Modeling Annual Groundwater Recharge Using Recharge Wells to Meet Ohio EPA Requirements of the Darby Watershed

1. Modeling Annual Groundwater Recharge Using Recharge Wells to Meet Ohio EPA Requirements of the Darby Watershed Presented by Doug Turney, PE, LEED AP

2. Big Darby Watershed Map HistoryNational Scenic RiverExceptional Warm Water Habitat and Cold Water HabitatSeveral Endangered Species5-year Moratorium on Sanitary Sewer Extensions Lifted in October of 2006EPA Construction Permit Effective Date: October 27, 2006

3. Groundwater Recharge Table Map

4. Table 1 Recharge Values

5. Table 2 Recharge Values

6. Groundwater Recharge Mitigation Example Problem Existing Conditions Proposed Conditions 10 Acres Row Crop 10 Acres High Density Residential Type C Soil Type C Soil Table 2 Recharge Area Table 2 Recharge Area Annual Recharge = 90 acre-in/yr Annual Recharge = 50 acre-in/yr Preferred Mitigation Option is Land Use Mitigation Convert 1 acre of Row Crop to Meadow yields 1.6 acre-in/yr of mitigation How many acres of row crop must be converted to meadow to mitigate for 40 acre-in/yr of groundwater recharge? 25 acres !

7. Mitigation Alternatives Bioretention Basins Use of the RECARGA model, developed by the University of Wisconsin, adaptable to Central Ohio http://dnr.wi.gov/runoff/stormwater/technote.htm Recharge Wells EPA has approved the use of recharge wells

8. Recharge Well System Layout

9. How do you model a recharge well? Find a model that can produce a continuous hydrograph for at least a years worth of data

10. WINSLAMM by PV & Associates Models continuous rainfall Uses small storm hydrology to estimate runoff volume, more accurate than TR-55 for small events Produces a usable hydrograph output, 6, 15, 60-minute output intervals

11. Case Study 168-Acre Warehouse Development 68 Acres of Roof 9 detention basins 3 of which are recharge well basins Roof water only Land mitigation area = 625 acres If recharge wells or bioretention not used Recharge volume deficit of 83.3 acre-ft, 3.6 million cubic feet

12. Step 1 Use WINSLAMM to produce an inflow hydrograph file for each watershed tributary to a recharge basin with a minimum 60-minute time step

13. Step 2

14. Step 3 Lake Evaporation Find mean monthly Class A pan evaporation data with at least 10 years of record Data below is from ODNR for a station at Ohio State University Convert to a constant flow rate

15. Step 4 Design water quality and peak flow rate control outlets assuming the following Normal pool is at 12” above recharge well outlet Normal pool is also equal to invert of water quality outlet Do not assume any runoff volume losses due to the recharge well

16. Step 5

17. Basin Elevation vs. Time

18. Step 6

19. Step 7 Hire a Geotechnical Engineer ! Borings required with pumping tests to determine how many recharge wells are needed for each basin to meet the target recharge rate requirement Number of recharge wells may vary considerably from site to site depending on subsurface geology Consider a subsurface exploration or literature research to determine recharge well potential during due diligence process when in the Darby watershed

20. Special EPA Requirements Monitoring may be required Recharge Volume Quality Roof water only unless pre-treated Submerged outlet