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3.2 Vapor Probe Construction <br /> 1. To protect interior surfaces,lay plastic sheeting around the probe location. <br /> 2. Use a rotary hammer drill to create an approximately 3-inch deep, 1 1/2-inch diameter <br /> hole that partially penetrates the slab. Use a piece of flexible tubing to blow or vacuum <br /> concrete debris and dust from the hole. Do not blow or vacuum after the slab has been <br /> completely penetrated. <br /> 3. Drill a smaller diameter inner hole in the center of the outer hole,periodically blowing <br /> dust and debris from the hole until the slab is penetrated. The diameter of the inner hole <br /> should exceed the diameter of the vapor probe tubing by the minimum amount <br /> practicable. The inner hole should be drilled completely through the slab and 3 to 4 <br /> inches into the subslab material(baserock or soil)to form a cavity(Figure 1). <br /> 4. Insert the capped vapor probe tubing through a tightly fitting rubber stopper or a Teflon <br /> disk and insert the stopper or disk into the bottom of the outer hole. The purpose of the <br /> stopper is to stop moisture from the annular seal from leaking into subslab materials.The <br /> fitting may either be constructed flush,or may protrude above the slab,depending on <br /> location and susceptibility to damage. If a lubricant is needed,use only high-vacuum <br /> silicone grease. <br /> 5. Clean the concrete surfaces in the borehole with a dampened towel to increase the <br /> potential of a good seal.Fill the remainder of the hole with hydrated bentonite(temporary <br /> probe)or hydrated bentonite topped with expanding cement(semi-permanent probe). <br /> Place a protective cap(temporary probe)or flush mounted well box(semi-permanent <br /> probe)over the probe to protect it from damage. <br /> 3.3 Vapor Sampling <br /> During vapor sampling,record all valve open/close times and canister/manifold vacuum readings <br /> at each step. Do not conduct sampling within 5 days following a significant rain event(0.5 <br /> inches of rainfall during any 24-hour period)or signficant irrigation adjacent to the building. <br /> Setup <br /> 1. Calculate and record the volume of the sampling assembly,tubing, vapor probe and void <br /> space created in subslab material. <br /> Volume=7E* r2 * L=3.14 x(1/2*ID)x(1/2*ID)*L, <br /> where ID=cavity,tubing or manifold inside diameter and L=length of cavity or <br /> tubing/manifold segment. <br /> 2. Wear latex or nitrile gloves while handling sampling equipment. Change gloves <br /> whenever a new sample is collected and after handling leak-check compound. <br /> 3. Replace the vapor probe cap with a closed Swagelok valve.Connect the sampling <br /> manifold to the vapor probe,sample Summa canister and vacuum pump using Swagelok <br /> fittings and stainless-steel,Teflon or Tygon tubing. Check all fittings for tightness(do not <br /> overtighten). <br /> 4. Close all valves.Record pre-test vacuum readings on summa canister. <br /> 2 <br />