2007 Stormwater Management Retrofit Plan

Transcription

1 2007 Stormwater Management Retrofit Plan Prepared by Thompson Lake Rainwater Garden during heavy rain, Spring 2004 Dakota County Soil and Water Conservation District Dakota County Operations Management th Street West, Suite Highway 55 Farmington, MN Hastings, Mn fax Page 1 of 38 Adopted 7/10/2007

2 Dakota County Stormwater Retrofit Review Sites Page 2 of 38 Adopted 7/10/2007

3 Dakota County Stormwater Management Plan Introduction Dakota County s lakes, rivers, and wetlands all depend on the replenishing waters of annual precipitation. However, when rain falls on land and impervious areas such as paved streets, parking lots, and building rooftops it can wash away soil and sediment. This is called runoff. Runoff can change both water quality and quantity affecting our water resources physically, chemically and biologically. Polluted runoff containing oil, grease, chemicals, nutrients, metals, litter, and pathogens for example, can severely reduce water quality. If left unmanaged, runoff stresses our streams, ages our lakes, and degrades and eliminates our wetlands. The proper treatment of stormwater is a national concern and stormwater regulations are administered by the U.S. Environmental Protection Agency (EPA) through the National Pollutant Discharge Elimination System (NPDES) permit program. In Minnesota, the EPA has delegated NPDES permitting authority to the Minnesota Pollution Control Agency (MPCA). The State s Stormwater Program is intended to reduce pollution and damage caused by runoff from construction sites, industrial facilities, and municipal separate storm sewer systems (MS4s). MPCA requires that all local jurisdictions with urbanized areas to participate in the MS4 program and to develop and implement a stormwater pollution prevention program (SWPPP). Dakota County is subject to this requirement for the urbanized portion of the County and adopted a stormwater pollution prevention program in The SWPPP must cover six areas of concern: Public education and outreach; Public participation/involvement; Illicit discharge, detection and elimination; Construction site runoff control; Post-construction site runoff control; and Pollution prevention/good housekeeping. The SWPPP must identify action steps or best management practices (BMP s) related to these six areas of concern. Each action step must contain a measurable goal and progress toward achieving the goals is to be reported on annually. One of the action steps identified in the Dakota County SWPPP is a review of potential stormwater retrofit opportunities for County building facilities. This report identifies these opportunities and makes recommendations and fulfills the requirement of that BMP. The identification of retrofit opportunities is only the first step. The Dakota County Board of Commissioners has set aside $25,000 in their annual Capital Improvement Program to construct stormwater improvements at County facilities. To date, the County has constructed a rain garden at the Wentworth Library and, using another funding source, constructed a rain garden at the Law Enforcement Center. The enclosed assessment, performed in 2004, did not attempt to prioritize stormwater improvement projects. Staff from Dakota County Soil and Water Conservation District, Dakota County Water Resources Office and Dakota County Operations Management have evaluated the potential stormwater retrofit projects and ranked the projects. The implementation chapter of this plan outlines the rating criteria and identifies the high priority retrofit projects. Funding for constructing the retrofit measures will predominately come from the County s Building CIP, however, this funding will be supplemented where appropriate from individual construction or Page 3 of 38 Adopted 7/10/2007

4 remodeling projects, annual landscape improvement funds and Environmental Management s education funds. Stormwater Management Retrofit Assessment The following assessments were performed by Dakota County Soil and Water Conservation District staff in 2004 as part of the Dakota County SWPPP. The conditions at each of the County facilities have not changes with the exception for the Wentworth Library and the LEC where new improvements have been installed. The assessments provide a simple list of potential stormwater management retrofit opportunities. The list is not intended to be inclusive and additional opportunities exist for all of the sites. The General Comments attempt to assign a preliminary prioritization to the site. No attempt has been made to prioritize the specific measures identified at each site. Cost for the improvements have not been identified and will vary depending upon when and how a measure is implemented and the specific site characteristics. For example, retrofitting a large bioretention facility at Thompson Lake Regional Park cost around $8000 plus in-kind match from the County. The Wentworth Library rain garden was constructed with County Transportation staff and cost only $8,200 for materials and equipment rental. Both features would have cost substantially more if an outside contractor had performed the work. See Appendix A for a glossary, example stormwater management practices, cost estimates, and an overview of how to protect water quality from urban runoff. Page 4 of 38 Adopted 7/10/2007

5 Stormwater Management Retrofit Assessment Site: Conservation and Extension Center Inspection Date: 6/15/2004 Potential Practice 1 Description: Bioretention Potential Practice 1 Location: Southwest corner of parking lot Potential Practice 2 Description: Bioretention Potential Practice 2 Location: Entrance driveway General Comments: Entrance practice would make good demo and address drainage problem. Page 5 of 38 Adopted 7/10/2007

