s 
 
 14.GS: 
 CIR 232 
 
 c. 1 
 
 Earth Science Department 
 state of Illinois I University 
 
 WILLiAM G. STRATTON, Governor 
 
 DEPARTMENT OF REGISTRATION AND EDUCATION 
 
 VERA M. BINKS, Director 
 
 GROUNDWATER GEOLOGY IN 
 WESTERN ILLINOIS, SOUTH PART 
 
 A Preliminary Geologic Report 
 
 Robert E. Bergstrom 
 Arthur J. Zeizel 
 
 Service activities concerning groundwater are performed 
 jointly by the Illinois State Geological Survey 
 and the Illinois State Water Survey. 
 
 DIVISION OF THE 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 JOHN C. FRYE, Chief URBANA 
 
 CIRCULAR 232 
 
 1957 
 
Digitized by the Internet Archive 
 
 in 2012 with funding from 
 
 University of Illinois Urbana-Champaign 
 
 http://archive.org/details/groundwatergeolo232berg 
 
GROUNDWATER GEOLOGY IN WESTERN ILLINOIS, SOUTH PART 
 
 A Preliminary Geologic Report 
 
 Robert E. Bergstrom and Arthur J. Zeizel 
 
 ABSTRACT 
 
 Geologic conditions controlling the availability of ground- 
 water in the south part of western Illinois range from unfavorable 
 to very favorable for domestic, municipal, and industrial supplies. 
 This report presents a summary of groundwater principles, eval- 
 uates the geology in terms of the availability of groundwater for 
 various purposes, and discusses methods of developing ground- 
 water supplies. The maps and figures show: 1) arealand vertical 
 distribution, type, and water -yielding character of upper bedrock 
 formations, and 2) probability of occurrence and nature of sand and 
 gravel aquifers. Summary logs of 16 key wells at selected loca- 
 tions give representative sequences of subsurface strata. 
 
 INTRODUCTION 
 
 The Mississippi and Illinois rivers and their tributaries are the most ob- 
 vious water resources in western Illinois. These two river systems, through 
 erosion, have also been mainly responsible for shaping the landscape. 
 
 Despite the vast amount of water available from the Mississippi and Illi- 
 nois rivers, withdrawal of water from these sources for use by cities, farms, 
 and industries in western Illinois has been relatively small. Most of the water 
 supplies utilized directly or indirectly by man in the area comes from the 
 great reservoir of water that is stored in the ground. 
 
 Water in the ground occurs in the soil zone within a few feet from the sur- 
 face and in the deeper, permanently saturated groundwater reservoir. Soil 
 water is utilized by crops and other vegetation, which are the greatest single 
 users of water. Groundwater, which occurs at some distance below the soil 
 moisture zone in most of western Illinois, is obtained by wells and is the major 
 source of water supply for farms, cities, and industries in the region. The de- 
 mand for groundwater is great because surface-water supplies are not always 
 present where needed, and even where present they commonly require consid- 
 erable capital outlay for collection and treatment. 
 
 The availability, quantity, and quality of groundwater depend upon the na- 
 ture and arrangement of the earth materials beneath the surface, that is, upon 
 geologic conditions. Any groundwater supply, whether for small domestic 
 needs or for the large requirements of a city or industry, can be obtained only 
 where there are rocks that can transmit water. Rocks which transmit water 
 are said to be permeable and are technically called aquifers. Because geologic 
 conditions change from place to place, in some areas groundwater is readily 
 available for all purposes, whereas in others it is difficult to obtain even small 
 supplies. 
 
 [1] 
 
ILLINOIS STATE GEOLOGICAL SURVEY 
 
 KEY 
 
 Detailed reports 
 
 Previously published 
 
 In progress 
 
 Area of general reports 
 outlined and identified 
 by Circular numbers 
 
 Fig. 1. - Index map showing areas for which reports on groundwater geology 
 in Illinois have been published since 1950 or are in progress. 
 
 Knowledge of the distribution and character of aquifers in any area is 
 necessary to develop groundwater supplies properly. This report provides 
 information on the availability of groundwater in the south part of western 
 Illinois and discusses principles of groundwater occurrence and development. 
 It is part of a program aimed at improving water supplies on Illinois farms, 
 in which the Illinois State Geological Survey is cooperating with the Extension 
 Service of the Agricultural Engineering Department, College of Agriculture, 
 University of Illinois. 
 
 The report is the seventh in a series.* It describes the south half of Agri- 
 cultural Extension District 2 and west part of District 4 and includes the fol- 
 lowing eleven counties: Adams, Brown, Calhoun, Cass, Greene, Hancock, 
 Jersey, Morgan, Pike, Schuyler, and Scott (figs. 1 and 2). 
 
 * Previous reports in the series, listed in "Suggested Reading" on page 28 
 and shown by area in figure 1, are available upon request from the Survey 
 in Urbana. 
 
GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 
 
 Fig. Z. - Western Illinois, south part, showing location of key wells. 
 
4 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 The region has an area of about 5,600 square miles and a population of 
 slightly more than a quarter of a million. Less than three -fourths of the land 
 is tillable because it has been extensively dissected by the Mississippi and 
 Illinois rivers and their tributaries. About three -fourths of the commercial 
 farms are livestock and grain farms. In Calhoun County and parts of Jersey, 
 Pike, and Adams counties, where the land is too rough for the cultivation of 
 annual crops, soil and climatic conditions favor the production of fruit, espe- 
 cially apples. Quincy and Jacksonville are the two largest cities in the region. 
 
 Drilling contractors in western Illinois have assisted in the preparation 
 of this report by providing large numbers of logs of water wells for the files 
 of the Geological Survey and by supplying information on specific problems of 
 occurrence of water -yielding materials and drilling conditions. 
 
 We are also pleased to acknowledge the assistance given by members of 
 the Groundwater Division and other divisions of the State Geological Survey. 
 Most of the data on water quality and well yields contained in this report have 
 been taken from records or published reports of the Illinois State Water Survey. 
 
 OCCURRENCE OF GROUNDWATER 
 
 Because groundwater occurs beneath the surface of the earth and is hidden 
 from view it is often regarded as somewhat mysterious. Throughout human 
 history many fanciful explanations have been presented to describe its source, 
 movement, and occurrence. Scientific study has shown, however, that ground- 
 water obeys certain physical laws or principles which are relatively simple 
 and easily understood, although complex in detail. Our present understanding 
 of the source, movement, and occurrence of groundwater and the relationship 
 of groundwater to other water sources are shown diagrammatically in figure 3. 
 
 The source of groundwater is rain, snow, or ice that falls on the earth from 
 the atmosphere and seeps into the ground. The tremendous quantity of water 
 that falls on the land surface by precipitation is seldom realized, but it is far 
 more than adequate to supply our vast groundwater reservoir. According to 
 records of the State Water Survey, during a year of average precipitation in the 
 vicinity of Quincy nearly a million gallons of water falls on each acre of land. 
 
 Most of the precipitation runs off in streams or is returned to the atmos- 
 phere by evaporation and transpiration. The remaining moisture filters slowly 
 down into the ground until it reaches a level below which all available openings 
 are filled with water. The top of this zone of saturation is called the water- 
 table. When a well is drilled or dug, it is dry until it penetrates the zone of 
 saturation; the position of the water-table is then shown by the level at which 
 water stands in the well. The water-table is not a level surface but conforms 
 more or less to the principal features of the land surface. Where the water- 
 table intersects the land surface, groundwater is discharged as seeps and 
 springs that feed perennial streams, lakes, and swamps. The water-table does 
 not remain stationary but fluctuates in response to the loss or gain of ground- 
 water. 
 
 Groundwater moves under the influence of gravity or in response to other 
 natural pressure differentials toward points of lowest pressure, which are 
 nearly always places of discharge, such as springs, marshes, or pumped wells. 
 
GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 
 
 Fig. 3. - Source, movement, and occurrence of groundwater. 
 
 This movement is slow because there is friction between the water and the 
 walls of the pores or crevices in the rock. 
 
 In places where the top of the zone of saturation is not confined and can 
 rise or fall freely as water is added or removed, groundwater is said to be 
 under water-table conditions. Under these conditions and under the influence 
 of gravity groundwater moves freely, hindered only by friction, in the direc- 
 tion of the slope of the water table. 
 
