Ground-Water Conditions and Studies in Georgia, 2002—03

U.S. Geological Survey Scientific Investigations Report 2005-5065

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Selected Ground-Water Studies in Georgia, 2002–03

The U.S. Geological Survey (USGS)—in cooperation with local, State, and other Federal agencies — conducted several studies in Georgia and adjacent states during 2002 – 03 to better define the occurrence and quality of ground water and to monitor hydrologic conditions. Summaries of current USGS studies in Georgia are provided in the following sections and include information regarding:

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Assessment of Ground-Water Flow near the Savannah River Site, Georgia and South Carolina

Study Chief Gregory S. Cherry

Cooperator U.S. Department of Energy

Year Started 2002

Problem

The U.S. Department of Energy (DOE) Savannah River Site (SRS) has manufactured nuclear materials for national defense since the early 1950s. A variety of hazardous materials — including radionuclides, volatile organic compounds, and trace metals — are either disposed of or stored at several locations at the SRS. As a result, contamination of ground water has been detected at several locations within the site and concern has been raised about the possible migration of water-borne contaminants offsite. Two issues have been raised: (1) is ground water flowing from the SRS and beneath the Savannah River into Georgia?; and (2) under what pumping scenarios could such ground-water movement occur? To address these concerns, the U.S. Geological Survey (USGS), in cooperation with the DOE, conducted a comprehensive study during 1991– 97 that simulated ground-water flow and stream- aquifer relations in the vicinity of the SRS. These ground-water simulations are limited by simplification of the conceptual model, which was based on available data through 1992. Large increases in ground-water pumping in Burke and Screven Counties, Georgia, since 1992 and a pronounced drought during 1998 –2002 may have changed hydraulic gra-dients near the river and affected the potential for transriver flow. To provide a more accurate and up-to-date evaluation of trans-river flow near the SRS, the earlier model is being updated to incorporate new data and simulate 2002 conditions. The revised model will be used to simulate a variety of water-management scenarios that could impact transriver flow in the SRS area.

Objectives

• Update the previously developed ground-water flow model to better define present-day (2002) ground-water flowpaths near SRS.
• Utilize the 2002 calibrated model to identify ground-water flowpaths and quantitatively describe current ground-water flowpaths near SRS under a variety of hypothetical pumping scenarios.

Progress and Significant Results, 2002–03

• Collected water-level measurements from 282 wells in Georgia and South Carolina during September 9–13, 2002, and constructed potentiometric-surface maps for four major aquifers. The potentiometric-surface maps were integrated into a Geographic Information System to determine the horizontal and vertical hydraulic gradients for the aquifers along with any interaction with streams and rivers. The water-level measurements were used to adjust boundary conditions and determine if any additional calibration is required to the model under 2002 hydrologic conditions.
• Updated ground-water use estimates within the eight-county study area to reflect the changes that have occurred since the previous study (Clarke and West, 1998). The major increase in ground-water use between 1995 and 2000 is evident for Burke, Jefferson, and Screven Counties, Ga.; and Allendale and Barnwell Counties, S.C. In these counties, ground-water use for irrigation increased from 16.7 million gallons per day (Mgal/d) during 1995 to 53.1 Mgal/d during 2000 and irrigated acreage increased from 61,690 acres during 1995 to 97,690 acres during 2000 (Fanning, 2003).
• Converted existing regional ground-water model to Graphical User Interface (GUI) environment to generate current model input for MODFLOW-2000 simulations. The new MODFLOW GUI incorporates the hydrogeologic framework (Falls and others, 1997) into the various model layers and is essential when performing three-dimensional particle-tracking analysis.
• Adjusted specified heads in the source-sink layer (A1) of the model to conform with the 2002 potentiometric-surface map of the Upper Three Runs aquifer, and lowered the specified heads along the lateral boundaries of the model in layers A2–A7 based on observation points in each aquifer. The specified heads in the source-sink layer were lowered to reflect the decline in water levels that resulted from the drought that occurred from 1998 to 2002.
• Evaluated ground-water model under steady-state conditions for 2002 to determine if additional calibration is necessary. The model simulations conducted using updated pumping estimates, observed aquifer heads, and recharge rates from the source-sink layer (A1), indicated that no additional calibration was required.

References Cited

Clarke, J.S., and West, C.T., 1998, Simulation of ground-water flow and stream-aquifer relations in the vicinity of the Savannah River Site, Georgia and South Carolina: U.S. Geological Survey Water-Resources Investigations Report 98-4062, 134 p.

Falls, W.F., Baum, J.S., Harrelson, L.G., Brown, L.H., and Jerden, J.L., 1997, Geology and hydrogeology of Cretaceous and Tertiary strata, and confinement in the vicinity of the U.S. Department of Energy Savannah River Site, South Carolina and Georgia: U.S. Geological Survey Water-Resources Investigations Report 97-4245, 125 p.

Fanning, J.L., 1997, Water use in Georgia by county for 1995: Georgia Geologic Survey Information Circular 101, 95 p.

Fanning, J.L., 2003, Water use in Georgia by county for 2000 and water use trends for 1980 – 2000: Georgia Geologic Survey Information Circular 106, 176 p.

The 5,147-square-mile study area (above) is in the Coastal Plain physiographic province, and is the same area investigated during the earlier 1991– 97 study, including the SRS and adjacent parts of Georgia and South Carolina. Coastal Plain sediments consist of layers of silt, clay, sand, and minor amounts of limestone ranging in age from Cretaceous to Tertiary. Sediments dip to the southeast away from the Fall Line and reach a maximum thickness of about 2,700 feet near the southern boundary of the study area.

