Pleasant Lake: Urban Subwatershed Stormwater Retrofit Assessment

Transcription

1 Pleasant Lake: Urban Subwatershed Stormwater Retrofit Assessment Prepared by: Wright Conservation District With assistance from: THE METRO CONSERVATION DISTRICTS for the City of Annandale

2

3 This report details a rapid, relative subwatershed stormwater retrofit assessment resulting in recommended catchments for placement of Best Management Practice (BMP) retrofits that address the goals of the Local Governing Unit (LGU) and stakeholder partners. No monitoring has been conducted in order to calibrate, verify and/or validate these results. That being said, given the existing data made available, all efforts have been made to provide the most accurate and precise estimates for pollutant loading and reduction along with estimated costs to reach these removal rates. This document should be considered as one part of an overall watershed restoration plan including educational outreach, stream repair, riparian zone management, discharge prevention, upland native plant community restoration, and pollutant source control. The methods and analysis behind this document attempt to provide a sufficient level of detail to rapidly assess sub-watersheds of variable scales and land-uses to identify optimal locations for stormwater treatment. The time commitment required for this methodology is appropriate for initial assessment applications. This report is a vital part of overall subwatershed restoration and should be considered in light of forecasting riparian and upland habitat restoration, pollutant hot-spot treatment, agricultural and range land management, good housekeeping outreach and education, and others, within existing or future watershed restoration planning. The assessment s background information is discussed followed by a summary of the assessment s results; the methods used and catchment profile sheets of selected sites for retrofit consideration. Lastly, the retrofit ranking criteria and results are discussed and source references are provided. Results of this assessment are based on the development of catchment-specific conceptual stormwater treatment best management practices that either supplement existing stormwater infrastructure or provide quality and volume treatment where none currently exists. Relative comparisons are then made between catchments to determine where best to initialize final retrofit design efforts. Final, site-specific design sets (driven by existing limitations of the landscape and its effect on design element selections) will need to be developed to determine a more refined estimate of the reported pollutant removal amounts reported here-in. This typically occurs after the procurement of committed partnerships relative to each specific target parcel slated for the placement of BMPs.

4

5 Contents Executive Summary... 3 Methods... 4 Selection of Subwatershed... 4 Subwatershed Assessment Methods... 4 Step 1: Retrofit Scoping... 4 Step 2: Desktop Retrofit Analysis... 4 Table 2. Summary of land use makeup by catchment area Table 3. Classified versus modeled land uses by catchment... 7 Table 3 (cont). Classified versus modeled land uses by catchment... 8 Tables 4 A-L. Development of aggregated new residential, undeveloped, industrial or commercial land use descriptions by catchment... 9 Step 3: Retrofit Reconnaissance Investigation Step 4: Treatment Analysis/Cost Estimates Step 5: Evaluation and Ranking Subwatershed Overview Figure 1 Catchments Figure 2 Land Use (see Table 2 for key or appendix 1 for detailed descriptions) Figure 3 Soils distribution for the Pleasant Lake subwatershed study area Subwatershed Results Figure 5 - Annual Runoff Volume Figure 6 - Annual Sediment Loading Figure 7 - Annual Phosphorous Loading Figure 8 - Annual Nitrogen Loading Figure 9 - Annual Aggregated Metals Loading Catchment Profiles Tree Box Curb-Cut Bioretention Moderately Complex Raingarden/Curb Cut Bioretention Pleasant Lake Moderately Complex Raingarden/Curb Cut Bioretention... 32

6 Pleasant Lake Moderately Complex Raingarden/Curb Cut Bioretention Pleasant Lake Moderately Complex Raingarden/Curb Cut Bioretention Intersection Bump out Bioretention Pleasant Lake 23 (21, 22, 23 & 25 combined) Moderately Complex Raingarden/Curb Cut Bioretention Intersection Bump out Bioretention Pleasant Lake School s Simple Raingardens/Curb Cut Bioretention Pleasant Lake School s Simple Raingardens/Curb Cut Bioretention Pleasant Lake Moderately Complex Raingardens/Curb Cut Bioretention Vegetated Swale Pleasant Lake Moderately Complex Raingarden/Curb Cut Bioretention Pleasant Lake References Appendix Appendix 1 WINSLAMM Standard Land Use Codes Appendix 2 Infiltration Rates... 51

7 Methods 3 Executive Summary Thirty-two catchments, and their existing stormwater management practices, were analyzed for annual pollutant loading. Stormwater practice options were compared, for each catchment, given their specific site constraints and characteristics. A stormwater practice was selected by weighing cost, ease of installation and maintenance and ability to serve multiple functions identified by the catchment. Thirteen of the 32 catchments were selected and modeled at various levels of treatment efficiencies. These catchments should be considered the low-hanging-fruit within the Pleasant Lake Subwatershed. Two existing pond modification analysis results from a previous study are also included and highly recommended. The following table summarizes the assessment results. Treatment levels (percent removal rates) for retrofit projects that resulted in a prohibitive BMP size, or number, or were too expensive to justify installation are not included. Reported treatment levels are dependent upon optimal siting and sizing. The recommended treatment levels/amounts summarized here are based on a subjective assessment of what can realistically be expected to be installed considering expected public participation and site constraints. Overall Catchment Treatment Catchment or Pond ID Retro Type *Qty of BMPs TP Reduction (%) TP Reduction (lb/yr) Volume Reduction (ac-ft/yr) Overall Est. Cost 1 O&M Term (years) Total Est. Term Cost/lb- TP/yr 2 15 A $10,534 $375 $ A $22,580 $938 $ A $20,112 $1,500 $ A $10,534 $375 $ A $18,618 $750 $343 23** A $18,618 $750 $ G $27,747 $2,175 $ A&D $47,586 $900 $ A $16,060 $630 $662 *Number of 250 sq-ft (at overflow elevation) equivalents live storage or treatment volumes vary **Catchments 21, 22, 23, and 25 were combined into Catchment 23 A = Bioretention (infiltration and/or filtration) (modeled as 250 sq-ft each at overflow elevation) D = Vegetated Swale (wet or dry) G = New [wet] Detention or Wetland creation 1 Estimated Overall Cost includes design, contracted soil core sampling, materials, contracted labor, promotion and administrative costs (including outreach, education, contracts, grants, etc), pre-construction meetings, installation oversight and 1 year of operation and maintenance costs. 2 Total Est. Term Cost includes Overall Cost plus 30 years of maintenance and is divided by 30 years of TP treatment.

