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TO E RO E K SOP No.026,REV.1 ASSOCIATES,INC INDOOR AIR AND SUB-SLAB SOIL GAS SAMPLING METHODS I PAGE 4 possible. Interior and exterior weather conditions can impact sample integrity. Initial and final weather conditions such as temperature,wind, precipitation,humidity, and barometric pressure should be documented and any major changes to those conditions that occur during the execution of sampling activities should be detailed. Sampling locations should be selected and prepared for sampling as described in a site- specific QAPP/FSP. Indoor air and soil gas samples should be paired to ensure data is representative of a specific sampling location.Indoor air samples will be collected within one to three feet of soil gas samples. Sub-slab soil gas samples may be collected from depths as shallow as 6 inches or as great as 50 feet below ground surface (bgs), depending on the objectives of the project, soil type encountered, and the type of drilling equipment used.The horizontal spacing of soil gas sampling points (grid size) may be only a few feet or more than 500 feet.Again, this is a function of project-specific objectives and site conditions. 2.2 EQUIPMENT AND SAMPLING SYSTEM PREPARATION Equipment used for monitoring air conditions and collecting air samples must be properly calibrated and/or tested prior to use. All equipment must be calibrated in accordance with the manufacture's specifications in a clean area on site. Instrument calibration schedules, as well as any deviations in performance criteria, must be recorded in the field logbook. Equipment for the collection of the indoor air and sub-slab soil gas may include the following: • Rotary hammer drill with smaller (e.g., 1/4-inch) and larger (e.g., 3/4-inch) bits capable of drilling holes at the sufficient diameter size and depth for installing sub-slab vapor probe through the building slab concrete to the sample target depth; • Sub-slab vapor probe or pin (either pre-fabricated or assembled on site) or an appropriate length of new dedicated tubing; • Teflon® or equivalent tubing of appropriate size for connecting the sampling port to pump (during gas point purging) and the sampling port to stainless steel canister (during sample collection); • Quick-drying Portland cement (no additives);