The following criteria are met in order to verify and maintain an upward hydraulic gradient in the producing aquifer: an effective confining layer must exist between the ground surface and the producing aquifer. This confining layer must have a lower hydraulic conductivity than the producing aquifer; and the potentiometric surface of the producing aquifer must remain higher in elevation than the potentiometric surface of the overlying aquifer. If there is no overlying aquifer, then the potentiometric surface of the producing aquifer must remain higher in elevation than the upper surface of the overlying confining layer. These criteria must be maintained during periods of maximum and long-term pumping and seasonal groundwater fluctuations. Not all confined aquifers in nature have an upward hydraulic gradient; however, for the purposes of R309-113, an upward hydraulic gradient must be maintained.