Hawthorne Army Depot

HWAAP-B29
BUILDING 103-41 ORDNANCE WASHOUT IMPOUNDMENT
(UNLINED PONDS)

SITE DESCRIPTION
HWAAP-B29 is a series of inactive unlined surface impoundments connected by steel troughs covering an area of approximately 0.25 square miles north of Building 103-41. Nine impoundments at this site, each measure approximately 25-ft x 100-ft x 3-ft, were used for TNT washwater from demilitarization. Five larger ponds measure approximately 100-ft x 100-ft x 10-ft. These larger impoundments were used for ammonium picrate washwater from demilitarization. The impoundments were constructed in 1957. From 1964 to 1968 the impoundments were used for disposal of explosives wastes. In addition sodium sulfate, other reaction products may have been discharged into the impoundments. Once the water evaporated from the small impoundments the remaining waste was burned in place. Ammonium picrate, TNT-stained soils, and black burn residue are evident in the impoundments. The impoundments have eroded and are partially filled with windblown sand. Groundwater sampling (1974 & 1980) at the site detected up to 620 ug/l of TNT and other organic and inorganic, nitrogen-bearing compounds. Groundwater sampling in 2000 detected up to 29 ug/L of TNT and other organic, inorganic, and nitrogen-bearing compounds. Current groundwater monitoring shows low levels (below action level) of explosives. Nitrate levels exceed MCLs. Groundwater samples from monitoring well IRPMW02 had nitrates at 57.9 mg/L.

Remedial investigation work in 1994 included groundwater sampling, surface soil and hand auger sampling, and cone penetrometer soundings. A pilot study successfully treated 300 cubic yards of ammonium picrate contaminated soil using windrow composting. During 2003, through a teaming effort with the NDEP, PRGs for ammonium picrate were raised from 7 ppm to 120 ppm for an industrial site to expedite cleanup of this site. A decision document approving bioremediation as the remedy was signed by regulators on September 9, 1995.

Aerial Photo (black & white --106KB)

PROPOSED PLAN
Approximately 49,000 cubic yards of explosives-contaminated soil were excavated from the site and treated using ex-situ windrow composting from 2001 through 2005. Additional investigation of explosives-contaminated groundwater at the site is required.

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