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Publications—Scientific Investigations Report

National Water-Quality Assessment Program

Development and Application of a Regression Equation for Estimating the Occurrence of Atrazine in Shallow Ground Water beneath Agricultural Areas of the United States

By Paul E. Stackelberg, Robert J. Gilliom, David M. Wolock, and Kerie J. Hitt


U.S. Geological Survey Scientific Investigations Report 2005-5287



The body of the report is available in PDF Format ( 3,357KB)



Results from 52 ground-water studies throughout the United States were used to examine relations between the occurrence of atrazine in shallow ground water in agricultural settings and explanatory variables that describe the natural setting, agricultural-management practices, and the type and amount of development in each area. The explanatory variables that were found to be correlated with atrazine occurrence were soil-infiltration rates, presence of artificial drainage (tile drains or trenches), available water-holding capacity of soils, soil permeability, amount of study area using ground water for irrigation source (as percentage of total area), amount of agricultural land (as percentage of total area), and intensity of atrazine use. Ordinary least-squares regression equations that used one or more of these explanatory variables describe as much as 58 percent of the variation in atrazine-detection frequencies. Application of a multivariate equation to unmonitored agricultural areas across the conterminous United States illustrates that atrazine use alone is insufficient for estimating the occurrence of atrazine in shallow ground water. Instead, areas in which soil characteristics and agricultural-management practices favor the movement of water from land surface to the water table and that also have intensive atrazine use are the most vulnerable to atrazine contamination.







Study Areas and Well Networks

Sampling and Analytical Methods

Statistical Methods

Ancillary Data

Estimating Atrazine Occurrence in Shallow Ground Water

Regression Equation

Residuals Analysis

Equation Performance

Estimation of Atrazine Occurrence



References Cited



1. Generalized locations of the 52 agricultural ground-water studies of the NAWQA (National Water-Quality Assessment) Program, 1991–2001

2. Distribution of (A) studentized residuals, (B) studentized residuals and estimated atrazine detection frequencies, and (C) observed and estimated atrazine detection frequencies

3. (A) Estimated 1992 agricultural use of atrazine throughout the conterminous United States, and (B) estimated frequency of atrazine occurrence in shallow ground water underlying agricultural areas throughout the conterminous United States.



1. Explanatory variables used for equation development

2. Statistics for ordinary least-squares regression equations


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For further information, contact:

Rafael Rodriguez, Director

U.S. Geological Survey

New York Water Science Center

425 Jordon Road

Troy, NY 12180-8349

(518) 285-5659


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