An aquifer is a water saturated permeable geologic layer, or fracture zone, that is able to transmit significant quantities of water. A geologic layer that cannot transmit significant quantities of water is usually referred to as an aquiclude. An aquitard is a rock unit that generally has a low permeability and hence will transmit only very limited quantities of water and are generally not suitable for production wells. The terms Aquifer or aquitards can be used to define most geologic strata. The most common aquifers include permeable sedimentary rocks such as sandstones, limestone’s, sand and gravel layers, and highly fractured volcanic and crystalline rocks. Common aquitards are un-fractured shale’s, clays and dense (un-fractured) crystalline rocks.
Sedimentary aquifers form layers and usually have a large lateral extent, whereas aquifers in fracture zones in igneous and crystalline rocks may have a very limited lateral extent. When searching for water using any geophysical method, including the Electro seismic method, the type of aquifer that may be present should be considered, both when planning a survey and especially when considering drilling.
- Confined—An aquifer overlain by one or more layers of impermeable rock or soil that restrict water to within the aquifer. The water is confined under pressure. Drilling a well into a confined aquifer releases that pressure and causes the water to rise in the well. These wells are sometimes called artesian wells.
- Unconfined—An aquifer that is not overlain by a layer of impermeable rock or soil. Water in a well will naturally stay at the level of the water table. As water is removed from the well, the water table at that place is lowered, causing the surrounding ground water to flow toward the well.
Southwest Groundwater Surveyor
Serving Southern California, Arizona, New Mexico, Utah.