STORMWATER ENGINEERING STANDARDS

Transcription

1 STORMWATER ENGINEERING STANDARDS RIVERTON CITY STORMWATER DIVISION SOUTH 4150 WEST Riverton, Utah 84065

2 TABLE OF CONTENTS 2.1 Precipitation 2.2 Modeling Methodologies 2.3 Design Storm 2.4 Run-off Design 2.5 Discharge Rates 2.6 Detention/Retention 2.7 Drawings: Concept Stage 2.8 Drawings: Preliminary and Final Stages 2.9 Storm Drain Pipe Location 2.10 Pipe Design, Material, Size, and Construction 2.11 Manholes (Clean-out Boxes) 2.12 Inlet and Combination Boxes 2.13 Water Quality Units 2.14 Easements 2.15 Stormwater Maintenance Plan for Post Construction 2.16 Low Impact Development(LID) 2.17 Land Disturbance Permit 2.18 Wetlands 2.19 Special Flood Hazard 2.20 Salt Lake County and Canal Facilities 2.21 East Riverton Drainage System 2.22 Irrigation Ditches 2.23 Class V Underground Injection Wells 2.24 Bonding

3 2.25 Impact Fee Reimbursement/Credit Policy 2.26 Impact Fee Exemption Policy 2.27 Quality Assurance 2.28 Value Engineering Submittals Definitions References Attachments

4 STORM WATER DESIGN STANDARDS Design Criteria: For developments and construction activities within Riverton City, the following engineering standards are required. 2.1 Precipitation: ARI* (years) 5 min 10 min 15 min POINT PRECIPITATION FREQUENCY ESTIMATES FROM NOAA ATLAS 14 Utah N W 4442 feet from "Precipitation-Frequency Atlas of the United States" NOAA Atlas 14, Volume 1, Version 4 G.M. Bonnin, D. Martin, B. Lin, T. Parzybok, M.Yekta, and D. Riley NOAA, National Weather Service, Silver Spring, Maryland, 2006 Extracted: Mon Jun min Precipitation Frequency Estimates (inches) 60 min 120 min 3 hr 6 hr 12 hr hr 48 hr 4 day 7 day 10 day 20 day 30 day 45 day 60 day

5 2.2 Design and Modeling Methodologies: A. Modified FAA Rational Method (Reference I). This method may be applied to watersheds less than 160 acres. B. Hydrograph routing methods. A hydrograph routing method approved by the City Engineer is required when modeling multiple connected ponds and water-sheds greater than 160 acres. (When using computer software for design approval, the applicant must provide the City with hardcopies of all input and output files in sufficient detail and format to perform a design review.) C. The latest edition of the applicable FHWA Hydraulic Engineering Circular shall be used when any hydraulic aspect of a project is not addressed in these standards Design Storm: The critical storm duration less than or equal to 24 hours shall be used. Table 1 - Storm Frequencies For Design Type of Structure Storm Drain (pipes, gutters, channels, boxes, streets etc.) Streets (surface route) Culvert (Creeks and Canals) Bridge(Creeks and Canals) Local Detention/Retention Systems Regional Detention/Retention Systems Commercial Detention/Retention Systems Residential/Commercial Temporary Retention Systems Private Residential Retention System(single and multifamily) Spillway Structures Minimum Design Storm Frequency 10% annual chance storm; Intensity based on time of concentration 10% annual chance storm flows routed over the surface with assumed complete pipe or inlet blockage. 1% annual chance storm or as required by regulating agency and property owner 1% annual chance storm or as required by regulating agency and property owner 10% annual chance storm or as required by stormwater master plans As required by Stormwater Master Plans 10% annual chance storm 10% annual chance storm 10% annual chance storm 10% annual chance storm flows (assume full pipe or inlet blockage) Table 2 Runoff Coefficients for Use with the Rational Method Surface Type 10% Annual Chance Storm 1% Annual Chance Storm Paved Roof Landscaped Other As Determined by the City Engineer

