U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007−5025

Prepared in cooperation with the 

CITY OF WICHITA, KANSAS, as part of the Equus Beds Ground-Water 

Recharge Project

Geochemical Effects of Induced Stream-Water and 

Artificial Recharge on the Equus Beds Aquifer, 

South-Central Kansas, 1995–2004

Recharge basins at

Sedgwick recharge

site

Settling

basin

N

Geochemical Effects of Induced StreamWater and Artificial Recharge on the Equus

Beds Aquifer, South-Central Kansas, 1995–

2004

By Heather C. Ross Schmidt, Andrew C. Ziegler, and David L. Parkhurst

Prepared in cooperation with the

CITY OF WICHITA, KANSAS, as part of the

Equus Beds Ground-Water Recharge Project

Scientific Investigations Report 2007–5025

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

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

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Schmidt, H.C. Ross, Ziegler, A.C., and Parkhurst, D.L., 2007, Geochemical effects of induced stream-water 

and artificial recharge on the Equus Beds aquifer, south-central Kansas, 1995–2004: U.S. Geological 

Survey Scientific Investigations Report 2007–5025, 58 p.

Front cover: Aerial photograph of Sedgwick recharge site (taken by Dave Stous, Burns and McDonnell 

Engineering Consultants, 1997).

Back cover: Photograph of recharge basins at Halstead recharge site (taken by Dave Stous, Burns and 

McDonnell Engineering Consultants, 1997).
Contents

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

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

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

Previous Studies ...................................................................................................................................3

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

Halstead Recharge System.................................................................................................................4

Sedgwick Recharge System...............................................................................................................5

Methods.........................................................................................................................................................11

Data Collection and Analysis............................................................................................................11

Water-Quality Data....................................................................................................................11

Continuous Data.........................................................................................................................12

Statistical and Mixing Models..........................................................................................................13

Flow and Solute-Transport Model....................................................................................................14

Geochemical Analysis and Simulations..........................................................................................14

Geochemical Effects of Induced Stream-Water Recharge at the Halstead Diversion Well Site ..16

Major Ion Chemistry and Tracers of Stream Water .....................................................................16

Selected Trace Metal Chemistry .....................................................................................................22

Geochemical Simulations..................................................................................................................26

Stream-Water Mixing in Adjacent Aquifer and Solute-Transport Model .................................28

Hydrologic Conditions...............................................................................................................28

Simple Mixing.............................................................................................................................28

Flow and Solute-Transport Model....................................................................................................31

Model Definitions and Flow Simulations ...............................................................................31

Solute Transport.........................................................................................................................33

Geochemical Effects of Artificial Recharge at Halstead Recharge Site............................................37

Major Ion Chemistry and Tracers of Recharge Water ................................................................37

Selected Trace Metal Chemistry .....................................................................................................39

Geochemical Simulations..................................................................................................................41

Geochemical Effects of Artificial Recharge at Sedgwick Recharge Site ..........................................42

Major Ion Chemistry and Tracers of Recharge Water .................................................................43

Selected Trace Metal Chemistry......................................................................................................47

Geochemical Simulations..................................................................................................................48

Summary and Conclusions.........................................................................................................................54

References Cited..........................................................................................................................................56

Figures

1. Maps showing location of study area in south-central Kansas ..........................................2

2. Maps showing features of Halstead recharge system including Halstead diversion 

well site and Halstead recharge site.........................................................................................6

3. Hydrogeologic section showing lithology at Halstead diversion well site.........................8

4. Hydrogeologic section showing lithology at Halstead recharge site .................................9

5. Map showing features of Sedgwick recharge site..............................................................10

6. Hydrogeologic section showing lithology at Sedgwick recharge site .............................11

iii
7. Graph showing relation between chloride concentrations and streamflow in Little 

Arkansas River at Highway 50 near Halstead during demonstration recharge period, 

April 1996–June 2002..................................................................................................................14

8. Graph showing estimated chloride concentrations in the Little Arkansas River at 

Highway 50 near Halstead using regression models based on streamflow and specific 

conductance measurements compared to measured chloride concentrations in water 

samples from the Little Arkansas River, 1995–2004 ..............................................................15

9. Piper diagrams describing major ion chemistry of water samples from monitoring wells 

and diversion well water at the Halstead diversion well site during March 1996, July 

1996, June 2001, and May 2003.................................................................................................17

10–16. Graphs showing:

10. Measured and estimated chloride concentrations in water samples from Little 

Arkansas River at Highway 50 near Halstead and from monitoring wells and 

diversion well water at Halstead diversion well site, February 1995–December

2004 ......................................................................................................................................21

11. Relation between chloride concentrations and specific conductance 

measurements in water from the diversion well at Halstead diversion well site, 

February 1995–May 2002 ..................................................................................................22

12. Measured and estimated atrazine concentrations in water from Little Arkansas 

River at Highway 50 near Halstead and from monitoring wells and diversion well 

water at Halstead diversion well site, February 1995–December 2004....................23 

13. Measured and estimated arsenic concentrations in water samples from Little 

Arkansas River at Highway 50 near Halstead and from monitoring wells and 

diversion well water at Halstead diversion well site, February 1995–December 

2004 ......................................................................................................................................25

14. Arsenic, iron, and manganese concentrations in deep monitoring well 

EB–145–PD5 at Halstead diversion well site, February 1995–December 2004........26

15. Iron concentrations in water samples from Little Arkansas River at Highway 50 

near Halstead and from monitoring wells and diversion well water at Halstead 

diversion well site, February 1995–December 2004.....................................................27

16. Water-level altitudes in monitoring wells at Halstead diversion well site and in 

Little Arkansas River at Halstead for November 1995–December 2004 and for 

January 2004–December 2004.........................................................................................30

17. Piper diagrams showing median major ion chemistry in water samples from Little 

Arkansas River at Highway 50 near Halstead, diversion well, and shallow monitoring 

well EB–145–A5 at the Halstead diversion well site ............................................................32

18. Computer screen capture showing model grid for the flow and solute-transport model 

at the Halstead diversion well site ..........................................................................................33

19. Maps showing simulated water-level contours for the upper and lower parts of the 

aquifer adjacent to the Little Arkansas River at the Halstead diversion well site...........34

20. Graphs showing simulated and measured water-level response to pumping at the 

Halstead well site .......................................................................................................................35

21. Computer screen capture showing initial chloride distribution for solute-transport 

model at the Halstead diversion well site...............................................................................36

22. Graph showing simulated fraction of stream chloride concentration in Halstead diversion well over a 100-year simulation ......................................................................................36

23. Piper diagrams showing major ion chemistry in water samples from the Halstead 

recharge site in May 1997, May 1999, and April 2003...........................................................38

iv
24–27. Graphs showing: 

24. Chloride concentrations in ground-water samples from the diversion well at 

Halstead diversion well site and monitoring wells at Halstead recharge site, 

May 1997–December 2004 ...............................................................................................41

25. Atrazine concentrations in ground-water samples from diversion well water at 

Halstead diversion site and monitoring wells at Halstead recharge site compared 

to concentra­tions in diverted recharge water, May 1997–December 2004.............42

26. Arsenic concentrations in ground-water samples from diversion well water at 

Halstead diversion site and monitoring wells at Halstead recharge site compared 

to concentrations in diverted recharge water, May 1997–Decem­ber 2004.............43

27. Iron concentrations in ground-water samples from diversion well water at 

Halstead diversion site and monitoring wells at Halstead recharge site compared 

to concentrations in diverted recharge water, May 1997–December 2004.............44

28. Piper diagrams showing major ion chemistry in water samples from the Sedgwick 

recharge site in July 1997, May 1999, and August 2002 .......................................................46

29–33. Graphs showing:

29. Measured and estimated chloride concentrations in water samples from Little 

Arkansas River near Sedgwick, treated diverted stream water, and monitoring 

wells at the Sedgwick recharge site, February 1995–Decem­ber 2004.....................49

30. Atrazine concentrations in water samples from Little Arkansas River near 

Sedgwick, treated diverted stream water, and monitoring wells at the Sedgwick 

recharge site, February 1995– December 2004 ............................................................50

31. Arsenic concentrations in water samples from Little Arkansas River near 

Sedgwick, treated diverted stream water, and monitoring wells at the Sedgwick 

recharge site, February 1995–December 2004 .............................................................51

32. Iron concentrations in water samples from Little Arkansas River near Sedgwick, 

treated diverted stream water, and monitoring wells at the Sedgwick recharge 

site, February 1995–December 2004...............................................................................52

33. Saturation indices for calcite and amorphous iron oxide, and modeled pH for theoretical mixing model of artificial recharge by injection of treated stream water 

into the Equus Beds aquifer.............................................................................................54

Tables 

1. Description of data-collection sites for Equus Beds Ground-Water Recharge Project, 

south-central Kansas, 1995–2004...............................................................................................7

2. Results of analysis of atrazine degradation products in water samples from the Little 

Arkansas River, from monitoring wells, and the diversion well at the Halstead diversion 

well site, south-central Kansas, 1995–2004............................................................................24

3. Saturation indices calculated for ground-water samples collected from Halstead 

diversion well site, south-central Kansas, March 1995–July 2003.....................................29

4. Saturation indices calculated for ground-water samples collected from monitoring 

wells at Halstead recharge site and Halstead diversion well, south-central Kansas, 

May 1997–April 2003...................................................................................................................45

5. Saturation indices calculated for ground-water samples collected from monitoring 

wells at Sedgwick recharge site and for samples of treated diverted stream water, 

south-central Kansas, July 1997–April 2003...........................................................................53
Conversion Factors, Abbreviations, and Datums

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi)

meter (m)

yard (yd)

1.609

3.28

0.9144

kilometer (km)

foot (ft)

meter (m)

Area

acre 4,047 square meter (m2)

square mile (mi2) 2.590 square kilometer (km2) 

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

foot per day (ft/d)

gallon per minute (gal/min)

inch per year (in/yr)

0.3048

0.06309

2.54

meter per day (m/d)

liter per second (L/s)

centimeters per year (cm/yr)

Volume

gallon (gal)

micrograms per liter (μg/L)

milligrams per liter (mg/L)

million gallons (Mgal)

0.003785

1.0

1.0

3,785

cubic meter (m3)

part per billion (ppb)

part per million (ppm)

cubic meter (m3)

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

 °F=(1.8×°C)+32.

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

 °C=(°F-32)/1.8.

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

25 °C).

Datums

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

(NAVD 88).

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

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

vi
Geochemical Effects of Induced Stream-Water and 

Artificial Recharge on the Equus Beds Aquifer, SouthCentral Kansas, 1995–2004

By Heather C. Ross Schmidt, Andrew C. Ziegler, and David L. Parkhurst

Abstract 

Artificial recharge of the Equus Beds aquifer is part of a 

strategy implemented by the city of Wichita, Kansas, to preserve future water supply and address declining water levels 

in the aquifer of as much as 30 feet caused by withdrawals 

for water supply and irrigation since the 1940s. Water-level 

declines represent a diminished water supply and also may 

accelerate migration of saltwater from the Burrton oil field to 

the northwest and the Arkansas River to the southwest into the 

freshwater of the Equus Beds aquifer. 

Artificial recharge, as a part of the Equus Beds GroundWater Recharge Project, involves capturing flows larger than 

base flow from the Little Arkansas River and recharging the 

water to the Equus Beds aquifer by means of infiltration or 

injection. The geochemical effects on the Equus Beds aquifer 

of induced stream-water and artificial recharge at the Halstead 

and Sedgwick sites were determined through collection and 

analysis of hydrologic and water-quality data and the application of statistical, mixing, flow and solute-transport, and 

geochemical model simulations. 

Chloride and atrazine concentrations in the Little Arkansas River and arsenic concentrations in ground water at the 

Halstead recharge site frequently exceeded regulatory criteria. During 30 percent of the time from 1999 through 2004, 

continuous estimated chloride concentrations in the Little 

Arkansas River at Highway 50 near Halstead exceeded the 

Secondary Drinking-Water Regulation of 250 milligrams per 

liter established by the U.S. Environmental Protection Agency. 

Chloride concentrations in shallow monitoring wells located 

adjacent to the stream exceeded the drinking-water criterion 

five times from 1995 through 2004. Atrazine concentrations 

in water sampled from the Little Arkansas River had large 

variability and were at or near the drinking-water Maximum 

Contaminant Level of 3.0 micrograms per liter as an annual 

average established by the U.S. Environmental Protection 

Agency. Atrazine concentrations were much smaller than the 

drinking-water criterion and were detected at much smaller 

concentrations in shallow monitoring wells and diversion 

well water located adjacent to the stream probably because 

of sorption on aquifer sediment. Before and after artificial 

recharge, large, naturally occurring arsenic concentrations 

in the recharge water for the Halstead diversion well and 

recharge site exceeded the Maximum Contaminant Level of 

10 micrograms per liter established by the U.S. Environmental Protection Agency for drinking water. Arsenic and iron 

concentrations decreased when water was recharged through 

recharge basins or a trench; however, chemical precipitation 

and potential biofouling eventually may decrease the artificial 

recharge efficiency through basins and trenches. 

At the Sedgwick site, chloride concentrations infrequently exceeded regulatory criteria. Large concentrations of 

atrazine were treated to decrease concentrations to less than 

regulatory criteria. Recharge of treated stream water through 

recharge basins avoids potentially large concentrations of arsenic and iron that exist at the Halstead diversion site. 

Results from a simple mixing model using chloride as a 

tracer indicated that the water chemistry in shallow monitoring 

well located adjacent to the Little Arkansas River was 

80 percent of stream water, demonstrating effective recharge 

of the alluvial aquifer by the stream. Results also indicated 

that about 25 percent of the water chemistry of the diversion 

well water was from the shallow part of the aquifer. Additionally, diverting water through a diversion well located adjacent 

to the stream removed about 75 percent of the atrazine, probably through sorption to aquifer sediment, and decreased the 

need for additional water treatment to remove atrazine. 

A flow and solute-transport model was developed using 

water-level and chloride concentration data to simulate and 

better evaluate the quantity of stream-water flow to the pumping diversion well. Simulation results indicate that chloride 

concentrations in the diversion well are dependent on the 

chloride distribution in the aquifer during the first few years 

of pumping. About 75 percent of the water in the diversion 

well originates from stream water after long-term continuous 

pumping for decades.

A theoretical geochemical model was developed to 

simulate the effects of artificially recharging fully oxygenated, 

treated stream water, by injection into the aquifer. Results 

indicate that chemical precipitation of calcite and iron oxyhydroxide are likely to occur and the potential increase of iron 

bacteria may combine to cause reduced efficiency of injection 

wells.
Introduction

The Wichita well field, developed in the 1940s in the 

Equus Beds aquifer, is one of the primary sources of water for 

the city of Wichita and the surrounding area in south-central 

Kansas (fig. 1). Historical water use for municipal supply and 

irrigation have caused water levels in the Equus Beds aquifer 

to decline more than 30 ft by 1993 in some areas (Aucott and 

others, 1998). Water-level declines represent a diminished 

water supply and also may accelerate migration of saltwater from the Burrton oil field to the northwest and from the 

Arkansas River to the southwest into the freshwater of the 

Equus Beds aquifer (Myers and others, 1996). 

Cheney Reservoir was first used in 1965 to supplement 

Wichita’s water supply from the Wichita well field (fig. 1). 

From 1965 through the mid-1990s, the city of Wichita’s 

water supply consisted of a mixture of 40 percent water from 

Cheney Reservoir and 60 percent water from the Equus Beds 

aquifer (Warren and others, 1995). Water-supply withdrawals were revised in the mid-1990s to use reservoir water for 

   Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

Study area

0 2 4 6 8 10 MILES

0 2 4 6 8 10 KILOMETERS

37 ̊45'

38 ̊

38 ̊15'

97 ̊45' 30' 97 ̊15'

Arkansas

River

River

Arkansas

Little

West

East

Emma

Emma

Sand 

Creek

Creek

Creek

RICECOUNTY

RENO

COUNTY

MARION

COUNTY

MCPHERSON

COUNTY

Approximate 

extent of High

Plains aquifer

system in 

Kansas

SEDGWICK

COUNTY

HARVEY

COUNTY

Hesston

Newton

Bentley

Mount

Hope

Patterson

Hutchinson

Alta Mills

Cr

Emma eek

Halstead

Index map

Cheney

Reservoir

KANSAS

Approximate extent of

Wichita well field

Andale

Valley

Center

Sedgwick

Wichita

Halstead

recharge site

Sedgwick

recharge

site

Intake for 

Sedgwick

recharge site

Base from U.S. Geological Survey digital data, 1:100,000, 1983 

Lambert Conformal Conic projection

Standard parallels 33 ̊ and 45 ̊, central meridian -98 ̊15'

EXPLANATION

Cow

Creek

Creek

Kisiwa

North

Fork

Burrton

Ninnescah River

Saltwater plume

Saltwater plume

Diversion

well site

Sedgwick treatment

facility

Approximate boundary of 

Equus Beds aquifer

(from Ross, 1991; Juracek

and Hansen, 1995)

Approximate location 

of McPherson channel

(from Williams and 

Lohman, 1949)

Boundary of Little

Arkansas River Basin

KINGMAN

COUNTY

Low-head

dam

Newton

McPherson

07143672

07143680

07144100

07144100 U.S. Geological Survey

 stream-gaging station 

 and number

Figure 1. Location of study area in south-central Kansas.
a larger percentage of the drinking-water supply because of 

declining water levels in the Equus Beds aquifer. Since 1993, 

ground-water levels have recovered more than 20 ft in some 

areas of the Wichita well field, primarily because of increased 

water use from Cheney Reservoir and decreased pumping in 

the well field area (Hansen and Aucott, 2004). In 2003, water 

from Cheney Reservoir was used for 60 percent of the water 

supply for the city of Wichita (Joan Kenny, U.S. Geological 

Survey, written commun., January 28, 2005). However, an 

expected increase in demand could cause supply shortages in 

the future (2050) (Jerry Blain, Water Supply Projects Administrator, city of Wichita Water and Sewer Department, oral 

commun., 2005). 

Artificial recharge of the Equus Beds aquifer will be 

used to augment the city of Wichita’s future water supply and 

help to preserve all existing aquifer uses from degradation by 

saltwater migration from the Burrton oil field and the Arkansas 

River by increasing water levels in the aquifer (fig. 1). Artificial 

recharge, as a part of the Equus Beds Ground-Water Recharge 

Project, involves capturing streamflows larger than base flow 

from the Little Arkansas River and recharging the water to the 

Equus Beds aquifer by means of infiltration or injection. The 

Equus Beds aquifer is recharged naturally by precipitation, 

subsurface inflow, streamflow losses, and irrigation return 

flow (Myers and others, 1996). Precipitation recharge, the 

major source of natural recharge for the Equus Beds aquifer, is 

estimated to be approximately 3 in/yr (Hansen, 1991). 

Artificial recharge adds a larger volume of water to the 

aquifer over a shorter period of time than would occur with 

natural infiltration. Artificially recharged water, however, 

may not have time to equilibrate to the existing ground-water 

chemical composition. Potential effects of artificial recharge 

include altering the pH and (or) dissolved oxygen concentration of the water, which could affect the solubility and mobility of ions important to water quality, such as calcium, bicarbonate, arsenic, and iron. Changes in dissolved oxygen could 

increase or decrease bacterial activity and potentially increase 

iron concentrations. Increased bacterial activity can create 

biofilms that reduce the effectiveness of artificial recharge. 

Dissolution of aquifer material can release constituents, such 

as arsenic, into ground water. Precipitation of minerals could 

reduce the size of aquifer pores, which could result in slower 

flow velocities through and smaller storage volumes in the 

aquifer (Drever, 1997).

A demonstration project for the Equus Beds GroundWater Recharge Project was conducted from April 1995 

through May 2002 to determine the feasibility of proposed 

artificial recharge methods, as well as to determine the effects 

of artificial recharge on the water quality of the aquifer. Different methods of capturing and recharging flows larger than base 

flow in the Little Arkansas River were used in two different 

recharge systems. The Halstead recharge system consisted of a 

diversion well, operated only when adjacent streamflows were 

larger than base flow, and a recharge facility 2 mi away where 

recharge water from the diversion well was distributed to surface-spreading basins, a recharge trench, or an injection well. 

In the Sedgwick recharge system, flows greater than base flow 

were diverted directly from the Little Arkansas River. The 

water then was treated and artificially recharged to the aquifer 

through surface-spreading recharge basins. 

The Equus Beds Ground-Water Recharge Project is a 

cooperative effort between the city of Wichita and the U.S. 

Geological Survey (USGS). The USGS role in the cooperative study is to document changes in historic hydrologic and 

water-quality conditions, identify probable causes of the 

changes in the study area, and define pre-recharge conditions 

for evaluating the effects of artificial recharge related to water 

quantity and water quality. Additional participants in the study 

are the Equus Beds Groundwater Management District No. 2 

(Halstead, Kansas), Bureau of Reclamation (U.S. Department 

of Interior), and the U.S. Environmental Protection Agency 

(USEPA). Project work is coordinated with the Kansas Department of Health and Environment (KDHE), the Kansas Water 

Office, and the Kansas Department of Agriculture, Division of 

Water Resources. Burns and McDonnell Engineering Consultants (Kansas City, Missouri) and Mid-Kansas Engineering 

Consultants (Wichita, Kansas) provide engineering expertise 

and project management. The maintenance and operation of 

the recharge facilities are performed by the city of Wichita. 

Purpose and Scope

This report describes the geochemical effects of induced 

stream-water recharge at the Halstead diversion site and 

artificial recharge on part of the Equus Beds aquifer at the 

Halstead and Sedgwick recharge sites. Effects of induced 

stream-water recharge through a pumping well at the Halstead diversion well site are described by analyses of water 

levels, water chemistry of stream and recharge water, a simple 

chloride-based mixing model to estimate the percentage of 

stream water in the adjacent aquifer over time, and a flow and 

solute-transport model to estimate the amount of stream water 

in the diversion well. 

Water-quality data collected during 1995–2004 from 

ground- and stream-water sites were used to describe the 

geochemical effects of artificial recharge processes. Changes 

in water chemistry as well as the multifunctional geochemical 

model PHREEQC (Parkhurst and Appelo, 1999) were used to 

describe geochemical processes caused by artificial recharge. 

Methods described in this report can be applied to similar 

recharge studies in other parts of the United States and foreign 

lands with similar hydrologic conditions.

Previous Studies

This report is one of several that are based upon the 

extensive data set collected as part of the Equus Beds GroundWater Recharge Project. Two previous reports presented 

results that are pertinent to the study described in this report. 

The first water-quality summary report, “Baseline Water Quality and Preliminary Effects of Artificial Recharge on Ground 

Introduction 
Water, South-Central Kansas, 1995–98” (Ziegler and others, 1999) presented results that indicate the initial effects of 

artificial recharge were minimal, that the water types involved 

in the recharge process were compatible, and that the primary 

constituents of concern for artificial recharge were chloride 

and atrazine because of generally larger concentrations of 

these constituents in stream water when compared to native 

ground water. Chloride and atrazine also were identified 

as constituents of concern because concentrations of these 

constituents in the stream water exceeded USEPA regulatory 

criteria. Other potential constituents of concern were sodium, 

nitrite plus nitrate, iron, manganese, and total coliform bacteria. 

