Hydrogeologic data from selected sites in the Piedmont and Blue Ridge provinces, Georgia

HYDROGEOLOGIC DATA FROM SELECTED SITES IN THE PIEDMONT AND BLUE RIDGE PROVINCES,
GEORGIA
David A. Brackett William M. Steele Thomas J. Schmitt Robert L. Atkins Madeleine F. Kellam Jerry A. Lineback

DEPARTMENT OF NATURAL RESOURCES ENVIRONMENTAL PROTECTION DIVISION GEORGIA GEOLOGIC SURVEY

INFORMATION CIRCULAR 86

Cover: Ltne art showing some of the complexities that one can encounter tn crystalline rock aquifers.

HYDROGEOLOGIC DATA FROM SELECTED SITES IN THE PIEDMONT AND BLUE RIDGE PROVINCES, GEORGIA
David A. Brackett William M. Steele Thomas J. Schmitt Robert L. Atkins Madeleine F. Kellam Jerry A. Lineback
Department of Natural Resources Joe D. Tanner, Commissioner
Environmental Protection Division Harold F. Rehel&, Director Georgia Geologic Survey
Wllllam H. McLemore, State Geologist
Atlanta 1991
INFORMATION CIRCULAR 86

CONTENTS
Page CON'fEN'TS ..... ... ...... .. .... .. ............ ... .... ... ... .. .... .. ... .. ..... ... ......... ......... .... .. ... ... ................... .. .... .. ... 1 LIST OF FIGURES ... .. ... ... .. ........ .. ........... ..... ..... .. ............... ....... .............. ... ... ........................ ... .. iv LIST OF T.ABLES ..... ... ..... .......... ..... .... ............... ... ...... .. ... ....... ...... ... ... ...... ... ............... ..... .......... X IN1RODUCTION .. .. ...... ... .. .. .. .............................................. .. ....................................... ...... .... .... 1
PURPOSE AND SCOPE OF STUDY .. ... .. ..... .. ... ... ... ...... ... .. ... ....... .. ... ... ... ....... .. .... .. ... .... .. ... 1 JUSTIFICATION FOR STIJDY........... .. ....... ...... .. ... ... .. .. .. ................................................... 1
DESCRIPTION OF STUDY AREA.................... ............................................................... ... 3
ME'ffiODS OF INVESTIGATION....................................................................................... 3 Geologic Mapping .... ... ... ... ... ... ... ... ... .... .. ... .... .. ... .... ... ......... ... .. .. .. .. .... .. ... ...... ..... .. . 3 Surface Geophysical Methods .. .. .. .. .. ... ... ... ... .... .. .... ..... .... .. ...... .... .. ... .... ...... ........ .. 3 Borehole Geophysical Logging.................................. ............................................ 4 Hydrologic Methods .. .. ..... .. ..... ...... ...... ... ... ...... ... .. .. .... .. ...... .. .... .. ... ... ..... .. ..... ....... . 4
PREVIOUS INVESTIGATIONS ..... ...... ... ... ............... ...... ............... ... ... ... ... ...... ... ........... .... ......... . 4 ACKNOWLEDGEMEN'TS ..... ... ...... ...... ... ... ... ... ... ......... ......... ...... ............ ...... ... ... ......... ......... ... .... 5 ASHlAND SUBDMSION, OCONEE COUN1Y .................... ........................... ............... .... .... .. .. .. 5
IN1RODUCTION .. .. ... ...... .... .. .... ... ... ... ... ... ... .. .... ... ... ... ... ... ... .. .... ... ... ... ... ... ... ... ... .... ... .... .... 5 GEOLOGY .............. .. .... ..... ..... .. .................... ...... ......... ............. ...... .. .... ..... ... ..... ...... .. .... .. 5 WA1'ERQUALITY ........... ................................................. ..... .. .................................. ... .. ... 7 HYDROLOGIC 1'ESTING ..... ......... ... .. .... .. ... ... .... ... ...... ...... ..... ................... .. ... ... .......... ...... 7 SUMMARY .. ...................................................... ...... .... .... ......... ........................................ 7 COLBERf, MADISON COUN1Y........ ... ... .. .... .. .... .. .... .. ... ... ... .. .. .. ... .... ... ...... .. ..... .. ... ... ... ........... .... 7 IN1RODUCTION .. ... .. ... .... ... .... .. .. ... ..... ..... ... .. ... ... .. .. .. .. .. .. ....... ...... ...... ... .. ... .... .. ..... .. ... ... ... 7 WELL SIDNG ....................................................................................... ................................... 7 GEOLOGY .. ................... .. ................. ............................................................................. .. 13 GEOPHYSICAL 1'ESTING ........................................ ..... .. ... ........................ ............... .... .... 13
i

CONTENTS
Page Surface Geophysical Testing .......................... .. ......... ....... ............................. ....... 13 Borehole Geophysical Logging ............................................................................. 13 HYDROWGIC TES'TING .................................................................................................24 SUMMARY .............,.......................................................................................................56 DAWSONVILLE, DAWSON COUNIY ....................................................,..................................... 56 IN1"RODUCTION ......................... ................ .. .... ...... .. ................... .. ................... .. .... ..... ... 56 WELL SmNG ....................................................................... ..... ... ....... ... .................. ...... 56 GEOWGY ......................................................................................................................56 WATER QUALI1Y ...........................................................................................................62 HYDROWGIC TES11NG ......... ........ ....... ..... ... ....... ............ ............ ........... ............ ... ...... .. 62 SUMMARY ......................................................................... ............. ............... ............ .... 62 LEXINGTON, OGLE1liORPE COUNIY ....... ....... ... .. .. .... ............................ ..................................62 IN1"RODUCTION ................................ .... ....... ....... .... .............. .. ............ .... ...... .... ..... ...... .. 62 GEOWGY ............................................ ..... ....... ..... .................. ... ..... .. .............. ............ ...62 WATER QUALI1Y ...........................................................................................................66 BOREHOLE GEOPHYSICS ............ ...... ................................... ... .......... ... ........................ 66 HYDROWGIC TESTING ............................. ... ...... .. ..... .......... ... ......... ....... .... ..... ...... ...... .. 66 SUMMARY ................................................................ ... ............ .... ......... ... ........ .... ..... ... .. 66 WCUST GROVE, HENRY COUNIY ........................................................ .. .... ..... ............ .... ......... 66 IN1"RODUCTION ............................................................................................................. 66 WELL SmNG .................................................................................................................78 GEOWGY ........................................................................ ........ .. ... ............................ ..... 78 WATER QUALI1Y .......................................................................... ...... ............ ............... 78 BOREHOLE GEOPHYSICS ............................................................. ........ ............. ........... 78
ii

CONTENTS
Page HYDROLOGIC 'JESTING ....................... ... ... ... ... ..... ... ....... .. .... ... ... ... ... ... .... .. ... .. ... ... .... .. .. 78 SUMMARY .................................................................................................................... 88 LOST MOUNT.AIN, COBB COUNIY .. ... .. ... .... .. .... ... ... ... ... ... ... ............ ..... ....... .. ... .... ... ... ... ... ... ... ... 88 IN"IRODUCTION .. ... ... ... ... ... ... ... ... .. ... .. .. ... .. ... ... ... ...... .... .. ............. ... ....... .. ... ... .. ... ... ... ... .. 88 GEOLOGY .... ...... ................... .. ............................................. .... ..................................... 88 HYDROLOGIC 'JESTING .. ... ... .. ... ...... ... ... ... .. .. .. ... .... ... ... .... .. .. ... ... .... .. ... ... ... ... ... .... ... ... ... . 92 SUMMARY ..................................................................................................................... 92 NEWNAN', COWETA COUNIY .. ... ... ... ...... .. ... ... .... .. .... .. .... .. ... .... ... ... ... .. .... .. ...... .. .... ... ... ... .... ... ... .. 92 IN"IRODUCTION .. .. .... ... .. .... .. ... ... ... .. .. .. .. .. ... ... .. .... .. ... .... ... ... ... ... .. ... ... ...... ... ... ... .... ... ... ... . 92 GEOLOGY ..................................................................................................................... 92 HYDROLOGIC 'JESTING .... ... ... .... ... ... ... ... ... ... ...... ... ... .. ... ... ... .... ... .. .... ... ... ...... ... ... ..... ... .. 97 SUMMARY .................................................. ... ...... ..... ... ............ .. .................................... 97 SHOAL CREEK SUBDIVISION, COWETA COUNIY.. ...... ... ... ... ... ... ... ... ... ... ... .. .... ...... ...... ... ... ... ... . 97 IN"IRODUCTION .. .. ... ... .... .. .... .. .... .. ... ... .... ... .. .... ... ... ... .. ... ...... ... .... .. .... ... .. ... ... .... .. ... ... ... .. 97 GEOLOGY ......................................... .............. .............................. ... ............................. 97 WAT'ER QUALI1Y ........................................................................................................... 103 GEOPHYSICAL 'JESTING ..................................................... ................................... ....... 103
Surface Geophysics ........................................................................................... 103 Borehole Geophysics .................................. ... ..................... ............................... 103 HYDROLOGIC 'JESTING ................................................................................................ 103 SUMMARY ............................... ...................................................................................... 103 UNICOI STA1"E PARK, WHITE COUNIY ..................................................................................... 118 IN"IRODUCTION ....................................................... ...................... ............... ..... ........... 118 GEOLOGY ..................................................................................................................... 118
iii

CONTENTS
Page WATER QUALflY............................................. ................................ ...................................... 118 GEOPHYSICAL TES11NG ................................................................ ... .................. ........... 118
Surface Geophysics ............................................................................................ 118 Borehole Geophysics .. ... ...... ... ........ ... .... .. ............ .... ... .. ....... .. ........ ................. .. .. 118 IIYDROWGIC TES11NG ........... .... .......................................................................... ........ 119 SUMMARY .................................................................................................. .. ....... ......... 144 WAT'KINSVIU..E, OCONEE COUNIY ........................................................................................... 144 INT'RODUC110N ......... ..... ...... ...... ......... ............................................................... ...... .... . 144 GEOWGY ....................................................................... .. ... ... ......... ..... ...... ....... ....... ..... 144 BOREHOLE GEOPHYSICS ................................................................. ............ ... .. .... ....... 144 IIYDROWGIC TES11NG ..... ... ..... ................................................................... ................. 153 SUMMARY .... .............. ... ..... ... ... ..... ......................... ... ...... .. .. .. .. ... ... ..... .. .... ...... .. .. ... .. .. ... . 153 GENERAL OBSERVATIONS ........ ..... .......... ....... ... ........... ..... ... ....... ....... .............. ..... ..... ..... ........ 153 WEU.. SITING ............................ .. ... .. ..... ...................... .. ................................................. 153 IIYDROWGIC 'fESTING ................................................................................................. 158 RECOMMENDATIONS ............... ................... ....... .............. .... ............... .......................... 158 REFERENCES ........................................................................................................................... 159

LIST OF FIGURES

Figure 1. Figure 2.
Figure 3. Figure 4.

Locations of hydrogeologic test sites. .. .. .. .. .. .. ..... ... ..... .... .. .. .. ... .... .. .... .. .. ....... .... .. .. 2
Geologic map of part of the Statham Quadrangle and locations of wells in the Ashland Subdivision, Oconee County... ....................................... .. ...... .. .... 6
Pumping rate of Ashland Subdivision well during the 24 hour pumping test. .. .... 9
Drawdown and recovery curve for Ashland Subdivision well. .. ............. .. ...... ... ..... 10

IV

LIST OF FIGURES
Page

FJgure 5. FJgure 6.
FJgure 7. FJgure 8. FJgure 9. FJgure 10. FJgure 11. FJgure 12. FJgure 13. FJgure 14. FJgure 15. FJgure 16. FJgure 17. FJgure 18. FJgure 19. FJgure 20. FJgure 21. FJgure 22. FJgure 23. FJgure 24. FJgure 25. FJgure 26. FJgure 27. FJgure 28.

Drawdown and recovery cutve for Ashland Subdivision obsetvation well 1. ......... 11 Geologic map of part of the Danielsville South Quadrangle and locations of wells in the Colbert area. .. .............................................................................. 12 Locations of wells and magnetic sutvey Unes at Colbert....................................... 14 Drift corrected magnetic proflle line 2 at Colbert. .. .............................................. 15 Drift corrected magnetic proflle line 3 at Colbert. .. .. .... .. .. .. ...... .. .... .. .... .. .. ........... 16 Sonic televiewer log of Colbert well 1, 62-75 ft...................................................... 17 Sonic televiewer log of Colbert well 1, 130-147 ft................................................. 18 Sonic televiewer log of Colbert well 1, 380-400 ft................................................. 19 Caliper log of Colbert well 1................................................................................. 20 Temperature log of Colbert well 1. ....................................................................... 21 Spontaneous potential log of Colbert well 1. ........................................................ 22 Acoustic velocity log of Colbert well 1. ................................................................. 23 Single- point resistivity log of Colbert well 1. ....................................................... 25 Natural gamma log of Colbert well 1.......................................................... .......... 26 Sonic televiewer log of Colbert well 1A, 365-375 ft............................................... 27 Sonic televiewer log of Colbert well 1A, 495-505 ft............................................... 28 Caliper log of Colbert well lA. .................................................................... ......... 29 Temperature log of Colbert well IA......................................................................30 Spontaneous potential log of Colbert well lA ...................................................... 31 Single- point resistivity log of Colbert well 1A ..................................................... 32 Natural gamma log of Colbert well lA.................................................................. 33 Caliper log of Colbert well 2............ :.......................... .......................................... 34 Temperature log of Colbert well 2........................................................................35 Spontaneous potential log of Colbert well 2......................................................... 36

v

LIST OF FIGURES
Page

Figure 29. Figure 30. Figure 31. Figure 32. Figure 33. Figure 34. Figure 35. Figure 36. Figure 37. Figure 38. Figure 39. Figure 40. Figure 41. Figure 42. Figure 43. Figure 44. Figure 45. Figure 46. Figure 47. Figure 48. Figure 49. Figure 50. Figure 51. Figure 52.

Single- point resistivity log of Colbert well2........................................................ 37 Natural ganuna log of Colbert well 2 .................................................................... 38 Sonic televiewer log of Colbert well3, 116-133 ft.................................................39 Sonic televiewer log of Colbert well3, 150-175 ft..... ............................................40 Sonic televiewer log of Colbert well 3, 180-200 ft. ............................................... .41 Caliper log of Colbert well 3................................................................................. 42 Temperature log of Colbert well3....................................................................... 43 Spontaneous potential log of Colbert well 3 .......................................... ............... 44 Acoustic velocity log of Colbert well 3 .................................................................. 45 Single- point resistivity log of Colbert well 3 ....................................................... .46 Natural ganuna log of Colbert well 3 ... ............... .... .............................................. 47 Sonic televiewer log of Colbert well4, 115-135 ft. ........................... .. .................. .48 Caliper log of Colbert well 4..... ............. ................ ......... ..... ... ..... .... ...... ............... 49 Temperature log of Colbert well 4........................................................................ 50 Spontaneous potential log of Colbert well 4............................................... .... ...... 51 Single- point resistMty log of Colbert well4........................................................ 52 Natural ganuna log of Colbert well 4.............................. ..... ................................. 53 Pumping rate during test of Colbert well 2 .......................................................... 54 Drawdown and recovery curves for Colbert well 2 . .. ............ ... .................... .. ...... .. 55 Pumping rate during test of Colbert well 3 ........... ...... .. ....................................... 57 Drawdown and recovery curves for Colbert well 3 .................................... .... ........ 58 Pumping rate during test of Colbert well 4 ................................. .. ........... ............ 59 Drawdown and recovery curves for Colbert well 4 ................... ........ ..................... 60 Geologic map of parts of the Dawsonville and Juno Quadrangles and location of Dawsonville municipal well 4........................................................ 61

Vl

LIST OF FIGURES
Page

Figure 53. Figure 54.
Figure 55. Figure 56. Figure 57. Figure 58. Figure 59. Figure 60. Figure 61. Figure 62. Figure 63. Figure 64. Figure 65.
Figure 66. Figure 67. Figure 68. Figure 69. Figure 70. Figure 71. Figure 72. Figure 73. Figure 74. Figure 75.

Drawdown and recovery curves for Dawsonville municipal well 4. .......................64 Geologic map of part of the Lexington Quadrangle and locations of wells in the Lexington area........................................................................................... 65 Sonic televiewer log ofLexington municipal well3, 86-100 ft. .............................. 68 Sonic televiewer log of Lexington municipal well 3, 211-225 ft............................. 69 Sonic televiewer log of Lexington municipal well 3, 486-498 ft... .. .... .................... 70 Caliper log of Lexington municipal well3. ............ ............. ........... ... .. .................. 71 Temperature log of Lexington municipal well 3 .................................................... 72 Acoustic velocity of Lexington municipal well 3 ........... .. ................................ .. .. .. 73 Single- point resistance log of Lexington municipal well3. .. ... ............................. 74 Natural ganuna log of Lexington municipal well 3 ....... .. ....................................... 75 Pumping rate during test of Lexington municipal well 3 . ............ .. ....................... 76 Drawdown and recovery curves for Lexington municipal well3 . ......... .. ........ ... ..... 77 Geologic map of part of the Locust Grove Quadrangle and the location of the new Locust Grove municipal well. ............................ .... .. ....................... ...... 79 Sonic televiewer log of Locust Grove municipal well. ...................... ...................... 81 Caliper log of Locust Grove municipal well. ....... .... ... ........... ... .... ... ............... ....... 82 Temperature log of Locust Grove municipal well.................................................. 83 Spontaneous potential log of Locust Grove municipal well. .......... .. .. ..... .... .... ....... 84 Acoustic velocity log of Locust Grove municipal well............................................ 85 Single- point resistivity log of Locust Grove municipal well.................................. 86 Natural ganuna log of Locust Grove municipal well............................................. 87 Pumping rate during test of Locust Grove municipal well. ............. ...................... 89 Drawdown and recovery curves for Locust Grove municipal well. .. ................ ..... .90 Geologic map of part of the Lost Mountain Quadrangle and location of the Lost Mountain well. .. ... ...... ... ............... .. ............................ ..... 91

Vll

LIST OF FIGURES
Page

Figure 76. Figure 77. Figure 78.
Figure 79. Figure 80. Figure 81. Figure 82.
Figure 83. Figure 84.
Figure 85.
Figure 86.
Figure 87.
Figure 88. Figure 89. Figure 90. Figure 91. Figure 92. Figure 93. Figure 94. Figure 95. Figure 96. Figure 97.

