Considerations for the use of topographic lineaments in siting water wells in the Piedmont and Blue Ridge physiographic provinces of Georgia

CONSIDERATIONS FOR THE USE OF TOPOGRAPmC LINEAMENTS
IN SITING WATER W. ELLS IN THE PIEDMONT AND BLUE RIDGE
PHYSIOGRAPmC PROVINCES OF GEORGIA
Madeleine F. Kellam David A. Brackett William M. Steele
----------
Georgia Geologic Smvey Environmental Protection Division Department of Natural Resources
INFORMATION CIRCULAR 91

CONSIDERATIONS FOR THE USE OF TOPOGRAPffiC LINEAMENTS.
IN SITING WATER WELLS IN THE PIEDMONT AND BLUE RIDGE
PHYSIOGRAPffiC PROVINCES OF GEORGIA
Madeleine F. Kellam David A Brackett William M. Steele

Georgia Department of Natural Resources

I .

Joe D. Tanner, Commissioner

Environmental Protection Division Harold F. Reheis, Director

Georgia Geologic Smvey William H. McLemore, State Geologist

Atlanta 1993
INFORMATION CIRCULAR 91

TABLE OF CONTENTS
IN'IRODUCTION .. ...... .. .... ... ... ...... ... ... ... ... ... .. .... ... ... ... ... ... ... ... ... ... ... ... ... ... .. ....... ... ...... ... ... ... ... ... .. 1 GEORGIA'S WA'IER RESOURCES ........................................................... ............. 1 WliT USE GROUND WA'IER? ........ ......................................................... .............. 1
.AREAOFSTUDY........................................................................................................................ 2 PHYSIOGRAPfiY AND SURFACE DRAINAGE .. ...................................................... 2 GEOWGY ........................................................................................................... 2
PRE'VIOUS WORK...................................................................................................................... 4 CRYSf.ALLINE-ROCK AQUIFERS ..... ... ........................ ............ .................................... ............... 4
WlfAT IS AN AQUIFER? ...................................... ................................................. 4 DEVEWPMENr OF CRYSf.ALUNE-ROCKAQUIFERS ........................................... 4 THE NATURE OF CRYSfALLINE-ROCKAQUIFERS ............................................... 6 UNEAMENTS AND THEIR USE IN WELL SITING IN THE PIEDMONT AND BLUE RIDGE PfiYSIOGRAPHIC PRO'VINCES .. ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... ... .. 6 RECOGNIZING UNEAMENTS ON TOPOGRAPHIC MAPS ................................ ....... 8 CON'TR.OLS ON LINEAMENT FORMATION ........... .................. ............ ................... 8
Discontinuities ................. ....................................... ...... ... ........................ 8 Joints ........................................................................................... 8 Faults ........................................................................................... 11 Lithologic Contacts ........................................................................ 11 Compositional Layering and Foliation ............................................. ll
Rock Type ................................................................................................ 11 WELL SITING USING TOPOGRAPHIC UNEAMENTS .................................................................... 16
WA'IER QUAI.JIY ISSUES .................................................................................... 16 PRACTICAL CONSIDERATIONS FOR WELL SmNG USING UNEAMENTS ..................................... 20
USE OF WElL-SITING PROFESSIONALS .............................................................. 20 COSf CONSIDERATIONS .................................................................................... 21 SUMMARY ................................................................................................................................. 21 REFERENCES ...........................................................................................................................22
iii

LIST OF FIGURES
Figure 1. Location of study area showing extent of the Piedmont and Blue Ridge Physiographic Provinces ................................... ............ ..................... ........................... 3
Figure 2. Representative rock textures: a. Sedimentary b. Igneous c. Metamorphic ....................... 5 Figure 3. A typical crystalline-rock aquifer (a). Schematic diagram showing saprolite and
fracture network yielding water to a well (b).............................................................. 7 Figure 4. Representative straight stream valley segments ............................ .... ........................... .. 9 Figure 5. Well-developed jointing in schist, Fulton County, Georgia ............................................... lO Figure 6. View across a linear topographic depression formed along the contact between a
sheared gneiss and a garnet-feldspar-quartz-muscovite schist in Carroll County, Georgia ........................................................................................................................ 12 Figure 7. A straight stream valley segment developed at the contact (dashed line) between a sheared gneiss and a garnet-feldspar-quartz-muscovite-schist ..................................... 13 Figure 8. Differential weathering along compositional layering in schist, Fulton County, Georgia ........................................................................................................................ 14 Figure 9. Drainage styles: a. Dendritic b. Rectangular ................................................................ 15 Figure 10. A structurally controlled stream segment, I..amar County, Georgia ................................ 17 Figure 11. Placement ofwells with respect to discontinuities ......................................................... 18 Figure 12. Proper well placement for maximum yield within a drainage basin ................................ 19
iv

CONSIDERATIONS FOR THE USE OF TOPOGRAPHIC LINEAMENTS IN SITING WATER WELLS IN THE PIEDMONT AND BLUE RIDGE PHYSIOGRAPHIC PROVINCES OF GEORGIA

Madeleine F. Kellam David A Brackett William M. Steele

INTRODUCTION
GEORGIA'S WATER RESOURCES

bility to pollution,smaller capital investment, and shorter development time. In addition, ground water development leaves the land free for other uses (Heath and Giese, 1980). Although suiface

North Georgia is blessed with an abundance of water. Rainfall is plentiful, and the area is drained bynumerousstreams and rivers that arise inits mountains.North Georgia's suifacewaterhas

water will continue to supply the bulk of water needs in north Georgia, in many cases ground water will represent the best option for additional water supplies.

beenharnessedfor powergenerationand storedfor industrial, municipal and recreational use by the WHY USE GROUND WATER?

construction of dams. Modem water systems deliverample amounts ofcleanwaterdirectlyto our

Why hasn't north Georgia's supply ofground

homes and places ofbusiness using a combination water been more extensively utilized? Because

of reservoirs, treatment plants and water lines.In ground water in the region has an unearned repu1990, suifacewaterusewas estimatedto begreater___tation for being difficult to locate in large quantities_ _~-~---
--- ------than 590 million gallons per day (Fanning et al., and unreliable in times of drought.

