Vertical Gradients in Water Chemistry in 

the Central High Plains Aquifer, 

Southwestern Kansas and Oklahoma 

Panhandle, 1999

By P.B. McMahon

Denver, Colorado

2001

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 01–4028
District Chief

U.S. Geological Survey

Box 25046, Mail Stop 415

Denver Federal Center

Denver, CO 80225–0046

For additional information write to:

District Chief

U.S. Geological Survey

Box 25046, Mail Stop 415

Denver Federal Center

Denver, CO 80225–0046

U.S. DEPARTMENT OF THE INTERIOR

GALE A. NORTON, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does 

not constitute endorsement by the U.S. Geological Survey.

Copies of this report can be purchased 

from:

U.S. Geological Survey

Information Services

Box 25286

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Denver, CO 80225
FOREWORD

III

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 the 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 sciencebased insights for current and emerging water issues and priorities. NAWQA results can contribute to informed 

decisions that result in practical and effective water-resource management and strategies that protect and restore 

water quality.

Since 1991, the NAWQA Program has implemented interdisciplinary assessments in more than 50 of the Nation’s 

most important river basins and aquifers, referred to as Study Units. 

(http://water.usgs.gov/nawqa/nawqamap.html). Collectively, these Study Units account for more than 60 percent 

of the overall water use and population served by public water supply, and are representative of the Nation’s major 

hydrologic landscapes, priority ecological resources, and agricultural, urban, and natural sources of contamination. 

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

assessments thereby build local knowledge about water-quality issues and trends in a particular stream or aquifer 

while providing an understanding of how and why water quality varies regionally and nationally. The consistent, 

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 on 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. 

The NAWQA Program recognizes that a national assessment by a single program cannot address all waterresource 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 V

Foreword................................................................................................................................................................................ III

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

Introduction............................................................................................................................................................................ 2

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

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

Description of Study Area ..................................................................................................................................................... 4

Geohydrologic Setting ................................................................................................................................................. 4

Land and Water Use..................................................................................................................................................... 5

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

Vertical Changes in Lithology ............................................................................................................................................... 12

Geophysical and Lithologic Logs................................................................................................................................ 12

Elemental and X-ray Diffraction Analyses.................................................................................................................. 18

Vertical Hydraulic Gradients ................................................................................................................................................. 20

Vertical Gradients in Water Chemistry .................................................................................................................................. 22

Tritium ......................................................................................................................................................................... 22

Dissolved Oxygen and Organic Carbon ...................................................................................................................... 31

Major Ions.................................................................................................................................................................... 31

Nitrate .......................................................................................................................................................................... 37

Arsenic......................................................................................................................................................................... 39

Pesticides ..................................................................................................................................................................... 40

Summary and Conclusions .................................................................................................................................................... 44

References Cited.................................................................................................................................................................... 45

FIGURES

1–5. Maps showing:

1. Land-surface elevations and locations of the southern, central, and northern parts of the 

High Plains aquifer............................................................................................................................................. 3

2. Ground-water elevations in the central High Plains aquifer and locations of monitoring wells ....................... 4

3. Geology underlying the central High Plains aquifer and locations of monitoring wells................................... 7

4. Saturated thickness of the central High Plains aquifer and locations of monitoring wells................................ 8

5. Land use overlying the central High Plains aquifer and locations of monitoring wells .................................... 9

6–17. Graphs showing:

6. Natural gamma and resistivity logs for water-table-well boreholes (a) Recon–1, (b) Recon–2, 

(c) Recon–3, (d) Recon–4, and (e) Recon–5...................................................................................................... 13

7. Natural gamma and resistivity logs for nested-well boreholes (a) Rolla, (b) Hugoton, (c) Liberal, and 

(d) Cimarron....................................................................................................................................................... 14

8. Ground-water elevations at the nested-well sites (a) Rolla, (b) Hugoton, (c) Liberal, and (d) Cimarron ......... 21

9. Relation between tritium concentrations and depth of the well-screen midpoint below the water table........... 30

10. Relation between dissolved (a) organic carbon and (b) oxygen concentrations and depth of the 

well-screen midpoint below the water table....................................................................................................... 32

11. Horizontal and vertical distribution of water types at the nested-well sites ...................................................... 33

12. Relation between calcite saturation indices and depth of the well-screen midpoint below the water table ...... 34

13. Relation between concentrations of dissolved solids and depth of the well-screen midpoint below the 

water table .......................................................................................................................................................... 35

CONTENTS
VI CONTENTS

14. Relation between bromide/chloride mass ratios and concentrations of dissolved chloride in 

water samples from the central High Plains aquifer and sediments of Permian age ......................................... 36

15. Relation between concentrations of dissolved nitrate and depth of the well-screen midpoint below 

the water table .................................................................................................................................................... 38

16. Relation between concentrations of dissolved arsenic and depth of the well-screen midpoint below 

the water table .................................................................................................................................................... 39

17. Relation between number of pesticide detections and depth of the well-screen midpoint below the 

water table.......................................................................................................................................................... 44

TABLES

1. Generalized section of the geologic units in southwestern Kansas and their relation to the central 

High Plains aquifer.................................................................................................................................................. 6

2. Construction details for monitoring wells and generalized land use around each well.......................................... 10

3. Methods used to analyze water samples ................................................................................................................. 12

4. Lithologic description of drill cuttings and core..................................................................................................... 15

5. Results of elemental and x-ray diffraction analyses................................................................................................ 19

6. Physical properties and concentrations of major ions, nutrients, trace elements, and tritium in water from 

the Cimarron River and sampled wells in the central High Plains aquifer and sediments of Permian age ............ 23

7. Pesticides and pesticide degradation products analyzed in water from sampled wells in the central 

High Plains aquifer and sediments of Permian age................................................................................................. 40

8. Pesticide usage in the study area and concentrations of pesticides and pesticide degradation products 

detected in water from sampled wells in the central High Plains aquifer and sediments of Permian age.............. 41

ABBREVIATIONS USED IN THIS REPORT

ft3/s cubic feet per second

DOC dissolved organic carbon

MCL maximum contaminant level

mg/L milligrams per liter

mg/L as N milligrams per liter as nitrogen

mg/L as P milligrams per liter as phosphorus

mi2 square miles

mL milliliters

mm millimeters

NAWQA National Water-Quality Assessment

TU tritium units

USGS U.S. Geological Survey

USEPA U.S. Environmental Protection Agency

μg/L micrograms per liter

μm micrometers

Sea level: In this report “sea level” refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)—a geodetic 

datum derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called 

Sea Level Datum of 1929.
Abstract 1

Vertical Gradients in Water Chemistry in the

Central High Plains Aquifer, Southwestern Kansas

and Oklahoma Panhandle, 1999

By P.B. McMahon

Abstract

The central High Plains aquifer is the 

primary source of water for domestic, industrial, 

and irrigation uses in parts of Colorado, Kansas, 

New Mexico, Oklahoma, and Texas. Water-level 

declines of more than 100 feet in some areas of 

the aquifer have increased the demand for water 

deeper in the aquifer. The maximum saturated 

thickness of the aquifer ranged from 500 to 

600 feet in 1999. As the demand for deeper water 

increases, it becomes increasingly important for 

resource managers to understand how the quality 

of water in the aquifer changes with depth. In 

1998–99, 18 monitoring wells at nine sites in 

southwestern Kansas and the Oklahoma 

Panhandle were completed at various depths in 

the central High Plains aquifer, and one monitoring well was completed in sediments of 

Permian age underlying the aquifer. Water 

samples were collected once from each well in 

1999 to measure vertical gradients in water chemistry in the aquifer. 

Tritium concentrations measured in ground 

water indicate that water samples collected in the 

upper 30 feet of the aquifer were generally 

recharged within the last 50 years, whereas all of 

the water samples collected at depths more than 

30 feet below the water table were recharged 

more than 50 years ago. Dissolved oxygen was 

present throughout the aquifer, with concentrations ranging from 1.7 to 8.4 mg/L.

Water in the central High Plains aquifer was 

predominantly a calcium-bicarbonate type that 

exhibited little variability in concentrations of 

dissolved solids with depth (290 to 642 mg/L). 

Exceptions occurred in some areas where there 

had been upward movement of mineralized water 

from underlying sediments of Permian age and 

areas where there had been downward movement 

of mineralized Arkansas River water to the 

aquifer. Calcium-sulfate and sodium-chloride 

waters dominated and concentrations of dissolved 

solids were elevated (862 to 4,030 mg/L) near the 

base of the aquifer in the areas of upward leakage. 

Dissolution of gypsum or anhydrite and halite in 

sediments of Permian age by ground water was 

the likely source of calcium, sulfate, sodium, and 

chloride in those waters. Calcium-sodium-sulfate 

waters dominated, and concentrations of 

dissolved solids were as large as 4,916 mg/L near 

the water table in the area of downward leakage. 

Dissolution of minerals in sedimentary deposits 

of marine origin in upstream areas of the 

Arkansas River drainage were the likely sources 

of calcium, sodium, and sulfate in those waters. 

Nitrate was detected throughout the aquifer 

and the background concentration was estimated 

to be 2.45 mg/L as N. The largest nitrate concentrations (8.28, 22, and 54.4 mg/L as N) occurred 

in recently recharged water collected adjacent to 

irrigated fields. Three pesticides (atrazine, metolachlor, simazine) and five pesticide degradation 

products (alachlor ethanesulfonic acid, alachlor 

oxanilic acid, deethylatrazine, metolachlor 

ethanesulfonic acid, metolachlor oxanilic acid) 

were detected in recently recharged water from 

six water-table wells. Five of the six wells were 
2 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

adjacent to irrigated fields. These data indicate 

that concentrations of nitrate and pesticides 

increased over time in some areas of the aquifer as 

a result of agricultural activities. 

Results from this study indicate that vertical 

gradients in water chemistry existed in the central 

High Plains aquifer. The chemical gradients 

resulted from chemical inputs to the aquifer from 

underlying sediments of Permian age, from the 

Arkansas River, and from agricultural activities. 

In areas where those chemical inputs occurred, 

water quality in the aquifer was impaired and may 

not have been suitable for some intended uses. 

INTRODUCTION

Knowledge of the quality of the Nation’s water 

resources is important because of the implications to 

human and aquatic health and because of the significant costs associated with decisions involving land and 

water management, conservation, and remediation. In 

1991, the U.S. Geological Survey began full implementation of the National Water Quality Assessment 

(NAWQA) Program. The long-term goals of the 

NAWQA Program are to describe the status and trends 

in the quality of the Nation’s surface- and groundwater resources and determine the natural and anthropogenic factors affecting the water quality (Gilliom 

and others, 1995). 

The High Plains Regional Ground Water study 

began in June 1998 and represents a modification of 

the traditional NAWQA design in that the groundwater resource is the primary focus of this investigation. The High Plains aquifer is a nationally important 

water resource that underlies about 174,000 mi2

 in 

parts of eight States (fig. 1). About 20 percent of agricultural land in the United States is in the High Plains, 

and about 30 percent of all the ground water used for 

irrigation in the United States is pumped from this 

aquifer (Weeks and others, 1988). Due to the large 

areal extent of the High Plains aquifer, three 

geographic regions have been delineated for logistical 

purposes (fig. 1): northern High Plains (96,500 mi2

); 

central High Plains (48,500 mi2); and southern High 

Plains (29,000 mi2

).

The central High Plains aquifer is the focus of 

this investigation. The aquifer is the primary source of 

water used for domestic, industrial, and irrigation 

purposes in parts of Colorado, Kansas, New Mexico, 

Oklahoma, and Texas. Water-level declines of more 

than 100 feet in some areas of the aquifer have 

increased the demand for water deeper in the aquifer. 

The maximum saturated thickness of the aquifer 

ranged from 500 to 600 feet in 1999. As the demand 

for water increases, it becomes increasingly important 

for resource managers to understand how the quality 

of water in the aquifer changes with depth. In previous 

studies, domestic, irrigation, and monitoring wells 

were sampled with the purpose of providing a broad 

areal assessment of water quality in the aquifer 

(Gutentag and others, 1981, 1984) or understanding 

specific water-quality problems like the intrusion of 

mineralized surface water into the aquifer (Whittemore, 1984). No studies had been designed specifically to document vertical changes in water chemistry 

in the aquifer. It is likely that vertical gradients in 

water chemistry exist in the central High Plains 

aquifer because of upward leakage of poor-quality 

water from underlying geologic units (Krothe and 

Oliver, 1982; Whittemore, 1984), infiltration of poorquality surface water (Whittemore, 1984), and landsurface activities (McMahon, 2000). 

Purpose and Scope

The purpose of this report is to describe vertical 

gradients in water chemistry in the central High Plains 

aquifer in southwestern Kansas and the Oklahoma 

Panhandle. In 1998–99, 18 monitoring wells at nine 

sites in southwestern Kansas and the Oklahoma 

Panhandle were completed in the aquifer and 1 monitoring well was completed in sediments of Permian 

age underlying the aquifer (fig. 2). The wells had 

single screens that were placed at various depths 

below the water table. In 1999, water samples were 

collected once from each well and analyzed for major 

ions, nutrients, trace elements, dissolved organic 

carbon (DOC), pesticides, and tritium. A water sample 

was collected from the Cimarron River and analyzed 

for major ions, trace elements, nutrients, and tritium 

during the same year.

Acknowledgments

The cooperation of landowners who agreed to 

the installation of monitoring wells on their property is
INTRODUCTION 3

Scottsbluff

North

Platte

Wayne

Garden

City

Colby

Guymon

Wichita

Amarillo

Lubbock

Midland

Odessa

Cheyenne

SOUTH DAKOTA

NEBRASKA

KANSAS

OKLAHOMA

TEXAS

WYOMING

COLORADO

NEW MEXICO

N. Platte River

South Platte River Platte River

EXPLANATION

0

0 50 100 150 200 KILOMETERS

50 100 150 200 MILES

35°

40°

105° 100°

Elevation, in

 feet above

 sea level

1,100

7,800

Canadian R

Cimarron R

Arkansas R

S. Fork Republican R

Republican River

North Loup R

Middle Loup R

South Loup R

Loup River

Elkhorn River

COLORADO

WYOMING SOUTH DAKOTA

NEBRASKA

NEW

MEXICO

TEXAS

KANSAS

OKLAHOMA

NORTHERN

AREA

SOUTHERN

AREA

CENTRAL

AREA

HIGH PLAINS AQUIFER

Figure 1. Land-surface elevations and locations of the southern, central, and northern parts of the High Plains aquife
4 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

gratefully acknowledged. David Young, Kansas 

Geological Survey, provided the geophysical log of 

the Liberal borehole. Roy Glass (U.S. Geological 

Survey), Allen Macfarlane (Kansas Geological 

Survey), and Margaret Townsend (Kansas Geological 

Survey) provided technical reviews of the manuscript.

DESCRIPTION OF STUDY AREA

The study area includes parts of Finney, Haskell, 

Morton, Seward, and Stevens Counties in southwestern Kansas and Texas County in the Oklahoma 

Panhandle (fig. 2). The area is characterized by flat to 

rolling terrain, except in the Cimarron River valley in 

Seward County where the land-surface elevation drops 

200 feet or more from the upland to the river. The 

study area is semiarid, receiving on average about 16 

to 20 inches of precipitation annually (Weeks and 

others, 1988). Natural vegetation is sparse and consists 

mostly of grasses. More detailed descriptions of the 

study area can be found in Smith (1940), Gutentag and 

others (1981, 1984), and Weeks and others (1988).

Geohydrologic Setting

The central High Plains aquifer consists of sediments of varying ages and compositions. The Ogallala 

Formation of Pliocene age is the largest geologic unit 

in the central High Plains aquifer (Smith, 1940; 

Gutentag and others, 1984). It consists primarily of 

unconsolidated clay, silt, sand, and gravel with scattered cemented zones consisting of calcium carbonate. 