 Commonly the permeable aquifer is overlain by a less permeable mate- 
 rial that restricts the upward movement of groundwater. Under these condi- 
 tions, the water in the confined aquifer is subject to pressure that causes the 
 water in a well to rise above the top of the aquifer. In this case groundwater 
 is said to be confined, or under artesian conditions. Where sufficient pres- 
 sures are encountered in an artesian well, the water may rise above the land 
 surface and make a flowing well. 
 
 To supply a pumped or flowing well, groundwater must move through the 
 earth materials toward the well. Under water-table conditions, pumping 
 lowers the water table in the vicinity of the well and induces the flow of ground- 
 water toward the well from adjacent areas. Under artesian conditions, pump- 
 ing causes a reduction of hydrostatic pressure in the vicinity of the well, which 
 induces the flow of groundwater toward the well. The depression in the water 
 table or in the artesian pressure surface, which results from pumping, is in 
 the form of an inverted cone with the well at the center. It is called the cone 
 of depression (fig. 3). 
 
 Groundwater is not everywhere available in sufficient quantities to satisfy 
 human requirements. The availability of groundwater in humid regions such as 
 western Illinois is basically dependent upon the presence of aquifers. Aquifers 
 such as sand and gravel store considerable water and transmit it readily. 
 Other earth materials, such as clay and shale, may contain even more water 
 per cubic foot than sand and gravel, yet retard movement of groundwater to 
 such a degree that they will not yield appreciable quantities of water to a well. 
 The value of an aquifer depends upon the type, size, number, and degree of 
 interconnection of the openings that may store and conduct groundwater. 
 
ILLINOIS STATE GEOLOGICAL SURVEY 
 
 SYSTEM 
 
 FORMATION 
 
 NORTH PART THlSAREA 
 W. ILLINOIS 
 
 GRAPHIC 
 LOG 
 
 ROCK TYPE 
 AND THICKNESS 
 
 WATER- YIELDING CHARACTERISTICS, DRILLING 
 AND WELL CONSTRUCTION DETAILS 
 
 PLEISTOCENE 
 SERIES 
 
 ■*Se: 
 
 Unconsoiidoted glacial 
 deposes, loess (wind- 
 blown silt) ond alluviurr 
 0-250' 
 
 Water yielding chorocler variable Lorge yields from thick sand ond 
 grovel deposits m bedrock volleys Wells usually require screens 
 and careful deveiopement 
 
 Mainly shale, with sond- 
 sfone, limestone ond 
 cool 
 
 0-430' 
 
 Generally unfavoroble as woter source Locally, domestic ond form 
 supplies obtained from thin sandstone, limestone, ond cool beds 
 Caving sholes require cosing 
 
 Ste Genevieve - 
 
 s; louis - 
 
 Salem 
 
 Sandy oolitic limestone 
 Dense limestone 
 
 Fossiliferous oolitic 
 limestone 0-325' 
 
 Thin, usually not water-yielding west of Illinois River Thicker, 
 occasionally woter- yielding eost of river ond in southern 
 Calhoun County 
 
 -I 4 
 
 Shale with some lime- 
 stone 0-125' 
 
 Not woter yielding ot most places Casing required 
 
 Keokuk- 
 Burlington 
 
 i , z: 
 
 T~£r~n- 
 
 , r 7fT , 
 
 Cherfy limestone, some 
 shole near base 
 0-275' 
 
 GeneroMy creviced ond woter-yielding Mom oquifier for domestic 
 supplies Wells penetrate limestone from 30 to 150 feet Tight 
 of some locations 
 
 ss 
 
 DEVO-\ 
 
 NIAN ^ 
 
 Shale and limestone 
 Some sandstone ond 
 
 siltstone 
 
 0-325' 
 
 Not water-yielding of most locations Locally, limestones yield small 
 quantifies of water Casing required 
 
 SILU- 
 RIAN 
 
 !\ /• / 
 
 Limestone, some sand- 
 stone 
 Cherfy limestone dolomite 
 0-225' 
 
 Not important groundwater source, except locolly for smoll supplies in Cal- 
 houn County Gos, oil, or salt woter found at some locofions. 
 
 l I l l t 
 
 Moquoketo 
 I 
 
 Greenish shole, some 
 
 dolomite and siltstone 
 
 0-250' 
 
 Mot woter-yielding ot most places Casing required. 
 
 Gaiena- 
 Decoroh- 
 
 Platteviile 
 (Trenton) 
 
 Kimmswick- 
 Decorah- 
 Plaffm- 
 joochim 
 
 ^S 
 
 Limestone, shaly zone m 
 upper part 
 
 Dolomite in lower part 
 0-340* 
 
 Commonly fight. Not important os aquifer Yields some domestic 
 supplies m Calhoun County. 
 
 Glenwood - St Peter 
 
 Clean, poorly cemented 
 sandstone 
 
 0-320' 
 
 Permeoble and woter-yielding Wafer rother strongly mineralized in 
 most of area Favorable aquifer m part of Calhoun County. 
 
 Shokopee 
 
 V?^ 
 
 Jefferson 
 
 City 
 
 Dolomite, cherty above, 
 sandy below 
 330-400" 
 
 Sandstone, some dolo- 
 mite 35-150' 
 
 7-r-/; 2 
 
 / 6 / / 
 
 6. ■ ' /i'i Cherty dolomite 
 I ;«-/<./«; 240-340 
 
 ,' -J _ ^ 
 
 1 . / a , , ' Sandstone and dolomite 
 
 .',' 
 
 Trempea- 
 
 /ironton- \ 
 \ Goiesville/ ' 
 
 Derby- 
 Doerun 
 
 T 7T7T, 
 
 /-- /■z--/-- 
 
 /—/—/- 
 
 7 1 
 
 Bonne 
 Terre 
 
 z=z r?r^ 
 
 ."• .'• :-:■':- 
 
 Rarely penetrated by woter wells in most of area because of great 
 depth and probability of obtaining highly mineialized water 
 
 Dolomite 
 
 90-250' 
 
 Dolomite 
 
 0-250' 
 
 Dolomite ond shole 
 140-360' 
 
 Limestone ond dolomite, 
 sandy m upper ond 
 lower parts 
 70-430' 
 
 Sondstone 
 
 0-440 
 
 PRE-CAMBRIAN : [■' \7."' Gronite ond other crystolme rocks extending to greot depth 
 
 Fig. 4. - Generalized column of rock formations in western Illinois, south part. 
 
GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 7 
 
 In western Illinois, the important aquifers are sand and gravel, limestone 
 and dolomite (a limestone -like rock rich in magnesium), and sandstone. Many 
 sand and gravel deposits are water -yielding because the openings between the 
 individual grains are large enough to allow relatively rapid movement of water. 
 Good water -yielding sand and gravel deposits are composed of grains that are 
 nearly all the same size and coarser than granulated sugar. If large amounts 
 of clay and silt are present in the sand and gravel deposits, the openings be- 
 tween the larger grains are clogged and the movement of water is retarded. 
 Sand and gravel deposits in the area of this report range in thickness from a 
 few inches to nearly a hundred feet. Deposits a few feet or more thick are 
 often suitable aquifers for drilled wells. Thinner deposits of sand and gravel 
 in otherwise tight earth materials are suitable aquifers only for dug or augered 
 wells of large diameter. 
 
 Water-yielding sandstone formations also transmit groundwater through 
 the openings between sand grains. As in sand and gravel deposits, any mate- 
 rial that clogs the openings between the sand grains reduces the water -trans- 
 mitting capacity of the formation. Sandstone formations contain variable 
 amounts of cement, and some sandstones are so thoroughly cemented that 
 whatever water is present moves primarily through joints and fractures. Rel- 
 atively few wells have been completed in sandstone in the area of this report. 
 Locally, however, the St. Peter sandstone (Ordovician) and thin fine-grained 
 Pennsylvanian sandstones are groundwater sources (figs. 4, 5, and 6). 
 
 Tight, compact rocks like limestone and dolomite yield groundwater to 
 wells from interconnected cracks and solution channels. Because these water- 
 filled openings are irregular in size and distribution, the yields of closely 
 spaced limestone or dolomite wells may be quite different. The Keokuk-Bur- 
 lington limestone (Mississippian) is fairly well creviced at most places in the 
 region and is usually a dependable source of groundwater for farm supplies 
 (figs. 4 and 6). 
 
 GEOLOGY 
 
 The branching and rebranching tributaries that cut into the uplands along 
 the main trunk valleys of the Mississippi and Illinois rivers have shaped much 
 of western Illinois into a landscape of bold bluffs, deep hollows, and narrow up- 
 land prairies. The most rugged part of the region is Calhoun County, which 
 stands as a high rocky divide between the Mississippi and Illinois rivers. 
 East of Illinois River, in eastern Jersey, Morgan, and Cass counties, the land 
 surface is less broken and merges into the flat prairies of central Illinois. 
 