A second water-quality summary report “Effects of Artificial Recharge on Water Quality in the Equus Beds Aquifer, 

South-Central Kansas, 1995–2000” (Ziegler and others, 2001) 

found that the overall effects of 3 years of artificial recharge 

did not substantially change ground-water quality. The report 

identified chloride, atrazine, total coliform bacteria, and 

additionally arsenic, as constituents of concern for recharge 

activities. Arsenic concentrations in the recharge water at 

Halstead ranged from 16 to 24 μg/L. Pre-artificial recharge 

arsenic concentrations in samples from monitoring wells at 

the Halstead recharge site ranged from less than 1 to 11 μg/L, 

and larger dissolved arsenic concentrations likely came from 

aquifer material (Ziegler and others, 2001). Arsenic was not 

included in the 1999 report because the USEPA Maximum 

Contaminant Level (MCL) for drinking water in 1999 was 

50 μg/L, and arsenic concentrations in water sampled as a 

part of the artificial recharge demonstration project did not 

approach 50 μg/L (Ziegler and others, 2001). In 2001, USEPA 

revised the arsenic MCL for finished drinking water to 

10 μg/L, effective in January 2006 (U.S. Environmental 

Protection Agency, 2004), and as a result, arsenic became a 

constituent of concern for artificial recharge.

Description of Study Area

The study area for the Equus Beds Ground-Water 

Recharge Project encompasses approximately 165 mi2 and 

extends northwest of the city of Wichita across parts of Harvey 

and Sedgwick Counties in south-central Kansas (fig. 1). The 

study area is bounded by the Arkansas River on the southwest 

and the Little Arkansas River on the northeast. The drainage 

area for the Little Arkansas River Basin near Sedgwick (site 

07144100) is about 1,165 mi2 (Ziegler and others, 1999). 

South-central Kansas has a continental climate that is 

characterized by large variations in seasonal temperatures, 

moderate precipitation, and windy conditions (Hansen and 

Aucott, 2004). In Wichita, Kansas, long-term daily average 

temperatures for 1971–2000 range from 30.2 °F in January to 81.0 °F in July (National Oceanic and Atmospheric 

Administration, 2002). The long-term annual mean precipitation for 1940–2005 at weather stations near the study area 

(at Halstead, Hutchinson, Mount Hope, Newton, Sedgwick, 

and Wichita) is 31.35 in. (National Oceanic and Atmospheric 

Administration, 1998–2005b). Most of this precipitation commonly occurs during spring and summer (May–September) 

(Hansen and Aucott, 2004).

Land use in the Little Arkansas River Basin is primarily 

agricultural and includes the production of livestock (pasture 

and rangeland) and field crops. Field crops produced include 

corn, sorghum, soybeans, and wheat (U.S. Department of 

Agriculture, 2002a,b). Agricultural chemicals applied to 

enhance crop production in the basin include fertilizers (such 

as nitrate, ammonia, and phosphorus) and pesticides (primarily 

alachlor and atrazine). 

The Equus Beds aquifer, the easternmost extension of 

the larger High Plains aquifer system, consists of unconsolidated silt, clay, sand, and gravel deposits of Quaternary 

age (Williams and Lohman, 1949). The Equus Beds aquifer 

includes alluvium adjacent to the streams in the study area. 

The McPherson channel (fig. 1), a trough of unconsolidated 

deposits about 200 ft thick within the Equus Beds aquifer, is a 

major flow path for ground-water movement within the aquifer 

and is important as it relates to the movement of chemical 

constituents (Williams and Lohman, 1949). 

The Equus Beds aquifer is an important source of ground 

water for the area because of generally shallow depth to the 

water table, large saturated thickness, and generally good 

water quality (Hansen and Aucott, 2004). Near the Arkansas 

River, the water table may be as little as 10 ft below land 

surface. Near the Little Arkansas River, the water table is at 

a greater depth, depending on the altitude of the land surface 

and the amount of water-level decline that has been caused by 

ground-water withdrawals. The maximum saturated thickness 

of the Equus Beds aquifer within the study area (almost 

250 ft) is near the Arkansas River and corresponds to the deepest areas of the underlying bedrock surface (Myers and others, 

1996). 

The direction of ground-water movement in the Equus

Beds aquifer generally is to the east (Aucott and others, 

1998). The Little Arkansas River primarily is a gaining stream 

within the study area as indicated by higher water levels in 

wells adjacent to the stream, which causes discharge from the 

aquifer to the stream during base-flow conditions (Myers and 

others, 1996; Aucott and others, 1998). However, in the vicinity of the Halstead diversion well site, a low-head dam on the 

river (fig. 1) has caused river elevation to be higher than water 

levels in the adjacent alluvium resulting in constant recharge 

of water from the Little Arkansas River to the aquifer (Ziegler 

and others, 1999). 

Halstead Recharge System 

The Halstead recharge system consists of the streamgaging station and water-quality monitoring site on the Little 

Arkansas River at Highway 50 near Halstead (site 07143672, 

fig. 1), a river-stage monitoring site on the Little Arkansas 

   Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer
River at Halstead (site 07143680, fig. 2A), the Halstead diversion well site (fig. 2A), and the Halstead recharge site (fig. 2B). 

During the demonstration phase of the recharge project, in 

accordance with Kansas Department of Agriculture, Division 

of Water Resources, permit conditions, the recharge water 

was diverted by pumping the diversion well adjacent to the 

Little Arkansas River only when flow exceeded 42 ft3/s at the 

upstream stream-gaging station (site 07143672, fig. 1) from 

April 1 through September 30 and when flow exceeded 20 ft3/s 

from October 1 through March 31 (Burns and McDonnell, 

written commun., 1998). Recent permit approval for Phase I 

of the full-scale artificial recharge and storage project 

(August 2005) by the Kansas Department of Agriculture, 

Division of Water Resources, requires minimum streamflow in 

the Little Arkansas River at Highway 50 near Halstead of 

57 ft3/s from April through September and 20 ft3/s from October through March (Kansas Department of Agriculture, Division of Water Resources, written commun., August 2005).

The Halstead diversion well site includes five shallow monitoring wells identified as EB–145–A1 through 

EB–145–A5, one deep monitoring well EB–145–PD5, and a 

pumping (diversion) well (table 1). The depths of the shallow wells range from 43 to 70 ft below land surface, and the 

wells are located approximately 45 to 1,600 ft from the river. 

Observation wells EB–145–PD3 and EB–145–PS3 (table 1, 

fig. 3) were used during aquifer tests conducted by Burns and 

McDonnell Concultants, Kansas City, Missouri, at the site and 

were not used for water-quality sampling. They are included 

in this report to describe the lithology at the site. All wells are 

constructed of 2-in. diameter polyvinyl chloride (PVC) and 

generally are screened in the lower 10 ft of the casing. The 

string of shallow wells trends in a southwest line that is roughly 

perpendicular to the stream at the site (fig. 2A). The deep monitoring well (EB–145–PD5) at the site is completed at a depth 

of approximately 120 ft and is located approximately 60 ft 

from the river. The deep monitoring well is screened over the 

lowest 5 ft of the well casing. The diversion well is a pumping 

well located approximately 150 ft north of the string of monitoring wells, and the depth of the well is approximately 136 ft. 

The diversion well is located approximately 70 ft from the 

Little Arkansas River. The pumping capacity of the diversion 

well is about 1,000 gal/min, and the well is screened throughout the lower 60 ft of the casing (table 1). 

Well logs indicate that the lithology at the diversion well 

site consists primarily of sand deposits interbedded with clay 

layers of varying thicknesses (fig. 3). A discontinuous clay 

layer occurs approximately 50 ft below land surface at the 

diversion well site. The clay layer extends laterally beneath 

the Little Arkansas River to the west (Burns and McDonnell, 

written commun., 1998) and pinches out between monitoring 

well EB–145–A2 and EB–145–A3 to the west (fig. 3). Where 

present, the lower permeability clay slows vertical movement 

of water from the upper part into the lower part of the aquifer. 

Although this clay layer alters direct flow of stream water into 

the lower part of the aquifer, it does not inhibit it entirely, and 

there is connectivity between the upper and lower parts of the 

aquifer (Burns and McDonnell, written commun., 1998). 

Recharge water from the diversion well was pumped 

about 2 mi through a pipeline to the Halstead recharge site 

where it was artificially recharged into the Equus Beds 

aquifer by one of three methods—surface-spreading recharge 

basins, a recharge trench, or a direct injection well (fig. 2B). 

Two recharge basins at the Halstead site are each capable of 

initially recharging 60 to 80 ft/d into the aquifer (Burns and 

McDonnell, written commun., 2005). However, a clay layer 

with some sand approximately 30 ft below land surface at 

the recharge site impedes vertical flow of recharge water into 

the aquifer (Ziegler and others, 1999) (fig. 4). This impediment caused water to rise to the bottom of the recharge basins, 

which resulted in lateral flow and slowed percolation through 

these basins to about 1 to 2 ft/d. The addition of passive 

recharge wells (2-in. well completed through the clay layer) 

increased infiltration rates to 6 to 8 ft/d (Burns and McDonnell, written commun., 2005). A recharge trench was installed 

by the city of Wichita to promote vertical movement of 

recharge water into the aquifer. The recharge trench is 

100 ft long, 3 ft wide, and approximately 15 ft deep; it has 

been tested at recharge rates of 60 to 80 ft/d (Burns and 

McDonnell, written commun., 2005). In addition, a direct 

injection well was used to recharge water into the lower part of 

the Equus Beds aquifer. The injection well is 225 ft deep and 

is capable of recharging about 900 gal/min to the aquifer. The 

vertical-flow problems associated with recharge basins at the 

site do not affect the injection well because the recharge water 

is injected beneath the clay layer. 

At the Halstead site, two shallow monitoring wells 

(SMW–H4 and SMW–H14) are completed at depths of 29 and 

27 ft, respectively; the wells are screened in the lowermost 

10 ft of the well casing. Two deep monitoring wells (DMW–

H1 and DMW–H13) also are located at the site and are completed to a depth of 220 ft. Deep monitoring wells H1 and H13 

are screened from 210 to 220 ft below land surface (table 1).

Artificial recharge began at the Halstead recharge site 

on May 29, 1997, and was discontinued in May 2002 when 

the demonstration phase of the Equus Beds Ground-Water 

Recharge Project ended. Almost 930 Mgal of water were 

recharged at the Halstead recharge site during the demonstration project (Burns and McDonnell, written commun., 2002). 

Sedgwick Recharge System

The Sedgwick recharge system consists of the streamgaging and water-quality-monitoring site in the Little Arkansas River near Sedgwick (site 07144100), a treatment facility, 

and the Sedgwick recharge site (fig. 1). For the Sedgwick 

recharge system, Kansas Department of Agriculture, Division of Water Resources, permit conditions allow water to be 

withdrawn from the river at all times when streamflow exceeds 

40 ft3/s at site 07144100 (Burns and McDonnell, written commun., 1998). 

Description of Study Area   
 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

0 

0 100 200 300 400 500 FEET 

50 100 METERS 

Base map modified from Burns and McDonnell, 1996 

EB–145–A5 

EB–145–A4 

EB–145–A3 

EB–145–A1 

EB–145–A1

EB–145–PD3 

EB–145–PS3 

07143680 

Levee 

Little 

Arkansas 

River 

 South Halstead Road

Diversion 

well 

Farm

pond 

Gravel road 

EXPLANATION 

EB–145–A2 

EB–145–PD5 

N

N 

DMW–H1 

SMW–H4 

DMW–H13 

SMW–H14 

Recharge 

trench 

Site boundary 

Recharge 

control 

building 

Recharge

basin 2

Recharge 

basin 1 

0 30 60 90 120 150 FEET 

0 10 20 30 40 METERS

County Road 574 

Monitoring well and number 

U.S. Geological Survey stream- 

 gaging station and number 

Trace of section shown in 

 figure 3 

Trace of section shown in 

 figure 4 

Sewage 

lagoon 

Base map modified from Burns and McDonnell, 1996 

Halstead diversion well site 

Halstead recharge site

07143680 

SW 30th Street 

B

A A'

B'

B B'

A‘

A 

Direct injection

 well

(B) 

(A)

Figure 2. Features of Halstead recharge system including (A) Halstead diversion well site and 

(B) Halstead recharge site.
Description of Study Area 



Table 1. Description of data-collection sites for Equus Beds Ground-Water Recharge Project, south-central Kansas, 1995–2004.[NAVD 88, North American Vertical Datum of 1988; --, not applicable or not available]

Site grouping Data-collection site number (figs. 1–6) U.S. Geological Survey site identification number Site name

Gage datum 

or top of 

well casing 

altitude 

(feet above 

NAVD 88)

Approximate 

well depth 

(feet)

Approximate 

depth of 

screened 

interval (feet)

Stream-water monitoring sites 07143672 07143672 Little Arkansas River at Highway 50 near 

Halstead,KS

1,370.55 -- --

07143680 07143680 Little Arkansas River at Halstead, KS 1,371.00 -- --07144100 07144100 Little Arkansas River near Sedgwick, KS 1,340.00 -- --

Halstead diversion well site Diversion well 380051097335501 Diversion well at TH–04–95 -- 136.5 75.9–136.5

EB–145–A1 380028097311001 Well #1 at TH–04–95 1,392.87 48 37.6–47.6EB–145–A2 380028097310901 Well #2 at TH–04–95 1,392.68 47 37–47

EB–145–A3 380028097311101 Well #3 at TH–04–95 1,392.82 70 60–70

EB–145–A4 380027097311401 Well #4 at TH–04–95 1,394.00 60 50–60EB–145–A5 380028097312701 Well #5 at TH–04–95 1,394.26 43 32–42

EB–145–PD5 380028097311002 Deep monitoring well 1,392.40 120 112–117EB–145–PD3 -- Deep observation well at TH–04–95 -- 124 114–124

EB–145–PS3 -- Shallow observation well at TH–04–95 -- 52 42–52

Halstead recharge site SMW–H4 380051097335601 Shallow monitoring well SMW–H4 1,429.22 29 19–29

SMW–H14 380053097335101 Shallow monitoring well SMW–H14 1,424.25 27 17–27

DMW–H1 380052097335701 Deep monitoring well DMW–H1 1,427.16 220 210–220DMW–H13 380053097335102 Deep monitoring well DMW–H13 1,424.31 220 210–220

Sedgwick recharge site Treated stream water 375331097285301 Treated stream water sampled at Sedgwick 

recharge site control building

-- -- --

SMW–S11 375327097285401 Shallow monitoring well SMW–S11 1,383.27 59 49–59SMW–S13 375332097284801 Shallow monitoring well SMW–S13 1,383.27 34.5 24.5–34.5

DMW–S10 375327097285402 Deep monitoring well DMW–S13 1,384.28 190 180–190DMW–S14 375332097284802 Deep monitoring well DMW–S14 1,384.03 195 185–195
   Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer 1,410 FEET 1,390 1,370 1,350 1,330 1,310 1,290 1,270 1,250 FEE 1,410

T

1,3901,3701,3501,3301,310

1,290

1,2701,250

A'

A 

0 0 

100 200 300 400 500 FEET 

50 100 METERS 

5 EB–145–A

EB–145–A4

EB–145–A3

EB–145–A2

est well (projected) T

EB–145–PD5 and EB–145–A1,

(composite)

(bend in section)

EB–145–PD3 and EB–145–PS3 

(composite) Levee Approximate land surface 

Screened interval 

Vertical exaggeration X 6 Datum is North American Vertical Datum of 1988 (NAVD 88)

Trace of section shown in figure 2A

Little Arkansas River

(1,376)

EB-145-A1

EB-145-PD5

EB-145-PS3

EB-145-PD3

(1,373.9)

(1,373.9)

(1,374) (1,374)

Clay Sand Silt Shale 

Approximate lithologic contactWater level—Number in parentheses ( ) is altitude of  water table in feet above NAVD 88, March 29, 1996Well-screen interval and identifier

EXPLANATION 

EB–145–PD5

Clay layer

Figure 3. Lithology at Halstead diversion well site.
Recharge water in the Sedgwick recharge system was 

diverted directly from the Little Arkansas River. After the 

water was diverted from the stream, it was treated with coagulants to remove sediment. Then, powdered activated carbon 

(PAC) was added to remove atrazine and other organic compounds from the water. After treatment, the water was pumped 

about 2 mi to the Sedgwick recharge site.

At the Sedgwick recharge site (fig. 5), the treated stream 

water was pumped to a settling basin to allow the remaining 

suspended sediment and PAC to settle out of the water. From 

the settling basin, treated stream water was pumped to one of 

three surface-spreading recharge basins and allowed to infiltrate into the Equus Beds aquifer. Shallow clay layers are not 

present to impede vertical movement of recharge water at this 

location; therefore, flow of recharge water to the water 

table occurs rapidly (fig. 6). Water levels in the shallow 

(wells SMW–S11 and SMW–S13) and deep (wells DMW–

S10 and DMW–S14) monitoring wells are the same and indicate hydraulic connection between the upper sand-and-gravel 

layers and the lower layers at the Sedgwick site. Infiltration 

rates through the recharge basins at this site averaged 8 to 

9 ft/d (Burns and McDonnell, written commun., 2005). Large 

permeability values of the sand-and-gravel layer underlying 

the recharge basins contribute to rapid infiltration. 

Artificial recharge at the Sedgwick recharge site began in 

April 1998 and continued through 2000. Approximately 

136 Mgal of treated stream water were artificially recharged to 

the aquifer at the Sedgwick recharge site (Burns and McDonnell, written commun., 2002). Artificial recharge activities 

ended in 2000 as the demonstration phase of the Equus Beds 

Ground-Water Recharge Project ended at the Sedgwick site. 

Description of Study Area   

Depth below land surface, in feet

30 feet 

225 feet 90 feet 75 feet

Recharge basin 2 

Clay 

Clay 

Clay 

Sand and gravel 

Clay with some sand 

Clay with some sand 

Sand with some clay 

220

230

240

210

200

190

180

170

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

10

Shale 

Vertical scale greatly exaggerated 

Not to scale horizontally 

Trace of section shown in figure 2B

Sand 

Sand 

Recharge 

trench 

Deep monitoring well 

DMW–H1 

Water level in nearby 0

shallow monitoring 

wells, May 13, 1997 

Land-surface

altitude 1,427.16 feet

Land-surface

altitude 1,427 feet Land-surface

altitude 1,424.31 feet

Screened interval 

for nearby shallow 

monitoring well 

SMW–H4 

Screened interval 

for nearby shallow 

monitoring well

SMW–H14 

Water level in deep 

monitoring wells, 

May 13, 1997 

Screened interval

for deep monitoring

well DMW–H1 Screened interval

for deep monitoring

well DMW–H13

B

Deep monitoring well 

DMW–H13 

B'

0 30 60 90 120 150 FEET 

0 10 20 30 40 METERS

Modified from Ziegler and others (1999)

Figure 4. Lithology at Halstead recharge site.
10 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

DMW–S10 

SMW–S11 

DMW–S14 

SMW–S13 

Site boundary 

Recharge 

control 

building 

Recharge 

basin 2 

Recharge 

basin 3 

Recharge 

basin 1 

N 

0 30 60 90 120 150 FEET 

0 10 20 30 40 METERS 

DMW–S10 Monitoring well and number

Trace of section shown in figure 6

EXPLANATION

119th Street West 

Base map modified from Burns and McDonnell, 1996 

C

C'

Sedgwick recharge site 

C C'

Modified from Ziegler and others (1999)

Settling

basin

Figure 5. Features of Sedgwick recharge site.
Methods

Data Collection and Analysis

Discrete water-quality samples as well as continuous 

water-quality, water-level, and streamflow data were used in 

this report to describe the geochemical effects of artificial 

recharge activities. Discrete water-quality samples were 

collected at monitoring well sites, at the diversion well, from 

treated diverted stream water from the settling basin at the 

Sedgwick recharge site, and at two stream-water sites on the 

Little Arkansas River. Real-time continuous water-quality data 

were collected at the Little Arkansas River at Highway 50 

near Halstead and at Sedgwick stream-gaging sites (07143672, 

07144100, fig. 1). 

Water-Quality Data 

Discrete stream- and ground-water-quality samples were 

collected from February 1995 through August 2004 throughout the study area. Stream-water samples were collected using 

depth- and width-integrating techniques (Wilde and Radtke, 

1998). Ground-water samples were collected with a submersible pump using methods described in Wood (1976), Koterba 

and others (1995), and Puls and Barcelona (1996). 

Analyses of water samples were performed to determine 

concentrations of dissolved solids, total and dissolved inorganic constituents, nutrients, organic compounds, volatile 

organic compounds (VOCs), radionuclides, and fecal-indicator 

bacteria in water samples (Ziegler and Combs, 1997). Arsenic speciation data also were collected and analyzed using 

methods described in Garbarino and others (2002). Dissolved 

concentrations of major ions; calcium, magnesium, sodium, 

Methods 11

Recharge basin 1 Recharge basin 3 

45 feet

210 feet 210 feet

C

Deep monitoring well

DMW–S10

C'

Deep monitoring well

DMW–S14

60 feet

Sand and gravel 

Clayey layer 

Sand and gravel 

Sand and gravel 

? 

? 

? 

Brown clay and sand 

Clay with some sand and gravel 

Clay with some sand 

Sand 

Shale 

190

180

170

160

150

140

130

120

110

100

90

80

70

60

50

40

30

20

10

0

45 feet 

Vertical scale greatly exaggerated 

Not to scale horizontally 

Trace of section shown in figure 5 

Depth below land surface, in feet

Water level in nearby

shallow monitoring

wells, July 17, 1997,

and deep monitoring

wells, June 19, 1997

Screened interval 

for nearby shallow 

monitoring well 

SMW–S11 

Screened interval 

for nearby shallow 

monitoring well

SMW-S13 

Screened interval 

for deep monitoring 

well DMW–S10 

Screened interval 

for deep monitoring 

well DMW–S14 

0 30 60 90 120 

0 10 20 30 40 METERS 

150 FEET

Land-surface

altitude 1,384.28 feet Land-surface

altitude 1,384.03 feet

Modified from Ziegler and others (1999)

Figure 6. Lithology at Sedgwick recharge site.
potassium, chloride, sulfate, and bicarbonate; trace metals; 

arsenic and its species; iron; and the organic compound, atrazine, are discussed in this report to describe the geochemical 

effects of artificial recharge. A discussion of all constituents 

sampled as a part of the Equus Beds Ground-Water Recharge 

Demonstration Project is included in Ziegler and others 

(1999). Samples were analyzed by the city of Wichita laboratory (Wichita, Kansas), the USGS National Water-Quality 

Laboratory (Denver, Colorado), and the USGS Organic Geochemistry Research Laboratory (Lawrence, Kansas).

