Oxon Cove Landfill Environmental Cleanup

 

Site Description and History

The Oxon Cove Landfill Site occupies an area within Oxon Cove Park located in Prince George’s County, Maryland, and Washington, DC. Oxon Hill Farm is a working farm located in the south-east portion of Oxon Cove Park. Oxon Cove Park & Oxon Hill Farm are managed by the National Capital Parks – East (NACE) administrative unit of the National Park Service (NPS). The 155-acre Oxon Cove Landfill Site consists of two areas: (1) the northern landfill area (88 acres) which straddles the boundary between Washington DC and Prince George’s County, Maryland; and (2) the eastern landfill area (67 acres) located entirely within Prince George’s County Maryland. The two areas are separated by Oxon Cove and Oxon Creek, which is a small tributary to the Potomac River. The Site was used by the District of Columbia (District) as a disposal area and landfill from the 1940s to 1972.

Before landfilling activities began, the northern area of the Site consisted of undeveloped wetlands and open water known as Oxon Bay and the eastern area consisted of agricultural fields and wetlands. Beginning in 1937, the District began filling the northern area with various materials including dredged sediments from Oxon Cove and the Potomac River channel, excess soil and construction materials from the construction of the I-295 highway, and possibly sludge/solids from the nearby Blue Plains Wastewater Treatment Plant.

In 1969, the District transitioned landfilling operations from the Kenilworth Park Landfill to the Oxon Cove Landfill. From October 1969 to June 1972, historical reports indicate that the District disposed of approximately 1,500,000 tons of municipal waste and 275,000 tons of incinerator ash at the Site. During this time, the District also disposed of sludge generated at the Blue Plains Wastewater Treatment Plant at the Site. In 1972, the landfill was closed and covered with soil that was likely mixed with wastewater treatment plant sludge to support revegetation. NPS mows portions of the eastern area of the Site to maintain the grass cover. The northern area and areas that are not mowed are currently covered with natural vegetation including grasses, wetlands, trees, and shrubs. The paved Oxon Hill Farm Hiker-Biker Trail, which is part of the Potomac Heritage National Scenic Trail, passes along the western edge of the eastern landfill area and crosses the eastern portion of the northern landfill area.

Oxon Cove Landfill Environmental Investigations

In 2002, NPS initiated environmental investigations of the Site pursuant to the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA). CERCLA and the regulations provided in the National Oil and Hazardous Substances Pollution Contingency Plan (NCP) provide the framework the federal government follows to assess and clean up contaminated sites. At the Oxon Cove Landfill Site, NPS is the federal government agency that is responsible for overseeing the CERCLA investigations. NPS has completed the first phase of the CERCLA process known as the preliminary assessment/site inspection or PA/SI. The PA/SI results indicated that Site soil, groundwater, and sediments are impacted by relatively low concentrations of hazardous substances typically found in municipal waste landfills and sludges generated from wastewater treatment plants. The Site contaminants are more concentrated below the soil cap (that is, within the waste fill) and therefore do not appear to pose a current risk to visitors using Oxon Cove Park or the hiker-biker trail. NPS has begun the next step of the CERCLA process called the remedial investigation, or RI. The purpose of the RI is to fully characterize the nature and extent of contamination present at the Site and will include assessments of risk posed by contamination to human health and wildlife. The RI results will allow NPS to determine if there are unacceptable risks or impacts posed by the Site that require cleanup.

Landfill Gas Migration Assessment

When wastes are placed in a landfill and covered, they decompose and generate gases, such as methane and hydrogen sulfide. This decomposition process and landfill gas generation is occurring at the Oxon Cove Landfill and is the cause for the rotten-egg smell (due to hydrogen sulfide gas) that can sometimes be noticed in the eastern landfill area. To determine if these landfill gases pose any risks to visitors or nearby structures, NPS completed assessments that included the collection of landfill gas samples at the surface of the former landfill, in the basement of the Oxon Hill Farm administration building, and along the perimeter of the landfill between the Site and the Forest Heights neighborhood. The assessments included testing for methane, volatile organic compounds, and combustible gas. Based on these assessments, NPS concluded that there are no risks to visitors or park staff associated with landfill gas escaping at the surface of the landfill or to nearby residences or buildings due to landfill gas migrating horizontally through the subsurface.

Next Steps

NPS is currently in the RI planning stage of the CERCLA response action. The RI will involve collection of surface and subsurface soil, surface water, and sediment samples; installation of monitoring wells; and collection of groundwater samples. NPS will conduct the RI in multiple phases and analyze the results of each phase to develop a conceptual site model and determine what additional data are needed to evaluate the Site. NPS anticipates the field work associated with Phase I of the RI will begin in early 2024. After the RI is completed, NPS will prepare an RI Report to summarize the results and provide the human health and ecological risk assessments. If the results of the risk assessments conclude that the contamination present at the Site poses unacceptable risks, NPS will prepare a Feasibility Study (FS) to identify and evaluate possible alternatives to address this risk.

Oxon Cove Landfill Documents

NPS has set-up an information repository for the Site at the Oxon Hill Farm visitor center. The repository includes the Oxon Cove Landfill administrative record (AR) file. The AR file contains all of the documents NPS will use to determine if the Site requires remediation and, if required, what is the best plan for cleaning up the Site. The AR file index lists all of the documents currently included in the Site’s AR file. The AR file will be periodically updated as the steps of the CERCLA process are completed. The public may review hard copies of all of the documents included in the information repository upon request when Oxon Hill Farm is open . Electronic versions of the documents may also be requested by contacting the NPS Project Manager, Donna Davies.

Community Involvement

NPS is interested in public feedback and works to maintain transparency in the CERCLA process. The public will have the opportunity to review and comment on any reports prepared for the Site and the proposed cleanup action. To communicate the current status of the work being completed at the Site, NPS will update this webpage and will also prepare Community Updates.

• Winter 2024 Community Update

Want to know more?

What is CERCLA?
What is a Risk Assessment?

Contact Information
Donna Davies
CERCLA Project Manager
Address: National Capital Parks-East
1900 Anacostia Drive, SE
Washington, D.C. 20020
Email Donna Davies
Phone: [phone]
Mon.-Fri. 9:00a.m. - 4:00p.m. ET