Lake Oswego Stormwater Management Manual. October 2012 DRAFT

Transcription

1 Lake Oswego Stormwater Management Manual October 2012 DRAFT

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3 Lake Oswego Stormwater Management Manual Prepared for City of Lake Oswego 380 A Avenue PO Box 369 Lake Oswego, OR (503) Prepared by Herrera Environmental Consultants 24 NW 2nd Avenue, Suite 204 Portland, OR Telephone (503)

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5 Table of Contents 1 Introduction Manual Purpose Statement Organization of this Manual Why Stormwater Matters Water Quantity Impacts on Lake Oswego s Receiving Waters and Conveyance System Water Quantity Impacts on Lake Oswego s Receiving Waters General Principles of Stormwater Management Structural Stormwater Best Management Practices Non-Structural Stormwater Best Management Practices Conveyance How Local Conditions Affect Stormwater Management Updates 12 2 Getting Started 13 3 Overview of Stormwater Requirements Applicability Requirements for all Residents, Property Owners, and Business Owners Prevent Illicit Discharge Maintain Existing Drainage Patterns Obtain Permits and Reduce Impacts Stormwater Management Requirements Overview of Project Classification Small Projects Medium Projects Large Projects Overview of Minimum Requirements Onsite Stormwater Management City of Lake Oswego Erosion Control Permit 22

6 3.5.3 Perform Site Assessment and Feasibility Analysis Underground Injection Control Review with Oregon Department of Environmental Quality System Designed by LIcensed Professional Downstream Analysis Drainage Report Required Recorded Operations and Maintenance Agreement/Plan and Deed Restriction Design for Infiltration/Design for Water Quality Design for Flow Control NPDES 1200-C Permit from Oregon Department of Environmental Quality Additional Guidance Exempt versus Non-Exempt Projects Waiver and Payment/Fee in-lieu Program Information 27 4 Stormwater Process Overview New or Remodeled Home Partitions, Commercial, and Multifamily Projects Land Use Planning - Full Review Overview of Interdepartmental Responsibilities Planning Department Engineering Department Building Department Public Works - Operations Division Parks and Recreation Department 35 5 Stormwater Management Criteria TMDL Approved Areas/303(d) Listed Receiving Waters Low Impact Development Design Practices LID Principle #1 38

7 5.2.2 LID Principle # LID Principle # LID Principle # Site Assessment and Feasibility Analysis Site Map Step 1 - City GIS Data Evaluation Step 2 - Site Visit Step 3 - Collect Other Data, if Available 44 6 Stormwater BMP Selection List of Approved Stormwater Best Management Practices Infiltration Best Management Practices Sensitive Areas Use and Approval of Proprietary Stormwater Best Management Practices Small and Medium Projects Large Projects 50 7 Stormwater BMP Standards and Specifications Performance Standards Pretreatment Onsite Stormwater Management Water Quality Flow Control Planting Design Why Plants Matter in Stormwater Design Vegetation Diversity and Its Effect on Water Quality Plant Selection Process: Steps and Considerations BMP Design Methods and Computations Soils Pollution/Flow Control Manhole Design 62

8 7.6 BMP Design Guidelines Sheet Flow Dispersion Swales Rain Gardens Planters Green Roofs Pervious Pavement Infiltration Trenches Drywells Rainwater Harvesting Filter Strips Sand Filters Constructed Wetlands Ponds Detention Pipes and Vaults Conveyance and Detention Design Standards General Provisions - Conveyance Extension of Public Conveyance Systems Conveyance Easements General Standard Conveyance Easement Width Reduced Conveyance Easement Widths Encroachments Flow Determination for Surface Water Conveyance Land Use Assumptions for Flow Determination Computational Methods for Runoff Calculations Surface Water Conveyance Design Considerations Design for Full Build Out Stormwater Conveyance Design Criteria 142

9 8.5.3 Materials Upstream Impacts Downstream Impacts Cross Lot Drainage Dissipation of Runoff Discharge Separation Alignment Other Requirements for Public Conveyance Systems Surveying Railroad Crossings Surfacewater/Stormwater Laterals General Provisions Planning Considerations Flood Management Design Standards Purpose Flood Management Areas Defined Flood Management Design Criteria Construction Phasing; Stormwater Pollution Prevention and Erosion and Temporary Sediment Control Legal Requirements City Code MS4 Permit C Permit General Considerations Poor Construction Practices Timing, Scheduling, and Staging of Work Wet Weather Season Erosion and Sediment Control Requirements Stage Work 151

10 9.4 Implementing Procedures Communication Prohibitions of activities Managerial Practices Consideration of Construction Impacts During Planning, Design, and Construction Planning Considerations Design Considerations Recommended Construction Practices Selecting Construction Best Management Practices Maintenance and Inspection Procedures Minimizing Disturbances Post Construction Documentation Erosion Control Plan Erosion and Sediment Control Drawing Inspection Log Maintenance Legal Requirements Maintenance Responsibilities Inspection Maintenance Access Transfer of Property Ownership Failure to Provide Adequate Maintenance Submittals and Reporting Operations and Maintenance Agreement/Plan Records of Maintenance Activities Maintenance Checklists Source Control 165

11 11.1 Overview Eliminate Illicit Connections to Storm Drains Perform Routine Maintenance for Surface Water Management System Catch Basins Other Facilities Dust Control General Recommendations Required Best Management Practices Proper Storage of Solid Wastes General Recommendations Required Best Management Practices Proper Disposal of Fluids and Wastes General Recommendations Required Best Management Practices Spill Prevention and Cleanup General Recommendations Required Best Management Practices Landscaping, Lawn, and Vegetation Management General Recommendations Required Best Management Practices Painting, Finishing, and Coating of Vehicles, Boats, Buildings, and Equipment General Recommendations Required Best Management Practices Parking Lot Maintenance and Storage of Vehicles and Equipment General Recommendations Required Best Management Practices Fueling at Dedicated Stations General Recommendations Automobile Repair and Maintenance 178

12 General Recommendations Required Best Management Practices Swimming Pool and Spa Maintenance General Recommendations Required Best Management Practices Vehicle, Equipment, and Building Washing General Recommendations Required Best Management Practices Outdoor Storage or Transfer of Solid Raw Materials, Byproducts, or Finished Products General Recommendations Required Best Management Practices References Definitions Abbreviations Definitions 186 Appendix A Approved Plant Lists and Seed Mixes City of Portland BES Stormwater Manual (2008) Appendix F.4 Plant LIst A -1 City of Portland BES Stormwater Management Manual (2004) Seed Specifications A -15 Appendix B Submittals Drainage Report Template B -1 Operations and Maintenance Plan Example B -10 Integrated Pest Management Plan Example B - 22 Appendix C Erosion Control Plan General Notes C - 1 Appendix D Infiltration Testing Guidance D - 1 Appendix E Rational Method Information E - 1 Appendix F Santa Barbara Urban Hydrograph (SBUH) Method Spreadsheet Input Data E - 1 Appendix G Reading the Soil G - 1 Appendix H Maintenance Checklists Swales H -1

13 Rain Gardens and Planters H - 6 Green Roofs H - 11 Permeable Pavement H - 14 Trenches and Drywells H - 18 Rainwater Harvesting H - 20 Filter Strip H - 21 Sand Filters H - 25 Constructed Wetlands H - 28 Ponds H - 32

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15 1 Introduction 1.1 Manual Purpose The goal of Lake Oswego s stormwater management program is to protect and improve Lake Oswego s watersheds and to protect the health of humans and other species that depend on healthy watersheds, as well as protect public and private property from adverse impacts of stormwater. This stormwater management manual summarizes requirements for stormwater management of the runoff produced by new and redeveloped lands in a way that will meet the intent of the City s National Pollution Discharge Elimination System (NPDES) Municipal Separate Storm Sewer System (MS4) permit and other legal requirements. This manual contains the minimum requirements for stormwater facilities and other best management practices (BMPs), including Low impact development (LID) techniques and facilities such as rain gardens, green roofs, and pervious pavement. Engineering criteria and design standards needed to implement the stormwater management program are provided in this manual. This manual is intended to be a dynamic rather than static document. As such, it will be updated periodically to reflect the state of stormwater practice and treatment technology. Best management practices, or BMPs, can be structural BMPs such as swales, rain gardens, or constructed wetlands. They can also be non-structural BMPs, such as the source control requirements to prevent pollution described in Chapter 11. The City of Lake Oswego (the City) is required to update the current manual to meet requirements in the NPDES MS4 permit issued on March 16, Table 2.1 summarizes requirements that apply for projects that exceed this threshold, along with where they are addressed in this manual. 1 Lake Oswego Stormwater Manual Draft

16 Introduction Table 1.1 NPDES MS4 Permit Requirements Addressed by this Manual. MS4 Permit Requirement Chapter 3 Minimum Requirements Overview Chapter 4 Stormwater Process Overview Chapter 5 Stormwater Management Criteria Chapter 6 Stormwater BMP Selection Chapter 7 Stormwater BMP Standards and Specifications Chapter 8 Conveyance and Detention Design Standards Chapter 9 - Construction and Stormwater BMPs Chapter 10 Stormwater BMP Maintenance Procedures Chapter 11 Source Control Implement the development and redevelopment project thresholds applicable to Lake Oswego: 3,000 square feet of new or redeveloped impervious area. Projects exceeding this threshold are referred to in this manual as large projects. Onsite stormwater management: Incorporate site specific management practices that target natural surface or pre-development hydrologic functions and optimize onsite retention based on site conditions. Design for water quality/design for flow control: Reduce site specific, postconstruction runoff volume, duration, and rates of discharges to the MS4 to minimize hydrological and water quality impacts from impervious surfaces. Capture and treat 80% of the annual average runoff volume. Reference design storm (or continuous simulation method) to demonstrate compliance with requirement to capture and treat 80% of average annual runoff volume. Include applicable LID and green infrastructure or equivalent approaches in the Stormwater Management Manual as well as the practical uses for these approaches. Include conditions where the implementation of LID, green infrastructure, or equivalent approaches may be impracticable. Include a list of BMPs including descriptions of site-specific design requirements, descriptions of design requirements that do not inhibit maintenance, conditions where the BMP applies. Include pollutant removal efficiency performance goals that maximize the reduction in discharge of pollutants. Lake Oswego Stormwater Manual Draft 2

17 Introduction MS4 Permit Requirement Chapter 3 Minimum Requirements Overview Chapter 4 Stormwater Process Overview Chapter 5 Stormwater Management Criteria Chapter 6 Stormwater BMP Selection Chapter 7 Stormwater BMP Standards and Specifications Chapter 8 Conveyance and Detention Design Standards Chapter 9 - Construction and Stormwater BMPs Chapter 10 Stormwater BMP Maintenance Procedures Chapter 11 Source Control City must review, approve, and verify proper implementation of post-construction site plans for new development and redevelopment projects. Include offsite stormwater quality management options where site constraints limit onsite stormwater management methods. Require erosion and sediment control (ESC) plans, require prevention and control of non-stormwater waste from construction, perform on-site inspections, and document enforcement procedures. Require effective operations and maintenance Identify and develop strategies, priorities, and tools for preventing or reducing hydromodification impacts to water bodies affected by the MS4s discharges. Total Maximum Daily Load or 303(d)-Listed water bodies In addition to meeting MS4 permit requirements, this manual was also a result of the findings of the Clean Streams Plan (Otak 2009) as well as a way to address numerous City Council Goals related to water quality improvement, LID, and protection of water resources. The goal with this manual is to improve performance, aesthetics, and maintenance of stormwater facilities, and to ensure that stormwater facilities are amenities that perform well over time, protect the City s water resources, and reflect community needs and values. This manual describes the requirements and methods for minimizing the impact of stormwater in Lake Oswego. The manual summarizes the City s current policies and procedures related to stormwater regulations and requirements, to streamline understanding of and compliance with stormwater requirements. This manual replaces the existing Surface Water Design Workbook (City of Lake Oswego 2003). This manual is intended for use by developers, designers of stormwater facilities, City staff, property owners, contractors, or others responsible for designing or implementing development or redevelopment projects in Lake Oswego. For simplicity, the term applicant is used throughout this manual to refer to the developer, designer, or other party proposing development or redevelopment that is subject to the stormwater regulations and requirements described in this manual. 3 Lake Oswego Stormwater Manual Draft

18 Introduction 1.2 Organization of the Manual Chapter 1 provides getting started guidance, which provide a quick overview of the planning, permitting, design, and construction requirements for projects in Lake Oswego. Applicants (including developers, designers of stormwater facilities, etc.) of proposed development or redevelopment projects should review this guidance. Chapter 2 summarizes background information on principles of stormwater management, the purpose and organization of this manual, and an overview of water quality and water quantity impacts on Lake Oswego s water bodies and conveyance system. Anyone who is interested in why stormwater management is important and how this manual addresses legal requirements should review this chapter. Chapter 3 helps applicants determine which minimum requirements apply, depending on the project type, area of disturbance, and amount of new or replaced impervious surface. Chapter 4 provides an overview of the stormwater review process, including flow charts that illustrate how stormwater review fits into other permitting and review at the City. Chapter 5 highlights the status of some of Lake Oswego s receiving waters that are listed as impaired on Oregon s 303(d) list (part of the Clean Water Act). Total maximum daily loads (TMDLs) have been or are being developed for the Tualatin River, Springbrook Creek, Tryon Creek, Oswego Lake, and the Willamette River. At the time of publication of this manual, there were no additional requirements for projects that drain to these receiving waters. Chapter 5 also provides an overview of LID site design concepts and requirements for the site assessment and feasibility analysis. Chapter 6 is intended to help applicants select stormwater facilities approved for use in Lake Oswego, depending on site characteristics and the stormwater management objective (e.g., flow control, onsite stormwater management, or water quality). Chapter 7 provides BMP standards and specifications, with information on hydraulic design, infiltration testing requirements, soil protection measures, and planting design. Chapter 8 provides requirements for conveyance facilities, including general provisions related to stormwater conveyance facilities, and technical design criteria for storm sewers and hydraulic structures. Chapter 9 provides information on construction practices required to ensure that receiving waters are protected and that stormwater BMPs function properly. Chapter 10 provides BMP maintenance checklists that summarize maintenance requirements to ensure effective performance and operation over time. Chapter 11 provides required source control requirements that prevent pollutants from leaving a site, facility, home, or business. Implementing applicable source control measures will help applicants and other residents, property owners, and businesses comply with the City s stormwater code. Chapter 12 includes a list of references cited in this manual. Chapter 13 provides abbreviations and definitions for key terms used in this manual. Lake Oswego Stormwater Manual Draft 4

19 1.3 Why Stormwater Matters Introduction Stormwater is the water that originates from rainfall and snowmelt. In urban areas, precipitation lands on surfaces such as roads, parking lots, and rooftops. When rain or snow lands on a surface that does not allow water to percolate into the ground (called an impervious surface), it cannot enter the soil through infiltration, so it flows overland as surface runoff. All surface water and runoff in Lake Oswego eventually finds its way to the Willamette River, the Tualatin River, or Oswego Lake. Each drainage basin is a complex system of topography, vegetation, and hydrology. Water flows through the drainage basins via a network of interconnected ditches, streams, and storm drains and eventually finds its way to the Willamette River and Tualatin River. The surface water management utility includes all natural and man made facilities used to manage the quantity and quality of surface water, including drainage easements, culverts, storm drains, ditches, catch basins, and other stormwater BMPs. Lake Oswego is different from many jurisdictions in that the surface water utility also includes natural systems such as stream corridors, rivers, ponds, wetlands, and impoundments. The City is responsible for managing and protecting its surface water management system through the implementation of the City s Stormwater Permit, TMDL implementation activities, and other natural resource programs. 5 Lake Oswego Stormwater Manual Draft

20 Introduction Water Quantity Impacts on Lake Oswego s Receiving Waters and Conveyance System The conversion of pervious surfaces to impervious surfaces through urbanization increases the volume of surface runoff, increases the maximum rate of flow of water during or after a precipitation event (called peak flow ), and changes the time at which peak flows occur. Development can affect the discharge of stormwater runoff as follows: Changing the timing at which the peak flow occurs, usually earlier in the storm Increasing the peak flow rate Increasing durations (the time period during which a receiving water experiences elevated flows) Increasing the runoff volume associated with a storm event Impacts on Conveyance System and Lake Oswego Residents and Property Owners Flooding Some areas of Lake Oswego have no storm drainage facilities, and other parts of the city have undersized pipe systems and open drainage ditches. During periods of heavy rainfall on areas with a large amount of impervious surface, local flooding, along with associated risks to health, public Stormwater flooding the streets. safety, and property, may occur. Reducing base flow discharge Cost and Feasibility between storms. Increasing the size of pipes is often infeasible due to conflicts with other utilities and the need to maintain gravity flow to receiving waters. Even where it is feasible, constructing larger pipes is a costly solution, requiring removal and restoration of the overlying pavement or other surface. Moving Problems Downstream Increasing pipe sizes or constructing detention facilities may alleviate flooding concerns in the immediate vicinity of these improvements, but these temporary fixes can ultimately exacerbate downstream problems if, for example, detention facilities delay the peak flow so that it coincides with peak flows downstream. Local Applicability and Solutions This manual prioritizes BMPs that promote infiltration of stormwater to groundwater. This reduces the volume and rate of stormwater discharged from a site, and has the additional benefit of supporting base flows in streams. Minimum requirements have been established to meet the legal requirements under the MS4 permit and to avoid exacerbating Lake Oswego s flooding problems as new development and redevelopment occur. This manual requires a downstream analysis to evaluate whether an individual project will affect downstream properties or infrastructure. The City is planning to update its 1992 Surface Water Master Plan to update built out conditions, with the reality of current and projected development densities to cover the next 20 years. Some of the undersized pipes and underserved areas will be addressed as part of this long-term planning effort. The City will be evaluating the need and feasibility of increasing, replacing, and constructing new stormwater management facilities as part of its long-term planning efforts under the stormwater management plan, but because the cost of such improvements must be borne by ratepayers, the City is promoting LID practices described in this manual to work with existing infrastructure. Lake Oswego Stormwater Manual Draft 6

21 Introduction Stormwater Runoff Impacts on Channel Processes and Relevancy to Lake Oswego Residents and Property Owners Streams and other receiving waters are affected in many complex ways by stormwater, as the timing, volume, and peak flows of stormwater that water bodies experience change due to development. As watersheds develop, soils are compacted and more surfaces are converted from native vegetation to impervious surfaces; this makes the hydrology become flashier, with a greater percentage of rainfall converted immediately to surface runoff, instead of contributing to evapotranspiration or infiltrating and recharging base flows. Pipes and ditches also shorten the time between when rainfall begins and when streams begin to rise. Some streams can experience elevated flow rates for a longer time period (duration). (Compared to a forested, undeveloped state, less rainfall volume contributes to evapotranspiration or infiltration into the ground.) Base flows in streams, which are sustained by groundwater and are critical to fish and other aquatic species during the summer, are commonly reduced. More complex and less intuitive is the relationship between streamflow and sediment in streams. Most of Lake Oswego s streams are considered alluvial (composed of channel and bank sediment that is mobilized and deposited by channel processes rather than hillslope processes). In an alluvial channel, the channel will respond to changes in flow and sediment supply by adjusting the channel may become steeper, wider, and/or deeper depending on the condition of the stream banks and streambed. Alternatively, or additionally, higher sediment loads or larger particles may be deposited in the channel (Lane 1955; Leopold and Maddock 1953). The impacts to stream channels resulting from changes in streamflow characteristics due to stormwater discharges are referred to as hydromodification, and they are important to residents, property owners, and business managers in Lake Oswego in the following ways: Property damage: Properties adjacent to stream channels can experience property damage, loss of trees, and other impacts as stream channels change alignment or geometry due to stormwater impacts. Flooding: Increased peak flows can result in an increased frequency of bank overtopping. If culverts or bridges are undersized or blocked with debris, properties or roads in the vicinity are likely to flood during storm events. Increased cost to ratepayers: As noted in Table 2.1, Lake Oswego s surface water management utility is legally required to address hydromodification under its MS4 permit. As hydromodification impacts associated with stormwater discharges get worse, the problems in receiving channels get more challenging to fix. Increased erosion and sedimentation: These can create substrate conditions that are inhospitable to the incubation and survival of salmonids. Bank erosion and sediment deposition can smother fish spawning and rearing habitats. Reduced habitat: Over-bank vegetation, large woody debris, and other important habitat-forming features, which are present in natural channels and are important for stream ecological health, are lost. Photo from ABR, Inc. Cutthroat fry from Springbrook Creek. 7 Lake Oswego Stormwater Manual Draft

22 Introduction Local Applicability and Solutions This manual prioritizes LID BMPs that promote infiltration. While this will not undo the hydromodification impacts that have already occurred, reducing the volume of surface runoff by promoting infiltration and reducing impervious surfaces will help decrease further impacts. In addition to this manual, the City, under the City s MS4 permit, is required to further address hydromodification by completing the following activities: Collect and maintain information that will inform future stormwater management decisions related to hydromodification based on local conditions and needs. Identify and develop strategies to address hydromodification information or data gaps related to water bodies within the City s jurisdiction Identify strategies and priorities for preventing or reducing hydromodification impacts related to stormwater discharges Identify or develop effective tools to reduce hydromodification Water Quality Impacts on Lake Oswego s Receiving Waters Beneficial uses include the following (OAR ): Domestic water supply Fishing Industrial water supply Boating Irrigation Water contact recreation Livestock watering Aesthetic quality Fish and aquatic life Hydropower Wildlife hunting Commercial navigation and transportation As stormwater flows over roads, roofs, and lawns, it collects and carries pollutants that are contained on those surfaces, including sediment, excess nutrients, pesticides, metals, bacteria, and fuel and oils. Recent watershed health indexing by the City of Lake Oswego indicates that these pollutants are reaching receiving waters. The receiving waters are showing signs of increased urbanization (sediment tolerant aquatic insects, or macroinvertebrates, bank erosion, bed scour and water quality trends). In addition to the health, recreational, aesthetic, and environmental concerns related to water quality, discharge of pollutants from stormwater can result in violation of state and federal water quality standards established by the Oregon Department of Environmental Quality (DEQ). These water quality standards have been established to protect the beneficial uses of water bodies. Beneficial uses are legally assigned by basin, and they are intended to establish goals and requirements for that water body, to make sure its water quality is supportive of the most sensitive beneficial use. The Clean Water Act requires the State of Oregon to develop a list of impaired or threatened waters within the state. To meet that mandate, DEQ prepares a list of impaired waters known as the 303(d) list that identifies water bodies that are failing to meet water quality standards that have been set by DEQ to protect beneficial uses. Lake Oswego Stormwater Manual Draft 8

23 Introduction To address water quality issues in 303(d)-listed waters, TMDLs must be established by DEQ for identified contaminants. A TMDL is the total amount of a contaminant a water body can accept without violating the water quality standard. Implementation plans are prepared to meet the TMDL goals and are implemented by Designated Management Agencies. The City of Lake Oswego is a Designated Management Agency for those reaches of the Tualatin River, Springbrook Creek, Tryon Creek, and the Willamette River within its jurisdiction and all of Oswego Lake these watersheds comprise nearly all of Lake Oswego. TMDL Water Quality Management Plans require the City to work toward reducing concentration of contaminants of concern, so BMPs that discharge to those water bodies should be directed toward the reduction of the TMDL contaminants. TMDLs and 303(d)-listed contaminants that have been identified for the water bodies in Lake Oswego s jurisdiction include phosphorus, bacteria, and dissolved oxygen, which are most frequently associated with stormwater. TMDL Water Quality Management Plans require the City to work toward reduction in concentration of contaminants of concern, so BMPs that discharge to those water bodies should be directed toward the reduction of the TMDL contaminants. As Water Quality Management Plans get developed, the City may require additional treatment to ensure that wasteload allocations approved for each water body are not exceeded. Local Applicability and Solutions The BMPs included in this manual have been selected based on their effectiveness at removing important pollutants from stormwater. The City is reviewing research that is underway funded by Washington s Stormwater Center, the Oregon Department of Transportation (ODOT), the Washington State Department of Ecology, and other agencies to make sure that BMPs and design standards reflect the best performing options based on the latest research. This manual includes maintenance schedules and guidance and source control requirements. One of the best ways that Lake Oswego residents and property owners can help protect the water quality of the City s receiving waters and keep it safe for recreation, fish, and other beneficial uses is by maintaining stormwater facilities to make sure that they keep functioning well and to adhere to the source control requirements in Chapter 11 to prevent pollutants from entering the storm system that will eventually reach streams or Oswego Lake. 1.4 General Principles of Stormwater Management Ideally, stormwater should be managed at its source by minimizing effective impervious surface area and using vegetation, amended soils, and infiltration to minimize the amount of stormwater runoff that leaves a site, entrains pollutants, and must be managed. Once stormwater runoff leaves a site, it is much more costly and less effective to transport, treat, and control the effects of stormwater. Low Impact Development: LID uses site design practices and/or BMPs that reduce the amount of stormwater to be managed through reducing impervious surface area; preserving vegetation and soil characteristics that promote infiltration and biological treatment processes; and designing small facilities, integrated into the landscape, that receive stormwater from small tributary areas, rather Effective impervious surfaces are those impervious surfaces that contribute runoff to the surface water management system. Runoff from these surfaces either enters catch basins and pipes directly or indirectly. A sidewalk that drains to a lawn or other landscaped area that is wide enough for stormwater runoff from the impervious surface to infiltrate is not considered effective impervious surface. 9 Lake Oswego Stormwater Manual Draft

24 Introduction than centralized facilities accepting stormwater from large areas. LID can be highly effective at reducing the impacts of development on streams, lakes, and other receiving waters. Examples of LID techniques. Greenroof The general principles of LID are described in Chapter 5 and include: 1. Understand the site 2. Reduce runoff through design 3. Reduce pollutants carried by runoff Pervious Pavement 4. Capture and treat runoff Cistern to collect and reuse roof runoff Linear rain gardens Riparian buffer Structural Stormwater Best Management Practices Structural stormwater BMPs are constructed facilities such as swales, ponds, or rain gardens that are designed to manage stormwater. LID stormwater management techniques capture, filter, store, evaporate, and infiltrate runoff near its source. LID BMPs should receive runoff from no more than 6,000 square feet of impervious surface area. Larger scale infiltration facilities may be appropriate for some parcels or projects, but the City prioritizes small, dispersed stormwater management facilities as the best way to manage runoff and meet City requirements. Flow control BMPs include detention ponds, tanks, or vaults that temporarily store stormwater and then release it at rates to match pre-development flow rates and/or durations. Flow control BMPs attempt to reduce the flooding and hydromodification impacts of development. Rainwater harvesting is an example of a flow control BMP that provides flow control by temporarily storing stormwater for later use for landscaping or approved building uses. LID flow control BMPs are typically small facilities, integrated into the landscape, that receive stormwater from small tributary areas, rather than centralized facilities accepting stormwater from large areas. They control flow through infiltration and/ or dispersion. LID can be highly effective at reducing the impacts of development on streams, lakes, and other receiving waters Non-Structural Stormwater Best Management Practices Non-structural BMPs are practices (rather than facilities) designed to prevent pollution. They include some erosion and sediment control measures, such as construction phasing, minimizing land disturbance, and stabilizing the site (see Chapter 9). Maintenance practices (Chapter 10) and source control measures described in Chapter 11 are also examples of important non-structural BMPs that are required to protect Lake Oswego s water bodies. Lake Oswego Stormwater Manual Draft 10

25 Introduction Additional non-structural BMPs also include education and outreach, illicit discharge detection and elimination, public involvement, and adaptive management. The City s website (raintoriver.org) provides more information on these ongoing stormwater programs Conveyance Conveyance facilities include inlets, catch basins, manholes, storm drains (pipes), and ditches used to safely convey, or transport, stormwater to a facility or an outfall to a stream or lake. The conveyance system is designed to convey a certain amount of stormwater, referred to as the capacity. Chapter 8 provides design information for conveyance facilities including size, location, structures, and materials. In Lake Oswego, catch basins with less than a 12-inch sump are considered a conveyance structure, while catch basins with a sump greater than or equal to 12 inches are considered a pretreatment facility that removes sediment via settling. 1.5 How Local Conditions Affect Stormwater Management Lake Oswego has many areas with high groundwater and shallow bedrock, both of which limit opportunities for LID. Many areas of the City also have steep slopes, which limit stormwater management options. Chapter 6 has site suitability criteria for stormwater BMPs, including tools for identifying areas that are appropriate for LID. Since the City is mostly residential, retrofit-type BMPs that are appropriate at the small site scale are and will be a priority. The City of Lake Oswego will be addressing stormwater runoff at different scales of land use and will be integrating stormwater management practices into those different scales to the maximum extent practicable. At the regional scale, this means working within the City and its neighboring jurisdictions to preserve open space and critical ecological features, encourage development in areas ripe for redevelopment, and using land efficiently. At the neighborhood scale, this means encouraging mixed-use and transit-oriented development where practicable, applying green street principles where resources allow, minimizing impervious surfaces, and making stormwater features public and private amenities where practicable. Commercial development in Lake Oswego tends to include landscaping and community amenities. Well-selected and designed stormwater BMPs can enhance the landscaping of a commercial site in addition to providing an important function. 11 Lake Oswego Stormwater Manual Draft

26 Introduction 1.6 Updates This manual was written in 2012 and reflects the current regulatory requirements and state of stormwater science and technology. Stormwater management is a dynamic and emerging science. There has been a surge of research related to stormwater in the past decade, particularly in the following areas: Compost and amended soil mixes that can improve BMP pollutant removal performance, especially for nutrients like phosphorus (current guidance is in Chapter 6, but as more information becomes available, updates will be provided via BMP sizing and analysis tools to streamline sizing of BMPs (current BMP selection and sizing guidance is described in Chapters 6 and 7. As the City addresses its hydromodification requirements in the MS4 permit, new sizing tools will likely be developed. Check for current BMP sizing requirements.) Proprietary BMPs that have been tested and approved under the Technology Assessment Protocol Ecology (TAPE) program, run by the Washington State Department of Ecology, are regularly updated on the TAPE program website: Proprietary BMPs are only allowed for use in Lake Oswego with prior approval from the City, and BMPs must be selected that have been approved for general use under the TAPE program. See Section for more information. The City is evaluating fee-in-lieu, incentive, and credit programs and other ways to add flexibility to its stormwater management program and comply with MS4 permit requirements. These programs are not yet in place, but updates will be provided on the City s website (raintoriver.org) as they are adopted. Lake Oswego Stormwater Manual Draft 12

27 2 Getting Started Planning a Project? Step 1 Review minimum project requirements table and description (Chapter 3) to determine whether the project is small, medium, or large, and which requirements apply. Step 2 Review Low Impact Development design practices and complete site assessment and feasibility analysis for the site (Chapter 5). Step 3 Consult with City staff - visit Planning and Engineering Departments. Bring the site assessment and feasibility analysis. Step 4 Plan the project to reduce runoff through design and reduce pollutants carried by runoff (LID principles #2 and #3 in Chapter 5). Step 5 Select onsite, water quality/infiltration, and flow control BMPs that are applicable for the site (Chapter 6). Step 6 Design stormwater management BMPs (Chapter 7) and complete submittals neccessary (Appendix B). 13 Lake Oswego Stormwater Manual Draft

28 Getting Started Planning a Project? Step 7 Make sure you have all permits and submittals BEFORE hiring a contractor. See Chapter 4 for an overview of permits and Appendix B for submittals. Step 8 Construct your project. See Chapter 9 for construction BMPs. Step 9 Request inspection by City staff, complete as-built plans and pay maintenance and landscape bonds as appropriate. (Chapter 4) Step 10 Maintain Stormwater BMPs (Chapter 10). Lake Oswego Stormwater Manual Draft 14

29 3 Stormwater Requirements 3.1 Applicability The requirements and guidance provided in this manual apply to the following activities: Overview Grading or earthwork, drainage, and erosion control activities, whether or not a permit is required Ground-disturbing activities, whether or not a permit is required Discharges directly or indirectly to a public storm drainage system Direct or indirect discharges into receiving waters within or contiguous to city limits New and existing land uses Creation or replacement of impervious surface areas Phased projects on a single site that exceed the thresholds in Table 3.1 with development occurring over a 5-year period are considered a single development and must meet applicable requirements from this manual based on cumulative areas of land disturbance and/or new/replaced impervious surface, as applicable. Developments approved prior to the implementation of this manual are not subject to these requirements. Specific requirements and exemptions are outlined in subsequent sections. The Lake Oswego Stormwater Management Manual is a policy document that the City reserves the right to modify. The City has the right to modify the standards and may establish supplemental requirements under a separate publication or policy that becomes an addendum to this Stormwater Management Manual. The City may also update additional requirements under a separate document. Any addendum to the Lake Oswego Stormwater Management Manual will be included in the latest online version of this document and updated in print when updates are made. 3.2 Requirements for all Residents, Property Owners, and Business Owners The activities noted in Section 3.1 include even minor activities of many people who work or live in Lake Oswego. That is because some activities, such as illicit discharge or rerouting stormwater to a neighbor s property, can cause significant damage even though there may be no associated increase in impervious surface area that would trigger the formal Small, Medium, and Large project classifications described in Section Prevent Illicit Discharges To voluntarily reduce stormwater impacts and help improve the health and quality of Lake Oswego s water bodies, stay informed by checking www. raintoriver.org regularly. All residents, property owners, and business owners in Lake Oswego must prevent illicit discharges in accordance with Lake Oswego Code (LOC) and must implement source control BMPs (Chapter 11) to avoid such discharges. Illicit discharges include pollutants resulting from a spill or deliberate dumping. 15 Lake Oswego Stormwater Manual Draft

30 Stormwater Requirements Overview Prohibited discharges are discharges that: a. Cause or contribute to a violation of the City s MS4 permit, or b. Cause or contribute to a violation of a waste load allocation contained in a TMDL approved by the US Environmental Protection Agency (US EPA), or c. Cause or contribute to a violation of a city, state, or federal law or regulation, or d. Cause or contribute to the endangerment of public health, safety, or welfare; the environment; or public or private property Maintain Existing Drainage Patterns Oregon has adopted the civil law doctrine of drainage. Adjoining landowners are entitled to have the normal course of natural drainage maintained. The downhill or downstream owner must accept water that naturally comes to their land from above, so long as the amount and pattern of drainage does not change significantly. Similarly, the downhill landowner may not obstruct the runoff from the upper property if the uphill landowner is properly discharging the water. Oregon drainage law, which originates from common law or case law, has developed without legislative action, and it is embodied in the decisions of the courts. Therefore, there are no Oregon Revised Statues to cite pertaining to Oregon drainage law. For more information on this topic, consult Section 2.2 of the ODOT Hydraulics Manual (ODOT 2011). For the uphill property owner, properly discharging the water means keeping the location of the discharge the same, avoiding substantial increases in the acceleration and concentration of stormwater, and preserving areas where water infiltrates, ponds, and/or evaporates rather than flows onto adjacent property Obtain Permits and Reduce Impacts Chapter 4 summarizes the stormwater review process and how it fits in with other planning and permit requirements in Lake Oswego (building permits, erosion control permits, land use review, and other requirements). The updated stormwater code (LOC 38.24) contains additional information on rights and responsibilities related to stormwater management. Enforcement and penalties for violations of stormwater requirements are summarized in LOC Stormwater Management Requirements The City of Lake Oswego has established requirements related to protecting public health or property, and avoiding or exacerbating flooding, downstream impacts, and drainage problems in the City or private drainage systems. Requirements that may apply fall into the following categories: Water quality treatment the City s MS4 permit requires that projects that exceed permit thresholds (3,000 square feet of new or replaced impervious surface) must provide stormwater facilities that capture and treat 80 percent of the average annual runoff. LID and onsite stormwater management practices must be given high priority. Chapters 6 and 7 provides information on how to select and design facilities that meet the MS4 permit requirements. Lake Oswego Stormwater Manual Draft 16

31 Stormwater Requirements Overview Detention or infiltration the City requires that projects that exceed permit thresholds (3,000 square feet of new or replaced impervious surface) must provide flow control to reduce the impacts of new impervious surface on the City s storm system and streams and Oswego Lake. 3.4 Overview of Project Classifications For the purposes of determining stormwater management requirements, Lake Oswego has three categories of projects: small, medium, and large Small Projects Small projects are defined as new or redevelopment projects that create or replace more than 200 square feet and less than 1,000 square feet of impervious area Medium Projects Medium projects are defined as new or redevelopment projects that create or replace 1,000 square feet or more but less than 3,000 square feet of impervious area Large Projects Large projects are defined as new or redevelopment projects that create or replace 3,000 square feet or more of impervious surface area. To minimize the stormwater management requirements that apply to a particular project, the City of Lake Oswego encourages applicants to reduce impervious surface area. Before determining the project classification, applicants should complete the impervious surface area reduction table (Table 3.1). 17 Lake Oswego Stormwater Manual Draft

32 Stormwater Requirements Overview Table 3.1 Impervious Surface Area Reduction Table. Step 1. Initial estimate of impervious surface area 1. Description Total new impervious surface area (sq.ft.) Total replaced impervious surface area (sq.ft.) Total new plus replaced impervious surface area (sq.ft.) Quantity Initial Estimate Step 2. Apply impervious surface area reduction credits. Description Total area of green roof (sq. ft.) Total area of porous pavement (sq. ft.) Other credits or reductions in impervious surface area (new/ protected trees, non-effective impervious surface 2 consult with planning and/or engineering department for details) (sq. ft.) Total impervious surface area reduction credits (sq. ft.) Quantity Reduction Step 3. Calculate remaining impervious surface area to be managed. Description Quantity Initial estimate (sq. ft.) Reduction (sq. ft.) Impervious surface area to be managed (sq. ft.) (Subtract reduction from initial estimate) sq. ft. = square feet 1 Impervious surface area: Any surface resulting for development activities that prevents the infiltration of water or results in more runoff than in the undeveloped condition. Common impervious surfaces include: building roofs, traditional concrete or asphalt paving on walkways, driveways, parking lots, gravel roads, and packed earthen materials. 2 Effective impervious surface area: Impervious surfaces that are connected via sheet flow or discrete conveyance to a drainage system. A sidewalk that drains to a lawn or other landscaped area where stormwater runoff from the impervious surface can infiltrate is not considered effective impervious surface. After calculating the area of impervious surface to be managed, refer to Table 3.2 to determine the project classification and applicable minimum requirements. Lake Oswego Stormwater Manual Draft 18

33 Stormwater Requirements Overview Table 3.2 Minimum Project Requirements. Minimum Project Requirements Onsite Stormwater Management 1 City of Lake Oswego Erosion Control Permit Perform Site Assessment and Feasibility Analysis UIC Review with DEQ Small Project New or redevelopment projects that create or replace >200 sq. ft. and <1,000 sq. ft. of impervious area Onsite Stormwater Management requirement shall apply. Stormwater facilities shall maximize onsite retention and be sized to infiltrate the 10 year 24 hour storm event, to the maximum extent practicable. See section of Stormwater Management Manual Erosion Control Permit required when activity disturbs >500 sq. ft. OR within 50 feet of pond, lake, river, stream corridor, canal, or wetland. Applicant to perform site assessment and feasibility analysis. Drywell design and construction shall be reviewed by registered engineer in State of Oregon. UIC registration may be required. See OAR Drywells shall conform to Oregon Plumbing Code. Project Classification Medium Project New or redevelopment projects that create or replace 1,000 sq. ft. and <3,000 sq. ft. of impervious area Onsite Stormwater Management requirement shall apply. Stormwater facilities shall maximize onsite retention and be sized to infiltrate the 10 year 24 hour storm event, to the maximum extent practicable. See section of Stormwater Management Manual Erosion Control Permit required when activity disturbs >500 sq. ft. OR within 50 feet of pond, lake, river, stream corridor, canal, or wetland. Applicant to perform site assessment and feasibility analysis. Drywell design and construction shall be reviewed by registered engineer in State of Oregon. UIC registration may be required. See OAR Drywells shall conform to Oregon Plumbing Code. Large Project New or redevelopment projects that create or replace 3,000 sq. ft. impervious surface Onsite Stormwater Management requirement shall apply. Stormwater facilities shall maximize onsite retention and be sized to infiltrate the 10 year 24 hour storm event, to the maximum extent practicable. See section of Stormwater Management Manual Erosion Control Permit required when activity disturbs >500 sq. ft. OR within 50 feet of pond, lake, river, stream corridor, canal, or wetland. Applicant to perform site assessment and feasibility analysis. Drywell design and construction shall be reviewed by registered engineer In State of Oregon. UIC registration may be required. See OAR Drywells shall conform to Oregon Plumbing Code. 19 Lake Oswego Stormwater Manual Draft

34 Stormwater Requirements Overview Project Classification Small Project Medium Project Large Project Minimum Project Requirements New or redevelopment projects that create or replace New or redevelopment projects that create or replace New or redevelopment projects that create or replace >200 sq. ft. and <1,000 sq. ft. of impervious area 1,000 sq. ft. and <3,000 sq. ft. of impervious area 3,000 sq. ft. impervious surface Professional engineer required for facility design and construction inspection. Landscape architect may design and inspect infiltration facility with review from professional engineer licensed in Oregon. System Designed by Licensed Professional Professional engineer may be required for facility design and construction inspection; requirement at City s discretion. Stormwater facilities (specifically, proprietary and subsurface infiltration systems) shall be designed and inspected by registered engineer in State of Oregon. Rain gardens for medium projects may be designed and inspected by a professional architect, or landscape architect Downstream Analysis Required Downstream Analysis required for all projects creating or redeveloping 1,000 sq. ft. of impervious area. Onsite Stormwater Management requirement shall apply. Stormwater facilities shall maximize onsite retention and be sized to infiltrate the 10 year 24 hour storm event, to the maximum extent practicable. See section of Stormwater Management Manual. See Design Manual and Article XXXX for Drainage Report Requirements. For projects 1,000 sq. ft., operations and maintenance plans must be prepared by a registered professional (licensed landscape architect or a licensed professional engineer) and recorded as a deed restriction in the county in which the property/facility is located. Downstream Analysis required for all projects creating or redeveloping 1,000 sq, ft, of impervious area. Onsite Stormwater Management requirement shall apply. Stormwater facilities shall maximize onsite retention and be sized to infiltrate the 10 year 24 hour storm event, to the maximum extent practicable. See section of Stormwater Management Manual. See Design Manual and Article XXXX for Drainage Report Requirements. For projects 1,000 sq. ft., operations and maintenance plans must be prepared by a registered professional (licensed landscape architect or a licensed professional engineer) and recorded as a deed restriction in the county in which the property/facility is located. Drainage Report Required Recorded Operations and Maintenance Plan Lake Oswego Stormwater Manual Draft 20

35 Stormwater Requirements Overview Project Classification Small Project Medium Project Large Project Minimum Project Requirements New or redevelopment projects that create or replace New or redevelopment projects that create or replace New or redevelopment projects that create or replace >200 sq. ft. and <1,000 sq. ft. of impervious area 1,000 sq. ft. and <3,000 sq. ft. of impervious area 3,000 sq. ft. impervious surface Recorded Maintenance Covenant All stormwater facilities must have a recorded maintenance agreement. See Design Manual for detail. All stormwater facilities must have a recorded maintenance agreement. See Design Manual for detail. Design for Infiltration/ Design for Water Quality Stormwater facilities shall be designed to capture and treat 80% of the average annual runoff volume, based on local rainfall frequency and intensity. Design for Flow Control Maintain peak flow rates at their pre-development levels for the 2-year, 5-year, and 10-year, 24- hour runoff events. NPDES 1200-C Permit from DEQ 1200-C DEQ permit required when construction activities including clearing, grading, excavation, materials or equipment staging and stockpiling that will disturb less than one acre that are part of a common plan of development or sale if the larger common plan of development or sale will ultimately disturb one acre or more and may discharge to surface waters or conveyance systems leading to surface waters of the state. DEQ = Oregon Department of Environmental Quality OAR = Oregon Administrative Rule UIC = underground injection contr 21 Lake Oswego Stormwater Manual Draft

