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CALIFORNIA GEOPHYSICAL GROUP, INC. <br />' O Box 578341, Modesto, CA 95357 Tel (209) 527-1247 <br /> May 15, 1998 Fax (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 1998 <br /> Darpetro, Inc USA Service Station <br /> 749 E Charter Way <br /> Stockton, CA <br /> ISite No 1060 <br /> This site was sampled on April 23, 1998 Sherwood Labs, Corp of Hilmar, California their <br />' report is attached <br /> Table 1 lists the history of the water table depths and elevations at this site since January <br /> 26, 1990 Table 2 lists the hydraulic gradients and bearings and Table 3 lists the analyses <br /> of the groundwater Also attached is a hydraulic gradient plot showng the approximate <br /> groundwater gradient on April 23, 1998 Sampling protocols are included <br /> FINDINGS <br /> The groundwater has risen approximately 5 5 feet since the last quarterly monitoring <br /> event The gradient bearing is to the northeast The gradient is 0 0011 Ft/ft The <br /> attached hydraulic gradient plot shows the bearing of the gradient See Figure 1 <br /> The wells were purged with a decontaminated pump and the measured field parameters <br /> I stabilized at the end of the purging Water samples were taken with a decontaminated <br /> bailer See Protocols Water samples were placed in appropriate glass containers with <br /> Teflon-lined seals <br /> The groundwater in all the wells was above California Drinking Water Standards for <br /> benzene and other hydrocarbon chemicals Just before we purged each well we removed <br /> the ORC treatment from all the wells There has been a decrease in contamination in <br /> wells MW-4, 5, 6, and 10 and an increase in wells MW-7, 9 and 11 Well MW-8 remains <br /> about the same <br /> Dissolved oxygen levels were recorded this quarter at this site The levels were <br /> measured with a calibrated YSI model 51 B meter by placing the sensor 5 feet below the <br /> surface of the water table before any bailing or other well disturbance occurred The <br /> measured levels are shown on Table 3A and Figure 3 <br /> Attached is a Hazardous Waste manifest showing the purged water was removed from <br /> this site <br />