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Cleanup in Vulnerable Communities'Initiative Discovery Project Reference:Favorite Cleaners and Enforcement Discovery Investigation Work Plan Project Number:60688620 depth of less than 16 feet bgs, deeper probe(15 ft.)implant depths will be adjusted to approximately 3 feet above groundwater to prevent capillary fringe from interfering with the collection of soil vapor. 4. The sand pack around the screen will extend 6 inches below and 6 inches above the screened interval. 5. Dry granular bentonite will be placed to 1 foot above the top of the sand pack. 6. The annular space will be filled with hydrated bentonite. The bentonite clay will be hydrated prior to placement in the borehole annular space. 7. An equilibration time(waiting time)of 48 hours will occur between probe completion and probe sampling to allow for the re-establishment of subsurface equilibrium. 8. The probes will be constructed with Teflon®or Nylaflow® tubing. 9. Each probe will be completed with a well box, and each tubing will be clearly labeled. 10. Post-run sampling methods will not be used for this investigation. Sub-Slab Vapor Probe/Pin Installation Permanent sub-slab vapor pins will be installed in accordance with the method described in Section 3.6 of the DTSC's Soil Gas Advisory(2015)and with the following procedures: 1. Six permanent sub-slab vapor pins will be installed within the interior of the former Boiler Room, Favorite Cleaners, J&S Flowers, and Carmen's Barber Shop, away from the edges of the building. 2. All sub-slab utilities will be located and clearly marked on the slab prior to drilling.All cuttings will be removed from the borehole. 3. Depending on the sub-slab probe construction, a sand pack may be installed to minimize disruption of airflow to the sampling tip. The probe will be placed midway in the sand pack. 4. Dry granular bentonite will be used to fill the borehole annular space to above the base of the concrete foundation. 5. Hydrated bentonite will be placed above the dry granular bentonite.The bentonite for this portion of construction will be hydrated at the surface prior to placement to ensure proper sealing. 6. The remainder of the hole will be filled with neat cement mixed with bentonite. Prior to the introduction of this material,the concrete surfaces in the borehole will be cleaned with a damp towel to increase the potential of a good seal; ideally, all concrete dust will be removed from the borehole. 7. All water used in the construction of the probe will be deionized. The cement will be contaminant-free and quick- drying, and all metal probe components will be thoroughly cleaned to remove manufacturer-applied cutting oils. 8. Each probe will be constructed with a gas-tight fitting and flush-mounted well box so that the probe completion is not a tripping hazard. Prepared for: California Department of Toxic Substances Control AECOM 15