Modeling of moisture movement through layered trench covers

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Authors:Johnson, T. M.; Cartwright, Keros; Herzog, B. L.; Larson, T. H.
Author Affiliations:Primary:
Ill. State Geol. Surv., Champaign, IL, United States
Volume Title:Role of the unsaturated zone in radioactive and hazardous waste disposal
Volume Authors:Mercer, James W., editor; Rao, P. S. C.; Marine, I. Wendell
Source:p.11-26; Role of the unsaturated zone in radioactive and hazardous waste disposal, Philadelphia, PA, May 31-June 4, 1982, edited by James W. Mercer, P. S. C. Rao and I. Wendell Marine. Publisher: Ann Arbor Sci. Publ., Ann Arbor, MI, United States. ISBN: 0-250-40620-9
Publication Date:1983
Note:In English. 14 refs.; illus.
Summary:Low-level radioactive wastes in the United States are currently buried in trenches in 11 major shallow land-burial grounds. Six of these sites - two federal and four commercial - are located in the relatively wet eastern part of the country. Tritium migration has been observed at five of these sites, and is thought to be caused by infiltration of precipitation through trench covers. Trench covers at all 11 sites consist of material excavated from the trenches. The material is typically mounded toa depth of 1-3 m and planted with grass. At sites in relatively wet regions, covers are compacted by earthmoving equipment, or material excavated from an adjacent trench is temporarily placed on the cover. At some sites, infiltration through trench covers has resulted in accumulation of water within the waste; at other sites, infiltration has caused migration of contaminants, although no free water has been observed in the trench. The results of laboratory experiments and computer simulations of several preliminary cover designs indicate that a layer of coarse-textured, unsaturated material overlain by fine-grained material serves as a barrier to moisture movement. The effectiveness of the barrier is related to the contrast in saturated hydraulic conductivity and texture between the two layers. These investigations also indicate that prior to breakthrough, moisture in the fine-grained layer overlying a coarse-textured layer in a sloping cover flows laterally downslope above the interface. It has been suggested previously that saturation of the overlying layer is required before moisture breakthrough will occur in such layered systems. However, these results indicate that moisture movement through layered systems of highly contrasting texture can occur when the moisture content of the overlying layer is less than saturation and the pressure head at the interface is less than zero. The significance of these results must be evaluated in terms of observed behavior in laboratory columns, field experiments, and present capability of instrument measurement of the parameters of interest. (See also W87-06947) (Lantz-PTT)
Subjects:Data processing; Engineering geology; Experimental studies; Finite difference analysis; Finite element analysis; Grain size; Ground water; Hydraulic conductivity; Infiltration; Laboratory studies; Layered materials; Low-level waste; Mathematical models; Moisture; Movement; One-dimensional models; Radioactive waste; Saturation; Soils; Statistical analysis; Textures; Theoretical studies; Two-dimensional models; Waste disposal; Water regimes; Trench covers
Record ID:1984003215
Copyright Information:GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from USGS product, Selected Water Resources Abstracts, Reston, VA, United States
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