GROUND WATER MINING--WHEN DISCHARGE EXCEEDS RECHARGE


From The Changing Illinois Environment: Critical Trends, Volume 2: Water Resources , Technical Report of the Critical Trends Assessment Project

INTRODUCTION

Ground water is an economically important, renewable resource. Each day Illinois uses large quantities of ground water to meet its supply needs for drinking water, industry, and power generation. Over one billion gallons of ground water are displaced and/or consumed daily for these uses (IWIP, 1991). Major metropolitan areas require vast amounts of water to sustain the needs of the people and businesses within their boundaries. No matter the size of these supplies, however, they are not infinite in their ability to meet demand. When the limits of renewability are exceeded, groundwater mining occurs. While some "overdrafts" in the hydrologic budget can be tolerated and might even be desirable, long-term mining of ground water should be avoided.

Understanding the availability of ground water in Illinois also requires understanding the concept of ground water and the processes associated with its availability. In general terms, ground water is any precipitation on the land surface that percolates down through the soil and reaches the water table or the zone of total saturation near the land surface. This zone is open to atmospheric pressures and responds quickly to fluctuations in precipitation. It also acts as a reservoir that slowly recharges the water bearing geologic materials beneath it. Some strata buried below the land surface store water in sufficient quantities to make it economically possible to withdraw this water. These formations are called aquifers. An aquifer is best defined as a saturated, permeable geologic unit that can transmit significant quantities of water under ordinary hydraulic gradients (Freeze and Cherry, 1979). The distribution of the materials that constitute aquifers is highly variable throughout Illinois, as are the amounts of ground water available within them.

Groundwater availability is highly dependent upon the geologic material within which it is stored. For exam- ple, sand and gravel formations found in the unconsolidated materials above bedrock store and release ground water with relative ease. Yield is determined by the interconnection of pore spaces between the sand and gravel particles and the amounts of clay and/or other claylike geologic materials blended within them. These clay or claylike materials will retard an aquifer's ability to release water when pumped. Limestone-type aquifers, on the other hand, can release large quantities of water, depending upon the degree and interconnection of the cracks and crevices found within the limestone. Sandstone aquifers are limited, inversely, in their ability to transmit ground water by the amount of cementation of the sand grains that make up the rock.

Groundwater scientists describe an aquifer's ability to transmit water in terms of transmissivity. Values can range from perhaps 300,000 down to 10,000 gallons per day per square foot (gpd/ft2). Usually the unconsolidated deposits of sand and gravel in Illinois have the highest transmissivity values. By contrast, the values for bedrock aquifers composed of sandstone or limestone usually are only a few thousand gpd/ft2.

Aquifers have existed for thousands and even millions of years. In fact, long before humans began using ground water, flowpaths were established within these aquifer systems. A kind of equilibrium or steady-state condition existed between recharge and discharge, even though the aquifers were completely full. Typically these two actions balance in an annual cycle. Thus, if more water flowed out of the system, then more ground water could be added during the next recharge part of the cycle, so that the overall amount of storage remained the same.

Recharge normally occurs throughout the entire state of Illinois on an annual cycle. During a drought, which may last several years, there may be little recharge to an aquifer, while demand for ground water is typically the greatest. During wet times, there may be so much water available for recharge, that it exceeds the infiltration rates and bypasses the groundwater system. The two key points to remember are that recharge is seasonal and that it varies in amount from year to year. Hydrologists can estimate an average annual recharge for an aquifer, and if pumpage data are available, they can predict with some certainty where problems may arise. This average would likely be based on 20 or perhaps even 30 years.

In several areas in Illinois, trends in groundwater use have prompted investigations of an aquifer's ability to supply a sustained yield of ground water for the required need. Bowman (1991) identified areas in Illinois where the groundwater use is approximately equal to or has exceeded the available yield of the aquifer system. Of the areas that were identified, only the Chicago region has experienced groundwater mining due to both the intense demand and the relatively low trans-missivity of the major aquifer supplying the region.

