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_ <br /> 1 <br /> 1 <br /> v <br /> t <br /> h : <br /> Quarterly Ground-Water Monitoring October 25, 1989 <br /> . R <br /> Beacon Station No. 502, Lodi, California AGS 46091-7 <br /> BC Laboratories, Inc., in Bakersfield, California (Hazardous Waste Testing Laboratory <br /> Certificate No. 102) analyzed the ground-water samples for total petroleum hydrocarbons <br /> (TPH) by Environmental Protection Agency (EPA) Method 8020, benzene toluene, <br /> ethylbenzene, and total xylene isomers (BTEX), chlorobenzene, and 1,4-dichlorobenzene <br /> by EPA Method 503.1. The results of these analyses and previous laboratory analyses are <br /> summarized in Table 2. Copies of the Laboratory Analysis Reports are attached to this <br /> letter report. <br /> The results of the laboratory analyses indicate that the BTEX concentrations in the giound,- <br /> water samples collected from monitoring wells MW-1, MW-3, MW-4, and MW-5 have <br /> increased slightly since the March 1989 sampling. Results indicated slight increases in <br /> concentrations of benzene and toluene with decrea-as in concentrations of ethylbenzene and <br /> xylene isomers for the MW-2 groundwater sample. Chlorobenzene, 1,4-dichlorobenzene <br /> and TPH concentrations were below the detection limits of the analytical"m4tnods used for <br /> each of the five samples. <br /> The ground-wafer gradient across the site was evaluated by combining measurements of the <br /> static water-level with the relative elevation of the top of the casing in each monitoring <br /> well. The relative elevation of the top of the casing in each well was previously evaluated . <br /> with a Lietz-Sokkisha C3E Automatic Level. The static water levels were adjusted using <br /> t the top of the casing in well MW-3 as a common datum. These data are summarized in <br /> Table 3, and were used to evaluate the gradient of the static potentierretric surface at the <br /> time of this quarterly monitoring event (Plate P-3). The groundwater gradient was <br /> evaluated to increase to the southwest with an average magnitude of 0.003, and the flow <br /> direction was toward the southwest_ The orientation of the ground-water gradient is similar <br /> to that in previous sampling events.' <br /> Applic: GeoSystems recommends that quarterly monitoring at the site be continued; the <br /> next sampling event has been scheduled for the week of September 25, 1989. <br /> 2 <br /> ADpl ed iGeaSysferrrs <br />