The Dover Gas Light Co. site covers 23 acres in Kent County, Dover, Delaware. It includes a former coal gas plant that operated from 1859 to 1948 and a former dry-cleaning facility. Buried coal tar residues and process equipment contaminated both soil and groundwater. EPA added the site to the National Priorities List in October 1989 after contamination was discovered in 1984 during drilling work.
Contaminants include volatile organic compounds such as benzene, toluene, ethylbenzene, xylene, and vinyl chloride, along with chlorinated solvents including trichloroethene and tetrachloroethene. Polycyclic aromatic hydrocarbons, including benzo(a)pyrene, are present in soil. Some contaminants exist as free-phase product in groundwater, meaning pure chemical sitting in the subsurface, not just dissolved traces. The city's drinking water supplies are currently unaffected by site contamination.
Soil cleanup, called Operable Unit 1, began in August 1998 and finished in September 2003. It involved soil vapor extraction, excavation of contaminated material from underground brick structures called gas holders, and construction of a paved asphalt cap. That capped area now serves as a parking lot for the adjacent Victrola Museum. A five-year review completed in July 2024 confirmed the soil remedy is working and protective of human health and the environment. EPA assessments also show that human exposure pathways are currently under control and groundwater contamination migration is stabilized.
Groundwater cleanup, Operable Unit 2, is still in progress. EPA completed a combined investigation and feasibility study in March 2023 and issued a cleanup decision that same month. The selected approach includes extraction wells, thermal treatment in place, off-gas treatment, groundwater and soil gas monitoring, and institutional controls. Remedial design work is scheduled to finish in September 2025, with active cleanup expected to run from September 2025 through approximately May 2027. The site is estimated to be ready for anticipated reuse between December 2026 and February 2027. Today, 69 on-site businesses employ 821 people and generate about $30.2 million in annual sales.
Community members can follow cleanup progress through fact sheets EPA has issued since 2003, with updates as recent as September 2025. For questions, community members can contact the EPA's Community Involvement Coordinator or Remedial Project Manager. Site documents are available at the Dover Public Library at 35 Loockerman Plaza or at the EPA Region 3 office in Philadelphia by appointment, by calling (215) 814-2396.
