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1.0 SUMMARY <br />1. This report presents the findings of Phase 2 of a geology and water resources <br />study of the Southern High Plains Ground Water Basin (Basin) on behalf of the <br />Southern High Plains Ground Water Management District (District). The Basin is <br />located in southeastern Colorado, south of the Arkansas River Basin in <br />southeastern Baca, Prowers and Las Animas counties. The investigation <br />involved an expansion upon the Phase 1 Study, including: (a) a more extensive <br />examination of water well records available at the State Engineer's Office; (b) a <br />further and more detailed assessment of geologic and hydrogeologic conditions; <br />and (c) further evaluation of water use in the District. <br />2. Available geologic and hydrogeologic information indicates there is effectively <br />one aquifer system which can be separated into four aquifer members, or units, <br />within the District: (a) High Plains; (b) Dakota; (c) Cheyenne; and (d) Dockum; <br />which range in age from Quaternary to Triassic. The High Plains Aquifer is <br />comprised of Quaternary age alluvium and eolian sands, and Tertiary age sands <br />and gravels of the Ogallala Formation. The Dakota Aquifer is comprised of the <br />Cretaceous age Dakota Sandstone, Kiowa Shale, and Cheyenne Sandstone. <br />The Dakota and Cheyenne being the aquifer members of the inclusive Dakota <br />Aquifer. The Dockum Aquifer is comprised of sandstones and siltstones of the <br />Triassic age Dockum Group. The High Plains Aquifer blankets most of the <br />District, although only five isolated areas were identified as still containing <br />recoverable ground water. The Dakota Aquifer underlies most of the District <br />except the southeast corner where the High Plains Aquifer lies directly over the <br />Dockum Aquifer. The areal extent of the Dockum Aquifer is not well known in the <br />District because of the general lack of wells and the greater depth of the Dockum <br />than the other two aquifers. <br />3. In 2001, about 126,300 acres of land were irrigated within the Basin. The total <br />ground water pumped for irrigation was estimated to be approximately 220,800 <br />acre-feet using weather data from the Plainsman Research Center near Walsh. <br />4. Generally, ground -water levels in the Basin have dropped approximately 100 feet <br />over the last 50 years. Water levels are measured each year from 97 monitoring <br />wells within the District. During the last ten years, these monitoring wells have <br />had an average water level decline of 5.4 feet. Between 2000 and 2001, water <br />levels declined in the majority of monitoring wells by —2.50 feet on average, as <br />compared to —1.12 feet in 2000 and —1.70 feet in 1999. Several wells showed an <br />1-1 <br />99-028.003\Phase 2 Report\SHP Summary <br />