POST-CONSTRUCTION STORM WATER

Transcription

1 POST-CONSTRUCTION STORM WATER 2013 Update for NPDES Permit #OHC Dan Bogoevski Ohio EPA Division of Surface Water June 20, 2013

2 Post-Construction Impacts degraded streams and Increased imperviousness and more efficient drainage leads to efficient pollutant conveyance.

3 Post-Construction BMPs Required for all projects where larger common plan disturbs 1 or more acre of land Exceptions: Projects that do not create impervious area Examples: soccer field, pipeline or utility line installation This is determined on a site-wide basis, not a drainage area basis Larger common plan disturbs < 5 ac and erosivity factor < 5 Abandoned mine land reclamation activities Stream and wetland restoration or mitigation activities Projects not subject to NPDES permitting Transportation project deemed routine maintenance and disturbs < 5 ac Discharges to combined sewers (sewer operator may still require)

4 Requirements for Large Construction Larger common plan disturbs 5 ac Structural BMPs must be sized to treat the Water Quality Volume (WQv) WQv = C * P * A / 12 [=] ac-ft C = runoff coefficient appropriate for storms < 1 inch P = 0.75 inches A = total contributing drainage area [=] acres BMP must be designed to drain the WQv (or EDv) in the specified target drawdown time Varies between 24 and 48 hours, depending on the BMP Additional storage volume must be provided for pollutants which will collect in the BMP Volume provided must be 20% WQv

5 BMP Design Guidance ODNR Rainwater and Land Development manual Chapter 2 Public transportation projects only May use ODOT Location & Design Vol 2 - Drainage Design manual

6 Structural Post-Construction BMPs Bioretention Area Permeable Pavement Sand Filter Dry Extended Detention Basin Infiltration Trench

7 Calculating Runoff Coefficient Use Table Land Use Runoff Coefficient Industrial & Commercial 0.8 High Density Residential (> 8 units/ac) 0.5 Medium Density Residential (4-8 units/ac) 0.4 Low Density Residential (< 4 units/ac) 0.3 Open Space and Recreational Areas 0.2 Where land use is mixed, calculate using a weighted average Or use formula c = 0.858i i i i = fraction of post-construction project area that is impervious

8 Standard BMPs & Drawdown Times Best Management Practice Infiltration Basin or Trench Permeable Pavement - Infiltration Permeable Pavement Extended Detention Dry Extended Detention Basin Wet Extended Detention Basin Constructed Wetland Sand & Other Media Filtration Bioretention Area Pocket Wetland Drain Time 48 hrs 48 hrs 24 hrs 48 hrs 24 hrs 24 hrs 24 hrs 24 hrs 24 hrs

9 What Happened to Enhanced Swales? BMP is still allowed Dry enhanced swale is now categorized as bioretention Wet enhanced swale is now categorized as constructed wetland Rainwater manual will be updated to reflect changes Dry Enhanced Swale Wet Enhanced Swale

10 What Happened to Filter Strips? Practice removed from list of standard practices Now listed as an alternative post-construction BMP Requires case-by-case approval and is not an acceptable standalone practice

11 Changes to Permeable Pavement Added as a standard post-construction BMP Designed to infiltrate the WQv, or Provide extended detention of the WQv Section 2.11 of Rainwater manual provides design guidance to meet NPDES permit requirements Permeable Pavers Oakwood Commons City of South Euclid

12 Changes to Bioretention Change in target drain time Reduction from 40 hours to 24 hours Consistent with latest research from NCSU Will lead to larger surface area Rainwater manual being updated OK to use existing guidance until new guidance available, but use 24 hour drain time Bioretention Cell Elyria High School City of Elyria

