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CLEARWATER <br /> G R o u n <br /> Environmental Services <br /> biodegradation processes are occurring within the contaminant plume in the upper water bearing <br /> zone <br /> Dissolved Oxygen Distribution <br /> Dissolved oxygen concentrations ranged from 3 7 mg/L (MW-5B) to 4 2 mg/1L (MW-8) The <br /> distribution of DO was examined with respect to the distribution of the known TPHg in the upper <br /> water-beanng zone (Figure 5) There appears to be an areal correlation between lowered DO <br /> concentrations and the center of the dissolved TPHg plume, thus suggesting that aerobic <br /> biodegradation processes within the core of the plume are occurring Monitoring data suggest <br /> that the oxidation-reduction potential in the center of the plume appears to be at the low end of <br /> optimum range to support aerobic biodegradation The more-elevated DO readings at the fringe <br /> of the TPHg plume suggest that aerobic biodegradation processes are likely occurring in the <br /> outer limits of the plume too The spatial correlation between reduced DO and elevated <br /> contaminant concentrations at the plume core is typical of many sites with older fuel releases <br /> a (i e >5 years), where intrinsic bioremediation has been confirmed <br /> Dr Randal von Wedel, biochemist for CytoCulture laboratories in Point Richmond, CA recently <br /> compared the historical NINA data for Clearwater and hypothesized to the variability of the <br /> NINA data " intrinsic bioremediation appears to be most active in the down-gradient portion <br /> of the hydrocarbon plume to the southeast of the former UST tanks in the vicinity of MW-5B <br /> The site may be consuming available nutrient levels faster than the normal recycling rate " <br /> Introducing " dilute concentrations of ammonia and phosphate solutions my help to rectify the <br /> nutrient depletion in the most active bioremediation zones Increasing dissolved oxygen <br /> concentrations in MW-1 and MW-5 would further enhance the aerobic biodegradation of <br /> residual petroleum hydrocarbons in these zones " Appendix D provides the full text of Dr <br /> Wedel's findings <br /> Anaerobic Electron Receptor Analytical Results <br /> Analytical results from selected wells for anaerobic electron receptors suggest that <br /> denitrification, iron, and possibly sulfate reduction are occurring within the contaminant plume <br /> ZB178C/4Q03 Monitoring Rpt 11 January 29,2004 <br />