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Ground water is one of the Nation’s most important natural resources. It is the principal source of drinking water for about 50 percent of the United States population, providing approximately 96 percent of the water used for rural domestic supplies and 40 percent of the water used for public supplies (Solley and others, 1998). In addition, more than 30 percent of the water used for agricultural purposes is withdrawn from wells. Ground water also is a significant, but often unrecognized, component of the Nation’s surface-water resources. Much of the flow in streams and the water in lakes and wetlands is sustained by the discharge of ground water, particularly during periods of dry weather.
Ground-water systems are dynamic and adjust continually to short-term and long-term changes in climate, ground-water withdrawal, and land use (Box A). Water-level measurements from observation wells are the principal source of information about the hydrologic stresses acting on aquifers and how these stresses affect ground-water recharge, storage, and discharge. Long-term, systematic measurements of water levels provide essential data needed to evaluate changes in the resource over time, to develop ground-water models and forecast trends, and to design, implement, and monitor the effectiveness of ground-water management and protection programs.
“Water-level measurements from observation wells are the principal source of information about the hydrologic stresses acting on aquifers and how these stresses affect ground-water recharge, storage, and discharge.”
The U.S. Geological Survey (USGS) has collected water-level data for more than a hundred years, and many State and other agencies have a long history of water-level monitoring. However, water-level monitoring in the United States is fragmented and largely subject to the vagaries of existing local projects. A stable, base network of water-level monitoring wells exists only in some locations. Moreover, agency planning and coordination vary greatly throughout the United States with regard to construction and operation of water-level observation networks and the sharing of collected data.
For many decades, periodic calls have been made for a nationwide program to obtain more systematic and comprehensive records of water levels in observation wells as a joint effort among USGS and State and local agencies. O.E. Meinzer described the characteristics of such a program over 65 years ago:
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The program should cover the water-bearing formations in all sections of the country; it should include beds with water-table conditions, deep artesian aquifers, and intermediate sources; moreover, it should include areas of heavy withdrawal by pumping or artesian flow, areas which are not affected by heavy withdrawal but in which the natural conditions of intake and discharge have been affected by deforestation or breaking up of prairie land, and, so far as possible, areas that still have primeval conditions. This nation-wide program should furnish a reliable basis for periodic inventories of the ground-water resources, in order that adequate provision may be made for our future water supplies.
—(O.E. Meinzer, 1935, Introduction to “Report of the Committee on Observation Wells, United States Geological Survey” (Leggette and others, 1935) |
More recently, the National Research Council (2000) reiterated, “An unmet need is a national effort to track water levels over time in order to monitor water-level declines.”
This report reviews the uses and importance of data from long-term ground-water-level monitoring in the United States. Case studies are presented to highlight the broad applicability of long-term ground-water-level data to water-resource issues commonly faced by hydrologists, engineers, regulators, and resource managers. It is hoped that this report will provide a catalyst toward the establishment of a more rigorous and systematic nationwide approach to ground-water-level monitoring—clearly an elusive goal thus far. The time is right for progress toward this goal. Improved access to water data over the Internet offers the opportunity for significant improvements in the coordination of water-level monitoring and the sharing of information by different agencies, as well as the potential means for evaluation of water-level monitoring networks throughout the United States.
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