Appendices - FB Environmental · pipes will then carry the water into the dry extended detention...
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WHITTEN BROOK WATERSHED RESTORATION PLAN Appendices Skowhegan Conservation Commission March 2011
Transcript of Appendices - FB Environmental · pipes will then carry the water into the dry extended detention...
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WHITTEN BROOK
WATERSHED RESTORATION PLAN Appendices
Skowhegan Conservation Commission
March 2011
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APPENDICES Appendix 1. Watershed Maps ..............................................................................................49
Map 1. Topography ....................................................................................................49
Map 2. Soils ...............................................................................................................50
Map 3. Soil Erodibility ...............................................................................................51
Map 4. Surficial Geology ...........................................................................................52
Map 5. Water Resources ............................................................................................53
Map 6. Land Use ........................................................................................................54
Map 7. Conservation Lands .......................................................................................55
Map 8. RRI Sites (Upper Madison Avenue Catchment) ............................................56
Map 9. RRI Sites (Lower Madison Ave Catchment) ..................................................57
Map 10. Road Jurisdiction .........................................................................................58
Appendix 2. Stormwater BMPs for Urban Watersheds .......................................................59
Appendix 3. List of Prioritized Stormwater Retrofit Sites...................................................61
Appendix 4. RRI Site Characteristics for Whitten Brook ....................................................63
Appendix 5. Methods for Calculating Percent of IC Treated and Nutrient Reductions ......64
Appendix 6. Estimated Pollutant Loading and Reduction Calculations for RRI Sites
in the Whitten Brook Watershed .....................................................................70
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Map 1
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Map 2
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Map 3
52 Map 4
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Map 5
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Map 6
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Map 7
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Map 8
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Map 9
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Map 10
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Bioretention/Biofilter: These shallow vegetated areas retain and filter stormwater runoff from impervious surfaces. Once stormwater infil-trates through the bioretention area, the water can be directed back into an existing storm drain, or back to the stream through a perforated pipe, allowing for additional subsurface treatment. Stormwater reaches the stream at a slower rate when bioretention is used thereby reducing pol-lutants and erosion along the stream bank.
Culvert/Outfall Armoring: If not properly installed, erosion can oc-cur around the openings of culverts and stormwater outfall pipes. This erosion poses a threat to stream water quality because the sediments and nutrients in the soil (such as phosphorus) go directly into the stream. The term “armoring” refers to the placement of rip-rap, or large angular stones, around the opening of a culvert or pipe. Rip-rap pro-tects the water by holding soil in its place, even during severe storm events.
Ditch Maintenance: Ditches should be lined with rip-rap (angular stones) or grassed-lined to reduce the potential for ditch erosion. Check dams, which are essentially piles of larger rocks creating a small dam across the ditch in varying intervals, are useful to prevent ditch erosion because they slow down the velocity of the water and trap sediment.
Dry Extended Detention Basin: These are large excavated depres-sions with raised outlet structures that are generally grass lined. The basins are constructed to withhold runoff from a specific catchment area, for a set period of time (e.g., 24 hours). Typically, a large area of impervious surface will have runoff collected in catchbasins, storm pipes will then carry the water into the dry extended detention basin, instead of sending it directly to a stream. When sized and constructed properly, dry extended detention basins can provide valuable peak flow volume reduction for urban streams, but must be designed properly in order to provide adequate reduction of high runoff temperatures. Permeable Pavers: Permeable pavers can serve as a replacement for concrete in walkways and patios as well as pavement in driveways and parking lots. These blocks reduce stormwater runoff by allowing rain-water to pass through them into the underlying soil. Pavers offer the same functional capabilities as typical impervious surfaces such as pavement or concrete, while reducing the negative impact that storm-water has on stream health.
Bioretention Area (Source: Urban Sub-watershed Restoration manual 3, CWP, 2007.)
Armored Culvert (Source: Tribal Habitat Conference Blog, blogs.nwifc.org.)
Appendix 2: Stormwater Best Management Practices (BMPs) for Urban Watersheds
Rock-lined Ditch with Check Dams (Source: lakecountyohio.gov)
Permeable Pavers on a Walkway (Source: pavingstonesupply.com )
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Rain Garden: These man-made shallow depressions in the soil are designed to capture and infiltrate stormwater flowing off impervious surfaces. Rain gardens are typically planted with native plants. Rain gardens are aesthetically and functionally appealing. By capturing and infiltrating runoff these gardens help to remove pollutants from storm-water and reduce stormwater runoff volume.
