Geophysical methods have been used during environmental studies conducted for the Corps of Engineers,<br>Sacramento District, to characterize potential sources of contamination at the U. S. Army base at Fort Ord,<br>California. Small-scale industrial operations have been ongoing since the base was established in 1917.<br>The most environmentally significant operations have been associated with military motor pools, landfills,<br>sewage plants, and bum pits. Fort Ord was added to the National Priorities List (Superfund) in February<br>1990 and has been targeted for closure. More than 50 site-specific or basewide investigations have been<br>conducted at the base, which covers over 23,000 acres on the Pacific Coast.<br>Geophysical methods have been used extensively for investigations at the base since 1985. Ground<br>penetrating radar and electromagnetic profiling were used to map the extent of subsurface debris during a<br>landfill investigation and to map underground storage tanks and associated utilities for the Underground<br>Storage Tank Management Program. Magnetometry was used to locate buried wellheads, and both<br>natural gamma and video logs were collected in old water supply wells prior to their destruction as part of<br>the Well Management Program.<br>For the Superfund investigations, an integrated program of geology, hydrogeology, and geophysics was<br>developed by Harding Lawson Associates, the Corps of Engineers, Fort Ord personnel, and the regulatory<br>agencies. Geophysical methods used in the investigations included high resolution seismic reflection<br>profiling, ground penetrating radar, electromagnetic profiling, magnetics, and geophysical borehole<br>logging. One or more of these methods was used for the following applications during the Superfund<br>investigations:<br>. Delineate suspected landfill areas<br>. Locate underground storage tanks and former tank locations<br>. Provide stratigraphic correlation and identify saturated sections in monitoring wells<br>. Clear borehole locations of subsurface utilities and obstructions, including unexploded ordnance<br>. Map subsurface geologic features such as an aquiclude layer, a fault, and a bedrock high.<br>Using geophysics at Fort Ord has reduced both cost and the number of intrusive activities and has aided<br>in the understanding of the subsurface geology and potential sources of contamination.


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