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

Rapid Recharge to Fractured Bedrock

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

Rapid Horizontal Recharge Linked with Flooding

Acknowledgments

Data:• Ohio EPA Staff• PWS Operators• ODNR Aquifer Map

GIS Support:• Ohio EPA, DDAGW GIS Unit