Atrazine concentrations in water samples for this study 

were determined by enzyme-linked immunosorbent assay 

(ELISA), which is a screen for triazine compounds that 

include atrazine, cyanazine, propazine, and their degradation 

products. In addition, selected samples were confirmed as 

atrazine by gas chromatography/ mass spectrometry (GC/MS) 

at the USGS Organic Geochemistry Research Laboratory, 

Lawrence, Kansas. The relation between triazine herbicide 

concentrations determined by ELISA and atrazine concentrations determined by GC/MS for water collected from the Little 

Arkansas River is expressed by the equation: 

 (1)

where x is the triazine herbicide concentration and y is the 

atrazine concentration (Ziegler and others, 1999). This relation 

between triazine and atrazine concentrations indicates that 

atrazine made up 81 percent of triazine concentrations. For 

the purposes of this report, triazine compounds detected by 

ELISA methodology will be referred to as atrazine. 

Discrete water-quality samples were collected at least 

monthly from two stream-water sites on the Little Arkansas 

River from 1995 through 2003. In 2004, eight samples per 

stream-water site were collected from March through July. 

Water-quality samples were collected at least quarterly from 

all monitoring wells at the Halstead and Sedgwick recharge 

sites and from selected monitoring wells at the Halstead diversion well site. Water from the diversion well was sampled at 

least monthly while in operation. The treated stream water at 

the Sedgwick recharge site also was sampled at least monthly 

during active artificial recharge activities. 

Further information regarding data-collection methods, 

preservation, sample holding times, analytical methods, and 

reporting limits can be found in Ziegler and Combs (1997). 

A description of the data-collection sites used in this study is 

provided in table 1. Data used for analysis in this report are 

available on the Web at http://waterdata.usgs.gov/ks/nwis/qw. 

Statistical summaries of water-quality data are available at 

http://ks.water.usgs.gov/Kansas/studies/equus/ (accessed 

December 2006).

Replicate, blank, and standard reference samples were 

quality-control samples collected as a part of the Equus Beds 

artificial recharge project. More than 200 quality-control 

samples were collected from 1995 through 2004; the majority 

of these samples were replicate and blank samples. Replicate samples were collected to identify the variability in the 

sampling and analysis system (Wilde and Radtke, 1998). A 

replicate sample set is a set of two (or more) samples that are 

collected closely in time and space so that the sample sets are 

thought to be representative of the ambient water composition at one collection time (Wilde and Radtke, 1998). More 

than 100 replicate samples were collected from 1995 through 

2004. Replicate samples were compared with their respective original sample by relative percentage difference (RPD) 

between the two samples. RPDs were calculated as the difference between the replicate and original sample concentrations 

divided by the average of the two values, multiplied by 100. 

Generally, replicate samples had RPDs of 10 percent or less 

and indicated that sampling and analysis methods were consistent and did not introduce large variability into the data set. 

More than 90 blank samples were collected as a part of 

the Equus Beds artificial recharge project from 1995 through 

2004. Dissolved solids and sodium were detected in 10 percent 

of the blank samples at concentrations greater than 5 and 

1 mg/L, respectively. Fluoride was detected in 15 percent of 

the blank samples. The detections of sodium were small and 

probably because of impurities in the acid used to the preserve 

the samples. Fluoride detections in blank samples ranged from 

0.04 to 0.10 mg/L, and fluoride detected in environmental 

samples ranged from less than 0.02 to 0.82 mg/L; therefore, 

fluoride concentrations in environmental samples could be 

affected by sampling and analytical errors. 

Standard reference samples were analyzed by the Wichita 

Municipal Water and Wastewater Laboratory on an annual 

basis and submitted to the USGS Branch of Quality Systems 

for analysis of results and evaluation of laboratory performance. A laboratory rating is assigned for each sample type 

and overall. Ratings are based on the number of F-pseudosigmas the reported value is from the most probable value 

(MPV), which is defined as the Z-value. A rating of excellent to unsatisfactory is assigned depending on the range of 

the Z-value. Absolute Z-value ranges from 0.00 to 0.50 were 

excellent, 0.51 to 1.00 were good, 1.01 to 1.50 were satisfactory, 1.51 to 2.00 were marginal, and greater than 2.00 were 

unsatisfactory (U.S. Geological Survey, 2006). Evaluations of 

the Wichita laboratory were consistently good to excellent in 

major and minor ion analysis. However, nutrient analysis was 

rated marginal during some years of the Equus Beds artificial 

recharge project. Results are available on the Web at http://

bqs.usgs.gov/srs/. 

Continuous Data

Data from continuous stream-gaging stations, continuous real-time water-quality monitors, and pressure transducers 

installed in monitoring wells to record real-time ground-water 

levels were used along with discrete-sample analytical data 

to aid in the interpretation of results presented in this report. 

Real-time monitoring of streamflow in the Little Arkansas 

River at Sedgwick stream-gaging site (07144100) began in 

October 1993. The stream-gaging site on the Little Arkansas 

River at Highway 50 near Halstead (site 07143672) began 

real-time monitoring of streamflow in May 1995. Real-time 

12 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

y . = 0 81x,
monitoring of river stage and nearby monitoring wells began 

in October 1995 at the Little Arkansas River at Halstead 

stream-gaging site (07143680). 

Continuous real-time monitoring of specific conductance, 

pH, and temperature using a multiparameter water-quality 

monitor began in May 1998 at the Little Arkansas River at 

Highway 50 near Halstead stream-gaging site (07143672) and 

in April 1998 at the Sedgwick stream-gaging site (07144100). 

Dissolved oxygen and turbidity sensors were added to the 

water-quality monitors at both sites in October 1998. Waterquality sensors were calibrated and maintained according to 

methods presented in Wilde and Radke (1998) and Wagner 

and others (2000). 

Pressure transducers were installed to record near realtime ground-water levels in monitoring wells EB–145–A1, 

A2, A3, and A4 in October 1995. Pressure transducers were 

installed in monitoring well EB–145–A5 in November 

1995 and in well EB–145–PD5 in February 1996. Realtime ground-water levels were recorded in monitoring wells 

EB–145–A2, A3, A4 and A5 through March 2002. Groundwater levels were recorded in monitoring wells EB–145–A1 

and EB–145–PD5 through December 2004. 

Streamflow, water-level, and water-quality data were 

transmitted by satellite to a downlink site and to a computer at 

the USGS Kansas Water Science Center in Lawrence, Kansas. 

Data are available upon request, and daily values are available 

on the Web at http://waterdata.usgs.gov/ks/nwis/qw.

Statistical and Mixing Models

Methods for development of statistical regression models 

used to estimate continuous chloride, arsenic, and atrazine 

concentrations in the Little Arkansas River are described in 

Christensen and others (2000, 2003). Simple statistical models 

using streamflow as an explanatory variable were used to 

estimate daily chloride concentrations from data collected 

from 1995 through 1998 from the Little Arkansas River and 

were developed using methods described in Helsel and Hirsch 

(1992). The use of statistical analysis was necessary to determine estimates of daily chloride concentrations in the stream 

water for use in the mixing model. 

Specific conductance is a good indicator of chloride 

concentrations in water and was used in a regression equation developed by Christensen and others (2003) to estimate 

chloride concentrations in water at the Little Arkansas River 

at Highway 50 near Halstead stream gage. This equation was 

used to estimate daily chloride concentrations from May 1998 

through December 2004 because continuous specific conductance data were available for this time period. The regression 

equation is:

 (2) 

where Cl equals chloride concentration in milligrams per liter 

(mg/L) and SC equals specific conductance measurements 

in microsiemens per centimeter at 25 oC. The coefficient of 

determination (R2) for this regression is 0.96 (Christensen and 

others, 2003). However, because it was necessary to establish 

an estimate of daily chloride concentrations in the stream from 

February 1995 through May 1998, before continuous specific 

conductance measurements were collected, another regression 

model was developed for estimating chloride concentrations 

on the basis of streamflow in the Little Arkansas River at 

Highway 50 near Halstead. The regression relates measured 

chloride values to streamflow recorded during sampling 

(fig. 7). The equation is:

 (3)

where Cl is the estimated chloride concentration in milligrams 

per liter, and Q is streamflow in cubic feet per second. Equation 3 has an R2

 of 0.64, indicating that specific conductance 

is a better estimator of chloride concentrations than streamflow. Figure 8 compares continuous chloride concentrations 

estimated by streamflow (blue line) and continuous chloride 

concentrations estimated by specific conductance (red line) to 

measured chloride concentrations in water sampled from the 

Little Arkansas River at Highway 50 near Halstead (gold line). 

As expected, figure 8 demonstrates that the regression model 

developed to estimate chloride concentrations using specific 

conductance measurements estimated chloride concentrations 

more accurately than the regression model developed using 

streamflow. However, when specific conductance measurements were not available, streamflow was determined to be an 

acceptable alternative with which to estimate chloride 

concentrations. Continuous specific conductance and streamflow data are available on the Web at http://ks.water.usgs.gov/

Kansas/rtqw/ (accessed December 2006). Chloride concentrations estimated using specific conductance measurements also 

are available at http://ks.water.usgs.gov/Kansas/rtqw/.

A simple mixing model using estimated chloride concentrations in stream water and measured chloride concentrations in water sampled at the Halstead diversion well site were 

used to estimate the fraction of stream water pumped from the 

diversion well. The equation derived from Fischer and others 

(1979) is:

 (4) 

where

 f is the relative concentration of the chloride in 

the pumped water (f = 0 for pure aquifer 

water and f = 1 for pure stream water);

C is the concentration of chloride in the pumped 

water;

Ca is the concentration of chloride in aquifer 

water; and

Cs is the chloride concentration in stream water.

Assumptions associated with the mixing model are 

related to the variable chloride concentrations in the stream 

water, which will be discussed further in the section “StreamWater Mixing in Adjacent Aquifer and Solute-Transport 

Model.”

Methods 13

Cl = -33.7 + 0.209 SC,

log10Cl = -0.44log10Q + 2.9,

( )

( ) a

s a

C C

f , C C

− = −
Flow and Solute-Transport Model

The program PHAST (Parkhurst and others, 1995; 

Parkhurst and Kipp, 2002) was used to simulate flow and 

transport of chloride from the stream through the aquifer into 

the diversion well. PHAST is a ground-water flow and reactive solute-transport simulator with capabilities to model a 

wide range of equilibrium and kinetic geochemical reactions 

(Parkhurst and others, 2004); however, no chemical reactions 

were included in the simulations described in this report. Flow 

parameters were calibrated to water-level altitudes measured 

during aquifer testing. Parameters were estimated using 

UCODE software (Poeter and Hill, 1998; Poeter and others, 

2005). UCODE performs nonlinear regression to estimate 

parameter values that result in the best fit between simulated 

values and observations. Estimated parameters included the 

hydraulic conductivity of the upper and lower sand and gravel 

aquifer, the hydraulic conductivity of the upper and lower clay 

layers, and the leakance of the streambed. These parameters 

were adjusted to accurately simulate the water levels in monitoring wells during the pumping and recovery periods of the 

aquifer test performed in 1996.

Geochemical Analysis and Simulations

Geochemical analysis of the effects of artificial recharge 

was accomplished by two analysis methods. First, an analysis 

of major ion and trace metal chemistry provided insight into 

environmental changes that may be occurring as a result of 

artificial recharge activities. Arsenic and iron are two constituents present in some of the ground water in the artificial 

recharge system and are sensitive to the pH and dissolved 

oxygen concentration in the system. Second, saturation indices 

were calculated using the computer program PHREEQC (version 2). PHREEQC version 2 is a computer program written 

in the C programming language that is designed to perform 

a wide variety of low-temperature aqueous geochemical 

calculations including speciation and saturation-index calculations (Parkhurst and Appelo, 1999). Data input in PHREEQC 

included water temperature, dissolved oxygen concentration, 

onsite alkalinity, and dissolved concentrations of calcium, 

magnesium, sodium, potassium, sulfate, chloride, arsenic, 

iron, and manganese. Measurements of the oxidation-reduction potential (Eh) were used when dissolved oxygen concentrations were less than 0.1 mg/L.

The saturation index (SI) indicates the degree of disequilibrium of a solution with respect to a certain mineral; if 

a solution is at equilibrium with a given mineral, the mineral 

will not dissolve or precipitate. The saturation index with 

respect to a certain mineral (such as calcite, discussed in the 

following paragraph) can be used to determine the likelihood 

of a mineral or phase dissolving into or precipitating from 

a solution. A negative (-) saturation index indicates that the 

solution is undersaturated with respect to the mineral. If the 

solution is undersaturated, it has the potential to dissolve the 

mineral if it is present and kinetics allow. If a saturation index 

is positive (+), the solution is oversaturated with respect 

to a mineral, and there is the potential for the mineral to 

14 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

Figure 7. Relation between chloride concentrations and streamflow in Little Arkansas River at Highway 50 near 

Halstead during demonstration recharge period, April 1996–June 2002.

1.0

10

100

1,000

1.0 10 100 1,000 10,000

Streamflow (Q), in cubic feet per second

Chloride (Cl) concentration, in milligrams per liter

log10 Cl = -0.44 log10 Q +2.9

R2 = 0.64
Methods 15

0

100

900800700600500400300200

1,000

Chloride concentration, in milligrams per liter

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Estimated chloride concentrationsin the Little Arkansas River usingregression model based on streamflow

Estimated chloride concentrationsin the Little Arkansas River usingregression model based on specificconductance measurements

Measured chloride concentrationsin the Little Arkansas River atHighway 50 near Halstead, Kansas

Figure 8. Estimated chloride concentrations in the Little Arkansas River at Highway 50 near Halstead using regression models based on streamflow (blue line) and specific conductance measurements (red line) compared to measured chloride concentrations (gold line) in water samples from the Little Arkansas River, 1995–2004.
precipitate. A saturation index near 0 indicates that the solution is near equilibrium with the mineral reacting fast enough 

to maintain equilibrium.

Saturation indices are calculated with respect to certain 

minerals. The saturation index (SI) is the log of the ion-activity product of a solution divided by the solubility product (Ksp) 

(Drever, 1997). For example, the saturation index of calcite 

(CaCO3) is:

 

2+ 2

3

sp(calcite)

log

Ca CO

SI

K

−         = (5) 

where [Ca2+] is the activity of the calcium ion, [CO3

2-] is the 

activity of the carbonate ion, and Ksp is the solubility product 

of calcite. 

The saturation indices for minerals reported herein were 

identified to be the most important minerals determined by 

predominant water types. These minerals include carbonate 

minerals [calcite (CaCO3) and dolomite (CaMg(CO3)

2

)] and 

iron hydroxides [iron hydroxide (amorphous) (Fe(OH)3(a)]. 

Geochemical Effects of Induced 

Stream-Water Recharge at the 

Halstead Diversion Well Site

A pumping diversion well in the aquifer adjacent to the 

stream was used to capture water for artificial recharge. Water 

collected at the Halstead diversion well site was pumped without treatment for recharge at the Halstead recharge site. The 

pumping diversion well was operated only when streamflow 

was greater than base-flow conditions described in the previous “Halstead Recharge System” section. Operating a pumping well adjacent to a stream causes a decline in ground-water 

levels adjacent to the stream, thereby increasing the hydraulic 

gradient into the adjacent aquifer. The larger hydraulic gradient “induces” stream water to flow into the aquifer toward the 

pumping well resulting in recharging the adjacent aquifer with 

stream water. Because all ground-water rights in the area were 

already fully appropriated, the pumping well was required 

to induce enough stream water into the adjacent aquifer to 

replace the water pumped from the well (Jerry Blain, Water 

Supply Projects Administrator, city of Wichita Water and 

Sewer Department, written commun., August 2005). The 

water from the diversion well then was piped 2 mi to the Halstead recharge site for use as recharge water (fig. 1). 

Operation of the diversion well will cause a large volume 

of water to flow to the lower part of the aquifer adjacent to the 

Little Arkansas River. This flow has the potential for causing changes in pH, water temperature, and dissolved oxygen 

concentrations, which can have an effect on the solubility and 

mobility of ions in the aquifer. Mixing two different types of 

water also can cause precipitation or dissolution of minerals. 

Major Ion Chemistry and Tracers of Stream 

Water

Piper diagrams (Piper, 1944) were created using calcium, 

magnesium, sodium, potassium, bicarbonate, sulfate, and chloride concentrations to illustrate major ion chemistry in water 

sampled from the Little Arkansas River, monitoring wells, and 

the diversion well at the Halstead diversion well site 

(fig. 9A–D). A Piper diagram is a way to classify water on 

the basis of relative proportions of the major ions in the water 

sample (Drever, 1997). Piper diagrams were constructed 

with water samples from March 1996 (fig. 9A), representing pre-pumping conditions; July1996 (fig. 9B), representing 

post aquifer-test conditions; June 2001 (fig. 9C), representing 

conditions after approximately 700 Mgal of water had been 

pumped from the diversion well; and May 2003 (fig. 9D), representing conditions after the end of the demonstration project. 

The dominant cation percentage of water sampled from all 

monitoring wells and the diversion well at the diversion well 

site ranged from no dominant type to calcium bicarbonate type 

water. The dominant anion was bicarbonate for water sampled 

from the monitoring wells and diversion well at the site. Water 

types for all monitoring wells trended toward the calcium 

bicarbonate fields for samples collected during and after artificial recharge activities. 

Chloride and the triazine herbicide, atrazine, generally 

occurred in larger concentrations in stream water than in 

ground water not affected by stream chemistry at the Halstead 

diversion well site. The source of dissolved chloride concentrations in the Little Arkansas River may be related to past oil 

and gas activities near McPherson and Burrton or wastewater-treatment and industrial discharges from McPherson and 

Newton (Donald Whittemore, Kansas Geological Survey, oral 

commun., 1999). USEPA has established a Secondary Drinking-Water Regulation (SDWR) of 250 mg/L for chloride concentrations in drinking water (U.S. Environmental Protection 

Agency, 2004). Chloride is a conservative constituent and does 

not degrade chemically or readily react with other constituents 

as it moves through the hydrologic system (Hem, 1992). The 

difference between the chloride concentrations in the ground 

water and stream water at the diversion well site were distinct 

enough to use chloride as a natural tracer of stream water into 

the adjacent aquifer. 

Chloride concentrations generally were larger in shallow 

monitoring wells EB–145–A1, EB–145–A2, and EB–145–A3, 

which are less than 500 ft from the Little Arkansas River and, 

therefore, are more affected by the stream-water chemistry 

(fig. 10A–B) than in shallow monitoring wells EB–145–A4 

and EB–145–A5. The shallow monitoring wells also are 

screened above the clay layer. Measured chloride concentrations in water sampled from the Little Arkansas River at 

Highway 50 near Halstead ranged from 5 to 930 mg/L with 

a median concentration of 153 mg/L (fig. 10A). Continuous 

chloride concentrations estimated from measured specific 

conductance values were available from 1999 through 2004 

for the Little Arkansas River at Highway 50 near Halstead 

16  Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer
(data available on the Web at http://ks.water.usgs.gov/Kansas/

rtqw/, accessed December 2006). Estimated chloride concentrations ranged from less than 5 to 445 mg/L with a median 

concentration of 193 mg/L. Estimated chloride concentrations exceeded the SDWR of 250 mg/L 30 percent of the time 

during the 6-year period. Chloride concentrations in water 

samples from shallow monitoring well EB–145–A1, located 

closest to the stream, were variable and ranged from 

80 to 275 mg/L with a median concentration of 159 mg/L 

(fig. 10B). Chloride concentrations in water samples from 

well EB–145–A1 exceeded the SDWR in 5 of 61 samples 

collected from 1995 through 2004. Chloride concentrations in 

water samples from monitoring wells EB–145–A2 

and EB–145–A3 were less variable than in samples from 

well EB–145–A1 and ranged from 139 to 203 mg/L with a 

median concentration of 164 mg/L and 88 to 178 mg/L with 

a median concentration of 146 mg/L, respectively (fig. 10B). 

Monitoring wells EB–145–A4 and EB–145–A5 were not 

affected by the stream-water chemistry and had small median 

chloride concentrations of 19 and 32 mg/L, respectively 

(fig. 10C), which are considered background concentrations 

in this part of the aquifer. 

Chloride concentrations were about 15 mg/L in water 

samples from deep monitoring well EB–145–PD5 prior to 

recharge activities beginning at the site (fig. 10C). Pumping 

at the site, which began with an aquifer test in April 1996, 

Geochemical Effects of Induced Stream-Water Recharge at the Halstead Diversion Well Site 17

0

10

20

30

40

50

60

70

80

90

100

Magnesium

0

10

20

30

40

50

60

70

80

90

100

Calcium

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100

Sulfate plus chloride

Calcium plus magnesium

Sodium plus potassium

Percent total, in milliequivalents per liter

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

Bicarbonate

Monitoring well EB–145–A1

Monitoring well EB–145–A2

Monitoring well EB–145–PD5

Diversion well

Little Arkansas River at 

 Highway 50 near Halstead

EXPLANATION

(A) March 1996

Chloride

Sulfate

0

10

20

30

40

50

60

70

80

90

100 0

10

20

30

40

50

60

70

80

90

100

Calcium

type

Magnesium type

Sodium

type

No dominant

type

Bicarbonate

type

Sulfate type

Chloride

type

No dominant

type

Figure 9. Major ion chemistry of water samples from monitoring wells and diversion well at the Halstead diversion well site 

during (A) March 1996, (B) July 1996, (C) June 2001, and (D) May 2003.
caused an increase in chloride concentrations in water sampled 

from well EB–145–PD5 as ground water affected by streamwater chemistry flowed into the deeper part of the aquifer. At 

the conclusion of the aquifer test in July 1996, the chloride 

concentrations in water samples from well EB–145–PD5 had 

increased from a background concentration of approximately 

15 to approximately 30 mg/L. When pumping resumed in 

May 1997 and continued intermittently until May 2002, the 

end of the demonstration project, chloride concentrations 

increased to a maximum concentration of about 130 mg/L in 

March 2002. Chloride concentrations in water sampled from 

well EB–145–PD5 steadily decreased to a concentration of 

about 40 mg/L after artificial recharge activities ended (fig. 10B). 

Chloride concentrations in water samples from the diversion well, the recharge water used at the Halstead recharge 

site, were initially about 20 mg/L but steadily increased to 

about 55 mg/L near the end of the aquifer test in July 1996 

(fig. 10C). When the pumping for the demonstration project 

resumed, chloride concentrations in water samples from the 

diversion well reached a stable median concentration of about 

60 mg/L from May 1997 through June 2002. 

Specific conductance in recharge water collected from the 

diversion well can be monitored on a real-time basis and provides a reliable estimate of chloride concentrations. Therefore, 

artificial recharge practices could be altered if estimated chloride concentrations in recharge water exceeded the SDWR of 

18 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

Figure 9. Major ion chemistry of water samples from monitoring wells and diversion well at the Halstead diversion well site 

during (A) March 1996, (B) July 1996, (C) June 2001, and (D) May 2003—Continued.

