Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Scientific Investigations Report 2022–5110

Prepared in cooperation with McHenry County, Illinois

Water Quality of Sand and Gravel Aquifers in McHenry

County, Illinois, 2020 and Comparisons to Conditions in 2010

U.S. Department of the Interior

U.S. Geological Survey

Cover: Photograph showing a U.S. Geological Survey hydrologist sampling a monitoring well

in Woodstock, McHenry County, Illinois. Photograph taken by Scott Kuykendall, Water Resource

Manager, McHenry County Planning and Development.

Water Quality of Sand and Gravel Aquifers

in McHenry County, Illinois, 2020 and

Comparisons to Conditions in 2010

By Amy M. Gahala, Lance R. Gruhn, Jennifer C. Murphy, and Lisa A. Matson

Prepared in cooperation with McHenry County, Illinois

Scientific Investigations Report 2022–5110

U.S. Department of the Interior

U.S. Geological Survey

U.S. Geological Survey, Reston, Virginia: 2022

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources,

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as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Gahala, A.M., Gruhn, L.R., Murphy, J.C., and Matson, L.A., 2022, Water quality of sand and gravel aquifers in

McHenry County, Illinois, 2020 and comparisons to conditions in 2010: U.S. Geological Survey Scientific Investigations

Report 2022–5110, 53 p., https://doi.org/10.3133/sir20225110.

Associated data for this publication:

Gahala, A.M., and Gruhn, L.R., 2022, Quality-assurance and quality-control data for discrete water-quality samples

collected in McHenry County, Illinois, 2020: U.S. Geological Survey data release, https://doi.org/10.5066/P9RBXV53.

U.S Geological Survey, 2020, USGS water data for the Nation: U.S. Geological Survey National Water Information

System database, https://doi.org/10.5066/F7P55KJN.

ISSN 2328-0328 (online)

iii

Acknowledgments

The authors would like to thank Scott Kuykendall, of the McHenry County Department of

Planning and Development, for his assistance with accessing each site and support of McHenry

County groundwater resource monitoring. The authors also thank the Planning, Environment,

and Development Committee and the McHenry County Board of McHenry County Planning

and Development for their support of this study and the groundwater monitoring network. The

authors also thank the McHenry County Conservation District for continuing to host the real-

time groundwater monitoring sites on conservation property. Also, thanks to the Illinois State

Geological Survey for allowing the U.S. Geological Survey (USGS) to use their existing monitor-

ing wells to increase the distribution of groundwater monitoring sites. The USGS appreciates

Daniel Abrams from the Illinois State Water Survey for contributing information regarding

production wells throughout McHenry County. The USGS appreciates this opportunity to provide

a water-quality update, along with continued support of the McHenry County Groundwater

Monitoring Network.

The authors greatly appreciate the assistance from colleagues Monica Hall and Carolyn

Soderstrom in sampling 47 monitoring wells and 3 surface-water sites during a pandemic and

summertime heat. We also would like to thank our colleague Jennifer Sharpe for her assistance

compiling figures for this report.

Contents

Acknowledgments ........................................................................................................................................iii

Abstract ...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................3

Description of Study Area ...................................................................................................................3

Previous Water-Quality Investigations..............................................................................................8

Methods of Study ...........................................................................................................................................8

Water-Quality Sampling .......................................................................................................................8

Statistical Analysis ...............................................................................................................................9

2020 Water Quality .........................................................................................................................................9

Field Properties ...................................................................................................................................10

Major Ions ............................................................................................................................................12

Trace Metals ........................................................................................................................................15

Nutrients ...............................................................................................................................................17

Contaminants of Emerging Concern ................................................................................................17

Suitability of Water for Drinking .......................................................................................................29

Comparison to 2010 Water-Quality Results .............................................................................................29

Statistical Comparison ................................................................................................................................29

Comparison of Chloride to Bromide Ratios .............................................................................................38

Summary........................................................................................................................................................41

References Cited..........................................................................................................................................42

Appendix 1. Quality Assurance and Quality Control of Water-Quality Results ..............................48

Figures

1. Map showing groundwater monitoring wells of the McHenry County

Groundwater Monitoring Network and U.S. Geological Survey National

Water-Quality Assessment Project and three surface-water-quality monitoring

sites sampled in June–July 2020 in McHenry County, Illinois...............................................2

2. Map showing distribution of sodium concentrations in samples from the

McHenry County Groundwater Monitoring Network wells and the National

Water-Quality Assessment Project monitoring wells, McHenry County,

Illinois, 2020 ..................................................................................................................................16

3. Graph showing dissolved solids concentrations by well depth in the McHenry

County Groundwater Monitoring Network wells and the National Water-Quality

Assessment Project monitoring wells, McHenry County, Illinois 2020 ..............................17

4. Map showing distribution of dissolved solids concentrations in the McHenry

County Groundwater Monitoring Network wells and the National Water-Quality

Assessment Project monitoring wells, McHenry County, Illinois, 2020 .............................18

5. Map showing distribution of chloride concentrations in the McHenry County

Groundwater Monitoring Network wells and the National Water-Quality

Assessment Project monitoring wells, McHenry County, Illinois, 2020 .............................19

6. Map showing distribution of arsenic concentrations in the McHenry County

Groundwater Monitoring Network wells and the National Water-Quality

Assessment monitoring wells, McHenry County, Illinois, 2020 ...........................................24

7. Map showing distribution of iron concentrations in the McHenry County

Groundwater Monitoring Network wells and the National Water-Quality

Assessment monitoring wells, McHenry County, Illinois, 2020 ...........................................25

8. Map showing distribution of manganese concentrations in the McHenry

County Groundwater Monitoring Network wells and the National Water-Quality

Assessment monitoring wells, McHenry County, Illinois, 2020 ...........................................26

9. Map showing number of detections for pharmaceuticals, pesticides, and

wastewater indicator compounds in the McHenry County Groundwater

Monitoring Network wells and four National Water-Quality Assessment

monitoring wells, McHenry County, Illinois, 2020 ..................................................................32

10. Graphs showing differences in the shallow, intermediate, and deep parts of the

sand and gravel aquifers for concentrations of selected constituents between

2010 and 2020 for water-quality samples in McHenry County, Illinois ...............................36

11. Diagrams showing major ions in wells from 2010 and 2020 in McHenry County,

Illinois ............................................................................................................................................37

12. Graph showing chloride-bromide ratio plotted against chloride concentrations

in the McHenry County Groundwater Monitoring Network wells and the

National Water-Quality Assessment monitoring wells, McHenry County,

Illinois, 2020 ..................................................................................................................................39

13. Graph showing chloride-bromide ratio plotted against chloride concentration

for wells that show shifts between 2010 and 2020 in the McHenry County

Groundwater Monitoring Network wells and the National Water-Quality

Assessment monitoring wells, McHenry County, Illinois, 2020 ...........................................40

Tables

1. Site information and water-quality sampling plan for field properties, major

ions, trace metals, nutrients, and contaminants of emerging concern analyzed

in the McHenry County Groundwater Monitoring Network, U.S. Geological

Survey National Water-Quality Assessment monitoring wells, and three

surface-water locations in Illinois, 2020 ...................................................................................4

2. Water use by category, volume of groundwater withdrawals, and population

served, McHenry County, Illinois, 2010 and 2015.....................................................................7

3. U.S. Environmental Protection Agency water-quality thresholds, number of

wells exceeding water-quality thresholds in samples collected in 2020, and

statistical description .................................................................................................................10

4. Results for field properties for the McHenry County Groundwater Monitoring

Network wells, 4 National Water-Quality Assessment Project monitoring wells,

and 3 surface-water sites, McHenry County, Illinois, 2020..................................................11

5. Results for concentrations of major ions from samples collected from

the McHenry County Groundwater Monitoring Network wells, 4 National

Water-Quality Assessment wells, and 3 surface-water sites in McHenry

County, Illinois, 2020 ...................................................................................................................13

6. Results for concentrations of trace metals from samples collected from

the McHenry County Groundwater Monitoring Network wells, 4 National

Water-Quality Assessment wells, and 2 surface-water sites in McHenry

County, Illinois, 2020 ...................................................................................................................20

vii

7. Results for concentrations of nutrients from samples collected from the

McHenry County Groundwater Monitoring Network wells, 4 National

Water-Quality Assessment wells, and 2 surface-water sites in McHenry

County, Illinois, 2020 ...................................................................................................................27

8. Concentrations of pharmaceuticals and wastewater indicator compounds

detected in samples collected from selected wells within the McHenry County

Groundwater Monitoring Network and three surface-water sites in McHenry

County, Illinois, 2020 ...................................................................................................................30

9. Summary statistics for selected constituents, results of the Wilcoxon

signed-rank test for groundwater-quality changes between 2010 and 2020 for

uncensored data and the paired Prentice-Wilcoxon test for uncensored data,

and evaluation of differences between the 2010 and 2020 aquifer-depth groups

of shallow, intermediate, and deep parts of the sand and gravel aquifers in

McHenry County, Illinois ............................................................................................................34

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi

) 259.0 hectare (ha)

square mile (mi

) 2.590 square kilometer (km

)

International System of Units to U.S. customary units

Multiply By To obtain

Mass

milligram (mg) 3.527×10

−5

ounce, avoirdupois (oz)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32.

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.

viii

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (µS/cm

at 25 °C).

Concentrations of chemical constituents in water are given in either milligrams per liter (mg/L),

micrograms per liter (µg/L), or nanograms per liter (ng/L).

Turbidity is given in nephelometric turbidity units (NTU).

Abbreviations

CEC contaminant of emerging concern

DEET N,N-Diethyl-m-toluamide

DWA drinking water advisory

EPA U.S. Environmental Protection Agency

MCGMN McHenry County Groundwater Monitoring Network

MCL maximum contaminant level

NAWQA National Water-Quality Assessment

NWQL National Water Quality Laboratory

p probability

PPW paired Prentice-Wilcoxon [test]

QAQC quality assurance and quality control

SMCL secondary maximum contaminant level

USGS U.S. Geological Survey

WIC wastewater indicator compound

WSR Wilcoxon signed rank [test]

< less than

Water Quality of Sand and Gravel Aquifers in

McHenry County, Illinois, 2020 and Comparisons to

Conditions in 2010

By Amy M. Gahala, Lance R. Gruhn, Jennifer C. Murphy, and Lisa A. Matson

bstract

McHenry County, Illinois, obtains most of its drinking

water from shallow sand and gravel aquifers (groundwater).

To evaluate this groundwater resource, the U.S. Geological

Survey, in cooperation with McHenry County, Illinois, col-

lected water-quality samples from 41 of 42 monitoring wells

in the McHenry County Groundwater Monitoring Network

and 4 monitoring wells from the U.S. Geological Survey

National Water-Quality Assessment Project. Additionally, a

subset of 12 monitoring wells was sampled and analyzed for

pharmaceuticals and wastewater indicator compounds (WICs),

collectively referred to as “contaminants of emerging con-

cern” (CECs). Results from this 2020 study were compared

to the 2010 results to assess changes in groundwater quality.

Statistical analyses and chloride-bromide ratio analyses also

were completed to assess changes in water quality.

Health-based benchmarks were exceeded for arsenic

(about 24 percent; 11 of 45 monitoring wells), sodium (40 per-

cent, 18 of 45), and manganese (about 2 percent, 1 of 45).

Aesthetically based benchmarks were exceeded for dissolved

solids (about 29 percent, 13 of 45), chloride (about 4 percent,

2 of 45), iron (about 87 percent, 39 of 45), and manganese

(about 29 percent, 13 of 45). CECs were detected at low or

estimated concentrations in 8 of the 12 (about 67 percent)

monitoring wells analyzed.

In addition to sampling the groundwater monitoring

wells, three surface-water-quality monitoring sites also were

sampled and analyzed for pharmaceuticals and WICs to pro-

vide a preliminary assessment of the presence of CECs in the

surface waters. CECs were detected in all three of the surface-

water-quality monitoring samples collected, and WICs were

more prevalent and more frequently detected than pharma-

ceutical compounds. These results provided a cursory under-

standing of the presence of CECs in surface waters and do not

constitute a robust analysis of sources, seasonality, range of

concentrations, persistence, or eects.

The 2020 groundwater-quality results had measurements

of eld properties, and concentrations of major ions, trace

metals, and nutrients that were consistent with 2010 results

with statistically signicant increases for calcium, magnesium,

and silica, and decreases for aluminum, ammonia, arsenic,

barium, bromide, calcium, molybdenum, phosphate, specic

conductance, sulfate, and dissolved solids. Increases generally

were detected in the intermediate and deep parts of the sand

and gravel aquifer, and decreases were detected in the shallow

parts of the sand and gravel aquifer. The mixed distribution

of increases and decreases among the various constituents

and aquifer-depth groups could be reecting dissolution and

mobility of some of the redox sensitive constituents and dilu-

tion of some constituents in the shallow aquifer depths. These

changes may be attributed to a combination of stable popula-

tion of the past decade (2010–20), land-use management prac-

tices, and the recent wet years of 2017 through 2019 causing a

dilution of the major ions in the shallow parts of the aquifer.

Introduction

McHenry County, Illinois, sources their drinking water

primarily from the shallow (less than 300 feet [ft]) sand and

gravel aquifers (groundwater). To evaluate this groundwa-

ter resource, a network of 42 groundwater monitoring wells

(referred to as the “McHenry County Groundwater Monitoring

Network” [MCGMN]) is used to monitor the water levels

and water quality in the sand and gravel aquifers (

g. 1). In

2010, water-quality samples were obtained at 41 monitoring

wells from the MCGMN, plus 5 additional monitoring wells

available from the U.S. Geological Survey (USGS) National

Water-Quality Assessment (NAWQA) Project were sampled

and analyzed for eld properties, major ions, trace metals, and

nutrients. In 2010, samples from a subset of the monitoring

wells also were analyzed for volatile organic compounds, pes-

ticides, and herbicides. The results of that study are presented

in Gahala (2017). In short, the ndings of that report indicated

health-based standards were exceeded for arsenic in 22 per-

cent of the monitoring wells sampled, sodium in 37 percent

of the monitoring wells sampled, and nitrates in 2 percent of

the monitoring wells sampled. Aesthetically based standards

were exceeded for total dissolved solids in 33 percent of the

wells sampled, chloride in 4 percent of the wells sampled,

iron in 85 percent of the wells sampled, and manganese in

2 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

WISCONSIN

ILLINOIS

BOONE CO

MC HENRY CO

DE KALB CO

MC HENRY CO

KANE CO

MC HENRY CO

LAKE CO

WALWORTH CO

MC HENRY CO

44N9E–20.7c

05548280

05438170

WOOD–08–01

HARV–09–01

HEBR–08–01

HEBR–08–02

HEBR–09–03

HUNT–09–03

MARN–09–01

MARN–09–02

MARN–10–03

MARN–10–04

MARS–09–01

MHEN–08–01

WAUC–02–12

WAUC–08–13

14–RIL–S

16–GRF–I/D

17–ALG–S/D

15–COR–S/I/D

10–MAR–S

11–SEN–I/D

13–NUN–I/D

7–HRT–S/I/D

9–MCH–S/D

8–GRN–I/D

1–CHE–S/D

4–RCH–S/I/D

3–HEB–I

43N8E–8.2c

43N8E–3.7d

45N7E–32.4d

NW–6–45–9

2–ALD–D

(Not sampled)

176

173

120

Fox Lake

Spring

Grove

Richmond

Hebron

Harvard

Pistakee

Highlands

Ringwood

Wonder

Lake

Greenwood

Johnsburg

Lakemoor

McCullom

Lake

McHenry

Woodstock

Bull Valley

Holiday

Hills

Prairie

Grove

Island

Lake

Marengo

Oakwood

Hills

Fox River

Valley

Gardens

Lakewood

Union

Cary

Huntley

Lake

in the

Hills

Fox

River

Grove

Trout Valley

Algonquin

Barrington

Hills

Hampshire

Carpentersville

Crystal

Lake

0 5 MILES1 2 3 4

0 5 KILOMETERS1 2 3 4

EXPLANATION

Base from U.S. Geological Survey 1:100,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 33˚ N. and 45˚ N.

Central meridian 89˚ W.

North American Datum of 1983

Marengo

City or town and identifier

U.S. Geological Survey surface-water-quality

monitoring site and identifier

McHenry County groundwater monitoring

well and identifier

National Water-Quality Assessment Project

well and identifier

05438170

14–RIL–S

43N8E–8.2c

MCHENRY COUNTY

ILLINOISILLINOIS

05550090

[D, deep; I, intermediate; S, shallow]

88°10'88°20'88°30'88°40'

42°30'

42°20'

42°10'

Figure 1. Groundwater monitoring wells of the McHenry County Groundwater Monitoring Network and U.S. Geological Survey

National Water-Quality Assessment Project and three surface-water-quality monitoring sites sampled in June–July 2020 in McHenry

County, Illinois.

Introduction 3

30 percent of the wells sampled. Volatile organic compounds

and pesticides were detected at trace levels in shallow wells

(less than 46 ft below land surface) near urban settings. To

identify changes in groundwater conditions in the shallow

sand and gravel aquifer since 2010, the USGS, in coopera-

tion with McHenry County, Illinois, and in collaboration with

the McHenry County Planning and Development Committee,

completed a decadal water-quality assessment of the sand and

gravel aquifers in June–July of 2020.

The MCGMN monitoring wells, along with four USGS

NAWQA Project shallow (less than about 46 ft) monitoring

wells in urban areas, were sampled and analyzed for eld

properties, major ions, trace metals, and nutrients (table 1).

Similar to the 2010 water-quality assessment, targeted

monitoring wells (12 total) were sampled for contaminants

of emerging concern (CECs). CECs can refer to many kinds

of chemicals, including medicines, personal care products,

cleaning products, and lawn care and agricultural products

(

U.S. Geological Survey, 2022). These CECs can enter our

groundwaters and surface waters through runo, septic

systems, discharges from wastewater-treatment plants, and

various industrial processes (

U.S. Geological Survey, 2022).

To identify if any CECs are present in the sand and gravel

aquifers, pharmaceuticals and wastewater indicator com-

pounds (WICs) were selected for analysis in the groundwater

at targeted monitoring wells. In addition to the groundwater

monitoring wells, three surface-water sites also were sampled

and analyzed for CECs, and two of the sites included analyses

for major ions, trace metals, and nutrients (table 1) to assess

general stream-water quality downstream from wastewater-

treatment plants and industries. Surface waters are the primary

drainage ways for groundwater, stormwater runo, and other

land-use discharges. This preliminary assessment of the pres-

ence of CECs provides a cursory understanding of concen-

trations detected but does not constitute a robust analysis of

sources, seasonality, range of concentrations, persistence, or

eects in surface water.

Purpose and Scope

The primary objectives of this study were to assess

changes in the water quality as it pertains to human health and

the environment and to identify potential eects of land use

on water quality. This investigation provides an update on the

water quality of the sand and gravel aquifers from the county-

wide network of groundwater monitoring wells and selected

surface-water sites. The purpose of this report is to summarize

and describe the ndings from the analysis of water-quality

samples collected during June and July of 2020 from the

MCGMN, plus four NAWQA monitoring wells and three

surface-water sites, and to complete the following:

• Describe the status of groundwater quality in 2020.

• Identify statistically signicant dierences in ground-

water quality by applying the Wilcoxon signed-rank

(WSR) test and paired Prentice-Wilcoxon (PPW) test.

• Provide an update on the sources of chloride (chloride-

bromide analysis) and compare results to the

2010 data.

• Summarize the results of the water-quality analysis

for CECs (pharmaceuticals and WICs) identied in

samples from targeted groundwater monitoring sites

and surface-water locations.

• Identify exceedances of drinking water standards and

statistically signicant dierences in concentrations

and potentially relate these results to land-use or other

eects near the well.

Description of Study Area

McHenry County, Ill. (611 square miles), is 35 miles

northwest of the Chicago metropolitan area. As described in

Gahala (2017), the county is generally geographically split by

type of land use. The western half of the county is dominated

by agricultural land use, and the eastern half is primarily urban

land use. Geologically, the land is described as hilly with

moraines, kames, eskers, and outwash plains resulting from

several glacial advances and retreats during the Quaternary

Period (Hackett and McComas, 1969; Berg and others, 1997;

Sti and Hansel, 2004). McHenry County is divided by two

hydrologic drainage basins, the Fox River drainage basin,

which drains towards the east, and the Kishwaukee River

drainage basin, which drains towards the west (Nicholas and

Krohelski, 1984; Berg and others, 1997; Illinois State Water

Survey, 2022; Gahala, 2017

, g. 3).

Precipitation ranged from 27.07 inches (in.) in 2012

to 49.9 in. in 2018, with an average of 44.51 in. over the

decade (2010–20) according to the Global Historical Climate

Network observation in Woodstock, Ill. (Woodstock 5NW)

(National Centers for Environmental Information, 2022a). The

legacy climatological period from 1981 to 2010 from weather

observation station Woodstock 5NW, in McHenry County,

Ill., indicates an average annual precipitation of 36.62 in.

(National Centers for Environmental Information, 2022b).

The most recent standard climatological period (1991–2020)

indicates an average annual precipitation of 38.68 in. (National

Centers for Environmental Information, 2022c), and the latest

15-year period from 2006 to 2020 indicates an average annual

precipitation of 41.18 in. (National Centers for Environmental

Information, 2022d). The average annual precipitation, cal-

culated from the daily values from 2010 to 2020 from data

downloaded for the observation station Woodstock 5NW is

slightly greater than the 2006–20 average annual precipita-

tion (44.51 in.) for the decade. Increases in precipitation can

aect water quality by increasing the amount of runo and

inltration of various land-use inputs through mobilization of

4 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 1. Site information and water-quality sampling plan for field properties, major ions, trace metals, nutrients, and contaminants of

emerging concern analyzed in the McHenry County Groundwater Monitoring Network, U.S. Geological Survey National Water-Quality

Assessment monitoring wells, and three surface-water locations in Illinois, 2020.

