Water-Resources Investigations Report 87-4145
This report is available online in pdf format (5 MB): USGS WRIR87-4145 (
)
D.W. Hicks, H.E. Gill, and S.A. Longsworth
U.S. Geological Survey Water-Resources Investigations Report 87-4145, 40 pages (Published 1987)
Large withdrawals of ground water in the 1,500- square-mile Albany area of southwestern Georgia have lowered water levels in deep aquifers as much as 140 feet and raised concern about the aquifers' ability to meet increasing demands. This study was conducted to evaluate the development potential of the shallow Upper Floridan aquifer as an alternate source of ground water, especially for public supply.
The study area lies mainly within the Dougherty Plain district of the Coastal Plain physiographic province. The Upper Floridan aquifer is the shallowest major ground-water reservoir, generally covered by only 20 to 80 feet (ft) of overburden. The aquifer includes units of sand, clay, limestone, and dolomite of middle Eocene age and younger, that form, in ascending order, the Lisbon Formation, the Clinchfield Sand, the Ocala Limestone, and the Suwannee Limestone. The aquifer is overlain by undifferentiated sediments of Miocene age and undifferentiated overburden of Quaternary age. The Upper Floridan ranges in thickness from about 50 ft in the northwestern part of the area to more than 370 feet in the southeastern part. The Upper Floridan stores and transmits large quantities of water, mainly in a zone of high permeability in the lower part of the aquifer. The transmissivity of the aquifer ranges from less than 10,000 feet squared per day northwest of Albany, to as much as 150,000 feet squared per day south and southeast of Albany. Twenty-eight years of agricultural and industrial pumping has not produced a long-term decline of the water level in the Upper Floridan; the aquifer system remains at equilibrium. The Upper Floridan yields hard, calcium bicarbonate-type water that contains no constituents in concentrations that exceed State drinking water standards.
The Upper Floridan aquifer is the primary source of irrigation, industrial, and rural domestic water supplies in the study area. The aquifer has not been developed as a public-supply source, however, largely because of concern over possible ground-water contamination by agricultural and industrial chemicals and landfill leachate. The development potential of the aquifer as a public-supply source depends on the quantity and the chemical quality of water available to wells. Near Albany, active and abandoned landfills, industrial and commercial sites, railroad yards, and gasoline and chemical storage tanks are potential sources of contaminants and, thus, make the area unsuitable for well sites. The areas of high transmissivity southeast of Albany, east of the Flint River, and southwest of Albany, west of the river, have the greatest development potential for public water supply. East of the river, yields of 12- to 16-inch-diameter wells reportedly exceed 2,000 gallons per minute (gal/min). West of the river, yields of 800 to 1,200 gal/min can be sustained by wells that tap the lower part of the aquifer, and some wells are reported to produce more than 2,500 gallons per minute. In these areas, it may be possible to develop several fields of properly spaced wells capable of supplying tens of millions of gallons of potable water per day without overstressing the aquifer.
In most of the study area, contaminants applied to or spilled on the land surface eventually can be expected to percolate through the overburden and reach the aquifer. Thus, it is important that wells be sited away from areas that have been used for the storage and disposal of potential contaminants and, probably to a lesser extent, the application of agricultural chemicals. In the northern part of the study area, the upper part of the Upper Floridan aquifer acts as a leaky confining unit, and wells that derive water exclusively from the lower part of the aquifer probably would have added protection against contaminants that penetrate the overburden. To the south, the confining unit is missing and the entire aquifer is permeable; contaminants on the land surface that percolate through the overburden and reach the aquifer in this area are more likely to be drawn into a pumped well.
In the area of greatest development potential east of the Flint River, wells may penetrate major groundwater conduits. Where this occurs, contamination from distant sources that recharge the aquifer, such as losing streams, is possible, because conduit flow in the aquifer is comparatively rapid and contaminants can be transported long distances without natural filtration or purification. Water in some conduits could become turbid, especially during wet periods, and cause quality problems. Also, wells located near the river could draw river water into the aquifer.
In karst terrane, such as the Dougherty Plain, drawing the water level in the aquifer down below the top of limestone by pumping could initiate sinkhole development. By limiting drawdown during well development and during production, the likelihood of causing sinkholes to form can be minimized.
Closed depressions, or sinks, throughout the Dougherty Plain probably are unsuitable as well sites, because (1) they are subject to flooding, (2) they collect water from upgradient areas and could concentrate potential contaminants, (3) water may percolate through their bottoms and could transport contaminants into the aquifer, and (4) the depressions may overlie limestone cavities filled with sand or clay that could interfere with well yield, development, and production.
Abstract
Introduction
Purpose and scope
Methods of investigation
Previous investigations
Well and surface-water station numbering systems
Acknowledgments
Description of the study area
Hydrogeology
Geology
Lisbon Formation
Clinchfield Sand
Ocala Limestone
Suwannee Limestone
Undifferentiated sediments of Miocene age
Undifferentiated overburden of Quaternary age
Hydraulic characteristics
Undifferentiated overburden
Upper Floridan aquifer
Recharge, discharge, and flow characteristics of the Upper Floridan aquifer
Ground-water levels
Seasonal water-level fluctuations
Long-term water-level changes and the effects of drought
Ground-water and surface-water relation
Ground-water quality
Development potential of the Upper Floridan aquifer
Quantity of available ground water
Potential for ground-water contamination
Geologic hazards
Conclusions
Selected references
Plates
Plate 1: Map showing locations of wells, letter and number designations of 7 1/2-minute topographic maps streamflow-measurement sites, and potentiometric surface of the Upper Floridan aquifer for November 1985, Albany area, Georgia 3.5 MB PDF)
Plate 2: Map showing lithology and thickness of the undifferentiated overburden, Albany area, Georgia (5 MB PDF)
Plate 3: Map showing locations of sinkholes and potential sources of contaminants, Albany area, Georgia (3.5 MB PDF)
This report is available online in pdf format (5 MB): USGS WRIR87-4145 ()
To view the PDF document, you need the Adobe Acrobat® Reader installed on your computer. (A free copy of the Acrobat® Reader may be downloaded from Adobe Systems Incorporated.)
Recent USGS publications on Georgia or Georgia Water-Resources Information
For more information, please contact webmaster-ga@usgs.gov .
U.S. Department of the Interior |
U.S. Geological Survey
URL: https://pubsdata.usgs.gov/pubs/wri/wri87-4145/index.html
Page Contact Information: USGS Publishing Network
Page Last Modified: Wednesday, 07-Dec-2016 13:14:16 EST
