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dt;artd at the wesrdets'of the"plume where'biociegiada- ACknOwledgrrlen#s
<br /> W.. ;a
<br /> tion ltas occurred: ;ower rroh eont?entrations occur in the 'l!'Fie research de'scrrbed in thinartrcle Vias supported in
<br /> midtlle'and bottom Oi`the plume where benzene is slowerto ;part by.the American Petroleum Instrtute ur;der Grant No.
<br /> degf$& .oxygen tnixes rvitli'the plume, BTEX may"be - GW-23A-04Q(F-38;We;would also.Aike,6 tftarik the North
<br /> biotransforrtt�pcl t+i pijitially oxidized intermediates"which 'Caroli ta:Division of Environmental Management for their
<br /> Are thiiiranaerobi y` e rgded via iron(eduction.Labors- ,assistance in mQmtorsng well installation and.Admah Leiner .
<br /> 4s
<br /> tory microcosm stirdres are beingconducted to resolve this and Heide Richardson for providiiig access to their prop
<br /> questaon arty:Special thanks to Colleen McCloskey for her work in
<br /> ;r, j' r rcollection and;analyats:of the soil gores..
<br /> CQnclUg.6!1S' 1
<br /> A-deiailed field rnyestagation has been completed at a. .References '
<br /> „ gasoLne-cordtamifisted'°agi*r hear Rocky Point,NC.Dis= Alvarez,P.J.J.and T.:141'Vogel 1991 Substrate interactions of
<br /> solved beitzenet�toldeho',elthylbenzene;`and xylene isomers benzene;Loluene,:40 para-xylene during microbial degra-
<br /> F. dation b ure cultures and mixed culture aquifer slurries. .
<br /> are being:contttiuously released from residual nonaqueous Y P
<br /> hese asoltrle tra ed beneath�the' ater table near the Appl.Environ:Microbiol,v:57;pp:2981-2985.
<br />' p B pp American Public Health;Association,:1992. Standard:Methods-
<br /> ongiTisd USTs'Tlie dissolved;B'T£X plume is biodegrading. for the.Examin on.of Water and Wisfe'Water. l8th ed:
<br /> Evidence for intrinsic biorer ediatiori.includes(1}depletiafi APHA-AWWA pF,Washington,:DC.
<br /> 4°of dissolved oit rt,-,#titrate and sulfate within'the$TEX Atlas, R K. 1986. MIG�robiology. f=undamentals and Applica-
<br /> (2).production of dissolved iron(Fe+z)and carbon tions.2nd ed..Nfh Milled Publishing tro.,New York.
<br /> ,. .- Barker,J.F.,-.G.C.Patrick,and D.Major.19$7.Natural attenua-
<br /> dioxr`de,'and(3)preferentral,removal of certain B'I'EX com tion of.aromatic':lydrocarbons in a shallow sand aquifer.
<br /> gonents: Toluene and =Xyl ene`decline-most rapidly with round Water Manrtoring Reyiew Vu ".pp.64-71.
<br /> _ distant e;#r'Ortc the source:'followed by.m.,'p=rtjileiie, and B�ckery TvI..1992 Iron reduction to aiaspllt ti�ontaminated aqui-
<br /> -benzene:':fltblbenurfe- appears'to degrade -very slowly ter Fontarning;gltrcotrite M$.'theses,.NC.State Univ.,
<br /> codec the`anaerobie:conditi&nsi present at the plume center.
<br /> Rat ' IYC:
<br /> 11ItYmtoring'of`"iissolved`carbon dioxide and the ver- Beller,H.R.,'
<br /> .,D.Grbit�Galio,and M.Reinhard,.,1992.Microbial
<br /> degradation of toluene under:sulfate-reducing conditions
<br /> iotti electrotf acceptors.provides a very useful tool for assess- and theinfluence of iron on the'process Appl..Environ.
<br /> ing the extent of biodegradation. Results from such moni- Microbiol 'v.58,pp:786-793.
