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Channel flow and trichloroethylene treatment in a partly iron-filled fracture: Experimental and model results

Cai, Zuansi; Merly, Corrine; Thomson, Neil R.; Wilson, Ryan D.; Lerner, David N.

Authors

Corrine Merly

Neil R. Thomson

Ryan D. Wilson

David N. Lerner



Abstract

Technical developments have now made it possible to emplace granular zero-valent iron (Fe0) in fractured media to create a Fe0 fracture reactive barrier (Fe0 FRB) for the treatment of contaminated groundwater. To evaluate this concept, we conducted a laboratory experiment in which trichloroethylene (TCE) contaminated water was flushed through a single uniform fracture created between two sandstone blocks. This fracture was partly filled with what was intended to be a uniform thickness of iron. Partial treatment of TCE by iron demonstrated that the concept of a Fe0 FRB is practical, but was less than anticipated for an iron layer of uniform thickness. When the experiment was disassembled, evidence of discrete channelised flow was noted and attributed to imperfect placement of the iron. To evaluate the effect of the channel flow, an explicit Channel Model was developed that simplifies this complex flow regime into a conceptualised set of uniform and parallel channels. The mathematical representation of this conceptualisation directly accounts for (i) flow channels and immobile fluid arising from the non-uniform iron placement, (ii) mass transfer from the open fracture to iron and immobile fluid regions, and (iii) degradation in the iron regions. A favourable comparison between laboratory data and the results from the developed mathematical model suggests that the model is capable of representing TCE degradation in fractures with non-uniform iron placement. In order to apply this Channel Model concept to a Fe0 FRB system, a simplified, or implicit, Lumped Channel Model was developed where the physical and chemical processes in the iron layer and immobile fluid regions are captured by a first-order lumped rate parameter. The performance of this Lumped Channel Model was compared to laboratory data, and benchmarked against the Channel Model. The advantages of the Lumped Channel Model are that the degradation of TCE in the system is represented by a first-order parameter that can be used directly in readily available numerical simulators.

Citation

Cai, Z., Merly, C., Thomson, N. R., Wilson, R. D., & Lerner, D. N. (2007). Channel flow and trichloroethylene treatment in a partly iron-filled fracture: Experimental and model results. Journal of Contaminant Hydrology, 93(1-4), 284-303. https://doi.org/10.1016/j.jconhyd.2007.04.001

Journal Article Type Article
Acceptance Date Apr 1, 2007
Online Publication Date Apr 19, 2007
Publication Date 2007-08
Deposit Date Apr 24, 2020
Journal Journal of Contaminant Hydrology
Print ISSN 0169-7722
Publisher Elsevier
Peer Reviewed Peer Reviewed
Volume 93
Issue 1-4
Pages 284-303
DOI https://doi.org/10.1016/j.jconhyd.2007.04.001
Keywords TCE treatment, Channel flow, Zero-valent iron, Fracture, Lumped parameter, Fracture reactive barrier, Modelling
Public URL http://researchrepository.napier.ac.uk/Output/2655198