Dispersivity in heterogeneous permeable media

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When one fluid displaces another through a one-dimensional porous medium, the composition changes from pure displacing fluid at the inlet to pure displaced fluid some distance downstream. The distance over which an arbitrary percentage of this change occurs is defined as the mixing zone length, which increases with increasing average distance traveled by the displacement front. For continuous injection, the mixing zone size can be determined from a breakthrough curve as the time required for the effluent displacing fluid concentration to change from, say, 10% to 90%. In classical dispersion theory, the mixing zone grows in proportion to the square ... continued below

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22 p.

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Chesnut, D.A. January 1, 1994.

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Description

When one fluid displaces another through a one-dimensional porous medium, the composition changes from pure displacing fluid at the inlet to pure displaced fluid some distance downstream. The distance over which an arbitrary percentage of this change occurs is defined as the mixing zone length, which increases with increasing average distance traveled by the displacement front. For continuous injection, the mixing zone size can be determined from a breakthrough curve as the time required for the effluent displacing fluid concentration to change from, say, 10% to 90%. In classical dispersion theory, the mixing zone grows in proportion to the square root of the mean distance traveled, or, equivalently, to the square root of the mean breakthrough time. In a multi-dimensional heterogeneous medium, especially at field scales, the size of the mixing zone grows almost linearly with mean distance or travel time. If an observed breakthrough curve is forced to fit the, clinical theory, the resulting effective dispersivity, instead of being constant, also increases almost linearly with the spatial or temporal scale of the problem. This occurs because the heterogeneity in flow properties creates a corresponding velocity distribution along the different flow pathways from the inlet to the outlet of the system. Mixing occurs mostly at the outlet, or wherever the fluid is sampled, rather than within the medium. In this paper, we consider the effects. of this behavior on radionuclide or other contaminant migration.

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22 p.

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INIS; OSTI as DE94007870

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  • International high-level radioactive waste management conference, Las Vegas, NV (United States), 22-26 May 1994

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  • Other: DE94007870
  • Report No.: UCRL-JC--114790
  • Report No.: CONF-940553--15
  • Grant Number: W-7405-ENG-48
  • Office of Scientific & Technical Information Report Number: 145203
  • Archival Resource Key: ark:/67531/metadc624466

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  • January 1, 1994

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  • June 16, 2015, 7:43 a.m.

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  • Feb. 23, 2016, 1:28 p.m.

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Chesnut, D.A. Dispersivity in heterogeneous permeable media, article, January 1, 1994; California. (digital.library.unt.edu/ark:/67531/metadc624466/: accessed November 12, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.