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Water-Quality Assessment of the Trinity River Basin, Texas—Ground-Water Quality of the Trinity, Carrizo-Wilcox, and Gulf Coast Aquifers, February–August 1994

By David C. Reutter and David D. Dunn

U.S. Geological Survey
Water-Resources Investigations Report 99–4233

National Water-Quality Assessment Program


Abstract

Ground-water samples were collected from wells in the outcrops of the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers during February–August 1994 to determine the quality of ground water in the three major aquifers in the Trinity River Basin study unit, Texas. These samples were collected and analyzed for selected properties, nutrients, major inorganic constituents, trace elements, pesticides, dissolved organic carbon, total phenols, methylene blue active substances, and volatile organic compounds as part of the U.S. Geological Survey National Water-Quality Assessment Program. Quality-control practices included the collection and analysis of blank, duplicate, and spiked samples.

Samples were collected from 12 shallow wells (150 feet or less) and from 12 deep wells (greater than 150 feet) in the Trinity aquifer, 11 shallow wells and 12 deep wells in the Carrizo-Wilcox aquifer, and 14 shallow wells and 10 deep wells in the Gulf Coast aquifer. The three aquifers had similar water chemistries—calcium was the dominant cation and bicarbonate the dominant anion. Statistical tests relating well depths to concentrations of nutrients and major inorganic constituents indicated correlations between well depth and concentrations of ammonia nitrogen, nitrite plus nitrate nitrogen, bicarbonate, sodium, and dissolved solids in the Carrizo-Wilcox aquifer and between well depth and concentrations of sulfate in the Gulf Coast aquifer. The tests indicated no significant correlations for the Trinity aquifer.

Concentrations of dissolved solids were larger than the secondary maximum contaminant level of 500 milligrams per liter established for drinking water by the U.S. Environmental Protection Agency in 12 wells in the Trinity aquifer, 4 wells in the Carrizo-Wilcox aquifer, and 6 wells in the Gulf Coast aquifer. Iron concentrations were larger than the secondary maximum contaminant level of 300 micrograms per liter in at least 3 samples from each aquifer, and manganese concentrations were larger than the secondary maximum contaminant level of 50 micrograms per liter in at least 2 samples from each aquifer. The pesticides atrazine, deethylatrazine, and pp'-DDE were detected in at least one sample from each aquifer. Diazinon was detected in 11 Trinity aquifer samples and 4 Carrizo-Wilcox aquifer samples. Each aquifer had one detection of a volatile organic compound—benzene in the Trinity aquifer, trichlorofluoromethane in the Carrizo-Wilcox aquifer, and trichloromethane in the Gulf Coast aquifer.

Table of Contents

Abstract

Introduction

Purpose and Scope

Physiographic and Hydrogeologic Setting

Trinity Aquifer

Carrizo-Wilcox Aquifer

Gulf Coast Aquifer

Acknowledgments

Data-Collection Methods

Well Selection

Sampling Methods

Quality Control

Ground-Water Quality

Trinity Aquifer

Carrizo-Wilcox Aquifer

Gulf Coast Aquifer

Comparisons Among Aquifers

Summary

References

Appendix 1. Water-Quality Data for Trinity, Carrizo-Wilcox, and Gulf Coast Aquifers

Figures

1.   Map showing location of major aquifers in relation to Integrated Land Resource Units in the Trinity River Basin study unit
2–4.   Maps showing location of wells sampled in the outcrop of the:
  2.   Trinity aquifer
  3.   Carrizo-Wilcox aquifer
  4.   Gulf Coast aquifer
5.   Boxplots showing distributions of depths for wells sampled in the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers in the Trinity River Basin study unit
6.   Trilinear diagrams of major constituents in samples from Trinity aquifer wells (a) 150 feet deep or less and (b) greater than 150 feet deep
7–8.   Boxplots showing range and distribution of concentrations of:
  7.   (a) Ammonia nitrogen, (b) nitrite plus nitrate nitrogen, (c) total phosphorus, and (d) orthophosphate phosphorus in samples from wells in the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers in the Trinity River Basin study unit
  8.   Major constituents in samples from wells in the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers in the Trinity River Basin study unit
  9.   Trace elements in samples from wells in the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers in the Trinity River Basin study unit
10–11.   Maps showing location of wells in the Trinity aquifer with:
  10. Pesticide detections in a sample
  11. Total phenols or volatile organic compound detections in a sample
12.   Trilinear diagrams of major constituents in samples from Carrizo-Wilcox aquifer wells (a) 150 feet deep or less and (b) greater than 150 feet deep
13–14.   Maps showing location of wells in the Carrizo-Wilcox aquifer with:
  13.   Pesticide detections in a sample
  14.   Total phenols or volatile organic compound detections in a sample
15.   Trilinear diagrams of major constituents in samples from Gulf Coast aquifer wells (a) 150 feet deep or less and (b) greater than 150 feet deep
16–17.   Maps showing location of wells in the Gulf Coast aquifer with:
  16.   Pesticide detections in a sample
  17.   Total phenols or volatile organic compound detections in a sample

Tables

1.   Description of wells sampled in the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers in the Trinity River Basin study unit
2.   National Water Quality Laboratory method detection limits for properties and constituents analyzed in samples from the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers in the Trinity River Basin study unit
3.   Constituents detected in field blanks, number of detections, and maximum concentrations
4.   Concentrations of inorganic constituents detected in quality-control sequential duplicate samples from the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers in the Trinity River Basin study unit
5.   Percent recoveries of volatile organic compound spiked samples from the Trinity, Carrizo-Wilcox, and Gulf Coast aquifers in the Trinity River Basin study unit
6–7.   Rank correlations between well depth and concentrations of nutrients and major inorganic constituents in the
  6.   Trinity aquifer samples
  7.   Carrizo-Wilcox aquifer samples
  8.   Gulf Coast aquifer samples

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