 Although the region has been sculptured primarily by running water, im- 
 portant developments in the landscape took place during the geologically recent 
 Ice Age (Pleistocene Epoch) when great continental glaciers advanced across 
 Illinois. The glaciers, advancing outward from centers of snow accumulation 
 in Canada, transported a great quantity of rock debris, and in melting deposited 
 it as a surface mantle which smoothed pre-existing irregularities and produced 
 broad, flat upland plains in much of western and central Illinois. The only part 
 of western Illinois which escaped glaciation was an area including most of Cal- 
 houn County and a small part of Jersey County, although all the surrounding 
 lands at one time or another were invaded by ice (see glacial boundary in fig. 7) 
 
ILLINOIS STATE GEOLOGICAL SURVEY 
 
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GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 9 
 
 Of the several glacial advances during the Ice Age only the earlier ones 
 (Illinoian and older) reached the region of the lower Illinois Valley. Subsequent 
 glaciations fell short of the region, although great volumes of meltwater from 
 the later ice sheets flowed down the Mississippi and Illinois river valleys. The 
 deposits left by the Illinoian and older glaciers have been extensively eroded 
 in western Illinois since their deposition. This is in contrast to northeastern 
 Illinois where the later glacial deposits (Wisconsin) have been subject to only 
 brief erosion, so that the rolling, hummocky topography is essentially as it 
 was when the ice melted. 
 
 The glacial deposits (drift) which have escaped erosion in the lower Illinois 
 Valley area are complex. Much of the upland is blanketed by unsorted rock 
 debris, called till, which was deposited by the ice during melting. In the valleys 
 and in some places on the uplands are beds of sand and gravel which meltwaters 
 carried away from the ice front and deposited. These deposits are called out- 
 wash. On the uplands, and especially near the river bluffs, are deposits of silt 
 and fine sand that were blown from barren river flats kept free of vegetation by 
 frequent glacial flooding. The windblown silt deposits (loess) occur throughout 
 the area, including Calhoun County which was largely unglaciated. Loess, till, 
 outwash, and the sediments of modern streams form a mantle over the bedrock 
 in much of western Illinois. 
 
 The nature of the bedrock and its relationship to the overlying mantle are 
 well shown in the steep bluffs that border Mississippi and Illinois rivers. Sim- 
 ilar information is obtained from records and samples of wells and borings in 
 areas where the bedrock is more or less completely buried. 
 
 The bedrock consists of layers of shale, coal, limestone, dolomite, and 
 sandstone, arranged one above the other like the pages of a book (figs. 4 and 5). 
 These rocks were originally deposited as loose sediments in shallow conti- 
 nental seas but were later buried and hardened. They are several hundred mil- 
 lion years old, whereas the glacial deposits which overlie them are probably 
 less than a million years old. During the long interval of time between the 
 deposition of the bedrock formations and the glacial deposits the area stood, as 
 now, above sea level and was subject to erosion. Tilting and warping of the 
 bedrock layers from their original horizontal position occurred at that time. 
 
 In southern Calhoun and Jersey counties the bedrock formations have been 
 sharply bent and in places broken along a line that extends from just north of 
 Brussels through Pere Marquette State Park (figs. 5 and 6). This structure is 
 called the Cap au Gres faulted flexure. As shown in figure 5, the rocks north 
 of the flexure lie about a thousand feet above the corresponding rocks to the 
 south. Along the flexure the rocks dip steeply southward and are broken by 
 fractures called faults. 
 
 The bedrock layers dip eastward or northeastward about 15 to 50 feet per 
 mile in the area of this report, although there are numerous local upfolds 
 (anticlines) and downfolds (synclines) that modify or reverse the regional dip. 
 Drilling for oil and gas has been concentrated mainly on anticline or dome 
 structures in accordance with established exploration practice in many oil pro- 
 ducing areas. Gas was formerly produced from Silurian rocks (fig. 4) along 
 an anticlinal structure west of Pittsfield (Pittsfield-Hadley anticline) and has 
 
10 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 Replacement for 
 Fig 6, p 10, Circular 232 
 
 Pennsylvonion 
 
 Mainly shale with thin sand- 
 stone, limestone, and coal 
 beds Small groundwater sap- 
 plies obtained from sandstone, 
 limestone, coal, or fractured shale 
 
 Pre-Pennsylvanian rocks, patterns shaded where 
 overlain by Pennsylvonion formations 
 
 Mississippian 
 
 7///\ St Louis limestone -Warsaw shale Limestone, water- 
 
 Y///A yielding where creviced. Shalenot woter-yielding. 
 
 Keokuk-Burlington limestone Creviced and water- 
 yielding at most locations 
 
 H Kinderhook shale Generally not water-yielding 
 
 Cop Au Gres 
 Faulted Flexure — 
 
 Devonian ond Silurian 
 
 \j Limestone and dolomite Water- 
 IN . WN yielding where creviced 
 
 Ordovicion 
 
 f Tvl Maquoketa shale, Kimmswick - Joachim dolomite, ond 
 
 wJfA St. Peter sandstone. Groundwatercondifions vonable 
 
 Description of bedrock formations is given in Fig. 4. 
 
 20 Miles 
 
 Fig. 6. - Areal distribution, type, and water-yielding character of upper bedrock 
 formations (modified from Geologic Map of Illinois, 1945). 
 
GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 11 
 
 Good to excellent, aquifers highly permeable 
 
 and widely distributed 
 Fair togood.oquifers differ widely in permeability 
 
 scattered and discontinuous 
 
 Areoof thicker drift in bedrock volley, little sub- 
 ,',' surface information avoiloble, area merits 
 
 ' further investigation 
 
 Poor, sond and grovel aquifers generally absent 
 
 Glociol boundary 
 
 Fig. 7. - Probability of occurrence and nature of sand and gravel aquifers. 
 
12 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 recently been discovered under similar conditions in a small area in Pike 
 County northwest of Pittsfield, between Baylis and Fish Hook near the south- 
 east corner of Adams County. Oil has been produced for many years from 
 Devonian rocks in the Colmar -Plymouth field, a low structural dome in south- 
 western McDonough, northwestern Schuyler, and southeastern Hancock coun- 
 ties. 
 
 Beneath the layered rocks, shown in figs. 4 and 5, are ancient crystalline 
 rocks which form the "basement." The basement rocks are mainly granitic in 
 composition, as is indicated by a few very deep borings in Illinois. In Pike 
 County two deep oil tests (wells 9 and 11, fig. 2 and table 1) reached granitic 
 rocks at depths of 3204 and 2221 feet respectively. 
 
 DISTRIBUTION OF AQUIFERS 
 
 Sand and gravel beds occur in the unconsolidated material that glaciers 
 and running water have deposited on the bedrock surface (fig. 3). Dolomite, 
 limestone, and sandstone aquifers occur in the bedrock. The vertical sequence 
 of earth materials in the area is given in figure 4. 
 
 Figure 6 shows the areal distribution and water -yielding properties of the 
 upper bedrock formations that are penetrated at land surface or beneath the 
 glacial material. Table 1 gives summary logs of 16 key wells to show the se- 
 quence of bedrock formations encountered at selected locations. 
 
 In many places, particularly along the courses of streams or of glacial or 
 preglacial drainage ways, sand and gravel deposits merit careful consideration 
 as a source of groundwater. Figure 7 shows the probability of occurrence of 
 sand and gravel aquifers. The areas shown as "good to excellent" are under- 
 lain by thick unconsolidated deposits containing sand and gravel, which occur 
 mainly in major bedrock valleys. Groundwater for domestic and farm supplies 
 may be obtained in this area from small-diameter drilled wells in sand and 
 gravel. Possibilities for municipal or industrial wells are good to excellent, 
 although test drilling is necessary to locate the best formation and site for the 
 construction of high-capacity wells and to obtain information on water quality. 
 
 The areas shown as "fair to good" in figure 7 have moderately thick gla- 
 cial deposits that border the deep channels of bedrock valleys or fill tributary 
 valleys and include some sand and gravel. Groundwater for domestic and farm 
 supplies may be obtained locally in these areas from drilled wells in sand and 
 gravel, but at some locations these deposits are absent and wells are usually 
 drilled into the bedrock. The probabilities for obtaining supplies of water for 
 industrial and municipal purposes are poor to fair. Extensive test-drilling is 
 likely to be necessary to locate water -yielding sand and gravel deposits suit- 
 able for such purposes. Areas outlined by dashes appear to be more promis- 
 ing but have not been sufficiently tested to be proved. 
 
