Mid-Atlantic Superfund

EPA Region 3 (Mid-Atlantic)

Delaware
New Castle County
10 miles south of Wilmington

EPA ID# DED000606079

1st Congressional District

Last Update: June 2008

Other Names

None

Current Site Status

The U.S. Environmental Protection Agency is overseeing the operation and maintenace of the cleanup of the Tybouts Corner Landfill Site. Construction activities for this site were completed in September 1995. Operation and maintenance activities associated with the landfill cap, gas extraction system, and the monitoring system(s) are ongoing. Groundwater monitoring results demonstrate that the concentration of contaminants in the ground water are approaching cleanup levels. The pumping wells were shut down in May 2007. EPA continues to monitor the groundwater and air to ensure the remedy remains protective.

Site Description

Tybouts Corner Landfill Site is located in New Castle County, Delaware approximately 10 miles south of Wilmington and four miles west of the Delaware River. The site was used by the New Castle County Department of Public Works as a municipal sanitary landfill that also accepted industrial wastes from December 1968 until July 1971. The landfill consisted of two noncontiguous sections, a west landfill that was about four acres in size and the main landfill that was about 47 acres, ranging from five to 40 feet thick. The first reported occurrence of contamination from the Tybouts Site was a domestic water well in May of 1976. A second private well was found to be contaminated in 1983. These are the only two water supply wells reported to be contaminated from the site to date.

Site Responsibility

Cleanup of this site is the responsibility of federal and state governments and parties potentially responsible for site contamination.

NPL Listing History

This site was proposed to the National Priorities List of the most serious uncontrolled or abandoned hazardous waste sites requiring long-term cleanup action on January 22, 1987. The site was formally added to the list on February 21, 1990, making it eligible for federal cleanup funds.

Threats and Contaminants

The site was ranked on the NPL in 1983 due to a threat of contamination of the regional aquifer, the primary source of water in this region in Delaware. The site also presented a threat to domestic wells in the immediate vicinity. In 1985, EPA installed a water line to supply homes in the vicinity of the site with public water. The contaminants of concern include vinyl chloride, benzene, and 1,2-dichloroethane, and various other organic and inorganic chemicals.

Contaminant descriptions and associated risk factors are available on the Agency for Toxic Substance and Disease Registry, an arm of the CDC, web site at http://www.atsdr.cdc.gov/hazdat.html

Cleanup Progress

The cleanup remedy, which was completed in 1995, included: a groundwater pumping system consiting of eight extraction wells to contain contaminated groundwater at the landfill; a subsurface slurry wall to prevent clean groundwater from entering the landfill; a multi-layer cap to prevent rain from entering the waste material in the landfill; and a passive venting system to prevent the build-up of landfill gases within the landfill.

Landfill gas was detected outside the boundaries of the landfill in 1996, and a temporary active gas venting system was installed. A permanent active gas venting system was installed in 2000.

During the last 12 years, quarterly sampling has been conducted to ensure the remedy is functioning as designed. Contaminant concentrations in groundwater decreased significantly and EPA and DNREC agreed to shut down the pumping wells in May 2007. Quartely monitoring of the groundwater is ongoing.

Samples were collected from the gas vents and the data was incorporated into an air model to evaluate any risk associated with exposure to the air emissions. The air modeling of the vent data demonstrated that emissions from the vents do not present an unacceptable risk to human health. The active gas venting system is effective in preventing the migration of underground landfill gas beyond the landfill property boundary. Annual monitoring of the passive landfill gas vents continues.

Contacts

Site Contacts

Administrative Record Locations