SITE INFORMATION AND CORRESPONDENCE

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Soll & Groundwater Investigation - 3 - 28 June 2006 Mountain House Sites #4 and # Mountain House, San Joaquin Co. Groundwater- Samples were collected from five of the seven borings and submitted for analysis. With the exception of boring MH4-6, TPHd concentrations ranging from ND to 170 pg/I were reported. BTEX compounds were also ND and ND to very low PAH concentrations was reported. The MH4-6 groundwater sample reported 2,400 pg/I TPHg, 130,000 pg/I TPHd, 1 pg/I benzene, 5.0 pg/l ethylbenzene, and 11 pg1I xylenes. Several PAHs were detected with naphthalene at 640 pg/I being somewhat elevated, two orders of magnitude greater than the PRG for tap water (6.2 pg/1) and nearly four times over the Cal-modified PRG of 0.093 pg/l. The petroleum hydrocarbons identified in MH4-6 appear to be related to a refined products pipeline(s) and these findings will be addressed separately. According to the results, it appears that the OVP crude oil leaks to soil has been adequately defined in the vicinity of boring MH4-1, is limited in width to approximately 150 feet and vertically less than 44-feet. Groundwater affected by crude oil leads from the OVP appears to be limited in extent and is generally contained within the approximate outline of impacted soil. Laboratory test results from other nearby Mountain House investigations reported that the shallow groundwater has high total dissolved solids (TDS) at up to 3,000 mg/I. In addition, use of the shallow groundwater in nearby Tracy is prohibited for domestic or municipal use by municipal Code, for administrative reasons unrelated to petroleum impacts from the OVP; use of the groundwater at the property does not present an environmental concern. Based on the results, the majority of impacted soil occurs either beneath and/or adjacent the north side of Byron Road and/or within the former OVP and/or current pipelines' right-of-way corridor. Site #5 Soil- SAIC installed seven soil borings in the vicinity of Condor borings GP-64 and GP-183 to evaluate the previously identified impacted areas and to delineate the lateral and vertical extent of impacts. MH5-1 was advanced near the center of highest TPHc concentrations (7,600 mg/kg at 16 feet) identified by Condor boring GP-64; the other SAIC borings were offsets for delineation purposes; borings were completed to depths ranging from 32 to 44 feet. Analysis for boring MH5-1 one, five, eight, ten and one-half, and 23.5-foot samples was 320, ND, 14, 32, and 1,100 mg/kg TPHc, respectively. TPHc in samples from the other borings ranged from ND to 25 mg/kg. With the exception of very low ethylbenzene and xylenes, BTEX compounds were non detect (ND). The majority of samples reported ND or had very low PAH concentrations. The 32-foot sample from MH5-1 was ND for TPH compounds, thus defining the vertical extent of TPH soil impact at Site #5. The low PAH concentrations reported are less than their respective US EPA Region 9 PRGs for direct residential exposure pathways through ingestion, dermal contact, and inhalation pathways.