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Soil and groundwater samples were collected during several previous <br /> environmental investigations in the area near the former condensate outlet pipe. Three soil <br /> borings and monitoring well MW-1 were installed in October 1996 directly beneath the former <br /> condensate outlet pipe. Soil samples collected to date indicate TCE in concentrations up to 5,900 <br /> micrograms per kilogram (µg/Kg) at 4 feet below ground surface (bgs) generally decreasing to a <br /> maximum of 1,500 mg/Kg at 10 feet bgs. TCE has not been detected in the groundwater samples <br /> collected from MW-1; however, because petroleum hydrocarbons have been detected in <br /> groundwater, laboratory detection limits have been elevated to 1,000 pg/L for TCE (GTI, 1996). <br /> 2.2 Geology <br /> Vernalis is located in the Central Valley Physiographic Province of California. <br /> The valley is about 40 miles wide, bounded by the Coastal Ranges to the west and the Sierra <br /> Nevada Range to the east. In the vicinity of Vernalis, unconsolidated Quaternary alluvial and <br /> fluvial sediments are found to a depth of at least 400 feet. Most of these soils were deposited in <br /> alluvial fans associated with rivers draining the Sierra Nevada Range. Coarser materials are <br /> associated with stream channel and natural levee deposits, while finer-grained soils are <br /> associated with floodplains and marshes, historically associated with rivers along the axis of the <br /> Central Valley (WHF, 1996). <br /> Soil borings at the site and the adjacent 35500 Welty Road property indicate that, <br /> to a depth of 40 feet bgs, soils are heterogeneous, consisting of relatively thin, discontinuous <br /> 4 <br />