U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2010–5047

Prepared in cooperation with the Oklahoma Department of Environmental Quality and the 

Ground-Water Protection Council

Arsenic-Related Water Quality with Depth and Water 

Quality of Well-Head Samples from Production Wells, 

Oklahoma, 2008
Arsenic-Related Water Quality with Depth 

and Water Quality of Well-Head Samples 

from Production Wells, Oklahoma, 2008

By Carol J. Becker, S. Jerrod Smith, James R. Greer, and Kevin A. Smith

Prepared in cooperation with the Oklahoma Department of Environmental Quality 

and the Ground-Water Protection Council

Scientific Investigations Report 2010–5047

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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

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Suggested citation:

Becker, C.J., Smith, S.J., Greer, J.R., and Smith, K.A., 2010, Arsenic-related water quality with depth and water quality of well-head samples from production wells, Oklahoma, 2008: U.S. Geological Scientific Investigations Report 

2010–5047, 38 p. 
iii

Contents

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

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

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

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

Study Aquifers ...............................................................................................................................................2

Rush Springs Aquifer ...........................................................................................................................6

Permian-Aged Undefined Aquifer .....................................................................................................6

Garber-Wellington Aquifer .................................................................................................................6

Arbuckle-Timbered Hills Aquifer .......................................................................................................7

Geochemical Processes Affecting Arsenic Concentrations in Groundwater ....................................8

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

U.S. Geological Survey Well Profiler ................................................................................................8

Candidate Well Selection ..........................................................................................................8

Geophysical Logs ......................................................................................................................13

Dye Tracer-Pulse Travel-Time Profile ....................................................................................13

Depth-Dependent Sampling ....................................................................................................13

Laboratory Analysis ..................................................................................................................15

Quality-Assurance Procedures ..............................................................................................15

Well-Head Sampling of Production Wells .....................................................................................15

Laboratory Analysis ..................................................................................................................15

Quality-Assurance Procedures ..............................................................................................15

Arsenic-Related Water Quality with Well Depth ...................................................................................16

Production Well RS-2X in the Rush Springs Aquifer ....................................................................16

Well Construction and Sampling Conditions ........................................................................16

Water Quality with Depth ........................................................................................................16

Production Well GW-7X in the Garber-Wellington Aquifer ........................................................18

Well Construction and Sampling Conditions ........................................................................19

Water Quality with Depth ........................................................................................................19

Arsenic-Related Water Quality in Well-Head Samples ........................................................................20

Arsenic in Relation to Physical Properties and Water Type .......................................................20

Arsenic in Relation to Other Trace Elements ................................................................................21

Summary .......................................................................................................................................................25

References ...................................................................................................................................................26

Appendixes 

1. Water-Property Measurements and Chemical-Constituent Concentrations 

Measured in Water from Depth-Dependent and Well-Head Samples, 

Oklahoma, 2008 .................................................................................................................29

2. Concentrations of Equipment-Blank Sample and Analytical Relative Percent 

Difference for Chemical Constituents Measured in Replicate Samples from 

Depth-Dependent and Well-Head Samples, Oklahoma, 2008 ...................................35
iv

Figures

1. Map showing location of production wells sampled and study aquifers, Oklahoma, 

2008 ................................................................................................................................................3

2. Chart showing geologic units and equivalent aquifer units .................................................7

3–6. Graphs showing: 

3. Estimated tracer-pulse travel times, depth-dependent sample locations, 

and well construction information for production well RS-2X in the Rush 

Springs aquifer, Oklahoma, 2008 ......................................................................................9

4. Estimated tracer-pulse travel times, depth-dependent sample locations, 

and well construction information for production well GW-7X in the GarberWellington aquifer, Oklahoma, 2008 ...............................................................................10

5. Concentrations of arsenic, bicarbonate, calcium, sodium, and sulfate in 

depth-dependent samples and well-head sample from production well RS-2X 

in the Rush Springs aquifer, Oklahoma, 2008 ...............................................................11

6. Concentrations of arsenic, calcium, and sodium in depth-dependent samples 

and well-head samples from production well GW-7X in the Garber-Wellington 

aquifer, Oklahoma, 2008 ...................................................................................................12

7. Diagram of perforated well GW-7X showing well construction, deployment of the 

U.S. Geological Survey well profiler, and the theoretical horizontal well cross 

section just above the pump shroud ......................................................................................14

8. Piper diagram showing percentages of major ions in well-head and depthdependent samples from production wells GW-7X in the Garber-Wellington aquifer 

and RS-2X in the Rush Springs aquifer, Oklahoma, 2008. ...................................................17

9. Graph showing relation of arsenic with pH in well-head samples from production 

wells, Oklahoma, 2008 ...............................................................................................................21

10. Piper diagram showing percentages of major ions in well-head samples from 

production wells, Oklahoma, 2008 ..........................................................................................22

11–12. Boxplots showing: 

11. Relation of barium, boron, chromium, and copper with arsenic in well-head 

samples from production wells, Oklahoma, 2008 ........................................................23

12. Relation of fluoride, nickel, uranium, and vanadium with arsenic in well-head 

samples from production wells, Oklahoma, 2008 ........................................................24

Tables

1. Site and completion information for production wells sampled for arsenic in 

depth-dependent and well-head samples, Oklahoma, 2008 .................................................4

2. Analysis methodologies, method references, and highest minimum reporting 

levels of water properties and chemical constituents measured in depthdependant and well-head water samples from production wells, Oklahoma, 2008 .........5

3. Sample location, water type, pH, and arsenic concentration of water from depthdependent and well-head samples from production wells, Oklahoma, 2008 ..................18
v

Conversion Factors, Datums, and Water-Quality Units

Inch/Pound to SI

Multiply By To obtain

Length

inch (in) 0.39 centimeter (cm)

inch (in) 0.039 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 0.621 kilometer (km)

Volume

gallon (gal) 0.264 liter (L) 

gallon (gal) 264.2 cubic meter (m3) 

cubic foot (ft3) 7.48 cubic meter (m3) 

Flow rate

gallon per minute (gal/min) 15.85 liter per second (L/s)

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

Datums

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

(NAVD 88).

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

Altitude, as used in this report, refers to distance above the North American Vertical Datum of 

1988 (NAVD 88).

Water-Quality Units

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

25 °C).

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

or micrograms per liter (μg/L). 

Minimum reporting level (MRL)—Smallest measured concentration of a constituent that may be 

reliably reported by using a given analytical method (Timme, 1995). 
vi
Abstract

The U.S. Geological Survey well profiler was used to 

describe arsenic-related water quality with well depth and 

identify zones yielding water with high arsenic concentrations 

in two production wells in central and western Oklahoma that 

yield water from the Permian-aged Garber-Wellington and 

Rush Springs aquifers, respectively. In addition, well-head 

samples were collected from 12 production wells yielding 

water with historically large concentrations of arsenic (greater 

than 10 micrograms per liter) from the Garber-Wellington 

aquifer, Rush Springs aquifer, and two minor aquifers: the 

Arbuckle-Timbered Hills aquifer in southern Oklahoma and a 

Permian-aged undefined aquifer in north-central Oklahoma. 

Three depth-dependent samples from a production well in 

the Rush Springs aquifer had similar water-quality characteristics to the well-head sample and did not show any substantial 

changes with depth. However, slightly larger arsenic concentrations in the two deepest depth-dependent samples indicate 

the zones yielding noncompliant arsenic concentrations are 

below the shallowest sampled depth. 

Five depth-dependent samples from a production well 

in the Garber-Wellington aquifer showed increases in arsenic 

concentrations with depth. Well-bore travel-time information 

and water-quality data from depth-dependent and well-head 

samples showed that most arsenic contaminated water (about 

63 percent) was entering the borehole from perforations adjacent to or below the shroud that overlaid the pump. 

Arsenic concentrations ranged from 10.4 to 124 micrograms per liter in 11 of the 12 production wells sampled at 

the well head, exceeding the maximum contaminant level of 

10 micrograms per liter for drinking water. pH values of the 

12 well-head samples ranged from 6.9 to 9. Seven production 

wells in the Garber-Wellington aquifer had the largest arsenic 

concentrations ranging from 18.5 to 124 micrograms per liter. 

Large arsenic concentrations (10.4–18.5) and near neutral to 

slightly alkaline pH values (6.9–7.4) were detected in samples 

from one well in the Garber-Wellington aquifer, three production wells in the Rush Springs aquifer, and one well in an 

undefined Permian-aged aquifer. All well-head samples were 

oxic and arsenate was the only species of arsenic in water 

from 10 of the 12 production wells sampled. Arsenite was 

measured above the laboratory reporting level in water from 

a production well in the Garber-Wellington aquifer and was 

the only arsenic species measured in water from the ArbuckleTimbered Hills aquifer. 

Fluoride and uranium were the only trace elements, 

other than arsenic, that exceeded the maximum contaminant 

level for drinking water in well-head samples collected for 

the study. Uranium concentrations in four production wells in 

the Garber-Wellington aquifer ranged from 30.2 to 99 micrograms per liter exceeding the maximum contaminant level of 

30 micrograms per liter for drinking water. Water from these 

four wells also had the largest arsenic concentrations measured 

in the study ranging from 30 to 124 micrograms per liter.

Introduction 

Arsenic is a known carcinogen (World Health Organization, 2001), and ingestion of inorganic arsenic, of which 30–90 

percent may be supplied by drinking water, is believed to 

cause bladder, kidney, lung, and liver cancer in humans (Smith 

and others, 1992). The risk of an individual dying from arsenic-related cancers as a result of lifetime ingestion of water 

with arsenic concentration at 50 micrograms per liter (μg/L) 

could be as great as 13 in 1,000 (Smith and others, 1992). To 

address this risk, the U.S. Environmental Protection Agency 

(EPA) in 2000 reduced the maximum contaminant level 

(MCL) for arsenic in drinking water from public water-supply 

systems from 50 to 10 μg/L (U.S. Environmental Protection 

Agency, 2001). The new arsenic rule became enforceable on 

January 23, 2006, affecting many municipalities and water districts in the United States, especially those in the West, Midwest, and Northeast (Welch and others, 2000). As many as 23 

public water-supply systems in Oklahoma have been affected 

by the reduced arsenic MCL of 10 μg/L for drinking water (J. 

Craig, Director Water Quality Division, Oklahoma Department of Environmental Quality, written commun., 2005). Most 

large communities in Oklahoma are financially able to address 

Arsenic-Related Water Quality with Well Depth and Water 

Quality in Well-Head Samples from Production Wells, 

Oklahoma, 2008

By Carol J. Becker, S. Jerrod Smith, James R. Greer, and Kevin A. Smith
2 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

noncompliant drinking water. Unfortunately, many small communities and rural water districts operate with small resources, 

maintain minimal conveyance infrastructure, and often have 

no secondary source of water. 

Selection of appropriate rehabilitation strategies for an 

individual well requires information about the heterogeneity 

and interconnectedness of aquifer materials, well construction 

details, especially the method of well completion, and, most 

valuably, changes in flow contribution and water quality with 

depth in the well. Wireline velocity logs and packer tests are 

the traditional methods for collecting depth-dependent flow 

and water-quality data, however these methods do not always 

provide representative information about aquifer characteristics during production and are time consuming, invasive, and 

expensive. 

A combined well-bore travel time and depth-dependent 

water sampler (Izbicki and others, 1999), referred to as the 

U.S. Geological Survey (USGS) well profiler, has been used 

by USGS investigators to evaluate well-bore travel time and 

collect samples at varying depths in a pumping well (Izbicki 

and others, 2008; Smith and others, 2009). The USGS wellprofiler method provides many technical advantages such as 

less operating down time, minimal modification to the well, 

and also can be considerably less expensive than traditional 

methods of data collection. In terms of data quality, the most 

important advantage is that all data collection is performed 

while the well is pumping.

A project was performed by the USGS, in cooperation 

with the Oklahoma Department of Environmental Quality 

and the Groundwater Protection Council, to describe arsenicrelated water quality with depth in two wells. The project 

used the USGS well profiler to determine if zones yielding 

water with high arsenic concentrations could be identified. 

The role of the Groundwater Protection Council in this project 

was to describe and evaluate the geohydrology of the aquifers studied and incorporate the geochemical results from the 

USGS well profiler into a generalized decision tree for identifying appropriate well-rehabilitation techniques. If the results 

showed that large arsenic concentrations in the borehole were 

related to stratigraphic zones or sedimentary layering, 

the USGS technique could be considered an option for identifying well-rehabilitation strategies that are less expensive than 

drilling new production wells or water treatment at the well 

head. 

An additional objective was to collect well-head samples 

from production wells producing arsenic contaminated water. 

These data could then be used to better define the spatial distribution of arsenic and the geochemical processes controlling 

the presence of arsenic in selected aquifers. 

Purpose and Scope

This report presents the results of an investigation that 

used the USGS well profiler to describe arsenic-related water 

quality with depth in two production wells in an attempt to 

identify zones yielding water with high arsenic concentrations. 

This report also describes groundwater quality of well-head 

samples from 12 production wells in arsenic-affected aquifers.

The USGS well profiler was used on two production 

wells in central and western Oklahoma that yield water from 

the Garber-Wellington aquifer (GW) and the Rush Springs 

aquifer (RS), respectively. Groundwater samples were collected at the well head from 12 production wells (fig. 1 and 

table 1) yielding water from the GW, RS, and two minor 

aquifers, the Arbuckle-Timbered Hills aquifer (TH) in southern Oklahoma and a Permian-aged undefined aquifer (PM) in 

north-central Oklahoma. 

