EPA Superfund Site

PALERMO WELL FIELD GROUND WATER CONTAMINATION

WA | EPA ID WA0000026534

About this site’s exposure pathways: As of June 2024, the Palermo Wellfield Superfund Site is considered “Insufficient Data to make a Human Exposure evaluation” (HEID) because of newly re-evaluated potential exposure pathways for vapor intrusion of trichloroethene (TCE) into residences and for vapor intrusion of tetrachloroethene (PCE) into commercial spaces. The tetrachloroethene (TCE) plume, which due to site topography impacts shallow groundwater within a residential neighborhood, may be causing detections of TCE in indoor air. The potentially responsible party (PRP) for Operable Unit 1 (OU-1, TCE plume) conducts indoor air sampling every 9 months at households in the residential neighborhood. In 2017 and 2018 there was a detection of TCE in indoor air at one residence that exceeded the Record of Decision (ROD) cleanup level of 1.46 micrograms per cubic meter (ug/m3). A vapor mitigation system was offered to the homeowner by the PRP, but the homeowner declined to allow the system to be installed. No detections exceeding the ROD cleanup level have been detected in indoor air in households sampled in the neighborhood since. However, the neighborhood has 48 households, and less than half of the house households typically allow sampling. The change in frequency and consistency in houses that allow sampling causes uncertainty in determining if groundwater to indoor air is a current completed pathway that is causing uncontrolled human exposure. PCE has been detected in sub-slab soil vapor samples at a commercial dry cleaning facility and adjacent businesses exceeding criteria that indicate a potential vapor intrusion risk, however, due to the prolonged use of PCE within the building, and connections between businesses and equipment that may have been used with PCE remaining on site, it is difficult to establish a pathway between sub slab soil vapor concentrations and indoor air concentrations. EPA is installing an soil vapor extraction (SVE) system and conducting a pilot test to determine the effectiveness of a horizontal extraction well for soil vapor extraction, which will eliminate the potential human exposure while operational and is developing a feasibility study and ROD Amendment to address soil vapor, groundwater and soil contaminates of concern that exceed remedial goals.
The activities planned to make the Human Exposure (HE) evaluation include continuing to monitor crawl space and living spaces for chlorinated solvents on a 9-month interval within the Palermo neighborhood, reaching out to the community to provide education about the site. EPA and the PRP, Washington Dept. of Transportation (WSDOT) are developing a focused feasibility study and ROD Amendment to address the TCE groundwater plume and any potential vapor intrusion pathways. EPA and WSDOT have an Administrative Settlement and Order on Consent (ASAOC) to address TCE detections that exceed acute exposure criteria of 2 ug/m3 with a time critical removal action (TCRA). An Action Memo has been signed to execute this TCRA if needed. A ROD Amendment is also being developed for OU-2 (PCE Plume) which will control and eliminate potential human exposure pathways. HE Under Control (HEUC) will be achieved for OU-2 once the SVE system is in place and vacuum influence is confirmed to be present within the vadose zone under the building, anticipated to be completed by October of 2024. HEUC will be achieved in OU-1 once an alternative has been selected, designed and implemented that reduces and/or controls TCE concentrations in indoor air, and sampling confirms levels are below the anticipated new CUL for that exposure pathway. TCE risk levels are anticipated to be adjusted lower to match the most current risk assessment guidance. HEUC control is anticipated in 2030.