Map showing land use in the study area

Data on ground-water use in the eight-county study area show a substantial increase since the earlier USGS study. Clarke and West (1998) reported that during 1987– 92 total ground-water use was about 80 Mgal/d. By 1995, the total ground-water use was about 85.4 Mgal/d (Fanning, 1997). Available data for 2000 (Fanning, 2003; W.J. Stringfield, U.S. Geological Survey, written commun., 2002) show that total ground-water use was about 117 Mgal/d.

The major increase in ground-water use between 1995 and 2000 is evident for Burke, Jefferson, and Screven Counties, Ga. In these counties, ground-water use for irrigation increased from 12.6 Mgal/d during 1995 to 43.8 Mgal/d during 2000, and irrigated acreage increased from 53,520 acres during 1995 to 76,380 acres during 2000 (Fanning, 2003). In the Georgia part of the study area, the majority of ground water used for irrigation is withdrawn from the Upper Three Runs aquifer in Jenkins and southern Screven Counties, and from the Upper Three Runs and Gordon aquifers in Jefferson, Burke, and northern Screven Counties.

Assessment of Surficial and Brunswick Aquifer Systems, Coastal Georgia

Location of test sites in coastal Georgia.

Study Chief Sherlyn Priest

Cooperators Georgia Department of Natural Resources

Environmental Protection Division

Camden County

Glynn County

Liberty County Development Authority

McIntosh County

City of Ludowici

Year Started 2002

Problem

The Upper Floridan aquifer is the primary source of water in the coastal area of Georgia. Declining water levels and localized occurrences of saltwater contamination in the Upper Floridan aquifer have resulted in the Georgia Environmental Protection Division capping permitted withdrawals at 1997 rates from the Upper Floridan aquifer in parts of the coastal area. These restrictions have prompted interest in developing supplemental sources of ground water, including the surficial and Brunswick aquifer systems. The surficial aquifer system includes the water table and semiconfined zones; the Brunswick aquifer system includes the upper and lower Brunswick aquifers (Clarke, 2003).

Objectives

• Characterize the geologic and water-bearing properties of the surficial and Brunswick aquifer systems.
• Characterize the water quality of the surficial and Brunswick aquifer systems.
• Develop monitoring network for management of the surficial and Brunswick aquifer systems.

Progress and Significant Results, 2002 – 03

• Old Sunbury Road site, Liberty County. Completed six test wells, conducted a 24-hour aquifer test in the semiconfined zone of the surficial aquifer and a 48-hour aquifer test in the lower Brunswick aquifer.
• City of Ludowici Prison site, Long County. Completed two test wells and completed 24-hour aquifer tests in wells completed in the semiconfined zone of the surficial aquifer and in the upper and lower Brunswick aquifers, combined.
• Waverly Fire Station No. 17 site, Camden County. Completed three test wells and completed 24-hour aquifer tests in wells completed in the semiconfined zone of the surficial aquifer and the upper Brunswick aquifer.
• Lawrence Road Fire Station site, St. Simons, Glynn County. Completed wells in the semiconfined zone of the surficial aquifer and in the lower Brunswick aquifer.
• Darien site, McIntosh County. Completed test wells in the surficial aquifer, semiconfined zone of the surficial aquifer, and lower Brunswick aquifer.
• References Cited

Clarke, J.S., 2003, The surficial and Brunswick aquifer systems-alternative ground-water resources for Coastal Georgia, in Proceedings of the 2003 Georgia Water Resources Conference held April 23–23, 2003, at The University of Georgia, Kathryn J. Hatcher, ed, Institute of Ecology, The University of Georgia, Athens, Georgia, CD–ROM.

Weems, R.E., and Edwards, L.E., 2000, Geology of Oligocene, Miocene, and younger deposits in the coastal area of Georgia: Georgia Geologic Survey Bulletin 131, 124 p.

Generalized lithologic, geologic, and hydrologic descriptions of the surficial and Brunswick aquifer systems at the Old Sunbury Road test site, Liberty County, Georgia.

A USGS hydrologist and drilling contractor taking water-level measurements during aquifer test of the lower Brunswick aquifer at Old Sunbury Road, Liberty County, Georgia, January 2002. The test is being conducted to better define the hydraulic properties of the surficial and Brunswick aquifer systems and to determine the usefulness of these aquifers as secondary sources of ground water. Photo by Sherlyn Priest, USGS.

Location and construction data for wells used in the study (gal/min/ft, gallons per minute per feet; —, no data; do., ditto).

¹OW, observation well; PW, pumping well
²CU, confining unit; LB, lower Brunswick aquifer; S, surficial aquifer; SS, semiconfined surficial aquifer; UB, upper Brunswick aquifer; WT, water table
³Negative value denotes below NAVD 88

City of Albany Cooperative Water-Resources Program

Study Chief Debbie Warner

Cooperator Albany Water, Gas, and Light Commission

Year Started 1977

Problem

Long-term heavy pumping from the Claiborne, Clayton, and Cretaceous aquifers, which underlie the Upper Floridan aquifer, has resulted in substantial water-level declines in the deep aquifers in the Albany area. These declines have raised concern about the capacity of the deep aquifers to meet the increasing demand for potable water supply. To provide additional water supply and reduce the demand on the deep aquifers, the Albany Water, Gas, and Light Commission has developed a large wellfield southwest of Albany. The supply wells at this location primarily tap the Upper Floridan aquifer, a karstic unit that is the uppermost reliable source of water in the area. Because of local recharge to the aquifer, water quality may be affected by land-use practices. Nitrate levels exceeding the 10-milligrams per liter Maximum Contaminant Level (U.S. Environmental Protection Agency, 2000) have been detected in some wells upgradient of the proposed wellfield. The ground-water flow system and water quality of the Upper Floridan aquifer in the vicinity of the wellfield are complex and poorly understood.

