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

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

• Create a Hydrologic Model for each basin with
  three outlets for each basin and import
  hydrograph data from WINSLAMM
• Recharge Well
• Lake Evaporation
• Detention Outlets

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

• Create Well Capacity vs. Annual Recharge Graph

17
Basin Elevation vs. Time
Runoff to stream
Runoff into recharge well or lost to evaporation
Evaporation losses
18
Step 6

• Select required recharge well capacity for each
  pond to meet target of 3.6 million cubic feet of
  recharge
• (1.80 1.46 0.43) 3.69 million cubic feet

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