Surficial Geology and Groundwater Investigation of The

SURFICIAL GEOLOGY AND GROUNDWATER INVESTIGATION OF THE

GARDEN PRAIRIE, IL 7.5 MINUTE QUADRANGLE

Logan C. Seipel

63 Pages August, 2015

Expansion and over pumping in the greater Chicago metropolitan area has raised concerns regarding groundwater resources. In McHenry County, municipal and domestic water supplies in the county are extracted exclusively from groundwater (Meyer, 1998) and largely from shallow sand and gravel aquifers. It is important to have an in depth understanding of the geology and processes affecting the surficial aquifer in order for best management practices to be implemented. Thus, the county has taken an aggressive approach to understanding these shallow aquifer systems though regional mapping and flow models.

This research focuses on understanding the characteristics and distribution of surficial geologic materials and impacts of heavy withdrawals on shallow aquifer systems in the Garden

Prairie 7.5 Minute Quadrangle. This project is composed of two main chapters: 1) a surficial geologic map and 2) a groundwater flow model.

The geologic map was produced to delineate the surficial geologic materials at the

1:24,000 scale. Construction of this map was completed using multiple data-sets such as traditional field mapping techniques, interpretation of well logs, high resolution LiDAR data, and

NRCS soils data. The Garden Prairie Quadrangle hosts geologic formations from both the Illinois and Wisconsin glacial episodes, and lies on the western extent of Wisconsin Glaciation. This

former geologic setting has left much of the quadrangle overlain by outwash sediments that used to fill former outwash valleys.

A groundwater flow model was developed to understand local groundwater flow systems impacted by an irrigation well within a shallow unconfined aquifer in McHenry County, Illinois.

Previous studies have look at regional effects of heavy groundwater withdrawals (Meyer, 2013), this study focuses on the local effects of unconfined aquifer pumping. These shallow unconfined aquifers, from which many high-capacity irrigation wells extract groundwater, are comprised of sand and gravel that fill former glacial outwash valleys. A local groundwater flow model was thus constructed to address the potential cumulative impacts of irrigation wells on groundwater drawdown and capture zones in the Kishwaukee River Valley.

SURFICIAL GEOLOGY AND GROUNDWATER INVESTIGATION OF THE

GARDEN PRAIRIE, IL 7.5 MINUTE QUADRANGLE

LOGAN C. SEIPEL

A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of

MASTER OF SCIENCE

Department of Geography-Geology

ILLINOIS STATE UNIVERSITY

2014

SURFICIAL GEOLOGY AND GROUNDWATER INVESTIGATION OF THE

GARDEN PRAIRIE, IL 7.5 MINUTE QUADRANGLE

LOGAN SEIPEL

COMMITTEE MEMBERS:

David Malone, Chair

Eric Peterson

Jason Thomason

ACKNOWLEDGMENTS

I would like to thank my family and friends for their support during my time completing this thesis research. Special thanks to all those who have contributed to my education over the years, without their support this would not have been possible.

In addition I would like to acknowledge my thesis committee members and thank them for their encouragement, guidance, and time spent working on this research. Their support was instrumental in the completion of this project.

Lastly I would like to thank the Illinois State Geological Survey and Jason

Thomason for the technical assistance and support. This project would not have been possible without the strong partnership between Illinois State University and the ISGS.

CONTENTS

Page

ACKNOWLEDGMENTS i

CONTENTS ii

TABLES iv

FIGURES v

CHAPTER

I. INTRODUCTION AND BACKGROUND 1

Introduction 1 Site Descriptions 3 Geology 4 Bedrock Geology 6 Geomorphology 8 Hydrogeologic Setting 9 Statement of the Problem 11 Research Questions 13

II. SURFICIAL GEOLOGIC MAP 14

Previous Work 14

Methodology 15 Discussion 21

iii

III. GROUNDWATER FLOW MODEL 28

Introduction 28 Previous Work 29 Conceptual Model 31

Model Setup 33 53 Initial Values 37 Adjustments 39

Sensitivity 39 Justification 40 Scenarios 40 Results 42 Discussion 46 IV. CONCLUSION 49

REFERENCES 80

APPENDIX A: Schematic of Borehole in Garden Prairie Quad 58 APPENDIX B: Surficial Geology of the Garden Prairie 7.5 Minute Quadrangle, IL 61

TABLES

Table Page

1. Garden Prairie Soil Series 18 2. Initial Values for Model Parameters 42

3. Results of Statistical Analysis 49

FIGURES

Figure Page

1.1 Location of Garden Prairie 7.5 Minute Quadrangle and Groundwater Flow Model Site 3 3

1.2 Figure 1.2 Quaternary Map of McHenry and Boone County with Garden Prairie Quadrangle and Groundwater Model Site Highlighted, Modified From ISGS Quaternary Map 6

1.3 Correlation of Stratigraphic Units in McHenry County, From Curry et al, 1997 8 1.4 McHenry County Surficial Aquifer Thickness Map, Modified from Thomason and Keefer 2013. Groundwater Flow Model Site Outlined in Black. 11 1.5 Shallow Aquifer Removal Rates in Northeastern Illinois, McHenry County Outlined in Red (Meyer, 2013) 13 2.1 Garden Prairie Quadrangle Unassigned Soils Polygons With County Line Left- Center 19 2.2 Garden Prairie Quadrangle with Soil Polygons Assigned Geologic Formations 20 2.3 DEM and Hillshade Combined to Show Geomorphology of Garden Prairie Quadrangle 22 2.4 Locations of Mapping Area and Moraines Showing Western Extents of Wisconsin Glaciation 25 2.5 Showing Approximate Ice Margins and Meltwater Pathways, Contributing to the Widespread Existence of the Henry Formation throughout the Mapping Area 27 2.6 Cross Section 1 of Kishwaukee Valley Road With Uppermost Units from Wisconsin Episode and Illinois Episode below. 28 2.7 Cross Section 2 from Dunham Road to Hwy 27 30 3.1 Perspective View of Study Area Highlighting Mr. Martin’s Irrigation Well in Yellow and Other Wells in White, Modified from Google Earth Image 32

3.2 Modified from Meyer, 2013 Showing Potentiometric Surface of Shallow Aquifer, Focused on Kishwaukee River Valley 34 3.3 Schematic Cross Section of Kishwaukee River Valley Sediments (Modified from Thomason and Keefer, 2013) 35 3.4 Theis Solution Calculated for Estimating Drawdown Near Thorne Road 38 3.5 Model Domain With Boundary Conditions, Potentiometric Surface Values, and Capture Zone for Irrigation Well Where Pumping Data Were Collected 44 3.6 Time dependent head data collected over first 8 hours of pumping. S-type curve is indicative of unconfined nature of the aquifer 46 3.7 Representing the six different model simulations with capture zones for each well. P-Values are representative of Layer 2 48

CHAPTER I

INTRODUCTION AND BACKGROUND

Introduction

McHenry County is a collar-county of the greater Chicago Metropolitan area in northeast Illinois, and is unique in the fact that all of its water is supplied from groundwater. Groundwater is withdrawn for municipal supply, domestic use, agricultural use, and commercial and industrial operations. In particular, shallow sand and gravel aquifers provide approximately 60% of the daily water requirements in the county. Rapid population growth and municipal expansion have been occurring for decades in this region. As such, sustainability of the local and regional aquifers has become a priority.

