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PHASE I HYDROGEOLOGIC ASSESSMENT WORK PLAN <br /> 7910 Lower Sacrunento Road, Stockton, California <br /> Delta Project No. 40-88-147 <br /> ' Page b <br /> 2.6 Regional Geology and Hvdroaeoloev <br /> Stockton lies within the Great Valley geomorphic province. The regional geology consists of <br /> unconsolidated deposits of sand, silts, and clays which were deposited in fluvial and deltaic <br /> environments. <br /> The regional map showing the ground water elevation contours for the unconfined aquifer for fall <br /> 1986, prepared by DWR, indicates that groundwater flows toward the southwest. <br /> 2.7 cite !GeQIQgy <br /> Subsurface geology at the site has been partially characterized from drilling and sampling eight soil <br /> borings. Soil borings B-I through B-4 were drilled near the existing underground storage tanks. Soil <br /> Lo borings B-5 through B-8 were located and drilled within the proposed location for the new tanks. <br /> �. <br /> All eight soil borings encountered a silty clay layer approximately 3 feet thick below the asphalt <br /> v w <br /> pa earlent. Belo the salty clay, the borings encountered layers of clayey salt (ML), salty clay (CL), <br /> and sandy silt (ML). Soil boring B-7 encountered a lense of silty sand (SM) between 4 and I 1 feet, <br /> w <br /> and soil boring B-8 encountered fine to medium sand (SP) between 8 and 11 feet. <br /> �. 3.0 WORK PLAN <br /> 3.1 Soil Borings <br /> Six soil borings will be drilled to characterize the subsurface geology and to evaluate the presence <br /> of petroleum constituents in the soils at the site. Three of the soil.borings will be completed within <br /> ` the uppermost water-bearing zone as ground water monitoring wells. Locations of the proposed <br /> monitoring wells and soil borings are presented in Figure 2. <br /> 3.2 Soil Sample Collection and„SGrgening <br /> A California modified split-barrel sampler will be used to extract soil samples from the soil borings. <br /> Three 6-inch brass tubes will be inserted into the California sampler to retain the soil sample. Upon <br /> retrieval, one brass tube will be capped, packaged, and preserved according to accepted EPA <br /> procedures for possible chemical analysis. One sample from each sampler will be extracted and <br /> placed in a sealed jar until completion of drilling activities. <br /> L. <br /> AW <br /> V <br />