36 Stormwater Requirements Overview 3.5 Overview of Minimum Requirements Onsite Stormwater Management Many of the City s storm drains are under capacity. There are also many areas that lack stormwater infrastructure. The City has been addressing these problems by requiring onsite stormwater management that infiltrates stormwater where feasible through use of rain gardens, infiltration trenches, or drywells. This requirement complies with the MS4 permit requirement to incorporate site-specific management practices that target natural surface or pre-development hydrologic functions as much as practicable. The site-specific management practices should optimize onsite retention based on the site conditions. See Chapter 6 for design criteria and options to meet onsite stormwater management requirements. Some projects may be able to meet onsite stormwater requirements through sheet flow dispersion. See Section for details City of Lake Oswego Erosion Control Permit All projects that disturb soil should take precautions to keep soil from leaving the site, but if projects exceed a certain threshold, they may be subject to submittal and permit requirements. An erosion control permit and plan are required for land disturbance of 500 square feet or more OR land disturbance within 50 feet of a pond, lake, river, stream corridor, canal, or wetland. For more information, consult the following sources: Lake Oswego Code (LOC) Chapter 52 for specific erosion and sediment submittal requirements, and required content for an Erosion Control Plan. Erosion Prevention and Sediment Control Planning and Design Manual (Clackamas County et al. 2008) for planning and design information for specific erosion and sediment control BMPs Perform Site Assessment and Feasibility Analysis As applicants perform the site assessment and feasibility analysis, they should keep in mind these LID principles: 1. Understand the site 2. Reduce runoff through design 3. Reduce pollutants carried by runoff 4. Capture and treat runoff. These principles are discussed in greater detail in Chapter 5. Lake Oswego Stormwater Manual Draft A site assessment and feasibility analysis is required for all project classifications. The goal of this analysis is to incorporate stormwater management into the landscape in a way that will preserve onsite drainage, soils, and native vegetation. Another important goal of the site assessment is to identify suitable locations for stormwater facilities before design actually begins on a project. The applicant will document soils, seasonal groundwater, existing topography, current hydrologic conditions and natural features, onsite vegetation, land use and zoning, and existing utilities. Completing the site assessment and feasibility analysis involves printing out a site map from LOMap (an interactive map website with geographic information system (GIS) data for these features), conducting a site visit, and gathering additional information as available. Section 5.3 has more guidance on performing the site assessment and feasibility analysis. 22

37 Stormwater Requirements Overview Underground Injection Control Review with Oregon Department of Environmental Quality Federal regulations require that owners/operators of certain types of stormwater facilities register them with the appropriate agency (DEQ in Oregon). The following facilities, which are included in this manual, are likely underground injection controls (UICs) that must be registered with DEQ: For confirmation of whether a specific facility is considered a UIC, refer to OAR and DEQ s website: state.or.us/wq/uic/uic.htm. Drywell Infiltration trench Proprietary Subsurface Facility Registration includes payment of a fee to DEQ based on the risk to groundwater and completion of a form that describes contributing area size and description, facility design information (e.g., depth and Owners/operators of such systems must complete the UIC General, Industrial and Commercial Stormwater Registration Application available at the DEQ website: ( deq.state.or.us/wq/uic/docs/ forms/genindcomsw.pdf). diameter, design infiltration rate), pretreatment, and site characteristics. Documentation of UIC registration with DEQ must be included with the drainage report prepared for a project that includes UIC(s) System Designed by Licensed Professional Because Lake Oswego is largely built out, only a limited amount of land is available for surface stormwater facilities, such as constructed wetlands and ponds. Since such facilities require a great deal of land area and will be placed within existing neighborhoods, it is essential that they fit in within the community context, reflect local aesthetics and character, and create a public amenity in addition to meeting water quality and flow control requirements. The City recommends that surface water facilities such as constructed wetlands, ponds, or rain gardens should be designed by a professional or team that understands how to incorporate the facility into the community context, improve aesthetics, and ensure water quality and flow control function. However, rain gardens for small projects do not need to be designed by a professional. Stormwater art in the landscape helps express local character. In addition, for medium and large projects with 1,000 square feet or more contributing impervious surface area, the City requires that designs of the following facilities must be stamped by a professional engineer: Drywell Infiltration trench Proprietary Subsurface Facility Detention pipes and vaults Detention ponds For large projects with 3,000 square feet or more contributing impervious surface area, designs of the facilities listed above and the following facilities must be stamped by a professional engineer: Rain garden (note that the maximum contributing area to a single rain garden is 6,000 square feet of impervious surface area). Planter Constructed wetland 23 Lake Oswego Stormwater Manual Draft

38 Stormwater Requirements Overview Wet pond Sand filter Pervious pavement (pervious concrete, porous asphalt, or pervious pavers) Swale Downstream Analysis In many parts of Lake Oswego, existing pipes are inadequate for the current level of development. When larger storm drains and new infrastructure must be constructed to accommodate increased flows from development, the costs are borne by all City ratepayers. The City of Lake Oswego has adopted a downstream analysis policy that links the relative contribution of the development activity and additional runoff to watershed area. The downstream analysis criterion is: Downstream analysis shall demonstrate adequate conveyance capacity to the distance where the project site contributes less than 10 percent of the upstream drainage basin area Drainage Report Required A drainage report must be submitted for all medium and large projects. The drainage report must document which minimum project requirements from Table 3.2 apply and must demonstrate that the project will meet applicable requirements. Calculations and drawings must be submitted as appendices to the report. The drainage report must address the following topics: Project Owner and Location Other Permits and Reviews (for all that apply) Project classification (small, medium, or large) Tree removal permit Land use planning review Sensitive lands overlay Special street setbacks Erosion control/1200-c permits Site Map (see Section for requirements) Minimum Project Requirements summarize which requirements apply and attach calculations demonstrating how they are met. Site Assessment and Feasibility Analysis Onsite stormwater management City of Lake Oswego Erosion Control Permit/ NPDES 1200-C Permit from DEQ Lake Oswego Stormwater Manual Draft 24

39 Stormwater Requirements Overview Underground Injection Control (UIC) review with DEQ Downstream analysis Recorded operations and maintenance plan Design for infiltration Design for flow control Attach the following: Infiltration test results UIC registration information (if applicable) Geotechnical report (if applicable) Soil testing results (if applicable) Calculations demonstrating sizing in conformance with BMP design guidelines Description of approved discharge location Appendix B contains a template for the drainage report with minimum submittal requirements Recorded Operations and Maintenance Agreement/Plan and Deed Restriction For projects that create or replace 1,000 square feet or more of impervious surface (medium and large projects), an operations and maintenance agreement/plan (OMP) is required. The OMP must describe how to properly maintain the facility, the frequency of maintenance required, and the party responsible for maintaining the facility. Chapter 10 provides information on recommended maintenance practices. However, the checklists in Chapter 10 are general and do not reflect site- and facility-specific criteria such as specific plants, maintenance access, and unique design features. An OMP that has been developed for a specific facility or site, such as the example provided in Appendix B, must be provided. In addition to registration with DEQ, owners/operators of facilities that manage stormwater from medium and large projects must file a deed restriction or recorded maintenance covenant in the county in which the property or facility is located. This step needs to be completed before the City will issue a Certificate of Occupancy. A copy of the deed restriction is provided in Appendix B Design for Infiltration/Design for Water Quality The City s MS4 permit requires that City- and development-related activities capture and treat 80 percent of the average annual runoff. LID and onsite stormwater management practices must be given high priority. New development must implement water quality facilities that reduce phosphorus by 65 percent, or to the maximum extent practicable. Phosphorus removal efficiency shall be calculated as summarized in the worksheet included with the drainage report template in Appendix B. Water quality design standard: Capture and treat 80 percent of the average annual runoff (1.0 inch in 24 hours) 25 Lake Oswego Stormwater Manual Draft

40 Stormwater Requirements Overview Because LID facilities, such as rain gardens, effectively capture stormwater in addition to treating it, the City prioritizes use of the following facilities. Medium and large projects, identified as design for infiltration/ design for water quality in Table 3.2, should implement the following facilities where feasible: Rain garden Planter Sheet flow dispersion Where sites are not suitable for infiltration, water quality treatment facilities that could be implemented include: Swale Constructed wetland Wet pond Sand filter Filter strip See Chapter 6 for stormwater facility selection guidance and Chapter 7 for design criteria and guidelines Design for Flow Control Flow control is required for Large Projects where soils are not suitable for infiltration. Where required, flow control facilities shall be designed to meet the following design standard: Flow control design standard: Maintain peak flow rates at their pre-development levels for the 2-year, 5-year, and 10-year, 24-hour runoff events. Chapter 7 has information on approved methods and rainfalls for these events NPDES 1200-C Permit from Oregon Department of Environmental Quality A 1200-C permit from DEQ is required for projects with land disturbance of 1 acre or more. An erosion control plan conforming to 1200-C requirements is acceptable for both City and DEQ requirements. These projects are also subject to the City s erosion control permit requirements, but a separate submittal is not required. The City will use the temporary erosion and sediment control documentation from the 1200-C permit to evaluate conformance with Lake Oswego s Erosion Control Permit. Refer to DEQ s website for information on the 1200-C permit: Lake Oswego Stormwater Manual Draft 26

41 3.6 Additional Guidance Exempt Projects Stormwater Requirements Overview The following developments are exempt from the minimum project requirements in Table 3.2: 1. Developments approved prior to implementation of the requirements in this manual are not subject to these requirements. 2. Repair or maintenance activities that are not considered to be replacement of impervious surfaces under the MS4 permit. These include repair or maintenance activities on structures or facilities taken to prevent decline, lapse, or cessation in the use of the existing impervious surface as long as no additional hydrologic impact results from the repair or maintenance activity Waiver and Payment/Fee in-lieu Program Information The City recognizes, as do state and federal regulators, that not all sites have suitable conditions for onsite stormwater management or preferred stormwater facilities that rely on infiltration. Conditions such as a high water table, shallow bedrock, steep slopes, and soils that are poorly drained or have low permeability characterize much of Lake Oswego. The City s MS4 permit requires the City to implement equivalent pollutant reduction measures for sites that cannot meet their stormwater management requirements onsite. Options identified in the MS4 permit include a payment-in-lieu program, a stormwater quality structural facility mitigation bank, or offsite mitigation within the same subwatershed as the project site. The City does not currently have a payment-in-lieu or offsite mitigation option. The City will be investigating options for providing equivalent pollutant reduction measures over the next several years and will update the stormwater program website, with any new information. 27 Lake Oswego Stormwater Manual Draft

42 Stormwater Process Overview 4.1 Review Process for Different Types of Projects New or Remodeled Home Figure 4.1 Lake Oswego Review Process - New or Remodeled Home Complete Site Assessment and Feasibility Worksheet See Appendix G Consultation with Engineering and Planning Staff Review minimum requirements in Stormwater Management Manual (Table 3.2) Discuss design options with Engineering and Planning (Chapter 7) Consultation with Planning Department Is the Property/Project subject to one or more of the permits, regulations, or requirements listed this chapter? YES See Land Use Review Process See Figure 4.3 Refer to Site Assessment and Feasibility Worksheet for site constraints and allowances NO Is a Building Permit Required? See Chapter 4.1 for Information YES NO Review Stormwater Management Manual for requirements that may apply even if your project is not subject to a land use or building permit. Submit construction documents describing your proposed work. Figure 4.1 provides an overview for the review process for a new or remodeled single-family home. When the applicant visits the City Planning counter, the Planning Department will review the proposed project to determine if there are land use and development review requirements. Most commonly, land use and development review will apply if one or more of the following apply: Lake Oswego Stormwater Manual Draft 28

43 Stormwater Process Overview Tree removal permit Tree protection plan Sensitive lands overlay Floodplain Heritage tree Zoning overlay Special street setback If land use and development review is not required, a building permit may be required. Building permits are needed for: All new construction Most remodeling projects, particularly when building safety may be affected Electrical, mechanical, or plumbing work that is subject to the Oregon Specialty Codes (Oregon Building Codes Division 2012). Construction documents describing the proposed work should be brought to meetings with the City s Engineering Department and should include: Two plan sets (legible and drawn to scale) including a site plan that shows the following: Property lines Lot dimensions Existing and proposed improvements with distances to property lines indicated Stormwater BMPs and drainage features with distances to property lines indicated Location and size of all trees located on the property Building permit application that includes the address of the existing building or, if for new construction, the legal description of the lot. Additional requirements apply for building, electrical, plumbing, and/or mechanical projects. See City website and consult Building Department for more information. Whether or not a building permit or land use and development review apply, the applicant should consult this manual to determine what stormwater management requirements apply. The City s Engineering Department can assist with stormwater requirements as well as the following: Utility location Driveways Street opening permits: All construction activities in the public right-of-way or within public utility easements require a street opening permit issued by the Engineering Department. For more information and submittal requirements, see street-opening-permit-application Erosion control permits Stormwater or sanitary sewer connection permits. 29 Lake Oswego Stormwater Manual Draft

44 Stormwater Process Overview Partitions, Commercial, and Multifamily Projects Figure 4.2: Lake Oswego Review Process 2-Lot Partition, New Commercial, Multi-Family, Subdivision, or Other Project Complete Site Assessment and Feasibility Worksheet See Appendix G Consultation with Engineering and Planning Staff Review minimum requirements in Stormwater Management Manual (Table 3.1) Discuss design options with Engineering and Planning (Chapter 7) Consultation with Planning Department Is the project a Minor or Major Development? (Planning Department will Determine Designation) OR Is the project subject to one or more of the permits, regulations, and/or requirements listed in Chapter 4.1? YES See Land Use Review Process See Figure 4.3 Refer to Site Assessment Worksheet for site constraints and allowances YES NO Is this project considered a ministerial development? <200 sq. ft. of impervious surface <10 ft. height Is a Building Permit Required? See Chapter 4.1 for Information YES NO Review Stormwater Management Manual for requirements that may apply even if your project is not subject to a land use or building permit. Submit construction documents describing your proposed work. See Chapter 4.1 Lake Oswego Stormwater Manual Draft 30

45 Stormwater Process Overview Figure 4.2 provides a simplified overview of the review process for other projects, such as two-lot partitions, new commercial, or multi-family projects. Land use and development review is not required for ministerial developments (less than 200 square feet of new or replaced impervious surface and less than 10 feet in height), unless one of the permits noted in Section is required. A building permit may still be needed, with the same triggers as noted in Section Stormwater management requirements will likely apply, depending on the amount of land disturbance and/ or new or replaced impervious surfaces. Section 3.4 of this manual provides guidance on determining which specific requirements apply Land Use Planning Full Review Projects that require land use and development review based on consultation with the Planning Department will be reviewed by staff from several departments throughout the application and design, construction, and operations and maintenance stages of project development. Figures 4.3, 4.4, and 4.5 provide an overview of activities and submittal and review responsibilities for both the applicant and City staff during all of these stages. Section 4.2 provides more information on the roles and responsibilities of different departmental staff related to stormwater management. 31 Lake Oswego Stormwater Manual Draft

46 Stormwater Process Overview Figure 4.3 Lake Oswego Review Process Application and Design Phase Phase 1: Applicant Preapplication Conference City Schedule preapplication conference with Planning Coordinator. Come prepared to discuss stormwater management including: How project will minimize impervious surface area How protect will protect and preserve native soils during construction (See Chapter 9) How project will meet onsite stormwater management requirments, if applicable (see Table 3..2). Proposed connection to City surface water management system. Plan to meet other minimum requirements that apply (Table 3.2). Applicant Planning Department will invite other department representatives as appropriate. Where stormwater management requirements apply (see Table 3.2), a representative from the Engineering Department will: Review stormwater management approach Convey stormwater standards and discuss stormwater management options Discuss site design options that can minimize stormwater management requirements and protect the native soils Discuss connections to City utilities Discuss right-of-way and sidewalk extension permits Discuss operations and maintenance requirements Visit the site, if appropriate City Phase 2: Project Application Submission The Applicant is responsible for submitting the following: The Planning Department will assign a land use casefile number and prepare a staff report Preliminary drainage report, including proposed BMPs (See Section 3.4 and Appendix B) Draft Operations and Maintenance Agreement/Plan (See Section 3.4 and Appendix B) Applicant City Phase 3: Land Use Decision If project is Approved: Proceed with design of project. Consult Stormwater Management Manual for submittal and design requirements related to stormwater. See Figure 4.4 for Construction Phase Review. If project is Approved with Conditions: Review conditions of approval. Contact Engineering Department if any of the conditions of approval related to stormwater are unclear. The Planning Coordinator will notify the Applicant of whether the application is approved, denied, or approved with conditions. Engineering Staff will start Stormwater Treatment Facilities (SWTF) file (for internal City use) if appropriate. If project is Denied: Consult with Planning and/or Engineer Coordinator for options. Lake Oswego Stormwater Manual Draft 32

47 Figure 4.4 Lake Oswego Review Process Construction Phase Stormwater Process Overview Applicant City Phase 1: Construction Plan Review Applicant submits construction plans and drainage report to Engineering. Submit two plan sets (legible and drawn to scale) that include all plan elements. Applicant Engineering Development Coordinator will: Review plans and applicable stormwater standards for SWTF per staff report conditions Issue construction permit for public infrastructure Schedule pre-construction meeting with contractors and owner City Phase 2: Construction Applicant pays 120% construction bond (engineer's public improvement cost estimate - EPICE) For public projects only Submit 9% project deposit for plan review Length: duration of construction phase Covers: contractor responsibilities Issued/released by: developer, includes letter of partial acceptance by Engineering Development Coordinator to developer/applicant's insurance company for release of bond. Applicant Engineering will: Ensure facility constructed per plans and sign off on completion Bond required to be posted before sign off by City Collect 120% construction bond City Phase 3: Post-Construction Applicant submits as-built drawings of facility. Applicant pays 10% two-year maintenance bond. Length: two years from issuance of Letter of Partial Acceptance Covers: public improvements Issued/released by: Engineering Applicant pays 5%-year and submits letter from landscaper to Planning Department. Length: two years from issuance of Partial Letter of Acceptance Covers: vegetation establishment, compost covering and functionality of the facility Issued/released by: Planning Department Engineering Development Coordinator Reviews as-built drawings of stormwater facilities Engineering and Planning Inspectors will coordinate final walk-through and punch list for compliance with conditions of approval Letter of Partial Acceptance Releases 120% construction bond Collects 10% maintenance bond and 5% landscape bond, as applicable. Engineering Staff updates SWTF file with bond dates and as-built numbers. Engineering Staff issues Final (100%) letter of acceptance 33 Lake Oswego Stormwater Manual Draft

48 Stormwater Process Overview Figure 4.5 Lake Oswego Review Process Operations and Maintenance Phase Phase 1: Applicant Operations and Maintenance Agreement Plan City Applicant submits operations and maintenance agreement/plan (OMP) to City. Final approved Stormwater Facility Operations and Maintenance Agreement shall be recorded with County Clerk by applicant. Applicant Engineering Staff will: Update SWTF file (add OMP) and submit to Engineering Development Coordinator Water Quality Program Coordinator will: File SWTF data for future inspections Enter project information in SWF database City Phase 2: One Year After Issuance of Letter of Partial Acceptance Owner submits one-year inspection and maintenance records in accordance with OMP Owner has 30-days to respond/rectify need and corrections notice(s) Phase 3: Applicant Ongoing Owner submits inspection and maintenance records in accordance with OMP. Engineering Inspector will: Perform one-year infrastructure inspection and prepare a needs and corrections list Engineering Development Coordinator will: Issue facility needs and corrections notice. City Water Quality Program Coordinator will: Schedule random inspections of 10% of facilities to ensure compliance with OMP Submit annual MS4 report to Oregon DEQ with information on each BMP: 4.2 Overview of Interdepartmental Responsibilities Several departments at the City are typically involved with review and permitting during planning, design, construction, and maintenance of new and rebuilding projects that include stormwater management requirements. This section provides a brief overview of City departmental responsibilities related to stormwater management Planning Department At the planning counter, applicants can learn what requirements apply to their project site (e.g., zoning, tree protection, and sensitive lands) and confirm whether the project is subject to land use review and building permitting requirements. Specific to stormwater, the Planning Department can provide information on the best locations to site a stormwater facility on a particular site to protect trees and meet setback requirements. Lake Oswego Stormwater Manual Draft 34

49 Stormwater Process Overview Engineering Department The Engineering Department provides stormwater review for the Building Department and for land use applications for partitions, subdivisions, and commercial development. The Engineering Department is the main point of contact for the following: Erosion control permit Street opening permit Confirming the locations of existing utilities, including stormwater Questions regarding capacity of existing storm drains or drainage ditches Clarifications on technical specifications related to stormwater facilities or conveyance facilities Stormwater submittals (e.g., drainage report, operations and maintenance plan) Building Department Building permits are required for most new construction and remodeling projects and for any projects that include electrical, mechanical, or plumbing work that is regulated by Oregon Specialty Codes (Oregon Building Codes Division 2012). Specific to stormwater, the Building Department will review any rainwater harvesting projects (other than rain barrels used strictly for landscape watering) to confirm that they conform to the Plumbing Specialty Code Public Works Operations Division Lake Oswego s Public Works Operations Division maintains public storm drains, ditches, storm drainage structures (e.g., catch basins and inlets), and non-vegetated stormwater facilities Parks and Recreation Department The Parks and Recreation Maintenance Division maintains public vegetated stormwater facilities, including rain gardens and planters located within street rights-of-way. 35 Lake Oswego Stormwater Manual Draft

50 Stormwater Management Criteria 5.1 TMDL Approved Areas/303(d) Listed Receiving Waters The Clean Water Act requires the State of Oregon to develop a list of impaired or threatened waters within the state. To meet that mandate, DEQ establishes water quality standards and prepares a list of impaired waters known as the 303(d) list. Waters are added to the 303(d) list if they do not meet the water quality standards set by DEQ. To address water quality issues in 303(d)-listed waters, DEQ must establish TMDLs for identified contaminants. A TMDL is the total amount of a contaminant a water body can accept without violating the water quality standard. Implementation plans are prepared to meet the TMDL goals and are implemented by Designated Management Agencies. The City of Lake Oswego is a Designated Management Agency for reaches of the Tualatin River, Springbrook Creek, Tryon Creek, and the Willamette River within the City s jurisdiction. The City is also the Designated Management Agency for Oswego Lake. TMDL Water Quality Management Plans require the City to work toward reduction in concentration of contaminants of concern, so stormwater facilities that discharge to those water bodies should be directed toward the reduction of the TMDL contaminants. Table 5.1 summarizes approved TMDLs and 303(d)-listed contaminants along with affected water bodies. Of the contaminants listed in Table 5.1, phosphorus, bacteria, and dissolved oxygen are most frequently associated with stormwater. New development must implement water quality facilities that reduce phosphorus by 65 percent, or to the maximum extent practicable. Phosphorus removal efficiency shall be calculated as summarized in the worksheet included with the drainage report template in Appendix B. The water bodies in Table 5.1 are within the City of Lake Oswego s jurisdiction and are listed as impaired on the 303(d) list or have an approved TMDL in place. These impaired watersheds account for nearly all of the City of Lake Oswego s area. For that reason, rather than adopt basin-by-basin approaches to targeting pollutants of concern, Lake Oswego is focusing on identifying stormwater facilities that are effective at targeting these pollutants and applying their use throughout the City. 5 Lake Oswego Stormwater Manual Draft 36

51 Stormwater Management Criteria Table 5.1 Total Maximum Daily Loads for Lake Oswego Water Bodies. Mangansese Iron Dieldrin DDT/DDE PAHs PCBs Mercury ph Phosphorus E.Coli Dissolved Oxygen Temperature Biological Criteria Fecal Coliform Chlorophyll a Ammonia Aldrin Aquatic Weeds or Algae Waterbody TMDL X X X X Oswego Lake/Oswego Creek X X X X X X X X X X X X X X X Fanno Creek Springbrook Creek Tryon Creek Tualatin River X X X Willamette River (and tributaries) 303(d) Oswego Lake/Oswego Creek X 37 Lake Oswego Stormwater Manual Draft Fanno Creek Springbrook Creek Tryon Creek X X Tualatin River X X X X X X X X Willamette River (and tributaries)

52 Stormwater Management Criteria 5.2 Low Impact Development Design Practices Low impact development is intended to reduce adverse hydrologic and water quality impacts of development on receiving waters and the environment by designing sites to mimic natural processes and replicate pre-development hydrology. LID is most effective when it is a strategy that is incorporated through all phases of site selection, planning, design, construction, and maintenance. While some LID techniques, such as permeable pavement, can have a higher construction cost than traditional methods, incorporating methods that reduce runoff generated or manage stormwater through dispersion or infiltration can save money by reducing downstream stormwater infrastructure costs relative to traditional development methods LID Principle #1 Understand the Site As applicants complete the site assessment and feasibility analysis (Section 5.3), they will collect information on onsite drainage, soils, native vegetation, depth to groundwater, existing topography, land use, zoning, and the surrounding site context. The goal of this analysis is to incorporate stormwater management into the landscape in a way that will preserve onsite drainage, soils, and native vegetation. Another important goal of the site assessment is to identify suitable locations for stormwater facilities before design begins on a project LID Principle #2 Reduce Runoff through Design LID can reduce the adverse ecological impacts associated with development. When there is less impervious area due to careful site planning and design, and native soils are protected or amended to preserve or promote infiltration, less stormwater enters streams as surface runoff. Consequently, hydrologic impacts to channels and other downstream receiving waters, such as increased peak flows or flow durations, are reduced. Reducing runoff through design means designing a project that is appropriate for and tailored to a particular site. It requires knowledge of the site, including localized depressions, soils with good infiltration capacity, and vegetation. Some key concepts include: Preserving and enhancing native vegetation to provide a high level of stormwater treatment Protecting native soils to preserve their infiltrative and treatment capacities Minimizing impervious surfaces through site design techniques In addition to minimizing impervious surface area and reducing runoff through design, careful site design techniques that work with natural topography, soils, and vegetation help create places that reduce impacts on the environment, are public amenities, increase habitat for native species, and beautify Lake Oswego. Stormwater BMPs included in this manual, including rainwater harvesting, green roofs, and pervious pavement, are options for further reducing stormwater impacts and stormwater management requirements. Lake Oswego Stormwater Manual Draft 38

53 Stormwater Management Criteria The following resources provide demonstrated effective methods for reducing runoff through design: Low Impact Development: Technical Guidance Manual for Puget Sound (PSAT and WSU 2005; update under development and scheduled to be released in Fall 2012): Green Streets: Innovative Solutions for Stormwater and Stream Crossings (Metro 2002): index.cfm/go/by.web/id=26335 Various publications, links, and resources available through the Oregon State University extension stormwater solutions webpage: LID Principle #3 - Reduce Pollutants Carried by Runoff Areas where water is currently infiltrating should be protected. Applicant should flag these areas so that construction vehicles do not compact soils. Soil retention. The duff layer and native topsoil should be retained in an undisturbed state to the maximum extent practicable. In any areas requiring grading/earthwork, remove and stockpile the duff layer and topsoil on site in a designated, controlled area, not adjacent to public resources and critical areas, to be reapplied to other portions of the site where feasible. Soil quality. All areas subject to clearing and grading that have not been covered by impervious surface, incorporated into a drainage facility, or engineered as structural fill or slope shall, at project completion, demonstrate: Topsoil layer has enough organic matter content (typically 10 percent in planting areas and 5 percent in turf areas) The correct ph balance (typically from and matching the ph of the original undisturbed soil) Existing and proposed improvements with distances to property lines indicated Additionally, subsurface layers should be scarified at least 4 inches with some incorporation of the upper material to avoid stratified layers, where feasible. Consider the quality of the compost and other materials used for planting beds. Typically, compost should have an organic matter content of 35 to 65 percent and a carbon:nitrogen ratio of 25:1-35:1. Mulch with a minimum of 2 to 3 inches of organic material. Additional information is provided in BMP T5.13 of the Stormwater Management Manual for Western Washington (Ecology 2012). 39 Lake Oswego Stormwater Manual Draft AND A minimum depth of 8 inches (except where tree roots limit the depth of incorporation of amendments Implementation. Consider the following when preserving and soil retention and quality. Leave undisturbed native vegetation and soil, and protect from compaction during construction.

54 Stormwater Management Criteria Amend existing site topsoil or subsoil either at the default recommended rates (listed above) or at custom-calculated rates based on tests of the soil and amendment. Stockpile existing topsoil during grading and earthwork, and replace it prior to planting. Stockpiled topsoil should be amended if needed to meet the organic matter or depth recommendations, either at the default recommended rates (listed above) or at a customcalculated rate based on tests of the soil and amendment. Import topsoil mix of sufficient organic content and depth to meet the recommendations listed above. To protect and improve the stormwater benefits provided by soils, including stormwater management and treatment, mulch existing landscape beds with materials such as shredded leaves, wood chips, and compost. Implement techniques like grass-cycling (leaving grass clippings on the lawn when mowing), and avoid overuse of soluble fertilizers and pesticides, which can damage beneficial soil life. More than one method may be used on different portions of the same site. Remember, soil that already meets the recommended depth and organic matter quality, and is not compacted, will likely not need to be amended. See and for more information on how to build soils, prevent weeds, reduce irrigation needs, and improve infiltration in existing soils LID Principle #4 Capture and Treat Runoff The applicant should keep runoff dispersed and design the site so that small areas of impervious surface either sheet flow to adjacent vegetation (sheet flow dispersion) or drain to a single bioretention facility (e.g., planter or rain garden) that is incorporated within overall site landscaping. Overflow routes shall be identified for all stormwater drainage from the proposed development, including overflows from BMPs. This information must be shown on the site map provided with the drainage report prepared for the project. Some design practices that can help to promote dispersion and avoid concentrating runoff include: Managing stormwater on site through infiltration to avoid impacting downstream receiving waters. Incorporating amended soils where existing soils lack sufficient organic matter or physical properties to remove pollutants through adsorption, filtration, or other processes remove pollutants. 5.3 Site Assessment and Feasibility Analysis LID Principle: Understand the Site Section 2.3 of this manual describes some of the results of urbanization and the impacts on water bodies in the City of Lake Oswego. These impacts include: Physical impacts to streams that degrade habitat and consequently threaten aquatic life Flooding of storm drains and ditches Discharge of pollutants that affect the water quality of rivers, streams and Oswego Lake Discharge of pollutants that affect human health as well as that of animals Lake Oswego Stormwater Manual Draft 40

55 Stormwater Management Criteria Many of these problems are attributable to the historic approach to development that transformed the landscape without considering all of the consequences. This approach frequently created impervious surfaces that severely affect the way water moves both above and below the ground and ignored stormwater runoff and associated pollutants as long as it could be safely transported away from development. Today, there is much greater awareness of the impacts of stormwater runoff and an understanding that development needs to be balanced to protect the natural resources that humans and other species depend on: clean water, soils, and vegetation. We effectively balance today s community needs with the need to preserve clean air, water and land resources for future generations. The built environment is designed to protect, enhance and be integrated with natural systems. -Lake Oswego Comprehensive Plan Selecting the right stormwater management technique should start as early as possible in the planning and design process. Before the site design is developed and before any construction commences, the City requires that applicants and/or site operators complete a site assessment and feasibility worksheet to evaluate site hydrology, topography, soils, vegetation (including vegetation that will be preserved) and any other features that demonstrate how stormwater moves through the site prior to development. This worksheet serves as an integral communication tool between the applicant and the City regarding existing stormwater runoff on the property and how the intended or proposed development activity may affect the existing runoff characteristics. The goal of the site assessment and feasibility analysis is to incorporate stormwater management into the landscape in a way that will preserve onsite drainage, soils, and native vegetation. Another important goal of the site assessment is to identify good locations for stormwater facilities before design actually begins on a project. Applicants must conduct the site assessment and feasibility analysis prior to consulting with City Building or Planning departments. Site assessment and feasibility analysis involves three steps, which are outlined in this section Site Map A site map is required as part of the drainage report. Much of the information required on the site map can be collected during the site assessment and feasibility analysis. Appendix G summarizes information needed for the site map, along with the corresponding step of the site assessment and feasibility analysis. At a minimum, the site map should document the following: Contours Property lines Lot dimensions Protected areas and preserved areas(trees to be preserved onsite, sensitive lands, water bodies) Building/land disturbance activity boundaries Proposed areas for stormwater management Drainage patterns (including depressions where stormwater appears to infiltrate and offsite drainage, if applicable) Appendix G provides a checklist for the site map and the other information that should be submitted as part of the site assessment and feasibility analysis. 41 Lake Oswego Stormwater Manual Draft

56 Stormwater Management Criteria Step 1 City Geographic Information System Data Evaluation Before conducting a site visit, printing a map that shows the locations of sensitive lands, structures, soil information, and other site information will provide helpful background information and will allow the applicant to field verify the GIS data during the site visit. To simplify this process for the applicant, the City has developed an interactive map website called LOMap. LOMap is an online tool that provides GIS data for many of the site attributes needed for a proper site analysis. GIS layers within the mapping tool include: Tax lot data Neighborhood associations Zoning information Environment layers (Federal Emergency Management Agency [FEMA] flood zones, USGS soil information, and fault lines) Utility locations Planning information (design districts, heritage trees, historic landmarks, permits, special street setbacks, commercial overlays, and sensitive lands) Fire information As-built drawings Parks Maps can be created with necessary data layers and printed or saved for future reference and sharing. The mapping tool is found online at: For instructions on how to use LOMap, go to: Step 2 - Site Visit If sandy or gravelly soils are observed, this may be a good site for a drywell or infiltration trench. Sandy or gravelly soils often have infiltration rates that are too high to provide effective treatment, so include a filter strip, swale, or other treatment BMP prior to infiltration BMP. Note that registration of a BMP with DEQ may be required if it is considered a UIC Soils Verify whether onsite soils match the USGS soil information or if further investigation is needed. To do this, the applicant should dig some small holes in a few representative areas scattered throughout the site to inspect the soils. By moistening a medium-sized handful of soil in their hand and rubbing a small amount between their fingers, the applicant can determine soil texture. Lake Oswego Stormwater Manual Draft 42

57 Identify whether site soils are predominantly: Sandy or a sandy loam Stormwater Management Criteria Individual sand particles can be distinguished between fingers and soil contains more sand than clay or loam? Does the soil appear to drain well? Silty or silty loam Does the soil feel smooth and chalky when moistened and rubbed between fingers? Clay or clay loam Does the soil feel sticky and hold together when moistened? Will the soil form a flat ribbon of 1 to 2 inches in length if kneaded and threaded through finger tips? See Appendix C for more information on how to read characteristics within site soils. Are there areas of protected native soils and/or amended soils that have been added for stormwater management function? These soils might be evident by the presence of healthy native vegetation. They would also be loose and uncompacted and infiltrating stormwater Topography To reduce construction and post-construction impacts, work should be conducted within the existing topography to the maximum extent practicable. The design should be developed in a way that works with existing grades: Plan the project to minimize land disturbance such as clearing and grading and cut and fill Keep cut and fill slopes as flat as practicable and consistent with soil stability Hydrology Where is the water draining? This will be easier to confirm on a rainy day, but even in dry conditions, general drainage patterns should be evident. Note the following: Locations of catch basins, inlets, ditches, and other stormwater facilities Depressions where water likely ponds and/or infiltrates during storms Offsite areas that slope toward the property and may contribute offsite drainage Areas where drainage from the site appears to drain to neighboring properties If ponding water is observed on areas of clay soils, confirm that area is not a jurisdictional wetland (consult with Planning Department). If not, and if stormwater facility is required, consider this area for constructed wetland or wet pond. If an onsite stormwater management or water quality treatment BMP is not needed, consider incorporating this wet area into landscaping plans through use of wetland plantings. 43 Lake Oswego Stormwater Manual Draft

58 Stormwater Management Criteria Vegetation Note location and size of all trees located on the property. Identify patches of native vegetation, invasive species and weeds, and dominant vegetation cover types. Several BMPs are not suitable near or on steep slopes (see Table 6.1). Confirm safe drainage route to prevent concentrated stormwater from draining down steep slopes. Confirm setbacks from sensitive areas. Select a vegetated BMP with habitat features and plant selection appropriate for the species and habitat present. If site was previously developed and site history is unknown, test soils for contamination Sensitive Areas Are there steep slopes (greater than 25 percent) on the site? Identify these areas on the site map. Are there wetlands, streams, areas with significant erosion, or other potentially critical areas observed? Development should be designed to avoid sensitive areas. In addition, construction activities should be planned to avoid discharge into sensitive areas (see Chapter 9) Existing structures Identify areas of existing structures, including parking areas, buildings, sheds, and any impervious surfaces Step 3 - Collect Other Data, if Available City staff may have information on previous site development as well as stormwater facilities observed during the site visit. Neighbors may be able to describe past land uses on and surrounding the site, and areas where they have noticed ponded water or water leaving or entering the site. They may also be willing to share observations about infiltration rates on their own site that may be representative of the area Soils Opportunities for infiltration are constrained by soil conditions. As noted in the Clean Streams Plan (Otak 2009), nearly half of the soils in Lake Oswego are classified as belonging to Natural Resources Conservation Service (NRCS) hydrologic soil group C. Another 30 percent of the soils are classified as group D, and the remainder of the soils are categorized as group B. Soil properties related to hydrologic soil groups affect infiltration potential as follows: Group B soils have a moderate infiltration rate. They include soils of moderately fine and moderately coarse texture and are generally most suitable for water quality treatment and disposal through infiltration. Group C soils are typically fine-textured soils (e.g., tills) with slow infiltration rates. These soils may be appropriate for infiltration facilities designed for treatment but are unlikely to have adequate infiltration rates to handle high runoff volumes. Group D soils, which include clays, have very slow infiltration rates or a high runoff potential and are not suitable for infiltration. Lake Oswego Stormwater Manual Draft 44

59 Stormwater Management Criteria Figure 5.1 provides a soils map of Lake Oswego. Check GIS data available from the City and online soils data from NRCS to evaluate whether soil conditions are likely to be favorable for infiltration. Test infiltration rates (Appendix D) and soil quality to assess suitability for infiltration and pick the best location for LID BMPs. Figure 5.1 Lake Oswego Soils Map. City Of Lake Oswego Soil Hydrologic Groups Soil Group A B C D Oswego Lake Miles 10/09/ Depth to Groundwater Information on depth to groundwater can be found on the USGS website: 45 Lake Oswego Stormwater Manual Draft

60 Stormwater BMP Selection 6 Lake Oswego is required to prioritize LID stormwater practices and reduce pollutants associated with 303(d)-listed and TMDL water bodies. The City prioritizes implementation of LID by requiring that all Small, Medium, and Large projects as defined in Section 3.4 use and prioritize onsite infiltration to the maximum extent practicable. Recent research by the Washington State Department of Transportation and the Washington Stormwater Center have found that LID stormwater facilities perform very well in reducing concentrations of total suspended solids, dissolved metals, fuel and oils, and other pollutants. However, preliminary water quality monitoring has found export of phosphorus from LID BMPs (concentrations are higher after treatment). The compost used as soil amendment in LID BMPs, which is critical to plant health, is high in nutrients such as phosphorus. Preliminary monitoring investigations suggest that export of pollutants is especially high in the months following installation. Ongoing research is being conducted by the Washington Stormwater Center and various municipalities on whether construction practices or soil mixes can be modified to reduce export of nutrients from these facilities. Given the sensitivity of Oswego Lake to phosphorus, the City is following this research and will be updating biofiltration soil mix recommendations and/or BMP design and construction practices based on research findings. 6.1 List of Approved Stormwater Best Management Practices Table 6.1 lists BMPs that are included in this manual and approved for use in Lake Oswego, and indicates which minimum project requirements they meet. (Applicable minimum project requirements are summarized in Table 3.2.) Infiltration Best Management Practices Soil Testing Some LID and infiltration BMPs are NOT appropriate for areas with contaminated soils. Restrictions apply to the following BMPs: Pervious pavement Sheet flow dispersion Rain garden infiltration Planter infiltration Drywell Infiltration trench If a potential infiltration facility drains into or is within 100 feet of a stream, lake, open water, or wetland, soils should be tested for toxic pollutants. Guidelines are being developed by the City as they develop water quality management plans to comply with TMDLs. Consult for current requirements and sampling protocols. Lake Oswego Stormwater Manual Draft 46

61 Stormwater BMP Selection Soil Testing Infiltration rate testing is required where infiltration facilities are proposed. Subsurface soil assessment and modified soil infiltration tests shall be conducted by using a pilot infiltration test (PIT). Guidance for conducting a PIT test is included in Appendix D Setbacks Stormwater facilities that meet the infiltration minimum project requirements per Table 6.1 are subject to the following horizontal setback requirements: Ten feet between the edge of the facility and the edge of the structure 100 feet from contaminated site 100 feet from drinking water supply wells or springs 10 feet from septic systems or drain fields 10 feet of underground storage tanks 5 feet from property lines without neighbor agreement A geotechnical report is required for to determine setbacks for infiltration facilities on slopes 15% or within 200 ft of a steep slope hazard area or landslide hazard area Underground Injection Control Devices If an applicant proposes a UIC, the applicant must demonstrate that the UIC is either authorized by rule or has a UIC permit associated with the facility. Additionally, if the UIC owner/operator cannot obtain DEQ approval, the UIC system must be formally closed and follow DEQ s guidelines for closing the UIC. See for more information Sensitive Areas Lake Oswego Code requires that a report evaluating soil conditions and potential hazards be submitted to the City Manager where development is to occur on a potential severe erosion or landslide hazard area. The report shall be prepared by a registered soils engineer or engineering geologist and shall contain the following: Evidence that a field investigation was made to determine the actual hazard. Statements regarding the exact nature and extent of the hazard. Recommendations on site preparation and construction methods to minimize the effects of the hazard. If erosion hazard exists, a specific erosion control plan to be approved by the City Manager, in accordance with LOC Chapter 52, Erosion Control. A description of any hazard area that should not be disturbed by construction. 47 Lake Oswego Stormwater Manual Draft

62 Stormwater BMP Selection If landslide hazard exists, a statement as to whether or not a proposed development constructed in accordance with the recommended methods is reasonably likely to be safe and to prevent landslide or damage to other property Use and Approval of Proprietary Stormwater Best Management Practices Proprietary devices are manufactured technologies that remove pollutants through hydrodynamic physical, chemical, or biological treatment processes. Lake Oswego allows use of proprietary stormwater facilities where other facilities are not feasible due to site constraints (e.g., steep slopes). City approval is required, and only facilities that have been tested and approved through the TAPE program run by the Washington State Department of Ecology will be permitted. (There is currently no comparable program in Oregon.) Under the TAPE program, technologies are field tested to evaluate whether they meet criteria for various levels of treatment (basic, dissolved metals, phosphorus, oil, and pretreatment). Basic treatment technologies remove 80 percent or more total suspended solids. Dissolved metals technologies meet basic treatment goal and remove 30 percent or more dissolved copper and 60 percent or more dissolved zinc for influent concentration ranges. Phosphorus meets basic treatment goal and removes total phosphorus. Technologies that have been or are being tested under the program are assigned use level designations as follows: Pilot Use Level Designation (PULD) laboratory data suggests that technology may meet the performance goal Conditional Use Level Designation (CULD) both laboratory and field data suggest likelihood of meeting performance goals General Use Level Designation (GULD) technology is approved by the Washington State Department of Ecology. Lake Oswego accepts proprietary technologies that have GULD for basic, dissolved metals, or phosphorus treatment as water quality treatment BMPs, as long as City has approved use of proprietary BMPs for the project. Lake Oswego allows use of proprietary technologies with GULD for pretreatment without approval by the City. Proprietary technology use level designations are posted the Washington State Department of Ecology s website at: Lake Oswego Stormwater Manual Draft 48

63 Table 6.1 Stormwater Management Best Practices. Stormwater BMP Selection Minimum Project Requirements from Table 3.2 Approval Manual Section Title Green roof Pervious pavement surface Pervious pavement facility (receives run-on) Sheet flow dispersion LID Site Design Technique On-Site Management Flow Control Water Quality Treatment Infiltration Rain garden infiltration Planter infiltration UIC Pretreatment Required? City Approval Required? Drywell or proprietary infiltration chamber Infiltration trench Constructed wetland Constructed wetland with detention storage Rainwater harvesting Sand filter Wet pond Infiltration pond Detention pond Detention pipes and vaults Filter strip Swale Proprietary treatment BMP 6.2 Small and Medium Projects Bioretention BMPs (e.g., rain gardens and planters) are the preferred BMPs for small sites because they provide treatment and flow control, are not considered UICs (unless they have an underdrain that discharges to a drywell or other UIC), and when well-designed can be a beautiful part of the landscape. Bioretention BMPS with underdrains are suitable in areas only where onsite soils have proven suitable for bioretention and there is not a risk of phosphorous export to surface water bodies. Compost-amended soils can export phosphorus as noted in Chapter Lake Oswego Stormwater Manual Draft

