National Water-Quality Assessment (NAWQA) Program
Several types of water-quality standards and guidelines for protection of human health, aquatic organisms, and wildlife are described. A few examples are discussed in detail, including the regulatory status, sampling medium, beneficial use and resource protected, technical basis, and underlying assumptions. Standards and guidelines are threshold values set by federal or state agencies or other institutions to indicate contaminant concentrations above which there may be potential effects on human health, aquatic organisms, or wildlife. Standards (legally enforceable threshold values) and guidelines (threshold values issued in an advisory capacity) are commonly used to assess the potential effects of pesticides and other contaminants on water quality by comparison with measured concentrations of individual contaminants in the environment. Effective use of these threshold values in water-quality assessment requires both an understanding of how individual standards and guidelines are derived, as well as information about the specific hydrologic system being studied. Specific questions that are addressed include: What factors should be considered in selecting appropriate standards and guidelines for comparison with the type of water quality data being assessed? What does each standard or guideline protect, and what does it mean when these values are exceeded? What is the technical basis for each standard or guideline, and how does this affect the conclusions regarding potential effects on water quality? What assumptions were made in deriving each standard or guideline and are they appropriate for the hydrologic system being studied? Recent changes in how some pesticide standards are developed, as mandated by the Food Quality Protection Act of 1996, are also discussed. Emphasis is placed on how individual standards and guidelines are developed, and how this affects the application of these standards and guidelines in water-quality assessment.