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May 4, 1993 Working To Restore Nature <br /> Unocal Station No 6981, Stockton, California <br /> A2 Site Geology and H dro eolo <br /> Sediments beneath the site consist primarily of clay, silt, and fine- to medium-grained sand <br /> Three generalized cross-sections A-A', B-B', and C-C' (Plates 4 through 6), were constructed <br /> using the Logs of Borings The surface trace of these cross-sections is shown on Plate 2 <br /> I <br /> Cross section A-A' shows our interpretation of the soil stratigraphy beneath the site in the <br /> east-west direction, and cross section B-B' shows our interpretation of the soil stratigraphy <br /> in the north-south direction The site is predominantly underlain by silt Lenses of poorly <br /> graded sand were encountered in borings B-1, B-3, B-5, B-14, and B-15 from approximately <br /> 22 to 65 feet below grade Lenses of silty sand were encountered in these borings and <br /> borings B-2, B-8, B-10, B-18, and B-19 The occurrence of these lenses are shown on Plates <br /> 4 and 5 <br /> 1 <br /> In January 1990, first ground water was encountered under unconfined conditions at <br /> approximately 50 feet below grade in sediments ranging from silt to fine-grained sand In <br /> October 1990, ground-water had dropped and monitoring wells MW-1 through MW-5 were <br /> dry. Ground water was encountered at approximately 55 feet below the existing ground <br /> surface in morutoring wells MW-6 through MW-13 which were installed in March and <br /> August of 1992 The direction of ground-water flow has consistently been to the northeast <br /> 1 <br /> with a hydraulic gradient ranging from 0 004 to 0 013 A Potentiometric Surface Map <br /> utilizing data collected on January 13, 1993 by GeoStrategies Inc is shown on Plate 7 <br /> Data from the pumping test were used to evaluate the hydraulic parameters transmissivity <br /> (T) and specific yield (Sy) and to provide information regarding aquifer boundary conditions <br /> and anisotropy The transmissivity for this zone was calculated to be approximately 0 4 to <br /> 0 8 feet2/minute and the specific yield is approximately 5 to 10 percent Using a pumping <br /> f� rate of 3 5 gallons per minute, the average calculated transmissivity, and the measured <br /> 38032-13 5 <br /> 1 <br />