64 Stormwater BMP Selection Where rain gardens and planters are not feasible due to site constraints, infiltration trenches, drywells, or proprietary infiltration chambers may be used. Since these technologies are considered UICs, they will need to be permitted through DEQ (see Section 3.5.4). Where an impervious surface is surrounded by lawn or landscaping, onsite stormwater management requirements may be met through sheet flow dispersion (see Section 7.4.1). Registration forms for UICs can be found on DEQ s website at: forms.htm) Submit documentation of registration along with drainage report. 6.3 Large Projects Large projects must meet water quality and flow control requirements, in addition to onsite stormwater management requirements, where applicable. Best management practices to minimize impervious surface and overall stormwater management requirements must be considered first. These include: Installation of green roof Installation of pervious pavement Rainwater harvesting Onsite preservation of vegetation Soils management to preserve onsite infiltration Minimizing the use of hard/impervious surfaces like impervious flat work (patios, driveways, walkways) Stormwater from remaining impervious surfaces should be managed with BMPs that provide both flow control and water quality. BMPs that will meet onsite stormwater management, water quality, and flow control requirements include: Rain garden Planter Combination of an infiltration or flow control BMP from Table 6.1 with a water quality treatment BMP from Table 6.1. If onsite stormwater management requirements apply, onsite stormwater management facilities should be sized to infiltrate 100 percent of the 10-year, 24-hour design storm (3.2 inches in 24 hours). If only water quality and flow control requirements apply, water quality BMPs should be sized to infiltrate the water quality design storm (1 inch in 24 hours.) Lake Oswego Stormwater Manual Draft 50

65 7 Stormwater BMP Standards and Specifications 7.1 Performance Standards Table 7.1 summarizes the performance standards that shall be used for BMP sizing. Table 7.1 Performance Standards for BMPs. BMP Category Performance Standard Precipitation Onsite stormwater management Infiltrate the runoff volume from 3.2 inches the 10-year, 24-hour storm event within 24 hours Water quality Capture and treat 80% of 1.0 inch average annual runoff Flow control Maintain peak flow rates at their pre-development levels for the 2 year, 24 hour storm: 2.38 inches 2-year, 5-year, and 10-year, 24- hour runoff events 5 year, 24-hour storm: 2.85 inches 10 year, 24-hour storm: 3.20 inches Pretreatment The following BMPs are approved for providing pretreatment where required (see Table 3.2): Filter strips Swales Proprietary BMPs approved under the TAPE program with a general use level designation for pretreatment Catch basins with a sump greater than or equal to 12 inches are considered to provide pretreatment via settling Onsite Stormwater Management Table 7.2 summarizes design considerations for onsite stormwater management facilities. 51 Lake Oswego Stormwater Manual Draft

66 Stormwater BMP Standards and Specifications Table 7.2 Onsite stormwater management facilities. Facility Design Performance Goal Design Considerations Rain garden/planter Capture and store the design storm in a surface pond for infiltration through the biofiltration soil medium. Where soil infiltration rates are not high enough to allow 100 percent infiltration, infiltration BMPs must be implemented to the maximum extent possible, and an approved discharge location must be identified. These facilities should be designed to drain in 24 hours. Drywell Infiltration trench Capture and store the design storm in a drywell for infiltration through the underlying soils Capture and store the design storm in a gravel-filled trench for infiltration through the underlying soils. Design as distributed facility with no more than 6,000 square feet of contributing impervious surface area. Rain gardens and planters with underdrains are suitable in areas only where onsite soils have proven suitable for bioretention and there is not a risk of phosphorous export to surface water bodies. Compostamended soils can export phosphorus as noted in Chapter 5. Where soil infiltration rates are not high enough to allow 100 percent infiltration, infiltration BMPs must be implemented to the maximum extent possible, and an approved discharge location must be identified. This facility is a UIC that must be registered with DEQ. Documentation of facility registration must be provided to the City. Where soil infiltration rates are not high enough to allow 100 percent infiltration, infiltration BMPs must be implemented to the maximum extent possible, and an approved discharge location must be identified. This facility is a UIC that must be registered with DEQ (unless constructed without an underdrain). Documentation of facility registration must be provided to the City. See Section 7.6 for design guidelines. Lake Oswego Stormwater Manual Draft 52

67 Stormwater BMP Standards and Specifications Water Quality Water quality BMPs must be to sized capture and treat 80 percent of the average annual stormwater runoff. This is equivalent to treating runoff from up to the first 1.0 inch of an individual storm event. Therefore, design storm volume for volume-based BMPs (constructed wetlands, wet ponds, planters, and rain gardens) can be calculated as the total runoff volume from a storm with 1.0 inch of precipitation. Similarly, design storm discharge for flow-based BMPs (swales, filter strips) can be calculated as the peak discharge from a 1.0-inch, 24-hour storm using the Santa Barbara Urban Hydrograph (SBUH) method and a synthetic NRCS Type 1A hyetograph. Table 7.3 Water Quality Treatment BMPs. Facility Design Performance Goal Other Considerations Rain garden/planter Capture and treat the design Design to drain in 24 hours. storm in a surface pond for infiltration through the Design as distributed facility with no more biofiltration soil medium. than 6,000 square feet of contributing impervious surface area. Bioretention facilities with underdrains are suitable in areas only where onsite soils have proven suitable for bioretention and there is not a risk of phosphorous export to surface water bodies. Compost-amended soils can export phosphorus as noted in Chapter 5. Swales/filter strips Wet ponds and constructed wetlands Sand filter Provide treatment through filtration by vegetation as water is conveyed through the facility. Capture and treat the runoff volume associated with the water quality design storm event. Capture and treat the peak flow associated with the water quality design storm event. Provide minimum residence time of 9 minutes. Remove pollutants through contact with sand media at a hydraulic rate sized to ensure drawdown time of 24 hours Flow Control Where soils are not suitable for infiltration, flow control may be needed for large projects. Where required, flow control facilities shall be designed to maintain peak flow rates at their predevelopment levels for the 2-year, 5-year, and 10-year, 24-hour runoff events (see Table 7.1). 53 Lake Oswego Stormwater Manual Draft

68 Stormwater BMP Standards and Specifications Table 7.4 Flow Control BMPs. Facility Design Performance Goal Other Considerations Infiltration pond, infiltration trench, drywell Detention pond or constructed wetland or wet pond with storage Detention pipes or vaults Rainwater harvesting 7.2 Planting Design Infiltrate all or part of stormwater runoff. If there is any surface discharge from facility, flow control standard must be met: Maintain peak flow rates at their pre-development levels for the 2-year, 5-year, and 10-year, 24- hour runoff events. Maintain peak flow rates at their pre-development levels for the 2-year, 5-year, and 10-year, 24- hour runoff events Maintain peak flow rates at their pre-development levels for the 2-year, 5-year, and 10-year, 24- hour runoff events Capture and store for reuse all or part of stormwater runoff. If there is any surface discharge from facility, flow control standard must be met: Maintain peak flow rates at their pre-development levels for the 2-year, 5-year, and 10-year, 24- hour runoff events Why Plants Matter in Stormwater Design Facility is a UIC that must be registered with DEQ. Constructed wetland or wet pond with storage also provides water quality treatment. Plants play several important roles in the function of stormwater Picking the Right Plant for the facilities while also providing the living components that contribute Right Place to the aesthetic quality of the landscape in Lake Oswego. Planting In order for plants to thrive and for design should respond to variable environmental conditions (e.g., soil a stormwater facility to achieve moisture conditions, sun exposure, existing infrastructure, setbacks long-term success, planting and site distances, pedestrian use and interaction, existing plant design must carefully consider communities and invasive species control, and visual buffering) in the placement of each plant within and around a facility. The design conjunction with surrounding community aesthetics and values. should consider the mature height For infiltration facilities, it is important to choose plants that do not and spread of each plant and require the use of fertilizers or pesticides to thrive. Plants should respond to environmental and also be adapted to local climate conditions and require little to no cultural site conditions. extra watering after the first two years of establishment. In addition to picking the right plant for the right place for environmental or social reasons, there are several other factors that can affect plant selection and planting design. This section describes some of the most critical factors to consider in planting design and outlines a strategy for ensuring appropriate plant selection. Lake Oswego Stormwater Manual Draft 54

69 Stormwater BMP Standards and Specifications Vegetation Diversity and Its Effect on Water Quality Diversifying vegetation in stormwater facilities can significantly improve water quality treatment effectiveness by enhancing the ecological function and unit treatment processes occurring in stormwater facilities. Diverse native vegetation improves water quality by: Reducing sediment load: The stems and leaf blades of vegetation intercept stormwater and act as physical filters by capturing sediment and associated pollutant particles. Emergent plant species are particularly suited to reducing sediment load because of their plant structure and adaptation to water inundation and saturated soils. Reducing water velocity: Vegetation reduces the velocity of water moving through a stormwater facility, allowing more time for pollutants to settle to the bottom and minimizing turbulence that may otherwise induce re-suspension of sediments previously deposited in the pond bottom. Plants play an important role in filtering sediment and pollutant particles from stormwater. Increasing ability of soil to absorb and filter pollutants: Root systems increase the potential for water to filter through soil, which increases the adsorption, sorption, and anion exchange interactions that remove pollutants in stormwater. Absorbing pollutants into plant matter: Plants will absorb some pollutants and heavy metals through their root systems and transfer them into their tissues. Plant species vary in their ability to assimilate pollutants and toxins into their tissues. For example, cattail species have demonstrated the ability to uptake a wide variety of pollutants, while burreed species have proven to be the most efficient at uptake of lead, zinc, and TPH (Seattle 1993 ). For stormwater facilities in which vegetation is used as a part of the pollution removal process, plants may have to be replaced and disposed of as hazardous waste. Vegetation growing in a stormwater facility can act both as a physical filter (causing gravity settling of particulates by regulating velocity of flow) and also as a biological sink (via direct uptake of dissolved pollutants) (Ecology 2012). The physical filtration process results in sediment removal, while the biological uptake component can result in removal of metals, phosphorus, and nitrogen from the water. Dense, healthy vegetation will provide good filtration and biological uptake in a stormwater facility. 55 Lake Oswego Stormwater Manual Draft

70 Stormwater BMP Standards and Specifications Indicators of degraded filtration and biological uptake include: Low plant density: bare soil and sparse vegetation on facility bottom and side slopes Unhealthy plant community: poor apparent health of the plant community. Monocultures: a planting comprised or dominated by a single species Visual indicators of plant stress or disease might include: Leaf cupping, curling, or rolling Himalayan blackberries dominate this plant community and are an indicator of poor plant community health. Yellowing, browning, or abnormally discolored leaves Wilting or abnormal drooping Unseasonal leaf drop Stunted leaf or plant growth An indicator of proper filtration and biological uptake functioning is a diverse and healthy plant community. Specifically, a diverse and healthy plant community comprises a variety of native species with little or no invasive species present and shows little to no stress, indicating plants are adapted to the site conditions and water fluctuations. This constructed wetland has a healthy variety of native trees, shrubs, and groundcover species simultaneously providing water quality benefits and a neighborhood amenity. Clean Water Services Lake Oswego Stormwater Manual Draft 56

71 Stormwater BMP Standards and Specifications Plant Selection Process: Steps and Considerations The following section describes one way to approach planting design for a stormwater facility. A summary of the plant selection process can be found in Figure 7.2. Figure 7.1 Plant Selection Process. Step 1 Information Gathering Conduct site analysis and collect relevant project information Step 2 Plant Selection Select appropriate plants for BMP and site location. REVISE PLANT SELECTION Step 3 Check Availability of Plant Selection with Local Nurseries Are the selected plants available, or is there enough time to contract a nursery to grow or aquire the plants needed? YES NO REVISE PLANT SELECTION Step 4 Review Maintenance Requirements of Plant Selection and Placement Does the plant selection align with long-term maintenance expectations, capabilities, and resources? NO YES Step 5 Update Construction Documents, Plans, and Specifications to Guide Installation and Establishment of Vegetation 57 Lake Oswego Stormwater Manual Draft

72 Stormwater BMP Standards and Specifications Step 1: Information Gathering Before plant selection can begin, the applicant needs to gather information about existing and proposed site conditions, the surrounding site context, desired future uses of the site, aesthetic requirements, and maintenance considerations that should influence design. Each stormwater facility should be designed in response to the unique characteristics and circumstances of its location. Information gathering should begin by evaluating the following site characteristics and site circumstances, including but not limited to: Determine hydrologic regime (micro-topography) (for example, infiltration facilities need plants that tolerate both saturated and dry periods) Is groundwater present (less drying/moist soils)? How does water move through and interact with the site? Evaluate site soils to determine soil composition and design characteristics Is a soil test needed to verify quantity of organic matter, identification of potential contamination, or nutrient contents? If amendments can be used rather than importing new soil, what types of amendments are appropriate for the proposed facility type? Determine the light duration and intensity of sunlight across the site Observe the surrounding context Determine if the site is near a natural area, designated sensitive area, within a neighborhood, or within a commercial district How can the planting design help the facility respond or adapt to the surrounding context? Access whether there are potential contaminant inputs and outputs from surrounding areas Are there any potential sources of contaminants that need to be mitigated in the site design (e.g. heavy road traffic, an industrial land use, car wash, etc.)? Document whether or not the site is adjacent to or near any of Lake Oswego s natural areas Is there an opportunity for the site to provide additional habitat connectivity or value for a fragmented natural area? Are there particular species that may be attracted to the site (bird populations, amphibians, butterflies, etc.) and that may benefit or be harmed by its location? See Parks Plans 2025: Lake Oswego s Parks, Recreation and Natural Areas System Plan for more information on Lake Oswego s parks and natural areas and how they relate to stormwater and habitat management goals for Lake Oswego (Lake Oswego 2012). Are there reference habitats nearby that provide clues to choosing an appropriate plant selection? Lake Oswego Stormwater Manual Draft 58

73 Determine desired future uses Stormwater BMP Standards and Specifications Is there a community desire or opportunity to incorporate multiple uses for the facility? For example, can trails, art, or wildlife viewing be incorporated into the design? Is the site highly visible? Will the site provide educational opportunities for neighborhood, community, or school groups? Should the facility blend into the surrounding context or make an artistic statement? Evaluate the aesthetic requirements and drivers for the site What personal or contextual ways can plants be organized? How can edges and borders be clearly organized around landscape facilities to ensure stewardship and not marginalization due to perceived messiness? Step 2: Plant Selection After gathering enough information about the site being designed, it is time to begin plant selection. As a rule, the applicant should select plants that will provide for year-round water quality and aesthetic functions. Native plants should always be considered first to meet design goals. (See following description of native This planting border has been overtaken by weeds and does not show clear signs of care. versus non-native vegetation to learn more about the advantages of planting native species.) If native species cannot meet the design needs of a site due to specific environmental or cultural goals, horticulturally appropriate species (that is, species that are well adapted to local site conditions and reliably perform well in stormwater facilities) can be used to supplement a native plant selection. All plant lists and species selections should be created based on species available from local nurseries. The justification for following this protocol is explained below. Native versus Non-Native Vegetation Planting native plants should be a priority for stormwater facilities for several reasons.: Native plants are adapted to local soil, hydrology, and climate conditions. Native plants compete with invasive species that threaten to overtake facilities and create monocultures. Native plants soften the transition from developed landscapes into natural areas. Native vegetation also provides the following aesthetic benefits: Native plant species placed in natural-looking clusters can better blend stormwater facilities into adjacent natural areas, open spaces, and neighborhoods. A diversity of native plants and use of trees and shrubs in addition to low-growing species creates a more park-like visual experience for the community. Native vegetation provides wildlife habitat and the presence of beneficial organisms (pollinators, food and forage, shelter). 59 Lake Oswego Stormwater Manual Draft

74 Stormwater BMP Standards and Specifications Native: A species that occurs naturally in a particular region, ecosystem, and habitat. Native (Other definition): Plant species that occurred naturally in a particular region, ecosystem, and habitat prior to European contact. Acceptable non-native or horticultural: Annual or perennial species that is not persistent or competitive with native vegetation. Some non-native, horticultural species are suitable for stormwater facilities. These species are usually chosen when a site is located within a highly developed area where an applicant has a specific design goal in mind. They are also beneficial when the mature size of native species is too large to be accommodated in a facility (e.g., narrow parking swales, flow-through planters alongside buildings, etc.) and a specific type of species is desired. For some BMPs, such as green roofs, there are only a few native species easily found in nurseries, and it is useful to augment the planting palette with nonnative, horticultural species. In these instances, plant lists should be reviewed and approved by a local botanist or landscape architect. Step 3: Review Availability of Plant List with Local Nurseries Naturalized species: Nonnative species that were introduced by humans to a region, ecosystem, and habitat, but have now become a part of natural native plant communities. Undesirable plant species: Plant species that are on the region s noxious weed list and plants that outcompete and dominate native plant communities. It is important to make sure that the plants selected for a design are available at a local nursery. If a plant list contains species that are not typically available or are requested in an unusual quantity, a nursery can often help find the plants needed if given enough time. Some nurseries can even grow species not normally within their selection if they are given at least a year of advance notice. If the project timeline is shorter than a year between design and installation, which is often the case, the need to verify availability of plant species is even more important. The more a designer can collaborate and communicate with local nurseries prior to plants being delivered to a project, the more likely a design will end up with the plants intended in the facility design. Step 4: Evaluate Maintenance Requirements for Preliminary Design During the design development process, it is important to consider the maintenance needs, limitations, and consequences of design decisions. Review operations and maintenance guidance for your facility design Assess available maintenance capabilities and resources to maintain the site Maintenance information and annual O & M checklists can found in Appendix H of this manual. Evaluate whether additional training or information is needed to properly maintain the facility Determine the maintenance needs of various planting design alternatives Will vegetation border walkways, driveways, or other surfaces where pedestrian or vehicle access will be an issue? What is the mature height and spread of each of the plant species? What are the critical lines of sight that need to be maintained at intersections, along sidewalks, and along bicycle paths for pedestrian and vehicular safety? Will vegetation border inlet or outlet structures, pervious pavement surfaces, drains, or other infrastructure that could be negatively affected by vegetation debris or root systems? Does the planting design maintain proper access in and around the stormwater facility? Lake Oswego Stormwater Manual Draft 60

75 Stormwater BMP Standards and Specifications Step 5: Update Construction Documents, Plans, and Specifications After the planting plan and list have been evaluated through all criteria in Steps 1 through 4, update the construction document plans and specifications in order to clearly guide the installation and establishment of vegetation. 7.3 BMP Design Methods and Computations The City s current guidance for sizing and hydraulic analysis of BMPs is to use the Santa Barbara Urban Hydrograph (SBUH) method. The SBUH method is a single-event model that estimates a flow hydrograph for a representative rainfall event. The SBUH method was developed by the Santa Barbara County Flood Control and Water Conservation District. Applicable to urban areas, it converts design storm incremental excess rainfall depths into instantaneous unit discharge hydrographs (Debo and Reese 2003). The SBUH method is appropriate for sizing most BMPs included in this manual. There are proprietary stormwater models available that may be used to conduct SBUH modeling. Alternatively, a spreadsheet may be used. See Appendix F for further information. The City is currently reviewing its sizing standards in light of NPDES MS4 permit requirements and the findings from the Clean Streams Plan (Otak 2009). However, the City uses the SBUH method to verify sizing of facilities, and is considering plans to develop and update sizing tools based on SBUH methodology Lake Oswego is currently updating design methods and computations to comply with state and federal permit guidelines. Check the website ( to find current guidance. Precipitation is one of the input parameters for using the SBUH method. The City currently uses the NRCS Type 1A, 24-hour rainfall distribution resolved into 10-minute time intervals as the standard design hyetograph. Table 7.5 summarizes precipitation for various design storms. Table 7.5 City of Lake Oswego Precipitation. Design Storm/Recurrence Interval 24-Hour Rainfall Depth (inches) (years) Water Quality year year year year year year year 5.55 Source: Otak Lake Oswego Stormwater Manual Draft

76 Stormwater BMP Standards and Specifications 7.4 Soils Soil health is fundamental to a functional stormwater facility. Soils play the most important role in treating water quality, successful plant establishment, and the long-term success of a site. A handful of soil can hold millions of microorganisms that are critical to recycling soil nutrients, maintaining soil structure, processing pollutants from runoff, and aiding plants in nutrient and water uptake. Soil should be treated as a community of living organisms, protected, and handled carefully during construction. NRCS Soil Biology Primer website: soil_biology/soil_food_web.html For an updated list of laboratories that serve Oregon in Soil, Water, Plant Tissue, and Feed Analysis, document the following Oregon State University Extension Service document: umatilla/mf/sites/default/files/ Nutrient_Management_Guide_ EM8677.pdf Rather than automatically incorporating soil amendments or new soil into a site, begin site analysis and pre-design with soil testing to assess soil structure and nutrient levels. (See Section ) If onsite soil is appropriate for the target design, protect and incorporate existing soil into the design. Avoid and minimize soil compaction and disturbance. If soil needs to be moved and stockpiled during construction, place soil in shallow linear mounds and sow a temporary cover crop over the mounds. Cover crops will stimulate soil activity and protect soils from erosion. The best protection for soil during construction is to move it from shallow mounds into its target area as quickly as possible. Leaving soil in large piles and covering it with plastic will result in sterile soil, devoid of beneficial organisms that treat water quality and aid in plant establishment. Salvaging Native Soil If possible, salvage litter and duff and store separate from the topsoil to prevent loss of seed bank in litter Do not mix topsoil with subsoil to prevent diluting of beneficial soil microorganism community Salvage when dry and keep dry for storage (cover with plastic if needed) Optimum size is 6 ft wide and 3 ft tall but larger long linear piles are better than large tall piles - Information adapted from Roadside Revegetation: An Integrated Approach to Establishing Native Plants US Department of Transportation, Western Federal Lands Highway Division, In order to practice sustainable design, consider methods to use and amend onsite soil first. If onsite soil is not appropriate for the facility design goals, consider a sustainable way to salvage soil for use at another local site. If soil or amendments need to be brought into a site from an outside source, research where the soil is coming from, what materials amendments are made from, and whether or not sustainable practices are being supported (See Chapter 6, page 46, for information regarding continued research on the use of compost in infiltration facilities). Lake Oswego Stormwater Manual Draft 62

77 7.5 Pollution/Flow Control Manhole Design Sheet Flow Dispersion Stormwater BMP Standards and Specifications Meeting flow control requirements requires both adequate detention storage volume and a control structure that releases stormwater at the design flow rate. Lake Oswego requires that detention facilities include a pollution/flow control manhole. CAD details for the City s pollution/flow control manhole are provided on the City s website, and the detention pipes and vaults BMP design guideline in Section 7.6 provides sizing guidance. 7.6 BMP Design Guidelines Note: This BMP guideline adapted from Seattle Public Utilities (2009b) Sheet flow dispersion is one of the simplest methods of runoff control. This BMP can be used for any impervious or pervious surface that is graded so as to avoid concentrating flows. Because flows are already dispersed as they leave the surface (i.e., not concentrated), they need only traverse a narrow band of adjacent vegetation for effective flow attenuation and treatment Applications and Limitations Sheet flow dispersion is applicable for impervious surfaces with slopes less than 15 percent, such as driveways, sport courts, patios, roofs without gutters, RV pads, or other situations where concentration of flows can be avoided Site Requirements Minimum requirements associated with dispersion area design include the following: A 2-foot-wide transition zone to discourage channeling shall be provided between the edge of the contributing impervious area and the downslope vegetation. This may be an extension of subgrade material (crushed rock), modular pavement, drain rock, or other material approved by the City. A vegetated buffer width of 10 feet of vegetation must be provided for up to 20 feet of width of contributing impervious surface. An additional 5 feet of width must be added for each additional 20 feet of width of contributing area or fraction thereof. The vegetated flow path must be covered with well-established lawn or landscape area (landscaping with well-established groundcover, or native vegetation with natural groundcover). The groundcover shall be dense enough to help disperse and infiltrate flows and to prevent erosion. Dispersion is typically not permitted within potential severe landslide areas. Dispersion is typically not permitted within 10 feet of a steep slope (greater than 25 percent) Dispersion is typically not permitted over contaminated sites or abandoned landfills. For sites with septic systems, the discharge point must be downgradient of the drain field primary and reserve areas. This requirement may be waived if site topography clearly prohibits flows from intersecting the drain field. 63 Lake Oswego Stormwater Manual Draft

78 Stormwater BMP Standards and Specifications Overflow Conveyance Minimum requirements associated with overflow conveyance design include the following: Dispersion area shall convey excess flow to an approved discharge point. Conveyance of large storms shall be considered. No erosion or flooding of downstream properties may result. Lake Oswego Stormwater Manual Draft 64

79 Swales Swales Definition: A long, linear, gently sloped channel that removes pollutants through sedimentation and filtration. Introduction A swale is an open, gently sloped, vegetated channel designed for treating stormwater. The primary pollutant removal mechanisms are filtration and sedimentation. These occur when vegetation intercepts stormwater and traps pollutants. Applicability Table BMP Parameters Appropriate for Pretreatment Onsite Swales generally do not remove dissolved pollutants effectively. Swales typically provide only incidental infiltration. Where soils are suitable for infiltration, consider a rain garden. Provides Flow Control Provides Water Quality Treatment Appropropriate for Residential UIC Permit Required A swale is designed so that water will flow evenly across the entire width of a densely vegetated area. For small contributing areas, a swale may Engineer Required be designed for both treatment and conveyance of onsite stormwater flow. This combined use can reduce development costs by eliminating the need for separate conveyance systems. Swales are best applied on a relatively small scale (generally less than 5 acres of impervious surface). They work well along roadways, driveways, and parking lots, and can be designed as beautiful public amenities. Graphic *Refer to section. Undeveloped Area Varied Side Slopes 3 Min. Bottom Width Outflow Dispersed Inflow Pavement Inflow 65 Lake Oswego Stormwater Manual Draft

80 Swales Site Requirements Sites must be large enough to incorporate a minimum of a 100-foot length. Swales may be located on a range of site conditions; from full sun to full shade. Plant selection should match site conditions. Edge of swales must be located a minimum of 5 feet from property lines. Edge of swales must be located a minimum of 10 feet from buildings. Swales are not appropriate for steep slopes Geometry Swales can be adapted to fit a wide variety of sites. Use the design steps and select from the plants and materials described in the following sections to ensure adequate treatment of stormwater. Swale Dimensions Length 100 feet Bottom width 3 feet Side slopes 4 horizontal: 1 vertical Flow depth 4 inches 0.5-4% Longitudinal Slope (for steeper sites, consider terracing) Mulch depth = 2-3 inches Top Width Optional benching above design ponding depth to integrate swale into the landscape 6 min. freeboard Bottom Width Design Ponding Depth Mulch Native Soil Biofiltration Soil Mix Lake Oswego Stormwater Manual Draft Figure 1. Swale Section (Typ). 66

81 Design Steps Swales Following is the procedure to confirm that a proposed swale has adequate capacity to treat water quality flows. Step 1: Design Storm Calculate water quality and conveyance design storm (Q WQ and Q Peak ) using an approved method (See Table 7.4 for rainfall depths). Step 2: Manning s Coefficient Select Manning s roughness coefficient (n) based on planting type and density. Parameter Units Range n Manning s Roughness Coefficient unitless Step 3: Site Geometry Establish preliminary geometry for the following criteria, considering specific site conditions. Parameter Units Range S L Longitudinal slope ft/ft to 0.04 b Bottom width ft 3 feet minimum Z Side slopes H:V (E.g., for 4H:1V side slopes, Z= 4) 4H:1V or flatter y Flow depth ft 0.33 feet (4 inches) maximum Step 4: Wetted Perimeter, Hydraulic Radius, and Flow Area Calculate the wetted perimeter, hydraulic radius, and flow area using Manning s equation (equations below are for a trapezoidal channel with equal side slopes). Parameter Equation P Wetted perimeter P= b + 2y(1+Z 2 ) 0.5 A Cross-section area A= by + Zy 2 R Hydraulic radius A P 67 Lake Oswego Stormwater Manual Draft

82 Swales Step 5: Velocity Calculate velocity using Chezy-Manning equation. Parameter Units Equation V Velocity fps (1.49/n)(R 2/3 )(S L 1/2 ) Step 6: Capacity Confirm that swale has adequate capacity. Q Swale VA Parameter Units cfs Is Q Swale Water Quality Design Flow? Step 7: Stability Check Perform stability check using n=0.04 and Q Peak (Step 1). Use trial and error to calculate the flow depth associated with Q Peak. Calculate P, A, and R from Step 4 corresponding to the peak flow depth. Then, calculate V Max from Step 5 and confirm that V<3 fps. Parameter Units Value n S Manning s n stability check Q Peak Conveyance Stability Flow cfs See Chapter 7 V MAX Maximum velocity for presumed stability fps 3 Lake Oswego Stormwater Manual Draft 68

83 Materials Mulch Vegetation Objective Swales Biofiltration Soil Mix Swale soil media must support long-term plant and soil health and provide treatment to water as it infiltrates. The following topsoil mixture should comprise at least the top 18 inches of soil depth and be placed on top of uncompacted native soil. This mixture can be achieved by amending native sandy soils with compost (See Section ##) or by purchasing a biofiltration soil mix. Component Percent by Volume Sandy loam 60-70% Composted plant-based organic matter 30-40% Fines are restricted to 2-5% and must pass through a size 200 sieve. Fine to medium hemlock bark or well-aged organic yard debris compost is recommended for swales. It should be placed in the facility only in areas above the designed flow depth. Keep mulch material out of the stormwater flow path to avoid clogging inlets or outlets. Mulch must be weed free and applied 2 to 3 inches thick to cover all soil between plants. It should not be over-applied. Establish dense plant growth of thin stemmed emergent native vegetation within the swale treatment area and a diversity of groundcovers, shrubs, and trees along edges and borders. Plant Selection and Diversity Swales often experience moist to saturated soil conditions during the wet, rainy season and dry soil conditions during warm summers. Plant selection should cater to specific site conditions for each facility. Select at least three species for the treatment area. Select species that are suitable for the hydrologic, light, and soil conditions in the proposed swale. Swales should be designed so that they do not require mowing. See Appendix A for a complete plant list with species for swale bottoms (Zone A) and side slopes (Zone B). Plant Quality Sedges and Rushes Grasses and forbs Shrubs Trees Nursery stock 10 inch plug, rhizome or tuber Nursery stock 1 gallon or equivalent; 4 inch pot allowed if the facility is left off-line for the first wet season, allowing plants an appropriate establishment period 1 gallon container or equivalent 3 gallon container or equivalent Lake Oswego Stormwater Manual Draft 69

84 Swales Grouping Plant Species Place plants in odd-numbered clumps (3s, 5s, 7s, etc) of the same species throughout the planting areas. Planting depth Plant bare-rooted plants 4 to 6 inches deep and plugs as deep as the pot or plug. Woody Vegetation Do not plant woody vegetation below the freeboard elevation of the swale. Swale Side Slope Planting Establish with low growing native groundcover and shrubs that allow adequate sunlight to the swale for plant growth. Locate shrubs to allow for maintenance access to the treatment area. Establish groundcover vegetation that is low growing, will protect slopes from erosion, and will not compete with low shrubs planted on the side slopes. Conveyance and Outlet/Overflow Swales must include outlets to an approved location. Construction Till soil to a depth of at least 8 inches prior to planting. Mark swale boundaries with stakes or flagging prior to construction and avoid any unnecessary soil compaction or disturbance. Maintenance Proper maintenance is essential for a functioning swale. Please refer to the operations and maintenance section (Chapter 10) for more information. Native grasses and sedges do not like to be cut or mowed. See Maintenance Checklists (Appendix H) for appropriate maintenance intervals. Herbicides should not be used as a weed control technique within stormwater facilities. Lake Oswego Stormwater Manual Draft 70

85 Rain Gardens Rain Gardens Definition: Introduction Vegetated depressions that provide stormwater treatment during the capture and infiltration of water runoff through a biofiltration soil medium. Applicability Table Rain gardens treat stormwater through BMP Parameters sedimentation of particles in ponded water; Appropriate for filtration and phytoremediation through contact Pretreatment with vegetation; and biodegradation and adsorption of pollutants through contact with Onsite soil organisms and chemical soil processes. Provides Flow Control Rain gardens are ideal for residential and small (When designed for commercial sites, within parking lots, along infiltration) roadways, and can help fulfill landscaping requirements. Linear rain gardens may look similar Provides Water Quality Treatment to swales, but they have a flat bottom and pond water to infiltrate it vertically through treatment Appropropriate for soils. Swales have a gently sloping bottom and Residential provide treatment through filtration by vegetation UIC Permit Required as water is conveyed through the swale. Through thoughtful plant selection and design, a rain Engineer Required garden can become a community and wildlife (If > 1,000 sq. ft. impervious asset in addition to treating stormwater; rain area) gardens can showcase sculpture, serve as a butterfly garden, or function as a sedge meadow, becoming a local source of pride and reinforcing neighborhood identity. 71 Lake Oswego Stormwater Manual Draft

86 Rain Gardens Site Requirements Cell bottom must be 1 foot above seasonal high ground water elevation or other layer that limits infiltration (e.g., bedrock, clay lens) if contributing area is less than 3,000 sf of impervious surface. Cell bottom must be 3 feet above seasonal high ground water elevation if contributing area is 3,000 sf or greater of impervious surface. Infiltration rate must be > 0.25 inches/hour for a rain garden. Otherwise, the rain garden will pond water longer than a 24 hour period. Infiltration rain gardens must meet requirements and setbacks in Section Geometry As a rule of thumb, the footprint of a rain garden will be approximately 10 percent of the impervious surface draining to the rain garden if infiltration rates are at least 1/2 inch per hour. This can provide an initial estimate of rain garden size, but final sizing must be determined using the criteria and methods below. Rain Garden Dimensions Minimum width: 2 feet Planted side slopes no steeper than 3 horizontal: 1 vertical (Rockery walls may be used for areas that require steeper side slopes) Minimum freeboard: 2 if contributing impervious area is < 5,000 sf; 6 for larger contributing areas Maximum ponding depth: 12 inches Top Width Optional benching above design ponding depth to integrate rain gardens into the landscape Freeboard Bottom Width Overflow Design Ponding Depth Mulch Native Soil Biofiltration Soil Mix Outlet to Approved Discharge Location Lake Oswego Stormwater Manual Draft Figure 1. Rain Garden Section (Typ). 72

87 Design Steps Rain Gardens Design Performance Goal Capture and store the design storm in a surface pond for infiltration through the biofiltration soil medium. Step 1: Site Suitability Determine infiltration rate for native soils where rain garden will be located. Conduct infiltration test. See Section Step 2: Determine Drainage Basin Characteristics Calculate the total drainage area and composite SCS Curve Number for both pervious and impervious surfaces in the basin. See Appendix F for SCS Curve Number calculations. Parameter Units Value A Drainage Area acres CN SCS Curve Number unitless Step 3: Design Storm Calculate the storm runoff volume of the on-site design storm or water quality storm (as applicable) using the equation below: V r [ = 3,360 * A * ( P * - 10] design CN ) P design ( [ - 10] ) CN Parameter P design Design Precipitation Depth Units in Values Water Quality: 0.96 Onsite: 3.20 V r Runoff Volume cf Step 4: Determine Rain Garden Treatment Depth Select the design depth for ponding in the rain garden before overflow. Parameter Units Values d Rain Garden Ponding Depth in Max Lake Oswego Stormwater Manual Draft

88 Rain Gardens Step 5: Develop Preliminary Rain Garden Geometry Select preliminary dimensions of the rain garden including length, width, and side slopes. Parameter Units Values L Length ft 3 Min W Width ft 3 Min S s Side slope ft/ft 3H:1V Max Step 6: Check Rain Garden Volume Calculate the storage volume of the rain garden using preliminary geometry. If volume is less than the design volume (V r ), adjust the facility geometry (e.g., increase area, ponding depth) and repeat this step. Step 7: Check Drawdown Time Calculate the storage volume of the rain garden using preliminary geometry. If volume is less than the design volume (V r ), adjust the facility geometry (e.g., increase area, ponding depth) and repeat this step. T D = d I = 24 hours max Parameter Units Values d Rain Garden Ponding Depth in Max 12 I Infiltration Rate in/hr Lake Oswego Stormwater Manual Draft 74

89 Materials Biofiltration Soil Mix Rain Gardens Rain garden soil media must support long-term plant and soil health and provide treatment to water as it infiltrates. The City of Portland s specification for Standard Blend for Public and Private Facilities (Appendix F.3 of the Portland Stormwater Manual) should comprise at least the top 18 inches of soil depth and be placed on top of uncompacted native soil. This mixture can be achieved by amending native sandy soils with compost (See Section 7.2 for information on amending onsite soils) or by purchasing a biofiltration soil mix. Mulch Fines are restricted to 5-15% and must pass through a size 200 sieve. Fine to medium hemlock bark or well-aged organic yard debris compost is recommended for rain gardens. It should be placed in the facility only in areas above the designed flow depth. Keep mulch material out of the stormwater flow path to avoid clogging inlets or outlets. Mulch must be weed free and applied 2 to 3 inches thick to cover all soil between plants. It should not be over-applied. Vegetation Objective Component Percent by Volume Sandy loam 60-70% Composted plant-based organic matter 30-40% Establish dense plant growth with a diversity of groundcovers, shrubs, and trees along edges and borders for maximum runoff treatment and weed control. Plant Selection and Diversity Rain gardens often experience moist to saturated soil conditions during the wet, rainy season and dry soil conditions during warm summers. Plant selection should be based on water level tolerances during the rainy season, as well as their ability to withstand dry summer conditions. Select at least seven species for the treatment area. Select species that are suitable for the hydrologic, light, and soil conditions in the proposed rain garden. Rain gardens should be designed so that they do not require mowing. See Appendix A for a plant list appropriate for rain gardens. Plant Quality Sedges and Rushes Grasses and forbs Shrubs Trees Nursery stock 10 inch plug, rhizome or tuber Nursery stock 1 gallon or equivalent; 4 inch pot allowed if the facility is left off-line for the first wet season, allowing plants an appropriate establishment period 1 gallon container or equivalent 3 gallon container or equivalent 75 Lake Oswego Stormwater Manual Draft

90 Rain Gardens Grouping Plant Species Place plants in odd-numbered clumps (3s, 5s, 7s, etc) of the same species throughout the planting areas. Planting depth Plant bare-rooted plants 4 to 6 inches deep and plugs as deep as the pot or plug. Woody Vegetation Do not plant woody vegetation below the freeboard elevation of the rain garden. Locate shrubs and trees to allow for maintenance access to the treatment area. Rain Garden Side Slope Planting Establish groundcover vegetation that will protect slopes from erosion and provide competition for invasive or weedy vegetation. Plantings along side slopes and tops of banks should maintain vehicular and pedestrian lines of sight near street crossings. Conveyance and Outlet/Overflow Rain gardens must include overflows that outlet to an approved discharge location. If native soil infiltration rates are less than 0.25 inches/hour, rain gardens shall include underdrains that conform to ODOT Standard Specification Underdrains are only permitted where onsite soils meet criteria in Section Construction Loosen native soil to a depth of at least 4 inches before placing biofiltration soil mix or amending native soils. Mark rain garden boundaries with stakes or flagging prior to construction and avoid any unnecessary soil compaction or disturbance. If soil is compacted, it is critical that it be uncompacted to ensure proper infiltration rates and function of rain garden. The rain garden and surrounding areas should be protected from sedimentation that will reduce Maintenance Proper maintenance is essential for a functioning rain garden. Please refer to the operations and maintenance section (Chapter 10) for more information. Native grasses and sedges do not like to be cut or mowed. See Maintenance Checklists (Appendix H) for further maintenance guidance. Herbicides should not be used as a weed control technique within stormwater facilities. Lake Oswego Stormwater Manual Draft 76

91 Planters Planters Definition: Vegetated reservoirs with structural walls that treat, and where soils are suitable, infiltrate stormwater through a biofiltration soil medium. Introduction Planters treat stormwater through sedimentation of particles in ponded water; filtration and phytoremediation through contact with vegetation; and biodegradation and adsorption of pollutants through contact with soil organisms and chemical soil processes. Planters are essentially rain gardens with structural walls. The following considerations may help you select the best facility for your site: Planters require less space to treat the same contributing area Planters are more costly to construct because they have structural walls Planters typically require an engineer to design (because of the structural walls) Applicability Table BMP Parameters Appropriate for Pretreatment Onsite Provides Flow Control (When designed for infiltration) Provides Water Quality Treatment Appropropriate for Residential UIC Permit Required Engineer Required (If > 1,000 sq. ft. impervious area) Flow-through (lined) planters have no setback requirements, so they can be constructed adjacent to buildings (for example, to treat roof runoff). Both rain gardens and planters can help fulfill a site s landscaping requirements Graphic Planter Width Overflow Roadway Design Ponding Depth Walkway Mulch Biofiltration Soil Mix To Approved Outlet Location Planter Drain Rock Underdrain to Run Length of Planter Where Required Native Soil 77 Lake Oswego Stormwater Manual Draft

92 Planters Site Requirements Bottom of planter must be 1 foot above seasonal high ground water elevation or other layer that limits infiltration (e.g., bedrock, clay lenses) if contributing area is less than 3,000 sf of impervious surface. Bottom of planter must be 3 feet above seasonal high ground water elevation or other impermeable layer if contributing area is 3,000 sf or greater of impervious surface. Geometry Planter Dimensions 12-inch maximum ponding depth Freeboard: 2 inches < 5,000 sq. ft. contributing area 6 inches for 5,000 sq. ft. contributing area 18 inch biofiltration soil mix Width 30 inch for infiltration planter Width 18 inch for flow-through planter Lake Oswego Stormwater Manual Draft 78

93 Design Steps Planters Design Performance Goal Capture and store design storm in surface pond for infiltration through biofiltration soil mix. Step 1: Determine Drainage Basin Characteristics Calculate the total drainage area and composite NRCS Curve Number for both pervious and impervious surfaces in the basin. See Appendix F for NRCS Curve Number calculations Parameter Units Value A Drainage Area acres CN SCS Curve Number unitless Step 2: Design Storm Calculate the storm runoff volume of the on-site design storm or water quality storm (as applicable) using the equation below: V r [ = 3,360 * A * ( P * - 10] design CN ) P design ( [ - 10] ) CN Parameter P design Design Precipitation Depth Units in Values Water Quality: 0.96 Onsite: 3.20 V r Runoff Volume cf Step 3: Determine Planter Treatment Depth Select the design depth for ponding in the planter before overflow Parameter Units Values d Planter Treatment Depth in Max Lake Oswego Stormwater Manual Draft

94 Planters Step 4: Calculate Planter Area Determine the surface area of the planter using the following equation: A s = V design d Parameter Units Values A s Surface Area of Planter sf Lake Oswego Stormwater Manual Draft 80

95 Materials Planters Planter Walls Planter walls shall be made of stone, concrete, brick, or other durable material. Chemically treated wood that can leach out toxic chemicals and contaminate stormwater shall not be used. Waterproof Liners If located adjacent to buildings, planters need waterproof liners placed along side walls to prevent potential lateral movement of water. Liners should be 30 mil PVC or equivalent. Gravel Drain Rock Drain rock is required below the bioretention soil mix. For infiltration planters, use 1½-inch ¾-inch washed drain rock. Drain rock shall conform to ODOT Standard Specifications All flow-through facilities shall use ¾-inch to ½-inch washed drain rock. Drain rock and biofiltration soil mix must be separated by a rock filter of 2- to 3-inch layer of special filter material per ODOT Standard Specification Underdrain Underdrains shall be perforated PVC pipe that meets ODOT Standard Specification , or approved equal. Piping installation must follow current Uniform Plumbing Code. Pipe shall be 4-inch minimum for private property and 6-inches minimum for streets.. Biofiltration Soil Mix Planter soil media must support long-term plant and soil health and provide treatment to water as it infiltrates. The City of Portland s specification for Standard Blend for Public and Private Facilities (Appendix F.3 of the Portland Stormwater Manual) should comprise at least the top 18 inches of soil depth and be placed on top of uncompacted native soil. This mixture can be achieved by amending native sandy soils with compost (See Section 7.2 for information on amending onsite soils) or by purchasing a biofiltration soil mix. Component Percent by Volume Sandy loam 60-70% Composted plant-based organic matter 30-40% Fines are restricted to 5-15% and must pass through a size 200 sieve. Mulch In high flow facilities, use washed rock mulch to a depth of 2 and add compost tea to planters as additional nutrients are needed. In regularly inundated facilities, apply fine to medium hemlock bark or well-aged organic yard debris compost. It should be placed in the facility only in areas above the designed flow depth. Keep mulch material out of the stormwater flow path to avoid clogging inlets or outlets. Mulch must be weed free and applied 2 to 3 inches thick to cover all soil between plants. It should not be over-applied. 81 Lake Oswego Stormwater Manual Draft

