oa A Geophysical Program To Aid In The Environmental Investigation Of The U.S. Army Base At Fort Ord, California

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.