Permeability is a material property that is determined by laboratory analysis, but is also commonly determined as a mass property through field testing. The mass property is more accurately known as the aquifer's hydraulic conductivity, which integrates all of the aquifer's characteristics to conduct water. See "Hydraulic conductivity".
The time available for attenuation in aquifer materials decreases as the permeability of the materials increases. Permeability may vary significantly among different types of materials or at different places within the same material. Permeability is often many times greater laterally than vertically. Ignored or undetected, a thin (0.5 inch or less) clay or shale seam in an otherwise uniform soil or rock aquifer can profoundly alter the outcome of mathematical analyses and design assumptions. Figure 7-11 shows the permeability of various geologic materials.
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