Stakeholder Meeting for Proposed Changes to Ohio Construction General Permit Jason Fyffe and John Mathews Ohio EPA, Division of Surface Water
Construction General Permit (Est. Timeline) 1. Internal draft (under construction) 2. Stakeholder outreach (November) 3. Public notice of draft renewal (December/January) • 45-52 days of public comment period 4. Review comments and incorporate changes (Feb/March) 5. Final package for Ohio EPA director signoff • Includes responsive summary (March) 6. Permit issued April 21, 2018
How to provide input: • All input is welcome, but specific, descriptive suggestions of modification or examples of issues are most helpful. Send email by December 6, 2017: Jason Fyffe Ohio EPA, Division of Surface Water SW Permits P.O. Box 43216-1049 Jason.Fyffe@epa.ohio.gov
Background of the Construction General Permit (CGP) • Between 1979 and 1983, the National Urban Runoff Program studied storm water runoff as a significant pollution source. The findings eventually led USEPA to initiate a National Pollutant Discharge Elimination System (NPDES) general permit.
Background of the Construction General Permit (CGP) • Ohio’s first Construction General Permit (1992) authorized the discharge of stormwater from construction sites. It largely focused on erosion and sediment control during construction, but also provided a general narrative for controlling storm water and pollutants after construction.
Background of the Construction General Permit (CGP) • The CGP requires development of a storm water pollution prevention plan (SWP3) and the implementation of this plan on all sites that disturb 1 acre or greater. • CGP renewal history • 1992, 2003, 2008, 2013, 2018
Background of the Construction General Permit (CGP) • The CGP requires development of a storm water pollution prevention plan (SWP3) and the implementation of this plan on all sites that disturb 1 acre or greater. • CGP renewal history • 1992, 2003, 2008, 2013, 2018 Post-construction requirement became more detailed and prescriptive for larger sites by incorporating an approach used by the 1998 WEF Manual of Practice.
Post-Construction (Current Permit) Aspects that apply to all construction sites: “So that receiving stream’s physical, chemical and biological characteristics are protected and stream functions are maintained, post-construction storm water practices shall provide perpetual management of runoff quality and quantity.” • …the SWP3 shall contain a description of the post- construction BMPs… • Detail drawings and maintenance plans shall be provided for all post-construction BMPs
Post-Construction (Current Permit) • Large sites require capturing & treating the water quality volume (WQv = C · P · A / 12)
Post-Construction (Current Permit) • Large sites require capturing & treating the water quality volume (WQv = C · P · A / 12) • Offsite mitigation may be authorized • Redevelopment: 20% WQv or 20% reduced imperviousness • Alternative practices may be approved provided they meet a tested standard (80% TSS testing using TARP; listed on NJStormwater; Mastep.net)
Post-Construction (Current Permit) • Small sites (<5 - 1ac.) describe measures …storm water detention structures...open vegetated swales and natural depressions; infiltration of runoff onsite; and sequential systems (which combine several practices). There is a variety of local interpretation on this, ranging from doing nothing to application of ineffective practices or application of more effective table 2 practices like bioretention. • The SWP3 shall include an explanation of the technical basis used to select the practices. Generally the rationale for selecting or how the practices meet the purposes is rarely shown in Storm Water Pollution Prevention Plans.
The Goal of Post-Construction BMPs • An important goal driving Ohio’s post-construction requirements is the target of providing 80% total suspended solids removal from average annual runoff • The goal of protecting channels from erosion is also provided through the extended detention of storm water
The Goal of Post-Construction BMPs Conclusions • This includes both concern for pollutants and the erosive effects on streams • It has a historic basis • It serves as a useful general target for pollution treatment goals (though specific watershed problems may require additional treatment approaches) • Other states also use some form of the 80% TSS target
Background of the Construction General Permit (CGP) • The CGP requires development of a storm water pollution prevention plan (SWP3) and the implementation of this plan on all sites that disturb 1 acre or greater. • CGP renewal history • 1992, 2003, 2008, 2013, 2018 So after 15 years, the post-construction criteria are being updated.
