A series of local and regional hydrogeologic investigations and modeling studies were used to characterize and remediate a site in northwestern Ohio where residual chemicals in groundwater potentially threatened the nearby village water supply. A fundamental component of these investigations was to use available data to develop an understanding of local geohydrology, and then to economically relocate the municipal water supply sufficiently upgradient of any potential contaminant sources to avoid future threats to the supply. LimnoTech’s expertise in developing an understanding of site geology, hydrogeological data and modeling results enabled them to successfully explore for and develop an alternative water supply that is more protected and more productive than the former village water supply.
Elevated concentrations of volatile organic compounds were identified in shallow groundwater within a system of stacked glacial aquifers. Downgradient municipal wells installed in a lower confined aquifer potentially were threatened by the impacted shallower groundwater, and an alternative location for the municipal supply was proposed by LimnoTech’s industrial client as a precaution. The village required an alternative water supply comparable in yield to the existing well field, and the industrial client needed an economic relocation of the municipal water supply sufficiently upgradient of any potential contaminant sources to avoid future threats to the supply.
To address these objectives, regional geological and hydrogeologic evaluations of the glacial sediments were conducted by integrating site-specific data collected through conventional drilling methods with existing residential well data. Logs were integrated into a single stratigraphic model to map the aerial extent and thickness of the village well field aquifer throughout a township-wide area. Among the well logs were a few that indicated the presence of a deeper and thicker aquifer, with a groundwater gradient similar in direction and magnitude as the shallower village well field aquifer. Further investigation showed that the deeper aquifer consisted of over 60 feet of very coarse sand and gravel deposits at the test location, suggesting a highly transmissive and extensive aquifer. Modeling predicted that a municipal well field at this location would not be threatened by downgradient contaminants.
By making extensive use of available data and highly targeted sampling within a well-designed modeling framework, the project balanced protectiveness and cost-effectiveness. Information from subsequent test monitoring wells confirmed that the test location was upgradient of the source of shallow groundwater impacts for both the village well field aquifer and the deeper aquifer. The results of the deep aquifer pumping tests demonstrated more than adequate flow and capacity, and minimal communication between the upper and lower aquifers.