[Data collected for sites in this table can be accessed in the U.S. Geological Survey (USGS) National Water Information System database (U.S. Geological

Survey, 2020b) using the USGS station identiers. ft, foot; NAVD 88, North American Vertical Datum of 1988; X, analyzed; —, no detection; Co, County;

CRN, Climate Response Network; IL, Illinois]

USGS station name USGS station identifier Field identifier Latitude Longitude

Land-surface elevation

(ft above NAVD 88)

Well depth

(ft)

43N5E–27.4h1 (14–RIL–S) 421056088380801 14–RIL–S 42.182 −88.636 806.75 20.4

43N7E–19.8d (HUNT–09–03) 421120088281801 HUNT–09–03 42.189 −88.472 878 150.7

43N7E–23.1d1 (16–GRF–I) 421122088222701 16–GRF–I 42.189 −88.374 879.51 99

43N7E–23.1d2 (16–GRF–D) 421122088222702 16–GRF–D 42.189 −88.374 879.51 139.1

43N8E–20.6h1 (17–ALG–S) 421145088194801 17–ALG–S 42.196 −88.330 880.03 47.3

43N8E–20.6h2 (17–ALG–D) 421145088194802 17–ALG–D 42.196 −88.330 880.03 187.8

43N6E–07.1g (MARS–09–01) 421321088341101 MARS–09–01 42.223 −88.570 928 190.3

43N6E–01.3b1 (15–COR–S) 421341088283701 15–COR–S 42.228 −88.477 851.23 55.1

43N6E–01.3b2 (15–COR–I) 421341088283702 15–COR–I 42.228 −88.477 851.48 103.3

43N6E–01.3b3 (15–COR–D) 421341088283703 15–COR–D 42.228 −88.477 851.23 116.1

44N5E–30.8c1 (10–MAR–S)

(McHenry Co CRN)

421533088421801 10–MAR–S 42.259 −88.705 780.93 20.3

44N9E–25.1d (WAUC–02–12) 421547088142301 WAUC–02–12 42.263 −88.240 835 192.3

44N6E–22.4c1 (11–SEN–I) 421626088311401 11–SEN–I 42.274 −88.521 830.63 75.4

44N6E–22.4c2 (11–SEN–D) 421626088311402 11–SEN–D 42.274 −88.521 830.63 153.2

44N5E–23.5g (MARN–09–02) 421653088370901 MARN–09–02 42.281 −88.619 827 110.6

44N7E–17.8h1 (WOOD–08–01) 421747088270701 WOOD–08–01 42.296 −88.452 943 202.3

44N8E–11.3d1 (13–NUN–I) 421820088154501 13–NUN–I 42.306 −88.263 785.32 113

44N8E–11.3d2 (13–NUN–D) 421820088154502 13–NUN–D 42.306 −88.263 785.32 152.2

44N9E–05.7d1 (WAUC–08–13) 421914088125301 WAUC–08–13 42.321 −88.215 766 105.3

45N7E–25.7a (MHEN–08–01) 422032088222001 MHEN–08–01 42.342 −88.372 860 103.3

45N6E–29.1h (MARN–09–01) 422120088330901 MARN–09–01 42.356 −88.552 909 100.7

45N6E–23.7d1 (7–HRT–S) 422142088303101 7–HRT–S 42.362 −88.509 924.14 62.3

45N6E–23.7d2 (7–HRT–I) 422142088303102 7–HRT–I 42.362 −88.509 924.14 114.9

45N6E–23.7d3 (7–HRT–D) 422142088303103 7–HRT–D 42.362 −88.509 924.14 165.7

45N8E–17.7h1 (9–MCH–S) 422308088195601 9–MCH–S 42.386 −88.332 863.18 25.9

45N8E–17.7h2 (9–MCH–D) 422308088195602 9–MCH–D 42.386 −88.332 863.18 180

45N7E–11.5a1 (8–GRN–I) 422308088231001 8–GRN–I 42.386 −88.386 855.97 70.3

45N7E–11.5a2 (8–GRN–D) 422308088231002 8–GRN–D 42.386 −88.386 855.97 153.1

45N7E–08.5a (HEBR–08–02) 422308088264201 HEBR–08–02 42.385 −88.445 898 100.3

45N5E–12.5h (HARV–09–01) 422358088360201 HARV–09–01 42.400 −88.601 942 120.1

45N9E–06.7e (NW–6–45–9) 422433088140601 NW–6–45–9 42.409 −88.235 855 73

46N5E–21.1d1 (1–CHE–S) 422704088385301 1–CHE–S 42.451 −88.648 896.24 40.3

46N5E–21.1d2 (1–CHE–D) 422704088385302 1–CHE–D 42.451 −88.648 896.24 110.8

46N6E–12.5d (HEBR–09–03) 422845088285401 HEBR–09–03 42.480 −88.481 949 120.6

46N8E–08.2e1 (4–RCH–S) 422848088191001 4–RCH–S 42.480 −88.320 844.15 24

46N8E–08.2e2 (4–RCH–I) 422848088191002 4–RCH–I 42.480 −88.320 844.15 98.3

46N8E–08.2e3 (4–RCH–D) 422848088191003 4–RCH–D 42.480 −88.320 844.15 176

46N7E–10.2f (HEBR–08–01) 422858088235601 HEBR–08–01 42.483 −88.399 898 145.3

46N7E–04.8b1 (3–HEB–I) 422925088255401 3–HEB–I 42.490 −88.432 867.93 66.3

44N5E–23.5g2 (MARN–10–03) 421653088370902 MARN–10–03 42.281 −88.619 828 160

Introduction 5

Table 1. Site information and water-quality sampling plan for field properties, major ions, trace metals, nutrients, and contaminants of

emerging concern analyzed in the McHenry County Groundwater Monitoring Network, U.S. Geological Survey National Water-Quality

Assessment monitoring wells, and three surface-water locations in Illinois, 2020.—Continued

[Data collected for sites in this table can be accessed in the U.S. Geological Survey (USGS) National Water Information System database (U.S. Geological

Survey, 2020b) using the USGS station identiers. ft, foot; NAVD 88, North American Vertical Datum of 1988; X, analyzed; —, no detection; Co, County; CRN,

Climate Response Network; IL, Illinois]

Average ground-

water level for

period of record

(ft below land

surface)

Aquifer unit

Water-quality analytes

Field properties Major ions Trace metals Nutrients

Contaminants of

emerging concern

7.78 Haeger-Beverly Unit X X X X —

26.39 Ashmore Sand Unit X X X X —

18.91 Ashmore Sand Unit X X X X —

21.27 Lower Glasford Sand Unit X X X X —

0.66 Yorkville-Batestown Unit X X X X —

99.32 Shallow Bedrock Aquifer

X X X X —

72.15 Upper Glasford Sand Unit X X X X —

9.08 Haeger-Beverly Unit X X X X —

9.64 Ashmore Sand Unit X X X X X

9.08 Ashmore Sand Unit X X X X —

4.96 Haeger-Beverly Unit X X X X X

97.27 Lower Glasford Sand Unit X X X X —

3.85 Ashmore Sand Unit X X X X —

5.11 Lower Glasford Sand Unit X X X X —

18.27 Upper Glasford Sand Unit X X X X —

78.11 Ashmore Sand Unit X X X X X

47.28 Yorkville-Batestown Unit X X X X —

47.38 Shallow Bedrock Aquifer and Lower Glasford Sand Unit X X X X —

20.93 Haeger-Beverly Unit X X X X —

34.01 Haeger-Beverly Unit X X X X —

32.95 Upper Glasford Sand Unit X X X X X

35.83 Haeger-Beverly Unit X X X X X

36.10 Upper Glasford Sand Unit X X X X —

37.61 Shallow Bedrock Aquifer and Lower Glasford Sand Unit X X X X —

10.53 Haeger-Beverly Unit X X X X X

53.96 Ashmore Sand Unit X X X X —

4.99 Haeger-Beverly Unit X X X X X

16.95 Shallow Bedrock Aquifer and Lower Glasford Sand Unit X X X X X

11.04 Haeger-Beverly Unit X X X X X

31.81 Ashmore Sand Unit X X X X X

31.27 Haeger-Beverly Unit X X X X —

7.40 Ashmore Sand Unit X X X X —

7.34 Shallow Bedrock Aquifer

X X X X —

24.54 Ashmore Sand Unit X X X X X

7.13 Haeger-Beverly Unit X X X X X

11.70 Upper Glasford Sand Unit X X X X —

11.00 Shallow Bedrock Aquifer and Lower Glasford Sand Unit X X X X —

27.85 Ashmore Sand Unit X X X X —

−12.95 Upper Glasford Sand Unit X X X X —

27.82 Lower Glasford Sand Unit X X X X —

6 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 1. Site information and water-quality sampling plan for field properties, major ions, trace metals, nutrients, and contaminants of

emerging concern analyzed in the McHenry County Groundwater Monitoring Network, U.S. Geological Survey National Water-Quality

Assessment monitoring wells, and three surface-water locations in Illinois, 2020.—Continued

[Data collected for sites in this table can be accessed in the U.S. Geological Survey (USGS) National Water Information System database (U.S. Geological

Survey, 2020b) using the USGS station identiers. ft, foot; NAVD 88, North American Vertical Datum of 1988; X, analyzed; —, no detection; Co, County;

CRN, Climate Response Network; IL, Illinois]

USGS station name USGS station identifier Field identifier Latitude Longitude

Land-surface elevation

(ft above NAVD 88)

Well depth

(ft)

44N5E–23.5g3 (MARN–10–04) 421653088370903 MARN–10–04 42.281 −88.619 827 82

46N6E–08.46l (2–ALD–D) 422828088333301 2–ALD–D 42.474 −88.559 1,176.35 344.4

43N8E–8.2c 421301088191501 43N8E–8.2c 42.217 −88.321 900 46.1

45N7E–32.4d 422002088263001 45N7E–32.4d 42.334 −88.442 900 30.4

43N8E–3.7d 421402088173501 43N8E–3.7d 42.234 −88.293 920 58.7

44N9E-20.7c 421633088125801 44N9E–20.7c 42.276 −88.216 750 26.1

Surface-water sites

Nippersink Creek Near Spring Grove, IL 05548280 Nippersink Creek 42.443 −88.248

— —

Fox River at Huntley Road at

Carpentersville, IL

05550090 Fox River 42.108 −88.290

— —

Kishwaukee River at Marengo, IL 05438170 Kishwaukee River 42.265 −88.608

— —

constituents into nearby surface waters (Hateld and Prueger,

2004) and potentially imparting geochemical changes and

transport within an aquifer.

Aquifers used to supply drinking water in McHenry

County were mapped and described in detail by Meyer

and others (2013). Drinking water supplies for McHenry

County are pumped from deeper bedrock aquifers such as the

Cambrian-Ordovician, Silurian dolomite, and the shallow sand

and gravel aquifers within glacial drift deposits (Woller and

Sanderson, 1976). Directions of groundwater ow were deter-

mined by Meyer and others (2013) and Gahala (2017) and are

briey summarized in this section. Groundwater is replenished

(recharge) from precipitation that falls onto the land surface

and inltrates through the soil and sediment to the water table,

where it ows downward and laterally through hydraulically

connected sediments over time. Some of the groundwater

ows laterally and discharges into local surface-water bodies.

Deeper parts of the sand and gravel aquifers that are overlain

by a low-permeability clay (till) can receive recharge through

downward transport through saturated clays or through pref-

erential, permeable ow paths made by thin or discontinuous

clay deposits.

This study focuses on the water quality within the shal-

low sand and gravel aquifers. The aquifer units within the

shallow sand and gravel aquifers that the monitoring wells

represent are described in detail in Meyer and others (2013)

and Gahala (2017) (table 1). Two wells are screened in the

upper 10 ft of the Shallow Bedrock Aquifer. The source of the

water is recharged from the sand and gravel aquifers.

The MCGMN and NAWQA wells are used to monitor

for the eects of various land uses and changes. Samples col-

lected from the MCGMN and NAWQA wells give a snapshot

of water quality at shallow, intermediate, and deep depths.

The depths of the MCGMN and NAQWA monitoring wells

range from 20.3 to 344.4 ft and are generally comparable to

the depth range of production and private (residential) wells

extracting drinking water from the shallow sand and gravel

aquifers. According to the Illinois State Water Survey, esti-

mates from the ILWATER database indicate about 58 percent

of production wells are extracting groundwater from the sand

and gravel aquifers at depths of 16 to 272 ft. About 69 percent

of private wells are extracting groundwater from sand and

gravel aquifers at depths from 8 to 372 ft (Daniel Abrams,

Illinois State Water Survey, written commun., March 23,

2022). It is important to note that these estimates from the

Introduction 7

Table 1. Site information and water-quality sampling plan for field properties, major ions, trace metals, nutrients, and contaminants of

emerging concern analyzed in the McHenry County Groundwater Monitoring Network, U.S. Geological Survey National Water-Quality

Assessment monitoring wells, and three surface-water locations in Illinois, 2020.—Continued

[Data collected for sites in this table can be accessed in the U.S. Geological Survey (USGS) National Water Information System database (U.S. Geological

Survey, 2020b) using the USGS station identiers. ft, foot; NAVD 88, North American Vertical Datum of 1988; X, analyzed; —, no detection; Co, County; CRN,

Climate Response Network; IL, Illinois]

Average ground-

water level for

period of record

(ft below land

surface)

Aquifer unit

Water-quality analytes

Field properties Major ions Trace metals Nutrients

Contaminants of

emerging concern

19.43

Upper Glasford Sand Unit X X X X —

218.31

Lower Glasford Sand Unit — — — — —

—

Haeger-Beverly Unit X X X X —

—

Haeger-Beverly Unit X X X X —

—

Haeger-Beverly Unit X X X X —

12.60

Haeger-Beverly Unit X X X X —

Surface-water sites

— —

X X X X X

— —

X X X X X

— —

X — — — X

Aquifer unit names originated from Illinois State Water Survey (Meyer and others, 2013) and are used in this report for consistency purposes. See Gahala

(2017) for further details on aquifer unit and monitoring well designations.

Wells screened in the Shallow Bedrock Aquifer are within the upper 5 or 10 feet of the bedrock and represent the interface between the two interconnected

aquifers.

ILWATER database are uncertain because the database does

not account for wells that have not been abandoned (sealed)

or categorized as both bedrock and unconsolidated (Daniel

Abrams, Illinois State Water Survey, written commun.,

March 23, 2022).

The 2020 population estimate for McHenry County

was 310,229, compared to the 2010 population of 308,760

(U.S Census Bureau, 2021). The USGS has estimated water

use for the United States every 5 years since 1950 at the State

level, and since 1985 at the county level. The most recent

estimate of water use was for 2015 (U.S. Geological Survey,

2020a). The water-use compilation includes data from produc-

tion wells, domestic-supply wells, irrigation wells, and other

sources (industrial, mining, livestock, and aquaculture) and

is reported at the county level. The population served and

water-use estimates for 2015 indicate that total groundwater

withdrawals have decreased by about 9 percent from 2010

(U.S. Geological Survey, 2020a; table 2). The USGS is tran-

sitioning from previous approaches of 5-year annual compila-

tions to a nationally consistent modeling platform to improve

Table 2. Water use by category, volume of groundwater withdrawals, and population served, McHenry County, Illinois, 2010 and 2015.

[Data from U.S. Geological Survey, 2020a. Mgal/d, million gallons per day; —, no data or not applicable]

Water-use category

Groundwater withdrawals (Mgal/d) Population served (thousands)

2010 2015 2010 2015

Public-supplied domestic 19.97 18.70 237 242

Self-supplied domestic 5.75 5.25 72 66

Irrigation 2.77 3.27 — —

Other

3.22 1.58 — —

Total 31.71 28.80 309 308

Includes industrial, mining, livestock, and aquaculture. Descriptions of estimation methodology are available at https://water.usgs.gov/watuse/data/index.

html.

8 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

temporal and spatial discretization of water use that is planned

to allow forecasting capability. Water-use data were not avail-

able for 2020 at the time of this publication.

As of 2009, land use in the county was 61 percent agri-

culture, 11 percent open spaces, and 16 percent residential,

and the remaining land use consisted of government/insti-

tutional, commercial retail, industrial, earth extraction, and

some designated as “vacant” (McHenry County Planning and

Development, 2020). It is estimated that by 2030, agricultural

land use will be reduced to 45 percent, and residential, open

spaces, and spaces designated as “environmentally sensitive”

together will account for 51 percent of the land use (McHenry

County Planning and Development, 2020).

Previous Water-Quality Investigations

Countywide water quality of the sand and gravel aquifers

of McHenry County was assessed from sampling of munici-

pal supply wells in 1976 (Woller and Sanderson, 1976) and

nearly quarterly sampling of residential wells from April 1979

through April 1980 (Nicholas and Krohelski, 1984), which

included major ions and nutrients. Results from these studies

indicated concentrations of major ions and nutrients were not

substantially variable and were generally consistent across

seasons. Dissolved iron had the greatest amount of uctuation

but could be aected by other factors, such as age of the resi-

dential well and piping. Health and aesthetically based water-

quality benchmarks were exceeded for sodium, nitrates, iron,

manganese, and dissolved solids in residential wells sampled

(Nicholas and Krohelski, 1984

). In 2010, 41 of 42 monitoring

wells in the MCGMN plus 5 NAWQA monitoring wells were

sampled for eld properties, major ions, metals, trace ele-

ments, and nutrients (Gahala, 2017). Health and aesthetically

based water-quality benchmarks were exceeded for arsenic,

sodium, nitrate (as nitrate plus nitrite), manganese, dissolved

solids, chloride, and iron.

Methods of Study

This section describes methods used to collect and ana-

lyze discrete water-quality samples, including sampling proce-

dures, data analysis, and quality assurance and quality control

(QAQC). The statistical analysis applied to the water-quality

results also is described.

Water-Quality Sampling

The MCGMN consists of 42 monitoring wells, of which

37 are equipped with pressure transducers that continuously

monitor the groundwater levels (1 reading every 15 min-

utes). These data are transmitted using satellite telemetry

to the USGS National Water Information System database

(

U.S. Geological Survey, 2020b) Water-quality samples were

collected from 41 of the 42 monitoring wells in the MCGMN

and 4 NAWQA monitoring wells during June–July 2020

(g. 1, table 1). The NAWQA monitoring wells were included

to assess eects from urbanization. Two monitoring wells

(2–ALD–D from MCGMN and 45N9E–7.6a from NAWQA)

were planned to be sampled in 2020 but were not sampled

because of site conditions and well integrity issues. All

groundwater monitoring wells were sampled for eld proper-

ties, major ions, trace metals, and nutrients. Field properties

included dissolved oxygen, pH, dissolved solids, specic

conductance, water temperature, turbidity, and alkalinity.

Additionally, 12 monitoring wells were sampled for the analy-

sis of CECs. Water-quality results can be retrieved from the

USGS National Water Information System database using the

station identiers in table 1. The chloride-bromide ratio analy-

sis from Gahala (2017) was used to help select which wells

would be sampled for CECs. Based on the chloride-bromide

ratio analyses, 9 of the 12 wells were identied as potentially

aected by sewage, and the remaining 3 wells were consid-

ered control wells and were not identied as being aected by

sewage (Gahala, 2017). Water-quality sampling procedures

generally adhered to the USGS “National Field Manual for the

Collection of Water-Quality Data” (U.S. Geological Survey,

variously dated).

Surface-water samples also were collected in 2020 to

preliminarily assess the presence of CECs downstream from

wastewater-treatment plants and other industrial discharges.

Five grab samples were collected along the cross-sectional

transect of each stream and composited with a precleaned

and prerinsed churn. This approach slightly deviated from the

recommended method described in the National Field Manual

(U.S. Geological Survey, variously dated), where streams

greater than 5 ft in width should have a minimum of 10 sample

points. Cross-sectional eld properties were measured within

the stream with a multiparameter device at intervals of 2–5 ft

at each surface-water-quality monitoring location to determine

if the stream was well mixed at that location. Water-quality

properties (major ions, trace elements, and nutrients) were

added at two of the three surface-water locations to assess gen-

eral water quality in the two streams that contribute to down-

stream (beyond McHenry County) drinking water sources.

Water-quality samples were collected following the

methods described in the USGS “National Field Manual

for the Collection of Water-Quality Data” (U.S. Geological

Survey, variously dated), and eld alkalinities were completed

in the eld using the inection-point method. Major ions, trace

metals, and nutrients were analyzed by the methods described

in Fishman (1993), Fishman and Friedman (1989), and

Garbarino and others (2006). WICs are a general category for

anthropogenically derived chemicals that include some phar-

maceuticals, pesticides, and some volatile organic compounds

all quantied in parts per billion (micrograms per liter).

Pharmaceuticals are quantied in parts per trillion (nanograms

per liter). Pharmaceuticals and WICs were analyzed by the

methods described in Furlong and others (2008 and 2014) and

2020 Water Quality 9

Zaugg and others (2006). Water-quality samples were shipped

with appropriate sample preservation to the USGS National

Water Quality Laboratory (NWQL) in Denver, Colorado, for

analysis. The NWQL uses method reporting conventions for

establishing the minimum concentration greater than which

a quantitative measurement can be made (Oblinger Childress

and others, 1999). These reporting conventions are the method

reporting level and the laboratory reporting level. The method

reporting level is dened by the NWQL as the smallest

measured concentration of a substance that can be reliably

measured using a given analytical method. The method detec-

tion level is the minimum concentration of a substance that

can be measured and reported with 99-percent condence

that the concentration is greater than zero (Oblinger Childress

and others, 1999; Barr and Davis, 2010). The laboratory

reporting level is the interim reporting level, which is typi-

cally two times the method detection level to minimize false

negative risks and is the smallest concentration of a chemical

that can be reported by the laboratory (Williams and others,

2015). QAQC results are summarized in appendix 1 and are

groundwater focused. No QAQC samples were collected for

the preliminary CEC assessment in the surface water. QAQC

samples include equipment blanks, eld blanks, and replicates

(replicate of the primary environmental sample) and were col-

lected almost weekly throughout the duration of the sampling

eort. For a total of 12 QAQC samples, 2 equipment blanks,

5 eld blanks, and 5 replicates were collected. The full results

of the QAQC samples and the full list of CECs sampled for

are summarized in Gahala and Gruhn (2022).

The water-quality results of the 2020 data are com-

pared to health-based and aesthetically based benchmarks in

water-quality samples established by the U.S. Environmental

Protection Agency (EPA), such as the drinking water advi-

sories (DWAs) and established maximum contaminant level

(MCL) and the secondary maximum contaminant level

(SMCL) (U.S. Environmental Protection Agency, 2009a, b,

2018). Aesthetically based benchmarks are derived from EPA

SMCLs, which are nonregulated, recommended criteria that

establish taste and odor quality. Surface-water-quality results

also were compared to aquatic ambient water-quality criteria

established by the EPA to assess suitability for aquatic life

(U.S. Environmental Protection Agency, 2021b).