Pumping rate during test of Lost Mountain well. ................................................. 93
Drawdown and recovery cmves for Lost Mountain well. .. .................. ...... .. .......... 94
Geologic map of part of the Newnan South Quadrangle and locations of the Newnan municipal wells. ..... ...... ............ ... ... ... ..... ...... ....... ...... ............ ...... . 95
Recovery cutve for Newnan test well. ................................................................... 98 Drawdown ~d recovery cutve for Newnan obsetvation well NE. .. ......... .... ..... ... ... 99
Drawdown and recovery cutve for Newnan obsetvation well S............ ..... ... .... .. ... 100
Geologic map of parts of the Madras and Tyrone Quadrangles and location of Shoal Creek Subdivision well4. ..... .............. .... ...... ... ...... ........... ....... ...... .... ... ... 101
Magnetic sutvey grtd at Shoal Creek Subdivision. ...... ........ ..... ....... ........ ....... ... ... 104
Changes in the magnetic field strength at the primary base station, Shoal Creek Subdivision site................................................................................ 105
Changes in the magnetic field strength at the secondary base station, Shoal Creek Subdivision test site. ....... .............. ................ .. ................................. 106
Magnetic sutvey showing the magnetic field caused by the well casing at the Shoal Creek Subdivision test site................ ........ ......... ... ... ................ .. ....... 107
Magnetic sutvey showing the magnetic field with the influence of the Shoal Creek Subdivision well removed.................................................................. 108
Magnetic anomaly map of the area around Shoal Creek Subdivision well 4......... 109
Caliper log of Shoal Creek Subdivision well 4......... ... .. .... ....... .. ...... .. ........ ..... ...... 110
Temperature log of Shoal Creek Subdivision well 4.............................................. 111
Spontaneous potential log of Shoal Creek Subdivision well 4 ............................... 112
Acoustic velocity log of Shoal Creek Subdivision well 4........................................ 113
Single- point resistivity log of Shoal Creek Subdivision well4............ .................. 114
Natural gamma log of Shoal Creek Subdivision wel14......................................... 115
Pumping rate during test of Shoal Creek Subdivision well 4................................ 116
Drawdown and recovery cutves for Shoal Creek Subdivision well4..................... 117
Geologic map of part of the Helen Quadrangle and the locations of the Unicoi State Park wells........................................................................................ 120

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LIST OF FIGURES
Page
Figure 98. Sonic televiewer log of Unicoi State Park well2, 643-650 ft. .. ... ...... .................... 122 Figure 99. Caliper log of Unicoi State Park well 2 ......... ..... .. ...... ....... ........ ... ......... .... ...... .. .. 123 Figure 100. Temperature log of Unicoi State Park well 2 ............... .... ... ... .. .. ..... ...... .... ... .. .. ... .. 124 Figure 101. Spontaneous potential log of Unicoi State Park well2 . ......... ... .. .. ... ....... .. .. ... .. ... . 125 Figure 102. Acoustic velocity log of Unicoi State Park well2 ...... ............................................. 126 Figure 103. Single- point resistivity log of Unicoi State Park well 2 .... ......... ....... ......... ..... ...... 127 Figure 104. Natural ganuna log of Unicoi State Park well2.................................................... 128 Figure 105. Sonic televiewer log of Unicoi State Park well5, 75-90 ft........... .. .......... ...... ... .... 129 Figure 106. Sonic televiewer log of Unicoi State Park well5, 145-155 ft. .... .. ....... .. ................ 130 Figure 107. Sonic televiewer log of Unicoi State Park well 5, 260-275 ft................................ 131 Figure 108. Sonic televiewer log of Unicoi State Park well5, 344-352 ft. ..... ... ... ............. ....... 132 Figure 109. Caliper log of Unicoi State Park well 5.................................... ........................ ..... 133 Figure 110. Temperature log of Unicoi State Park well 5....................................................... 134 Figure 111. Spontaneous potential log of Unicoi State Park well 5 ..................... .... ... ....... .... .. . 135 Figure 112. Acoustic velocity log of Unicoi State Park well 5... .................. ...... ........................ 136 Figure 113. Single- point resistivity log of Unicoi State Park well 5...................... ...... .. .......... 137 Figure 114. Natural ganuna log of Unicoi State Park well 5... .... .. ..... ....... .. .. ......... ...... .. .. ... .. .. 138 Figure 115. Pumping rate during test of Unicoi State Park well2 ....... ..................... ... .... .. ..... 139 Figure 116. Drawdown and recovery cmves for Unicoi State Park well 2. .. ...... ...................... 140 Figure 117. Drawdown and recovery cuxves for observation Unicoi State Park well 1. ............ 141 Figure 118. Drawdown and recovery cuxves for obsexvatlon Unicoi State Park well2 ............ 142 Figure 119. Drawdown cuxve for Unicoi State Park wel15 during 41-day pumping test..... .. .. 143 Figure 120. Geologic map of part of the Watkinsville Quadrangle and locations of the
test well and obsexvation well............................................................................. 145 Figure 121. Sonic televiewer log of three intexvals in Watkinsville well. ........ .......... .. .. ... .. .... .. . 147
IX

LIST OF FIGURES
Page

Figure 122. Caliper log of Watkinsville well............................................. ............................... 148 Figure 123. Temperature log of Watkinsville well. .. ........ ... .. ...... ..... ........ .... .... .... ........... ...... ... 149 Figure 124. Spontaneous potential log ofWatkinsville well............... .......................... ............ 150 Figure 125. Acoustic velocity log ofWatkinsville well................................................ .. ...... ...... 151 Figure 126. Single- point resistivity log of Watkinsville well.................................................... 152 Figure 127. Natural gamma log ofWatkinsville well.. ... .... .. .... ..... ... ................. ....... ...... .... .. .... 154 Figure 128. Pumping rate during test of Watkinsville well. .... .... ...... ......... .... ......... ..... ............ 155 Figure 129. Drawdown and recovery cmves for Watkinsville well. ............................... .... .... ... 156 Figure 130. Drawdown and recovery cmves for Watkinsville obsetvation well... ..... .. ... ... ...... .. 157

LIST OF TABLES

Table 1. Table 2. Table 3. Table 4. Table 5. Table 6. Table 7. Table 8. Table 9. Table 10. Table 11.

Ashland Subdivision, joint orientations and descriptions. ..... ........ ... ... .. ... .. ... ....... 8 Ashland Subdivision well, water-quality analysis. .. ..... ....... .......... .... ... ... ... ......... .. 8 Dawsonville, joint orientations and descriptions. ..... ............... .. ......................... .. 63 Dawsonville municipal well 4, water-quality analysis. .. ... ........ ............ ........ .... ..... 63 Lexington municipal well 3, water-quality analysis. ............... .... ... ... .......... ... .. .. .. . 67 Locust Grove municipal well 1, water-quality analysis. ........ ... ..... .... ......... .. ... .. ... . 80 Newnan, joint orientations and descriptions. .. ... ... ............... .. .. .... ... ... ....... ... ........ 96 Shoal Creek Subdivision, joint orientations and descriptions. ........ ........ ....... .. .. ... 102 Shoal Creek Subdivision well, water-quality analysis... .... ..... .... ... .... .. ... ...... ......... 102 Unicoi State Park wells 2 and 5, water-quality analyses................ .................... ... 121 Watkinsville, joint orientations and descriptions................... .. .......................... ... 146

X

HYDROGEOLOGIC DATA FROM SELECTED SITES IN THE PIEDMONT AND BLUE RIDGE -PROVINCES, GEORGIA

David A. Brackett. Willlam M. Steele. Thomas J. Schmitt. Robert L. Atklns. Madeleine F. Kellam. & Jerry A. Lineback

INTRODUCTION
PURPOSE AND SCOPE OF STUDY
The purpose of this study is to provide data (with some interpretations) on the principal hydrogeologic controls on the occurrence and movement ofground water at ten hydrologic test sites in the Piedmont and Blue Ridge Physiographic Provinces of Georgia (Fig. 1). These sites are the Ashland Subdivision (Oconee County). the Shoal Creek Subdivision (Coweta County), a private well at Lost Mountain (Cobb County), and the cities of Colbert, Locust Grove, Lexington, Newnan, and Watkinsville, all located in the Piedmont Province. Two sites are located in the Blue Ridge Province, the city of Dawsonville and Unicoi State Park. The knowledge gained from the test sites may assist in more effective development of the ground-water resources elsewhere in these provinces. Studies at the ten sites indicate that the keyto obtaining additional ground water in the Piedmont and Blue Ridge is the proper siting of new wells with respect to those geological and hydrological criteria that most stronglyinfluence ground-water availability.
This report presents geologic, geophysical, and hydrologic test data gathered from the ten test sites. All sites were investigated because one or more of the wells at these sites had a potential yield in excess of 50 gpm. Wells at four of these siteswere drilled at locations selected by the Georgia Geologic Survey as potentially having high-yield possibilities. The Survey sited these wells in response to requests from cities or municipal water systems seeking to develop additional ground water. Wells drilled at random locations in the Piedmont and Blue Ridge have an average yield of less than 20 gpm, a yield sufficient for domestic use but not for reliable public water supplies.

The types ofinformation collected at the ten test sites include:
1. Geologic mapping within a one-m1le radius of the well and field measurements of geologic structures such as foliation, joints, faults, linear stream segments, discontinuities,and compositional layering.
2. Descriptions of the major lithologies in the map area.
3. Surlace geophysical studies at three sites.
4. Borehole geophysical logging at six sites. 5. Test pumping of at least one well per site. 6. Water quality data. In addition to presenting this information, this report includes some general obsetvations on siting wells in the Piedmont and Blue Ridge and suggests avenues for further research.
JUSTIFICATION FOR STUDY
Rapid growth ofboth population and industry in north Georgia in recent years has increased the demand for potable water in this region. Regional water needs currently are being met primarily through the use of surlace-water resources. The effects ofsevere rainfall shortages in 1980, 1981, 1986, and 1988 suggest that existing surlace-water supplies may be unable to meet all of the future water demands of the area during periods of drought.
Ground water can provide a viable alternative or supplement to surface-water supplies in the future. In some cases, but not all, development of ground water is less environmentally disruptive than constructing surface-water reservoirs and may have economic advantages over surface-water systems in many cases. For example, extensive land areas need not be purchased, roads need not be rerouted nor wetlands

1

CUMBERLAND PLATEAU

N
t
Ot::==::::::E===350, MILES Ot:=:J=:=::360. KILOMETERS

I I DECATUR CRADY

THOMAS

FLA.

Figure 1. Locations of hydrogeologic test sites. 2

flooded. Ground-water resources in the Piedmont
and Blue Ridge Provinces currently are under utilized, due primarily to the difficulty ofreliably and predictably locating wells having adequate yields. The North Georgia Hydrology Program was established in December, 1986, bythe Georgia Geologic Survey to aid in developing the resource potential of ground water in north Georgia. One of the most important goals of this study was to identify what hydrogeologic criteria are most significant and necessary to reliably locate sites for high yield wells in the two provinces.
DESCRIPTION OF STUDY AREA
The Piedmont Province is a broad upland developed on complexly deformed Late Precambrian and Paleozoic metamorphic and igneous rocks. The topography of the province is rolling to rugged with elevations ranging from approximately 2000 ft in the Dahlonega area to 500 ft or less along the Fall Line, the southern margin of the province. Crystalline bedrock in the province has little intergranular porosity. Ground water in the bedrock is in open spaces formed through jointing or fracturing, along discontinuities formed by compositional layering or faulting, and in zones of weathering extending from the surface to more than 100 ft into the bedrock in places. The bedrock is overlain by a variable thiclmess (averaging 50ft) ofresidual weathered rock called saprolite.
The Blue Ridge Province is a highland of conical peaks and broad summits. The highest elevation in the Blue Ridge in Georgia is Brasstown Bald (elevation, 4, 784 ft). Intermountain plateaus average 1,600 to 1,700 ft in elevation. The topography is controlled largely by lithology. Valleys are developed on easily weathered lithologies, or on highly fractured rocks, and peaks are produced by more resistant rocks. Saprolite thiclmess is generally less than in the Piedmont because ofthe steeper slopes.
The climate ofthe Piedmont and Blue Ridge provinces is warm and moist. Average rainfall is 53 in. per year and is much higher in some mountainous areas. Significant rainfall deficits in the spring and summer months were recorded in 1980, 1981, 1986, and 1988.
The population of the Piedmont and Blue Ridge Provinces of Georgia was approx.lmately

3,420,400 in 1985 (Bachtel, 1987). The largest population center is the Atlanta metropolitan area. Projections of population for the study area in the 1990's show that continued growth is expected.
METHODS OF INVESTIGATION
Geologic Mapping
A geologic map was constructed at each site, extending at least one mile from each well studied. Field maps, constructed at the scale of 1:24,000, showed major rock types and the orientation ofjoint sets, compositional layering, fold axes, and mineral lineations. Geologic descriptions included the nature of the saprolite and the length, spacing, aperture opening and mineralization ofjoints and otherdiscontinuities. Analysis of structural trends included plotting data. such as the orientations ofjoints, compos1tlonallayering, and mineral lineations on equal area stereonets. The orientations of linear stream segments in the vicinity of each test site were measured on 7. 5 minute topographic quadrangle maps. Summaries and interpretations of the geologic and structural data appear in each site report.
Surface Geophysical Methods
Surface geophysical investigations carried out at three sites included magnetic smveys and electrical resistivity soundings. Magnetic surveys at the Colbert, Shoal Creek Subdivision, and Unicoi State Park sites attempted to locate geologic contacts suspected from geologic mapping. Tape and compass methods were used to establish the survey lines and a station spacing of 16.5 ft (5 m) min1mized background noise. An EG&G Geometries GSD-856 proton precession magnetometerrecorded magnetic measurements in Its internal memory. Base station readings taken at regular time intervals during the survey corrected for the diurnal fluctuations in the earth's magnetic field.
The electrical resistivity survey conducted at Unicoi State Park utilized a Bison Signal Enhancement Earth Resistivity System, Model 2390, and the Bison Offset Sounding System (BOSS). Soundings were oriented parallel and perpendicular to structurally controlled valley segments.

3

Borehole Geophysical Logging
A suite of geophysical logs were run on test wells where possible. The logging was done by the Water Resources Division, U. S. Geological Sutvey (USGS), Doraville, Georgia, as part of Georgia Geologic Sutvey's cooperative agreement. Logs obtained included: Sonic televiewer, caliper, temperature, spontaneous potential, acoustic velocity, single-point resistance, and natural gamma.
Borehole logs show the depth of discontinuities which may yield water to the well. The logs were compared to the drillers log on which the driller noted water-bearing zones. Many water-bearing zones appeared as discontinuities on one or more of the borehole logs. Discontinuities obsetved by borehole logging have various origins. Many of these discontinuities are joints or fractures in the crystalline rocks which represent openings along which ground water can easily move. Other discontinuities have been interpreted as weathered zones that extend some distance into the bedrock along joints, fractures, orcompositional layering. Compositional layering in the metamorphic and igneous rocks ofthe Piedmont and Blue Ridge may provide permeable pathways for ground-water flow. Differential weathering along susceptible compositional layers may result in water-bearing discontinuities. The drilling process itself produced apparent discontinuities because the borehole diameter increases in softer lithologies.
Sonic televiewer logs provide a 3600 image of the borehole and allow measurement of the structural orientation of discontinuities. Discontinuities interpreted asjoints orfractures usually appear as very dark gray to black areas with sharp boundaries on televiewer logs. Weathered zones or discontinuities caused by compositional layering often appear as gray mottled or gray and black mottled areas with uneven and indistinct boundaries on televiewer logs. The orientation of discontinuities in the boreholes as measured on the sonic televiewer logs was compared to the orientation of compositional layering and jointing measured during geologic mapping.
Hydrologic Methods
Hydrologic testing methods varied some-

what from site to site reflecting such factors as the availability of equipment and the incompleteness of knowledge of the yield characteristics of the wells. The hydrologic tests employed included constant-head tests (stress tests), constant-rate pumping tests, and step-tests.
Lack of previous quantitative hydrologic testing ofthe test wells required stress tests to be conducted in order to accurately define the yield characteristics ofthe wells. Accurate yield information proved to be a necessary precursor to a successful constant-rate pumping test. Nine of the site investigations included at least one constant-rate pumping test. In this type oftest. a well is pumped at a constant rate of discharge for the duration of the test and the drawdown is measured periodically in the pumped well and in any obsetvation wells. The water levels are again measured after pumping while they recover to pre-pumping levels. Most constant-rate pumping tests continued for a 24 hour period plus recovery time. Two 72- hour tests and one 41 day test were also carried out.
Throttling the pump engines or adjustment of in-line valves regulated flow from the wells during the tests. Measurements of the flow rate were made using either a standard 4in. by 2. 5in. orifice weir or an orifice bucket. Air lines were installed in some wells to measure water levels, otherwise a conductive probe indicatorwas used. Stilling wells allowed accurate water level measurements in wells exhibiting cascading water. The rate of drawdown dictated the time tntetval between water level measurements. Measurements were often taken more frequently than the logarithmic measurement schedule employed for most tests. Nearby wells at some test sites, used as obsetvation wells, allowed additional water level data to be collected.
PREVIOUS INVESTIGATIONS
One of the earliest descriptions of ground water in the Piedmont and Blue Ridge provinces of Georgia was provided by McCallie (1908). The ground-water resources ofthe Atlanta area were described by Herrick and LeGrand (1949) and Carter and Herrick (1951). Stewart and Herrick (1963) described emergency water supplies for the Atlanta area. Sever (1964) reported on the ground-water resources of Dawson County. McCollum (1966) studied ground water in Rockdale County.

4

A general oveiView of ground-water occurrence and availability, along with a rnethcx:l of selectingfavorable drilling sites in crystalline rocks of the southeastern United States, was presented by LeGrand (1967). Cressler and others (1979) reported on the geohydrology of Bartow, Cherokee and Forsyth Counties. Groundwaterinthe greater Atlanta region was described by Cressler and others (1983) and included the results of several pumping tests conducted for the study. Watson (1984) studied the hydrology of Greene, Morgan and Putnam Counties. A regional study of the hydrogeology of northern Georgia was conducted by the Georgia Geologic Survey as part of the Survey's application for primacy over the UndergroundInjectionControl Program (Arora,..OO., 1984). Radtke and others (1986) investigated the occurrence and availability of ground water in an 11 county region surrounding Athens, Georgia; three pumping tests were conducted for this study. The hydrogeology of Lamar County was studied by Gorday (1989).
ACKNOWLEDGEMENTS
The authors wish to thank the following individuals for their assistance and cooperation during the field study portion of this project: Mr. James C. Adams, Adams-Massey Co.; Mr. Richard Brown. Shoal Creek SubdMsion; Mr. Ellis Chastain. Virginia Well Co.Inc.; Mr. Dan Elder, Oconee Well Drillers: Mayor Jeny M. Elkins, City of Locust Grove: Mr. Jeny Fordham, Unicoi State Park: Commissioner William C. Madden, Madison County; Mr. Jerome Martin, Martin Well Co., Inc.; Mr. WA Martin, Grosch Irrfgation Co.; Mayor William G. Murray, City of Lexington; Mayor Howard Roper, City of Dawsonville; Mr. David Sibley, City of Newnan; and Mr. Ray Ward, Ward Well Drilling Co., Inc. Dr. Charles W. Cressler of the U.S. Geological Survey (Ret.) and Mr. Thomas Crawford of West Georgia College also provided valuable advice and guidance.
ASHLAND SUBDIVISION, OCONEE COUNTY
INTRODUCTION
A constant-rate pumping test was conducted on a high-yield community-supply well for the Ashland Subdivision, Oconee County, located approximately 12 rni southwest of the

city of Athens (Fig. 1). The subdivision water supply well was sited by Oconee Well Drillers at the head of an intermittent northeast trending stream. The driller reported that the well could produce more than 100 gprn. The Georgia Geologic Survey obtained access to the well to conduct a pumping test.
GEOLOGY
Ashland Subdivision lies in the Winder Slope District of the Piedmont Physiographic Province (Clark and Zisa, 1976). Stream valleys in the vicinity of the well are gently concave, and hill tops are gently convex to flat (Fig. 2). Local relief is approximately 240 ft. The largest streams in the Ashland SubdMsion area are the Apalachee River and Barber Creek, which have floodplains up to one halfrnlle wide. Large streams, such as the Apalachee River, exhibit dendritic drainage patterns: whereas smaller streams, such as Barber Creek, and intermittent streams have rectangular ortrellis-style drainage. Straight stream valley segments in the area are oriented N27E, N62E, N23W, and N59W. The Ashland Subdivision well is in a northeast-trending valley of an intermittent stream.
Rocks within a mile radius of the test well include a red to light tan saprolite developed from biotite gneiss, a red to purple saprolite developed from a mica or sillimanite mica schist, an ocher to yellow-brown saprolite weathered from a hornblende plagiocl~se amphibolite, and a black saprolite developed from a garnet-rich quartzite. The mica schist, amphibolite and garnet quartzite are interlayered on a scale of a few feet. Dikes and sills of light-colored, coarsegrained, equtgranular biotite granite intruded the abovementioned rocks in the Ashland area. These tabular intrusions range from less than one foot thick to several hundred feet thick. Pods and blebs of granite also occur along cornpositional layering.
The rocks in the Ashland Subdivision area have been polydeforrned, and they exhibit northsouth and east-west trending open upright warping folds. The geologic map (Fig. 2) illustrates the complexity of the structures in the study area. Compositional layering strikes to the northeast and northwest and dips generally greater than 45.
Several steeply inclined joint sets can be

5

N
t

EXPLANATION

Base from U.S. Geological Survey Statham 1:24,000, photorevised 1985.

