Why Do Some "Artesian" Wells Flow?
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figure 1. Click on image for larger view.
Wells that are drilled into confined aquifers can flow naturally under the higher pressure created by ground water trapped beneath confining layers.

The artesian well shown in Figure 1 is a special kind of artesian well because it is a flowing artesian well. Like a pipe full of water, the confined aquifer into which this well is drilled sustains higher water pressure than in the unconfined aquifer above it, so that water is forced to rise higher in the artesian well than the local water table around it. If the water level rises above the top of the well, the well flows under natural water pressure.

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