Bridge Stormwater Runoff Analysis and Treatment Options (2014) / Chapter Skim
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E-1 BMP Evaluation Tool Modeling Methodology This appendix summarizes the modeling methodology and underlying data used in the BMP Evaluation Tools. Introduction and Purpose This document summarizes the modeling methodology, assumptions, and default parameters used in the development of the BMP Evaluation Tools.
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E-2 As indicated by the confidence intervals in Table E-4, there does not appear to be a clear relationship between AADT and pollutant concentration except for possibly dissolved phosphorus, total copper, and total zinc, particularly when comparing the low traffic AADT (<25K) against the high traffic AADT (>50K)
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E-3 parametric statistics for this analysis. The Wilcoxon signed rank test was used to evaluate whether the influent and effluent concentrations are statistically different and the Spearman's rho correlation coefficient was used to evaluate whether a monotonic relationship exists (Helsel and Hirsch 2002)
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E-4 measurement pairs was set. PFC was the only BMP with only one study in the BMP Database.
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E-5 quality. To do this, the Spearman's rho test was applied to each BMP-pollutant combination.
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E-6 Regression Analysis of the Relationship between Influent and Effluent Based on the results of the Wilcoxon and Spearman's rho tests, several BMPs appear to provide statistically significant reductions in pollutant concentrations along with monotonic influent/effluent relationships. These results together indicate that regression analyses can be conducted to develop functional relationships that can be used to predict BMP performance.
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Pollutant Bioretention Grass Swale Detention Basin Sand Filter PFC TSS 3 3 3 3 8 NO3- 4 1 1 1 4 TKN 2 4 1 1 8 TN 9 9 9 9 9 DP 8 1 4 1 4 TP 4 2 2 2 8 TCu 3 3 3 3 8 TPb 4 3 1 1 8 TZn 3 3 3 3 8 FC 3 4 3 3 4 E coli 3 4 3 7 4 1 - KTRL regression of Ceff vs.
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E-8 In addition to the 343 COOP rain gages, 40 Automated Surface Observing System (ASOS) rain gages with 5 minute rainfall data were analyzed.
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E-9 When evaluating capture efficiency and volume reduction, each BMP can be considered to consist of a set of storage compartments, each with a distinct volume, discharge rate, and pathway by which water discharges, i.e., surface discharge, infiltration, evapotranspiration (ET)
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E-10 rates (i.e., storage drained by ET) , the concept of a representative drawdown time is not applicable.
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E-11 • Tributary area imperviousness • Tributary area soil type Table E-15 provides a summary of the supporting model runs that were executed to provide the database to support the tool. Key results from each SWMM run were extracted using automated routines to develop lookup databases indexed by the key parameters described in the table above.
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E-12 Parameter Number of Increments Consistent Drawdown Model Runs (Infiltration, Surface Discharge) Climate Regions 343 Modeled Imperviousness of Tributary Area 1 Supported Imperviousness 0 to 100% (analog scale; more reliable above 25%)
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E-13 normalized by the 85th percentile, discrete storm event for the selected rain gage. These normalized values can be used to scale the nomographs for the selected rain gage to a particular location.
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E-14 Graphical operations supporting solution: 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Pe rc en t Vo lu m e Ca pt u re Storage BMP Design Volume (in) 1-Hour DDT 2-Hour DDT 3-Hour DDT 6-Hour DDT 12-Hour DDT 24-Hour DDT 36-Hour DDT 48-Hour DDT 72-Hour DDT 96-Hour DDT 120-Hour DDT 180-Hour DDT 240-Hour DDT 300-Hour DDT 360-Hour DDT 480-Hour DDT 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 Pe rc en t Vo lu m e Ca pt u re Storage BMP Design Volume (in)
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E-15 Given: Drainage area = 1.5 acres Runoff coefficient of drainage area = 0.86 (computed) Effective area of bioretention = 1000 ft2 Depth of bioretention media = 3 ft Porosity of bioretention media = 0.4 Field capacity of bioretention media (fc)
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E-16 Whole Life Cost Tool Whole life costing (also known as life cycle cost analysis) is about identifying future costs and referring them back to present day costs using standard accounting techniques such as present value (PV)
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E-17 The methodology and issues in determining these costs are presented in the following sections. Capital Costs Capital costs for BMPs include construction costs and various associated costs.
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E-18 An important consideration when assessing cost is what would be constructed in lieu of the selected practice. For instance, engineered swales are typically a much less expensive option for stormwater conveyance than the curb and gutter systems they replace, which leads to the conclusion that these water quality benefits facilities are effectively free, since some type of system is required for drainage purposes.
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E-19 Table E-17. BMP routine maintenance tasks.
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E-20 and the stormwater retrofit-specific costs were estimated to be $102,040, resulting in a 13% increase from the estimated new construction cost due to the project being built as a retrofit. This lower percent difference from the average found in the URS report is likely due to the fact that this is a much larger retrofit project compared to the 16 projects evaluated for the URS report, with corresponding lower unit prices.
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E-21 facility had the BMP not been built should also be computed and subtracted as appropriate from the final BMP WLC. Costs are calculated using unit prices developed from DOT bid tabulations that reflect average values of costs, RS Means 100.
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E-22 in improving the accuracy of a user-created cost estimate would be for the user to multiply these unit costs by the appropriate location factor, adjust to the current year using a similar factor, then enter the product in the "user entered" column. As a minimum, the assumptions and costs components should be reviewed for appropriateness prior to model application in a generic mode.
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E-23 Table E-21. Example capital cost worksheet.
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Table E-22. Example maintenance worksheet.
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E-25 WLC Tool Outputs The WLC model summarizes the expected annual costs on the Whole Life Cost worksheet (hidden by default) as shown in Table E-23.
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E-26 Whole Life Cycle Costs Summary Total Facility Base Cost Total Associated Capital Costs (e.g., Engineering, Land, etc.) Capital Costs Inspection, Reporting & Information Management 0.5 $180 $360 Vegetation Management with Trash & Minor Debris Removal 0.5 $1,380 $2,760 add additional activities if necessary 0 $0 $0 add additional activities if necessary 0 $0 $0 Totals, Regular Maintenance Activities $3,120 Corrective Maintenance 4 $6,740 $1,685 add additional activities if necessary 0 $0 $0 add additional activities if necessary 0 $0 $0 Totals, Corrective & Infrequent Maintenance Activities $1,685 Capital Costing Method Assumed Level of Maintenance Estimated Capital Cost, $ (2013)
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E-27 shown in Figure E-10. The WLC for a variety of BMPs can then be calculated and compared to determine the least cost alternative for a given scenario.
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Abbreviations and acronyms used without definitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005)
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