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Mr.Michael J.Infurna,Jr.—San Joaquin County Public Health Services—Environmental Health Division <br /> November 7,2002 <br /> GR has presented no documentation in the various CAPS or quarterly monitoring <br /> reports that dissolved oxygen concentrations increased as a result of the short-term <br /> operation of the DPE unit. <br /> Dissolve oxygen (DO) measurements were not collected during the previous Dual Phase <br /> Extraction (DPE) event at the site. However, DO concentrations can increase as a result <br /> of a DPE event. During a typical DPE event, groundwater extraction forms a cone of <br /> depression while the vapor extraction (VE) draws vapors/air through the formerly <br /> saturated, now exposed medium. The oxygen levels in the area of impact are typically <br /> low due to aerobic activity in the vadose and capillary fringe zones. By replacing the <br /> pore air containing depleted oxygen levels with new air containing higher levels of <br /> oxygen, aerobic activity can be enhanced, with a continuance of biodegradation. <br /> Dissolved oxygen levels in groundwater are likely increased through the same process. <br /> During the groundwater extraction activities, aquifer material is exposed to the effects of <br /> the VE process. Introduction of oxygen rich air to the exposed aquifer medium does <br /> increase the available oxygen and results in an increase in DO concentrations in that area <br /> influenced by the dual-phase extraction. <br /> Starting with the quarterly monitoring and sampling event scheduled for November, <br /> 2002, GR will collect dissolved oxygen measurements in monitoring wells MW-3, MW-6 <br /> and MW-7. In addition, GR will also collect specific bio-parameter groundwater samples <br /> in attempt to support GR's hypothesize regarding the degradation of MtBE to TBA <br /> observed at the site. <br /> There has been no presentation of data indicating that biodegradation of any gasoline <br /> components has occurred on the site or that site conditions are suitable for selective, <br /> biodegrading bacteria to propagate. <br /> Starting with the quarterly monitoring and sampling event scheduled for November, <br /> 2002, GR will collect bioparameter measurements in monitoring wells MW-3,MW-6 and <br /> MW-7. Bioparameter measurements will include oxidation-reduction potential, sulfate, <br /> nitrate, iron and dissolved oxygen. GR will review the bioparameter data and prepare our <br /> evaluation of the results. Bioparameter data evaluation will be included in subsequent <br /> quarterly summary reports. <br /> The shift from high MtBE concentrations to high TBA concentrations was abrupt and <br /> indicates a significant composition change that permeated the local subsurface at a <br /> rate that intuitively appears to be more rapid than normal groundwater velocity, <br /> diffusion rates of dissolved oxygen, and initiation and completion of a phase of <br /> biological processes that hitherto appeared to have been dormant. <br /> It is unfortunate that DO and other bio-parameters were not taken in conjunction with the <br /> recent DPE event in order to help document any mass transfer from MtBE to TBA. The <br /> DPE event artificially accelerated the movement of groundwater (velocity) and potential <br /> diffusion rates of oxygen above those considered normal. The increase of oxygen very <br /> well could have accelerated the biological process that was considered dormant according <br /> to EHD. Therefore, the degradation process likely continued while sufficient oxygen was <br /> available (resulting from the DPE), and may have slowed significantly when the oxygen <br /> levels were depleted (post DPE) by the same degradation process. Hence, the <br /> 140245.08 2 <br />