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a� <br /> 1. Direct-push soil vapor sampling probes (implant type) <br /> An implant consists of a tubular, stainless steel screen with a length of 6 inches, diameter <br /> of 1/8 to '/4 inch, and a pore size of 0.0057 inches. Note that the implant is not retrievable <br /> and at site closure must be abandoned in place. The implant is connected to a nylon <br /> sampling tube of sufficient length to enable soil vapor sampling at the ground surface. A <br /> direct-push rig (i.e., Geoprobel) is used to push a series of drive rods to a designated <br /> depth. When this depth is reached,the implant is slid down the bore of the drive rods and <br /> is attached to the drive point at the bottom. Then the drive rods are removed, leaving the <br /> implant and drive point in the subsurface (Figure 2). As the drive rods are removed the <br /> borehole may collapse around the sampling probe. Also, as the drive rods are removed a <br /> sand pack can be installed around the implant, followed by a hydrated granular bentonite <br /> seal extending to the ground surface. A surface seal of hydrated granular bentonite is <br /> applied where the drive rods meet the ground surface. <br /> One of the potential drawbacks of these implants is the difficulty in installing a sand pack <br /> and hydrated granular bentonite seal through the drive rods as they are removed from the <br /> borehole. Avoid lateral movement of the sampling tubes and drive rods to prevent <br /> atmospheric air from entering the soil vapor sample. <br /> P,.be Rod <br /> lubny <br /> Reim Rolde <br /> I <br /> Yo�oe <br /> S <br /> ImpWnd <br /> �mpinl ` <br /> Figure 2. Direct-push soil vapor <br /> samplingrobe (implant type; <br /> Geoprobe). <br /> ETC Soil Vapor Sampling Technical Toolkit 9 <br /> Version 1.4, September 7,2005 <br />