GROUND-WATER RESOURCES OF THE SOUTH METROPOLITAN ATLANTA REGION, GEORGIA by JohnS. Clarke and Michael F. Peck U.S. Department of the Interior U.S. Geological Survey EXPLANATION ~:; ~~..] 0 UNIT 8--Granilic gneiss UNIT C- Schlst f.:~::;-\d UNIT F..Granile - UNIT G-Caladasllc rocks I':.:::.::] UNIT 0--Blotile gneiss - UNIT H- Ouartzlte ~ THRUST FAULT--Teeth on upper plate SITE YIELDING 100 GALLONS PER MINUTE OR MORE Well ..,_ Spring 0 5 10 MILES 0 5 10 KILOMETERS Geology from Higgins and others, 1988 DEPARTMENT OF NATURAL RESOURCES ENVIRONMENTAL PROTECTION DIVISION GEORGIA GEOLOGIC SURVEY INFORMATION CIRCULAR 88 GROUND-WATER RESOURCES OF THE SOUTH METROPOLITAN ATLANTA REGION, GEORGIA by John S. Clarke and Michael F. Peck U.S. DEPARTMENT OF THE INTERIOR U.S. GEOWGICAL SURVEY Prepared in cooperation with the U.S. ARMY CORPS OF ENGINEERS SAVANNAH DISTRICT GEORGIA DEPARTMENT OF NATURAL RESOURCES Joe D. Tanner, Commissioner ENVIRONMENTAL PROTECTION DMSION Harold F. Reheis, Assistant Director GEORGIA GEOWGIC SURVEY William H. McLemore, State Geologist Atlanta, Georgia 1991 INFORMATION CIRCULAR 88 CONTENTS Abstract.............................................................................................................................................................................. 1 Introduction....................................................................................................................................................................... 2 Purpose and scope............................................................................................................................................. 2 Methods.............................................................................................................................................................. 2 Previous studies....................................................................................... .......................................................... 4 Well and spring numbering system................................................................................................................. 4 Acknowledgem.ents............................................................................................................................................ 4 Description of the study area.......................................................................................................................................... 4 Geologic setting...................................................................................................... ........................................... 4 Hydrologic setting.............................................................................................................................................. 5 Water use............................................................................................................................................................ 5 Ground-water resources.................................................................................................................................................. 8 Hydrogeologic units........................................................................................ .................................................. 8 Ground-water levels........................................................................................... ............................................... 9 Ground-water availability................................................................................................................................. 9 Well yields and factors affecting yields............................................................................................12 Spri:ngs ....... .................. .... ...... ........... ............................ ........................................................................ 14 Occurrence of high-yielding wells and springs................................................................................17 Well-perforntance tcsts................................................................ ......................................................18 Water quality......................................................................................................................................................21 Summary and conclusions...............................................................................................................................................23 Selected references...........................................................................................................................................................25 Appendix A--Record of wells..........................................................................................................................................27 Plate 1. Figure Figures Figure ILLUSTRATIONS [Plate is in pocket] Map showing hydrogeologic units and locations of wells and springs in the south Metropolitan Atlanta region, Georgia 1. Map showing location of study area, physiographic provinces, and the Flint River Basin................................................................................................................................. 3 2. Graphs showing water use in the south Metropolitan Atlanta region, 1985................ 7 3. Hydrograph showing cumulative departure from the long-term average of precipitation at the National Weather Service Station Atlanta WSO, AP, and periodic water levels a well llAAOl, Spalding County, 1979-88.............................10 4.-5. Graphs showing: 4. Topographic setting and selected well and site characteristics ...............................13 5. Average yield and selected well and site characteristics ..........................................15 6. Boxplots of selected chemical constituents in ground water in the south metropolitan Atlanta region..................................................................................................................22 Table 1. 2. 3. 4. 5. 6. 7. TABLES Water use, 1985................................................................................................................................... 6 Ground-water use by cities and towns, 1985 ................................................................................... 8 Summary of welJ data.........................................................................................................................12 Regression models for well groupings.............................................................................................16 Summary of spring data.....................................................................................................................19 Summary of data for high-yielding wells.........................................................................................20 Physical and chemical characteristics of ground-water [in pocket in back of report) iii CONVERSION FACTORS, ABBREVIATIONS, DEFINITIONS, AND VERTICAL DATUM Multiply inch (in.) foot (ft) mile (mi) by Length 25.4 0.3048 1.609 to obtain millimeter (mm) meter (m) kilometer (km) square mile (ml2) gallon (gal) gallon per minute (galjmln) million gallons per day (Mgalfd) inch per year (injyr) gallon per day (gal/d) cubic foot per day (tt3 /d) 2.590 Volume 3.785 0.003785 Flow 0 .06309 0.04381 43.81 25.4 3.785 0.02832 square kilometer (km2) liter (L) cubic meter (m3) liter per second (Lfs) cubic meter per second (m3js) liter per second (L/s) millimeter per year (mmjyr) liter per day (L/d) cubic meter per day (m3jd) iv CONVERSION FACTORS, ABBREVIATIONS, DEFINITIONS, AND VERTICAL DATUM MuHiply foot per day (ft/d) by Hydraulic conductivity 0.3048 to obtain meter per day (m/d) gallon per minute per foot [(galjmin}/ft] Specific capacity 0.2070 liter per second per meter [(Ljs}/m] Temperature in degrees Celsius (C} may be converted to degrees Fahrenheit (F} as follows: Additional abbreviations JLg/L micrograms per liter mgjl milligrams per liter JLS/cm at 2sc = microslemen per centimeter at 25 degrees Celsius Sea level:--ln this report "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929}--a geodetic datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerty called "Sea Level Datum of 1929." v GROUND-WATER RESOURCES OF THE SOUTH METROPOLITAN ATLANTA REGION, GEORGIA By JohnS. Clarke and Michael F. Peck U.S. Geological -Survey ABSTRACT Ground-water resources of the ninecounty south metropolitan Atlanta region were evaluated in response to an increased demand for water supplies and concern that existing surfacewater supplies may not be able to meet future supply demands. Previous investigations have suggested that crystalline rock in the study area has low permeability and can not sustain well yields suitable for public supply. However, the reported yield for 406 wells drilled into crystalline rock units in this area ranged from less than 1 to about 700 gallons per minute, and averaged 43 