Hawthorne Army Depot

HWAAP-B04
BUILDING 101-44 IMPOUNDMENT

SITE DESCRIPTION
HWAAP-B04 is a double-lined surface impoundment approximately 140-ft x 240-ft x 15-ft, having a capacity of 586,000 gallons designed to collect explosive-contaminated wash-down water from demilitarization operations. The impoundment was never used, but was constructed using soil from a previous unlined impoundment that had collected explosive wash-down water from 1944 to 1977. The newer lined impoundment was constructed at the same location as the older unlined impoundment. A 1989 Remedial Investigation included collecting near surface, subsurface, and groundwater samples from within and adjacent to the impoundment. Explosives and petroleum hydrocarbons were detected in the soil samples and explosives were detected in groundwater samples at levels up to 30 mg/L above the regulatory standards.

Additional remedial investigation work in 1994 included 4 surface samples collected from within the impoundment, where visual staining of explosives were observed, and ground water samples from existing wells. Elevated concentrations of explosives (240 mg/kg of RDX, and 22 mg/kg of 1,3,5-trinitrobenzene) were detected in the soil samples. Groundwater samples detected high levels of explosives (2600 ug/L of RDX, 3.6 ug/L of 1,3,5-TNB, 18 ug/L of 4-Amino-DNT, 40 ug/L of picric acid). Explosive contamination exceeds state of Nevada action levels. Annual groundwater monitoring began in 1997. Currently, only well, DZB101-44MW3, (upgradient) shows elevated explosives (RDX) levels.

Aerial Photo (black & white --156KB)

PROPOSED PLAN
Remaining explosive-contaminated soil was excavated in 2009, and the impoundment was backfilled. Investigation to determine the extent of RDX contamination in groundwater surrounding the SWMU will begin in FY2011

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