Limestone beds of Eocene, Oligocene, and lower Miocene age, called the principal artesian aquifer, are the chief source of ground water for Colquitt County. Because streams are small, undependable and relatively inaccessible to most users, ground water is the most important source for increased industrial and agricultural water use. INTRODUCTION Colquitt County, Ga., largely depends on ground water for domestic and industrial use. Water-well drillers, however, have experienced difficulty in obtaining adequate supplies in some parts of the county. The drillers noted anomalous groundwater heads and water-quality problems. Studies in other counties in southwestern Georgia suggested that these anomalies might be related to poorly defined structural features. These were among the reasons that Colquitt County was selected for study in 1967. Location and Extent of the Area Colquitt County (fig. 1) includes an area of 536 mil (1,458 km 2) in south-central Georgia. The county lies in the lower Coastal Plain physiographic province. The principal towns include the county seat, Moultrie (1970 population, 14,302); Doerun (1,157); Norman Park (912); Berlin (422); Ellenton (337); Funston (293); and Crosland (158). Colquitt County is bordered on the north by Worth and Tift Counties, on the east by Cook County, on the south by Brooks and Thomas Counties, and on the west by Mitchell County. FIGURE I.-LOCATION OF COLOUITT COUNTY Purpose and Scope of the Investigation Although surface water is still the main source of irrigation water, ground water is the principal source of domestic, industrial, and stock water in Colquitt County. Responsible governmental and service organizations in Colquitt County hope for and expect continued economic expansion in industry and agriculture. This expansion will almost certainly be accompanied by a greatly increased demand for water. The only source likely to meet this demand is ground water. It is necessary to evaluate the magnitude of this resource in order to properly plan for continued development. To aid in this evaluation, the Georgia Department of Natural Resources, Geologic and Water Resources Division, maintains a statewide cooperative program with the U.S. Geological Survey to appraise Georgia's water resources. The objectives of this investigation were: 1. To map and study the subsurface formations that constitute the principal artesian aquifer and its water-bearing zones, and to determine their hydrologic properties. 2. To map and study the beds making up lesser aquifer systems and to determine their hydrologic properties. 3. To determine geologic structure and its hydrologic significance. 4. To determine the sustained yield of wells and the quality of the water available in the various aquifer systems. Previous Investigations Colquitt County, as a part of the Coastal Plain of Georgia, has been discussed in a number of reports covering south Georgia or the Southeast. These include, "Artesian water in Tertiary limestone in the southeastern States" (Stringfield, 1966) and "Subsurface geol...
Water from a brackish-water zone (1,050-1,350 ft) has concentrations as high as 2,150 milligrams per liter chloride, and concentrations are suspected to be higher than 3,000 milligrams per liter chloride. This brackish water has been identified as the source of the water that contaminates the upper and lower freshwater bearing zones of the principal artesian aquifer. The confining unit separating the fresh and brackish water seems to contain breaks that act as vertical conduits for the movement of brackish water into the freshwater zones of the aquifer. Faults are suspected to be responsible for the breaks in the confining unit. The rate of upward movement of brackish water seems to be a function of the rate of water-level decline in the aquifer. There are two main areas of brackish-water intrusion. One area is near Bay and Prince Streets, and the other area is near Reynolds and Q Streets. Successive maps showing chloride ion concentration trace the movement of the chloride front northward in the Bay Street area at the rate of about 350 feet per year toward the center of pumping. An average of about 400 gallons per minute of water containing 2,000 milligrams per liter chloride invaded the upper water-bearing zone between December 1962 and December 1966. A like amount may have entered the lower water-bearing zone. Maximum chloride concentration in the upper water-bearing zone is 1,540 milligrams per liter in the Bay Street area and 640 milligrams per liter in the Reynolds Street area. In a few areas, where individual wells have been drilled deep enough to penetrate the confining unit over the brackish-water zone, the well furnishes a conduit for brackish water to recharge the freshwater aquifer. Plugging the lower part of these wells usually reduces the chloride concentration of the water. Dl D2 CONTRIBUTIONS TO THE HYDROLOGY OF THE UNITED STATES The chloride concentration of water in the principal artesian aquifer can probably be reduced by use of interceptor wells, relief wells, or well-field spacing. Interceptor wells would prevent laterally moving brackish water from contaminating a well field. A relief well would tap and withdraw poor quality water from only the brackish-water zone to lower the head in that zone and decrease the rate of leakage into the freshwater aquifer. Wider spacing of wells would prevent the development of a deep cone of depression and the steeper hydraulic gradients that accompany it. The brackish water pumped by the interceptor or relief wells could be used for industry, aquaculture, recreation, or for other processes in which the chloride content is not critical.
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