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of PCE (10,000 ppb) These compounds are thought to be an artifact result of migration of a more regional plume from an upgradient source 2.4 Geology/Hydrogeology Subsurface investigations indicate that lithology beneath the site consists of interbedded sedi- ments primarily of low to moderate permeability clayey silt, silty clay, clay, and silt, and higher permeability sand, silty sand, and sandy clay Groundwater elevation trends were analyzed to provide information regarding the association between groundwater elevation changes and dissolved hydrocarbon concentration changes The analysis was performed using average groundwater elevations from September 1990 to October 1994 Histoncally, average groundwater elevations have ranged from -43 47 to -35 61 feet MSL Between September 1990 and June 1992, minimum and maximum groundwater elevation events closely followed the cycle of dry and wet seasons typical of northern California, aver- age groundwater elevations demonstrated seasonal fluctuations between -41 and -44 feet MSL Since June 1992, groundwater elevations have been steadily increasing to a maximum of-35 61 feet MSL in June 1994 The average groundwater elevation for the entire data set was -40 75 feet MSL with an standard deviation of 2 61 feet, suggesting the hydrocarbon smear zone is approximately 5 2 feet thick A clear association between changes in groundwater elevation and changes in dissolved hydrocarbon concentrations is demonstrated at the most heavily impacted well, Monitoring Well MW-2 Typically, dissolved hydrocarbon concentrations increased during periods of higher groundwater elevation and decreased during periods of lower groundwater elevation 2.5 Remediation Site remediation has included the removal of product storage tanks and associated piping, and the removal of a waste oil storage tank in December 1986 New product storage tanks were installed in the southwestern corner of the site, and a new waste oil storage tank was placed in the northwestern corner of the site 2.6 Exposure Pathway Since gasoline constituents have been detected in groundwater beneath the site, it is reason- able to expect groundwater flow to be the primary exposure pathway The most likely expo- sure point would be a downgradient water-supply well located near the site and the primary exposure route would be ingestion Two wells identified in the well survey, a domestic well • 3201357BNCAP 4 April 4, 1995