U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2013–5055

Prepared in cooperation with the City of Norman, Oklahoma

Pilot Study of Natural Attenuation of Arsenic in Well Water 

Discharged to the Little River Above Lake Thunderbird, 

Norman, Oklahoma, 2012
Front cover:

Top, Trees on the normal shoreline of Lake Thunderbird near Norman, Oklahoma, showing diminished 

lake levels, February 2013 (photograph by Stanley T. Paxton).

Bottom, U.S. Geological Survey hydrologist Samuel H. Rendon measuring streamflow in the Little River 

near Norman, Oklahoma, May 2012 (photograph by Kevin A. Smith).

Back cover:

Top, Little River near Norman, Oklahoma, May 2012 (photograph by Samuel H. Rendon).

Bottom right, Water-quality sampling at City of Norman well, May 2012 (photograph by Stanley T. 

Paxton).

Bottom left, U.S. Geological Survey hydrologic technician Kevin A. Smith measuring water quality in the 

Little River near Norman, Oklahoma, May 2012 (photograph by Samuel H. Rendon).
Pilot Study of Natural Attenuation of 

Arsenic in Well Water Discharged to 

the Little River Above Lake Thunderbird, 

Norman, Oklahoma, 2012

By William J. Andrews, Jason R. Masoner, Samuel H. Rendon, Kevin A. Smith, 

James R. Greer, and Logan A. Chatterton

Prepared in cooperation with the City of Norman, Oklahoma

Scientific Investigations Report 2013–5055

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

Suggested citation:

Andrews, W.J., Masoner, J.R., Rendon, S.H., Smith, K.A., Greer, J.R., and Chatterton, L.A., 2013, Pilot study of natural 

attenuation of arsenic in well water discharged to the Little River above Lake Thunderbird, Norman, Oklahoma, 2012: 

U.S. Geological Survey Scientific Investigations Report 2013–5055, 31 p., http://pubs.usgs.gov/sir/2013/5055/. 

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iii

Acknowledgments

The authors thank Scott Aynes, Chris Mattingly, and Mark Daniels of the City of Norman for their 

assistance and encouragement during this study.

v

Contents

Acknowledgments .......................................................................................................................................iii

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

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

Overview of Arsenic Chemistry .........................................................................................................2

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

Description of Study Area ...........................................................................................................................3

Methods of Sampling and Analysis ...........................................................................................................3

Sample Collection and Measurement of Well Discharge and Streamflow ...............................3

Sample Analysis ...................................................................................................................................6

Data Analysis ........................................................................................................................................7

Well Construction and Discharge .....................................................................................................7

Streamflow ..........................................................................................................................................10

Attenuation of Arsenic and Selected Trace Elements ..........................................................................11

Well-Water Quality ............................................................................................................................11

Surface-Water Quality ......................................................................................................................11

Streambed Sediments .......................................................................................................................20

Summary .......................................................................................................................................................21

References Cited .........................................................................................................................................21

Appendixes

1. Quality Control and Assurance ................................................................................................27

2. Stream Distances, Moving-Average Stream Velocities, and Arrival Times from 

the Upstream Streamflow-Gaging Station (12th Avenue Northwest) Water-Quality 

Sampling of the Little River near Norman, Oklahoma, May 2012 .......................................29

Figures

1. Map showing location of the central Oklahoma aquifer and groundwaterarsenic concentrations measured in the aquifer, 1977–2004 ...............................................4

2. Map showing study area and sites sampled in or near Norman, Oklahoma, 

April–June 2012 ............................................................................................................................5

3. Graph showing pumping rates for six city wells, Norman, Oklahoma, May 7–18, 

2012 ................................................................................................................................................8

4. Graph showing streamflow measured at a streamflow-gaging station and daily 

precipitation in or near Norman, Oklahoma, April–June 2012 .............................................9

5. Graphs showing concentrations of selected trace elements with time 

discharged at six city wells in Norman, Oklahoma, May 7–18, 2012 .................................12

6. Graph showing arsenic concentration and pH values in water samples 

collected from six city wells in Norman, Oklahoma, May 7–18, 2012 ...............................13

7. Barchart showing dissolved arsenic loads produced by six city wells in Norman, 

Oklahoma, May 7–18, 2012 .......................................................................................................14

8. Graphs showing dissolved arsenic concentrations, loads, and yields, and 

daily precipitation at four sites on the Little River sampled in or near Norman, 

Oklahoma, April–June 2012 ......................................................................................................15
vi

9. Graphs showing dissolved arsenic concentrations with concentrations of 

chromium, selenium, and vanadium in surface-water samples collected at four 

sites on the Little River in or near Norman, Oklahoma, April–June 2012 .........................17

10. Graph showing estimated traveltimes of surface water from the Little River at 

12th Avenue Northwest near Norman, Oklahoma, streamflow-gaging station to 

three downstream streamflow-gaging stations in and near Norman, Okla., 

May 2012 .....................................................................................................................................18

11. Graph showing estimated cumulative arsenic load discharged from six city 

wells and two streamflow-gaging stations on the Little River in or near Norman, 

Oklahoma, April 16–June 1, 2012 .............................................................................................19

12. Boxplots showing distributions of selected trace-element concentrations in 

streambed sediments collected before and after well discharges to the Little 

River at nine sites in or near Norman, Oklahoma, April–June 2012 ..................................20

Tables

1. Groundwater, surface-water, and streambed-sediment sample site locations in 

or near Norman Oklahoma, April–June 2012 ..........................................................................6

2. Physical properties and constituents analyzed in well water, surface water, 

and streambed sediment in or near Norman, Oklahoma, April–June 2012 .......................7

3. Selected characteristics of city wells discharged to the Little River in Norman, 

Oklahoma, May 7–18, 2012 .........................................................................................................8

4. Initial and final amount of discharge and percentage change in discharge rate 

for the six city wells in Norman, Oklahoma, May 7–18, 2012 ................................................9

5. Mean discharges of the six city wells in Norman, Oklahoma, May 7–18, 2012 ................9

6. Selected characteristics of surface-water sites sampled in or near Norman, 

Oklahoma, April–June 2012 ......................................................................................................10

7. Instantaneous stream velocities by date, time, and location for surface-watersampling sites in or near Norman, Oklahoma, May 8–22, 2012 ..........................................10

8. Stream-interval lengths and 2-point or 3-point moving-average stream velocities 

in each interval used to calculate arrival times for surface-water sampling 

dates of the Little River in or near Norman, Oklahoma, May 8–22, 2012 ..........................11

9. Summary statistics of dissolved concentrations of selected trace elements in 

24 samples of water discharged by six city wells in Norman, Oklahoma, 

May 7–18, 2012 ...........................................................................................................................13

10. Dissolved concentrations of selected arsenic types in water samples collected 

from six city wells in Norman, Oklahoma, May 18, 2012 .....................................................14

11. Coefficient of determination (r2) of linear regressions of dissolved concentrations 

of selected trace elements in 30 water samples collected at four sites on the 

Little River in or near Norman, Oklahoma, April–June 2012 .................................................18

12. Sampling dates and times shown with calculated arrival dates and traveltimes 

downstream and corresponding samples from the Little River at 12th Avenue 

Northwest near Norman, Oklahoma, streamflow-gaging station, May 2012 ..................19

13. Two-sided Wilcoxon rank-sum test statistics comparing the trace-element 

content of streambed-sediment samples collected before and after well-water 

discharge to the Little River, April–May 2012, at nine sites in or near Norman, 

Oklahoma ....................................................................................................................................21
vii

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2) 

Volume

gallon (gal) 3.785 liter (L) 

Flow rate

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

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

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

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

SI to Inch/Pound

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2) 247.1 acre

square kilometer (km2) 0.3861 square mile (mi2)

Volume

liter (L) 0.2642 gallon (gal)

Mass

kilogram (kg) 2.205 pound avoirdupois (lb)

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

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

(NAVD 88).

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

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

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

or micrograms per liter (μg/L).

Pilot Study of Natural Attenuation of Arsenic in Well 

Water Discharged to the Little River Above Lake 

Thunderbird, Norman, Oklahoma, 2012

By William J. Andrews, Jason R. Masoner, Samuel H. Rendon, Kevin A. Smith, James R. Greer, and 

Logan A. Chatterton

Abstract

The City of Norman, Oklahoma, wanted to augment its 

water supplies to meet the needs of an increasing population. 

Among the city’s potential water sources are city wells that 

produce water that exceeds the 10 micrograms per liter 

primary drinking-water standard for arsenic. The City of 

Norman was interested in investigating low-cost means 

of using natural attenuation to remove arsenic from well 

water and augment the water supply of Lake Thunderbird, 

the primary water source for the city. The U.S. Geological 

Survey, in cooperation with the City of Norman, conducted 

a preliminary investigation (pilot study) to determine if 

discharge of water from those wells into the Little River over 

a 12-day period would reduce arsenic concentrations through 

natural-attenuation processes. Water in the Little River flows 

into Lake Thunderbird, the principal water source for the city, 

so the discharged well water would improve the water balance 

of that reservoir.

During this pilot study, 150–250 gallons per minute 

from each of six city wells were discharged to the Little 

River over a 12-day period. Water-quality samples were 

collected from the wells during discharge and from the river 

before, during, and after well discharges. Streambed-sediment 

samples were collected at nine sites in the river before and 

after the well-discharge period. Water discharge from the six 

wells added 0.3 kilogram per day of arsenic to the river at the 

nearest downstream streamflow-gaging station. Dissolved 

arsenic concentration in the Little River at the closest 

downstream sampling site from the wells increased from about 

4 micrograms per liter to as much as 24 micrograms per liter. 

Base flow in the river increased by about 1.7 cubic feet per 

second at the nearest downstream streamflow-gaging station. 

Streamflow in the river was two-thirds of that expected from 

the amount of water discharged from the wells because of 

seepage to soils and evapotranspiration of well water along 

drainage ways to the river. Arsenic concentrations at the 

nearest downstream streamflow-gaging station were less than 

arsenic concentrations measured in many of the well-water 

samples during the well-pumping period.

Arsenic concentrations, loads, and yields in the Little 

River generally decreased downstream from the closest 

streamflow-gaging station to the wells by 50 percent or more, 

indicating removal of about 0.25 kilogram or 0.53 pound 

per day of arsenic during base-flow conditions. Measured 

river-water arsenic concentrations near the confluence of the 

Little River with Lake Thunderbird were in compliance with 

the primary drinking-water standard. Arsenic concentrations 

measured at four downstream stations in the Little River 

also were less than established criteria set for protection of 

aquatic biota. After well discharges to the Little River were 

stopped, arsenic concentrations, loads, and yields in the river 

gradually decreased over 14 days to concentrations measured 

prior to the well-water discharges. Cumulative loads of 

arsenic discharged at the wells and the closest and farthest 

downstream streamflow-gaging stations indicated removal of 

about 2.5 kilograms of arsenic as well-water flowed to and 

down the river. Arsenic concentrations in streambed-sediment 

samples collected before and after the well-water discharges 

were not significantly different. Results of this pilot study 

indicate that using natural-attenuation processes to remove 

arsenic from water and supplement city water supplies may 

be a viable, relatively low-cost method for attenuating arsenic 

in well water and for augmenting the water supply of Lake 

Thunderbird.

