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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 matrix sampling and analyses planned for this DI.The proposed groundwater sample locations are depicted on Figure 4. The sampling protocol for groundwater samples is discussed in Section 3.2.5.4 below.The analytical methods for water samples are summarized in Section 3.2.6.2 below and Table 5.The field QC samples to be collected are discussed in Sections 3.2.5.6 and 3.2.6.4 below. 3.2.4 Indoor and Ambient Air Sampling Indoor air sampling will be conducted in accordance with Programmatic QAPP which was prepared for the Evaluation and Mitigation of Subsurface Vapor Intrusion to Indoor Air(2011). Five active indoor air samples plus one duplicate and three active ambient air samples will be collected upwind, downwind, and crosswind plus duplicate.Table 1 presents a summary of the air matrix sampling and analyses planned for this DI.Three of the indoor air samples will be co-located with sub-slab soil vapor pins,with one located near the reception desks and workers of the His Will Insurance office, one in the utility room, and one in the restroom. In the Best Foot Massage parlor one in the reception area near workers and one in the restrooms.The proposed indoor and ambient air sample locations are depicted on Figures 4A and 4B. The sampling protocol for Indoor"ir s'mples 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 1. 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 gas, sub-slab soil gas, indoor air, and ambient air samples.All samples will be collected and handled in accordance with approved procedures specified herein and in applicable sections of Programmatic QAPP. 3.2.5.1 Utility Clearance The utility clearance will include a 48-hour prior notification of Underground Service Alert(USA)and a geophysical survey at the Site.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 Site, will be notified of the intent to conduct subsurface investigations at least 72 hours prior to initiation of intrusive field tasks.All proposed locations of 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 site 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-augered to 5 feet bgs to check for utilities. 3.2.5.2 Soil Gas and Sub-Slab Soil Gas Sampling A qualified company will conduct the soil gas survey using a direct push Geoprobe-type rig (unless a hollow-stem rig is needed due to lithologic conditions), and hand tools.A general description of the probe installation and soil gas sampling is presented below.Any requirement not specifically written below is incorporated by reference to the Programmatic QAPP. Soil Gas Boreholes and Probe Installation The permanent soil gas probe emplacement method described in Section 3.2 of the of the Programmatic QAPP will be used. In addition,the following items 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 minus16 feet deep. 2. A minimum of one borehole per location will be continuously cored, and a borehole lithologic log will be prepared. Prepared for: Department of Toxic Substances Control AECOM 12