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Applied —G–'Osystems x191-E Power Inn Road, Sacr,unentp, CA 95826 49161 452-2401 • FREMONT • IRVINE • HOUSTON • BOSTON • SACRAMENTO •CULVER CITY •SAN JOSE April 15, 1991 1226gdem AGS 86102-5 Mr. Glenn Dembroff Ultramar Inc. 525 West Third Street Hanford, California 93230 Subject: Fourth Quarter 1990 Quarterly Ground-Water Monitoring at Beacon Service Station No. 492, 470 North Main Street, Manteca, California. Mr. Dembroff: This report presents the results of the fourth quarter 1990 groundwater sampling that Applied GeoSystems, Inc. conducted at the request of Ultramar Inc. (Ultramar) at the subject site (see the Site Vicinity Map, Plate P-1). The purpose of this sampling program is to monitor the concentratiorts of hydrocarbons in ground water at the site. Work included measuring depths to water,sampling ground water for subjective and laboratory analyses of hydrocarbons, and evaluating the groundwater gradient beneath the site. The locations of the monitoring wells are shown on the Generalized Site Plan, Plate P-2. Presentound-Water am lin On December 18, 1990, a geologist from Applied GeoSystems, Inc.conducted the quarterly monitoring event at the subject site following methods summarized in an attachment to this letter report. Water levels were measured in the monitoring wells.A geologist from Applied GeoSystems, Inc. returned to the site on remeasure water levels on January 3. 1991, in response to a discrepancy in groundwater elevation that arose during the calculation of a ground-water gradient map. These latter water levels (see Table 1) were used to evaluate the groundwater gradient. We evaluated the ground-water gradient on January 3, 1991, to be flat,which is consistent with the gradient evaluated during previous sampling events. We collected groundwater samples from each monitoring well and examined the samples for floating product, sheen, and other subjective evidenc-- of hydrocarbons. No subjective - -- -- - evidence of hydrocarbons was observed in any of the samples from the monitoring wells see Table 2).