National Water-Quality Assessment (NAWQA) Program
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Each stream sampled by NAWQA was classified according to the dominant land uses in its watershed. The land-use data set used for these classifications was an enhanced version of the 1992 National Land Cover Data (NLCD), which classified land use for each 30-by-30-meter area of land in the conterminous United States. The original and enhanced versions of the NLCD are described, respectively, by Vogelmann and others (2001) and Nakagaki and Wolock (2005).
The most common unique mixtures of pesticides and degradates found in stream water and ground water illustrate the diversity and complexity of mixtures that occur in agricultural and urban areas. The mixtures detected most frequently for each number of compounds are shown for each land use, with all detections included, regardless of concentration. These most common unique mixtures serve as examples, rather than as a comprehensive compilation of all the most important mixtures, because other mixtures occurred almost as frequently.
The most common unique mixtures of organochlorine pesticide compounds found in fish tissue were dominated by compounds derived from commercial formulations of DDT, DDD, and chlordane, as well as dieldrin The mixtures detected most frequently for each number of compounds are shown for each land use. These most common mixtures serve as examples, rather than having unique importance, because many other mixtures occur almost as frequently.
Most wells sampled for agricultural and urban land-use studies were shallow observation wells that are not used for drinking water, but about 29 percent of wells sampled in agricultural areas were domestic wells. Most wells sampled for the major aquifer studies are used for drinking water; about 13 percent were public-supply wells, and 71 percent were domestic wells. Overall, about 1 percent of all domestic and public-supply wells had concentrations of a pesticide greater than a human-health benchmark.
Selected studies of pesticide mixtures containing diazinon illustrate the spectrum of possible responses for such mixtures The types of compounds included are two organophosphate insecticides (OP), a pyrethroid insecticide (P), a triazine herbicide (T), and a nutrient.
Appendix 1. Pesticide compounds analyzed in NAWQA samples
Appendix 2. Properties affecting the transport and fate of selected pesticide compounds
Appendix 3. Water-quality benchmarks for pesticide compounds analyzed in NAWQA samples
Appendix 4. List of abbreviations, acronyms, and units of measurement
Appendix 5. NAWQA sampling sites and their characteristics
Appendix 6. Downloadable water-quality data files
Appendix 7. Statistical summaries of water-quality data
Appendix 8. Methods and approach for NAWQA pesticide data analysis
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