Site 4 - Benzene, Toluene, Ethylbenzene, and Xylene Plume
A benzene, toluene, ethylbenzene, and xylene (BTEX) plume is associated with releases from maintenance activities at the former Transportation Building and a 7,600-gallon UST which was formerly located there. The BTEX plume in groundwater has migrated to the north of NWIRP Bedford, to an off-property wetland area. Most of the Site 4 plume is comingled with the Site 3 plume.
The UST and approximately 75 to 100 cubic yards of oil-contaminated soil were removed in 1989.
Groundwater impacts were delineated through a series of phased investigations that occurred from 1989 through 1997. BTEX were identified as the COCs in site groundwater. In 1999, the BTEX plume extended over 0.75 acres (approximately 50 feet in width and 700 feet in length) in shallow overburden groundwater.
An RI/RA identified risks if site groundwater was to be used as a drinking water supply. Three rounds of in situ chemical oxidation were conducted from 2000 to 2002, and the changes in groundwater concentrations were monitored. This treatment did not reduce BTEX concentrations sufficiently to achieve the cleanup goal, but helped to reduce contamination. Source area reduction, conducted from 2003 to 2004 with electrical resistance heating, reduced BTEX concentrations by 82.2 to 99.7 percent. Subsequent groundwater monitoring through 2008 showed a rebound in Site 4 plume groundwater BTEX concentrations because of the release of soil-bound BTEX.
The Site 4 ROD was signed in 2009. Selective excavation of the source area described in the ROD was not necessary based on pre-design investigation results. LUCs were implemented to restrict future use of the site to industrial/commercial scenarios, to prohibit the use of groundwater as drinking water, to restrict building occupancy because of the potential for vapor intrusion from soil, and to require annual inspections of the site to ensure that LUCs are continuing to be implemented. Quarter groundwater monitoring for the residual groundwater plume was initiated in 2012 and is ongoing. The site cleanup goals have nearly been achieved; consequently, the Navy is planning on optimizing the LTM program as part of the second FYR, reducing the sampling frequency, number of wells, and the analysis.
Previous investigations, plans and documentation at this site are: IAS; RI/RA; FS; and a ROD.
LUCs have been implemented; Quarterly Groundwater Monitoring is being conducted.