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Mr. Carl Knowles 2 17 July 2018 2016 letter. In a letter dated 23 March 2017, Central Valley Water Board staff requested sampling of recently discovered domestic wells downgradient of the Site and a work plan addendum "evaluating the feasibility and cost effectiveness of constructing a land disposal system for the proposed GWE system." On 20 April 2017, Stratus submitted the Work Plan Addendum; however, it did not include a cost estimate for the land disposal system nor justification for Stratus' claim that "we are confident that the ground surface at the site will readily accept groundwater at a rate up to 8 gpm." Following additional Central Valley Water Board staff requests for a land disposal cost estimate, Stratus provided cost estimate values in an email dated 15 June 2017. To date. Stratus has not provided justification for their claim that discharged groundwater will readily infiltrate at the Site, nor plans for testing this claim. Comments on Proposed Remediation Plan Central Valley Water Board staff has the following comments on the proposed remediation plan presented in the Work Plan and Work Plan Addendum: 1 The Work Plan and Work Plan Addendum do not present rationale for the proposed SVE system, and the need for the SVE system is not clear to Central Valley Water Board staff. The Work Plan proposes the installation of two SVE wells within the footprint of the 1990 soil excavation, with screens from 17 to 37 feet below ground surface (bgs). The 1990 excavation was completed to a depth of 35 to 40 feet bgs. Therefore, Central Valley Water Board staff expect that vadose zone mass removal by the SVE wells will be negligible. Stratus did not operate an SVE system during ozone injections from 2012 to 2015. It is unclear why SVE might be needed to capture air sparging vapors, but not needed to capture vapors produced during sparging with ozone, which is a stronger oxidant than the oxygen produced during air sparging. Central Valley Water Board staff does not approve of the proposed SVE remedy. If Stratus wishes to proceed with SVE at the Site, please submit a letter report presenting their rationale for SVE operation and additional system design details (including drawings). Additionally, address the items in Comment No. 2. 2. The Work Plan and Work Plan Addendum do not present Stratus' plans for managing water produced by the SVE system, nor do they mention a moisture separator in the SVE design. Moisture separators are a standard component of SVE systems that are needed to prevent extracted water from entering GAO vessels. The Work Plan states that the SVE wells will be screened from approximately 17 to 37 feet bgs. On 6 March 2018, Stratus measured depth-to-groundwater at on-Site wells MW-11 and MW-12 at 28.58 feet bgs and 30.11 feet bgs, respectively. Therefore, proposed SVE wells may have up to 7 to 8 feet of submerged screen depending on the drawdown produced by groundwater extraction. The Work Plan also proposes to spray extracted groundwater (estimated at 2 to 3 gallons per minute per well) on the ground surface at the Site, which would introduce approximately 7,000 gallons per day into the vadose zone. The proposed SVE design and approach is inadequate for handling the substantial volume of water that will be produced during SVE. The Work Plan states "Submersible pumps will be installed within wells EX-1 and EX-2, and should pump groundwater at a fixed rate (estimated at about 2-3 gallons per minute from each well)." The Work Plan Addendum states "...Stratus estimates that a total of about 3 gallons per minute (gpm), or 1.5 gpm from each of the two extraction wells, will be achieved." It is unclear why the documents present conflicting values. It is also unclear whether Stratus intends to target these specific flow rates, or whether they