Unconsolidated materials range from loose gravel, sand, silt or clay. Most people are aware how water can travel through unconsolidated aquifers such as gravel, but many people don't know that groundwater moves in consolidated aquifers in much the same way. Open spaces, pores or fractures, can transmit water at varying rates. The decisions about what formation your well will be completed in can affect how much water your well can supply. Aquifers can be classified as unconfined or confined.
Unconfined aquifers are water table aquifers that are at atmospheric pressure.
Confined aquifers are overlain by an impermeable layer, such as clay or shale, that prevents the upward movement of water. The overlying confining layer allows aquifers to develop pressures that result in artisan aquifers. Most confined aquifers are actually semi-confined because the confining layer is not completely impermeable. The depth to groundwater in many shallow wells is directly influenced by water levels in nearby streams, and can fluctuate several feet in response to seasonal stream changes. Seasonal variations can also cause water quality changes.