Statistical Analysis

To identify changes in water quality between 2010 and

2020, two analyses were completed. Using paired samples,

dierences between 2010 and 2020 were assessed across all

wells for each constituent. For constituents that did indicate

a statistically signicant dierence across all wells, dier-

ences between 2010 and 2020 also were assessed for three

groups of wells in either deep, intermediate, or shallow

aquifers. A total of 20 constituents were measured in 43 wells

in 2010 and 2020. The wells also were grouped according

to aquifer depth; 10, 19, and 14 wells were designated as

“shallow” (13.6–58.7 ft below ground surface), “intermediate”

(62.3–120.6 ft below ground surface), and “deep” (139–344 ft

below ground surface), respectively. Of the constituents,

nine had at least one censored (less than the reporting level)

observation. An alpha level of 0.05 was used for determining

statistical signicance. All statistical analyses were completed

using the R statistical software program (R Core Team, 2019),

specically the NADA (Lopaka and Helsel, 2020). NADA2

(Julian and Helsel, 2021) and Wilcox (R Core Team, 2021)

R packages, which include statistical tests for censored data.

The applicable statistical test depended on the presence

of censored values in the dataset. The WSR test (Helsel, 2012)

was used to assess changes when the data were all uncensored

values. The PPW test was used when data were a mix of

censored and uncensored values. Both tests are nonparametric,

require no assumptions about the distribution of the data, and

have a null hypothesis that the dierence between paired sam-

ples is zero. Rejection of the null hypothesis indicates samples

collected in 2020 dier from those collected in 2010. The

PPW test is a score test and allows for left-censored values

to have multiple reporting levels, meaning recensoring data

to the highest reporting level is not required (Helsel, 2012).

These two tests also were used when testing for dierences in

concentration between 2010 and 2020 for each aquifer group.

Because three comparisons (one for each aquifer group) were

made for each parameter, probability values (p-values) from

the WSR and PPW tests were adjusted using the Benjamini

and Hochberg correction, which controls the false discovery

rate when completing multiple comparison tests (Benjamini

and Hochberg, 1995). The combination of testing for dier-

ences between 2010 and 2020 across all wells and testing for

dierences within each aquifer group helped to identify at

what depth changes were likely.

2020 Water Quality

Results of the 2020 decadal water-quality sampling are

presented in this section and include eld properties, major

ions, trace metals, and nutrients. Selected monitoring wells

were sampled for CECs, which include pharmaceuticals,

pesticides, and WICs. The results for three surface-water sites

sampled also are included in tables in this report. The surface-

water results did not have any detected concentrations of

major ions, metals, or nutrients greater than any aquatic ambi-

ent water-quality criteria. Groundwater water-quality results,

including the implications on the suitability for drinking water,

are discussed in the following sections. The following sec-

tions compare constituents with the health-based standards and

aesthetically based recommendations by the EPA and include

the enforceable MCLs, nonenforceable SMCLs, and DWA

(U.S. Environmental Protection Agency, 2009a, 2018; table 3).

10 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 3. U.S. Environmental Protection Agency water-quality thresholds, number of wells exceeding water-quality thresholds in

samples collected in 2020, and statistical description (maximum, minimum, median).

[MCL, maximum contaminant level; µg/L, microgram per liter; DWA, drinking water advisory; mg/L, milligram per liter; SMCL, secondary maximum contami-

nant level; >, greater than]

Constituent

Water-quality standard

and benchmark

concentration

Concentration

Number of sites

exceeding drinking

water benchmark

Common sources of

constituent

Potential effect of

exceedance on health

Health-based benchmark

Arsenic MCL= 10 µg/L Maximum = 70.29

Minimum = 0.10

Median = 0.75

11 Aquifer sediments and

rocks, fertilizer

Skin damage; circula-

tory system prob-

lems, potentially

carcinogenic.

Sodium DWA = 20 mg/L

(20,000 µg/L)

Maximum = 180

Minimum = 4.32

Median = 14.6

18 Road salt, septic leach-

ate, water softener,

aquifer sediment,

and rocks

May increase blood

pressure in at-risk

individuals.

Manganese DWA = 0.3 mg/L (300

µg/L)

Maximum = 740

Minimum = 0.50

Median = 25.6

1 Aquifer sediments and

rocks, industrial

discharges, sewage,

landll leachate

Toxicity to nervous

system.

Aesthetically based benchmark

Dissolved

solids

SMCL = 500 mg/L Maximum = 1,358

Minimum = 272

Median = 419

13 Road salt, brines, septic

leachate, dissolved

aquifer minerals

Objectional tastes

and laxative eect

at concentrations

>1,000 mg/L.

Chloride SMCL = 250 mg/L Maximum = 517

Minimum = 0.55

Median = 16.9

2 Dissolved aquifer

minerals, road salt,

brines, septic leach-

ate

Imparts salty taste and

corrosive to metal

infrastructure.

Iron SMCL = 300 µg/L Maximum = 3,478

Minimum = 10

Median = 1,640

39 Aquifer sediments and

rocks

Discolors laundry

and stains xtures;

imparts metallic

taste.

Manganese SMCL = 50 µg/L Maximum = 740

Minimum = 0.50

Median = 25.6

13 Aquifer sediments and

rocks

Dark-brown or black

staining on xtures

and laundry, black

particulates at high

concentrations.

Water-quality standards and benchmark concentrations are from U.S. Environmental Protection Agency (2018).

Data summarized from U.S. Geological Survey (2020b).

Field Properties

Results for eld properties are presented in table 4.

Dissolved oxygen concentrations at groundwater wells ranged

from 0.0 to 7.0 milligrams per liter (mg/L) with a median

0.20 mg/L but were typically (80 percent) less than 1.0 mg/L.

According to McCallum and others (2008), denitrication

becomes more favorable at a dissolved oxygen concentration

of less than 2.0 mg/L. Dissolved oxygen at surface-water sites

ranged from 8.4 to 14.3 mg/L.

The pH collected at groundwater wells ranged from 6.5 to

7.6 standard pH units with a median of 7.2, and eld alkalini-

ties ranged from 268 to 429 mg/L as calcium carbonate with a

median of 340 mg/L as calcium carbonate. Surface-water sites

had higher pH values than wells and ranged from 8.0 to 8.9;

no eld alkalinities were measured at the surface-water sites.

Specic conductance measured at groundwater sites

ranged from 489 to 2,343 microsiemens per centimeter at

25 degrees Celsius (µS/cm) with a median of 719 µS/cm, and

specic conductance at surface-water sites ranged from 688

to 803 µS/cm. Some of the groundwater sites had elevated

measurements of specic conductance and may be aected

by the application of salt and salt brines on roads that can

inltrate into the groundwater. Elevated specic conductance

was especially noticeable at shallow well sites that are closer

to roadways.

2020 Water Quality 11

Table 4. Results for field properties for the McHenry County Groundwater Monitoring Network wells, 4 National Water-Quality

Assessment Project monitoring wells, and 3 surface-water sites, McHenry County, Illinois, 2020.

[Data available from U.S. Geological Survey, 2020b. mg/L, milligram per liter; std, standard; µS/cm, microsiemens per centimeter at 25 degrees Celsius; °C,

degree Celsius; NTU, nephelometric turbidity unit; CaCO

, calcium carbonate; IL, Illinois; —, no data]

Field identifier

Dissolved oxygen

(mg/L)

pH,

std units

Specific conductance

(µS/cm)

Water temperature

(°C)

Turbidity

(NTU)

Field alkalinity

(mg/L as CaCO

)

14–RIL–S 2.1 7.1 1,123 12.6 7.0 268

HUNT–09–03 0.1 7.4 726 11.8 0.4 377

16–GRF–I 0.1 6.6 996 11.8 5.9 325

16–GRF–D 2.5 7.3 606 13.6 0.9 294

17–ALG–S 0.4 7.1 818 22.7 10.0 391

17–ALG–D 1.1 7.5 605 18.3 2.1 276

MARS–09–01 1.9 7.2 564 13.2 0.4 353

15–COR–S 0.1 7.3 750 13.4 15.6 335

15–COR–I 0.1 7.4 743 12.7 4.3 341

15–COR–D 0.2 7.4 738 12.8 3.4 349

10–MAR–S 3.0 7.1 719 11.8 4.0 271

WAUC–02–12 0.2 7.6 534 13.3 5.8 302

11–SEN–I 0.2 7.0 679 12.3 0.6 306

11–SEN–D 0.2 7.1 592 12.0 1.9 348

MARN–09–02 0.2 7.0 678 13.3 9.6 356

WOOD–08–01 0.3 7.3 698 13.3 1.9 404

13–NUN–I 0.2 7.2 621 12.9 1.0 314

13–NUN–D 0.2 7.2 646 13.6 1.4 332

WAUC–08–13 0.1 7.1 727 12.8 0.7 355

MHEN–08–01 0.1 6.5 909 13.4 0.7 361

MARN–09–01 0.5 7.3 715 12.9 5.2 363

7–HRT–S 0.2 7.2 1,093 12.8 56.6 372

7–HRT–I 0.5 7.1 592 12.9 1.2 340

7–HRT–D 0.1 7.2 623 12.3 2.3 369

9–MCH–S 7.0 7.1 1,120 15.6 40.9 425

9–MCH–D 0.2 7.5 489 15.1 1.9 300

8–GRN–I 0.3 7.1 1,141 14.1 2.6 389

8–GRN–D 0.1 7.4 616 12.7 3.4 277

HEBR–08–02 0.1 7.3 798 12.5 4.0 322

HARV–09–01 0.4 7.1 782 12.6 2.2 331

NW–6–45–9 0.4 7.0 986 15.0 0.7 358

1–CHE–S 0.1 6.9 620 12.6 11.2 312

1–CHE–D 0.2 7.6 513 16.0 1.8 276

HEBR–09–03 0.7 7.3 753 12.6 7.1 322

4–RCH–S 3.7 7.2 1,983 25.3 13.6 373

4–RCH–I 0.1 7.3 543 12.3 5.2 311

4–RCH–D 0.5 7.4 527 12.6 12.9 302

HEBR–08–01 0.0 7.0 561 12.2 0.8 331

3–HEB–I 0.1 7.2 722 12.8 20.8 381

MARN–10–03 0.2 7.4 604 13.0 2.0 320

MARN–10–04 1.8 7.4 701 12.7 1.0 407

12 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 4. Results for field properties for the McHenry County Groundwater Monitoring Network wells, 4 National Water-Quality

Assessment Project monitoring wells, and 3 surface-water sites, McHenry County, Illinois, 2020.—Continued

[Data available from U.S. Geological Survey, 2020b. mg/L, milligram per liter; std, standard; µS/cm, microsiemens per centimeter at 25 degrees Celsius; °C,

degree Celsius; NTU, nephelometric turbidity unit; CaCO

, calcium carbonate; IL, Illinois; —, no data]

Field identifier

Dissolved oxygen

(mg/L)

pH,

std units

Specific conductance

(µS/cm)

Water temperature

(°C)

Turbidity

(NTU)

Field alkalinity

(mg/L as CaCO

)

43N8E–8.2c 3.6 7.0 1,269 13.9 77.0 354

45N7E–32.4d 0.2 6.8 918 12.8 7.3 331

43N8E–3.7d 0.2 6.7 2,343 13.8 12.1 375

44N9E–20.7c 0.2 6.7 1,663 13.3 6.2 429

Nippersink Creek Near

Spring Grove, IL

10.3 8.3 703 25.4 — —

Fox River at

Huntley Road at

Carpentersville, IL

14.3 8.9 688 28.2 — —

Kishwaukee River at

Marengo, IL

8.4 8.0 803 21.3 — —

Water temperature in groundwater wells ranged from

11.8 to 25.3 degrees Celsius (°C) with a median of 12.85 °C.

Most wells were in the 11–16 °C range, but two wells were

considerably higher and more similar to surface-water sites

(17–ALG–S and 4–RCH–S), potentially from heating of the

pump discharge line and ow-through chamber because of

incomplete shading on sunny days or from the lower pumping

rates allowing the water to warm within the discharge lines.

Surface-water sites had water temperatures ranging from 21.3

to 28.2 °C, which is typical of many Midwest streams and riv-

ers in June and July.

Turbidity at groundwater sites was generally low and

ranged from 0.4 to 77.0 nephelometric turbidity units (NTU),

and the median was 3.4 NTU. No turbidity measurements

were made at surface-water sites.

Major Ions

Major ions were analyzed in the groundwater samples

and two surface-water samples to compare to applicable

drinking water standards, determine changes in groundwater

sources, and identify potential land-use eects. Constituents

included calcium, magnesium, potassium, chloride, sodium,

dissolved solids, bromide, uoride, silica, and sulfate. Results

from the analysis of these samples are presented in

table 5 and

further described in the following paragraphs.

Calcium in monitoring wells ranged from 41.8 to

184 mg/L with a median of 85.9 mg/L, and at the two

surface-water sites, results were 44.5 mg/L and 72.5 mg/L.

Magnesium in wells ranged from 27.8 to 95.0 mg/L with a

median of 44.9 mg/L, and concentrations in surface-water

sites were 34.8 mg/L and 37.9 mg/L. Calcium and magnesium

are dissolved from soils, sediments, and rock, particularly

limestone and dolomite; these constituents can cause water

hardness and scale formation on pipes and plumbing (National

Ground Water Association, 2010).

Potassium in groundwater wells ranged from 0.83 to

8.00 mg/L with a median of 1.54 mg/L, and concentrations in

surface-water sites were 2.39 mg/L and 2.73 mg/L. Potassium

is not only commonly detected in clays, rocks, and soils, but

also can be detected in fertilizers (Mullaney and others, 2009).

High concentrations of potassium (greater than 500 mg/L) are

usually indicative of a road salt source, especially if potas-

sium chloride is applied as a deicer (National Ground Water

Association, 2010; Gahala, 2017).

Sodium ranged from 4.3 to 180 mg/L with a median of

14.64 mg/L, and concentrations in surface-water sites were

29.3 mg/L and 52.3 mg/L. High occurrences of sodium were

often incidental with high occurrences of chloride, which

could indicate that sodium chloride is being used as a deicer

for roadways.

Bromide in the groundwater wells ranged from an esti-

mated 0.011 to 0.254 mg/L with a median of 0.031 mg/L, and

concentrations at the two surface-water sites were 0.032 mg/L

and 0.036 mg/L. Fluoride in groundwater ranged from 0.05 to

0.68 mg/L with a median of 0.29 mg/L, and concentrations at

the surface-water sites were 0.14 mg/L and 0.16 mg/L. Silica

in groundwater ranged from 8.8 to 25.3 mg/L with a median of

19.96 mg/L, and concentrations at the surface-water sites were

1.1 mg/L and 15.9 mg/L. Bromide is a trace element in sea-

water, or naturally dissolved from sedimentary rocks such as

evaporites, carbonates, and shales (Salameh and others, 2016).

Anthropogenic sources of bromide can come from septic

tanks, deicers, agricultural chemicals, solvents, and gaso-

line additives (Davis and others, 1998). Fluoride in ground-

water is from weathering and leaching of uoride-bearing

minerals from rocks and sediments (Jha and others, 2013).

2020 Water Quality 13

Table 5. Results for concentrations of major ions from samples collected from the McHenry County Groundwater Monitoring Network wells, 4 National Water-Quality

Assessment wells, and 3 surface-water sites in McHenry County, Illinois, 2020.

[Data available from U.S. Geological Survey, 2020b. mg/L, milligram per liter; <, less than reporting level; E, estimated; —, no data; IL, Illinois]

Field identifier

Calcium

(mg/L)

Magnesium

(mg/L)

Potassium

(mg/L)

Chloride

(mg/L)

Sodium

(mg/L)

Bromide

(mg/L)

Fluoride

(mg/L)

Silica

(mg/L)

Sulfate

(mg/L)

Dissolved solids

(mg/L)

Chloride/

bromide ratio

14–RIL–S 68.3 35.6 1.53 187 114 0.084 0.13 11.7 15.3 548 2,338

HUNT–09–03 92.1 46.8 1.32 11.9 14.6 0.028 0.32 22.3 21.3 417 396

16–GRF–I 96.8 49.1 2.69 120 50.1 0.073 0.34 23.5 26.0 563 1,714

16–GRF–D 56.8 42.9 1.54 18.3 18.2 0.029 0.57 19.8 22.9 348 610

17–ALG–S 88.1 46.1 1.17 28.1 28.9 <0.020 0.24 15.0 34.0 450

E2,811

17–ALG–D 43.4 36.4 2.06 48.8 28.3 0.056 0.68 20.7 0.24 303 865

MARS–09–01 63.2 39.4 1.53 1.24 17.9 0.040 0.29 24.4 0.05 330 31

15–COR–S 96.1 47.3 1.34 14.1 7.4 0.049 0.35 19.4 86.9 466 282

15–COR–I 96.6 48.6 1.36 12.4 7.6 0.046 0.37 20.5 79.3 461 247

15–COR–D 93.2 48.5 1.43 11.7 7.4 0.048 0.40 20.6 77.6 465 235

10–MAR–S 85.8 39.0 1.92 31.3 21.1 0.033 0.11 8.8 97.7 424 1,043

WAUC–02–12 43.4 36.4 1.75 5.37 28.3 0.023 0.65 20.7 0.69 303 233

11–SEN–I 85.9 43.5 1.68 20.7 5.4 0.032 0.17 19.3 56.8 398 689

11–SEN–D 68.1 40.8 1.92 2.2 11.9 0.017 0.32 19.9 0.07 276 111

MARN–09–02 70.8 40.2 1.88 1.38 22.2 0.022 0.38 25.3 0.40 272 69

WOOD–08–01 79.6 47.3 1.60 1.53 12.0 E0.011 0.45 23.0 0.07 389

E153

13–NUN–I 72.1 42.4 1.06 1.99 10.8 0.015 0.53 22.0 22.0 341 133

13–NUN–D 71.7 44.9 1.46 4.32 13.8 0.034 0.45 21.4 44.7 363 127

WAUC–08–13 96.4 48.4 1.27 3.12 5.7 0.021 0.18 23.8 60.7 415 156

MHEN–08–01 112 55.8 2.08 65.9 11.9 0.050 0.15 20.8 52.0 533 1,317

MARN–09–01 92.3 45.3 0.89 17.2 5.2 0.021 0.22 19.7 35.4 419 817

7–HRT–S 131 60.8 1.40 107 16.9 0.026 0.14 22.3 60.8 618 3,567

7–HRT–I 76.8 37.4 1.09 0.79 8.3 <0.020 0.29 21.7 0.05 339

E79

7–HRT–D 75.6 40.7 1.35 3.53 8.7 0.022 0.30 22.2 0.26 349 160

9–MCH–S 109 50.6 1.84 121 84.4 0.057 0.15 17.9 29.3 676 2,017

9–MCH–D 41.8 27.8 1.48 0.55 29.8 0.012 0.62 16.8 0.05 284 46

8–GRN–I 126 62.0 3.89 120 35.5 0.060 0.12 17.6 79.7 632 2,017

8–GRN–D 79.7 39.2 1.14 5.07 4.3 0.037 0.17 20.0 62.9 362 137

HEBR–08–02 104 49.2 1.94 24.8 9.4 0.045 0.14 20.0 96.3 505 547

HARV–09–01 96.2 46.9 2.46 37.2 12.2 0.024 0.14 14.5 51.9 455 1,537

14 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 5. Results for concentrations of major ions from samples collected from the McHenry County Groundwater Monitoring Network wells, 4 National Water-Quality

Assessment wells, and 3 surface-water sites in McHenry County, Illinois, 2020.—Continued

[Data available from U.S. Geological Survey, 2020b. mg/L, milligram per liter; <, less than reporting level; E, estimated; —, no data; IL, Illinois]

Field identifier

Calcium

(mg/L)

Magnesium

(mg/L)

Potassium

(mg/L)

Chloride

(mg/L)

Sodium

(mg/L)

Bromide

(mg/L)

Fluoride

(mg/L)

Silica

(mg/L)

Sulfate

(mg/L)

Dissolved solids

(mg/L)

Chloride/

bromide ratio

NW–6–45–9 102 49.5 3.91 83.6 41.8 0.045 0.11 15.3 44.3 562 1,672

1–CHE–S 96.9 43.7 8.00 26.6 11.8 0.024 0.16 14.7 78.9 464 1,332

1–CHE–D 50.6 29.0 1.01 0.76 21.3 0.014 0.37 11.0 0.39 274 76

HEBR–09–03 97.7 46.5 0.83 29.6 6.4 0.037 0.09 13.5 78.5 448 740

4–RCH–S 135 65.9 1.74 417 180 0.060 0.26 20.4 41.4 1,063 6,950

4–RCH–I 60.6 35.7 1.44 2.10 12.1 <0.020 0.39 18.9 0.04 303

E210

4–RCH–D 58.2 35.4 1.40 0.83 9.7 0.012 0.38 20.6 0.04 304 83

HEBR–08–01 69.0 38.4 1.00 2.31 6.6 0.025 0.33 18.0 21.1 326 621

3–HEB–I 84.8 46.8 1.13 16.9 12.8 0.038 0.26 22.1 16.0 404 423

MARN–10–03 61.7 35.2 1.69 1.94 24.8 0.023 0.38 21.3 0.46 283 —

MARN–10–04 76.7 43.4 1.74 1.99 17.4 0.031 0.39 23.8 0.03 392 —

43N8E–8.2c 94.6 43.2 3.08 183 118 0.035 0.10 15.3 29.8 685 5,229

45N7E–32.4d 109 48.5 1.78 69.2 25.8 <0.020 0.15 16.6 42.3 518

E6,920

43N8E–3.7d 184 95.0 7.37 517 170 0.254 0.05 18.7 73.0 1,358 2,035

44N9E–20.7c 121 56.5 2.06 227 129 0.044 0.10 15.4 35.5 802 5,675

Nippersink Creek

Near Spring

Grove, IL

72.5 37.9 2.39 52.8 29.3 0.036 0.16 15.9 30.7 403 —

Fox River at

Huntley Road at

Carpentersville, IL

44.5 34.8 2.73 89.6 52.3 0.032 0.14 1.1 24.5 385 —

Kishwaukee River at

Marengo, IL

— — — — — — — — — — —

Chloride/bromide ratios are calculated by assigning one-half of the reporting level and are agged as estimated.

2020 Water Quality 15

Anthropogenic sources of uoride can include coal burning,

oil rening, steel productions, brick-making industries, and

phosphatic fertilizer plants (Jha and others, 2011).

