Arrays of Unpumped Wells for Plume Migration Control by Semi-Passive In Situ Remediation |
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| Authors: | Ryan D. Wilson Douglas M. Mackay John A. Cherry |
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| Affiliation: | Ryan D. Wilson;is a research associate and Ph.D. student in the Department of Earth Sciences at the University of Waterloo, Waterloo, Ontario. His research interests include field and modeling studies of semi-passive remediation technologies and the behavior of gaseous tracers. Wilson received his B.Sc. in geology from the University of Alberta in 1987, and his M.Sc. in earth sciences (hydrogeology) from the University of Waterloo in 1993. Douglas M. Mackay;is a research associate professor in the Department of Earth Sciences at the University of Waterloo, Waterloo, Ontario. His research focuses on field studies of transport and fate of organic chemicals in ground water and ground water decontamination technologies. Dr. Mackay received a B.S. in engineering and M.S. and Ph.D. degrees in civil engineering from Stanford University in 1970, 1973, and 1981, respectively. John A. Cherry;is professor and chair of contaminant hydrogeology in the Department of Earth Sciences at the University of Waterloo, where he is also an associate of Waterloo Centre for Groundwater Research. His research interests focus on the hydrogeology of clayey aquitards and various aspects of subsurface contaminant migration in aquitards and aquifers. He is a co-author of a textbook on hydrogeology, titled Groundwater, published by Prentice-Hall in 1979, and co-editor of a new reference book titled Dense Chlorinated Solvents and other DNAPLs in Groundwater, published by Waterloo Press in 1995. |
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| Abstract: | Arrays of unpumped wells can be used as discontinuous permeable walls in which each well serves both as a means to focus ground water flow into the well for treatment and as a container either for permeable reactive media which directly destroy dissolved ground water contaminants or for devices or materials which release amendments that support in situ degradation of contaminants within the aquifer downgradient of the wells. This paper addresses the use of wells for amendment delivery, recognizing the potential utility of amendments such as electron acceptors (e.g., oxygen nitrate), electron donors (primary substrates), and microbial nutrients for stimulating bioremediation, and the potential utility of oxidizers, reducers, etc., for controlled abiotic degradation. Depending on its rate and constraints, the remedial reaction may occur within the well and/or downgradient. For complete remediation of ground water passing through the well array, the total flux of amendment released must meet or exceed the total flux demand imposed by the plume. When there are constraints on the released concentration of amendment (relative to the demand), close spacing of the wells may be required. If the flux balance allows wider spacing, it is likely that limited downgradient spreading of the released amendment will then be the primary constraint on interwell spacing. Divergent flow from the wells, roughly two times the well diameter, provides the bulk of downgradient spreading and constrains maximum well spacing in the absence of significant lateral dispersion. Stronger lateral dispersion enhances the spreading of amendment, thereby increasing the lateral impact of each well, which allows for wider well spacing. |
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