The carbonate-cemented zones typically occur near 

the top of the formation. The sediments largely were 

deposited in a braided-stream environment. The thickness of the Ogallala Formation in the study area ranges OKLAHOMA

TEXAS

NEW

MEXICO

COLORADO KANSAS

NORTHERN HIGH PLAINS AQUIFER

SOUTHERN

HIGH PLAINS AQUIFER

Amarillo

Guymon

Garden

City

Recon–3

Recon–2

Recon–4

Recon–5

Recon–1

Hugoton

Cimarron

Liberal

Rolla

Haskell

Stevens Seward

Texas

Finney

Morton

River

Canadian

River

Cimarron

Arkansas

River

2600

2200

1800

EXPLANATION

Extent of High Plains

aquifer

Nested well and site

name

Water-table well and

site name

Surface-water sampling

site

Line of equal water-table

elevation, in feet above

sea level

Contour interval 400 feet,

based on 1999

measurements

0 25 50 MILES

0 25 50 KILOMETERS

Recon–5

Rolla

Figure 2. Ground-water elevations in the central High Plains aquifer and locations of monitoring wells. 

Elevations are based on 1999 measurements (V.L. McGuire, U.S. Geological Survey, written 

commun., 2000).
DESCRIPTION OF STUDY AREA 5

from 0 to about 500 feet. Younger sedimentary 

deposits that comprise a lesser proportion of the 

aquifer in the six-county study area include alluvial 

and windblown deposits of Pleistocene and Holocene 

age (Smith, 1940; Gutentag and others, 1981, 1984). 

The contact between the Ogallala Formation and 

younger deposits has not been mapped throughout the 

study area, and mapping that contact was beyond the 

scope of this project. A generalized section of the 

geologic units in southwestern Kansas and their relation to the central High Plains aquifer is shown in 

table 1.

The central High Plains aquifer in the study area 

is underlain by rocks ranging in age from Permian to 

Late Cretaceous (fig. 3). The Permian rocks consist of 

interbedded red shale, siltstone, sandstone, limestone, 

dolomite, gypsum, anhydrite, and halite (Gutentag and 

others, 1984). Dissolution of halite and gypsum/anhydrite in rocks of Permian age by ground water and 

subsequent discharge of this mineralized water to the 

aquifer is known to occur in Seward County (Gutentag 

and others, 1981; Whittemore, 1984).

The Arkansas and Cimarron Rivers (fig. 2) are 

the two principal drainages in the study area. Both 

rivers flow from west to east. Flow in the Arkansas 

River was intermittent before the late 1990’s because 

of the large quantities of water directly diverted from 

the river and pumped from its alluvial aquifer for irrigation in Colorado and Kansas. Since the late 1990’s, 

a reduction in pumping from the alluvial aquifer in 

Colorado has resulted in increased flow in the river in 

Kansas during the irrigation season, although flow in 

the river at Garden City during 2000 still was intermittent. The Arkansas River is a losing river in the study 

area and contains brackish water (Whittemore, 2000); 

therefore, infiltration of Arkansas River water impairs 

the water quality in the central High Plains aquifer. 

Flow in the Cimarron River is intermittent upstream 

from southeastern Seward County. Flow in the 

Cimarron River becomes perennial downstream from 

that area because of discharge from the central High 

Plains aquifer. 

In 1999, the depth to water in the central High 

Plains aquifer ranged from about 50 to 300 feet below 

land surface and the saturated thickness ranged from 0 

to about 600 feet (fig. 4). Declines of about 100 feet in 

the saturated thickness have occurred in some areas 

between the Arkansas and Cimarron Rivers since irrigation pumping began in the 1950’s and 1960’s 

(McGuire and Sharpe, 1997). In the areas of greatest 

saturated thickness in Seward, Stevens, and Texas 

Counties, water-level declines have been less than 

50 feet since pumping began (McGuire and Sharpe, 

1997).

Hydraulic gradients in the central High Plains 

aquifer indicate that ground-water movement generally was from west to east (fig. 2). Gutentag and others 

(1984) estimated that water moved through the aquifer 

at an average rate of about 1 foot per day. However, 

directions and rates of ground-water movement in the 

aquifer were likely to vary areally depending on the 

intensity of well pumpage, sediment lithology, 

recharge and discharge rates, and other hydrologic 

factors.

Recharge to the central High Plains aquifer 

occurs by infiltration of irrigation water, areally 

diffuse infiltration of precipitation, infiltration of 

stormwater runoff through streambeds, and upward 

movement of water from underlying aquifers. Luckey 

and Becker (1999) estimated that mean recharge rates 

from precipitation ranged from 0.068 to 0.69 inch per 

year. 

Discharge from the aquifer occurs by well 

pumping, discharge to streams and underlying aquifers, diffuse ground-water flow across the eastern 

boundary of the aquifer, and evapotranspiration. 

Pumping for irrigation accounted for about 95 percent 

of the discharge from the aquifer in 1997 (Luckey and 

Becker, 1999). Large-scale development of irrigated 

agriculture in the study area began in the 1950’s and 

1960’s, and since that time a net depletion of water 

stored in the aquifer has occurred. The estimated 

decrease in volume of water stored in the High Plains 

aquifer in Kansas and Oklahoma between 1980 and 

1995 was about 24 million acre-feet (McGuire and 

Sharpe, 1997). In Kansas and Oklahoma, about 84 and 

90 percent of the predevelopment saturated thickness 

remained as of 1995 (McGuire and Sharpe, 1997).

Land and Water Use

Land in the study area is used primarily for 

grazing (rangeland) and the production of crops (irrigated and dryland cropland) (fig. 5). Wheat, corn, 

sorghum, and alfalfa are the main crops. Confined 

animal-feeding operations are an important industry in 

the study area, and many of the crops grown there are 

used for animal feed. The top five pesticides used in 

the study area (in terms of pounds applied) were atra
6 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999 Table 1. Generalized section of the geologic units in southwestern Kansas and their relation to the central High Plains aquifer [Modified from Gutentag and others, 1981, 1984; Macfarlane and others, 1993] Era System Series Geologic unit Thickness, feet R

central Hi

Cenozoic Quaternary Pleistocene and Holocene Alluvium 0–80 Forms part of the aqu

connected to undeTertiary deposits. Dune sand 0–75 Forms part of the aqu

Loess 0–45 Generally lies above 

Pleistocene Undifferentiated deposits 0–550 Forms part of the aqu

connected to Terti

Tertiary Pliocene Ogallala Formation 0–500 Primary geologic uni

Mesozoic Cretaceous Upper Cretaceous Niobrara Chalk 0–250 These geologic units 

part of the aquifer 

Carlile Shale 0–330 Greenhorn Limestone 0–200 Graneros Shale 0–130 Lower Cretaceous Undifferentiated rocks 0–450 Triassic-Jurassic Undifferentiated rocks 0–350 Paleozoic Permian Upper Permian Big Basin Formation 0–160 Day Creek Dolomite 0–80 Whitehorse Formation 100–350 Lower Permian Dog Creek Formation 15–60 Blaine Formation 20–150 Flowerpot Shale 1-- Cedar Hills Sandstone 1 --

1Not reported.
METHODS OF INVESTIGATION 7

zine, 2,4-D, metolachlor, alachlor, and butylate (U.S. 

Department of Agriculture, 1999).

Irrigation is the primary use of ground water in 

the study area. Of the approximately 4.7 million acrefeet of water withdrawn from the High Plains aquifer 

in Kansas and Oklahoma in 1990, 96 percent was used 

for irrigation (McGuire and Sharpe, 1997). Pumping 

for irrigation in the central High Plains began in the 

1940’s, but it was not until the 1960’s that the installation of irrigation wells proceeded at a rapid pace 

(Luckey and Becker, 1999). 

METHODS OF INVESTIGATION

Monitoring wells sampled during this study 

were installed by the U.S. Geological Survey in 1998 

and 1999. Water samples for chemical analysis were 

collected from the wells by the U.S. Geological 

Survey in 1999. An additional sample was collected 

from one of the wells (Cimarron–436) in 2000 to 

verify the chemical analysis of the 1999 sample. The 

following section of the report describes the methods 

used in the well-site-selection process, well installation, geophysical logging, water-level measurements, 

sediment-sample collection, water-sample collection, 

methods of chemical analysis, and quality-control of 

the water-quality data.

Well-site selection. Nineteen monitoring wells 

were installed at nine sites for the collection of water 

levels and samples. A single water-table well was 

installed at each of five sites, and nested wells (wells 

screened at different depths below the water table) 

were installed at four sites (fig. 2). The well sites were 

selected based on the following criteria: OKLAHOMA

TEXAS

NEW

MEXICO

COLORADO

KANSAS

NORTHERN HIGH PLAINS AQUIFER

SOUTHERN

HIGH PLAINS AQUIFER

Amarillo

Guymon

Garden

City

EXPLANATION

Geologic units underlying the

central High Plains aquifer

Upper Cretaceous

 rocks

Lower Cretaceous

 rocks

Jurassic/Triassic rocks

Permian rocks

Nested well

Water-table well

0 25 50 MILES

0 25 50 KILOMETERS

Figure 3. Geology underlying the central High Plains aquifer and locations of monitoring wells. 

Map modified from Gutentag and others (1984).
8 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

1. Water-table wells were located adjacent to irrigated 

cropland (fig. 5 and table 2).

2. Nested wells were located in areas of the aquifer 

that overlie sediments of Permian age (fig. 3). 

3. Nested wells were located in the thickest saturated 

section of the aquifer (fig. 4).

The water-table wells were located adjacent to 

irrigated cropland because water-table wells generally 

sample the most recently recharged ground water 

(McMahon, 2000) and because it was assumed that 

rates of water and agricultural-chemical application in 

that land-use setting would represent the maximum 

rates to be expected in most of the study area. Areas 

with the largest saturated thickness of the central High 

Plains aquifer were selected as nested-well sites 

because those areas may represent the most long-term 

ground-water supply in the study area. Those areas 

also overlie sediments of Permian age that contain 

mineralized water (Gutentag and others, 1981; Krothe 

and Oliver, 1982).

One surface-water sampling site was located on 

the Cimarron River (fig. 2). That site was located 

about 0.5 mile northeast of the Cimarron nested-well 

site. The land-surface elevation of the river site was 

about 75 feet lower than that at the nested-well site. 

Well installation. Boreholes used for well 

installation were drilled in 1998–99 by the U.S. 

Geological Survey using a mud-rotary drill rig. Wells 

were installed using established well-installation 

protocols (Lapham and others, 1995). Generally, wells 

were installed by placing polyvinyl chloride (PVC) 

well screen and casing in the borehole after drilling to 

the target depth, placing a sand filter in the annular 

space around the well screen and a bentonite plug on 

top of the sand filter, and sealing the annular space 

from the top of the plug to land surface using a 

high-density bentonite grout. At the nested-well sites, 

two wells were placed in each borehole. The annular 

space between well screens was sealed with bentonite.The wells were developed by bailing and pumping 

Figure 4. Saturated thickness of the central High Plains aquifer and locations of monitoring wells. 

Thicknesses based on 1999 water-level measurements and U.S. Geological Survey base-of-aquifer map 

(V.L. McGuire, U.S. Geological Survey, written commun., 2000; Gutentag and others, 1984).

TEXAS

NEW

MEXICO

COLORADO

OKLAHOMA

KANSAS

NORTHERN HIGH PLAINS AQUIFER

SOUTHERN

HIGH PLAINS AQUIFER

Amarillo

Guymon

Garden

City

EXPLANATION

Nested well

Water-table well

0 25 50 MILES

0 25 50 KILOMETERS

Saturated thickness of the central

High Plains aquifer, in feet, based

on 1999 measurements

0 to 200

200 to 400

400 to 600
METHODS OF INVESTIGATION 9

(water-table wells) or by air lifting and pumping (wells 

screened beneath the water table) immediately after 

drilling and again at least one month before sample 

collection. During the second well-development 

period, the pH, temperature, specific conductance, and 

turbidity of the water were monitored to determine 

when the well began producing water representative of 

the aquifer. Water was considered to be representative 

of the aquifer after a minimum of five casing volumes 

of water had been pumped and the change in fieldparameter values between three successive measurements (taken at 30-minute intervals) was less than 5 

percent. Well construction details are listed in table 2.

Geophysical logging. Natural gamma and 

electrical resistivity logs were obtained for each borehole before the well casings were installed. Only the 

deepest borehole was logged at the nested-well sites. 

The borehole at the Liberal nested-well site was 

logged by the Kansas Geological Survey, Lawrence, 

Kansas. The boreholes at the Cimarron, Hugoton, and 

Rolla nested-well sites were logged by Reeves Wireline, Inc., Liberal, Kansas. All other boreholes were 

logged by the U.S. Geological Survey.

Water-level measurement. Water levels in all 

of the wells were measured before water-sample 

collection by using an electric tape. Water levels were 

measured in the nested wells monthly for about 1 year.

Sediment-sample collection. Sediment 

samples were collected during drilling of the nestedwell sites. Cuttings were collected from the drillingmud return flow every 10 feet by using a wire mesh 

screen. The cuttings were rinsed in clean tap water to 

remove excess drilling mud and stored in sealed 

plastic bags after the lithology was determined. Cores 

of sediments of Permian age were collected from 

depths of 361 to 376 feet and from 421 to 425 feet 

below land surface at the Cimarron site. The 4-inchdiameter cores were wrapped in plastic and stored in 

cardboard boxes after the lithology was determined.

Figure 5. Land use overlying the central High Plains aquifer and locations of monitoring wells. 

Land-use data from Fegeas and others (1983). The data were collected from about 1977 to 1982.

KANSAS

Guymon

Liberal

Garden

City

OKLAHOMA

EXPLANATION

Generalized land use overlying

the central High Plains aquifer

Urban/Built up

Outside study area

Rangeland

Water

Wetlands

Barren land

Nested well

Water-table well

Agricultural

Irrigated lands (greater

 than 30 percent of

 cropland irrigated)

0 5 10 15 20 MILES

0 5 10 15 20 KILOMETERS
10 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999 Table 2. Construction details for monitoring wells and generalized land use around each well [All depths relative to land surface; n.d., not determined; Sch., Schedule; PVC, polyvinyl chloride; CRP, Conservation Reserve Program] Site identification Well name Construction date Elevation of land surface (feet above mean sea level) Depth to base of central High Plains aquifer (feet) Depth to water at time of construction (feet) Total depth of well (feet) Well diameter (inches) Casing and screen material Depth of open interval (feet) Dep

of scr

midpoint 

water t

(fee

Water-table well sites, central High Plains aquifer 375855100484001 Recon–1 11/12/98 2,837 n.d. 72 94 2 Sch. 40 PVC 68 to 88 6 

375734100452301 Recon–2 11/13/98 2,904 n.d. 120 133 2 Sch. 40 PVC 107 to 127

–3 

374220100422501 Recon–3 11/14/98 2,801 n.d. 161 190 2 Sch. 40 PVC 164 to 184 13 365610101484301 Recon–4 11/16/98 3,494 n.d. 274 300 2 Sch. 40 PVC 254 to 294 0 363817101213101 Recon–5 11/18/98 3,032 n.d. 282 303 2 Sch. 40 PVC 277 to 297 5 

Nested-well sites,

central High Plains aquifer

370402101394402 Rolla–193 05/25/99 3,361 399 179 198 2.5 Sch. 80 PVC 173 to 193 4 370402101394401 Rolla–366 05/26/99 3,361 399 179 371 2.5 Sch. 80 PVC 356 to 366 182 370130101180904 Hugoton–140 06/19/99 3,112 635 126 145 2.5 Sch. 80 PVC 120 to 140 4 370130101180903 Hugoton–313 06/18/99 3,112 635 127 318 2.5 Sch. 80 PVC 303 to 313 181 370130101180902 Hugoton–495 06/15/99 3,112 635 126 500 2.5 Sch. 80 PVC 485 to 495 364 370130101180901 Hugoton–617 06/14/99 3,112 635 128 627 2.5 Sch. 80 PVC 607 to 617 484 370033100534204 Liberal–160 05/07/99 2,814 576 119 165 2.5 Sch. 80 PVC 140 to 160 31 370033100534203 Liberal–319 05/06/99 2,814 576 138 324 2.5 Sch. 80 PVC 309 to 319 176 370033100534202 Liberal–436 05/03/99 2,814 576 138 441 2.5 Sch. 80 PVC 426 to 436 293 370033100534201 Liberal–570 04/30/99 2,814 576 137 581 2.5 Sch. 80 PVC 560 to 570 428 370434100405204 Cimarron–65 05/23/99 2,444 345 58 70 2.5 Sch. 80 PVC 45 to 65

–3 

370434100405203 Cimarron–210 05/20/99 2,444 345 53 215 2.5 Sch. 80 PVC 200 to 210 152 370434100405202 Cimarron–336 05/22/99 2,444 345 56 341 2.5 Sch. 80 PVC 326 to 336 275 

Sediments of Permian age

370434100405201 Cimarron–436 05/19/99 2,444 345 56 441 2.5 Sch. 80 PVC 396 to 436 360 
METHODS OF INVESTIGATION 11

Water-sample collection. A grab sample of 

water was collected from the right bank of the main 

channel of the Cimarron River near the Cimarron 

nested-well site (fig. 2) using clean 1-liter polypropylene bottles. The Cimarron River at that site occupied a broad valley, and the main channel, which was 

about 15 feet wide, flowed through a marshy area 

sustained by discharge from the central High Plains 

aquifer. The sample bottles containing river water 

were carried back to a mobile water-quality laboratory 

mounted on a truck for processing. Samples were 

processed for analyses of major ions, nutrients, trace 

elements, and tritium using the methods described 

below for the ground-water samples.

