From The Changing Illinois Environment: Critical Trends, Volume 2: Water Resources , Technical Report of the Critical Trends Assessment Project
The purpose of this report is to begin to examine the records of groundwater quality for temporal trends in selected portions of Illinois. Increasingly, groundwater contamination is discussed in the news media, and it may seem that the entire groundwater resource has been impacted. However, these contamination events are often localized and may not represent widespread degradation of the groundwater resource. By examining the temporal trends in groundwater quality of county- sized regions, it may be possible to determine if large scale degradation of the groundwater resource has occurred.
The general term "groundwater quality" refers to the chemical composition of ground water. Ground water originates as precipitation that filters into the ground. As the water infiltrates, it begins to change chemically due to reactions with air in the soil and with the earth materials through which it flows. In addition, human-induced chemical changes can also occur. Contamination of ground water generally refers to human-induced chemical changes and not naturally occurring processes.
As a general rule, local groundwater quality tends to remain nearly constant under natural conditions because of long groundwater travel times. Therefore, significant changes in groundwater quality can often indicate degradation of the groundwater resource.
Two distinct types of information, water quality and aquifer delineation, have been used in the preparation of this report. The water quality data come from two sources: private wells and municipal wells. The private well water quality data are compiled by the Chemistry Division of the Illinois State Water Survey (ISWS) as part of their water testing program and are maintained by the Office of Groundwater Information in a water quality database. The municipal well data come from Water Survey analyses and from the Illinois Environmental Protection Agency (IEPA) Laboratories. The combined database now contains about 50,000 records of chemical analyses from samples analyzed at the Water Survey laboratories and the IEPA laboratories. Some of these analyses date to the early part of the century, but most are from 1970 to the present. Before 1987, most analyses addressed inorganic compounds and physical parameters. Since then, many organic analyses have been added to the database from the IEPA Safe Drinking Water Act compliance monitoring program.
The geologic information, including approximate depth, thickness, and boundaries of various aquifer units, was obtained from the Illinois State Geological Survey.
Several limitations to the data must be understood before any meaningful interpretation can begin:
1. Representativeness of the sample 2. Location information 3. Charge balance check of the laboratory analysis 4. Extrapolation to larger areas
The private well samples are likely not completely representative of regional groundwater quality. In most cases, private well owners submit samples for analysis only when they believe there may be a problem such as high iron or an odd odor or taste. This suggests that perhaps one or more constituents may not be representative, but in general, the remainder of the chemical information will be accurate and useful. As a result, the composite data may be skewed toward analyses with higher than normal concentrations.
On the other hand, the private well information probably provides a better picture of the spatial distribution of chemical groundwater quality than municipal well information because of the larger number of samples spread over a large area. The recent IEPA data from municipal wells will not be skewed because each well is sampled and analyzed on a regular basis. While this produces a much more representative sample overall, samples are generally limited to specific areas where municipalities are located. Therefore, these data may not be good indicators of regional groundwater quality.
Much of the location information for the private wells is based solely on the location provided by the driller at the time the well was constructed. Generally, the locations are given to the nearest 10 acre plot of land. For our purposes here, that degree of resolution is adequate. However, it is not uncommon for the given location to be in error by up to as much as 6 miles. To circumvent the possible location errors, this report presents results on a county basis.
The validity of water quality data was checked by calculating a charge balance for each analysis. Charge balance is a simple measure of the quality of a water quality analysis. It measures the deviation from the constraint of electrical neutrality of the water by comparing total cations (positively charged ions) with total anions (negatively charged ions). Because many of the early analyses were performed for specific chemical constituents, a complete chemical analysis is not always available from which to calculate a charge balance. Based on a search of the water quality database for analyses with sufficient chemical constituents to perform an ion balance, it was found that more than 98 percent of the analyses produced an acceptable mass balance. This gives us confidence that the chemical analyses are accurate.
The question of extrapolation of a point value (a well water sample) to a regional description of groundwater quality is difficult and theoretically beyond the scope of this report. However, several general points can be raised. First, none of the data provide a uniform spatial coverage. Therefore, it seemed best to summarize the data on a county basis to ensure that an adequate number of values would be available. The private well analyses are more numerous and will likely provide better spatial coverage than the municipal well data, which are concentrated in isolated locations.