Introduction

In January 2006, the U.S. Environmental Protection 

Agency (USEPA) reduced the primary drinking-water 

standard for arsenic from 50 to 10 micrograms per liter (μg/L) 

in response to new information about the risk of lung and 

bladder cancers caused by ingestion of arsenic (Morales and 

others, 2000). About 5 percent of public-supply water systems 

in the United States, serving about 11 million people, were 

expected to exceed the new drinking-water standard (Tiemann, 

2001), including several municipal water systems that produce 

water from the Central Oklahoma aquifer (COA). Well water 

produced from parts of the COA has arsenic concentrations 
2 Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird

exceeding the primary drinking-water standard of 10 μg/L 

(Schlottmann and others, 1998; Smith, 2005; Smith and 

others, 2009; Smith and Becker, 2011; U.S. Environmental 

Protection Agency, 2012). Concentrations of arsenic in excess 

of the new primary drinking-water standard have reduced the 

availability of groundwater for several communities, including 

the rapidly growing City of Norman, Okla. (Smith, 2005).

The City of Norman, Okla., idled about one-third of its 

large-capacity wells in the mid-2000s because concentrations 

of arsenic in water from those wells exceeded the primary 

drinking-water standard and the high cost of removing arsenic 

from that water (Smith, 2005). The principal water source for 

Norman is Lake Thunderbird (which supplied 2.96 billion 

gallons in 2010), which is supplemented by water pumped 

from wells (about 1.30 billion gallons in 2010) to supply 

approximately 110,000 residents with water (Bryan Hapke, 

City of Norman, written commun., 2012; Steven Barker, 

Oklahoma Department of Commerce, written commun., 

2011). Increased demand for water by the city and recent 

droughts have lowered the lake level, limiting the amount 

of water that the city water utility can pump from Lake 

Thunderbird. 

The City of Norman was interested in investigating 

low-cost means of using natural attenuation to remove arsenic 

from well water and augment the water supply of Lake 

Thunderbird. One option was to pump water with high arsenic 

concentration from selected city wells into the Little River, a 

major tributary to Lake Thunderbird, with expectations that 

arsenic in the added water would be diluted by river water 

and removed by sorption of aqueous arsenic to streambed 

sediments. If that method was successful, the city could use 

water from several idle wells to augment the supply of water 

in Lake Thunderbird with minimal infrastructure changes. 

Supplementing water in Lake Thunderbird with well-water 

discharges to the Little River, particularly during dry periods, 

would enable the city to withdraw additional water from the 

lake during other times of the year (Chris Mattingly, City of 

Norman, written commun., 2012). Results from this study may 

be relevant to other areas with elevated arsenic concentration 

in groundwater and combined groundwater/surface-water 

public-supply systems, though local conditions are likely to 

affect the extent of natural attenuation of arsenic.

Overview of Arsenic Chemistry

Arsenic is a common element in rocks of the Earth’s 

crust and tends to be associated with iron, manganese, and 

aluminum minerals (Pierce and Moore, 1980; Stollenwerk, 

2003). Arsenic is present in small concentrations in many 

hydrogeologic settings and can occur naturally in groundwater 

in concentrations sufficiently large to be detrimental to 

human health. Arsenic compounds have been used in a 

wide range of industrial products including medicines, 

herbicides, and poultry-feed supplements. Chronic ingestion 

of arsenic in drinking water or other substances can cause 

nausea and vomiting, decreased production of blood cells, 

abnormal heart rhythm, damage to blood vessels, fetal 

deformations, neurological effects, cancers, and death 

(Agency for Toxic Substances and Disease Registry, 2007; 

Eisler, 1988). The most common forms of arsenic in water 

are the inorganic arsenite and arsenate ions and the organic 

forms monomethylarsonate and dimethylarsinate (U.S. 

Environmental Protection Agency, 1985).

Although arsenic exists in nature in the -3, 0, +3, and 

+5 valence states, only arsenic in the +3 or +5 valence states 

(As-III and As-V, respectively) is common in natural waters. 

These valence states form the oxyanion species arsenite 

(H3-xAsO3

-x), and arsenate (H3-xAsO4-x) (Rai and Zachara, 1984; 

Hem, 1985). As-III is the stable form of aqueous arsenic in 

moderately reduced (oxygen depleted) water, and As-V is 

the stable form of arsenic in oxic water. As-III and As-V may 

co-occur in water because conversions of As-III to As-V, or 

As-V to As-III, are slow reactions (Welch and others, 2000). 

Inorganic arsenic compounds generally are more toxic than 

organic arsenic compounds, with the As-III form of arsenic 

being more toxic than the As-V form (Eisler, 1988; Hughes, 

2002).

The arsenate form of arsenic precipitates with or 

adsorbs on hydrous iron oxides, and calcium, sulfur, 

aluminum, and barium minerals (U.S. Environmental 

Protection Agency, 1980; Barringer and others, 2010). 

Adsorption of arsenic on naturally occurring aluminum- and 

iron-oxide coatings on mineral grains in the unsaturated zone 

was measured during groundwater recharge by Izbicki and 

others (2008). Such coatings are most abundant on finegrained sediments. Streambed sediments commonly contain 

oxides and oxyhydroxides of aluminum, iron, barium, and 

other trace elements that may be effective for lowering 

dissolved arsenic concentrations (Barringer and others, 2010). 

Sulfide in reduced streambed or lakebed sediments also can 

cause precipitation and sorption of iron compounds and 

arsenic (Kobayashi and Lee, 1978). Sediments of the Little 

River are expected to contain many of the arsenic-sorbing 

phases of trace metals and other cations. Accordingly, well 

water discharged to the Little River was expected to lose some 

portion of dissolved arsenic as the well water and river water 

contacted sediment.

Purpose and Scope

The purpose of this report is to describe results of a 

pilot study to investigate the potential to use the naturalattenuation capacity of the Little River to lower arsenic 

concentrations in water discharged from six municipal wells 

in Norman, Okla. This report describes analyses of well and 

stream discharges, water quality, and streambed-sediment 

chemistry for samples collected in or near the Little River 

from April through June 2012.
Methods of Sampling and Analysis 3

Description of Study Area

The COA, also known as the Garber-Wellington 

aquifer, consists of a westward-dipping complex mixture 

of discontinuous mudstones, siltstones, and channelized 

sandstones of Permian age (Parkhurst and others, 1996). 

Overlying the Garber Sandstone and Wellington Formation 

is the Hennessey Group, a leaky confining unit that consists 

of mudstones and siltstones (Parkhurst and others, 1996). 

Sandstones in the Garber Sandstone and Wellington 

Formation, which underlie about 3,000 square miles in 

central Oklahoma (fig. 1), provide most of the groundwater 

withdrawn from the COA.

Large dissolved concentrations of arsenic and other trace 

elements in parts of the COA are attributed to mobilization 

from sediment that forms the aquifer in response to 

geochemical conditions. Trace-element concentrations tend to 

increase with depth in the aquifer; larger concentrations also 

are common in confined zones in the upper parts of the aquifer 

(Schlottmann and others, 1998). Increased concentrations of 

trace elements in the aquifer-mineral matrix are associated 

with goethite-cemented sandstone, mudstones, and chemically 

reduced zones (Schlottmann and others, 1998). Generally, 

oxidizing conditions and pH exceeding 8.5 facilitate release 

of arsenic, chromium, and selenium (Schlottmann and others, 

1998). Given the complex stratigraphy and groundwater 

flow paths of the COA, adjoining layers of sandstones 

and siltstones can contain water of substantially different 

composition (Schlottmann and others, 1998; Smith, 2005; 

Smith and Becker, 2011). Thus, adjacent wells in the same 

well field can produce water with arsenic concentrations 

greater or less than the primary drinking-water standard.

The Little River (fig. 2) receives storm runoff and natural 

discharge from the COA near Norman, Okla. The four Little 

River water-quality and nine sediment-sampling sites sampled 

for this report were on the segment of the river between 

streamflow-gaging stations 07229451 (Little River at 12th 

Avenue Northwest near Norman, Okla.) and 07229480 (Little 

River near Franklin, Okla.), a channel distance of about 10.5 

miles (fig. 2). The headwaters of the 230-square-mile Little 

River watershed are north and west of Norman (fig. 1). The 

river, which is ephemeral in the headwaters of the watershed 

(upstream from the uppermost streamflow-gaging station), 

flows eastward and is the main tributary to Lake Thunderbird. 

Elm Creek (fig. 2) is a perennial tributary of the Little River, 

which flows southward from Lake Stanley Draper into the 

Little River about 0.5 mile upstream from streamflow-gaging 

station 07229480. Unconsolidated streambed sediment in the 

channel of the Little River consists of clays, silts, and fine 

sands from erosion of soils weathered from bedrock of the 

COA, which consists of reddish-brown shales, mudstones, and 

sandstones containing carbonate rock fragments, feldspars, 

chlorite, and micas that are dissolving and iron oxides, 

manganese oxides, kaolinite, and quartz that are precipitating 

(Parkhurst and others, 1996). Groundwater in the COA is oxic, 

as indicated by relatively large dissolved concentrations of 

oxygen and nitrate and oxidized forms of arsenic, chromium, 

selenium, vanadium, and uranium (Parkhurst and others, 

1996). The interconnection of groundwater and surface water 

through the streambed sediments in the hyporheic zone (the 

zone of mixing of groundwater and surface water in streambed 

and bank sediments) of this river provides opportunities for 

changes in water chemistry (pH and redox-conditions) and 

granular (mineral) substrates suitable for naturally attenuating 

arsenic concentrations in water. The city wells pumped for 

this pilot study were at distances of 0.1 to 1.0 mile from the 

Little River (fig. 2); discharges from the wells flowed over 

grasslands and through small, grassed drainage ditches to the 

river.

Methods of Sampling and Analysis

Sample Collection and Measurement of Well 

Discharge and Streamflow

During April, 2012, 4 surface-water-quality and 18 

streambed-sediment samples were collected from the Little 

River (at 4 sites and 9 sites, respectively), and 4 instantaneousdischarge measurements were made in the river using 

methods described in Wilde and others (2012) and Rantz and 

others (1982). From May 7 to 18, 2012, well-water samples 

were collected periodically at each well head by attaching a 

Teflon-tube adaptor to standard spigots and transferring the 

water through Teflon tubing to a preservation chamber. The 

preservation chamber was used to limit exposure to airborne 

contamination. Well-water samples were filtered in the field 

using 0.45-micron pore-size disposable filters. Surface-water 

samples were collected from equal-width intervals across the 

stream channel and composited in a churn splitter. Samples 

were decanted from the churn to precleaned sample bottles. 

A peristaltic pump with Teflon tubing was used to filter 

surface-water samples. Water samples collected for cation 

and metal analyses were preserved using premeasured 

purified acids. Stream-discharge measurements were made 

coincident with collection of each water-quality sample. 

