SITE INFORMATION AND CORRESPONDENCE

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Soil & Groundwater Investig -4- 28 June 2006 Mountain House Sites #4 an fr Mountain House, San Joaquin Co. Groundwater - Samples were collected from five of the seven borings and submitted for analysis. The centrally located boring, MH5-1 reported TPHd at 670 pg/l, BTEX compounds were ND; PAHs were ND to very low concentrations slightly over the Method Detection Limits (MDLs) for the respective PAH compounds. Groundwater samples for the lateral and upgradient borings, were ND for TPH compounds. However, 350 pg/I TPHc was reported in downgradient boring, MH5-7, which is 125 feet north of MH5-1; BTEX and PAHs were ND. According to the results, it appears that the OVP crude oil leaks to soil has been adequately defined, is limited in width to less than 150 feet and vertically less than 32-feet. Petroleum- impacted groundwater appears to be limited in extent but has not been adequately defined at MH5-7 where TPH was reported downgradient of boring MH5-1. Well Surve A well survey for domestic wells identified four private wells within a one-half mile radius of Sites #4 and #5. Two are approximately 3,400 feet downgradient of Site #5 and the other two are 3,000 and 4,900 feet southeast (crossgradient) of Site #4. According to Department of Water Resources well completion records, the wells were completed with at least a 35 to 50- foot sanitary surface seal; well depths range between 85 and 160 feet. Thus, these surface seals would extend below the shallow groundwater (approximately 8 to 18 feet) that occurs at these sites. Summa Site #4 - Overall, it appears that impacted soil and groundwater has been defined and is limited in extent to beneath Byron Road and/or within the pipeline right-of-way corridor next to Byron Road. With the exception of the potential leaks from a refined product pipeline, I agree that soil and groundwater impacted by OVP leaks has been adequately delineated. The petroleum hydrocarbons identified at this site by fuel fingerprint analysis appear to be related to a refined products pipeline(s) and these findings will be addressed separately. Site #5 - Similarly, it appears that TPH in soil impacts has been defined and limited in extent to beneath Byron Road and/or within the pipeline right-of-way corridor next to Byron Road. However, groundwater has not been adequately delineated downgradient, north of boring MH5-7 and additional analysis is needed. I agree that impacted soil conditions have been adequately defined. However, additional characterization borings and analysis are needed to complete delineation of impacted groundwater north of boring MH5-7. SAIC recommended two additional borings north of MH5- 7 to assess downgradient conditions of groundwater. In addition to the borings proposed by SAIC, I recommend that a third boring be included approximately 75 feet northwest of proposed boring location MH5-8.