THE Metropolitan Land Planning Act (amended 1995)

Transcription

1 Chapter - Water Resources Water Supply Background THE Metropolitan Land Planning Act (amended 1995) requires local governments to prepare comprehensive plans and submit them to the Metropolitan Council to determine their consistency with metropolitan system plans. One element of these plans must address municipal water systems. Minnesota Statute requires Water Supply Plans (also referred to as Water Emergency and Conservation Plans) to be completed as part of the local comprehensive planning process. Additionally, Minnesota Statute 3G.291 requires all public water suppliers that serve more than 1,000 people to have a Water Supply Plan approved by the Minnesota Department of Natural Resources (DNR). An approved Water Supply Plan is also a requirement to obtain a Water Appropriations Permit Amendment from the DNR. Chapter Contents Water Supply Water Supply System Surface Water Management Sanitary Sewer Stillwater s Water Department is owned and operated by the city; however, it is under the control and management of the independent Stillwater Board of Water Commissioners. Stillwater s Water Supply Plan was submitted to and approved by the DNR and Met Council in The Water Supply Plan consists of four parts: Part 1: Water supply system description and evaluation Part 2: Emergency response procedures Part 3: Conservation plan Part 4: Metropolitan Land Planning Act requirements. The purpose of this chapter of the comprehensive plan is to Chapter : Water Resources -1

2 provide a summary of the Water Supply Plan. For brevity and security reasons, the more detailed document is not included in this 2030 Comprehensive Plan. Forecasts Water usage within the city has remained relatively steady during the last years. In 2004, the City of Stillwater pumped approximately 721 million gallons of water into the system. Peak day water demand in 2004 was 4.7 million gallons per day (MGD). Stillwater s Water Supply Plan contains a detailed analysis of existing water usage, including historic water demand and high volume users. Water usage in Stillwater is projected to remain relatively steady and even decline after 2020 due to projection of fewer people per household as the city ages. The projected water demand for 2030 is a daily average of 2.3 MGD with an estimated daily maximum of.0 MGD as shown in Table.1 Projected Water Demands. Projections were found by using the methodology from Stillwater s Water Supply Plan. The average day projections were found using population projections and 11 gallons per capita per day (average of last years). Maximum day was found by applying a factor of 2. to the projected average day. Water conservation is discussed later in this chapter. Table.1: Projected Water Demands Total Projected Population 1,400 21,300 19,900 Avg. Day Demand (MGD) Max. Day Demand (MGD) 5..5 Projected Demand (MG per Year) Water Supply System The city presently obtains its raw water supply from 7 wells. An eighth well (well #) is to be developed on the Legends Park site with plans for it to be operational in All wells draw water from the Jordan aquifer. Well #1 also draws water from the Mt. Simon aquifer. The total firm capacity of the wells is 5,400 gallons per minute (gpm) or 7.7 MGD. Firm capacity is defined as the total system capacity with the largest well out of service. Because Stillwater s water source meets or exceeds all Federal and State drinking water standards, minimal treatment is required. Water from the supply wells is pumped into the distribution system, after chlorine and fluoride are added to disinfect and prevent tooth decay, respectively. Polyphosphate is also added to the water before it reaches the distribution system. Four storage facilities stabilize pressure during peak water demands and also serve as a source of water during fires or power outages. There is a total existing storage volume of 3.25 million gallons. Emergency Response Procedures Stillwater has prepared a water system vulnerability assessment and emergency response plan in accordance with the Safe Drinking Water Act, as modified by the Bioterrorism Preparedness and Response Act of These documents identify contacts for emergency situations, emergency response procedures, describe water sources and services areas, and provide procedures for augmenting water supplies in the event of an emergency. The Water Supply Plan identifies triggers for implementing demand reduction procedures in the event of a water system emergency. Water use is rationed in accordance with water use priorities established by state statute. These triggers and water use priorities are regularly reviewed and adjusted as needed. Demand reduction measures are instituted by the Board of Water Commissioners -2 Chapter : Water Resources

