Geology topics

Research about Iowa, Illinois, Indiana, Michigan, Minnesota, Missouri, Wisconsin

Source-linked reports with geographic coverage including Iowa, Illinois, Indiana, Michigan, Minnesota, Missouri, Wisconsin.

3 recordsLinked to original sources

USGS1992

Summary of ground-water hydrology of the Cambrian-Ordovician aquifer system in the northern Midwest, United States

The Cambrian-Ordovician aquifer system contains very productive aquifers throughout an area of about 161,000 square miles in the northern Midwest. The aquifer system is used extensively for industrial and rural water supplies and is the primary source of water for many municipalities in most of its area of occurrence, except in Indiana, central and southern Illinois, and western Iowa, where the aquifer system contains saline water. About 680 million gallons per day was withdrawn from drilled wells in the aquifer system in 1980. Rocks of Cambrian and Ordovician age, mainly marine sandstones and carbonate rocks, constitute most of the bedrock and subcrop beneath glacial drift in southeastern Minnesota, northeastern Iowa, Wisconsin, northern Illinois, and extreme northwestern Indiana. These strata dip generally to the south and east off the Transcontinental arch in Minnesota and the Wisconsin arch, which are structurally high areas of the Precambrian basement, into the structural lows of the Forest City basin of southwestern Iowa, the Illinois basin, and the Michigan basin. The Cambrian and Ordovician rocks are buried by younger rocks in the remainder of Iowa, Illinois, and Indiana and in most of northern Missouri. Silurian and Devonian carbonate rocks immediately overlie the Cambrian and Ordovician rocks in those areas and are termed the "Silurian-Devonian aquifer" in this study. The balance of the Devonian rocks and the overlying Mississippian and Pennsylvanian rocks generally are fine-grained sediment or dense carbonate rocks and collectively are considered to be a regional confining unit. Most of the area is covered by a veneer of glacial drift, which, along with Cretaceous sandstone in northwestern Iowa, is treated as a regional water-table aquifer. The Cambrian-Ordovician aquifer system is composed of six hydrogeologic units, which are, in descending order, the Maquoketa confining unit, St. Peter-Prairie du Chien-Jordan aquifer, St. Lawrence- Franconia confining unit, Ironton-Galesville aquifer, Eau Claire confining unit, and Mount Simon aquifer. The uppermost confining unit is the least permeable; it consists primarily of the Maquoketa Shale but includes the dense carbonate rocks of the Galena Dolomite and the Decorah, Platteville, and Glenwood Formations where they are overlain by the Maquoketa Shale. The presence of the Maquoketa in Iowa, eastern Wisconsin, northeastern Illinois, and Indiana effectively confines the entire aquifer system below. The aquifer system is a leaky-artesian system in which movement of ground water is controlled partly by the internal confining units. In the northern outcrop area, unconfined conditions prevail in shallow parts of the aquifer system and where the system is thin. Much of the recharge in upland areas discharges to streams through local flow systems, which are no more than a few miles in length. The remainder of the recharge moves slowly downward to deeper formations and downgradient to form or join the regional flow system. Computer simulations of regional ground-water flow improve understanding of the regional character of the Cambrian-Ordovician aquifer system. Ground-water flow in the confined part of the aquifer system is mainly horizontal, away from the structural highs in the north, toward the structural basins in the south and east. The rate of ground-water movement is very slow, and the flux along flow paths into the basins decreases because of a progressive loss of head and small but widespread upward leakage. Saline water in the basins restricts movement of freshwater into the deeper parts of the basins, thereby forcing flow upward through confining units. Principal regional discharge areas are the Mississippi and Missouri Rivers, the Illinois and Michigan structural basins, and Lake Michigan. However, the lake is not in direct hydraulic connection with the Cambrian-Ordovician aquifer system and receives flow primarily from the Silurian-Devonian aquifer, which it directly overlies. The longest regional flow paths originate in recharge areas in northwestern Iowa and extend southeastward as much as 400 miles toward the Illinois basin. Simulated predevelopment recharge and discharge for the Cambrian- Ordovician aquifer system balance at 351 million gallons per day. Development of the aquifer system began in various parts of the northern Midwest in the 1860's and 1870's with the drilling of deep, generally flowing artesian wells near Lake Michigan in eastern Wisconsin and northeastern Illinois and along the valleys of the Mississippi River and its tributaries. Initial heads of 186 and 130 feet above Lake Michigan at Milwaukee and Chicago, respectively, have been reported. Large-scale pumping has produced cones of depression in these two areas, with respective head declines of as much as 375 and 900 feet. Other major pumping centers generally have had much smaller declines. The largest withdrawals from the aquifer system were about 180 million gallons per day in each of the major metropolitan areas of Chicago and Minneapolis-St. Paul (Twin Cities). However, the total decline in head in the St. Peter-Prairie du Chien-Jordan aquifer in the Twin Cities by 1980 was only 90 feet because the aquifer is unconfined. Most of the eastern two-thirds of Iowa, where the aquifer system is tightly confined, is characterized by more than 50 feet of head decline, with 200 feet or more at Mason City and the Quad Cities. Pumpage from the Cambrian-Ordovician aquifer system throughout the study area averaged 683 million gallons per day for the period 1976-80. Results of a transient-model simulation show that recharge increased over predevelopment recharge by 447 million gallons per day. Natural discharge decreased by 99 million gallons per day, and 137 million gallons per day was released from aquifer storage. Mineralization of ground water in the aquifer system increases from slightly mineralized calcium magnesium bicarbonate water in the northern recharge areas, through more mineralized, mixed water types with increased sodium and sulfate, to highly mineralized sodium chloride brines in the deeper parts of the structural basins.

