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Identifying Sensitive Aquifers in Ohio
Chris Kenah, Michael. W. Slattery, Linda. D. Slattery, and Michael Eggert
Ohio EPA, Division of Drinking and Ground Waters
DMT’06
Outline
• Logic for identifying sensitive aquifers• Suspected sensitive aquifers• Water Quality/SWAP data - Impacted PWSs• Analysis of ODNR glacial aquifer attributes
and location of impacted PWSs– Differences between geologic setting and lithologic
attributes
• Ohio Sensitive Aquifers
Data Sources
• Geologic Information– Recharge Pathways – ODNR Aquifer Maps
• PWS Compliance and Ambient Data – Nitrate, VOC, SOC
• Special Study Knowledge
Logic for Sensitive Aquifer ID
• Short or Rapid Recharge Pathways
• Areas of Ground Water - Surface Water Interaction
• Recharge through Glacial Drift– Identify glacial settings with rapid recharge
Sensitive Glacial Settings
• Buried Valleys - sand & gravel aquifers– Fine to coarse grained material– Buried valley, alluvial, out wash/kame, and
beach ridge geologic settings
• Thin Glacial Drift - over bedrock aquifers– Fined grained - tills and lacustrine deposits – Lacustrine, ground and end moraine settings
Ohio SWAP Program
• SWAP Susceptibility Analysis– Includes evaluation of compliance data;
• 516 PWSs Highly Susceptible – Based on water quality compliance data
• Nitrate > 2.0 mg/L• VOC or SVOC detections
WQ Impacts in Sensitive Aquifers?
• Attach glacial aquifer attributes to PWS locations
• Evaluate PWS WQ impact association with:– Glacial geologic settings– Glacial lithologies
• Compare percentage of PWSs impacted
Data Limitations
• ODNR aquifer maps thickness are ranges not well depths– If glacial drift < 25’, bedrock production well likely– If glacial drift > 25’, production may be in drift
• In thicker glacial sand and gravels, well depth may not approach glacial drift thickness
• In thicker till lithologies, production may come from sand lenses or bedrock
• Utilizing statewide generalizations
PWS Water Quality Impacts - Geologic Settings
Thickness ofGlacial Unit (Feet)
Number of PWSs in Glacial Unitwith Impacts
Total Number of GW Based PWSs in Glacial Unit
Percentage ofImpacted PWSs
Sand and Gravel Aquifer Settings
0-25 10 39 25.6 %
25-100 92 487 18.9 %
>100 153 1066 14.4 %
Bedrock Aquifers Below Thin Uplands and Lacustrine Deposits
0-25 133 904 14.7 %
25-100 103 1032 10.0 %
>100 8 28 28.6 %
Moraine Deposits
0-25 0 0 0.0 %
25-100 27 704 3.8 %
>100 13 559 2.3 %
Thickness ofGlacial Unit (Feet)
Number of PWSs in Glacial Unitwith Impacts
Total Number of GW Based PWSs in Glacial Unit
Percentage ofImpacted PWSs
Sand and Gravel Lithologies
0-25 6 9 66.7 %
25-100 50 133 37.6 %
>100 113 495 22.8 %
Fine Grained Lithologies
0-25 4 36 11.1 %
25-100 44 405 10.9 %
>100 37 464 8.0 %
Till Lithologies
0-25 133 898 14.8 %
25-100 128 1682 7.6 %
>100 24 697 3.4 %
PWS Water Quality Impacts – Lithologic Association
Sensitive Aquifers
• PWSs with WQ impacts associated with:– Coarse S&G aquifers– Thin Tills (0-25 ‘)
• Aquifers composed of fines provide more protection than S&G aquifers and thin tills over bedrock aquifers;
• Thick tills are associated with low % of PWSs with WQ impacts (3-4 %)
Future Activities - Sensitive Aquifers
• Attach glacial drift thickness, DRASTIC ranking, and soil properties to PWS locations for analysis of WQ impacts
• Incorporate well casing length and depth as analysis factors
• Evaluate dissolved vs particulate sensitivity• Identify areas where horizontal flow pro-vides
rapid recharge• Short term sampling in sensitive aquifers