3 is rationed in accordance with water use priorities established by state statute. These triggers and water use priorities are regularly reviewed and adjusted as needed. Demand reduction measures are instituted by the Board of Water Commissioners Water Conservation Plan Water conservation programs are intended to reduce the demand for water, improve the efficiency in use and reduce loss and waste of water. Conserving water can be a cost-effective way to reduce the need to construct and operate additional water supply facilities. Stillwater s water conservation goals include the following: Maintain low unaccounted for water use Reduce overall water use (residential and total per capita water use) Maintain low peak day water usage. Stillwater s Water Conservation Plan (contained in the Water Supply Plan) details each of the conservation goals and how Stillwater compares to benchmark metrics for each of the goals. The conservation plan also details existing and proposed conservation programs. These programs include: Metering of water usage. All wells and customers in Stillwater are metered, so that Stillwater has an accurate account of water pumped and water sold. Water audits. Stillwater regularly compares water pumped to water sold, and estimates un-metered water use (such as construction and hydrant flushing). Leak detection programs. These are currently conducted every 2 years. Conservation oriented water rates such as Stillwater s increasing block rate for residential meters. Regulation and enforcement of federal, state and local regulations such as: plumbing codes, rain sensors on irrigation systems, water efficient plumbing fixtures and watering restrictions. Education programs such as Consumer Confidence Reports and Community Newsletters. Implementation Future System Needs The future design system for Stillwater consists of the following improvements: Additional water supply wells. The Water Supply Plan contains a more detailed analysis on the sustainability of the Jordan aquifer to sustain Stillwater s current and projected demands. There are currently no plans to construct new storage facilities. Additional trunk and lateral water distribution mains, added with development. Capital Improvement Plan Stillwater annually updates the trunk water system Capital Improvement Plan (CIP). The current CIP is included in Stillwater s Water Supply Plan. Costs for constructing, operating and maintaining Stillwater s water system are recovered from water availability charges and water rates. Chapter : Water Resources -3

4 Surface Water Management Background The City of Stillwater s Local Surface Water Management Plan (LSWMP) was completed and adopted in January 200. It is incorporated into the 2030 Comprehensive Plan by reference only. The LSWMP will serve as a comprehensive planning document to guide the city in conserving, protecting, and managing its surface water resources. It has been created to meet the requirements detailed in Minnesota Statutes 3B and Minnesota Rules 4, administered by the Minnesota Board of Water and Soil Resources. It is also consistent with the goals and policies of the Metropolitan Council s Water Resources Management Policy Plan, and the three watershed management organizations having jurisdiction within the city: Brown s Creek Watershed District, Middle St. Croix Watershed Management Organization and Carnelian-Marine- St. Croix Watershed District. Rules, policies, and other information on the various watershed management organizations in the City can be found on their respective websites. Brown s Creek Watershed District Middle St. Croix Watershed Management Organization Carnelian-Marine-St. Croix Watershed District Section 2 of the LSWMP describes the physical setting; the history, natural resources and land uses within the city. Sections 3 through 5 describe the regulatory agencies having jurisdiction in Stillwater, and past studies and agreements related to surface water resources. Section summarizes the inventories, assessments and modeling completed for the plan, and provides a current assessment of surface water management in Stillwater. Section 7 lists the goals and policies identified to address surface water management needs in the city. Section summarizes current ordinances and capital projects planned to implement the goals and policies listed in Section 7. Section 9 outlines the continued administration of the plan. Natural landscape features are a strong element in defining Stillwater s character. Figure 2.2 in Appendix A of the LSWMP shows the topography within the city. In addition to the St. Croix River, Brown s Creek, Lily Lake, McKusick Lake and Long Lake, surface water resources within Stillwater include several more ponds and wetlands. The preparation of the LSWMP included a full review of the current surface water system in Stillwater. The physical system was mapped to establish watershed sub-basins and runoff paths. This information was used to create a hydrologic model of the entire city, using HydroCAD modeling software. The modeled sub-basins and system layout are shown on Map 1 attached to the LSWMP. Overall, the city has effectively managed the conveyance of stormwater runoff. Based on discussions with the City Engineer, flooding problems are localized and minor. This determination is supported by the hydrologic model completed for this plan. Portions of the City of Stillwater have water quality assessment models either completed or currently under development. As part of the LSWMP, the three remaining basins in the city have been modeled using P Urban Catchment Model software. Figure.1 of the LSWMP shows the basins modeled for water quality, as well as the modeler and date. Table.4 in Appendix B contains the P model results on a sub-basin basis, including watershed area, BMP area, BMP type, and BMP percent load reductions of total phosphorus, total suspended sediment, and water volume. The preparation of the LSWMP also included an inventory and assessment of wetlands within the city. Wetland inventories have been partially Chapter : Water Resources

