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Soil, Plant and Structural considerations for Surface Barriers in Arid Environments: Application of Results from Studies in the Mojave Desear near Beatty, Nevada
Pages 68-78

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From page 68...
... A prevalent assumption is that little or no precipitation will percolate to buried wastes at an arid site. Thick unsaturated zones, which are common to arid regions, are thought to slow water movement and minimize the risk of waste migration to the underlying water table.
From page 69...
... ~ [~ i ~MONA ~. ~: N_, Location of waste-burial site, Death Valley, and Mojave Desert of southwestern WATER MOVEMENT THROUGH DEEP UNSATllRATED ZONE BENEATH UNDISTURBED, VEGETATED AREA Field investigations to define the rates and directions of water movement through the deep unsaturated zone beneath an undisturbed' vegetated area began in the early 1980's and continue today.
From page 70...
... Calculations based on either of the two deposition rates indicate that if the only source of chloride in the soils is from atmospheric deposition, then considerable time is needed to accumulate the quantity of measured chloride. The low chloride concentrations below 10 m indicate either that the deeper soils were flushed with dilute water in the past or that chloride never accumulated in the soils.
From page 71...
... The smaller hydraulic heads estimated from core samples near land surface may result from soil drying during firming or sampling. Nevertheless, hydraulic heads in the upper 50 m are less than the hydraulic head at the water table, Indicating a Hying trend and upward liquid flow.
From page 72...
... . Within the zone of higher chloride concentrations, water content is not measurably changing, but water pressures, temperatures, and vapor densities change seasonally (Fischer, 19921.
From page 73...
... , and daily water pressures (c) measured at four sites.
From page 74...
... Rapid percolation for the undisturbed soils, both vegetated and nonvegetated, resulted in high water pressures during the springs of 1988, 1991, and 1992. Pressures for the east trench show that the wetting front did not reach the 0.75-m depth until June 1988, and pressures for the west trench show that the wetting front did not reach that depth until June 1992.
From page 75...
... Unlike the native soil profile, the fill provides no textural stratification to impede deep percolation of infiltrated water. Changes in the structural integrity of trench covers through erosion or subsidence can reduce the waste-isolation potential of a burial site.
From page 76...
... Ongoing investigations indicate that, under present climatic conditions, the natural soil-plant system effectively limits the potential for deep percolation. The stratified soil profile, in combination with native plants, provides for rapid infiltration, which reduces runoff; limited depth of percolation; high storage capacity for infiltrated water; and effective seasonal depletion of water accumulated in the root zone.
From page 77...
... Natural revegetation processes at arid sites may be extremely slow, however, and studies to develop strategies for establishment of native vegetation on trench covers are needed. To date, studies at the Mojave Desert site have focused on present-day climatic conditions.
From page 78...
... 1994b. Effects of temperature on water movement at the and disposal site for low-level radioactive wastes near Beatty, Nevada fabs.~.


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