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4.3 INDOOR AND OUTDOOR AIR SAMPLING Up to two indoor air samples may be collected from residential buildings and up to three indoor air samples may be collected from commercial/industrial buildings. Indoor air samples shall be collected focusing on the lowest habitable/usable space. However, if a building has a crawlspace, air samples will be collected from within the crawlspace. It is anticipated that most commercial/industrial and some residential buildings in the retained areas have a slab-on grade foundation type. Buildings with this foundation type or buildings that have a basement (not anticipated) may have an indoor air sample collected with a co-located sub-slab soil vapor sample. Indoor air samples shall be collected over an 8-hour period (commercial/industrial building)or 24-hour period (residential building). If sub-slab soil vapor is to be evaluated at a subject building, once the indoor air sample has been collected, a sub-slab soil vapor sample will be collected as described in the following section. Indoor air samples will be collected within the breathing zone height (3 to 5 feet above the floor surface) in an area of the building that is mutually agreed upon with the building occupants.Sampling in closets, corners, adjacent to hot air/air conditioning vents, or other locations not reasonably representative of breathing conditions will be avoided. An outdoor ambient air sample will also be collected over the same time period as collection of indoor air samples. Indoor and outdoor air samples shall be collected in 6-liter passivated canisters, individually certified as clean. Sub-slab soil vapor shall be collected in 1-liter certified-clean canisters.Sample canisters and flow controllers shall be obtained from Eurofins Test America, Sacramento, California. The following information will be recorded for each sampling location: • The initial and final dates and times of sample collection; • Canister serial number and flow controller serial number; • Canister field vacuum prior to and immediately following sample collection; and • Confirmation of the building layout sketch with depiction of the sample location. Weather(temperature, moisture conditions,wind direction/speed, barometric pressure, and whether regional barometric pressure is rising or falling) will be recorded. Other data will be collected to support the sampling, such as measurements made using a photoionization detector(RAE Systems ppbRAE or equivalent), pressure differential meter(Dwyer DigiMax-1000 or equivalent), and/or other field data. Field equipment will be calibrated daily according to manufacturer's instructions and checked during the day. Appendix C contains the indoor and outdoor air sampling procedures to be following for this VI pathway evaluation. 4.4 SUB-SLAB SOIL VAPOR SAMPLING Sub-slab soil vapor sampling will be conducted in general accordance with the California Environmental Protection Agency/Department of Toxic Substances Control (CaIEPA/DTSC)Advisory—Active Soil Gas Investigations, dated July 2015 (CaIEPA/DTSC Advisory). Up to two sub-slab soil vapor samples may be collected from residential buildings, and up to three sub-slab soil vapor samples may be collected from commercial/industrial buildings. Sub-slab soil vapor MICH