Groundwater samples collected with the well profiler 

and at the well head were analyzed for the dissolved major 

ions and trace elements including the arsenic species; arsenite, arsenate, dimethylarsinate (DMA), monomethylarsonate 

(MMA), and total arsenic shown on table 2. Selected water 

properties—specific conductance, pH, water temperature, dissolved oxygen, and alkalinity also were measured (table 2). In 

this report, unless otherwise noted, the word arsenic refers to 

dissolved arsenic regardless of oxidation state. 

Acknowledgments 

The authors would like to thank Robert Pistole, Steve 

Ray, and Keith Wright for their willingness to assist and cooperation on this project. Gratitude also is expressed to the managers and well operators of the communities who graciously 

allowed USGS personnel to access and sample their production wells. Appreciation is extended to Mark Hildebrand and 

David Pruitt with the Oklahoma Department of Environmental 

Quality and Jim Roberts, Mike Nickolaus, and Mike Paque 

with the Ground Water Protection Council. Stan Paxton and 

William Andrews of the USGS Oklahoma Water Science 

Center and Christina Stamos-Pfeiffer of the USGS California 

Water Science Center provided suggestions for improving the 

manuscript. 

Study Aquifers

The rock units most widely used as aquifers for drinkingwater supply in central and western Oklahoma are the Garber 

Sandstone and the Rush Springs Formation (Christenson, 

1998). These rock units and other Permian-aged rock units 

exposed at the surface in central and western Oklahoma are 

commonly referred to as “redbeds” because of the pronounced 

red color from iron oxide coatings on the mineral grain surfaces. Arsenic and the association with iron oxide and the 

geochemical processes controlling the adsorption and release 

of arsenic in the Garber Sandstone unit of the Garber-Wellington aquifer were studied extensively by the USGS National 

Water Quality Assessment (NAWQA) program. However, 

arsenic in other aquifers in Oklahoma, with regard to the 

source and related geochemical processes, has not been 

investigated.
Study Aquifers 

3Figure 1. Location of production wells sampled and study aquifers, Oklahoma, 2008. 

!(

!(

!(

!(

!(

!(

!(

!( !(

!P

!P RS-2X

GW-7X

GW-1

GW-2

TH-1

RS-3

GW-5

GW-3

PM-1

GW-6

RS-1

GW-4

-96° -97° -98° -99°

37°36°35°

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

Albers Equal Area Conic projection, North American Datum 1983

Central Oklahoma

aquifer boundary

(Christenson, 1998)

0 50 Miles0 50 Kilometers

!P

Well sampled at well 

head and well identifier

Well sampled at well 

head and by using downhole interval sampler

RS-1

Hennessey Group(overlies and confines

the Garber-Wellington

aquifer in this area)

Permian-aged undefined

aquifers (Garber Sandstone

and the Wellington Formation yield minor amounts

of water in this area)

Arbuckle-Timbered 

Hills aquifer 

Oklahoma

Rush Springs aquifer

Permian-aged redbeds

Garber-Wellingtonaquifer
4 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells Table 1. Site and completion information for production wells sampled for arsenic in depth-dependent and well-head samples, Oklahoma, 2008. [USGS, U.S. Geological Survey; ID, identifier; --, not available; lds, land surface; slotted, well casing is slotted near bottom of well; open, well is completed with no casing below surface casing; perforated, casing is perforated at selected zones] USGS site ID Well ID Aquifer Sample location Land 1 surface altitude (feet) Well depth (feet below lds) Pump depth (feet below lds) Static water level (feet below lds) Pumping water level (feet below lds) Completion type 352934097271502 355034097145201 353308097290701 352934097271502 352604097370901 351914097320201 351853097284701 364824097311601 353237098403901 352822098233801 351754098331501 343706098451201 GW-1 GW-2 GW-3 GW-4 GW-5 GW-6 GW-7X PM-1 RS-1 RS-2X RS-3 TH-1 Garber- Wellington Garber- Wellington Garber- Wellington Garber- Wellington Garber- Wellington Garber- Wellington Garber- Wellington Permian-aged undefined Rush Springs Rush Springs Rush Springs Arbuckle Timbered Hills well head well head well head well head well head well head well head; depth dependent well head well head well head; depth dependent well head well head 1,105 1,015 1,120 1,245 1,233 1,285 1,210 1,091 1,638 1,676 1,521 1,365 --2 310 750 265 854 782 811 120 320 294 375 620 ---- 683-- 680 760 732 100 260 270 260 595 ------------ 402---- 169---- ------------ 521---- 220---- slotted slotted perforated slotted perforated perforated perforated slotted open open open perforated

1 Distance above North American Vertical Datum of 1988.2 Probably less than 300 feet below land surface based on a comparison to wells within a radius of 1.5 miles. 
Study Aquifers 5

Table 2. Analysis methodologies, method references, and highest minimum reporting levels of water properties and chemical 

constituents measured in depth-dependant and well-head water samples from production wells, Oklahoma, 2008. All constituents are 

dissolved unless otherwise noted—Continued.

Water properties and chemical constituents 

(units)

Maximum 

contaminant level

(US EPA, 2009)

Secondary maximum 

contaminant level

(US EPA, 2009)

Method references Highest minimum 

reporting level

Oxygen, field, (mg/L) -- -- Wilde and Radtke (1998) 0.1 

pH, field, (standard units) -- 6.5 to 8.5 Wilde and Radtke (1998) .1 standard units

Specific conductance, field, (μS/cm at 25 oC) -- -- Wilde and Radtke (1998) 3 significant digits

Water temperature, field, (oC) -- -- Wilde and Radtke (1998) .5 

Calcium, (mg/L) -- -- Fishman (1993) .02

Magnesium, (mg/L) -- -- Fishman (1993) .012

Potassium, (mg/L) -- -- Fishman and Friedman (1989) .06

Sodium, (mg/L) -- -- Fishman (1993) .12

Alkalinity, field, (mg/L as CaCO3

) -- -- Rounds and Wilde (2001) 3 significant digits

Bicarbonate, field, (mg/L) -- -- Rounds and Wilde (2001) 3 significant digits

Carbonate, field, (mg/L) -- -- Rounds and Wilde (2001) 3 significant digits

Bromide, (μg/L) -- -- Fishman and Friedman (1989) .02 

Chloride, (mg/L) -- 250 Fishman and Friedman (1989) .12 

Fluoride, (mg/L) 4 2 Fishman and Friedman (1989) .08 

Silica, (mg/L) -- -- Fishman (1993) .02 

Sulfate, (mg/L) -- 250 Fishman and Friedman (1989) .18 

Dissolved solids, total, (mg/L) -- 500 Fishman and Friedman (1989) 3 significant digits

Aluminum, (μg/L) -- 50 to 200 Garbarino and others (2006) 4 

Antimony, (μg/L) 6 -- Garbarino and others (2006) .14 

Arsenate, (μg/L) -- -- Garbarino and others (2002) .8 

Arsenic, (μg/L) 10 -- Garbarino and others (2006) .06 

Arsenic, total, (μg/L) 10 -- Garbarino and others (2006) .2 

Arsenite, (μg/L) -- -- Garbarino and others (2002) 1.2 

Dimethylarsinate, (μg/L) -- -- Garbarino and others (2002) .6 

Monomethylarsonate, (μg/L) -- -- Garbarino and others (2002) 1.8 

Barium, (μg/L) 2,000 -- Garbarino and others (2006) .4 

Beryllium, (μg/L) 4 -- Garbarino and others (2006) .02 

Boron, (μg/L) -- -- Garbarino and others (2006);

Garbarino (1999)

4 

Cadmium, (μg/L) 5 -- Garbarino and others (2006) .04 

Chromium, (μg/L) 100 -- Garbarino and others (2006) .12 

Cobalt, (μg/L) -- -- Garbarino and others (2006) .02 

Table 2. Analysis methodologies, method references, and highest minimum reporting levels of water properties and chemical 

constituents measured in depth-dependant and well-head water samples from production wells, Oklahoma, 2008. All constituents are 

dissolved unless otherwise noted.

[US EPA, U.S. Environmental Protection Agency; μS/cm, microsiemens per centimeter; °C, degree Celsius; --, not applicable; mg/L, milligram per liter; μg/L, 

microgram per liter; CaCO3, calcium carbonate] 
6 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

Rush Springs Aquifer

The Rush Springs aquifer (RS) is equivalent to the Rush 

Springs Formation in west-central Oklahoma (fig. 2). The 

aquifer is generally less than 250-foot thick and composed of 

very fine-grained to fine-grained sandstone with interbedded 

dolomite or gypsum (Becker and Runkle, 1998). Sand grains 

composing the Rush Springs Formation in Caddo County are 

loosely cemented with iron oxide and calcite (Tanaka and 

Davis, 1963). Overlying the aquifer in the western part are 

beds of massive gypsum interbedded with shale and siltstone. 

Well yields from the Rush Springs aquifer vary depending 

on location and depth. Well yields generally are high in the 

aquifer with most irrigation wells producing more than 1,000 

gallons per minute (gpm) (Becker and Runkle, 1998). 

Permian-Aged Undefined Aquifer

In north-central Oklahoma, groundwater is produced 

from minor aquifers that consist of intermittent layers of 

permeable sandstone and limestone in rocks that are predominantly composed of shale (Beldon, 1997). The Garber 

Sandstone and Wellington Formation make up more than 

half of the rock units in this part of the state, but are not 

considered a major source of groundwater because of the 

high percentage of shale (Beldon, 1997). Groundwater 

from the Permian-aged rock units in this area is calcium 

magnesium-bicarbonate water type with dissolved solids 

ranging from 500 to 2,000 mg/L (Bingham and Bergman, 

1980). 

Garber-Wellington Aquifer

The Garber-Wellington aquifer (GW) is composed of 

the Garber Sandstone and the Wellington Formation and 

together these two formations yield the greatest quantities of 

usable water in central Oklahoma (fig. 1 and fig. 2). Both formations are part of a larger aquifer system, used for domestic 

and public supply, referred to as the Central Oklahoma aquifer 

(COA). The rock units that compose the COA, including the 

Garber Sandstone and the Wellington Formation, extend north 

and southwest, but typically are not used for drinking-water 

supply beyond the COA boundaries because of inadequate 

yields. 

Table 2. Analysis methodologies, method references, and highest minimum reporting levels of water properties and chemical 

constituents measured in depth-dependant and well-head water samples from production wells, Oklahoma, 2008. All constituents are 

dissolved unless otherwise noted—Continued.

Water properties and chemical constituents 

(units)

Maximum 

contaminant level

(US EPA, 2009)

Secondary maximum 

contaminant level

(US EPA, 2009)

Method references Highest minimum 

reporting level

Copper, (μg/L) 11,300 1,000 Garbarino and others (2006) 1 

Iron, (μg/L) -- 300 Fishman (1993) 8 

Lead, (μg/L) 115 -- Garbarino and others (2006) .06 

Lithium, (μg/L) -- -- Garbarino and others (2006);

Garbarino (1999)

1 

Manganese, (μg/L) -- 50 Garbarino and others (2006) .2 

Molybdenum, (μg/L) -- -- Garbarino and others (2006) .02 

Nickel, (μg/L) -- -- Garbarino and others (2006) .20 

Selenium, (μg/L) 50 -- Garbarino and others (2006) .04 

Silver, (μg/L) -- 100 Garbarino and others (2006) .1 

Strontium, (μg/L) -- -- Garbarino (1999); Garbarino 

and others (2006)

.8 

Uranium, (μg/L) 30 -- Garbarino and others (2006) .006 

Vanadium, (μg/L) -- -- Garbarino and others (2006) .16 

Zinc, (μg/L) -- 5,000 Garbarino and others (2006) 2 

1

 Copper and lead are regulated by a treatment technique that requires systems to control the corrosiveness of the water. If more than 10 percent of tap water 

samples exceed the maximum contaminant level, water systems must take corrective steps. For copper, the action level is 1,300 μg/L, and for lead is 15 μg/L (US 

EPA, 2009).
Study Aquifers 7

The hydrogeology of the GW has been studied and 

described at length by Parkhurst and others (1996), Christenson and others (1992), Christenson (1998), and Harrington 

and Roberts (2005). In brief, the total thickness of the Garber 

Sandstone and Wellington Formation ranges from 1,100 to 

1,600 feet (ft) (Christenson and others, 1992) and consists of 

stacked channel bars, floodplain deposits, and related fluvial 

facies (Stanley Paxton, U.S. Geological Survey, written 

commun., 2005) that grade into one another vertically and 

horizontally. 

Most domestic, stock, and irrigation wells in the aquifer 

draw water from less than 300 ft below land surface. Most 

public-supply wells, however, bypass the shallow aquifer 

system and produce water from greater than 300 ft below 

land surface. Deep wells that tap the confined aquifer system in the western one-quarter of the COA, where the GW 

is overlain by the Hennessey Group, are more likely to 

exceed the arsenic MCL than wells in the unconfined part 

of the aquifer (Schlottmann and others, 1998). Schlottmann 

and others (1998) estimated that about 30 percent of deep 

wells in the confined GW produced water with arsenic 

concentrations exceeding 50 μg/L, and only 2.4 percent of 

deep wells in the unconfined aquifer system produced water 

with arsenic concentrations exceeding 50 μg/L.

The geochemistry of trace elements in the COA, including arsenic, was studied by the USGS NAWQA program in 

detail. Schlottman and others (1998) showed that arsenic in 

the Garber Sandstone is adsorbed onto iron oxide probably 

in the form of goethite and hematite coatings on mineral 

surfaces. The highest percentage of arsenic and iron are contained by the clays in the Garber Sandstone and decreases 

with an increase in mineral grain size (Gromadzki, 2004). 

The clays have a high cation-exchange capacity, permitting 

sodium ions in the clays to exchange with calcium and 

magnesium ions in the water (Parkhurst and others, 1996). 

