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RECEAD v_=:% n� <br /> Water Boards MAY B 12012 <br /> Central Valley Regional Water Quality Control Boa VARONMENTALHEALTH <br /> ERMIT/SERVICES <br /> 18 May 2012 ` ty✓� <br /> Mr. Jeff Baker , ' ►1/� <br /> Tesoro Companies, Inc. <br /> 3450 South 344`" Way, Suite 100 <br /> Auburn, WA 98001-5931 <br /> OXYGEN INJECTION PILOT STUDY AND WELL DESTRUCTION WORKPLAN, TESORO <br /> STOCKTON TERMINAL, PORT OF STOCKTON, SAN JOAQUIN COUNTY <br /> California Regional Water Quality Control Board, Central Valley Region (Central Valley Water <br /> Board) staff reviewed the following documents: <br /> 27 February 2012 Oxygen Injection Pilot Study Status Report (Pilot Study Report) <br /> 4 May 2012 Well Destruction Work Plan (Work Plan) <br /> Stantec Consulting Corporation (Stantec) submitted the reports on behalf of Tesoro <br /> Environmental Resources Company (Tesoro) for Tesoro's Stockton Terminal. <br /> On 25 January 2011, Tesoro began a one-year oxygen injection pilot study in wells <br /> TS/MW-3DR and TS/MW-4D to evaluate injecting oxygen into the "D" groundwater zone. The <br /> Pilot Study Report shows decreases in petroleum hydrocarbon concentrations in the treatment <br /> wells; however, little change in concentration was observed in the downgradient well <br /> TS/MW-2D. Tesoro recommends continuing the D zone pilot study for an additional year and <br /> increasing the amount of oxygen being injected. <br /> Tesoro is expanding the tank farm area during the second and third quarters of 2012. The Work <br /> Plan proposes the destruction of 25 ozone injection wells and five D zone monitoring wells that <br /> are within the area of the new tank farm. Tesoro states that because the wells will be within the <br /> containment area, the wells will present a potential conduit to groundwater following an <br /> accidental release from the tanks. <br /> Our comments are: <br /> 1. Central Valley Water Board staff concurs with the destruction of the 25 ozone sparge <br /> wells and D zone monitoring wells within the proposed tank farm expansion area. <br /> However, the Work Plan proposes destruction of all D zone monitoring wells in the area, <br /> which are necessary to monitor source area contamination in the D zone. Tesoro needs <br /> to either keep one existing D zone monitoring well or install a new D zone monitoring <br /> .icD. P L- .i _,-. C i:F¢coy F' L EGCC. 'rv- c,rn cF <br />