Objectives

• Monitor water-level fluctuations in the four aquifers used in the Albany area and relate water-level trends to changes in climatic conditions and pumping patterns.
• Describe the ground-water flow and water quality of the Upper Floridan aquifer in the southwestern Albany area: identify ground-water flow directions and gradients for the Upper Floridan aquifer; determine if there is a rapid hydrologic response of ground-water levels to rainfall; describe the distribution of ground-water ages for the Upper Floridan aquifer in the study area; and describe ground-water quality, with a particular emphasis on nitrate concentrations.

Progress and Significant Results, 2002 – 03

• Continued hydrologic and water-quality monitoring, operation of continuous ground-water-level monitoring network, and added two wells to continuous recorder network in the vicinity of the wellfield. The network consists of 28 wells tapping four aquifers.
• Collected water-level measurements from 68 wells in the southwestern Albany area, October 1– 3, 2002, and constructed a potentiometric-surface map.
• Collected water-level measurements from 74 wells in the southwestern Albany area, September 8 –  9, 2003, and constructed a potentiometric-surface map.
• Collected water samples from 12 wells in the southwestern Albany area, November 18 – 20, 2002, and analyzed samples for cations, anions, and nutrients. Collected water samples on May 13, 2003, from four wells —  two upgradient and two downgradient from the wellfield. Collected a sample from the Flint River on May 13, 2003, to compare the water-quality characteristics of ground and surface water. These data were used to construct a trilinear diagram showing the percentage composition of major cations and anions.
• Collected water samples from 14 wells in the southwestern Albany area, November 3 –  5, 2003, and analyzed samples for cations, anions, and nutrients. Collected a sample from the Flint River on November 4, 2003, to compare the water-quality characteristics of ground and surface water. These data were used to construct a trilinear diagram showing the percentage composition of selected major cations and anions.
• Updated the Web site for the Albany program to provide the public with hydrologic information in the Albany area. Included on the Web site is information on ground-water activities; references and publications; ground-water, surface-water, and drought monitoring; ground-water- quality data; and links to other Web pages related to Albany's water issues. The Web site may be accessed at http://ga.water.usgs.gov/projects/albany/

References Cited

U.S. Environmental Protection Agency, 2000, Maximum contaminant levels (Part 143, National Secondary Drinking Water Regulations): U.S. Code of Federal Regulations, Title 40, Parts 100 –149, revised as of July 1, 2000, p. 612 – 614.

The USGS continuously records water levels at 30 wells and 3 streamgages in the Albany area, shown on the map above. Data from four of these wells and the three streamgages are available in real time at http://ga.waterdata.usgs.gov/nwis

Albany program Web site

Visit the Albany program Web site at http://ga.waterdata.usgs.gov/projects/albany

City of Brunswick and Glynn County Cooperative Water-Resources Program

Study Chief David C. Leeth and Gregory S. Cherry

Cooperator City of Brunswick

Glynn County

Jekyll Island Authority

Year Started 1959

Problem

In the Brunswick area, saltwater has contaminated the Upper Floridan aquifer for nearly 50 years. Currently (2003) within an area of several square miles of downtown Brunswick, the aquifer yields water that has a chloride concentration greater than the 250 milligrams per liter (mg/L) State and Federal drinking-water standard (Georgia Environmental Protection Division, 1997; U.S. Environmental Protection Agency, 2000) and in some areas exceeds 2,250 mg/L. Saltwater contamination has constrained further development of the Upper Floridan aquifer in the Brunswick area and prompted interest in the development of alternative sources of water supply, primarily from the shallower surficial and Brunswick aquifer systems, and from the deeper Lower Floridan aquifer.

Objectives

• Better define mechanisms of ground-water flow and movement of saltwater in the Floridan aquifer system.
• Define the vertical geometry of the high-chloride plume.
• Assess alternative sources of water supply from the surficial and Brunswick aquifer systems, and the Lower Floridan aquifer.
• Monitor long-term ground-water levels and quality, and develop and maintain a comprehensive ground- water database.

