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� i ULEARWATE.LV G R 0 U P aerobic biodegradation processes are hkelp ooeulrfing aiin Ahe outer limits of the plume too. The ;.sad r_ spatial correlation between reduced D4 and elevated contaminant concentrations at the plume core is typical of many sites with older fuel releases (i.e. >5 years), where intrinsic bioremediation has been confirmed. ''�3 I t Dr. Randal von Wedel, biochemist for CytoCulture laboratories in Point Richmond, CA recently compared the historical NINA data for Clearwater and hypothesized to the variability of the AWA data. "...intrinsic bioremediation appears to be most active in the down-gradient portion of the hydrocarbon plume to the southeast of the former UST tanks in the vicinity of MW-5B. -- 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." 2.3.6 Anaerobic Electron Receptor Analytical Results Analytical results from selected wells for anaerobic electron receptors suggest that denitrification, iron, and possibly sulfate reduction are occurring within the contaminant plume. i 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 i of the following anaerobic parameters: nitrate, ortho-phosphate, sulfate, and ferrous iron. Sulfate concentrations are depleted and ferrous iron is elevated within the plume at well MW-5B rye; compared to background well MW-4. This suggests that denitrification, sulfate reduction, and iron reduction have occurred, or are occurring within the core of the contaminant plume. 2.3.7 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. The total aerobic heterotrophs to hydrocarbon i ZBI78E iSOC System Installation/Start-u 8Nov qq� 004 229 Tewksbury Avenue ® Point Richmond,California 94801 ® Telephone: 510-307-9943 ® Fax: 510-232�$A <<:'=