Regrade Pavement: Regrading pavement in parking lots or drive-ways redirects stormwater into vegetated areas or other stormwater treatment alternatives rather than running down adjacent roads, storm drains, or nearby ditches, all of which lead to the stream. This BMP is a good option for paved areas because it reduces overall pollutant load and volume of stormwater reaching the stream during storm events.
Remove Pavement: If pavement is never or very rarely used, remov-ing it will have a positive effect on the water quality of the stream. By replacing pavement with vegetation the potential pollutants being washed off the pavement would infiltrate into the soil, rather than washing into the stream. Tree Box Filter: These are manufactured concrete structures that are installed along a parking lot or street. They are designed to control stormwater runoff and filter pollutants and are typically connected to existing stormwater pipes. Water from the impervious area enters the filter base, much like a catch basin. The roots and filter media in the base help to remove pollutants from stormwater before it reaches the stream. Vegetative Buffer: Having a buffer, or naturally vegetated area along the stream corridor, is a simple and effective means of protecting stream water quality. Native plants, shrubs and trees growing along the stream help reduce bank erosion, increase stormwater infiltration, and offer shade to the stream which moderates temperature in runoff. Buffers can be created by planting native trees and shrubs along the stream corridor. These plants can be found at most local nurseries. Water Diverters: Stormwater running directly off an impervious sur-face into a catch basin or ditch receives minimal treatment before reaching the stream. Water diverters force stormwater into a treatment system before entering the stream allowing for pollutant removal as well as flow and volume control. Examples of water diverters include appropriately placed speed bumps, sand filled fire hoses or pavement curbs.
Pavement Removal (Source: OregonLive.com)
Rain Garden (Source: Herring Run Water-shed Association, baywatersheds.org.)
Appendix 2: Stormwater Best Management Practices (BMPs) for Urban Watersheds, cont.
Tree Box Filter (Source: Bohler Engineering, bohlereng.com).
Vegetated Buffer (Source: treevitalize.net).
Appendix 3: List of Prioritized Stormwater Retrofit Sites for the Whitten Brook Watershed
Site ID Proposed BMPsValue to Stream
(1 High, 5 Low) 1
Ease of Implementation (A high, E Low)
Overall Priority (HH=Highest)
BasinDivert pipe from CB to existing pond, reconstruct outlet structure, dredge pond
1 A HH
2B‐10
Define parking for 6‐7 cars; remove asphalt from beside north end of building & re‐vegetate w/conservation mix. Install diverter to rain garden. Fence seeded area to limit compaction.
1 A HH
2BW‐8Install tree boxes to capture runoff from 201 and adjacent res/com homes & driveways
1 ? HH
Tree
Boxes/2012Install tree boxes to capture runoff from 201 and adjacent res/com homes & driveways
1 ? HH
2CW‐1 Two tree boxes ‐ one on each side of storm drain 1 ? HH
1AE‐6Hotspot ‐ no containment for spills. Install small rain garden or vegetative planter near road.
1 E H
2BW‐7Drop inlet or curb cut to rain garden where Boynton's sign is located or tree box filter w/underdrain pipe to storm drain
1 ? H
1BW‐2ARemove pavement and re‐vegetate area in front of parking between road & spots 300 sq. ft
2 A H
2AW‐2Install diverter to bioretention in grassy area @ front and behind where new pavement will be
2 B H
2BW‐5
1. Remove pavement (broken) on south‐east corner of Whitten Ct along cement retaining wall. Design would require engineering not to destabilize existing culvert that connects Whitten Bk.
2 C Hculvert that connects Whitten Bk. 2. For gas station‐catch basin. 3. For storm drain on road ‐ tree b
2CW‐3Rain garden in area adjacent to sign; tree box filter above storm drain on Madison Ave.
2 C? H
2CE‐1Install bioretention / grass swale islands to define parking areas and breakup pavement; not to reduce parking area.
2 A town/ D business H
2CE‐4Install rain garden in the center to define parking areas better.
2 D M/H
1A‐2Remove pavement, replace with vegetation or permeable pavers.
3 D M
1AE‐3Vegetate no parking area; reduce parking or use permeable pavers.
