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San Joaquin County DIRECTOR <br /> Donna Heran,REHS <br /> Environmental Health Department� - •oG p ASSISTANT DIRECTOR <br /> r: .y 600 East Main Street Laurie Cotulla, REHS <br /> =� Stockton, California 95202-3029 PROGRAM COORDINATORS <br /> Carl Borgman,REHS <br /> Mike Huggins,REHS, RDI <br /> "AQ Website: yyyyyy sJgov.arg/ehd Margaret Lagorio,REHS <br /> Phone: (209)468-3420 Robert McClellon,REHS <br /> Fax: (209)464-0138 Jeff Carruesco,REHS, RDI <br /> !Casey Foley,REHS <br /> MS. KELLY ESTER <br /> CHEVRON MANAGEMENT COMPANY <br /> PO BOX 6012, ROOM K 2236 <br /> SAN RAMON CA. 94583 <br /> RE: Chevron USA Products#9-8264 Site Code:1418 <br /> 3775 Tracy Blvd. <br /> Tracy, Ca.95376 <br /> WORK PLAN: Oxygen Injection Workplan <br /> DATED: April 23,2007 <br /> PREPARED BY: Conestaga-Rovers and Associates(CRA) <br /> APPROVED• M <br /> ADEQUATE AND NECESSARY ELEMENTS OF THE WORK PLAN [HSS 25296.10(c)(3)1: <br /> 1. To inject oxygen Into the groundwater at MW-4 to increase dissolved oxygen concentrations. <br /> 2. To attempt to enhance biodegradation of hydrocarbon and aid in groundwater cleanup. <br /> 3. Approximately every two weeks,CRA will Inject oxygen into groundwater In on-site MW-4 <br /> utilizing a mobile system. <br /> 4. Approximately 125 cubic feet of oxygen will be delivered to the bottom of MW-4 during each <br /> event. <br /> 5. The injection period will last for 6 months and an evaluation will be conducted at the end of <br /> that period. <br /> 6. Groundwater samples will be collected for analysis to establish a be <br /> and additional <br /> samples will be analyzed as the process continues. <br /> 7. Dissolved oxygen concentrations will be measuredlanalyzed to determine Increased oxygen <br /> concentrations In the groundwater during the Injection period. <br /> 8. Samples will be analyzed using:EPA Method 8015M,EPA Method 8260B,and appropriate <br /> dissolved metals analysis. <br /> COMMENTS AND CONDITIONS: <br /> 1. Based upon prior soil and groundwater assessment completed at this site over the pass 12 <br /> years,the contamination plume appears to be localized the area of MW-4 with some <br /> migration towards MW-3. Both MW-3 and MW-4 are located on-site and screen properly at <br /> groundwater table. Groundwater contaminant concentrations have declined over time and <br /> this proposed phase of work seems appropriate. <br /> 2. END has reviewed the CRA Case Closure Request dated August 15,2007, but can not grant <br /> closure at this time. <br /> 3. After completion of this proposed phase of work and with the vertical extent of the <br /> groundwater plume in the area of MW-4 Is defined(possibly a grab groundwater sample <br /> collected for analysis),EHD will evaluate closure and NFAR. <br /> 4. Until closure is granted,quarterly groundwater monitoring must continue. <br /> DATEDZ4- <br /> Harlin Knoll Senior RENS(209)468-3442 <br /> Cc:CRA <br />