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e r <br /> V <br /> y <br /> 02 <br /> 06 <br /> + 0.4 <br /> D E <br /> °a osos • le <br /> °6 °: :2 <br /> +D.1 ` <br /> 111 0.3 <br /> DI• e°3 oD <br /> / IEr <br /> Q. EER POH COnCEMMTON <br /> —in— ME EQM.nK=D M_EMM <br /> EnpyryssxED.ERE MEERRED) - <br /> ' CCMCUII MEMX-OSmpL <br /> -:. yu,Figure.3 Fedgous--iron in ground water, Patrick AFB, Florida.` <br /> downgradient in the plume. BTEX concen- BTEX biodegraded. Between points B and <br /> trations are listed in Table 2. Methane pro- C the relative decrease in TMB had a re- <br /> duced from BTEX and TMB = (measured duction rate similar to BTEX. Therefore, we <br /> BTEX + TMB) x (0.78). Ground water isop- chose not to use TMB as a surrogate tracer <br /> leth maps for BTEX, dissolved oxygen, fer- and concluded that BTEX/TMB ratios did <br /> rous iron and methane are shown in Fig- not substantiate that intrinsic bioremedia- <br /> ures 1, 2, 3 and 4, respectively. Both meth- tion occurred. <br /> ane and trimethylbenzene (TMB) were se- <br /> lected as surrogate tracers. It was assumed GROUND WATER <br /> that all methane was both stable and pro- GEOCHEMISTRY <br /> duced from BTEX components (Table 3). <br /> For example, methane at point A as a The redox potential at the site ranged from <br /> tracer was 14000 + 6282 = 20282 µg/L. 54 to -293 mV. Low redox potential coin- <br /> Our usual approach has been to use cided with sampling points of high BTEX <br /> trimethylbenzene (TMB) as a recalcitrant contamination, low dissolved oxygen, some <br /> compound to correct BTEX concentrations ferrous iron, and elevated methane concen- <br /> for dispersion, dilution, sorption and volatili- trations. Water temperature was a warm <br /> zation. For some reason benzene was 26°C, which suggested that bacterial <br /> higher at point B than at point A, which in- growth rates could be high. Total alkalinity <br /> dicated that TMB was, under these site ranged from 148 to 520 mg/L, which would <br /> conditions, not entirely recalcitrant. How- suffice to buffer pH changes caused by <br /> ever, the TMB corrected toluene, ethylben- BTEX biooxidation reactions. pHs near 7 <br /> zene and xylenes decreased 30 to 60 per- were in the optimal range of BTEX- <br /> cent between point A and B, which con- degrading microbes. Nitrate was very low <br /> firmed that biodegradation occurred (Table so denitrification for BTEX removal was not <br /> 4). Even though some biodegradation of viable. Sulfate at levels up to 86 mg/L were <br /> TMB may have occurred, the corrected fairly high, but a relationship between sul- <br /> values would underestimate the percent fate and BTEX changes was not apparent. <br /> Proceedings of the 10th Annual Conference on Hazardous Waste Research 5 <br />