During the exchange, the water becomes undersaturated 

with respect to dolomite and in response, more dolomite 

dissolves and more calcium and magnesium are available 

for cation exchange (Parkhurst and others, 1996). As cation 

exchange and dolomite dissolution continue at depth, the 

pH gradually increases (Parkhurst and others, 1996) and 

at a pH value of 8.5, arsenic begins to desorb from the iron 

oxide coatings (Schlottmann and others, 1998). In general, 

cation exchange between water and clay minerals in the 

Garber Sandstone becomes more prevalent as water becomes 

older with depth. These conditions are most frequently found 

where the Garber Sandstone is confined by the Hennessey 

Group (Christenson, 1998). The confined conditions tend to 

cause this part of the aquifer to be poorly flushed by fresh 

water and as a result the water has a longer residence time 

and has been altered by cation exchange to a greater degree 

(Schlottman and others, 1998). As a consequence, large 

arsenic concentrations in this part of the aquifer are characteristically associated with sodium-rich water types and high pH 

values.

Arbuckle-Timbered Hills Aquifer

The Arbuckle-Timbered Hills aquifer (TH) is considered a minor aquifer in Oklahoma because of limited areal 

extent and the small number of wells completed in the aquifer. The aquifer is composed of a thick sequence of Cambrianto Ordovician-aged limestone, dolomite, sandy dolomite, mudstone, conglomerate, and shale about 6,000 ft thick (Havens, 

1977). Wells completed in the TH produce groundwater from 

solution openings, fractures, and faults in the limestone and 

dolomite sections in the aquifer. Groundwater is of sodiumbicarbonate and sodium-chloride type with some sulfate 

(Havens, 1983). Fluoride concentrations are elevated in the 

TH and usually exceed the EPA MCL of 4 milligrams per liter 

(mg/L) in drinking water (Havens, 1983). 

Pe mr ai n

Whi et horse

Group

Rush Springs Formation

Marlow Formation

Dog Creek Shale

Blaine Gypsum

Salt Plains Formation

Fairmont Shale

El Reno

Group Hennessey

Group

Sumner

Group

Ordov ci ai n Cambr ai n

Upper part of

Arbuck el Group

Lower part of Arbuck el

Group and T mi bered

Hil sl Group

Upper part of Arbuckle 

Group undifferentiated

West Spring Creek 

Formation and Kindblade 

Formation

Cool Creek Formation 

and McKenzie Hill 

Formation

Signal Mountain Formation

Royer Dolomite

Fort Sill Limestone

Honey Creek Formation

Reagan Sandstone

Arbuckle-Timbered 

Hills aquifer (TH)

Rush Springs 

aquifer (RS)

Garber-Wellington 

aquifer (GW);

undefined aquifers 

in north-central 

Oklahoma (PM)

Chase, Council Grove,

and Admire Groups, 

undivided Central Oklahoma aquifer

(Christenson (1998)

System Stratigraphic unit Aquifer

Garber Sandstone

Wellington Formation

Figure 2. Geologic units and equivalent aquifer units. 
8 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

Geochemical Processes Affecting 

Arsenic Concentrations in 

Groundwater

Sources of arsenic in groundwater can be anthropogenic or naturally occurring. Anthropogenic sources include 

abandoned mines and mine waste, agricultural pesticides, and 

wood preservatives. Naturally occurring sources of arsenic 

include geothermal waters, oxidation of arsenic sulfide minerals, and arsenic adsorbed onto iron oxides, aluminum oxides, 

and clay minerals (Welch and others, 2000; Sracek and others, 

2004). 

Arsenic in groundwater is commonly in two oxidation 

states: arsenite and arsenate. Arsenite, the most toxic of the 

arsenic species, is 4 to 10 times more soluble than arsenate 

and most likely to be in groundwater during reducing conditions (U.S. Environmental Protection Agency, 2002). Arsenate 

is most prevalent in oxygenated water at neutral and alkaline 

pH values. Both arsenic species adsorb onto a variety of metal 

oxides. However, iron oxide is the most adsorbent substrate 

because of chemistry and prevalence of iron oxide throughout 

the hydrogeologic environment (Hinkle and Polette, 1998), 

especially in Oklahoma aquifers. 

Geochemical processes affecting the desorption of arsenic from iron oxides are pH of the water, structural changes of 

crystalline iron oxide, and dissimilatory iron reduction (Welch 

and others, 2000). Arsenate adsorbs to iron oxide in neutral 

and lower pH water but desorbs as pH values become alkaline. 

Because the pH increases, the surface charge of the iron oxide 

becomes negative and repels arsenate and other negatively 

charged ions that compete for adsorption sites (Sracek and others, 2004; Kresse and Fazio, 2003). Desorption of arsenic from 

iron oxide has been shown as the largest source of arsenic to 

water in other aquifers throughout the United States (Robertson, 1989; Welch and others, 2000). Desorption of arsenic 

also happens during the conversion of crystalline iron oxide to 

other mineral phases. Changes in the crystalline structure can 

decrease the number of adsorption sites releasing arsenic and 

other ions (Hinkle and Polette, 1998; Fuller and others, 1993). 

Desorption of arsenic from iron oxide also results from the 

biologically mediated process of dissimilatory iron reduction, 

which happens in reducing environments with large amounts 

of decaying organic matter. During those conditions, bacteria 

cause arsenic as arsenite to desorb from available iron oxide 

into groundwater (Stollenwerk, 2003). The organoarsenicals 

DMA and MMA also are found in groundwater during these 

conditions, being biologically mediated forms of arsenic 

indicative of reducing conditions. 

Methods of Study

The USGS well profiler was used to describe changes 

in water quality with depth in two production wells; RS-2X 

in the RS and GW-7X in the GW. Tracer-pulse travel-time 

profiles were constructed to determine appropriate depths for 

depth-dependent sampling between zones contributing flow. 

Tracer-pulse travel-time profiles are shown on graphs (figs. 3 

and 4) and the zones sampled are shown on plots with measured concentrations of arsenic and selected major ions (figs. 5 

and 6). 

Water samples were collected at the well head from 12 

production wells: GW-1 through GW-6 and GW-7X in the 

GW; PM-1 in the PM; RS-1, RS-3, and RS-2X in the RS; and 

TH-1 in the TH (fig. 1 and table 1). The water-quality data 

were grouped by water type and by aquifer to study relations 

between arsenic and the other trace elements. Percentages of 

the major-ion concentrations, in milliequivalents, were used to 

determine water type and to construct Piper diagrams (Piper, 

1944) to illustrate water-quality characteristics and common 

trends in water quality. Cations and anions were considered 

dominant when composing 50 percent or more of the total ion 

concentration expressed in milliequivalents per liter. Ions were 

considered to be secondary when composing between 25 and 

49 percent of the total ion concentration.

U.S. Geological Survey Well Profiler 

Candidate Well Selection 

The RS-2X and GW-7X production wells were selected 

from a list of candidate production wells with arsenic concentrations exceeding the MCL of 10 μg/L and by using criteria 

that were considered necessary to facilitate safe and efficient 

access to the well:

• The ability of the community to manage water-supply 

needs without the use of the well during the testing 

period. 

• A minimum 10-inch diameter cased or open borehole 

with greater than 2 inches of clearance between the 

production pipe and borehole wall or casing.

• A minimum 1.5-inch diameter access port at the well 

head that allows direct vertical access inside the casing.

• A sampling port in the production line (preferably at 

the well head) that allows collection of representative 

samples of produced water.

• A blow-off valve that allows produced water to be 

discharged at the surface without entering the distribution system. 

Some additional criteria that were not necessary to 

facilitate access to the production wells by using the USGS 

well profiler, but were considered to increase the likelihood of 

sampling success were:

• A 1.25-inch diameter slotted polyvinylchloride (PVC) 

access tube attached to the pump column. 
Methods of Study 

9

TRACER-PULSE TRAVEL TIME, IN SECONDS

DEPTH, IN FEET BELOW LAND SURFACE

Pumping water level

Pump 

Tracer-pulse travel time 

200210220230240250260270280290300

0 100 200 300 400 500 600 700 800 900

Pumping water level

NATURAL GAMMA,

IN API UNITS

40 90 14040 90 140

Increasing

clay content

open-hole completion

16.5- to 17-inchdiameterborehole

bottom of well

7.1

10.4

10.1

Depth-dependent sample location and measured arsenic concentration inmicrograms per liter (μg/L)

7.1

10.5 μg/L

Arsenic concentrationat pump intake measuredat well head

API, American Petroleum Institute

Figure 3. Estimated tracer-pulse travel times, depth-dependent sample locations, and well construction information for production well RS-2X in the Rush Springs aquifer, Oklahoma, 2008. 
10 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells 112 feet 190 seconds 500 520 540 560 580 600 620 640 660 680 700 720 740 760 780 800 200 300 400 500 600 700 800 TRACER-PULSE TRAVEL TIME, IN SECONDS

DEPTH BELOW LAND SURFACE, IN FEET

Pumping water level

112 feet 190 seconds = 0.6 foot/second

NATURAL GAMMA,

 IN API UNITS

20 60 100

20 60 100

Increasing

clay content

140 gpm

10-inchdiametercasing

0.49

0.65

0.85

0.9

1.4

23.7 μg/L

Arsenic concentrationmeasured at well head

Perforations in well casing

Pump shroud and pump

0.9 Depth-dependent sample location and measured

arsenic concentration inmicrograms per liter (μg/L)

Tracer-pulse travel time

API American Petroleum Institute

gpm Gallon per minute

Velocity of dye flowing to pump intake is calculated:

Figure 4. Estimated tracer-pulse travel times, depth-dependent sample locations, and well construction information for production well GW-7X in the Garber-Wellington aquifer, Oklahoma, 2008. 
Methods of Study 11

10 20 30 40 50

SULFATE, IN MILLIGRAMS PER LITER

300

290

280

270

260

250

BICARBONATE, IN MILLIGRAMS PER LITER

335 345 355 365 375

50 60 70 80

7 8 9 10 11

ARSENIC, IN MICROGRAMS PER LITER

CALCIUM AND SODIUM, IN

MILLIGRAMS PER LITER

Pump

intake

DEPTH BELOW LAND SURFACE, IN FEET

240

230

220

325

90

Pumping 

water 

level

Bottom of well

NATURAL GAMMA,

IN API UNITS

40 90 140

40 90 140

6

Increasing

clay content

open-hole completion

Sodium

Calcium

Arsenic

Bicarbonate

Sulfate

Open symbols

are well-head 

concentrations

Maximum Contaminant 

Level for arsenic in drinking 

water (U.S. Environmental 

Protection Agency, 2009)

API American Petroleum Institute

Figure 5. Concentrations of arsenic, bicarbonate, calcium, sodium, and sulfate in depth-dependent samples and well-head sample 

from production well RS-2X in the Rush Springs aquifer, Oklahoma, 2008. 
12 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

0 20 40 60 80 100 120

700

650

600

550

0 10 20

ARSENIC, IN MICROGRAMS PER LITER

CALCIUM AND SODIUM, 

IN MILLIGRAMS PER LITER

Pump

intake

DEPTH BELOW LAND SURFACE, IN FEET

750

800

500

Pumping 

water 

level

Top of pump shroud

Bottom of well

NATURAL GAMMA,

 IN API UNITS

20 60 100

Sodium

Arsenic

Calcium

Maximum Contaminant 

Level for arsenic in 

drinking water 

(U.S. Environmental 

Protection Agency, 2009)

30

140

Estimated arsenic concentration 

in water mixture originating from 

adjacent to and just below the 

pump shroud

40 50

Perforated

intervals in

casing

60 70 80

Increasing

clay content

Open symbol

is well-head

concentration

Shroud

API American Petroleum 

 Institute

Figure 6. Concentrations of arsenic, calcium, and sodium in depth-dependent samples and well-head samples from production well 

GW-7X in the Garber-Wellington aquifer, Oklahoma, 2008. 
Methods of Study 13

• A submersible pump set high in the well rather than 

lower. 

• The production well must be able to pump continuously for 10 hours per day for as many as 5 days.

Geophysical Logs

Prior to depth-dependent sampling the RS-2X well, the 

down-hole pump and production casing were removed from 

the non-cased hole and a gamma-ray dual-induction caliper 

logging tool was run by Hayes Evaluation Logging and Perforating from Anadarko, Oklahoma. The gamma-ray is used 

as an indicator of rock lithology and was used to determine 

boundaries between the sandstones and clayey zones in the 

borehole. In general, clays have a larger content of radioactive 

materials whereas sandstones have smaller amounts of clay 

and can be identified as having low natural gamma radiation 

(Keys, 2005a). This type of log is commonly used in perforated well completions after the casing has been set to locate 

water producing sandstones for perforation. The dual-induction log is used to measure the resistivity of the formation, 

which provides information about the pore fluids and porosity of the rocks. This information is also used to determine 

boundaries between rock layers (Keys, 2005b). The caliper log 

provides a continuous measure of the borehole diameter and 

also provides information about rock lithology and fracturing 

(Keys, 2005c). 

After the geophysical log had been run, the pump and 

production casing were put back into the hole and tracer-pulse 

travel times were collected. Zones having higher sand content 

and less clay were identified on the geophysical logs, this 

information along with the travel-time information were used 

to identify the depths or stratigraphic zones contributing water 

to the well for depth-dependent sampling. 

The GW-7X well had an existing geophysical log 

(gamma-ray neutron) with casing perforations provided by the 

well operator. The geophysical log had been run after the well 

originally was drilled and cased to locate stratigraphic zones 

having high sand/low clay content for perforating. The traveltime information and the geophysical log were used to identify 

the depths for depth-dependent sampling. 

