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High Plains Aquifer <br />As shown on Map 4, the current estimate of ground -water storage in the High Plains <br />aquifer is 3,102,000 acre-feet, with a combined surface area of about 565,000 acres and <br />a remaining sand/silt saturated thickness of only 35 feet. This estimate is an increase <br />from the volume estimated in the Phase 1 Study and is based upon more accurate well <br />logs. Due to the relatively small remaining saturated thickness, the resulting estimate of <br />recoverable ground -water storage in the aquifer is 1,002,000 acre-feet. Most of the <br />reduction in aquifer storage is likely due to leakage into the underlying Dakota and <br />Dockum aquifers induced by extensive irrigation pumping from these underlying bedrock <br />aquifers. <br />Dakota Member <br />The current estimate of ground -water storage is 3,740,700 acre-feet, the resulting <br />estimate of recoverable ground water in the aquifer is 1,496,300 acre-feet, and a <br />remaining saturated thickness of only 52 feet. <br />Cheyenne Member <br />This lower member of the Dakota aquifer is generally fully saturated. The current <br />estimate of ground -water storage is 8,660,500 acre-feet. The economically recoverable <br />ground water resource is estimated to be 3,464,000 acre-feet. This member has an <br />estimated remaining saturated thickness of 98 feet. <br />Dockum aauifer <br />The Dockum aquifer is estimated to be between 300 and 570 feet thick beneath the <br />District. For the purposes of this study the Dockum has been separated into two water <br />resource categories, proven and possible. The upper 200 feet of the Dockum is proven <br />by many existing large capacity wells. The lower portion of the Dockum is rarely <br />penetrated and of unknown characteristics from a water production standpoint. <br />However, significant water reserves are possible within the lower portion of the Dockum <br />and additional development/exploration is needed to confirm this resource. The aquifer <br />likely underlies most of the District, but access may be more than 500 feet below the <br />ground surface and beyond the financial means of many irrigators in the District. The <br />estimated proven volume of ground water stored in the proven Dockum aquifer is <br />12,844,353 of which 6,422,000 acre-feet is economically recoverable. The estimated <br />possible volume of ground -water stored in the unexplored portion of the Dockum aquifer <br />is 19,267,000 acre-feet, of which, 9,633,000 acre-feet is economically recoverable. <br />VI 1-3 <br />99-028.003\Phase 2 Report\SHP GW Resources <br />