6 2.4 Run-off Design: A. Design two independent stormwater systems 1) Minor System: a) Design to drain vehicle and pedestrian paths for flood control, safety and public convenience, e.g. the road, pipe and gutter system. b) Design the minor system to a 10% annual chance storm. 2) Major System: a) Design for managing storm events exceeding 10% annual chance storm and failed minor systems. b) Design the surface route to convey flows to a safe termination point, e.g. detention/retention areas, creeks, canals, rivers and approved RW and private property locations. Surface routes may include but not limited to: roads, channels, swales, open space, parkways etc., and must be above ground. c) The major route for public runoff must be contained within the public R/W or stormwater drainage easements throughout its route. d) Design the major system for the 10% annual chance storm flows assuming 100% pipe and inlet blockage. e) The cost of the major system is the responsibility of the developer. B. Gutter grades are 0.5% min. 2.5 Discharge Rates A. Design per the General Permit for Discharges from Small Municipal Separate Storm Sewer System. Summary: Design the site to mirror the pre-development hydrology. B. The runoff in excess of the pre-development hydrology must not exceed the flood control discharge rates and return periods according to City Stormwater Master Plans*, summarized in the Riverton City Stormwater Restriction Map* as regulated by City Design Standards. C. Address the entire watershed area per the Stormwater Master Plans this may require accounting for area outside the project site, as well as areas that may become tributary as a result of the Stormwater Master Plans. Depending on the flood hazards, upstream runoff may pass through or require impoundment. D. *Riverton City Webpage Locations Stormwater Master Plans and Riverton City Stormwater Restriction Map: stormwater_master_plans.php MS4 Permit: pdf 2.6 Detention/Retention and Appurtenance (Requirements apply to Public and Private unless specifically noted). A. Development shall infiltrate, evaporate or harvest and reuse the 90 th percentile precipitation required by the latest revision of the General Permit for Discharges from Small Municipal Separate Storm Sewer Systems (MS4s). Requirement on Hold. B. Development must manage its stormwater impact onsite, unless allowed to discharge to a regional system. C. Detention Systems 1) Design detention systems to receive the peak flow rate and volume for the tributary area.

7 2) Detention impoundment system must reach maximum before bypass is allowed. 3) The infiltration rate is not allowed to govern the flood control volume. 4) Design for soil saturation influence area within 20 of foundations or less per soil report. Provide barriers when necessary. 5) Provide barriers when necessary. D. Retention Systems 1) Design retention systems to receive the peak flow rate and volume for the tributary area. 2) Retention impoundment system must reach maximum before bypass is allowed. 3) Underground retention systems using infiltration shall receive pretreatment. 4) The infiltration rate is not allowed to govern the flood control volume. 5) Retention systems using infiltration shall distribute the runoff load, be balanced across the site and receive pretreatment. (This requirement is intended to better mimic the predevelopment infiltration pattern as much as reasonably practical and to minimize water that ponds for long periods of time. This will improve infiltration rates and minimize mosquito habitat.) 6) Design for soil saturation influence area within 20 of foundations or less per soil report. Provide barriers when necessary. E. Spillway 1) Design spillway structures at safe locations to pass peak flows from the entire tributary area assuming the outlet pipe or inlet is inoperative. 2) No structures are allowed to be constructed within the flood route. F. Public Detention/Retention Systems 1) Detention systems may include but not limited to: ponds, swales, wet ponds, tank, pipe, drywell, perforated pipe... 2) Detention system infiltration rate is not allowed to govern flood control volume. 3) Retention systems may include but not limited to: drainage fields, ponds, swales, wet ponds, drywell, perforated pipe... 4) Above ground retention systems must be designed to drain within 48 hours following storm event. 5) Retention volume is not allowed to be stored in gravel or equivalent media. 6) Hydraulic depth 4 feet maximum. 7) Freeboard 1 foot minimum 8) Side slopes 3:1 minimum 9) Slope/Grade 2% minimum 10) Corner radii 10 minimum 11) Site must drain into itself 12) Detention systems must be maintainable by jet hose, 8 vacuum tube or be open to surface 13) Retention systems must be maintainable by an 8 vacuum tube or be open to surface maintenance equipment. G. Public outfall structures 1) Cast in place box conforming to the pond embankment slope and flush to grade. 2) Option 1: Grate bar orientation parallel to slope and less than 2 apart. Bar gauge no less than 3/8 and cross support sufficient to prevent instability to pedestrian traffic. Option determined by City. 3) Option 2: Outfall box surrounded by 8 wrought iron fence, 6 mow strip and gate with locking mechanism for 3/8 padlock. Option determined by City. 4) Splash pad sloping back into box with low flow or drywell. Prevent mosquito hazards unless approved with water quality device/system. 5) Submit detail