Physical properties of water, including temperature, specific 

conductance, dissolved-oxygen concentration, and pH, were 

measured in the field using a YSI 556 multimeter calibrated 

with known standard solutions. At the wells, a flow-through 

cell was used to measure physical properties. At surface-water 

sites, the measurement probe of the multimeter was placed in 

the stream to measure physical properties. Streamflow-gaging 

stations were installed on the Little River at 12th Avenue 

Northwest (07229451, farthest upstream streamflow-gaging 

station) and at the Little River near Franklin (07229480, 

farthest downstream streamflow-gaging station) (fig. 2, 

table 1). Data from those stations were transmitted by satellite 

telemetery into the USGS National Water Information System 

(NWIS) database (U.S. Geological Survey 2012a).
KINGFISHER COUNTY LOGAN COUNTY PAYNE COUNTY LINCO

COUN

CANADIAN COUNTY 

MCCLAIN COUNTY GRADY COUNTY PONTOTOC COUNTY OKLAHOMA COUNTY CLEVELAND COUNTY POTTAWATOMIE COUNTY

Base modified from U.S. Geological Survey digital dataHydrography from Oklahoma Water Resources BoardAlbers Equal-Area Conic projectionNorth American Datum of 1983

M

36°00'35°45'35°30'35°15'35°00'

97°45' 97°30' 97°15' 97°00' 

0 4 8 12 16 20 MILES

0 4 8 12 16 20 KILOMETERS

Central Oklahoma

aquifer

OKLAHOMA

Central Oklahoma aquifer Confined UnconfinedStudy area watershed boundaryCity of Norman boundaryArsenic concentrations, in micrograms per liter Total Nondetection to 10.00 10.01 to 50.00 50.01 to 232.0 Dissolved Nondetection to 10.00 10.01 to 50.00 50.01 to 110.0

EXPLANATION

Elm

Creek

Canadian River Lake Thunderbird

D

Little River

North

Canadian River

Washita

River

Cimarron River

Figure 1. Location of the central Oklahoma aquifer and groundwater-arsenic concentrations measured in the aquifer, 1977–2004.
Figure 2. Study area and sites sampled in or near Norman, Oklahoma, April–June 2012. 

97°29' 97°27' 97°25' 97°23' 97°21' 9

35°19'35°18'35°17'35°16'35°15'35°14'35°13'

Aerial photograph from U.S. Department of Agriculture (2010)Hydrography from Oklahoma Water Resources Board (2012)Study area boundary from U.S. Geological Survey (2012a,b)

07229480

07229451

07229453

07229458

07229460

07229475

07229470 07229463

07229456

W11

W13

W12

W15

W16

W18

Lake Stanley

Draper

Little

River

Elm Creek

Study area boundary (Little River watershed)U.S. Geological Survey streamflow-gaging station, surface-water-quality and streambed-sediment sampling site and  station numberSurface-water-quality and streambed- sediment-sampling site and station numberStreambed-sediment sampling site and  station numberCity well and well numberOklahoma Mesonet station—Norman Mesonet 2 NW 

EXPLANATION

a

W15

07229458

07229456

N

U

07229480

BN

!

0 1 2 KILOMETERS

0 1 

a

U

U U

U

U BN

BN

N

! N

!

!

!!

!
6 Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird

During a 12-day well-discharge period (May 7–18, 

2012), water from six wells (Norman city wells 11, 12, 13, 

15, 16, and 18) was pumped at rates of about 150 to 250 

gallons per minute (gal/min) and entered the Little River 

upstream from the streamflow-gaging station at 12th Avenue 

Northwest (fig. 2, table 1). During the well-discharge period, 

four measurements of instantaneous streamflow were made 

at the four surface-water sampling sites (fig. 2), six to eight 

measurements of well discharges were made with stopwatches and graduated buckets, and well-water-quality and 

surface-water-quality samples were collected. From May 22 

to June 1, 2012, surface-water-quality samples were collected 

and streamflow was measured at each of the four water-quality 

sites to monitor post-well-discharge changes. A second set of 

18 streambed-sediment samples was collected on May 29–31, 

2012.

Sample Analysis

Well-water and surface-water-quality samples were 

analyzed for physical properties and constituent concentrations 

of filtered (dissolved) and unfiltered (total) major ions 

(Fishman and Friedman, 1989; Fishman, 1993), filtered 

trace elements, unfiltered trace elements, (Hoffman and 

others, 1996; Fishman and Friedman, 1989; Garbarino, 1999; 

Garbarino and Struzeski, 1998; Garbarino and Damrau, 2001; 

Garbarino and others, 2002, 2006), and arsenic compounds 

(Garbarino and others, 2006; table 2). Quality-control samples 

were collected and analyzed for quality assurance—the 

quantification of reproducibility and reliability of field data 

(appendix 1).

Streambed-sediment samples were sieved to collect 

sediments less than 2 millimeters in diameter. Those sieved 

Table 1. Groundwater, surface-water, and streambed-sediment sample site locations in or near Norman Oklahoma, April–June 2012.

[USGS, U.S. Geological Survey; no shading for city wells, blue shading for surface-water-quality sampling sites, brown shading for streambed-sediment 

sampling sites]

USGS 

site number Site name Site type Sampling 

dates code1

351538097283401 09N-03W-13 BBA 1, City well 11 City well A

351550097283801 09N-03W-12 CCB 1, City well 13 City well A

351559097283601 09N-03W-11 DAD 1, City well 12 City well A

351643097285601 09N-03W-02 DCA 1, City well 16 City well A

351648097285101 09N-03W-11 AAC 1, City well 15 City well A

351726097290901 09N-03W-02 BAA 1, City well 18 City well A

07229451 Little River at 12th Avenue Northwest near Norman, Okla. Streamflow-gaging station and surfacewater quality sampling siteB

07229456 Little River at 12th Avenue Northeast near Norman, Okla. Surface-water quality sampling site C

07229463 Little River at 36th Avenue Northeast near Norman, Okla. Surface-water quality sampling site C

07229480 Little River near Franklin, Okla. Streamflow-gaging station and surfacewater quality sampling siteB

07229451 Little River at 12th Avenue Northwest near Norman, Okla. Streambed-sediment sampling site D

07229453 Little River at Porter Avenue near Norman, Okla. Streambed-sediment sampling site D

07229456 Little River at 12th Avenue Northeast near Norman, Okla. Streambed-sediment sampling site D

07229458 Little River at 24th Avenue Northeast near Norman, Okla. Streambed-sediment sampling site D

07229460 Little River above Lake Thunderbird near Norman, Okla. Streambed-sediment sampling site D

07229463 Little River at 36th Avenue Northeast near Norman, Okla. Streambed-sediment sampling site D

07229470 Little River above Elm Creek near Norman, Okla. Streambed-sediment sampling site D

07229475 Little River at 60th Avenue Northeast near Franklin, Okla. Streambed-sediment sampling site D

07229480 Little River near Franklin, Okla. Streambed-sediment sampling site D

1

A, May 7, 10, 15, and 18, 2012; B, April 16, 29, 23, and 25, May 8, 14, 17, 22, 25, 29, and June 1, 2012; C, May 8, 14, 17, and 22, 2012; D, April 17–18, and 

May 27–28, 2012. 
Methods of Sampling and Analysis 7

samples were analyzed for trace-element concentrations 

using a Niton XL3t 950 X-ray fluorescence (XRF) analyzer 

(table 2) at the USGS Oklahoma Water Science Center in 

Oklahoma City, Okla. Elemental concentrations determined 

by XRF were measures of the sediment coatings and not the 

elemental concentrations of the entire sediment particles, 

providing elemental concentrations of the reactive surface of 

the particles (Jenkins and others, 1995). XRF analysis was 

done following USEPA Method 6200 (U.S. Environmental 

Protection Agency, 2007). All water-quality samples were 

analyzed by the USGS National Water Quality Laboratory 

(NWQL) in Lakewood, Colorado. Stream-discharge 

measurements were made prior to the collection of surfacewater samples as described in Wilde and others (2012). All 

streamflow, water-quality, and streambed-sediment data 

summarized in this report are available at the USGS NWIS 

Web site at http://waterdata.usgs.gov/ok/nwis.

Data Analysis

Water-quality, streamflow, well-discharge, and 

streambed-sediment data are summarized in tables in this 

report. The data are grouped to represent conditions before, 

during, and after well discharge, and comparisons of selected 

data are made between those periods. Loading of arsenic to 

the river system as well as estimates of evapotranspiration/

seepage loss of well water were done as a preliminary 

quantification of the hydrologic and geochemical properties 

of this system before, during, and after the well-discharge 

period. In addition to summary tables of data, ranges of 

trace-element concentrations measured in streambed-sediment 

samples are shown in boxplots. Time-series graphs are 

shown for concentrations, loads (concentration multiplied 

by streamflow), and yields (load divided by drainage area) 

of selected constituents. Drainage areas for each surfacewater station were determined using U.S. Geological Survey 

(2012c). Graphs of associations of selected constituents 

are shown with regression analysis. The nonparametric 

two-sided Wilcoxon rank-sum test (Wilcoxon, 1945) was 

used to compare locations of distributions of trace-element 

concentrations in paired groups of streambed-sediment 

samples. The TIBCO Spotfire S-plus 8.1 program (TIBCO 

Software, 2008) was used to compute data summaries and 

comparative tests and to create graphs for this report. A 

coefficient of determination describes the fraction of variance 

explained by a regression between variables (Helsel and 

Hirsch, 1992). The p-value of statistical tests denotes the 

probablility of obtaining the computed test statistic when the 

null hypothesis (expected result) of a statistical test is true 

(Helsel and Hirsch, 1995).

Well Construction and Discharge

The six wells discharged for this pilot study were more 

than 600 feet (ft) deep, had perforated-casing zones ranging 

from 295–478 ft long, had diameters from 10.00–10.75 

inches, and are believed to have been drilled in the 1940s 

and 1950s (table 3). With the exceptions of city wells 16 

and 18, pumping rates generally decreased from the start of 

discharge on May 7 to the cessation of well discharge on May 

18, 2012 (fig. 3, table 4). Those decreases in pumping rates 

may have been caused by reduction in available water in the 

aquifer with increasing drawdown. Given that the sum of 

mean discharge of the six wells was 1,169 gal/min (2.60 ft3/s) 

(table 5), and base flow at the upstream streamflow-gaging 

station on the Little River increased by about 1.70 ft3/s 

during the well-discharge period (fig. 4), about 35 percent 

of the water discharged from the wells seeped into soils or 

was evapotranspired prior to reaching the Little River at that 

upstream station. Discharging the six city wells continuously 

for a year, assuming a loss of 35 percent before reaching the 

Little River, would produce an additional flow into the lake 

of about 400 million gallons, representing 13.6 percent of 

the 2.96 billion gallons of water withdrawn from the lake 

every year or 1.76 percent of the 22.9 billion gallons of water 

in storage at the conservation pool elevation of the lake of 

1,039 ft (U.S. Army Corps of Engineers, 2012). 

Table 2. Physical properties and constituents analyzed in well 

water, surface water, and streambed sediment in or near Norman, 

Oklahoma, April–June 2012.