Chemical Components Selected for Trend Analysis
In many cases, groundwater contamination refers to the introduction into ground water of industrial or agricultural chemicals such as organic solvents, heavy metals, fertilizers, or pesticides. However, recent evidence suggests that many of these contamination occurrences are localized and form finite plumes that extend downgradient from the source. Much of this information is relatively recent, dating back a few decades, but long term records at any one site are rare. As mentioned earlier, changes in the concentrations of naturally occurring chemical elements such as chloride, sulfate, or nitrate also can be indicative of contamination. Increasing chloride concentrations may indicate contamination from road salt or oil field brine. Increasing sulfate concentrations may be from acid wastes, for example metal pickling. Increasing nitrate concentrations may result from fertilizer application, feed lot runoff, or leaking septic tanks. These naturally occurring substances are the major components of mineral quality in ground water and are routinely included in groundwater quality analyses. Fortunately, the Illinois State Water Survey has maintained records of routine water quality analyses of private and commercial wells that extend as far back as the 1890s. After examination of these records, six chemical constituents (table 1) were chosen for trend analyses based on the large number of available analyses and because they may be indicators of human-induced degradation of groundwater quality.
Aquifer Unit Delineation
Ground water occurs in many types of geological materials and at various depths below the land surface. This variability results in significant differences of natural groundwater quality from one part of Illinois to another and from one aquifer to the next even at the same location. For the purposes of trend analyses, six aquifer designations were delineated: alluvial valley aquifers, bedrock valley aquifers, shallow drift aquifers, deep drift aquifers, shallow bedrock aquifers, and deep bedrock aquifers. Each of these aquifer designations represents a unique set of conditions that are of interest for assessing overall trends in groundwater quality.
Alluvial Valley Aquifers. These aquifers underlie many of the major rivers and streams in Illinois, such as the Illinois River, the Wabash River, and the Mississippi River. The aquifers tend to be near the land surface and of limited lateral extent. These aquifers are made up of a variety of materials in grain sizes ranging from sand and gravel to clay. Some of these aquifers tend to be vulnerable to contamination because they are near the land surface and often in proximity to intense industrial activity located along the rivers.
Bedrock Valley Aquifers. Bedrock valley aquifers occur along former river channels. The major bedrock valley aquifers are largely sand and gravel and can be several hundred feet thick. Some of these aquifers are exposed at the land surface, such as in Mason County, while others, such as the Mahomet Valley aquifer, are buried beneath more than 200 feet of fine-grained material that provides protection in some areas. The shallow bedrock valley aquifers are just as vulnerable to contamination as the alluvial valley aquifers, but the more deeply buried aquifers tend to be less vulnerable.
Shallow Drift Aquifers. These aquifers were formed by glacial meltwater and tend to be more laterally extensive than the valley aquifers. They are composed of unconsolidated sand and gravel and are typically very permeable. In general, the shallow drift less than 100 feet deep is potentially more vulnerable from a contamination perspective.
Deep Drift Aquifers. Although of similar geologic origin as the shallow drift aquifers, the greater depth of the deep drift aquifers provides more protection from human-induced contamination.
Shallow Bedrock Aquifers. Bedrock aquifers are lithified materials such as limestone, dolomite, or sand-stone. "Shallow" in this context generally refers to the uppermost bedrock unit, even though it may be buried by several hundred feet of glacial material. These aquifers, where covered by fine grained material, are generally less vulnerable to contamination. However, in regions where the bedrock is at or near the land surface, the potential for contamination is much greater.
Deep Bedrock Aquifers. Deep bedrock aquifers are typically more than 500 feet below land surface. As a general rule, the water in the deep aquifers tends to be more highly mineralized than some of the shallow aquifers, but it varies from location to location. The potential for contamination by vertical migration of chemicals from the land surface is low. Other contamination pathways, such as abandoned wells, are probably a much greater threat to the groundwater quality in deep bedrock aquifers.
Counties Selected for Analysis
Two counties were selected for trend analysis of shallow drift aquifers. Three counties were selected for trend analysis of the other aquifer categories. The counties associated with each aquifer designation are given in table 2, along with the associated well depths from which samples were taken. The locations are also shown in figure 1.
Alluvial Valley Aquifers
Winnebago County. The alluvial aquifer associated with the Rock River runs north and south through the county. Much of the aquifer system underlies the Rockford metropolitan area, creating a high potential for groundwater contamination. In fact, one portion of the aquifer was recently designated as the "Southeast Rockford Superfund Site" because of a large plume of volatile organic contaminants.
