ARCHIVED REPORTS_XR0002476 - Laserfiche WebLink

Home Browse Search

CLEARWATER G R o u r • Environmen(RI Servrces Results are summarized on Table 2 and the laboratory report and cham-of-custody form is included in Appendix C Sulfate concentrations are depleted and ferrous iron is elevated within the plume at well MW-513 compared to background well MW-4 (Figure 7) 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) Microbial Counts and Additional Bioattenuatmon 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 4 1 (MW-8) to 25 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 bioremediation is occurring at the plume core Results of the microbial enumeration study indicate the ratio between total heterotrophs and hydrocarbon degraders had reversed in one sample analyzed for this quarter compared to last quarter According to CytoCulture, a microbiological laboratory, this happens in approximately 10% of the time Some possible explanations to this occurrence might be 1) The hydrocarbon degrading bacterial population had preexisted before testing 2) A prior spill had provided the hydrocarbon degraders enough fuel for consumption to create an indigenous heterotrophic community in the saturated zone beneath the site, or 3) A prior exposure to a carbon source had occurred . prior to testing, for example, a sewage spill or an agriculture overflow Populations of total anaerobic heterotrophs and anaerobic hydrocarbon degrading heterotrophs were not collected this quarter due to a communication problem with the laboratory With the electron receptor concentration analytical data and lowered DO concentrations indicate that anaerobic bioremediation processes are prevalent at the plume's center Concentrations of ammonia, which range from 0 60 to 12 mg/L (Table 2), are sufficient concentrations to indicate biodegradation conditions do indeed exist (m a iron reduction, sulfate reduction, and methanogenesms) Discussion Most MNA parameters and indicators appear favorable for bioremediation It should be noted that field measurements of DO, Eh, pH and conductivity were collected after the wells were purged and sampled so values obtained would reflect aquifer conditions surrounding the sample point While heterotrophic populations indicate that favorable conditions exist for aerobic hydrocarbon degradation at the plume edges, the conditions seem to favor the slower anaerobic processes at the core of the plume SUMMARY AND CONCLUSIONS Results from this quarterly monitoring event appear to confirm results reported from previous groundwater monitoring activities, that the contaminant plume is stable and delineated . Contaminant concentrations appear to be highest in the in the area of monitoring well MW-5B ZB178C/3Q03 Morutommg Rpt 9 October 14, 2003