SPOON River AREA ASSESSMENT

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SPOON RIvER AREA ASSESSMENT

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VOLUME 2: WATER RESOURCES

Illinois Department ofNatural Resources Office of Scientific Research and Analysis llIinois State Water Survey 2204 Griffith Drive Champaign, Illinois 61820 (217) 244-5459

1998

300 Printed by the authority ofthe State of lliinois Other CTAP Publications

The Changing Illinois Environment: Critical Trends, summary and 7-volume technical report Illinois Land Cover, An Atlas, plus CD-ROM Inventory ofEcologically Resource-Rich Areas in Illinois Rock River Area Assessment, 5-volume technical report The Rock River Country: An Inventory ofthe Region's Resources Cache River Area Assessment, 5-volume technical report The Cache River Basin: An Inventory ofthe Region's Resources Mackinaw River Area Assessment, 5-volume technical report The Mackinaw River Country: An Inventory ofthe Region's Resources The Illinois Headwaters: An Inventory ofthe Region's Resources Headwaters Area Assessment, 5-volume technical report The Illinois Big Rivers: An Inventory ofthe Region's Resources Big Rivers Area Assessment, 5-volume technical report The Fox River Basin: An Inventory ofthe Region's Resources Fox River Area Assessment, 5-volume technical report The Kankakee River Valley: An Inventory ofthe Region's Resources Kankakee River Area Assessment, 5-volume technical report The Kishwaukee River Basin: An Inventory ofthe Region's Resources Kishwaukee River Area Assessment, 5-volume technical report Embarras River Area Assessment, 5-volume technical report Upper Des Plaines River Area Assessment, 5-volume technical report Illinois River Bluffs Area Assessment, 5-volume technical report Annual Report 1997, Illinois EcoWatch Stream MonitoringManual, Illinois RiverWatch ForestMonitoring Manual, Illinois ForestWatch Illinois Geographic Information System, CD-ROM of digital geospatial data

AIl CTAP and Ecosystems Program documents are available from the DNR Clearinghouse at (217) 782-7498 or TOO (217) 782-9175. Selected publications are also available on the World Wide Web at http://dnr.state.il.us/ctap/ctaphome.htm, or http://dnr.state.il.us/c2000/manage/partner.htm, as well as on the EcoForum Bulletin Board at 1 (800) 528-5486 or (217) 782-8447.

For more information about CTAP, call (217) 524-0500 or e-mail [email protected]; for information on the Ecosystems Program call (217) 782-7940 or e-mail at [email protected]. About This Report

The Spoon River Area Assessment examines the Spoon River basin in west central Illinois, an area that encompasses parts of nine counties. This report is part ofa series of reports on areas ofIllinois where a public-private partnership has been formed to protect natural resources. These assessments provide information on the natural and human resources ofthe areas as a basis for managing and improving their ecosystems. The determination ofresource rich areas and development of ecosystem-based information and management programs in Illinois are the result ofthree processes - the Critical Trends Assessment Program, the Conservation Congress, and the Water Resources and Land Use Priorities Task Force.

Background

The Critical Trends Assessment Program (CTAP) documents changes in ecological conditions. In 1994, using existing information, the program provided a baseline of ecological conditions. 1 Three conclusions were drawn from the baseline investigation:

1. the emission and discharge of regulated pollutants over the past 20 years has declined, in some cases dramatically, 2. existing data suggest that the condition of natural ecosystems in Illinois is rapidly declining as a result offragmentation and continued stress, and 3. data designed to monitor compliance with environmental regulations or the status of individual species are not sufficient to assess ecosystem health statewide.

Based on these findings, CrAP has begun to develop methods to systematically monitor ecological conditions and provide information for ecosystem-based management. Five components make up this effort:

I. identify resource rich areas, 2. conduct regional assessments, 3. publish an atlas and inventory ofIllinois landcover, 4. train volunteers to collect ecological indicator data, and 5. develop an educational science curriculum which incorporates data collection

At the same time that CTAP was publishing its baseline findings, the Illinois Conservation Congress and the Water Resources and Land Use Priorities Task Force were presenting their respective findings. These groups agreed with the CTAP conclusion that the state's ecosystems were declining. Better stewardship was needed, and they determined that a voluntary, incentive-based, grassroots approach would be the most appropriate, one that

1 See The Changing Illinois Environment: Critical Trends, summary report and volumes 1-7.

·111 recognized the inter-relatedness ofeconomic development and natural resource protection and enhancement.

From the three initiatives was born Conservation 2000, a six-year program to begin reversing ecosystem degradation, primarily through the Ecosystems Program, a cooperative process of public-private partnerships that are intended to merge natural resource stewardship with economic and recreational development. To achieve this goal, the program provides financial incentives and technical assistance to private landowners. The Rock River and Cache River were designated as the first Ecosystem Partnership areas.

At the same time, CTAP identified 30 Resource Rich Areas (RRAs) throughout the state. In RRAs and other areas where Ecosystem Partnerships have been formed, CTAP is providing an assessment ofthe area, drawing from ecological and socio-economic databases to give an overview ofthe region's resources - geologic, edaphic, hydrologic, biotic, and socio economic. Although several ofthe analyses are somewhat restricted by spatial and/or temporal limitations ofthe data, they help to identity information gaps and additional opportunities and constraints to establishing long-term monitoring programs in the partnership areas.

The Spoon River Assessment

The East Fork of the Spoon River rises to the north ofNeposet in Bureau County and the West Fork rises to the east ofKewanee in Henry County. The forks join near the center of Stark County to form the main channel. The river flows in a southerly direction for 161 miles before it empties into the I1linois River at Havana. For about 100 miles it runs nearly parallel to the I1linois River. The area covered in this report encompasses the entire Spoon River basin as determined by the I1linois Environmental Protection Agency. This basin is an approximately 1,180,951 acre watershed that includes virtually all of Stark County and portions ofBureau, Fulton, Henry, Knox, McDonough, Marshall, Peoria, and Warren counties in west-central I1linois. These are also the boundaries of the Spoon River Ecosystem Partnership.

This assessment is comprised offive volumes. In Volume 1, Geology discusses the geology, soils, and minerals in the assessment area. Volume 2, Water Resources, discusses the surface and groundwater resources and Volume 3, Living Resources, describes the natural vegetation communities and the fauna of the region. Volume 4 contains three parts: Part I, Socio-Economic Profile, discusses the demographics, infrastructure, and economy ofthe area, focusing on the five counties with the greatest

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Vll

Contributors

Project Coordinator Nani Bhowmik

Maps Kathleen J. Brown

Editor and Report Coordinator Christopher Wellner

Introduction Physiography, Rivers and Streams, Lakes H. Vernon Knapp Wetlands Michael Miller, Liane Suloway, Laura Keefer' Land Use Laura Keefer

Climate and Trends in Climate James Angel, Wayne Armstrong

Streamflow H. Vernon Knapp, Gana Ramamurthy, Kenneth Nichols

Erosion and Sedimentation Misganaw Demissie, Renjie Xia, William Bogner

Water Use and Availability Ground-Water Resources Kenneth Hlinka, John Blomberg, Kay Charles Surface Water Resources H. Vernon Knapp

Ground-Water Quality Kenneth Hlinka, John Blomberg, Thomas Holm

, Contributor Affiliations: Michael Miller, Illinois State Geological Survey; Liane Suloway, Illinois Natural History Survey; Laura Keefer, Illinois State Water Survey.

Table of Contents

Introduction 1 Physiography 1 Rivers and Streams 3 Lakes 4 Wetlands 5 Land Use 10 Climate and Trends in Climate 13 Overview : 13 Temperature 13 Precipitation 17 Precipitation Deficits and Excesses 20 Severe Weather 20 Tornadoes 20 Hail 20 Thunderstorms 21 Summary 21 Streamflow 23 Stream Gaging Records 23 Human Impacts on Streamflows in the Spoon River Basin 23 Annual Streamflow Variability 25 Statistical Trend Analysis 26 Daily and Seasonal Flow Variability 27 Flooding and High Flows 29 Statistical Trend Analysis 29 Seasonal Distribution of Flood Events 30 Drought and Low Flows 31 Seven-Day Low Flows 31 Multi-Year Low Flows 33 Erosion and Sedimentation 35 Instream Sediment Load 35 Sedimentation 44 Water Use and Availability 47 Ground-Water Resources 47 Data Sources 48 Data Limitations 48 Ground-Water Availability 49 . 1995 Ground-Water Use 50 Ground-Water Use Trends 50

xi Surface Water Resources 51 Present Water Use 51 Potential for Development of Surface Water Sources 51 Ground-Water Quality 55 Data Sources 55 Data Limitations 56 Chemical Components Selected for Trend Analysis 57 Aquifer Unit Analysis 58 Discussion and Results 58 Iron (Fe) 61 Total Dissolved Solids (TDS) 61 Sulfate (S04) 62 Nitrate (N03) 63 Chloride (CI) 63 Hardness (as CaC03) 64 Summary 65 References 67

List of Figures

Introduction Figure 1. Major Streams and Lakes in the Spoon River Basin 2 Figure 2. Stream Profiles for the Spoon River and Three Tributaries 4 Figure 3. Wetlands from the National Wetlands Inventory and Quadrangle Map Boundaries for the Spoon River Assessment Area 8 Figure 4. National Wetlands Inventory Information from the London Mills 7.5-minute Quadrangle Map Showing Wetlands, Deepwater Habitat, and NWI Codes 9 Figure 5. Acreages of Selected Crops in the Spoon River Basin Based on lAS Data 11

Climate and Trends in Climate Figure 6. Average Annual Temperature for Peoria, illinois, 1901-1996 14 Figure 7. Annual Number of Days with Maximum Temperatures Equal to or Above 90°F at Peoria, 1901-1996 15 Figure 8. Annual Number of Days with Minimum Temperatures Equal to or Below 32°F at Peoria, Winters 1901-1902 to 1995-1996 16 Figure 9. Annual Number of Days with Minimum Temperatures Equal to or Below OaF at Peoria, Winters 1901·1902 to 1995-1996 16 Figure 10. Annual Precipitation at Peoria, 1901-1996 18

xii Figure 11. Annual Number ofDays with Measurable Precipitation at Peoria, 1901-1996 18 Figure 12. Annual Snowfall at Peoria, Winters 1903-1904 to 1995-1996 19 Figure 13. Annual Number ofDays with Measurable Snowfall at Peoria, Winters 1903-1904 to 1995-1996 19 Figure 14. Annual Number ofDays with Thunderstorms at Peoria, 1948-1995 21

Streamflow Figure 15. Stream Gaging Stations in the Spoon River Basin 24 Figure 16. Average Annual Streamflow for Selected Gages in the Spoon River Basin 26 Figure 17. Flow Duration Curves (Discharge Versus Probability) 28 Figure 18. MontWy Flow Probabilities for the Spoon River at Seville 28 Figure 19. Annual Peak Discharges at Four Stream Gages in the Spoon River Basin 29 Figure 20. Annual 7-Day Low Flows for a) the Illinois River, and b) the tributaries in the Spoon River Basin 32

Erosion and Sedimentation Figure 21. Sediment Monitoring Stations in the Spoon River Basin 36 Figure 22. Variabilities ofInstantaneous Flow Discharge, Suspended Sediment Concentration, and Suspended Sediment Load for the Spoon River at London Mills 38 Figure 23. Variabilities ofFlow Discharge and Instantaneous Suspended Sediment Concentration and Load for the Spoon River at Seville 39 Figure 24. Variabilities ofFlow Discharge and Instantaneous Suspended Sediment Concentration and Load for Indian Creek near Wyoming ...... 40 Figure 25. Variabilities ofFlow Discharge and Instantaneous Suspended Sediment Concentration and Load for Big Creek at S1. David 41 Figure 26. Variabilities ofFlow Discharge and Instantaneous Suspended Sediment Concentration and Load for Big Creek near Bryant 42 Figure 27. Variabilities ofFlow Discharge and Instantaneous Suspended Sediment Concentration and Load for Slug Run near Bryant 43

Water Use and Availability Figure 28. Location ofPotential Reservoir Sites in the Spoon River Basin 53

xiii List of Tables

Introduction Table I. Distribution of Land Slopes for Stark and Knox Counties I Table 2. Tributaries in the Spoon River Basin and Location of Confluence with the Spoon River 3 Table 3. Significant Lakes and Reservoirs in the Spoon River Basin 5 Table 4. Wetlands in the Spoon River Basin 6

Climate I, :\ Table 6. Temperature Summary for Peoria 14 Table 7. Average Annual Temperature during Consecutive 30-Year Periods IS Table 8. Precipitation Summary for Peoria 17

Streamflow Table 9. USGS Stream Gaging Stations in the Spoon River Basin having Continuous Discharge Records 25 Table 10. Trend Correlations for Annual and Seasonal Flows 27 Table II. Trend Correlations for Flood Volume and Peak Flow 30 Table 12. Monthly Distribution of Top 25 Flood Events at Selected Stations 30 Table 13. Minimum Flows Experienced During Major Droughts (in cfs), Spoon River at Seville, 1915-1996 31

Erosion and Sedimentation Table 14. Sediment Monitoring Stations in the Spoon River Basin 35 Table IS. Annual Sediment Load for the Spoon River Basin 45 Table 16. Lake Sedimentation Rates in the Spoon River Basin 46

Water Use and Availability Table 17. Number of Reported Private Wens in the Spoon River Basin 49 Table 18. Ground-Water Use Trends in the Spoon River Basin 51

Ground-Water Quality Table 19. Chemical Constituents Selected for Trend Analysis, Unconsolidated Systems 59 Table 20. Chemical Constituents Selected for Trend Analysis, Bedrock Aquifer Systems 60

XIV Introduction

The Spoon River basin in west-centrallllinois covers approximately 1,855 square miles, with drainage in 9 counties: Bureau, Fulton, Henry, Knox, Marshall, McDonough, Peoria, Stark, and Warren. Figure I provides the general location of the basin and its major streams. The Spoon River has its headwaters in Bureau County, and flows generally south by southwest through Stark, Knox, and Fulton Counties, before turning southeast to join the lllinois River near Havana.

