Analysis of Field Data for Risk Assessment of Vapor Intrusion at a Trichloroethylene-Contaminated Site - A Case Study in Taiwan

The potential risks of vapor intrusion (VI) can arise from low bulk soil contaminant concentration existing in shallow soils beneath a building foundation. To assess VI risks for such a contamination scenario, a comprehensive study was conducted on a factory building located at a trichloroethylene (TCE)-contaminated site. This study involved the integration of various types of field data, including groundwater, bulk soil, soil gas and indoor air data, along with the utilization of the Vapor Intrusion Screening Level (VISL) calculator. Previously observed high TCE concentrations in soil gas are attributed to accumulation of TCE vapor within the unsaturated soil beneath the building floor, since ground surface is extensively paved at this site. These soil gas data do not directly correlate with the magnitudes of bulk soil and/or groundwater TCE concentration with the linear adsorption model. Soil gas TCE concentration exceeding 107 mu g/m3 (or bulk soil concentration exceeding 18.9 mg/kg) observed in shallow soils (at a depth of less than 1 m ) may pose health risk to the workers inside the building due to VI, as we have detected TCE vapor concentrations exceeding indoor air screening level several times in the past. This bulk soil TCE concentration, however, falls below soil pollution control standards for TCE, i.e., 60 mg/kg, in Taiwan. As a result, soil remediation is not considered at this site. Soil gas TCE concentrations have reduced to less than 106 mu g/m3 after two years of groundwater remediation work at this site. However, we have observed significantly higher soil gas TCE levels at a depth of 0.5 m compared to other depths. This discrepancy raises suspicions that an amount of TCE may still be trapped within the shallow soils that are not reached by groundwater table.