Madison/St. Clair Counties. The alluvial aquifer located in the region known as the American Bottoms along the Mississippi River near St. Louis has been intensely developed for many years. Many industries concentrated near the river contribute contaminants to the aquifer. Further east, the area is largely agricultural. This region is similar to Winnebago County because of the high potential for groundwater contamination.
Gallatin County. The aquifer along the Wabash River differs from the other two because this is a largely rural county, and industrialization is not expected to be a significant source of contamination.
Bedrock Valley Aquifers
Bureau County. Located in the ancestral valley of the Mississippi River, this aquifer is increasingly being used for irrigation. This additional usage is currently within the safe yield of the aquifer. Leaching of agrichemicals, particularly nitrate, is of some concern in this area.
Mason County. Also located along the ancestral Mississippi River, now the Illinois River, this aquifer is essentially exposed at the land surface. It is an area of significant irrigation and may represent an analog to future conditions in Bureau County.
Champaign County. The Mahomet Bedrock Valley aquifer extends from the Illinois/Indiana border to the Illinois River. Near Champaign, the aquifer is buried beneath some fine grained glacial material that provides protection. The aquifer in Champaign County is less vulnerable to contamination than in the other two counties.
Shallow Drift Aquifers
DuPage County. Several aquifers are present in DuPage County, and the three uppermost ones will be examined. This will be particularly interesting because DuPage County has undergone a tremendous amount of urbanization over the past 100 years. As a result, the impact of human activity on the quality of the ground water may be documented. It is anticipated that the shallowest aquifer will show the greatest impact, while the deepest aquifers may not. The shallow drift aquifer is used primarily by private, low-capacity wells, whereas the deeper aquifers are the major source of water to many of the municipalities.
Effingham County. Agricultural activities and shallow, domestic large-diameter wells dominate the picture in Effingham County because of the paucity of good sand and gravel deposits. Recent ISWS research suggests that shallow large diameter wells are particularly susceptible to contamination.
Deep Drift Aquifers
DuPage County. This is probably a continuation of the overlying shallow drift aquifer, but being somewhat deeper, less human-induced chemical changes should be evidenced in the ground water.
McLean County. The largely agricultural activity in this county provides a nice contrast to the urbanized land use of DuPage County.
Macon County. The county is a mixture of rural and urban land uses. The aquifer is composed of sand and gravel deposits at depths of 100 to 300 feet.
Shallow Bedrock Aquifers
DuPage County. The shallow dolomitic limestone of Silurian age has been heavily used throughout this county for domestic, municipal, and industrial purposes. It underlies the sand and gravel deposits of the deep drift aquifer, and the groundwater qualities of these two systems should provide a good contrast.
Kankakee County. The shallow Silurian dolomite has become a major aquifer system for irrigation needs in this area. The area is mainly used for specialty crop production and is similar to the other counties in this category in regard to the depth and thickness of the aquifer system.
Whiteside County. The deeper water bearing bed rock formations in this county consist of the Silurian dolomite and the Galesville sandstone. This county differs from the others of this group in that it is predominantly agricultural. Deep Bedrock Aquifers
Winnebago County. The unconsolidated material of this county overlies more than 2,000 feet of Cambrian sandstones and less than 600 feet of Ordovician dolomite providing ground water for multiple needs. These aquifer systems have been used throughout the history of this area, and water quality is generally dependent on the types of geologic material within which the water is stored.
Cook County. This county is similar to Winnebago County in that its industrial activity is centered over the deep Cambrian-Ordovician aquifer system. The depths of these deeper systems should prove to better protect them from contamination by surface activities.
Knox County. In contrast to Winnebago and Cook Counties, this county has mostly agricultural activities. The deep Glenwood-St. Peter and Ironton- Galesville sandstones are groundwater sources for municipal wells and are the most dependable aquifers for high-capacity wells in the county.
Although many reports on the groundwater resources of Illinois summarize the chemical quality of the water, relatively few look at temporal trends in groundwater quality. One of the earliest studies to examine temporal trends in Illinois groundwater quality was presented by Gibb and O'Hearn (1980). They lumped data for the period 1940 to 1979 into five aquifer categories: 1) drift wells < 50 feet deep, 2) drift wells > 50 feet deep, 3) Pennsylvanian aquifers, 4) shallow limestone and dolomite aquifers, and 5) deep sandstone aquifers. They calculated median chemical concentrations per township for six parameters: 1) total dissolved solids (TDS), 2) hardness as CaCO3, 3) sulfate, 4) nitrate, 5) chloride, and 6) iron. Their results suggest that, as expected, natural variability characterizes the spatial distribution of groundwater quality.
