Water-Quality Assessment of the Potomac River Basin: Water-Quality and Selected Spatial Data, 1992-96
By A.L. Derosier, J.W. Brakebill, J.M. Denis, and S.K. Kelley
Excerpt from Introduction
The U.S. Geological Survey (USGS) implemented the National Water-Quality Assessment (NAWQA) Program to describe the status and trends in the quality of the Nation's surface water and ground water and to provide scientific understanding of the natural and human-induced factors that affect water quality. In 1991, twenty study units were started. Additional study units began in 1994 and 1997. Data collection and analysis in each study unit follows national guidelines for the NAWQA Program, but also addresses the issues most important to that study unit. NAWQA is designed to produce a wealth of water-quality information to assist policy makers and managers at the national, state, and local levels in making more informed decisions.
In 1991, the Potomac River Basin study unit began planning assessment activities. The basin was subdivided into eight subunits based on physiographic and geologic characteristics, which were determined to be the most influential natural factors affecting water quality. Water-quality sampling began in 1992. The first high-intensity data-collection phase of the study unit spanned from 1993 to 1995; much of the data collection focused on the Great Valley Carbonate, Piedmont, Triassic Lowlands, and Valley and Ridge subunits. Hundreds of water-quality characteristics were measured in different media during this time, including ground water, streamwater, streambed sediments, and aquatic biological tissues. Fish communities and stream habitat also were sampled. In addition, spatial data such as geology, land use, hydrography, and other watershed characteristics were compiled into a geographic information system (GIS) to support the assessment. After 1995 the project entered a period of less frequent sampling called the low-intensity phase.
