In many parts of the state groundwater aquifers exist at various depths below land surface. Such aquifers or groups of such aquifers may demonstrate a natural hydraulic separation to a significant degree over local or regional areas as evidenced, in part, by differing hydraulic heads and variable responses to pumping stress. The upper aquifer or upper aquifer zone often will not yield water in sufficient or sustainable quantities for uses which require a large volume of water. Therefore, they have often been traditionally used for domestic water supplies, stockwatering and other uses that require only minimal water supplies and for which it is not cost effective to tap deeper aquifers. Further, the uppermost aquifers also commonly contribute to spring and stream flows. In some cases, the withdrawal of water from the lower aquifers causes the depletion of the upper aquifers through cascading waters or simultaneous withdrawals from both upper and lower aquifers, and in such cases, poor quality waters from one zone can also contaminate a different aquifer zone.