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Show GROUND WATER 59 reason to justify leaving the basin entirely full in areas where there is a demand for the water. Therefore, a second determination of major importance is the ex- tent to which the ground water basin should be drawn down, and then stabilized. This determination is essentially one of economics. It might be that some water users can afford to pump from a depth of 500 feet, and, if that is so, then water could be withdrawn and Used until the level of the basin is lowered to 500 feet, and the res- ervoir level then stabilized by limiting withdrawals to the amount by which the reservoir is recharged each year. But it is difficult to apply the same economic criteria to each type of use. Higher valued uses can justify pumping costs that are much higher than lower valued uses can afford to pay. And sometimes there is a variance between the costs which individual users for the same purpose of use can afford to pay. This is particularly true in agriculture, where in some areas holders of earlier well rights operate relatively small farms which are rather inefficient, and only econom- ically marginal in the best of times. Then, when subsequent irriga- tion users drill large wells into the basin at substantial depth, and farm large acreages using modern equipment and methods, their efficiency in farming is often much greater than the earlier, smaller operators. The result is that the larger and more efficient operators can afford to pay the costs of pumping from greater depths; whereas the holders of the earlier (senior) rights simply go out of business and discontinue farming because the increased pump cost to them is more than they can afford to pay. This illustrates the fact that even between users for the same type of use there will be difficult policy decisions as to the depth to which the water level of the underground water basin should be lowered in order to permit optimum utilization of the water in the reservoir. (2) PROBLEMS ASSOCIATED WITH MINING GROUND WATER A further determination to be made, again essentially as a matter of economic policy, is whether a ground water basin should be totally mined. If water in an underground basin is withdrawn and used to the extent that the level of the basin is reduced to a level approach- ing a maximum economic pump lift, then, to that extent, the eco- nomic supply of water in the reservoir has already been largely mined. But if a decision is made to use all of the water in a reservoir which economically can be recovered, then the reservoir supply will be totally exhausted, at least for all practical economic purposes, and no longer will yield any significant amounts of water (except to the extent that the annual recharge is available for withdrawal and use). In some areas the annual recharge might be sufficient to contribute a rather significant supply of water, but in many areas the annual recharge is negligible. There is thus a difference between withdrawing the water in a reservoir down to the point where the efficient user for low valued uses can economically afford to pump, and mining the reservoir beyond that to the point where only the efficient higher valued uses |