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4 u 0 0 AdddiorW Site Assessment Report and Work Plan for Aditm l Subsurface Inwestigatm 3 The Southland Corporation,Store#19976,1399 N Main St Manteca California June 5 1998 ' (TPH-G) using EPA methods 8020/modified 8015 One sample from each soil boring was also analyzed for the oxygenates, methyl-tert butyl-ether(MTBE),tert-butanol (TBA),dasopropyl ether(DIPE), ethyl-tert-butyl ether(ETBE),and tert-amylmethyl ether(TAME) using EPA method 8260 3.3 Groundwater Sampling Methods Following completion of the borings,grab groundwater samples were collected from soil borings GP-1,GP- 2,and GP-3 using disposable bailers, then decanted into 40-milliliter glass vials treated with hydrochloric acid to preserve the samples The samples were sealed using Teflon®-septum caps, labeled, placed on ice in an insulated container,and transported under chain-of-custody manifest to Core Laboratory The groundwater samples were analyzed for BTEX, MTBE, and TPH-G, using EPA methods 8020/modified 8015,and for oxygenates MTBE,TBA, DIPE, ETBE,and TAME using EPA method 8260 ' Following collection of soil and groundwater sam les,each soil boring was routed back to surface rade p 9 9 9 with neat cement i ' 4.0 RESULTS OF SOIL AND GROUNDWATER SAMPLE ANALYSES 4.1 Site Geology The site is located in the middle of the northern San Joaquin Valley Shallow stratigraphic units in the vicinity of Manteca are mapped as Quaternary dune sand overlying the Quaternary Modesto Formation which consists dominantly of arkosic alluvium (California Division of Mmes and Geology, 1991, Geologic Map of the San Francisco-San Jose Quadrangle, 1250,00) ' The materials encountered during recent drilling at the site consisted of sand and silty sand to approximately 10 feet BGS underlain by clayey silty sand and silt to approximately 25 feet BGS and fine to coarse sand,clayey silt and clayey silty sand to approximately 40 feet BGS(Appendix A) Static ' groundwater level in the bonngs was approximately 13 feet BGS 4 2 Results of Soil Sample Analyses Table 1 summarizes the laboratory analytical results for the soil samples collected from the three soil ' bonngs drilled April 29, 1998 The highest concentrations of benzene, MTBE and TPH-G were reported in sample GP-3-35 at 15 milligrams per kilogram (mg/kg), 27 rng/kg and 2,600 mg/kg, respectively MTBE, TBA, DIPE, ETBE, and TAME, using EPA method 8260 were not detected in the three samples analyzed ' Copies of laboratory analyses reports and chain-of-custody are included in Appendix C 1 19976=r rpt ' FLUOR DANIEL GTI r