EFFECTIVENESS OF ELECTRICAL RESISTIVITY IN DELINEATING LEACHATE PLUME AT THE FORMER SHELBY COUNTY LANDFILL IN MEMPHIS, TENNESSEE

Ground-water contamination from waste stored in landfills and other waste sites is a global threat to fresh water supplies. The Shelby County landfill at Shelby Farms in Memphis, Tennessee, lies in the flood plain of the Wolf River and is known to be the source of low-level contamination in the underlying alluvial and Memphis aquifers. The unlined municipal and industrial waste landfill was in operation from the early 1960s to 1988. Prior to closure, discovery of a hydrogeologic “window” in the upper Claiborne confining unit overlying the Memphis aquifer 0.2 km north of the landfill led to several ground-water investigations by the U.S. Geological Survey to evaluate the threat posed to the Memphis aquifer, the regional source for municipal water supplies.

Identification of ground-water contamination is commonly achieved by chemical analysis of water sampled from monitoring wells; however, the distribution of monitoring wells does not always satisfactorily reflect the extent of ground-water contamination. This pilot study gauged the effectiveness of an electrical resistivity survey to identify the extent of contamination in a shallow aquifer beneath a landfill. Seven resistivity lines were completed north of the landfill using a SuperSting© R8/IP with an array of 28 electrodes at 10 meter spacing. Historical geochemical data and geologic logs were used to constrain resistivity data collected and produce a two-dimension cross-section of the subsurface. Preliminary results of the resistivity survey indicate impacted ground water in the shallow aquifer immediately north of the landfill, which is consistent with elevated specific conductance values and poor water quality observed in monitoring wells in the same vicinity during the July 2011 ground-water sampling event. Application of a full-scale resistivity survey may also improve the definition of the window orientation and lithology.