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sample locations may be co-located with indoor air sample locations (if collected). Sub-slab soil vapor samples will be collected from below the building if a slab is present(slab-on grade or basement foundation types) and permission to install a sub-slab vapor probe is granted by the property owner. The installation of sub-slab soil vapor sampling points shall be completed directly after indoor air sampling has been completed, if applicable. Based on the condition of the slab, one sub-slab soil vapor monitoring point will be installed near the center of the building slab. A second location will be installed between the first sub-slab location and the wall nearest the Site, at least three feet from the foundation wall.The slab thickness of the subject buildings is unknown but is assumed to be approximately three to five inches for planning purposes. Prior to drilling through building floors,a utility survey will be conducted to identify subsurface utilities.A hand-held rotary hammer drill will be used to install the sub-slab soil vapor probes.The hammer drill will be fitted with a 1.5-inch-diameter drill bit and used to drill through the top two inches of the concrete slab.A vacuum equipped with HEPA filtration,will be used to capture concrete dust while drilling into the concrete. Once a depth of two inches has been reached, the hammer drill will be fitted with a 5/8-inch-diameter drill bit and used to advance the hole from two inches through to the bottom of the concrete slab.The drill bit will then be advanced an additional one inch into the fill material below the concrete slab to form a void space. After the 5/8-inch-diameter hole has been cored through the concrete slab, a stainless-steel Vapor Pin° fitted with a silicone sleeve will be installed directly into the drilled 5/8-inch hole.The Vapor Pin® will be tapped into place using a dead blow hammer with the protection of the Vapor Ping installation/extraction tool to protect the barb fitting. Once the Vapor Pin® is in place, a protective cap will be placed on top to prevent vapor loss prior to sampling.The Vapor Pin°will be covered with a flush-mounted cover. Each sampling location will be allowed to equilibrate for a minimum of two hours prior to collection of sub-slab soil vapor samples. Prior to sample collection, each sub-slab soil vapor sample probe will be leak-tested using helium, and then purged in generally accordance with DTSC. The sub-slab soil vapor samples will be collected using laboratory-provided, certified 1-liter canisters equipped with dedicated 200 milliliters per minute flow controllers. The following information will be recorded for each sub-slab soil vapor sample collected: • Pressure differential measurement collected at each location; • Initial and final dates and times of sample collection; • Canister and flow controller serial numbers; • Canister vacuum prior to and immediately following sample collection; • A building layout sketch with depiction of sample locations; and • Photographs showing the sampling location and surrounding areas. Appendix D contains the sub-slab probe installation and sub-slab soil vapor sampling operating procedures for this VI pathway evaluation.An example canister sampling form is also provided in Appendix D. Ambient temperature, moisture conditions, and regional barometric pressure will also be recorded. Once the samples have been collected,the vapor pins shall be removed, and the slab penetration filled with concrete. 8RICH