What is a Confined Aquifer?
Confined aquifers are those that are overlain by an impermeable material, such as clay or shale, resulting in the water being under pressure. The impermeable nature of this overlying material restricts the amount of water that can move freely through it. For the most part, the water located within these confining layers does not intermingle with the waters of other aquifers or surface water systems, and thus do not have meaningful natural recharge rates. In the diagram below, the confined aquifer can only gain meaningful recharge from a small area at the outcrop location (or where it becomes unconfined), such as in the western portion of our county. The amount of recharge is limited to 10% or less of precipitation, and often cannot move quickly to the lower portions of the confined aquifer. When ground water withdrawal rates exceed the natural recharge rates (more gallons pulled out than are naturally recharged), the aquifer is being mined or depleted. A majority of the aquifers of the