Ground-water samples were collected and 

processed in a mobile water-quality laboratory 

mounted on a truck. Water was pumped from the wells 

using a submersible piston-type pump made of stainless steel and Teflon. Sampling protocols used in this 

study are described in detail in Koterba and others 

(1995). To minimize the risk of sample contamination, 

all sample collection and preservation took place in 

dedicated environmental chambers consisting of clear 

polyethylene bags supported by tubular PVC frames. 

Sampling equipment was thoroughly decontaminated 

after sampling each well. Polyethylene bags forming 

the sample and preservation chambers were replaced 

after each sampling event.

Prior to sampling, wells were purged of stagnant 

water by pumping at least three casing volumes of 

water from the well. After the initial pumping period, 

field measurements of water temperature, specific 

conductance, pH, and dissolved oxygen were monitored every 5 minutes in a closed-cell, flow-through 

chamber until stable readings were obtained. Turbidity 

also was measured every 5 minutes using a portable 

turbidity meter. Once stable field measurements were 

obtained, water flow was redirected to the clean 

sampling chamber where water was immediately 

collected for analysis according to the NAWQA 

Program protocol (Koterba and others, 1995). 

Water samples collected for the analysis of 

major cations and trace elements were filtered using a 

0.45-μm disposable capsule filter and collected in 

precleaned plastic bottles that were rinsed with filtered 

ground water. Samples for major cations and trace 

elements were acidified to a pH of less than 2 using 

ultrapure nitric acid. Samples for major anions and 

nutrients were filtered using the capsule filter, 

collected in field-rinsed plastic bottles, and stored on 

ice with no other preservation. Additionally, a filtered 

sample was collected for field titration of carbonate 

alkalinity. Unfiltered 1-liter water samples were 

collected in the sampling chamber in unrinsed plastic 

bottles and were capped leaving 2 mL of headspace 

for the analysis of tritium. The bottle caps were 

secured with electrical tape and stored at room temperature until delivered to the laboratory for analysis. 

Water samples collected for the analysis of 

pesticides and pesticide degradation products were 

passed through a methanol-rinsed stainless steel filter 

chamber containing a baked 0.7-μm glass fiber filter. 

Pesticide samples were collected in cleaned and baked 

amber-colored glass bottles and immediately chilled 

on ice until delivery to the laboratory for analysis. 

Samples for the analysis of DOC were passed through 

0.45-μm silver filters, collected in baked amber glass 

bottles, and immediately chilled on ice until delivery 

to the laboratory for analysis. 

Elemental and X-ray diffraction analysis of 

sediment samples. Selected subsamples of the sediment cuttings and core were analyzed for their 

carbonate and organic carbon contents and their bulk 

mineralogy. The sediments used for carbon measurements were dried, sieved to remove the fraction 

greater than 2 mm in diameter, and ground using a 

mortar and pestle. Carbonate and organic carbon 

contents were determined at Huffman Laboratories, 

Golden, Colo., by (a) directly measuring the total 

carbon content using a Leco Model CR12 carbon 

analyzer, (b) directly measuring the carbonate content 

using a UIC/Coulometrics System 140 carbonate 

carbon analyzer, and (c) calculating organic carbon 

content as the difference between total and carbonate 

contents.

Bulk mineralogy was qualitatively estimated by 

using X-ray powder diffraction analysis. Sediment 

samples were dried and ground to a fine powder prior 

to X-ray analysis. Each mineral type in the sediment 

samples was classified as comprising a major, minor, 

or trace portion of the bulk mineralogy based on the 

diffraction signal intensity.

Chemical analysis of water samples. Chemical analyses of water samples were performed at the 

USGS National Water-Quality Laboratory located in 

Lakewood, Colo., with the exception of the analyses 

for tritium (USGS Tritium Laboratory, Menlo Park, 

Calif.) and chloroacetanilide herbicide degradation 

products (USGS Pesticide Research Laboratory, 

Lawrence, Kan.). Table 3 lists references for the 

methods used for each chemical analysis. 

Quality control of water-quality data. The 

quality of sample collection, processing, and analysis 
12 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

was checked by collecting quality-control samples. 

The number of quality-control samples was approximately 30 percent of the number of environmental 

samples. Quality-control samples included field 

blanks, replicate environmental samples, and field 

matrix spike samples. Field blanks verified that decontamination procedures were adequate and that field 

and laboratory procedures did not contaminate 

samples. Replicate samples assessed the combined 

effects of field and laboratory procedures on measurement variability. Matrix spike samples assessed the 

recovery bias of analytes in the spike solution.

Blank samples were collected for major ions, 

nutrients, trace elements, DOC, and pesticides. The 

source solution for blank samples was specially 

prepared organic-free or inorganic-free water provided 

by the USGS for the NAWQA Program. Blank solution was passed through all sampling equipment, and 

then a sample of the blank solution was collected 

using the same procedures as for environmental 

samples. 

Replicate samples were collected sequentially 

for all analyses except pesticides. Replication of pesticides was accomplished during the field matrix 

spiking process where replicate environmental 

samples were injected with known concentrations of 

selected pesticides. 

VERTICAL CHANGES IN LITHOLOGY

Vertical changes in lithology in the central High 

Plains aquifer were determined from geophysical and 

lithologic logs (figs. 6 and 7; table 4). The general 

lithologic descriptions were derived from examination 

of geophysical logs, cuttings, and cores and were 

supplemented by elemental carbon and X-ray diffraction analyses.

Geophysical and Lithologic Logs

Resistivity and natural-gamma logging tools 

record the electrical resistivity and natural gamma 

radioactivity of sediment, and the output from those 

logs can be used to evaluate lithologic variability in 

aquifers. Sands and gravels are resistive to the flow of 

electrical current used in resistivity logging; therefore, 

one can generally attribute the increase in resistivity in 

those logs to increased proportions of sand and gravel 

in the aquifer. However, other factors beside lithology 

can affect resistivity logs, including degree of water 

saturation, sediment mineralogy, and salinity of water. 

The presence of mineralized water in sandy deposits 

would produce small resistivities, possibly leading 

to the incorrect conclusion that the aquifer consisted 

of fine-grained material. Mineralized ground water 

affected the resistivity logs from the Recon–1 (below 

the 70-foot depth; fig. 6a), Recon–2 (below the 

120-foot depth; fig. 6b), and Cimarron (below the 

285-foot depth; fig. 7d) boreholes. Natural gamma 

logs record the gamma radioactivity emitted by naturally occurring radioactive elements in shale and clay. 

The increase in gamma activity recorded by natural 

gamma logs generally is attributed to increased 

proportions of clay in the aquifer or changes in clay 

mineralogy. 

Table 3. Methods used to analyze water samples

Constituent or

constituent group Analytical method Reference

Pesticides and metabolites, National 

Water-Quality Laboratory

Solid phase extraction using a C–18 cartridge and capillary-column gas 

chromatography/mass spectrometry

Zaugg and others (1995)

Pesticide metabolites, Pesticide 

Research Laboratory

High performance liquid chromatography/mass spectrometry Hostetler and Thurman 

(1999)

Dissolved organic carbon Ultraviolet-light promoted persulfate oxidation and infrared spectrometry Brenton and Arnett (1993)

Major ions Atomic absorption spectrometry Fishman (1993)

Trace elements Inductively coupled plasma-mass spectrometry Faires (1993)

Nutrients Various methods Fishman (1993)

Tritium Electrolytic enrichment with gas counting Michel and Schroeder 

(1994)
VERTICAL CHANGES IN LITHOLOGY 13 Figure 6. Natural gamma and resistivity logs for water-table-well boreholes (a) Recon–1, (b) Recon–2, (c) Recon–3, (d) Recon–4, and (e) 

300 0 50 100 150 0 50 100 150 0 50 100 

0 50 100 150 0 50 100 150

250200150100

50

0

(a) (b) (c) (d) 

Water level attime of drilling

Well screen

Resistivity

Natural gamma

DEPTH BELOW LAND SURFACE, IN FEET

NATURAL GAMMA LOG, IN COUNTS PER SECOND, AND RESISTIVITY LOG, IN OHM-METERS
14 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999 

100 150 0 50 100 150 0 50

700600500400300200100

0

0 50 0 50 100 150

NATURAL GAMMA LOG, IN COUNTS PER SECOND, AND RESISTIVITY LOG, IN OHM-M

DEPTH BELOW LAND SURFACE, IN FEET

(a) (b) (c) 

Water level attime of drilling

Base of aquifer Well screen

Natural gamma

Resistivity

Figure 7. Natural gamma and resistivity logs for nested-well boreholes (

a) Rolla, (

b) Hugoton, (

c) Liberal, and (

d) Cimarron.
VERTICAL CHANGES IN LITHOLOGY 15

Table 4. Lithologic description of drill cuttings and core

[All depths relative to land surface; n.d., not determined]

Borehole name: Recon–1

Completion date: 11/12/98

Depth to base of aquifer (feet): n.d.

Depth to water at time of drilling (feet): 72

Total depth of borehole (feet): 101

Depth interval

(feet below 

land surface)

Lithology

0–5 Silty sand, dark brown

 5–10 Clayey silt, tan

10–15 Fine silty sand with some clay, tan

15–17 Fine sand, reddish brown

17–18 Clay, tan 

18–30 Medium sand with some silt, tan

30–40 Sandy clay, light tan

40–50 Clayey sand, tan

50–55 Medium gravelly sand

55–70 Medium to coarse sand

70–75 Medium sand with some silt

75–101 Fine to medium silty sand

Borehole name: Recon–3

Completion date: 11/14/98

Depth to base of aquifer (feet): n.d.

Depth to water at time of drilling (feet): 161

Total depth of borehole (feet): 195

Depth interval

(feet below 

land surface)

Lithology

0–10 Silty sand with some clay, dark brown

10–20 Light brown silty sand, light brown

20–35 Fine silty sand, tan

35–55 Fine to medium sand, tan

55–125 Medium to coarse sand, tan

125–130 Sandy clay

130–135 Medium to coarse sand

135–140 Sandy clay

140–165 Medium to coarse sand

165–175 Clayey sand

175–195 Fine to medium silty sand

Table 4.—Continued

Borehole name: Recon–4

Completion date: 11/16/98

Depth to base of aquifer (feet): n.d.

Depth to water at time of drilling (feet): 274

Total depth of borehole (feet): 305

Depth interval

(feet below 

land surface)

Lithology

0–5 Clayey sand, dark reddish brown

5–30 Clayey sand, reddish brown

30–100 Silty sand, light reddish brown

100–130 Fine silty sand, tan

130–140 Fine silty sand with caliche, tan

140–160 Clayey sand, light tan

160–165 Clayey sand with caliche, light tan

165–180 Silty sand, light tan

180–210 Silty sand with caliche, light tan

210–220 Sand with caliche, light tan

220–240 Silty sand with clay, light tan

240–260 Silty sand, light tan

260–280 Medium sand

280–305 Silty sand

Borehole name: Recon–5

Completion date: 11/18/98

Depth to base of aquifer (feet): n.d.

Depth to water at time of drilling (feet): 282

Total depth of borehole (feet): 305

Depth interval

(feet below 

land surface)

Lithology

0–5 Sandy clay, dark brown

5–10 Sandy clay, light brown

10–40 Caliche and sand, light brown

40–50 Fine sand with caliche stringers

50–60 Fine to medium sand

60–65 Medium sand

65–90 Sandy clay, light brown

90–100 Medium sand

100–145 Clay, light brown, with sand stringers

145–150 Sandy clay

150–170 Medium sand

170–180 Clay, light brown, with sand stringers

180–195 Sandy clay

195–215 Medium sand

215–220 Sandy clay

220–230 Medium sand

230–290 Sandy silty clay

290–295 Dense clay

295–305 Clayey sand
16 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

Table 4. Lithologic description of drill cuttings and 

core—Continued

[All depths relative to land surface; n.d., not determined]

Borehole name: Rolla

Completion date: 05/26/99

Depth to base of aquifer (feet): 399

Depth to water at time of drilling (feet): 179

Total depth of borehole (feet): 400

Depth interval

(feet below 

land surface)

Lithology

0–30 Fine sand, red

30–40 Fine silty sand

40–50 Fine silty sand with gravel

50–70 Fine sand with caliche, light tan

70–90 Medium to coarse sand with gravel and 

caliche

90–100 Coarse sand and gravel

100–110 Sandy silt with clay, tan

110–140 Silty sand with caliche, light red

140–150 Coarse sand

150–210 Fine silty sand

210–230 Fine sand with caliche

230–240 Fine sand with clay stringers

240–250 Silty sand

250–260 Interbedded fine sand and clay

260–280 Interbedded sandy silt and clay

280–320 Silty sand

320–330 fine to medium sand

330–340 Fine to medium sand, light pinkish red

340–360 Fine sand, light pinkish red

360–390 Medium to coarse sand, light pinkish red 

390–399 Medium sand, light pinkish red

399–400 Hard sandy clay, red and yellow

Table 4.—Continued

Borehole name: Hugoton

Completion date: 06/14/99

Depth to base of aquifer (feet): 635

Depth to water at time of drilling (feet): 128

Total depth of borehole (feet): 640

Depth interval

(feet below 

land surface)

