Site 1 is situated adjacent to the North Branch Potomac River, along the northern border of the developed portion of Plant 1 at ABL. The site boundary encompasses a total of 13.9 acres with the Active Burning Ground (ABG) consisting of 8.5 acres and the Outside Active Burning Ground (OABG) consisting of 5.4 acres. The ABG is a fenced area currently used for burning reactive wastes and is regulated under a RCRA permit. The burning of reactive material at the ABG began in 1959. Historical disposal of spent acids and solvents generated by plant operations during the 1970s and 1980s occurred in three former disposal pits located in the ABG. Reportedly, trichloroethene (TCE) was the primary spent solvent that was disposed in the pits, which are known to be a source of contamination to groundwater.
The OABG consists of a 5.4-acre parcel outside of the fenced area that was historically used for the disposal of various wastes (demolition debris, drums, and rocket casings), as well as for burning waste and spreading ash from the early 1960s until approximately 1981. The OABG is no longer in use and the area is not included within the boundaries of the active RCRA permit.
Site 1 has been characterized through several investigations and studies since 1983. The results of a Focused Remedial Investigation for Site 1 indicated that volatile organic compounds were the most widespread contaminants detected in Site 1 media, with TCE detected most often and at the highest concentrations in soil and groundwater.
In the early to mid-1990s, management of the environmental remediation of Site 1 was separated in two Operable Units (OU) due to the size and complexity of total site cleanup. Site 1 soil (OU-4) was investigated separately from the groundwater, surface water, and sediment (OU-3). A Record of Decision (ROD) was signed in May 1997 for Site 1 groundwater, surface water, and sediment (OU-3). A ROD was signed in September 2014 for Site 1 soil (OU-4).
The selected remedy for Site 1 OU-3 (groundwater and the surface water and sediment of the North Branch Potomac River adjacent to Site 1) is site-wide alluvial and bedrock groundwater containment (i.e., capture and removal) with subsequent onsite treatment and discharge of treated water to the river. Construction of a groundwater treatment plant was completed in September 1997. Extraction and treatment of contaminated groundwater began in September 1998 and continues today. The plant has treated a volume between 100 and 200 gallons per minute of groundwater extracted from Site 1 since 1998.
Long-term monitoring (LTM) of groundwater, surface water, and sediment have been implemented as part of the LTM program since 1998. LTM activities have been conducted on a tri-quarterly basis, and the results are documented in progress reports. However, LTM activities have been temporarily suspended during the implementation of the Site 1 soil (OU-4) remedial action. The LTM program will be scoped and implemented following the completion of the construction activities related to the Site 1 Soil Remedial Action.
In accordance with the Site 1 OU-4 ROD, the selected remedy for the ABG consists of excavation and offsite disposal of contaminated soil, land-use controls, and long-term management. The remedial action for the ABG was completed in August 2017. The selected remedy for the OABG consists of removal of surface debris, excavation and offsite disposal of contaminated soil, land-use controls, and long-term management. The excavation and soil removal activities at the OABG were conducted from June 2017 to October 2019, followed by site restoration activities, which are expected to be completed in 2020.
Detailed information from previous investigations conducted at Site 1 is available in the Administrative Record.