Progress and Significant Results, 2002 – 03

• During 2002 and 2003, a network of 22 continuous ground-water-level monitoring wells was operated (13 in the Upper Floridan aquifer, 4 in the Lower Floridan aquifer, 4 in the Brunswick aquifer system, and 1 in the surficial aquifer system). Nine wells were removed from service during January 2004 because of the rising cost of monitoring.
• Potentiometric surfaces of the upper Floridan aquifer were mapped:
  • During June 2002, based on water-level measurements collected in 95 wells.
  • During June 2003, based on water-level measurements collected in 56 wells.
• Choropleths of the Upper Floridan aquifer were mapped:
  • During June 2002, based on analysis of chloride samples collected in 66 wells.
  • During June 2003, based on chloride samples collected in 88 wells.
• New well information was incorporated into the U.S. Geological Survey (USGS) National Water Information System database, including seven additional Miocene wells and three Floridan aquifer wells.
• During 2003, the Georgia Geologic Survey installed three wells at a site on St. Simons Island (Lawrence Road site). Drilling and geophysical logging revealed the confined portion of the surficial aquifer system was present from 110 feet (ft) to 170 ft below land surface (bls); the upper Brunswick aquifer at this site was present from 360 to 370 ft bls, and the lower Brunswick aquifer was from 445 to 525 ft bls. An Upper Floridan aquifer monitor well also was installed and was completed from 640 to 780 ft as open hole.
• Geophysical logs were collected from 10 wells during 2002 and 2003.
• The Web site was updated for the Brunswick program that may be accessed at http://ga2.er.usgs.gov/brunswick/

References Cited

Georgia Environmental Protection Division, 1997, Secondary maximum contaminant levels for drinking water: Environmental Rule 391-3-5-19, revised October 1997: Official Code of Georgia Annotated Statutes, Statute 12-5-170 (Georgia Safe Drinking Water Act), variously paginated.

U.S. Environmental Protection Agency, 2000, Maximum contaminant levels (Part 143, National Secondary Drinking Water Regulations): U.S. Code of Federal Regulations, Title 40, Parts 100–149, revised as of July 1, 2000, p. 612–614.

Fluid resistivity log being collected from an observation well completed in the surficial aquifer at Brunswick, Georgia. The log is being collected to determine the integrity of the well casing and to locate zones where saltwater may be entering the well. Photo by Michael F. Peck, USGS.

Examples of geophysical logs collected from an unused production well on Jekyll Island using a multiparameter logging tool. The natural-gamma (NG) and electric (E) logs are used to determine different water-bearing zones and well construction, the fluid resistivity (F) log indicates zones of higher conductivity, and the temperature (T) log measures borehole fluid temperature.

A geologist for the Georgia Department of Natural Resources, Environmental Protection Division, processes geophysical logs collected from a surficial aquifer well at Brunswick, Georgia. These logs are being used to determine the source of saltwater entering the well. Photo by Michael F. Peck, USGS.

An unused production well on Jekyll Island is being converted into an observation well for continuous monitoring of ground-water levels. The 751-foot-deep well is completed in the Upper Floridan aquifer. Geophysical logs were collected to assess the integrity of the well casing and suitability for incorporation into the Georgia statewide ground-water-level monitoring network. A continuous ground-water-level recorder was installed at the well on October 25, 2004, at which time the water level was 21.83 feet above land surface. Photo by Michael F. Peck, USGS.

Georgia Coastal Sound Science Initiative

Study Chief Dorothy F. Payne

Cooperator Georgia Department of Natural Resources Environmental Protection Division

Year Started 2000

Problem

Pumping from the Upper Floridan aquifer has resulted in substantial water-level decline and saltwater intrusion at the northern end of Hilton Head Island, South Carolina, and at Brunswick, Georgia. This saltwater contamination has constrained further development of the Upper Floridan aquifer in the coastal area and created competing demands for the limited supply of water. The Georgia Environmental Protection Division has capped permitted withdrawal from the Upper Floridan aquifer at 1997 rates in parts of the coastal area, prompting interest in the development of alternative sources of water supply, primarily from the shallower surficial and Brunswick aquifer systems.

Objectives

• Better define mechanisms of ground-water flow and movement of saltwater.
• Delineate paths and rates of ground-water flow and intrusion of saltwater into the Upper Floridan aquifer and develop models to simulate a variety of water-management scenarios.
• Delineate areas where saltwater is entering the Floridan aquifer system offshore of the Savannah – Hilton Head Island area.
• Assess long-term ground-water levels and quality, and de-velop and maintain a comprehensive ground-water database.
• Assess alternative sources of water supply from:
  1. seepage ponds connected to the surficial aquifer,
  2. the Lower Floridan aquifer, and
  3. the Brunswick aquifer system.

Progress and Significant Results, 2002 – 03

• Collected and acquired geophysical logs at multiple sites throughout study area in wells completed in the Brunswick aquifer system, and the Upper and Lower Floridan aquifers;
• Collected Lower Floridan aquifer water-quality samples at St. Marys and St. Simons Island.
• Installed continuous water-level recorders in Upper Floridan aquifer wells in Glynn and Camden Counties and in Lower Floridan aquifer wells at Pineora, Effingham County, and Pembroke, Bryan County.
• Completed assessments of pond-aquifer flow and water availability at seepage pond sites in Glynn and Bulloch Counties.
• Developed model database: acquired well-specific pumping rate data for Beaufort, Colleton, Jasper, and Hampton Counties in South Carolina, for the city of Savannah and industrial wells in Chatham County, and for the city of Brunswick and industrial wells in Glynn County; incorporated data into pumping distributions for models; incorporated hydrostratigraphy and water-quality data into a geographic information system database for Savannah–Hilton Head Island, and Brunswick solute-transport models.
• Calibrated single-density (MODFLOW) regional ground-water model to 1980 and 2000 conditions; began sensitivity testing of final model, including transient response and boundary condition testing.
• Continued development of solute-transport models; tested mechanism of saltwater transport in offshore area, and estimated predevelopment saltwater-freshwater interface.

