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20 March 1996 <br /> ' AGE-NC Project No, 95-0108 <br /> Page 2 of 7 <br /> ' 2.3. GROUND WATER DEPTH AND FLOW DIRECTION <br /> Based on the San Joaquin County Flood Control and Water Conservation District map entitled Litres <br /> of Equal Elevation in Water Wells, Fall 1993, ground water depth at the site is approximately 55 feet <br /> below surface grade (bsg). Regional flow direction in the area of the site is west to southwest. <br /> ' However, flow direction can vary locally and with seasonal changes of ground water depth. <br /> ' 2.4. REGIONAL GEOLOGICAL.AND HYDROGEOLOGICAL SETTING <br /> The subject site is located in the central portion of the Great Valley geomorphic province of <br /> ' California. The valley is a nearly flat, elongate trough trending northwest and southeast for <br /> approximately 450 miles. The valley is enclosed by the granitic Sierra Nevada Mountains on the east <br /> ' and the sedimentary and metamorphic Franciscan Coast Range on the west. The surficial and upper <br /> several thousand feet of subsurface layers consist primarily of unconsolidated and consolidated <br /> alluvial and floodplain sheet deposits (predominantly sand, silt and clay) of Quaternary age, which <br /> lie <br /> is derived from the Sierra Nevada Mountains. Beneath the upper sedimentary deposits lies a thick <br /> sequence of marine deposits of Mesozoic age, which in turn are underlain by a pre-Jurassic complex <br /> of igneous and metamorphic rock. <br /> 3.0. ASSESSMENT OF HYDROCARBON-11%IPACTED SOIL <br /> 3.1. SOIL BORING DRILLING, JULY AND SEPTEMBER 1992 <br />' On 06 July 1992, four soil borings were advanced at the site under the direction of T & T Earth <br /> Services of Jackson, California. Each boring was advanced to a depth of 35 feet below surface grade <br /> (bsg) by Hunt Drilling of Jackson. Petroleum hydrocarbon odors were noted in samples from each <br />' soil boring. <br /> A total of twelve soil samples were submitted to State-certified laboratory for analysis. TPH-g and <br /> TPH-d were detected in soil samples from each boring at concentrations up to 2,600 ppm (B1-37- <br /> 55"). No BTE&X were.detected in any of the soil-samples; however, method detection/reporting <br />' linuts for BTE&X were above PHS-END acceptable concentrations. Analytical results of boring soil <br /> samples are included in Table 2. <br />' At the request of the PHS-EHD, two additional soil borings were advanced at the site by T&T on <br /> • 08 September 1992, Borings LCSB-1D and LCSB4-ID were placed immediately adjacent to borings <br /> SB 1 and SB4 to obtain duplicate samples for analysis using acceptable method detection/reporting <br />' limits for BTE&X. A PHS-EHD inspection report indicates that no hydrocarbon odors were noted <br /> in samples collected from the duplicate borings. However, analytical results of TPH-d for soil samples <br />