During those millions of years of formations, the forces of nature created different layers of minerals and rocks. Each of these layers have either high permeability or low to none permeability. In a hydraulic sense, there are two confining layers that affect permeability. Each of these layers can be staggered in any order, depending on the geology of the local region. Figure 3- Example of Layers in the subsurface sectional view of the layers before mining occurs.
Water infiltrates through the soil and unconsolidated material, entering the aquifer.
This can be made up of such materials as sandstone or gravel depending on the location. It then travels slowly through an aquitard, into another aquifer. The water is unable to infiltrate the aquifuge and this acts as a bottom to the aquifer. Appendix II shows an example of how mountain layers may have been formed. Notice in the graphic in Appendix II the different layers, most importantly the limestone, sandstone, and shale.