Lithology

0–10 Silty sand with clay, dark brown

10–30 Fine silty sand, light brown

30–50 Fine sand

50–100 Fine silty sand with caliche

100–110 Clay, brown

110–120 Silty clay, brown

120–140 Fine sand with caliche

140–180 Clay with caliche, brown

180–190 Sandy clay

190–200 Silty sand

200–230 Medium to coarse sand with clay stringers

230–240 Clayey sand

240–260 Sandy clay, brown

260–270 Silty sand with gravel

270–300 Fine to medium silty sand

300–310 Fine sand

310–325 Medium to coarse sand

325–370 Brown clay

370–375 Fine sand

375–390 Sandy clay

390–410 Fine silty sand with clay stringers

410–460 Medium to coarse sand with gravel

460–470 Sandy clay, brown

470–520 Medium to coarse sand

520–550 Clayey sand with caliche, brown and gray

550–580 Clay, blue/gray/brown

580–590 Medium clayey sand

590–600 Medium to coarse clayey sand

600–635 Fine to coarse sand with gravel near base

635–640 Medium sandy clay, red
VERTICAL CHANGES IN LITHOLOGY 17

Table 4. Lithologic description of drill cuttings and 

core—Continued

[All depths relative to land surface; n.d., not determined]

Borehole name: Liberal

Completion date: 04/30/99

Depth to base of aquifer (feet): 576

Depth to water at time of drilling (feet): 137

Total depth of borehole (feet): 583

Depth interval

(feet below 

land surface)

Lithology

0–5 Silty sand, dark brown

5–20 Fine sandy silt, brown

20–50 Fine sandy silt with caliche, tan

50–60 Fine silty sand, brown

60–80 Fine sandy silt, tan

80–95 Fine to medium sand

95–115 Clayey silt

115–130 Fine clayey sand

130–135 Clay, tan and white

135–150 Silty clay, tan and white

150–160 Clay and caliche, white

160–170 Brown clay 

170–180 Fine silty sand

180–190 Fine to medium sand

190–240 Fine sand, silty near top, with caliche

240–260 Fine to medium sand, yellow

260–270 Fine to medium sand, brown

270–310 Fine clayey and silty sand

310–330 Fine to medium sand

330–350 Silty sand

350–360 Fine to medium sand

360–390 Medium to coarse sand with caliche

390–400 Silty sand

400–440 Medium to coarse sand

440–460 Siltstone, becoming sandier near bottom

460–470 Fine sand

470–480 Fine to medium sand

480–490 Siltstone

490–510 Medium sand

510–550 Interbedded sand and siltsone

550–560 Sand, yellow

560–570 Medium sand with 5 percent red clay

570–576 Medium sand and 40 percent red clay

576–582 More than 50 percent red clay, weathered red 

bed

582–583 Hard, dense red clay, unweathered red bed

Table 4.—Continued

Borehole name: Cimarron

Completion date: 05/19/99

Depth to base of aquifer (feet): 345

Depth to water at time of drilling (feet): 56

Total depth of borehole (feet): 441

Depth interval

(feet below 

land surface)

Lithology

0–15 Fine sand and silt, light red

15–30 Sandy clay, brown

30–50 Clay, brown

50–60 Sandy clay, brown, with gravel

60–70 Medium to coarse sand

70–90 Sandy clay, brown

90–120 Gray clay with some silt

120–130 Fine sandy clay, brown

130–140 Clayey sand, brown

140–160 Medium to coarse sand

160–170 Clayey sand, brown

170–290 Medium to coarse sand with some clay 

stringers

290–300 Silty sand with gravel 

300–340 Sandy clay

340–345 Medium sand with red clay

345–360 Dense clay, clayey sand, silt, pink weathered 

redbed

360–362 Sandy silty clay, pink, with carbonate-filled 

fracture,

362–365 Dense clay, red, with gray reduced spots, 

unweathered red bed

365–375 Interbedded soft clay and hard claystone, 

carbonate-filled fractures, gray reduction 

spots, one fracture with slickensides

375–441 Interbedded clay and siltsone, red
18 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

The geophysical and lithologic logs indicate that 

the central High Plains aquifer at the well sites was a 

mix of clay, silt, sand, and gravel that was largely 

unconsolidated, except for cemented caliche layers 

that occurred in some places in the aquifer (table 4). 

There was no obvious trend in lithology toward finer 

or coarser grained material with depth in the aquifer. 

Fine to coarse sand was penetrated, however, at the 

base of the aquifer at the Rolla, Hugoton, and Liberal 

boreholes (table 4). The occurrence of basal sand and 

gravel also was reported in the southern High Plains 

aquifer (Seni, 1980). The geophysical and lithologic 

logs indicate that intervals of sand and gravel occurred 

at various depths in the unsaturated zone and aquifer. 

For example, several layers of medium to coarse 

sand were penetrated in the unsaturated zone at the 

Recon–3 site (table 4 and fig. 6c). Coarse-grained 

sediments under dry conditions in the unsaturated 

zone may actually inhibit the movement of water and 

solutes from land surface to the water table compared 

with fine-grained sediments. This is because the 

hydraulic conductivity of coarse-grained sediments 

may be smaller than that of finer grained sediments 

under dry conditions (Tindall and Kunkel, p. 189, 

1999). Relatively thick layers of coarse-grained sediment were present below the water table in the 

Hugoton borehole at depths from about 290 to 330, 

410 to 450, 470 to 520, and 600 to 635 feet below 

land surface (table 4 and fig. 7b). For the most part, 

the intervals of medium to coarse sand and gravel 

below the water table were less than 50 feet thick. One 

exception was a 120-foot-thick medium to coarse 

sand interval in the Cimarron borehole at the 170- to 

290-foot depth interval. Those intervals of coarsegrained sediment are the principal water-bearing units 

in the aquifer at those sites.

Thick clay layers were penetrated during 

drilling at most sites. In the unsaturated zone at the 

Recon-5 site, sandy clay and clay were penetrated 

from 65 to 90 and 100 to 145 feet below land surface 

(table 4 and fig. 6e). In the Hugoton borehole, a brown 

clay was penetrated below the water table in the 325 to 

370 foot depth interval (table 4 and fig. 7b). A tan and 

white silty clay was penetrated in the 130- to 150-foot 

depth interval in the Liberal borehole (table 4 and 

fig. 6c). Water-level data indicate that clay intervals 

such as those created locally confined conditions in 

the aquifer (see discussion in the section “Vertical 

Hydraulic Gradients”).

The Cimarron borehole was the only one that 

penetrated the unweathered sediments directly below 

the aquifer to any appreciable depth, approximately 

80 feet. Cuttings and cores were available for that site. 

Limited lithologic information from cuttings was 

available for the sediments underlying the aquifer at 

the Rolla, Hugoton, and Liberal boreholes. Sediments 

underlying the aquifer in those locations are Permian 

in age (fig. 3; Macfarlane and others, 1993). Sediment 

retrieved from the drill bit at the bottom of the Liberal 

borehole indicated that the unweathered sediments of 

Permian age at that site consisted of hard, dense, red 

clay with no evidence of fractures. About 6 feet of 

weathered sediment of Permian age overlies the 

unweathered sediment. The unweathered sediments of 

Permian age at the Cimarron borehole were quite variable lithologically, ranging from dense clay to fractured siltstone (table 4). The numerous fractures in the 

unweathered sediment were either lined or completely 

filled with carbonate cement. The presence of 

secondary cement in the fractures indicates that water 

had moved through the fractures.

Elemental and X-Ray Diffraction Analyses

Measured amounts of carbonate and organic 

carbon in the sediments ranged from less than 0.02 to 

3.22 and less than 0.05 to 0.60 weight percent, respectively (table 5). Carbonate carbon in the aquifer 

occurred as caliche layers and cemented nodules, 

whereas carbonate in the sediments of Permian age 

occurred as pore- and fracture-filling cements and as 

fine-grained matrix material. The carbonate carbon in 

the aquifer and in the cements in sediments of Permian 

age was calcite. The fine-grained carbonate carbon 

matrix in sediments of Permian age was dolomite. The 

largest measured organic carbon content, 0.60 weight 

percent, occurred in a sandy brown clay from the 

Cimarron borehole. However, the five other finegrained sediments that were measured contained less 

than 0.25 weight percent organic carbon. Organic 

carbon tends to be concentrated in fine-grained sediments; therefore, sand and gravel in the aquifer also 

probably contained less than 0.25 weight percent 

organic carbon. The one medium to coarse sand 

sample analyzed for organic carbon contained less 

than 0.05 weight percent (table 5). The general lack of 

organic carbon in the aquifer probably limits the 

amount of natural microbial activity in the aquifer that 

could affect water quality.
VERTICAL CHANGES IN LITHOLOGY 19

Table 5. Results of elemental and X-ray diffraction analyses

[--, not measured; <, less than indicated value]

Borehole

Depth

(feet below

land surface)

Lithology

X-ray diffraction results Carbon content

(weight percent)

Mineral

phase

Relative

abundance Carbonate Organic

Rolla 360 Medium to coarse sand, 

light pinkish red

Quartz Major -- --

Potassium feldspar Major -- --

Albite Minor -- --

Calcite Minor -- --

Muscovite Trace -- --

Montmorillonite Trace -- --

Hugoton 200 Medium to coarse sand 

with clay stringers

-- -- 3.22 <0.05

240 Sandy clay, brown -- -- 1.77 0.06

380 Sandy clay -- -- 0.68 0.12

610 Fine to coarse sand Quartz Major -- --

Anorthoclase Major -- --

Calcite Minor -- --

Albite Minor -- --

Liberal 430 Medium to coarse sand Quartz Major -- --

Potassium feldspar Major -- --

Albite Minor -- --

Muscovite Trace -- --

520 Siltstone -- -- <0.02 <0.05

Cimarron 80 Sandy clay, brown -- -- 1.71 0.60

160 Clayey sand, brown -- -- 0.65 0.21

200 Medium to coarse sand Quartz Major -- --

Potassium feldspar Major -- --

Albite Minor -- --

Calcite Trace -- --

Muscovite Trace -- --

361 Sandy, silty clay Quartz Major 0.19 <0.05

Microcline Minor -- --

Montmorillonite Minor -- --

Muscovite Minor -- --

Albite Minor -- --

Hematite Trace -- --

Chlorite Trace -- --

Kaolinite Trace -- --

361 Carbonate-filled fracture Calcite Major -- --

Quartz Minor -- --

Microcline Minor -- --

Muscovite Trace -- --

Albite Trace -- --

422 Siltstone, red Quartz Major 0.74 0.07

Dolomite Minor -- --

Orthoclase Minor -- --

Albite Minor -- --

Muscovite Minor -- --

Montmorillonite Minor -- --

Kaolinite Trace -- --
20 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

Quartz was the major mineral detected by X-ray 

diffraction analysis of the aquifer sediments (table 5). 

Various feldspar minerals were next largest in abundance after quartz. Less abundant minerals in the 

aquifer included calcite, muscovite, and montmorillonite. Quartz also was the major mineral detected in 

the detrital sediments of Permian age. However, 

calcite was the major authigenic mineral in the fracture-filling cement. Neither halite, anhydrite, nor 

gypsum was detected in the sediments of Permian age 

using X-ray diffraction analysis. Those minerals are 

known to occur in the sediments of Permian age and 

may occur in sediments at the base of the Ogallala 

Formation (Smith, 1940; Gutentag and others, 1981). 

VERTICAL HYDRAULIC GRADIENTS

The potential for upward or downward water 

movement at any given location in an aquifer can be 

determined by measuring water-surface elevations in 

wells screened at different depths in the aquifer at that 

location. Those measured water-surface elevations are 

referred to as “hydraulic heads.” Ground water moves 

from areas of high hydraulic head to areas of low 

hydraulic head. The vertical hydraulic gradient in an 

aquifer is defined as the difference in hydraulic head 

divided by the distance between screened intervals in 

two wells screened at different depths in the aquifer. 

The potential for upward or downward water movement in an aquifer is directly proportional to the 

hydraulic gradient.

Vertical hydraulic gradients in the central High 

Plains aquifer varied spatially and temporally in the 

aquifer (fig. 8) and were affected by lithology and 

pumping in nearby wells. A large downward gradient 

that existed between the shallowest well and the three 

deeper wells at the Liberal site probably was created 

by pumping from the nearby City of Liberal well field, 

which lowered heads in the deep part of the aquifer 

where those supply wells were screened. A clay layer 

at a depth of 130 to 170 feet (table 4, fig. 7c) isolated 

the shallow part of the aquifer from the pumping 

effects (fig. 8c). The downward gradient at that site 

probably persisted over time because the municipal 

wells pumped throughout the year. Superimposed on 

the drawdown caused by pumping at the municipal 

well field was seasonal pumping of irrigation wells, 

which produced additional drawdowns during the 

summers of 1999 and 2000. 

Seasonal pumping of a nearby irrigation well 

produced downward hydraulic gradients between the 

shallowest well and the three deeper wells at the 

Hugoton site that did not persist throughout the year 

(fig. 8b). An irrigation well was located about 0.3 mile 

from the nested wells and was screened in the bottom 

250 feet of the aquifer. Pumping of that well during the 

1999 and 2000 irrigation seasons (typically from about 

the end of May through the middle of September) 

caused water levels in the three deep monitoring wells 

to drop from about 20 to 60 feet relative to the water 

level in the shallow well. The water levels in the 

deeper monitoring wells recovered to within 1 foot of 

the shallow water level after the irrigation season 

ended in 1999 (fig. 8b). Clay layers at depths of 180 to 

190, 240 to 260, and 325 to 370 feet (table 4) probably 

helped to isolate the shallow monitoring well from the 

effects of pumping deeper in the aquifer.

The water-level data from the Liberal and 

Hugoton sites indicate that clay layers in the aquifer 

caused local confinement of the deep ground water. 

That local confinement may help protect deep water in 

the aquifer from the downward movement of contaminants. However, in the absence of clay layers, 

pumping could draw more water, as well as more 

contaminants, deeper into the aquifer. The lowering of 

heads that was produced by pumping deep in the 

aquifer could also have induced the upward migration 

of mineralized water into the aquifer from underlying 

geologic units.

Unlike the Liberal and Hugoton sites, where the 

hydraulic gradients were downward, the hydraulic 

gradients at the Cimarron site were upward from the 

two deeper wells screened in the aquifer to the watertable well (fig. 8d). The apparent difference in 

hydraulic head between the two deep wells was less 

than 1 foot, whereas the head difference between the 

two deep wells and the water-table well was about 2 to 

2.5 feet. On the basis of the depth of the water table 

below land surface in Cimarron–65 (about 55 feet) and 

the land-surface elevation difference between the river 

and Cimarron–65 (about 75 feet), it is likely that there 

also was an upward hydraulic gradient between the 

aquifer and the river at that site. The Cimarron River 

was located about 0.5 mile northeast of the Cimarron 

well site. The hydraulic-head and elevation data indicate that there was potential for deep water in the 

aquifer to discharge to the river in the vicinity of the 

Cimarron well site. A seepage run conducted on the
VERTICAL HYDRAULIC GRADIENTS 21 Date Date

5/1/99 11/1/99 5/1/00 11/1/00 5/1/99 11/1/99 55/1/99 11/1/99 5/1/00 11/1/00 5/1/99 11/1/99 5

3,1843,1833,1823,1813,180

2,9902,9802,9602,9502,9702,9402,9302,9202,3922,3912,3902,3892,3882,387

2,7002,6952,6902,6852,6802,6752,6702,665

GROUND-WATER ELEVATION, 2,660

IN FEET ABOVE SEA LEVEL

GROUND-WATER ELEVATION,

IN FEET ABOVE SEA LEVEL

(a) 

(c) 

Hugoton–Hugoton–Hugoton–Hugoton–

Cimarron–65 CCimarron–210 C

Rolla–193Rolla–366

Liberal–160Liberal–319Liberal–436Liberal–570

Figure 8. Ground-water elevations at the nested-well sites (

a) Rolla, (

b) Hugoton, (

c) Liberal, and (

d) Cimarron. Well Cimarron

sediments of Permian age. All other wells were screened in the central High Plains aquifer.
22 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

Cimarron River near the Cimarron site by Gutentag 

and others (1981) indicated that ground-water 

discharge from the aquifer contributed flow to the 

river at a rate of about 1.7 ft3/s per mile of stream 

channel. It is likely that the rate of ground-water 

discharge decreased since those measurements were 

taken because of water-level declines in the aquifer. 