0

.5 MILES

E3 E3 E3

0

.5 KILOMETERS

HHH

45 -"--
+
>----i ~19
x



Strike and dip of compositional layering Strike and dip of vertical compositional layering Strike and dip of inclined joint Strike and dip of vertical joint Trend and plunge of upright fold axis Outcrop Observation well Pumping well

Figure 2. Geologic map of part of the Statham Quadrangle and locations of wells in the Ashland Subdivision, Oconee County.

6

observed in the vicinity of Ashland Subdivision (Fig. 2, Table 1). Some straight valley segments of at least a mile in length parallel these joint trends.
WATER QUALITY
Water quality analysts indicates that water from the Ashland Subdivision well meets Safe Drinking Water Standards (Table 2). Tests were performed by the Agricultural Service Laboratoxy of the Extension Poultzy Science Department in Athens, Georgia.
HYDROLOGIC TESTING
The pumping rate of the Ashland Subdivision well averaged 138 gpm during a 24-hour constant-rate pumping test. A drilled well owned by the subdivision (observation well 1) is located 820 ft southwest of the pumping well and a shallow bored well (observation well2) is located on adjacent property approximately 1200 ft southeast of the test well (Fig. 2). Water pumped from the well during the test was directed onto the ground. Because ofthe short duration ofthe test and the clayey nature of the soil at the site, recirculation of water discharged from the test well did not appear to significantly influence the test results.
The Ashland Subdivision well could not sustain the initial pumping rate of 150 gpm rate after the first few hours of the test (Fig. 3). The production rate was dropped gradually to 132 gpm at the end of the test giving an average rate of 138 gpm for the test.
Drawdown in the test well totalled 171 ft at the end of the 24-hour test. A graph of drawdown versus time for this well plots as a smooth curve (Fig. 4). The recovery curve also is smooth and is symmetrical to the drawdown curve.
Drawdown was first observed in observation well 1 after three hours of pumping. Observation well 1 showed a total of 1.4ft of drawdown during the test (Fig. 5). A bottle found floating in this well during the recovexy portion of the test apparently interfered with the conductive probe used to measure the water level, causing the data to be somewhat erratic. Observation well 2 recorded no drawdown for the duration of the test.

SUMMARY
The hydrologic test results show that the Ashland Subdivision well had a yield of 138 gpm for 24 hours. A total of 171 ft of drawdown was observed in the pumped well. Observation well 1 had a drawdown of 1.4 ft and observation well 2 showed no effects of the pumping. Waterquality analysts indicates that ground water from the Ashland Subdivision well meets drinking water standards.
COLBERT. MADISON COUNTY
INTRODUCTION
The city of Colbert is located in southern Madison County (Fig. 1). Madison County officials requested that the Geologic Survey assist in locating new municipal well sites for Colbert. Three wells were drilled at sites designated by the Geologic Survey and two add1Uonal wells were drilled at sites selected by the water well contractor hired by the city.
WELL SITING
The Geologic Survey sited three wells for the city ofColbert. The first step in identifying potential high-yielding well sites was to examine the locations and yields of existing wells in the vicinity of Colbert. The yields of these wells ranged from 0 to 35 gpm with the highest yielding well located at the head of a northwesttrendtngvalley. This northwest topographic trend Is prominent in the Colbert area and could indicate the orientation of discontinuities which may channel ground water to wells.
The criteria used in the selection ofthe site for Colbert well 1 included the intersection of topographic features trending parallel to discontinuities (Fig. 6). Well site 2 is located 1n a northwest-trending topographic feature near an intersecting north-south discontinuity. The drill rig could not reach the site due to wet conditions, and so well2 was drilled about 150 ft north of the chosen site. The site for well3 was selected because ofintersecting topographic features and its location downdtp from a perennial stream.
1\vo additional wells drilled at Colbert are

7

Table 1. Ashland Subdivision. joint orientations and descriptions.

1Qint

Ja

Spacim~

Surface

N27E

60-80

2 in-1ft

smooth to irregular

N59W

50-90

2 in-4ft

irregular

N62E

60-90

0.5 in-1ft

smooth to irregular

E-W

60-90

0.5 in-4 in

smooth to irregular

Coatin~
manganese none none none

Table 2. Ashland Subdivision well. water-quality analysis.

Parameter

Results

Parameter

Ag

<0.05 mg/1

As

<0.05 mg/1

Ba

<0.05 mg/1

Cd

<0.005 mg/1

C02

2.6 mg/1

Cr

<0.01 mg/1

Cu

0.01 mg/1

F

0.1 mg/1

Fe

0.059 mg/1

Hg

<0.001 mg/1

Mg

1.23 mg/1

< =below laboratory detection limits

Na Nitrate Pb Se S04 Zn Turbidity (NTU) Alkalinity (as CaCO) Hardness (as CaC03) Chloride

Results
6.9 mg/1 0.843 mg/1 <0.02 mg/1 <0.001 mg/1 2.4 mg/1 0.34 mg/1 <1.00
52 mg/1
15.1 mg/1 3.00 mg/1

8

180

160

:::!: 140
A.
"-z 120
UJ
~ 100 a:

"az: 80

\0

:::!: 60

::)

A.

40

20

0

0

300 600 900 1200 1500 1800 21 00 2400 2700

TIME SINCE START IN MINUTES

Figure 3. Pumping rate of Ashland SubdMsion well during the 24-hour pumping test.

(.

TIME SINCE PUMP START IN MINUTES 0 300 600 900 1200 1500 1800 2100 2400 2700 0

20

40

1wwu.-. 60

z 80 z

......
0

~
0c 100

~
ct

120

140

160

180

Figure 4. Drawdown and recovery cutve for the Ashland Subdivision well.

TIME SINCE PUMP START IN MINUTES 0 300 600 900 1200 1500 1800 2100 2400 2700 0

0.2

... 0.4

w w
u.

0.6

-z

~ 0.8

-

0 c
~ 1

ca:

1.2

1.4

1.6

Figure 5. Drawdown and recovery curve for Ashland Subdivision observation well 1.

N
t

0

.5 MILES

R R R

0

.5 KILOMETERS

RRR

, ...

Base from U.S. Geological Survey

Danielsville South 1:24,000, 1972.

EXPLANATION

I bgn, msch, A ~oarse-grained biotite plagioclase gneiss; coarse-grained graphite-bearing mica schist;

I .

. and coarse-grained hornblende plagioclase amphibolite

lbgn, msch + pegj Coarse-grained biotite plagioclase gneiss; coarse-grained graphite-bearing mica schist

.

. with pods and lenses of pegmatite

15 -"-

Strike and dlp of compositional layering

Strike and dip of vertical joint

Strike and dip of inclined joint

x

Outcrop



Well location

4

Well number

C-1

Existing city well

Contact

Figure 6. Geologic map of part of the Danielsville South Quadrangle and locations of wells in the Colbert area.
12

located at sites selected by the driller. Well 1A was picked at a T-intersection of two drainageways across the valley from well 1. The criteria for selection ofthe site ofwell4 included convenience factors; the city owned the well site and possessed easy access. Well 4 is located between topographic features that curve away from each other in the upslope direction indicating a convergent dip configuration for the discontinuities responsible for these topographic features.
GEOLOGY
The city of Colbert lies in the Winder Slope District, a subdivision of the Piedmont Physiographic Province (Clark and Zisa, 1976). Stream valleys are gently concave with floodplains as wide as several hundred feet (Fig. 6). HUl tops are gently convex with interstream divides approximately 200 ft wide. Most land surface slopes gently, with a total reliefofabout 100ft. Straight valley segments apparent on the 7. 5 minute topographic map in the vicinity of Colbert are oriented N40W, N66W, N25, N40E, N6E, and N85E. The wells located by the Geologic Survey are at intersections of tributaries to Beaverdam Creek in an area of rolling topography.
The site is mostly underlain by red to tan saprolite weathered from a coarse-grained biotite gneiss. This saprolite is interlayered with red to tan saprolite weathered from graphitebearing mica schist and ocher-colored saprolite weathered from an amphibolite. Coarse-grained, equigranular biotite granite and quartz feldspar pegmatite intruded the mica schist.
Compositional layering generally strikes northeast and dips to the southeast and northwest near Colbert (Fig. 6). The compositional layering at well site 1 trends northwest with a southwest dip. Near well site 2, compositional layering strikes north-south and dips to the west. Compositional layering strikes northeast with a southeast dip in the vicinity of well site 3. A fold trending northeast, and plunging to the southwest, may be present in the Colbert area (Fig. 6).
Joints strike N72Wwith dips from 54NE to vertical; N65'W and N-S with vertical dip; and N23'W dipping 55 to 75SW (Fig. 6). At well 2, joint sets strike N22E dipping 78SE and N800W with vertical dip. Ajoint set strikes N56Wwith vertical dip near well 3.

GEOPHYSICAL TESTING
Sur;/ace Geophysical Testing
A magnetic survey conducted at Colbert near the well sites consisted of four profile lines (Fig. 7). Individual magnetic readings were subtracted from an average of readings at the site in order to identify magnetic anomalies. Profile line 1 showed a smooth increase in field values to the south, with no large magnetic anomalies near thesitesofwells 1 and 1A. Neitherwereanylarge anomalies detected in profile line 4. Profile line 2 showed an anomaly of about 120 gamma near well2 (Fig. 8). This anomaly is spike-shaped and is superimposed on a smooth decrease in the field values to the west. Profile line 3 shows a 50 gamma drop to the north near well3 (Fig. 9). The 50 gamma anomaly on line 3 is much greater than the average 10-15 gamma variation in the magnetic field common over most of the site.
The magnetic anomaly in profile 2 is most likely due to a magnetic unit interlayered in the metamorphic sequence. The anomaly in profile 3 is a much more significant feature and may represent a geologic contact near well 3. Well 3 produced 210 gpm during a 72-hour pumping test and penetrated numerous discontinuities. The steepness of the change suggests that the contact is dipping at a high angle and is possibly vertical. The geographic locations ofthe anomalies suggest that lithologic boundaries may coincide with linear stream segments.
Borehole Geophysical Logging
A suite of borehole geophysical logs, including sonic televiewer, caliper, temperature, spontaneous potential, acoustic velocity logs, single-point resistivity and natural gamma were runonColbertWells 1, 1A, 2, 3, and4. These logs aided in identification of discontinuities in the wells that may represent water-bearing zones.
Discontinuities are visible on the sonic televiewer log of Colbert well 1 at 68 ft, 140-145 ft and 383-385 ft (Figs. 10-12). Anomalies on the caliper, temperature, spontaneous potential, and acoustic velocity logs correlate with the discontinuity visible on the sonic televiewer log at 68 ft (Figs. 13-16). The caliper log shows an increase in borehole diameter at 140-145 ft. correlating with the discontinuity zone visible on the sonic

13

/

EXPLANATION

/

Magnetometry survey line

Ell Well

Station number

-....

~ .

Base from U.S. Geological Survey Danielsville South 1:24,000, 1972.

N

0

.5 MILES

t

F3 Fd Fd

R R R 0

.5 KILOMETERS

Figure 7. Locations of wells and magnetic survey lines at Colbert. 14

0
~------------------------------------------~~ 9-

0
CD
9-

0
II)
9-

aw :

0
~
9-

a2
::::!!E ::::)

z

z

- 0n 0
~ 9-
1-
~

0 N
9-

-0
9-

0

0

0 0
(J)

aa0no

0
a0 o

a0 n
~

0 0
~

a0 n
CD

o-
0 CD

N

N

N

N

N

N

N

II)

II)

II)

II)

II)

II)

II)

SVWWVD

Figure 8. Drift corrected magnetic profile line 2 at Colbert. 15

.0....
N

a::

UJ

0 al

0 N

:!
:z l

-z
0 0
.0...). .~... C/)

0
.C..IO..

0

0

0

0

0

0

0

c.C.D-

0

I()

0

I()

0

I()

0

0)

CIO

CIO

I'

I'

CD

CD

N

N

N

N

N

N

N

I()

I()

I()

I()

I()

I()

I()

SVWWVD

Figure 9. Drift corrected magnetic profile line 3 at Colbert. 16

N

62

63 64

65

66

67

w1-

w

-LL
z

68

:::z:::
1c.-. 69
c w

70

71

72

73

74 75

COMPASS QUADRANTS

E

s

w

N

. ... . . ,.~

' '

. ..li .. . . . ... j.: . .

. ~

.-t.-:. ~~

Figure 10. Sonic televiewer log of Colbert well 2, 62-75 ft. 17

COMPASS QUADRANTS

N

E

s

w

N

130

131

132 133

134 135

136

1uww-.
z

137 138

J:
w1cc-.

139 140

141

142

143

144

145

...

146

~II!' & .. .

._-:;.'t - I ......."-t..".'.. ,,: "'I.I

147

p

-- ~--. - ~...:.. ~

I

II f

~ , ~ - ... .

c.-.. ' ...... ,., . .. . ~ . :..! '

Figure 11. Sonic televiewer log of Colbert well 1, 130-147 ft.

18

COMPASS QUADRANTS

N

E

S

W

N

380 381 382 383 384 385 386 387 388
1ww- 389
LL
-z 390
l:
1ccw.-. 391
392 393 394 395 396 397 398 399 400

Figure 12. Sonic televiewer log of Colbert well 1, 380-400 ft.

19

HOLE DIAMETER IN INCHES 0 1 2 3 4 5 6 7 8 9 10
0+-T-~r-~~~-4-T-+~~~~~~~4-~
100
200
uwtw-. 300
z
400
~
t-
cwll. 500
600
700
800._----------------------------------~
Figure 13. Caliper log of Colbert well 1.
20

TEMPERATURE <Co)

14

15

16

17

18

19

20

o~~~~~~T4~~~~,-rT4-rr~r+~~~

100

200
w1uw-. 300
z
:::1: 400
1caw-.
500

600

700

Figure 14. Temperature log of Colbert welll. 21

MILLIVOLTS

200

.....

w w

300

u.

z

:..I..:. 400
11.
c w

500

600

700

800~--------------------------------~

Figure 15. Spontaneous potential log of Colbert well I.
22

MICROSECONDS PER FOOT

0

100

200

300

400

500

0+---~--~~~-4--~--~--~--4---~~

100 .......
200
w.w...
II. 300
z
:.r..::.
c0w. 400
500

600

Figure 16. Acoustic velocity log of Colbert well 1.
23

televiewer log. This depth interval also correlates with anomalies on the spontaneous potential, single-point resistance (Fig. 17), and acoustic velocity logs.
The fractured zone visible on the some televiewer log at 383-385 ft in well 1 correlates with anomalies on the caliper, spontaneous potential, single-point resistance and acoustic velocity logs. Not all anomalies seen on borehole geophysical logs of well 1 could be ascribed to discontinuities, however. The caliper and resistance logs both contained anomalies which could not be correlated with discontinuities visible on sonic televiewer logs, and the gamma-ray anomalies on the natural gamma log showed no apparent correlationwith any discontinuity seen on the some televiewer logs (Fig. 18).
The some televiewer logs from Colbert well 1A show discontinuities at 369-370 and 500-501 ft (Figs. 19 - 20). These zones are marked by anomalies on the caliper. single- point resistivity and spontaneous potential logs (Figs. 21, 23, and 24). Caliper and single-point resistance logs from Colbert well 1A indicate a possible waterbearing zone at 266-277 ft (Figs. 21 and 24). Temperature and natural ganuna logs were not useful in identifying discontinuities in this well (Figs. 22 and 25).
Colbert well2 was geophystcally logged, but the well driller reported that the major waterbearing zone was penetrat ed at 450ft. which was below the reach of the logging equipment (Figs. 26-30). The driller reported a minor weathered zone between 323 and 332 ft. The spontaneous potential log shows an increase at 310-330 ft and the single -point resistance values decrease slightly between 320 and 360ft. These anomalies could suggest a minor water-bearing zone near 320ft.
Anomalies on the some televiewer, caliper, spontaneous potential, single-point resistance, and acoustic velocity logs ofColbertwell3indicate the presence of a discontinuity at 123-125 ft (Figs. 31-34, 36-38) . Another discontinuity is indicated at 161-163 ft by anomalies on the some televiewer, caliper, resistance, and acoustic velocity logs. At 185-190 ft. the some televiewer shows a discontinuity that appears to be a weathered zone. The caliper, spontaneous potential, resistance, and acoustic velocity logs also show anomalies at or near this depth. A possible fractured or weathered zone may be indicated between 201 and 23 7 ft by anomalies on the spontaneous potential, resistance, and acoustic velocity logs. Natural gamma anoma-

lies also occur near this interval (Fig. 39). Spontaneous potential and acousticvelocitylogs show discontinuities at 248-254 ft. No temperature anomalies were logged in this well (Fig. 35).
The some televiewer log, and other logs, indicate a major discontinuity at 123-125 ft in Colbert well 4 (Figs. 40-45). A sign1ficant increase in borehole diameter occurs at this depth (Fig. 41) and the single-point resistance log shows an anomaly near this depth (Fig. 44). An increase in borehole diameter at 169 ft. along with an increase inground-watertemperature at 170 ft (Fig. 42), indicates a probable waterbearing zone. The single-point resistance log also shows a sign1ficant negative shift at 169 ft. A spontaneous potential log and a natural ganuna log were also run on Colbert well 4 (Figs. 43 and 45).
The orientations of subsurface discontinuities were measured from some televiewer logs of Colbert wells 1, 1A, 2, 3 and 4. These orientations were plotted on equal area diagrams and compared with the orientations of foliation, joints, and straight valley segments.
Wells 1, 3 and 4 penetrated northwestdipping discontinuities which are parallel or subparallel to the major structural features in the Colbert area. The strike and dip of foliation measured at the land surface are within 28 and 12, respectively, of the strike and dip of subsurface discontinuitiesmeasuredfrom televiewer logs. Well 3, the highest yielding of the five Colbert wells, intercepted numerous discontinuities of varying orientations.
HYDROLOGIC TESTING
Air lift tests on Colbert wells 1 and 1A indicated well yields of 15 and 10 gpm, respectively. No further hydrologic tests were performed on these wells. Stress tests, using a submersible pump powered by a generator, were performed on Colbert wells 2, 3, and 4in order to estimate production capacity for these wells.
The stress test conducted on Colbert well 2 lasted for 72-hours. Outflow was directed to the floodplain of the creek 15 feet from the well. The pumping rate is shown in Figure 46. The drawdown and recovery curves generated from the data gathered during the test are irregular and asymmetrical (Fig. 47).
A 72-hour well stress test was also carried out on Colbert well 3. Variations in the power

24

OHMS 1000 1500 2000 2500 3000 3500
o~~~~rT~~~~~~~~~~~~-r~~
100 200
w.w.... 300
IL
z
.:aw.:z...:.: 400 c
500 600 700
800~----------------------------------~
Figure 17. Single- point resistivity log of Colbert well 1.
25

API GAMMA UNITS
100 200 300 400 500 eoo

100

200

1ww- 300
LL
z

::1:

1-
wDc.