Average annual precipitation for the basin in 36.25 inches. The corresponding average annual streamflow is about 9 inches.

Physiography . \ The Spoon River basin falls within the physiographic region called the Galesburg Till Plain, as described by Leighton et al. (1948). The topography is characterized by rolling upland prairies, broken up by streams that have eroded 50 to 100 feet below the general level of the adjacent uplands. The rolling nature of the area is shown by the distribution of land slopes for the area, given in Table 1. The average elevation of the upland areas generally follows the slope of the river, being greatest in the northern part of the watershed, with elevations exceeding 800 feet above mean sea level (msl), and least to the south (650 feet ms/). The maximum elevation in the basin is 870 feet msl, located in Stark County, and the minimum is 425 feet msl at the Spoon's confluence with the ,',,' lllinois River.

Table 1. Distribution of Land Slopes for Stark and Knox Counties Percent of land in slope category

Percent of land in slope category Slo e Stark Count Knox Count 0- 2% 37.3 29.8 2-4 28.4 25.6 4-7 15.6 11.9 7 - 12 10.5 16.7 12 18 5.1 5.9 18 - 30 2.6 10.1 > 30 0.6 0.1

Source: Runge et al. (1969)

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Figure 1. Major Streams and Lakes in the Spoon River Basin .'

Rivers and Streams , ",

The Spoon River basin has about 2,750 miles of rivers and streams. Larger streams (those with watersheds greater than 10 square miles) account for about 32% of this total, or approximately 881 river miles. The three largest tributaries to the Spoon River are Cedar Creek, Walnut Creek, and Haw Creek, draining areas of 288 square miles (mi\ 2 2 171 mi and 113 mi , respectively. These streams are shown in Figure 1. Other major tributaries having drainage areas in excess of 40 square miles are listed in Table 2.

Table 2. Tributaries in the Spoon River Basin and Location of Confluence with the Spoon River

Drainage area Spoon Stream Name Counties s mi) River (mile) Big Creek Fulton 66.5 17.2 Shaw Creek Fulton, McDonough 52.0 39.3 Put Creek Fulton 91.8 43.6 Coal Creek Fulton 42.1 59.0 CedarCreek Fulton, Warren, Knox 288 68.7 Littlers Creek Knox, Fulton 42.9 73.2 Haw Creek Knox 113 75.6 French Creek Knox, Peoria 69.4 85.2 Court Creek Knox 96.3 101.6 Walnut Creek Peoria, Stark, Knox 171.0 115.6 Indian Creek Stark, Henry 73.8 127.0 Camp RunlMud Run Stark, Marshall 93.7 129.9 East Fork Spoon River Stark, Bureau 94.1 146.5

The total length of the Spoon River is 142 miles. For much of its length, the river has a deep and narrow channel, with a width of less than 100 feet. The width eventually broadens to 150 feet downstream, as the river approaches its confluence with the lllinois River. Its tributaries generally have widths proportional to the size of their watersheds, ranging from 20 to 30 feet. The banks of the Spoon River are usually quite steep, as the river is typically entrenched into the alluvial floodplain to a depth of more than 20 feet. The width of its floodplain varies: In Stark County it is generally no more than 1000 feet wide, but as the river flows farther south the floodplain fluctuates between a few thousand feet to as much as 1.5 miles. The river can meander considerably where the floodplain is wide. The floodplain also broadens downstream as the Spoon River approaches the lllinois River.

The channel slope of the Spoon River is moderate for a stream its size, averaging about 1.5 feet per mile (ft/mi) for most of its length. Only near its headwaters does the channel slope steepen, exceeding 30 ftlmi in the upper 5 miles of the river. Figure 2 illustrates the channel slope of the Spoon River and three selected tributaries. Most major tributaries have a steeper channel slope (approximately 5 ftlmi) and also approach or exceed 30 ftlmi in their upper reaches. Walnut Creek (not shown) has the most gentle slope of the major tributaries, averaging approximately 3 ftlmi for most of its length.

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400 0 20 40 60 80 100 120 140 160 180 DISTANCE. miles

Figure 2. Stream Profiles for the Spoon River and Three Tributaries

The streams in the Spoon River basin are generally well developed and incised so as not to require channelization. Mattingly and Herricks (1991) indicate that there are only 21 stream miles in the basin that have been channelized, which makes it one of the least channelized watersheds in lllinois.

Lakes

The Spoon River basin has approximately 260 lakes, as identified by I: 100,000 scale topographic mapping. In addition, there are hundreds of other small lakes and ponds, having surface areas generally less than 2 acres. Most of the 260 lakes identified in the watershed are located in modified terrain, left over from coal mining. Over half of these lakes in surface-mined areas are located in Fulton County near the city of Canton, including the two largest (Lake Marie and Lake Wee-Ma-Tuk).

Table 3 lists the lakes in the Spoon River basin having a surface area of greater than 100 acres. Most of the largest lakes were formed by the impoundment of streams and are located on the western side of the basin. Though all these lakes currently serve a recreational function, the oldest were originally built for water supply. The total surface area of all 260 lakes is approximately 5,000 acres, or about 4 percent of the basin's total area.

4 Table 3. Significant Lakes and Reservoirs in the Spoon River Basin

Surface Year Name Count area (acres) built Functionff Lake Bracken Knox 181 1922 Recreation/Stream impoundment Snakeden Hollow Lake Knox 148 1978 Recreation/Stream impoundment Spoon Lake Knox 680 1971 Recreation/Stream impoundment Little Swan Lake Warren 226 1968 Recreation/Stream impoundment Lake Wee-Ma-Tuk Fulton 178 1965 Recreation/Surface-mined Lake Marie Fulton 128 1959 Recreation/Surface-mined Lake Wildwood Haven Fulton 98 1971 Recreation/Stream impoundment Calhoun Lake Knox 50 1923 Recreation/Stream impoundment Lake Rice Knox 51 1895 Residential-recreation/Stream impoundment

Wetlands

Wetlands are an important part of our landscape because they provide critical habitat for many plants and animals and serve an important role in mitigating the effects of storm flow in streams. They are also government-regulated landscape features under Section 404 of the Clean Water Act. In general, wetlands are a transition zone between dry uplands and open water; however, open-water areas in many upland depressional wetlands are dry at the surface for significant portions of the year.

The Spoon River basin has only about 1.7% (20,034 acres) of its total area in wetlands (Table 4). Approximately 43% (8,536 acres), 33% (6,553 acres), and 11 % (2,267 acres) of these wetlands exist in stream corridors and are classed as openwater, bottomland forest or riverine, and shallow marsh/wet meadow wetlands, respectively. (For wetland categories, see the table describing wetland and deepwater habitat in Volume 3: Living Resources.)

The hydrogeology of wetlands allows water to accumulate in them longer than in the surrounding landscape, with far-reaching consequences for the natural environment. Wetland sites become the locus of organisms that require or can tolerate moisture for extended periods of time, and the wetland itself becomes the breeding habitat and nursery for many organisms that require water for early development. Plants that can tolerate moist conditions (hydrophytes) can exist in these areas, whereas upland plants cannot successfully compete for existence. Given the above conditions, the remaining wetlands in our landscape are refuges for many plants and animals that were once widespread but are now restricted to existing wetland areas.

5 Table 4. Wetlands in the Spoon River Basin

Subbasin Wetlands % of %of % of total Subbasin Name Acres area Acres subbasin wetlands Big Cr. 37,370 3.2 1,921.23 5.1 9.6 Brush Cr. 31,056 2.6 462.75 1.5 2.3 Cedar Cr. 120,466 10.2 1,438.41 1.2 7.2 Coal Cr. 26,957 2.3 913.74 3.4 4.6 Court Cr. 61,607 5.2 1,219.93 2.0 6.1 E. Fk. Spoon R. 60,544 5.1 153.03 0.3 0.8 East Cr. 7,597 0.6 96.93 1.3 0.5 French Cr. 44,445 3.8 458.13 1.0 2.3 Haw Cr. 40,230 3.4 449.95 1.1 2.2 Indian Cr. 46,994 4.0 215.28 0.5 1.1 Littlers Cr. 27,438 2.3 1,211.74 4.4 6.0 Lost Grove Cr. 10,369 0.9 148.71 1.4 0.7 Put Cr. 30,314 2.6 1,361.72 4.5 6.8 ShawCr. 33,309 2.8 232.55 0.7 1.2 Slug Run 5,153 0.4 389.04 7.5 1.9 Spoon R. cntr. 47,693 4.0 1,359.14 2.8 6.8 Spoon R. lwr. 32,111 2.7 1,113.12 3.5 5.6 Spoon R. lwr. cntr. 97,212 8.2 2,189.76 2.3 10.9 Spoon R. upr. 98,615 8.4 711.92 0.7 3.6 Spoon R. upr. cntr. 93,952 8.0 1,897.77 2.0 9.5 Swan Cr. 62,874 5.3 627.84 1.0 3.1 Turkey Cr. 17,103 1.4 173.17 1.0 0.9 W. Fk. Spoon R. 38,165 3.2 194.58 0.5 1.0 Walnut Cr. 109,374 9.3 1,093.83 1.0 5.5 Totals 1,180,948 100.0 20,034.27 1.7 100.0

The configuration of wetlands enables them to retain excess rainwater, extending the time the water spends on the upland area. The effect of this retention on the basin is to delay the delivery of water to the main stream. This decreases the peak discharges of storm flow Qr floods, thus reducing flood damages and the resulting costs. It is important to realize that the destruction of wetland areas has the opposite effect, increasing peak flood flows and thereby increasing flood damages and costs.

The location of wetlands affects many day-to-day decisions because wetlands are considered "Waters of the United States" (Clean Water Act) and are protected by various legislation at the local, state, and federal levels (for example, the Rivers and Harbors Act of 1899, Section 10; the Clean Water Act; and the TIlinois Interagency Wetlands Act of 1989). Activities by government, private enterprise, and individual citizens are subject to regulations administered by the U.S. Army Corps of Engineers. Under a Memorandum of Agreement between federal regulatory agencies with jurisdiction over wetlands, the Natural Resources Conservation Service takes the lead in regulating wetland issues for agricuituralland, and the U.S. Army Corps of Engineers takes the lead for all nonagricultural lands.

6 In contexts where wetland resources are an issue, the location and acreage of a wetland will be information required by any regulatory agency, whether local, state, or federal. Currently, there are two general sources of wetland location information for lllinois: the National Wetland Inventory (NWO, completed in 1980, and Illinois Land Cover, an Atlas (ILCA) by the lllinois Department of Natural Resources (1996). The State of lllinois used the NWI information to publish the Wetland Resources ofIllinois: An Analysis and Atlas (Suloway and Hubbell, 1994). While this atlas is not of suitable scale for landowners or government agencies to use for individual wetland locations, it can be used by agencies or groups that consider wetlands in an administrative or general government manner and focus on acreage and not individual wetland boundaries.

The NWI program involved identifying wetlands on aerial photographs of 1:58,000 scale and publishing maps of this information using USGS 1:24,000-scale topographic (. \ quadrangle maps as the base. NWI quadrangle maps for the Spoon River basin are shown in Figure 3. Individual quadrangles can be purchased from:

Center for Governmental Studies Wetland Map Sales Northern lllinois University De Kalb, IL 60115 Telephone: (815) 753-1901

Digital data by quadrangle are available from the NWI Web site: www.nwLfws.gov.

The ILCA inventory used Landsat Thematic Mapper satellite data as the primary source for interpretation. National Aerial Photography Program photographs verified the land cover classification and helped ensure consistency from area to area in lllinois. The ILCA and companion compact disc can be purchased from:

lllinois Department of Natural Resources 524 South Second Street Lincoln Tower Plaza Springfield, IL 62701-1787 Telephone: (217) 524-0500 E-mail: [email protected] Web site: http://dnr.state.il.us/ctap/ctaphome.htm

Although the ILCA and NWI programs were not meant for regulatory purposes, they are the only state or regional wetland map resources available and are the logical sources for beginning a wetland assessment. The presence or absence of wetlands as represented by the wetland maps is not certified by either the ILCA or the NWI mapping program. Figure 4, taken from the London Mills Quadrangle in the Spoon River basin, exemplifies the information that can be expected from NWI maps.

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Figure 4. National Wetlands Inventory information from the London Mills 7.5-minute quadrangle map showing wetlands, deepwater habitat, and NWI codes. In some areas with intense economic development and significant wetland acreage, the NWI maps have been redone or updated for use in designating or locating wetland areas. Whatever the source of wetland map information, the user should be aware that this information is a general indication of wetland locations, and the boundaries and exact locations should be field-verified by persons trained or certified in wetland delineation.

