Barrier Technologies for Environmental Management Summary of a Workshop (1997) / Chapter Skim
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Natural Physical and Biological Processes Compromise the Long-term Performance of Compacted Soil Caps
Natural Physical and Biological Processes Compromise the Long-term Performance of Compacted Soil Caps
Pages 79-88
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From page 79... ...
PHYSICAL PROCESSES INFLUENCING BARRIER INTEGRITY Physical phenomena that affect the integrity of compacted soil barriers in shallow land burial facilities and remediation sites are related to natural cycles of temperature and precipitation. Cycling occurs over three distinct hme scales: diurnal (hourly changes)
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From page 80... ...
Very little variation in cap water content was found through several multi-year simulations, although baIrier water contents were lower for years with lower rainfall than normal (Luxmoore and Tharp, 1992~. An experimental study of compacted soil caps In a mesic environment in Germany suggests, however, that field performance would be less than predicted by the model.
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From page 81... ...
The hazardous and radioactive wastes typically found at remedial sites are less susceptible than municipal waste to subsidence due to decomposition, but poor initial compaction of waste can lead to cap subsidence unless wastes are stabilized prior to cap placement. BIOLOGICAL PROCESSES INFLUENCING BARRIER INTEGRITY Without continual human intervention, ecological succession will occur on waste sites resulting in the establishment of a series of biotic comm unities that will modify soil barriers.
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From page 82... ...
The occurrence of plant root penetration into caps depends on the plants established by revegetation and subsequent ecological succession, the rooting depth of the plants, and the roots' ability to penetrate the cap material. Radioactive waste sites provide strong evidence for root penetration of soil caps because monitoring readily detects radionuclides in above-ground plant tissues.
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From page 83... ...
Oxygen diffusion to roots may limit root respiration In dense clay layers with high water content due to low gas filled porosity. There is evidence that roots become less effective in penetrating a dense soil layer as soil aeration is diminished (Russell, 1977~.
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From page 84... ...
At the Idaho National Engineering Laboratory, several species of rodents and their surface castings have been contaminated by burrowing into trenches of radioactive waste even in areas with 1.2-m caps (Arthur and Markham, 19834. The extent to which burrowing damages soil barriers depends on the depth of burrows, and in particular, whether the burrows extend through the soil cover of a compacted layer or even further through the cap.
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From page 85... ...
in humid areas, earthworms probably cause more significant damage to soil barriers than vertebrates because they are abundant and may burrow deeply (Table 21. In addition, the extensive burrowing of earthworms provides
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From page 86... ...
nor example, vlemauer at al. ~-' reported formation of desiccation cracks in a compacted soil layer below an intact synthetic membrane battier, probably due to natural thermal cycles and the exothermic decomposition of underlying wastes.
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From page 87... ...
1992. Simulation of baITier heterogeneity and preferential flow effects on the performance of shallow land burial facilities.
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From page 88... ...
1993. Compacted soil barriers at abandoned landfill sites are likely to fad!
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