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"r CALIFORNIA GEOPHYSICAL GROUP, INC. P O Box 691, Poway, CA 92074 Tel- (619) 486-1323 FAX. (619) 486-2329 November 20, 1992 REAft fAM DEC 0 1992 Public Health Services ENVIRONMEN11#, t, San Joaquin County � RM1T/ rj P. O, Box 2009 Stockton, Ca 95307 $ V RE= Quarterly Report October 1992 - rte Darpetro Service Station 749 E Charter Way Stockton, Ca Site # 1060 The site was sampled on October 27, 1992 and the laboratory analysis of the water samples were done by Sherwood Labs of Hilmar, California. The water table measurements, sampling parameters and chain of custody are attached. Table I lists the history of the water analysis taken at the site since Jan 26, 1990. Table II is the history of the water table measurements, and Table III list the history of Hydraulic Gradients Attached is one water table elevation plot showing the approximate groundwater gradient. The water samples were obtained by using a pre-cleaned teflon bailer and new section of rope This was performed after the measured field parameters had stabilized during the purging operation. See protocols Water samples were placed in appropriate glass containers with teflon-lined lids. EISDINO The water table has gone down about 2 feet since the last measurement The gradient direction has shifted 20 degrees to the north The slope of the gradient has increased 15 times ! The groundwater contamination has increased in wells 5 and 6 and decreased in well 4 Since the gradient has shifted slightly away from well 4 we believe this is the cause of the reduction in contaminants. Both odor and sheen were noted in wells 5 and odor was noted in well 6 ! The statistical evaluation of the combined data indicate a true gradient will be found if there is a difference across the sampled site of 0, 5 feet This is the case and therefore we can be assured the gradient is correct