This chapter examines groundwater use in the Chicago region and contrasts it with three other areas in the state (Peoria region, eastern Kankakee and Northern Iroquois Counties, and the American Bottoms region) where major changes in groundwater use have occurred. It examines the hydrogeologic factors associated with these areas, the potential yield of each aquifer system, and the impacts caused by demand for the groundwater resource. These four high use areas were chosen because data are available and because ground water meets the demand of a significant segment of their population, important industries, or irrigation needs. Groundwater mining has the potential to be of critical concern to each of these areas.

THE CHICAGO REGION

Problem Statement

The Chicago region has been a focus of groundwater research for decades. In one of the best overall assess-ments of the region, Suter et al. (1959) noted that some of the bedrock aquifers that underlie the area had been used for nearly 100 years. That early report, known as Cooperative Report No. 1, between the Illinois State Water and Geological Surveys, correctly recognized that the diversity of underground water sources (aqui-fers) had helped promote the industrial expansion of the area. It also recognized that withdrawals from the key aquifer, the Ironton Galesville Sandstone, were outstripping the sustained yield of the aquifer. That is, groundwater mining had begun.

The inevitable consequence of groundwater mining is that critical water levels will be reached and well yields will decline significantly. This situation was recognized in the early 1960s in the Chicago region and resulted in a lawsuit being brought by the state of Wisconsin against the state of Illinois. Consequently, in 1966 the U.S. Supreme Court issued a decree concerning groundwater withdrawals in the Chicago region. As a result of an amendment to that decree, planners for Illinois had to formally recognize the need to reduce pumpage from the Cambrian-Ordovician aquifer system in northeastern Illinois (Fetter, 1981). Accordingly, the 81st General Assembly directed the Illinois Department of Transportation/Division of Water Resources (IDOT/DWR) to implement a long term program for allocating Lake Michigan water. The program regulates the use of Lake Michigan water by Illinois and has funded impact studies of pumpage from the deep sandstone aquifer underlying northeastern Illinois.

The allocation program initiated two hydrogeologic modeling studies (Prickett and Lonnquist, 1971; Burch, 1991) in an attempt to characterize water level trends, pumpage, and recharge rates of this system. These computer models were (and currently are) used as tools in the management of the groundwater resource. The first model, developed by Prickett and Lonnquist, was a predictive or deterministic one. Like all models, it solves equations numerically and is useful in describing certain cause and effect relationships. Because it uses simplifying assumptions about groundwater flow equations, aquifer boundaries, and initial starting conditions, the model can be used to predict water levels. Conclusions about groundwater drawdowns or recoveries can then be made by comparing the results of different simulations.

Burch (1991) redeveloped the original Chicago model partly because computer hardware has moved beyond the mainframes and punch cards that Prickett and Lonnquist used. Burch sought to use the model in a microcomputer/personal computer (PC) environment, which allows low cost preprocessing of input data and postprocessing of model calculations. With this new version of the Chicago model, Burch was able to determine the impact of substituting Lake Michigan water for ground water in the Chicago region. His investigation made use of the detailed pumpage and hydrogeologic data available by merging classical methods with new mapping techniques.

Water Use in the Chicago Region

Since 1980, the Water Survey has maintained computer records of groundwater pumpage. Prior to that, however, only penciled notations on paper forms were kept for most communities, industries, and golf courses in northeastern Illinois. The Water Survey periodically published summaries of these notes, which generally represented annual compilations for each usage type by county. These early records, which were diligently maintained between 1964 and 1980, were combined with computer data to form the best available record of groundwater pumpage in northeastern Illinois.

Figure 1 illustrates the modern history of groundwater pumpage from public and industrial wells in the Chicago region. It clearly indicates that major pumpage from this area increased for several decades until the 1980s and 1990s.

Water-Level Trends: Lesson in Responsiveness to Lake Michigan Substitutions

Each year since 1959, the heavy demand on the most significant aquifer in northeastern Illinois has exceeded the resource's ability to recharge. Consequently, pump age has had an ever increasing effect on groundwater levels. By 1960, the drawdowns at the pumping centers associated with each community had overlapped enough to produce a regional cone of depression. Groundwater levels declined by more than 1,000 feet at some locations. In many parts of the Chicago region, the groundwater level had fallen to elevations below sea level.