Given the limitations of most existing wetland maps, more complete information can be obtained by comparing mapped wetlands with other regional attributes such as shallow aquifers, subsurface geology, and placement in the landscape. When these comparisons show consistent regional patterns (for example, placement in the landscape or correlation with a particular geologic material), any parcels of land with similar landscape positions or geologic materials can be considered potential wetland sites even if maps do not show them as wet.

Land Use

Agriculture is the major land use in the nine counties (Bureau, Fulton, Henry, Knox, Marshall, McDonough, Peoria, Stark, and Warren) in the Spoon River basin. The lllinois Department of Agriculture, lllinois Agricultural Statistics (lAS) data indicate that in 1995 agricultural acreage accounted for approximately 64% of the total surface area in the Spoon River assessment area, an increase of 18% from 671,0667 acres in 1925 to 751,666 acres in 1995. Figure 5 shows the changes in the harvested acres of selected crops in the basin from 1925 to 1995.

In 1925 the dominant crops were grassy crops (wheat, oats, and hay) and com, accounting for 98% of the agricultural crops grown in the basin (336,033 acres for com and 324,572 for grassy crops). Com acreage has remained fairly steady over time, increasing only slightly to levels above 500,000 acres in 1976, with a significant drop in 1983 to 331,532 acres. In 1925 soybeans were confined to 1346 acres; however, it steadily increased to 313,668 acres in 1995, which is the highest to date. The average grassy crop acreage from 1925 to 1954 was 266,500 and from this time steadily decreased to approximately 50,000 acres in 1995. The inverse relationship between soybean and grassy crop acreage can be seen in figure 5, where the trends in acreage cross during 1964-66. In 1995, the dominant crops were com and soybeans as opposed to com and grassy crops in 1925. Ninety-three percent of acres harvested in the Spoon River basin in 1995 were com and soybeans.

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Figure 5. Acreages ofSelected Crops in theSpooon River Basin Based on lAS Data

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11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 Climate and Trends in Climate

This chapter reviews climate trends in and around the Spoon River basin since the tum of the century. Climate parameters examined are: annual average temperature, the number of days with highs above or equal to 90oP, the number of days with lows below or equal to 32°P, the number of days with lows below or equal to oop, annual precipitation, the number of days with measurable precipitation, annual snowfall, and the number of days with measurable snowfall. Extreme weather events examined in this report are tornadoes, hail, and thunderstorms.

Overview

The Spoon River basin in north-central TIlinois occupies portions of Henry, Bureau, Stark, Marshall, Knox, Peoria, Warren, McDonough, and Pulton counties. The climate of this area is typically continental, as shown by its changeable weather and the wide range of temperature extremes. Summer maximum temperatures are generally in the 80s or 90s, with lows in the 60s or 70s, while daily high temperatures in winter are generally in the 20s or 30s, with lows in the teens or 20s. Based on the latest 30-year average (1961 1990), the average first occurrence of 32°P in the fall is October 17, and the average last occurrence of 32°P in the spring is April 22.

Precipitation is normally heaviest during the growing season and lightest in midwinter. Thunderstorms and associated heavy showers are the major source of growing season precipitation, and they can produce gusty winds, hail, and tornadoes. The months with the most snowfall are November, December, January, Pebruary, March, and April. However, snowfalls have occurred as early as October and as late as May. Heavy snowfalls rarely exceed 12 inches.

The climate data used in the following discussions originate from Peoria, Illinois (Peoria County), the National Weather Service (NWS) Coop site with the longest record (1901 1996), located near the eastern portion ofthe basin. Supportive data and analyses for nearby Illinois sites can be found in reports by the Illinois Department of Energy and Natural Resources (1994) and Changnon (1984).

Temperature

The average January maximum temperature at Peoria is 30°F and the minimum is 13°P, whereas the average July temperatures are 86°P and 65°F, respectively (Table 6). The average annual temperature is 50.7°P. The warmest year of record since 1901 was 1901, with an average of 57.2°P, while the coldest year was 1917, averaging 47.8°P.

13 Table 6. Temperature Summary for Peoria (Averages are from 1961-1990 and extremes are from 1901-1996. Temperatures are inOP)

Record Record # of days # of days # of days Average Average high low with high with low with low Month high low (year) (year) >90°F S32°P

Although there is a great deal of year-to-year variability, mean annual temperatures at Peoria show warming from 190I to 1930, followed by a cooling trend until 1960, before temperatures warmed through 1996 (Figure 6).

55 G:' ~54 ~ :> 1'1 e 53 Q) a. 11\ ~ E 52 ~ I (ij 51 .JA :> c: vyv \A ~ 50 IN ~v c: ,r ct:l Q) 49 ~ 48

47 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Figure 6. Average Annual Temperaturejor Peoria, Illinois, 1901-1996

14 Examination of average temperatures over time is one way to clarify trends. The NWS has adopted 30-year averages, ending at the beginning of the latest new decade, to represent climate "normals." These averages were adopted to filter out some of the smaller scale features and yet retain the character of the longer term trends. Consecutive, overlapping "normals" for the last seven 30-year periods at Peoria are presented in Table 7. The consecutive averages demonstrate the slight warming through the 1931-1960 period, followed by cooling through the 1961-1990 period.

Table 7. Average Annual Temperature during Consecutive 30-Year Periods

Averaging Average temperature period (oF) 1901-1930 51.4 1911-1940 51.8 1921-1950 51.9 1931-1960 51.9 1941-1970 51.0 1951-1980 50.5 1961-1990 50.5

The frequency of extreme events sometimes conveys a clearer picture of trends than average values. The annual number of days with temperatures equal to or above 90°F is shown in Figure 7. The time series resembles annual temperature (Figure 6), even though the number of days with temperatures above 90°F represents only the high summer temperature extremes. Figure 7 data shows an increase through 1938, followed by a slow decline through 1970, before returning to somewhat higher numbers from 1971 to 1996.

60 LL a C) II 50 1\ .r:: :c.940 .r:: ~ '?E- 30 l/l IV ~ 0 20 Mil '0 \ '**' ~ 10 11 " o 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Figure 7. Annual Number ofDays with Maximum Temperatures Equal to or Above 90°F at Peoria. 1901-1996

15 Figure 8 shows the winter frequency of daily minimum temperatures equal to or below 32°P. The frequency of such temperatures shows no trends. Figure 9 shows the number of days per year when the minimum temperature was equal to or below OaF, beginning with the 1903-1904 winter. No long-term trends are evident; however, there is a large degree of variability from year to year.

160

150 LL ~ 140 r\; ~ I 1\ r\J ;;: 130 V a ~ ...J V N \I" E 120 7 ;;: V ~ 110 ottl 15 100 '110 90

80 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Figure 8. Annual Number ofDays with Minimum Temperatures Equal to or Below 32°F at Peoria, Winters 1901-1902 to 1995-1996 35

30 LL a II 25 v ;;: .3 20 E ;;: 15 ~ o 1111 15 10 N '110 ~ u~ ~ 5 fi If{ I II' o 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Figure 9. Annual Number ofDays with Minimum Temperatures Equal to or Below O°F atPeoria. Winters 1901-1902 to 1995-1996

16 Precipitation

Average annual precipitation at Peoria is 36.25 inches, with more rainfall in the spring and summer than in fall and winter (Table 8). Late spring, summer, and early fall precipitation is primarily convective in nature, often associated with short thunderstorms (1-2 hours in duration). During the remainder of the year, the precipitation is of longer duration and associated with synoptic-scale weather systems (cold fronts, occluded fronts, and low-pressure systems). The wettest year of record was 1990 (55.35 inches). The driest year was 1988 (22.17 inches).

Table 8. Precipitation Summary for Peoria (Avera es are from 1961-1990 and extremes are from 1901-1996. Precipitation is in inches.)

Record Record Largest one- #of high low day amount days Month ( ear) ( ear) ear) Snowfall wI reci January 1.51 8.11 (1965) 0.07 (1919) 4.43 (1965) 7.3 9 February 1.42 4.95 (1942) 0.14 (1907) 2.83 (1942) 5.9 8 March 2.91 6.95 (1973) 0.40 (1958) 2.88 (1944) 3.4 11 April 3.77 8.66 (1947) 0.71 (1971) 5.06 (1950) 1.2 12 May 3.70 11.49 (1915) 0.47 (1934) 5.52 (1927) 0 12 June 3.99 11.69 (1974) 0.45 (1936) 4.74 (1911) 0 10 July 4.20 10.15 (1993) 0.33 (1988) 3.56 (1953) 0 9 August 3.10 8.61 (1955) 0.25 (1992) 4.32 (1955) 0 9 September 3.87 13.09 (1961) 0.03 (1979) 4.11 (1961) 0 9 October 2.65 10.53 (1941) 0.03 (1964) 3.62 (1969) 0.1 8 November 2.69 7.62 (1985) 0.07 (1917) 4.26 (1990) 1.9 9 December 2.44 6.34 (1949) 0.29 (1930) 2.52 (1965) 6.4 9

The annual precipitation at Peoria is shown in Figure 10. There are no trends in the data. However, the last 10 years of data have the highest degree of variability.

The number of days per year with measurable precipitation (i.e., more than a trace) is shown in Figure 11. No trend is evident from 1901 to 1960. From 1961 to 1996, the variability in the number of days has increased dramatically. The much lower values in the first few years of the record may be due to changes in exposure, location, or observer. The annual precipitation (Figure 10) shows no such pattern, suggesting that the changes shown in Figure II mainly impact the very light precipitation events. Precipitation is more frequent during summer months than during winter months.

17 55

45 ~ =c \J II " I. 'i V '\

20 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Figure 10. Annual Precipitation at Peoria, 1901-1996

150

140 c o '.p 130 .~ c. 'u 120 II ~ IP 0.. II .. .<::110 II :!::: u ;:;: , V 11"1 ~ 100 «l Cl a 90 '*to 80

70 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Figure 11. Annual Number ofDays with Measurable Precipitation at Peoria, 1901-1996 ,· "., Average winter snowfall at Peoria is 26.2 inches, but there is great year-to-year variability. The most winter snowfall was 52.3 inches during the 1977-1978 winter, whereas the least was only 5.8 inches during the 1916-1917 winter. Snowfall from the 1903-1904 winter season through the 1995-1996 season is shown in Figure 12. A similar upward trend was evident through the mid-1980s, followed by a slight decline through the winter of 1995-1996.

18 60

40 "2 '= II ~ 30 a enc I~~y ~ 20 ... M IAN V\ 1\ I' II 10 " o 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Figure 12. Annual Snowfall at Peoria. Winters 1903-1904 to 1995-1996

Figure 13 shows the number of days each winter with snowfall, from 1903-1904 through 1995-1996. The number of days with snow shows a somewhat different pattern than that for total snowfall with increases through 1966-1967, followed by decreases through 1995 1996. A snowfall of more than 6 inches occurs about once a year. Snow cover is frequently experienced at Peoria, lasting from a few days at a time to up to three months.

35 , I. (\l 30 3: III~ g 25 N\ en ,\ ~ 20 rn > MI .1 1\ V i:5 15 a A rv\ \..1 ~ 10 V , ~V'4

5 II o 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Figure 13. Annual Number ofDays with Measurable Snowfall at Peoria. Winters 1903-1904 to 1995-1996

19 Precipitation Deficits and Excesses

Following are the driest years in the Spoon River basin in terms of annual precipitation shortfall, starting with the driest: 1988, 1989, 1910, 1930, 1914,1962, 1994, 1956, 1963, and 1901. The driest summer seasons (June, July, and August) include: 1988, 1936, 1910, 1922, 1930, 1991, 1912, 1920, 1914, and 1933. Significantly above average precipitation fell at Peoria in 1990, 1993,1927, 1973, 1926,1902, 1965, 1982, 1970, and 1985. No single decade dominated in terms of years with excessive precipitation.

Severe Weather

Tornadoes

Although tornadoes are not uncommon in illinois, most people do not expect to be affected directly, even if they live in the state for a lifetime. This is because tornadoes are generally only one-quarter mile in diameter, travel at roughly 30 miles per hour for only 15-20 minutes, and then dissipate, directly affecting a total area less than 2 square miles. Since lllinois observes an average of 28 tornadoes a year (though the actual number varies from fewer than ten to about 100 during the last 35 years), the total area directly affected by tornadoes annually is only about 55 square miles, 0.001 % the total area of the state. Even with 96 tornadoes reported in lllinois in 1974 (the greatest number reported in the last 30 years), the affected area was only about 0.003% the total area of the state. These numbers do not diminish the effect on those experiencing property damage, injury, or worse, but they demonstrate the extremely low probability of direct impact at any given location.

The most recent study on tornadoes in illinois (Wendland and Guinan, 1988) examined events from 1955 to 1986 and found no apparent trends in tornado frequency or intensity.! On average, the Spoon River basin experiences about one tornado every three years.