3 C M
1AE‐7 Remove composted grass and install rain garden. 3 C M
1C‐3AInstall vegetative buffers at entrance and exits on both sides of building
3 D M
2AE‐1 Install a grassed swale at end of road 3 C M
2BW‐6 Install tree box above storm drain 3 C M
Appendix 3: List of Prioritized Stormwater Retrofit Sites for the Whitten Brook Watershed
Site ID Proposed BMPsValue to Stream
(1 High, 5 Low) 1
Ease of Implementation (A high, E Low)
Overall Priority (HH=Highest)
2BW‐9
Reduce impervious area by creating vegetated area in center along east side where current designated parking spots are located. Grade such that runoff flow to vegetated area (no curb).
3 D M
2BE‐1Install drip line trench & plants between buildings and paved parking
3 D M
2CE‐3 Extend garden feature to collect all roof drainage 3 A M
2D‐1Remove pavement adjacent to the stream and install buffer. Remove 30 x 40' of pavement adjacent to white garage. Rototill to loosen packed soil.
3 B M
1AW‐11. Install Tree box filters @ edge of lot‐length of lot.2. Underground storage w/use of isolator row (50% removal)
4 B M
1AE‐4Separate parking with veg. plantings/beds; reduce paved area; about 200 sq ft to remediate.
4 C L
1AE‐5 Install grassed swale in ROW. 4 C L
1AE‐8Remove parking pavement at side of building ‐ 6,000 sq ft treatment area; re‐vegetate
4 D L
1AW‐2
1. Install rain garden in eastern corner ‐ remove 2nd drive.2. Permeable pavers3. Install swale in pavement to drain to bioretention
4 ? L
areas4. Alt tree box filter
1B‐1A Biofilter along southern edge of pavement 4 D L
2BW‐5aRepair eroding culvert/protect outlet & stream; find source of black water pipe.
4 ? L
2CW‐2 Install tree box filter above storm drain 4 C? L2AW‐1 Install Tree Box Filter 5 ? L
1A‐1Utilize existing grassy area. Regrade pavement towards treatment area.
5 E L
1AW‐3Use bioretention around storm drains ‐ infiltrating bioretention cell w/underdrain
5 D L
2CE‐2Remove pavement or replace with permeable pavers in area periodically for overflow parking
Not Feasible Not Feasible L1 Ratings assume that the Dry Extended Detention Basin (Basin) will be installed.
2 GIS analysis depicts a total of 30 catch basins within the watershed along Rt. 201. There are a total of 10 TB filters in the RRI survey. Three ofthese 10 are NOT along Rt. 201. Therefore, 7 TB filters were subtracted from the total number of catch basins along Rt. 201. Therefore, 23 TB filterswere used for these calculations.
Appendix 4: RRI Site Characteristics for Whitten Brook
Site IDImpervious Area (sq ft)
Estimated Runoff Treated on Site (%)
Estimated Low Cost Per Site
Estimated High Cost Per Site
1A‐1 5,130 60 $2,870 $2,870
1A‐2 10,688 60 $8,552 $10,157
1AE‐3 26,220 55 $20,972 $24,904
1AE‐4 3,960 60 $1,600 $1,900
1AE‐5 3,000 20 $1,500 $2,500
1AE‐6 21,600 92 $32,400 $38,880
1AE‐7 2,000 92 $4,000 $4,800
1AE‐8 13,500 70 $16,500 $25,500
1AW‐1 17,500 95 $63,025 $81,745
1AW‐2 950 98 $9,761 $16,161
1AW‐3 125,000 60 $112,000 $170,000
1B‐1A 25,000 81 $43,543 $82,085
1BW‐2A 10,000 50 $2,400 $2,850
1C‐3A 40,000 25 $8,000 $9,500
2AW‐1 11,400 90 $6,000 $12,000
2AW‐2 15,000 81 $28,125 $45,000
2AE‐1 800 20 $1,500 $2,500
2BW‐5 15,000 95 $33,225 $39,225
2BW‐5a N/A N/A $3,200 $3,200
2BW‐6 5,000 90 $6,000 $12,000
2BW‐7 9,000 97 $21,000 $29,700
2BW‐8 TBD 90 $12,000 $24,000
2BW‐9 8,000 65 $8,000 $9,500
2B‐10 49,005 71 $79,000 $94,000
2BE‐1 5,400 92 $3,630 $4,155
2CW‐1 3,325 90 $6,000 $12,000
2CW‐2 11,880 90 $6,000 $12,000
2CW‐3 9,000 97 $19,000 $28,200
2CE‐1 11,020 20 $1,500 $2,500
2CE‐2 1,000 15 $2,722 $2,722
2CE‐3 2,000 25 $600 $825
2CE‐4 12,000 92 $18,000 $21,600
2D‐1 4,000 70 $9,600 $10,500
Basin1 358,499 90 $70,000 $100,000
Tree Boxes2 TBD 90 $138,000 $276,000
2 GIS analysis depicts a total of 30 catch basins within the watershed along Rt. 201. There are a total of 10 TB filters in the RRI survey. Three of these 10 are NOT along Rt. 201. Therefore, 7 TB filters were subtracted from the total number of catch basins along 201. Therefore, 23 TB filters were used for these calculations.