With the deliveries of Lake Michigan water to communities in Cook County in the 1980s, however, the trend began to reverse. Sasman et al. (1986) reported that water levels were rising in some areas that previously had relied on the deep Cambrian-Ordovician aquifer system. Figure 1 shows the impact of this trend on pumpage. More conversions to Lake Michigan water in the late 1980s at Des Plaines, Arlington Heights, and Mt. Prospect resulted in even more areas of rising water levels according to Visocky's 1991 observations (Visocky, 1993). This trend is expected to continue as more Lake Michigan water is delivered to DuPage County and parts of Lake County. The computer simulation by Burch (1991) predicts that this trend may result in a 650 foot rise centered on the community of Elmhurst by the year 2010.

Other changes in Illinois pumpage patterns are likely to occur during the model simulation period (1986- 2010). The most notable change will occur when the Joliet and Wilmington public water supply systems shift their pumpage from ground water to the Kankakee River. Other decreases in pumpage from the Cambrian-Ordovician aquifer are also anticipated at Aurora, Batavia, Geneva, Montgomery, North Aurora, and Crystal Lake as these communities diversify their sources of water. A few communities (Sugar Grove, Cary, and Rockdale) are expected to hold their Cambrian-Ordovician pumpage steady at present levels and meet future growth from shallower aquifers.

The key observation to be made, however, is that if pumpage is decreased to a level equal to the average annual recharge, then groundwater mining will cease. As a result of aggressive resource evaluation and management, Illinois has an opportunity to match Cambrian-Ordovician pumpage in the Chicago region with the practical sustained yield of the aquifer. If this occurs, it will mark the first time since the late 1950s that the system has been in balance.

THE PEORIA REGION

Groundwater mining is not currently a problem in the Peoria region. Although it too has a long history of industrial development and heavy demand for groundwater supplies, the area has not experienced the water resource problems described for the Chicago region. Although the aquifer properties and reasons for problems in the two areas differ, the regions share a responsiveness to water level declines.

The Peoria region is located in north-central Illinois and includes parts of Peoria, Tazewell, and Woodford Counties. It covers about 600 square miles and is approximately 30 miles long and 20 miles wide. The region has had a great history of industrial growth, mainly in the manufacture of heavy earth moving equipment and in the distillation of alcoholic beverages, which requires large amounts of water. Fortunately, this area lies over the very prolific Sankoty aquifer. This deposit of unconsolidated sand averages 100 feet in thickness and is an order of magnitude more transmissive than the major aquifer supplying the Chicago region.

Even with this great resource, heavy pumpage lowered water levels in certain well fields and prompted concern for resource management as early as the 1940s. Many of the industrial facilities located in the Peoria region required low temperature water. Ground water became the favored resource of the area because of its availability and temperature. The Illinois River was only used on a limited basis, due to its traditional pollution problems (prior to environmental regulations of the 1970s) and its high summer temperatures. As a consequence of the ever increasing demand for ground water, water levels in the well fields declined steadily, partly because pumpage exceeded replenishment by natural recharge and partly because the wells were too closely spaced. By 1940 local concern had reached such an alarming level that the Illinois State Water Survey was asked to study the situation (Horberg et al., 1950; Suter and Harmeson, 1960).

The Water Survey subsequently determined that the overpumpage of ground water was between 8 and 10 million gallons per day (mgd) and demonstrated the need to adopt conservation measures and some method of artificial recharge. Several methods were investigated, including induced infiltration (using natural water bodies to increase flow), landflooding (inundating a tract of land with water), channel construction (modification of a stream channel), recharge wells (induced flow directly into the aquifer), and recharge pits (gravity flow from excavated pits into the aquifer).

