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1 ' First Quarter 1999 Post-Remediation Monitoring and Sampling Report/Request for Closure_ 2 IpThe Southland Corporation Store 020304 455 Grant Line Road,Tracy CA April 15, 1999 Groundwater Monitoring Data ' Groundwater monitoring was performed on March 17 1999 Prior to monitoring, the we l)caps were opened to allow the water level in each well to stabilize to atmospheric pressure The DTW was measured to the nearest 0 01 foot from the top of the well casing using an Interface probe ' Water table elevations, calculated from the March 17, 1999 monitoring data, were used to prepare a potentiometric surface map (Figure 2) The groundwater flow direction is generally toward the northeast at a hydraulic gradient of 0 003 ft/ft Groundwater monitoring results from the monitoring and sampling event ' are presented in Table 1, and historical results are summarized in Table 1A(Attachment 2) Field data sheets are Included in Attachment 3 Dissolved oxygen data obtained from this monitoring and sampling event indicate a depletion of oxygen levels due to intrinsic biodegradation Dissolved oxygen readings taken range from a high of 5 64 milligrams per liter(mg/L) in well MW-4 to a low of 0 10 mg/L in well MW-16 High dissolved oxygen levels ' have been typical of wells located upgradient of the former UST pit and former pump island areas, which have historically had non-detectable levels of dissolved hydrocarbons Wells with lower dissolved oxygen levels are located within or downgradient from the hydrocarbon plume i 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 150 gallons of purge water was generated during this sampling event and will be disposed of by a licensed waste hauler during the early portion of the second quarter, 1999 Waste hauler documentation will be forwarded upon receipt Monitoring Well Sampling and Analytical Results ' Groundwater samples were collected from wells MWA through MW-6, MWA 1, MWA 5, MWA 6, GWE-1, and GWE-2 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 lob 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 Core Laboratories in Anaheim, California 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(DIPS), ethyl-tert-butyl ether(ETRE) and tert-amylmethyl ether(TAME) using EPA method 8260 ' 20304gi99 RPT