6 Stormwater Management Retrofit Assessment Site: Dakota County Government Center Inspection Date: 6/3/2004 Potential Practice 1 Description: Bioretention and native plantings Potential Practice 1 Location: Southeast turf depressional area - appears to receive runoff from majority of site and drains well. Opportune retrofit location. Potential Practice 2 Description: Bioretention - curb cut with speed bump diversion Potential Practice 2 Location: Northeast employee parking area - north portion drains untreated off site Potential Practice 3 Description: Impervious reduction, recessed island, and/or porous parking Potential Practice 3 Location: W side of main parking lot Potential Practice 4 Description: Dry wells or cisterns. Potential Practice 4 Location: Below roof downspouts Potential Practice 5 Description: Porous pavement or below ground infiltration systems Potential Practice 5 Location: New pavement and parking areas General Comments: Excellent examples of natural landscaping and stormwater management currently located at southwest corner of site. Page 6 of 38 Adopted 7/10/2007

7 Stormwater Management Retrofit Assessment Site: Northern Service Center Inspection Date: 5/28/2004 Potential Practice 1 Description: Pavement reduction or porous parking Potential Practice 1 Location: West lot. Could be used primarily as overflow because of limited use. Potential Practice 2 Description: Native landscaping and soil restoration Potential Practice 2 Location: West of west lot. Potential Practice 3 Description: Bioretention Potential Practice 3 Location: West lot - west side of building. Potential Practice 4 Description: Bioretention, Filter Swale, or Infiltration Trench Potential Practice 4 Location: East lot and southeast corner of site. Southeast swale is opportune location. Potential Practice 5 Description: Dry wells or cisterns. Potential Practice 5 Location: Below roof downspouts General Comments: Good site for demonstrations. Sand accumulation at northeastern corner of east parking lot. Page 7 of 38 Adopted 7/10/2007

8 Stormwater Management Retrofit Assessment Site: Western Service Center Inspection Date: 5/28/2004 Potential Practice 1 Description: Bioretention or native plantings Potential Practice 1 Location: South of southeast lot - along County Road 42 Potential Practice 2 Description: Porous pavement Potential Practice 2 Location: All low use parking areas Potential Practice 3 Description: Bioretention island or Infiltration Trench Potential Practice 3 Location: Staff lot west of library Potential Practice 4 Description: Roof runoff treatment or native plantings Potential Practice 4 Location: West side of WSC Potential Practice 5 Description: Dry wells or cisterns. Potential Practice 5 Location: Below roof downspouts General Comments: Good site for demonstrations - large impervious areas with potential for pretreatment Page 8 of 38 Adopted 7/10/2007

9 Stormwater Management Retrofit Assessment Site: Burnhaven Library Inspection Date: 6/15/2004 Potential Practice 1 Description: Bioretention Potential Practice 1 Location: Southeast corner of parking lot near inlet Potential Practice 2 Description: Bioretention or Filter Swale Potential Practice 2 Location: Southwest edge of parking lot near curb cut General Comments: Priority site for ultra-urban retrofit and treatment for Early Lake. Page 9 of 38 Adopted 7/10/2007

10 Stormwater Management Retrofit Assessment Site: Farmington Library Inspection Date: 6/15/2004 Potential Practice 1 Description: Bioretention - recessed islands Potential Practice 1 Location: Parking lot General Comments: Great demo site - direct drainage to vermillion river trout stream. Page 10 of 38 Adopted 7/10/2007

11 Site: Heritage Library Inspection Date: 5/28/2004 Stormwater Management Retrofit Assessment Potential Practice 1 Description: Enhanced bioretention or native plantings Potential Practice 1 Location: West and south of library Potential Practice 2 Description: Bioretention Potential Practice 2 Location: East of parking lot - ideal location Potential Practice 3 Description: Dry wells or cisterns. Potential Practice 3 Location: Below roof downspouts General Comments: Drains to tributary of Vermillion River. Priority site - opportune site for bioretention east of main parking lot, between the City lot and the Library lot. Page 11 of 38 Adopted 7/10/2007

12 Stormwater Management Retrofit Assessment Site: Inver Glen Library Inspection Date: 6/15/2004 Potential Practice 1 Description: Bioretention Potential Practice 1 Location: Adjacent to parking lot inlets Potential Practice 2 Description: Native landscaping Potential Practice 2 Location: Front lawn area General Comments: Parking lot drainage conveyed to pond. Good demo site. Page 12 of 38 Adopted 7/10/2007

