oa Application of Geophysics for Environmental Characterization, Remedial Design, and Remedial Implementation at Three Fractured Bedrock Sites Impacted by Chlorinated Solvents in New England

Over the last sixteen years, geophysical methods have been used at multiple sites to characterize fractured bedrock impacted with chlorinated solvents and dense non-aqueous phase liquids (DNAPLs). Borehole geophysical data is essential to develop accurate site conceptual models (CSM) for bedrock contaminant source areas and plumes. these data must be integrated with other hydrophysical and chemical data in order for the CSM to support remedial design decisions. the importance of this integrated characterization approach lies in the recognition that at many older DNAPL impacted fractured bedrock sites, the original DNAPL mass has been transferred from the fracture network to the rock matrix through DNAPL dissolution and matrix diffusion. Three case studies are presented to illustrate how geophysical data including 1) borehole geophysics (caliper, temperature, electric logs, acoustic televiewer (ATV), digital borehole image processing systems (BIPs), heat pulse flow meter (HPFM) logging), 2) interwell test data (HPFM interference testing, electrical resistivity Tomography (ERT)), and 3) surface methods (azimuthal resistivity) have been successfully integrated with other primary data, including: straddle packer groundwater data, methanol extracted rock matrix data, conservative interwell tracer tests (CITT), and partitioning interwell tracer tests (PITT). the platform for the CSM is a dynamic three dimensional (3-D) visualization tool that allows a comprehensive Interpretation approach by Integrating these independent, multi-characteristic data. the visualizations relate the distribution of contaminants in specific fractures and rock matrix porosity to the hydraulic characteristics of the fracture network. <br>the three sites to be presented include two sites in Maine and one in Massachusetts. Geophysical data in one of these case studies was used to support regional scale fractured flow contaminant fate and transport models and two Technical Impracticality (TI) waiver evaluations. the geophysical data at the other two sites supported detailed source area characterizations for evaluating and implementing remedial actions supported by tracer studies.