Sulfate from wells ranged from 0.03 to 97.7 mg/L with a

median of 29.7 mg/L, and concentrations at the two surface-

water sites were 24.5 mg/L and 30.7 mg/L. Hydrogen suldes

commonly are associated with a “rotten egg” odor and can

impart a foul smell at higher concentrations (Agency for Toxic

Substances and Disease Registry, 2011). Sni tests at the

time of sampling can often determine if there is a presence of

hydrogen suldes. Additional discussion later in this report

relates these values to health-based benchmarks, implica-

tions to drinking water suitability, and aquatic life criteria for

surface water.

Results for major ions did not exceed any health-based

benchmarks except sodium, which exceeded the DWA

of 20 mg/L in 40 percent (18 of 45 groundwater sites) of

samples (g. 2, table 5). Sources of sodium include dissolu-

tion of sediments and rocks, road salt, and septic-system

leachate solutions (

U.S. Environmental Protection Agency,

2002; Panno and others, 2006). Excess ingestion of sodium

can increase blood pressure in at-risk individuals (Centers

for Disease Control and Prevention, 2022). DWAs are not

legally enforceable, and the 20 mg/L benchmark applies only

to people on a 500-milligram-per-day restricted sodium diet

(

U.S. Environmental Protection Agency, 2018).

Dissolved solids are a measure of the dissolved ion

concentrations in water. Groundwater samples ranged from

272 to 1,358 mg/L with a median of 417 mg/L, and concen-

trations at surface-water sites were 385 and 403 mg/L. The

EPA has established an SMCL for dissolved solids because

they can aesthetically aect groundwater, leave objectionable

tastes, and have laxative eects when consumed at concentra-

tions greater than 1,000 mg/L (table 3). Additionally, higher

concentrations of dissolved solids can cause foaming and

corrosion of metals. Dissolved solids can distinguish types

of aquifers or indicate contamination from landll leachate

or road salt (Clark and Piskin, 1977). Shallower wells gener-

ally having higher dissolved solids concentrations than deeper

wells (

g. 3); 29 percent of the groundwater wells (13 of

45 sites) exceeded the SMCL of 500 mg/L and 4 percent (2 of

45 sites) exceeded the 1,000-mg/L concentration (g. 4). The

two surface-water sites had similar concentrations of dissolved

solids and did not exceed any thresholds of concern.

Chloride in groundwater ranged from 0.55 to 517 mg/L

with a median of 16.9 mg/L, and concentrations at surface-

water sites were 52.8 mg/L and 89.6 mg/L (table 5). Chloride

was variable across wells, and the highest concentrations

were near roadways. High concentrations of chloride are

often attributed to road salt being applied as a deicer during

winter weather events. Chloride has an SMCL of 250 mg/L,

and greater concentrations can impart a salty taste on drink-

ing water and can contribute to the corrosion of infrastructure

(Shi and others, 2009; Pieper and others, 2018). Detections of

chloride were variable across the MCGMN, and the high-

est concentrations were detected near roadways. A total of

4 percent of the wells (2 of 45 wells) exceeded the SMCL, and

several shallow wells have elevated concentrations of chloride

(

g. 5).

Trace Metals

Metals and trace elements are naturally occurring in

the environment, although natural concentrations can vary

depending on local geology and contributions from anthro-

pogenic activities (

U.S. Geological Survey, 2019). Some

metals are essential nutrients, but all metals can be toxic at

some level, and for some metals, it only takes small amounts

to cause toxicity (

U.S. Environmental Protection Agency,

2022a). During the 2020 sampling campaign, a variety of

metals and trace elements were analyzed for, and these results

are presented in table 6. These results are discussed in relation

to health-based benchmarks and compared to the 2010 results

later in this report to determine suitability of the groundwater

and surface water for drinking and the potential implications

on aquatic life in surface water. In general, most metals and

trace elements were less than the reporting level or detected

at low concentrations and did not exceed any health-based

benchmarks (

table 3); however, arsenic, iron, and manganese

did exceed a benchmark and are discussed individually in this

section.

Results for arsenic in groundwater and surface water

were variable and ranged from less than 0.20 to 70.3 micro-

grams per liter (µg/L). Arsenic is a naturally occurring

element that is detected in sediments and rocks, and it dis-

solves in anoxic groundwater (Hem, 1985; Lin and Puls,

2000). Chronic ingestion of arsenic at concentrations greater

than the EPA MCL of 10 µg/L has been linked to increased

risk of lung, bladder, skin, liver, kidney, and prostate can-

cer (

U.S. Environmental Protection Agency, 2018; table 3).

Arsenic concentrations exceeded the MCL in about 24 per-

cent (11 of 45) of the monitoring wells, and most locations

had concentrations similar to what was measured in 2010,

with slight increases in 17–ALG–D from 16.1 µg/L in 2010

to 20.7 µg/L in 2020 and in 1–CHE–D from 62 µg/L in 2010

to 70.3 µg/L in 2020 (g. 6). The screen interval at monitor-

ing well 1–CHE–D is open to the top of the limestone bed-

rock aquifer and had low dissolved oxygen (0.2 mg/L). The

geochemically reducing conditions may increase the dissolu-

tion of arsenic-bearing minerals within the limestone aquifer

(Renard and others, 2015

). MARN–10–03 (10.1 µg/L) and

MARN–10–04 (16.3 µg/L) were sampled in 2020 but were

not available to sample in 2010; both wells had detections of

arsenic greater than the MCL. Detections for arsenic at the two

surface-water sites that were sampled did not exceed the MCL

for arsenic.

Iron concentrations in groundwater ranged from less than

10 to 3,478 µg/L with a median of 1,739 µg/L. Groundwater

in McHenry County has naturally elevated iron from the

dissolution of glacial aquifer material and is consistent with

previous water-quality investigations and this 2020 decadal

16 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

WISCONSIN

ILLINOIS

BOONE CO

MC HENRY CO

DE KALB CO

MC HENRY CO

KANE CO

MC HENRY CO

LAKE CO

WALWORTH CO

MC HENRY CO

Fox Lake

Spring

Grove

Richmond

Hebron

Harvard

Pistakee

Highlands

Ringwood

Wonder

Lake

Greenwood

Johnsburg

Lakemoor

McCullom

Lake

McHenry

Woodstock

Bull Valley

Holiday

Hills

Prairie

Grove

Island

Lake

Marengo

Oakwood

Hills

Fox River

Valley

Gardens

Lakewood

Union

Cary

Huntley

Lake

in the

Hills

Fox

River

Grove

Trout Valley

Algonquin

Barrington

Hills

Hampshire

Carpentersville

Crystal

Lake

44N9E–20.7c

WOOD–08–01

HARV–09–01

HEBR–08–01

HEBR–08–02

HEBR–09–03

MARN–09–01

MHEN–08–01

WAUC–02–12

WAUC–08–13

14–RIL–S

17–ALG–D

17–ALG–S

10–MAR–S

9–MCH–D

9–MCH–S

8–GRN–I

8–GRN–D

1–CHE–D

1–CHE–S

3–HEB–I

43N8E–8.2c

43N8E–3.7d

45N7E–32.4d

NW–6–45–9

HUNT–09–03

MARS–09–01

–

SEN

–

SEN

–

GRF

–

GRF

–

COR

–

COR

–

COR

–

–NUN–

7–HRT–

4–RCH–S

4–RCH–

MARN

–

MARN

–

MARN

–

88°10'88°20'88°30'88°40'

42°30'

42°20'

42°10'

0 5 MILES1 2 3 4

0 5 KILOMETERS1 2 3 4

EXPLANATION

[D, deep; I, intermediate; S, shallow]

City or town and identifier

Monitoring well sodium concentration,

in milligrams per liter, and identifier

Less than 20

Greater than 20

16–GRF–D

14–RIL–S

Marengo

Base from U.S. Geological Survey 1:100,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 33˚ N. and 45˚ N.

Central meridian 89˚ W.

North American Datum of 1983

Figure 2. Distribution of sodium concentrations in samples from the McHenry County Groundwater Monitoring Network wells and the

National Water-Quality Assessment Project monitoring wells, McHenry County, Illinois, 2020.

2020 Water Quality 17

100

150

200

250

Depth of well below land surface,

in feet

200 400 600 800 1,000 1,200 1,400

Dissolved solids, in milligrams per liter

Figure 3. Dissolved solids concentrations by well depth in

the McHenry County Groundwater Monitoring Network wells

and the National Water-Quality Assessment Project monitoring

wells, McHenry County, Illinois 2020.

update (Groschen and others, 2008; Gahala, 2017). Iron has an

SMCL of 300 µg/L, and concentrations exceeding the SMCL

can cause staining of household xtures and laundry (National

Ground Water Association, 2010). Concentrations greater than

1,800 µg/L can impart a metallic taste in water (Fetter, 1980,

p. 355). A total of 87 percent (39 of 45 wells) exceeded the

300-µg/L SMCL, and 40 percent (18 of 45 wells) exceeded

the 1,800-µg/L concentration (g. 7). Iron in surface-water

samples was less than the reporting level of 10 µg/L.

Manganese ranged from 0.5 to 740 µg/L with a median

of 25.6 µg/L (table 6). Manganese naturally occurs in aqui-

fer sediments but also can have anthropogenic sources

such as industrial euent, acid-mine drainage, sewage, and

landll leachate (Nádaská and others, 2010; World Health

Organization, 2011). Long-term exposure to DWA exceed-

ances of manganese can cause toxicity to the nervous system

(World Health Organization, 2011). Manganese has a DWA

of 300 µg/L (exceeded at one well) and an SMCL of 50 µg/L.

Similar to iron, manganese is naturally abundant in groundwa-

ter in McHenry County because of dissolution of manganese-

oxide coatings on glacial aquifer material (Groschen and

others, 2008). Concentrations greater than the SMCL can

cause dark brown or black staining on household xtures

and laundry. About 29 percent (13 of 45 wells) exceeded the

SMCL, and the highest concentration was nearly 15 times the

SMCL (740 µg/L at 10–MAR–S; g. 8; table 3). Manganese

concentrations in surface water did not exceed the aesthetic or

health benchmarks.

Nutrients

Nitrogen (nitrate plus nitrite as nitrogen, hereafter

referred to as “nitrate”) and phosphorus naturally occur in the

environment but also can come from anthropogenic sources

such as fertilizers, animal manure, and sewage (Gahala,

2017). Anthropogenic sources of nutrients, such as fertilizers,

have increased the concentrations of nitrate in many streams

and aquifers (

U.S. Geological Survey, 1999; Dubrovsky and

others, 2010; Domagalski and Johnson, 2012). In total, 8 of

45 wells, or about 18 percent of the sampled monitoring wells,

had detections for nitrate (0.08 to 5.33 mg/L) and all were

shallow (less than a 50-ft depth) (table 7). Nitrite ranged from

less than the reporting level of 0.001 to 0.054 mg/L with a

median of less than 0.001 mg/L as nitrogen. Orthophosphate

ranged from less than the reporting level of 0.004 to

0.141 mg/L as phosphorus with a median of 0.010 mg/L

as phosphorus. Ammonia ranged from less than 0.01 to

2.04 mg/L as nitrogen with a median of 0.34 mg/L as nitro-

gen. Nippersink Creek and Fox River were the two surface-

water sites sampled for nutrients (

table 7). Nitrate, nitrite, and

orthophosphate were detected at Nippersink Creek, but the

concentration of ammonia was less than the reporting level of

0.01 mg/L as nitrogen.

No detections of nitrate exceeded the MCL of 10 mg/L in

2020. Nitrate concentrations ranged from less than the report-

ing level to 5.33 mg/L as nitrogen. Although no nitrate sam-

ples exceeded the MCL of 10 mg/L, a few sites did indicate

slight increases. Well 17–ALG–S increased from 0.71 mg/L

as nitrogen in 2010 to 1.57 mg/L as nitrogen in 2020 and

10–MAR–S increased from 0.23 mg/L as nitrogen in 2010 to

1.52 mg/L as nitrogen in 2020. Nitrite concentrations ranged

from less than the reporting level of 0.001 to 0.054 mg/L as

nitrogen and did not exceed the MCL of 1 mg/L for the health-

based benchmark in any samples. Nitrite is unstable in aerated

water and is generally considered to be an indicator of contam-

ination from sewage or organic waste (Hem, 1985) if present.

Results for all nutrients are summarized in

table 7.

A dissolved oxygen concentration of 2.0 mg/L is a

common threshold for denitrication to exist; below this

concentration, denitrication becomes favorable (McCallum

and others, 2008). In all but one well, detections of nitrate

were coincident with dissolved oxygen concentrations greater

than 2.0 mg/L, and most of these wells were shallow wells

(20–48 ft). The one exception is well 17–ALG–S, where the

dissolved oxygen concentration was 0.4 mg/L and the nitrate

concentration of 1.57 mg/L as nitrogen was relatively high.

One potential explanation for the lower dissolved oxygen and

elevated nitrate concentration may be that groundwater can

move quickly through sand and gravel aquifer materials along

a preferential ow path or that dissolved oxygen decreases at a

faster rate than denitrication.

Contaminants of Emerging Concern

CECs are pharmaceuticals, detergents, natural and

synthetic hormones, pesticides, and other chemicals such as

WICs, plastic components, surfactant metabolites, and re

retardants (

U.S. Environmental Protection Agency, 2009b;

Tomasek and others, 2012) that are not typically treated for

in wastewater-treatment plants. CECs that may be removed

at wastewater-treatment plants are incidental to biological

treatment and disinfection processes (

U.S. Environmental

Protection Agency, 2009b; U.S. Geological Survey, 2018).

18 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

WISCONSIN

ILLINOIS

BOONE CO

MC HENRY CO

DE KALB CO

MC HENRY CO

KANE CO

MC HENRY CO

LAKE CO

WALWORTH CO

MC HENRY CO

Fox Lake

Spring

Grove

Richmond

Hebron

Harvard

Pistakee

Highlands

Ringwood

Wonder

Lake

Greenwood

Johnsburg

Lakemoor

McCullom

Lake

McHenry

Woodstock

Bull Valley

Holiday

Hills

Prairie

Grove

Island

Lake

Marengo

Oakwood

Hills

Fox River

Valley

Gardens

Lakewood

Union

Cary

Huntley

Lake

in the

Hills

Fox

River

Grove

Trout Valley

Algonquin

Barrington

Hills

Hampshire

Carpentersville

Crystal

Lake

44N9E–20.7c

WOOD–08–01

HARV–09–01

HEBR–08–01

HEBR–08–02

HEBR–09–03

MARN–09–01

MHEN–08–01

WAUC–02–12

WAUC–08–13

14–RIL–S

17–ALG–D

17–ALG–S

10–MAR–S

9–MCH–D

9–MCH–S

8–GRN–I

8–GRN–D

1–CHE–D

1–CHE–S

3–HEB–I

43N8E–8.2c

43N8E–3.7d

45N7E–32.4d

NW–6–45–9

HUNT–09–03

MARS–09–01

–

SEN

–

SEN

–

GRF

–

COR

–

COR

–

COR

–

–NUN–

7–HRT–

4–RCH–S

4–RCH–

MARN–09–02

MARN

–

MARN

–

16–GRF–D

88°10'88°20'88°30'88°40'

42°30'

42°20'

42°10'

0 5 MILES1 2 3 4

0 5 KILOMETERS1 2 3 4

EXPLANATION

City or town and identifier

Monitoring well dissolved solids concentration,

in milligrams per liter, and identifier

0 to 500

501 to 1,000

Greater than 1,000

Marengo

[D, deep; I, intermediate; S, shallow]

–

ALG

–

S17

–

ALG

–

43N8E–3.7d

–

RIL

–

S14

–

RIL

–

Base from U.S. Geological Survey 1:100,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 33˚ N. and 45˚ N.

Central meridian 89˚ W.

North American Datum of 1983

Figure 4. Distribution of dissolved solids concentrations in the McHenry County Groundwater Monitoring Network wells and the

National Water-Quality Assessment Project monitoring wells, McHenry County, Illinois, 2020.

2020 Water Quality 19

WISCONSIN

ILLINOIS

BOONE CO

MC HENRY CO

DE KALB CO

MC HENRY CO

KANE CO

MC HENRY CO

LAKE CO

WALWORTH CO

MC HENRY CO

Fox Lake

Spring

Grove

Richmond

Hebron

Harvard

Pistakee

Highlands

Ringwood

Wonder

Lake

Greenwood

Johnsburg

Lakemoor

McCullom

Lake

McHenry

Woodstock

Bull Valley

Holiday

Hills

Prairie

Grove

Island

Lake

Marengo

Oakwood

Hills

Fox River

Valley

Gardens

Lakewood

Union

Cary

Huntley

Lake

in the

Hills

Fox

River

Grove

Trout Valley

Algonquin

Barrington

Hills

Hampshire

Carpentersville

Crystal

Lake

44N9E–20.7c

WOOD–08–01WOOD–08–01

HARV–09–01HARV–09–01

HEBR–08–01HEBR–08–01

HEBR–08–02HEBR–08–02

HEBR–09–03HEBR–09–03

MARN–09–01MARN–09–01

MARN–09–02

MARN–10–03

MARN–10–04

MHEN–08–01

WAUC–02–12WAUC–02–12

WAUC–08–13

14–RIL–S

17–ALG–D17–ALG–D

17–ALG–S17–ALG–S

10–MAR–S10–MAR–S

9–MCH–D

9–MCH–S

8–GRN–I

8–GRN–D

1–CHE–D1–CHE–D

1–CHE–S1–CHE–S

3–HEB–I3–HEB–I

43N8E–8.2c

43N8E–3.7d

45N7E–32.4d

NW–6–45–9

HUNT–09–03HUNT–09–03

MARS–09–01MARS–09–01

11–SEN–I

11–SEN–D

11–SEN–I

11–SEN–D

16–GRF–I

16–GRF–D

15–COR–S

15–COR–I

15–COR–D

15–COR–S

15–COR–I

15–COR–D

13–NUN–I

13–NUN–D

13–NUN–I

13–NUN–D

7–HRT–S

7–HRT–I

7–HRT–D

4–RCH–S

4–RCH–I

4–RCH–D

88°10'88°20'88°30'88°40'

42°30'

42°20'

42°10'

0 5 MILES1 2 3 4

0 5 KILOMETERS1 2 3 4

EXPLANATION

[D, deep; I, intermediate; S, shallow]

City or town and identifier

Monitoring well chloride concentration,

in milligrams per liter, and identifier

0 to 50

50.1 to 250

Greater than 250

Marengo

–

ALG

–

S17

–

ALG

–

43N8E–3.7d

–

RIL

–

S14

–

RIL

–

Base from U.S. Geological Survey 1:100,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 33˚ N. and 45˚ N.

Central meridian 89˚ W.

North American Datum of 1983

Figure 5. Distribution of chloride concentrations in the McHenry County Groundwater Monitoring Network wells and the National

Water-Quality Assessment Project monitoring wells, McHenry County, Illinois, 2020.

20 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 6. Results for concentrations of trace metals from samples collected from the McHenry County Groundwater Monitoring

Network wells, 4 National Water-Quality Assessment wells, and 2 surface-water sites in McHenry County, Illinois, 2020.