gallons per minute. The reported flow from 13 springs ranged from 0.5 to 679 gallons per minute. The yield of 43 wells and flow from five springs was reported to exceed 100 gallons per minute. Most of the highyielding wells and springs were near contact zones between rocks of contrasting lithologic and weathering properties. The high-yielding wells and springs are located in a variety of topographic settings: hillsides, upland draws, and hilltops were most prevalent. The study area, which includes Henry, Fayette, Coweta, Spalding, Lamar, Pike, Meriwether, Upson and Talbot Counties, is within the Piedmont physiographic province except for the southernmost part of Talbot County, which is in the Coastal Plain physiographic province. In the Pi~dmonl, ground-water storage occurs in joints, fractures and other secondary openings in the bedrock, and in pore spaces in the regolith. The most favorable geologic settings for siting highyielding wells are along contact zones between rocks of contrasting lithology and permeability, major zones of fracturing such as the Towaliga and Auchumpkee fault zones, and other numerous shear and microbreccia zones. Although most wells in the study area are from 101 to 300 feet deep, the highest average yields were obtained from wells 51 to 100 feet deep, and 301 to 500 feet deep. Of the wells inventoried, the average diameter of well casing was largest for wells located on hills and ridges, possibly indicating a preference for such topographic locations by cities and industrial users who typically develop larger diameter wells than do domestic users. Generally, for a given depth range or well diameter, the highest yielding wells were obtained in draws and valleys, followed by hills and ridges and slopes and flats. In 1985, wells and springs supplied about 16 million gallons per day or 37 percent of the total water withdrawn in the area. Average recharge to the aquifers in the upper Flint River basin, which constitutes 66 percent of the area, was estimated to be about 575 million gallons per day. Groundwater recharge in this basin ranged from 414 million gallons per day during an average dry year, to 771 million gallons per day during an average wet year. During the severe drought of 1954, the estimated recharge was 70 million gallons per day. Ground water in the study area generally is suitable for most uses. With the exception of local occurences of excessive iron, fluoride, and manganese, concentrations of total and/or dissolved constituents generally meets State and Federal drinking water standards. Ground-water quality may be affected by the presence of radionuclides associated with the decay of uranium found in igneous and metamorphic rocks. 1 INTRODUCTION The south Metropolitan Atlanta region (south metro region) of the Piedmont physiographic province is undergoing rapid population growth. As the population grows, the demand for water supplies in the region will increase. Most municipal and industrial supplies in the south metro region are derived from surfacewater sources, but expected increases in the demand for water are causing concern that the surface-water resources may not be able to meet the demand. Ground water in the area may offer a potential source of water to supplement the available surface-water resources. Ground water in the Piedmont is contained in openings in the otherwise impermeable crystalline bedrock, and in the overlying semi-consolidated to unconsolidated material. Until recently, ground-water yields in the Piedmont were considered too small to provide substantial amounts of water for municipal and industrial supply. A study by Cressler and others {1983), however, showed that large supplies of ground water may be obtained from a variety of geologic and topographic settings in the greater Atlanta region--the area north of and including the northern part of the south metro region. More recent work by the Georgia Geologic Survey (Brackett and others, 1990a) has located highyielding wells in a number of communities in the Piedmont. To determine the development potential of ground water in the south metro region, the U.S. Geological Survey {USGS), in cooperation with the U.S. Army Corps of Engineers, Savannah District, and the Georgia Department of Natural Resources, Environmental Protection Division (EPD), Georgia Geologic Survey (GGS), conducted a study of the ground-water resources in the area during 1988-89. Purpose and Scope This report provides a general evaluation of the ground-water resources of the south metro region and their development potential. The evaluation describes existing ground-water supplies in the region, including domestic, agricultural, municipal, and industrial wells and springs; their yield; hydrogeologic and topographlc setting; conslruction specifications; and quality of water. Although this report giws a general overview of hydrogeologic conditions favorable for attaining high-yielding wells in the area, more detailed studies to better define local hydrogeologic conditions would be necessary to locate actual drilling sites. The study area (fig. 1) includes the upper Flint River basin and, with the exception of extreme southern Talbot County in the Coastal Plain, lies within the Piedmont physiographic province. The 2,808 mi2 study area includes Fayette, Henry, Spalding, Coweta, Pike, Upson, Meriwether, Talbot, and Lamar Counties. Methods Prior to this study, data and information on the geology, hydrology, and water quality of aquifers in the south metro region were insufficient for a thorough evaluation of the ground-water resources. For this reason, an extensive file search and field inventory of wells were conducted to collect additional data and information in the region. These data were used to demonstrate the yield potential of aquifers in the region. Files of well drillers, municipalities, county tax offices, county health departments, the USGS, the GGS, and EPD were searched and reviewed for pertinent information. Well data obtained from these sources were plotted on 7 1/2-minute topographic quadrangle maps and locations were verified by USGS personnel in the field. As new sites were field inventoried, data were entered into the U.S. Geological Survey's Ground-Water Site Inventory (GWSI) system, a computerized system for ground-water data storage and retrieval. At each new well site, the following data were obtained, where available. (1) well construction specifications, (2) well yield or spring discharge, (3) static and pumping water levels, (4) water use, (5) quality of water, (6) topographic setting, (7) soil thickness, (8) depths of water-bearing zones and their characteristics, and (9) depth and character of lithologic changes. 2 I / I , I oNEWNAN t COWETA \ ( \ I MERIWETHER G'' ~JLLE 3300' \ \ DURAND 0 , EXPLANATION D 6 PIEDMONT PHYSIOGRAPHIC PROVINCE COASTAL PLAIN PHYSIOGRAPHIC PROVINCE FLINT RIVER DRAINAGE BASIN BOUNDARY I SPALDING 'o_ GRIFFIN \. PIKE ZEB0ULON UPSON l LAMAR ( \. 0 BA RNESVfLLE ) I \ THOM0ASTON GEORGIA Figure 1.--Location of study area, physiographic provinces, and the Flint River Basin. 3 This inventory resulted in the addition of 201 well sites and 12 springs to the existing data base of 280 wells and 1 spring. Previous Studies The ground-water resources in the northern half of the south metro region, which includes Coweta, Henry, Fayette, and Spalding Counties, were described in a report on the ground water resources in the greater Atlanta region by Cressler and others (1983). Their report assessed the quantity and chemical quality of ground water in the region, and discussed methods for locating high-yielding wells throughout the region. In Lamar County, Gorday {1989) assessed the availability and chemical quality of ground water, and investigated siting techniques for high-yielding wells. Hewett and Crickmay (1937) described geohydrologic controls on the warm springs of Georgia and presented a geologic map of the Warm Springs area. White (1965) described bauxite deposits and the geology of the Warm Springs district of Meriwether County. Reinhardt and others (1984) discussed evidence for Cenozoic tectonism in the southwest Georgia Piedmont near Warm Springs. Schamel and others (1980) described the geology of the Pine Mountain Window and adjacent terranes in Georgia and Alabama in a fieldtrip guidebook. Clarke (1952) described and mapped the geology and mineral resources of the Thomaston 15-minute quadrangle, which includes parts of Upson, Talbot, Pike, and Lamar Counties. Higgins and others (1988) described the structure, stratigraphy, tectonostratigraphy, and evolution of the southernmost part of the Appalachian orogen, which included all of the south metro region; and revised, adopted, and simplified the stratigraphic nomenclature of the region. Well and Spring Numbering System Wells and springs in this report are numbered according to a system based on the USGS index to topographic maps of Georgia. Each 7 1/2-minute topographic