 The areas shown as "poor" are primarily bedrock upland with glacial de- 
 posits thin, absent, or composed mainly of tight till. Sand or gravel capable 
 of supplying groundwater is rare, and most wells obtain water from the bed- 
 rock. 
 
GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 13 
 
 DEVELOPMENT OF GROUNDWATER SUPPLIES 
 Geologic Conditions that Affect Groundwater Development 
 
 The amount and quality of groundwater available in an area are controlled 
 by geologic factors that must be considered in developing groundwater supplies. 
 These factors, which are discussed relative to individual occurrences in other 
 sections of this report, are summarized as follows: 
 
 1) Distribution of aquifers, including presence or absence, depth and 
 thickness, and areal extent. 
 
 2) Nature of aquifers, including type of material, kind of openings (pores 
 or crevices), and presence of substances which affect water quality. 
 
 3) Geologic structure, including regional and local dip of beds, faults, 
 and jointing. 
 
 4) Distribution and nature of non- water -yielding materials. 
 
 The mere presence of an aquifer is not in itself enough to assure that a 
 satisfactory groundwater supply can be obtained in a given area. Care must be 
 taken to select the aquifer most suitable for the water supply required, to adapt 
 the type and manner of construction of the well to the geologic conditions, and 
 to place the well where it will best maintain the required standards of quality 
 and quantity of water. 
 
 Unconsolidated Deposits 
 
 Where extensive water -yielding sand and gravel deposits are present, con- 
 sideration should usually be given to developing wells in them rather than in 
 the underlying bedrock. Sand and gravel wells may have one or more of the 
 following advantages over bedrock wells, particularly over deep bedrock wells: 
 shallower water levels, colder water, greater water yields to specific wells, 
 and, locally, water of better mineral quality. A disadvantage of sand and gravel 
 wells is the special construction needed to take full advantage of the water- 
 yielding capacity of the aquifer. 
 
 Illinois State Water Survey records show that considerable iron may be 
 found in sand and gravel wells locally along the Mississippi and Illinois rivers. 
 The areas of iron concentration are not clearly defined because data are incom- 
 plete; however, the possibility of encountering water with objectionably high 
 iron content must be considered in planning groundwater developments in the 
 valley areas. Water-well drillers who operate in these areas report that com- 
 monly water from the deeper deposits is "rusty" and therefore most farm wells 
 in the bottomlands are finished at depths as shallow as possible. 
 
 High-capacity sand and gravel wells require the use of screens, which 
 allows the flow of sand -free water into the well bore. It is important, in the 
 development of sand and gravel wells, that the size of the screen openings or 
 slots be chosen on the basis of the size of the material to be screened. There- 
 fore it is necessary that samples of the aquifer be obtained and analyzed for 
 particle size to determine the correct size of the screen opening. 
 
 Development necessarily follows construction of a sand and gravel well. 
 In proper development, the finer grained materials in the immediate vicinity 
 of the well bore are drawn through the screen and removed, which leaves a 
 natural graded filter that prevents pumping of sand and silt. Better results and 
 
14 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 yields may be obtained from some sand and gravel deposits by placing an 
 "envelope" or "pack" of selected gravel or coarse sand between the deposit 
 and the screen. The grain size of the particles in the gravel pack must have 
 the proper relationship to the grain size and sorting of the formation and to 
 the screen slot size to achieve the best results (see Smith, H. F., Gravel 
 packing water wells, Illinois State Water Survey Circ. 44). The use of open 
 pipe, or slotted pipe, or pipe filled with gravel should be avoided except in 
 very coarse deposits where the well will yield far more water than is pumped. 
 
 The physical characteristics of sand and gravel deposits are generally 
 more variable than those of bedrock formations. For this reason, groundwater 
 development from sand and gravel sources usually requires test drilling prior 
 to well design and construction. In areas where the presence of suitable aqui- 
 fers is uncertain, a test-drilling program is necessary to determine whether 
 suitable deposits are present and, if present, the best location for the well. 
 Data on the suitability of water quality at specific sites should also be obtained 
 in the exploration program. 
 
 Test-drilling is generally done by drilling small-diameter holes with cable 
 tool (percussion) or with rotary drilling equipment. The test-driller's report 
 is an important part of the groundwater development program and should in- 
 clude the following information when obtainable: 1) driller's log of formations 
 penetrated, 2) static water level and changes in water levels during drilling, 
 3) drilling time of the individual formations, 4) weight and viscosity of drilling 
 mud, and 5) loss of mud or fluid during drilling. Samples of drill cuttings 
 should be saved at a five -foot interval and also where there are changes in the 
 type of material. 
 
 Conditions favorable for drilled wells in sand and gravel in western Illinois 
 are found mainly in and along the Illinois, Mississippi, La Moine, Mill, Macoupin 
 and Apple Valleys (fig. 2). 
 
 Driving a sand point is the quickest and most economical method of well 
 construction but is practical only where small supplies of groundwater are 
 needed and where such supplies are available from sand and gravel at shallow 
 depths. Conditions are suitable for driven wells in the Illinois, Mississippi, 
 and La Moine valley -bottoms and locally in minor tributaries. 
 
 Large -diameter (2 to 5 feet) dug wells are most suitable in areas where 
 the unconsolidated materials are fine-grained and cannot yield water readily 
 to a drilled or driven well; therefore they are used widely throughout much of 
 the area in which glacial material is thin and tight and is underlain by Pennsyl- 
 vanian rocks of low permeability. Large -diameter wells are excavated by hand 
 or by power auger, shovel, or bucket and can be excavated to depths up to about 
 100 feet. In areas where conditions are favorable for drilled or driven wells, 
 the use of large -diameter dug wells is not recommended because of pollution 
 and maintenance problems. The chief advantage of a large -diameter well is 
 that it can store relatively large quantities of water. Short intermittent pump- 
 ing of a large -diameter well does not require immediate release of water from 
 the surrounding materials, and the well can refill slowly between times of 
 pumping. Special sanitary precautions should be taken with large -diameter 
 wells. (See Illinois State Department of Public Health Circ. 14A.) 
 
GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 15 
 
 Bedrock Formations 
 
 Wells constructed in bedrock aquifers are generally less difficult to de- 
 sign because the well bore is usually left uncased and because the aquifers are 
 more consistent over wider areas. Test drilling in bedrock aquifers is seldom 
 done, particularly where records of prior drilling in the area are available. 
 
 In western Illinois the most important geologic factors affecting well con- 
 struction in bedrock aquifers are: 1) type, thickness, depth, and permeability 
 of aquifers; 2) ability of formations to sustain open hole without casing or lin- 
 ing; 3) tendency of formations to yield silt or sand during pumping; and 4) dif- 
 ferences in the quality of water contained in different formations. 
 
 Creviced dolomite and limestone do not normally require casing or lining. 
 However, where groundwater supplies are obtained from near-surface dolomite 
 or limestone formations with less than about 35 feet of overburden, there is 
 danger of bacterial pollution. The open crevices provide little filtering or other 
 purifying action, and polluted water may travel long distances through these 
 openings. 
 
 Normal drilling procedure in the development of bedrock aquifers is to 
 install surface casing to firm bedrock and to continue into the bedrock with an 
 open hole. Where a bedrock formation is too weak to sustain an open hole, it 
 may be necessary to continue the surface casing through the weak formation 
 into a more competent underlying formation or to set liners. The most impor- 
 tant caving zones requiring casing are in the Pennsylvanian, Warsaw, and 
 Kinderhook shales (fig. 4). 
 
 Conditions are generally favorable in western Illinois for drilled wells in 
 bedrock. The main aquifers exploited for farm supplies are the Keokuk-Bur- 
 lington limestone and in Calhoun County the Devonian-Silurian, Kimmswick- 
 Joachim, and St. Peter formations (figs. 4 and 6, and table 1). 
 
 Large Groundwater Supplies 
 
 Development of groundwater supplies for municipal, industrial, and irri- 
 gation purposes requires technical advice and careful planning based on all 
 available geologic and hydrologic data. The type, extent, thickness, depth, dis- 
 tribution, and water -yielding characteristics of aquifers in the area should be 
 determined so that the available quantity of water may be estimated and plans 
 made for proper well construction. Hydrologic data, such as yields of existing 
 wells, pressure potential of various formations, and water quality, should also 
 be determined as accurately as possible. 
 
