U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2006–5196

National Water-Quality Assessment Program

Ground-Water Quality Beneath Irrigated Cropland 

of the Northern and Southern High Plains Aquifer, 

Nebraska and Texas, 2003−04

0 50 100 150 200 MILES

0 50 100 150 200 KILOMETERS

Colorado

Wyoming

South Dakota

Nebraska

Kansas

New Mexico

Texas

Oklahoma

Iowa

Canadian R

Southern High Plains

agricultural land-use

study area

Northern High Plains

agricultural land-use

study area

NORTHERN

CENTRAL

SOUTHERN

Boundary of

High Plains

aquifer
Ground-Water Quality Beneath Irrigated 

Cropland of the Northern and Southern 

High Plains Aquifer, Nebraska and Texas, 

2003–04

By Jennifer S. Stanton and Lynne Fahlquist

National Water-Quality Assessment Program

Scientific Investigations Report 2006–5196

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: 2006

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Suggested citation:

Stanton, J.S., and Fahlquist, Lynne, 2006, Ground-water quality beneath irrigated cropland of the northern and southern High Plains aquifer, Nebraska and Texas, 2003–04: U.S. Geological Survey Scientific Investigations Report 2006–

5196, 95 p.
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: 

What is the condition of our Nation’s streams and ground water? How are the conditions changing over time? 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 waterresource 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, multi-scale approach helps to 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, volatile organic compounds, trace metals, 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 that the most recent and available knowledge about water resources can 

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

you 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 ..............................................................................................................................3

Acknowledgments................................................................................................................................3

Methods of Investigation..............................................................................................................................3

Site Selection and Well Installation...................................................................................................3

Sample Collection and Analysis.........................................................................................................5

Data Treatment......................................................................................................................................8

Quality Control.......................................................................................................................................8

Field-Blank Samples....................................................................................................................8

Replicate Samples.......................................................................................................................9

Environmental-Matrix Spike Samples....................................................................................10

Hydrogeologic Setting.................................................................................................................................10

Northern High Plains..........................................................................................................................10

Southern High Plains..........................................................................................................................11

Land-Use Setting..........................................................................................................................................12

Northern High Plains..........................................................................................................................12

Southern High Plains..........................................................................................................................14

Ground-Water Quality Beneath Irrigated Cropland...............................................................................14

Nitrate ..................................................................................................................................................14

Northern High Plains.................................................................................................................16

Southern High Plains.................................................................................................................20

Pesticides.............................................................................................................................................21

Northern High Plains.................................................................................................................21

Southern High Plains.................................................................................................................24

Dissolved Solids..................................................................................................................................27

Northern High Plains.................................................................................................................27

Southern High Plains.................................................................................................................29

Comparison of Ground-Water Quality in Two Study Areas ..................................................................32

Summary........................................................................................................................................................33

References Cited..........................................................................................................................................34

 Appendixes ..................................................................................................................................................39

Figures

1–6. Maps showing:

1. Location of High Plains aquifer and boundaries of northern and southern High 

Plains agricultural land-use study areas, Nebraska and Texas ..................................2

2. Distribution of irrigated cropland and location of wells installed to evaluate 

ground-water quality in northern and southern High Plains, Nebraska and Texas, 

2003–04 ..................................................................................................................................4
vi

3. Distribution of major crops grown, by county, in northern and southern High 

Plains agricultural land-use study areas, Nebraska and Texas, 2002 ........................6

4. Distribution of primary land-use types in northern and southern High Plains 

agricultural land-use study areas, Nebraska and Texas, 1992 ..................................13

5. Ground-water withdrawals for irrigation, by county, in northern and southern 

High Plains agricultural land-use study areas, Nebraska and Texas, 2000.............15

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

fertilizer, by county, and nitrate concentrations in ground-water samples 

collected from northern and southern High Plains agricultural land-use study 

areas, Nebraska and Texas, 2003–04 .............................................................................17

7–8. Graphs showing:

7. Nitrogen isotope ratio values of nitrate in nitrogen sources and ground-water 

samples collected from northern and southern High Plains agricultural land-use 

study areas, Nebraska and Texas, 2003–04. .................................................................19

8. Concentrations of pesticide compounds in ground-water samples collected from 

northern and southern High Plains agricultural land-use study areas, Nebraska 

and Texas, 2003–04............................................................................................................22

9. Maps showing number of pesticide compounds detected at concentrations equal to 

or greater than laboratory reporting level in ground-water samples collected from 

northern and southern High Plains agricultural land-use study areas, Nebraska and 

Texas, 2003–04.............................................................................................................................23

10. Graphs showing frequency of pesticide detections at concentrations equal to or 

greater than 0.05 microgram per liter in ground-water samples collected from northern 

High Plains agricultural land-use study area, where primarily corn and soybeans 

are grown, and from southern High Plains agricultural land-use study area, where 

primarily cotton is grown, relative to samples collected from other National WaterQuality Assessment study areas where the same crops are grown.................................24

11. Map showing location of National Water-Quality Assessment agricultural study areas 

across the United States ...........................................................................................................25

12. Trilinear diagrams showing relative proportions, in percentage equivalents, of major 

ions in ground-water samples collected from northern and southern High Plains 

agricultural land-use study areas, Nebraska and Texas, 2003–04.....................................30

Tables

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

water-quality constituents in northern and southern High Plains agricultural land-use 

study areas, Nebraska and Texas, 2003–04 .............................................................................7

2. Constituents detected in field-blank samples collected for northern and southern High 

Plains agricultural land-use study areas, Nebraska and Texas, 2003–04...........................9

3. Summary of relative percentage differences for replicate samples collected for 

northern and southern High Plains agricultural land-use study areas, Nebraska and 

Texas, 2003–04.............................................................................................................................10

4. Median values of average soil properties within 1,640 feet of monitoring wells in 

northern and southern High Plains agricultural land-use study areas, Nebraska and 

Texas.............................................................................................................................................11

5. Ten most frequently applied pesticides in northern and southern High Plains 

agricultural land-use study areas, Nebraska and Texas, 1997 ...........................................14
vii

6. Summary statistics for nitrogen and phosphorus compounds and nitrogen and oxygen 

isotopes of nitrate in ground-water samples collected from northern and southern 

High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04................16

7. Relations between nitrate concentrations in ground-water samples and borehole and 

soil characteristics in northern and southern High Plains agricultural land-use study 

areas, Nebraska and Texas, 2003–04 ......................................................................................20

8. Pesticide compound detections in ground-water samples related to borehole and soil 

characteristics in northern and southern High Plains agricultural land-use study areas, 

Nebraska and Texas, 2003–04...................................................................................................26

9. Summary statistics for physical properties, major ions, selected trace elements, and 

dissolved organic carbon in ground-water samples collected from northern 

and southern High Plains agricultural land-use study areas, Nebraska and Texas, 

2003–04 .........................................................................................................................................28

10. Dissolved-solids concentrations in ground-water samples related to borehole and soil 

characteristics in northern and southern High Plains agricultural land-use study areas, 

Nebraska and Texas, 2003–04...................................................................................................31

11. Major ions and trace elements related to nitrate concentrations in ground-water 

samples collected from northern and southern High Plains agricultural land-use study 

areas, Nebraska and Texas, 2003–04 ......................................................................................31

Conversion Factors, Abbreviations, and Datum

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

micrometer (μm) 0.00003937 inch (in.)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

acre-foot (acre-ft) 1,233 cubic meter (m3)

milliliter (mL) 0.338 ounce, fluid (oz)

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

gallon (gal) 0.003785 cubic meter (m3) 

Flow rate

gallon per minute (gal/min) 0.06309 liter per second (L/s)

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

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Radioactivity

picocurie per liter (pCi/L) 0.312 tritium unit 
viii

Multiply By To obtain

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

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)

Concentration

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

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

milligram per liter (mg/L) 0.058 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.

Datum

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

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

(NAVD 1988). 
Abstract

A study of the quality of ground water beneath irrigated 

cropland was completed for the northern and southern High 

Plains aquifer. Ground-water samples were collected from 

30 water-table monitoring wells in the northern agricultural 

land-use (NAL) study area in Nebraska in 2004 and 29 watertable monitoring wells in the southern agricultural land-use 

(SAL) study area in Texas in 2003. The two study areas 

represented different agricultural and hydrogeologic settings. 

The primary crops grown in the NAL study area were corn 

and soybeans, and the primary crop in the SAL study area was 

cotton. Overall, pesticide and fertilizer application rates were 

larger in the NAL study area. Also, precipitation and recharge 

rates were greater in the NAL study area, and depths to water 

and evapotranspiration rates were greater in the SAL study 

area.

Ground-water quality beneath irrigated cropland was 

different in the two study areas. Nitrate concentrations were 

larger and pesticide detections were more frequent in the NAL 

study area. Nitrate concentrations in NAL samples ranged 

from 1.96 to 106 mg/L (milligrams per liter) as nitrogen, with 

a median concentration of 10.6 mg/L. Water in 73 percent of 

NAL samples had at least one pesticide or pesticide degradate 

detected. Most of the pesticide compounds detected (atrazine, 

alachlor, metolachlor, simazine, and degradates of those pesticides) are applied to corn and soybean fields. Nitrate concentrations in SAL samples ranged from 0.96 to 21.6 mg/L, with 

a median of 4.12 mg/L. Water in 24 percent of SAL samples 

had at least one pesticide or pesticide degradate detected. The 

pesticide compounds detected were deethylatrazine (a degradate of atrazine and propazine), propazine, fluometuron, and 

tebuthiuron. Most of the pesticides detected are applied to 

cotton fields.

Dissolved-solids concentrations were larger in the SAL 

area and were positively correlated with both nitrate and 

chloride concentrations, suggesting a combination of human 

and natural sources. Dissolved-solids concentrations in NAL 

samples ranged from 272 to 2,160 mg/L, with a median of 

442 mg/L, and dissolved solids in SAL samples ranged from 

416 to 3,580 mg/L, with a median of 814 mg/L.

Introduction

The High Plains aquifer underlies about 174,400 mi2

in the central United States in parts of Colorado, Kansas, 

Nebraska, New Mexico, Oklahoma, South Dakota, Texas, 

and Wyoming (fig. 1). Ground water is the primary source 

for drinking water, irrigation, industry, and water supplies for 

animal production in the High Plains region. In 1990, the 

High Plains aquifer supplied drinking water to 2.2 million 

people or about 82 percent of High Plains residents (Dennehy, 

2000). The area’s economy has been dominated by agriculture for over a century. About 27 percent of irrigated land in 

the United States is in the High Plains, and about 30 percent 

of ground water used for irrigation in the United States is 

pumped from the High Plains aquifer (Dennehy, 2000).

About 41 percent of the land in the High Plains is 

cropland and 12 percent is irrigated (U.S. Geological Survey, 

1992; Qi and others, 2002). Ground water provides most of 

the water used for irrigation. The number of irrigated acres 

has increased substantially since the mid-1900s because of 

advancements in well drilling and pumping technology and the 

development of center-pivot irrigation systems. The number 

of irrigated acres increased from about 2 million acres in 

1949 to about 13 million acres in 1992 (Gutentag and others, 

1984; Qi and others, 2002). As irrigated agriculture increased, 

producers were able to grow crops with larger water demands 

and economic returns; hence, the types of crops grown in the 

region have changed over time (U.S. Department of Agriculture, variously dated).

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 irrigated cropland. Application of agricultural amendments directly introduces nutrients, 

pesticides, and dissolved solids to the hydrologic system. 

Changes in soil structure and application of irrigation water 

Ground-Water Quality Beneath Irrigated Cropland of the 

Northern and Southern High Plains Aquifer, Nebraska and 

Texas, 2003–04

By Jennifer S. Stanton and Lynne Fahlquist
Figure 1. Location of High Plains aquifer and boundaries of northern and southern High Plains agricultural land-use 

study areas, Nebraska and Texas.

!

!

!

! !

!

!

!

!

!

!

!

! !

!

!

Colorado

Wyoming

South Dakota

Nebraska

Kansas

New Mexico

Texas

Oklahoma

Iowa North Loup

Middle Loup

South Loup

Arkansas

Canadian 

R

Cimarron

Elkhorn

Kansas

Missouri

North Platte River

Platte

Red

Republican

South Platte

Alliance

Amarillo

Bird City

Cheyenne Columbus

Dodge City

Grand

Island

Guymon

Kearney

Lubbock

McCook

Midland

North

Platte

Ogallala

Valentine

York River

River

River

River

River

River

River

River

River

River

River

River

108° 106° 104° 102° 100° 98° 96°

32°

34°

36°

38°

40°

42°

NORTHERN

CENTRAL

SOUTHERN

Base from U.S. Geological Survey 

1:100,000 Digital Line Graphs (DLG)

EXPLANATION

Northern High Plains agricultural land-use study area (Eastern Nebraska hydrogeologic unit)

Southern High Plains agricultural land-use study area (Ogallala Formation hydrogeologic unit)

High Plains aquifer

Boundary of High

Plains aquifer

0 50 100 150 200 MILES

0 50 100 150 200 KILOMETERS

   Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
increase recharge rates, which aid movement of human and 

natural (such as nitrogen in soil organic matter and dissolved 

solids) chemical constituents past the root zone to ground 

water (Scanlon and others, 2005). Indirect effects of agriculture 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). As part of the NAWQA Program, a 

study of the ground-water quality of the High Plains aquifer 

was conducted. Because of its large geographic extent and the 

logistical challenges associated with regional ground-water 

quality studies, the High Plains aquifer was subdivided into 

three regions—northern High Plains, central High Plains, and 

southern High Plains (fig. 1).

To assess the effects of selected irrigated crops and 

hydrogeologic settings on ground-water quality in the High 

Plains aquifer, samples of ground water were collected from 

water-table monitoring wells in three agricultural land-use 

areas. Monitoring wells were located in an irrigated crop 

setting in each of the High Plains regions—corn and soybeans 

(northern High Plains), corn (central High Plains), and cotton 

(southern High Plains). Results from the study in the central 

High Plains were reported in Bruce and others (2003) and are 

not discussed here.

Purpose and Scope

This report describes and compares the quality of ground 

water at the water table beneath irrigated cropland in the 

northern High Plains (NHP) and southern High Plains (SHP). 

The two regions are located in different hydrogeologic and 

agricultural settings. Thirty water-quality monitoring wells 

were installed in the NHP agricultural-land use (NAL) study 

area, and 30 wells were installed in the SHP agricultural landuse (SAL) study area near irrigated fields. The wells were 

constructed with short well screens (typically 10 ft) near the 

water table to intercept ground water and, therefore, observe 

the effects of nearby irrigated cropland on ground-water 

quality. Ground-water samples were collected once from the 

30 wells in the NAL study area in 2004 and once from 29 of 

the 30 wells in the SAL study area in 2003. One well in the 

SAL study area went dry after installation and, therefore, was 

not sampled. Water from all sites was analyzed for physical 

properties, and concentrations of nitrogen and phosphorus 

compounds, nitrogen isotopes of nitrate, pesticides and pesticide degradates, dissolved solids, major ions, trace elements, 

dissolved organic carbon, and tritium. In addition, water 

samples collected from the NAL study area also were analyzed 

for oxygen isotopes of nitrate.

Acknowledgments

The authors are grateful to the many landowners who 

allowed installation of a monitoring well on their property. 

This study could not have been conducted without their support. The authors also thank the Plains Cotton Growers, Inc.; 

Texas Cooperative Extension county offices in the southern 

High Plains study area; Texas A&M Agricultural Research 

and Extension Center, Lubbock; Texas Tech University, Lubbock; High Plains Underground Water Conservation District 

No. 1; Llano Estacado Underground Water Conservation District; Sandy Land Underground Water Conservation District; 

South Plains Underground Water Conservation District; Conservation and Survey Division of the University of Nebraska; 

and the Upper Big Blue Natural Resources District.

Methods of Investigation

Site Selection and Well Installation

Water-table monitoring wells were located and constructed with the purpose of evaluating the effect of irrigated 

agriculture on ground-water quality in the NHP and SHP 

regions. Gutentag and others (1984) describe the boundaries 

and settings of the NHP and SHP regions; however, the western boundaries of the regions have been revised for the High 

Plains ground-water-quality studies. Changes to the boundary 

were made to exclude areas of the unfractured Brule Formation in the NHP region and to account for better geologic 

information that became available for the SHP region.

The NHP region can be divided into five major hydrogeologic units—the Arikaree and Brule Formations, Ogallala 

Formation, Eastern Nebraska, Platte River Valley, and Sand 

Hills. These units represent unique depositional time periods, depositional settings, geologic materials, and hydrologic 

characteristics. The NAL study area was located within the 

Eastern Nebraska hydrogeologic unit (fig. 1)—a unit underlying extensive irrigated agriculture. The SAL study area was 

located within the Ogallala Formation—the major hydrogeologic unit of the High Plains aquifer in the SHP region.

Wells were installed in areas where irrigated agriculture 

was greater than 30 percent of the local land use. The percentage of irrigated agriculture was determined by overlaying a 

1.24- by 1.24-mi grid on maps classified from Landsat Thematic Mapper satellite images that showed irrigated agriculture (nominal 1980 and 1992) (fig. 2) (Thelin and Heimes, 

1987; Qi and others, 2002). McMahon (2000) showed that 

the effect of agriculture on ground-water quality was more 

likely to be observed in areas with depths to ground water of 

less than 200 ft; therefore, study areas also were limited to 

those regions where depth to water was less than 200 ft below 

land surface. In the most densely irrigated part of the SAL 

study area, depths to water were generally greater than 200 ft, 

and the primary crops grown were corn and wheat rather than 

Methods of Investigation   
Figure 2. Distribution of irrigated cropland (nominal 1980) and location of wells installed to evaluate ground-water quality in (A) northern and (B) southern High 

Plains, Nebraska and Texas, 2003–04.

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7

8

9 6 5

4

3 2

1

17

22

30

16

15 29

18 19 28

27 20

14

21 10 26 25 13 24 11

23

12

104° 103° 102° 101°

35°34°33°32°

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7

8 6

9

5 4 3

2

1

19

20

18 30 21

29 17

28 16

22

23 10 27

26

15 11

14

24 12 25 13

100° 99° 98° 97°

43°42°

41°40°

Base information from U.S. Geological Survey 1:100,000 Digital Line Graphs (DLG) 

EXPLANATION

Density of irrigated cropland,in percent of 1.24-mile grid cell

! Monitoring well and identifier

0 25 50 75 100 KILOMETERS

0 25 50 75 100 MILES

15−29

30−4950−6970−100

0−14

Irrigated cropland data from Thelin and Heimes (1987)

Kansas

23

(A) Northern High Plains study area

Texas

Boundary of High Plainsaquifer

Nebrask

a

South Dakot

a

(B) Southern High Plains study are

a

New Mexico

Boundary of High Plainsaquifer

   Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
cotton (fig. 3B). As a result, SAL sites were not located in the 

areas with the most irrigated cropland (fig. 2B). The extent of 

the NAL study area was modified further to avoid duplication 

of effort by a similar NAWQA study (U.S. Geological Survey, 

2006) in the northern part of the Eastern Nebraska unit.

Potential monitoring well locations were selected using 

a grid-based, random site-selection computer program (Scott, 

1990). Each study area was divided into 30 equal-area cells. 

The computer program randomly selected one primary and 

one alternate location from a large population of potential sites 

within each cell. Areas near each randomly selected location 

were visited to determine the placement of monitoring wells. 

Monitoring well sites were selected with the following criteria: 

(1) within 4 mi of the randomly selected location; (2) next to 

a field that had been irrigated for approximately 20 years or 

more; (3) downgradient from the irrigated field on the basis of 

the direction of regional ground-water flow; (4) crops grown 

in the upgradient field were primarily corn and soybeans 

in the NAL area and primarily cotton in the SAL area; (5) 

located away from surface-water bodies, irrigation wells, or 

potential sources of contamination such as chemical storage, 

farm buildings, abandoned wells, and septic fields; (6) not in a 

water-gathering depression; (7) accessible to a well drilling rig 

and mobile laboratory; (8) did not receive direct application of 

irrigation water; and (9) land owner granted permission to drill 

a well. If no sites within the 4-mi radius were suitable, sites 

near the alternate randomly selected location were considered.

Well installation methods were used to maximize the 

likelihood that water-quality samples reflected the effects of 

irrigated agriculture on ground-water quality, that water-quality samples represented aquifer conditions, and that equipment and construction materials were not a source or sink of 

sampled analytes. Wells were installed with a hollow-stem 

auger using no drilling fluids in the NAL study area. In the 

SAL study area, wells were installed using an air rotary-casing advance technique. The air was filtered to minimize the 

possibility of introducing contaminants during the drilling 

process. Well casings were constructed of 2-in. diameter 

polyvinyl chloride (PVC) in the NAL study area and 2.5-in. 

PVC in the SAL study area. Typically, wells were constructed 

with 10-ft screens with a 5-ft blank casing with end cap below 

the screen. Effects of land-use activities on ground-water 

chemistry generally are observed at the shallowest part of the 

aquifer; therefore, the top of the well screen was placed about 

5 ft below the estimated water table. The annular space from 

the bottom of the well to a few feet above the water table was 

filled with a silica-sand gravel pack. A bentonite well plug at 

least 2 ft thick was placed in the annular space above the silica 

sand to provide a seal. The remaining annular space was filled 

with bentonite/cement grout, and a concrete pad and protective 

steel cover were placed at the land surface around the well.

Sample Collection and Analysis

Ground-water samples were collected from 30 monitoring wells in the NAL study area, and 29 monitoring wells 

in the SAL study area (Appendixes 1 and 2). Ground-water 

samples were collected using procedures described by Koterba 

and others (1995) and the USGS national field manual (U.S. 

Geological Survey, variously dated). Water samples were processed onsite in a mobile laboratory using methods designed 

to minimize changes to the water-sample chemistry. Water 

was pumped from wells with a stainless-steel submersible 

pump and delivered to the mobile laboratory through Teflon 

tubing with stainless-steel connections. Prior to sample collection, stale water was flushed from the well by purging at 

least three casing volumes from the well. While purging, specific conductance, pH, water temperature, turbidity, and dissolved oxygen 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 1).

Water samples were analyzed to determine physical properties and concentrations of nitrogen and phosphorus compounds, nitrogen isotopes of nitrate, pesticides and pesticide 

degradates, dissolved solids, major ions, carbonate alkalinity, 

trace elements, dissolved organic carbon, and tritium. Water 

samples collected from the NAL study area also were analyzed for oxygen isotopes of nitrate. Forty-seven pesticides 

and seven pesticide degradates were analyzed for all samples 

collected from the NAL and SAL study areas (Appendixes 1 

and 2). Additional pesticide compounds specific to the crops 

grown in each area also were analyzed. Pesticide degradates 

of atrazine, acetochlor, alachlor, dimethanamid, flufenacet, 

metolachlor, and propachlor were analyzed for NAL samples 

only. Fluometuron, norflurazon, prometryn, propazine, and 

their associated degradates were analyzed for SAL samples 

only. Laboratory analytical methods are briefly summarized 

for measured water-quality constituents in table 1.

Eleven SAL wells were resampled because dissolved 

organic carbon concentrations in water samples from those 

wells were one to two orders of magnitude larger than other 

samples and were deemed unreliable. Potential dissolved 

organic carbon contamination sources were not discovered. 

When those wells were resampled, dissolved organic carbon 

concentrations were generally within the same order of magnitude as other previously collected samples. Therefore, the 

dissolved organic carbon concentrations from the second set of 

samples were considered to be representative of aquifer conditions and were used in interpretations in this report. With the 

exception of dissolved organic carbon, water-quality data from 

Methods of Investigation 
 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04

Figure 3. Distribution of major crops grown, by county, in (A) northern and (B) southern High Plains agricultural land-use study areas, Nebraska and Texas, 2002. (Distributions shown are relative percentages by crop of the total acreage harvested.)

104° 103° 102° 101°

35°34°33°32°

100° 99° 98° 97°

43°42°

41°40°

Base information from U.S. GeologicalSurvey 1:100,000 Digital Line Graphs (DLG) 

EXPLANATIO

N 0 25 50 75 100 KILOMETERS

0 25 50 75 100 MILES

CornCottonHayPeanuts

SorghumSoybeansWheatOther

Crop data from U.S. Department of Agriculture (variously dated)

(A) Northern High Plains study are

a

Texas

Boundary of High Plainsaquifer

Nebrask

a

South Dakota

(B) Southern High Plains study are

a

New Mexico

Boundary of High Plainsaquifer

Kansas
Table 1. Laboratory analysis and onsite treatment and preservation methods for measured water-quality constituents in northern and 

southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04.

[USGS, U.S. Geological Survey; NWQL, National Water Quality Laboratory; μm, micrometer; 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, turbidity, 

dissolved oxygen

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 4 o

C.

Nitrogen and oxygen 

isotopes of nitrate

USGS Stable Isotope 

Laboratory, Reston, VA

Continuous flow isotope 

ratio mass spectrometry

Casciotti and others, 2002 Filter sample through 

0.45-μm filter, freeze 

sample until shipment 

to laboratory.

Pesticides and pesticide 

degradates

USGS NWQL, 

Lakewood, CO

C-18 solid-phase extraction and capillarycolumn GC/MSZaugg and others, 1995; 

Lindley and others, 

1996; Madsen and 

others, 2003

Filter through 0.7-μm 

baked glass fiber filter, 

chill sample and maintain at 4 o

C.

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 capillary-column 

GC/MS with selectedion monitoring

Zimmerman and Thurman, 1999; Kish and 

others, 2000; Lee and 

Strahan, 2003

Filter through 0.7-μm 

baked glass fiber filter, 

chill sample and maintain at 4 o

C.

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 sample 

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 4 oC.

Tritium USGS Isotope Tracers 

Laboratory, Menlo 

Park, CA

Electrolytic enrichment 

and liquid scintillation

Thatcher and others, 1977 Completely fill bottle to 

exclude air bubbles. 

Fill bottle with minimal 

splashing.

Methods of Investigation 
the first set of samples were used in interpretations found in 

this report.

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) to minimize both false positive and false negative errors. LT-MDLs and LRLs vary among constituents and 

analytical methods. The 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. The 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 the NWQL on the basis of laboratory spikesample 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. Pesticide and volatile organic compounds 

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, it is qualified with an 

“E” remark code.

Water-quality data characteristically include “outliers” 

(observations much larger or smaller than most of the data), 

censored data, and positive skewness (most data occur at 

small values but a few extreme large values are present). For 

these reasons, nonparametric statistical methods were used in 

this report. 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 0.05 or less indicated sufficient evidence 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 was used to test the correlation between 

variables in a data set (Bhattacharyya and Johnson, 1977). 

In this report, a p-value of 0.05 or less indicated sufficient 

evidence that two variables were correlated. Fisher’s Exact 

test (Agresti, 1990) was used to detect group differences in 

categorical data. A p-value of 0.05 or less indicated that there 

was a 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 blank samples were collected, sample bottles were 

filled with water that was specially prepared at the NWQL 

instead of water from the sampled well. Prior to use, the 

prepared water was analyzed and certified to be free of the 

environmental sample analytes. Field-blank samples were 

otherwise collected using the same procedures and equipment 

as environmental samples. Blank 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 tritium or 

isotope blank samples; therefore, tritium and isotope blank 

samples were not collected.

