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Scientific Investigations Report 2006-5299

In cooperation with the Texas Commission on Environmental Quality

Recent (2003–05) Water Quality of Barton Springs, Austin, Texas, With Emphasis on Factors Affecting Variability

By Barbara J. Mahler, Bradley D. Garner, MaryLynn Musgrove, Amber L. Guilfoyle, and Mohan V. Rao

Report cover and link to PDF

Report PDF (12.4 MB)

Appendix 1 PDF (1.9 MB)

Appendix 2 PDF (1.6 MB)

Appendix 3 PDF (385 kB)

Appendix 4 PDF (2.6 MB)

Appendix 5 PDF (3.3 MB)

 

Abstract

From 2003 to 2005, the U.S. Geological Survey, in cooperation with the Texas Commission on Environmental Quality, collected and analyzed water samples from the four springs (orifices) of Barton Springs in Austin, Texas (Upper, Main, Eliza, and Old Mill Springs), with the objective of characterizing water quality. Barton Springs is the major discharge point for the Barton Springs segment of the Edwards aquifer. A three-pronged sampling approach was used: physicochemical properties (including specific conductance and turbidity) were measured continuously; samples were collected from the four springs routinely every 2 weeks (during August-September 2003) to 3 weeks (during June 2004-June 2005) and analyzed for some or all major ions, nutrients, trace elements, soluble pesticides, and volatile organic compounds; and samples were collected from the four springs at more closely spaced intervals during the 2 weeks following two storms and analyzed for the same suite of constituents. Following the two storms, samples also were collected from five of the six major streams that provide recharge to Barton Springs. Spring discharge during both sample collection periods was above average (60 cubic feet per second or greater). Barton Springs was found to be affected by persistent low concentrations of atrazine (an herbicide), chloroform (a drinking-water disinfection by-product), and tetrachloroethene (a solvent). Increased recharge from the major recharging streams resulted in increased calcium, sulfate, atrazine, simazine, and tetrachloroethene concentrations and decreased concentrations of most other major ions, nitrate, and chloroform at one or more of the springs. These changes in concentration demonstrate the influence of water quality in recharging streams on water quality at the springs even during non-stormflow conditions. The geochemical compositions of the four springs indicate that Upper Spring is more contaminated and is influenced by a contributing flow path that is separate from those leading to other springs under all but stormflow conditions. Main, Eliza, and Old Mill Springs share at least one common flow path that contributes contaminants to the three springs. Old Mill Spring, however, is less affected by anthropogenic contaminants than the other springs and receives a greater component of water from a flow path whose geochemistry is influenced by water from the saline zone of the aquifer. At Main Spring, atrazine, simazine, chloroform, and tetrachloroethene concentrations increased following storms, describing breakthrough curves that peaked 2 days following rainfall; at Upper Spring, atrazine and simazine concentrations described breakthrough curves that peaked 1 day following rainfall. At both Main and Upper Springs, additional anthropogenic compounds were detected following storms. The geochemical response of the springs to recharge indicates that much of the transport occurs through conduits. When there is no flow in the recharging streams, ground water advects from the aquifer matrix into the conduits and is transported to the springs. When there is flow in the streams, recharge through the streambeds directly enters the conduit system and is transported to the springs. Following storms, surface runoff recharges through both interstream recharge features and streambeds, delivering runoff-related contaminants to Barton Springs.


Suggested citation:

Mahler, B.J., Garner, B.D., Musgrove, M., Guilfoyle, A.L., and Rao, M.V., 2006, Recent (2003–05) water quality of Barton Springs, Austin, Texas, with emphasis on factors affecting variability: U.S. Geological Survey Scientific Investigations Report 2006–5299, 83 p., 5 appendixes.



Contents

Abstract

Introduction

Purpose and Scope

Overview of Karst Systems

Study Area Description and Previous Studies

Geologic Setting

Sources of Recharge

Discharge From the Aquifer

General Ground-Water-Flow Direction

Saline Zone Boundary

Water Quality in the Barton Springs Segment of the Edwards Aquifer

Chemical Species and Contaminants of Interest

Nutrients

Pesticides

Volatile Organic Compounds

Acknowledgments

Methods

Study Design

Discharge Measurements

Recharge Estimation

Physicochemical Property Measurements

Water-Quality Sample Collection

Analytical Methods

Water Quality of Barton Springs (2003–05)

Continuous Discharge and Physicochemical Measurements

Spring Discharge

Specific Conductance

Turbidity

Temperature

pH

Dissolved Oxygen

Water Quality Over an Annual Cycle

Major Ions

Differences in Geochemistry Among Spring Orifices

Temporal Variability in Major Ion Concentrations and Relation to Recharge and Discharge

Nutrients

Differences in Nitrate Concentrations Among Spring Orifices

Temporal Variability in Nitrate Concentrations and Relation to Recharge and Discharge

Trace Elements

Soluble Pesticides

Detection Frequencies and Concentrations

Differences in Pesticide Concentrations Among Spring Orifices

Temporal Variability in Pesticide Concentrations and Relation to Recharge and Discharge

Volatile Organic Compounds

Detection Frequencies and Concentrations

Differences in Volatile Organic Compound Concentrations and Detection Frequencies Among Spring Orifices

Temporal Variability in Volatile Organic Compound Concentrations and Relation to Recharge and Discharge

Comparison of Pesticide and Volatile Organic Compound Concentrations in Spring Waters and Ground Waters

Pharmaceuticals

Annual Loads of Ubiquitous Contaminants

Response of Barton Springs to Stormflow

Variation in Physicochemical Properties in Response to Storms

Streamflow and Spring Discharge

Specific Conductance and Turbidity

Major Ions

Nutrients

Soluble Pesticides

Volatile Organic Compounds

Pharmaceuticals

Storm-Related Loads of Contaminants

Synthesis—Factors That Affect Water-Quality Variability

Water Quality

Relation of Spring Geochemistry to Flow Paths

Sources of Water to Barton Springs

Aquifer Functioning in Response to Flow Conditions

Limitations of This Investigation

Summary

References

Appendix 1—Review of Historical (1974–2003) Water-Quality Data

Appendix 2—Historical Data

Appendix 3—Quality-Assurance/Quality-Control Data

Appendix 4—Routine Sampling Data

Appendix 5—Storm Sampling Data

 


For additional information contact:
Director, Texas Water Science Center
U.S. Geological Survey
8027 Exchange Drive
Austin, Texas 78754-4733
 
World Wide Web: http://tx.usgs.gov/
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