Permeability clay contamination

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. 

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... 

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. 

Passive perimeter gas control systems are designed to alter the path of contaminant flow through the use of trenches or wells, and typically include synthetic flexible membrane liners (FMLs) and/or natural clays as containment materials. The membrane is held in place by a backfilled trench, the depth of which is determined by the distance to a limiting structure, such as groundwater or bedrock. A permeable trench installation functions to direct lateral migration to the surface, where the gases can be vented (if acceptable) or collected and conveyed to a treatment system (Figure 10a and 10b). 

Low-permeability passive perimeter gas control systems (Figure 16.7) effectively block gas flow into the areas of concern by using barriers (such as synthetic membranes or natural clays) between the contaminated site and the area to be protected. In the low-permeability system, gases are not collected and therefore cannot be conveyed to a point of controlled release or treatment. The low-permeability system can also alter the paths of convective flow. 

Plume No. 3 (areas 4 and 5) is located in low permeable, partially fractured clay from 0 - 10m bgs (k = 4 x 10" m/s), over a layer of sand and gravel (k = 5 x 10" m/s) down to 18m bgs, and underlain by clay. The groundwater table is at 1 Om bgs in the sand and gravel. In areas where this layer is absent, only perched groundwater occurs, at depths of between 2 and 12m bgs. Contamination was found throughout the whole profile, in concentrations between 15mg/l to free phase, with most of the free phase found in the upper clay layer. 

The PF technology also has several potential limitations. Fractures do not always propagate in the direction or to the distances expected. Fractures may open new pathways for the unwanted spread of contaminants. Pockets of low permeability may remain after fracturing. Surface heave and stress resulting from the process can create hazards for buildings or other structures at a site. If the moisture content of the contaminated media is not controlled, the formation may swell and close the fractures. PF is not applicable at sites with high natural permeabilities. Fractures will close in soils with low clay content. In addition, PF should not be used in areas of high seismic activity. 

The EiAD technology works most effectively on clay-type soils where the hydraulic permeability is small. Results indicate that the EiAD technology can remove inorganic contaminants such as zinc and cadmium from clay sods. Soil contaminants may be cations, such as cadmium, chromium, and lead, or anions, such as cyanide, chromate, and dichromate. 

Electrokinetic treatment can be used to remediate soils, sludges, and sediments contaminated with heavy metals and organic hydrocarbons. Electrokinetic treatment works well on clay-type soils with low hydraulic permeability, which are difficult to treat using other in sitn technologies. Electrokinetic permeabilities for aqueous systems in clays have been demonstrated to be up to 1000 times greater than normal hydraulic permeabilities, and some heavy metals have exhibited removal efficiencies of up to 100%. 

This technology is not suitable for very dense, low-permeability soils and sediments. However, electrokinetic transport could be used to remediate contaminated clay formations within a more permeable aquifer. 

Recent variations include the use of backfilled caissons media-filled, hollow-vibrating beams and emplaced reaction vessels. The funnel typically consists of sheet pilings, slurry walls, or some other material and is preferably keyed into an impermeable layer (clay, bedrock) to prevent contaminant underflow. Particular care is required in designing and constructing the connection between the impermeable funnel section and the permeable gate section in order to avoid bypass of contaminated ground water. 

The vadose zone soils at the New Mexico State Highway and Transportation Department (NMSHTD) District 2 Maintenance Patrol Yard in Artesia, New Mexico (Artesia Yard) consist primarily of massive to poorly stratified silty clay, clay, or clayey silt. Soils of such low permeability (<10 10 square centimeters) are generally not amenable to the use of SVE (U.S. EPA 1995). However, as this case history shows, operation of a high-vacuum SVE system, with periodic monitoring and adjustment, can be very successful in removing sizeable secondary sources of petroleum hydrocarbons (both PSH and residual soil contamination) from the subsurface. 

Clays are generally considered to be effective barriers for flow of water and solutes due to their low permeability and high ion adsorption capacity. However, as environmental criteria for the emission of contaminants and water from clay barriers become increasingly stringent, it is crucial to be aware of all relevant driving forces and fluxes and to take them into account in model assessments. In this respect the processes of chemical and electro-osmosis may not be neglected in clayey materials of hydraulic conductivity < 10-9 m/s [7], At these low conductivities the surface charge of the clay particles and the counter-ion accumulation in diffuse double layers enable explanation and quantification of osmotic processes and semi-permeability in clays [1],... 

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