1 There are 15.5 acres of impervious draining to the No. Madison Ave outfall, where the proposed extended detention basin is located. The sq ft of IC sent to this BMP accounts for the 7.27 acres of IC within this catchment already being treated by other BMPs. The number 358,499 is the 8.23 acres of IC that would go untreated within this catchment without the extended detention basin.
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Appendix 5: Methods for Calculating Percent of IC Treated
and Nutrient Reductions
The methodology employed by FB Environmental to calculate the estimated annual runoff volume treated and nutrient reductions at the 35 RRI sites in the Whitten Brook watershed is described below.
SOIL SUITABILITY
The Whitten Brook watershed is dominated by Madawaska soils (type B). Research into the infiltration rate for Madawaska soils found that the Ksat was estimated at 0.6 inches / hour in the upper horizon to as much as 20.0 inches / hour in the lower horizon. This is a fairly well drained soil.1 The medium high to high infiltration rate for this soil was taken into account when assigning a percentage of runoff volume treated to the BMPs.
RESEARCH – FLOW REDUCTION
Literature research provided information on the estimated annual percentage of runoff volume treated by BMPs recommended for the RRI sites, the following BMP types were researched;
• bioretention/filtration
• pervious pavers/ pavement
• tree box filters
• rain gardens
• sending runoff to vegetated areas
Attachment 1 documents the findings from this research, while Attachment 2 lists the sources.
The literature research provided the numbers that would be used to calculate the percentage of IC each BMP treated on its site. For example, one source estimated that properly sized rain gardens in well drained soils (such as Madawaska soils) could treat the runoff on a site by 90%, while another estimated this rate to be 85-94%, and another estimated the rate to be 99%. Therefore, the number that was applied to rain gardens, when sized properly, was 92%, an average of all these rates.
For several of the BMPs where there was a range of values within the research, in these cases an average of the values was used. The numbers used in the calculations are provided below.
• Bioretention – 81%
• Pervious Pavers / Pavement – 72%
1 The Society of Soil Scientists of Northern New England "Ksat Values for New Hampshire Soils" SSSNNE Special Publication No. 5, September, 2009 available online at: http://www.sssnne.org/KsatNH.pdf. Accessed online on October 7, 2010
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• Tree Box Filters – 90%
• Rain Gardens – 92%
• Vegetation – 50 – 75% depending on vegetation / IC ratio
Much of this research also suggested optimum BMP size to IC drainage area ratios. For example, a rain garden’s surface area should be 20% of its drainage area for optimum runoff volume treated.2 These numbers were taken into account when calculating the cost for each BMP, since most BMP cost estimates were based off of sq ft of rain garden constructed etc.
CALCULATING PERCENTAGE OF IC TREATED
1. The estimated sq ft of IC at each treatment site was determined.
2. The BMP(s) recommended at the site was / were considered and an estimate for area of IC treated on each site was calculated.
a. If there was only one BMP on the site, the percentage of runoff treated by the BMP (taken from the literature research) was multiplied by the IC area. This provided an area of IC treated annually on the site.
b. If there was more than one BMP, the cumulative percentage of runoff treated by all BMPs on the site (taken from the literature research) was multiplied by the IC area. This provided an area of IC annually treated on site.