5 completed by each of the three watershed districts/ management organizations with jurisdiction in the city. The goal of the wetland inventory was to provide a unified wetland management plan to facilitate the city s role as Local Governing Unit (LGU) for the Wetland Conservation Act (WCA.) In the months and years ahead, the city will face multiple challenges in surface water management. Having just applied for NPDES permit coverage, the city must now begin to implement new programs to address stormwater pollution. The governing watershed districts/management organizations within the city will continue to implement surface water standards that impact city reconstruction and development projects. The MPCA will complete local TMDL studies that will lead to challenging implementation projects throughout the city. Growth in and around the city will put additional pressure on local surface water resources, while the aging infrastructure will require significant reconstruction and capital investment. resources. Section 7.5 Citywide Program Elements - Goals and policies for managing water resources and drainage systems on a citywide scale, to effectively achieve surface water management goals. Section 7. Support of Other Agencies - Goals and policies to coordinate local surface water management with the work of watershed management organizations and state agencies. The Surface Water Management Plan is incorporated into the city s 200 Comprehensive Plan update by reference and will be applicable until 201, at which time an updated plan will be required. Periodic amendments may be required to incorporate changes in local practices. In particular, changes in the three applicable Watershed Management Plans may require revisions to the plan. The city has a strong interest in protecting and managing its valuable water and natural resources, recognizing the relationships between resource protection, land use management, development, redevelopment and fiscal responsibility. The goals and policies outlined in the LSWMP are grouped by their relationship to the key issues listed below: Section 7.2 Land Development and Redevelopment Goals and policies to prevent flooding and adverse impacts to water resources from land disturbance and impervious surfaces. Section 7.3 Water Resource Management Goals and policies for managing Stillwater s wetlands, lakes, streams and groundwater, to preserve the functions and values of these resources. Section 7.4 Management of Floodplains, Shorelands and Natural Areas Goals and policies for managing these areas, to preserve the functions and values of these Chapter : Water Resources -5

6 Sanitary Sewer Background The Comprehensive Plan is required to include a sanitary sewer element covering the collection and disposal of wastewater generated by the community. Similarly, the Metropolitan Sewer Act requires local governments to submit a Comprehensive Sewer Plan (CSP) which describes the current and future service needs required from Metropolitan Council Environmental Services (MCES). In March 2005 the Metropolitan Council adopted a revised Water Resources Management Policy Plan (WRMPP). The 2030 WRMPP includes the metropolitan wastewater system plan with which local comprehensive plans must conform. The method Stillwater has chosen to demonstrate its conformance is through this sanitary sewer chapter. This chapter updates the City of Stillwater s Comprehensive Sanitary Policy Plan or CSPP. The city last updated its CSPP in 1995 and described the expansion of the city s trunk system (in particular within the annexation areas extending west to County Highway ) and the demands this expansion places on the Metropolitan Disposal System operated by Metropolitan Council Environmental Services (MCES). MCES also uses Table.2A -- Metropolitan Council Projections for Sewered Areas - the CSPP to determine whether capacity upgrades will be needed at the Metropolitan Wastewater Treatment Plant. This update is necessary to reflect land use changes that have occurred since the 1995 CSPP was prepared and to reflect land use changes proposed in the Comprehensive Plan for the 2030 period. Stillwater s sewer system connects to Met Council Interceptor 91 at meter number 0 on the southern border of the city. Interceptor 91 travels south and arrives at the St Croix Valley Wastewater Treatment Plant in Oak Park Heights. Forecasts Table.2A present s projections of sewered population, households, and employees for the City of Stillwater, as prepared by Metropolitan Council and presented in its 2030 WRMPP. A decline in overall population is projected after 2020 due to an anticipated reduction of people per household as the city ages. The City of Stillwater has its own sewered population projections which are shown in Table.2B. These projections are based on vacant, underutilized and undeveloped parcels remaining in the city. The city arrives at its projections based upon an inventory of existing underutilized lots and a mix of development densities to achieve the Metropolitan Land Planning Act obligations. Sewered Total Sewered Total Total Year Population Population Households Households Employment 20 1,300 19,0 7,250 7,500 11, ,550 21,300 7,00,0, ,200 19,900,300,00 13,00 1 Metropolitan Council Water Resources Management Policy Plan, May, 2005 Table.2B -- City-preferred Projections Year Sewered Population Total Population Sewered Households Total Households Total Employment 20 1,0 1,400 7,0 7,200 11, ,170 21,300,050,0, ,70 19,900,550,00 13,00 Chapter : Water Resources