In addition to looking at the spatial distribution of water quality, Gibb and O'Hearn also examined the temporal trends in groundwater quality for 21 well fields around the state. At five locations (Champaign- Urbana, Clinton, Edwardsville, Fairbury, and Farmer City) no long-term trends in chloride, hardness, sulfate, nitrate, or TDS were observed. Two municipalities for which trends in groundwater quality were observed, Bethalto in Madison County and Gibson City in Ford County, have well fields in sand and gravel aquifers. Increases in chloride and TDS were noted at Bethalto. Gibb and O'Hearn suggest that the increases near Bethalto are caused by a leaky surface water runoff retention pond near the well field. At Gibson City, only nitrate was not observed to increase. Again, Gibb and O'Hearn suggest a local source for the contamination, possibly a leaking storm sewer line. The observed increases in the concentrations of chemical constituents in the well water at Gibson City and Bethalto appear to be due to a local, human-induced source, rather than widespread degradation of the groundwater resource.
Gibb and O'Hearn found no trends in the Enfield well field, which taps Pennsylvanian-age rocks in White County. Of the four well fields tapping shallow dolomite or limestone aquifers that Gibb and O'Hearn examined, only Millstadt in St. Clair County did not show a trend of deteriorating groundwater quality. The other three cities (LaGrange, Libertyville, and Naperville) showed increases in concentrations in two or more of the five constituents examined. It is important to recognize that each of these communities is part of the rapidly urbanizing Chicago metropolitan area in northeastern Illinois. Gibb and O'Hearn hypothesized that the expanded use of road salt beginning in about 1960 in the Chicago metropolitan area led to a regional degradation of groundwater quality in the shallow Silurian dolomite aquifer.
Of the nine municipalities with deep sandstone well fields that Gibb and O'Hearn examined, seven had no long-term trends in groundwater quality (Dixon, Elgin, Geneva, Monmouth, Ottawa, Peru, and Rockford). A trend of increasing chloride in one of the wells at Bensenville in DuPage County is likely due to nearby improperly abandoned wells that are allowing poorer quality ground water from the overlying carbonate aquifers to migrate downward to the deep sandstone aquifer. A similar degradation of water quality in the well field at Freeport, Stephenson County, is also likely related to leakage in the wells, which is allowing poorer quality water from overlying units to migrate downward.
Several preliminary conclusions can be drawn from the work of Gibb and O'Hearn (1980). First, degradation of groundwater quality is more of a problem for shallow aquifers and less of a problem for deeper aquifers. Second, many cases of groundwater quality degradation can be traced to local problems, such as improperly constructed or abandoned wells or some nearby source such as an infiltration pond or leaking sewer line. The rapid urbanization of large portions of northeastern Illinois appears to have caused a more widespread degradation in groundwater quality, particularly in regard to chloride from road salt.
DISCUSSION AND RESULTS
The temporal trends of the six chemical constituents in the six types of aquifers are summarized in this section. Box plot representations are used because they summarize both the average behavior and the variability in the data. Figure 2 explains the box plot representation of the data. The center line of each box is the median concentration for the samples in that category. For example, the median hardness concentration for the decade of 1940-1949 from alluvial valley aquifers is about 500 milligrams per liter (mg/L) as CaCO3 (figure 3). This means that one-half of the samples have hardness greater than 500 mg/L, and one-half have hardness less than 500 mg/L. The top and bottom of each box represent the 75 percent and 25 percent values, respectively. The 75 percent value, about 750 mg/L as CaCO3 in the example above, implies that three-quarters of the analyses had hardness less than 750 mg/L. Beyond the box are a whisker and a dot at each end. The upper and lower whiskers represent the 90 percent and 10 percent levels, respectively. The circles are the 95 percent and 5 percent levels. The whiskers and circles provide valuable information about variability within the data and can be useful in identifying outliers in the data. Outliers are loosely defined as data values that are so much larger or smaller than the majority of the data that they should be viewed with caution. Outliers may indicate an erroneous data point, but they may also represent an anomalous local condition.
Outliers were not plotted in figures 3-8. The data are plotted in figures 3-8 by decade, beginning with 1900- 1909 (decade 1), 1910-1919 (decade 2), etc., through the 1990s. Therefore, the decade of the 1990s is plotted as decade 10. Each decade covers the corresponding ten-year period, except for the partial decade of the 1990s. The data from the three counties in each aquifer classification were combined to yield a composite view of the groundwater quality.
