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� `•.�"""�filr�ss �. .m.-. s.�t.',uwtr�„^ur �r rr�.+w>.,n*. �A .d <br /> 6 <br /> Quarterly Ground-Water Monitoring January 8, 1990 <br /> Beacon Station No. 492, Manteca, California AGS 36102-4 <br /> Mobile Chem Labs, Inc., in Lafayette, California (Hazardous Waste Testing 1 ab3.atory <br /> Certificate No. 195), analyzed the ground-water samples for total petroleum hydroca-buns <br /> (TPH) as gasoline by California Department of health Services Leaking Underground <br /> ® Fuel Tanks (LUF I) Method and for benzene, toluene, ethylbenzene, and total xylene <br /> isomers (BTEX) by Environmental Protection Agency Method 602. The results of these <br /> analyses and previous laboratory analyses are summarized in Table 2. Copies of the <br /> laboratory Analysis Reports are attached. <br /> The results of the laboratory analyses indicate that hydrocarbon constituents were not <br /> ® detected in the ground-water sample collected from MW-3 but were detected in the samples <br /> from MW-1 and MW-2. TPH as gasoline was detected at 1..20 parts per million (ppm) in <br /> the sample from MW-1 and at 0.300 ppm in the sample from MW-2. Concentrations of <br /> BTEX compounds ranged from 0.0025 ppm to 0.130 ppm, The laboratory analysis of <br /> - previous samplings have given similar results. <br /> f8 <br /> Applied GeoSystems evaluated the groundwater gradient across the site. The elevation of <br /> i the top of the casing in each well was evaluated previously by Moldenhauer Engineering <br /> Company,a licensed land surveyor of Davis, California on November 27, 1989. Elevations <br /> .x� were measured in feet relative to mean sea level, using a local U.S. Geological Survey <br /> benchmark as datum. The measurements of the depths to ground water were combined <br /> with the casing elevations io calculate the elevations of the ground-water surface. These <br /> data are summarized in Table 3. We interpreted that the groundwater gradient was flat, <br /> which is consistent with previous sampling events. <br /> Applied GeoSystems recommends that monitoring of ground water at the site be continued <br /> on a quarterly basis. The next sampling has been scheduled for the week of December 18, <br /> 1989. <br /> V <br /> - <br /> 2 <br />