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How the Kd Approach Undermines Ground Water Cleanup

How the Kd Approach Undermines Ground Water Cleanup Environmental scientists have long appreciated that the distribution coefficient (the “Kd” or “constant Kd”) approach predicts the partitioning of heavy metals between sediment and ground water inaccurately; nonetheless, transport models applied to problems of environmental protection and ground water remediation almost invariably employ this technique. To examine the consequences of this practice, we consider transport in one dimension of Pb and other heavy metals through an aquifer containing hydrous ferric oxide, into which many heavy metals sorb strongly. We compare the predictions of models calculated using the Kd approach to those given by surface complexation theory, which is more realistic physically and chemically. The two modeling techniques give qualitatively differing results that lead to divergent cleanup Strategies. The results for surface complexation theory show that water flushing is ineffective at displacing Pb from the sorbing surface. The effluent from such treatment contains a persistent “tall” of small but significant levels of contamination. Subsurface zones of Pb contamination, furthermore, do not migrate rapidly or far in flowing ground water. These results stand in sharp contrast to the predictions of models constructed using the Kd approach, yet are consistent with experience in the laboratory and field. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Ground Water Wiley

How the Kd Approach Undermines Ground Water Cleanup

Ground Water , Volume 38 (3) – May 1, 2000

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References (22)

Publisher
Wiley
Copyright
Copyright © 2000 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0017-467X
eISSN
1745-6584
DOI
10.1111/j.1745-6584.2000.tb00230.x
Publisher site
See Article on Publisher Site

Abstract

Environmental scientists have long appreciated that the distribution coefficient (the “Kd” or “constant Kd”) approach predicts the partitioning of heavy metals between sediment and ground water inaccurately; nonetheless, transport models applied to problems of environmental protection and ground water remediation almost invariably employ this technique. To examine the consequences of this practice, we consider transport in one dimension of Pb and other heavy metals through an aquifer containing hydrous ferric oxide, into which many heavy metals sorb strongly. We compare the predictions of models calculated using the Kd approach to those given by surface complexation theory, which is more realistic physically and chemically. The two modeling techniques give qualitatively differing results that lead to divergent cleanup Strategies. The results for surface complexation theory show that water flushing is ineffective at displacing Pb from the sorbing surface. The effluent from such treatment contains a persistent “tall” of small but significant levels of contamination. Subsurface zones of Pb contamination, furthermore, do not migrate rapidly or far in flowing ground water. These results stand in sharp contrast to the predictions of models constructed using the Kd approach, yet are consistent with experience in the laboratory and field.

Journal

Ground WaterWiley

Published: May 1, 2000

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