8 4 Methods Methods Selection of Subwatershed Before the subwatershed stormwater assessment begins, a process of identifying a high priority water body as a target takes place. Many factors are considered when choosing which subwatershed to assess for stormwater retrofits. Water quality monitoring data, non-degradation report modeling, and TMDL studies are just a few of the resources available to help determine which water bodies are a priority. In areas without clearly defined studies, such as TMDL or officially listed water bodies of concern, or where little or no monitoring data exist, metrics are used to score subwatersheds against each other. In large subwatersheds (e.g., greater than 2500 acres), a similar metric scoring is used to identify areas of concern, or focus areas, for a more detailed assessment. Subwatershed Assessment Methods The process used for this assessment is outlined below and was modified from the Center for Watershed Protection s Urban Stormwater Retrofit Practices, Manuals 2 and 3 (Schueler, 2005, 2007). Locally relevant design considerations were also included into the process (Minnesota Stormwater Manual). Step 1: Retrofit Scoping Retrofit scoping includes determining the objectives of the retrofits (volume reduction, target pollutants, etc) and the level of treatment desired. It involves meeting with local stormwater managers, city and watershed district staff to determine the issues in the subwatershed. This step also helps to define preferred retrofit treatment options and retrofit performance criteria. In order to create a manageable area to assess in large subwatersheds, a focus area may be determined. Step 2: Desktop Retrofit Analysis The desktop analysis involves computer-based scanning of the subwatershed for potential retrofit catchments and/or specific sites. This step also identifies areas that won t require further assessment for several reasons (e.g., sufficient existing treatment, lack of retrofitting space, etc.). Accurate GIS data are extremely valuable in conducting the desktop retrofit analysis. Some of the most important GIS layers include: 2-foot or finer topography, hydrology, soils, watershed/subwatershed boundaries, parcel boundaries, high-resolution aerial photography and the storm drainage infrastructure. Each catchment is initially investigated for several land position opportunities that are conducive to stormwater retrofitting (Table 1). Table 1 - Subwatershed Metrics and Potential Retrofit Project Site/Catchment Screening Metric Potential Retrofit Project Existing Ponds Open Space Roadway Culverts Outfalls Conveyance system Large Impervious Areas (campuses, commercial, parking) Neighborhoods Add storage and/or improve water quality by excavating pond bottom, modifying riser, adding an enhanced filtration bench, raising embankment, and/or modifying flow routing. New regional treatment (pond, bioretention). Add wetland or extended detention water quality treatment upstream. Split flows or add storage below outfalls if open space is available. Add or improve performance of existing swales, ditches and nonperennial streams. Stormwater treatment on site or in nearby open spaces. Utilize right of way, roadside ditches or curb-cut raingardens or filtering systems to treat stormwater before it enters storm drain network.

9 Methods 5 Pleasant Lake Desktop Assessment In this assessment, each catchment was initially defined using the newest delineations provided by the city of Annandale. Each catchment was scrutinized considering existing stormwater infrastructure, level of current treatment within any existing stormwater infrastructure, practicality of retrofitting, etc. After an initial field investigation, it was determined that catchments 11, 12, 15, 19, 20-29, 30 and 31 would provide the greatest possibilities for stormwater retrofitting and the remaining catchments were eliminated from further analysis. The elimination of the remaining catchments was due primarily to their relative isolated hydrologic nature (in regards to the lake), their existing level of treatment combined with limited to no BMP modification potential, or given their land use incompatibility to stormwater retrofitting. For practicality, catchments 21, 22, 23 and 25 were combined as one catchment and ID d as 23. For those catchments not eliminated from further analysis, each was subdivided into unique land use types (WINSLAMM codes; Appendix 1) using aerial imagery and visually confirmed and/or corrected via field observation. In nearly all cases, catchments were made up of several land use types. Because the current version of WINSLAMM allows for only one representative specific land use per land use family (i.e., Residential, Commercial, Industrial, Institutional, Other Urban Land Uses and Freeway), we aggregated specific land uses of similar family s into a customized land use file (Tables 2-4, next page). Results of this land use classification scheme were reviewed with aerial photography to roughly determine the accuracy of WINSLAMM s allocation of proportional area by individual source areas. Base-loading estimates were made for each catchment for several parameters: runoff volume, TSS, TP TKN, Metals (Figures 5-9). The Minneapolis airport data from the year 1959 was used as the representative average precipitation year in lieu of more locally-available precipitation data at the time of analysis. For the annual loading of metals (copper, lead, zinc and cadmium), an aggregated index of loading for each catchment was generated by normalizing the load to the highest sum on a scale of ).

10 6 Methods Table 2. Summary of land use makeup by catchment area.

11 Methods 7 Table 3. Classified versus modeled land uses by catchment

12 8 Methods Table 3 (cont). Classified versus modeled land uses by catchment

13 Methods 9 Tables 4 A-L. Development of aggregated new residential, undeveloped, industrial or commercial land use descriptions by catchment Table A Catchment 12, new residential and undeveloped NEW OSUD LDR Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas Table B Catchment 19, new residential and undeveloped NEW OSUD LDR SUB Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas

14 10 Methods Table C Catchment 20, new residential and undeveloped NEW OSUD MDRNA OSUD Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas Table D Catchment 23, new residential and undeveloped NEW OSUD MDRNA LDR Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas

15 Methods 11 Table E Catchment 24, new residential and undeveloped NEW OSUD MFRNA LDR OSUD PARK ADD.(1) Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas (1) An isolated water body and a portion of road separately delineated in the desktop analysis were defined as noted here. Table F Catchment 26, new residential and undeveloped NEW OSUD HRR OSUD CEM Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas

16 12 Methods Table G Catchment 26, new commercial NEW COM OFPK CDT Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas Table H Catchment 26, new institutional NEW INST INST SCH Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas

17 Methods 13 Table I Catchment 28, new residential and undeveloped NEW OSUD SUB Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas Table J Catchment 31, new residential and undeveloped NEW OSUD LDR OSUD Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas

18 14 Methods Table K Catchment 31, new commercial NEW COM OFPK SHOP Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas Table L Catchment 32, new residential and undeveloped NEW OSUD MDRNA OSUD Source Area/acres Roofs Paved Parking/Storage Unpaved Prkng/Storage Playground Driveways Sidewalks/Walks Street Area Large Landscaped Area Undeveloped Area Small Landscaped Area Isolated Area Other Pervious Area Other Dir Cnctd Imp Area Other Part Cnctd Imp Area Pavd Lane & Shldr Area Large Turf Areas

