Georgia Water Science Center

USGS Water-Resources Investigations Report 93-4161


This report is available online in pdf format (1.0 MB): USGS WRIR 93-4161 (Opens the PDF file in a new window. )

Melinda J. Chapman, Barbara J. Milby, and Michael F. Peck

U.S. Geological Survey Water-Resources Investigations Report 93-4161, 27 pages (Published 1993)


The current (1991) surface-water source of drinking-water supply for the city of Zebulon, Pike County, Georgia, no longer provides an adequate water supply and periodically does not meet water-quality standards. The hydrogeology of crystalline rocks in the Zebulon area was evaluated to assess the potential of ground-water resources as a supplement or alternative source of water to present surface-water supplies. As part of the ground-water resource evaluation, well location and construction data were compiled, a geologic map was constructed, and ground water was sampled and analyzed.

Three mappable geologic units delineated during this study provide a basic understanding of hydrogeologic settings in the Zebulon area. Rock types include a variety of aluminosilicate schists, granitic rocks, amphibolites/hornblende gneisses, and gondites. Several geologic features that may enhance ground-water availability were identified in the study area. These features include contacts between contrasting rock types, where a high degree of differential weathering has occurred, and well-developed structural features, such as foliation and jointing, are present. High-yielding wells (greater than 25 gallons per minute) and low-yielding wells (less than one gallon per minute) were located in all three geologic units in a variety of topographic settings. Well yields range from less than one gallon per minute to 250 gallons per minute. The variable total depths and wide ranges of casing depths of the high-yielding wells are indicative of variations in depths to water-bearing zones and regolith thicknesses, respectively. The depth of water-bearing zones is highly variable, even on alocal scale.

Analyses of ground-water samples indicate that the distribution of iron concentration is as variable as well yield in the study area and does not seem to be related to a particular rock type. Iron concentrations in ground-water samples range from 0.02 to 5.3 milligrams per liter. Both iron concentration and well yield varies substantially over a relatively small area.




Purpose and scope

Description of study area

Methods of investigation

Previous studies

Ground-water availability

Ground-water quality

Well and spring numbering system



Regional geology

Local geology

Unit A

Unit B

Unit C

Ground-water resources

Relation of geology to occurrence and availability of ground water

Unit A

Unit B

Unit C

Well yield

Ground-water sampling results

Factors affecting ground-water quality


Sources of potential contamination

Summary and conclusions




This report is available online in pdf format (1.0 MB): USGS WRIR 93-4161 (Opens the PDF file in a new window. )
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