Skip Links

USGS - science for a changing world

Scientific Investigations Report 2009–5147

Prepared as part of the
National Water-Quality Assessment Program

Factors Affecting Water Quality in Domestic Wells in the Upper Floridan Aquifer, Southeastern United States, 1998-2005

By Marian P. Berndt and Christy A. Crandall

Thumbnail of link to report image cover(192 KB)

Abstract

The Floridan aquifer system is a highly productive carbonate aquifer that provides drinking water to about 10 million people in Florida, Georgia, and South Carolina. Approximately 1.6 million people rely on domestic wells (privately owned household wells) for drinking water. Withdrawals of water from the Floridan aquifer system have increased by more than 500 percent from 630 million gallons per day (2.38 cubic meters per day) in 1950 to 4,020 million gallons per day (15.2 cubic meters per day) in 2000, largely due to increases in population, tourism, and agriculture production.

Water samples were collected from 148 domestic wells in the Upper Floridan aquifer in Florida, Georgia, South Carolina, and Alabama during 1998-2005 as part of the U.S. Geological Survey (USGS) National Water-Quality Assessment Program. The wells were located in different hydrogeologic settings based on confinement of the Upper Floridan aquifer. Five networks of wells were sampled con-sisting of 28 to 30 wells each—two networks were in unconfined areas, two networks were in semiconfined areas, and one network was in the confined area. Physical properties and concentrations of major ions, trace elements, nutrients, radon, and organic compounds (volatile organic compounds and pesticides) were measured in water samples. Concentrations were compared to water-quality benchmarks for human health, either U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Levels (MCLs) for public water supplies or USGS Health-Based Screening Levels (HBSLs). The MCL for fluoride of 4 milligrams per liter (mg/L) was exceeded for two samples (about 1 percent of samples). A proposed MCL for radon of 300 picocuries per liter was exceeded in about 40 percent of samples.

Nitrate concentrations in the Upper Floridan aquifer ranged from less than the laboratory reporting level of 0.06 to 8 mg/L, with a median nitrate concentration less than 0.06 mg/L (as nitrogen). Nitrate concentrations did not exceed the MCL of 10 mg/L. Statistical comparisons indicated that median nitrate concentrations were significantly different by degree of confinement where the highest median nitrate concentration was 1.46 mg/L for 58 samples from unconfined areas, and by network, where the highest median nitrate concentration was 2.43 mg/L in 28 samples from unconfined areas in southwestern Georgia. Nitrate concentrations in unconfined areas were positively correlated to: (1) the percentage of agricultural land use around the well, (2) the amount of nitrogen fertilizer applied, and (3) the dissolved oxygen concentrations in groundwater.

Volatile organic compounds (VOCs) were detected in about 63 percent of all samples. Chloroform, carbon disulfide, and 1,2-dichloropropane were the most frequently detected VOCs. Chloroform, a byproduct of water chlorination, was most frequently detected in unconfined urban areas. Carbon disulfide, a solvent, was most frequently detected in confined areas in southeastern Georgia. Pesticides were detected in about 21 percent of all samples, but were detected in about 69 percent of the 28 samples from unconfined areas in southwestern Georgia. The herbicides atrazine, deethylatrazine, and metolachlor were the most frequently detected pesticides.

Posted January 2010

For additional information contact:
Marian P. Berndt mberndt@usgs.gov
U.S. Geological Survey
2639 North Monroe Street - Suite A-200
Tallahassee, FL 32303

Part or all of this report is presented in Portable Document Format (PDF); the latest version of Adobe Reader or similar software is required to view it. Download the latest version of Adobe Reader, free of charge.


Suggested citation:

Berndt, M.P., and Crandall, C.A., 2009, Factors Affecting Water Quality in Domestic Wells in the Upper Floridan Aquifer, Southeastern United States, 1998-2005: U.S. Geological Survey Scientific Investigations Report 2009-5147, 39 p.



Contents

Foreword

Acknowledgments

Abstract

Introduction

Purpose and Scope

Description of Study Area

Hydrogeologic Setting

Land Use, Population, and Water Use

Methods

Sample Collection and Processing

Quality Assurance and Quality Control

Water-Quality Benchmarks for Human Health

Geochemical Analysis

Statistical Analysis

Compilation of Ancillary Data

Characteristics of Sampling Networks

Groundwater Geochemistry

Dissolved Solids, Dissolved Oxygen, Major Ions, and pH

Mineral Saturation Indices

Trace Elements and Radon

Occurrence and Distribution of Selected Contaminants

Nitrate

Occurrence and Distribution of Nitrate

Factors Affecting Nitrate Concentrations

Volatile Organic Compounds

Occurrence and Distribution

Comparison to Water-Quality Benchmarks for Human Health

Factors Affecting Volatile Organic Compound Detections

Pesticides

Occurrence and Distribution

Comparison to Water-Quality Benchmarks for Human Health

Factors Affecting Pesticide Detections

Summary

References Cited

Appendix 1. Volatile organic compounds analyzed in water samples

Appendix 2. Pesticides analyzed in water samples



Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://pubs.usgs.gov/sir/2009/5147/
Page Contact Information: GS Pubs Web Contact
Page Last Modified: Thursday, 10-Jan-2013 19:44:05 EST