Filtered and 

unfiltered wellwater and surfacewater samplesFiltered surfacewater samples

X-ray fluorescence 

analysis of 

streambed 

sediment

Dissolved oxygen Calcium Aluminum

pH, laboratory Magnesium Antimony

Specific conductance Phosphorus Arsenic

Temperature Arsenate Barium

Aluminum Arsenite Cadmium

Arsenic Dimethylarsinate Cobalt

Barium Monomethylarsonate Copper

Chromium Iron

Iron Lead

Magnesium Manganese

Manganese Molybdenum

Selenium Nickel

Vanadium Selenium

Uranium

Vanadium

Zinc
8 Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird

Table 3. Selected characteristics of city wells discharged to the Little River in Norman, Oklahoma, May 7–18, 2012.

[USGS, U.S. Geological Survey; --, unknown; (Chris Mattingly, City of Norman, written commun., 2013)]

USGS and City of 

Norman well numbers

Well depth

(feet below land surface)

Depth to first 

casing perforation

(feet below land surface)

Well 

casing diameter

(inches)

Date drilled

351538097283401, Well 11 635 312 10.75 November 11, 1944

351559097283601, Well 12 671 376 10.00 December 1944

351550097283801, Well 13 -- -- -- --

351648097285101, Well 15 674 220 10.75 May 1953

351643097285601, Well 16 679 291 10.75 June 1, 1953

351726097290901, Well 18 698 220 10.00 --

7

May 2012

8 9 10 11 12 13 14 15 16 17 18

100

150

175

125

200

250

225

275

Pumping rate, in gallons per minute

EXPLANATION

City well 11

City well 12

City well 13

City well 15

City well 16

City well 18 

Figure 3. Pumping rates for six city wells, Norman, Oklahoma, May 7–18, 2012.
Methods of Sampling and Analysis 9

Table 4. Initial and final amount of discharge and percentage 

change in discharge rate for the six city wells in Norman, 

Oklahoma, May 7–18, 2012.

[USGS, U.S. Geological Survey; gal/min, gallons per minute]

USGS and City 

Norman well numbers

Initial 

discharge 

rate

(gal/min)

Final 

discharge 

rate

(gal/min)

Change in 

discharge 

rate

(percent)

351538097283401, Well 11 178 166 -6.74

351559097283601, Well 12 236 198 -16.1

351550097283801, Well 13 171 142 -17.0

351648097285101, Well 15 266 180 -32.3

351643097285601, Well 16 171 237 38.6

351726097290901, Well 18 195 200 2.56

Mean 203 187 -7.88

Table 5. Mean discharges of the six city wells in Norman, 

Oklahoma, May 7–18, 2012.

[USGS, U.S. Geological Survey; gal/min, gallons per minute; ft3/s, cubic feet 

per second; L/d, liters per day]

USGS and City of 

Norman well numbers

Mean wellwater discharge

(gal/min) (ft3/s) (L/d)

351538097283401, Well 11 171 0.381 933,000

351559097283601, Well 12 213 0.474 1,160,000

351550097283801, Well 13 154 0.343 839,000

351648097285101, Well 15 235 0.523 1,280,000

351643097285601, Well 16 200 0.445 1,090,000

351726097290901, Well 18 196 0.437 1,070,000

Sum of mean well-water 

discharge

1,169 2.60 6,372,000

20

Streamflow, in cubic feet per second

10

1

0.1

Daily precipitation,

in inches

0

0.4

0.8

1.2

2012

Apr. 16 Apr. 23 Apr. 30 May 7 May 14 May 21 May 28 June 4

Well-discharge

period

EXPLANATION

Daily precipitation, in inches, at

 Norman, Oklahoma—Norman

 Mesonet 2 NW station (Oklahoma

 Climatological Survey, 2012)

Streamflow, in cubic feet per second, at

 U.S. Geological Survey streamflow-gaging

 station 07229451 Little River at 12th Avenue

 Northwest near Norman, Oklahoma

Figure 4. Streamflow measured at a streamflow-gaging station and daily precipitation in or near Norman, Oklahoma, April–June 2012.
10 Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird

Streamflow

Streamflow measured at the upstream streamflowgaging station (Little River at 12th Avenue Northwest) from 

April–June 2012, varied from less than 1 to nearly 20 ft3/s, 

with streamflow peaks coinciding with six rainfall events 

having amounts ranging from less than 0.2 inch to nearly 

1.5 inches (fig. 4). Continuous streamflow was available 

from the farthest rated upstream streamflow-gaging station 

whereas synoptic streamflow measurements (measured at 

the time of water-quality sampling) were available at the 

other three streamflow-gaging stations (table 6). Despite 

different amounts of rainfall among those precipitation events, 

streamflow peaks coinciding with rainfall consistently reached 

about 15 ft3/s at the Little River at 12th Avenue Northwest 

streamflow-gaging station following each of those events 

(fig. 4). Base flow generally decreased during the April to 

June period of this study, though base flow increased from 

about 1.0 ft3/s before wells discharged to the river to about 

2.7 ft3/s during well discharge (fig. 4), with the well discharge 

increasing streamflow at that station by about 1.7 ft3/s during 

the discharge period. 

Streamflow-transport times were calculated from the 

farthest upstream streamflow-gaging station (Little River 

at 12th Avenue Northwest) to the farthest downstream 

streamflow-gaging station (Little River near Franklin). The 

distance between the farthest upstream and downstream gages 

was divided into 34 intervals of about 1,640 ft (500 meters; 

appendix 2). Intervals at 0, 16,400, 32,800, and 55,800 ft 

were the distances of downstream surface-water sampling 

sites (Little River at 12th Avenue Northeast, at 36th Avenue 

Northeast, and near Franklin, respectively) from the upstream 

site. Measured instantaneous stream velocities (table 7) were 

used to calculate 2-point and 3-point moving-average stream 

velocities (table 8) that were applied when estimating watertransport times for each 1,640-ft stream increment between 

the farthest upstream and downstream streamflow-gaging 

station (appendix 2). Two-point average calculations were 

done only for the farthest upstream (12th Avenue Northwest) 

and downstream (Little River Near Franklin) sampling sites, 

whereas 3-point average calculations were done for sampling 

sites in between the farthest upstream and downstream sites 

(12th Avenue Northeast and 36th Avenue Northeast).

Table 6. Selected characteristics of surface-water sites sampled in or near Norman, Oklahoma, April–June 2012.

[USGS, U.S. Geological Survey]

USGS site 

number Site name and gaging status

Latitude and 

longitude 

(decimal degrees)1, 2

Upstream 

contributing area

(square miles)1

07229451 Little River at 12th Avenue Northwest near Norman, Okla. (gaged, streamflow rated) 35.268N, 97.459W 18.0

07229456 Little River at 12th Avenue Northeast near Norman, Okla. (ungaged) 35.274N, 97.424W 41.3

07229463 Little River at 36th Avenue Northeast near Norman, Okla. (ungaged) 35.279N, 97.388W 47.9

07229480 Little River near Franklin, Okla. (gaged, streamflow unrated) 35.276N, 97.340W 88.8

1

U.S. Geological Survey (2012b, c). 

2

Latitude and longitude were computed using the North American Datum of 1983.

Table 7. Instantaneous stream velocities by date, time, and location for surface-water-sampling sites in or near Norman, Oklahoma, 

May 8–22, 2012.

[Stream velocities, in feet per hour]

Sampling date 

and time

Farthest upstream 

streamflow-gaging station

12th Avenue Northwest 

near Norman, Okla.

(0)1

Farthest downstream 

streamflow-gaging station

Little River Near 

Franklin, Okla.

(55,800)1

12th Avenue Northeast 

near Norman, Okla.

(16,400)1

36th Avenue Northeast 

near Norman, Okla.

(32,800)1

5/8/12 17:30 684 576 1,440 252

5/14/12 9:30 1,872 648 360 540

5/17/12 16:00 720 792 252 360

5/22/12 12:30 1,513 900 468 1,224

1

Values in parenthesis refer to distance in feet from the upstream streamflow-gaging station.
Attenuation of Arsenic and Selected Trace Elements 11

Attenuation of Arsenic and Selected 

Trace Elements

Well-Water Quality

Four water samples collected from each of the wells 

in May, 2012, contained a median dissolved arsenic 

concentration of 42.1 μg/L. All of the well-water samples 

contained dissolved arsenic concentration greater than the 

primary drinking-water standard of 10 μg/L (fig. 5, table 9). 

Concentrations of the other analyzed trace elements were 

less than primary or secondary drinking-water standards 

(aluminum, 50 to 200 μg/L; barium, 2,000 μg/L; chromium, 

100 μg/L; manganese, 50 mg/L; and selenium, 50 μg/L; 

U.S. Environmental Protection Agency, 2012; table 9). 

Concentrations of aluminum, arsenic, barium, chromium, 

manganese, selenium, and vanadium varied during the 

well-discharge period (fig. 5). Some of the most substantial 

changes in trace-element concentrations during the welldischarge period were increases of about 7 μg/L in aluminum 

concentration in water from city well 11, and increases 

of more than 100 μg/L of barium and about 10 μg/L of 

chromium in water from city well 13, decrease of manganese 

concentration of about 2 mg/L with subsequent increase of 

about 1 mg/L in water from city well 12, and increase in 

manganese concentration of about 2 mg/L in water from city 

well 16 (fig. 5). Arsenic concentration generally decreased 

slightly in water discharged from most of the city wells during 

the discharge period (fig. 5), which may have been caused by 

gradual flushing of more readily soluble arsenic on aquiferparticle rims in the COA surrounding the wells. Similar to 

results described in Schlottmann and others (1998), well water 

with larger (more alkaline) values of pH contained greater 

arsenic concentrations, as shown in some samples from wells 

with pH measured and arsenic concentration determined 

(fig. 6).

Concentrations of arsenic compounds, including arsenite, 

arsenate, monomethylarsonate, and dimethylarsinate, were 

analyzed in well-water samples collected on May 18, 2012, 

from each of the six city wells. Arsenate was the only form of 

detectable arsenic in those six well-water samples (table 10).

With mean discharges from the six city wells ranging 

from 0.343 to 0.523 ft3/s (table 5), the total load of arsenic in 

pumped well water decreased from 0.314 kilograms per day 

(kg/d) on May 7, 2012, to 0.255 kg/d on May 18, 2012. Those 

decreases coincided with decreases in well-water discharges 

and arsenic concentrations (figs. 3, 5, and 7). 

Surface-Water Quality

The dissolved arsenic concentration of water samples 

collected in the Little River increased at the four sampled 

surface-water sites after discharge of wells to the Little River 

began on May 7 (fig. 8). The greatest increase in arsenic 

concentration was measured at the streamflow-gaging station 

nearest to the discharging wells (Little River at 12th Avenue 

Northwest) with the arsenic concentrations in surface water 

being less than the arsenic concentrations in the pumped well 

water from most of the wells (figs. 5 and 8). As the water 

flowed downstream, the dissolved arsenic concentration 

decreased by 50 percent or more in the river with none of the 

downstream water samples having arsenic concentrations 

exceeding the primary drinking-water standard of 10 μg/L 

(fig. 8). In addition, the concentrations of arsenic in wellwater and surface-water samples collected for the study 

did not exceed the National Recommended Water Quality 

Criteria of 340 μg/L (Criteria Maximum Concentration) or 

150 μg/L (Criteria Continuous Concentration) set to protect 

aquatic life (U.S. Environmental Protection Agency, 2006). 