13 Stormwater Management Retrofit Assessment Site: Pleasant Hill Library Inspection Date: 6/3/2004 Potential Practice 1 Description: Bioretention, Infiltration Trench, and/or Recessed Island Potential Practice 1 Location: Parking lot treatmen Potential Practice 2 Description: Native landscaping Potential Practice 2 Location: Front turf area Potential Practice 3 Description: Dry wells or cisterns. Potential Practice 3 Location: Below roof downspouts General Comments: Relatively small site. Lower priority from a water quality perspective. Good demo opportunity however. Page 13 of 38 Adopted 7/10/2007

14 Stormwater Management Retrofit Assessment Site: Wentworth Library Inspection Date: 5/28/2004 Potential Practice 1 Description: Bioretention Potential Practice 1 Location: North side of building, to treat roof runoff proir to entering adjacent lake. Potential Practice 2 Description: Bioretention - high priority Potential Practice 2 Location: Northwest corner of parking lot, to treat roof runoff proir to entering adjacent lake. General Comments: Priority site entire property drains directly to adjacent lake without any treatment. Opportune site for bioretention west of parking lot. Sand accumulation in northeast corner of parking lot. Page 14 of 38 Adopted 7/10/2007

15 Site: Wescott Library Inspection Date: 5/28/2004 Stormwater Management Retrofit Assessment Potential Practice 1 Description: Bioretention, Recessed Islands, and/or Infiltration Trench Potential Practice 1 Location: Along wescott and west end of lot Potential Practice 2 Description: Native plantings Potential Practice 2 Location: West and south sides of building Potential Practice 3 Description: Dry wells or cisterns. Potential Practice 3 Location: Below roof downspouts General Comments: Much of the parking lot islands recently landscaped - bioretention along north side of parking lot would make a good demo site. Page 15 of 38 Adopted 7/10/2007

16 Stormwater Management Retrofit Assessment Site: South St. Paul Library/Museum Inspection Date: 6/8/2004 Potential Practice 1 Description: Porous parking Potential Practice 1 Location: Both lots Potential Practice 2 Description: Small bioretention Potential Practice 2 Location: South lot inlet Potential Practice 3 Description: Bioretention Potential Practice 3 Location: Small raingarden in front Potential Practice 4 Description: Dry well or other subsurface practice Potential Practice 4 Location: TBD Potential Practice 5 Description: Infiltration trench Potential Practice 5 Location: Adjacent to parking areas General Comments: Very tight site. Difficult to retrofit. Possible green roof site? Page 16 of 38 Adopted 7/10/2007

17 Stormwater Management Retrofit Assessment Site: Empire Transportation Facility Inspection Date: 5/28/2004 Potential Practice 1 Description: Native plantings Potential Practice 1 Location: Throughout site, esp in swales and around ponds (if not already planned) General Comments: Thorough runoff treatment system already in place. Swales and ponds could use vegetative enhancement. Page 17 of 38 Adopted 7/10/2007

18 Stormwater Management Retrofit Assessment Site: Farmington Transportation Facility Inspection Date: 6/15/2004 Potential Practice 1 Description: Bioretention or Filter Swale Potential Practice 1 Location: Northeast corner of parking lot General Comments: Existing ponds treat storage barn. Much of site drains to vegetated swales, so lower priority with current conditions. Page 18 of 38 Adopted 7/10/2007

19 Stormwater Management Retrofit Assessment Site: Hastings Transportation Facility Inspection Date: 6/3/2004 Potential Practice 1 Description: Filtration or bioretention Potential Practice 1 Location: Between impervious surfaces and vermillion river - Northwest corner of site before runoff reaches culvert Potential Practice 2 Description: Native plantings Potential Practice 2 Location: Swale in front of facility General Comments: Priority site simple and inexpensive retrofit. Page 19 of 38 Adopted 7/10/2007

20 Stormwater Management Retrofit Assessment Site: Lebanon Hills Regional Park Inspection Date: 5/28/2004 Potential Practice 1 Description: Filtration swale already in place, south portion of parking lot goes directly to riprap channel. Future lot improvements could route southern lot to swale. Potential Practice 1 Location: Jensen lake trail-head parking lot Potential Practice 2 Description: Bioretention Potential Practice 2 Location: Campground roads, especially near lodge. Potential recessed bioretention island demonstration near main entrance? General Comments: Main visitor center is a model of innovative design and stormwater management for the state and region. Many practices already in place throughout park system. High number of visitors provides a good opportunity for additional ddemonstrations. Page 20 of 38 Adopted 7/10/2007