Dye Tracer-Pulse Travel-Time Profile

To obtain tracer-pulse travel-time data, the well profiler 

used a slim, high-pressure, multipurpose hose filled with a 

dilute, nontoxic, rhodamine-dye tracer solution. Figure 7 

shows a generalized diagram of a perforated production well, 

similar to GW-7X, showing the well profiler and deployment 

of the hose into the pumping well. The hose was lowered as 

deep as possible and a small amount of the tracer solution was 

injected into the water column. The hose was subsequently 

raised several feet and another pulse of tracer solution was 

injected into the well. The tracer pulse travels to the pump 

intake at the same velocity as water traveling in the well 

borehole or casing. A small part of the well-head discharge 

from the pumping well was routed through a field fluorometer 

(Turner Designs model 10-AU), which reports the tracer concentration (in micrograms per liter) at one-second intervals. 

The difference in time between tracer injection and detection 

at the surface was recorded as the travel time in seconds for 

the given depth. The travel times were plotted in relation to 

well depth and combined with ancillary information, such 

as well diameter, the following were concluded: (1) depth of 

the pump intake (minimum travel time), (2) changes in water 

velocities in the well, (3) estimated depths of contributing 

intervals, and (4) the pumping water level. 

Depth-Dependent Sampling

After contributing intervals were identified, the wellprofiler hose was drained of tracer solution and a stainlesssteel-reinforced Teflon sample hose was attached to the end of 

the multipurpose hose. A check valve separated the two hoses 

and prevented contamination of the sample hose by residual 

tracer solution. A second check valve was attached to the other 

end of the sample hose and both hoses were pressurized with 

compressed nitrogen gas. When a sample depth was reached, 

samples were collected by opening the manual valve on the 

surface end of the hose. When the hose depressurized, the 

hydrostatic pressure of the water column in the well exceeded 

the pressure inside the hose. The in-line check valves opened 

and sample water filled the hose to about the pumping water 

level. The manual valve at the surface was closed and the 

water-filled hose was reeled to the surface. The pressure of the 

water column inside the hose was great enough to close the 

in-line check valves during hose retrieval. The sample hose 

was 50 ft in length and contained a storage volume of about 

0.33 gallon. Once at the surface, the sample-hose attachment 

(including check valves) was disconnected from the multipurpose hose and compressed nitrogen was used to force the 

sample water out of the sample hose through plastic tubing 

and a filter into polyethylene bottles. To completely fill the 

sample hose and obtain enough water to fill sample bottles, 

the end of the sample hose had to be at least 50 ft below the 

pumping water level.

An enclosed chamber was used to prevent wind-borne 

contamination of the sampled water. Trace elements samples 

were preserved by acidification to a pH of 2 or less by using 

2 milliliters of nitric acid. The arsenic speciation sample was 

preserved by acidification with 100 microliters of ethylenediaminetetraacetic acid (EDTA). 

Each sample collected with the well profiler represented 

conditions at a discrete depth in the pumping well, not a 

specific hydrogeologic zone in the formation. The sample 

was a mixture of water from several contributing zones, with 

the number of zones represented in the mixture increasing in 

the direction of the pump. Without reliable estimates of zonal 

production, a mass-balance approach could not be used to estimate constituent concentrations from each zone. As a result, 

the depth-dependent water-quality data were only used to draw 

qualitative comparisons between zones. 
14 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

Figure 7. Diagram of perforated well GW-7X showing well construction, deployment of the U.S. Geological Survey well profiler, and the 

theoretical horizontal well cross section just above the pump shroud. 

Well head

U.S. Geological 

Survey well 

profiler

Fluorometer

Steel casing

Pump intake

Slotted PVC

access tube

Perforated interval

Pump motor

Slotted PVC 

access tube

Electrical 

cable (A ) cab

Above pump shroud

Aash

g in s Ca

Not to scale

EXPLANATION

Aash

Acas

Acol

Acab

cross-sectional 

production pipe, in square feet

area of the 

cross-sectional 

electrical cable, in square feet

area of the 

cross-sectional area of the well

casing above the pump shroud, 

in square feet

cross-sectional area of the empty

casing, in square feet

Pump shroud

Sandstone

Mudstone

Perforations

Cement annulus (Arrow 

indicates 

water flow)

THEORETICAL CROSS SECTION

Production pipe

Production 

pipe

(A ) col

(A

) cas

vash

downward velocity of water above 

the pump shroud, in feet per second

Electrical 

cable

vash

Qtot

Qtot well discharge in gallons per minute

PVC polyvinyl chloride 
Methods of Study 15

Laboratory Analysis

All samples were processed by using established USGS 

protocols described in Wilde and others (2004). Water properties of the depth-dependent samples were measured in a YSI 

XL multiprobe meter cup and recorded after there was less 

than a 10-percent variation in specific conductance and less 

than 0.2-unit variation in pH (appendix 1). Dissolved oxygen 

and water temperature were recorded but were not necessarily representative of the water in the aquifer. Alkalinity, 

bicarbonate, and carbonate concentrations were measured by 

using an inflection point titration method described by Rounds

and Wilde (2001). Water samples were analyzed at the USGS 

National Water Quality Laboratory in Denver, Colorado, for 

dissolved concentrations of the major ions, trace elements, and

arsenic species shown on table 2.

Quality-Assurance Procedures

Laboratory decontamination of sampling equipment 

was performed by using USGS standard methods (Wilde, 

2004). The same procedures were applied to sample hoses 

and fittings with one exception. The sample-hose attachment 

is Teflon-lined and would normally be rinsed with a 5-percent hydrochloric-acid solution. This step was not applied 

because the acid rinse would damage the permanently attache

stainless-steel fittings. 

Quality-control samples for samples collected by using 

the well profiler consisted of one replicate and an equipment 

blank. A replicate sample is an extra sample set collected with

the environmental sample to determine the accuracy of laboratory analytical procedures. 

The analytical accuracy between the environmental and 

replicate samples collected by the depth dependent sampler 

was computed as the relative percent difference (RPD) of constituent concentrations by using the following equation: 

RPD = [(C1-C2) / ((C1+C2)/2)] * 100

Where;

 C1 = larger of the two concentrations

 C2 = smaller of the two concentrations 

Relative percent difference values were not calculated if 

one constituent had an estimated concentration or a concentration less than the minimum reporting level. 

The RPD values for major ions measured in the depthdependent samples (well RS-2X) ranged from 0 to 19 percent 

and for trace elements the RPD values ranged from 0 to 150 

percent (appendix 2). The RPD value for arsenic was 0.

Large RPD values can result from sequential and not 

simultaneous collection of environmental and replicate 

samples. Large RPD values also can be caused by small concentrations reported with few significant figures. For example,

concentrations of 2 and 3 would give an RPD of 40 percent; 

whereas, if the concentrations were reported with more signifi

cant figures, such as 2.4 and 2.6, the RPD would be 8 percent. 

d 

-

An equipment blank was collected to determine if 

samples were contaminated by the sampling equipment or 

bottles. An equipment blank sample showed contamination 

of calcium, fluoride, silica, aluminum, barium, copper, lead, 

nickel, silica, and zinc (appendix 2). The only constituents 

measured at elevated concentrations of importance in the blank 

sample were copper, lead, and zinc. Concentrations of these 

trace elements in the equipment blank sample were larger than 

concentrations measured in the depth-dependent samples from 

GW-7X.

Well-Head Sampling of Production Wells

The 12 production wells were operating and purged 

before sampling. All wells were sampled from a garden-hose 

spigot on the well head by using a length of plastic tubing with 

a polypropylene adaptor that screwed onto the spigot. The 

water properties specific conductance, pH, temperature, and 

dissolved oxygen were measured every 5-7 minutes during 

the purging process by using a flow-through chamber with an 

YSI multi-probe meter. The meter calibrations were performed every morning before use. The specific conductance 

and pH calibrations used standard solutions that bracketed the 

expected values. Samples were collected after water properties 

had stabilized during the purging process. 

The criteria for stabilization were less than a 10-percent variation in specific conductance, less than 0.2-unit variation in 

pH, and less than 0.3-mg/L variation in dissolved oxygen. 

Filtered water was collected in polyethylene bottles in an 

enclosed sampling chamber to prevent wind-borne contamination. Trace elements samples were preserved by acidification 

to a pH of 2 or less by using 2 milliliters of nitric acid. The 

arsenic speciation sample was preserved by acidification with 

100 microliters of ethylenediaminetetraacetic acid (EDTA). 

Laboratory Analysis

Well-head samples were analyzed for dissolved concentrations of the major ions, trace elements, and arsenic species shown on table 2. Alkalinity, bicarbonate, and carbonate 

concentrations were measured by using an inflection point 

titration method described by Rounds and Wilde (2001). 

Water-quality samples were collected and processed by 

using established USGS protocols described in U.S. Geological Survey (2006) and Wilde and others (2004). Samples were 

shipped on ice over night to the USGS National Water Quality 

Laboratory in Denver, Colorado.

Quality-Assurance Procedures

Equipment for well-head sampling was cleaned at the 

USGS Oklahoma Water Science Center by using a nonphosphate detergent, plastic brush, and peristaltic pump, and 

rinsed with tap water followed by deionized water. Equipment 
16 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

was then rinsed with an acid solution consisting of 5 percent 

hydrochloric acid and rinsed again with deionized water. 

Equipment was air dried, then wrapped in new plastic bags 

and used one time between each cleaning. 

Quality-control samples for well-head sampling 

consisted of one replicate and a matrix spike for arsenate, 

arsenite, DMA, and MMA. Two replicates were collected; 

however one was lost in shipment. The analytical accuracy 

between the environmental and replicate sample collected at 

the well head was computed as the RPD of constituent concentrations. The RPD values for major ions measured in water 

from well-head samples from GW-3 ranged from 0 to 6.9 

percent and for trace elements measured in well-head samples, 

the RPD values ranged from 0 to 20 percent. The RPD value 

for arsenic was 2.1 percent (appendix 2). 

The matrix spike is a quality-control sample used to 

evaluate the effects of the sample-water chemistry on the 

performance of the laboratory-analytical method (Sandstrom 

and Lewis, 2009). Three samples were collected from well 

GW-3 on August 7, 2008; an environmental sample, a replicate, and a third sample that was spiked with 20 μg/L each of 

arsenate, arsenite, DMA, and MMA. Arsenic concentrations 

in the environmental and replicate samples from GW-3 were 

about 4.7 μg/L. The measured concentrations of arsenite, 

DMA, and MMA in the spiked sample each should have been 

20 μg/L and arsenate around 24.7 μg/L. The measured concentrations in the spiked sample were arsenate 31.5 μg/L, arsenite 

17.5 μg/L, DMA 22.1 μg/L, and MMA 21.9 μg/L.

Arsenic-Related Water Quality with 

Well Depth

Production Well RS-2X in the Rush Springs 

Aquifer 

The RS-2X production well was selected for sampling 

with the well profiler based on the selection criteria and that it 

had historical arsenic concentrations averaging around 10 μg/L 

(Keith Wright, City of Hinton, Oklahoma, personal commun., 

2008). A well-head sample collected prior to this study in 

2008 by USGS personnel had a total arsenic concentration of 

11.4 μg/L. 

Well Construction and Sampling Conditions 

The RS-2X production well was cased from land surface 

to about 20 ft with 16.5- to 17-inch diameter surface casing 

(fig. 3). Below 20 ft, the well was open hole in sandstone and 

finer-grained sediments down to a total depth of 294 ft. The 

borehole averaged about 16.5 to 17 inches in diameter to a 

depth of 254 ft where the formation was washed out and the 

diameter increased to about 21 inches. The well had a 5-ft long 

submersible pump that was set at 270 ft below land surface. 

The static water level was 169 ft below land surface and 

the pumping water level was 220 ft below land surface. Prior 

to sampling, the production pipe and submersible pump 

were temporarily removed from the borehole and natural 

gamma dual-induction caliper log was run. 

Water Quality with Depth

Three intervals contributing flow were selected for 

sampling on the basis of the tracer-pulse travel-time profile, 

the natural gamma log curve, and the completion information 

shown on figure 3. Aided by this information, three depthdependent samples were collected at 267 ft, 275 ft, and 285 

ft. There were no samples collected below 285 ft because of 

entanglement of the well-profiler hose with electrical wiring 

on the production casing. 

The well-head sample collected from the RS-2X production well had an arsenic concentration of 10.5 μg/L, a dissolved oxygen concentration of 9.2 mg/L, and a near neutral 

pH of 7.2 (appendix 1). Arsenic concentrations in the depthdependant samples ranged from 7.1 to 10.4 μg/L with pH 

values ranging from 7.2 to 7.4 (table 3). Dissolved oxygen 

concentrations ranged from 7 to 15.4 mg/L (appendix 1) in 

the depth-dependent samples but probably were not accurate 

because of exposure to air. 

The Piper diagram (Piper, 1944) on figure 8 illustrates 

that the well-head and depth-dependent samples have similar water-quality characteristics by the close proximity of 

the sample points on the plot and does not show any apparent water-quality trends with depth. Constituent concentrations that varied between the well-head and depth-dependent 

samples were arsenic, sodium, and sulfate. The shallow depthdependent sample (267 ft) had the smallest arsenic and largest 

sodium concentrations compared to the well-head and the two 

deeper samples (275 and 285 ft) (fig. 5) and may indicate that 

zones yielding noncompliant arsenic concentrations are below 

267 ft. 

