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CLEARWATER ' G R O U P Ewvironmentef Services ' of the hydrocarbon plume to the southeast of the former UST tanks in the vicinity of MW-5B Y p Y ' The site may be consuming available nutrient levels faster than the normal recycling rate " Introducing " dilute concentrations of ammonia and phosphate solutions my help to rectify the ' nutrient depletion in the most active bioremediation zones Increasing dissolved oxygen concentrations in MW-1 and MW-5 would further enhance the aerobic biodegradation of residual ' petroleum hydrocarbons in these zones " Appendix C provides the full text of Dr von Wedel's findings 1 2 3 7 Anaerobic Electron Receptor Analytical Results ' Analytical results from selected wells for anaerobic electron receptors suggest that denitnfication, iron, and possibly sulfate reduction are occurring within the contaminant plume ' Three wells, two generally upgradient of the plume (MW-4 and MW-1), one in the center of the plume (MW-513), and one downgradient of the plume (MW-8) were sampled for concentrations of the following anaerobic parameters nitrate, ortho-phosphate, sulfate, and ferrous iron ' Analytical Results are summarized on Table 2 and the laboratory report and cham-of-custody form is included in Appendix B Sulfate concentrations are depleted and ferrous iron is elevated within the plume at well MW-513 ' compared to background well MW-4 This suggests that denitrification, sulfate and iron reduction are occurring at the center of the contaminant plume, despite the fact that Eh values ' appear to be slightly high to facilitate the sulfate reduction (Table 2) ' 2 3 8 Microbial Counts and Additional Bioattenuation Parameters Results of microbial enumeration indicate the existence of an indigenous heterotrophic ' community in the saturated zone beneath the site (Table 2) The total aerobic heterotrophs to hydrocarbon degraders ratios range from 3 1 (MW-5B) to 300 1 (MW-4) with larger populations ' of aerobic hydrocarbon degraders present in samples from the plume core wells and depleted populations at the plume perimeter This supports the argument that ongoing aerobic ZB178C RAP 12 May 18,2004 I