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Third Quarter 1998 Post-Remediation Monitoring and Sampling Report/Request for Closure 2 r The Southland corporation,Store#20304,455 Grant Line Road.,Tracy,CA October 15,1998 Separate-phase hydrocarbons were not detected in any of the monitoring wells. Water table elevations, calculated from the August 18, 1998 monitoring data,were used to prepare a potentiometric surface map (Figure 2). The groundwater flow direction is generally toward the north at a hydraulic gradient of 0.003 ft/ft. Groundwater monitoring results from the monitoring and sampling event are presented in Table 1,and L, historical results are summarized in Table 1A(Attachment 2). field data sheets are included in Attachment 3. Purge Water Transportation and Disposal �- The purge water was stored onsite in Department of Transportation (DOT)approved 55-gallon drums pending characterization and proper disposal. Approximately 34 gallons of purge water was generated F during this sampling event and vv:.,'.' be c;by a licensed waste hauler during the early portion of the fourth quarter. Waste hauler documentation will be forwarded upon receipt. r ` Monitoring Well Sampling and Analytical Results Groundwater samples were collected from wells MW-4,MW-5,and MW-16. Before sampling, at least four well-casing volumes of groundwater was removed from each monitoring well, unless the well was purged dry. Field measurements of temperature, conductivity,and pH were recorded during well purging. The groundwater samples were collected using disposable bailers and placed in analysis-specific sample containers with analysis-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 L„ samples were stored on ice in an insulated container and transported under chain-of-custody manifest to Care Laboratories in Anaheim,Califomia. The groundwater samples were analyzed for BTEX, MTBE and TPH-G using Environmental Protection Agency(EPA) methods 8020/modified 8015, and the oxygenates, methyl-tert-butyl ether(MTBE),tert-butanol (TBA),diisopropyl ether(DIPE), ethyl-tert-butyl ether(ETBE) and tert-amylmethyl ether(TAME) using EPA method 8260. Groundwater purged during the third quarter monitoring and sampling event was pumped through the groundwater extraction system. Dissolved benzene and TPH-G were detected in groundwater samples from monitoring well MW-16 at concentrations of 75 micrograms per liter(ug/L) and 5,000 ug/L, respectively(Figure 3). MTBE was not detected in any of the wells sampled. Analytical results from the groundwater samples collected on August 18, 1998 are presented in Table 1, and historical analytical results are summarized in Table 1A. The laboratory analytical reports and the chain-of-custody records for this sampling event are included in Attachment 4. La 203Wg398,RPT FLUOR DANIEL GTI A L