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Geosptec consultants Conditions,products,or activities that may affect or interfere with the indoor air quality evaluation may be discussed with the owner/occupant. Owners/occupants may be requested to remove,to the extent possible, products or materials that may confound the indoor air quality evaluation prior to sample collection. In addition, potential preferential pathways will be identified and noted. Potential preferential pathways include utility conduits and other penetrations in the building floor/slabs as determined by visual inspection in the areas where samples will be collected. Indoor air samples will be collected over an approximate 8-hour period to represent concentrations of VOCs that may be encountered over the anticipated daily exposure period, in accordance with the Supplemental Guidance (CaIEPA, 2023). Three samples will be collected from each of the two suites, as well as a duplicate sample at one location. Three outdoor air samples will be collected at the Site to assess local ambient conditions. Samples will be collected concurrently with indoor air samples, starting one hour before deploying and ending one hour after indoor air samples. Indoor and outdoor air samples will be collected in individually certified six-liter Summa'm canisters fitted with a 10-hour flow controller. The outdoor air samples will be submitted to the laboratory under proper chain-of-custody protocol and will be analyzed for VOCs by TO-15 selective ion monitoring (SIM). Indoor and outdoor air samples will be collected in accordance with the indoor and outdoor air sampling SOP (Appendix B). 3.4.2 Sub-Slab Probe Installation and Sampling Three temporary sub-slab Vapor Pins®will also be installed in each of the two suites, collocated with and near to the indoor air sample locations. Sub-slab probes will be installed by drilling a small diameter hole through the concrete slab and placing'/4-inch Teflon®tubing fitted with a stainless-steel filter or Vapor Pin® through the hole. The sub-slab probes will be constructed in accordance with the soil vapor probe sampling SOP provided in Appendix B. Sub-slab probes will be installed and sampled following the completion of indoor air sampling in accordance with the Supplemental Guidance to prevent contamination of indoor air via slab penetrations and allowed to equilibrate at least two hours prior to sampling. Sub-slab samples will be collected from the probes using 1L Summa' canisters. Prior to purging and sampling activities, a shut-in test and leak check will be completed in accordance with the SOP(Appendix B). Approximately three volumes will be purged from the sub-slab probe. One purge volume includes the internal volume of the tubing and Vapor Pin®.Purging and sampling will commence following a successful shut-in and leak test(i.e. no evidence of leaks is found during the tests). Sub-slab soil vapor samples will be analyzed for VOCs by EPA Method TO-15, and helium by modified ASTM Method D-1946. 3.5 Quality Assurance and Quality Control The following sections describe the quality assurance/quality control(QA/QC)procedures to be completed in the field and during the laboratory analytical process, and the procedures for data verification and validation. A detailed Quality Assurance Project Plan(QAPP) is included as Appendix C. 3.5.1 Field Quality Assurance Measures Quality control measures for soil vapor sampling will include shut-in testing,leak testing,collection of field quality assurance samples, and proper sample handling and custody procedures as described below. The shut-in and leak testing will be performed in accordance with the Geosyntec SOPS in Appendix B and described in Section 3.4.2 above. 9 September 2025