Mid-Atlantic Superfund

EPA Region 3 (Mid-Atlantic)

Delaware
New Castle County
2 miles southwest of the City of New Castle

EPA ID# DED000605972

1st Congressional District

Last Update: June 2008

Other Names

Delaware Sand & Gravel Co. Landfill
Delaware Sand & Gravel-Llangollen
Army Creek Landfills

Current Site Status

All construction work is finished at this site. The site is now in the operations and maintenance phase. This phase includes operating the soil treatment system, plus quarterly groundwater and vapor testing to ensure the cleanup continues to be effective.

Site Description

The Delaware Sand & Gravel Landfill site covers 27 acres and is located approximately two miles from the City of New Castle, Delaware. Formerly a sand and gravel quarry, the site is now an inactive industrial waste landfill located adjacent to another National Priorities List site, the Army Creek Landfill. This privately-owned facility began landfilling operations in 1968. During its years of operation, approximately 550,000 cubic-yards of industrial wastes and construction debris were disposed of at the site. This included thousands of drums containing organic and inorganic hazardous substances. Three major waste disposal areas exist at the site: the Grantham South Area, the Drum Disposal Area, and the Inert Disposal Area. Shallow soil in a fourth area, known as the Ridge Area, became contaminated during the temporary storage of drummed chemical wastes at that location.

The 3-acre Drum Disposal Area was a repository for at least 13,000 drums containing liquids and sludge from chemical production, manufacturing, and petroleum refining processes. The one-half-acre Ridge Area included “hot spots” of contaminated surface soil due to chemical spills. The 2-acre Grantham South Area and 11-acre Inert Disposal Area each contain debris and mixed-chemical wastes buried 20-40 feet thick.

Hazardous substances buried at both the Delaware Sand & Gravel Landfill and the Army Creek Landfill have migrated into underlying groundwater. The Potomac Aquifer, which is used as a public source of water, lies beneath the site. Public water supply wells are located about one mile south of the site. Groundwater recovery wells, installed as part of the cleanup, are located between the site and the public supply wells. The recovery well network was designed in order to capture groundwater-borne contaminants migrating from both the Delaware Sand & Gravel and Army Creek Landfill sites. Recovered groundwater is routed through a treatment plant located on the Army Creek Superfund Site before being discharged to Army Creek (stream). The treatment plant was constructed as part of the Army Creek Landfill site cleanup work.

Site Responsibility

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

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 December 30, 1982. The site was formally added to the list on September 8, 1983, making it eligible for federal cleanup funds.

Threats and Contaminants

Contaminants found in groundwater include benzene, bis(2-chloroethyl)ether and 1,2-dichloroethane. Contaminants found in soil included benzene, bis(2-chloroethyl)ether, 1,2-dichloroethane, methylene chloride, polychlorinated biphenyls (PCBs), arsenic, antimony and lead.

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

In 1983-84, EPA removed 1,644 drums containing flammable solids and PCBs from the surface of the Drum Disposal Area. During that time, a temporary security fence was installed, and site studies began.

EPA issued its initial Record of Decision (ROD) for cleanup of the site in 1988 and amended the ROD in 1993 based on new information that came to light during pre-design field investigations.

The Grantham South Area was used for the disposal of construction debris and mixed chemical wastes. Work in this area included installation of a security fence and construction of a multi-layer landfill cap with a gas-venting system. All of this work was finished by September 1991.

The Drum Disposal Area was a major source of the organic compound contamination in the groundwater. Cleanup work in this area included the construction of a slurry wall to contain wastes, the removal and treatment of water from the containment area within the slurry wall, excavation of wastes and drums, construction of a soil treatment cell and installation of a security fence. Approximately 13,000 drums and an estimated 2,300 cubic yards of PCB-contaminated soils were excavated and taken off-site. All of this work was completed by July 1997. Contaminated soils from the Drum Disposal Area and the Ridge Area are still being treated in the soil treatment cell, using bioventing. Bioventing is a process where oxygen is supplied to bacteria in the soil, enabling the microbes to break down hazardous substances in the soil. EPA anticipated that the PRPs would have to operate this system for approximately eight years. Currently the system is in its eleventh year of operation and although a significant contaminant mass has been removed from the soil (based on results of ground water and soil gas monitoring), attainment of the soil cleanup standards has not been demonstrated. EPA, the State and parties responsible for the cleanup are evaluating options for addressing the remaining contamination.

The Ridge Area contained “hot spots” of contaminated surface soil due to liquid chemical spills. Work in this area included excavation of contaminated surface soil and transfer of this material to the Drum Disposal Area, treatment of the soil at the Drum Disposal Area as described above and backfilling of the area with clean soil followed by revegetation. While soils are still being treated, the rest of this work was completed by September 1996.

The Inert Disposal Area was used for the disposal of construction debris and various industrial wastes. Work in this area included removal of surface debris, construction of a multi-layer landfill cap, including a gas-venting system, and installation of a security fence. All of this work was finished by July 1997.

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