8 H. Public maintained system access ramp criteria 1) Road & ramp 15 wide 2) Ramp slopes per APWA driveway approach break over angles at top and bottom per 216, 221, 222, 225 conforming to the subdivision standard. 2) Road & ramp shall be all weather access for 40,000lb load that is compatible with the pond uses. Including but not limited to: Reinforced sod, traversable architectural rock slabs, concrete 4) Jet Truck work zone relative to structure a. Work zone may not block vehicle lane b. Jet Truck front access: Work zone edge no more than 7 to farthest box inside wall c. Jet Truck side access: Work zone edge no more than 15 to farthest box inside wall 6) Provide description, including but not limited to drawing and details I. Private Detention/Retention Systems specific limitations/allowances 1) Detention/Retention systems may include but not limited to drainage fields, ponds, swales, wet ponds, tanks, pipe, drywell, perforated pipe. 2) Flood control requirement: Road and parking area surfaces must impound a minimum of 6 of the storm that exceeds the capacity of the detention/retention pond and underground systems before spilling beyond the property boundary. This is so the property owner can evaluate the performance of unmaintained or failing the detention/retention systems. 3) Commercial development may not include gravel pore space towards required storage volume unless the following conditions are met: a) Satisfy the requirements of 2.6 general requirements b) The system must be designed and constructed in accordance with the manufacturer s specifications. c) Provide a pre-treatment system with off-line pollutant storage to capture and treat storm water flow before it enters the subsurface detention system. d) Provide a plan for maintaining and monitoring the system performance. e) Design impoundment systems to receive the peak flow rate and volume for the tributary area and to fall at site sag locations. f) Provide specifications for aggregate used in the subsurface system, particularly regarding void space. g) Comply with infiltration requirements established by site approved stormwater drainage and geotechnical studies. h) Commercial stormwater storage systems may choose to exceed 3:1 side slopes and depths but only where these systems have a 20 buffer from public R/W. J. Flow Rate Restrictions 1) Small discharge orifices are allowed to be increased to 3.14 square inches as allowed by the City Engineer when flood concerns nonexistent. In such cases, the maximum release rate, may exceed the maximum release rate otherwise required by this Standard. However, in such cases, every effort shall be made by the designing engineer to minimize the head over the orifice. Designs with excessive head, in the sole judgment of the City Engineer, shall not be allowed. K. Canal 1) The latest version of Canal regulations and design standards apply to design and construction affecting this canal. 2) A copy of the construction/discharge permit from the Canal Company and Salt Lake County Flood Control where applicable is required to release stormwater runoff into a canal. 2.7 Drawings: Preliminary Stage.

9 A. Provide adequate information to determine the site drainage patterns affecting the entire project area. Drawings should include but not be limited to: 1) Existing topography showing all existing drainage features within 100 feet (City Engineer may increase this amount) of the project site including but not limited to: existing watercourses, storm drains, canals, irrigation ditches, springs, culverts, etc. 2) Any surrounding areas outside the project site that influence the project or that the project may influence downstream or adjacent to the project. 3) Detention/Retention Locations, volume and area required. 4) Major system route (surface route). 5) Delineate the FEMA 100 year flood plain. 6) Existing structures of any kind. 2.8 Drawings: Final Stages. A. Provide adequate information to determine the site drainage patterns affecting the entire project area. Drawings should include but not limited to: 1) Topography at 1-foot minimum contour intervals (proposed and existing). a. Existing topography showing all existing drainage features with-in 100 feet (City Engineer may increase this amount) of the project boundary including but not limited to: location of existing watercourses, storm drains, canals, irrigation ditches, springs and culverts etc. b. Proposed watercourses. 2) Tributary drainage areas, flow directions, inlets, conveyance system, outlets, catch basins, waterways, culverts, detention basins, elevations, grades, capacities, orifice plates etc. 3) The major system route and termination point. 4) Delineate the 100-year flood plain as designated by FEMA and Salt Lake County 100 year flows. 5) Detention or retention volume and area, high flood mark, and freeboard noted, including max depth, side slopes, and spillways. For commercial sites, delineate 100-year detention boundaries in parking area or its designed location. 6) Any surrounding areas outside the project site that influence the project or that the project may influence downstream or adjacent to the project. 7) Plan and profile drawings. 8) Existing structures 9) Soil, geotechnical, or exploratory report 10) Previously redlined plan sets 2.10 Pipe Design, Material, Size, and Construction: A. For pipe type see APWA Standard Specifications, Section B. 15 minimum pipe diameter or as dictated on Stormwater Master Plan. C. Install storm drain pipe per APWA Plan No D. Minimum depth: 2-foot cover. May include asphalt. E. Slope requirements: 0.5% City minimum but can allow slopes per HEC22 minimums as approved by City Engineer. F. Match pipe crowns G. Testing requirement: video inspection of the entire system including joints prior to acceptance. H. Install pipe within roadway between top back of curbs. I. Public stormwater pipe is not allowed on private property. City Engineer approved exceptions require stormwater easement. Provide 7.5 easement each side of storm drain lines that are

