In 1991 the U.S. Geological Survey (USGS) initiated the National Water-Quality Assessment (NAWQA) Program to assess the status and trends in the quality of freshwater streams and aquifers, and to provide a sound understanding of the natural and human factors that affect the quality of these resources. The design is based on balancing the unique assessment requirements of individual hydrologic systems with a nationally consistent design structure that incorporates a multiscale, interdisciplinary approach for ground water and surface water.
The "building blocks" of the NAWQA
Program are the individual hydrologic systems -- called
study units-- which presently include 59 areas located
throughout the Nation. These study units provide the framework
for a national and regional water-quality assessment. Together,
these areas account for 60-70 percent of the Nation's water use
and population served by public water supplies, and cover about
one-half of the land area of the Nation. Twenty study-unit
investigations were started in 1991, an additional 16 were
started in 1994, 15 were started in 1997, and 2 were started in
1999. An additional seven study-unit investigations are planned
for the future.
As part of the NAWQA
Program, the USGS is evaluating water quality in the
Allegheny and Monongahela (ALMN) River Basins. The ALMN
Study-Unit Investigation was started in 1994. The ALMN drainage
basin is the largest stream system in southwestern Pennsylvania.
The Study Unit covers an area of about 19,145 square miles in
part or all of 16 counties and four states, including
Pennsylvania, Maryland, New York, and West Virginia. The Study
Unit is home to more than 3.1 million people who rely on surface
and ground-water resources that originate within the basin. In
1990, water withdrawn from aquifers and surface-water bodies in
the Study Unit averaged 3 billion gallons per day, most of which
was from surface-water sources
(McAuley and others, 1997). Additional information on the
Study Unit environmental setting
The quality of the surface water, ground water, and aquatic life in the ALMN Study Unit can be significantly affected by several principal issues, including:
For information on the ALMN Project Study-Unit Design see the Project Overview, for description of each surface water and ground water study component, or see the Summary Table, for an overview of all the study components.
Initial ALMN Project
activities included detailed planning during the first year and
analysis of existing data during the second year. The suceeding 3
years are for intensive data collection and analysis. The sixth
year is for completion of data analysis and reports. These
activities will be followed by a period of low-level assessment,
mainly intermittent water-quality monitoring, at selected sites.
The next cycle of intensive data collection and analysis will
follow the low-level assessment period (McAuley and others, 1997).
Nationally, about one-third of the study units are in the
intensive-study phase at any given time.