7 Table.3 presents projected sewer flows for the entire service area represented in Figure.1. Both Stillwater and Metropolitan Council Projections are provided. Stillwater has based average flow projections on the 2007 meter data and adding the proposed flow from the small portion of future development remaining in the city. The flow from the future development areas was generated by applying the unit rates from Table.4 to the proposed land uses. Based on the Proposed Land Use Plan, the city will be fully developed by ; therefore this flow is carried through to Metropolitan Council s projected flows for the years 20, 2020, and 2030 are from its Water Resources Management Policy Plan (updated 2005). The city s projections generally correspond with the Met Council projections. The projected flows in Table.3 vary from the 1995 CSP due to a decrease in the 20 population projections by Met Council and the city. A detailed description of the change is provided in the Land Use Chapter earlier in this 2030 Comprehensive Plan. Table.3 - Wastewater Flow Projections Year MCES Projected Average Flow (MGD) 1 City Projected Average Flow (MGD) MGD MGD 2.53 MGD MGD MGD 2. MGD MGD MGD 2. MGD 1. Metropolitan Council s Water Resources Management Policy Plan (May 2005). 2. Based on metered data MGD = Million Gallons per Day. Sanitary Sewer Design Criteria The land use plan for the City of Stillwater served as the basis for the development of the sanitary sewer flow projections and analysis of the trunk system. Using the land use plan, the area of each land use was determined for each sewer district. Existing land uses used in this plan include low density, low/ medium density, medium density, and high density residential, commercial, research and development (R&D)/industrial, public and open space. Several types of commercial and residential land use are proposed. For the purposes of generating sewer flows, these are lumped into the general categories. Detailed descriptions of the various land uses are found earlier in this Comprehensive Plan. Municipal wastewater is made up of a mixture of domestic sewage, commercial and industrial wastes, groundwater infiltration, and surface water inflows. With proper design and construction, groundwater infiltration and surface water inflows, often called infiltration/inflow (I/I), can be minimized. The flows due to I/I are accounted for in the analysis and design of the trunk sewer system. The anticipated average wastewater flows from the various subdistricts were determined by applying unit flow rates to each of the land use categories. The system design unit flow rates are presented in Table.4. For all land uses unit rates/acre were used to generate average flow projections. The units per acre assumptions for Low, Low/Medium, Medium, and High Density Residential, Commercial, R&D/ Industrial were based in part on information from the 1995 CSP and city staff regarding projected number of units for each land use. Open Space was assumed to not generate any sewer flows. Stillwater s system design flow projections originate from the land use statistics based directly on the land use plan. Certain reductions in land use area are made to account for wetlands, steep slopes etc. and a net developable acreage for each land use category is thus created. The net acreage is multiplied by standard unit flow rates to obtain an average flow for each sewershed. Chapter : Water Resources -7