400

500

800

700

Figure 18. Natural gamma log of Colbert well!.
26

N
365 366 367 368
.ww... 369
LL
-z 370
.:cw:.:.t..: 371
Q
372 373 374 375

COMPASS QUADRANTS

E

s

w

N

Figure 19. Sonic televiewer log of Colbert welllA, 365-375 feet. 27

COMPASS QUADRANTS

N

E

s

w

N

495 496 497 498
1ww- 499
LL
z
:I: 500 1-
cQw. 501
502 503 504 505

Figure 20. Sonic televiewer log of Colbert well lA, 495-505 feet.
28

HOLE DIAMETER IN INCHES 0 1 2 3 4 5 6 7 8 9 10
0+-~+-~r-r-~~--~~-+~,+-r~~~~
100
200
.ww....
LL 300
z
:..I..:.
0.
w 400
0
500
600
700._------------------------------------~
Figure 21. Caliper log of Colbert well lA
29

TEMPERATURE (Co)

15

16

17

18

19

20

100
200
...
w w
II,. 300
z
...:::t:
wa. 400
Q
500
600
700~----------------------------------~

Figure 22. Temperature log of Colbert well lA
30

MILLIVOLTS

-800

-400

0

400

800

OT-~,-,-~-r-r-r-+~==~~r-r-r-~

100

200

1ww-
II.

300

z

2:
1caw-. 400

500

800

700~--------------------------------~

Figure 23. Spontaneous potential log of Colbert well lA. 31

OKMS

. .... . 1000

1500

2000

2500 ' I

3000 I '

350 ' I

0 .

.

.

4000

50

-

100

1- 150-r-
1w1.1

1.1.

z 200

X

J-

w0.

1-

c 250

1-

300

350

400
J
450~--------------------------~~------~

Figure 24. Single- point resistivity log of Colbert well lA. 32

API GAMMA UNITS

0

100 200 300 400 500 600

or-~~~~~~~~-+~~+-~~

100

200
1ww-
u.
z 300
::I: 1-
Dw . c 400

500

600

Figure 25. Natural gamma log of Colbert well IA. 33

HOLE DIAMETER IN INCHES

5

6

7

8

9

10

0+---~--~~---4--~--~------~----~

50

100

... 150
w w
IL. 200
-z
...X
wA. 250
Q
300

350

400

450~----------------------------------~

Figure 26. Caliper log of Colbert well2. 34

TEMPERATURE <Co)

14

15

18

17

18

18

20

O~-r~~rT~~~-r~~rT~~~-r~~rT4

50

100

150

1ww-

IL
z

200

::1: 1-
wD. 250
c

300

350

400

450~----------------------~----------~

Figure 27. Temperature log of Colbert well 2. 35

MILLIVOLTS

-800

-400

0

400

800

0+-~-r-,--~~,--r~~~~,-~~--~~

50

100
.ww.... 150
II.
z 200 :..r.:.:.
Q.
cw 250
300

350

400

Figure 28. Spontaneous potential log of Colbert we112. 36

OHMS 1000 1500 2000 2500 3000 3500 4000
o~~~~~~~~~~~~~~==~~
100
....;...
200
1ww-
LL
z 300
:I: 1-
0w.. c 400
500
600
Figure 29. Single- point resistivity log of Colbert well 2.
37

API GAMMA UNITS

0

100 200 300 400 500 600

0+-~----~r--+--~~~~--+-~--~--~-i

50

100

tww- 150
lL
z
200 ::z:: t-
wD..
c 250

300

350

400

Figure 30. Natural gamma log of Colbert well 2.
38

COMPASS QUADRANTS

N

E

s

w

N

116

117

118

119 120

121

122

tww- 123

u. 124

-z

:::t: t-

125

c0w.

126

127

128

129

130

131 132

133

Figure 31. Sonic televiewer log of Colbert well 3, 116-133 ft.

39

COMPASS QUADRANTS

N

E

s

w

N

150

151

152

153

154

155

156

157

158

159

160

ww1-
LL

161 162

z 163

J:

1ccw-.

164 165

166

167

168

169

170

171

172

173

174

175

Figure 32. Sonic televiewer log of Colbert well 3, 150-175 ft.

40

COMPASS QUADRANTS

N

E

s

w

N

180 181 182 183 184
185 186 187 188
w1w- 189
LL
z 190 :I:
1caw-. 191
192 193 194 195 196 197 198 199 200

Figure 33. Sonic televiewer log of Colbert well 3, 180-200 ft.

41

HOLE DIAMETER IN INCHES 0 1 2 3 4 5 6 7 8 9 10
0+-~+-~~~~-4---+~~~_.~~~4-~

50

100

1ww-
u.

150

z

X

1-

Q.
w

200

c

250

300

Figure 34. Caliper log of Colbert well 3. 42

TEMPERATURE (C0 )

14

15

16

17

18

19

20

o~~~~rT~rr~~~,-rT~~~~~,-~

50

100
1ww-
LL 150
z
X 1-
ll.
ld 200
Q
250

300

FJgure 35. Temperature log of Colbert well 3. 43

MILLIVOLTS

-800

-400

0

400

800

0+-~-T~~+-~~~--~~------~~----~

50

100
1Ill Ill 1&.
z 150
%
1aw . -
Q 200

250

300

Figure 36. Spontaneous potential log of Colbert well3.
44

MICROSECONDS PER FOOT

0

100

200

300

400

500

o~--~--~~---4--~--~--~--4---~~

50

100
1ww-
Ll. 150
z
:::1: 1-
wDc. 200
250

300

350~----------------------------------~

Figure 37. Acoustic velocity log of Colbert we113. 45

OHMS
1000 1500 2000 2500 3000 3500 4000 0
......,.
IuU..
-z:
:.a.1...:.
w
Q
3 5 0 . __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ j
Figure 38. Single- point resistivity log of Colbert we113.
46

API GAMMA UNITS

0

100 200 300 400 500 600

0+--.--~~r--r--.--+--~~--~--~~~

50

100
1ww-
1.1.
z 150
::1:
1aw . c 200

250

300

350 ._----------------------------------~

Figure 39. Natural gamma log of Colbert well 3.
47

COMPASS QUADRANTS

N

E

s

w

N

115

116

117

118

119

120

121

122

123

1w w 124

LL.

z 125

J:

1a-.
c w

126

127

128 129

130 131

132

133

134

135

Figure 40. Some televiewer log of Colbert well 4, 115-135 ft.

48

HOLE DIAMETER IN INCHES
0 1 2 3 4 5 e 7 8 8 10
0+-~~~~~~-+-r~~~~~r-~~~~
100
.. 200
~
Ill IL.
..-z 300
.X~..
Q
400
500
800~----------------------------------~
Figure 41. Caliper log of Colbert well 4.
49

TEMPERATURE {Co)

14

15

16

17

18

19

20

o~,~~~~~,~~~~~~~~~

100

200
1ww-
II.
z
X 300
1wa.c
400

500

600~------------------------------------~

Figure 42. Temperature log of Colbert well 4. 50

MILLIVOLTS

-800

-400

0

400

800

0+-~~~--~~~~~--r-~~-+~--r-~~

tOO
~-,
w1- 200 w
II.
-z::
...X 300
D.
c w
400

500

FJgure 43. Spontaneous potential log of Colbert well 4. 51

OHMS 1000 1500 2000 2500 3000 3500 4000
0~-r~-r~~~~-r~~~~~~~~-r~~
100
... 200
&LI
&uL..I
z
:::t ... 300
11.
c&LI
400
500
600._------------------------------------~
Figure 44. Single- point resistivity log of Colbert well 4. 52

API GAMMA UNITS

0

100 200 300 400 500 600

0+--,--~~~~--~-+--~~--~--r--r-4

100

1ww- 200
LL.
z
:::r:::
1- 300
awD.
400

500

Figure 45. Natural gamma log of Colbert well 4.
53

0I I
0

I

I

I

1440

I

I

I

2880

I

I I

4320

I

I

I

5760

I

I

I

7200

TIME SINCE START IN MINUTES

I

I

8640

Figure 46. Pumping rate during test of Colbert well 2.

TIME SINCE PUMP START IN MINUTES

0 0I I

1440

i

I I

2880

I

I

I

4320

I

I I

5760
1 I '

7200

I

I

I

8640

I

I

50

1-
"'11.1 100
IL
-z
;z: 150

0

Ul Ul

0
~a: 200

0

250

300~--------------------------------------------~

FJgure 47. Drawdown and recovery cwves for Colbert well2.

output by the generator caused minor fluctuations in the pumping rate (Fig. 48). Discharge directed into the flood plain ofthe creek, 15 feet from the well, flowed away from the well. Rapid drawdown in well3. noted during the first hours of testing, quickly transitioned into relative stability (Fig. 49}. The total drawdown was 117 ft for a pumping rate of 210 gpm. The fluctuations in drawdown match fluctuations in the pumping rate. The water.level in test well3 rose rapidly during the first hours of the recovery period, followed by a short transition into a slow final recovery.
Discharge was directed onto the floodplain of a nearby perennial stream during a 24-hour stress test conducted on Colbert well 4. The pump maintained a rate of83 gpm for most ofthe test period with a total drawdown of 66 ft recorded. Two major fluctuations in the pumping rate did occur during the test. however (Fig. 50). A truck severed the power line to the pump 230 minutes into the test. At the end of the test period, the driller requested that the well capacity be tested under a simulated water-system load. With the well at maximum drawdown, the pumping rate was varied in order to emulate well capacity at varying head values. Drawdown and recovery observed in the pumped well plot as asymmetrical and irregular curves (Fig. 51).
SUMMARY
Three wells sited for the city of Colbert by the Geologic Survey were selected on structural and topographic criteria. The three wells (wells 1, 2, and 3) produced yields of 15, 153, and 210 gpm, respectively. Two additional wells, sited and drilled, by the contractor produced yields of 10 and 83 gpm.
Well3 penetrated numerous discontinuities which are parallel or subparallelto foliations and joints mapped in the Colbert area. This well produced the highest yield of the Colbert wells (210 gpm} suggesting that enhanced recharge may be available through the numerous discontinuities noted in the well bore.
DAWSO~LE,DAWSONCOUNTY
INTRODUCTION
Dawsonville is located in central Dawson

County (Fig. 1} which lies in the Dahlonega Upland District of the Blue Ridge Physiographic Province (Clark and Zisa, 1976). The Geologic Survey selected a site for a new Dawsonville municipal water well at the request of the city. The Geologic Survey conducted a 24-hour constant rate pumping test on a well drilled on this site. No geophysical studies were carried out at the Dawsonville well site.
WELL SITING
The most productive ofDawsonville's previously drilled wells was located in a topographic low, at the intersection oftwo streams. A similar topographic situationwas sought as the location for the new well. An examination of the Dawsonville area indicated that a northwest structural trend with a vertical dip was the most frequent in the area (Fig. 52). The Geologic Survey selected the new well site (well 4) at the intersection ofa northwest-trending valley and a northeasterly trending valley oriented parallel to compositional layering. The well site is topographically low and is located in a large drainage basin.
GEOLOGY
Valleys near the Dawsonville well site are narrow and v-shaped and appear to be structurally controlled (Fig. 52). Ridge tops are narrow and irregular in shape. Most streams have rectangular or trellis drainage patterns, but the larger streams have dendritic drainage patterns. Relief in the study area is approximately 300 ft. Stream valley segments near Dawsonville are oriented N50"W, N44W, N22W, and N32E.
Three mappable rock units occur in the study area. All three strike northeast and dip southeast. These are:
1} A unit contatntng mica schist, biotite gneiss, and amphibolite. These rocks consist of a coarse-grained tan- to purple-colored mica schist saprolite and coarse-grained tan to yellowbrown biotite gneiss and quartz-rich gneiss saprolite. The mica schist is interlayered with the biotite gneiss on a 1-2 ft scale. The mica schist locally contains thin layers of ocher-colored amphibolite saprolite.
2) A unit characterized by button mica schist and biotite gneiss. This unit consists of a coarse-grained tan to purple garnet bearing

56

2~r---------------------------------------

200

:E

D.

" z

~

w ~

150
~

a:

"-z 100!
D.

Ul -.1

:E
:l

~

D.

50

0

0

1440

2880

4320

5760

7200

8640

TIME SINCE START IN MINUTES

Figure 48. Pumping rate during test of Colbert well 3.

TIME SINCE PUMP START IN MINUTES

0

1440

2880

4320

5760

7200

8640

0+-~--~~~--~-+--~~~--~~--~~~--+-~--r-~

20

1-
ww 40
~

-z
;z= 60

VI 00

c 0

c~a: 80

100

120~:=~====~--------~------------------~

FJgure 49. Drawdown and recovery curves for Colbert well 3

90
~
80 -Fr

::!1 70
0..
CJ
-z 60
w ~ 50 a:

CzJ 40 r-

Ul

-- 0:
::!1 30
:;::)

\0

0..

20 -

10--.... 0 r, 0

. . ..

300

600

'
900

.I o o

I

I I

I I

1200 1500 1800 2100

.I I I
2400

.I I
2700

TIME SINCE START IN MINUTES

Figure 50. Pumping rate during test of Colbert well 4.

TIME SINCE PUMP START IN MINUTES

0 300 600 900 1200 1500 1800 2100 2400 2700

0 I I I I I I I I I I I I I I

I II I

I II I

I I I I

II II

I I I I

II II

II II

II II

I I I

10

1- 20
w w

LL

-z 30
z

3:

~

0 40
0

~

a:

0 50

60

70~----------------------------------------------~

Figure 51. Drawdown and recovery cwves for Colbert well4.

N
t

X
rs;5
..

EXPLANATION
sch, A Schist, amphibolite

sch Schist
I I sch, bgn Schist, biotite gneiss

Strike and dip of vertical joint

X

Outcrop

Strike and dip of compositional layering



Well location

Strike and dip of inclined joint

- - - Inferred contact

0

.5 MILE

H E3 E3

0

.5 KILOMETER

HRR

Figure 52. Geologic map of parts of the Dawsonville and Juno Quadrangles and location of Dawsonville municipal well.

61

button mica schist saprolite that is thinly interlayered with a tan to yellow-brown biotite gneiss saprolite. Garnets are less than 0.1 in. in diameter. The stze of "buttons" in the schist varies. The gneiss is a coarse-grained massive to foliated biotite-quartz plagioclase gneiss. The gneiss forms shoals in Flat Creek and along tributaries to Flat Creek west of the well site.
3) A unit of mica schist. This sequence consists of a fine- to coarse-grained red to tan garnet mica schist saprolite with purple- to tanweathered quartz-rich gneiss saprolite. Garnets in this schist have a diameter of up to 0.25 in.
The geologic map (Fig. 52) Ulustrates the northeast strike and southeast dip of compositional layering. Joints near the well site are spaced from one inch to several feet apart and their strike length varies from an inch to several feet (Table 3). Joint sets are oriented N45'W, N50E, N62W, and Nl8W, and all dip vertically (Fig. 52). Aperture Ooint opening) is less than 0. 1 in. in saprolite and manganese commonly coats joint surfaces.
WATER QUALITY
A water-quality analysis conducted by the Water Supply Laboratory of the Environmental Protection Division indicates water from this well meets Safe Drinking Water Standards (Table
4).
HYDROLOGIC TESTING
Dawsonville's municipal well4 was drilled to a depth of 200ft and had an air lift yield of 100 gpm. The Geologic Smvey conducted a 24-hour constant-rate test on the well using a submersible production pump and utility power. No observation wells were available for the test. A nearby stream received the discharge from the pumped well. The pumping rate remained constant at approximately 75 gpm for the duration of the test with only 9.43 ft of drawdown observed. Drawdown and recovery curves constructed from the test data are smooth (Fig. 53). The shape ofthe drawdown curve for the test well can be matched to an exponential integral (Theis Well Function) but the meaning oftransmissivity and storativity values which could be derived from this methodology are unknown because the assumptions which govern the Theis method are

not met in this crystalline rock aquifer.
SUMMARY
The Geologic Survey located a well site for the City of Dawsonville (municipal well 4). The site selected lies in a topographically low area at the intersection of two discontinuities. Hydrologic tests indicate that the well can easily sustain a pumping rate of 75 gpm for a period of 24 hours.
LEXINGTON,OGLETHORPECOUNTY
INTRODUCTION
The city of Lexington is located in central Oglethorpe County, about 20 miles east ofAthens (Fig. 1). The Georgia Geologic Survey was asked by the city of Lexington to test municipal well3 to evaluate the well's production capacity. Although the well site was not selected by the Geologic Survey, it is a moderately high-yield well located next to, but not on, a prominent linear stream segment.
GEOLOGY
The city ofLexington lies in the Washington Slope District, a subdivision of the Piedmont Physiographic Province (Clark and Zisa, 1976). Stream valleys in the Lexington area are gently concave and hill tops are gently convex to flat. Relief is roughly 120 ft, and most land slopes gently. Drainage patterns of the larger streams, such as Town Creek, are dendritic but have long straight valley segments (Fig. 54). Intermittent streams have dendritic or trellis drainage patterns. Straight valley segments near Lexington are orientated Nil0 E, N25E, N84E, and N68'W. Municipal we113 is located on the west side of a northeast-trending straight valley segment.
Rocks within a mile radius of municipal well 3 are mainly light gray, medium-grained, massive, equigranular, biotite granite gneiss with intrusions of light-colored, medium-grained, equigranular granite. The granite is porphyritic in places, with feldspar phenocrysts up to 0.5 in in diameter. Medium- to coarse-grained chloritic

62

Table 3. Dawsonville. joint orientations and descriptions.

1Wn1

Illil

Spacin~

Surface

N50W

90

2 in-1ft

straight smooth

NSOOE

900

1-3ft

smooth to irregular

N62W

900

1ft

straight

smooth

N18W

900

1ft

smooth to

curvilinear

Coatin~
manganese clay
manganese
manganese clay
manganese clay

Table 4. Dawsonville municipal well 4. water quality analysis.

Parameter

Results

Parameter

pH Ag As Ba Cd Cr
Cu
F Fe Hg Nitrate

6.4 <25 ~gil <25 ~gil <50 ~gil
<5 ~gil <25 ~gil <50 ~gil <0.1 mgll <50 ~gil <0.5 ~gil
0.80 mgll

< =below laboratory detection limits

Pb Mn Na Se Zn Spec.Cond. Alkalinity Hardness Total Dissolved Solids

Results
<25 ~gil <25 ~gil
2.3 mgll <5 ~gil 640 ~gil
34~o/cm
14 ~gil 10 ~gil
24mgll

63

TIME SINCE PUMP START IN MINUTES
0 300 600 900 1200 1500 1800 2100 2400 2700 0

1

2

1ww- 3
IL 4
-z
z 5

~

=0c= 6

~

ca: 7

8

9

10

F1gure 53. Drawdown and recovery curves for Dawsonville city well 4.

N
t
/ .

/

Base from U.S. Geological Survey

Crawford 1:24,000, 1971; Lexington 1:24,000, 1971;

EXPLANATION

Maxeys 1:24,000, 1971; and Sandy Cross 1:24,000, 1971.

Ibggn, brg j Light-colored medium-grained equagranular biotite granite gneiss;

light-colored medium- to coarse-grained biotite granite

>----<

Strike and dip of vertical joint

Strike and dip of inclined joint

X

Outcrop



Well location

Or-----.-----..-~-5
E3 E3 E3

MILES

H H H 0~,__.--,-,_.::;5 KILOMETERS

Figure 54. Geologic map of part of the Lexington Quadrangle and locations of wells in the Lexington area.

