USGS Open-File Report 00-515
Contrasting geologic features and landforms of the physiographic provinces
of Georgia (table 2, fig.
1) result in substantial differences in
ground-water conditions from one part of the State to another. These
features that make up the framework of the aquifers affect the quantity
and quality of ground water throughout the State.
Surficial aquifers are present in each of the physiographic provinces. In the Piedmont, Blue Ridge, and Valley and Ridge Provinces (fig. 1), the surficial aquifers consist of soil, saprolite, stream alluvium, colluvium, and other surficial deposits. In the Coastal Plain Province, the surficial aquifers consist of intermixed layers of sand, clay, and limestone. The surficial aquifers usually are under water-table (unconfined) conditions and are used for domestic and livestock supplies. These aquifers are semiconfined locally in the coastal area.
In the Piedmont and Blue Ridge Provinces, rocks are complex and consist of structurally deformed metamorphic and igneous rocks. Ground water is transmitted through secondary openings along fractures, foliation, joints, contacts, or other features in the crystalline bedrock. In the Valley and Ridge Province, ground water is transmitted through both primary and secondary openings in folded and faulted sedimentary and metasedimentary rocks of Paleozoic age.
The most productive aquifers in Georgia are in the Coastal Plain Province in the southern part of the State. The Coastal Plain is underlain by alternating layers of sand, clay, dolomite, and limestone that dip and thicken to the southeast. Coastal Plain aquifers generally are confined except near their northern limits, where they crop out or are near land surface. Aquifers in the Coastal Plain include the upper and lower Brunswick aquifers, the Floridan aquifer system, the Claiborne aquifer, the Gordon aquifer, the Clayton aquifer, and the Cretaceous aquifers and aquifer systems.
Table 2. Aquifer and well characteristics
in Georgia
[modified from Clarke and Pierce
(1984) and Peck and others (1992); ft,
feet; gal/min, gallons per minute]
| Well characteristics | ||||
|---|---|---|---|---|
| Depth (ft) | Yield (gal/min) | |||
| Aquifer name and description | Common range | Common range | May exceed | Remarks |
| Surficial
aquifer: Unconsolidated sediments; residuum, generally unconfined |
11-72 | 2-25 | 25 | Primary source of water for domestic and livestock supply in rural areas. Supplemental source of water in coastal Georgia. |
| Upper and
lower Brunswick aquifers: Phosphatic and dolomitic quartz sand, generally confined |
85-390 | 10-30 | 180 | Not a major source of water in coastal Georgia, but considered a supplemental water supply to the Upper Floridan aquifer. Most wells are multi-aquifer, tapping the upper and lower Brunswick aquifers and the Upper Floridan aquifer. The lower Brunswick aquifer currently is not monitored (Clarke and others, 1990, p. 26-28). |
| Floridan aquifer
system: Limestone, dolomite, and calcareous sand, generally confined |
40-900 | 1,000-5,000 | 11,000 | Supplies 50 percent of ground water in Georgia. The aquifer system is divided into the Upper and Lower Floridan aquifers. In the Brunswick area, the Upper Floridan aquifer includes two freshwater-bearing zones, the upper water-bearing zone and the lower water-bearing zone. The Lower Floridan aquifer is not considered a major aquifer. In the Brunswick area and in southeastern Georgia, the Lower Floridan aquifer includes the brackish-water zone, the deep freshwater zone, and the Fernandina permeable zone (Krause and Randolph, 1989). The Lower Floridan aquifer extends to more than 2,700 ft and yields high-chloride water below 2,300 ft (Jones and Maslia, 1994). |
| Gordon aquifer
system: Sand and sandy limestone, generally confined |
270-530 | 87-1,200 | 1,800 | Major source of water for irrigation, industrial, and public-supply use in east-central Georgia. |
| Claiborne
aquifer: Sand and sandy limestone, generally confined |
20-450 | 150-600 | 1,500 | Major source of water for irrigation, industrial, and public-supply use in southwestern Georgia. |
| Clayton
aquifer: Limestone and sand, generally confined |
40-800 | 250-600 | 2,150 | Major source of water for irrigation, industrial, and public-supply use in southwestern Georgia. |
| Cretaceous
aquifers and aquifer systems: Sand and gravel, generally confined |
30-750 | 50-1,200 | 3,300 | Major source of water in east-central Georgia. Supplies water for kaolin mining and processing. Includes the Providence aquifer in southwestern Georgia, and the Dublin, Midville, and Dublin-Midville aquifer systems in east-central Georgia. |
| Paleozoic-rock
aquifers: Sandstone, limestone, and dolostone |
15-2,100 | 1-50 | 3,500 | Not laterally extensive. Limestone and dolostone aquifers are most productive. Storage is in regolith, primary openings, and secondary fractures and solution openings in rock. Springs in limestone and dolostone aquifers discharge at rates of as much as 5,000 gal/min. Sinkholes may form in areas of intensive pumping. |
| Crystalline-rock
aquifers: Granite, gneiss, schist, and quartzite |
40-600 | 1-25 | 500 | Not laterally extensive. Storage is in regolith and fractures in rock. Hydrogeology of crystalline-rock aquifers is not well understood. |
GROUND-WATER LEVELS
Short-term fluctuations and long-term trends in ground-water levels result
from variations in recharge and discharge. Recharge varies in response to
precipitation and surface-water infiltration into an aquifer. Discharge
occurs as natural flow from an aquifer to streams and springs, as
evapotranspiration, and as withdrawal from wells.
Discussions of ground-water levels in Georgia are grouped by aquifer and subdivided into areas and subareas in which wells have similar water-level fluctuations and trends.
Water-level fluctuations in 1999 are shown for 130 continuously monitored wells, which are considered to be representative of ground-water levels throughout the State. For each well, well-site information is listed, record high and low water levels for the period of record, monthly mean water levels are shown in hydrographs for the period of record, daily mean water levels are shown in hydrographs for 1999, and monthly and annual water-level statistics (minimum, mean, and maximum daily mean water levels) are tabulated for 1999. Monthly statistics are not computed for months having less than 25 days of record. Extreme water levels for the period of record listed in the well-site information and tabulated water-level statistics are reported to the nearest 0.01 ft, reflecting the accuracy of the recorders used. Land-surface data generally are determined from the best available topographic map, and are accurate to about one-half the contour interval. Some land-surface data were determined by surveying methods or Global Positioning System (GPS) and are more accurate. In this report, an extreme water level refers to the lowest or highest daily mean water level for the period of record of a particular well. Thus, any instantaneous water-level measurement on a given day may be lower or higher than the extreme water level reported in the text, the daily mean water level shown on the hydrograph, or the minimum or maximum values tabulated.
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Observation wells for which hydrographs are included in this report:
Recent USGS publications on Georgia
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Georgia Water-Resources Information
Last updated Monday, 26-Jun-2000 15:14:12 EDT
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