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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 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 and these 2 wells have carbon filtration units which remove contamination before delivering the treated water to the community of Millsboro.
Based upon a removal site evaluation, the OSC proposed and EPA Region III approved a Removal Action at the Site. An Action Memorandum was signed on July 14, 2009, and included funding in the amount of $420,000 to conduct sampling of drinking water and drinking water sources (ground water) and to change carbon filtration units in which contaminated ground water is treated before delivery to the community of Millsboro. The required sampling was initiated in September 2009 and the EPA response contractor was mobilized to the Site September 9, 2009 in order to initiate activities enabling EPA to be ready to change the carbons when needed.
The Site was proposed to the National Priorities List and was subsequently finalized on that List during the timeframe of the Removal Action. A Remedial Project Manager was assigned and initiated the process of identifying potentially responsible parties (PRPs) and seeking to get those parties to assume responsibility for the activities conducted under the Removal Action. An Order requiring response actions from PRPs was signed by the Region on May 10, 2010. The PRPs initiated routine sampling in May 2010 and are now preparing for future carbon changeout activities.
The sampling occurred weekly between September 2009 through April 2010. The carbon filtration units were changed in one well in November and in the other well in December 2009. Now that the PRPs are assuming the activities of the EPA Removal Action, the scope and intent of the Removal Action as selected in the July 2009 Action Memorandum are completed.
Weekly ground water and drinking water sampling and analytical activities were initiated in September 2009 and were routinely conducted by the EPA START contractor (Tetra Tech) through April 2010. The samples were analyzed for volatile organic compounds by laboratories participating in the EPA Contract Laboratory Program (CLP). Notably, TCE and its breakdown products were analyzed in each sample. Ultimately, the sampling and analytical responsibilities were transferred in May 2010 to a contractor engaged by potentially responsible parties identified by EPA.
During the Removal Action, samples were collected from 2 public wells and from 2 points in the distribution system, At each public well, a sample was collected before the 2 carbon units at each well ("lead" sample), from between the 2 units present at each well site ("middle" sample), and from a point after the carbon units at each well ("lag" sample). The highest concentration found at well #1 was 230 ug/L detected on 2/22/10. The highest concentration detected at well #2 was 280 ug/L on 9/9/09. Concentrations after the carbon units did not exceed 0.5 ug/L..
Over the course of the response action, the analytical results were routinely reviewed by EPA and the Town of Millsboro. The analytical results were also sent to the Delaware Department of Natural Resources and Environmental Control (DNREC). The responsibility for determining the need for a carbon change in order to assure the protection of the residents of the Town of Millsboro was, by agreement, that of the Town of Millsboro.
The carbon units attached to the 2 contaminated wells were changed over a 3 day period in November and December 2009 by Siemens under subcontract to the EPA ERRS contractor (Guardian Environmental). The spent carbon was shipped off-Site to Siemens Water Technologies for regeneration/re-use.
The Site is now on the National Priorities List (NPL). The sampling and analysis of the ground water and drinking water as well as the future changeout of the carbon filter units is addressed pursuant to an Order to potentially responsible parties. No further Removal Actions are expected and the Action is completed.
Await final costs.
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