65

epidote amphibolite and light-colored granite gneiss underlie the biotite granite gneiss. Borehole logs suggest that the contact between these two units is at 190-200 ft in municipal well3.
Foliation was not apparent in the massive granite gneiss unit. The granite contains biotite schlieren: however, orientation data are insufficient to determine a trend. Joint surfaces are smooth, spacing is from Sin. to 10ft. and joints commonly are 1 to 5 ft in length. Joirit sets are oriented N36"W, N50"E, N29E, NSO"W, and N2E, all with vertical dips (Fig. 54).
WATER QUALITY
A water quality analysts performed by Law and Company indicates that water from this well has sulfate and TDS levels that exceed Secondary Maximum Contaminant Levels (Table 5).
BOREHOLE GEOPHYSICS
Sonic televiewer, caliper, temperature, acoustic velocity, single-point resistance and natural gamma logs were run on municipal well 3 (Figs. 55-62). The logs show discontinuities at 91-94, 211-225, and 486-498 ft.
The sonic televiewer log (Fig. 55) shows a discontinuity at 91-94 ft. Anomalies on the caliper, temperature, natural gamma, and to a lesser extent, the single-point resistance log, also indicate a discontinuity at this depth. A weathered zone at 211-225 ft is apparent on the sonic televiewer log (Fig. 56) and is also represented by anomalies in borehole diameter, water temperature, natural gamma and acoustic velocity. Observations made by the well driller. as well as the sonic televiewer log (Fig. 57), indicate that a water-bearing weathered zone lies between 486 and 498 ft. An increase in borehole diameter at this depth, in addition to a slight decrease in ground-water temperature, support this interpretation. The single-point resistance log also shows an anomaly at this depth (Fig. 61).
Increases in borehole diameter at 250-265 and 358-380 ft (Fig. 58) could not be correlated with water-bearing zones. Significant increasing anomalies on the natural gamma log (Fig. 62) occur at 113, 157, 215, and 309ft, only one of which could be correlated with a water-bearing zone.
The orientations of subsurface

discontinuities were measured from the sonic televiewer log of the Lexington well. These orientations were plotted on an equal area diagram and compared with the orientations ofjoints and straight streamvalley segments measured at the surface near the well site. Discontinuities measured on the televiewer log strike within 11oof a surface joint set that strikes N500E with vertical dip. Northwest-strtldng discontinuitiesmeasured on the televiewer log strike within 5o of a straight stream valley segment.
HYDROLOGIC TESTING
A 24-hour constant-rate pumping test was conducted on Lexington municipal well 3 using a submersible production pump and utility power. No observation wells could be located to monitor the test. The outflow from the test well was directed onto the ground and flowed to a nearby stream.
A drawdown of 186ft took place during the test. carried out at a constant pumping rate of 60 gpm (Fig. 63). The drawdown curve formed by the data gathered during the test is irregular (Fig. 64). The recovery curve, while smoother than the drawdown curve, was not a smooth exponential integral curve.
SUMMARY
Lexington municipal well3 is located on the side of a northeast-trending linear valley segment. Sonic televiewer logs indicate that the well penetrated several northeast-striking discontinuities. The well sustained a pumping rate of 60 gpm durtng a 24-hour test with ~n observed drawdown of 186ft.
LOCUST GROVE, HENRY COUNTY
INTRODUCTION
The City of Locust Grove, in Henry County, obtains its municipal-supplywater from a spring (Fig. 1). During the drought of 1986, the yield of the spring dropped and the city had to purchase water from Henry County. The mayor requested that the Geologic Survey locate a well to

66

Table 5. Lexington municipal well 3, water-quallty analysis.

Parameters
pH Ag As Ba Cd Cl C02 Cr Cu F Fe Hg Mn

Results
7.0 <0.04mg/l < 0.02 mg/1 <0.05 mg/1 <0.005mg/l 11 mg/1
7.0 mg/1 <0.04 mg/1 <0.04mg/l
1.2 mg/1 <0.04 mg/1 <0.001 mg/1 <0.04 mg/1

< = below laboratory detection limit

Parameters
Na Pb Se
so 3
Zn Total Dissolved Solids Nitrate Nitrogen (N) Turbidity (NTU) Alkalinity (as CaC03} Total Hardness (as CaC03 )

Results
32 mg/1 <0.02 mg/1 <0.01 mg/1 200mg/l 0.20mg/l
503 mg/1
0.55 mg/1 2.7
38 mg/1
240mg/l

67

N
86 87 88 89 90 91
ww1- 92
LL.
z 93
:I:
1ccw.- 94
95 96 97 98 99 100

COMPASS QUADRANTS

E

s

w

N

Figure 55. Sonic televiewer log of Lexington municipal well 3, 86-100 ft. 68

N
211 212 213 214 215 216
w1w- 217
LL.
z 218
.J..:.
wcc. 219
220 221 222 223 224 225

COMPASS QUADRANTS

E

s

w

N

Figure 56. Sonic televiewer log of Lexington municipal well 3, 211-225 ft.
69

N
486 487 488 489 490
1wwu-. 491
z 492
l:
1cwc.- 493
494 495 496 497 498

COMPASS QUADRANTS

E

s

w

N

Figure 57. Some televiewer log of Lexington mun1cipal well 3, 486-498 ft.
70

HOLE DIAMETER IN INCHES 0 1 2 3 4 5 6 7 8 9 10
0~,-;-,-;-~+-T-+-~+-~~r-~r-~r-~~
100
200
tww-
lL
z
:r: 300
t-
wD.
0
400
500
Figure 58. Caliper log of Lexington municipal well 3.
71

TEMPERATURE (C0 )

14

15

16

17

18

19

20

o~~~~~~~~~~~~~~~~~~~~

100

200
1UJ UJ
"z"' 300
:..I..:.
Q.
cUJ
400

500

Figure 59. Temperature log of Lexington municipal well 3. 72

MICROSECONDS PER FOOT

0

100

200

300

400

500

0+---T---~--~--~~~~~~--~--~--~

100

200
1ww-
IL
z
X 300
1-
Dc w .
400

500

600~----------------------------------~

Figure 60. Acoustic velocity log of Lexington municipal well3.
73

OHMS
1000 1500 2000 2500 3000 3500 4000
0~-r~~rT~r+~-r~-r~,-~~~~-r~~
100
200
tUJ UJ
LL
z
300 X:
at-.
Uc J
400
500
Figure 61. Single- polnt resistance log of Lexington municipal well3. 74

API GAMMA UNITS

0

100 200 300 400 500 800

0+-~--+-~--4-~--4-~--~~~~~~~

100

1ww- 200
IL
z
::1:
1- 300
Q.
a w
400

500

800._--------------~~----------------~

Figure 62. Natural gamma log of Lexington municipal well 3. 75

70

60

"'

:E
D.
"- 50-
z
w ~ 40+
a:

" z
it

30-

:E

~

-....]
0\

D. 20

10-

0 '-

I t

l

I I

I

0

300 600 900 1200 1500 1800 2100 2400 2700

TIME SINCE START IN MINUTES

Figure 63. Pumping rate during test of Lexington municipal well 3.

TIME SINCE PUMP START IN MINUTES 0 300 600 900 1200 1500 1800 2100 2400 2700 0

20

40

.....
w

60

w

-u.
z

80

z 3:

100

-..1 -..1

0 c
~

120

ca: 140

160

180

200

FJgure 64. Drawdown and recove:ry curves for Lexington municipal well 3.

supplement their spring.
WELL SITING
Four well sites were chosen for the city of Locust Grove. Three of these sites were rejected by the city for drilling because they were too far from existing water lines or were located on property not owned by the city. A fourth site was accepted for drilling. This well site (municipal well 1) was located in a topographic low at the intersection of a structurally controlled, northeast-trending stream and a northwest-trending discontinuity.
GEOLOGY
The city of Locust Grove lies in the Washington Slope District, a subdivision of the Piedmont Physiographic Province (Clark and Zisa, 1976). Valleys in the vicinity ofLocust Grove are concave (Fig. 65). Floodplains range between 100 and 200 ft wide, with gently convex interstream divides. Relief is approxtmately 190 ft. Intermittent streams in the Locust Grove area have trellis-style drainage patterns, and perennial streams have dendritic to rectangular drainage patterns. Straight stream valley segments in the Locust Grove area, measured on 7.5 minute topographic map~. are oriented N06'W', N54'W', N28'W', and N50-70E. The well site is in a northeast-trending segment of the valley of Brown Branch.
Rocks within a mile radius of the Locust Grove well include coarse-grained biotite schist, coarse-grained sillimanite mica schist, and coarse-grained biotite gneiss. These rocks are interlayered on a scale of one inch to a few feet. The saprolite shows layering on a s1milar scale.
Compositional layering in the rocks strikes northeast and dips southeast (Fig. 65). Joint sets strike N780W, E-W, N59W, and N21E. All joints have vertical to nearly vertical dips. Joint spacing ranges up to several feet and persistence along strike varies up to several feet. Joint planes are smooth to rough curvoplanar and joint aperture in weathered rock is less than 0.1 in.
WATER QUALITY
A water quality analysis indicates that

water from this well is acceptable as a drinking water source (Table 6). The tests were performed by Law and Company. Clarkston, Georgia.
BOREHOLE GEOPHYSICS
Asuite ofborehole geophysical logs, includLng sonic televiewer, caliper. temperature. spontaneous potential, acoustic velocity. singlepoint resistance and natural gamma logs were run at Locust Grove municipal well 1 (Figs. 6672). Ge.ophysLcal logs and the well driller's observations indicate that probable water-bearing zones lte at 109-110 and 153-154 ft.
The sonic televiewer log shows a discontinuity at 109-110 ft (Fig. 66a). The temperature log indicates an increase in ground-water temperature at this depth probably resulting from water flowing into the borehole (Fig. 68). The spontaneous potential log changes character abruptly at approximately 100-110 ft. possibly due to the presence ofa water-filled discontinuity at this depth.
The driller's report indicates that the discontinuity at 153-154 ft yields the largest quantity ofwater (Fig. 66b). This corresponds with an increase in borehole diameter on the caliper log (Fig. 67). The temperature log also shows an increase in temperature at this depth, suggesting that water enters the borehole from a waterbearing discontinuity at or near this depth. Although othergeophysical logs (natural gamma, resistance, and acoustic velocity) were run, their results could not be correlated to water-beartng zones.
The orientations of ten discontinuities measured from the sonic televiewer log of the Locust Grove well are "scattered" when plotted on an equal-area diagram and no average orientation could be measured. The water-bearing discontinuity at 109-110 ft is oriented N03W and dips 27SW, subparallel to the N06W orientation of straight valley segments near the well. The major water-bearing discontinuity at 153154 ft strikes N90E and dips 11N. This strike is parallel to the E-W striking joint set. but the joints have vertical dips at the surface.
HYDROLOGIC TESTING
A 24-hour constant-rate pumping test was conducted on Locust Grove municipal well1

78

....

. xxX
X

bgn, msch .



li'VI.<

: t'...

!.IJI.

..,

~ l'to <.J.., , o

..t .
..,. ' " "

~ -~~

1

-~~

.. ....
~! 4~ {5

P l/lCt:

I,Jl\' .~

".

;?x7rx~,

...

. . . ., !,

... , I

ol

/'

.'

/
' \ ''


.

~"~ X~

~ J
21

1( ~

X 30

- ... . . ~.......

/

..., '.' ~.' !.;$"'Wt.4,.~3~ ---:--

5~
t ,
.X

..;...~

',,. ./.

/
w.
' I

EXPLANATION

Base from U.S. Geological SuNey Locust Grove 1:24,000, 1964.

sg

White to yellow brown weathering graphite sillimanite mica schist

I IRed weathering biotite plagioclase gneiss, sillimanite gneiss and sillimanite

bgn, msch

.

. mica schist

..4...5.._

Strike and dip of foliation

N

Strike and dip of vertical joint

t

Strike and dip of inclined joint

X

Outcrop



Well location

0
Fd R

.5 MILE
H

0

.5 KILOMETER

R RR

Contact

Figure 65. Geologic map of part of the Locust Grove Quadrangle and the location of the new Locust Grove city well.

79

Table 6. Locust Grove municipal well 1, water-quality analysis.

Parameter

Results

Parameter

Results

pH

7.5

Na

6.9 mg/1

Ag

<0.04mg!l

Pb

<0.02 mg/1

As

<0.02mg/l

Se

<0.001 mg/1

Ba

<0.1 mg/1

S03

Cd

<0.005 mg/1

Zn

7.6 mg/1 <0.02 mg/1

C02

5.6 mg/1

Color (Pt-Co

Cl

3.3 mg/1

Units)

5

Cr

<0.04mg/l

Turbidity

0.56

Cu

<0.04mg!l

(NTU)

F

<0.4 mg/1

Alkalinity (as

76 mg/1

Fe

0.18 mg/1

CaC03)

Hg

<0.001 mg/1

Nitrate

<0.3 mg/1

Mn

0.09 mg/1

Nitrogen

Total hardness

68 mg/1

(as CaC03 ) Total disolved

150 mg/1

solids

< =below laboratory detection limit

80

COMPASS QUADRANTS

N

E

s

w

N

a) 105

106

107
1ww- 108
LL.
z 109

:I: I-

110

cwC.. 111

112

113

114

b) 149

150

151
twu 152
zLL. 153
:I: 154 I-
wcC.. 155
156

157

158

Figure 66. Some televiewer log of Locust Grove municipal well, (a) 105-114 ~t., (b) 149-158 ft. 81

HOLE DIAMETER IN INCHES 0 1 2 3 4 5 6 7 8 9 10
o~~+---~~~-4---+~~--~--~--~~

50

100

150

....
1&.1 200
1u&...1

z
250

.::.:.1.:

Q.

1&.1
0

300

350

Figure 67. Caliper log of Locust Grove municipal well. 82

TEMPERATURE <Co)

14

15

16

17

18

19

20

O~rr~-r~,-r+~rr~-r~,-~~~~-r~

100

200
1wwu.
z
X 300
1-
lcwl.
400

500

600~------------------------------------~

Figure 68. Temperature log of Locust Grove municipal well.
83

MILUVOLTS

-400

0

400

800

100
.wwu..... 200 z :::c
..... 300
1wc1.
400
500
600~--------------------------------~

Figure 69. Spontaneous potential log of Locust Grove municipal well. 84

MICROSECONDS PER FOOT

0

100

200

300

500

0+---~--+---r---r-~~~~~---4--~--~

50

100

150
1ww-
II.
z 200
X 1-
0w. 250 c
300

350

450~-------------------------------------J

Figure 70. Acoustic velocity log of Locust Grove municipal well.
85

OHMS 1000 1500 2000 2500 3000 3500 4000
o~~~~~~~~~~~~~~~~~~~~
100
1ww- 200
u.
z ::r:
1- 300
Dc w .
400
500
Figure 71. Single-point reslstMty log of Locust Grove municipal well.
86

API GAMMA UNITS

0

100

200

300

400

500

600

0+-~--~-,--~--~~--~--+-~~~--~~

100

1ww- 200 u..
z
X
1- 300
w ~
0
400

500

600._----------------------------------~

Figure 72. Natural gamma log of Locust Grove municipal well.
87

using a four-inch, shaft-driven turbine pump powered by a diesel engine. No observation wells could be located. An intermittent stream located about 300 ft northwest of the test well received the outflow from the test pumping. The well was pumped at a constant rate of 180 gpm (Fig. 73) which produced a total of 139 ft of drawdown. Drawdown and recovery curves formed by the test data are smooth but asymmetrical (Fig. 74).
SUMMARY
The Geologic Survey located municipal well 1 for the city of Locust Grove at the intersection of a structurally controlled stratght stream valley segment and a discontinuity trend. The well had a yield of 180 gpm after a 24-hour pumping test (F.tg. 74). The total drawdown recorded was 139ft.
LOST MOUNTAIN, COBB COUNTY
INTRODUCTION
The community ofLost Mountain is located in western Cobb County (Fig. 1). A domestic well in Lost Mountain was tested for its hydrologic properties by the Geologic Survey because a report by the well driller indicated that the well produced a large volume ofwater from what may be a bottom-hole fracture at a depth of616 feet. Bottom-hole fractures are a class of inferred, near- horizontal discontinuities that may have developed at depths of hundreds of feet due to stress relief as overburden is naturally removed from the crystalline rocks of the Piedmont by eroston(Cressler, Thurmond. and Hester, 1983). The Geologic Survey obtained access to this well in order to test the hydrologic properties of one of these presumed bottom-hole discontinuities. Geophysical logs were not run on this well.
GEOLOGY
The community of Lost Mountain lies in the Central Uplands District. a subdivision of the Piedmont PhysiographicProvince (Clark and Zlsa, 1976). Total relief in the area is approximately 520 ft {F.Ig. 75). With the exception of Lost Mountain, the hill tops are gently convex and

stream valleys are gently concave. Intermittent streams in the Lost Mountain area have trellisstyle drainage patterns: whereas, larger streams commonly show dendritic drainage. Straight valley segments near Lost Mountain are oriented N50"E, N70"E, N20"E, N20"W, N45'W, and N85E. The well site is located on an interstream divide on the southeastern flank of Lost Mountain and is several hundred feet higher than the surrounding area (Fig. 75).
Two mappable lithologic units are present in the vicinity of the Lost Mountain well. One is a unit containing amphibolite, biotite gneiss and garnet quartzite. Roughly 85-90 percent of this unit Is a dark-green coarse-grained epidotechlorite-plagioclase-hornblende amphibolite. Amphibolite weathersto a yellow-brown to ochercolored saprolite with a boxwork texture. Gray coarse-grained biotite plagioclase granite gneiss makes up 5-10 percent of this unit. Scattered quartz and feldspar porphyroblasts are present and range in diameter up to 0.1 in. The gneiss contains a few garnets that are 0.1 in. in diameter. These two llthologles are interlayered on a scale one inch to a few feet. The remaining 5 percent of this unit consists of a reddish-brown weathered, garnet quartzite. Garnets range in diameter up to 0.4 in. The quartzite exhibits a "spotted" texture in places and is 10 to 30ft in thiclmess.
The other unit in the vicinity of Lost Mountain is predominantly a coarse-grained, silvergrey to green, garnet-chlorite schist. The garnets range in diameter up to lin. Locally this unit has a "button schist texture with buttons ranging from 1 to 3 in. The chlorite schist weathers to a red-brown or tan saprolite. The schist is a massive unit with a crude foliation characterized by chlorite wrapped around garnet porphyroblasts. Quartzite comprises a very small percent of this unit. The quartzite contains pyrite and possibly chalcopyrite. Outcrops of quartzite commonly are less than 5 ft wide in this map unit.
The geologic map (F.Ig. 75) illustrates the northeast strike and the southeast and northwest dip ofthe rocks. Joint spacing is from 2 in. to 1 ft and persistence along strike varies from 1 in. to 20ft. Joints occur as en echelon fractures and as straight, curving, or irregular planes that are manganese coated in places. Most joints, however, are straight with smooth surfaces. Joint aperture in weathered rock is 0.1 in. or less. Joint sets oriented N50"W, N700W, and N54E are

88

200

180

----

:E 160

D..

"-z 140

UJ
!;(

120

a:
100+

"-z

1-

D.. 80

:!E

::::)

00

D.. 60+

\0

40

20

0 0 300 600 900 1200 1500 1800 2100 2400 2700 TIME SINCE START IN MINUTES

Figure 73. Pumping rate during test of Locust Grove city well.

TIME SINCE PUMP START IN MINUTES 0 300 600 900 1200 1500 1800 21 00 2400 2700
0 Ia 111 I 1 a v a I 1 a; a I a a a a I a a 1 t I a 1 a a I 1 a 1 I a a 1 I as a a I ~ 1

20

wtw- 40

LL

-z
;z: 60

\0
0

c 0

~
ca:

80

100

120~------------------------------------------------~

Figure 74. Drawdown and recovezy curves for Locust Grove city well.

""\."~-->--cr---.~--+7-___..;.k---/ Base from U.S. Geological Survey Lost Mountain 1:24,000, photorevised 1982.