Reference Cited

Peck, M.F., and McFadden, K.W., 2004, Potentiometric surface of the Upper Floridan aquifer in the coastal area of Georgia, September 2000: U.S. Geological Survey Open-File Report 2004-1030. Available only online at https://pubs.usgs.gov/of/2004/1030/

Coastal area ground-water-level monitoring network.

Geophysical logging and water-quality sampling of the Lower Floridan aquifer well 39Q024 on Tybee Island in Chatham County, December 2003. Photo by Edward H. Martin, USGS.

Potentiometric surface estimated from field measurements

Potentiometric surface estimated from simulated potentiometric surface during 2000.

Effects of Impoundment of Lake Seminole on Water Resources in the Lower Apalachicola–Chattahoochee– Flint River Basin and in parts of Alabama, Florida, and Georgia

Study Chief Lynn J. Torak

Cooperator Georgia Department of Natural Resources

Environmental Protection Division

Year Started 1999

Problem

Multiple uses of freshwater supplies in the lower Apalachi-cola– Chattahoochee – Flint (ACF) River Basin have concerned water managers in the States of Alabama, Florida, and Georgia for many years. Numerous studies have been conducted to understand the complex relations between hydrologic-system components and natural stresses, and to answer questions regarding the effects on those relations caused by human intervention. Although previous studies addressed important water-resource issues in the lower ACF River Basin, by design, none collected hydrologic data needed to develop and maintain a monthly water budget for Lake Seminole and the corresponding stream-lake-aquifer flow system. None of these studies investi-gated the hydrologic and hydrogeologic implications of Lake Seminole impoundment by construction of Jim Woodruff Lock and Dam and the effects of the lake on other flow-system components. Therefore, the U.S. Geological Survey — in cooperation with the Georgia Department of Natural Resources, Environmental Protection Division — developed a monthly water budget for Lake Seminole, estimated the volume of water flowing into Florida before and after construction of the dam, and assessed karst solution features to evaluate the potential for sinkhole collapse beneath the lake, followed by catastrophic lake drainage.

Objectives

• Develop a water budget for Lake Seminole that will result in reasonable understanding of the effect of the lake on the overall flow system in the lower ACF River Basin.
• Compare current (2001) and pre-Lake Seminole ground-water and surface-water flow to determine whether the volume of water flowing out of Georgia has changed significantly after construction of Jim Woodruff Lock and Dam and filling of the lake.
• Evaluate the possibility of a substantial amount of water entering the ground-water system from Lake Seminole, flowing beneath Jim Woodruff Lock and Dam, and entering Florida downstream of the dam.
• Assess the likelihood of failure of dissolution features in the karst limestone of the lake bottom, such as sinkhole collapse, and the likelihood of sudden partial or complete draining of the lake. If these events are likely, then propose a data-collection system to monitor conditions that might lead to sudden draining of Lake Seminole.

Progress and Significant Results, 2002 – 03

• Streamflow comprises nearly 81 percent of total lake inflow and about 89 percent of outflow.
• Ground water constitutes 10 percent of total inflow and about 5 percent of outflow, as lake leakage.
• Precipitation and evaporation comprise about 1 and 2 percent of the total water budget, respectively.
• Techniques used to estimate lake leakage resulted in a 4-percent error in lake outflow, which is within the acceptable error for streamflow measurements, defining the largest water-budget component.
• Apalachicola River flow is nearly the same for pre- and postimpoundment conditions. Prior to impoundment, ground water flowed from Florida to Georgia, discharging to the Flint River then into the Apalachicola River, back into Florida. After impoundment, ground water flows from Lake Seminole as leakage to the Upper Floridan aquifer that discharges to the Apalachicola River directly downstream of the dam.
• Solution features located near the lakeshore and along the lake bottom facilitate lake-water leakage into the Upper Floridan aquifer and ground-water inflow to the lake.
• Lake-water chemistry is conducive to limestone dissolution along ground-water flowpaths beneath the lake.
• Preimpoundment photographs show numerous karst features in the lake bottom that promote lake-aquifer interaction.
• Minimal potential for sinkhole collapse and sudden lake drainage exists because of small hydraulic gradients between the lake and aquifer.

References Cited

Jones, L.E., and Torak, L.J., 2004, Simulated effects of impoundment of Lake Seminole on ground-water flow in the Upper Floridan aquifer in southwestern Georgia and adjacent parts of Alabama and Florida: U.S. Geological Survey Scientific Investigations Report 2004-5077, 22 p. Available only online at http://water.usgs.gov/pubs/sir/2004/5077/

Mosner, M.S., Aulenbach, B.T., and Torak, L.J., 2004, Ground-water and surface-water flow and estimated water budget for Lake Seminole, southwestern Georgia and northwestern Florida: U.S. Geological Survey Scientific Investigations Report 2004-5073, 54 p. Available only online at http://water.usgs.gov/pubs/sir/2004/5073/

Simulated potentiometric surface and directions of ground-water flow in the Upper Floridan aquifer from simulation of (A) hypothetical preimpoundment conditions; and (B) postimpoundment conditions (modified from Jones and Torak, 2004).

Monthly water budget for Lake Seminole and relative contributions of inflow and outflow components (modified from Mosner and others, 2004).