8 Table.4 - System Design Wastewater Unit Flow Rates Land Use Type Gal/Unit/ Day Units /Acre Gal/Acre/ Day Low Density Residential ,020 Low/Medium DensityResidential Medium Density Residential ,320 1,0 High Density Residential 190 2,50 Commercial ,300 Institutional Downtown/MU ,000 R&D/Industrial ,000 Sanitary Sewer Trunk System The trunk sewer system layout for the City of Stillwater is presented in the Trunk Sewer System Map, Figure.1. This map shows the main sanitary sewer districts, existing and proposed trunk sanitary sewers, and existing and proposed lift stations and force mains. The modeling of the sanitary sewer system was based on a variety of parameters, such as: land use, population density, standard wastewater generation rates, topography, and future land use plans. Based on the topography of the undeveloped areas, the sewer subdistricts were created and the most costeffective locations for future trunk line facilities were determined. The location of smaller sewer laterals and service lines are dependent upon future land development plats and cannot be accurately located from a study of this type. Both the existing and proposed pipe systems were evaluated and broken up into design segments. Each end of a design segment has a node assigned to it. The nodes were designated for the following reasons: Flow from a subdistrict entering the pipe network. Significant grade change has occurred. Change in pipe size. Two or more trunks connect. Manmade elements (roads, railroads, etc.) affecting location and installation costs for the trunk system or lateral service of the subdistricts. The proposed alignments shown on the Trunk Sewer System Map generally follow the natural drainage of the land to minimize the use of lift stations and consequently provide the city with the most economical ultimate design sanitary sewer system. Minor adjustments in the routing and size of the trunk facilities will take place as determined by the specific land use and development conditions at the time of final design. Any such adjustments are expected to deviate minimally from this plan. Each subdistrict contains at least one collection point where the subdistrict s sewage is defined to enter the pipe network. Upstream of that collection point, a lateral network of gravity lines can serve unserviced areas. - Chapter : Water Resources

9 Table.5 - Capacity and Design Flows for Trunk System y g y Node From S-1 S-3 S-4 S-5 S-2 S- To S-2 S-4 S-5 S- S- M0 Pipe Size (in) FM Pipe Slope 1 (%) Capacity (MGD) Average Flow (MGD) Peak Flow 2 (MGD) ) Where data was not available, minimum pipe slopes have been assumed based on Ten States Standards 2) After applying a standard peak flow factor 3) FM = Force Main Table.5 represents capacities of existing and proposed trunk pipes shown on Figure.1. As shown in Table.5, all sanitary sewer trunk pipes have adequate capacity for the peak flows. The majority of the sewer system for Stillwater was originally designed to accommodate both sanitary sewage and stormwater runoff. Sewer separation was accomplished in 1972 and 1973 throughout the original city. The remaining sewer was designed to serve sanitary sewage only. Since the older sewer was designed as a part of the combined system, the majority of the sanitary sewer has excess capacity as illustrated in Table.5. As of December 31, 200, less than 0 scattered individual on-site septic systems still existed in Stillwater. The city is committed to the proper design, location, installation and ongoing maintenance of these systems. The Stillwater City Code requires that all new individual on-site septic systems be installed according to Minnesota Pollution Control Agency (MPCA) rule 700 permit requirements. Groundwater conditions, soil borings, distance to surface water, percolation tests, and design and type of system are further factors included in the developer s site evaluation. Permitting and maintenance is handled by Washington County due to the small number of on-site systems in the city. Chapter : Water Resources -9

10 Figure.1 : Trunk Sewer System Map Brown's Creek S December, 200 I:/5/507001/gis/maps/sanitary system.mxd S Open Water S-5 Gravity Pipe 3 3 Forcemain S- 0 1 Manhole Kolliner Park 4 Sanitary Node 1 S5 Sanitary Districts Lift Station S-1 30 S S City Limit S3 9 1,00 Feet Existing City Gravity Trunk Pipe Met Council Meter M S Lily Lake 1 0 Long Lake 1 S St. Croix River S Lake McKusick 30 S1 200 Comprehensive Plan S 4 1 Trunk Sanitary Sewer System South Twin Lake 95 3 December, 200 Chapter : Water Resrouces I:/5/507001/gis/maps/sanitary system.mxd -