Eisler (1988), in a review of arsenic toxicity data, concluded 

that a freshwater quality criteria of 40 μg/L would be more 

protective of most forms of aquatic life. The largest arsenic 

concentration measured in surface water was less than 

30 μg/L, indicating that no known toxic risk to aquatic biota 

would be expected from these well discharges according to 

Eisler (1988) and U.S. Environmental Protection Agency 

(2006) (fig. 8).

Table 8. Stream-interval lengths and 2-point or 3-point movingaverage stream velocities in each interval used to calculate 

arrival times for surface-water sampling dates of the Little River in 

or near Norman, Oklahoma, May 8–22, 2012.

[Units are in feet per hour, bold font signifies 2-point moving average of 

stream velocity, regular font signifies 3-point moving-average of stream 

velocity]

Stream interval, 

in distance from 

input of well 

discharge

(feet)

Surface-water sampling dates

5/8/2012 5/14/2012 5/17/2012 5/22/2012

0 to 8,200 630 1,260 756 1,210

9,840 to 24,600 900 960 588 960

26,200 to 44,300 756 516 468 864

45,900 to 55,800 846 450 306 846
12 Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird Dissolved barium concentration, in micrograms per liter Dissolved aluminum concentration, in micrograms per liter Dissolved vanadium concentration, in micrograms per liter Dissolved manganese concentration, in micrograms per liter Dissolved chromium concentration, in micrograms per liter Dissolved arsenic concentration, in micrograms per liter Dissolved selenium concentration, in micrograms per liter

0

100

200

320

300

0

5

10

15

20

22.5

0

50

100

150

200

250

300

325

0.0

0.5

1.0

1.5

2.0

2.5

10

15

20

25

27.5

0

20

40

60

80

100

0

10

20

30

35

7 8 9 10 11 12 13 14 15 16 17 18

May 2012

7 8 9 10 11 12 13 14 15 16 17 18

May 2012

Primary drinking-water standard

EXPLANATION

City well 11

City well 12

City well 13

City well 15

City well 16

City well 18 

Figure 5. Concentrations of selected trace elements with time discharged at six city wells in Norman, Oklahoma, May 7–18, 2012.
Attenuation of Arsenic and Selected Trace Elements 13

Table 9. Summary statistics of dissolved concentrations of selected trace elements in 24 samples of water discharged by six city wells 

in Norman, Oklahoma, May 7–18, 2012.

[μg/L, micrograms per liter; <, less than]

Trace element Range of data

Percentage of 

nondetectable data 

of 24 samples

Mean 

concentration

(μg/L)

Median 

concentration

(μg/L)

Aluminum 2.80–21.1 0.00 7.57 5.70

Arsenic 12.7–94.1 0.00 46.8 42.1

Barium 58.6–313 0.00 119 102

Chromium 13.3–27.1 0.00 20.9 20.6

Iron <3.20–8.80 45.8 3.38 3.25

Manganese <0.160–2.56 4.17 0.683 0.530

Selenium 3.80–30.5 0.00 15.4 14.0

Vanadium 48.8–298 0.00 167 147

1

Nondetectable data converted to one-half of reporting limit to compute mean value.

8.4 8.6 8.8 9.0 9.2

pH, in standard units

9.3

0

20

40

60

80

100

Arsenic concentration, in micrograms per liter

EXPLANATION

City well 11

City well 12

City well 13

City well 15

City well 16

City well 18 

Figure 6. Arsenic concentration and pH values in water samples collected from six city wells in Norman, Oklahoma, May 7–18, 2012.
14 Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird

Decreased arsenic concentration downstream from the 

area of well-water discharge to the river likely was caused 

by a combination of natural-attenuation processes. These 

processes include dilution from water added to the river by 

base-flow seepage along the streambank and inflows from 

tributaries, sorption of dissolved arsenic to mineral surfaces, 

and seepage of surface water into the hyporheic zone in 

streambed and streambank sediments. Arsenic concentration 

in water in the river generally decreased after the discharge of 

well water ceased. An exception was the farthest downstream 

station (Little River near Franklin, Okla.), where arsenic 

concentration in the river continued to increase for 10 days 

after the well-water discharge ceased (fig. 8). The later peak of 

arsenic concentration may have been caused by: (1) additional 

time needed for water to flow downstream, (2) outseepage of 

high-arsenic river water that had seeped into the hyporheic 

zone, and (3) desorption of arsenic from mineral phases that 

equilibrated with higher-arsenic river water during the wellwater discharge with subsequent release of arsenic to lowerarsenic river water after discharge. Arsenic concentration 

in the Little River returned to near background (conditions 

prior to well-water discharge) at the farthest upstream and 

downstream surface-water sampling sites by June 1, 2012, 14 

days after the well-water discharges to the river had ceased 

(fig. 8). Although arsenic concentrations decreased in the 

downstream direction, increasing streamflow at downstream 

stations tended to make arsenic loads relatively similar at the 

three downstream stations during and immediately following 

the well-discharge period (fig. 8).

Discharge of arsenic from the wells and the smaller 

upstream basin area of the farthest upstream station (Little 

River at 12th Avenue Northwest) caused the yield of arsenic to 

be considerably larger at that station than for the downstream 

stations (fig. 8). Arsenic yields decreased more than 50 percent 

in the downstream direction.

Precipitation falling during the sampling period also 

affected transport of arsenic in the river (fig. 8). The rainfall 

event of about 1–2 inches near the end of May, in particular, 

may have caused the increases in arsenic loads and yields in 

the Little River by increasing overland flow, inflows from 

tributaries, and resuspension of arsenic in streambed sediments 

(figs. 4 and 8).

Table 10. Dissolved concentrations of selected arsenic types in water samples collected from six city wells in Norman, Oklahoma, 

May 18, 2012.

[USGS, U.S. Geological Survey; all concentrations in micrograms per liter; <, less than]

USGS and City of 

Norman well numbers Arsenite Arsenate Monomethylarsonate Dimethylarsinate

351538097283401, Well 11 <2.00 56.0 <16.0 <3.00

351559097283601, Well 12 <2.00 93.5 <16.0 <3.00

351550097283801, Well 13 <0.40 12.5 <3.20 <0.60

351648097285101, Well 15 <0.40 38.2 <3.20 <0.60

351643097285601, Well 16 <0.40 28.7 <3.20 <0.60

351726097290901, Well 18 <0.40 13.8 <3.20 <0.60

May 2012

7 10 15 18

0

0.1

0.2

0.3

0.35

Dissolved arsenic load, in kilograms per day

EXPLANATION

City well 11

City well 12

City well 13

City well 15

City well 16

City well 18 

Figure 7. Dissolved arsenic loads produced by six city wells in 

Norman, Oklahoma, May 7–18, 2012.
Attenuation of Arsenic and Selected Trace Elements 15

April May

16 23 30 7 14 21 28 1

June

2012

Daily precipitation,

in inches

0

0.4

0.8

1.2

30

10

5

1

0.4

0.1

0.01

0.003

0.001

0.004

0.0001

0.00006

Dissolved arsenic concentration,

in micrograms per liter

Dissolved arsenic load, in kilograms per day Dissolved arsenic yield, in kilograms

per day per square kilometer

Well-discharge

period

Well-discharge

period

Well-discharge

period

Dissolved arsenic concentration, load, or yield,

 by U.S. Geological Survey (USGS) sampling 

 site (USGS station number)

 Little River at 12th Avenue Northwest near 

 Norman, Oklahoma (7229451)

EXPLANATION

 Little River at 12th Avenue Northeast near 

 Norman, Oklahoma (7229456)

 Little River at 36th Avenue Northeast near 

 Norman, Oklahoma (07229463)

 Little River near Franklin, Oklahoma (07229480)

Daily precipitation, in inches, at

 Norman, Oklahoma—Norman

 Mesonet 2 NW station

 (Oklahoma Climatological

 Survey, 2012)

Figure 8. Dissolved arsenic concentrations, loads, and yields, and daily precipitation at four sites on the Little River sampled in or near 

Norman, Oklahoma, April–June 2012.
16 Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird

Comparing dissolved arsenic concentration to streamflow 

in the Little River during the study period indicated generally 

greater dissolved arsenic concentration during well-water 

discharge, and slightly greater concentrations of arsenic after 

well-water discharge than in the period before well-water 

discharge (figs. 4 and 8). Summarizing the effects of wellwater discharge to water quality in the Little River:

1. The smallest dissolved arsenic concentrations were 

measured before well-water discharge began;

2. The largest arsenic concentrations were measured in the 

river at the end of well-water discharge;

3. Arsenic concentration decreased in the downstream 

direction, indicating the effects of dilution, sorption, and 

other natural-attenuation processes; and

4. Dissolved arsenic concentration measured in the Little 

River gradually decreased to concentrations similar to 

those measured in the period before well-water discharge 

over a 14-day period after well-water discharge to the 

river ceased. 

Concentrations of other measured trace elements 

with substantial correlations with arsenic in water samples 

collected from the Little River included chromium, selenium, 

and vanadium (fig. 9, table 11). These trace elements have 

chemical properties similar to those of arsenic and are 

expected to occur as dissolved oxyanions in the COA. 

Schlottmann and others (1998) described coincident increases 

of concentrations of arsenic, chromium, and selenium in 

water with depth in parts of the COA. In addition to concerns 

about elevated concentration of arsenic in well water, concern 

has been expressed about the concentration of hexavalent 

chromium (Cr+6) in city drinking water (Environmental 

Working Group, 2010; City of Norman, 2012). Filtered 

(dissolved) and unfiltered (total) concentrations of chromium 

were analyzed in well water and surface water. Although Cr+6

concentration was not analyzed in those samples, given the 

oxic conditions of this aquifer, much of the chromium in water 

may be in the Cr+6 form.

To further investigate the decrease in arsenic 

concentration in the Little River through natural attenuation 

processes, streamflow transport times from the farthest 

upstream streamflow-gaging station (Little River at 12th 

Avenue Northwest near Norman, Okla.) to the farthest 

downstream streamflow-gaging station (Little River near 

Franklin, Okla.) were estimated from moving averages of 

water velocities measured at the four surface-water sites 

during sampling from May 8 to May 22, 2012 (fig. 10, table 8, 

appendix 2). Water traveltime between the two streamflowgaging stations on May 8, 2012 was approximately 2.9 days 

(fig. 10, table 12). On May 14 and 17, 2012, which were in the 

middle of the well-water-discharge period, traveltimes were 

somewhat greater at about 3.6 days and 4.9 days, respectively 

(fig. 10, table 12). Increased traveltimes may have been caused 

by backwater effects or pooling of water at downstream gages 

from rain events or the pumping of groundwater discharged 

into Little River. On May 22, 2012, 3 days after discharge of 

well water to the Little River had ceased, the water traveltime 

was about 2.5 days (fig. 10, table 12), similar to traveltime on 

May 8.