Preliminary tests in August and September 1941 (Suter and Harmeson, 1960) on an abandoned gravel pit indicated that these pits, if refilled by river water, would increase groundwater levels with an acceptable increase in groundwater temperature. Water levels within Water Survey monitoring wells reacted almost immediately to this recharge method. This became the method of choice primarily because other methods were more expensive, the required mechanisms for them were unavailable, or the increase in groundwater temperature associated with them was unacceptable.

Consequently, in 1949 funds were appropriated for the Water Survey to construct and operate a research pit with a capacity of 0.3 mgd. Pit 1 was built on the property of the Water Survey Laboratory, and began operation on October 4, 1951. This pit was operated for seven more seasons through 1959. Pit 2 (2.0 mgd capacity) was built in 1956 on leased land adjoining Water Survey property, and artificial recharge within the pit was initiated in October 1957. Both pits yielded recharge rates higher than expected.

The successful operation of the first Water Survey recharge pits led to the construction of two other similar installations. The Bemis Bros. Bag Company and the Peoria Water Works Company both built artificial recharge pits to reestablish groundwater levels for their pumping needs during the 1950s. Construction and operation of the Water Survey pits and privately owned pits was deemed very successful in relieving the stress, at least for a few years, caused by heavy groundwater pumpage in a small area of Peoria.

Water Level Trends: The Lesson of Artificial Recharge

Today, our water use data reveal that industrial pump age has declined, while public water supply use has remained relatively steady since 1968 (in the Peoria region). Groundwater mining is not a problem here. In fact, water levels in this region are higher today than they were 50 years ago. The experience at Peoria is relevant, however, because it shows how overpumpage and poor spacing of high capacity wells can lead to problems. It also reveals that, like the experience in Chicago, the resource can recover when pumpage stops.

Today the privately owned utility supplying water to Peoria and many of its industries is concerned about future growth. Estimates through the year 2005 indicate that the current Illinois-American Water Company facilities may be inadequate to handle the estimated peak demand for the year 2005 from their central well field. As a result, they funded a Water Survey hydrologic investigation of this well field (Schicht, 1992). That study found that the required need could be met, with little or no impact to the current well field, by developing a new well field to the north of the existing field. The study considered inputs to the hydrologic system (by observing scientific aquifer tests) and balanced them against estimated withdrawals. It also concluded that induced recharge from the Illinois River would play an important role in balancing supply and demand.

Fortunately, the Water Survey has a long history of monitoring and study at Peoria. Thus it can more confidently calculate the long term yield of the Sankoty aquifer in that area. But the Water Survey does not always have necessary background information when asked pointed questions about groundwater mining in other areas. The following section differs from the first two because it describes a situation in which little was known until a problem arose.

EASTERN KANKAKEE AND NORTHERN IROQUOIS COUNTIES

In the late 1980s, the Kankakee/Iroquois County area was rife with highly charged emotions regarding groundwater use. The concerns arose in response to increased irrigation during a period of low rainfall. Water supply interruptions in area domestic wells were perceived by some to mean that too much water being removed from the ground. A competition for ground water among uninformed users began in an area served by multiple aquifers.

The area, located south of the Chicago region and along the eastern border of Illinois, has two distinct aquifers (Cravens et al., 1990). A reasonably productive bedrock aquifer consisting of Silurian and Devonian age dolomite is frequently used by irrigators. This aquifer is overlain by a surficial sand and gravel aquifer system that sometimes is used to provide ground water for domestic use and livestock watering. At the time of the study, no high capacity irrigation wells were using the surficial deposits for their supply, although the sand has the potential in some areas to serve as a viable source of irrigation water.

The issue of groundwater mining came about because water supply interruptions in domestic supply wells began to be reported in the early 1980s. These interruptions were temporary (lasting from hours to months), which made it necessary for some well owners to replace or deepen their wells, lower their pump intakes, or change the type of pump being used. Soon the linkage to irrigation pumpage was made, and the inevitable "finger-pointing" began. The conflict grew to such an extent that the area was specifically identified by an amendment to the Water Use Act of 1983 (P.A. 85-1330). Not only were the groundwater interruptions observed and emergency restrictions contemplated in Illinois, but also in two adjacent counties in Indiana. Basch and Funkhouser (1985) reported that an intensive irrigation project in the dolomite aquifer in these two Indiana counties affected nearly 130 domestic wells. These problems resulted in litigation and legislation protecting small well owners in Indiana.

