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Quarterly Ground-Water Monitoring October 25, 1989 Beacon Station No. 502, Lodi, California AGS 86091-7 BC Laboratories, Inc., in Bakersfield, California (,Hazardous Waste Testing Laboratory Certificate No. 102) analyzed the ground-water samples for total petroleum hydrocarbons (TPH) by Environmental Protection Agency (EPA) Method 8020, benzene toluene, ethylbenzene, and total xylene isomers (BTEX). chlorobenzene, and 1,4-dichlorobenzene by EPA Method 503.1. The results of these analyses and previous laboratory analyses are summarized in Table 2. Copies of the Laboratory Analysis Reports are attached to this letter report. The results of the laboratory analyses indicate that the BTEX concentrations in the ground- water samples collected from monitoring wells MW-1, MW-3, MW-4, and MW-5 have increased slightly since the March 1989 sampling. Results indicated slight increases in concentrations of benzene and toluene with decreases in concentrations of ethylbenzene and xylene isomers for the MW-2 groundwater sample. Chlorobenzene, 1,4-dichlorobenzene and TPH concentrations were below the detection limits of the analytical methods used for each of the five samples. The groundwater gradient across the site was evaluated by combining measurements of the static water-level with the relative elevation of the top of the casing in each monitoring well. The relative elevation of the top of the casing in each well was previously evaluated with a Lietz-Sokkisha C3E Automatic Level. The static water levels were adjusted using- the top of the casing in well MW-3 as a common datum. These data are summarized in ' Table 3, and were used to evaluate the gradient of the static potentiometric surface at the time of this quarterly monitoring event (Plate P-3). The ground-water gradient was evaluated to increase to the southwest with an average magnitude of 0.003, and the flow direction was toward the southwest. The orientation of the ground-water gradient is similar to that in previous sampling events. Applied GeoSystems recommends that quarterly monitoring at the site be continued, the next sampling event has been scheduled for the week of September 25, 1989. 2 ,4pjp/fed 4a6POS,j St&JnS