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a <br /> s <br /> f <br /> x gn <br /> KEI-P91-0202.P2 <br /> April 9, 1991 <br /> Page 4 <br /> Delta area. The Central Valley is a large, northwestward- <br /> trending, asymmetric structural trough that ha8 been filled <br /> with up n six vertical less of sediment sediment in he SanJoaquin <br /> Valley and up <br /> Valley. <br /> Based on review of regional geologic ,naps (U.S. Geological <br /> Survey Miscellaneous Fieldu Delta, !a F-1 01"Geoloa" bygi anaFs <br /> of the Sacramento-San Joaquin <br /> Atwater, 19a2) , the subject site is underlain by the Pleisto- <br /> cene Modesto Formation (¢m) • The Modesto Formation in the <br /> vicinity of the site is described as typically consisting of <br /> loose sand and silt, which is chiefly fluvial, representing an <br /> alluvial fan deposit of the Mokelumne River which I-as a <br /> reported average thickness of about l0 to 3.5 feet and is <br /> commonly underlain by compact, unweathered silt.Formation is considered to be underlain by the Pleistocene <br /> Riverbank Formation. <br /> PROPOSED FIELD WORK <br /> PHASE i - DEFINING THE EXTENT OF SUBSURFACE CONTAMINATION <br /> 1. KEI proposes ,to, install th ele.atn o- nch ..diams er moria a!rite <br /> tiie�ask; designated as MWl, d MW3 on the attached Site <br /> quipment. Permits <br /> Plan, Figure 3, using hollow stem auger e <br /> will be obtained from the SanJoaquin County Local Health <br /> Department prior to beginning <br /> The wells will be drilled about 10ta' 15 'feet into <br /> - <br /> satat urated_zon0of the first encountered ground viat w unless a <br /> 5 foot thick clay a,4uitard is encountered Zirst, Yt Bch time <br /> drilling will be terminated. <br /> 2. Soil samples will be collected at a maximum spacing of 5 foot <br /> intervals, significant changes in lithology, at obvious areas <br /> of contamination, ana atfd r h iofl about 4 to the /5r feet below <br /> water <br /> interface beginning Pt <br /> grade. Sampling for laboratory analyses and lithologic <br /> lagging purposes will continue until the first water table is <br /> encountered. Sampling for lithologic logging purposes only <br /> will continue below the water table to the total depth <br /> drilled. However, the first boring drilled will be sampled at <br /> approximately 2.5 foot intervals to provide a better under- <br /> standing of he subsurface soils. Classification of soil will <br /> -- ----- - -- --- ---- - - - -be-done-using-the Unif ied-Soils Classification Sy ) <br /> by KEI's field engineer or geologist. Samples-wr -- <br /> lected in a California modified split-spoon sampler with two <br /> �� n�ne�e�INI1Al1•rn <br />