Use of Vapor Extraction System and its Subsequent Reduction of Worker Exposure to Carbon Tetrachloride During Retrieval of Hanfords Legacy Waste

摘要

The Hanford Site is a decommissioned nuclear productions complex located in south eastern Washington and is operated by the Department of Energy (DOE). From 1955 to 1973, carbon tetrachloride (CCl(sub 4)), used in mixtures with other organic compounds, was used to recover plutonium from aqueous streams at Z Plant located on the Hanford Site. The aqueous and organic liquid waste that remained at the end of this process was discharged to soil columns in waste cribs located near Z Plant. Included in this waste slurry along with CCl(sub 4) were tributyl phosphate, dibutyl butyl phosphate, and lard oil. (Truex et al., 2001). In the mid 1980's, CCl(sub 4) was found in the unconfined aquifer below the 200 West Area and subsequent ground water monitoring indicated that the plume was widespread and that the concentrations were increasing. It has been estimated that approximately 750,000 kg (826.7 tons) of CCl(sub 4) was discharged to the soil from 1955 to 1973. (Truex et al., 2001). With initial concentration readings of approximately 30,000 parts per million by volume (ppmv) in one well field alone, soil vapor extraction began in 1992 in an effort to remove the CCl(sub 4) from the soil. (Rohay, 1999). Since 1992, approximately 78,607.6 kg (86.65 tons) of CCl(sub 4) have been extracted from the soil through the process of soil vapor extraction and 9,409.8 kg (10.37 tons) have been removed from the groundwater. (EPA, 2006). The success of this environmental cleanup process benefited not only the environment but also workers who were later involved in the retrieval of solid waste from trenches that were in or near the CCl(sub 4) plume.