13 Requirements for Redevelopment Reduce impervious area by 20% Create open space where pavement previously existed Use green roof or permeable pavement for 1:1 reduction credit Or, treat 20% of the WQv Treat 100% of the WQv generated by 20% of the project area Or, a combination of reducing impervious area and treating WQv that totals to 20% For linear public transportation projects Area within existing right-of-way is redevelopment (20% of WQv) Even if it is not currently impermeable surface Development within newly-acquired right-of-way is new development (100% of WQv)

14 What if Project is a Mix of New and Redevelopment? Calculate a WQv for site Weighted average based on acreage Newly-developed areas at 100% Redeveloped areas at 20% Structural BMPs provided must total to the WQv for site Each BMP must be sized at 100% of the WQv for its drainage area Flexibility to select which drainage areas receive treatment, but should treat areas with largest expected pollutant load, i.e., parking lot Provide enough BMPs so that their WQv(s) total or exceed the WQv for the site

15 Example: School Expansion Parking Lot Building Existing Condition Total acreage = 10 ac Existing developed area = 7 ac New developed area = 3 ac

16 Example: School Expansion DA1 = 5 ac WQv of DA1 = 0.8*0.75*5/12 = 0.25 ac-ft WQv provided = WQv of DA1 (0.25 ac-ft) > WQv required (0.22 ac-ft) Post-Construction Condition WQv = 0.8 * 0.75 * 10/12 = 0.5 ac-ft WQv for site = 3/10(1) + 7/10(.2) = 0.44 WQv = 0.22 ac-ft

17 Example: School Expansion WQv provided = WQv of DA1 + DA2 + DA3 = 0.25 ac-ft WQv provided (0.25 ac-ft) > WQv required (0.22 ac-ft) DA1 = 3 ac WQv of DA1 = 0.15 ac-ft DA2 = 1 ac WQv of DA2 = 0.05 ac-ft DA3 = 1 ac WQv of DA3 = 0.05 ac-ft Post-Construction Condition WQv = 0.8 * 0.75 * 10/12 = 0.5 ac-ft WQv for site = 3/10(1) + 7/10(.2) = 0.44 WQv = 0.22 ac-ft

18 Requirements for Small Construction Larger Common Plan disturbs 1 5 ac Ohio EPA does not set minimum design standards, but We recommend that the same practices and design standards be used as with large construction Regulated MS4s may set standards SWP3 must provide technical basis for BMP selection Bioretention at CVS Pharmacy City of Lorain

19 What if Project Cannot Meet These Requirements? Options include: Off-Site Mitigation of Post-Construction BMPs Non-Structural Post-Construction BMPs Alternative Post-Construction BMPs These options should only be pursued when a standard practice is infeasible Physical site constraint Inability to achieve a functional design Must obtain approval from Ohio EPA Obtain prior to submitting the Notice of Intent (NOI) Obtaining NPDES permit coverage does not mean that Ohio EPA has approved the non-standard post-construction plan Regulated MS4 plan approval authority should withhold plan approval until proof of Ohio EPA approval is submitted.

20 Off-Site Mitigation Requirements Maintenance agreement is established to ensure operations and treatment in perpetuity Location of off-site mitigation is in same HUC-14 watershed unit Must treat 1.5 times WQv at off-site location or the WQv at the point of retrofit, whichever is greater

21 HUC-14 Map

22 Non-Structural Post-Construction BMPs Conservation Development Mixed Use/Compact Development Narrower Streets/ Reduced Parking Requirements Downspout Disconnection with Extended Conveyance Meadow Planting Riparian Setbacks

23 Non-Structural Post-Construction BMPs Currently, no minimum requirement except in Big Darby Creek and portions of Olentangy River watersheds Riparian setbacks Groundwater recharge requirement (Darby only) Use in lieu is not a stand-alone option for the site as a whole Ohio EPA can only consider for portions of the site not draining to a common drainage system Rear yard runoff, e.g., provide riparian buffer where rear yards drain toward a stream Use will reduce the size of structural practices because WQv will be smaller Runoff coefficient from open spaces and recreational areas is lower than developed areas Protected natural areas and undeveloped areas don t have to be directed through structural BMPs But, if they are, must count toward total contributing drainage area

