SITE INFORMATION AND CORRESPONDENCE

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Mr. Thomas Kosel - 3 - 25 July 2007 the plume has resulted in significant conversion of MTBE to TBA. In some cases the MTBE is non-detect (ND) at the downgradient edge of the plume, and vertical definition of MTBE may no longer be required. However, the MW-2 and MW-14 data show that significant concentrations of TBA remain in the source area. The TBA in monitoring well MW-18C exceeds the WQO of 12 pg/L and therefore is not vertically delineated. We concur that source area remediation is needed to prevent the further downward and downgradient migration of this contaminant. However, ConocoPhilips will also need to provide evidence that the full vertical extent of the TBA plume will be addressed by the proposed remedial technology. 2. The reduction of TPHg in monitoring wells MW-8 and MW-14 indicate that the hydrogen peroxide and ozone (HiPDX) pump and treat system was effective at addressing this contaminant. ConocoPhillips removed this system in August 2006 despite Regional Water Board staff comments citing non-concurrence with plans for system removal, as stated in our 28 March 2006 letter. This action is contrary the spirit of cooperation between responsible party (RP) and regulatory agency necessary for effective site management and oversight. This could result in enforcement action against ConocoPhilips. Since the COC concentrations at this Site are declining Regional Water Board staff will not recommend enforcement at this time but may do so in the future if it becomes necessary. As requested in our 21 July 2006 letter, baseline groundwater sampling will be conducted before the pilot test system becomes operational, reported in the report of system startup, and submitted to this office no more than four weeks after the system startup date. This suite of laboratory analyses will be repeated after 10 weeks and 26 weeks of system operation. System operation will be monitored on a weekly basis for the first four weeks and every two weeks for the remainder of the pilot test. According to the Proposed Schedule provided in the Annual Report, a Startup Report is due to be submitted two months following startup sampling and a Summary Report is proposed for submittal about eight months after baseline sampling. 3. Earthtech's 4 April 2006 Work Plan stated that a summary report will be prepared at the end of the pilot test activities. Earthtech plans on including data collected during the pilot test and providing conclusions regarding the effectiveness and recommendations for the final remedial alternative. We request the summary report include an analysis of the pilot study data to verify conclusions regarding system adequacy. The analysis should include (1) a stoichemetric analysis of biochemical oxygen demand (BOD) to verify that the quantity of oxygen supplied was sufficient to address naturally occurring organic matter as well as the oxidizable fuel hydrocarbons present in subsurface, (2) a radius of influence (ROI) analysis to confirm that the 12 injection wells and the 10-foot ROI resulted in an adequate distribution of dissolved oxygen in the plume, and (3) a comparison of MTBE to TBA ratios before and after initiation of the pilot study to establish that observed degradation resulted from application of the injected oxygen. 4. The monitoring frequency revisions, proposed for MRP No. R5-2004-0824 in the First QMR, contradict the baseline, six week, and monthly monitoring frequency proposed for the Pilot Study wells. While there is an abundance of groundwater data at this Site, it is more appropriate to postpone MRP revisions at least until the data from the pilot study can be evaluated before applicable monitoring frequency revisions can be identified.