Iowa, Illinois, Indiana, Michigan, Minnesota, Miss↗

USGS1992

Hydrogeology of the Cambrian-Ordovician aquifer system in the northern Midwest, United States with a section on ground-water quality

The Cambrian-Ordovician aquifer system contains the most extensive and continuous aquifers in the northern Midwest of the United States. It is the source of water for many municipalities, industries, and rural water users. Since the beginning of ground-water development from the aquifer system in the late 1800's, hydraulic heads have declined hundreds of feet in the heavily pumped Chicago-Milwaukee area and somewhat less in other metropolitan areas. The U.S. Geological Survey has completed a regional assessment of this aquifer system within a 161,000-square-mile area encompassing northern Illinois, northwestern Indiana, Iowa, southeastern Minnesota, northern Missouri, and Wisconsin. Consolidated sedimentary rocks in the northern Midwest range in age from Precambrian to Cretaceous and crop out in generally concentric, arcuate patterns, dipping away from structural highs (arches) on the Precambrian basement in northern Minnesota and Wisconsin toward structural lows (basins) to the south and east. The sedimentary bedrock is generally overlain by a veneer of glacial drift. Thickness of the sedimentary sequence increases to about 5,000 feet in the Forest City basin of southwestern Iowa and to about 14,000 and more than 15,000 feet in the Illinois and Michigan basins, respectively. Cambrian and Ordovician age rocks, mainly marine sandstone and carbonate rocks, compose much of the sedimentary sequence and form the Cambrian-Ordovician aquifer system. The aquifer system lies on the Precambrian basement, regarded as a regional confining unit. Six hydrogeologic units are defined; they are arranged as alternating pairs of an aquifer and an overlying confining. unit. The units are named using the predominant geologic nomenclature of the upper Mississippi Valley, which includes most of the study area. In the southern quarter of the area, the hydrogeologic units consist of equivalent formations of the Ozark area (mostly carbonate rocks). The uppermost part of the aquifer system is the Maquoketa confining unit, which consists of the Maquoketa Shale and the underlying dolomite and shale of the Galena Dolomite and the Decorah, Platteville, and Glenwood Formations. The underlying St. Peter-Prairie du Chien-Jordan aquifer is an important source of ground water in the western part of the area in Iowa and Minnesota, where the uniform Jordan Sandstone is hydraulically connected to overlying fractured dolomite of the Prairie du Chien Group. The unit is less important in the eastern part of Wisconsin and Illinois because the Jordan Sandstone is absent and the Prairie du Chien Group is thin or absent due to pre-St. Peter Sandstone erosion. Equivalent rocks in northern Missouri-the Roubidoux Formation and the Gasconade and Eminence Dolomites-are mainly carbonate rocks that are somewhat permeable and contain some sandstone. The St. Lawrence and Franconia Formations underlying the St. Peter-Prairie du Chien-Jordan aquifer consist generally of silty and shaly, fine-grained, poorly sorted, and dolomitic sandstones that restrict vertical movement of ground water and form a regional confining unit. In the southern and eastern parts of the area, the Potosi and Derby-Doerun Dolomites and the upper part of the Davis Formation are the equivalent rocks (mainly carbonate rocks). In the east-central part of the area in Illinois and Wisconsin, the Ironton-Galesville aquifer forms the most important aquifer of the Cambrian-Ordovician aquifer system, contributing about one-third of the yield from wells in the aquifer system in the Chicago area. The aquifer