24 Ohio Balanced Growth Program Conservation Development Compact Development Stream and Wetland Protection Source Water Protection Natural Areas Management Brownfield Redevelopment Steep Slope Protection Transfer of Development Rights

25 Alternative BMPs Must demonstrate that standard BMPs are infeasible Physical site constraint Inability to achieve a functional design

26 Guidance on Manufactured Systems Must show 80% TSS removal for both laboratory & field conditions MTD Certifications and Guidance Stormwater Technologies Clearinghouse Must obtain permission from Ohio EPA on large construction sites (LCP 5 acres) If manufactured system is an add-on above and beyond what is required to meet Ohio EPA post-construction requirements, e.g., a hydrodynamic separator preceding a wet extended detention basin, Ohio EPA does not need to provide approval

27 OK NO NJCAT Guidance

28 May be NO MASTEP Guidance

29 MASTEP Guidance OK!

30 But, is hydrologic impact negligible? Negligible if BMP infiltrates the entire WQv < 1 acre of imperviousness created within the larger common plan of development or sale Redevelopment in an ultra-urban setting (imperviousness already 100% with discharge to MS4) Direct discharge to a 4 th order or larger stream, lake or other large waterbody and development area < 5% of watershed area upstream of development If not, then you must also add a structure to control the discharge rate Target = WQv/24 hours

31 Filter Cartridge-Based Manufactured BMP Contech StormFilter Unit Eaton Blvd City of Beachwood

32 Underground Detention

33 Storm Tech Isolator Row System Evaluated by NJCAT, but no report on website Evaluated by MASTEP, but rated a 2 Tenn Tech U lab test data from 60 95% TSS removal UNH field test data shows 80% TSS removal Substantially, but not fully TARP-compliant Ohio EPA has allowed system if it is designed to either: Infiltrate the WQv with 48 hr drawdown time, or Provide extended detention of the WQv with 24 hr drawdown time This essentially mimics requirements for permeable pavement, a standard BMP

34 Storm Tech Isolator Row System

35 Storm Tech at Solon Village All chambers discharge through control structure WQv stored between elevation and orifice at elevation provides 24 hr drawdown of WQv Additional depth below underdrains provided to promote infiltration as well

36 Long-Term Maintenance Plans Required for all postconstruction BMPs Should include non-structural as well as structural BMPs Is a required component of the SWP3, but must be a stand-alone document Developer must provide to responsible party Regulated MS4s must ensure it is being implemented

37 Long-Term Maintenance Plans Required content Party responsible for inspection and maintenance Routine and non-routine maintenance tasks Schedule for inspection and maintenance Maintenance and access agreements Map showing location of easements Suggested content Map identifying location and type of BMP Detail drawing of BMP/outlet structure w/ parts labeled Checklist to conduct inspections

38 Post-Construction: Future Federal Rule National performance standards were expected June 2013 Focus expected to be on runoff reduction BMPs ODNR and Ohio EPA working to develop the Runoff Reduction Method for Ohio in anticipation of rule Will accept once published in the Rainwater manual Federal rules would go into effect 18 months after final rule is promulgated Ohio EPA must incorporate into construction general permit and MS4 general permits issued after the federal effective date This would be no earlier than April 2018

39 For More Information Websites Ohio EPA US EPA Ohio EPA Contacts at NEDO Cuyahoga, Geauga, Lake & Lorain Dan Bogoevski (330) Medina, Summit, Portage & Wayne Molly Drinkuth (330) Ashtabula, Columbiana, Mahoning, Trumbull & Holmes Chris Moody (330) Stark & Carroll Phil Rhodes (330)

40 Additional Guidance Ohio EPA Post-Construction Q&A Not yet updated for OHC000004, but will be soon Responsiveness Summary for OHC NEOSWTC MS4 Workshops or USEPA Webcasts