19 Methods 15 Table 5 WINSLAMM modeling parameters and files used in the assessment File Name Date Created/ Last Modified Created By Description CPZ: These files contain the sediment particle size distributions developed from monitored data. The files area used in the evaluation of control practices that rely upon particle settling for pollution control. NURP.CPZ 5/16/88 Pitt/UA Summarizes NURP outfall particle size data PPD (Pollutant Probability Distribution) files describe the pollutant concentrations found in source areas. USGS/DNR pollutant probability distribution file from Wisconsin WI_GEO01.ppd 11/26/02 Horwatich/USGS monitoring data. PRR (Particulate Residue Reduction) files describe the fraction of total particulates that remains in the drainage system (curbs and gutters, grass swales, and storm drainage) after rain events end due to deposition. This fraction of the total particulates does not reach the outfall, so the outfall values are reduced by the fraction indicated in the.prr file. USGS/DNR particulate residue reduction file for the delivery WI_DLV01.prr 7/8/01 Horwatich/USGS system from Wisconsin monitoring data. RSV (Runoff coefficient file). These coefficients, when multiplied by rain depths, land use source areas, and a conversion factor, determine the runoff volumes needed by WinSLAMM. WI_SL06 Dec06.rsv 12/18/06 Horwatich/USGS USGS/DNR runoff volumetric coefficient file from Wisconsin monitoring data. Use for all versions of WinSLAMM starting from v STD (Street Delivery File): These files describe the fraction of total particulates that are washed from the streets during rains, but are subsequently redeposited due to lack of energy in the flowing water. WI_Com Inst Indust Dec06.std WI_Res and Other Urban Dec06.std Freeway Dec06.std 12/12/06 Horwatich/USGS 12/07/06 Horwatich/USGS 7/12/05 Pitt/UA USGS/DNR street delivery file from Wisconsin monitoring data. Use for all versions of WinSLAMM starting from v for Industrial, Commercial and Institutional land uses. USGS/DNR street delivery file from Wisconsin monitoring data. Use for all versions of WinSLAMM starting from v for Residential and Other Urban land uses. Street delivery file developed to account for TSS reductions due to losses in a freeway delivery system based upon early USDOT research. Renamed Freeway.std PSC (Particulate Solids Concentration): Values in this file, when multiplied by source area runoff volumes and a conversion factor, calculate particulate solids loadings (lbs). USGS/DNR particulate solids concentration file from Wisconsin WI_AVG01.psc 11/26/02 Horwatich/USGS monitoring data. RAN (Rain Files): MN Minneapolis 59.RAN Parameter Start/End Date Winter Season Range Drainage System NA NA A n event-record of rainfall for the year 1959, considered as an average year, in the form of Start Date, Start Time, End Date, End Time and Rainfall (in inches). Settings Description Defines the modeling period in reference to the rain file data. In this case, the entire one year period was selected (i.e., 01/02/59-12/28/59). Set to begin on November 7 th and end on March 17 th. Set to Curb and gutter, valleys, or sealed swales in fair condition.

20 16 Methods Step 3: Retrofit Reconnaissance Investigation After identifying potential retrofit sites through this desktop search, a field investigation was conducted to evaluate each site. During the investigation, the drainage area and stormwater infrastructure mapping data were verified. Site constraints were assessed to determine the most feasible retrofit options (Table 6) as well as eliminate sites from consideration. The field investigation may have also revealed additional retrofit opportunities that could have gone unnoticed during the desktop search. Table 6 - Stormwater Treated Options for Retrofitting Area Best Management Treated Practice Potential Retrofit Project Extended Detention hr detention of stormwater with portions drying out between events (preferred over Wet Ponds). Mau include multiple cell design, infiltration benches, sand/peat/iron filter outlets and modified choker outlet features. Wet Ponds Permanent pool of standing water with new water displacing pooled water from previous event. Wetlands Depression less than 1-meter deep and designed to emulate wetland ecological functions. Residence times of several days to weeks. Best constructed off-line with low-flow bypass. Bioretention Use of native soil, soil microbe and plant processes to treat, evapotranspirate, and/or infiltrate stormwater runoff. Facilities can either be fully infiltrating, fully filtering or a combination thereof Filtering Filter runoff through engineered media and passing it through an under-drain. May consist of a combination of sand, soil, compost, peat, compost and iron. Infiltration A trench or sump that is rock-filled with no outlet that receives runoff. Stormwater is passed through a conveyance and pretreatment system before entering infiltration area. Swales A series of vegetated, open channel practices that can be designed to filter and/or infiltrate runoff. Other On-site, source-disconnect practices such as rain-leader raingardens, rain barrels, green roofs, cisterns, stormwater planters, dry wells or permeable pavements acres acres Step 4: Treatment Analysis/Cost Estimates Treatment analysis Sites most likely to be conducive to addressing the LGU goals and appear to be simple-to-moderate in design/install/maintenance considerations are chosen for a cost/benefit analysis in order to relatively compare catchments/sites. Treatment concepts are developed taking into account site constraints and the subwatershed treatment objectives. Projects involving complex stormwater treatment interactions or pose a risk for upstream flooding require the assistance of a certified engineer. Conceptual designs, at this phase of the design process, include a cost estimate and estimate of pollution reduction. Reported treatment levels are dependent upon optimal site selection and sizing.

21 Methods 17 Modeling of the site is done by one or more methods such as with P8, WINSLAMM or simple spreadsheet methods using the Rational Method. Event mean concentrations or sediment loading files (depending on data availability and model selection) are used for each catchment/site to estimate relative pollution loading of the existing conditions. The site s conceptual BMP design is modeled to then estimate varying levels of treatment by sizing and design element. This treatment model can also be used to properly size BMPs to meet LGU restoration objectives. Pleasant Lake Treatment Analysis For the Pleasant Lake treatment analysis, each catchment, and each parcel within them, was first assessed for BMP family type applicability given specific site constraints and soil types. Pedestrian and car traffic flow, parking needs, snow storage areas, obvious utility locations, existing landscaping, surface water runoff flow, project visibility, cues of care in relation to existing landscape maintenance, available space and several other factors dictated the selection of one or more potential BMPs for each site. A previous retrofit study (Bolton and Menck, Inc., 2004) was performed identifying 2 new pond retrofits: catchments 12 and 26. For both scenarios developed to concept phase by the previous study, we recreated the design parameters within WINSLAMM so that the removal estimates we used for relative comparison to other recommendations within this study were meaningful (it is not possible to compare results from one model to the next). This by no means suggests that the previous study s findings were inaccurate or invaluable. WINSLAMM 9.5 was used to model the pollutant removal efficiency of at least one retrofitting scenario and treatment level by assigning variable numbers of specific BMP types in each land use type. The sum of the combined treatment was considered and scaled to the 10%-30% TP-reduction from base loading conditions. Infiltration Rates County soils survey data was used to identify a modeling estimate for infiltrating BMP s. For each Land Use within a catchment receiving a specific BMP treatment, or at the outfall of the catchment, the survey documentation was referenced. The most limiting soil layer in the profile was selected to be representative of the site. If the limiting layer was found to be within 3-ft, overexcavation was considered in order to access the more rapidly draining sub layer. A tally of each limiting layer found in the area was used along with a mean bulk density estimate to determine an areaweighted infiltration rate (Appendix 2; Rawls, et al).

