SITE INFORMATION AND CORRESPONDENCE

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M. Scott Mansholt - 2 - Chevron Environmental 27 October 2005 Mountain House#3 Benzene, toluene, ethylbenzene, and xylenes (BTEX) was non detect(ND) to very low concentrations in the majority of the soil samples; TPH as crude oil (TPHc) was ND in four borings and ranged from 4.7 to 4,700 mg/kg in the other borings at depths between 2 and 54 feet with the higher concentrations reported at less than 33 feet. The highest TPHc concentration (4,700 m ed in boring MH3-1 at six feet. Coincidentally, the highest polycyclic aromatic hydrocarbon na(PAH)t fluor ne at 2.8 mg/kg, was reported in this same sample. Low concentrations of other PAHs were detected in the borings reporting TPHc. Five of the six groundwater samples collected were submitted for TPH constituents of concern and total dissolved solids (TDS) analysis. The TDS results from the samples ranged from 1,260 to 1,700 mg/L. Depth to groundwater encountered this investigation ranged between I 1 and 25 feet. BTEX was not detected in any of the samples; 830 pg/L TPH gasoline (TPHg) was reported in MH3-1A; the remaining samples were ND for TPHg. Low concentrations of PAHs were reported. TPH diesel (TPHd) was ND in one of the samples and the others ranged from 50 pg/L in MH3-7 to 500,000 pg/L in MH3-2. The sixth groundwater sample (at 50 feet) from hydropunch MH3-1B, reported elevated FAH concentrations, 1,000 pg/L TPHg, and 160,000 pg/L TPHd; BTEX was ND. The report proposes to install five additional and two contingency borings both up- and down-gradient of the recently installed borings to collect soil and groundwater samples for analysis. Based on our review, we have the following comments; • Three domestic wells were identified within the 2,000-foot radius of the site. Based on their respective locations and distances relative to the site and the sanitary seals extending to at least 50-feet, it is unlikely these wells were affected by OVP leaks. • The lithology log for boring M113-2 states that "staining"was present in the upper part of the hole but"fades" by the time the 20-foot samples are collected. The corresponding soil sample from 20 feet was ND for TPHc and BTEX compounds. However, the analysis for groundwater sample MH3-2-W20 (at 20 feet) reported elevated concentrations of TPHd at 500,000 gg/L and virtually no PAHs. The visual observation of no staining reported at 20 feet appears to be consistent with the ND soil results but not the elevated TPHd concentrations reported for groundwater. • Groundwater analysis reported on Table 3 state that water sample MW3-2-W20 had a pH of 7 when received at the laboratory; apparently the vial(s) were not properly acidified to pH<2. If this sample was not properly preserved, was the "holding time"exceeded before the TPH analysis was conducted? It appears the TPHg analysis was completed five days after sample collection. Clarification of these items needs to be provided and/or borings need to be advanced at or immediately down-gradient of this location to determine the lateral extent of the highly impacted groundwater(and soil) in the area of MH3-2. • Concentrations of TPHg at 830 and 1,000 pg/L were reported in two of the groundwater samples. Considering the active refined product pipelines nearby, future samples submitted need to be