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Mr. Shelby Lathrop - 3 - 3 April 2008 <br /> Former Tosco Bulk Terminal No. 1( <br /> thousands of pg/L in source area wells MW-14 and MW-8, have been significantly diminished <br /> in recent groundwater monitoring events. During baseline monitoring some of the highest <br /> concentrations of these CDCs were detected in MW-2 and MW-16. However, quarterly <br /> monitoring was not required for these wells during the fourth quarter. <br /> Our comments are provided below. <br /> 1. The Addendum proposed to discuss the progress of the oxygen injection system with <br /> Regional Water Board staff after 60 days, and to submit a progress report after three <br /> months of operation. The system has been operated for about three and a half months. <br /> Therefore, I contacted Mr. Sean Coyle of SECOR on 1 and 2 April 2008 to inquire about <br /> preparation of the three-month report and whether the groundwater monitoring data <br /> continue to indicate that additional oxygen injection points are necessary. Mr. Coyle <br /> returned my call on 2 April. After a discussion about the progress of the remedial activities, <br /> he stated that the three-month report would be submitted by 25 April 2008. <br /> 2. Arsenic detections at the Site varied from 59 pg/L in background well MW-10, to 170 pg/L <br /> in downgradient well MW-20. The similarity in site-wide concentrations indicate that the <br /> source of arsenic may not be anthropogenic. The high concentration of Fe (II) and the low <br /> heterotrophic plate counts indicate that the naturally-occurring arsenic may be due to <br /> abiotic iron reduction of Fe (III) to Fe (ll). Although the mechanism(s) for mobilizing arsenic <br /> in groundwater at the Site is presently unknown, we are concerned that oxidizing the <br /> groundwater may exacerbate this condition. Therefore, the groundwater analytical data <br /> should be closely monitored for increases in the arsenic concentrations. Increases that <br /> greatly exceed background concentrations will trigger discussions on whether termination <br /> of this technology is warranted. <br /> If you have any questions regarding this letter, you may contact me at (916) 464-4811 or <br /> betaylor@waterboards.ca ov. <br /> BRIAN TAYLOR P. <br /> ll� <br /> Engineering Geolo ist <br /> cc: Mr. Sean Coyle, SECOR International Incorporated, Rancho Cordova <br /> Mr. Harlin Knoll, San Joaquin County Environmental Health Department, Stockton <br /> Ms. Debbie Callie, Port of Stockton, Stockton <br /> Mr. Mark O'Brien, Port of Stockton/ERSC, Alamo <br /> Mr. Richard Stiffler, City of Stockton — Department of Municipal Utilities, Stockton <br /> Mr. Jeff Kasper, Deputy Port Director, Environmental Planning & Facilities, Stockton <br /> Ms. Carol Campagna, Shell OPUS, Carson <br /> Mr. Joe Aldridge, NuStar Energy, Texas <br />