Results of blank sample analyses are summarized in 

table 2. Concentrations of analytes detected in blank samples 

were compared with concentrations of analytes in environmental samples to determine the potential for environmental 

sample contamination. If the magnitude of the blank sample 

concentrations approached the environmental sample concentrations, environmental sample concentrations may have 

been affected by sampling contamination. Concentrations of 

aluminum, copper, manganese, nickel, and dissolved organic 

carbon in at least one field-blank sample were larger than 

the smallest concentration 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 

 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
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:

RPD = −

 +



 





×

Sample 1 Sample 2

Sample 1 Sample 2

2

100 . (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 median RPDs of the 

constituent groups ranged from 0.3 to 5.1 percent (table 3). 

With the exception of trace elements and dissolved organic 

carbon, about 90 percent of the RPDs were less than 5 percent. 

The larger RPDs for trace elements might be explained by 

many constituents with small concentrations near the LRL. 

With small concentrations and less precision, small differences can yield 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. The individual constituents having the largest 

average RPDs were chromium (16.0 percent), silver (15.4 percent), lithium (13.2 percent), fluoride (11.1 percent), and iron 

(10.2 percent). In general, small RPDs for constituents indicated that the amount of variability between paired environmental and replicate samples was within acceptable limits.

Table 2. Constituents detected in field-blank samples collected for northern and southern High Plains agricultural 

land-use study areas, Nebraska and Texas, 2003–04.

[<, less than; E, estimated; --, only one detection in field-blank samples, median not calculated]

Constituent

Number of detections1/ 

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)

Nitrate 1/6 -- 0.08 0.65 – 106

Pesticide compounds

None detected

Major ions (concentrations in milligrams per liter)

Calcium 4/4 0.06 .10 29.9 – 473

Magnesium 1/4 -- .009 6.83 – 198

Sodium 3/4 .14 .17 9.18 – 735

Silica 3/4 .16 .84 20.9 – 81.7

Trace elements (concentrations in micrograms per liter)

Aluminum 1/6 -- 10 <2 – E2

Boron 2/6 17 19 23 – 943

Copper 4/6 .65 1.3 0.4 – 5.2

Lithium 1/6 -- .7 8.1 – 278

Manganese 3/6 .3 .5 <0.2 – 621

Nickel 6/6 .06 .75 0.7 – 52.1

Strontium 2/6 .6 .64 237 – 7,250

Vanadium 3/6 .4 .6 2.4 – 118

Dissolved organic carbon (concentrations in milligrams per liter)

Dissolved organic carbon 1/6 -- .5 E0.3 – 16.2

1

Equal to or greater than the highest laboratory reporting level (LRL).

Methods of Investigation 
Environmental-Matrix Spike Samples

Environmental-matrix spikes typically are utilized to 

quantify the gain or loss of organic-compound analytes due 

to water-matrix properties, sample holding time, or onsite and 

laboratory procedures. A spike recovery of 100 percent suggests no matrix interference or degradation and good analytical recovery. Environmental-matrix pesticide spike samples 

were prepared by injecting known amounts of 52 pesticide 

compounds into replicate samples while onsite. The average 

percentage recovery of individual pesticide compounds was 

calculated from the four matrix spike samples and is reported 

in Appendix 3. Forty-one of the 52 pesticide compounds 

analyzed were within an acceptable range of 60 to 120 percent 

recovery (Furlong and others, 2001). Of the 11 pesticide 

compounds analyzed that did not fall into the range of acceptable recovery, three (deethylatrazine, carbaryl, and carbofuran) 

always were reported as estimated values by NWQL because 

of known problems with gas chromatography or extraction 

or because they did not otherwise meet method performance 

criteria (Zaugg and others, 1995).

Hydrogeologic Setting

Northern High Plains

The NAL study area was limited to the Eastern Nebraska 

hydrogeologic unit in the NHP region. For this report, the 

Eastern Nebraska unit refers to the Pleistocene and Pliocene 

deposits in the eastern part of the NHP where the underlying 

Ogallala Formation is thin or absent. According to previous 

studies (Johnson and Keech, 1959; Richmond and others, 

1994; Gosselin and others, 1996; Verstraeten and others, 

1998), the Eastern Nebraska unit consists primarily of sand 

and gravel but also includes wind-deposited silt and clay 

(loess), paleosols, and unsorted and unstratified glacial till. 

The earlier Pliocene sediments consist of granite, anorthosite, 

and quartz sediment eroded from the Laramie Range and Medicine Bow Mountains in Wyoming to the west. Later, glacial 

processes transported Pleistocene sand and gravel, composed 

primarily of quartz, from the north. The hydrologic conditions 

in the NAL study area can be unconfined, perched, semiconfined, or confined. The thickness of the Eastern Nebraska unit 

is variable and ranges from 0 to more than 300 ft. Either the 

Ogallala Formation or bedrock of Cretaceous age underlies 

this unit. It is hydraulically connected to the Ogallala Formation where it is present (Johnson and Keech, 1959; Richmond 

and others, 1994; Gosselin and others, 1996; Verstraeten and 

others, 1998).

Table 3. Summary of relative percentage differences for replicate samples collected for northern and southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04.

[--, percentile not calculated]

Compound class

Number of 

samples

Number 

of replicate pairs 

used in 

calculation1

Minimum

Percentile

Maxi10 25 50 75 90 mum

Environmental sample replication (relative percentage differences)

Nitrogen and phosphorus compounds 

(5 constituents) 4 9 0 -- -- 0.3 -- -- 10.6

Nitrogen and oxygen isotopes of nitrate 

(2 constituents) 2 3 0 -- -- 2.3 -- -- 3.4

Pesticides and pesticide degradates 

(81 compounds) 4 2 0 -- -- 5.1 -- -- 10.2

Dissolved solids 4 4 .35 -- -- .83 -- -- 1.86

Major ions (10 constituents) 4 39 0 0 0.5 1.2 2.3 4.4 40.0

Trace elements (23 constituents) 6 91 0 0 .5 1.9 5.5 15.4 42.9

Dissolved organic carbon 6 6 0 -- -- 3.2 -- -- 23.2

Tritium 2 2 2.7 -- -- 4.4 -- -- 6.1

1

Percentage difference was not calculated if the laboratory results of either the environmental or replicate sample were qualified with “E” or “<”. Only the 

50th percentile was reported if there were fewer than 10 percentage-difference values calculated in a compound class.

10 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Depths to ground water in the Eastern Nebraska unit 

range from less than 5 to over 300 ft below land surface 

(Sharon Qi, U.S. Geological Survey, written commun., 2005). 

Hydraulic conductivity in this area generally varies from less 

than 25 to 200 ft/d and averages about 70 ft/d (Gutentag and 

others, 1984; Sharon Qi, U.S. Geological Survey, written commun., 2006). Well yields in this area range from just a few 

gallons per minute (gal/min) in small-capacity domestic and 

stock wells to more than 2,000 gal/min in irrigation and public 

supply wells (Nebraska Department of Natural Resources, 

2003).

Thick layers of glacial till and (or) loess and soils of low 

permeability between the land surface and the water table 

limit the amount of precipitation that enters ground water 

as recharge. For these reasons, most precipitation is lost to 

surface runoff or evapotranspiration. Ground-water recharge 

in the NAL study area is estimated to be about 20 percent of 

mean annual precipitation (Dugan and Zelt, 2000). Average percentage of sand, silt, and clay, bulk density, organic 

matter content, and vertical and horizontal permeability for 

soils within a 1,640-ft radius around each of the 30 wells was 

calculated from the 1994 State soil geographic (STATSGO) 

database (U.S. Department of Agriculture, 1994; Schwarz and 

Alexander, 1995; Wolock, 1997). STATSGO soil mapping 

unit identifiers were averaged on a coarse (1-km, 0.6214-mi) 

resolution grid prior to calculating average properties within 

1,640-ft of each monitoring well. The median of the 30 average values calculated for each soil characteristic is presented 

in table 4.

The land surface in the NAL study area is characterized 

by flat plains or gently rolling loess hills that have been dissected by stream channels. Streams are relatively abundant 

compared with other areas of the High Plains. Many small 

reservoirs that catch precipitation runoff are located in the area 

and typically are used to water livestock.

The climate is subhumid, and the area receives mean 

annual precipitation of between about 25 in/yr in the west to 

about 27 in/yr in the east (Johnson and Keech, 1959). Most 

precipitation falls from thunderstorms during the summer 

growing season (May through September). Mean annual pan 

evaporation rates range from about 65 to 75 in/yr (Gutentag 

and others, 1984). Natural ground-water recharge rates (not 

including recharge from irrigation) have been estimated to be 

between 4 and 6 in/yr (Dugan and Zelt, 2000).

Southern High Plains

The SAL study area was limited to the areal extent of 

the Ogallala Formation of Tertiary age within the SHP region. 

Previous studies provided hydrogeologic characteristics of the 

study area (Seni, 1980; Gutentag and others, 1984; Fahlquist, 

2003). The Ogallala Formation is made of stream-deposited 

gravel, sand, silt, and clay originating from the Rocky Mountains to the west (Seni, 1980). Sediments were deposited in a 

complex, braided-stream alluvial-fan environment. Paleovalleys incised into the underlying bedrock generally contain 

coarser sand and gravel. The Ogallala Formation is primarily unconfined but may be locally confined or semiconfined 

where extensive clay layers are present. Layers of caliche are 

common. The saturated thickness of the Ogallala Formation 

varies from less than 20 to more than 500 ft. In the study 

area, this unit overlies bedrock of Cretaceous or Triassic age 

and may be hydraulically connected to these bedrock units in 

some areas. The Blackwater Draw Formation overlies and is 

considerably less extensive than the Ogallala Formation but, 

where saturated, is considered to be part of the High Plains 

aquifer. It consists of aeolian, fluvial, and lacustrine sediment 

and lies between the Ogallala Formation and the land surface 

in some areas. For this report, the Blackwater Draw Formation is part of the study area.

Depth to ground water ranges from less than 100 ft in 

the south to more than 400 ft in parts of the north (Fahlquist, 

2003). Hydraulic conductivity in the SAL study area typiTable 4. Median values of average soil properties within 1,640 feet of monitoring wells in northern and southern High Plains agricultural land-use study areas, Nebraska and Texas.

[Source: 1994 STATSGO database (U.S. Department of Agriculture, 1994; Schwarz and Alexander, 1995; Wolock, 1997). NAL, northern High Plains agricultural land use; SAL, southern High Plains agricultural land use; <, less than]

Variable NAL study area SAL study area p-value (Wilcoxon rank-sum)1

Average sand content of soils, in percent 3.9 44.8 <0.001

Average silt content of soils, in percent 62.4 28.9 <.001

Average clay content of soils, in percent 33.9 26.3 .066

Average bulk density of soils, in grams per cubic centimeter 1.33 1.52 <.001

Average organic matter content, in percent by weight .54 .17 <.001

Average vertical permeability of soils, in inches per hour .57 1.36 <.001

Average horizontal permeability of soils, in inches per hour .83 1.56 <.001

1

p-values indicate the statistical probability that there was a real difference between two groups of data. Variables were considered to be significantly different 

between the two study areas if p was less than or equal to 0.05.

Hydrogeologic Setting 11
cally varies from 1 to 100 ft/d, with a geometric mean of about 

7 ft/d (Blandford and others, 2003). Paleovalleys filled with 

coarse gravel and sand typically have greater hydraulic conductivity than the finer sediments located in the interchannel 

regions. Well yields range from a few gallons per minute to 

about 1,000 gal/min (Texas Water Development Board, 2002).

The land surface is a gently sloping plateau that grades 

from the highest altitude of about 5,600 ft in the northwest 

to about 2,700 ft in the southeast (Fahlquist, 2003). Playas 

(closed-basin depressions) cover about 2 percent of the land 

surface and capture rainfall and irrigation runoff. Only a 

few streams exist in the area, and most are ephemeral. Some 

streams are captured by reservoirs to supply water to municipalities. The median values for average percentage of sand, 

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

and horizontal permeability of soils within a 1,640-ft radius of 

the 29 sampled monitoring wells are found in table 4.

The SAL study area is semiarid to subhumid, receiving a 

mean annual precipitation between 13 in/yr in the southwest 

to about 20 in/yr in the northeast (Bomar, 1983). Evaporation 

rates are some of the highest in the Nation. Mean annual pan 

evaporation rates range from about 95 to more than 105 in/yr 

(Gutentag and others, 1984). Natural ground-water recharge 

rates have been estimated to be from no recharge to about 

1 in/yr (Dugan and Zelt, 2000; Scanlon and others, 2005).

Land-Use Setting

To examine the effect of irrigated agriculture on groundwater quality at the water table, the NAL and SAL study 

areas were located in regions where irrigated agriculture was 

currently greater than 30 percent of the local land use. In 

addition to irrigation water, fertilizers and pesticides are commonly applied in these areas to produce consistent crop yields. 

There are no easily obtainable historical data to evaluate the 

changes in nutrient, pesticide, and irrigation-water applications. However, it is generally thought that because of more 

efficient farming practices, application rates are less today 

than 30 or 40 years ago. For example, application of irrigation 

water has moved from primarily flood and furrow methods to 

more efficient center-pivot systems. Also, many crop producers now are testing soils for nitrogen levels to adjust fertilizer 

application rates and prevent overapplication of nutrients to 

cropland. Although the estimated application rates presented 

in the following sections 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 nutrients, pesticides, and irrigation water that are applied.

Northern High Plains

In 1992, an estimated 83 percent (4.9 million acres) of 

the land in the NAL study area was used for cropland and 

12 percent was rangeland. The remaining 5 percent was classified as forest, wetlands, open water, or urban (fig. 4A) (U.S. 

Geological Survey, 1992). Land-use classes were estimated 

from Landsat Thematic Mapper satellite images as part of 

the National Landcover Dataset (NLCD). The most common 

crops grown in the study area in 2002 were corn and soybeans. 

Secondary crops included hay, sorghum, and wheat (fig. 3A) 

(U.S. Department of Agriculture, variously dated). About 

34 percent of the study area was irrigated in 1980 (Thelin and 

Heimes, 1987).

Nitrogen fertilizers commonly are applied to cropland 

in the NAL study area. The amount of nitrogen applied to 

cropland from manure (Barb Ruddy and David Lorenz, U.S. 

Geological Survey, written commun., 1997) in 1997 and commercial fertilizer (David Lorenz, U.S. Geological Survey, written commun., 1998) in 1998 in the NAL study area was about 

558 million lb. The total nitrogen divided by the total number 

of cropland acres yields an average nitrogen application rate 

of about 114 lb/acre of cropland. Fertilizer application rates 

were based on state-level fertilizer sales obtained from the 

Statistical Reporting Service (SRS) of the U.S. Department of 

Agriculture (Alexander and Smith, 1990). 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. Manure application rates were calculated 

from county-level livestock populations obtained from the 

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 not accounted for when estimating 

animal manure nitrogen.

The estimated nitrogen application rate within 1,640 ft of 

sampled wells in the NAL ranged from 52 to 136 lb/acre, with 

a median of 104 lb/acre. Nitrogen applications within 1,640 ft 

of each monitoring well were calculated using average estimated county-level manure data from 1992 to 1997 and commercial fertilizer application data from 1992 to 2001 coupled 

with the 1992 NLCD data enhanced with Geographic Information Retrieval and Analysis System (GIRAS) data (Kerie Hitt, 

U.S. Geological Survey, written commun., July 2005). For 

each well, the estimated county-level nitrogen application was 

multiplied by the fraction of the county’s cropland that was in 

the 1,640-ft buffer of the well.

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

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). An average of 1.62 lb/acre of pesticides was applied to 

cropland in the NAL study area in 1997 (table 5) (Naomi Nakagaki, U.S. Geological Survey, written commun., July 2005). 

Atrazine and metolachlor were the pesticides most commonly 

applied to crops. The types and amounts of pesticides applied 

to each area are related to the types of crops grown.

Most water used in the northern High Plains is for 

cropland irrigation. In 2000, an estimated 1,940 Mgal/d was 

12 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
104° 103° 102° 101°

35°34°33°32°

100° 99° 98° 97°

43°42°

41°40°

Base information from U.S. Geological Survey 1:100,000 Digital Line Graphs (DLG) 

EXPLANATION 0 25 50 75 100 KILOMETERS

0 25 50 75 100 MILES

UrbanAgricultureRangeland

ForestWater

Land use

Monitoring well

Land cover from U.S. Geological Survey (1992)

(A) Northern High Plains study area

Texas

Boundary of High Plainsaquifer

South Dakota

(B) Southern High Plains study area

New Mexico

Boundary of High Plainsaquifer

Kansas

Nebraska

Figure 4. Distribution of primary land-use types in (A) northern and (B) southern High Plains agricultural land-use study areas, Nebraska and Texas, 1992.

Land-Use Setting 13
used for that purpose in the NAL study area (U.S. Geological Survey, 2004). Ground-water withdrawals for irrigation 

varied by county and ranged from 15 to 315 Mgal/d (fig. 5A). 

Irrigation water is applied mainly during the summer months 

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

Other water uses include publicly supplied drinking water 

(41 Mgal/d), livestock (16 Mgal/d), industrial (13 Mgal/d), and 

rural household drinking water (8 Mgal/d).

Southern High Plains

According to the NLCD, cropland covered about 53 percent (9.8 million acres) of the SAL study area in 1992. Fortysix percent of the study area was designated as rangeland, and 

the remaining 1 percent was classified as forest, wetlands, 

open water, or urban (fig. 4B) (U.S. Geological Survey, 1992). 

In 2002, cotton was the primary crop grown in the area. Secondary crops were wheat and sorghum (fig. 3B) (U.S. Department of Agriculture, variously dated). About 11 percent of the 

study area was irrigated in 1992 (Qi and others, 2002).

Fertilizers and pesticides are commonly applied to cropland in this area. Nitrogen application rates were calculated 

using the same method as in the NAL study area. Over the 

entire SAL study area, the total amount of nitrogen applied 

to cropland from manure (Barb Ruddy and David Lorenz, 

U.S. Geological Survey, written commun., 1997) in 1997 and 

commercial fertilizer (David Lorenz, U.S. Geological Survey, 

written commun., 1998) in 1998 was about 712 million lb. 

Dividing the total nitrogen application by the total number 

of cropland acres within the extent of the hydrogeologic unit 

yields an average application rate of 73 lb/acre of cropland. 

The nitrogen application rate within 1,640 ft of the monitoring wells in the SAL study area ranged from 32 to 189 lb/acre, 

with a median of 58 lb/acre. Application rates of the 10 

pesticides most often applied in 1997 are shown in table 5. 

An average of about 0.73 lb/acre of pesticides was applied to 

cropland. The pesticides most commonly applied were trifluralin, malathion, and 2,4–D.

Similar to the northern High Plains, water use in the 

southern High Plains is dominated by cropland irrigation. In 

2000, an estimated 3,680 Mgal/d was used for that purpose 

(U.S. Geological Survey, 2004). Ground-water withdrawals for irrigation varied by county in the SAL study area and 

ranged from less than 2 to about 420 Mgal/d (fig. 5B). Irrigation water is applied mainly during the summer months (May 

through September) when crop water demands are largest. 

Other water uses in the study area include publicly supplied 

drinking water (59 Mgal/d), livestock (50 Mgal/d), mining 

(27 Mgal/d), and industrial (16 Mgal/d).

Ground-Water Quality Beneath 

Irrigated Cropland

Nitrate

Nitrogen in the form of nitrate is of interest in ground 

water because it is mobile, persistent, and exceeds the upper 

concentration limit for public drinking water more often 

than any other agricultural chemical. Sources of nitrogen 

Table 5. Ten most frequently applied pesticides in northern and southern High Plains agricultural land-use study areas, Nebraska 

and Texas, 1997.

[Pesticide application rates on crops were estimated from the National Center of Food and Agricultural Policy (NCFAP) (1997) and county-level information 

of harvested crops in the 1997 Census of Agriculture (U.S. Department of Agriculture, 1999); lb/acre, pound per acre; a.i., active ingredient]

NAL study area SAL study area

Pesticide name Average amount applied to cropland 

(lb/acre of a.i.) Pesticide name Average amount applied to cropland (lb/acre of a.i.)

Atrazine 0.46 Trifluralin 0.17

Metolachlor .44 Malathion .09

Acetochlor .18 2,4–D1 .09

Glyphosate1 .18 Atrazine .08

Alachlor .08 Pendimethalin .07

Cyanazine .06 Sodium-chlorate1 .06

Pendimethalin .06 Metolachlor .05

2,4–D1 .06 Ethephon1 .05

Terbufos .05 Glyphosate1 .04

Carbofuran .05 Tribufos1 .03

TOTAL 1.62 TOTAL .73

1

Not analyzed in water samples collected as part of this study.

14 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
104° 103° 102° 101°

35°34°33°32°

100° 99° 98° 97°

43°42°

41°40°

Base information from U.S. Geological Survey 1:100,000 Digital Line Graphs (DLG) 

EXPLANATION

0 25 50 75 100 KILOMETERS

0 25 50 75 100 MILES

1−5051−100101−150

151−200Greater than 200

Ground-water withdrawals for irrigation,in million gallons per day

Monitoring well

Ground-water withdrawal data from U.S. Geological Survey (2004)

(A) Northern High Plains study area

Texas

Boundary of High Plainsaquifer

South Dakota

(B) Southern High Plains study area

New Mexico

Boundary of High Plainsaquifer

Kansas

Nebraska

Figure 5. Ground-water withdrawals for irrigation, by county, in (A) northern and (B) southern High Plains agricultural land-use study areas, Nebraska and Texas, 2000.

Ground-Water Quality Beneath Irrigated Cropland 15
include manure, commercial fertilizers, septic system effluent, 

atmospheric deposition, some minerals, and natural grassland 

soils. Converting natural grasslands to cultivated cropland can 

release naturally occurring soil nitrogen from the soil horizon 

(Scanlon and others, 2005). McMahon and others (2006) 

estimated that in some parts of the High Plains as much as 

57 percent of nitrate in the unsaturated zone under cropland 

was from natural soil nitrogen. Although nitrate 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 representing naturally occurring sources in ground water has been estimated to be about 2 to 4 mg/L (Madison and Brunett, 1985; 

Gosselin, 1991; Mueller and Helsel, 1996; McMahon, 2001; 

Becker and others, 2002).

Water samples were analyzed for nitrite (reported as 

nitrogen), nitrite plus nitrate (as nitrogen), ammonium (as 

nitrogen), ammonium plus organic nitrogen (as nitrogen), and 

orthophosphate (as phosphorus) (Appendixes 1 and 2, table 6). 

Nitrate is the dominant form of nitrogen in oxygenated water, 

whereas nitrite, ammonium, and organic nitrogen are more stable when oxygen concentrations are small. Dissolved oxygen 

concentrations indicated that almost all ground-water samples 

collected in the NAL and SAL study areas were oxygenated 

(greater than 1.0 mg/L dissolved oxygen). Nitrite concentrations ranged from less than 0.008 to 0.116 mg/L, composing a 

maximum of 2.2 percent of the nitrite plus nitrate concentration where nitrite was detected. Therefore, nitrate plus nitrite 

concentrations will be referred to as nitrate concentrations in 

this report.

Northern High Plains

Nitrate concentrations of samples collected in the NAL 

study area ranged from 1.96 to 106 mg/L, with a median of 

10.6 mg/L (table 6, Appendix 1). Nitrate concentrations in 

27 samples (90 percent) were greater than 4.00 mg/L, suggesting that human activities have affected nitrate concentrations 

in ground water at the water table over a large portion of the 

NAL study area. Although the sampled wells are not used 

as a source of drinking water, concentrations were compared 

with U.S. Environmental Protection Agency (USEPA) drinking-water standards (U.S. Environmental Protection Agency, 

2004) to relate the quality of ground-water samples at the 

water table to nationally recognized public water-supply criteria. Concentrations in 16 samples (53 percent) were larger 

than 10.0 mg/L, the USEPA Maximum Contaminant Level for 

nitrate in drinking water (fig. 6A).

Table 6. Summary statistics for nitrogen and phosphorus compounds and nitrogen and oxygen isotopes of nitrate in ground-water 

samples collected from northern and southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04.

[Constituents are dissolved; NAL, northern High Plains agricultural land-use study area; SAL, southern High Plains agricultural land-use study area; USEPA, 

U.S. Environmental Protection Agency; mg/L, milligrams per liter; <, less than; MCL, Maximum Contaminant Level; --, no data; E, estimated; 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; NA, not analyzed]

Constituent or property

Concentrations USEPA 

drinkingwater 

standard/ 

type of 

standard1

p-value 

(Wilcoxon 

rank-sum)2

NAL samples SAL samples

Minimum Median Maximum Minimum Median Maximum

Nitrite as N, in mg/L <0.008 <0.008 <0.008 <0.008 <0.008 0.116 1 / MCL --

Nitrite plus nitrate as N, in 

mg/L 1.96 10.6 106 .65 4.12 21.6 10 / MCL <0.001

Ammonia as N, in mg/L <.04 <.04 .05 <.04 <.04 E.04 30 / LTHA --

Ammonia plus organic 

nitrogen as N, in mg/L NA NA NA <.1 <.1 .21 -- --

Orthophosphate as P, in mg/L .078 .27 .513 <.007 E.01 .03 -- <.001

Nitrogen isotope ratio (δ15N) 

of nitrate, in per mil 2.23 6.31 11.59 4.3 6.1 10.3 -- .964

Oxygen isotope ratio (δ18O) of 

nitrate, in per mil -2.40 3.08 5.66 NA NA NA -- --

1

Source: U.S. Environmental Protection Agency, 2004.

2

p-values indicate the statistical probability that there was a real difference between two groups of data. Variables were considered to be significantly different between the two study areas if p was 0.05 or less. p-values were not calculated when more than 50 percent of the concentrations were less than the largest 

laboratory reporting level.

16  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Ground-Water Quality Beneath Irrigated Cropland 

17

104° 103° 102° 101°

35°34°33°32°

100° 99° 98° 97°

43°42°

41°40°

Base information from U.S. Geological Survey 1:100,000 Digital Line Graphs (DLG) EXPLANATION

0 25 50 75 100 KILOMETERS

0 25 50 75 100 MILES

0−2526−5051−75

Less than or equal to 4.004.10 to 10.0Greater than 10.0

76−100Greater than 100

Average nitrogen application rates frommanure and fertilizer, in pounds per acreof cropland per year

Nitrate concentration, inmilligrams per liter as N

Application rates from Barbara Ruddy and David Lorenz,U.S. Geological Survey, written commun., 1997, andDavid Lorenz, U.S. Geological Survey, written commun., 1998

(A) Northern High Plains study area

Texas

Boundary of High Plainsaquifer

South Dakota

(B) Southern High Plains study area

New Mexico

Boundary of High Plainsaquifer

Kansas

Nebraska

 Figure 6. Distribution of average nitrogen application rates from manure and commercial fertilizer, by county, and nitrate concentrations in ground-water samples collected from (A) northern and (B) southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04.
Nitrogen isotope ratio (δ15N) of nitrate was analyzed to 

indicate the possible sources of nitrate in ground water. δ15N 

values represent the ratio of stable-isotopic abundances of 

15N/14N of nitrate in a sample to those of atmospheric nitrogen. 

The units of δ15N are per mil (parts per thousand) and are computed using the formula (Kendall and McDonnell, 1998):

δ15N= 1 1 000 R(sample)

R(standard)

− 



 



 × , , (2)

where R(sample) is the ratio of the heavier stable isotope (15N) 

to the lighter stable isotope (14N) of nitrate in the ground-water 

sample, and R(standard) is the ratio of 15N to 14N in atmospheric nitrogen.