0

10

20

30

40

50

60

70

80

90

100

Magnesium

0

10

20

30

40

50

60

70

80

90

100

Calcium

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100

Sulfate plus chloride

Calcium plus magnesium

Sodium plus potassium

Percent total, in milliequivalents per liter

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

Bicarbonate

(B) July 1996

Chloride

Sulfate

0

10

20

30

40

50

60

70

80

90

100 0

10

20

30

40

50

60

70

80

90

100

Calcium

type

Magnesium type

Sodium

type

No dominant

type

Bicarbonate

type

Sulfate type

Chloride

type

No dominant

type

Monitoring well EB–145–A1

Monitoring well EB–145–A2

Monitoring well EB–145–A3

Monitoring well EB–145–A4

Monitoring well EB–145–A5

Monitoring well EB–145–PD5

Diversion well

Little Arkansas River at 

 Highway 50 near Halstead

EXPLANATION
250 mg/L, which would help prevent degradation of the Equus

Beds aquifer by chloride. A regression model was developed 

for future monitoring which relates specific conductance 

measurements to chloride concentrations in the water sampled 

from the diversion well (fig. 11). The model equation is:

 (6)

 

where Cl is chloride concentration in milligrams per liter and 

SC is specific conductance in microsiemens per centimeter at 

25 oC. The regression has an R2 of 0.86.

Atrazine is a broadleaf, pre-emergent herbicide that is 

used for weed control in corn and grain sorghum. Atrazine 

commonly is applied to crops in the study area and is detected 

frequently in the Little Arkansas River, especially during the 

growing season (April–September). Atrazine has an MCL of 

3.0 μg/L as an annual average (U.S. Environmental Protection 

Agency, 2004). Atrazine degrades chemically in the environment and does not occur naturally. Therefore, the presence 

of atrazine in the pumped diversion well water indicates 

movement of stream-affected ground water towards the deep 

pumping well. In addition to chloride, the presence of atrazine 

concentrations was used as evidence of the movement of shallow ground water into the deeper part of the aquifer.

Atrazine concentrations in discrete water-quality samples 

collected from the Little Arkansas River at Highway 50 ranged 

from less than 0.10 to 47 μg/L (fig. 12A). Continuous atrazine 

Geochemical Effects of Induced Stream-Water Recharge at the Halstead Diversion Well Site 19

0

10

20

30

40

50

60

70

80

90

100

Magnesium

0

10

20

30

40

50

60

70

80

90

100

Calcium

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100

Sulfate plus chloride

Calcium plus magnesium

Sodium plus potassium

Percent total, in milliequivalents per liter

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

Bicarbonate

Chloride

Sulfate

0

10

20

30

40

50

60

70

80

90

100 0

10

20

30

40

50

60

70

80

90

100

Calcium

type

Magnesium type

Sodium

type

No dominant

type

Bicarbonate

type

Sulfate type

Chloride

type

No dominant

type

(C) June 2001

Monitoring well EB–145–A1

Monitoring well EB–145–A2

Monitoring well EB–145–A3

Monitoring well EB–145–A4

Monitoring well EB–145–A5

Monitoring well EB–145–PD5

Diversion well

Little Arkansas River at 

 Highway 50 near Halstead

EXPLANATION

Figure 9. Major ion chemistry of water samples from monitoring wells and diversion well at the Halstead diversion well site 

during (A) March 1996, (B) July 1996, (C) June 2001, and (D) May 2003—Continued.

Cl = -45.8 + 0.131 SC,
concentrations were estimated by the regression model: 

 

 (7) 

where atrazine is in micrograms per liter, D equals the julian 

day of year, and SC equals specific conductance measurements 

in microsiemens per centimeter at 25 oC (Christensen and others, 2000, 2003). Continuous data are available on the Web 

at http://ks.water.usgs.gov/Kansas/rtqw/ (accessed December 2006). 

Annual averages calculated from daily estimates of atrazine were equal to the MCL of 3.0 μg/L in 1999 and smaller 

than 3.0 μg/L from 2000 through 2004. Average rather than 

median concentrations of atrazine are discussed in this report 

to facilitate a direct comparison of measured and estimated 

atrazine concentrations to the MCL, which is defined as an 

annual average. Atrazine concentrations in water samples 

from shallow monitoring wells EB–145–A1, EB–145–A2, and 

EB–145–A3 were the largest when compared to all samples 

from the monitoring wells at the diversion well site, and 

concentrations fluctuated from less than 0.10 to about 2.6 μg/L 

(fig. 12B). Atrazine was not detected in water from shallow 

monitoring wells EB–145–A4 and EB–145–A5.

Atrazine concentrations in water samples from deep 

monitoring well EB–145–PD5 were less than or equal to 0.10 

μg/L from October 1995 through May 1996 (fig. 12C). Detec20 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

Figure 9. Major ion chemistry of water samples from monitoring wells and diversion well at the Halstead diversion well site 

during (A) March 1996, (B) July 1996, (C) June 2001, and (D) May 2003—Continued.

0

10

20

30

40

50

60

70

80

90

100

Magnesium

0

10

20

30

40

50

60

70

80

90

100

Calcium

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100

Sulfate plus chloride

Calcium plus magnesium

Sodium plus potassium

Percent total, in milliequivalents per liter

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

Bicarbonate

Chloride

Sulfate

0

10

20

30

40

50

60

70

80

90

100 0

10

20

30

40

50

60

70

80

90

100

Calcium

type

Magnesium type

Sodium

type

No dominant

type

Bicarbonate

type

Sulfate type

Chloride

type

No dominant

type

(D) May 2003

Monitoring well EB–145–A1

Monitoring well EB–145–A2

Monitoring well EB–145–A3

Monitoring well EB–145–A4

Monitoring well EB–145–A5

Monitoring well EB–145–PD5

Little Arkansas River at 

 Highway 50 near Halstead

EXPLANATION

365 log10atrazine = 0.430 - 0.643 cos

0.359 sin

+

- 0.00079SC,

2πD ( )

365

2πD ( )
tions of atrazine larger than 0.10 μg/L increased after September 1997 with the largest concentration of 0.33 μg/L occurring 

in December 1998. The increase in atrazine concentrations 

in water from well EB–145–PD5 corresponded with the 

increase in chloride concentrations and indicates the presence 

of ground water from the upper part of the adjacent aquifer 

flowing to the lower part of the aquifer. Pumping of ground 

water at the Halstead diversion well site has caused increased 

chloride concentrations from 15 to 130 mg/L and increased 

atrazine concentrations from less than 0.10 to 

0.33 μg/L in deep monitoring well EB–145–PD5. 

Geochemical Effects of Induced Stream-Water Recharge at the Halstead Diversion Well Site 21

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Monitoring well EB–145–A4

Monitoring well EB–145–A5

Monitoring well EB–145–PD5

Diversion well water

0

0

0

100

100

100

50

50

200

200

200

150

150

300

300

300

250

250

400

500

600

700

800

900

1,000 (A)

(B)

(C)

Chloride concentration, in milligrams per liter (mg/L)

Measured chloride concentrations

in Little Arkansas River

U.S. Environmental Protection Agency (2004)

Secondary Drinking-Water Regulation (250 mg/L) 

U.S. Environmental Protection Agency (2004) Secondary

Drinking-Water Regulation (250 mg/L) 

Estimated continuous

chloride concentrations

in Little Arkansas River

U.S. Environmental Protection Agency (2004) Secondary

Drinking-Water Regulation (250 mg/L) 

Monitoring well EB–145–A1

Monitoring well EB–145–A2

Monitoring well EB–145–A3

Diversion well

pumping period

Diversion well

pumping period

Diversion well

pumping period

Figure 10. Measured and estimated chloride concentrations in water samples from (A) Little Arkansas River at Highway 50 near 

Halstead (site 07143672, fig. 1), (B) shallow monitoring wells EB–145–A1, EB–145–A2, and EB–145–A3, and (C) shallow monitoring wells 

EB–145–A4 and EB–145–A5, deep monitoring well EB–145–PD5, and diversion well water at Halstead diversion well site, February 

1995–December 2004.
Atrazine was detected in 48 of 282 (17 percent) water 

samples from the diversion well. Atrazine initially was 

detected about 4 months after pumping began at the site and 

was detected periodically throughout the remainder of the 

demonstration project with the largest detection of 0.42 μg/L 

occurring in June 2000.

Deethylatrazine and deisopropylatrazine are degradation 

products of atrazine (table 2). Deethylatrazine concentrations 

in water sampled from the Little Arkansas River ranged from 

less than 0.05 to 1.8 μg/L (table 2). The largest detection of 

deethylatrazine was 0.17 μg/L in water from well EB–145–A1 

and 0.08 μg/L in water from well EB–145–A2 (table 2). Concentrations of deisopropylatrazine ranged from less than 0.05 

to 1.2 μg/L in stream water. There were two detections in 

32 samples analyzed for deisopropylatrazine in the water 

samples from monitoring well EB–145–A1 at the Halstead 

diversion well site. Deisopropylatrazine was not detected in 

water from any other monitoring well or in water sampled 

from the diversion well at the site. Detections of atrazine 

degradation products were rare, which indicates decreases in 

atrazine concentration are more likely because of adsorption 

by aquifer material than because of degradation. 

Selected Trace Metal Chemistry

The influx of stream water caused by operation of the 

pumping well could affect the mobility of dissolved arsenic at 

the diversion well site. Also, induced stream-water recharge 

could stimulate growth of iron bacteria and cause precipitation of iron minerals from ground water. If arsenic is dissolved 

from the aquifer material, it could increase the dissolved 

arsenic concentration in the local ground water; dissolved 

arsenic has an MCL of 10 μg/L in drinking water established 

by USEPA (U.S. Environmental Protection Agency, 2004). 

Arsenic is a trace element that occurs naturally in the 

environment; however, large concentrations of arsenic have 

been shown to be detrimental to human health (Hem, 1992). 

In 2004, USEPA revised the arsenic drinking-water criterion 

for arsenic from 50 to 10 μg/L. The new criterion became 

effective on January 23, 2006 (U.S. Environmental Protection 

Agency, 2004). Adsorption or coprecipitation by iron oxyhydroxide and association with sulfide in reduced bottom mud 

appear to be major inorganic factors that can maintain arsenic 

at very small concentrations in water (Hem, 1992). Arsenic 

is considered to be naturally occurring in clay layers in the 

Equus Beds aquifer.

The mobility of arsenic in the hydrologic environment 

generally is controlled by two categories of processes—

adsorption and desorption reactions and solid-phase precipitation and dissolution reactions (Hinkle and Polette, 1999). 

These processes are affected by pH, redox reactions, and 

the presence of competing anions in the water, all of which 

could be altered as a result of artificial recharge activities. The 

adsorption of arsenic to iron-oxide surfaces tends to decrease 

as pH increases; therefore, changes in ground-water pH can 

promote adsorption or desorption of arsenic. The redox state 

in which arsenic occurs has an important effect on the mobility 

of arsenic. Arsenate (As V) is dominant under oxidizing con22 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

Cl = -45.8 + 0.131 SC

R2 = 0.86

Chloride (Cl) concentration, in millgrams per liter

0

10

20

30

40

50

60

70

80

90

0 100 200 300 400 500 600 700 800 900

Specific conductance (SC), in microsiemens per centimeter at 25 degrees Celsius

Figure 11. Relation between chloride concentrations and specific conductance measurements in water from 

diversion well at Halstead diversion well site, February 1995–May 2002.
Geochemical Effects of Induced Stream-Water Recharge at the Halstead Diversion Well Site 23

Figure 12. Measured and estimated atrazine concentrations (A) in water from Little Arkansas River at Highway 50 near Halstead 

(station 07143672, fig. 1) and from (B) shallow monitoring wells EB–145–A1, EB–145–A2, and EB–145–A3, (C) deep monitoring 

well EB–145–PD5, and diversion well water at Halstead diversion well site, February 1995–December 2004.

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

Diversion well pumping period

 Atrazine concentrations

Little Arkansas River at Highway 50

near Halstead, KS

Estimated continuous atrazine 

 concentration

Monitoring well EB–145–A1 

Monitoring well EB–145–A2

Monitoring well EB–145–A3

Monitoring well EB–145–PD5

Diversion well water

0

0.5

1.0

1.5

2.0

2.5

3.0 (B) Monitoring well EB–145–A1, EB–145–A2, and EB–145–A3

5

0

10

15

20

25

30

35

40

45

50

Atrazine concentration, in micrograms per liter (μg/L) as atrazine

(A) Little Arkansas River at Highway 50 near Halstead

U.S. Environmental Protection

Agency (2004) Maximum

Contaminant Level for atrazine

(3.0 μg/L as an annual average) 

Measured atrazine 

concentration Estimated atrazine concentration

U.S. Environmental Protection

Agency (2004) Maximum Contaminant Level for atrazine

(3.0 μg/L as an annual average) 

EXPLANATION

U.S. Environmental Protection

Agency (2004) Maximum Contaminant Level for atrazine

(3.0 μg/L as an annual average) 

0

0.5

1.0

1.5

2.0

2.5

3.0 (C) Monitoring well EB–145–PD5 and diversion well water
ditions, and arsenite (As III) is dominant under more reducing 

conditions. 

Arsenic concentrations in 13 percent of the 54 discrete 

water-quality samples from the Little Arkansas River at 

Highway 50 near Halstead exceeded the MCL of 10 μg/L 

(fig. 13A). Arsenic speciation data were collected for selected 

samples from March 2003 through July 2004. Arsenate (AsO4

-3) 

was the dominant arsenic species in samples collected from 

the Little Arkansas River at Highway 50 near Halstead, which 

is typical of oxygenated water. Continuous arsenic concentrations were estimated by the regression model:

 (8)

 

where arsenic is in micrograms per liter and Q is streamflow 

in cubic feet per second from the Little Arkansas River at 

Highway 50 near Halstead. The regression R2 is 0.66 (Christensen and others, 2003). Data are available on the Web at 

http://ks.water.usgs.gov/Kansas/rtqw/ (accessed December 

2006). Estimated arsenic concentrations exceeded the MCL 

10 percent of the days from 1999 through 2004. Larger arsenic 

concentrations in stream water generally occurred during 

times of low streamflow when base flow to the stream is supplied from the ground water.

Initial water samples from well EB–145–A1 had arsenic 

concentrations of 10 and 5 μg/L, but arsenic was not detected 

in the remainder of the water samples from this well. Arsenic 

concentrations in samples from shallow monitoring wells 

EB–145–A2 and EB–145–A3 were slightly larger than the 

detection limit and did not vary substantially throughout the 

study period indicating that the induced stream-water recharge 

at this site did not transport dissolved arsenic or mobilize 

sorbed arsenic near this well.

Arsenic concentrations consistently were larger than the 

MCL in water from shallow monitoring wells EB–145–A4 

and EB–145–A5 (fig. 13B). Median arsenic concentrations 

were 16 and 25 μg/L in water samples from wells EB–145–A4 

and EB–145–A5, respectively. Arsenite (As III), the dominant 

species in more reducing conditions, was the dominant arsenic 

species in these two wells. Stream water does not appear to 

migrate as far as wells EB–145–A4 and A5 as demonstrated 

by chloride and atrazine concentrations; therefore, it is not 

expected that arsenic concentrations in water sampled from 

these two wells would be affected by diversion activities. 

The median arsenic concentration calculated from water 

sampled from deep monitoring well EB–145–PD5 was 

22 μg/L throughout the entire study period. However, there 

was a substantial increase in concentrations from March 2001 

through July 2003 after the majority of pumping of the diversion well ended. Arsenic concentrations in water samples from 

well EB–145–PD5 reached a maximum concentration of 

49 μg/L in July 2003 and steadily decreased to concentrations 

of about 37 μg/L through July 2004. The arsenic peak in 

July 2003 followed peak concentrations in iron and manganese 

in November 2002 (fig. 14). Guo and others (1997) found that 

arsenic was released after iron and manganese had dissolved 

during experiments where spiked sediment columns were 

progressively reduced, suggesting that dissolution rather than 

desorption was the dominant process (Smedley and Kinniburgh, 2002). The increase in iron and manganese concentrations followed by the increase in arsenic at this site indicates 

the local area became more reducing temporarily and caused 

dissolution of arsenic from aquifer material. The increase in 

arsenic concentrations also corresponded to the lowest naturally occurring (not caused by pumping of diverion well) water 

levels recorded at the site. Arsenic speciation data collected 

24 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

Table 2. Results of analysis of atrazine degradation products in water samples from the Little Arkansas River, from monitoring wells, 

and the diversion well at the Halstead diversion well site, south-central Kansas, 1995–2004.

[μg/L, micrograms per liter; <, less than; ND, not detected]

Sampling site (fig. 2)

Deethylatrazine Deisopropylatrazine

Number of 

samples

Number of 

detections

Range in 

concentration 

(μg/L)

Number of 

samples

Number of 

detections

Range in 

concentration 

(μg/L)

Little Arkansas River at Highway 50 near 

Halstead

77 43 <0.05–1.8 47 35 <0.05–1.2

Shallow monitoring well EB–145–A1 40 8 <0.05–0.17 32 2 <0.05–0.06

Shallow monitoring well EB–145–A2 17 2 <0.05–0.08 14 0 ND

Shallow monitoring well EB–145–A3 19 0 ND 15 0 ND

Shallow monitoring well EB–145–A4 10 0 ND 7 0 ND

Shallow monitoring well EB–145–A5 14 0 ND 11 0 ND

Deep monitoring well EB–145–PD5 28 0 ND 19 0 ND

Diversion well 82 0 ND 61 0 ND

10 10 log 1 arsenic . = − 16 0. Q 227log ,
Geochemical Effects of Induced Stream-Water Recharge at the Halstead Diversion Well Site 25

Figure 13. Measured and estimated arsenic concentrations in (A) water samples from Little Arkansas River at Highway 50 near Halstead 

and from shallow monitoring wells EB–145–A1, EB–145–A2, and EB–145–A3 and (B) shallow monitoring wells EB–145–A4, EB–145–A5, 

deep monitoring well EB–145–PD5, and diverted recharge water at Halstead diversion well site, February 1995–December 2004. Location 

of wells shown in figure 2A. 

Diverson well pumping period

 Arsenic concentration

Little Arkansas River at Highway 50

 near Halstead, KS (site 07143672,

 fig. 1) 

Monitoring well EB–145–A1

Monitoring well EB–145–A2

Monitoring well EB–145–A3

Monitoring well EB–145–A4

Monitoring well EB–145–A5

Monitoring well EB–145–PD5 

Diversion well water

Dissolved arsenic concentration, in micrograms per liter (μg/L)

EXPLANATION

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

0

20

10

30

40

50

U.S. Environmental Protection

Agency (2004) Maximum

Contaminant Level for arsenic

(10 μg/L, effective 2006) 

Estimated continuous arsenic

concentration for Little Arkansas

River at Highway 50

0

20

10

30

40

50

U.S. Environmental Protection

Agency (2004) Maximum

Contaminant Level for arsenic

(10 μg/L, effective 2006) 

(A)

(B)
from May 2003 through July 2004 indicate arsenite (As III) is 

the dominant species in monitoring well EB–145–PD5, which 

is the dominant species under more reducing conditions. 

Water sampled from the diversion well had a median 

arsenic concentration of 20 μg/L, and arsenic concentrations 

did not change substantially during pumping. Arsenic concentrations in water from the diversion well were consistent 

with concentrations in water from shallow monitoring 

wells EB–145–A4 and EB–145–A5 and in water from 

well EB–145–PD5 prior to March 2001. 

Iron concentrations also are affected by the pH and dissolved oxygen concentrations of a hydrologic system. Iron 

is a trace metal that generally occurs in small concentrations 

in water. The chemical reactions of iron and its solubility in 

water depend largely on the degree of oxidation and the bacterial activity in the hydrologic system (Hem, 1992). USEPA 

established a SDWR of 300 μg/L for iron in finished drinking water because iron can cause taste-and-odor problems, 

corrosion of pipes, deposits of scale or sediment, and staining 

of laundry (U.S. Environmental Protection Agency, 2004). 

Iron bacteria can have an effect on dissolved iron concentrations in an aquifer and can be of particular concern in artificial 

recharge operations. The addition of oxygenated water to a 

system could create favorable conditions for increased bacterial activity. In turn, increased biological activity can produce 

a biofilm that can clog well screens and reduce the efficiency 

of injection wells. Bacterial activity may increase or decrease 

dissolved iron concentrations in water intercepted by wells 

(Hem, 1992). 

Dissolved iron concentrations observed in the Little 

Arkansas River, monitoring wells, and the diversion well at the 

Halstead diversion well site varied from less than 5 to 

6,250 μg/L (fig. 15A–B). The largest and most variable concentrations of iron occurred in water samples from shallow 

monitoring well EB–145–A1, which is closest to the stream. 

Iron concentrations in water from this well ranged from 1,600 

to 6,250 μg/L. Iron concentrations increased in water samples 

from well EB–145–A1 beginning in July 2003 after the end of 

diversion well pumping. Samples from monitoring well EB–

145–A2 also had relatively large iron concentrations, ranging 

from 1,600 to 2,700 μg/L. The iron concentrations in shallow 

monitoring wells EB–145–A3, EB–145–A4, and EB–145–A5 

increased in response to pumping from less than or equal to 

300 μg/L to between 300 and 1,000 μg/L. Iron concentrations 

in water samples from deep monitoring well EB–145–PD5, 

initially less than 10 μg/L, increased in response to pumping 

and continued to increase to a maximum of 740 μg/L until 

2003, and have decreased from 2003 through 2004 (fig. 15B). 

