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Additional Site Assessment Report and Wait Plan for Additional Subsurface Investigation 6 The Southland Ce ration Store#19976,1399 N Main St Manteca California June 5 1998 ' 5.3 Reporting and Schedule VViithin four to six weeks of receipt of all field and analytical findings, Fluor Daniel GTI will prepare a report summarizing the data collected under the scope of work detailed above The report will document the methods and results of the work,summarize laboratory analytical results, and include appropriate maps Field work will commence within four weeks of written regulatory agency approval of this scope of work 6.0 CONCLUSION AND CLOSURE ABSTRACT Three geoprobe points were drilled at the subject site to a vertical depth of between 40 and 47 feet BGS (Figure 2) A total of 19 soil samples and three groundwater samples were collected for analysis Analytical results indicate the groundwater near the former USTs contains elevated concentrations of BTEX,TPH-G,and MTBE The highest concentrations of BTEX.MTBE,and TPH-G were found beneath the northeastern section of the UST pad (GP-3) Concentrations of BTEX, MTBE,and TPH-G in soil samples from GP-1 and GP-2 were low to non-detectable Sod samples from GP-3 contained non- detectable to moderate levels of BTEX,MTBE and TPH-G The lateral extent of hydrocarbons in sod beneath the site appears restricted to the immediate area of the former USTs Low to moderate benzene,MTBE, and TPH-G concentrations(up to 0 93 mg/kg,2 7 mg/kg, and 220 mg/kg, respectively)were detected in sod samples collected beneath the former USTs Benzene and TPH-G concentrations decrease to the south of the former USTs in sod samples collected from the floor of the excavation for the newly installed USTs and are below method detection limit in the southernmost samples collected from the excavation To the northwest and northeast of the former USTs, ' sod containing hydrocarbons are delineated by soil bonngs GP-1 and GP-2,which contained TPH-G concentrations of 0 26 mg/kg and 4 6 mg/kg, respectively in samples collected at 20 feet BGS Verbcal delineation of hydrocarbon containing sod at the site Is uncertain due to what appears to be anomalous data collected from sod boring GP-3 installed within the former tank pit location Analytical results from soil samples collected from soil boring GP-3 show fluctuating hydrocarbon concentrations with ' depth Benzene and TPH-G were not detected in sample collected at 30 feet and 40 feet BGS but were detected in samples collected at 25 feet, 35 feet,and 45 feet(TPH-G only) MTBE in sod boring GP-3 was ' not detected or detected at low concentrations in samples collected at 25 feet,30 feet,40 feet, but was detected in samples collected at 35 feet and 45 feet at concentrations of 27 mg/kg and 3 mg/kg, respectively by EPA method 8020 ' The elevated hydrocarbon concentrations may be due to a matrix interference with the shallow groundwater at the site (approximately 13 It) and may not represent actual hydrocarbon concentrations at depth ' beneath the site Unless groundwater elevation beneath the site has fluctuated significantly over time, it is 1997Btarrpt ' FLUOR DANIEL GTI