Arsenic load was estimated in approximately the same 

parcel of water as it flowed from the farthest upstream 

streamflow-gaging station to the other three downstream 

streamflow-gaging stations, though sampling was not 

specifically designed to measure the same parcels of water 

with flow downstream, and there is uncertainty regarding 

traveltime of water downstream, given limited measurement of 

streamflow velocities. Only 3 out of 13 downstream samples 

had calculated arrival times of water that could be paired 

within several hours of the estimated arrival times (based on 

moving average of flow velocities) to an upstream sample 

(table 12). Water sampled at the farthest upstream streamflowgaging station on May 14 at 09:30 was estimated to arrive at 

the farthest downstream station on May 18 at 00:45 and was 

paired to a sample collected on May 17 at 08:30. The arsenic 

load from the water sample collected at the farthest upstream 

station on May 14 was 0.135 kg/d, whereas the load from the 

paired sample at the farthest downstream station was 0.059 

kg/d, a loss of 0.076 kg/d or -56.3 percent (fig. 8). Water 

sampled at the farthest upstream streamflow-gaging station 

on May 17 at 16:00 was estimated to arrive at the farthest 

downstream station on May 22 at 14:00 and was paired to 

a sample collected at that downstream station on May 22 

at 09:00. The arsenic load from the sample at the farthest 

upstream station on May 17 was 0.147 kg/d, whereas the load 

from the sample at the farthest downstream station was 0.216 

kg/d, an increase of 0.069 kg/d or 46.9 percent (fig. 8). Water 

sampled at the farthest upstream streamflow-gaging station 

on May 22 at 12:30 was estimated to arrive at the farthest 

downstream station on May 25 at 00:45 and was paired to 

a sample collected at the downstream station on May 25 at 

08:00. The arsenic load of the upstream sample collected on 

May 22 was 0.152 kg/d, whereas the load at the downstream 

station was 0.056 kg/d, a decrease of 0.096 kg/d or -63.2 

percent (fig. 8). The total amount of arsenic removed from 

the well water as it flowed to the farthest downstream gaging 

station after well discharge was about 0.24 kg or 0.53 pound 

per day during base-flow conditions (figs. 7 and 8).

The increase in dissolved arsenic load in the downstream 

direction of the May 17 and May 22 paired samples may be 

related to the rainfall event of about one-half inch on May 20 

and 21, 2012 (figs. 4 and 8). That rainfall, in addition to the 

well water discharged to the Little River, may have produced 

additional runoff containing arsenic (fig. 11). No rainfall was 

recorded during flow of the paired samples collected from 

May 14 through May 18, 2012, and May 22 through May 25, 

2012.
Attenuation of Arsenic and Selected Trace Elements 17

0 5 10 15 20 25

Dissolved arsenic concentration, in micrograms per liter

Dissolved chromium concentration, in micrograms per liter Dissolved selenium concentration, in micrograms per liter Dissolved vanadium concentration, in micrograms per liter

0

2

4

6

8

0

2

4

6

8

10

0

20

40

60

80

Figure 9. Dissolved arsenic concentrations with concentrations of chromium, selenium, and vanadium in surface-water samples 

collected at four sites on the Little River in or near Norman, Oklahoma, April–June 2012. 
18 Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird

Table 11. Coefficient of determination (r2) of linear regressions of dissolved concentrations of selected trace elements in 30 water 

samples collected at four sites1 on the Little River in or near Norman, Oklahoma, April–June 2012.

[Values of one-half of reporting limits substituted for nondetectable values; p-value in parentheses, p-value greater than 0.05 indicates no correlation] 

Trace 

element Aluminum Arsenic Barium Chromium Iron Manganese Phosphorus Selenium Vanadium

Aluminum 1.00

Arsenic 0.07

(0.161)

1.00

Barium 0.25

 (0.005)

0.25

(0.005)

1.00

Chromium 0.05

(0.255)

0.87

(<0.001)

0.19

(0.017)

1.00

Iron 0.50

 (<0.001)

0.06

(0.206)

0.37

(<0.001)

0.04 

(0.267)

1.00

Manganese 0.20

(0.013)

0.04

(0.270)

0.02

(0.430)

0.04 

(0.284)

0.09

(0.103)

1.00

Phosphorus 0.17

(0.023)

0.06

(0.179)

0.12 

(0.063)

0.10 

(0.091)

0.38 

(<0.001)

0.04

(0.271)

1.00

Selenium 0.05

(0.216)

0.97

(<0.001)

0.29

(0.002)

0.88 

(<0.001)

0.05 

(0.216)

0.04 

(0.315)

0.07 

(0.169)

1.00

Vanadium 0.08

(0.125)

0.99

(<0.001)

0.24

(0.005)

0.87

(<0.001)

0.06

<0.183)

0.03 

(0.349)

0.05 

(0.236)

0.96

(<0.001)

1.00

1

Little River at 12th Avenue Northwest near Norman, Oklahoma, at 12th Avenue Northeast near Norman, Okla., at 36th Avenue Northeast near Norman, 

Okla., and near Franklin, Okla.

Distance downstream from the Little River at 12th Avenue Northwest near Norman, Oklahoma,

streamflow-gaging station, in thousands of feet

0 5 10 15 20 25 30 35 40 45 50 55

Estimated date of water travel downstream from the Little River at 12th

Avenue Northwest near Norman, Oklahoma, streamflow-gaging station

in May 2012

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

May 8

May 14

May 17

May 22

EXPLANATION

U.S. Geological Survey (USGS) 

 streamflow-gaging station

 name (USGS station number)

 Little River at 12th Avenue

 Northeast near Norman, 

 Oklahoma (7229456)

 Little River at 36th Avenue

 Northeast near Norman,

 Oklahoma (07229463)

 Little River near Franklin, 

 Oklahoma (07229480)

Figure 10. Estimated traveltimes of surface water from the Little River at 12th Avenue Northwest near Norman, Oklahoma, streamflowgaging station to three downstream streamflow-gaging stations in and near Norman, Okla., May 2012. 
Attenuation of Arsenic and Selected Trace Elements 19

Table 12. Sampling dates and times shown with calculated arrival dates and traveltimes downstream and corresponding samples from 

the Little River at 12th Avenue Northwest near Norman, Oklahoma, streamflow-gaging station, May 2012.

[Yellow, green, and blue shades are estimated to be the same mass of water transported downstream; na, not applicable]

Little River streamflow-gaging station

12th Avenue 

Northwest near 

Norman, Okla.

12th Avenue Northeast 

near Norman, Okla.

36th Avenue Northeast 

near Norman, Okla. Near Franklin, Okla.

Sample date 

and time

Sample date 

and time

Estimated 

arrival from 

12th Avenue 

Northwest

Sample date 

and time

Arrival from 

12th Avenue 

Northwest

Sample date 

and time

Estimated 

arrival from 

12th Avenue 

Northwest

5/8/2012 17:30 5/8/2012 15:30 5/9/2012 15:00 5/8/2012 11:30 5/10/2012 11:30 5/8/2012 8:30 5/11/2012 16:00

5/14/2012 9:30 5/14/2012 13:00 5/15/2012 1:00 5/14/2012 15:00 5/16/2012 1:00 5/14/2012 17:00 5/18/2012 0:45

5/17/2012 16:00 5/17/2012 14:00 5/18/2012 17:00 5/17/2012 10:30 5/20/2012 0:15 5/17/2012 8:30 5/22/2012 14:00

5/22/2012 12:30 5/22/2012 16:00 5/23/2012 4:00 5/22/2012 14:00 5/23/2012 22:00 5/22/2012 9:00 5/25/2012 0:45

5/25/2012 10:30 no sample na no sample na 5/25/2012 8:00 na

Apr. 16 Apr. 23 Apr. 30 May 7 May 14 May 21 May 28

2012

Cumulative arsenic load, in kilograms

0

1

2

3

4

4.5

Six city wells

Little River at 12th Avenue Northwest

 near Norman, Oklahoma

 streamflow-gaging station

 (upstream)

Little River near Franklin, Oklahoma

 streamflow-gaging station

 (downstream)

EXPLANATION

Figure 11. Estimated cumulative arsenic load discharged from six city wells and two streamflow-gaging stations on the Little River in 

or near Norman, Oklahoma, April 16–June 1, 2012.
20 Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird

The cumulative load of dissolved arsenic added by 

the discharge of well water was greater than the change 

of cumulative dissolved arsenic load at the downstream 

streamflow-gaging stations during the period of well discharge 

(fig. 11). Cumulative arsenic loading at the upstream 

streamflow-gaging station, during that 12-day period was 

about 1 kg, compared to 3.5 kg discharged at the wells 

(fig. 11). Allowing for about 2.5 days of lag time between well 

discharge and water arriving at the downstream streamflowgaging station, about 1.5 kg of dissolved arsenic load flowed 

by that station coinciding with the well-water-discharge 

period (fig. 11). Inflow of surface water from Elm Creek and 

groundwater seepage comprising base flow between these two 

stations may have been the source of the additional 0.5 kg of 

dissolved arsenic load flowing past the downstream station in 

the periods coinciding with well-water discharge.

Streambed Sediments

Concentrations of selected trace elements in streambedsediment samples collected at nine sites on the Little River did 

not change significantly from before well discharges began 

to after well discharges ceased (fig. 12, table 13). Such lack 

of change indicates that relatively small amounts of arsenic 

and other selected trace elements were sorbed to streambed 

sediments in the Little River during the study period. This 

lack of change is to be expected as ambient streambed 

sediment arsenic content was about 2,000 times the arsenic 

concentration in water, as arsenic concentration in water 

is expressed in micrograms per liter (or parts per billion) 

and arsenic concentration in sediment is expressed in 

milligrams per liter (or parts per million) (figs. 8 and 12). 

In addition, some of the streambed-sediments containing 

sorbed arsenic and other trace metals may have been 

resuspended and transported farther downstream during 

several rainfall events that occurred during the sampling 

period. Additional sampling of sediments and water flowing 

into the lake during a longer discharge period would be 

useful for developing better understanding of the fate and 

transport of arsenic and related trace metals in this alluvial 

and lacustrine system.

Trace element and collection time relative to well discharges 

Arsenic Chromium Barium Iron Manganese

Before

After

Before

After

Before

After

Before

After

Before

After

Trace element concentration, in milligrams per kilogram

10,000

100,000

1,000

100

10

1

0.1

9 9 9 9 9 9 9 9 9 9

9

EXPLANATION 

 Schematic boxplot

 Number of sites

 Upper detached

 Upper adjacent

 75th percentile

 Median

 25th percentile

 Lower adjacent

 Lower detached

Figure 12. Distributions of selected trace-element concentrations in streambed sediments collected before and after well discharges 

to the Little River at nine sites in or near Norman, Oklahoma, April–June 2012. 
References Cited 21

Summary

The City of Norman, Oklahoma, wanted to augment 

its water supplies to meet water demands of an increasing 

population. The city stopped using water from wells that 

produced water exceeding the 10 micrograms per liter primary 

drinking-water standard for arsenic in the mid-2000s, leaving 

Lake Thunderbird as the primary water supply for the city. 

The U.S. Geological Survey, in cooperation with the City 

of Norman, Okla., conducted a pilot study to investigate if 

discharging well water with elevated arsenic concentration 

into the Little River, the major tributary to Lake Thunderbird, 

would lower dissolved arsenic concentrations through naturalattenuation processes that may occur in the stream channel.

