SITE INFORMATION AND CORRESPONDENCE

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Ms. Shelby Lathrop - 3 - 16 September 2009 Former Tosco Bulk Terminal l' 0013 Our comments are presented below. 1. Existing environmental literature sources cite an oxygen to hydrocarbon mass ratio of 3 to 1 as being adequate for the biodegradation of petroleum hydrocarbons. In the area of MW-2, bounded by injection wells IP-1 through IP-3 and IP-14, Central Valley Water Board staff estimate that during 2008 the average mass of TBA dissolved in groundwater was about 0.03 lbs. During 2008, ConocoPhillips injected about 720 lbs of oxygen in this area. Therefore, during 2008, the oxygen to TBA ratio was about 24,000 to 1. If we assume that only about 2% of the oxygen will actually dissolve into the aquifer', the oxygen to TBA mass ratio drops to 490 to 1 but still should be more than adequate to promote remediation. However, the groundwater monitoring data do not show any increases in TBA attenuation rates in MW-2. An evaluation of the pilot study data is needed to determine whether the elevated TPHd and TBA and the continued low DO concentrations can be attributed to unanticipated additional contaminant mass in the subsurface (such as the TBA and TPHd concentrations observed in the newly installed IP wells), IP well construction, or other contributing factors. 2. The Report does not specify the method used to sparge the oxygen below the groundwater table. On 2 September 2009, 1 spoke via telephone with Stantec's project manager to request clarification on this matter. He stated that the oxygen is not being injected below the water table. It is being pumped into the wells through a fitting on the well cap. As such, the oxygen is being applied to the water table in the well. It is not clear to us how the oxygen could be delivered to the base of the A zone, and to the B and C zones at depths that range from 20 to 60 feet below the water table, if it is not being injected below the water table. In addition, a minimum level of sustained pressure is required to deliver injected oxygen downward to the target aquifers. If oxygen is being delivered under the supply bottle pressure, the application pressure would decrease as the bottle is emptied. Table 1 of the 2008 Annual Report documents that DO concentrations were recorded at their highest levels in wells MW-2, MW-8, and MW-16 during May and June of 2008. It was during this period that ConocoPhillips had retrofitted IP-1 through IP-9 with diffuser tips to deliver oxygen near the bottom of each well. It is not clear when the diffuser tips were removed from these injection wells. Although not all these wells attained the target DO concentration of 10 mg/L, the increased concentrations indicated that a more targeted delivery may enhance system efficacy. Based on the current low DO levels, it may be appropriate for ConocoPhillips to begin sparging the oxygen below the water table at the base of depths of the A, B, and C zones at injection pressures that are sufficient to overcome the well and aquifer pressures. If necessary, flow-through packers could be deployed in the injection wells to isolate oxygen delivery to specific depths. Practical Design Calculations for Groundwater and Soil Remediation,Jeff Kuo,1999.