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18 July 2008 AGE-NC Project No. 95-0137 Page 5 of 6 y 3.2. COLLECTION OF SOIL VAPOR SAMPLES / Soil vapor samples will be obtained at a depth of approximately three to four feet bsg in each boring. Samples will be collected using a Geoprobe soil vapor assembly. An expendabl6 vapor point will be placed into a point holder at the bottom of an assembly of 1.25-inch diameter hollow drive rods.The assembly will then be advanced to the specified depth and retracted approximately six to twelve inches in order to disengage the expendable point and expose a column of sgata from which soil vapor can be extracted. Single use, '/a-inch diameter disposable polyethylene tubing is then attached to a tubing adapter equipped with an O-ring to ensure a vacuum- tight seal. The adapter assembly is then lowered through the center of the hollow drive rods to the specified depth and secured by threading into the expendable vapor point holder. Above ground, the surface around the soil vapor sampler will be sealed with a bentonite sealant to prevent ambicot air intrusion. An isopropyl alcohol (IPA) tracer gas (liquid IPA) will be exposed within a plastic sheeting over the sampling equipment to detect leakage of ambient air into the sampling train. The end of the polyethylene tubing is attached by a two-way inlet port to a Tedlar bag placed inside an SKC Vac-U-Chamber("lung box")vacuum chamber.A vacuum pump attached to a purge port of the vacuum chamber is then used to purge the exposed soil column, through the sampling tubing and inlet port, until approximately three volumes of soil vapor or ambient air is evacuated through the sampling system. The vacuum chamber is then sealed and the vacuum pump is attached to a vacuum outlet port of the chamber. When vacuum is applied to the chamber, a negative pressure is created around the Tedlar bag, which inflates, allowing the soil vapor sample to enter directly into the bag via the inlet port. When the sample is collected,the negative pressure in the chamber is reduced and the sample bag is sealed,labeled,logged on a chain of custody form, '" and placed into a dry cooler(cool temperature). Then soil vapor will be collected onto the carbon coalescent tuba and sealed for semi-volatile analysis(TO 17 analysis),labeled and transported within a dry cooler. Subsequently,,all of the collected soil vapor samples and carbon media will be delivered to a State of California-certified laboratory for analysis of the chemical constituents listed in Section 2.2. All soil vapor samples will be analyzed within 72 hours of the sampling time. After collection of the sample, soil vapor from the polyethylene tubing will be monitored for the presence of volatile organics using a photo-ionization detector(PID)pre-calibrated to isobutylene. Advanced GeoEnvironmental,Inc.