Some possible sources of nitrate in ground water include 

fertilizer, natural soil nitrogen, and animal manure (including human waste). In general, fertilizer has δ15N values in 

the range of 0 to +6 per mil, natural soil nitrogen has δ15N 

values in the range of +4 to +8 per mil, and δ15N values larger 

than +10 per mil generally indicate an animal manure source 

(Heaton, 1986; Clark and Fritz, 1997; Mengis and others, 

2001; Böhlke, 2002). The use of nitrogen isotopes to identify sources of nitrate in ground water may be complicated 

by several factors. For example, the ranges of δ15N values of 

natural soil nitrogen and fertilizer partially overlap, making 

it difficult to distinguish between these two sources of nitrate 

in some cases. Ground water containing a mixture of nitrate 

from fertilizer and manure sources could produce nitrate δ15N 

values that are similar to values for natural soil nitrogen, possibly resulting in an incorrect interpretation of the isotope data. 

Additionally, microbial processes such as denitrification in 

the soil and aquifer, and volatilization of anhydrous ammonia 

can alter the original δ15N of the nitrogen source (Mengis and 

others, 2001). Despite these potential complications, nitrogen 

isotope data can provide useful source information for groundwater nitrate in many circumstances.

Concentrations and δ15N values of nitrate in NAL 

samples ranged from 1.96 to 106 mg/L and +2.23 to +11.59 

per mil, respectively (fig. 7). For comparison, the median 

concentration and δ15N values of nitrate in old ground water 

in western Nebraska were 2.17 mg/L as N and +3.5 per mil, 

respectively (fig. 7) (McMahon and Böhlke, 2006). Nitrate in 

the old ground water was derived from natural soil nitrogen. 

Only two NAL samples appear to have δ15N values that can 

be clearly associated with a particular nitrate source. Nitrate 

in the sample with the smallest δ15N value (+2.23 per mil) 

appears to have been derived from fertilizer, and nitrate in the 

sample with the largest δ15N value (+11.59 per mil) appears to 

have been derived from animal waste. The remaining samples 

could contain a mixture of nitrate from fertilizer, soil nitrogen, 

and (or) animal waste sources, on the basis of the isotope data. 

One sample was not evaluated because the dissolved oxygen 

concentration was less than 2.0 mg/L and the δ15N value may 

have been affected by denitrification. All the other samples 

had dissolved oxygen concentrations larger than 2.0 mg/L. 

The nitrate concentration data could help to differentiate 

between nitrate derived from fertilizer and soil nitrogen if the 

median concentration in old ground water in western Nebraska 

is representative of nitrate derived from soil nitrogen in the 

NAL study area. All but one of the NAL samples contained 

nitrate concentrations larger than 2.17 mg/L, the median 

concentration in old ground water, indicating that soil nitrogen 

was not a major source of nitrate in the NAL ground water. If 

this interpretation is correct, then fertilizer and manure could 

be the primary sources of nitrate in those samples with mixed 

sources.

Hydrogeologic variables were examined to determine 

their relation to nitrate concentrations in the NAL study area. 

Water levels were measured at each well immediately before 

sample collection. Measurements ranged from 35.10 to 

164.41 ft, with a median of 84.58 ft below land surface. The 

relation between nitrate concentrations and depth to water was 

evaluated using the Spearman’s rho correlation test. Nitrate 

was not statistically correlated with depth to water in the NAL 

samples (rho= –0.278, p=0.134). However, the three largest 

nitrate concentrations were found in samples from monitoring 

wells that had depths to water of less than 75 ft below land 

surface.

The relation between tritium and nitrate concentrations 

was examined to evaluate the effect of residence time on 

nitrate concentrations. Tritium occurs naturally but also was 

released to the atmosphere in large quantities during aboveground nuclear weapons testing in the 1950s and 1960s. As of 

2000, recharge water that had been exposed to the atmosphere 

since the 1950s would be expected to have more than 

1.5 pCi/L tritium (Thatcher, 1962; Clark and Fritz, 1997). 

Thus, tritium concentrations greater than or equal to 1.5 pCi/L 

indicate that at least a portion of the sample water entered 

the aquifer within the last 50 years. Widespread irrigation 

and application of agricultural chemicals generally have been 

used in the High Plains for about 50 years. Therefore, tritium 

concentrations can indicate whether water entered the aquifer 

recently enough to be affected by agricultural chemicals.

In NAL samples, tritium concentrations indicated that 

at least a portion of the water from 27 of the 30 samples was 

recharged in the last 50 years. Tritium concentrations ranged 

from values that were less than the LRL (1 pCi/L) to 34 pCi/L, 

with a median of 14 pCi/L. Nitrate concentrations were 

larger (p=0.020) in samples with a residence time of less than 

50 years; the median nitrate concentration in samples with a 

residence time of less than 50 years was 12.4 mg/L, and the 

median nitrate concentration in samples with a residence time 

of more than 50 years was 4.32 mg/L. Nitrate concentrations 

also were positively correlated with tritium concentrations 

(rho=0.517, p=0.006) in the NAL study area. Because tritium 

concentrations in precipitation have been decreasing since 

the 1960s, this result may indicate that nitrate concentrations 

in recharge water also may have been larger previously but 

that more recent recharge water contained smaller quantities of nitrate. Another possible explanation is that ground18  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Figure 7. Nitrogen isotope ratio (δ15N) values of nitrate in nitrogen sources and in groundwater samples collected from (A) northern and (B) southern High Plains agricultural land-use 

study areas, Nebraska and Texas, 2003–04.

Ground-Water Quality Beneath Irrigated Cropland 19

(A) Northern High Plains study area

(B) Southern High Plains study area

0

5

10

15

20

0 5 10 15 20 25 40 60 80 100 120

Nitrate concentration, in milligrams per liter as N

0

5

10

15

20

Median concentration

in old ground water

(western Nebraska)

(McMahon and Böhlke, 2006)

Median 15N value

in old ground water

(western Nebraska)

(McMahon and Böhlke, 2006)

Median concentration

in old ground water

(northern Texas)

(McMahon and Böhlke, 2006) Median 15N value in old ground water

(northern Texas)

(McMahon and Böhlke, 2006)

Ground-water sample

Nitrogen isotope ratio ( 15N) value, per mil

Ground-water sample

Fertilizer

Soil nitrogen

Animal waste

Fertilizer

Soil nitrogen

Animal waste
water samples containing smaller tritium concentrations are 

receiving a smaller portion of recently recharged water and a 

larger portion of older water that is not affected by agricultural 

activities at the land surface.

The percentage of coarse-grained materials in each well 

borehole and average values for percentage of sand, silt, and 

clay, bulk density, organic matter content, and vertical and 

horizontal permeability for soils within a 1,640-ft radius 

around each well were compiled to determine their effect on 

nitrate concentrations. Borehole descriptions were obtained 

from the well driller’s logs, and soil characteristics were determined from the 1994 STATSGO database (U.S. Department 

of Agriculture, 1994; Schwarz and Alexander, 1995; Wolock, 

1997). The relations between nitrate concentrations and borehole and soil characteristics were determined statistically with 

the Spearman’s rho correlation test (table 7). Nitrate concentrations were not significantly correlated to the examined borehole and soil characteristics (Spearman’s rho p-values were 

greater than 0.05). The lack of correlation between nitrate and 

soil characteristics may be related to the coarse spatial resolution (1-km, 0.6214-mi) or the effect of vertically averaged soil 

properties of the soils dataset.

Domestic wells draw water from a range of depths across 

the aquifer, and a set of samples from randomly selected 

domestic wells provides a good indication of the variability 

of water quality with depth and an evaluation of the overall 

water-quality conditions within the aquifer. Alternatively, 

samples collected from water-table wells usually have the 

highest concentrations of human-related contaminants and 

other chemical constituents that originate from above the aquifer. Nitrate concentrations in NAL samples were compared 

with nitrate concentrations in rural domestic wells to determine whether concentrations were different at the water table 

than throughout the aquifer. The median nitrate concentration 

in 30 randomly distributed domestic wells throughout the 

Eastern Nebraska hydrogeologic subunit was 1.92 mg/L (Stanton, in press), and the median concentration in the 30 watertable wells was 10.6 mg/L (p<0.001). Domestic well samples 

were collected at depths ranging from 19.60 to 179.10 ft below 

the water table, and all NAL samples were collected at depths 

of about 5 ft below the water table. The larger nitrate concentrations in samples collected from water-table wells located 

near irrigated cropland provide evidence that nitrogen applied 

to irrigated agricultural land is reaching ground water but may 

not be reaching rural domestic wells in the area.

Southern High Plains

Nitrate concentrations in the SAL samples ranged from 

0.65 to 21.6 mg/L, with a median concentration of 4.12 mg/L 

(table 6, Appendix 2). Nitrate concentrations in 16 samples 

(55 percent) were larger than 4.00 mg/L, and concentrations 

in five samples (17 percent) were larger than the USEPA 

Maximum Contaminant Level of 10.0 mg/L (fig. 6). δ15N 

values of nitrate ranged from about +4.3 to +10.3 per mil in 

SAL samples (fig. 7, table 6, appendix 2). None of the SAL 

samples had a δ15N value that could indicate conclusively a 

specific source of nitrogen. Two samples were not assessed 

because dissolved oxygen concentrations were less than 

2.0 mg/L. The median nitrate concentration in old ground 

water representing nitrate from natural soil nitrogen in northern Texas was 1.48 mg/L (fig. 7) (McMahon and Böhlke, 

2006). Nitrate concentrations in 24 (83 percent) SAL samples 

were larger than the median concentration in old ground water, 

Table 7. Relations between nitrate concentrations in ground-water samples and borehole and soil characteristics in northern and 

southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04.

[NAL, northern High Plains agricultural land use; SAL, southern High Plains agricultural land use]

Variable NAL study area SAL study area

Spearman’s rho p-value3 Spearman’s rho p-value3

Percentage of coarse-grained sediments in well borehole1 0.198 0.288 0.239 0.206

Average sand content of soils, in percent2 .075 .687 –.129 .493

Average silt content of soils, in percent2 –.027 .883 .123 .517

Average clay content of soils, in percent2 –.185 .317 .131 .489

Average bulk density of soils, in grams per cubic centimeter2 .170 .361 –.050 .790

Average organic matter content of soils, in percent by weight2 –.229 .216 .713 .360

Average vertical permeability of soils, in inches per hour2 .011 .956 –.128 .498

Average horizontal permeability of soils, in inches per hour2 .117 .530 –.131 .488

1

Source: well driller’s logs.

2

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

3

p-values indicate the statistical probability confidence that there was a real correlation between two variables. Variables were considered to be significantly 

correlated with nitrate if p was 0.05 or less. 

20 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
suggesting that nitrate in SAL samples primarily is the result 

of human activities.

Hydrogeologic variables were examined to determine 

their relation to nitrate concentrations in the SAL study area. 

Depth to ground water in the SAL study area ranged from 

78.85 to 195.24 ft, with a median of 153.16 ft below land surface (Appendix 2). Nitrate concentrations in the SAL samples 

were inversely correlated (rho= –0.417, p=0.027) with depth to 

water, indicating that nitrate concentrations at the water table 

decreased as the thickness of the unsaturated zone increased. 

In SAL samples, tritium concentrations indicated that at least 

a portion of the water from 17 of the 29 (59 percent) samples 

had been recharged in the last 50 years (young water). Tritium 

concentrations ranged from less than the LRL (1 pCi/L) to 

41 pCi/L, with a median of 3 pCi/L (Appendix 2). Nitrate 

concentrations were larger (p=0.009) in samples with a residence time of less than 50 years; the median nitrate concentration in samples containing young water was 4.70 mg/L, and 

the median nitrate concentration in samples with old water 

was 2.24 mg/L. Nitrate concentrations also were positively 

correlated with tritium concentrations (rho=0.479, p=0.011) 

in the SAL study area. The relations between nitrate and 

borehole and soil characteristics were evaluated statistically 

with the Spearman’s rho correlation test (table 7). Nitrate 

concentrations in the SAL study area were not significantly 

correlated to the borehole and soil characteristics (all p-values 

greater than 0.05).

Nitrate concentrations in SAL wells were compared 

with nitrate concentrations in rural domestic wells. Sample 

collection depths at domestic wells ranged from about 5 to 

200 ft below the water table, and all SAL wells were sampled 

at depths of around 5 ft below the water table. The median 

nitrate concentration in 48 randomly distributed domestic 

wells throughout the Ogallala Formation in the SHP was 

2.98 mg/L (Fahlquist, 2003), and the median concentration in 

the 29 SAL wells was 4.12 mg/L. Although the median concentration in SAL wells was slightly larger, the difference in 

nitrate concentrations between domestic and SAL monitoring 

wells was not statistically significant (p=0.202).

Pesticides

Northern High Plains

Figure 8 shows pesticide concentrations both greater 

than and less than the largest laboratory reporting level 

(LRL). Pesticide concentrations not qualified with a “less 

than” remark code are presented. However, for this report, 

a pesticide concentration was only identified as a detection 

if the value was equal to or greater than the largest LRL for 

that compound. Twenty-two NAL samples (73 percent) had 

at least one pesticide compound detected at a concentration 

equal to or greater than the largest LRL (fig. 9). Pesticides 

detected were: atrazine (20 samples), alachlor (one sample), 

metolachlor (one sample), and simazine (one sample). These 

pesticides are herbicides that control broadleaf and grassy 

weeds. Atrazine is used primarily on corn and sorghum fields. 

Alachlor is used on corn, soybeans, and peanuts. Metolachlor is used for corn, soybeans, peanuts, sorghum, cotton, 

and other crops. Simazine typically is applied to field, fruit, 

vegetable, and ornamental crops (Cornell University Cooperative Extension, 2005). Pesticide degradates detected were 

deethylatrazine (17 samples), alachlor ethanesulfonic acid 

(ESA) (16 samples), metolachlor ESA (10 samples), alachlor 

ethanesulfonic acid second amide (ESA SA) (seven samples), 

metolachlor oxanilic acid (OA) (five samples), alachlor OA 

(one sample), and acetochlor/metolachlor ESA SA (one 

sample). The pesticide degradates of alachlor and metolachlor 

were detected more frequently than their associated parent 

pesticide compounds. Pesticide concentrations were small and 

did not exceed public drinking-water standards where established. The largest pesticide compound concentration was 

3.09 μg/L (alachlor ESA).

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 0.05 μg/L. 

When examining pesticide detections at concentrations equal 

to or greater than 0.05 μg/L, pesticide degradate compounds 

were more frequently detected than parent compounds. Parent 

compounds detected were atrazine (10 samples) and metolachlor (one sample). Pesticide degradate compounds detected 

were alachlor ESA (12 samples), deethylatrazine (11 samples), 

metolachlor ESA (eight samples), alachlor ESA SA (four samples), metolachlor OA (two samples), acetochlor/metolachlor 

ESA SA (one sample), and alachlor OA (one sample) (fig. 8).

Figure 10 compares the frequencies of pesticides detected 

in ground water at concentrations equal to or greater than 

0.05 μg/L in samples collected from the NAL study area and 

in 345 samples collected from 14 NAWQA agricultural study 

areas (fig. 11) across the Nation where corn and soybeans 

were the primary crops (Appendix 4). The pesticide compounds shown are those that were analyzed in all NAWQA 

corn and soybean study areas. Except for deethylatrazine, 

only pesticide parent compounds are compared. Atrazine and 

deethylatrazine were detected more than twice as frequently 

in NAL samples than in other NAWQA study area samples; 

whereas metolachlor was detected more frequently in samples 

from other NAWQA study areas. Acetochlor, alachlor, carbofuran, metribuzin, prometon, propyzamide, and simazine were 

detected in samples collected from other NAWQA study areas 

but not in samples collected from the NAL study area.

The relation between pesticides and water depth was 

investigated by comparing measured water levels at sites with 

no pesticides detected and sites with at least one pesticide 

compound detected using the Wilcoxon rank-sum statistical 

test. Samples collected in areas with shallower depths to water 

were more likely to have detectable pesticides (p=0.018). 

Water samples containing at least one detectable pesticide 

(22 samples) had a median depth to water of 82.82 ft, whereas 

Ground-Water Quality Beneath Irrigated Cropland 21
samples with no detected pesticides (8 samples) had a median 

depth to water of 110.36 ft. The number of pesticide 

detections increased as the depth to water decreased 

(rho= –0.467, p=0.012).

The effect of ground-water residence time on pesticide 

detections was evaluated using tritium concentrations. In 

NAL samples, at least one pesticide was detected in 22 of 

the 27 water samples with residence times of 50 years or 

less (young water) and in none of the three water samples 

with residence times of more than 50 years (old water). The 

Fisher’s Exact test for independence between categorical variables indicated that samples with young water were statistically more likely to have a pesticide compound detection than 

samples with old water (p=0.014). In addition, water samples 

containing at least one detectable pesticide compound had a 

median tritium concentration of 15 pCi/L, whereas samples 

with no detected pesticide compounds had a median tritium 

concentration of 8 pCi/L (p=0.019). The number of pesticide 

compound detections also increased as tritium concentrations 

increased (rho=0.508, p=0.006).

The relations between pesticides and borehole and 

soil characteristics were investigated by comparing averMetribuzin

Simazine

Alachlor OA

Alachlor

Acetochlor/metolachlor ESA SA

Metolachlor

Metolachlor OA

Alachlor ESA SA

Metolachlor ESA

Alachlor ESA

Deethylatrazine

Atrazine

0.001

ESA

SA

OA

0.01 0.10 1.0 10 100

Malathion

Fluometuron

Tebuthiuron

Propazine

Deethylatrazine

Concentrations in this range are less than the laboratory 

 reporting level (LRL)

U.S. Environmental Protection Agency (2004) Maximum 

 Contaminant Level

Estimated concentration of pesticide compound

Concentration of pesticide compound

Ethanesulfonic acid

Second amide

Oxanilic acid

EXPLANATION

Concentration, in micrograms per liter (μg/L)

(A) Northern High Plains study area

(B) Southern High Plains study area

Common 

assessment

level (0.05 μg/L)

Figure 8. Concentrations of pesticide compounds in ground-water samples collected from (A) northern 

and (B) southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04. 

Pesticides are listed in order of decreasing detection frequency.

22 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
!

! !

!

!

!

! ! ! ! ! ! !! ! ! !

!

! !! ! !! ! !

!

!

!

!

! ! ! ! !

!

!

! ! ! ! ! ! ! ! ! !

! ! ! !

!! ! ! ! !

!

!

9 61 1 4

4 1 5 2

3 3

2

2

2

2

6 3 4 1

1

1

1

1

4

6 2 4

3 6

104° 103° 102° 101°

35°34°33°32°

100° 99° 98° 97°

43°42°

41°40°

Base information from U.S. Geological Survey 1:100,000 Digital Line Graphs (DLG) EXPLANATION 0 25 50 75 100 KILOMETERS

0 25 50 75 100 MILES

Monitoring well

No pesticide detectedPesticides detected and  number of detections

(A) Northern High Plains study area

Texas

Boundary of High Plainsaquifer

South Dakota

(B) Southern High Plains study area

New Mexico

Boundary of High Plainsaquifer

Kansas

Nebraska

!

!6

Figure 9. Number of pesticide compounds detected at concentrations equal to or greater than laboratory reporting level in ground-water samples collected from 

(A) northern and (B) southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04.

Ground-Water Quality Beneath Irrigated Cropland 23
age soil properties near NAL wells with no pesticide compound detections and NAL wells with at least one detectable 

pesticide compound using the Wilcoxon rank-sum statistical 

test (table 8). The difference between the two groups was 

considered to be significant if the test statistic p-value was 

0.05 or less. Samples that had at least one detectable pesticide 

were located in areas with soils having a smaller percentage 

of silt content (p=0.017) and smaller horizontal permeability 

rates (p=0.022). These results are counterintuitive and may 

be related to the coarse spatial resolution of the soils dataset 

or the effect of vertically averaged soil properties from the 

STATSGO database.

The number of pesticide compound detections in the 

water-table monitoring wells was compared with detections in 

domestic wells. Similar to the difference in nitrate concentrations, pesticides were detected more often in NAL wells than 

in domestic wells (p=0.002) — 30 percent of samples collected from domestic wells (Stanton, in press) and 73 percent 

of samples collected from NAL wells had at least one detectable pesticide compound.

Southern High Plains

Seven SAL samples (24 percent) contained at least one 

pesticide compound detected at or above the LRL (figs. 8 

and 9). Pesticides detected were propazine (two samples), 

fluometuron (one sample), and tebuthiuron (one sample). Propazine is an herbicide that controls broadleaf and grassy weeds 

and is used on sorghum fields. Fluometuron is used to control 

weeds in cotton fields. Tebuthiuron is a broad-spectrum herbicide that is used to control weeds in noncropland areas such 

as rangelands, rights-of-way, and industrial sites (Cornell University Cooperative Extension, 2005). The pesticide degradate 

deethylatrazine was detected in six samples. Deethylatrazine 

usually is formed from degradation of atrazine, a pesticide 

that generally is not used on cotton but may have been used on 

(A) Corn and soybeans (NAL)

Frequency of detections at concentrations equal to or

greater than 0.05 microgram per liter, in percent

Recently recharged ground water from other 

 NAWQA study areas growing the same crops

 (appendix 4)

Recently recharged ground water from northern 

 and southern High Plains study areas

(B) Cotton (SAL)

EXPLANATION

Carbofuran

Propyzamide

Acetochlor

Simazine

Alachlor

Prometon

Tebuthiuron

Metribuzin

Metolachlor

Deethylatrazine

Atrazine

Tebuthiuron

0 10 20 30 40

Deethylatrazine

Simazine

Fluometuron

Norflurazon

Atrazine

Metolachlor

Figure 10. Frequency of pesticide 

detections at concentrations equal to 

or greater than 0.05 microgram per liter 

in ground-water samples collected 

from northern High Plains agricultural 

land-use study area, where primarily 

corn and soybeans are grown, and 

from southern High Plains agricultural 

land-use study area, where primarily 

cotton is grown, relative to samples 

collected from other National WaterQuality Assessment study areas where 

the same crops are grown. Pesticides 

are listed in order of decreasing detection frequency.

24 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Georgia-Florida Coastal Plain

Mobile River Basin

Lower Tennessee River Basin

Lower Illinois River Basin

Upper Illinois

River Basin

Eastern Iowa Basins

Upper Mississippi River Basin

San Joaquin-Tulare Basins

Albemarle-PamlicoDrainage Basin

Santee River Basin and Coastal Drainages

Apalachicola-Chattahoochee-Flint River Basin

Potomac River

Basin

White River Basin

Lake Erie-Lake

Saint Clair Drainages

Lower Susquehanna

River Basin

Great and LittleMiami River Basins

Long IslandNew JerseyCoastal Drainages

Delmarva Peninsula

125° 120° 50° 115° 110° 105° 100° 95° 90° 85° 80° 75° 70° 65°

45°

40°

35°

30°

25°

0 150 300 450 600 MILES

0 150 300 450 600 KILOMETERS

Canada

Mexico The Bahamas 

Base from U.S. Geological Survey digital data, 1:2,000,000, 1991Albers Equal Area Conic projectionStandard parallels 29°30' and 45°30', central meridian 96°Horizontal coordinate information is referenced to theNorth American Datum of 1983 (NAD 83)

Figure 11. Location of National Water-Quality Assessment (NAWQA) agricultural study areas across the United States.

Ground-Water Quality Beneath Irrigated Cropland 25
corn and sorghum grown in the SHP prior to conversion to cotton or may have been used for Conservation Reserve Program 

(CRP) land or roadside areas (U.S. Environmental Protection 

Agency, 2001). Deethylatrazine also can be a degradate of 

propazine (Barbash and Resek, 1996). Pesticide concentrations were considerably less than respective concentration 

limits for public drinking-water supplies. The largest pesticide 

concentration detected in ground-water samples collected 

from the SAL study area was 0.392 μg/L (estimated) of deethylatrazine.

Three pesticide compounds were detected at concentrations equal to or greater than the 0.05-μg/L common assessment level in SAL samples — deethylatrazine (three samples), 

propazine (two samples), and fluometuron (one sample) 

(fig. 8). These results were compared with the detection 

frequencies in 41 ground-water samples collected from three 

NAWQA agricultural study areas where cotton was a primary crop (fig. 10, Appendix 4). The pesticide compounds 

shown are those that were analyzed in all NAWQA cotton 

study areas. Except for deethylatrazine, only pesticide parent 

compounds were compared. Propazine concentrations were 

not analyzed in samples collected from other NAWQA cotton 

study areas, and therefore, the detection frequencies could not 

be compared. Deethylatrazine was detected about twice as 

frequently at concentrations equal to or larger than 0.05 μg/L 

in SAL samples as in samples collected from other NAWQA 

study areas. Fluometuron was detected less frequently in 

SAL samples (3 percent) than in other NAWQA samples 

(5 percent). Atrazine, metolachlor, norflurazon, simazine, and 

tebuthiuron were detected at concentrations equal to or greater 

than 0.05 μg/L in other NAWQA cotton study samples but not 

in SAL samples. One reason that most pesticide compounds 

were detected less frequently in the SAL samples than in 

samples collected from other cotton studies might be the large 

evaporation rates in the SHP. All but one of the other cotton 

studies were completed in the southeast part of the country 

where recharge is greater and downward movement of chemicals may be more likely.

In the SAL study area, depth to water did not have a 

significant effect on pesticide compound detections. Water 

samples containing at least one detectable pesticide compound 

(7 samples) had a median depth to water of 153.36 ft, and 

samples with no detected pesticide compounds (22 samples) 

had a median depth to water of 149.45 ft (p=0.862). The 

number of pesticide compound detections was not correlated 

with depth to water in the SAL area (rho= –0.003, p=0.987).

Table 8. Pesticide compound detections in ground-water samples related to borehole and soil characteristics in northern and southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04.

[NAL, northern High Plains agricultural land use; SAL, southern High Plains agricultural land use]

Variable

NAL study area SAL study area

Median 

value near 

wells 

with no 

pesticides 

detected

Median 

value near 

wells 

with one 

or more 

pesticides 

detected

p-value 

(Wilcoxon 

rank-sum)1

Median value 

near wells 

with no pesticides detected

Median 

value near 

wells with 

one or more 

pesticides 

detected

p-value 

(Wilcoxon 

rank-sum)1

Percentage of coarse-grained sediments in 

well borehole2

4.5 12.0 0.424 4.2 5.8 0.733

Average sand content of soils, in percent3 4.4 3.2 .136 44.8 44.8 .610

Average silt content of soils, in percent3 70.5 62.4 .017 28.9 28.9 .684

Average clay content of soils, in percent3 24.8 34.8 .084 26.3 26.3 .573

Average bulk density of soils, in grams per 

cubic centimeter3

1.38 1.33 .587 1.52 1.52 .851

Average organic matter content of soils, in 

percent by weight3

.56 .53 .869 .18 .16 1.000

Average vertical permeability of soils, in 

inches per hour3

1.20 .77 .210 1.36 1.36 .809

Average horizontal permeability of soils, in 

inches per hour3

1.13 .47 .022 1.56 1.56 .573

1

p-values indicate the statistical probability that there was a real difference between two groups of data. Variables were considered to be significantly different 

between the two groups if p was less than or equal to 0.05. 

2

Source: well driller’s logs.

3

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

26  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
At least one pesticide compound was detected in 29 percent of SAL samples that also contained water recharged less 

than 50 years ago (samples with tritium concentrations equal 

to or greater than 1.5 pCi/L) and in 17 percent of samples 

with water recharged more than 50 years ago (samples with a 

tritium concentration less than 1.5 pCi/L). Although a larger 

percentage of samples with young water had at least one 

detectable pesticide, it was not a statistically significant difference (p=0.369). However, tritium concentrations were significantly different (p=0.019) between samples with and without 

pesticide detections; SAL water samples containing at least 

one detectable pesticide compound had a median tritium concentration of 15 pCi/L, and samples with no detected pesticide 

compounds had a median tritium concentration of 3 pCi/L. It 

should be expected that any sample with a detectable pesticide 

compound should have a residence time of less than 50 years 

because pesticide applications, at least as a large-scale agricultural practice, have only been in use for about 50 years. 