quadrangle in Georgia has been given a number and letter designation begining at the southwest corner of the State, and increase numerically eastward. The letters progress alphabetically northward. Because the alphabet contains fewer letters than there are quadrangles, those in the northern part of the State are designated by double letters, AA follows Z, and so forth. The letters "1", "0", "II", and "00" are not used. Wells and springs inventoried in each quadrangle are numbered consecutively, beginning with 1. Thus, the fourth well scheduled in the 11AA quadrangle is designated 11AA04. Locations of wells and springs in the study area are shown in plate 1. Acknowledgements The authors extend their appreciation to the many well owners, drillers, city clerks, and managers of municipal and industrial waterworks who readily furnished information about wells. In particular, the writers wish to thank Mrs. Hoyt W. Waller of Waller Drilling Co., Grifftn, Ga., and Mr. James Breakey and Mr. Mike Smith of Middle Georgia Water Systems Inc., Zebulon, Ga. DESCRIPTION OF THE STUDY AREA Geologic Setting Previous investigators have divided the various igneous and metamorphic rock units of the south metro region into more than 40 named formations and unnamed mappable units that range in thickness from less than 10 ft to possibly more than 10,000 ft (Cressler and others, 1983, p. 7). Regional tectonic stresses have warped the rocks into complex and refolded folds that have been injected by younger igneous plutons and dikes and broken by faults (Cressler and others, 1983, p. 7). The rocks are characterized by several distinct regions that are separated from each other by thrust faults (Higgins and others, 1988). A generalized geologic map of the area is shown in plate 1. The Towaliga and Auchumpkee are major fault zones that cut across the southern part of the south metro region. The Towaliga is a normal fault that dips to the northwest and extends for at least 125 mi across Georgia and Alabama (Clarke, 1952, p. 72). In the study area, the fault cuts across central Lamar and southern Meriwether and Pike 4 Counties, and is marked by a discontinuous zone of mylonite, blastomylonite, button schist, and mylonite gneiss as much as 1 mi wide (Higgins and others, 1988, p. 23). The Auchumpkee fault of Higgins and others (1988, p. 67), crosses northcentral Talbot and south-central Upson Counties in the southern part of the study area. The Auchumpkee is a thrust fault that locally coincides with what has been mapped previously as the Goat Rock fault (Clarke, 1952, p. 73). The fault is marked by a zone 1 to 2 mi wide that is characterized throughout its length by sheared rocks, mylonite, ultramylonite, and blastomylonite. The area north of the Towaliga fault is characterized by metamorphic rocks intruded by granite subsequent to metamorphism. Rocks in the area between the Towaliga and Auchumpkee faults consist chiefly of schist, gneiss, and quartzite that were intruded by granite and charnockite (Higgins, 1988). South of the Auchumpkee fault, the principal rocks are hornblende-biotite granite and biotite-oligoclase gneiss and epidote-amphibolite gneiss (Clarke, 1952, p. 6). Other major faults in the south metro region include the Shiloh fault (Schamel and Bauer, 1980; Sears and others, 1981), a normal fault cutting across northern Talbot County, and the Warm Springs fault (Christopher and others, 1980), a normal fault in southern Meriwether County. Hydrologic Setting Average annual precipitation in the south metro region for the period 1941-70 ranged from less than 48 in. in eastern Lamar County to more than 52 in. in Talbot, and parts of Meriwether, Coweta, and Fayette Counties (Carter and Stiles, 1983). Maximum rainfall generally occurs during the winter and midsummer. Average annual runoff for the same period ranged from less than 16 in. in Spalding and eastern Lamar and Fayette Counties, to more than 24 in. in southeastern Talbot County, which lies within the Coastal Plain physiographic province (Carter and Stiles, 1983). Ground-water recharge rates in the upper Flint River basin were estimated by Faye and Mayer (1990) using a hydrograph separation technique for the Flint River near Culloden stream gage site (site 02347500, plate 1). The upper Flint River basin lies in th~ Piedmont, and covers an area of about 1,850 mi , or about 66 percent of the study area. Although ground-water contribution from outside the river's drainage basin through faults, fracture systems, or contact zones transecting the basin boundary is possible, it is likely that the largest percentage of recharge is derived from precipitation within the basin. The estimated mean annual ground-water recharge rate in the Flint River basin is about 6.5 in/yr (575 Mgal/d), but is higher during wet years and lower during dry years (Faye and Mayer, 1990). Average wet and dry years were determined by examining streamflow records for 1911-87. During an average dry year (1941), the recharge rate was about 4.7 in/yr (415 Mgaljd); whereas, during an average wet year (1949), the recharge rate was about 8.8 in/yr (770 Mgal/d). During extreme droughts, the recharge rate is well below the average. During the severe drought of 1954, ground-water recharge was estimated to be only about 0.8 in/yr (70 Mgaljd). Differences in recharge rates during wet and dry years determine the relative amounts of water available from the regolith and from deeper fracture systems for baseflow to streams and yield to wells. During wet years, the regolith is more saturated, and there is more water in ground-water storage. During dry years, however, the regolith is less saturated or is completely dry, and groundwater storage largely is limited to fracture systems in the bedrock. Thus, recharge during the severe drought of 1954 (0.8 in/yr), probably did little to recharge the regolith, but primarily contributed to storage in deep fracture systems within the drainage basin. Although the amount of recharge exceeds current ground-water withdrawals in the basin (16 Mgal/d), only a small percentage of the estimated annual recharge can be economically recovered by wells. The actual amount that can be recovered will depend on utilization of systematic waterprospecting techniques to locate sites favorable for the development of high-yielding wells. Water Use Water-use data for the south metro region were compiled from Turlington and others (1987) (table 1, fig. 2). In the study area, approximately 43.3 Mgal/d was withdrawn from surface- and ground-water sources during 1985. Of this total, about 63 percent (27 Mgaljd) was from surfacewater sources and 37 percent (16 Mgal/d) was from ground-water sources. 5 Table 1.--Water use in the study area, 1985 [Data from Turlington and others, 1987) County and source Withdrawals, in million gallons per day Domestic Public and supply commercial Industry and mining Irrigation Livestock Totals Coweta County Ground water Surface water County totals Fayette County Ground water Surface water County totals Henry County Ground water Surface water County totals Lamar County Ground water Surface water County totals Meriwether County Ground water Surface water County totals Pike County Ground water Surface water County totals Spalding County Ground water Surface water County totals Talbot County Ground water Surface water County totals Upson County Ground water Surface water County totals Ground water totals, all counties Surface water totals, all counties 0.38 2.03 3.08 0.00 3.46 2.03 .27 .76 .43 .00 .70 .76 .21 1.46 3.25 .00 3.46 1.46 .01 .50 1.68 .00 1.69 .50 .36 .91 .98 .00 1.34 .91 .16 .53 .12 .00 .28 .53 0.08 1.47 5.45 .00 5.53 1.47 .11 .34 .00 .00 .11 .34 .14 .80 1.79 .00 1.93 .80 1.72 8.80 16.78 .00 0.03 0.02 .53 .04 .56 .06 .01 .02 .00 .06 .01 .08 .00 .00 .00 .25 .00 .25 .00 .06 .00 .24 .00 .30 .35 .00 .00 .08 .35 .08 .00 .13 .00 .14 .00 .27 0.00 0.00 .00 .25 .00 .25 .00 .06 .00 .04 .00 .10 .01 .27 2.97 .31 2.98 .58 .40 .56 3.50 1.41 0.00 .12 .12 .00 .07 .07 .01 .10 .11 .55 .64 1.19 .81 .96 1.77 .11 .19 .30 0.01 .08 .09 1.14 1.19 2.33 2.06 2.09 4.15 4.69 5.44 2.46 3.77 6.23 1.06 .56 1.62 1.68 3.60 5.28 1.12 2.56 3.68 2.43 2.02 4.45 .93 .45 1.38 1.56 5.78 7.34 1.65 1.23 2.88 3.28 7.16 10.44 16.17 27.13 6 GROUND-WATER USE lJ'SCN TALBOT SPALDING > PI~<<<<"~<'..<<<\<'~<<1 > PHWATER tt:IIR'( -..-.. -~....".,;',<~~<<'~<._..~<<'~1 m_ ~ .. FAYETTE , ,,............. .......,...............' , ..:'...' ,..................', COWETA 0 2 4 6 8 PUMPAGE, IN MILLION GALLONS PER DAY 27.13MgaVd rn PUBLIC SUPPLY D DOMESTIC AND COMMERCIAL INDUSTRY AND MINING ~ IRRIGATION g LIVESTOCK mGROUND WATER D SURFACE WATER Figure 2.