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12 June 1996 <br /> AGE-NC Project No. 95-0130 <br /> Page 2of5 <br /> i <br /> . 2.3. INITIAL INVESTIGATION <br /> On 28 and 29 December 1994, five soil borings (B 1 through B5) were advanced.at the site. Borings <br /> B1, B3, and B5 were advanced to depths of 35 feet below surface grade (bsg) near the area of the <br /> I-= former USTs. Borings B2 and B4 were advanced to depths of 50 and 65 feet bsg, respectively. <br /> Petroleum hydrocarbons were detected in soil samples throughout each boring. <br /> l <br /> On 08 and -1,09 January 1995 four additional soil borings (MW MW-2, MW-3. and B6) were <br /> j. advanced at the site. Boring B6 was advanced to a depth of 65 feet bsg. Borings MW-1 through <br /> MW-3 were advanced to depths of 80 feet bsg and completed as 2-inch diameter ground water <br /> r" monitoring wells. Petroleum hydrocarbon-.impacted soil and ground water were detected in samples <br /> collected from each monitoring well. Table 1 summarizes the analytical results of all boring and <br /> monitoring well soil samples. <br /> i <br /> '. 2.4, REGIONAL GEOLOGIC SETTING <br /> � . <br /> The site is situated within the Great Valley.Geomorphic Province of California, a large, elongate <br /> i <br /> northwest tending, asymmetric structural trough. The Great Valley Province has been filled with <br /> thick sequences of sediments ranging in age from Jurassic to Recent, creating a nearly flat lying <br /> ii alluvial plain, which extends from the Tehachapi Mountains in the south to the Klamath Mountains <br /> 1 . . <br /> in the north_ The western and eastern boundaries of this province are comprised of the California <br /> Coast Range and the Sierra Nevada Mountains, respectively. Rocks composing the basement floor <br /> of the province have not been completely defined but are believed to be of metamorphic and igneous <br /> origin, The Great Valley Province is split into-two major divisions which are identified as the <br /> ` Sacramento and San Joaquin Valleys. . <br /> ' 2.5. GROUND WATER DEPTH AND GRADIENT <br /> ^ ' The water-table surface beneath the site currently occurs at a depth of approximately.51 feet bsg. The <br /> . uppermost ground water flows in an unconfined aquifer. With depth, the aquifer becomes semi- <br /> confined due to the presence of heterogeneous layers of sediment. <br /> .f <br /> Review of Lines o Equal Depth Of Water Wells Fall 1993.published'by the San Joaquin County <br /> { <br /> Flood Control and Water Conservation District suggests that.regio nal ground water flow.is towards <br /> the northeast. Conversely,previous quarterly ground watermonitoring events have indicated that <br /> .�`. <br /> ards the southeast. <br /> local ground water flow beneath the site is tow <br />