Protection of ground water meeting UPUS Determining ground water zones – Ground water definition – Determining how many zones Examples POGWMUPUS and GW Zones

Protection of Ground Water Meeting Unrestricted Potable Use Standards Ground water meeting UPUS is “clean” ground water “Clean” ground water required to be protected from future UPUS exceedance per ORC Cannot demonstrate or assume ground water exceeds UPUS without sampling and analysis

Determine division or separation of ground water zones How should subsurface saturated zones be grouped or divided Determine if confining units are present If confining units, how do they separate ground water zones Ground Water Zones

Ground Water Definition Yield > 1.5 gallons of water within 8 hours after purging In situ hydraulic conductivity > 5 x 10 6 cm/sec

Is it a ground water zone? May assume saturated zone is ground water May demonstrate saturated zone does not contain ground water – Bias demonstrations to highest outcome – Ground water yield – In situ hydraulic conductivity Uppermost Saturated Zone

Protection of Ground Water Zones Investigate each zone (GW zone and confining units) from the surface down, as needed Determine which zones exceed UPUS Determine which zones meet UPUS and need to be protected

Protection of “Clean” Ground Water Buried Valley Aquifer Glacial Till Dayton Vadose Zone What is the next lower ground water zone requiring protection? Saturated Sand and Gravel (meets UPUS)

Protection of “Clean” Ground Water Buried Valley Aquifer Glacial Till Piketon Vadose Zone What is the next lower ground water zone requiring protection? Contaminated Ground Water Zone

Protection of “Clean” Ground Water Regional Sandstone Aquifer Glacial Till Wooster Vadose Zone Sand lens and Regional Sandstone Aquifer must be protected from exceeding UPUS Contaminated Ground Water Zone Sand Lens

Water Zone Examples Be specific describing zones Avoid terms upper or lower zone unless clearly defined in text (e.g., highest, second zone encounter below the highest and separated by a confining unit) Use hydrostratigraphy or hydrogeology Differentiate units on cross sections

Central Ohio Delaware and Columbus Limestone Weathered Bedrock - Gravel Unconsolidated Sand Delaware Clay

Southwest Ohio Clay Overconsolidated Clay Clay Bedrock Lowest Sand and Gravel Highest Sand and Gravel

Northeast Ohio Berea Sandstone Unconsolidated Alluvium Sharon Sandstone Cuyahoga Formation

POGWMUPUS Demonstration Demonstrate chemicals of concern in subsurface won’t migrate to ground water zone at concentrations that exceed UPUS Evaluate Leaching Potential – Compare to leach based soil values – Weight-of-evidence

Evaluate Leaching Potential Compare to leach-based soil values – Generic Ohio EPA derived LBSV – Calculate Site/Property Specific LBSVs

Weight of Evidence Nature and age of release Type and concentration of COCs Separation distance between COCs and GW Physical properties of soil Engineering controls/preferential pathways Modeling results Impacts from off-property source

Example Eastern Ohio site – Contaminated river gravels – Flow direction towards Ohio River – Did not sample “lower” GW or install deep well – Ohio EPA was not convinced with weight of evidence provided in NFA letter

Eastern Ohio Pottsville Group Shale with Sandstone Ohio River River Gravel

Eastern Ohio Concern was for contamination domestic wells completed in bedrock (Pennsylvanian sandstone) Site conceptual model had flow from bedrock, to river gravel, and river Upward gradient (higher hydraulic head) from bedrock to river gravels and then river COCs not over standards for discharge to surface water body

Summary Identify GW zones – Determine GW connectivity – Determine confining units Determine highest GW zone that meets UPUS – Must continue to meet UPUS or remediation required Questions?