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7.0 GROUND -WATER RESOURCES <br />7.1 GENERAL <br />The Phase 1 report presented a revised conceptual model of the Basin aquifer system <br />from the model first described by Beck in 1967. This change of viewpoint was due <br />largely to a preponderance of new hydrogeologic and water -use data from the Basin that <br />was created after 1967. Notwithstanding this new paradigm, important physical factors <br />remain that have, and will, continue to affect the availability of ground water in the Basin. <br />These factors include the following: <br />• The overall movement of ground water in the Basin is down -dip from west to east <br />and into Kansas. <br />• Local ground -water flows and water -table elevations are influenced significantly <br />by high-volume pumping for irrigation and municipal use. <br />• Water levels will continue to decline in the aquifers, particularly the High Plains <br />and Dakota, as irrigation pumping continues and expands. <br />• Significant long-term pumping in one aquifer can affect water levels in the <br />overlying aquifer due to the hydraulic communication between the aquifers in <br />many places of the Basin. For example, high-volume irrigation pumping from the <br />Dakota and Dockum aquifers likely affects the water levels in the overlying High <br />Plains aquifer. This has occurred in southwest Kansas as reported by the <br />Kansas Geological Survey. Future development of the Dockum aquifer in the <br />northern, central, and western part of the Basin may also affect water levels in <br />the overlying Dakota aquifer <br />This section describes how these factors have affected the availability of ground water in <br />the Basin. Notable reinterpretations include the Dakota and Cheyenne formations that <br />have been combined into the Dakota Aquifer in this report, and the underlying Dockum <br />has been included as a major aquifer. Until recently, the Dockum aquifer has not been <br />recognized as a potential major source of ground water in the District. <br />7.2 Recoverable Ground -Water Resources <br />In this report, the recoverable ground -water resource for the Dakota is 50 percent of the <br />estimated in-place ground -water volume. This definition is conservative and consistent <br />with current industry views. At 50 percent level drawdown and loss of storage, high- <br />volume pumping for irrigation is assumed to be uneconomical with current technology, <br />energy costs, and income from irrigated agricultural ventures (a fundamental <br />assumption). However, for the High Plains Aquifer Unit, the percentage varies <br />depending upon the remaining saturated thickness. For this study, the largest average <br />VII -1 <br />99-028.003\Phase 2 Report\SHP GW Resources <br />