U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007–5228

Prepared as part of the 

National Water-Quality Assessment Program

Occurrence of Agricultural Chemicals in Shallow

Ground Water and the Unsaturated Zone, Northeast

Nebraska Glacial Till, 2002–04
Occurrence of Agricultural Chemicals in 

Shallow Ground Water and the Unsaturated 

Zone, Northeast Nebraska Glacial Till, 

2002–04

By Jennifer S. Stanton, Gregory V. Steele, and Jason R. Vogel

Prepared as part of the National Water-Quality Assessment Program

Scientific Investigations Report 2007–5228

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Stanton, J.S., Steele, G.V., and Vogel, J.R., 2007, Occurrence of agricultural chemicals in shallow ground water and 

the unsaturated zone, northeast Nebraska glacial till, 2002–04: U.S. Geological Survey Scientific Investigations 

Report 2007–5228, 51 p.

Front cover: (top left) Collecting water from monitoring well W–18, northeast Nebraska, to be processed in mobile 

laboratory. (bottom right) Developing a monitoring well in northeast Nebraska glacial till. Photographs by G.V. Steele, 

U.S. Geological Survey.

Back cover: (top left) Typical agricultural setting in northeast Nebraska glacial till looking northwest from Well D–26. 

(bottom right) Monitoring well and sample delivery line at the monitoring well. Photographs by G.V. Steele, U.S. 

Geological Survey.
iii

Foreword

The U.S. Geological Survey (USGS) is committed to serve the Nation with accurate and timely 

scientific information that helps enhance and protect the overall quality of life and facilitates 

effective management of water, biological, energy, and mineral resources (http://www.usgs.

gov/). Information on the quality of the Nation’s water resources is of critical interest to the 

USGS because it is so integrally linked to the long-term availability of water that is clean and 

safe for drinking and recreation and that is suitable for industry, irrigation, and habitat for fish 

and wildlife. Escalating population growth and increasing demands for multiple water uses 

make water availability, now measured in terms of quantity and quality, even more critical to the 

long-term sustainability of our communities and ecosystems.

The USGS implemented the National Water-Quality Assessment (NAWQA) Program to support 

national, regional, and local information needs and decisions related to water-quality management and policy (http://water.usgs.gov/nawqa/). Shaped by and coordinated with ongoing 

efforts of other Federal, State, and local agencies, the NAWQA Program is designed to answer: 

(1) What is the condition of our Nation’s streams and ground water? (2) How are the conditions changing over time? (3) How do natural features and human activities affect the quality 

of streams and ground water, and where are those effects most pronounced? By combining 

information on water chemistry, physical characteristics, stream habitat, and aquatic life, the 

NAWQA Program aims to provide science-based insights for current and emerging water issues 

and priorities. NAWQA results can contribute to informed decisions that result in practical and 

effective water-resource management and strategies that protect and restore water quality.

Since 1991, the NAWQA Program has implemented interdisciplinary assessments in more 

than 50 of the Nation’s most important river basins and aquifers, referred to as “study units” 

(http://water.usgs.gov/nawqa/nawqamap.html). Collectively, these “study units” account for 

more than 60 percent of the overall water use and population served by public water supply and 

are representative of the Nation’s major hydrologic landscapes, priority ecological resources, 

and agricultural, urban, and natural sources of contamination. 

Each assessment is guided by a nationally consistent study design and methods of sampling 

and analysis. The assessments thereby build local knowledge about water-quality issues and 

trends in a particular stream or aquifer while providing an understanding of how and why water 

quality varies regionally and nationally. The consistent, multiscale approach helps determine 

if certain types of water-quality issues are isolated or pervasive and allows direct comparisons 

of how human activities and natural processes affect water quality and ecological health in the 

Nation’s diverse geographic and environmental settings. Comprehensive assessments of pesticides, nutrients, trace metals, volatile organic compounds, and aquatic ecology are developed 

at the national scale through comparative analysis of the study-unit findings (http://water.usgs.

gov/nawqa/natsyn.html). 

The USGS places high value on the communication and dissemination of credible, timely, and 

relevant science so the most recent and available knowledge about water resources can be 

applied in management and policy decisions. We hope this NAWQA publication will provide the 

needed insights and information to meet your needs and thereby foster increased awareness 

and involvement in the protection and restoration of our Nation’s waters. 
iv

The NAWQA Program recognizes that a national assessment by a single program cannot 

address all water-resource issues of interest. External coordination at all levels is critical for 

a fully integrated understanding of watersheds and for cost-effective management, regulation, 

and conservation of our Nation’s water resources. The program, therefore, depends extensively on the advice, cooperation, and information from other Federal, State, interstate, tribal, 

and local agencies, non-government organizations, industry, academia, and other stakeholder 

groups. The assistance and suggestions of all are greatly appreciated.

Robert M. Hirsch

Associate Director for Water
Contents

Foreword ........................................................................................................................................................iii

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

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

Purpose and Scope ..............................................................................................................................2

Acknowledgments................................................................................................................................2

Description of Study Area ............................................................................................................................2

Hydrogeologic Setting .........................................................................................................................2

Land-Use Setting...................................................................................................................................5

Methods of Investigation..............................................................................................................................7

Site Selection and Well Installation...................................................................................................7

Sample Collection and Analysis.........................................................................................................9

Data Treatment......................................................................................................................................9

Quality Control.....................................................................................................................................15

Field-Blank Samples..................................................................................................................15

Replicate Samples.....................................................................................................................15

Environmental-Matrix Spike Samples....................................................................................16

Occurrence of Agricultural Chemicals in Shallow Ground Water ......................................................17

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

Pesticides.............................................................................................................................................19

Occurrence of Chemicals in the Unsaturated Zone ..............................................................................24

Factors Related to Occurrence of Agricultural Chemicals in Shallow Ground Water.....................25

Water Depth.........................................................................................................................................26

Aquifer-Sediment and Soil Characteristics....................................................................................26

Land Use...............................................................................................................................................26

Geologic Unit .......................................................................................................................................26

Well Type..............................................................................................................................................28

Summary........................................................................................................................................................30

References Cited..........................................................................................................................................30

Appendix 1. Pesticides analyzed in ground-water samples collected from northeast Nebraska 

glacial till, 2003–04..........................................................................................................................36

Appendix 2. Unsaturated-zone borehole-sediment sample results, northeast Nebraska glacial 

till, May–October 2002...................................................................................................................42

Appendix 3. Nitrate as nitrogen and pesticide concentrations in ground-water samples 

collected from domestic wells, northeast Nebraska glacial till, 1994–95.............................48

Figures

1–6. Maps showing:

1. Location of study area, northeast Nebraska glacial till ................................................3

2. Distribution of primary land-use types overlying northeast Nebraska glacial till, 

1992, and location of flow-path study site .......................................................................4

3. Distribution of major crops grown, by county, northeast Nebraska glacial till, 

2002 ........................................................................................................................................6
vi

4. Use of ground water, by county, northeast Nebraska glacial till, 2000.......................8

5. Distribution of average nitrogen application rates from manure and commercial 

fertilizer, by county, and nitrate as nitrogen concentrations in ground-water 

samples, northeast Nebraska glacial till, spring 2003 and May 2004 .......................21

6. Number of pesticide compounds detected in ground-water samples, northeast 

Nebraska glacial till, spring 2003 and May 2004...........................................................22

7. Graphs showing concentrations of pesticide compounds in ground-water samples, 

northeast Nebraska glacial till, 2003–04 .................................................................................25

8. Map showing nitrate as nitrogen concentrations in ground-water samples collected 

from domestic wells, northeast Nebraska, 1994–95 .............................................................29

Tables

1. Ten most frequently applied pesticides over northeast Nebraska glacial till, 1997 ..........7

2. Monitoring wells sampled in 2003, northeast Nebraska glacial till....................................10

3. Monitoring wells sampled in 2004, northeast Nebraska glacial till....................................12

4. Laboratory analysis and onsite preservation and treatment methods for measured 

water-quality constituents, northeast Nebraska glacial till, 2003–04................................14

5. Constituents detected in field-blank samples, northeast Nebraska glacial till, 

2003–04 .........................................................................................................................................16

6. Apparent recharge date of ground-water samples collected from monitoring wells, 

northeast Nebraska glacial till, 2003–04 .................................................................................18

7. Descriptive statistics for nitrogen and phosphorus compounds in ground-water 

samples, northeast Nebraska glacial till, 2003 ......................................................................19

8. Concentrations of nitrogen and phosphorus compounds in ground-water samples 

from flow-path wells and selected glacial-till network wells, northeast Nebraska glacial till, Maple Creek watershed, 2004 ....................................................................................20

9. Pesticide detections in ground-water samples collected in May and October 2004, 

northeast Nebraska glacial till, Maple Creek watershed....................................................24

10. Relations between nitrate as nitrogen concentrations in ground-water samples collected from glacial-till network wells and well-borehole and surficial soil characteristics, northeast Nebraska glacial till, 2003...............................................................................27

11. Pesticide compound detections in ground-water samples collected from glacial-till 

network wells related to well-borehole and surficial soil characteristics, northeast 

Nebraska glacial till, 2003..........................................................................................................27

12. Distribution of median nitrate as nitrogen concentrations and pesticide compound 

detections in glacial-till network wells, by land-use feature, northeast Nebraska glacial till, 2003..................................................................................................................................28

13. Distribution of nitrate as nitrogen concentrations and pesticide compound detections 

in ground-water samples collected from glacial-till network wells, by geologic unit, 

northeast Nebraska glacial till, 2003 .......................................................................................28
vii

Conversion Factors, Abbreviations, and Datum

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

micron (μm) 0.00003937 inch (in.)

mile (mi) 1.609 kilometer (km)

millimeter (mm) 0.03937 inch (in.)

Area

acre 4,047 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

million gallons per day (Mgal/d) 3,785 cubic meter per day (m3/d)

gallon (gal) 0.003785 cubic meter (m3) 

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Density

gram per cubic centimeter (g/cm3) 62.43 pound per cubic foot (lb/ft3)

Application rate

pound per acre (lb/acre) 1.121 kilogram per hectare (kg/ha)

Flow rate

inch per hour (in/h) 25.4 millimeter per hour (mm/h)

Concentration

microgram per liter (μg/L) 1 part per billion (ppb)

milligram per kilogram (mg/kg) 1.601x10-5 ounce per pound (oz/lb)

milligram per liter (mg/L) 1 part per million (ppm)

milligram per liter (mg/L) 0.05841 grain per gallon (gr/gal)

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

°F=(1.8×°C)+32.

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

°C=(°F-32)/1.8.

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

Agricultural chemicals applied at the land surface in 

northeast Nebraska can move downward, past the crop root 

zone, to ground water. Because agricultural chemicals applied 

at the land surface are more likely to be observed in the shallowest part of an aquifer, an assessment of shallow groundwater and unsaturated zone quality in the northeast Nebraska 

glacial till was completed between 2002 and 2004. Groundwater samples were collected at the first occurrence of ground 

water or just below the water table at 32 sites located in areas 

likely affected by agriculture. Four of the 32 sites were situated along a ground-water flow path with its downgradient 

end next to Maple Creek. Twenty-eight sites were installed 

immediately adjacent to agricultural fields throughout the 

glacial-till area. In addition to those 32 sites, two sites were 

installed in pastures to represent ground-water conditions in 

a non-cropland setting. Ground-water samples were analyzed 

for physical properties and concentrations of nitrogen and 

phosphorus compounds, selected pesticides and pesticide 

degradates, dissolved solids, major ions, trace elements, and 

dissolved organic carbon. Chlorofluorocarbons (CFCs) or sulfur hexafluoride (SF6

) concentrations were analyzed at about 

70 percent of the monitoring wells to estimate the residence 

time of ground water. Borehole-core samples were collected 

from 28 of the well boreholes. Sediment in the unsaturated 

zone was analyzed for nitrate, chloride, and ammonia concentrations.

Analytical results indicated that the agricultural chemicals most often detected during this study were nitrates and 

herbicides. Nitrate as nitrogen (nitrate–N) concentrations 

(2003 median 9.53 milligrams per liter) indicated that human 

activity has affected the water quality of recently recharged 

ground water in approximately two-thirds of the wells near 

corn and soybean fields. The principal pesticide compounds 

that were detected reflect the most-used pesticides in the area 

and included parent or degradate compounds of acetochlor, 

alachlor, atrazine, and metolachlor. Overall, pesticide concentrations in ground-water samples collected in 2003 and 

2004 were small and did not exceed public drinking-water 

Occurrence of Agricultural Chemicals in Shallow Ground 

Water and the Unsaturated Zone, Northeast Nebraska 

Glacial Till, 2002–04

By Jennifer S. Stanton, Gregory V. Steele, and Jason R. Vogel

standards where established. On average, more pesticides were 

detected in the flow-path wells than in the glacial-till network 

wells. The presence of a perennial stream within 1,640 feet 

of a well was correlated to smaller nitrate–N concentrations 

in the well water, and the presence of a road ditch within 

164 feet of the well was correlated to the presence of detectable pesticides in the well water. All other variables tested 

showed no significant correlations to nitrate–N concentrations 

or pesticide detections.

Unsaturated zone soil cores collected in 2002 from well 

boreholes indicated that nitrogen in the forms of nitrate–N 

and ammonia as nitrogen (ammonia–N) was available in the 

unsaturated zone for transport to ground water. Concentrations 

of nitrate–N and ammonia–N in these soil cores were inversely 

correlated to depth, and nitrate–N concentrations were correlated to chloride concentrations.

Introduction

Ground water is the primary source for drinking water, 

irrigation, industry, and water supplies for animal production in the glacial-till area of northeast Nebraska. Row-crop 

agriculture is the dominant land use in this area. Applications 

of agricultural amendments (such as fertilizers, pesticides, 

and soil conditioners), changes in soil structure from tillage, 

increased recharge, and changes to ground-water flow patterns 

are associated with cropland (Böhlke, 2002). Agricultural 

amendments directly introduce nutrients and pesticides to the 

hydrologic system. Changes in soil structure and application 

of irrigation water increase recharge rates. Increased recharge 

aids movement of human-related and natural chemical constituents (such as nitrogen in soil organic matter and dissolved 

solids) past the root zone to ground water (Scanlon and others, 

2005). Indirect effects of row-crop agriculture may include 

increased rates of mineral weathering, mineral solubility, and 

trace element dissolution rates (Böhlke, 2002).

In 1991, the U.S. Geological Survey (USGS) implemented the National Water-Quality Assessment (NAWQA) Program to provide scientifically sound information for 
managing the Nation’s water resources. The goals of the 

NAWQA Program are to assess the status and long-term 

trends of the Nation’s surface- and ground-water quality and to 

understand the natural and human factors that affect it (Gilliom and others, 1995). To evaluate the effects of cropland 

and hydrogeologic settings on ground-water quality, samples 

were collected from monitoring wells installed as part of two 

studies conducted within the Central Nebraska Basins (CNBR) 

Study Unit of the NAWQA Program (fig. 1). Because agricultural chemicals applied at the land surface are more likely 

to be observed in the shallowest part of an aquifer, shallow 

ground-water samples were collected from monitoring wells 

that were constructed with screens placed just below the 

anticipated lowest depth of the water table.

The Agricultural Chemicals Transport (ACT) study, 

conducted as part of the NAWQA Program, was designed to 

understand the transport and fate of agricultural chemicals 

through the hydrologic cycle in selected agricultural settings, 

including the Maple Creek watershed (fig. 1). As part of the 

ACT study, four clusters of monitoring wells were installed 

along a ground-water flow path with its downgradient end next 

to Maple Creek (flow-path study site, fig. 2). Water-quality 

results from ground-water samples collected from the shallowest well at each of the four well clusters were used in this 

report to assess the ground-water quality near the water table. 

In this report, these wells will be referred to as the flow-path 

wells.

The Agricultural Land-Use (AgLUS) study also was 

conducted as part of the NAWQA Program to specifically 

determine the effect of agriculture on ground-water quality. 

Wells were installed immediately adjacent to agricultural 

fields throughout the glacial-till area and were screened open 

to either the first occurrence of ground water or just below 

the water table to provide a broad-scale evaluation of recently 

recharged ground water that would most likely be affected by 

nearby land use. These wells will be referred to as glacial-till 

network wells in this report.

Purpose and Scope

This report describes the occurrence of agricultural 

chemicals in the shallow ground water beneath and adjacent 

to cropland in the northeast Nebraska glacial till and in the 

unsaturated zone. Specifically, agricultural chemicals include 

nutrients and pesticides. Ground-water samples were collected 

from 34 monitoring wells from spring 2003 through fall 2004. 

Ground-water samples were analyzed for physical properties 

and concentrations of nitrogen and phosphorus compounds, 

selected pesticides and pesticide degradates, dissolved solids, 

major ions, trace elements, and dissolved organic carbon. 

Twenty-four of the 34 monitoring wells also were sampled 

for chlorofluorocarbons (CFCs) or sulfur hexafluoride (SF6) 

concentrations to estimate the residence time of ground water. 

Borehole core samples were collected during well installation at 28 well sites in 2002. Sediment in the unsaturated zone 

was analyzed for nitrate as nitrogen (nitrate–N), ammonia as 

nitrogen (ammonia–N), and chloride concentrations. The relation between ground-water quality and selected land-use and 

hydrogeologic variables was examined.

Acknowledgments

The authors thank the many landowners who allowed 

installation of a monitoring well on their property. This study 

could not have been conducted without their support.

Description of Study Area

The study area is within the boundaries of the glacial till 

north of the Platte River in northeast Nebraska (fig. 1). This 

area of glacial till covers approximately 2,700 square miles 

(mi2) in the lower Elkhorn River Basin. The study area has 

a continental climate receiving mean annual precipitation of 

28.5 inches (in.) between 1971 and 2000. Total precipitation at 

Columbus, Nebraska, was 25.6 in. in 2003 and 28.4 in. in 2004 

(National Climatic Data Center, 2007). Most of the area has a 

somewhat low permeable surface and subsurface. Topography 

consists of mostly rolling hills with areas of flat terraces and 

flood plains along larger streams (Newport, 1957).

Hydrogeologic Setting

The hydrogeology of the study area is a very complex 

mixture of deep to shallow regional and local aquifers located 

in the glaciated area of eastern Nebraska. Aquifer units in the 

study area include regional units that, because they are too 

deep, are untapped by the monitoring wells used in this study. 

These units, consisting of sand and gravel deposits of Pliocene 

and Pleistocene age, have been identified as Plio-Pleistocene 

deposits by Gosselin and others (1996) and are hydraulically 

connected locally to shallower aquifers and streams. Consequently, where these deeper aquifers discharge to shallower 

ones, they can play an important role in the water quality of 

the shallower deposits in which the monitoring wells for this 

study are installed. The regional ground-water-flow direction 

in the study area is from northwest to the southeast (Flowerday 

and others, 1998).

Hydrologic units in the study area vary from confined to 

unconfined systems of which bedrock of Cretaceous age—

including the Dakota Sandstone, Graneros Shale, Greenhorn 

Limestone, Carlile Shale, Niobrara Formation, and the Pierre 

Shale—typically serves as the lower limit of the regional 

unconsolidated aquifers. Bedrock of Tertiary age is located in 

the extreme northwestern part of the study area (Bentall and 

others, 1971; Gosselin and others, 1996). In most of the study 

area, the Cretaceous-age bedrock units generally do not yield a 

sufficient amount of freshwater for most uses. In the eastern part of the study area, potable water can be found in the 

   Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Figure 1. Location of study area, northeast Nebraska glacial till.

Description of Study Area 

PLATTE

BURT

PIERCE

DODGE

POLK

CUMING

BUTLER

WAYNE

DIXON

MADISON

SAUNDERS

CEDAR

COLFAX

STANTON

KNOX

THURSTON

DAKOTA

WOODBURY

WASHINGTON

NANCE

DOUGLAS

MERRICK

SARPY

K–05

P–04

P–03

W–07

W–08

W–R1 P–02

W–15 W–09

W–18

W–14

S–10

B–28

S–01 B–27

S–11

D–21

D–26

D–22

D–24

CE–17

DI–16

CU–30

CU–19

CU–29

CU–20

CO–13

DG–23

FS1–4A FS1–3A

FS1–2A

FS1–1A

S–R2

CE–06

IO

NEBRASK

WA

A

Missouri River

Platte River

Loup River

Shell

Creek

West Fork Maple Creek

Elkhorn

River

Logan

Creek

Index map

Columbus

East Fork Maple Creek

97°50' 40' 30' 20' 10' 97° 50' 40' 30' 96°20'

41°10'

20'

30'

40'

50'

42°

10'

20'

42°30'

WOODBURY

IOWA

MISSOURI

KANSAS

WYOMING

COLORADO

Big Blue River

NEBRASKA

SOUTH DAKOTA

Maple Creek watershed

boundary

0 5 10 15 20 MILES

0 1 5 0 15 20 KILOMETERS

Boundary of Central Nebraska Basins Study Unit

Boundary of Central Nebraska

Basins Study Unit

Boundary of Central Nebraska

Basins Study Unit

Study area

EXPLANATION

D–22

D–24

FS1–1A

Study area for agricultural chemicals S–R2

 in shallow ground water

Other areas of Central Nebraska Basins

 Study Unit

Glacial-till network well and identifier

 (sampled in 2003)

Reference well and identifier (sampled in 2003)

Flow-path well and identifier (sampled in 2004)

Glacial-till network well within Maple Creek

 watershed and identifier (sampled in 2003

 and 2004)

Base from Nebraska Department of Natural Resources in work

share agreement with U.S. Geological Survey, 1:12,000 digital data

Albers Equal-Area Conic projection

Standard parallels 29°30’, and 45°30’, central meridian -96°

Horizontal coordinate information is referenced to the North American

 Datum of 1983 (NAD 83)
PLATTE

BURT

PIERCE

DODGE

POLK

CUMING

BUTLER

WAYNE

DIXON

MADISON

SAUNDERS

CEDAR

COLFAX

STANTON

KNOX

THURSTON

DAKOTA

WASHINGTON

NANCE

DOUGLAS

MERRICK

SARPY

K–05

P–04

P–03

W–07

W–08

W–R1 P–02

W–15 W–09

W–18

W–14

S–10

B–28

S–01 B–27

S–11

D–21

D–26

D–22

D–24

CE–17

DI–16

CU–30

CU–19

CU–29

CU–20

CO–13

DG–23

FS1–4A FS1–3A

FS1–2A FS1–1A

S–R2

CE–06

IOWA

NEBRASKA

Platte River

Loup River

Shell

Creek

Elkhorn River

Logan

Creek

Inset

Missouri River

PLYMOUTH UNION

WOODBURY

West Fork Maple Creek

East Fork Maple Creek

97°50' 40' 30' 20' 10' 97° 50' 40' 30' 96°20'

41°10'

20'

30'

40'

50'

42°

10'

20'

42°30'

Big Blue River

Maple Creek watershed

boundary

0 5 10 15 20 MILES

0 1 5 0 15 20 KILOMETERS

Boundary of Central Nebraska

Basins Study Unit

Boundary of Central Nebraska

Basins Study Unit

EXPLANATION

Cropland

Pasture / Hay

Forest / Shrubland / Grasslands

Urban

Open water and wetlands

Other areas of Central Nebraska 

 Basins Study Unit

D–22

D–24

FS1–1A

S–R2

Glacial-till network well and

 identifier (sampled in 2003)

Reference well and identifier (sampled in 2003)

Flow-path well and identifier

 (sampled in 2004)

Glacial-till network well within

 Maple Creek watershed and

 identifier (sampled in 2003 and 2004)

Land use

Base from Nebraska Department of Natural Resources in work

share agreement with U.S. Geological Survey, 1:12,000 digital data

Albers Equal-Area Conic projection

Standard parallels 29°30’, and 45°30’, central meridian -96°

Horizontal coordinate information is referenced to the North American

 Datum of 1983 (NAD 83)

96°33’

41°33’55”

41°33’35”

50”

45”

40”

55” 50” 45” 96°32’40”

FS1–4A

FS1–3A

FS1–2A

FS1–1A

Inset

Flow-path study site

Corn field Corn field

Riparian

area

Pasture

Maple Creek

Land use from U.S. Geological Survey, 1992

0 240 480 FEET

0 60 120 METERS

Inset base from U.S. Department of Agriculture

Farm Service Agency digital aerial photography, 2003, 1:12,000

Universal Transverse Mercator projection, Zone 14

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

Columbus

Figure 2. Distribution of primary land-use types overlying northeast Nebraska glacial till, 1992, and location of flow-path study site.

   Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Dakota Sandstone. Although dissolved-solids concentrations 

there generally are less than 500 mg/L (Ellis, 1984), elsewhere the Dakota Sandstone typically contains water that is 

highly mineralized. The primary source of water to the Dakota 

Sandstone is the several sand-and-gravel units that overlie 

it. Bentall and others (1971) reported that beneath Cuming 

and Thurston Counties the Greenhorn Limestone is a waterbearing unit and the Carlile Shale is also a known local source 

of water supply. The Niobrara Formation provides a local 

water supply in the study area. However, neither the Graneros 

Shale nor the Pierre Shale are known to yield water to wells 

(Bentall and others, 1971). In the extreme northwestern part of 

the study area, the Ogallala Formation of Tertiary age yields 

some water to wells.

Aquifers in the study area also include coarse-grained 

alluvial deposits that lie in paleovalleys beneath glacial till of 

Pleistocene age. Where upland areas overlie the paleovalleys, 

ground-water levels can be more than 130 feet (ft) deep (Fredrick and others, 2006). Gosselin and others (1996) report that 

the thickness of these coarse-grained alluvial deposits varies 

from location to location but generally is less than 300 ft. The 

paleovalley deposits can be as much as 5 mi wide and 200 ft 

thick in the Maple Creek area (Fredrick and others, 2006). 

Coarse-grained alluvial deposits also can be localized within 

the glacial till (Verstraeten and Ellis, 1995). These localized 

deposits vary substantially in thickness and areal extent and 

typically occur as perched or semi-perched aquifers within 

the glacial-till deposits. Available data are not sufficient to 

adequately delineate the occurrence and distribution of these 

localized deposits, but in most of the study area they collectively are considered discontinuous aquifers (Verstraeten 

and Ellis, 1995). Ground-water levels in these discontinuous 

aquifers vary substantially depending on the source. Water 

levels in perched aquifers can be located near the land surface, 

whereas water levels in the paleovalleys can be located hundreds of feet below the land surface.

Aquifers also are found in alluvium in the major river 

valleys and the adjacent terraces. Numerous stream valleys, 

which have incised the glacial sediment, contain alluvium 

deposited by these streams that locally can be tens of feet 

thick. These alluvial aquifers consist of coarse-grained alluvium of Quaternary age that is found beneath the flood plains 

and in the terraces, which generally are capped with loess. The 

alluvial aquifers are permeable sand-and-gravel deposits with 

intermixed and interbedded silt and clay deposits (Verstraeten 

and Ellis, 1995). Moreover, these deposits are capable of 

yielding large amounts of water to irrigation wells (Gosselin 

and others, 1996). The primary sources of recharge for these 

aquifers are precipitation, runoff from upland areas, and infiltration during times of high river stage (Verstraeten and Ellis, 

1995). Fredrick and others (2006) report that ground-water 

levels range from near surface to about 70 ft along the loesscapped terraces.

In the area of the flow-path wells, the primary aquifer 

unit is the alluvial material and terrace deposits described in 

the preceding paragraph. Depths below land surface for the 

aquifer in this area vary from about 70 ft under the loesscapped terraces (Fredrick and others, 2006) to less than 1 ft 

adjacent to Maple Creek. The thickness of the alluvial aquifer, 

obtained from a driller’s log of nearby irrigation wells, is 

about 175 ft (Nebraska Department of Natural Resources, 

2007).

Land-Use Setting

Land use in the study area is dominated by agriculture. 

According to interpreted Landsat Thematic Mapper satellite 

images composing the National Land Cover Dataset (NLCD), 

in 1992 about 81 percent of the study area was used for row 

crops, and 16 percent was used for pasture or hay (fig. 2). The 

remaining 3 percent of the study area was classified as forest, urban, open water, or wetlands (U.S. Geological Survey, 

1992). The crops most commonly grown in the study area in 

2002 were corn and soybeans (fig. 3). Planted pasture or hay 

and oats also were grown (U.S. Department of Agriculture, 

variously dated).

Nitrogen fertilizers are applied to cropland in the study 

area. The amount of nitrogen applied to cropland from manure 

and commercial fertilizer has been estimated for each county 

in the study area (Ruddy and others, 2006). Average nitrogen application rates from commercial fertilizer and manure 

between 1987 and 1997 ranged from 44 (Knox County) to 

123 pounds per acre (lb/acre) (Cuming County). Fertilizer 

application estimates were based on State-level fertilizer sales 

compiled by the Association of American Plant Food Control 

Officials (AAPFCO). Estimates of county fertilizer use were 

calculated by multiplying the total State fertilizer sales by the 

portion of the State’s fertilized acreage that was in each county 

as determined by the Census of Agriculture. Manure application rates were calculated from county-level livestock populations obtained from the 1997 Census of Agriculture (U.S. 

Department of Agriculture, 1999). Nitrogen content of manure 

was estimated using methods described by Goolsby and others 

(1999). Loss of nitrogen through volatilization was accounted 

for when estimating animal manure nitrogen. According to 

the farm operator at the flow-path study site, nitrogen fertilizer was applied to the corn field surrounding flow-path well 

FS1–1A after planting (May 8, 2004) (fig. 2). No fertilizer or 

manure was applied to the land surface around the other flowpath wells. However, cattle were grazed near wells FS1–3A 

and FS1–4A during parts of the year.

Pesticides (insecticides, herbicides, and fungicides) commonly are applied to cropland to control weeds and insects. 

The types and amounts of pesticides applied to each area are 

related to the types of crops grown. When pesticides move 

past the soil profile to a ground-water resource that is used for 

drinking water, they can cause potential health concerns (U.S. 

Environmental Protection Agency, 2004). Atrazine and metolachlor were the pesticides most commonly applied to crops in 

1997 in the study area (table 1) (National Center for Food and 

Agricultural Policy, 1997; U.S. Department of Agriculture, 

Description of Study Area 
Big Blue River

PLATTE

BURT

PIERCE

DODGE

POLK

CUMING

BUTLER

WAYNE

DIXON

MADISON

SAUNDERS

CEDAR

COLFAX

STANTON

KNOX

THURSTON

DAKOTA

WOODBURY

PLYMOUTH

WASHINGTON

NANCE

DOUGLAS

MERRICK

SARPY

IOWA

NEBRASKA

River

Platte River

UNION

Missouri

97°50' 40' 30' 20' 10' 97° 50' 40' 30' 96°20'

41°10'

20'

30'

40'

50'

42°

10'

20'

42°30'

0 5 10 15 20 MILES

0 1 5 0 15 20 KILOMETERS

Boundary of Central Nebraska

Basins Study Unit

Boundary of Central Nebraska

Basins Study Unit

EXPLANATION

Base from Nebraska Department of Natural Resources in work

share agreement with U.S. Geological Survey, 1:12,000 digital data

Albers Equal-Area Conic projection

Standard parallels 29°30’, and 45°30’, central meridian -96°

Horizontal coordinate information is referenced to the North American

 Datum of 1983 (NAD 83)

Study area for agricultural chemicals

 in shallow ground water

Other areas of Central Nebraska Basins

 Study Unit

Corn

Soybeans

Planted pasture or hay

Other crops

Crop type, in percent

Crop data from U. S. Department of Agriculture,

variously dated

MONONA

Figure 3. Distribution of major crops grown, by county, northeast Nebraska glacial till, 2002.

 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
1999; Naomi Nakagaki, U.S. Geological Survey, written commun., July 2005). Although the estimated application rates do 

not necessarily represent conditions during the time that water 

composing the ground-water samples was recharged, they 

do provide a general idea of the types and relative amounts 

of pesticides that are applied. According to the landowner, 

0.6 lb/acre of metolachlor and 0.8 lb/acre of atrazine were 

applied to the corn field at the flow-path study site at the time 

of planting (May 9, 2004), 1 lb/acre of atrazine was applied 

about 5 days after planting, and 0.5 lb/acre of chlorpyrifos was 

applied in July 2004.

Most water used in the study area is for cropland 

irrigation. In 2000, an estimated 218 million gallons per day 

(Mgal/d) were used for that purpose in the study area (U.S. 

Geological Survey, 2004). Ground-water withdrawals for 

irrigation varied by county and ranged from 8 to 118 Mgal/d. 

Irrigation water is applied mainly during the summer months 

(June through August) when crop water demands are largest. 

Other primary water uses include publicly supplied drinking 

water, self-supplied domestic drinking water, industrial, and 

livestock (fig. 4). At the flow-path study site, an estimated 

10 in. of irrigation water were applied in each of 2003 and 

2004 during a 6-week period in July and August.

Methods of Investigation

Water samples were collected from 34 monitoring wells 

(fig. 1). Four of the wells were installed between September 

2003 and March 2004 as part of a flow-path ACT study in 

Maple Creek Valley, and 28 wells distributed throughout the 

glacial-till area of northeast Nebraska were installed in 2002 

as part of an AgLUS. Additionally, two reference wells were 

installed to represent background, or naturally occurring, 

ground-water-quality conditions.

Site Selection and Well Installation

The flow-path wells sampled as part of this study were 

located in the southern part of the glaciated area of northeast 

Nebraska about 5 mi upstream from the confluence of Maple 

Creek and the Elkhorn River. The flow-path study site was 

chosen to represent localized ground-water flow from agricultural lands to discharge points at a nearby stream flanked 

by riparian woodland areas (fig. 2). Specific site descriptions for this study site are provided in Fredrick and others 

(2006). The flow path begins in a cropped field (corn in 2004) 

(well FS1–1A) with additional wells located adjacent to the 

corn field (well FS1–2A), in a pasture (well FS1–3A), and 

in a riparian woodland area adjacent to Maple Creek (well 

FS1–4A). Each well location is within a cluster of three wells 

with the shallowest well located just below the anticipated 

lowest depth of the water table. Two additional piezometers 

were placed at depth below the shallowest well at each site 

but are not discussed in this report. All samples not collected 

specifically from the flow-path wells were collected from the 

glacial-till network of wells or were reference wells.

The glacial-till network wells sampled in this study were 

located in the glacial-till areas of northeastern Nebraska where 

soil zones are poorly drained. A primary criterion for site 

selection was location of the wells in areas characterized by 

intrinsic aquifer susceptibility as indicated by selected hydrologic landscape regions (Winter, 2001; Wolock and others, 

2004) and land use that was at least 20 percent corn and soybeans. Therefore, the boundaries of the study area were based 

primarily on hydrologic landscape regions with modifications 

to exclude areas where land use was not classified as having 

greater than 20 percent corn and soybean production.

Site locations for the glacial-till well network were 

selected using a stratified random approach (Scott, 1990). 

Using a geographical information system (GIS), the study 

area was divided into 30 cells of equal area, and each of these 

30 cells then was subdivided into 30 equal-area subcells. From 

the 30 subcells, one random primary polygon and four random 

alternate polygons were chosen by a scripted GIS algorithm. 

Thus, within each of the 30 cells, there were 30 subcells from 

which one primary and four alternate subcells were randomly 

chosen. Following the selection of the random points (centers 

of the subcells), land use within about a 2-mi radius of the 

random point was screened to ensure the monitoring wells fit 

the criteria of the study. If the land use fell within the guidelines of the study, landowners were contacted for permission 

to install a monitoring well.

Two reference wells were located in areas of no cultivated 

crop production for the past 5 years. Both reference wells were 

Table 1. Ten most frequently applied pesticides over northeast 

Nebraska glacial till, 1997.

[Pesticide application rates on crops were estimated from the National 

Center for Food and Agricultural Policy (NCFAP) (1997) and county-level 

information on harvested crops in the 1997 Census of Agriculture (U.S. 

Department of Agriculture, 1999); lb/acre, pound per acre; a.i., active 

ingredient]

Pesticide name Average amount applied to 

cropland (lb/acre of a.i.)

Metolachlor 0.33

Atrazine .32

Acetochlor .14

Glyphosate1 .14

Alachlor .08

Pendimethalin .07

Trifluralin .06

Cyanazine .05

Terbufos .04

Carbofuran .04

Total 1.27

1

Not analyzed in samples collected as part of this study.

Methods of Investigation 
PLATTE

BURT

PIERCE

DODGE

POLK

CUMING

BUTLER

WAYNE

DIXON

MADISON

SAUNDERS

CEDAR

COLFAX

STANTON

KNOX

THURSTON

DAKOTA

WOODBURY

MONONA

PLYMOUTH

WASHINGTON

NANCE

DOUGLAS

MERRICK

SARPY

IOWA

NEBRASKA

River

Platte River

UNION

Missouri

97°50' 40' 30' 20' 10' 97° 50' 40' 30' 96°20'

41°10'

20'

30'

40'

50'

42°

10'

20'

42°30'

0 5 10 15 20 MILES

0 1 5 0 15 20 KILOMETERS

Boundary of Central Nebraska

Basins Study Unit

Boundary of Central Nebraska

Basins Study Unit

EXPLANATION

Base from Nebraska Department of Natural Resources in work

share agreement with U.S. Geological Survey, 1:12,000 digital data

Albers Equal-Area Conic projection

Standard parallels 29°30’, and 45°30’, central meridian -96°

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

Study area for agricultural chemicals

 in shallow ground water

Other areas of Central Nebraska Basins

 Study Unit

Irrigation

Public supply

Self-supplied domestic

Industrial

Livestock

Water-use categories,

 in percent

Water-use data from U. S. Geological Survey, 2004

Water-use category is shown only when

composing greater than 1 percent of total

water use.

Figure 4. Use of ground water, by county, northeast Nebraska glacial till, 2000.

 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
targeted for placement in pastures that were at least 1,640 ft 

from any cropped field. However, one well (SR–2) was located 

within 700 ft of a corn field but upgradient from crops with 

respect to the estimated ground-water flow direction.

Wells were installed using methods that maximized the 

likelihood that water-quality samples represented aquifer 

conditions and that equipment and construction materials 

were not a source or sink of sampled analytes (Lapham and 

others, 1997). Wells were installed using hollow-stem auger 

techniques that introduced no drilling fluids. Well casings and 

screens were constructed of 2-in. diameter polyvinyl chloride 

(PVC). Because agricultural chemicals applied at the land 

surface are more likely to be observed in the shallowest part 

of an aquifer, monitoring wells were constructed with short 

screens placed at the first occurrence of ground water (most 

of the glacial-till network sites) or just below the anticipated 

lowest depth of the water table (tables 2 and 3). The annular 

space above the well screen and filter pack was filled with 

bentonite grout, and a concrete pad and protective steel cover 

were placed around the well.

Sample Collection and Analysis

 Fifty-eight ground-water samples were collected from 

the 34 monitoring wells in 2003 and 2004 (tables 2 and 3). 

Water samples were analyzed to determine physical properties 

and concentrations of nitrogen and phosphorus compounds, 

selected pesticides and pesticide degradates, dissolved solids, 

major ions, trace elements, and dissolved organic carbon. 

Samples from the 28 glacial-till network wells distributed 

throughout the glaciated area and samples from two reference 

wells were collected during April, May, and June 2003 to 

coincide with the approximate time that agricultural chemicals 

would be applied to crops (table 2). In 2004, samples from the 

four flow-path wells plus samples from three of the glacialtill network wells within the Maple Creek watershed were 

collected in March (pre-plant), May (post-plant), August and 

early September (growing season), and October (post-harvest) 

(table 3). Samples from those seven sites were only analyzed 

for pesticides and pesticide degradates in May and October 

of 2004. Twenty-four of the ground-water samples collected 

in spring of 2003 and 2004 were analyzed for either CFCs 

(CFC–11, CFC–12, and CFC–113) or SF6 concentrations to 

estimate the approximate recharge date of the water sample. 

Sediment-core samples were collected at 28 well boreholes 

during installation between May and October 2002. Analytical laboratories for water samples and laboratory analytical 

methods are briefly summarized for measured water-quality 

constituents in table 4.

Ground-water samples were collected from monitoring 

wells using procedures described in the USGS national field 

manual (U.S. Geological Survey, variously dated) and by the 

U.S. Geological Survey Reston Chlorofluorocarbon Laboratory (U.S. Geological Survey, 2005). Water samples were processed onsite in a mobile laboratory using methods designed 

to minimize changes to the water-sample chemistry. Water 

samples for nutrient, pesticide, and major ion analysis were 

pumped from wells using a stainless-steel submersible pump 

and delivered to the mobile laboratory through Teflon tubing 

with stainless-steel connections. Water samples for CFCs and 

SF6 analyses were delivered to the mobile laboratory using 

refrigerator-grade copper tubing. Prior to sample collection, 

stagnant water was flushed from the well by purging at least 

three casing volumes from the well. While purging, specific 

conductance, pH, water temperature, dissolved oxygen, and 

turbidity were measured until readings were stable (U.S. 

Geological Survey, variously dated). Once measurements 

stabilized, water samples were collected in precleaned bottles 

within an enclosed chamber to prevent sample contamination. 

To prevent degradation of water samples and to maintain the 

initial concentration of compounds between the time of sample 

and laboratory analyses, bottles were preserved according to 

the requirements of the laboratories. Preservation practices 

differ among analytes and may include chilling, filtration, and 

(or) chemical treatment (table 4).

Continuous sediment-core samples were collected prior 

to well installation using a 4-in. split-core sampler. Sediment 

samples then were collected from the continuous-core samples 

at 10-ft intervals or at major changes in lithology. Chemical 

analyses of sediment samples were performed by the University of Nebraska Soil and Plant Analytical Laboratory in 

Lincoln, Nebraska (Carolyn Bossung, University of NebraskaLincoln, written commun., June 2004). Particle-size analyses 

were performed by a combination of laser diffraction and sieving by the U.S. Geological Survey in Menlo Park, California 

(Gee and Or, 2002).

Data Treatment

In 1998, the USGS National Water-Quality Laboratory 

(NWQL) began implementing a new method for reporting 

analytical results (Childress and others, 1999). Two concentration levels are used in the new method; the long-term method 

detection level (LT–MDL) and the laboratory reporting level 

(LRL) minimize both false-positive and false-negative errors. 

LT–MDLs and LRLs vary among constituents and analytical 

methods. LT–MDL is determined from the standard deviation of long-term laboratory spike-sample measurements and 

is set to the level at which false-positive errors are minimized 

to no more than 1-percent probability. LRL is set to the level 

at which false-negative errors are minimized to no more 

than 1-percent probability and is generally equal to twice 

the LT–MDL. Using this reporting convention, if a reported 

concentration is greater than both the LRL and the smallest 

laboratory calibration standard, it is not censored or qualified. 

If a reported concentration is smaller than the LT–MDL, it is 

coded as “less than” the LRL, unless information-rich laboratory methods (organic constituent methods that have additional 

qualitative information provided by the instrumentation) 

are used. LT–MDLs and LRLs are reevaluated annually by 

Methods of Investigation 
Table 2. Monitoring wells sampled in 2003, northeast Nebraska glacial till.

[NA, not applicable]

Well 

identifier 

(fig. 1)

U.S. Geological 

Survey site number Well type Geologic unit

Latitude 

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Sample 

date

Depth of 

well (feet 

below 

land 

surface)

Depth to 

top of well 

screen 

(feet below land 

surface) 

Depth to 

bottom of 

well screen 

(feet below 

land 

surface) 

Depth to 

water 

level (feet 

below 

land 

surface)

Watercollecting road 

ditch 

within 

164 feet

B–27 414931096321101 Glacial-till network Pleistocene loess 41.82530 -96.53637 June 5 25 15 25 8.79 noB–28 415220096214801 Glacial-till network Pleistocene loess 41.87219 -96.36326 April 28 17 7 17 10.13 yesCE–06 422947097142701 Glacial-till network Pleistocene sand and gravel 42.49663 -97.24098 May 20 23.5 13.5 23.5 9.46 yesCE–17 422802097031601 Glacial-till network Holocene alluvium 42.46747 -97.05469 May 19 20 15 20 2.10 yesCO–13 414343096595801 Glacial-till network Holocene alluvium 41.72866 -96.99968 June 4 25 15 25 11.05 yes

CU–19 420024096485901 Glacial-till network Holocene alluvium 42.00670 -96.81637 May 28 22 17 22 9.41 noCU–20 415558096434501 Glacial-till network Pleistocene loess 41.93300 -96.72929 April 29 45 35 45 38.48 yesCU–29 415918096350501 Glacial-till network Pleistocene glacial till 41.98857 -96.58498 April 30 32 22 32 18.42 yesCU–30 420248096300901 Glacial-till network Pleistocene glacial till 42.04663 -96.65237 May 29 30 20 25 27.55 yesD–21 414401096531301 Glacial-till network Pleistocene loess 41.73376 -96.88711 June 2 29.5 19.5 29.5 13.16 yesD–22 413853096483801 Glacial-till network Pleistocene loess 41.64808 -96.81053 June 4 32 27 32 26.10 noD–24 413340096402701 Glacial-till network Holocene alluvium 41.56108 -96.67425 May 15 24.5 19.5 24.5 21.04 yesD–26 414141096371701 Glacial-till network Pleistocene loess 41.69483 -96.62150 June 4 57 52 57 50.31 noDG–23 411733096185501 Glacial-till network Holocene alluvium 41.29259 -96.31530 June 9 15 10 15 4.02 noDI–16 422011096595401 Glacial-till network undifferentiated Pleistocene deposits 42.33641 -96.99834 May 5 65 60 65 58.13 yes

K–05 422756097334901 Glacial-till network Pleistocene sand and gravel 42.46561 -97.56350 May 20 45 40 45 22.11 noP–02 421357097243201 Glacial-till network Pleistocene glacial till 42.23239 -97.40900 May 27 25 20 25 8.31 yesP–03 422156097314301 Glacial-till network Pleistocene glacial till 42.36556 -97.52864 May 21 39 29 39 34.02 yesP–04 422441097404601 Glacial-till network Pleistocene glacial till 42.41133 -97.67950 May 20 60 50 60 51.02 yesS–01 414948097212601 Glacial-till network undifferentiated Pleistocene deposits 41.83015 -97.35736 May 13 35 30 35 32.10 yesS–10 420425097101301 Glacial-till network Pleistocene loess 42.07361 -97.17028 May 7 30 20 30 22.35 noS–11 414527097094101 Glacial-till network Pleistocene glacial till 41.75758 -97.16146 June 3 65 55 65 47.17 yesW–07 422031097043501 Glacial-till network Pleistocene sand and gravel 42.34199 -97.07663 May 6 73 68 73 62.30 yesW–08 421829097112401 Glacial-till network Pleistocene loess 42.30811 -97.18997 May 8 35 25 35 22.23 yesW–09 421149097121301 Glacial-till network Pleistocene loess 42.19694 -97.20361 May 7 37 32 37 31.92 noW–14 420526096543901 Glacial-till network undifferentiated Pleistocene deposits 42.09056 -96.91083 May 1 35 25 35 13.69 yes

W–15 421303097011601 Glacial-till network Holocene alluvium 42.21750 -97.02111 May 7 34.8 29.8 34.8 15.61 noW–18 420922096514401 Glacial-till network Pleistocene loess 42.15622 -96.86235 May 5 39 34 39 26.84 yesS–R2 415458097142201 Reference Holocene alluvium 41.91623 -97.23966 June 3 29 24 29 17.25 NAW–R1 421445097123801 Reference Pleistocene loess 42.24575 -97.21067 May 28 53 48 53 45.47 NA

10 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Methods of Investigation 11

Table 2. Monitoring wells sampled in 2003, northeast Nebraska glacial till.—Continued[NA, not applicable]

Well 

identifier 

(fig. 1)

U.S. Geological 

Survey site number Well type Geologic unit

Latitude 

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Sample 

date

Perennial 

stream 

within 

1,640 

feet

Farmhouse 

within 

164 

feet

Manure 

storage or 

pasture 

within 

164 

feet

Irrigation 

well 

within 

1,640 

feet

Irrigated 

cropland 

within 

1,640 

feet

B–27 414931096321101 Glacial-till network Pleistocene loess 41.82530 -96.53637 June 5 no no no yes yesB–28 415220096214801 Glacial-till network Pleistocene loess 41.87219 -96.36326 April 28 no no no yes noCE–06 422947097142701 Glacial-till network Pleistocene sand and gravel 42.49663 -97.24098 May 20 no no no no yesCE–17 422802097031601 Glacial-till network Holocene alluvium 42.46747 -97.05469 May 19 no no no no noCO–13 414343096595801 Glacial-till network Holocene alluvium 41.72866 -96.99968 June 4 yes no no no noCU–19 420024096485901 Glacial-till network Holocene alluvium 42.00670 -96.81637 May 28 no no no no noCU–20 415558096434501 Glacial-till network Pleistocene loess 41.93300 -96.72929 April 29 no yes no no noCU–29 415918096350501 Glacial-till network Pleistocene glacial till 41.98857 -96.58498 April 30 no no no no noCU–30 420248096300901 Glacial-till network Pleistocene glacial till 42.04663 -96.65237 May 29 no no no no noD–21 414401096531301 Glacial-till network Pleistocene loess 41.73376 -96.88711 June 2 no no no no noD–22 413853096483801 Glacial-till network Pleistocene loess 41.64808 -96.81053 June 4 no no no no noD–24 413340096402701 Glacial-till network Holocene alluvium 41.56108 -96.67425 May 15 yes no no yes yesD–26 414141096371701 Glacial-till network Pleistocene loess 41.69483 -96.62150 June 4 no no no no noDG–23 411733096185501 Glacial-till network Holocene alluvium 41.29259 -96.31530 June 9 no no yes no yesDI–16 422011096595401 Glacial-till network undifferentiated Pleistocene deposits 42.33641 -96.99834 May 5 no no no yes yesK–05 422756097334901 Glacial-till network Pleistocene sand and gravel 42.46561 -97.56350 May 20 no no yes no noP–02 421357097243201 Glacial-till network Pleistocene glacial till 42.23239 -97.40900 May 27 no yes yes no noP–03 422156097314301 Glacial-till network Pleistocene glacial till 42.36556 -97.52864 May 21 no no yes no noP–04 422441097404601 Glacial-till network Pleistocene glacial till 42.41133 -97.67950 May 20 yes yes no no yesS–01 414948097212601 Glacial-till network undifferentiated Pleistocene deposits 41.83015 -97.35736 May 13 yes no no no noS–10 420425097101301 Glacial-till network Pleistocene loess 42.07361 -97.17028 May 7 no no no no noS–11 414527097094101 Glacial-till network Pleistocene glacial till 41.75758 -97.16146 June 3 yes no no no noW–07 422031097043501 Glacial-till network Pleistocene sand and gravel 42.34199 -97.07663 May 6 no no no yes yesW–08 421829097112401 Glacial-till network Pleistocene loess 42.30811 -97.18997 May 8 no no no no noW–09 421149097121301 Glacial-till network Pleistocene loess 42.19694 -97.20361 May 7 no no no no noW–14 420526096543901 Glacial-till network undifferentiated Pleistocene deposits 42.09056 -96.91083 May 1 no no no no noW–15 421303097011601 Glacial-till network Holocene alluvium 42.21750 -97.02111 May 7 no no no yes yesW–18 420922096514401 Glacial-till network Pleistocene loess 42.15622 -96.86235 May 5 no no no no noS–R2 415458097142201 Reference Holocene alluvium 41.91623 -97.23966 June 3 NA NA NA NA NAW–R1 421445097123801 Reference Pleistocene loess 42.24575 -97.21067 May 28 NA NA NA NA NA
Table 3. Monitoring wells sampled in 2004, northeast Nebraska glacial till.