21 Stormwater Management Retrofit Action Plan In order to prioritize and insure the effective use of the funds set aside to implement retrofit projects, staff from Dakota County Soil and Water Conservation District, Dakota County Water Resources Office, and Dakota County Operations Management have evaluated the potential stormwater retrofit projects and ranked the projects. Due to the availability of resources, both financial and manpower, it has been assumed that only 2 to a maximum of 3 projects could be implemented each year. Project staff developed three criteria to rank each potential project. The criteria are: 1. Identifiable Water Resource Does the drainage from the facility discharge directly to a water body, wetland or watercourse. Facilities that directly discharged were given higher priority. 2. Site Suitability Factors such compatible site conditions, visibility, ease of installation, access, available land area, etc. were weighed for each potential project. 3. Perceived Benefit Projects that generated the greatest benefit were given higher priority. Factors such as water quality improvement, resource protection, public education, demonstration potential, and public outreach were all considered in staff s rating of perceived benefit. Each potential project was given a value from 1 (low) to 3 (high) for each criterion. Figure 1 summarizes the staff ranking. The first two projects listed on Figure 1, the Wentworth Library and the LEC, have already been implemented. The next set of high priority projects are recommended to be implemented over the next three years ( ), depending upon funding and staff availability. The second set of projects will be considered after Figure 1 also lists two Park projects. These projects have other available funding sources and are, therefore, listed separately. Figure 2 provides a visual graphic of the highest ranked projects. In addition to the retrofit projects, the Stormwater Retrofit Program has identified other lower cost best management practices opportunities that will be investigated further and implemented as time and funding allows. These opportunities are listed on Figure 3. Figure 4 provides Fact Sheets on completed projects. Page 21 of 38 Adopted 7/10/2007

22 Figure 1 Page 22 of 38 Adopted 7/10/2007

23 Figure 2 Page 23 of 38 Adopted 7/10/2007

24 Page 24 of 38 Adopted 7/10/2007

25 Page 25 of 38 Adopted 7/10/2007

26 Figure 3 Page 26 of 38 Adopted 7/10/2007

27 Figure 4 Page 27 of 38 Adopted 7/10/2007

28 APPENDIX A Glossary Bioretention: On-lot retention of stormwater through the use of vegetated depressions engineered to collect, store, and infiltrate runoff. Sometimes referred to as rain water gardens. Cisterns: Below-ground tanks designed to collect and store rooftop runoff. Often used to collect water for irrigation purposes. Dry Well: Small excavated trenches filled with stone to control and infiltrate rooftop runoff. Filter Strips: Bands of closely-growing vegetation, usually grass, planted between pollution sources and downstream receiving water bodies. Impervious Area: A hard surface area (e.g., parking lot or rooftop) that prevents or retards the entry of water into the soil, thus causing water to run off the surface in greater quantities and at an increased rate of flow. Infiltration: The downward movement of water from the land surface into the soil. Native vegetation: Native plants with deep roots that are adapted to local climate conditions. Many function very effectively to treat runoff and maximize infiltration. NPDES: National Pollutant Discharge Elimination System; a regulatory program in the Federal Clean Water Act that prohibits the discharge of pollutants into surface waters of the United States without a permit. Permeable: Soil or other material that allows the infiltration or passage of water or other liquids. Porous pavement: Devices and practices to promote infiltration in parking areas. Porous pavers, reinforced grass, and porous concrete are potential options. Subgrade below porous pavement is prepared to maximize infiltration. Rain Barrels: Above-ground barrels designed to collect and store rooftop runoff. Rain water garden: Another common term for bioretention. Runoff: Water from rain, melted snow, or irrigation that flows over the land surface. Swale: An open drainage channel designed to detain or infiltrate stormwater runoff. Vegetated roof: Rooftop system that insulates the building and filters/retains runoff. One of the best examples in the mid-west is at the Lebanon Hills Regional Park Visitor s Center. Page 28 of 38 Adopted 7/10/2007

29 APPENDIX B Examples of Stormwater Management Practices Bioretention Source: Maryland Stormwater Manual Page 29 of 38 Adopted 7/10/2007

30 Bioretention Thompson Lake Bioretention, 2004 Burnsville Rainwater Garden Rushmore Ave, 2004 Page 30 of 38 Adopted 7/10/2007

31 Infiltration Trench Source: Maryland Stormwater Manual Page 31 of 38 Adopted 7/10/2007

32 Dry Well Rain Barrels/Cisterns Page 32 of 38 Adopted 7/10/2007

33 Filter Swale Source: Maryland Stormwater Manual Page 33 of 38 Adopted 7/10/2007

34 Filter Swale Thompson Lake Filter Swale, 2004 Hastings Government Center Filter Swale, 2004 Page 34 of 38 Adopted 7/10/2007

