SITE INFORMATION AND CORRESPONDENCE

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Soil & Groundwater Investig _ Mountain House Sites #4 an 2 28 June 2006 Mountain House, San Joaquin Co. Curr Investigation In November 2005, an additional soil and groundwater investigation was performed w included borings to collect soil and groundwater samples for analysis. hich In addition to analysis of samples for delineation purposes, soil and groundwater samples were analyzed for the TPH constituents of concern (TPH as diesel [TPH-d aromatic hydrocarbons [PAHs], and BTEX, i.e. benzene, toluene, ethylbenzene,polynuclear xylenes) to support a future Human Health Risk Assessment (HHRA). For the purposes of the HH a different analytical method having lower detection levels was used for the BTEX analysis. The groundwater samples were also analyzed for TPH as gasoline (TPHg). y Soil samples for HHRH purposes were obtained from one, three, five, eight, and/or ten or eleven feet; lateral and vertical characterization samples were obtained at depths of 16 to 44 feet. Consistent with previous investigations, depth to groundwater ranges between 12 an feet and the gradient is north. d $ Site #4 Soil - SAIC installed seven soil borings in the vicinity of Condor borings GP-53 and GP-180 to identify/confirm previously identified impacted areas and to delineate thelateral and vertical extent of impacts. MH4-1 was advanced near the center of highest TPHc concentrations identified by Condor and the remaining borings were offsets for delineation purposes. SAIC's borings were completed to depths ranging from 32 to 44 feet. Analyses for boring MI-14-1 samples taken at one, three, five, eight, eleven, and 16-feet was 740, 34, 1,600, 300, and 19,000 mg/kg TPHc, respectively. With the exception of ethylbenzene at 0.016 mg/kg, BTEX compounds were non detect (ND). The 44-foot sample was ND for TPH compounds, thus defining the vertical extent of TPH impacts at Site #4. With the exception of boring MH4-6, samples from the other five offset borings reported TPHc at ND to 13 mg/kg and ND or very low concentrations of the TPH compounds. Low concentrations of PAHs were reported in the majority of the samples. The low concentrations of PAHs reported are less than their respective Preliminary Remediats through Goals (PRGs) established by the US EPA Region 9 for direct residential exposure pathway ingestion, dermal contact, and inhalation pathways. Only one PAH slightly exceeded its PRG which was detected in MH-1 at 8.5 and 16 feet, which corresponds to samples having elevated TPHc concentrations. Boring MH4-6, approximately 75 feet north of MI-14-1 and near the Kinder Morgan and Bay Area Products pipelines, reported TPHc between one and eleven feet up to 26,000 mg/kg and TPI-Ig as high as 3,200 mg/kg at 8.5-feet. Benzene and toluene was ND and ethylbenzene and xylenes concentrations ranged from ND to 7.1 mg/kg at 8.5-feet. The sample collected at 23 feet in this boring was ND for TPH compounds. A soil sample from 8-feet was submitted for fuel fingerprint and chromatogram analysis. The analysis reported that the hydrocarbons in the C 11 - C20 range makes up and that the type of fuel found is weathered jet fuel and not from San Joaquin a Valley crude oil.