ARCHIVED REPORTS_XR0002476 - Laserfiche WebLink

Home Browse Search

CLEARWATEX G R o u P Enwronmentai Servicrs biodegradation processes are occurring within the contaminant plume in the upper water bearing zone Dissolved Oxyyseen Distribution Dissolved oxygen concentrations ranged from 4 98 mg/L (MW-1) to 11 32 mg/L (MW-3) in field, down-well measurements, and 3 60 mg/L (MW-8) to 5 00 mg/L (MW-1) in samples tested at the laboratory 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 lowered DO concentrations and the center of the dissolved TPHg plume, thus suggesting that aerobic biodegradation processes within the core of the plume are already occurring 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 too The spatial correlation between low DO and elevated contaminant concentrations at the plume core is typical of many sites with older fuel releases (i a >5 years), where intrinsic bioremediation has been confirmed Dr Randal von Wedel, biochemist for CytoCulture laboratories in Point Richmond, CA recently compared the historical MNA data for Clearwater and hypothesized to the variability of the MNA 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 " Appendix D provides the full text of Dr Wedel's findings Reduction-Oxidation Potential Distribution Reduction-oxidation potential data ranges from 43 6 millivolts (MW-5B) to 393 millivolts (MW- 4), 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 Anal3qical 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 ZB178C/3Q03 Monitoring Rpt 8 October 14,2003