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27 September 2024 AdvancedGeo <br /> p An Employet-Owned Company <br /> Project No. 23-7573 ' <br /> Page 4 of 6 <br /> 4.1. PRE-SAMPLING BUILDING INSPECTIONS <br /> Prior to IA sampling, each building will be inspected for potential volatile chemical sources <br /> and commercial and household products will be inventoried. Products that contain volatile <br /> chemicals or other chemicals that can potentially bias the results of the sampling will be <br /> listed on Building Survey and Indoor Air Source Screen Forms (Appendix B). The Building <br /> Survey and Indoor Air Source Screen Forms are presented in Attachment 6 of <br /> Supplemental Guidance: Screening and Evaluating Vapor Intrusion Final Draft (February <br /> 2023), prepared by the California Department of Toxic Substances Control (DTSC) and <br /> California Water Resources Control Boards. Indoor contaminant sources and products <br /> that could potentially bias the sampling results will be located using an organic vapor <br /> meter (OVM) equipped with a photo-ionization detector (PID) calibrated to a detection <br /> limit of parts per billion by volume (ppb MiniRAE 3000). Any identified sources of indoor <br /> contamination will be removed from the building or sealed, if feasible, and the areas will <br /> be re-monitored. <br /> 4.2. INDOOR AIR, AMBIENT AND CRAWL SPACE SAMPLE COLLECTION <br /> AGI proposes to collect indoor air samples in both commercial suites. Crawl space <br /> samples are proposed underneath raised foundations of the residential structures. A <br /> single ambient air sample will be collected near the rear of the subject building suite as <br /> part of this investigation. Additional sample locations will be evaluated based on results <br /> from this investigation. <br /> 4.2.1. Indoor Air Sampling Method <br /> The indoor and ambient air samples will be collected in six-liter Summa canisters using <br /> passive integrated sampling procedures. Each canister's initial vacuum will be measured <br /> and recorded to ensure the initial vacuum is greater than 25 inches of mercury (in hg). <br /> The sampling inlet on the canisters will be connected to a mass flow controller containing <br /> a particulate filter and calibrated to 11.7 milliliters/minute (ml/min) so that indoor and <br /> ambient air samples are passively collected over an approximate 8-hour period. <br /> Indoor air samples will be collected by placing laboratory prepared Summa cannisters <br /> approximately 3-5 feet above the ground surface in the breathing zone; the outside <br /> ambient air samples will be collected from approximately 6 feet above the ground surface. <br /> Once the air sampling canisters are placed and positioned properly, the Summa canister <br /> valves will be opened to begin air sample collection. Ambient air sample containers will <br /> be opened approximately 60 minutes before the indoor air sample cans. <br /> Following approximately 8-hours of sample time, the indoor air and ambient air sample <br /> containers will be retrieved, closed, and sealed. The sample containers will then be <br />