Geochemical Simulations

Saturation indices were calculated for water samples collected before, during, and after diversion activities to determine the effect on mineral solubility. Saturation indices (SI) 

were calculated using PHREEQC from constituent concentrations in water samples from all monitoring wells and the diversion well from March 1995 through May 2003 (table 3). The 

March 1995 and March 1996 samples were collected before 

the April 1996 aquifer test at the site (Burns and McDonnell, 

written commun., 1998) and, therefore, are considered prediversion samples because they were not affected by diver26  Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

0

200

400

600

800

1,000

1,200

6/15/1994 10/28/1995 3/11/1997 7/24/1998 12/6/1999 4/19/2001 9/1/2002 1/14/2004 5/28/2005

Dissolved iron and manganese concentrations, in micrograms per liter (μg/L) 

0

10

20

30

40

50

60

Dissolved arsenic concentrations, in micrograms per liter (μg/L)

Iron

Manganese

U.S. Environmental Protection Agency (2004)

Maximum Contaminant Level for arsenic 

(10 μg/L, effective 2006)

U.S. Environmental Protection 

Agency (2004) Secondary DrinkingWater Regulation for iron (300 μg/L)

Arsenic

Figure 14. Arsenic, iron, and manganese concentrations, in deep monitoring well EB–145–PD5 at 

Halstead diversion well site, February 1995–December 2004. 
Geochemical Effects of Induced Stream-Water Recharge at the Halstead Diversion Well Site 27

Dissolved iron concentration, in micrograms per liter (μg/L)

Diversion well pumping period

 Iron concentrations

 Little Arkansas River at Highway 50

near Halstead

 Monitoring well EB–145–A1

 Monitoring well EB–145–A2

 Monitoring well EB–145–A3

Monitoring well EB–145–A4

Monitoring well EB–145–A5

Monitoring well EB–145–PD5 

Diversion well water

EXPLANATION

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

0

5,000

4,000

3,000

2,000

1,000

6,000

7,000

U.S. Environmental Protection

Agency (2004) Secondary

Drinking-Water Regulation

(300 μg/L)

0

1,300

1,200

1,100

1,000

900

800

700

600

500

400

300

200

100

(B) Deep monitoring well EB–145–PD5 and diversion well water

(A) Little Arkansas River at Highway 50 near Halstead and shallow monitoring wells

U.S. Environmental Protection

Agency (2004) Secondary

Drinking-Water Regulation

(300 μg/L)

Figure 15. Iron concentrations in water samples from (A) Little Arkansas River at Highway 50 near Halstead and from shallow 

monitoring wells and (B) deep monitoring well EB–145–PD5 and diversion well water at Halstead diversion well site, February 1995–

December 2004. 
sion activities. Saturation indices with respect to calcite and 

dolomite (table 3) indicate the potential for dissolution if the 

minerals are present in the aquifer. However, the absence of 

water samples with near-equilibrium saturation indices probably indicate that calcite and dolomite are not present in the 

aquifer at this site. 

Saturation indices with respect to amorphous ferric (iron) 

oxyhydroxide [Fe(OH)3(a)] were oversaturated in water samples from wells EB–145–A1, EB–145–A2, and EB–145–A4 

indicating that amorphous iron oxyhydroxide could precipitate 

from the water. Amorphous iron oxyhydroxide saturation indices in water from well EB–145–A3 were near equilibrium in 

the July 1996 sample and were oversaturated for the remainder 

of the study period. The July 1996 sample was collected at the 

end of the 75-day aquifer test. Saturation indices with respect 

to amorphous iron oxyhydroxide in water sampled from 

well EB–145–A5 were undersaturated in the July 1996 sample 

and oversaturated in all remaining samples throughout the 

study period. However, dissolved iron concentrations in shallow monitoring wells EB–145–A1 through A5 were variable 

(fig. 15) and did not change in response to diversion activities 

at the site.

Dissolved iron present in water sampled from the diversion well along with mostly oversaturated saturation indices with respect to amorphous iron hydroxides indicate the 

potential for iron oxyhydroxide to precipitate from this water. 

However, the dissolved iron in the diversion well samples is 

assumed to be mostly ferrous (reduced) iron because ferric 

iron oxyhyroxides have extremely small solubilities. Thus, the 

precipitation of ferric oxyhydroxides is expected to be limited 

unless dissolved oxygen (or other oxidants, such as nitrate) 

is introduced into the recharge water. Iron oxide precipitates 

were observed on the floors of the recharge basin and trench at 

the Halstead recharge site where water from the diversion well 

is exposed to atmospheric oxygen before being recharged into 

the Equus Beds aquifer.

Stream-Water Mixing in Adjacent Aquifer and 

Solute-Transport Model

Hydrologic Conditions

The Little Arkansas River is a gaining stream throughout most of its length in the study area, meaning that ground 

water flows into the river. However, at the diversion well site, 

a low-head dam on the river about 2 mi downstream (fig. 1) 

causes stream elevation at the site to be higher than groundwater levels in the adjacent aquifer resulting in waterflow from 

the Little Arkansas River to the aquifer (fig. 16A). During 

both pumping and nonpumping conditions, water levels in 

monitoring wells at the diversion well site responded within a 

few days to water-level changes in the Little Arkansas River 

(fig. 16B). Operation of the pumping well caused water levels 

in monitoring wells completed in the adjacent aquifer to 

decline. Maximum drawdown was 16 ft in monitoring well 

EB–145–PD5, the well screened closest to the pumping well 

(fig. 16A). Water levels in well EB–145–A1, the well nearest 

to the stream, declined as much as 8 ft during pumping. 

 The effect of the clay layer (described previously in 

“Description of Study Area”) on the hydrological response 

of the adjacent aquifer to pumping of the diversion well was 

analyzed in detail by Burns and McDonnell (written commun., 

1998) during an aquifer test of the diversion well that occurred 

before full-scale demonstration activities began. It was found 

that two cones of depression formed in the aquifer as a result 

of pumping the well. One formed in the lower part of the 

aquifer, beneath the clay layer, and centered over the pumping 

well. The other formed in the upper part of the aquifer, above 

the clay layer, and the center was offset to the west of the 

pumping well by the clay layer (Burns and McDonnell, written commun., 1998). 

Simple Mixing

Piper diagrams were constructed using the median concentrations of calcium, magnesium, sodium, potassium, bicarbonate, sulfate, and chloride in water samples from the Little 

Arkansas River, the diversion well, and shallow monitoring 

well EB–145–A5 throughout the study period. The Piper diagram in figure 17 shows that median chemical concentrations 

in the diversion well water plot along a line drawn between the 

stream-water and ground-water samples, indicating that water 

sampled from the diversion well is a mixture of stream and 

ground water.

A simple mixing model (described in previous “Methods” 

section) was used to estimate the percentage of stream water 

entering the aquifer adjacent to the stream above the clay layer 

and also to estimate the percentage of ground water from the 

upper part of the adjacent aquifer reaching the diversion well 

in the deeper part of the aquifer. Increases in water levels in 

well EB–145–A1 following periods of high flow in the Little 

Arkansas River illustrate that the stream effectively recharges 

the adjacent aquifer at this site (fig. 16A). Chloride concentrations in the Little Arkansas River were temporally variable, 

which made it difficult to define a stream-water end member 

for use in the mixing model. Therefore, the median value 

(193 mg/L) from estimated chloride concentrations for the 

Little Arkansas River at Highway 50 near Halstead for 1995–

2004 was used in the mixing model (fig. 10). This median was 

calculated from daily chloride concentrations estimated from 

continuous specific conductance or streamflow measurements. 

The ground-water end member chloride concentration was 

32 mg/L (fig. 10), the median chloride concentration from 

monitoring well EB–145–A5.

The estimated mixture of water sampled from monitoring well EB–145–A1 was about 80 percent stream water and 

about 20 percent ground water on the basis of the end members mentioned in the previous paragraph and the median 

value of 159 mg/L for chloride concentrations from monitoring well EB–145–A1. This estimated mixture of water along 

28 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer
Geochemical Effects of Induced Stream-Water Recharge at the Halstead Diversion Well Site 29

 

Table 3. Saturation indices calculated for ground-water samples collected from 

Halstead diversion well site, south-central Kansas, March 1995–July 2003.

[--, not available or not calculated]

Date of sample

Mineral (chemical formula) saturated indices

Calcite

(CaCO3)

Dolomite

(MgCa(CO3)

2

)

Amorphous iron

(Fe(OH)3(a))

Shallow monitoring well EB–145–A1 (fig. 2) 

March 1995 -0.35 -1.37 1.62

March 1996 -.27 -1.20 1.67

July 1996 -.84 -2.32 .85

June 2001 -.67 -1.91 .90

May 2003 -.69 -1.98 1.07

Shallow monitoring well EB–145–A2 (fig. 2) 

March 1995 -- -- --

March 1996 -.16 -.99 1.58

July 1996 -.64 -1.97 .26

June 2001 -.46 -1.56 1.20

May 2003 -.29 -1.23 1.78

Shallow monitoring well EB–145–A3 (fig. 2) 

March 1995 -- -- --

March 1996 -- -- --

July 1996 -.41 -1.53 -.02

June 2001 -.47 -1.58 .89

May 2003 -.14 -.93 1.39

Shallow monitoring well EB–145–A4 (fig. 2) 

March 1995 -- -- --

March 1996 -- -- --

July 1996 -.33 -1.36 .40

June 2001 -.22 -1.10 1.88

May 2003 -.15 -.98 1.54

Shallow monitoring well EB–145–A5 (fig. 2)

March 1995 -- -- --

March 1996 -- -- --

July 1996 -.41 -1.57 -.12

June 2001 -.28 -1.25 1.00

May 2003 -.34 -1.37 .81

Deep monitoring well EB–145–PD5 (fig. 2)

March 1995 -- -- --

March 1996 -.05 -.73 .79

July 1996 -.63 -1.90 .57

June 2001 -.33 -1.26 1.23

May 2003 -.07 -.74 2.09

Diversion well (fig. 2)

March 1995 -- -- --

April 1996 -.30 -- 1.83

July 1996 -.45 -- .58

May 2000 -.18 -- .25
with water-level evidence demonstrate recharge of the adjacent 

aquifer by the stream. The estimated mixture of water sampled 

from the diversion well (median concentration 60 mg/L) was 

about 25 percent water from monitoring well EB–145–A1 and 

about 75 percent from ground water. 

The presence of atrazine in water samples from deep 

monitoring well EB–145–PD5 and in water samples from the 

diversion well indicates the migration of stream water into the 

deeper part of the adjacent aquifer. One advantage of using 

the induced stream-water recharge approach to capture stream 

water for use in artificial recharge is that organic compounds, 

such as atrazine, are sorbed by or attached to aquifer material 

as the water moves into the adjacent aquifer. The average concentration of atrazine in the Little Arkansas River at Highway 

50 near Halstead from 1999 through 2004 was 2.4 μg/L. The 

average atrazine concentration in monitoring well EB–145–A1 

was 0.45 μg/L. If mixing model percentages of 80 percent 

surface water and 20 percent ground water in monitoring well 

EB–145–A1 are applied to average atrazine concentrations 

from the surface water (2.4 μg/L) and ground water 

(0.05 μg/L), the resulting estimated average atrazine concentrations in well EB–145–A1 is 1.93 μg/L. The estimated atra-

30 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

Figure 16. (A) Water-level altitudes in monitoring wells at Halstead diversion well site and in Little Arkansas River at Halstead 

(site 07143680) for November 1995–December 2004 and (B) for January 2004–December 2004. Location of monitoring wells 

shown in figure 2B. Location of stream-gaging site shown in figure 1. 

1,355

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

1,360

1,365

1,370

1,375

1,380

1,385

1,390

1,395

Water-level altitudes, in feet above North American Vertical Datum of 1988

Diversion well pumping period

Water-level altitudes

 Monitoring well EB–145–A1

 Monitoring well EB–145–A2

 Monitoring well EB–145–A3

 Monitoring well EB–145–A4

 Monitoring well EB–145–A5

 Monitoring well EB–145–PD5

 Little Arkansas River at Halstead, KS

EXPLANATION

(A) November 1995–December 2004
zine concentration is much larger than the measured average 

atrazine concentration of 0.45 μg/L in water sampled from this 

well, indicating a large amount (about 75 percent) of atrazine 

likely is sorbed to the aquifer material.

Flow and Solute-Transport Model

Flow and transport simulations were performed with the 

solute-transport model PHAST (Parkhurst and others, 2004) 

to better evaluate the quantity of flow between the Little 

Arkansas River and the diversion well at the Halstead diversion well site. The model was calibrated to drawdown data at 

six monitoring wells and then used to simulate the transport of 

stream-derived chloride to the diversion well over a period of 

10 years. Results are used to provide a preliminary estimate of 

mixing of stream water and ground water at the diversion well.

Model Definitions and Flow Simulations

Burns and McDonnell (written commun., 1998) conducted aquifer tests and developed a subregional model for 

the area including the Halstead diversion site. The hydraulic 

conductivity (K) in subregional model was 60 ft/d for sand and 

gravel layers. Transmissivity of clay layer was 359 ft2/d and a 

storativity of 0.02. The grid spacing was 1,000 ft. 

The flow model described in this report was developed 

in metric units with an assigned vertical datum of 50 m. For 

this report, spatial data from the model have been converted to 

feet and rounded to the nearest 0.1 ft. Altitudes and hydraulic 

heads are reported relative to NAVD 88, and the 50-m vertical 

datum represents an altitude of 1,390 ft, which is approximately land-surface altitude at the Halstead recharge site. The 

model considered the effects of pumpage on an initially flat 

water table and a stream that was maintained at a water level 

2 ft above the initial water table. Water was allowed to flow 

in through the side boundaries of the model domain through 

leaky boundary conditions. Precipitation recharge and the 

regional hydraulic-head gradients were ignored. 

Horizontal model-grid coordinates ranged from -8,202.1 

to +8,202.1 ft in the x and y directions, with coordinate x=0, 

y=0 at the diversion well. Horizontal grid nodes were variably 

spaced with closest spacing near the diversion well (13.1 ft), 

fractionally increasing to the largest spacing at the borders 

(1,380.4 ft). Constant node spacing of 32.6 ft was overlaid 

on the x axis from x=0 to x=300 to enhance resolution in the 

vicinity of the Little Arkansas River. The y axis of the grid 

was rotated about 15 degrees counterclockwise relative to 

north so that it was aligned with the Little Arkansas River 

north of the observation wells (fig. 18). Vertical grid coordinates (z direction) ranged from 1,252.9 to 1,390.0 ft. Vertical 

grid spacing was 16.4 ft below 1,324.4 ft altitude and 8.2 ft 

above that altitude. The total numbers of grid nodes in each 

direction were 70 (x direction), 53 (y direction), and 12 

(z direction).

Geochemical Effects of Induced Stream-Water Recharge at the Halstead Diversion Well Site  31

Figure 16. (A) Water-level altitudes in monitoring wells at Halstead diversion well site and in Little Arkansas River at 

Halstead (site 07143680) for November 1995–December 2004 and (B) for January 2004–December 2004. Location of 

monitoring wells shown in figure 2B. Location of stream-gaging site shown in figure 1—Continued. 

1,372

1,374

1,376

1,378

1,380

1,382

1,384

1,386

1,388

1,390

1,392

11/25/2003 1/14/2004 3/4/2004 4/23/2004 6/12/2004 8/1/2004 9/20/2004 11/9/2004 12/29/2004 2/17/2005

Water-level altitudes, in feet above North American Vertical Datum of 1988

Monitoring well EB–145–A1

Monitoring well EB–145–PD5

Little Arkansas River 

at Halstead, KS

(B) January 2004–December 2004
Moving upward from an assumed impermeable shale 

boundary at 1,252.9 ft, the hydrologic units considered in the 

model included a lower sand and gravel aquifer from 1,252.9 

to 1,324.4 ft, a lower clay layer from 1,324.4 to 1,340.8 ft, an 

upper sand and gravel aquifer from 1,340.8 to 1,365.4 ft, and 

an upper clay layer from 1,365.4 to 1,390.0 ft. On the basis of 

lithologic information from the monitoring wells and the offset 

in the drawdown cones in the upper and lower aquifers during 

the April 1996 aquifer test, a sand and gravel window in the 

lower clay layer was included that ranged from -1,148.3 to 

-164.0 ft in the x direction and -328.1 to 328.1 ft in the 

y direction.

The model had a free-surface boundary condition (unconfined flow), which uses the porosity as the specific storage in a 

cell that contains the water table and zero for specific storage 

in all cells not containing the water table. The stream boundary ran from top to bottom of the simulation area with a kink 

near the pumping well (light blue line, fig. 18). The multicolored patches surrounding the stream (fig. 18) defined hydraulic conductivity to be equal to the aquifer hydraulic conductivity from 1,365.4 to 1,390.0 ft altitude. For the rest of the 

domain, this altitude corresponds to the upper clay layer. Thus, 

the stream connects directly to the aquifer (not the upper clay 

layer), and all the resistance to flow from stream to aquifer is 

represented by the streambed hydraulic conductivity. 

Leaky boundaries were applied at all four vertical sides 

of the domain. These boundaries had a constant hydraulic head 

(1,373.9 ft) at a distance of 3,280.8 ft from the edges. The 

diversion well pumped 978 gal/min over a 114.5-day period 

representing April 1 through July 24, 1996, with an off period 

of 6 days in early May when pumping was suspended. 

Drawdown data at six monitoring wells [EB–145–A1, 

EB–145–A2, EB–145–A3, EB–145–A4, EB–145–A5, and 

EB–145–PD5 (line of yellow dots in fig. 18)] were used to 

32 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

0

10

20

30

40

50

60

70

80

90

100

Magnesium

0

10

20

30

40

50

60

70

80

90

100

Calcium

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100

Sulfate plus chloride

Calcium plus magnesium

Sodium plus potassium

Percent total, in milliequivalents per liter

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

Bicarbonate

Chloride

Sulfate

0

10

20

30

40

50

60

70

80

90

100 0

10

20

30

40

50

60

70

80

90

100

Calcium

type

Magnesium type

Sodium

type

No dominant

type

Bicarbonate

type

Sulfate type

Chloride

type

No dominant

type

Little Arkansas River at 

 Highway 50 near Halstead

Diversion well

Monitoring well EB–145–A5

EXPLANATION

Mixing line

Figure 17. Median major ion chemistry in water samples from Little Arkansas River at Highway 50 near Halstead, diversion well, and 

shallow monitoring well EB–145–A5 at the Halstead diversion well site.
calibrate the flow model. Simulated hydraulic heads were 

calibrated to 13 points spaced at 10-day intervals at each of the 

six monitoring wells that spanned the pumping and recovery 

period (last 2 points) of the 1996 aquifer test. All data were 

given a 0.33-ft standard deviation for the fitting except the 

data at day 40, which were given a 3.28-ft standard deviation 

because of the sensitivity of the hydraulic heads to the time 

pumping was restarted on day 39, following the end of downtime in early May. 

Parameters fit by UCODE (Poeter and Hill, 1998) 

included a single hydraulic conductivity for the upper and 

lower aquifer, which applied to the sand and gravel window in 

the upper clay as well and the zones connecting the stream to 

the aquifer; a single hydraulic conductivity for the upper and 

lower clay layers; and the streambed leakance. Other fixed 

parameters were as follows: porosity, 0.3; isotropic dispersivity, 16.4 ft; initial hydraulic head, 1,373.9 ft; stream width, 

98.4 ft; streambed thickness, 3.28 ft; and stream altitude, 

1,375.9 ft (2 ft above initial hydraulic head). The total simulation time was 130 days, with a time step of 2 days. 

Fit values were aquifer hydraulic conductivity (K), 

50.1 ft/d; clay layer hydraulic conductivity, 0.069 ft/d; and 

streambed leakance, 0.029 (1/d). These values are similar 

to those used by Burns and McDonnell (written commun., 

1998). Contours for the simulated drawdown at the end of the 

pumping period of the aquifer test (maximum drawdown) are 

shown in figure 19A for the upper and figure 19B for the lower 

aquifer units along with measured drawdowns in the observation wells. The general features of the measured drawdown are 

captured by the model, but there are discrepancies at individual wells. Figures 20 A–F show the measured drawdowns 

compared to the simulated drawdowns for each monitoring 

well. Actual and simulated drawdowns are similar for all 

monitoring wells. The lack of recovery of water levels in 

well EB–145–A5 after pumping was not possible to simulate; 

however, this well was the farthest from the pumping well, and 

during the rest of the study, water levels at this well did not 

always respond to pumping at the diversion well. Therefore, 

other factors may affect water levels in well EB–145–A5.

Solute Transport 

The calibrated parameters for the flow system were used 

in the simulation of chloride transport. For the initial condition, chloride was distributed linearly with distance from the 

stream (fig. 21); fractional concentration was 1 at the stream 

and 0 at a distance of 656.2 ft, which is consistent with 

chloride concentrations in the monitoring wells. This profile 

applied to water in the upper clay layer (1,332.6 ft) to the land 

surface. Pumping at a rate of 978 gal/min was simulated for a 

period of 10 years. The model time step was variable from 

Geochemical Effects of Induced Stream-Water Recharge at the Halstead Diversion Well Site  33

Figure 18. Model grid for the flow and solute-transport model at the Halstead diversion well site.
34 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

1,354

1,362

1,370

Water-level altitude, 

in feet above North

American Vertical

Datum of 1988

Water-level altitude, 

in feet above North

American Vertical

Datum of 1988

1,366

1,358

1,362

1,370

1,366

EB–145–A5

(1,370.7)

EB–145–A4

(1,363.5)

EB–145–A3

(1,362.6)

EB–145–A2

(1,364.2)

Diversion

well

Simulated Little

Arkansas River

1,370

1,368

1,364

1,362

1,366 EB–145–A1 (shallow, 

 1,366.1)

EB–145–PD5 (deep)

EB–145–A5 EB–145–A4

EB–145–A3

EB–145–A2

Diversion

well

Simulated Little

Arkansas River

EB–145–A1 (shallow)

EB–145–PD5 (deep, 1,356.6)

1,370

1,368

1,364

1,362

1,360

1,366

1,358

1,356

1,354

(A) Shallow observation wells

(B) Deep observation wells 

EXPLANATION

1,370 Water-level contour—Shows altitude of water level.

 Contour interval 2 feet. Datum is North American

 Vertical Datum of 1988

Observation well—Upper number is observation well

 identifier. Number in parentheses ( ) is water-level 

 altitude, in feet above North American Vertical Datum 

 of 1988

EB–145–A5

(1,370.7)

0 100 200 300 400 500 FEET

0 50 100METERS

0 100 200 300 400 500 FEET

0 50 100METERS

N

N

Figure 19. Simulated water-level contours for the (A) upper and (B) lower parts of the aquifer 

adjacent to the Little Arkansas River at the Halstead diversion well site.
1 minute to 0.05 year. All induced recharge from the stream 

had a fractional concentration of 1.0. The distribution of chloride with time and the concentration of chloride in the pumping well were simulated. 

Initially, the simulated rate of induced recharge, as 

determined by flow through the river boundary condition, is 

about 55 percent of the pumping rate; the remainder of the 

water pumped is taken from storage within the aquifer. The 

simulated rate of induced recharge increases over several years 

of pumping. After 10 years, the simulated rate of induced 

recharge is about 75 percent of the pumping rate; the rate of 

flow through the leaky boundaries at the edges of the domain 

is about 24 percent of the pumping rate; and the rate of change 

in storage is about 1 percent of the pumping rate. Thus, the 

simulation results indicate that the flow system is nearly at 

steady state after 10 years of continuous pumpage.

Chloride concentrations in the diversion well increase 

rapidly in the simulation and are similar to measured chloride 

concentrations in water sampled from the well (fig. 22 and 

fig. 10). The initial plateau in measured chloride concentration 

at the diversion well was about 20 percent of the concentration in stream water; the simulated concentration is less than 

25 percent. However, the similarity is based on the assumed 

initial chloride concentrations in the aquifer. At steady state in 

the model, the concentration of chloride at the diversion well 

will be equal to the fraction of water derived from the stream. 