The experience in eastern Kankakee and northern Iroquois counties illustrates that the issue of groundwater mining can have interstate ramifications. This was also the case in the Chicago region when Wisconsin sued Illinois in the U.S. Supreme Court and won.

Seasonal Impacts of Intensive Water Use

In 1987, a near normal year for precipitation, public water supply pumpage (typically for communities) amounted to approximately 16 percent of the total groundwater use, or 493.77 million gallons for the area. Rural domestic use accounted for about another 17 percent (586 million gallons) of the annual pump age. Industrial facilities accounted for only 1.6 percent of the total use (54.86 million gallons). Irrigation, however, accounted for more than 63 percent of the total groundwater use, or approximately 2,122 million gallons. Unlike other water uses, irrigation water demands are entirely seasonal. Most irrigation water withdrawals occur during the summer months, June- August. This intense short-term usage places enormous stress on the aquifer system, which in turn creates the potential for supply interruption of domestic wells finished in the upper part of the bedrock aquifer.

But in 1988, groundwater pumpage rose dramatically for most users in Illinois in response to the drought conditions. By July 7 that year, total groundwater withdrawals for irrigation in this area amounted to 2,227 million gallons; by midsummer withdrawals for this area had already exceeded the irrigation pumpage for the previous year by 105 million gallons. By the end of 1988, total groundwater use for irrigation was estimated to be 5,658 million gallons. During this time, approximately 120 complaints of well supply interruptions were filed in the study area. Detailed investigation of 71 of these complaints revealed that 25 pertained to Silurian age dolomite wells (the bedrock aquifer), 37 pertained to shallow sand and gravel wells (the surficial aquifer), and 9 were fictitious. Remedial actions to reestablish water supplies were undertaken by the owners of four dolomite wells and four sand and gravel wells.

Water Level Trends: Lesson of Timing, Area, and the Potential for Conflicts

The "use-to-yield" concept is a somewhat crude strategy that Illinois, and more specifically the Water Survey (Bowman and Collins, 1987), developed for locating areas of the state where groundwater conflicts might arise. It involves examining the actual use in the township and contrasting it with the township's potential aquifer yield. This use-to-yield percentage, expressed as "use/yield" represents a qualitative assessment of the percentage of the total resource being used. Although not meant to be used as the basis for site specific technical analysis, this use/yield comparison has the potential to help identify those regions where an aquifer may be overdeveloped.

Water Survey investigators (Cravens et al., 1990) considered three different scenarios in evaluating the long-term viability of the dolomite aquifer of eastern Kankakee and northern Iroquois Counties. Each scenario involved the "use/yield" concept, and in each case, difficulties were encountered in applying this statewide tool to a specific area. The first scenario considered the effects of precipitation on the previously predicted use/yield ratio. It found that in a near normal precipitation year, the use/yield ratio was determined to be 0.12 over the 414-square-mile (sq mi) study area, and in 1988 this value increased to 0.25.

But when the Cravens team looked more closely at the area from which water was being diverted (the second scenario) and contrasted it with the total pumpage during the 90-day irrigation season, they calculated a different use/yield ratio. They determined the ratio to be 0.32 and 0.77 in 1987 and 1988, respectively. Clearly, seasonal impacts can modify the ratio, especially when considering only the area (271 sq mi) from which ground water was being diverted to the irrigated area.

In the third scenario for the dolomite aquifer, the Cravens study examined the use/yield ratio when only the irrigated lands in the study site were considered. They found that the ratio increased dramatically when viewed with such a narrow focus. A ratio of 2.00 was determined for 1987, while a ratio of 4.54 was found for the entire year of 1988. That is, when narrowly viewed, use of ground water on irrigated lands exceeded the aquifer's ability to keep up with demand. But in the real world, not all lands overlying an aquifer are irrigated, so this scenario is unrealistic. Bowman (1991) had assumed that a use/yield ratio of 1.0 or more indicated a potential problem area and that a ratio of 0.5 to 0.999 indicated the possibility (not the probability) of overdevelopment. She determined that a ratio of less than 0.5 indicated an area where over pumpage probably does not occur. It is clear that her larger view of demand, which was tied to 30-year averages for precipitation, found fewer conflict areas.