This inconsistency might be explained by the difference in the 

way that pesticide compounds and tritium may be affected by 

mixing of water having a residence time of less than 50 years 

and water having a residence time of more than 50 years in 

the aquifer. Pesticide compounds can be detected at small 

concentrations. Therefeore, even when a water sample contains a small amount of young water, the presence of pesticide 

compounds may still be detectable. Conversely, if mixing of 

young and old water is occurring and only a small portion of 

the sampled water in a well has a residence time of less than 

50 years, the tritium concentration may be diluted such that 

the concentration is less than 1.5 pCi/L, and the sample may 

be classified as having old water.

The relations between pesticides and borehole and soil 

characteristics were examined by comparing the soil characteristics near SAL wells with no pesticide compound detections and SAL wells with at least one detectable pesticide 

compound (table 8). The difference between the two groups 

of samples was considered to be significant if the test statistic 

p-value was 0.05 or less. Borehole and soil characteristics did 

not differ significantly between the two groups of samples.

The number of pesticide compound detections in the 

SAL wells was compared with detections in domestic wells. 

Pesticides were detected more often in SAL wells, but the 

difference in frequencies was not statistically significant 

(p=0.554)—24 percent of samples collected from SAL wells 

and 17 percent of samples collected from domestic wells 

(Fahlquist, 2003) had at least one detectable pesticide compound.

Dissolved Solids

The concentration of dissolved solids is an indicator of 

ground-water quality. High concentrations of dissolved solids 

can limit the use of ground water for drinking water, application to crops, and industrial purposes. Major ions account 

for the bulk of dissolved solids in a water sample. The major 

cations in ground water typically are calcium, magnesium, 

sodium, and potassium. The major anions in ground water 

typically are carbonate alkalinity [reported as calcium carbonate (CaCO3

) equivalent], sulfate, chloride, and fluoride. 

When nitrate is present in substantial quantities, it also can 

be a major anion. Trace elements (mostly metals) make up a 

component of dissolved solids but at concentrations so small 

that they are relatively negligible when compared to concentrations of major ions. Measurements of water properties and 

concentrations of major ions and selected trace elements are 

presented in Appendixes 1 and 2 and summarized in table 9.

Ground water contains dissolved solids derived mostly 

from dissolution of soil or rock minerals that come in 

contact with water. Fertilizers also contain minerals and trace 

elements that, when applied at the land surface, can move 

downward to the aquifer. In addition to the direct application 

of dissolved solids that are contained in commercial fertilizers, fertilizers can have an indirect effect on concentrations 

of dissolved solids. The biochemical process of converting 

manure and commercial fertilizer to nitrate lowers the pH of 

pore water, thereby increasing the dissolution and mobility of 

ions and metals that are present in soils and geologic materials 

(Böhlke, 2002). Consequently, concentrations of major ions 

and trace elements sometimes are positively correlated with 

nitrate concentrations.

Northern High Plains

Dissolved-solids concentrations in ground water collected 

from the NAL study area ranged from 272 to 2,160 mg/L, 

with a median of 442 mg/L. The relative proportions of the 

major cations and anions are shown in figure 12. A cation or 

anion is referred to as dominant if it accounts for more than 

60 percent of the total cations or anions. The dominant cation 

was most commonly calcium, and the dominant anion was 

most commonly carbonate alkalinity, principally in the form of 

bicarbonate (HCO3

–

). Some samples had no dominant cation 

or anion but had nearly equal mixtures of more than one cation 

or anion. One sample (NAL-205, Appendix 1) was dominated 

by chloride; this sample had the largest dissolved-solids concentration of all NAL samples. Nitrate was sufficiently large 

in one sample (NAL-113, Appendix 1) to be the dominant 

anion.

Dissolved-solids, major ion, and trace element concentrations were compared with USEPA drinking-water standards 

(U.S. Environmental Protection Agency, 2004) to relate the 

quality of water-table samples to nationally recognized public 

water-supply criteria. However, because the wells sampled 

as part of this study were screened near the water table and 

located adjacent to irrigated cropland, water-quality results do 

not represent the water quality that might be found in water 

collected from wells that are used for drinking-water purposes. 

Eight NAL samples had dissolved-solids concentrations 

greater than the USEPA Secondary Drinking-Water Regulation 

(SDWR) of 500 mg/L (U.S. Environmental Protection Agency, 

2004). One sample (NAL-205) exceeded the USEPA SDWRs 

Ground-Water Quality Beneath Irrigated Cropland 27
Table 9. Summary statistics for physical properties, major ions, selected trace elements, and dissolved organic carbon in ground-water 

samples collected from northern and southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04.

[Constituents are dissolved. NAL, northern High Plains agricultural land use; SAL, southern High Plains agricultural land use; USEPA, U.S. Environmental 

Protection Agency; <, less than; μS/cm, microsiemen per centimeter; oC, degrees Celsius; SDWR, Secondary Drinking-Water Regulation; NTU, nephelometric 

turbidity unit; >, greater than; TT, Treatment Technique; mg/L, milligrams per liter; CaCO3, calcium carbonate; 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]

Constituent or property

NAL samples SAL samples USEPA drinking 

water standard/ 

type of 

standard1

p-value 

(Wilcoxon 

rank-sum) Minimum Median Maximum Minimum Median Maximum 2

Physical properties

Water level, in feet 

below land surface

35.10 84.58 164.41 78.85 153.16 195.24 -- <0.001

Specific conductance, in 

μS/cm at 25 oC

421 709 3,320 676 1,260 4,630 -- <.001

pH, in standard units 6.0 7.1 7.3 7.0 7.2 7.4 6.5-8.5/SDWR .001

Temperature, in oC 13.0 14.5 21.1 17.5 19.0 21.2 -- <.001

Turbidity, in NTU .1 .6 >1,000 .2 .9 5.9 5/TT .220

Oxygen, in mg/L 1.3 6.5 8.0 .8 6.5 8.8 -- .671

Dissolved solids (concentrations in milligrams per liter)

Dissolved solids 272 442 2,160 416 814 3,580 500/SDWR <.001

Major ions (concentrations in milligrams per liter)

Carbonate alkalinity, as 

CaCO3

46 232 418 155 234 355 -- .612

Calcium 48.4 89.4 473 29.9 79.4 195 -- .255

Magnesium 6.83 14.8 70.1 24.6 65.9 198 -- <.001

Sodium 9.18 31.45 114 29.0 59.4 735 -- <.001

Potassium 3.79 6.91 26.3 2.16 9.08 27.5 -- .048

Sulfate 14.0 32.5 255 17.4 160 1,300 250/SDWR <.001

Bromide .04 .11 2.13 .11 .95 4.86 -- <.001

Chloride 3.08 13.3 502 11.2 165 701 250/SDWR <.001

Fluoride <.2 .3 .5 .98 2.80 5.55 4/MCL <.001

Silica 20.9 35.5 53.7 28.4 51.1 81.7 -- <.001

Selected trace elements (concentrations in micrograms per liter)

Arsenic 1.3 4.2 9.3 1.7 7.5 25.9 10/MCL <.001

Barium 43 230 741 14 56 196 2,000/MCL <.001

Boron 23 35 68 108 226 943 600/LTHA <.001

Cobalt .125 .311 1.68 .102 .310 1.20 -- .964

Copper .4 .9 5.2 .6 1.4 4.9 1,300/TT .010

Iron <10 <10 1,020 <10 <10 55 300/SDWR --

Lithium 8.1 16.7 47.5 43.6 119 278 -- <.001

Manganese <.2 .7 331 <.2 6 621 300/LTHA <.001

Molybdenum .2 1.8 22.7 .9 5.3 52.9 40/LTHA <.001

28  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
for both sulfate (250 mg/L) and chloride (250 mg/L) concentrations. Trace elements exceeding drinking-water standards 

were uranium (two samples), iron (one sample), manganese 

(one sample), and selenium (one sample).

The relations between dissolved-solids concentrations 

and depth to water and residence time were tested. Dissolved 

solids were inversely correlated with water depth in samples 

from the NAL study area (rho= –0.447, p=0.016), indicating 

that dissolved-solids concentrations were larger in areas where 

the water table was closer to the land surface. Dissolvedsolids concentrations also were related to tritium concentrations (p=0.032); the median dissolved-solids concentration in 

samples with water recharged in the last 50 years was 

452 mg/L, and the median dissolved-solids concentration in 

samples with water recharged more than 50 years ago was 

298 mg/L.

The relations between dissolved-solids concentrations 

and borehole and soil characteristics were examined with the 

same method as nitrate concentrations. Dissolved solids in 

ground water were not significantly correlated to the examined 

borehole or soil characteristics (table 10).

Application of nitrogen fertilizers may have affected 

dissolved-solids concentrations. As mentioned previously, the 

process of converting nitrogen fertilizer to nitrate produces 

acidity that can dissolve minerals in the soil and increase the 

concentration of dissolved solids that eventually recharges 

ground water (Böhlke, 2002). The relation between nitrate 

and major ion and trace element concentrations in ground 

water was examined statistically with the Spearman’s rho correlation test. If the test statistic p-value was less than or equal 

to 0.05, nitrate was considered to be positively correlated with 

the ion or metal. Nitrate was not correlated with pH but was 

positively correlated with dissolved solids, carbonate alkalinity, calcium, magnesium, sodium, potassium, bromide, barium, 

cobalt, copper, lithium, and strontium (table 11). Several 

factors may explain the lack of correlation between nitrate and 

pH. Acidity is consumed by the biogeochemical reactions in 

the soil and subsoil (prior to recharge) that cause dissolved ion 

and metal concentrations to increase. In addition, the buffering capacity of ground water and aquifer sediments also could 

have raised the pH of acidic recharge water.

Southern High Plains

In the SAL study area, dissolved-solids concentrations 

ranged from 416 to 3,580 mg/L, with a median of 814 mg/L 

(table 9). Most samples had no dominant cation or anion 

(fig. 12). The dominant cation was sodium in one sample; 

this sample had the largest dissolved-solids concentration of 

all SAL samples. In three samples, the dominant anion was 

carbonate alkalinity, principally in the form of bicarbonate 

(HCO3

–

); in one sample, the dominant anion was sulfate. In 

general, as dissolved-solids concentrations increased, the 

anion balance shifted from carbonate alkalinity to chloride to 

sulfate.

The USEPA concentration standards for publicly supplied 

drinking-water quality were exceeded for several constituents in the SAL study area (table 9). Twenty-five samples 

exceeded the USEPA SDWR of 500 mg/L for dissolved-solids 

Table 9. Summary statistics for physical properties, major ions, selected trace elements, and dissolved organic carbon in ground-water 

samples collected from northern and southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04.—Continued

[Constituents are dissolved. NAL, northern High Plains agricultural land use; SAL, southern High Plains agricultural land use; USEPA, U.S. Environmental 

Protection Agency; <, less than; μS/cm, microsiemen per centimeter; oC, degrees Celsius; SDWR, Secondary Drinking-Water Regulation; NTU, nephelometric 

turbidity unit; >, greater than; TT, Treatment Technique; mg/L, milligrams per liter; CaCO3, calcium carbonate; 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]

Constituent or property

NAL samples SAL samples USEPA drinking 

water standard/ 

type of 

standard1

p-value 

(Wilcoxon 

rank-sum) Minimum Median Maximum Minimum Median Maximum 2

Selected trace elements (concentrations in micrograms per liter)—Continued

Selenium 1.4 9.4 90.2 1.1 14.4 93.5 50/MCL 0.211

Strontium 237 409 1,820 1,050 2,500 7,250 4,000/LTHA <.001

Uranium .04 3.90 83.0 1.95 9.25 30.8 30/MCL .001

Dissolved organic carbon (concentrations in milligrams per liter)

Dissolved organic 

carbon

E.3 1.3 16.2 .8 2.2 10.8 -- <.001

1

Source: U.S. Environmental Protection Agency, 2004.

2

p-values indicate the statistical probability that there was a real difference between two groups of data. Variables were considered to be significantly different 

between the two study areas if p was less than or equal to 0.05. p-values were not calculated when more than 50 percent of the concentrations were less than the 

largest laboratory reporting level.

Ground-Water Quality Beneath Irrigated Cropland 29
concentrations, nine samples exceeded the SDWR of 

250 mg/L for sulfate concentrations, and five samples 

exceeded the SDWR of 250 mg/L for chloride concentrations. 

The SDWRs for each of these constituents are nonenforceable guidelines. Trace elements that exceeded their respective 

USEPA public drinking-water standard were: arsenic (11 samples), strontium (six samples), boron (three samples), manganese (three samples), molybdenum (one sample), selenium 

(one sample), and uranium (one sample).

Likely sources of dissolved solids in the SAL study 

area include fertilizers, natural minerals, and underlying 

bedrock units. As mentioned previously, fertilizers containing dissolved solids are commonly at the land surface in the 

SAL study area and can potentially move past the root zone 

into ground water. Dissolved solids that are concentrated in 

the subsoil by evaporative processes potentially are another 

substantial source of larger dissolved-solids concentrations in 

ground water in the SAL study area. Evidence of this is suggested by the positive correlation between concentrations of 

dissolved solids and chloride in the SAL samples (rho=0.800, 

p<0.001). 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). The presence of large chloride concentrations 

in SAL ground-water samples indicates that prior to widespread irrigation, recharge rates were much smaller in the SAL 

study area and caused dissolved solids to concentrate in the 

unsaturated zone. Because the wells sampled as part of this 

study were located adjacent to irrigated cropland, irrigation 

water may have transported dissolved solids from the unsaturated zone to ground water. However, potassium chloride 

(KCl) also is known to have been applied as a nutrient source 

in parts of the SAL study area and may be a source of chloride in ground water (McMahon and others, 2006). Another 

source of dissolved solids in ground water of the SAL study 

area may be the underlying mineralized bedrock. In an area 

where irrigation wells pumped water from the lower part of 

Percent

Calcium

 100 

 80

 60

 40

 20

 0 

 0 

 20 

 40 

 60 

 80 

 100 

Magnesium

 0 

 20

 40 

 60 

 80 

 100 

Sodium plus potassium

Chloride, fluoride, nitrite plus nitrate

 0 

 20 

 40 

 60 

 80 

 100 

 100 

 80

 60

 40

 20

 0 

Carbonate plus bicarbonate

 100 

 80 

 60 

 40 

 20

 0 

Sulfate

 0 

 20 

 40

 60

 80 

 100

Sulfate plus chloride

 0 

 20

 40

 60

 80

 100 

Calcium plus magnesium

 100 

 80 

 60

 40 

 20 

 0 

 100 

 80

 60

 40

 20

 0 

Percent

Percent

EXPLANATION

Sample from northern High Plains agricultural land-use study area

Sample from southern High Plains agricultural land-use study area

Figure 12. Relative proportions, in 

percentage equivalents, of major 

ions in ground-water samples collected from northern and southern 

High Plains agricultural land-use 

study areas, Nebraska and Texas, 

2003–04.

30 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Comparison of Ground-Water Quality in Two Study Areas 31

Table 10. Dissolved-solids concentrations in ground-water samples related to borehole and soil characteristics in northern and 

southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04.

[NAL, northern High Plains agricultural land use; SAL, southern High Plains agricultural land use]

Variable NAL study area SAL study area

Spearman’s rho p-value1 Spearman’s rho p-value1

Percentage of coarse-grained sediments in well borehole2 –0.109 0.558 0.023 0.905

Average sand content of soils, in percent3 .125 .502 .333 .078

Average silt content of soils, in percent3 .188 .313 –.331 .080

Average clay content of soils, in percent3 –.268 .148 –.332 .079

Average bulk density of soils, in grams per cubic centimeter3 .278 .134 .500 .008

Average organic matter content of soils, in percent by weight3 –.354 .056 –.279 .140

Average vertical permeability of soils, in inches per hour3 .331 .075 .269 .155

Average horizontal permeability of soils, in inches per hour3 .194 .297 .332 .080

1

p-values indicate the statistical probability that there was a correlation between two variables. Variables were considered to be significantly correlated with 

dissolved solids if p was less than or equal to 0.05. 

2

Source: well driller’s logs.

3

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

Table 11. Major ions and trace elements related to nitrate concentrations in ground-water samples collected from northern and 

southern High Plains agricultural land-use study areas, Nebraska and Texas, 2003–04.

[NAL, northern High Plains agricultural land use; SAL, southern High Plains agricultural land use; <, less than]

NAL study area SAL study area

Constituent1 Spearman’s rho p-value Constituent1 Spearman’s rho p-value

Dissolved solids 0.781 <0.001 Dissolved solids 0.485 0.010

Carbonate alkalinity .469 .012 Magnesium .526 .005

Calcium .711 <.001 Sodium .412 .029

Magnesium .732 <.001 Boron .408 .031

Sodium .457 .014 Lithium .502 .008

Potassium .551 .003 Selenium .485 .010

Bromide .525 .005 Strontium .629 .001

Barium .641 .001

Cobalt .535 .004

Copper .584 .002

Lithium .450 .016

Strontium .683 <.001

1

 Constituents listed are those positively correlated with nitrate as indicated by the Spearman’s rho test statistic (p-value less than or equal to 0.05).
the High Plains aquifer, McMahon and others (2004) observed 

an upward hydraulic gradient between the bedrock and the 

aquifer during the irrigation season.

Irrigation practices may be mobilizing sources of dissolved solids in the unsaturated zone. The introduction of 

widespread irrigation has increased the downward movement 

of water, providing a mechanism for transporting dissolved 

solids to ground water. McMahon and others (2006) reported 

that ground-water flux rates in the SHP were much larger 

under irrigated cropland (between about 0.66 and 1.3 in/yr) 

than rangeland (about 0.008 in/yr).

The relations between dissolved-solids concentrations 

and depth to water and residence time were inspected. Dissolved solids were inversely correlated with water-table depth 

in samples collected from the SAL study area (rho= –0.495, 

p=0.009), indicating that dissolved-solids concentrations 

are larger in areas where the water table is closer to the land 

surface. Unlike the NAL samples, dissolved-solids concentrations in SAL samples were not related to residence time 

as determined from tritium concentrations; concentrations 

were not significantly different between old and young water 

(p=0.166) and not correlated with tritium concentrations 

(rho=0.098, p=0.605). This result may indicate that recent 

agricultural activities may not be the source of elevated dissolved-solids concentrations presently observed at the water 

table.

The relations between dissolved-solids concentrations 

and borehole and soil characteristics also were examined. 

Dissolved-solids concentrations in SAL samples were significantly correlated only with bulk density (rho=0.500, p=0.008) 

(table 10). However, dissolved solids were positively (but not 

significantly) correlated with horizontal permeability and percentage of sand, and negatively correlated with percentage of 

silt and clay at slightly larger p-values (p=0.080, 0.078, 0.080, 

and 0.079, respectively).

The relation between nitrate and major ion and trace 

element concentrations was examined with the Spearman’s 

rho correlation test. Nitrate concentrations were positively 

correlated with dissolved solids, magnesium, sodium, boron, 

lithium, selenium, and strontium concentrations (table 11), 

indicating that major ion and trace element concentrations 

may be affected by the indirect effects of fertilizer applications 

at the land surface.

Eleven (38 percent) SAL samples exceeded the enforceable drinking-water standard for arsenic (10 μg/L); more 

often than for any other constituent analyzed in ground-water 

samples collected from the SAL study area. Arsenic concentrations ranged from 1.7 to 25.9 μg/L, with a median of 

7.5 μg/L. Sources of arsenic can be natural or introduced by 

humans. Arsenic is naturally present in some geologic formations such as marine shales, volcanic rocks, and metamorphic 

rocks formed from sedimentary deposits. Human sources of 

arsenic include organic and inorganic pesticide compounds. 

Pesticides containing arsenic have been used historically 

on cotton in the SHP (Hudak, 2000) and may be a potential 

source to ground water. Arsenic concentrations were not 

significantly different between the SAL water-table wells and 

domestic wells (Fahlquist, 2003) (p=0.287), indicating that 

arsenic concentrations are similar at all depths in the aquifer. 

This result may provide some evidence that the primary source 

of arsenic is natural geologic deposits and not a source at the 

land surface.

Comparison of Ground-Water Quality in 

Two Study Areas

Land use and hydrogeologic variables in the NAL and 

SAL study areas were compared to evaluate their potential 

effect on nitrate, pesticides, and dissolved-solids concentrations in ground water. Many factors in the NAL study area 

are more favorable for movement of chemicals applied at the 

land surface into ground water than in the SAL study area. 

Depths to water are less, precipitation is greater, evapotranspiration rates are smaller, and recharge rates are greater in the 

NAL study area than in the SAL study area. About twice the 

amount of pesticides was applied to cropland in the NAL study 

area than in the SAL study area, and nitrogen application rates 

near monitoring wells also were estimated to be greater in the 

NAL study area.

The effect of irrigated agriculture on ground water at the 

water table was more apparent in samples collected from the 

NAL study area. Samples collected in the NAL study area 

had larger nitrate concentrations and more detectable pesticide 

compounds than samples collected in the SAL study area. The 

median nitrate concentration of NAL samples (10.6 mg/L) 

was significantly larger (p<0.001) than the median concentration in SAL samples (4.12 mg/L). Twenty-two NAL samples 

(73 percent) and seven SAL samples (24 percent) had at least 

one pesticide compound detected at concentrations greater 

than the largest LRL.

The primary crops grown near wells in the NAL area are 

corn and soybeans, whereas the primary crop in the SAL area 

is cotton. The types of pesticides detected in the two areas 

were related to the types of crops grown. Atrazine, alachlor, 

metolachlor, simazine, and degradates of those compounds 

were detected most frequently in ground-water samples collected from the NAL study area. Except for simazine, these 

pesticides commonly are applied to corn or soybean fields 

and are on the list of most applied pesticides in the NAL area 

(table 5). In the SAL study area, deethylatrazine (a degradate 

of atrazine and propazine) was detected most often in groundwater samples. Although atrazine is not applied to cotton 

fields, it may have been applied in or near those same fields, 

for example when sorghum was the dominant cash crop. 

Propazine may have been applied to cotton fields and was 

the second most frequently detected pesticide compound in 

ground-water samples.

Although elevated nitrate concentrations and pesticide 

compound detections in ground water likely resulted from 

agricultural activities, dissolved solids were probably from a 

32 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
combination of natural and human sources. SAL samples had 

larger dissolved-solids, major ion, and trace element concentrations than NAL samples. Dissolved-solids concentrations 

in SAL samples were correlated with chloride concentrations 

(rho=0.800, p<0.001), indicating that evaporative processes 

potentially are a significant source of dissolved solids. There 

was, however, a relation between nitrate and dissolved solids, 

indicating a human source of both. Dissolved solids probably 

were not significantly affected by evaporative processes in the 

NAL study area. With the exception of one sample (NAL205, 502 mg/L, Appendix 1), chloride concentrations were 

small (less than 60 mg/L) in the NAL samples and were not 

significantly correlated with concentrations of dissolved solids 

(rho=0.315, p=0.090).

Summary

To observe the effect of irrigated agriculture on groundwater quality at the water table, monitoring wells screened 

at the top of the High Plains aquifer were installed adjacent 

to irrigated cropland areas of the northern and southern High 

Plains (NHP and SHP, respectively) regions of Nebraska 

and Texas. Water samples were collected from monitoring 

wells in 2003 and 2004; 30 samples were collected from the 

northern High Plains agricultural land-use (NAL) study area, 

and 29 samples were collected from the southern High Plains 

agricultural land-use (SAL) study area.

The NAL study area is located within the Eastern 

Nebraska hydrogeologic unit of the NHP region. This unit is 

located in an area affected by past glacial activity. The unit 

consists primarily of sand and gravel that is overlain by a mantle of low permeability glacial till and (or) loess. Mean annual 

pan evaporation rates range from 65 to 75 in/yr, and estimated 

recharge rates range from 4 to 6 in/yr. About 83 percent of 

the land in the NAL study area was used for cropland in 1992, 

and about 34 percent of the land in the study area was irrigated in 1980. In 2000, an estimated 1,940 Mgal/d of water 

was used for irrigation. The most common crops grown in 

the area in 2002 were corn and soybeans. In 1997–98, the 

average amount of nitrogen fertilizer applied in the study area 

was 114 lb/acre, and the median amount of nitrogen applied 

within 1,640 ft of the sampled monitoring wells was estimated 

to be 104 lb/acre. In 1997, an average of about 1.62 lb/acre of 

pesticides was applied to cropland in the NAL study area. The 

pesticides applied most (in pounds of active ingredient) were 

atrazine and metolachlor.

The SAL study area is located within the Ogallala Formation hydrogeologic unit of the SHP region. The Ogallala 

Formation consists of gravel, sand, silt, and clay sediment that 

were deposited in a complex stratigraphy. Mean annual pan 

evaporation rates range from about 95 to more than 105 in/yr, 

and estimated recharge rates range from no recharge to about 

1 in/yr. About 53 percent of the area was used for growing crops in 1992. Approximately 11 percent of land in the 

study area was irrigated. In 2002, cotton was the primary 

crop grown. In 1997–98, the average amount of nitrogen 

fertilizer applied over the study area was 73 lb/acre, and the 

median estimated rate of nitrogen application within 1,640 ft 

of the sampled wells was 58 lb/acre. In 1997, an average of 

0.73 lb/acre of pesticides was applied to cropland. The three 

pesticides applied most (in pounds of active ingredient) were 

trifluralin, malathion, and 2,4–D.

Nitrate concentrations in NAL ground-water samples 

ranged from 1.96 to 106 mg/L, with a median of 10.6 mg/L. 

Ninety percent of the samples had a concentration greater 

than 4.00 mg/L, indicating that elevated nitrate concentrations 

were likely a result of human activities. More than one-half 

(53 percent) of the samples had nitrate concentrations larger 

than the USEPA drinking-water Maximum Contaminant Level 

(MCL) of 10 mg/L. Nitrate concentrations decreased with 

depth below land surface, were larger in samples containing water recharged in the last 50 years, and were larger than 

nitrate concentrations observed in domestic wells.

Nitrate concentrations in the SAL samples ranged 

from 0.65 to 21.6 mg/L, with a median concentration of 

4.12 mg/L. Nitrate concentrations in 55 percent of samples 

were larger than 4.00 mg/L, and concentrations in five 

(17 percent) samples were larger than the drinking-water 

MCL. Nitrate concentrations decreased with depth below land 

surface and were larger in samples containing water recharged 

within the last 50 years. Nitrate concentrations in SAL wells 

were not significantly larger than in domestic wells.

Seventy-three percent (22 samples) of NAL samples contained at least one detectable pesticide or pesticide degradate. 

The compounds detected were primarily atrazine, alachlor, 

metolachlor, simazine, and their degradates. Concentrations 

of detected pesticides ranged up to 3.09 μg/L. When detection frequencies of pesticide compounds were compared at a 

common assessment level of 0.05 μg/L, pesticide degradates 

were detected more frequently than parent compounds. Pesticide concentrations did not exceed their respective USEPA 

drinking-water standards. Atrazine and deethylatrazine were 

detected more than twice as frequently in NAL samples than 

in other NAWQA study area samples where corn and soybeans were the primary crops grown, whereas metolachlor 

was detected more frequently in samples collected from 

other NAWQA study areas. Acetochlor, alachlor, carbofuran, 

metribuzin, prometon, propyzamide, simazine, and tebuthiuron were detected in samples collected from other NAWQA 

study areas but not in samples collected from the NAL study 

area. Samples collected in areas with smaller depths to water 

were more likely to have detectable pesticides. Pesticides also 

were more likely to be detected in samples containing water 

that had been recharged in the last 50 years. NAL monitoring wells more frequently had at least one detectable pesticide 

than domestic wells.

