National Water-Quality Assessment (NAWQA) Program
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by Anthony J. Tesoriero and Frank D. Voss
[Ground Water, v. 35, no. 6, November-December 1997, p. 1029-1039.]Abstract
The occurrence and distribution of elevated nitrate concentrations (greater than or equal to 3
mg/l) in ground water in the Puget Sound Basin, Washington, were
determined by examining existing data from more than 3000 wells.
Models that estimate the probability that a well has an elevated
nitrate concentration were constructed by relating the occurrence of
elevated nitrate concentrations to both natural and anthropogenic
variables using logistic regression. The variables that best explain
the occurrence of elevated nitrate concentrations were depth,
surficial geology, and the percentage of urban and agricultural land
within a radius of 3.2 kilometers of the well. From these relations,
logistic regression models were developed to assess aquifer
susceptibility (relative ease with which contaminants will reach
aquifer) and ground-water vulnerability (relative ease with which
contaminants will reach aquifer for a given set of land-use
practices). Both models performed well at predicting the probability
of elevated nitrate concentrations in an independent data set. This
approach to assessing aquifer susceptibility and ground-water
vulnerability has the advantages of having both model variables and
coefficient values determined on the basis of existing water quality
information and does not depend on the assignment of variables and
weighting factors based on qualitative criteria.
Table of Contents
Introduction
Regional hydrology
Methods
Data analysis and discussion
Single variable models
Multiple variable models
Summary and conclusions
Acknowledgments
References