--Water use in the south metropolitan Atlanta region, 1985. Of the 16 Mgal/d withdrawn from groundwater sources in 1985, 54 percent was for domestic and commercial uses, 29 percent was for livestock, 11 percent was for public supply, 3.5 percent was for irrigation, and 2.5 percent was for industrial and mining uses. In 1985, Upson County used the most ground water (3.28 Mgal/d or 20 percent) in the nine-county study area. Almost all the ground water in the study area is obtained from wells, except where a few municipalities are withdrawing water from large springs. See tables 1 and 2 and figure 2 for a complete summary of source and use for 1985. Table 2.--Ground-water use by cities and towns in the study area, 1985 [Data from Turlington and others, 1987] GROUND-WATER RESOURCES Ground water in the Piedmont part of the study area, which includes all but the southern part of Talbot County, occurs primarily in the regolith and in areas where secondary permeability has developed along geologic discontinuities in the otherwise impermeable crystalline bedrock. Regolith is the semi-consolidated to unconsolidated material that occurs as a layer on top of the bedrock. The regolith is composed of soil, saprolite (weathered rock), stream alluvium, colluvium, and other surficial deposits. The availability of water in the Coastal Plain part of the study area (extreme southern Talbot County) is similar to that in the Piedmont to the north, because the Coastal Plain sediments in this area, like the regolith, are comparatively thin and overlie crystalline rocks. County Coweta Fayette Henry Meriwether Pike Spalding Talbot Upson City or town Daily water use (million gallons Source per day) Grantville Moreland Turin well 0.08 well .02 well .03 Brooks well .03 Hampton well .08 McDonough well .03 Greenville well .11 Lone Oak well .05 Luthersville well .04 Warm Springs spring .10 Concord Meansville Molena Williamson spring .06 well .03 well .03 well .04 Orchard Hill well .01 Geneva well .02 Junction City well .01 Talbotton well .08 Yatesville well .04 Hydrogeologic Units Many of the rock units in the south metro region exhibit similar physical properties and yield comparable quantities of water and similar chemical quality. On the basis of these similarities, Cressler and others (1983) grouped rock units of the Greater Atlanta region, which includes the northern half of the study area, into nine principal hydrogeologic units (plate 1). These hydrogeologic units consist of (1) unit A (amphibolite, gneiss, and schist), (2) unit B (granitic gneiss), (3) unit C (schist), (4) unit D (biotite gneiss), (5) unitE (mafic rocks), (6) unit F (granite), (7) unit G (cataclastic rocks), (8) unit H (quartzite), and (9) unit J (metamorphosed carbonate rocks) . During the current study, these units were extended throughout the Piedmont part of the south metro region, and all Coastal Plain sediments were grouped into a single unit (K). Thus, a total of 10 hydrogeologic units (units A-K) were included as a part of this study. These hydrogeologic units, as described by Higgins and others (1988); Georgia Geologic Survey (1976); and Cressler and others (1983), are shown in plate 1. 8 Ancient alluvial-fan, landslide, and debrisflow deposits are present in the Pine Mountain area (H.W. Markewich, U.S. Geological Survey, written commun., 1989). These deposits occur along the mountainous ridges, have thick weathering and soil profiles, and probably are from early Pleistocene to late Miocene in age. The alluvial fan deposits may serve as a source of water supply due to their relatively high permeability. The deposits consist of stacked fming-upward sequences of cobble-gravel to medium sand, that range in thickness from several inches to greater than 50 ft (H.W. Markewich, U.S. Geological Survey, written commun., 1989). The alluvial fans occur along numerous quartzite ridges (unit H, plate 2) and have been identified along north-, east-, and south-facing slopes. Alluvial deposits along the Flint River and its tributaries also may serve as sources of ground water. Alluvium along the Flint River terraces in the Pine Mountain area generally is less than 20 ft thick (much of the alluvium is 8 to 10 ft thick), and commonly consists of a fming-upward sequence of coarse sand and pebble gravel, to medium and fine sand and no gravel (H.W. Markewich, U.S. Geological Survey, written commun., 1989). Alluvial deposits along tributaries of the Flint River commonly are from 2 to 5 ft thick, and channel deposits are up to 15 ft thick. Sediments of the Coastal Plain in southern Talbot County consist of layers of sand, gravel, and clay that attain a maximum thickness of at least 260 ft, the depth penetrated by well 10U006 at Junction City (appendix A). The sediments generally strike from east to west and dip southward. The sediments overlie igneous and metamorphic basement rocks that are a subsurface extension of the rocks of the Piedmont province. In parts of the Piedmont part of the study area, erosional remnants of Coastal Plain sediments are present. The largest and most northern of these erosional remnants is located north of Pine Mountain near Warm Springs in Meriwether County. In this area, about 30 mi north of the inner margin of the Coastal Plain, sediments of Paleocene age have been isolated from correlative Coastal Plain deposits by high-angle reverse faults and subsequent erosion (Reinhardt and others, 1984, p. 1, 176). Ground-Water Levels Ground-water levels in the south metro region are influenced primaily by changes in precipitation, evapotranspiration, and local pumping. Water-level fluctuations in the shallow regolith are shown by the hydrograph for well llAAOl (Georgia Experiment Station) near Griffin in Spalding County (fig. 3). The ground-water level in the 30-ft deep well is affected mainly by precipitation and evapotranspiration as can be seen by comparing the hydrograph with the rainfall graph in figure 3. Rainfall in the area generally is heavy in the winter and midsummer and relatively light in spring and fall. The ground-water level shows a rapid rise with the onset of late winter rains and reduced evapotranspiration, and generally attains the highest level for the year in March or April. Heavy rainfall in midsummer results in small rises in the water level, but much of this rainfall is lost to evapotranspiration and runoff. The water level in the regolith declines in the spring and early fall owing to increases in evapotranspiration and decreases in rainfall, and the annual low generally occurs in October or November. Three droughts during the 1980's resulted in lower-than-normal water level in the fall of 1981, in the fall of 1986, and in the summer of 1988 (fig. 3). Ground-Water Availability In the Piedmont province, ground water occurs in joints, fractures, and other secondarily formed openings in the bedrock, and in pore spaces in the regolith. In this area, the ground-water reservoirs are recharged by water flowing directly into openings in the exposed rock or by seeping through the regolith. The quantity of water that can be withdrawn from wells depends on the amount of available recharge, the thickness of saturated regolith (available storage), and the extent to which openings in the rock are interconnected with the regolith. The size, spacing, and interconnection of openings vary from one rock type to another. Generally, the largest and most interconnected openings occur in hard, brittle rocks such as quartzite and metagraywacke, and in carbonate rocks such as marble (Cressler and others, 1983, p. 9). 9 WELL 11AA01 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 Figure 3.--Cumulative departure from the long-tern1 average of precipitation at the National Weather Service Station Atlanta WSO AP and periodic water levels at wellllAAOl, Spalding County, 1979-88. 10 Cressler and others (1983) described the factors that influence the availability of ground water in the greater Atlanta region, which includes the northernmost counties of the south metro region (Coweta, Fayette, Spalding, and Henry). They concluded that high-yielding wells may be found near certain structural, stratigraphic, and topographic features that are associated with increased permeability of the rock. These features include (1) contact zones between rock units of contrasting character, (2) contact zones within multilayered rock units, (3) fault zones, (4) stress relief fractures, and (5) shear zones. Other features, such as rock type, depth of weathering, saturated thickness of the regolith, and topographic setting, also are factors that influence the availability of water from wells. Similar observations were made by Brackett and others (1990a). The present study determined that many of the above features were factors influencing well yield throughout the Piedmont part of the south metro region. Thus, numerous locations may be favorable for the development of high-yielding wells. There are more than 4,000 mi of contact zones between rocks of contrasting lithologies in the south metro region that may favor greater permeability of the rock. Greater permeability along such contacts results from differential weathering of the contrasting rock types. For example, along a contact between a foliated schist unit and a