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_,j-5-2000 17:57 FR*RECISION SAMPLING TO • i�1ed��4�� r.e� <br /> Method of Analysis of Soil Gas <br /> - Onsite gas chromatography analysis/gas detector <br /> - Off-site laboratory <br /> Method of Purging <br /> -Syringes <br /> -Vacuum vessel <br /> Equipment, Tools, or Materials <br /> Vacuum vessels., SV-1 and SV-2 (complete with a battery and pump) <br /> Teflon, polyethylene and silicone tubing <br /> 1" Geoprobe rods <br /> Detailed Explanation of Procedure <br /> The two-inch OD Geoprobe rods are advanced to a pre-determined depth. The Teflon <br /> tubing is then attached to a nipple which is threaded at the opposite end. The tubing <br /> with the threaded end is lowered down the interior of the casing. When resistance is <br /> encountered the reverse threaded end can be screwed onto the sub containing the <br /> retractable tip. Once the threaded end is snug, the casing can be withdrawn about three <br /> or four inches to allow the retractable tip to be pulled out of the sub. An "O"-ring holds <br /> the retractable tip in place- Once the tip is out of the sub, the open end of the casing is <br /> exposed to the soil formation interval where the soil gas sample is to be collected. As <br /> above, purging is conducted for a predetermined amount of time prior to sample <br /> collection. The sample then can be collected in either a Summa canister or a Tedlar bag. <br /> A certain amount of tame is necessary to purge the casing of unwanted vapors from the <br /> surface. The client determines the purge volume, or we perform purge volume <br /> calculations based on the diameter of the casing and the depth of the boring. The <br /> purging can be conducted with either of two methods. The first method is with a syringe <br /> that is used to withdraw air from the casing. This method is used with smaller diameter <br /> casing, as the volume withdrawn by the syringe is quite small (50 cubic centimeters). <br /> EC-4 soil&s 10 <br />