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2.2.7.2 Nitrate <br /> After dissolved oxygen has been depleted in the microbiological treatment zone,nitrate maybe used as an <br /> electron acceptor for anaerobic biodegradation via denitrification. Nitrates were either not detected or <br /> detected at low concentrations. The low concentrations suggest that denitrification will not bean important <br /> ` biodegradation process for fuel hydrocarbons. <br /> 2.2.7.3 Ferrous Iron <br /> Conversion offerriciron to ferrous iron results in dissolved iron concentrations.Under reducing conditions, <br /> ferrous iron(Fe')occurs. Under oxidizing conditions,ferric iron(Fe+3)dominates. Ferric iron,although <br /> ` relatively insoluble, forms complexes with other chemicals or with suspended material. <br /> Ferrous iron concentrations ranged from 0.2 to 2.5 mg/L. The highest iron concentration was detected in <br /> the source well MW-2A,which was screened across contaminated soil. Iron is an electron acceptor for <br /> a uaerobicbiodegradation.Iron is elevated in well MW-2A,suggesting that biodegradation ofhydrocarbons <br /> 6. by iron reduction is occurring. <br /> 2.2.7.4 Sulfate <br /> Sulfate concentrations ranged from 2.3 to 91 mg/L. The lowest sulfate concentration was detected in the <br /> source well MW-2A. Sulfate is another potential electron acceptor that may be used for anaerobic <br /> ` <br /> biodegradation ofpetroleum hydrocarbons. The association ofelevated BTEX compounds with depleted <br /> sulfate concentrations is a strong indication that anaerobic biodegradation of BTEX compounds through <br /> L sulfanogenesis is occurring. <br /> 2.2.7.5 Methane <br /> During methanogenesis,an anaerobic biodegradation process,carbon dioxide is used as an electron <br /> acceptor and methane is produced. The presence of methane in the groundwater plume relative to <br /> ` background is indicative of strongly reducing conditions. Because methane is not present in fuel,the <br /> presence ofinethane in groundwater in contact with fuels is indicative ofmicrobial degradation of fuel <br /> hydrocarbons. <br /> Methane concentrations ranged from 0.032 mg/L to 0.38 mg/L. The highest methane concentration was <br /> detected in the source well MW-2A,which also had elevated BTEX concentrations. This is a strong <br /> indication that anaerobic biodegradation ofthe BTEX compounds is occurring at the site through microbial <br /> bioremediation. <br /> r <br /> 6 <br />