96 Planters Vegetation Objective Establish dense plant growth with a diversity of groundcovers, shrubs, and trees along edges and borders for maximum runoff treatment and weed control. Plant Selection and Diversity Planters often experience moist to saturated soil conditions during the wet, rainy season and dry soil conditions during warm summers. Plant selection should be based on water level tolerances during the rainy season, as well as their ability to withstand dry summer conditions. Select at least five species for small treatment areas and add diversity for medium to larger facilities. Select species that are suitable for the hydrologic, light, and soil conditions in the proposed planter. Planters should be designed so that they do not require mowing. See Appendix A for a plant list appropriate for stormwater planters. Plant Quality Sedges and Rushes Nursery stock 10 inch plug, rhizome or tuber Grasses and forbs Nursery stock 1 gallon or equivalent; 4 inch pot allowed if the facility is left off-line for the first wet season, allowing plants an appropriate establishment period Shrubs 1 gallon container or equivalent Trees 3 gallon container or equivalent Grouping Plant Species Place plants in odd-numbered clumps (3s, 5s, 7s, etc) of the same species throughout the planting areas. Planting depth Plant bare-rooted plants 4 to 6 inches deep and plugs as deep as the pot or plug. Woody Vegetation Do not plant woody vegetation below the freeboard elevation of the planter. Locate shrubs and trees to allow for maintenance access to the treatment area. Planter Side Slope Planting Establish ground cover vegetation that will protect slopes from erosion and provide competition for invasive or weedy vegetation. Plantings along side slopes and tops of banks should maintain vehicular and pedestrian lines of sight near street crossings. Lake Oswego Stormwater Manual Draft 82

97 Conveyance and Outlet/Overflow Planters must include overflow outlets that discharge to an approved location. Planters Where required, underdrains shall be provided along the length of the planter. Construction Till soil to a depth of at least 8 inches prior to planting. Mark planter boundaries with stakes or flagging prior to construction and avoid any unnecessary soil compaction or disturbance. Maintenance Proper maintenance is essential for a functioning stormwater planter. Please refer to the operations and maintenance section (Chapter 10) for more information. Native grasses and sedges do not like to be cut or mowed. See Maintenance Checklists (Appendix H) for further maintenance guidance. Herbicides should not be used as a weed control technique within stormwater facilities. 83 Lake Oswego Stormwater Manual Draft

98 Green Roofs Green Roofs Definition: A building roof that is partially or completely covered with vegetation, and growing media, atop a waterproof membrane (also called: ecoroof, vegetated roof) Introduction A green roof is a thin, layered system of waterproofing, drainage layers, growing media, and planting to cover impervious roof areas and allow water to be absorbed, detained, and evaporated back into the atmosphere. Green roofs are not used to manage stormwater directly, but rather, similar to pervious pavements, reduce the overall area of impervious surfaces. The strategy is employed often on tight sites where other stormwater management strategies are not possible due to lack of area. Applicability Table BMP Parameters Appropriate for Pretreatment Onsite Provides Flow Control (When designed for infiltration) Provides Water Quality Treatment Appropropriate for Residential UIC Permit Required Green roofs are mostly extensive meaning they are low-maintenance and lightweight, primarily designed for stormwater management, with aesthetics as a secondary goal. Semiintensive projects have somewhat deeper soils Engineer Required (If > 1,000 sq. ft. or more expansive plantings. These should be impervious area) differentiated from accessible roof gardens and terraces which include deeper soils, paved areas, seating, furnishings - have more intensive plantings or areas for growing food and other items that are used as an amenity and not primarily for stormwater management. Examples Flat Commercial/Mixed Use Roof Lake Oswego Stormwater Manual Draft Sloped Residential Roof 84

99 Site Requirements Green Roofs Flat or slightly sloped roofs on large institutional, commercial, or residential projects. Green Roofs work on sloped roofs up to a maximum of 4:12 without additional engineering - and can be steeper with intermediate support of soils. Structural considerations: Must be able to carry additional loads of at least 15 pounds per square foot (ideal is 30 pounds per square foot) when fully saturated. Access to roof via crane, lift or other device is recommended to load heavy & bulky materials up to rooftop surface. Geometry Green roofs can be adapted to fit a wide variety of roofs. Use the design steps and select from the plants and materials described in the following sections to ensure adequate treatment of stormwater. Green Roof Dimensions Min. Growing Media Depth: 4 inches Max. Growing Media Depth: 8 inches Min. Roof Slope: 1/4 per foot Max. Roof Slope: 4:12 (greater slopes allowed with engineering/stabilization) Perimeter edges and access pavers should count for no greater than 10% of green roof area Mulch: Rock mulch (non-organic) to avoid wind and water erosion. Vegetation to cover 100% of soil areas Metal Edging Gravel Mulch Approved Plantings Growing Media Drainage Layer with Filter Fabric 4 min. Waterproofing Protection/ Root Barrier Building Structure Drain to Approved Outfall Location Figure 1. Green Roof Section (typ.) 85 Lake Oswego Stormwater Manual Draft

100 Green Roofs Design Steps Following is the procedure to confirm that a proposed green roof has adequate capacity to manage the impervious roof surfaces. Step 1: Determine Green Roof Area Determine area of roof that will contain vegetated rooftop area (s.f.) Step 2: Calculate non-vegetated Green Roof areas Gravel perimeter edging, pavers, drains and other areas of the green roof can be included in the overall square footage of green roof up to 10%. Step 3: Calculate Impervious Area Reduction To calculate the total impervious area reduction, sum the total vegetated area with any nonvegetated green roof elements (up to 5%) to calculate the total impervious area reduction. The following table is an example of the calculation to obtain the quantity to be entered for impervious area reduction: Parameter Vegetated Areas Non-vegetated Areas (pavers, gravel, drains) Units s.f. s.f. Range 1, (max) IMPERVIOUS AREA REDUCTION s.f. 1,050 s.f. Materials Root Barrier / Protection Layer Synthetic, non-biodegradable layer to protect waterproofing layers and provide additional protection from roots. Should not use copper or copper hydroxide for root inhibitor. Drainage Layer / Filter Fabric Synthetic or mineral layer to provide water movement under growing media. 1/2 depth with void space of at least 50%, covered by non-woven (needle-punched) filter fabric separation from growing media. Growing Medium The following engineered growing media mix should be placed to a depth of at least 4 inches to meet requirements - and should contain no fines, weed seeds, or other materials. Provide documentation of saturated weight (field moisture capacity) tested and documented by a third party Mineral Mulch Pumice / Lightweight Aggregate 80-90% Composted plant-based organic matter 10-20% Washed gravel or non-decompostable material (no fines) that will not be moved by wind or water movement Lake Oswego Stormwater Manual Draft 86

101 Vegetation Objective Green Roofs Establish dense plant growth of low-maintenance, low-water use succulent vegetation supplemented with some hardy perennials, grasses, and other native, non-woody vegetation. Plant Selection and Diversity Extensive green roofs should consist of a foundation of succulents (i.e. sedums, sempervirum) and other Crassulacean acid metabolism (CAM) species. This designates plants that photosynthesize, and thus evapotranspire, at night, which reduces the amount of water lost during hot, sunny days. These low-growing species provide dense coverage to aid in erosion control and weed suppression. A minimum of 10 species should be included to promote microclimatic diversity and resilience to the roof - allowing for species to fill in if others are slow to perform. No monocultures. Use 10% deciduous species distributed throughout the roof to See Appendix A for a complete plant list with species for green roofs Plant Quality & Space Cuttings Container Plants Small pieces of sedums and other succulents broadcast onto soil surface to root in place lbs/ 1000 s.f. typical. Plugs or 4 inch pots of pre-grown species (4-12 o.c.), should have a full crown and be free of weeds or other materials. If possible, pre-grow in green roof soil or installed as bareroot plugs to avoid weed contamination and importation of organic soils on to roofs. Conveyance and Outlet/Overflow Green roofs must include outlets to an approved location from roof drains, scuppers and other drainage devices. Construction Ensure waterproofing is installed and protected prior to construction Install drainage layer, edging, filter fabric, and irrigation prior to soil installation. Do not install in heavy rains to avoid erosion. Install plants in spring or fall (or irrigate as needed) - do not install during freezing temperatures. Maintenance Proper maintenance is essential for a functioning green roof. Please refer to the operations and maintenance section (Chapter 10) for more information. See Maintenance Checklists (Appendix H) for further maintenance guidance for green roof vegetation Herbicides should not be used as a weed control technique within stormwater facilities. 87 Lake Oswego Stormwater Manual Draft

102 Pervious Pavement Pervious Pavement Definition: Pervious pavement is pavement designed to allow rainfall to percolate into the underlying soil or aggregate storage reservoir beneath the pavement. Introduction There are several options for wearing course, or the surface layer of pervious pavement, including porous asphalt, pervious concrete, or pavers. Porous asphalt is open-graded asphalt that allows water to percolate or infiltrate into underlying soils. Porous concrete omits fines in the aggregate to create stable air pockets that allow water to drain to the base below. There is an inverse relationship between porosity and strength.* Pavers are generally suitable for pedestrian areas and low traffic parking areas and are available in a variety of configurations (rigid concrete or durable plastic grid filled with gravel or a mixture of gravel, sand, and topsoil suitable for vegetation). Pervious pavement may be designed as a surface, that receives only direct rainfall, or facility, that receives runoff of stormwater from adjacent impervious surfaces. * As porosity is increased, the structural strength is reduced. BMP Parameters (appropriate for) Appropriate for Pretreatment Onsite Applicability Table Flow Control (If suitable soils and designed for infiltration only [no underdrains]) Water Quality Treatment Residential UIC Permit Required? Engineer Required? Oswego Lake Watershed Design Modification* Yes No Graphic Lake Oswego Stormwater Manual Draft 88

103 Site Requirements Pervious Pavement To be considered for pervious pavement, a site must meet the following design criteria: Surface slope no greater than 5% Not receiving high sediment loads (leaf litter can cause clogging, so avoid pervious pavement underlying large deciduous trees) Vertical separation to underlying water table, bedrock or other impermeable layer 4 feet from ground surface Not appropriate for areas at risk of hazardous spills such as gas stations Not appropriate for construction over fill soils Geometry Types Wearing Course Porous Concrete The wearing course of a porous concrete section shall meet the following: 4-inch thickness for residential driveway, pedestrian only, private street, parking lot or fire lane 7-inch thickness for public street Porous Asphalt The minimum thickness of the wearing course of a porous asphalt section shall be as follows: 2.5-inch thickness for residential driveway or pedestrian only 3 inches for private street, parking lot or fire lane 6 inches for public street Aggregate Storage Reservoir Minimum base depth for structural support should be 6 inches for vehicular loading Design depth is typically determined by storage depth needed to manage design storm. Leveling Course Where pervious pavement installations are proposed over fine sediments, provide a 1 to 3-inch thick leveling course if the pervious pavement surface is open-celled paving grids, interlocking concrete pavers or porous asphalt concrete. 89 Lake Oswego Stormwater Manual Draft

104 Pervious Pavement Design Steps Pavement design is outside of the scope of these guidelines. Pavement design shall demonstrate that pavement structure has the structural strength for anticipated vehicle loadings. The following resources can provide guidance on structural pavement design: National Asphalt Pavement Association Design, Construction and Maintenance Guide AASHTO Guide for Design of Pavement Structures Step 1: Determine Site Infiltration Rate Step 2: Determine Design Flow and Volume for Storage (Q design ) Calculate 10-year, 24-hour discharge and runoff volume using approved single-event methods Step 3: Calculate Thickness of Storage Layer Using and approved model, route the design storm through the pervious pavement storage area, and determine the maximum ponding depth (considering infiltration and void ratio of storage layer material). This maximum ponding depth is the design storage layer thickness. Lake Oswego Stormwater Manual Draft 90

105 Materials Choker Course Pervious Pavement Choker Course should be 1-3 of 3/4 to 2 uniformly graded washed aggregate (AASHTO No. 57). Aggregate Storage Reservoir The aggregate storage reservoir shall conform to ODOT standard specifications granular drain backfill material, AASHTO No. 57, or approved equal. Porous Asphalt The surface wearing course for porous asphalt shall conform to open graded ½ inch or ¾-inch asphalt design from ODOT standard specification or approved equal. Content: % by weight of total (dry aggregate) mix. Performance Grade (PG): Do not use an asphalt cement performance grade less than for open graded, porous asphalt mixes. Leveling Course The leveling course shall conform to Section of the Technical specifications. Construction For a pervious pavement installation to be approved in Lake Oswego, designers must demonstrate that construction will be performed by a qualified contractor ideally one who has had prior experience with successful installations. Examples include performance-based specifications or requiring certification through a national training program. During construction, the pervious pavement site must be protected from sediment and runoff. The subgrade should be protected from truck traffic. Compaction will reduce the permeability of soils and should be done with caution. The subgrade shall be scarified prior to setting the aggregate storage reservoir. Compaction shall meet the following criteria: Compact to 95 percent for public roadways No compaction required for residential driveway or pedestrian only surfaces over native fill. Maintenance Remove vegetation, debris, sediment, and other materials promptly. If there is moss growth on surface of pervious pavement, pressure wash or vacuum sweep the surface during the dry season to preserve infiltration capacity. Review checklists in Appendix H for complete maintenance schedule. 91 Lake Oswego Stormwater Manual Draft

106 Infiltration Trench Infiltration Trench Definition: A linear, gravel-filled trench that distributes stormwater to underlying soils. Introduction An infiltration trench provides flow control only, so pretreatment is required. Infiltration trenches are classified as underground injection chambers (UICs), unless they are constructed without an underdrain, so they must be registered with the Oregon Department of Environmental Quality (DEQ). These guidelines cover infiltration trenches for both small and large projects. Some differences are: Observation wells are required for infiltration trenches serving large contributing areas (>3,000 sf) Applicability Table BMP Parameters Appropriate for Pretreatment Onsite Provides Flow Control Provides Water Quality Treatment Appropropriate for Residential UIC Permit Required Engineer Required GRAPHIC Washed gravel used for construction of infiltration trenches. Lake Oswego Stormwater Manual Draft 92

107 Site Requirements Infiltration Trench Trenches are not approved for slopes greater than 25% Trenches must be located a minimum of 10 feet from building foundations Trench must be located a minimum of 5 feet from property lines Infiltration trenches are not allowed in the public right-of-way Trenches should not be located where they will be subject to vehicular traffic Soil surrounding trenches must be native, uncompacted soil Separation from seasonal high groundwater elevation 5 feet Geometry Infiltration trenches are rectangular in shape, and can be any length. Infiltration Trench Dimensions Depth of drain rock 12 inches Width = 2 to 5 feet Observation Well (if required) Finish Grade Underdrain Maintain 6 Washed Drain Rock Below Pipe Inlet 2-3 inches Rock Filter 2 to 5 Figure 1. Infiltration Trench Section (Typ). 93 Lake Oswego Stormwater Manual Draft

108 Infiltration Trench Design Steps The required storage capacity of an infiltration system shall be determined by subtracting the volume of water that can infiltrate from the facility within a 24-hour period from the contributing basin during a 24- hour, 10-year storm event. Step 1: Site Suitability Confirm that site meets the criteria for infiltration facilities (Chapter 7), perform infiltration test, and confirm that you are willing to register the drywell as a UIC with Oregon DEQ. A geotechnical report is required for infiltration facilities on slopes 15% or within 200 ft of a steep slope hazard area or landslide hazard area. Step 2: Determine Drainage Basin Characteristics Calculate the total drainage area and composite SCS Curve Number for both pervious and impervious surfaces in the basin. See Appendix F for SCS Curve Number calculations. A CN Parameter Drainage Area SCS Curve Number Units acres unitless Value Step 3: Calculate Runoff Volume Calculate the volume of runoff during a 10-year, 24-hour storm using the equation below: 1000 V r = 3,360 * A * ( P * [ ] design CN ) P design * 1000 ( [ - 10] ) CN Parameter Units Values V r Runoff Volume cf P design Design Precipitation Depth in 3.2 Lake Oswego Stormwater Manual Draft 94

109 Step 4: Establish Preliminary Geometry Establish infiltration trench depth, width and length for preliminary evaluation. Infiltration Trench Parameter Units Values H Trench Depth ft W Trench Width ft L Trench Length ft Step 5: Calculate Infiltration Volume Calculate the volume that can infiltrate from the infiltration trench to groundwater in a 24-hour period using the trench geometry and the percolation rate determined through the Falling Head Percolation Test. ( ) V = A dw * T * 60 R perc Parameter Units Values R perc Percolation Rate min/in A dw Surface Area of Infiltration Trench sf V i Infiltration Volume cf T Time hr 24 Step 6: Calculate Storage Volume Subtract the volume calculated in Step 5 from the runoff volume calculated in Step 3. This is the required storage volume for the infiltration trench. If the required storage volume is not met by the preliminary geometry assumed in Step 4, adjust and repeat steps 5 and 6 until the criteria are met. 95 Lake Oswego Stormwater Manual Draft

110 Infiltration Trench Materials Drain Rock Drain rock shall be 3/4-1 1/2 granular drain backfill material. Drain rock shall conform to ODOT Standard Specifications Underdrain Underdrain shall be perforated 6 in diameter PVC that conforms to ODOT Standard Specification ; the invert elevation must be 2 feet below finished grade. Rock Filter A rock filter, 2 to 3 inches of special filter material per ODOT Standard Specification , shall be placed between the drain rock and native soils. Conveyance and Outlet/Overflow An observation well is required for infiltration trenches constructed for large projects - See Chapter 3 An underdrain is required unless infiltration rates of native soils are 2 inches/hour. Construction The location of the proposed infiltration trench shall be clearly marked prior to land disturbance to ensure that the area is protected from construction vehicle traffic (construction vehicles shall be restricted within 10 feet of trench). The bottom of the infiltration trench shall be level. Infiltration rates shall be tested after construction to confirm that they are consistent with the design infiltration rates. Maintenance Protect trench from vehicle traffic to avoid compaction. If ponding is observed in observation well or at the surface of facility, clear underdrain of debris. Avoiding planting large shrubs or tree adjacent to trench to prevent damage from large root systems. See Chapter 10 for additional maintenance guidance. Lake Oswego Stormwater Manual Draft 96

111 Drywell Drywell Definition: Perforated precast concrete cylinders that discharges stormwater into underlying soils. Introduction Drywells are Class V Injection Wells under the federal Underground Injection Control (UIC) Program. These facilities must be registered with DEQ and classified as exempt, authorized by rule, or authorized by permit. Drywells do not provide water quality treatment, so water quality treatment is required before stormwater discharges into drywells. For drywells used exclusively for residential roof runoff from three units or less, a silt trap is the only pretreatment necessary. They must be registered with DEQ since they are considered to be Class V injection wells. Where space is available, rain gardens are preferred to manage residential runoff since they provide both treatment and flow control (and are not considered UICs). Applicability Table BMP Parameters (appropriate for) Appropriate for Pretreatment Onsite Flow Control Water Quality Treatment Residential UIC Permit Required? Engineer Required? Yes No Photo from huffcut.com 97 Lake Oswego Stormwater Manual Draft

112 Drywell Site Requirements Drywells must meet the infiltration design criteria described in Chapter 7 Drywells must be 10 feet above seasonal groundwater or impermeable layer The center of the drywell must be 10 feet from building foundations The center of the drywell must be 5 feet from property lines Depth: top of drywell shall be lower than the floor elevation of basements in immediately adjacent buildings Drywells are not allowed on slopes 25% Photo from nylandsolutions.com Drywells are not allowed in the public right-of-way Soil surrounding drywells must be native, uncompacted soil Pretreatment is required unless the drywell is only receiving roof runoff Geometry Drywell Dimensions Diameter 2 feet Lake Oswego Stormwater Manual Draft 98

113 Design Steps Drywell The required storage capacity of a drywell/infiltration system shall be determined by subtracting the volume of water that can infiltrate out of the facility within a 24-hour period from the contributing basin during a 24-hour, 10-year storm event. Step 1: Site Suitability Confirm that site meets the criteria for infiltration facilities (Chapter 7), perform infiltration test, and confirm that you are willing to register the drywell as a UIC with Oregon DEQ. A geotechnical report is required for drywells on slopes 15% or within 200 ft of a steep slope hazard area or landslide hazard area; Step 2: Determine Drainage Basin Characteristics Calculate the total drainage area and composite SCS Curve Number for both pervious and impervious surfaces in the basin. See Appendix F for SCS Curve Number calculations. Parameter Units Values A Drainage Area acres CN SCS Curve Number unitless Step 3: Calculate Runoff Volume Calculate the volume of runoff during a 10-year 24-hour storm using the equation below: 1000 V r = 3,360 * A * ( P * [ ] design CN ) P design * 1000 ( [ - 10] ) CN Parameter Units Values V r Runoff Volume cf P design Design Precipitation Depth in Lake Oswego Stormwater Manual Draft

114 Drywell Step 4: Establish Preliminary Geometry and Number of Drywells Establish drywell depth and diameter, and number of units for preliminary evaluation. Parameter Units Values D Drywell Diameter ft Range H Drywell Depth ft Min. Max. N Number of Drywell Units each Step 5: : Calculate Infiltration Volume Calculate the volume that can infiltrate from the drywell(s) to groundwater in a 24-hour period using the drywell geometry and the percolation rate determined through the Falling Head Percolation Test. ( ) V = A dw * T * 60 R perc Parameter Units Values R perc Percolation Rate min/in A dw Area of Drywell(s) sf V i Infiltration Volume cf T Time hr 24 Step 6: Calculate Storage Volume Subtract the volume calculated in Step 5 from the runoff volume calculated in Step 3. This is the required storage volume for the drywell(s). If the required storage volume is not met by the preliminary geometry/number of drywells assumed in Step 4, adjust and repeat steps 5 and 6 until the criteria are met. Lake Oswego Stormwater Manual Draft 100

115 Materials Drywell Gravel Drain Rock Place 12-inch minimum layer of 3/4 to 1-1/2 round rock that conforms to ODOT Standard Specifications between pit lining and earth wall, up to the lid. Construction The location of the proposed drywell shall be clearly marked prior to land disturbance to ensure that the area is protected from construction vehicle traffic (construction vehicles shall be restricted within 10 feet of drywell). The bottom of the drywell shall be level. Infiltration rates shall be tested after construction to confirm that they are consistent with the design infiltration rates. Maintenance Proper maintenance and regular inspection is essential for a functioning drywell. Please refer to the operations and maintenance section (Chapter 10) for more information. 101 Lake Oswego Stormwater Manual Draft

116 Rainwater Harvesting Rainwater Harvesting Photo provided by RainBank Definition: Collection of stormwater in rain barrels or cisterns for reuse either for landscape irrigation or non-potable household or building use, such as toilet flushing or cold water laundry. Introduction Rain barrels are BMPs that collect stormwater for reuse, typically for landscape irrigation. Rain barrels typically have a small capacity, or storage volume, so they cannot completely meet onsite stormwater management or flow control requirements. The usefulness of rain barrels for flow control is also limited because of the nature of storms in the Pacific Northwest, where frequent storms occur in the fall, spring and winter, when irrigation needs are much lower. Cisterns are generally larger facilities that can supply storage for non-potable household or building uses as well as irrigation. Any stormwater reuse within a house or building must obtain plumbing approval from the building department. System containment backflow protection in the form of a reduced pressure (RP) type of backflow Applicability Table BMP Parameters Appropriate for Pretreatment Onsite Provides Flow Control Provides Water Quality Treatment Appropropriate for Residential UIC Permit Required Engineer Required assembly must be provided. System containment RPs must be located on private property at the property line, immediately adjacent to the point of water service connection. (Depends on Cistern Size and Location) Graphic Photo provided by RainBank Lake Oswego Stormwater Manual Draft 102

117 Site Requirements To protect the water quality of the rainwater harvested, rainwater should not be harvested from roofs containing copper or zinc or materials treated with fungicides or herbicides. Rainwater Harvesting Rainwater harvesting should only be used for stormwater collected from roofs if approved by the building department. Reuse of stormwater for non-potable uses is restricted by the Oregon Plumbing Specialty Code and by the building department. Do not use rainwater harvested from rooftops to water vegetable gardens or edible crops. Geometry Types Cisterns may be installed either at grade, below ground, under a deck, or in a basement or crawl space. Multiple cisterns may be installed to provide increased storage capacity. Photo provided by RainBank 103 Lake Oswego Stormwater Manual Draft

118 Rainwater Harvesting Design Steps Supplemental calculations are not required for rain barrels. For cisterns, an engineered design may be required. For all cisterns that are proposed to meet onsite stormwater management or flow control requirements, the following information must be submitted: Tank size and material Water storage facility details and specifications Pretreatment facility details Pump and associated electrical details and specification Piping size, material, and placement details and specifications Average daily water use documentation Hydraulic calculations demonstrating compliance with stormwater management requirements Where cisterns are proposed to supplement domestic greywater uses, conduct a water balance calculation between domestic greywater uses and precipitation to determine the appropriate cistern size. See the Oregon Smart Guide to Rainwater Harvesting (Oregon Department of Consumer and Business Services) for information on how to perform these calculations. Lake Oswego Stormwater Manual Draft 104

119 Materials Rainwater Harvesting Rainwater harvesting includes the following elements: Collection System Typically gutters and downspouts along with any piping needed to route harvested water to the cistern. Debris Screen A leaf guard or screen should be provided to reduce sediment and other debris from entering the cistern. Cisterns Cisterns can be constructed of concrete, fiberglass, or plastic. Opaque containers must be used for aboveground cisterns to minimize algae growth. Delivery and Distribution System Delivery may be accomplished by a gravity system or include the pumps and pipes needed to move water from the storage system to the end use area. Consider designing a potable water back-up that can operate without electricity in emergency conditions. Water must be drawn from at least 4 inches above the bottom of the tank. Pretreatment Water quality treatment is typically required to protect the delivery and distribution system and to improve the quality of the collected water for the reuse. The extent of water treatment depends on both the quality of the water entering the storage system and the intended water use. Systems must protect the functions of delivery valves and fixtures and range from simple screens to cartridge filters, UV light, and chlorination. Screen systems and/or basic mechanical filtration are typically adequate for irrigation and toilet flushing reuse. Approval is required by the building department for any project routing harvesting water to an indoor plumbing system. Conveyance and Outlet/Overflow The cistern must have a designated overflow when the volume of the tank meets capacity. The minimum overflow is 4 inches in diameter. Overflows must discharge to an approved location. Construction All cisterns must be installed in accordance with manufacturer s installation instructions and the City s building code and all applicable laws. 105 Lake Oswego Stormwater Manual Draft

120 Rainwater Harvesting Maintenance Cistern/storage systems must have both access points and drains to allow inspections and cleaning. Openings shall be designed to restrict entry from unauthorized personnel and/or appropriate signage shall be provided. Cleaning of any accumulated sediment on the bottom of the cistern must be possible by flushing through a drain, vacuuming or another approved method. Cistern/storage systems that are buried below ground level must have a manhole riser that sticks out a minimum of 8 inches above the surrounding ground. Manhole covers must be secured and locked to prevent tampering. Lake Oswego Stormwater Manual Draft 106

121 Filter Strips Filter Strips Definition: a gently sloped vegetated strip that removes pollutants through filtration, sedimentation, and infiltration. Introduction A filter strip is a section of vegetated area adjacent to an uncurbed impervious surface. Stormwater flows at a low velocity and depth evenly across the entire width of the filter strip. Pollutants are removed through stormwater contact with vegetation and underlying soils. Filter strips are appropriate for meeting landscaping requirements, but plant selection must be consistent with their stormwater treatment function (see Appendix A). Filter strips must be protected from disturbance to preserve healthy vegetation and soil conditions in order to maintain water quality function. These facilities are a good choice for roads in Lake Oswego, and are complimented by the shoulder gravel strip that helps to distribute flow. Filter strips can also be good choices for small projects, for example to provide water quality treatment for roof or driveway runoff before it is discharged into a drywell, infiltration trench, or other facility. Applicability Table BMP Parameters Appropriate for Pretreatment Onsite Provides Flow Control Provides Water Quality Treatment Appropropriate for Residential UIC Permit Required Engineer Required Graphic 107 Lake Oswego Stormwater Manual Draft

122 Filter Strips Site Requirements There must be an approved overflow route Filter strips are appropriate for all soil types Filter strips may be located on a range of site conditions from full sun to full shade. Plant selection should match site conditions (see Appendix A) Filter strips must be a minimum of 5 feet from the property line Filter strips must be a minimum of 5 feet from structures Filter strips must be a minimum of 50 feet from wetlands, rivers, streams, and creeks Filter strip monitoring. Geometry Filter Strip Dimensions Dimensions and slopes: Filter strips shall slope between 0.5 and 10 percent. If slope is greater than 5 percent, check dams are required. Slope of pavement area draining to the strip shall be less than 6 percent. Filter strips shall have a minimum width of 5 feet, measured in the direction of flow. Filter strip monitoring troughs. Lake Oswego Stormwater Manual Draft 108

123 Design Steps Filter Strips Following is the procedure to confirm that a proposed filter strip has adequate capacity to treat water quality flows. Step 1: Calculate Design Discharge Estimate peak discharge rate (Q design ) in cubic feet per second for water quality design storm Parameter Q design Design Discharge Units cfs Value Step 2: Determine preliminary facility parameters Determine width and slope of filter strip Parameter Units Value T Filter Strip Width ft S Filter Strip Slope ft/ft Step 3: Calculate flow depth Calculate flow depth (y in feet) using the following equation (must be less than 1 inch [0.083 feet]): y= Q design * n ( ) 1.49 * T * S 0.6 Parameter Units Value y Flow Depth ft Max (1 inch) n Mannings Roughness unitless 0.25 T Flow Width ft S Longitudinal Slope ft/ft If flow depth is greater than one inch, adjust width and/or slope and recalculate. 109 Lake Oswego Stormwater Manual Draft

124 Filter Strips Step 4: Check Velocity Calculate velocity of flow using the following equation (V in feet per second) Parameter V = Q T * y V Flow Velocity Units Value ft/s Max 0.5 If velocity is greater than 0.5 ft/s, adjust width and/or slope and recalculate. Step 5: Calculate Flow Path Length Calculate the flow path length of the filter strip (L in feet) using the equation below: L = * 5 n Parameter L Filter Strip Flow Path Length Units Value ft Lake Oswego Stormwater Manual Draft 110

125 Materials Filter Strips Biofiltration Soil Mix Filter strip soil media must support long-term plant and soil health and provide treatment to water as it infiltrates. The City of Portland s specification for Standard Blend for Public and Private Facilities (Appendix F.3 of the Portland Stormwater Manual) should comprise at least the top 18 inches of soil depth and be placed on top of uncompacted native soil. This mixture can be achieved by amending native sandy soils with compost (See Section 7.2 for information on amending onsite soils) or by purchasing a biofiltration soil mix. Mulch Component Percent by Volume Sandy loam 60-70% Composted plant-based organic matter 30-40% Fines are restricted to 5-15% and must pass through a size 200 sieve. Fine to medium hemlock bark or well-aged organic yard debris compost is recommended for filter strips. It should be placed in the facility only in areas above the designed flow depth. Keep mulch material out of the stormwater flow path to avoid clogging inlets or outlets. Mulch must be weed free and applied 2 to 3 inches thick to cover all soil between plants. It should not be over-applied. Vegetation Objective Establish dense plant growth of groundcovers and shrubs with a goal of 95% coverage. Plant Selection and Diversity Filter strips often experience moist to saturated soil conditions during the wet, rainy season and dry soil conditions during warm summers. Plant selection should respond to specific site conditions for each facility. See Appendix A for a complete plant list. Plant Quality Sedges and Rushes Grasses and forbs Nursery stock 10 inch plug, rhizome or tuber Nursery stock 1 gallon or equivalent; 4 inch pot allowed if the facility is left off-line for the first wet season, allowing plants an appropriate establishment period Grouping Plant Species Place plants in odd-numbered groups or clumps (3s, 5s, 7s, etc) of the same species throughout the planting areas. Planting depth Plant bare-rooted plants 4 to 6 inches deep and plugs as deep as the pot or plug. 111 Lake Oswego Stormwater Manual Draft

126 Filter Strips Conveyance and Outlet/Overflow Filter strips must drain to an approved outlet location. If soils are suitable for infiltration, route flows to an infiltration trench or drywell (note that these are UICs and would need to be registered with DEQ). Construction Till soil to a depth of at least 8 inches prior to planting. Mark filter strip boundaries with stakes or flagging prior to construction and avoid any unnecessary soil compaction or disturbance. Maintenance Proper maintenance and regular inspection are essential for a functioning filter strip. Please refer to the operations and maintenance section (Chapter 10) for more information. Native grasses and sedges do not like to be cut or mowed, see plant maintenance section for further maintenance guidance. Herbicides should not be used as a weed control technique within stormwater facilities. Lake Oswego Stormwater Manual Draft 112

127 Sand Filter Sand Filters Definition: Introduction Structural landscaped reservoirs used to collect, filter, and infiltrate stormwater, allowing pollutants to settle and filter out as the water percolates through the sand and gravel. Note: guidance adapted from Portland (2008). A sand filter includes pre-treatment, a flow spreader, a sand bed, and an underdrain collection system. Sand filters can be constructed above, at, or below grade. Depending on site conditions, sand filters can be designed to completely infiltrate all the stormwater they receive or designed as flowthrough facilities where only a portion of the flow is infiltrated, and overflow is directed to an approved discharge point. If plants are used, sand filters can be used to help fulfill a site s required landscaping area requirement and should be integrated into the overall site design. Numerous design variations of shape, wall treatment, and planting scheme can be used to fit the character of a site. Applicability Table BMP Parameters Appropriate for Pretreatment Onsite Provides Flow Control Provides Water Quality Treatment Appropropriate for Residential UIC Permit Required Engineer Required Graphic Maximum Ponding Depth Overflow Sand Filter Depth is 12 Inches Filter Material 2-3 Inches Washed Drain Rock 8 Inches Native Soil Perforated Underdrain 113 Lake Oswego Stormwater Manual Draft

128 Sand Filter Site Requirements Infiltration sand filters must be located a minimum of 5 feet from property lines Infiltration sand filters must be located a minimum of 10 feet from building foundations. No setbacks are required for lined flowthrough sand filters where the height above finished grade is 30 inches or less. 4 feet of hydraulic head required from inlet to outlet. Pretreatment required Geometry Sand Filter Dimensions Width 18 inches (flow through) and 30 inches (infiltration). Depth of sand filter bed 12 inches. Depth of filter material 2-3 inches. Depth of drain rock (underlying sand filter and filter material) 8 inches. Storage depth: Where the facility is at or above grade, the storage depth must be at least 12 inches between the top of the filter medium and the base of the overflow. Length to width ratio of 2:1 minimum. Slope 0.5 percent in any direction. For subgrade facilities, the filter medium must be 30 inches deep, with 8 inches of gravel above and below for conveyance. A minimum of 2 inches of freeboard (vertical distance between the overflow inlet elevation and overtopping elevation) shall be provided. Lake Oswego Stormwater Manual Draft 114

129 Sand Filter Design Steps Sand filters can be designed in 2 ways: Route stormwater hydrographs through a proposed facility to demonstrate that it meets the design criteria using an approved SBUH hydrologic model Calculate sand filter surface area using the simplified method described below. Step 1: Design Storm Size sand filters to treat the water quality design storm. Parameter P design Design storm Units in Value 0.96 Step 2: Contributing Drainage Area Measure or estimate total drainage area that will discharge to the proposed sand filter. Parameter Units Value A t Drainage Area sf Step 3: Facility Parameters Determine the sand bed depth and maximum ponding depth for the proposed sand filter. Parameter Units Value L Sand Filter Media Depth ft Min. 1.5 D Maximum Ponding Depth ft Step 4: Hydraulic Gradient Calculate the hydraulic gradient (I [unitless]) across the sand filter media using the following equation: I = ( D 2 + L ) L 115 Lake Oswego Stormwater Manual Draft

130 Sand Filter Step 5: Sand Filter Surface Area Calculate the sand filter surface area (A sf [sf]) required using the following equation: A sf = A t *P design *R K*I*T Parameter Units Value R Routing Factor unitless 0.7 T Drawdown Time hr 24 Method derived from Eastern Washington Stormwater Management Manual (Ecology 2004) Lake Oswego Stormwater Manual Draft 116

131 Materials Sand Filter Sand filters should have vegetated side slopes (maximum 3H:1V slope) if space allows. If not feasible, vertical walls can be used around the filter. Sand Media The sand in a filter must consist of a medium sand meeting the size gradation (by weight) given in the Table below. The contractor must obtain a grain size analysis from the supplier to certify that the No. 100 and No. 200 sieve requirements are met. Sand Media Specification U.S. Sieve Number Percent Passing <4 200 <2 Source: King County Surface Water Design Manual, September 1998 Sand Filter Walls Sand filter walls shall be made of stone, concrete, brick, or other durable material. Chemically treated wood that can leach out toxic chemicals and contaminate stormwater shall not be used. Waterproof Liners Flow-through facilities require a waterproof liner. There are many liner options and installation varies. Liner shall be 30 mil PVC or equivalent. Gravel Drain Rock Drain rock is required below the sand. For infiltration facilities where drain rock is specified to retain stormwater prior to infiltration, the specification is 1½-inch ¾-inch washed drain rock (ODOT ). All flow-through facilities shall use ¾-inch - 1/2-inch layer of washed drain rock (ODOT ). Drain rock and sand must be separated by a 2- to 3-inch layer of special filter material per ODOT Standard Specification Underdrains Underdrains shall be perforated PVC pipe that meets ODOT Standard Specification , or approved equal. Piping installation must follow current Uniform Plumbing Code. Pipe shall be 4-inch minimum for private property and 6-inches minimum for streets.. Vegetation Objective Plantings are recommended in sand filters. Plants enhance infiltration, prevent erosion, and compete with weeds. Establish dense plant growth of groundcovers and shrubs with a goal of 95% coverage.see Appendix A for a list of species appropriate for sand filters. 117 Lake Oswego Stormwater Manual Draft

132 Sand Filter Plant Selection and Diversity Sand filters will experience extreme dry soil conditions during warm summers. Plant selection should respond to specific site conditions for each facility. See Appendix A for a complete plant list. Plant Quality Sedges and Rushes Nursery stock 10 inch plug, rhizome or tuber Grasses and forbs Nursery stock 1 gallon or equivalent; 4 inch pot allowed if the facility is left off-line for the first wet season, allowing plants an appropriate establishment period Grouping Plant Species Place plants in odd-numbered groups or clumps (3s, 5s, 7s, etc) of the same species throughout the planting areas. Planting depth Plant bare-rooted plants 4 to 6 inches deep and plugs as deep as the pot or plug. Conveyance and Outlet/Overflow Sand filters must be located off-line. An overflow or bypass structure is required for larger storm events. For public sand filters, the following additional criteria apply: The sand filter must consist of an inlet structure, sand bed, underdrain piping, and liner. The inlet structure shall spread the flow of incoming water uniformly across the surface of the filter medium during all anticipated flow conditions. This flow shall be spread in a manner that prevents roiling or otherwise disturbing the filter medium. Where a collector manifold with perforated lateral branch lines is used, lateral branch line spacing shall not exceed 10 feet. The underdrain laterals shall be placed with positive gravity drainage to the collector manifold. The collector manifold shall have a minimum 1 percent grade toward the discharge joint. All laterals and collector manifolds shall have cleanouts installed, accessible from the surface without removing or disturbing filter media. Construction Special attention should be paid to the structural waterproofing if the facility is constructed adjacent to building structures. The location of the infiltration sand filter shall not be subject to compaction prior to, during, and after the construction of the facility. Maintenance See Appendix H for a sand filter maintenance requirements. Lake Oswego Stormwater Manual Draft 118

133 Constructed Wetland Constructed Wetland Definition: Stormwater treatment facilities that are designed to emulate natural wetlands, with natural, irregular shapes, shallow water that varies in depth, and varied side slopes. They are saturated or have standing water for part of the year. They are often shallower than ponds. Introduction Constructed wetlands present a wonderful opportunity to integrate habitat and a beautiful public amenity into the landscape of a large residential or commercial development. Constructed wetlands with healthy, thriving plants provide excellent water quality treatment. They require a large surface area and a large contributing area to ensure that wetland conditions are maintained. Although this guidance describes a stormwater BMP most applicable for large developments, planting and soil recommendations are also suitable for smaller sites. If residential or other small property owners have moist soil conditions on site, consider designing to enhance those wetland conditions. Applicability Table BMP Parameters Appropriate for Pretreatment Onsite Provides Flow Control (When designed for infiltration) Provides Water Quality Treatment Appropropriate for Residential UIC Permit Required Engineer Required (Depends on drainage area size) Graphic 119 Lake Oswego Stormwater Manual Draft

134 Constructed Wetland Site Requirements Adequate space for wetland footprint and maintenance access Edge of wetland must be located a minimum of 5 feet from property lines Edge of wetland must be located a minimum of 10 feet from buildings Appropriate for Group C or D soils Appropriate site hydrology to sustain saturated conditions for part of the year and maintain wetland vegetation. Geometry Constructed wetlands should be irregularly shaped, with a sinuous flow path and a variety of side slopes and benches incorporated to maximize plant establishment and diversity. See Figure 1 and Vegetation for an overview of wetland planting zone information. Constructed Wetland Dimensions Two cells required, with the first cell, the sediment forebay, containing 10% of the design volume, unless pretreatment is provided in a different facility. Where space permits, a sediment forebay with a staff gauge is strongly encouraged since it provides a clear visual indicator of when maintenance is needed. Bottom width 3 feet Slopes and depths should vary to provide a variety of habitat and maximize treatment. Flow depth 4 inches Ponding depth 2.5 feet Side slopes 5 horizontal: 1 vertical below maximum ponding depth Side slopes 3 horizontal: 1 vertical above maximum ponding depth Lake Oswego Stormwater Manual Draft Upland Seed Mix Slope Planting Emergent Planting Wetland Planting Emergent Planting Wetland Planting Emergent Planting Wetland Planting Shrub and Tree Planting Upland Seed Mix Figure 1. Constructed Wetland Section (Typ). A constructed wetland and its surrounding site context showing varying topographic conditions and plant communities. 120

135 Design Steps Constructed Wetland Constructed wetland sizing follows the same design steps for sizing a pond. However, constructed wetlands will have a larger surface area, varied side slopes, and shallower ponding areas to maximize water quality treatment. Step 1: Determine Drainage Basin Characteristics Calculate the total drainage area and composite SCS Curve Number for both pervious and impervious surfaces in the basin. See Appendix F for SCS Curve Number calculations. Parameter Units Values A Drainage Area acres CN SCS Curve Number unitless Step 2: Design Storm Calculate the runoff volume associated with the water quality storm: 1000 V r [ = 3,360 * A * ( P * - 10] design CN ) P design ( [ - 10] ) CN 2 Parameter P design Design Precipitation Depth Units in Values 0.96 V r Runoff Volume cf Step 3: Grading and Site Design Design varied side slopes, water depths, and planting zones to compliment site characteristics. Step 4. Determine Wetland Permanent Pool Depths Permanent water depth in a wetland will vary in the different cells. Determine the average, maximum, and minimum depths for permanent pool in each cell of the wetland. Parameter d wetland Permanent Pool Depth Units ft Values Lake Oswego Stormwater Manual Draft

136 Constructed Wetland Step 5: Refine Wetland Grading Using design criteria as guidance, adjust the layout of the wetland cells, verifying that max depths do not exceed those in Step 2. Calculate the permanent pool volume from the preliminary grading layout and adjust if the volume is less than the design storm volume. Lake Oswego Stormwater Manual Draft 122

137 Materials Constructed Wetland Growing Medium Constructed wetlands are best for Type C and D soils or in areas with a high groundwater table. Soils must be saturated for a long enough duration to maintain wetland vegetation. Investigate the soil profile and determine whether appropriate site soils exist and if any soil amendments need to be added in order to assist with initial plant establishment. See Chapter 7 for soil testing and amendment requirements. Mulch Fine to medium hemlock bark or well-aged organic yard debris compost is recommended for constructed wetlands. It should be placed in the facility only in areas above the designed flow depth. Keep mulch material out of the stormwater flow path to avoid clogging inlets or outlets. Mulch must be weed free and applied 2 to 3 inches thick to cover all soil between plants. It should not be over-applied. Vegetation Objective Establish dense plant growth of native submergent and emergent native vegetation within the constructed wetland and a diversity of groundcovers, shrubs, and trees along edges and borders. Maintain a 20 minimum distance between water-seeking species and inlets or outlets to prevent blocking structures or obstructing maintenance efforts. Plant Selection and Diversity Constructed wetlands often experience long periods of saturated soil conditions during the wet, rainy season, but may dry out during warm summers. Plant selection should cater to specific site conditions for each facility. Select at least nine species for the treatment area. Select species that are suitable for the hydrologic, light, and soil conditions in the proposed constructed wetland. Constructed wetlands should be designed so that they do not require mowing. See Appendix A for a complete plant list of species appropriate for constructed wetlands. Plant Quality Sedges and Rushes Grasses and forbs Shrubs Trees Nursery stock 10 inch plug, rhizome or tuber Nursery stock 1 gallon or equivalent; 4 inch pot allowed if the facility is left off-line for the first wet season, allowing plants an appropriate establishment period 1 gallon container or equivalent 3 gallon container or equivalent 123 Lake Oswego Stormwater Manual Draft