22 18 Methods Cost Estimates Each resulting BMP (by percent TP-removal dictated sizing) was then assigned estimated design, installation and first-year establishment-related maintenance costs given its ft 2 of treatment, or similar units (Table 7). An annual cost/tp-removed for each treatment level was then calculated for the lifecycle of said BMP which included promotional, administrative and life-cycle operations and maintenance costs. Table 7 -Average BMP Cost Estimates BMP Median Inst. Cost ($/sq ft) Marginal Annual Maintenance Cost (contracted) O & M Term Pond Retrofits $3.00 $500/acre 30 Extended Detention $5.00 $1000/acre 30 Design Cost ($70/hr) Installation Oversight Cost ($70/hr) 1 40% above $210 construction (3 visits) 3 $2800/acre $210 (3 visits) Wet Pond $5.00 $1000/acre 30 3 $2800/acre $210 (3 visits) Stormwater Wetland $5.00 $1000/acre 30 3 $2800/acre $210 (3 visits) Water Quality Swale 6 $12.00 $250/100 ln ft 30 $1120/100 ln ft $210 (3 visits) Cisterns $ $ NA $210 (3 visits) French Drain/Dry Well $ $ % above $210 construction (3 visits) Infiltration Basin $15.00 $500/acre 30 $1120/acre $210 (3 visits) Rain Barrels $ $25 30 NA $210 (3 visits) Structural Sand Filter (including peat, compost, iron amendments, or similar) 6 Impervious Cover Conversion $20.00 $250/25 ln ft 30 $300/25 ln ft $210 (3 visits) $20.00 $500/acre 30 $1120/acre $210 (3 visits) Stormwater Planter $27.00 $50/100 sq ft 30 20% above $210 construction (3 visits) Rain Leader Disconnect $ $25/150 sq ft 30 $280/100 sq ft $210 Raingardens (3 visits) Simple Bioretention (no $10.00 $0.75/sq ft 30 $840/1000 sq ft $210 engineered soils or (3 visits) under-drains, but w/curb cuts and forebays) Moderately Complex Bioretention (incl. engineered soils, underdrains, curb cuts, no retaining walls) Complex Bioretention (incl. engineered soils, under-drains, curb cuts, forebays, 2-3 ft retaining $12.00 $0.75/sq ft 30 $1120/1000 sq ft $210 (3 visits) $14.00 $0.75/sq ft 30 $1250/1000 sq ft $210 (3 visits) Total Installation Cost (Includes design & 1-yr maintenance) Design-dependent Drainage Areadependent calculation $14/sq ft $16/sq ft $15/sq ft $15/sq ft $25/cu ft $22/sq ft $20/sq ft $33/sq ft $6/sq ft $12/sq ft $15/sq ft $18/sq ft

23 Methods 19 Table 7 -Average BMP Cost Estimates BMP Median Inst. Cost ($/sq ft) Marginal Annual Maintenance Cost (contracted) O & M Term walls) Highly Complex Bioretention (incl. engineered soils, underdrains, curb cuts, forebays, 3-5 ft retaining walls) $16.00 $0.75/sq ft 30 Underground Sand Filter $65.00 $0.75/sq ft 30 Design Cost ($70/hr) Installation Oversight Cost ($70/hr) 4 $1400/1000 sq ft $210 (3 visits) Total Installation Cost (Includes design & 1-yr maintenance) $25/sq ft 1 40% above $210 $92/sq ft construction (3 visits) Stormwater Tree Pits $70.00 $0.75/sq ft % above $210 $100/sq ft construction (3 visits) Grass/Gravel Permeable $12.00 $0.75/sq ft % above $210 $18/sq ft Pavement (sand base) construction (3 visits) Permeable Asphalt $9.00 $0.75/sq ft % above $210 $14.00/sq ft (granite base) construction (3 visits) Permeable Concrete $12.00 $0.75/sq ft % above $210 $18/sq ft (granite base) construction (3 visits) Permeable Pavers $25.00 $0.75/sq ft % above $210 $36/sq ft (granite base) construction (3 visits) Extensive Green Roof $ $500/1000 sq ft % above $210 $320/sq ft construction (3 visits) Intensive Green Roof $ $750/1000 sq ft % above construction $210 (3 visits) $500/sq ft 1 Likely going to require a licensed, contacted engineer. 2 Assumed landowner, not contractor, will maintain. 3 LRP would only design off-line systems not requiring an engineer. For all projects requiring an engineer, assume engineering costs to be 40% above construction costs. 4 If multiple projects are slated, such as in a neighborhood retrofit, a design packet with templates and standard layouts, element elevations and components, planting plans and cross sections can be generalized, design costs can be reduced. 5 Not included in total installation cost (minimal). 5 Assumed to be 15 feet in width. Step 5: Evaluation and Ranking The results of treating each site by at least one stormwater BMP were analyzed for cost/treatment (30- yr) and ranked from the most cost-efficient level of treatment of TP to the least (see Executive Summary Table The Executive Summary table (page 3) summarizes that level of treatment for each catchment selected for either the lowest cost/treatment, or by the lowest levels that sum to the treatment goals identified by the City or Watershed District. The table is sorted in terms of the annual, 30-yr cost per pound of TP treated. However, it is recommended that the City consults the Value Index to, in a very real sense, address three public issues with the same dollar spent.

24 20 Subwatershed Results Subwatershed Overview The following illustrations describe the Pleasant Lake urban(-ized/-izing) subwatershed and its makeup. Figure 1 Catchments

25 Subwatershed Results 21 Figure 2 Land Use (see Table 2 for key or appendix 1 for detailed descriptions)

26 22 Subwatershed Results Figure 3 Soils distribution for the Pleasant Lake subwatershed study area See Appendix 3 for key to soil series descriptions

27 Subwatershed Results 23 Subwatershed Results Figure 5 - Annual Runoff Volume

28 24 Subwatershed Results Figure 6 - Annual Sediment Loading

29 Subwatershed Results 25 Figure 7 - Annual Phosphorous Loading

30 26 Subwatershed Results Figure 8 - Annual Nitrogen Loading

31 Subwatershed Results 27 Figure 9 - Annual Aggregated Metals Loading

32 28 Catchment Profiles Catchment Profiles The following pages provide catchment-specific information that was analyzed for stormwater BMP retrofit treatment at various levels. The recommended level of treatment reported in the Executive Summary Table is determined by weighing the cost-efficiency vs. site specific limitations and expected public buy-in (partnership). Each Catchment Profile includes a table showing the data relevant to various levels of treatment. The recommended treatment level (or expected success in establishing a certain amount of practices in the catchment) is highlighted. The table below is an example of such a table recommending the 43% treatment level to be achieved by modifying the existing pond with a enhanced iron sand filter. If the decision is made to move to the next level of treatment, by adding approximately 28 ea of 12 X 6 Tree Pits, then the expected treatment increases yet its value potentially decreases relative to other treatment levels found within other catchments in the study. EXISTING CONDITIONS RETROFIT OPTIONS Cost/Benefit Analysis Base Loading Treatment* Network Treatment By BMP Level 1 Level 2 Level 3 Existing BMP performance (%TP) 34% New Net % New Net % New Net % Treatment TP (lb/yr) % % NA TSS (lb/yr) % % NA Volume (acre-feet/yr) % 0% NA Square feet of practice (or, CU FT of storage for WP, ED, SW) BMP Type Wet Pond Pond Retrofits Stormwater Tree Pits Marginal Costs Materials/Labor/Design $5,000 $144,210 Unit Promotion & Admin Costs $500 $2,416 Total Project Cost $5,500 $179,006 Annual O&M $1,500 $1,080 Term Cost/lb/yr (30 yr) $318 $698