11 Infiltration and Inflow The City of Stillwater has a proactive program directed at identifying and correcting I/I, including the following: City Code regarding I/I first passed in 1973 and has been updated several times since then.(city Code Section 29.-5) 20% of the city sanitary sewer lines are televised annually for potential I/I sources. Five total flow meters are set up to identify areas of town with potential inflow. Replacement of vented sanitary manhole lids (estimated -20 replaced annually) Visual inspections of manholes in low lying areas to assure lids are sealed. Installation of external manhole seals on all new sanitary sewer manholes and replacement of seals and castings on street projects (estimated annually). Ongoing annual review of flows to develop the next stage of improvements. The city spent over $20,000 on I/I reduction measures in The Metropolitan Council has instituted its Inflow/ Infiltration Surcharge Program since Stillwater s previous plan. The fundamental policy statement summarizing this program is that Metropolitan Council will not provide additional capacity within its interceptor system to serve excessive inflow and infiltration. The Council establishes inflow and infiltration thresholds for each of the communities that use its system. Communities that exceed this threshold are required to eliminate this excess flow within a reasonable timeframe. The Metropolitan Council annual I/I surcharge for the City of Stillwater is $4,000. The city has been able to show adequate progress through its numerous programs to reduce I/I over the past two years to not be charged. City Code Section Prohibiting deposit of stormwater in sewer system. Subd. 1. Discharge of surface water. No person shall discharge or cause to be discharged any stormwater, surface water, groundwater, cooling water or industrial process waters into any sanitary sewer. No rainspout or other form of surface drainage and no foundation drainage shall be connected to any sanitary sewer. Subd. 2. Inspections. The public works director and other authorized employees of the city, bearing proper credentials and identifi cation, shall at reasonable times be permitted to enter upon all properties connected to the city sanitary sewer system or the city storm sewer system for the purpose of inspection, observation, measurement, sampling and testing. Subd. 3. Separate connection required. When separate sewer mains and storm sewer mains have been constructed and are available to property, the owner of the property shall take all action to separate the sewers and connect them separately to the sanitary sewer and the storm sewer in accordance with the provisions of this section within 90 days after the date of mailing or delivery of offi cial notice to do so. The notice shall be given to the owner or occupant in writing by the public works director on the order of the city council. Subd. 4. Interceptors. Grease, oil and sand interceptors shall be provided when they are necessary for the proper handling of any liquid waste containing grease in excess amounts of any fl ammable waste, sand or other harmful ingredients. Interceptors shall be located so as to be easily accessible for cleaning and inspection. If necessary, in the opinion of the public works director, a suitable control manhole in the building sewer shall be installed to facilitate observation and sampling of the waste. The manhole shall be constructed by the owner in accordance with plans approved by the city engineer. The owner shall maintain the manhole so as to be safe and accessible at all times. The owner shall take action to install the interceptor in accordance with this section within 90 days after the date of mailing or delivery of notice to do so. The notice shall be given to the owner or occupant by the public works director on the order from the city council. Subd. 5. Connection by city. Whenever any owner or occupant fails to comply with the written notice, the city council shall, by resolution, direct that the sewers be separated and installed and connections made with the sanitary and storm sewer systems or that a grease, oil and sand interceptor be installed, and the cost of the installation be paid in the fi rst instance out of the general fund, and then assessed against the property benefi tted in accordance with subdivision of this section. Subd.. Assessment. After the installation and connection have been completed pursuant to city council resolution, the clerk shall serve a written notice of the assessment upon the owner or the owner s representative directing the owner to pay the assessment to the treasurer within ten days. If it is not paid, the clerk shall certify the amounts to the county auditor for collection in the same manner as other special assessments and real estate taxes. The city council may, by resolution, spread the assessment over a three-year period. Chapter : Water Resources -11

12 Flood-related Infiltration and Inflow Due to the proximity of the St. Croix River to the city s trunk sanitary sewer main, flood-related I/I reduction needs to be addressed. To that end, the city is replacing all vented sanitary manhole lids with closed sanitary manhole lids and is also sealing the manholes in low lying areas impacted by flood related I/I. Within the next three years the city plans to undertake a slip lining project of the sanitary sewer main adjacent to the St. Croix River. This work will likely be completed in conjunction with the Phase III Downtown Stillwater levy project being completed by the US Army Corps of Engineering. It is currently estimated that the sewer lining project will cost $00,000. During remodeling and construction projects, the city will continue to inspect and require property owners to disconnect drain tiles, roof leaders, and other non-sanitary water sources so they do not discharge into the sanitary sewer system. - Chapter : Water Resources