Water system managers often express a desire for an upper estimate of the amount of water that may be
withdrawn from an aquifer unit. The concept of safe yield was introduced by O. E. Meinzer to estimate the maximum supply
of water that can be pumped perennially from an aquifer without causing a decrease in overall water quantity or quality.
Walton (1970, p. 608) used the term, "practical sustained yield" to describe essentially the same concept.
It was accepted that safe yield was limited by the long-term mean annual recharge of the groundwater reservoir.
It was also recognized that safe yield could be further reduced by the transmissive properties of the aquifer unit.
Under the assumptions of this concept, storage depletion or groundwater "mining" occurred when withdrawals continually
exceeded the mean annual recharge.
Because an estimate of safe yield also depended upon, among other things, an unchanging balance between pumping,
recharge, and natural discharge, changes in any of these factors would cause changes in the estimate of safe yield.
The inability to control or predict changes in the many variables was a major deficiency of the concept.
As a result, safe yield was a subject of controversy regarding its pseudohydrologic character (Kazmann, 1965, p. 161), and
has now fallen into disuse. Therefore, no safe yield values were estimated for communities in the study area [the
Central Coastal Plain of North Carolina].