Pumping of about 150–250 gallons per minute from each 

of six city wells discharged a total of about 0.3 kilograms per 

day of arsenic, increased base flow at the farthest upstream 

streamflow-gaging station nearest to the wells by 1.7 cubic 

feet per second, and increased dissolved arsenic concentration 

in the Little River by as much as 24 micrograms per liter. 

Approximately two-thirds of the water discharged from 

the wells reached the farthest upstream streamflow-gaging 

station nearest to the wells, with arsenic concentrations at that 

station being less than the arsenic concentrations measured 

in many well-water samples. Arsenic concentrations, loads, 

and yields continued to generally decrease in the downstream 

direction by 50 percent or more, indicating removal of about 

0.25 kilogram per day of arsenic during base-flow conditions. 

At the farthest upstream streamflow-gaging station, the 

arsenic concentration exceeded the primary drinking-water 

standard of 10 micrograms per liter during well discharge. At 

downstream streamflow-gaging stations, arsenic concentration 

was less than the primary drinking-water standard. All of the 

surface-water samples had arsenic concentrations below the 

thresholds expected to have adverse effects on aquatic biota. 

After well-water discharges to the Little River were stopped, 

arsenic concentrations, loads, and yields gradually decreased 

over a period of about 14 days to values measured prior to the 

well-water discharge. Cumulative loads of arsenic discharged 

from the wells and the farthest upstream streamflow-gaging 

station indicated removal of about 2.5 kilograms of the 3.5 

kilograms of discharged dissolved arsenic between the wells 

and the farthest upstream streamflow-gaging station at 12th 

Avenue Northwest. About 1.5 kilograms of dissolved arsenic 

flowed past the farthest downstream streamflow-gaging station 

near Franklin, Okla., during the period corresponding to wellwater discharge. The extra 0.5 kilogram of arsenic loading 

compared to the station at 12th Avenue Northwest probably 

was related to inflow of surface water from Elm Creek and 

seepage of groundwater along the stream channel between 

those two stations. Streambed-sediment samples collected 

before and after the well-water discharges did not have 

significant increases in arsenic concentration. Some of the 

streambed sediments containing sorbed arsenic may have been 

resuspended and transported to the lake during the increased 

streamflows following several rainfall events that occurred 

during the sampling period.

Results of this pilot study indicate that using naturalattenuation processes to remove arsenic from well water and 

supplement city water supplies may be a viable, relatively 

low-cost treatment method. Longer-term testing of this method 

would be needed to better evaluate potential accumulation 

of arsenic and other trace metals in streambed sediments and 

the ultimate capacity of this fluvial system for attenuating 

elevated arsenic concentration in pumped groundwater. 

Results from this study may be transferable to other areas 

with elevated arsenic concentrations in groundwater and 

combined groundwater/surface-water public-supply systems, 

though local conditions are likely to affect the extent of natural 

attenuation of arsenic.

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Chromium 83 0.546

Barium 93 0.863

Iron -0.3978 0.691

Manganese 90 0.730
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Appendixes

Appendix 1 27

Appendix 1. Quality Control and Assurance

Quality-control samples are used for quality assurance, 

which quantifies reproducibility and reliability of field data. 

Field water and streambed-sediment samples were collected 

using protocols described in Wilde and others (2012) and 

streamflow measurements were made using protocols 

described in Rantz and others (1982). Sample analyses were 

done using methods and equipment described in published 

USGS reports and USEPA methods. The NWQL and USGS 

Sediment Laboratory routinely run calibration standards, 

spikes, and blanks for quality-control purposes (Pritt and 

Raese, 1995).

In addition to quality-control procedures of those 

laboratories, all streambed-sediment samples were analyzed 

twice by XRF to account for heterogeneity of metals contents 

in those samples, and two field-replicate water samples and 

one field-blank water sample were analyzed for the same 

constituents as field-water samples. Relative percent difference 

(RPD) between replicate samples was computed as follows:

RPD= (|a - b|/(a + b/2))*100 percent (1)

where

a is the trace-element concentration analyzed in 

the first analysis, and 

b is the trace-element concentration analyzed in 

the second analysis.

RPDs of replicate samples typically were less than 

10 percent (tables A1–1 and A1–2), indicating good 

reproducibility of data. RPDs of constituents measured in 

replicate well-water samples were slightly greater than those 

of surface-water samples, which may have been caused by 

relatively high pumping rates and heterogeneous contributions 

of producing zones of those wells with time. Most constituents 

analyzed in the field blank water sample were not detected 

(table A1–3). Constituents detected in the blank sample (total 

barium, and dissolved iron) were detected at concentrations 

substantially less than those typically measured in river-water 

samples.

Table A1–1. Relative percent differences of selected traceelement concentrations in 36 pairs of field and field replicate 

streambed-sediment samples collected in Norman, Oklahoma, 

May–June 2012.

[RPD, relative percent difference]

Constituent Sample medium Median 

RPD

Range 

of RPDs

Relative percent differences between replicate analyses

Arsenic Streambed sediment 20.8 0.0760–119

Chromium Streambed sediment 14.4 1.37–200

Barium Streambed sediment 3.2 0.146–28.6

Iron Streambed sediment 0.855 0.00657–13.7

Manganese Streambed sediment 3.13 0.0718–27.0

Table A1–2. Relative percent differences of selected constituent 

concentrations in one pair of field and field replicate well-water 

samples and one pair of field and field replicate surface-water 

samples collected in Norman, Oklahoma, May–June 2012.

[RPD, relative percent difference; “Dissolved” refers to filtered sample and 

“Total” refers to an unfiltered sample; RPDs not calculated for data pairs with 

one censored value, designated by “NA”; SW, surface water; WW, well water]

Constituent Sample 

medium RPD

Hardness as calcium carbonate WW 3.33

Dissolved phosphorus SW\WW 2.82\0

Dissolved calcium SW\WW 1.08\3.08

Total calcium SW\WW 1.32\1.58

Dissolved magnesium SW\WW 0.56\3.24

Total magnesium SW\WW 0.56\1.51

Dissolved arsenic SW\WW 0\0.21

Total arsenic SW\WW 0\0.22

Dissolved arsenate WW 10.2

Dissolved arsenite WW 0

Dissolved dimethylarsinate WW 0

Dissolved monomethylarsonate WW 0

Dissolved aluminum SW\WW 44.4\8.33

Total aluminum SW\WW 16.9\6.15

Dissolved barium SW\WW 1.93\1.87

Total barium SW\WW 0.59\3.7

Dissolved chromium SW\WW 0\0.52

Total chromium SW\WW 9.52\0.49

Dissolved iron SW\WW 13.8\NA.

Total iron SW\WW 14.1\23.0

Dissolved manganese SW\WW 19.4\22.9

Total manganese SW\WW 2.75\NA

Dissolved selenium SW\WW 1.00\0.59

Total selenium SW\WW 1.04\1.36

Dissolved vanadium SW\WW 6.82\0.60

Total vanadium SW\WW 2.35\0.61

Total alpha-emitting isotopes of radium SW\WW 42.5\3.08

Appendix 1
28 Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird

Table A1–3. Constituent concentrations measured in field blank 

water sample collected at the Little River near Franklin, Oklahoma, 

streamflow-gaging station on April 19, 2012.

[mg/L, milligrams per liter; <, less than; μg/L, micrograms per liter]

Constituent Constituent 

concentration

Dissolved phosphorus, in mg/L <0.004

Dissolved calcium, in mg/L <0.022

Total calcium, in mg/L <0.021

Dissolved magnesium, in mg/L <0.011

Total magnesium, in mg/L <0.007

Dissolved arsenic, in μg/L <0.03

Total arsenic, in μg/L <0.28

Dissolved barium, in μg/L <0.07

Total barium, in μg/L 0.15

Dissolved chromium, in μg/L <0.60

Total chromium, in μg/L <0.60

Dissolved iron, in μg/L 0.21

Total iron, in μg/L <0.40

Dissolved vanadium, in μg/L <0.60

Total vanadium, in μg/L <0.60

Dissolved aluminum, in μg/L <2.2

Total aluminum, in mg/L <3.8

Dissolved selenium, in μg/L <0.03

Total selenium, in μg/L <0.05
Appendix 2 29

Table A2–1. Stream distances, moving-average stream 

velocities, and arrival times from the upstream streamflow-gaging 

station (12th Avenue Northwest) during the May 8, 2012, sampling 

event of the Little River near Norman, Oklahoma.—Continued 

[Start time 17:30 on May 8, 2012; ft, feet; hr, hour; 12th Avenue NW, Little 

River at 12th Avenue NW near Norman Okla.; 12th Avenue NE, Little River 

at 12th Avenue Northeast near Norman, Okla.; 36th Avenue NE, Little River 

at 36th Avenue Northeast near Norman, Okla.; near Franklin, Little River near 

Franklin, Okla.]

Sampling 

station

Stream 

distance 

(ft)

Moving 

average 

velocity 

(ft/hr)

Hours Days Arrival from 

12th Avenue NW

12th 

Avenue 

NW

0 630 0.0 0.0 5/8/2012 17:30

1,640 630 2.6 0.1 5/8/2012 20:06

3,280 630 5.2 0.2 5/8/2012 22:42

4,920 630 7.8 0.3 5/9/2012 1:18

6,560 630 10.4 0.4 5/9/2012 3:54

8,200 630 13.0 0.5 5/9/2012 6:30

9,840 900 14.8 0.6 5/9/2012 8:20

11,500 900 16.7 0.7 5/9/2012 10:09

13,100 900 18.5 0.8 5/9/2012 11:58

14,800 900 20.3 0.8 5/9/2012 13:48

12th 

Avenue 

NE

16,400 900 22.1 0.9 5/9/2012 15:37

18,000 900 23.9 1.0 5/9/2012 17:26

19,700 900 25.8 1.1 5/9/2012 19:16

21,300 900 27.6 1.1 5/9/2012 21:05

23,000 900 29.4 1.2 5/9/2012 22:54

24,600 900 31.2 1.3 5/10/2012 0:44

26,200 756 33.4 1.4 5/10/2012 2:54

27,900 756 35.6 1.5 5/10/2012 5:04

29,500 756 37.7 1.6 5/10/2012 7:14

31,200 756 39.9 1.7 5/10/2012 9:24

Appendix 2. Stream Distances, MovingAverage Stream Velocities, and Arrival Times 

from the Upstream Streamflow-Gaging Station 

(12th Avenue Northwest) Water-Quality 

Sampling of the Little River near Norman, 

Oklahoma, May 2012 

Appendix 2

Table A2–1. Stream distances, moving-average stream 

velocities, and arrival times from the upstream streamflow-gaging 

station (12th Avenue Northwest) during the May 8, 2012, sampling 

event of the Little River near Norman, Oklahoma. 

[Start time 17:30 on May 8, 2012; ft, feet; hr, hour; 12th Avenue NW, Little 

River at 12th Avenue NW near Norman Okla.; 12th Avenue NE, Little River 

at 12th Avenue Northeast near Norman, Okla.; 36th Avenue NE, Little River 

at 36th Avenue Northeast near Norman, Okla.; near Franklin, Little River near 

Franklin, Okla.]