This in turn has led to recognition that a better understanding of the surficial geology and shallow aquifer systems is necessary in order to implement sustainable management practices.

This research aims to improve the overall understanding of the surficial deposits in the Garden Prairie 7.5 Minute Quadrangle as well as the implications of anthropogenic impacts on shallow groundwater systems. Previous geologic investigations have proved to be valuable tools in making informed decisions regarding best management practices in McHenry County. This research aims to contribute towards the current scientific knowledge of the area. To accomplish this, two individual research exercises were completed. The first is a surficial geologic map of the Garden Prairie 7.5 1

Minute Quadrangle. The second is a groundwater flow model aimed at better understanding the impacts of high-capacity irrigation wells in the shallow aquifer. The first objective of this project is a surficial geologic map, characterizing and describing

Quaternary materials in the Garden Prairie 7.5 Minute Quadrangle. This is part of a larger collective effort to map the state of Illinois at the 1:24,000 scale. The Garden

Prairie Quad marks the extent of the Wisconsin Episode of glaciation in Illinois and detailed mapping of the deposits in the area can lead to not only informed decisions regarding resource management, but also insight as to glacial depositional environments and conditions that once existed there.

The second objective is a groundwater flow model aimed at understanding the local effects of high-capacity pumping wells on the surficial aquifer. While the population of McHenry County is expanding, there still exists a vibrant agricultural industry. Within the Kishwaukee River Valley, the surficial aquifer is heavily used to meet these agricultural demands, and possess a high potential for contamination. A more complete understanding of the groundwater flow patterns in this aquifer and of the potential effects of pumping will lead to more informed water-management policies.

Together these two efforts will contribute to a better understanding of the local geology and groundwater flow regime.

Figure 1.1 Location of Garden Prairie 7.5 Minute Quadrangle and Groundwater Flow Model Site

Site descriptions

This project includes two study sites located in north-eastern Illinois. The site of the surficial geologic map is the Garden Prairie 7.5 Minute Quadrangle. This quadrangle lies on the border between Boone and McHenry Counties and is outlined in Figure 1.2

The second site, located in the southeast corner of the Garden Prairie Quadrangle, within the Kishwaukee River Valley, serves as the domain for the groundwater flow model. The model was developed in response to the high concentration of irrigation wells that are screened in the glacial outwash sediments of the river valley. The domain of the model is highlighted in red and can be seen in Figure 1.2.

Geology

Prior to the Quaternary Period, streams and rivers dissected the bedrock landscape and produced a paleo-topography that is similar to the driftless area 100km to the west.

During the subsequent glacial periods, further modification of the valleys occurred by means of glaciers, glacial outwash, and melt-water rivers (Curry et al, 1997). Along with more erosion, these valleys were also being filled in with glacial outwash sediments

(Ritzi et al, 1994). Glacial sediments such as sand, gravel, diamicton and clay were deposited in these bedrock valleys and serve as aquifers in McHenry County (Berg and

Curry, 1999).

The landscape of McHenry County has been molded by previous glaciations that occurred over the past 730,000 years (Curry et a, 1997). The Illinois Episode of glaciation occurred between 190,000 and 130,000 years ago (Johnson, 1986; Curry and

Pavich, 1996). Although most of the deposits associated with this episode are deeply buried in McHenry County, they are present at the surface in the western half of the

Garden Prairie Quadrangle.

Following the Illinois Episode the global climate warmed, and the area represented by McHenry County entered an interglacial period from 130,000 to 55,000 years ago. The Sangamon Episode is characterized by the Sangamon Geosol, which is an

4 ancient soil horizon commonly buried throughout McHenry County and an important marker unit for subsurface geologic interpretation (Curry et al., 1997).

During the most recent Wisconsin Episode of glaciation, the Laurentide Ice

Sheet, which covered much of the Great Lakes region, expanded and retracted lobes of ice through McHenry County three separate times. During those times the ice sheet deposited glacial sediments up to 100 meters thick and buried any pre-existing surfaces

(Hansel and Johnson, 1996). The western extent of Wisconsin Episode glaciation is marked by the Marengo Moraine. Subsequent fluctuations of the Laurentide Ice Sheet in

McHenry County are represented by the Barlina and Woodstock Moraines (Figure 1.2)

Particle sizes ranging from boulders to clay are included within the glacial deposits, and these sediments have proven to be valuable resources for the area, such as sand and gravel aggregate for construction, aquifer formations for extracting groundwater, and nutrient-rich loam for the abundant, excellent agricultural soils (Curry et al., 1997).

However, understanding the distribution, characteristics, and relationships among the units is critical for making decisions regarding engineering, resource extraction, groundwater removal and quality, and waste disposal (Hansel and Johnson, 1996).

Figure 1.2 Quaternary Map of McHenry and Boone County with Garden Prairie Quadrangle and Groundwater Model Site Highlighted, Modified From Stiff, 2000.

Bedrock

The bedrock geology of McHenry County is an important contributor to the groundwater flow system. The oldest unit that comprises the bedrock surface is the

Galena Group, composed of an Ordovician fossiliferous dolomite. On average this 6 dolomite is 60 m (200 ft.) thick and can provide water for public use in certain areas in

McHenry and Boone Counties, but is more frequently utilized to the west where overlying glacial drift is thin (Curry et al., 1997). The Maquoketa Group lies above the

Galena Group and consists of shaly dolomite and limestone. Its thickness ranges from 45-

60 m (150-200 ft.) when Silurian rocks are present. The overlying Silurian formations form the youngest bedrock layer. In the western area of the county where this project is focused, thicknesses are usually greater than 30 m (100 ft.). Fractures within these layers of dolomite allow connectivity with the overlying glacial sediments (Curry et al., 1997).

Where present, the lowermost unconsolidated aquifer, basal drift aquifer, overlies the bedrock and is in direct contact. Another instance of interaction occurs when glacial sediments have filled in bedrock paleo-valleys. The unconsolidated units are in contact with the bedrock on the sides of the paleo-valleys. Where the contacts between sand and gravel aquifers and bedrock exist, these units are most likely hydraulically connected and may act as one single aquifer system (Thomason and Keefer, 2013).

Figure 1.3 Correlation of Stratigraphic Units in McHenry County, From Curry et al.,

1997.

Geomorphology

The Garden Prairie Quadrangle on the western side of the county includes parts the western edge of the Marengo Moraine and associated glacial outwash sediments.

Much of the geomorphology consists of fragmented alluvial terraces composed of sand and gravel that were likely deposited away from the ice front. These broad outwash valleys, which now include the modern Kishwaukee River and its tributaries, were likely reoccupied numerous times during each glacial event. Thus, multiple-aged successions of glacio-fluvial outwash sediments fill the modern stream valleys. The fragmented

8 terraces likely record different fluctuations of sediment deposition associated with respective glacial events.

