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455 Grant Line Road, Tracy, California April 22, 1994 The Southland Corporation Page 2 Separate-phase hydrocarbons were not detected in any of the monitoring wells. The water-table elevations calculated from the March 31, 1994 monitoring data were used to prepare a potentiometric surface map (Figure 3). No significant change in the potentiometric surface elevation is observed since the previous quarter's monitoring event. The groundwater flow direction is toward the northeast with a hydraulic gradient of approximately 0.003 foot/foot. The historical and current water-level measurements are presented in Table 1. MONITORING WELL SAMPLING AND ANALYTICAL RESULTS Per the reduced sampling schedule approved by the California Regional Water Quality Control Board-Central Valley Region (CRWQCB-CVR), on March 31, 1994, groundwater samples were collected only from 5 monitoring wells (MW-4, 5, 8, 9 and 10) and one groundwater extraction well. MW-2 was not sampled because the well casing was clogged-with tree bark. Before sampling, at least four well-casing volumes of groundwater was removed from each of the monitoring wells, unless the wells were purged dry. Field measurements of temperature, conductivity, and pH were recorded during well purging (Attachment 1). The groundwater samples were collected using a Teflon® sampler and placed in analyses-specific sample containers with analyses-specific preservatives. The samples were then sealed and labeled with the job identification number, the sample number, date, time, and type of laboratory analysis required. The samples were stored on ice in an insulated container and transported under chain-of-custody manifest to GTEL Environmental Laboratories, Inc. in Concord, California. The groundwater samples were analyzed for BTEX, and TPH-G using EPA methods 8020/8015. Dissolved BTEX and TPH-G were detected in all groundwater samples with the exception of MW-4. The highest concentrations of benzene (13,000 parts per billion [ppb)) and TPH-G (44,000 ppb) were detected in the groundwater samples collected from well MW-10. Figure 4 illustrates the distribution of dissolved benzene and TPH-G concentrations in groundwater. Review of the historical data shows that the BTEX and TPH-G concentrations, detected in the samples collected on March 31, 1994, are within the same order of magnitude as previous results (Table 1). The laboratory analytical reports and the chain-of-custody records for the March 31, 1994 sampling event are included in Attachment 2. CONCLUSIONS AND RECOMMENDATIONS The potentiometric surface elevation as measured in the groundwater monitoring wells has not changed significantly since the previous quarter's monitoring event. • Based on the groundwater monitoring and analytical data collected to date, Groundwater a h.''`� .f JLE'GROUNDWATER i_ '� - TECHNOLOGY