Cravens et al. (1990) found that the volumes of recharge and discharge can vary widely at different locations within the eastern Kankakee and northern Iroquois County study area. Recharge to the dolomite aquifer is much greater in areas where the surficial sand directly overlies the bedrock than where clay or till separates the bedrock from the surficial system. They also determined that the presence of major river systems and their effect on the groundwater recharge regime are not taken into account. These systems increase water levels and recovery rates both during and after the irrigation season.

Groundwater mining is not a problem in eastern Kankakee and northern Iroquois Counties. The resources are adequate to provide ground water to present users without causing long-term depletion of the resource. Although record declines in the potentiometric surface (the surface to which water rises in a well under normal conditions) occurred during the drought of 1988, long-term depletion of the resource will only occur if irrigation continues to be developed without regulation and if precipitation continues at below normal levels (Cravens et al., 1990). We should recognize that short term extremes in demand, which could exceed one year, do not constitute mining of the groundwater resource. Groundwater managers must keep in mind the long view and base any decisions on average annual figures of supply and demand.

AMERICAN BOTTOMS REGION

The American Bottoms area in southwestern Illinois is one of the most heavily populated, industrialized areas in the state. It encompasses the communities of Alton, Wood River, Granite City, Collinsville, East St. Louis, and Cahokia. The groundwater resource of the sand and gravel aquifer underlying the area once was developed extensively. These deposits range in depth from several feet near the bluff edge and the Chain of Rocks reach of the Mississippi River to more than 170 feet, with an average depth of 120 feet across the entire area. The experience in the American Bottoms area, as it is known on topographic maps, is presented here because it is the exact opposite of groundwater mining. The difficulties that water managers face, though, are similar to those described in the three preceding regions. The problem is that groundwater levels are rising, in fact, so much so that they are causing flooded basements and highway underpasses. The Illinois Department of Transportation even has a network of dewatering wells to keep roadways in some areas from being inundated by ground water. Some 10 million gallons are pumped to waste each day!

This is an uncommon situation because ground water is typically an economic asset to a region, not a liability. Although the problem in the American Bottoms is not mining, the problem of rising groundwater levels is due largely to the intense development of a resource without an understanding of equilibrium conditions; that is, predevelopment water levels, groundwater flow patterns, future total pumpage, and estimates of average annual recharge.

The first significant withdrawal of ground water in the American Bottoms started in the late 1890s. Prior to 1900, ground water was primarily used for domestic and farm supplies. Since then groundwater withdrawals have been mostly for industrial and municipal use. Increasing pumpage in the area continually lowered water levels throughout the entire region until the 1960s. During this time, infrastructure maintenance and construction designs allowed for only the current water level safety margins. When the demand for ground water declined in the late 1960s, however, groundwater levels rose and kept rising. The rising groundwater levels are believed to have resulted in costly destruction of household basements and sewer and gas lines, as well as foundation problems. The situation has become so dire that the U.S. Army Corps of Engineers initiated a feasibility study (USACOE, 1987) and an environmental impact statement concerning the design of a proposed groundwater withdrawal plan to reduce the damages caused by groundwater flooding.

