Drilling a Deep Geologic Test Well at

Hilton Head Island, South Carolina

The U.S. Geological Survey (USGS), in cooperation 

with the South Carolina Department of Health and Environmental Control (SCDHEC), is drilling a deep geologic test well at Hilton Head Island, S.C. The test well 

is scheduled to run between mid-March and early May 

2011. When completed, the well will be about 1,000 feet 

deep. The purpose of this test well is to gain knowledge 

about the regional-scale Floridan aquifer, an important 

source of groundwater in the Hilton Head area (fig. 1). 

Also, cores obtained during drilling will enable geologists to study the last 60 million years of Earth history in 

this area.

Why Is the Drilling at Hilton Head Island?

The USGS has undertaken a 5-year study of 

the geology of the greater Hilton Head region. This 

endeavor combines mapping of the surface geology with 

detailed study of the subsurface geology. The Hilton 

Head site was chosen to complete a series of test wells 

in Georgia and South Carolina that parallel the Savannah River from the Savannah River Nuclear Site to the 

Atlantic Coast. The data gathered from these wells will 

be combined with published information from other 

wells in the area to enable us to model the subsurface 

geology in this area.

Why Are We Doing This Study?

Groundwater is a vital natural resource in the southeastern Atlantic Coastal Plain. The Floridan aquifer, 

one of the most productive aquifers in the world, is a 

regional-scale source of groundwater that has been used 

locally for more than 100 years. Recently, heavy use of 

this resource has caused some wells along the coast to 

experience saltwater intrusion, rendering them unsuitable for drinking water (fig. 2). As water use increases in 

response to growing municipal, industrial, and agricultural demand, State and local governments will face difficult decisions about future use of the Floridan aquifer. A 

primary goal of the USGS is to make information on the 

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2011–3032

March 2011

aquifer available to decisionmakers. Defining the internal 

character and boundary of the aquifer in the subsurface 

requires detailed knowledge of the rock types, their ages, 

and their physical characteristics. This information will 

help water resource specialists to model groundwater 

flow and to correlate subsurface characteristics across 

State and local boundaries. The results from the test well 

at Hilton Head will be added to the larger database that 

describes the Floridan aquifer.

SOUTH

CAROLINA

GEORGIA

MISS. ALABAMA

Hilton Head

Island

Atlantic

Ocean

Gulf of Mexico FLORIDA

Figure 1. Extent of the Floridan aquifer. In the Savannah, Ga., area, 

the Floridan is about 400 feet thick and the top is about 200 feet 

below the surface.
Figure 2. Floridan aquifer 

groundwater flow models. A, Before 

the 1880s; B, As of 2005. Modified 

from Falls and others, 2005.

NE

 Area of freshwater recharge Area of freshwater discharge

from the surficial aquifer to from the Upper Floridan aquifer SW the Upper Floridan aquifer toward the saline water

of the surficial aquifer

Sea level

Predevelopment (before 1880s) NOT TO SCALE

Land surface

surficial aquifer

upper confining unit

Atlantic Ocean Upper Floridan aquifer

Lower Floridan aquifer 

middle 

c.f.

lower semiconfining unit

 semiconfining unit

Area of freshwater recharge Area of saline water recharge

from the surficial aquifer to from the ocean and surficial aquifer

the Upper Floridan aquifer toward the Upper Floridan aquifer

 Upper Floridan aquifer

SW NE

Sea level

NOT TO SCALE

Land surface

surficial aquifer

upper confining unit

lower semiconfining unit

Atlantic Ocean

Water-supply wells for

Chatham County

middle 

c.f.

Lower Floridan aquifer 

 semiconfining unit

Present Day (2005)

EXPLANATION

Fresh groundwater

Very saline groundwater

Moderately saline 

groundwater 

Seawater

Confining unit

Potentiometric surface of

the Upper Floridan aquifer

General direction of

groundwater flow

NE

SW

Trace of cross section on 

inset map

[c.f., channel fill (permeable)]

SOUTH

CAROLINA

GEORGIA

FLORIDA

Area of freshwater recharge

from the surficial aquifer to

the Upper Floridan aquifer

Area of saline water recharge

from the ocean and surficial aquifer

toward the Upper Floridan aquifer

 Upper Floridan aquifer

SW NE

Sea level

NOT TO SCALE

upper confining unit

surficial aquifer

Land surface

lower semiconfining unit

Atlantic Ocean

Lower Floridan aquifer 

Present Day (2005)

middle 

 semiconfining unit

c.f.

Water-supply wells for

Chatham County

EXPLANATION

Fresh groundwater

Very saline groundwater

Moderately saline 

groundwater 

Seawater

Potentiometric surface of

the Upper Floridan aquifer

General direction of

groundwater flow

Trace of cross section on 

it 

NE

SW

GEORGIA

SOUTH

CAROLINA

NE

 Area of freshwater recharge

from the surficial aquifer to

the Upper Floridan aquifer

Area of freshwater discharge

from the Upper Floridan aquifer

toward the saline water

of the surficial aquifer

SW

Sea level

NOT TO SCALE Predevelopment (before 1880s)

upper confining unit

surficial aquifer

Land surface

Atlantic Ocean Upper Floridan aquifer

Lower Floridan aquifer 

lower semiconfining unit

middle semiconfining unit

c.f.

