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F <br /> CALIFORNIA GEOPHYSICAL GROUP, INC. <br /> O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 <br /> May 16 , 1997 Fox (209) 527-4810 <br />' Public Health Services <br /> San Joaquin County <br />' P.O. Box 388 <br /> Stockton, Ca 95201 <br />' RE: Quarterly Report April , 1997 <br /> Darpetro Service Station <br /> 749 E. Charter Way <br /> Stockton, Ca. <br /> Site # 1060 <br />' The site was sampled on April 24 , 1997 and the water samples were <br /> analyzed by Sherwood Labs of Hilmar. The water table <br /> measurements, sampling parameters and chain of custodies are <br />' attached. <br /> Table 1 lists the water levels and depths to water, since January <br /> 261 1990. Table 2 lists the hydraulic gradients and bearings and <br />' Table 3 list the chemical analyses taken each quarter. Also <br /> attached is a plot of the water table contours and dissolved <br /> oxygen concentrations on April 24 , 1997. <br /> The water purging was performed with a decontaminated pump and <br /> the measured field parameters stabilized during the purging. <br />' Water samples were taken with a decontaminated bailer. See <br /> protocols. Water samples were placed in appropriate glass <br /> containers With teflon lined lids. The Laboratory Certificate <br /> indicates a blank was taken and tested. This blank was taken at <br />' the end of the purging and testing in order to test the <br /> performance of new tubing. The test indicated that the tubing <br /> used did not react as indicated by the supplier and will not be <br /> used in the future. <br /> Wells MW-1 , 2 and 3 were not measured or sampled, authorized by <br /> Mr. Steve Sasson, the county regulator. <br />' FINDINGS <br /> The groundwater flow is Northerly at a gradient of 0 . 0079 Ft/Ft. <br /> The groundwater level has risen about 2.2 feet, since the last <br /> quarterly reading. The water this quarter is the highest it has <br /> been at this site since January, 1990. Figure 1 shows the water <br /> table elevations. <br /> Benzene contamination is present in all of the wells above the <br /> California Action Levels. The oxygen levels were measured using <br /> a YSI Model 51B oxygen level meter. The meter was calibrated the <br /> day before performing the testing. The oxygen level was measured <br /> Page 1 <br />