terminates to the west, south, and east, where the sandstones grade into less permeable carbonate rocks in central Iowa, central Illinois, and northwestern Indiana, respectively. The underlying Eau Claire Formation and its partial equivalent to the southwest, the Bonneterre Formation, form an important confining unit above the Mount Simon aquifer throughout much of the study area. Siltstone and shale are fairly common in the upper part of the Eau Claire Formation but less so in its northernmost extent in Wisconsin. Dolomite content increases southward and westward, where a middle dolomite facies grades laterally into the Bonneterre in Missouri, southwestern Minnesota, extreme south-central Wisconsin, and possibly in western Iowa. The basal unit in the Cambrian-Ordovician aquifer system, the Mount Simon aquifer, is present throughout the study area, except where it is absent over local highs of the Precambrian basement. It consists primarily of the Mount Simon Sandstone in the north and its equivalent in northern Missouri, the Lamotte Sandstone. The underlying Hinckley Sandstone of Precambrian age is included in Minnesota, as is the overlying Elmhurst Sandstone Member of the Eau Claire Formation in northern Illinois. The aquifer increases greatly in thickness and the water is progressively more saline away from the northern structural highs toward the basins. Much of the movement and discharge of ground water in the northern Midwest occurs in local, unconfined, shallow flow systems within a few miles of points of recharge. The rest of the water is semiconfined or confined in intermediate or regional flow systems within the bedrock, where flow is deeper, slower, and traverses much longer distances from recharge areas to discharge areas. The major areas of recharge to regional confined flow are in northwestern Iowa, southeastern Minnesota, western, southern, and eastern Wisconsin, and northern Illinois. Although the rate of flow is small, significant recharge to the Cambrian-Ordovician aquifer system also occurs as leakage through the Maquoketa confining unit, where the vertical hydraulic gradient is downward. Ground water in much of the confined aquifer system moves laterally from recharge areas toward the major river valleys and Lake Michigan or down dip toward the structural basins. The longest flow paths extend as much as 400 miles from northwestern Iowa southeast toward the Illinois basin or to the Mississippi River and Missouri River valleys near their confluence. Other major confined flow is from eastern Wisconsin toward the Michigan basin and southward flow from northeastern Illinois toward the Illinois basin. Regional ground-water discharge from the aquifer system is mainly diffuse upward leakage from confined aquifers along flow paths toward the structural basins. Very saline water around and brines within the basins restrict regional flow into the basins, forcing ground water to discharge upward. Water in intermediate flow systems discharges upward to the major river valleys. Original heads of more than 100 feet above land surface were recorded in the aquifer system near Lake Michigan in eastern Wisconsin and at Dubuque, Iowa, along the Mississippi River. The Cambrian-Ordovician aquifer system was developed rapidly in the late 1800's after the first deep well was drilled in Chicago in 1864. Many flowing wells were not controlled, which caused water levels in deep wells to decline, and many no longer flowed by the early 1900's. Heads in the aquifers have declined very little in most of the recharge or unconfined areas since ground-water withdrawal began, but major declines have occurred in confined areas. The largest declines in head are at Chicago, Illinois, Milwaukee and Green Bay, Wisconsin, and