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Site 5: Inert (Non-Ordnance) Landfill

Background

The Site 5 inert landfill operated from the early-1960s to 1985, accepting inert wastes generated by ABL. The landfill is located on a terrace above the North Branch Potomac River southwest of Plant 1. Inert wastes were defined as wastes neither contaminated with explosives nor generated at an area on the facility where explosives were managed.

Several investigations were performed to evaluate the nature and extent of contamination in environmental media at Site 5. In general, low levels of volatile organic compounds, pesticides, and inorganics were detected in soil samples collected around the perimeter of the landfill. In addition, trichloroethene (TCE) was detected in Site 5 groundwater downgradient of the landfill.

The remediation at Site 5 is managed as two separate Operable Units (OUs). A Record of Decision (ROD) for Site 5 landfill contents and surface soil (OU-1) was signed in February 1997. The selected remedy was an impermeable landfill cap, land-use controls, a landfill gas venting system, and post-closure requirements. Landfill cap construction was completed in September 1997, and landfill operations and maintenance (O&M) is ongoing as specified in the ROD.

The Site 5 human health and ecological risk assessments were revised in 2004 for groundwater, surface water, and sediment based on additional data collected since the initial risk assessments were prepared during the 1994 Phase II Remedial Investigation. A ROD for Site 5 groundwater, surface water, and sediment (OU-2) was signed in February 2006. The selected remedy included installation of a permeable reactive barrier wall filled with zero-valent iron to treat TCE in alluvial groundwater downgradient of the Site 5 landfill. This remedy also included land-use controls and monitored natural attenuation. The permeable reactive barrier was installed in June 2006. A background study to determine iron and manganese concentrations, as well as a TCE investigation are scheduled to take place in fall 2020.

A long-term monitoring (LTM) program for groundwater was implemented in 1998 in addition to the O&M activities of the landfill cap remedy. LTM activities including groundwater sampling are conducted on an annual basis and the results are documented in progress reports.

Detailed information from previous investigations conducted at Site 5 is available in the Administrative Record.

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