1992).

For centuries, wells have been used for water

In additionto its surface-watersupplies, north supplyin nort:J:,l Georgia. Inthe past, wellswere dug

Georgia also has large reserves of ground water by hand, down to the water table. Water was

which can be tapped using water wells. Ninety-six brought to the surface with a rope and bucket, or

million gallons per day of ground water were used by means of a hand-turned crank. And how was

in 1990 (Fanning et al., 1992). This represents only the site for a well chosen? The well was simply dug

a fraction of the ground water available for use in close to the house for the sake of convenience.

the region. But with north Georgia's abundant Sometimes the local dowser, or "water witch,"

suiface-watersupplies, whywould anyone want to chose a site using a forked stick Some of these

use ground water in this day and age?

shallow wells yielded enough water; some did not.

The reason is that the population of north

The development of technology has changed

Georgia is growing at a rapid rate. Population was the business of drilling water wells. Modem wells

estimatedat3,300,000in 1985, andanincreaseof in north Georgia are drilled using powerful pneu-

1,000,000 is projected by the year 2000 (Bachtel, matic rigs that can drill hundreds of feet through

1987). This growth brings increased demand for solid rock in a single day. Electric pumps can

water. Surface water resources are already heavily deliver water to the suiface without the need for

utilized. Newsourceswill have to be found to supply manual labor. These deeper wells rarely go dry in

future needs. Also,the cost ofdeveloping newwater times of drought. And how is the modem well site

supplies will have to be carefully considered. In chosen? Today many well sites are still chosen for

many cases, ground water supplies can be devel- convenience, orbythelocaldowser. Some ofthese

oped at a lower per unit cost than suiface water. wells yield enough water; some do not.

Some of the benefits of developing ground

Well sites chosen for convenience rather than

water supplies include a simpler permitting for sound geological reasons often do not produce

process,Iower water treatment cost, less suscepti- large, sustainable amounts of water. Although

1

generally adequate for household supply, these poorly sited, low-yielding wells help to perpetuate the idea that ground water is not a viable watersupply option where large yields are required for municipal, or industrial supply. Because ground water may represent the best, or only, option for manycommunities andindustriesinsome areas of north Georgia, there has been concern over how to reliably locate adequate supplies.
In recentyears, hydrogeologists have focused their attention on ways to define areas in which high well yiel9.s can be expected. This has entailed studying the geologic factors which influence the occurrence of ground water in the metamorphic and igneous rocks of north Georgia in order to recognize areas where such geologic factors produce good potential for high well yields. Using features observed on the land surface, geologists are able to concentrate their search for ground water in the areas with the best potential for high yields. There are numerous examples, among geologically sited wells, of yields in excess of 100 gallons per minute (gpm) sustainable for many years(Cressleretal., 1983). Everyyearthevolume ofgeologic knowledge increases, further improving the probability of scientifically locating adequate and reliable sources of ground water in north Georgia.
The Geologic Survey Branch of the Georgia Environmental Protection Division initiated a program in 1987 to study the occurrence of ground water in North Georgia and to develop methods to site high-yielding wells using geological criteria. Thispapersummarizes some ofthosefindings. The following discussion focuses on the use of topographic lineaments, one type ofgeologic feature, to aid in siting wells.
There are a number of definitions of lineaments, but all have certain things in common. Lineaments are linear features that are visible on aerial photographs ortopographicmaps. Theycan include such features as straight segments of streams, linear valleys, linear depressions, and aligned gaps in ridges. Most lineaments are negative, or topographically low, features; although sometimes straight ridges are also called lineaments. Cultural features, such as roads, do not qualify as lineaments.
This study focused primarily on lineaments visible on topographic maps, and their use in well siting in north Georgia. Evaluation of the siteselection criteria, for over 190 well sites in 36 counties in the Piedmont and Blue Ridge Physiographic Provinces, revealed some useful observations about the use of topographic lineaments in well siting. Although far from definitive, this paper outlines some ofthe practical considerations, posi-

tive and negative, inherent in this method of well siting. The use of lineaments in well siting has evolved over a number of years, in a number of geologic settings around the world. Although still being refined inthe Southeast, this method can be useful to those attempting to locate sites for potentially high-yielding wells.
Thispublicationwaswrittenforthosewho are not trained in geology or hydrogeology, but who will, nevertheless, be called upon to make wellsiting decisions. These include well drillers, water system managers, engineers, and others in industry, government and the general public who are seeking to develop _ground water supplies. Although not a "how-to" manual, it introduces the conceptsbehindwell sitingincrystalline-rockaquifers, particularly with regard to the use of lineaments. It also explores some of the issues which should be considered in any well-siting decision. Finally, it offers guidelines for selecting a registered professional geologist to aid inwell siting and a well drilling contractor to drill the well.
AREA OF STUDY
The study area encompasses the Piedmont and Blue Ridge Physiographic Provinces (Figure 1). These Provinces extend across the greater part of 62 Georgia counties, an area of approximately 19,500 square miles. Data were collected from numerous well siteswithinthis region; however, no attemptcouldbe made to provide complete or equal coverage of all 62 counties within the study area. The largest cities located within the Piedmont and Blue Ridge include Atlanta, Athens, Carrollton, Cartersville, Decatur, Douglasville, Gainesville, Griffin, LaGrange, Marietta, Newnan, Roswell, and Toccoa.
PHYSIOGRAPHY AND SURFACE DRAINAGE
In Georgia, the Piedmont and Blue Ridge Physiographic Provinces are bounded on the west bythe Emerson-Great SmokyFault. The Piedmont is a rolling upland, bounded on the south by the Fall Line and on the north by the Blue Ridge. The Blue Ridge is a rugged upland, distinguished from the Piedmont Province chiefly on the basis of its greater topographic relief.
Most of the major river systems of Georgia arise inthe Piedmont and BlueRidge Physiographic Provinces. Major rivers which drain these provinces include the Chattahoochee, Flint, Ocmulgee, and Savannah Rivers and their tributaries.
GEOLOGY
The Blue Ridge and Piedmont Physiographic Provinces are underlain by geologically complex

