The mission of the U.S. Geological Survey is to assess the quantity and the quality of the earth resources of the Nation and to provide information that will assist resource managers and policy makers at the Federal, the State, and the local levels in making sound decisions. Assessment of water-quality conditions and trends is an important part of this overall mission. The history of the earth sciences demonstrates that the ''scale'' at which scientists examine the Earth has a major effect on the kinds of insights gained from their studies. In geology, for example, roles exist for investigations at the quadrangle map scale (1 :24,000) and for continental or global scale studies focused on plate tectonics. Furthermore, geologic studies at one scale often enhance the understanding of the phenomena examined at the other scales. Similarly, in meteorology, there is a role for microscale climatic studies over distances of less than a mile, mesoscale studies of regional weather systems, and global circulation studies. Again, the overall science would be weakened by the lack of any one of these scales of study. Investigations at different temporal scales also are needed. Some studies of earthquake phenomena, for example, measure processes that last for seconds or even milliseconds, and others chart the buildup of the stresses responsible for earthquakes over periods of decades to centuries. This document defines an approach for examining the quality aspects of water resources at a unique combination of spatial and temporal scales. The spatial scale is primarily regional (several thousands of square miles), and the temporal scale is primarily multiyear and decadal. The study design stems from the view that insights about water quality, which would be of great value to resource managers and policy makers, can be best achieved by examining water quality at these scales and by aggregating the findings of the studies with time and across the Nation. These assessments would rely on many of the data already being collected as part of smaller scale studies focused on local problems, although the questions under investigation would be quite different. The primary questions would concern the natural and human factors that give rise to different types of widespread waterquality conditions and the long-term fate of contaminants stored in aquifers, sediments, or biota. Throughout its history, the Nation has made major investments in assessing natural resources, such as soils, minerals, and hydrocarbons, and human resources in terms of the health, the education, the employment, and the economic status of the population. The reason for these investments in information is that decisions our society makes about using or conserving these resources, investing in their improvement, or regulating their use will be better if they are based on sound information. The maintenance and the improvement of water quality is now one of the major areas of public investment and government regulation. Therefore, it is appropriate that serious attempts be...
