ARCHIVED REPORTS XR0001734 - Laserfiche WebLink

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Quarterly vround-Water Monitoring January 22. 1990 Beacon Station No. 502, Lodi, California AGS 86091-7 Mobil. Chem Labs, Inc., in Lafayette, California (Hazardous Waste Testing Laboratory Certificate No. 195), analyzed the ground-water 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 1. The results of the laboratory analyses indicate that hydrocarbon constituents were not detected in the ground-water samples collected from MW-4 and MW-5. TPH as gasoline was detected at 0.050 parts per million (ppm) in the samples from MW-1 and NSW-2'and at 0.100 ppm in the s2-nple from MW-3. Concentrations of the BTEX compounds were below detection limits, with the exception of 0.023 ppm of toluene and 0.018 ppm of total xylene isomers in the sample from MW-3. 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 a datum. The measurements of the depths to ground water were combined with the casing elevations to calculate the groundwater elevations. These data are summarized in Table 2 and were used to evaluate the ground-water gradient at the time of this quarterly monitoring event (Plate P-3). The average groundwater gradient was evaluated to be 0.004, with a flow direction towards the southwest; the magnitude of the gradient appears to be greater ir_ :he northeastern portion of the site. The orientation of the groundwater. gradient is similar to that evaluated in previous sampling events. Applied GeoSystems recommends that monitoring of ground water at the site be continued on a quarterly basis. The next sampling event has been scheduled for the week of March 19, 1990. 2