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Cleanup in Vulnerable Communities'Initiative Discovery Project Reference:Favorite Cleaners and Enforcement Discovery Investigation Work Plan Project Number:60688620 3.2.4 Indoor and Outdoor Ambient Air Sampling Indoor air sampling will be conducted in accordance with the Programmatic QAPP,which was prepared for the evaluation and mitigation of subsurface vapor intrusion to indoor air(AECOM 2022c). Eight active indoor air samples plus one duplicate will be collected within the commercial building.Additionally,three active outdoor ambient air samples will be collected upwind, downwind, and crosswind plus a duplicate.These active outdoor ambient air sample locations will be determined by the wind direction during the day of sampling. Table 3 presents a summary of the air matrix sampling and analyses planned for this Discovery Investigation. Six of the indoor air samples(IA-1, IA-2, IA-3, IA-4, IA-5, and IA-6)will be co-located with one sub-slab vapor sample in the former Boiler Room/current Kitchen,two sub-slab vapor samples in the former Favorite Cleaners'building,two sub- slab vapor samples in J&S Flowers shop, and one sub-slab vapor sample in Carmen's Barber shop. Two extra indoor air samples(IA-7 and IA-8)will be collected in J&S Flowers shop. The proposed indoor and outdoor ambient air sample locations are depicted on Figures 4A and 4B. The sampling protocol for indoor air samples is discussed in Section 3.2.5.5 below.The analytical methods for indoor air samples are summarized in Section 3.2.6.3 below and Table 3. Field QC samples to be collected are discussed in Sections 3.2.5.6 below.Active indoor air samples will be collected using 6-liter Summa®canisters with 8-hour flow regulators. 3.2.5 Sampling Methods and Procedures This section describes the methods and procedures that will be used to collect soil vapor, sub-slab vapor, indoor air, outdoor ambient air, and groundwater(If encountered)samples.All samples will be collected and handled in accordance with approved procedures specified herein and in applicable sections of the Programmatic QAPP. 3.2.5.1 Utility Clearance The utility clearance will include a 72-hour prior notification of Underground Service Alert(USA)and a geophysical survey at the Subject Property.The geophysical survey will be conducted using electromagnetic or potential field methods to clear each boring location.Any utility companies not covered by USA that may have underground utilities at the Subject Property,will be notified of the intent to conduct subsurface investigations at least 72 hours prior to initiation of intrusive field tasks by USA.All proposed locations of the subsurface investigation will be clearly marked with white paint or surveyor's flagging as required by USA. USA will contact all utility owners of record within the Subject Property vicinity and notify them of the intention to conduct subsurface investigations in proximity to buried utilities.All utility owners of record,or their designated agents, will be expected to clearly mark the position of their utilities on the ground surface throughout the area designated for investigation. In addition, each borehole will be hand-augured to 5 feet bgs to clear for potential utilities or subsurface obstructions. 3.2.5.2 Soil Vapor and Sub-Slab Vapor Sampling A qualified company will conduct the soil vapor survey using a direct-push Geoprobe-type rig (unless a hollow-stem- auger[HSA] rig is needed due to lithologic conditions), and hand tools.A general description of the probe installation and soil vapor sampling is presented below.Any requirement not specifically written below is incorporated by reference to the Programmatic QAPP. Soil Vapor Boreholes and Probe Installation The permanent soil vapor probe emplacement method described in Section 3.2 of the of the Programmatic QAPP will be used. In addition,the following activities will be performed. 1. Boreholes will be drilled with direct-push methods. If lithological conditions do not allow for direct-push methods, DTSC will be informed. Boreholes will be drilled to plus or minus 16 feet bgs. 2. A minimum of one borehole at the Subject Property will be continuously cored, and a borehole lithologic log will be prepared. 3. Two screened intervals will be installed within one borehole with screens set at 5 and 15 feet bgs.A bentonite plug will be set in each borehole to pneumatically isolate the screens. Deeper soil vapor probe implants will be installed to a depth of at least 10 feet bgs where possible. However, if shallow groundwater is encountered at a Prepared for: California Department of Toxic Substances Control AECOM 14