RCRA Corrective Action – TSDF Initial Subsurface Characterization


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RCRA Corrective Action – TSDF Initial Subsurface Characterization

The site is a commercial hazardous waste TSDF facility located in the Midwest. The facility’s RCRA Hazardous Waste Management Part B Permit requires site-wide RCRA Corrective Action for releases from solid waste management units. As a first step in the Corrective Action process the state agency required the facility to prepare a current conditions report (CCR). Due to the complete lack of subsurface data and understanding of site hydrogeology conditions, the state agency requested the facility conduct subsurface characterization and develop the site conceptual model (CSM) as part of the CCR. Cox-Colvin was selected by the facility in 2013 to conduct site characterization and develop the CSM. The site is on the edge of a complex glacial buried valley with regionally interbedded clays, sand, and gravel layers, including a sole-source aquifer.

Subsurface characterization was conducted through a phased approach that included a desktop review, lithologic profiling using rapid assessment tools, vadose zone sampling, monitor well installation, and water level collection. Lithology profiling consisted of continuous soil core collection and electrical and hydraulic conductivity logging using the Geoprobe Hydraulic Profiling Tool (HPT). Based on the results of lithologic profiling and soil sampling, monitor well locations were proposed for the uppermost perched zones. Results of the HPT work provided strong evidence of a thick low permeable confining unit which served to protect the underlying sole source drinking water aquifer and regional water supply, and limited investigation to the shallow perched zones. Targeted monitor wells were installed in the perch zoned to determine if releases from site SWMUs to groundwater had occurred. This information was presented in the form of a CSM as part of the CCR.