conception, NAWQA was the largest water resources program ever undertaken by USGS (R. J. Gilliom and R. M. Hirsch, personal communication, May 13, 2009).


In the first decade of water-quality monitoring (Cycle 1, 1991-2001) NAWQA set out to (1) accumulate high-quality, multidisciplinary, water-quality data and (2) generate a national synthesis of those data focusing on analysis of the highest-priority issues that cuts across the geography and answers the question, “How is the nation’s water quality changing?” The program demonstrated considerable progress toward a national water-quality assessment in Cycle 1. For thoroughness and to place this report in context, the committee notes key components of Cycle 1 here. (For a detailed review of Cycle 1 see NRC [2002].)

The Study Unit Concept

The Cycle 1 study units accounted for 60 to 70 percent of the nation’s water use and population served by public water supplies and covered about one-half of the land area of the United States. A broad suite of physical, chemical, and biological constituents was selected based on relevance to water-quality issues and existing analytical methods including measurements of:

  • streamflow,
  • pH,
  • temperature,
  • dissolved oxygen,
  • specific conductance,
  • major ions,
  • nutrients,
  • trace elements,
  • organic carbon,
  • pesticides, and
  • volatile organic compounds (VOCs) (NRC, 2002).

Also, descriptions of biological communities were made based on different taxonomic groups and habitat conditions (NRC, 2002). A suite of surface water reference sites, a sampling site selected for relatively undisturbed conditions, was built into the surface water network design. At the end of Cycle 1, monitoring at 51 study units plus a study of the High Plains Aquifer in the central United States were completed. (The geographic scope of

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