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ERI 205503 R03 Tosco 76 Seryion <br /> RESULTS OF INVESTIGATION <br /> Site Geology <br /> Sediments encountered in off-site borings BI I through B 19 typically consisted of heterogeneous <br /> mixtures of silt, clay, and fine- to coarse-grained sand Groundwater was initially encountered at <br /> approximately 9 to 14 feet bgs, with static groundwater elevations ranging from approximately 6 0 to 6 5 <br /> feet bgs Saturated zones were encountered at depths ranging from approximately 10 to 30 feet bgs <br /> Using depth to groundwater data collected on April 14 and 15, 1999, groundwater flow direction was <br /> ' towards the southwest at a calculated gradient of approximately 0 004 <br /> Based upon ERI's evaluation of, 1) the samples collected from borings 1311 (MW8D), B14 (MW9D), <br /> and B17 (MW10D) (Attachment D), 2) a review of the boring logs of wells MW1 through MW7S & D, <br /> soil borings B8 through B10, and cone penetrometer (CPT) borings CPTI through CPT3 <br /> (Attachment F), 3) a review of groundwater monitoring and sampling data collected from wells <br /> MW8S/I/D through MW10SII/D, and, 4) a review of the quarterly groundwater monitoring data with <br /> respect to the groundwater elevations in single-casing wells MW1 through 3, and nested wells MW4S <br /> & D through MW7S & D, the water bearing zone presently being evaluated beneath and in the vicinity <br /> 1 of the site appears to consist of a single unconfined aquifer of variable permeability ERI's <br /> interpretation of the geology and hydrogeology beneath and in the vicinity of the site is shown on Cross <br /> Sections A-A' and B - B' (Plate 3 and Plate 4, respectively) The locations of cross-sections A-A' and <br /> B-B' are shown on Plate 2 <br /> Groundwater Conditions <br /> 1 Dissolved gasoline and diesel hydrocarbons and oxygenated compounds (MTBE, methanol, and <br /> ethanol) were not detected at or above laboratory method detection limits in groundwater samples <br /> 1 collected from groundwater monitoring well MW9S However, low concentrations of dissolved <br /> hydrocarbons were detected in groundwater samples collected form the remaining wells Analytical <br /> laboratory results are summarized in Table 1 and shown on Plate 2 Copies of laboratory reports for <br /> groundwater samples obtained during this investigation are included in Attachment E <br /> Groundwater samples collected from wells MW8S/IID through MW 10SII/D were not subjected to a <br /> silica gel cleanup process prior to Environmental Protection Agency (EPA) Method 8015 modified <br /> laboratory analysis for TEPHd Laboratory report notes indicate that diesel range hydrocarbons <br /> detected in groundwater samples collected from well MW8S through MW8D, MW91, and MW10D <br /> were classified as unknown hydrocarbons or were reported as diesel based upon a single analyte peak <br /> because a fuel hydrocarbon pattern was not present <br /> SOIL STOCKPILE DISPOSAL <br /> At the request of Tosca, Manley & Sons Trucking, Inc of Sacramento, California transported <br /> approximately eleven 55-gallon drums (4 Tons) of stockpiled soil to the Forward, Inc Landfill in <br /> Manteca, California for disposal Soil disposal documentation is included in Attachment G <br /> 4 <br />