138 Constructed Wetland Grouping Plant Species Place plants in odd-numbered clumps (3s, 5s, 7s, etc) of the same species throughout the planting areas. Planting depth Plant bare-rooted plants 4 to 6 inches deep and plugs as deep as the pot or plug. Woody Vegetation Utilize woody vegetation to provide shade to standing water and provide structural diversity within the constructed wetland. Do not plant woody vegetation within 20 of inlet and outlet structures. Conveyance and Outlet/Overflow Constructed wetlands must overflow to an approved outlet structure. Emergency Overflow Spillway All ponds shall have an emergency overflow spillway or other overland location that will safely pass runoff from the 100-year storm event over the pond embankment in the event of control structure failure or for storm events exceeding design of the control structure. Spillways shall meet the following criteria: Locate the spillway from the top of the berm embankment to a City approved downstream conveyance system. Design the spillway to carry the 100-year storm event for the total upstream drainage area. The invert elevation of the spillway shall be at least 12 inches above the primary overflow elevation. The minimum spillway depth shall be 12 inches from the top of the berm. Provide a vegetated spillway designed to protect the spillway from erosion should an overflow event occur. Construction Planting designer shall place the plants during construction and create as-builts. Mark wetland boundaries with stakes or flagging prior to construction and avoid any unnecessary soil compaction or disturbance. When stockpiling soils, place them in shallow linear mounds to preserve soil microorganisms and vitality - see Chapter 7 for more information. Maintenance Maintain access routes to the constructed wetland for maintenance purposes. A public wetland facility should include a minimum 8-foot-wide access route with no greater than 10% slope. Staff gauges required at inlet and outlet. Bat and bird boxes are encouraged to help with pest control. Lake Oswego Stormwater Manual Draft 124

139 Ponds Ponds Definition: Stormwater ponds approved for use in Lake Oswego include wet ponds, infiltration ponds, and detention ponds. Ponds detain and/or infiltrate stormwater. Ponds are a good choice where there is a large contributing area draining to a single facility, where there is adequate space to design a pond that can be integrated into the landscaping, and where it is accessible for maintenance. Introduction WET PONDS Wet ponds have a permanent pool of standing water. Pollutants are removed through settling and biological processes. They are a good choice where soil infiltration rates are not adequate for an infiltration pond or rain garden, where there is a large enough contributing area that the pond will not be stagnant, and where they can be incorporated into the landscape as a beautiful amenity. INFILTRATION PONDS Infiltration ponds are vegetated depressions that temporarily pool stormwater before it percolates into underlying soils. Infiltration ponds may be solely for flow control, if soils are granular (type A and B soils - see Section 2.5.1), in which case a pretreatment facility is required. If soils have appropriate characteristics (organic content, soil sorptive capacity), infiltration facilities may also provide runoff treatment through physical filtration, adsorption, and precipitation. They are suitable where infiltration rates are adequate, and where the contributing area exceeds 5 acres. Applicability Table BMP Parameters Appropriate for Pretreatment Onsite Provides Flow Control (When designed for infiltration) Provides Water Quality Treatment Appropropriate for Residential UIC Permit Required Engineer Required WP= Applies to Wet Ponds DP= Applies to Detention Ponds IP=Applies to Infiltration Ponds DP, IP WP, IP DETENTION PONDS Detention ponds are ponds that temporarily store water then release it slowly over time, through control structures that control the rate and time of release. There may be incidental infiltration, but generally soils are not adequate for complete infiltration. 125 Lake Oswego Stormwater Manual Draft

140 Ponds Site Requirements Minimum contributing area = 5 acres Site must have adequate space for pond and maintenance access Pond selection should be appropriate for soil characteristics (e.g., if soils have adequate infiltration capacity, design an infiltration pond rather than a lined wetpond) Edge of water surface shall be 20 feet from property lines and structures Edge of water surface shall be 200 feet from tops of slopes > 15% Geometry Pond Dimensions Where space is available, include two cells, with the first cell (forebay) containing approximately 10% of the design surface area. Maintenance access must be provided to forebay. Maximum side slopes 3H: 1V Length:width ratio 3:1 Vegetated Side Slopes Max Ponding Depth Permanent Pool Depth (Wet Pond) Figure 1. Pond Section (TYP). Infiltration (Infiltration Ponds) Lake Oswego Stormwater Manual Draft 126

141 Design Steps Ponds Detention Ponds: Use an approved model to route post-developed flows through the pond. See design steps for Detention Pipes and Vaults. Infiltration Ponds: Use method described for Infiltration Trench to determine pond size. Wet Ponds: The following steps apply to wet ponds. Step 1: Determine Drainage Basin Characteristics Calculate the total drainage area and composite SCS Curve Number for both pervious and impervious surfaces in the basin. See Appendix F for SCS Curve Number calculations. Parameter Units Values A Drainage Area acres CN SCS Curve Number unitless Step 2: Design Storm Calculate the runoff volume associated with the water quality storm: 1000 V r [ = 3,360 * A * ( P * - 10] design CN ) P design ( [ - 10] ) CN 2 Parameter P design Design Precipitation Depth Units in Values 0.96 V r Runoff Volume cf Step 3: Grading and Site Design Design varied side slopes, water depths, and planting zones, to compliment site characteristics and transition site in with surrounding context. Step 4. Determine Wetland Permanent Pool Depths Permanent water depth will vary in the different cells. Determine the average, maximum, and minimum depths for permanent pool in each cell. Parameter Units Values d pond Permanent Pool Depth ft Lake Oswego Stormwater Manual Draft

142 Ponds Step 5: Refine Pond Grading Using design criteria as guidance, adjust the layout of the pond cells, verifying that maximum depths do not exceed those in Step 2. Calculate the permanent pool volume from the preliminary grading layout and adjust if the volume is less than the design storm volume. Lake Oswego Stormwater Manual Draft 128

143 Materials Ponds Growing Medium Investigate the soil profile and determine whether appropriate site soils exist for healthy vegetation and if any soil amendments need to be added in order to assist with initial plant establishment. See Section 7.6 for soil testing and amendment requirements. Mulch Fine to medium hemlock bark or well-aged organic yard debris compost is recommended around the base of plantings in areas along the tops of banks and side slopes above the high water mark. Mulch must be weed free and applied 2 to 3 inches thick to cover all soil between plants. It should not be over-applied. Vegetation Objective Detention Ponds: It is difficult to establish vegetation in areas that experience inundation for longer than a 48- to 72-hour period of time. Establish dense plant growth in areas along side slopes and tops of banks where water levels and soil conditions are amenable to vegetation. Consider using rock or similar surfacing along the pond bottoms and side slopes that will experience prolonged inundation and then, may or may not dry out during the warm, dry seasons. This will help prevent weed establishment and soil erosion. Infiltration Ponds: Infiltration ponds are designed to drain within a 24-hour period. Follow the vegetation guidance for rain gardens when designing an infiltration pond, while adjusting planting zones to the appropriate water depth tolerances along pond side slopes. Wet Ponds: Establish dense plant growth of native submergent and emergent native vegetation along pond side slopes and a diversity of groundcovers, shrubs, and trees along edges and borders of the facility. Added water quality treatment can be integrated into a pond system by adding a shallower wetland bench prior to the pond outlet. For all ponds, maintain a 20 minimum distance between water-seeking shrub species and inlets or outlets to prevent blocking structures or obstructing maintenance efforts. The remaining guidance for vegetation in ponds refers to vegetation for wet ponds. Plant Selection and Diversity Wet ponds will have fairly consistent soil moisture characteristics along side slopes. Depending on site soil and drainage characteristics, the side slopes and top of bank plantings may experience moist to saturated winter soil conditions and dry summer conditions. Plant selection should cater to specific site conditions for each facility. Select at least nine species for the treatment area. Select species that are suitable for the hydrologic, light, and soil conditions of the proposed pond. Ponds should be designed so that they do not require mowing. See Appendix A for a complete plant list of species appropriate for various types of ponds. 129 Lake Oswego Stormwater Manual Draft

144 Ponds Plant Quality Sedges and Rushes Grasses and forbs Shrubs Trees Nursery stock 10 inch plug, rhizome or tuber Nursery stock 1 gallon or equivalent; 4 inch pot allowed if the facility is left off-line for the first wet season, allowing plants an appropriate establishment period 1 gallon container or equivalent 3 gallon container or equivalent Grouping Plant Species Place plants in odd-numbered clumps (3s, 5s, 7s, etc) of the same species throughout the planting areas. Planting depth Plant bare-rooted plants 4 to 6 inches deep and plugs as deep as the pot or plug. Woody Vegetation Utilize woody vegetation to provide shade to standing water and provide structural diversity surrounding the pond borders. Do not plant woody vegetation within 20 of inlet and outlet structures. Conveyance and Outlet/Overflow Overflow must be to a City approved downstream conveyance system. For detention ponds, the following criteria apply: Primary overflow (D) elevation shall be set at the 10-year design release rate. Emergency Overflow Spillway All ponds shall have an emergency overflow spillway or other overland location that will safely pass runoff from the 100-year storm event over the pond embankment in the event of control structure failure or for storm events exceeding design of the control structure. Spillways shall meet the following criteria: Locate the spillway from the top of the berm embankment to a City approved downstream conveyance system. Design the spillway to carry the 100-year storm event for the total upstream drainage area. The invert elevation of the spillway shall be at least 12 inches above the primary overflow elevation. Lake Oswego Stormwater Manual Draft 130

145 Ponds The minimum spillway depth shall be 12 inches from the top of the berm. Provide a vegetated spillway designed to protect the spillway from erosion should an overflow event occur. Construction Planting designer shall place the plants during construction and create as-builts. Encourage the use of onsite soils when constructing berms or surrounding pond topography. Mark pond boundaries with stakes or flagging prior to construction and avoid any unnecessary soil compaction or disturbance. When stockpiling soils, place them in shallow linear mounds to preserve soil microorganisms and vitality - see Section 7.6 for more information. Maintenance Maintain access routes to the pond for maintenance purposes. A public pond facility should include a minimum 8-foot-wide access route with no greater than 10% slope. Consider using reject rock and/or low-growing native prairie species for maintenance access roads. Using the rock for access roads will avoid hauling costs and native prairie species will not need mowing, but may be mowed prior to maintenance activities without experiencing excessive damage. Staff gauges required at inlet and outlet. Bat and bird boxes are encouraged to help with pest control. 131 Lake Oswego Stormwater Manual Draft

146 Detention Pipes and Vaults Definition: Underground storage facilities that temporarily store water before releasing it to reduce runoff rates from new developments to meet design standards (typically to match predevelopment flow rates for specified design storms). Introduction Detention pipes and vaults are appropriate for residential developments, commercial and industrial sites, and roads, where large development projects are required to meet detention standards, and there is inadequate space or unsuitable site conditions for an infiltration pond, constructed wetland with storage, or detention pond. Detention pipes and vaults do not provide water quality treatment, so a separate water quality treatment BMP will be required to meet water quality treatment requirements. Detention facilities must be designed by an engineer, with designs demonstrating that they have adequate maintenance access, they can withstand vehicular and other structural loadings, they will be stable and have been designed to counteract buoyancy forces in areas of high groundwater, and the materials can withstand chemical properties of soils. Applicability Table BMP Parameters Appropriate for Pretreatment Onsite Provides Flow Control Provides Water Quality Treatment Appropropriate for Residential UIC Permit Required Engineer Required To demonstrate that detention facilities will perform their primary flow control function, an engineer must submit calculations from an approved hydrologic model or method. Lake Oswego Stormwater Manual Draft 132

147 Site Requirements Detention Pipes and Vaults Underground storage facilities must be located to avoid conflicts with other underground utilities. Regular maintenance is essential to ensure continued function of underground detention facilities. Therefore, they must be accessible by maintenance vehicles. Tanks and vaults shall be placed on stable, consolidated native soil with suitable bedding. Tanks and vaults shall not be allowed in fill slopes, unless a geotechnical analysis is performed for stability and construction practices. Geometry Detention Pipe Diameter 36 inches Pipe bottom shall be flat or gently sloped (slope 0.5%) Maximum distance between pipe bottom and finish grade = 20 Sediment storage depth 6 inches Freeboard (distance between design headwater elevation and overflow elevation in control structure) 6 inches Detention Vault Vault bottom shall be flat or gently sloped (slope 0.5%) to the center, forming a v Sediment storage depth 6 inches Freeboard 6 inches Pollution/Flow Control Manhole The minimum allowable diameter for an orifice used to control flows in a public facility is 2 inches. Private facilities may use a 1-inch diameter orifice if additional clogging prevention measures are implemented. Orifice diameter shall be greater than or equal to the thickness of the orifice plate. Orifices less than 3 inches shall not be made of concrete. A thin material (e.g. stainless steel, HDPE, or PVC) shall be used to make the orifice plate; the plate shall be attached to the concrete or structure. 133 Lake Oswego Stormwater Manual Draft

148 Detention Pipes and Vaults Design Steps Detention facilities shall be designed by an engineer, with calculations submitted to demonstrate that the facility meets the following design criteria: Post-development peak discharge rate must match the predeveloped peak discharge rate specified in Section 7.1 using an approved single-event hydrologic model. In soils where groundwater may induce flotation and buoyancy, measures shall be taken to counteract these forces. Ballasting with concrete or earth backfill, providing concrete anchors, or other counteractive measures shall be required. Calculations shall be required to demonstrate stability. All vaults, and pipes shall meet structural requirements for overburden support and traffic loadings, if appropriate. H-20 live loads shall be accommodated for tanks and vaults under roadways and parking areas. End caps shall be designed for structural stability at maximum hydrostatic loading conditions. Step 1: Design Flows Calculate pre-development peak flows (Q pre ) and post-development peak flows (Q post, Q 100 ) using approved model (see Section 7.1). Step 2: Establish Preliminary Geometry Determine initial values for detention pipe or vault geometry parameters. Step 3: Establish Preliminary Outlet Structure Configuration Determine initial values for orifice diameter and overflow depth. Orifice Sizing Equation: Q = C A (2 g h) 0.5 Parameter Units Value Q Orifice Discharge Rate cfs C Coefficient of discharge ft 0.60 for plate orifices A Area of Orifice sq ft h Hydraulic Head ft g Acceleration of Gravity ft/sec Lake Oswego Stormwater Manual Draft 134

149 Detention Pipes and Vaults The diameter of plate orifices is typically calculated from the given flow. The orifice equation is often useful when expressed as an equivalent orifice diameter in inches. where: d = Q h Parameter Units Q Flow cfs Value d h Orifice Diameter Hydraulic Head inches ft Step 4: Route Design Storm Use an approved model to route the post development design storm (Q post ) through the detention facility, and compare peak outflow to the predevelopment design storm peak flow (Q pre ) Step 5: Refine Facility Adjust facility geometry, orifice size, and overflow elevation until design criteria are met. Step 6: Check 100-year Flow Check overflow design to ensure safe conveyance of the 100-year runoff discharge. 135 Lake Oswego Stormwater Manual Draft

150 Detention Pipes and Vaults Materials Detention Pipe Galvanized metals leach zinc into the environment, especially in standing water situations. This can result in zinc concentrations that can be toxic to aquatic life. Therefore, galvanized materials shall not be used in stormwater facilities and conveyance systems. For public facilities, detention pipe materials and joints shall conform to the technical specifications. For private facilities, the pipe material shall conform to the Oregon Plumbing Specialty Code. Detention Vault Detention vaults shall be constructed of structural reinforced concrete (3000 psi, ASTM 405). All construction joints shall be provided with water stops. Flow Control Structure Orifices shall be protected within a manhole structure or by a minimum 18-inch- thick layer of 1½ - 3-inch evenly graded, washed rock. Orifice holes shall be externally protected by stainless steel or galvanized wire screen (hardware cloth) with a mesh of ¾ inch or less. Chicken wire shall not be used for this application. Orifices less than 3 inches shall not be made of concrete. A thin material (e.g., stainless steel, HDPE, or PVC) shall be used to make the orifice plate; the plate shall be attached to the concrete or structure. Conveyance and Outlet/Overflow Pollution/ Flow Control Manhole Design Pollution/Flow control manholes must be provided that regulate outflow from the underground detention facilities. Pollution/Flow control manholes must comply with the specifications outlined in the City s Standard Plans numbers B-1.08A and B-1.08B. Additional general requirements are presented below. Permit submittal must include flow control structure rim elevation, the storage pipe invert elevation, the outlet pipe invert elevation, and, the elevation of the top of the storage pipe, and the elevation of the top of the overflow pipe. Maintenance Detention Pipe End Plates and Connections The upstream end of the detention pipe must have a maintenance hole or watertight end plate or plug of standard manufacture (not constructed in the field) and must be made from the same material as the detention pipe. Access The following access requirements apply to detention pipes: Lake Oswego Stormwater Manual Draft 136

151 Detention Pipes and Vaults Detention pipes more than 100 feet long must have access risers at each end to allow for maintenance and repair. Detention pipes over 200 feet long must have an access riser at the upstream end and a cleanout at least every 100 feet. Detention pipes and vaults must have access provided that meet the following criteria: Detention pipes more than 50 feet long must provide a cleanout. Detention pipes more than 100 feet long must have access risers at each end to allow for maintenance and repair. Detention pipes over 200 feet long must have an access riser at the upstream end and a cleanout at least every 100 feet. Access openings shall be positioned a maximum of 50 feet from any location within the detention pipe or vault. All detention pipe access openings shall have round, solid locking lids (usually 1/2 to 5/8-inch diameter Allen-head cap screws). Thirty-six-inch minimum diameter CMP riser-type manholes of the same gage as the detention pipe material may be used for access along the length of the detention pipe and at the upstream terminus of the detention pipe in a backup system. The top slab is separated (1-inch minimum gap) from the top of the riser to allow for deflections from vehicle loadings without damaging the riser pipe. All detention pipe and vault access openings must be readily accessible by maintenance vehicles. Detention pipes and vault must comply with the OSHA and Oregon OSHA confined space requirements, which include, but are not limited to, the preparation of ventilation plans and clearly marking entrances to confined space areas. Access for detention vaults may be provided by use of removable panels, hatches, or ring and cover. Internal structural walls of large vaults shall be provided with openings sufficient for maintenance access between cells. The openings shall be sized and situated to allow access to the maintenance v in the vault floor. The recommended minimum internal height is 7 feet from the highest point of the vault floor (not sump), and the recommended minimum width is 4 feet. However, concrete vaults may be a minimum 3 feet in height and width if there are access manholes at each end, and if the width is no larger than the height. Minimum internal height requirement do not apply for any areas covered by removable panels. 137 Lake Oswego Stormwater Manual Draft

152 Conveyance and Detention Design Standards 8 Note: Most of the design standards in this Chapter have been adapted from Clean Water Services (2007). Lake Oswego s conveyance standards have been developed to protect public safety, to minimize flooding risk, and to protect water quality. 8.1 General Provisions - Conveyance General provisions regarding conveyance and detention standards are as follows: The provisions of this chapter shall apply to all public and private surface water conveyance systems within City s jurisdiction. Interpretations of such provisions and their application in specific circumstances shall be made by the City. In addition to these rules, all surface water conveyances shall be designed and constructed to DEQ rules. Where these rules conflict with DEQ rules, DEQ rules shall apply. The City requires the applicant to provide an acceptable point of surface water discharge from the developed site. The acceptable point of discharge shall be deemed acceptable by the City prior to acceptance of the site assessment and feasibility analysis. Except as otherwise provided, the extension of the public conveyance systems to serve any parcel or tract of land shall be done by and at the expense of the property owner or applicant and done in a manner that utilizes the natural drainage patterns while considering future planning concerns. The City reserves the legal right to perform the work or cause it to be performed and bill the property owner for the cost or to pursue special assessment proceedings as otherwise provided by City ordinance or permit conditions. Refer to the City s technical specifications for conveyance systems, including all acceptable materials Design, including materials, size, and location of surface water mains and service lines, shall be in accordance with City Engineering Division s policies, design standards, technical specifications, and standard details and be approved by the City Manager. Variances from the standard details and/or technical specifications shall require written approval of the City. Please contact the City for the most current version of technical specifications and standard details. 8.2 Extension of Public Conveyance Systems A development requiring connection to the public surface water system shall extend the public storm conveyance systems to allow all adjacent uphill parcels to be served by the public systems. Under some circumstances, the City may waive this requirement for surface water conveyance if one of the following conditions is met: The proposed connection to the public surface water conveyance system is for an existing building. Topography prevents uphill parcels from being effectively served by the required conveyance extension. Lake Oswego Stormwater Manual Draft 138

153 Conveyance and Detention Design Standards Uphill parcels are outside the urban growth boundary, and in the City s view, the boundary is not likely to be expanded in the future to include uphill parcels. An analysis demonstrates that the uphill parcels are likely to be served via another routing of the conveyance system, and the City agrees with this analysis. When the physical extension of the conveyance system is not required for reasons other than topography, the City may require an easement for future surface water conveyance. 8.3 Conveyance Easements General Easements and public rights-of-way are outlined in LOC and LOC In general, the following conditions apply to surface water easements. Public surface conveyance facilities, not located within public right-of-way, shall be located within an easement granted to the City. The City may require that a minimum area of 7.5 feet in all directions from the edge of a manhole, catch basin, cleanout, or field inlet be encompassed in a public right-of-way or easement granted to the City. Access easements shall be provided to manholes, where required by the City. Proposed encroachments shall not prevent access to, cover, or block the flow of water to or into catch basins, ditches, or swales, and shall not otherwise alter the natural drainage pattern or adversely affect adjacent property. Where drainage is involved, the City Manager or his designee may set specific requirements. Utility construction within easements shall minimize disturbance to existing conditions, especially trees and other vegetation. Any disturbed areas within easements shall be restored to a condition similar to the condition prior to construction, including the replacement of plants of similar species as those removed or damaged. Replacement trees shall be of similar species and be a minimum of one and one-half inches in caliper. Applicants and reviewers shall review LOC and LOC for more detail Standard Conveyance Easement Width Standard utility easement widths are located in LOC (4). In general, when designing a surface water conveyance system and associated easements, designers shall consider the following: Utility easements created on undeveloped real property and located outside public or private waterways or right-of-way, widths shall be a minimum of 15 feet (7.5 feet on each side of the easement centerline). Widths shall be the minimum width possible to facilitate utility installation and maintenance. For easements created over real property and located within or adjacent to public or private waterways, minimum easements, shall be a minimum of 10 feet (5 feet on each side of the easement centerline). Easements widths will consider many factors, including method of utility construction, ordinary depth of water over the conveyance, and the type of equipment used for utility construction, maintenance and repair or replacement. 139 Lake Oswego Stormwater Manual Draft

154 Conveyance and Detention Design Standards Reduced Conveyance Easement Widths Conveyance easement widths may be reduced if all the following conditions are met to the satisfaction of the City: A reduced easement width is needed due to the location of existing buildings that prevent a standard easement width. Another conveyance route within the development site and public right-of-way is not possible due to topography. Furthermore, when reduced conveyance easements are allowed, the City may condition the reduced easement width on site specific and other design factors Encroachments In general, the following encroachment conditions shall be considered in the design of the surface water conveyance system. The designer should consider, at a minimum, LOC 42.18, Public Rights-of-Way and Easements, when the possibility of easement encroachment exists. Structures constructed within conveyance easements or vegetation or landscaping materials in, over or upon any dedicated public right-of-way or easement shall require an encroachment agreement with the City. Approval of the encroachment is at the discretion of the City. The encroachment agreement shall allow or City to remove the structure, as needed, to access the conveyance system. Replacement of the structure shall be at the property owner s expense. The City may require special protection for the conveyance system in the vicinity of the encroachment, including but not limited to: Clearance to manholes and underground pipelines and storm drains shall be 7.5 feet. When the City Manager or designee determines that permitting the requested encroachment may subject the City to potential liability, a condition of permit issuance shall be the filing with the City Recorder of a policy of insurance and form of policy issued by an insurance company licensed to do business in Oregon. 8.4 Flow Determination for Surface Water Conveyance In general, the designer shall consider the following information regarding flows when designing the surface water conveyance system Land Use Assumptions for Flow Determination Ten- to 100-year flows for design of conveyance systems shall be based on full build-out of the upstream basin based upon the most recent approved county or City comprehensive land use plan and realistic estimates of development densities in areas included in recent additions to the urban growth boundary. Lake Oswego Stormwater Manual Draft 140

155 Conveyance and Detention Design Standards Computational Methods for Runoff Calculations Unless an alternative method is approved by the City in writing, calculation of storm runoff used for conveyance design shall be based on one of the following methods with the limitations on use of each listed Rational Method The Rational Method is a simple equation that estimates peak runoff discharge and is commonly used for sizing conveyance systems and stormwater facilities in small basins. The Rational Method formula is: Q=CfCIA Where: Q = peak flow, cubic feet per second (cfs) C f = runoff coefficient adjustment factor to account for reduction of infiltration and other losses during large storm events C = runoff coefficient, dimensionless I = rainfall intensity (function of time of concentration), inches per hour (in/hr) A = drainage area (acres) Appendix E provides a table of runoff coefficients, rainfall intensity-duration-recurrence interval curves to determine rainfall intensity, and formulas for calculating the time of concentration. For a more detailed discussion of the Rational Method, refer to Appendix 7-F of the ODOT Hydraulics Manual (ODOT 2011) Santa Barbara Urban Hydrograph (SBUH) SBUH methods shall be based on the following information: The rainfall distribution to be used within the City is the design storm of 24-hour duration based on the standard NRCS Type 1A rainfall distribution using the chart in Appendix F Soil types shall be derived from the NRCS Soil Survey for the appropriate county (Multnomah, Clackamas/Washington County). See Appendix F for reference. 8.5 Surface Water Conveyance Design Considerations In general, the designer shall consider the following when designing the conveyance system. 141 Lake Oswego Stormwater Manual Draft

156 Conveyance and Detention Design Standards Design for Full Build Out Storm drainage facilities shall be designed and constructed to accommodate all future full build-out flows generated from upstream property Stormwater Conveyance Design Criteria Sizing Design Storm The design storm to be used for sizing of conveyance facilities depends on the contributing area. Refer to Table 8.1 for guidance. Table 8.1. Contributing Area Recurrence Interval < 40 acres 10-year without surcharge 40 acres-640 acres 25-year without surcharge 640 acres 100-year without surcharge Materials Lake Oswego s complete design and construction specifications for storm sewers are provided in the Technical Specifications, section Table 8.2 summarizes approved materials for storm sewers. Table 8.2. Approved Storm Drain Materials. Material Specification Reinforced concrete pipe ASTM C-76, Class III Non-reinforced concrete pipe ASTM C-14, Class 3 (max. size 18 ) Ductile iron pipe See Technical Specifications PVC ASTM D3034, SDR 35 HDPE AASHTO M294 Type S (12 to 36 in diameter) or AASHTO 252 Type S (4 to 10 in diameter). Lake Oswego Stormwater Manual Draft 142

157 Conveyance and Detention Design Standards Minimum Diameters Storm sewers shall conform to the following minimum diameters: 10-inch from inlets to catch basins and manholes 12-inch or greater for main lines Minimum Cleansing Velocity The pipe shall be set at a minimum slope to assure that a minimum cleansing velocity of 3 feet per second is maintained under full flow conditions Upstream Impacts Modifications to the existing on-site storm drainage facilities shall not restrict flows thereby creating backwater onto offsite property to levels greater than the existing situation, unless approved by the affected offsite property owner(s) and the City. When approved, the offsite property owner(s) shall agree to and sign a permanent easement legally describing the location of the backwater storage and authorizing the use of their property for stormwater drainage and detention purposes. The easement shall be in a form approved by the City Downstream Impacts The City may require the applicant to remove downstream restrictions that create backwater during the 25-year design storm in the current or post-development condition, at the City s discretion. Removal of downstream obstructions shall not be allowed if the removal will cause, contribute, or exacerbate damage from flooding to existing buildings or dwellings in the 100-year design storm. When downstream restrictions are not removed, an on-site detention facility shall be required Cross Lot Drainage Developments shall not materially increase or concentrate runoff onto adjacent properties, except when the runoff is contained in an existing drainage way. Developments shall accommodate existing off-site drainage entering a development site so as to not negatively affect upstream property owners Dissipation of Runoff Discharge Runoff exiting a development site shall be discharged with adequate energy dissipaters to prevent downstream damage Separation Unless approved by City, the minimum separation distance between parallel surface water conveyances shall be 5 feet clear. If vertical separation between utilities is greater than 3 feet, additional horizontal spacing may be required to allow for maintenance access. 143 Lake Oswego Stormwater Manual Draft

158 Conveyance and Detention Design Standards Alignment Public surface water utility conveyance shall be laid on a straight alignment and at uniform grade. See section for minimum slope for cleansing velocity. 8.6 Other Requirements for Public Conveyance Systems Surveying The applicant s engineer or surveyor shall be responsible for establishing the location of the surface water utility conveyance system by means of construction stakes offset along the center lines prior to commencement of construction. Moving upstream, there shall be a construction stake placed within 25 feet of each manhole, and at no more than 100-foot intervals along the mainline. Each lateral location shall be staked Railroad Crossings Crossing of railroad rights-of-way shall be done in conformance with the requirements of the railroad having jurisdiction. If bonds or certificates of insurance protection are required, they shall be furnished by the contractor or applicant to the railroad company concerned. The City shall be named as an additional insured. Actual permits or easements for such crossings shall be obtained by the applicant and all terms for such permits or easements shall be met by the applicant and contractor. 8.7 Surfacewater/Stormwater Laterals General Provisions The specifications contained herein, together with the State of Oregon Uniform Plumbing Code and all other applicable requirements of federal, state, and local law shall govern the installation of laterals. The provisions of City ordinances requiring permits, fees, and other requirements shall be complied with prior to the start of work on any portion of the sanitary or storm pipeline systems Planning Considerations Where a parcel requiring connection to a public surface water utility conveyance system cannot connect through a lateral meeting the requirements of this section, then extension of the public conveyance system shall be required. This extension of the public system is in addition to the requirements of Section 8.2. Two adjacent single-family dwellings or two duplexes may be served by a single surface water utility upon consideration and written approval of the City. 8.8 Conveyance and Detention Design Standards Purpose The purpose of these standards is to reduce the risk of flooding, prevent or reduce the risk to human life and property, and maintain the functions and values of floodplains, such as allowing for the storage and conveyance of stream flows through existing and natural flood conveyance systems. Lake Oswego Stormwater Manual Draft 144

159 Conveyance and Detention Design Standards Flood Management Areas Defined Flood management areas shall include, but are not limited to, the following: Land identified within the 100-year floodplain and floodway as shown on the FEMA flood insurance maps. See City website for details and maps. Land identified in updated flood studies or any other authoritative data documenting flood elevations as approved by the City. Applicants shall use the most recent and technically accurate watershed model information, should one exist, available from the City, or other updated data as approved by the City, to determine flood areas Flood Management Design Criteria The standards that apply to the flood management areas apply in addition to local, state, and federal restrictions governing floodplains and flood hazard areas. All fill placed in a floodplain shall be balanced with an equal amount of soil material removal and shall not decrease floodplain storage capacity at any stage of a flood (2-, 25-, or 100-year storm event). No net fill in any floodplain is allowed except when all of the following conditions are met: When an area has received special protection from floodplain improvement projects which either lower the floodplain or otherwise protect affected properties; Where the exceptions comply with adopted master plans, watershed management plans, or subbasin plans, if any; and When all required permits and approvals have been obtained in compliance with FEMA rules and other local, state, and federal laws regarding fill in floodplains. Large areas may not be excavated in order to gain a small amount of fill in a floodplain. Excavation areas shall not exceed the fill areas by more than 50 percent of the square footage, unless approved by the City. Any excavation dug below the winter low water elevation shall not count toward compensating for fill since these areas would be full of water in the winter and not available to hold stormwater following a rain. Winter low water elevation is defined as the water surface elevation during the winter when it has not rained for at least three days and the flows resulting from storms have receded. This elevation may be determined from records, studies, or field observation. Any fill placed above the 100- year floodplain will not count toward the fill volume. The excavated area shall be designed to drain if it is an area identified to be dry in the summer, for example, if it is used for a park or mowed in the summer. Excavated areas identified to remain wet in the summer, such as a constructed wetland, shall be designed not to drain. For areas that are to drain, the lowest elevation shall be at least 6 inches above the winter low water elevation, and sloped to drain. One percent slopes will be allowed in areas less than 1,000 square feet Excavation to balance a fill shall be located on the same parcel as the fill unless it is not reasonable or practicable to do so. In such cases, the excavation shall be in the same drainage basin, within points of constriction on the conveyance system, if any, as near as practical to the fill site, and shall be constructed as a part of the same development project. 145 Lake Oswego Stormwater Manual Draft

160 Conveyance and Detention Design Standards Short-term parking (motor vehicles remain parked for less than 18 hours per day) in the floodplain may be located at an elevation of no more than one foot below the 10-year floodplain so long as the parking facilities do not occur in a sensitive area. Long-term parking (motor vehicles remain parked for greater than 18 hours without being moved) in the floodplain may be located at an elevation of no more than one foot below the 100-year floodplain so long as the parking facilities do not occur in a sensitive area. Temporary fills permitted during construction shall be removed upon completion of construction prior to the close of the in-stream work window as defined by Oregon Department of Fish and Wildlife or other local, state, or federal authority. Excavation and fill required for the construction of detention facilities or other facilities, such as levees, shall be specifically designed to reduce or mitigate flood impacts. Levees shall not be used to create vacant buildable land. Excavation and fill required to restore or enhance floodplains, riparian areas, wetlands, uplands, and streams, including but not limited to the planting of vegetation and day-lighting of existing storm pipes, shall be permitted as long as the design complies with applicable federal, state, and local standards. The floodplain may not be modified to increase water velocities such that stream bank erosion will be increased, unless the stream banks are protected to prevent the increased erosion. Uncontained areas of hazardous materials are prohibited within flood management areas. Existing nonconforming uses are allowed to continue in the flood management area. Existing nonconforming uses may be modified with approval from the City. Any proposed work within or modification to a floodway shall be certified by an Oregon-registered professional engineer as to how it conforms to these standards and all other local, state, and FEMA regulations. For streams, creeks, rivers, and other watercourses where the floodway has not been identified, the entire floodplain shall be treated as a floodway unless a study has been prepared by an Oregonregistered professional engineer and approved by the City to define the floodway limits for a stream section. Lake Oswego Stormwater Manual Draft 146

161 9 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control This chapter describes construction practices that are required to ensure that construction activities do not cause unacceptable impacts to stormwater runoff and water bodies. 9.1 Legal Requirements City Code Temporary erosion and sediment control requirements can be found in Chapter 52 of the Lake Oswego Code MS4 Permit Under the City s MS4 permit, contractors have the following responsibilities: Construction site operators must develop erosion prevention and sediment control site plans and must implement and maintain effective erosion prevention and sediment control BMPs. Construction site operators must prevent or control nonstormwater waste that may cause adverse impacts to water quality, such a discarded building materials, concrete truck washout, chemicals, litter, and sanitary waste C Permit Under the NPDES 1200-C permit, the following observations are considered significant and should be documented with photographs and notes and reported to the City and DEQ: a. Earth slides or mud flows that leave the construction site and are likely to discharge to surface waters. More information may be found in the Erosion Control permit application, available on the Engineering website at engineer/forms.htm and in Chapter 38 and Chapter 52 of the Lake Oswego Code, at CityCode/. For information on the Erosion Control program, please call: Delynn Clark at (503) or at dclark@ci.oswego.or.us. For information on the Surface Water Management System, please contact: David Gilbey at (503) or by at dgilbey@ci.oswego.or.us. b. Evidence of concentrated flows of water causing erosion when such flows are not filtered or settled to remove sediment prior to leaving the construction site and are likely to discharge to surface waters. Evidence includes the presence of rills, gullies, or channels. Flow to stormwater inlets or catch basins located on the site will be considered leaving the site if there are no sediment control structures downstream of the inlets or catch basins that are under the permittee s control. 147 Lake Oswego Stormwater Manual Draft

162 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control c. Turbid flows of water that are not filtered or settled to remove sediment prior to leaving the construction site and are likely to discharge to surface waters. Flow to stormwater inlets or catch basins located on the site will be considered leaving the site if there are no sediment control structures downstream of the inlets or catch basins that are under the permittee s control. d. Deposits of sediment at the construction site in areas that drain to unprotected stormwater inlets or catch basins that discharge to surface waters. Inlets and catch basins with failing sediment controls due to lack of maintenance or inadequate design will be considered unprotected. e. Deposits of sediment from the construction site on public or private streets outside of the permitted construction activity that are likely to discharge to surface waters. f. Deposits of sediment from the construction site on any adjacent property outside of the permitted construction activity that are likely to discharge to surface waters General Considerations Stay familiar with current erosion prevention and sediment control requirements. The contractor is responsible for knowing and following local, state, and federal requirements. Most local regulations are mandated by the federal Clean Water Act; the City does not have the ability to waive these requirements. 9.2 Poor Construction Practices There are many construction and development activities that adversely affect stormwater runoff during and after development. They include: Clearing all vegetation and exposing all soils on a project site; scraping the organic layer of soil and hauling off site Soil compaction of site and BMP areas from construction equipment Failing to protect locations of stormwater facilities from construction activities Using stormwater runoff and treatment facilities as temporary erosion and sedimentation BMPs or construction debris collection areas Stockpiling soils and other materials in unsuitable locations or without adequate protection and management Ineffective erosion control. These activities not only create construction site management issues (that cost time and resources) but also affect the long-term functionality of any stormwater facilities located on the site and affect the site s natural ability to treat and infiltrate stormwater. For example, failing to protect locations of stormwater BMPs from construction traffic can lead to overly compacted soils onsite. These compacted soils, unless remedied at extra cost, lead to poorly or non-functioning stormwater facilities. Non-functioning or poorly functioning facilities become long-term, costly maintenance problems for the ultimate owner of the property. Lake Oswego Stormwater Manual Draft 148

163 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control One of the keys to success in protecting local water resources from the impacts of construction and development related stormwater runoff is minimizing land disturbance. For this reason, the City has assembled this chapter on construction phasing and sequencing and implementation of construction BMPs. For more information on how construction practices cause water quality and water quantity problems in receiving waters, please see Section 2.3 of this manual. There are some important general principles that should govern erosion and sediment control plans and effective erosion and sediment control in general. These principles include: Timing, scheduling, and staging of work to minimize overall impacts Implementing procedures to ensure compliance with effective construction BMPs Considering construction impacts during preliminary design and prior to onsite grading Minimizing disturbances by establishing and protecting buffers and reducing grading activities Documentation throughout the life of the project 9.3 Timing, Scheduling, and Staging of Work Scheduling can be a very effective means of reducing impact from development and building activities as well as protecting existing site features that are critical in the overall infiltration and treatment of stormwater. Construction activities should be planned and implemented to minimize the extent and duration of exposed soils and to maximize the preservation and protection of site features that will be used for stormwater management. Scheduling activities should take into account the season and daily weather forecast. Grading activities should occur during dry periods, and disturbed If wet weather is forecast, grading activities should be postponed and disturbed areas should be stabilized as quickly as possible using appropriate physical BMPs. See Section for more information. areas should be stabilized as quickly as possible. Furthermore, the site operator or developer should consider the following when scheduling development and construction activities. Schedule structural BMP installation and implementation activities before any site activity starts. The schedule should consider how runoff and preservation and protection areas will be managed during each phase of the development, and which elements should be installed and implemented before other activities are started. Plan, site, and develop in a manner that minimizes impacts and protects areas that provide important water quality benefits or are particularly susceptible to erosion or sediment loss. Consider water, sewer, and other utility connections at each phase of the project to minimize the amount of additional land disturbance. 149 Lake Oswego Stormwater Manual Draft

164 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control Wet Weather Season Erosion and Sediment Control Requirements The City requires that contractors and developers implement supplemental erosion and sediment control requirements if construction activities are planned between October 1 and May 31 and during all rainy periods. Soil and sediment are leading pollutants damaging the quality of rivers, streams, lakes, and other water bodies. These pollutants degrade water quality and reduce the ability of waterways to support aquatic life by encouraging higher water temperatures and by providing a vehicle that transports other pollutants into lakes and streams. Because the rate of erosion on construction sites is up to 500 times greater than on natural rates, the City of Lake Oswego has adopted stringent requirements meant to reduce erosion and sediment from construction sites while allowing construction to continue. Wet weather measures must be fully implemented and remain effective throughout the winter months (October 1 through May 31). The approved erosion control plans contain details and information pertaining to wet weather measures that must be implemented on your site. Erosion control base measures, including sediment fence or wattles around the perimeter, catch basin inserts, and a construction entrance, do not constitute the additional required measures during the wet weather season. Inspection staff requires strict compliance with City ordinances and wet weather measures outlined in the erosion control plans for the project site. Citations may be issued for failure to install and/or maintain required erosion control measures, or for allowing sediment or other pollutants to enter the surface water system. To avoid a citation, contractors and developers must proactively maintain all erosion and sediment control measures, and educate subcontractors and crew members about City requirements. Wet weather erosion prevention requirements are as follows (Lake Oswego 2011): All stockpiled material must be fully covered with secured plastic sheeting and isolated with silt fencing or check dams/wattles at the toe of the slope unless being worked. All exposed/disturbed soil must be covered at the end of each work day. Approved ground cover includes a 3-inch minimum depth of straw, compost mulch, wood chips, or gravel. Plastic sheeting, overlapped and securely staked, may also be used as a ground cover. All vehicles must be parked on the gravel construction entrance or driveway or other graveled parking pads. Do not park vehicles on soils protected with approved cover. All concrete wash-out, mortar, and wet saw slurry, and all liquid waste must be dumped into leakproof pans. No ground/pit dumping is allowed on any site this is a year-round requirement. Lake Oswego Stormwater Manual Draft 150

165 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control All construction waste, garbage, and debris must be collected at the end of each work day and stored in containers or enclosed facilities until disposed of this is a year-round requirement. All erosion control facilities and practices described in the project erosion control plan must be properly installed, monitored for effectiveness, and maintained throughout the project. If the facilities and practices in the erosion control plan are not effective, additional measures must be implemented. Information regarding maintenance can be found in the Lake Oswego Code, section 52. Information regarding approved measures and installation procedures is contained in the Erosion Prevention and Sediment Control Planning and Design Manual (Clackamas County et al. 2008). Hard copies of this manual may be obtained through Clean Water Services or Clackamas County Water Environment Services. Alternatively, an electronic copy can be downloaded free of charge from the Clackamas County Water Environment Services web site. ( htm) Other measures may be required by the inspector to address site conditions. All measures must be maintained in good working order, with all accumulations of sediment removed as necessary. To preserve ground cover, it is recommended that temporary plywood, plank, or gravel walkways be placed around the job site to provide access to the structure without further disturbing covered soils. The Wet Weather Requirements are in addition to standard erosion and sediment control requirements. All contractors, subcontractors, property owners, and anyone working on the construction site is expected to know local, state, and federal requirements related to erosion and sediment control and water quality. All regulations must be adhered to at all times Stage Work Construction phasing or sequencing is a critical step in minimizing land disturbance and protecting longterm infiltration and treatment of runoff on the site to prevent construction (as well as post construction) stormwater impacts and pollution. Construction sequencing and phasing activities are simple and cost-effective ways of mitigating many of the stormwater impacts that originate with construction activities. Construction phasing and sequencing requires that developers and contractors follow and implement a scheduled plan and implement nonstructural BMPs during the development and construction phases of a project and after development. Developers and contractors should consider the procedures listed in Section 9.4, below, when performing construction sequencing. 151 Lake Oswego Stormwater Manual Draft