Hydrogeologic setting

Within a regional hydrogeological context, there are four major aquifer systems that are present. These systems can be divided into bedrock aquifers and major sand and gravel aquifers. While minor sand and gravel aquifers do exist, the scope of this project does not warrant their discussion.

In McHenry County, the lowermost system present is comprised of Silurian-

Ordovician bedrock aquifers that can be over 60 meters below the land surface. As stated earlier, they are an important aspect in groundwater interactions and are often in hydraulic connectivity with the overlying basal drift aquifer near the bedrock/basal drift interface.

The basal aquifer is comprised mostly of sand and gravel deposits that were associated with glacial meltwater deposition. Given the landscape at the time of deposition, most sediments filled lowlands and bedrock valleys. Therefore, these aquifers are usually in direct contact with the bedrock and their thickness is generally less than 10 meters but can exceed 30 meters in some areas. Typically this aquifer is utilized for both domestic and municipal water supply in the county.

The Pearl-Ashmore aquifer is an important water resource in McHenry County for both municipal and domestic withdrawal. The sediments composing the aquifer are associated with the retreat of Illinois-Episode deposits and the advance of Wisconsin-

Episode glaciation. Typical of outwash sediments the Pearl-Ashmore is composed of coarse sands and gravels and may include fine to medium sands. Its thickness is variable ranging from less than 10 meters to over 30 meters but is thin or non-existent in the study areas of this project.

Lastly, the uppermost aquifer in this succession is the surficial aquifer. Not unlike the other aquifers in the area, it is composed of sand and gravel deposits that area often quite shallow and exposed at the surface. Given its composition is from meltwater streams during the Wisconsin Episode depositing sediments, the surficial aquifer is often located in glacial meltwater valleys, which are represented by the modern alluvial valleys in McHenry County today (Figure 1.4). Thickness of the aquifer ranges from 1 meter along valley edges to over 36 meters in other parts of the valley. Utilization of this aquifer is widespread and supplies water for domestic, municipal, and agricultural needs.

Specifically, in the Kishwaukee River Valley where this project is focused, large amounts of water are removed from the aquifer for agricultural use.

Figure 1.4 McHenry County Surficial Aquifer Thickness Map, Modified from Thomason and Keefer 2013. Groundwater Flow Model Site Outlined in Black.

Statement of the Problem

McHenry County derives 100 percent of its water supplies (drinking and agricultural) from groundwater (Curry et al. 1997). Shallow sand and gravel aquifers supply 60 percent of municipal drinking water and account for an even larger portion of agricultural irrigation use. Collectively, these withdrawals put high usage and contamination stresses on the shallow, sand and gravel aquifer systems. The impacts of groundwater withdrawal and contamination potential cannot be adequately addressed without a better understanding of the extent of the deposits and the flow patterns that exist in them.

Figure 1.5 Shallow Aquifer Removal Rates in Northeastern Illinois, McHenry County Outlined in Red (Meyer, 2013).

Research Questions

1. What is the structure and stratigraphy of surficial geologic units in the Garden

Prairie 7.5 Minute Quadrangle?

2. What is the capture zone of large-scale irrigation wells in the Kishwaukee

River Valley?

3. What is the collective impact of these irrigation wells on local groundwater

flow patterns?

Chapter II

Surficial Geologic Map

The first aspect of this project completed is a surficial geologic map of the

Garden Prairie 7.5 Minute Quadrangle, located on the western side of McHenry County, and eastern edge of Boone County. Geologic maps can be highly useful tools for many aspects such as land-use planning, resource evaluation, and groundwater investigation.

This project is part of the large-scale effort being undertaken to map the entire State of

Illinois at the 1:24,000 scale.

Previous work

For over ten years, Illinois State University students and faculty have developed a strong relationship with the Illinois State Geological Survey (ISGS) regarding geologic investigations in Illinois. This partnership has resulted in the production and publication of over a dozen geologic maps throughout the state. This project is also a continuation of the numerous geologic studies that have been carried out in McHenry County over the past 50 years.

Previous studies in McHenry County have been conducted regarding sand and gravel resources (Anderson and Block, 1962; Specht and Westerman, 1976) and regional stratigraphy (Berg et al, 1985) Geologic investigations regarding groundwater resources

(Curry et al, 1997: Meyer 1998; Meyer 2013: Thomason and Keefer 2013) and glacial history (Curry and Yansa, 2004) are some of the more recent studies that have been completed in McHenry County. Surficial mapping at the 1:24,000 scale has been extensive throughout McHenry County. Some of the previously mapped 7.5 Minute

Quadrangles include the Marengo South Quadrangle (Stravers and Curry, 1995), Fox

Lake Quadrangle (Kulczycki et al, 2001), Barrington Quadrangle (Stravers et al, 2002),

Richmond Quadrangle (Stravers et al, 2003), McHenry Quadrangle (Stravers et al, 2003),

Huntley Quadrangle (Curry and Thomason, 2012), Marengo North Quadrangle (Stravers et al, 2006), and Hebron Quadrangle (Carlock et al, 2009). Multiple M.S. projects at

Illinois State University have also included geologic mapping and have assisted in guiding the approach to constructing the map (Roche, 2009: McEvoy, 2006, and Bowen,

2007, Flaherty, 2013, Lau 2011).

Methodology

The surficial geologic map was constructed using multiple data sources and software platforms. The data sets included Natural Resources Conservation Service

(NRCS) soils data, water-well records, previous geologic investigations, field investigation, and high-resolution LiDAR data for geomorphic evaluation. ESRI’s

ArcGIS 10.2 program was utilized for the construction and modification of the surficial map. Once completed, the surficial map was imported and redrafted in ACD’s Canvas 15.

Lastly, the map was combined with contour elevations into a GeoPDF, provided by the

USGS, using Adobe Illustrator.

The first step in completing this map was collecting and interpreting the NRCS soils data. The data were imported into ArcGIS from both Boone and McHenry Counties

(Figure 2.1). These data were then interpreted using Soil Survey of Boone County and

Soil Survey of McHenry County (NRCS, 2000: NRCS 1997). Using the descriptions of the soils and their parent material, geologic formations were assigned to each respective

16 soil within the study area (Table 1). This provided the base-data for the geologic map

(Figure 2.2). Where soils descriptions lacked detail enough or were inadequate, they were not assigned a formation until they were compared against neighboring polygons and local geomorphology.

Table 1 Example of Some of the Soil Series Located in the Garden Prairie 7.5

Minute Quadrangle Including Parent Material and Lithostratigraphic Unit.

