Conceptual Site Model Development and Capture Zone Analysis for An MTBE-Impacted Aquifer within Fractured Granitic Bedrock

A fractured granitic bedrock aquifer has been contaminated with methyl tert-butyl ether (MTBE) at depths of up to 527 feet below ground surface (bgs).  Two nearby drinking water supply wells have become impacted above the regulated concentration for MTBE.  Geophysical logging and packer testing  was conducted on several monitoring wells drilled up to 527 feet bgs and results suggest that bedrock hydraulic conductivity is very low (10^-4 to 10^-6 centimeters per second) and flow is conducted through a network of very small fractures in specific intervals.  Pump testing was also conducted and results suggest interconnectivity between fractures, showing influence on water levels at wells over 200 feet apart (horizontally).   The results from the pump testing are used to examine the geophysical logging and packer testing data and to develop a conceptual site model that identifies specific fate and transport pathways.  Using this conceptual model, a capture zone analysis is performed to assess hydraulic containment.  The results of these characterization efforts and the evaluation of a remedial approach to address the source zone is presented.