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CLEARWA" TER <br /> G R O U P <br /> Enrofry Hiner tri Servecea <br />' bioremediation is occurring at the PlUrne core The total anaerobic heterotrophs to hydrocarbon <br />' degraders ratios range from 500 3 (MW-4) to 3 2 (MW-8) Electron receptor concentration <br /> analytical data and lowered DO concentrations indicate that anaerobic bioremediation processes <br />' are prevalent at the plume's center <br />' Concentrations of ammonia, which range from 0 9 to 14 mg/L (Table 2), are sufficient to <br /> indicate biodegradation conditions do indeed exist (i e iron reduction, sulfate reduction, and <br />' methanogenesis) <br />' 2 3 9 Discussion <br /> Most MNA parameters and indicators appear favorable for bioremediation It should be noted <br />' that field measurements of DO, pH and conductivity were collected after the wells were purged <br /> and sampled so values obtained would reflect aquifer conditions surrounding the sample point <br /> While heterotrophic populations indicate that favorable conditions exist for aerobic hydrocarbon <br /> degradation at the plume edges, the conditions seem to favor the slower anaerobic processes at <br />' the core of the plume Results from this quarterly monitoring event appear to confirm results <br /> reported from previous groundwater monitoring activities, that the contaminant plume is stable <br />' 'and delineated) Contaminant concentrations appear to be highest in the in the area of monitoring <br /> well-MW-5B <br /> 3.0 SUMMARY OF HYDROGEOLOGY AND CONTAMINATION <br /> I <br /> 3.1 Hydrogeology <br />' The site is underlain predominantly by sediments characterized by silts, clays and silt, clay and <br /> sand mixtures and discontinuous sand lenses Based on field observations and literature values, <br />' the average hydraulic conductivity of subsurface sediments is likely on the order of 10-3 cm/sec <br /> (Table 4 5, Fetter, C W "Applied Hydrogeology", 1988) <br /> Groundwater is present in unconfined conditions beneath the site Depth to water ranges from <br /> approximately 8 to 12 feet bgs annually The water table is historically at its highest elevation in <br /> 1 <br />' ZB171C RAP 13 May LS,2004 <br />