Well 

identifier 

(fig. 2)

U.S. Geological 

Survey site number Well type Geologic unit

Latitude 

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Sample date

Depth of 

well (feet 

below land 

surface 

datum)

Depth to 

top of well 

screen (feet 

below land 

surface) 

Depth to bottom of well 

screen (feet 

below land 

surface)

Depth to water level (feet 

below land 

surface)

FS1–1A 413334096325301 Flow path Pleistocene sand and gravel 41.55958 -96.54808 March 30 79 74 79 70.39

May 19 not availableAugust 16 71.09October 4 71.47

FS1–2A 413341096325501 Flow path Pleistocene sand and gravel 41.56139 -96.54853 March 29 81.1 76.1 81.1 69.51

May 18 not availableAugust 17 70.21October 7 70.38

FS1–3A 413348096324801 Flow path Pleistocene sand and gravel 41.56325 -96.54678 March 31 60 55 60 51.05

May 20 not available

August 18 51.83October 6 52.03

FS1–4A 413350096324701 Flow path Pleistocene sand and gravel 41.56395 -96.54655 April 1 18.2 13.2 18.2 12.80

May 24 10.00

August 17 14.05October 5 14.22

D–24 413340096402701 Glacial-till 

network

Holocene alluvium 41.56108 -96.67425 March 23 24.5 19.5 24.5 18.50

May 25 18.46

September 8 18.84October 13 18.11

12 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Table 3. Monitoring wells sampled in 2004, northeast Nebraska glacial till.—Continued

Well 

identifier 

(fig. 2)

U.S. Geological 

Survey site number Well type Geologic unit

Latitude 

(decimal 

degrees)

Longitude 

(decimal 

degrees)

Sample date

Depth of 

well (feet 

below land 

surface 

datum)

Depth to 

top of well 

screen (feet 

below land 

surface) 

Depth to bottom of well 

screen (feet 

below land 

surface)

Depth to water level (feet 

below land 

surface)

CO–13 414343096595801 Glacial-till 

network

Holocene alluvium 41.72866 -96.99968 March 25 25 15 25 11.95

41.72866 -96.99968 May 26 25 15 25 8.44

September 9 12.24October 12 12.45

S–11 414527097094101 Glacial-till 

network

Pleistocene glacial till 41.75758 -97.16146 March 24 65 55 65 46.80

May 25 46.83

August 19 43.13October 14 42.49

Methods of Investigation 13
Table 4. Laboratory analysis and onsite preservation and treatment methods for measured water-quality constituents, northeast Nebraska glacial 

till, 2003–04.

[USGS, U.S. Geological Survey; NWQL, National Water Quality Laboratory; μm, micron; oC, degrees Celsius; C-18, carbon 18; GC/MS, gas chromatography/

mass spectrometry; LC/MS, liquid chromatography/mass spectrometry; <, less than; UV, ultraviolet; mL, milliliter]

Constituent or 

constituent group Analyzing laboratory Analytical method(s) Reference(s) Onsite treatment and preservation method(s)

Depth to water, 

specific conductance, 

pH, temperature, 

dissolved oxygen, 

and turbidity

Measured onsite Various methods USGS, variously dated None.

Nitrogen and 

phosphorus 

compounds

USGS NWQL, 

Lakewood, CO

Various methods Fishman, 1993; Patton 

and Kryskalla, 2003

Filter through 0.45-μm 

filter, chill, and 

maintain at 4oC.

Pesticides and pesticide 

degradates

USGS NWQL, 

Lakewood, CO

C-18 solid-phase 

extraction and 

capillary-column GC/MS

Zaugg and others, 1995; 

Lindley and others, 

1996; Furlong and 

others, 2001; Madsen 

and others, 2003

Filter through 0.7-μm 

baked glass-fiber filter, 

chill, and maintain at 

4oC.

Selected pesticide 

degradates

USGS Organic 

Geochemistry 

Research Laboratory, 

Lawrence, KS

Online solid-phase extraction and LC/MS; 

solid-phase extraction 

and GC/MS; solid-phase 

extraction and capillarycolumn GC/MS with 

selected-ion monitoring

Zimmerman and 

Thurman, 1999; Kish 

and others, 2000; Lee 

and Strahan, 2003

Filter through 0.7-μm 

baked glass-fiber filter, 

chill, and maintain at 

4oC.

Dissolved solids and 

major ions

USGS NWQL, 

Lakewood, CO

Inductively coupled plasma Fishman and Friedman, 

1989; Fishman, 1993; 

American Public 

Health Association, 

1998

Anions, filter through 

0.45-μm filter; cations, 

filter through 0.45-μm 

filter, acidify sample to 

pH <2 with nitric acid 

(HNO3).

Carbonate alkalinity Analyzed onsite Inflection-point titration USGS, variously dated Filter through 0.45-μm 

filter.

Trace elements USGS NWQL, 

Lakewood, CO

Inductively coupled plasma, 

atomic absorption 

spectrometry

Fishman and Friedman, 

1989; Faires, 1993; 

McLain, 1993; 

Garbarino, 1999 

Filter through 0.45-μm 

filter and acidify to 

< 2 with nitric acid 

(HNO3).

Dissolved organic 

carbon

USGS NWQL, 

Lakewood, CO

UV-light promoted 

persulfate oxidation and 

infrared spectrometry

Brenton and Arnett, 

1993

Filter through 0.7-μm 

baked glass-fiber filter, 

acidify to pH < 2 with 

1 mL of 4.5N sulfuric 

acid (H2SO4), chill, and 

maintain at 4oC.

Chlorofluorocarbons USGS Chlorofluorocarbon 

Laboratory, Reston, VA

Purge-and-trap, gas 

chromatography with 

electron-capture 

detector

Bullister, 1984; 

Bullister and Weiss, 

1988; Busenberg and 

Plummer, 1992; 

Plummer and 

Busenberg, 1999

No contact with 

atmosphere.

Sulfur hexafluoride USGS 

Chlorofluorocarbon 

Laboratory, Reston, VA

Purge-and-trap, gas 

chromatography with 

electron-capture 

detector

Busenberg and Plummer, 

2000

No contact with 

atmosphere.

14 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
NWQL on the basis of laboratory spike-sample measurements 

and may change with time.

Concentrations are qualified as estimated in several 

situations. If a reported concentration is smaller than either 

the LRL or the smallest laboratory calibration standard but 

greater than the LT–MDL, the value is qualified as estimated 

using an “E” remark code. An “E” remark code also is used if 

the reported concentration is larger than the largest laboratory 

calibration standard. Pesticides were analyzed and reported 

using information-rich laboratory methods. These methods 

report concentrations smaller than the LT–MDL if an analyte 

is positively identified and all other laboratory quality-control 

criteria are satisfied. The reported concentrations smaller than 

the LT–MDL are qualified with an “E” remark code. Finally, 

if a compound does not meet method-specific performance 

criteria, reported concentrations are qualified with an “E” 

remark code.

Water-quality data commonly are positively skewed 

(most data occur at small values but a few extreme large values 

are present). For this reason, nonparametric statistical methods 

were used in this report to evaluate the analytical results. The 

nonparametric Wilcoxon, or Mann-Whitney, rank-sum test 

(two-sided) was used to compare observations between groups 

of data (Wilcoxon, 1945). In this report, a p-value of less than 

0.10 indicates that there was a significant difference between 

two groups of data. If more than 50 percent of the values were 

censored, no statistical comparison was attempted. The nonparametric Spearman’s rho test was used to correlate observations between variables in a dataset (Bhattacharyya and Johnson, 1977). Rho is the “linear correlation coefficient computed 

on the ranks of the data” (Helsel and Hirsch, 1992). In this 

report, a p-value of less than 0.10 indicates that the correlation of the two variables was statistically significant. Fisher’s 

exact test (Agresti, 1990) was used to detect group differences in categorical data. A p-value of less than 0.10 indicates 

there was a statistically significant difference between the two 

groups of data.

To apply statistical tests, it was sometimes necessary to 

substitute censored (“less than”) values with a numeric value. 

Substitutions were applied using methods described by Helsel 

(2005) and were dependent upon the laboratory reporting 

methods of each constituent. Censored data were set to a value 

smaller than the smallest LT–MDL to effectively be treated as 

a tied rank that was smaller than any estimated or uncensored 

value. Estimated values were treated as quantitative results.

Quality Control

Additional samples were collected to assess the reliability 

of sample processing and analytical methods. These qualitycontrol samples included field-blank, replicate, and environmental-matrix spike samples.

Field-Blank Samples

Field-blank samples were collected to determine the 

occurrence and magnitude of sample contamination during 

sample collection, equipment cleaning, transport, and analysis. When field-blank samples were collected, sample bottles 

were filled with ultrapure water prepared at NWQL instead 

of well water. Prior to use, the prepared water was analyzed 

and certified to be free of the environmental sample analytes. 

Field-blank samples otherwise were collected using the same 

procedures and equipment as environmental samples. Fieldblank samples were collected and analyzed for nitrogen and 

phosphorus compounds, pesticide compounds, major ions, 

trace elements, and dissolved organic carbon. It is not possible 

to prepare meaningful age-dating field-blank samples; therefore, age-dating field-blank samples were not collected.

Results of field-blank sample analyses are summarized 

in table 5. Concentrations of analytes detected in field-blank 

samples were compared with concentrations of analytes in 

environmental samples to determine the potential for environmental sample contamination. If the magnitude of the fieldblank sample concentrations approached the environmental 

sample concentrations, environmental sample concentrations 

may have been affected by sampling contamination. Concentrations of metolachlor, aluminum, manganese, zinc, and 

dissolved organic carbon in at least one field-blank sample 

were larger than the smallest concentrations found in environmental samples. Therefore, at small concentrations, it was 

not possible to determine if environmental concentrations of 

these constituents were representative of aquifer conditions 

or the result of sampling contamination. Because relatively 

few analytes were detected in field-blank samples, equipment 

decontamination and sample handling procedures adequately 

prevented positive bias of reported concentrations.

Replicate Samples

Replicate samples are two environmental samples collected sequentially to represent a duplication of the same 

sample water. They are collected to determine variability of 

the data as a result of sampling and analytical procedures. The 

relative percentage difference (RPD) between concentrations 

of paired replicate samples was calculated using the formula:

( ) 1 2 x 100 . 1 2

2

Sample Sample RPD Sample Sample− = +

(1)

When there is no variability between the paired analyses, the RPD is zero. The RPD was not calculated if one or 

both of the paired replicate concentrations were less than the 

largest laboratory reporting level (LRL) or identified as an 

estimated value by the laboratory. The individual constituents 

having the largest average RPDs were atrazine (25.0 percent), 

Methods of Investigation 15
copper (22.9 percent), metolachlor ethanesulfonic acid (ESA) 

(12.3 percent), ammonia (11.3 percent), dissolved organic 

carbon (10.5 percent), and manganese (10.4 percent). The 

larger RPDs for these constituents might be explained by their 

small concentrations near the LRL. With small concentrations 

and few significant figures, small differences can have large 

calculated variability. For example, an environmental sample 

concentration of 0.01 mg/L and a replicate sample concentration of 0.02 mg/L yield an RPD of 50 percent. Except for 

nickel, RPDs were 5 percent or less for constituents with measured concentrations greater than 10 times the LRL.

Environmental-Matrix Spike Samples

Environmental-matrix spike samples typically are used 

to quantify the gain or loss of organic-compound analytes 

because of water-matrix properties, sample holding time, 

or onsite and laboratory procedures. A spike recovery of 

100 percent indicates no matrix interference or degradation 

and good analytical recovery. Environmental-matrix pesticide 

spike samples were prepared by adding known amounts of 

99 pesticide compounds into replicate samples while onsite. 

The average percentage recovery of individual pesticide 

compounds was calculated from the environmental-matrix 

spike samples and is reported in Appendix 1. Eighty-six of 

the 99 pesticide compounds analyzed were within an acceptable range of 60 to 120 percent recovery (Furlong and others, 

2001). Of the 13 pesticide compounds analyzed that did not 

fall into the range of acceptable recovery, 10 always were 

reported as estimated values by NWQL because of known 

problems with gas chromatography or extraction or because 

Table 5. Constituents detected in field-blank samples, northeast Nebraska glacial till, 2003–04.

[P, phosphorus; E, estimated; ND, not detected; --, median not calculated; M, presence verified but not quantified]

Constituent

Number of detections/

number of field-blank 

samples

Median concentration 

of detected analytes in 

field-blank samples 

Maximum concentration 

in field-blank samples 

Range of concentrations 

in environmental samples 

Nitrogen and phosphorus compounds (concentrations in milligrams per liter)

Orthophosphate as P 3/8 E0.005 0.007 ND–1.28

Pesticide compounds (concentrations in micrograms per liter)

Metolachlor 1/6 -- E.006 ND–E0.002

Major ions (concentrations in milligrams per liter)

Calcium 4/5 .04 .09 11.2–406

Magnesium 2/5 E.004 E.004 2.49–90.5

Sodium 4/5 .11 .16 4.50–281

Silica 5/5 .22 2.27 19.4–50.4

Trace elements (concentrations in micrograms per liter)

Aluminum 2/4 -- 11 ND–28

Barium 3/4 -- M 14–664

Cobalt 1/4 -- E.007 0.045–9.11

Copper 2/4 .3 .4 0.5–11.5

Iron 1/5 -- 10 ND–5,810

Manganese 4/7 1.0 1.8 ND–18,300

Nickel 3/4 .15 .16 0.76–16.2

Silver 1/4 -- .2 ND

Strontium 2/3 .29 .34 50–2,160

Vanadium 1/4 -- E.1 0.5–9.6

Uranium 1/4 -- E.01 0.02–162

Zinc 3/4 E.9 2.7 E0.6–14.3

Dissolved organic carbon (concentrations in milligrams per liter)

Dissolved organic carbon 2/4 1.1 1.6 0.4–4.8

16  Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
they did not otherwise meet method performance criteria 

(Zaugg and others, 1995; Furlong and others, 2001).

Occurrence of Agricultural Chemicals 

in Shallow Ground Water

Agricultural chemicals applied at the land surface are 

more likely to be observed in the shallowest part of an aquifer 

because recently recharged ground water generally is located 

at the top of an aquifer near chemical sources. Ground-water 

samples were collected from 34 monitoring wells from spring 

2003 through spring 2004. Ground-water samples were analyzed for physical properties and concentrations of nitrogen 

and phosphorus compounds, selected pesticides and pesticide 

degradates, dissolved solids, major ions, trace elements, and 

dissolved organic carbon. Laboratory results have previously 

been reported in U.S. Geological Survey water-data reports 

(Hitch and others, 2004; Hitch and others, 2005; U.S. Geological Survey, 2006).

Samples from a portion of the sites were analyzed for 

CFCs (CFC–11, CFC–12, and CFC–113) or SF6 to determine 

the apparent date the water was isolated from the atmosphere 

(recharge date). Age-dating techniques can be affected by 

processes such as mixing of waters within the aquifer, the time 

it takes for atmospheric gases to reach deep saturated zones, 

microbial degradation, sorption onto organic carbon and 

minerals, and contamination from sources other than atmospheric gases (Plummer and Busenberg, 1999). Therefore, 

ages are referred to as “apparent ages.” The results from this 

analysis indicated that all analyzed water samples contained 

at least a portion of water that had resided in the aquifer for 

less than 50 years, and most had an apparent recharge date that 

was within the past 30 years (table 6). Because widespread 

application of agricultural chemicals primarily has been within 

the past 50 years, samples likely represent water that has been 

exposed to potential agricultural contaminants.

Nutrients

Nitrogen and phosphorus are nutrients commonly 

applied to agricultural lands to improve the fertility of soils 

and improve crop yields. These nutrients can migrate past 

the soil horizon and to ground water. Nitrogen and phosphorus compounds can exist as different forms in water. Water 

samples were analyzed for nitrite reported as nitrogen, nitrite 

plus nitrate as nitrogen, ammonia as nitrogen, ammonia plus 

organic nitrogen as nitrogen (2003 samples only), and orthophosphate as phosphorus (tables 7 and 8). Dissolved orthophosphate concentrations are typically small in ground water 

because phosphorus has a very low solubility and readily sorbs 

to soil particles (Miller and Donahue, 1990). Therefore, most 

of the following discussion will focus on nitrogen compounds.

Nitrate is the dominant form of nitrogen in oxygenated 

water, whereas nitrite, ammonia, and organic nitrogen are 

more stable when oxygen concentrations are small. Dissolved oxygen concentrations indicated that about 62 percent 

of ground-water samples collected in the study area were 

oxygenated (greater than 1.0 mg/L dissolved oxygen) (Hitch 

and others, 2004). Nitrite was detected in 13 of the 58 (22 percent) ground-water samples collected in 2003 and 2004 with 

concentrations up to 0.021 mg/L (tables 7 and 8) (Hitch and 

others, 2004). Nitrite composed a maximum of 3.5 percent of 

the nitrite plus nitrate concentration as nitrogen where nitrite 

was detected and nitrite plus nitrate as nitrogen concentrations 

were not estimated. Therefore, nitrite plus nitrate concentrations will be referred to as nitrate as nitrogen (nitrate–N) concentrations in this report. Ammonia was detected in 15 of the 

58 samples (26 percent), with concentrations up to 0.90 mg/L 

(tables 7 and 8). Three of the five samples collected from the 

glacial-till well network in 2003 that contained detectable 

ammonia also had a dissolved-solids concentration larger than 

1,000 mg/L. Ammonia plus organic nitrogen concentrations in 

samples collected in 2003 ranged from undetected to 1.3 mg/L 

(table 7).

Nitrogen in the form of nitrate–N is mobile, persistent, 

and is the most common ground-water contaminant in the 

Nation (Mueller and Helsel, 1996). Although, nitrate–N is 

found naturally in ground water, elevated concentrations 

generally are caused by human-related sources (Spalding 

and Kitchen, 1988; Bruce and others, 2003; McMahon and 

Böhlke, 2006). The maximum background concentration of 

nitrate–N representing naturally occurring sources in ground 

water is estimated to be about 2 to 4 mg/L nationwide (Madison and Brunett, 1985; Gosselin, 1991; Mueller and Helsel, 

1996; McMahon, 2001; Becker and others, 2002). Nitrate–N 

concentrations in samples collected in spring 2003 from 

the 28 glacial-till network wells ranged from undetected to 

69.5 mg/L, with a median of 9.53 mg/L (table 7). Nitrate–N 

concentrations in 19 samples (68 percent) were greater than 

4 mg/L, indicating that human activity has affected nitrate–N 

concentrations in recently recharged ground water near corn 

and soybean fields. Although the sampled wells are not 

representative of wells typically used as a source of drinking 

water, concentrations in 13 samples (46 percent) were larger 

than 10 mg/L, the USEPA Maximum Contaminant Level 

for nitrate–N in drinking water (fig. 5) (U.S. Environmental 

Protection Agency, 2004). Nitrate–N concentrations in the 

two reference wells sampled in 2003 were 1.71 and 8.96 mg/L 

(table 7).

The four flow-path and three glacial-till network wells in 

the Maple Creek watershed were sampled four times during 

2004—March (pre-plant), May (post-plant), August and early 

September (growing season), and October (post-harvest). 

Although the flow-path wells were located within a small area, 

nitrate–N concentrations in ground-water samples collected 

from those wells were variable (table 8). In May 2004, the 

largest nitrate–N concentration from the flow-path wells was 

in shallow ground water beneath the pasture (21.1 mg/L as N, 

Occurrence of Agricultural Chemicals in Shallow Ground Water 17
well FS1–3A). Nitrate–N also was detected in ground water 

beneath the cropped field (13.0 mg/L as N, well FS1–1A) 

but was not detected in the shallow ground water on the 

edge of the cropped field (well FS1–2A) and in the riparian 

zone (well FS1–4A). Nitrate–N concentrations in May 2004 

beneath the pasture and cropped field at the flow-path study 

site were larger than the median concentration in samples 

collected from the glacial-till network wells during the same 

time period in 2003 (table 7). The larger nitrate–N concentration in water from well FS1–3A during May 2004 may have 

resulted from the absence of the loess cap that would impede 

the downward movement of water. The loess cap is present at 

wells FS1–1A and FS1–2A. Concentrations generally were 

similar throughout the growing season with the exception of 

samples collected from well FS1–3A. In March, the nitrate–N 

concentration of the ground-water sample from well FS1–3A 

was less than the reporting level of 0.06 mg/L (undetected), 

whereas ground-water samples collected in May, August, and 

October ranged from 19.4 to 21.1 mg/L (table 8). Nitrate–N 

concentrations in water from wells FS1–1A and FS1–4A 

decreased slightly during the summer months (May and 

August).