The sulfate concentration was about two times greater 

in the well-head sample, 41.2 mg/L, than the depth-dependent 

samples collected above and below the pump. The reason 

for the discrepancies in sodium, sulfate, and arsenic in 

samples is unknown. Water with elevated sulfate concentrations may have entered the well from the zone (269–272 ft) 

adjacent to the pump intake (fig. 5). During production, this 

water would travel horizontally to the pump intake and not be 

captured in depth-dependent samples from above and below 

the pump intake. However, more samples would be needed 

below the pump to better define any water-quality trends with 

depth and locate where arsenic-contaminated water is entering 

the borehole. This additional information may help determine 

whether zonal isolation would be a feasible option to lower 

arsenic concentrations in this well.
Arsenic-Related Water Quality with Well Depth 17

Figure 8. Percentages of major ions in well-head and depth-dependent samples from production wells GW-7X in the GarberWellington aquifer and RS-2X in the Rush Springs aquifer, Oklahoma, 2008. 

CALCIUM CHLORIDE

SULFATE PLUS CHLORIDE

CALCIUM PLUS MAGNESIUM

SULFATE

SODIUM PLUS POTASSIUM

MAGNESIUM

CARBONATE PLUS BICARBONATE

 0 

 20 

 40 

 60 

 80 

 100 

100

80

60

40

20

0

100

80

60

40

20

0

100

80

60

40

20

0

100

20

40

60

80

0

 0 

 20 

 40 

 60 

 80 

 100 

100

80

60

40

20

0

100

80

60

40

20

0

100

80

60

40

20

0

100

80

60

40

20

0

EXPLANATION

GW-7X

RS-2X

GW-7X

RS-2X

RS-2X

?

?

GW-7X

582ft

WH

710ft

Outline of trend showing cation exchange process in samples from 

the GW-7X production well 

?

Well-head sample from RS-2X in the Rush Springs aquifer

Depth-dependent sample from RS-2X in the Rush Springs aquifer (the 267-foot 

sample did not have a bicarbonate measurement and is absent in the right (anion) triangle 

Well-head sample from GW-7X in the Garber-Wellington aquifer

Depth-dependent sample from GW-7X in the Garber-Wellington aquifer

Probable composition of water originating from adjacent to and 

below the pump shroud in GW-7X (based on wells with similar 

construction and water quality with depth S.J. Smith, written commun., 2009)

Percentage of total milliequivalents per liter
18 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

Production Well GW-7X in the GarberWellington Aquifer

The USGS well profiler was used to collect dye tracerpulse travel-time information and five depth-dependent 

samples in the GW-7X production well in the GW. At the 

time of testing, the production well had been out of operation for 2.5 years because historical arsenic concentrations 

ranging from about 25 to 28 μg/L resulted in the well being 

noncompliant (Robert Pistole, Project Manager, Veolia Water 

North America, oral commun., 2008). The well was purged for 

about 72 hours before any samples were collected. 

Table 3. Sample location, water type, pH, and arsenic concentration of water from depth-dependent and well-head samples from 

production wells, Oklahoma, 2008.

[μg/L, micrograms per liter; --, not available; ID, identifier; lds, land surface] 

Well ID Aquifer Sample location

(feet below lds) Water type

pH

(standard 

units)

Arsenic

dissolved

(μg/L)

GW-1 Garber-Wellington well head sodium bicarbonate 8.8 30

GW-2 Garber-Wellington well head sodium bicarbonate 7.8 124

GW-3 Garber-Wellington well head sodium-magnesium 

bicarbonate-chloride

8.0 4.8

GW-4 Garber-Wellington well head sodium-calcium bicarbonate 7.1 18.5

GW-5 Garber-Wellington well head sodium bicarbonate 8.5 59.9

GW-6 Garber-Wellington well head sodium bicarbonate-chloride 8.6 37.7

GW-7X Garber-Wellington well head before depthdependent samplessodium bicarbonate 8.7 22.9

GW-7X Garber-Wellington 582 sodium-magnesium bicarbonate 7.8 .49

GW-7X Garber-Wellington 610 sodium bicarbonate 8.0 .65

GW-7X Garber-Wellington 653 sodium-magnesium bicarbonate 8.2 .85

GW-7X Garber-Wellington 686 sodium bicarbonate 8.1 .9

GW-7X Garber-Wellington 710 sodium bicarbonate 8.1 1.4

GW-7X Garber-Wellington well head after depthdependent samplessodium bicarbonate 8.7 23.7

PM-1 Permian-aged undefined well head calcium-sodium 

bicarbonate-chloride

6.9 10.4

RS-1 Rush Springs well head calcium-sulfate bicarbonate 7.4 18.2

RS-2X Rush Springs well head calcium-sodium bicarbonate 7.2 10.5

RS-2X Rush Springs 267 -- 7.4 7.1

RS-2X Rush Springs 275 calcium-sodium bicarbonate 7.3 10.4

RS-2X Rush Springs 285 calcium-sodium bicarbonate 7.2 10.1

RS-3 Rush Springs well head calcium bicarbonate 7.4 15.7

TH-1 Arbuckle Timbered Hills well head sodium bicarbonate 9.0 11.6
Arsenic-Related Water Quality with Well Depth 19

Well Construction and Sampling Conditions

The production well GW-7X was completed with casing 

that was perforated at intervals from 522 ft to the bottom of 

the well at 783 ft (Steve Ray, City of Moore, Oklahoma, written commun., 2009) (fig. 4). For this type of well completion, 

the casing is cemented to the formation borehole and perforations (opening through which water enters the well) are made 

through the casing and cement annulus at permeable aquifer 

zones, usually identified from a natural gamma geophysical 

log after the casing has been installed. 

An 8-inch diameter PVC shroud overlaid the pump at 

718 ft (fig. 6). The shroud is similar to an open-bottom tube 

that surrounds the submersible pump and forces water to flow 

past the motor to reach the pump intake, keeping the motor 

cool during production (Cheapa Pumps, 2009; Driscoll, 1986). 

The pump intake was about 14 ft below the top of the shroud 

at 732 ft with about 5 ft of pump motor extending below the 

pump intake. There was about 51 ft of formation below the 

bottom of the pump. The static water level was 402 ft below 

land surface before testing began and 521 ft below land surface while the well was pumping (fig. 6).

Obstructions and irregularities of the casing wall and 

pump column can impede the movement of the sampling hose 

into and out of the well. To circumvent potential problems, 

the pump column was pulled from the well and a 1.25-inch 

diameter, 0.375-inch slotted PVC access tube was installed 

to guide the sample hose down the borehole. The bottom end 

of the access tube was open, cut at an angle, and ended at the 

top of the shroud that was not removed for sampling (fig. 7). 

There was insufficient space between the shroud and casing to 

extend the PVC or well-profiler sample hose below the pump. 

As a result there were no tracer-pulse travel-time data or 

depth-dependent samples collected below the shroud.

Water Quality with Depth 

In well GW-7X, five depths were selected for sampling 

on the basis of information obtained from the tracer-pulse 

travel-time profile and natural gamma log curve shown on 

figure 4. Two well-head samples were collected to measure 

arsenic concentrations, one before and another after the depthdependent samples were collected to see if concentrations 

had changed in produced water with time. Depth-dependent 

samples were collected above the shroud at 582 ft, 610 ft, 653 

ft, 686 ft, and 710 ft. 

All samples from well GW-7X, well head and depth 

dependent, were oxic with dissolved oxygen ranging between 

5.3 to 8.6 mg/L (appendix 1). However, measurements of dissolved oxygen in depth-dependent samples were probably not 

accurate because of exposure to air during sampling. 

There was a distinct difference in pH values, major-ion 

composition, and arsenic concentrations between the depthdependent and well-head samples from well GW-7X. Wellhead samples showed higher pH values (appendix 1), smaller 

concentrations of calcium, and larger concentrations of arsenic 

and sodium than depth-dependent samples (fig. 6). pH values 

at the well head were 8.7, while pH values in depth-dependent 

samples ranged from 7.8 (582 ft) to 8.2 (653 ft) and increased 

with depth (table 3). Arsenic concentrations in well-head 

samples stayed relatively constant in produced water, ranging from 22.9 μg/L before testing and 23.7 μg/L after testing. 

Depth-dependent sample concentrations were substantially 

smaller, ranging from 0.49 μg/L (582 ft) to 1.4 μg/L (710 

ft), and similar to pH, increased with depth. The oxic conditions and arsenate in all samples, indicated that pH-activated 

desorption from iron oxide coatings is most likely the source 

and mechanism for release of arsenic, which is consistent with 

the NAWQA study findings relating to arsenic in the COA 

(Christenson, 1998).

Water type of samples from GW-7X was sodium-bicarbonate except for samples from 582 ft and 653 ft, which had 

slightly larger percentages of magnesium and were sodiummagnesium bicarbonate. The percentages of sodium and 

calcium ions in the depth-dependent samples show an inverse 

relation; as the percentage of sodium ions increases with 

depth, the calcium ions decrease. This trend is shown on the 

Piper diagram on figure 8 and corresponds to the exchange of 

sodium ions in the clays with calcium ions in the water, which 

becomes more prevalent as the water becomes older with 

depth. The effects from cation exchange also are seen in the 

increase of pH values and arsenic concentrations with depth. 

In addition to sodium and arsenic, well-head samples also 

had markedly larger concentrations of boron, chromium, lead, 

molybdenum, selenium, vanadium, and uranium than depthdependent samples (appendix 1). These findings, in addition 

to the other water quality discrepancies between the well-head 

and depth-dependent samples, indicate that noncompliant 

produced water was entering the borehole from perforations adjacent to or below the shroud (fig. 7). This conclusion was supported by the calculations shown in this section 

that estimate that about 63 percent of the water produced at 

the well head originated adjacent to or below the shroud. By 

using this estimate and the arsenic concentrations in the wellhead samples and the sample collected just above the shroud 

(710 ft), the water mixture in the borehole below the shroud 

was estimated to have an arsenic concentration of 36 μg/L, in a 

probable range of 30 to 56 μg/L.

From the tracer-pulse travel time in figure 4, the maximum downward velocity of water flowing through the well 

just above the pump shroud was 0.6 foot per second (ft/sec). 

This velocity can be converted to a volumetric flow rate, by 

using the equation:

Qash = Vash * Aash * 60 seconds per minute 

* 7.48 gallons per cubic foot

where

Qash is the maximum flow rate of water above the shroud, in 

gallons per minute,

Vash is the velocity of water above the pump shroud (0.6 foot 

per second; fig. 7), and
20 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

Aash is the theoretical cross-sectional area of the well casing 

above the pump shroud in square feet (fig. 7).

The theoretical cross sectional area of the well casing 

above the pump shroud (Aash) can be computed as the cross 

sectional area of the empty well casing (Acas), minus the areas 

of the production pipe (Acol) and electrical cable to the pump 

motor (Acab), by using the equation;

Aash = Acas - Acol - Acab

where

Aash is the cross-sectional area of the well casing above the 

pump shroud, in square feet,

Acas is the cross sectional area of the empty well casing, in 

square feet,

Acol is the cross sectional area of the production pipe, in 

square feet, and

Acab is the cross sectional area of the electrical cable, in 

square feet. 

For well GW-7X, which has a 10-inch diameter casing, 

a 4.5-inch outside diameter production pipe with 5.5-inch 

outside diameter collars (at the pipe joints), and a 1.5-inch 

diameter electrical cable, the idealized cross-sectional area 

of the well casing above the pump shroud was about 0.4 ft2 

(fig. 7). However, because of turbulence, friction loss, well 

scale buildup, and eddies created around the many objects in 

the well, the effective cross-sectional area was probably less 

than 0.4 ft2. Smith and others (2009), by using an empirical approach on wells of identical construction to GW-7X, 

estimated that the effective cross-sectional area of the well 

casing above the pump shroud can range from 0.14 to 0.36 ft2, 

and was about 0.21 ft2 on average. By using these estimates 

of effective cross-sectional area, the downward flow rate just 

above the pump shroud could range from 90.5 to 37.1 gallons 

per minute (gpm), with an average downward flow rate of 55.6 

gpm. Given that the total discharge of the well was about 150 

gpm (Steve Ray, City of Moore, Oklahoma, oral commun., 

2009) this equates to a flow contribution range of 60.3 to 24.7 

percent of the total well discharge, with an average of 37.1 

percent of the total discharge coming from above the pump.

Given the well-head arsenic concentration (Cwh) of 22.9 

μg/L and the arsenic concentration (Cash) of 1.4 μg/L from the 

depth-dependent sample collected from just above the pump 

shroud (fig. 6), the arsenic concentration of the water mixture 

originating from the zones adjacent to and below the pump 

shroud (Cbsh) was estimated at 36 μg/L by using the equation:

Cbsh = Cwh – ((Pash) (Cash)) / Pbsh

where 

Cbsh is the arsenic concentration, in micrograms per liter, 

of the water mixture originating from the zones 

adjacent to and below the pump shroud,

Cwh is the concentration of arsenic in water produced at the 

well head (22.9 in micrograms per liter), 

Cash is the concentration of arsenic in depth-dependent 

sample collected just above the shroud (1.4 in 

micrograms per liter), 

Pash is the percentage of the total well discharge that 

originates from zones adjacent to or below the 

pump shroud, and

Pbsh is the percentage of the total well discharge (150 

gallons per minute) that originates from zones 

above the shroud.

Arsenic-Related Water Quality in WellHead Samples 

Most of the 12 production wells sampled had historical arsenic concentrations exceeding 10 μg/L, and except for 

production well GW-7X, were on line and used for water 

supply (fig. 1). The well-head sample collected from GW-7X 

before testing was used to describe the water quality from this 

well. The arsenate, arsenite, DMA, and MMA water sample 

from well GW-3 collected in August 2008 was compromised 

and was not used in the report. A partial sample analysis from 

this well with concentrations of these arsenic species (collected September 2008) was used with the measured physical 

properties and major ion concentrations from the August 2008 

sample for comparison in the report. 

