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itai a11Vll <br /> Chevron - 2 - 22 October 2008 <br /> Mountain House Site #4 <br /> Analysis of MH4-1 samples from 8.5, 11, and 16 feet detected benzo(a)pyrene <br /> at <br /> concentrations of 0.13, 0.054, and 0.074 mg/kg at 8.5, 11, and 16 feet bgs, res ective! . <br /> sample from 44 feet bgs was ND for TPH constituents which define the vertical e y The <br /> affected soil, xtent of <br /> Analytical results for soil samples from downgradient boring MH4-6 completed <br /> withinUPRR ROW and near the approximate location of the BAPL pipeline, detected concentrations the <br /> Of petroleum hydrocarbons as follows: concentrations <br /> • TPHc at 17, 3,500, 26,000, and 9,100 mg/kg, from depths of 1, 5, 8.5, and 11 feet <br /> respectively; benzene was ND, and xylenes were ND, 0.055, 7.1, and 1.6 mg/kg, <br /> bgs <br /> respectively. Naphthalene was detected at concentrations between 0.001 to 43 mg/kg. <br /> The remaining PAHs were ND. Analysis of the 23-foot sample was ND for TPH <br /> constituents. TPH as gasoline (TPHg) was detected at the same depths, respective) <br /> at ND, 990, 3,200, and 3,000 mg/kg. y <br /> Analysis of the MH4-6 groundwater sample detected 130,000 microgramser liter <br /> as diesel (TPHd), 2,400 pg/L TPHg, and benzene and xylenes at 1 and 11 P (Ng/L) TPH <br /> Naphthalene was detected at 640 Pg/L. A subsequent fuel fingerprint evaluation determined <br /> that petroleum hydrocarbons present in boring MH4-6 soil and groundwater samples was <br /> consistent with weathered jet fuel or kerosene, diesel, heating fuel, and/or a jet fuel <br /> combination. SAiC indicated this was attributable to another source and not the historical <br /> crude oil pipelines. Reports documenting the possible leak of refined petroleum h drocarbo <br /> have been forwarded to the Sacramento Central Valley Water Board office. y ns <br /> Depth to groundwater was observed at approximately 13 to 19 feet bgs and based on <br /> groundwater elevations from nearby Mountain House Development sites, the gradient is <br /> northeast. There are no groundwater monitoring wells at the Site. <br /> Based on the findings, SAIC concluded the lateral extent of crude oil affected soil was defined <br /> with an approximate radius of 50 feet, centered near boring MH4-1. The vertical extent was <br /> defined by ND results for the 44-foot bgs sample from this boring. The area of crude oil <br /> affected groundwater was slightly larger, elongated around MH4-1 with approximate <br /> dimensions of 80 by 120 feet. Affected soil and groundwater is delineated beneath and within <br /> the Byron Road ROW easement. <br /> The future Site use and access is not anticipated to change and will likely be limited to <br /> construction/maintenance activities associated with the highway and/or possibly utilities. <br /> Consequently, SAIC conducted an environmental risk evaluation (ERE) based on the most <br /> likely potential exposure by a construction/trench maintenance worker associated with features <br /> within the highway ROW easement. <br /> According to the May 2008 ERE report, SAiC concluded that the residual crude oil compounds <br /> remaining at the site do not pose a threat to human health and do not exceed applicable TPH <br /> screening values described in - Screening for Environmental Concerns of Sites with <br /> Contaminated Soil and Groundwater, interim Final 2008a (ESLs), San Francisco Bay Regional <br /> Wafer Quality Control Board, May for a construction/trench worker exposure scenario. Central <br />