Twenty-four percent (six samples) of SAL samples contained at least one detectable pesticide or pesticide degradate. 

The compounds detected were primarily deethylatrazine (a 

degradate of atrazine and propazine), propazine, fluometuron, 

Summary 33
and tebuthiuron. The maximum concentration of any pesticide 

was an estimated 0.392 μg/L. When detection frequencies of 

pesticide compounds were compared at a common assessment 

level of 0.05 μg/L, deethylatrazine was detected most often 

(10 percent of samples). Except for deethylatrazine, pesticide 

compounds were detected less frequently in the SAL study 

area than in other NAWQA study areas where cotton was a 

primary crop. Pesticide concentrations did not exceed their 

respective USEPA drinking-water standards. Depth to water 

and residence time were not significantly related to pesticide 

detections. There also was no significant difference in the 

frequency of pesticide detections in SAL monitoring wells and 

domestic wells.

Dissolved-solids concentrations in ground-water samples collected from the NAL study area ranged from 272 to 

2,160 mg/L, with a median of 442 mg/L. The relative proportions of the major ions composing the dissolved solids indicated that most ground water was a calcium bicarbonate type. 

Water generally was acceptable for drinking-water purposes 

with respect to dissolved solids, major ions, and trace elements. Dissolved-solids concentrations decreased with depth 

below land surface and were larger in samples with a residence 

time of 50 years or less.

Dissolved-solids concentrations in ground-water samples collected from the SAL study area ranged from 416 to 

3,580 mg/L, with a median of 814 mg/L. The relative proportions of the major ions composing the dissolved solids 

indicated that ground water generally was nearly equally 

codominated by mixtures of more than one cation or anion. 

Eighty-six percent of samples exceeded the USEPA nonenforceable SDWR for dissolved solids (500 mg/L). Sulfate 

and chloride concentrations in some samples exceeded their 

respective SDWR (250 mg/L) as well. Dissolved-solids concentrations decreased with depth below land surface but were 

not significantly larger in samples with a residence time of 

50 years or less.

Land use and hydrogeologic variables in the NAL and 

SAL study areas were compared to evaluate their potential 

effect on nitrate, pesticide, and dissolved-solids concentrations 

in ground water. Many factors in the NAL study area are more 

favorable than in the SAL study area for movement of chemicals applied at the land surface into ground water. Depths to 

water are less, precipitation is greater, evapotranspiration rates 

are smaller, and recharge rates are greater in the NAL study 

area than in the SAL study area. More than twice the amount 

of pesticides was applied to cropland in the NAL study area 

than in the SAL study area. Manure and commercial fertilizer application rates near monitoring wells were greater in 

the NAL study area. The occurrence of nitrate and pesticide 

compounds indicates more extensive human effects on ground 

water at the water table in the NAL study area than in the SAL 

study area. Samples collected from the SAL study area had 

larger dissolved-solids concentrations. Larger dissolved-solids 

concentrations in the SAL study area may be related to evapotranspiration and recharge rates.

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38  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendixes

Appendixes 39
Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Site number Site name Field 

identifier

Sample 

date 

(month-dayyear)

Nitrite, 

filtered 

(mg/L as N)

Nitrite plus 

nitrate, 

filtered 

(mg/L as N)

Ammonia, 

filtered 

(mg/L as N)

Ammonia plus 

organic nitrogen, filtered 

(mg/L as N)

1 400757098325401 2N 11W15CDDD1 NAL–201 08–17–04 <0.008 13.6d <0.04 --

2 402154098512601 5N 14W26DDDD1 NAL–202 08–18–04 <.008 4.32 <.04 --

3 402708098534901 6N 14W28DDCD1 NAL–103 08–18–04 <.008 3.15 <.04 --

4 402943098284801 6N 10W 7DDDC1 NAL–204 08–17–04 <.008 17.1d <.04 --

5 403330098545101 7N 14W20DADA1 NAL–205 08–19–04 <.008 106d .04 --

6 405047098133201 10N 8W10CCBB1 NAL–106 07–21–04 <.008 40.0d <.04 --

7 410247097533601 12N 5W 4BAAA1 NAL–107 07–20–04 <.008 10.4d <.04 --

8 405353097572601 11N 6W25BACC1 NAL–108 08–16–04 <.008 13.5d <.04 --

9 404525097515101 9N 5W10DDDD1 NAL–109 07–22–04 <.008 18.8d <.04 --

10 404020098052401 8N 7W10DDAA1 NAL–110 07–21–04 <.008 12.4d <.04 --

11 403314097532801 7N 5W21CDAD1 NAL–111 07–14–04 <.008 3.53 <.04 --

12 401853097550101 4N 5W18DAAA1 NAL–112 07–15–04 <.008 9.56d <.04 --

13 401329097444501 3N 4W15DADA1 NAL–113 08–19–04 <.008 76.2d <.04 --

14 402103097404201 5N 3W32DCDC1 NAL–114 07–15–04 <.008 20.1d <.04 --

15 403502097460101 7N 4W10CCCB1 NAL–115 07–14–04 <.008 1.96 .05 --

16 405224097414401 11N 3W31DDCD1 NAL–116 07–22–04 <.008 10.8d <.04 --

17 405941097515301 12N 5W22DAAD1 NAL–117 09–06–04 <.008 15.3d <.04 --

18 410710097454201 13N 4W10BAAA1 NAL–118 07–19–04 <.008 14.5d <.04 --

19 413850097425801 19N 3W 6CBCB1 NAL–119 07–19–04 <.008 6.93d <.04 --

20 411256097301101 14N 2W 2ADDA1 NAL–120 07–13–04 <.008 6.14d <.04 --

21 410520097344501 13N 2W20BBBC1 NAL–221 07–20–04 <.008 13.3d <.04 --

22 404445097322201 9N 2W15CBCC1 NAL–122 08–19–04 <.008 7.82d <.04 --

23 404117097253301 8N 1W 4DADD1 NAL–123 07–18–04 <.008 8.46d <.04 --

24 401918097195301 4N 1E 8DDDD1 NAL–224 08–20–04 <.008 7.68d <.04 --

25 401715097083601 4N 2E25ADAA1 NAL–125 07–16–04 <.008 21.3d <.04 --

26 403520097013901 7N 3E12ADDD1 NAL–126 07–16–04 <.008 14.3d <.04 --

27 403759097130101 8N 2E29ADDD1 NAL–127 07–18–04 <.008 4.30 <.04 --

28 405304097103901 11N 2E34AADA1 NAL–128 07–17–04 <.008 7.09d <.04 --

29 410410097220601 13N 1W25DAAD1 NAL–129 07–13–04 <.008 8.07d <.04 --

30 410552097220501 13N 1E18BCCC1 NAL–130 07–12–04 <.008 8.22d <.04 --

40 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Orthophosphate, 

filtered 

(mg/L as 

P)

d15N of 

nitrate, 

filtered 

(per mil)

d18O of 

nitrate, 

filtered 

(per mil)

2,6-Diethylaniline, 

filtered 

(μg/L)

3-trifluomethylaniline, 

filtered 

(μg/L)

3-trifluoromethylphenylurea, 

filtered 

(μg/L)

Acetochlor, 

filtered 

(μg/L)

Acetochlor ESA, 

filtered 

(μg/L)

Acetochlor OA, 

filtered 

(μg/L)

Acetochlor SAA, 

filtered 

(μg/L)

Acetochlor/

metolachlor 

ESA SA, 

filtered 

(μg/L)

1 0.210d 7.52 2.78 <0.006 -- -- <0.006 <0.02 <0.02 <0.02 0.05

2 .078 8.15 .06 <.006 -- -- <.006 <.02 <.02 <.02 <.02

3 .199 6.36 -2.40 <.006 -- -- <.006 <.02 <.02 <.02 <.02

4 .307d 3.63 1.06 <.006 -- -- <.006 <.02 <.02 <.02 <.02

5 .154 9.51 4.96 <.006 -- -- <.006 <.02 <.02 <.02 <.02

6 .277d 2.23 2.84 <.006 -- -- <.006 <.02 <.02 <.02 --

7 .325d 4.93 1.64 <.006 -- -- <.006 <.02 <.02 <.02 <.02

8 .270d 5.30 1.60 <.006 -- -- <.006 <.02 <.02 <.02 <.02

9 .368d 4.28 3.07 <.006 -- -- <.006 <.02 <.02 <.02 --

10 .414d 6.03 1.56 <.006 -- -- <.006 <.02 <.02 <.02 --

11 .188 8.36 3.36 <.006 -- -- <.006 <.02 <.02 <.02 <.02

12 .207d 6.91 3.52 <.006 -- -- <.006 <.02 <.02 <.02 <.02

13 .269d 6.58 5.66 <.006 -- -- <.006 <.02 <.02 <.02 <.02

14 .299d 4.75 3.27 <.006 -- -- <.006 <.02 <.02 <.02 <.02

15 .146 6.46 4.06 <.006 -- -- <.006 <.02 <.02 <.02 <.02

16 .347d 6.33 2.46 <.006 -- -- <.006 <.02 <.02 <.02 --

17 .140 6.28 2.82 <.006 -- -- <.006 <.02 <.02 <.02 <.02

18 .303d 5.92 3.47 <.006 -- -- <.006 <.02 <.02 <.02 <.02

19 .186 7.35 1.53 <.006 -- -- <.006 <.02 <.02 <.02 <.02

20 .271d 5.49 1.01 <.006 -- -- <.006 <.02 <.02 <.02 <.02

21 .513d 4.51 2.90 <.006 -- -- <.006 <.02 <.02 <.02 <.02

22 .360d 5.98 3.38 <.006 -- -- <.006 <.02 <.02 <.02 <.02

23 .154 9.22 3.46 <.006 -- -- <.006 <.02 <.02 <.02 <.02

24 .352d 6.89 3.59 <.006 -- -- <.006 <.02 <.02 <.02 <.02

25 .156 11.59 4.84 <.006 -- -- <.006 <.02 <.02 <.02 <.02

26 .508d 5.10 3.09 <.006 -- -- <.006 <.02 <.02 <.02 <.02

27 .228d 8.52 3.12 <.006 -- -- <.006 <.02 <.02 <.02 <.02

28 .329d 6.53 3.19 <.006 -- -- <.006 <.02 <.02 <.02 <.02

29 .271d 5.82 3.30 <.006 -- -- <.006 <.02 <.02 <.02 <.02

30 .229d 5.31 2.19 <.006 -- -- <.006 <.02 <.02 <.02 <.02

Appendix 1 41
Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Alachlor, 

filtered 

(μg/L)

Alachlor 

ESA, 

filtered 

(μg/L)

Alachlor 

ESA SA, 

filtered 

(μg/L)

Alachlor 

OA, 

filtered 

(μg/L)

Alachlor 

SAA, 

filtered 

(μg/L)

alphaHCH, 

filtered 

(μg/L)

Atrazine, 

filtered 

(μg/L)

Azinphosmethyl, 

filtered 

(μg/L)

Benfluralin, 

filtered 

(μg/L)

Butylate, 

filtered 

(μg/L)

Carbaryl, 

filtered 

(μg/L)

1 <0.005 0.04 <0.02 <0.02 <0.02 <0.005 0.012 <0.050 <0.010 <0.004 <0.041

2 <.005 <.02 <.02 <.02 <.02 <.005 <.007 <.050 <.010 <.004 <.041

3 <.005 <.02 <.02 <.02 <.02 <.005 <.007 <.050 <.010 <.004 <.041

4 <.005 .03 <.02 <.02 <.02 <.005 .319 <.050 <.010 <.004 <.041

5 <.005 <.02 <.02 <.02 <.02 <.005 <.007 <.050 <.010 <.004 <.041

6 <.005 <.02 <.02 <.02 <.02 <.005 .052 <.050 <.010 <.004 <.041

7 <.005 <.02 <.02 <.02 <.02 <.005 .015 <.050 <.010 <.004 <.041

8 <.005 .41 .04 <.02 <.02 <.005 .578 <.050 <.010 <.004 <.041

9 <.005 .11 <.02 <.02 <.02 <.005 .047 <.050 <.010 <.004 <.041

10 <.005 .33 .08 <.02 <.02 <.005 .125 <.050 <.010 <.004 <.041

11 <.005 <.02 <.02 <.02 <.02 <.005 .007 <.050 <.010 <.004 <.041

12 <.005 .20 <.02 <.02 <.02 <.005 .207 <.050 <.010 <.004 <.041

13 <.005 3.09 .14 <.02 <.02 <.005 <.007 <.050 <.010 <.004 <.041

14 <.005 .53 .21 <.02 <.02 <.005 .478 <.050 <.010 <.004 <.041

15 <.005 <.02 <.02 <.02 <.02 <.005 <.007 <.050 <.010 <.004 <.041

16 <.005 .33 .02 <.02 <.02 <.005 .171 <.050 <.010 <.004 <.041

17 <.005 .81 .03 <.02 <.02 <.005 .631 <.050 <.010 <.004 <.041

18 <.005 <.02 <.02 <.02 <.02 <.005 <.007 <.050 <.010 <.004 <.041

19 <.005 <.02 <.02 <.02 <.02 <.005 <.007 <.050 <.010 <.004 <.041

20 <.005 <.02 <.02 <.02 <.02 <.005 <.007 <.050 <.010 <.004 <.041

21 <.005 .62 .03 <.02 <.02 <.005 .236 <.050 <.010 <.004 <.041

22 <.005 .04 <.02 <.02 <.02 <.005 .049 <.050 <.010 <.004 <.041

23 <.005 <.02 <.02 <.02 <.02 <.005 .018 <.050 <.010 <.004 <.041

24 <.005 <.02 <.02 <.02 <.02 <.005 .009 <.050 <.010 <.004 <.041

25 <.005 <.02 <.02 <.02 <.02 <.005 <.007 <.050 <.010 <.004 <.041

26 <.005 .35 <.02 <.02 <.02 <.005 .021 <.050 <.010 <.004 <.041

27 <.005 .06 <.02 <.02 <.02 <.005 .010 <.050 <.010 <.004 <.041

28 <.005 .03 <.02 <.02 <.02 <.005 <.007 <.050 <.010 <.004 <.041

29 <.005 <.02 <.02 <.02 <.02 <.005 .011 <.050 <.010 <.004 <.041

30 .012 1.08 <.02 .11 <.02 <.005 .766 <.050 <.010 <.004 <.041

42 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Carbofuran, 

filtered 

(μg/L)

Chlorpyrifos, 

filtered 

(μg/L)

cis-Permethrin, 

filtered 

(μg/L)

Cyanazine, 

filtered 

(μg/L)

Cyanazine 

amide, 

filtered 

(μg/L)

DCPA, 

filtered 

(μg/L)

Deethylatrazine, 

filtered 

(μg/L)

Deisopropylatrazine, 

filtered 

(μg/L)

Deisopropylprometryn, 

filtered 

(μg/L)

Demethylfluometuron, 

filtered 

(μg/L)

Demethyl 

norflurazon, 

filtered 

(μg/L)

1 <0.020 <0.005 <0.006 <0.018 -- <0.003 E0.021 -- -- -- --

2 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

3 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

4 <.020 <.005 <.006 <.018 -- <.003 E.392 -- -- -- --

5 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

6 <.020 <.005 <.006 <.018 -- <.003 E.071 -- -- -- --

7 <.020 <.005 <.006 <.018 -- <.003 E.004n -- -- -- --

8 <.020 <.005 <.006 <.018 -- <.003 E.428 -- -- -- --

9 <.020 <.005 <.006 <.018 -- <.003 E.066 -- -- -- --

10 <.020 <.005 <.006 <.018 -- <.003 E.093 -- -- -- --

11 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

12 <.020 <.005 <.006 <.018 -- <.003 E.111 -- -- -- --

13 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

14 <.020 <.005 <.006 <.018 -- <.003 E.125 -- -- -- --

15 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

16 <.020 <.005 <.006 <.018 -- <.003 E.098 -- -- -- --

17 <.020 <.005 <.006 <.018 -- <.003 E.308 -- -- -- --

18 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

19 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

20 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

21 <.020 <.005 <.006 <.018 -- <.003 E.088 -- -- -- --

22 <.020 <.005 <.006 <.018 -- <.003 E.032 -- -- -- --

23 <.020 <.005 <.006 <.018 -- <.003 E.006 -- -- -- --

24 <.020 <.005 <.006 <.018 -- <.003 E.009 -- -- -- --

25 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

26 <.020 <.005 <.006 <.018 -- <.003 E.011 -- -- -- --

27 <.020 <.005 <.006 <.018 -- <.003 E.008 -- -- -- --

28 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

29 <.020 <.005 <.006 <.018 -- <.003 <.006 -- -- -- --

30 <.020 <.005 <.006 <.018 -- <.003 E.429 -- -- -- --

Appendix 1 43
Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Desulfinyl 

fipronil, 

filtered 

(μg/L)

Desulfinylfipronil amide, 

filtered 

(μg/L)

Diazinon, 

filtered 

(μg/L)

Dieldrin, 

filtered 

(μg/L)

Dimethenamid, 

filtered 

(μg/L)

Dimethenamid 

ESA, 

filtered 

(μg/L)

Dimethenamid 

OA, 

filtered 

(μg/L)

Disulfoton, 

filtered 

(μg/L)

EPTC, 

filtered 

(μg/L)

Ethalfluralin, 

filtered 

(μg/L)

Ethoprop, 

filtered 

(μg/L)

1 <0.012 <0.029 <0.005 <0.009 <0.02 <0.02 <0.02 <0.02 <0.004 <0.009 <0.005

2 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

3 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

4 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

5 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

6 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

7 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

8 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

9 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

10 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

11 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

12 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

13 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

14 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

15 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

16 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

17 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

18 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

19 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

20 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

21 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

22 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

23 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

24 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

25 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

26 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

27 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

28 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

29 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

30 <.012 <.029 <.005 <.009 <.02 <.02 <.02 <.02 <.004 <.009 <.005

44 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Fipronil 

filtered 

(μg/L)

Fipronil 

sulfide, 

filtered 

(μg/L)

Fipronil 

sulfone, 

filtered 

(μg/L)

Flufenacet, 

filtered 

(μg/L)

Flufenacet ESA, 

filtered 

(μg/L)

Flufenacet OA, 

filtered 

(μg/L)

Fluometuron, 

filtered 

(μg/L)

Fonofos, 

filtered 

(μg/L)

Lindane, 

filtered 

(μg/L)

Linuron, 

filtered 

(μg/L)

Malathion, 

filtered 

(μg/L)

1 <0.016 <0.013 <0.024 <0.02 <0.02 <0.02 -- <0.003 <0.004 <0.035 <0.027

2 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

3 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

4 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

5 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

6 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

7 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

8 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

9 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

10 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

11 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

12 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

13 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

14 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

15 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

16 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

17 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

18 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

19 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

20 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

21 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

22 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

23 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

24 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

25 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

26 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

27 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

28 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

29 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

30 <.016 <.013 <.024 <.02 <.02 <.02 -- <.003 <.004 <.035 <.027

Appendix 1 45
Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Methyl 

parathion, 

filtered 

(μg/L)

Metolachlor, 

filtered 

(μg/L)

Metolachlor ESA, 

filtered 

(μg/L)

Metolachlor OA, 

filtered 

(μg/L)

Metribuzin, filtered 

(μg/L)

Molinate, 

filtered 

(μg/L)

Napropamide, 

filtered 

(μg/L)

Norflurazon, 

filtered 

(μg/L)

p-p’-DDE, 

filtered 

(μg/L)

Parathion, 

filtered 

(μg/L)

Pebulate, 

filtered 

(μg/L)

1 <0.015 <0.013 0.44 0.02 <0.006 <0.003 <0.007 -- <0.003 <0.010 <0.004

2 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

3 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

4 <.015 <.013 .17 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

5 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

6 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

7 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

8 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

9 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

10 <.015 <.013 .12 .03 <.006 <.003 <.007 -- <.003 <.010 <.004

11 <.015 E.006t <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

12 <.015 <.013 .30 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

13 <.015 <.013 .22 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

14 <.015 <.013 .66 .06 <.006 <.003 <.007 -- <.003 <.010 <.004

15 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

16 <.015 <.013 .04 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

17 <.015 E.008n <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

18 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

19 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

20 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

21 <.015 <.013 .09 .03 <.006 <.003 <.007 -- <.003 <.010 <.004

22 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

23 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

24 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.005 <.010 <.004

25 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

26 <.015 <.013 .04 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

27 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

28 <.015 <.013 <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

29 <.015 E.007n <.02 <.02 <.006 <.003 <.007 -- <.003 <.010 <.004

30 <.015 .976 1.41 .35 E.005n <.003 <.007 -- <.003 <.010 <.004

46  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Pendimethalin, 

filtered 

(μg/L)

Phorate, 

filtered 

(μg/L)

Prometon, 

filtered 

(μg/L)

Prometryn, 

filtered 

(μg/L)

Propyzamide, 

filtered 

(μg/L)

Propachlor, 

filtered 

(μg/L)

Propachlor ESA, 

filtered 

(μg/L)

Propachlor OA, 

filtered 

(μg/L)

Propanil, 

filtered 

(μg/L)

Propargite, 

filtered 

(μg/L)

Propazine, 

filtered 

(μg/L)

1 <0.022 <0.011 <0.01 -- <0.004 <0.025 <0.05 <0.02 <0.011 <0.02 --

2 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

3 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

4 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

5 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

6 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

7 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

8 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

9 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

10 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

11 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.03 --

12 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

13 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

14 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

15 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

16 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

17 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

18 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

19 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

20 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

21 <.022 <.011 Mn -- <.004 <.025 <.05 <.02 <.011 <.02 --

22 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

23 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

24 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

25 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

26 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

27 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

28 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

29 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

30 <.022 <.011 <.01 -- <.004 <.025 <.05 <.02 <.011 <.02 --

Appendix 1 47
48  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04

Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Simazine, 

filtered 

(μg/L)

Tebuthiuron, 

filtered 

(μg/L)

Terbacil, 

filtered 

(μg/L)

Terbufos, 

filtered 

(μg/L)

Thiobencarb, 

filtered 

(μg/L)

Triallate, 

filtered 

(μg/L)

Trifluralin, 

filtered 

(μg/L)

Depth of 

well (feet 

below 

LSD)

Depth to 

water 

level (feet 

below 

LSD)

Specific 

conductance, 

unfiltered 

(μS/cm)

pH, 

unfiltered 

(standard 

units)

1 <0.005 <0.02 <0.034 <0.02 <0.010 <0.002 <0.009 118.3 97.27 701 6.9

2 <.005 <.02 <.034 <.02 <.010 <.002 <.009 158.43 137.67 574 7.2

3 <.005 <.02 <.034 <.02 <.010 <.002 <.009 129.39 113.70 451 7.2

4 <.005 <.02 <.034 <.02 <.010 <.002 <.009 118.53 97.79 960 7.1

5 <.005 <.02 <.034 <.02 <.010 <.002 <.009 77.37 60.62 3,320 6.7

6 <.005 <.02 <.034 <.02 <.010 <.002 <.009 92.39 71.09 1,260 7.1

7 <.005 <.02 <.034 <.02 <.010 <.002 <.009 122.5 99.18 888 7.3

8 <.005 <.02 <.034 <.02 <.010 <.002 <.009 114.07 82.02 806 7.1

9 <.005 <.02 <.034 <.02 <.010 <.002 <.009 106.5 86.70 824 7.1

10 <.005 <.02 <.034 <.02 <.010 <.002 <.009 118.21 95.57 815 6.9

11 <.005 <.02 <.034 <.02 <.010 <.002 <.009 118.5 90.92 495 6.9

12 <.005 <.02 <.034 <.02 <.010 <.002 <.009 112.4 79.95 605 6.9

13 <.005 <.02 <.034 <.02 <.010 <.002 <.009 58.47 38.30 844 6.0

14 <.005 <.02 <.034 <.02 <.010 <.002 <.009 108.79 88.08 778 6.8

15 <.005 <.02 <.034 <.02 <.010 <.002 <.009 123.5 83.67 591 6.9

16 <.005 <.02 <.034 <.02 <.010 <.002 <.009 98.23 79.59 727 7.2

17 <.005 <.02 <.034 <.02 <.010 <.002 <.009 114.8 84.53 716 6.8

18 <.005 <.02 <.034 <.02 <.010 <.002 <.009 114.1 87.12 789 7.1

19 <.005 <.02 <.034 <.02 <.010 <.002 <.009 193.06 164.41 614 7.2

20 <.005 <.02 <.034 <.02 <.010 <.002 <.009 133.5 114.40 484 7.2

21 <.005 <.02 <.034 <.02 <.010 <.002 <.009 93.57 67.98 884 7.2

22 <.005 <.02 <.034 <.02 <.010 <.002 <.009 53.63 35.10 875 6.7

23 <.005 <.02 <.034 <.02 <.010 <.002 <.009 100.71 73.18 616 7.0

24 <.005 <.02 <.034 <.02 <.010 <.002 <.009 128.38 111.77 421 6.7

25 <.005 <.02 <.034 <.02 <.010 <.002 <.009 128.5 107.01 744 7.2

26 <.005 <.02 <.034 <.02 <.010 <.002 <.009 114.0 84.63 617 6.8

27 <.005 <.02 <.034 <.02 <.010 <.002 <.009 113.57 77.36 517 7.1

28 <.005 <.02 <.034 <.02 <.010 <.002 <.009 102.2 75.80 494 6.8

29 <.005 <.02 <.034 <.02 <.010 <.002 <.009 116.47 83.61 610 7.0

30 .031 <.02 <.034 <.02 <.010 <.002 <.009 98.5 73.87 535 7.1
Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Temperature (o

C)

Turbidity, 

unfiltered 

(NTU)

Dissolved 

oxygen 

(mg/L)

Dissolved 

solids, 

filtered 

(mg/L)

Hardness 

(mg/L as 

CaCO3)

Alkalinity, 

filtered, 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Sodium 

adsorption ratio

Sodium 

(percent)

