249 Hydrogeology (Posters)

Wednesday, 3 November 2010
8:00 AM - 6:00 PM
Hall D

REVISITING THE FORMER SHELBY COUNTY LANDFILL IN MEMPHIS, TENNESSEE, TO ASSESS ATTENUATION AND EXTENT OF GROUNDWATER CONTAMINATION IN A STEADY-STATE SYSTEM

Paper number: 249-2
Program: Technical Sessions
Time: 8:00 AM – 6:00 PM

Authors

Abstract

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 municipal and industrial waste landfill was in operation from the early 1960’s to 1988, and has undergone semi-annual post-closure monitoring since 1988. Prior to closure, discovery of a hydrogeologic “window” in the upper Claiborne confining unit overlying the Memphis aquifer north of the landfill led to several investigations by the U.S. Geological Survey (USGS). Results of those studies showed groundwater flow in the alluvial aquifer away from the river, through the landfill, and toward the window in the confining unit. The USGS studies and subsequent well construction and environmental tracer sampling indicate a downward vertical gradient to the Memphis aquifer and elevated concentrations of contaminants in the alluvial aquifer near the window and within the upper Memphis aquifer. Potentiometric surface maps constructed from water-level measurements in the alluvial and Memphis aquifers obtained over the past 22 years consistently show a steady-state groundwater system with little variation in groundwater flow.

Assessment of data collected over the past 20 years shows how groundwater contamination has evolved within the aquifer system. Since the initial comprehensive sampling that defined the horizontal extent of contamination, current monitoring consists of semi-annual sampling of four monitoring wells (two in the alluvial aquifer and two in the Memphis aquifer). A Geographic Information System (GIS) database was constructed to spatially evaluate groundwater sampling results from the USGS online database, state regulatory agencies, and other data sources. Future work will investigate the use of non-invasive (geophysical) methods, such as electrical resistivity tomography and electromagnetic induction, to identify the vertical and horizontal extent of contamination in the alluvial aquifer as well as build upon previous work to identify other windows in the confining unit.