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8.0 CONCLUSIONS <br />1. The study indicates about 126,300 acres of irrigated land within the Basin using <br />an estimated 220,800 acre-feet of ground water in 2001. <br />2. The SHPGWMD has four aquifers, which effectively act as one aquifer unit due <br />to leakage of the intervening aquitards. The aquifer "members" include the High <br />Plains Aquifer, the Dakota and Cheyenne members (which are part of the larger <br />Dakota Aquifer), and the underlying Dockum Group. <br />3. Most groundwater recharge is directly from precipitation and irrigation returns. <br />With the conversion from flood irrigation to more efficient center pivot sprinkler <br />systems, the recharge from irrigation has been reduced. <br />4. Generally, water levels in the Basin have declined about 100 feet in the last 50 <br />years. Site-specific change in the potentiometric surface is dependent on the <br />proximity to heavy irrigation, recharge, and the source aquifer systems. In 2001, <br />the composite potentiometric surface declined by approximately -1.14 feet as <br />compared to —1.12 feet in 2000 and —1.70 feet in 1999. <br />5. The study suggests the proven economically recoverable groundwater resources <br />of about 12.4 million acre-feet. At current withdrawal rates of 220,000 acre-feet <br />annually, the ground -water reserves are estimated to have an economical life <br />expectancy of about 56 years. New irrigation technology such as drip systems <br />would extend the economic life of the aquifer system, if irrigators consider this <br />technology to be economically viable. <br />6. The study suggests the combination of the proven economically recoverable <br />ground water (12.4 million acre-feet) with the possible reserves (9.6 million acre- <br />feet) in the Dockum aquifer system would increase the overall reserves to about <br />22 million acre-feet. At current withdrawal rates of 220,000 acre-feet annually, <br />the ground -water reserves are estimated to have a life of about 100 years. The <br />cost of energy, commodity prices, irrigation technology are factors that may affect <br />the economic viability of pumping water from the lower Dockum aquifer unit and <br />this estimate of the life of these reserves. <br />7. Many of the existing monitor wells have limited completion information available <br />to confirm affected hydrostratigraphic intervals and their overall distribution, <br />VIII -1 <br />99-028.003\Phase 2 Report\Conclusions <br />