35 Porous Parking Porous Pavers Schmelz VW Porous Pavers Installation (Uni Ecostone) Page 35 of 38 Adopted 7/10/2007

36 Porous Parking Reinforced Turf Reinforced grass overflow parking Reihbein Netlawn Grass Pavers Page 36 of 38 Adopted 7/10/2007

37 APPENDIX C Stormwater Best Management Practices Cost Estimates* BMP Family BMP List BMP Type Estimated Cost Building Comments etc Site Comments Project-Source etc Retention Wet Pond $ /cf treated water volume EPA website, adapted from Brown & Schueler 1997b Extended Storage Pond Roof Storage Dry Pond $ /cf treated water volume Green Roof (Extensive) $ /cf treated water volume $13.70 /sf membrane thru plants $12 /sf average membrane thru plants Detention Oversized Pipes $ cf $ cf $ cf Oil/Grit Separator Dry Swale Multi-chamber treatment tank Stormceptor $38,000 /ac of impervious $15,000 /ac of impervious Extensive type on sloped roof on woodframe bldg, Carlisle Roofing systemmembrane, Mn Native L scapes Extensive type Concrete pipes, boxes HDPE CSP, aluminum pipe Costs per cu ft stored volume, depends on materials/storage type. EPA website, adapted from Brown & Schueler 1997b Lebanon Hills RP Visitor Center, Eagan, 2003, est based on 6,200+ sf roof area From NEMO website EPA website, adapted from Brown & Schueler 1997b Adapted fr Parsons Eng Sci, Source EPA website Bannerman 2000, adapted from SEWRPC 1991 Bannerman 2000, adapted from SEWRPC 1991 $4.90 to 9.00 /lf Schueler, 1987 CWP On-lot Infiltration Permeable Unit Paving $8.50+ /lf, $0.50 /cf of treated water vol $6.50 to 8 /sf mechanical laying $12.50 /sf hand laying Depending on swale depth and width, assumes 6 storage in filter Uni EcoStone, and 15 of engineered permeable base SEWRPC, 1991 & EPA website adapted from above Estimates from Jay Riggs, DCSWCD, 11/03; Jay Michels, MECA, 12/03 Page 37 of 38 Adopted 7/10/2007

38 BMP Family BMP List BMP Type Estimated Cost Building Comments etc Site Comments Project-Source etc Infiltration $10 /sf Urban retrofit, inc soil Thompson Lake Infiltration Basin Rain Garden correction, plants, etc Park 2003, DCSWCD $14.25 /sf Urban retrofits Prince Georges Cnty Maryland, 1993, Infiltration Trench Rain Garden Reinforced Turf $5.50 /sf Geocells, Grassypavers, Netlawn $1.30 /cf of Based on 0.25 ac basin treated water typical costs volume $2.50 to 6.66 /cy or $18 /sf ave (7.50 to /sf), $4 /cf of treated water volume $3 to 6 /cf of treated water volume Sand Filters varies $17,500 /ac of impervious Est costs include site clearing thru estab of veg filter strip 1200 cf volume, 4 w x 3 d x 100 l, $3,000 to $8,000 est 1993 costs Cost varies depending on type, lowest=perimeter, higher=surface, undergr source EPA website Jay Michels, MECA, 12/03 EPA website, adapted from SEWRPC 1991 SE Wisc Reg Plann Comm 1991, source EPA website & EPA, adapted from SEWRPC 1991 EPA website, adapted from Brown & Schueler 1997b Bannerman 2000, adapted from SEWRPC 1991 Wetland Underground Filters Delaware Filter $20 /sf or $44,000 /ac of impervious Bioretention $5.30 /cf of treated water vol $0 to $1.30 /cf of treated water volume Assumes 6 of storage, highest cost assumes sod used to estab filter strips Bannerman 2000, adapted from SEWRPC 1991 EPA website, adapted from Brown & Schueler 1997b EPA wesite, adapted from SEWRPC 1991 G. Pates, 12/12/03 *Note: Little MN/Twin Cities cost estimates/data available. Estimates for cost/cf of treated water volume were based on typical 50 ac residential developments or 5 ac commercial sites in 1991 and 1996/7. Extrapolating this data and estimates to larger and smaller sites will not provide accurate project level cost estimates due to differences of scale, mobilization costs, etc. Publications that this information was taken from suggest that the information be used for planning purposes only. Page 38 of 38 Adopted 7/10/2007