1 16.9 0.8 5.6 452 290 169 91.6 14.8 26.3 0.7 16

2 16.1 3.9 2.3 298 260 228 81.8 12.5 16.0 .4 12

3 19.9 36 5.5 272 190 204 66.3 6.83 16.6 .5 15

4 14.5 .7 6.8 482 370 378 123 16.1 64.1 1 26

5 13.6 .3 7.3 2,160 1,500 351 473d 70.1d 114d 1 14

6 14.3 .6 6.5 769 480 415 154 22.8 99.7 2 31

7 15.2 1.1 6.6 562 400 418 130 18.4 37.9 .8 17

8 14.2 .3 7.9 437 330 330 106 16.3 37.8 .9 19

9 14.1 .2 7.7 499 380 337 125 15.8 28.0 .6 14

10 15.0 .3 7.0 532 380 258 120 19.9 25.3 .6 12

11 16.2 13 6.6 315 170 128 52.1 8.80 28.0 .9 26

12 14.1 .6 6.4 396 210 227 69.9 8.90 44.0 1 30

13 13.7 1.2 5.3 667 340 46 102 21.6 12.4 .3 7

14 14.5 .5 5.9 503 270 230 87.2 13.3 49.8 1 28

15 13.7 .9 1.3 384 210 159 70.6 8.42 31.4 .9 23

16 14.5 1.3 7.1 466 280 317 85.8 15.0 47.6 1 27

17 16.8 >1,000 6.5 460 340 306 110 15.9 37.8 .9 19

18 14.9 .2 8.0 482 310 297 97.3 15.4 47.9 1 25

19 16.5 1.6 6.1 400 290 276 92.4 14.8 9.18 .2 6

20 17.1 .2 6.6 320 200 209 67.9 8.26 22.9 .7 19

21 14.0 .2 6.9 508 340 403 99.2 21.1 63.7 2 29

22 13.0 .5 4.2 602 370 256 110 21.9 42.5 1 20

23 21.1 52 4.3 412 250 198 79.5 11.6 27.3 .8 19

24 14.3 1.7 7.6 283d 150 144 48.4 7.59 24.4 .9 25

25 15.8 3.3 6.6 447 330 245 106 15.0 19.2 .5 11

26 14.8 .1 5.5 412 230 173 67.9 13.8 39.9 1 27

27 14.5 .3 4.4 341 210 192 65.3 11.3 25.1 .8 20

28 13.3 .2 4.8 332 180 188 56.4 8.76 35.9 1 30

29 14.3 .2 5.7 409 240 222 74.1 12.1 31.5 .9 22

30 15.4 .2 6.5 332 230 233 69.4 12.9 29.3 .8 22

Appendix 1 49
50 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04

Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Potassium, 

filtered 

(mg/L)

Sulfate, 

filtered 

(mg/L)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Bromide, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Aluminum, 

filtered 

(μg/L)

Antimony, 

filtered 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Barium, 

filtered 

(μg/L)

Beryllium, 

filtered 

(μg/L)

1 7.25 47.5 58.5 0.2 0.26 34.2 <2 <0.20 2.8 234 <0.06

2 5.27 23.1 24.5 .2 .15 41.0 <2 E.13n 2.4 144 <.06

3 5.42 14.9 5.65 .2 .04 30.5 Mn .23 2.3 182 <.06

4 12.1 53.5 20.4 .3 .17 30.6 <2 <.20 2.9 448 <.06

5 26.3d 255d 502d .4 2.13d 27.4d <3d E.21nd 9.3 219d <.12d

6 10.8 99.1 18.8 .4 .14 27.2 E1n E.12n 1.9 326 <.06

7 7.63 27.0 7.82 .4 .08 32.8 <2 E.17n 6.2 176 <.06

8 6.87 27.7 17.4 .4 .14 35.2 <2 E.12n 3.5 275 <.06

9 7.95 32.1 22.7 .3 .16 43.7 <2 E.14n 4.7 393 <.06

10 8.42 53.3 46.7 .3 .27 46.1 Mn E.14n 4.6 249 <.06

11 4.14 31.0 47.0 <.2 .14 37.9 Mn E.15n 1.3 68 <.06

12 6.47 31.0 16.4 .3 .13 36.9 <2 E.13n 4.4 329 <.06

13 10.7 35.5 15.0 <.2 .12 53.7 <2 <.20 1.7 741 <.06

14 8.95 38.6 37.3 .3 .19 35.9 <2 E.15n 2.9 394 <.06

15 9.22 103 20.4 .3 .12 20.9 <2 .21 3.3 175 <.06

16 6.95 26.3 6.90 .4 .11 35.2 <2 E.14n 4.0 282 <.06

17 10.3 23.7 5.27 .5 .10 35.6 <2 E.20n 4.4 316 <.06

18 8.21 36.1 8.56 .4 .07 33.7 <2 E.12n 4.7 169 <.06

19 5.75 14.0 10.4 .2 .08 51.5 <2 <.20 5.1 224 <.06

20 5.09 15.8 3.08 .3 .05 40.0 <2 .25 4.5 338 <.06

21 9.57 24.0 7.08 .4 .10 34.6 <2 E.17n 6.1 384 <.06

22 11.2 162 11.5 .4 .11 37.3 <2 E.16n 5.8 43 <.06

23 6.21 65.0 13.2 .3 .10 35.5 E1n <.20 2.5 192 <.06

24 4.35 24.0 8.17 .3 .10 33.0 <2 E.11n 4.1 123 <.06

25 3.79 15.1 33.1 .2 .18 33.7 <2 <.20 2.8 337 <.06

26 5.26 69.6 13.3 .2 .10 37.0 <2 E.11n 5.5 226 <.06

27 4.07 40.9 12.0 .3 .09 38.2 <2 <.20 5.9 83 <.06

28 5.63 32.8 3.32 .3 .07 36.3 <2 E.18n 6.0 134 <.06

29 5.81 60.0 5.68 .3 .06 35.4 <2 E.14n 4.2 157 <.06

30 4.72 15.8 3.76 .4 .06 31.3 <2 E.19n 3.6 330 <.06
Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Boron, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Chromium, 

filtered 

(μg/L)

Cobalt, 

filtered 

(μg/L)

Copper, 

filtered 

(μg/L)

Iron, 

filtered 

(μg/L)

Lead, 

filtered 

(μg/L)

Lithium, 

filtered 

(μg/L)

Manganese, 

filtered 

(μg/L)

Molybdenum, 

filtered 

(μg/L)

Nickel, 

filtered 

(μg/L)

1 44 E0.03n 0.8 0.364 1.3 <6 0.09 17.4 0.7 1.2 2.58

2 35 <.04 20.5 .167 .7 E5n <.08 14.9 .5 2.5 .70

3 36 <.04 15.8 .155 .6 E5n E.04n 12.4 1.2 2.4 2.65

4 53 <.04 2.1 .503 1.3 E4n E.06n 20.5 1.1 2.6 3.37

5 43d .17d 3.7 1.68d 5.2d <19d <.16d 47.5d 1.3d 15.2d 6.36d

6 52 .10 1.8 .489 2.1 E3n <.08 23.4 1.0 22.7 2.92

7 34 <.04 12.1 .429 1.0 E3n <.08 14.5 .3 3.4 2.99

8 34 <.04 3.0 .254 .9 <6 E.07n 15.4 <.2 3.0 1.71

9 34 E.03n 2.1 .365 1.0 <6 <.08 18.1 E.2n 1.9 1.65

10 34 E.02n 3.3 .383 1.2 <6 <.08 17.6 .5 1.5 2.30

11 34 E.04n 1.2 .232 .8 7 <.08 10.1 2.8 1.0 4.03

12 33 <.04 1.2 .247 .9 <6 <.08 15.4 .3 1.6 2.19

13 23 <.04 1.5 .279 1.5 <6 E.06n 20.2 3.7 E.2n 1.60

14 35 <.04 E.6n .343 .9 <6 <.08 20.3 .3 1.7 2.97

15 32 .07 <.8 1.13 .9 1,020 <.08 23.3 331 .8 2.55

16 26 E.02n 5.2d .274 2.2 <6 E.08n 15.4 .6 3.7 1.75

17 29 .07 E.5n 1.55 1.9 17 E.05n 18.9 32.5 14.5 52.1

18 35 .04 4.4 .342 .9 <6 <.08 17.6 .4 2.2 2.46

19 45 <.04 5.2 .386 .7 E6n <.08 18.2 2.3 1.6 3.45

20 29 <.04 5.4 .198 E.4n <6 <.08 12.9 .3 2.0 1.60

21 37 E.02n 6.0 .338 .8 <6 <.08 13.8 .2 4.5 2.74

22 68 .04 1.4 .283 2.3 <6 <.08 29.9 .5 5.1 1.59

23 42 E.03n 1.9 .575 1.4 E3n <.08 15.0 8.8 1.5 5.73

24 32 <.04 1.1 .125 .6 <6 <.08 8.1 .3 1.5 1.12

25 36 <.04 6.0 .363 .7 E6n <.08 15.9 .5 1.5 3.83

26 38 E.02n E.8n .274 .8 <6 <.08 14.1 8.0 1.2 2.34

27 38 <.04 .9 .205 .7 <6 <.08 18.4 .7 1.3 1.66

28 35 <.04 1.5 .170 .6 <6 <.08 17.6 E.2n 1.1 1.22

29 32 <.04 7.3 .232 .6 <6 <.08 12.1 1.0 1.0 1.87

30 65 <.04 1.7 .199 .6 <6 <.08 12.6 1.1 2.7 1.64

Appendix 1  51
Appendix 1. Results of physical and chemical analyses of ground-water samples collected from northern High Plains agricultural 

land-use study area, Nebraska, 2004.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map identifier (fig. 2)

Selenium, 

filtered 

(μg/L)

Silver, 

filtered 

(μg/L)

Strontium, 

filtered 

(μg/L)

Thallium, 

filtered 

(μg/L)

Uranium, 

filtered 

(μg/L)

Vanadium, 

filtered 

(μg/L)

Zinc, filtered 

(μg/L)

Organic carbon, filtered 

(mg/L)

Tritium, 

unfiltered 

(pCi/L)

1 6.4 <0.2 486 <0.04 3.88 7.9 1.1 1.9 30

2 8.9 <.2 340 <.04 1.55 10.1 1.3 .5 <1

3 11.2 <.2 301 <.04 4.11 14.8 1.1 E.3n <1

4 5.4 <.2 496 <.04 9.51 7.4 .8 1.8 16

5 90.2d <.4d 1,820d <.08d 69.1d 25.3d 1.3d 16.2 13

6 15.3 <.2 687 <.04 83.0 5.6 1.2 2.3 34

7 3.5 <.2 640 <.04 14.5 12.8 1.8 1.6 17

8 5.9 <.2 461 <.04 8.21 9.6 E.4n 1.3 22

9 10.4 <.2 462 <.04 4.46 11.8 <.6 1.4 18

10 14.9 <.2 550 <.04 3.46 8.8 1.1 1.8 12

11 12.1 <.2 292 <.04 .29 7.0 11.8 1.3 12

12 5.0 <.2 298 <.04 2.44 10.9 1.2 1.4 25

13 1.4 <.2 633 <.04 .04 3.3 1.7 .8 20

14 13.0 <.2 377 <.04 3.35 10.0 .6 1.9 16

15 30.1 <.2 362 <.04 1.16 2.4 .7 1.3 16

16 4.1 <.2 381 <.04 8.73 11.0 .9 1.2 9

17 8.3 <.2 448 <.04 4.77 9.0 3.4 1.4 14

18 12.3 <.2 453 <.04 11.9 10.0 1.5 1.5 16

19 32.9 <.2 508 <.04 6.46 10.6 E.5n .6 <1

20 3.7 <.2 301 <.04 1.83 12.4 1.5 .9 12

21 4.4 <.2 505 <.04 15.9 12.6 E.4n 1.4 18

22 8.7 <.2 421 <.04 21.4 10.8 .8 1.3 13

23 22.7 <.2 397 <.04 1.17 4.8 2.1 1.1 12

24 2.3 <.2 237 <.04 .46 6.9 E.5n .5 7

25 9.8 <.2 519 <.04 1.96 6.4 2.0 .8 3

26 25.8 <.2 347 <.04 .95 7.2 E.5n 1.2 14

27 9.0 <.2 359 <.04 2.70 4.6 1.0 .5 6

28 14.8 <.2 263 <.04 4.55 9.0 E.3n .8 11

29 44.4 <.2 365 <.04 1.50 10.4 5.1 .9 13

30 1.5 <.2 295 <.04 3.92 11.3 E.4n .7 22

52 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, land 

surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3

, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Site number Field 

identifier Site name

Sample 

date 

(month/

day/year)

Nitrite, 

filtered 

(mg/L as N)

Nitrite plus 

nitrate, 

filtered 

(mg/L as N)

Ammonia, 

filtered 

(mg/L as N)

Ammonia plus 

organic 

nitrogen, 

filtered 

(mg/L as N)

Orthophos–

phate, 

filtered 

(mg/L as P)

1 324148102541801 SAL–201 KD–27–17–612 02–28–03 E0.005 3.74 <0.04 E0.06 <0.02

2 324723102504901 SAL–202 KD–27–10–716 02–28–03 E.007 3.92 <.04 .10 E.01

3 325034102325101 SAL–203 KD–27–12–21 02–28–03 .116 10.5 <.04 .13 <.02

07–29–03 .008 11.5 <.04 .17 <.02

4 330635103011201 SAL–104 ZT–25–64–303 03–01–03 <.008 2.35 <.04 E.09 <.02

SAL–104 ZT–25–64–303 07–29–03 <.008 2.67 <.04 .22 <.02

5 333830102491701 SAL–105 DP–24–18–804 02–23–03 <.008 2.52 <.04 .14 .02

07–30–03 <.008 3.65 <.04 .23 <.02

6 334043102365501 SAL–106 DP–24–20–404 02–21–03 <.008 3.78 <.04 <.10 .03

07–30–03 <.008 3.84 <.04 .17 E.01

7 340012102273501 SAL–107 RU–10–61–703 02–27–03 <.008 4.12 <.04 <.10 <.02

08–01–03 E.005 4.02 <.21 E.06 <.02

8 334905102545001 SAL–108 DP–24–09–605 02–22–03 <.008 4.64 <.04 E.07 <.02

9 334309102380201 SAL–209 DP–24–19–304 02–23–03 <.008 6.17 <.04 E.06 .02

10 333922102392701 SAL–110 DP–24–19–903 02–22–03 <.008 1.34 <.04 <.10 .02

11 333014102261401 SAL–111 LX–24–29–801 02–18–03 <.008 .65 <.04 <.20 E.01

12 331609102181501 SAL–212 XY–24–46–803 03–01–03 <.008 5.69 <.04 E.05 E.01

13 333458102184801 SAL–213 LX–24–30–503 02–18–03 E.004 6.03 <.04 <.50 <.02

14 334517102181201 SAL–114 LX–24–14–803 02–19–03 <.008 14.7 <.04 .17 E.01

07–30–03 E.006 16.5 <.21 .26 <.02

15 340430102150001 SAL–215 RU–10–63–407 02–15–03 .100 4.53 E.04 .13 <.02

16 341350102213101 SAL–116 RU–10–54–101 02–27–03 <.008 1.95 <.04 <.10 .02

17 344030102184701 SAL–117 DD–10–22–503 02–26–03 <.008 4.03 <.04 .12 .03

18 340324102141501 SAL–118 RU–10–63–406 02–15–03 <.008 4.90 <.04 E.09 <.02

07–31–03 <.008 5.62 <.21 .11 <.02

19 340040102163401 SAL–219 RU–10–62–903 02–14–03 .013 3.96 <.04 .13 .03

07–31–03 .107 2.90 <.21 .31 <.02

20 335655102191801 SAL–120 RU–24–06–513 02–14–03 <.008 3.43 <.04 E.08 <.02

Appendix 2  53
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, land 

surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3

, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Site number Field 

identifier Site name

Sample 

date 

(month/

day/year)

Nitrite, 

filtered 

(mg/L as N)

Nitrite plus 

nitrate, 

filtered 

(mg/L as N)

Ammonia, 

filtered 

(mg/L as N)

Ammonia plus 

organic 

nitrogen, 

filtered 

(mg/L as N)

Orthophos–

phate, 

filtered 

(mg/L as P)

21 334122102062101 SAL–121 LX–24–24–407 02–19–03 <0.008 4.70 <0.04 E0.05 <0.02

22 332946102135701 SAL–122 LX–24–39–102 dry -- -- -- -- --

23 332402101561801 SAL–123 SP–23–33–802 02–12–03 <.008 21.6 <.04 .21 E.01

24 333415102010301 SAL–224 SP–24–32–607 02–17–03 <.008 5.55 <.04 E.05 E.01

07–31–03 <.008 5.35 <.04 .13 <.02

25 333525101414901 SAL-225 SP–23–27–212 02–17–03 .008 13.0 <.04 .12 E.01

07–30–03 .015 13.7 <.04 .15 E.01

26 333755102032601 SAL-226 SP–24–24–803 02–16–03 <.008 8.40 <.04 E.07 <.02

27 335808102084401 SAL-227 RU–24–07–302 02–13–03 <.008 .85 <.04 <.10 E.01

28 335836102081001 SAL-228 RU–24–07–303 02–13–03 <.008 10.1 <.04 .11 E.01

07–31–03 <.008 8.14 <.21 .29 <.02

29 340358101434101 SAL-229 KY–11–56–406 02–11–03 <.008 1.15 <.04 <.10 E.01

30 342402101384301 SAL-130 XT–11–35–913 02–26–03 <.008 1.35 <.04 E.07 E.02

54 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, 

degrees Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

d15N of 

nitrate, 

filtered 

(per mil)

d18O of 

nitrate, 

filtered 

(per mil)

2,6-Diethylaniline, 

filtered 

(μg/L)

3-trifluoromethylaniline, 

filtered 

(μg/L)

3-trifluoromethylphenylurea, 

filtered 

(μg/L)

Acetochlor, 

filtered 

(μg/L)

Acetochlor 

ESA, 

filtered 

(μg/L)

Acetochlor OA, 

filtered 

(μg/L)

Acetochlor 

SAA, 

filtered 

(μg/L)

Acetochlor/

metolachlor 

ESA SA, 

filtered 

(μg/L)

Alachlor, 

filtered 

(μg/L)

1 7.3 -- <0.006 <0.05 <0.05 <0.006 -- -- -- -- <0.004

2 5.9 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

3 4.9 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

-- -- -- -- -- -- -- -- -- -- --

4 4.7 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

-- -- -- -- -- -- -- -- -- -- --

5 5.4 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

-- -- -- -- -- -- -- -- -- -- --

6 5.3 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

-- -- -- -- -- -- -- -- -- -- --

7 6.5 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

-- -- -- -- -- -- -- -- -- -- --

8 5.9 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

9 7.8 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

10 7.7 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

11 10.3 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

12 6.1 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

13 6.1 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

14 4.5 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

-- -- -- -- -- -- -- -- -- -- --

15 4.9 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

16 7.4 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

17 9.1 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

18 5.1 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

-- -- -- -- -- -- -- -- -- -- --

19 5.8 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

-- -- -- -- -- -- -- -- -- -- --

20 7.9 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

21 4.3 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

Appendix 2  55
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, 

degrees Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

d15N of 

nitrate, 

filtered 

(per mil)

d18O of 

nitrate, 

filtered 

(per mil)

2,6-Diethylaniline, 

filtered 

(μg/L)

3-trifluoromethylaniline, 

filtered 

(μg/L)

3-trifluoromethylphenyl-urea, 

filtered 

(μg/L)

Acetochlor, 

filtered 

(μg/L)

Acetochlor 

ESA, 

filtered 

(μg/L)

Acetochlor OA, 

filtered 

(μg/L)

Acetochlor 

SAA, 

filtered 

(μg/L)

Acetochlor/

metolachlor 

ESA SA, 

filtered 

(μg/L)

Alachlor, 

filtered 

(μg/L)

22 -- -- -- -- -- -- -- -- -- -- --

23 6.3 -- <0.006 <0.05 <0.05 <0.006 -- -- -- -- <0.004

24 7. -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

-- -- -- -- -- -- -- -- -- -- --

25 5.6 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

-- -- -- -- -- -- -- -- -- -- --

26 7.1 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

27 5.6 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

28 5.3 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

-- -- -- -- -- -- -- -- -- -- --

29 9.9 -- <.006 <.05 <.05 <.006 -- -- -- -- <.004

30 10.3 -- <.006 <.05 <.05 <.006 -- -- -- -- <.010

56  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Alachlor 

ESA, 

filtered 

(μg/L)

Alachlor 

ESA SA, 

filtered 

(μg/L)

Alachlor 

OA, 

filtered 

(μg/L)

Alachlor 

SAA, 

filtered 

(μg/L)

alphaHCH, 

filtered 

(μg/L)

Atrazine, 

filtered 

(μg/L)

Azinphosmethyl, 

filtered 

(μg/L)

Benfluralin, 

filtered 

(μg/L)

Butylate, 

filtered 

(μg/L)

Carbaryl, 

filtered 

(μg/L)

Carbofuran, 

filtered 

(μg/L)

1 -- -- -- -- <0.005 <0.007 <0.050 <0.010 <0.002 <0.041 <0.020

2 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

3 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

-- -- -- -- -- -- -- -- -- -- --

4 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

-- -- -- -- -- -- -- -- -- -- --

5 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

-- -- -- -- -- -- -- -- -- -- --

6 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

-- -- -- -- -- -- -- -- -- -- --

7 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

-- -- -- -- -- -- -- -- -- -- --

8 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

9 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

10 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

11 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

12 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

13 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

14 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

-- -- -- -- -- -- -- -- -- -- --

15 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

16 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

17 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

18 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

-- -- -- -- -- -- -- -- -- -- --

19 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

-- -- -- -- -- -- -- -- -- -- --

20 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

21 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

22 -- -- -- -- -- -- -- -- -- -- --

23 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

Appendix 2  57
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Alachlor 

ESA, 

filtered 

(μg/L)

Alachlor 

ESA SA, 

filtered 

(μg/L)

Alachlor 

OA, 

filtered 

(μg/L)

Alachlor 

SAA, 

filtered 

(μg/L)

alphaHCH, 

filtered 

(μg/L)

Atrazine, 

filtered 

(μg/L)

Azinphosmethyl, 

filtered 

(μg/L)

Benfluralin, 

filtered 

(μg/L)

Butylate, 

filtered 

(μg/L)

Carbaryl, 

filtered 

(μg/L)

Carbofuran, 

filtered 

(μg/L)

24 -- -- -- -- <0.005 <0.007 <0.050 <0.010 <0.002 <0.041 <0.020

-- -- -- -- -- -- -- -- -- -- --

25 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

-- -- -- -- -- -- -- -- -- -- --

26 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

28 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

-- -- -- -- -- -- -- -- -- -- --

29 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

30 -- -- -- -- <.005 <.007 <.050 <.010 <.002 <.041 <.020

58  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Chlorpyrifos, 

filtered 

(μg/L)

cis-Permethrin, 

filtered 

(μg/L)

Cyanazine 

amide, 

filtered 

(μg/L)

Cyanazine, 

filtered 

(μg/L)

DCPA, 

filtered 

(μg/L)

Deethylatrazine, 

filtered 

(μg/L)

Deisopropylatrazine, 

filtered 

(μg/L)

Deisopropyl 

prometryn, 

filtered 

(μg/L)

Demethylfluometuron, 

filtered 

(μg/L)

Demethyl 

norflurazon, 

filtered 

(μg/L)

Desulfinyl 

fipronil, 

filtered 

(μg/L)

1 <0.005 <0.006 <0.05 <0.018 <0.003 <0.006 <0.05 <0.05 <0.05 <0.05 <0.004

2 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

3 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

-- -- -- -- -- -- -- -- -- -- --

4 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

-- -- -- -- -- -- -- -- -- -- --

5 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

-- -- -- -- -- -- -- -- -- -- --

6 <.005 <.006 <.05 <.018 <.003 E.261 <.05 <.05 <.05 <.05 <.004

-- -- -- -- -- -- -- -- -- -- --

7 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

-- -- -- -- -- -- -- -- -- -- --

8 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

9 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

10 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

11 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

12 <.005 <.006 <.05 <.018 <.003 E.005 <.05 <.05 <.05 <.05 <.004

13 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

14 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

-- -- -- -- -- -- -- -- -- -- --

15 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

16 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

17 <.005 <.006 <.05 <.018 <.003 E.392 <.05 <.05 <.05 <.05 <.004

18 <.005 <.006 <.05 <.018 <.003 E.012 <.05 <.05 <.05 <.05 <.004

-- -- -- -- -- -- -- -- -- -- --

19 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

-- -- -- -- -- -- -- -- -- -- --

20 <.005 <.006 <.05 <.018 <.003 E.022 <.05 <.05 <.05 <.05 <.004

21 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

22 -- -- -- -- -- -- -- -- -- -- --

Appendix 2  59
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Chlorpyrifos, 

filtered 

(μg/L)

cis-Permethrin, 

filtered 

(μg/L)

Cyanazine 

amide, 

filtered 

(μg/L)

Cyanazine, 

filtered 

(μg/L)

DCPA, 

filtered 

(μg/L)

Deethylatrazine, 

filtered 

(μg/L)

Deisopropylatrazine, 

filtered 

(μg/L)

Deisopropyl 

prometryn, 

filtered 

(μg/L)

Demethylfluometuron, 

filtered 

(μg/L)

Demethyl 

norflurazon, 

filtered 

(μg/L)

Desulfinyl 

fipronil, 

filtered 

(μg/L)

23 <0.005 <0.006 <0.05 <0.018 <0.003 <0.006 <0.05 <0.05 <0.05 <0.05 <0.004

24 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

-- -- -- -- -- -- -- -- -- -- --

25 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

-- -- -- -- -- -- -- -- -- -- --

26 <.005 <.006 <.05 <.018 <.003 E.066 <.05 <.05 <.05 <.05 <.004

27 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

28 <.005 <.006 <.05 <.018 <.003 E.013 <.05 <.05 <.05 <.05 <.004

-- -- -- -- -- -- -- -- -- -- --

29 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

30 <.005 <.006 <.05 <.018 <.003 <.006 <.05 <.05 <.05 <.05 <.004

60 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Diazinon, 

filtered 

(μg/L)

Dieldrin, 

filtered 

(μg/L)

Dimethenamid, 

filtered 

(μg/L)

Dimethenamid 

ESA, 

filtered 

(μg/L)

Dimethenamid 

OA, 

filtered 

(μg/L)

Desulfinylfipronil 

amide, 

filtered 

(μg/L)

Disulfoton, 

filtered 

(μg/L)

EPTC, 

filtered 

(μg/L)

Ethalfluralin, 

filtered 

(μg/L)

Ethoprop, 

filtered 

(μg/L)

Fipronil, 

filtered 

(μg/L)

1 <0.005 <0.005 <0.05 -- -- <0.009 <0.02 <0.002 <0.009 <0.005 <0.007

2 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

3 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

-- -- -- -- -- -- -- -- -- -- --

4 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

-- -- -- -- -- -- -- -- -- -- --

5 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

-- -- -- -- -- -- -- -- -- -- --

6 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

-- -- -- -- -- -- -- -- -- -- --

7 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

-- -- -- -- -- -- -- -- -- -- --

8 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

9 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

10 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

11 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

12 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

13 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

14 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

-- -- -- -- -- -- -- -- -- -- --

15 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

16 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

17 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

18 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

-- -- -- -- -- -- -- -- -- -- --

19 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

-- -- -- -- -- -- -- -- -- -- --

20 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

21 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

22 -- -- -- -- -- -- -- -- -- -- --

Appendix 2  61
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Diazinon, 

filtered 

(μg/L)

Dieldrin, 

filtered 

(μg/L)

Dimethenamid, 

filtered 

(μg/L)

Dimethenamid 

ESA, 

filtered 

(μg/L)

Dimethenamid 

OA, 

filtered 

(μg/L)

Desulfinylfipronil 

amide, 

filtered 

(μg/L)

Disulfoton, 

filtered 

(μg/L)

EPTC, 

filtered 

(μg/L)

Ethalfluralin, 

filtered 

(μg/L)

Ethoprop, 

filtered 

(μg/L)

Fipronil, 

filtered 

(μg/L)

23 <0.005 <0.005 <0.05 -- -- <0.009 <0.02 <0.002 <0.009 <0.005 <0.007

24 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

-- -- -- -- -- -- -- -- -- -- --

25 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

-- -- -- -- -- -- -- -- -- -- --

26 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

27 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

28 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

-- -- -- -- -- -- -- -- -- -- --

29 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

30 <.005 <.005 <.05 -- -- <.009 <.02 <.002 <.009 <.005 <.007

62 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Fipronil 

sulfide, 

filtered 

(μg/L)

