Multi-Method Geophysical Approach for Characterizing a Deep Fractured Bedrock Aquifer, Anniston Army Depot, Anniston, Alabama

The correct positioning of deep wells to monitor groundwater and entrained contaminants is greatly aided by using remote sensing methods. The geologic setting at the Anniston Army Depot (ANAD) consists of a sequence of fractured dolostones and clastic rocks that have been thrust-faulted, creating a highly complex and heterogeneous aquifer. The drilling of deep bedrock groundwater monitoring wells at this site is expensive due to depth, the nature of the rock, and the required use of casing-advancement drilling techniques; thus, well positioning is critical. A geophysical program consisting of seismic reflection, seismic refraction, electrical imaging (EI), and magnetotellurics (MT) has been used at ANAD to position groundwater monitoring wells at locations selected to intercept fractured bedrock. In addition, borehole geophysical and hydrophysical logging has been completed to assess flow conditions and to calibrate the geophysical survey measurements.