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The Millsboro TCE Site includes a probable source area, a TCE-contaminated ground water plume, and the public drinking water supply system operated by the Town of Millsboro. The probable TCE source area is located at the intersection of Wharton Street and South Dupont Highway. The area is presently a vacant lot. Formerly, the property at the probable source area included a laboratory facility which manufactured poultry vaccines between approximately 1952 and 1999. The facility included an underground tank suspected to be the probable source of the TCE contamination to the public water supply wells. The Site additionally includes a plume of TCE-contaminated groundwater migrating from the probable source area towards and into public drinking water supply wells serving the Town of Millsboro. There are two supply wells known to be contaminated by TCE. The entire area of the Site is located on relatively flat ground and under both residentially and commercially populated areas of Millsboro, DE.
The analytical results of the routine analysis of water samples collected from the public supply wells indicate the presence of trichloroethylene. Since 2005, TCE in the most contaminated well has been detected at concentrations as high as about 800 ug/L; but within the past year TCE has been routinely detected between approximately 200 and 350 ug/L. The area of contaminated groundwater is estimated to be approximately 1500 feet long and 300 feet wide.
Several response actions were conducted at the Site between the late 1980’s and the late 1990’s that involved the removal of underground and above-ground storage tanks. However, it is unknown if any of these actions involved the removal of any source of TCE. Additionally, environmental evaluations of the Site were performed in1997, but the suspected source of TCE was not established. After discovery of the elevated TCE in the drinking water supply of the Town of Millsboro in 2005, the public wells were initially taken out of service and then ultimately fitted with granular activated carbon units to remove TCE from the wells. Following an investigation in 2005 by a Delaware Department of Natural Resources and Environmental Control (DNREC) contractor, the probable source area was identified. The DNREC conducted an interim action at the Site which involved the removal of underground tanks and piping which were suspected to function as drywell, septic, or leaching tanks. The sludge in at least one of these tanks contained elevated concentrations of TCE. DNREC removed the sludge and approximately 209 tons of contaminated soils surrounding the underground tanks.
EPA has initiated activities to investigate the potential for potentially responsible parties to assume responsibility for the provision of carbon.
The EPA OSC completed a removal site evaluation at this Site utilizing the existing ground water sampling information supplied by DNREC. The threat evaluation is summarized in the Action Memorandum and indicates that the public could be adversely impacted by the release of TCE should the carbon filter units at the public wells not be routinely changed.
The EPA approved an Action Memorandum and CERCLA funding in the amount of $420,000 for response activities at this Site. The funding is basically focused on the sampling of the water and the provision of fresh carbon for the existing carbon filter units when needed.
The OSC visited the Site on August 25, 2009, to meet with the Town of Millsboro and initiate coordination for the assumption of responsibilities by the EPA.
The OSC issued documents to engage the services of a technical contractor (Tetra Tech) to conduct sampling activities and a response contractor (Guardian Environmental Services) to manage the provision of carbon for the filter units at the Site.
The sampling effort will occur weekly and begin September 9, 2009. The response contractor will also be present to collect information which will be used to prepare a work plan relating to the provision of carbon.
Conduct routine sampling of ground water and drinking water.
Change carbon in filter units when data indicate that breakthrough could cause TCE contaminatio exceed Safe Drinking Water standards.
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