Nitrate–N concentrations in two of the glacial-till network wells in the Maple Creek watershed stayed about the 

same throughout the growing season in 2004. Nitrate–N concentrations in well CO–13 (fig. 1) were always less than the 

Table 6. Apparent recharge date of ground-water samples collected from monitoring wells, northeast Nebraska glacial till, 2003–04.

[CFCs, chlorofluorocarbons; SF6, sulfur hexafluoride]

Well identifier 

(fig. 2)

U.S. Geological Survey 

site number Sample date Well type Age-dating method Apparent date of recharge

B–27 414931096321101 June 5, 2003 Glacial-till network CFCs mid- to late 1980s

B–28 415220096214801 April 28, 2003 Glacial-till network CFCs around 1990

CE–06 422947097142701 May 20, 2003 Glacial-till network CFCs 1989 or older

CE–17 422802097031601 May 19, 2003 Glacial-till network CFCs mid-1970s or older

CO–13 414343096595801 June 4, 2003 Glacial-till network CFCs mid-1960s to mid-1970s

D–21 414401096531301 June 2, 2003 Glacial-till network CFCs late 1970s to early 1980s

D–22 413853096483801 June 4, 2003 Glacial-till network CFCs mid-1980s

D–24 413340096402701 May 15, 2003 Glacial-till network CFCs mid-1980s

DI–16 422011096595401 May 5, 2003 Glacial-till network CFCs late 1970s 

FS1–2A 413341096325501 August 17, 2004 Flow path SF6 late 1980s

FS1–3A 413348096324801 August 18, 2004 Flow path SF6 late 1980s to early 1990s

FS1–4A 413350096324701 August 17, 2004 Flow path SF6 early 1990s

K–05 422756097334901 May 20, 2003 Glacial-till network CFCs early to mid-1980s

P–02 421357097243201 May 27, 2003 Glacial-till network CFCs mid-1970s 

P–03 422156097314301 May 21, 2003 Glacial-till network CFCs mid-1980s to early 1990s

P–04 422441097404601 May 20, 2003 Glacial-till network CFCs mid- to late 1980s

S–10 420425097101301 May 7, 2003 Glacial-till network CFCs mid- to late 1980s

S–11 414527097094101 June 3, 2003 Glacial-till network CFCs early to mid-1980s

S–R2 415458097142201 June 3, 2003 Reference CFCs mid-1980s

W–07 422031097043501 May 6, 2003 Glacial-till network CFCs mid-1980s

W–08 421829097112401 May 8, 2003 Glacial-till network CFCs mid- to late 1980s

W–14 420526096543901 May 1, 2003 Glacial-till network CFCs mid-1960s to 1970

W–15 421303097011601 May 7, 2003 Glacial-till network CFCs mid- to late 1970s

W–18 420922096514401 May 5, 2003 Glacial-till network CFCs mid- to late 1960s or older

18  Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
reporting level of 0.06 mg/L, and concentrations in well S–11 

(fig. 5) were close to 4.0 mg/L. Well D–24 (fig. 5) had variable nitrate–N concentrations that were largest in the spring 

(38.9 mg/L as N on March 23, 2004) and declined throughout 

the growing season to less than one-half the original concentration (16.5 mg/L as N on October 13, 2004). The nitrate–N 

concentration in ground water collected from this well in May 

of the previous (2003) growing season as part of the glacial-till 

well network was 11.4 mg/L.

Orthophosphate as phosphorus (P) concentrations in 

ground-water samples collected in spring 2003 from the 

glacial-till well network ranged from undetected to 0.24 mg/L 

(table 7). Orthophosphate–P concentrations were larger in the 

two reference wells (0.12 and 0.36 mg/L) than in most of the 

other glacial-till network samples. A nitrate–N concentration 

larger than background levels and the detection of orthophosphate–P in reference wells might indicate that enrichment is 

a result of county and (or) region-wide application of these 

nutrients; the reference well with the larger nitrate–N concentration was located in a county that had larger amounts of 

nitrogen applied at the land surface (fig. 5). Other explanations 

likely include historical land use (grazing) or perhaps unreported fertilizer applications near these wells.

In the Maple Creek area in 2004, orthophosphate–P concentrations in shallow ground water were similar and consistent throughout the year beneath the corn field (well FS1–1A: 

mean=0.24 mg/L as P, standard deviation=0.01 mg/L as P) 

and the riparian area (well FS1–4A: mean=0.23 mg/L as 

P, standard deviation=0.05 mg/L as P) and were similar to 

the maximum orthophosphate–P concentration detected in 

the nearby glacial-till network well (well D–24, located in 

similar proximity to Maple Creek as well FS1–1A, about 

6.5 mi upstream). Concentrations of orthophosphate–P in 

shallow ground water beneath the pasture (well FS1–3A: 

mean=0.45 mg/L as P, standard deviation=0.03 mg/L as P) 

were consistent throughout the year but at concentrations 

nearly twice as large as the maximum concentration detected 

in the glacial-till network wells in 2003. The shallow groundwater samples collected from the edge-of-field well FS1–2A 

in March and May had the largest concentrations of orthophosphate-P of any sample collected during the ACT study 

(0.86 and 0.87 mg/L as P), whereas concentrations in samples 

from that site collected in August and October 2004 were both 

less than the reporting level. The maximum orthophosphateP concentration was 1.28 mg/L in water from well CO–13 

(May 26, 2004).

Pesticides

 Pesticides can migrate to ground water as the original 

compound or break down into degradation products. Water 

samples collected in 2003 were analyzed for 90 pesticides and 

17 pesticide degradates, and water samples collected in 2004 

were analyzed for 43 pesticides and 39 pesticide degradates 

(Appendix 1) (Hitch and others, 2004, 2005).

Thirteen (46 percent) of the 28 samples collected in 

spring 2003 from wells in the glacial-till network had at 

least one detectable pesticide concentration (fig. 6). Pesticides detected were atrazine (triazine class) (five samples), 

bentazon (one sample), flumetsulam (sulfonanilide class) (one 

Table 7. Descriptive statistics for nitrogen and phosphorus compounds in ground-water samples, northeast Nebraska glacial till, 2003.

[Constituents are dissolved; USEPA, U.S. Environmental Protection Agency; N, nitrogen; mg/L, milligrams per liter; ND, not detected; MCL, Maximum Contaminant Level; LTHA, Lifetime Health Advisory, the concentration of a chemical in drinking water that is not expected to cause any adverse noncarcinogenic 

effects for a lifetime of exposure; --, no data or not calculated; P, phosphorus; E, estimated]

Constituent or property

Concentrations Number of 

detections

Number of 

drinking-water 

exceedances

USEPA drinkingwater standard/ 

type of standard Minimum Median Maximum 1

Glacial-till network wells (28 samples analyzed)

Nitrite as N, in mg/L ND ND 0.017 3 0 1 / MCL

Nitrite plus nitrate as N (nitrate–N), in mg/L ND 9.53 69.5 27 13 10 / MCL

Ammonia as N, in mg/L ND ND .90 5 0 30 / LTHA

Ammonia plus organic nitrogen as N, in mg/L ND .14 1.3 18 -- --

Orthophosphate as P, in mg/L ND .06 .24 24 -- --

Reference wells (2 samples analyzed)

Nitrite as N, in mg/L ND -- ND 0 0 1 / MCL

Nitrite plus nitrate as N (nitrate–N), in mg/L 1.71 -- 8.96 2 0 10 / MCL

Ammonia as N, in mg/L ND -- ND 0 0 30 / LTHA

Ammonia plus organic nitrogen as N, in mg/L ND -- .21 1 -- --

Orthophosphate as P, in mg/L .12 -- .36 2 -- --

1

Drinking-water standards from U.S. Environmental Protection Agency (2004).

Occurrence of Agricultural Chemicals in Shallow Ground Water 19
Table 8. Concentrations of nitrogen and phosphorus compounds in ground-water samples from flow-path wells and selected glacial-till network 

wells, northeast Nebraska glacial till, Maple Creek watershed, 2004.

[Constituents are dissolved. Nitrate-N, nitrate as nitrogen; mg/L, milligrams per liter; N, nitrogen; P, phosphorus; ND, not detected; E, estimated; <, less 

than]

Well identifier 

(fig. 2) Sample date Nitrite (mg/L as N) Nitrate-N (mg/L) Ammonia (mg/L as N) Orthophosphate (mg/L as P)

Flow-path wells

FS1–1A March 30 0.021 13.4 ND 0.232

May 19 .011 13.0 ND .248

August 16 .014 11.1 ND .231

October 4 .009 11.7 ND .243

FS1–2A March 29 ND ND 0.24 .858

May 18 ND ND .28 .867

August 17 .014 ND .24 <.006

October 7 ND ND .26 E.003

FS1–3A March 31 ND ND ND .408

May 20 ND 21.1 ND .448

August 18 ND 19.4 ND .476

October 6 ND 19.9 ND .476

FS1–4A April 1 .014 .88 ND .230

May 24 E.004 ND ND .174

August 17 .016 .55 ND .243

October 5 .030 .85 ND .288

Glacial-till network wells

D–24 March 23 ND 38.9 ND .238

May 25 ND 28.4 E.02 .249

September 8 ND 20.2 ND .241

October 13 ND 16.5 E.03 .236

CO–13 March 25 ND ND .66 .94

May 26 ND ND .58 1.28

September 9 ND ND .71 .98

October 12 .014 E.04 .87 .356

S–11 March 24 ND 4.01 ND .042

May 25 ND 3.86 ND .042

August 19 ND 3.87 ND .040

October 14 ND 3.95 ND .043

20 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Base from Nebraska Department of Natural Resources in work

share agreement with U.S. Geological Survey, 1:12,000 digital data

Albers Equal-Area Conic projection

Standard parallels 29°30’, and 45°30’, central meridian -96°

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

PLATTE

BURT

PIERCE

DODGE

POLK

CUMING

BUTLER

WAYNE

DIXON

MADISON

SAUNDERS

CEDAR

COLFAX

STANTON

KNOX

THURSTON

DAKOTA

PLYMOUTH UNION

WASHINGTON

NANCE

DOUGLAS

MERRICK

SARPY

IOWA

NEBRASKA

Missouri River

Platte River

WOODBURY

Missouri River

97°50' 40' 30' 20' 10' 97° 50' 40' 30' 96°20'

41°10'

20'

30'

40'

50'

42°

10'

20'

42°30'

Maple Creek watershed

boundary

0 5 10 15 20 MILES

0 1 5 0 15 20 KILOMETERS

Boundary of Central Nebraska

Basins Study Unit

Boundary of study area

Boundary of study area

EXPLANATION

Average nitrogen application rates

 from manure and fertilizer (1987–

 97), in pounds per acre of cropland

 per year

Nitrate as nitrogen concentrations, in milligrams per liter

0–50

51–75

76–100

Greater than 100

Less than or equal to 4.00

4.01 to 10.0

Greater than 10.0

Flow-path well (May 2004 sample)

Less than or equal to 4.00

4.01 to 10.0

Greater than 10.0

Glacial-till network well 

 (spring 2003 sample)

Less than or equal to 4.00

4.01 to 10.0

Reference well (spring 2003 sample)

Boundary of study area

Boundary

of study

area

Nitrogen application rates from

Ruddy and others (2006)

Big Blue River

Boundary of Central Nebraska

Basins Study Unit

96°33’

41°33’55”

41°33’35”

50”

45”

40”

55” 50” 45” 96°32’40”

0 240 480 FEET

0 60 120 METERS

Inset

Inset base from U.S. Department of Agriculture

Farm Service Agency digital aerial photography,

2003, 1:12,000 Universal Transverse Mercator projection,

Zone 14

Horizontal coordinate information is referenced

 to the North American Datum of 1983 (NAD 83)

Inset

Flow-path study site

Maple Creek

FS1–4A

FS1–3A

FS1–2A

FS1–1A

K–05

P–04

P–03

W–07

W–08

W–R1 P–02

W–15 W–09

W–18

W–14

S–10

B–28

S–01 B–27

S–11

D–21

D–26

D–22

D–24

CE–17

DI–16

CU–30

CU–19

CU–29

CU–20

FS1–4A FS1–3A

FS1–2A FS1–1A

S–R2

CE–06

DG–23

CO–13

Figure 5. Distribution of average nitrogen application rates from manure and commercial fertilizer, by county, and nitrate as nitrogen concentrations in 

ground-water samples, northeast Nebraska glacial till, spring 2003 and May 2004.

Occurrence of Agricultural Chemicals in Shallow Ground Water 21
Shell Creek

Elkhorn River

Logan Creek

Loup

River

PLATTE

BURT

PIERCE

DODGE

POLK

CUMING

BUTLER

WAYNE

DIXON

MADISON

SAUNDERS

CEDAR

COLFAX

STANTON

KNOX

THURSTON

DAKOTA

PLYMOUTH UNION

WASHINGTON

NANCE

DOUGLAS

MERRICK

SARPY

IOWA

NEBRASKA

Missouri River

Platte River

WOODBURY

Missouri River

97°50' 40' 30' 20' 10' 97° 50' 40' 30' 96°20'

41°10'

20'

30'

40'

50'

42°

10'

20'

42°30'

Big Blue River

Maple Creek watershed

boundary

0 5 10 15 20 MILES

0 1 5 0 15 20 KILOMETERS

Boundary of Central Nebraska

Basins Study Unit

EXPLANATION

Reference well and identifier (spring 2003 sample)

Pesticides or degradates not detected

 Pesticides or degradates detected, with number of 

 pesticide compounds detected in parentheses ( )

Flow-path well and identifier (May 2004 sample)

 Pesticides or degradates detected, with number of

 pesticide compounds detected in parentheses ( )

Study area for agricultural chemicals in shallow ground water

Other areas of Central Nebraska 

 Basins Study Unit

Glacial-till network well and

identifier (spring 2003 sample)

Pesticides or degradates not detected

 Pesticides or degradates detected, with

 number of pesticide compounds detected 

 in parentheses ( )

Columbus

West Fork Maple Creek

East Fork Maple Creek

96°33’

41°33’55”

41°33’35”

50”

45”

40”

55” 50” 45” 96°32’40”

0 240 480 FEET

0 60 120 METERS

(2)

(1)

(1)

(1)

(1)

(0)

(1)

(1)

(1)

(1)

(1)

(2)

(1)

(8)

(1)

(8)

(2)

(3)

(2)

(3)

(4)

(4)

Inset

Inset base from U.S. Department of Agriculture

Farm Service Agency digital aerial photography,

2003, 1:12,000

Universal Transverse Mercator projection, Zone 14

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

(1)

Inset

Flow-path study site

Maple Creek

FS1–4A

FS1–3A

FS1–2A

FS1–1A

Boundary of Central Nebraska

Basins Study Unit

K–05

P–04

P–03

W–07

W–08

W–R1

W–R1

S–R2

P–02

W–15

W–09 W–18

W–14

S–10

B–28

S–01 B–27

S–11

D–21

D–26

D–22

D–24

CE–17

DI–16

CU–30

CU–19

CU–29

CU–20

B–27

CU–20

FS1–4A

FS1–3A

FS1–2A FS1–1A

FS1–4A

FS1–3A

S–R2

CE–06

DG–23

CO–13

Base from Nebraska Department of Natural Resources in work

share agreement with U.S. Geological Survey, 1:12,000 digital data

Albers Equal-Area Conic projection

Standard parallels 29°30’, and 45°30’, central meridian -96°

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

FS1–3A

Figure 6. Number of pesticide compounds detected in ground-water samples, northeast Nebraska glacial till, spring 2003 and May 2004.

22 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
sample), imazethapyr (imidazolinone class) (one sample), 

malathion (organothiophosphate acaricides or aliphatic 

organothiophosphate insecticides class) (one sample), and 

picloram (pyridine herbicides) (one sample). Pesticide 

degradates detected were compounds that can form from the 

breakdown of atrazine—deethylatrazine (five samples) and 

deethyldeisopropylatrazine (five samples). Deethylatrazine 

also is a degradate of propazine.

Atrazine and its degradation compounds were the most 

frequently detected pesticides in water samples from wells 

in the glacial-till well network, and atrazine was the second 

most frequently applied pesticide in the glacial-till area in 

1997 (table 1). The median concentration of atrazine (estimated 0.004 μg/L) was equal to the median concentration of 

deethylatrazine (estimated 0.004 μg/L) and smaller than the 

median concentration of deethyldeisopropylatrazine (estimated 0.14 μg/L). About one-half of the samples containing 

degradation compounds of atrazine did not contain detectable concentrations of either atrazine or propazine. Thirty-six 

percent of the samples contained at least one of the atrazine 

or atrazine degradation compounds, similar to what was 

found in other agricultural areas across the Nation (Gilliom 

and others, 2006).

Ground-water samples collected between 1992 and 

2001 as part of 52 studies across the Nation were evaluated to 

determine which human and natural factors (such as pesticide 

use, soil characteristics, hydrology, and climate) were related 

to atrazine detection frequencies. The result of this evaluation was a statistical model that estimated the frequency of 

pesticide detections in areas where pesticide concentrations 

had not been measured (Gilliom and others, 2006). In northeast Nebraska, the estimated frequency of atrazine detections 

as a percentage of shallow wells was greater than 75 percent. 

The actual frequency of atrazine detections in the glacialtill network was 18 percent (5 of 28 wells). If degradation 

products of atrazine are combined with atrazine detections, 

the detection frequency is 36 percent (10 of 28 wells). One 

reason the model did not accurately estimate the actual detection frequency in northeast Nebraska might be that the factors 

affecting pesticide detections in most areas of the country are 

not the same factors that affect pesticide detections in northeast Nebraska. The most important factors that explained 

variability in pesticide detections in the national model were 

the proportion of land with subsurface tile-drain systems and 

the average vertical permeability of soil. Another, less important, factor was atrazine use. These three factors explained 

55 percent of the variability in atrazine detection frequencies 

in the areas where pesticide concentrations were measured 

between 1992 and 2001. The only factor tested that affected 

pesticide detections in the Nebraska glacial-till study area was 

the presence of a road ditch within 164 ft of the well, which is 

explained further in the section on “Factors Related to Occurrence of Agricultural Chemicals in Shallow Ground Water.”

Because the two reference wells were located away from 

cropland, it was expected that the two reference wells would 

have few detectable pesticide compounds. However, eight 

pesticide compounds (acetochlor, atrazine, deethylatrazine, 

desulfinylfipronil amide, diuron, fipronil sulfone, metolachlor, 

and prometon) were detected at well W–R1, more compounds 

than any other site. Possible explanations could be historical 

land use, unreported applications, or movement from upgradient applications.

Ground-water samples collected from the Maple Creek 

watershed in 2004 (four flow-path wells and three glacial-till 

network wells) were analyzed for pesticides in May and October (table 9). The only parent pesticide compound detected 

was atrazine in shallow ground water under the cropped field 

(well FS1–1A), adjacent to the cropped field (well FS1–2A), 

and in the riparian area (well FS1–4A). Pesticide degradates 

detected in water from the four flow-path wells were acetochlor ethanesulfonic acid (ESA), acetochlor oxanilic acid 

(OXA), alachlor ESA, deethylatrazine, metolachlor ESA, and 

metolachlor OXA. In general, concentrations of atrazine and 

its degradates decreased slightly from May to October 2004, 

whereas concentrations of acetochlor, alachlor, and metolachlor compounds increased slightly from May to October. 

Only pesticide degradates were detected in the three glacial-till 

network wells sampled in 2004. In May, alachlor ESA was 

detected in two wells, and metolachlor ESA was detected in 

one well. More pesticides were detected in October; deethylatrazine was detected in one well, alachlor ESA was detected 

in two wells, alachlor ESA second amide was detected in one 

well, and metolachlor ESA was detected in one well (table 9).

Pesticide concentrations in ground-water samples collected in 2003 and 2004 were small and did not exceed public 

drinking-water standards where established. Deethyldeisopropylatrazine, a pesticide degradate that does not have a public 

drinking-water standard, had the largest pesticide compound 

concentration in a ground-water sample (estimated 0.76 μg/L 

in water from well CE–06). The well with the largest number 

of pesticide detections in one sample was well W–R1, with 

eight different pesticide compounds detected (fig. 6).

The LRL can affect the detection frequency of pesticide 

compounds; analytes with smaller LRLs are likely to have 

greater detection frequencies. To remove the effect of variable 

LRLs, detection frequencies of pesticide compounds were 

compared using a common assessment level of 0.04 μg/L. 

In samples collected from wells in the glacial-till network 

in 2003, deethyldeisopropylatrazine was detected in five 

samples at concentrations greater than or equal to 0.04 μg/L 

(fig. 7). Diuron was detected in one of the reference wells. The 

pesticide compounds detected at greater than or equal to the 

0.04-μg/L assessment level in flow-path samples in May 2004 

were alachlor ESA (three samples) and metolachlor ESA (two 

samples) (table 9). In October, pesticide compounds detected 

in flow-path wells equal to or greater than 0.04 μg/L were 

acetochlor ESA (one sample), acetochlor OXA (one sample), 

alachlor ESA (three samples), and metolachlor ESA (two 

samples). In ground-water samples collected in May 2004 

from the three glacial-till network wells in the Maple Creek 

watershed, alachlor ESA was detected in one well, and metolachlor ESA was detected in one well at concentrations greater 

Occurrence of Agricultural Chemicals in Shallow Ground Water 23
than or equal to the 0.04-μg/L assessment level. In October, 

alachlor ESA was detected in two wells, metolachlor ESA 

was detected in one well, and alachlor ESA second amide was 

detected in one well at concentrations greater than or equal 

to the 0.04-μg/L assessment level (table 9). Overall, the ESA 

degradates of alachlor and metolachlor accounted for 14 of 

the 17 pesticide compounds detected in 2004 at concentrations greater than or equal to the common assessment level of 

0.04 μg/L.

The presence of pesticides in ground water collected 

near crop fields provides evidence that agricultural chemicals are moving downward and affect ground-water quality. 

The primary pesticide compounds detected were the parent 

compound or degradates of acetochlor, alachlor, atrazine, and 

metolachlor. Overall, pesticide degradates were more commonly detected and were detected at larger concentrations than 

parent compounds.

Occurrence of Chemicals in the 

Unsaturated Zone

Unsaturated-zone sediment samples were collected 

at 28 of the 30 glacial-till network and reference well 

sites between May and October 2002. Sediment cores were 

analyzed for texture and chemical constituents (nitrate–N, 

ammonia–N, and chloride) (Appendix 2). Nitrate–N and 

ammonia–N concentrations in sediment-core samples can 

indicate that nitrogen fertilizers are stored in the unsaturated 

zone and that nitrogen may move downward to ground water 

(Spalding and Kitchen, 1988). Nitrate–N was detected in 

unsaturated-zone sediment samples at concentrations ranging from 1.86 to 27.4 mg/kg, with a median of 4.04 mg/kg. 

Ammonia concentrations in sediment samples ranged from 

0.84 to 17.8 mg/kg, with a median of 2.65 mg/kg. These 

concentrations were calculated by weight and, therefore, are 

not directly comparable to dissolved concentrations in water. 

However, data indicate that nitrogen in the forms of nitrate–N 

and ammonia–N is available in the unsaturated zone for transport to ground water. Nitrate–N and ammonia–N 

Table 9. Pesticide detections in ground-water samples collected in May and October 2004, northeast Nebraska glacial till, Maple Creek 

watershed.

[Constituents are dissolved; ESA, ethanesulfonic acid; OXA, oxanilic acid; SA, second amide; E, estimated; ND, not detected]

Well identifier (fig. 2) Pesticide compound Concentration in

May 2004 (μg/L)

Concentration in

October 2004 (μg/L)

Flow-path wells

FS1–1A Atrazine

Deethylatrazine

Alachlor ESA

Metolachlor ESA

0.037 

E.031

.20

.20

0.028 

E.021

.26

.26

FS1–2A Atrazine

Deethylatrazine

Alachlor ESA

Metolachlor ESA

.009

E.014

.25

.16

.008

E.013

.34

.17

FS1–3A Deethylatrazine

Alachlor ESA

Metolachlor ESA

E.006

.05

.03

ND

.06

.03

FS1–4A Atrazine

Acetochlor ESA

Acetochlor OXA

Metolachlor OXA

ND

ND

.02

.02

E.006

.07

.07

ND

Glacial-till network wells

D–24 Alachlor ESA

Deethylatrazine

Metolachlor ESA

.11

ND

.04

.13

E.006

.06

CO–13 None detected

S–11 Alachlor ESA

Alachlor ESA SA

.03

ND

.05

.08

24 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
concentrations in sediment samples were inversely correlated 

with sample depth (rho= -0.194, p=0.017 and rho= -0.306, 

p=0.004, respectively).

