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A4OM • Ambient air sampling will be conducted concurrently with indoor air sampling. Sample locations will be outside and adjacent to the targeted building. Per USEPA (2015), ambient air sampling will begin prior to (e.g., approximately 2 hours before) indoor air sampling to account for building air exchange rates. • Each ambient air sample will be collected in evacuated, batch-certified stainless-steel canisters and submitted to an accredited, off-site analytical laboratory for USEPA TO-15 analysis using full-scan GC/MS. • The canister for ambient air sample collection will be placed such that the inlet is at a sampling location that is representative of the heating, ventilation, and air conditioning (HVAC) system inlet air for the building, if an HVAC system is operating. o If the HVAC inlet is on the side of the building, locate the Summa® canister inlet within approximately 10-feet of the HVAC inlet. If the HVAC inlet is on the roof of the building, locate the Summa® canister inlet on the roof using the safest method available, if possible. o If no HVAC inlet or safely accessible roof inlet is present, the canister can be located immediately upwind of the building, avoiding sampling near walls, under trees, or other areas with obstructed air flow. • Ambient samples should be located away from gasoline stations, automobiles, gasoline-powered engines, fuel and oil storage tanks, chemical storage areas, and dry cleaners. • Sampling devices should be placed at least 10 feet beyond a tree's drip line. • Ambient air samples should be collected on the upwind side of a building at a distance equal to twice the height of the building. Once canisters are in place, sample as described in Section 2.3. 2.5 Field Equipment Calibration Equipment used during the sampling event will require in-field calibration. However, if required; routine calibration will be completed in compliance with the equipment manual. Calibration records and copies of the manufacturer manuals for each field instrument will be kept in the field and project files. 3 LABORATORY ANALYTICAL PROCEDURES 3.1 Analytical Methods Indoor/ambient air samples will be submitted for laboratory analysis of VOCs using USEPA Test Method TO-15 SIM, which provides lower reporting limits that are necessary for risk assessment.