Hail

Hail events are somewhat rare and typically affect a very small area (from a single farm field up to a few square miles). Unfortunately, very few NWS Coop sites measure hail. The combination of small, infrequent events being measured by a sparse climate network makes for very few reliable, long-term records of these events, particularly for large areas. Based on Changnon (1995), the Spoon River basin experiences two hail days per year, with the actual number varying greatly from year to year. The years with the most hail days were 1927, 1950, and 1954, each with seven. There are no indications of trends in hail days, based on the records from Peoria, illinois from 1901 to 1994.

20 Thunderstorms

On average, the Spoon River basin experiences about 40 days with thunderstorms each year. The annual number of days with thunder over the Spoon River basin since 1948 is shown in Figure 14, which is composed of data from Peoria (1948-1995). There is substantial year-to-year variation in thunderstorm days, ranging from as many as 56 in 1975 to as few as 23 in 1968. There is no significant trend in thunderstorm days over the 1948-1995 period at Peoria.

~ ~ 50 c f'.j ::> ~ 45 VI ,!;; \ ~ " (1 .~ 40 ·u • lfl A \A V iii' 35 -y o ~lJ '""\J '030 \ '"' 25 --.;;;; 20 1940 1950 1960 1970 1980 1990 2000

Figure 14. Annual Number ofDays with Thunderstorms at Peoria. 1948-1995

Summary

The average annual temperature for Peoria shows a warming trend through 1930, followed by a cooling trend until the early 1960s before warming through 1996. The number of days with temperatures above or equal to 90°F shows an increase through 1938, followed by a slow decline through 1970, before returning to somewhat higher numbers from 1971 to 1996. The number of days with temperatures below or equal to 32°F and O°F showed no trends.

21 For precipitation, there are no trends. There were no trends in the number of days with measurable precipitation. For snowfall and the number of days with snow, there was an upward trend through the 1980s, followed by a downward trend through 1996.

Records extending back to 1901 show no clear trends in hail events. Similarly, there are no apparent trends in tornado events, although records date only to 1955. The number of days with thunderstorms has been recorded since 1948 with no significant trends.

22 Streamflow

Surface water resources are an essential component of any ecosystem because they provide different types of habitats for aquatic and terrestrial biota. In addition to their natural functions, they are sources of water supply for domestic, industrial, and agricultural use. Changes in natural and human factors, such as climate, land and water use, and hydrologic modifications, can greatly affect the quantity, quality, and distribution (both in space and time) of surface waters in a river basin.

There are about 2,750 miles of rivers and streams in the Spoon River basin. The status of these rivers and streams is monitored by stream gaging stations, which measure the flow of water over time, providing information on the amount and distribution of surface water passing the station. Since it is not feasible to monitor all streams in a basin, gaging stations are established at selected locations, and the data collected are transferred to other parts of the watershed by applying hydrologic principles. Streamflow records are used to evaluate the impacts of changes in climate, land use, and other factors on the water resources of a river basin.

Stream Gaging Records

Figure 15 shows the location of eight stream gages in the Spoon River basin presently or previously operated by the U.S. Geological Survey that have ten or more years of continuous daily flow data. These stations are listed in Table 9 with the Drowning Fork gage at Bushnell, which is located less than 3 miles from the boundary of the Spoon River basin and provides a representative flow record for tributaries in the southwestern portion of the basin. The gages on Big Creek, Evelyn Branch, and Slug Run are located in surface-mined areas and provide useful information to determine the impacts of surface mining on the stream hydrology.

Human Impacts on Streamflows in the Basin

The characteristics of streamflow in any moderately developed watershed vary over time because of the cumulative effect of human activities in the region. Like most locations in llIinois, the Spoon River basin has experienced considerable land use modification since European settlement, including cultivation, removal of wetland areas, and deforestation. However, because most modifications began prior to the onset of streamgaging activities, their impact cannot usually be detected in the gaging records. Of the recent modifications to the landscape, surface mining for coal has the most noticeable impact on streamflows and watershed hydrology. These impacts are discussed at various points in this chapter.

23 Scale 1:833800 b=====~'O=====_"~====~30MI" 0 'b===,l,!,0:'-==;;!"6==",;'!":'-=~40 KlIom.t...

N Basin Boundary • Lakes

N Streams A Gaging stations

Figure 15. Location of Gaging Stations in the Spoon River Basin Table 9. USGS Stream Gaging Stations in the Spoon River Basin having Continuous Discharge Records

Record Drainage Length Period 2 USGS ill Station name area (mi ) ( ears) of record 05568800 Indian Creek near Wyoming 62.7 37 1959-present 05569000 Brush Creek at Lake Bracken near Galesburg' 9.1 26 1932-1958 05569500 Spoon River at London Mills 1072 54 1942-present 05570000 Spoon River at Seville 1636 82 1914-present 05570350 Big Creek at St. David 28.0 14 1972-1986 05570360 Evelyn Branch near Bryant 5.8 20 1972-1992 05570370 Big Creek near Bryant 41.2 20 1972-1992 05570380 Slug Run near Bryant 7.1 17 1975-1992 05584400 Drowning Fork near Bushnell 26.3 22 1960-1982

Notes: a) Monthly discharge estimates only

Climate variability causes the greatest influence on the changes in streamflows from year to year and decade to decade. Its influence is usually large enough to help mask the impacts of the less obtrusive human modifications to the rivers' flows, including many '.} types of land use modification. The major changes to the climate during this century are assumed to occur from natural climatic variability, but it is possible that in the future they may be shown to also have human influences. '

Other modifications to the watershed, such as reservoir construction, point withdrawals, and discharges into the streams, normally have definable impacts on stream flows. However, the reservoirs in the Spoon River basin are generally small and the amount of water withdrawn from or discharged into streams is also small. Therefore, the streamflow records do not display any noticeable impacts from these sources.

Annual Streamflow Variability

Average streamflow varies greatly from year to year, and can also show sizable variation between decades. Figure 16 shows the annual series of average streamflow for the Spoon River at Seville and selected gaged tributaries. Flows are presented in units of inches of runoff over each stream's watershed. Of the 36 inches of precipitation that falls in the basin in an average year, roughly 9 inches of water becomes streamflow. Average annual runoff from surface-mined lands is essentially the same as that from other areas.

As shown in Figure 16, the series of average annual streamflows are almost identical for all gaging stations, although streams in the smaller watersheds can show a wider variability. The greatest annual runoff in the watershed was almost 30 inches, and occurred in 1993. The least annual runoff, less than 1.5 inches, occurred four year earlier

25 30.------....,...---,

--e-Indian Creek near Wyoming 25 ~ Big Creek near Byrant '" -e-Drowning Fork at Bushnell -Ir-Spoon River at Seville £.E; ~ 20

::; iii 15 a: ~ w

0+---+---1-----\---+---+----1----+----+-----1 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

Figure 16. Average Annual Streamflow for Selected Gages in the Spoon River Basin in 1989. The average flow for the Spoon River gage was particularly high during the 11 year period 1973-1983, and particularly low from 1930 to 1941. The variability in these flows can be attributed to coincident fluctuations in average annual precipitation. Overall, there has been a slight increasing trend in streamflow since the early part of this century, although there has also been a decreasing trend over the last 20 years.

Statistical Trend Analysis

Table 10 shows the trend coefficients estimated for the annual flow record for individual stations in the basin. The trend analysis identifies a statistically-significant increase in average flow for the Spoon River. Trend coefficients in the tributary streams are highly variable, ranging from 0.174 to -0.326. Trend coefficients can vary significantly depending on the period being analyzed, and the negative trend coefficient for the Big Creek gage occurs primarily because of its gaging period. The lower half of Table 10 illustrates the impact of the period of record on the trend coefficients for the Spoon River at Seville. The coefficients indicate that, while there is a long-term increasing trend in . average streamflow for the Spoon River, there has also been a decreasing trend since the 1970s.

Of additional interest is the season during which the flow increases have occurred. Trend statistics for the long-term stations on the Spoon River display an increasing trend in fall streamflows, however none of the short-term tributary stations show such a trend. There was a sizable increase in spring and summer flows between the 1960s and early 1980s, followed by a decrease in these flows.

26 Table 10. Trend Correlations for Annual and Seasonal Flows

Period of Kendall trend correlation Station Name record Annual Fall Winter S rin Summer Indian Creek near Wyoming 1959-1996 0.174 0.191 0.141 0.059 0.123 Brush Creek at Lake Bracken 1932-1958 -0.214 Big Creek near Bryant 1972-1992 -0.326 -0.189 -0.074 -0.411 -0.347 Drowning Fork near Bushnell 1960-1982 0.056 -0.030 -0.048 0.160 0.134 Spoon River at London Mills 1942-1996 0.160 0.242 0.059 0.078 -0.020 Spoon River at Seville 1914-1996 0.151 0.061 0.045 0.146 0.058 Spoon River at Seville 1932-1958 -0.003 -0.089 -0.009 -0.071 0.280 Spoon River at Seville 1943-1996 0.136 0.195 0.059 0.051 -0.026 Spoon River at Seville 1959-1996 0.096 0.073 0.119 0.062 0.066 Spoon River at Seville 1960-1982 0.281 0.065 -0.013 0.273 0.411 Spoon River at Seville 1972-1992 -0.263 0.053 0.011 -0.358 -0.253

Daily and Seasonal Flow Variability

Figure 17 plots the flow duration curves for the gages in the Spoon River basin. The flow duration curve provides an estimate of the frequency (probability) with which the given flows are exceeded. Streamflows, or discharges, for each frequency level are given in cubic feet per second (cfs). The curves for the Spoon River stations, at Seville and London Mills, look almost identical with the exception that there is consistently more flow at the Seville gage because of its larger drainage area. The slopes of the flow duration curves for Indian Creek and Drowning Fork, which are slightly steeper, display the typical flow relationships expected of smaller tributaries. Flows for smaller tributaries can be highly variable, with high flows being as much as fifteen times greater than the "normal" 50 percent flow and low flows being zero during the late summer and fall.

The flow duration curves for streams in the surface-mined areas (Big Creek, Evelyn Branch, and Slug Run) have a noticeably different shape. The overall variability of flow in these streams is less, as evidenced by a more gradual slope. These streams have a considerably greater amount of discharge during low flows, i.e. those flows where the probability of exceedence is greater than 80 percent. For example, the low flows for Big Creek are almost three times greater than that for Indian Creek, even though Indian Cleek has a much larger watershed. High flows (those flows where the probability of exceedence is less than 10 percent) in the surface-mined areas are also noticeably lower than the unimpacted, similarly-sized watersheds. The uneven topography in the mined areas and storage provided by surface-mine lakes, results in much less storm runoff.

27 10000 Tir:::::;;;=--r-I-rT-rII-r7==g~~~~=~=;::::==i::;l --e-Indian Creek near Wyoming ~ Spoon River at London Mills ., --&-Spoon River at Seville ____ Evelyn Branch near Bryant -.-Big Creek near Bryant 1000 --.-Slug Run near Bryant ~ Drowning Fork at Bushnell I I .!! Q 100 ui ~ a: ~ ~ o 10

0.1 J--' -'-_-'---'--'-+--+_-'---'-_+--'--+--+.....:;:_+-_-'-~---'--' 10 20 30 50 70 80 90 99

PERCENT CHANCE OF EXCEEDENCE Figure 17. Flow Duration Curves (Discharge Versus Probability)

As with all other locations in Illinois, streams in the Spoon River basin have a well-defined seasonal cycle. Figure 18 shows the probability offlow rates on the Spoon River at Seville. As shown, flows tend to be greatest during the spring and early summer months, March through June, dropping to their minimum values by late summer and fall. Nevertheless, there is significant variation in the flows for each month. For example, during wet years the flows in the fall can be greater than the average spring.

10000

~- ~ ~ 1000 -&. 1l - ui ~ r a: " I / ...... "-... ~ ()"" (f) ~ 0 ~ 100 / ~. .. ------ ---'-50% -A-90% -'-10%

10 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Figure 18. Monthly Flow Probabilities for the Spoon River at Seville

28 Flooding and High Flows

The magnitude of flooding in the Spoon River basin is generally similar to that experienced in other watersheds in western and centrallllinois. Figure 19 shows the annual series of peak: flood discharges for the Spoon River at Seville and three smaller streams. Peak: discharges are given in cubic feet per second Ccfs). The three highest floods on record for the Spoon River occurred in 1924, 1974, and 1993. The average peak: flows for the Spoon River have been slightly greater since 1970; however, in general there is little overall trend in the 80 years of record even though average strearnflows have increased over the same period of time.

100000

.. ~ 1M Jt • .!II ~~ ~ " ~tN XI ~ \~ 10000 L. tl\./A. .. f'

Cil ~ .~ ~ 7'i9 I~ ~ Indian Creek near Wyoming Jt~ 1000 I~~'-~ f .....,:,. Spoon River at Seville I -+-Big Creek near Bryant I f--- -e--Drowning Fork at Bushnell

100 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Figure 19. Annual Peak Discharges at Four Stream Gages in the Spoon River Basin

There is no detectable trend in the flooding at the Drowning Fork and Big Creek gages. The Indian Creek gage shows a noticeable increasing trend in peak flows. The peak: flow rates for Big Creek are noticeably smaller than the other watersheds. As indicated earlier, high flows and peak: discharges in surface-mined areas are significantly less than in unimpacted watersheds as a result of the additional storrnwater storage provided by topographic depressions in surface-mined areas.

