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�. uista 1 Quarterly Monitoring Report June 1, 1989 Former UNOCAL station No. 2$59, Stockton, California AGS e 1, 12-2 98 nondetectable in well �. ]-1, and that concentrations of these constituents had increased in a ground-water sample collected from monitoring well MW-2, and remained near initially detected concentrations in a ground-water sample collected from monitoring well M IW-3, At your request, a geologist from Applied GeoSystems was present onsite March 2 and 3, 1989, to collect ground-water samples from monitoring wells MW-1 through MW-3. The depth to the ground- water surface in each monitoring well was measured to the nearest 0.01--foot with a Solinst water-level indicator. The ground water was found to be approximately 1/2-foot shallower in the recent sampling event than previously measured. The water-level data, summarized in Table 1, were used to construct a Ground-Water Potentiometric Surface Map across the site (Plate P-3) . Evaluation of depth-to-water data collected on March 2, 1989, indicate that the direction of ground-water flow at the site is northeast. The evaluated direction of ground-water flow on June 6, 1988, and October 26, 1989, was also northeast. The average gradient at the time of measurement was 0.0021. This value is similar to the ground-water gradient evaluated during the sampling event of June 6, 1988, and less than the ground- water gradient evaluated from data collected on October 26, 1989. In June 1988 the average gradient was 0.0017; the average gradient in October 1988 was 0.0068. _.4 Ground-water samples were collected from near the air-fluid interface in the monitoring wells for subjective analysis by lowering approximately half'tFe length of a clean Teflon bailer past the interface. The bailer was then retrieved and the water sample was examined for floating product, sheen, and other subjective evidence of hydrocarbon contamination. No floating product, product sheen, or emulsion was noted in samples from the monitoring wells. The results of these subjective analyses are presented in Table 2. Approximately 3 well volumes (30 gallons) of ground water were purged from the wells using a submersible pump. Recharge to the t wells was relatively rapid. Ground-water samples for laboratory analysis were then collected from the monitoring wells by gently lowering a clean Teflon bailer past_the.--.air water.-....interface--to--a-----_..-____.-- --------------.._.-._..---._-- ----------- -- - -- --- ----point--immediately bel-ow--the top of the water column. The bailer was then recovered and the sample slowly transferred to laboratory-cleaned, 40-milliliter glass vials to which concentrated hydrochloric acid had been added as a preservative. -- 2 AVP114erl G'e0Systerms