EXPLANATION
I I gmq Garnet mica quartzite

0

Amphibolite, biotite gneiss

8

Garnet chlorite schist

N
t

.2. Strike and dip of compositional layering

Strike and dip of inclined joint Strike and dip of vertical joint

0
E3 H

.5 MILE
H

0

.5 KILOMETER

HHR

x

Outcrop



Well location

Inferred contact

Figure 75. Geologic map of part of the Lost Mountain Quadrangle and location of the Lost Mountain well.
91

vertical andjoints oriented N15W dip 70NE (Fig. 75).
HYDROLOGIC TESTING
A 24-hour step test was conducted on the Lost Mountain well using a submersible pump and generator supplied by the driller. No observationwells could be located for this test. The pumping rate during the test was very irregular due to intermittent failure of the generator, but averaged 60 gpm (Fig. 76). Pumping at this rate produced a total drawdown of only 9.5 ft during the test period. Drawdown and recovery curves generated from the test data are irregular and asymmetrical (Fig. 77). The curves are atypical in that they have a low slope and a linear shape. The well had not recovered to tts pre-pumping water level after 6 days.
SUMMARY
The Lost Mountainwell sustained an average pumping rate of 60 gpm for 24 hours. The drawdown was minimal, indicating that a considerable amount of water was stored in the bottom-hole fracture. However, full recovery of the well did not take place during the six days of monitoring. The very slow rate ofrecovery ofthis well was attributed to its high topographic position and limited recharge.
NEWNAN, COWETA COUNTY
INTRODUCTION
The city of Newnan is located in central Coweta County (Fig. 1). Newnan relies primarily on surface water to meet its municipal-supply needs, but withdraws ground water from three wells to supplement surface-water supplies. The Geologic Survey asked to be allowed to use one ofthese wells to conduct a pumping test because the other two wells could be used as observation wells. A 24-hour pumping test was conducted on well P, and wells Sand NE (Geologic Survey designation) were used as observation wells (Fig. 78). Information on well construction was not available for any of these wells.

GEOLOGY
The city of Newnan lies in the Greenville Slope District (Clark and Zisa, 1976), a subdivision of the Piedmont Physiographic Province. Total relief in the Newnan area is approximately 200 ft (Fig. 78). Hilltops are gently convex, and stream valleys are gently concave. The largest streams in the area exhibit dendritic drainage patterns. Smaller intermittent streams have trellis-style drainage patterns. Straight valley segments identified on topographic maps near Newnan are oriented N29W, N04E, N74W, and N40E. The three municipal wells are all located in the valley of a northwest-trending tributary of Sandy Creek 1n an area of rolling topography.
The floodplain of the tributary where the wells are located is underlain by alluvium which in turn overlies the Clarkston Formation. The alluvium consists of tan. micaceous, sandy silt. The alluvium along the tributary to Sandy Creek ranges from 0 to 5 ft thick. A six-inch bed of colluvial and alluvial cobbles underlies the alluvium and marks the contact between the alluvium and bedrock.
The Clarkston Formation is the bedrock unit in which the Newnan city wells are completed. The formation consists of a tan to purple saprolite derived from a sillimanite-garnet-mica schist and a tan to purple saprolite derived from a biotite-plagioclase gneiss. These two lithologies are interlayered on a scale of one to several feet. The gneiss locally contains feldspar porphyroblasts and layers of manganese garnet quartzite and manganese garnet schist. Ochercolored saprolite derived from a dark-green to black coarse-grained hornblende-plagioclase amphibolite also Js present (Higgins and Atkins, 1981). Amphibol1te layers are commonly less than one foot thick and comprise only about 5 percent ofthe outcrop area. All ofthese lithologies contain intrusions ofgranite and quartz-feldspar pegmatite in places.
The geologic map illustrates the northwest strike and northeast dip of the compositional layering (Fig. 78). Shearing parallels the compositional layering. Joints are spaced from one inch to several feet apart and persistence along strike varies from an inch to several feet (Table 7). Joint aperture tn weathered rock is less than 0.1 in. Joint sets that strike E-W. N250W, and N52E all d1p vertically. Joints striking N22E dip 54NW and some of the E-W joints dip 34N.

92

90

80 -~

70

~ -~

,.........

a:::.!

-z~ 60 -~ 1~

"'-~ '---

w~ 50
a:

~ 40
z

i[

~

:::! 30

\0 Vl

:a:.J

20

10

0 .

0

300

. .

. .I

I

I o

I

I

600 900 1200 1500 1800 2100 2400

TIME SINCE START IN MINUTES

I
2700

FJgure 76. Pumping rate during test of Lost Mountain well.
\

TIME SINCE PUMP START IN MINUTES 0 300 600 900 1200 1500 1800 2100 2400 2700 0

1

2

tw- 3 w

-IL
z

4

:z= 5

\0
+:-.

0c 6

~

ca: 7

8

9

10

FJgure 77. Drawdown and recovery curves for Lost Mountain well.

.. { .
. ... ~

.,
I
I '
. I'
,/ . f1'"1\ .' /'

EXPLANATION
0 Alluvium 0 Clarkston Formation
~ Strike and dip of compositional layering
Strike and dip of inclined joint

~";

' \nr\\ :.\ ' /~ ~' '
.. ' ~ -

' ~ ,.:t.

'

Base from U.S. Geological SuNey Newnan South 1:24,000, 1965.

__.,o Trend and plunge of mineral lineation

-+++-45 Trend and plunge of fold axis
N

p Well location

t

X Outcrop

~ Strike and dip of vertical joint

Contact

0 H

.5 MILE
E3 H

0

.5 KILOMETER

HHR

Figure 78 . Geologic map of part of the Newnan South Quadrangle and locations of the Newnan municipal wells.

95

Table 7. Newnan, joint orientations and descriptions.

1.Qiru
East-West
Northwest Northeast Northeast East-West

om SpacinQ

900

2 in-1ft

"
II
NW
N

"
II
2in
3-6 in

Surface
smooth to irregular curving
smooth curving
smooth
weathered surface
curving smooth

Coatin~
none
manganese manganese manganese manganese

96

HYDROLOGIC TESTING
Two pumping tests were conducted at well P, a capacity test to measure the maximum pumping rate sustainable by the well over a period offour hours and a 24-hour constant-rate test during which the well was pumped at a rate of30 gpm. Wells S and NE served as observation wells during these tests.
Drawdown in the pumping well could not be adequately measured because of cascading water (Fig. 79). The water level in well NE dropped over 2 ft in 24 hours while water level in wellS dropped just over0.5 ft in the same period of time (Figs. 80, 81). Recovery of wells NE and P was monitored after the constant discharge test. Recovery ofwell S was not recorded due to its limited drawdown during pumping. The test well has a sustainable pumping rate of 30 gpm after 24 hours of pumping.
SUMMARY
The Newnan well sustained a pumping rate of 30 gpm for 24 hours. Drawdown could not be recorded in well P due to cascading water. Only 2 ft of drawdown was noted in an observation well located 345 ft from well P and a little more than 0.5 ft of drawdown in a second observation well located 214ft from P.
SHOAL CREEK SUBDIVISION, COWETA COUNTY
INTRODUCTION
Shoal Creek Subdivision, in Coweta County, is located about 35 miles south ofAtlanta and 2 mi west of Peachtree City (Fig. I). The Geologic Survey asked to be allowed to measure the hydrologic properties of Shoal Creek community-supply well4 because of its high-yield potential.
GEOLOGY
The Shoal Creek Subdivision lies in the Greenville Slope District, a subdivision of the PiedmontPhysiographic Province (Clarkand Zisa,

1976). Hilltops in the area are convex: to flat and are 800 to 1000 ft across (Fig. 82). The remaining area is gently sloping. Local relief is roughly 120 ft. Stream valleys in the vicinity of Shoal Creek are gently concave with floodplains between 200 and 400 ft wide. Drainage patterns range from dendritic to rectangular. Straight stream valley segments in the area, measured from topographic quadrangle maps, trend N350W, N53"W, N13E, N3SOE, and N79E. Shoal Creek Subdivision well 4 is located at the intersection of a northeast-trending intermittent stream and a northwest-trending segment of the valley of perennial Shoal Creek.
Two major geologic units are present in the Shoal Creek area, the Promised Land Formation and the Clarkston Formation (Higgins and others, 1987; Higgins and Atkins, 1981). The well is located at the contact between the two formations.
The Promised Land Formation crops out east of Shoal Creek. It consists of granite gneiss (approximately 90 percent) and amphibolite (approximately 10 percent). The granite gneiss is a light-colored, medium-grained, equigranular, foliated, biotite, quartz, plagioclase granite gneiss. The amphibolite is represented by a red-orange to ocher-colored amphibolite saprolite.
The Clarkston Formation crops out west of Shoal Creek. It consists ofinterlayered mediumto coarse-grained garnet, biotite, quartz, plagioclase gneiss: tan- to purple-weatheringmediumto coarse-grained mica schist; and yellow- to ocher-weathering medium- to coarse-grained amphibolite. These metamorphic rocks were intruded by a coarse-grained equigranular biotite granite.
The study area is located in the southwestem nose of the Newnan- Tucker Synform, a northeast trending regional fold. This fold has been refolded by a north trending upright fold (Scott Creek fold generation; Higgins and Atkins, 1981; Atkins and Higgins, 1980). The general strike of the compositional layering is northeast with a southeast dip (Fig. 82). The rocks along Shoal Creek, however, strike northwest and dip to the northeast.
Joints are spaced from 2 to 6 in. apart, and persistence along strike varies from 1 in. to 70 ft (Table 8). Joint aperture in weathered and exposed rock is less than 0.1 in. Joints in the Shoal Creek area are commonly vertical and

97

TIME SINCE PUMP START IN MINUTES 0 300 600 900 1200 1500 1800 2100 2400 2700 0

5

... 10
w ~ 15

z -
z 20

\0 00

0==
0
3:. 25

C(

a:

0

30

35

40

Figure 79. Drawdown and recovery cwve for Newnan test well.

TIME SINCE PUMP START IN MINUTES

0 300 600 900 1200 1500 1800 2100 2400 2700

0 I I I I I I I I I I I I I I

II II

I II I

I I I I

I II I

I I I I

II II

I I I I

I II I

II I

0.5

....

w w

-IL
z

1

z

3:

\0 \0

0 0 1.5
~

a:

0

2

2.5._------------------------------------------------~

Figure 80. Drawdown and recove:ry curve for Newnan observation well NE.

TIME SINCE 'PUMP START IN MINUTES 0 300 600 900 1200 1500 1800 2100 2400 2700 0 I I I I I I I I IiI 1' I I I I I I' I I I I I IiI I I I IiI I I I' IiI' iII I IiI

0.1

w.w... 0.2

1L

-z 0.3
z

8 -

3= 0c 0.4
~

ca: 0.5

0.6

0.7._--------------------------------------------------

Figure 81. Drawdown and recovery cle for Newnan obsrvatlon well S.

~<.,

. .X ""~
msch,ibgp, A
00

.\f. ~~ .-.~.*.....:.... --.:;._..o. ___..

t

'.,

' ,.

,

l'lt/l.~(tJ/1

'I_.ak'

N
I
t \\~~
- 33~'00" '
I
.\
'/
I \

I

'

EXPLANATION

ggn,A

Promised Land Formation:

I I granite gneiss, amphibolite

msch, bgn, A Clarkston Formation: mica schist,

.

. biotite gneiss, amphiholite

Strike and dip of compositional layering

Strike and dip of inclined joint

Strike and dip of vertical joint

Base from US. Geological Survey Madras 1:24,000, photorevised 1983 and Tyrone 1:24,000, photorevised 1982.

X

Outcrop

Well location

- - - Inferred contact

0

.5 MILE

Fd F3 Fd

0

.5 KILOMETER

HHR

Figure 82. Geologic map of parts of the Madras and Tyrone Quadrangles and location of Shoal Creek Subdivision well4.
101

Table 8. Shoal Creek. joint orientations and descriptions.

IQim

LenQth

Spacin~

Surface

N55E

50-60ft

6 in-2ft

smooth

N41W

60-70 ft

4-6in

curvoplanar

N35E

1 in-5 ft

3-6 in

irregular

CoatinQ none none
none

Table 9. Shoal Creek Subdivision well. water-quality analysis.

Parameters

Results

Parameters

pH

8.0

Ni

Ag

nd

Pb

A

nd

Se

Ba

nd

S04

Cd

nd

Zn

Cl

40 mg/1

Hardness

Cr

nd

(as CaC03)

Cu

0.016mg/1

Turbidity (N1U)

F

0.500mg/l

Nitrate

Fe

0.43 mg/1

Total Solids

Mg

nd

(as NaCl)

Mn

0.010 mg/1

Na

0.009 mg/1

nd =not detected

Results
nd nd nd nd 0.009 mg/1
120 mg/1 1.6 nd
259 mg/1

102

strike N55E, N41OW, N35E, and N59"W (Fig. 82).
WATER QUALITY
A water-quality analysis from Shoal Creek Subdivision well 4 indicates that the water is high in iron, turbidity, and hardness (Table 9). The Shoal Creekwater analyses were performed by West Georgia Water Analysis of Carrollton.
GEOPHYSICAL TESTING
Sw:face GeophJJSics
A series of magnetic profiles were conducted at Shoal Creek Subdivision well 4 to determine whether any magnetic anomalies are associated with this high-yielding well. Measurements were conducted on a 330x 330ft (100 x 100m) grid centered on the well and laid out by pace and compass (Fig. 83). Figures 84 and 85 show the drift in the base station during the measurement period.
The most prominent feature in the survey is the large magnetic anomaly produced by the well casing (Fig. 86). Figure 87 shows the data with the well casing anomaly removed. Figure 88 is a contour map of the cleaned magnetic data. The most prominent feature on the map is a magnetic anomaly in the southwest part of the survey area (Fig. 88). The magnitude of the anomaly isgreaterthan 40 gammas, which is ten Urnes the normal ambient variation in the magnetic field seen over the rest of the site. This anomaly suggests a consistent contrast in magnetic properties between the rocks to the southwest and those to the northeast of the survey area.
Borehole Geophysics
A suite of borehole geophysical logs, including caliper, temperature, spontaneous potential, acoustic velocity, single-point resistance and natural gamma logs were run at Shoal Creek Subdivision well 4 (Figs. 89-94). A waterbearing discontinuity was reported by the well driller at approximately 228 ft, corresponding with anomalies on borehole geophysical logs.

The caliper log (Fig. 89) suggests a relatively smooth borehole surface of constant diameter until about 220 ft. From 220 to 228 ft, the borehole diameter becomes smaller. The apparent reduction in hole diameter is caused by a pipe lodged in the borehole. The caliper log indicates a great increase in borehole diameter at 228 ft. Anomalies on the spontaneous potential and single-point resistance logs occur from about 210 to 230ft (Figs. 91 and 93). These anomalies may be related to the water-bearing discontinuity at 228 ft. However, the metal pipe lodged in the borehole probably produced some ofthis activity. The acoustic velocity log (Fig. 92) shows one major anomaly at about 231ft.
HYDROLOGIC TESTING
The Geologic Survey conducted two pumping tests. a stress test and a 24-hour constantrate pumping test on Shoal Creek Subdivision well 4, using a four-inch shaft-driven turbine pump powered by a gasoline engine. Discharge from the test well was directed into Shoal Creek, 50ft away, via a drainage ditch. No observation wells could be located near the site.
The appropriate pumping rate for the 24hour constant-rate test was calculated from the results of a four-hour stress test. During the constant-rate test, the well sustained a pumping rate of 104 gpm for 24 hours (Fig. 95). The total drawdown observed during the constantrate test was 143 ft. Drawdown and recovery curves generated by the data gathered from the constant-rate test are irregular but synunetrical (Fig. 96). The well was somewhat unusual in that, prior to pumping, the well had an artesian flow rate of 5 gpm. The well again began to flow several days after testing, but at a lower rate.
SUMMARY
The Shoal Creek Subdivision well is located at the contact between the Promised Land and Clarkston Formations. The well was test pumped at a rate of 104 gpm for 24 hours with a drawdown of 143 ft. A plot of drawdown versus recovery produced synunetrtcal curves.

103





























































!.













-




























SHOAL

CREEK



..,...



:'l






















20










15










10







5

1

EXPLANATION

eWell Survey point 5 Line number

N

t

0 0

30 meters 98 feet

Figure 83. Magnetic smvey grid at Shoal Creek Subdivision. 104

52410~--------------------------------------~~----~

en
<C

52405

:E

:E

<C

C)

-z 52400

w

...1

<C

0

tn 52395

-0
Vt

-w
> ~

w...1 a:

52390

523851 I I I I ' I I ' I I I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

I

600 650 700 750 800 850 900 950 1000

TIME OF DAY IN MINUTES

Figure 84. Changes in the magnetic field strength at the prtmary base station, Shoal Creek SubdMsion site.

52415

52410

52405

52400

tn

c(

:! :!

52395

c(

CJ

-0

52390

0\

52385

52380

52375

550

600

650

700

750

800

850

TIME OF DAY IN MINUTES

Figure 85. Changes 1n the magnetic field strength at the secondary base station, Shoal Creek SubdMsion site.

400~--------------------------------------~

300
U)

cC

:::!

200t ~ :::!
c(
CJ
-z

w
..J

100

-

<nBi

12
11 10 9 8

cC

0

U)

~
0 -....l

-w
> ~

0

.aw.:J -100

-200 0I

I 2

I 4

I 6

I 8

I
10

I
12

1
14

1
16

1
18

2I0

2I2

STATION NUMBER

Figure 86. Magnetic suiVey showing the magnetic field caused by the well casing at the Shoal Creek Subdivision test site.

\.'

400

350 300 250

-=~~~~~~~-~~~-~~==-~~-==-~--------=--~-~---;--------=----=----=---~-----;---=--:--;---~--~-~---=---~--~---~--~--~---~--~--~--~--~1-1~12~21=8970j~

-- Cl)

c(
:e

200

:e

c( (!)

150

-

~----------12

-------------

11

-=========.=-=====~-----------------=-=--=-==================8~

.....

100

------------------------------ 7

0
00

------------------------------- 6

50

-------------------------------- 5

------------------------------------------------- 4
0 ======================================~

-50 0

------------------------------------------------- 1
2 4 6 8 10 12 14 16 18 20 22
STATION NUMBER

Figure 87. Magnetic survey showtng the magnetic field with the infiuence of the Shoal Creek Subdivision well removed.

0

,\\J
\J~o

to~

EXPLANATION
0 Magnetic anomaly gamma
Well location

N

t

0 0

30meters 98 feet

Figure 88. Magnetic anomaly map of the area around Shoal Creek Subdivision well 4. 109

HOLE DIAMETER IN INCHES
0 1 2 3 4 5 6 7 8 9 10
0+-~+-~.-4:~-4~~.--~:--.-4~~:~.~~~~~

50-~

1ww-
u.

100
-

z

:c
1-
wc0.. 150
. ~

I

200-~

250~----------------------------------~

Figure 89. Caliper log of Shoal Creek Subdivision well 4. 110

TEMPERATURE (C0 ) 14 14.5 15 15.5 16 16.5 17 17.5 18 18.5 19
O+Trn~nn+r~+n~~Tr~~~~~~~~~~
50
.ww.... 100
I.L
z
.:.:.:.t.:
A.
~ 150
200
250._----------------------------------~
Figure 90. Temperature log of Shoal Creek Subdivision we114.
111

MILLIVOLTS

-800

-400

0

400

800

OT-~~~~,-,-~~~--~-r-r-r~~

50
wu~ w. 100
z
:I:
~
g.
w c
150

200

Figure 91. Spontaneous potential log of Shoal Creek Subdivision well4. 112

MICROSECONDS PER FOOT

0

100

200

300

400

500

0+---~--+---T-.--~~--~~~:~~~~--~--~

>
50~

....
wwu..

