Overview of the CD-ROM

The WQN data base contains water-quality and streamflow data collected at 679 locations in the United States including 63 HBN stations for the approximate period 1962-95 and 618 NASQAN stations for 1973-95 (two stations have belonged to both networks during the period of operations). Supporting information identifies and describes the water-quality and streamflow stations and watersheds, water-quality constituents, and the methods, remarks, laboratories, sample-collection agencies, and the laboratory measurement accuracy associated with the water-quality data. The WQN data sets on the CD-ROMs include the following elements:

• Uniformly-sampled (i.e., semi-annually to monthly) stream water-quality data for 63 physical, chemical, and biological properties of water (122 water constituents including the dissolved, suspended, and total forms). This includes physical/field measurements (e.g, temperature, instantaneous streamflow, pH, suspended sediment), major ions, nutrients, organic carbon, radiochemicals, biological measurements (e.g., fecal bacteria, phytoplankton, and periphyton), and inorganic trace elements. With the exception of the periphyton data, which reflect substrate conditions, all measurements reflect conditions in the water column.

• Daily mean values of streamflow for time periods corresponding to the water-quality records. These data can be used with the water-quality data to derive estimates of flux or load.

• Water-quality and streamflow station attributes including drainage area, latitude, longitude, the dates of station operation, county, state, and hydrologic unit code (HUC) identifiers, and drainage basin population for 1990 and land- cover statistics for 1987.

• The sample-collection agencies, laboratories, and laboratory analytical methods associated with the stream water-quality data. In addition to national network documents describing these characteristics, information on the collection agencies, laboratories, and analytical methods has been stored with the water-quality data values in digital data files since the early to mid 1980s.

• Laboratory quality-control data for 34 contstituents for water years 1985-95 (Oct. 1, 1984 to Sept. 30, 1995) for estimating the measurement bias and variability of national network stream water-quality data. The quality-control data were collected through a USGS program (the Blind Sample Program) responsible for regularly-submitting stable, homogeneous standard reference water samples to the USGS laboratory for measurement.

• Documentation of changes in field and laboratory methods, constituent coverage, network operations, reporting conventions, and sample contamination that may affect the use and interpretation of WQN stream water-quality data. The documentation includes USGS water-quality memoranda describing national network operations and important changes in field and laboratory methods.

• Copies of this Open-File Report. This report provides important background information on the national networks, characteristics of the water-quality, streamflow, and quality- assurance data, and statistical methods for using the Blind Sample Program reference sample data to evaluate the accuracy of the stream water-quality data.

• A bibliography of publications of national network field and laboratory methods, network historical background, interpretations of network data at the national, regional, and local levels, and statistical methods and computer software that have been developed for use with data having characteristics similar to those of the national network data.