Nevertheless, the upward hydraulic gradient at the 

Cimarron site and the observed perennial flow in the 

Cimarron River near the Cimarron site indicate that 

water in the central High Plains aquifer still discharged 

to the river in 1999.

Some hydraulic heads in the aquifer at the 

Cimarron site were lower than the heads in the underlying sediments of Permian age (fig. 8d). Thus, there 

was an upward gradient directed from the sediments of 

Permian age to the aquifer. Estimating the magnitude 

of the upward gradient and the amount of upward flow 

was hampered because water in the sediments of 

Permian age was more dense than freshwater in the 

aquifer. The density of the water in the sediments of 

Permian age was 1.012 grams per cubic centimeter. 

For comparison, the densities of freshwater and 

seawater are 1 and 1.023 grams per cubic centimeter, 

respectively. Although it is possible to calculate an 

equivalent freshwater head for the deep Cimarron 

well, that freshwater head could be used to calculate 

the hydraulic gradient between that and another well 

only if the two wells were screened at the same elevation (Reilly, 1993). Nevertheless, the uncorrected head 

data and chemical data (discussed in the following 

sections) indicate that there was diffusion or advective 

movement of mineralized water from the sediments of 

Permian age to the aquifer.

VERTICAL GRADIENTS IN WATER

CHEMISTRY

Concentrations of tritium, major ions, nitrate, 

arsenic, and pesticides varied with depth in the central 

High Plains aquifer. Some of those chemical gradients 

were the result of chemical inputs from the land 

surface, upward leakage of mineralized water from the 

underlying sediments of Permian age, and recharge of 

mineralized water from the Arkansas River. This 

section presents the chemical data and discusses 

processes that could explain the observed vertical 

gradients in water chemistry.

Tritium

Determining the apparent age of ground water is 

important because it can be indicative of an aquifer’s 

vulnerability to contamination from sources at the land 

surface. Aquifers that contain recently recharged water 

are more vulnerable to contamination originating at 

land surface than are aquifers containing no recently 

recharged water. Several methods are available for 

age-dating ground water, although the suitability of the 

methods differs depending on various factors 

including the recharge age of the water and the thickness of the unsaturated zone. Results of a tritium 

method of age-dating are discussed in this section. 

Tritium is a radioactive isotope of hydrogen that is 

present in some water molecules. Tritium in ground 

water of the central High Plains aquifer ultimately 

came from precipitation that recharged the aquifer. 

Because tritium is radioactive, with a half-life of 

12.43 years, its concentration in water decreases over 

time due to radioactive decay. Before the onset of 

atmospheric testing of nuclear weapons in the early 

1950’s, the tritium content of precipitation in the study 

area was probably on the order of 8 TU (Thatcher, 

1962). Therefore, ground water totally derived from 

precipitation that fell before the early 1950’s would 

contain less than 0.5 TU in 1999. The tritium content 

of precipitation increased substantially after the onset 

of atmospheric nuclear weapons testing but has slowly 

decreased since its peak in the early 1960’s. For 

example, the tritium content of precipitation at a 

measurement site in Albuquerque, New Mexico, the 

closest tritium measurement site to the study area, 

peaked at about 2,000 to 4,500 TU in 1963–64, 

whereas the tritium content in precipitation ranged 

from about 6 to 10 TU in 1991 (the most recent data) 

(International Atomic Energy Agency/World Meteorological Organization, 1998). Even with the variability 

in the tritium content of precipitation over time, 

ground water totally derived from precipitation that 

fell since the early 1950’s would contain more than 

0.5 TU in 1999. 

At the time of sampling in 1999, all of the water 

samples collected from more than 30 feet below 

the water table contained less than 0.5 TU of tritium 

(table 6 and fig. 9), indicating that water was 

recharged by precipitation that fell before the early 

1950’s. In contrast, all but two of the water samples 

collected from less than 30 feet below the water table 

contained more than 0.5 TU (fig. 9), indicating that
VERTICAL GRADIENTS IN WATER CHEMISTRY 23

Table 6. Physical properties and concentrations of major ions, nutrients, trace elements, and tritium in water from the Cimarron River and sHigh Plains aquifer and sediments of Permian age[μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, Celsius; mg/L, milligrams per liter; CaCO3, calcium carbonate; μg/L, micrograms per liter; --, not analyzed 

Station identification Well name Sample date

Depth to water

(feet below

land surface)

Depth of screen 

midpoint below

water table

(feet)

Specific

conductance

(μS/cm)

pH, whole 

water, field

(standard

units)

Tem

370434100405205 Cimarron River 09/01/99 -- -- 1,044 8.04 

Water-table well sites,

central High Plains aquifer

375855100484001 Recon–1 02/03/99 70 8 5,130 6.96 375734100452301 Recon–2 02/02/99 121 −4 1,635 7.00 374220100422501 Recon–3 02/04/99 161 13 1,001 7.19 365610101484301 Recon–4 02/05/99 273 1 632 7.69 363817101213101 Recon–5 02/17/99 279 8 619 7.73 

Nested-well sites,

central High Plains aquifer

370402101394402 Rolla–193 08/30/99 179 4 459 7.70 2370402101394401 Rolla–366 08/30/99 180 181 1,136 7.47 370130101180904 Hugoton–140 08/29/99 133 −3 704 7.65 2370130101180903 Hugoton–313 08/29/99 154 154 602 7.50 370130101180902 Hugoton–495 08/28/99 172 318 560 7.66 2370130101180901 Hugoton–617 08/28/99 175 437 578 7.64 2370033100534204 Liberal–160 08/27/99 117 33 540 7.65 2370033100534203 Liberal–319 08/27/99 149 165 513 7.72 370033100534202 Liberal–436 08/26/99 147 284 504 7.59 2370033100534201 Liberal–570 08/26/99 147 418 583 7.47 2370434100405204 Cimarron–65 09/01/99 56 −1 645 7.59 370434100405203 Cimarron–210 08/31/99 54 151 671 7.50 370434100405202 Cimarron–336 09/01/99 54 277 6,360 7.13 

Sediments of Permian age

370434100405201 Cimarron–436 08/31/99 55 361 23,200 7.15 2

10/18/00 55 361 22,700 7.30 
24 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999 Table 6. Physical properties and concentrations of major ions, nutrients, trace elements, and tritium in water from the Cimarron River and s

High Plains aquifer and sediments of Permian age—Continued

[μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, Celsius; mg/L, milligrams per liter; CaCO3, calcium carbonate; μg/L, micrograms per liter; --, not analyzed 

Station identification Well name

Alkalinity, 

filtered, field

(mg/L as CaCO3)

Calcium,

dissolved

(mg/L as Ca)

Magnesium,

dissolved

(mg/L as Mg)

Sodium,

dissolved

(mg/L as Na)

Potassium,

dissolved

(mg/L as K)

C

di

(mg

370434100405205 Cimarron River -- 81.4 27.7 87.9 6.69 

Water-table well sites,

central High Plains aquifer

375855100484001 Recon–1 290 486 260 525 17.2 2375734100452301 Recon–2 340 145 69.6 81.6 8.89 1374220100422501 Recon–3 240 113 17.0 73.5 3.95 365610101484301 Recon–4 142 36.3 30.7 47.5 6.07 363817101213101 Recon–5 168 44.2 31.5 26.5 6.79 

Nested-well sites,

central High Plains aquifer

370402101394402 Rolla–193 174 42.8 6.52 42.5 4.21 370402101394401 Rolla–366 144 133 41.6 47.9 3.60 370130101180904 Hugoton–140 206 39.1 11.7 74.3 8.32 370130101180903 Hugoton–313 149 70.5 21.5 19.8 3.42 370130101180902 Hugoton–495 162 63.7 18.9 19.7 3.32 370130101180901 Hugoton–617 160 66.9 19.3 20.2 3.29 370033100534204 Liberal–160 208 38.6 34.6 17.9 3.49 370033100534203 Liberal–319 174 44.2 23.7 25.2 3.48 370033100534202 Liberal–436 162 41.8 22.5 26.5 3.78 370033100534201 Liberal–570 182 46.7 24.1 36.1 3.88 370434100405204 Cimarron–65 157 54.4 14.1 48.8 4.66 370434100405203 Cimarron–210 162 67.1 18.8 41.8 3.67 370434100405202 Cimarron–336 144 300 148 761 10.7 1,8

Sediments of Permian age

370434100405201 Cimarron–436 88 776 431 3,836 17.7 7,6

92 749 431 4,051 20.0 7,8
VERTICAL GRADIENTS IN WATER CHEMISTRY 25

Table 6. Physical properties and concentrations of major ions, nutrients, trace elements, and tritium in water from the Cimarron River and s

High Plains aquifer and sediments of Permian age—Continued

[μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, Celsius; mg/L, milligrams per liter; CaCO3, calcium carbonate; μg/L, micrograms per liter; --, not analyzed 

Station identification Well name

Bromide,

dissolved

(mg/L as Br)

Fluoride,

dissolved

(mg/L as F)

Silica,

dissolved

(mg/L as SiO2)

Ammonium,

dissolved

(mg/L as N)

Nitrit

dissol

(mg/L a

370434100405205 Cimarron River 0.13 0.76 24.8 0.02 0.0

Water-table well sites,

central High Plains aquifer

375855100484001 Recon–1 1.48 0.61 39.6 0.04 <0.0375734100452301 Recon–2 0.25 0.69 46.8 <0.02 <0.0374220100422501 Recon–3 0.26 0.28 24.5 <0.02 <0.0365610101484301 Recon–4 0.27 1.8 23.5 <0.02 <0.0363817101213101 Recon–5 0.14 1.9 29.4 <0.02 <0.0

Nested-well sites,

central High Plains aquifer

370402101394402 Rolla–193 0.07 0.18 29.4 0.25 0.1370402101394401 Rolla–366 0.16 0.27 30.3 <0.02 <0.0370130101180904 Hugoton–140 0.13 0.49 34.1 1.07 0.0370130101180903 Hugoton–313 0.14 0.33 31.8 <0.02 <0.0370130101180902 Hugoton–495 0.13 0.34 30.0 <0.02 <0.0370130101180901 Hugoton–617 0.13 0.34 30.5 <0.02 <0.0370033100534204 Liberal–160 0.10 3.5 54.3 <0.02 <0.0370033100534203 Liberal–319 0.11 0.84 31.4 <0.02 <0.0370033100534202 Liberal–436 0.11 0.55 28.7 <0.02 <0.0370033100534201 Liberal–570 0.09 0.57 27.4 <0.02 <0.0370434100405204 Cimarron–65 0.08 0.88 22.9 0.18 0.0370434100405203 Cimarron–210 0.14 0.55 26.9 <0.02 <0.0370434100405202 Cimarron–336 0.42 0.47 26.9 <0.02 <0.0

Sediments of Permian age

370434100405201 Cimarron–436 0.26 0.26 38.4 <0.02 <0.0

1.36 0.25 36.1 0.05 <0.0
26 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999 Table 6. Physical properties and concentrations of major ions, nutrients, trace elements, and tritium in water from the Cimarron River and s

High Plains aquifer and sediments of Permian age—Continued[μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, Celsius; mg/L, milligrams per liter; CaCO3, calcium carbonate; μg/L, micrograms per liter; --, not analyzed 

Station identification Well name

Nitrite plus nitrate,

dissolved

(mg/L as N)

Orthophosphate,

dissolved

(mg/L as P)

Phosphorus,

dissolved

(mg/L as P)

Organic carbon,

dissolved

(mg/L as C)

Solids, re

at 180

dissol

(mg/

370434100405205 Cimarron River 0.79 0.04 0.058 -- 64

Water-table well sites,

central High Plains aquifer

375855100484001 Recon–1 8.28 0.03 0.023 -- 4,91375734100452301 Recon–2 54.4 0.02 0.009 -- 1,05374220100422501 Recon–3 22.0 0.02 0.007 -- 64365610101484301 Recon–4 3.38 0.02 0.013 -- 37363817101213101 Recon–5 3.80 <0.01 0.005 -- 39

Nested-well sites,

central High Plains aquifer

370402101394402 Rolla–193 5.71 <0.01 0.009 -- 29370402101394401 Rolla–366 2.40 <0.01 0.004 0.5 86370130101180904 Hugoton–140 2.24 <0.01 0.01 1.6 37370130101180903 Hugoton–313 2.56 <0.01 0.004 1.5 39370130101180902 Hugoton–495 2.50 <0.01 <0.004 0.3 36370130101180901 Hugoton–617 2.30 <0.01 <0.004 0.4 38370033100534204 Liberal–160 1.90 <0.01 0.004 0.5 33370033100534203 Liberal–319 3.15 <0.01 0.008 0.4 31370033100534202 Liberal–436 3.06 <0.01 0.009 0.4 30370033100534201 Liberal–570 2.36 <0.01 0.007 0.5 36370434100405204 Cimarron–65 2.06 <0.01 0.007 0.4 37370434100405203 Cimarron–210 3.06 <0.01 0.008 0.3 41370434100405202 Cimarron–336 2.30 <0.01 <0.004 0.3 4,03

Sediments of Permian age

370434100405201 Cimarron–436 0.39 <0.01 0.008 <0.1 15,43

0.32 0.01 0.006 -- 15,43
VERTICAL GRADIENTS IN WATER CHEMISTRY 27

Table 6. Physical properties and concentrations of major ions, nutrients, trace elements, and tritium in water from the Cimarron River and s

High Plains aquifer and sediments of Permian age—Continued

[μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, Celsius; mg/L, milligrams per liter; CaCO3, calcium carbonate; μg/L, micrograms per liter; --, not analyzed 

Station identification Well name

Antimony,

dissolved

(μg/L as Sb)

Arsenic,

dissolved

(μg/L as As)

Barium,

dissolved

(μg/L as Ba)

Beryllium,

dissolved

(μg/L as Be)

Cadmium,

dissolved

(μg/L as Cd)

Chr

dis

(μg/

370434100405205 Cimarron River <1 1.5 103 <1 <1 <

Water-table well sites,

central High Plains aquifer

375855100484001 Recon–1 -- -- -- -- -- 375734100452301 Recon–2 -- -- -- -- -- 374220100422501 Recon–3 -- -- -- -- -- 365610101484301 Recon–4 -- -- -- -- -- 363817101213101 Recon–5 -- -- -- -- -- 

Nested-well sites,

central High Plains aquifer

370402101394402 Rolla–193 <1 2.3 78 <1 <1 <370402101394401 Rolla–366 <1 1.8 15 <1 <1 370130101180904 Hugoton–140 <1 3.7 38 <1 <1 370130101180903 Hugoton–313 <1 2.0 31 <1 <1 370130101180902 Hugoton–495 <1 1.7 30 <1 <1 370130101180901 Hugoton–617 <1 1.6 29 <1 <1 370033100534204 Liberal–160 <1 4.6 108 <1 <1 370033100534203 Liberal–319 <1 1.7 53 <1 <1 370033100534202 Liberal–436 <1 3.6 52 <1 <1 370033100534201 Liberal–570 <1 2.6 39 <1 <1 370434100405204 Cimarron–65 <1 <1.0 99 <1 <1 370434100405203 Cimarron–210 <1 1.0 43 <1 <1 370434100405202 Cimarron–336 <3 <1.0 48 <3 <3 <

Sediments of Permian age

370434100405201 Cimarron–436 <10 12 32 <10 <10 <

<10 9.4 27 <10 <10 
28 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999 Table 6. Physical properties and concentrations of major ions, nutrients, trace elements, and tritium in water from the Cimarron River and s

High Plains aquifer and sediments of Permian age—Continued[μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, Celsius; mg/L, milligrams per liter; CaCO3, calcium carbonate; μg/L, micrograms per liter; --, not analyzed 

