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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
© 2014 Logan Seipel
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
i
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.
ii
iii
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
iv
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
v
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
vi
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
1
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
2
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.
3
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.
4
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
5
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).
6
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
7
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).
8
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
9
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.
10
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.
11
Figure 1.4 McHenry County Surficial Aquifer Thickness Map, Modified from Thomason
and Keefer 2013. Groundwater Flow Model Site Outlined in Black.
12
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.
13
Figure 1.5 Shallow Aquifer Removal Rates in Northeastern Illinois,
McHenry County Outlined in Red (Meyer, 2013).
14
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?
15
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
16
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
17
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.
18
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
Number
Series Parent material Lithostratigraphic
Unit
777A Adrian muck Herbaceous organic
material over sandy
outwash or alluvium
Grayslake Peat
188A Beardstown loam Outwash and loamy
and sandy sediments
Henry
332A Billett sandy loam Outwash Henry
624B Caprell silt loam, 2-4% Thin mantle of silty
material and the
underlying loamy till
Glasford
3776A Comfrey loam, freq. flood Loamy alluvium Cahokia
87B2 Dickinson sandy loam Loamy and sandy
outwash
Henry
62A
Herbert silt loam, Silty material and the
underlying loamy till
Tiskilwa
103A Houghton muck Herbaceous organic
material
Grayslake Peat
527C2 Kidami loam, 4-6%, eroded Till with or without a
thin mantle of loess or
other silty material
Tiskilwa
623B Kishwaukee silt loam, 2-5% Thin layer of loess
over loamy and
gravelly outwash
Tiskilwa
60C2 La Rose loam, 5-10%,
eroded
Loamy till Tiskilwa
528A Lahoguess loam Outwash Henry
766A Lamartine silt loam Outwash Henry
8082A Millington silt loam, occ.
flooded
Calcareous loamy
alluvium
Cahokia
1100A Palms Muck, undrained Herbaceous organic
material over loamy
material or alluvium
Grayslake Peat
1529A Selmass loam, undrained Loamy outwash Henry
618E Senachwine silt loam, 12-
20%
Till Tiskilwa
19
Figure 2.1 Garden Prairie Quadrangle Unassigned Soils Polygons With County Line
Left-Center
20
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
21
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).
22
Figure 2.3 DEM and Hillshade Combined to Show Geomorphology of Garden
Prairie Quadrangle
23
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
24
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
25
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
26
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 south-
east 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
27
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).
28
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
29
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
30
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.
31
Figure 2.7 Cross Section 2 from Dunham Road to Hwy 27
32
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
33
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.
34
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.
35
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
36
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).
37
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.
38
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.
39
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).
40
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
41
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
42
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.
43
Table 3 Initial and Final Values for Model Parameters
Parameter Initial
Value
Final
Value
Layer 1
Kx
of .0003
m/s
.0012 m/s
Ky of .0003
m/s
.0012 m/s
Kv of .0003
m/s
.0012 m/s
Layer 2
Kx
of .0035
m/s
0.0058 m/s
Ky of .0035
m/s
0.0058 m/s
Kv of .0035
m/s
0.0058 m/s
Layer 3
Kx
.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
Kx
3x10-8 m/s 1x10-7 m/s
Ky 3x10-8 m/s 1x10-7 m/s
44
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
45
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.
46
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
47
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
1.
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.
48
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).
49
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
50
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-
Value
Degrees of
Freedom
p-Value 2
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
51
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
52
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.
53
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
54
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.
55
REFERENCES
Anderson, Richard C., and Block, Douglas A., 1962 Sand and gravel resources of
McHenry County, Illinois: Illinois State Geological Survey, 15p, Circular 336
Artimo, A. (2002). Application of flow and transport models to the polluted Honkala
aquifer, Sakyla, Finland. Boreal Environment Research, 7(2), 161-172.
Berg, R. C., Curry, B. B., & Olshansky, R. (1999). Tools for groundwater protection
planning: An example from McHenry County, Illinois, USA. Environmental
Management, 23(3), 321-331.
Berg, Richard C., Kempton, John P., Follmer, Leon R., and McKenna, Dennis R., 1985,
Illinoian and Wisconsinan stratigraphy and environments in northern Illinois: the
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APPENDIX A
SCHEMATICS OF BOREHOLES IN GARDEN PRAIRIE 7.5 MINUTE
QUADRANGLE, IL
60
61
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APPENDIX B
SURFICIAL GEOLOGIC MAP OF THE GARDEN PRAIRIE 7.5 MINUTE
QUADRANGLE, IL
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PLATE 1
See back cover
