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Mr. Jeff Baker -2 - 22 April2009 <br /> •Stockton Terminals Technic*mmittee <br /> Ozone degrades too quickly to be used to remediate pollution below 100 feet bgs. <br /> The Letter does not provide a timetable for reducing the frequency of biodegradation <br /> parameter data collection. <br /> Our comments are presented below. <br /> 1. We concur that the detection of 56 pg/L of TPHd near boring TS/MW-3D essentially <br /> delineates the vertiGaF extent of the plume. However, additional vertical investigation <br /> may be required if!he•TPHd detections persist or increase after remediation is <br /> implemented. <br /> 2. Without sampling data gaps specifically identified in the cross-section, it is doubtful <br /> that any competent interpretations can be judged to be more valid than the next. <br /> Based on the multitude of possible interpolations of groundwater-bearing unit <br /> continuity, the most critical concerns governing respective interpretations may be the <br /> potential financial and regulatory consequences. <br /> 3. We concur with STTC's proposed strategy for conducting the tracer test and <br /> subsequent installation of TS/MW-4D as well as the potential installation of TS/MW- <br /> 3DR, as described in the Letter. <br /> 4. The 13 pounds of oxygen falls slightly short of the 3:1. ratio rule oxygen to petroleum <br /> hydrocarbon rule but may be adequate where the mass has been overestimated. As <br /> stated in the Letter, however, the minimum ratio does not account for possible <br /> hydrocarbons sorbed to soil, other sources of biological oxygen demand, or <br /> locations where the hydrocarbon mass may be.as much as 29 pounds, as estimated <br /> by Stantec. In addition, studies show that as little as 2% of the total oxygen injected <br /> may dissolve into groundwater. Based on these uncertainties, STTC must be <br /> prepared for the possibility of having to significantly increase the mass of oxygen <br /> necessary to bring about hydrocarbon mass removal. <br /> 5. Because uncertainties prevent STTC from including a finalized oxygen injection pilot <br /> test monitoring schedule in the Letter, STTC must provide a 30-day notice to Central <br /> Valley Water Board staff so that the changes may be assessed. STTC may not <br /> implement reductions in monitoring frequency without Central Valley Water Board <br /> concurrence. <br /> We concur with the 29 January 2009 Pilot Study Work Plan as modified by the Letter <br /> and the comments in this letter. By 1 May 2009, please submit an implementation <br /> schedule for the pilot study. If you have any questions regarding this letter, you may <br /> contact me at (91 464-4811 or by email at betaylor@waterboards.ca.gov. <br /> BRIA T LOR, P.G. <br /> Engi ring Geologist <br /> cc list on Page 3 <br />