10 approved for side lot or rear lot installation. Templates are available at the Stormwater Division. Provide space for vehicular access for all manholes and storm drain lines that are approved for side lot or rear lot installation Manholes (Clean-out Boxes): A. Design per APWA Plan No.-331, 341, 302 or approved equivalent. B. Place manholes, at all changes in pipe size, alignment, and slope. Typical spacing to be 500 feet maximum. C. Public manholes are not allowed on private property. City Engineer approved exceptions require stormwater easement. Easement templates are available at the Stormwater Division. Manhole lids used for this application must be bolt down lids with PENTA-HEAD bolts. D. Design boxes to be self cleaning, except when specified by the City Engineer Inlet and Combination Boxes: A. Design per APWA Plan No.-315 through APWA Plan No Provide casting with water quality markings that either by word or symbol prohibits pollutants to be discharged into drain. B. Design spacing per time of concentration calculations for the 10% annual chance storm intensity with spread not exceeding ½ the driving lane. C. Design double inlet box at low points in vertical curves and at the low points of downgrade culde-sacs or dead ends. Force the sag to property boundaries. D. Locate inlet boxes at intersections and capture gutter flow to minimize pedestrian inconvenience. E. Locate inlet boxes at property lines to property boundaries to prevent conflict with driveway access. F. Design boxes to be self cleaning, except when specified by the City Engineer. G. Design to eliminate water channels in roadways Water Quality Device: A. Water quality device are required for all sites discharging stormwater to the public system. B. Private systems designs must include realistic maintenance configurations. C. The system, water quality device and Long-Term Stormwater Maintenance Plan(LTSWMP) must together mirror or perform better than the historical undisturbed condition. D. Provide engineering or the manufacturers test results supporting the effectiveness for containment of pollutants relative the flow rate and velocity designed for the device. E. Provide drawings and the maintenance requirements necessary to maintain the designed water quality results. The water quality device or system must also trap enough residual stormwater for testing. F. The annual LTSWMP reports must ultimately validate the performance of the system(device and LTSWMP Easements: A. Provide a legal easement for all public storm drain facilities allowed on private property by the City Engineer. Easement templates are available by the Stormwater Division. B. Provide 7.5 minimum each side of storm drainpipe. C. Provide 20 minimum surface route easements. D. Extend easements 10 feet beyond the last manhole or inlet boxes on the line. E. All easements shall be submitted and approved by City Engineer and recorded before final