Nitrate–N concentrations were correlated with chloride 

concentrations (rho=0.303, p=<0.001). However, ammonia–N 

concentrations were not correlated with chloride (rho=0.022, 

p=0.833). Chloride is considered to be a conservative constituent that will accumulate in soils where evapotranspiration 

rates are large and recharge rates are small (Allison and others, 

1985; Scanlon and Goldsmith, 1997; Scanlon and others, 

2005; McMahon and others, 2006). Stored nitrate–N accompanied by chloride in the unsaturated zone can imply that the 

source of nitrate–N is, at least in part, naturally occurring salts 

that have accumulated as a result of evapotranspiration. However, this is not likely in this study area because its recharge 

rate is greater than the regions where this commonly occurs.

Factors Related to Occurrence of 

Agricultural Chemicals in Shallow 

Ground Water

Several factors were examined to determine their relation to the occurrence of agricultural chemicals in shallow 

ground water. Only samples collected from the 28 wells in the 

glacial-till network in 2003 were used as part of these analyses 

because random site-selection procedures were used for these 

wells. The variables considered for this analysis were water 

depth, aquifer-sediment and soil characteristics, land use, 

geologic unit, and well type. The residence time (amount of 

time since water has been isolated from contact with the atmosphere) of ground water typically is related to ground-water 

chemistry (McMahon and others, 2007). However, because of 

Concentration, in micrograms per liter

Prometon

Picloram

Metolachlor

Malathion

Imazethapyr

Flumetsulam

Fipronil sulfone

Diuron

Desulfinylfipronil amide

Deisopropylatrazine

Deethyldeisopropylatrazine

Deethylatrazine

Bentazon

Atrazine

Acetochlor

(A) Samples collected in 2003

(B) Samples collected in 2004

0.001 0.01 0.1 1.0 10

Metolachlor oxanilic acid

Metolachlor ethanesulfonic acid

Deethylatrazine

Atrazine

Alachlor ethanesulfonic acid second amide

Alachlor ethanesulfonic acid

Acetochlor oxanilic acid

Acetochlor ethanesulfonic acid

Common assessment level

(0.04 microgram per liter)

Common assessment level

(0.04 microgram per liter)

EXPLANATION

Concentrations in this range are less than the laboratory reporting level (LRL)

U.S. Environmental Protection Agency (2004) Maximum Contaminant Level for atrazine

Concentration of pesticide compound—Squares ( ) designate reference well

Estimated concentration of pesticide compound—Squares ( ) designate reference well

Figure 7. Concentrations of pesticide compounds in ground-water samples, northeast Nebraska glacial till, 2003–04.

Factors Related to Occurrence of Agricultural Chemicals in Shallow Ground Water 25
the study design, all ground-water samples had short residence 

times (less than 50 years) as determined by CFC and SF6

results, and therefore, residence time could not be used as a 

variable to explain differences in ground-water quality.

Water Depth

Water levels were measured onsite at each well immediately before sample collection. Larger concentrations of agricultural chemicals typically are found in areas where ground 

water is closer to the land surface. In spring 2003, water levels 

in the study area ranged from 2.10 to 62.30 ft below land 

surface, with a median of 22.17 ft below land surface (table 2). 

No correlation was found between nitrate–N concentrations 

and depth to water using Spearman’s rank correlation test 

(rho= -0.061, p= 0.751). The median depth to water in wells 

with no pesticide detections (22.23 ft; n=15) was not significantly different than the median depth to water in wells with 

pesticide detections (22.11 ft; n=13) using the Wilcoxon ranksum statistical test (p= 0.928). One possible reason for the 

lack of relation with depth to water is that water levels in all 

of the wells were shallow (within 65 ft below the land surface) 

and may represent similar conditions. Pesticide detections in 

ground water at these sites could also be the result of recharge 

from other areas. Another possible reason for the lack of a 

relation could be that ground water was sampled during a time 

of the year when many of the pesticides that were analyzed 

in this study were not typically present in the shallow ground 

water; pesticides applied in spring 2003 may have not reached 

ground water at the time of sampling, and pesticides applied 

the previous year may have already degraded.

Aquifer-Sediment and Soil Characteristics

Aquifer-sediment (well borehole) and soil characteristics 

were measured at wells in the glacial-till network and compared to nitrate–N concentrations and pesticide detections in 

ground water from these wells. Sediment collected from the 

well boreholes indicated that most of the wells were bored 

through sediment that was predominantly (at least 70 percent) silt (Appendix 2). Only one glacial-till network well 

(well S–01, fig. 1) was completed in sediment that was less 

than 50 percent silt (Appendix 2). Mean characteristics of surficial soils within a 1,640-ft radius of the well, including sand 

content, silt content, clay content, bulk density, organic matter 

content, vertical permeability of soils, and horizontal permeability were determined from the 1994 State Soil Geographic 

(STATSGO) database (U.S. Department of Agriculture, 1994; 

Schwarz and Alexander, 1995; Wolock, 1997). Nitrate–N concentrations were not related to either aquifer sediment in the 

well borehole or soil characteristics (table 10). Additionally, 

a Wilcoxon rank-sum statistical test indicated that the occurrence of pesticides was not related to either aquifer sediment 

or soil characteristics (table 11).

Land Use

Land-use characteristics were documented in the 

vicinity of each well within 164- and 1,640-ft buffers. Landuse characteristics included the presence of water-collecting 

ditches, perennial streams, farm house, manure storage or 

pasture, irrigation wells, and irrigated cropland. Nitrate–N 

concentrations and pesticide detections were compared for 

well sites where these land-use characteristics were present 

or absent (tables 2 and 12). The percentage of various land 

uses such as cropland also was estimated within 1,640-ft of 

each well using aerial photography and onsite visual inspection. The only characteristic significantly related to nitrate–N 

concentrations was the presence or absence of a perennial 

stream within 1,640 ft of the well site. The median nitrate–N 

concentration at sites where a perennial stream was present 

was 1.96 mg/L, whereas the median nitrate–N concentration 

in samples collected from sites where a perennial stream was 

not present was 10.5 mg/L (p=0.053, table 12). In northeastern Nebraska, areas draining to streams often are steeper and 

therefore kept as pasture, woodland, or grassland rather than 

cropland. For comparison, at the flow-path wells, the average nitrate–N concentration in May 2004 was 7.1 mg/L at the 

wells within 1,640 ft of Maple Creek (wells FS1–2A, FS1–3A, 

and FS1–4A) and 13.0 mg/L at the well farther than 1,640 ft 

away from Maple Creek (well FS1–1A).

The only characteristic significantly related to the presence of pesticide compounds was the presence or absence of 

a road ditch within 164 ft of the well site. Sixty-three percent 

of the samples collected from the glacial-till network wells 

located near a road ditch had at least one pesticide compound 

detected, and 11 percent of the samples collected from the 

wells not located near a road ditch had at least one detectable 

pesticide compound (p=0.016, table 12). For comparison, 

all of the flow-path wells were more than 164 ft from a road 

ditch, with all four wells having at least one pesticide detected 

in May 2004. Larger concentrations of agricultural chemicals 

near road ditches are expected because road ditches provide a 

setting that promotes focused recharge. Runoff from precipitation and (or) applied irrigation water can carry chemicals 

to road ditches where the water will collect and eventually 

infiltrate downward to the saturated zone.

Geologic Unit

Differences in geologic units also may explain differences 

in nitrate–N concentrations and pesticide detections. Wells 

in the glacial-till network were completed in five geologic 

units—Holocene-age alluvium and Pleistocene-age loess, sand 

and gravel, glacial till, and undifferentiated deposits (table 13). 

The median nitrate–N concentration was largest in groundwater samples collected from the Pleistocene-age loess. Loess 

deposits in central and southwest Nebraska have been known 

to contain naturally occurring nitrogen (Boyce and others, 

1976) and if the loess in northeast Nebraska is similar, the unit 

26  Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Table 10. Relations between nitrate as nitrogen (nitrate–N) concentrations in ground-water samples collected from glacial-till network wells and 

well-borehole and surficial soil characteristics, northeast Nebraska glacial till, 2003.

Variable (characteristics within 1,640 feet of borehole) Range of values Spearman’s rho p-value1

Percentage of sand and gravel in well borehole2 10.8–46.1 -0.023 0.909

Percentage of silt in well borehole2 47.9–79.5 -.017 .929

Percentage of clay in well borehole2 6.0–9.8 .157 .435

Average sand content of soils, in percent3 3.94–22.87 .118 .542

Average silt content of soils, in percent3 48.58–71.73 .058 .765

Average clay content of soils, in percent3 23.38–32.26 .100 .606

Average bulk density of soils, in grams per cubic centimeter3 1.27–1.48 –.204 .289

Average organic matter content, in percent by weight3 0.85–3.17 .133 .492

Average vertical permeability of soils, in inches per hour3 0.79–1.46 –.097 .612

Average horizontal permeability of soils, in inches per hour3 0.89–2.50 –.142 .458

1

p-values measure the probability that there is not a real correlation between two variables. Variables were considered correlated with nitrate–N if p-value 

was less than 0.10. 

2

Source: Well-borehole sediment-core samples.

3

Source: 1994 STATSGO database (U.S. Department of Agriculture, 1994; Schwarz and Alexander, 1995; Wolock, 1997).

Table 11. Pesticide compound detections in ground-water samples collected from glacial-till network wells related to well-borehole and surficial 

soil characteristics, northeast Nebraska glacial till, 2003.

Variable

(characteristics within 1,640 feet of borehole)

Median value near 

wells with no 

pesticides detected

Median value near wells 

with one or more 

pesticides detected

p-value 

(Wilcoxon rank-sum 

test)1

Percentage of sand and gravel in well borehole2 19.48 17.59 0.643

Percentage of silt in well borehole2 73.19 72.81 .940

Percentage of clay in well borehole2 7.95 9.07 .643

Average sand content of soils, in percent3 5.19 5.22 .853

Average silt content of soils, in percent3 66.93 66.93 .890

Average clay content of soils, in percent3 26.51 27.55 .404

Average bulk density of soils, in grams per cubic centimeter3 1.33 1.32 .331

Average organic matter content, in percent by weight3 1.35 1.56 .308

Average vertical permeability of soils, in inches per hour3 1.27 1.23 .308

Average horizontal permeability of soils, in inches per hour3 1.28 1.23 .211

1

p-values measure the probability that there is not a real difference between two groups. Groups were considered different if p-value was less than 0.10. 

2

Source: Well-borehole sediment-core samples.

3

Source: 1994 STATSGO database (U.S. Department of Agriculture, 1994; Schwarz and Alexander, 1995; Wolock, 1997).

Factors Related to Occurrence of Agricultural Chemicals in Shallow Ground Water 27
may be contributing to nitrate–N concentrations in ground 

water in this unit. In addition, 60 percent of the ground-water 

samples collected from the loess also had at least one pesticide 

detected, indicating that agricultural chemicals are present in 

the unit and are very likely a contributing factor to the elevated 

nitrate–N concentrations. Samples collected from Pleistocene-age sand and gravel and undifferentiated deposits had 

the highest percentages of samples with at least one detectable pesticide compound. Statistical tests were not performed 

because the number of water samples collected from each 

geologic unit was small.

Well Type

Nitrate–N and pesticide concentrations in the 28 glacial-till network samples collected in 2003 were compared 

with water samples collected by the Nebraska Department of 

Health and Human Services in 1994 and 1995 from 62 rural 

domestic wells in the Lower Elkhorn Natural Resources 

District (fig. 8, Appendix 3) (University of Nebraska, 2000). 

Samples collected from domestic wells typically draw water 

from a range of depths across the aquifer and provide a good 

indication of the variability of water quality with depth. Thus, 

samples from domestic wells provide an evaluation of the 

overall water-quality conditions within the aquifer. Alternatively, because samples collected from water-table monitoring wells are closest to the source of agricultural chemicals 

Table 12. Distribution of median nitrate as nitrogen concentrations and pesticide compound detections in glacial-till network wells, by 

land-use feature, northeast Nebraska glacial till, 2003.

[Nitrate–N, nitrate as nitrogen; mg/L, milligrams per liter; >, greater than]

Land-use feature

Number 

of sites 

where 

feature is 

present 

(out of 28)

Median 

nitrate–N 

concentration at sites 

where feature 

is present 

(mg/L)

Median 

nitrate–N 

concentration at 

sites where 

feature 

is absent 

(mg/L)

p-value 

(Wilcoxon 

rank-sum 

test)1

Percentage 

of sites 

that have a 

pesticide 

detected 

where 

feature is 

present 

Percentage of sites 

that have a 

pesticide 

detected 

where 

feature is 

absent 

p-value 

(Fisher’s 

exact 

test)2

Water-collecting road ditch within 164 feet 19 9.46 11.3 0.357 63 11 0.016

Perennial stream within 1,640 feet 5 1.96 10.5 .053 20 52 .333

Farmhouse within 164 feet 3 17.2 9.46 .391 33 48 >.5

Manure storage or pasture within 164 feet 4 12.6 9.53 >.5 0 54 .102

Irrigation well within 1,640 feet 6 15.85 7.81 .126 33 50 >.5

Irrigated cropland within 1,640 feet 8 10.5 9.18 >.5 25 55 .221

1

Wilcoxon (1945).

2

Agresti (1990).

Table 13. Distribution of nitrate as nitrogen concentrations and pesticide compound detections in ground-water samples collected from glacial-till 

network wells, by geologic unit, northeast Nebraska glacial till, 2003.

[nitrate–N, nitrate as nitrogen; mg/L, milligrams per liter; ND, not detected]

Geologic 

system

Geologic 

series Geologic unit Number of samples

Minimum 

nitrate–N 

concentration

(mg/L)

Median nitrate–N 

concentration

(mg/L)

Maximum 

nitrate–N 

concentration

(mg/L)

Percentage of 

samples with 

at least one 

pesticide 

compound 

detected

Quaternary

Holocene alluvium 6 ND 6.14 29.5 17

loess 10 1.14 19.3 69.5 60

Pleistocene sand and gravel 3 1.07 4.91 6.35 67

glacial till 6 .91 2.51 28.9 33

undifferentiated deposits 3 8.9 9.6 15.1 67

28  Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
MONONA

Big Blue River

PLATTE

BURT

PIERCE

DODGE

POLK

CUMING

BUTLER

WAYNE

DIXON

MADISON

SAUNDERS

CEDAR

COLFAX

STANTON

KNOX

THURSTON

DAKOTA

UNION PLYMOUTH

WASHINGTON

NANCE

DOUGLAS

MERRICK

SARPY

IO

NEBRASK

WA

A

WOODBURY

Missouri River

Platte River

97°50' 40' 30' 20' 10' 97° 50' 40' 30' 96°20'

41°10'

20'

30'

40'

50'

42°

10'

20'

42°30'

Maple Creek watershed

boundary

0 5 10 15 20 MILES

0 1 5 0 15 20 KILOMETERS

Boundary of Central Nebraska

Basins Study Unit

Boundary of Central Nebraska

Basins Study Unit

Boundary of study area

Boundary of study area

EXPLANATION

Average nitrogen application rates from manure and fertilizer (1987–97), in 

 pounds per acre of cropland per year

Nitrate as nitrogen (nitrate-N) 

 concentration, in milligrams 

 per liter

26–50

51–75

76–100

Greater than 100

Domestic well and map number—Data presented in Appendix 3

Less than or equal to 4.00

4.01 to 10.0

Greater than 10.0

Boundary of study area

Boundary

of study area

Base from Nebraska Department of Natural Resources in work

share agreement with U.S. Geological Survey, 1:12,000 digital data

Albers Equal-Area Conic projection

Standard parallels 29°30’, and 45°30’, central meridian -96°

Horizontal coordinate information is referenced to the North American

 Datum of 1983 (NAD 83)

Nitrogen application rates from Ruddy and others (2006)

Nitrate-N concentrations from University of Nebraska (2000)

1

2

61

60

58 59 53

57

62

54

55

56

3

35

33

36

32

34

37

39

42

41

40

38

4

8

19

28

31

32

29

26

27

24

25

17

46

43

51

50

52

44

45 48

49

47

14

20

21 22

23

18

12

11

10

9

16

13

15

6

7

5

5

Figure 8. Nitrate as nitrogen concentrations in ground-water samples collected from domestic wells, northeast 

Nebraska, 1994–95.

Factors Related to Occurrence of Agricultural Chemicals in Shallow Ground Water 29
that originate from above the aquifer, they are more likely to 

have the largest concentrations of those constituents. Depths 

of these 62 domestic wells had a wider range (20 to 330 ft 

below land surface, Appendix 3) and deeper median depth 

(120 ft below land surface) than the wells in the glacial-till 

network (15 to 73 ft; median depth 33.4 ft; table 2). The 

median nitrate–N concentration in water collected from wells 

in the glacial-till network in 2003 (9.53 mg/L, table 7) was 

significantly larger (p=0.069) than the median concentration 

in water collected from domestic wells in 1994 and 1995 

(4.12 mg/L, Appendix 3).

Domestic well samples were analyzed for 12 pesticides—alachlor, atrazine, butylate, chlorpyrifos, cyanazine, 

ethyl parathion, fonofos, methyl parathion, metolachlor, 

metribuzin, terbufos, and trifluralin (Appendix 3). Except for 

ethyl parathion, all of these compounds also were analyzed in 

the 2003 samples from the glacial-till network wells and were 

used for comparison. Because the LRL can affect the detection 

frequency of pesticide compounds, a common LRL was used 

for each pesticide compound. The LRLs of the pesticides analyzed in domestic-well samples were larger (0.05 to 2.5 μg/L) 

than the LRLs of the same pesticides analyzed in glacial-till 

network samples (0.003 to 0.02 μg/L). Therefore, if the pesticide concentration in a glacial-till network sample was less 

than the domestic well LRL for that pesticide, it was not considered to be a detection for comparison purposes. Using this 

method of comparison, one domestic-well sample had detectable concentrations of one pesticide (atrazine), and none of the 

glacial-till network samples had detectable concentrations of 

any of the 11 pesticides compared. Water-quality comparisons 

by well type should be considered with caution because the 

amounts of nitrogen (Ruddy and others, 2006) and pesticides 

(Nebraska Agricultural Statistics Service, 2005) used in the 

study area have changed between 1994–95 and 2003–04, and 

these comparisons, therefore, could be skewed.

Summary

Because agricultural chemicals applied at the land surface 

are more likely to be observed in the shallowest part of an 

aquifer, shallow ground-water samples were collected and 

analyzed in 2003 and 2004 from 34 wells in the glaciated area 

of northeast Nebraska. Land use in this area was 97 percent 

agriculture, predominately corn and soybeans. Ground-water 

age dating indicated that the water in the samples from these 

shallow wells had recharged less than 50 years ago.

Analytical results indicated that the agricultural chemicals are present in recently recharged ground water. Nitrate–N 

concentrations indicated that human activity has affected 

approximately two-thirds of the wells near corn and (or) 

soybean fields. Nitrate–N concentrations in samples collected 

in spring 2003 from the 28 glacial-till network wells ranged 

from undetected to 69.5 mg/L, with a median of 9.53 mg/L. In 

May 2004, the largest nitrate–N concentration from the flowpath wells was in shallow ground water beneath the pasture 

(21.1 mg/L as N, well FS1–3A). Nitrate–N also was detected 

in ground water beneath the cropped field (13.0 mg/L as N, 

well FS1–1A) but was not detected in the shallow ground 

water on the edge of the cropped field (well FS1–2A) and in 

the riparian zone (well FS1–4A).

The principal pesticide compounds that were detected in 

samples collected from the 34 wells reflect the most-used pesticides in the area and include parent or degradate compounds 

of acetochlor, alachlor, atrazine, and metolachlor. Overall, 

pesticide concentrations in ground-water samples collected in 

2003 and 2004 were small and did not exceed public drinking-water standards where established. Deethyldeisopropylatrazine, a pesticide degradate with no public drinking-water 

standard, was the pesticide compound with the largest concentration (estimated 0.76 μg/L).

Unsaturated-zone soil cores indicated that nitrogen in 

the forms of nitrate–N and ammonia–N was available in the 

unsaturated zone for transport to ground water. Additionally, the concentrations of nitrate–N and ammonia–N in these 

soil cores were inversely correlated to depth, and nitrate–N 

concentrations were correlated to chloride concentrations. 

For ground-water samples, the presence of a perennial stream 

within 1,640 ft of the well was correlated to smaller nitrate–N 

concentrations, and the presence of a road ditch within 164 ft 

of the well was correlated to the presence of detectable pesticides. All other variables tested showed no significant correlations to nitrate–N concentrations or pesticide detections.

Nitrate-N was the principal agricultural contaminant 

found in the shallow ground water and unsaturated zone 

beneath northeast Nebraska glacial till, particularly at concentrations that may be of concern to resource managers or 

planners. The median concentration in shallow ground water 

was not far below the drinking-water MCL, and the presence 

of elevated nitrate concentrations in ground water and unsaturated zone solids greater than concentrations present in the 

aquifer presently used for supplying domestic drinking water 

could have implications for attentive monitoring of the fate of 

these contaminants in the ground-water system of northeast 

Nebraska.

References Cited

Agresti, Alan, 1990, Categorical data analysis: New York, 

John Wiley, 576 p.

Allison, G.B., Stone, W.J., and Hughes, M.W., 1985, Recharge 

in karst and dune elements of a semi-arid landscape as indicated by natural isotopes and chloride: Journal of Hydrology, v. 76, p. 1–25.

30 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
American Public Health Association, 1998, Standard methods 

for the examination of water and wastewater (20th ed.): 

Washington, D.C., American Public Health Association, 

American Water Works Association, and Water Environment Federation, p. 3–37—3–43.

Becker, M.F., Bruce, B.W., Pope, L.M., and Andrews, W.J., 

2002, Ground-water quality in the central High Plains aquifer, Colorado, Kansas, New Mexico, Oklahoma, and Texas, 

1999: U.S. Geological Survey Water-Resources Investigations Report 02–4112, 64 p.

Bentall, Ray, and others, 1971, Water supplies and the land, 

the Elkhorn River Basin of Nebraska: Lincoln, University 

of Nebraska-Lincoln Conservation and Survey Division 

Resource Atlas No. 1, 51 p.

Bhattacharyya, G.K., and Johnson, R.A., 1977, Statistical 

concepts and methods: New York, John Wiley, 639 p.

Böhlke, J.K., 2002, Groundwater recharge and agricultural 

contamination: Hydrogeology Journal, v. 10, p. 153–179.

Boyce, J.S., Muir, John, Edwards, A.P., Seim, E.C., and 

Olson, R.A., 1976, Geologic nitrogen in Pleistocene loess 

of Nebraska: Journal of Environmental Quality, v. 5, no. 1, 

p. 93–96.

Brenton, R.W., and Arnett, T.L., 1993, Methods of analysis by 

the U.S. Geological Survey National Water Quality Laboratory—determination of dissolved organic carbon by UVpromoted persulfate oxidation and infrared spectrometry: 

U.S. Geological Survey Open-File Report 92–480, 12 p.

Bruce, B.W., Becker, M.F., Pope, L.M., and Gurdak, J.J., 

2003, Ground-water quality beneath irrigated agriculture in 

the central High Plains aquifer, 1999–2000: U.S. Geological Survey Water-Resources Investigations Report 02–4219, 

39 p.

Bullister, J.L., 1984, Atmospheric chlorofluoromethanes as 

tracers of ocean circulation and mixing—studies in the 

Greenland and Norwegian Seas: San Diego, University of 

California, Ph.D. dissertation, 172 p.

Bullister, J.L., and Weiss, R.F., 1988, Determination of CCl3F 

and CClF2 in seawater and air: Deep-Sea Research, v. 35, 

no. 5, p. 839–854.

Busenberg, Eurybiades, and Plummer, L.N., 1992, Use of 

chlorofluorocarbons (CCl3F and CCl2F2) as hydrologic tracers and age-dating tools—the alluvium and terrace system 

of central Oklahoma: Water Resources Research, v. 28, 

no. 9, p. 2257–2283.

