Seepage, reduced

CeUulosic fibers, powdered limestone, gHsonite, and asphalt are frequently added to both water and oH muds at levels of 10 to 25 kg/m (4—10 lb /bbl) when high differential pressures are encountered to control seepage losses to the formation. This treatment also is used to improve the quaHty of the mud filter cake to reduce the chance of differential pressure sticking. 

The primary characteristic necessary for a liner, cover, or cutoff wall is low permeability, which essentially enables them to slow down the seepage or diffusion of chemicals. Clay is therefore the main material used to construct these containment systems. The thickness and chemical compatibility of containment systems are of concern in assessing the performance of a system. For example, clay liners are constructed as a simple liner that is 2 to 5 ft thick. In composite and double liners, the compacted clay layers are usually between 2 and 5 ft thick, depending on the characteristics of the underlying geology and the type of liner to be installed. Regulations specify that the clay used can only allow water to penetrate at a rate of less than 1.2 in./yr. However, the effectiveness of clay liners can be reduced by fractures induced by freeze-thaw cycles, drying out, and the presence of some chemicals. 

Fig. 7-2. Summary of environmental pathways by which terrestrial plants may become contaminated with radionuclides. In the case of an input from atmosphere, or as a result of the process of resuspension , any external radionuclide burden may be reduced by field loss mechanisms conversely, an initially external radionuclide deposit (Rat) may become internalised (i int) following foliar absorption and translocation. Radioactive contaminants of soils may be derived either from atmospheric inputs or from seepage in ground waters. Partitioning of radionuclides in soil—soil water systems controls their availability for root absorption, which normally occurs exclusively from the liquid phase. The chemical speciation of the nuclide in this phase, however, provides a further control on bioavailability which is highly radionuclide specific.

Two problems with the canal required correcting. One was excessive water seepage that made the surrounding farmland unusable. The other was heavy weed growth that reduced the water-carrying capacity of the canal and required that the canal be weeded periodically. 

After a full irrigation season the canal has remained free of weeds. Seepage has been reduced to the point where the adjacent land is usable. Some cracks in the lining have developed, but they have not effected seriously the performance of the liner. Analysis has shown most of the cracks to be the result of ... 

Sorption to iron-oxyhydroxide can be computed with the surface complexation model of Dzombak and Morel (1990). This model assembles the results of numerous laboratory experiments on sorption of trace elements to ferrihydrite (Hfo, hydrous ferric oxide, EeOOH). Eerrihydrite is a more or less amorphous substance which is found in nature in seepage zones of reduced, iron containing groundwater. Probably, it will be representative for the iron-oxyhydroxide which forms during in situ iron removal in aquifers, but this has not been verified yet. 

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