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1 <br /> Report on Additional Site Assessment and First Quarter 2000 Monitoring and Sampling Report 5 <br /> • 7-Eleven Inc Store#19976 1399 N Main St Manteca California February 4 2000 <br /> transported under chain-of-custody to a state-certified laboratory The groundwater samples were <br /> analyzed for BTEX, and TPH-G using EPA Methods 80201modified 8015, and for TBA, MTBE, DIPS, <br /> ETBE, and TAME by EPA Method 8260 <br /> All purge water generated during the monitoring and sampling event was stored in a Department of <br /> Transportation (DOT)-approved 55-gallon drum pending characterization and proper disposal Waste <br /> documentation will be forwarded if requested <br /> 40 RESULTS <br />' 41 Geology and Hydrogeology <br /> The site is located in the middle of the northern San Joaquin Valley Shallow stratigraphic units in the <br /> vicinity of Manteca are mapped as Quaternary dune sand overlying the Quaternary Modesto Formation <br /> which consists dominantly of arkosic alluvium (California Division of Mines and Geology, 1991, Geologic <br /> Map of the San Francisco-San Jose Quadrangle, 1 250,00) <br /> Subsurface soils consist of sand and silty sand to approximately 10 feet below grade, underlain by clayey <br /> Isilty and silt to approximately 25 feet below grade and fine-to coarse-grained sand, clayey silt and clayey <br /> silty sand to the total depth of investigation The recent boring log is included in Appendix A, historical <br /> data are included in the previous reports <br /> Groundwater was first encountered In the borings at 20 -25 feet below grade (equilibrated groundwater <br /> levels range between about 13 and 18 feet below grade Groundwater flow in the shallow and deeper <br /> parts of the water bearing zone as mapped from data collected on January 24, 2000, is to the north- <br /> northwest at a hydraulic gradient ranging from 0 001 to 0 002 foot per foot (Figures 2 and 3) Soils <br /> encountered during drilling at the site consist of interbedded sand, silty fine sand, clayey silt, and silty <br /> I clay <br /> 1 <br /> 1 <br /> 19976 3SA <br /> 1 <br />