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Stantec Consulting Corporation <br /> 3017 Kilgore Road Suite 100 <br /> Rancho Cordova CA 95670 <br /> Tel: (916)861-0400 <br /> Fax: (916)861-0430 n f�Fc—�n �7 <br /> Stantec <br /> JUL 2 3 �0 i0 <br /> ENVIRU HENT NEA[M <br /> July 21, 2010 pEWITISERVICES <br /> Mr. Brian Taylor, P.G. <br /> Engineering Geologist <br /> California Regional Water Quality Control Board — Central Valley Region <br /> 11020 Sun Center Drive Suite #200 <br /> Rancho Cordova, California 95670 <br /> Reference: Addendum to Remedial Action Plan <br /> Former Tosco Bulk Terminal No. 10013 <br /> 3505 Navy Drive <br /> Stockton, California <br /> Dear Mr. Taylor: <br /> This addendum letter, prepared on behalf of the ConocoPhillips Company by Stantec Consulting <br /> Corporation (Stantec), supplements our Remedial Action Plan (RAP), dated April 30, 2010, for the site <br /> referenced above (Figures 1 and 2) and has been prepared in response to regulatory correspondence <br /> from the California Regional Water Quality Control Board — Central Valley Region (CRWQCB-CVR), <br /> dated June 14, 2010 (Attachment 1). <br /> The general conclusion of the recently submitted RAP was to continue oxygen injections through the <br /> fourth quarter 2010. At which time, if the recent concentration trends are unchanged, monitored natural <br /> attenuation will be initiated until remedial objectives are met or until MNA parameters are projected to <br /> meet water quality objectives (WQOs) in a reasonable timeframe. <br /> The comments presented in the June 14, 2010 CRWQCB-CVR letter pertaining to the RAP and <br /> ongoing oxygen injection activities which require a reply are listed in bold below followed by details and <br /> discussion to support the response. <br /> Specify the remedial objectives. <br /> The site location is in a predominantly commercial/industrial area and is physically located on an <br /> human altered/constructed island which was formed largely due to the dredging/creation of the San <br /> Joaquin River deep water channel (located approximately 600 feet north of the subject site). Previous <br /> receptor surveys did not readily identify the presence of water production wells or other sensitive <br /> receptors within a close proximity of the subject site. <br /> In addition, previous assessments at the site have yielded estimated total dissolved solids (TDS) as <br /> ranging near 1,500 milligrams per liter (mg/1). When applying the formula TDS = A X C (where A is the <br /> conversion factor averaging out to be 0.65, and C is the specific conductance (pmhos/cm)) a general <br />