The western part of the Salt River Valley area (WSRV) is a large
alluvial basin in central Arizona. The WSRV includes the city of Phoenix and
much of the surrounding metropolitan area, which had a population of 2.1
million residents in 1990. In addition to being a major population center,
large parts of the valley have been intensively farmed since the early part of
the century. Both agricultural and non-agricultural activities have affected
the quality of ground water in the basin. Ground water in several areas of the
valley exceeds the 10 mg/L (as N) maximum contaminant level set by the U.S.
Environmental Protection Agency (USEPA). Although in some areas high nitrate
concentrations have a natural source, in other areas nitrates are the result of
one or more human activities.
The purposes of the project, which began in 1990 in cooperation with
the Arizona Department of Environmental Quality, were
- to attempt to develop a geochemical technique to identify sources of
contaminants in ground water on the basis of the chemical and isotopic
composition of both the ground water and suspected nitrate sources, and
- to establish the best geostatistical methods for unbiased and reproducible
spatial estimates (maps) of existing nitrate contamination in ground water.
Because ground-water under large areas of the valley contains more than 10 mg/L
nitrate nitrogen, accurate estimates of nitrate distribution are beneficial to
effective management or at least monitoring of the problem.
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