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21 March 2003 AGE-NC Project No. 95-0114 Page 11 of 11 4.5. SOIL-GAS PROBE BORING INSTALLATION Each soil-gas probe boring will be advanced to depth of 35 feet bsg using a van-mounted Geoprobe 5400 probing unit equipped with 1.125-inch diameter rods. Soil-gas samples will be obtained at depths of 20 and selectively at 35 feet bsg using a Geoprobe soil-vapor assembly. An expendable vapor point will be placed into a point holder at the bottom of a string of 1-inch diameter hollow drive rods. The assembly will then be advanced to the specified depth and retracted approximately six inches in order to engage the expendable point and expose a column of strata from which soil gas can be extracted. A post-run tubing adapter equipped with an O-ring to ensure a vacuum-tight seal is then attached to a'/a-inch diameter,single use,disposable polyethylene tubing.The sampling tube is then lowered through the center of the hollow drive rods and secured by threading into the expendable point holder. Above ground, the polyethylene tubing is attached to a stainless steel T-valve that is connected to a vacuum pump contained within the GeoProbe 5400 soil sampling machine;the third end of the T- valve is attached to a sampling point inside a vacuum chamber. The vacuum pump will apply negative pressure to the exposed soil column until approximately three volumes of soil vapor or ambient air is evacuated through the sampling system. Inside the vacuum chamber, a Tedlar bag will be attached directly to the sampling point through a collapsible,air-tight port. The vacuum chamber will then be sealed,and a negative pressure will be applied to the chamber through a second port by the vacuum pump, forcing the soil-vapor sample to enter directly into the Tedlar bag.Upon collection of the gas sample,the negative pressure in the chamber will be reduced and the sampling bag sealed, properly labeled, log on a chain-of-custody form, and place into a dry cooler. All soil-vapor samples will be delivered to a State-certified laboratory for analysis by EPA methods 8015 and 8260,which includes all target compounds. After soil-vapor sample collection,soil gas from the polyethylene tubing will then be monitored for the presence of volatile organics using a photo-ionization detector (PID) pre-calibrated to isobutylene. At the completion of soil-vapor sampling, each probe boring location will be backfilled to surface grade using portland cement. Advanced GeoEnviron mental,Inc.