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,1 } Fourth ouarter 1994 Monitoring and Sampling Report January 13, 1995 The Southland Corporation, 455 Grant Line Rd.,Tracy, CA 2 Separate-phase hydrocarbons were not detected in any of the monitoring wells. The water-table elevations calculated from the December 23, 1994 monitoring data were used to prepare a potentiometric surface map (Figure 3, Attachment 1). The groundwater flow is toward the northeast at a hydraulic gradient of approximately 0.005 ft/ft. The historical and current water-level measurements are presented in Table 1 (Attachment 2). MONITORING WELL SAMPLING AND ANALYTICAL RESULTS Groundwater samples were collected from ten site-related monitoring wells (MW-1, 3 through 6, 8 through 15 and GWE-1). MW-2 was not sampled this quarter 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 3). The groundwater samples were collected using a Teflon® sampler and placed in analysis-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. • Dissolved BTEX and TPH-G were detected in groundwater samples from monitoring wells MW-1 8 through 10, and GWE-1. The highest concentrations of benzene and TPH-G were detected in MW- 10 at 5,600 parts per billion (ppb) and 21,000 ppb, respectively. Figure 4 illustrates the distribution of dissolved benzene and TPH-G concentrations in groundwater (Attachment 1). The laboratory analytical reports and the chain-of-custody records for the December 23, 1994 sampling event are included in Attachment 4. CONCLUSIONS AND RECOMMENDATIONS The potentiometric surface continues to show a gradient to the northeast and has not changed significantly since the previous quarter's monitoring event. Based on the groundwater monitoring and analytical data collected to date, Groundwater Technology recommends that quarterly monitoring continue through 1995. 4094-M&S.RPT(STHL-5) ❑❑`� GROUNDWATER ❑❑❑ TECHNOLOGI' .