3. The estimated IC from all of the sites was summed in sq ft and then converted to acres.
4. The estimated IC annually treated on all sites was summed and converted to acres.
5. Using these numbers, the estimated annual percentage of IC treated on all of the sites was determined. (IC treated/IC total) * 100 = % of IC treated from all sites
CALCULATING NUTRIENT REDUCTIONS: BMP PERFORMANCE EXTRAPOLATION TOOL
The nutrient reductions were calculated with the aid of the “BMP Performance Extrapolation Tool (BMP-PET) for New England.” This was provided to FBE by EPA. To use the tool:
1. Select the source area where your BMP will be installed:
a. Commercial, Industrial, High Density Residential, Low Density Residential, Medium Density Residential
2. Select the BMP type you will be installing:
2 Hinman, C. and Beyerlein, D "Modeling Assumptions and Results for the Western Washington Rain Garden Handbook" Technical Memorandum, Washington State University, Tacoma, WA, 2007 available online at: www.pierce.wsu.edu/lid/raingarden/RainGardenFlowControlModeling.pdf , accessed online on October 25, 2010
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a. Bio-retention, Dry Pond, Glass swale, Gravel wetland, Infiltration basin-static method, Infiltration trench, porous pavement, or wet pond
3. Select the pollutant you would like to get the removal efficiency for:
a. Total Phosphorous (TP), Total Suspended Solids (TSS), or Total Zinc (Zn)
4. For the infiltration basin-static method and infiltration trench you can select the infiltration rate in inches / hour), this does not apply to any other BMP types in this tool.
5. For the porous pavement you can select the depth (in inches) of your filter course, this does not apply to any other BMP types in this tool
6. You then specify A or B:
a. The specific size of BMP; by selecting the depth of runoff it will be built to treat (between 0 and 2 inches).
b. Specific target BMP removal efficiency for the pollutant (between 0 – 100%)
7. Click the button “extrapolate from curves”
8. If you chose category A (size of BMP) then you will receive a number corresponding to the BMP removal efficiency for the specific nutrient you chose.
9. If you chose category B (target removal efficiency) you will receive the corresponding BMP size (in depth of runoff it should be built to treat).
This was done for all of the BMPs located in the RRI sites, except for Tree Box Filters (because they were not included in the tool). The source area for each BMP on every site was selected as commercial. The tool was run three times for each BMP to extrapolate the removal efficiency for; TP, TSS, and Zn. The tool was run for each BMP using category A with a depth of one inch. The following assumptions were made:
• Removal efficiencies for porous pavement were equivalent to pervious pavers and when pervious pavers were recommended the tool was used based off of porous pavement.
• Removal efficiencies for bio-retention were equivalent to rain gardens and when rain gardens were recommended the tool was used based off of bio-retention.
• Removal efficiencies for grass swales were equivalent to vegetation and when vegetation was recommended the tool was used based off of grass swales.
CALCULATING NUTRIENT REDUCTIONS: FOR EACH SITE AND ALL SITES
The removal efficiencies generated for each BMP were then placed into a spreadsheet in a row corresponding to the BMP or site and the removal efficiencies in a column under the corresponding pollutant type.
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• If there was more than one BMP recommended for a site the highest removal efficiency generated for each pollutant type was used in the calculation.
• The removal efficiencies for Tree Box Filters came from the same source as the annual percentage of runoff treated (UDT, information provided in Attachment 2). The numbers were; TSS: 85%, TP: 74%, and Zn: 82%
Annual loads (in lb/acre-year) of the three pollutants considered were gathered from a document prepared for EPA by Tetra Tech titled “Stormwater Best Management Practices (BMP) Performance Analysis.” The numbers used for each site were from a commercial source; TSS: 1117.77 lb/acre-year, TP: 1.66 lb/acre-year, and Zn: 2.33 lb/acre-year
1. These numbers were then multiplied by the overall acreage of IC on each site to get an estimated load for each pollutant from each site in lb/acre-year.
2. The load for each site was then multiplied by the corresponding removal efficiency for each pollutant type to obtain an estimated reduction from each site in lb/acre-year.
3. The estimated loads on each site were summed for each pollutant type.
4. The estimated load reduction on each site was summed for each pollutant type.
5. An estimated percent reduction in each pollutant was then calculated.
a. Ex. (SUM TSS Reduction / SUM TSS Load) * 100 = % Reduction in TSS from all Sites.