granite gneiss unit, water flowing along the foliation of the schist unit (oriented toward the contact) would travel until it was obstructed by the lower permeability gneiss unit. Here, water would travel along the contact to reach a lower potential head. The flow of water along this contact could result in chemical weathering of the rock units and enhanced permeability. The most productive contacts generally are ones in which a resistant rock is overlain by a rapidly weathering rock. Where the rocks overlying the resistant rock are foliated, have a high feldspar content, differ mineralogically, and occupy a topographic position favorable to recharge (Cressler and others, 1983, p. 11), higher yields to wells are possible. Cressler and others (1983, p. 43), stated that potentially permeable contact zones between rocks of contrasting character occur wherever units B, D, and F are in contact with units A, C, and E and locally with unit G. In addition, they stated that some contact zones between unit C and units E, H, and G also may be permeable. These contact zones are shown on plate 1. As more detailed geologic maps become available, better definition of potentially permeable contact zones in the area will be possible. Cressler and others (1983, p. 15) stated that high well yields also are available from areas where faults bring into contact two or more rock types that respond differently to weathering, much the same as occurs in permeable contact zones. Their study (1983) concluded that the largest yields generally are available from faults that involve both resistant rocks, such as massive gneiss or granite (units B and F) and less resistant rocks, such as feldspathic schist (unit C). The Towaliga fault and Auchumpkee fault are major fault zones that cut across the southern part of the south metro region. Although fractures produced by movement of the faults typically have been healed by mineralization and are no longer fully open (Clarke, 1952, p. 73), shearing and mixing of rock types along the fault plane may result in increased permeability. In parts of the south metro region, there are shear zones and microbreccia zones that may be associated with increased permeability of the rock. This increased permeability occurs where the sheared rock is in contact with native rock producing a zone of contrasting weathering properties. Cressler and others (1983, p. 37) reported that some of the highest yields in the greater Atlanta region (100 gal/min to more than 200 gal/min) were found near shear zones, including some in Spalding County. These zones of crushed, angular rock are the result of stresses that cause contiguous parts of a rock body to slide relative to each other in a direction parallel to their plane of contact. The sheared rock consists of flinty crush rock and sheared native rock. In the south metro region, shear zones are prominent south of the Auchumpkee fault in rock unit D (plate 1). Flinty crush rock associated with shearing occurs in unit G west and southwest of Talbotton in Talbot County. Microbreccia zones are indicated on plate 1 as rock unit G in northwestern Spalding County, in southeastern Fayette County, and in northwestern Talbot County. 11 Well yields and factors affecting yields The reported yield for 406 wells ranged from less than 1 to 700 gal/min, and averaged 43 gal/min. Many of the well sites in the south metro region were located for convenience, i.e., near towns, manufacturing plants, homes, and so forth, and without regard to hydrologic well-site selection criteria. It is likely that greater well yields could be obtained by following proper well-siting techniques. For a complete discussion of well-siting criteria as related to topography, the reader is referred to LeGrand (1967) and Cressler and others (1983). The relations among well yield, wellconstruction characteristics, water-bearing unit, and topographic setting were evaluated based on information from 481 wells (table 3; appendix A) . Statistics for hydrogeologic units E, G, H, J, and K are not listed because fewer than 15 well records were available for each of the units. Information for these units were, however, included in the summary statistics. To evaluate the influence of topographic setting on well yield, data for wells were grouped into three topographic categories that corresponded to those used in Daniel's (1987) statistical analysis of well data in the North Carolina Piedmont and Blue Ridge: draws and valleys, hills and ridges, and slopes and flats. Construction and yield characteristics varied over the study area based on differences in topographic setting and geologic unit. A graphical summary of selected site and well characteristics for the south metro region is shown in figure 4. The average well in the data base had a total depth of 288 ft, had 6.5 in. casing to a depth of 70 ft, and yielded 43 gal/min. As would be expected, average values of land-surface altitude, well depth, and depth to water were greatest for wells located on hills and ridges, and lowest for wells in draws and valleys. In the study area, depth of casing is an approximation of the thickness of regolith. Although the thickness of regolith would be expected to be greater for wells located on hills and ridges, the depth of casing (thickness of regolith) averaged about 70 ft for each of the three topographic settings. The saturated thickness of regolith can be estimated for a well by subtracting the depth to water from the casing depth. The average saturated thickness was greatest for wells located in draws and valleys (59 ft), and least for Table 3.--Summary of well data in the study area Hydrogeologic unit Yield (gallons per minute) Range Number of Average wells Total depth (feet) Number of Range Average wells Casing depth (feet) Number of Range Average wells A -Amphiboli te- ~ eiss-schis t B- anitic gneiss C--Scltist D- Biotite gneiss F-Granite All wells!/ 0.0-200 1-200 1.5-700 6-100 2.5-150 0.0-700 40 230 30-780 297 246 6-446 71 201 48 58 85-675 247 59 8-140 54 45 76 31 31-745 307 33 19-205 80 32 30 23 67-547 295 30 7-160 77 25 24 34 26-605 277 38 17-121 27 33 43 406 26-780 288 441 6-446 70 360 1/Jncludes units A, B, C, D, E, F, G, H, J, and K 12 es ~7 219 1000 800 m iii i!f 600 ~ c ~ 400 II: c ~ 200 DV HR SF TOPOGRAPHIC SETIING 93 i 50 237 . DV HR SF TOPOGRAPHIC SETTING eo ., ,.. - , 00 ~.w. !~ 60 u-:c ~~ 40 ~ w cCl 20 w0: ~ 50 67 11 4 179 DV HR SF TOPOGRAPHIC SETIING 54 84 17 ' DV HR SF TOPOGRAPHIC SETIING 9 59 98 DV HR SF TOPOGRAPHIC SETTING 116 70 179 DV HR SF TOPOGRAPHIC SETTING EXPLANATION 85 Number Indicates total number of wells in each topographic setting. DV Draws and Valleys HR Hills and ridges SF Slopes and flats DV HR SF TOPOGRAPHIC SETTING Figure 4.--Topographic setting and selected well and site characteristics in the south metropolitan Atlanta region. 13 wells located on hills and ridges (44ft). Although each topographic setting had similar regolith thickness, the saturated thickness in draws and valleys (59 ft) was greater owing to a shallower depth to water. The average diameter of well casing was largest for wells located on hills and ridges (6.8 in.). This may reflect a preference for such topographic locations by cities and industrial users who usually develop larger diameter wells than do domestic users. The relations among well yield, well diameter, and well depth for the various topographic settings and geologic units were compared by using bar graphs showing average yield for various ranges of well depth and well diameter (fig. 5). Although most wells in the south metro region were from 101 to 300 ft deep, the highest average yields were obtained from wells 51 to 100ft deep (62 gal/min), and 301 to 500ft deep (57 gal/min). Most wells in the south metro region were cased with 6 in. casing (299 wells) and had an average yield of 40 gal/min. The highest average yields were obtained from 10-in. diameter wells (453 gal/min). Generally, for a given depth range or well diameter, the highest yielding wells were obtained in draws and valleys, followed by hills and ridges and slopes and flats. Hydrogeologic units B and C generally had the largest yielding wells for a given depth range or well diameter. To remove the variation in well yield attributed to differences in well depth and diameter, calculations were performed following the procedures described by Daniel (1987, p. 41). Daniel (1987) conducted a statistical analysis of 6,200 wells to identify factors associated with highyielding wells in the Piedmont and Blue Ridge of North Carolina. His study used a least squares regression analysis in which yield and yield-per-foot of well depth were treated as dependent variables to be explained in terms of well depth and well diameter. A similar analysis was applied to 484 wells in the south metro region, in which well yield was explained in terms of well depth, well diameter, altitude of land surface, and well volume. The regression analysis was made to