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Nature's Response to Land Contamination
Published in Daniel T. Rogers, Environmental Compliance Handbook, 2023
Specific geologic factors affecting migration of pollutants in soil include (Rogers 1996; USGS 2006a; Rogers et al. 2007, 2012): Composition. Soil type has a significant influence on the migration of contaminants. In general, coarse-grained soils, such as sand and gravel, do not impede the migration of contaminants nearly as much as soils composed of clay.Porosity and permeability. Direct evidence of migration potential is hydraulic conductivity. Soils composed of sand and gravel have a hydraulic conductivity 100s to 1,000s of times higher than soils composed of clay. Although soils or sediments composed of clay may have a high relative porosity, they are usually not as permeable because the porosity is generally not interconnected.
Groundwater Flow — Art Or Science?
Published in Gregory D. Boardman, Hazardous and Industrial Wastes, 2022
The volume and velocity of groundwater flow are evaluated by using the empirically derived Darcy equation, familiar to groundwater scientists. Figure 1 shows the principle of laminar flow (or pipeflow)(2), as defined by the Darcy equation. The volume or rate of groundwater flow is proportional to the slope of the groundwater table and the hydraulic conductivity. Hydraulic conductivity is mathematically defined as the constant of proportionality in the Darcy equation. Conceptually, hydraulic conductivity is defined as a “measure of the capacity of a porous medium to transmit water”(3).
Experiences with Liners Using Natural Materials
Published in T. H. Christensen, R. Cossu, R. Stegmann, Landfilling of Waste: Barriers, 2020
The most important property of a compacted clay liner is its hydraulic conductivity. Designers make use of liner hydraulic conductivity to predict contaminant flux from a landfill in order to assess compliance at a specified boundary. Approvals for operation are based on whether or not compliance can be achieved. However, in spite of its importance, the hydraulic conductivity of compacted clay and methods to measure it are generally poorly understood.
Hydraulic conductivity estimation of sandy soils: a novel approach
Published in ISH Journal of Hydraulic Engineering, 2023
Mohammad Aasif Khaja, Shagoofta Rasool Shah, Ramakar Jha
Hydraulic conductivity depends upon both the physical properties of flowing fluid, which include density, viscosity, and temperature, as well as the intrinsic features of a porous medium, such as particle size distribution, porosity, specific surface, angularity, tortuosity, the shape of pores, degree of compaction, etc. (Todd and Mays 2005). However, in many natural occurrences, like in temperate regions, the sub-surface fluid properties remain practically constant, so it depends on medium characteristics alone (Cashman and Preene 2001; Masch and Denny 1966). The dependence of hydraulic conductivity on the PSD of sandy soils has long been well recognized (Shepherd 1989). As a result, various empirical models for the K estimation have been developed across the globe based on grain size distribution. The work of Hazen (1892) provides the oldest empirical equation where hydraulic conductivity is represented as a function of squared particle size at 10% passing (noted as d10, unit in centimeters to get K in ) as follows:
On the permeability of layered soil system: experimental study
Published in International Journal of Geotechnical Engineering, 2022
Abdulla A. Sharo, Mohammaed S. Al-Zoubi, Areen M. Al-Ababneh
Permeability, known also as hydraulic conductivity, is the capacity of a soil to permit the passage of fluids through its interconnected voids, where the flow of fluids is from a point of high energy to a point of lower energy. Permeability is an important soil property in geotechnical engineering, and it is usually expressed in terms of a related coefficient named the coefficient of permeability,. The value of the coefficient of permeability of soils plays a significant role in the field of geotechnical analysis such as analysing and designing earth dams, studying and controlling soil slopes, designing retaining structures, and checking and controlling the soil settlement and groundwater flow (Das and Sobhan 2013). For homogeneous soil deposits, various factors affect the coefficient of permeability including fluid viscosity, fluid polarity, unit weight, particle size and particle size distribution, soil mineralogy, void ratio, soil structure, and the degree of saturation (Das and Sobhan 2013; Mesri and Olson 1971).
Raw and modified clays and clay minerals for the removal of pharmaceutical products from aqueous solutions: State of the art and future perspectives
Published in Critical Reviews in Environmental Science and Technology, 2020
Hence, in order to improve the hydraulic conductivity of swelling clays, the nature of the main compensating cations is very important. Na-compensated clay minerals are unfavorable for such applications due to their very high swelling capacity, leading to potential delamination (Laird, 2006), whereas Ca and K-compensated cations have limited swelling properties. However, K-compensated clay minerals are largely considered as non-swelling clay minerals and K+ is very hard to exchange (Missana, Benedicto, García-Gutiérrez, & Alonso, 2014; Shainberg, Alperovitch, & Keren, 1987). As a result, Ca-compensated clay minerals may be an appropriate solution. When the variable swelling properties of smectites were tested in order to verify the impact of compensating cations, it was found that the hydraulic conductivity of Ca-SWy2 was three times as high as that of Na-SWy2, with hydraulic conductivities of 6.0 × 10−13 and 1.9 × 10−12 m·s−1 respectively (Thiebault, Boussafir, Guégan, et al., 2016). This difference is generated by the axial swelling strain, which is about 37% for Na-SWy2 and 1.5% for Ca-SWy2 (Ghayaza, 2012). Although significant, the hydraulic conductivity of Ca-SWy2 remains far higher than the classical limit of 10−9 m·s−1 for waterproof materials.