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CLEARWATER <br /> C R O U P <br /> • Environmental Services <br /> Results of microbial enumeration indicate the existence of an indigenous heterotrophic <br /> community in the saturated zone beneath the site (Table 2) The total aerobic heterotrophs to <br /> hydrocarbon degraders ratios range from 1 5 1 (MW-8) to 4 1 (MW-1) with larger populations of <br /> aerobic hydrocarbon degraders present in samples from the plume perimeter wells and depleted <br /> populations at the plume core This supports the argument that ongoing aerobic bioremediation <br /> is occurring at the plume fringe Populations of total anaerobic heterotrophs versus hydrocarbon <br /> degrading heterotrophs are present at a 25 2 ratio in MW-5B This combined with the electron <br /> receptor concentration analytical data and lowered DO concentrations indicate that anaerobic <br /> bioremediation processes are prevalent at the plume's center <br /> Concentrations of ammonia, which range from 0 90 to 2 40 mg/L (Table 2), are sufficient <br /> concentrations to indicate biodegradation conditions do indeed exist (i a iron reduction, sulfate <br /> reduction, and methanogenesis) <br /> Discussion <br /> Most MNA parameters and indicators appear favorable for bioremediation It should be noted <br /> that field measurements of DO, Eh, pH and conductivity were collected after the wells were <br /> purged and sampled so values obtained would reflect aquifer conditions surrounding the sample <br /> point While heterotrophic populations indicate that favorable conditions exist for aerobic <br /> hydrocarbon degradation at the plume edges, the conditions seem to favor the slower anaerobic <br /> processes at the core of the plume <br /> SUMMARY AND CONCLUSIONS <br /> Results from this quarterly monitoring event appear to confirm results reported from previous <br /> groundwater monitoring activities, that the contaminant plume is stable and delineated <br /> Contaminant concentrations appear to be highest in the in the area of monitoring well MW-5B <br /> PROJECT STATUS AND RECOMMENDATIONS <br /> Clearwater recommends continuation of groundwater monitoring for MNA parameters in wells <br /> MW-1, MW-4, MW-5B, and MW-8 for two more quarters, and for contaminant concentration in <br /> wells MW-1 through MW-8 to confirm results reported herein and to determine contaminant <br /> concentration and distribution trends over the near future <br /> ZB178C/2Q03 Monitoring Rpt 9 September 15,2003 <br />