ARCHIVED REPORTS_XR0002477 - Laserfiche WebLink

Home Browse Search

br Y CLEAR-WATER G R o v P • Ersvrrommeniuf Services Dissolved Ox en Distribution Dissolved oxygen concentrations ranged from 2 55 mg/L (MW-4) to 6 87 mg/L (MW-7) in field, down-well measurements, and 2 6 mg/L (MW-8) to 5 9 mg1L (MW-4) in samples tested at the laboratory (these discrepancies are discussed below) The distribution of DO was examined with respect to the distribution of the known TPHg in the upper water bearing zone (Figure 5) There appears to be an areal correlation between lower DO concentrations and the center of the dissolved TPHg plume, thus suggesting that aerobic biodegradation processes within the core of the plume have already gone through an aerobic stage and exhausted DO in this location Monitoring data suggest that the reduction-oxidation potential in the center of the plume appears to be at the low end of optimum range to support aerobic biodegradation The more-elevated DO readings at the fringe of the TPHg plume suggest that aerobic biodegradation processes are likely occurring in the outer limits of the plume The spatial correlation between low DO and elevated contaminant concentrations at the plume core is typical of many sites with older fuel releases (1 a >5 years), where intnnsic bioremediation has been confirmed Reduction-Oxidation Potential Distribution Reduction-oxidation potential data ranges from 182 millivolts (MW-8) to 258 5 millivolts (MW- 2), and has a similar distribution with respect to the contaminant plume as DO This style of Eh distribution suggests that more reducing conditions are present within the center of the plume, corroborating the interpretation that aerobic biodegradation processes are likely occurring in this area Eh values at the site are too great to accommodate sulfate reduction Interpretations regarding anaerobic pathways are further examined using anaerobic electron receptor analytical data below 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 Three wells, two generally upgradient of the plume (MW-4 and MW-1), one in the center of the plume (MW-5B), and one downgradient of the plume (MW-8) were sampled for concentrations of the following anaerobic parameters nitrate, ortho-phosphate, sulfate, and ferrous iron The trends of these analyte concentrations through the plume are shown on Figure 7 Analytical Results are summarized on Table 2 and the laboratory report and chain-of-custody form is included in Appendix C Nitrate and sulfate are depleted and ferrous iron is elevated within the plume at well MW-5B 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 Bioattenuation Parameters ZB178C/2Q03 Morutonng Rpt 8 September 15, 2003