In 1991, the U.S. Geological Survey (USGS) began to implement a full-scale National Water-Quality Assessment (NAWQA) program. The three major objectives of the NAWQA program are to provide a consistent description of current waterquality conditions for a large part of the Nation's water resources, define long-term trends in water quality, and identify, describe, and explain the major factors that affect water-quality conditions and trends. The program will produce water-quality information that will be useful to policy makers and managers at the national, State, and local levels. The program will be implemented through 60 separate investigations of river basins and aquifer systems, called study units. These study-unit investigations will be conducted at the State and local level, and will form the foundation on which national- and regional-level assessments are based. The 60 study units are hydrologic systems that include parts of most major river basins and aquifer systems. The study-unit areas range from 1,200 to more than 65,000 square miles and include about 60 to 70 percent of the Nation's water use and population served by public water supply. In 1991, the Lower Susquehanna River basin was among the first 20 NAWQA study units selected for study under the full-scale implementation plan.