Seven production wells produced water from the GW, 

three from the RS, one from the TH, and one from PM (fig. 1 

and table 3). The production wells ranged in depth from 120 to 

854 ft (table 1). Four production wells (GW-1, GW-2, GW-4, 

PM-1) had slotted casing at the bottom of the well similar to 

completion techniques used to construct domestic wells. To 

maximize the volume of produced water for this type of well 

completion, the annulus between the casing and formation is 

filled with sand from the bottom of the well to near land surface which permits groundwater to flow into the slotted casing 

from the full saturated thickness of the aquifer penetrated. 

Five wells had perforated casing open to the formation at 

varying intervals (GW-3, GW-5, GW-6, GW-7X, TH-1). Three 

production wells in the RS (RS-1, RS-2X, and RS-3) had 

open-hole completions, a common well-completion method 

in the RS for domestic, irrigation, and public-supply wells. 

For this type of well completion, casing is not installed below 

surface casing which allows groundwater to move towards the 

pump from all water bearing zones in the borehole. 

Arsenic in Relation to Physical Properties and 

Water Type 

Arsenic concentrations in well-head samples were larger 

than 10 μg/L, except for GW-3 at 4.8 μg/L, and ranged from 

10.4 to 124 μg/L (table 3). Six of the seven production wells 

in the GW had the largest arsenic concentrations ranging from 

18.5 to 124 μg/L. Large arsenic concentrations (10.4–18.5) 
Arsenic-Related Water Quality in Well-Head Samples 21

and near neutral to slightly alkaline pH values (6.9–7.4) were 

detected in samples from production wells in the RS (RS-1, 

RS-2X, RS-3) in addition to GW-4 in the GW and PM-1 in 

the PM (fig. 9 and table 3). Schlottmann and others (1998) 

reported arsenic is not mobile at pH values below 8.5 in the 

GW and the coincidence of low pH values and large arsenic 

concentrations may be due to water mixing in the borehole 

from multiple zones.

All well-head samples were oxic and arsenate was the 

only species of arsenic in water from 10 of the 12 production 

wells sampled. Arsenite was measured above the laboratory 

reporting level in water from GW-4 and was the only arsenic 

species measured in water from TH-1. Arsenite is generally 

present in water during reducing conditions. However, the 

dissolved oxygen concentration of the sample was 3.7 mg/L, 

indicating oxic conditions. This discrepancy might be the 

result of water mixing in the borehole or the introduction of air

from the sampling process.

Most samples showed larger concentrations of dissolved 

arsenic than total arsenic, which was not anticipated, because 

total arsenic is a measure of the dissolved and undissolved 

forms. This discrepancy might be attributed to analytic error 

or to the different analytical techniques used to measure total 

and dissolved arsenic (David Mueller, U.S. Geological Survey, 

written commun., 2009). The average difference between 

total and dissolved concentrations was only 0.5 percent and 

was considered in an acceptable range. The small difference 

between dissolved and total arsenic concentrations in wellhead samples (and depth-dependant samples) indicates that 

arsenic was dissolved in groundwater and not associated with 

particulate material (appendix 1).

Sodium and bicarbonate were the predominant ions of 

all well-head samples from the GW. Magnesium and chloride 

were secondary ions in GW-3 and chloride was a secondary 

anion in GW-6. The Piper diagram on figure 10 shows that 

the percentages of calcium plus magnesium and sodium plus 

potassium in the GW samples plot along a trend similar to the 

depth-dependent samples from GW-7X on figure 8 indicating 

the transition from a calcium to a sodium dominated water 

type.

Unlike the GW where sodium was the dominant cation, 

calcium composed the greatest percentage of cations in water 

from the RS production wells (49 to 68 percent) with sodium 

a dominant secondary cation only in RS-2X. Sulfate was the 

dominant anion in RS-1 and bicarbonate the dominant anion in 

water from RS-2X and RS-3 (fig. 10). Arsenic concentrations 

in the three RS production wells ranged from 10.5 to 18.2 

μg/L with near neutral to slightly alkaline pH values of 7.2 and 

7.4 (table 3). The largest arsenic concentration, 18.2 μg/L from 

RS-1, was associated with calcium-sulfate bicarbonate type 

water. 

Water from production well TH-1 was sodium-bicarbonate type with sodium composing almost 100 percent of the 

cations and bicarbonate 65 percent of the anions (fig. 10 and 

table 3). The total dissolved solids concentration of 511 mg/L 

and the pH value of 9.0 exceeded the secondary maximum 

contaminant level of 500 mg/L and a value 8.5, respectively, 

for drinking water (U.S. Environmental Protection Agency, 

2009). Arsenic and fluoride were measured at concentrations 

of 11.6 μg/L and 7.44 mg/L, respectively, and exceeded the 

MCLs of 10 μg/L and 4 mg/L, respectively, for drinking water 

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

Water from the production well PM-1 was calcium 

sodium-bicarbonate chloride type with calcium composing 

43 percent and sodium 36 percent of the total cations in the 

water sample. Total dissolved solids were measured at a 

concentration of 937 mg/L and exceeded the secondary maximum contaminant level of 500 mg/L for drinking water (U.S. 

Environmental Protection Agency, 2009). Arsenic was measured at a concentration of 10.4 μg/L and exceeded the MCL 

for drinking water (U.S. Environmental Protection Agency, 

2009).

Arsenic in Relation to Other Trace Elements 

In the COA, Schlottmann and others (1998) generally found that high concentrations of arsenic occurred with 

chromium, selenium, and vanadium. Figures 11 and 12 show 

Figure 9. Relation of arsenic with pH in well-head samples 

from production wells, Oklahoma, 2008. 

6.5 7.0 7.5 8.0 8.5 9.0

0

20

40

60

80

100

120

Maximum Contaminant

Level for arsenic in 

drinking water 

(U.S. Environmental

Protection Agency,

 2009) 

pH at which arsenic 

becomes mobile in 

the Central Oklahoma

aquifer (Schlottmann and 

others, 1998) 

GW-2

PM-1

GW-1

GW-3

GW-4

GW-6

GW-7X TH-1

RS-1

RS-2X

RS-3

GW-5

Arsenic concentration, in micrograms per liter

pH, in standard units

Garber-Wellington aquifer

Rush Springs aquifer

Permian-aged undefined aquifer

EXPLANATION

Arbuckle-Timbered Hills aquifer
22 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

CALCIUM CHLORIDE

SULFATE PLUS CHLORIDE

CALCIUM PLUS MAGNESIUM

SULFATE

SODIUM PLUS POTASSIUM

MAGNESIUM

CARBONATE PLUS BICARBONATE

 0 

 20 

 40 

 60 

 80 

 100 

100

80

60

40

20

0

100

80

60

40

20

0

100

80

60

40

20

0

100

20

40

60

80

0

 0 

 20 

 40 

 60 

 80 

 100 

100

80

60

40

20

0

100

80

60

40

20

0

100

80

60

40

20

0

100

80

60

40

20

0

EXPLANATION

GW-7X

RS-2X

GW-7X

GW-7X

RS-2X

RS-2X

TH-1

RS-3

GW-6

GW-5

GW-4

GW-3

GW-2

GW-1

PM-1

RS-1

RS-1

RS-1

RS-3

RS-3

PM-1

PM-1

GW-4 GW-4

GW-5

GW-5

GW-6

GW-6

TH-1

TH-1

GW-3 GW-3

GW-1

GW-1

GW-2

GW-2

Arbuckle-Timbered Hills aquifer

Cation exchange 

Percentage of total millequivalents per liter

Represents the process of cation exchange 

occurring in the Garber-Wellington aquifer 

and the transition from a calcium to a sodium 

dominated water type.

Garber-Wellington aquifer

Rush Springs aquifer

Permian-aged undefined aquifer

Figure 10. Percentages of major ions in well-head samples from production wells, Oklahoma, 2008. 
Arsenic-Related Water Quality in Well-Head Samples 23

Figure 11. Relation of barium, boron, chromium, and copper with arsenic in well-head samples from production wells, Oklahoma, 2008. 

EXPLANATION

10 100 1,000

Boron concentration, in micrograms per liter

1

10

100

10 100

1

10

100

Barium concentration, in micrograms per liter

GW-3

1 500

Maximum contaminant level

for arsenic in drinking water 

(U.S. Environmental

Protection Agency, 2009) 

TH-1

1

Copper concentration, in micrograms per liter

PM-1

GW-3

1

10

100

0.1 1 10

Chromium concentration, in micrograms per liter

GW-3

GW-2

1

10

100

100 0.4 6

Garber-Wellington aquifer

Rush Springs aquifer

Permian-aged undefined aquifer

Arbuckle-Timbered Hills aquifer

Arsenic concentration, in micrograms per liter Arsenic concentration, in micrograms per liter

Arsenic concentration, in micrograms per liter Arsenic concentration, in micrograms per liter
24 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

Figure 12. Relation of fluoride, nickel, uranium, and vanadium with arsenic in well-head samples from production wells, Oklahoma, 

2008. 

1

Fluoride concentration, in milligrams per liter

1

10

100

Maximum contaminant 

level for fluoride in 

drinking water 

(U.S. Environmental

Protection Agency, 

2009) 

TH-1

GW-3

GW-2

GW-5

0.1 10

1

10

100

1 10 100

Uranium concentration, in micrograms per liter

1

10

100

Maximum contaminant 

level for uranium in 

drinking water 

(U.S. Environmental

Protection Agency, 

2009) 

GW-3

GW-2

GW-5

GW-1

GW-6

0.3

1

Nickel concentration, in micrograms per liter

1

10

100

0.1

1 10 100 1,000

Vanadium concentration, in micrograms per liter

1

10

100

0.1

GW-3

TH-1

EXPLANATION

Maximum contaminant level

for arsenic in drinking water 

(U.S. Environmental

Garber-Wellington aquifer Protection Agency, 2009) 

Rush Springs aquifer

Permian-aged undefined aquifer

Arbuckle-Timbered Hills aquifer

Arsenic concentration, in micrograms per liter

Arsenic concentration, in micrograms per liter Arsenic concentration, in micrograms per liter

Arsenic concentration, in micrograms per liter
Summary 25

that chromium and vanadium (selenium is not shown) in 

addition to barium, boron, fluoride, copper, and uranium have 

a positive relation to arsenic in samples from most of the 

12 production wells. In an oxyanion form these trace elements 

can compete with arsenic for sorption sites on iron oxides 

and be released into groundwater during similar conditions 

(Hem, 1992). Unlike the other trace elements, nickel showed 

a negative relation to arsenic (fig. 12). The sample from TH-1 

tends to diverge from the trend on most plots that may be an 

indication of different geochemical processes occurring in the 

TH compared to the other aquifers. Samples from GW-2 and 

GW-3, which have the largest and smallest arsenic concentrations, also tend to diverge from trends on selected plots 

(figs. 11 and 12). Copper had a strong positive relation with 

arsenic except for two samples, GW-3 and PM-1 (fig. 11). 

Concentrations of dissolved iron ranged from E2.0 to 

10.0 μg/L in six samples and showed no correlation to arsenic 

in well-head samples (not shown), including water from the 

GW where arsenic concentrations are related to the iron oxide 

in the rocks. Dissolved iron has been found in previous studies 

to have a weak correlation with arsenic (Kresse and Fazio, 

2003; Anawar and others, 2004) or similar to this study, no 

relation (Robertson, 1989). These findings may be the result 

of an association between arsenic and iron in an undissolved 

state. Bahadur and others (2007) showed a substantial correlation between total arsenic and total iron in a nationwide study 

of surface water and groundwater.

Twelve of the 21 trace elements analyzed have MCLs 

and six trace elements have secondary maximum contaminant levels for drinking water (table 2) (U.S. Environmental 

Protection Agency, 2009). Fluoride and uranium were the only 

trace elements, other than arsenic, that exceeded the MCLs for 

drinking water in well-head samples collected for the study 

(fig. 12). Uranium concentrations in four GW production 

wells (GW-1, GW-2, GW-5, and GW-6) ranged from 30.2 to 

99 μg/L, exceeding the MCL of 30 μg/L for drinking water 

(fig. 12). Samples from GW-1, GW-2, GW-5, and GW-6 wells 

also had the largest arsenic concentrations measured in the 

study, ranging from 30 to 124 μg/L (fig. 9 and table 3).

Summary 

In Oklahoma, as many as 23 public water-supply systems 

have been affected by the reduced arsenic maximum contaminant level of 10 μg/L for drinking water. Most large communities in Oklahoma are financially able to address noncompliant 

drinking water. However, many small communities and rural 

water districts, which operate with small resources, maintain 

minimal conveyance infrastructure, and often have no secondary source of water. 

A project was performed by the USGS, in cooperation 

with the Oklahoma Department of Environmental Quality 

and the Groundwater Protection Council. The objective of 

the project was to describe arsenic-related water quality 

with depth in two wells by using the USGS well profiler to 

determine if the findings could be used to identify zones yielding water with high arsenic concentrations. If findings show 

that large arsenic concentrations in the borehole are related 

to stratigraphic zones or sedimentary layering, this technique 

could be considered an option in a generalized decision tree 

for identifying appropriate well-rehabilitation strategies that 

are less expensive than drilling new production wells or water 

treatment at the well head. 

In addition, samples were collected at the well head 

from 12 production wells yielding water with historically 

large concentrations (greater than 10 μg/L) of arsenic from 

the Garber-Wellington aquifer, Rush Springs aquifer, and 

two minor aquifers; the Arbuckle-Timbered Hills aquifer in 

southern Oklahoma and a Permian-aged undefined aquifer in 

north-central Oklahoma.