166 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control 9.4 Implementing Procedures Communication Project success in meeting stormwater management objectives depends on communicating the intent of site and stormwater design, as well as the preservation of existing site features that help reduce the overall impact of stormwater runoff. Developers and builders should not only install physical BMPs to mitigate construction and development stormwater impacts, they should also implement procedural practices in accordance with a planned schedule. Developers, builders, and contractors are responsible for implementing the following non-structural BMPs to ensure that stormwater facility design is implemented as intended and that permanent stormwater facility areas are protected during construction and site development. This communication is also critical in ensuring that structural construction BMPs are implemented and maintained throughout the life of the project Prohibitions of activities Developers and contractors planning construction activities should also consult Chapter 11 for source control BMPs related to construction practices. These include: Dust control Proper storage of solid wastes Spill prevention and cleanup Proper disposal of fluids and wastes Painting, finishing, and coating of vehicles, boats, buildings, and equipment Outdoor storage or transfer of solid raw materials, byproducts, or finished products Other source control BMPs may apply depending on the construction project. Consult Chapter 11 for more information. Prohibiting activities that affect the long-term success of design and implementation of stormwater management on the site can greatly influence the design success of stormwater facilities and the ability of the entire site to manage stormwater. Some prohibited activities related to construction that are required to protect water bodies from construction impacts are discussed in Chapter Managerial Practices Managerial practices BMPs include administrative and procedural practices during development and construction. The applicant should consider, at a minimum, the following managerial practices when developing a site. Train staff and contractors Ensure responsibility by implementing agreements with subcontractors requiring them to adhere to legal requirements and permits, construction practices described in this chapter, the erosion control plan, and the Erosion Prevention and Sediment Control Planning and Design Manual (Clackamas County et al. 2008). Implement the project erosion control plan, SWPPP, and other procedures before construction starts Conduct inspections and maintain BMPs Update and evaluate the project erosion control plan or SWPPP For more information on each of these managerial BMPs, please see Lake Oswego Stormwater Manual Draft 152

167 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control 9.5 Consideration of Construction Impacts during Planning, Design, and Construction This section provides an overview of some of the erosion and sediment control principles, but the Erosion Prevention and Sediment Control Planning and Design Manual (Clackamas County et al. 2008) should be reviewed in its entirety for more information on erosion prevention and sediment control considerations during all stages of project planning, design, and construction Planning Considerations Land disturbance at a construction site accelerates erosion dramatically. Factors that influence accelerated erosional processes include: Presence or absence of vegetation and ground cover Rainfall and climate Slope length and steepness Surface texture Soil type Drainage basin area In general, soil particle size also influences erosional processes. Soil erodibility increases as the percent of silt increases and the percent of fine sand increases. Soil erodibility also generally decreases as the percent of clay increases and the percent of organic matter increases. Slope length and gradient also greatly influence soil erosion. Doubling erosional slope length increases erosional potential by four times, and doubling the slope gradient increases erosional potential by five times Erosion and Sediment Impacts Erosion and sedimentation cause both environmental and economic impacts. Environmental Impacts include introducing more nutrients (such as nitrogen and phosphorus) into already nutrientlimited waters within the City. Economic impacts include expensive construction delays because of sedimentation and site damage. Although these processes and erosion and sediment control practices are focused on typical construction practices, they are also applicable to any parcel where erosional issues may have become or could become an issue in the future Design Considerations Vegetation is the most effective form of erosion control. Very little erosion occurs on soil covered with undisturbed natural vegetation. 153 Lake Oswego Stormwater Manual Draft

168 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control Designers should try to integrate existing trees and other natural vegetation into the site improvement plan and should clearly denote the vegetated areas that should be protected from disturbance. The City s website offers more information on the preservation and protection of trees during development. Plan, site, and develop in a manner that minimizes impacts and protects areas that provide important water quality benefits or are particularly susceptible to erosion or sediment loss. Plan grading to work with existing topography so that cut and fill slopes are as flat as practicable and consistent with soil stability. Slopes of 2:1 or steeper may require special design Recommended Construction Practices The Erosion Prevention and Sediment Control Planning and Design Manual (Clackamas County et al. 2008) is the primary reference for construction practices to minimize the amount of disturbed land area and to protect soils and sensitive areas from sediment during construction. During construction, existing vegetation should be retained whenever possible and only areas necessary for construction activities should be cleared Selecting Construction Best Management Practices Temporary erosion and sediment control BMPs are implemented to protect and prevent soil disturbed from construction activities from moving offsite and into the surface water management system. These construction BMPs are temporary and are not intended as a permanent practice to prevent stormwater runoff. BMPs should be selected in consideration of the site, the nature of construction activities, and the proposed sequencing of construction activities. A detailed discussion of these topics along with guidelines for design, installation, inspection, and maintenance of applicable BMPs are in the Erosion Prevention and Sediment Control Planning and Design Manual (Clackamas County et al. 2008) Stabilized Construction Entrance The primary access point (s) for construction traffic should be identified on plans and stabilized before earthwork begins to prevent sediment and construction debris from leaving the site. If there will be a large amount of earthwork and construction vehicle traffic, a tire wash facility may be required. BMP: construction entrance BMP: tire wash facility General considerations: Keep construction entrances (including the existing driveway) clean and swept free of debris. Sweep up any visible debris immediately; never rinse or power wash debris from the driveway into the street or into storm drains. Clean up any tracking on street surfaces at the end of each work day. Keep parking limited to hard-surfaced or properly graveled areas. Do not block the construction entrance with trailers or materials. Crew parking areas are a common source of soil disturbance and tracking. Lake Oswego Stormwater Manual Draft 154

169 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control Put plywood or steel sheeting down on construction pathways and try to load and unload materials on the jobsite, not in the street. Even small Bobcat -style equipment can cause serious soil disturbance; running on wood or steel sheeting can reduce soil disturbance and limit damage to existing root systems Perimeter and Sediment Controls Perimeter controls should be installed along borders of sensitive areas, around areas of proposed stormwater management facilities that need to be protected, and at the limits of clearing and construction activities. They should be installed downslope of proposed construction activities, and should be installed at a set elevation rather than sloping to avoid generating channelized runoff. If development substantially changes the natural drainage conditions on a site, merely protecting the drainage channels on a project site may not be sufficient to prevent erosion. Sediment is required to be trapped on site. An example of the implementation of a protective stormwater BMP is protecting areas from compaction and clogging by clearly identifying locations of BMPs on construction plans and including construction notes on the plans similar to the following: All stormwater BMP areas shall be clearly marked before site work begins to avoid soil disturbance during construction. No vehicular construction traffic, except that specifically used to construct the stormwater facility, shall be allowed within 10 feet of infiltration areas. Some erosion during construction is unavoidable. The function of a sediment barrier is to prevent sediment from leaving a site; the barrier detains sediment-laden stormwater on the site long enough for soil particles to settle out before the runoff enters receiving waters. At a minimum, sediment control shall include: Locate sediment basins and traps at low points below disturbed areas. Use earth dikes or swales to route drainage from disturbed areas into acceptable discharge locations. Place sediment barriers and sediment fences below small, disturbed areas on gentle to moderate slopes. Stormwater BMP locations should be clearly marked with stakes or flagging prior to construction. BMP: buffer zone BMP: preserve natural vegetation BMP: sediment fence BMP: wattles BMP: filter berm 155 Lake Oswego Stormwater Manual Draft

170 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control Stabilize Slopes and Disturbed Areas Areas that have been cleared should be stabilized through use of seed and mulch as soon as possible after grading is completed. Mulch helps seedlings become established and protects the soil from raindrop splash until vegetation takes over. Soils may be planted with temporary or permanent vegetation. If the soil will be exposed during the winter months, protective measures other than vegetation must be used. See the Erosion Prevention and Sediment Control Planning and Design Manual (Clackamas County et al. 2008) for more information. Exposed slopes are a potential source of sediment in the event of storm events if they are not stabilized through one of the following methods: Protect existing vegetation and limit soil disturbance whenever possible. Re-seed exposed soils as quickly as possible, and consider the use of deep-rooted native vegetation to help restabilize soils. BMP: seeding (temporary/permanent) BMP: pipe slope drain BMP: surface roughening Stockpile Areas Clearly identify stockpile areas and cover controls. Designate places to stage and store construction materials. These areas should be protected with a gravel base, plywood, concrete, or another hard surface. Store piles of compost, bark dust, topsoil, or other amendments on tarps; try not to order these materials until immediately before they will be used on the site. Cover stockpiles with plastic sheeting during the wet weather season, and in summer whenever the stockpiles will remain unworked for 14 days or longer. Cover exposed soils with 3 inches of straw, compost mulch, wood chips, gravel, or other ground cover to minimize disturbance and reduce the potential for tracking. BMP: matting BMP: plastic sheeting Runoff Control Runoff should be diverted from exposed soils or steep slopes. Construction changes the characteristics of runoff. The creation of impervious surfaces, removal of plant cover, and compaction of soil by construction traffic allows less water to percolate into the soil and, therefore, increases the volume of runoff. Drainage ways and outlets must be prepared to handle concentrated or increased runoff. See the Erosion Prevention and Sediment Control Planning and Design Manual (Clackamas County et al. 2008) for more information. Lake Oswego Stormwater Manual Draft 156

171 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control Where construction stormwater concentrates, the following can be used to reduce runoff velocities: BMP: check dam BMP: diversion dike/swale BMP: grass-lined swale BMP: outlet protection BMP: sediment basin BMP: sediment trap Control Pollutants Provide adequate, well-marked garbage disposal containers. Litter, debris, scrap materials, and other waste are considered pollutants and must be contained on the site. Containers should be leak-proof. Small containers should be emptied weekly; larger containers/dumpsters should be emptied as needed. Provide leak-proof pans for concrete rinse water and left-over mortar and masonry materials. New regulations require these materials be contained and hauled offsite. Small kiddie swimming pools work very well for this purpose. Remember: these materials are harmful to landscaping and trees, and may pollute the water table. Do not rinse any material into the storm drain. Remember: Only rain goes down the drain! Temporary and Permanent Stormwater Facilities Know where the nearest storm drains are located, and keep them protected with non-woven filter inserts. Clean up and properly dispose of any material that accumulates in the filter, and remove and dispose of all filters at the end of the project. BMP: biofilter bag BMP: inlet protection Maintenance and Inspection Procedures Another critical non-structural BMP is maintenance and inspection procedures. Site operators should consider the following, at a minimum, when identifying construction stormwater maintenance procedures. Outline all structural BMP maintenance and inspection procedures in the erosion control plan, SWPPP, or other BMP documents. Implement the maintenance procedures to keep physical BMPs in good working order at all times. If an erosion control permit has been issued for the site (either issued by the City issued or an NPDES 1200-C) the permit requires that you conduct regular inspections and document the findings of those inspections. Personnel selected to conduct inspections should be knowledgeable in the principles and practices of erosion and sediment controls and preservation and protection controls, possess the technical skills to 157 Lake Oswego Stormwater Manual Draft

172 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control assess conditions at the construction site that could impact stormwater quality, and assess the effectiveness of any sediment and erosion control measures selected. Ensure that maintenance and inspection of construction BMPs occurs regularly (that is, outlined on a schedule as described in this chapter) Implement corrective action whenever an inspection (formal or informal) identifies a problem or potential issue. Document all inspection and maintenance activities. At a minimum this should include the date, BMP, location, and maintenance performed City Inspection City inspectors will visit construction and development sites to ensure that the approved erosion prevention and sediment control plan is properly implemented and that additional physical BMPs are in place, as necessary. At a minimum, inspectors will observe and document: Disturbed areas of the site Material and waste storage areas Stockpile areas Construction site entrances and exits Sensitive areas Tree protection Discharge locations to public storm drains Discharges to receiving waters, if appropriate Inspections will be documented with photographs and monitoring results as appropriate. Please see the City s website for more examples and tools. 9.6 Minimizing Disturbances Vegetation is the most effective form of erosion control. Very little erosion occurs on a soil covered with undisturbed natural vegetation. During construction, existing vegetation should be retained whenever possible and only areas necessary for construction activities should be cleared. Designers should try to integrate existing trees and other natural vegetation into the site improvement plan and should clearly denote the vegetated areas that should be protected from disturbance. The City s website offers more information on the preservation and protection of trees during development. Lake Oswego Stormwater Manual Draft 158

173 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control General design and construction considerations to minimize disturbances on construction sites are: Where applicable and appropriate, locate construction pollutant sources (including sediment) away from drainage swales, wetlands, or water bodies. Sediment removed from sediment control facilities should be placed in non-critical flat areas of the site. In no instance should the removed sediment be placed in a position where subsequent rainfall could return it to the sediment control devices. Minimize land disturbance, such as clearing and grading and cut and fill, to reduce erosion and sediment loss Post Construction Before removing temporary erosion and sediment control measures, ground cover or permanent landscaping shall be established. 9.7 Documentation Erosion Control Plan Developers or site operators are required to submit an erosion control plan with their 1200-C application to DEQ, if the project includes 1 acre or less of land disturbance. Although erosion control plans are common with larger developments, they are not as common for smaller development activities. However, the plan elements and procedural BMPs are relevant to all sizes of development and construction activities, so developers or site operators of smaller Activities that are violations of local, state, or federal laws Activities that damage or alter physical BMPs Erosion control plans area referred to as stormwater pollution prevention plans (SWPPP) in Washington state and some other jurisdictions. SWPPP guidance and templates can be found at: Please see the City s website for more examples and tools. Approval of a construction erosion and sediment control plan by the City does not relieve the applicant from the responsibility to ensure that erosion control measures are constructed, implemented and maintained to contain sediment on the construction site. projects should also consider drafting and implementing an erosion control plan. This plan will help the site operator manage the site and avoid damage to the stormwater facility areas and preservation or protection areas. Erosion control plans typically include good housekeeping information for the site operators and contractors. The erosion control plan is designed to identify prohibited activities as well how to conduct activities with the correct physical BMPs. At a minimum, site operators and developers should consider the following prohibited activities when drafting procedural BMPs. 159 Lake Oswego Stormwater Manual Draft

174 Construction Phasing, Stormwater Pollution Prevention and Erosion and Temporary Sediment Control Erosion and Sediment Control Drawing The erosion and sediment control plan should include a drawing that will be part of the contract documents for the project. Applicable BMPs are in the Erosion Prevention and Sediment Control Planning and Design Manual (Clackamas County et al. 2008) and summarized in Section 9.3. At a minimum, the drawing must include the following information: Primary access point (s) for construction traffic: Access points must be stabilized with crushed rock (reject rock from site construction is acceptable). Limits of clearing and construction activities: Show perimeter controls that will be used to prevent sediment or construction debris from leaving the site. Sensitive areas, such as streams or wetlands: Show buffer protection measures that will be installed prior to any land disturbing activities. Areas of proposed stormwater management facilities: Effective erosion control. The location of stormwater BMPs shall not be subject to compaction prior to, during, and after the construction of the facility. Plan should delineate protection buffer and method of protecting from construction traffic. Show sediment control measures that will be used on and at toes of slopes. Clearly identify stockpile areas and cover controls. Show existing and proposed stormwater facilities, including inlets, catch basins, and how they will be protected. Show temporary stormwater collection, conveyance, and treatment facilities. Include general notes for erosion and sediment control (Appendix H provides a current list of required construction notes. Please see the City s website for any updates and more examples and tools.) Inspection Log Contractors should maintain an inspection log that documents that silt fence, covers, and construction BMPs are intact and functioning well and that notes rainfall, observed problems, corrective actions, and results. Lake Oswego Stormwater Manual Draft 160

175 10 Maintenance Regular and appropriate inspection and maintenance of stormwater management facilities is critical to their continued function. This chapter describes maintenance requirements for stormwater facilities, including access, submittals, reporting, and penalties in the event of violations. Detailed checklists with required maintenance activities are provided for each of the flow control, water quality, and LID BMPs included in Chapter 7. The specific maintenance activities during the calendar year and following storm events depend on the facility type and its design Legal Requirements The City surface water code (LOC ) outlines legal requirements related to maintenance of stormwater facilities, including inspection, access, and considerations in the event of transfer of property ownership. Requirements are briefly summarized in this chapter, but property owners and managers should review the code for detailed legal requirements Maintenance Responsibilities Public Facilities Lake Oswego s Public Works, Operations Division, maintains public storm drain, ditches, storm drainage structures (e.g., catch basins and inlets), and non-vegetated stormwater facilities. The Parks and Recreation Maintenance Division maintains public vegetated stormwater facilities, including rain gardens and planters located within street rights-of-way Private Facilities Maintenance of private facilities is the responsibility of the property owner, unless a different responsible party is identified in the OMP. Under Lake Oswego s surface water code, responsibilities include: Maintain stormwater management facilities in good condition, with facilities operating at design capacity and performing the function for which they were designed while in continuous working order. Inspect and maintain at an appropriate frequency and level to avoid nuisance conditions in or adjacent to the stormwater management facility that suggest that the facility is not in good working order, such as uncontrolled runoff and overflow, stagnant water with concomitant algae growth, insect breeding, odors, discarded debris, or safety hazards created by the facility s operation. Inspect stormwater facilities according to the schedule included in the maintenance checklists provided in this chapter or a facility-specific OMP. Promptly repair and restore stormwater management facilities in accordance with the maintenance checklists provided in this chapter. 161 Lake Oswego Stormwater Manual Draft

176 Maintenance Provide and maintain all necessary access routes from the public right-of-way in accordance with this chapter or the OMP Inspection Under Lake Oswego s surface water code, when stormwater management facilities are privately owned and maintained, the City shall be granted reasonable access rights by license or easement to the facilities. The City reserves the right to inspect private facilities to confirm that they are in conformance with Lake Oswego s stormwater management requirements. Examples of inspections may include but are not limited to: Routine inspections Random inspections Inspections based upon complaints or other notice of possible violations Inspection of areas generating or sites generating higher than typical sources of sediment or other pollutants Inspections of businesses or industries with discharges that are more likely than the typical discharge to cause violations of state or federal water or sediment quality standards or the City s MS4 stormwater permit based on the City s evaluation of businesses and industries Joint inspections with other agencies inspecting under environmental or safety laws Inspection of Facilities Operating Under Partial Letter of Acceptance Maintenance Access All stormwater BMPs (except those that serve only a single-family residence) shall have maintenance access that meets the following criteria: Provide a maintenance access road that allows maintenance vehicles to perform needed maintenance activities. Needed maintenance activities include vacuum cleaning of pollution control manholes and similar structures, removal of debris from major debris control structures, removal of sediment collected in the facility, and grading needed to restore proper function of the facility. Provide a maintenance access path that allows a person with hand equipment to perform maintenance and inspection services. These services typically require access to inlets and outlet structures. Provide a flat area adequate for a person to stand above all outlet debris control structures Access by the City All stormwater management facilities, whether located on private or public property, shall be accessible at all times for City inspection. When stormwater management facilities are accepted by the City for maintenance, access easements shall be provided at a width meeting the criteria in the following sections to allow access by maintenance and inspection equipment. Lake Oswego Stormwater Manual Draft 162

177 Maintenance Maintenance Access Roads All ponds shall have an access road and ramp that meet the following criteria: The road grade shall be 15 percent, maximum. The road cross slope shall be 3 percent, maximum. The road width shall be 12 feet on straight sections and 15 feet on curves. The outside turning radius shall be 40 feet, minimum. The road surface load capacity shall be H-20 loading with an assumed California bearing ratio of 3 or greater. Road surfaces shall be pervious pavement (see BMP design guidelines) or gravel. Gravel examples include: 2 inches of ¾-0 crushed rock over 10 inches of 2 0 crushed rock over Mirafi 550X geotextile fabric. For access road surfaces, consider using reject rock from site construction or a low-growing native prairie seed mix that does not need to be mowed but can withstand mowing prior to dredging operations. Paver stones may be incorporated into access roads at larger facilities Maintenance Access Paths Maintenance access paths shall meet the following design criteria: The path grade shall be 33 percent, maximum, or have approved steps. The path cross slope shall be 3 percent, maximum. The path width shall be 3 feet, minimum. The path surface shall provide an all-weather, mud free, walkable access. Acceptable path surface examples include grass, gravel, and wood chips Transfer of Property Ownership An agreement with the City shall be required when the stormwater management facility will be owned, operated, or maintained by the City. When ownership of stormwater management facilities are transferred to and accepted by the City, the transfer shall include access easements of a width acceptable to the City Engineer that is sufficient to allow access by maintenance and inspection equipment. If property is transferred to another owner, the responsible party must inform the new owner(s) or responsible party of the existence of stormwater management facilities on the site, of restrictions of the stormwater management facilities (including design capacity and setbacks), and of the requirements for inspection and maintenance of the stormwater management facilities. If the responsible party changes due to the transfer of the property, an updated OMP should be submitted to the City. 163 Lake Oswego Stormwater Manual Draft

178 Maintenance 10.2 Failure to Provide Adequate Maintenance In the event the City Engineer has reason to believe that the stormwater management facility has not been maintained or that it has become a threat to public safety or health, the City Engineer shall notify the responsible party by certified mail. The notice shall specify the suspected non-maintenance or conditions giving rise to the threat to public safety or health, and the measures the City Engineer deems needed to comply with the OMP. The notice shall specify that the responsible party has thirty (30) days, or a shorter time period established by the City Engineer as needed under the circumstances to protect the public safety and health, within which time such measures shall be completed. The surface water code establishes enforcement provisions in the event of failure to provide adequate maintenance or respond to a notice of violation. Enforcement may include being charged for the cost of repair work, a lien on the property in the Municipal Lien Docket, and/or fines according to the current fine schedule Submittals and Reporting Operations and Maintenance Agreement/Plan An OMP that has been developed for a specific facility or site, such as the example provided in Appendix B, must be provided. For projects that create or replace 1,000 square feet or more of impervious surface (medium and large projects), an OMP is required. The OMP must describe how to properly maintain the facility, the frequency of maintenance required, and the party responsible for maintaining the facility. Owners/operators of facilities that manage stormwater from medium and large projects must file a deed restriction or recorded maintenance covenant in the County in which the property or facility is located. This step needs to be completed before the City will issue a Certificate of Occupancy. A copy of the deed restriction is provided in Appendix B Records of Maintenance Activities The owner or responsible party identified in the OMP is required to keep all records of maintenance activities as described in this chapter or the OMP. The responsible party shall make records of the installation, and of all maintenance and repairs, and shall retain the records for at least five years. These records shall be made available to the City Engineer during inspection of the stormwater management facility and at other reasonable times upon request. In the event of transfer of property ownership, the initial responsible party shall transfer maintenance records to the new owner/responsible party Maintenance Checklists Maintenance checklists for each facility are included in Appendix H. The checklists include descriptions of items to inspect during specific times of the year and following storms, and corrective action items to address problems observed during inspection. Lake Oswego Stormwater Manual Draft 164

179 11 Source Control Note: content from this chapter was adapted from Seattle Director s Rules (Seattle Public Utilities 2009a) Overview Water quality treatment BMPs described in Chapter 7 remove pollutants after they have entered stormwater. They are typically more expensive and often cannot remove 100 percent of the pollutants. The City s MS4 permit requires that the City prevent illicit discharges and reduce pollutants from industrial and commercial facilities. The use of source control BMPs is the first line of defense in stormwater pollution prevention for several reasons: In most cases, source control BMPs are sufficient to correct stormwater pollution problems. Most source control BMPs are relatively inexpensive and easy to implement. The source control BMPs included in this chapter include both required BMPs to comply with the City stormwater code and the City s MS4 permit, and recommended BMPs. Source control BMPs prevents contaminants from entering stormwater runoff and the surface water utility by controlling them at their source. Source control BMPs are options that prevent or reduce stormwater contamination with or without the aid of permanent structures. They can include process changes, such as changes in raw material and products, and the recycling of wastes. Many source control BMPs are common sense housekeeping practices; for example, dust and debris can be swept or vacuumed from a work area and put into the garbage instead of using a hose to wash it into a storm drain or other drainage conveyance. Examples of source control BMPs include: Implementing good housekeeping practices Implementing preventive maintenance procedures Writing and implementing a spill plan (SWPPP or procedural BMPs) Covering material Isolating pollutant sources to prevent uncontaminated stormwater from flowing onto those areas and becoming a source of contamination Moving pollution-generating activities inside or under a covered area Using a berm or deflector curb to keep contaminated water from entering the surface water management system Erecting a permanent roof or structure over storage and working areas Installing a wash pad that is connected to the sanitary sewer Table 11.1 lists source control activities that can be used by residents, all types of commercial businesses, institutions, and land uses in Lake Oswego. 165 Lake Oswego Stormwater Manual Draft

180 Source Control Table 11.1 Summary of Source Control Strategies. Applies To Eliminate illicit connections to storm drains Perform routine maintenance for drainage systems and stormwater facilities Dust control Proper storage of solid wastes Proper disposal of fluids and wastes Spill prevention and cleanup Landscaping and lawn and vegetation management Painting, finishing, and coating of vehicles, boats, buildings and equipment Parking lot maintenance and storage of vehicles and equipment Fueling at dedicated stations Automobile repair and maintenance Swimming pool and spa maintenance Vehicle, equipment, and building washing Outdoor storage or transfer of solid raw materials, byproducts, or finished products Chapter Section All residents and property owners/ managers Landscaping service providers and nurseries Swimming pool/ spa maintenance providers Contractors Painting Food service establishment Car washing establishments, car dealerships Fleet vehicle yards and maintenance facilities Automotive repair and maintenance; gas stations Golf courses Lake Oswego Stormwater Manual Draft 166

181 11.2 Eliminate Illicit Connections to Storm Drains Source Control Some properties and residences have internal building drains, sump overflows, process wastewater discharges, and even sanitary sewer and septic system pipes that are incorrectly plumbed to the Lake Oswego surface water management system. These storm drain connections allow a variety of pollutants to flow directly to the surface water ultimately receiving drainage instead of to the sanitary sewer or septic system. Frequently, such connections are not intentional, but they can be very harmful to the environment and must be eliminated. All building owners or managers in Lake Oswego should examine their plumbing systems to identify any illicit connections. A good place to start is an examination of the site plans. If any toilets, sinks, appliances, showers, bathtubs, floor drains, industrial process waters, or other water-using equipment are connected to the Lake Oswego surface water management system, those connections must either be permanently plugged or disconnected and rerouted as soon as possible. If it is not obvious through observation or examination of site plans, one method of determining where a pipe or structure drains is to perform a dye test with a nontoxic dye or a smoke test. These tests are typically best performed by qualified personnel such as a plumbing contractor. If it is found that sanitary facilities, such as toilets and sinks, are hooked up to the Lake Oswego surface water management system, a connection permit must be obtained from the City Building Department to reroute them to the sanitary sewer. Other options for correcting discharges to the drainage system include using a holding tank or installing a process treatment system. Restrictions on certain types of discharges may require pretreatment before they enter the sanitary sewer. It is the responsibility of the property owner or business operator to obtain the necessary permits and to follow through on rerouting the connection from the storm drain to the sanitary sewer. Contact the City of Lake Oswego Engineering Division if you suspect a cross-connection Perform Routine Maintenance for Surface Water Management System Sediment and pollutants can accumulate over time in various components of drainage collection, conveyance, and treatment systems, such as catch basins, ditches, storm drains, and oil/water separators. These pollutants can include sediment and other substances such as oils, debris, and sludge. When a storm event occurs, the pollutants can become mobilized and carried into the surface water ultimately receiving drainage water. Regular maintenance of the drainage system decreases the amount of pollutants available to contaminate the stormwater. Many properties in Lake Oswego have privately owned catch basins and other surface water management facilities. It is the property owner s responsibility to maintain these assets. Please contact the City of Lake Oswego Operations Division to find out if the catch basin or other facility is publicly or privately owned. The required elements of this citywide BMP are described below Catch Basins Routine cleaning of catch basins is one of the most important stormwater source control measures that can be implemented. Clean catch basins when they are more than half full or when the sediment is within 18 inches of the bottom of the outlet pipe. Scheduled maintenance activities (for example, cleaning a catch basin once per year) is a cost-effective way to maintain a catch basin. 167 Lake Oswego Stormwater Manual Draft

182 Source Control Catch basins are typically located beneath low spots in parking lots, along curbs and roadway edges, and where flows from more than one storm drain pipe are combined. Most catch basins have some storage in the bottom (called a sump) to trap sediments, debris, and other particles that can settle out of stormwater, thereby preventing clogging of downstream pipes and washing of these solids into the surface water ultimately receiving drainage water. When catch basins are about 60 percent full of sediment, they stop removing sediment from stormwater. Oils and grease, petroleum hydrocarbons, debris, metals, sediment, and contaminated water are found in catch basins, oil/water separators, and settling basins. At a minimum, catch basins should be inspected and maintained at least once each year Other Facilities Other facilities can include both structural and non-structural stormwater BMPs. They all require routine maintenance to ensure they remain functional. Frequency and level of maintenance varies based on the facility location, function, and exposure to impacts and, for most facilities, should be described in the OMP. Checklists in Chapter 10 provide more details on operation and maintenance procedures for specific facilities Dust Control This BMP applies to residents, businesses, and public agencies that pursue dust control measures in disturbed land areas or on unpaved roadways and parking lots. All land-disturbing activity must comply with the Erosion Control Code (LOC Chapter 52). Dust can result in air and water pollution, particularly at demolition sites, in disturbed land areas, and on unpaved roadways and parking lots. Chemicals applied to dust-prone areas to minimize dust production can also pollute stormwater and the surface water ultimately receiving drainage water if they are not properly selected or applied General Recommendations Minimize dust generation and apply environmentally friendly and government- approved dust suppressant chemicals, if necessary. The use of motor oil or other oils for dust control on unpaved roadways and parking lots is prohibited Required Best Management Practices The following BMPs or equivalent measures are required of all businesses and public agencies engaged in activities that generate dust: Street gutters, sidewalks, driveways, and other paved surfaces in the immediate area of the demolition must be swept regularly to collect and properly dispose of loose debris and garbage. Install catch basin filters onsite and in surrounding catch basins to collect sediment and debris. Maintain the filters regularly (weekly or as needed) to prevent plugging. Remove catch basin filters when development activity is complete. Oil is prohibited be used for dust control. Lake Oswego Stormwater Manual Draft 168

183 11.5 Proper Storage of Solid Wastes Source Control This BMP applies to properties that store solid wastes, including food wastes and ordinary garbage, outdoors. If improperly stored in this climate, these wastes can contribute a variety of pollutants to stormwater. Pollutants of concern include toxic organic compounds; fats, oils, and greases; metals; nutrients; suspended solids; substances that increase chemical oxygen demand; and substances that increase biological oxygen demand. These pollutants must not be discharged to the drainage system or directly into receiving waters. Dangerous solid wastes must be stored and handled according to special guidelines and may require a permit. Businesses and public agencies that store dangerous wastes must follow specific regulations outlined by DEQ. For the specific requirements and permitting information, contact DEQ General Recommendations Store wastes in suitable containers with leak-proof lids. Sweep or shovel loose solids. Educate employees about the need to check for and replace leaking containers. Consider implementing the following practices: Store containers such that wind will not be able to knock them over. Use waterproof liners to prevent leaks from the solid waste container. Designate a storage area, pave the area, and slope the drainage to a holding tank or sanitary sewer drain. If a holding tank is used for storing wastewater, the contents must be pumped out before the tank is full and disposed of appropriately to a sanitary sewer or wastewater treatment system. Compost appropriate wastes or recycle solid wastes Required Best Management Practices The following BMPs or equivalent measures are required of all properties engaged in the storage of solid wastes: Store solid wastes in suitable containers with leak-proof lids. Containers must be replaced if they are leaking, corroding, or otherwise deteriorating. The waste storage area must be swept or otherwise cleaned frequently to collect all loose solids for proper disposal in a storage container. Do not hose the area to collect or clean solids. Drain dumpsters, dumpster pads, and trash compactors to the sanitary sewer. Use spill cleanup materials to clean up fats, oil, grease, or other contaminants. 169 Lake Oswego Stormwater Manual Draft

184 Source Control 11.6 Proper Disposal of Fluids and Wastes This BMP applies to all residents, businesses, property owners, and public agencies engaged in pressure washing of non-vehicular engines, equipment, and portable objects. It also applies to businesses that clean or wash manufacturing equipment, such as saws, grinders, screens, and other processing devices, outside of buildings General Recommendations To contain fluids and wastes generated from these activities, use of a wash pad is highly recommended. Sumps or holding tanks may be useful for storing liquid wastes temporarily. The contents must be disposed of properly. Solid and liquid wastes and contaminated stormwater must be disposed of using one of the following acceptable methods: Recycling facilities Municipal solid waste disposal facilities Hazardous waste treatment, storage, and disposal facilities Sanitary sewer Required Best Management Practices The following BMPs or equivalent measures are required of all businesses engaged in cleaning or washing of tools, engines, equipment, and portable objects: All wash water must be discharged to a sanitary sewer, process treatment system, or holding tank and must never be discharged to the surface water management utility. If a holding tank is used for the storage of wash water, the contents must be pumped out before the tank is full and disposed of appropriately to a sanitary sewer or wastewater treatment system (pretreatment and/or permit requirements may apply). Pressure washing must be conducted in a designated area (such as a wash pad) that is provided with a sump drain connected to a sanitary sewer or treatment system, or a blind sump or holding tank. The wash area must have a means for stormwater run-on prevention (such as a berm or sump). For wash pads that discharge directly to the sanitary sewer, the uncovered portion of the wash pad must be no larger than 200 square feet or must have an overhanging roof. This is to prevent excess stormwater from entering the sanitary sewer. A connection permit is needed to connect to the City s sanitary sewer system. For information about connection permits, call the City Building Department. Many liquid wastes and contaminated stormwater (depending on the pollutants and associated concentrations) can be discharged to the sanitary sewer system, but are subject to approval and permitting by the wastewater treatment plant. Please contact the Lake Oswego Engineering Division for more details. If wastes cannot be legally discharged to a sanitary sewer, dangerous and hazardous wastes must be properly transported to an appropriate hazardous waste disposal, treatment, and storage facility. Lake Oswego Stormwater Manual Draft 170

185 11.7 Spill Prevention and Cleanup Source Control Spills can contribute a variety of pollutants to the drainage system and nearby waterways and are often preventable if appropriate practices for chemical and waste handling and spill response are implemented. Promptly contain and clean up leaks and spills of solid and liquid pollutants including oils, solvents, fuels, and dust from manufacturing operations on any exposed soil, vegetation, or paved area. The specific requirements for complying with this citywide BMP are described below. A spill can be a one-time event, a continuous leak, or frequent small spills. All types must be addressed General Recommendations To reduce the potential for spills, implement the following practices and have spill cleanup kits available at activity locations where spills may occur: Clearly label all containers that contain potential pollutants. Store and transport liquid materials in appropriate containers with tight- fitting lids. Place drip pans underneath all containers, fittings, and valves where materials are likely to spill or leak. Use tarpaulins, ground cloths, or drip pans in areas where materials are mixed, carried, and applied to capture any spilled materials. Train employees on the safe techniques for handling materials used on the site and encourage them to check for leaks and spills Required Best Management Practices All businesses identified in Table 11.1 and any other businesses or institutions that store or use chemicals shall meet the requirements identified in this section Spill Plan Develop and implement a spill plan (Spill Prevention and Control Plan) and update it annually or whenever there is a change in activities or staff responsible for spill cleanup. Post a written summary of the plan at appropriate points in the building, such as loading docks, product storage areas, waste storage areas, and near a phone. The spill plan may need to be required to be posted at multiple locations. Describe the facility including the owner s name, address, and telephone number; the nature of the facility activity; and the general types of chemicals used in the facility. Designate spill response employees to be on the site during business activities. Provide a current list of the names, addresses, and telephone numbers (office and home) of designated spill response employee(s) who are responsible for implementing the spill plan. Provide a site plan showing the locations of storage areas for chemicals, storm drains, and other relevant drainage or materials information. Describe the emergency cleanup and disposal procedures. 171 Lake Oswego Stormwater Manual Draft

186 Source Control List the names and telephone numbers of public agencies to contact in the event of a spill. All employees must have annual training of spill control procedures. New employees must be trained upon hiring. All training must be documented. For templates and guidance on preparing spill control plans, refer to the following resources: cfm?action=factsheet_results&view=specific&bmp=62&minmeas ure=4 general/1200indswpcpchecklist.pdf Spill Cleanup Kit The City operates the Watershed Hotline ( ), a call number for citizens to report watershed concerns, illicit discharges or spill activity. This hotline is advertised on the City s website and periodically in the City s monthly newsletter Hello LO. During normal business hours, the City s Engineering staff answer this phone line and respond to non-emergency calls within one business day. Emergency calls taken during normal office hours are redirected to the City of Lake Oswego Fire Department. All calls reporting a spill are forwarded to LOCOM ( Lake Oswego Non-Emergency Number) for Fire Department dispatch, and all calls are initially responded to as a Level 1 Emergency. Store spill cleanup kits near areas with a high potential for spills so that they are easily accessible in the event of a spill. The contents of the spill kit must be appropriate to the types and quantities of materials stored or otherwise used at the facility and refilled when the materials are used. For example: Absorbent pads Sorbent booms, or socks Absorbent granular material such as kitty litter Protective clothing such as latex gloves and safety goggles Thick plastic garbage bags Drain cover Spill Cleanup and Proper Disposal of Material In the event of a spill, implement the following procedures: Implement your spill plan immediately. Contact the employee(s) responsible for implementing the spill plan. Block off and seal the nearby inlet(s) to the drainage system to prevent materials from entering the drainage system. Use an appropriate material to clean up spills. Do not use emulsifiers or dispersants such as liquid detergents or degreasers. Lake Oswego Stormwater Manual Draft 172

187 Source Control Immediately report all spills that could reach storm drains, the sanitary sewer, streams, rivers, or Oswego Lake to the City. Do not wash absorbent material into interior floor drains or exterior storm drains. Dispose of used spill control materials in accordance with the hazardous waste management guidance on DEQ s website: and applicable laws Landscaping, Lawn, and Vegetation Management This BMP applies to businesses and public agencies that perform landscaping including grading, landscape materials storage piles, soil transfer, vegetation removal, pesticide and fertilizer applications, and watering. Lawn and vegetation management can include control of objectionable weeds, insects, mold, bacteria, and other pests by means of chemical pesticides and is conducted commercially at commercial, industrial, and residential sites. Examples of landscaping and lawn and vegetation management include weed control on golf courses, access roads, and utility corridors; removal of moss from rooftops; killing of nuisance rodents; application of fungicides on patio decks; and residential lawn and plant care. Stormwater contaminants from landscaping and lawn and vegetation management activities include toxic organic compounds, metals, oils, suspended solids, ph, coliform bacteria, fertilizers, and pesticides. Pesticides such as pentachlorophenol, carbonates, and organometallics can be released to the environment as a result of leaching and dripping from treated plants, container leaks, product misuse, and outside storage of pesticide-contaminated materials and equipment. Inappropriate management of vegetation and improper application of pesticides or fertilizers can result in stormwater contamination. These pollutants must not be discharged to the drainage system or directly into receiving waters, except as permitted by DEQ. Pesticides are prohibited for use in stormwater facilities General Recommendations Avoid fertilizer and pesticide application, soil erosion, and site debris. Cover and contain exposed, erodible soils. Develop and implement an integrated pest management (IPM) plan (see Appendix B for example) and use pesticides prudently. If pesticides or herbicides are used, they must be carefully applied in accordance with label instructions and the Federal Insecticide, Rodenticide and Fungicide Act and applicable state laws. In Oregon, pesticide use is regulated by the Department of Agriculture. For information on pesticide investigation and enforcement, refer to this website: For an investigation district map with contact information, refer to this website: To control erosion and the discharge of stormwater pollutants, maintain appropriate vegetation, properly apply fertilizer where necessary, or consider the use of pest-resistant varieties when possible. Also, where practical, grow plant species appropriate for the site. 173 Lake Oswego Stormwater Manual Draft

188 Source Control Required Best Management Practices The following BMPs or equivalent measures are required of all businesses and public agencies engaged in landscaping or lawn and vegetation management activities. To report violations or ask questions about pesticide use, contact the Oregon Department of Agriculture Landscaping Do not dispose of collected vegetation in the surface water management system, waterways, receiving waters, or sensitive lands or protected areas, taking care to avoid contamination or site disturbance. Use mulch or other erosion control measures when soils are exposed for more than one week during the dry season (June 1 to September 30) or two days during the rainy season (October 1 to May 31) Pesticides Develop an IPM plan that, at a minimum, includes the requirements outlined in Appendix B, Example of Integrated Pest Management Program and Plan. Choose the least toxic pesticide that is capable of reducing the infestation to acceptable levels. Conduct any pest control during the life stage when the pest is most vulnerable. For example, if it is necessary to use a Bacillus thuringiensis (Bt) application to control tent caterpillars, it must be applied before the caterpillars form their cocoons or it will be ineffective. The pest control method should be site-specific rather than generic. When necessary to use pesticides, apply according to the directions on the label and use the following BMPs: Conduct spray applications according to specific label directions and the applicable local and state regulations. Some applications may require a Pesticide Applicators license. Please see Do not apply pesticides if it is raining or immediately before expected rain (unless the label directs such timing). Ensure that the pesticide application equipment is capable of immediate shutoff in the event of an emergency. Do not apply pesticides within 100 feet of open waters including wetlands, ponds, streams, sloughs, or any drainage ditch or channel that leads to open water except when approved by DEQ and the City (all sensitive areas including wells, streams, and wetlands must be flagged prior to spraying). Take care to avoid contamination or site disturbance during applications. Never apply pesticides in quantities that exceed the manufacturer s instructions. Mix pesticides and clean the application equipment under cover in an area where accidental spills will not enter surface water or ground water and will not contaminate the soil. The City Sensitive Lands ordinance also restricts certain described pesticide use within buffer zones of certain sensitive areas. Please contact the City Planning Department for more information on Sensitive Lands. Lake Oswego Stormwater Manual Draft 174

189 Source Control Storage: Store pesticides in enclosed areas or in covered impervious containment. Do not hose down the paved areas to a storm drain or street or other conveyance. Ensure that pesticide-contaminated waste materials are kept in designated covered and contained areas, and disposed of properly. Rinsate from equipment cleaning and/or triple-rinsing of pesticide containers should be used as product or recycled into product Fertilizer Do not pour rinsate down the drain! Ensure that all fertilizers are applied by properly trained personnel. Document and keep all training records. For commercial and industrial facilities, ensure that fertilizers are not applied to grass swales, filter strips, or buffer areas that drain to sensitive receiving waters Painting, Finishing, and Coating of Vehicles, Boats, Buildings, and Equipment This BMP applies to businesses and public agencies that perform outdoor surface preparation and application of paints, finishes, and coatings to vehicles, boats, buildings, and equipment. Potential pollutants include organic compounds, oils and greases, metals, and suspended solids. These pollutants must not be discharged to the surface water management system or directly into any receiving waters General Recommendations Cover and contain exterior surface preparation, painting, and sanding operations and apply good housekeeping and preventive maintenance practices to prevent the contamination of stormwater with paint overspray and grit from sanding. Conduct activities indoors whenever possible. The following BMPs are recommended to further prevent and minimize the contamination of stormwater resulting from activities related to the painting, finishing, and coating of vehicles, boats, buildings, and equipment: Recycle paints, paint thinner, solvents, wash water from pressure washers, and any other recyclable materials. Use efficient spray equipment such as electrostatic, air-atomized, high- volume/low-pressure, or gravity-feed spray equipment. Purchase recycled paints, paint thinner, solvents, and other products if feasible. Dispose of unused paint promptly. Unused paint may be recycled at the Metro Recycling and Paint Disposal Facility: go/by.web/id/ Lake Oswego Stormwater Manual Draft

190 Source Control Required Best Management Practices The following BMPs or equivalent measures are required of all businesses and public agencies engaged in activities related to the painting, finishing, and coating of vehicles, boats, buildings, and equipment Preparation and Application Train employees in the application and cleanup of paints, finishes, and coatings to reduce misuse and overspraying. Document and keep all training records. Use ground cloths or drop cloths underneath outdoor painting, scraping, and sandblasting work, and properly clean and temporarily store collected debris. Porous drop cloths are recommended for exterior surface preparation work to capture solids and allow rainwater to seep through. Use a storm drain cover, catch basin filter, or similarly effective runoff control device if dust, sediment, or other pollutants may escape the work area. If a catch basin filters are used on site, maintain the filter regularly (weekly, or as needed) to prevent plugging. Do not conduct spraying, blasting, or sanding activities over open water or where wind may blow paint into water. If windy conditions are present, use a curtain to contain the activity. While using a spray gun or conducting sand blasting, enclose and/or contain all work in compliance with applicable air pollution control requirements and those of the Occupational Safety and Health Administration Cleanup Wipe up spills with rags and other absorbent materials immediately. Do not hose down the area. On marine dock areas, sweep rather than hose down debris. Collect any water that is generated and convey it to an appropriate treatment and disposal facility. Use a ground cloth, pail, drum, drip pan, tarpaulin, or other protective device for activities such as paint mixing and tool cleaning outside or where spills can contaminate stormwater. Whenever possible, conduct these activities inside or in an enclosed area. Clean paint brushes and tools covered with water-based paints in sinks connected to sanitary sewers or in portable containers that can be dumped into a sanitary sewer drain. Collect solvents used to clean brushes and tools covered with non-water-based paints, finishes, or other materials. Used solvents (e.g., paint thinner, turpentine, and xylol) must be recycled or be disposed of properly Material Storage and Disposal Unused paint may be recycled at the Metro Recycling and Paint Disposal Facility: cfm/go/by.web/id/571 Dispose of all wastes and prevent all uncontrolled releases to the air, ground, or water. Store all paints, finishes, or solvents inside a building or in covered secondary containment. All containers must have tight-fitting lids. Lake Oswego Stormwater Manual Draft 176

