SITE INFORMATION AND CORRESPONDENCE

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Lee Kggins - 2 - is 9 July 2010 f Chevron Mountain House Site#3 the PEA guidance, the Screening Evaluation used analytical results for benzene, toluene, ethyl-benzene, and xylenes (BTEX) and polynuclear aromatic hydrocarbons (PAH) for 23 samples from 15 borings with crude oil affected soil obtained from depths of 2 to 10 feet below ground surface (bgs). • Soil and groundwater affected with San Joaquin Valley (SJV) crude oil beneath the Site are attributable to leaks from the historical OVP and/or TAOC pipelines located on the property. The crude oil affected areas are beneath/within the former OVP and TAOC pipeline easements, the Byron Road right-of-way, and the active refined product pipeline easements. Concentrations of total petroleum hydrocarbons as crude oil (TPHc) was detected in soil at approximate depths between 2 and 54 feet bgs. TPHc concentrations ranged from 4.7 milligrams per kilogram (mg/kg) at sample depth of two feet bgs to a high of 4,700 mg/kg at six feet bgs; most samples were non-detect (ND) for TPHc. The vertical extent of crude oil affected soil was defined by the 54 feet bgs sample having a TPHc concentration of 46 mg/kg. The lateral and vertical extent of crude oil affected soil has been defined. • Analytical total petroleum hydrocarbons as diesel (TPHd) results for groundwater samples from the 2001 borings were primarily ND. However, three samples with petroleum sheen present on groundwater, had detections of TPHd from 20,000 micrograms per liter (pg/L) to 310,000 pg/L and total petroleum hydrocarbons as gasoline (TPHg) from 660 to 43,000 pg/L. BTEX compounds were ND with the exception of benzene and toluene detected at 2.0 and 1.2 pg/L, respectively. PAH concentrations were detected in the samples up to 110 pg/L (flourene in two samples). The area of separate phase crude oil in soil and groundwater has an approximate dimension of 100 feet across and lies beneath and within the Byron Road right-of-way. • During 2004 and 2007, workplans were approved and additional borings drilled to obtain soil and groundwater samples for TPH characterization and delineation purposes. The lateral extent of affected groundwater was delineated by analytical results of ND, at or slightly above the taste and odor water quality objective' of 100 pg/L TPHd, or below applicable environmental screening levels. Laterally, the extent of crude oil affected groundwater was thus delineated by sample analytical results from the downgradient borings. There are no groundwater monitoring wells at the Site. • Duplicate samples were submitted for general minerals analysis to determine water quality parameters. Analysis of onsite groundwater samples indicated that the shallow, crude oil affected groundwater contains concentrations of total dissolved solids (TDS) ranging from 1 ,120 milligrams per liter (mg/L) to 2,130 mg/L. In accordance with the Water Quality Control Plan for the Sacramento River Basin and the San Joaquin River Basin (Basin Plan), groundwater having a TDS of less than 3,000 mg/L is considered a potential drinking water source. However, the State of California Department of Health Services Recommended Maximum Contaminant Level for TDS in drinking water is 500 mg/L. ' - The United States Environmental Protection Agency, Suggested No Adverse Response Levels, 1980, describes 100 pg/L as the taste and odor groundwater quality objective threshold for diesel.