Geochemical Effects of Induced Stream-Water Recharge at the Halstead Diversion Well Site  35

1,366

1,367

1,368

1,369

1,370

1,371

1,372

1,364

1,365

1,366

1,367

1,368

1,369

1,370

1,371

1,361

1,362

1,363

1,364

1,365

1,366

1,367

1,368

1,369

1,370

1,371

4/5/1996

4/25/1996

5/15/1996

6/4/1996

6/24/1996

7/14/1996

8/3/1996

8/23/1996

1,363

1,364

1,365

1,366

1,367

1,368

1,369

1,370

1,370

1,371

1,372

1,373

1,374

1,356

1,358

1,360

1,362

1,364

1,366

1,368

1,370

1,372

4/5/1996

4/25/1996

5/15/1996

6/4/1996

6/24/1996

7/14/1996

8/3/1996

8/23/1996

(A) EB–145–A1 (D) EB–145–A4

(C) EB–145–A3 (F) EB–145–PD5

(B) EB–145–A2 (E) EB–145–A5

Measured

water level

Simulated

water level

Measured

water level

Simulated

water level Measured

water level

Simulated

water level

Measured

water level

Simulated

water level

Measured

water level

Simulated

water level

Measured

water level

Simulated

water level

Water-level altitudes, in feet above North American Vertical Datum of 1988

Figure 20. Simulated and measured water-level response to pumping at the Halstead diversion well site.
36  Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer Fraction of stream chloride concentration at diversion well

0

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0 10 20 30 40 50 60 70 80 90 100

Years of continuous simulated pumping

Figure 22. Simulated fraction of stream chloride concentration in Halstead diversion well over a 100-year simulation.

1.00

Simulated

chloride

concentration,

in milligrams 

per liter

0.75

0.50

0.25

0

Figure 21. Initial chloride distribution for solute-transport model at the Halstead diversion well site.
Thus, ultimately (after decades) the water pumped will have 

a chloride concentration approximately equal to 75 percent of 

the concentration of water in the stream. 

In summary, flow and transport simulation results indicate that with continuous pumpage the flow system requires 

decades to achieve steady state. At steady-state flow, the rate 

of induced recharge is simulated to be about 75 percent of the 

pumping rate. Initial chloride concentrations in the diversion 

well are dependent on the chloride distribution in the aquifer at 

the beginning of pumpage. It requires a decade for simulated 

chloride concentrations in the diversion well to be representative of the rate of induced stream-water recharge.

This model is limited to qualitative application and is a 

simplification of the natural system. This model simulates continuous pumping of the diversion well, which will not occur 

because of the permit restrictions; therefore, it likely will take 

more time to reach equilibrium. Regional gradients to and 

along the river, natural recharge, evapotranspiration, and other 

factors have been ignored. This model and the simple mixing 

model both qualitatively illustrate that a substantial portion 

of water in the diversion well originates from the stream. 

However, the initial pumped water contains a large proportion 

of water from the aquifer, and many years may be required to 

reach steady-state conditions with the larger contribution from 

the stream.

Geochemical Effects of Artificial 

Recharge at Halstead Recharge Site

The Equus Beds aquifer at the Halstead recharge site 

was artificially recharged through surface-spreading recharge 

basins, a recharge trench, and a direct injection recharge well 

(fig. 2B); therefore, possible geochemical effects depend on 

the method of artificial recharge. Potential issues for artificial recharge through the injection well at the Halstead site 

include the formation of mineral precipitates because of 

reactions between the recharge water and the existing ground 

water. Changes in pH and redox potential caused by artificial 

recharge could affect the mobility of dissolved arsenic concentrations at the Halstead site. Also, the precipitation of iron 

minerals from existing ground water is a potential concern 

because the recharge of water with pH and redox potential in 

the range of ferric iron could stimulate growth of iron bacteria. 

Major Ion Chemistry and Tracers of Recharge 

Water

Piper diagrams were created for water sampled from shallow and deep monitoring wells at the Halstead recharge site. 

The diagrams presented in figures 23A–C depict the major 

ion chemistry in May 1997, May 1999, and April 2003 at the 

Halstead recharge site. Samples collected during May 1997 

were collected before artificial recharge began at the site and 

are considered baseline samples at the site. The water type for 

samples from shallow and deep monitoring wells SMW–H4, 

DMW–H1, and DMW–H13 is calcium bicarbonate, meaning that calcium is the dominant cation and bicarbonate 

is the dominant anion. Initial chloride concentrations in 

wells SMW–H4, DMW–H1, and DMW–H13 were less than 

50 mg/L before artificial recharge operations began in 

May 1997 (fig. 24). 

Water sampled from the shallow monitoring well 

SMW–H14 is a sodium chloride type water and noticeably 

different than water sampled from the other monitoring wells 

at the Halstead site. The initial chloride concentration in 

water from shallow monitoring well SMW–H14 was about 

280 mg/L, which was greater than the 250-mg/L SDWR. The 

larger chloride concentrations and the sodium chloride water 

type in the sample from well SMW–H14 can be attributed to 

the well’s proximity to the sewage treatment lagoon located to 

the southeast of the recharge site (Ziegler and others, 1999). 

Piper plots show that water samples from well SMW–H14 

evolved to calcium-bicarbonate-type water during artificial 

recharge and reverted to sodium-chloride-type water after 

artificial recharge activities ended (fig. 23). During the period 

of artificial recharge through the basins, trench, and direct 

injection, all monitoring wells had essentially the same major 

ion composition. 

Water sampled from shallow monitoring wells showed 

evidence of recharge water soon after artificial recharge began 

through the recharge basins and trench. Chloride concentrations 

decreased in samples from shallow monitoring well SMW–H14 

from 280 mg/L and increased in chloride concentrations in 

samples from shallow monitoring well SMW–H4 from 20 mg/L 

to about 60 mg/L, the concentration of chloride in recharge 

water (fig. 24). Deep monitoring wells showed evidence of 

recharge water after the injection well was used for artificial 

recharge. Chloride concentrations in water sampled from deep 

monitoring wells DMW–H1 and DMW–H13 increased from 

about 8 to about 60 mg/L and remained constant throughout 

the study period except for a concentration of about 130 mg/L 

in a sample from well DMW–H13 in April 1999 (fig. 24). 

Chloride concentrations in samples from all monitoring 

wells remained similar to recharge water concentrations during active artificial recharge through the recharge basins and 

trench from May 1997 through August 2000. After artificial 

recharge ended through the recharge basins and trench in 

2001, the chloride concentrations in water sampled from 

well SMW–H14 increased to before-recharge concentrations of between 100 and 420 mg/L. Chloride concentrations 

decreased from about 50 to about 30 mg/L in water sampled 

from well SMW–H4. The response of chloride concentrations in water from the shallow monitoring wells indicates a 

displacement of the ground water in the immediate area at the 

site rather than mixing. Chloride concentrations in the deep 

monitoring wells have remained around 60 mg/L since the end 

of recharge operations. 

Atrazine concentrations in water from the shallow monitoring wells at the Halstead recharge site also indicate when 

Geochemical Effects of Artificial Recharge at Halstead Recharge Site  37
artificial recharge began through the recharge basins 

(May 1997), and concentrations in water from the deep 

monitoring wells indicate when recharge by injection well 

began (August 1997) (fig. 25). The before-recharge concentration in the sample from well SMW–H4 was 0.14 μg/L, 

which was larger than the average concentration in samples of 

recharge water (less than 0.10 μg/L), and the before-recharge 

concentration in a sample from well SMW–H14 was less than 

0.10 μg/L and equal to the average concentration in recharge 

water. After recharge began, atrazine concentrations in water 

from the shallow monitoring wells at the Halstead recharge 

site were similar to concentrations in the recharge water. Concentrations in shallow monitoring wells generally were 

0.15 μg/L or less, but occasionally concentrations ranged 

between 0.25 and 0.50 μg/L; large concentrations were measured more frequently toward the end of the sampling period. 

Atrazine concentrations in the final samples from the shallow monitoring wells (2004) were approximately 0.25 μg/L. 

Atrazine concentrations in deep monitoring wells increased 

when artificial recharge by injection began in August 1997. 

Concentrations were variable, occasionally in the range of 

0.10 to 0.20 μg/L. Atrazine concentrations in all samples were 

considerably less than the USEPA MCL of 3.0 μg/L as an 

annual average. The changes in atrazine concentrations correspond with the changes in chloride concentrations and indicate 

the presence of recharge water in the Equus Beds aquifer at 

the Halstead site.

38 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

0

10

20

30

40

50

60

70

80

90

100

Magnesium

0

10

20

30

40

50

60

70

80

90

100

Calcium

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100

Sulfate plus chloride

Calcium plus magnesium

Sodium plus potassium

Percent total, in milliequivalents per liter

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

Bicarbonate

(A) May 1997

Chloride

Sulfate

0

10

20

30

40

50

60

70

80

90

100 0

10

20

30

40

50

60

70

80

90

100

Calcium

type

Magnesium type

Sodium

type

No dominant

type

Bicarbonate

type

Sulfate type

Chloride

type

No dominant

type

Monitoring well SMW–H14

Monitoring well SMW–H4

Monitoring well DMW–H1

Monitoring well DMW-H13

EXPLANATION

Figure 23. Major ion chemistry in water samples from the Halstead recharge site in (A) May 1997, (B) May 1999, and (C) April 2003.
Selected Trace Metal Chemistry

At the Halstead recharge site, the pre-recharge concentrations of arsenic were less than 5.0 μg/L in samples from the 

shallow monitoring wells (fig. 26). Arsenic concentrations 

in water from the shallow monitoring wells did not increase 

because of artificial recharge at the site despite the median 

arsenic concentration of 20 μg/L in the recharge (diversion 

well) water (fig. 26). Ferric oxyhydroxide percipitates have 

been observed in the recharge basins and trench at the Halstead recharge site, and it is likely that sorption or co-precipitation of arsenic with ferric oxyhydroxides sequesters arsenic 

(Welch and others, 2000) before water recharges through the 

basins and trench. 

The initial arsenic concentrations in water sampled from 

monitoring wells DMW–H1 and DMW–H13 were 8.6 and 

11 μg/L, respectively. Arsenic concentrations in water from 

the deep monitoring well DMW–H1 increased because of 

artificial recharge. Median concentrations increased to 

20 μg/L in samples from well DMW–H1 after injection 

began in August 1997 (fig. 26). Arsenic concentrations at this 

monitoring well were similar to concentrations in the recharge 

(diversion well) water and increased in a similar pattern as 

the conservative constituent chloride. Arsenic concentrations 

likely increased as a result of the influx of the recharge water 

near monitoring well DMW–H1. Direct injection of recharge 

water likely allowed less contact with the atmosphere than 

water recharge through the basins and trench. Thus, precipiGeochemical Effects of Artificial Recharge at Halstead Recharge Site  39

0

10

20

30

40

50

60

70

80

90

100

Magnesium

0

10

20

30

40

50

60

70

80

90

100

Calcium

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100

Sulfate plus chloride

Calcium plus magnesium

Sodium plus potassium

Percent total, in milliequivalents per liter

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

Bicarbonate

Chloride

Sulfate

0

10

20

30

40

50

60

70

80

90

100 0

10

20

30

40

50

60

70

80

90

100

Calcium

type

Magnesium type

Sodium

type

No dominant

type

Bicarbonate

type

Sulfate type

Chloride

type

No dominant

type

(B) May 1999

Monitoring well SMW–H14

Monitoring well SMW–H4

Monitoring well DMW–H1

Monitoring well DMW–H13

Diversion well

EXPLANATION

Figure 23. Major ion chemistry in water samples from the Halstead recharge site in (A) May 1997, (B) May 1999, and (C) April 2003—

Continued.
tation of ferric oxyhydroxides did not occur, which allowed 

large arsenic concentrations in the recharge water to be introduced directly into the aquifer. 

Iron was detected only four times in water collected 

from shallow monitoring wells SMW–H4 and SMW–H14. 

Concentrations in the shallow monitoring wells ranged from 

less than 5 to 46 μg/L and were substantially less than the 

USEPA SDWR of 300 μg/L (U.S. Environmental Protection 

Agency, 2004) (fig. 27). The iron concentrations in shallow 

monitoring wells at the site also were substantially less than 

the median iron concentration of 430 μg/L in the recharge 

(diversion well) water. 

Iron concentrations in water from the deep monitoring 

wells at the Halstead recharge site were larger than in shallow monitoring wells and increased after injection of recharge 

water. Iron concentrations in water samples from monitoring well DMW–H1 were about 20 μg/L before injection but 

increased steadily to greater than 200 μg/L after injection 

recharge began in August 1997. Similar to arsenic concentrations, the iron concentrations in samples from deep 

well DMW–H1 indicated mixing with the recharge water and 

not necessarily a change in the geochemical environment. 

Iron concentrations in the water sampled from deep monitoring well DMW–H13 increased after injection recharge began 

and were substantially larger than iron concentrations in the 

recharge (diversion well) water (fig. 27). This mobilization 

of iron could be caused by reduction of ferric oxyhydroxides, increased bacterial activity, or some other change in the 

40 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

Figure 23. Major ion chemistry in water samples from the Halstead recharge site in (A) May 1997, (B) May 1999, and (C) April 2003—

Continued.

0

10

20

30

40

50

60

70

80

90

100

Magnesium

0

10

20

30

40

50

60

70

80

90

100

Calcium

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100

Sulfate plus chloride

Calcium plus magnesium

Sodium plus potassium

Percent total, in milliequivalents per liter

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

Bicarbonate

(C) April 2003

Chloride

Sulfate

0

10

20

30

40

50

60

70

80

90

100 0

10

20

30

40

50

60

70

80

90

100

Calcium

type

Magnesium type

Sodium

type

No dominant

type

Bicarbonate

type

Sulfate type

Chloride

type

No dominant

type

Monitoring well SMW–H14

Monitoring well SMW–H4

Monitoring well DMW–H1

Monitoring well DMW–H13

EXPLANATION
geochemical environment related to the injection of recharge 

water. 

The method by which the aquifer is recharged is particularly important with respect to dissolved iron concentrations 

in the water. Iron in the diversion well water will react with 

oxygen as evidenced by the precipitation of ferric oxyhydroxides 

in the spreading basins and trench at the Halstead recharge 

site. Iron-oxidizing bacteria also could thrive under these 

conditions and create biofilms that can reduce permeability in 

well screens or aquifer material. The water from the diversion 

well contains little oxygen. If it is directly injected through a 

well, it may have little contact with atmospheric oxygen, and 

the iron in the recharge water would have little opportunity 

to oxidize. However, problems could occur if the receiving 

aquifer water contains oxygen and the injection well provides 

a source of reduced iron. Diversion well water introduced 

through spreading basins and trenches becomes oxygenated 

and then mineral precipitation occurs, possibly mediated by 

iron-oxidizing bacteria. Mineral precipitation and biofouling 

eventually could decrease the efficiency of artificial recharge 

by spreading basins and trenches. In addition, oxygenated 

water could react in the aquifer by mixing with ground water 

with large iron concentrations or by direct reaction with 

reduced iron in the aquifer material. 

Geochemical Simulations

Saturation indices were calculated for water samples 

from all the monitoring wells at the Halstead recharge site collected during May 1997, May 1998, June 2001, August 2002, 

and April 2003 (table 4). Artificial recharge activities began 

at the Halstead recharge site on May 15, 1997; therefore, 

May 13, 1997, samples are considered pre-recharge samples. 

The August 2002 and April 2003 samples were collected after 

the end of the artificial recharge demonstration project and are 

representative of post-recharge conditions. 

Geochemical Effects of Artificial Recharge at Halstead Recharge Site 41

Figure 24. Chloride concentrations in ground-water samples from diversion well at Halstead diversion site and monitoring wells at 

Halstead recharge, May 1997–December 2004.

Artificial recharge period

Chloride concentrations

 Shallow monitoring well SMW–H4

 Shallow monitoring well SMW–H14

 Deep monitoring well DMW–H1

 Deep monitoring well DMW–H13

 Diversion well water

EXPLANATION

1996 1997 1998 1999 2000 2001 2002 2003 2004 0

50

450

400

300

350

200

250

100

150

U.S. Environmental Protection

Agency (2004) Secondary

Drinking-Water Regulation

(250 mg/L)

Chloride concentration, in milligrams per liter (mg/L)
Saturation indices for calcite in diversion well water 

samples were negative (-0.15 to -0.80) indicating undersaturation with respect to calcite. Saturation indices for calcite and 

dolomite in shallow monitoring wells SMW–H4 and SMW–

H14 were undersaturated throughout the entire study period. 

Saturation indices increased after artificial recharge began 

but remained negative. Saturation indices for initial samples 

indicated undersaturation with respect to calcite and dolomite 

in deep monitoring wells DMW–H1 (-1.12 and -2.80) and 

DMW–H13 (-0.65 and -2.01). Saturation indices increased 

in samples from the deep monitoring wells after injection 

recharge began, and some saturation indices approached equilibrium; the May 1998 sample was at or near equilibrium with 

respect to calcite. The initial undersaturation with respect to 

calcite and dolomite in samples from all wells probably indicates limited carbonate minerals in aquifer sediments; thus, the 

increase in saturation indices probably is related to changes in 

water chemistry caused by the mixing of aquifer water with 

recharge water rather than dissolution of carbonate minerals. 

Iron was measurable in one water sample from the 

shallow monitoring wells and all of the samples from the 

deep monitoring wells. All saturation indices calculated for 

these samples indicated supersaturation and the potential for 

amorphous ferric oxyhydroxide precipitation. Precipitation 

of amorphous ferric oxyhydroxides is expected to be limited 

unless oxygen is introduced to the water. Iron oxyhydroxide 

precipitates on the recharge basin and trench floors at the 

Halstead recharge site demonstrate that diversion well water, 

when in contact with oxygen, will precipitate ferric oxyhydroxides. 

Geochemical Effects of Artificial 

Recharge at Sedgwick Recharge Site

Recharge water at the Sedgwick recharge site was 

diverted directly from the Little Arkansas River, treated to 

reduce turbidity and organic compounds, then artificially 

recharged through surface-spreading recharge basins (fig. 5). 

The major ion composition of water sampled from the two 

shallow and two deep monitoring wells on the site as well as 

42 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

Artificial recharge period

Atrazine concentrations

 Shallow monitoring well SMW–H4

 Shallow monitoring well SMW–H14

 Deep monitoring well DMW–H1

 Deep monitoring well DMW–H13

 Diversion well water

EXPLANATION

1996 1997 1998 1999 2000 2001 2002 2003 2004

0

0.50

0.25

0.75

3.0

U.S. Environmental Protection Agency (2004) Maximum Contaminant Level for atrazine (3.0 μg/L as an annual

average)

Atrazine concentration, in micrograms per liter (μg/L) as atrazine

Figure 25. Atrazine concentrations in ground-water samples from diversion well at Halstead diversion site and monitoring wells at 

Halstead recharge site compared to concentrations in diverted recharge water, May 1997–December 2004.
the treated recharge water was analyzed using Piper diagrams 

to access the geochemical effects of artificial recharge at this 

site. Additionally, atrazine, arsenic, and iron concentrations 

were examined to determine effects of artificial recharge. 

Saturation indices calculated with respect to calcite, dolomite, 

and amorphous iron oxide also were examined. Simulations to 

model injection of treated stream water into the Equus Beds 

aquifer also were conducted. 

Major Ion Chemistry and Tracers of Recharge 

Water

Piper diagrams were constructed using major ion chemistry to compare major ion concentrations during artificial 

recharge activities in water sampled from all monitoring wells 

at the Sedgwick recharge site, the treated diverted stream 

water, and the Little Arkansas River. Piper diagrams were 

constructed using data from July 1997 (fig. 28A), representing 

water chemistry before recharge; May 1999 (fig. 28B), representing water chemistry during recharge; and August 2002 

(fig. 28C), representing the water chemistry after recharge. 

Piper diagrams show that water samples from the shallow 

monitoring wells at the Sedgwick recharge site increase in 

chloride proportion during artificial recharge and then revert 

to low chloride water types after the end of artificial recharge 

activities. Water samples from the deep monitoring wells show 

little variation in the proportions of major cations and anions. 

Chloride concentrations in water samples collected from 

the Little Arkansas River near Sedgwick were variable and 

ranged from 5 to 305 mg/L with a median concentration of 

70 mg/L (fig. 29A). Measured chloride concentrations 

exceeded the USEPA SDWR of 250 mg/L (U.S. Environmental Protection Agency, 2004) in 2 of 135 samples from 1995 

through 2004. Chloride concentrations were estimated for 

the Little Arkansas River near Sedgwick using the regression 

model:

 (9)

 

where Cl is chloride concentration in milligrams per liter, SC

equal specific conductance in microsiemens per centimeter at 

25 degrees Celsius, and Q equals streamflow in cubic feet per 

Geochemical Effects of Artificial Recharge at Sedgwick Recharge Site 43

Artifical recharge period

Arsenic concentrations

 Shallow monitoring well SMW–H4

 Shallow monitoring well SMW–H14

 Deep monitoring well DMW–H1

 Deep monitoring well DMW–H13

 Diversion well water

EXPLANATION

1996 1997 1998 1999 2000 2001 2002 2003 2004

0

5

10

15

20

30

25

35

40

U.S. Environmental Protection Agency (2004) Maximum

Contaminant Level for arsenic (10 μg/L, effective 2006)

Arsenic concentration, in micrograms per liter (μg/L)

Figure 26. Arsenic concentrations in ground-water samples from diversion well at Halstead diversion site and monitoring wells at 

Halstead recharge site compared to concentrations in diverted recharge water, May 1997–December 2004.

10 Cl = −112 + + 0. S 203 C . 25 7log Q,
second. The regression has an R2

 of 0.94 (Christensen and others, 2003). 

Chloride concentrations in the Little Arkansas River near 

Sedgwick estimated from the regression with specific conductance exceeded the SDWR one time from 1999 through 2004, 

and the median value was 99 mg/L (data available on the Web 

at http://ks.water.usgs.gov/Kansas/rtqw/, accessed December 

2006). Chloride concentrations in samples of treated diverted 

stream water were similar to concentrations found in samples 

from the stream because treatment did not affect chloride 

concentrations. Chloride concentrations in treated diverted 

stream water ranged from 13 to 220 mg/L with a median 

concentration of 62 mg/L (fig. 29). Chloride concentrations in 

the treated diverted stream water did not exceed the drinkingwater criterion for chloride. However, chloride concentrations 

in the stream may have exceeded the SDWR of 250 mg/L 

between samplings of the treated diverted stream water, and it 

would be expected that chloride concentrations in the treated 

diverted stream water also would exceed the SDWR at these 

times. 

Chloride concentrations in water sampled from the deep 

monitoring wells were larger than concentrations in water 

sampled from shallow monitoring wells before artificial 

recharge began at the Sedgwick recharge site in April 1998. 