Soil Series Parent material Lithostratigraphic Number Unit 777A Adrian muck Herbaceous organic Grayslake Peat material over sandy outwash or alluvium 188A Beardstown loam Outwash and loamy Henry and sandy sediments 332A Billett sandy loam Outwash Henry 624B Caprell silt loam, 2-4% Thin mantle of silty Glasford material and the underlying loamy till 3776A Comfrey loam, freq. flood Loamy alluvium Cahokia 87B2 Dickinson sandy loam Loamy and sandy Henry outwash Herbert silt loam, Silty material and the Tiskilwa 62A underlying loamy till 103A Houghton muck Herbaceous organic Grayslake Peat material 527C2 Kidami loam, 4-6%, eroded Till with or without a Tiskilwa thin mantle of loess or other silty material 623B Kishwaukee silt loam, 2-5% Thin layer of loess Tiskilwa over loamy and gravelly outwash 60C2 La Rose loam, 5-10%, Loamy till Tiskilwa eroded 528A Lahoguess loam Outwash Henry 766A Lamartine silt loam Outwash Henry 8082A Millington silt loam, occ. Calcareous loamy Cahokia flooded alluvium 1100A Palms Muck, undrained Herbaceous organic Grayslake Peat material over loamy material or alluvium 1529A Selmass loam, undrained Loamy outwash Henry 618E Senachwine silt loam, 12- Till Tiskilwa 20%

Figure 2.1 Garden Prairie Quadrangle Unassigned Soils Polygons With County Line Left-Center

Figure 2.2 Garden Prairie Quadrangle with Soil Polygons Assigned Geologic Formations.

Where possible, water-well records were also used to validate the existing soils polygons. Local well data are available through the Illinois State Geologic Survey for over 400 wells within the mapping area. These logs were examined where necessary to help constrain the local geology and compare to the soils interpretations. However

20 sometimes water-well records were either incomplete or could not offer sufficient geologic descriptions, where this occurred these data were not utilized.

The efforts of previous mapping excercises in McHenry County were also used to aide in the construction of the map. Previous geologic maps of Boone (Berg et al, 1984) were digitized and imported into ArcGIS. This map and other geologic investigations

(Curry et al, 1997) served as a template from which a more detailed map was constructed.

The final dataset used was the high-resolution LiDAR made available from the

Illinios State Geologic Survey. These data were incorporated as a Digital Elevation

Model (DEM) and coupled with a hillshade aspect to better reveal the geomorphology.

The Dem and hillshade were incorporated as layers underlying the map in ArcGIS, providing additional insight towards delineating geologic contacts and geomorphic landforms. With this high-resolution of the topography, delineating contacts becomes more accurate. Visualization of prevoiusly unknown geomorphic features continues to enhance our understanding of the glacial depositional environments and settings of the past (Figure 2.3).

Figure 2.3 DEM and Hillshade Combined to Show Geomorphology of Garden

Prairie Quadrangle

Discussion

The results of the Garden Prairie 7.5 Minute Quadrangle are interesting in the fact that Quaternary sediments from both Wisconsin and Illinois Episodes are present

(Plate 1). The extent of the Wisconsin advance can be seen on the eastern side of the quadrangle as the Tiskilwa Formation forming the Marengo Moraine. The results of this map are also presented in Plate 1. Eight lithostratigraphic units were observed in the

Garden Prairie 7.5 Minute Quadrangle geologic map and are discussed in stratigraphic order from oldest to youngest.

Illinois Episode The Glasford Formation is the oldest surficial formation found in the Garden Prairie Quadrangle. In McHenry County the presence of the Glasford

Formation is limited, but does extend westward into Boone County where it is more prolific. Within the mapping area, it is found predominantly in the west-central and north central portions. It is topographically marked by the northeast trending regions of higher elevation between Rush Creek and Piscasaw Creek (Figure 2.3). Where present at the surface, the Glasford Formation is characterized as silt-clay diamicton but can also contain lenses of silt and gravel or even lake-sediments. Its composition can be described as loam to sandy loam diamicton with inclusions of silt, sand, and gravel (Curry et al,

1997).

In the subsurface, the Glasford can be further broken up into two separate lithology’s including glacial meltwater derived sand and gravel units along with ice- contact sediments that are clay-rich and poorly sorted. These separate lithology’s within

23 the Glasford Formation are further subdivided into confining units and aquifer units

(Thomason and Keefer, 2013). The uppermost confining unit (G1) is comprised of a dense silty-clay diamicton. On the western edge of McHenry County and within the

Garden Prairie Quadrangle, it is the primary confining unit and overlies the Glasford aquifer (GS1). This unit is primarily found on the western edge of McHenry County and its composition is primarily outwash sands and gravels associated with the Illinois

Episode glaciation (Willman and Frye, 1970). Typically, its presence is confined to buried bedrock valleys with its principal uses being for domestic water supply.

Underlying the uppermost Glasford Aquifer is another sequence of silty-clay diamicton with lenses of lake sediments or gravel units possible. This unit is referred to as the basal confining unit. Thickness of this unit is variable but can reach up to 55 meters in the western portion of McHenry County (Thomason and Keefer, 2013). The lowermost aquifer unit in the Glasford succession is the basal aquifer and is an important resource for municipal as well as domestic supply. Typically these sediments are deeply buried and confined to bedrock valleys where glacial meltwater streams and rivers once flowed.

Its composition is variable from silty sand to coarse gravel and cobbles (Thomason and

Keefer, 2013).

The Winnebago Formation is found only in the upper northwest corner of the mapping area, capping a succession of glacial deposits known as Capron Ridge (Figure

2.3). A distinct change in elevation between the alluvium of Piscasaw Creek and the

Capron Ridge reveals the presence of the Winnebago Formation. This topographically distinct feature can be described as an erosional remnant of the Illinois till plain. The

Winnebago consists of loam to sandy loam diamicton with inclusions of clay, silt, sand and gravel, with thicknesses ranging from 0 to over 22 meters thick. (Curry et al, 1997).

Wisconsin Episode Following the Sangamon Episode, the onset of glaciation returned during the Wisconsin Episode (55,000-10,000 years ago). The landscape and geomorphology that exists within the Garden Prairie Quadrangle is a direct result of this glacial episode, and the associated glacial deposits are the most relevant to groundwater protection and planning in McHenry County. During the Wisconsin Episode, glaciers entered and retreated from this region at least three times. These glaciers were part of the

Harvard Sublobe of the Lake Michigan Lobe, which generally advanced westward across the region.

The Wisconsin Episode glacial deposits have been divided into the Mason and

Wedron Groups. The Mason Group is primarily outwash sediments consisting of sand and gravel, silt, or silty clay that exist above, below and intertongue with the Wedron

Group deposits (Curry et al, 1997). Of the four primary Mason Group units found in

McHenry County, only the Henry and Equality Formations are present at the surface in the mapping area. The Wedron Group differs in that these sediments are directly deposited by glaciers. They consist primarily of diamicton that is inter-bedded with sands and gravels.

The first glacial advance of the Wisconsin Episode occurred 25,000 to 23,500 years ago and is known as the Marengo Phase. This advance resulted in the deposition of the Marengo Moraine in the western part of McHenry County. The study area for this project incorporates the western edge of this moraine and areas further west of it. The

25 moraine is largely composed of the Tiskilwa Formation. Lithologically the till is described as a reddish-brown to pinkish clay-loam diamicton with lenses of gravel, sand, silt and clay (Hansel and Johnson, 1996). The Marengo Moraine is located in the southeast quadrant of the mapping area and is one of the more topographically distinct units.