191 Source Control Parking Lot Maintenance and Storage of Vehicles and Equipment This BMP applies to businesses and public agencies that own or operate public and commercial parking lots and sidewalks, such as those associated with retail stores, apartment buildings, fleet vehicles (including car rental lots and car dealerships), and equipment sale and rental facilities. It also includes properties where vehicles or equipment are stored outside. Potential pollutants produced by the parking and storage of vehicles and equipment include petroleum hydrocarbons and other organic compounds, oils and greases, metals, and suspended solids General Recommendations Prevent stormwater contamination by avoiding and reducing washing. Do not use soap or other chemicals unless the area drains to a sanitary sewer. When wash water is discharged to the sanitary sewer, check if pretreatment is necessary before being discharged. Some sites may be required to obtain a wash water permit from DEQ. For example, the washing of roads, parking lots, sidewalks, and other paved surfaces is permitted provided: Surfaces are swept prior to washing and There is no runoff off the site or discharge to surface waters, storm sewers, or dry wells. Please see provisions of DEQ 1700B permit at and or contact DEQ s Northwest Region Permit Office for more details Required Best Management Practices The following BMPs or equivalent measures are required for activities related to the parking and storage of vehicles and equipment: Sweep or vacuum parking lots, storage areas, sidewalks, and driveways regularly to collect dirt, waste, and debris and dispose of as solid waste. Do not hose down or pressure wash areas that drain to a storm drain, drywell, or to the surface water ultimately receiving drainage water. If a parking lot must be washed, discharge the wash water to a sanitary sewer or other approved wastewater treatment system, if allowed by the City, or collect it for offsite disposal. Please contact the City for more information. Cover or plug storm drains to prevent wash water from entering the surface water management utility. In some cases, contaminated stormwater may need to be pretreated before it is discharged to the sanitary sewer. Make sure all outside materials that have the potential to leach or spill to the drainage system are covered, contained, or moved to an indoor location. An oil removal system is recommended for high-use parking lots. 177 Lake Oswego Stormwater Manual Draft

192 Source Control Fueling at Dedicated Stations This BMP applies to businesses and public agencies that operate a facility used exclusively for the transfer of fuels from a stationary pumping station to vehicles or equipment. This type of fueling station includes aboveground or underground fuel storage facilities, which may be permanent or temporary. Permanent fueling stations include facilities such as, but not limited to, commercial gasoline stations, 24-hour convenience stores, car washes, warehouses, manufacturing establishments, maintenance yards, marinas and boatyards, and private fleet fueling stations. Temporary fueling stations include facilities such as, but not limited to, construction sites and any other site on which fuel is temporarily stored and dispensed into vehicles or equipment. A spill can be a one-time event, a continuous leak, or frequent small spills. All kinds must be prevented. Typically, stormwater contamination at fueling stations is caused by leaks or spills of fuels, lubrication oils, radiator coolants, and vehicle wash water. These materials contain organic compounds, oils and greases, and metals that can be harmful to humans and aquatic life. These pollutants must not be discharged to the surface water management system or directly into receiving waters. Direct or indirect discharges of antifreeze, oil, gasoline, grease, and all other automotive and petroleum products and flammable or explosive materials into the surface water management system are prohibited discharges under the City s Stormwater Code. These types of discharges are also prohibited according to state regulations General Recommendations All new fueling stations must be constructed on an impervious concrete pad under a roof to keep out rainfall and to prevent stormwater run-on. A treatment BMP must be used for contaminated stormwater and wastewaters in the fueling containment area Automobile Repair and Maintenance This BMP applies to businesses and public agencies on whose premises oil, fuel, engine oil, and other fluids such as battery acid, coolants, and transmission and brake fluids are removed and replaced in vehicles and equipment. It also applies to mobile vehicle maintenance operations, such as those at construction sites. A spill can be a one-time event, a continuous leak, or frequent small spills. All kinds must be prevented. Pollutants of concern are toxic petroleum hydrocarbons, toxic organic compounds, oils and greases, ph, and metals. These pollutants must not be discharged to the surface water management system or directly into receiving waters General Recommendations Leaks and spills of fluids can be prevented and contained by the use of good housekeeping measures and the use of cover and containment BMPs. Compliance can be achieved more easily with sewer and stormwater requirements by running a dry shop, thereby reducing consumption and discharge of liquids. Soiled rags and other cleanup material must be properly managed in accordance with Lake Oswego Fire Code and Solid Waste regulations or cleaned and reused by a professional cleaning service. Lake Oswego Stormwater Manual Draft 178

193 Although not required, the following BMPs can provide additional pollution protection: Source Control Recycle oil, antifreeze, batteries, and air conditioning coolant. Recover air conditioning gases. Use reusable cloth rags to clean up drips and small spills instead of disposable materials. Use absorbent pillows or booms in or around storm drains and catch basins to absorb oil and fuel. Unused paint may be recycled at the Metro Recycling and Paint Disposal Facility: go/by.web/id/ Required Best Management Practices The following BMPs or equivalent measures are required of all businesses and public agencies engaged in automotive repair and maintenance activities: Employees must be educated annually about the need for careful handling of automotive fluids. New employees must be trained upon hiring. Employees at businesses or public agencies that routinely change or handle these fluids must be trained in spill prevention and cleanup. All training must be documented. For information on training, see Spill cleanup materials, such as rags and absorbent materials, must always be kept close at hand when changing oil and other fluids. Soiled rags and other cleanup material must be properly disposed of or professionally cleaned and reused. Maintenance and repair activities must be conducted indoors. Drain all fluids that have the potential to leak from wrecked vehicles and equipment when they arrive. Store and dispose of fluids properly. If the work must be performed outdoors or at a mobile location (such as a as a construction site), drip pans or other containment devices must be used beneath the vehicle or equipment to capture all spills. Make sure all outside materials that have the potential to leach or spill to the drainage system are covered, contained, or moved to an indoor location. Maintenance and repair areas cannot be hosed down. Instead, they must be swept weekly or more often as needed to collect dirt, and spills must be wiped up with rags and other absorbent materials. If pressure washing is necessary, the wastewater must be collected and disposed of properly. It cannot be discharged to the stormwater drainage system. Drains located inside buildings must be connected to the sanitary sewer. Do not allow drains inside maintenance buildings to connect to the sanitary sewer without prior approval from the City. A connection permit is needed to connect to the City s wastewater system. For information about connection permits, call the City Building Department. In most cases, stormwater collected on fuel containment pads will need to be pretreated before it is discharged to the sanitary sewer. If floatable components are present, use an oil/water separator or other appropriate treatment to treat all runoff from the fluid changing area prior to discharge to the sanitary sewer. 179 Lake Oswego Stormwater Manual Draft

194 Source Control If extensive staining and oily sheen is present, absorbent pillows or booms must be used in or around catch basins and properly maintained to prevent oil from entering the stormwater drainage system Swimming Pool and Spa Maintenance This BMP applies to all private, public and commercial swimming pools and spas. Pools and spas at hotels, motels, apartments, and condominium complexes are also covered. Pollutants of concern include nutrients, suspended solids, chlorine, ph, and substances that increase chemical oxygen demand General Recommendations Dispose of pool or spa water to the sanitary sewer, if approved by the City. Although not required, the following BMP can further help to reduce the potential for stormwater contamination: Hire a professional pool-draining service to collect all pool water for offsite disposal Required Best Management Practices The following BMPs or equivalent measures are required for all swimming pool and spa cleaning and maintenance activities. In some cases, contaminated stormwater from swimming pool and spa cleaning and maintenance activities may need to be pretreated before it is discharged to the sanitary sewer. For approval before discharging wash water to the wastewater system, contact Public Works Operations ( ) at least 48 hours in advance. Pool water may not be discharged to a receiving water or the surface water management system unless there are no detectable levels of chlorine, because even at low concentrations chlorine is harmful to fish and other aquatic life. If pool discharge water is discharged to the ground, discharge must be slow enough to allow infiltration of all water into the ground and not produce surface runoff. Diatomaceous earth used in pool filters cannot be discharged to receiving waters, drainage systems, septic systems, or the ground Vehicle, Equipment, and Building Washing The City has charity car wash kits available at no cost to reduce the impacts of carwash fundraisers General Recommendations This BMP applies to the washing of vehicles, aircraft, vessels, industrial equipment, and large buildings. Discharges resulting from scrubbing, sanding, pressure washing, and steam cleaning are also included in this category of cleaning and washing activities. Vehicle washing by private citizens and fund-raising groups such as schools, churches, and scouting groups is permitted. However, fund-raising groups must employ the best management practices outlined in DEQ s fact sheet on non-profit activities. Lake Oswego Stormwater Manual Draft 180

195 Source Control Wash water from cleaning activities can contain soaps and detergents, oils and greases, suspended solids, metals, and soluble organic compounds that can contaminate stormwater. These pollutants must not be discharged to the drainage system or directly into receiving waters. Although not required, the following BMPs can provide additional pollution control for businesses and public agencies that perform washing operations for vehicles, equipment, and building structures. To reduce potential overall pollution load to the sanitary sewer: Minimize water and detergent use in all washing operations. Use phosphate-free detergents when practical. Consider recycling the washwater by installing a closed-loop water recycling system. For intermittent uses, such as at commercial parking lots and at gasoline stations used for charity car washes where it is not possible to discharge the wash water to an indoor sanitary connection (such as to an indoor toilet or utility sink), a temporary plug or a temporary sump pump can be used at the storm drain to collect the wash water for offsite disposal, such as discharge to a nearby sanitary sewer. At industrial sites, contact DEQ for NPDES permit requirements related to washing trucks. New and used car dealerships may wash vehicles in the parking stalls as long as a temporary plug system is used to collect the wash water for disposal as stated above or an approved treatment system for the wash water is in place Required Best Management Practices Cleaning, pressure washing, and steam cleaning wastewater must be discharged into a sanitary sewer drain at a site that is approved for discharge. It is illegal to discharge the dirty solution to the drainage system; however, the activity may be permitted for disposal in the wastewater system if approved by the City. For more information and to determine whether a type of chemical and an amount of water are permitted for discharge to the sanitary sewer system, contact the City Operations Division. If sanitary sewer disposal is not available or not allowed, the collected wastewater must be treated or transferred to a holding tank, where it must be picked up for disposal by a licensed waste hauler. The following BMPs or equivalent measures are required of all businesses and public agencies engaged in washing, pressure washing, or steam cleaning of vehicles, equipment, and building structures: Conduct indoor vehicle and equipment washing operations in an area that drains to the wastewater system and that prevents the wash water from running outside and entering the surface water management system. Conduct outdoor vehicle and equipment washing operations in a designated wash area that drains to a sump (like a grit separator) or a catch basin and then to the sanitary or another appropriate wastewater treatment or recycling system. 181 Lake Oswego Stormwater Manual Draft

196 Source Control If adjacent to a building or constructed over hazardous material storage areas, roofs and covers are also regulated by the Fire Code. At gasoline stations, multi-family residences, and any other business and public agency where vehicles are washed, clearly mark the washing area. A connection permit is required to connect to the City s wastewater system. For information about connection permits, call the City Building Department. In some cases, wash water may need to be pretreated before it is discharged to the sanitary sewer Outdoor Storage or Transfer of Solid Raw Materials, Byproducts, or Finished Products This BMP applies to businesses and public agencies on whose premises there will be outdoor storage and transfer of solid raw materials, byproducts, or products such as, but not limited to, gravel, sand, salts, topsoil, compost, logs, sawdust, wood chips, lumber and other building materials, concrete, and metal products typically stored outside in large piles or stacks at commercial or industrial establishments. If stormwater comes in contact with the stockpiled materials listed above, pollutants can be leached or erosion of the stored materials may occur. Potential pollutants include suspended solids, substances that increase biological oxygen demand, organic compounds, and dissolved salts (e.g., sodium chloride, calcium chloride, and magnesium chloride). These pollutants must not be discharged to the drainage system or directly into receiving waters General Recommendations Cover and contain materials to prevent erosion. Erosion results in stormwater contamination and loss of valuable product Required Best Management Practices The following BMPs or equivalent measures are required of all businesses and public agencies engaged in the outdoor storage or transfer of solid raw materials, byproducts, or finished products: Do not hose down the contained stockpile area if the discharge will flow into a storm drain or a drainage conveyance. Sweep paved storage areas daily or more often as necessary to collect and dispose of loose solid materials. For stockpiles containing more than 5 cubic yards of erodible or water- soluble materials such as soil, deicing salts for roads, compost, unwashed sand and gravel, and sawdust; and for outside storage areas for solid materials such as logs, bark, lumber, and metal products, choose one or more of the following BMPs: Store in a building or a covered, paved area, preferably surrounded by a berm. Place temporary plastic sheeting (polyethylene, polypropylene, hypalon, or equivalent material) over the material. Lake Oswego Stormwater Manual Draft 182

197 12 References Center for Watershed Protection: Solutions for Clean Water and Healthy Natural Resources < Clackamas County, Water Environment Services, Clean Water Services, Oak Lodge Sanitary District, City of Gladstone, City of Happy Valley, City of Lake Oswego, City of Milwaukie, City of Oregon City, City of West Linn, and City of Wilsonville, Erosion Prevention and Sediment Control Planning and Design Manual. Revised December Clean Water Services The Low Impact Development Approaches Handbook. Clean Water Services Design and Construction Standards. Debo, Thomas N. and Andrew J. Reese Municipal Stormwater Management, 2nd ed. Lewis Publishers, CRC Press LLC. Boca Raton, Florida. DEQ Oregon TMDLs Approved by EPA May 2000 through April Web page accessed on April 2, 2012, at: < DEQ Willamette Basin TMDL. Oregon Department of Environmental Quality. Ecology Stormwater Management Manual for Western Washington. Publication Number Washington State Department of Ecology. Olympia, Washington. Available for download at: wa.gov/programs/wq/stormwater/manual.html Kitsap County Kitsap County Stormwater Pond Retrofit Design Guidance Manual. Kitsap County Public Works Department. Port Orchard, WA. Lane, E.W Design of Stable Channels. Transactions of the American Society of Civil Engineers, Volume 120, pages Lake Oswego, City of Parks Plan 2025: Lake Oswego Parks, Recreation and Natural Areas System Plan. Webpage accessed on October 4, 2012, at < fileattachments/parksrec/cityprojects/13445/lo_parksplan2025_adopted_073112_high.pdf> Lake Oswego, City of Wet Weather Season Erosion and Sediment Control Requirements: Minimum effective dates: October 1st through May 31st and during all rainy periods. City of Lake Oswego Public Works Department. March 23, Lake Oswego City of Lake Oswego Surface Water Management Design Workbook. December 2003 Edition. Leopold, L.B., and Maddock, T The Hydraulic Geometry of Stream Channels and some Physiographic Implications. US Geological Survey Professional Paper, 252. Metro Green Streets: Innovative Solutions for Stormwater and Stream Crossings. ODOT Hydraulics Manual. Oregon Department of Transportation. Oregon Building Codes Division Oregon Specialty Codes Online. Webpage accessed on April 27, 2012, at: < Otak Clean Streams Plan. 183 Lake Oswego Stormwater Manual Draft

198 References Portland, City of Sewer and Drainage Facilities Design Manual. Portland, City of Stormwater Management Manual. PSAT and WSU Low Impact Development: Technical Guidance Manual for Puget Sound. Puget Sound Action Team and Washington State University Pierce County Extension. Available for download at: < Seattle Public Utilities. 2009a. Director s Rules for Seattle Municipal Code Chapters Volume 1: Source Control Technical Requirements Manual. Department of Planning & Development. Seattle Public Utilities. 2009b. Director s Rules for Seattle Municipal Code Chapters Volume 3: Stormwater Flow Control & Water Quality Treatment Technical Requirements Manual. Department of Planning & Development. Stormwater Solutions. Oregon State University extension webpage: < stormwater/> WES Erosion Prevention and Sediment Control: Planning and Design Manual. Clackamas County Water Environment Services. Lake Oswego Stormwater Manual Draft 184

199 13 Definitions 13.1 Abbreviations BMP - best management practice CFR Code of Federal Regulations DEQ Oregon Department of Environmental Quality ESC erosion and sediment control FEMA Federal Emergency Management Agency GIS geographic information system IPM integrated pest management LID low impact development LOC Lake Oswego Code MS4 - municipal separate stormwater system NPDES - National Pollutant Discharge Elimination System NRCS Natural Resource Conservation Service OAR Oregon Administrative Rule ODOT Oregon Department of Transportation OMP operations and maintenance plan SBUH Santa Barbara Urban Hydrograph SWPPP stormwater pollution prevention plan TAPE Technology Assessment Protocol Ecology TMDL total maximum daily load UIC underground injection control US EPA US Environmental Protection Agency USGS US Geological Survey 185 Lake Oswego Stormwater Manual Draft

200 Definitions 13.2 Definitions 303(d) List A list developed in conformance with Section 303(d) of the federal Clean Water Act that identifies waters that do not meet water quality standards and where a total maximum daily load (TMDL) needs to be developed. Adsorption Adsorption is the process by which dissolved pollutants adhere to suspended particulates, bottom sediments, vegetation surfaces, or other media (such as activated carbon). Some filtration media help remove charged pollutant particles, such as metal cations, by adsorption. Bedrock The native, contiguous, consolidated rock underlying the surface of the Earth. Above bedrock is usually an area of broken and weathered unconsolidated rock, usually called sediment. Occasionally bedrock is exposed on the surface indicating that sediment has been removed by streamflow or some other sediment transport process (e.g., landsliding). Best Management Practices (BMPs) The schedule of activities, controls, prohibition of practices, maintenance procedures, and other management practices designed to prevent or reduce pollution. BMPs also include treatment requirements, operating procedures and practices to control stormwater runoff. Built out Most land is already developed rather than undisturbed. Capacity See design capacity Channel The land features (bed and banks) that confine a stream. Channel straightening The modification of the natural drainage patterns of a channel and elimination of sinuosity, braiding, and other natural features. Design capacity The flow volume or rate that a stormwater management facility is designed to safely contain, receive, convey, reduce pollutants from, or infiltrate to meet a specific performance standard. Detention The temporary storage of stormwater runoff in a facility (typically a pond, vault, or large pipe) which is used to control the peak discharge rates. The entire stormwater volume is ultimately released, but at a lower discharge rate. Direct discharge Stormwater that enters receiving water through a point source, such as a pipe, outfall, or ditch. Discharge As defined in 40 CFR 122.2, discharge when used without qualification means the discharge of a pollutant. Lake Oswego Stormwater Manual Draft 186

201 Definitions Discharge of a pollutant means: (a) Addition of any pollutant or combination of pollutants to Waters of the State from any point source, or (b) Addition of any pollutant or combination of pollutants to the waters of the contiguous zone or the ocean from any point source other than a vessel or other floating craft which is being used as a means of transportation. Drywell Perforated precast concrete cylinders that discharge stormwater into underlying soils. Effective Impervious Surface Impervious surfaces that are connected via sheet flow or discrete conveyance to a drainage system. A sidewalk that drains to a lawn or other landscaped area where stormwater runoff from the impervious surface can infiltrate is not considered effective impervious surface. Entrain To carry. Erodible or leachable materials Erodible or leachable materials, wastes, or chemicals are those substances which, when exposed to rainfall, measurably alter the physical or chemical characteristics of the rainfall runoff. Examples include erodible soils that are stockpiled, uncovered process wastes, manure, fertilizers, oily substances, ashes, kiln dust, and garbage dumpster leakage. Fish spawning and rearing habitats Habitats associated with vulnerable life stages of important fish species. The timing of construction activities that could potentially affect these areas is typically restricted. Gravel bars Elongated depositions of alluvium within a channel that are not permanently vegetated. Groundwater Subsurface water that occurs in soils and geological formations that are fully saturated. Groundwater fluctuates seasonally and includes perched groundwater. Hydrograph A hydrograph graphically displays the discharge of stormwater runoff over time. The area under the hydrograph represents the total volume of stormwater runoff during that storm. Hydromodification Impacts to stream channels resulting from changes in stream flow, volume, and duration due to stormwater discharges. These may include bank erosion, incision, channel scour, and channel straightening. These changes result in loss of aquatic habitat and impairments to water quality. Hyetograph A graphical representation of the distribution of rainfall over time. 187 Lake Oswego Stormwater Manual Draft

202 Definitions Illicit discharge Any discharge to a municipal separate storm sewer system that is not composed entirely of stormwater except discharges authorized under Section A.4.axii, discharges permitted by a NPDES permit or other state or federal permit, or otherwise authorized by DEQ. Impervious surface Any surface resulting for development activities that prevents the infiltration of water or results in more runoff than in the undeveloped condition. Common impervious surfaces include: building roofs, traditional concrete or asphalt paving on walkways, driveways, parking lots, gravel roads, and packed earthen materials. Indirect discharge Stormwater that enters receiving waters via surface runoff or via groundwater. Industrial Activities Activities such as manufacturing, transportation, mining, and steam electric power industries; scrap yards, landfills, certain sewage treatment plants, and hazardous waste management facilities. Infiltration The downward movement of rainwater or surface water through the soil. Infiltration pond A vegetated depression that temporarily pools stormwater before it percolates into underlying soils. Infiltration trench A linear, gravel-filled trench that distributes stormwater to underlying soils. Invert elevation The elevation of the lowest part of the inside of a pipe, culvert, or ditch. Land disturbance Large project(s) New or redevelopment projects that create or replace 3,000 square feet or more of impervious surface area. Large woody debris The accumulation of trees and large branches that have fallen into a stream. Large woody debris serves many purposes in a stream that are vital to life history of many native species of fish, plants, and animals. Low impact development (LID) A stormwater management approach that seeks to mitigate the impacts of increased runoff and stormwater pollution using a set of planning, design and construction approaches and stormwater management practices that promote the use of natural systems for infiltration, evapotranspiration, and reuse of rainwater and can occur at a wide range of landscape scales (i.e. regional, community and site) Maximum extent practicable Medium project(s) New or redevelopment projects that create or replace between 1,000 and 3,000 square feet of impervious surface area. Lake Oswego Stormwater Manual Draft 188

203 Definitions Municipal separate storm sewer system (MS4) The regulatory definition of an MS4 (40 CFR (b)(8)) is a conveyance or system of conveyances (including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains): (i) Owned or operated by a state, city, town, borough, county, parish, district, association, or other public body (created to or pursuant to state law) including special districts under state law such as a sewer district, flood control district or drainage district, or similar entity, or an Indian tribe or an authorized Indian tribal organization, or a designated and approved management agency under section 208 of the Clean Water Act that discharges into waters of the United States. (ii) Designed or used for collecting or conveying stormwater; (iii) Which is not a combined sewer; and (iv) Which is not part of a Publicly Owned Treatment Works (POTW) as defined at 40 CFR In practical terms, operators of MS4s can include municipalities and local sewer districts, state and federal departments of transportation, public universities, public hospitals, military bases, and correctional facilities. National Pollutant Discharge Elimination System (NPDES) The NPDES program was initiated by the U.S. Congress in 1972 and amended in 1987 as part of the Clean Water Act. It regulates discharges of stormwater pollutants into navigable or regulated waters from municipalities and many types of industrial sites. Over-bank vegetation Vegetation that extends over the channel, providing shading and wood supply. Overflow elevation The elevation that water is allowed to rise in a pond before it flows into an outlet pipe. Peak Flow The maximum rate of flow of water during or after a precipitation event Pervious Surface Pollutant generating impervious surface Pollutant Pollutant means dredged spoil, solid waste, incinerator residue, filter backwash, sewage, garbage, sewage sludge, munitions, chemical wastes, biological materials, concrete wash water, paint, radioactive materials (except those regulated under the Atomic Energy Act of 1954, as amended [42 U.S.C et seq.]), heat, wrecked or discarded equipment, rock, sand, cellar dirt and industrial, municipal, and agricultural waste discharged into water. Pool Deep area in a stream channel. Potential Severe Erosion Hazard Area Surface areas where erosion can be easily caused by removal of vegetation cover, stripping topsoil, or placing fill, whether by natural causes such as streams or surface runoff or by development activities. The placement of any new fill in such an area shall be considered as creating a potentially severe erosion hazard. (Known Potential Severe Erosion Hazard Areas are described and mapped in the Engineering Geology chapter of the Lake Oswego Physical Resources Inventory, March, 1976, on file at City Hall; specifically in Table II, Characteristics and Limitations of Earth Materials and Engineering Geology map, and the Relative Slope Instability Hazard Map of the Lake Oswego Quadrangle, prepared by the State of Oregon Department of Geology and Mineral Industries (DOGAMI), published in 1995.) 189 Lake Oswego Stormwater Manual Draft

204 Definitions Potential Severe Landslide Hazard Area Areas where earth movement or failure, such as slumps, mud flows, debris slides, rock falls or soil falls, are likely to occur as a result of development activities. These activities include excavation which removes support of soils by changes in runoff or groundwater flow or vibration loading such as pile driving or blasting. Prohibited material Prohibited materials include pollutants or other material that is not explicitly identified as authorized discharges per Schedule A(4)(a)(xii) of the City s NPDES MS4 permit that are discharged to the surface water management system. Public nuisance Nuisance conditions include improper function resulting in uncontrolled runoff and overflow; stagnant water with concomitant algae growth, insect breeding, and odors; discarded debris; and safety hazards created by a facility s operation. Replace or Replacement The removal of an impervious surface that exposes soil followed by the placement of an impervious surface. Replacement does not include repair or maintenance activities on structures or facilities taken to prevent decline, lapse or cessation in the use of the existing impervious surface as long as no additional hydrologic impact results from the repair or maintenance activity. Receiving water A receiving water is the ultimate destination for stormwater leaving a particular site. Virtually all receiving waters are Waters of the State, and include lakes, bays, ponds, impounding reservoirs, springs, wells, rivers, streams, creeks, estuaries, marshes, inlets, canals, the Pacific Ocean within the territorial limits of the State of Oregon, and all other bodies of surface or underground waters, natural or artificial, inland or coastal, fresh or salt, public or private (except those private waters that do not combine or effect a junction with natural surface or underground waters) that are located wholly or partially within or bordering the state or within its jurisdiction. (ORS 468B.005(10)). Redevelopment A project on a previously developed site that results in the addition or replacement of impervious surface. Riffles Shallow areas in a stream channel where the surface of flowing water is broken by waves or ripples. Santa Barbara Urban Hydrograph (SBUH) A hydrologic model that converts design storm incremental excess rainfall depths into instantaneous unit hydrographs and routes them through an imaginary reservoir. Sedimentation Deposition of sediment. Sensitive Lands Those areas that the City has designated as sensitive lands within the sensitive lands zoning overlay. These include lands containing natural resources that have environmental significance within the Lake Oswego planning area (Urban Service Boundary) including wetlands, stream corridors, and tree groves. Such lands are more sensitive or easily damaged by development impacts than non-resource lands. Lake Oswego Stormwater Manual Draft 190

205 Definitions Small project(s) New or redevelopment projects that create or replace greater than 200 square feet and less than 1,000 square feet of impervious surface area. Spillway An armored surface outlet from detention pond or other surface BMP to allow stormwater to discharge even in the event of outlet plugging or higher than design flows. Steep slope A steep slope is an average slope of 25 percent or more. Storm drain A pipe that transports stormwater. Stormwater The water that originates from precipitation, primarily rainfall and snowmelt. Stormwater management facilities Facilities intended to collect or convey stormwater runoff, reduce pollutants from stormwater, or reduce hydrologic impacts associated with stormwater by detaining or infiltrating stormwater. Substrate Material underlying the portion of the streambed that receives direct flow. Surface water management utility The surface water management utility is the entity that plans, designs, constructs, maintains, administers, and operates all City surface water conveyances and facilities, and the regulations for facility control. The surface water management utility also establishes standards for design and construction. Surface Water Management System Includes all natural and manmade facilities utilized by the Surface Water Utility to regulate the quantity and quality of surface water, including drainage easements, culverts, storm drains, catch basins, stream corridors, rivers, ponds, wetlands and impoundments. Total maximum daily load (TMDL) DEQ develops TMDLs for water quality limited or impaired water bodies (on the 303(d) list) in accordance with OAR , which defines how much of an identified pollutant a specified water body can receive and still meet water quality standards 191 Lake Oswego Stormwater Manual Draft

206

207 Appendix A Approved Plant LIsts and Seed Mixes From City of Portland Bureau of Environmental Services Stormwater Manual (2008) Appendix F.4 and Seed Specifications for Stormwater Management Manual (2004)

208

209 APPENDIX F.4 PLANT LISTS Zone A: Area of the facility defined as the bottom of the facility to the designed high water mark. This area has moist to wet soils and plants located here shall be tolerant of mild inundation. Zone B: Area of the facility defined as the side slopes from the designed high water line up to the edge of the facility. This area typically has dryer to moist soils, with the moist soils being located further down the side slopes. Plants here should be drought tolerant and help stabilize the slopes.. Swale Planting Zones Zone B Zone A Zone B Planter Planting Zones Zone A Basin Planting Zones Zone B Zone A Saturated Appendix F.4: Planting Templates and Plant Lists F.4-1 Portland Stormwater Management Manual - August 1, 2008 A - 1

210 Ecoroof Planting Zones 4-12 soil depth Zone C Zone D soil depth Grassy Swale Native Seed Mix Percentages are by weight: Hordeum brachyantherum (Meadow Barley) = 25% Danthonia californica (California Oat-grass) = 15% Elymus glaucus (Blue Wild Rye) = 10% Bromus carinatus (California Brome) = 10% Festuca romerii (Roemer's fescue) = 10% Deschampsia cespitosa (Tufted hairgrass) = 10% Agrostis exarata (Spike bentgrass) = 10% Alopecurus geniculatus (Water foxtail) = 5% Deschampsia elongata (Slender hairgrass) = 5% Appendix F.4: Planting Templates and Plant Lists F.4-2 Portland Stormwater Management Manual - August 1, 2008 A - 2

211 Facility Plant List Plant Name Proposed Facility Type Characteristics Private Public Botanic name, Common Name Zone Swale Planter Basin Dry Pond Wet Pond Basin NW Native Evergreen Potential Hgt. O.C. Spacing Herbaceous Plants Aster suspicatus, Douglas' Aster B X X Y N 36" 12" Athyrium felix-femina, Lady Fern B X X X Y N 36" 24" Blechnum spicant, Deer Fern B X X X Y N 24" 24" Bromus carinatus, Califonia Brome Grass A X X Y Y 18" 12" Bromus sitchensis, Alaska Brome A X X Y Y 18" 12" Bromus vulgaris, Columbia Brome A X X Y Y 18" 12" Camassia leichtlinii, Camas Lily A X X X Y N 24" 12" Camassia quamash, Common Camas A/B X X X X Y N 24" 12" Carex deweyanna, Dewey Sedge A X X X X Y Y 36" 12" Carex densa, Dense Sedge A X X X X Y Y 24" 12" Carex obnupta, Slough Sedge A X X X X Y Y 4' 12" Carex rupestris, Curly Sedge A X X X N Y 14" 12" Carex stipata, Sawbeak Sedge A X X X N N 20" 12" Carex testacea, New Zealand Orange Sedge A X X X X N Y 24" 12" Carex vesicaria, Inflated Sedge A X X X X Y N 36" 12" Deschampsia cespitosa, Tufted Hair Grass A/B X X X X Y N 36" 12" Eleocharis acicularis, Needle Spike Rush A X X X X Y Y 30" 12" Eleocharis ovata, Ovate Spike Rush A X X X X Y Y 30" 12" Eleocharis palustris, Creeping Spike Rush A X X Y Y 30" 12" Elymus glaucus, Blue Wild Rye B X X X Y Y 24" 12" A - 3

212 Facility Plant List Plant Name Proposed Facility Type Characteristics Private Public Botanic name, Common Name Festuca occidentalis, Western Fescue Grass A X X X Y N 24" 12" Festuca rubra, Red Fescue B X X X Y Y 24" 12" Glycera occidentalis, Western Manna Grass A X X Y Y 18" 12" Hebe 'Autumn Glory', Hebe B X X N Y 14" 12" Iris douglasiana, Douglas Iris B X X X Y N 18" 12" Iris sibirica, Siberian Iris A X X X N N 36" 12" Iris tenax, Oregon Iris B X X X Y N 18" 12" Juncus balticus, Baltic Rush A X X X N N 20" 12" Juncus effusus var. pacificus, Soft rush A X X X X Y Y 36" 12" Juncus ensifolius, Daggerleaf Rush A X X X X N N 10" 12" Juncus patens, Spreading Rush A X X X X N Y 36" 12" Juncus tenuis, Slender Rush A X X X X Y Y 36" 12" Lupinus micranthus, Small Flowered Lupine B X X X Y N 18" 12" Lupinus polyphyllus, Largeleaved Lupine A/B X X Y N 36" 12" Polypodium glycrrhiza, Licorice Fern A X X X Y Y 12" 12" Polystichum munitum, Sword Fern A/B X X X Y Y 24" 24" Pteridium aquilinum, Bracken Fern B X X Y Y 5' 12" Scriptus acutus, Hardstem Bulrush A X X X N N 10" 12" Scriptus americanus, American Bulrush A X X X X Y Y 30" 12" Scriptus microcarpus, Small Fruited Bulrush A X X Y Y 24" 12" Scriptus validus, Softstem Bulrush A X X X N N 5' 12" Sedum oreganum, Oregon Stonecrop B X Y Y 4" 12" Sisyrinchium californicum, Yellow-eyed Grass A/B X X X N Y 6" 12" Zone Swale Planter Basin Dry Pond Wet Pond Basin NW Native Evergreen Potential Hgt. O.C. Spacing A - 4

213 Facility Plant List Plant Name Proposed Facility Type Characteristics Private Public Botanic name, Common Name Veronica liwanensis, Speedwell A X X N N 2" 12" Large Shrubs and Small Trees Zone Swale Planter Acer circinatum, Vine Maple A/B X X X X Y N 15' 10' Amelanchier alnifolia, Western Serviceberry B X X X Y N 20' 10' Ceanothus sanguineus, Oregon Redstem Ceanothus B X X X Y Y 7' 4' Holodiscus discolor, Oceanspray B X X X Y N 6' 4' Lonicera involucrata, Black Twinberry B X X X Y N 5' 4' Oemleria cerasiformis, Indian Plum B X X X Y N 6' 4' Philadelphu lewisii, Wild Mock Orange B X X X Y N 6' 4' Ribes sanguineum, Red- Flowering Current B X X X Y N 8' 4' Rubus parviflorus, Thimbleberry B X X X Y N 8' 4' Rubus spectabilis, Salmonberry A X X X X Y N 10' 4' Salix fluviatalis, Columbia Willow A/B X X X X N N 13' 6' Salix lucida var. 'Lasiandra', Pacific Willow A X X X X Y N 13' 6' Salix purpurea nana, Blue Arctic Willow B X X N N 8' 6' Salix stichensis, Sitka Willow A X X X X Y N 20' 6' Sambucus cerulea, Blue Elderberry B X X X Y N 10' 10' Sambucus racemosa, Red Elderberry B X X X Y N 10' 10' Spriaea douglasii, Douglas Spiraea A/B X X X X Y N 7' 4' Viburnum edule, Highbush Cranberry A/B X X X X Y N 6' 4' Basin Dry Pond Wet Pond Basin NW Native Evergreen Potential Hgt. O.C. Spacing A - 5

214 Facility Plant List Plant Name Proposed Facility Type Characteristics Private Public Botanic name, Common Name Zone Swale Planter Basin Dry Pond Wet Pond Basin NW Native Evergreen Potential Hgt. O.C. Spacing Shrubs Ceanothus velutinus, Snowbrush B X X X Y Y 4' 3' Cornus sericea, Red-twig Dogwood A X X X X Y N 6' 4' Cornus sericea 'Kelseyii', Kelsey Dogwood B X X X N N 24" 24" Gaultheria shallon, Salal B X X X Y Y 24" 24" Mahonia aquifolium, Oregon Grape B X X X Y Y 5' 3' Mahonia nervosa, Dull Oregon Grape B X X X Y Y 24" 24" Physocarpus capitatus, Pacific Ninebark A/B X X X Y N 10' 3' Rosa gymnocarpa, Baldhip Rose B X X X Y N 3' 3' Rosa nutkana, Nootka Rose B X X X Y N 8' 3' Rosa pisocarpa, Swamp Rose A/B X X X X Y N 8' 3' Symphoricarpos alba, Common Snowberry B X X X Y N 6' 3' Groundcovers Arctostaphylos uva-ursi, Kinnickinnick B X X Y Y 6" 12" Fragaria chiloensis, Coastal Strawberry B X X Y Y 6" 12" Fragaria vesca, Woodland Strawberry B X X N Y 10" 12" Fragaria virginiana, Wild Strawberry B X X N Y 10" 12" Helictotrichon sempervirens, Blue Oat Grass B X X N Y 24" 12" Mahonia repens Creeping Oregon Grape B X X Y Y 12" 12" Trees Abies grandis, Grand Fir B X X Y Y 150' A - 6

215 Facility Plant List Plant Name Proposed Facility Type Characteristics Private Public Botanic name, Common Name Acer griseum, Paperbark Maple B X X N N 30' Acer macrophyllum, Big Leaf Maple B X X X Y Y 60' Alnus rubra, Red Alder A X X X Y N 80' Arbutus menziesii, Madrone B X X Y N 35' Crataegus douglasii, Black Hawthorn A X X X Y N 40' 10' Fraxinus latifolia, Oregon Ash A/B X X X Y N 30' Malus fusca, Pacific Crabapple A X X X X Y N 30' 10' Metasequoia glyptostroboides, Dawn Redwood B X X N N 80' Populus tremuloides, Quaking Aspen A X X Y N 40' Prunus emarginata var. mollis, Bitter Cherry A/B X X X X Y N 50' Pseudotsuga menziesii, Douglas Fir B X X X Y Y 200' Quercus garryana, Oregon White Oak B X X X Y N 100' Rhamnus purshiana, Cascara A/B X X X X Y N 30' Salix hookeriana, Hooker's Willow A/B X X X X Y N 15' Salix scouleriana, Scouler's Willow A/B X X X X Y N 15' Thuja plicata, Western Red Cedar A X X Y Y 150' Tsuga hetrophylla, Western Hemlock A X X X Y Y 125' Tsuga mertensiana, Mountain Hemlock B X X X Y Y 125' Zone Swale Planter Basin Dry Pond Wet Pond Basin NW Native Evergreen Potential Hgt. O.C. Spacing A - 7

216 Ecoroof Plant List Plant Name Characteristics Botanic name, Common Name Zone NW Native Evergreen Potential Hgt. O.C. Spacing Full Sun Partial Shade Sedums and Succulents Delosperma ssp., Ice Plant C N Y 4" X Malephora crocea var. purpureo crocea 'Tequila Sunrise', Coppery Mesemb C N Y 10" X Sedum 'Autumn Joy' C N N 24" X Sedum acre, Biting Stonecrop C N Y 2" X Sedum album, White Stonecrop C N Y 3" X Sedum divergens, Pacific Stonecrop C N Y 3" X Sedum hispanicum, Spanish Stonecrop C N Y 3" X Sedum kamtschaticum, Kirinso C N N 6" X Sedum oreganum, Oregon Stonecrop C Y Y 4" X X Sedum sexangular, Tasteless Stonecrop C N Y 4" X Sedum spathulifolium, Stonecrop C Y Y 4" X Sedum spurium, Two-row Stonecrop C N Y 6" X X Sempervivum tectorum, Hens and Chicks C N Y 6" X Herbaceous Plants Achillea millefolium, Common Yarrow C N N 36" X Achillea tomentosa, Wooly Yarrow C N N 8" X Arenaria montana, Sandwort C N N 4" X Artemesia 'Silver Mound', Artemesia C N N 12" X Aurinia saxatilis, 'Compacta' C N N 6" X Castilleja foliosa, Indian Paintbrush C Y N 10" X A - 8

217 Ecoroof Plant List Plant Name Characteristics Botanic name, Common Name Dianthus ssp. C N N 12" X X Erigeron discoideus, Fleabane C N N 12" X X Festuca glauca, Blue Fescue C N Y 12" X X Fragaria chiloensis, Coastal Strawberry C Y Y 10" X X Fragaria virginiana, Wild Strawberry C Y Y 10" X X Gaillardia aristata, Birds-eye gilia C N N 20" X X Gazania linearis 'CO Gold', Gazania C N N 6" X Gilia capitata, Blue Thimble Flower C Y N 12" X Koelaria macrantha, June Grass C N N 24" X X Linaria reticulate, Purplenet Toadflax C N N 20" X Lobularia maritima, Sweet Alyssum C N N 12" X Polypodium glycrrhiza, Licorice Fern C Y Y 12" X X Polystichum munitum, Sword Fern C Y Y 24" X X Potentilla nepalensis, Nepal Cinquefoil C N N 14" X X Potentilla neumanniana, Cinquefoil C N N 14" X Thymus serphyllum, Creeping Thyme C N N 3" X Veronica liwanensis, Speedwell C N N 2" X X Shrubs and Small Trees Amalanchier alnifolia, Saskatoon Serviceberry D Y N 20' X Berberis thunbergii, Japanese Barberry D N N 4' X Zone NW Native Evergreen Potential Hgt. O.C. Spacing Full Sun Partial Shade A - 9

218 Ecoroof Plant List Plant Name Characteristics Botanic name, Common Name Zone NW Native Evergreen Potential Hgt. O.C. Spacing Full Sun Partial Shade Gaultheria shallon, Salal D Y Y 24" X X Lavandula angustifolia 'Hidcote', Dwarf English Lavander D N Y 30" X Mahonia aquifolium, Oregon Grape D Y Y 5' X X Mahonia nervosa, Dull Oregon Grape D Y Y 24" X X Mahonia repens, Creeping Oregon Grape D Y Y 12" X X Nanadina domestica, Heavenly Bamboo D N N 4' X X Ribes sanguineum, Red- Flowering Current D Y N 12' X X Rosa nutkana, Nootka Rose D Y N 10' X Symphoricarpos mollis, Creeping Snowberry D Y N 18" X X Thymus vulgaris, Common Thyme D N Y 12" X X A - 10

219 Pond Plant List Planting Plant Name Zone Characteristics Botanic name, Common Name Wet to Saturated Moist to Dry Dry/Upland NW Native Evergreen Potential Hgt. O.C. Spacing Herbaceous Plants Alisma plantago-aquatica, Water Plantain X Y N 24" 12" Alopecurus geniculatus, Water Foxtail X Y Y 18" 12" Aster suspicatus, Douglas' Aster X X Y N 36" 12" Bidens cernua, Nodding Beggerticks X Y N 24" 12" Blechnum spicant, Deer Fern X X Y N 24" 24" Bromus sitchensis, Alaska Brome X X Y Y 18" 12" Camassia quamash, Common Camas X Y N 24" 12" Carex deweyanna, Dewey Sedge X X Y Y 36" 12" Carex obnupta, Slough Sedge X Y Y 4' 12" Deschampsia cespitosa, Tufted Hair Grass X Y N 36" 12" Eleocharis ovata, Ovate Spike Rush X Y Y 30" 12" Eleocharis palustris, Creeping Spike Rush X Y Y 30" 12" Elymus glaucus, Blue Wild Rye X Y Y 24" 12" Glycera occidentalis, Western Manna Grass X X Y Y 18" 12" Lemna minor, Common Lesser Duckweed X Juncus effusus var. pacificus, Soft rush X X Y Y 36" 12" Juncus ensifolius, Dagger-leaf Rush X X Y Y 24" 12" Juncus oxymeris, Pointed Rush X X Y Y 24" 12" A - 11

