USGS banner

Ground-Water Flow and Water Quality in the Upper Floridan Aquifer, Southwestern Albany Area, Georgia, 1998–2001

Debbie Warner and Stephen J. Lawrence

U.S. Geological Survey Scientific Investigations Report 2005-5047, 77 pages (Published July 2005) ONLINE ONLY

ABSTRACT

photoDuring 1997, the Dougherty County Health Department sampled more than 700 wells completed in the Upper Floridan aquifer in Dougherty County, Georgia, and determined that nitrate as nitrogen (hereinafter called nitrate) concentrations were above 10 milligrams per liter (mg/L) in 12 percent of the wells. Ten mg/L is the Georgia primary drinking-water standard. The ground-water flow system is complex and poorly understood in this predominantly agricultural area. Therefore, the U.S. Geological Survey (USGS) — in cooperation with Albany Water, Gas and Light Commission — conducted a study to better define ground-water flow and water quality in the Upper Florida aquifer in the southwestern Albany area, Georgia.

Ground-water levels were measured in the southwestern Albany area, Georgia, during May 1998 and March 1999 (spring), and October 1998 and September 1999 (fall). Groundwater levels measured in 75 wells open only to the Upper Floridan aquifer were used to construct potentiometric-surface maps for those four time periods. These maps show that ground water generally flows from northwest to southeast at gradients ranging from about 2 to greater than 10 feet per mile. During spring and fall 1998, ground-water levels were high and mounding of the potentiometric surface occurred in the central part of the study area, indicating a local recharge area. Water levels declined from December through February, and by March 1999 the mound in the potentiometric surface had dissipated.

Of the 75 wells in the potentiometric network, 24 were selected for a water-quality network. These 24 wells and 1 spring were sampled during fall 1998 and spring 1999. Samples were analyzed for major chemical constituents, selected minor constituents, selected nutrients, and chlorofluorocarbons (CFC). Water-quality field measurements — such as water temperature, pH, specific conductance (SC), and dissolved oxygen (DO) — were taken at each well. During August 2000, a ground-water sample was collected and analyzed for selected sewage tracers. During March 2001, water samples from selected wells were analyzed for nitrogen and oxygen isotopes. Age-dating analysis using CFCs yield apparent groundwater ages that range from modern to greater than 50 years.

The chemistry of ground water in the Upper Floridan aquifer varies widely throughout the southwestern Albany area, Georgia, and in general represents the chemistry commonly found in recharge areas. From fall 1998 through spring 1999, median values of pH, SC, and DO concentration were 7.6 standard units, 266 microsiemens per centimeter at 25 degrees Celsius (μS/cm), and 5.6 mg/L, respectively. The SC is highest (350 – 400 μS/cm) where mounding of the potentiometric surface exists. Specific DO concentrations indicate an area of anoxic ground water in the north-central part of the study area.

Water samples indicate that ground water in the study area is dominated by calcium and bicarbonate ions, which is consistent with the limestone lithology of the aquifer. About 25 percent of the samples contained sodium and chloride at ratios similar to those in rainfall, indicating a close proximity to recharge areas. The remaining water samples, however, had sodiumchloride ratios less than 0.90, the ratio in Tift County, Georgia, rainfall samples. These low sodium-chloride ratios are consistent with chloride enrichment. Minor constituent and nutrient concentrations typically are below laboratory reporting limits; however, the maximum nitrate concentration measured during the study period was 12.2 mg/L, and the median concentration for the study period was 3.0 mg/L. Samples collected during 1999 had a higher median nitrate concentration than the 1998 samples. Regression analysis indicated that nitrate concentrations are related exponentially to chloride concentrations.

Four distinct groups of ground-water-quality samples, plus four unique samples, were identified using cluster analysis. Water-quality groups I and II occur in the north-central part of the study area and generally are chemically similar. These groups represent an area of anoxic ground water where reducing conditions prevail. Water-quality group III occurs in the central part of the study area and represents a mixing zone where three chemically different ground waters merge. Water-quality group IV occurs in the south-central part of the study area, has nitrate concentrations less than 2.5 mg/L, and probably represents background conditions of the Upper Floridan aquifer in this area. The four unique samples collected from two wells represent ground water with elevated nitrate concentrations. Ground water drawn from one well possibly is contaminated by the application of biosolids in fields upgradient from the study area. Ground water from the other well apparently is influenced by agricultural fertilizer.


TABLE OF CONTENTS

Abstract

Introduction

Purpose and Scope

Description of Study Area

Previous Investigations

Acknowledgments

Methods of Investigation

Well and Spring Naming System

Well Inventory and Measurement of Ground-Water Levels

Collection and Chemical Analysis of Water Samples

Age-Dating Ground Water Using Chlorofluorocarbons

Statistical Analysis of Water-Quality Data

Hydrogeology of the Upper Floridan Aquifer

Undifferentiated Overburden

Upper Floridan Aquifer

Lisbon Confining Unit

Ground-Water Flow in the Upper Floridan Aquifer

Water Levels

Flow Directions and Gradients

Recharge and Ground-Water Ages

Ground-Water Chemistry and Water Quality in the Upper Floridan Aquifer

Description of Ground-Water Chemistry and Water Quality

pH, Specific Conductance, and Dissolved Oxygen

Major Chemical Constituents

Minor Chemical Constituents

Dissolved Nutrient Concentrations

Nitrate

Nitrogen and Oxygen Isotopes

Emerging Contaminants

Spatial Patterns in Ground-Water Chemistry and Water Quality

Spatial Distribution of Specific Conductance

Spatial Distribution of Nitrate as Nitrogen

Identification and Spatial Distribution of Water-Quality Groups

Unique Samples

Water-Quality Groups I and II

Water-Quality Group III

Water-Quality Group IV

Summary and Conclusions

References Cited

Appendix A

Appendix B

 


REPORT AVAILABILITY

This report is available online in pdf format: Scientific Investigations Report 2005-5047 (2.3 MB), cover (1.5 MB)
To view this document, you need the Adobe Acrobat® Reader installed on your computer. (A free copy of the Acrobat® Reader may be downloaded from Adobe Systems Incorporated.)


Recent USGS publications on Georgia or Georgia Water-Resources Information

For more information, please contact webmaster-ga@usgs.gov .


U.S. Department of the Interior, U.S. Geological Survey
Persistent URL:
Page Contact Information: Contact USGS
Last modified: Thursday, January 10 2013, 04:54:19 PM
FirstGov button  Take Pride in America button