USGS Georgia Water Science Center
This report is available online in pdf format (2 MB): USGS OFR 2004-1366 (
)
Lester J. Williams, Phillip N. Albertson, Donna D. Tucker, and Jaime A. Painter
U.S. Geological Survey Open-File Report 2004-1366, 38 pages (Published 2004)
Thirty-two wells, ranging in depth from 180 to 630 feet, were used to study the bedrock lithology, fracture, and water-yielding characteristics in the Lawrenceville, Georgia, area. These data were compiled to determine what geologic structures,
if any, contribute to the development of increased permeability
and high ground-water yield in the area. Methods used in this study include test-well drilling, geophysical logging and borehole-camera surveys, flowmeter surveys, aquifer testing, packer testing, and water-level monitoring.
Water-bearing fractures identified in open boreholes of wells include: joints, open joints, and zones of joint concentration; foliation partings and major foliation openings along foliation and layering of the rock; dissolution openings along mineral infillings; and irregular voids and fractures. Most of the joints observed in the boreholes appeared as tight hairline fractures and typically were not significant water-bearing zones. Moderate to small amounts of water—from 1 to 5 gallons per minute (gal/min)—are produced from open, steeply-dipping joints and zones of joint concentration. Foliation partings and major foliation openings, which form "foliation parallel-parting systems" in the area, yielded large quantities of water to open boreholes. Foliation partings typically yielded from 1 to 15 gal/min, with a maximum value of about 63 gal/min. In some boreholes, groups of foliation partings form significant water-bearing zones yielding as much as 50 gal/min. Major foliation openings yield substantially more water than the smaller foliation partings, with a typical range from 50 to 100 gal/min. Major foliation openings are the primary water-producing features responsible for high-yield wells in the area. In a few wells, dissolution openings along mineral infilled joints or veins had yields as much as 35 gal/min, indicating the potential importance of dissolution features in the bedrock.
Flowmeter surveys, aquifer tests, packer tests, and water-level monitoring provided additional hydrologic information on water-bearing fractures in the study area. These data were used to help confirm the depth and yield contribution from various types of water-bearing fractures, indicate the hydraulic characteristics of these fractures, and show the hydraulic response of the aquifer system to pumping.
Collectively, the data from this study indicate that foliation parallel-parting systems, consisting of discontinuous zones of foliation partings and major foliation openings, strongly influence
the yields of wells in the Lawrenceville area. Wells tapping these systems are capable of sustaining large ground-water withdrawals for extended periods of time, as indicated from the continuous operation of the Rhodes Jordan Wellfield since 1995. Open-hole water levels, flowmeter surveys, and preferential drawdown parallel to foliation and compositional layering all indicate a general hydraulic confinement of foliation parallel-parting systems, and indicate a strong lithologic and structural control on the development of these water-bearing fracture systems.
Foliation parallel-parting systems are easily identified in boreholes using geophysical methods described in this report. The yield potential of foliation parallel-parting systems within an individual topographic basin or several topographic basins can be large, depending on the areal extent of the water-bearing zones and the interconnectivity of these zones with sources of recharge.
Abstract
Introduction
Purpose and Scope
Description of the Study Area
Water Use
Geologic Setting
Hydrogeologic Setting
Well-Naming System
Supplemental Data on CD–ROM
Acknowledgments
Methods of Data Collection and Analysis
Test-Well Drilling
Air-Percussion Rotary Drilling and Well Construction
Lithologic Sampling and Determination of Rock Type
Well Development and Short-Term Yield
Geophysical Logging and Borehole-Camera Surveys
Caliper Logging
Natural-Gamma Logging
Resistivity Logging
Fluid-Temperature and Fluid-Resistivity Logging
Borehole-Televiewer Imaging
Borehole-Camera Surveys
Characterization of Fractures in Open Boreholes
Determination of Type, Depth, and Orientation of Fractures
Identification of Water-Bearing Fractures
Estimating Yield Contribution from Individual Water-Bearing Fractures
Estimating Yield during Drilling
Flowmeter Surveys
Aquifer Testing
Packer Testing
Water-Level Monitoring
Hydrogeologic Data
Fracture Data
Individual Fracture Yield
Joints, Open Joints, and Zones of Joint Concentration
Foliation Partings and Major Foliation Openings
Dissolution Openings
Irregular-Shaped Voids and Fractures
Flowmeter Surveys
Aquifer-Test Data
Aquifer-Test Yield, Drawdown, and Recovery
Direction and Magnitude of Drawdown
Packer-Test Data
Water-Level Data
Summary and Conclusions
References Cited
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