Fipronil 

sulfone, 

filtered 

(μg/L)

Flufenacet, 

filtered 

(μg/L)

Flufenacet ESA, 

filtered 

(μg/L)

Flufenacet OA, 

filtered 

(μg/L)

Fluometuron, 

filtered 

(μg/L)

Fonofos, 

filtered 

(μg/L)

Lindane, 

filtered 

(μg/L)

Linuron, 

filtered 

(μg/L)

Malathion, 

filtered 

(μg/L)

Methyl 

parathion, 

filtered 

(μg/L)

1 <0.005 <0.005 <0.05 -- -- <0.05 <0.003 <0.004 <0.035 <0.027 <0.006

2 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

3 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

-- -- -- -- -- -- -- -- -- -- --

4 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

-- -- -- -- -- -- -- -- -- -- --

5 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

-- -- -- -- -- -- -- -- -- -- --

6 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

-- -- -- -- -- -- -- -- -- -- --

7 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

-- -- -- -- -- -- -- -- -- -- --

8 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

9 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

10 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

11 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

12 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

13 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

14 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

-- -- -- -- -- -- -- -- -- -- --

15 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

16 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

17 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

18 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

-- -- -- -- -- -- -- -- -- -- --

19 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

-- -- -- -- -- -- -- -- -- -- --

20 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

21 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

22 -- -- -- -- -- -- -- -- -- -- --

23 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

Appendix 2  63
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Fipronil 

sulfide, 

filtered 

(μg/L)

Fipronil 

sulfone, 

filtered 

(μg/L)

Flufenacet, 

filtered 

(μg/L)

Flufenacet ESA, 

filtered 

(μg/L)

Flufenacet OA, 

filtered 

(μg/L)

Fluometuron, 

filtered 

(μg/L)

Fonofos, 

filtered 

(μg/L)

Lindane, 

filtered 

(μg/L)

Linuron, 

filtered 

(μg/L)

Malathion, 

filtered 

(μg/L)

Methyl 

parathion, 

filtered 

(μg/L)

24 <0.005 <0.005 <0.05 -- -- <0.05 <0.003 <0.004 <0.035 <0.027 <0.006

-- -- -- -- -- -- -- -- -- -- --

25 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

-- -- -- -- -- -- -- -- -- -- --

26 <.005 <.005 <.05 -- -- .06 <.003 <.004 <.035 <.027 <.006

27 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

28 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

-- -- -- -- -- -- -- -- -- -- --

29 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 E.006n <.006

30 <.005 <.005 <.05 -- -- <.05 <.003 <.004 <.035 <.027 <.006

64 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Metolachlor, 

filtered 

(μg/L)

Metolachlor 

ESA, 

filtered 

(μg/L)

Metolachlor OA, 

filtered 

(μg/L)

Metribuzin, 

filtered 

(μg/L)

Molinate, 

filtered 

(μg/L)

Napropamide, 

filtered 

(μg/L)

Norflurazon, 

filtered 

(μg/L)

p,p’-DDE, 

filtered 

(μg/L)

Parathion, 

filtered 

(μg/L)

Pebulate, 

filtered 

(μg/L)

Pendimethalin, 

filtered 

(μg/L)

1 <0.013 -- -- <0.006 <0.002 <0.007 <0.05 <0.003 <0.010 <0.004 <0.022

2 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

3 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

-- -- -- -- -- -- -- -- -- -- --

4 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

-- -- -- -- -- -- -- -- -- -- --

5 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

-- -- -- -- -- -- -- -- -- -- --

6 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

-- -- -- -- -- -- -- -- -- -- --

7 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

-- -- -- -- -- -- -- -- -- -- --

8 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

9 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

10 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

11 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

12 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

13 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

14 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

-- -- -- -- -- -- -- -- -- -- --

15 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

16 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

17 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

18 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

-- -- -- -- -- -- -- -- -- -- --

19 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

-- -- -- -- -- -- -- -- -- -- --

20 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

21 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

22 -- -- -- -- -- -- -- -- -- -- --

23 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

Appendix 2  65
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Metolachlor, 

filtered 

(μg/L)

Metolachlor 

ESA, 

filtered 

(μg/L)

Metolachlor OA, 

filtered 

(μg/L)

Metribuzin, 

filtered 

(μg/L)

Molinate, 

filtered 

(μg/L)

Napropamide, 

filtered 

(μg/L)

Norflurazon, 

filtered 

(μg/L)

p,p’-DDE, 

filtered 

(μg/L)

Parathion, 

filtered 

(μg/L)

Pebulate, 

filtered 

(μg/L)

Pendimethalin, 

filtered 

(μg/L)

24 <0.013 -- -- <0.006 <0.002 <0.007 <0.05 <0.003 <0.010 <0.004 <0.022

-- -- -- -- -- -- -- -- -- -- --

25 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

-- -- -- -- -- -- -- -- -- -- --

26 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

27 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

28 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

-- -- -- -- -- -- -- -- -- -- --

29 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

30 <.013 -- -- <.006 <.002 <.007 <.05 <.003 <.010 <.004 <.022

66  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Phorate, 

filtered 

(μg/L)

Prometon, 

filtered 

(μg/L)

Prometryn, 

filtered 

(μg/L)

Propyzamide, 

filtered 

(μg/L)

Propachlor, 

filtered 

(μg/L)

Propachlor ESA, 

filtered 

(μg/L)

Propachlor OA, 

filtered 

(μg/L)

Propanil, 

filtered 

(μg/L)

Propargite, 

filtered 

(μg/L)

Propazine, 

filtered 

(μg/L)

1 <0.011 <0.01 <0.05 <0.004 <0.010 -- -- <0.011 <0.02 <0.05

2 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

3 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

-- -- -- -- -- -- -- -- -- --

4 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

-- -- -- -- -- -- -- -- -- --

5 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

-- -- -- -- -- -- -- -- -- --

6 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 .31

-- -- -- -- -- -- -- -- -- --

7 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

-- -- -- -- -- -- -- -- -- --

8 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

9 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

10 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

11 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

12 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

13 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

14 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

-- -- -- -- -- -- -- -- -- --

15 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

16 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

17 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

18 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

-- -- -- -- -- -- -- -- -- --

19 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

-- -- -- -- -- -- -- -- -- --

20 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

21 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

22 -- -- -- -- -- -- -- -- -- --

23 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

24 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

-- -- -- -- -- -- -- -- -- --

Appendix 2  67
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Phorate, 

filtered 

(μg/L)

Prometon, 

filtered 

(μg/L)

Prometryn, 

filtered 

(μg/L)

Propyzamide, 

filtered 

(μg/L)

Propachlor, 

filtered 

(μg/L)

Propachlor ESA, 

filtered 

(μg/L)

Propachlor OA, 

filtered 

(μg/L)

Propanil, 

filtered 

(μg/L)

Propargite, 

filtered 

(μg/L)

Propazine, 

filtered 

(μg/L)

25 <0.011 <0.01 <0.05 <0.004 <0.010 -- -- <0.011 <0.02 <0.05

-- -- -- -- -- -- -- -- -- --

26 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

27 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

28 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 .06

-- -- -- -- -- -- -- -- -- --

29 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

30 <.011 <.01 <.05 <.004 <.010 -- -- <.011 <.02 <.05

68  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Simazine, 

filtered 

(μg/L)

Tebuthiuron, 

filtered 

(μg/L)

Terbacil, 

filtered 

(μg/L)

Terbufos, 

filtered 

(μg/L)

Thiobencarb, 

filtered 

(μg/L)

Triallate, 

filtered 

(μg/L)

Trifluralin, 

filtered 

(μg/L)

Depth of 

well (feet 

below 

LSD)

Depth to 

water 

level 

(feet 

below 

LSD)

Specific 

conductance, unfiltered 

(μS/cm)

pH, unfiltered 

(standard 

units)

1 <0.005 <0.02 <0.034 <0.02 <0.005 <0.002 <0.009 190 165.86 766 7.3

2 <.005 <.02 <.034 <.02 <.005 <.002 <.009 120.3 98.73 1,490 7.1

3 <.005 <.02 <.034 <.02 <.005 <.002 <.009 128 108.91 1,610 7.2

-- -- -- -- -- -- -- 128 110.15 1,640 7.3

4 <.005 .03 <.034 <.02 <.005 <.002 <.009 158 140.03 1,600 7.0

-- -- -- -- -- -- -- 158 142.54 -- --

5 <.005 <.02 <.034 <.02 <.005 <.002 <.009 215.8 190.25 1,980 7.2

-- -- -- -- -- -- -- 215.8 196.43 2,010 7.4

6 <.005 <.02 <.034 <.02 <.005 <.002 <.009 171.04 153.36 1,260 7.3

-- -- -- -- -- -- -- 171.04 <156.25 1,310 7.5

7 <.005 <.02 <.034 <.02 <.005 <.002 <.009 169.5 154.70 1,030 7.1

-- -- -- -- -- -- -- 169.5 155.33 1,070 7.0

8 <.005 <.02 <.034 <.02 <.005 <.002 <.009 159.15 139.86 2,040 7.0

9 <.005 <.02 <.034 <.02 <.005 <.002 <.009 195.8 173.63 2,220 7.1

10 <.005 <.02 <.034 <.02 <.005 <.002 <.009 166.3 145.73 1,160 7.3

11 <.005 <.02 <.034 <.02 <.005 <.002 <.009 179.1 154.59 1,030 7.2

12 <.005 <.02 <.034 <.02 <.005 <.002 <.009 154.1 132.13 1,350 7.3

13 <.005 <.02 <.034 <.02 <.005 <.002 <.009 154.9 135.45 1,490 7.1

14 <.005 <.02 <.034 <.02 <.005 <.002 <.009 114.7 90.24 2,800 7.0

-- -- -- -- -- -- -- 114.7 91.40 2,860 7.5

15 <.005 <.02 <.034 <.02 <.005 <.002 <.009 179.6 161.30 863 7.2

16 <.005 <.02 <.034 <.02 <.005 <.002 <.009 209.8 192.56 733 7.1

17 <.005 <.02 <.034 <.02 <.005 <.002 <.009 210.8 187.14 744 7.4

18 <.005 <.02 <.034 <.02 <.005 <.002 <.009 176.5 157.55 1,340 7.1

-- -- -- -- -- -- -- 176.5 158.85 1,450 7.4

19 <.005 <.02 <.034 <.02 <.005 <.002 <.009 148.9 128.57 4,630 7.0

-- -- -- -- -- -- -- 148.9 129.00 4,930 7.1

20 <.005 <.02 <.034 <.02 <.005 <.002 <.009 143.8 124.44 1,230 7.0

21 <.005 <.02 <.034 <.02 <.005 <.002 <.009 188.3 169.50 1,220 7.3

22 -- -- -- -- -- -- -- 160.1 -- -- --

Appendix 2  69
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Simazine, 

filtered 

(μg/L)

Tebuthiuron, 

filtered 

(μg/L)

Terbacil, 

filtered 

(μg/L)

Terbufos, 

filtered 

(μg/L)

Thiobencarb, 

filtered 

(μg/L)

Triallate, 

filtered 

(μg/L)

Trifluralin, 

filtered 

(μg/L)

Depth of 

well (feet 

below 

LSD)

Depth to 

water 

level 

(feet 

below 

LSD)

Specific 

conductance, unfiltered 

(μS/cm)

pH, unfiltered 

(standard 

units)

23 <0.005 <0.02 <0.034 <0.02 <0.005 <0.002 <0.009 99.6 78.85 2,070 7.1

24 <.005 <.02 <.034 <.02 <.005 <.002 <.009 174.3 153.16 915 7.4

-- -- -- -- -- -- -- 174.3 156.28 1,090 7.6

25 <.005 <.02 <.034 <.02 <.005 <.002 <.009 135.0 107.89 1,480 7.2

-- -- -- -- -- -- -- 135.0 108.91 1,530 7.3

26 <.005 <.02 <.034 <.02 <.005 <.002 <.009 137.9 121.15 1,040 7.2

27 <.005 <.02 <.034 <.02 <.005 <.002 <.009 176.0 157.99 1,010 7.3

28 <.005 <.02 <.034 <.02 <.005 <.002 <.009 174.7 154.76 1,520 7.1

-- -- -- -- -- -- -- 174.7 155.65 1,690 6.9

29 <.005 <.02 <.034 <.02 <.005 <.002 <.009 153.0 118.97 1,010 7.0

30 <.005 <.02 <.034 <.02 <.005 <.002 <.009 218.5 195.24 676 7.2

70 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Temperature, 

water (oC)

Turbidity, 

unfiltered 

(NTU)

Dissolved 

oxygen, 

(mg/L)

Dissolved 

solids, 

filtered 

(mg/L)

Hardness 

(mg/L as 

CaCO3)

Alkalinity, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Sodium 

adsorption ratio

1 20.4 2.6 4.9 480 260 175 61.9 24.6 53.2 1 

2 18.9 .8 5.1 977 550 245 112 64.4 96.8 2 

3 20.1 .4 5.5 1,010 610 239 79.4 100 90.3 2 

20.5 .4 6.1 -- -- -- -- -- -- -- 

4 19.0 .6 5.3 1,070 680 187 193 47.4 70.9 1 

-- -- -- -- -- -- -- -- -- -- 

5 19.2 1.1 7.5 1,080 840 173 126 128 52.3 .8 

20.4 -- 6.2 -- -- -- -- -- -- -- 

6 19.3 2.6 8.5 814 420 229 66.4 60.2 95.1 2 

19.6 -- 6.4 -- -- -- -- -- -- -- 

7 19.1 .4 7.2 560 380 183 83.4 42.1 44.5 1 

19.7 2.0 5.0 -- -- -- -- -- -- -- 

8 18.9 .2 7.1 1,210 780 155 159 91.1 117 2 

9 19.6 1.5 5.8 1,420 880 309 74.9 167 126 2 

10 20.3 .7 5.9 781 490 165 79.5 70.6 52.5 1 

11 21.2 .2 1.7 667 450 265 44.1 81.6 46.6 1 

12 19.0 .3 7.3 893 470 279 57.3 79.3 101 2 

13 20.6 1.1 2.9 852 580 250 82.9 90.5 66.3 1 

14 17.8 .6 7.3 1,830 1,300 168 195 198 118 1 

20.0 -- 6.3 -- -- -- -- -- -- -- 

15 18.2 1.8 3.2 558 370 230 84.7 38.9 29.0 .7 

16 18.7 1.4 6.0 416 270 208 51.6 33.3 41.2 1 

17 17.5 1.0 6.5 464 340 355 29.9 62.9 35.8 .9 

18 18.7 .5 8.8 834 570 175 147 49.3 42.3 .8 

20.3 .6 5.9 -- -- -- -- -- -- -- 

19 -- 2.8 3.2 3,580 1,100 326 187 154 735 10 

20.9 1.5 2.6 -- -- -- -- -- -- -- 

20 18.6 5.0 7.1 732 470 257 93.2 56.3 59.4 1 

21 19.1 2.4 7.5 763 400 245 48.7 65.9 105 2 

22 -- -- -- -- -- -- -- -- -- --

Appendix 2  71
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Temperature, 

water (oC)

Turbidity, 

unfiltered 

(NTU)

Dissolved 

oxygen, 

(mg/L)

Dissolved 

solids, 

filtered 

(mg/L)

Hardness 

(mg/L as 

CaCO3)

Alkalinity, 

filtered 

(mg/L as 

CaCO3)

Calcium, 

filtered 

(mg/L)

Magnesium, 

filtered 

(mg/L)

Sodium, 

filtered 

(mg/L)

Sodium 

adsorption ratio

23 19.0 -- 7.8 1,600 830 212 109 134 145 2 

24 19.9 0.9 7.8 543 270 320 31.5 46.9 84.2 2 

19.6 -- 9.8 -- -- -- -- -- -- -- 

25 20.3 .4 .8 936 580 248 71.3 96.1 67.3 1 

18.4 -- .9 -- -- -- -- -- -- -- 

26 18.5 .6 7.3 621 450 267 66.1 68.5 34.4 .7 

27 19.6 4.5 7.9 606 360 234 54.7 54.4 56.0 1 

28 -- 5.9 6.5 953 640 218 96.3 95.2 59.0 1 

21.1 5.2 5.5 -- -- -- -- -- -- -- 

29 18.4 -- 6.0 539 370 207 68.5 47.6 43.6 1 

30 18.0 .7 4.8 445 270 301 36.5 43.0 45.4 1 

72 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Sodium 

(percent)

Potassium, 

filtered 

(mg/L)

Sulfate, 

filtered 

(mg/L)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Bromide, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Aluminum 

filtered 

(μg/L)

Antimony, 

filtered 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Barium, 

filtered 

(μg/L)

1 31 3.27 77.7 76.2 2.79 0.61 53.6 <2 <0.30 16.2 43

2 28 4.34 260 207 2.28 1.85 57.4 <2 <.30 12.6 58

3 24 8.28 250 218 4.40d 1.72 57.8 <2 <.30 25.9 63

-- -- -- -- -- -- -- -- -- -- --

4 18 4.00 297 239 .98 1.92 64.5 <2 <.30 5.9 66

-- -- -- -- -- -- -- -- -- -- --

5 12 6.05 244 396 2.02 2.15 48.3 <2 E.18 6.6 44

-- -- -- -- -- -- -- -- -- -- --

6 33 8.45 198 137 3.60d 1.11 48.1 M E.28 9.7 25

-- -- -- -- -- -- -- -- -- -- --

7 20 2.16 46.4 176 1.46 1.09 41.5 <2 <.30 3.2 118

-- -- -- -- -- -- -- -- -- -- --

8 25 9.08 302 401 2.88d 2.30 32.9 <2 <.30 3.0 94

9 23 23.1 388 334 2.76 .91 41.5 E2 <.30 6.6 30

10 19 8.60 267 115 2.30 .92 53.1 M <.30 8.9 21

11 18 12.4 160 80.1 3.48d .70 48.2 M <.30 21.3 35

12 31 12.0 252 119 4.44d .92 50.6 <3 E.15 12.7 22

13 20 6.45 141 219 5.05d 1.46 50.8 E1 <.30 10.9 50

14 16 13.6 542 521 3.44d 3.03 50.1 <3 <.60 6.3 68

-- -- -- -- -- -- -- -- -- -- --

15 14 5.83 104 55.6 1.41 .43 51.5 E1 .34 6.1 98

16 25 6.86 30.4 80.9 1.59 .43 28.4 2 <.30 1.7 174

17 19 5.08 24.5 11.2 2.80d .11 72.5 <2 <.30 5.3 161

18 14 7.10 151 218 1.25 1.26 53.8 <2 <.30 5.2 60

-- -- -- -- -- -- -- -- -- -- --

19 58 27.5 1,300 701 2.92d 4.86 57.6 <3 <.60 6.0 14

-- -- -- -- -- -- -- -- -- -- --

20 21 14.1 73.2 185 1.42 1.77 52.9 <2 <.30 5.1 54

21 36 10.4 150 139 5.20d .94 49.6 M <.30 11.1 30

22 -- -- -- -- -- -- -- -- -- -- --

23 27 17.0 689 92.6 3.80d .95 56.1 E1 E.18 13.2 22

24 39 9.48 51.9 50.0 5.55d .41 43.7 E1 <.30 14.9 56

-- -- -- -- -- -- -- -- -- -- --

Appendix 2  73
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Sodium 

(percent)

Potassium, 

filtered 

(mg/L)

Sulfate, 

filtered 

(mg/L)

Chloride, 

filtered 

(mg/L)

Fluoride, 

filtered 

(mg/L)

Bromide, 

filtered 

(mg/L)

Silica, 

filtered 

(mg/L)

Aluminum 

filtered 

(μg/L)

Antimony, 

filtered 

(μg/L)

Arsenic, 

filtered 

(μg/L)

Barium, 

filtered 

(μg/L)

25 20 23.6 218 174 2.86d 0.99 59.2 M <0.30 16.3 28

-- -- -- -- -- -- -- -- -- -- --

26 14 10.4 77.3 117 2.96d .90 51.1 E1 <.30 10.3 83

27 24 12.7 98.4 117 1.73 .76 49.2 <2 E.17 8.0 54

28 16 15.5 214 219 1.32 1.03 53.5 <2 <.30 6.9 56

-- -- -- -- -- -- -- -- -- -- --

29 20 10.1 17.4 165 2.22 .90 45.3 M <.30 2.6 196

30 26 8.17 29.3 13.6 3.86d .12 81.7 M <.30 7.5 110

74 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Beryllium, 

filtered 

(μg/L)

Boron, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Chromium, 

filtered 

(μg/L)

Cobalt, 

filtered 

(μg/L)

Copper, 

filtered 

(μg/L)

Iron, 

filtered 

(μg/L)

Lead, 

filtered 

(μg/L)

Lithium, 

filtered 

(μg/L)

Manganese, 

filtred 

(μg/L)

Molybdenum, 

filtered 

(μg/L)

1 <0.06 108 0.04 E0.7 0.231 1.0 <10 <0.08 48.3 4.1 7.8

2 <.06 147 E.03 <.8 .674 2.4 40 <.08 108 49.5 4.3

3 <.06 393 .04 <.8 .405 2.4 <10 <.08 146 10.5 7.6

-- -- -- -- -- -- -- -- -- -- --

4 <.06 136 E.02 <.8 .776 1.5 25 <.08 67.0 30.1 2.2

-- -- -- -- -- -- -- -- -- -- --

5 E.04 168 E.02 1.0 .334 1.8 <10 .09 107 8.6 2.5

-- -- -- -- -- -- -- -- -- -- --

6 <.06 392 <.04 E.6 .147 1.1 <10 <.08 133 1.2 4.7

-- -- -- -- -- -- -- -- -- -- --

7 <.06 206 E.04 1.3 .801 1.0 <10 <.08 43.6 70.5 5.1

-- -- -- -- -- -- -- -- -- -- --

8 <.06 245 E.02 E.6 .310 1.5 <10 <.08 150 .5 5.6

9 E.04 450 E.02 <.8 .551 1.8 <10 <.08 225 569 7.2

10 E.03 167 <.04 1.1 .160 1.1 <10 <.08 122 2.7 5.1

11 <.06 226 E.02 <.8 .945 1.0 55 <.08 94.3 341 9.2

12 <.06 687 .04 E.7 .180 1.7 <50 E.07 160 4.7 13.7

13 <.06 429 .04 E.8 .237 1.2 <10 <.08 118 7.3 11.7

14 <.12 375 <.07 E.7 .510 3.6 <30 <.16 199 .4 2.7

-- -- -- -- -- -- -- -- -- -- --

15 <.06 118 E.02 E.4 1.20 .9 <10 E.05 68.3 157 1.7

16 <.06 139 E.02 E.4 .287 .9 <10 <.08 75.0 68.4 5.5

17 <.06 146 <.04 E.7 .102 .7 <10 <.08 263 1.2 2.0

18 <.06 134 E.03 .8 .687 1.4 <10 <.08 79.8 14.1 .9

-- -- -- -- -- -- -- -- -- -- --

19 <.12 766 .13 <.8 .720 4.9 <10 <.16 278 101 52.9

-- -- -- -- -- -- -- -- -- -- --

20 <.06 249 <.04 E.6 .278 .9 <10 <.08 56.5 .4 3.4

21 <.06 376 E.04 E.7 .136 1.3 <10 <.08 119 E.1 13.1

22 -- -- -- -- -- -- -- -- -- -- --

23 <.06 943 E.03 E.5 .567 3.2 <10 <.08 170 .9 9.7

24 <.06 401 E.02 1.2 .167 .7 <10 <.08 111 .7 10.1

-- -- -- -- -- -- -- -- -- -- --

Appendix 2  75
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Beryllium, 

filtered 

(μg/L)

Boron, 

filtered 

(μg/L)

Cadmium, 

filtered 

(μg/L)

Chromium, 

filtered 

(μg/L)

Cobalt, 

filtered 

(μg/L)

Copper, 

filtered 

(μg/L)

Iron, 

filtered 

(μg/L)

Lead, 

filtered 

(μg/L)

Lithium, 

filtered 

(μg/L)

Manganese, 

filtred 

(μg/L)

Molybdenum, 

filtered 

(μg/L)

25 <0.06 336 E0.03 <0.8 0.601 1.7 <10 <0.08 126 621 5.3

-- -- -- -- -- -- -- -- -- -- --

26 <.06 141 E.02 E.5 .209 .7 <10 <.08 132 .7 4.9

27 <.06 217 .06 .9 .198 1.7 <10 <.08 137 9.7 5.8

28 <.06 201 E.02 E.5 .339 1.5 <10 <.08 154 6.0 1.6

-- -- -- -- -- -- -- -- -- -- --

29 <.06 207 E.03 E.8 .144 .6 <10 <.08 77.0 .6 4.0

30 <.06 257 E.03 <.8 .125 1.5 <10 <.08 110 4.2 6.4

76  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Nickel, 

filtered 

(μg/L)

Selenium, 

filtered 

(μg/L)

Silver, 

filtered 

(μg/L)

Strontium, 

filtered 

(μg/L)

Thallium, 

filtered 

(μg/L)

Uranium 

natural, 

filtered 

(μg/L)

Vanadium, 

filtered 

(μg/L)

Zinc, 

filtered 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Tritium, 

unfiltered 

(pCi/L)

1 2.71 5.2 <0.2 1,050 E0.03 3.78 83.2 1.1 0.8 <1

2 5.27 14.9 <.2 2,160 .06 7.78 59.8 1.8 2.0 3

3 3.88 18.7 .2 3,460 .07 8.30 118 2.0 -- 12

-- -- -- -- -- -- -- -- 1.8 --

4 9.03 17.7 <.2 2,190 .07 8.07 26.2 1.8 -- 3

-- -- -- -- -- -- -- -- 2.9 --

5 4.83 21.2 1.2 4,100 <.04 5.63 33.7 5.8 -- <1

-- -- -- -- -- -- -- -- 7.8 --

6 2.66 49.9 .7 2,390 <.04 10.1 42.3 11.3 -- 37

-- -- -- -- -- -- -- -- 7.1 --

7 4.34 8.6 <.2 1,760 .06 5.59 14.0 8.6 -- 7

-- -- -- -- -- -- -- -- .8 --

8 4.95 21.9 2.8 4,270 <.04 5.88 22.2 1.1 1.4 <1

9 3.42 28.1 <.2 4,940 .05 8.48 46.2 3.0 2.2 12

10 2.71 35.2 1.1 2,500 <.04 5.38 45.1 3.8 1.9 <1

11 3.22 1.1 <.2 2,220 <.04 9.14 27.9 1.7 3.0 <1

12 3.00 93.5 <.2 3,080 <.04 21.9 49.7 1.8 1.5 21

13 4.11 12.3 1.5 3,170 E.03 13.4 48.1 2.1 2.3 1

14 9.30 49.5 3.2 7,250 E.08n 17.1 29.6 5.8 -- 10

-- -- -- -- -- -- -- -- 3.1 --

15 4.03 8.4 <.2 1,720 E.03 5.67 30.8 7.8 2.4 6

16 2.62 3.5 <.2 1,200 .04 10.7 8.7 6.3 .8 <1

17 2.29 3.4 <.2 1,450 <.04 18.3 18.5 3.0 3.9 15 

18 5.23 19.9 E.1 2,280 .06 6.21 23.1 7.1 -- 1

-- -- -- -- -- -- -- -- 10.8 --

19 7.32 3.8 E.2n 5,800 .10 30.8 13.5 6.1 -- 3

-- -- -- -- -- -- -- -- 4.2 --

20 3.29 15.9 <.2 2,530 E.04 10.3 17.6 1.8 2.3 41

21 2.51 14.0 <.4 2,570 E.03 11.7 49.8 1.4 2.4 10

22 -- -- -- -- -- -- -- -- -- --

23 6.10 45.0 <.2 5,730 E.03 26.1 45.8 3.7 2.2 4

24 1.93 9.0 <.2 2,390 E.02 27.1 72.1 9.5 -- 34

Appendix 2  77
Appendix 2. Results of physical and chemical analyses of ground–water samples collected from southern High Plains agricultural 

land–use study area, Texas, 2003.—Continued

[mg/L, milligrams per liter; --, no data; <, less than; d, diluted sample, method high range exceeded; μg/L, micrograms per liter; d15N, nitrogen isotope ratio; 

d18O, oxygen isotope ratio; ESA, ethanesulfonic acid; SA, second amide; OA, oxanilic acid; SAA, sulfynil acetic acid; E, estimated; t, below the long-term 

method detection level; n, below the laboratory reporting level and above the long-term method detection level; M, presence verified, not quantified; LSD, 

land surface datum referenced to North American Vertical Datum of 1988 (NAVD 88); μS/cm, microsiemens per centimeter at 25 degrees Celsius; oC, degrees 

Celsius; NTU, nephelometric turbidity units; >, greater than; CaCO3, calcium carbonate; pCi/L, picocuries per liter]

Map 

identifier 

(fig. 2)

Nickel, 

filtered 

(μg/L)

Selenium, 

filtered 

(μg/L)

Silver, 

filtered 

(μg/L)

Strontium, 

filtered 

(μg/L)

Thallium, 

filtered 

(μg/L)

Uranium 

natural, 

filtered 

(μg/L)

Vanadium, 

filtered 

(μg/L)

Zinc, 

filtered 

(μg/L)

Organic 

carbon, 

filtered 

(mg/L)

Tritium, 

unfiltered 

(pCi/L)

24 -- -- -- -- -- -- -- -- 1.3 --

25 3.10 17.9 <.2 3,130 0.08 1.95 31.0 2.3 -- 3

-- -- -- -- -- -- -- -- 1.6 --

26 2.20 8.9 <.2 3,190 E.04 13.3 40.5 2.3 1.6 21

27 3.97 7.8 E.1 2,110 <.04 9.26 28.4 29.8 1.8 <1

28 5.87 14.4 E.2 3,650 E.02 9.25 29.2 1.8 -- <1

-- -- -- -- -- -- -- -- 4.3 --

29 4.21 1.5 E.1 1,790 E.04 8.79 12.7 3.0 .8 <1

30 2.63 6.7 <.2 1,280 <.04 9.97 33.0 4.3 2.4 <1

78  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 3. Pesticides analyzed in ground-water samples collected from northern and southern High Plains aquifer, Nebraska and 

Texas, 2003–04.