The thickness of the Tiskilwa Till is variable throughout McHenry, typically ranging from 0 to over 60 meters, but it does reach a maximum thickness of over 90 meters in the northern reaches of the Marengo Moraine (Curry et al, 1997).

Figure 2.4 Locations of Mapping Area and Moraines Showing Western Extents of

Wisconsin Glaciation

The Harvard Sublobe then retreated and re-advanced about 16,500 years ago during the Livingston Phase of the Wisconsin Episode. During this advance, the ice

26 margin extended as far west as the current location of Woodstock. The primary deposit associated with this advance is the Yorkville Diamicton of the Lemont Formation, which is a fine-grained till that, comprises the Barlina Moraine (Figure 2.4). Less extensive, unnamed outwash deposits are often associated with the Livingston Phase. After this advance the sublobe again retreated (Curry et al. 1997) In areas west of the moraine, glacial melt-water streams deposited sand and gravel likely in broad, high-discharge outwash streams (Hansel and Johnson, 1996).

The last glaciers that moved into McHenry County were associated with the

Woodstock Phase (about 15,500 years ago) and advanced generally from the northeast and covered the northeast half of the county. This phase deposited the Haeger Member of the Lemont Formation, which most often a coarse-grained diamicton. This diamicton comprises the northwest-southeast trending Woodstock Moraine, which is the modern watershed divide between the Fox and Kishwaukee River Valleys. Thick sequences of sand and gravel of the Henry Formation were also deposited during this most recent advance (Hansel and Johnson, 1996). These deposits are found largely within the modern river and stream valleys and comprise the surficial drift aquifer in McHenry County

(Figure 1.3).

Figure 2.5 Showing Approximate Ice Margins and Meltwater Pathways, Contributing to the Widespread Existence of the Henry Formation Throughout the Mapping Area.

The Henry Formation can be found throughout the quadrangle due to its deposition as glacial outwash from fluctuations of the ice margin during the Wisconsin

Episode. The Henry Formation is predominantly found in the Rush Creek and

Kishwaukee River Valleys (Figure 2.6). The valleys served as meltwater pathways and outwash plains. The outwash channel that cuts through the Marengo Moraine and forms the present-day Kishwaukee River valley resulted in thick deposits of outwash sediments that comprise the present day surficial drift aquifer in this location. The depositional environment resulted in the lithology being mostly stratified sand and gravel. Thickness

28 of the Henry Formation is variable from 0 to 21m, with the thickest being seen in the northern reaches of the mapping area near Rush Creek (Appendix A, GARP-09-01).

Figure 2.6 Cross Section 1 of Kishwaukee Valley Road With Uppermost Units from

Wisconsin Episode and Illinois Episode below.

The uppermost unit associated with the Wisconsin Episode is the Equality

Formation. During the stages of Wisconsin glaciation, deposition of Equality Formation sediments was also occurring. It can be seen only on the western side of the quadrangle, to the north and south of the large area encompassed by the Glasford Formation, and is associated with outwash waters from the last recession of the Wisconsin Episode. This resulted in its occurrence being constrained to the lowland areas on the western side of the mapping area. The Equality Formation is described as bedded silts and clays containing massive to fine bedding and laminae (Hansel and Johnson, 1996). These sediments are mostly fine-grained silts and clays. Where found they may also exhibit

29 lamination as well as fossil content, and reach a maximum thickness of 34m (Curry et al,

1997).

Alluvium and Colluvium Throughout McHenry and Boone counties there are several more recently deposited (Holocene) formations that exist as surficial units. In the study area, there are three distinct units that are present. Grayslake Peat is defined by its composition of peat and muck with some interbedded silt and clay deposits. Typically it is found in small scattered areas located in swampy depressions as well as lake fillings or margins. The Cahokia Formation is generally described as sandy alluvium; however it can exist as bedded silts, clays, and sand and gravel deposits. The Cahokia Alluvium is the most prolific of the surficial deposits in the mapping area. It is located predominantly in the river valleys and floodplains where modern surface drainages have re-worked the uppermost materials. Specifically, Cahokia Alluvium can be found in the vicinity of Rush

Creek (Figure 2.6), the Kishwaukee River, and in the northwest corner of the mapping area along Piscasaw Creek. Lastly the Peyton Formation, comprised of diamicton or sorted sediments, exists as colluvium or material moved downslope. Its occurrence in the mapping area is local and constrained to the north-central portion.

Figure 2.7 Cross Section 2 from Dunham Road to Hwy 27

CHAPTER III

GROUNDWATER FLOW MODEL

Introduction

As previously stated, McHenry County has a complete reliance on groundwater.

Coupled with the fact that the population has been rapidly increasing since the 1930’s, groundwater resources have become an important resource of investigation in McHenry

County (Meyer, 1998). Of particular interest are the widespread sand and gravel aquifers. These aquifers provide about 75% of the water withdrawn for public water use in McHenry County. About 70% of these sand and gravel aquifers lie within 30 meters

(100 ft.) of land surface (Curry et al, 1997). The county can be roughly divided into two halves with the western side seeing more agricultural use and the eastern side being more municipal withdrawals. However, total agricultural land use however is about 75% (Berg,

1999). Given the shallow unconfined nature and high agricultural use, there exists a moderate to high contamination potential for many aquifers in the area (Thomason, 2013,

Hwang et al, 2007, Berg et al, 1999). Along with contamination, growing concerns over unsustainable withdrawals have prompted investigation into what the effects of current pumping activities will have on future resources (Meyer et al, 2013).

The study area for this model is located on the western side of McHenry County, in the southeast corner of the Garden Prairie Quadrangle (Figure 1.3). The land use is primarily agricultural and lies within the Kishwaukee River Valley. The Kishwaukee

River is located in a paleo-valley of bedrock that has been filled with glacial sediments.

The succession of glacial sediments deposited in this valley in recent stages of glaciation

32 host the surficial drift aquifer and many other units. This project focuses on the effects of high-capacity irrigation wells located in the river valley and screened in the surficial drift aquifer. Figure 3.1 offers a perspective view of the local study area including the irrigation well used for data collection and other known wells. In order to gain a better understanding of the effects of pumping, a steady-state groundwater flow model was constructed using MODFLOW to simulate the current pumping regime and to simulate the effects of different drought scenarios.

Figure 3.1 Perspective View of Study Area Highlighting Mr. Martin’s Irrigation Well in

Yellow and Other Wells in White, Modified from Google Earth.