2

BLUE RIDGE
F:igure 1. Location of study area showing extent of the Piedmont and Blue Ridge Physiographic Provinces. 3

metamorphic and :Igneous rocks. The most common rocks are gneisses and schists, into which :Igneous rocks, chiefly granite, have been intruded. Otherintrusive rocks include pegmatite, and mafic and ultramafic intrusives. Thin dikes of diabase are also common and tend to cut across regional strike (Herrick and LeGrand, 1949). The rocks of the Piedmont andBlueRidgehavebeenextensively folded and faulted, further complicating the already complex geologic picture.
PREVIOUS WORK
Inthe search for ground water in north Georgia, itwasrecognized quite earlythat a relationship existedbetweentopographyandwellyield. LeGrand (1967) used this relationship to develop a means of siting wells with an increased probability of large yield. He recommended a method of siting wells with regard to topographic setting combined with soil thickness. He noted that draws and valleys, combined with thick soil, produced higher yields than slopes and ridges with thin soil. By rating topographic setting and soil thickness independently, potential well sites could be ranked and compared.
Cressler et al. (1983), in a comprehensive .study of ground water in the Greater Atlanta Region, described well yields as being influenced by various geologic features, some of which were expressed topographically. Among these were lithologic contacts, faults, and small-scalefeatures such asjoints, compositional layers, and foliation.
The study of lineaments as a class of topographic feature was developed by La.ttman (1958), using aerialphotographs. A studybyLa.ttmanand Parizek (1964) related well yield to proximity to single fracture traces and fracture trace intersections. The use of lineaments and fracture trace analysis rapidlygained acceptance as a method for identifying sites for potential high-yielding wells and has resultedinnumerous otherstudies onthe use of lineaments to locate areas where good well yields can be expected.
CRYSTALLINE-ROCK AQUIFERS
WHAT IS AN AQUIFER?
The concept of an aquifer is fundamental to the understanding ofany method ofwell siting: An aquifer is a rock unit that stores water and transmits thatwaterto wells. In sedimentary rock areas such as the Coastal Plain of south Georgia, rocks are formed of individual grains which have been cementedtogether. A great deal ofpore space is left between these grains (Figure 2a). The porous nature ofthese rocks allows them to act much like

giant sponges, taking in and storing great quantities ofwater in a process called recharge. Porousrock aquifers yield the stored water easily to wells tapping the rocks.
The Piedmont and Blue Ridge Physiographic Provinces of north Georgia are composed ofmetamorphic and :Igneous, or crystalline, rocks. Most metamorphic and :Igneous rocks contain very little primary, or original, pore space. Weathering and fracturing, however, produce secondary openings in these rocks which allow them to store and transmitwater:. Thus,the deformationalandweathering history of metamorphic and :Igneous rocks determine their properties as aquifers.
DEVELOPMENT OF CRYSTALLINE-ROCK
AQUIFERS
To understand the nature ofa crystalline rock aquifer, let us examinethe "life history" ofa crystalline rock. The earth is a dynamic place, and movementswithin its rocky crust result from enormous forces. When these forces act on rocks, tremendous strain results. Igneous rocks are formed when heat and pressure within the earth increase to the point at which materials of the earth's crust melt. The resulting liquid cools and crystallizes into solid rock as it comes nearer the surface ofthe earth. The rock textures that result are interlocking grains (Figure 2b). Metamorphic rocks are formed when sedimentary or :Igneous rocks are subjectedtoheatorpressurehigh enough to cause the grains ofthe rockto recrystallize. The resulting rocks also have a texture composed of interlocking grains (Figure 2c) and are often more dense and less porous than the original rock.
The conditions that produce crystalline rocks occur deep within the earth. Sooner or later, however, these rocks are exposed at the surface of the earth. They are pushed up and uncovered slowlythrough erosionofthe overlyingmaterial. As these rocks approach the surface, weathering begins. Weathering is a complex series of processes which combine to cause rocks to decompose mechanically and chemically.
Mechanical weathering occurs when rocks are broken by physical forces. One type of mechanical weathering is expansion of rock due to unloading. As erosion lessens the confining pressure on rock which was once deep in the ground, the rock responds to the decrease in pressure by breaking into sheetlike layers parallel to the surface. Another important type ofphysical weatherIng is the expansion of water as it freezes. The freezing water acts as a wedge to break the rock apart.

4

a.

-----1----

b.

c.

Figure 2. Representative rock textures: a. Sedimentazy b. Igneous c. Metamorphic. 5

One type ofchemicalweathering occurswhen rain water combines with other elements in the earth's atmosphere or in the soil to produce acids that chemically alter the rock. Chemical weathering changes the composition and texture of the rock, usually resulting in a more porous material than the original rock.
Mechanicalandchemicalweatheringtogether produce soil and a mass of decayed rock called saprolite. The porous nature of soil and saprolite allows it to store water. In the Piedmont and Blue Ridge, where the rocks themselves are too dense to store s:lgnificant quantities of water, the overlying soil and saprolite act as an :Important reservoir for ground water storage. They are, thus, a vital component ofccystalline-rock aquifers. The depth and extent ofthis soil and saprolite reservoir determines, in large part, the amount ofwater a ccystalline-rock aquifer will yield.
Weathering and development ofsaprolitegenerallyproceedfromthe surfacedownwards. Weathering processes do not proceed unifonnly in all directions, however. Many factors influence the rate ofweathering, and, thus, the extent ofsaprolite development in any given area. Joints and faults, two types of fractures, are among these factors.
Joints are plane fractures or sets of parallel plane fractures inthe rocks, alongwhich there has beenno movement. Intersectingjointsetsproduce angular blocks within a rock mass.
Faults are fractures along which there has been movement parallel to the break. Rocks on either side of the fault may have moved past each other ho~ntally or have been pushed up or dropped down relative to each other. Rocks in the vicinity of a fault may be broken or crushed.
Fractures such as joints and faults also provide paths of attack for both mechanical and chemical weathering. The more highly fractured a rock is the more surface area it presents to chemical weathering. Because of this, highly fractured areas often develop a thick layer of saprolite. The porous saprolite receives and stores water from precipitation which, in turn, allows more chemical weathering. Through progressive decomposition, weathering can also widen the openings of individual fractures.
Other types of openings in metamorphic and igneous rocks can also present opportunities for enhanced rates ofchemicalweathering. Metamorphic and :Igneous rocks may contain layers of vacying mineral composition. Metamorphism can also produce a type of layering called foliation. These planarlayers ofvacying composition present opportunities for chemical reactions. These features of the rock, along with fractures, are collectively called discontinuities.

