Mid-Atlantic Superfund

EPA Region 3 (Mid-Atlantic)

Delaware
Kent County
Dover

EPA ID# DE8570024010

1st Congressional District

Last Update: November 2008

Other Names

None

Current Site Status

All the remedial actions are in-place at Dover Air Force Base (AFB) and the site is considered construction complete. The Basewide Remedial Investigation and Feasibility Studies were completed in 2005. The Record of Decision (ROD) for Land-use Control (LUC) at SD12 was signed in November, 2006. The ROD for the South Management Unit ( SMU) was signed in January 2006 and remedial action workplans were completed and remedial work started in January 2006 and were completed September 2006. For Area 6 in the West Management Unit, the ROD was signed in January 2006, workplans were completed in February 2006, and remedial work started in late February 2006 and was completed in September 2006. The ROD for Area 5 in the West Management Unit was signed in April 2006, a remedial action workplan was approved in April 2006 and remedial work started in May 2006 and was completed in September 2006. The ROD for LUCs at Multiple-sites was signed in May 2006 and all LUCs were put in place by September 2006, including LUCs for Site SD-12. The ROD for the final sites, SS08 and LF25, was signed in May, 2006 with the workplans completed later that month and remedial action started in June, 2006 and completed in September 2006. The main components of the selected remedies for the SMU, Areas 5 and 6, SS08 and LF25 are injection of organic carbon material to enhance biodegradation, natural attenuation with long-term monitoring and institutional controls. A Preliminary Close-out Report was signed in September 2006 indicating all remedies were in-place and Dover AFB was in the Construction Complete phase of the Superfund program. All sites are under long-term monitoring.

Site Description

The 3,700-acre Dover AFB site in Dover, Delaware, is the base of operation for the 436th Airlift Wing. The base contains 23 areas on site that were used for disposing of industrial waste. An estimated 23,000 cubic feet of waste were disposed of from 1951 to 1970. The base's operations generated numerous wastes, some in drums, including paints, solvents, waste fuels, and oil. These wastes were disposed of in various on-base locations including 12 landfills and three fire training areas. Access to the site is restricted. There are approximately 1,000 people living on base, and 39,000 people living within a three-mile radius of the site. The distance from the base to the nearest residence is a half mile, and the site is located in a commercial and residential area that is densely populated. The base groundwater well system serves about 10,000 people and is routinely monitored by the Air Force. No contaminants have ever been reported in this system.

Shallow on-site groundwater is contaminated with volatile organic compounds (VOCs) from former waste disposal practices and site operations. A variety of VOCs have been detected in both on- and off-site groundwater including trichloroethylene (TCE), tetrachloroethylene (PCE) and carbon tetrachloride. VOCs also have been detected in the sediments. VOCs and heavy metals including mercury, chromium, and cadmium have been detected in on-site stream waters.

Site Responsibility

This site is being addressed through Federal actions.

NPL Listing History

Proposed Date: 10/15/1984.
Final Date: 03/13/1989.

Threats and Contaminants

Twelve contaminant plumes have been identified in shallow, on-site and off-site ground water. The contaminants are primarily petroleum, volatile organic compounds (VOCs) and to a lesser extent, metals and pesticides. The VOCs include fuel-related components (benzene, toluene, ethylbenzene, and xylene) and industrial-use compounds such as tetrachloroethylene, trichloroethylene, 1,2-dichloroethylene and carbon tetrachloride. Petroleum hydrocarbons, VOCs, metals, pesticides, and semi-volatile organic compounds have also been detected in on-site soils, drainage ditches, surface water and sediments. Potential health threats include exposure and ingestion to contaminated ground water used for potable purposes. Direct contact with contaminated soil by workers and potential residents may also be a concern. Freshwater wetlands are located on site.

Contaminant descriptions and associated risk factors are available at: (ATSDR web site).

Cleanup Progress

The Air Force has already cleaned up several industrial waste basins, a drum site, and has provided an alternate water supply to affected residents. A landfill and some hazardous waste areas were excavated during the runway extension in 1988 and 1989.

