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e a r --� Quarterly Ground-Water Monitoring January 22, 1990 Beacon Station No. 492, Manteca, California AGS 86102-4 Mobile Chem Labs, Inc., in Lafayette, California (Hazardous Waste Testing Laboratory Certificate No. 195), analyzed the groundwater samples for total petroleum hydrocarbons (TPH) as gasoline by California Department of Health Services Leaking Underground Fuel Tanks (LUPI) Method and for benzene, toluene, ethylbenzene, and total xylene isomers (BTEX) by Environmental Protection Agency Method 602. Copies of the laboratory Analysis Reports are attached. The results of these analyses and previous laboratory analyses are summarized in Table 2. The results of the laboratory analyser indicate that hydrocarbon constituents were not detected in the ground-water sample collected from MW-3. TPH as gasoline was detected at 0.100 parts per million(ppm)in the sample from MW-1 and at 0.053 ppm in the sample from MW-2. Concentrations of BTEX compounds were below detection limits, with the exception of 0.013 ppm of toluene in the sample from MW-1. Applied GeoSystems evaluated the ground-water gradient across the site. The elevation of the top of the casing in each well was surveyed by Moldenhauer Engineering Company, a licensed land surveyor from Davis, California, on November 27, 1989. Elevations were measured in feet relative to mean sea level,using a local U.S.Geological Survey benchmark as datum. 'Ihe measurements of the depths to ground water were combined with the casing elevations to calculate the elevations of the ground-water surface. These data are ® summarized in Table 3. We interpreted that the ground-water gradient was flat, which is con.3istent with !aur interpretation from previous sampling events. Applied GeoSystems recommends that monitoring of ground water at the site be continued on a quarterly basis. The next sampling has been scheduled for the week of March 19, ® 1990. 2 1.