National Water-Quality Assessment--Potomac River Basin: Study Design for Assessing the Occurrence and Distribution of Water-Quality Conditions in the Potomac River Basin, Study Unit of the National Water-Quality Assessment Program
By James M. Gerhart
The Potomac River Basin study unit of the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) program has been designed to describe and explain the water-quality conditions of streams and aquifers in a large part of the 14,670-square-mile basin, the western two-thirds of which is included in the Mid-Atlantic Highlands Area. The design of the study unit consists of four major components--(1) retrospective analysis of water-quality data, (2) assessment of the occurrence and distribution of water-quality conditions, (3) long-term monitoring of water-quality conditions, and (4) case studies of the source, transport, and effect of contaminants. The occurrence and distribution assessment is the major component of the middle years (1993-95) of the initial 6-year intensive phase of the study unit.
The objectives of the second major component, the occurrence and distribution assessment, include the description of the occurrence, spatial distribution, and temporal variation of selected surface-water, ecological, and Groundwater water-quality characteristics, as well as the explanation of how natural and human factors influence those characteristics. To facilitate meeting these objectives, the Potomac River Basin has been divided, or stratified, into eight geographic subunits. Each of the eight subunits represents a distinctly different combination of physiographic, geologic, ecologic, and hydrologic settings, thereby establishing a convenient framework for the description and explanation of water-quality conditions.
Surface-water, ecological, and Groundwater sampling approaches for the occurrence and distribution assessment have been designed to enable the description and explanation of water quality at basinwide, subunit, and small watershed scales. Surface-water and ecological approaches include (1) a basinwide survey of contaminants in bed sediments and aquatic biological tissues, (2) a fixed network of stream sites throughout the basin for water- column sampling and ecological surveys, (3) a synoptic water-column sampling of major tributaries, (4) synoptic water-column samplings and ecological surveys at numerous sites in four of the eight subunits, and (5) synoptic water-column samplings and ecological surveys at numerous sites in a small watershed in an important subunit. Groundwater approaches include (1) the sampling of numerous shallow domestic wells at randomized locations in four of the eight subunits, and (2) the installation, instrumentation, and sampling of shallow observation wells in a small watershed in an important subunit. Analytes for most surface-water and Groundwater samples include major ions, nutrients, and pesticides. Ecological surveys generally include the description of habitat and algal, benthic-macroinvertebrate, and fish communities.
Gerhart, J. M. 1994, Study design for assessing the occurrence and distribution of water-quality conditions in the Potomac River Basin study unit, NAWQA program [abs.] : Abstract Booklet, Mid-Atlantic Highlands Area Environmental Monitoring and Assessment Conference, Hershey, Pennsylvania, February 23-25, 1994, p. 39.