Station identification Well name

Copper,

dissolved

(μg/L as Cu)

Iron,

dissolved

(μg/L as Fe)

Lead,

dissolved

(μg/L as Pb)

Manganese,

dissolved

(μg/L as Mn)

Molybdenum,

dissolved

(μg/L as Mo)

N

di

(μg

370434100405205 Cimarron River <1 <10 <1 26 9.2 

Water-table well sites,

central High Plains aquifer

375855100484001 Recon–1 -- <30 -- <12 -- 375734100452301 Recon–2 -- <10 -- <3 -- 374220100422501 Recon–3 -- <10 -- <3 -- 365610101484301 Recon–4 -- <10 -- <3 -- 363817101213101 Recon–5 -- <10 -- 8.0 -- 

Nested-well sites,

central High Plains aquifer

370402101394402 Rolla–193 <1 <10 <1 24 4.1 370402101394401 Rolla–366 1.4 <10 <1 <3 1.1 370130101180904 Hugoton–140 <1 <10 <1 6.7 12 370130101180903 Hugoton–313 <1 <10 <1 <3 1.8 370130101180902 Hugoton–495 <1 <10 <1 <3 1.8 370130101180901 Hugoton–617 <1 <10 <1 <3 1.8 370033100534204 Liberal–160 <1 <10 <1 <3 3.0 370033100534203 Liberal–319 <1 <10 <1 <3 3.7 370033100534202 Liberal–436 <1 <10 <1 <3 4.3 370033100534201 Liberal–570 <1 <10 <1 7.8 5.4 370434100405204 Cimarron–65 <1 <10 <1 4.9 5.8 370434100405203 Cimarron–210 <1 <10 <1 <3 2.5 370434100405202 Cimarron–336 <3 <50 <3 130 3.4 

Sediments of Permian age

370434100405201 Cimarron–436 <10 <200 <10 111 11 

5.1 <120 <10 68 11 
VERTICAL GRADIENTS IN WATER CHEMISTRY 29

Table 6. Physical properties and concentrations of major ions, nutrients, trace elements, and tritium in water from the Cimarron River and s

High Plains aquifer and sediments of Permian age—Continued

[μS/cm, microsiemens per centimeter at 25 degrees Celsius; °C, Celsius; mg/L, milligrams per liter; CaCO3, calcium carbonate; μg/L, micrograms per liter; --, not analyz

Station identification Well name

Silver,

dissolved

(μg/L as Ag)

Uranium,

dissolved

(μg/L as U)

Zinc,

dissolved

(μg/L as Zn)

370434100405205 Cimarron River <1 6.6 <1 

Water-table well sites,

central High Plains aquifer

375855100484001 Recon–1 -- -- -- 375734100452301 Recon–2 -- -- -- 374220100422501 Recon–3 -- -- -- 365610101484301 Recon–4 -- -- -- 363817101213101 Recon–5 -- -- -- 

Nested-well sites,

central High Plains aquifer

370402101394402 Rolla–193 <1 2.5 <1 370402101394401 Rolla–366 <1 7.4 1.1 370130101180904 Hugoton–140 <1 6.3 2.5 370130101180903 Hugoton–313 <1 4.7 <1 370130101180902 Hugoton–495 <1 4.7 1.1 370130101180901 Hugoton–617 <1 4.5 2.0 370033100534204 Liberal–160 <1 8.3 3.4 370033100534203 Liberal–319 <1 6.8 1.7 370033100534202 Liberal–436 <1 8.0 1.0 370033100534201 Liberal–570 <1 9.6 3.2 370434100405204 Cimarron–65 <1 5.2 1.1 370434100405203 Cimarron–210 <1 4.8 1.8 370434100405202 Cimarron–336 <3 11.0 <3 

Sediments of Permian age

370434100405201 Cimarron–436 <10 <10 <10 

<10 8.4 <10 
30 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

those samples contained at least a portion of water 

recharged less than 50 years ago. The two water-table 

wells that produced water with less than 0.5 TU 

tritium had relatively large depths to water of 179 and 

279 feet below land surface (Rolla–193 and Recon–5; 

table 6). 

The tritium data indicate a vertical gradient in 

ground-water ages exists in the aquifer at the sampling 

sites. Most of the water at the water table was 

recharged less than 50 years ago, whereas all of the 

deep water was recharged more than 50 years ago. 

Better definition of the age gradient below the water 

table will require the use of other techniques and will 

be the subject of future investigations. Shallow ground 

water at most of the sampling sites was recharged 

since the onset of widespread irrigated agriculture in 

the 1950’s and 1960’s; therefore, that water could be 

susceptible to contamination from agricultural chemicals. The lack of recently recharged water at depth 

below the water table probably was the result of 

various factors that limited the amount of recharge to 

the aquifer, including the relatively large depths to 

water (median depth of 147 feet below land surface at 

the time of sampling), the semiarid climate, and the 

presence of thick clay layers in some areas which 

isolate shallow from deep zones in the aquifer.

Water from the Cimarron River, which was 

collected during base-flow conditions in the late 

summer of 1999, contained 0.9 TU of tritium (table 6). 

In comparison, the tritium concentrations in water 

from the nearby Cimarron nested wells were 4.4 TU in 

the water-table well and less than 0.3 TU in the deeper 

wells. Those data indicate that ground water 

discharging to the river at that site was a mixture of 

relatively old (deep) water having little or no tritium 

and recently recharged (shallow) water. It is unlikely 

that the tritium content of Cimarron River water was 

substantially affected by isotopic exchange with water 

vapor in the atmosphere because that exchange 

process is slow relative to the residence time of most

500

400

300

200

100

0

0 2 4 6 8 10 12 14

CONCENTRATION OF TRITIUM, IN TRITIUM UNITS

DEPTH OF WELL-SCREEN MIDPOINT BELOW

WATER TABLE, IN FEET

Recon–1

Recon–2

Recon–3

Recon–4

Recon–5

Rolla site

Hugoton site

Liberal site

Cimarron site

Detection level = 0.3 tritium unit

Figure 9. Relation between tritium concentrations and depth of the well-screen midpoint below the 

water table. Concentrations of tritium less than 0.3 tritium unit were set to zero.
VERTICAL GRADIENTS IN WATER CHEMISTRY 31

river water (Michel and Schroeder, 1994). Thus, the 

tritium concentration in the river under base-flow 

conditions should have been controlled primarily by 

the tritium concentration in ground-water discharge.

Dissolved Oxygen and Organic Carbon

Several chemicals of environmental concern in 

the central High Plains aquifer may be used by naturally occurring microorganisms under anoxic conditions, including nitrate, arsenate, and sulfate. In the 

absence of dissolved oxygen, microbes may reduce 

dissolved nitrate, arsenate (the primary form of arsenic 

in oxygenated ground water), and sulfate to less 

oxidized forms (Chapelle, 1993). Microbial reduction 

of those chemicals is beneficial because it lowers their 

concentration in water by converting them into less 

soluble or less toxic forms. In oxygenated ground 

water, microbes may oxidize other chemicals of environmental concern in the aquifer, such as atrazine, to 

carbon dioxide (McMahon and others, 1992). The role 

of dissolved oxygen in microbial processes makes 

measuring its distribution in ground water important if 

the fate of potentially harmful chemicals is to be 

understood.

Dissolved oxygen is readily removed from 

ground water by microbes if suitable electron donors 

are available. Typically, those electron donors are 

DOC in ground water or solid organic carbon in the 

aquifer sediments. Concentrations of DOC in the 

aquifer were relatively small (table 6 and fig. 10a), 

ranging from 0.3 to 1.6 mg/L, with a median concentration of 0.4 mg/L. The single measured value of 

DOC in the sediments of Permian age was less than 

0.1 mg/L. For comparison, Thurman (1985) reported a 

median DOC concentration of 0.7 mg/L for ground 

water from several other aquifers. Concentrations of 

solid organic carbon in the aquifer also were relatively 

small (median concentration was 0.06 weight percent, 

table 5). Sediments that are enriched in organic carbon 

typically contain more than about 0.2 percent organic 

carbon by weight (McMahon and others, 1999). Only 

two samples of clay contained more than 0.2 percent 

organic carbon by weight (table 5). The data indicate 

that the supply of DOC and solid organic carbon to 

support microbial oxygen reduction in the aquifer was 

limited; therefore, dissolved oxygen in the aquifer was 

likely to persist. 

Dissolved oxygen was detected in water 

throughout the aquifer, as well as in water from the 

sediments of Permian age (table 6 and fig. 10b). 

Concentrations of dissolved oxygen in the aquifer 

ranged from 1.7 to 8.4 mg/L. The general trend of 

decreasing dissolved oxygen concentrations with 

increasing depth below the water table at three of the 

four nested-well sites indicates that some oxygen 

reduction probably occurred along flow paths in the 

aquifer. However, the reduction rate was not fast 

enough to use all of the oxygen. The presence of 

dissolved oxygen throughout the aquifer indicates that 

chemicals like sulfate, nitrate, and arsenate would not 

be reduced by microbes to any significant extent; 

therefore, those chemicals would persist in the aquifer. 

The lack of a vertical gradient in dissolved oxygen 

concentrations at the Hugoton site probably was 

caused by vertical mixing of ground water during 

pumping of the nearby irrigation well that was 

screened in the lower one-half of the aquifer.

Major Ions

Calcium and bicarbonate were commonly the 

most abundant dissolved major ions in the aquifer 

(fig. 11), which reflects the dissolution of calcite 

(CaCO3) in the aquifer. Calcite was not a major 

mineral phase in the aquifer in terms of abundance 

(table 5), but it is readily soluble in water compared to 

more abundant minerals in the aquifer like quartz and 

feldspars. Calcite dissolution apparently occurred 

during the movement of water through the unsaturated 

zone, or very shallow in the flow system, because 

water throughout the aquifer was in thermodynamic 

equilibrium with respect to calcite (fig. 12). The saturation index (SI) is defined as:

where

 IAP is the ion activity product of the components of 

the mineral phase (dissolved calcium and 

carbonate in the case of calcite), and

KT is the solid phase solubility equilibrium product at 

the specified water temperature.

If SI = 0, water is at equilibrium with respect to the 

mineral phase; if SI<0, water is undersaturated with respect to the mineral phase, 

and the mineral has the potential to 

dissolve; if SI>0, water is supersaturated 

with respect to the mineral phase, and the 

mineral has the potential to precipitate.

SI IAP/KT = log( )
32 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

500

400

300

200

100

0

500

400

300

200

100

0

0123456789

CONCENTRATION OF DISSOLVED OXYGEN,

IN MILLIGRAMS PER LITER

CONCENTRATION OF DISSOLVED ORGANIC 

CARBON, IN MILLIGRAMS PER LITER

DEPTH OF WELL-SCREEN MIDPOINT BELOW

WATER TABLE, IN FEET

DEPTH OF WELL-SCREEN MIDPOINT BELOW

WATER TABLE, IN FEET

0 0.4 0.8 1.2 1.6 2.0

(b)

(a)

Rolla site

Hugoton site

Liberal site

Cimarron site

Recon–1

Recon–2

Recon–3

Recon–4

Rolla site

Hugoton site

Liberal site

Cimarron site

Detection level = 0.1 milligram per liter

Figure 10. Relation between dissolved (a) organic carbon and (b) oxygen concentrations 

and depth of the well-screen midpoint below the water table. Concentrations of dissolved 

organic carbon less than 0.1 milligram per liter were set to zero.
VERTICAL GRADIENTS IN WATER CHEMISTRY 33

Figure 11. Horizontal and vertical distribution of water types at the nested-well sites. Water types were based on relative 

percentages of the major-ion concentrations expressed in milliequivalents per liter.

10 20 30 40 50 60 70 80

3,800

3,600

3,400

3,200

3,000

2,800

2,600

2,400

2,200

2,000

1,800

HORIZONTAL DISTANCE, IN MILES

ELEVATION, IN FEET ABOVE SEA LEVEL

Rolla site

Ca-Na-HCO3

Ca-SO4

3

4

Na-HCO3

Ca-HCO3

Ca-HCO3

Ca-HCO3 Ca-Mg-HCO3

Ca-Mg-HCO3

Ca-Mg-HCO3 Ca-Na-HCO3

Na-Cl

Na-Cl

Ca-Na-HCO3

Mg-Ca-HCO3

Central

High Plains

aquifer

Sediments of Permian age

Land surface

Water table

Liberal site

Hugoton site

Cimarron site

Well screen midpoint

Ca, calcium

Mg, magnesium

Na, sodium

HCO , bicarbonate

Cl, chloride

SO ,sulfate

Base of aquifer

Water type

The SI values in figure 12 were calculated using 

the WATEQFP speciation model in the computer 

program NETPATH (Plummer and others, 1994). 

Because of the salinity of water from Cimarron–436, 

the computer program PHRQPITZ (Plummer and 

others, 1988), a computer program for calculating 

geochemical reactions in brines, was used to calculate 

the calcite SI for that sample. Calcite SI values within

± 0.25 of the zero value were assumed to indicate that 

water was in equilibrium with respect to calcite due to 

uncertainties in the water-temperature measurements. 

Caliche, a calcite-bearing deposit, was detected in the 

unsaturated zone at many of the drill sites and is one 

possible source of the dissolved calcium and bicarbonate. If the dissolved major ions in the aquifer were 

largely derived from the unsaturated zone or shallow 

part of the flow system, then there should have been 

very little change in the concentrations of dissolved 

solids with depth in the aquifer. The concentrations of 

dissolved solids in water samples from the Hugoton 

and Liberal nested-well sites did exhibit very little 

variability with depth (fig. 13). However, that was not 

the case at the Rolla or Cimarron sites.

Concentrations of dissolved solids at the Rolla 

and Cimarron sites increased from 290 and 370 mg/L 

near the water table to 862 and 4,030 mg/L at the 

bottom of the aquifer (fig. 13 and table 6). In addition, 

the relative proportions of major ions at the top and 

bottom of the aquifer at those sites changed. At the 

Rolla site, the water type changed from calciumsodium-bicarbonate at the top to calcium-sulfate at the 

bottom. At the Cimarron site, the water type changed
34 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

Figure 12. Relation between calcite saturation indices and depth of the well-screen midpoint below the water 

table. Water samples with saturation indices within ±0.25 of the zero value were considered to be in equilibrium 

with respect to calcite due to uncertainties in the measurement of water temperatures.

500

400

300

200

100

0

-0.5 -0.4 -0.3 -0.2 -0.1 0 -0.1 0.2 0.3 0.4 0.5

CALCITE SATURATION INDEX

DEPTH OF WELL-SCREEN MIDPOINT BELOW

WATER TABLE, IN FEET

Undersaturated Supersaturated

Recon–1

Recon–2

Recon–3

Recon–4

Recon–5

Rolla site

Hugoton site

Liberal site

Cimarron site

Equilibrium

from calcium-sodium-bicarbonate at the top to 

sodium-chloride at the bottom. The vertical changes in 

dissolved solids and water type at those sites could be 

the result of the dissolution of a different mineral 

assemblage at the bottom of the aquifer or from the 

upward movement of mineralized water from underlying geologic units. For example, the calcium-sulfate 

and sodium-chloride waters at those sites could have 

been derived from the dissolution of gypsum 

(CaSO4

.2H2O) and halite (NaCl). Neither of those 

minerals was detected in sediments at the bottom of 

the aquifer using X-ray diffraction analysis (table 5); 

however, it is possible that small amounts of gypsum 

in reworked sediments of Permian age could exist at 

the base of the aquifer (Smith, 1940). It is unlikely that 

small amounts of halite, which is very soluble, would 

persist in the aquifer. Therefore, the change in 

dissolved solids and water types with depth at those 

sites probably resulted from a combination of the 

dissolution of reworked Permian sediments near the 

base of the aquifer and the upward movement of 

mineralized water from sediments underlying the 

central High Plains aquifer. 