This region has been of major interest to the Water Survey for many years. As a result, a network was created of 19 observation wells, five of which are monitored continuously by water level recorders. The Water Survey has also established a practice of measuring more than 200 wells throughout this area about every five years. The most recent, widespread measurement was conducted in 1990. The results of the pre-vious measurements are summarized periodically in Water Survey publications. Figure 2 illustrates the historical trend of groundwater pumpage in the American Bottoms area. It shows that the estimated pumpage from wells increased from 2.1 mgd in 1900 to 111.0 mgd in 1956. Pumpage then declined sharply to 92.0 mgd in 1958, and by 1964 it had again increased to 110.0 mgd. After 1966, pumpage steadily declined to 54.4 mgd in 1981, before slowly increasing to 60.1 mgd in 1985. Recent pumpage increases appear to be associated with the IDOT dewatering well networks along roadways in the area. This dewatering effort prevents water levels from rising above the road surfaces. These continuing efforts have created a cone of depression in the groundwater level's surface centered on the metropolitan East St. Louis (Metro East) area.

Water Level Trends: Reverse Lesson of Groundwater Mining

Groundwater levels in the American Bottoms have been measured periodically for more than 45 years by the Water Survey and other concerned public and private parties. As mentioned above, the Water Survey still maintains a network of monitoring wells in this area. Some of these wells were established when pumping was at its peak in the region. The hydrograph of one such well (Water Survey well No. 01081, Marathon Oil observation well) is detailed in figure 3, which clearly indicates the rising trend of groundwater levels since 1965 due to the overall decrease in groundwater use.

Recharge in this area is from precipitation, induced infiltration from the Mississippi River and lesser water bodies in the area, and subsurface flow from the bluffs bordering the surface materials and into the sand and gravel deposits (Kohlhase, 1987). Recharge by induced infiltration occurs where pumpage from wells has low-ered the level of the ground water below the elevation of the surface water body. All the available information indicates that lack of recharge of the sand and gravel deposits is not a concern. The construction of major underground infrastructures during the high- use era has set the stage for destruction by rebounding groundwater levels.

The U.S. Army Corps of Engineers has been charged with initiating some type of plan to help minimize the destruction of property from rising water levels. To this end, they have detailed a major plan (USACOE, 1987) that will withdraw 41.25 mgd from wells in 57 locations. The initial cost is estimated at almost $8 million with a yearly maintenance cost of more than $1 million. Obviously, the cost of rising water levels can have economic consequences.

SUMMARY AND CONCLUSIONS

Ground water is a finite resource that is not uniformly distributed throughout the state. In some areas of Illinois, demand for this resource has caused it to become well developed. Demand can exceed supply, especially in urbanized areas of Illinois, and potential problems can arise from competition for the resource. The major concern is that annual use, in the long term, should not exceed the average annual recharge available to a specific aquifer system. When annual use does exceed average annual recharge over a prolonged period, groundwater mining occurs.

This chapter summarizes the hydrologic situations in four industrial centers of Illinois: Chicago, Peoria, eastern Kankakee and northern Iroquois Counties, and the American Bottoms. The use of ground water in each region is summarized, along with a discussion of any problems associated with this use.

In Illinois the most significant problem, in terms of groundwater "mining," occurs in the Chicago region. This problem started during the 1950s when demand exceeded what the natural systems could effectively recharge. Groundwater levels in one of the major aquifer systems of this region have declined by almost 1,000 feet since pumping began. The economic result has been increased pumping costs due to increased lift requirements. (A lawsuit brought by Wisconsin ultimately required the state of Illinois to decrease its pumpage from the major aquifer supplying the Chicago region.) The mining of the natural system also puts it at risk of compaction, which could permanently damage the aquifer.

No other area in Illinois has had a more historically adverse impact on groundwater levels than has the Chicago region. While heavy groundwater use has affected the groundwater flow system in the other areas discussed, none appear to equal the Chicago situation. Steps are being taken to relieve the stress on the aquifer system. The substitution of Lake Michigan water for ground water is having positive impacts, but this strategy will only buy a few years. Burch (1991) projected that by the year 2005, groundwater mining of the principal aquifer supplying the Chicago region will resume.

The issue of groundwater mining involves lengthy study and continuous, long-term monitoring of pump age and groundwater levels. From the four case studies presented in this chapter, it is possible to make some suggestions about how to avoid groundwater mining: Determine average annual recharge for each aquifer.

Maintain adequate spacing between high capacity wells.

Establish a long-term program for measuring groundwater levels.

