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Mr. Jeff Baker - 5 - • 11 March 2009 Stockton Terminals TechnicalOmittee 5. We do not concur with the STTC's proposal to make installation of TS/MW-4D contingent on having to mobilize a drill rig to the site to install TS/MW-3DR. As discussed during our 10 December 2008 meeting, TS/MW-3D is screened about 35 feet shallower than it should have been. Therefore, installation of deeper remediation and/or monitoring wells to address and verify cleanup of the full vertical extent of the dissolved phase petroleum hydrocarbon plume in this vicinity is required. The installations must be performed regardless of whether the proposed helium-oxygen tracer test shows that there is sufficient communication between TS/MW-3D and TS/MW-2D. We are willing to delay installation of the deeper wells until after the tracer test, but are not willing to make the installations dependent on the outcome of the test. 6. Table 2 in the Assessment Report appears to contain a discrepancy regarding the dates on Which groundwater sampling occurred. The lower portion of the table shows that the TS/MW-3D grab groundwater sample was obtained from a depth of 140 feet bgs on 7 October 2008, and that deeper samples from 155 feet bgs and 160 feet bgs were obtained on 6 October. STTC needs to clarify whether this is a mistake and explain how deeper sampling was performed before shallower sampling. 7. We concur with the terms of the Revised Contingency Plan. The section on Page 3 entitled Contingency Plan Language makes implementation contingent on confirmation from a monitored natural attenuation (MNA) study that natural biodegradation will not occur at a rate sufficient to destroy remaining petroleum hydrocarbons and MTBE downgradient of the A and B zone ozone sparge systems. After unsuccessfully attempting to locate the results of this MNA-study, Regional Water Board contacted Stantec personnel who stated that the MNA study had already been conducted back in 2004 or 2005. An email correspondence in our file from about April 2004 discusses evaluating baseline data in anticipation of conducting the nitrate-sulfate injection, enhanced bioremediation pilot study at the BP property in 2005. Therefore, in the event that the Contingency Plan has to be implemented in the future, STTC's decision to proceed with the nitrate-sulfate injections serves as confirmation that the STTC and the Regional Water Board have reached a consensus that natural biodegradation is not occurring at a rate sufficient to destroy remaining petroleum hydrocarbons. 8. For the proposed TS/MW-2D oxygen-injection pilot study, we are concerned that there may be significant limitations to using bottled oxygen to deliver the oxygen to groundwater. This proposed methodology was employed at a nearby site last year where bi-weekly injections of 13-pound oxygen bottles were used to attempt to attain a DO concentration of 10 milligrams per liter (mg/L) to promote biodegradation. Results were mixed, even after equipping the injection wells with diffuser tips designed to deliver the oxygen directly to water bearing units considerably shallower than the D zone units that will be targeted at STTC. The STTC must supplement the description of the oxygen-injection pilot study to show (1) how they calculated that the oxygen will be delivered with sufficient