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0 <br /> CONESTOGA-ROVERS <br /> &ASSOCIATES <br /> A CRA geologist will supervise the drilling and describe encountered soils in the borings using the <br /> Unified Soil Classification System and Munsell Soil Color Charts. Soil samples will be collected <br /> continuously for soil description and possible chemical analysis. Soil samples will be screened in the <br /> field for organic vapors using a photo-ionization detector (PID). Exploratory boring logs will be <br /> prepared for each boring. PID measurements will be recorded on the boring logs. <br /> The soil borings will be drilled in the known source areas and soil samples will be collected at 3, 5, and <br /> 10 feet below grade (fbg) for chemical analyses. If groundwater is encountered prior to 10 fbg, then a <br /> sample will be collected at first encountered groundwater and not at 10 fbg. Additionally, two soil <br /> samples will be collected from each of the vapor borings from approximately 0.5 and 4.5 fbg for <br /> chemical analyses. Soil samples designated for chemical analysis will be retained in stainless steel or <br /> brass sample tubes. The tubes will be covered on both ends with TeflonTM sheets and plastic end caps. <br /> Soil samples will be labeled,entered onto a chain-of-custody record, and placed into a cooler with ice for <br /> transport to a State of California certified laboratory for analysis. <br /> After the soil vapor borings are advanced, fixed vapor-sampling points will be installed in each boring <br /> using '/<-inch diameter Teflon tubing. Two nested vapor-sampling points will be installed within each <br /> boring. Each point will use a 3-inch screen interval manufactured by Geoprobe attached to the Teflon <br /> tubing. Screened intervals will be set at 4 and 8 feet in borings V-1 through V-6, and 3 and 6 feet in <br /> borings V-7 through V-10. To ensure the tubing does not curl or kink during installation, CRA will first <br /> straighten out each length of tubing prior to installation, and then use a small-diameter PVC guide pipe to <br /> hold the tubing in place within the boring while packing the annulus with sand. A clean, fine-grained <br /> silica sand filter pack will be installed approximately 1.5 inches below to 1.5 inches above the screened <br /> interval, and the guide pipe will be lifted as the sand pack is installed to ensure the pack stabilizes the <br /> tubing within each boring. Bentonite layers will be placed between screened intervals. The annulus will <br /> then be sealed to the surface using bentonite slurry, set atop a two-inch base of bentonite pellets. Each <br /> soil probe will be completed at the surface using a traffic-rated well box set in concrete at grade. Soil <br /> vapor probe construction details are presented on Figure 3. <br /> At least two weeks after probe installation, soil vapor samples will be collected from each sampling point <br /> in Summa canisters according to CRA's vapor sampling protocol. Isopropyl alcohol will be used as a <br /> tracer gas at each sampling location to insure that the samples are not representative of ambient air. <br /> Confirmation samples will be collected approximately two weeks after the initial sampling event. Purge <br /> and sampling rates will be between 100 and 200 millimeters per minute to limit stripping and to prevent <br /> ambient air intrusion. Installation and sampling is effected by rain and onsite watering. We will allow 2 <br /> days or more after a heavy rain event or onsite watering prior to collecting soil vapor samples. <br /> 1729 3 <br /> Worldwide Engineering, Environmental, Construction,and IT Services <br />