SITE INFORMATION AND CORRESPONDENCE

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Ms. Shelby Lathrop -2 - 31 December 2008 r Former Tosco Bulk Terminal No. 10013 well MW-20 and to convert monitoring well MW-22C into an injection point using downhole inflatable packers. Oxygen injection events are scheduled to be completed twice a month by injecting 300 ft3 of bottled oxygen per event over a two-day period in each of the nine injection points. DO concentration monitoring will be conducted in 12 monitoring wells, including eight A zone wells (MW-2, MW-8, MW-14, MW-16, MW-20, and P-1 through P-3), three B zone wells (MW-17B, P-4, and P-5) and one C zone well (MW-19C) prior to and immediately following each injection event. The Work Plan does not propose petroleum hydrocarbon monitoring specifically for the oxygen injections. ConocoPhillips conducts groundwater monitoring at the Site pursuant to Monitoring and Reporting Program (MRP) No. R5-2004-0824. The 30 October 2008 Quarterly Status Summary Report, Third Quarter 2008 describes groundwater monitoring activities performed in August 2008. The groundwater flow directions in the A, B, and C zones were to the southwest. The gradients ranged from 0.001 feet per foot (ft/ft) in the C zone to 0.004 ft/ft in the A zone. During the second quarter, TPHg was non-detect (ND) in all but one well, MW-3, which contained 96 micrograms per liter (pg/L) of TPHg. The highest concentration of TPHd was in MW-17B at 190 pg/L. MW-2 contained the highest concentration of TBA at 420 pg/L, and MW- 17B had the highest concentration of MTBE at 18 pg/L. Our comments are presented below. 1. The Work Plan does not propose a specific length of time over which this phase of the pilot study will be performed or whether DO injection has been selected as the groundwater remedy for this Site. If the proposed work is a continuation of the pilot study that began in December 2007, a termination date has to be established. If ConocoPhillips has selected oxygen injection as a the groundwater remedy for this site, then the technology must be clearly identified as such in a Remedial Action Plan, so that the Regional Water Board can provide concurrence, if appropriate. 2. The A and B zone injection points that the Work Plan recommends installing near MW-20 are positioned cross-gradient of this monitoring well. It seems that, an upgradient position would be more advantageous for optimizing the delivery of oxygen to this well. ConocoPhillips needs to provide the rationale behind selecting the cross-gradient location for these injection points. 3. During pilot testing, monitoring results obtained from MW-17B showed that DO levels did not increase, DIPE and TBA concentrations increased slightly, and TPHd levels were ND. Third quarter monitoring results, however, show that the TPHd concentration in this well increased to 190 pg/L. In the 25 July 2008 Oxygen Injection Pilot Study Report (Report), ConocoPhillips recommended installing an oxygen injection well in the vicinity of MW-17B to address the deficient DO and elevated DIPE and TBA concentrations. However, that recommendation is absent from the Work Plan. ConocoPhillips needs to explain why an injection point in the vicinity of MW-17B is no longer being considered.