Original Methodology The WQv approach for Ohio was adapted in 2003, from from Urban Runoff Quality Management (1998). The assumptions and methodology have been examined to see if they are still valid and able to meet the goal
Original Methodology As documented in Ohio EPA’s Post-Construction Q & A (2007):
WQv Equation and Inputs WQv = C · P · A/12, where: WQv = extended detention volume to be captured P = 0.75 C = watershed runoff coefficient A = contributing drainage area (acres) Approach endorsed by ASCE to reasonably maximize treatment for water quality. • Balance retention and readiness • Knee-of-the-curve optimization • NOT flood control Goal: capture of 80% of TSS (annual basis)
WQv Equation and Inputs WQv = C · P · A/12, where: WQv = extended detention volume to be captured P = 0.75 C = watershed runoff coefficient A = contributing drainage area (acres) Questions: 1. Does this reach the 80% TSS goal? 2. Does the precipitation (P) reflect up-to-date rainfall data? 3. Is C the most appropriate and relevant way to relate imperviousness to runoff?
Does This Meet the 80% TSS Goal? • Assuming several BMPs can achieve 90% TSS removal (wet ED basins, wetland ED basins, bioretention and permeable pavement) • Then we achieve 80% TSS removal on an annual basis by capturing and treating 90% of annual runoff volume 90% annual runoff volume · 90% treatment efficiency = TSS reduction 0.9 · 0.9 = 0.81 (or 81% TSS removal) 19
Does This Meet the 80% TSS Goal? • Assuming several BMPs can achieve 90% TSS removal (wet ED basins, wetland ED basins, bioretention and permeable pavement) • Then we achieve 80% TSS removal on an annual basis by capturing and treating 90% of annual runoff volume 90% annual runoff volume · 90% treatment efficiency = TSS reduction 0.9 · 0.9 = 0.81 (81% TSS removal) P= 0.75 was estimated to be about 85% of rainfall events and is actually lower (near 80%) 20
Does Precipitation (P) Reflect Current Rainfall Data & Approaches? (From figure 5.3 Mean Estimated statewide mean = 0.50” storm precipitation 24 hr maximized detention multiplier depth. See WEF, 1998 pages 175-177) x (1.582) = 0.80” (range 0.73” to 0.89”) 48 hr maximized detention multiplier x (1.963) = 0.98” (range 0.90” to 1.10”)
Does This Meet the 80% TSS Goal? • Conclusion: The precipitation value needed to be reviewed and updated 22
Is C the Best Volumetric Runoff Coefficient? • C = 0.858i 3 – 0.78i 2 + 0.774i + 0.04 • Used in Ohio, California and Denver, Colorado • Rv = 0.05 + 0.9i • More common usage (8 nearby states) • Rv (impervious) = 0.95 • Rv (pervious) = 0.05
Is C the Best Volumetric Runoff Coefficient?
Is C the Best Volumetric Runoff Coefficient? Credit: Jay Dorsey
Is C the Best Volumetric Runoff Coefficient? Undisturbed Soils Renovated Soils
Is C the Best Volumetric Runoff Coefficient? Volumetric runoff coefficients (Rv) adjusted for impervious, disturbed soils and natural soils Battiata, J., K. Collins, D. Hirschman, and G. Hoffman. 2010. The Runoff Reduction Method. J. Contemporary Water Research and Education 146: 11-21.
Potential Changes to the Permit 1. Electronic submittal of all plans (SWP3) 2. Sediment basins and sediment barriers clarifications 3. Update post-construction requirements A. Capture WQv in a Table 2 practice for all developments > 1 ac B. Adjust the WQv Calculation: i. Change the volumetric runoff coefficient equation (Rv) with options for natural soils or restored soils ii. Increasing the precipitation value to 0.9 inches C. Table 2: Add underground detention; full WQv for Wet E-D D. Credit green infrastructure practices that can reduce the WQv E. Redevelopment – reduce imperviousness by 20%; provide 20% of the WQv with a green infrastructure practice; or provide 40% of the WQv with standard extended detention practices F. Alternative practices: acceptable testing, PSD and appropriate water quality flow 4. On-site infiltration may be used for Big Darby groundwater recharge
Potential Changes to the Permit 1. Request electronic submittal of all plans (SWP3)
Potential Changes to the Permit 1. Request electronic submittal of all plans (SWPPP) 2. Sediment basins and sediment barrier clarifications • All sed basins have drain times of 48 hours • (misconception – 48 hr only applied to sites >5 ac) • Sediment basins are appropriate for sites < 10 ac • (misconception – sed basins only for sites >10 ac)
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