Post-Remediation Source Assessment and Data Interpretation to Achieve Regulatory Closure at a Trichloroethylene and Petroleum Hydrocarbon Site

摘要

Background/Objectives. Trichloroethylene (TCE) was detected in the water supply wells for the Municipality of Skagway, Alaska, in 1987. In 1991 the Alaska Department of Environmental Conservation retained a consultant to assess the potential source of the TCE in the water supply wells. A railroad maintenance yard located 700 metres hydraulically up gradient of the wells was identified as a potential source. In 1996 investigations at the railroad maintenance yard were conducted and a co-mingled petroleum hydrocarbon and TCE plume was identified extending 100 metres off-site. A combination of source removal and in situ air-sparging with soil vapour extraction (AS-SVE) was used to remediate a co-mingled plume between 1998 and 2003. Annual post remediation groundwater monitoring and supplemental investigations have been conducted at the site since the remedial activities were completed in 2003. The remedial excavation and ASSVE system was successful in reducing the size of two co-mingled plumes to within the property boundaries; however, annual groundwater monitoring data obtained since completion of the remediation suggested a possible increasing trend in TCE concentration at one on-site groundwater monitoring well. Obtaining regulatory closure for the site with TCE concentrations at one location showing a potentially increasing trend was problematic.