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Weston Solutions, Inc. Remedial Action Work Plan for the San Joaquin County Human Services Agency Site—Stockton, California PROPOSED IMPLEMENTATION PLAN tight grid spacing of 6 feet will be used for injection to obtain adequate coverage and contact with contaminants within the source area. Prior to injection, BOS 200 slurries will be prepared in mixing tanks housed in a mobile injection trailer. The components of BOS slurry will include BOS 200, supplemental gypsum, bacterial culture, and water. The source of water for preparing the slurry will be local hydrant or water truck/tank. The design volumes of BOS 200, supplemental gypsum, and bacteria concentrate are summarized in Table 6-1. These design volumes are based on empirical calculations performed by the vendor using current contaminant concentration data,adsorption capacities, and experience with design loadings at similar sites. Gypsum will be added as a source of time-release sulfate to facilitate biodegradation of petroleum hydrocarbon contaminants in the medium to long term. The injection of BOS 200 amendment into each point will be conducted using direct push technology(DPT) across the vertical treatment interval of approximately 18 feet to 43 feet bgs and at a vertical spacing of every 2 feet. The injection interval is selected to inject the treatment reagent in the capillary fringe (December 2020 water table depth at well MW-2 was 20.9 feet bgs) and below water table corresponding to the screen interval (30 to 45 feet bgs) of well MW-2. Prior to drilling, concrete coring will be used to remove concrete. In addition, each injection location will be hand-augered to 5 feet before the initiation of direct push drilling to minimize the risk of contact with shallow subsurface utilities. The injection using DPT will be conducted using a top-down approach. This approach includes driving the injection rod to the top of the injection interval (approximately 18 feet bgs) and injecting a batch of BOS 200 slurry (30 gallons). Once the injection at the first level is complete, the injection rod is pushed to the next target depth and a fresh batch of slurry is injected. This process is repeated until the lower limit of the injection interval (approximately 43 feet bgs) is reached. 6-3 February 2021