33 Catchment Profiles 29 This page intentionally left blank

34 30 Catchment Profiles Pleasant Lake 11 Existing Catchment Summary Model Inputs Acres 36.9 Parameter Input Volume (acre-feet/yr) 14.3 Primary Area Hydraulic Conductivity (in/hr) 2.5 TP (lb/yr) 23.8 WINSLAMM SLU file MDRNA TSS (lb/yr) WINSLAMM SLU file LI WINSLAMM SLU file OSUD DESCRIPTION This catchment is comprised of primarily medium-high density, single family housing units on quarter to half acre lots. Open space and turfs are ideally suited for formal bioretention retrofitting if willing landowners can give up these ideal locations and install Best Management Practices (BMP) to treat stormwater runoff. Sandy soils in these areas are conducive to infiltration and the treatment of stormwater runoff. RETROFIT RECOMMENDATION A combination of 2 to 6 tree planter/bioretention cells and partially-retaining walled bioretention cells taking street runoff from the curb line are recommended in this catchment. For modeling purposes, box practices were designed as an average top and bottom surface area between the typical. The dollar value for Moderately Complex was used to estimate cost for the 10% level suggesting that the first projects that should go in are the easiest of the regular bioretention cells (see illustration, following page). The 20% treatment level includes the more complex gardens including Tree Planters and, therefore reflects a higher cost/sq ft. The following design elements were used for modeling purposes, along with the WINSLAMM parameters discussed herein, and must be incorporated in any future design to meet this catchment s estimated value. Tree Box Curb-Cut Bioretention Various custom sizes (60 ft 2 avg) Sump forebay Vertical walls around entire perimeter 1-ft ponding depth 6-in curb and wall provide 6-in of potential freeboard No underdrain Amended, de-compacted soils Moderately Complex Raingarden/Curb Cut Bioretention 250 ft 2 top edge perimeter and project area / 160 ft 2 basin floor Retaining wall on back and possibly sides of garden Rainguardian forebay, or similar 1-ft ponding depth 6-in curb and wall provide 6-in of potential freeboard No underdrain Amended, de-compacted soils

35 Catchment Profiles 31 Cost/Benefit Analysis EXISTING CONDITIONS Base Loading Treatment Existing BMP performance (%TP) 0.0% New RETROFIT OPTIONS Marginal Network Treatment By BMP Level 1 (2 cells) New % New Level 2 (6 cells) Level 3 New % New New % Treatment TP (lb/yr) TSS (lb/yr) Volume (acre-feet/yr) Square feet of practice (or, CU FT of storage for WP, ED, SW) Marginal Costs BMP Type No Treatment Moderately Complex Bioretention Highly Complex Bioretention Materials/Labor/Design $7,710 $37,710 Unit Promotion & Admin Costs $565 $254 Total Project Cost $10,534 $41,513 Annual O&M $375 $1,125 NA Term Cost/lb/yr (30 yr) $301 $492

36 32 Catchment Profiles Pleasant Lake 12 Existing Catchment Summary Model Inputs Acres 41.6 Parameter Input Volume (acre-feet/yr) 30.1 Primary Area Hydraulic Conductivity (in/hr) 1.0 TP (lb/yr) 37.3 Secondary Area Hydraulic Conductivity (in/hr) TSS (lb/yr) WINSLAMM SLU file MDRNA WINSLAMM SLU file LDR WINSLAMM SLU file INST DESCRIPTION The area has several quarter acre parcels with vast areas of green space available along the road frontage. These parcels have adequate storage to treat stormwater runoff through the use of bioretention. Larger tracts of land exist in the subcatchment under the ownership of the City of Annandale. An open ditch is located in the center of the cities property with open space to allow expansion for storage and settling. RETROFIT RECOMMENDATION Strong consideration of retrofitting in new ponding and/or filtering storage within the park area (treating the drainage ditch as per Bolton and Menk, Inc. 2004) is recommended. If this option is not pursued, then we recommend retrofitting 4 bioretention cells taking street runoff from the curb line within the MDRNA portions (Willow Dr and Knollwood St) areas within this catchment. For modeling purposes Moderately Complex was used to estimate cost for the various treatment levels. The following design elements were used for modeling purposes, along with the WINSLAMM parameters discussed herein, and must be incorporated in any future design to meet this catchment s estimated value. Moderately Complex Raingarden/Curb Cut Bioretention 210 ft 2 top edge perimeter and project area / 100 ft 2 basin floor 3:1 side slopes, the majority without any retaining walls Rainguardian forebay, or similar 0.75-ft ponding depth 6-in curb and slopes/wall provide 6-in of potential freeboard No underdrain Amended, de-compacted soils

37 Catchment Profiles 33 Cost/Benefit Analysis EXISTING CONDITIONS Base Loading Treatment Existing BMP performance (%TP) 0.0% New RETROFIT OPTIONS Marginal Network Treatment By BMP Level 1 (4 cells) Level 2 Level 3 New % New New % New New % Treatment TP (lb/yr) TSS (lb/yr) Volume (acre-feet/yr) Square feet of practice (or, CU FT of storage for WP, ED, SW) 840 Marginal Costs BMP Type No Treatment Moderately Complex Bioretention Materials/Labor/Design $12,810 Unit Promotion & Admin Costs $387 Total Project Cost $16,060 NA NA Annual O&M $630 Term Cost/lb/yr (30 yr) $662

38 34 Catchment Profiles Pleasant Lake 15 Existing Catchment Summary Model Inputs Acres 36.9 Parameter Input Volume (acre-feet/yr) 29.2 Primary Area Hydraulic Conductivity (in/hr) 2.5 TP (lb/yr) 36.2 Secondary Area Hydraulic Conductivity (in/hr) TSS (lb/yr) WINSLAMM SLU file MDRNA WINSLAMM SLU file OFPK WINSLAMM SLU file INST DESCRIPTION This catchment is comprised of primarily medium-high density, single family housing units on quarter of an acre lots. Open space and turfs are ideally suited for formal bioretention retrofitting if willing landowners can give up these ideal locations and install landscaping. There is also a relatively large commercial property which contains large tracts of impervious surfaces between rooflines and pavement. A church property within the catchment currently has a water quality swale servicing its 2- acre parking lot. RETROFIT RECOMMENDATION No significant gain in retrofitting the church s parking lot presented itself during the analysis. We therefore recommend retrofitting between 2 to 12 bioretention cells taking street runoff from the curb line within the MDRNA portions (Willow Dr and Knollwood St) areas within this catchment. For modeling purposes Moderately Complex was used to estimate cost for the various treatment levels. The following design elements were used for modeling purposes, along with the WINSLAMM parameters discussed herein, and must be incorporated in any future design to meet this catchment s estimated value. Moderately Complex Raingarden/Curb Cut Bioretention 250 ft 2 top edge perimeter and project area / 160 ft 2 basin floor 3:1 side slopes, the majority without any retaining walls Rainguardian forebay, or similar 1.0-ft ponding depth 6-in curb and slopes/wall provide 6-in of potential freeboard No underdrain (although opportunity exists on several locations to tie into the existing storm sewer if soils prove unsuitable upon soil sampling) Amended, de-compacted soils