Statistical Trend Analysis

Results of the statistical trend analysis of flood records are given in Table II. Trend coefficients are computed for both the annual peak discharges at the gage, as well as the annual series of 7-day high flows, which is the average maximum flow rate over seven consecutive days. Analysis of the annual high flows provides an indication of the trend in flow volume. The peak flows and high flows for most gaging stations show a small

29 increasing trend. In most cases, these trend coefficients are not statistically significant (a 90% level of confidence). The Indian Creek gaging record shows a significant trend in peak discharge; however, the trend coefficient computed for the high flows is considerably less. Conversely, Big Creek near Bryant shows a downward trend in high flows over the period 1972-1992, but no trend in peak flows. The detection of flood trends is greatly impacted by the period of record being analyzed.

Table 11. Trend Correlations for Flood Volume and Peak Flow

Period Kendall trend correlation Stream Ga in Station of record 7-da hi h flow eak flow Indian Creek near Wyoming 1960-1996 0.111 0.293 Spoon River at London Mills 1943-1996 0.029 0.021 Spoon River at Seville 1918-1996 0.108 0.135 1943-1996 0.043 0.017 Big Creek near Bryant 1972-1992 -0.221 0.053 Drowning Fork near Bushnell 1961-1991 0.090 0.022

Seasonal Distribution of Flood Events

Table 12 presents the monthly distribution of the top 25 flood events for five gaging stations. For the Spoon River, major flooding usually occurs during the first half of the year. For most smaller tributaries, such as Indian Creek and the Drowning Fork, floods most commonly occur in summer and are usually caused by local convective storms. For Big Creek and streams in surface-mined areas, spring is the most common flooding season. ,~

Table 12. Monthly Distribution of Top 25 Flood Events at Selected Stations

Month Jan Feb Mar Jun Ju1 Au Oct Nov Dec Indian Creek 2 2 5 5 4 2 0 1 0 near Wyoming Spoon River 4 2 3 4 2 5 2 0 2 0 1 0 at London Mills Spoon River 1 3 3 2 3 5 3 1 2 1 0 at Seville Big Creek 0 1 2 6 4 7 0 0 0 2 2 near Bryant Drowning Fork 3 1 3 1 8 4 0 2 0 1 near Bushnell

30 Drought and Low Flows

Minimum flows during droughts are defined by the average flow experienced during a critical period of low streamflow. The average flow experienced during a short critical period, such as with a I-day or 7-day low flow, is useful for evaluating short-term impacts of low streamflow on water quality, aquatic habitat, and direct water withdrawals from streams. The average flow experienced during a long critical period, ranging from 18 to 42 months in duration, is useful in analyzing drought impacts on reservoir supplies. In the Spoon River basin and other parts of western illinois, minimum levels in water supply reservoirs may not be reached until as many as 4 years after the onset of a drought, depending on both the size of the reservoir and water demand. Table 13 lists the most severe, lowest magnitude flows experienced on the Spoon River at Seville for the critical periods discussed in the following sections.

Table 13. Minimum Flows Experienced During Major Droughts (in cfs), Spoon River at Seville, 1915·1996

Duration of critical period Drou ht Years 7-da 18-month 30-month 42-month 1922-1923 24.6 321 489 452 1930-1931 34.7 292 451 573 1933-1934 18.0 260 63 I 1940-1941 10.7 182 373 539 1955-1956 20.3 271 383 476 1963-1964 14.9 252 352 694 1988-1989 6.8 129 358 588

Seven-Day Low Flows

Figure 20 presents the 7-day low flows computed for a) the Spoon River gages, and b) four tributary gages. As shown in this figure, low flows on the Spoon River have generally increased since the early part of this century, when drought periods were more common. But the magnitude of low flows have been decreasing since the 1970s, with the exception of 1993 when flows were high all year. The minimum low flows for the period of record for the Spoon River occurred in the drought of 1988-1989, although there is a newspaper account that indicates the Spoon River experienced zero flow during an extended drought in the 1870s. Some of the other lowest flows occurred during 1940, 1936, 1963, and 1934.

Most of the smaller tributaries in the Spoon River basin have flows near zero during most summers and any extended dry period. Some of the largest tributaries have at least a small amount of flow throughout the entire year except during droughts. Streams in surface-mined areas of the basin, such as Big Creek and Evelyn Branch, have much higher levels of sustained flow in dry periods than do similarly-sized watersheds in the remainder of the basin.

31 '/' "

600,------,

500 -'1!r--Spoon River at Seville -+-Spoon River at London Mills

400 ~ u.i Cl ~ 300 :I: U W Ci 200

100

O+---+---...-.,.;=-"'I'------'-"!-...... -= 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000

18 -Er-lndian Creek near Wyoming ~ Evelyn Branch near Byrant 16 ~ Big Creek near Bryant ~ Drowning Fork at Bushnell 14

l!! q 12 w Cl a: 10 :I:"" Uw Ci 8

0 1960 1965 1970 1975 1980 1985 1990 1995

Figure 20. Annual7-Day Low Flowsfor a) the Illinois River, and b) the tributaries in the Spoon River Basin

32 Multi-Year Drought Flows

Table 13 also illustrates that the severity of a drought, and its overall impact on water supplies, can vary over time. For example, the 1988-1989 drought was the drought of record for shorter durations (l8-months and less). Several other droughts, such as those in 1922-1923,1940-1941, and 1955-1956 were not as acute or intense, but had persistent low flows lasting several years.

As shown by the first column of Table 13, major droughts occurred in every decade since streamgaging was initiated on the Spoon River through the mid-I 960s. Analyses of water supply and precipitation records have also shown that major droughts were regularly experienced prior to this time. Thus, the occurrence of only one major drought since the mid-1960s is a significant change. Though the future is difficult to predict, the infrequent occurrence of drought and the absence of persistent droughts is expected if the climate remains cooler and wetter, as predicted by recent climate models.

Erosion and Sedimentation

Instream Sediment Load

Instream sediment load is the component of soil eroded in the watershed and from the streambanks that is transported to and measured at a gaging station. It indicates the actual amount of soil generated upstream of the gaging station and eventually transported to downstream reaches of the river. Given the complex dynamic process of soil erosion, sediment transport, and deposition, it is very difficult to quantify how much of the soil eroded from uplands and streambanks actually moves to downstream reaches.

The sediment transported by a stream is a relatively small percentage of the total erosion in the watershed. However, the amount of sediment transported by a stream is the most reliable measure of the cumulative results of soil erosion, bank erosion, and sedimentation in the watershed upstream of a monitoring station.

Table 14 summarizes information about the six gaging stations in the Spoon River basin where instream sediment was monitored for some time. As shown in Figure 21, two of these stations are located on the Spoon River, one on Indian Creek, two on Big Creek, and the sixth on Slug Run.

Table 14. Sediment Monitoring Stations in the Spoon River Basin

USGS station Drainage area Station name number s . mi.) Period of record Spoon River at London Mills 05569500 1,072 Oct. 1980-Sept. 1987 Spoon River at Seville 05570000 1,636 Oct. 1980-Sept. 1981 Oct. 1994-Sept. 1996 Indian Creek near Wyoming 05568800 63 Oct. 1980-Sept. 1981 Big Creek at St. David 05570350 28 Nov. 197 I-Sept. 1980 Big Creek near Bryant 05570370 41 Dec. 1971-Dec. 1986 Slug Run near Bryant 05570380 5 Oct. 1975-Sept. 1980

The U.S. Geological Survey (USGS) monitored sediment yield at the Spoon River at Seville for three water years (1981, 1995, and 1996). USGS also monitored sediment yield at Indian Creek near Wyoming for one water year (1981), at Big Creek at St. David for nine water years (1972-1980), at Big Creek near Bryant for fifteen water years (1972 1986), and at Slug Run near Bryant for five water years (1976-1980). Data collected by the USGS were reported as daily average concentrations; therefore, daily and annual sediment loads at the stations can be calculated.

35 Scale 1:633600 ',======~"======~"1",,=====~30MI..

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Figure 21. Sediment Monitoring Stations in the Spoon River Basin 25000,------, 05569500 Spoon River at London Mills 20000

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38 25000 r------, 05570000 Spoon River at Seville 20000 f----

35000 f------ u ~ &. 0000 _._- .- __ .- _ _-- ..----.---.------.------..----.- .."---.. "-.-"--.-~" -- ,------.-. , __ .

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,- Figure 23. Variabilities ofFlow Discharge and Instantaneous Suspended Sediment Concentration and Loadfor the Spoon River at Seville

39 1500~------, 05568800 Indian Creek near Wyoming

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1 10/l/80 10/1/81 Date

Figure 24. Variabilities ofFlow Discharge and Instantaneous Suspended Sediment Concentration and Loadfor Indian Creek near Wyoming

40 1200,------, 05570350 Big Creek at 51. David 1000

SOO ~ ~ u ~ 600 ~ 0 400

200 ------11

10000

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lUAJUU-"-L IOllnl 1OIIn2 IOnn3 10ltn4 10ltnS lO/In6 lO/In7 IOllnS lOltn9 1011lS0 Date

Figure 25. Variabilities ofFlow Discharge and Instantaneous Suspended Sediment Concentration and Load for Big Creek at St. David

41 1200r------, 05570370 Big Creek near Bryant 1000 e.-... . .

800 e.- ..

600 e. .

&400 e.-.

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1 10/1171 1011/73 1011175 10/1177 1011179 1011181 1011183 1011185 1011187 Date

,., Figure 26. Variabilities ofFlow Discharge and Instantaneous Suspended Sediment Concentration and Loadfor Big Creek near Bryant

42 100',------, 055703S0 Slug Run near Bryant so .. ------

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Figure 27. Variabilities ofFlow Discharge and Instantaneous Suspended Sediment Concentration and Loadfor Slug Run near Bryant

43 Similarly, annual sediment load can be calculated for all stations but the Spoon River at London Mills. As shown in Table 15, annual sediment load at the Spoon River at Seville varied from a low of 1,026,099 tons in 1996 to a high of 2,049,265 tons in 1981, with an annual average of 1,486,247 tons. Annual sediment load at Big Creek at St. David varied from a low of 9,571 tons in 1979 to a high of 46,859 tons in 1973, with an annual average of 17,682 tons. Annual sediment load at Big Creek near Bryant varied from a low of 13,727 tons in 1984 to a high of 44,240 tons in 1973, with an annual average of 22,202 tons. Annual sediment load at Slug Run near Bryant varied from a low of 442 tons in 1980 to a high of 1,006 tons in 1978, with an annual average of 792 tons. Note that the 1972 load for Big Creek at St. David was only for a period of nine months and the 1972 load for Big Creek near Bryant was only for a period of ten months.

The corresponding sediment yield per square mile ranged from 627 tons per square mile in 1996 to 1,253 tons per square mile in 1981, with an average of 909 tons per square mile for the Spoon River at Seville. The sediment yield per square mile at Big Creek at St. David ranged from 342 tons per square mile in 1979 to 1,674 tons per square mile in 1973, with an average of 632 tons per square mile. At Big Creek near Bryant, it ranged from 335 tons per square mile in 1984 to 1,079 tons per square mile in 1973, with an average of 542 tons per square mile. Finally, at Slug Run near Bryant, it ranged from 63 tons per square mile in 1980 to 144 tons per square mile in 1978, with an average of 113 tons per square mile.

Sedimentation

Sedimentation is the process by which eroded soil is deposited in stream channels, lakes, wetlands, and floodplains. In natural systems that have achieved dynamic equilibrium, the rates of erosion and sedimentation are in balance over a long period of time. This results in a stable system, until disrupted by extreme events. However, in ecosystems where there are significant human activities (farming, construction, or hydraulic modifications) the dynamic equilibrium is often disturbed, resulting in increased rates of erosion in some areas and a corresponding increased rate of sedimentation in other areas.

Erosion rates are measured by estimating soil loss in upland areas and measuring streambank and bed erosion along drainageways. These measurements are generally not very accurate and thus are estimated indirectly, most often through evaluation of sediment transport rates based on instream sediment measurements and empirical equations. Similarly, measurement of sedimentation rates in stream channels is very difficult and expensive.

Lake sedimentation surveys provide the most reliable sedimentation measurements. Since lakes are typically created by constructing dams across rivers, creating a stagnant or slow-moving body of water, they trap most of the sediment that flows into them. The " I continuous accumulation of eroded soils in lake beds provides a good measure of how much soil has been eroded in the watershed upstream of the lake.

44 Table 15. Annual Sediment Load for the Spoon River Basin

Water discharge Sediment load Station name Water ear (cfs) (tons) Spoon River at Seville 1981 542,495 2,049,265 1995 640,820 1,383,378 1996 370,744 1,026,099

Indian Creek near Wyoming 1981 21,089 138,806

Big Creek at St. David 1972 5,666 4,847* 1973 14,394 46,859 1974 16,047 28,951 1875 8,765 16,508 1976 8,320 15,531 1977 5,892 11,866 1978 10,633 10,598 1979 9,746 9,571 1980 6,454 14,407

Big Creek near Bryant 1972 8,631 6,874** 1973 20,586 44,240 1974 23,613 43,206 1975 12,975 21,121 1976 11,784 24,912 1977 8,695 25,408 1978 16,303 18,551 1979 13,843 15,141 1980 9,084 18,655 1981 13,120 21,090 1982 16,120 23,709 1983 21,579 24,712 1984 15,564 13,727 1985 11,130 14,199 1986 14,212 17,484

Slug Run near Bryant 1976 1,657 779 1977 767 736 1978 2,230 1,006 1979 2,057 995 1980 1,000 442

Note: * and ** represent eleven- and ten-month totals, respectively.

