Permeability clays

Understanding the basic hydraulic mechanisms for synthetic liners and clay liners is very important in appreciating the advantages of a composite liner. Clay liners are controlled by Darcy s law (Q = kiA). In clay liners, the factors that most influence liner performance are hydraulic head and soil permeability. Clay liners have a higher hydraulic conductivity and thickness than do synthetic liners. Additionally, leachate leaking through a clay liner will undergo chemical reactions that reduce the concentration of contaminants in the leachate. 

Gas-collector systems are installed directly beneath the low-permeability clay cap in a hazardous waste landfill. Landfills dedicated to receiving only hazardous wastes are relatively new and gas has never been detected in these systems. It may take 40 years or more for gas to develop in a closed secure hazardous waste landfill facility. Because the long-term effects of gas generation are not known, and costs are minimal, U.S. EPA strongly recommends the use of gas-collector systems. 

The NATA site consists of tailings overlying relatively low permeability clay soil, gravel-sand, and bedrock units. There are two aquifers one is confined between the bedrock and clay, and another unconfined aquifer which developed within the NATA tailings. Vertical exchange between aquifers is limited due to the clay separation. This is demonstrated by the higher piezometric levels of the unconfined aquifer compared to the confined one. 

Site permeability, clay content, depth to water table, and organic content can impact technology performance. 

The technology can be used in any type of soil, including low-permeability clays. According to the vendor, this technology can be used to treat polychlorinated biphenyls (PCBs), dioxins, chlorinated solvents, pesticides, and herbicides. The thermal blanket technology has been demonstrated to remediate PCB-contaminated soil to a level of 2 ppm. 

EO could be used as an alternative technology for remediation of contaminants in low permeability clay-rich soils, and represents an in situ, abiotic physical and chemical treatment process which utilizes the Eh-pH gradients established in the subsurface as a result of electrolysis reactions at... 

Alternatives to batch testing include the use of diffusion cells or flowthrough columns. Diffusion cells are easier to operate, but are less representative of field conditions where some advection may occur. However, operation of columns at very low flow rates is difficult and subject to artifacts. To minimize possible wall effects associated with shrink/swell behavior of low-permeability clay materials, several researchers have utilized column devices that provide a confining pressure, such as flexible wall permeameters (e.g., Acar and Haider, 1990 Smith and Jaffe, 1994 Shackelford and Redmond, 1995 Khandelwal et al., 1998 Khandelwal and Rabideau, 2000). 

Figure 13 Concentration profiles for groundwater at the Galloway Township gasoline study site in July 1990 and April 1991(after Cozzarelli et al, 1999). The two shallow samples are within the sandy sediments (3.26 m and 3.81 m bis) and one deeper sample (at 4.72 m bis) is within the low-permeability clay-rich layer.

Operating Limitations. The landfill (or treatment) site should be lined with a very low permeability clay or a synthetic liner to prevent migration of oil or leachates covered to prevent any nuisance such as blowing sand and designed so that any leachate, contaminated surface water, or groundwater can be contained and treated before release. 

Abstract To better understand the coupling of thermal (T), hydraulic (H) and mechanical (M) processes (T-H-M processes) and their influence on the system behaviour, models allowing T-H-M coupling are developed. These models allow simulations in the near-field of the system. Such a model has been developed within the simulator RockFlow/RockMech. This paper concentrates on the thermal and hydraulic processes. For those processes, the material parameters and state variables are highly non-linear and mostly functions of temperature, saturation and pressure. This paper shows how these dependencies are formulated mathematically and are implemented into RockFlow/RockMech. The implementation allows phase changes between the fluid phases (gas and liquid) to occur explicitly. The model allows the simulation of very low permeability clays with high capillary pressures. An example for code validation is shown, where low permeability clay is desaturated, lastly, current work on the calculations performed in the near field study (BMTl) of the DECOY ALEX III project is outlined. 

Engineered barriers generally include a waste form (spent nuclear fuel or glass containing radioactive wastes) encapsulated within a metallic container (e.g., steel and copper), which may be surrounded by a low-permeability, clay-rich buffer and backfiU. Natural barriers include the repository host rock and a volume of rock between the repository and biosphere. The engineered barriers and immediately adjacent host rock are referred to as the near field [1]. 

Keywords Porosity Permeability Clay-modified electrodes ... 

In Fig. 9.3, the effect of inorganic fillers with different aspect ratios on the membrane permeability to methanol and proton conductivity is compared [34]. For the same filler concentration, the layered silicate was more effective in reducing methanol permeability. Clays and layered silicates such as laponite have been used by different groups for the development of fuel cell membranes. Examples are Nafion/ mordenite [35] and Nafion/montmoriUonite [36], Nafion/sulfonatedmontmorillonite [37], SPEEK/montmorillonite [38,39], SSEBS/montmoriUonite [40]. 

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