Discontinuities are :Important in water well siting. They include any feature, at any scale, that interrupts the homogeneity of a rock mass. Discontinuitiesincludevariations inrockcomposition such as foliation, compositional layers, and lithologic contacts, as well as breaks in the rocks such as joints and faults. These features all have the potential to provide pathwaysfor ground-water movement.
THE NATURE OF CRYSTALLINE-ROCK AQUIFERS
Ccystalline-rockaquifersare a combinationof a soil and saprolite reservoir that collects and stores recharge water from precipitation, and a network of discontinuities in less weathered bedrock that acts to deliver water to the well. When a well is drilled, these two components will influence the amount ofwater the well will yield over t:fme. A larger soil and saprolite reservoir means that more water is potentially available to the well (Figure 3). This factor alone, however, can't guarantee a good well. A network of discontinuities intercepting the saprolitemust also bepresentin orderforthewater to be delivered.to the well. And, naturally, the more extensive this. network is, the larger the area of saprolite reservoir the well will tap. Also, the well must intercept one or more of the individual discontinuities in this network, or there will be no pathway for water to enter the bore hole.
Thus, the areas with the greatest potential for high-yielding wells are those which are most permeable, which allowrecharge and storage ofground water, and those areas which have a network of discontinuities to deliver water to the well. The difficulty in choosing such areas in metamorphic and igneous rocks ofthe Piedmont and Blue Ridge Physiographic Provinces is that most ofthegeologic factors which will dete~e the success of wells are covered by soil and vegetation and so are difficultto see and measure. Surfacefeatures such as topographic lineaments can provide valuable clues to the nature of the aquifer. Lineament analysis can help indicate areas with high wellyield potential when used in combinationwith field inspection of the local geology.
LINEAMENTS AND THEIR USE IN WElL SITING IN THE
PIEDMONT AND BLUE RIDGE PHYSIOGRAPHIC PROVINCES
North Georgia is heavily wooded and possesses considerable relief developed on complexly foldedandfaultedmetamorphic and igneousrocks. In this area, topographic lineament analysis com-

6

a. b.
~Well
BEDROCK Figure 3. Atypical cxystalline-rock aquifer: (a) Schematic diagram showing saprolite andfracture network yielding water to a well (b). (After Heath and Giese, 1980.)
7

bined with geologic mapping, is a useful technique for well siting. In order to apply this technique successfully, it is necessary to learn to recognize lineaments on topographic maps and to understand the factors which control their formation.
RECOGNIZING LINEAMENTS ON TOPOGRAPHIC MAPS
Recognizing lineaments ontopographicmaps is not a matter of absolutes. In most cases, a lineament is evaluated by its relative appearance, that is, how it compares with other features ofthe surroundingtopography. Itshouldbe kept inmind that learning to recognize lineaments on topographic maps is not an end in itself, but a means to focus a complete investigation.
The most common type oftopographic lineament is a straight stream valley segment. All streams change direction many times over their length, butwhere a planardiscontinuityintersects the land surface, a stream may conform to the discontinuity, resultinginadistinctlylinearstream segment (Figure 4). Faults, joints, lithologic contacts, compositional layers or any other type of discontinuity can produce such straight stream segments.
Not all topographic lineaments are stream valley segments. Some lineaments will be linear valleys, or11series ofalignedvalleys, oralignedgaps in ridges. Breaks in slope or abrupt changes in the characterofthe topographymay alsobeconsidered topographic lineaments. A lineament may be continuous across several topographic features. For example, a linear stream segment may be aligned with a gap in a ridge and with a linearvalley across the ridge. Linear changes in natural vegetation are considered lineaments on aerial photographs, but they are not often visible on topographic maps.
Because locatingwells at lineament intersections has the potential to improve well yields, recognizingtheseintersections ontopographicmaps is important. Intersections can be of two types: truncating, or "T"-shaped intersections and transcending, or "X'-shaped intersections. Well siting experience bythe Georgia Geologic Surveytends to confirm that transcending intersections produce higher well yields than truncating intersections, but this observation has not been quantified.
In rare cases, there are certain cultural features visible on topographic maps which may be mistaken for lineaments. Examples include abandoned roads and channelized streams that can be mistaken forjoint-controlled streams. Linear vegetational changes on topographic maps are often the result ofland-clearing activity orfence lines. In

most cases, inspection of the site will make clear the cultural origin of these features.
CONTROLS ON LINEAMENT FORMATION
Dlscontlnuitles
Discontinuities in rocks fall into two broad types, fractures and compositional differences. Manylinearfeatures inthe Piedmont are causedby steeply dippingfractures inthe rock, such asjoints and fault zones. Other causes include differential weathering along lithologic contacts, tilted layers of vru:ying composition, and foliation produced by metamorphism. All of these are discussed below.
Joints
Joints are the most common type offracture seen in rocks (Lahee, 1961). They are produced when rocks are subjected to compression, tension, or torsion. These stresses can be accompanied by emplacement of igneous rock masses, and are a part of the same processes which produce folding and faulting of rocks. Although intrusive igneous rocks can containjoints, well-developedjointing is more common in layered rocks (Figure 5).
The importance ofjointsinthe development of topography is stated by Lahee (1961, p. 282). "In promoting erosion they Uoints] are of the utmost importance, for they serve as channels for decomposition, they facilitate the wedge action of ice in disintegration...and they invite concentrated attackby abrasive agents." He further states that"... ithas been demonstrated thatthe patternofdrainage and topography in a region often reveals a marked dependence upon the existing fracture systems."
Joints are produced in sets, all the joints in one sethaving approximatelythe same orientation. Sometimes a series, or set, of lineaments is developed on a joint set, all the lineaments having similarorientations. Becausejoints are so numerous and tend to be concentrated in a given area, it is common to see linear stream segments or linear valleys developed on an area ofconcentratedjointing. These areas may produce very high wellyields because intensified weathering may produce a thick layer of soil and saprolite which will store water, and the joints provide a network of discontinuities to channel the water to wells.
Intersectlngjoint sets are oftenperpendicular to one another. Angular relationships between two or more lineaments or sets of lineaments, such as abrupt changes in the courses of streams, suggest joint control. Lahee (1961, p. 282) states that"... the elbow turns in many young streams are not