Busenberg, Eurybiades, and Plummer, L.N., 2000, Dating 

young ground water with sulfur hexafluoride—natural 

and anthropogenic sources of sulfur hexafluoride: Water 

Resources Research, v. 36, p. 3011–3030.

Childress, C.J., Oblinger, Foreman, W.T., Connor, B.F., and 

Maloney, T.J., 1999, New reporting procedures based on 

long-term method detection levels and some considerations 

for interpretation of water-quality data provided by the U.S. 

Geological Survey National Water Quality Laboratory: U.S. 

Geological Survey Open-File Report 99–193, 19 p.

Ellis, M.J., 1984, Overview of the Dakota aquifer system 

in Nebraska, in Jorgensen, D.G. and Signor, D.C., eds., 

Geohydrology of the Dakota aquifer: Worthington, Ohio, 

National Water Well Association, Proceedings of Symposium held October 5–6, 1982, Lincoln, Nebraska, p. 48–55.

Faires, L.M., 1993, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—determination of metals in water by inductively coupled plasmamass spectrometry: U.S. Geological Survey Open-File 

Report 92–634, 28 p.

Fishman, M.J., ed., 1993, Methods of analysis by the U.S. 

Geological Survey National Water Quality Laboratory—

determination of inorganic and organic constituents in water 

and fluvial sediments: U.S. Geological Survey Open-File 

Report 93–125, 217 p.

Fishman, M.J., and Friedman, L.C., 1989, Methods for 

determination of inorganic substances in water and fluvial 

sediments: U.S. Geological Survey Techniques of WaterResources Investigations, book 5, chap. A1, 545 p.

Flowerday, C.A., Kuzelka, R.D., and Pederson, D.T., 1998, 

The groundwater atlas of Nebraska (2d ed.): University 

of Nebraska–Lincoln, Conservation and Survey Division, 

Resource Atlas No. 4A, 44 p.

Fredrick, B.S., Linard, J.I., and Carpenter, J.L., 2006, Environmental setting of Maple Creek watershed, Nebraska: U.S. 

Geological Survey Scientific Investigations Report 2006–

5037, 22 p.

Furlong, E.T., Anderson, B.D., Werner, S.L., Soliven, P.P., 

Coffey, L.J., and Burkhardt, M.R., 2001, Methods of 

analysis by the U.S. Geological Survey National Water 

Quality Laboratory—determination of pesticides in water 

by graphitized carbon-based solid-phase extraction and 

high-performance liquid chromatography/mass spectrometry: U.S. Geological Survey Water-Resources Investigations 

Report 01–4134, 73 p.

Garbarino, J.R., 1999, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—determination of dissolved arsenic, boron, lithium, selenium, 

strontium, thallium, and vanadium using inductively 

coupled plasma-mass spectrometry: U.S. Geological Survey 

Open-File Report 99–093, 31 p.

References Cited  31
Gee, G.W., and Or, Dani, 2002, Particle-size analysis, in

Dane, J.H., and Topp, G.C., eds., Methods of soil analysis, 

part 4—physical methods: Madison, Wisconsin, Soil Science Society of America, Book Series No. 5, p. 255–293.

Gilliom, R.J., Alley, W.M., and Gurtz, M.E., 1995, Design of 

the National Water-Quality Assessment Program—occurrence and distribution of water-quality conditions: U.S. 

Geological Survey Circular 1112, 33 p.

Gilliom, R.J., Barbash, J.E., Crawford, C.G., Hamilton, P.A., 

Martin, J.D., Nakagaki, Naomi, Nowell, L.H., Scott, J.C., 

Stackelberg, P.E., Thelin, G.P., and Wolock, D.M., 2006, 

The quality of our Nation’s waters—pesticides in the 

Nation’s streams and ground water, 1992–2001: U.S. Geological Survey Circular 1291, 172 p.

Goolsby, D.A., Battaglin, W.A., Lawrence, G.B., Artz, 

R.S., Aulenbach, B.T., Hooper, R.P., Keeney, D.R., and 

Stensland, G.J., 1999, Flux and sources of nutrients in the 

Mississippi-Atchafalaya River Basin—topic 3 report for the 

integrated assessment on hypoxia in the Gulf of Mexico: 

Silver Spring, Maryland, National Oceanic and Atmospheric Administration, Coastal Ocean Program, Decision 

Analysis Series No. 17, 130 p.

Gosselin, D.C., 1991, Bazile Triangle groundwater quality 

study: University of Nebraska–Lincoln, Conservation and 

Survey Division, Water-Supply Paper 68, 29 p.

Gosselin, D.C., Headrick, Jacqueline, Chen, Xun-Hong, Summerside, Scott, and Tremblay, Rod, 1996, Northeast glacial 

drift area hydrogeologic summary from domestic well-water 

quality in rural Nebraska: University of Nebraska–Lincoln, 

Conservation and Survey Division GIM–98, 4 p.

Helsel, D.R., 2005, Nondetects and data analysis—statistics 

for censored environmental data: Hoboken, New Jersey, 

John Wiley, 250 p.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in 

water resources: Amsterdam, The Netherlands, Elsevier Science B.V., 529 p.

Hitch, D.E., Hull, S.H., Walczyk, V.C., Miller, J.D., and Drudik, R.A., 2004, Water resources data, Nebraska, water year 

2003: U.S. Geological Survey Water-Data Report NE–03–

01, 470 p.

Hitch, D.E., Walczyk, V.C., Drudik, R.A., Miller, J.D., 

and Hull, S.H., 2005, Water resources data, Nebraska, 

water year 2004: U.S. Geological Survey Water-Data 

Report NE–04–1, 673 p.

Kish, J.L., Thurman, E.M., Scribner, E.A., and Zimmerman, 

L.R., 2000, Methods of analysis by the U.S. Geological 

Survey Organic Geochemistry Research Group—determination of selected herbicides and their degradation products 

in water using solid-phase extraction and gas chromatography/mass spectrometry: U.S. Geological Survey Open-File 

Report 00–385, 13 p.

Lapham, W.W., Wilde, F.D., and Koterba, M.T., 1997, Guidelines and standard procedures for studies of ground-water 

quality—selection and installation of wells, and supporting 

documentation: U.S. Geological Survey Water-Resources 

Investigations Report 96–4233, 110 p., available on Web, 

accessed August 8, 2007, at http://water.usgs.gov/owq/pubs/

wri/wri964233/wri964233.pdf

Lee, E.A., and Strahan, A.P., 2003, Methods of analysis by the 

U.S. Geological Survey Organic Geochemistry Research 

Group—determination of acetamide herbicides and their 

degradation products in water using online solid-phase 

extraction and liquid chromatography/mass spectrometry: 

U.S. Geological Survey Open-File Report 03–173, 17 p.

Lindley, C.E., Stewart, J.T., and Sandstrom, M.W., 1996, 

Determination of low concentrations of acetochlor in water 

by automated solid-phase extraction and gas chromatography with mass selective detection: Journal of Association 

of Official Analytical Chemists International, v. 79, no. 4, 

p. 962–966.

Madsen, J.E., Sandstrom, M.W., and Zaugg, S.D., 2003, 

Methods of analysis by the U.S. Geological Survey National 

Water Quality Laboratory—a method supplement for the 

determination of fipronil and degradates in water by gas 

chromatography/mass spectrometry: U.S. Geological Survey Open-File Report 02–462, 11 p.

Madison, R.J., and Brunett, J.O., 1985, Overview of the occurrence of nitrate in ground water of the United States, in

National water summary 1984—hydrologic events, selected 

water-quality trends, and ground-water resources: U.S. Geological Survey Water-Supply Paper 2275, p. 93–105.

McLain, Betty, 1993, Methods of analysis by the U.S. Geological Survey National Water Quality Laboratory—determination of chromium in water by graphite furnace atomic 

absorption spectrophotometry: U.S. Geological Survey 

Open-File Report 93–449, 16 p.

McMahon, P.B., 2001, Vertical gradients in water chemistry 

in the central High Plains aquifer, southwestern Kansas and 

Oklahoma Panhandle, 1999: U.S. Geological Survey WaterResources Investigations Report 01–4028, 35 p.

McMahon, P.B., Böhlke, J.K., and Carney, C.P., 2007, Vertical 

gradients in water chemistry and age in the northern High 

Plains aquifer, Nebraska, 2003: U.S. Geological Survey 

Scientific Investigations Report 2006–5294, 58 p.

32 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
McMahon, P.B., and Böhlke, J.K., 2006, Regional controls on 

the isotopic composition of nitrate in ground water, High 

Plains, USA: Environmental Science & Technology, v. 40, 

no. 9, p. 2965–2970.

McMahon, P.B., Dennehy, K.F., Bruce, B.W., Böhlke, J.K., 

Michel, R.L., Gurdak, J.J., and Hurlbut, D.B., 2006, Storage 

and transit time of chemicals in thick unsaturated zones 

under rangeland and irrigated cropland, High Plains, United 

States: Water Resources Research, v. 42, no. 3, WO3413, 

18 p.

Miller, R.W., and Donahue, R.L., 1990, Soils—an introduction 

to soils and plant growth (6th ed.): Englewood Cliffs, New 

Jersey, Prentice–Hall Inc., 767 p.

Mueller, D.K., and Helsel, D.R., 1996, Nutrients in the 

Nation’s waters—too much of a good thing?: U.S. Geological Survey Circular 1136, 24 p.

National Center for Food and Agricultural Policy, 1997, 

National pesticide use database: Washington, D.C., National Center for Food and Agricultural Policy, information 

available on Web, accessed December 29, 2004, at 

http://www.ncfap.org/database/default.php

National Climatic Data Center, 2007, Annual climatological 

summary, station 251825, Columbus 3 NE: National Climatic Data Center data available on Web, accessed August 

8, 2007, at http://cdo.ncdc.noaa.gov/ancsum/ACS

Nebraska Agricultural Statistics Service, 2005, Pesticide use 

trends: Nebraska Department of Agriculture, information 

available on Web, accessed January 28, 2007, at http://www.

agr.state.ne.us/division/bpi/pes/html_files/trends.htm

Nebraska Department of Natural Resources, 2007, Registered groundwater wells data retrieval: Lincoln, Nebraska 

Department of Natural Resources, information available on 

Web, accessed May 29, 2007, at http://dnrdata.dnr.ne.gov/

wellssql/

Newport, T.G., 1957, Reconnaissance of the groundwater resources of the Elkhorn River basin above Pilger, Nebraska: U.S. Geological Survey Water-Supply 

Paper 1360–I, p. 713–754.

Patton, C.J., and Kryskalla, J.R., 2003, Methods of analysis by 

the U.S. Geological Survey National Water Quality Laboratory—evaluation of alkaline persulfate digestion as an alternative to Kjeldahl digestion for determination of total and 

dissolved nitrogen and phosphorus in water: U.S. Geological Survey Water-Resources Investigations Report 03–4174, 

33 p.

Plummer, L.N., and Busenberg, Ed, 1999, Chlorofluorocarbons—tools for dating and tracing young groundwater, 

chap. 15, in Environmental tracers in subsurface hydrology: 

Boston, Kluwer Academic Publishers, p. 441–478.

Ruddy, B.C., Lorenz, D.L., and Mueller, D.K., 2006, Countylevel estimates of nutrient inputs to the land surface of 

the conterminous United States, 1982–2001: U.S. Geological Survey Scientific Investigations Report 2006–5012, 

17 p., available on Web, accessed June 13, 2006, at 

http://pubs.usgs.gov/sir/2006/5012/

Scanlon, B.R., and Goldsmith, R.S., 1997, Field study of 

spatial variability in unsaturated flow beneath and adjacent 

to playas: Water Resources Research, v. 33, no. 10, p. 2239–

2252.

Scanlon, B.R, Reedy, R.C., Stonestrom, D.A., Prudic, D.E., 

and Dennehy, K.F., 2005, Impact of land use and land 

cover change on groundwater recharge and quality in the 

southwestern United States: Global Change Biology, v. 11, 

p. 1577–1593.

Schwarz, G.E., and Alexander, R.B., 1995, State soil geographic (STATSGO) database for the conterminous United 

States: U.S. Geological Survey Open-File Report 95–449, 

digital data available on Web, accessed August 25, 2006, at 

http://water.usgs.gov/GIS/metadata/usgswrd/XML/

ussoils.xml

Scott, J.C., 1990, Computerized stratified random siteselection approaches for design of a ground-water-quality 

sampling network: U.S. Geological Survey Water-Resources 

Investigations Report 90–4101, 109 p.

Spalding, R.F., and Kitchen, L.A., 1988, Nitrate in the intermediate vadose zone beneath irrigated cropland: GroundWater Monitoring Review, v. 8, no. 2, p. 89–95.

University of Nebraska, 2000, Quality-assessed agrichemical 

contaminant database for Nebraska ground water: Nebraska 

Department of Natural Resources, digital data available 

on Web, accessed August 18, 2006, at http://dnrdata.dnr.

ne.gov/clearinghouse/index.asp

U.S. Department of Agriculture, 1994, State soil geographic 

(STATSGO) database for Nebraska: U.S. Department of 

Agriculture digital data, available on Web, accessed August 

25, 2006, at http://www.ncgc.nrcs.usda.gov/

products/datasets/statsgo/index.html

U.S. Department of Agriculture, 1999, 1997 Census of agriculture, volume 1, geographic area series, U.S. summary 

and county level data: U.S. Department of Agriculture, 

digital data available on Web, accessed June 12, 2006, at 

http://www.nass.usda.gov/Census_of_Agriculture/1997/

index.asp

U.S. Department of Agriculture, variously dated, National 

Agricultural Statistics Service data base: U.S. Department 

of Agriculture, information available on Web, accessed 

June 22, 2005, at http://www.nass.usda.gov/census/

References Cited  33
U.S. Environmental Protection Agency, 2004, 2004 Edition of 

the drinking water standards and health advisories: Washington, D.C., Office of Water, EPA 822–R–04–005, 12 p.

U.S. Geological Survey, 1992, National land characteristics 

data set, nominal 1992: U.S. Geological Survey, information 

available on Web, accessed March 3, 2005, at

http://eros.usgs.gov/products/landcover/nlcd.html

U.S. Geological Survey, 2004, Water use in the United States: 

U.S. Geological Survey, data available on Web, accessed 

July 29, 2004, at http://water.usgs.gov/watuse/

U.S. Geological Survey, 2005, CFC sampling method: 

U.S. Geological Survey, information available on Web, 

accessed July 23, 2007, at http://water.usgs.gov/lab/

chlorofluorocarbons/sampling/bottles/

U.S. Geological Survey, 2006, Water resources data, Nebraska, 

water year 2005: U.S. Geological Survey Water Data 

Report NE–05, available on Web, accessed August 8, 2007, 

at http://web10capp.er.usgs.gov/adr_lookup/wdr-ne-05/

U.S. Geological Survey, variously dated, National field manual 

for the collection of water-quality data: U.S. Geological 

Survey Techniques of Water-Resources Investigations, book 

9, chaps. A1–A9, available on Web, accessed August 8, 

2007, at http://pubs.water.usgs.gov/twri9A

Verstraeten, I.M., and Ellis, M.J., 1995, Reconnaissance of 

ground-water quality in the Papio-Missouri River Natural 

Resources District, eastern Nebraska, July–September 1992: 

U.S. Geological Survey Water-Resources Investigations 

Report 94–4197, 90 p.

Wilcoxon, Frank, 1945, Individual comparisons by ranking 

methods: Biometrics, v. 1, p. 80–83.

Winter, T.C., 2001, The concept of hydrologic landscapes: 

Journal of the American Water Resources Association, 

v. 37, no. 2, p. 335–349.

Wolock, D.M., 1997, STATSGO soil characteristics for the 

conterminous United States: U.S. Geological Survey OpenFile Report 97–656, digital data.

Wolock, D.M., Winter, T.C., and McMahon, Gerard, 2004, 

Delineation and evaluation of hydrologic landscape regions 

in the United States using geographic information system 

tools and multivariate statistical analyses: Environmental 

Management, v. 34, suppl. 1, p. s71–s88.

Zaugg, S.D., Sandstrom, M.W., Smith, S.G., and Fehlberg, 

K.M., 1995, Methods of analysis by the U.S. Geological 

Survey National Water Quality Laboratory—determination 

of pesticides in water by C–18 solid-phase extraction and 

capillary-column gas chromatography/mass spectrometry 

with selected-ion monitoring: U.S. Geological Survey 

Open-File Report 95–181, 60 p.

Zimmerman, L.R., and Thurman, E.M., 1999, Method of 

analysis by the U.S. Geological Survey Organic Geochemistry Research Group—determination of triazine and chloroacetanilide herbicides in water by solid-phase extraction 

and capillary-column gas chromatography/mass spectrometry with selected-ion monitoring: U.S. Geological Survey 

Open-File Report 98–634, 21 p.

34 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Appendixes
Appendix 1. Pesticides analyzed in ground-water samples collected from northeast Nebraska glacial till, 2003–04.

[USGS, U.S. Geological Survey; CAS, Chemical Abstracts Service; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; MCL, 

Maximum Contaminant Level; ESA, ethanesulfonic acid; OXA, oxanilic acid; SAA, sulfynil acetic acid; ESA SA, ethanesulfonic acid second amide; LTHA, 

Lifetime Health Advisory; --, not determined or not applicable]

Pesticide name

USGS 

parameter 

code

CAS number Sample 

year

Highest 

laboratory 

reporting 

level

(μg/L)

Mean fieldmatrix spike 

recovery

(percent)

Pesticide type

USEPA 

drinkingwater 

standard 

(μg/L) / type 

of standard1

1-Naphthol 49295 90–15–3 2004 0.09 -- degradate --

2-Chloro-2,6-diethylacetanilide 61618 6967–29–9 2004 .005 -- degradate --

2-Ethyl-6-methylaniline 61620 24549–06–2 2004 .004 -- degradate --

2-Hydroxyatrazine (OIET)2 50355 2163–68–0 2003 .008 -- degradate --

2,4-D 39732 94–75–7 2003 .02 138.1 herbicide 70 / MCL

2,4-DB2 38746 94–82–6 2003 .02 74.8 herbicide --

2,4-D methyl ester 50470 1928–38–7 2003 .009 73.3 herbicide --

2,6-Diethylaniline 82660 579–66–8 2003, 2004 .006 103.1 degradate --

3-Hydroxycarbofuran 49308 16655–82–6 2003 .006 83.9 degradate --

3-Ketocarbofuran2 50295 16709–30–1 2003 1.5 0.0 degradate --

3,4-Dichloroaniline 61625 95–76–1 2004 .004 -- degradate --

4-Chloro-2-methylphenol 61633 1570–64–5 2004 .006 -- degradate --

Acetochlor 49260 34256–82–1 2003, 2004 .006 113.5 herbicide --

Acetochlor ESA 61029 -- 2004 .02 -- degradate --

Acetochlor OXA 61030 -- 2004 .02 -- degradate --

Acetochlor SAA 62847 -- 2004 .02 -- degradate --

Acetochlor / metolachlor ESA SA 62850 -- 2004 .02 -- degradate --

Acifluorfen 49315 50594–66–6 2003 .007 96.0 herbicide --

Alachlor 46342 15972–60–8 2003, 2004 .005 106.9 herbicide 2 / MCL

Alachlor ESA 50009 -- 2004 .02 -- degradate --

Alachlor ESA SA 62849 -- 2004 .02 -- degradate --

Alachlor OXA 61031 -- 2004 .02 -- degradate --

Alachlor SAA 62848 140939–16–8 2004 .02 -- degradate --

Aldicarb2 49312 116–06–3 2003 .04 7.5 insecticide 3 / MCL

Aldicarb sulfone2 49313 1646–88–4 2003 .02 59.9 degradate 3 / MCL

Aldicarb sulfoxide2 49314 1646–87–3 2003 .008 56.7 degradate 4 / MCL

Alpha-HCH 34253 319–84–6 2003 .005 104.7 insecticide / 

degradate

--

Atrazine 39632 1912–24–9 2003, 2004 .007 107.9 herbicide 3 / MCL

Azinphos-methyl2 82686 86–50–0 2003, 2004 .05 75.4 insecticide --

Azinphos-methyl, oxygen analog 61635 961–22–8 2004 .02 -- degradate --

36  Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Appendix 1. Pesticides analyzed in ground-water samples collected from northeast Nebraska glacial till, 2003–04.—Continued

[USGS, U.S. Geological Survey; CAS, Chemical Abstracts Service; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; MCL, 

Maximum Contaminant Level; ESA, ethanesulfonic acid; OXA, oxanilic acid; SAA, sulfynil acetic acid; ESA SA, ethanesulfonic acid second amide; LTHA, 

Lifetime Health Advisory; --, not determined or not applicable]

Pesticide name

USGS 

parameter 

code

CAS number Sample 

year

Highest 

laboratory 

reporting 

level

(μg/L)

Mean fieldmatrix spike 

recovery

(percent)

Pesticide type

USEPA 

drinkingwater 

standard 

(μg/L) / type 

of standard1

Bendiocarb 50299 22781–23–3 2003 0.03 75.9 insecticide --

Benfluralin 82673 1861–40–1 2003, 2004 .01 81.8 herbicide --

Benomyl 50300 17804–35–2 2003 .004 54.5 fungicide --

Bensulfuron 61693 83055–99–6 2003 .02 116.7 herbicide --

Bentazon2 38711 25057–89–0 2003 .01 53.8 herbicide 200 / LTHA

Bromacil2 04029 314–40–9 2003 .03 68.7 herbicide 90 / LTHA

Bromoxynil2 49311 1689–84–5 2003 .02 83.2 herbicide --

Butylate 04028 2008–41–5 2003 .004 105.2 herbicide 400 / LTHA

Carbaryl2 82680 63–25–2 2003, 2004 .041 98.0 insecticide 700 / LTHA

Carbofuran2 82674 1563–66–2 2003 .02 108.1 insecticide 40 / MCL

Chloramben methyl ester2 61188 7286–84–2 2003 .02 74.1 herbicide --

Chlorimuron 50306 90982–32–4 2003 .01 90.4 herbicide --

Chlorothalonil2 49306 1897–45–6 2003 .04 9.4 fungicide --

Chlorpyrifos 38933 2921–88–2 2003, 2004 .005 91.6 insecticide 20 / LTHA

Chlorpyrifos, oxygen analog 61636 5598–15–2 2004 .06 -- fungicide --

cis-Permethrin 82687 54774–45–7 2003, 2004 .006 62.0 insecticide --

Clopyralid 49305 1702–17–6 2003 .01 92.6 herbicide --

Cyanazine 04041 21725–46–2 2003 .018 118.4 herbicide 1 / LTHA

Cycloate2 04031 1134–23–2 2003 .01 72.5 herbicide --

Cyfluthrin 61585 68359–37–5 2004 .008 -- insecticide --

Cypermethrin 61586 52315–07–8 2004 .009 -- insecticide --

Dacthal monoacid 49304 887–54–7 2003 .01 116.5 degradate --

DCPA 82682 1861–32–1 2003, 2004 .003 104.8 herbicide 70 / LTHA

Deethylatrazine (CIAT)2 04040 6190–65–4 2003, 2004 .006 65.7 degradate --

Deethyldeisopropylatrazine(CAAT)2 04039 3397–62–4 2003 .04 -- degradate --

Deisopropylatrazine (CEAT)2 04038 1007–28–9 2003 .04 53.3 degradate --

Desulfinylfipronil 62170 -- 2003, 2004 .012 -- degradate --

Desulfinylfipronil amide 62169 -- 2003, 2004 .029 -- degradate --

Diazinon 39572 333–41–5 2003, 2004 .005 103.7 insecticide 0.6 / LTHA

Diazinon, oxygen analog 61638 962–58–3 2004 .01 -- degradate --

Appendix 1  37
Appendix 1. Pesticides analyzed in ground-water samples collected from northeast Nebraska glacial till, 2003–04.—Continued

[USGS, U.S. Geological Survey; CAS, Chemical Abstracts Service; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; MCL, 

Maximum Contaminant Level; ESA, ethanesulfonic acid; OXA, oxanilic acid; SAA, sulfynil acetic acid; ESA SA, ethanesulfonic acid second amide; LTHA, 

Lifetime Health Advisory; --, not determined or not applicable]

