Client: Shelby County Landfill
Project: Shelby County Landfill Groundwater Sampling
A major threat to the Memphis aquifer is contamination. Though the Memphis aquifer is protected mostly by a thick overlying clay unit (aquitard), there are breaches in this clay that offer connectivity to the shallow aquifer. One such breach exists directly north of the former Shelby County Landfill at Shelby Farms, a landfill that was developed and closed prior to any EPA regulations that required in the least a liner and separation of household waste from hazardous waste. Because of leachate entering into the shallow aquifer, CAESER conducts groundwater sampling of the shallow and Memphis aquifers at this site.
The landfill is reaching the end of its 30-year post closure monitoring. However, multiple site investigations including a comprehensive groundwater sampling event in 2011 and annual sampling at wells within the aquitard breach show a continual deterioration of groundwater quality in the Memphis aquifer at the breach.
Efforts have been made to define the extent of the aquitard breach including near-surface geophysics. A S-wave seismic investigation conducted by CAESER in 2005 indicated potential paleochannels (ancient streams) that may act as a conduit for leachate to move into the Memphis aquifer. A more recent resistivity study (2012) shows the impact of leachate in groundwater in the area north of the landfill and mirrors the results of the seismic study and groundwater sampling events. A conceptual model is in the works that will incorporate well boring and near-surface geophysics data to get a better idea of what is happening in the subsurface.
Project Status and Deliverables:
CAESER is working closely with Shelby County government to reduce the impacts leachate may have on the Memphis aquifer. The County used results from our 2012 investigation to address localized erosion of the landfill cap and pooling of rain water along the landfill skirt. By reducing the amount of infiltration into the landfill, this in turn reduces the amount of leachate that is produces and leaves off-site.
The former Shelby County Landfill is just one of many sites in and around aquitard breaches in Shelby County. The breaches pose a threat to the high quality of water found in the Memphis aquifer; thus, it is imperative for the community to identify the location of these breaches and the threat posed by contaminated sites nearby.