Hydrogeologic Assessment and Simulation of Stream-Aquifer Relations in the Lower Apalachicola–Chattahoochee–Flint River Basin

Study Chief Lynn J. Torak

Cooperator Georgia Department of Natural Resources

Environmental Protection Division

Year Started 2000

Problem

Current hydrologic information and ground-water flow modeling in the lower Apalachicola – Chattahoochee –  Flint (ACF) River Basin (map below) are insufficient to describe effects of time-variant irrigation pumping on streamflow. Therefore, existing models cannot accurately predict ground-water or streamflow conditions during a growing season. The Georgia Department of Natural Resources, Environmental Protection Division (GaEPD) has implemented a hydrologic assessment of the Upper Floridan aquifer in southwestern Georgia to obtain new information and to further understanding of stream-aquifer relations and the effects of ground-water pumping on streamflow in a karst hydrologic setting. The U.S. Geological Survey (USGS) has engaged in a cooperative effort with GaEPD to develop a ground-water flow model that can account for stream-aquifer interaction and streamflow reduction because of agricultural pumping. Information obtained from the model is vital for the State's management of ground-water resources and for providing early indications of low-streamflow conditions that would affect delivery of water to downstream, out-of-state users.

Objectives

• Develop new data for the stream-aquifer system by evaluating well-drilling and aquifer-test information.
• Obtain accurate locations of pumped wells for municipal, industrial, and irrigation purposes.
• Collect and compile ground-water-level, stream-seepage, and off-stream spring-discharge data.
• Synthesize newly collected and existing hydrologic data into a transient finite-element model of ground-water flow that can simulate seasonal ground-water levels, stream-aquifer interaction, and pumpage-induced streamflow reduction, and assess the sensitivity of streamflow to ground-water pumping.

Progress and Significant Results, 2002 – 03

• Collected new hydrogeologic data defining aquifer and semiconfining-unit thickness and extent, and evaluated results of aquifer-performance tests; incorporated new information into Ground-Water-Site-Inventory database.
• Compiled recent (post-1986) hydrogeologic information on aquifer and semiconfining-unit thickness and extent, hydraulic properties, and pumpage, from GaEPD records.
• Incorporated well coordinates from agricultural wells, obtained by GaEPD using global-positioning-system tech-nology, into local database used for developing model inputs.
• Analyzed agricultural withdrawal data for spatial and temporal relations.
• Evaluated ground-water-level measurements, stream-discharge data, hydrograph-separation methods, and off-stream springflow for October 1999, April 2000, and August 2000 conditions to define ground-water flow to streams.
• Installed five real-time streamgaging stations and upgraded one station for water-quality and acoustic velocity metering.
• Added 12 sites to monitor-well network of hourly ground-water-level recorders and one real-time satellite station.
• Initiated application of USGS transient finite-element model, MODFE, and development of automated input/output graphical user interface.

Streamflow gaging network in the lower Apalachicola–Chattahoochee–Flint River Basin and new/upgraded stations (labeled on map).

Chemigation/irrigation apparatus installed in well tapping the Upper Floridan aquifer southeast of Lake Seminole, Decatur County, Georgia. Well is 700 feet deep and was used in an aquifer-performance test. Photo by Lynn J. Torak, USGS.

Typical center-pivot spray-irrigation system used in the lower Apalachicola – Chattahoochee – Flint River Basin, southwestern Georgia. Photo by L. Elliott Jones, USGS.

Control panel and time totalizer for monitoring usage of center-pivot irrigation system. Photo by L. Elliott Jones, USGS.

Flowmeter installed in discharge line of irrigation system. Photo by L. Elliott Jones, USGS.

Real-time streamflow data-collection platform

Real-time streamflow data-collection platform installed at station 02353265, Ichawaynochaway Creek at Georgia Highway 37, near Morgan, Georgia, and graph of data that can be accessed at http://ga.waterdata.usgs.gov/nwis/current/?type=flow&group_key=basin_cd

Ground-Water Information and Project Support

Study Chief David C. Leeth

Cooperator Georgia Department of Natural Resources

Environmental Protection Division

Abany Water, Gas, and Light Commission

City of Brunswick

Glynn County

Jekyll Island Authority

St. Johns Water Management District, Florida

Year Started 1938

Problem

Ground water accounts for about 22 percent of freshwater withdrawals in Georgia — more than 2.7 billion gallons per day. More than 1.8 million people are served by ground- water supplies, and 734 million gallons per day are with-drawn for irrigation (Julia L. Fanning, U.S. Geological Survey, oral commun., 2004). The distribution and quality of ground water are highly variable and directly related to geology, and natural and human stresses. Monitoring ground-water levels and ground-water quality is essential for the management and development of this resource.

Objectives

• Collect ground-water-level and ground-water-quality data to assess the quantity, quality, and distribution of ground water.
• Provide date to address water-management needs and evaluate the effects of national and local management and conservation programs.
• Advance the knowledge of the regional hydrologic system.
• Advance field or analytical methodology.
• Advance the understanding of hydrologic processes.
• Provide data or results useful to multiple parties in potentially contentious interjurisdictional conflicts about water resources.
• Provide hydrologic data required for interstate and international compacts, Federal law, court decrees, and congressionally mandated studies.
• Provide water-resource information that can be used by multiple parties for planning and operational purposes.
• Contribute data to national databases that will be used to advance the understanding of regional and temporal variations in hydrologic conditions.