produce the most significant regression models based on groupings of all wells, topographic setting, and geologic unit. The resulting models are listed in table 4. The regression coefficient R2 in table 4 is an indicator of the fit of a regression model to the variations in the data. For example, an R2 of 0.95 indicates that 95 percent of the variation of the data may be explained by the regression model. Similarly, the amount of change in R2 resulting from the incorporation of an independent variable into a model, gives an indication of the relative signficance of that variable. For example, a change in R2 of 0.23 for well diameter and 0.01 for well depth indicates that well diameter is more significant than well depth. For each model, well diameter and well depth were the most significant variables (as indicated by the change in R2) influencing reported well yield. For the 10 geologic units, only the models for units A and C are listed in table 4 because R2 values for each of the other units were less than 0.001, and were, thus, considered statistically insignificant. The average well yield was adjusted by using the equations listed in table 4, and by using the data base average values of well depth (288ft), casing diameter (6.46 in.), altitude (820ft) and well volume (64.12 ft3 or 480 gal). Using this procedure, the adjusted average yield for all wells was 53 gal/min. The adjusted yield was 32 gal/min for unit A and 56 gal/min for unit C. The highest adjusted yields were found in draws and valleys (54 gal/min); slopes and flats and hills and ridges had the same average yield (37 gal/min). Higher well yields near hills and ridges in the Greater Atlanta region (including the northern part of the south metro region), were attributed by Cressler (1983) to be the result of nearly horizontal fractures. These fractures occur mainly at depths of 150 ft to more than 600 ft, and are not revealed by structural and stratigraphic features normally associated with increased bedrock permeability (Cressler and others, 1983, p. 26). Six wells tapping these lowangle fractures were identified by Cressler and others (1983, p. 24-25) in Coweta, Fayette, Henry, and Spalding Counties. Springs In the study area, 13 major springs were inventoried from topographic maps, historical records, and from a published report by Hewett and Crickmay (1937). Hewett and Crickmay (1937) conducted an extensive study of the springs in a 32 mi2 area near Pine Mountain. Data from 13 of these springs were evaluated in this study (1990) to determine if any correlations could be made between yield and rock unit, topographic setting, and water temperature (table 5, plates 1 and 2). Most of the springs occur near contact zones between units A and H (four springs) and between units C and H (three springs), and within unit A (three springs) (plate 1). One spring 14 ALL WELLS >500 1 42 .. ~ 12 2 401-500 1 43 3 301-400 1 64 201-300 1 122 ' 101-200 1102 UJ 51-100 ~ 0 a: 1 16 20 40 60 eo ::J CJ) 0 z >500 '///. '/. :53: 401-500 '/./. 9cUoJ 301-400 f: 21 32 6 15 7 19 fUJ 201-300 UJ LL. ~ 101-200 54 13 SLOPES AND FLATS 0 45 ~ 23 HILLS AND RIDGES 0 55 22 DRAWS AND VALLEYS I 5:UJ 51-100 ' / ht 0 25 10 5 3 ::1 0 20 40 60 80 100 UJ 3: 17"12 >500 1 3 ~ 3 30 =4 401-500 3 4 26 6 301-400 ~74 9 32 201-300 ~2 64 18 101-200 -- ... ..... 71 8 5 7 20 53 6 IWJ UNIT A D UNITS D UNIT C ~ UNIT D 51-100 1---------, 1 [ill UNIT F 4 11 CJ) UJ J: () ~ 6 ~ r:C UJ 0 f- UJ ~ <( Ci _J _J UJ 3: 10 8 6 0 ALL WELLS 100 200 300 400 500 2 [ ] SLOPES AND FLATS ~ HILLS AND RIDGES EJ DRAWS AND VALLEYS 200 400 600 BOO D !z::: ::I a0 c 0 ..1 0w B (.!) 2 43 2 2 WELL DIAMETER ~ 121NCH D 101NCH ~ 8 INCH A D 6 INCf-1 0 100 200 0 200 400 600 800 AVERAGE YIELD, IN GALLONS PER MINUTE AVERAGE YIELD, IN GALLONS PER MINUTE Number at end of bar indicates total number of wells in each category. Figure 5.--Average yield and selected well and site characteristics in the south metropolitan Atlanta region . 15 Table 4.--Regression models for well groupings in the study area [Independent variables: TD, well depth in feet; DIA, well diameter in inches; VOL, well volume in cubic feet; ALT, land surface altitude in feet . R2, coefficient of determination] Group Number Change in R2 of Independent values variables Variable Model Regression model All wells 309 Wells located 57 in draws and valleys Wells located 99 on hills and ridges Wells located 151 on slopes and flats Wells tapping 177 unit A Wells tapping 21 unit C TD DIA VOL ALT TD DIA VOL ALT TD DIA VOL ALT TD DIA VOL ALT TD DIA VOL ALT TD DIA VOL ALT 0.000 .226 .009 .000 0.2256 .009 .1558 .069 .043 .095 .015 .6040 .407 .194 .005 .035 .1861 .143 .013 .016 .008 .2656 .148 .049 .076 .038 .9182 .705 .154 .037 Yield = -0.152178 (TD) + 18.6116 (DIA) + 0.600898 (VOL) -0.00553663 (ALT)- 57.3247 Yield = -.235638 (TD)- 30.0033 (DIA) + 1.09589 (VOL) -0.151751 (ALT) + 369.904 Yield = -0.984676 (TD) - 67.4724 (DIA) + 4.68029 (VOL) + 0.0783363 (ALT) + 392.29 Yield "" -0.157991 (TD) - 2.96015 (DIA) + 0.530056 (VOL) + 0.0505922 (ALT) + 26.5582 Yield = -0.221068 (TD) - 21.7362 (DIA) + 0.914495 (VOL) + 0.14387 (ALT) + 59.9007 Yield = -1.14025 (TD)- 62.184 (DIA) + 5.46151 (VOL) -0.204655 (ALT) + 604.331 was within unit D, one was within unit C, and one was near the contact between units C and G. The 13 springs were located in three topographic settings; upland draw (six springs) was the most prevalent topographic setting. Five of the springs were located near the northern base of Pine Mountain; one was located near the southern base of Oak Mountain (plate 1). During the period 1933-35, the 13 springs had discharge rates that ranged from 0.5 to 679 gal/min, and water temperatures that ranged from 16.6 to 31.2 C. Hewett and Crickmay (1937, p. 4) classified springs having water temperatures higher than 18.8 C as "warm" and those having water temperatures lower than 18.8c as "cold". Seven of the 13 springs inventoried had water temperatures greater than 18.8 C, and thus were classified as warm springs. 16 Occu"ence of high-yielding wells and springs High-yielding wells and springs are herein defined as those having yields greater than or equal to 100 galjmin. Forty-three high-yielding wells and five high-yielding springs were inventoried in the south metro region (tables 5, 6; plate 1). The high-yielding wells had reported yields from 100 to 7oo gal/min, ranged in depth from 85 to 550ft, and were cased with 14 to 300ft of casing. Most of the wells were drilled near contact zones between rocks of contrasting lithologic and weathering properties (24 wells), and within rock unit A (14 wells). The high-yielding wells were located in a variety of topographic settings; hillsides (14 wells), upland draws (14 wells), and hilltops (12 wells) were the most prevalent. With the exception of well 12Y009 in Lamar County, all the highyielding wells were located north of the Towaliga fault. This study (1991) found no high-yielding wells in Talbot or Upson Counties. The highest yielding wells were in southwestern Meriwether County near Durand. Reported yields from wells 07X001 and 07X002 were 600 and 700 galjmin, respectively (table 6), which are among the highest reported yields in the entire Piedmont province of Georgia. The wells supply an industrial user and are located on a hilltop within unit C, about 2 mi northwest of the Towaliga fault (plate 1). A geologic map by Higgins and others (1988, plate 2) indicates that the two wells are located on the underriding plate of a thrust fault. This fault has thrust interlayered amphibolite, gneiss, and schist of Unit A over schist of unit C (plate 1). It is likely that fracturing and differential weathering associated with this thrust fault and the nearby Towaliga fault has resulted in increased permeability in the area and the higher well yield. Well 07X001 is 400ft deep and is cased with 10-in. steel casing to a depth of 78 ft. In August 1975, the well was pumped at a rate of 600 galjmin for 6 hours, producing a drawdown of 90 ft, which resulted in a specific capacity of 6.7 (gal/min)/ft. Well 07X002 is 475 ft deep and is cased with 10-in. steel casing to a depth of 88 ft. The well was pumped at a rate of 700 gal/min for 6 hours in July 1975, producing a drawdown of 85 ft, which resulted in a specific capacity of 8.2 (galjmin)/ft. Although the two wells may supply higher yields, water demand at the industrial site requires only 60,000 gal/d, or an average of 42 galjmin. The wells have been pumped nearly continuously (24 hours per day) at that combined rate with no reported decrease in yield since 1975. Wells 08Y002 and 09Y005, also in Meriwether County, had reported yields of 110 and 100 galjmin, respectively. Well 08Y002, located northwest of Greenville, was drilled in an upland draw into unit A to a depth of 325 ft and was cased to an unknown depth. After 3 hours of pumping at a rate of 110 galjmin, the drawdown stabilized at 162 ft, resulting in a specific capacity of 0.68 (gal/min)/ft. Well 09Yo05, at Gay, was drilled on a hillside into unit A, to a depth of 385 ft, and is cased to a depth of 75 ft. The well sustained a yield of 100 gal/min during a 24-hour test in 1988. The five high-yielding springs had discharges ranging from 125 to 679 galjmin during the period 1933-35 (table 5). With the exception of Cold Spring (08X007) and Clearwater Spring (10Y014), all the high-yielding springs were classified warm. One of the high-yielding springs was located near the contact between units A and H, three were located near the contact between units C and H, and one was located within unit C (plate 1). The springs were located in valleys (two springs), hillsides (two springs), and upland draws (one spring). With the exception of Clearwater Spring (10Y014), each of the high-yielding springs were south of the Towaliga fault. The two highest yielding springs in the study area occur in southwestern Meriwether County on the north side of Pine Mountain at the town of Warm Springs, near the contact between units C and H (plate 1). Hewett and Crickmay (1937, p. 7-12) reported that Warm Springs (08X008) discharged from 596 gal/min in February 1935 to 679 galjmin in August 1934, and Cold Spring (08X007) discharged from 238 galjmin in March 1935 to 451 gal/min in March 1934. Warm Springs has several openings, one of which is a large fissure in quartzite from which about 200 gal/min flows (Hewett and Crickmay, 1937, p. 5). The discharge rate of the spring is affected by precipitation, and has a 6- to 7-week lag between rainfall in the area and a corresponding increase in the discharge of the spring (Hewett and Crickmay, 1937, p. 32). The spring is recharged by precipitation on Pine Mountain, where water enters the ground-water system along the contact between the Hollis Quartzite (unit C) and the Woodland Gneiss (unit D), and flows to a depth of about 17 3,800 ft (Hewett and Crickmay, 1937). At this depth, the flow of water is bounded by the Towaliga fault and is diverted to land surface along the contact between the Hollis Quartzite (unit C) and the Manchester Schist (unit H). Rose (1990) made an analysis of the carbon-14 activity of water from Warm Springs and estimated the age of the water to be 3,620 (102) years and estimated the flow rate to be about 10ft/yr. The temperature of water from Warm Springs was the highest recorded in the study area, and ranged from 30.6 o C to 31.2 o C during the period 1933-35 (Hewett and Crickmay, 1937). The relatively high temperature of water from the spring was attributed to the heating of the water as it percolated deeply into the rock along the contact between units H and D. The temperature of the water at Cold Spring, which is about 1 mi from Warm Springs, ranged from 17.4C to 18.3c during November 1933. Water from this spring has a lower temperature because it does not penetrate as deeply into the rock as does water from Warm Springs, and thus is not heated by the higher temperature of the rocks at depth. We/1-peifomance tests Long-term well performance tests provide information on the ability of wells to sustain high yields for extended periods without drawing the water level below the pump intake. In addition, the rate of water-level recovery after pump shutdown reflects the efficiency of recharge to the fracture system(s) that supplies the well. Thus, the rate of recovery is indicative of the amount of time that a well can maintain a certain yield. Wellperformance tests were conducted by the GGS in five wells in the south metro region as part of their evaluation of the ground-water resources of the Piedmont and Blue Ridge provinces (Brackett and others, 1990a; 1990b). The following discussion summarizes results of those tests. Well 13AA06 at Locust Grove, Henry County, was tested by the GGS in July 1987 (Brackett and others, 1990a). The well was drilled to a total depth of 500 ft and was cased with 63 ft of 6-in. casing (appendix A). Two primary production zones were encountered during drilling--one at 109 ft that yielded about 5 gal/min, and one at 152 ft that yielded about 100 gal/min. The upper production zone was a contact between rock layers and the lower production zone was either a joint or a fault in the rock. The well was pumped for 24 hours at rates ranging from 180 to 300 gal/min so that drawdown was maintained at about 67 percent of the available drawdown to the top of the deepest production zone. During the test, fluctuations in yield at this drawdown level were monitored. A pumping rate of 300 gal/min was maintained for about 8 hours, after which the pumping rate quickly dropped to 220 gal/min. The yield continued to decline slowly for 5 hours before stabilizing at about 180 gal/min for an additional 11 hours at which time the pump was shut off. After pump shutdown, the water level recovered about 18 percent within an hour and was fully recovered within 24 hours. Well 08BB20 at Shoal Creek, Coweta County was tested by the GGS in August 1987 (Brackett and others, 1990a). The 225-ft deep well was cased with 21 ft of 6-in. casing and taps two primary production zones--one at 100 ft that yielded 8 gal/min, and one at 218 ft that yielded 150 galfmin. Two tests were run in the well during August 1987. During the first test, the well was pumped for 5 hours at 150 gal/min, resulting in a drawdown of 140 ft, or 63 percent of the available drawdown above the deepest production zone. Drawdown had not stabilized after 5 hours and the drawdown curve continued to be steep, resulting in the test being discontinued. During the second test, the well was pumped at 100 gal/min for 24 hours, resulting in a drawdown of 143ft, which was 65 percent of the available drawdown above the 218-ft production zone. Drawdown at that pumping rate was nearly stable. After pump shutdown, the water level in the well recovered about 24 percent within an hour, and was 96 percent recovered 24 hours after pump shutdown. Three wells at Barnesville, Lamar County were tested by the GGS in August 1988 (W.M. Steele, Georgia Geologic Survey, written commun., 1989). Well12Y015 was drilled to a depth of 600ft and cased to 24 ft with 8-in. casing. Although specific water-bearing zones were not delineated during testing, caliper and acoustic televiewer logs indicate that there are numerous openings in the rock (fractures or bedding planes) at depths of 37 to 70 ft, 110 to 165 ft, and 370 to 383 ft. Pumping the well at a rate of 60 gal/min produced a drawdown of 193 ft, which was below the two uppermost intervals of openings in the well (37 to 70 ft and 110 to 165 ft), but above the deepest interval (370 to 383ft). Drawdown in the well was nearly stable after 24 hours of pumping, and 18 Table 5.--Summary ofspring data in the study area [gal/min, gallons per minute; o C, degrees Celsius; --, no data available; Topographic setting: V, Valley; S, Hillside; W, Upland draw] Spring number Spring name Yield (gal/min) Date TemP.Crature measured (0 C) Date measured Topographic setting Remarks Meriwether Coun!Y 07X004 White Sulphur Spring 08W007 Parkman Spring 08X007 Cold Spring 08X008 Wann Springs 09W008 Brown Spring 09W009 Chalybeate Spring Pike Couno/ 10Y014 Clearwater Spring 11Y017 Lifsey Spring 11Y018 Taylor Spring Spalding Coun!Y 11AA19 Hammonds Spring Talbot Couno/ 08W006 Oak Mountian Spring Upson Couno/ 10X011 Thundering Spring 10X012 Barker Spring 0.65 1.62 75 451 238 678.6 595.5 15 30 12 24 1933 16.6 1933 17.3 12-10-1933 24.8 03-24-1934 17.4 03- -1935 18.3 08-24-1934 30.6 02-17-1935 312 12- -1933 20.5 12- -1934 20.0 1933 18.5 1933 182 125 08-22-1958 18.0 83 06-15-1935 25.8 385 06-15-1935 23.7 15 10-11-1988 54 12-08-1933 17.1 .94 12-08-1933 380 23.2 06-12-1935 23.4 06-12-1935 30 11- -1933 23.0 23.4 06-12-1935 v 12-08-1933 06-14-1935 12-10-1933 v v 11-30-1933 11-30-1933 s 12-08-1933 w 06-14-1935 12-08-1930 w 06-14-1935 Within unit A. Underlain by Carolina gneiss. Spring has four openings. Within unit A. Spring has one opening which is presently under a lake. Near contact between units C and H. Spring has four openings. Near contact between units C and H. Spring has several openings, main opening is a large nssure In qWlltzite. Near contact between units A and H. Spring has three openings, some gas bubbles appear In the water. Near contact between units A and H. Analyses show high levels of dissolved solids, silica, and iron. Spring has four opening~~. 10-22-1958 w 06-15-1930 w 06-15-1935 v Within unit C. Associated with a tourmaline-bearing pegmatite. Called Concord Spring by Hewett and Crickmay (1937). Near contact between units C and G. Spring occurs in the Towaliga fault zone. Bubbles of gas are present in the water. Spring has several openings. Near contact between units C and H. Spring has several openings and bubbles of gas are given oil by the largest source. w Within unit D. Yield reported by owner. Spring hu never gone dcy. 12-08-1933 w Within unit A. Spring underlain by Manchester schist. Water has elevated levels of iron. Spring hill! one opening. 