The central High Plains aquifer at the Rolla site 

was underlain by sediments of Permian age younger 

than the Cedar Hills Sandstone (table 1), on the basis 

of the elevation of the aquifer base (table 2) and the 

elevations of the tops of the bedrock units underlying 

the aquifer near that site (Macfarlane and others, 

1993). It was beyond the scope of this project to determine which of those Permian units were actually 

present at the Rolla site; however, several of them 

contain gypsum and anhydrite (Day Creek Dolomite, 

Dog Creek Formation, Blaine Formation, Flowerpot 

Shale) and halite (Blaine Formation, Flowerpot Shale) 

(Gutentag and others, 1981; Macfarlane and others, 

1993). The Day Creek Dolomite in Morton County is 

reported to contain elevated concentrations of 

dissolved calcium and sulfate (Gutentag and others, 

1981). The calcium-sulfate-bearing mineral phases
VERTICAL GRADIENTS IN WATER CHEMISTRY 35

Figure 13. Relation between concentrations of dissolved solids and depth of the well-screen midpoint below the 

water table.

500

100 1,000 10,000 100,000

400

300

200

100

0

DEPTH OF WELL-SCREEN MIDPOINT BELOW

WATER TABLE, IN FEET

CONCENTRATION OF DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

Recon–1

Recon–2

Recon–3

Recon–4

Recon–5

Rolla site

Hugoton site

Liberal site

Cimarron site

(and possibly water) in sediments of Permian age at 

the Rolla site are possible sources of the elevated 

concentrations of dissolved calcium and sulfate at the 

base of the aquifer. Water-level data for the sediments 

of Permian age were not available in the vicinity of the 

Rolla nested-well site; therefore, the hydraulic 

gradient across the Permian/High Plains-aquifer 

contact was not known. However, water-level data 

from the Rolla nested wells indicate that water levels 

at the base of the aquifer declined during the irrigation 

season (fig. 8a), which might have induced the upward 

movement of water from the sediments of Permian age 

to the aquifer.

At the Cimarron site, water-quality data from 

the well screened in sediments of Permian age indicate 

the presence of a sodium-chloride water in those sediments (table 6). Furthermore, the water-level data indicate that the hydraulic gradient at that site was directed 

upward from the sediments of Permian age to the 

aquifer during at least part of the measurement period 

(fig. 8d). Thus, the chemical and water-level data 

demonstrate that the sodium-chloride water at the base 

of the aquifer could have come from the underlying 

sediments of Permian age. 

Bromide/chloride mass ratios are useful for 

understanding the origin of saline waters (Whittemore, 

1995). Bromide/chloride mass ratios were plotted for 

water from the central High Plains aquifer, water from 

well Cimarron–436 (screened in sediments of Permian 

age), halite-dissolution brines in sediments of Permian 

age in south-central Kansas (Whittemore, 1993), and 

oil brines in southwestern Kansas (Whittemore, 1984) 

to further aid in the identification of possible sources 

of salinity in wells Cimarron-336 and Cimarron–436 

(fig. 14). All but one of the water samples from the 

aquifer plotted in the mixing zone defined by freshwater and halite-dissolution brine, thus indicating that 

water from well Cimarron–336 was derived from the 

mixing of freshwater and halite-dissolution brine from 

the Permian section. Calculations indicate that mixing
36 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

Figure 14. Relation between bromide/chloride mass ratios and concentrations of dissolved chloride in water samples 

from the central High Plains aquifer and sediments of Permian age. For comparison, bromide/chloride mass ratios 

were plotted for halite-dissolution brines in sediments of Permian age from south-central Kansas (Whittemore, 1993), 

seawater, and oil brines in southwestern Kansas (Whittemore, 1984). The solid lines define a zone of mixing of freshwater in the aquifer and halite-dissolution brine. The percentages refer to the amount of halite-dissolution brine in the 

mixture.

of about 5 percent halite-dissolution brine with freshwater would produce water with the chloride concentration and bromide/chloride ratio measured in water 

from well Cimarron–336. Whittemore (1995) and 

Mehta and others (2000) also concluded that upward 

movement of halite-dissolution brine was an important 

mechanism for salinization of water in the High Plains 

aquifer of Kansas, Oklahoma, and Texas. Whittemore 

(1984) proposed that dissolution of halite beds in the 

Lower Permian Blaine Formation was the source of 

sodium chloride water in Seward County, Kansas, the 

location of the Cimarron nested-well site. 

The bromide/chloride ratio measured in water 

collected from Cimarron–436 in August 1999 plotted 

below the zone of mixing of freshwater and halitedissolution brine shown in figure 14. However, 

Cimarron–436 was resampled in October 2000 to 

check that earlier measurement. The bromide/chloride 

ratio measured in water collected from Cimarron–436 

in October 2000 plotted within the mixing zone. 

Calculations indicate that mixing of about 20 percent 

halite-dissolution brine with freshwater would produce 

water with the chloride concentration and 

bromide/chloride ratio measured in water collected 

from well Cimarron–436 in October 2000.

Calcium-sulfate or sodium-chloride waters were 

not detected at the base of the aquifer at the Hugoton 

or Liberal nested-well sites, even though sediments of 

Permian age underlie both sites (fig. 3) and well 

pumping lowered water levels in the deeper part of the 

20%

5%

1%

CONCENTRATION OF DISSOLVED CHLORIDE,

IN MILLIGRAMS PER LITER

BROMIDE/CHLORIDE MASS RATIO

1

0.00001

0.0001

0.001

0.01

0.1

10 100 1,000 10,000 100,000 1,000,000

Zone of mixing of freshwater

with halite-dissolution brine

Cimarron–336

Cimarron–436

Recon–1

Central High Plains aquifer

Sediments of Permian age

Seawater

Halite-dissolution brine, south-central Kansas

Oil brine, southwestern Kansas
VERTICAL GRADIENTS IN WATER CHEMISTRY 37

aquifer (figs. 8b and 8c), increasing the potential for 

upward movement of water. Those findings indicate 

that sediments at the top of the Permian section at 

those sites probably had small hydraulic conductivities, which limited the upward movement of mineralized water. The sample of sediment of Permian age 

retrieved from the Liberal borehole consisted of dense 

red clay (table 4), which likely did have a small 

hydraulic conductivity. Another possibility is that the 

hydraulic gradient between the aquifer and sediments 

of Permian age was horizontal or directed downward 

at the Hugoton and Liberal sites. 

Sediments of Permian age were not the only 

source of mineralized water in the aquifer. The water 

sample from well Recon–1 also had a large concentration of dissolved solids, with the dominant ions being 

calcium-sodium-sulfate. However, the bromide/chloride ratio in water from Recon–1 lies above the zone 

of mixing of freshwater and halite-dissolution brine 

shown in figure 14, indicating that halite-dissolution 

brine was not the source of mineralized water in 

Recon–1. Recon–1 was screened at the water table and 

was located about 2.5 miles north of the Arkansas 

River, which contains large concentrations of calciumsodium-sulfate water (Whittemore, 2000). Whittemore 

proposed that the source of dissolved solids in 

Arkansas River water was the dissolution of minerals 

in marine shales in southeastern Colorado by irrigation 

water. In fact, the bromide/chloride ratio in water 

from Recon–1 is intermediate in value to the ratios 

for freshwater and seawater (fig. 14). Leakage of 

Arkansas River water into the underlying central High 

Plains aquifer has occurred since the 1970’s (Whittemore, 2000). The similarity in chemical compositions 

between water from Recon–1 and the Arkansas River, 

their proximity to each other, and the presence of a 

hydraulic gradient directed from the river toward the 

aquifer indicate that the Arkansas River is the source 

of the mineralized water in well Recon–1. Whittemore 

(2000) also concluded that the Arkansas River is a 

source of mineralized water in the central High Plains 

aquifer in the study area. In summary, the data 

presented in this section indicate that there are chemically distinct sources of mineralized water above and 

below the aquifer that produced vertical gradients in 

dissolved solids and water types in the aquifer.

Nitrate

Nitrogen occurs naturally in relatively small 

concentrations in rocks, soils, organic material, and 

the water that comes in contact with them (Holloway 

and Dahlgren, 1999). It also occurs in relatively large 

concentrations in animal manure and fertilizers and in 

treated sewage effluent from municipalities. Nitrate, 

the most commonly occurring form of nitrogen in 

ground water, is of environmental concern because its 

discharge to surface water can support eutrophication. 

Nitrate is a health concern because ingestion of large 

concentrations of nitrate in drinking water by infants 

can cause low levels of oxygen in the blood (Fan and 

Steinberg, 1996). For this reason, the USEPA established an MCL of 10 mg/L as N in drinking water 

(U.S. Environmental Protection Agency, 2001a). 

Other adverse health effects from the ingestion of 

nitrate might include spontaneous abortion among 

some women (Centers for Disease Control and 

Prevention, 1996) and increased risk of non-Hodgkins 

lymphoma (Ward and others, 1996). 

Concentrations of dissolved nitrate in water 

from the aquifer ranged from 1.90 to 54.4 mg/L as N, 

and the water samples from the sediments of Permian 

age contained from 0.32 to 0.39 mg/L as N (table 6 

and fig. 15). Only 2 of the 20 samples had nitrate 

concentrations greater than the MCL. The median 

concentration of nitrate in the 10 samples from the 

aquifer that contained no measurable tritium was 

2.45 mg/L as N. That nitrate concentration might be 

representative of the background nitrate concentration 

in the aquifer in the study area because ground water 

represented by those samples was recharged before the 

onset of modern (post-1950’s) anthropogenic activity 

in the study area. 

The three largest nitrate concentrations occurred 

in water samples that were collected at the water table 

beneath irrigated fields. Those samples also contained 

pesticides, indicating that the nitrate probably was 

derived from agricultural activities. In contrast to 

those shallow samples, water samples collected from 

farther below the water table generally contained less 

nitrate and no detectable tritium. McMahon and others 

(2000) concluded that concentrations of dissolved 

nitrate in recently recharged water were significantly 

larger than the concentrations in older water in the 

aquifer, on the basis of 123 analyses of ground water 

collected in 1999. In addition, they concluded that the 

smaller nitrate concentrations in older water were not
38 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

the result of extensive denitrifying activity at depth in 

the aquifer because of the generally oxidizing conditions present in the aquifer. The implications of the 

findings from this study and that of McMahon and 

others (2000) are that (a) anthropogenic activity in the 

study area during the last 50 years has resulted in an 

increase in nitrate concentrations in the aquifer and (b) 

nitrate in the aquifer is likely to persist because 

geochemical conditions in the aquifer are not conducive to extensive denitrification, which would substantially decrease nitrate concentrations.

Not all of the water samples collected at the 

water table near irrigated fields contained elevated 

nitrate concentrations. Samples from wells Recon–4, 

Recon–5, and Hugoton–140 contained from 2.20 to 

3.80 mg/L as N of nitrate, even though all three wells 

were screened at the water table below irrigated fields. 

Two of the wells, Recon–4 and Recon–5, had depths to 

water greater than 250 feet and produced water that 

contained little or no tritium; therefore, those samples 

may have predated significant agricultural activity in 

the study area. It is unclear why water from Hugoton–

140 only contained 2.20 mg/L as N of nitrate, given 

that the depth to water was only 133 feet and the water 

contained 12.3 TU of tritium. One possibility is that 

the amount of nitrogen applied to cropland at the 

Hugoton–140 site was much less, or was not applied 

until more recently, than the nitrogen applied at the 

three irrigated sites having larger nitrate concentrations at the water table. Records of nitrogen applications at those sites are needed to evaluate that 

possibility.

Figure 15. Relation between concentrations of dissolved nitrate and depth of the well-screen midpoint below 

the water table. MCL refers to the maximum contaminant level permitted in drinking water, as established by 

the U.S. Environmental Protection Agency (2001a).

500

400

300

200

100

0

0 6 2 4 10 8 20 30 40 50 60 MCL

CONCENTRATION OF DISSOLVED NITRATE, IN MILLIGRAMS 

PER LITER AS NITROGEN

DEPTH OF WELL-SCREEN MIDPOINT BELOW WATER

TABLE, IN FEET

Recon–1

Recon–2

Recon–3

Recon–4

Recon–5

Rolla site

Hugoton site

Liberal site

Cimarron site
VERTICAL GRADIENTS IN WATER CHEMISTRY 39

Arsenic

Arsenic occurs naturally in rocks, soils, and the 

water that comes in contact with them. It also occurs in 

anthropogenic products such as wood preservatives 

and herbicides. Long-term exposure to small concentrations of arsenic in drinking water can lead to skin, 

bladder, lung, and prostate cancer. Other effects of 

ingesting arsenic at low levels include cardiovascular 

disease, diabetes, and anemia, as well as reproductive 

and developmental, immunological, and neurological 

effects. The U.S. Environmental Protection Agency 

may lower the MCL for arsenic from 50 to 10 μg/L 

(U.S. Environmental Protection Agency, 2001b).

None of the water samples collected from the 

central High Plains aquifer exceeded the proposed 

MCL of 10 μg/L for arsenic (table 6). A water sample 

collected from sediments of Permian age contained 

12 μg/L arsenic, but the elevated dissolved-solids 

concentration of that water made it unsuitable for 

human consumption anyway. Based on the hydraulichead and arsenic data (figs. 8d and 16), water relatively enriched in arsenic had the potential to move 

upward from the sediments of Permian age to the 

aquifer in the area of the Cimarron nested-well site. 

However, the arsenic concentration in water from 

Cimarron–336 (less than 

1 μg/L), the well screened just above the High 

Plains/Permian contact, did not indicate that water 

with elevated arsenic concentrations was entering the 

aquifer. At least two mechanisms could attenuate 

arsenic concentrations in water from the sediments of 

Permian age—dilution and adsorption. The median 

arsenic concentration in water from the aquifer (1.8 

μg/L) was smaller than the concentration in water 

from the sediments of Permian age; therefore, mixing

Figure 16. Relation between concentrations of dissolved arsenic and depth of the well-screen 

midpoint below the water table. 

500

400

300

200

100

0

0 5 10 15

CONCENTRATION OF DISSOLVED ARSENIC, IN MICROGRAMS PER LITER

DEPTH OF WELL-SCREEN MIDPOINT BELOW WATER

TABLE, IN FEET

Rolla site

Hugoton site

Liberal site

Cimarron site
40 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

of those waters would reduce the arsenic concentration 

in the upwelling water. Interestingly, the arsenic 

concentration in Cimarron–336 was smaller than the 

median concentration in the aquifer, indicating that 

dilution was not the only mechanism attenuating 

arsenic concentrations in the upwelling water. Adsorption of arsenate in oxygenated water onto ferric ironand manganese-oxide grain coatings is an important 

mechanism in some hydrologic settings (Welch and 

Lico, 1998) and may be responsible for further 

reducing the concentration of arsenic in water entering 

the aquifer from underlying sediments. Other trace 

elements that had relatively elevated concentrations in 

water from the sediments of Permian age included 

chromium, copper, manganese, molybdenum, and 

nickel (table 6).

