A FRACTURE TRACE, VERY LOW FREQUENCY AND TEMPERATURE PROFILE INVESTIGATION TO DETERMINE LOCATIONS OF LATERAL INFLOW BENEATH A SUPERFUND SITE, BLOOMINGTON, INDIANA

The Lemon Lane Landfill [a Superfund site] is a former municipal solid waste disposal site contaminated with polychlorinated biphenyls [PCBs] located on the Mitchell Plain, in south-central Indiana. Highly fractured Mississippian carbonates of the Blue River and Sanders Groups form the bedrock under the landfill. These carbonates contain surface and subsurface karst features such as sinkholes, springs and conduits.

During 1950 to 1964, disposal of capacitors manufactured by the former Westinghouse Corporation occurred at the site. These capacitors were manufactured with PCB-containing oil. Leaking oil entered the groundwater system through soil macropores and fractures and discharged at the Illinois Central emergence, a karst spring. Numerous investigations have been performed to locate the source and quantify the extent of contamination. Results of these investigations suggest that concentrated pockets of PCB contaminated soil and water are flushed from the rock below during rain events. This is supported by the spring hydrograph, which shows that the highest concentration of PCBs occurs at the peak of spring outflow. In 1987, a hypalon cover was placed over the landfill to stop infiltrating precipitation from flushing more PCBs into the bedrock and to prevent exposure to nearby residents. A set of studies was designed to determine if significant horizontal groundwater flow was occurring beneath the cover.

We performed a fracture trace analysis which shows two prominent fractures intersecting the landfill. These fracture locations coincide with temperature and Very Low Frequency [VLF] anomalies. Thermistors installed at one fracture location monitored soil temperature for any changes during rain events. Results showed a decrease in soil temperature during several rain events, which suggest a dendritic flow pattern of groundwater entering the system below the landfill. Two other temperature anomalies also suggest lateral inflow. The VLF surveys illustrate a sharp gradient in the VLF values; these gradients indicate the locations of shallow groundwater flow zones.