[Data available from U.S. Geological Survey, 2020b. µg/L, microgram per liter; <, less than reporting level; E, estimated; IL, Illinois; —, no data]

Field identifier

Aluminum

(µg/L)

Barium

(µg/L)

Beryllium

(µg/L)

Cadmium

(µg/L)

Chromium

(µg/L)

Iron

(µg/L)

Manganese

(µg/L)

Molybdenum

(µg/L)

14–RIL–S <6 75.8 <0.02 <0.06 <1 <10 10.2 0.61

HUNT–09–03 <3 78.4 <0.01 <0.03 0.6 2,667 12.2 2.33

16–GRF–I <3 207 <0.01 <0.03 <0.5 2,185 25.6 1.65

16–GRF–D <3 115 <0.01 <0.03 <0.5 526 6.4 0.70

17–ALG–S <3 93.7 <0.01 <0.03 <0.5 471 36.6 3.25

17–ALG–D <3 88.4 <0.01 <0.03 <0.5 849 11.4 4.25

MARS–09–01 <3 126 <0.01 <0.03 <0.5 1,914 14.0 3.98

15–COR–S <3 129 <0.01 <0.03 <0.5 3,020 54.1 2.27

15–COR–I <3 126 <0.01 <0.03 <0.5 2,689 42.7 1.70

15–COR–D <3 124 <0.01 <0.03 <0.5 2,518 39.5 1.59

10–MAR–S <3 52.1 <0.01 <0.03 <0.5 <10 740 2.02

WAUC–02–12 <3 92.4 <0.01 <0.03 <0.5 772 11.4 1.60

11–SEN–I <3 78.1 <0.01 <0.03 <0.5 946 45.4 1.07

11–SEN–D <3 75.7 <0.01 <0.03 <0.5 1,689 22.4 1.09

MARN–09–02 <3 125 <0.01 <0.03 <0.5 1,927 18.5 4.05

WOOD–08–01 <3 59.0 <0.01 <0.03 1.1 1,277 32.5 1.78

13–NUN–I <3 101 <0.01 <0.03 <0.5 1,796 13.8 1.32

13–NUN–D <3 64.4 <0.01 <0.03 <0.5 604 8.4 1.87

WAUC–08–13 <3 78.1 <0.01 <0.03 0.7 1,509 29.6 0.32

MHEN–08–01 <3 80.3 <0.01 <0.03 <0.5 2,434 72.8 1.37

MARN–09–01 <3 55.1 <0.01 <0.03 <0.5 3,478 29.8 1.23

7–HRT–S <6 84.2 <0.02 <0.06 <1 2,530 58.1 2.16

7–HRT–I <3 35.6 <0.01 <0.03 <0.5 2,525 11.2 1.58

7–HRT–D <3 44.6 <0.01 <0.03 <0.5 2,176 17.3 0.97

9–MCH–S <6 62.2 <0.02 <0.06 <1 <10 0.9 0.65

9–MCH–D <3 87.4 <0.01 <0.03 <0.5 2,372 26 2.79

8–GRN–I <6 131 <0.02 <0.06 <1 1,861 61.6 1.89

8–GRN–D <3 32.9 <0.01 <0.03 <0.5 775 222 2.12

HEBR–08–02 <3 109 <0.01 <0.03 <0.5 1,629 53.1 1.69

HARV–09–01 <3 59.7 <0.01 <0.03 <0.5 915 50.5 2.69

NW–6–45–9 <3 72.0 <0.01 <0.03 <0.5 1,406 54.2 2.57

1–CHE–S <3 148 <0.01 <0.03 <0.5 1,357 141 0.89

1–CHE–D <3 78.6 <0.01 <0.03 <0.5 1,256 8.1 6.04

HEBR–09–03 <3 45.5 <0.01 <0.03 <0.5 2,060 33.6 0.96

4–RCH–S <6 173 <0.02 <0.06 <1 1,206 28.8 0.95

4–RCH–I <3 51.8 <0.01 <0.03 <0.5 2,044 9.9 1.34

4–RCH–D <3 52.4 <0.01 <0.03 <0.5 1,142 5.1 1.14

HEBR–08–01 <3 59.6 <0.01 <0.03 <0.5 1,640 24.2 1.04

3–HEB–I <3 68.0 <0.01 <0.03 0.8 1,764 13.5 0.30

MARN–10–03 <3 284 <0.01 <0.03 <0.5 1,714 8.4 7.13

MARN–10–04 <3 103 <0.01 <0.03 <0.5 2,382 22.5 3.34

2020 Water Quality 21

Table 6. Results for concentrations of trace metals from samples collected from the McHenry County Groundwater Monitoring

Network wells, 4 National Water-Quality Assessment wells, and 2 surface-water sites in McHenry County, Illinois, 2020.—Continued

[Data available from U.S. Geological Survey, 2020b. µg/L, microgram per liter; <, less than reporting level; E, estimated; IL, Illinois; —, no data]

Nickel

(µg/L)

Silver

(µg/L)

Antimony

(µg/L)

Arsenic

(µg/L)

Selenium

(µg/L)

Uranium

(µg/L)

Lithium

(µg/L)

Strontium

(µg/L)

Boron

(µg/L)

0.44 <2 <0.12 <0.20 0.24 0.59 2.61 87 16

E1.35 <1 <0.06 24.5 <0.05 0.04 3.08 475 37

0.28 <1 <0.06 0.13 <0.05 <0.03 8.63 874 45

<0.20 <1 <0.06 0.20 <0.05 <0.03 6.06 3,349 197

0.87 <1 0.11 0.19 <0.05 1.32 10.98 592 76

E1.20 <1 0.06 20.7 <0.05 <0.03 2.74 1,680 175

0.26 <1 <0.06 21.7 <0.05 <0.03 7.85 466 91

<0.20 <1 <0.06 0.42 <0.05 <0.03 5.03 265 36

<0.20 <1 <0.06 0.71 <0.05 0.04 5.16 302 37

<0.20 <1 <0.06 0.54 <0.05 0.05 5.44 315 39

E2.40 <1 0.18 0.24 0.18 3.80 1.61 109 21

E0.40 <1 <0.06 0.80 <0.05 <0.03 10.72 1,680 175

<0.20 <1 <0.06 0.59 <0.05 0.10 3.14 186 29

<0.20 <1 <0.06 3.82 <0.05 <0.03 3.01 721 90

<0.20 <1 <0.06 12.4 <0.05 <0.03 6.95 669 128

0.41 <1 <0.06 0.62 <0.05 <0.03 6.70 641 73

<0.20 <1 <0.06 0.30 <0.05 <0.03 5.77 1,526 83

<0.20 <1 <0.06 0.10 <0.05 0.05 6.22 1,318 107

0.29 <1 <0.06 0.22 <0.05 0.05 3.20 175 24

0.46 <1 <0.06 0.36 <0.05 0.06 4.08 159 21

<0.20 <1 <0.06 8.40 <0.05 <0.03 1.24 314 17

0.87 <2 <0.12 0.58 <0.1 0.15 4.98 125 93

0.54 <1 <0.06 18.2 <0.05 <0.03 1.61 535 39

<0.20 <1 <0.06 9.72 <0.05 <0.03 2.44 700 41

0.67 <2 <0.12 0.21 0.48 0.88 3.37 190 64

<0.20 <1 <0.06 5.38 <0.05 <0.03 1.44 2,341 264

E1.08 <2 <0.12 1.04 <0.1 0.25 11.89 148 22

<0.20 <1 <0.06 1.14 <0.05 0.22 3.28 112 14

0.83 <1 0.56 3.23 <0.05 0.26 4.76 135 19

0.27 <1 <0.06 0.56 <0.05 0.59 4.27 92 21

0.72 <1 0.07 0.48 0.07 0.93 6.98 76 19

0.66 <1 <0.06 0.36 <0.05 1.03 3.17 204 32

<0.20 <1 <0.06 70.3 <0.05 <0.03 0.45 393 48

0.31 <1 <0.06 0.21 <0.05 <0.03 2.07 82 17

0.59 <2 <0.12 0.27 <0.1 0.14 9.37 271 26

0.59 <1 <0.06 15.5 <0.05 <0.03 1.99 1,190 79

<0.20 <1 <0.06 16.7 <0.05 <0.03 3.03 1,052 58

<0.20 <1 <0.06 5.07 <0.05 <0.03 2.23 513 42

0.25 <1 <0.06 13.3 <0.05 <0.03 1.90 559 55

0.31 <1 <0.06 10.1 <0.05 <0.03 7.19 437 135

0.34 <1 <0.06 16.3 <0.05 <0.03 4.85 831 99

22 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 6. Results for concentrations of trace metals from samples collected from the McHenry County Groundwater Monitoring

Network wells, 4 National Water-Quality Assessment wells, and 2 surface-water sites in McHenry County, Illinois, 2020.—Continued

[Data available from U.S. Geological Survey, 2020b. µg/L, microgram per liter; <, less than reporting level; E, estimated; IL, Illinois; —, no data]

Field identifier

Aluminum

(µg/L)

Barium

(µg/L)

Beryllium

(µg/L)

Cadmium

(µg/L)

Chromium

(µg/L)

Iron

(µg/L)

Manganese

(µg/L)

Molybdenum

(µg/L)

43N8E–8.2c <6 38.3 <0.02 <0.06 <1 <10 0.5 0.37

45N7E–32.4d <3 43.4 <0.01 <0.03 0.6 <10 63.3 3.55

43N8E–3.7d <6 175 <0.02 <0.06 <1 2,479 78.3 1.97

44N9E–20.7c <6 85.0 <0.02 <0.06 <1 13 113 2.01

Nippersink Creek

Near Spring Grove,

IL <3 55.9 <0.01 <0.03 <0.5 <10 18.7 1.18

Fox River at

Huntley Road at

Carpentersville, IL 3.9 53.0 <0.01 <0.03 <0.5 <10 1.6 1.52

Kishwaukee River at

Marengo, IL

— — — — — — — —

The release of CECs to the environment is a growing concern

because of the potential to cause adverse eects in humans and

other nontargeted organisms (Kolpin and others, 2002), and

the use of pharmaceuticals has increased by 2.8 percent since

2015 (Martin and others, 2019; Centers for Disease Control

and Prevention, 2021). The most commonly prescribed

medications include analgesics, antihyperlipidemic agents,

and dermatological agents (Centers for Disease Control and

Prevention, 2021). WICs are a general category for anthro-

pogenically derived chemicals that include some pharma-

ceuticals, pesticides, and some volatile organic compounds

all quantied in parts per billion (micrograms per liter).

Pharmaceuticals were analyzed in parts per trillion (nanograms

per liter) and include the most commonly used prescription

drugs for antibiotics, opioids, diabetes, anti-inammatories,

and high blood pressure and cholesterol (statins) medication.

Atrazine is also used as an antihistamine and is referred to in

the results as “pharmaceutical atrazine,” and thiabendazole is

an antiworm medication (Drugs.com, 2021; WebMD, 2021).

In 2020, a subset consisting of 12 monitoring wells and

3 surface-water sites was sampled and analyzed for CECs,

including pharmaceuticals, pesticides, and WICs. Chloride-

bromide ratio analyses completed in Gahala (2017) identied

wells that plotted near the sewage mixing curve or indicated

a mix of sewage and dilute road salt. Monitoring wells with

chloride-bromide ratio results in 2010 that plotted near the

sewage mixing curve or mixture of sewage and dilute road

salt were HEBR–09–03, 15–COR–I, 10–MAR–S, 9–MCH–S,

MARN–09–01, 8–GRN–I, HARV–09–01, 4–RCH–S, and

HEBR–08–02. Designated background wells were selected

based on their chloride-bromide ratio plotting near high road

salt mixing curves (7–HRT–S) or within the dilute ground-

water range or with no clear proximity towards a particular

mixing curve (8–GRN–D and WOOD–08–01).

A total of 172 CECs were analyzed for in the ground-

water monitoring wells, and only 5 percent of the CECs were

detected in either low or estimated concentrations, indicating

a lack of widespread presence of CECs in the shallow ground-

water resource and supporting the overall good quality of the

shallow groundwater resource (

table 8). A total of 9 CECs

were detected at low concentrations in groundwater samples

from 8 of the 12 (about 66 percent) monitoring wells (g. 9;

table 8); however, 3 of the 9 CECs also were detected in at

least 1 blank QAQC sample (appendix 1, table 1.2; Gahala

and Gruhn, 2022). These CECs are formatted in bold italics

and agged as a potential but not veried detection (

table 8).

The most common uses of the pharmaceuticals are provided

in the parentheses in

table 8 and were obtained from search-

ing the database available at

ht tps://www. drugs.com/ (Drugs.

com, 2021

). Of the 111 pharmaceuticals analyzed, 2 (2 per-

cent) pharmaceuticals were detected in groundwater samples;

caeine was detected in 1 well and nicotine was detected in

6 wells (table 8). Of the 61 WICs analyzed, 7 (about 11 per-

cent) were detected in ve groundwater samples, 10–MAR–S

and 9–MCH–S had detections of 2 WICs. A total of three

WIC detections are agged because they also were detected

in at least one blank QAQC sample (

appendix 1, table 1.2;

Gahala and Gruhn, 2022). N,N-Diethyl-m-toluamide (com-

monly known as DEET) was detected in every groundwater

sample and surface-water sample, including all the QAQC

samples (

appendix 1, table 1.2; Gahala and Gruhn, 2022). This

compound was removed from the results tables and discus-

sions because of its ubiquitous detection and questionable

source. The low level and often estimated concentrations not

only indicate the vulnerability of groundwater with respect

to sewage and septic euents but also highlight the potential

capacity of the aquifer to degrade or mitigate some of the

detected CECs.

2020 Water Quality 23

Table 6. Results for concentrations of trace metals from samples collected from the McHenry County Groundwater Monitoring

Network wells, 4 National Water-Quality Assessment wells, and 2 surface-water sites in McHenry County, Illinois, 2020.—Continued

[Data available from U.S. Geological Survey, 2020b. µg/L, microgram per liter; <, less than reporting level; E, estimated; IL, Illinois; —, no data]

Nickel

(µg/L)

Silver

(µg/L)

Antimony

(µg/L)

Arsenic

(µg/L)

Selenium

(µg/L)

Uranium

(µg/L)

Lithium

(µg/L)

Strontium

(µg/L)

Boron

(µg/L)

E1.06 <2 <0.12 <0.20 0.50 0.41 6.21 107 35

E2.08 <1 <0.06 0.17 <0.05 1.55 6.79 84 33

<0.20 <2 <0.12 0.53 <0.1 0.36 10.87 175 161

E3.23 <2 <0.12 <0.20 0.18 1.50 9.72 156 28

E1.77 <1 0.12 1.52 0.32 0.85 2.70 146 38

E1.14 <1 0.23 1.63 0.19 0.60 3.11 278 43

— — — — — — — — —

Nickel concentrations near the method report limit are qualied because similar concentrations were detected in the equipment and eld blanks (appendix 1).

Italicized values are unrelated to the laboratory designated estimated values.

The surface-water sampling and analysis of CECs pro-

vide a general indication of the presence of CECs at locations

downstream from multiple or specic wastewater-treatment

discharges. The results are based on a single sample collec-

tion at three surface-water sites and do not constitute a robust

analysis of the sources, range in concentrations, seasonal-

ity, and persistence. Of the 172 CECs analyzed, 35 (about

20 percent) CECs were detected in at least 1 surface-water

sample and 18 were detected at all 3 surface-water sites. Of

the 111 pharmaceuticals analyzed, 20 were detected in the

surface-water samples, including the pharmaceutical atrazine.

Of the 61 WICs analyzed, 15 were detected in surface-water

samples, including the pesticide atrazine (table 8). Surface

waters indicated the highest concentrations and most frequent

detection of CECs. These locations were selected based on

proximity to wastewater-treatment plant euent, and the

detections highlight the limits of the treatment systems.

The analytical methods for pharmaceutical compounds,

in nanograms per liter, and WICs, in micrograms per liter,

naturally create high variability in the quantied results of

detections. For detailed discussion of the groundwater QAQC

results, refer to

appendix 1. The groundwater results discussed

consider only the constituents that were detected at low or

estimated quantities in the sample or replicate and omit con-

sideration or discussion of constituents detected in the blank

samples. No equipment blanks were collected for the surface-

water sample collection. Surface-water results are considered

acceptable for discussion of general presence and frequency of

detections among the three samples.

Pharmaceuticals are used by individuals for health

reasons and include over-the-counter medication such as

aspirin and pseudoephedrine, and medications prescribed

by a physician such as Lipitor, albuterol, amoxicillin, and

many others (

U.S. Environmental Protection Agency, 2009b).

Most ingested pharmaceuticals are not fully metabolized,

so parts are excreted in human waste. Metabolized and

unmetabolized pharmaceuticals are discharged in domes-

tic sewage (

U.S. Environmental Protection Agency, 2009b;

U.S. Geological Survey, 2021a, b). Carbamazepine is an anti-

convulsant used to prevent and control seizures (Drugs.com,

2021

) and was detected (2.9 nanograms per liter [ng/L]) in the

replicate sample from 9–MCH–S, but was not detected in the

primary environmental sample (

appendix 1, table 1.2; Gahala

and Gruhn, 2022). Caeine was detected in HEBR–09–03,

estimated at 5.5 ng/L. Pharmaceutical atrazine was detected

in the replicate of 10–MAR–S at 5.03 ng/L (appendix 1,

table 1.2; Gahala and Gruhn, 2022) but was not detected in the

environmental sample at 10–MAR–S. Nicotine was detected

at low and estimated concentrations in 50 percent (6 out of 12)

of the groundwater samples. The number of CEC detections in

the MCGMN are shown in

gure 9.

Fox River and Kishwaukee River had the greatest number

of pharmaceuticals detected (18 in each), whereas Nippersink

Creek had 16 pharmaceutical detections. The highest con-

centrations detected in the three surface-water sites were for

methylbenzotriazole, hexamethylenetetramine, fexofenadine,

metformin, sulfamethoxazole, carbamazepine, and caeine.

The Kishwaukee River had the higher detections of lido-

caine, methocarbamol, tramadol, metoprolol, venlafaxine,

famotidine, and desvenlafaxine than the other two surface

water sites. Nippersink Creek had higher concentrations of

atrazine, cotinine, and acetaminophen than the Fox River or

Kishwaukee River. Of the 13 pharmaceuticals detected in all

3 surface-water samples, concentrations were generally high-

est in Fox River and Kishwaukee River.

24 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

WISCONSIN

ILLINOIS

BOONE CO

MC HENRY CO

DE KALB CO

MC HENRY CO

KANE CO

MC HENRY CO

LAKE CO

WALWORTH CO

MC HENRY CO

Fox Lake

Spring

Grove

Richmond

Hebron

Harvard

Pistakee

Highlands

Ringwood

Wonder

Lake

Greenwood

Johnsburg

Lakemoor

McCullom

Lake

McHenry

Woodstock

Bull Valley

Holiday

Hills

Prairie

Grove

Island

Lake

Marengo

Oakwood

Hills

Fox River

Valley

Gardens

Lakewood

Union

Cary

Huntley

Lake

in the

Hills

Fox

River

Grove

Trout Valley

Algonquin

Barrington

Hills

Hampshire

Carpentersville

Crystal

Lake

44N9E–20.7c

WOOD–08–01

HARV–09–01

HEBR–08–01

HEBR–08–02

HEBR–09–03

MARN–09–01

MARN

–

MARN

–

MARN

–

MHEN–08–01

WAUC–02–12

WAUC–08–13

14–RIL–S

17–ALG–D

17–ALG–S

10–MAR–S

9–MCH–D

9–MCH–S

8–GRN–I

8–GRN–D

1–CHE–D

1–CHE–S

3–HEB–I

43N8E–8.2c

43N8E–3.7d

45N7E–32.4d

NW–6–45–9

HUNT–09–03HUNT–09–03

MARS–09–01

–

SEN

–

SEN

–

GRF

–

GRF

–

COR

–

COR

–

COR

–

–NUN–

7–HRT–

4–RCH–S

4–RCH–

88°10'88°20'88°30'88°40'

42°30'

42°20'

42°10'

0 5 MILES1 2 3 4

0 5 KILOMETERS1 2 3 4

EXPLANATION

City or town and identifier

Monitoring well arsenic concentration,

in micrograms per liter, and identifier

Less than 0.2

0.2 to 10

Greater than 10

14–RIL–S14–RIL–S

1–CHE–D

Marengo

1–CHE–S

[D, deep; I, intermediate; S, shallow]

Base from U.S. Geological Survey 1:100,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 33˚ N. and 45˚ N.

Central meridian 89˚ W.

North American Datum of 1983

Figure 6. Distribution of arsenic concentrations in the McHenry County Groundwater Monitoring Network wells and the National

Water-Quality Assessment monitoring wells, McHenry County, Illinois, 2020.

2020 Water Quality 25

WISCONSIN

ILLINOIS

BOONE CO

MC HENRY CO

DE KALB CO

MC HENRY CO

KANE CO

MC HENRY CO

LAKE CO

WALWORTH CO

MC HENRY CO

Fox Lake

Spring

Grove

Richmond

Hebron

Harvard

Pistakee

Highlands

Ringwood

Wonder

Lake

Greenwood

Johnsburg

Lakemoor

McCullom

Lake

McHenry

Woodstock

Bull Valley

Holiday

Hills

Prairie

Grove

Island

Lake

Marengo

Oakwood

Hills

Fox River

Valley

Gardens

Lakewood

Union

Cary

Huntley

Lake

in the

Hills

Fox

River

Grove

Trout Valley

Algonquin

Barrington

Hills

Hampshire

Carpentersville

Crystal

Lake

44N9E–20.7c

WOOD–08–01

HARV–09–01

HEBR–08–01

HEBR–08–02

HEBR–09–03

MARN–09–01

MARN

–

MARN

–

MARN

–

MHEN–08–01

WAUC–02–12

WAUC–08–13

14–RIL–S

17–ALG–D

17–ALG–S

10–MAR–S

9–MCH–D

9–MCH–S

8–GRN–I

8–GRN–D

1–CHE–D

1–CHE–S

3–HEB–I

43N8E–8.2c

43N8E–3.7d

45N7E–32.4d

NW–6–45–9

HUNT–09–03HUNT–09–03

MARS–09–01

–

SEN

–

SEN

–

GRF

–

GRF

–

COR

–

COR

–

COR

–

–NUN–

7–HRT–

4–RCH–S

4–RCH–

88°10'88°20'88°30'88°40'

42°30'

42°20'

42°10'

0 5 MILES1 2 3 4

0 5 KILOMETERS1 2 3 4

EXPLANATION

[D, deep; I, intermediate; S, shallow]

City or town and identifier

Monitoring well total iron concentration,

in milligrams per liter, and identifier

Less than 10

10 to 300

301 to 1,800

Greater than 1,800

14-RIL-S14-RIL-S

1-CHE-D

Marengo

44N9E–20.7c

7-HRT

-D

Base from U.S. Geological Survey 1:100,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 33˚ N. and 45˚ N.

Central meridian 89˚ W.

North American Datum of 1983

Figure 7. Distribution of iron concentrations in the McHenry County Groundwater Monitoring Network wells and the National

Water-Quality Assessment monitoring wells, McHenry County, Illinois, 2020.

26 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

WISCONSIN

ILLINOIS

BOONE CO

MC HENRY CO

DE KALB CO

MC HENRY CO

KANE CO

MC HENRY CO

LAKE CO

WALWORTH CO

MC HENRY CO

Fox Lake

Spring

Grove

Richmond

Hebron

Harvard

Pistakee

Highlands

Ringwood

Wonder

Lake

Greenwood

Johnsburg

Lakemoor

McCullom

Lake

McHenry

Woodstock

Bull Valley

Holiday

Hills

Prairie

Grove

Island

Lake

Marengo

Oakwood

Hills

Fox River

Valley

Gardens

Lakewood

Union

Cary

Huntley

Lake

in the

Hills

Fox

River

Grove

Trout Valley

Algonquin

Barrington

Hills

Hampshire

Carpentersville

Crystal

Lake

44N9E

–

20.7c

WOOD–08–01

HARV

–

HEBR–08–01

HEBR

–

HEBR–09–03

MARN–09–01

MARN

–

MARN

–

MARN

–

MHEN

–

WAUC–02–12

WAUC–08–13

14–RIL–S

17–ALG–D

17–ALG–S

10–MAR–S

9–MCH–D

9–MCH–S

–

GRN

–

GRN

–

1–CHE–D

–

CHE

–

3–HEB–I

43N8E–8.2c

43N8E

–

3.7d

45N7E

–

32.4d

–

HUNT–09–03

MARS–09–01

–

SEN

–

SEN

–

GRF

–

GRF

–

15–COR–S

–

COR

–

COR

–

–NUN–

–

HRT

–S

7–HRT–

4–RCH–S

4–RCH–

88°10'88°20'88°30'88°40'

42°30'

42°20'

42°10'

0 5 MILES1 2 3 4

0 5 KILOMETERS1 2 3 4

EXPLANATION

City or town and identifier

Monitoring well manganese concentration,

in micrograms per liter, and identifier

0 to 50.00

50.01 to 300

Greater than 300

14–RIL–S14–RIL–S

1–CHE–D

Marengo

–

ALG

–

[D, deep; I, intermediate; S, shallow]

Base from U.S. Geological Survey 1:100,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 33˚ N. and 45˚ N.

Central meridian 89˚ W.

North American Datum of 1983

Figure 8. Distribution of manganese concentrations in the McHenry County Groundwater Monitoring Network wells and the National

Water-Quality Assessment monitoring wells, McHenry County, Illinois, 2020.

2020 Water Quality 27

Table 7. Results for concentrations of nutrients from samples collected from the McHenry County Groundwater Monitoring Network

wells, 4 National Water-Quality Assessment wells, and 2 surface-water sites in McHenry County, Illinois, 2020.