Previous Work

Studies of Quaternary materials in McHenry county date back to the 1960’s and explore different facets such as sand and gravel resources (Anderson and Block, 1962;

Specht and Westerman, 1976), groundwater (Curry et al. 1997; Meyer 1998), general stratigraphy (Berg et al. 1985) and glacial history (Curry et al, 1997). More recently, groundwater investigations have been completed focusing on local aquifers (Thomason and Keefer, 2013) as well as simulation modeling and potentiometric surface mapping in

McHenry County (Meyer et al, 2013). In a recent study by Meyer et al, 2013, drought simulations were modeled in the shallow and deep aquifer systems of the McHenry

County region in an attempt to predict future drawdown scenarios. Over 8700 wells are represented in the model completed by Meyer et al, 2013. Drought scenarios modeled in this report (Meyer, 2013) show drawdown levels in the shallow aquifer ranging from 0 to

10 meters and being predominantly located in areas of municipal withdrawal for public use. The effect of this could result in reductions of natural groundwater discharge, thus affecting baseflow levels in streams and lakes. There is also the potential for well failure in the shallow aquifer where drawdown levels are highest. The results of Meyer et al,

2013, shown as a potentiometric surface map of the shallow aquifer system in the

Kishwaukee River valley and surrounding area, are represented in Figure 3.2. Studies such as the Meyer report focus on the larger scale impacts of current groundwater withdrawals. This project aims to understand the more localized impacts of heavy pumping on the widespread surficial aquifers in the Kishwaukee River Valley.

Figure 3.2 Modified from Meyer, 2013 Showing Potentiometric Surface of Shallow Aquifer, Focused on Kishwaukee River Valley.

Conceptual Model

The aquifer system being studied is referred to as the surficial drift aquifer in

McHenry County (Thomason and Keefer, 2013). It is an unconfined system composed of various layers of high-conductivity glaciofluvial outwash sediments that have been deposited in the Kishwaukee River Valley. Underlying these units are overlapping layers of both high and low hydraulic conductivity (K) sediments from the previous glacial episodes. The model domain is defined by the Kishwaukee River to the south, Rush

Creek, which trends southwest-northeast on the west portion of the boundary, and a constant head boundary to the north which connects the Kishwaukee River and Rush

Creek. The model domain was divided into four hydrologically distinct units. The three uppermost units consist of materials such as alluvium, sand and gravel, and gravel. These units are respectively considered Layer 1, Layer 2, and Layer 3 in the model set-up. A fourth unit below, Layer 4, was assigned a relatively much lower conductivity value in an attempt to separate it from the units above. Layer 4 represents a combination of the underlying sediments, which can be comprised of lenses of till, lake sediments, and bedrock. Thicknesses of these layers can variable, especially outside the model domain.

Layer 1 is about 5 meters thick in this area. Layer 2 ranges from 0 to about 18 meters in some areas. Layer 3 is similar with thicknesses ranging from 0-20 meters. The underlying Layer 4 ranges from 60 to 80 meters in the model domain. These units are represented in Figure 3.3 in cross sectional view. Hydraulic conductivity values for each layer were estimated from the pumping data collected, lithological descriptions, and field observations.

Figure 3.3 Schematic Cross Section of Kishwaukee River Valley Sediments (Modified from Thomason and Keefer, 2013).

The boundary conditions were assigned based on available model domain and hydrologic condition information that was available. The Kishwaukee River bounds the model to the south and can easily be defined as a constant head boundary. The same can be said for Rush Creek to the west. These classifications were done by interpreting topographic maps at the upstream and downstream extents of these boundary conditions to determine elevation head values. To the north, another constant head boundary was assigned. This designation was based on both a previously constructed GFLOW model and the results of Meyer et al, 2013 (Figure 3.1) which identifies potentiometric values near the same location. The bedrock also begins to steeply rise and comes closer to the land surface as one travels northward from the Kishwaukee River (Figure 3.3). Due to this, it was important to assign the constant head boundary on the south side of this rise in bedrock and subsequent desaturation of the aquifer (Figure 3.1).

Recharge to the system was estimated based off of precipitation data for McHenry

County. This area receives roughly .91 meters of precipitation a year (NRCS, 1997). To account for runoff and evapotranspiration one-tenth of the annual precipitation was simulated as recharge in the model, in Layer 1. In order to gain a better understanding of the aquifer’s response to irrigation, it was necessary to obtain pumping data from one of these irrigation wells. Mr. Martin is a local farmer in McHenry County and graciously agreed to allow installation of monitoring wells on his property in order to gain a better understanding of the local effects of pumping.

Model Setup

After the model domain was defined, attempts were made at estimating the equilibrium drawdown caused by a pumping well. The irrigation well of interest is screened at a level of approximately 18 meters (60 feet) below land surface. This puts the well in Layer 3 (gravel), based on the cross section (Figure 3.3). It is assumed that all wells located in the river valley are also screened at this elevation as it corresponds to a productive sand and gravel zone. After discussing with Mr. Martin, the drawdown in the well casing was estimated to be roughly 3.65 meters and was later confirmed to hold steady at this level during a pumping event. From these data, a solution was found using the Theis equation in order to estimate drawdown at distances extending outward from the well. While the Theis equation is traditionally used for confined aquifers, it provided an acceptable solution to aid in decisions regarding well placement (Figure 3.4). Based on these calculations, it was determined that two piezometers would be installed 14.6 meters (48 ft.) and 61 meters (200 ft.) away from the irrigation well, and will be referred to as piezometer 1 and piezometer 2 respectively. Installation was completed by hand, using 1.9 cm steel pipe, post driver, hand auger, and an 45 cm stainless steel screened tip.

These were screened at 8.2 meters (26 ft.) and 8.5 meters (28 ft.) below the land surface, or, 3.65 meters (12 ft.) below the water table in order to capture the time dependent drawdown data during a pumping event. Each pumping even occurs for approximately

48 hours. This is the time required for the center-pivot to complete one full rotation. The data taken from the pumping event are represented in Figure 3.5. Due to unforeseen circumstances and a particularly wet summer, irrigation was sparse and data were not able to be collected again. 38

Figure 3.4 Theis Solution Calculated for Estimating Drawdown Near Thorne Road.

A groundwater flow model was constructed to understand the cumulative effect of the irrigation wells in this region and how different climatic scenarios alter drawdown.

The model was developed using the software platform of Groundwater Vistas, built by

Environmental Simulations Inc., which utilizes the MODFLOW simulation (McDonald and Harbaugh, 1988,). MODFLOW has been used in modeling exercises for numerous purposes such as flow through a leaky aquitard (Chen et al, 2005), estimation of extent and probability of aquifer contamination (Meriano and Eyles, 2002 and Witkowski et al,

2003), and stream-aquifer seepage (Osman and Bruen, 2002). Some other examples include contaminant transport and attenuation modeling (Artimo, 2002) and delineating areas of recharge (Wang et al, 2014).

In addition to MODLFOW, MODPATH (McDonald and Harbaugh 1988; Pollock

1989) was also used to delineate capture zones for each respective well. MODPATH is a post-processing program designed to work with MODFLOW in particle tracking analysis. Results of running MODPATH can represent travel times and flow paths of particles. Both forward and reverse tracking can be computed as well as velocity of the particles (Shamsuddin et al, 2014). For this project, reverse particle tracking was utilized at each individual well. After running the MODFLOW simulation, particles were assigned in a circular pattern around each well, and a reverse particle tracking analysis was computed. This allowed visualization of where each of the particles originated in the model domain and their respective travel paths back to the wells, thus revealing their capture zones.

Layer elevations for the tops of the four units, as described previously, were obtained from the ISGS as part of the large-scale 3-D model of McHenry County

(Thomason and Keefer, 2013). These layers were imported from Esri ArcGIS into

Groundwater Vistas as shape-files. These shape-files were converted from raster files in

ArcGIS. Once imported into Vistas, not all cells had correct elevation data after importation and were modified manually.