<br /> toning can- o-used to identify'factors that-may control the . Berry;,D. F.,*.J..Fta'ncb, andJ-M. Bollag: 1987.`Microbial
<br /> rate of biodegradation in different portions of the dissolved metabolism of hairrocyclic and,3teterocyc3ie,aromaticcom-
<br /> hydrocarbon plume. Carbon dioxide.is'ari indicator of bac- pounds under anaerobic colsdit. i Microbiol.Rev.y.51,
<br /> Yp•43-59
<br /> erial respiration and,-,therefore,of biodegradation that has Borden, R. C .199x: Nafriral bioremediation bf hydrocarbon-
<br /> already occurred. However,monitoring for dissolved CO2 contamrnated,grraund water.In:Handbook of Bioremedia-
<br /> as a sole indicator of biodegradation may not be appro- tion.CRC Press,Boca Raton,-FL.pp. 177-199.
<br /> priate in aquifers that contain carbonate minerals. . Borden,R.C.,P.B.Bedient;M.D:.Lee,C. H.Ward,and"J..T.
<br /> Intrinsic bioremediation appears to occur in.three distinct Wilson.1986:Transport of dissolved hydrocarbons influ-
<br /> enced by reae'r'ation"and oxygen limited biodegradation:2,
<br /> zones at the Rocky Point"site:Immediately upgradient and Field application.,Water Resour.Res.v.22,pp. 1983-1990.
<br /> downgradient of the source where oxygen,nitrate,and sul- Chiang,C.Y.,J.P.Salanitro,E.Y.Chai,J.D.Colthart,and C.L.
<br /> fate are present, biodegradation is rapid. Once these elec- Klein. 1989.Aerobic biodegradation of benzene,toluene,
<br /> tron acceptors are consumed, the rate of biodegradation and xylene in a sandy aquifer—data analysis and computer
<br /> slows considerably. Ferric iron is present in the aquifer modeling:Ground Water.v.27,pp.823-834.,. .
<br /> Domenico,P.A.and F.W.Schwartz.1990.Physical and Chemi-
<br /> diments as an'."iron-rich,. rnixed-valence, clay'
<br /> mineral' gy.John Wiley and Sons,Inc.,New York.
<br /> -se Y cal Hydrogeolo ,
<br /> "(glauconite), but this iron does'not appear to be'readily 824 pp.
<br /> Available for"use by the aquifer microorganisms. At the Edwards,E.A.,L.LWills,M. Reinhard,and D:Grbtl:-Galib.
<br /> downgradient end.of the plume, some methanogenic bio- 1992. Anaerobic degradation of toluene and xylene by
<br /> degradation is occurring.The change from iron-reducing to aquifer microorganisms under sulfate-reducing conditions.
<br /> Appl.Environ.Microbiol.v.58,pp.794-800.
<br /> .. methanogenic conditions appears to be controlled by an Ehrlich,G.G.,R.A.Schroeder,and P.Martin. 1985.Microbial
<br /> increase in the carbonate content of the aquifer material in populations in a" fuel-contaminated shallow aquifer at
<br /> this portion of the site. Tustin,California U.S.Geological Survey in cooperation
<br /> ' The rate and extent of intrinsic bioremediation appears with the U.S.Marine Corps,Sacramento,CA.U.S.Geol.
<br /> to be limited by.the type and;quantity of electron acceptors. Surv.Open File Rep.85-335.
<br /> Gomez, C. I993. Characterization of a dissolved hydrocarbon.
<br /> Certain hydrocarbons(toluene, o-xylene, and possibly m-, plume.M.S.thesis,NC State Univ.,Raleigh,NC_
<br /> ,'p'-xylene)are being degraded under anaerobic conditions in Grbi6-Gali6,D.and T M.Vogel.1987.Transformation of toluene
<br /> the plume censer.This degradation reduces the total biolog- and benzene by mixed methanogenic cultures. Appl.
<br /> ical oxygen demand allowing greater aerobic biodegrade- Environ.Microbiol.v.53,pp.254-260.
<br /> Hadley,P.W.and R, Armstrong. 1991."Where's the benzene?"
<br /> tion of the more recalcitrant compounds (benzene and Examining California ground-water quality surveys.
<br /> ethylbenzene).Transverse spreading of the.plume is limited Ground Water.v.29,pp.3540.
<br /> *aerobic biodegradation of the dissolved hydrocarbons at Hult,M.F. 1991.Overview of research on contamination of the
<br /> the plume edges. subsurface by crude oil at the Bemidji, Minnesota,toxic
<br /> 188
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