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<br /> <br />Sustainability of <br />Ground-Water Resources <br /> <br />by William M. Alley <br />Thomas E. Reilly <br />O. Lehn Franke <br /> <br />INTRODUCTION <br /> <br />Ground water is one of the Nation's most <br />important natural resources. It provides about <br />40 percent of the Nation's public water supply. In <br />addition, more than 40 million people, including <br />most of the rural population, supply their own <br />drinking water from domestic wells. As a result, <br />ground water is an important source of drinking <br />water in every State (Figure 1). Ground water is <br />also the source of much of the water used for irriga- <br />tion. It is the Nation's principal reserve of fresh- <br />water and represents much of the potential future <br />water supply. Ground water is a major contributor <br />to flow in many streams and rivers and has a strong <br />influence on river and wetland habitats for plants <br />and animals. <br /> <br />The pumpage of fresh ground water <br />in the United States in 1995 was estimated <br />to be approximately 77 billion gallons per <br />day (Solley and others, 1998), which is about <br />8 percent of the estimated 1 trillion gallons <br />per day of natural recharge to the Nation's <br />ground-water systems (Nace, 1960). From an <br />overall national perspective, the ground-water <br />resource appears ample. Locally, however, the <br />availability of ground water varies widely. <br />Moreover, only a part of the ground water <br />stored in the subsurface can be recovered by <br />wells in an economic manner and without <br />adverse consequences. <br /> <br />Ground water is one of the Nation's most <br />important natural resources. <br /> <br />1 <br />