IN SITU THERMAL DESORPTION (ISTD) OF PCBs

A field demonstration is described in which a new in-situ thermal desorption soil remediation process (ISTD–Thermal Wells) is shown to remove high-concentration PCB contamination from clay soils. The demonstration was conducted at the Missouri Electric Works (MEW) Superfund site in Cape Girardeau, Missouri, from April 21 through June 1, 1997. For this demonstration, twelve heater/vacuum wells were completed in a multiple triangular array with a 5-foot well spacing to a depth of 12 feet. During the remediation, electrical-resistance heating and vacuum were applied to the wells for a period of 42 days. Soil temperatures were monitored throughout the experiment, and soil samples were taken with a split-spoon sampler fitted with six-inch brass coring sleeves to verify the removal of contaminants. Temperatures above 1000°F were achieved in the interwell regions, and PCB concentrations in the treated area were reduced from a maximum concentration of approximately 20,000 ppm to non-detect (i.e., <33 ppb) by EPA Method 8080. The system destruction removal efficiency (DRE) for PCBs was 99.9999998%.