39 Catchment Profiles 35 Treatment Cost/Benefit Analysis EXISTING CONDITIONS Base Loading Treatment Existing BMP performance (%TP) 2.2% RETROFIT OPTIONS Marginal Network Treatment By BMP Level 1 (2 cells) Add. Treat. New % (total) Level 2 (6 Cells) Add. Treat. New % (total) Level 3 (12 cells) New New % TP (lb/yr) TSS (lb/yr) Volume (acre-feet/yr) Square feet of practice (or, CU FT of storage for WP, ED, SW) Marginal Costs BMP Type Water Quality Swale Moderately Complex Bioretention Moderately Complex Bioretention Moderately Complex Bioretention Materials/Labor/Design $7,710 $22,710 $45,210 Unit Promotion & Admin Costs $565 $254 $153 Total Project Cost $10,534 $26,513 $49,799 Annual O&M $375 $1,125 $2,250 Term Cost/lb/yr (30 yr) $259 $324 $395

40 36 Catchment Profiles Pleasant Lake 23 (21, 22, 23 & 25 combined) Existing Catchment Summary Model Inputs Acres 38.4 Parameter Input Volume (acre-feet/yr) 28.7 Primary Area Hydraulic Conductivity (in/hr) 2.5 TP (lb/yr) 36.8 WINSLAMM SLU file MDRWA TSS (lb/yr) WINSLAMM SLU file CDT WINSLAMM SLU file OSUD DESCRIPTION This catchment is comprised of primarily medium-high density, single family housing units on half acre lots. Open space and turfs are ideally suited for formal bioretention retrofitting. A large portion of this catchment is consumed by Annandale City Park. These grounds could be a prime location to treat stormwater runoff, educate the public, and attract wildlife. There is a dominant commercial, downtown area with a boulevard-sized road running from the highway all the way to the lake. Some medium density single family residential homes are located within the subcatchment and the public ball field is nearby. RETROFIT RECOMMENDATION We recommend retrofitting between 4 to 9 bioretention cells taking street runoff from the curb line within the residential areas within this catchment during the first phase of city stormwater retrofitting. After similar levels of treatment have been achieved throughout the City, moving into retrofitting 8 intersection bumps outs, to be designed as curb-cut raingardens, should be considered. Bump outs add the benefits of road surface reduction (reduction of pollutant loading), traffic-stilling at intersections (improved pedestrian safety) and aesthetic enhancement of the downtown area. Losses to parking can be compensated by switching the existing parallel parking to angled parking. For modeling purposes Moderately Complex was used to estimate cost for the 10-20% TP-treatment levels and w weighted average of costs was generated for the inclusion of the intersection bump outs. The following design elements were used for modeling purposes, along with the WINSLAMM parameters discussed herein, and must be incorporated in any future design to meet this catchment s estimated value. Moderately Complex Raingarden/Curb Cut Bioretention 250 ft 2 top edge perimeter and project area / 160 ft 2 basin floor 3:1 side slopes, the majority without any retaining walls Rainguardian forebay, or similar 1.0-ft ponding depth 6-in curb and slopes/wall provide 6-in of potential freeboard No underdrain (although opportunity exists on several locations to tie into the existing storm sewer if soils prove unsuitable upon soil sampling) Amended, de-compacted soils Intersection Bump out Bioretention 160 ft 2 top and bottom edge Rainguardian forebay, or similar 1.0-ft ponding depth 6-in curb and slopes/wall provide 6-in of potential freeboard No underdrain (although opportunity exists on several locations to tie into the existing storm sewer if soils prove unsuitable upon soil sampling) Amended, de-compacted soils

41 Catchment Profiles 37 Cost/Benefit Analysis EXISTING CONDITIONS Base Loading Treatment Level 1 (4 cells) Existing BMP performance (%TP) 0.0% New New % New RETROFIT OPTIONS Marginal Network Treatment By BMP Level 2 (9 cells) New % Level 3 (+8 bump outs) New New % Treatment TP (lb/yr) TSS (lb/yr) Volume (acre-feet/yr) Square feet of practice (or, CU FT of storage for WP, ED, SW) Marginal Costs BMP Type No Treatment Moderately Complex Bioretention Moderately Complex Bioretention +Intersection Bump Outs Materials/Labor/Design $15,210 $33,960 $70,600 Unit Promotion & Admin Costs $341 $189 $136 Total Project Cost $18,618 $38,205 $75,396 Annual O&M $750 $1,688 $2,648 Term Cost/lb/yr (30 yr) $351 $386 $481

42 38 Catchment Profiles Pleasant Lake 24 Existing Catchment Summary Model Inputs Acres Parameter Input Volume (acre-feet/yr) 24.7 Primary Area Hydraulic Conductivity (in/hr) 2.5 TP (lb/yr) 39.8 WINSLAMM SLU file MDRNA TSS (lb/yr) WINSLAMM SLU file LDR WINSLAMM SLU file MFRNA WINSLAMM SLU file PARK DESCRIPTION The large boulevard which starts south of downtown off the highway extends north through this catchment s western edge. This park is used heavily by the residents of Annandale and surrounding communities which could act as an excellent education resource tool and offers an opportunity to visually tie the downtown area to the lake as a uniform boulevard. The remaining proposed projects are to be constructed in medium density single family residential neighborhood on Cherry Avenue. The majority of catchment 24 is undeveloped/-able. We discuss treatment only within the urbanized areas. RETROFIT RECOMMENDATION We recommend retrofitting between 4 to 8 bioretention cells taking street runoff from the curb line within the residential areas within this catchment during the first phase of city stormwater retrofitting. After similar levels of treatment have been achieved throughout the City, moving into retrofitting 6 intersection bumps outs near the park, to be designed as curb-cut raingardens, should be considered. Bump outs add the benefits of road surface reduction (reduction of pollutant loading), traffic-stilling at intersections (improved pedestrian safety) and aesthetic enhancement of the downtown area. Losses to parking can be compensated by switching the existing parallel parking to angled parking. For modeling purposes Moderately Complex was used to estimate cost for the 10-20% TP-treatment levels and w weighted average of costs was generated for the inclusion of the intersection bump outs. The following design elements were used for modeling purposes, along with the WINSLAMM parameters discussed herein, and must be incorporated in any future design to meet this catchment s estimated value. Moderately Complex Raingarden/Curb Cut Bioretention 250 ft 2 top edge perimeter and project area / 160 ft 2 basin floor 3:1 side slopes, the majority without any retaining walls Rainguardian forebay, or similar 1.0-ft ponding depth 6-in curb and slopes/wall provide 6-in of potential freeboard No underdrain (although opportunity exists on several locations to tie into the existing storm sewer if soils prove unsuitable upon soil sampling) Amended, de-compacted soils Intersection Bump out Bioretention 160 ft 2 top and bottom edge Rainguardian forebay, or similar 1.0-ft ponding depth 6-in curb and slopes/wall provide 6-in of potential freeboard No underdrain (although opportunity exists on several locations to tie into the existing storm sewer if soils prove unsuitable upon soil sampling) Amended, de-compacted soils