Progress and Significant Results, 2002–03

• Continuous water-level recorders were operated in 185 wells during 2002 and 177 wells during 2003; data from 159 wells during 2002 and 156 wells during 2003 (map, above) were included in annual data reports (Coffin and others, 2003; 2004). Periodic water-level measurements were made in more than 729 wells throughout the State during this period. Water-level data were collected to define potentiometric surfaces and to assess long-term trends. Water samples for chloride analysis were collected from 72 wells during 2002 and 87 wells during 2003 in the Brunswick area, 4 wells during 2003 in the Savannah area, and 6 wells during 2002 and 2003 in Camden County. Borehole-geophysical logs were collected from 9 wells in the Lawrenceville area, 9 in Rockdale County, and 18 in the coastal area. The types of logs collected include caliper, natural gamma, electric (lateral, long and short-normal resistivity) fluid-temperature, fluid-resistivity, electromagnetic induction, full-waveform sonic, acoustic televiewer, optical televiewer, and spinner-flowmeter.
• Well-inventory, water-level, and geologic data were verified for entry into the National Water Information System (NWIS) database. Field inventories were conducted to assist projects, and 186 sites were added to the NWIS Ground-Water Site Inventory to improve ground-water data coverage in the State. Five wells were instrumented with real-time transmission (satellite relay) of continuous water-level records to aid in drought planning. Currently, 18 wells are equipped for real-time transmission of continuous water-level data. The NWIS database may be accessed on the Web at http://waterdata.usgs.gov/ga/nwis/current/?type=gw

References Cited

Coffin, Robert, Grams, S.C., Leeth, D.C., and , and Peck, M.F., 2003, Continuous ground-water-level data, and periodic surface-water- and ground-water-quality data, calendar year 2002, v. 2 in Alhadeff, S.J., and McCallum, B.E. (compilers), Water resources data – Georgia, 2002: U.S. Geological Survey Water-Data Report GA-02-2, CD –ROM.

Coffin, Robert, Grams, S.C., Peck, M.F., and Cressler, A.M., 2004, Continuous ground-water-level data, and periodic surface-water- and ground-water-quality data, calendar year 2003, v. 2 in Alhadeff, S.J., McCallum, B.E., Landers, M.N., (compilers), Water resources data–Georgia, 2003: U.S. Geological Survey Water-Data Report GA-03-2, CD –ROM.

A downhole continuous recorder in Gwinnett County, Georgia, which is part of the ground-water-level monitoring network for an ongoing study. The equipment consists of a data logger, battery, and 15-pounds-per-square-inch transducer — all installed inside of a 6-inch-diameter casing. The recorder is set to collect data on an hourly basis, and processed and stored in National Water Information System. Photo by Alan M. Cressler, USGS.

A typical real-time continuous recorder well in DeKalb County, which is part of the ground-water-level monitoring network. The equipment consists of a data logger, 30-pounds-per-square-inch transducer, a radio and antenna for transmitting data, and a solar panel and battery. Real-time data are typically recorded at 60-minute intervals, stored on site, and then transmitted to USGS offices from every 1 to 4 hours via satellite, telephone, or radio relay. The NWIS database may be accessed on the Web at http://waterdata.usgs.gov/ga/nwis/current/?type=gw Photo by Alan M. Cressler, USGS.

A hydrologic technician from the Ground-Water Informa-tion and Project Support Unit collects a water sample for chloride analysis from a well in Glynn County, Georgia. The sampling trailer contains a 5-horsepower centrifugal pump, reel with 100 feet of suction hose, and pipe fittings and adapters. The samples are collected annually in support of the Brunswick and Glynn County Cooperative Water-Resources Program. Photo by Alan M. Cressler, USGS.

A public supply well in Glynn County is shown flowing at about 30 gallons per minute while spinner flowmeter logs were collected to estimate the percentages of water from different water-bearing zones. This well is completed in the confined surficial, upper Brunswick, and lower Brunswick aquifers, and the flowmeter logs help to quantify the ground-water contribution from each zone. Photo by Michael F. Peck, USGS.

Ground-Water Resources and Hydrogeology of Crystalline-Rock Aquifers in Rockdale County, North-Central Georgia

Study Chief Lester J. Williams

Cooperator Rockdale County

Year Started 2001

Problem

Ground water in crystalline rocks of the State has not been extensively tapped as a source of public drinking water. This source, however, may prove to be a valuable resource to communities wishing to supplement their existing surface-water supplies and augment the amount of available drinking water in rapidly-growing areas of north Georgia, such as in Rockdale County (map, right). Little information is available to evaluate fully the quantity and quality of ground-water resources in the area. Because geology is the principal control on the availability of ground water, the U.S. Geological Survey (USGS) is conducting this study, in cooperation with Rockdale County, to determine the rock types and geologic structures that influence ground-water availability. Ultimately, this information will increase the understanding of how ground water flows through complex crystalline-rock aquifer systems and provide critical information for the future development and manage-ment of this resource.

Objectives

• Evaluate the hydrogeology and ground-water resources of the study area.
• Provide baseline geologic and hydrologic information for a typical crystalline-rock aquifer setting in northern Georgia.
• Determine the hydraulic characteristics and storage potential of water-bearing zones/hydrogeologic units at various well sites.
• Define the best methods and approaches to characterize the availability of ground water in crystalline-rock areas.
• Develop a better understanding of crystalline-rock aquifer systems so that State and local water-management agencies can use this information when developing ground-water use policies.

