SITE INFORMATION AND CORRESPONDENCE

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No Further Action Required Deter ation -2 - 5 May 2099 Mountain House Development S4 Source: Historical leaks from crude oil pipeline(s) installed in the early 1900's. The pipelines were removed from service during the late 1960's and early 1970's. Actions: Preliminary Site investigations were conducted between 2001 and 2005. • In 2001, six exploratory borings were advanced and soil samples collected were analyzed for TPH constituents of concern. Affected soil was noted in samples from two of the borings at depths ranging from 8 to 16 feet bgs. Analyses reported TPHc at concentrations of 13,000 milligrams per kilogram (mg/kg) in a sample from a depth of 13.5 feet bgs and 3,600 mg/kg in the sample from a depth of 15 feet bgs. Groundwater samples were not collected for analysis. • During 2005, an additional investigation included seven borings (MW4-1 to MH4-7) and collection of 28 soil and 5 groundwater samples for analysis to further delineate soil and groundwater impacts. In boring MH4-1, TPHc concentrations detected in soil samples from depths of between 1 and 16 feet bgs ranged from 740 mg/kg to 19,000 mg/kg. BTEX constituents were non-detect (ND). Polynuclear aromatic hydrocarbons (PAHs) were ND and/or detected at slightly over respective method detection limits (MDLs) except in the MH4-1 soil samples. PAH analysis of MH4-1 samples for benzo(a)pyrene were reported at concentrations of 0.13, 0.054, and 0.074 mg/kg at depths of 8.5, 11, and 16 feet bgs, respectively. The sample from a depth of 44 feet bgs was ND for TPH constituents which defined the vertical extent of affected soil. • The analytical results for soil samples from downgradient boring MH4-6 completed within the UPRR ROW and near the approximate location of the BAPL pipeline, reported concentrations of TPHc, xylenes, and naphthalene. The remaining PAHs were ND. Analysis of the soil sample from a depth of 23 feet bgs was ND for TPH constituents. TPH as gasoline (TPHg) concentrations between 990 and 3,200 mg/kg was detected in samples at depths up to 11 feet bgs. • Analytical results of the MH4-6 groundwater sample were reported at 130,000 micrograms per liter (pg/L) TPH as diesel (TPHd), 2,400 lag/L TPHg, and benzene and xylenes at 1 and 11 pg/L, respectively. Naphthalene was detected at a concentration of 640 pg/L. Fuel fingerprint evaluation determined that petroleum hydrocarbons present in the soil and groundwater samples from this boring were consistent with weathered jet fuel or kerosene, diesel, heating fuel, and/or a jet fuel combination. SAIC concluded these analytical results for samples from this boring were attributable to another source and not the historical crude oil pipelines. Reports documenting the possible leak of refined petroleum hydrocarbons to soil and/or groundwater have been forwarded to the Sacramento office of the Central Valley Regional Water Quality Control Board (Central Valley Water Board). • Analytical results for the remaining groundwater samples attributable to crude oil from OVP leaks, did not exceed applicable screening levels with one exception of TPHd at a concentration of 170 lag/L which exceeds the taste and odor water quality objective threshold (100 lag/L) for drinking water. This sample came from a soil boring that is adjacent to Byron Road; the lateral extent of the affected groundwater extends beneath the road and is limited to within the ROW easement. • In 2008, SAIC completed the ERE to evaluate exposure by comparing the analytical soil results to the 2008 ESLs for a construction/trench worker scenario. As noted above, TPHc, BTEX, and PAH constituent concentrations reported in samples taken in 2001