43 Catchment Profiles 39 Cost/Benefit Analysis EXISTING CONDITIONS Base Loading Treatment RETROFIT OPTIONS Marginal Network Treatment By BMP Level 1 (4 cells) Level 2 (8 cells) Level 3 (+6 bump outs) Existing BMP performance (%TP) 0.0% New New % New New % New New % Treatment Marginal Costs TP (lb/yr) TSS (lb/yr) Volume (acre-feet/yr) Square feet of practice (or, CU FT of storage for WP, ED, SW) BMP Type No Treatment Moderately Complex Bioretention Moderately Complex Bioretention +Intersection Bump Outs Materials/Labor/Design $15,210 $30,210 $59,200 Unit Promotion & Admin Costs $341 $206 $154 Total Project Cost $18,618 $34,322 $63,773 Annual O&M $750 $1,500 $2,220 Term Cost/lb/yr (30 yr) $343 $326 $358

44 40 Catchment Profiles Pleasant Lake 26 Existing Catchment Summary Model Inputs Acres 87.6 Parameter Input Volume (acre-feet/yr) 76.0 Primary Area Hydraulic Conductivity (in/hr) 2.5 TP (lb/yr) 88.0 WINSLAMM SLU file MDRNA TSS (lb/yr) WINSLAMM SLU file HRR WINSLAMM SLU file OFPK WINSLAMM SLU file CDT WINSLAMM SLU file WINSLAMM SLU file WINSLAMM SLU file WINSLAMM SLU file SCH INST OSUD DESCRIPTION This subwatershed contains a topography which drains towards Pleasant Lake and has a long in conveyance run along the city street. This is a highly variable land-use area with both public and private land retrofitting options and should be considered a valuable project area in terms of highly-visible, educational opportunity projects. RETROFIT RECOMMENDATION Strong consideration of retrofitting in new ponding and/or filtering storage within the park area (treating the drainage ditch as per Bolton and Menk, Inc. 2004) is recommended. If this option is not pursued, then we recommend starting by retrofitting 2 practices: a large bioretention cell on the school property (intersection of Cherry Ave and Birch St) which would treat both the school s runoff and a portion of the Commercial Downtown area; and a very simple and effective double-street disconnect to a linear raingarden is possible along the ball-fields northern edge. Although less valuable relative to the rest of the projects identified in this and Wenk s study, other bioretention (curb-cut) options exist as well (see illustration, next page). In addition, the City of Annandale Fire Hall would be another option to place a BMP on public property with high visibility. This area has soils suitable for infiltration and plenty of green space for storage to treat stormwater runoff. For modeling purposes SImple was used to estimate cost for the various treatment levels. The following design elements were used for modeling purposes, along with the WINSLAMM parameters discussed herein, and must be incorporated in any future design to meet this catchment s estimated value. School s Simple Raingardens/Curb Cut Bioretention Ball Fields: 2000 ft 2 top edge perimeter / 1500 ft 2 basin floor; NW corner: 900 ft 2 / 540 ft 2 3:1 side slopes Rainguardian forebay, or similar Ball Fields: 1-ft ponding depth; NW corner: 0.5-ft 6-in curb and slopes and 6-in freeboard No underdrain Amended, de-compacted soils CEM

45 Catchment Profiles 41 Cost/Benefit Analysis EXISTING CONDITIONS Base Loading Treatment RETROFIT OPTIONS Marginal Network Treatment By BMP Level 1 Level 2 Level 3 Treatment Existing BMP performance (%TP) 0.0% TP (lb/yr) TSS (lb/yr) Volume (acre-feet/yr) Square feet of practice (or, CU FT of storage for WP, ED, SW) New New % New New % New New % 2900 BMP Type No Treatment *Simple Bioretention MA NA Marginal Costs Materials/Labor/Design $23,200 Unit Promotion & Admin Costs $157 Total Project Cost $27,747 Annual O&M $2,175 Term Cost/lb/yr (30 yr) $371 *It was assumed that school volunteers would spread delivered mulch and plant these projects thereby reducing the unit cost.

46 42 Catchment Profiles Pleasant Lake 27 Existing Catchment Summary Model Inputs Acres 65.2 Parameter Input Volume (acre-feet/yr) 59.3 Primary Area Hydraulic Conductivity (in/hr) 2.5 TP (lb/yr) 69.2 WINSLAMM SLU file SCH TSS (lb/yr) DESCRIPTION This site is primarily school (institutional) grounds in nature with a little residential cover type. It is highly impervious, comprised of large parking lots and buildings. Drainage patterns flow towards the city streets and fills the ditch located on the northern edge of the parking lot. There is somewhat limited open space to work with, but those available areas, in particular on the north side of the school, are nicely positioned to treat stormwater. This project area should be considered a valuable project area in terms of highly-visible, educational opportunity projects. RETROFIT RECOMMENDATION We recommend starting by retrofitting 2 bioretention practices along Hemlock St that service that street and the school s parking lots. Secondary retrofitting options along Park Street and perimeter buffers and/or raingardens along the southern edge of the property (treating surface runoff before entering the ditch system to the south) would provide value as well (not analyzed in this study). The following design elements were used for modeling purposes, along with the WINSLAMM parameters discussed herein, and must be incorporated in any future design to meet this catchment s estimated value. School s Simple Raingardens/Curb Cut Bioretention 2 ea ft 2 top edge perimeter / 715 ft 2 basin floor 3:1 side slopes Rainguardian forebay, or similar 1.5-ft ponding depth No underdrain Amended, de-compacted soils

47 Catchment Profiles 43 Cost/Benefit Analysis EXISTING CONDITIONS Base Loading Treatment RETROFIT OPTIONS Marginal Network Treatment By BMP Level 1 Level 2 Level 3 Existing BMP performance (%TP) 0.0% New New % New New % New New % Treatment TP (lb/yr) TSS (lb/yr) Volume (acre-feet/yr) Square feet of practice (or, CU FT of storage for WP, ED, SW) 2000 BMP Type No Treatment *Simple Bioretention NA NA Marginal Costs Materials/Labor/Design $16,000 Unit Promotion & Admin Costs $206 Total Project Cost $20,112 Annual O&M $1,500 Term Cost/lb/yr (30 yr) $294 *It was assumed that school volunteers would spread delivered mulch and plant these projects thereby reducing the unit cost.

