The Great Lakes Regions, as a whole, has abundant supplies of water. Nearly 805•,000 billion cubic feet of water is contained in the Great Lakes. An additional 35,000 billion cubic feet of potable ground water is available from storage in the region. Estimated ground-water discharge to the streams and lakes of the region is 26 billion gallons per day.Despite this abundance of water, the United States part of the Great Lakes basin is faced with many water-related problems, most of which involve water quality and water supply. Other problems concern periods of low flow in streams, preservation of wetlands, detrimental effects of erosion, and flooding. The significance of ground water in thes.e problems is often overlooked.Ground water can be an alternative to surface water as a source of supply, or it can be used conjunctively with surface water to provide flexibility in water-supply management. Ground water supplied approximately 1,800 million gallons per day of the 39,900 million gallons. per day used in the Great Lakes Region in 1970. The ground-water contribution was only 4.5 percent of the water used. Thus, ground water represents a potential source of supply for much of the region. It also can be used, where conditions permit, to maintain lake levels and flow in streams, to dilute poor quality surface water, and to maintain or create wetlands and ponds.In managing water resources, ground water and surface water should be considered parts. of a single system. Management includes not only planning and controlling the development but also monitoring the effects of this development. Recent advances in ground-water hydrology have provided methods to resolve some of the development and management questions that formerly slowed the development of ground water.All of the States in the Great Lakes Region have some regulations to control the development or protect the quality of the ground water. These regulations, however, are not as comprehensive as those governing surface water. Future legislation could be designed to encourage the development of ground water and, at the same time, to protect the resource.Efficient development and management of ground-water resources requires a through knowledge of the system. Reports on ground water are available for about 80 percent of tbe Great Lakes Region. Most of these reports., however, are not sufficiently detailed to be useful in comprehensive planning. As ground-water development continues, quantitative groundwater studies, utilizing models as predictive tools, will enable this development to proceed in an efficient manner.

Introduction. _______________ Methods of investigation. Well-numbering system... Acknowledgments. _ ______ Geologic units...__________-Basin-fill deposits. ___.__-Silt and sand facies __ Limestone facies_ Alluvial deposits. ________ Terrace alluvium___. Flood-plain alluvium.

Previous work_________________________________ ___________ 2 Methods of investigation_______________________________________ 3 Well-numbering system______________________________________ 4 Acknowledgments.

__________________________________________ _ ______________ Jl Introduction ______________________________________________________ Geography ________________________________________________________ General geology.__________________________________________________ Summary of stratigraphy_______________________________________ . Geologic .history. ___________________________________________ _ __ Occurrence of ground \vater_______________________________________ Principles-__ ________________________________________________ Water ,table_________ __________________________________________ Hydraulic properties of water-bearing materials.______________________ Water-level fluctuations.___________________________________________ Recharge of;ground water._________________________________________ Discharge of ground \vater__________________________________________ Well construction and pumping equipment____________________________ Utilization of water._______________________________________________ Domestic and stock supplies___________-________-______-_-______ Public supplies._______________________________________________ Irrigation supplies.____________________________________________ Possibilities of additional development of large supplies of water from wells .__________________________________________________ Quality of water_________________________________________________ Chemical constituents in relation to use of water-_________________ Sanitary considerations_______-_____-___--_-_________-__-____-Geologic formations and their water-bearing properties.________________ 41 Cretaceous system..___________________________________________ 41 .Upper Cretaceous series-___________________________________ 41 Pierre shale___________________________________________ 41 Tertiary system.______________________________________________ Pliocene series___________________________________________ Ogallala formation..___________________________________ Quaternary system.___________________________________________ Pleistocene series___-___________-_________-_______________-Grand.Island(?) formation____________________________ Sappa(?) formation_ ___________________________________ Peorian loess________________________________________ Pleistocene and Recent series. ___--______-_-___-_______--_--Dune sand__________________________________________ Alluvium. _ ___________________________________________ 51 References cited___________________________________________________ 52 Index.___________________________________________________________ 55 in IV CONTENTS ILLUSTRATIONS [Plates are in separate volume] PLATE 1. Geologic map of Yuma County. 2. Fence diagram of Yuma County. 3-7. Maps of Yuma County 3. Contours on the water table, 1958-59. 4. Depth to water and location of wells. 5. Depth to bedrock. 6. Saturated thickness of the water-bearing materials. 7. Contours on the bedrock surface. Page FIGURE 1. Index map of Yuma County, Colo., and vicinity.__________ J3 2. Sketch showing system of numbering wells in Colorado____ 3-6. Aerial photo...

Topography and drainage._ ____________________________________ Climate ______________________________________________________ Economy.-___________________________________________________ Geologic units and their water-bearing properties-_____________________ 7 Undifferentiated Paleozoic and Mesozoic rocks.___________________ Cretaceous System.