An added feature of the box plot is an indication of the number of data points used to create the respective box. As noted in figure 2, a single horizontal line signifies that less than four data points were available. If only the box is present, four to ten data points were found. Adding the whiskers indicates 11 to 20 values. If more than 20 data points are present, then the full box plot and the circles are used. This representation of the number of data points is helpful for assessing the results. If only a few data points are known for a three-county area over an entire decade, little confidence can be given to those results.
Hardness, given as mg/L of CaCO3, is presented in figure 3. Typically, the water in the shallower aquifers tends to be slightly harder than in the deeper aquifers. Median concentrations fluctuate from decade to decade for each aquifer classification. Some trends are observable, such as the apparent increase in hardness over time in the shallow bedrock aquifers and a corresponding decrease in the shallow drift and deep bedrock. Given the limitations of the data however, it is very difficult to know if these trends are significant.
Iron concentrations for each of the aquifer classifications are given in figure 4. With the exception of the deep bedrock aquifers, the median iron concentrations are often well above the class I potable ground water standard of 0.5 mg/L. Iron tends to be quite variable, with a few values in the range of 50 to 60 mg/L. This clearly indicates a great deal of spatial variability in the iron concentrations of ground water.
By ignoring boxes with fewer than 20 data points, it is clear that there are no significant temporal trends in the iron concentrations in ground water over the past century. The reader should recall that each box represents the data from three counties over a ten-year period. The lack of temporal trends indicates that when viewed in large scale, ground water quality with respect to iron has remained stable. However, it must be recognized that on a local scale (on the order of several acres), significant degradation of groundwater quality may have occurred.
Median sulfate concentrations (figure 5) do not appear to be changing with time, except for concentrations in the deep bedrock aquifers. A trend of decreasing sulfate is evident, from near 400 mg/L at the beginning of the century to 100 mg/L by the 1980s. This trend, however, may be an artifact because the last two decades have less that 20 data points each, which may not be an adequate number of samples. The significant fluctuations in the median concentrations from decade to decade, especially for the deep drift and bedrock valley aquifers, are symptoms of the data limitations. These fluctuations typify the difficulties of working with data that do not come from a specially designed monitoring program.
Of the constituents examined in this report, chloride is one of the most likely to indicate the impacts of anthropogenic activity on ground water. Yet, if one examines figure 6 and discounts the boxes with fewer than 20 data points, there are no noticeable trends in chloride concentrations. Despite documented cases of road salt contamination of ground water, no large-scale degradation due to chloride is apparent.
One might expect nitrate to show significant trends over the past 50 years because of increased fertilizer application. Nonetheless, no significant trends in nitrate concentrations (figure 7) suggest long-term, widespread degradation of groundwater quality. On the other hand, the ISWS has documented numerous cases of elevated nitrate levels associated with rural private wells (Wilson et al., 1992). The evidence may suggest that rural well contamination is associated more with farmstead contamination of the local ground water or well rather than regional contamination of major por- tions of an aquifer from the land application of fertilizers. However, this is an active research topic, and it requires a great deal of additional study before definitive conclusions can be drawn.
Total Dissolved Solids
The total dissolved solids concentration (figure 8) is a lumped measure of the total amount of dissolved chemical constituents in ground water. As such, it will not be a sensitive indicator of trace level contamination, but is a good indicator of major inputs of ions or cations to ground water. As with the other constituents, significant variability exists in the mean concentration, but no clear trend is apparent. As noted above, the fluctuations from one decade to the next are more likely related to the data limitations and not to any inherent changes in groundwater quality.
This work was undertaken to examine long-term temporal trends in groundwater quality over selected areas of Illinois. The data from private and municipal wells were the primary source of information used to construct figures that showed the trends in six chemical constituents in ground water from six aquifer classifications. These figures demonstrate that on a county-wide scale, ground water has not been degraded with respect to the six chemicals examined. Because of data limitations, trace-level contaminants were not studied, but it is imperative that such an assessment be undertaken in the future. It is clear from the earlier work of Gibb and O'Hearn (1980) that the quality of some ground water, particularly in the metropolitan Chicago area, has been degraded by anthropogenic activity, resulting in increases of chloride and total dissolved solids.
Much of the contamination of Illinois ground water is generally localized. Nonetheless, this contamination can render a private or municipal groundwater supply unusable. Once contaminated, ground water is very difficult and expensive to clean and may take many years to complete. Clearly, it is in the best interests of the people of Illinois to protect their groundwater resource through prevention of contamination.