48 44 Catchment Profiles Pleasant Lake 28 Existing Catchment Summary Model Inputs Acres 76.5 Parameter Input Volume (acre-feet/yr) 58.8 Primary Area Hydraulic Conductivity (in/hr) 1.5 TP (lb/yr) 61.9 WINSLAMM SLU file MOBH TSS (lb/yr) WINSLAMM SLU file SUB WINSLAMM SLU file OSUD DESCRIPTION This residential area is occupied by multiple small modular homes with extensive parking area. Impervious surfaces dominate the land use with open spaces with the exception of the area along Hemlock St. The current drainage network is undeveloped roadside swales with estimated little infiltration capacity. Although space is somewhat limited, there is potential to incorporate extensive BMP s to treat a large portion of stormwater runoff which currently travels untreated into the major ditch system along the catchment s southern edge. RETROFIT RECOMMENDATION We recommend retrofitting between 8 to 18 small bioretention cells taking runoff from the streets and parking areas within the residential areas of this catchment during the first phase of city stormwater retrofitting. In addition, in combination with at least 8 of the bioretention cells, retrofitting the existing drainage swale along Hemlock St by deeply ripping, then vegetating with Canada Bluejoint Grass, Prairie Cordgrass, Rice Cut Grass and/or Switch Grass would be valuable. For modeling purposes Moderately Complex was used to estimate cost for the 10-20% TP-treatment levels of the bioretention cells. Moderately Complex Raingardens/Curb Cut Bioretention 150 ft 2 top edge perimeter / 40 ft 2 basin floor 3:1 side slopes Rainguardian forebay, or similar 0.75-ft ponding depth New 6-in curb surrounding plant beds and slopes and 6-in freeboard No underdrain Amended, de-compacted soils Vegetated Swale Servicing 10-acres of catchment Total swale length = 1050 ln ft Bottom width 10 ft Side slopes 5:1 Longitudinal slope 0.02 (V/H) Swale retardence factor = B Grass height = 36-in Dynamic infiltration rate = 0.05 (in/hr)

49 Catchment Profiles 45 Treatment Cost/Benefit Analysis EXISTING CONDITIONS Base Loading Treatment RETROFIT OPTIONS Marginal Network Treatment By BMP Level 1 (8 RG+VS) Level 2 (18 RG+VS) Level 3 Existing BMP performance (%TP) 0.0% New New % New New % New New TP (lb/yr) TSS (lb/yr) Volume (acre-feet/yr) Square feet of practice (or, CU FT of storage for WP, ED, SW) Marginal Costs BMP Type No Treatment Moderately Complex Bioretention + Vegetated Swale Moderately Complex Bioretention + Vegetated Swale Materials/Labor/Design $40,950 $46,200 Unit Promotion & Admin Costs $57 $52 Total Project Cost $47,586 $53,057 Annual O&M $900 $2,025 Term Cost/lb/yr (30 yr) $380 $424 #DIV/0! Cost estimates are a reflection of pooling unit costs of two dissimilar practices together NA

50 46 Catchment Profiles Pleasant Lake 29 Existing Catchment Summary Model Inputs Acres 70.2 Parameter Input Volume (acre-feet/yr) 40.2 Primary Area Hydraulic Conductivity (in/hr) TP (lb/yr) 59.3 WINSLAMM SLU file 2.5 MDRN A TSS (lb/yr) WINSLAMM SLU file SCOM WINSLAMM SLU file INST WINSLAMM SLU file OSUD DESCRIPTION This area of Annandale consists of a predominately medium density residential population. There is currently adequate open space for new BMP installation. Large portions of impervious surfaces travel untreated into a neighboring sod farm which is transported through a ditch system into surrounding wetlands. RETROFIT RECOMMENDATION Primary consideration for retrofitting this catchment would be to open the curb line along Poplar Lane thereby allowing runoff from the street and contributing uplands to drain into the open area surrounding the ditch. The design of a shallow-ponding vegetated buffer area to the ditch would provide treatment benefits, but were beyond the scope of this analysis. More detailed site surveying and determination of easement allowance will be required before taking on the modeling effort. What is modeled for his catchment was allowances for the installation of 5 to 12 curb-cut bioretention cells servicing the residential areas. For modeling purposes Moderately Complex was used to estimate cost for the various treatment levels. The following design elements were used for modeling purposes, along with the WINSLAMM parameters discussed herein, and must be incorporated in any future design to meet this catchment s estimated value. Moderately Complex Raingarden/Curb Cut Bioretention 250 ft 2 top edge perimeter and project area / 160 ft 2 basin floor 3:1 side slopes, the majority without any retaining walls Rainguardian forebay, or similar 1.0-ft ponding depth 6-in curb and slopes/wall provide 6-in of potential freeboard No underdrain (although opportunity exists on several locations to tie into the existing storm sewer if soils prove unsuitable upon soil sampling) Amended, de-compacted soils

51 Catchment Profiles 47 Treatment Marginal Costs Cost/Benefit Analysis EXISTING CONDITIONS Base Loading Treatment RETROFIT OPTIONS Marginal Network Treatment By BMP Level 1 (5 cells) Level 2 (12 cells) Level 3 Existing BMP performance (%TP) 0.0% New New % New New % New New % TP (lb/yr) TSS (lb/yr) Volume (acre-feet/yr) Square feet of practice (or, CU FT of storage for WP, ED, SW) BMP Type No Treatment Moderately Complex Bioretention Moderately Complex Bioretention Materials/Labor/Design $18,960 $45,210 Unit Promotion & Admin Costs $290 $153 Total Project Cost $22,580 $49,799 Annual O&M $938 $2,250 NA Term Cost/lb/yr (30 yr) $286 $322

52 48 Catchment Profiles

53 Catchment Profiles 49 References Minnesota Stormwater Steering Committee Minnesota Stormwater Manual. Minnesota Pollution Control Agency. St. Paul, MN. Panuska, J Drainage System Connectedness for Urban Areas. Memo. Wisconsin Dept of Natural Resources. Madison, WI. Pitt, R., Voorees,J.and C.Burger WINSLAMM v9.4: Source Loading and Management Model for Windows. Rawls et. al Use of Soil Texture, Bulk Density, and Slope of the Water Retention Curve to Predict Saturated Hydraulic Conductivity. Transactions of the ASAE. Vol 41(4): St. Joseph, MI. Schueler et. al Methods to Develop Restoration Plans for Small Urban Watersheds. Manual 2, Urban Subwatershed Restoration Manual Series. Center for Watershed Protection. Ellicott City, MD. Schueler et. al Urban Stormwater Retrofit Practices. Manual 3, Urban Subwatershed Restoration Manual Series. Center for Watershed Protection. Ellicott City, MD. USDA Urban Hydrology for Small Watersheds TR-55. Second Edition. Washington, DC. Walker, W.W P8: Urban Catchment Model, V 3.4. Developed for the USEPA, Minnesota PCA and the Wisconsin DNR. Wenck Associates, Inc City of Stillwater Lake Management Plans Lily Lake and McKusick Lake. Prepared for City of Stillwater and Brown s Creek Watershed District. Stillwater, Minnesota.

54 50 Appendices Appendix Appendix 1 WINSLAMM Standard Land Use Codes