Remedial investigations of karst aquifers: a case study at former Marietta Air Force Station, Lancaster County, Pennsylvania
A phased multi-disciplinary approach was used to investigate potential environmental impact on the overburden aquifer and karst (bedrock) aquifer from the historic use of a suspected fire training pit at the former Marietta Air Force Station in Lancaster County, Pennsylvania. Investigation techniques have included direct push technology, real-time sample analysis via use of a mobile laboratory, earth resistivity imaging/induced polarization, geophysical borehole logging, packer testing, installation of one multi-port well with five sampling ports set in the karst aquifer, installation of multiple conventional monitoring wells, and completion of multiple rounds of groundwater sampling and data analysis. Both the vertical and lateral extents of groundwater contamination by chlorinated volatile organic compounds were delineated in the overburden and karst aquifer. The pathway-focused human health risk assessment has indicated that groundwater remediation is required to meet the federal and state health standards for volatile organic compounds. Based on the hydrogeological conditions and the nature and extent of the delineated contamination, plumes in both the overburden and karst aquifers, chemical oxidation (in the karst aquifer), and enhanced bioremediation (in the overburden aquifer) have been selected as the preferred alternatives for groundwater remediation, with monitored natural attenuation included as a common component of both alternatives.