45 Lake sedimentation rates for four lakes surveyed in the Spoon River basin are presented in Table 16. The sedimentation rates (in percent per year) for these four lakes are moderate to high in comparison to most lllinois lakes. The higher sedimentation rate for Lake Calhoun is due primarily to a large watershed draining into a relatively small lake.

Avon Lake is shown as Avondale Lake on the 7.5 minute map. The lake was built by the CB&Q Railroad in 1906. By the 1930's the lake was no longer used on a regular basis for water supply and was leased out for recreational use. In 1946, the lake was purchased by the village of Avon for use as a water supply reservoir. Also in 1946, the village raised the spillway thereby increasing the level of the lake.

Lake Bracken

Lake Bracken was constructed in 1923 by the CB&Q Railroad. The lake was purchased by the surrounding landowners in the early 1960's for recreational use. In the 1990's concerns have been raised about the impact of numerous watershed contamination sites on the lake.

Lake Calhoun

Lake Calhoun was constructed by the Galva Country Club in 1926. Problems were experienced with the spillway of the lake in the mid 1940's and the spillway was raised 2.9 feet in 1946. The spillway failed in 1950 and the lake drained completely. The spillway has been rebuilt.

EwanPond

Ewan Pond is a small private pond about one mile south of Elmira, lllinois.

46 " Water Use and Availability

Statewide, water use has increased a modest 27% since 1965 (lllinois Department of Energy and Natural Resources, 1994). Most of that increase is in power generation.

< , Water use for PWS has risen only about 7% during that time, less than the concurrent percentage increase in population. The number of public ground-water supply facilities in lllinois has risen significantly during that time, yet the total amount supplied by ground water remains near 25%.

A dependable, adequate source of water is essential to meeting existing and potential population demands and industrial uses in lllinois. Modifications to and practical management of both surface and ground-water use have helped make lllinois' water resources reliable. As individual facilities experience increases in water use, innovative alternative approaches for adequate water supplies must be developed, such as use of both surface and ground waters. Major metropolitan centers (such as the Chicago area, Peoria, Decatur, and some smaller communities) have already developed surface and ground water sources to meet their development needs and to sustain growth. The construction of impounding reservoirs has become and will remain economically and environmentally expensive, making it a less common approach.

Proper management of water resources is necessary to ensure a reliable, high quality supply for the population. Water conservation practices will become increasingly important to reduce demand and to avoid exceeding available supplies. Both our ground water resources and surface reservoir storage must be preserved to maintain reliable sources for future generations.

Ground-Water Resources

Ground water provides approximately one-third of lllinois' population with drinking water. The sources of this water can be broken down into three major units: I) sand and gravel, 2) shallow bedrock, and 3) deep bedrock. Most ground-water resources are centered in the northern two-thirds of lllinois.

Sand-and-gravel aquifers are found along many of the major rivers and streams across the state and also in "buried bedrock valley" systems created by complex glacial and interglacial episodes of surface erosion. There are also many instances of thin sand-and gravel deposits in the unconsolidated materials above bedrock. These thin deposits are used throughout lllinois to meet the water needs of small towns. Shallow bedrock units are more commonly used in the northern third of lllinois, whereas deep bedrock units are most widely used in the northeastern quarter (in and around the Chicago area). The variety of uses and the volume of water used vary widely throughout the state. This report describes ground-water availability and use in the Spoon River area.

47 Data Sources

Private Well Information The llIinois State Water Survey (ISWS) has maintained well construction information since the late 1890s. Selected information from these documents has been computerized and is maintained in the Private Well Database. These data are easily queried and summarized for specific needs and form the basis of well distribution studies in the area.

Public Well Information Public Water Supply (PWS) well information has been maintained at the ISWS since the late 1890s. Municipal well books (or files) have been created for virtually all of the reported surface and ground-water PWS facilities in llIinois. Details from these files are assembled in the Public-Industrial-Commercial Database, which was created to house water well and water use information collected by the ISWS.

Ground-Water Use Information The water use data given in this report come from the records compiled by the ISWS' llIinois Water Inventory Program (IWlP). This program was developed to document and facilitate planning and management of existing water resources in llIinois. Information is collected through an annual water use summary mailed directly to each PWS facility.

Data Limitations

Several limitations must be taken into consideration when interpreting these data:

1. Information is reported by drillers and each PWS facility. 2. Data measuring devices are generally not very accurate. 3. Participation in the lWlP is voluntary.

Information assembled from well construction reports and from the lWlP is considered "reported" information. This means that the data are as accurate as the reliability of the individual reporting or as mechanical devices dictate. The quality of the reported information depends upon the skill or budget of the driller or facility, respectively. Moreover, the ISWS estimates that only one-third to one-half of the wells in the state are on file at the Survey, mainly due to the lack ofreporting regulations prior to 1976.

In general, water use measuring devices, such as the meters used by PWS facilities, are not very accurate. In fact, errors of as much as 10% are not uncommon. Much of the information reported in the lWlP is estimated by the water operator or by program staff. Participation in the program is not required by the State of llIinois, and each facility voluntarily reports its information through a yearly survey. However, not all facilities know of or respond to the water use questionnaire. After several mail and telephone attempts have been made to gather this information, estimates are made using various techniques. To help reduce errors associated with the program, reported water use

48 infonnation is checked against usage from previous years to identify any large-scale reporting errors.

Ground-Water Availability

The Spoon River basin encompasses portions of 9 counties: Knox, Fulton, Stark, Bureau, Henry, Warren, McDonough, Peoria, and Marshall. The portion of each county in the watershed varies from less than I% (Peoria County) to 99% (Stark County). This section summarizes ground-water availability in the area, taking into consideration only those portions of each county that are actually in the watershed.

Domestic and Fann Wells Available regional infonnation indicates that ground water for domestic and farm use is obtained from shallow unconsolidated materials and from deeper lying bedrock units. Table 17 summarizes the number of reported private wells in the watershed by county and depth.

Table 17. Number of Reported Private Wells in the Spoon River Basin (Source: ISWS Private Well Database)

Depth range, feet Count 0-50 51-100 101-150 151-200 201-250 251-300 301-350 351-400 400+ Bureau 5 2 6 4 I I 6 Fulton 466 211 69 43 36 30 27 35 90 Henry 21 3 5 6 2 3 3 19 62 Knox 273 195 113 97 63 47 24 5 157 McDonough 59 15 11 1 4 5 14 4 4 Marshall 2 3 1 3 1 Peoria 96 45 15 11 6 3 8 2 21 Stark 424 123 65 57 30 12 7 4 81 Warren 23 46 40 58 69 22 25 14 20 Total 1,364 648 320 280 214 126 110 64 398

Public Water Supply Wells Infonnation from the ISWS' Public-Industrial-Commercial Database indicates that most ground water for PWS use in the area comes from wells finished in the Cambrian Ordovician systems, which supplies about 63% of the ground water withdrawn. The unconsolidated systems contribute 25%, with the Pennsylvanian and Silurian systems providing the remaining 12%.

Unconsolidated wells range in depth from 15 to 205 feet, while bedrock wells range in depth from 87 to 2,595 feet. A total of 29 public water supplies withdraw 2.96 million gallon~ per day (mgd), servicing a reported 37,704 residents at an average per capita daily water use of 86.5 gallons per day (gpd).

49 1995 Ground-Water Use

Ground water constitutes a major portion of the total water used in the basin. Total ground-water use in the basin during 1995 is estimated to be 5.74 mgd, with 2.96 mgd for PWS facilities, 0.13 mgd for self-supplied industries (SS!), 0.80 mgd for rural/domestic uses, and 1.85 mgd for livestock watering.

Public Water Supply In 1995, municipal residential use for 29 communities using ground water was reported to be 2.96 mgd, serving a combined population of 37,704. The average per capita use from these municipalities is 86.5 gpd.

Self-Supplied Industry Self-supplied industries are defined as those facilities that meet all or a portion of their water needs from their own sources. In the Spoon River area, 5 SSI facilities reported pumping 0.13 mgd of ground-water during 1995.

RurallDomestic There is no direct method for determining rural/domestic water use in the basin. To obtain an estimate, several assumptions were made using existing information. The population served and number of services reported by PWS facilities were used to calculate an average population per service for all PWS facilities in the area. This number was used as an estimate of population per reported domestic well. The average PWS per capita use was then used as a multiplier to determine the total rural/domestic water use from each well. Based on information from the ISWS Private Well Database, which shows 3,524 reported wells in the Spoon River area, an average of 2.6 people per service (well), and an average of 86.5 gpd per person, total rural/domestic water use was estimated to be 0.80 mgd.

Livestock Watering Water withdrawals for livestock use in 1995 were estimated to be 1.85 mgd. Water use estimates for Iivestock are based on a fixed amount of water use per head for each type of animal. Percentages of the total animal population (illinois Department of Agriculture, 1995) for the major livestock (cattle and hogs) in the counties were calculated based upon the percentage of county acres in the Spoon River area. Daily consumption rates provided the basis for these calculations (beef cattle = 12 gpd, all other cattle =35 gpd, and hogs = 4 gpd; see Ensminger and Olentine, 1978).

Ground-Water Use Trends

Ground-water use in the Spoon River area has remained relatively constant over the last six years. During this period, total ground-water use has averaged 3.44 mgd and ranged from 2.83 to 4.08 mgd; PWS use has averaged 3.28 mgd and ranged from 2.72 to 3.96 mgd; and SSI use has averaged 0.15 mgd and ranged from 0.12 to 0.30 mgd. Table 18

50 shows the individual totals per year since 1990. No significant trends are evident in terms of water withdrawals in the basin.

Table 18. Ground-Water Use Trends in the Spoon River Basin (in million gallons per day, mgd) Year PWS SSI Total 1990 3.96 0.13 4.08 1991 3.50 0.12 3.62 1992 3.40 0.30 3.70 1993 2.72 0.12 2.83 1994 3.17 0.12 3.29 1995 2.96 0.13 3.09 Average 3.28 0.15 3.44 ... , /J

"1 e ,. , Surface Water Resources

The rivers, streams, and lakes of the Spoon River basin serve a wide variety of purposes, including public water supply, recreation (boating/canoeing and fishing), and habitat for aquatic life. The primary focus of this section is on water withdrawn from streams, lakes, and ponds for public and industrial water supply and the surface water resources available for potential uses of this type.

Present Water Use

As indicated in the previous section, the total amount of water withdrawals in the Spoon River basin is small, amounting to just over 4 million gallons per day (mgd). The largest water withdrawal in the basin, and the only surface water withdrawal, is used for processing in a coal mining operation, in which an average of 0.9 mgd is obtained and discharged to/from a strip-mined lake. There are no public water supply withdrawals from streams or reservoirs in the basin. However, Canton Lake, located immediately east of the basin, supplies water to the communities of Canton and Cuba, both located in the Spoon River basin.

Potential for Development of Surface Water Sources

Water supply systems generally obtain surface water in one of three manners: I) direct withdrawal from a stream, 2) impoundment of a stream to create a storage reservoir, or 3) creation of an off-channel (side-channel) storage reservoir into which stream water is pumped. As described below, there are limited locations available for sustainable direct withdrawals from streams. The region has several potential locations for impounding reservoirs, and the potential for side-channel storage also exists along most streams. Development of these resources is unlikely unless there is considerable growth in water use that would expand above the supply provided by local groundwater.

51 Direct Withdrawals from Streams The Spoon River is the only stream in the area that is able to support a direct withdrawal for water use. The greatest sustainable flow in the river occurs downstream in Fulton County, where the minimum observed daily flow is 3 cubic feet per second Ccfs), or roughly equivalent to 2 mgd.

Impounding Reservoirs The streams in the Spoon River basin provide a number of possible reservoir sites, primarily because of its their steep valley slopes. Figure 28 shows the locations of 38 potential reservoir sites in the region, as given in Dawes and Terstriep (1966). Many of the potential reservoir sites could safely support a yield in excess of 2 mgd. In general, the construction of impounding reservoirs has become less common primarily because of costs and environmental concerns. As a result, the proximity of alternative sources should be considered in the proposed development of reservoirs.

Side-Channel Reservoirs There are no side-channel reservoirs in the Spoon River basin, although several side channel reservoirs exist in the adjacent McDonough County. The construction of side channel reservoirs is generally not limited by local topography and could be a viable water supply option for a small water supply along most of the tributary streams in the basin. The amount of water a side-channel reservoir can provide is limited primarily by flow in the stream over time and the size of the storage reservoir.

52 Scale 1:633600 '"""====,s"=====~z,,,,====';".'"

N Basin Boundary • Potential reservoirs

N Streams

Figure 28. Location of Potential Reservoirs in the Spoon River Basin

, ,

Ground-Water Quality

This section examines ground-water quality records to determine temporal trends and to provide baseline water quality parameters in the Spoon River area. Increasingly, ground water contamination is discussed in the news media, and it may seem that the entire ground-water resource has been affected. However, these contamination events are often localized and may not represent widespread degradation of the ground-water resource. By examining the temporal trends in ground-water quality in the area, it may be possible to determine whether large-scale degradation of the ground-water resource has occurred.

