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Shell Mountain House Pipeline -2 - 3 November 2811 <br /> Mountain House Parkway and , _,nt Line Road, Tracy <br /> Neighborhoods C and D and in July 2005, 3,200 lineal feet of the pipelines were removed from <br /> beneath Neighborhood B. <br /> Neighborhoods C&D <br /> Liquid phase hydrocarbon (LPH) was observed in soil during a 2004 investigation along the <br /> pipelines. Shell completed a series of excavations along the pipeline alignment between July <br /> and November 2006 to remove soil impacted above a cleanup goal of 5,000 milligrams per <br /> kilogram (mg/kg). Shell deepened excavations where sample concentrations of petroleum <br /> hydrocarbons were above the cleanup goal. Final excavation depths ranged from 2 to 24 bgs <br /> and confirmation samples collected from the excavation sidewalls and the floor demonstrated <br /> that soil had either been remediated to the cleanup goal, or to the extent that was practical <br /> and safe. <br /> Shell excavated approximately 131,000 cubic yards of soil from beneath Neighborhoods C <br /> and D and transported about 68,000 cubic yards to the Altamont Landfill for disposal. One of <br /> 179 soil samples collected from the deepened excavations contained petroleum hydrocarbons <br /> in excess of the cleanup goal of 5,000 mg/kg of total petroleum hydrocarbons. In addition, <br /> elevated levels of TPHc in excess of the cleanup level were encountered while installing one <br /> monitoring well. Central Valley Water Board staff reviewed the excavation confirmation results <br /> and approved backfilling the excavations in Neighborhoods C and D. <br /> Neighborhood B <br /> Shell observed hydrocarbon staining and odor during a 2005 soil investigation and completed <br /> a series of excavations along the pipeline alignment to depths ranging from 7 to 34 bgs in <br /> June and July 2007 to remove the impacted soil. Shell deepened excavations where sample <br /> concentrations were above the cleanup goal. Final confirmation samples collected from the <br /> excavation sidewalls and the floor demonstrated that soil had either been remediated to the <br /> cleanup goal, or excavated to the extent that was practical and safe. <br /> Shell excavated approximately 35,000 cubic yards of soil from beneath Neighborhood B and <br /> transported about 10,000 cubic yards to the Altamont Landfill for disposal. One of 117 soil <br /> samples collected from the excavations contained elevated concentrations of petroleum <br /> hydrocarbons in excess of the cleanup goal. Central Valley Water Board staff reviewed the <br /> excavation confirmation results and approved backfilling of the excavations. <br /> SOIL AND GROUNDWATER INVESTIGATIONS <br /> Soil beneath the Site consists primarily of silty clay and clayey silt. Inter-bedded sand lenses <br /> occur between 16 and 21 feet bgs in the center of the Site. The maximum hydrocarbon <br /> concentrations observed in soil were detected during an October 2004 investigation in <br /> Neighborhoods C and D that preceded the removal action, and are listed on Table 1. <br /> Table 1 - Greatest Soil Concentrations (in mg/kg) <br /> Volatile Organic Compounds <br /> TPH-c TPH-d Benzene Toluene Ethyl- Total <br /> benzene Xylenes <br /> 130,000 42,000 0.88 1.0 3.7 11 <br /> TPHc and TPH-d =total petroleum hydrocarbons as crude and as diesel <br />