During the 1970s, national environmental concern focused on those resources that were impacted by contaminants that could be seen or smelled. Surface and air contamination was the primary concern, whereas ground water was not considered to be at risk because it was hidden from view. Historically, protection of water supplies was centered on keeping those contaminants that carried disease out of the drinking supply. Some inorganic chemicals and a few common industrial chemicals also made the protection list.
However, a major shift in definition of the term "unsafe drinking water" began to emerge in the early 1980s. The need to protect the population from the potential threat of very small doses of chemicals was and currently is the primary driving force for groundwater protection in the nation. Today, groundwater contamination by a variety of commonly used toxic chemicals, such as volatile organic compounds, is considered a major environmental issue at both the national and state levels.
Since the mid to late 1980s, national concern has focused on groundwater contamination and its potential impacts to those individuals who rely on it for their drinking water. This concern has led to the initiation of several laws and agency policy shifts to help ward off this imposing threat or to help create a monetary base for research and remediation of existing contamination. Illinois is one of only a handful of states that has adopted legislation in an attempt to respond to this concern. In 1987, P.A. 85-0863 was introduced as a comprehensive, prevention-based policy focused on beneficial uses of ground water and preventing degradation. This act, known as the Illinois Groundwater Protection Act (IGPA), relies upon a state and local partnership and, although directed toward protection of ground water as a natural and public resource, it specifically targets drinking water wells in Illinois.
The act details the process in which the environmental agencies in the state shall initiate and develop educational, investigation, and management techniques to protect Illinois' ground water. The monitoring of this process was organized with the establishment of the Interagency Coordinating Committee on Groundwater. This committee is responsible for reporting the progress of the agencies cooperating in the IGPA initiatives to the Governor on a regular basis and for publishing this progress in a biennial report.
The Illinois State Water Survey is one of several agencies involved in the research and educational aspects of this act. The agencies involved include:
Illinois Environmental Protection Agency (Chair), Illinois Department of Energy and Natural Resources, Illinois Department of Mines and Minerals, Office of the State Fire Marshal, Illinois Department of Transportation - Water Re- sources Division, Illinois Department of Agriculture, Illinois Emergency Services and Disaster Agency, Illinois Department of Nuclear Safety, Illinois Department of Commerce and Community Affairs.
The act details several preventative initiatives to be handled by various environmental agencies and calls for several activities related to education, management, and research of ground water in Illinois. It sets the policy framework for the management of the resource and responds to the need to protect groundwater quality under a unified groundwater protection program. In short, the act:
Sets a groundwater protection policy Enhances cooperation Establishes water well protection zones Provides for surveys, mapping, and assessments Establishes recharge area protection Requires new groundwater quality standards
Currently, two short-term projects mandated by the IGPA have been completed: the recharge area delineation and prioritization, and an initial report on the impacts of pesticides on ground water. The site surveys of each public water supply are near completion. These surveys detail the well location and the land surface activities around it.
The Illinois Environmental Protection Agency has conducted a synoptic analysis of the public water supply wells, which indicated that the quality of the state's ground water is generally good. The analysis of the information used for this paper also tends to support this view. The IEPA and the ISWS also agree that in some areas in Illinois chemical levels are limiting use of the resource. The IEPA reported that 4.6 percent of the tested public water wells had detectable levels of organic chemical contamination (Interagency Coordinating Committee on Groundwater, 1990).
The IGPA was established to ultimately protect Illinois' groundwater resources. The work currently being completed will help guide this protection. However, the fiscal resources needed for statewide assessment and management of this nature are not now available. Ultimately, the concept of protection versus cleanup is sound. The cost of cleanup of ground water is far greater than that of protection. This act is one step toward the protection of these vital resources.
Gibb, J.P., and M. O'Hearn. 1980. Illinois Groundwater Quality Data Summary, Illinois State Water Survey Contract Report 230, Champaign, IL.
Interagency Coordinating Committee on Groundwater. 1990. Illinois Groundwater Protection Program: A Biennial Report.
Wilson, S.D., K.J. Hlinka, J.M. Shafer, J.R. Karny, and K.A. Panczak. 1992. Agricultural Chemical Contamination of Shallow-Bored and Dug Wells, in Research on Agricultural Chemicals in Illinois Groundwater: Status and Future Directions II, Proceedings of the second annual conference, Illinois Groundwater Consortium, Southern Illinois University, Carbondale, IL, pp.140- 148.
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