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Fourth Quarter 1998 Monitoring and Sampling Report and Work Plan for Additional Subsurface Investigation 2 The Southland Corporation,Store#19976, 1399 North Main Street Manteca CA January 29 1999 have been corrected (Table 1) With last quarter's data corrected the WTE, groundwater flow direction and ' analytical results conform more logically with fourth quarter monitoring and sampling data Groundwater monitoring results from September 16 and December 30, 1998 monitoring and sampling events are presented In Table 1 Field data sheets are included in Attachment 3 MONITORING WELL SAMPLING AND ANALYTICAL RESULTS ' On December 30, 1998, groundwater samples were collected from four wells Before sampling, at least four well-casing volumes of groundwater were removed from each monitoring well unless the well was purged dry The groundwater samples were collected using disposable bailers Groundwater samples were placed in analysis-specific containers with analysis-specific preservative The samples were then sealed using Teflon septum caps, labeled with the job Identification number, the sample number, date, time, and type of laboratory analysis required The samples were stored on Ice and transported with a chain-of-custody record to Core Laboratories, Inc , in Anaheim, California Groundwater samples were ' analyzed for BTEX and TPH-G using Environmental Protection Agency(EPA) method 8020/modified 8015 and for the oxygenates TBA, MTBE, DIPE, ETBE and TAME using EPA method 8260 Laboratory analytical results and historical reports for groundwater samples collected on December 30, ' 1998 are summarized in Table 1 The highest concentrations of benzene and TPH-G were reported in groundwater sampled from MW-2 at 3,150 micrograms per liter(pg/L) and 38,400 Vg/L, respectively The highest concentration of MTBE was found in well MWA at 383 pg/L Benzene and TPH-G concentrations Increased In wells MWA(crossgradient) and MW-2 (downgradlent),while MTBE Increased In MW-1 and decreased in MW-2 between the third and fourth quarters Dissolved hydrocarbon concentrations decreased in MWAA(the deep monitoring well)to below detection limits Dissolved hydrocarbon concentrations have remained low to non-detectable in well MW-3 (upgradlent) over the two quarters sampled The laboratory analytical reports for the groundwater samples are Included In Attachment 4 Dissolved oxygen data taken from the four monitoring wells on December 30, 1998, indicate depletion of dissolved oxygen through ongoing Intrinsic biodegradation Dissolved oxygen levels decreased in all ' wells between the third and fourth quarters Dissolved oxygen levels ranged from 0 4 milligrams per liter (mg/L)to 1 2 mg/L(Table 1) PURGE WATER TRANSPORTATION AND DISPOSAL All purge water generated during this quarterly monitoring and sampling event was stored in 55-gallon ' Department of Transportation (DOT)-approved drums pending characterization and proper disposal Approximately 48 gallons of purged water generated during this sampling event will be removed from the site during the next quarter by Belshlre Environmental Services, Inc and transported to a licensed treatment ' and disposal facility Waste disposal documentation will be forwarded once received BACKGROUND ' Underground storage tank replacement and associated soil sampling activities were conducted in 1996 On September 19, 1996, a total of five soil samples were collected from the tank pit area (Figure 2) Table 1 IT CORPORA710N