MULTIMEDIA RISK-BASED SOIL CLEANUP AT A GASOLINE-CONTAMINATED SITE USING VAPOR EXTRACTION

At a utility service center, gasoline from an underground storage tank had leaked into subsurface vadose zone soils for several years. To re mediated the site, a soil vapor extraction (SVE) system was installed and operated. At the completion of the SVE operation, gasoline-contain ing residues in several confirmation soil borings exceeded agency-mand ated cleanup levels. Rather than continue with SVE, a risk-based appro ach was developed to evaluate what levels of gasoline-containing resid ues could be left in the soil and still protect human health. The risk -based approach consisted of simulating the fate of chemical residues through the vadose zone and then into both the ground water and atmosp here. Receptor point concentrations were predicted, and health risks w ere assessed. The risk assessment concluded that ingestion of contamin ated ground water and inhalation of air while showering were the large st potential contributors to risk, and that risks associated with inha lation of vapor-containing ambient air are small. However, all predict ed risks are below the acceptable risk levels of 10(-6) individual can cer risk probability and 1.0 hazard index. Therefore, the lead agency accepted the recommendation that the site requires no further remediat ion. The service center continues normal operations today.