[Data available from U.S. Geological Survey, 2020b. mg/L, milligram per liter; N, nitrogen; NO

, nitrate; NO

, nitrite; P, phosphorus; <, less than; U, nondetect;

M, detect; IL, Illinois; —, no data]

Field identifier

Nitrate (NO

+ NO

)

(mg/L as N)

Nitrite

(mg/L as N)

Orthophosphate

(mg/L as P)

Ammonia

(mg/L as N)

Hydrogen sulfide

(sniff test)

14–RIL–S 4.74 0.005 <0.004 <0.05 U

HUNT–09–03 <0.04 0.001 0.096 0.80 U

16–GRF–I <0.04 <0.001 0.017 0.77 U

16–GRF–D <0.04 0.006 0.011 1.01 M

17–ALG–S 1.57 0.027 0.009 0.37 U

17–ALG–D <0.04 <0.001 0.007 0.57 U

MARS–09–01 <0.04 <0.001 0.008 1.49 U

15–COR–S <0.04 <0.001 0.012 0.22 M

15–COR–I <0.04 <0.001 0.012 0.24 U

15–COR–D <0.04 <0.001 0.025 0.24 M

10–MAR–S 1.52 0.054 <0.004 0.02 U

WAUC–02–12 <0.04 <0.001 0.012 0.58 M

11–SEN–I <0.04 <0.001 0.005 0.17 U

11–SEN–D <0.04 <0.001 0.008 1.11 U

MARN–09–02 <0.04 <0.001 0.023 1.54 U

WOOD–08–01 <0.04 0.001 0.027 1.04 M

13–NUN–I <0.04 <0.001 0.011 0.32 U

13–NUN–D <0.04 <0.001 0.015 0.26 M

WAUC–08–13 <0.04 <0.001 0.014 0.16 M

MHEN–08–01 <0.04 <0.001 0.004 0.11 U

MARN–09–01 <0.04 <0.001 0.035 0.76 U

7–HRT–S <0.04 0.001 0.008 0.09 U

7–HRT–I <0.04 <0.001 0.009 0.78 U

7–HRT–D <0.04 <0.001 0.011 0.98 M

9–MCH–S 5.33 <0.001 <0.004 <0.01 U

9–MCH–D <0.04 <0.001 0.141 1.55 M

8–GRN–I <0.04 <0.001 0.005 0.09 U

8–GRN–D <0.04 <0.001 0.005 0.09 M

HEBR–08–02 <0.04 <0.001 0.004 0.07 U

HARV–09–01 <0.04 <0.001 0.016 0.02 M

NW–6–45–9 0.16 0.007 0.005 0.03 U

1–CHE–S <0.04 0.002 0.005 0.11 U

1–CHE–D <0.04 <0.001 0.008 1.84 M

HEBR–09–03 <0.04 <0.001 0.004 0.04 M

4–RCH–S 0.08 0.003 0.014 0.4 U

4–RCH–I <0.04 <0.001 0.073 0.95 U

4–RCH–D <0.04 <0.001 0.026 0.71 U

HEBR–08–01 <0.04 0.001 0.059 0.53 U

3–HEB–I <0.04 <0.001 0.017 1.1 M

MARN–10–03 <0.04 <0.001 0.056 0.89 M

MARN–10–04 <0.04 0.001 0.047 2.04 U

28 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 7. Results for concentrations of nutrients from samples collected from the McHenry County Groundwater Monitoring Network

wells, 4 National Water-Quality Assessment wells, and 2 surface-water sites in McHenry County, Illinois, 2020.—Continued

[Data available from U.S. Geological Survey, 2020b. mg/L, milligram per liter; N, nitrogen; NO

, nitrate; NO

, nitrite; P, phosphorus; <, less than; U, nondetect;

M, detect; IL, Illinois; —, no data]

Field identifier

Nitrate (NO

+ NO

)

(mg/L as N)

Nitrite

(mg/L as N)

Orthophosphate

(mg/L as P)

Ammonia

(mg/L as N)

Hydrogen sulfide

(sniff test)

43N8E–8.2c 2.47 0.001 0.010 0.01 U

45N7E–32.4d <0.04 <0.001 0.004 <0.05 U

43N8E–3.7d <0.04 <0.001 0.007 0.04 U

44N9E–20.7c 0.13 0.004 0.008 <0.01 U

Nippersink Creek Near Spring

Grove, IL 1.96 0.036 1.992 <0.01

—

Fox River at Huntley Road at

Carpentersville, IL

<0.04 <0.001 <0.004 <0.01 —

Kishwaukee River at Marengo, IL — — — — —

Wastewater indicators are chemical compounds that

indicate the presence of domestic and industrial waste in

water sources such as streams and aquifers (

U.S. Geological

Survey, 2021b). Domestic WICs include caeine and cotinine

(a byproduct of nicotine metabolism in the liver; Bradley

and others, 2007). Industrial wastewater indicators include

compounds used in plastic components, surfactant metabo-

lites, re retardants, and many others (Tomasek and oth-

ers, 2012). Several WICs were detected in the groundwater

samples from the MCGMN, and many more were detected

in surface-water samples from Nippersink Creek, Fox River,

and the Kishwaukee River. The following paragraphs discuss

the results of WICs that are classied as “organic other” and

do not fall under the pharmaceutical or pesticide/herbicide

categories discussed in the previous sections.

FYROL FR 2 (0.05 µg/L) was detected in the groundwa-

ter at 10–MAR–S and is a common additive ame retardant

in commercially used exible and rigid polyurethane foams

(Chemical Book, 2021

). Indole (0.08 µg/L) was detected in

the groundwater at 8–GRN–D and has many uses (cleaning

agent, food additive, veterinary drug, fragrance, and more;

PubChem, 2021a). A common food additive and fragrance

(PubChem, 2021b

), 2,6-Dimethylnapththalene (0.01 µg/L),

was detected in the groundwater at HEBR–09–03.

Detections of WICs in surface water were most frequent

and at greater concentrations in the Fox River but were gener-

ally ubiquitous in all three surface-water locations (

table 8).

WICs (organics/other, not including pesticides) detected

in samples from all three surface-water locations include

β-sitosterol (cosmetics, detergent, veterinary drug; PubChem,

2021c) and diethyl phthalate (plasticizer, solvent, household

products, and more; PubChem, 2021d). No endocrine disrupt-

ing compounds such as 4-nonylphenols were detected at con-

centrations greater than reporting level in any of the surface-

water samples. Endocrine disrupting compounds are known to

cause various hormone and reproductive eects on aquatic life

(

U.S. Environmental Protection Agency, 2022b).

Pesticides are chemicals used to prevent, destroy, or

repel living organisms from where they are not wanted

(

U.S. Environmental Protection Agency, 2009b). Pesticides are

frequently used to increase crop yields and improve the quality

of the crops; however, they can be transported to groundwater

and surface water (U.S. Geological Survey, 1999, 2021a).

Results for pesticide analyses are presented in

table 8.

Four pesticides (prometon, atrazine, metolachlor,

and pentachlorophenol) were detected in the water sam-

ples collected in 2020. Prometon is an herbicide used to

control the emergence of most annual and many peren-

nial broadleaf weeds and grasses in nonagricultural areas

(

U.S. Environmental Protection Agency, 1990). Prometon was

detected in 9–MCH–S (estimated 0.04 ng/L; table 8) and also

was detected in the associated replicate sample (0.04 ng/L;

table 1.2). No detections of prometon were in the surface-

water samples.

Atrazine is a common and widely used herbicide that can

be applied before and after planting to control broadleaf and

grassy weeds (

U.S. Environmental Protection Agency, 2021a).

Atrazine is used primarily in agriculture, but to a lesser extent,

it is sometimes used on residential lawns and golf courses

(

U.S. Environmental Protection Agency, 2021a). As indicated

table 8, atrazine also can be used as antianxiety medica-

tion; therefore, atrazine has two results, the pharmaceutical

method analyzed concentrations in parts per trillion (nano-

grams per liter), and the WIC analysis measured concentra-

tions in parts per billion (micrograms per liter). Atrazine was

not detected in any environmental samples from groundwater

wells, although it was detected in the replicate sample for 9–

MCH–S (3.29 µg/L) and the replicate sample for 10–MAR–S

at the parts per trillion concentration of 5.03 ng/L (table 1.2).

This inconsistency in detection between the parts per billion

and parts per trillion concentrations and between the envi-

ronmental and replicate samples highlights the variability of

Statistical Comparison 29

detections at these low levels with the laboratory methods

applied as described in the “Methods of Study” section and

detailed in the cited references.

All three surface-water sites had detections for atrazine

(table 8). Atrazine was highest in Nippersink Creek with a

concentration of 299 ng/L, as detected with the pharmaceuti-

cal method, and also was detected at 0.31 µg/L (315 ng/L)

with the WIC analytical method. Consistent concentrations

of atrazine between the pharmaceutical analysis and WIC

analytical method also were noted for the Fox River and

Kishwaukee River. Metolachlor is a broad-spectrum herbicide

used for general weed control in numerous agricultural crops,

lawns and turf, ornamental plants, trees, shrubs, right of ways,

fence and hedge rows, and in forestry (U.S. Environmental

Protection Agency, 1995). Metolachlor was not detected in

any of the groundwater wells, although it was detected at all

surface-water sites. One surface-water site (Fox River) had

a detection for pentachlorophenol (estimated 0.13 μg/L), but

no other detections of this pesticide were in surface water or

groundwater.

Suitability of Water for Drinking

The largest concern for causing negative eects to

the quality of groundwater as a source of drinking water is

for arsenic, iron, manganese, and dissolved solids, which

are naturally occurring in the sand and gravel aquifers in

McHenry County (table 3). The MCL of 10 µg/L for arsenic

was exceeded in about 24 percent of the wells, and chronic

ingestion of arsenic in exceedance of the MCL has been

linked to increased risk of lung, bladder, skin, liver, kid-

ney, and prostate cancer (U.S. Environmental Protection

Agency, 2018; table 3). Manganese, which can cause toxic-

ity to the nervous system, has a health-based drinking water

advisory of 300 µg/L, and that was exceeded at one loca-

tion (U.S. Environmental Protection Agency, 2018; table 3).

Aesthetically, the SMCL of 500 mg/L for dissolved solids was

exceeded at 13 locations (about 29 percent). Dissolved solids

in exceedance of the SMCL can cause objectionable taste and,

at concentrations greater than 1,000 mg/L, can have laxative

eects (U.S. Environmental Protection Agency, 2018; table 3).

Two sites had dissolved solids concentrations that exceeded

1,000 mg/L (4–RCH–S and 43N8E–3.7d) (table 5). Aside

from health concerns, the main concern with most of these

constituents is that treatment would be needed to prevent dam-

age to infrastructure and staining of household appliances and

laundry. Another major concern for drinking water is nutrient

concentrations, especially nitrate and nitrite, which have an

MCL of 10 mg/L and 1 mg/L, respectively. No exceedances of

the MCL were measured for either nitrate or nitrite. In general,

the groundwater in McHenry County is suitable for drinking

water, and some of the aesthetic issues could be mitigated

with home water-treatment systems such as water softeners.

The concentrations of many of these constituents could also

be reduced with an at-home water-treatment system such as a

carbon ltration, ion-exchange systems, and reverse-osmosis

systems (Thomas and Eckberg, 2015).

The implications of low concentrations of CECs in

surface water on drinking water and aquatic life are unknown,

and it is important to reiterate that these results are a single

sample at three sites and do not constitute a robust understand-

ing of the distribution and persistence of these CECs. These

pharmaceuticals, pesticides, and low concentrations of WICs

are potentially ingested by consumers of stream-sourced

drinking water and aquatic biota within the streams (Wilson

and others, 2011). In a study by Benson and others (2017),

the potential long-term toxicity of CECs to humans for the

most frequently detected and highest concentrations of WICs

and pharmaceuticals were quantied with a risk-assessment

analysis. The study concluded that the exposure to these

CECs is not likely to pose a public health concern; however,

additional toxicity data would be helpful to improve the

calculated risks (Benson and others, 2017). Also, studies have

determined that many of these CECs may degrade naturally in

the streams (Bradley and others, 2007) whereas others persist

miles downstream (Barber and others, 2013), including some

of the contaminants detected in this study (sulfamethoxazole

and carbamazepine). The persistence, seasonality, sources, and

range in concentrations and eects of CECs in surface water

were not investigated as part of this study. Frequent testing by

water-treatment facilities provides the data on exposure levels

and baseline understanding for potential eects.

Comparison to 2010 Water-Quality

Results

The following sections compare the 2020 water-quality

results to the baseline results of 2010. Dierences in water

quality on the decadal time scale were evaluated with the

WSR test (Helsel, 2012) to identify statistically signicant

dierences. Shifts in chloride to bromide ratio plots also are

evaluated to identify potential changes in water quality.

Statistical Comparison

The results of the WSR to assess changes in the water-

quality results between 2010 and 2020 indicated a few statisti-

cally signicant dierences between the two sampling events

(table 9). Dierences were statistically signicant among

all wells for concentrations of aluminum, ammonia, arsenic,

barium, bromide, calcium, magnesium, molybdenum, ortho-

phosphate, silica, specic conductance, sulfate, and dissolved

solids. Statistically signicant dierences (p-value of less than

[<] 0.05) were calculated among shallow (20.3–58.7 ft below

ground surface), intermediate (62.3–120.6 ft below ground

surface), or deep (139–344.4 ft below ground surface) aquifer

30 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 8. Concentrations of pharmaceuticals and wastewater indicator compounds detected in samples collected from selected wells

within the McHenry County Groundwater Monitoring Network and three surface-water sites in McHenry County, Illinois, 2020.

[Data available from U.S. Geological Survey, 2020b. Bold values are detections greater than the detection or reporting level. Bold italic values had a detection

in one or more blank quality assurance and quality control samples. CEC, contaminant of emerging concern; Pharm, pharmaceuticals; ng/L, nanogram per liter;

<, less than the reporting level; E, estimated; WIC, wastewater indicator compound; µg/L, microgram per liter; HHCB, Hexahydrohexamethyl cyclopentabenzo-

pyran; TBEP, Tris(2-butoxyethyl) phosphate]

CEC type Constituent Units 15–COR–I 10–MAR–S WOOD–08–01 MARN–09–01 7–HRT–S

Pharm Hexamethylenetetramine (urinary antiseptic) ng/L <110 <110 <110 <110 <110

Pharm Guanylurea (metformin transformation product) ng/L <140 <140 <140 <140 <140

Pharm Gabapentin (anticonvulsant) ng/L <160 <160 <160 <160 <160

Pharm Acetaminophen (pain relief) ng/L <20 <20 <20 <20 <20

Pharm Caeine (stimulant) ng/L <91 <91 <91 <91 <91

Pharm Carbamazepine (anticonvulsant) ng/L <11 <11 <11 <11 <11

Pharm Cotinine (nicotine metabolite) ng/L <6.4 <6.4 <6.4 <6.4 <6.4

Pharm Sulfamethoxazole (antibiotic) ng/L <20 <20 <20 <20 <20

Pharm Lidocaine (skin conditions) ng/L <8 <8 <8 <8 <8

Pharm Triamterene (diuretic) ng/L <5.2 <5.2 <5.2 <5.2 <5.2

Pharm Metformin (antidiabetic) ng/L <20 <20 <20 <20 <20

Pharm Nicotine (stimulant) ng/L <80 <80

E35.3 E35.2 E36.5

Pharm Methocarbamol (muscle relaxant) ng/L <20 <20 <20 <20 <20

Pharm Fexofenadine (antihistamine) ng/L <44 <44 <44 <44 <44

Pharm Methylbenzotriazole (corrosion inhibitors) ng/L <80 <80

<80 <80 <80

Pharm Tramadol (pain relief) ng/L <7.4 <7.4 <7.4 <7.4 <7.4

Pharm Metoprolol (cardiac) ng/L <10 <10 <10 <10 <10

Pharm Venlafaxine (antidepressant) ng/L <5.2 <5.2 <5.2 <5.2 <5.2

Pharm Famotidine (gastric) ng/L <34 <34 <34 <34 <34

Pharm Desvenlafaxine (antidepressant) ng/L <84 <84 <84 <84 <84

Pharm (pesticide) Atrazine (antianxiety)

ng/L <20 <20 <20 <20 <20

WIC (pesticide) Atrazine (pesticide)

µg/L <0.16 <0.16 <0.16 <0.16 <0.16

WIC Diethyl phthalate µg/L <0.4

0.11

<0.4 <0.4 <0.4

WIC Fluoranthene µg/L <0.02 <0.02 <0.02 <0.02 <0.02

WIC Isophorone µg/L <0.05 <0.05 <0.05 <0.05 <0.05

WIC Phenanthrene µg/L <0.02 <0.02 <0.02 <0.02 <0.02

WIC FYROL FR 2 µg/L <0.32

0.05

<1.92 <0.32 <1.92

WIC Triclosan µg/L <0.32 <0.32 <0.32 <0.32 <0.32

WIC β-Stigmastanol µg/L <3.4 <3.4 <3.4 <3.4 <3.4

WIC 2,6-Dimethylnaphthalene µg/L <0.04 <0.04 <0.04 <0.04 <0.04

WIC 9,10-Anthraquinone µg/L <0.04 <0.04 <0.04 <0.04 <0.04

WIC

β-Sitosterol µg/L <4.8 <4.8 <4.8 <4.8 <4.8

WIC Cholesterol µg/L <1.6 <1.6 <1.6 <1.6 <1.6

WIC HHCB µg/L <0.04 <0.04 <0.04 <0.04 <0.04

WIC Indole µg/L <0.04 <0.04 <0.04 <0.04 <0.04

WIC TBEP µg/L <0.64 <0.64 <1.92 <0.64 <1.92

WIC Triethyl citrate µg/L <0.16 <0.16 <0.16

E0.05

<0.16

WIC Triphenyl phosphate µg/L <0.08 <0.08 <0.08 <0.08 <0.08

WIC (pesticide) Pentachlorophenol µg/L <1.6 <1.6 <1.6 <1.6 <1.6

WIC (pesticide) Prometon µg/L <0.16 <0.16 <0.16 <0.16 <0.16

WIC (pesticide) Metolachlor µg/L <0.04 <0.04 <0.04 <0.04 <0.04

Statistical Comparison 31

Table 8. Concentrations of pharmaceuticals and wastewater indicator compounds detected in samples collected from selected

wells within the McHenry County Groundwater Monitoring Network and three surface-water sites in McHenry County, Illinois, 2020.—

Continued

[Data available from U.S. Geological Survey, 2020b. Bold values are detections greater than the detection or reporting level. Bold italic values had a detection

in one or more blank quality assurance and quality control samples. CEC, contaminant of emerging concern; Pharm, pharmaceuticals; ng/L, nanogram per liter;

<, less than the reporting level; E, estimated; WIC, wastewater indicator compound; µg/L, microgram per liter; HHCB, Hexahydrohexamethyl cyclopentabenzo-

pyran; TBEP, Tris(2-butoxyethyl) phosphate]

9–MCH–S 8–GRN–I 8–GRN–D HEBR–08–02 HARV–09–01 HEBR–09–03 4–RCH–S

Nippersink

Creek

Fox River

Kishwaukee

River

<110 <110 <110 <110 <110 <110 <110

E14 E212 E35.1

<140 <140 <140 <140 <140 <140 <140

29 32 171

<160 <160 <160 <160 <160 <160 <160 <160

53 36.5

<20 <20 <20 <20 <20 <20 <20

E22.8

<20 <20

<91 <91 <91 <91 <91

E5.5

<91

E24.5 E24 E12.4

<11 <11 <11 <11 <11 <11 <11

4.85 9 6.5

<6.4 <6.4 <6.4 <6.4 <6.4 <6.4 <6.4

4.36

<6.4 <6.4

<20 <20 <20 <20 <20 <20 <20

E13.10 E32 E25.3

<8 <8 <8 <8 <8 <8 <8

6.24 17 30.4

<5.2 <5.2 <5.2 <5.2 <5.2 <5.2 <5.2

0.98 3.6 3.4

<20 <20 <20 <20 <20 <20 <20

33.8 64.1 59.6

23.2 E38.5 E38.6

<80 <80 <80 <80 <80 <80 <80

<20 <20

<20 <20 <20 <20 <20

17.8 9.9 19.6

<44 <44 <44 <44 <44 <44 <44

E20.31 E70.8 E65.3

<80 <80 <80 <80 <80 <80 <80

E38.1 E113 E28.3

<7.4 <7.4 <7.4 <7.4 <7.4 <7.4 <7.4 <7.4

6.2 10.7

<10 <10 <10 <10 <10 <10 <10 <10

6.4 18.1

<5.2 <5.2 <5.2 <5.2 <5.2 <5.2 <5.2

3.76 3.8 13.2

<34 <34 <34 <34 <34 <34 <34 <34

E9.8 E12.5

<84 <84 <84 <84 <84 <84 <84

E8.01 E9.7 E30.7

<20 <20 <20 <20 <20 <20 <20

299 159 84.9

<0.16 <0.16 <0.16 <0.16 <0.16 <0.16 <0.16

0.31 0.16 0.13

<0.4 <0.4 <0.4 <0.4 <0.4 <0.4 <0.4

0.17 0.12 0.29

<0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02 <0.02

0.05 0.01

<0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05

0.02

<0.05

<0.02 <0.02 <0.02 <0.02 <0.02 <0.02

<0.02 <0.02

0.02 0.02

<0.32 <0.32 <0.32 <0.32 <1.92 <0.32 <0.32 <1.92 <1.92 <1.92

<0.32 <0.32 <0.32 <0.32 <0.32 <0.32 <0.32 <0.32

E0.06

<0.32

<3.4 <3.4 <3.4 <3.4 <3.4 <3.4 <3.4 <3.4

E0.47 E0.45

<0.04 <0.04 <0.04 <0.04 <0.04

0.01

<0.04 <0.04 <0.04 <0.04

<0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04

E0.03

<0.04

<4.8 <4.8 <4.8 <4.8 <4.8 <4.8 <4.8

E0.66 E0.84 E0.58

E0.09

<1.6 <1.6 <1.6 <1.92 <1.6 <1.6 <1.92 <1.92 <1.92

<0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04

0.02

<0.04

0.07

<0.04 <0.04

0.08

<0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04

<0.64 <0.64 <0.64 <0.64 <1.92 <0.64 <0.64

E0.95 E0.71

<1.92

<0.16 <0.16 <0.16 <0.16 <0.16 <0.16 <0.16 <0.16 <0.16

E0.13

<0.08 <0.08 <0.08 <0.08 <0.08 <0.08 <0.08 <0.08 <0.08

0.04

<2.56 <1.6 <1.6 <1.6 <1.6 <1.6 <1.6 <1.6

E0.13

<1.6

E0.04

<0.16 <0.16 <0.16 <0.16 <0.16 <0.16 <0.16 <0.16 <0.16

<0.04 <0.04 <0.04 <0.04 <0.04 <0.04 <0.04

0.36 0.12

0.09

Common use of pharmaceutical from Drugs.com, 2021.