As previously mentioned, the northern constant head boundary condition was determined by a few factors, including a previously constructed GFLOW model and the

Meyer report. GFLOW (Haitjema, 1995) uses an analytic element to model, and was used to better understand groundwater flow in the surficial aquifer. Analytic element models have been used effectively to provide boundary conditions and simulate the flow system

40 for extraction into a local three-dimensional model in the past (Hunt et. al., 1998). The analytic element model differs from a MODFLOW approach in that GFLOW does not use a model grid, rather, it represents wells and surface waters by point sinks and line sinks (Haitjema, 2010). An analytical solution exists for each individual element added.

These solutions are then combined to create one large solution for the groundwater flow system. Due to the fact that no grid is present in this model, heads and flows can be calculated anywhere in the model domain (Hunt et al, 2003). Often times these models are developed as screening models for a fast hydrologic analyses of an area (Hunt, 2006).

The results of the GFLOW model confirm the potentiometric contours produced by

Meyer et al, 2013 (Figure 3.2) and was deemed an appropriate model for the purpose of this project.

Initial Values

Given the desire to merge the underlying low conductivity units into a low-flow boundary, layer 4 was assigned a value of 3x10-8 m/s. Above this; Layer 3 represents the gravel lense in which the irrigation well is screened. As such, a value of .035 m/s was initially given. Layer 2 is slightly more diverse in its composition (sand and gravel).

Estimating its conductivity then resulted in an initial value of .0035 m/s. The uppermost unit in this sequence is a combination of alluvium in the river valley along with the terraces found on the northern extent of the model domain. Given this merging of the different lithologies, a conductivity of .0003 m/s was assigned. Average precipitation values for McHenry County was obtained from the Natural Resource Conservation

Society soil survey and adjusted for evapotranspiration, helped provide the initial recharge values in the model of .00025 m/day. The initial values for the constant head 41 boundaries representing the Kishwaukee River and Rush Creek were selected using topographic maps to determine elevation head at the upstream and downstream locations.

The northern boundary was initially assigned a head value of 239 meters based on the

GFLOW model and Meyer, 2013.

Table 3 Initial and Final Values for Model Parameters

Parameter Initial Final

Value Value

Layer 1 of .0003 .0012 m/s

Kx m/s

Ky of .0003 .0012 m/s

m/s

Kv of .0003 .0012 m/s

m/s

Layer 2 of .0035 0.0058 m/s

Kx m/s

Ky of .0035 0.0058 m/s

m/s

Kv of .0035 0.0058 m/s

m/s

Layer 3 .035 m/s 0.0116 m/s

Ky .035 m/s 0.0116 m/s

Kv .035 m/s 0.0116 m/s

Layer 4 3x10-8 m/s 1x10-7 m/s

Ky 3x10-8 m/s 1x10-7 m/s

Kv 3x10-8 m/s 1x10-7 m/s

Recharge .00025 m/d .00025 m/d

Adjustments

The constant head boundaries were each individually adjusted from their original values to try and simulate baseline elevation head values at the pumping well. The northern reaches of the model where the bedrock rises steeply in elevation most often proved the most difficult area to assign head elevations due to the differences in hydraulic conductivity between the layers. Hydraulic conductivity values were also adjusted for this same purpose of model justification. The conductivity values were not adjusted until after the constant head boundaries had been modified to simulate the most realistic scenario.

Initial and final values are each parameter are displayed in Table 2.

Sensitivity

Sensitivity analyses consisted of individually adjusting parameters and evaluating the results of head values compared against the target value. Results of this sensitivity analysis revealed that the model appeared to be most sensitive to adjustments in the constant head boundaries. Adjustments were made in .5 to one meter increments and produced noticeable change in the target value of piezometer 2. In some instances, model convergence would fail if head boundaries were assigned either too high or low, or were forced into certain layers. Changes made to the hydraulic conductivity values typically did not result in as much change in the model as modification of constant head boundaries. The upper three layers were modified due to the heterogeneous nature of the 44 units and therefore possible variation in conductivities. However, the lowermost unit was only slightly adjusted in order to simulate very low flow. The initial and final values for the adjusted hydraulic conductivity are presented in Table 3.

Justification

The initial model was constructed using MODFLOW and the conditions and adjustments described above. Justification was provided by a target values taken from piezometer 2 (located 61 meters from the irrigation well). In piezometer 2, drawdown was measured to be 8 inches after 8 hours of pumping, at which time the system had begun to reach equilibrium. The model was adjusted until it could simulate this drawdown at the given pumping rate of 4360 m3/day at the target location. Once this was justification using MODFLOW, MODPATH was applied in order to visualize the capture-zone of the irrigation well. These results can be visualized in Figure 3.5.

Figure 3.5 Model Domain With Boundary Conditions, Potentiometric Surface Values, and Capture Zone for Irrigation Well Where Pumping Data Were Collected.

Scenarios

After an initial model was set up and justified as explained above, six additional scenarios were modeled using MODFLOW in an attempt to understand the system’s response to pumping under different conditions. Using Google Earth to locate irrigation circles, and information gathered from Mr. Martin, four other wells were added to the initial simulation. These wells were assumed to be screened at the same depth and withdrawing at the same rate as Mr. Martin’s. Therefore, the first simulation represented shows all five wells in the Kishwaukee River Valley pumping at 800 gal/min under normal recharge conditions. This is meant to be representative of base conditions under a normal climatic scenario. The next five simulations were an attempt to model different degrees of drought conditions. Each simulation included a progressive decrease in recharge by 10% coupled with an increase in pumping rate by 10%. Historical stream gauge data for the Kishwaukee River (USGS, 2013) revealed that stream levels were constant, even in times of drought. Therefore, only the final simulation includes a lowering of the constant head boundary representing the Kishwaukee River (.15 meters lower). This last simulation also includes a 50% decrease in recharge as well as the respective 50% increase in pumping. After running these simulations using MODFLOW,

MODPATH was used to generate capture zone of each well under the respective conditions.

In addition to visual representation, a statistical analysis of cell-by-cell head values between the model runs was also completed. This was done by comparing the head levels in each cell of Scenario 1 (normal recharge and pumping rates) against the

46 head levels of the same cells in Scenario 2-6. Therefore, the change in head levels could be compared and contrasted for each individual simulation alongside normal conditions.

These data were then analyzed using a standard t-test and two-tailed p-value with a confidence interval of 95%. The results of the statistical analyses are presented in Table

Results

The results of the pumping data collected over an eight hour period are presented in Figure 3.6. The data were plotted on a logarithmic scale against time and show that after 10 hours, the system begins to reach equilibrium and drawdown measurements begin to become more constant.

Figure 3.6 Time dependent head data collected over first 8 hours of pumping. S-type curve is indicative of unconfined nature of the aquifer.