Median chloride concentrations in the monitoring wells were 

12 mg/L in well SMW–S11, 11 mg/L in well SMW–S13, 

64 mg/L in well DMW–S10, and 46 mg/L in well DMW–

S14. Chloride concentrations in the shallow monitoring wells 

were variable during recharge activities (April 1998 through 

November 2000), ranging from 12 to 156 mg/L. Generally, 

when large chloride concentrations were detected in samples 

of treated diverted stream water, large chloride concentrations were detected in the samples from the shallow monitoring wells. Chloride concentrations in the shallow monitoring 

wells were less than the treated diverted stream water because 

of mixing with the existing shallow ground water. Chloride 

concentrations in the shallow monitoring wells never exceeded 

USEPA SDWR of 250 mg/L (U.S. Environmental Protection 

Agency, 2004) during the study period (fig. 29B). 

Chloride concentrations in deep monitoring well DMW–

S10 ranged from 56 to 70 mg/L with a median concentration 

of 63 mg/L and remained relatively stable throughout the 

demonstration project. Chloride concentrations in monitoring 

well DMW–S14 ranged from 19 to 52 mg/L with a median 

concentration of 23 mg/L. Chloride concentrations in this well 

decreased after artificial recharge activities began, which may 

44 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

Artifical recharge period

Iron concentrations

 Shallow monitoring well SMW–H4

 Shallow monitoring well SMW–H14

 Deep monitoring well DMW–H1

 Deep monitoring well DMW–H13

 Diversion well water

EXPLANATION

1996 1997 1998 1999 2000 2001 2002 2003 2004

0

200

400

600

800

1,000

1,400

1,200

U.S. Environmental Protection Agency (2004)

Secondary Drinking-Water Regulation (300 μg/L)

Iron concentration, in micrograms per liter (μg/L)

Figure 27. Iron concentrations in ground-water samples from diversion well at Halstead diversion site and monitoring wells at 

the Halstead recharge site compared to concentrations in diverted recharge water, May 1997–December 2004.
indicate the displacement of deep aquifer water with water 

from the shallow part of the aquifer.

Atrazine concentrations in the Little Arkansas River near 

Sedgwick ranged from 0.10 to 41 μg/L with an average concentration of 4.0 μg/L (fig. 30A), which exceeds the USEPA 

MCL of 3.0 μg/L as an annual average. The regression model 

is:

 (10)

where atrazine is in micrograms per liter, D is the julian day of 

the year, and SC is specific conductance in microsiemens per 

centimeter at 25 degrees Celsius. The regression has an R2 of 

0.60 (Christensen and others (2000, 2003).

Annual averages calculated from estimated daily atrazine concentrations developed for the Sedgwick recharge site 

(fig. 30A) from 1999 through 2004 did not exceed the drinking-water criterion. Measured atrazine concentrations in the 

treated diverted stream water ranged from 0.10 to 6.8 μg/L 

with an average concentration of 0.30 μg/L (fig. 30B). The 

maximum concentration of 6.8 μg/L occurred on a day when 

the PAC treatment malfunctioned (Jerry Blain, Water Supply Projects Administrator, city of Wichita, Water and Sewer 

Department, written commun., August 2005), demonstrating 

Geochemical Effects of Artificial Recharge at Sedgwick Recharge Site 45

 

Table 4. Saturation indices calculated for ground-water samples collected from 

monitoring wells at Halstead recharge site and Halstead diversion well, south-central 

Kansas, May 1997–April 2003.

[--, not calculated]

Date of sample

Mineral (chemical formula) saturation indices

Calcite

(CaCO3)

Dolomite

(CaMg(CO3)

2

)

Amorphous iron

(Fe(OH)3(a))

Shallow monitoring well SMW–H4 (fig. 2B)

May 1997 -2.10 -4.79 --

May 1998 -.40 -1.41 --

June 2001 -.99 -2.43 --

August 2002 -1.22 -2.88 --

April 2003 -1.04 -2.54 --

Shallow monitoring well SMW–H14 (fig. 2B)

May 1997 -.93 -2.46 0.89

May 1998 -.47 -1.58 --

June 2001 -.51 -1.58 --

August 2002 -.67 -1.90 --

April 2003 -.46 -1.50 --

Deep monitoring well DMW–H1 (fig. 2B)

May 1997 -1.12 -2.80 .71

May 1998 0 -.60 2.50

June 2001 -.27 -1.14 2.43

August 2002 -.28 -1.15 2.51

April 2003 -.11 -.81 2.75

Deep monitoring well DMW–H13 (fig. 2B)

May 1997 -.65 -2.01 2.63

May 1998 -.03 -.73 3.25

June 2001 .01 -.59 2.73

August 2002 -.26 -1.14 2.98

April 2003 -.09 -.80 3.17

Diversion well (fig. 2)

May 1997 -.80 -- -.42

May 1998 -.35 -- -.87

June 2001 -.15 -- 1.42

365 log10atrazine = 0.237 - 0.745 cos +

2πD ( )

0.504 sin - 0.000647SC, 365

2πD ( )
the need for treatment of diverted stream water for atrazine 

removal. The average atrazine concentration in shallow 

monitoring well SMW–S11 before artificial recharge began 

was 0.17 μg/L. This well was the only monitoring well where 

atrazine was detected before artificial recharge began in 

April 1998. Atrazine concentrations increased in water 

samples from both shallow monitoring wells after artificial 

recharge began at the Sedgwick recharge site. The maximum 

concentration of 1.1 μg/L occurred in a sample from well 

SMW–S11 in August 1998. Generally larger concentrations 

of atrazine in the shallow monitoring wells were observed 

when large concentrations occurred in the treated diverted 

stream water (fig. 30B). Atrazine concentrations in the treated 

diverted stream water exceeded USEPA MCL of 3.0 μg/L for 

drinking water in three discrete samples. However, the annual 

average concentration in water from the shallow monitoring 

wells was considerably less than 3.0 μg/L. Atrazine was not 

detected in water samples from the deep monitoring wells at 

this site. 

The increase in chloride and atrazine concentrations 

in water from the shallow wells after recharge began at the 

Sedgwick site indicates the presence of treated diverted stream 

water in the shallow parts of the aquifer; however, the minimal 

change in the chloride concentrations in water sampled from 

the deep monitoring wells indicates that the treated diverted 

stream water did not reach the deeper parts of the aquifer at 

the Sedgwick recharge site. 

46  Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

0

10

20

30

40

50

60

70

80

90

100

Magnesium

0

10

20

30

40

50

60

70

80

90

100

Calcium

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100

Sulfate plus chloride

Calcium plus magnesium

Sodium plus potassium

Percent total, in milliequivalents per liter

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

Bicarbonate

Chloride

Sulfate

0

10

20

30

40

50

60

70

80

90

100 0

10

20

30

40

50

60

70

80

90

100

Calcium

type

Magnesium type

Sodium

type

No dominant

type

Bicarbonate

type

Sulfate type

Chloride

type

No dominant

type

(A) July 1997

Monitoring well SMW–S11

Monitoring well SMW–S13

Monitoring well DMW–S10

Monitoring well DMW–S14

Treated diverted stream water

Little Arkansas River near

 Sedgwick

EXPLANATION

Figure 28. Major ion chemistry in water samples from the Sedgwick recharge site in (A) July 1997, (B) May 1999, and (C)

August 2002.
Selected Trace Metal Chemistry

At the Sedgwick recharge site, concentrations of arsenic 

in samples from the treated diverted stream water ranged from 

2.1 to 5.9 μg/L. The larger concentrations in this range usually 

corresponded with larger concentrations in water from the 

Little Arkansas River near Sedgwick, which ranged from 

1.1 to 14 μg/L. Arsenic concentrations were less than 

5.0 μg/L in all water samples from the monitoring wells at the 

Sedgwick recharge site. However, arsenic concentrations were 

slightly larger in samples from the deep monitoring wells, 

ranging from 1.8 to 5.0 μg/L, than in the shallow monitoring 

wells, ranging from less than 1.0 to 2.7 μg/L (fig. 31). The 

concentrations in all monitoring wells and treated diverted 

stream water were less than the USEPA MCL of 10 μg/L. 

Arsenic concentrations in ground water did not change substantially during recharge operations, indicating that, if arsenic 

is present in aquifer material at this site, the artificial recharge 

process did not mobilize arsenic.

With the exception of a few large concentrations in water 

samples from monitoring well SMW–S11, dissolved iron concentrations in water samples from all monitoring wells 

at the Sedgwick recharge monitoring site were small, if 

detected at all (fig. 32B). Dissolved oxygen concentrations 

in well SMW–S11 ranged from 3.1 to 6.8 mg/L in the water 

samples with the large iron concentrations. These concentrations indicate that the source of the iron is not the aquifer 

water in the vicinity of well SMW–S11 because dissolved 

Geochemical Effects of Artificial Recharge at Sedgwick Recharge Site 47

0

10

20

30

40

50

60

70

80

90

100

Magnesium

0

10

20

30

40

50

60

70

80

90

100

Calcium

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100

Sulfate plus chloride

Calcium plus magnesium

Sodium plus potassium

Percent total, in milliequivalents per liter

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

Bicarbonate

Chloride

Sulfate

0

10

20

30

40

50

60

70

80

90

100 0

10

20

30

40

50

60

70

80

90

100

Calcium

type

Magnesium type

Sodium

type

No dominant

type

Bicarbonate

type

Sulfate type

Chloride

type

No dominant

type

(B) May 1999

Monitoring well SMW–S11

Monitoring well SMW–S13

Monitoring well DMW–S10

Monitoring well DMW–S14

Treated diverted stream water

Little Arkansas River near

 Sedgwick

EXPLANATION

Figure 28. Major ion chemistry in water samples from the Sedgwick recharge site in (A) July 1997, (B) May 1999, and (C)

August 2002—Continued.
iron likely would be oxidized and precipitate in the presence 

of large dissolved oxygen concentrations. The large iron concentrations initially detected in water from the well could be 

an artifact of insufficient well development. The development 

of wells before water-quality sampling is necessary to remove 

the loose sediment in the well that may have been introduced 

during drilling. Metals, such as iron, can be associated with 

the sediment that could have been disturbed during well installation. Field notes recorded during the first several samplings 

at this well indicated large sediment concentrations in the 

water from well. 

Geochemical Simulations

Saturation indices were simulated for water samples 

collected during July 1997, May 1999, June 2000, and 

June 2001 for all monitoring wells at the Sedgwick recharge 

site as well as the treated diverted stream water (table 5). Artificial recharge activities began at the Sedgwick recharge site in 

April 1998; therefore, the samples collected during July 1997 

were considered representative of pre-recharge conditions. 

Calcite and dolomite saturation indices in the treated 

diverted stream water ranged from -0.54 to 0.21 and from 

-1.26 to 0, respectively. For initial water samples from the 

48 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

0

10

20

30

40

50

60

70

80

90

100

Magnesium

0

10

20

30

40

50

60

70

80

90

100

Calcium

100 90 80 70 60 50 40 30 20 10 0 0 10 20 30 40 50 60 70 80 90 100

Sulfate plus chloride

Calcium plus magnesium

Sodium plus potassium

Percent total, in milliequivalents per liter

0

10

20

30

40

50

60

70

80

90

100

100

90

80

70

60

50

40

30

20

10

0

Bicarbonate

Chloride

Sulfate

0

10

20

30

40

50

60

70

80

90

100 0

10

20

30

40

50

60

70

80

90

100

Calcium

type

Magnesium type

Sodium

type

No dominant

type

Bicarbonate

type

Sulfate type

Chloride

type

No dominant

type

(C) August 2002

Monitoring well SMW–S11

Monitoring well SMW–S13

Monitoring well DMW–S10

Monitoring well DMW–S14

Treated diverted stream water

Little Arkansas River near

 Sedgwick

EXPLANATION

Figure 28. Major ion chemistry in water samples from the Sedgwick recharge site in (A) July 1997, (B) May 1999, and 

(C) August 2002—Continued.
Geochemical Effects of Artificial Recharge at Sedgwick Recharge Site 49

Figure 29. Measured and estimated chloride concentrations in water samples from (A) Little Arkansas River near Sedgwick 

(site 07144100, fig. 1), treated diverted stream water, and (B) monitoring wells at the Sedgwick recharge site, February 1995–

December 2004.

0

250

200

150

100

50

300

350

U.S. Environmental Protection Agency (2004) Secondary

Drinking-Water Regulation (250 mg/L)

U.S. Environmental Protection Agency (2004) Secondary

Drinking-Water Regulation (250 mg/L)

0

300

200

250

100

50

150

Chloride concentration, in milligrams per liter (mg/L)

Artifical recharge period

 Chloride concentrations

 Little Arkansas River near Sedgwick

 Treated diverted stream water

 Shallow monitoring well SMW–S11

 Shallow monitoring well SMW–S13

Deep monitoring well DMW–S10

Deep monitoring well DMW–S14

Estimated chloride concentration

 in Little Arkansas River near

 Sedgwick

EXPLANATION

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

(B) Monitoring wells

(A) Little Arkansas River near Sedgwick (site 07144100, fig.1) and treated diverted stream water
50 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

0

30

35

25

20

15

5

10

40

45

U.S. Environmental Protection Agency

(2004) Maxmium Contaminant Level for 

atrazine (3.0 μg/L as an annual average)

0

8

5

6

7

2

3

1

4

(B) Treated diverted stream water and monitoring wells

(A) Little Arkansas River near Sedgwick (site 07144100, fig.1) and treated diverted stream water

Atrazine concentration, in micrograms per liter (μg/L) as atrazine

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

U.S. Environmental Protection Agency (2004) Maxmium Contaminant

Level for atrazine (3.0 μg/L as an annual average)

Artificial recharge period

 Atrazine concentrations

 Little Arkansas River near Sedgwick

 Treated diverted stream water

 Shallow monitoring well SMW–S11

 Shallow monitoring well SMW–S13

Deep monitoring well DMW–S10

Deep monitoring well DMW–S14

Estimated continuous atrazine

 concentrations from Little Arkansas

 River near Sedgwick

EXPLANATION

Figure 30. Atrazine concentrations in water samples from (A) Little Arkansas River near Sedgwick, treated diverted stream 

water, and (B) monitoring wells at the Sedgwick recharge site, February 1995–December 2004.
shallow monitoring wells, saturation indices for calcite 

(-0.46 and -0.81) and dolomite (-1.6 and -2.27) indicated 

undersaturation. Saturation indices for samples collected from 

shallow wells during and after artificial recharge also indicated 

undersaturation, except for one near-zero saturation index 

for calcite in water from well SMW–S11. Calcite saturation 

indices indicated slight undersaturation in water sampled from 

deep monitoring wells DMW–S10 and DMW–S14, whereas 

dolomite saturation indices indicated undersaturation. The 

saturation indices for the few samples in which iron was measurable indicated supersaturation with respect to amorphous 

ferric hydroxide. 

The initial negative saturation indices for calcite and 

dolomite for samples from the shallow monitoring wells 

indicate that carbonate minerals probably are not present in the 

shallow aquifer. Similarly dolomite is probably not present in 

the deeper aquifer, but calcite may be reacting in the deeper 

aquifer to produce saturation indices that approach equilibrium. 

The saturation index for calcite is greater than zero for at 

least one sample of the treated diverted stream water, which 

indicates the potential for calcite precipitation. The introduction of oxygen with the treated diverted stream water combined with saturation indices in the aquifer that indicate supersaturation with respect to amorphous ferric hydroxide indicate 

the possibility of precipitation of ferric oxyhydroxides.

Simulations to model injection of treated stream water 

into the Equus Beds aquifer were conducted using PHREEQC. The stream water is oxygenated, which when injected 

into ground water with low dissolved oxygen concentrations, 

could result in alterations in the redox condition of the ground 

water. Direct injection of stream water was not tested during 

the demonstration phase of the Equus Beds Ground-Water 

Recharge Project. The model simulates mixing the treated 

stream water from the Sedgwick site (median concentrations) with pre-recharge ground water from deep monitoring well DMW–H13 at the Halstead site. 

Geochemical Effects of Artificial Recharge at Sedgwick Recharge Site 51

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

0

5

10

15

20

25

30

35

40

U.S. Environmental Protection Agency (2004) Maximum 

Contaminant Level for arsenic (10 μg/L, effective 2006)

Arsenic concentration, in micrograms per liter (μg/L)

Artificial recharge period

 Arsenic concentrations

 Little Arkansas River near Sedgwick

 Treated diverted stream water

 Shallow monitoring well SMW–S11

 Shallow monitoring well SMW–S13

Deep monitoring well DMW–S10

Deep monitoring well DMW–S14

EXPLANATION

Figure 31. Arsenic concentrations in water samples from Little Arkansas River near Sedgwick, treated diverted stream water, 

and monitoring wells at the Sedgwick recharge site, February 1995–December 2004. 
52 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

0

500

600

400

300

100

200

700

U.S. Environmental Protection Agency (2004)

Secondary Drinking-Water Regulation (300 μg/L)

0

1,500

1,000

1,100

1,200

1,300

1,400

400

500

600

700

100

200

300

800

900

(B) Monitoring wells

(A) Little Arkansas River near Sedgwick (site 07144100, fig.1) and treated diverted stream water

Iron concentration, in micrograms per liter (μg/L) 

1995 1996 1997 1998 1999 2000 2001 2002 2003 2004

U.S. Environmental Protection Agency (2004)

Secondary Drinking-Water Regulation (300 μg/L)

Artificial recharge period

 Iron concentrations

 Little Arkansas River near Sedgwick

 Treated diverted stream water

 Shallow monitoring well SMW–S11

 Shallow monitoring well SMW–S13

Deep monitoring well DMW–S10

Deep monitoring well DMW–S14

EXPLANATION

Figure 32. Iron concentrations in water samples from (A) Little Arkansas River near Sedgwick, treated diverted stream water, 

and (B) monitoring wells at the Sedgwick recharge site, February 1995–December 2004.
Results of the simulation indicate that calcite oversaturation is likely only in mixtures that are greater than 90 percent 

treated recharge water from the Little Arkansas River (fig. 33). 

The treated stream water is oversaturated with respect to calcite, the receiving ground water is undersaturated with respect 

to calcite, and the calculations indicate it is possible that calcite precipitation may occur. Calcite precipitation could reduce 

permeability and reduce effectiveness of artificial recharge. 

Amorphous iron oxyhyrdoxide may precipitate as oxygenated treated stream water is injected into the ground water, 

which has small dissolved oxygen concentrations and an 

average dissolved iron concentration of 845 μg/L. Calculations 

indicate oversaturation for all mixtures of the two waters 

(fig. 33). In addition, iron bacteria could be a cause for concern for injection of oxygenated water into the aquifer. It is 

possible that biofouling of the injection well could occur causing increased precipitation of iron and creation of a biofilm 

associated with iron bacteria activity (Hem, 1992). The precipitation and biofouling could decrease the efficiency of the 

injection well as well as reduce the permeability of the aquifer 

material in vicinity of the well.

Geochemical Effects of Artificial Recharge at Sedgwick Recharge Site 53

Table 5. Saturation indices calculated for ground-water samples collected from 

monitoring wells at Sedgwick recharge site and for samples of treated diverted 

stream water, south-central Kansas, July 1997–April 2003.

[--, not calculated]

Date of sample

Mineral (chemical formula) saturation indices

Calcite 

(CaCO3)

Dolomite 

(CaMg(CO3)

2

)

Amorphous iron 

(Fe (OH)3(a))

Shallow monitoring well SMW–S11 (fig. 5)

July 1997 -0.46 -1.6 2.58

May 1999 .02 -.47 --

June 2000 -.97 -2.46 1.30

June 2001 -1.27 -3.07 .88

Shallow monitoring well SMW–S13 (fig. 5)

July 1997 -.81 -2.27 --

May 1999 -1.12 -2.79 --

June 2000 -.89 -2.25 --

June 2001 -1.16 -2.81 --

Deep monitoring well DMW–S10 (fig. 5)

July 1997 -.12 -.74 --

May 1999 -.05 -.60 --

June 2000 -.10 -.66 --

June 2001 -.20 -.90 --

Deep monitoring well DMW–S14 (fig. 5)

July 1997 -.14 -.76 --

May 1999 -.09 -.67 --

June 2000 -.19 -.85 --

June 2001 -.18 -.82 --

Treated diverted water (collected from settling basin, fig. 5)

July 1997 -.01 -.55 --

May 1999 .21 0 --

June 2000 -.54 -1.26 --

June 2001 -- -- --
Summary and Conclusions

The Wichita well field, developed in the 1940s in the 

Equus Beds aquifer, is one of the primary sources of water 

for the city of Wichita and the surrounding area in south-central Kansas. Historical water use for municipal supply and 

irrigation had caused water levels in the Equus Beds aquifer 

to decline more than 30 ft by 1993 in some areas. Water-level 

declines represent a diminished amount of available water but 

also may accelerate migration of saltwater from the Burrton 

oil field to the northwest and from the Arkansas River to the 

southwest into the freshwater of the Equus Beds aquifer. 

Artificial recharge of the Equus Beds aquifer will augment the city of Wichita’s future water-supply needs and help 

to preserve all existing aquifer uses from degradation of the 

aquifer from saltwater migration by increasing water levels in 

the aquifer. The Equus Beds Ground-Water Recharge Project 

is a cooperative effort between the city of Wichita and the U.S. 

Geological Survey (USGS). Artificial recharge, as a part of the 

Equus Beds Ground-Water Recharge Demonstration Project, 

involved capturing flows larger than base flow from the Little 

Arkansas River and recharging the water to the Equus Beds 

aquifer by means of infiltration or injection. The project used 

two methods of stream-water diversion for recharge water and 

three methods of artificial recharge. The USGS role in the 

cooperative study is to document changes in historic hydrologic water-quality conditions, to identify the probable causes 

of the changes in the study area, and to define pre-recharge 

conditions for evaluating the effects of artificial recharge 

related to water quantity and water quality. 

This report examines the geochemical effects of induced 

stream-water and artificial recharge activities that were a part 

of the Equus Beds Ground-Water Recharge Demonstration 

Project, which was conducted April 1995 through May 2002. 

Geochemical effects were determined through collection and 

analysis of hydrologic and water-quality data, application of 

statistical, mixing, flow, and solute-transport, and geochemical 

model simulations.

At the Halstead diversion site a pumping well in the 

aquifer adjacent to the stream was used to capture water for 

artificial recharge. Water collected at this site was pumped 

without treatment to the Halstead recharge site. 

Estimated chloride concentrations in the Little Arkansas 

River at Highway 50 near Halstead exceeded the SDWR of 

250 mg/L established by USEPA about 30 percent of the time. 

Chloride concentrations were slightly smaller than stream concentrations at shallow monitoring wells nearest the stream at 

the Halstead diversion well site and decreased to background 

concentrations (19 to 32 mg/L) in shallow monitoring wells 

500 ft or more from the stream. Chloride concentrations in the 

deep monitoring well (EB–145–PD5) at the Halstead diversion 

well site increased from background concentrations of 

15 mg/L to a maximum of 130 mg/L during the pumping 

phase of the demonstration project and decreased to about 

40 mg/L after pumping ceased. Chloride concentrations in the 

diversion well increased from 20 to about 60 mg/L during the 

pumping phase of the demonstration project.

