PCB Soil Solvent Extraction

By Mark Meckes, EPA Risk Reduction Engineering Laboratory

The EPA Superfund Innovative Technology Evaluation Program (SITE Program) has successfully demonstrated the Terra-Kleen solvent extraction system's ability to reduce polychlorinated biphenyl (PCB) concentration in soils to less than 2 milligrams per kilogram (mg/kg). This is equivalent to the Toxic Substance Control Act's (TSCA) incineration performance guidance level. The Terra-Kleen solvent extraction system has overcome many of the soil handling, contaminant removal and regulatory restrictions that have made it difficult to implement a cost-effective PCB soil treatment system.

The Terra-Kleen system is a batch process that operates at ambient temperatures and removes organic contaminants from soils using proprietary solvents. After soils are washed with solvent, contaminated solvent passes through a solvent recovery unit, where contaminants are separated from the solvent and concentrated, reducing the contaminant volume for disposal. Terra-Kleen maximizes its waste reduction potential by: (1) recycling the extraction solvent as part of the routine system operations; (2) maintaining a closed-loop process to reduce volatile emissions; and (3) concentrating organic contaminants. For the initial treatability studies portion of the

demonstration, the SITE Program obtained 1-ton batches of soil from each of three PCB-contaminated sites and shipped the soil to Terra-Kleen's testing facility in Okmulgee, Oklahoma. Soils were also obtained from Sites 4 and 6 at the Naval Air Station North Island (NASNI) near San Diego, California and from a third site in Anchorage, Alaska. Analyses of all demonstration soils revealed that Aroclor 1260 was the only PCB mixture present. PCB concentrations in untreated soils ranged from 17 to 640 mg/kg. Following treatment, PCB removal efficiencies ranged from 95 to 99%.

Successful removal of PCBs during the treatability study led to a pilot-scale demonstration at NANSI in June 1994. Treated soil concentrations for the NASNI Site 4 pilot-scale demonstration were consistently below 2mg/kg. Untreated PCB concentrations in the soil had ranged from 129 to 168 mg/kg; removal efficiency rates ranged from 98.7 to 98.9%. Completion of the pilot-scale demonstration at NASNI has encouraged the U.S. Navy to select Terra-Kleen to implement full-scale remediation at three NANSI PCB-contaminated sites, totalling about 5,000 cubic yards of soil.

Additionally, as a result of the PCB pilot-scale results at NANSI, the Navy has chosen TERRA-Kleen to implement a full-scale system to remediate 500 tons of pesticide contaminated soils at NCS-Stockton. There, analytical results of samples collected from the first 20-cubic-yard container of treated soil showed 98% removal for dichlorodiphenyldichloroethane (12.2 mg/kg in untreated soil); 99.4% removal for dichlorodiphenyldichloroethene (1.5 mg/kg in untreated soil); and 98.9% removal of dichlorodiphenyltrichloroethane (80.5 mg/kg in untreated soil). Full-scale remediation began in July 1994.

In addition to PCBs and the pesticides discussed above, the Terra-Kleen system is designed to remove petroleum hydrocarbons, chlorinated hydrocarbons, polynuclear aromatic hydrocarbons, polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans from soils, sludges and sediments.

For more information and to get on the mailing list for reports, call Mark Meckes at EPA's Risk Reduction Engineering Laboratory at 513-569-7348 by phone or at 513-569-7676 by FAX.