Pesticides

Of the 53 compounds analyzed for in the water 

samples (table 7), 3 pesticides (atrazine, metolachlor, 

and simazine) and 5 pesticide degradation products 

(alachlor ethanesulfonic acid, alachlor oxanilic acid, 

deethylatrazine, metolachlor ethanesulfonic acid, and 

metolachlor oxanilic acid) were detected in samples 

from six water-table wells (table 8). Five of the six 

wells were adjacent to irrigated fields. The frequency 

of detection of the compounds that were measured 

in all samples was, in order of decreasing frequency;

Table 7. Pesticides and pesticide degradation products analyzed in water from sampled wells in the central High Plains 

aquifer and sediments of Permian age

[*, only analyzed in water samples from Recon wells; μg/L,micrograms per liter]

Constituent

Analytical method

reporting limit

(μg/L)

Constituent

Analytical method

reporting limit

(μg/L)

2,6-diethylaniline 0.003 Acetochlor 0.002

Acetochlor ethanesulfonic acid* 0.050 Acetochlor oxanilic acid* 0.050

Alachlor 0.002 Alachlor ethanesulfonic acid* 0.050

Alachlor oxanilic acid* 0.050 Atrazine 0.001

Azinphos-methyl 0.001 Benfluralin 0.002

Butylate 0.002 Carbaryl 0.003

Carbofuran 0.003 Chlorpyrifos 0.004

Cyanazine 0.004 DCPA 0.002

Deethylatrazine 0.002 Diazinon 0.002

Dieldrin 0.001 Disulfoton 0.017

EPTC 0.002 Ethalfluralin 0.004

Ethoprophos 0.003 Fonofos 0.003

Lindane 0.004 Linuron 0.002

Malathion 0.005 Metolachlor 0.002

Metolachlor ethanesulfonic acid* 0.050 Metolachlor oxanilic acid* 0.050

Metribuzin 0.004 Molinate 0.004

Napropamide 0.003 Parathion 0.004

Parathion-methyl 0.006 Pebulate 0.004

Pendimethalin 0.004 Phorate 0.002

Prometon 0.018 Propachlor 0.007

Propanil 0.004 Propargite 0.013

Propyzamide 0.003 Simazine 0.005

Tebuthiuron 0.010 Terbacil 0.007

Terbufos 0.013 Thiobencarb 0.002

Triallate 0.001 Trifluralin 0.002

alpha-HCH 0.002 cis-Permethrin 0.005

p,p'-DDE 0.006
VERTICAL GRADIENTS IN WATER CHEMISTRY 41

Table 8. Pesticide usage in the study area and concentrations of pesticides and pesticide degradation products detected in water from sHigh Plains aquifer and sediments of Permian age[μg/L, micrograms per liter; ESA, ethanesulfonic acid; OA, oxanilic acid; E, estimated concentration; <, less than indicated concentration; --, not analyzed or not applica

Station identification Well name Sample date

Depth to water

(feet below

land surface)

Depth of screen 

midpoint below

water table

(feet)

Alachlor,

dissolved

(μg/L)

Alachlor E

dissolv

(μg/L)

Pesticide usage, ranked according to pounds of active 

ingredient applied in the study area1

-- -- -- 4 -- 

Water-table well sites,

central High Plains aquifer

375855100484001 Recon–1 02/03/99 70 8 <0.002 0.44 375734100452301 Recon–2 02/02/99 121 −4 <0.002 <0.05 374220100422501 Recon–3 02/04/99 161 13 <0.002 1.5 365610101484301 Recon–4 02/05/99 273 1 <0.002 0.12 363817101213101 Recon–5 02/17/99 279 8 <0.002 <0.05 

Nested-well sites,

central High Plains aquifer

370402101394402 Rolla–193 08/30/99 179 4 <0.002 -- 370402101394401 Rolla–366 08/30/99 180 181 <0.002 -- 370130101180904 Hugoton–140 08/29/99 133 −3 <0.002 -- 370130101180903 Hugoton–313 08/29/99 154 154 <0.002 -- 370130101180902 Hugoton–495 08/28/99 172 318 <0.002 -- 370130101180901 Hugoton–617 08/28/99 175 437 <0.002 -- 370033100534204 Liberal–160 08/27/99 117 33 <0.002 -- 370033100534203 Liberal–319 08/27/00 149 165 <0.002 -- 370033100534202 Liberal–436 08/26/99 147 284 <0.002 -- 370033100534201 Liberal–570 08/26/99 147 418 <0.002 -- 370434100405204 Cimarron–65 09/01/99 56 −1 <0.002 -- 370434100405203 Cimarron–210 08/31/99 54 151 <0.002 -- 370434100405202 Cimarron–336 09/01/99 54 277 <0.002 -- 

Sediments of Permian age

370434100405201 Cimarron–436 08/31/99 55 361 <0.002 -- 
42 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999 Table 8. Pesticide usage in the study area and concentrations of pesticides and pesticide degradation products detected in water from sam

central High Plains aquifer and sediments of Permian age—Continued[μg/L, micrograms per liter; ESA, ethanesulfonic acid; OA, oxanilic acid; E, estimated concentration; <, less than indicated concentration; --, not analyzed or not applicabl

Station identification Well name

Atrazine,

dissolved

(μg/L)

Deethylatrazine,

dissolved

(μg/L)

Metolachlor,

dissolved

(μg/L)

Metolachlor ESA,

dissolved

(μg/L)

Metolach

disso

(μg

Pesticide usage, ranked according to pounds of active 

ingredient applied in the study area1

1 -- 3 -- -- 

Water-table well sites,

central High Plains aquifer

375855100484001 Recon–1 0.006 20.014 E <0.002 <0.05 <0.0375734100452301 Recon–2 5.0 1.7 E 0.096 2.8 1.2 374220100422501 Recon–3 1.2 0.60 E <0.002 <0.05 <0.0365610101484301 Recon–4 0.40 0.12 E <0.002 <0.05 <0.0363817101213101 Recon–5 <0.001 <0.002 <0.002 <0.05 <0.0

Nested-well sites,

central High Plains aquifer

370402101394402 Rolla–193 0.007 0.002 E <0.002 -- -- 370402101394401 Rolla–366 <0.001 <0.002 <0.002 -- -- 370130101180904 Hugoton–140 0.072 0.009 E <0.002 -- -- 370130101180903 Hugoton–313 <0.001 <0.002 <0.002 -- -- 370130101180902 Hugoton–495 <0.001 <0.002 <0.002 -- -- 370130101180901 Hugoton–617 <0.001 <0.002 <0.002 -- -- 370033100534204 Liberal–160 <0.001 <0.002 <0.002 -- -- 370033100534203 Liberal–319 <0.001 <0.002 <0.002 -- -- 370033100534202 Liberal–436 <0.001 <0.002 <0.002 -- -- 370033100534201 Liberal–570 <0.001 <0.002 <0.002 -- -- 370434100405204 Cimarron–65 <0.001 <0.002 <0.002 -- -- 370434100405203 Cimarron–210 <0.001 <0.002 <0.002 -- -- 370434100405202 Cimarron–336 <0.001 <0.002 <0.002 -- -- 

Sediments of Permian age

370434100405201 Cimarron–436 <0.001 <0.002 <0.002 -- -- 

1Data from U.S. Department of Agriculture, 1999.2Concentrations of deethylatrazine are estimated because of their poor recoveries from the water samples (see text).
VERTICAL GRADIENTS IN WATER CHEMISTRY 43

atrazine = deethylatrazine > simazine > metolachlor. 

The median concentration for the compounds that 

were detected was 0.12 μg/L. The reported 

concentrations of deethylatrazine probably underestimated the actual concentrations because recoveries of 

deethylatrazine in water samples spiked with known 

concentrations of deethylatrazine only averaged 59 

percent. Recoveries for the other spiked compounds 

were 106 percent for simazine, 89 percent for atrazine, 

86 percent for alachlor, and 84 percent for metolachlor. Only the water sample from Recon–2 

contained a pesticide concentration (atrazine at 5.0 

μg/L) that exceeded an MCL (3 μg/L for atrazine) 

(U.S. Environmental Protection Agency, 2001a). The 

monitoring wells are not water-supply wells, but the 

aquifer is an important source of water to domestic 

and public-supply wells in the central High Plains.

The pesticide data indicate that the degradation 

products are an important component of the pesticide 

mass balance in the aquifer. For example, 12 of the 

21 detections were of pesticide degradation products. 

The mass ratio of parent compound/degradation 

product ranged from 0 to 0.024 for alachlor and metolachlor, indicating that the mass of degradates far 

outweighed the masses of alachlor and metolachlor. 

The atrazine/deethylatrazine ratio was greater than 1, 

but that ratio probably was affected by the relatively 

poor recovery of deethylatrazine from the water 

samples compared with atrazine. These results indicate that measurement of pesticide degradation products is necessary in order to accurately assess the 

effects of pesticides on water quality in the aquifer. 

Similar conclusions were reached in other studies of 

pesticide occurrences in ground water in the 

Midwestern United States (Kolpin and others, 1996; 

Kalkhoff and others, 1998).

Application of synthetic organic pesticides to 

cropland in the United States largely began after 

World War II (Barbash and Resek, 1996). Because of 

the relatively recent introduction of pesticides to the 

environment, pesticide detections can be used as an 

indicator of ground water that contains at least a 

component of recently recharged water. The top five 

pesticides used in the study area, in terms of pounds of 

active ingredient applied and listed in order of 

decreasing usage, are atrazine > 2,4-D > metolachlor > 

alachlor > butylate (U.S. Department of Agriculture, 

1999). The list of pesticides analyzed for in this study 

includes all of the top five pesticides used in the study 

area except 2,4-D (table 7). Three of the top five pesticides used in the study area, or their degradation products, were detected in the water samples (table 8).

Pesticides, or their degradation products, were 

only detected in water samples collected from wells 

screened near the water table (fig. 17), similar to the 

distribution of tritium (fig. 9), providing additional 

evidence that recently recharged water probably did 

not penetrate deeply into the aquifer at the well sites. 

The lack of pesticide detections at depth in the aquifer 

at the well sites might indicate that clay/silt layers in 

the aquifer inhibited the downward movement of 

contaminants. Other studies of the central High Plains 

aquifer have reported pesticide detections in water 

samples from domestic and public-supply wells that 

were screened as much as 160 feet below the water 

table (M.F. Becker, U.S. Geological Survey, written 

commun., 1999; B.W. Bruce, U.S. Geological Survey, 

written commun., 1999). Thus, it appears that in some 

areas of the aquifer, pesticides penetrated to greater 

depths than those observed in this study.
44 Vertical Gradients in Water Chemistry in the Central High Plains Aquifer, Southwestern Kansas and Oklahoma Panhandle, 1999

Figure 17. Relation between number of pesticide detections and depth of the well-screen midpoint below 

the water table.

500

400

300

200

100

0

0 1 2 3 4 5 67

NUMBER OF PESTICIDE DETECTIONS

DEPTH OF WELL-SCREEN MIDPOINT BELOW WATER

TABLE, IN FEET

Recon–1

Recon–2

Recon–3

Recon–4

Recon–5

Rolla site

Hugoton site

Liberal site

Cimarron site

SUMMARY AND CONCLUSIONS

The central High Plains aquifer is the primary 

source of water for domestic, industrial, and irrigation 

uses in parts of Colorado, Kansas, New Mexico, Oklahoma, and Texas. Water levels have declined in some 

areas, increasing the demand for water deeper in the 

aquifer. The maximum saturated thickness of the 

aquifer ranged from about 500 to 600 feet in 1999. As 

the demand for water builds, it becomes increasingly 

important for resource managers to understand how 

the quality of water in the aquifer changes with depth. 

In 1998–99, 18 monitoring wells at nine sites in southwestern Kansas and the Oklahoma Panhandle were 

completed at various depths in the central High Plains 

aquifer, and 1 monitoring well was completed in sediments of Permian age underlying the aquifer. Water 

samples were collected once from each well in 1999 to 

measure vertical gradients in water chemistry in the 

central High Plains aquifer. 

Geophysical and lithologic logs indicate that the 

aquifer largely consists of unconsolidated clay, silt, 

sand, gravel, and caliche. There was no apparent trend 

in grain size with depth in the aquifer. Relatively thick 

intervals of clay/silt and sand/gravel were penetrated 

in the unsaturated and saturated zones at several sites. 

Quartz and feldspars were the major minerals identified in the aquifer, and calcite was observed in trace 

amounts except in caliche beds, in which case it was 

the major mineral phase.

Water-level data indicate that vertical hydraulic 

gradients varied spatially and temporally in the aquifer 

and were affected by pumping in nearby wells and 

lithology. Seasonal irrigation pumping caused waterlevel declines of 20 to 60 feet in deep monitoring wells 

at the Hugoton site. However, the water levels recovered to within 1 foot of prepumping levels after the 

irrigation season. Clay layers in the aquifer caused 

local confinement of the deep ground water and may 

help protect deep ground water from the downward
REFERENCES CITED 45

movement of contaminants. In the absence of clay 

layers, pumping could draw contaminants deeper into 

the aquifer. Pumping in the aquifer could also induce 

the upward migration of mineralized water from 

underlying geologic units.

Vertical gradients in ground-water age were 

present in the aquifer. Most of the water samples 

collected from the upper 30 feet of the aquifer were 

recharged in the last 50 years, whereas all of the 

water samples collected from depths more than 30 feet 

below the water table were recharged more than 

50 years ago, on the basis of tritium concentrations 

measured in ground water. Despite the presence of 

relatively old water at depth in the aquifer, dissolved 

oxygen was present throughout the thickness of the 

aquifer, with concentrations ranging from 1.7 to 

8.4 mg/L. The presence of dissolved oxygen 

throughout the aquifer indicates that some redoxsensitive chemicals of environmental concern (nitrate, 

arsenic, sulfate) had the potential to persist in the 

ground water.

Major-ion data indicate that water in the aquifer 

was predominantly a calcium-bicarbonate type that 

showed little variability in concentrations of dissolved 

solids with depth (290 to 642 mg/L). Exceptions 

included two areas (Rolla and Cimarron) of the aquifer 

where there had been upward movement of mineralized water from underlying sediments of Permian age 

and one area (near Garden City, Kansas) where there 

had been downward movement of mineralized 

Arkansas River water. In the areas of upward leakage, 

calcium-sulfate and sodium-chloride waters dominated and concentrations of dissolved solids were 

elevated at the base of the aquifer (862 to 4,030 mg/L). 

Dissolution of gypsum or anhydrite and halite in sediments of Permian age by ground water were the likely 

sources of calcium, sulfate, sodium, and chloride in 

these areas.

Poor-quality Arkansas River water infiltrated 

the aquifer near Garden City, Kansas (Recon–1), 

calcium-sodium-sulfate waters dominated, and 

concentrations of dissolved solids near the water table 

were as large as 4,916 mg/L. Dissolution of minerals 

in sedimentary deposits of marine origin in upstream 

areas of the Arkansas River drainage were the likely 

sources of calcium, sodium, and sulfate in this area. 

Nitrate was detected throughout the aquifer, and 

the background concentration was estimated to be 

2.45 mg/L as N. The largest concentrations (8.28, 

22.0, and 54.4 mg/L as N) occurred in recently 

recharged water collected adjacent to irrigated fields. 

These data indicate that concentrations of nitrate 

increased over time in some areas of the aquifer as a 

result of agricultural activities. The pesticide data also 

indicate that agricultural activity has affected water 

quality in the aquifer. Three pesticides (atrazine, metolachlor, simazine) and five pesticide degradation products (alachlor ethanesulfonic acid, alachlor oxanilic 

acid, deethylatrazine, metolachlor ethanesulfonic acid, 

and metolachlor oxanilic acid) were detected in water 

samples from six water-table wells. Five of the six 

wells were adjacent to irrigated fields. Three of the top 

five pesticides used in the study area (in terms of 

pounds applied), or their degradation products, were 

detected in the water samples. Atrazine was present in 

water from one of the water-table wells at a concentration of 5 μg/L, which exceeded the 3-μg/L MCL. 

Results from this study indicate that vertical 

gradients in water chemistry existed in the central 

High Plains aquifer. The chemical gradients were the 

result of chemical inputs to the aquifer from underlying sediments of Permian age, from the Arkansas 

River, and from agricultural activities. In areas where 

those chemical inputs occurred, water quality in the 

aquifer was impaired and may not have been suitable 

for some intended uses.

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