 Information on geologic conditions pertaining to groundwater supplies at 
 prospective well locations is available upon request from the State Geological 
 Survey. The Survey maintains a current file of subsurface information includ- 
 ing drillers' logs and samples of drill cuttings, from which specific data on 
 formation characteristics are available for many areas in Illinois. It also 
 publishes basic geologic studies of a regional nature. Information on well 
 yields, water levels, and water quality is furnished by the State Water Survey. 
 
16 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 Domestic Groundwater Supplies 
 
 Development of groundwater supplies for domestic and stock use differs 
 from municipal, industrial, and irrigation developments in three important as- 
 pects: 1) the quantity of water needed for domestic and stock purposes is con- 
 siderably smaller and may, therefore, be provided from considerably thinner 
 and less permeable aquifers; 2) the area within which a well can be constructed 
 for domestic or stock purposes is normally small, usually a farmyard or a 
 suburban lot; and 3) the cost of well construction must be low, which prohibits 
 deep drilling. 
 
 In much of the area of this report geologic conditions are generally favor- 
 able for obtaining private water supplies at reasonable cost. Throughout most 
 of the area, creviced dolomite and limestone are at sufficiently shallow depth 
 to be within reach of private wells. Water -yielding sand and gravel are present 
 in some areas. Sandstone, coal, and fractured shale in the Pennsylvanian sys- 
 tem yield sufficient water for small wells in many localities. 
 
 Subsurface geologic conditions generally vary little within the limited area 
 of an individual homesite or farm. However, there may be great changes in 
 geologic conditions with depth. Information on depth of aquifers is valuable for 
 planning the type, depth, and size of a well. 
 
 Perhaps the most important considerations in locating private wells are 
 those of sanitation and convenience of location. Wells should be placed with 
 regard to geologic conditions, surface drainage, topography, and land usage so 
 as to provide maximum protection from harmful bacteria and objectionable in- 
 organic material. 
 
 The following suggestions may be helpful in planning for individual or farm 
 supplies. 
 
 1) Inventory the water requirements - estimate the amount of water needed 
 for domestic use, stock use, milk cooling, washing, and fire protection. 
 
 2) Obtain all available information on the occurrence of water -yielding 
 formations at the location. The maps in this report are designed to give a 
 fundamental understanding of the occurrence and distribution of the water - 
 yielding formations in this area so that the most suitable type of well can be 
 planned. If additional more specific information is desired, address the State 
 Geological Survey, Urbana, Illinois, giving: a) location of property by section, 
 township, and range; b) intended use of the water supply; c) estimate of the 
 quantity needed; and d) all information on existing wells on the property or 
 previous drilling attempts. 
 
 3) Select a well driller with a reputation for constructing wells that have 
 proved to be trouble-free. Make sure the driller is capable of properly han- 
 dling the types of aquifers he may encounter at the location. If the well is to 
 be finished in sand and gravel, select a driller experienced in setting well 
 screens. 
 
 4) Check with the State Department of Public Health for regulations and 
 suggestions on proper well construction and location and proper pump housing. 
 The State Department of Public Health discourages the use of well pits on 
 Grade A milk farms unless they are built to very rigid specifications. Prop- 
 erly constructed well pits are more expensive than other approved methods of 
 pump installation. 
 
GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 17 
 
 5) Make periodic bacterial analyses of the water supply. Dug wells are 
 more difficult to keep sanitary than are properly constructed drilled wells. 
 Wells drilled into creviced dolomite and limestone formations are, however, 
 also susceptible to bacterial pollution, particularly where the creviced forma- 
 tions are overlain by thin overburden. 
 
 Role of the Drilling Contractor 
 
 Much of the success of any drilled well depends on the skill and knowledge 
 of the drilling contractor. A drilling contractor has certain duties and respon- 
 sibilities to his customers. 
 
 1) The driller should provide an accurate log of the well or test hole at the 
 time it is completed. The log should include a description of the formations, 
 information on the static water level, basic construction features of the well 
 (length and size of well casing and screen, etc.), and an indication of the ca- 
 pacity of the well as determined by a pumping test. Copies of the driller's log 
 containing an accurate location should be filed with the State Geological Survey. 
 Log books may be obtained by drillers, without charge, from the State Geolog- 
 ical Survey. 
 
 2) The well should be constructed in accordance with accepted safe sani- 
 tary practices. The top of the well should be constructed to prevent surface 
 pollution from entering the well or seeping downward around the casing. It is 
 also desirable that well construction allow for measurement of the depth to 
 water without requiring removal of the pumping equipment. 
 
 3) The driller should endeavor to take full advantage of any water -yielding 
 formations he may encounter. In areas where groundwater conditions are gen- 
 erally unfavorable, it takes a skillful driller to obtain the maximum amount of 
 water from a poor formation. Where sand and gravel aquifers are used as a 
 source of groundwater, the driller should select a well screen on the basis of 
 size and sorting of the formation material. After construction the well should 
 be properly developed. A properly screened and developed well in sand and 
 gravel will not pump an objectionable amount of sand or silt during service. 
 
 4) It is desirable to save samples at 5-foot intervals for the total depth of 
 drilling, especially for municipal, industrial, irrigation, and school wells. The 
 State Geological Survey files samples of drill cuttings received from drillers. 
 The samples may be sent express collect to the Survey where they will be 
 studied and kept on file for reference. Information obtained from samples is 
 vital in effective rehabilitation of old wells. 
 
 COUNTY GROUNDWATER SUMMARIES 
 
 Detailed information on groundwater supplies in the counties of western 
 Illinois, south part, follows. These discussions supplement the geologic in- 
 formation shown on the maps in figures 6 and 7 and given in table 1. 
 
 Adams County 
 
 In Adams County thick permeable sand and gravel deposits suitable for 
 high-capacity wells are present at many locations in the valley of the Missis- 
 sippi River where the fill is as much as 125 feet thick. Drillers report mainly 
 
18 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 coarse material below 45 feet. Deposits of sand and gravel are locally present 
 along tributaries of the Mississippi such as Mill Creek, Ursa Creek, and Bear 
 Creek. Deposits are not always confined to the valley along these tributaries, 
 but in some cases also occur below the bordering upland. East of Quincy, por- 
 tions of the Mill Creek bedrock valley underlie the upland and contain water - 
 yielding deposits that are more than 150 feet below the surface. 
 
 Thin sand and gravel deposits containing considerable amounts of chert 
 occur in the lower part of the drift on the upland in the west half of the county. 
 These are suitable water sources for drilled or dug farm wells at some loca- 
 tions. 
 
 The Keokuk-Burlington limestone, present beneath the entire upland in the 
 county, is the main source of private water supplies. Water is generally ob- 
 tained from wells penetrating the limestone for 120 to 140 feet, and ranging in 
 depth from ZOO to 350 feet. At some places the upper, weathered part of the 
 formation, composed of well-creviced rock and pockets of loose chert, is a 
 source of water. The limestone is suitable mainly for small private ground- 
 water supplies and commonly yields water more or less charged with hydrogen 
 sulfide. Payson and Loraine obtain water from the Keokuk-Burlington lime- 
 stone with wells ranging from 300 to 330 feet in depth. 
 
 Groundwater possibilities in deeper bedrock formations are fair to poor. 
 The Devonian-Silurian limestone, which is absent near the southwestern corner 
 and is less than 50 feet thick in much of the county, is not highly creviced and 
 at some locations contains shows of gas, associated with saline water. Simi- 
 larly, the Kimmswick- Joachim dolomite is "tight" or yields water of poor 
 quality. 
 
 The St. Peter sandstone, encountered at depths ranging from 650 to more 
 than 900 feet, yields water that is too salty for most purposes, according to 
 analyses by the Illinois Geological Survey (Meents, et al., 111. Pet. 66, 1952, 
 p. 36). Analyses of water from the St. Peter sandstone from two wells in sec. 
 11, T. 2 S., R. 6 W., and sec. 26, T. 2 S., R. 8 W., show 8210 ppm total solids 
 with 3876 ppm chlorides and 12,258 ppm total solids with 6398 ppm chlorides 
 respectively. 
 
 Brown County 
 
 In Brown County the Illinois Valley, containing river deposits up to 75 feet 
 thick, is the most favorable area for developing municipal and industrial ground- 
 water supplies, though consideration must be given to water quality. Wells less 
 than 50 feet deep penetrating more than 20 feet of sand and gravel have been 
 constructed in the valley near the bluffs by the Village of Versailles, located 
 on the upland about two miles west of the valley. 
 
