Abstract

Tooele Army Depot, Tooele County, Utah has developed a hydrogeological model to predict spatio-temporal changes in trichloroethylene contamination originating from sources on the base. Established in 1942 to store World War II supplies, ammunition, and combat vehicles, the Depot is situated in the Basin and Range Providence about 50 km west of Salt Lake City, Utah. In order to better define this hydrogeological framework, a helicopter-borne, time-domain electromagnetic system, known as SkyTEM, was used to survey a 64-km2 area of the Depot. Areas where carbonate basement is known from prior studies to be at or near the surface were clearly delineated in the SkyTEM data as a high resistivity zone, which begins near the ground surface and continues to the deepest samples at about 200 m. In some places the basement appears to be conductive rather than resistive. In areas where unconsolidated sedimentary cover is known to be thick, such as in the northwest part of the survey area, resistivities were low throughout the sample intervals. The SkyTEM data supports the existence of some, but not all, of the hydrological boundaries hypothesized from potentiometric information. Shallow high-resistivity layers in the east and southeast portions of the survey area appear to be underlain by more conductive sediments, and so should not necessarily be interpreted as shallow bedrock, but possibly as resistive sediments such as dry sand and gravel. One of the most significant results of the survey is the delineation of a narrow unit, interpreted as a paleochannel, at depths greater than 100 m that may be responsible for migration of contamination to the northwest.

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