54 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer

-1.0

-0.5

0

0.5

1.0

1.5

2.0

2.5

3.0

0 10 20 30 40 50 60 70 80 90 100

Percentage of treated stream water 

Saturation index

6.8

7.0

7.2

7.4

7.6

7.8

8.0

pH, in standard units

Calcite

pH

Amorphous iron oxide

Figure 33. Saturation indices for calcite, amorphous iron oxide, and modeled pH for the theoretical mixing model of artificial 

recharge by injection of treated stream water into the Equus Beds aquifer.
The annual average of estimated atrazine concentrations 

in the Little Arkansas River at Highway 50 was equal to 

the 3.0 μg/L for 1999 and was smaller than 3.0 μg/L for 

2000 through 2004. The USEPA MCL for atrazine is 

3.0 μg/L as an annual average. Although atrazine concentrations diminish as the induced stream-water recharge migrates 

through the aquifer, the removal of atrazine is not complete. 

Atrazine initially was detected in samples from the diversion 

well 4 months after pumping began, and atrazine was detected 

periodically at concentrations up to 0.42 μg/L in the diversion 

well and the deep monitoring well at the diversion well site. 

Detections of atrazine degradation products were rare, which 

indicates decreases in atrazine concentration are more likely 

because of sorption processes than degradation.

Thirteen percent of the 54 discrete water-quality samples 

from the Little Arkansas River at Highway 50 near Halstead 

exceeded the MCL of 10 μg/L for arsenic. Arsenate was the 

dominant species in surface-water samples. Arsenic concentrations for samples from the three shallow monitoring wells 

nearest to the stream at the diversion well site generally were 

near or less than the detection limit. Naturally occurring arsenic concentrations consistently exceeded the MCL in water 

from shallow monitoring wells more than 500 ft from the 

stream, the deep monitoring well, and the diversion well, with 

median concentrations ranging from 16 to 25 μg/L. Arsenate 

was the dominant species in surface-water samples. Arsenic 

concentrations in water samples from these wells did not 

change in response to pumping the diversion well.

Dissolved iron concentrations observed in the Little 

Arkansas River at Highway 50 near Halstead generally were 

less than the 300-μg/L SDWR established by the USEPA. The 

two shallow monitoring wells nearest the stream had large 

iron concentrations, ranging from 1,600 to 6,250 μg/L. Iron 

concentrations in samples from all other wells increased in 

response to pumping from less than or equal to 300 μg/L to 

between 300 and 1,000 μg/L. 

Saturation indices for calcite and dolomite for water 

samples from the Halstead diversion site indicate that these 

minerals probably are not present in the aquifer adjacent to the 

Little Arkansas River. Saturation indices for amorphous ferric 

oxyhydroxide indicate the potential for precipitation of the 

mineral from diversion well water; however, precipitation is 

expected to be limited in the absence of oxygen.

Piper diagrams indicate that water sampled from the 

diversion well is a mixture of water from the Little Arkansas 

River and water in the aquifer adjacent to the stream. Water 

levels and chemistry indicate that the shallow part of the 

aquifer adjacent to the stream was constantly recharged by the 

Little Arkansas River and that the water chemistry of the shallow aquifer was similar to the chemistry of the Little Arkansas 

River. A simple chloride-based mixing model indicates that 

water sampled from monitoring well EB–145–A1 was about 

80 percent stream water and 20 percent ground water. The 

estimated mixture of water sampled from the diversion well 

was about 25 percent water from monitoring well EB–145–A1 

and about 75 percent from ground water. Using these percentages, an estimated 75 percent of atrazine is sorbed to aquifer 

sediments, decreasing the need for additional water treatment 

to remove atrazine before recharge. A flow and solute-transport model was developed to simulate flow of the stream water 

to the pumping well using water levels and chloride concentrations. Flow and transport-model simulation results indicate that at steady state—after decades—the rate of induced 

stream-water recharge is about 75 percent of the pumping rate. 

Water captured by the diversion well was pumped to the 

Halstead recharge site and artificially recharged to the aquifer 

through surface-spreading recharge basins, a recharge trench, 

or a direct-injection recharge well. The water composition of 

the recharge (diversion well) water and water from all monitoring wells was a calcium bicarbonate type, except for shallow monitoring well SMW–H14, which contained a sodium 

chloride type water. The different water type is attributed to 

the well’s proximity to a sewage treatment lagoon. After artificial recharge through the basins and trench began, chloride 

concentrations in water from the shallow monitoring wells 

approximated the chloride concentration in recharge (diversion 

well) water (60 mg/L). After artificial recharge through the 

basins and trench ended, chloride concentrations in water from 

shallow monitoring well SMW–H14 increased to greater than 

pre-recharge concentrations. The effects of artificial recharge 

were not evident in water from the deep monitoring wells until 

artificial recharge through the direct injection well began, after 

which chloride concentrations increased to about 60 mg/L, and 

remained at that concentration for the duration of the study. 

The average atrazine concentration in recharge (diversion 

well) water for the Halstead recharge site was less than 0.1 μg/L. 

Atrazine concentrations in all water samples from monitoring 

wells were considerably less than the USEPA MCL of 

3.0 μg/L as an annual average. After artificial recharge through 

the basins and trench began, atrazine concentrations in water 

from the shallow monitoring wells at the Halstead recharge 

site were similar to concentrations in the recharge water, generally 0.15 μg/L or less, but occasionally were between 0.25 

and 0.50 μg/L. Atrazine concentrations in water from the deep 

monitoring wells increased when artificial recharge by injection began. Concentrations were variable, occasionally in the 

range of 0.1 to 0.2 μg/L. 

The median arsenic concentration in the recharge (diversion well) water for the Halstead recharge site was 20 μg/L. 

Arsenic concentrations in water samples from the shallow 

monitoring wells did not increase because of artificial recharge 

despite the large arsenic concentrations in the recharge water. 

Ferric oxyhydroxide precipitates observed in the recharge 

basins and recharge trench may have sorbed or co-precipitated 

arsenic. Arsenic concentrations in samples from deep monitoring well DMW–H13 remained relatively constant (approximately 10 μg/L) with no apparent change because of recharge 

activities. Arsenic concentrations in samples from deep 

monitoring well DMW–H1 increased to about 20 μg/L after 

injection recharge began, which was attributed to conservative 

transport of arsenic in the injected recharge (diversion well) 

water. 

Summary and Conclusions 55
Iron concentrations in water samples from the shallow 

monitoring wells at the Halstead recharge site were substantially less than the USEPA SDWR of 300 μg/L. Iron concentrations in water samples from deep monitoring well DMW–

H1 increased steadily to larger than 200 μg/L after artificial 

recharge by direct injection began and is attributed to conservative transport of iron in the injected recharge (diversion 

well) water. Iron concentrations in the water sampled from 

deep monitoring well DMW–H13 increased after injection 

recharge began to levels substantially larger than iron concentrations in the recharge water. This mobilization of iron could 

be caused by reduction of ferric oxyhydroxides, increased 

bacterial activity, or some other change in the geochemical 

environment related to the injection of recharge water. 

Saturation indices for calcite and dolomite for prerecharge water samples from monitoring wells at the Halstead 

recharge site indicate limited carbonate minerals in the aquifer 

sediments at the site; therefore, increases in saturation indices 

probably were related to changes in water chemistry caused 

by mixing of the aquifer water with the recharge water rather 

than dissolution of carbonate minerals. Ferric oxyhydroxide 

precipitates on the recharge basin and trench floors at the 

Halstead recharge site demonstrate that the recharge (diversion 

well) water, when contacted by oxygen from the atmosphere, 

will precipitate ferric oxyhydroxides.

Direct diversion of water from the Little Arkansas River 

was used to capture flows greater than base flow for the Sedgwick recharge system. The stream water was treated to reduce 

turbidity and organic compounds and piped to the Sedgwick 

recharge site for artificial recharge through surface-spreading 

recharge basins.

Chloride concentrations in water samples from the shallow monitoring wells at the Sedgwick recharge site increased 

after artificial recharge operations began. Chloride concentrations in one deep monitoring well did not change because of 

artificial recharge activities, whereas chloride concentrations 

decreased in the other deep monitoring well, which may indicate the displacement of deep aquifer water by shallow aquifer 

water as water in the shallow aquifer is in turn displaced by 

recharge water.

Annual averages calculated from estimated daily atrazine concentrations for the Little Arkansas River at Sedgwick 

did not exceed the USEPA MCL of 3.0 μg/L (as an annual 

average) from 1999 through 2004. Atrazine concentrations in 

the treated diverted stream water exceeded 3.0 μg/L in three 

discrete samples. At the Sedgwick recharge site, atrazine 

concentrations increased in water sampled from both shallow 

monitoring wells after artificial recharge began. Atrazine was 

not detected in water sampled from the deep monitoring wells 

at this site. 

Arsenic concentrations were less than 5.0 μg/L in all 

water samples from the monitoring wells at the Sedgwick 

recharge site. Arsenic concentrations did not change during 

recharge operations, indicating that the artificial recharge did 

not mobilize arsenic. Iron concentrations were small in water 

sampled from all monitoring wells at the Sedgwick recharge 

site. 

Saturation indices calculated for water sampled from 

the shallow monitoring wells at the Sedgwick recharge site 

indicate carbonate minerals probably are not present in the 

shallow part of the aquifer. However, calcite may be reacting 

in the deeper part of the aquifer to produce saturations indices 

that approach equilibrium. 

Simulations to model injection of treated stream water 

into the Equus Beds aquifer were conducted using PHREEQC. 

These simulations examined the effects of mixing treated 

stream water with deep ground water on the saturation indices 

of calcite and amorphous ferric oxyhydroxide. Results of the 

simulations indicate that calcite oversaturation is likely only 

for mixtures that are greater than 90 percent recharge water. 

Calcite precipitation could reduce permeability and reduce 

effectiveness of artificial recharge. Amorphous ferric oxyhydroxide oversaturation is possible in all mixtures of the two 

waters. In addition, iron bacteria could be a cause for concern 

for injection of oxygenated water into the aquifer. It is possible that biofouling of the injection well could occur causing 

increased precipitation of iron and creation of a biofilm associated with iron bacteria activity. The precipitation and biofouling could decrease the efficiency of the injection well as well 

as reduce the permeability of the aquifer material in vicinity of 

the well.

References Cited

Aucott, W.R., Myers, N.C., and Dague, B.J., 1998, Status of 

ground-water levels and storage in the Wichita well field 

area, south-central Kansas, 1997: U.S. Geological Survey 

Water-Resources Investigations Report 98–4095, 15 p.

Burns and McDonnell, 1996, Equus Beds Groundwater 

Recharge Demonstration Project: Kansas City, Missouri, 

Burns and McDonnell Engineering Consultants, prepared 

for the city of Wichita Water and Sewer Department, various pagination. 

Christensen,V.G., Jian, Xiaodong, and Ziegler, A.C., 2000, 

Regression analysis and real-time water-quality monitoring 

to estimate constituent concentrations, loads, and yields in 

the Little Arkansas River, south-central Kansas, 1995–99: 

U.S. Geological Survey Water-Resources Investigations 

Report 00–4126, 36 p.

Christensen, V.G., Ziegler, A.C., Rasmussen, P.P., and Jian, 

Xiaodong, 2003, Continuous real-time water-quality 

monitoring of Kansas streams, in Proceedings of 2003 

Spring Specialty Conference on Agricultural Hydrology and 

Water Quality, May 12–14, 2003, Kansas City, Missouri: 

Middleburg, Virginia, American Water Resources Association, AWRA Technical Publication Series No. TPS–03–1, 

compact disc.

56  Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer
Drever, J.L., 1997, The geochemistry of natural waters—surface and groundwater environments (3rd ed.): Upper Saddle 

River, New Jersey, Prentice Hall, 436 p. 

Fetter, C.W., 1994, Applied hydrogeology: Englewood Cliffs, 

New Jersey, Prentice Hall, 517 p. 

Fischer, H.B., List, E.J., Koh, R.C.Y., Imberger, J., and 

Brooks, N.H., 1979, Mixing in inland and coastal waters: 

New York, Academic Press, Inc., 483 p.

Garbarino, J.R., Bednar, A.J., and Burkhardt, M.R., 2002, 

Methods of anaysis by the U.S. Geological Survey National 

Water Quality Laboratory—arsenic speciation in naturalwater samples using laboratory and field methods: U.S. 

Geological Survey Water-Resources Investigations 

Report 02–4144, 47 p.

Guo, T.Z., DeLaune, R.D., and Patrick, W.H., 1997, The 

influence of sediment redox chemistry on chemically active 

forms of arsenic, cadmium, chromium, and zinc in estuarine 

sediment: Environmental International v. 23, p. 305–316.

Hansen, C.V., 1991, Estimates of freshwater storage and 

potential natural recharge for principal aquifers in Kansas: 

U.S. Geological Survey Water-Resources Investigations 

Report 87–4230, 100 p.

Hansen, C.V., and Aucott, W.R., 2004, Status of ground-water 

levels and storage volume in the Equus Beds aquifer near 

Wichita, Kansas, January 2000–January 2003: U.S. Geological Survey Water-Resources Investigations 

Report 03–4298, 36 p.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in 

water resources: New York, Elsevier, 522 p.

Hem, J.D., 1992, Study and interpretation of chemical characteristics of natural water (3rd ed.): U.S. Geological Survey 

Water-Supply Paper 2254, 263 p.

Hinkle, S.R., and Polette, D.J., 1999, Arsenic in ground water 

of the Willamette Basin, Oregon: U.S. Geological Survey 

Water-Resources Investigations Report 98–4205, 29 p.

Juracek, K.E., and Hansen, C.V., 1995, Digital maps of the 

extent, base, top, and 1991 potentiometric surface of the 

High Plains aquifer in Kansas: U.S. Geological Survey 

Open-File Report 95–758, map scales 1:500,000 and 

1:100,000.

Koterba, M.T., Wilde, F.D., and Lapham, W.W., 1995, 

Ground-water data-collection protocols and procedures for 

the National Water-Quality Assessment Program—collection and documentation of water-quality samples and related 

data: U.S. Geological Survey Open-File Report 95–399, 113 p.

Myers, N.C., Haragadine, G.D., and Gillespie, J.B., 1996, 

Hydrologic and chemical interactions of the Arkansas 

River and the Equus Beds aquifer between Hutchinson and 

Wichita, south-central Kansas: U.S. Geological Survey 

Water-Resources Investigations Report 95–4191, 100 p.

National Oceanic and Atmospheric Administration, 1998, 

Climatological data, annual summary, Kansas, 1997: Asheville, North Carolina, v. 111, no. 13, 35 p.

National Oceanic and Atmospheric Administration, 1999, 

Climatological data, annual summary, Kansas, 1998: Asheville, North Carolina, v. 112, no. 13, 31 p.

National Oceanic and Atmospheric Administration, 2000, 

Climatological data, annual summary, Kansas, 1999: Asheville, North Carolina, v. 111, no. 13, 35 p.

National Oceanic and Atmospheric Administration, 2001, 

Climatological data, annual summary, Kansas, 2000: Asheville, North Carolina, v. 114, no. 13, 33 p.

National Oceanic and Atmospheric Administration, 2002, 

Climatological data, annual summary, Kansas, 2001: Asheville, North Carolina, v. 115, no. 13, 36 p.

National Oceanic and Atmospheric Administration, 2003, 

Climatological data, annual summary, Kansas, 2002: Asheville, North Carolina, v. 116, no. 13, 32 p.

National Oceanic and Atmospheric Administration, 2004, 

Climatological data, annual summary, Kansas, 2003: Asheville, North Carolina, v. 117, no. 13, 32 p.

National Oceanic and Atmospheric Administration, 2005a, 

Climatological data, annual summary, Kansas, 2004: Asheville, North Carolina, v. 118, no. 13, 32 p.

National Oceanic and Atmospheric Administration, 2005b, 

Daily precipitation data for United States cooperative and 

National Weather Service sites: Asheville, North Carolina, 

North Climatic Data Center, accessed February 21, 2006, at 

http://www.ncdc.noaa.gov/oa/climate/stationlocator.html

Parkhurst, D.L., and Appelo, C.A.J, 1999, User’s guide to 

PHREEQC (version 2)—a computer program for speciation, batch-reaction, one-dimensional transport, and inverse 

geochemical calculations: U.S. Geological Survey WaterResources Investigations Report 99–4259, 312 p.

Parkhurst, D.L., Engesgaard, P., and Kipp, K.L., 1995, Coupling the geochemical model PHREEQC with a 3D multicomponent solute-transport model, in V.M. Goldschmidt 

Conference, State College, Pennsylvania: Program and 

Abstracts, p. 77–78. 

References Cited 57
Parkhurst, D.L., and Kipp, K.L., 2002, Parallel processing for 

PHAST—a three-dimensional reactive-transport simulator, 

in Hassanizadeh, S.M., Schotting, R.J., Gray, W.G., and 

Pinder, G.F., eds., Developments in water science—computational methods in water resources: Amsterdam Elsevier, 

no. 47, v. 1, p. 711–718.

Parkhurst, D.L., Kipp, K.L., Engesgaard, P., and Charlton, 

S.R., 2004, PHAST—a program for simulating groundwater flow, solute transport, and multicomponent geochemical reactions: U.S. Geological Survey Techniques and Methods, book 6, chap. A8, 154 p.

Piper, A.M., 1944, A graphic procedure in the geochemical 

interpretation of water analyses: American Geophysical 

Union Transactions, v. 25, p. 914–923.

Poeter, E.P., and Hill, M.C., 1998, Documentation of UCODE, 

a computer code for universal inverse modeling: U.S. 

Geological Survey Water-Resources Investigations 

Report 98–4080, 116 p.

Poeter, E.P., Hill, M.C., Banta, E.R., Mehl, Steffen, and Christensen, Steen, 2005, UCODE_2005 and six other computer 

codes for universal sensitivity analysis, calibration, and 

uncertainty evaluation: U.S. Geological Survey Techniques 

and Methods, book 6, chap. A11, 283 p.

Puls, R.W., and Barcelona, M.J., 1996, Low-flow (minimal 

drawdown) ground-water sampling procedures: U.S. Environmental Protection Agency, Ground Water Issue, 

EPA 540/S–95/504, April 1996, 12 p.

Ross, J.A., compiler, 1991, Geologic map of Kansas: Kansas 

Geological Survey Map M–23, 1 sheet, scale 1:500,000.

Smedley, P.L., and Kinniburgh, D.G., 2002, A review of the 

source, behavior, and distribution of arsenic in natural 

waters: Applied Geochemistry, v. 17 no. 5, p. 517–568.

U.S. Department of Agriculture, 2002a, 2002 Census of agriculture county profile, Harvey, Kansas: U.S. Department 

of Agriculture, National Agricultural Statistics Service, 

information available on Web, accessed June 16, 2005, 

at http://www.nass.usda.gov/census/census02/profiles/ks/

cp20079.PDF

U.S. Department of Agriculture, 2002b, 2002 Census of agriculture county profile, Sedgwick, Kansas: U.S. Department 

of Agriculture, National Agricultural Statistics Service, 

information available on Web, accessed June 16, 2005, 

at http://www.nass.usda.gov/census/census02/profiles/ks/

cp20173.PDF

U.S. Environmental Protection Agency, 2004, 2004 edition 

of the drinking water standards and health advisories: U.S. 

Environmental Protection Agency, Report EPA 822–R–

04–005, winter 2004, information available on the Web, 

accessed July 10, 2005, at http://www.epa.gov/waterscience/

drinking/standards/dwstandards.pdf

U.S. Geological Survey, 2006, U.S. Geological Survey Standard Reference Sample Project-Performance Evaluation of 

Analytical Labortories: U.S. Geological Survey, Branch of 

Quality Systems, information available on Web, accessed on 

August 21, 2006, at http://bqs.usgs.gov/srs/FactSheet.htm

Wagner, R.J., Mattraw, H.C., Ritz, G.F., and Smith, B.A., 

2000, Guidelines and standard procedures for continuous 

water-quality monitors—site selection, field operation, calibration, record computation, and reporting: U.S. Geological 

Survey Water-Resources Investigations Report 2000–4252, 

53 p. 

Ward, J.R., and Harr, C.A., eds., 1990, Methods for collection 

and processing of surface-water and bed-material samples 

for physical and chemical analysis: U.S. Geological Survey 

Open-File Report 90–140, 79 p.

Warren, D.R., Blain, G.T., Shorney, F.L, and Klein, L.J., 1995, 

IRP—a case study from Kansas: Journal of the American 

Water Works Association, June 1995, p. 57–71.

Welch, A.H., Westjohn, D.B., Helsel, D.R., and Wanty, R.B., 

2000, Arsenic in ground water of the United States—occurrence 

and geochemistry: Ground Water, v. 38, no. 4, p. 589–604.

Wilde, F.D., and Radke, D.B., eds., 1998, Field measurements, 

in National field manual for the collection of water-quality 

data: U.S. Geological Survey Techniques of Water-Resource 

Investigations, book 9, chap. A6, p. 3–20.

Williams, C.C., and Lohman, S.W., 1949, Geology and 

ground-water resources of a part of south-central Kansas 

with special reference to the Wichita municipal water supply: Kansas Geological Survey Bulletin 79, 455 p. 

Wood, W.W., 1976, Guidelines for collection and field analysis 

of ground-water samples for selected unstable constituents: 

U.S. Geological Survey Techniques of Water-Resources 

Investigations, book 1, chap. D2, 24 p.

Ziegler, A.C., Christensen, V.G., and Ross, H.C., 1999, 

Baseline water-quality and preliminary effects of artificial 

recharge on ground water, south-central Kansas, 1995–98: 

U.S. Geological Survey Water-Resources Investigations 

Report 99–4250, 74 p.

Ziegler, A.C., and Combs, L.J., 1997, Baseline data-collection 

and quality control protocols and procedures for the Equus

Beds Ground-Water Recharge Demonstration Project near 

Wichita, Kansas, 1995–96: U.S. Geological Survey OpenFile Report 97–235, 57 p.

Ziegler, A.C., Ross, H.C., Trombley, T.J., and Christensen, 

V.G., 2001, Effects of artificial recharge on water quality in 

the Equus Beds aquifer, south-central Kansas, 1995–2000: 

U.S. Geological Survey Fact Sheet 096–01, 4 p.

58 Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer
Prepared by Lawrence Publishing Service Center.

Edited by Lanna Combs.

Graphics by Jeff Hartley and Michael Kemppainen.

Layout and design by Michael Kemppainen.

For more information concerning the research 

described in this report, contact:

 U.S. Geological Survey

 4821 Quail Crest Place

 Lawrence, KS 66049

 (785) 842-9909

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Schmidt and others—Geochemical Effects of Induced Stream-Water and Artificial Recharge on the Equus Beds Aquifer, 

South-Central Kansas, 1995–2004 —USGS/SIR 2007−5025

Recharge basins at

Halstead recharge site

N