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GEOMATRIX <br /> APPENDIX B <br /> ' INDICATOR PARAMETERS FOR INTRINSIC BIOREMEDIATION <br /> ' The processes of intrinsic bioremediation of dissolved petroleum hydrocarbons in the <br /> subsurface depend on the available terminal electron acceptors. The dominant terminal- <br /> electron accepting processes typically start from aerobic respiration, then to denitrification, <br /> ' metal (i.e., iron and manganese) reduction, sulfate reduction, and methanogenesis. Since the <br /> natural biodegradation rate of petroleum hydrocarbons in the subsurface is typically slow and <br /> ' difficult to measure, parameters of the various biodegradation processes in groundwater have <br /> been monitored and used to evaluate intrinsic bioremediation at the site. These indicator <br /> ' parameters are described below. <br /> • Dissolved Oxygen (DO): Microbes use oxygen as an electron acceptor in aerobic <br /> ' respiration processes. Lower DO concentrations within affected groundwater <br /> compared to adjacent areas indicate aerobic biodegradation activities. <br /> ' • Nitrate: Nitrate may be used as an alternative electron acceptor in anaerobic <br /> (anoxic) denitrification processes. In such conditions, nitrate may be reduced to <br /> nitrite and subsequently to nitrogen and/or nitrous oxide gases. Lower nitrate <br /> concentrations within affected groundwater compared to adjacent areas indicate <br /> 10 denitrification activities. <br /> ' • Dissolved Iron: Iron may be used as an electron acceptor instead of oxygen during <br /> anaerobic iron reduction processes. In these conditions, ferric iron(Fe 3+) can be <br /> reduced to the ferrous (Fe2+) form, which is more soluble in water. Higher <br /> ' dissolved iron concentrations within affected groundwater compared to adjacent <br /> areas indicate iron reduction activities. <br /> ' • Sulfate: Sulfate is another alternative electron acceptor in anaerobic sulfate <br /> reduction processes. Sulfate may be reduced to sulfide and subsequently to <br /> hydrogen sulfide gas in these conditions. Lower sulfate concentrations within <br /> ' affected groundwater compared to adjacent areas indicate sulfate reduction <br /> activities. <br /> ' • Oxidation-Reduction Potential (ORP): ORP of groundwater is a measure of <br /> electron activity; ORP values typically are positive under oxidizing conditions <br /> (losing electrons) and negative under reducing conditions (gaining electrons). <br /> Anaerobic biodegradation generally creates a reducing condition. <br /> • Alkalinity: Total alkalinity is a measure of hydroxides, carbonates, and <br /> bicarbonates. Microbial activities can increase alkalinity concentrations in <br /> 0 groundwater. <br /> I:\PRO]EC1V000sI2463\DOCUMENI\2463 12-02 tpt.dm B-1 <br />