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T1JI GROUNDWATER. TECHNOLOGY, INC. �„ ntChu tirEhyhu.,r. n,c„nf.Cahi:�LnE4351G71-'_':Eti7 July 23, 1991 Job No.020300167 Mr. Clint Rogers Chevron U.S.A.Inc. P.O.Box 5004 San Ramon,CA 94583 r Subject: Groundwater Monitoring Report Chevron Facility No. 9-0557 139 South Center Stockton,California Dear Mr.Rogers; This letter report has been prepared for Chevron U.S.A., Inc. (Chevron)and summarizes the results of - routine groundwater monitoring and sampling performed by Groundwater Technology, !no. at the above- referenced site. The four monitoring wells at this Chevron facility were monitored on June 27, 1991,to determine depth- to-groundwater(DTWb hydraulic gradient,and to check for the presence of separate-phase hydrocarbons. Table 1 presents the current and historical groundwater-monitoring data. Figure 1 shows well locations and groundwater potentiometric-surface lines. The calculated gradient is.002,and slopes to the southeast. After measuring the DTW,the four monitoring wells were purged and sampled. All of the groundwater san:;lles wore analyzed for the presence of benzene, toluene,ethylbenzene and xylenes (BTBX)and total petroleum hydrocarbons (TPH)-as-gasoline. Also,the water samples collected from monitoring wells MW.1 and MW-2 were analyzed for the presence of fecal coliform. The analytical results Indicated that the benzene concentrations were below the method detection limit of <0.5 parts per billion (ppb)In MW-3 and MW-4, but were detected in the samples collected from MWA and MW?.at 31 ppb and 140 ppb, respectively. The analytical results indicated that TPH-as-gasoline was detected in MW-1 at 1,300 ppb, MW-2 at .,Boo ppb, and MvV-3 at 130 ppb,and <50 ppb In MW-4. The analytical results for the two samples analyzed for the presence of fecal coliform were below the method detection limit. Copies of the analytical reports are attached. z l)f&rs rhmaUhaur Nig•VS..Canada and0verseas