8

53ase map from _u._S. G._~ 1 :24!000 topog~apl]ic_117_ap,_Locust Grove, G,tJ..~_L96!14 photorevised_1973_._ _~-1E=-3r--,---,E=-3--,---TE=-13/-2-~--TE=-3---r--oE=-3--~---r0~----------------------------------~ MILE
CONTOUR INTERVAL 20 FEET NATIONAL GEODETIC VERTICAL DATUM OF 1929
Figure 4. Representative straight stream valley segments. A Locust Grove municipal well located on the NE-trending segment yielded 180 gpm (air lift yield). Locust Grove topographic quadrangle.
9

Figure 5. Well-developed jointing in schist, Fulton County, Georgia. 10

infrequently due to a shift of the current from one joint set to another." Other causes could include a shift from a joint set to any other planar feature, such as compositional layering or lithologic contacts.
Faults

developed on the schist is charactertzed by linear valleys. Outcrops for the most part are confined to road cuts and stream valleys. Wells completed in the schist are adequate for household supply. But one well near the contact, sited using geologic criterta, yielded in excess of 100 gpm (Crawford, personal communication).

Abrupt offsets of drainages and streams, or Compositional Layering and Foliation abrupt changes in linear topography can some-

times indicate the presence ofa fault (Cressler et al. 1983). But, although theytypicallycontainbroken rock, faults do not always produce lineaments, or result in increased well yields. The heat and pressure generated along a fault canproduce rocks that are more dense and more resistant to weathering than the original rocks. In some cases, however, rocks ofvery different weathering characteristics are brought together along a fault, and enhanced weathering of the less resistant rock occurs. In such cases, weathering of the less resistant rock may produce a linear valley or depression along the trend of the fault, or there may

Although they are produced in different ways, compositional layering and foliation have sim:ilar effects on the weathering characteristics of rocks. Because these discontinuities are layers ofvarying mineral composition, they provide avenues for chemicalweatheringto proceed more rapidly inthe less resistant layers (Figure 8). Compositional layering and foliation can be areally extensive and may produce large weathered zoneswith considerable potential for high yielding wells. However, the scale ofsuch discontinuities is not large enough to produce topographic lineaments.

be a change in the character of the topography

Rock Type

across the fault. Faults that juxtapose different rock types may result in differential weathering, thus ,producing areas of enhanced permeability with good well-yield potential.

Rocktype exerts a fundamental control onthe development of topographic lineaments. First, it affects the probability that rocks will be layered or jointed, two factors that favor lineament develop-

Lithologic Contacts

ment. Second, rock type determines the relative degree of weathering that the rocks will undergo.

A lithologic contact is the surface between two

Massive crystalline rocks, such as granite,

-----contiguous rockmasses ofdifferent lithologic char- produce fewer topographic lineaments than lay- - - -

acter (Lahee, 1961). The two contiguous rock types eredrocks. Massiverockscontainfewdiscontinuities

often have very different physical and chemical along which differential weathering can occur to

charactertstics, and these contacts can be areas of produce lineaments. This is illustrated.by studies

enhanced chemical weathering. In such cases, of drainage patterns in massive igneous rocks.

lithologic contact zones may be represented on the These rocks usually exhibit a dendritic drainage

land surface by linear topographic depressions or pattern, in which stream valleys have a randomly

linear changes in slope or topography (Figure 6). branched pattern (Figure 9a). The dendritic drain-

Wells drilled into the zone of enhanced weathering age pattern occurs in areas where structural con-

along the contact may produce higher well yields trol, such as jointing, faulting or inclined layering,

than those drilled into either ofthe less weathered is not well developed (Lahee,l961). The dendritic

rocks even a short distance from the contact.

drainage pattern common in massive rocks can be

The contact between a sheared gneiss and a . contrasted with that ofjointed and foliated rocks

garnet-feldspar-quartz-muscoVite schist in Carroll such as schis~. which t~nd to exhibit a rectangular

Countyillustrates enhancedweathering and higher drainage pattern (Figure 9b). This drainage pattern

well yield, along a lithologic contact. The contact is contams many topographic lineaments. Where

visible on the topographic map as a linear stream . stream courses are influenced by the regular pat-

valley, with a marked_~erence in the character of terns ofjointing and/or layering tl:}.atare common

the topography on either side (Figure 7). The in these rocks, streatl1S follow. a few preferred

gneiss, on the northwest side of the valley.- fS.. ortentations making obvious lineaments.

massive and reSists weathering, which produces

Inthe Piedmont and Blue Ridge Physiographic

rolling topography with rounded hills and pave- Provirlces, the jll1d:aposition. of numerous rock

ment outcrops. There are few records ofsuccessful types often produces a complex drainage pattern

wells drilled in the gneiss. The schist, on the ~hichcombines elements ofseveral different drain-

southeast side of the v~ey'. is both layered and age. patterns. The development of lineaments in

jointed, and it weatherS more deeply. Topography

suc.h

areas,

while

influenced

by

rock

type, -

is

not

11. .