Progress and Significant Results, 2002-03

• Compiled data on approximately 450 wells (primarily rural domestic) including field confirmation of well location, casing diameter, well yield, casing depth, total depth, and static/pumping water level.
• Obtained geophysical logs from 19 wells to characterize the lithology, fracture, and yield characteristics of various rock units throughout Rockdale County.
• Collected ground-water samples from three wells to characterize water quality.
• Completed detailed geologic mapping throughout much of Rockdale County and began subsurface correlation with geophysical log data; hydrogeologic units and storage capabilities are being compiled from these data.
• Identified likely high-yielding water-bearing zones/hydrogeologic units in several parts of Rockdale County.
• Currently compiling a geographic information system database to combine well data with existing geologic, topographic, hydrographic, and other geographic data.

Although well inventories are time consuming and require a site visit, it is the only available means to obtain accurate location and water-level data for area wells. Depth, yield, and water level are obtained from wells. Map (A) shows wells inventoried during previous studies. Map (B) shows approximately 450 wells inventoried during this study.

Water-quality sampling— Samples were collected from three wells to determine water quality. A pump is set into the well to collect the samples. Water-quality properties are monitored during the process of purging the well prior to sampling. Photo by Lester J. Williams, USGS.

Geologic mapping — Rock types, joints, fractures, and other water-bearing features are mapped by walking along roads, riverbeds, power lines and other access points. The above photo shows a prominent set of joints aligned parallel to the streambed of the Yellow River near Milstead, Georgia. Photo by Lester J. Williams, USGS.

Well refurbishment
Photo of an air-rotary drilling rig, after 30 minutes | Photo of an air-rotary drilling rig, after 4 hours
Photos of an air-rotary drilling rig used to refurbish and clean out an old (unused) water-supply well in Conyers, Georgia. Photo A was taken after about 30 minutes (reddish color is iron scaling), and Photo B was taken after approximately 4 hours of development. The refurbishment was necessary to prepare the open portion of the borehole for logging and down-hole camera surveys. The drilling rig was air-lifting approximately 250 gallons of water per minute at the end of refurbishment. Photo by Lester J. Williams, USGS.

Borehole geophysical logging—Borehole geophysical tools and down-hole cameras provide the most effective means to study the nature of water-bearing openings.

USGS employees calibrate a three-arm caliper tool. The caliper tool (right) measures diameter by pressing mechanical arms out against the borehole wall. Geophysical tools measure the physical properties of the rock surrounding the well. Photo by Lester J. Williams, USGS.

A caliper log is the simplest log to interpret. Peaks show where the borehole is enlarged and indicate sections of the borehole where a fracture opening may be present. Down-hole camera images of a fracture formed parallel to rock layering at a depth of 73 feet.

Sustainability of Ground-Water Resources in the City of Lawrenceville area

Study Chief Phillip N Albertson

Cooperator City of Lawrenceville, Georgia

Year Started 2002

Problem

The city of Lawrenceville overlies an igneous and metamorphic-rock aquifer that supplies about 6 percent of the city's current water use. Lawrenceville plans to increase ground-water withdrawal from wells located in the upper Alcovy River Basin and from wells in the Redland–Pew Creek River Basin. Long-term effects of the withdrawal of ground water in this area are largely unknown. For this reason the U.S Geological Survey (USGS), in cooperation with the city of Lawrenceville, began a study to investigate the sustainability of ground-water resources as additional municipal wells become operational.

Concern about the possible effects of ground-water withdrawal has led the city of Lawrenceville to install a monitoring network to assess changes in the hydrologic system that pumping may initiate. These changes possibly include a decrease in ground-water levels, cross-basin transfer of ground water, dewatering of the overlying saprolite, and a decline in streamflows. As ground-water development continues to increase in the Piedmont region of Georgia, it is important to monitor the effects of ground-water withdrawal to better manage the resource.

Objectives

• Monitor the effect of increased ground-water withdrawals by additional municipal wells on surrounding ground-water levels and streamflow.
• Determine pre- and postpumping hydrologic budgets of the Alcovy and Pew–Redland Creek Basins.
• Provide drawdown data from surrounding monitoring wells to the city of Lawrenceville and estimate the zone of influence of active municipal wells.

Progress and Significant Results, 2002 – 03

• Installed 11 new monitoring wells during July 2003 to form a network of 27 wells to monitor long-term water levels in areas of increased ground-water withdrawal.
• Installed continuous water-level recorders on a well pair in the upper Alcovy River Basin, on a well pair in the Redland–Pew Creek River Basin, and on a single well in the upper Apalachee River Basin.
• Obtained weekly water-level measurements at 21 monitoring wells.
• Installed continuous-recording streamgages at the outflow of both the upper Alcovy River and the Redland–Pew Creek River Basins.
• Installed staff gages at four additional streamflow monitoring sites.
• Obtained weekly staff-gage readings and stream- flow measurements at the four periodic streamflow measurement sites.
• Obtained seepage measurements during the low-flow period in the fall of 2003 to quantify the ground-water contribution to streamflow in areas to be pumped.
• Developed a project internet site, that may be accessed at http://ga.water.usgs.gov/projects/lawrencevillegw

Location of the Lawrenceville study area in the Piedmont physiographic province of Georgia.

Ground-water wells and streamflow monitoring sites for three river basins located near Lawrenceville, Georgia.

The USGS is monitoring streamflow weekly at four sites in the study area, one of these being Redland Creek, shown above. Photo by Phillip N. Albertson, USGS.

Staff gage on Cedar Creek. Photo by Phillip N. Albertson, USGS.

Drillers install a new regolith monitoring well. Photo by Phillip N. Albertson, USGS.

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