11 approval will be granted. F Natural drainage and irrigation water 2.15 Long-Term Stormwater Management Plans: A. Commercial Development must enter into a Long-Term Stormwater Management Agreement. B. Private developments expected to establish HOA s must enter into a Long-Term Stormwater Management Agreement, C. Small Private Developments(determined upon case by impact) not expected function under a Home Owners Association (HOA), have two options: 1. Private residential subdivisions proposing a Low-Impact Development (LID) with no direct connection to the City piped, open ditch or gutter system may file a Covenant to Maintain to preserve and protect the LID in lieu of the LTSWMP. 2. Private residential subdivisions proposing direct connections to the City piped, open ditch or gutter system must enter into a Long-Term Stormwater Management Agreement (LTSWMP) unless determined by the City Engineer a case of impact that a Covenant to Maintain will be sufficient. D. As required by the Clean Water Act and resultant local regulations, including Riverton City s Municipal Separate Storm Sewer Systems (MS4) permit, those who develop land are required to build and maintain systems that will prevent contaminated water from reaching waters of the state. E. A Long-Term Stormwater Management Plan (LTSWMP) is necessary to prevent contaminated water, both stormwater and non-stormwater, from reaching the City s storm drain system, which is connected to creeks, canals, and the Jordan River. F. The LTSWMP must identify the minimum standard operating procedures (SOPs) necessary to accomplish this purpose. G. All other activities and site operations not identified in this LTSWMP that pollutes runoff entering the City s storm drain system must be prohibited Low Impact Development (LID): A. Commercial development must include a LID analysis that meets the objective of mirroring the predevelopment hydrology(ms4 Permit UTR090000, However, development must infiltrate, evaporate or harvest and reuse the 90 th percentile storm events minimum(requirement on HOLD). No LID limits are defined for private systems except designs must not negatively impact surrounding properties. Analysis must include the list of LIDs considered, the reasons for incorporating the LIDs selected and the reasons why the other LIDs where not used. (MS4 Permit UTR The Stormwater Utility Fee is directly proportional to impervious area and is reduced by minimizing the impervious area. Also the Stormwater Utility Fee can be further reduced up to 45% for sites that retain all runoff up to a 100 year event. Submit the LID report with the stormwater calculations report. B. Public residential development must include an LID analysis that meets the objective of mirroring the predevelopment hydrology. The LID infrastructure parameters are defined in Section 2.6 of this document. Analysis must include the list of LIDs considered, the reasons for incorporating the LIDs selected and the reasons why the other LIDs where not used. (MS4 Permit UTR The incentive for incorporating LIDs is the potential infrastructure and land cost saved by the elimination or reduction of the stormwater detention or retention systems. Submit the LID report with the stormwater calculation report. C. Utility Fee Adjustment Application: Request an application

12 D. LID reference sites: E. Suggested LID approaches: 1) Reduce the amount of impervious area 2) Reduce the amount of directly connected impervious acreage. 3) Connect roof drains to landscaping. 4) Slope dumpster enclosure pads towards landscaping. 5) Minimize concentrating large volumes runoff in one location rather, uniformly distribute over the site and direct runoff to wide open flat landscaping areas that will maintain shallow depths improving on infiltration and evaporation. 6) Distribute drywells across the site minimizing the large tributary areas to single drywells intended to better mimic the conditions of the predevelopment hydrology. F. LID evaluation must include: 1) List of LID s considered 2) The reasons for the selection of each LID considered e.g. why and why not the LID was selected. G. LID design has few limits but the selected LID must be defined and maintained via the requirements of the Long-Term Stormwater Management Plan (LTSWMP) and Agreement. 1) Retention/infiltration designs shall include systems that minimize above ground standing water that foster mosquito populations Land Disturbance Permit: A. Construction projects require Land Disturbance Permits (LDP) and, where required by State Law, a Notice of Intent (NOI) for Storm Water Discharges Associated with Construction Activity under the UPDES General Permit (GCP) No. UTRC and UTRH The Land Disturbance and NOI applications can be found online at: B. Stormwater Pollution Prevention Plans (SWPPPs) must be prepared in accordance to the LDP and the GCP requirements. SWPPP templates are available online at: Contact the Riverton City Stormwater Divisions for web links. C. SWPPPs must be managed via an internet-based system with the following privileges: 1) Public accessibility and view rights to your current SWPPP, inspection reports, corrective actions and all other permit requirements. 2) City staff accessibility and view rights to your current SWPPP, inspection reports, corrective actions and all other permit requirements. 3) City staff accessibility for purpose of SWPPP assessments, audits, and data collection Wetlands: A. 10-9a-521; A municipality may not designate or treat land as wetland unless the United States Army Corps of Engineers or other agency of the federal government has designated the land as wetland. However, municipalities and other agencies have an obligation to protect the health, safety and welfare of adjacent properties whether or not wetlands exist. Adjacent property must be protected during and after construction Special Flood Hazard: A. Comply with SECTION AREAS OF SPECIAL FLOODHAZARDS GENERAL PROVISIONS.

