Lennon, Smith, Souleret Engineering, Inc. Civil Engineers and Surveyors Page 1 of 8 05/2013 LENNON, SMITH, SOULERET ENGINEERING, INC. (LSSE) SPEARHEADS FIRST OF ITS KIND GREEN INFRASTRUCTURE DEMONSTRATION PROGRAM In the last decade(s) Low Impact Development (LID) and Green Infrastructure (GI) Best Man- agement Practices (BMP’s) have been widely utilized as a method of erosion and sedimenta- tion and water pollution control predominantly for land development programs and, to a lesser degree, urban storm water runoff. However the focus is shifting from “green field” development practices to application of GI BMP’s in mature urban neighborhoods. With the emergence of integrated watershed based planning encompassing Long Term Control Plans (LTCP’s), Municipal Storm Sewer Systems (MS4) Stormwater permit requirements and Total Maximum Daily Load (TMDL) limits for specific pollutant constituents on local streams, inclusion of GI – particularly retrofit GI in urban/ wet-weather/CSO facilities planning – has gained the interest of the regulators, permittees and diverse environmental interest groups. At the national level, application of various forms of GI is being promoted as an alternative to conventional grey solutions in combined system LTCP’s. For instance, in Allegheny County, Pennsylvania, the regional conveyance and treatment authority’s (ALCOSAN’s) recent release of its Draft Regional Wet Weather Plan was met with immediate demands for use of GI as an alternative to the selected plan, which relies on grey technologies. While there has been a groundswell of interest in application of GI, there is little hard data, and less in the way of engineering assessment tools available to municipal engineers to facilitate an area wide evaluation of GI for comparison to conventional wet weather control technologies. In the absence of well defined regional screening practices, engineers are hard pressed to render opinions on Green vs. Grey in routine practice, let alone in a regulatory context which requires compliance with enforceable Consent Orders. To attempt to address this issue in Allegheny County, PA, 3 Rivers Wet Weather (3RWW) com- missioned its Program Management Team, including LSSE, to develop and implement a demonstration project to assist municipal engineers and affected municipalities by developing practicable engineering protocols, performance assessment criteria, and cost estimating tools, sufficient for use in the PaDEP/ ACHD mandated Municipal Feasibility Studies. Three test basins were analyzed to develop the process of evaluating sites for potential GI projects. The Nine Mile Run Sewershed (785 acres), Girty’s Run Sewershed subdivided into Millvale (277 acres) and Lennon, Smith, Souleret Engineering, Inc. Civil Engineers and Surveyors Est. 1985 Bio-retention Basin at Findlay Industrial Park, Allegheny County, PA
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Lennon, Smith, SouleretEngineering, Inc.Civil Engineers and Surveyors
Page 1 of 805/2013
LENNON, SMITH, SOULERET ENGINEERING, INC. (LSSE) SPEARHEADS FIRST OF ITS KIND GREEN INFRASTRUCTURE DEMONSTRATION PROGRAM
In the last decade(s) Low Impact Development (LID) and Green Infrastructure (GI) Best Man-agement Practices (BMP’s) have been widely utilized as a method of erosion and sedimenta-tion and water pollution control predominantly for land development programs and, to a lesser degree, urban storm water runoff. However the focus is shifting from “green fi eld” development practices to application of GI BMP’s in mature urban neighborhoods. With the emergence of integrated watershed based planning encompassing Long Term Control Plans (LTCP’s), Municipal Storm Sewer Systems (MS4) Stormwater permit requirements and Total Maximum Daily Load (TMDL) limits for specifi c pollutant constituents on local streams, inclusion of GI – particularly retrofi t GI in urban/wet-weather/CSO facilities planning – has gained the interest of the regulators, permittees and diverse environmental interest groups.
At the national level, application of various forms of GI is being promoted as an alternative to conventional grey solutions in combined system LTCP’s. For instance, in Allegheny County, Pennsylvania, the regional conveyance and treatment authority’s (ALCOSAN’s) recent release of its Draft Regional Wet Weather Plan was met with immediate demands for use of GI as an alternative to the selected plan, which relies on grey technologies.
While there has been a groundswell of interest in application of GI, there is little hard data, and less in the way of engineering assessment tools available to municipal engineers to facilitate an area wide evaluation of GI for comparison to conventional wet weather control technologies. In the absence of well defi ned regional screening practices, engineers are hard pressed to render opinions on Green vs. Grey in routine practice, let alone in a regulatory context which requires compliance with enforceable Consent Orders. To attempt to address this issue in Allegheny County, PA, 3 Rivers Wet Weather (3RWW) com-missioned its Program Management Team, including LSSE, to develop and implement a demonstration project to assist municipal engineers and affected municipalities by developing practicable engineering protocols, performance assessment criteria, and cost estimating tools, suffi cient for use in the PaDEP/ACHD mandated Municipal Feasibility Studies.
Three test basins were analyzed to develop the process of evaluating sites for potential GI projects. The Nine Mile Run Sewershed (785 acres), Girty’s Run Sewershed subdivided into Millvale (277 acres) and
Lennon, Smith, SouleretEngineering, Inc.Civil Engineers and Surveyors
Est. 1985
Bio-retention Basin at Findlay Industrial Park, Allegheny County, PA
Lennon, Smith, SouleretEngineering, Inc.Civil Engineers and Surveyors
Page 2 of 8 05/2013
West View (542 acres), and McNeilly Run (285 acres) Sewersheds were the test areas 3RWW identi-fi ed as having signifi cant potential to be benefi cially impacted by GI projects, due to their relative sizes, combined sewers, and number of overfl ow structures. The technologies or Best Management Practices (BMPs) being considered for application in the municipal systems include: bio-retention basins, infi ltra-tion basins, grass swales, vegetated fi lter strips, constructed wetlands, and permeable pavement.