Mason City, Iowa, where the aquifer system is confined by the Maquoketa confining unit. The composite head in the aquifer system declined more than 900 feet in the deepest cones of depression in the Chicago area from 1864 to 1980 and about 375 feet in the cone at Milwaukee from 1880 to 1980. More than 200 feet of decline has occurred at Mason City. The head declined as much as 440 feet in Green Bay from 1886 to 1957, when the city discontinued use of its deep wells and began using water from Lake Michigan. The largest centers of pumping are in the Chicago and Twin Cities (Minneapolis-St. Paul, Minnesota) metropolitan areas about 180 million gallons per day each in 1980. Pumpage exceeded 10 million gallons per day in only a few other areas in 1980. Ground water in the Cambrian-Ordovician aquifer system in the northern Midwest is characterized by an extreme range of mineralization, but its quality in most of the area is good. The major cations are calcium, magnesium, and sodium, and the major anions are bicarbonate, sulfate, and chloride. Sodium, sulfate, and chloride distributions are closely related to the distribution pattern of dissolved solids but not in the same proportion. Dissolved-solids concentration is generally less than 1,000 milligrams per liter in the recharge areas of Wisconsin, southern Minnesota, northeastern Iowa, and north-central Illinois where the aquifer system crops out or subcrops beneath glacial drift. Ground water there is the Ca-Mg-HC03 type, derived from and identical to that in the overlying glacial drift. In northwestern Iowa and southwestern Minnesota, the water in both the glacial drift and the Cambrian-Ordovician aquifer system is a Ca-Na-S04HC03 type, derived from oxidation of pyrite in the overlying Cretaceous Dakota Formation. Transition to higher dissolved solids in the confined areas commonly is accompanied by increased sulfate concentration and· the occurrence of Ca-Na-S04-type water. Salinity of the ground water increases progressively toward the .basins, where dissolved solids exceed 200,000 milligrams per liter. Saline water is present in the Mount Simon aquifer near Lake Michigan in eastern Wisconsin and northeastern Illinois but occurs in successively younger rocks to the east and south as they dip toward the basins. Similarly, salinity increases down dip in Iowa to the southwest and south; however, regional ground-water flow in Iowa is from northwest to southeast. Much of the ground water in the confined aquifer system is isotopically depleted in 0180 and OD with respect to modern precipitation-an indication that the water originated as precipitation in a much colder climate than the present and probably was derived from recharge of glacial meltwater. On the basis of o34S values for sulfur in sulfate, it is believed that isostatic loading from glacial ice over the Michigan basin reversed the hydraulic gradient to trend westward, opposite from the present gradient, causing saline water in the Michigan basin to discharge westward through the present recharge areas. Natural water-quality problems in the Cambrian-Ordovician aquifer system are mainly the high dissolved-solids concentrations and associated high concentrations of sulfate and chloride, which limit the use of the water for municipal and domestic purposes in much of the confined aquifer system in central and southern Illinois, Indiana, southern and western Iowa, and northern Missouri. Another concern is that radium activity exceeds normal background concentrations of a few picocuries per liter in much of the confined aquifer system in eastern Wisconsin, northeastern Illinois, and central Iowa. Other common problems are high hardness and locally excessive concentrations of iron and hydrogen sulfide.

