Over the past two decades, NAWQA has used nationally consistent procedures for site selection, sampling, chemical analysis, and data management to examine the natural factors and land-management practices that control the quality of ground water and surface water, encompassing a broader range of spatial scales, contaminants, and environmental settings than any other large-scale sampling program to date. NAWQA also examines temporal trends in ground- and surface-water quality across the Nation.
Early NAWQA accomplishments included the publication of summaries of existing information on environmental settings and water quality in major hydrologic basins across the Nation, as well as overviews of current understanding regarding the occurrence, sources, transport, and fate of a wide range of contaminants in the hydrologic system. These summaries provided guidance for selecting the locations, environmental media, and contaminants upon which the program has focused its sampling. The program has also assembled an extensive body of ancillary data—mostly from non-USGS sources—on chemical releases, environmental characteristics, and land use from local to national scales. These data have been combined with the NAWQA sampling results to construct statistical and mechanistic models for predicting contaminant occurrence in ground water throughout the Nation. NAWQA also helped bring national attention to the detection in ground water of several contaminants whose occurrence in the hydrologic system had not been widely reported—including the gasoline additive MTBE; chloroform; the herbicides prometon, acetochlor, and glyphosate; and several pesticide degradates—as well as to potential contaminant sources that had not yet received much scrutiny, such as road salt, ground-water recharge facilities, and atmospheric deposition.