Record of Decision System (RODS)
DOVER GAS LIGHT CO.
|Site Name:||DOVER GAS LIGHT CO.|
|City & State:||DOVER DE 19904|
|NPL Status:||Currently on the Final NPL|
Please note that the text in this document summarizes the Record of Decision for the purposes of facilitating searching and retrieving key text on the ROD. It is not the officially approved abstract drafted by the EPA Regional offices. Once EPA Headquarters receives the official abstract, this text will be replaced.
The Dover Gas Light site is in Kent County, Delaware, within the City of Dover. It occupies the western half of the city block bounded by New Street, Bank Lane, North Street, and Governor's Avenue. From 1859 to 1948, the site was used for the production of gas from coal through a process known as coal gasification. The gas was used primarily for lighting and cooking purposes. During this time, various buildings, gas holders, and storage areas used in the gasification process were located at the site. When the plant was closed in 1948, all the structures, except for one, were demolished. Much of the plant was removed, but sections of process equipment containing coal oil and/or coal tar were buried on-site. The remaining building was used by the Delaware State Museum for storage until it was destroyed by fire in 1982. The site is currently an unpaved parking area used by the Delaware State Museum and other nearby businesses.
The size of the former coal gas plant is approximately one acre while the size of the site is approximately 23 acres due to the spread of contamination in the groundwater. Only the plant area itself has contamination from the coal gas process in soil near the surface. Contamination was first discovered at the site in 1984 when the State conducted studies in preparation for the construction of a Family Court building. Remains of the coal gasification plant were found buried on-site and oily soil samples yielded significant contamination levels. As a result, the State installed and sampled 16 monitoring wells on and near the site at varying depths below the ground surface. The shallow groundwater beneath and to the southeast of the former plant location was contaminated with several volatile organic compounds (VOCs) and polynuclear aromatic hydrocarbons (PAHs). A portion of the groundwater contained an oily layer of contamination called a non-aqueous phase liquid (NAPL).
The Environmental Protection Agency (EPA) proposed to put the site on the National Priorities List (NPL) in January 1987. The site was formally added to the NPL in October 1989.
Operable Unit 1 (OU1):
A Record of Decision (ROD) was completed in August 1994, which addressed soil contamination at the location of the former coal gas plant and groundwater contamination in the Columbia Aquifer associated with the former coal gas plant. In December 1997, a ROD Amendment was issued which specifically modified the portion of the 1994 ROD selected remedy which addressed the contaminated soil.
The goal of this alternative would be to protect museum workers from surficial soil contamination and to prevent the soil contamination from being a potential and/or continuing source of groundwater contamination. To protect museum workers from exposure to soil contamination, the parking lot would be paved, thereby preventing contact with any contamination. As an added benefit, the pavement would also decrease the amount of infiltrating rain water, reducing the potential for contamination to migrate to the groundwater.
Under this alternative, the tar-filled soil contaminated in the gas holders would be excavated (they are approximately 8-10 feet in depth) and shipped off-site for thermal treatment. Heavy contamination outside the gas holders would be addressed by soil vapor extraction (SVE). SVE would remove the more volatile contaminants (which are also the most mobile in groundwater) and would increase the biodegradation of contaminants in the soil by pulling more oxygen below the surface. The SVE system would continue to operate until it was no longer removing contamination and was no longer aiding subsurface biodegradation.
The top several feet of the groundwater aquifer which contains the non-aqueous phase liquid (NAPL) material would be addressed as part of the groundwater cleanup rather than excavated as in the original clean-up plan. This alternative also includes institutional controls (for example, the existing agreement between the State of Delaware and Chesapeake Utilities Corporation) to prevent future development of the former coal gas plant location in a way that could harm the public.
Estimated Capital Cost: $1,300,000
Present Worth Cost of O&M: $200,000
Estimated Annual O&M Cost: Not Documented
Estimated Present Worth Cost: $1,500,000
Estimated Present Worth Cost (combined including groundwater cleanup): $2,700,000
Overall Estimated Site Cleanup Cost: $4,200,000
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