Scientific Investigations Report 2004-5145
U.S. Geological Survey Scientific Investigations Report 2004-5145, 27 pages (Published 2004)
By James L. Robinson
This report is available online in pdf format.: USGS SIR 2004-5145: Cover (3 MB), Contents (1 MB)
Water from wells and springs accounts for more than 90 percent of the public water supply in Calhoun County, Alabama. Springs associated with the Jacksonville Thrust Fault Complex are used for public water supply for the cities of Anniston and Jacksonville. The largest ground-water supply is Coldwater Spring, the primary source of water for Anniston, Alabama. The average discharge of Coldwater Spring is about 32 million gallons per day, and the variability of discharge is about 75 percent.
Water-quality samples were collected from 6 springs and 15 wells in Calhoun County from November 2001 to January 2003. The pH of the ground water typically was greater than 6.0, and specific conductance was less than 300 microsiemens per centimeter. The water chemistry was dominated by calcium, carbonate, and bicarbonate ions. The hydrogen and oxygen isotopic composition of the water samples indicates the occurrence of a low-temperature, water-rock weathering reaction known as silicate hydrolysis. The residence time of the ground water, or ground-water age, was estimated by using analysis of chlorofluorocarbon, sulfur hexafluoride, and regression modeling. Estimated ground-water ages ranged from less than 10 to approximately 40 years, with a median age of about 18 years.
The Spearman rho test was used to identify statistically significant covariance among selected physical properties and constituents in the ground water. The alkalinity, specific conductance, and dissolved solids increased as age increased; these correlations reflect common changes in ground-water quality that occur with increasing residence time and support the accuracy of the age estimates. The concentration of sodium and chloride increased as age increased; the correlation of these constituents is interpreted to indicate natural sources for chloride and sodium. The concentration of silica increased as the concentration of potassium increased; this correlation, in addition to the isotopic data, is evidence that silicate hydrolysis of clay minerals occurred.
The geochemical modeling program NETPATH was used to investigate possible mixing scenarios that could yield the chemical composition of water collected from springs associated with the Jacksonville Thrust Fault Complex. The results of NETPATH modeling suggest that the primary source of water in Coldwater Spring is a deep aquifer, and only small amounts of rainwater from nearby sources are discharged from the spring. Starting with Piedmont Sports Spring and moving southwest along a conceptual ground-water flow path that parallels the Jacksonville Thrust Fault Complex, NETPATH simulated the observed water quality of each spring, in succession, by mixing rainwater and water from the spring just to the northeast of the spring being modeled. The percentage of rainwater and ground water needed to simulate the quality of water flowing from the springs ranged from 1 to 25 percent rainwater and 75 to 99 percent ground water.
Abstract
Introduction
Purpose and Scope
Previous Investigations
Acknowledgments
Description of the Study Area
Climate and Rainfall
Hydrogeology
Study Design and Methods
Water-Quality Samples
Quality-Assurance and Quality-Control Procedures
Graphical and Statistical Methods
Geochemical Modeling
Physical Properties, and Chemical and Isotopic Composition of Water Samples
Physical Properties
Major Ions
Nutrients
Isotopic Composition
Saturation State with Respect to Minerals
Age of Water Associated with the Jacksonville Thrust Fault Complex
Estimates of Ground-Water Age
Chlorofluorocarbons and Sulfur Hexafluoride
Regression Modeling
Relations Between Ground-Water Age and Ground-Water Quality
Source of Water in Springs Associated with the Jacksonville Thrust Fault Complex
Analysis of Water-Quality Variability of Selected Springs
Relation Between Rainfall and Discharge of Coldwater Spring
Geochemical Modeling
Summary
References Cited
This report is available online in pdf format.: USGS SIR 2004-5145: Cover (3 MB), Contents (1 MB)
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Robinson, J.L., 2004, Age and source of water in springs associated with the Jacksonville Thrust Fault Complex, Calhoun County, Alabama: U.S. Geological Survey Scientific Investigations Report 2004–5145, 27 p.
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