Table A2–1. Stream distances, moving-average stream 

velocities, and arrival times from the upstream streamflow-gaging 

station (12th Avenue Northwest) during the May 8, 2012, sampling 

event of the Little River near Norman, Oklahoma.—Continued 

[Start time 17:30 on May 8, 2012; ft, feet; hr, hour; 12th Avenue NW, Little 

River at 12th Avenue NW near Norman Okla.; 12th Avenue NE, Little River 

at 12th Avenue Northeast near Norman, Okla.; 36th Avenue NE, Little River 

at 36th Avenue Northeast near Norman, Okla.; near Franklin, Little River near 

Franklin, Okla.]

Sampling 

station

Stream 

distance 

(ft)

Moving 

average 

velocity 

(ft/hr)

Hours Days Arrival from 

12th Avenue NW

36th 

Avenue 

NE

32,800 756 42.1 1.8 5/10/2012 11:35

34,500 756 44.3 1.8 5/10/2012 13:45

36,100 756 46.4 1.9 5/10/2012 15:55

37,700 756 48.6 2.0 5/10/2012 18:05

39,400 756 50.8 2.1 5/10/2012 20:15

41,000 756 52.9 2.2 5/10/2012 22:25

42,600 756 55.1 2.3 5/11/2012 0:36

44,300 756 57.3 2.4 5/11/2012 2:46

45,900 846 59.2 2.5 5/11/2012 4:42

47,600 846 61.1 2.5 5/11/2012 6:38

49,200 846 63.1 2.6 5/11/2012 8:35

50,900 846 65.0 2.7 5/11/2012 10:31

52,500 846 67.0 2.8 5/11/2012 12:27

54,100 846 68.9 2.9 5/11/2012 14:24

Near 

Franklin

55,800 846 70.8 3.0 5/11/2012 16:20
30 Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird

Table A2–2. Stream distances, moving-average stream 

velocities, and arrival times from the upstream streamflow-gaging 

station (12th Avenue Northwest) during the May 14, 2012, sampling 

event of the Little River near Norman, Oklahoma.

[Start time 09:30 on May 14, 2012; ft, feet; hr, hour; 12th Avenue NW, Little 

River at 12th Avenue Northwest near Norman Okla.; 12th Avenue NE, Little 

River at 12th Avenue Northeast near Norman, Okla.; 36th Avenue NE, Little 

River at 36th Avenue Northeast near Norman, Okla. ; near Franklin, Little 

River near Franklin, Okla.]

Sampling 

station

Stream 

distance 

(ft)

Moving 

average 

velocity 

(ft/hr)

Hours Days Arrival from 12th 

Avenue NW

12th 

Avenue 

NW

0 1,260 0.0 0.0 5/14/2012 9:30

1,640 1,260 1.3 0.1 5/14/2012 10:48

3,280 1,260 2.6 0.1 5/14/2012 12:06

4,920 1,260 3.9 0.2 5/14/2012 13:24

6,560 1,260 5.2 0.2 5/14/2012 14:42

8,200 1,260 6.5 0.3 5/14/2012 16:00

9,840 960 8.2 0.3 5/14/2012 17:42

11,500 960 9.9 0.4 5/14/2012 19:25

13,100 960 11.6 0.5 5/14/2012 21:07

14,800 960 13.3 0.6 5/14/2012 22:50

12th 

Avenue 

NE

16,400 960 15.0 0.6 5/15/2012 0:32

18,000 960 16.8 0.7 5/15/2012 2:15

19,700 960 18.5 0.8 5/15/2012 3:57

21,300 960 20.2 0.8 5/15/2012 5:40

23,000 960 21.9 0.9 5/15/2012 7:22

24,600 960 23.6 1.0 5/15/2012 9:05

26,200 516 26.8 1.1 5/15/2012 12:16

27,900 516 29.9 1.2 5/15/2012 15:26

29,500 516 33.1 1.4 5/15/2012 18:37

31,200 516 36.3 1.5 5/15/2012 21:48

36th 

Avenue 

NE

32,800 516 39.5 1.6 5/16/2012 0:58

34,500 516 42.7 1.8 5/16/2012 4:09

36,100 516 45.8 1.9 5/16/2012 7:20

37,700 516 49.0 2.0 5/16/2012 10:31

39,400 516 52.2 2.2 5/16/2012 13:41

41,000 516 55.4 2.3 5/16/2012 16:52

42,600 516 58.6 2.4 5/16/2012 20:03

44,300 516 61.7 2.6 5/16/2012 23:13

45,900 450 65.4 2.7 5/17/2012 2:52

47,600 450 69.0 2.9 5/17/2012 6:31

49,200 450 72.7 3.0 5/17/2012 10:09

50,900 450 76.3 3.2 5/17/2012 13:48

52,500 450 80.0 3.3 5/17/2012 17:27

54,100 450 83.6 3.5 5/17/2012 21:05

Near 

Franklin

55,800 450 87.2 3.6 5/18/2012 0:44

Table A2–3. Stream distances, moving-average stream 

velocities, and arrival times from the upstream streamflow-gaging 

station (12th Avenue Northwest) during the May 17, 2012, sampling 

event of the Little River near Norman, Oklahoma. 

[Start time 16:00 on May 17, 2012; ft, feet; hr, hour; 12th Avenue NW, Little 

River at 12th Avenue Northwest near Norman Okla.; 12th Avenue NE, Little 

River at 12th Avenue Northeast near Norman, Okla.; 36th Avenue NE, Little 

River at 36th Avenue Northeast near Norman, Okla.; near Franklin, Little 

River near Franklin, Okla.]

Sampling 

station

Stream 

distance 

(ft)

Moving 

average 

velocity 

(ft/hr)

Hours Days Arrival from 12th 

Avenue NW

12th 

Avenue 

NW

0 756 0.0 0.0 5/17/2012 16:00

1,640 756 2.2 0.1 5/17/2012 18:10

3,280 756 4.3 0.2 5/17/2012 20:20

4,920 756 6.5 0.3 5/17/2012 22:30

6,560 756 8.7 0.4 5/18/2012 0:40

8,200 756 10.8 0.5 5/18/2012 2:50

9,840 588 13.6 0.6 5/18/2012 5:38

11,500 588 16.4 0.7 5/18/2012 8:25

13,100 588 19.2 0.8 5/18/2012 11:12

14,800 588 22.0 0.9 5/18/2012 14:00

12th 

Avenue 

NE

16,400 588 24.8 1.0 5/18/2012 16:47

18,000 588 27.6 1.1 5/18/2012 19:34

19,700 588 30.4 1.3 5/18/2012 22:22

21,300 588 33.2 1.4 5/19/2012 1:09

23,000 588 35.9 1.5 5/19/2012 3:56

24,600 588 38.7 1.6 5/19/2012 6:44

26,200 468 42.2 1.8 5/19/2012 10:14

27,900 468 45.7 1.9 5/19/2012 13:44

29,500 468 49.3 2.1 5/19/2012 17:15

31,200 468 52.8 2.2 5/19/2012 20:45

36th 

Avenue 

NE

32,800 468 56.3 2.3 5/20/2012 0:15

34,500 468 59.8 2.5 5/20/2012 3:45

36,100 468 63.3 2.6 5/20/2012 7:16

37,700 468 66.8 2.8 5/20/2012 10:46

39,400 468 70.3 2.9 5/20/2012 14:16

41,000 468 73.8 3.1 5/20/2012 17:46

42,600 468 77.3 3.2 5/20/2012 21:17

44,300 468 80.8 3.4 5/21/2012 0:47

45,900 306 86.1 3.6 5/21/2012 6:08

47,600 306 91.5 3.8 5/21/2012 11:30

49,200 306 96.9 4.0 5/21/2012 16:52

50,900 306 102.2 4.3 5/21/2012 22:13

52,500 306 107.6 4.5 5/22/2012 3:35

54,100 306 112.9 4.7 5/22/2012 8:56

Near 

Franklin

55,800 306 118.3 4.9 5/22/2012 14:18
Appendix 2 31

Table A2–4. Stream distances, moving-average stream 

velocities, and arrival times from the upstream streamflow-gaging 

station (12th Avenue Northwest) during the May 17, 2012, sampling 

event of the Little River near Norman, Oklahoma. 

[Start time 12:30 on May 22, 2012; ft, feet; hr, hour; 12th Avenue NW, Little 

River at 12th Avenue Northwest near Norman Okla.; 12th Avenue NE, Little 

River at 12th Avenue Northeast near Norman, Okla.; 36th Avenue NE, Little 

River at 36th Avenue Northeast near Norman, Okla.; near Franklin, Little 

River near Franklin, Okla.]

Sampling 

station

Stream 

distance 

(ft)

Moving 

average 

velocity 

(ft/hr)

Hours Days Arrival from 12th 

Avenue NW

12th 

Avenue 

NW

0 1,210 0.0 0.0 5/22/2012 12:30

1,640 1,210 1.4 0.1 5/22/2012 13:51

3,280 1,210 2.7 0.1 5/22/2012 15:13

4,920 1,210 4.1 0.2 5/22/2012 16:34

6,560 1,210 5.4 0.2 5/22/2012 17:56

8,200 1,210 6.8 0.3 5/22/2012 19:17

9,840 960 8.5 0.4 5/22/2012 21:00

11,500 960 10.2 0.4 5/22/2012 22:42

13,100 960 11.9 0.5 5/23/2012 0:25

14,800 960 13.6 0.6 5/23/2012 2:07

12th 

Avenue 

NE

16,400 960 15.3 0.6 5/23/2012 3:50

18,000 960 17.0 0.7 5/23/2012 5:32

19,700 960 18.8 0.8 5/23/2012 7:15

21,300 960 20.5 0.9 5/23/2012 8:57

23,000 960 22.2 0.9 5/23/2012 10:40

24,600 960 23.9 1.0 5/23/2012 12:22

26,200 864 25.8 1.1 5/23/2012 14:16

27,900 864 27.7 1.2 5/23/2012 16:10

29,500 864 29.6 1.2 5/23/2012 18:04

31,200 864 31.5 1.3 5/23/2012 19:58

36th 

Avenue 

NE

32,800 864 33.4 1.4 5/23/2012 21:52

34,500 864 35.3 1.5 5/23/2012 23:46

36,100 864 37.2 1.5 5/24/2012 1:40

37,700 864 39.1 1.6 5/24/2012 3:34

39,400 864 41.0 1.7 5/24/2012 5:27

41,000 864 42.9 1.8 5/24/2012 7:21

42,600 864 44.8 1.9 5/24/2012 9:15

44,300 864 46.7 1.9 5/24/2012 11:09

45,900 846 48.6 2.0 5/24/2012 13:05

47,600 846 50.5 2.1 5/24/2012 15:02

49,200 846 52.5 2.2 5/24/2012 16:58

50,900 846 54.4 2.3 5/24/2012 18:54

52,500 846 56.4 2.3 5/24/2012 20:51

54,100 846 58.3 2.4 5/24/2012 22:47

Near 

Franklin

55,800 846 60.2 2.5 5/25/2012 0:43
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Andrews and others—Pilot Study of Natural Attenuation of Arsenic in Well Water Discharged to the Little River Above Lake Thunderbird—SIR 2013–5055

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