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Cleanup in Vulnerable Communities'Initiative Final Project Reference:Bobson Cleaners Discovery and Enforcement Discovery Project Number:60688620-5.1 Investigation Work Plan Soil gas samples will be collected and analyzed for the full suite of VOCs to assess for vapor intrusion from the subsurface resulting from former/current dry-cleaning activities. Seven on-site soil gas probe locations are planned. Soil gas samples will be collected at 5 and 15 feet bgs at each location, as required by DTSC, and as appropriate based on Site geology. If shallow groundwater is encountered at a depth less than 16 feet bgs, deeper probe implant depths will be adjusted to at least 10 feet bgs and approximately 3 feet above groundwater to prevent capillary fringe from interfering with the collection of soil vapor. If groundwater is encountered at proposed sampling depths or shallower, or if groundwater is shallower than 5 feet bgs,the proposed soil gas samples may be cancelled and grab groundwater samples will be collected,with DTSC concurrence. First groundwater beneath the Site is expected at a depth of approximately 14 to 24 feet bgs. Additionally, three sub-slab soil gas samples will be collected within the Bobson Cleaners Inc.facility, per the May 16, 2023, access agreement discussion with the Site owner. Two soil gas samples will be collected adjacent to the former LUST site,two will be collected from parking spaces to the west of the commercial building, one is located southeastern corner of the building near the waterline, and two will be located west of the carport near the storm drain and southwestern corner of the carport.The three sub-slab soil vapor pins locations will be split between the His Will Insurance office and Best Foot Massage. Of the two locations in the His Will Insurance office,one will be located behind the door in the utility closet, and the other will be located behind the door in the restroom. Within Best Foot Massage Parlor, the sample location will be placed in the restroom. These locations were chosen as they are unlikely to be disturbed and are out of the general footpath and are in rooms with floor penetrations. Table 1 presents a summary of the active soil gas and sub-slab soil gas sampling and analyses planned for this DI. The proposed soil gas and sub-slab soil gas sample locations are depicted on Figures 4A and 4B. The sampling protocol for soil gas samples is discussed in Section 3.2.5.2 below.The analytical methods for soil gas samples are summarized in Section 3.2.6.1 and Table 1. Field QC samples to be collected are discussed in Sections 3.2.5.6 and 3.2.6.4. 3.2.2 Soil No soil matrix samples will be collected for laboratory analyses.To assist in planning soil gas sampling depths, seven boreholes will be advanced at the soil gas sampling location(s). Continuously cored borehole(s)will be completed to 16 feet bgs.The lithology of the cored samples will be logged in the field.The soil boring will be logged to terminal depth using the United Soil Classification System. Headspace testing will be performed using a photoionization detector(PID)to assess the presence of VOCs in recovered soil samples. Lithologic description and headspace testing will be documented on the boring logs. 3.2.3 Groundwater If encountered, grab groundwater sampling will be performed in accordance with the Programmatic QAPP,which was prepared in accordance with the following Programmatic QAPPs for groundwater investigations: • "Representative Sampling of Ground Water for Hazardous Substances," February 2008; • "Drilling, Logging, and Sampling at Contaminated Sites," November 2013; • "Well Design and Construction for Monitoring Groundwater at Contaminated Sites,"September 2014; and • "Guidelines for Planning and Implementing Groundwater Characterization of Contaminated Sites,"June 2012. If groundwater is encountered during advancement of boreholes for soil vapor well installation, grab groundwater samples will be collected from the boreholes. Groundwater samples will be collected in appropriate containers, stored in properly chilled coolers and delivered to an California Environmental Laboratory Accreditation Program (ELAP)-certified laboratory. Groundwater samples will be analyzed for VOCs(including fuel oxygenates)using USEPA Method 8260B. In addition if needed, equipment rinsate blank samples will be collected as set forth in Section 3.2.5.6 below.Table 2 presents a summary of the water Prepared for: Department of Toxic Substances Control AECOM 11