USGS

 

Estimating the Susceptibility of Surface Water in
Texas to Nonpoint-Source Contamination
by Use of Logistic Regression Modeling

By William A. Battaglin, Randy L. Ulery, Thomas Winterstein, and Toby Welborn

Available from the U.S. Geological Survey, Branch of Information Services, Box 25286, Denver Federal Center, Denver, CO 80225, USGS Water-Resources Investigations Report 03-4205, 24 p., 2 figs.

This document also is available in pdf format: Adobe Acrobat Icon WRIR 03-4205.pdf (1.7 MB)
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The citation for this report, in USGS format, is as follows:
Battaglin, W.A., Ulery, R.L., Winterstein, T., and Welborn, T., 2003, Estimating the Susceptibility of Surface Water in Texas to Nonpoint-Source Contamination by Use of Logistic Regression Modeling: U.S. Geological Survey Water-Resources Investigations Report 03-4205, 24 p.


Abstract

In the State of Texas, surface water (streams, canals, and reservoirs) and ground water are used as sources of public water supply. Surface-water sources of public water supply are susceptible to contamination from point and nonpoint sources. To help protect sources of drinking water and to aid water managers in designing protective yet cost-effective and risk-mitigated monitoring strategies, the Texas Commission on Environmental Quality and the U.S. Geological Survey developed procedures to assess the susceptibility of public water-supply source waters in Texas to the occurrence of 227 contaminants. One component of the assessments is the determination of susceptibility of surface-water sources to nonpoint-source contamination. To accomplish this, water-quality data at 323 monitoring sites were matched with geographic information system-derived watershed- characteristic data for the watersheds upstream from the sites. Logistic regression models then were developed to estimate the probability that a particular contaminant will exceed a threshold concentration specified by the Texas Commission on Environmental Quality. Logistic regression models were developed for 63 of the 227 contaminants. Of the remaining contaminants, 106 were not modeled because monitoring data were available at less than 10 percent of the monitoring sites; 29 were not modeled because there were less than 15 percent detections of the contaminant in the monitoring data; 27 were not modeled because of the lack of any monitoring data; and 2 were not modeled because threshold values were not specified.


Contents

Abstract

Introduction

Texas Source Water Assessment Project

Purpose and Scope

Surface-Water Nonpoint-Source Component

Surface-Water Sites

Water-Quality Data

Watershed-Characteristics Data

Logistic Regression Models

Estimating the Susceptibility of Surface Water to Nonpoint-Source Contamination

Summary of Modeled Contaminants

Examples of Modeling Results

Summary

References

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