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-05-2000 17:58 FRO RECISION SAMPLING TO 1J11�tiS�457� r.e4 The second method of purging is the vacuum vessel. Purging is conducted by switching on the vacuum pump that withdraws air from the casing_ The vacuum is not strong enough to remove solids such as soil. A pressure gauge is mounted on top of the vacuum vessel. The gauge measures the amount of vacuum pressure within the vacuum vessel in inches of mercury or kiloPascals. The maximum amount of vacuum pressure should not exceed 17 of inches of mercury, or 58 kiloPascals. Use the valve stem to regulate vacuum pressure. If the vacuum pressure exceeds these figures the plexiglas cover will crack or completely fail by imploding_ The soil vapor from the casing pass through the vessel and out through the exhaust line. Most clients prefer to perform air monitoring with their photo-ionization detectors (PID) or organic vapor monitors (OVM) positioned at the exhaust hose. Sample Collection in a Tedlar Bag A tedlar bag is connected by tubing from the casing inserted through compression fitting through the top of the plexiglas. The vacuum pressure on the bag causes it to expand which draws soil vapor into the bag. As soon as the bag fills, deactivate the pump. Remove the bag and dose the bag so no vapor is lost. Upon completion of sample collection, dispose of the used tubing and replace with fresh tubing for the next sample location. Withdraw the casing as normal. If you have advanced the casing with a slide hammer(usually used with the one-inch rods), you will need to extract the casing with a jack, chain, or vice grips, and or pipe wrenches. Sample Collection in a Summa Canister A different set up is used for sample collection in the Summa canister. A new piece of tubing is inserted into the casing and the other end is attached to a 'T" or"Y"junction- The split line ends up at the intake tubing which is attached to the line inserted at the compression fitting on top of the vacuum vessel. The other split is attached to the hardware provided with the Summa canister that is then screwed into the vacuum vessel. You may want to gently tighten this fitting with a crescent wrench. Once the desired amount of purging is completed, the tubing leading to the vessel is damped off. The tubing leading to the canister is undamped so that flow from the casing to the canister is unobstructed (the Summa canisters are provided with attachment hoses and hardware). Open the canister- The canister is under vacuum so it will passively EC-4 soil gis 11