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surficial recharge from stream flow and precipitation. In portions of T. 28 S., R. 43 W. <br />and T. 31 S., R. 48 W., the underlying Dakota Aquifer is fully saturated and likely <br />recharges the overlying High Plains Aquifer. In the southeastern part of Baca County, <br />the Dakota Aquifer pinches out and ground water in the Dakota Aquifer appears to flow <br />laterally into the High Plains. Similarly, in the southeast corner of Baca County, the <br />Dockum Aquifer is fully saturated and composite water levels are well up into the <br />overlying High Plains Aquifer. The High Plains thickens dramatically to the southeast <br />into Kansas, Oklahoma and Texas where the saturated thickness is several hundred <br />feet. <br />In the northern part of the District, the Ogallala Formation overlies the Graneros Shale of <br />the Colorado Group. Southeast of Stonington, the Ogallala generally lies directly on top <br />of the Dockum Aquifer. In the remaining area of the Basin, the Ogallala lies on top of the <br />Dakota Formation. These relationships are important in determining where the High <br />Plains Aquifer may recharge the underlying aquifer, or may be recharged by the <br />underlying aquifer. For example, in Cross-section A—A', west of well #5231, the static <br />water level is below the High Plains Aquifer but in the Dakota Aquifer. Conversely, east <br />of #5231, the Dakota Aquifer appears to charge the High Plains Aquifer. The composite <br />water level rises into the High Plains Aquifer as the Dakota Aquifer is truncated. <br />Research by the Kansas Geological Survey has similarly shown that the juxtaposed <br />water -bearing formations (whether High Plains/Dakota or High Plains/Dockum) each <br />function as single aquifer systems with water -well development (Macfarlane and Sawin, <br />1995). <br />The saturated thickness maps and the cross-sections (Figures 1 through 5) show the <br />composite water table crosses formation boundaries indicating there is hydraulic <br />communication between hydrostratigraphic units. For example, several wells in T. 28 S., <br />R. 43 W. completed in both the High Plains and Dakota aquifers suggest the Dakota is <br />fully saturated with the composite water table in the High Plains Aquifer. Specifically, <br />monitor wells #5025 and #5026, in Sections 21 and 29, respectively, are also high- <br />volume irrigation wells that were completed in both aquifers. These wells have historic <br />water -level declines of 56 feet and 47 feet, respectively, which in turn lowered the <br />composite water level below the High Plains Aquifer and into the underlying Dakota <br />Aquifer in Section 29. <br />Historic records indicate a major basin -wide drop of the water levels in the High Plains <br />Aquifer. The average decline in about 300 wells in Region I, of Southwestern Kansas, is <br />over 50 feet since predevelopment, with some wells losing over 200 feet of saturation. <br />In the Basin, High Plains wells have experienced over 12 feet of water -level decline in <br />VI 8 <br />99-028.003\Phase 2 Report\Hydrogeology <br />