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Soil and Groundwater Investigation Report Mountain House Development Site#6 July 2008 • Subcontracted Cruz Brothers Locators, a private utility locator,to survey the site and proposed boring locations for any potential overhead and underground hazards and/or other potential obstacles. 3.2 FIELD INVESTIGATION ACTIVITIES SAIC supervised the advancement of 29 soil borings(SB-1 through SB-29) at the site from March 17 through April 1, 2008,to define the extent of petroleum-affected soil and groundwater. A SAIC field geologist observed RSI Drilling,Inc. (C57#802334)advance the soil borings to depths ranging from 12 to 40 feet bgs using a direct-push, dual-tube Geoprobe 6600 rig. Prior to advancement, each boring was hand cleared to a minimum depth of 8 feet bgs using a hand auger. Borings were cored from 8 feet bgs to total depth using a sampler equipped with 4-foot acetate liners. All samples were inspected and logged according to the Unified Soil Classification System(USCS)under the supervision of a California Professional Geologist. Soil cores were field screened for the presence of organic vapors using a photoionization detector(PID) and recorded on the boring logs(Appendix Q. In accordance with the work plan,up to three soil intervals at each boring location were to have been sampled: (1)the top 10 feet bgs for risk assessment, (2)below 10 feet bgs to assess the magnitude of CDCs in the most affected soil, and(3)beneath the affected zone to determine the vertical extent. Soil samples collected from a desired interval were sealed on each end with Teflon sheets and plastic end caps. The samples were immediately labeled and placed in an ice-cooled chest pending analysis. All down-hole boring equipment was either steam cleaned or decontaminated with a Liquinox/water solution and rinsed between borings using deionized water. All soil borings were abandoned on completion by backfilling with neat-cement grout placed from total depth to 3 feet bgs using a tremie pipe in accordance with SJCEHD guidelines. The remaining 3 feet were backfilled with native soil. An inspector with SJCEHD was provided with a daily update regarding the field investigation activities. Soil boring locations are shown on Figure 2. All soil and groundwater samples were submitted to Lancaster Laboratories,Inc. (Lancaster; a California State-certified laboratory,ELAP#2116)under SAIC chain-of-custody protocol. Selected soil samples were analyzed for the following COCs: • TPHc (carbon range CIO to C36)by EPA Method 8015 Modified; • BTEX by EPA Method 826013; and • PAHs by EPA Method 8270C using selective ion monitoring. SAIC collected grab groundwater samples from borings SB-1 through SB-4, SB-6 through SB-8, SB-10, SB-12, SB-15, SB-17 through SB-20, and SB-23 through SB-28. Each soil boring was generally advanced several feet past first-encountered groundwater before a sample was collected. Immediately after collection,the samples were labeled and placed in an ice-cooled chest pending analysis. Groundwater samples were analyzed for the following COCs: • TPHd(carbon range CIO to C25)by EPA Method 8015 Modified with and without silica-gel cleanup; • BTEX by EPA Method 8260B using a 25-milliliter purge to attain HPP Risk Assessment Detection Limits; and • PAHs by EPA Method 8270C(using large-volume injection to attain HPP Risk Assessment Detection Limits). Select groundwater samples were also analyzed for the following water quality parameters: Xorl4 merit`& From Science to Solutions