[USGS, U.S. Geological Survey; CAS, Chemical Abstracts Service; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; NAL, northern 

High Plains agricultural land use; SAL, southern High Plains agricultural land use; ESA, ethanesulfonic acid; OA, oxanilic acid; SAA, sulfynil acetic acid; ESA 

SA, ethenesulfonic acid second amide; MCL, Maximum Contaminant Level; LTHA, Lifetime Health Advisory; --, no data]

Pesticide compound 

name

USGS 

parameter 

code

CAS number

Study 

area(s) 

sampled

Highest 

laboratory 

reporting level 

(μg/L)

Mean fieldmatrix spike 

recovery 

(percent)

Pesticide type

USEPA drinkingwater standard 

(μg/L) /type of 

standard1

2,6-Diethylaniline 82660 579–66–8 NAL,SAL 0.006 98.3 degradate --

3-trifluoromethylaniline 

(TFMA)

61742 98–16–8 SAL .05 -- degradate --

3-trifluoromethylphenylurea (TFMPU)61741 13114–87–9 SAL .05 -- degradate --

Acetochlor 49260 34256–82–1 NAL,SAL .006 107.5 herbicide --

Acetochlor ESA 61029 -- NAL .02 -- degradate --

Acetochlor OA 61030 -- NAL .02 -- degradate --

Acetochlor SAA 62847 -- NAL .02 -- degradate --

Acetochlor/metolachlor 

ESA SA

62850 -- NAL .02 -- degradate

Alachlor 46342 15972–60–8 NAL,SAL .005 106.7 herbicide 2/MCL

Alachlor ESA 50009 -- NAL .02 -- degradate --

Alachlor ESA SA 62849 -- NAL .02 -- degradate --

Alachlor OA 61031 -- NAL .02 -- degradate --

Alachlor SAA 62848 140939–16–8 NAL .02 -- degradate --

Alpha-HCH 34253 319–84–6 NAL,SAL .005 88.0 insecticide / 

degradate

Atrazine 39632 1912–24–9 NAL,SAL .007 118.3 herbicide 3/MCL

Azinphos-methyl3 82686 86–50–0 NAL,SAL .050 2128.3 insecticide --

Benfluralin 82673 1861–40–1 NAL,SAL .010 83.6 herbicide --

Butylate 04028 2008–41–5 NAL,SAL .004 98.7 herbicide 400/LTHA

Carbaryl3 82680 63–25–2 NAL,SAL .041 2120.9 insecticide 700/LTHA

Carbofuran3 82674 1563–66–2 NAL,SAL .020 2121.4 insecticide 40/MCL

Chlorpyrifos 38933 2921–88–2 NAL,SAL .005 93.3 insecticide 20/LTHA

cis-Permethrin 82687 54774–45–7 NAL,SAL .006 65.3 insecticide --

Cyanazine 04041 21725–46–2 NAL,SAL .018 2121.0 herbicide 1/LTHA

Cyanazine amide 61709 -- SAL .05 -- degradate --

DCPA 82682 1861–32–1 NAL,SAL .003 109.1 herbicide 70/LTHA

Deethylatrazine (CIAT)3 04040 6190–65–4 NAL,SAL .006 245.7 degradate --

Deisopropylatrazine 

(CEAT)

04038 1007–28–9 SAL .05 -- degradate --

Deisopropyl prometryn 61752 -- SAL .05 -- degradate --

Appendix 3  79
Appendix 3. Pesticides analyzed in ground-water samples collected from northern and southern High Plains aquifer, Nebraska and 

Texas, 2003–04.—Continued

[USGS, U.S. Geological Survey; CAS, Chemical Abstracts Service; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; NAL, northern High Plains agricultural land use; SAL, southern High Plains agricultural land use; ESA, ethanesulfonic acid; OA, oxanilic acid; SAA, sulfynil acetic acid; 

ESA SA, ethenesulfonic acid second amide; MCL, Maximum Contaminant Level; LTHA, Lifetime Health Advisory; --, no data]

Pesticide compound name

USGS 

parameter 

code

CAS number

Study 

area(s) 

sampled

Highest laboratory reporting 

level (μg/L)

Mean fieldmatrix spike 

recovery 

(percent)

Pesticide 

type

USEPA drinkingwater standard 

(μg/L) /type of 

standard1

Demethylfluometuron 

(DMFM)

61753 -- SAL 0.05 -- degradate --

Demethylnorflurazon 61754 -- SAL .05 -- degradate --

Desulfinyl fipronil 62170 -- NAL,SAL .012 117.5 degradate --

Desulfinylfipronil amide 62169 -- NAL,SAL .029 2139.8 degradate --

Diazinon 39572 333–41–5 NAL,SAL .005 98.7 insecticide 0.6/LTHA

Dieldrin 39381 60–57–1 NAL,SAL .009 94.5 insecticide --

Dimethenamid 61588 87674–68–8 NAL,SAL .05 -- herbicide --

Dimethenamid ESA 61951 -- NAL .02 -- degradate --

Dimethanamid OA 62482 -- NAL .02 -- degradate --

Disulfoton 82677 298–04–4 NAL,SAL .02 225.3 insecticide 0.3/LTHA

EPTC 82668 759–94–4 NAL,SAL .004 96.9 herbicide --

Ethalfluralin 82663 55283–68–6 NAL,SAL .009 95.9 herbicide --

Ethoprop 82672 13194–48–4 NAL,SAL .005 95.3 insecticide --

Fipronil 62166 120068–37–3 NAL,SAL .016 2137.9 insecticide --

Fipronil sulfide 62167 120067–83–6 NAL,SAL .013 116.2 degradate --

Fipronil sulfone 62168 120068–36–2 NAL,SAL .024 109.8 degradate --

Flufenacet 62481 142459–58–3 NAL,SAL .05 -- herbicide --

Flufenacet ESA 61952 -- NAL .02 -- degradate --

Flufenacet OA 62483 -- NAL .02 -- degradate --

Fluometuron 38811 2164–17–2 SAL .05 -- herbicide 90/LTHA

Fonofos 04095 944–22–9 NAL,SAL .003 90.8 insecticide 10/LTHA

Lindane 39341 58–89–9 NAL,SAL .004 90.5 insecticide 0.2/MCL

Linuron 82666 330–55–2 NAL,SAL .035 2121.1 herbicide --

Malathion 39532 121–75–5 NAL,SAL .027 112.0 insecticide 100/LTHA

Methyl parathion 82667 298–00–0 NAL,SAL .015 97.9 insecticide 2/LTHA

Metolachlor 39415 51218–45–2 NAL,SAL .013 107.5 herbicide 100/LTHA

Metolachlor ESA 61043 -- NAL .02 -- degradate --

Metolachlor OA 61044 -- NAL .02 -- degradate --

Metribuzin 82630 21087–64–9 NAL,SAL .006 90.4 herbicide 200/LTHA

Molinate 82671 2212–67–1 NAL,SAL .003 96.9 herbicide --

80 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 3. Pesticides analyzed in ground-water samples collected from northern and southern High Plains aquifer, Nebraska and 

Texas, 2003–04.—Continued

[USGS, U.S. Geological Survey; CAS, Chemical Abstracts Service; USEPA, U.S. Environmental Protection Agency; μg/L, micrograms per liter; NAL, northern High Plains agricultural land use; SAL, southern High Plains agricultural land use; ESA, ethanesulfonic acid; OA, oxanilic acid; SAA, sulfynil acetic acid; 

ESA SA, ethenesulfonic acid second amide; MCL, Maximum Contaminant Level; LTHA, Lifetime Health Advisory; --, no data]

Pesticide compound 

name

USGS 

parameter 

code

CAS number

Study 

area(s) 

sampled

Highest laboratory reporting 

level (μg/L)

Mean fieldmatrix spike 

recovery 

(percent)

Pesticide type

USEPA drinkingwater standard 

(μg/L) /type of 

standard1

Napropamide 82684 15299–99–7 NAL,SAL 0.007 95.2 herbicide --

Norflurazon 50332 27314–13–2 SAL .05 -- herbicide --

p,p’-DDE 34653 72–55–9 NAL,SAL .003 77.8 degradate --

Parathion 39542 56–38–2 NAL,SAL .010 106.9 insecticide --

Pebulate 82669 1114–71–2 NAL,SAL .004 99.2 herbicide --

Pendimethalin 82683 40487–42–1 NAL,SAL .022 97.3 herbicide --

Phorate 82664 298–02–2 NAL,SAL .011 246.3 insecticide --

Prometon 04037 1610–18–0 NAL,SAL .01 106.0 herbicide 100 / LTHA

Prometryn 04036 7287–19–6 SAL .05 -- herbicide --

Propyzamide 82676 23950–58–5 NAL,SAL .004 104.5 herbicide 50 / LTHA

Propachlor 04024 1918–16–7 NAL,SAL .025 115.8 herbicide 90 / LTHA

Propachlor ESA 62766 -- NAL .05 -- degradate --

Propachlor OA 62767 -- NAL .02 -- degradate --

Propanil 82679 709–98–8 NAL,SAL .011 112.3 herbidide --

Propargite 82685 2312–35–8 NAL,SAL .03 89.9 acaricide --

Propazine 38535 139–40–2 SAL .05 -- herbicide 10 / LTHA

Simazine 04035 122–34–9 NAL,SAL .005 106.3 herbicide 4 / MCL

Tebuthiuron 82670 34014–18–1 NAL,SAL .02 2124.8 herbicide 500 / LTHA

Terbacil3 82665 5902–51–2 NAL,SAL .034 102.3 herbicide 90 / LTHA

Terbufos 82675 13071–79–9 NAL,SAL .02 80.8 insecticide 0.9 / LTHA

Thiobencarb 82681 28249–77–6 NAL,SAL .010 104.4 herbicide --

Triallate 82678 2303–17–5 NAL,SAL .002 89.9 herbicide --

Trifluralin 82661 1582–09–8 NAL,SAL .009 86.8 herbicide 5 / LTHA

1

Source: U.S. Environmental Protection Agency, 2004.

2

Mean percentage recovery of compounds did not fall within the acceptable performance range (60 to 120 percent).

3

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 3  81
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Corn/Soybeans

Albemarle-Pamlico Drainage Basin 344950076381901 94–04–12

345434076301501 94–04–12

345516077190001 94–03–30

350522077133401 94–03–30

352305077321701 94–03–25

352905077594501 94–03–24

353241077521601 94–03–29

360913076173101 94–05–16

361702076330101 94–04–28

Delmarva Peninsula 380358075292901 03–01–15

381245075404002 03–01–16

381543075273802 01–08–08

381754075083603 01–08–09

382403075233202 01–08–21

382824075081502 03–01–04

382833075213701 03–01–06

383308075382301 01–08–28

384150075265301 01–07–24

384323075393201 01–07–25

384637075153201 02–12–19

391832075560803 01–07–12

391927076000301 01–07–03

Eastern Iowa Basins 405405091335001 97–07–02

405601091551901 97–07–10

411511091155101 97–06–24

411843092105101 97–07–14

412755091114101 97–06–25

412927092575201 97–07–14

413248092011301 97–07–07

413540091341201 97–06–10

82 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Corn/Soybeans—Continued

Eastern Iowa Basins—Continued 414208092312601 97–07–09

414912093284201 97–07–15

414958090230301 97–06–12

415527092190301 97–07–17

420117092505601 97–07–09

421115091250501 97–07–24

421705092142501 97–07–22

422518092144701 97–07–22

422629092345001 97–07–23

423419093172401 97–07–08

423557091560501 97–08–27

423639092350901 97–06–17

424203092551301 97–07–31

424548092101701 97–08–26

425401093135201 97–07–31

425756092162401 97–08–21

430159093403201 97–07–29

430525093023501 97–07–30

431222093313301 97–07–29

431339093155901 97–07–30

432946093161901 97–08–18

433815093000001 97–08–04

435221093001901 97–08–05

Lake Erie-Lake Saint Clair Drainages 413053084565100 98–06–18

413140084442300 98–06–15

413148084472200 98–06–10

413520084460500 98–07–06

413719084361000 98–06–11

413746084341400 98–06–09

413923084472000 98–06–08

414125084360800 98–07–07

Appendix 4  83
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Corn/Soybeans—Continued

Lake Erie-Lake Saint Clair Drainages—

Continued

414320084161200 98–07–08

414519084161600 98–07–24

414520084374800 98–06–17

414611084262000 98–06–19

414728084390400 98–06–16

414907084243100 98–07–10

415026084220000 98–07–22

415456084095500 98–07–20

420047084234900 98–07–09

420054084024000 98–07–23

420303084040300 98–07–21

421125083533800 98–06–25

421225083593300 98–06–26

421237083523500 98–06–23

421244083492000 98–06–24

425204083011600 98–07–13

425758083040100 98–07–13

430336083012700 98–08–04

431328082520100 98–07–14

431730082492900 98–07–14

433501082452500 98–08–05

Long Island-New Jersey Coastal Drainages 393015075054501 96–10–30

393050075180001 96–12–20

393413075141901 96–10–16

393516075164701 96–10–28

393523075132801 96–10–30

393542075110501 96–10–16

393625075112501 96–09–05

393712075121201 96–10–16

393818075132401 96–09–03

393916075122201 96–09–03

84 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Corn/Soybeans—Continued

Lower Illinois River Basin 395626089024901 97–07–23

400736088344701 97–07–31

401216088482301 97–07–09

401945088400701 97–06–18

402727088464201 97–08–05

402912088515101 97–06–23

402920088401301 97–07–15

403025088273201 97–07–07

403759088422601 97–06–24

403808089065901 97–07–01

404004088485501 97–07–08

404139088195901 97–07–28

404603088563501 97–06–30

404737089093201 97–08–06

404849088281001 97–08–04

404906088404901 97–06–25

405100089214701 97–07–30

405218088462401 97–07–29

405638089360801 97–07–02

405832088592001 97–07–24

405837089033701 97–07–10

410502089392501 97–07–21

410857089442301 97–07–22

410947089044101 97–08–07

412136088571001 97–07–17

412442089025701 97–07–16

412654089133301 97–07–14

395553088441401 97–11–03

395853088364401 97–09–22

400033088300301 97–09–09

400111088550501 97–08–19

Appendix 4  85
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Corn/Soybeans—Continued

Lower Illinois River Basin—Continued 400345088444901 97–10–22

400512089022601 97–08–21

400601088553401 97–10–21

400725088300201 97–09–23

400846088491001 97–08–25

401020089252801 97–10–29

401100089004701 97–10–23

401151088423401 97–10–22

401152088454801 97–09–11

401203089203201 97–10–29

401226088234101 97–09–25

401322089153901 97–08–13

401327089025201 97–09–18

401508088293201 97–08–27

401601089154401 97–10–28

401751088214101 97–09–08

401753088120701 97–09–24

401805088361801 97–08–28

401810089010101 97–09–10

401813089165601 97–10–28

402059088571701 97–09–17

402210088215701 97–09–15

402213088132201 97–09–16

402250088551201 97–08–27

402304089032601 97–08–20

Lower Susquehanna River Basin 395143076525201 93–07–12

395346076502901 93–07–12

400033076344901 93–07–12

Lower Tennessee River Basin 343530086213801 00–06–01

343613086441701 00–05–25

344407086273401 00–06–01

86  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Corn/Soybeans—Continued

Lower Tennessee River Basin—Continued 344615086272201 00–06–01

345112086313401 00–06–01

345222086303301 00–06–07

345247086415001 00–05–31

345539086241301 00–05–31

345822086254001 00–06–06

345912086243901 00–05–31

352627086002601 00–05–30

353341086074501 00–05–30

354014086093401 00–05–30

Great and Little Miami River Basins 391636084452800 00–08–03

392018084371800 00–08–02

392756084300900 00–08–02

393421084003300 00–07–26

393831085043500 00–08–09

394233083576000 00–07–26

394420084463001 00–08–16

394650084320300 00–07–17

394745085051300 00–08–25

394759085071000 00–08–10

395135085070000 00–08–09

395213085052200 00–08–24

395248084491600 00–08–16

395911084422700 00–07–24

400019083412000 00–07–19

400145084106000 00–08–01

400850083404700 00–07–13

401040084154000 00–07–28

401238084144400 00–07–27

401240083492600 00–07–19

401307083450600 00–07–18

Appendix 4  87
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Corn/Soybeans—Continued

Great and Little Miami River Basins—

Continued

401359083493100 00–07–25

401837083492900 00–07–20

Potomac River Basin 384556078385101 93–07–21

385521078281601 93–09–20

391200077520401 93–09–09

391317077555801 93–07–27

392033077530301 93–06–10

Santee River Basin and Coastal Drainages 323759080283701 97–11–25

324349081092801 97–09–23

324412080485501 97–09–16

324507081061901 97–09–23

324754080573801 97–09–24

325129080453601 97–09–22

325435080530601 97–10–23

325618081054101 97–09–29

325812081090901 97–10–01

330540080490701 97–10–29

330656080365201 97–09–09

330715081192501 97–11–24

331038080545601 97–10–02

331043081022101 97–10–02

331303080464101 97–11–25

331305080231301 97–09–11

331842080215301 97–08–28

331934080283701 97–09–22

332056080293501 97–09–08

332219080390501 97–09–10

332224080123601 97–08–27

332355080410401 97–09–10

332446080242201 97–08–28

332534080155701 97–08–27

88  Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Corn/Soybeans—Continued

Santee River Basin and Coastal Drainages—

Continued

332641080032201 97–08–26

332706080332001 97–09–08

Upper Illinois River Basin 405145087044701 99–07–07

405343087091501 99–09–09

405458087484601 99–09–08

405524087152701 99–07–08

405732087282301 99–07–19

410030087263101 99–07–19

410123087385601 99–07–21

410253087280701 99–07–22

410309087381501 99–07–14

410422088000001 99–07–13

410505087201201 99–07–20

410510087224201 99–06–29

410511087295201 99–08–24

410600087113501 99–06–29

410702087310201 99–07–21

410715087072301 99–06–14

410748087060901 99–06–14

410812087423401 99–08–23

410859087370001 99–07–13

410925087333201 99–06–30

410947087050501 99–06–15

411029087172401 99–06–01

411119087143601 99–06–02

411123088061201 99–08–23

411248087304901 99–07–20

411329087121201 99–06–15

411511087214501 99–06–16

411719087171301 99–06–01

413141088402401 99–07–12

Appendix 4  89
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Corn/Soybeans—Continued

Upper Mississippi River Basin—Continued 451730093423001 98–05–20

451811093445601 98–05–19

451822093413201 98–05–27

451835093400401 98–05–27

451915093463901 98–05–26

451921093445101 98–05–26

451924093474601 98–05–18

451953093484901 98–05–18

451957093483201 98–05–18

452007093413001 98–05–20

452030093511403 98–08–11

452036093423701 98–05–20

452040093463101 98–05–19

452111093523401 98–05–19

452210093523701 98–05–21

452215093481001 98–05–14

452229093525801 98–05–21

452324093541601 98–05–21

452335093504301 98–05–14

452335093504501 98–05–14

452408093552901 98–05–12

452408093553001 98–05–13

452428093591601 98–05–13

452543093544801 98–05–12

452545093571002 98–05–15

452609093553001 98–05–12

452610093553001 98–05–11

452711093565501 98–05–11

452720093552202 98–05–11

White River Basin 393119086154101 94–07–27

393223085534001 94–07–18

90 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) SIte number Date sampled (year–month–day)

Corn/Soybeans—Continued

White River Basin—Continued 393230085375301 94–08–01

393405086322001 94–07–28

393433085320301 94–08–01

394032085543101 94–06–30

394157085430401 94–08–03

394226085275601 94–07–19

394516086555601 94–08–10

394849086273001 94–08–11

395253086314001 94–09–07

395633085460801 94–08–03

395656086191601 94–09–20

395713085202901 94–09–20

400356085562101 94–06–29

400401085044701 94–07–26

400713086132801 94–09–21

400718085042201 94–07–26

400746084551101 94–07–25

400838085205801 94–09–01

400844086095201 94–09–21

401945085321501 94–08–02

401952085460101 94–08–02

382833087193201 94–09–14

383115086590701 94–09–13

383221087293301 94–08–23

383457087015601 94–08–29

383525087175001 94–06–22

383801087270901 94–08–24

383803086584701 94–08–30

383817087211101 94–08–23

384038087055501 94–09–13

385057086565601 94–08–18

Appendix 4  91
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Corn/Soybeans—Continued

White River Basin—Continued 385201087033601 94–08–18

385533086582801 94–08–17

385941087012101 94–09–12

390138086591201 94–08–16

390722087054501 94–09–15

390858086580701 94–08–16

391531087123001 94–07–20

391643087082201 94–07–21

391937087134501 94–07–05

392103087000301 94–09–08

392448087062801 94–07–21

393025087063701 94–08–15

382629087362101 95–07–31

383014086581801 95–07–18

383858087141001 95–08–02

384520086224201 95–07–17

385243086043901 95–07–17

385358087061101 95–07–18

390244086593401 95–07–19

390505085513301 95–07–25

391209087074601 95–07–03

391558086461401 95–07–27

391811085551001 95–07–26

391943087091901 95–07–03

392211086283701 95–07–27

393038086222101 95–05–17

393350085561701 95–06–01

393455086562101 95–07–05

393622085483301 95–06–01

394012086124401 95–07–20

394026085240301 95–05–31

92 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Corn/Soybeans—Continued

White River Basin—Continued 395549085172401 95–05–15

395709086040101 95–06–12

400805085525801 95–05–08

400949085154301 95–05–10

401027085314301 95–05–09

Cotton

Apalachicola-Chattahoochee-Flint River 

Basin

310913084195301 93–08–24

315009083571001 93–09–02

Georgia–Florida Coastal Plain 312025083401101 94–03–24

312356083462001 94–04–01

313209083464801 94–03–28

313324083450601 94–04–01

313435083390101 94–03–16

313630083385001 94–03–17

313822083311901 94–04–05

313950083425401 94–04–05

314123083391301 94–04–05

314421083281601 94–03–29

314847083360301 94–03–29

315043083401901 94–03–31

315059083350901 94–03–31

315747083312901 94–03–30

Lower Tennessee River Basin 343919087182201 00–05–24

344127087212001 00–05–23

344131087335201 00–05–22

344154087171201 00–05–24

344217087283601 01–04–17

344557087253201 01–04–17

Mobile River Basin 322131085554301 01–09–20

322229086445801 01–07–18

322434085555601 01–06–26

Appendix 4  93
Appendix 4. Ground–water monitoring sites from 14 National Water–Quality Assessment (NAWQA) agricultural study areas where 

corn and soybeans primarily are grown and from 5 NAWQA agricultural study areas where cotton primarily is grown.—Continued

[Source: NAWQA data warehouse (U.S. Geological Survey, 2002)]

Study unit (fig. 11) Site number Date sampled (year–month–day)

Cotton—Continued

Mobile River Basin—Continued 322500085551201 01–06–25

322547086072101 01–08–21

322616086365601 01–09–19

322648085541601 01–09–07

322655085551501 01–07–24

322744086104801 01–09–19

322801085555101 01–06–19

322818085560601 01–06–19

322831086124601 01–07–23

322834085542201 01–10–07

322842085562901 01–06–18

323405086214101 01–09–18

323457086193001 01–09–18

San Joaquin-Tulare Basins 361519119433401 95–05–25

361852119350601 95–05–24

361948119412201 95–05–24

94 Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, 2003–04
Prepared by Lawrence Publishing Service Center.

Edited by Lanna Combs.

Illustrations and cover design by Jeff Hartley and Mike Kemppainen.

Layout and design by Kristi Hartley.

For more information concerning the research described in this report, 

contact:

U.S. Geological Survey

5231 South 19th Street

Lincoln, NE 68512

(402) 328–4100

http://ne.water.usgs.gov
Author—Spine Title—Report Series Name 0000

ISBN

Printed on recycled paper Printed on recycled paper

Stanton and Fahlquist—Ground-Water Quality Beneath Irrigated Cropland of the Northern and Southern High Plains Aquifer, Nebraska and Texas, 2003−04—USGS/SIR 2006–5196

Northern High Plains study area

Southern High Plains study area

05

10

15

20

0 5 10 15 20 25 40 60 80 100 120

Nitrate concentration, in milligrams per liter as N

05

10

15

20

Median concentration

in old ground water

(western Nebraska)

(McMahon and Böhlke, 2006)

Median 15N value

in old ground water

(western Nebraska)

(McMahon and Böhlke, 2006)

Median concentration

in old ground water

(northern Texas)

(McMahon and Böhlke, 2006) Median 15N valu

e

in old ground water (northern Texas)

(McMahon and Böhlke, 2006)

Ground-water sample

Nitrogen isotope ratio ( 15N) value, per mil

Ground-water sample

Fertilizer

Soil nitrogen

Animal waste

Fertilizer

Soil nitrogen

Animal waste