SITE INFORMATION AND CORRESPONDENCE

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w+. Jcott Mansholt • Mountain House Site #2 - 2 - • 4 May 2007 were not detected except for 0.2 mg/kg toluene in the s-foo boring having TPHc present to at least 27-feet. t sample from MH2-6 which is the Polynuclear aromatic hydrocarbons (PAH) concentrations at or slightly above the method detection limits for the respective compounds were re borings. Similar to the BTEX compounds, ported in samples from five of the nine porting Groundwater The depth to groundwater is approximately 12 to 18 fee Five groundwater samples were submitted for petroleu detected in three samples with value, t and the gradient is north-northeast. Petroleum hydrocarbon analysis and TPHd was in MH2-1. TPH as of 58 lag/1 in PVIH2-6, 82 pg/1 in [OH2-4, and 69,000 p /! gasoline (TPHg) was not detected in four samples and was re pg /l Pg/l also in MH2-1. BTEX compounds were not detected ethylbenzene and 0.19 pg/l xylenes in borin MH2-1. d except for 0.01 Pg/!ported at compounds reported correspond to samplesfromMH2 1 Generally, the petroleum hydrocarbon ch has elevated TPH in soil. Low concentrations of PAHs were detected at or slightly above the laboratory for the respective compounds in each of the groundwater samples. hehi reporting limits concentrations were reported in groundwater sample MH2-1 (TPHd e t PAH @ 59,,0000()o pg/1). Department of Water Resources (DWR) well completion records report three private within 2,000-feet of the site were completed with a minimum sanitary surface seal of 35 fe One of the three wells was verified in the field at approximately 1,850-feet cr feet. site. Considering the depths of the sanitary seals, the limited extent of affected ssoildand of the groundwater coupled with the distance from the project site, dissolved petroleum constituents likely will not affect these domestic wells. Comments Based on review of the May 2005 characterization report, Regional Water Board staff concurred in our 14 July 2005 response to Chevron that the extent of affected soil and groundwater had been adequately delineated. Additionally, according to the report, affected soil is limited in extent with approximate dimensions of 100-feet across with the distribution in groundwater slightly larger than the outline of affected soil. Vertically, soil and groundwater impacts are defined by non detect for TPH compounds in the 44-foot sample from boring MH2-1. The data indicates affected soil and groundwater occurs within the Byron Road right-of-way, primarily beneath Byron Road and the former OVP alignment located on the southwest side of Byron Road. Additionally, Regional Wafter Board staff concurred that removal of impacted soil is not generally feasible given that the majority lies beneath Byron Road and/or within the Byron Road right-of-way. Groundwater samples from the investigation were submitted for total dissolved solids (TDS) determination with values ranging from 1,350 milligrams per liter (mg/1) to 1,410 mg/I.