Cleanup activities for the operable unit at Fire Training Area #3 began early in 1992. An underground storage tank, and oil/water separator, along with all associated piping were removed from the site. Contaminated soils surrounding the tanks and underlying the fire training pit also were removed. The area was capped with clean soil in late 1992.

In September 1995, the Air Force began cleanup operations in the Industrial Area. Contaminant sources in this area include waste treatment units, buildings, hangars, and industrial sewer lines. Also in 1995, the Air Force initiated removal of contamination on the surface of the water table at two former landfills and the recovery of jet fuel on the water table surface at two other locations. A removal action for a portion of a landfill located on a golf course was completed in 1998.

All Records of Decision (RODs) have been issued for the 20 operable units (OUs) established at the Dover AFB. Remediation, including LUCs is underway at all of these units - OU1 (Fire Training Pit #3 Remediated), OU2 (Free Product Removed from Groundwater at Landfills), OU3 (Oil/Water Separator Removed), OU4 (Underground Storage Tank Removed), OU5 (Pesticide Source in Industrial Soils Removed), OU6, OU8, and OU10 (Industrial Area Source VOC Monitored Natural Attenuation of Groundwater Contamination), and OU7 (Golf Course Landfill Soil Removed). Construction of the remedy for OU9 (East Management Unit, WP14 LF15), OU11 and OU12 (Industrial Area Source VOC Monitored Natural Attenuation of Groundwater Contamination), OU13 ( East Management Unit, LF22, LF23, WP24), OU14 (WP21), OU15 (South Management Unit, FT01, SS07, LF17, LF18), OU16 (West Management Unit, Area 6), and OU17 (West Management Unit, Area 5 and Area 4).

Most recently, the ROD for OU23 (Multi-site Land-use Controls) was signed in May 2006 and along with Land-use Controls at OU24 (SD12), was implemented in September 2006. The ROD for the final sites, SS08 and LF25 (OU19), was signed in May 2006 with the remedial workplans completed later that month and remedial action started in June 2006 and completed in September 2006. The main components of the selected remedies for OUs 15, 16, 17, and 19 are injection of organic carbon material to enhance biodegradation in the source areas, natural attenuation with long-term monitoring of the dissolved portion of the groundwater plumes, and institutional controls. The second round of carbon injections were completed by November 2007. This round of injections included approximately four times the amount of carbon into the subsurface relative to the first round. The third round of carbon injections began in Spring 2008. The most recent monitoring data shows good progress is being made. As part of the final groundwater remedies, over 600 wells and injection points have been installed and by the end of September 2006, over 10,000,000 gallons of amended water has been injected. All sites are under long-term monitoring.

An interim remedial action was undertaken for Building 719 (West Management Unit) in 2000, where an accelerated anaerobic biodegradation (AAB) recirculation system was put in place. Building 719 is the single largest chlorinated solvent source area for the Area 6 plume. In early 2007, the system was turned off and is currently in passive mode, to determine whether or not rebound occurs. Monitoring data from the 2008 semi-annual report shows that MCLs have been nearly reached in all of the wells within the reactive zone and progress towards MCLs continues to be made in the wells not within the source area.

The Air Force submitted a vapor intrusion assessment report in December 2007. Buildings above the areas with the highest shallow groundwater contaminant concentrations were selected to assess “worst case” scenarios. The assessment revealed that vapor intrusion does not appear to be a significant exposure pathway at the locations sampled during the study, under current land use conditions. Building 760 in Area 5 was not included in the original assessment, due to ongoing interior renovations and was sampled in Spring 2008. The addendum was submitted in September 2008 and is currently under review.

A basewide Five-Year Review was completed in October 2008. Groundwater monitoring data of South Management Unit Site FT01 indicate that the RAOs have been achieved, where benzene and chlorobenzene have not been detected in the past four (biannual) sampling events. FT01 will be closed and monitoring will be suspended; however, groundwater restrictions will remain. In addition, residential risk screening for groundwater was performed for seven of the 22 LUC sites and no unacceptable human health risk was identified. These seven sites (OT43, OT46, OT47, OT57, WP29, WP32, and OT55) will be closed and excluded from future five-year reviews for LUCs. Furthermore, the selected remedies were found to remain protective of human health and the environment.

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