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1S .� tiv��, • : nr 3336 Data Drive ute 100 ��. Delta rj;t 'P ?c-� P� 1' 5 Raincho Cordova,CA 95670 Environmental 9161638-2085 Consultants,Inc. ;=AX:916/638-8385 March 17, 1994 Ms. Marla GuensIer Exxon Company, U.S.A. Post Office Box 4032 Concord, California 94524-2032 Subject: Quarterly Ground Water Monitoring Report, First Quarter 1994 Exxon Retail Station No. 7-3330 - 3128 West Benjamin Holt Drive Stockton, California Delta Project No. 40-93-810 Dear Ms. Guensler: Delta Environmental Consultants, Inc. (Delta), has been authorized by Exxon Company, U.S.A. (Exxon), to conduct quarterly ground water monitoring at Exxon Retail Station No. 7-3330, located at 3128 West Benjamin Holt Drive, Stockton, California. This letter report p ents the �.' results of quarterly ground water monitoring and sampling conducted on February 10,-1994. The location of the site is shown in Figure 1 and site features are illustrated in Figure 2. All work conducted at the site by Delta was performed in accordance with the field methods and procedures described in Enclosure A. i Ground Water Table Elevations Flow Direction and Hydraulic Gradient i Ground water table elevations were measured in each of the four existing monitoring wells at the sile on February 10, 1994. Depths to ground water in the monitoring wells ranged from 11.55 to 11.80 feet below the tops of the well casings. Ground water table measurements are presented in Table 1. A water table contour map constructed from the ground water table elevations recorded on February 10, 1994, is included'as Figure 3. The water table contours illustrated in Figure 3 indicate that ground water flowed toward the northeayt with a hydraulic gradient of-approximately_0.091. Subjective Analysis No liquid-phase petroleum hydrocarbons or hydrocarbon sheens were present in the wells during the February 1994 site visit. Analytical Results Ground water samples collected from monitoring wells MW-3, MW-4, MW-5, and MW-6, on February 10, 1994, were submitted to a California-certified laboratory for analysis of benzene, toluene, ethylbenzene, total xylenes, and total petroleum hydrocarbons as gasoline. Analytical test results are summarized in Table 2. Ground water samples collectedAom monitoring wells MW-3, MW-4, MW-5, and MW-6 did not contain detectable concentrations f petroleum hydrocarbons. The concentration of benzene in the ground water sample collected from monitoring well MW-5 has decreased since the previous sampling event in November 1993. A dissolved benzene concentration Delta Delivers Solutions