Figure 6. View across a linear topographic depression formed along the contact between a sheared gneiss and a garnet-feldspar-quartz-muscovite schist in Carroll County, Georgia.
12

~~
~~~---, ,.-- ..,, ,o'~o'
,----'

Base map from U.S.G.S. 1:24.000 topographic map, Carrollton, GA., 1973. photorevised 1982.

0

MILE

CONTOUR INTERVAL 20 FEET NATIONAL GEODETIC VERTICAL DATUM OF 1929

Figure 7. A straight streamvalley segment developed at the contact (dashed line) between a sheared gneiss and a garnet-feldspar-quartz-muscovite-schiSt. A well sited on this contact by T.J.Crawford yielded over 100 gpm. (Carrollton,GA topographic quadrangle)

13

Figure 8. Differential weathering along compositional layering in schist, Fulton County, Georgia. The pedestal in the center of the photo is all that remains of the non-resistant layer.
14

a.

b.

Figure 9. Drainage styles: a. Dendritic b. Rectangular.

15

straight forward. Another way in which rock type affects the
development oflineaments isthrough theirvarying susceptibility to weathering. Differential weathering occurs where adjacent rocks ofdifferent chemical composition and physical characteristics are exposed at the surface. Negative lineaments can form along the units which weather more readily than the surrounding rocks.
WELL SITING USING TOPOGRAPlllC
LINEAMENTS
Many lineaments, such as the Wa.rwoman Uneament in Rabun County, Georgia, are of such large scalethattheyare hmnediatelyvisible evenon satellite imagery. Others are so small orsubtlethat they can be verified only by field inspection. The prominence oflineaments on a topographic map is only one factor to consider when evaluating the well-yield potential of an area. One must also consider the size of the area from which a well derives its water, known as the recharge area, and the origin ofthe lineament.
Inthe Piedmont and Blue RidgePhysiographic Provinces, the size of recharge areas is highly variable. The recharge area includes allthe soil and saprolite that supply ground water to a well via a network ofdiscontinuities. The recharge area may extend only a few hundred feet from the well, in the case of very low-yielding wells. In areas with a sizeable network of discontinuities, the recharge area may include soil and saprolite hundreds to thousands of feet from the well.
In order to evaluate the size of the recharge area, the relationship of the lineament with a prominent discontinuity such as a well-developed joint set or a lithologic contact should be established. The area around the lineament should be geologicallymapped to provide data onthe orientation of such discontinuities. This is to insure that the linear feature seen on the topographic map is really the result of a geologic structure. When examining stream valley lineaments, for example, one should verify that the valley orientation is structurally controlled by measuring the orientations ofnearbydiscontinuities and comparingthem with the orientation of the stream valley segment (Figure 10). Recharge areas are usually identified bylow-lyingtopographydeveloped ondeeplyweathered rocks. Often such deeplyweathered areas are near streams or drainages, with few, if any, outcrops. It is important to have enough structural data to allow interpolation across the area without outcrops.

Outcrops can provide other information important in selecting well sites. Information regarding the movement of water can be obtained from observing the spacing, persistence, and openness ofjoint sets. Spacing refers to the distance between joints; persistence describes the relative surface area of the individual fractures. Closely spaced, persistent joints will allow the movement of more water than widely spaced joints of limited extent. Joints which are open will allow the movement of more water than those which are closed. Staining onjoint surfaces orweathering ofthejoint surfaces may indicatejoint sets which have the potential to be water bearfug. Any of these factors may influence a decision on well site selection.
Once a general area has been identified as a candidate well site, certain factors can be used to help maximize well yield. Identifying a topographic lineament and drilling in the center of it is not enough, although this technique is probablybetter than drilling at random.
The orientation of the discontinuities in the subsurface should be kept in mind when siting wells. Because the discontinuities control the direction of ground-water flow, wells should be sited in such a way that the discontinuities direct watertowards, not away from, the well (Figure 11). Further, The inclination ofthe discontinuities will affect decisions concerning the depth of the well.
Streamvalleys also directsurfacewaterdownwards from the valley's head and inward from its walls. For this reason the most water will be available to wells which are located nearthe center ofvalleys, close to the valley floor (Figure 12).
WATER QUALITY ISSUES
The overall quality of ground water in north Georgia is quite good; however, there are two major factors which can adversely affect the quality of ground water. One is the type of rock and degree ofweathering, and the otherisman-made pollution within the recharge area of the well.
Rocks in the Piedmont and Blue Ridge Physiographic Provinces can yield natural concentrations ofiron, sulfate or manganese high enough to be objectionable. It is not always possible to determine before a well is drilled whetherthe water willcontain high levels ofthese constituents. Information on the quality ofwater from other wells in the area is helpful. A Georgia registered professional geologist (P.G.) with well-siting experience in the area should be able to offer advice on avoiding potential water quality problems.
An important part ofselecting a potential well site is assessing the possibility ofman-made pollution. A careful examination of the surrounding

16

-~--~

~-----

Figure 10. A structurally controlled stream segment, Lamar County, Georgia. The stream flows parallel to the joint set visible at lower left, and subparallel to the strike of the foliation.

17

Figure 11. Placement of wells with respect to discontinuities. Well 1 intercepts discontinuities at approximately 100ft depth. Well 2 does not intercept discontinuities.
18

Saprolite Bedrock

Best Well Sites

Water Table

Figure 12. Properwell placementformaximumyieldwithin a dra:fi?.age basin. After Heath and Giese, 1980.

19

area should be made in order to discover whether activities such as farming, waste disposal, or indusby are likely to contribute pollutants to the groundwater. Itis oftenhelpfulto speakwith longtime residents ofthe areawho may remember past activities of which there is no longer any obvious evidence.
Thefuture qualityofgroundwatershould also be considered. In addition to steps taken to site wells awayfrom present sources ofpollution, it will be necessru:y to safeguard the vicinity ofnew wells from potential pollution.
PRACTICAL CONSIDERATIONS FOR
WELL SITING USING LINEAMENTS