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Attachment 1: Annual Percentage of Runoff Volume Treated
Proposed BMP % of Annual Runoff Treated Notes
(Source)
Bioretention / Filtration
82 (1) This number is based on a specific system built at the UNH Stormwater Center. The bioretention's total area was 272 square feet and the catchment area was 1 acre.
80 (4)
Based on designs that rely of full infiltration. Given the type B soils in the watershed, bioretention would be designed for full infiltration. If an underdrain was necessary the subsequent runoff treated would be significantly lower.
52 to 56 (5) Based on a bioretention system installed in poorly drained soils where an underdrain was needed to transport runoff that was unable to infiltrate into soils.
Pervious Pavers / Pavement
75 (4)
Based on designs that rely of full infiltration. Given the type B soils in the watershed, pervious pavement would be designed for full infiltration. If an underdrain was necessary the subsequent runoff treated would be around 45%.
72 (7) Based on pervious paver driveway. The infiltration rate for the pervious pavers was measured at 11.2 cm/hour.
68 (2) Based on porous asphalt installation at UNH Stormwater Center. The system is installed over clay soils will naturally poor infiltration. Surface area is 5,200 square feet and catchment area is 5,500 square feet.
Tree Box Filters 90 (3) Based on a 6’X6’ Filterra tree box filter system. When sized to treat ¼ acre it will treat around 90% of the annual runoff volume.
Rain Gardens
99 (6) Rain garden designed to treat 2.54 cm or 1in of runoff in well drained soils. If an underdrain is necessary to transport water off site runoff reduction would be much less.
85 to 94 (10) When rain garden surface area is 20% of the impervious area.
90 (9) When conditions are initially dry and rain gardens are between 100 and 300 square feet.
Sending Runoff to Vegetated Area:
Pavement Regrading Water Diverter
50 to 75 (4)
Any of the associated BMPs that send runoff to a vegetated area could expect a runoff reduction. The less concentrated the runoff (such as sheet flow), less runoff volume and the higher the infiltration rate of the soil, will lead to a greater runoff reduction.
Whitten Brook's watershed is dominated by Madawaska soils. Madawaska soils are in Hydrologic Soil Group B. These soil types have moderately low runoff potential when thoroughly wet. (8)
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Attachment 2: Annual Percentage Treated - Sources
Source ID Reference
1 University of New Hampshire Stormwater Center, Bioretention System (Bio II), Durham, NH, 2008 available online at: http://www.unh.edu/erg/cstev/fact_sheets/bio_ii_fact_sheet_08.pdf. Accessed online on October 18, 2010.
2 University of New Hampshire Stormwater Center, Porous Asphalt, Durham, NH, 2008 available online at: http://www.unh.edu/erg/cstev/fact_sheets/pa_fact_sheet_08.pdf. Accessed online on October 18, 2010.
3 Urban Design Tools, Low Impact Development Techniques, “Tree Box Filter Summary Table” available online at: http://www.lid-stormwater.net/treeboxfilter_sizing.htm Accessed online on October 24, 2010.
4 Hirschman, D. Collins, K. and Schueler, T., Technical Memorandum: The Runoff Reduction Method, Appendix A, The Center For Watershed Protection, Ellicot City, ME. 18 April, 2008. B1-B11.
5 Hunt, W. A. Jarret, J. Smith and L. Sharkey. 2006. Evaluating bioretention hydrology and nutrient removal at three field sites in North Carolina. Journal of Irrigation and Drainage Engineering. 6: 600-612.
6 Dietz, M. and J. Clausen. 2006. Saturation to improve pollutant retention in a rain garden. Environmental Science and Technology. 40(4): 1335-13340.
7 Gilbert, J. and J. Clausen. 2006. Stormwater runoff quality and quantity from asphalt, paver and crushed stone driveways in Connecticut. Water Research 40: 826-832.
8 The Society of Soil Scientists of Northern New England "Ksat Values for New Hampshire Soils" SSSNNE Special Publication No. 5, September, 2009 available online at: http://www.sssnne.org/KsatNH.pdf. Accessed online on October 7, 2010.
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Charles River Watershed Association, Low Impact Best Management Practice (BMP) Information Sheet: Rain Gardens, Weston, MA, 2008 available online at: http://www.crwa.org/projects/bmpfactsheets/crwa_raingarden.pdf , Accessed online on October 25, 2010.
