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Mr. Jeff Tierney, E.I.T. GeOSynteC D July 1, 2022 consultants Page 4 the hand auger. The annular space of the borehole will be filled with filter pack sand, granular bentonite, hydrated bentonite, and cement grout according to the details presented in Figure 4. After installing the SVPs, the borehole will be surface completed using a 6-inch diameter traffic- rated well vault set in concrete, which will be mounted flush with the existing grade of the surrounding asphalt or concrete surface. Soil Physical Properties Sampling Undisturbed soil samples will be collected during installation of the SVPs to evaluate the physical properties of soil at the off-site location. During boring advancement, hand augering will be stopped at 4.5 ft bgs to allow for collection of an undisturbed soil sample from 4.5 to 5 ft bgs using a slide hammer. Hand augering will then continue until 9.5 ft bgs, at which point a second undisturbed soil sample will be collected from 9.5 to 10 ft bgs. The borehole will then be reamed using the hand auger to ensure a consistent borehole diameter to total depth. The soil samples will be collected in stainless-steel liners and sealed on each end with Teflon® tape and slip-on end caps. The samples will be labeled with project identification, sample location and depth, analytical method, and time and date of sampling. Samples will be transported under chain-of-custody procedures to Cooper Testing Laboratory (Cooper Testing) of Palo Alto, California, for analysis. Soil Vapor Sampling Soil vapor samples will be collected from each of the on- and off-site SVPs in a manner consistent with that described in the Work Plan(sections 4.4.1 to 4.4.5). Soil vapor sampling techniques will include leak testing, shut-in testing, and purging in accordance with Department of Toxic Substances Control (DTSC) guidance, including the Advisory (DTSC, 2015). New SVPs will be sampled a minimum of 48 hours following probe installation. Sampling of the off-site SVPs will be performed in the same mobilization as the planned sampling of the four on-site SVPs,which will be conducted no more than 48 hours in advance of the routine Q3-2022 groundwater monitoring event at the site (planned to be performed in the second half of August). Soil vapor samples collected from each of the on-site and off-site SVPs will then be submitted to a California-certified laboratory, Eurofins Air Toxics of Folsom, California, for analysis of the four selected VOCs of interest: 1,2-DCP, 1,2,3-trichloropropane (1,2,3-TCP), 1,2- dibromo-3-chloropropane (DBCP), and chloroform. 5 Department of Toxic Substances Control.2015.Advisory—Active Soil Gas Investigations. California Environmental Protection Agency,Department of Toxic Substances Control,Los Angeles Regional Water Quality Control Board, and San Francisco Regional Water Quality Control Board,July 2015. engineers I scientists I innovators