The results of the initial simulation containing only one irrigation well are visually represented using potentiometric surface contours and the capture zones in

Figure 3.4. This simulation provided the template for the following model trials as well as gave insight into the local effect the irrigation well has on the system as a whole. The results of this model trial were not included in the statistical analysis. The purpose of this trial was to provide justification for future model simulations and also provide additional insight into the local effects of Mr. Martin’s single irrigation well at this location. The results of the additional six simulations are visually represented below in Figure 3.7.

Potentiometric surface contours and capture zones for each well provide additional understanding of how the current pumping regime could alter flow patterns in each modeled scenario. The potentiometric contours show localized cones of depression around each well in some scenarios. As the recharge drops and pumping rates increase, more change is noticed in the contours. The capture zone results of the six scenarios are similar to those of the potentiometric contours. Scenario A shows more separation between capture zones of each respective well and a relatively small portion being drawn from the Kishwaukee River. Scenario F however reveals that the size of the capture zones has increased, with the zones beginning to merge and a larger area in contact with the

Kishwaukee River (Figure 3.7).

Figure 3.7 Representing the six different model simulations with capture zones for each well. p-Values are representative of Layer 2.

The results of the statistical analysis performed between model runs are represented in Table 3. The p-Value can be compared between each different scenario to analyze whether or not the change in head values in these cells is statistically significant.

It should be noted that the p-Value is fairly consistent across all four layers per each scenario. It is also important to note that the first two scenarios do not produce changes in head values that are significant. Only when recharge is dropped 30% and pumping is 49 increased 30% (Scenario 3) is significant change witnessed, with the most occurring in the final Scenario. The statistical analysis supports the visual representation of the flow patterns. Only the results of the two tailed p-value contrasting the last three simulations to normal conditions produced statistically significant results. Therefore, slight changes in recharge and pumping do not have a statistically significant on the change in head levels.

Table 3: Results of Statistical Analysis on Head Levels Compared With Simulation 1.

Scenario 1-2 Layer T- Degrees of p-Value 2 Value Freedom Tail 1 0.738 7410 0.461 2 0.740 7412 0.460 3 0.739 7412 0.460 4 0.747 7410 0.455 Scenario 1-3 1 1.555 7410 0.120 2 1.559 7412 0.119 3 1.559 7412 0.119 4 1.466 7410 0.143 Scenario 1-4 1 2.410 7410 <.05 2 2.417 7412 <.05 3 2.410 7412 <.05 4 2.323 7410 <.05 Scenario 1-5 1 3.267 7410 <.05 2 3.276 7412 <.05 3 3.269 7412 <.05 4 3.205 7410 <.05 Scenario 1-6 1 7.328 7410 <.001 2 7.350 7412 <.001 3 7.329 7412 <.001 4 7.246 7410 <.001

Discussion

The groundwater flow model was developed in order to better understand the singular and cumulative effect of high-capacity irrigation wells located in the

Kishwaukee River Valley. More specifically, those screened and withdrawing from the surficial drift aquifer. The results presented in Figure 3.5 show potentiometric surface contours and capture zones for each respective model run. It is important to note that while there are noticeable changes in the contour patterns, the overall flow pattern is not significantly altered by slight changes in recharge and pumping rates. Local change in the contours is present around the wells, but does not extend to great lengths beyond their pivot radius. Also, more change can be seen on the eastern side of the model area as compared to the west. This is hypothesized to be a result of the diminishing width of the surficial aquifer as it extends northward from the Kishwaukee River on the eastern side.

The fact that the contours are not as altered on the west side is hypothesized to be the effect of the confluence of the Kishwaukee River and Rush Creek.

In regards to the capture zone analysis, this same hypothesis can be applied. The diminishing width of the surficial drift aquifer in the eastern area of the model domain results in less water available to each well, therefore, they must draw more from the

Kishwaukee River to meet the pumping demand. Also, the cumulative effect of the higher concentration of wells in this area could also be influencing the capture zone sizes.

It is also essential to acknowledge the sources of error that are present that could potentially influence results. One aspect to note is that more target data could be beneficial in enhancing the overall accuracy of the model. Also, using pumping data

51 from one pumping event has limitations, for example potential seasonal variations in water table elevations. More insight could also be gained as to the local impact of the irrigation wells by obtaining post-pumping recovery data.

Estimations such as those made for hydraulic conductivity values and the constant head boundary along the northern transect are also possible sources of error.

Installation of monitoring wells along the currently utilized boundaries could provide more reliable data.

Given the time-frame and data available, the conditions modeled were considered acceptable. However, the simulations are not a perfect representation of actual conditions, specifically in regards to those simulating drought and increased pumping. Typically, drought conditions show a decrease in precipitation which in turn is assumed to lead to an increase in pumping. This respective increase is difficult to quantify and therefore may not be modeled in a manner most representative of actual conditions. Lastly, this simulation provides results for steady-state conditions. It is difficult to determine then what the effects of extended drought and increased pumping over longer time-steps will have on the shallow aquifer system.

CHAPTER IV

CONCLUSION

In conclusion, there were two chapters of this thesis; a surficial geologic map and a groundwater flow model. Collectively these two aspects describe the structure and stratigraphy of the Quaternary materials present in the Garden Prairie 7.5 Minute

Quadrangle as well as the local groundwater flow patterns in the Kishwaukee River

Valley. While this project did answer the research questions presented, it is not a complete investigation and is meant to enable a better scientific understanding of the available resources in northeastern Illinois.

The geologic map reveals the extent of glaciation during the Wisconsin Episode in the Marengo Moraine, and provides a detailed (1:24,000) delineation and characterization of the surface materials present in the mapping area. The relatively large exposure of outwash sediments present in the mapping area reveals that the Kishwaukee

River and Rush Creek probably served as outwash channels for multiple fluctuations of the ice front in McHenry County. Not only can this map aid in the understanding of the geology and glacial history in the area, it can also be useful in groundwater protection planning and resource evaluation in the future.

The groundwater flow model can be an appropriate tool in assessing the impacts of high-capacity irrigation wells in local unconfined aquifers of McHenry County. This project focused on the quantitative assessment of these wells, and gave insight into the sustainability of the aquifer given the current conditions. However, this research also adds to the collective knowledge about unconfined, unconsolidated aquifer systems and

53 anthropogenic impacts. Given the widespread nature of these aquifers throughout the

Midwest and their prolific use, the approach taken in this research project may be a simple and effective way to understand sustainable use in similar aquifers.

Future studies could build on this work by examining this same system and taking a more qualitative approach. Given the nature of the sediments composing the aquifer, there is potential for investigation regarding nutrient cycling and contamination.

Chemical analysis of water samples over time take from this aquifer could prove insightful as to the fate and transport of contaminants. In the modeled scenarios, only drastic recharge and pumping alterations produce a distinct change in the flow regime.

However, it is important to note that many other factors play into determining the impacts of groundwater withdrawal and this study is by no means all encompassing.

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APPENDIX A

SCHEMATICS OF BOREHOLES IN GARDEN PRAIRIE 7.5 MINUTE

QUADRANGLE, IL

APPENDIX B

SURFICIAL GEOLOGIC MAP OF THE GARDEN PRAIRIE 7.5 MINUTE

QUADRANGLE, IL

PLATE 1 See back cover