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CONESTOGA-ROVERS & ASSOCIATES May 4, 2009 2 Reference No. 632277 Historical depth to groundwater in site wells has ranged from approximately 5 to 9 feet below top of casing (BTOC), with an average depth of approximately 7 feet BTOC. The groundwater flow direction beneath the site has been consistently to the northwest (Figure 2) . Previous Investigations: Numerous investigations have been performed at the site beginning in 1994. To date, 15 cone penetration testing borings and 8 monitoring wells have been installed at the site. A summary of previous investigations conducted to date at the site is presented as Attachment B. PROPOSED SCOPE OF WORK To evaluate vapor intrusion to indoor air pathways at the site where soil has exceeded the San Francisco Bay Regional Water Quality Control Board (RWQCB) risk-based screening Ievels for soil vapor, CRA proposes to advance four hand-augered soil borings. Cumulative historical soil analytical results are summarized in Table 1 . The soil borings will be completed as permanent soil vapor wells and will be used to collect soil vapor to determine if concentrations exceed the San Francisco Bay RWQCB risk-based screening levels for soil vapor. The locations of the proposed borings and soil vapor wells are shown on Figure 2. CRA's Standard Field Procedures are presented as Attachment C. Underground Utility Location: CRA will notify Underground Service Alert prior to initiating field work to clear boring locations with utility companies. A private utility line locator will be contracted to additionally-clear-boring locations-of-utrlity4ines.-All-borings will be-advanced using a 34nch diameter hand auger. Site Health and Safety Platt: CRA will prepare a site safety plan to inform site workers of known hazards and to provide health and safety guidance. The plan will be kept on-site at all times during field activities and signed by all site workers and visitors. Permits: CRA will obtain the necessary permits from SJCEHD prior to beginning field operations. A minimum of 72 hours notice will be given to SJCEHD and the Central Valley RWQCB prior to soil boring advancement, vapor well installation, and vapor well sampling activities. Drilling Company: V&W Drilling Inc., of Stockton, California (C57720904), will install the four vapor wells. Vapor Probe Installation: CRA proposes to advance two soil borings along the south side of the site, one soil boring in the central portion of the site, and one soil boring adjacent to the sales building using a 3-inch hand auger to depths up to 5 fbg. Worldwide Engineering, Environmental, Construction, and IT Services