EXPLANATION

Fresh groundwater

Very saline groundwater

Moderately saline 

groundwater 

Seawater

Confining unit

Potentiometric surface of

the Upper Floridan aquifer

General direction of

groundwater flow

Trace of cross section on 

inset map

NE

SW

GEORGIA

SOUTH

CAROLINA

FLORIDA

NE

 Area of freshwater recharge

from the surficial aquifer to

the Upper Floridan aquifer

Area of freshwater discharge

from the Upper Floridan aquifer

toward the saline water

of the surficial aquifer

SW

Sea level

NOT TO SCALE Predevelopment (before 1880s)

upper confining unit

surficial aquifer

Land surface

Atlantic Ocean Upper Floridan aquifer

Lower Floridan aquifer 

lower semiconfining unit

middle semiconfining unit

c.f.

Area of freshwater recharge

from the surficial aquifer to

the Upper Floridan aquifer

Area of saline water recharge

from the ocean and surficial aquifer

toward the Upper Floridan aquifer

 Upper Floridan aquifer

SW NE

Sea level

NOT TO SCALE

upper confining unit

surficial aquifer

Land surface

lower semiconfining unit

Atlantic Ocean

Lower Floridan aquifer 

Present Day (2005)

middle 

 semiconfining unit

c.f.

Water-supply wells for

Chatham County
What Exactly Are We Doing? 

 The test well is obtained using a technology called 

wireline core drilling (fig. 3). A hollow drill stem (pipe) 

is carefully drilled through the soil into the underlying 

variably indurated sands, silts, clays, and limy sediments, 

which are collected in an inner core barrel in 10-foot 

sections. These sections are pulled back to the surface 

and the collected core is boxed for study (fig. 4). On site, 

the freshly cored sediments are described and sampled 

for laboratory analysis. The inner barrel is then put 

back down the hole to drill and collect the next 10-foot 

section. The Hilton Head test well will take about two 

months to drill. After the hole is completed, we will conduct a variety of tests in the open hole. These are referred 

to as “downhole geophysics” and involve lowering several instruments on cables in order to measure physical 

properties of the sand, silt, clay, and limy sediment layers 

such as electrical resistance and natural radiation. Finally, 

we will place a small groundwater monitoring instrument 

Figure 3. U.S. Geological Survey drill rig and crew conducting 

wireline core drilling on the Atlantic Coastal Plain.

at a specific level in the hole and connect it to a surface 

graph. We will transport the collected core and samples 

back to USGS laboratories for completion of testing and 

descriptions. Paleontologists at the USGS will examine 

the core for microfossils that help explain the geologic 

history (fig. 5).

What Will Be the Final Products of This Study?

Following analysis of all the information gathered 

from the Hilton Head test well, the USGS will publish a 

set of reports and make them available to the public. These 

reports will include technical descriptions of the entire 

1,000-foot corehole as well as assessments of fossil content, chemical characteristics, and ages of the sediments. 

This information will be correlated with data from other 

test wells in the Floridan aquifer. Information gathered 

from the groundwater monitoring instrument will be available as these data are accumulated.

Figure 4. Section of poorly indurated limestone core recovered 

from a well drilled into the Floridan aquifer, Pineora, Ga. Box 

contains core from 473.4 to 481.2 feet down. This well was 

completed in April 2009 and is part of our USGS project work. 

Photograph by Colleen Durand, USGS.
How Is the Drilling Funded? 

Funding for the Hilton Head test well comes from 

the USGS National Cooperative Geologic Mapping Program. This program is funded by Congress through the 

Department of the Interior and includes components that 

fund Federal, State, and academic research. Additional 

support comes from the SCDHEC. Funding covers all 

costs associated with drilling, salaries for science staff, 

and final publication of the results.

Figure 5. Photomicrographs of microfossils from the Atlantic 

Coastal Plain. A, Dinoflagellate; B, Calcareous nannofossil.

Cordosphaeridium

cantharellus

50μm

A

7μm

Pemma sp.

B

B

Reference Cited

Falls, W.F., Ransom, Camille, Landmeyer, J.E., Reuber, E.J., 

and Edwards, L.E., 2005, Hydrogeology, water quality, 

and saltwater intrusion in the Upper Floridan aquifer in 

the offshore area near Hilton Head Island, South Carolina, 

and Tybee Island, Georgia, 1999–2002: �.�. Geologi� –2002: �.�. Geologi� 2002: U.S. Geological �urvey �cientific Investigations Report 2005–5134, 

48 p. (available only at http://pubs.er.usgs.gov/usgspubs/sir/

sir20055134).

By Arthur P. Schultz and Ellen L. Seefelt

Who Will Benefit From This Information?

1. Federal, State, and local water management agencies

2. Environmental and geological consultants

3. State and local academic institutions

4. The general public

For additional information, please contact:

Camille Ransom Art Schultz, Project Chief

Department of Health and Environmental Control U.S. Geological Survey

2600 Bull Street 926A National Center 

Columbia, SC 29201 12201 Sunrise Valley Drive

Telephone: (803) 898–3575 Reston, VA 20192 

E-mail: ransmoc@dhec.sc.gov Telephone: (703) 648–6501

E-mail: aschultz@usgs.gov