SELECTION AND APPLICATION OF INVESTIGATIVE METHODS FOR A CHLORINATED SOLVENT IMPACTED KARST AQUIFER

A hydrogeologic investigation of chlorinated solvent (cVOC) impacted groundwater was conducted in the karst Knox Group dolomite aquifer in East Tennessee. Previous site investigations were limited to karst features and impacted groundwater in shallow bedrock (< 50 feet). This investigation focused on evaluating deep bedrock groundwater quality and the distribution of primary and secondary porosity features present in the karst aquifer that influence groundwater flow, dissolved-phase and DNAPL contaminant transport. Given the lack of clear and consistent guidance on investigating contaminated karst, selecting the appropriate investigative tools was critical to designing the study and ensure the collection of reliable data without excessive cross contamination between transmissive zones in the aquifer.

Eight bedrock core holes, up to 176 feet deep, were advanced by wire line coring. Rock cores provided a direct assessment of lithology and integrity. Transmissive intervals, inferred by drilling water loss, were isolated by packers or low-flow sampling techniques through the core barrel to obtain vertically discrete groundwater samples. The ColorTec Ground-Water Tester provided semi-quantitative, dissolved cVOC concentrations in real-time to assess the presence of DNAPL, the potential for vertical contaminant transport from continued coring, and the need for a temporary vertical seal upon completion. Confirmation samples, analyzed at a fixed-base laboratory, were evaluated in conjunction with passive groundwater samples obtained from the open core holes using polyethylene diffusion bag (PDB) samplers, resulting in separate vertical cVOC profiles for each core hole. A borehole geophysical tool suite (mechanical caliper, acoustic and optical televiewer, and natural gamma) was deployed at four core holes to evaluate bedrock structure and lithology. Heat pulse flowmeter testing indicated the presence of vertical groundwater flow zones in the core holes, and fluid temperature and resistivity data addressed overall groundwater character.

Collectively, the investigative tools maximized core hole information, minimized vertical cross contamination, and provided vertically discrete data for the design and installation of multi-level Water FLUTe monitoring wells in seven core holes.