The well-head and depth-dependent samples from a 

production well in the Rush Springs aquifer had similar 

water-quality characteristics but did not show any substantial 

changes with depth. Zones yielding noncompliant arsenic concentrations appear to be below the shallowest depth-dependent 

sample. However, more samples would be needed below the 

pump to determine whether zonal isolation would be a feasible 

option for this well. 

Changes in water quality with depth were seen in five 

depth-dependent samples collected from a production well in 

the Garber-Wellington aquifer. The depth-dependent samples 

showed an increase in arsenic concentrations with depth. Data 

showed that most of arsenic contaminated water (about 63 

percent) was entering the borehole from perforations adjacent 

to or below the shroud that overlies the pump. The water mixture in the borehole below the shroud was estimated to have an 

arsenic concentration of 36 μg/L.

Arsenic concentrations ranged from 10.4 to 124 μg/L in 

eleven well-head samples. Six of the seven production wells in 

the Garber-Wellington aquifer had the largest arsenic concentrations ranging from 18.5 to 124 μg/L. All well-head samples 

were oxic and arsenate was the only species of arsenic in water 

from 10 of the 12 production wells sampled. Arsenite was 

measured above the minimum reporting level in water from a 

production well in the Garber-Wellington aquifer and was the 

only arsenic species measured in water from the ArbuckleTimbered Hills aquifer. Studies have shown that desorption 

from iron oxide coatings on mineral grains is the source of 

arsenate in the Garber-Wellington aquifer. Desorption from 

iron oxide also may be the source of arsenic as arsenate in 

groundwater samples from wells in the Rush Springs aquifer 

and the Permian-aged undefined aquifer. However, the source 

and incidence of arsenic in aquifers other than the GarberWellington in Oklahoma have not been studied.

Barium, boron, fluoride, chromium, copper, selenium, 

uranium, and vanadium showed a positive relation to arsenic 

in well-head samples from most of the 12 production wells. In 

an oxyanion form, these trace elements compete with arsenic for sorption sites on iron oxides and can be released into 

groundwater during similar chemical conditions as arsenic. 

Unlike other trace elements, nickel showed a strong inverse 
26 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

relation to arsenic concentrations. Iron showed no relation 

to arsenic in well-head samples, including water from the 

Garber-Wellington where arsenic concentrations are related to 

the iron oxide in the rocks. 

Fluoride and uranium were the only trace elements, 

other than arsenic, that exceeded the maximum contaminant 

level for drinking water in well-head samples collected for 

the study. Uranium concentrations in four production wells in 

the Garber-Wellington aquifer ranged from 30.2 to 99 μg/L 

exceeding the maximum contaminant level of 30 μg/L for 

drinking water. Water from these four wells also had the largest arsenic concentrations measured in the study ranging from 

30 to 124 μg/L.

References 

Bahadur, Rakesh, Samuels, William, Cameron, Tara, and 

Smith, Ben, 2007, Assessment of the co-occurrence of 

drinking water contaminants: About arsenic co-occurrence, 

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Appendix 1—Water-Property Measurements and ChemicalConstituent Concentrations Measured in Water from DepthDependent and Well-Head Samples, Oklahoma, 2008

Appendix 1

Appendix 1 31

Appendix 1. Water-property measurements and chemical-constituent concentrations measured in water from depth-dependent and well-head samples, Oklahoma, 2008. All concentrations are dissolved unless otherwise noted.[USGS, U.S. Geological Survey; ID, identifier; E, estimated; <, less than; --, not available; mg/L, milligram per liter; μg/L, microgram per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; GW, Garber-Wellington aquifer; PM, Permian-aged undefined aquifer; RS, Rush Springs aquifer; TH, Arbuckle Timbered Hills aquifer; lds, land surface; WH, well-head sample; DMA, dimethylarsinate; MMA, monomethylarsonate; c, sample was contaminated and constituent was not measured]

USGS 

site ID Well ID Date Time Aquifer Sample type Well depth (feet below lds) Sample location (feet below land surface) Dissolved oxygen (mg/L) pH

355110097240301 GW-1 Oct. 28, 2008 1100 GW Regular -- WH 2.3 8.8355034097145201 GW-2 Oct. 9, 2008 1030 GW Regular 310 WH 3.2 7.8353308097290701 GW-3 Aug. 7, 2008 1200 GW Regular 750 WH 6.0 8.0353308097290701 GW-3 Aug. 7, 2008 1201 GW Replicate 750 WH -- --353308097290701 GW-3 Sep. 11, 2008 1030 GW Regular 750 WH 5.0 7.6352934097271502 GW-4 Jul. 25, 2008 1130 GW Regular 265 WH 3.8 7.1352604097370901 GW-5 Jul. 22, 2008 1100 GW Regular 854 WH 2.9 8.5352604097370901 GW-5 Aug. 29, 2008 1345 GW Regular 854 WH -- 8.6351914097320201 GW-6 Jul. 16, 2008 1500 GW Regular 782 WH 4.0 8.6351853097284701 GW-7X Dec. 12, 2008 1000 GW Regular 811 WH 8.6 8.7351853097284701 GW-7X Dec. 13, 2008 1100 GW Regular 811 582 7.7 7.8351853097284701 GW-7X Dec. 13, 2008 0800 GW Regular 811 610 5.3 8.0351853097284701 GW-7X Dec. 12, 2008 1430 GW Regular 811 653 7.2 8.2351853097284701 GW-7X Dec. 12, 2008 1330 GW Regular 811 686 8.4 8.1351853097284701 GW-7X Dec. 12, 2008 1030 GW Regular 811 710 8.5 8.1351853097284701 GW-7X Dec. 13, 2008 1500 GW Replicate 811 WH 8.3 8.7364824097311601 PM-1 Jul. 31, 2008 1300 PM Regular 120 WH 6.1 6.9353237098403901 RS-1 Jul. 15, 2008 1100 RS Regular 320 WH 8.6 7.4352822098233801 RS-2X Nov. 25, 2008 1600 RS Regular 294 285 7.0 7.2352822098233801 RS-2X Nov. 25, 2008 1630 RS Regular 294 WH 9.2 7.2352822098233801 RS-2X Nov. 25, 2008 1700 RS Regular 294 275 10.2 7.3352822098233801 RS-2X Nov. 26, 2008 1300 RS Regular 294 267 15.4 7.4352822098233801 RS-2X Nov. 26, 2008 1301 RS Replicate 294 267 -- --351754098331501 RS-3 Sep. 5, 2008 1030 RS Regular 375 WH 10.7 7.4343706098451201 TH-1 Sep. 5, 2008 1400 TH Regular 620 WH 3.7 9.0
32 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells Appendix 1. Water-property measurements and chemical-constituent concentrations measured in water from depth-dependent and well-head samples, Oklahoma, 2008. All concentrations are dissolved unless otherwise noted.—Continued [USGS, U.S. Geological Survey; ID, identifier; E, estimated; <, less than; --, not available; mg/L, milligram per liter; μg/L, microgram per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; GW, Garber-Wellington aquifer; PM, Permian-aged undefined aquifer; RS, Rush Springs aquifer; TH, Arbuckle Timbered Hills aquifer; lds, land surface; WH, well-head sample; DMA, dimethylarsinate; MMA, monomethylarsonate; c, sample was contaminated and constituent was not measured] USGS site ID Well ID Spe- cific con- duc- tance (μS/ cm) Tem- per- ature (°C) Cal- cium (mg/L) Mag- ne- sium (mg/L) Potas- sium (mg/L) Sod- ium (mg/L) Alka- linity (mg/L) Bicar- bonate (mg/L) Car- bo- nate (mg/L) Bro- mide (μg/L) Chlor- ide (mg/L) Fluor- ide (mg/L) Silica (mg/L) Sul- fate (mg/L) Total dis- solved solids (mg/L) Al- um- inum (μg/L) An- tim- ony (μg/L) Ar- sen- ate (μg/L) 355110097240301 GW-1 742 17.9 2.02 0.877 0.48 173 300 342 11 0.08 42.4 0.78 8.90 29.4 440 8.3 E.03 28.1 355034097145201 GW-2 1,010 18 20.3 12.9 .87 211 494 599 2 .14 21.8 .52 11.4 24 602 <4 E.02 125 353308097290701 GW-3 665 18.3 25 20.3 1.99 82.3 209 251 2 .05 59.2 .30 14 35 365 E1.6 <.14 c 353308097290701 GW-3 -- -- 24 19.6 1.97 87.4 -- -- -- .05 58.3 .28 13.7 34.5 -- E.8 <.14 c 353308097290701 GW-3 732 18 -- -- -- -- 206 250 0 -- -- -- -- -- -- -- -- <.8 352934097271502 GW-4 919 18.1 72.5 28.3 2.02 88.3 355 433 0 .12 52.1 .38 16.7 70 545 2 <.14 16.2 352604097370901 GW-5 681 19.7 -- -- -- -- 283 337 4 -- -- -- -- -- -- -- -- 53.5 352604097370901 GW-5 -- -- 7.34 2.42 .57 159 283 329 8 .04 16.1 .53 10.5 63.9 -- 1.9 <.14 59.9 351914097320201 GW-6 982 19.7 10.6 8.85 1.31 191 312 362 9 .19 125 1.18 11.8 17.6 555 2.3 <.14 36.7 351853097284701 GW-7X 504 18.5 10.5 8.55 1.21 100 258 305 4 .03 6.22 .55 11.7 11.3 307 E2.2 <.04 20.9 351853097284701 GW-7X 377 13.0 20.9 19.8 1.91 43 210 254 9 .04 7.53 .33 13.4 7.20 249 <4 <.04 <.8 351853097284701 GW-7X 404 12.4 13.9 12.3 1.56 63.5 200 E241 E1 .02 7.37 .31 12.8 7.11 239 <4 <.04 E.5 351853097284701 GW-7X 408 12.4 14.9 13.2 1.58 58.8 203 246 0 .02 7.21 .33 12.9 7.19 239 <4 <.04 E.7 351853097284701 GW-7X 405 13.4 14.9 13.3 1.61 60.1 205 249 0 E.02 7.39 .32 13 7.46 242 E4 <.04 E.7 351853097284701 GW-7X 404 10.8 14.6 13.2 1.59 61.4 209 252 1 .02 7.20 .32 12.9 7.24 245 E3.3 <.04 1.2 351853097284701 GW-7X 509 18.7 10.2 8.27 1.15 102 326 378 10 .02 6.12 .57 11.9 11.5 349 E2.4 <.04 21.9 364824097311601 PM-1 1,630 16.9 145 40.7 1.18 140 418 510 0 .68 216 .17 32.9 108 937 <1.6 <.14 9.7 353237098403901 RS-1 758 17.8 105 13.2 1.30 31.4 127 154 0 .20 14.3 .50 21.2 219 483 <1.6 <.14 17.2 352822098233801 RS-2X 634 16.8 64.5 8.04 1.31 60 290 353 0 .03 16.5 .18 32.4 26.2 384 <4 .06 9.2 352822098233801 RS-2X 659 17.1 73.4 9.23 1.42 63.3 281 342 0 .03 17.8 .18 26.8 41.2 402 <4 E.03 9.3 352822098233801 RS-2X 626 11.1 71.6 9.01 1.36 62.6 286 348 0 .04 17.6 .17 30.5 25.5 390 <4 E.03 9.5 352822098233801 RS-2X 672 10.2 67.7 7.34 1.56 82 -- -- -- .02 16.9 .16 29.2 21.7 -- 10.3 .05 6.3 352822098233801 RS-2X -- -- 66.2 7.23 1.56 82.7 -- -- -- .02 17 .17 24.2 21.8 -- <4 .06 6.2

351754098331501 RS-3 328 18.1 41.6 9.76 .90 10.1 157 191 0 .06 5.03 .27 20.9 6.61 191 E1.3 <.14 14.4

343706098451201 TH-1 875 19.7 1.38 .473 .78 200 303 343 13 .19 51 7.44 9.31 57.4 511 3.5 <.14 <.8
Appendix 1 33

Appendix 1. Water-property measurements and chemical-constituent concentrations measured in water from depth-dependent and well-head samples, Oklahoma, 2008. All concentrations are dissolved unless otherwise noted.—Continued[USGS, U.S. Geological Survey; ID, identifier; E, estimated; <, less than; --, not available; mg/L, milligram per liter; μg/L, microgram per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; GW, Garber-Wellington aquifer; PM, Permian-aged undefined aquifer; RS, Rush Springs aquifer; TH, Arbuckle Timbered Hills aquifer; lds, land surface; WH, well-head sample; DMA, dimethylarsinate; MMA, monomethylarsonate; c, sample was contaminated and constituent was not measured]

USGS 

site ID

Well

ID

Arsenic 

dissolved

(μg/L)

Arsenic

total

(μg/L)

Arsenite

(μg/L)

Barium

(μg/L)

Beryllium

(μg/L)

Boron

(μg/L)

Cadmium

(μg/L)

Chromium

(μg/L)

Cobalt

(μg/L)

Copper

(μg/L)

Iron

(μg/L)

Lead

(μg/L)

Lithium

(μg/L)

Manganese

(μg/L)

Molybneum

(μg/L)

Nickel

(μg/L)

Selenium

(μg/L)

