Study GuideGeology–Groundwater1. PermeabilityPermeabilitydescribes how easily fluids, such as water, oil, or gas, can move through a rock. Itdepends on how well the tiny spaces inside the rock are connected to each other.It’s important to know thatporosity and permeability are not the same thing. A rock can havemany pore spaces (high porosity) but still not allow fluids to flow easily if those spaces are poorlyconnected.1.1 How permeability works•Permeability measures connectivity, not just empty space.•If pore spaces link together well, fluids can flow freely.•If pore spaces are small or isolated, fluid movement is slow or blocked.1.2 Examples of different rocks•Sandstoneusually has bothhigh porosity and high permeability. Its grains are relativelylarge, and the pore spaces connect well,allowing fluids to pass through easily.•Shalecan be quiteporous, but it haslow permeability. This is because its very fine grainscreate tiny pore spaces that do not connect well.•Igneous rocksgenerally havelow porosity and low permeability. However, if they areheavily cracked or fractured by tectonic forces, fluids can move through those fractures moreeasily.2. The Water TableGroundwater does not just appear underground—it gets there by moving slowly downward throughsoil and rock.Gravitypulls water down through the ground until it reaches a depth of about5Preview Mode
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