The technical assessment process developed by LSSE starts with the EPA’s SUSTAIN program Frame-work Manager, an ArcGIS methodology utilized to identify potential sites for BMPs within a given sewer-shed based on design specifi c criteria such as slope, drainage area, soil conditions, groundwater depth, and isolation distances to roads, streams and buildings. Utilizing Allegheny County specifi c criteria the SUSTAIN BMP siting tool analysis yielded mapping of potential GI BMP features (polygons) where all eight siting criteria were met for each of the six BMP under consideration. Exhibit 1 presents a screen shot of a portion of the Nine Mile Run sewershed wherein the siting tool analysis identifi ed 7,500 “BMP features” of varying sizes and shapes. These 7,500 features were then further screened through multiple engineering screening criteria to develop “sites” deemed conceptually feasible at the desktop planning level, for implementation of a Green Infrastructure solution. These sites were categorized as “Candidate Municipal Projects” that were deemed feasible to be owned, operated, and maintained by a municipal entity, “Institutional/ Commercial Projects” for large private sites, and “Non-Municipal Infi ltration Features” for residual BMP features that were not incorporated into either of the other categories, but that offer po-tential for community rain garden installations.
Once the BMP features were identifi ed in each test basin a subsequent analysis, performed on each SWMM Model sub-catchment within each test basin, consolidated the features into “candidate projects” utilizing a second set of screening criteria. In the Nine Mile Run shed this process identifi ed 321 GI proj-ects. Exhibit 2 presents a screenshot of the Municipal Candidate Projects” identifi ed for the same area presented in Exhibit 1. The resulting “conceptual projects” were then analyzed in 3RWW’s web based “RainWays®” application to identify the surface drainage areas tributary to the individual GI projects (Exhibit 3) to evaluate effectiveness in reducing runoff and to develop pre-design, conceptual capital and operating cost estimates associated with specifi c BMPs. Table 1 presents the output analysis from
Total Combined Sewer Area 785.08 acresTotal Annual Combined Sewer Area Runoff (RainWays) 237.25 MG
NOTE: RESULTS ASSUME UNDERFLOW FROM GI PROJECTS IS NOT RETURNED TO COMBINED SYSTEM.
Candidate GI Project ParametersPermeable Pavement Bioretention
Infiltration Basin
Grass Swales***
Vegetated Filter Strips
Constructed Wetland Totals
Effective Design Area of Candidate GI Projects Used to Capture First 1.0 inch of Runoff from Tributary Drainage Area (acres) 3.86 1.51 0.09 0.00 0.00 0.02 5.47Total GI Project Area Available (Acres) 28.09 11.29 0.84 0.28 0.00 0.14 40.64Percentage of GI Area used to Capture First 1.0 inch of Runoff from Tributary Drainage Area (%) 14% 13% 10% 0% 0% 13% 13%Number of Candidate GI Projects 46 264 9 1 0 1 321Portion of Drainage Area Tributary to Candidate GI Projects (acres) 77.50 77.74 4.58 0.00 0.00 1.31 161.12
****3RWW RAINWAYS TOOL BMP COST: EXCLUDES SEPARATION COSTS TO DIVERT FLOW TO GI PROJECT AND TO OUTLET UNDERFLOW FROM GI PROJECT.
**Present Worth calculated assuming a 20 year term at 1% interest.*Capture value assumes all catch basins / inlets in tributary drainage area are closed off and all roof leaders in tributary drainage area are disconnected.
***Capture values for these Candidate GI Projects w ere negligible in this subcatchment.
Opinion of Probable Cost****
Table 13RWW GI Project
Candidate Municipal Project Evaluation SummaryNine Mile Run - December 31, 2012
Lennon, Smith, SouleretEngineering, Inc.Civil Engineers and Surveyors
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this process for the Nine Mile Run shed. As noted in the table GI BMP’s were sized to capture the fi rst inch of runoff for the drainage areas tributary to the individual GI Projects. The upper section of the table presents the effective design size (area) of each BMP type as well as the drainage area tributary to each. In this instance, as an example, a total of 28.6 acres of permeable pavement candidate project area was identifi ed, however only 3.86 acres of the permeable pavement candidate project area is required to treat or capture, the fi rst inch of runoff from 77.5 acres of drainage area. This provides a great deal of fl exibility in locating the BMP to best serve the area. In practice, the local municipal or designated engineer will need to “ground-truth” these candidate sites to determine optimal locations in consideration of numer-ous factors including constructability, operations and maintenance, environmental sensitivity, aesthetics, secondary impacts (e.g. displacement of existing infrastructure, parking, etc.) to capture only the fi rst inch of runoff from the total area tributary to all Candidate Municipal BMP projects identifi ed is estimated to reduce the annual runoff volume by about 21 percent.
As noted above, in addition to the Candidate Municipal GI projects identifi ed, the process also defi ned Commercial / Institutional permeable pavement and green roof projects (Exhibit 4) and Non-municipal infi ltration type BMP features (Exhibit 5) for subsequent analysis.
Using the process developed by LSSE and the 3RWW PM Team, local municipalities will now have a method to identify, screen, size, cost, and evaluate effectiveness of GI projects at the conceptual level on a large scale basis within their own sewer systems.
For more information contact: Lawrence J. Lennon, P.E., D.WRE at [email protected].
Lennon, Smith, SouleretEngineering, Inc.Civil Engineers and Surveyors