The general term "ground-water quality" refers to the chemical composition of ground water. Ground water originates as precipitation that filters into the ground. As the water infiltrates the soil, it begins to change chemically due to reactions with air in the soil and with the earth materials through which it flows. Human-induced chemical changes can also occur. In fact, contamination of ground water is generally the result of human induced chemical changes and not naturally occurring processes.

As a general rule, local ground-water quality tends to remain nearly constant under natural conditions because of long ground-water travel times. Therefore, significant changes in ground-water quality can indicate degradation of the ground-water resource.

Data Sources

The ground-water quality data that are used in this report come from two sources: private wells and municipal wells. The private well water quality data are compiled by the Chemistry Division of the lllinois State Water Survey (ISWS) as part of its water testing program and are maintained by the Office of Ground-Water Information in a water quality database. The municipal well data come from ISWS analyses and from the lllinois Environmental Protection Agency (IEPA) laboratories.

The combined database now contains more than 50,000 records of chemical analyses from samples analyzed at the ISWS and 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. This report presents information for only a portion of the chemical parameters in the ISWS database.

55 Data Limitations

Several limitations must be understood before meaningful interpretation of the water quality data can begin:

1. Representativeness of the sample 2. Location information 3. Data quality (checked by charge balance) 4. Extrapolation to larger areas

Generally, private well samples are not representative of regional ground-water 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. However, while one or more constituents may not be representative, 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, private well information probably gives a better picture of the spatial distribution of chemical ground-water quality than municipal well information because of the larger number of samples spread over a large area. Recent lEPA 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 ground-water 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, locations are given to the nearest IO-acre plot of land. For this discussion, that degree of resolution is adequate. However, it is not uncommon for a given location to be in error by as much as 6 miles. To circumvent possible location errors, this report presents results on a watershed basis.

The validity of water quality data was not checked for this report. However, previous charge balance checking of these data was conducted for a similar statewide project (lliinois Department of Energy and Natural Resources, 1994). Charge balance is a simple measure of the accuracy 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.

56 The statewide study searched the water quality database for analyses with sufficient chemical constituents to perform an ion balance. The charge balance checking of those data found that more than 98 % of the analyses produced acceptable mass balance, which suggests that the chemical analyses are accurate in the database. Using that assumption for this report, we feel confident that most of the analyses used are accurate and give representative water quality parameters for the Spoon River area. However, this may be true only for large samples, a factor that should be considered when reviewing the results, as this report presents data from ten decades and a wide range of sample sizes.

Extrapolating a point value (a well water sample) to a regional description of ground water quality is difficult theoretically and beyond the scope of this report. However, none of the data provide a uniform spatial coverage. Therefore, it seems best to summarize the data on a watershed basis to ensure an adequate number of values. 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, ground-water contamination involves the introduction into ground water of industrial or agricultural chemicals such as organic solvents, heavy metals, fertilizers, and pesticides. However, recent evidence suggests that many of these contamination occurrences are localized and form finite plumes that extend down gradient from the source. Much of this information is relatively recent, dating back a few decades, and long-term records at anyone site are rare.

As mentioned earlier, changes in the concentrations of naturally occurring chemical elements such as chloride, sulfate, or nitrate also can indicate contamination. For instance, increasing chloride concentrations may indicate contamination from road salt or oil field brine, while increasing sulfate concentrations may be from acid wastes such as metal pickling, and 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 ground-water quality analyses.

Fortunately, the ISWS 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 were chosen for trend analyses based on the large number of available analyses and because they may be indicators of human-induced degradation of ground-water quality. These components are iron (Fe), total dissolved solids (IDS), sulfate (S04), nitrate (N03), chloride (Cl), and hardness (as CaC03).

S7 Aquifer Unit Analysis

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 ground-water quality from one part of lllinois to another and from one aquifer to the next even at the same location. For the purpose of this trend analysis, wells that were finished in the unconsolidated sand and gravel units were grouped together, as were wells finished in the bedrock units. The unconsolidated units are by far the most frequently used in the Spoon River basin. Out of the more than 3,524 private wells reported in the watershed, 62% of the classified wells report penetration into the bedrock units. From the water quality analyses in the ISWS water quality database, 696 (68%) of 1,024 wells indicated that the water for the sample came from the bedrock units. In this report, unconsolidated and bedrock aquifers are discussed separately in the descriptions of each chemical constituent.

Discussion and Results

Temporal trends in the six chemical constituents from unconsolidated and bedrock materials are summarized in this section. Tables 19 and 20 present the results of each decade's analyses, including the maximum, minimum, mean, and median for each of the six chemical constituents for unconsolidated and bedrock materials, respectively.

Median values are given in the tables by decade, beginning with 1900-1909 (Decade 0), 1910-1919 (Decade 1), and so on through the 1990s (Decade 9). Each decade covers the corresponding ten-year period, except for the partial decade of the 1990s. Median concentrations are given per decade so that temporal trends can be identified in the data set. Median values are the midpoints of a set of data, above which lie half the data points and below which is found the remaining half. These values are used to look at the central tendency of the data set. Although the arithmetic mean would also look at this statistic, it incorporates all data points into its analysis, which can move the mean value in one direction or another based upon maximum or minimum values.

Outliers occur in many data sets. These are extreme values that tend to stand alone from the central values of the data set. They may lead to a false interpretation of the data set, whereas the median values are true values that are central to the data set. By looking at the median we can determine trends in the central portions of the data. However, for data sets with a small number of samples, the median may not necessarily be representative of the water quality in the area.

It is important to recognize that the values included in these tables are reported values. While every attempt to verify the values was made, the validity of each value with regard to method error, etc. is not known. For this reason, the tables include every analysis in the database and all analysis results regardless of whether a value seems excessive and regardless of the sample size in the decade.

58 Table 19. Chemical Constituents Selected for Trend Analysis, Unconsolidated Systems

Decade* Chemical constituent 0 2 3 4 5 6 7 8 9 Iron (Fe) Sample size (N) 0 0 0 17 27 21 21 175 42 16 Minimum (mg/L) N/A N/A N/A 0.0 0.0 0.0 0.0 0.0 0.0 0.1 Maximum (mg/L) N/A N/A N/A 15.0 23.0 7.1 11.0 32.0 36.0 8.2 Mean (mg/L) N/A N/A N/A 2.1 2.0 1.6 1.3 1.5 2.0 1.5 Median (mg/L) N/A N/A N/A 0.6 0.5 0.9 0.4 0.2 0.4 0.3 IDS Sample size (N) 0 0 0 19 28 21 21 177 43 16 Minimum (mgll) N/A N/A N/A 250.0 215.0 329.0 227.0 47.0 259.0 170.0 Maximum (mgll) N/A N/A N/A 906.0 994.0 942.0 1114.0 2068.0 747.0 729.0 Mean (mgll) N/A N/A N/A 513.1 445.8 502.0 530.0 655.8 430.6 402.6 Median (mgll) N/A N/A N/A 467.0 368.5 454.0 492.0 540.0 417.0 430.0 Sulfate (SO,) Sample size (N) 0 0 0 19 13 0 2 41 35 16 Minimum (mgll) N/A N/A N/A 0.0 23.0 N/A 62.0 0.4 0.2 10.0 Maximum (mgll) N/A N/A N/A 220.0 254.0 N/A 65.0 253.8 152.0 81.0 Mean (mgll) N/A N/A N/A 57.0 101.5 N/A 63.5 89.9 59.6 52.7 Median (mgll) N/A N/A N/A 28.0 94.0 N/A 63.5 72.0 55.0 57.0

Nitrate (N03) Sample size (N) 0 0 0 18 7 II 15 168 II 0 Minimum (mgll) N/A N/A N/A 1.5 2.6 0.0 0.5 0.0 0.5 N/A Maximum (mgll) N/A N/A N/A 150.0 53.8 81.6 69.0 351.0 47.3 N/A Mean (mgll) N/A N/A N/A 25.3 17.8 14.4 21.1 53.9 17.8 N/A Median (mg/I) N/A N/A N/A 9.5 13.8 4.9 13.2 27.1 1.1 N/A Chloride (C1) Sample size (N) 0 0 0 19 28 21 21 176 43 16 Minimum (mgll) N/A N/A N/A 1.0 3.0 1.0 1.0 0.0 0.0 1.0 Maximum (mgll) N/A N/A N/A 102.0 89.0 83.0 280.0 260.0 53.0 38.0 Mean (mgll) N/A N/A N/A 22.2 15.5 24.8 36.2 35.8 15.6 17.5 Median (mgll) N/A N/A N/A 12.0 11.0 13.0 11.0 18.5 10.0 18.0

Hardness (as CaC03) Sample size (N) 0 0 0 18 28 21 21 172 33 9 Minimum (mg/I) N/A N/A N/A 104.0 148.0 116.0 55.0 28.0 178.0 290.0 Maximum (mgll) N/A N/A N/A 768.0 701.0 856.0 608.0 1510.0 586.0 363.0 Mean (mgll) N/A N/A N/A 415.6 349.6 401.2 365.0 491.2 352.3 330.0 Median (mgll) N/A N/A N/A 421.5 304.0 376.0 372.0 422.0 345.0 328.0

*Note: Decade 0=1900-1909, Decade 1=1910-1919, and so on.

59 Table 20. Chemical Constituents Selected for Trend Analysis, Bedrock Aquifer Systems

Decade* Chemical constituent 0 2 3 4 5 6 7 8 9 Iron (Fe) Sample size (N) 14 14 12 54 66 55 35 272 137 26 Minimum (mg/L) 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.1 Maximum (mg/L) 12.5 2.8 2.4 20.0 8.1 18.0 39.0 39.0 32.0 4.6 Mean (mgIL) 2.2 0.7 0.6 2.4 1.2 2.3 2.6 1.6 1.3 0.8 Median (mg/L) 0.7 0.4 0.4 0.6 0.6 0.8 0.7 0.4 0.3 0.3 TDS Sample size (N) 14 15 12 62 67 57 35 273 136 26 Minimum (mgll) 415.0 543.0 1132.0 355.0 155.0 433.0 382.0 335.0 352.0 157.0 Maximum (mgll) 1544.0 2955.0 2941.0 2757.0 3704.0 3611.0 3676.0 3785.0 2628.0 2030.0 Mean (mgll) 1142.1 1614.7 1873.5 1312.4 1385.0 1537.1 1244.0 1223.3 1348.2 795.8 Median (mg/I) 1280.0 1632.0 1679.0 1288.5 1324.0 1527.0 1198.0 1146.0 1350.0 508.0 Sulfate (S04) Sample size (N) 10 18 12 58 47 18 12 157 124 26 Minimum (mgll) 0.0 82.0 0.0 0.0 0.0 7.0 0.0 0.0 5.0 10.0 Maximum (mgll) 540.0 1327.0 1277.0 1400.0 1346.0 1170.0 419.0 1200.0 1515.0 771.0 Mean (mgll) 236.8 699.2 608.1 358.0 373.4 323.4 137.1 292.4 336.0 273.1 Median (mgll) 243.0 738.0 548.5 307.0 274.0 239.0 111.5 216.0 223.5 112.0 Nitrate (NO,) Sample size (N) 12 12 12 50 26 17 24 192 21 0 Minimum (mgll) 0.0 0.0 0.2 0.0 0.0 0.0 0.0 0.0 0.4 N/A Maximum (mgll) 2.2 5.3 40.8 363.0 87.3 46.0 131.0 32.0 4.7 N/A Mean (mgll) 0.3 2.2 4.2 10.8 6.4 6.6 10.4 1.4 1.2 N/A Median (mg/I) 0.0 1.9 0.8 1.4 0.9 0.4 0.6 0.2 0.8 N/A Chloride (CI) Sample size (N) 14 18 12 62 67 57 34 273 137 26 Minimum (mgll) 6.0 19.0 155.0 1.0 3.0 1.0 0.0 0.0 1.0 1.0 Maximum (mg/I) 580.0 830.0 855.0 1000.0 1600.0 1700.0 1700.0 1950.0 1067.0 800.0 Mean (mgll) 246.4 253.4 398.1 234.2 290.8 356.9 293.9 269.2 283.9 177.3 Median (mgll) 230.0 207.5 342.5 200.5 270.0 280.0 255.0 185.0 240.0 150.5 Hardness (as CaCO,) Sample size (N) 14 15 II 62 67 58 35 261 101 I I Minimum (mgll) 30.0 28.0 42.0 1.0 11.0 1.0 2.0 6.0 8.0 37.0 Maximum (mgll) 460.0 908.0 956.0 1567.0 919.0 1090.0 592.0 1592.0 769.0 476.0 Mean (mgll) 269.2 410.8 440.5 348.5 248.3 240.7 213.6 203.4 214.6 298.8 Median (mgll) 276.5 338.0 355.0 326.5 182.0 114.5 184.0 152.0 166.0 335.0

*Note: Decade 0=1900-1909, Decade 1=1910-1919, and so on.