 Thinner, less continuous sand and gravel deposits in the La Moine River 
 valley have been developed as supplementary water sources at Mt. Sterling. 
 In the remainder of the county, where the glacial drift is generally less than 
 50 feet thick, consists mainly of tight till, and is extensively dissected by trib- 
 utaries of the Illinois River, water-bearing sand and gravel deposits are rarely 
 encountered. 
 
 The Keokuk-Burlington limestone is the primary source of groundwater 
 for domestic supplies. In most of the county it is within 250 feet of land surface 
 
GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 19 
 
 but is overlain by Pennsylvania!! rocks, Kinderhook shale, or both (fig. 6). 
 Drilling into the limestone about 130 feet is usually necessary to penetrate the 
 most favorable water -yielding zones, although at a few locations where the 
 limestone is highly fractured in its upper few feet good wells result with only 
 shallow penetration. Oil and gas shows and associated highly-mineralized 
 water have been reported in the Devonian-Silurian rocks in the area. 
 
 The permeable St. Peter and deeper Cambrian sandstones which occur 
 interbedded with thick dolomite formations below a depth of 1000 feet (fig. 4) 
 are potential water sources, though high mineralization (4076.4 ppm residue 
 with 1310 ppm chlorides) is reported by the State Water Survey for a water 
 sample from an old well at Mt. Sterling drilled more than Z000 feet deep and 
 penetrating the sandstones (Illinois Water Survey Bull. 21, 1925, p. 455). 
 
 Calhoun County 
 
 In Calhoun County groundwater conditions are highly variable because of 
 the intense dissection of the upland and the strong deformation of the bedrock 
 along the Cap au Gres faulted flexure (fig. 5). 
 
 Water supplies from sand and gravel are generally available in the Mis- 
 sissippi and Illinois River valleys. Deposits in the latter are 150 feet thick 
 near the east river bank opposite Hardin, and consist mainly of sand below a 
 depth of about 30 feet. Shallow deposits are reported to yield water of better 
 mineral quality, with less iron, than the deeper deposits. Small supplies of 
 water may be obtained from thin beds of sand and gravel at depths less than 
 50 feet in river terrace deposits of tributary valleys south of the Cap au Gres 
 faulted flexure. Glacial deposits are absent on the uplands, except for a small 
 area in the vicinity of Batchtown. Here water has been obtained from glacial 
 gravels at depths ranging from 35 to 65 feet. 
 
 Wells on the uplands obtain water from the Keokuk-Burlington limestone 
 in the northern quarter of the county, in the Devonian-Silurian dolomite from 
 near Kampsville to five or six miles south of Hardin, in the Kimmswick- 
 Joachim dolomite from east of Batchtown south to the Cap au Gres flexure, 
 and in the St. Louis limestone south of the flexure. The limestones and dolo- 
 mites are not extensively creviced and consequently yield water supplies suit- 
 able only for small domestic wells. 
 
 Springs are abundant in the limestone uplands, and have been extensively 
 used as sources of private, school, and community water supply. 
 
 The St. Peter sandstone is more permeable than the shallower limestone 
 and dolomite formations, and in some areas is an excellent source of ground- 
 water, particularly near its area of outcrop along the Mississippi River north 
 of the Cap au Gres flexure. 
 
 The State Water Survey records the following water analysis in parts per 
 million from a 453 -foot well open to the Kimmswick- Joachim dolomite and St. 
 Peter sandstone at Batchtown: residue, 402; hardness, 310; alkalinity, 392; 
 chlorides, 7; and sulphates, 17.8. The quality of water in the St. Peter declines 
 sharply to the north and east as the formation gets deeper. South of the Cap 
 au Gres flexure the St. Peter is more than 1000 feet deep and yields salt water. 
 
 Detailed information on the geology of Calhoun County is available in 
 United States Geological Survey Professional Paper 218 (Rubey, 1952). 
 
20 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 Cass County 
 
 Sand and gravel deposits suitable for small to large groundwater supplies 
 are present in the drift and river valley fill in more than half of Cass County. 
 Drilling in the Illinois River valley in the vicinity of Beardstown shows de- 
 posits at least 100 feet thick, consisting mainly of sand and gravel. Wells 
 show a gradation downward from sand through fine gravel to medium or, lo- 
 cally, coarse gravel. Although the deposits thin and become finer near the 
 bluffs, the entire flood-plain area is considered favorable for exploration for 
 sites for high-capacity wells. Similar deposits and groundwater conditions 
 exist along the wide Sangamon River flood plain in the northern part of the 
 county. 
 
 In the upland area, drift more than 150 feet thick occurs in a bedrock val- 
 ley 3 to 4 miles wide that passes eastward from the Illinois Valley between 
 Virginia and the southern edge of the county (fig. 7). Records of wells in the 
 valley show the fill to be composed almost entirely of glacial till or of glacial 
 till interbedded with deposits of sand and gravel that have accumulative thick- 
 ness of as much as 50 feet. 
 
 In the northern part of Cass County the drift has been intensively dissected 
 by tributaries of Sangamon River and most drilled wells go into the Pennsylvan- 
 ian or Keokuk-Burlington bedrock. South and east of Chandlerville many wells 
 obtain water from just below the No. 2 coal at depths less than 100 feet. The 
 Pennsylvanian rocks thicken eastward, and extend to a depth of about 400 feet 
 along the east county line. 
 
 Mississippian limestones underlie the drift in the western part of the 
 county but are seldom penetrated for water supplies because of the availabil- 
 ity of water in the shallower sand and gravel deposits. 
 
 The Devonian-Silurian formations, Kimmswick- Joachim dolomite, and St. 
 Peter sandstone have been penetrated in several wells at Beardstown and in 
 oil tests on the uplands. These horizons are considered unfavorable ground- 
 water sources because they are likely to yield highly mineralized water. 
 
 Greene County 
 
 Deposits in the Illinois River valley in Greene County range up to 150 feet 
 thick and include highly permeable sand and gravel. Macoupin and Apple Creek 
 valleys, as well as other smaller tributaries, also contain thin, discontinuous 
 deposits of sand and gravel that locally provide adequate groundwater for farm 
 and small municipal supplies, such as at Greenfield. 
 
 The glacial drift on the uplands averages about 50 feet in thickness and has 
 scattered pockets of sand and gravel that yield water. A number of these are 
 reported east of Carrollton to the vicinity of Greenfield and Fayette. 
 
 The principal source of private and municipal supplies of groundwater in 
 the county is the creviced Keokuk-Burlington limestone. Municipal supplies 
 at Carrollton have been obtained for many years from springs that issue from 
 fissures in the limestone cropping out along a small tributary of Apple Creek. 
 Roodhouse obtained water from similar springs along a tributary of Sandy Creek, 
 but later drilled 150-foot wells into the Keokuk-Burlington limestone near the 
 springs and secured yields of more than 400 gpm (Illinois Water Survey Bull. 
 40). 
 
GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 21 
 
 Water is also obtained from Pennsylvanian rocks and the Salem limestone 
 (fig. 4) in the eastern half of the county. East of Roodhouse many domestic wells 
 are finished in fractured shales or sandstones above or a few feet below coal 
 beds at a depth less than 100 feet. In wells where suitable water supplies are 
 not obtained in the Pennsylvanian rocks in this area drilling is extended into 
 the underlying Salem or Keokuk -Burlington limestones. 
 
 Drilling for private water supplies rarely goes below the Keokuk-Burling- 
 ton limestone, although the 200-foot thick Devonian-Silurian limestone and dol- 
 omite is a potential source of small to moderate amounts of groundwater along 
 the western edge of the county. Deeper horizons, including the St. Peter sand- 
 stone, are considered unfavorable groundwater sources because of poor quality 
 of the water. 
 
 Hancock County 
 
 In Hancock County permeable sand and gravel deposits occur along the 
 Mississippi River south of Warsaw where the valley flat attains a width of 4 
 miles, but are thin and restricted north of Warsaw where the river flows 
 through a narrow channel cut in Mississippian limestone. Less extensive, lo- 
 cally thick, permeable sand and gravel deposits also occur associated with the 
 valleys of Bear Creek, LaMoine River, and LaHarpe Creek and with a buried 
 bedrock valley which is partially outlined by dashes in figure 7. 
 
