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<br />-27- <br /> <br /> <br />O. f) l'\ q ,":j I. <br />t lJ () -j ,~ <br /> <br />major watercourses. Also, extensive quantities of relatively <br />shallow ground water underlie large portions of Nebraska, western <br />Kansas, eastern Wyoming and Colorado, and parts of Missouri and <br />South Dakota. In all, reserves lying at less than 1,000 feet <br />deep are estimated at greater than 3 billion acre-feet.2 <br />Further, large amounts of ground water are known to exist in <br />extensive sandstones and limestones at depths greater than 1,000 <br />feet. Although these deeper deposits contain more water than the <br />more accessible shallow aquifers, its use is limited by excessive <br />pumping costs and variable quality. <br /> <br />Water tables in some areas of the basin are declining due to <br />withdrawals in excess of recharge. Areas experiencing <br />significant adverse effects include northwestern Kansas, eastern <br />Colorado and Wyoming, northwestern Nebraska, portions of the <br />Platte and Blue Basins in Nebraska, and parts of eastern <br />Missouri. On the other hand, the ground water level is rising in <br />portions of south central Nebraska due to irrigation canal <br />seepage and infiltration from irrigated lands. <br /> <br />Ground Water Quality <br /> <br />The quality of ground water in the basin is variable. Water <br />of highest quality is generally deri~ed from dune sand, such as <br />that found in north central Nebraska, and from deep igneous and <br />metamorphic rock formations. Major sources of ground water are <br />generally sedimentary deposits and valley alluviums. In the <br />former, abundant shallow sandstone and limestone deposits <br />generally yield water of adequate quality for most uses. Water <br />recovered from valley alluviums is influenced by the quali ty of <br />the surface water, the rock types in the valley, and the <br />surrounding vegetation. Alluviums along many streams contain <br />water with high sulfate concentrations. <br /> <br />Ground water containing concentrations of total dissolved <br />solids exceeding 2,000 miligrams/liter, considered very poor <br />quality, is found in highly developed aquifers in eastern <br />Montana, central South Dakota, western Iowa, and northwestern <br />Missouri. <br /> <br />Interrelationship of Surface and Ground Water <br /> <br />With increasing development of bOth surface and ground-water <br />resources, their hydrologic interrelationship is becoming <br />increasingly more important to users. Several types of effects <br />have resulted from public and private water and land resource <br />