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Scientific Investigations Report 2010—5158

Revised Hydrogeologic Framework of the Floridan Aquifer System in the Northern Coastal Area of Georgia and Adjacent Parts of South Carolina

Lester J. Williams and Harold E. Gill (USGS Hydrologist, Retired)

ABSTRACT

Thumbnail of and link to report PDF (10.4 MB)

The hydrogeologic framework for the Floridan aquifer system has been revised for eight northern coastal counties in Georgia and five coastal counties in South Carolina by incorporating new borehole geophysical and flowmeter log data collected during previous investigations. Selected well logs were compiled and analyzed to determine the vertical and horizontal continuity of permeable zones that make up the Upper and Lower Floridan aquifers and to define more precisely the thickness of confining beds that separate these aquifers.

The updated framework generally conforms to the original framework established by the U.S. Geological Survey in the 1980s except for adjustments made to the internal boundaries of the Upper and Lower Floridan aquifers and the individual permeable zones that compose these aquifers. The revised boundaries of the Floridan aquifer system were mapped by taking into account results from local studies and regional correlations of geologic and hydrogeologic units. Because the revised framework does not match the previous regional framework along all edges, additional work will be needed to expand the framework into adjacent areas.

The Floridan aquifer system in the northern coastal region of Georgia and parts of South Carolina can be divided into the Upper and Lower Floridan aquifers, which are separated by a middle confining unit of relatively lower permeability. The Upper Floridan aquifer includes permeable and hydraulically connected carbonate rocks of Oligocene and upper Eocene age that represent the most transmissive part of the aquifer system. The middle confining unit consists of low permeability carbonate rocks that lie within the lower part of the upper Eocene in Beaufort and Jasper Counties, South Carolina, and within the upper to middle parts of the middle Eocene elsewhere. Locally, the middle confining unit contains thin zones that have moderate to high permeability and can produce water to wells that tap them. The Lower Floridan aquifer includes all permeable strata that lie below the middle confining unit and above the base of the aquifer system. Beneath Hilton Head Island, South Carolina, the middle Floridan aquifer is now included as part of the Lower Floridan aquifer. The base of the Floridan aquifer system generally is located at the top of lower Eocene rocks in Georgia and the top of Paleocene rocks in South Carolina.

The Upper and Lower Floridan aquifers are interconnected to varying degrees depending on the thickness and permeability of the middle confining unit that separates these aquifers. In most places, hydraulic head differences between the two aquifers range from a few inches to a few feet or more. Monitoring at several vertically clustered well-point sites where wells were set at different depths in the aquifer revealed variations in the degree of hydraulic separation with depth. In general, the head separation between the Upper and Lower Floridan aquifers increases with depth, which indicates that the deeper zones are more hydraulically separated than the shallower parts of the Lower Floridan aquifer.

First posted August 6, 2010

The report is presented here in pdf format (print quality). Plates are about 2 Mb in size.

  • Report (5 Mb)
  • Plate 1 (24" x 33"): Location of wells used in study in the northern coastal area of Georgia and parts of South Carolina
  • Plate 2 (36" x 40"): Geohydrologic cross sections A–A' through D–D', northern coastal area of Georgia and parts of South Carolina
  • Plate 3 (30" x 30"): Geohydrologic cross sections E–E' through G–G', northern coastal area of Georgia and parts of South Carolina

For additional information contact:
Director, Georgia Water Science Center
U.S. Geological Survey
3039 Amwiler Rd.
Suite 130
30360-42824
http://ga.water.usgs.gov/

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:

Williams, L.J., and Gill, H.E., 2010, Revised hydrogeologic framework of the Floridan aquifer system in the northern coastal area of Georgia and adjacent parts of South Carolina: U.S. Geological Survey Scientific Investigations Report 2010–5158, 103 p., 3 plates.



Contents

Abstract

Introduction

Purpose and Scope

Description of Study Area

Previous Studies

Methods

Acknowledgments

Geologic Setting

Geologic Units

Paleocene Unit

Lower Eocene Unit

Middle Eocene Unit

Upper Eocene Unit

Oligocene Unit

Miocene Unit

Structural Features

Hydrogeologic Units

Hydrogeologic Framework of the Floridan Aquifer System

Previous Interpretation of the Hydrogeologic Framework

Hydrogeologic Data from Selected Test Sites

Test Sites from Previous U.S. Geological Survey Studies

Hilton Head Test Sites

City of Richmond Hill Test Sites

Berwick Plantation Test Site

City of Rincon Test Site

City of Savannah Well No. 5 Test Site

Pineora Test Site

Hunter Army Airfield Test Site

Revised Interpretation of the Hydrogeologic Framework

General Configuration and Extent of the Floridan Aquifer System

Upper Confining Unit and Lower Brunswick Aquifer

Upper Floridan Aquifer

Thickness and Extent

Permeable Zones

Hydraulic Properties

Middle Confining Unit of the Floridan Aquifer System

Thickness and Extent

Hydraulic Properties

Lower Floridan Aquifer

Thickness and Extent

Permeable Zones

Hydraulic Properties

Aquifer Interconnection

Regional Correlation

Summary

Selected References

Appendix A. Summary of Hydrogeologic Data for Selected Wells Used in This Study


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