Electrical Resistance Heating Remediation at a Carbon Tetrachloride Site

摘要

Carbon tetrachloride was used as a carrier for the fumigant carbon disulfide in the grain industry during the 1950s to early 1980s. This practice left a carbon tetrachloride legacy at a number of grain storage facilities across the United States. At this Kansas facility, a significant source remained, including undissolved product extending 52 ft below grade adjacent to a grain elevator. Geology was dominated by clays. Those below 39 ft were associated with heaving clays. An estimated 3,220 lbs of carbon tetrachloride was present within the source area. Given the difficult geology and a stringent performance standard of mass reduction of carbon tetrachloride to less than 19 lbs total and less than 7 mg/kg remaining in all soil samples, the remedial technology selected was Electrical Resistance Heating. Carbon tetrachloride undergoes a hydrolysis reaction at elevated temperatures resulting in destruction in situ, and thus negating the need for off-gas treatment. In addition, a remedial groundwater goal of achieving 0.5 mg/L carbon tetrachloride and 0.5 mg/L chloroform in the source area was agreed upon with the regulatory agency. The geology resulted in variable heating within the source area. From the increase in chlorides in the source area monitoring wells, an estimated 8,100 pounds of carbon tetrachloride was destroyed via the hydrolysis reaction. However, the reaction rate proved slower than the literature suggested. Not all carbon tetrachloride was destroyed by hydrolysis, and an estimated 1,000 to 2,500 lbs of carbon tetrachloride and chloroform was extracted by a near-surface soil vapor extraction system. Overall destruction of contaminants exceeded 99.4 percent, resulting in meeting the mass remedial goal for carbon tetrachloride (8 lbs remaining) and meeting the 7 mg/kg goal on average, but not on every individual soil sample.