32 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

WISCONSIN

ILLINOIS

BOONE CO

MC HENRY CO

DE KALB CO

MC HENRY CO

KANE CO

MC HENRY CO

LAKE CO

WALWORTH CO

MC HENRY CO

Fox Lake

Spring

Grove

Richmond

Hebron

Harvard

Pistakee

Highlands

Ringwood

Wonder

Lake

Greenwood

Johnsburg

Lakemoor

McCullom

Lake

McHenry

Woodstock

Bull Valley

Holiday

Hills

Prairie

Grove

Island

Lake

Marengo

Oakwood

Hills

Fox River

Valley

Gardens

Lakewood

Union

Cary

Huntley

Lake

in the

Hills

Fox

River

Grove

Trout Valley

Algonquin

Barrington

Hills

Hampshire

Carpentersville

Crystal

Lake

WOOD

–

HARV–09–01

HEBR

–

HEBR

–

MARN–09–01

–

MAR

–

MCH

–

15–COR–I

–

HRT

–S

–

RCH

–

8–GRN–I

8–GRN–D

88°10'88°20'88°30'88°40'

42°30'

42°20'

42°10'

0 5 MILES1 2 3 4

0 5 KILOMETERS1 2 3 4

EXPLANATION

[D, deep; I, intermediate; S, shallow]

9–MCH–S

8–GRN–D

City or town and identifier

Number of detections of contaminants of

emerging concern in monitoring

wells and identifier

8–GRN–I8–GRN–I

Marengo

15–COR–I

Base from U.S. Geological Survey 1:100,000-scale digital data

Albers Equal-Area Conic projection

Standard parallels 33˚ N. and 45˚ N.

Central meridian 89˚ W.

North American Datum of 1983

Figure 9. Number of detections for pharmaceuticals, pesticides, and wastewater indicator compounds in the McHenry County

Groundwater Monitoring Network wells and four National Water-Quality Assessment monitoring wells, McHenry County, Illinois, 2020.

Statistical Comparison 33

groups between the 2010 and 2020 water-quality results.

Statistically signicant dierences were noted for aluminum

(deep), arsenic (shallow), barium (deep and intermediate),

calcium (deep and intermediate), magnesium (deep and inter-

mediate), manganese (intermediate), molybdenum (deep and

intermediate), orthophosphate (deep and shallow), and silica

(deep and intermediate) (table 9). In gure 10, a change plot

shows pairs of linked points that are the two samples collected

in 2010 and 2020 for a given well. If both samples for a given

well were censored, the lower value was recensored to the

higher value. If only one of the samples was uncensored but

less than the other sample’s reporting level, the uncensored

value was censored to match the censored sample. These

“within pair” recensored values were only computed and used

for plotting; they were not used in the statistical analyses.

Censored values are indicated with open circles. Whether the

change between 2010 and 2020 was downward, upward, or the

same (common when both values were censored) is indicated

by the color of the points and line.

Increases generally were detected in the intermediate

and deep parts of the sand and gravel aquifer, and decreases

were generally detected in the shallow part of the sand and

gravel aquifer (g. 10). The mixed distribution of increases

and decreases among the various constituents and aquifer-

depth groups could be reecting dissolution and mobility of

some of the redox sensitive constituents and dilution of some

constituents in the shallow aquifer depths. These dierences

may be attributed to a combination of stable population of the

past decade (2010–20), to land-use management practices,

or potentially to the recent wet years of 2017 through 2019

causing a dilution of the major ions in the shallow parts of the

aquifer.

The descriptive statistics and a trilinear Piper diagram

(Piper, 1944; g. 11A, B) also were reviewed to identify rela-

tive changes in the range and average of selected constituents

of interest. A slight shift was seen in the anions in the Haeger-

Beverly Unit (shallow aquifer) between 2010 and 2020 with a

decrease in sulfate and chloride (g. 11A). The trilinear Piper

diagram for all other wells in the network indicates overall

consistency in concentrations of major ions from 2010 to 2020

(g. 11B). The minimum, median, and maximum for selected

constituents for 2010 and 2020 are listed in table 9. Only

calcium, magnesium, and silica indicated a slight increase in

minimum, median, and maximum concentrations.

34 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 9. Summary statistics (minimum, maximum, and median) for selected constituents, results of the Wilcoxon signed-rank test for groundwater-quality changes between

2010 and 2020 for uncensored data and the paired Prentice-Wilcoxon test for uncensored data, and evaluation of differences between the 2010 and 2020 aquifer-depth groups of

shallow, intermediate, and deep parts of the sand and gravel aquifers in McHenry County, Illinois.

[Bold denotes statistically signicant; p-value, probability value; µg/L, microgram per liter; <, less than reporting level; PPW, paired Prentice-Wilcoxon test; —, no data or not applicable; mg/L, milligram per

liter; N, nitrogen; WSR, Wilcoxon signed-rank test; µS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent Year

Number of

censored

Percent

censored

Minimum Median Maximum Test type

p-value for

all wells

Deep wells

p-value

Intermediate

wells p-value

Shallow wells,

p-value

Aluminum, µg/L 2010 27 63 <1.7 <1.7 38.9 PPW

0.0456 0.0462

— —

Aluminum, µg/L 2020 43 100 <3 <3 <6 — — — — —

Ammonia and ammonium,

mg/L as N

2010 4 9 <0.01 0.28 1.88 PPW

0.0432

0.3054 0.7778 0.4971

Ammonia and ammonium,

mg/L as N

2020 5 12 <0.01 0.26 1.84 — — — — —

Arsenic, µg/L 2010 0 0 0.15 0.88 62 PPW

0.0013

0.1637 0.5869

0.0471

Arsenic, µg/L 2020 3 7 <0.12 0.58 70.3 — — — — —

Barium, µg/L 2010 0 0 40.1 89.6 239 WSR

<0.0001 0.003 0.0424

0.0745

Barium, µg/L 2020 0 0 32.9 78.4 207 — — — — —

Bromide, mg/L 2010 0 0 0.013 0.039 0.119 PPW

0.0014

0.1796 0.1035 0.1796

Bromide, mg/L 2020 4 9 <0.011 0.032 0.254 — — — — —

Calcium, mg/L 2010 0 0 38.4 85.1 176 WSR

0.0247 0.0036 0.0447

0.1685

Calcium, mg/L 2020 0 0 41.8 88.1 184 — — — — —

Chloride, mg/L 2010 0 0 0.49 15.2 521 WSR 0.6814 0.1641 0.1712 0.1641

Chloride, mg/L 2020 0 0 0.55 17.2 517 — — — — —

Inorganic nitrogen

(nitrate and nitrite),

mg/L

2010 36 84 <0.02 <0.02 10 PPW 0.2646 — 0.3359 0.3359

Inorganic nitrogen

(nitrate and nitrite),

mg/L

2020 35 81 <0.04 <0.04 5.33 — — — — —

Iron, µg/L 2010 0 0 4.9 1,480 3,450 PPW 0.0551 0.2967 0.1755 0.3017

Iron, µg/L 2020 5 12 <10 1,630 3,480 — — — — —

Magnesium, mg/L 2010 0 0 25.9 43.3 83.9 WSR

0.0026 0.003 0.0105

0.2207

Magnesium, mg/L 2020 0 0 27.8 45.2 95 — — — — —

Manganese, µg/L 2010 0 0 0.45 30.2 667 WSR 0.0504 0.1264

0.0423

0.5076

Manganese, µg/L 2020 0 0 0.5 28.8 740 — — — — —

Molybdenum, µg/L 2010 0 0 0.388 2 33.8 WSR

0.0001 0.003 0.0345

0.2026

Molybdenum, µg/L 2020 0 0 0.297 1.65 6.04 — — — — —

Statistical Comparison 35

Table 9. Summary statistics (minimum, maximum, and median) for selected constituents, results of the Wilcoxon signed-rank test for groundwater-quality changes between

2010 and 2020 for uncensored data and the paired Prentice-Wilcoxon test for uncensored data, and evaluation of differences between the 2010 and 2020 aquifer-depth groups of

shallow, intermediate, and deep parts of the sand and gravel aquifers in McHenry County, Illinois.—Continued

liter; N, nitrogen; WSR, Wilcoxon signed-rank test; µS/cm, microsiemens per centimeter at 25 degrees Celsius]

Constituent Year

Number of

censored

Percent

censored

Minimum Median Maximum Test type

p-value for

all wells

Deep wells

p-value

Intermediate

wells p-value

Shallow wells,

p-value

Orthophosphate, mg/L 2010 0 0 0.02 0.067 0.468 PPW

<0.0001 0.003

0.099

0.0071

Orthophosphate, mg/L 2020 3 7 <0.012 0.028 0.433 — — — — —

Potassium, mg/L 2010 0 0 0.78 1.63 7.15 WSR 0.1801 0.6477 0.6873 0.2778

Potassium, mg/L 2020 0 0 0.83 1.53 8 — — — — —

Silica, mg/L 2010 0 0 8 18.2 23.6 WSR

<0.0001 0.0015 0.0012

0.7595

Silica, mg/L 2020 0 0 8.8 19.9 25.3 — — — — —

Sodium, mg/L 2010 0 0 3.87 11.6 181 WSR 0.9182 0.6669 1 0.6669

Sodium, mg/L 2020 0 0 4.33 13.8 180 — — — — —

Specic conductance,

µS/cm

2010 0 0 512 754 2,260 WSR

0.0179

0.297 0.3341 0.2235

Specic conductance,

µS/cm

2020 0 0 488 724 2,340 — — — — —

Sulfate, mg/L 2010 4 9 <0.09 37.2 117 PPW

0.0071

0.1394 0.1341 0.1394

Sulfate, mg/L 2020 0 0 0.03 34 97.7 — — — — —

Dissolved solids, mg/L 2010 0 0 285 465 1,220 WSR

0.0015

0.1117 0.1418 0.1117

Dissolved solids, mg/L 2020 0 0 272 419 1,360 — — — — —

36 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

500

1,000

0.1

0.2

0.3

0.4

120

500

1,000

1,500

2,000

200

400

600

2020

Deep ShallowInter.

2010

2020

2010

2020

2010

2020

Deep ShallowInter.

2010

2020

2010

2020

2010

2020

Deep ShallowInter.

2010

2020

2010

2020

2010

Aluminum, in µg/L

Ammonia, in mg/L

Arsenic, in µg/L

Barium, in µg/L

Bromide, in mg/L

Calcium, in mg/L

Chloride, in mg/L

Iron, in µg/L

Magnesium, in mg/L

Manganese, in µg/L

Molybdenum, in µg/L

2.5

5.0

7.5

10.0

Nitrate plus nitrite, in mg/L

Phosphate, in mg/L

Potassium, in mg/L

Silica, in mg/L

100

150

2020

Deep ShallowInter.

2010

2020

2010

2020

2010

Sodium, in mg/L

Specific conductance, in

microsiemens per centimeter

at 25 degrees Celsius

Sulfate, in mg/L

Dissolved solids, in mg/L

0.05

0.10

0.15

0.20

0.25

100

150

0.5

1.0

1.5

100

200

300

400

500

100

150

200

1,000

2,000

3,000

[Inter., intermediate; mg/L, milligram per liter; µg/L, microgram per liter]

EXPLANATION

Blue background indicates

change plot is statistically

significant (probability

value less than 0.05)

Direction of change

Down

Same

Censored value

False

True

Year and aquifer depth group

Figure 10. Differences in the shallow, intermediate, and deep parts of the sand and gravel aquifers for concentrations of selected

constituents between 2010 and 2020 for water-quality samples in McHenry County, Illinois.

Statistical Comparison 37

100

Calcium

Chloride + fluoride

Sodium + potassium

Magnesium

Sulfate + chloride

Calcium + magnesium

Bicarbonate

Sulfate

EXPLANATION

Haeger-Beverly unit

2010

2020

PERCENT

Figure 11. Major ions in wells from 2010 and 2020 in McHenry County, Illinois. A, wells completed in the Haeger-Beverly Unit;

B, all other wells in the network.

38 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

100

Calcium

Chloride + fluoride

Sodium + potassium

Magnesium

Sulfate + chloride

Calcium + magnesium

Bicarbonate

Sulfate

EXPLANATION

All other wells in

the network

2010

2020

PERCENT

Figure 11. Major ions in wells from 2010 and 2020 in McHenry County, Illinois. A, wells completed in the Haeger-Beverly Unit;

B, all other wells in the network.—Continued

Comparison of Chloride to Bromide

Ratios

The methods for chloride-bromide ratio analyses used in

Gahala (2017) were repeated for the 2020 samples. Bromide

is a conservative ion (similar to chloride) that can be depos-

ited from precipitation and inltrate into groundwater (Davis

and others, 1998) or dissolved from sedimentary rock such

as carbonates, shale, and evaporites (Salameh and others,

2016). Concentrations of bromide in groundwater are usually

40–8,000 times less than concentrations of chloride, so small

changes in the mass of bromide produce large variations in

the ratios of chloride to bromide, which can help trace the

source of the chloride (Davis and others, 1998; Gahala, 2017).

The 2020 sample results were used, and the chloride-bromide

ratios were plotted on the same graph as the source binary

mixing curves to evaluate sources aecting water quality

and assess any changes in water quality at each monitor-

ing well since 2010 (

gs. 12 and 13). The proximity of the

Comparison of Chloride to Bromide Ratios 39

plotted chloride-bromide ratio to the source-mixing curve

indicates the potential source for the chloride in the surround-

ing groundwater. Chloride-bromide ratios were estimated for

monitoring wells with bromide concentrations less than the

reporting level (<0.020 mg/L) by halving the reporting level

(0.01) to estimate a point on the curve. Plot points for 17–

ALG–S, 7–HRT–I, 4–RCH–I, and 45N7E–32.4d are estimated

and do not plot on any curves but plot to the left of the curves.

In general, the 2020 chloride-bromide ratios plotted simi-

larly to where they plotted in 2010, indicating the source of

the chloride had not changed. CECs identied in 10–MAR–S,

MARN–09–01, 9–MCH–S, 8–GRN–D, and HEBR–09–03

are consistent with the source water identied in the chloride-

bromide ratio analysis. A few locations did indicate shifts

toward a specic binary-mixing curve, and these locations

are discussed in this section (

g. 13). The chloride-bromide

100

1,000

10,000

0.1 1 10 100 1,000 10,000 100,000

Chloride-bromide ratio

Chloride, in milligrams per liter

EXPLANATION

Animal waste

Brine

Dilute groundwater and potassium chloride

Dilute groundwater and road salt, high

Dilute groundwater and road salt

Dilute groundwater and sewage, low

Dilute groundwater and water softener

Sewage

Sewage and road salt, high

Sewage and road salt, low

Chloride source Well

14–RIL–S

44N9E–20.7c

17–ALG–D

43N8E–8.2c

MARS–09–01

15–COR–S

15–COR–I

15–COR–D

43N8E–3.7d

10–MAR–S

WAUC–02–12

11–SEN–I

11–SEN–D

MARN–09–02

WOOD–08–01

13–NUN–I

13–NUN–D

WAUC–08–13

45N7E–32.4d

MHEN–08–01

MARN–09–01

7–HRT–S

7–HRT–I

7–HRT–D

9–MCH–S

9–MCH–D

8–GRN–I

8–GRN–D

HEBR–08–02

HARV–09–01

NW–6–45–9

1–CHE–S

1–CHE–D

HEBR–09–03

4–RCH–S

4–RCH–I

4–RCH–D

HEBR–08–01

3–HEB–I

HUNT–09–03

16–GRF–I

16–GRF–D

17–ALG–S

Figure 12. Chloride-bromide ratio plotted against chloride concentrations in the McHenry County Groundwater Monitoring Network

wells and the National Water-Quality Assessment monitoring wells, McHenry County, Illinois, 2020.

40 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

100

1,000

10,000

0.1 1 10 100 1,000 10,000 100,000

Chloride-bromide ratio

Chloride, in milligrams per liter

EXPLANATION

Animal waste

Brine

Dilute groundwater and potassium

chloride

Dilute groundwater and road salt, high

Dilute groundwater and road salt

Dilute groundwater and sewage, low

Dilute groundwater and water

softener

Sewage

Sewage and road salt, high

Sewage and road salt, low

Chloride source

Well

17–ALG–D

MARS–09–01

43N8E–3.7d

WAUC–02–12

11–SEN–I

MARN–09–01

7–HRT–D

HARV–09–01

Figure 13. Chloride-bromide ratio plotted against chloride concentration for wells that show shifts between 2010 and 2020 in

the McHenry County Groundwater Monitoring Network wells and the National Water-Quality Assessment monitoring wells,

McHenry County, Illinois, 2020.

ratio analysis for monitoring well 11–SEN–I indicated a shift

from the dilute groundwater and sewage (low) mixing curve to

plotting close to the sewage mixing curve (

g. 13). Monitoring

wells 11–SEN–I and 11–SEN–D are near a septic eld for

a municipal building. Chloride and sulfate concentrations

slightly increased since 2010 in 11–SEN–I. Increased sulfate

concentrations could be indicative of increased microbial

activity, possibly from sewage (

table 5). Chloride concentra-

tions increased at 11–SEN–I from 8.53 to 20.7 mg/L, and sul-

fate concentrations increased from 45.9 to 56.8 mg/L (Gahala,

2017;

table 5). The shift more towards the sewage mixing

curve may be indicative of ongoing and potentially increasing

septic-eld eect at this location.

Monitoring well HARV–09–01 shifted from near the

sewage source curve in 2010 towards the dilute groundwater

and water-softener curve in 2020. Other constituents, such

as alkalinity, pH, nutrients, major ions, and metals, were

reviewed to observe if any changes were consistent with this

change. In general, no dierences were statistically signicant

despite there being slight decreases in nutrient concentra-

tions and slight increases in iron concentrations. This well

also was sampled and analyzed for CECs in 2020 because it

previously plotted near the sewage mixing curve. The results

of the CEC analyses were all less than the reporting level,

indicating sewage is not likely aecting the groundwater

quality at HARV–09–01. The shift to another source curve

could be highlighting the uncertainty of the chloride-bromide

ratio analysis, or the source of the groundwater at this location

could be from a mixture of sources; future sampling events

may clarify this result.

The chloride-bromide ratios for 17–ALG–D shifted from

plotting on the dilute groundwater and potassium chloride

curve to plotting on the sewage curve. The surroundings of

this well are split between agriculture and urban land (Gahala,

2017). A few other constituents that either increased or

decreased (not signicantly) could explain the shift from the

Summary 41

dilute groundwater and potassium chloride curve to the sew-

age curve. Manganese nearly doubled in concentrations from

6 to 11.4 mg/L, magnesium increased from 28.6 to 36.4 mg/L,

sulfate decreased from 3.28 to 0.24 mg/L, and sodium

decreased from 49.4 to 28.3 mg/L (Gahala, 2017; tables 5

and 6). Nutrients such as ammonia and orthophosphate also

decreased. This well is a candidate for future sampling for

CECs to monitor for any continued changes or eects.

NAWQA monitoring well 43N8E–3.7d shifted from

between the dilute groundwater and water softener and the

sewage and road salt (high) curves in 2010 to nearly on the

curve for the sewage and road salt (low) mixing curve in 2020.

Chloride concentrations increased from 149 mg/L in 2010

to 517 mg/L in 2020, sodium concentrations increased from

57.3 mg/L in 2010 to 170 mg/L in 2020, and bromide con-

centrations increased from 0.061 mg/L in 2010 to 0.254 mg/L

in 2020 (Gahala, 2017; table 5). Other constituents also have

changed with increases in sodium, iron, manganese, magne-

sium, potassium, barium, and dissolved solids, all of which

indicate a potential eect on water quality and subsequent

shift in geochemistry. This well is in an urban area and could

receive anthropogenic eects from leaky sewers and road salt

inltration. Previous investigations that analyzed for vola-

tile organic compounds did not indicate detectable levels of

contaminants.

MARN–09–01 shifted from between the curves of sew-

age and dilute groundwater and potassium chloride in 2010

to nearly on the curve for the dilute groundwater and water-

softener curve in 2020. Few constituents indicated increases

in concentrations except for chloride, calcium, sulfate, and

iron, which were slight increases. The land use surround-

ing MARN–09–01 is agriculture and urban (Gahala, 2017).

This well also was selected for analysis of CECs because the

orthophosphate detected in this well in 2010 was the high-

est of any of the other wells sampled that year. The 2020

orthophosphate results indicated a reduction from 0.152 mg/L

in 2010 to 0.035 mg/L in 2020 (table 7). It was previously

concluded that this well may have been under the eect of a

previous septic eld from a former house near the monitor-

ing well (Gahala, 2017). The CEC analysis detected nicotine

(estimated 35.2 ng/L; table 8). The compound triethyl citrate

was detected, but this compound was detected in the equip-

ment blank (associated with 10–MAR–S); therefore, it is a

suspected detection but not conrmed (appendix 1, table 1.2;

Gahala and Gruhn, 2022). Nicotine is a likely detection

because this constituent was not detected in eld blanks or

equipment blanks. The source of the chloride in 2010 plot-

ted near the sewage mixing curve, but in 2020, the source is

indicated as being aected by water softeners. In either case,

an anthropogenic source of the chloride is implicated.

Summary

McHenry County, Illinois, obtains most its drinking water

from the shallow sand and gravel aquifers (groundwater).

To evaluate this groundwater resource, the U.S. Geological

Survey collected water-quality samples from 41 of the

42 monitoring wells in the McHenry County Groundwater

Monitoring Network, 4 monitoring wells from the National

Water-Quality Assessment program, and 2 surface-water

sites for analysis of nutrients, major ions, and trace metals.

Additionally, a subset of 12 monitoring wells and 3 surface-

water sites was sampled and analyzed for contaminants of

emerging concern (CECs). The 2020 results were summarized

and compared to the 2010 water-quality data to identify any

dierences in the water quality of the sand and gravel aquifers

in McHenry County, Illinois, which is the primary source of

drinking water.

