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389. National Ambient Water Quality in Rivers and Streams -- Violation Rate

[In percent. Violation level based on U.S. Environmental Protection Agency water quality criteria. Violation rate represents the proportion of all measurements of a specific water quality pollutant which exceeds the "violation level" for that pollutant. "Violation" does not necessarily imply a legal violation. Data based on U.S. Geological Survey's National Stream Quality Accounting Network (NASQAN) data system; for details, see source. Years refer to water years. A water year begins in October and ends in September. @mg=micrograms; mg=milligrams]

POLLUTANT Violation level 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995
Fecal coliform bacteria....... Above 200 cells per 100 ml 31 30 33 34 30 28 24 23 22 30 26 15 28 31 28 35
Dissolved oxygen............ Below 5 mg per liter 5 4 5 4 3 3 3 2 2 3 2 2 2 (Z) 2 1
Phosphorus, total,
  as phosporous............ Above 1.0 mg per liter 4 4 3 3 4 3 3 3 4 2 3 2 2 2 2 4
Lead, dissolved ............. Above 50 @mg per liter (Z) (Z) (Z) (Z) (Z) (Z) (Z) (Z) (Z) (Z) (Z) (Z) (Z) (NA) (NA) (NA)
Cadmium, dissolved............ Above 10 @mg per liter 1 1 1 (Z) (Z) (Z) (Z) (Z) (Z) (Z) (Z) (Z) (Z) (NA) (NA) (NA)

NA Not available. Z Less than 1.

Source: U.S. Geological Survey, national-level data, unpublished; state-level data, level data in Water-Data Report, annual series prepared in cooperation with the state governments.

* NASQUAN (National Stream Quality Accounting Network

During the past 30 years, the U.S. Geological Survey (USGS) has operated two national stream water-quality networks, the Hydrologic Benchmark Network (HBN) and the National Stream Quality Accounting network (NASQAN). These networks were begun in the 1960s and 1970s, respectively, to document stream water-quality conditions and trends for watersheds throughout the United States and to improve our understanding of the effects of the natural environment and human activities on water quality. The enactment of significant environmental legislation during these decades, including the Water Quality Act of 1965 and the Clean Water Act of 1972 and its subsequent amendments, increased the need for comprehensive water-quality monitoring data at all levels of government. The networks were designed to address these needs at the national and regional levels by providing systematically-collected information on the quality of the nation's rivers (Leopold, 1962b; Briggs and Ficke, 1975).

Since their inception, the national networks have provided water-quality data for numerous watersheds with diverse climatic, physiographic, and cultural characteristics, which has benefited efforts to investigate the causes of spatial and temporal variations in water quality (Smith and others, 1987a; Smith and Alexander, 1983). The watersheds range from the relatively small, minimally disturbed basins in the HBN to the larger, more culturally-influenced drainage basins of NASQAN. During the operation of the networks, considerable changes have occurred in terrestrial and atmospheric sources of water pollutants in the United States brought about, in part, by regulatory actions. Examples include changes in fertilizer use, atmospheric sources of sulfur and nitrogen, and wastewater discharges from municipal sewage treatment plants. The national networks have provided some of the best available information for investigating the influences of these pollutant sources on national and regional water quality (e.g., Smith and others, 1987a; Smith and Alexander, 1986; Kramer and others, 1986; Lins, 1986; Smith and others, 1993). In addition, national network data have been used to quantify trends in stream water quality (e.g., Lettenmaier and others, 1991; Smith and others, 1993), estimate the rates of chemical flux from watersheds (e.g., Alexander and others, 1996a; Peters, 1984), and investigate relations between water quality and streamflow (e.g., Smith and others, 1982) and between water quality and various physical characteristics of the watersheds (Biesecker and Leifeste, 1975; Peters, 1984). Numerous state and local investigations of stream water quality have also used NASQAN and HBN data to examine stream water-quality conditions and trends (e.g., Schertz, 1990; Schertz and others, 1994; Hay and Campbell, 1990; Hainly and Ritter, 1986).

The national networks have provided stream measurements for a relatively consistent and comprehensive set of water properties. Approximately 85 physical, chemical, and biological properties have been analyzed during more than 60,000 visits to 679 stream locations. Relatively consistent sampling and analytical methods have been used at national network sites during their operation. The water-quality data reflect sampling over a wide range of streamflow conditions. As of 1995, expenditures for the two national networks have totaled approximately $95 million, including $80 million for NASQAN and $15 million for the HBN.

Documentation and quality-assurance information on network operations and historical records of sample-collection agencies, laboratories, analytical methods, and estimates of laboratory measurement error are available to assist in the proper use of the stream water-quality data. This information is especially useful for documenting changes in network operations and sampling and analytical methods that may affect the use and interpretation of the ambient water-quality data. Much of this information is contained in USGS publications and previously unpublished USGS internal technical memoranda. Estimates of laboratory measurement error (i.e., variability and bias) have been previously published as part of the Blind Sample Program, an external USGS laboratory quality- assurance program (Maloney and others, 1994). These data have been used to systematically assess the accuracy of USGS laboratory methods and national network stream water-quality data (see for example, Maloney and others, 1994; Alexander and others, 1993). *

These tables are based on figures supplied by the United States Census Bureau, U.S. Department of Commerce and are subject to revision by the Census Bureau.

Copyright © 2006 Photius Coutsoukis and Information Technology Associates, all rights reserved.