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, state, and local levels in making sound decisions. Assessment of water-quality conditions and trends is an important part of this overall mission, and the survey has recently released the report Concepts for a National Water-Quality Assessment Program by Robert M. Hirsch, William M. Alley, and William G. Wilber as U.S. Geological Survey Circular 1021.
The authors define 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 best be achieved by examining water quality at these scales and by aggregating the findings of the studies with time and across the country. 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 water- quality conditions and the long-term fate of contaminants stored in aquifers, sediments, or biota.