13 2.20 Salt Lake County and Canal Facilities: A. The latest version of Salt Lake County ordinances and/or canal design standards apply to design and construction activities, for the following systems under Salt Lake County Control: Jordan River, Midas Creek, Rose Creek, Beckstead Canal, South Jordan Canal, Utah and Salt Lake Canal, and Utah Lake Distributing Canal East Riverton Drainage System: A. Design per APWA Plan No.-341 or approved equivalent. B. Manhole lid label to be marked East Riverton Drain C. Place manholes, at all changes in pipe size, alignment, and slope. Typical spacing to be 500 feet maximum. D. No City manholes allowed on private property. Exceptions require written easement (request templates at the Engineering Department). E. Design boxes to be self cleaning, except when specified by the City Engineer. F. Use RCP gasketless pipe, match existing size, 12 minimum. Insert spigot and bell to insure the gap ranges between , Section G. Install storm drain pipe per APWA Plan No Pipe zone, 1 to 1/2 crushed gravel completely fully wrapped with GEOTEX 451 or approved equivalent, Section H. Slope requirements: 0.5% minimum or as per calculated scouring velocities. I. Match pipe crowns J. Testing requirement: video inspection of the entire system prior to acceptance. K. Easement 20 wide minimum, pipe within the middle third Irrigation Ditches: A. Pipe open irrigation ditch within or adjacent to the boundary of the development. B. Relocate irrigation pipes to front yards where possible. C. Investigate all existing irrigation systems (pipe or ditch) within or adjacent to the project limits and determine if they are to be perpetuated. Notify the respective irrigation users of all public hearing dates and provide the City with all the names and addresses of affected shareholders. Coordinate with the respective shareholders or representative and provide a written document, which identifies the agreements between the two parties. Include pipe sizes, known flows and any other relevant information. D. Irrigator permission is not required to pipe ditches E. Irrigator permission is required for elimination of ditches or runoff discharges to them. F. Design piping of sufficient size to handle the anticipated flow in existing ditch minimum. G. Design appropriate boxes, diversions, gratings, and covers to minimize irrigation hazards. Design 4 maximum grate opening. H. Design clean-out boxes per the agreements with irrigators. Design irrigation structures in public R/W in accordance with city standards. Irrigation lids are to be bolted. I. Community diversion boxes and clean out boxes are not allowed in back yards and any allowed will require city approval. Irrigation system not in the public R/W requires an easement. J. Provide easements on plat not less than 7.5 each side of pipe. Identify as Irrigation Easement K. Connection to City systems requires a sediment and debris containment system. Minimum design parameters or equal:

14 1. System must trap sediment and debris generated on the irrigated area. 2. System must be maintainable and configured so the water user will recognize when maintenance is necessary. 3. Safety systems preventing child injury and drowning. 4. Include a permit and terms of discharge, including but not limited to; maintenance agreement and plan, inspection reports, easement for City access of system Class V Underground Injection Wells: A. Compliance per Utah 1422 Underground Injection Control Program (UIC) B. C. Permit Application: D. Obtain an Underground Injection Control (UIC) permit and include a copy with the Stormwater Report for any projects designed to include underground storage or infiltration system Bonding: A. Bond all public facilities Impact Fee Reimbursement/Credit Policy in accordance to State Code 11-36a: Impact fee reimbursements and credits must be based on the calculation methodologies of the Impact Fee Analysis. Developments are responsible for their own project cost except where the Impact Fee Facilities Plan accounts for reimbursements or credits in which case the land is reimbursed at purchase cost and the project improvements are reimbursed at approved actual cost. However, land necessary for system improvements for the greater service area beyond the project boundaries may be reimbursed at opportunity cost amounts proportionate to land necessary to accommodate the additional service area runoff volumes. When the project area is within a larger service area, where stormwater infrastructure is absent and in the absence of an Impact Fee Facilities Plan, development must temporally or permanently mitigate for all runoff at their cost. This means to either construct system improvements, construct temporary flood control systems or enter into a pioneering agreement and build system improvements for the greater service area. Definitions: Project improvements: Stormwater infrastructure necessary to manage the developments stormwater impact in accordance to City development standards. System improvements: Stormwater infrastructure necessary to manage a greater stormwater service area in accordance to City development standards. A. Reimbursements for land opportunity cost must be supported by a certified appraisal for the specific land opportunity loss. B. Actual cost must be accompanied by receipts and comply with City Procurement Policy ensuring competitive cost Impact Fee Exemption Conditions: A. Sites to be considered no impact to the system must satisfy the following conditions for this exemption: 1. Site must retain all runoff for the 100 year 24hour storm and require no City stormwater

15 capital improvement projects. 2. Private sites must enter into a stormwater agreement and create a Long-Term Stormwater Management Plan per City Standards Quality Assurance: A. Perform work in accordance with City requirements as described herein. Design work shall be accomplished under the direct supervision of a Utah Registered Professional Engineer, and shall carry the seal of the same supervising Professional Engineer Value Engineering: A. Riverton City promotes concepts and designs that may improve the overall performance, life and aesthetics of the City as a whole. All Value Engineering concepts and designs require review and approval by the City Engineer.