Health-based benchmarks were exceeded for arsenic

(about 24 percent; 11 of 45 monitoring wells), sodium (40 per-

cent, 18 of 45), and manganese (about 2 percent, 1 of 45).

Aesthetically based benchmarks were exceeded for dissolved

solids (about 29 percent, 13 of 45), chloride (about 4 percent,

2 of 45), iron (about 87 percent, 39 of 45), and manganese

(about 29 percent, 13 of 45). CECs were detected at low or

estimated concentrations in 8 of the 12 (about 67 percent)

monitoring wells analyzed.

In addition to sampling the groundwater monitoring

wells, three surface-water-quality monitoring sites also were

sampled and analyzed for pharmaceuticals and wastewater

indicator compounds to provide a preliminary assessment

of the presence of CECs in the surface waters. CECs were

detected in all three of the surface-water-quality monitoring

samples collected, and wastewater indicator compounds were

more prevalent and more frequently detected than pharma-

ceutical compounds. These results provided a cursory under-

standing of the presence of CECs in surface waters and do not

constitute a robust analysis of sources, seasonality, range of

concentrations, persistence, or eects.

The 2020 groundwater-quality results had measurements

of eld properties and concentrations of major ions, trace

metals, and nutrients that were consistent with 2010 results

with statistically signicant increases for calcium, magnesium,

and silica and decreases for aluminum, ammonia, arsenic,

barium, bromide, calcium, molybdenum, phosphate, specic

conductance, sulfate, and dissolved solids. Increases generally

were detected in the intermediate and deep parts of the sand

and gravel aquifer, and decreases were detected in the shallow

part of the sand and gravel aquifers. The mixed distribution

of increases and decreases among the various constituents

and aquifer-depth groups could be reecting dissolution and

42 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

mobility of some of the redox sensitive constituents and dilu-

tion of some constituents in the shallow aquifer depths. These

changes may be attributed to a combination of stable popula-

tion of the past decade (2010–20), to land-use management

practices, and to the recent wet years of 2017 through 2019

causing a dilution of the major ions in the shallow parts of

the aquifer.

In addition to comparing the 2020 water-quality data to

the 2010 data, an analysis for the source of chloride ions in

the groundwater was completed by applying the 2020 chlo-

ride and bromide concentrations to the chloride-bromide ratio

analysis. The results indicate the sources of chloride remained

similar to 2010, where many of the chloride concentrations

in the groundwater are from road salt applications. A few of

the wells indicated some shift from road salt towards sewage

or from sewage towards road salt. The change in potential

sources may indicate a change in the mixture of sources within

that part of the aquifer.

A total of 172 CECs were analyzed for in the ground-

water monitoring wells, and only 5 percent of the CECs were

detected in low or estimated concentrations, indicating a lack

of widespread presence of CECs and supporting the overall

good quality of the shallow groundwater resource. CECs were

identied in about 66 percent (8 of 12) of the monitoring wells

sampled and in all 3 surface-water samples. CECs identied

in 10–MAR–S, MARN–09–01, 9–MCH–S, 8–GRN–D, and

HEBR–09–03 are consistent with the source water identied

in the chloride-bromide ratio analysis. The low level and often

estimated concentrations not only indicate the vulnerability of

groundwater with respect to sewage and septic euents but

also highlight the potential capacity of the aquifer to degrade

or mitigate some the detected CECs. Surface waters indicated

the highest concentrations and most frequent detection of

CECs. These locations were selected based on proximity to

wastewater-treatment plant euent, and the detections high-

light the limits of the treatment systems.

The suitability of the groundwater for drinking water is

generally good; however, some naturally occurring miner-

als, such as arsenic, manganese, and iron, would likely need

some ltration or treatment system to reduce the potential

toxicity (arsenic) and taste objections (iron and manganese).

The suitability of surface water for drinking water is gener-

ally good. However, the longer-term eects of chronically low

concentrations of CECs are unknown and the sources, range of

concentration, and persistence of the CECs would benet from

additional studies.

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48 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Appendix 1. Quality Assurance and Quality Control of Water-Quality Results

Quality Assurance and Quality Control

for Major Ions, Nutrients, Metals, and

Trace Elements

Quality assurance and quality control (QAQC) of the

water-quality results were completed by collecting blank (eld

and equipment) and replicate (duplication of the environ-

mental sample for analysis of variability) samples about once

per week during the sampling period between June and July

of 2020 to evaluate variability and control bias in analytical

results (table 1.1; Gahala and Gruhn, 2022). One equipment

blank was collected for each sampling pump type before any

eld sampling. A total of four eld equipment blanks were

collected following the decontamination procedures, three

for the analysis of nutrients, major ions, and metals and one

for the analysis of pharmaceuticals and wastewater indicator

compounds (WICs). A total of ve replicate samples were col-

lected to verify the laboratory results: two for nutrients, major

ions, and metals/trace elements; one for pharmaceuticals and

WICs; one for pharmaceuticals; and one for WICs.

Pre-eld equipment blanks were collected before any

eld use or mobilization. Pumps and associated tubing were

washed with liquid Alconox solution, rinsed with tap water,

and rinsed a third time with de-ionized water. Inorganic blank

water was then passed through the pumps and tubing and

the lter, and blank samples were collected in their respec-

tive prelabeled sample bottles, preserved with nitric acid,

and placed in an ice-bath cooler and sent overnight to the

U.S. Geological Survey National Water Quality Laboratory in

Denver, Colorado, for analysis. Field blanks were collected to

test for the quality of decontamination procedures. Field blank

samples were collected in a similar manner after the collec-

tion of the environmental and replicate samples, following the

decontamination procedures and addition of a new lter for

ltered samples.

The pre-eld equipment blank from the Fultz pump

detected low concentrations of several constituents. Cobalt,

copper, lead, nickel, zinc, antimony, and bromide were

detected at low concentrations but were within the range

of concentrations detected in the environmental samples.

Calcium, uoride, silica, barium, and strontium also had some

low-level detections but were below the range of concentra-

tions detected in the environmental samples. Subsequent

eld rinse equipment blanks from the Fultz pump did not

have detections greater than the reporting level for lead, and

antimony, and therefore, the environmental sample results

are considered acceptable. One eld-rinse equipment blank

sample (7–HRT–D) detected bromide just above the report-

ing limits (less than [<] 0.010 and <0.020) of 0.011 mg/L and

is within the range of some of the environmental samples.

This detection could be attributed to the uctuating reporting

limit for many of the results and may increase the uncertainty

of concentrations less than 0.020 mg/L. It is possible that the

initial pre-eld equipment blank had remnant tap water and

(or) de-ionized water inadvertently collected in the samples.

Equipment blanks from the Grundfos pump detected many of

the same constituents as detected in the Fultz pump, and there-

fore, detections of some of these constituents with similar low

concentrations in the environmental samples for 17–ALG–D

and WAUC–02–12 collected with the Grundfos are estimated.

These detections within the blanks, regardless of the pump,

indicate the source is potentially from tubing or laboratory

interference or tap/de-ionized rinse water. Of the three eld

blanks, low-level detections were noted for several constitu-

ents, including many of the same constituents detected in the

blank samples. Except for copper, cobalt, and zinc, no other

detections were within the range of the concentrations detected

in the environmental samples. Results with detections in the

pre-eld equipment blanks and eld blanks are estimated.

Statistical analyses for cobalt, copper, nickel, and zinc were

not evaluated (table 1.1).

Replicate samples were collected to assess the reproduc-

ibility of the sample-collection procedures and laboratory

analysis to provide a measure of variability. Replicate samples

were collected immediately after the environmental sample.

Of the 34 comparisons between major ions, trace metals, and

nutrients analyzed, 4 constituents (orthophosphate, cobalt,

copper, and bromide) had dierences greater than 10 percent.

Cobalt and copper were routinely detected in blank samples

and are excluded from further analysis or considerations. The

dierences in orthophosphate greater than 10 percent were

because of low concentrations near the method detection level,

but the environmental results are reliable enough to determine

water types and would not alter the determination of whether a

constituent exceeded water-quality standards.

Bromide had larger variability in detected concentration

results (23- and 37-percent dierence) between replicates

and environmental samples. The replicate value for bromide

in 9-MCH–S was 0.036 microgram per liter (µg/L), and the

replicate chloride concentration was 123 milligrams per liter

(mg/L). The environmental sample for 9–MCH–S had a

detected bromide concentration of 0.057 µg/L and the chloride

concentration of 121 mg/L was consistent with the replicate

concentration. The dierences in detection of bromide concen-

tration aected where the environmental and replicate results

plotted on the chloride-bromide source curves. The 9–MCH–S

environmental sample chloride-bromide ratio plotted ambigu-

ously between the “sewage and road salt high curve” and

“dilute groundwater and softener” curves. Previous samples

from 2010 through 2015 showed 9–MCH–S chloride-bromide

Appendix 1. Quality Assurance and Quality Control of Water-Quality Results 49

Table 1.1. Chemical characteristics of selected quality-control samples collected in McHenry County, Illinois, June and July 2020.

[mg/L, milligram per liter; N, nitrogen; <, less than reporting level; NR, not reported; P, phosphorous; µg/L, microgram per liter; 180C, laboratory dissolved solids dried at 180 degrees Celsius; NA, not available]

Constituent

Field identifier

10–MAR–S WAUC–02–12 43N8E–8.2c

45N8E–17.7h1

(9–MCH–S)

45N6E–23.7d3

(7–HRT–D)

45N8E–17.7h1

(9–MCH–S)

45N6E–23.7d3

(7–HRT–D)

45N8E–17.7h1

(9–MCH–S)

45N6E–23.7d3

(7–HRT–D)

Sample type

Fultz pump

equipment

blank

Grundfos pump

equipment blank

Field blank Field blank Field blank Replicate Replicate

Environmental

sample

Environmental

sample

Sample date (month/day/year) and time

6/8/2020 13:30 6/29/2020 16:00 6/22/2020 16:00 7/20/2020 12:00 7/13/2020 11:30 7/20/2020 14:00 7/13/2020 11:30 7/20/2020 14:00 7/13/2020 11:30

Ammonia (mg/L as N) <0.01 0.01 <0.01 <0.01 <0.01 <0.01 1.01 <0.01 0.97

Nitrite (mg/L as N) <0.001 <0.001 <0.001 <0.001 <0.001 0.002 <0.001 <0.001 <0.001

Nitrate + nitrite (mg/L as N) <0.04 <0.04 0.12 <0.040 <0.04 5.42 <0.04 5.33 <0.04

Orthophosphate (mg/L as P) <0.004 <0.004 0.005 <0.004 <0.004 0.011 0.006 <0.004 0.011

Calcium (mg/L) 0.48 0.17 0.07 0.09 0.09 108 77.6 109 75.6

Magnesium (mg/L) <0.01 0.07 0.02 0.01 0.02 51.4 40.5 50.6 40.7

Sodium (mg/L) <0.4 0.45 <0.4 <0.4 <0.4 84.3 8.60 84.4 8.65

Potassium (mg/L) <0.30 <0.30 <0.30 <0.30 <0.30 2.02 1.27 1.84 1.35

Chloride (mg/L) <0.02 0.02 <0.02 <0.02 <0.02 123 3.52 121 3.53

Sulfate (mg/L) <0.02 0.045 <0.02 <0.02 <0.02 29.75 0.28 29.3 0.26

Fluoride 0.05 <0.01 <0.01 0.02 <0.01 0.14 0.32 0.15 0.30

Silica 0.09 <0.05 <0.05 0.05 <0.05 18.0 22.1 17.9 22.1

Arsenic (µg/L) <0.1 <0.1 <0.1 <0.1 <0.1 <0.2 9.96 0.21 9.72

Barium (µg/L) 2.06 2.25 3.59 2.8 3.15 62.4 44.5 62.2 44.6

Beryllium (µg/L) <0.01 <0.01 <0.01 <0.01 <0.01 <0.02 <0.01 <0.02 <0.01

Boron (µg/L) 2.0 <2.0 <2 <2 <2 64.6 39.9 64.1 40.5

Cadmium (µg/L) <0.03 <0.03 <0.03 <0.03 <0.03 <0.06 <0.03 <0.06 <0.03

Chromium (µg/L) <0.5 0.5 <0.5 <0.5 <0.5 <1 <0.5 <1 <0.5

Cobalt (µg/L) 0.32 0.074 <0.03 0.08 <0.03 0.09 0.1 0.081 0.09

Copper (µg/L) 1.9 6.1 10.4 3 3.8 4.2 0.7 5.3 0.4

Iron (mg/L) <10 <10 <10 <10 <10 <10 2,175 <10 2,176

Lead (µg/L) 0.06 <0.02 <0.02 0.03 <0.02 <0.04 <0.02 <0.04 <0.02

Manganese (µg/L) 0.93 0.28 <0.2 0.24 <0.2 0.93 17.5 0.91 17.3

Molybdenum (µg/L) <0.05 0.08 <0.05 <0.05 <0.05 0.63 0.97 0.65 0.97

Nickel (µg/L) 0.30 0.40 0.27 <0.20 0.20 0.60 <0.20 0.67 <0.20

Silver (µg/L) <1 <1 <1 <1 <1 <2 <1 <2 <1

Strontium (µg/L) 0.6 5.5 2.2 2.9 3.6 189 705 190 700

50 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 1.1. Chemical characteristics of selected quality-control samples collected in McHenry County, Illinois, June and July 2020.—Continued

Constituent

Field identifier

10–MAR–S WAUC–02–12 43N8E–8.2c

45N8E–17.7h1

(9–MCH–S)

45N6E–23.7d3

(7–HRT–D)

45N8E–17.7h1

(9–MCH–S)

45N6E–23.7d3

(7–HRT–D)

45N8E–17.7h1

(9–MCH–S)

45N6E–23.7d3

(7–HRT–D)

Sample type

Fultz pump

equipment

blank

Grundfos pump

equipment blank

Field blank Field blank Field blank Replicate Replicate

Environmental

sample

Environmental

sample

Sample date (month/day/year) and time

6/8/2020 13:30 6/29/2020 16:00 6/22/2020 16:00 7/20/2020 12:00 7/13/2020 11:30 7/20/2020 14:00 7/13/2020 11:30 7/20/2020 14:00 7/13/2020 11:30

Zinc (µg/L) 9.1 <2 4.3 3.9 2.1 <4 <2 <4 <2

Antimony (µg/L) 0.09 <0.06 <0.06 <0.06 <0.06 <0.12 <0.06 <0.12 <0.06

Aluminum (µg/L) <3 <3 <3 <3 <3 <6 <3 <6 <3

Lithium (µg/L) <0.15 <0.15 <0.15 <0.15 <0.15 3.34 2.46 3.37 2.44

Selenium (µg/L) <0.05 <0.05 <0.05 <0.05 <0.05 0.5 <0.05 0.48 <0.05

Uranium (µg/L) <0.03 <0.03 <0.03 <0.03 <0.03 0.89 <0.03 0.89 <0.03

Bromide mg/L 0.010 <0.010 <0.020 <0.010 0.011 0.036 0.027 0.057 0.022

Laboratory dissolved solids,

dry, 180C, (mg/L)

424 <26.8 <27.8 NA NA 684 360 676 NA

Appendix 1. Quality Assurance and Quality Control of Water-Quality Results 51

ratios plotting near and along the “sewage and road salt, high”

curve (Gahala, 2017). The 2020 environmental and replicate

chloride-bromide ratio results shifted the datapoints away

from the “sewage and road salt, high” curve towards and near

the “dilute groundwater and softener” curve. The environmen-

tal sample for 7–HRT–D plotted near the dilute groundwater

and sewage (low) curve, whereas the replicate was slightly

farther away from that curve and slightly closer to the 2010

data point where it was between the curves of dilute ground-

water and sewage (low) and the curve for brine within the

dilute range. The shift was not substantially dierent enough

to change the interpretation of the source.

Quality Assurance and Quality Control

for Contaminants of Emerging Concern

For the contaminants of emerging concern (CECs),

ve QAQC samples were collected (one eld blank, three

replicates [one full, one for only pharmaceuticals, and one

for only WICs], and one equipment blank). The Fultz pump

was the only pump used for the collection of samples for the

analysis of organic compounds (pharmaceuticals and WICs).

After the equipment decontamination steps of wash, tap water

rinse, and de-ionized water rinse, laboratory grade methanol

was run through the Fultz pump and tubing and followed by

certied organic blank water. After the methanol wash passed

through the tubing, the certied organic blank water was then

collected in the appropriate sample containers for the analysis

of pharmaceuticals and WICs. Samples collected for pharma-

ceutical analysis were ltered with a 25-millimeter disposable

lter. Field blank samples were collected in a similar man-

ner after the collection of the environmental and replicate

samples, following the decontamination procedures, and a new

25-millimeter lter was used. Samples were placed in an ice-

bath cooler and sent overnight to the National Water Quality

Laboratory for analysis. All detections, reported and estimated,

are presented in table 1.2.

Two replicate samples were collected for the analysis

of pharmaceuticals and WICs. Of the 155 comparisons for

pharmaceuticals and 74 comparisons for WICs, 8 dierences

were detected. Two constituents, prometon and nicotine, had

detections in the environmental sample and the replicate and

no detections in the equipment blank or eld blank. Other

constituents (atrazine, less than 0.16 nanogram per liter [ng/L];

carbamazepine, 2.9 ng/L) had detections in either the sample

or the replicate, but not both; and the remaining constituents

had detections in either the equipment blank or eld blank.

Based on these results, prometon, nicotine, atrazine, and car-

bamazepine are considered as likely detections in the ground-

water monitoring well samples.

Results from groundwater wells were variable, and some

detections in the QAQC samples were not detected in the pri-

mary environmental samples. This variability was represented

in the results of the analysis of the environmental sample and

the associated replicate QAQC samples where a detection in

one sample was not detected in the other in every instance. In

other words, a detection occurred in either the environmental

sample or the replicate sample, but not in both. This pattern

was detected in 9–MCH–S sample results for carbamaze-

pine and atrazine. Other types of QAQC samples (equipment

and eld blanks) also unexpectedly resulted in detections of

several CECs. This pattern could potentially be caused by

ineective de-ionization of water at the local laboratory where

equipment for sampling is cleaned and stored. If water was not

being completely de-ionized, some of these CECs were poten-

tially being detected in tap water that is not fully processed

through de-ionization. Nicotine was detected in six monitoring

wells, including the three hypothesized background monitor-

ing wells. Detections were less than the reporting level of

80 ng/L and ranged from 23.2 to 38.6 ng/L. Replicate results

for nicotine were less than 10-percent dierent (6 percent).

N,N-Diethyl-m-toluamide (DEET) also was detected in every

environmental sample and every QAQC sample despite

personnel adhering to eld sampling protocol of avoiding

the use of any repellent (or pharmaceutical and personal care

products). The cross contamination is suspected to be from the

laboratory machines and the ubiquitous and persistent nature

of DEET. The results for DEET are therefore not considered in

the tally of detections or any further discussion.

52 Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010

Table 1.2. Detections of contaminants of emerging concern in quality assurance and quality control samples.

[CEC, contaminant of emerging concern; pharm, pharmaceuticals; WIC, wastewater indicator compound; OOT, organics other; ng/L, nanogram per liter; E, estimated; <, less than reporting level; —, no data;

μg/L, microgram per liter; OPE, organics pesticides]

CEC type Group Constituent Units

10–MAR–S

equipment blank

10–MAR–S replicate

(pharm only)

7–HRT–S replicate

(WIC only)

9–MCH–S

replicate

9–MCH–S

field blank

Pharm OOT Hexamethylenetetramine ng/L E21.1 <110 — <110 <110

Pharm OOT Carbamazepine ng/L <11 <11 — 2.9 <20

Pharm OOT Nicotine ng/L <80 <80 — 24.6 <80

WIC OOT Diethyl phthalate µg/L <0.4 — <0.4 0.05 0.17

WIC OOT Phenanthrene µg/L 0.01 — <0.02 <0.02 0.02

WIC OOT Pyrene µg/L <0.02 — <0.02 <0.02 0.01

WIC OOT Naphthalene µg/L <0.02 — <0.02 <0.02 0.06

WIC OOT Bis(2-ethylhexyl) phthalate µg/L 1.9 — <3 <2 1.39

WIC OOT Cholesterol µg/L E0.13 — <1.9 <1.6 E0.08

WIC OOT 4-Nonylphenol (all Isomers) µg/L E0.15 — <1.6 <1.6 <1.6

WIC OOT Triethyl citrate µg/L E0.05 — <0.16 <0.16 <0.16

WIC OOT Isopropylbenzene µg/L E0.03 — <0.04 <0.04 E0.08

WIC OOT 1-Methylnaphthalene µg/L < 0.04 — <0.04 <0.04 0.01

WIC (pesticide) OPE

N,N-Diethyl-m-toluamide (DEET)

µg/L E0.14 — 0.04 0.06 0.17

WIC (pesticide) OPE Prometon ng/L <0.16 — <0.16 0.04 <0.16

WIC (pesticide) OOT Atrazine µg/L <0.16 — <0.16 3.29 <0.16

Pharm (pesticide) OPE Atrazine ng/L <0.16 5.03 <0.16 <0.16 <0.16

Appendix 1. Quality Assurance and Quality Control of Water-Quality Results 53

References Cited

Gahala, A.M., 2017, Hydrogeology and water quality of

sand and gravel aquifers in McHenry County, Illinois,

2009–14, and comparison to conditions in 1979 (ver.

1.1, August 2022): U.S. Geological Survey Scientic

Investigations Report 2017–5112, 91 p., accessed

August 26, 2022, at https://doi.org/ 10.3133/ sir20175112.

Gahala, A.M., and Gruhn, L.R., 2022, Quality-assurance and

quality-control data for discrete water-quality samples col-

lected in McHenry County, Illinois, 2020: U.S. Geological

Survey data release, https://doi.org/ 10.5066/ P9RBXV53.

For more information about this publication, contact:

Director, USGS Central Midwest Water Science Center

405 North Goodwin

Urbana, IL 61801

217–328–8747

For additional information, visit: h ttps://www .usgs.gov/

centers/ cm- water

Publishing support provided by the

Rolla Publishing Service Center

ISSN 2328-0328 (online)

https://doi.org/ 10.3133/ sir20225110

Gahala and others—Water Quality of Sand and Gravel Aquifers in McHenry County, Illinois, 2020 and Comparisons to Conditions in 2010—SIR 2022–5110