Pesticide name

USGS 

parameter 

code

CAS number Sample 

year

Highest 

laboratory 

reporting 

level

(μg/L)

Mean fieldmatrix spike 

recovery

(percent)

Pesticide type

USEPA 

drinkingwater 

standard 

(μg/L) / type 

of standard1

Dicamba 38442 1918–00–9 2003 0.01 90.9 herbicide --

Dichlorprop 49302 120–36–5 2003 .01 94.6 herbicide/

insecticide/

fumigant

--

Dichlorvos 38775 62–73–7 2004 .01 -- degradate --

Dicrotophos 38454 141–66–2 2004 .08 -- insecticide --

Dieldrin 39381 60–57–1 2003, 2004 .009 83.4 insecticide --

Dimethenamid 61588 87674–68–8 2004 .02 -- herbicide --

Dimethenamid ESA 61951 -- 2004 .02 -- degradate --

Dimethanamid OXA 62482 -- 2004 .02 -- degradate --

Dimethoate 82662 60–51–5 2004 .006 -- insecticide --

Dinoseb 49301 88–85–7 2003 .01 94.4 herbicide 7 / MCL

Diphenamid 04033 957–51–7 2003 .03 79.9 herbicide 200 / MCL

Disulfoton 82677 298–04–4 2003 .02 35.3 insecticide 0.3 / LTHA

Diuron 49300 330–54–1 2003 .01 105.8 herbicide 10 / LTHA

EPTC 82668 759–94–4 2003 .01 88.9 herbicide --

Ethalfluralin 82663 55283–68–6 2003 .009 94.4 herbicide --

Ethion 82346 563–12–2 2004 .004 -- insecticide --

Ethion monoxon 61644 17356–42–2 2004 .03 -- degradate --

Ethoprop 82672 13194–48–4 2003 .005 81.5 insecticide --

Fenamiphos 61591 22224–92–6 2004 .03 -- nematocide 2 / LTHA

Fenamiphos sulfone 61645 31972–44–8 2004 .008 -- degradate --

Fenamiphos sulfoxide 61646 31972–43–7 2004 .03 -- degradate --

Fenuron 49297 101–42–8 2003 .03 61.2 herbicide --

Fipronil 62166 120068–37–3 2003, 2004 .016 -- insecticide --

Fipronil sulfide 62167 120067–83–6 2003, 2004 .013 -- degradate --

Fipronil sulfone 62168 120068–36–2 2003, 2004 .024 -- degradate --

Flufenacet 62481 142459–58–3 2004 .02 -- herbicide --

Flufenacet ESA 61952 -- 2004 .02 -- degradate --

38  Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Appendix 1. Pesticides analyzed in ground-water samples collected from northeast Nebraska glacial till, 2003–04.—Continued

[USGS, U.S. Geological Survey; CAS, Chemical Abstracts Service; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; MCL, 

Maximum Contaminant Level; ESA, ethanesulfonic acid; OXA, oxanilic acid; SAA, sulfynil acetic acid; ESA SA, ethanesulfonic acid second amide; LTHA, 

Lifetime Health Advisory; --, not determined or not applicable]

Pesticide name

USGS 

parameter 

code

CAS number Sample 

year

Highest 

laboratory 

reporting 

level

(μg/L)

Mean fieldmatrix spike 

recovery

(percent)

Pesticide type

USEPA 

drinkingwater 

standard 

(μg/L) / type 

of standard1

Flufenacet OXA 62483 -- 2004 0.02 -- degradate --

Flumetsulam2 61694 98967–40–9 2003 .01 119.9 herbicide --

Fluometuron 38811 2164–17–2 2003 .03 89.0 herbicide 90 / LTHA

Fonofos 04095 944–22–9 2003, 2004 .003 101.5 insecticide 10 / LTHA

Fonofos, oxygen analog 61649 -- 2004 .002 -- degradate --

Hexazinone 04025 51235–04–2 2004 .013 -- herbicide 400 / LTHA

Imazaquin2 50356 81335–37–7 2003 .02 111.3 herbicide --

Imazethapyr2 50407 81335–77–5 2003 .02 120.0 herbicide --

Imidacloprid 61695 138261–41–3 2003 .007 108.2 insecticide --

Iprodione 61593 36734–19–7 2004 1 -- fungicide --

Isofenphos 61594 25311–71–1 2004 .003 -- insecticide --

Lindane 39341 58–89–9 2003 .004 103.7 insecticide 0.2 / MCL

Linuron 38478 330–55–2 2003 .01 98.1 herbicide --

Malaoxon 61652 1634–78–2 2004 .008 -- degradate --

Malathion 39532 121–75–5 2003, 2004 .027 91.5 insecticide 100 / LTHA

MCPA 38482 94–74–6 2003 .02 93.1 herbicide 4 / LTHA

MCPB2 38487 94–81–5 2003 .01 110.6 herbicide --

Metalaxyl 50359 57837–19–1 2003 .02 76.2 fungicide --

Metalaxyl 61596 57837–19–1 2004 .005 -- fungicide --

Methidathion 61598 950–37–8 2004 .006 -- insecticide --

Methiocarb2 38501 2032–65–7 2003 .008 91.2 insecticide --

Methomyl2 49296 16752–77–5 2003 .004 77.2 insecticide 200 / LTHA

Methyl paraoxon 61664 950–35–6 2004 .03 -- degradate --

Methyl parathion 82667 298–00–0 2003, 2004 .015 100.0 insecticide 2 / LTHA

Metolachlor 39415 51218–45–2 2003, 2004 .013 103.0 herbicide 100 / LTHA

Metolachlor ESA 61043 -- 2004 .02 -- degradate --

Metolachlor OXA 61044 -- 2004 .02 -- degradate --

Metribuzin 82630 21087–64–9 2003, 2004 .006 102.4 herbicide 200 / LTHA

Metsulfuron2 61697 74223–64–6 2003 .03 33.9 herbicide --

Molinate 82671 2212–67–1 2003 .003 89.9 herbicide --

Appendix 1  39
Appendix 1. Pesticides analyzed in ground-water samples collected from northeast Nebraska glacial till, 2003–04.—Continued

[USGS, U.S. Geological Survey; CAS, Chemical Abstracts Service; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; MCL, 

Maximum Contaminant Level; ESA, ethanesulfonic acid; OXA, oxanilic acid; SAA, sulfynil acetic acid; ESA SA, ethanesulfonic acid second amide; LTHA, 

Lifetime Health Advisory; --, not determined or not applicable]

Pesticide name

USGS 

parameter 

code

CAS number Sample 

year

Highest 

laboratory 

reporting 

level

(μg/L)

Mean fieldmatrix spike 

recovery

(percent)

Pesticide type

USEPA 

drinkingwater 

standard 

(μg/L) / type 

of standard1

Myclobutanil 61599 88671–89–0 2004 0.008 -- fungicide --

3-(4-Chlorophenyl)-1-methyl urea 61692 5352–88–5 2003 .02 77.4 degradate --

Napropamide 82684 15299–99–7 2003 .007 72.3 herbicide --

Neburon 49294 555–37–3 2003 .01 98.1 herbicide --

Nicosulfuron2 50364 111991–09–4 2003 .01 147.0 herbicide --

Norflurazon2 49293 27314–3–2 2003 .02 99.9 herbicide --

Oryzalin 49292 19044–88–3 2003 .02 76.3 herbicide --

Oxamyl 38866 23135–22–0 2003 .01 77.7 insecticide 200 / MCL

p,p’-DDE 34653 72–55–9 2003 .003 62.1 degradate --

Parathion 39542 56–38–2 2003 .01 112.3 insecticide --

Pebulate 82669 1114–71–2 2003 .004 89.6 herbicide --

Pendimethalin 82683 40487–42–1 2003, 2004 .022 73.7 herbicide --

Phorate 82664 298–02–2 2003, 2004 .011 61.2 insecticide --

Phorate, oxygen analog 61666 2600–69–3 2004 .1 -- degradate --

Phosmet 61601 732–11–6 2004 .008 -- insecticide --

Phosmet, oxygen analog 61668 3735–33–9 2004 .06 -- degradate --

Picloram 49291 1918–02–1 2003 .02 94.5 herbicide 500 / MCL

Prometon 04037 1610–18–0 2003, 2004 .01 115.6 herbicide 100 / LTHA

Prometryn 04036 7287–19–6 2004 .005 -- herbicide --

Propachlor 04024 1918–16–7 2003 .025 98.8 herbicide 90 / LTHA

Propachlor ESA 62766 -- 2004 .05 -- degradate --

Propachlor OXA 62767 -- 2004 .02 -- degradate --

Propanil 82679 709–98–8 2003 .011 95.1 herbicide --

Propargite 82685 2312–35–8 2003 .02 75.2 acaricide --

Propham 49236 122–42–9 2003 .01 95.2 herbicide 100 / LTHA

Propiconazole 50471 60207–90–1 2003 .02 85.3 fungicide --

Propoxur 38538 114–26–1 2003 .008 92.6 insecticide --

Propyzamide 82676 23950–58–5 2003, 2004 .004 92.7 herbicide 50 / LTHA

Siduron 38548 1982–49–6 2003 .02 87.2 herbicide --

Simazine 04035 122–34–9 2003, 2004 .005 101.9 herbicide 4 / MCL

40 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Appendix 1. Pesticides analyzed in ground-water samples collected from northeast Nebraska glacial till, 2003–04.—Continued

[USGS, U.S. Geological Survey; CAS, Chemical Abstracts Service; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; MCL, 

Maximum Contaminant Level; ESA, ethanesulfonic acid; OXA, oxanilic acid; SAA, sulfynil acetic acid; ESA SA, ethanesulfonic acid second amide; LTHA, 

Lifetime Health Advisory; --, not determined or not applicable]

Pesticide name

USGS 

parameter 

code

CAS number Sample 

year

Highest 

laboratory 

reporting 

level

(μg/L)

Mean fieldmatrix spike 

recovery

(percent)

Pesticide type

USEPA 

drinkingwater 

standard 

(μg/L) / type 

of standard1

Sulfometuron2 50337 74222–97–2 2003 0.009 134.7 herbicide --

Tebuthiuron 82670 34014–18–1 2003, 2004 .02 110.7 herbicide 500 / LTHA

Terbacil2 82665 5902–51–2 2003 .034 99.9 herbicide 90 / LTHA

Terbufos 82675 13071–79–9 2003, 2004 .02 70.9 insecticide 0.9 / LTHA

Terbufos, oxygen analog sulfone 61674 56070–15–6 2004 .07 -- degradate --

Terbuthylazine 04022 5915–41–3 2004 .01 -- herbicide --

Thiobencarb 82681 28249–77–6 2003 .005 100.2 herbicide --

Triallate 82678 2303–17–5 2003 .002 92.9 herbicide --

Triclopyr 49235 55335–06–3 2003 .02 101.9 herbicide --

Trifluralin 82661 1582–09–8 2003, 2004 .009 85.8 herbicide 5 / LTHA

1

Source: U.S. Environmental Protection Agency (2004).

2

These pesticides are qualitatively identified and reported with an E (estimated value) because of problems with gas chromatography or extraction or do not 

meet laboratory method performance criteria (Zaugg and others, 1995).

Appendix 1 41
Appendix 2. Unsaturated-zone borehole-sediment sample results, northeast Nebraska glacial till, May–October 2002.

[Nitrate–N, nitrate as nitrogen; Ammonia–N, ammonia as nitrogen; <, less than; >, greater than; mg/kg, milligrams per kilogram; mm, millimeter; NA, not analyzed]

Well 

identifier 

(fig. 1)

U.S. Geological 

Survey site number

Sample 

depth 

(feet 

below 

land 

surface)

Nitrate–N 

(mg/kg)

Ammonia–

N (mg/kg)

Chloride 

(mg/kg)

Percentage of sample composed of indicated grain size

Clay (<2 

microns) 

(<0.002 

mm)

Silt 

(2–50 

microns) 

(0.002–

0.05 mm)

Very fine 

sand 

(50–100 

microns) 

(0.05–0.1 

mm)

Fine sand 

(100–250 

microns) 

(0.1–0.25

mm)

Medium 

sand 

(250–500 

microns) 

(0.25–0.5

mm)

Coarse 

sand 

(500–1,000 

microns) 

(0.5–1 mm)

Very coarse 

sand 

(1,000–2,000 

microns) 

(1–2 mm)

Gravel 

(>2,000 

microns) 

(>2 mm)

B–27 414931096321101 0 7.96 2.54 10.8 7.12 63.8 22.0 5.18 1.08 0.81 0 0B–27 414931096321101 10 4.67 3.64 12.0 10.2 78.9 9.75 1.20 0 0 0 0

B–27 414931096321101 20 NA NA NA 10.2 82.9 6.85 .03 0 0 0 0B–28 415220096214801 0 7.01 3.53 8.76 7.32 69.6 22.6 .44 0 0 0 0

B–28 415220096214801 10 NA NA NA 10.0 77.8 10.6 1.52 0 0 0 0B–28 415220096214801 20 NA NA NA 11.3 83.9 4.86 0 0 0 0 0

CE–06 422947097142701 0 6.74 2.11 10.2 6.88 65.0 24.5 3.45 .16 0 0 0CE–06 422947097142701 10 NA NA NA 6.51 68.1 24.3 1.08 0 0 0 0CE–06 422947097142701 20 NA NA NA 10.4 76.7 12.9 .01 0 0 0 0

CE–17 422802097031601 0 5.15 2.27 27.6 6.60 70.6 22.1 .76 0 0 0 0

CE–17 422802097031601 8 NA NA NA 11.3 81.0 7.21 .36 0 0 0 .08CE–17 422802097031601 22 NA NA NA 2.41 11.8 3.01 26.4 42.2 13.7 .50 0CO–13 414343096595801 0 5.96 2.63 15.1 7.05 73.1 18.3 .06 0 0 0 1.44

CO–13 414343096595801 10 6.39 2.79 8.77 6.47 73.8 19.1 .58 0 0 0 0CO–13 414343096595801 20 NA NA NA 9.94 81.0 9.06 .01 0 0 0 0

CU–19 420024096485901 0 24.6 2.79 11.5 6.87 64.3 22.9 5.54 0 0 0 .48

CU–19 420024096485901 10 7.00 4.00 6.62 8.87 81.5 9.63 0 0 0 0 0CU–19 420024096485901 20 NA NA NA 9.98 83.9 6.14 0 0 0 0 0

42 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Appendix 2. Unsaturated-zone borehole-sediment sample results, northeast Nebraska glacial till, May–October 2002.—Continued

[Nitrate–N, nitrate as nitrogen; Ammonia–N, ammonia as nitrogen; <, less than; >, greater than; mg/kg, milligrams per kilogram; mm, millimeter; NA, not analyzed]

Well 

identifier 

(fig. 1)

U.S. Geological 

Survey site number

Sample 

depth 

(feet 

below 

land 

surface)

Nitrate–N 

(mg/kg)

Ammonia–

N (mg/kg)

Chloride 

(mg/kg)

Percentage of sample composed of indicated grain size

Clay (<2 

microns) 

(<0.002 

mm)

Silt 

(2–50 

microns) 

(0.002–

0.05 mm)

Very fine 

sand 

(50–100 

microns) 

(0.05–0.1 

mm)

Fine sand 

(100–250 

microns) 

(0.1–0.25

mm)

Medium 

sand 

(250–500 

microns) 

(0.25–0.5

mm)

Coarse 

sand 

(500–1,000 

microns) 

(0.5–1 mm)

Very coarse 

sand 

(1,000–2,000 

microns) 

(1–2 mm)

Gravel 

(>2,000 

microns) 

(>2 mm)

CU–20 415558096434501 0 2.96 2.37 13.2 9.06 75.6 13.7 1.62 0 0 0 0CU–20 415558096434501 10 2.92 1.66 6.74 9.95 78.8 11.2 .02 0 0 0 0

CU–20 415558096434501 20 3.52 1.86 4.71 10.5 81.0 8.22 .26 0 0 0 0

CU–20 415558096434501 30 3.98 1.41 11.0 9.48 82.5 8.02 .01 0 0 0 0

CU–29 415918096350501 0 5.59 2.36 3.09 8.68 76.0 11.4 1.87 .24 0 0 1.80

CU–29 415918096350501 10 3.15 17.8 2.84 9.73 67.8 10.9 6.92 1.39 0 0 3.29CU–29 415918096350501 20 NA NA NA 14.8 72.2 7.83 3.94 0 0 0 1.24CU–29 415918096350501 30 NA NA NA 14.8 84.1 .02 0 0 0 0 1.12

CU–30 420248096300901 0 4.53 4.02 11.4 7.82 61.4 20.2 6.66 1.32 1.13 0 1.42CU–30 420248096300901 10 4.46 2.96 9.89 9.82 78.9 7.65 .47 0 0 0 3.19

CU–30 420248096300901 20 4.22 3.62 10.20 9.12 84.1 6.65 .03 0 0 0 .06

CU–30 420248096300901 30 NA NA NA 11.1 75.9 11.9 .50 0 0 0 .67D–21 414401096531301 0 8.53 3.81 16.5 6.74 58.9 13.6 1.88 0 0 0 19.0

D–21 414401096531301 10 3.24 1.74 8.55 9.47 78.5 12.0 .01 0 0 0 0D–21 414401096531301 20 NA NA NA 10.3 85.1 4.53 0 0 0 0 0D–21 414401096531301 30 NA NA NA 9.71 83.4 6.56 .36 0 0 0 0

D–22 413853096483801 0 3.72 2.11 9.85 8.28 76.0 15.3 .39 0 0 0 0

D–22 413853096483801 10 5.18 2.79 6.30 10.1 80.2 9.71 0 0 0 0 0D–22 413853096483801 20 27.4 2.84 48.9 9.81 81.1 7.72 1.34 0 0 0 0

D–22 413853096483801 30 NA NA NA 10.5 85.2 4.33 0 0 0 0 0D–22 413853096483801 35 NA NA NA 9.35 80.9 9.30 .44 0 0 0 0

Appendix 2 43
Appendix 2. Unsaturated-zone borehole-sediment sample results, northeast Nebraska glacial till, May–October 2002.—Continued

[Nitrate–N, nitrate as nitrogen; Ammonia–N, ammonia as nitrogen; <, less than; >, greater than; mg/kg, milligrams per kilogram; mm, millimeter; NA, not analyzed]

Well 

identifier 

(fig. 1)

U.S. Geological 

Survey site number

Sample 

depth 

(feet 

below 

land 

surface)

Nitrate–N 

(mg/kg)

Ammonia–

N (mg/kg)

Chloride 

(mg/kg)

Percentage of sample composed of indicated grain size

Clay (<2 

microns) 

(<0.002 

mm)

Silt 

(2–50 

microns) 

(0.002–

0.05 mm)

Very fine 

sand 

(50–100 

microns) 

(0.05–0.1 

mm)

Fine sand 

(100–250 

microns) 

(0.1–0.25

mm)

Medium 

sand 

(250–500 

microns) 

(0.25–0.5

mm)

Coarse 

sand 

(500–1,000 

microns) 

(0.5–1 mm)

Very coarse 

sand 

(1,000–2,000 

microns) 

(1–2 mm)

Gravel 

(>2,000 

microns) 

(>2 mm)

D–24 413340096402701 0 3.89 3.07 4.33 4.91 52.4 29.7 10.2 1.79 1.01 0 0D–24 413340096402701 8 3.45 3.56 12.3 9.06 79.1 10.6 1.13 0 0 0 .07

D–24 413340096402701 13 3.20 1.41 3.88 4.67 37.6 14.1 36.6 6.84 0 0 .22

D–26 414141096371701 0 4.65 3.20 9.57 6.80 63.1 28.2 1.90 0 0 0 0

D–26 414141096371701 10 11.9 2.92 61.2 8.00 78.7 13.3 .01 0 0 0 0

D–26 414141096371701 20 3.42 2.12 11.5 8.18 78.0 13.1 .59 0 0 0 0D–26 414141096371701 28 3.63 2.16 3.92 8.97 82.1 8.91 0 0 0 0 0

D–26 414141096371701 40 3.82 2.19 4.90 NA NA NA NA NA NA NA NA

DI–16 422011096595401 0 4.61 1.99 14.1 6.09 66.2 21.9 4.45 .78 .53 0 0

DI–16 422011096595401 10 3.34 2.48 8.76 8.70 79.0 12.3 .01 0 0 0 0DI–16 422011096595401 20 3.31 2.84 20.6 8.51 79.8 11.5 .20 0 0 0 0

DI–16 422011096595401 30 3.39 1.51 14.77 9.17 79.5 11.4 .01 0 0 0 0DI–16 422011096595401 40 3.69 2.85 14.05 NA NA NA NA NA NA NA NA

DI–16 422011096595401 55 3.12 1.24 3.43 NA NA NA NA NA NA NA NA

K–05 422756097334901 0 5.70 2.74 7.25 5.85 60.4 28.0 5.44 .25 0 0 .09

K–05 422756097334901 10 3.91 2.00 4.05 10.7 82.0 6.24 .18 0 0 0 .91K–05 422756097334901 20 3.45 1.89 5.03 12.51 82.6 4.88 0 0 0 0 0

K–05 422756097334901 30 NA NA NA 8.46 75.3 10.3 5.68 0 0 0 .30

P–02 421357097243201 0 6.02 3.45 4.32 6.99 67.7 25.3 .08 0 0 0 0P–02 421357097243201 10 NA NA NA 10.3 71.3 13.7 .04 0 0 0 4.71P–02 421357097243201 15 NA NA NA 10.5 73.0 15.3 .78 0 0 0 .44P–02 421357097243201 20 NA NA NA 10.4 73.1 13.8 2.68 0 0 0 0

44 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Appendix 2. Unsaturated-zone borehole-sediment sample results, northeast Nebraska glacial till, May–October 2002.—Continued

[Nitrate–N, nitrate as nitrogen; Ammonia–N, ammonia as nitrogen; <, less than; >, greater than; mg/kg, milligrams per kilogram; mm, millimeter; NA, not analyzed]

Well 

identifier 

(fig. 1)

U.S. Geological 

Survey site number

Sample 

depth 

(feet 

below 

land 

surface)

Nitrate–N 

(mg/kg)

Ammonia–

N (mg/kg)

Chloride 

(mg/kg)

Percentage of sample composed of indicated grain size

Clay (<2 

microns) 

(<0.002 

mm)

Silt 

(2–50 

microns) 

(0.002–

0.05 mm)

Very fine 

sand 

(50–100 

microns) 

(0.05–0.1 

mm)

Fine sand 

(100–250 

microns) 

(0.1–0.25

mm)

Medium 

sand 

(250–500 

microns) 

(0.25–0.5

mm)

Coarse 

sand 

(500–1,000 

microns) 

(0.5–1 mm)

Very coarse 

sand 

(1,000–2,000 

microns) 

(1–2 mm)

Gravel 

(>2,000 

microns) 

(>2 mm)

P–03 422156097314301 0 2.40 2.66 5.41 5.87 59.7 30.3 4.02 0.04 0 0 0

P–03 422156097314301 10 1.86 2.13 4.08 8.01 65.6 20.8 5.41 .01 0 0 .21P–03 422156097314301 20 1.99 1.33 2.62 4.51 25.0 4.05 31.6 32.4 2.33 0 0

P–03 422156097314301 23 2.35 2.35 5.52 NA NA NA NA NA NA NA NAP–03 422156097314301 30 2.68 1.87 15.8 12.1 72.3 13.1 .83 0 0 0 1.79

P–04 422441097404601 0 6.08 3.01 9.06 6.69 65.0 25.7 2.43 .06 0 0 .09P–04 422441097404601 10 4.09 3.19 3.18 10.1 75.5 12.5 .04 0 0 0 1.88

P–04 422441097404601 20 3.94 1.96 3.92 11.0 76.6 12.4 0 0 0 0 0P–04 422441097404601 30 4.43 1.93 2.69 11.2 78.8 9.96 0 0 0 0 0

P–04 422441097404601 40 4.51 1.54 5.15 NA NA NA NA NA NA NA NA

P–04 422441097404601 50 4.18 1.45 3.36 NA NA NA NA NA NA NA NA

S–01 414948097212601 0 5.26 2.42 9.54 6.28 63.1 24.9 4.94 0 0 0 .76

S–01 414948097212601 10 6.36 1.73 7.35 10.1 77.9 11.9 .03 0 0 0 0S–01 414948097212601 18 3.68 1.09 5.82 4.66 32.6 11.5 23.6 23.9 3.65 0 0