16 SUBMITTALS (pertaining to stormwater management) A. Stormwater Report: Provide pdf formatted for an 8 ½" x 11" and 11 x 17 size paper. Include all calculations and support data necessary to demonstrate the site stormwater system is adequate to manage stormwater onsite, outside runoff sources and its impact to the existing City conveyance system. B. Include the LID analysis describing the LID selection process. Provide calculations supporting the selected LID performance at control and containment. Include maintenance instruction or refer to the Long-Term Stormwater Management Plan for the maintenance necessary to ensure the LID will perform long term. B. Required permits governing the permanent stormwater system. May include but are not limited to: County Flood Control, Stream Alterations, Army Corp of Engineer permits, etc. End of Section

17 DEFINITIONS To shorten this document certain words or phrases are defined as follows unless stated otherwise in said document: A. Detention Storage: The storage of storm water runoff for controlled release during or immediately following the design storm event. B. Discharge Point: A point or location where surface or pipe storm water runoff is concentrated before being released from the project area. C. Easement: An interest in land created by grant or agreement, which confers a right upon owners (private or public) to some profit, benefit, dominion, or lawful use of another. D. City Engineer: Riverton City Engineer or authorized representative. E. Emergency: Unforeseen circumstance that presents immediate danger to persons or property. This also includes loss of utility services. F. Groundwater: Water beneath the earth s surface between the saturated soil and rock that supplies wells and springs. G. Infiltration: That portion of the rainfall, which percolates into the ground surface. H. Percolation: The process by which fluid passes through a porous substance. I. Pocket Pond: Above or below ground stormwater detention or retention systems, including WQCV systems, located on a parcel that is smaller than the minimum standard residential subdivision lot size allowed in that zone. J. Pre-development Hydrology: The combination of runoff, infiltration rates, and natural retention volumes that existed on a site before human-induced land disturbance occurred. K. Retention Storage: The storage of storm water runoff where the only outlet is infiltration and evaporation. L. Runoff Volume: The total volume of runoff from the surface of a property or runoff from the surface that is collected by a man made conveyance systems on the same property above or below ground. M. Spillway: A waterway in or about a hydraulic structure, for the release of excess water. N. Subdivision: Any division of a property within a parcel (residential or commercial) O. Storm Water Runoff: Water resulting from precipitation running off the surface of a drainage area during and immediately following a cloudburst event. P. Tributary Watershed: The entire catchment area that receives storm water runoff for specific concentration point(s). Q. Waters of the State: All streams lakes, ponds, marshes, watercourses, wells, springs, irrigation

18 systems, drainage systems, and all other bodies of water, surface and underground, natural or artificial, public or private, which are contained within, flow through, or border upon this State or any portion thereof, except those bodies of water confined to and retained within the limits of private property, and which do not develop into or constitute a nuisance, or a public health hazard.

19 REFERENCES A. American Society of Civil Engineers, Design and Construction of Urban Stormwater Management Systems. B. Soil Conservation Service, Urban Hydrology for Small Watersheds. Technical Release No. 55, U.S. Department of Agriculture. C. TRC North American Weather Consultants, Rainfall Intensity Duration Analysis Salt Lake County, Utah. D. Federal Emergency Management Agency. Flood Insurance Study Guidelines and Specifications for Study Contractors. Washington, D.C., Federal Emergency Management Agency. E. Salt Lake County Flood Control. Best Management Practices. F. U.S. Department of Transportation, Federal Highway Administration, Hydraulic Design of Highway Culverts. Washington D.C., U.S. Department of Transportation. G. Virginia Department of Conservation and Historic Resources, Virginia Erosion and Sediment Control Handbook. 3 rd ed. Richmond, Virginia. Virginia Department of Conservation and Historic Resources. H. U.S. Department of Transportation, Federal Highway Administration, Urban Drainage Design Manual. Washington D.C., U.S. Department of Transportation. I. Guo, James C.Y., Detention Basin Sizing For Small Urban Catchments, ASCE Journal of Water Resources Planning and Management, Volume 125, No. 6, November.