1 OOt-

z

.X...
Q.
wc 150

200

250------------------------------------~

Figure 92. Acoustic velocity log of Shoal Creek SubdMsion well4. 113

OHMS
1000 1500 2000 2500 3000 3500 4000
o~~~rr~~~~rir~~~~=-~~T4
50
.ww...
u. 100
z
.X...
caw.
150
200
250._----------------------------------~
Figure 93. Single-point resistivity log of Shoal Creek Subdivision well 4.
114

API GAMMA UNITS

0

100 200 300 400 500 600

0+-~~~--~-4--~--~~--4-~~~--~~

50
....
~ 100
II.
z
:I: I-
wD.
Q 150

200

250~----------------------------------~

Figure 94. Natural gamma log of Shoal Creek Subdivision well 4. 115

120

100

::!

D.

CJ

1-

-z 80

w !;(

f

a: 60"t

Cz J

~ 40!

............

D.

0'1

20

0 I ' I I I I, I I ' It I I I I I

I I II

I ' I I

I I' I

I I I

I' I I

I II

I I I

I I' 1

I I I

0

300 600 900 1200 1500 1800 2100 2400 2700

TIME SINCE START IN MINUTES

Figure 95. Pumping rate du11ng test of Shoal Creek Subdivision well 4.

TIME SINCE PUMP START IN MINUTES 0 JOO 600 900 1200 1500 1800 2100 2400 2700 0

20

40

w w ~
u.

60

-

-z
;z:: 80
c 0

-..J

~ 100

ca:

120

140

160

Ftgure 96. Drawdown and recovery curves for Shoal Creek SubdMsion well 4.

~COISTATEPARK,~TE
COUNTY
INTRODUCTION
Unicoi State Park is located in northern White County, about 80 miles northeast of Atlanta (Fig. 1). The yield of the park's watersupply well 1 declined from approximately 100 gpm to 30 gpm during the summer drought of 1986, forcing the park to curtail activities for part of the summer. In an effort to obtain adequate supplies of potable water, the park drilled 4 new wells. two ofwhich were sited by the Geologic Survey (wells 2 and 5). Two additional wells were sited, one by the well driller (well 3) and another by a dowser (well4) (Fig. 97).
GEOLOGY
Unicoi State Park is located in the Blue Ridge Mountain District, a subdivision of the Blue Ridge Physiographic Province (Clark and Zisa, 1976). Ridges trend northeast and are steep-sided with small rounded hill tops (Fig. 97). Local reltefts approximately 1200 ft. Most of the land surface is sloping. Many ofthe stream valleys in the vicinity of the park are v-shaped with little or no floodplain. Streams exhibit trellis-style drainage patterns. Straight stream valley segments near Unicoi State Park trend N50"\V, N76E, N48E, and Nl0E. Well 2 is located at the intersection of northwest- and northeast-trending tributary streams of Smith Creek. Well5 is located south of Unicoi Lake in a straight, north-south-trending segment of the valley of Smith Creek. The park's original well (well 1) is located northeast of well 2 in a northeast-trending tributary of Smith Creek.
Three major mappable lithologic units can be identified in the vicinity of Unicoi State Park (Gil1on, 1982, and German, 1985). Biotite gneiss consists of slabby, gray-weathering, coarsegrained biotite plagioclase gneiss with thin (1 in.) crenulated mica schist layers. Gneissic layeringvaries in thickness from one inch to several feet in this unit.
A second unit contains interlayered mica schist, biotite gneiss. and amphibolite.Tan- to silvery-weathering, coarse-grained mica schist is interlayered with coarse-grained biotite gneiss

on a scale of 1 to 20 ft. One- to two-foot wide units of ocher-colored. coarse-grained amphibolite are also present. The occurrence of amphibolite distinguishes this sequence from the others.
The third unit is interlayered biotite gneiss and mica schist. Lithologies are a grayish-white weathering coarse-grained biotite feldspar gneiss interlayered with crenulated mica schist. Schist layers are 0.5 to 1ft thick. The gneiss weathers to a distinct white sandy saprolite with feldspar porphyroblasts 0.5in. in length. This sequence comprises 50 percent of the area studied.
The geologic map 1llustrates the northeast strike and the northwest and southeast dips of the compositional layering (Fig.97). Joints are spaced from one to several feet apart. Joints at Unicoi are straight to curvilinear with smooth surfaces. The joint sets strike N18E, vertical; N05E, SE dip; N500W, vertical, and N-S with east or west dip.
WATER QUALITY
Water-quality analyses performed by the Georgia Erwironmental Protection Division Water Quality Laboratories indicate that well 2 is high in iron and that well 5 is high in calcium, sulfate, strontium, and zinc as compared to well 2 (Table 10). The sulfate content renders water from well 5 non-potable.
GEOPHYSICAL TESTING
Sur:face Geophysics
Nine vertical resistivity soundings and three magnetic proflles were conducted at the site of well 5. Electrical and magnetic surveys indicate anomalies parallel to the north-south topographic trend and parallel to a north-south joint set. Both resistivity and magnetic surveys support the existence of a narrow fracture zone. Schmitt and others (1991) describe the results of the surface geophysical investigations in the Unicoi area.
Borehole Geophysics
A suite of borehole geophysical logs, including sonic televiewer, caliper, temperature, spontaneous potential, acoustic velocity, single-

118

point resistance. and natural gamma logs were run on Unicoi Wells 2 and 5 (Figs. 98-114). Unicoi well2 (Figs. 98-104) contains two potential water-bearing zones at 10S and 643-6SO ft. The caliper log (Fig. 99) shows an increase in borehole diameter at 90-10S ft. The spontaneous potential and single-point resistance logs also show anomalies at 10S ft. A potential waterbearing zone at 643-6SO ft is indicated by the televiewer log (Fig. 98). From 10S to SOO ft, resistance values are stable, and then the values decrease from SOO to 6SO ft.
A flow meter was used at Unicoi well S, in additionto borehole geophysical logs, in orderto locate water-bearing zones. Several such zones were identified (Figs. 10S-114). At 79-80 ft, the sonic televiewer log shows a discontinuity which the flow meter indicates to be water-bearing (Fig. 10S). Borehole diameter also increases at this depth and anomalies occur on the single-point resistance and acoustic velocity logs. The sonic televiewer and caliper logs show a weathered discontinuity at 84-88 ft: that also produces water. The single-point resistance and acoustic velocity logs show anomalies at this depth. Minor water-bearing zones were identified at 1481SO and 265-268 ft on the basis of sonic televiewer, caliper, single-point resistance, and acoustic velocity logs, along with flow meter data. The flow meter indicates the presence of another minor water-bearing weathered discontinuity at 301-342 ft. This zone Is also indicated by changes in borehole diameter, stngle-polnt resistance and acoustic velocity. A more sJgnlficant water-bearing zone is located at 34S-3S2 ft. The flow meter and temperature log both indicate that ground water enters the borehole at this depth. The sonic televiewerlog shows a weathered discontinuity, and the borehole diameter increases at this depth.
The orientation ofsubsurface discontinuities were measured from sonic televiewer logs of Unicoi wells 2 and S. These orientations were plotted on equal area diagrams and compared with the orientations of compositional layering, joints, and straight valley segments mapped at the surface. Subsurface discontinuities in Unicoi wells 2 and S strike northeast. The strikes ofthe discontinuities in the two wells are within go of each other. Northeast-striking, northwest-dipping compositional layering was measured at

the land surface. The strike and dip of the surface compositional layering are within 23 and 18, respectively, of the strike and dip of northwest-dipping subsurface discontinuities measured from sonic televiewer logs. The subsurface discontinuities of this orientation may, therefore, be related to compositional layering. The three northeast-striking discontinuities observed in the sonic televiewer logs strike within l7ofalinearstreamvalleytrend(N7S0 -80"E). The discontinuities from 148 to 1SO ft: and 26S to 268 ft in the Unicoi wellS are water-bearing and dip about S5 and S9, respectively, to the northwest. These dips correspond to the dip direction of compositional layering and may represent zones of differential weathering.
HYDROLOGIC TESTING
A total of four new wells were drilled at Unicoi State Park. Well3 (drtller) and 4 (dowser), sited without using geological or structural criteria, had air-lift yields of approximately S gpm. Well 2 was sited by the Geologic Survey on the basis of prox1mity to existing water lines at the request of park officials. A 24-hour constantrate pumping test conducted on Unicoi well 2 utilized a submersible pump powered by utility power. The discharge from the well was directed into a nearby creek. The pumping rate was held constant at approximately 10 gpm except during the very early portion of the test (Fig. 115). Drawdownandrecoverycurvesconstructed from data gathered at well 2 illustrate the characteristics of the well (Fig. 116). Curves generated from the data on two observation wells (wells 3 and 4) are irregular and asymmetrical (Figs. 117 and 118).
Unicoi well S was sited by the Geologic Smvey using geologic and structural criteria. It was test pumped at a constant rate of 130 gpm for 41 days, except when power was down, in an attempt to reduce sulfate levels in the ground water from this well. Testing was conducted using a submersible pump powered by utility power. The discharge from wellS flowed into a nearby stream. Drawdown stabilized during the test and remained constant except durtng periods of interrupted power (Fig. 119). Sulfate levels did not decline significantly during the 41 days of pumping. Recovery was not monitored at wellS.

119

N
t

EXPLANATION

Base from U.S. Geological Survey Helen 1:24,000, photorevised 1985.

at

Undifferentiated cobbles of alluvium and colluvium sand and silt

Slabby, gray weathering coarse-grained biotite plagioclase gneiss with thin (1 inch) crenulated bgn L - - - - - - - - ' mica schist layers

Tan to silvery weathering coarse-grained mica schist interlayered with coarse-grained biotite msch, bgn, A
gneiss, locally contains 1-2 foot thick ocher-colored coarse-grained amphibolite

bgn, msch

Grayish-white weathering coarse-grained biotite feldspar gneiss int~rlayered with thin ( < 1 foot) crenulated mica schist

Red-brown to gray weathering biotite gneiss (1-1 0 feet thick) and tan to silver to purple bgn, msch, A
weathering quartz biotite schist (6 inches-1 foot thick), locally contains thin (1-2 feet) layers of

ocher -colored amphibolite

Jt Strike and dip of compositional layering
>--< Strike and dip of vertical joint Strike and dip of inclined joint

X Outcrop
Well location
Contact

0

.5 MILE

I II II I

0

.5 KILOMETER

H 1::::::1 ~

~14 Trend and plunge of upright open fold

Inferred contact

Figure 97. Geologic map of part of the Helen Quadrangle and the locations of the Unicoi State Park wells.

120

Table 10. Unicoi State Park wells 2 and 5. water-quality analyses.

Well Number Date Sampled

2 9/15/86

5 8/15/86

5

5

9/15/86 3/5/87

faram~t"'rs
pH
Spec. Cond.
Cl
S04 N02+N03

4.5 50
1 <2 <0.02

Results

5.0

5.2

1100

328

1

3

850

125

<0.002

<0.02

7.2 834
1 400
<0.5

liniU
J.Lmho/cm mg!l mg!l mg.N/1

ICAfScreen

Ca

6.2

250

56.6 185

mg!l

K

0.8

3.4

1.1

mg!l

Mg

0.6

1.4

0.6

1.2 mg!l

-; .....

Na

3.2

24.7

8.9

21.7 mg!l

Ag

<10

<10

<10

<25

Jlg/l

AI

105

<20

<20

Jlg/l

As

<40

<40

<40

<25

Jlg/l

Au

<25

<25

<25

Jlg/l

Ba

<10

<10

<10

<50

Jlg/l

Be

<10

<10

<10

Jlg/l

Bi

<50

<50

<50

Jlg/l

Cd

<10

<10

<10

<5

Jlg/l

Co

<10

<10

<10

Jlg/l

Cr

<10

<10

<10

<25

Jlg/l

Cu

<10

<10

<10

<50

Jlg/l

Fe

23

20

<50

Jlg/l

Mn

40

68

49

40

Jlg/l

Mo

<10

<10

<10

<10

Jlg/l

Ni

<20

<20

<20

Jlg/l

Pb

<25

<25

<25

<25

Jlg/l

Sb

<50

<50

<50

Jlg/l

Se

<3

<8

<3

<5

Jlg/l

Sn

<50

<50

<50

Jlg/l

Sr

27

1230

270

Jlg/l

Ti

13

<10

<10

Jlg/l

T1

<50

<50

<50

Jlg/l

v

<10

<10

<10

Jlg/l

y

<10

<10

<10

Jlg/l

Zn

<10

87

135

120

Jlg/l

Zr

<10

<10

<10

Jlg/l

< = below laboratory detection limits

121

N 643

644

645

1ww-
LL

646

z

:J:
1ccw-. 647

648

649

650

COMPASS QUADRANTS

E

s

w

N

Figure 98. Sonic televiewer log of Unicoi State Park well 2, 643-650 ft. 122

HOLE Dl AMETER IN INCHES 0 1 2 3 4 5 6 7 8 9 10
0+-~+-~~r-~~~~~-+~-+~~~~~~
100
200
1w -
w
LL 300
z ::r:
1-
Qw. 400 c
500
600
700~------------------------------------~
Figure 99. Callper log of Unicoi State Park well 2.
123

TEMPERATURE <Co)

14

15

16

17

18

19

20

o~~~-r~-r~~~,-rT~rT~rT~rr~~~

50

100

wtw- 150
II.
z 200
l:
wcat-. 250

300

350

Figure 100. Temperature log of Unicoi State Park well 2. 124

MILLIVOLTS

-800

-400

0

400

800

0+-~~~~+-~~~--+-~~~--~~~~~

50

100

150 1w w IL 200
z
:::1:
1aw.- 250
Q
300

350

400

450

Figure 101. Spontaneous potential log of Unicoi State Park well 2. 125

MICROSECONDS PER FOOT

100

200

300

500

100

200

1wwu-. 300
z

:r:

1aw . -
Q

400

500

600

700~----------------------------------~

Figure 102. Acoustic velocity log of Unicoi State Park well2. 126

OHMS 1000 1500 2000 2500 3000 3500 4000
0~-r~~rT~~~-r~-r~,-~~~+,-r~~
100 200
...
w w
LL
z 300
.:a..:
0wc.. 400
500 600
Figure 103. Single-point resistMty log of Unicoi State Park we112. 127

API GAMMA UNITS

0

100 200 300 400 500 600

0+-~--~--~~-,--~-,--4--,--~-,r-~

100

200
wtwu..
z
X
otw-.
0

Figure 104. Natural gamma log of Unicoi State Park well 2. 128

COMPASS QUADRANTS

N

E

s

w

N

75

76 77

78

79

80

utww-.
-z

81 82

J:

t-
cQw.

83

84

85

86 87

88

89 90

Figure 105. Sonic televiewer log of Unicoi State Park well 5, 75-90 ft. 129

COMPASS QUADRANTS

N

E

s

w

N

145 146 147 148
1ww- 149
LL.
-z 150 J: 1-
c0w. 151
152 153 154 155

Figure 106. Sonic televiewer log of Unicoi State Park well 5, 145-155 ft. 130

COMPASS QUADRANTS

...... N

E

.. . w~:'"

..~

260

~~- :~

s

w

N

261

262

263 264

265

266

"ww"""'
LL.

267

-z

:X: 268

c"w"".".'

0

269

270

271

272

273

274 275

Figure 107. Sonic televiewer log of Unicoi State Park well 5, 260-275 ft. 131

N

344

345

346

u1ww-. 347

:z:

:::t: 348

w1c.c

349

350

351

352

COMPASS QUADRANTS

E

s

w

N

Figure 108. Sonic televiewer log of Unicoi State Park well 5, 344-352 ft. 132

HOLE DIAMETER IN INCHES 0 1 2 3 4 5 6 7 8 9 10
0+-~+-~~~~~~-4~-+~-+-r~~~~
50
100
1ww- 150
u.
z 200
J: 1-
Q.
wc 250
300
350
Figure 109. Caliper log of Unicoi State Park well 5.
133

TEMPERATURE (Co)

14

15

16

17

18

19

20

0~~--~--~~~~rT~~~~-r~-r~-r~~

100

200

1ww-
1.1.

300

z

X
1caw.- 400

500

600

700~------------------------------------~

Figure 110. Temperature log of Unicoi State Pa1k well 5. 134

MILLIVOLTS

-800

-400

0

400

800

0+--r~~--~~-r~-4--r-~-r-+~--r-~~

50
~--
100

..... 150
w w
IL
z 200

.X....

G.

w
0

250

300

350

400

450~--------------------------------~

Figure 111. Spontaneous potential log of Unicoi State Park well 5. 135

MICROSECON.DS PER FOOT
ww.....
LL
z
X
ot-. w
Q
Figure 112. Acoustic velocity log of Unicoi State Park well 5. 136

OHMS 1000 1500 2000 2500 3000 3500 4000
0~-r~~~~r+~~~-r~~~~rT~~~~
50 100
.ww.... 150
IL
z 200 :..:.c..
Qwc. 250
300 350 400
Figure 113. Single-point resistivity log of Unicoi State Park well 5.
137

API GAMMA UNITS

0

100 200 300 400 500 800

0~~~~--~~--~--~~--+-----~----~

50

100

tww-
LL

150

z

X

t-
Qcw.

200

250

300

350

Figure 114. Natural gamma log of Unicoi State Park well 5. 138

70 ~

60

:::!

D.
C!J

50

-z

w
!ci

40

a:

Cz!J 30

I[

:E

....... w

::;)
D. 20

\0

J l

_,..

0 I I I I I I I I I I ' I I I I

III I

III I

I' I I

I I I I

I III

III I

I II I

II II

I I

0

300 600 900 1200 1500 1800 2100 2400 2700

TIME SINCE START IN MINUTES

Figure 115. Pumping rate during test of well 2 at Unicoi State Park.

TIME .SINCE PUMP START IN MINUTES 0 300 600 900 1200 1500 1800 2100 2400 2700 0

20

40

w ~ w LL 60

-~
0

-z

z 3:

80

0 c

~ 100

cC

120

140

160

Figure 116. Drawdown and recovery curves for well 2 at Unicoi State Park.

TIME SINCE PUMP START IN MINUTES 0 300 600 900 1200 1500 1800 2100 2400 2700 0

0.1

0.2

1ww-
lL 0.3

--~

-z
;z: 0.4
0
Q
~ 0.5

a:

Q

0.6

0.7

0.8

Figure 117. Drawdown and recovery curves for observation well 1 at Unicoi State Park.

TIME SINCE PUMP START IN MINUTES

0

300 600 900 1200 1500 1800 2100 2400 2700

0 L I I I I I I I I I i I I I

I Ii I

I' II

i II I

I' II

II iI

i ' i I

iI' I

I I I I

I ' I

0.1

...... 0.2 w w
u..

-~
N

-z 0.3
;z :
0c 0.4
~

a:

c 0.5

0.6
0.7......__ _ _ _ _ _ _ _ __l__ _ _ _ _ _ _ _ __j

Figure 118. Drawdown and recovery curves for observation well 2 at Unicoi State Park.

TIME SINCE PUMP START IN MINUTES

0

14400

28800

43200

57600

0

20

40

.....

w

w
1.1.

60

-z
z 80

-w+:o.

0=c=
~ 100

ca:

120

140

160

F1gure 119. Drawdown curve for wellS at Urucoi State Park during 41-day pumping test.

