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Workplan for Additional Offsite Assessment,Fate and Transport Evaluation Addendum, 2 <br /> Sensitive Receptor Survey and Fourth Quarter 2002 Monitoring And Sampling <br /> 7-Eleven Store No 14117,2725 Country Club Blvd,Stockton,CA January 30,2003 <br /> A corrective action plan (CAP) (Shaw, June 2002)was submitted to the SJCPHS Agency response <br /> indicated that completion of lateral delineation to the east and north of the site will be required prior to CAP <br /> review by the SJCPHS In addition, site hydraulic parameters applied in the fate and transport evaluation <br /> submitted with the CAP were based on literature values for soil types logged at the site, and the SJCPHS <br /> has asked for further verification <br /> In response to the SJCPHS's request, a synopsis of regional assessment data, including investigations <br /> north and east of the site pursued by the neighboring service station facility, and a more detailed hydraulic <br /> parameter evaluation relative to the fate and transport model have been completed and are discussed in <br /> this report <br /> 30 GEOLOGYIHYDROGEOLOGY <br /> 1 The site is located in the northern part of the San Joaquin Valley at an elevation of approximately 1 foot <br /> above mean sea level Shallow stratigraphy in the area consists of Quaternary alluvial/deltaic deposits <br /> Materials encountered during previous drilling at the site (Figures 3 and 4) generally consist of <br /> interbedded clayey fine-grained sand, silty clay, and clayey silt, with laterally-discontinuous lenses of <br /> silty sand to very fine-grained sand encountered from about 18 to 28 feet below grade (bg) During <br /> drilling of deeper well MW-2, fine-to medium-grained sand was encountered from 38 to 51 feet bg (the <br /> maximum drilling depth) <br /> The sand units are generally fresh-water-bearing east and southeast of Stockton, but increasingly <br /> brackish or saline water has been reported westward The saline and brackish-water/fresh-water <br /> boundary trends north to south across the western part of Stockton The brackish/saline water west of <br /> this boundary is often overlain by a layer of fresh groundwater to about 50 feet bg, therefore, shallower <br /> groundwater monitoring wells may encounter fresh water on both sides of the boundary Historically, <br /> groundwater has been encountered at the site at about 10 feet bg, static levels are at similar depths <br /> During the current sampling event, equilibrated depth to groundwater ranged from 8 60 to 9 43 feet below <br /> top of casing (TOC) <br /> Historic flow9 radients have fluctuated, with flow directions ranging from the south to the east, to the <br /> ' northwest The fluctuation of flow directions may be due to tidal action, thus the net gradient may be near <br /> zero The shallow groundwater and proximity of some of the monitoring wells to the former and current <br /> UST pits likely contribute to local perturbations and fluctuations in groundwater flow direction <br /> 14117Q24 SAR doe <br /> t <br />