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ADVISORY- ACTIVE SOIL GAS INVESTIGATIONS 3.5 DECONTAMINATION Decontaminate all reusable equipment to prevent cross contamination. Tubing is not reusable and should not be decontaminated. Instead, use new or unused sampling tubing for each probe location. Decontamination may consist of steam cleaning or a three-stage decontamination process consisting of a wash with a non-phosphate detergent, a rinse with tap water and a final rinse with distilled water. Collect one equipment blank at the beginning of sampling and at least one each day after decontamination. Equipment should be air- dried before reuse. The most common method of collecting an equipment blank is to pour distilled water over recently decontaminated piece of equipment and collect the water in an appropriate container for analysis of site constituents. Drill rods contacting contaminated soil should be decontaminated before reuse and blank tested as appropriate. If soil gas samplers arrive at the site after drill rig demobilization, equipment blanks should be provided by the drilling contractor. As discussed in Section 3.2.2, an equipment blank is recommended for probe tubing and probe tips. A syringe blank may be collected by sampling ultra-pure air as it passes through the syringe, and a syringe blank is not an acceptable substitute for the driller's equipment blank. The equipment blanks demonstrate there is no residual contaminant carryover from other sites or the manufacturing process. 3.6 SUB-SLAB INVESTIGATION METHODS The procedures for collecting sub-slab soil gas samples directly under a building's foundation are the same as for collecting subsurface soil gas samples. When collecting sub-slab samples, if a building is determined to have a moisture barrier and/or a tension slab, special care should be given when hand-drilling through the concrete slab. In particular, for tension foundation slabs, the tension cables within the slab should be located prior to drilling either through visual observation or through remote-sensing with either a metal detector or ground penetrating radar. The cutting of a tension cable within a slab during drilling could disrupt the integrity of the slab and potentially cause injury to the field crew. When evaluating sub-slab soil gas for a building, permanent sampling points should be installed so repeated sampling can be conducted, as necessary, to evaluate seasonal or temporal variations. For sub-slab samples, after removal of the floor covering, a small-diameter hole should be drilled through the concrete of the foundation slab. Typically, holes are 1.0 to 1.25 inches in diameter. Either an electric hand drill or concrete corer is used to drill the holes. All sub-slab utilities, such as water, sewer, and electrical, should be located and clearly marked on the slab prior to drilling. Sub-slab holes should be advanced three to four inches into the engineering fill below the slab. All drill cuttings should be removed from the borehole. A typical sub-slab probe design is shown in Figure 2. The sampling probe should be constructed with the following specifications: July 2015 15