Maintain records of well locations and how much they pump.

Recognize that seasonal extremes may cause interruptions to inadequately constructed wells, but this problem is not indicative of mining.

Recognize that groundwater level declines can have interstate consequences.

By following these guidelines, resource managers can avoid long-term groundwater mining so that Illinois can make the best use of its vast groundwater resources.

REFERENCES

Basch, M.E., and R.V. Funkhouser. 1985. Irrigation Impacts on Groundwater Levels in Jasper and Newton Counties, Indiana, 1981-1984. Water Resource Assessment 85-1. Division of Water, Indiana Department of Natural Resources. Indianapolis, IN.

Bowman, J.A. 1991. State Water Plan Task Force Special Report on Groundwater Supply and Demand in Illinois. Illinois State Water Survey Report of Investigation 116. Champaign, IL.

Bowman, J.A., and M.A. Collins. 1987. Impacts of Irrigation and Drought on Illinois Groundwater Resources. Illinois State Water Survey Report of Investigation 109. Champaign, IL.

Burch, S.L. 1991. The New Chicago Model: A Reassessment of the Impacts of Lake Michigan Allocations on the Cambrian-Ordovician Aquifer System in Northeastern Illinois. Illinois State Water Survey Research Report 119. Champaign, IL.

Cravens, S.J., S.D. Wilson, and R.C. Barry. 1990. Regional Assessment of the Groundwater Resources in Eastern Kankakee and Northern Iroquois Counties. Illinois State Water Survey Report of Investigation 111. Champaign, IL. Fetter, C.W. 1981. Interstate Conflict over Ground Water: Wisconsin-Illinois. Ground Water 19(2):201-213.

Freeze, R.A., and J.A. Cherry. 1979. Groundwater. Prentice-Hall, Inc. Englewood Cliffs, NJ.

Horberg, L., M. Suter, and T.E. Larson. 1950. Groundwater in the Peoria Region. A cooperative research project conducted by the Illinois State Water and Geological Surveys. Illinois State Water Survey Bulletin No. 39. Champaign, IL.

Illinois Water Inventory Program (IWIP). 1991. Statewide Water Withdrawal Information, 1978-1993. Unpublished report, Illinois State Water Survey, Champaign, IL.

Kohlhase, R.C. 1987. Groundwater Levels and Pumpage in the East St. Louis Area, Illinois, 1981-1985. Illinois State Water Survey Circular 168. Champaign, IL.

Prickett, T.A., and C.G. Lonnquist, 1971. Selected Digital Computer Techniques for Groundwater Resource Evaluation. Illinois State Water Survey Bulletin 55. Champaign, IL.

Sasman, R. T., R. S. Ludwigs, C. R. Benson, and J. R. Kirk. 1986. Water Level Trends and Pumpage in the Cambrian and Ordovician Aquifers in the Chicago Region, 1980-1985. Illinois State Water Survey Cir-cular 166. Champaign, IL.

Schicht, R.J. 1992. Groundwater Investigation at Peoria, Illinois: Central Well Field Area, Illinois State Water Survey Contract Report 537. Champaign, IL.

Suter, M., R.E. Bergstrom, H. F. Smith, G.H. Emrich, W. C. Walton, and T. E. Larson, 1959. Preliminary Report on Groundwater Resources of the Chicago Region, Illinois. Cooperative Report 1, Illinois State Water Survey and Illinois State Geological Survey. Champaign, IL.

Suter, M., and R.H. Harmeson. 1960. Artificial Groundwater Recharge at Peoria, Illinois. Illinois State Water Survey Bulletin 48. Champaign, IL.

U.S. Army Corps of Engineers. 1987. American Bottoms, Illinois: Feasibility Report and Environmental Impact Statement. St. Louis District, Lower Mississippi Valley Division, draft document. St. Louis, MO.

Visocky, A. P. 1993. Water Level Trends and Pumpage in the Deep Bedrock Aquifers in the Chicago Region, 1985- 1991. Illinois State Water Survey Circular 177. Champaign, IL.

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