220 Pond Plant List Planting Plant Name Zone Characteristics Wet to Saturated Botanic name, Common Name Juncus patens, Spreading Rush X X N Y 36" 12" Juncus tenuis, Slender Rush X X Y Y 36" 12" Lupinus polyphyllus, Largeleaved Lupine X Y N 36" 12" Myosotis laxa, Small-flowered Forget-Me-Not X Y N 18" 12" Polystichum munitum, Sword Fern X X Y Y 24" 24" Sagittaria latifolia, Wapato X Y N 24" 12" Potamogeton natans, Floatingleafed Pondweed X Y Y 18" 12" Scriptus acutus, Hardstem Bulrush X N N 10" 12" Scriptus microcarpus, Small Fruited Bulrush X Y Y 24" 12" Sisyrinchium idahoense Blueeyed Grass X N Y 6" 12" Sparganium emersum, Narrowleaf Bur-reed X Y N 24" 12" Veronica liwanensis, Speedwell X X N N 2" 12" Viola palustris, Marsh Violet X X Y N 6" 6" Large Shrubs and Small Trees Acer circinatum, Vine Maple X X Y N 15' 10' Amelanchier alnifolia, Western Serviceberry X Y N 20' 10' Holodiscus discolor, Oceanspray X Y N 6' 4' Lonicera involucrata, Black Twinberry X Y N 5' 4' Oemleria cerasiformis, Indian Plum X X Y N 6' 4' Philadelphu lewisii, Wild Mock Orange X Y N 6' 4' Moist to Dry Dry/Upland NW Native Evergreen Potential Hgt. O.C. Spacing A - 12

221 Pond Plant List Planting Plant Name Zone Characteristics Wet to Saturated Botanic name, Common Name Ribes sanguineum, Red- Flowering Current X Y N 8' 4' Rubus parviflorus, Thimbleberry X Y N 8' 4' Rubus spectabilis, Salmonberry X X Y N 10' 4' Salix fluviatalis, Columbia Willow X X N N 13' 6' Salix lucida var. 'Lasiandra', Pacific Willow X X Y N 13' 6' Salix stichensis, Sitka Willow X X Y N 20' 6' Sambucus racemosa, Red Elderberry X Y N 10' 10' Spriaea douglasii, Douglas Spiraea X Y N 7' 4' Viburnum edule, Highbush Cranberry X Y N 6' 4' Shrubs Cornus sericea, Red-twig Dogwood X X Y N 6' 4' Fragaria vesca, Woodland Strawberry X X N Y 10" 12" Fragaria virginiana, Wild Strawberry X X N Y 10" 12" Mahonia aquifolium, Oregon Grape X X Y Y 5' 3' Mahonia nervosa, Dull Oregon Grape X Y Y 24" 24" Physocarpus capitatus, Pacific Ninebark X Y N 6' 3' Rosa gymnocarpa, Baldhip Rose X Y N 3' 3' Rosa nutkana, Nootka Rose X Y N 8' 3' Rosa pisocarpa, Swamp Rose X Y N 8' 3' Moist to Dry Dry/Upland NW Native Evergreen Potential Hgt. O.C. Spacing A - 13

222 Pond Plant List Planting Plant Name Zone Characteristics Wet to Saturated Botanic name, Common Name Spiraea betulifolia, Birchleaf Spiraea X Y N 24" 24" Symphoricarpus alba, Snowberry X Y N 3' 3' Trees Abies grandis, Grand Fir X Y Y 150' Acer macrophyllum, Big Leaf Maple X Y Y 60' Alnus rubra, Red Alder X X Y N 80' Arbutus menziesii, Madrone X Y N 35' Cornus nuttalii, Western flowering Dogwood X X Y N 20' Crataegus douglasii, Black Hawthorn X Y N 40' Fraxinus latifolia, Oregon Ash X X Y N 30' Malus fusca, Pacific Crabapple X X Y N 30' Pinus ponderosa, Ponderosa Pine X Y Y 70' Pinus monticola, Western White Pine X X Y Y 90' Prunus emarginata var. mollis, Bitter Cherry X Y N 50' Pseudotsuga menziesii, Douglas Fir X Y Y 200' Quercus garryana, Oregon White Oak X Y N 100' Rhamnus purshiana, Cascara X Y N 30' Salix hookeriana, Hooker's Willow X X Y N 15' Salix scouleriana, Scouler's Willow X X Y N 15' Thuja plicata, Western Red Cedar X X Y Y 150' Moist to Dry Dry/Upland NW Native Evergreen Potential Hgt. O.C. Spacing A - 14

223 Stormwater Management Manual Adopted July 1, 1999, revised September 2004 A - 15 Page F-14

224 Appendix B Submittals Drainage Report Template Operations and Maintenance Plan Example Integrated Pest Management Plan Example

225

226 City of Lake Oswego Drainage Report Project Name Project Number

227 Project Overview Please provide the following information along with a brief description for the proposed project. Project Owner and Location Property Owner/Land Owner Address Phone Project Owner/Developer Address Phone Project Engineer (If applicable) Name of Supervising Engineer Company Phone Name of Licensed Landscape Architect or Landscape Designer Company Phone Project Name Project Type 1 Development Name Site Address Tax Lot # Legal description of the lot (if new construction): 1 Examples of project types include 2-lot partition, new commercial, multi-family, and single-family residential. B - 1 Page of

228 Other Permits and Reviews (Answer All That Apply) Building Permit #: LU #: Has a land use planning review been conducted? (Circle One) Yes No Is a tree removal permit needed? (Circle One) Yes No Tree removal permit #: Is there a sensitive lands overlay? (Circle One) Yes No What is the zoning overlay? Are there special street setbacks? (Circle One) Yes No Setback distances: City of Lake Oswego Erosion Control Permit #: 1200-C Permit #: Is the project classified as a Small, Medium, or Large Project according to Lake Oswego Stormwater Code? (Circle One) Small Project New or redevelopment projects that create or replace >200 sq ft and <1000 sq ft of impervious surface Medium Project New or redevelopment projects that create or replace 1000 sq ft and <3000 sq ft of impervious surface Large Project New or redevelopment projects that create or replace 3000 sq ft Site Map Criteria Attach a site map that includes any of the listed applicable attributes for each drainage facility. Provide additional descriptions for each item if appropriate. Property lines Contour lines and critical elevations (City Datum) Lot dimensions Onsite and offsite drainage patterns (indicate with arrows) and features Project location (Township and Range) Stormwater Management Subbasin (Available on Web) Total Impervious Area (TIA) of project Effective Impervious Area (EIA) of project site Existing and proposed improvements with dimensions and distance from property lines Proposed stormwater collection, conveyance, treatment and flow control features Areas of protected native soils and/or amended soils that have been added for stormwater management function Sensitive lands delineation Floodplain delineation Wetland delineation B - 2 Page of

229 Minimum Project Requirements Project Type? (Circle One) New development Redevelopment Project classification? Refer to previous page for description of Small, Medium, or Large project classification descriptions. (Circle One) Small Project Medium Project Large Project See Stormwater Design Manual to determine which of the following minimum requirements apply. Check All Minimum Project Requirements that apply: Minimum Project Requirement Site Assessment and Feasibility Analysis Onsite Stormwater Management City of Lake Oswego Erosion Control Permit UIC Review with DEQ System Designed by Licensed Professional Downstream Analysis Drainage Report Required Recorded Operations and Maintenance Plan Recorded Maintenance Covenant Design for Infiltration Design for Water Quality Design for Flow Control NPDES 1200 C Permit form DEQ B - 3 Page of

230 Minimum Requirements Summary In the following section, describe how each applicable minimum requirement will be met. Site Assessment and Feasibility Analysis The goal of the site assessment and feasibility analysis is to incorporate stormwater management into the landscape in a way that will preserve onsite drainage, soils, and native vegetation. Another important goal of the site assessment is to identify good locations for stormwater facilities and BMPs BEFORE design actually begins on a project. Applicants must conduct the feasibility assessment prior to consulting with building or planning departments. In order to simplify this process, the city has developed an interactive map website called LOMap. LOMap is an online tool that provides GIS data for many of the site attributes needed for a proper site analysis. GIS layers within the mapping tool include: Tax lot data Neighborhood associations Zoning information Environment layers (FEMA boundaries, soil information, and fault lines) Utility locations Planning information (Design districts, Heritage trees, historic landmarks, permits, special street setbacks, commercial overlays, and sensitive lands) Fire information As-Builts Parks Maps can be created with necessary data layers and printed or saved for future reference and sharing. The mapping tool is found online at: For instructions on how to use the City of Lake Oswego s Flex Map, go to: In addition to the information found on LOMaps, consideration of the following site attributes should be documented and considered within the site assessment: Existing vegetation (native vegetation, invasive species and weeds, existing trees, and dominant vegetation cover types) Surrounding land use Existing drainage patterns and features Attach site assessment and feasibility analysis. B - 4 Page of

231 Onsite Stormwater Management Onsite stormwater management facilities must be sized to infiltrate 100 percent of the stormwater runoff for a 10-year, 24-hour design storm based on tested infiltration rates (Inches/Hour). Which approved BMPs will be used to meet the onsite stormwater management requirement? Onsite Stormwater Management BMPs Rain garden Infiltration trench Planter Drywell Refer to BMP design guideline(s) for selected BMP(s). Attach the following: Infiltration test results UIC registration information (where applicable) Geotechnical report (where applicable) Soil testing results (where applicable) Calculations demonstrating sizing in conformance with BMP design guidelines Description of approved discharge location City of Lake Oswego Erosion Control Permit/ NPDES 1200-C Permit from DEQ Describe how the project will meet erosion and sediment control requirements. Attach the following: Erosion Control Plan 1200-C permit (if applicable) B - 5 Page of

232 Underground Injection Control (UIC) Review with Oregon Department of Environmental Quality Stormwater controls that qualify as UIC systems include, but are not limited to: Drywells and drill holes Trenches with depth from ground surface that is greater than width regardless of the presence of gravel fill or soil cap Infiltration trenches trenches Does the project include a BMP that is an underground injection control (UIC) that must be registered with the Oregon Department of Environmental Quality (DEQ)? (Circle one) Yes No If the answer to the above question is yes, the project needs to conform with all applicable regulations. Attach the following: Documentation of UIC registration with DEQ Downstream Analysis Attach the following: Calculations for downstream analysis Recorded Operations and Maintenance Plan Attach the following: Approved Operations and Maintenance (O & M) Plan Deed restrictions B - 6 Page of

233 Design for Water Quality Which approved BMPs will be used to treat water quality? Water Quality BMPs Swale Planter Rain garden Constructed wetland Wet pond Sand filter Filter strip Refer to BMP design guideline(s) for selected BMP(s). Attach the following: Infiltration test results UIC registration information (if applicable) Geotechnical report (if applicable) Soil testing results (if applicable) Calculations demonstrating sizing in conformance with BMP design guidelines B - 7 Page of

234 Design for Flow Control Refer to the Lake Oswego BMP design guidelines within the Lake Oswego Stormwater Design Manual for selection of appropriate BMP(s). Which approved BMPs will be used for flow control? Flow Control BMPs Infiltration trench Drywell or Infiltration chamber (UIC) Infiltration pond Constructed wetland with detention storage Rainwater harvesting Detention pond Detention pipes and vaults Attach the following: Infiltration test results UIC registration information (if applicable) Geotechnical report (if applicable) Soil testing results (if applicable) Calculations demonstrating sizing in conformance with BMP design guidelines B - 8 Page of

235 Phosphorous Removal Efficiency for New Development Projects For new development projects, include phosphorous removal effiency calculations. Calculate the phosphorus removal efficiency as follows (OAR ): R P = R v Where: R P Required phosphorous removal efficiency R v Average site runoff coefficient The average site runoff coefficient can be calculated from the following equation: R v = (0.7 x A1) + (0.3 x A2) + (0.7 x A3) + (0.5 x A 4) + (A5 x 0.0) Where: A1 A2 Fraction of total area that is paved streets with curbs and that drain to storm sewers or open ditches. Fraction of total area that is paved streets that drain to water quality swales located on site. A3 Fraction of total area that is building roof and paved parking that drains to storm sewers. A4 A5 Fraction of total area that is grass, trees and marsh areas. Fraction of total area for which runoff will be collected and retained on site with no direct discharge to surface waters. B - 9 Page of

236 Project Name Date Operations & Maintenance Manual GREEN ROOF PROJECT OPERATIONS & MAINTENANCE MANUAL DATE 1. General Operations & Maintenance a. Introduction b. General Operations & Maintenance c. O&M Contacts 2. Operations and Maintenance Requirements a. Irrigation b. Vegetation Management c. Soil Substrate/Growing Medium d. Aesthetics e. Insect Control f. Structural Components g. Debris & Litter h. Spill Prevention i. Training/Written Guidance j. Access & Safety 3. O&M Schedule & Documentation a. Activity Matrix b. Maintenance Calendar c. O&M Form Sample O&M prepared by: APPENDICES A. Construction Documents (As-Builts) B. Product Documentation 3435 NE 45 th Avenue Suite E Portland, Oregon OPERATIONS AND MAINTENANCE MANUAL (SAMPLE) Page 1 of 8 B - 10

237 Project Name Date Operations & Maintenance Manual 1. GENERAL OPERATIONS & MAINTENANCE 1a. Introduction This manual will serve as a guideline for operations and maintenance of. The goal of this document is to identify the need for regular specified maintenance and inspection to: Identify any potential issues and develop a well-documented site history Add to the collective knowledge of ecoroof techniques and technology Improve scheduling efficiency for maintenance and irrigation Develop preventative maintenance techniques to avoid future problems The following sections provide specific Operational & Maintenance requirements for areas related to the Green Roof. Section II summarizes best management practices for O&M. Section III summarizes all of the project components, necessary maintenance or inspection, routine schedules, and conditions/activities that would trigger unscheduled visits. Appendices include Construction Documents and Product Documentation to ensure a complete understanding of all system components. 1b. General Operations & Maintenance An O&M log should be created and maintained to document all operations and maintenance activities and inspections. Inspection records will be used to: 1) Determine where special maintenance conditions exist, 2) Determine optimal frequencies for future inspection and maintenance, 3) generate scheduled and unscheduled (i.e. repair) orders, and 4) assure facility operation and aesthetics. Documentation of operations and maintenance should be conducted according to appropriate standards and best management practices for green roofs, including the following elements: 1. Full inspection should occur on a quarterly basis for a period of the first 2 years, and a minimum of semi-annually thereafter. More frequent spot inspections are recommended, depending on site-specific conditions as shown in the matrix in Section III 2. Inspection records should include: o General condition of vegetation areas, predominant plant species, distribution and success rate o Soil condition and erosion areas o Areas of standing water or potential drainage problem areas o Condition of roof drains o Operation of irrigation timing, moisture sensors, Et module o Observed unscheduled maintenance needs o Components which do not meet the performance criteria and require immediate maintenance 1c. O&M Contacts CONTACT PHONE EXT./PAGER Name/Title # # OPERATIONS AND MAINTENANCE MANUAL (SAMPLE) Page 2 of 8 B - 11

238 Project Name Date Operations & Maintenance Manual 2. OPERATIONS & MAINTENANCE REQUIREMENTS 2a. Irrigation Irrigation will be accomplished through the use of spray rotors. System layout and as-builts are found in Appendix A and data sheets are included in Appendix B. Download of ET data and water usage should be checked once per month and recorded in the operations log. This will provide critical baseline information for future years operations. Irrigation will be used to supplement natural rainfall, primarily in low-water months from June to September. The irrigation timing will be based on the site conditions and augmented by the ET Controller for optimal water usage. Main lines should be drained in fall from internal point of connection. 2b. Vegetation Management During the establishment period, areas where soil coverage leaves bare patched greater than 4 shall be supplemented with additional cuttings to match. Fallen leaves and debris shall be removed from planted areas and located in designated compost area. Any noncompost or surplus materials should be removed from roof surface and disposed of in an acceptable manner. Nuisance and prohibited vegetation from the Portland Plant List shall be removed when discovered. A copy of the nuisance & prohibited plants is located online at Dead vegetation shall be removed and replaced. Dead-heading of flower stalks from sedums should be done once per year in the late fall. Weeds will be removed manually. Pre-emergent or other herbicides shall not be used. Weeds shall be removed regularly and not allowed to accumulate or spread. The following groupings of vegetation should be the goal of maintenance: Sedums should be allowed to colonize freely in the areas established on the planting plan in three distinct diverse mix (not monocultural). While banding is part of the design intent, it is understood that vegetation will change over time and does not need to be highly maintained to keep this intact. 2c. Soil Substrate/Growing Medium Inspection should be conducted for evidence of erosion from wind or water. o o o 2d. Aesthetics Any erosion should be stabilized with additional substrate and/or growing medium similar in nature to the original material (not to exceed 2.5 soil depth) Areas should be planted immediately with appropriate material to hold soils in place; use erosion control netting and/or sterile straw mulch if necessary to provide immediate coverage of areas. Sources of erosion damage (shedding from other roofs, channeling of surface runoff, obstructions) should be identified & corrected immediately. The desired aesthetic of the green roof is to maintain a healthy mix of succulent vegetation, that is free of weeds and that each band is not dominated by a single species. Irrigation is for maintenance of plant health, and should allow for seasonal variation of plants, not to maintain a lush surface year round. Weeding and litter control should be done to maintain a neat appearance of vegetation and common areas and to avoid colonization by non-sedum species. OPERATIONS AND MAINTENANCE MANUAL (SAMPLE) Page 3 of 8 B - 12

239 Project Name Date Operations & Maintenance Manual 2e. Insect Control Every attempt shall be made not to harbor detrimental insects on the green roof and to encourage the colonization by beneficial insects. Standing water that creates an environment for development of insect larvae shall be eliminated by manual means. Chemical sprays shall not be used. 2f. Structural Components Maintain clear drainage of rooftop drains to prevent accumulation of water in ponds Protect and preserve the integrity of roofing system and Green Roof by adhering to all requirements from manufacturer when performing activities on roof, specifically relating to excavation or modification to edge areas. Do not penetrate the roof membrane during any rooftop activity 2g. Debris and Litter Remove litter periodically to prevent clogging of inlet drains and interference with plant growth this includes some trimming of flower stalks from sedums. Remove all litter from roof at the time of removal. 2h. Spill Prevention Any maintenance of rooftop equipment and building that requires handling of substances that can contaminate groundwater or damage plantings or green roof system should: o o 2i. Training and Written Guidance exercise safe spill prevention measures according to manufacturers specifications identify and correct any damage or releases of pollutants as soon as possible Information in this Operation & Maintenance report shall be provided to all maintenance personnel, and multiple copies should be available from. A specific safety program, compliant with all OSHA regulations, should be developed for maintenance staff while working on open roof systems in zones that have lower than 42 parapet heights and/or do not have adequate tie-offs for elevated worker safety. 2j. Access and Safety Access should be safe and efficient. Due to low parapet height, maintenance staff should take adequate safety precautions while working on rooftop. Any rooftop work should follow Oregon Occupational Safety & Health Division standards for preventing falls from Elevation. Egress and ingress routes shall be maintained to design standards clear of debris that would cause tripping Walkways shall be clear of obstructions and maintained to design standards OPERATIONS AND MAINTENANCE MANUAL (SAMPLE) Page 4 of 8 B - 13

240 Project Name Date Operations & Maintenance Manual 3. O&M SCHEDULE + DOCUMENTATION 3a. Activity Matrix The following table summarizes operations and maintenance activities. Each section is divided by the component or area that is addressed. Specific activities are listed, each including a routine schedule for regular maintenance, as well as possible triggers that will necessitate unscheduled checks. All activities should be recorded in an O&M manual for a complete record of adjustments, upkeep, repairs, and water usage. Area Activity Unscheduled Trigger Schedule First 2 years Schedule Long Term Irrigation Inspect system for correct operation, water coverage and/or broken lines; Evaluate irrigation timing with plant water needs. Record schedule Check for breaks Check valves for operation Replace damaged connections, pipe accessories Flush irrigation system and winterize system; insulate live supply lines Noticeable dry or brown patches/ die-back of vegetation Noticeable dry or brown patches/ die-back of vegetation Reduction of line pressure System degradation on controller Every month during irrigation season; Once weekly during hot, dry periods Every month during irrigation season Twice yearly (once at system startup in spring); spot check during hot, dry periods 3 times yearly during irrigation season One monthly during irrigation season Once monthly during irrigation season Twice yearly during Twice yearly during irrigation season irrigation season as needed as needed as needed n/a End of irrigation season (Nov 1) End of irrigation season (Nov 1) Vegetation Management Check for dead plants and replace; Survey for nuisance and/or prohibited vegetation Remove fallen leaves/debris complaints Once per month Once per year (Spring) debris interferes with Once per month Every three months roof drains Mow sedums cuttings from existing n/a Once per year As needed plants to encourage colonization Cutting back & removal of flower heads n/a Once per year (Fall) Once per year (Fall) Manually remove weeds in planted areas Complaints Once per month Twice per year Apply additional sedum cuttings to cover exposed soil areas complaints; notice erosion as needed Every spring as needed Contain plantings that are colonizing areas not specified such as ballasted areas and flashings along parapet n/a Twice per growing season Once per growing season Soil Substrate/ Growing Medium Identify potential erosion (by wind or water) areas and take measures to stabilize Measure for potential settling & stability issues of material; maintain 4 profile Rainfall event greater than 1 in 24 hour period Once per month Twice per year n/a Once per month Once per year OPERATIONS AND MAINTENANCE MANUAL (SAMPLE) Page 5 of 8 B - 14

241 Project Name Date Operations & Maintenance Manual Area Activity Unscheduled Trigger Schedule First 2 years Schedule Long Term Insect Control Survey for presence of detrimental insects Eliminate standing water that could harbor insect larvae noted presence of insects noted presence of standing water Twice per season as needed Twice per season as needed Aesthetics Examine and note general aesthetic conditions of rooftop, including plant health, litter, and necessary maintenance n/a Every visit Once per month Structural Components Examine rooftop drains for proper functioning Examine Green Roof System for damage, necessary repairs, or other structural issues ponding is noted Once per month Twice per year n/a Once per month Twice per year Debris/ Litter Pick up litter on roof area and check drains for clogging Complaints or noticeable accumulation Once per month Once per month Spill Prevention Exercise safe spill prevention measures if using chemicals that could damage roof, vegetation or contaminate groundwater work scheduled on rooftop equipment as needed when activity is triggered as needed when activity is triggered Training Provide input on safety program and O&M manual if problem is noted as needed (review yearly for compliance) as needed (review every three years for compliance) Access/ Safety Maintain clear walkways to design standards Take adequate safety precautions while working in low parapet zone n/a Once per month Every 3 months always always always OPERATIONS AND MAINTENANCE MANUAL (SAMPLE) Page 6 of 8 B - 15

242 Project Name Date Operations & Maintenance Manual 3b. Maintenance Calendar The following is recommended schedule for O&M for the first two years (augment annually based on site observations and project maturity) and long term, to focus on the primary maintenance issues that will arise at different times of the year. While this outlines scheduled required activities, there should be regular visits and observation (monthly walk through) to observe unscheduled triggers and identify potential problems before they escalate. Every visit should include review for access/safety, litter removal, and updating O&M logs accordingly. MONTH ESTABLISHMENT (2 YEARS) LONG TERM January February March Check for Erosion/Exposed Soil/Standing Water Check drains for obstructions Litter Removal Spot Check for Erosion Issues, Standing Water, Drain Function & Litter Removal April Spring Cleaning/Heavy Weeding Survey for Nuisance Vegetation & Remove Provide Additional Sedum Cuttings in Exposed Areas Mow Sedum areas to promote colonization Fill any soil areas that settled more than 1 Spring Cleaning/Light Weeding Survey for Nuisance Vegetation & Remove Add sedum cuttings (if needed) May Startup Irrigation System, Set Timer & Test Moderate Weeding Startup Irrigation System, Set Timer & Test Light Weeding as needed June Monitor and Adjust Irrigation Timing Moderate Weeding Light Weeding as needed July Monitor and Adjust Irrigation Timing Light Weeding Monitor Irrigation (critical dry months) August Monitor and Adjust Irrigation Timing Light Weeding Monitor Irrigation (critical dry months) September Monitor and Adjust Irrigation Timing Moderate Weeding Light Weeding as needed October Remove Flower Stalks/Additional Leaf Litter Moderate Weeding Survey for Nuisance Vegetation & Remove Drain Irrigation System, Flush & Winterize Remove Flower Stalks/Excess Leaf Litter Light Weeding as needed Survey for Nuisance Vegetation & Remove Drain Irrigation System, Flush & Winterize November December Check for Erosion/Exposed Soil Check Drains for obstructions Litter Removal Spot Check for Erosion Issues, Standing Water, Drain Function & Litter Removal OPERATIONS AND MAINTENANCE MANUAL (SAMPLE) Page 7 of 8 B - 16

243 Project Name Date Operations & Maintenance Manual 3c. O&M Form Maintenance: Record date, description, and contractor (if applicable) for all structural repairs, landscape maintenance, and facility cleanout activities. Log #: Date: Work Performed By: Initials: Description of Work Performed: Scheduled? (Y/N) Required Follow up Activities and Date: Log #: Date: Work Performed By: Initials: Description of Work Performed: Scheduled? (Y/N) Required Follow up Activities and Date: Log #: Date: Work Performed By: Initials: Description of Work Performed: Scheduled? (Y/N) Required Follow up Activities and Date: Log #: Date: Work Performed By: Initials: Description of Work Performed: Scheduled? (Y/N) Required Follow up Activities and Date: OPERATIONS AND MAINTENANCE MANUAL (SAMPLE) Page 8 of 8 B - 17

244 Project Name Date Operations & Maintenance Manual Make additional copies as needed and keep in a binder for reference OPERATIONS AND MAINTENANCE MANUAL (SAMPLE) Page 9 of 8 B - 18

245 OHSU C-Wing Green Roof Project April 2011 Operations & Maintenance Manual APPENDIX A. Construction Documents Include Table of Contents B - 19

246 OHSU C-Wing Green Roof Project April 2011 Operations & Maintenance Manual APPENDIX B. Product Documentation Include Table of Contents B - 20

247 OHSU C-Wing Green Roof Project April 2011 Operations & Maintenance Manual B - 21

248 Integrated Pest Management Plan Example Source: Seattle Public Utilities. 2009a. Director s Rules for Seattle Municipal Code Chapters Volume 1: Source Control Technical Requirements Manual. Used with permission. An Integrated Pest Management Plan (IPM) is a natural, long-term, ecologically based systems approach to controlling pest populations. This system uses techniques either to reduce pest populations or maintain them at levels below those causing economic injury, or to so manipulate the populations that they are prevented from causing injury. The goals of IPM are to encourage optimal selective pesticide use (away from prophylactic, broad spectrum use) and to maximize natural controls to minimize the environmental side effects by creating and maintaining healthy landscapes: Design for a healthy landscape. A landscape should be designed to maximize intended uses of the land and to minimize potential pest problems. Design considers such plant health factors as site usage, soils, topography, hydrology and drainage, proximity to sensitive or critical areas, and existing vegetation as well as known pest sensitivity. Awareness of potential pest problems. Certain plants have known pest problems. Likewise, certain cultural conditions or landscape situations can encourage the infestation of pests. Maintenance for maximum landscape health. A well-designed and maintained landscape dramatically reduces the need for pest control. Appropriate selection of plants, pruning, proper irrigation, applications of mulch and fertilizer, appropriate mowing techniques, and other practices all promote landscapes that resist pest pressures and support natural predators. Minimize disturbance of naturally occurring biological controls. Pests have natural predator and control operating on them at all times. Disruption of these systems through poor maintenance practices can cause more new pest problems to develop. The step-by-step comprehensive IPM process is provided below as a guide. The Integrated Pest Management Plan Process Step One: Correctly identify problem pests and understand their life cycle. Learn more about the pest. Observe it and pay attention to any damage that may be occurring. Learn about the life cycle. Many pests are only a problem during certain seasons or can only be treated effectively in certain phases of the life cycle. Step Two: Establish tolerance thresholds for pests. Every landscape has a population of some pest insects, weeds, and diseases. This is good because it supports a population of beneficial species that keeps pest numbers in check. Beneficial organisms may compete with, eat, or parasitize disease or pest organisms. Decide on the level of infestation that must be exceeded before treatment needs to be considered. Pest populations under this threshold should be monitored but do not need treatment. For instance, European crane flies usually do not do serious damage to a lawn unless there are between 25 and 40 larvae per square foot feeding on the turf in February (in normal weather years). Also, most people consider a lawn healthy and well-maintained even with up to 20 percent weed cover, so treatment, other than continuing good maintenance practices, is generally unnecessary. B - 22

249 Step Three: Monitor to detect and prevent pest problems. Regular monitoring is a key practice to anticipate and prevent major pest outbreaks. It begins with a visual evaluation of the lawn or landscape s condition. Take a few minutes before mowing to walk around and look for problems. Keep a notebook, record when and where a problem occurs, then monitor the problem at about the same time in future years. Specific monitoring techniques can be used in the appropriate season for some potential problem pests, such as European crane fly. Step Four: Modify the maintenance program to promote healthy plants and discourage pests. A healthy landscape is resistant to most pest problems. Lawn aeration and overseeding along with proper mowing height, fertilization, and irrigation will help the grass out-compete weeds. Correcting drainage problems and letting soil dry out between watering in the summer may reduce the number of crane fly larvae that survive. Step Five: If pests exceed the tolerance thresholds. Use cultural, physical, mechanical, or biological controls first. If those prove insufficient, use the chemical controls described below that have the least non- target impact. When a pest outbreak strikes (or monitoring shows one is imminent), implement IPM and then consider control options that are the least toxic or have the least non-target impact. Here are two examples of an IPM approach: Red thread disease is most likely under low nitrogen fertility conditions and most severe during slow growth conditions. Mow and bag grass clippings to remove diseased blades. Fertilize lightly to help the grass recover, then begin grass-cycling and change to fall fertilization with a slow-release or natural-organic fertilizer to provide an even supply of nutrients. Chemical fungicides are not recommended because red thread disease cannot kill the lawn. Crane fly damage is most prevalent on lawns that stay wet in the winter and are irrigated in the summer. Correct the winter drainage and/or allow the soil to dry between irrigation cycles; larvae are susceptible to drying out so these changes can reduce their numbers. It may also be possible to reduce crane fly larvae numbers by using a power de-thatcher on a cool, cloudy day when feeding is occurring close to the surface. Studies are being conducted using beneficial nematodes that parasitize the crane fly larvae; this type of treatment may eventually be a reasonable alternative. UOnly after trying suitable non-chemical control methods or determining that the pest outbreak is causing too much damage should chemical controls be considered. Study to determine what products are available and choose a product that is the least toxic and has the least non-target impact. Step Six: Evaluate and record the effectiveness of the control, and modify maintenance practices to support lawn or landscape recovery and prevent recurrence. Keep records. Note when, where, and what symptoms occurred, or when monitoring revealed a potential pest problem. Note what controls were applied and when, and the effectiveness of the control. Monitor each year for the same problems. Review landscape maintenance and cultural practices to see if they can be modified to prevent or reduce the problem. A comprehensive IPM program should also include the proper use of pesticides as a last resort, and vegetation/fertilizer management to eliminate or minimize the contamination of stormwater. B - 23

250 Appendix C Erosion Control Plan General Notes

251

252 Erosion Control Plan General Notes List current as of March 25, Check City website for any updates: From October 1st through May 31st, the wet weather erosion prevention measures will be in effect for any exposed soils or soils not fully established. See the Erosion Prevention and Sediment Control Planning and Design Manual (Chapter 4) for requirements. All stockpiled sediment will be covered with plastic sheeting and isolated with silt fencing or check dam at the toe of slope when not in use. All exposed soils will be protected with an adequate ground cover at the end of construction each day. (Straw, mulch, compost, wood chips, plastic sheeting, etc. Consult the detail sheet in the permit or the manual for specifications) Owner or designated person shall be responsible for proper installation and maintenance of all erosion and sediment control measures and compliance with water quality laws, in accordance with LOC Chapter 52, State, and Federal regulations. Garbage and debris, including litter, food wrappers & cans, construction scraps and material packaging must be collected and contained in secured garbage containers at the end of each work day. Containers should be emptied as needed; small containers and garbage cans (less than 55 gallons) should be emptied on a weekly basis. Concrete wash-out, tile saw & mortar slurry must be contained in leak proof pans and properly disposed of. No ground or pit dumping allowed. Implementation of the Erosion & Sediment Control (ESC) plan, maintenance, replacement, and upgrading of ESC measures is the responsibility of the contractor until all construction is completed, the site has been stabilized, and approved by the City Manager or his designee. All measures will comply with specifications provided in the Erosion Prevention and Sediment Control Planning and Design Manual (Revised December 2008), available at ESC measures shown on this plan must be installed prior to all clearing and grading activities, and in such a manner as to ensure that sediment and sediment laden water does not enter the storm water management system, roadways, or violate applicable water quality standards. ESC measures shown on this site plan are minimum requirements for anticipated site conditions. During the process of construction, these measures shall be upgraded as needed to ensure that sediment and sediment-laden water does not leave the site. During active construction, ESC measures shall be inspected daily by an Erosion Control Plan Manager (specifically designated by the owner or contractor) and maintained as necessary to ensure their continued effectiveness. ESC measures will be inspected every 2 weeks or 24 hours following a rain event of 0.5 inches or greater, during inactive periods. C - 1

253 All catch basins and conveyance lines shall be cleaned prior to paving. The cleaning operations shall not flush sediment- laden water into the storm water management system. Stabilized gravel entrances shall be installed at the beginning and maintained for the duration of the project. Single-family residential projects will have a minimum 20 x 20 entrance. Commercial and development projects will install a minimum 20 x 50 entrance made of 4 clean crushed rock (1 ½ for Single Family Residential). All catch basins and area drains that have the potential to receive runoff from the construction site must be protected until pavement surfaces are completed or vegetation is re-established. All dewatering discharges will be treated using a discharge line filter in addition to inlet protection at the 1st downstream catch basin. Unfiltered dewatering discharge cannot be disposed of in the storm system. Exposed soils that will remain unworked for 14 days or more shall be immediately protected with an appropriate ground cover. Disturbed land that will remain unworked for two months or longer shall also be seeded with an approved seed mixture. Temporary seeding for site stabilization will be applied by September 1st. Public streets will be swept daily, if necessary, to alleviate sediment discharge to the storm water management system. Unfiltered wash water cannot be discharged to the storm system. A spill kit is required to be maintained on site to prevent spills of hazardous or harmful substances from entering the storm water management system. Crews must be trained on the location and use of the kit. The boundaries of the clearing limits shown on this plan shall be clearly flagged in the field prior to construction. During the construction period, no disturbance beyond the flagged clearing limits shall be permitted. The flagging shall be maintained by the applicant/contractor for the duration of construction. C - 2

254 Appendix D Infiltration Testing Guidance City of Seattle Modified Procedure for Conducting a Pilot Infiltration Test

255

256 Infiltration Testing Report Note adapted from Portland Stormwater Management Manual (Portland 2008). Include the following information in the Infiltration Testing Report. The Infiltration Testing Report should be attached to the project s Design Report: 1. Statement of project understanding (proposed stormwater system) 2. Summary of subsurface conditions encountered 3. Summary of infiltration testing including location and number of tests and testing method used. Discussion of how the tests were performed (i.e. pipe type or diameter or test pit dimensions) 4. Infiltration testing results in inches per hour 5. Recommended design infiltration rate 6. Groundwater observations within exploration and an estimate of the depth to seasonal high groundwater 7. Site plan showing location of infiltration tests 8. Boring or test pit logs. The logs should include an associated soil classification consistent with ASTM D , Standard Practice for Classification for Description and Identification of Soils (Visual- Manual Procedure). The logs should also include any additional pertinent subsurface information, such as soil moisture conditions, depth and description of undocumented or engineered fill, soil color and mottling conditions, soil stiffness or density, and approximate depth of contact between soil types. 9. Infiltration Test Data Tables (see following pages for example and blank tables) D - 1

257 Lot number and Location Test Hold Location and Number Dimension of hole: Test method Proposed BMP Date Depth to bottom of hole: Tester s name, company, and phone number Depth (feet) Soil Texture Notes Pre-saturation start time Pre-saturation end time Time Time interval (minutes) Drop in water level (feet) Notes D - 2

258 Appendix E Rational Method Information

259

260 E - 1

261 E - 2

262 E - 3

263 E - 4

264 E - 5

265 E - 6

266 E - 7

267 E - 8

268 E - 9

269 E - 10

270 Appendix F Santa Barbara Urban Hydrograph (SBUH) Method Spreadsheet Input Data

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272 Santa Barbara Urban Hydrograph Method The Santa Barbara Urban Hydrograph (SBUH) method is a single-event model that estimates a flow hydrograph for a representative rainfall event. The SBUH method was developed by the Santa Barbara County Flood Control and Water Conservation District. Applicable to urban areas, it converts design storm incremental excess rainfall depths into instantaneous unit hydrographs and routes them through an imaginary reservoir (Debo and Reese 2003). Elements of the SBUH Method The SBUH method depends on several variables: Pervious (Ap) and impervious (Aimp) land areas Time of concentration (Tc) calculations Runoff curve numbers (CN) applicable to the site Design storm Assumptions for these variables must be explained and justified in the design report. Land Area The total area, including the pervious and impervious areas within a drainage basin, shall be quantified in order to evaluate critical contributing areas and the resulting site runoff. Each area within a basin shall be analyzed separately and their hydrographs combined to determine the total basin hydrograph. Areas shall be selected to represent homogenous land use/development units. Time of Concentration Time of concentration, Tc, is the time for a theoretical drop of water to travel from the furthest point in the drainage basin to the facility being designed. (In this case, Tc is derived by calculating the overland flow time of concentration and the channelized flow time of concentration.) Tc depends on several factors, including ground slope, ground roughness, and distance of flow. The formula for determining Tc is found in Appendix E (Chart 1). When calculating Tc, the following limitations apply: Overland sheet flow (flow across flat areas that does not form into channels or rivulets) shall not extend for more than 300 feet. For flow paths through closed conveyance facilities such as pipes and culverts, standard hydraulic formulas shall be used for establishing velocity and travel time. (See Chapter 8 for more data on pipe flow rates and velocities.) Flow paths through lakes or wetlands may be assumed to be zero (i.e. Tc = 0). Runoff Curve Numbers Runoff curve numbers were developed by the Natural Resources Conservation Service (NRCS) after studying the runoff characteristics of various types of land. Curve numbers (CN) were F- 1

273 developed to reduce diverse characteristics such as soil type, land usage, and vegetation into a single variable for doing runoff calculations. The runoff curve numbers approved by the City for water quantity/quality calculations are included as Table ## of this appendix. The curve numbers presented in Table C-2 are for wet antecedent moisture conditions. Wet conditions assume previous rainstorms have reduced the capacity of soil to absorb water. Given the frequency of rainstorms in the Lake Oswego area, wet conditions are most likely, and give conservative hydrographic values. Design Storm The SBUH method also requires a design storm to perform the runoff calculations. For flow control calculations, the City uses a NRCS Type 1A 24-hour storm distribution. This storm is shown in Table F-1. The depth of rainfall for the 2 through 100-year storm events is shown below in Table F-2. Table F-1. NRCS Type 1A Storm Distribution. Time Step No. Rainfall Distribution Time # minutes % of Pt % % % % % % % % % % % % % % % % % % % % % % % % % % % % F- 2

274 % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % F- 3

275 % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % F- 4

276 % % % % % % % % % % % % % % % % % % % % % % % % % % % Table F-2. City of Lake Oswego Precipitation Design Storm/Recurrence Interval (years) 24-Hour Rainfall Depth (inches) Water Quality year year year year year year year 5.55 F- 5

277 Source: Otak Soils and Curve Numbers Soil information can be found in the latest Soil Survey for Lincoln County, Oregon Soil information may be obtained electronically from the USDA Natural Resources Conservation Services (NRCS) websoil survey Select Start WSS Navigate by: State and County (Oregon; Lincoln) Define your area of interest (AOI) using the graphic tool Determine the portions of the site that fall under each of the 4 hydrologic soil groups - Hydrologic Soil Groups Group A. Group B. Group C. Group D. Soils having a high infiltration rate (low runoff potential) when thoroughly wet (deep, well drained to excessively drained sands or gravelly sands). Soils having a moderate infiltration rate when thoroughly wet (moderately deep or deep, moderately well drained or well drained soils that have moderately fine texture to moderately coarse texture) Soils having a slow infiltration rate when thoroughly wet (soils having a layer that impedes the downward movement of water or soils of moderately fine texture or fine texture) Soils having a very slow infiltration rate (high runoff potential) when thoroughly wet (clays that have a high shrink-swell potential, soils that have a high water table, soils that have a claypan or clay layer at or near the surface, and soils that are shallow over nearly impervious material) Curve Numbers for Hydrologic Soil Group - Description A B C D Open space (lawns, parks, golf courses, cemetaries) Poor condition (< 50% grass coverage) Fair condition (50 to 75% grass coverage) Good condition (>75% grass coverage) Impervious Areas Paved areas (parking lots, roofs, driveways) Streets and roads Urban Districts Paved with curbs Paved with open ditches Gravel Dirt F- 6

278 Commercial and business (85% impervious) Industrial (72% impervious) Residential districts by average lot size 1/8 acre or less (65% impervious) /4 acre (38% impervious) /3 acre (30% impervious) /2 acre (25% impervious) Source: SCS Urban Hydrology for Small Watersheds. USDA Soil Conservation Service Engineering Division TR-55. June F- 7

279 Appendix G Reading the Soil From Kitsap County Stormwater Pond Retrofit Design Guidance Manual

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281 Reading the Soil Complex chemical interactions occur within soil when it comes in contact with water and air. The color and characteristics of a soil can provide general information about how long it has been saturated or inundated. This portion of the manual is a guide to recognizing these soil characteristics, but a soil and/or wetland professional should be contacted to verify what has been observed and to obtain more information. Redoximorphic Features Soils with dark backgrounds and rusty and/or yellow splotches could indicate soils were saturated for a temporary period of time (2 weeks or a month) and then dried out allowing air to enter the soil pores. The rust and yellow splotches are referred to as redoximorphic features. These features indicate that iron has gone into solution and then been exposed to air; oxidizing the iron and creating rust colors in the soil. If you observe soils with these characteristics, contact a soil or wetland professional to get more information. Depleted Soils Soils that have a light grey background can be what is referred to as depleted soils. Depleted soils often also contain redoximorphic features (rust and yellow splotches). Soils exhibiting these characteristics are likely to have been saturated for a longer period (up to several months) than the soils shown in Photo 11. Much of the iron in these soils has been leached out and down the soil column during the time they are saturated. When soils dry out, air enters the soil s pores and creates redoximorphic features (rusty/yellow splotches). Soils with this characteristic may indicate shallow groundwater is present and affecting drainage of the stormwater facility. Gleyed Soils Soils that are saturated or inundated all year round typically have light grey-greenish or bluish colors. Nearly all of the iron and manganese in these soils have been leached down the soil column leaving the light grey-greenish, bluish color, indicating permanent or long term saturation. Soils that have this characteristic could indicate that shallow groundwater is present and may affect the drainage of the stormwater facility. Saturated Soils Soils are saturated when 100 percent of the soil pores are filled with water. It can be difficult to determine whether soils are saturated just by looking at them. Once a hole is excavated, soils may be seen glistening or water may be pouring out of the side of the hole. This is an indication that soils are saturated, but closer observation of the soils is best. If you can squeeze water out of the soil easily, it is likely saturated even if you do not see water pouring out of the side of the hole. Contact a soils or wetland scientist to assist with verification of soil saturation. G-1

282 Shallow Water Table A shallow groundwater table may be present beneath a stormwater pond, at least for part of the year. It is important to recognize that the water levels can rise with rainwater from winter storms, adversely affecting drainage of the stormwater facility. Shallow water tables are typically in low elevation areas near streams or other water bodies. The presence of shallow groundwater can be determined during the dry season (May through September in western Washington) when the stormwater pond is not receiving much inflow. While the surface of the stormwater facility may be dry, the water table may be just below the surface. Excavate soils to a depth of at least 24 inches to determine if shallow groundwater is present. Leave the soil pit open for at least 30 minutes or an hour to allow the water (if present) to fill up part of the hole, especially if soils are fine-textured such as clay and silt that transmit water slowly. If shallow groundwater fills the soil pit during this test, dig another soil pit elsewhere in the pond bottom, and allow time for water to fill it in. If pooled water is observed in one or more test pits, it is likely that a shallow water table is present at a similar elevation beneath the entire pond. Well-drained Soils Soils may also be dry below the surface indicating they are well-drained. Excavate a soil pit to at least 24 inches to determine whether soils are well-drained. Soils that are light or bright in color and that do not have redoximorphic features also indicate well-drained soils. Well-drained soils are typically coarse-textured such as sandy soils, unless there is a high water table that keeps soils saturated near the soil surface. Soils that are well drained should be dry during most of the year except within a couple days after a rainstorm has occurred. Well-drained soils typically infiltrate rainwater within a short period of time (no longer than a week). G - 2