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f � � CALIFORNIA GEOPHYSICAL GROUP, INC. P O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 August 19 , 1997 Fax (209) 527-4810 Public Health Services San Joaquin County P.O. Box 388 Stockton, Ca 95201 ' RE: Quarterly Report July, 1997 Darpetro Service Station 749 E. Charter Way Stockton, Ca. Site # 1060 The site was sampled on JLX1;y—lB, ''1'9;97 and the water samples were analyzed by Sherwood Labs of Hilmar. The water table measurements, sampling parameters and chain of custodies are ' attached. Table 1 lists the water levels and depths to water, since January 26, 1990 . Table 2 lists the hydraulic gradients and bearings and ' Table 3 list the chemical analyses taken each quarter. Also attached is a plot of the water table contours and dissolved oxygen concentrations on July 18, 1997 . The water purging was performed with a decontaminated pump and the measured field parameters stabilized during the purging. Water samples were taken with a decontaminated bailer. See ' protocols. Water samples were placed in appropriate glass containers with teflon--lined lids. The Laboratory Certificate indicates a blank was taken and tested. This blank was taken at the end of the purging and testing; in order to test the performance of new tubing. The test indicated that the tubing was not cleaned completely. ' Wells MW-1, 2 and 3 were not measured or sampled, authorized by Mr. Steve Sasson, the county regulator. ' FINDINGS The groundwater flow is to the northeast at a gradient of 0.0018 ' Ft/Ft. The groundwater level has fallen about 0 .6 feet, since the last quarterly reading. Figure 1 and Table 1 show the water table elevations. ' Benzene contamination is present in all of the wells above the California Action Levels. The oxygen levels were measured using a YSI Model 51B oxygen level meter. The meter was calibrated the ' day before performing the testing. The oxygen level was measured 5 feet below the surface of the water table. ' L Page 1