Process-Based BMP Design Tool for Post-Construction. October 18, 2012

Transcription

1 Process-Based BMP Design Tool for Post-Construction October 18, 2012

2 EPA s Stated Goal + Reduce, through regulation, the impacts of new development and redevelopment storm water runoff to the Nation s waters. EPA NPDES website How? + Require completed projects to be designed, built, and maintained so as to retain the sites pre-development hydrologic characteristics to the extent technically feasible NRC publication - Urban Stormwater Management in the United States, October 15, 2008 What? + Make the developed site act like it did before it was developed

3 First flush w/ extended detention Regulatory Approaches % reduction Annual loads Volume control w/ infiltration Effluent concentrations w/ annual loads Nothing Better Good Best stormo

4 Regulatory Status + Current EPA Rulemaking + SEPTEMBER NOVEMBER DECEMBER MAY 2011 June 2013 Draft Regulation and public comment + NOVEMBER 2012 December 2014 Final Rule + EISA (Energy Independence and Security Act of 2007) + 95 th percentile storm infiltration for federal building projects + MS4 Permit Improvement Guide (April 2010) + Site Performance Standards + NPDES MS4 Permit for Washington DC + Site Performance Standards

5 EPA Performance Standard Examples + Annual pollutant loading + Post-development loading pre-development loading + Examples: + post-construction annual pollutant loads are not allowed to exceed predevelopment levels for pollutants of concern + OCRM and SCDHEC Strengths Direct connection to pollutants of concern (no surrogates) Allows for site specific conditions to be taken into account Perceived Weaknesses Too hard to calculate Too hard to regulate Less controversial (policy driven) Allows design characteristics of BMPs to be taken into account Overly prescriptive design standards are not needed Facilitates TMDL restrictions

6 Integrated Design and Evaluation Assessment of Loadings + History/Background of IDEAL + Modeling Approach + Current Development + Demo

7 IDEAL + A first of its kind post-construction water quality model for designing stormwater BMPs and calculating their trapping efficiencies. + Uses + BMP design for small to large developments projects + TMDL compliance + Antidegradation restrictions + Watershed master planning + LID design

8 What makes IDEAL unique? + Target Users + Site Design Community + Regulators + Process-based BMP computations + Flexibility in design + Allows engineers to design BMPs + Meet regulatory and owner goals + Easy to use + Object-oriented, drag-n-drop + Quick setup and input + Isotherms

9 Development History

10 OCRM Spreadsheet version + A Developed by Woolpert with J.C. Hayes and Associates as a subcontractor + Drs. Bill Barfield and John Hayes + Response to antidegradation restrictions for Coastal SC OCRM version + User group site design engineers + Initially a spreadsheet program + Greenville County adopted and funded upgrades + Now a.net computer language program

11 Object Oriented VB.Net version

12 Summary of versions Pollutants OCRM Spreadsheet (2002) IDEAL (2011) Sediments, Nutrients, Bacteria Watersheds BMPs Conveyances Isotherms & Rainfall Analysis Wet/Dry Ponds, VFS None SC Coast Wet/Dry Ponds, VFS, Bioretention cells, Sand filters, Bioswales, Porous pavement, Cisterns, Infiltration trenches, Engineered devices Pipes, channels, and simple translation SC, VA, WV, NC, GA, FL

13 Current Developments + Expansion of isotherms to more geographic areas + User-defined rainfall and soil databases + Annual continuous simulation + Increase scope of model + Current geographical areas served

14 Modeling Framework

15 Watershed Modeling Framework ID

16 Model Introduction

17 Rainfall Statistics + Design Storms + Annual Distribution of Storms Precip Amount Prob P 12 Storms 0.25 to 10.5 Growing Season P=0.664 Dormant Season P=0.336 AMC 1 AMC 2 AMC 3 AMC 1 AMC 2 AMC 3 P=0.797 P=0.104 P=0.100 P=0.543 P=0.231 P=0.226

18 Hydrology + SCS Runoff Curve Number Method + Excess Runoff Hydrograph from + Gamma distribution unit hydrograph + Unit rainfall for Storm Type (I, Ia, II, III) + Precipitation Options + Single/Design event + Probabilistic Distribution ID

19 Sediment Yield - Particle Size Matters Size Time to settle 1 foot Large Aggregate mm 15 seconds Sand mm 16 seconds Small Aggregate mm 11 minutes Silt mm 1 hour Clay mm 1+ day Can t see clay particle, even at this scale (~ 1:100) ID

20 Sediment Yield + Pervious Areas - MUSLE + Impervious Areas - EMC Approach + EMC varies with type of impervious area + Modeling dependability improves as local data is collected + Model Sediment Size Distribution + Used to determine sediment trapping in Vegetated Filter Strip and in ponds + Nutrients and bacteria are sorbed on the exchange phase of the clay particles, hence need to know concentration of clay size particles + Pervious areas based on CREAMS equations + Impervious areas based on NURP data ID

21 Nutrient and Bacteria Loading + Modeling Nutrients + Yield based on event mean concentrations (EMCs) for each chemical + EMCs vary based on land use + Modeling Indicator Bacteria + Yield based on event mean concentrations (EMCs) for bacteria + EMCs highly variable + National average ~ 15,000 number/100ml + Death and growth modeled using 1 st order decay ID

22 BMP Trapping + Predicts trapping of sediments in ponds through settling and infiltration for 5 particle classes, silt, sand, clay, large and small aggregate. + Predicts nutrient trapping by settling of particulate matter, sorbed portion on trapped active clay content based of the sediment by isotherms, and infiltration. + Predicts bacteria trapping using isotherms and mortality.

23 IDEAL BMP Types Dry Pond

24 IDEAL BMP Types Wet Pond ID

25 IDEAL BMP Types - Bioretention ID

26 IDEAL BMP Types - Bioswale ID

27 IDEAL BMP Types Enhanced Bioswale ID

28 IDEAL BMP Types Sand Filter ID

29 IDEAL BMP Types - Cisterns ID

30 IDEAL BMP Types Porous Pavement ID

31 IDEAL BMP Types Infiltration ID

32 IDEAL BMP Types - VFS ID

33 IDEAL BMP Types - Misc Devices ID

34 IDEAL Additional functionality + Flexibility in output formats and export + Background image + Interface with Civil 3D + SWMM Routing Engine ID

35 Output + Graphical and + Text (PDF or HTML ID

36 First flush w/ extended detention Regulatory Approaches % reduction Annual loads Volume control w/ infiltration Effluent concentrations w/ annual loads Nothing Better Good Best stormo