From 1953 until 1992, the Missouri Electric Works Inc. (MEW) operated a 6.4 acre site, located in an industrial area in Cape Girardeau, Missouri. MEW sold, serviced, and maintained electric motors, transformers, and transformer controls at this facility. Historical operations included salvaging transformer oil and materials from old equipment; copper wire was sold and the transformer oil was filtered and reused. It was estimated that 28,000 gallons of oil were released at the site. The results of a Remedial Investigation (RI), conducted between September 1989 and March 1990, showed PCBs in the surface and subsurface soils (as high as 58,000 mg/kg in soils found on site and 2,030 mg/kg in off-site soils). The areal extent of PCB concentrations in the soil that were greater than 10 mg/kg was estimated to be 295,000 square feet (ft2) or 6.8 acres. A Record of Decision (ROD), signed in 1990, specified excavation of PCB-contaminated soil followed by incineration, and extraction and treatment of groundwater. However, the MEW PRP Steering Committee proposed in situ thermal desorption of the soil, and an Explanation of Significant Differences (ESD) was issued for this site in January 1995 which included thermal desorption as an acceptable process for treating site soils. In January 1997, EPA and MDNR accepted a Demonstration Test Plan for this technology.
TerraTherm's in situ thermal desorption (ISTD) technology was demonstrated at MEW to treat subsurface soil contamination in an area near a former PCB storage pad. The objectives of the demonstration were to clean soils to below cleanup levels and achieve a destruction and removal efficiency (DRE) of greater than 99.9999% for PCBs. Twelve heater/vacuum wells were installed in a triangular pattern, spaced 5 ft apart. A vapor seal was constructed over the entire test area to insulate and reduce heat loss, and to seal the surface of the test area against vapor emissions. The MU-125 mobile process unit used for the demonstration was equipped with a particulate cyclone, a Thermatrix ES-125 flameless thermal oxidizer, and two carbon canisters in series. Three distinct temperature phases were recorded during the heating process. During the third (superheating) phase soil temperatures rose to over 1000°F. The vendor used this data to estimate that about 50% of the total soil volume reached a temperature of over 1100°F. The results of soil samples taken after completion of the 42-day demonstration showed that the concentration of PCBs in all samples was below the 2 mg/kg cleanup goal and that PCB concentrations were below the detection limit in the majority of samples. Results of stack testing showed that the DRE for PCBs was 99.9999998%, meeting the goal of 99.9999%.
The vendor used data from the demonstration to estimate that the cost for a full-scale application is between $120 and $200 per cubic yard for "most standard sites." According to the RPM, the Missouri Electric Works Steering Committee has retained another experienced vendor to perform the full-scale work at the Missouri Electric Works site. The vendor submitted a lower cost proposal than TerraTherm.