SITE INFORMATION AND CORRESPONDENCE

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Ms. Shelby Lathrop -2 - 16 September 2009 Former Tosco Bulk Terminal - 10013 - ConocoPhillips began implementing a mobile oxygen injection pilot study at the Site in December 2007 to clean up the groundwater pollution. At the time the Second QMR was prepared, ConocoPhillips had conducted a total of 12 oxygen injection events twice monthly. The objective is to attain a dissolved oxygen (DO) concentration of 10 micrograms per liter (mg/L) to attenuate TPHd and TBA in source area and downgradient wells. However, the groundwater monitoring data tabulated in Appendix B of the Second QMR do not indicate that the oxygen injection pilot study has been effective in reducing COC concentrations. To address the recalcitrant TPHd and TBA concentrations ConocoPhillips increased the volume of oxygen injections from 150 ft3 to 300 ft3 per bi-weekly event in May 2008. However, TPHd in MW-2 continues to show an increasing concentration trend. The TBA concentration in MW-2 shows an overall decreasing trend. However, this trend began in 2004. In downgradient wells MW-16 through MW-21 B, however, TBA has remained relatively stable and continues to exceed the water quality objective (WQO) of 12 pg/L. Based on these results ConocoPhillips proposed additional modifications in the 18 November 2008 Workplan for Continuation of Mobile Oxygen Injection and Installation of Additional Oxygen Injection Points (Work Plan). The Work Plan proposed to utilize existing wells MW-22C and P6 as additional oxygen injection points. The Work Plan also proposed to install five onsite injection points (IP-13 through IP-17) and destroy nine improperly constructed injection points (IP-1 through IP-9). In the Report, ConocoPhillips states that proposed well installations and abandonments were performed between 9 and 14 July 2009. Due to access restrictions at the Site, however, IP-13 could not be installed, the proposed modifications to P6 could not be performed, and IP-2 and IP-3 could not be abandoned. ConocoPhillips continues to correspond with the Port of Stockton to resolve the access issues and complete the proposed work. Groundwater samples from IP-14 through IP-17 contained TPHd, TBA, and minor concentrations of MTBE and di-isoprpryl ether. IP-14 contained the maximum concentrations of TPHd and TBP., which were 370 ug/L and 560 ug/L, respectively. On 27 and 28 July, 13 pounds (Ibs) of bottled oxygen were injected into IP-11, IP-14 through IP-17, and MW-22 over a one hour period. ConocoPhillips reports that the injection event caused DO concentrations in nearby monitoring wells to increase from an overall average of 1 .26 mg/L to 1.71 mg/L. ConocoPhillips estimates that about 2,964 pounds of oxygen have been injected at the Site. The 30 January 2009 Response to RWQCB-CVR December 31, 2008 Letter, Addendum to November 18, 2008 Work Plan recommended performing the pilot study until the fourth quarter of 2009, after which a final remedial action plan (RAP) would be submitted to the Central Valley Water Board. In the Report, however, ConocoPhillips proposes to extend the pilot study until the first quarter of 2010 before preparing the RAP.