Superfund Information Systems: Site Profile

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The 23-acre Dover Gas Light Co. site is located in Dover, Delaware. From 1859 to 1948, the Dover Gas Light Company processed coal to produce gas for use in street lamps on site. Operators buried process materials containing coal tar residues on the site. After the plant closed in 1948, all structures except a brick garage were demolished. Much of the plant was removed, but sections of the tanks and other process equipment were buried on site. These underground structures contained coal oil and/or coal tar. These waste disposal activities contaminated soil and groundwater with hazardous chemicals.

Approximately 10,000 people live within one mile of the site and an estimated 45,000 people are served by public and private wells within three miles of the site.

EPA proposed the Site to the National Priorities List (NPL) in January 1987.  It was listed on the NPL in October 1989, making it eligible for federal cleanup funds.

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What Has Been Done to Clean Up the Site?

EPA's decisions on how to address site contamination are formally outlined in legal documents known as Records of Decision. The First Record of Decision (ROD) for this site was issued on August 16, 1994. In it, EPA called for the excavation of contaminated soils and off-site treatment. Also, EPA selected a combination of containment and natural attenuation for the groundwater.  An amendment to the ROD was issued in December 1997.

In May 1995, EPA ordered Chesapeake Utilities Corporation and to General Public Utilities Corporation, ordering them to implement the ROD. Only Chesapeake Utilities Corporation complied with this May 1995 order.

In the December 1997 ROD amendment, EPA modified the soil cleanup requirements. Contaminated soil would be excavated from within the three underground brick structures called gas holders. Remaining soil contamination would be addressed by using soil vapor extraction (SVE) technology and capping the one-acre lot with an asphalt parking lot.

In 1998, Chesapeake finished excavating soils from inside the gas holders. In 2000, the SVE system finished removing soil contamination from the remaining soil. This work included: non-aqueous phase liquid (NAPL) monitoring and recovery, soil vapor extraction and gas holder remediation and involved constructing a parking lot.

On April 25, 2002, Chesapeake Utilities Corporation (CUC) began the parking lot construction. The parking lot construction, among other things, restricts exposure to soils and limits storm water infiltration in soils. CUC completed soil cleanup work in September 2002. EPA completed its second five-year review on this remedy in July 2009.

In 2000 design for the groundwater containment system was stopped to further reconsider the releases of perchloroethene from a nearby dry cleaner. First Energy (formerly General Public Utilities Corporation) completed a groundwater investigation to define the extent of the perchloroethene contamination. EPA formally accepted the results of this study in December 2005.

EPA used the 2005 groundwater investigation completed by First Energy to plan a site-wide supplementary groundwater investigation, intended to fill any remaining data gaps.

EPA completed groundwater sampling for the first phase of this investigation in April 2006, and completed the second phase of groundwater sampling in January 2008.

EPA also conducted an initial round of vapor intrusion testing at several locations in Dover between April and July 2008.


A second vapor intrusion study was completed in 2010. EPA completed the field investigation of groundwater contamination beneath the City of Dover in 2011.

EPA completed the Supplementary Groundwater Remedial investigation on July 12, 2013.


EPA completed the Human Health and Ecological Risk Assessments in December 2014.





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What Is the Current Site Status?

EPA is currently conducting a Five-Year Review of the soil remedy at the Dover Gas Light Site, to be completed in July 2019.

EPA is currently conducting a Feasibility Study at the Dover Gas Light Site to determine the best approaches to address groundwater contamination at the site. That effort should be completed in early 2019.


Tests confirm that the City of Dover's drinking water supplies currently remain unaffected by site contamination.

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