355110097240301 GW-1 30 27.8 <0.8 93 <0.02 1,780 0.02 56.8 <0.02 <1.0 <4 0.11 7.2 <0.2 4 <0.12 49.6

355034097145201 GW-2 124 111 <.8 106 E.01 1,600 E.01 8.2 E.02 4.5 E2 .51 9.4 <.2 1.7 .13 3.1

353308097290701 GW-3 4.8 4.7 c 74 <.01 330 <.04 20.2 E.02 2.2 <8 .18 7.2 .4 .9 .66 2

353308097290701 GW-3 4.7 4.6 c 75 <.01 303 <.04 20.4 E.02 1.8 E8 .17 6.4 .4 .8 E.15 2353308097290701 GW-3 1 1 <.6 -- -- -- -- -- -- -- -- -- -- -- -- -- --352934097271502 GW-4 18.5 18.0 1.5 52 <.01 106 <.04 1.6 .05 1.4 <8 1.14 18.4 27.6 1 .27 .52352604097370901 GW-5 -- -- <.6 -- -- -- -- -- -- -- -- -- -- -- -- -- --352604097370901 GW-5 59.9 57.9 <1.2 67 E.01 1,250 <.04 32.8 <.02 2.2 <8 E.07 9.5 .6 6.1 <.20 31.1351914097320201 GW-6 37.7 35.3 <.6 385 .01 181 .05 14.3 <.02 1.7 <8 .17 9.3 E.2 25 <.20 49.4

351853097284701 GW-7X 22.9 21.9 <.8 208 <.02 868 <.02 66.2 E.01 E.83 5 .23 6.6 E.2 3.4 <.12 25.8

351853097284701 GW-7X .49 .60 <.8 316 <.02 236 <.02 44.2 .03 <1.0 E4 E.04 7.3 .7 .4 .50 .8351853097284701 GW-7X .65 .64 <.8 282 <.02 266 <.02 45.9 .02 <1.0 E3 .09 7.9 .4 .4 .32 .93351853097284701 GW-7X .85 .86 <.8 291 <.02 255 <.02 44.4 E.02 <1.0 <4.0 <.06 7.8 .2 .3 .27 .94351853097284701 GW-7X .90 .86 <.8 290 <.02 255 <.02 44.8 .02 <1.0 E3 E.04 7.8 .2 .3 .28 .96351853097284701 GW-7X 1.4 1.4 <.8 284 <.02 277 <.02 45.5 .02 <1.0 5 .09 8.0 .4 .4 .31 1.6351853097284701 GW-7X 23.7 22.9 <.8 202 <.02 927 E.01 66 E.01 1.9 5 .24 6.6 E.2 3.5 .17 25364824097311601 PM-1 10.4 10.1 <.6 97 <.01 115 <.04 .38 .07 5.0 <8 .94 34.2 <.2 .7 .63 8.9353237098403901 RS-1 18.2 17.5 <.6 47 <.01 179 <.04 1.7 .05 1.4 10 .37 14.4 1.0 3 .46 .4352822098233801 RS-2X 10.1 9.7 <.8 162 <.02 35 <.02 2.9 .05 <1.0 <4 .25 17.3 .9 .1 .70 .69352822098233801 RS-2X 10.5 9.9 <.8 148 <.02 36 <.02 2.7 .04 E.56 E3 .32 17.1 <.2 .1 .36 .83352822098233801 RS-2X 10.4 10 <.8 155 <.02 34 <.02 2.5 .04 <1.0 <4 .14 16.3 .5 .1 .51 .82352822098233801 RS-2X 7.1 7.7 <.8 147 <.02 31 <.02 3.8 .05 <1.0 E4 .19 17.6 .8 .1 .69 .55352822098233801 RS-2X 7.1 7.7 <.8 144 <.02 33 E.01 3.9 .06 3.8 7 1.33 18.9 .9 .1 .80 .59351754098331501 RS-3 15.7 15 <.6 154 <.01 24 <.04 .83 .04 E.98 <8 .51 6.2 <.2 .5 .37 .24343706098451201 TH-1 11.6 10.8 10.8 3 .01 1,470 E.03 <.12 <.02 E.62 E7 .13 22.2 .5 14.4 <.20 <.04
34 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells Appendix 1. Water-property measurements and chemical-constituent concentrations measured in water from depth-dependent and well-head samples, Oklahoma, 2008. All concentrations are dissolved unless otherwise noted.—Continued [USGS, U.S. Geological Survey; ID, identifier; E, estimated; <, less than; --, not available; mg/L, milligram per liter; μg/L, microgram per liter; μS/cm, microsiemens per centimeter; °C, degrees Celsius; GW, Garber-Wellington aquifer; PM, Permian-aged undefined aquifer; RS, Rush Springs aquifer; TH, Arbuckle Timbered Hills aquifer; lds, land surface; WH, well-head sample; DMA, dimethylarsinate; MMA, monomethylarsonate; c, sample was contaminated and constituent was not measured] USGS site ID Well ID Silver (μg/L) Strontium (μg/L) Thorium (μg/L) Vanadium (μg/L) Zinc (μg/L) DMA (μg/L) MMA (μg/L) Uranium (μg/L) 355110097240301 GW-1 <0.008 55.6 <0.04 361 E1.7 <0.6 <1.8 58.8 355034097145201 GW-2 <.008 237 <.04 901 4.6 <.6 <1.8 99 353308097290701 GW-3 <.1 1,000 <.04 55.9 3.3 c c 6.63 353308097290701 GW-3 <.1 1,020 <.04 54.2 3.1 c c 6.62 353308097290701 GW-3 -- -- -- -- -- <.6 <1.8 -- 352934097271502 GW-4 <.1 678 <.04 6.5 4.2 <.6 <1.8 1.9 352604097370901 GW-5 -- -- -- -- -- <.6 <1.8 -- 352604097370901 GW-5 <.1 140 <.04 293 E1.6 <1.2 <3.6 30.2 351914097320201 GW-6 <.1 373 <.04 33.7 3.6 <.6 <1.8 51 351853097284701 GW-7X <.008 331 <.04 267 <2 <.6 <1.8 9.79 351853097284701 GW-7X <.008 661 <.04 8.3 <2 <.6 <1.8 4.61 351853097284701 GW-7X <.008 440 <.04 7.9 <2 <.6 <1.8 4.08 351853097284701 GW-7X <.008 466 <.04 10.8 <2 <.6 <1.8 4.16 351853097284701 GW-7X <.008 467 <.04 11.8 <2 <.6 <1.8 4.14 351853097284701 GW-7X <.008 467 <.04 16.5 <2 <.6 <1.8 4.38 351853097284701 GW-7X <.008 317 <.04 302 E1.8 <.6 <1.8 10.1 364824097311601 PM-1 <.1 937 <.04 11.4 12.7 <.6 <1.8 6.28 353237098403901 RS-1 <.1 925 <.04 28.8 3.3 <.6 <1.8 1.31 352822098233801 RS-2X <.008 208 <.04 13.4 3.9 <.6 <1.8 1.16 352822098233801 RS-2X <.008 266 <.04 13.5 2 <.6 <1.8 1.66 352822098233801 RS-2X <.008 203 <.04 12.5 9 <.6 <1.8 1.22 352822098233801 RS-2X <.008 119 <.04 14.3 3.2 <.6 <1.8 .54 352822098233801 RS-2X <.008 121 <.04 14.5 10.4 <.6 <1.8 .54

351754098331501 RS-3 <.1 1,220 <.04 13.6 30.9 <.6 <1.8 .46343706098451201 TH-1 <.1 26.1 <.04 .09 1.8 <.6 <1.8 .83
Appendix 2—Concentrations of Equipment-Blank Sample 

and Analytical Relative Percent Difference for Chemical 

Constituents Measured in Replicate Samples from DepthDependent and Well-Head Samples, Oklahoma, 2008

Appendix 2

Appendix 2 37

Appendix 2. Concentrations of equipment-blank sample and analytical relative percent difference of chemical constituents replicate 

samples for measured in water from depth-dependent and well-head samples, Oklahoma, 2008. Unless noted, all concentrations are 

dissolved.

[USGS, U.S. Geological Survey; <, constituent was not detected or concentration was less than the reporting level; E, estimated; mg/L, milligram per liter; 

μg/L, microgram per liter; na, not analyzed; DMA, dimethylarsinate; MMA, monomethylarsonate; --, not calculated; Relative percent difference values were not 

calculated if one constituent had an estimated concentration or a concentration less than the reporting level; c, sample was contaminated and constituent was not 

measured] 

USGS station

identifier

Well

identifierDate Sample 

type

Calcium,

(mg/L)

Magnesium,

(mg/L)

Potassium,

(mg/L)

Sodium,

(mg/L)

Bromide

(μg/L)

352822098233801 RS-2X Nov. 26, 2008 Sample 67.7 7.34 1.56 82.0 0.02

352822098233801 RS-2X Nov. 26, 2008 Replicate 66.2 7.23 1.56 82.7 .02

Relative percent 

difference 2.2 1.5 0 -.8 0

353308097290701 GW-3 Aug. 7, 2008 Sample 25.0 20.3 1.99 82.3 .05

353308097290701 GW-3 Aug. 7, 2008 Replicate 24.0 19.6 1.97 87.4 .05

Relative percent 

difference 4.1 3.5 1.0 -6.0 0

Equipment blank .04 <.02 <.02 <.12 <.02

Spiked sample from 

GW-3 GW-3 Aug. 7, 2008 na na na na na

USGS station

identifier

Well

identifier

Chloride

(mg/L)

Fluoride

(mg/L)

Silica

(mg/L)

Sulfate

(mg/L)

Aluminum

(μg/L)

Antimony

(μg/L)

Arsenate

arsenic

(μg/L)

Arsenic, 

dissolved

(μg/L )

Arsenic

total

(μg/L)

Arsenite 

arsenic

(μg/L)

Barium

(μg/L)

352822098233801 RS-2X 16.9 0.16 29.2 21.7 10.3 0.05 6.3 7.1 7.7 <0.8 147

352822098233801 RS-2X 17.0 .17 24.2 21.8 <4.0 .06 6.2 7.1 7.7 <.8 144

Relative percent 

difference

-.6 -6.1 19 -.5 -- -18 1.6 0 0 -- 2.1

353308097290701 GW-3 59.2 .30 14.0 35.0 E1.6 <.14 c 4.8 4.7 c 74

353308097290701 GW-3 58.3 .28 13.7 34.5 E.8 <.14 c 4.7 4.6 c 75

Relative percent 

difference

1.5 6.9 2.2 1.4 -- -- -10 2.1 2.2 -12.4 -1.3

Equipment blank <.12 E.07 E.02 <.18 E1.2 <.1 -- <.06 <.6 -- E.2

Spiked sample from 

GW-3

GW-3 na na na na na na 31.5 na na 17.5 na
38 Arsenic-Related Water Quality with Well Depth and Water Quality in Well-Head Samples from Production Wells

Appendix 2. Concentrations of equipment-blank sample and analytical relative percent difference of chemical constituents replicate 

samples for measured in water from depth-dependent and well-head samples, Oklahoma, 2008. Unless noted, all concentrations are 

dissolved.—Continued

[USGS, U.S. Geological Survey; <, constituent was not detected or concentration was less than the reporting level; E, estimated; mg/L, milligram per liter; 

μg/L, microgram per liter; na, not analyzed; DMA, dimethylarsinate; MMA, monomethylarsonate; --, not calculated; Relative percent difference values were not 

calculated if one constituent had an estimated concentration or a concentration less than the reporting level; c, sample was contaminated and constituent was not 

measured] 

USGS station

identifier

Well

 identifier

Beryllium

(μg/L)

Boron

(μg/L)

Cadmium

(μg/L)

Chromium

(μg/L)

Cobalt

(μg/L)

Copper

(μg/L)

Iron

(μg/L)

Lead

(μg/L)

Lithium

(μg/L)

Manganese

(μg/L)

Molybdenum

(μg/L)

Nickel

(μg/L)

352822098233801 RS-2X <0.02 31 <0.02 3.8 0.05 <1.0 E4 0.19 17.6 0.80 0.1 0.69

352822098233801 RS-2X <.02 33 E.01 3.9 .06 3.8 7 1.33 18.9 .9 .1 .80

Relative percent 

difference

-- -6.25 -- -2.6 -18.2 -- -- -150 -7.1 -11.8 0 -14.8

353308097290701 GW-3 <.01 330 <.04 20.2 E.02 2.2 <8 .18 7.2 .4 .9 .66

353308097290701 GW-3 <.01 303 <.04 20.4 E.02 1.8 E8 .17 6.4 .4 .8 E.15

Relative percent 

difference

-- 8.5 -- -1.0 -- 20 -- 5.7 11.8 0 11.8 --

Equipment blank <.008 <6 <.04 <.1 <.02 1.06 <8 .39 <1 <.2 <.2 E.18

Spike sample from 

GW-3

GW-3 na na na na na na na na na na na na

USGS station

identifier

Well

 identifier

Selenium,

(μg/L)

Silica,

(μg/L)

Strontium,

(μg/L)

Thallium,

(μg/L)

Vanadium,

(μg/L)

Zinc,

(μg/L)

DMA,

(μg/L)

MMA,

(μg/L)

Uranium,

(μg/L)

352822098233801 RS-2X 0.55 <0.008 119 <0.04 14.3 3.2 <0.6 <1.8 0.54

352822098233801 RS-2X .59 <.008 121 <.04 14.5 10.4 <.6 <1.8 .54

Relative percent 

difference

-7.0 -- -1.7 -- -1.4 -105.9 -- -- 0

353308097290701 GW-3 2.0 <.1 1,000 <.04 55.9 3.3 c c 6.63

353308097290701 GW-3 2.0 <.1 1,020 <.04 54.2 3.1 c c 6.62

Relative percent 

difference

0 -- -2.0 -- 3.1 6.2 -- -- .1

Equipment blank <.04 E.02 <.8 <.04 <.04 5.3 na na <.02

Spiked sample from 

GW-3

GW-3 na na na na na na 22.1 21.9 na

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