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Hinman, C. and Beyerlein, D "Modeling Assumptions and Results for the Western Washington Rain Garden Handbook" Technical Memorandum, Washington State University, Tacoma, WA, 2007 available online at: www.pierce.wsu.edu/lid/raingarden/RainGardenFlowControlModeling.pdf , accessed online on October 25, 2010.
Appendix 6: Estimated Pollutant Loading and Reduction Calculations for RRI Sites in the Whitten Brook Watershed
Site IDEst. IC (Acres)
% Reduction TSS
% Reduction TP
% Reduction Zn
TSS Load (lb/acre‐year)
TP Load (lb/acre‐year)
Zn Load (lb/acre‐year)
Reduction TSS (lb/acre‐year)
Reduction TP (lb/acre‐year)
Reduction Zn (lb/acre‐year)
1A‐1 0.12 80 21 95 131.64 0.20 0.27 105.31 0.04 0.261A‐2 0.25 80 21 95 274.25 0.41 0.57 219.40 0.09 0.541AE‐3 0.60 80 21 95 672.82 1.00 1.40 538.25 0.21 1.331AE‐4 0.09 80 21 95 101.62 0.15 0.21 81.29 0.03 0.201AE‐5 0.07 80 21 95 76.98 0.11 0.16 61.59 0.02 0.151AE‐6 0.50 99 76 97 554.27 0.82 1.16 548.72 0.63 1.121AE‐7 0.05 99 76 97 51.32 0.08 0.11 50.81 0.06 0.101AE‐8 0.31 80 21 95 346.42 0.51 0.72 277.13 0.11 0.691AW‐1 0.40 85 74 82 449.06 0.67 0.94 381.70 0.49 0.771AW‐2 0.02 99 76 97 24.38 0.04 0.05 24.13 0.03 0.051AW‐3 2.87 99 76 97 3207.56 4.76 6.69 3175.48 3.62 6.491B‐1A 0.57 99 76 97 641.51 0.95 1.34 635.10 0.72 1.301BW‐2A 0.23 80 21 95 256.60 0.38 0.53 205.28 0.08 0.511C‐3A 0.92 80 21 95 1026.42 1.52 2.14 821.13 0.32 2.032AW‐1 0.26 85 21 82 292.53 0.43 0.61 248.65 0.09 0.502AW‐2 0.34 99 76 97 384.91 0.57 0.80 381.06 0.43 0.782AE‐1 0.02 80 21 95 20.53 0.03 0.04 16.42 0.01 0.042BW‐5 0.34 85 74 95 384.91 0.57 0.80 327.17 0.42 0.762BW‐5a N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A2BW 5a N/A N/A N/A N/A N/A N/A N/A N/A N/A N/A2BW‐6 0.11 85 74 82 128.30 0.19 0.27 109.06 0.14 0.222BW‐7 0.21 99 76 97 230.94 0.34 0.48 228.63 0.26 0.472BW‐8 TBD 85 74 82 TBD TBD TBD TBD TBD TBD2BW‐9 0.18 80 21 95 205.28 0.30 0.43 164.23 0.06 0.412B‐10 1.13 99 76 97 1257.49 1.87 2.62 1244.92 1.42 2.542BE‐1 0.12 99 89 99 138.57 0.21 0.29 137.18 0.18 0.292CW‐1 0.08 85 74 82 85.32 0.13 0.18 72.52 0.09 0.152CW‐2 0.27 85 74 82 304.85 0.45 0.64 259.12 0.34 0.522CW‐3 0.21 99 76 97 230.94 0.34 0.48 228.63 0.26 0.472CE‐1 0.25 80 21 95 282.78 0.42 0.59 226.22 0.09 0.562CE‐2 0.02 18.4 12.4 17 25.66 0.04 0.05 4.72 0.00 0.012CE‐3 0.05 40 10.5 47.5 51.32 0.08 0.11 20.53 0.01 0.052CE‐4 0.28 99 76 97 307.93 0.46 0.64 304.85 0.35 0.622D‐1 0.09 80 21 95 102.64 0.15 0.21 82.11 0.03 0.20
Basin1 15.5 30 15 25 9570.39 18.76 19.30 2871.12 2.81 4.821Calculation of pollutant load entering the extended detention basin from the entire catchment. The pollutant load from all of the sites after treatment was taken into account, as well as the pollutant load from the 8.23ac that are untreated in the catchment.
