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•' i 455 Grant Line Road, Tracy, California July 27, 1994 j The Southland Corporation Page 2 Separate-phase hydrocarbons were not detected in any of the monitoring wells. The water-table elevations calculated from the June 30, 1994 monitoring data were used to prepare a potentiometric surface map (f=igure 3). No significant change in the potentiometric surface elevation has occurred since the previous quarter's monitoring event. The groundwater flow is toward the northeast at 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 June 30, 1994, groundwater samples were collected from only five monitoring wells (MW-4, 5, 8, 9 and 10). MW-2 and extraction well GWE-1 were not sampled this quarter because the MW-2 well casing was clogged with tree bark, and the GWE-1 well cap was stuck tight. 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 method 8020. Dissolved BTEX and TPH-G were detected in all groundwater samples with the exception of MW-5. The highest concentrations of benzene (13,000 parts per billion [ppb]) and TPH-G (50,000 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 June 30, 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 June 30, 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 quarters monitoring event. GROUNDWATER ❑0❑ TECHNOLOGY