SUMMARY
The Georgia Geologic SuiVey sited two wells for Unicoi State Park, wells 2 and 5. Well 2 has a yield of 10 gpm after pumping for 24 hours. Wells 3 and 4, sited by others, had yields less than 5 gpm each and were used as obseiVation wells during the pumping test of well 2. Well 5 produced 130 gpm from numerous discontinuities and it sustained this yield for over 4 months of pumping. Well 5 produces more than the amount of water needed to sustain the park: however, the water is not potable due to a high sulfate content.
WATKINSVILLE, OCONEE COUNTY
INTRODUCTION
A high-yield, private water-supply well owned by Oconee Well Dr1llers, located in Watkinsville, Oconee County, about 8 mi south of Athens, was made avatlable to the Geologic SuiVey for testing to measure its hydrologic properties (Fig. 1). A second drtlled well, located 400 ft northwest. and a shallow bored well, located 1000 ft southwest of the pumping well, were used as monitoring wells.
GEOLOGY
Watkinsville lies in the Winder Slope District, a subdivision ofthe Piedmont Physiographic Province. Stream valleys in the Watkinsville area are gently concave and hlll tops are flat to gently convex. Valley floodplains are narrow, usually less than 100ft in width (Fig. 120). Most of the land surface is gently sloping. Relief is approximately 100ft. Intermittent streams exhibit trellis or rectangular drainage patterns. Straight streamvalleysegments nearWatkinsville trendN40"W, N15E, N50"E, andN78E. The test well is located in the valley of an intermittent, northwest-trending tributary of southeastflowing Porters Creek.
The study area is underlain by a redweathering biotite gneiss, red- to tan-weathering mica schist, red-weathering biotite granite, and ocher- to yellow-brown weathering amphibolite. Biotite granite occurs as dikes and pods in the

gneiss. Biotite schist is interlayered with the biotite gneiss on the scale of one inch to a few feet. Amphibolite occurs locally. Slllimanite mica schist occurs northeast of Watkinsville. Slllimanite mica schist and amphibolite are interlayered on a one foot scale.
Rocks in the study area have been polydeformed. The geologic map (Fig. 120) Ulustrates the complexity ofthe structures. Compositional layering strikes northeast and dips to the southeast and northwest.
Joints are spaced from one inch to several feet apart and their persistence along strike varies from one inch to several feet. Joint aperture in weathered and exposed rock is less than 0.1 in. Joints strike N40"E, N60"-80"E, and N36"W and have vertical to near vertical dips (Fig. 120, Table 11).
BOREHOLE GEOPHYSICS
Geophysical logs, including sonic televiewer, caliper, temperature, spontaneous potential, acoustic velocity logs, single-point resistance, and natural gamma, were run at the Watkinsville well (121-127). Examination ofthe logs indicates the presence ofwater-bearing zones at depths of 140-146ft, 150-152 ft. 347-348 ft. and 400-410 ft. Another water-bearing zone may be present at 20-21 ft.
The sonic televiewer log (Fig. 121a) and the caliper log (Fig. 122) indicate what appears to be a discontinuity at a depth of 20-21 ft. This, however, may actually be a zone where saprolite has "washed out" just below the base of the casing (16 ft). The sonic televiewer log indicates a potential water-bearing zone at 140-146 ft. consisting of a low-angle discontinuity dipping 29 SE, intersecting a high-angle discontinuity that dips 84SW (Fig. 121b). This zone also is characterized by increased borehole diameter on the caliper log, decreasing water temperature, and by anomalies on the spontaneous potential, single-point resistance, and acoustic velocity logs (Figs. 122-126). Two other potential waterbearing zones appear at 150-152 and 347-348 ft on the sonic televiewer logs (Figs. 121b and 121c) and are also indicated by anomalies on the caliper, temperature, spontaneous potential, resistance, and acoustic velocity logs. A large anomaly at 400-410 ft on the single-point resistance log correlates with anomalies on temperature, natural gamma, and acoustic velocity

144

N
t

-.-x :
A'xx
46
'

Base from

U.S. Geological SuNey

Watkinsville 1:24,000,

EXPLANATION

photorevised 19.86.

msch, A

Medium- to coarse-grained mica schist and medium- to coarse-grained amphibolite

I I bgn, bsch bgr + peg Coarse-grained contorted biotite gneiss and biotite schist intruded by coarse- grained

.

. porphyritic biotite granite and pegmatite

Strike and dip of compositional layering in metamorphic rock

Strike and dip of flow banding in granite

Strike and dip of vertical joint

Strike and dip of inclined joint

X

Outcrop

Pavement outcrop

Inferred contact



Pumping well



Observation well

0

.5 MILE

H H H

0

:5 KILOMETER

HHH

Figure 120. Geologic map of part of the Watkinsville Quadrangle and locations of the test well and obseiVation well.

145

Table 11. Watkinsville, joint orie11tatlons and descriptions

Imn1

om

N400E

900

N60" -800 E

900

N36W

900

Spacinq 1-2ft
1-2ft
2-6 in

Surface
curvilinear trend with smooth to irregular surface
curvilinear trend with irregular surface
curvilinear trend with smooth to irregular surface

Coatin~:
none
none
none

146

COMPASS QUADRANTS

N

E

s

w

N

ja) 20 21

22 b) 140
141

142 143

144
1wwu-. 145
z
146 :I:
1cwc.- 147
148

149

150

151
152
~ c) 346 347

348

Figure 121. Sonic televiewer log of the Watkinsvtlle well. 147

HOLE DIAMETER IN INCHES

0 0

1

2

3 I

4

5

.6 7
I

8
J

1

9 10

50 .

~~

100 ...
150
w.w.... 200
lL
z 250..
.X....
Q.
cw 300


.~ -
(
~

350 ..

~

400
J~
j
450 I-

500

Figure 122. Caliper log of Watkinsville well. 148

TEMPERATURE (Co)

14

15

16

17

18

19

20

o~~rT~rr~~rr~~rT~~~~~~~~

50

100

,..--

150

1ww- 200
u..
z
250
%
1acw.- 300

350

400

450

500._----------------------------------~

F1gure 123. Temperature log of Watkinsville well. 149

MILLIVOLTS

-800

-400

0

400

800

04-~~~--~~~-T~--r-~~-+~--r-~~

100

200
1ww-
u..
z 300
X 1-
Iwll.
Q 400

500

600

700~----------------------------------~

Figure 124. Spontaneous potential log of Watkinsville well. 150

MICROSECONDS PER FOOT

0

100

200

300

400

500

0+---~--~~~-4---T---+--~--~--~~

50

100

150
1ww- 200
u.
z
250
::J: 1-
c1w1. 300

350

400

450

500._----------------------------------~

Figure 125. Acoustic velocity log of Watkinsville well. 151

OHMS 1000 1500 2000 2500 3000 3500 4000
o~~~~~~~~~T4~~~~~~+-~~~
50 100 150
.wwu..... 200
z
.:.:.1..: 250 1w1. c
300 350 400 450
500~------------------------------------~
Figure 126. Single- point resistivity log of Watkinsville well.
152

logs. suggesting that this interval is another potential water-bearing zone not detected on sonic televieweror caliper logs. S1gniftcant natural gamma anomalies occur at about 275, and 332 ft (Fig. 127): however. their relationship, if any, to water-bearing characteristics of the well are unlmown.
The orientations of subsurface discontinuities were measured from the sonic televiewer log of the Watkinsville well. These orientations were plotted on equal area diagrams and compared with the orientations of compositional layering, joints, and straight valley segments measured at the surface. The strikes of discontinuities measured on the televiewer log (N75E and N80"E) are parallel to the strike of one joint set (N60"-80E) and nearly parallel to one linear streamvalleytrend (N80"-85 E) mapped
0
on the surface. This could indicate that the discontinuities observed on the sonic televiewer logs are joints and that the northeast-trending streams are structurally controlled. However, dips measured on the televiewer vary greatly (27NW, 29SE, and 84SW) and generally are of lower angle than dips of the corresponding surface joint set.
HYDROLOGIC TESTING
A 24-hour constant-rate pumping test was completed on the Watkinsville well using a submersible production pump and utility power. Discharge from the well flowed into a valley head. A pumping rate of 83 gpm was used throughout the test (Fig. 128). Drawdown and recovery curves generated from the test well data are somewhat irregular and asymmetrical (Fig. 129). Curves generated from the drilled observation well data are more regularbut also asymmetrical (Fig. 130). The bored observation well did not respond to the pumping.
SUMMARY
Hydrologic results indicate that the pumping well had a yield of 83 gpm for 24 the hours of the pumping test. Water was produced from discontinuities that were oriented parallel or subparallel to surface joint orientations but have varying degrees of dip.

GENERAL OBSERVATIONS
The Georgia Geologic Survey's efforts to locate high yield well sites and the testing of these and other wells in the Piedmont and Blue Ridge have yielded interesting preliminary hydrogeologic findings which merit comment and further investigation. The following is a discussion of some of the observations made during this phase of the project and of some of the possible future avenues for investigation.
WELL SITING
Certain factors have been identified which appear to aid in maximizing well yield when siting Piedmont wells. LeGrand (1967) described physiographic characteristics, such as topography and soil thickness, which appeared to correlate with high well yields in the Piedmont. Observations made during this study in the Piedmont and Blue Ridge confirm this relationship and have further refined well-siting methodology for these regions.
Wells completed in the crystalline rocks of the Blue Ridge and Piedmont Physiographic Provinces produce water from soil and saprolite and from voids in the unweathered rock. Ground water is channeled to wells via fractures, joints, weathered intervals, contacts or any other rock discontinuities intercepted by the well. The performance of a well, therefore. is controlled by the following factors:
1) the storage and transmission capabllities of the soil,
2) the storage and transmission capabilities ofthe discontinuity network, and
3) the hydraulic efficiency of the connection between the well bore and the discontinuities it intercepts.
An ideal Piedmont or Blue Ridge well would be constructed in a place where the well bore will intercept numerous discontinuities that are hydraulically connected to a thick, permeable regolith which is, in tum, hydraulically connected to one or more perennial streams. The ideal well would be ofrelatively large diameter (e.g., greater than 6 in.}, in order to intercept a larger surface area of water-bearing discontinuities to allow more efficient transmission of water to the well.

153

API GAMMA UNITS

0

100 200 300 400 500 600

0+-~--~~~~--~-+--~-4--~~~~~

50

100

150
.ww....
LL 200
z

.:.r..:. caw.

250

300

350

400

450

500~----------------------------------~

Figure 127. Natural gamma log ofWatldnsville well. 154

180~----------------------------------------------~

140

:::E 120
ID.
CJ

3 100
w t( a: 80

-VI

zaCJ:
:::E

60

::::)

ID.

VI

40

20

0 I I I ' I I I I I I I I I I I

I I I I

II I

III I

I' I I

I I II

II II

I I I'

I' I'

II I

0 300 600 900 1200 1500 1800 2100 2400 2700

TIME SINCE START IN MINUTES

Figure 128. Pumping rate durtng test of Watkinsville well.

TIME SINCE PUMP START IN MINUTES 0 300 600 900 1200 1500 1800 2100 2400 2700 0

10

20

1-

Hi 30

u..

z z 40

-VI

3: 0c 50

C1\

~

~ 60

c

70

80

90

F1gure 129. Drawdown and recovery cwves for Watklnsv1lle well.

TIME SINCE PUMP START IN MINUTES

0

300 600 900 1200 1500 1800 2100 2400 2700

o~ucc:: l l ,l l l . , , , , , , , , l l l

1

1w- 2 w

1.1.

-z 3

-Ul

z 0c== 4

-...I

~

c~ 5

6

7._------------------------------------------------~

Figure 130. Drawdown and recovery curves for Watldnsv11le observation well.

This well also would be close enough to required utilities to reduce development costs, and it would be shallow (less than 400 ft) to minimize construction costs.
Ideal conditions rarely occur. Compromises are necessary, but the hydrogeologic siting criteria for the well system should not be the area for compromise. Wells must be properly placed if they are expected to produce high reliable yields. Almost certainly, wells sited on the basis of convenience will have lower yields.
Well performance factors, such as those discussed above, reflect soU and btdrock characteristics which can not be observed directly prior to completion of a well. Thus, well siting in the Piedmont and Blue Ridge Provinces is difficult, but possible, using a comprehensive geological approach. Methods of topographic analysis, such as the LeGrand Method, only indirectly address geologic factors critical to well performance. Geologic structure, compositional layering and the weathering characteristics of the rocks, which are observable and mappable in the field, must also be considered.
The topographic features of the Piedmont and Blue Ridge Provinces, when closely examined, reflect the geologic structure and weathering characteristics of the rocks on which they are developed. Areas offractured and highly weathered rock are frequently expressed topographically as valleys and draws, serve to trap and channel water, and should be exploited in the placement ofwells. The lowest elevations within these valleys appear to produce the highest yields, possibly due to a combination of high water table and, in many cases, a thick soil/ saprolite or alluvium acting as a ground-water reservoir.
Rock discontinuities, such as foliations, compositional layering, joints and fractures, may serve to channel ground water from the soil/ saprolite reservoir to the well. Locating wells at intersections of such discontinuities will generally maximize yield. Soil thickness at the well head itself, long regarded as a predictor of well yield, can not always guarantee a good yield. Wells located in areas ofshallow soil may intercept discontinuities which drain ground-water reservoirs located some distance away or, conversely, a well may penetrate a thick soU which does not readily transmit water because of limited discontinuities in the underlying bedrock.
Astructural analysis ofrockdiscontinuities, along with topographic analysis, has been the

most reliable method found by this study for siting wells in the Piedmont and Blue Ridge Provinces. The relationship between topography and bedrock characteristics is complex, but it must be understood if a well .is to be optimally sited.
HYDROLOGIC TESTING
Pumping tests conducted by the Geologic Survey on wells in the Piedmont and Blue Ridge have yielded some interesting results. Each test yielded a unique set of results indicating the highly variable nature of the hydrogeologic system in the Piedmont and Blue Ridge Provinces. The importance of monitoring water-level recovery, rather than just drawdown, was demonstrated by pumping test results. Recovery response may present a truer picture of long term well yield than does the drawdown curve, because the effects of pump performance, variations in pumping rate, and turbulence caused by the pumping are not present. Drawdown and recovery curves demonstrate another signJftcant aspect of crystalline rock hydrology: well behavior can not be reliably predicted using classical analytical methods. Since the assumptions governing the application of the Theis equation are not met, transmissivity and storativity have no clear physical meaning in aquifers formed of discontinuities in crystalline rocks. Further, such a well changes performance characteristics over time as the well is pumped and the discontinuities are de-watered.
RECOMMENDATIONS
This study demonstrates that ground water in the Piedmont and Blue Ridge Provinces has the potential to be a reliable source for public drinking water supplies and for light industrial and commercial uses. Further refinements in well-siting methodology are needed, as well as a more complete understanding of the performance characteristics of crystalline-rock wells. Development of ground water to provide or supplement water supplies in the future will depend on the accuracy with which high-yielding wells can be sited and on the degree to which the long-term performance of such wells can be predicted. Further research in crystalline-rock hydrology should address the question of how

158

best to site high-yielding wells without the need for expensive preliminary investigations or testing.
Many drillers familiar with finding water in the Piedmont and Blue Ridge report that approximately 5-7 percent of randomly drilled domestic wells have a high yield potential (greater than 50 gpm). Observations from this study indicate that the high yield wells lie in identifiable geologic structures. The structures which can be identified as representing potential highyield sites probably occupy only 5 percent of the land area or less. Thus, rational development of ground-water resources in the Piedmont/Blue Ridge may require developers of water supplies to obtain drilling sites or water rights in places more remote from their treatment or distribution systems than they usually have in the past.
Since almost all ground-water in the Piedmont/Blue Ridge can be considered as being part of the surface or water table aquifer, it is quite prone to pollution from man-made sources. Special ground-water protection efforts should be directed towards those geological environments in which the high yield well sites may be located.
REFERENCES
Arora, R., ed., 1984, Hydrogeologic evaluation for underground injection control in north Georgia: Georgia Geologic Survey, Hydrologic Atlas 12, 18 plates.
Atkins, R L., and Higgins, M. W., 1980, Superimposed folding and its bearing on the geologic history of the Atlanta, Georgia
m. area, Excursions in Southeastern Geol-
ogy: American Geological Institute, v. 1, p. 19-40.
Carter, R W., and Herrick, S. M., 1951, Water resources of the Atlanta metropolitan area: U.S. Geological Survey, Circular 148, 19 p.
Clark, W.Z., Jr., and Zisa, A.C., 1976, Physiographic map of Georgia: Georgia Geologic Survey, scale 1:2,000,000.
Cressler, C. W., Blanchard, H. E.,Jr., and Hester, W. G., 1979, Geohydrology of Bartow,

Cherokee, and Forsyth Counties, Georgia: Georgia Geologic Survey, Information Circular 50, 45 p.
Cressler, C. W., Thurmond, C. J., and Hester, W. G., 1983, Ground water in the Greater Atlanta Region, Georgia: Georgia Geologic Survey, Information Circular 63, 144 p.
German, J. M., 1985, The geology of the northeastern portion of the Dahlonega gold belt: Georgia Geologic Survey, Bulletin 100, 41 p.
Gillon, K. A, 1982, Structural, metamorphic and economic geology of the Cowrock and Helen, Georgia 7 1/2' quadrangles: M.S. Thesis, University of Georgia (unpublished), 236 p.
Gorday, L. L., 1989, Hydrogeology of Lamar County, Georgia: Georgia Geologic Survey, Information Circular 80, 40 p.
Higgins, M. W., and Atkins, R L., 1981, The stratigraphy of the Piedmont southeast of the Brevard zone in the Atlanta, Georgia, area: .1n Wigley, P. B., ed., Latest thinking on the stratigraphy of selected areas in Georgia: Georgia Geologic Survey, Information Circular, 54-A. p. 3-40.
Higgins, M. W., Atkins, R L., Crawford, T. J., Crawford, R. F., Brooks, Rebekah, and Cook, R. B., 1986, The structure, stratigraphy, tectonostratigraphy, and evolution of the southernmost part of the Appalachian orogeny: U.S. Geological Survey, Open File Report 86-372, 162 p.
Keys, W. S.. and MacCary, L. M., 1971, Application of borehole geophysics to water-resources investigations: Techniques of Water-Resources Investigations of the U. S. Geological Survey, Book2, ChapterE1, 126 p.
LeGrand, H. E.. 1967, Ground water of the Piedmont and Blue Ridge Provinces in the

159

southeastern States: U. S. Geological Survey, Circular 538, 11 p.
McCallie, S. W., 1908, A preliminary report on the underground waters of Georgia: Georgia Geologic Survey, Bulletin 15, 370 p.
McCollum, M.J., 1966, Ground-water resources and geology of Rockdale County, Georgia: Georgia Geologic Survey, Information Circular 33, 93 p.
Radtke, D. B., Cressler, C. W., Perlman, H. A, Blanchard, H. E., Jr., McFadden, K, W., and Brooks, Rebekah, 1986, Occurrence and avatlabllity of ground water in the Atijens region, northeastern Georgia: U. S. 6~o logical Survey, Water-Resources Investigations Report 86-4075, 79 p.
Schmitt, T. J., Atkins, R L., Gorday, L. L., and Lineback, J. A, 1991, Geophysical and geologic investigations ofwater-well sites at Unicoi and Amicalola Falls State Parks: Georgia Geologic Survey Open File Report 91-2.
Sever, C. W., 1964, Geology and groundwater resources of crystall1ne rocks, Dawson County, Georgia: Georgia Geologic Survey, Information Circular 30, 32 p.
Steele, W. M., Atkins, R L., Brackett, D. A. and Schmitt, T. J., 1988, Orientation of fractures measured from sonic televiewerlogs of selected crystalline rock wells in the Piedmont and Blue Ridge Physiographic Provinces of Georgia: International Conference on Fluid Flow in Fractured Rocks, in press.
Stewart,J. W., and Herrick, S.M., 1963, Emergency water supplies for the Atlanta area in a national disaster: Georgia Geologic Survey, Special Publication No. 1, 24 p.
160

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