Locating wells in the vicinity of topographic lineaments has been shown empiricallyto improve well yields. Although lineament analysis cannot predictthe actualyield ofa well, it canbe a valuable means to reduce the risk of drilling a low-yielding well. One researcher has described the risk ofa dry hole as 1 chance in 4 for randomly located wells, and 1 in 72 for wells located on fractures or lineaments (Snipes, 1981). There is some evidence that wells sited on the intersections of fractures produce higher yields than those located on single fractures (Schmitt, 1988). Intersecting lineaments are indicative of these intersecting fractures.
Uneament analysis is a usefultoolforlocating high-yielding wells. It has become increasingly popular as a means for choosing well sites. It should be noted, however, that there are some drawbacks to relying exclusively on these techniques when siting wells.
Uneament analysis can indirectly indicate geologic characteristicswhich favor high well yield. However, many potentially high-yielding well sites will be overlooked or misinterpreted by relying on lineament analysis alone. For example, lineament analysiswillgiveno indications ofhorizontalstressrelieffractures ofthe type documented by Cressler et al. (1983), or distinguish rock types whose weathering characteristics produce higher-thanaverage well yields. Additionally, simple proximity to lineaments does not assure the maximum well yield. For instance, in many cases, drilling slightly to one side or the other ofa lineament can produ'ce very different well yields, depending, in part, on the direction in which the discontinuities are inclined. Knowledge ofthe detailed geology ofthe well site is critical for gaining the maximum benefit from the use of lineaments in well siting.
Uneaments analysis does not address water quality issues. The chemical and mineral compo-

sitionofa rockcan adverselyaffectthe quality ofthe water that it produces. Common water-quality problems in igneous and metamorphic rocks include high natural concentrations of iron, sulfate and manganese. Inspection of the rocks in the vicinity ofthe proposed wells can screen out potential well sites where water quality may be of concern.
USE OF WElL-SITING PROFESSIONALS
The drilling of a water well requires a certain amount of expense and risk. The best way to reduce this risk, and perhaps the overall cost, is to seek qualified professional assistance in selecting and drilling a well site.
The seiVices of a Georgia registered professionalgeologist, onewho has experience in locating well sites in your area, can be an excellent investment, particularly where large well yields are required. A qualified professional geologist will take into account all the pertinent geologic factors in order to obtain the highest and most reliable well yield.
Should you decide to hire a professional, it is importantto assesstheir experience and success in locating wells in your area. The geologist should have a knowledge of the local geology. All the factors mentioned in this paper should be taken into consideration, including topography, local drainage patterns, rocktypes, depth ofweathering, geologic structure, and all discontinuities. In addition, a professional geologist will take care to choose well sites that are not located near potential sources of contamination.
Once the well sites have been selected, the geologist will mark the sites using a stake or other marker. It is very important that all parties involved, including the well drilling contractor, realize that the well must be drilled at the point specified. In cases where well sites are chosen to intercept a sp~ific discontinuity, even a few feet one way orthe other can adversely affect well yield.
It is preferable that the geologist be available for advice during the drilling of the well. The professional geologist that you choose should have an understanding ofdrilling techniques and a good rapport with your well driller. Most registered geologists who specialize in well siting maintain professional relationships with one or more licensed well drilling contractors.
The geologist should be able to inform the driller about the drilling conditions he is likely to encounter and be ready to advise on the best drilling method for the area. Thewell driller should have confidence in the ability of the geologist to make decisions regarding the progress of drilling,

20

setting of casing, and whether it may (or may not) most difficult to access. Difficulty ofaccess, and the

be necessruy to abandon the hole. Unless the attendant expense, must be weighed against the

geologist is knowledgeable and has the confidence yield potential of the well, and the possibility of a
of the well driller, the best well sites may be "dry hole" in a.. more easily reached site. Even if

abandoned before high-yieldingzones are reached. some unsuccessfulwells are drilled duringground-

Conversely, the geologist should know when to water development, the overall cost of a surface-

save the client money by curtailing drilling at a site water system may far outweigh that of a ground-

that proves to have less potential than expected. water system.

It is well to note that all geologists offering

Well construction represents a considerable

professional seiVices to the public in Georgia must part of the cost of developing a ground water

hold a professional geologist's license issued bythe supply. When choosing a licensed well-drilling

state of Georgia. In a like manner, all water well contractor, cost-per-foot should not be the only

contractors must hold .a valid State license and consideration. A well-drilling contractor with con-

must construct all wells in accordance with the siderable experience in your particular area, and

provisions of the Georgia Water Well Standards onewho is willing to rely on the recommendation of

Act.

professional geologists when choosing a well site,

COST CONSIDERATIONS

maybe a bargain at a somewhat higher price than competitors who are not experienced in the area or

are less willing to accept advice.

When deciding whether to develop ground

Other expenses include a suitable pump, the

water or surface water to meet the needs of a cost ofwater lines, and the cost ofgetting power to

community or industry, one ofthe most important the well site. Awell house is usuallyconstructed for

factors to consider is cost. There are many compo- security. Testing for both water quality and well

nents to the total cost of a water system, and they capacity are additional expenses.

differ depending on which resource is utilized.

The cost of water treatment must also be

When considering ground water as a source of considered. Inmanycases,groundwaterqualityis

water supply, the following should be taken into such that it may be used for virtually any purpose

account. Professional assistance in selecting drill- with little or no treatment. The cost advantages of

ing sites can be viewed as a one-time expenditure such a situation are obvious. In some areas,

which may ultimately eliminate costly mistakes. It however, higher-than-normal concentrations of

represents a good investment in risk reduction. A such natural substances as iron or sulfate require

low-yielding well costs just as much to drill as a. treatment... Man-made pollutantscan also find _ _ __ --~high-yielding well; often mote:- High~yielding we11S~-tlieirway1nto ground waterand require ti-eat:nlent.

cost less on a per-gallon-obtained basis than do

