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Soil Excavation and Second Quarter Post-Treatment Monitoring and Sampling Report 4 • The Southland Corporation,Store#20304,455 Grant Line Road,Tracy,CA June 9,1998 The excavation limits were determined based on soil and groundwater analytical data from previous site investigations The purpose of the excavation was to remove a majority the sod containing the highest residual hydrocarbon concentration beneath the site Soils encountered in the two excavations consisted of sandy silty clay to a depth of 3 feet BGS,followed by sandy silt to 7 feet BGS and silty clay(western side of excavation near store building)and fine sand (eastern side of excavation near store budding and beneath for dispenser island)to a depth of 9 feet BGS Static groundwater level was approximately 4 5 feet BGS in the two excavations 3 1 Soil Sample Collection A total of 13 soil samples were collected from the floor and sidewalls of the two excavations at depths ranging from 2 feet to 9 feet BGS (Figure 2) The samples were collected under the direction and observation of Mr Harlin Knoll of the SJCPHS The samples were collected in 2-inch-diameter by 6-inch- long brass tubes directly into the soil brought up by the backhoe The sample tubes were sealed with Teflon film, plastic caps and tape, labeled, and placed on ice in an insulated cooler The samples were transported under chain-of-custody(COC)to state-certified West Laboratory in Davis, California for analysis Samples were analyzed for benzene,toluene, ethyl-benzene and xylenes(BTEX), methyl tert- butyl-ether(MTBE), and TPH-G by Environmental Protection Agency(EPA) methods 8020/8015 In addition,the sample containing the highest hydrocarbon concentration by EPA methods 8020/8015 was analyzed for tert-butanol (TBA),MTBE,diisopropyl ether(DIPE), ethyl-tert-butyl ether(ETBE), and tert- amylmethyl ether(TAME) by EPA method 8260 3 2 Soil Analytical Results Table 1 summarizes the analytical results of the soil samples collected during the recent excavation, along with historical sod analytical results from previous site investigabons The highest benzene and TPH-G concentrations were detected in sample E-24, collected at a depth of 6 feet BGS from the southern sidewall in the excavation northeast of the former tank pit,at 71 mg/kg and 1,700 mg/kg, respectively MTBE was not detected in any of the 13 samples collected TBA, MTBE, DIPE, ETRE, and TAME were not detected in the one sample (E-2-6) analyzed by EPA 8260 A copy of the analytical report and COC is included in Appendix D 3.3 Backfill and Compaction The two excavations were backfilled with pea gravel and paved with asphalt The pea gravel was compacted in each excavation to approximately 6 inches BGS Compaction tests were not performed on the backfill material FLUOR DANIEL GTI 20304exrpt �5_