SITE INFORMATION AND CORRESPONDENCE

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Ms. Shelby Lathrop -2 - 8 March 2011 Former Tosco Bulk Terminal No. 'iuJ13 150 cubic feet (ft) to 300 ft3 per bi-weekly event. ConocoPhillips has continued this schedule and estimates that about 9,105 pounds of oxygen have been injected at the Site since the pilot study began. Oxygen injections and DO measurements have not been performed in MW-22 since August 2009 due to a damaged screen. During the fourth quarter, DO concentrations generally averaged about 2 milligrams per liter (mg/L). In February 2010, DO concentrations increased to as much as 46 mg/L in MW-17B and MW-20. Elevated concentrations were not sustained in MW-1713, but were in MW-20 through the fourth quarter. The pilot study was terminated on 31 December 2010. The Addendum responds to our comments on ConocoPhillips' 22 December 2010 Work Plan for Human Health Risk Assessment. The Addendum proposes to • Consider the ingestion, dermal contact, and inhalation of volatiles from groundwater -- - exposure pathways as well as potential exposures to volatiles from soil vapor in the - Human Health Risk Assessment (HHRA); • Collect shallow soil gas samples at two locations onsite and one offsite to assist in the risk evaluations; • Use the USEPA's ProUCL 4.0 statistical software package to calculate baseline threshold values of COCs and present non-parametric approaches for consideration; • Consider all detected analytes as potential COCs; and • Consider potential exposures to ecological receptors as part of the Tier 1 HHRA. Our comment is presented below: Central Valley Water Board staff concurs with the Addendum and the use of ProUCL 4.0. The Fact Sheet for this software package, provided in Attachment 3, states that ProUCL 4.0 employs non-parametric methods such as regression on order statistics (ROS) and Kaplan- Meier (K-M) to compute upper confidence limits (UCL 95) for censored data sets. ConocoPhillips should use ROS for this task. By 6 May 2011, please submit the HHRA. If you have any questions regarding this letter, you may contact me at (916) 464-4811 or betaylor@waterboards.ca.gov. BRIANlfiAY R, P.G. Engineering Geologist cc: Mr. Harlin Knoll, San Joaquin County Environmental Health Department, Stockton Mr. Richard Stiffler, City of Stockton - Department of Municipal Utilities, Stockton Ms. Debbie Callie, Port of Stockton, Stockton Mr. Mark O'Brien, Port of Stockton/ERSC, Alamo Mr. Jeff Kasper, Deputy Port Director, Environmental Planning & Facilities, Stockton Mr. Sean Coyle, Stantec, Rancho Cordova Mr. Joe Aldridge, NuStar Energy, Texas Ms. Carol Campagna, Shell OPUS, Carson