 Glacial deposits within the buried valley are not well known. In eastern 
 Hancock and southwestern McDonough counties sand and gravel deposits more 
 than 50 feet thick underlie the surficial glacial till. Favorable water -yielding 
 deposits are also present locally in the lower part of the valley, more or less 
 coincident with Bear Creek. North of Carthage, in the central part of the county, 
 the fill appears to be largely tight glacial till. 
 
 The Keokuk-Burlington limestone is within 200 feet of the surface in most 
 of the county and is the main source of groundwater supplies in the bedrock. At 
 some locations water is obtained from a weathered creviced zone at the top of 
 the limestone, but more commonly penetration of more than 100 feet is neces- 
 sary to obtain adequate water for domestic or farm supplies. Water -yielding 
 zones are rarely encountered in the Salem and Warsaw formations which over- 
 lie the Keokuk-Burlington. Pennsylvanian rocks are generally absent, although 
 along the east edge of the county and in isolated outliers to the west thin Penn- 
 sylvanian rocks occur beneath the drift and include sandstones that yield ground- 
 water. At Bowen a 42-foot Pennsylvanian sandstone is encountered at a depth 
 of 48 feet. 
 
 The Devonian-Silurian rocks and the Kimms wick- Joachim dolomite are re- 
 ported to be poorly to only moderately creviced, and therefore are not con- 
 sidered favorable horizons in which to attempt to obtain groundwater supplies, 
 in view of the depth of drilling necessary to test these formations. Depth to the 
 Devonian-Silurian rocks ranges from 450 to as much as 750 feet. The Kimms - 
 wick- Joachim is 100 to 200 feet deeper. 
 
 Water from the Kimmswick- Joachim dolomite, St. Peter sandstone, and 
 deeper Cambrian formations was formerly obtained at Carthage from wells 
 ranging in depth from 847 to 1700 feet (Illinois Water Survey Bull. 21, 1925, 
 
22 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 p. 114). This source was abandoned in favor of a surface supply, and at pres- 
 ent.drilling into the deeper formations is undertaken only in the course of oil 
 exploration. 
 
 Jersey County 
 
 In Jersey County water -yielding sand and gravel deposits suitable for 
 drilled wells are found mainly in the Illinois River valley and locally in Otter 
 and Macoupin Creek valleys. Extensive test-drilling in Otter Creek valley by 
 the City of Jerseyville showed permeable deposits less than 50 feet below the 
 valley flat in T. 7 N., R. 12 W., west of the city's limestone springs, and finer 
 grained, less permeable material in the lower part of the valley adjacent to 
 Illinois River. Sand is commonly encountered below 30 feet in the Illinois 
 River valley, and coarse sand usually below 50 feet. 
 
 Many farm wells in the eastern half of Jersey County obtain small supplies 
 of water from fractures in Pennsylvanian shales within a depth of 180 feet 
 (fig. 6). In wells drilled into underlying Mississippian limestones the Pennsyl- 
 vanian rocks are commonly cased off to prevent caving of the shales. 
 
 The Keokuk-Burlington limestone is the source of private groundwater sup- 
 plies in much of the county, with wells ranging in depth from less than 50 feet 
 in some of the hollows east of the confluence of the Illinois and Mississippi 
 rivers to more than 350 feet on the upland east of Jerseyville. At shallower 
 depths in the eastern two-thirds of the county the St. Louis -Salem limestone 
 (fig. 4) is sufficiently thick and creviced at some places to yield water for farm 
 wells. 
 
 Devonian-Silurian rocks are extensively exposed along the Illinois River 
 bluffs above the confluence with the Mississippi in the southwestern part of 
 Jersey County, and locally yield water. The Kimmswick- Joachim rocks which 
 occur about 150 feet below the base of the Silurian rocks in the same area com- 
 monly contain water unsuitable for domestic use. 
 
 In Jerseyville's old 1542 -foot well into the St. Peter sandstone, salt water 
 was reported in the Kimmswick- Joachim at a depth of 1040 feet, and after cas- 
 ing was set to a depth of 1367 feet, a water analysis by the Illinois Water Survey 
 showed a mineral content of 3012 ppm with 1347 ppm chlorides (Bull. 40, 1950). 
 Analysis by the Illinois Geological Survey of a water sample from the St. Peter 
 at a depth of 1700 feet seven miles east of Jerseyville showed 9040 ppm total 
 solids and 5234 ppm chlorides (Illinois Geol. Survey 111. Pet. 66, 1952, p. 37). 
 
 Morgan County 
 
 Sand and gravel deposits, which outside of the Illinois River valley are 
 generally thin and discontinuous, are more common in the northern half of 
 Morgan County where the glacial drift is from 50 to 150 feet thick. In the bed- 
 rock valley area outlined by dashes in figure 7, sand and gravel up to 35 feet 
 in thickness is reported, but little information is available on the nature or 
 productivity of the deposits. Mauvaise Terre Creek locally contains sand and 
 gravel which formerly was utilized by Jacksonville as a source of water supply. 
 
 Pennsylvanian rocks, which underlie the drift in the uplands, range in 
 thickness from 25 to 50 feet near the river bluffs to more than 400 feet in the 
 
GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 23 
 
 southeastern part of the county. At some locations private wells are finished 
 in sandstone or fractured coal, shale, or limestone in the Pennsylvanian rocks 
 within 200 or 300 feet of land surface. 
 
 The Salem limestone underlies the Pennsylvanian rocks and in many places 
 is penetrated for domestic groundwater supplies. Water-bearing crevices in 
 the Salem are not abundant, with the result that yields are generally low. Depth 
 to the Salem ranges from 175 to about 550 feet from northwest to southeast. 
 
 The Keokuk-Burlington limestone is usually more than 200 feet below the 
 top of the Salem and is rarely reached in domestic wells. Depths of the Devon- 
 ian-Silurian and St. Peter rocks in the eastern part of the county are shown in 
 table 1. 
 
 Drilling for water in the bedrock is somewhat restricted by the presence 
 of gas in the lower Pennsylvanian and Salem rocks in T. 15 N., R. 9 W. and in 
 Devonian rocks in T. 13 N., R. 8 W. The water associated with the gas in these 
 areas is usually not potable. Analysis of water from the Devonian-Silurian rocks 
 at a depth of 1020-1039 feet in sec. 22, T. 13 N., R. 8 W. shows 30,584 ppm 
 total solids with 16,635 ppm chlorides (Illinois Geol. Survey 111. Pet. 66, 1952, 
 p. 35). 
 
 Jacksonville formerly supplemented a surface supply with 3100-foot wells 
 that penetrated the St. Peter sandstone between depths of 1540 and 1837 feet and 
 passed into Cambrian sandstones at a depth of 2080 feet (Illinois Water Survey 
 Bull. 21, 1925, p. 297). According to Water Survey analysis this water had a 
 mineral content of 2431 ppm with 1000 ppm chlorides. Mineralization of water 
 from these formations increases eastward as the formations get deeper. 
 
 Pike County 
 
 Extensive water -yielding sand and gravel deposits occur only in the Mis- 
 sissippi River valley and, in the northeastern part of Pike County, in the Illi- 
 nois River valley. Municipal water supplies are obtained from sand and gravel 
 in the Mississippi Valley from wells commonly less than 75 feet deep at Pleas- 
 ant Hill, New Canton, Barry, Kinderhook, and Hull. The valley fill near the 
 river, composed mainly of sand and gravel below a depth of 20 to 40 feet, at- 
 tains a thickness of more than 130 feet. In the Illinois River valley in the north- 
 eastern part of the county, the fill thickens from less than 20 feet near the bluff 
 to about 80 feet near the river. 
 
 Tributary valleys such as Bay Creek and McKee Creek locally contain 
 water -yielding sand and gravel suitable for small municipal supplies, such as 
 at Nebo, Griggsville, and Perry. Favorable deposits on the uplands are thin 
 and discontinuous. 
 
 The Keokuk-Burlington limestone (figs. 4 and 6) is the primary source of 
 groundwater for private supplies in Pike County. Drillers report that water is 
 obtained in the upper 60 feet of the formation where crevicing is most exten- 
 sive. At some locations, particularly east of Pittsfield, the upper 25 to 30 feet 
 of the formation is composed of broken, rubbly rock which yields water readily. 
 The formation is less favorable for obtaining water west of the anticlinal belt 
 running northwestward through Pittsfield, including the area of the old Pitts - 
 field gas field. 
 