S–01 414948097212601 30 2.69 1.19 4.58 2.71 18.0 7.47 32.3 34.5 5.05 .02 0

S–10 420425097101301 0 4.45 5.30 3.57 5.63 60.2 30.7 3.41 .06 0 0 0

S–10 420425097101301 10 3.36 3.06 1.78 8.40 78.1 13.0 .44 0 0 0 0S–10 420425097101301 20 NA NA NA 10.0 78.8 11.2 0 0 0 0 0S–10 420425097101301 30 NA NA NA 10.2 79.6 9.13 1.11 .01 0 0 0 Appendix 2 

45
Appendix 2. Unsaturated-zone borehole-sediment sample results, northeast Nebraska glacial till, May–October 2002.—Continued

[Nitrate–N, nitrate as nitrogen; Ammonia–N, ammonia as nitrogen; <, less than; >, greater than; mg/kg, milligrams per kilogram; mm, millimeter; NA, not analyzed]

Well 

identifier 

(fig. 1)

U.S. Geological 

Survey site number

Sample 

depth 

(feet 

below 

land 

surface)

Nitrate–N 

(mg/kg)

Ammonia–

N (mg/kg)

Chloride 

(mg/kg)

Percentage of sample composed of indicated grain size

Clay (<2 

microns) 

(<0.002 

mm)

Silt 

(2–50 

microns) 

(0.002–

0.05 mm)

Very fine 

sand 

(50–100 

microns) 

(0.05–0.1 

mm)

Fine sand 

(100–250 

microns) 

(0.1–0.25

mm)

Medium 

sand 

(250–500 

microns) 

(0.25–0.5

mm)

Coarse 

sand 

(500–1,000 

microns) 

(0.5–1 mm)

Very coarse 

sand 

(1,000–2,000 

microns) 

(1–2 mm)

Gravel 

(>2,000 

microns) 

(>2 mm)

S–11 414527097094101 0 5.03 3.17 12.7 8.01 72.1 17.6 2.25 0 0 0 0.08

S–11 414527097094101 10 2.22 1.97 8.08 9.61 81.0 9.2 .22 0 0 0 0S–11 414527097094101 20 2.36 2.31 8.02 9.14 80.3 10.0 .56 0 0 0 0

S–11 414527097094101 28 4.20 3.09 4.90 9.02 80.0 10.7 .26 0 0 0 0

S–11 414527097094101 40 3.45 5.73 3.62 9.55 77.7 9.19 3.41 .15 0 0 .04

S–R2 415458097142201 0 4.24 1.95 7.31 2.60 24.8 11.5 4.0 18.7 2.24 .01 0S–R2 415458097142201 10 3.01 .84 2.55 1.53 6.07 7.91 5.3 29.0 5.14 .01 0

S–R2 415458097142201 17 3.54 1.35 4.13 2.11 6.71 9.01 62.2 17.8 2.13 0 0

W–07 422031097043501 0 5.52 2.59 4.56 7.26 69.9 21.4 .03 0 0 0 1.43

W–07 422031097043501 10 3.71 3.13 19.6 9.53 80.2 10.3 0 0 0 0 0

W–07 422031097043501 20 4.71 2.66 22.7 14.6 70.9 6.29 0 0 0 0 8.12W–07 422031097043501 30 4.40 3.04 4.30 14.1 73.7 7.78 2.86 0 0 0 1.49

W–07 422031097043501 40 4.16 3.59 3.92 NA NA NA NA NA NA NA NAW–07 422031097043501 50 5.24 3.94 3.23 NA NA NA NA NA NA NA NA

W–07 422031097043501 58 5.12 6.26 1.95 NA NA NA NA NA NA NA NA

W–07 422031097043501 60 4.11 1.86 3.68 NA NA NA NA NA NA NA NA

W–08 421829097112401 0 4.12 4.30 9.11 7.53 67.0 23.0 2.17 0 0 0 .34W–08 421829097112401 10 3.67 3.93 8.98 10.3 76.4 13.0 .04 0 0 0 .27

W–08 421829097112401 20 3.79 2.90 7.90 10.8 79.2 10.0 0 0 0 0 0

W–08 421829097112401 30 NA NA NA 9.45 76.0 14.5 .01 0 0 0 0

46  Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Appendix 2. Unsaturated-zone borehole-sediment sample results, northeast Nebraska glacial till, May–October 2002.—Continued

[Nitrate–N, nitrate as nitrogen; Ammonia–N, ammonia as nitrogen; <, less than; >, greater than; mg/kg, milligrams per kilogram; mm, millimeter; NA, not analyzed]

Well 

identifier 

(fig. 1)

U.S. Geological 

Survey site number

Sample 

depth 

(feet 

below 

land 

surface)

Nitrate–N 

(mg/kg)

Ammonia–

N (mg/kg)

Chloride 

(mg/kg)

Percentage of sample composed of indicated grain size

Clay (<2 

microns) 

(<0.002 

mm)

Silt 

(2–50 

microns) 

(0.002–

0.05 mm)

Very fine 

sand 

(50–100 

microns) 

(0.05–0.1 

mm)

Fine sand 

(100–250 

microns) 

(0.1–0.25

mm)

Medium 

sand 

(250–500 

microns) 

(0.25–0.5

mm)

Coarse 

sand 

(500–1,000 

microns) 

(0.5–1 mm)

Very coarse 

sand 

(1,000–2,000 

microns) 

(1–2 mm)

Gravel 

(>2,000 

microns) 

(>2 mm)

W–09 421149097121301 0 3.10 4.68 2.74 9.95 74.1 12.8 1.87 0.16 0 0 1.11W–09 421149097121301 10 2.28 2.46 3.23 NA NA NA NA NA NA NA NA

W–09 421149097121301 20 5.34 1.96 2.42 9.95 80.4 9.61 .03 0 0 0 0

W–09 421149097121301 30 4.90 1.88 2.50 9.80 80.4 9.78 0 0 0 0 0W–14 420526096543901 0 4.75 5.56 3.57 8.34 70.7 19.9 1.02 0 0 0 0

W–14 420526096543901 10 2.47 3.52 6.04 10.7 78.0 9.74 .57 0 0 0 .98

W–14 420526096543901 20 NA NA NA 10.0 84.6 5.34 .04 0 0 0 0W–14 420526096543901 30 NA NA NA 9.82 81.1 8.70 .32 0 0 0 .05W–15 421303097011601 0 5.09 7.46 3.34 7.70 63.7 21.8 6.35 .43 0 0 0W–15 421303097011601 10 4.83 4.55 1.71 10.8 78.5 10.6 .06 0 0 0 0

W–15 421303097011601 20 NA NA NA 10.6 78.3 10.7 .38 0 0 0 0W–15 421303097011601 30 NA NA NA 5.03 35.6 7.20 12.1 13.4 12.6 6.51 7.71W–R1 421445097123801 0 3.08 3.33 7.84 9.03 72.4 16.9 .07 0 0 0 1.58

W–R1 421445097123801 10 3.14 3.44 3.92 10.1 79.3 10.5 .04 0 0 0 0

W–R1 421445097123801 20 2.87 2.20 8.14 9.71 79.6 10.7 .05 0 0 0 0W–R1 421445097123801 30 3.35 2.81 7.11 10.4 81.7 7.88 .01 0 0 0 0

W–R1 421445097123801 40 3.98 1.43 8.42 NA NA NA NA NA NA NA NA

Appendix 2 47
Appendix 3. Nitrate as nitrogen and pesticide concentrations in ground-water samples collected from domestic wells, northeast Nebraska glacial 

till, 1994–95. 

[Source: University of Nebraska (2000). Nitrate–N, nitrate as nitrogen; mg/L, milligrams per liter; μg/L, micrograms per liter; <, less than]

Map 

identifier 

(fig. 8)

Database 

number

County

Well 

depth 

(feet 

below 

land 

surface)

Date 

sampled 

(month/day/

year)

Longitude 

(decimal 

degrees)

Latitude 

(decimal 

degrees)

Nitrate–N 

(mg/L)

Alachlor 

(μg/L)

Atrazine 

(μg/L)

Butylate 

(μg/L)

Chlorpyrifos 

(μg/L)

Cyanazine 

(μg/L)

1 115912 Burt 50 3/23/1995 -96.40028 41.75997 1.4 <0.2 <0.1 <0.2 <0.4 <2.5

2 115992 Cedar 250 5/11/1995 -97.2857 42.36977 2.0 <.2 <.1 <.2 <.4 <2.5

3 115993 Cedar 250 5/11/1995 -97.23723 42.39881 8.7 <.2 <.1 <.2 <.4 <2.5

4 116018 Cedar 180 5/9/1995 -97.09855 42.47099 33.0 <.2 <.1 <.2 <.4 <2.5

5 115819 Colfax 120 1/25/1995 -97.03495 41.52887 8.3 <.2 <.1 <.2 <.4 <2.5

6 115853 Colfax 320 1/25/1995 -97.07339 41.63012 2.6 <.2 <.1 <.2 <.4 <2.5

7 115856 Colfax 305 2/15/1995 -96.92979 41.60842 3.3 <.2 <.1 <.2 <.4 <2.5

8 115885 Colfax 40 1/25/1995 -96.98784 41.67397 197 <.2 <.1 <.2 <.4 <2.5

9 113649 Cuming 150 4/17/1995 -96.92744 41.75366 1.0 <.2 <.1 <.2 <.4 <2.5

10 113650 Cuming 100 4/17/1995 -96.90814 41.78264 3.2 <.2 <.1 <.2 <.4 <2.5

11 113651 Cuming 52 4/13/1995 -96.72362 41.8401 <.1 <.2 .26 <.2 <.4 <2.5

12 113652 Cuming 100 4/13/1995 -96.79171 41.8695 <.1 <.2 <.1 <.2 <.4 <2.5

13 113653 Cuming 140 4/13/1995 -96.77279 41.74624 1.9 <.2 <.1 <.2 <.4 <2.5

14 113654 Cuming 55 4/17/1995 -96.60824 41.88356 27.1 <.2 <.1 <.2 <.4 <2.5

15 113655 Cuming 66 4/17/1995 -96.5596 41.95571 5.9 <.2 <.1 <.2 <.4 <2.5

16 113657 Cuming 80 4/13/1995 -96.69528 41.79673 15.1 <.2 <.1 <.2 <.4 <2.5

17 113659 Cuming 150 4/17/1995 -96.95648 41.90592 11.5 <.2 <.1 <.2 <.4 <2.5

18 113660 Cuming 30 4/13/1995 -96.79178 41.9131 <.1 <.2 <.1 <.2 <.4 <2.5

19 113661 Cuming 70 4/13/1995 -96.85913 42.03611 4.4 <.2 <.1 <.2 <.4 <2.5

20 113663 Cuming 235 4/18/1995 -96.58865 41.95588 .6 <.2 <.1 <.2 <.4 <2.5

21 115977 Dixon 96 5/9/1995 -96.8861 42.2825 <.1 <.2 <.1 <.2 <.4 <2.5

22 115978 Dixon 40 5/9/1995 -96.77027 42.29661 9.4 <.2 <.1 <.2 <.4 <2.5

23 115979 Dixon 72 5/9/1995 -96.74092 42.29646 13.5 <.2 <.1 <.2 <.4 <2.5

24 115824 Dodge 70 11/2/1994 -96.83329 41.56467 1.1 <.2 <.1 <.2 <.4 <2.5

25 115831 Dodge 320 2/27/1995 -96.58222 41.52791 <.1 <.2 <.1 <.2 <.4 <2.5

26 115834 Dodge 22 2/28/1995 -96.45827 41.51313 15.3 <.2 <.1 <.2 <.4 <2.5

27 115857 Dodge 100 2/27/1995 -96.83323 41.5792 .1 <.2 <.1 <.2 <.4 <2.5

28 115859 Dodge 220 2/28/1995 -96.77544 41.65177 <.1 <.2 <.1 <.2 <.4 <2.5

29 115860 Dodge 107 2/28/1995 -96.62172 41.62927 .1 <.2 <.1 <.2 <.4 <2.5

30 115888 Dodge 110 2/28/1995 -96.85311 41.69537 4.2 <.2 <.1 <.2 <.4 <2.5

48  Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Appendix 3. Nitrate as nitrogen and pesticide concentrations in ground-water samples collected from domestic wells, northeast Nebraska glacial 

till, 1994–95.—Continued

[Source: University of Nebraska (2000). Nitrate–N, nitrate as nitrogen; mg/L, milligrams per liter; μg/L, micrograms per liter; <, less than]

Map 

identifier 

(fig. 8)

Database 

number

County

Well 

depth 

(feet 

below 

land 

surface)

Date 

sampled 

(month/day/

year)

Longitude 

(decimal 

degrees)

Latitude 

(decimal 

degrees)

Nitrate–N 

(mg/L)

Alachlor 

(μg/L)

Atrazine 

(μg/L)

Butylate 

(μg/L)

Chlorpyrifos 

(μg/L)

Cyanazine 

(μg/L)

31 115896 Dodge 326 2/28/1995 -96.61249 41.72379 9.9 <0.2 <0.1 <0.2 <0.4 <02.5

32 116016 Knox 280 5/18/1995 -97.50936 42.52199 .5 <.2 <.1 <.2 <.4 <2.5

33 116017 Knox 305 5/18/1995 -97.58784 42.51443 9.0 <.2 <.1 <.2 <.4 <2.5

34 116019 Knox 200 5/18/1995 -97.62693 42.45633 <.1 <.2 <.1 <.2 <.4 <2.5

35 116021 Knox 160 5/18/1995 -97.75434 42.46326 15.8 <.2 <.1 <.2 <.4 <2.5

36 116061 Knox 330 5/17/1995 -97.54877 42.55088 2.2 <.2 <.1 <.2 <.4 <2.5

37 113664 Pierce 280 4/25/1995 -97.45998 42.34772 .4 <.2 <.1 <.2 <.4 <2.5

38 113665 Pierce 110 4/25/1995 -97.41144 42.28993 33.9 <.2 <.1 <.2 <.4 <2.5

39 113669 Pierce 265 4/25/1995 -97.54797 42.42013 5.2 <.2 <.1 <.2 <.4 <2.5

40 113672 Pierce 165 4/25/1995 -97.43061 42.33327 12.6 <.2 <.1 <.2 <.4 <2.5

41 113676 Pierce 100 4/25/1995 -97.6058 42.36916 13.9 <.2 <.1 <.2 <.4 <2.5

42 115994 Pierce 90 5/9/1995 -97.66427 42.39104 6.1 <.2 <.1 <.2 <.4 <2.5

43 115872 Platte 120 10/26/1994 -97.34479 41.73243 9.6 <.2 <.1 <.2 <.4 <2.5

44 115873 Platte 100 10/25/1994 -97.39197 41.71796 5.3 <.2 <.1 <.2 <.4 <2.5

45 115874 Platte 120 10/25/1994 -97.39193 41.71082 13.1 <.2 <.1 <.2 <.4 <2.5

46 115875 Platte 93 10/25/1994 -97.4306 41.73986 .2 <.2 <.1 <.2 <.4 <2.5

47 115876 Platte 210 10/25/1994 -97.47953 41.6747 3.8 <.2 <.1 <.2 <.4 <2.5

48 115877 Platte 120 10/25/1994 -97.46987 41.66739 109.2 <.2 <.1 <.2 <.4 <2.5

49 115879 Platte 250 10/25/1994 -97.49867 41.70377 2.1 <.2 <.1 <.2 <.4 <2.5

50 113679 Stanton 60 4/19/1995 -97.22869 42.07266 13.6 <.2 <.1 <.2 <.4 <2.5

51 113680 Stanton 237 4/19/1995 -97.32417 41.76855 <.1 <.2 <.1 <.2 <.4 <2.5

52 113681 Stanton 65 4/19/1995 -97.07257 41.81184 8.7 <.2 <.1 <.2 <.4 <2.5

53 113688 Wayne 125 4/24/1995 -96.92524 42.18836 11.1 <.2 <.1 <.2 <.4 <2.5

54 113689 Wayne 144 4/24/1995 -96.83759 42.19552 3.9 <.2 <.1 <.2 <.4 <2.5

55 113691 Wayne 100 4/24/1995 -96.84721 42.17445 <.1 <.2 <.1 <.2 <.4 <2.5

56 113692 Wayne 208 4/19/1995 -97.0614 42.13059 .1 <.2 <.1 <.2 <.4 <2.5

57 113693 Wayne 32 4/27/1995 -97.20732 42.14506 17.5 <.2 <.1 <.2 <.4 <2.5

58 113694 Wayne 190 4/27/1995 -97.23684 42.19563 <.1 <.2 <.1 <.2 <.4 <2.5

59 113695 Wayne 20 4/27/1995 -97.27558 42.1956 6.9 <.2 <.1 <.2 <.4 <2.5

60 113698 Wayne 220 4/24/1995 -96.96378 42.2391 .4 <.2 <.1 <.2 <.4 <2.5

61 113699 Wayne 180 4/27/1995 -97.12957 42.31872 3.8 <.2 <.1 <.2 <.4 <2.5

62 113700 Wayne 55 4/19/1995 -97.11029 42.10876 32.7 <.2 <.1 <.2 <.4 <2.5

Appendix 3  49
Appendix 3. Nitrate as nitrogen and pesticide concentrations in ground-water samples collected from domestic wells, northeast Nebraska glacial till, 

1994–95.—Continued 

[Source: University of Nebraska (2000). Nitrate–N, nitrate as nitrogen; mg/L, milligrams per liter; μg/L, micrograms per liter; <, less than]

Map 

identifier 

(fig. 8)

Database 

number

County

Well 

depth 

(feet 

below 

land 

surface)

Date 

sampled 

(month/day/

year)

Longitude 

(decimal 

degrees)

Latitude 

(decimal 

degrees)

Ethyl 

parathion 

(μg/L)

Fonofos 

(μg/L)

Methyl 

parathion 

(μg/L)

Metolachlor 

(μg/L)

Metribuzin 

(μg/L)

Terbufos 

(μg/L)

Trifluralin 

(μg/L)

1 115912 Burt 50 3/23/1995 -96.40028 41.75997 <0.1 <0.05 <0.1 <2.1 <0.8 <0.2 <0.4

2 115992 Cedar 250 5/11/1995 -97.2857 42.36977 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

3 115993 Cedar 250 5/11/1995 -97.23723 42.39881 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

4 116018 Cedar 180 5/9/1995 -97.09855 42.47099 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

5 115819 Colfax 120 1/25/1995 -97.03495 41.52887 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

6 115853 Colfax 320 1/25/1995 -97.07339 41.63012 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

7 115856 Colfax 305 2/15/1995 -96.92979 41.60842 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

8 115885 Colfax 40 1/25/1995 -96.98784 41.67397 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

9 113649 Cuming 150 4/17/1995 -96.92744 41.75366 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

10 113650 Cuming 100 4/17/1995 -96.90814 41.78264 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

11 113651 Cuming 52 4/13/1995 -96.72362 41.8401 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

12 113652 Cuming 100 4/13/1995 -96.79171 41.8695 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

13 113653 Cuming 140 4/13/1995 -96.77279 41.74624 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

14 113654 Cuming 55 4/17/1995 -96.60824 41.88356 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

15 113655 Cuming 66 4/17/1995 -96.5596 41.95571 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

16 113657 Cuming 80 4/13/1995 -96.69528 41.79673 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

17 113659 Cuming 150 4/17/1995 -96.95648 41.90592 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

18 113660 Cuming 30 4/13/1995 -96.79178 41.9131 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

19 113661 Cuming 70 4/13/1995 -96.85913 42.03611 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

20 113663 Cuming 235 4/18/1995 -96.58865 41.95588 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

21 115977 Dixon 96 5/9/1995 -96.8861 42.2825 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

22 115978 Dixon 40 5/9/1995 -96.77027 42.29661 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

23 115979 Dixon 72 5/9/1995 -96.74092 42.29646 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

24 115824 Dodge 70 11/2/1994 -96.83329 41.56467 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

25 115831 Dodge 320 2/27/1995 -96.58222 41.52791 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

26 115834 Dodge 22 2/28/1995 -96.45827 41.51313 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

27 115857 Dodge 100 2/27/1995 -96.83323 41.5792 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

28 115859 Dodge 220 2/28/1995 -96.77544 41.65177 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

29 115860 Dodge 107 2/28/1995 -96.62172 41.62927 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

30 115888 Dodge 110 2/28/1995 -96.85311 41.69537 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

50 Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04
Appendix 3. Nitrate as nitrogen and pesticide concentrations in ground-water samples collected from domestic wells, northeast Nebraska glacial till, 

1994–95.—Continued 

[Source: University of Nebraska (2000). Nitrate–N, nitrate as nitrogen; mg/L, milligrams per liter; μg/L, micrograms per liter; <, less than]

Map 

identifier 

(fig. 8)

Database 

number

County

Well 

depth 

(feet 

below 

land 

surface)

Date 

sampled 

(month/day/

year)

Longitude 

(decimal 

degrees)

Latitude 

(decimal 

degrees)

Ethyl 

parathion 

(μg/L)

Fonofos 

(μg/L)

Methyl 

parathion 

(μg/L)

Metolachlor 

(μg/L)

Metribuzin 

(μg/L)

Terbufos 

(μg/L)

Trifluralin 

(μg/L)

31 115896 Dodge 326 2/28/1995 -96.61249 41.72379 <0.1 <0.05 <0.1 <2.1 <0.8 <0.2 <0.4

32 116016 Knox 280 5/18/1995 -97.50936 42.52199 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

33 116017 Knox 305 5/18/1995 -97.58784 42.51443 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

34 116019 Knox 200 5/18/1995 -97.62693 42.45633 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

35 116021 Knox 160 5/18/1995 -97.75434 42.46326 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

36 116061 Knox 330 5/17/1995 -97.54877 42.55088 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

37 113664 Pierce 280 4/25/1995 -97.45998 42.34772 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

38 113665 Pierce 110 4/25/1995 -97.41144 42.28993 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

39 113669 Pierce 265 4/25/1995 -97.54797 42.42013 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

40 113672 Pierce 165 4/25/1995 -97.43061 42.33327 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

41 113676 Pierce 100 4/25/1995 -97.6058 42.36916 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

42 115994 Pierce 90 5/9/1995 -97.66427 42.39104 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

43 115872 Platte 120 10/26/1994 -97.34479 41.73243 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

44 115873 Platte 100 10/25/1994 -97.39197 41.71796 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

45 115874 Platte 120 10/25/1994 -97.39193 41.71082 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

46 115875 Platte 93 10/25/1994 -97.4306 41.73986 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

47 115876 Platte 210 10/25/1994 -97.47953 41.6747 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

48 115877 Platte 120 10/25/1994 -97.46987 41.66739 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

49 115879 Platte 250 10/25/1994 -97.49867 41.70377 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

50 113679 Stanton 60 4/19/1995 -97.22869 42.07266 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

51 113680 Stanton 237 4/19/1995 -97.32417 41.76855 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

52 113681 Stanton 65 4/19/1995 -97.07257 41.81184 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

53 113688 Wayne 125 4/24/1995 -96.92524 42.18836 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

54 113689 Wayne 144 4/24/1995 -96.83759 42.19552 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

55 113691 Wayne 100 4/24/1995 -96.84721 42.17445 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

56 113692 Wayne 208 4/19/1995 -97.0614 42.13059 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

57 113693 Wayne 32 4/27/1995 -97.20732 42.14506 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

58 113694 Wayne 190 4/27/1995 -97.23684 42.19563 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

59 113695 Wayne 20 4/27/1995 -97.27558 42.1956 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

60 113698 Wayne 220 4/24/1995 -96.96378 42.2391 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

61 113699 Wayne 180 4/27/1995 -97.12957 42.31872 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

62 113700 Wayne 55 4/19/1995 -97.11029 42.10876 <.1 <.05 <.1 <2.1 <.8 <.2 <.4

Appendix 3  51
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Stanton and others—Occurrence of Agricultural Chemicals in Northeast Nebraska Glacial Till, 2002–04—Scientific Investigations Report 2007–5228

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