03-23-1934 s 03-23-1934 s Near contact between units A and H. Spring hBB four openings with a large amount of gas bubbles rising from the water. Near contact between units A and H. Spring occurs near a ridge of Hollis quartzite. The spring has several sources with gas bubbles rising from them. 19 Table 6.--Summary ofdata for high-yielding wells in the study area [gal/min, gallons per minute; --,no data available; S, Hillside; V, Valley; H, Hilltop; W, Upland draw; F, Flat] Grid number Well name Yield (gal/min) Depth of well (feet) Casing Casing Topodepth diameter graphic (feet) (inches) setting Remarks Coweta County 06AA02 Sue Rickenbacker 100 06BB09 Plant Yates 115 06BB10 Do. 100 07AA10 City of Newnan 100 07AA11 Do. 100 07AA16 Holiday Inn 100 07BB02 F.L. Schronder 150 07BB11 G.C. Watkins 100 07BB15 Bpoe-Eiks-Oub 124 08BB20 Shoal Creek, Ga. 100 08CC04 W.H. Johnston 150 Fayette County 09BB06 H.D. Sowell 150 09BB15 Marnell Mobile Home Park 125 09BB16 C.B. Pyke 120 10AA05 E.N. Gray 120 10AA09 John Crews 200 lOBBll C.C. Rogers Construction Company 100 10CC01 W.T.Turner 150 10CC03 J & S Water Company 100 10CC06 Allgood Construction Company 100 10CC07 T.J. Busey 150 10CC08 Dix Leon Subdivision 110 Henrv County 11BB15 Frank Ritchie 200 12BB05 Selmans Dairy 100 12BB12 Southern Railroad 200 12BB13 McDonough, Ga 200 12CC14 Hugo Kirk 150 12CC20 Morgan Auto Parts 100 12CC24 J.B. Gleaton 100 12CC26 Safari Motor Inn 100 12DD01 Frank Stokes 200 13AA01 Six Star Mobile Home Village 100 13AA06 Locust Grove, Ga. 180 Lamar County 12Y001 Milner School 105 12Y005 Liz Acres Subdivision 100 12Y009 Barnemile 300 Meriwether County 07X001 Georgia Pacific Durand No.1 600 07X002 Georgia Pacific Durand No.2 700 08Y002 Mead (shallow well) 110 09Y005 City of Gay, Ga. No.2 100 Pike County 10Y004 The Ceaders Golf Course 125 11Z003 Williamson, Ga., 1 214 Spalding County 12AA02 Arnold Mcintire 100 90 23 6 w Near contact between units A and E 307 43 6 w Near contact between units B and G 146 42 6 s Near contact between units B and G 350 w Within unit A 350 s Within unit A 223 68 6 H Near contact between units A and B 255 65 6 H Within unit A 212 30 6 s Within unit A 265 72 6 w Within unit A 225 21 6 v Within unit A 125 33.5 6 s Near contact between units A and F 210 62 6 H Within unit A 400 87 6 w Within unit A 148 H Near contact between units A and B 145 45 6 s Near contact between units B and D 175 v Near contact between units A, E, and H 85 60 6 s Within unit A 85 42 6 s Within unit B 122 22 6 w Near contact between units B and E 123 93 6 v Near contact between units A and E 96 58 6 s Near contact between units A and E 96 49 6 s Near contact between units B and E 415 14 6 105 55 6 550 300 12 500 280 12 146 126 6 220 59 6 146 17 6 300 38 6 368 38 6 258 102 6 500 63 6 H Near contact between units A and C H Near contact between units A and C s Near contact between units A and C w Within unit A w Near contact between units B and D H Near contact between units B, C, and D s Within unit A H Near contact between units A and D s Within Unit B w Near contact between units A and C w Near contact between units A and C 263 87 6 H Within unit A 165 s Near contact between units A and G 400 30 6 w Near contact between units C and H 400 78 10 H Within unit C 475 88 10 H Within unit C 325 6 w Within unit A 385 75 6.25 s Within unit A 165 74 6 w Within unit C 400 95 8 H Near contact between units C and J 130 24 w Near contact between units A and F 20 recovered relatively rapidly. The water level had recovered 84 percent one hour after shutdown, and was 98 percent recovered 8 hours after shutdown. Well12Y016 at Barnesville was drilled to a depth of 400 ft and cased to 47 ft with 8-in. casing. Specific water-bearing zones were not delineated in this well during drilling. Openings in the rock were indicated on caliper and acoustic televiewer logs at numerous depths in the well, particularly in the intervals 75 to 78 ft, 82 to 88 ft, 122 to 129 ft, 135 to 144ft, 164ft, 172ft, 229ft, 254 to 259ft, 270 to 271 ft, 367 ft, and 395 to 397 ft. At a pumping rate of 75 gal/min, the drawdown was 190 ft, which was below the six uppermost openings, but above the five lowermost openings. Drawdown was stable after 24 hours of pumping and the well recovered rapidly following pump shutdown (W.M Steele, Georgia Geologic Survey, written commun., 1989). One hour after pump shutdown, the water level had recovered 98 percent. Well12Y017 at Barnesville was drilled to a depth of 405 ft and cased to an unknown depth. Specific water-bearing zones were not delineated during drilling of the well. Caliper and acoustic televiewer logs indicate the presence of openings in the rock at depths of 152 ft, 255 to 256 ft, 264 ft; 338 ft, 347 to 348 ft, 362 to 363 ft, and 396 ft. At a pumping rate of 40 gal/min, the drawdown was 175 ft, which was below the uppermost opening (152ft) but above the remaining six openings. Drawdown was stable after 24 hours of pumping and the well recovered rapidly (W.M. Steele, Georgia Geologic Survey, written commun., 1989). An hour after pump shutdown the water level had recovered 99 percent. The five well-performance tests indicate that (1) the wells were capable of sustaining their respective test yields for periods of 24 hours without exceeding the available drawdown, and (2) water levels in four of the five wells were almost fully recovered within 24 hours of pump shutdown; the fifth well recovered about 96 percent. These factors indicate that the wells probably are capable of sustaining their respective test yields under hydrologic conditions similar to those at the time of the tests. It is important to note that yields from the wells may vary seasonally, and that the tests reflect the climatic and hydrologic conditions at the time of the tests. Generally, yields are lower during dry periods, and higher during wet periods. Other conditions, such as interference from nearby pumping wells or the diversion of surface drainage and subsequent loss of recharge may lower the yield of a well. Water Quality Ground-water-quality data for the study area are scarce. Of the 54 water-quality analyses included in this report, 23 are from wells in Lamar County (table 7, in the pocket of this report). The water samples were collected during the period from 1958-88 and were analyzed by different laboratories, including those of the USGS, EPD, and two private firms (table 7). Information concerning these wells and water-quality data are stored in the USGS's National Water Information System (NWIS). Ground water in the south metro region generally is a calcium magnesium sodium bicarbonate type water that is low in dissolved solids and suitable for most uses. Hardness commonly ranges from soft to hard, and pH commonly ranges from 4.8 to 8.3. With the exception of iron, fluoride, and manganese, concentrations of total and/or dissolved constituents generally do not exceed State and Federal Drinking Water Standards (Georgia Department of Natural Resources, 1977; U.S. Environmental Protection Agency, 1986). A summary of selected water-quality constituents is shown in figure 6. The boxplots in figure 6 show that ground water in the south metro region has low median concentrations of dissolved solids (83 mg/L), total iron (100 Jl.g/L), and total manganese (17 J.&g/L). Although the median concentration of total iron (100 J.&g/L) does not exceed the recommended State drinking-water standard of 300 J.&g/L (Georgia Department of Natural Resources, 1977), eight wells had concentrations exceeding the standard, seven of which occur in rock unit A and one of which occurs in rock unit D. Six of the eight wells are in Lamar County, where a maximum total iron concentration of 43,000 J.&g/L was detected in water from well 12Y011. High concentrations of iron may be due to local mineralized zones, contamination from surface water, or from iron fiXing bacteria (Cressler and others, 1983). Although the median concentration of manganese did not exceed the State drinking-water standard of 50 #.Lg/L, six wells had concentrations exceeding the standard, four of which are in Lamar County. Five of the wells were drilled in water- 21 NUMBER OF ANALYSES 1 ,ooo ~~2~5~~2~5~__~2~5 --~2~5--~2~5____s~o~--~sa~___2~5~__~45~----~4~2 ______~28~~ 100 . 10 w a0 : 1 ' $ 0 :::> li w w 0.1 o.01 L~-----------------------------5wIL--f ---~:goa0:c~: --~------------------------~ ~ NUMBER OF ANALYSES 100,0001". --2~ 9 -__, 25;~-~24--, ~ffi ~~ 10,000 ; ~ ~~ ogf21-"W LL:~::E 1,000 ~a: ~~ 100 ~ 10 L-~--~--L-- NUMBER OF ANALYSES 12 r - - - - ----=2=3_ _ _ __ _--, 10 8- 4 2 - o ~-----L~----~ NUMBER OF ANALYSES 25r---------"3~8_ __ _ _ _- , 101 L__ __ _ _ _ _ __ _ _ __ J NUMBER OF ANALYSES 8.5 r-------=2~9_______ , 8 :. - - 5 - 4.5 '----------------~ EXPLANATION PERCENTILE--Percentage of analyses equal to or less than indicated values ~ Maximum 25th .50th 75th Minimum GEORGIA ENVIRONMENTAL PR.OTECI10N DMSION (1977) AND U.S. ENVIRONMENTAL PR