How do unconfined and confined aquifers differ?
An unconfined aquifer contains groundwater at atmospheric pressure and is not overlain by adequate confining (clay) layers. The upper limit of the zone of saturation below land surface is commonly referred to as the water table. The depth to the water table usually fluctuates to some extent depending on the season of the year and the amount of local precipitation that directly recharges such aquifers. Because the water table generally conforms to the local surface topography, the depth to water increases in areas of higher relief and decreases in areas of lower elevation. Groundwater contained in confined aquifers is isolated by relatively impermeable confining layers and is subjected to pressures (or artesian heads) higher than atmospheric pressure. This phenomenon allows groundwater under natural pressure to rise to some level above the actual top of the aquifer. Confined aquifers typically are found in most areas of the state at depths of 200 feet or more.
