SITE INFORMATION AND CORRESPONDENCE

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M. Scott Mansholt -2 - 14 July 2005 ChevronTexaco Mountain House Site#2 SOIL Concentrations of TPH-c were non detect in the soil samples obtained from 4 of the 8 soil borings. However, concentrations of TPH-c were detected ranging from 16 to 1,400 mg/kg in samples from the remaining borings. The highest TPH-c, 1,400 mg/kg, was reported at 27 feet in boring MH2-6. The vertical extent of petroleum-impacted soil was defined by boring MH2-1 at 44 feet, which was non detect for petroleum hydrocarbons. In conjunction, a sample was obtained and submitted for fuel fingerprint analysis, which reported features characteristic of San Joaquin Valley crude oil. With the exception of toluene at 0.2 mg/kg in one boring at 6 feet, BTEX compounds were non detect in the soil samples. Low PAH concentrations were reported in samples from five of the soil borings with the highest concentration detected at 20 feet in boring MH2-1, which was 0.089 mg/kg anthracene. GROUNDWATER Depth to groundwater is approximately 13 to 17.5 feet and the gradient is northeast. With one exception, TPH-d concentrations were non detect, 58 and 82 pg/L. TPH as gasoline (TPH-g) and TPH-d concentrations at 140 pg/L and 59,000 pg/L were reported in boring MH2-1. This boring is near former Condor boring GP-175, which reported elevated concentrations of TPH-d in soil at 20 feet. Low PAH concentrations were reported at or slightly over the method detection limits (HDLs) in the groundwater samples. A toluene concentration of 0.1 gg/L (the MDL for toluene) was reported in two samples, otherwise the remaining results were non detect for BTEX compounds. Generally, the presence of petroleum hydrocarbon compounds concentrations in groundwater corresponds to samples/locations having elevated TPH in soil. A groundwater sample from one boring was submitted for general minerals analysis including nitrate and total dissolved solids (TDS). The general minerals results and the TDS value, reported at 1,280 mg/L,were consistent with results from other nearby OVP sites. Hydrocarbon-impacted groundwater appears to be limited in extent and generally coincides with the approximate outline of impacted soil located in close proximity to the former Condor borings, which coincides with an area of crude oil saturated soil. According to the results, the outline of impacted soil and groundwater delineated is generally 100 feet across with the distribution in groundwater slightly larger than the area of impacted soil. Vertically, soil and groundwater impacts are defined by non detect for TPH compounds in the 44-foot soil sample from boring MH2-1. A well survey for domestic wells within a 2,000-foot radius of Mountain House Sites 1 and 2 revealed that three private wells were identified cross-gradient to the site (> 1,000 feet); two are southeast and one is northwest. Review of Department of Water Resources well completion records indicate that the three wells were completed with at least a 35 to 50-foot sanitary surface seal. These surface seals extend below the shallow groundwater(occurs approximately 7 to 17 feet) that occurs at this site. Considering the depths of the sanitary seals coupled with the distance from the project site, dissolved petroleum constituents likely will not affect these domestic wells.