24 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 The Devonian and Silurian rocks (fig. 4) have been extensively tested for 
 oil and gas and are not considered favorable groundwater sources. Along the 
 Pittsfield anticline they locally contain gas and yield salt water. An analysis 
 of water from the interval in sec. 12, T. 3 S., R. 2 W., in northeastern Pike 
 County, shows 9764 ppm total solids with 5262 ppm chlorides (Illinois Geol. 
 Survey 111. Pet. 66, 1952, p. 35). 
 
 The St. Peter sandstone, which is encountered at depths from 600 to 1000 
 feet below land surface, is permeable and water-yielding, but at most locations, 
 especially from Pittsfield eastward, the water is probably highly mineralized. 
 Somewhat more favorable water quality is to be expected west of Pittsfield 
 where the St. Peter formation is shallower. Casing off the Kimmswick- Joachim 
 formations and penetrating the sandstone only for 25 to 50 feet is recommended 
 for water wells attempted in the St. Peter formation. Formations below the 
 St. Peter yield water too highly mineralized for most purposes, according to 
 analyses of waters from wells over 2000 feet deep at Barry and Pittsfield 
 (Illinois Water Survey Bull. 21, 1925, p. 54, 521). 
 
 Schuyler County 
 
 In Schuyler County the Keokuk-Burlington limestone, which is encountered 
 at depths ranging from 50 feet along LaMoine River to more than 350 feet on 
 the uplands just east of Rushville, is the main source of domestic groundwater 
 supplies. It is commonly 200 feet thick, although drilling usually penetrates 
 only the upper two-thirds of the limestone, the part reported to be the best 
 creviced. At some locations water is obtained from limestone and chert rubble 
 at the top of the formation. 
 
 On the uplands the Keokuk-Burlington is overlain by Warsaw shale, thin 
 Salem limestone, Pennsylvanian rocks, and glacial drift (figs. 4 and 6). At a 
 few locations drilled wells obtain water from the Salem limestone or Pennsyl- 
 vanian fractured shales, limestone, or coals, but these rocks are generally 
 less likely sources of groundwater than the Keokuk-Burlington. The Devonian- 
 Silurian rocks at some locations in the county contain minor amounts of oil and 
 gas, commonly associated with saline water. Water in the deeper bedrock for- 
 mations (St. Peter sandstone and below) is of uncertain quality and in some 
 places not potable. Analysis of water from a well drilled into the St. Peter 
 formation at Rushville shows 4284.8 ppm residue with 1485 ppm chlorides 
 (Illinois Water Survey Bull. 21, 1925, p. 577). 
 
 Sand and gravel, which occurs extensively only in the Illinois River valley, 
 is the best source of large groundwater supplies for industrial and municipal 
 use in the county. Deposits in the valley are less than 75 feet thick, but they 
 contain coarse permeable material within 10 to 25 feet of the surface. One of 
 the Rushville municipal wells, located on the valley flat near the bluffs 6 1/2 
 miles southeast of the city, is 50 feet deep and has been tested at 300 gallons 
 per minute with 11/4 feet of drawdown (Illinois Water Survey Bull. 40, 1950). 
 
 Thinner, discontinuous sand and gravel deposits, which occur in the valley 
 of LaMoine River, are potential sources of moderate industrial and municipal 
 groundwater supplies. The upland is underlain by well-dissected, thin imper- 
 meable glacial drift in which sand and gravel deposits capable of supplying 
 even domestic wells are rarely encountered. 
 
GROUNDWATER IN WESTERN ILLINOIS (SOUTH) 25 
 
 Scott County 
 
 In Scott County excellent water -yielding sand and gravel deposits occur in 
 the Illinois River valley at depths less than 125 feet. Test-drilling by the City 
 of Jacksonville adjacent to the river a mile south of the north county -line 
 showed nearly continuous sand and gravel below a depth of about 25 feet. The 
 following section was penetrated in one of the test wells: 
 
 Description Thickness (ft.) Depth (ft.) 
 
 Silt, fine, sandy 25 25 
 
 Sand, medium, traces of gravel 9 34 
 
 Sand, medium, with 15% pea gravel, 
 
 5% medium gravel 16 50 
 
 Sand, medium, with 10% pea gravel, 
 
 clay balls 
 Sand, medium, traces of gravel 
 Sand, gray, with 10% medium gravel 
 Sand, medium, with 15% medium 
 
 coarse gravel 
 Sand, medium, with 40% medium 
 
 coarse gravel 
 Sand and gravel, cemented 
 
 Thinner, less continuous sand and gravel deposits occur in the valley of 
 Sandy Creek. Winchester obtains groundwater from deposits 20 to 30 feet 
 thick encountered at a depth of 20 feet in the valley a mile south of town. 
 Water -yielding sand and gravel deposits on the upland are rare, although a few 
 successful private wells have been completed in sand and gravel west of Win- 
 chester. 
 
 Most drilled wells in Scott County are completed in Mississippi lime- 
 stone bedrock at depths less than 300 feet (fig. 4). The Keokuk -Burlington 
 limestone occurs at shallow depths in the west part of Scott County and east 
 of Winchester (fig. 6). In the northeast and southeast townships where thin 
 Pennsylvanian rocks overlie Mississippian rocks it is customary to finish 
 wells in the Keokuk-Burlington and case off the overlying shales and drift. At 
 some locations in these townships water is obtained from coal beds, sandstones, 
 or fractured limestones or shales in the Pennsylvanian rocks. 
 
 2 
 
 52 
 
 8 
 
 60 
 
 9 
 
 69 
 
 
 
 89 
 
 6 
 
 95 
 
 2 
 
 97 T.D. * 
 
 * Limestone bedrock at 97 feet. 
 
26 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
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28 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 SUGGESTED READING 
 
 Bedrock topography of Illinois: Leland Horberg, Illinois Geol. Survey Bull. 73, 
 1950. 
 
 Cisterns: Illinois Dept. of Public Health Circ. 129, 1949. 
 
 Disinfection of water: Illinois Dept. of Public Health Circ. 97, 1950. 
 
 Geology and mineral resources of the Hardin and Brussels quadrangles (in 
 Illinois): "William W. Rubey, U. S. Geol. Survey Prof. Paper 218, 1952. 
 
 Gravel packing water wells: H. F. Smith, Illinois "Water Survey Circ. 44, 1954. 
 
 Illinois water supply: "Water Resources Committee, Illinois State Chamber of 
 Commerce, 1956. 
 
 Individual water supply systems: Recommendations of the Joint Committee on 
 Rural Sanitation, U. S. Public Health Service Publication 24, 1950. 
 
 Public ground-water supplies in Illinois: compiled by G. C. Habermeyer, 
 Illinois Water Survey Bull. 21, 1925. 
 
 Public ground-water supplies in Illinois: compiled by Ross Hanson, Illinois 
 "Water Survey Bull. 40, 1950. 
 
 Significance of Pleistocene deposits in the groundwater resources of Illinois: 
 J. W. Foster, Econ. Geol., v. 48, no. 7, November 1953. 
 
 Wells, dug, drilled, driven: Illinois Dept. of Public Health Circ. 14, 1951. 
 
 Other general reports on groundwater geology in Illinois similar in purpose 
 and scope to the present study include the following circulars: C. 192, 
 Water wells for farm supply in central and eastern Illinois; C. 198, 
 Groundwater possibilities in northeastern Illinois; C. 207, Groundwater 
 in northwestern Illinois; C. 212, Groundwater geology in southern Illinois; 
 C. 222, Groundwater geology in western Illinois, north part; and C. 225, 
 Groundwater geology in south-central Illinois. These circulars, published 
 by the Illinois State Geological Survey, are available free on request. 
 
 Topographic maps are available for the area covered in this report. These 
 
 maps are on a scale of approximately 1 inch to the mile. They are printed 
 by quadrangles and may be obtained from the Illinois State Geological 
 Survey, Urbana, Illinois, or from the United States Geological Survey, 
 Washington 25, D. C, for 30 cents each. Index maps showing the topo- 
 graphic map coverage of the State are free on request. 
 
 Detailed geologic reports have been published or are in preparation for the 
 
 following quadrangles: Colchester, Macomb, Tallula, Springfield, Hardin, 
 Brussels, and Beardstown. Information on these reports may be obtained 
 from the Illinois State Geological Survey in Urbana. 
 
 Illinois State Geological Survey Circular 232 
 28 p., 7 figs., 1 table, 1957 
 
immzi} 
 
 JCandofJUncofa/ii 
 
 CIRCULAR 232 
 
 ILLINOIS STATE GEOLOGICAL SURVEY 
 
 URBANA