60 , Iron (Fe)

Iron in ground water occurs naturally in the soluble (ferrous) state. However, when exposed to air, iron becomes oxidized into the ferric state and forms fine to fluffy reddish-brown particles that will settle to the bottom of a container if allowed to sit long enough. The presence of iron in quantities much greater than 0.1 to 0.3 milligrams per liter (mg/I) usually causes reddish-brown stains on porcelain fixtures and laundry. The drinking water standards recommend a maximum limit of 0.3 mg/I iron to avoid staining (Gibb, 1973).

Unconsolidated Systems Iron concentrations for unconsolidated systems in the watershed are given for each decade in Table 19. Minimum and maximum concentrations for all ten decades are 0.0 and 36.0 mg/I, respectively. These values clearly indicate a great deal of spatial variability in iron within the watershed. The median values range from 0.2 to 0.9 mg/I for all ten decades. While these median values show relatively high concentrations that could cause staining of porcelain fixtures (greater than 0.3 mgll), they generally pose no threat to human health. In addition, most median values are close to the Class I potable ground-water supply standard of 0.5 mgll. Table 19 suggests no significant trend in iron concentrations in the area.

Bedrock Aquifer Systems Iron concentrations for bedrock aquifer systems in the watershed are given for each decade in Table 20. Minimum and maximum concentrations for all ten decades are 0.0 and 39.0 mgll, respectively. These values clearly indicate a great deal of spatial variability in iron within the watershed. The median values range from 0.3 to 0.8 mgll for all ten decades. While some median values show relatively high concentrations that could cause staining of porcelain fixtures (greater than 0.3 mg/I), they generally pose no threat to human health. Table 20 suggests no significant trend in iron concentrations in the area.

Total Dissolved Solids (TDS)

The TDS content of ground water is a measure of the mineral solutes in the water. Water with a high mineral content may taste salty or brackish depending on the types of minerals in solution and their concentrations. In general, water containing more than 500 mg/l TDS will taste slightly mineralized. However, the general public can become accustomed to the taste of water with concentrations of up to 2,000 mg/1. Water containing more than 3,000 mg/l TDS generally is not acceptable for domestic use, and at 5,000 to 6,000 mg/l, livestock should not drink the water. Because TDS concentration is a lumped measure of the total amount of dissolved chemical constituents in the water, it will not be a sensitive indicator of trace-level contamination. However, it is a good indicator of major inputs of ions or cations to ground water.

61 Unconsolidated Systems IDS concentrations in the unconsolidated systems in the watershed are given for each decade in Table 19. Minimum and maximum concentrations for all ten decades are 47.0 and 2,068.0 mgll, respectively. Median values range from 368.5 to 540.0 mgll for all ten decades. There are no significant trends in TDS concentrations indicated in these aquifer systems in the watershed.

Bedrock Aquifer Systems TDS concentrations for bedrock aquifer systems in the watershed are reported for each decade in Table 20. Minimum and maximum concentrations for all ten decades are 155.0 and 3,785.0 mgll, respectively. Median values range from 508.0 to 1,679.0 mg/I for all ten decades. Generally, there are no significant trends in TDS concentrations within bedrock aquifer systems in the watershed. Any fluctuations from one decade to the next are more likely related to data limitations than to any inherent changes in ground water quality.

Water with high sulfate concentrations often has a medicinal taste and a pronounced laxative effect on those not accustomed to it. Sulfates generally are present in aquifer systems in one of three forms: as magnesium sulfate (sometimes called Epsom salt); as sodium sulfate (Glauber's salt); Qr as calcium sulfate (gypsum). They also occur in earth materials in a soluble form that is the source for natural concentrations of this compound. Human sources similar to those for chloride also can contribute locally to sulfate concentrations. Coal mining operations particularly are a common source of sulfate pollution, as are industrial wastes. Drinking water standards recommend an upper limit of 250 mgll for sulfates. Upward trends in sulfate concentrations can suggest potential ground-water pollution.

Unconsolidated Systems Sulfate concentrations for unconsolidated systems in the watershed are reported for each decade in Table 19. Minimum and maximum concentrations for all ten decades are 0.0 and 254.0 mg/I, respectively. Median values are all well below the drinking water standard (250 mgll), and range from 28.0 to 94.0 mg/l for all ten decades. Fluctuations from one decade to the next are more likely related to data limitations than to any inherent changes in ground-water quality.

Bedrock Aquifer Systems Sulfate concentrations for bedrock aquifer systems in the watershed are reported for each decade in Table 20. Minimum and maximum concentrations for all ten decades are 0.0 and 1,515.0 mg/I, respectively. Median values are all well below the drinking water standard, and range from 111.5 to 738.0 mgll for all ten decades. Table 20 indicates variability, but no significant trends in sulfate concentrations in the watershed. Fluctu'ations from one decade to the next are more likely related to data limitations than to any inherent changes in ground-water quality.

62 Nitrate (N03)

Nitrates are considered harmful to fetuses and children under the age of one when concentrations in drinking water supplies exceed 45 mgll (as N03), or the approximate equivalent of 10 mgll nitrogen (N). Excessive nitrate concentrations in water may cause "blue baby" syndrome (methmoglobinemia) when such water is used in the preparation of infant feeding formulas. Inorganic nitrogen fertilizer has proven to be a source of nitrate pollution in some shallow aquifers, and may become an even more significant source in the future as ever increasing quantities are applied to lllinois farmlands. Upward trends in concentrations of nitrate may be a good indication that farm practices in the area are affecting the ground-water environment.

Unconsolidated Systems Nitrate concentrations for unconsolidated systems in the watershed are reported for each decade in Table 19. Minimum and maximum concentrations for all ten decades are 0.0 and 351.0 mgll' respectively. The maximum concentration (351.0) is a reported value; however, it should be viewed as an outlier of the dataset, and not as representative of the water quality in the area. The median values, which are all below the drinking water standards, range from 1.1 to 27.1 mg/l for all ten decades and are more indicative of representative concentrations in the unconsolidated materials. The ISWS has documented numerous cases of elevated nitrate levels associated with rural private wells (Wilson et al., 1992). The evidence suggests that rural well contamination is associated more with farmstead contamination of the local ground water or well than with regional contamination of major portions of an aquifer from land application of fertilizers. This topic is actively being studied.

Bedrock Aquifer Systems Nitrate concentrations for bedrock aquifer systems in the watershed are reported for each decade in Table 20. Minimum and maximum concentrations for all ten decades are 0.0 and 363.0 mgll' respectively. As in the case of the unconsolidated materials, the maximum value should be considered an outlier and not a representative concentration in the watershed. Median values are well below the drinking water standards, and range from 0.0 to 1.9 mgll for all ten decades.

Chloride (CI)

Chloride is generally present in aquifer systems as sodium chloride or calcium chloride. Concentrations greater than about 250 mgll usually cause the water to taste salty. Chloride occurs in earth materials in a soluble form that is the source for normal concentrations of this mineral in water. Of the constituents examined in this report, chloride is one of the most likely to indicate the impacts of anthropogenic activity on ground water. Increasing chloride concentrations may indicate contamination from road salt or oil field brine. The drinking water standards recommend an upper limit of 250 mgll for chloride. In sand and gravel aquifers throughout most of the state, chloride concentrations are usually less than 10 mgll.

63 Unconsolidated Systems Chloride concentrations for unconsolidated systems in the watershed are reported for each decade in Table 19. Minimum and maximum concentrations for all ten decades are 0.0 and 280.0 mgll, respectively. Median values are well below the drinking water standard, and range from 10.0 to 18.5 mgll for all ten decades. Table 19 indicates no significant trends in chloride concentrations in the watershed.

Bedrock Aquifer Systems Chloride concentrations for bedrock aquifer systems in the watershed are reported for each decade in Table 20. Minimum and maximum concentrations for all ten decades are 0.0 and 1,950.0 mgll, respectively. Median values range from 150.5 to 342.5 mgll for all ten decades. Table 20 indicates no significant trends in median chloride concentrations in the watershed. Fluctuations from one decade to the next are more likely related to data limitations than to any inherent changes in ground-water quality.

Hardness (as CaCOJ)

Hardness in water is caused by calcium and magnesium. These hardness-forming minerals generally are of major importance to users since they affect the consumption of soap and soap products and produce scale in water heaters, pipes, and other parts of the water system. The drinking water standards do not recommend an upper limit for hardness. The distinction between hard and soft water is relative, depending on the type of water a person is accustomed to. The ISWS categorizes water from 0 to 75 mgll as soft, 75 to 125 mgll as fairly soft, 125 to 250 mgll as moderately hard, 250 to 400 mgll as hard, and over 400 mgll as very hard.

Unconsolidated Systems Hardness concentrations for unconsolidated systems in the watershed are reported for each decade in Table 19. Minimum and maximum concentrations for all ten decades are 28.0 and 1,510.0 mgll, respectively. Median values range from 304.0 to 422.0 mgll for all ten decades indicating hard to very hard water in this area.

Bedrock Aquifer Systems Hardness concentrations for bedrock aquifer systems in the watershed are reported for each decade in Table 20. Minimum and maximum concentrations for all ten decades are 1.0 and 1,592.0 mg/I, respectively. Median values range from 114.5 to 355.0 mgll for all ten decades. Water with these concentrations are considered moderately hard to hard. No trends are observed in hardness concentrations from the bedrock in this area.

64 Summary

This work was undertaken to examine long-term temporal trends in ground-water quality in the Spoon River area. Data from private and municipal wells were the primary sources of information used to show the trends in six chemical constituents of ground water in the area. These data demonstrate that on a watershed scale, ground water has not been degraded with respect to the six chemicals examined. Fluctuations from one decade to the next are more likely related to data limitations than to any inherent changes in ground water quality. It is also evident that the sample size in each decade can playa role in trend analysis.

Much of the contamination of illinois' ground water is localized. Nonetheless, this contamination can render a private or municipal ground-water supply unusable. Once contaminated, ground water is very difficult and expensive to clean, and clean-up may take many years to complete. Clearly it is in the best interests of the people of lllinois to protect their ground-water resource through prevention of contamination.

Although no significant trends in water quality for these six constituents are apparent, the information provides baseline water quality for the watershed. This information can be used in future studies of the area as a reference to determine whether the local ground water quality is degrading.

References

Introduction lllinois Department of Natural Resources. 1996. Illinois Land Cover, An Atlas. IDNR 96/05. Springfield, ll-. lllinois Department of Natural Resources. 1996. Illinois Land Cover, An Atlas. Compact Disc. Springfield, ll-. Mattingly, R.L., and E.E. Herricks. 1991. Channelization of Streams and Rivers in Illinois: Procedural Review and Selected Case Studies. Illinois Department of Natural Resources Report ILENRIRE-WR-91101. Su!oway, L., and M. Hubbell. 1994. Wetland Resources of Illinois: An Analysis and Atlas. lllinois Natural History Survey Special Publication 15. Champaign, ll-.

Climate and Trends in Climate

Changnon, S.A., Jr. 1984. Climate Fluctuations in Illinois: 1901-1980. Illinois State Water Survey Bulletin 68. Champaign, ll-. Changnon, S.A., Jr. 1995. Temporal Fluctuations of Hail in Illinois. lllinois State Water Survey Miscellaneous Publication 167. Champaign, ll-. Illinois Department of Energy and Natural Resources. 1994. The Changing lllinois Environment: Critical Trends. Volume I: Air Resources. ll-ENRIRE-EA-94/05(l). Springfield, ll-. Wendland, W.M., and Guinan, P. 1988. A Tornado and Severe Weather Climatology for lllinois: 1955-1986. Transactions of the Illinois Academy of Science 81 (I &2): 131 146.

Water Use and Availability

Dawes, J.H., and M.L. Terstriep. 1966. Potential Surface Water Resources of North Central Illinois. lllinois State Water Survey Report of Investigation 56. Ensminger, M.E., Olentine, C.G., Jr., 1978. Feeds and Nutrition. Clovis, CA. Illinois Department of Agriculture. 1995. Illinois Agricultural Statistics: Annual Summary, 1995. Springfield, ll-. Illinois Department of Energy and Natural Resources. 1994. The Changing Illinois Environment: Critical Trends. Volume 2: Water Resources. ll-ENRIRE-EA 94/05(2). Springfield, ll-.

67 Ground-Water Quality

Gibb, J.P. 1973. Water Quality and Treatment of Domestic Groundwater Supplies. lllinois State Water Survey Circular 118. Champaign, IL. lllinois Department of Energy and Natural Resources. 1994. The Changing lllinois Environment: Critical Trends. Volume 2: Water Resources ILENRJRE-EA 94/05(2). Springfield, IL. 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 lllinois Groundwater: Status and Future Directions II. Proceedings of the second annual conference, lllinois Groundwater Consortium, Southern lllinois University, Carbondale, IL.

68 The llIinois Department of Natural Resources receives federal financial assistance and therefore must comply with federal anti-discrimination laws. In compliance with the Illinois Human Rights Act, the Illinois Constitution, Title VI of the 1964 Civil Rights Act, Section 504 of the Rehabilitation Act of 1973 as amended, and the U.S. Constitution, the Illinois Department of Natural Resources does not discriminate on the basis of race, color, sex, national origin, age or disability. lfyou believe you have been discriminated against in any program, activity or facility please contact the Eqnal Employment Opportunity Officer, Department of Natural Resources, 524 S. Second St., Springfield, 1L 62701-1787, (217) 782-7616, or the Office ofHuman Rights, U.S. Fish & Wildlife Service, Washington, D.C. 20240.

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