Usually, several wells are required to supply

low-yielding wells. The cost of a professional the needs ofa community or industry. However, it

geologist's assistance shouldbe more than offset by maybe feasible to add wells to a system only as they

paying forfewerfeet ofhole pergallon ofyield. Even are needed. In this way, ground water can supply

though some well sites will cost more to drill than the growing water needs of a community without a

others, the difference in cost between them may be large up-front investment.

minimal when compared to the difference in yield.

Potential water users are reminded that a

Most individual homeowners and businesses ground-water withdrawal permit is required to

developinggroundwatersupplieswillberestricted withdraw more than 100,000 gallons or more of

to well sites on their own property. Industries and water per day. Wells used for community water

local governments requiring large well yields, how- supplies must also have a permit and must meet

ever,mayfinditnecessruytolookbeyondtheirown standards set by the Georgia Safe Drinking Water

property in order to obtain the needed amount of Act. Water use and drinking water permits are

water. Obtaining legal access to the property on issuedbytheWaterResourcesManagementBranch

which the well site is located may entail buying or of the Environmental Protection Division of the

leasing of property. In many cases rights-of-way .Georgia Departm~nt of Natural Resources in

must also be considered. It may be necessruy to Atlanta.

obtain easements from adjacent property owners for physical access to the site orfor the construction

SUMMARY

ofwater or power lines to the site.

Aquifers in the .Piedmont and Blue Ridge

Physical access to the drilling site may require Physiographic Provinces are complex systems com-

the removal oftreesand undergrowth, heavyequip- posed of a subsurface reservoir of porous soil and

ment rental, and in some cases, road construction. saprolite overlying a network of discontinuities in

Often the well sites with the most potential are the relatively non-porous metamorphic and igneous

21

rocks. Discontinuitiesinthe rocks serveto channel water from the overlying soil/saprolite reservoir to water wells which intercept the discontinuities. Obtaining large well yields in the Piedmont/Blue Ridge depends on selecting well sites which have both an adequate soil and saprolite reservoir and a network of discontinuities in the less weathered rock to facilitate water movement.
Topographic lineament analysis has evolved as an indirect means of locating areas with good well-yield potential in crystalline rock aquifers. Surface lineamentscanreveal the presence ofsuch underground features as faults, joints, lithologic contacts and compositional layeling which may channel water to wells.
There are both positive and negative aspects to the use oftopographic lineaments in well siting. Lineament analysis as part of a well- siting methodology can greatly enhance the probability of drilling a high-yielding well. However, reliance strictlyonlineamentanalysis is notrecommended. There are many other geologic factors which influence well yield, and all of them should be considered in making well siting decisions.
On-site verification of the nature of topographic lineaments is necessary in order to maximize well yields. Considerations in the siting of wells include rock type, depth ofweatheling, prox:lmity to discontinuities, extent of discontinuities, positionwithinthe drainagebasin, andpresence of potential pollutants within the recharge area ofthe well.
Careful attention to geologic factors can significantly reduce the risk of drilling a low-yielding well, and, thus, can reduce the overall cost of developing a ground-water system. Georgia registered professional geologists with well-siting experience canprovidevaluableguidance inthisregard. Cooperationbetweenthe licensed well drilling contractor and the geologist is essential. Even small deviations from the chosen well site or drilling depth can result in lowered well yields.
When deciding whether to develop a ground water system, there area number ofcost factors to consider. They include siting assistance, property acquisition, access, drilling, pumping system, water lines, and possibly, water treatment.

1983, Ground water in the greater Atlanta region, Georgia: Georgia Geologic Survey Information Circular 63, 144 p. Heath, RC. and Giese, G.L., 1980, What about ground water in North Carolina: Are large supplies feasible?: "Popular Publications of the U.S. Geological Survey" series, 15 p.
Herrick, S.M., and LeGrand, H.E., 1949, Geology and ground-water resources of the Atlanta area, Ge9rgia: Georgia Geologic Survey Bulletin 55, 124 p.
Lahee, F.H., 1961, Field Geology: McGraw-Hill, 926p.
Lattman, L.H., 1958, Technique of mapping geologic fracture traces and lineaments on aerial photographs: Photogrammetric Engineeling, v. 24, p. 568-577.
Lattman, L.H. and Parizek, RR, 1964, Relationship between fracture traces and the occurrence of ground water in carbonate rocks: Jour. of Hydro., v. 2, p. 73-91.
LeGrand, H.E., 1967, Ground water of the Piedmont and Blue Ridge Provinces in the SoutheastemStates: U.S. Geological Survey Circular 538, 11 p.
Schmitt, T.J., 1988, Correlationofwaterwellyields and remote sensing lineaments in the crystalline rocks of Rabun County, Georgia in Symposium Proceedings of International Conference onFluidFlowinFracturedRocks: Georgia State University, p. 136-148.
Snipes; D.S., 1981, Ground water quality and quantity in fracture zones in the Piedmont of northwestern North Carolina: Water Resources Research Institute Report No. 93, 87 p.
Fanning,J.L., and Doonan, GA, and Montgomery, L.T., 1992, Water use in Georgia by County for 1990: Georgia Geologic Survey Information Circular 90, 98 p.

REFERENCES
Bachtel, D. C. ,ed., 1987, The Georgia countyguide: The University ofGeorgia Cooperative Extension Service, Athens, Ga., 171 p.

U.S. Geological Survey, 1983, Useoffracturetraces inwaterwell location: Ahandbook: Washington, D.C., Office ofWaterResearch andTechnology (OWRTTI/82 1), 55 p.

Cressler, C.W., Thurmond, C.J., and Hester, W.G.,

22

For convenience in selecting our reports from your bookshelyes, they are color-~eyed across the spine by subject as follows:

Red Dk. Purple Maroon Lt. Green Lt. Blue Dk. Green Dk. Blue Olive
Yellow
Dk. Orange Brown Black Dk. Brown

Valley and Ridge mapping and structural geology Piedmont and Blue Ridge mapping and structural geology Coastal Plain mapping and stratigraphy Paleontology Coastal Zone studies Geochemical and geophysical studies Hydrology Economic geology Mining directory Environmental studies Engineering studies Bibliographies and lists of publications Petroleum and natural gas Field trip guidebooks Collections of papers

Colors have been selected at random, and will be augmented as new subjects are published.

Publications Consultant: Patricia Allgood Cartographers: Melynda D. Lewis and Michael T. Laitta

The Department of Natural Resources is an equal opportunity employer and offers all persons the opportunity to compete and participate in each area of DNR employment regardless of race, color, religion, sex, national origin, age, handicap, or other non-merit factors.

$965/500