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Us. Shelby Lathrop - 3 - 30 July 2010 <br /> Former Tosco Bulk Terminal No. 3 <br /> wells ranged from 35 micrograms per liter (Ng/L) to 120 pg/L. In addition, methanol was <br /> detected at concentrations that exceed the WQO of 3,500 pg/L in these wells. <br /> CocncoPhillips has theorized that the methanol detections are anomalous. The risk-based <br /> modeling to determine appropriate site specific cleanup goals for Site CDCs must include <br /> methanol if the elevated concentrations are sustained, and should be based on data from <br /> these wells because they present the highest level of risk. <br /> 5. After reviewing ConocoPhillips' proposed criteria of five times the site specific risk-based <br /> cleanup goals to define rebound compliance levels, we have determined that the statistical <br /> methodologies sets forth by the California Code of Regulations (CCR) Title 27, Section <br /> 20415 (e) (8) are more applicable for determining concentrations that are statistically <br /> significantly different from site specific cleanup goals. Therefore, ConocoPhillips must select <br /> one of the methods suggested in Section 20415 (e) (8), (A) through (E) to calculate baseline <br /> concentrations and rebound compliance levels for TBA, and methanol, if applicable using <br /> the historical concentrations for monitoring wells MW-2, MW-8, MW-11, MW-16 and MW- <br /> 22C. <br /> 6. We concur with the proposed contingency plan to resume oxygen injections and believe that <br /> it should be implemented after three consecutive statistically significantly quarterly <br /> exceedences of the calculated risk-based cleanup goals. <br /> Shortly after this letter is issued, Central Valley Water Board staff will contact Nustar and the <br /> Port of Stockton to determine whether they concur with ConocoPhillips' proposed strategy, as <br /> modified by the comments in this letter, and whether a meeting should be convened to <br /> determine if either (1) additional modifications are necessary or (2) the plan is unacceptable and <br /> a new strategy must be formulated. <br /> If you have any questions regarding this letter, you may contact me at (916) 464-4811 or <br /> betaylor@waterbo�,rds.ca.gov. <br /> BRIAN TALOR P.G. <br /> Engineering Geologist <br /> cc: Mr. Harlin Knoll, San Joaquin County Environmental Health Department, Stockton <br /> Mr. Richard Stiffler, City of Stockton — Department of Municipal Utilities, Stockton <br /> Ms. Debbie Callie, Port of Stockton, Stockton <br /> Mr. Mark O'Brien, Port of Stockton/ERSC, Alamo <br /> Mr. Jeff Kasper, Deputy Port Director, Environmental Planning & Facilities, Stockton <br /> Mr. Sean Coyle, Stantec, Rancho Cordova <br /> Mr. Joe Aldridge, NuStar Energy, Texas <br /> Ms. Carol Campagna, Shell OPUS, Carson <br />