Iowa, Illinois, Indiana, Michigan, Minnesota, Miss↗

USGS1992

Simulation of regional ground-water flow in the Cambrian-Ordovician aquifer system in the northern Midwest, United States: in Regional aquifer-system analysis

A six-State area in the northern Midwest of the United States has become increasingly dependent on ground water from the Cambrian-Ordovician aquifer system, which consists of a sequence of sandstones, carbonate rocks, and shales. Ground-water withdrawals from the aquifer system began in the late 1800's and increased to approximately 684 million gallons per day (1,058 cubic feet per second) by 1980. This withdrawal has caused more than 900 feet of decline in the potentiometric surface of the aquifer system in parts of the Chicago, Ill., area. Pumping in Minneapolis-St. Paul, Minn., Milwaukee, Wis., and central Iowa has produced a few hundreds of feet of water-level decline. A quasi-three-dimensional ground-water flow model was developed to improve understanding of the regional ground-water flow system by simulating the aquifer system under the conditions that existed before and during ground-water development. The Cambrian-Ordovician aquifer system and the overlying rocks were incorporated in the conceptual model as five aquifer layers with four intervening confining layers. The aquifer layers, from top to bottom, are as follows: Quaternary deposits and Cretaceous rocks (aquifer layer 5); basal Devonian carbonate rocks and underlying Silurian carbonate rocks (aquifer layer 4); Middle Ordovician St. Peter Sandstone, Lower Ordovician Prairie du Chien Group, and Upper Cambrian Jordan Sandstone (aquifer layer 3); Upper Cambrian Ironton and Galesville Sandstones (aquifer layer 2); and Upper Cambrian Mount Simon Sandstone and Precambrian Hinckley Sandstone (aquifer layer 1). The effects on the flow system of ground water having variable density and the individual aquifer layer contribution of flow to wells open to several aquifer layers were simulated by incorporating appropriate terms in the ground-water flow equation and corresponding modifications in the ground-water flow model. Results of steady-state simulations are shown as maps of freshwater head and as flow-rate vectors. A comparison was made of available predevelopment head data and simulated predevelopment heads for the Mount Simon, St. Peter-Prairie du Chien-Jordan, and Silurian-Devonian aquifers. The root mean square of the differences between observed and simulated heads for these aquifers was 53, 36, and 44 feet, respectively. Steady-state model simulation indicates that regional recharge areas are located in northwestern Iowa, southeastern Minnesota, much of Wisconsin, northern Illinois, and central Missouri. Regional discharge areas are located near the Mississippi River and its tributaries, the Missouri River, Lake Michigan, and the Illinois basin. Results of a transient simulation of the period 1861 to 1980 are shown as maps of freshwater head and freshwater-head decline. The root mean square of the differences between observed and simulated heads for the St. Peter-Prairie du Chien-Jordan aquifer was 63 feet. In addition, hydrographs of simulated hydraulic head were compared with hydrographs of observed head in wells open to various combinations of aquifers. The numerous head measurements within a model node display a wide range in magnitude; however, their historical trend generally follows the trend of the simulated heads. The simulated recharge from the glacial drift to the immediately underlying bedrock aquifers averages 0.03, 0.06, 0.24, and 0.02 inch per year, respectively, to the Mount Simon, Ironton-Galesville, St. Peter- Prairie du Chien-Jordan, and Silurian-Devonian aquifers for predevelopment conditions and 0.03, 0.07, 0.45, and 0.07 inch per year, respectively, to the same aquifers for 1976-80. These recharge rates are less than 1.5 percent of average annual precipitation of about 30 inches per year. Most of the recharge from precipitation discharges to streams as base flow through local and intermediate ground-water flow systems. Only a small fraction of the precipitation recharges the deeper, regional flow system. The simulated predevelopment recharge of 571 cubic feet per second is balanced by an equivalent discharge. For the period 1976-80, simulated recharge increased to 1,398 cubic feet per second. Total discharge, including pumpage from the four bedrock aquifers, increased to 1,619 cubic feet per second. The difference in recharge and discharge during this period is from aquifer storage. Results of variable-density simulations indicate that the rate of ground-water movement is small in areas where ground water is highly mineralized. The rates and directions are controlled by the intrinsic permeability of the rock, freshwater head gradients, and gravitational force.

Iowa, Illinois, Indiana, Michigan, Minnesota, Miss↗