U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2012–5117

Prepared in cooperation with the Wyoming Department of Environmental Quality

Water-Quality Characteristics and Trend Analyses for 

the Tongue, Powder, Cheyenne, and Belle Fourche River 

Drainage Basins, Wyoming and Montana, for Selected 

Periods, Water Years 1991 through 2010
Cover. Clear Creek, Wyoming. Photograph by Melanie L. Clark.
Water-Quality Characteristics and 

Trend Analyses for the Tongue, Powder, 

Cheyenne, and Belle Fourche River 

Drainage Basins, Wyoming and Montana, 

for Selected Periods, Water Years 1991 

through 2010

By Melanie L. Clark

Prepared in cooperation with the Wyoming Department of Environmental Quality

Scientific Investigations Report 2012–5117

U.S. Department of the Interior

U.S. Geological Survey
ISBN 978-1-4113-3428-1

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Clark, M.L., 2012, Water-quality characteristics and trend analyses for the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, for selected periods, water years 1991 through 2010: 

U.S. Geological Survey Scientific Investigations Report 2012–5117, 70 p.
iii

Acknowledgments

Thanks are extended to U.S. Geological Survey (USGS) colleagues in the Casper, Wyoming, 

Field Office and the Billings, Montana, Field Office for collecting data used in this report. Many 

private landowners allowed access to sampling sites. Thanks also are extended to Bill DiRienzo 

of the Wyoming Department of Environmental Quality for his support of the study; and Janet 

Carter, Elizabeth Ciganovich, Keith Lucey, Kirk Miller, and Steve Sando of the USGS for providing 

reviews of the manuscript. Suzanne Roberts assisted in the preparation of illustrations and the 

layout of the report.
iv

Contents

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

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

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

Purpose and Scope ..............................................................................................................................6

Study Area Description........................................................................................................................6

Data Collection and Analysis.....................................................................................................................10

Field and Analytical Methods ...........................................................................................................10

Data Analysis Methods......................................................................................................................12

Quality Assurance...............................................................................................................................13

Water-Quality Characteristics ...................................................................................................................15

Streamflow...........................................................................................................................................15

Specific Conductance........................................................................................................................18

Sodium Adsorption Ratios.................................................................................................................20

Trend Analyses of Selected Water-Quality Characteristics.................................................................22

Trend Analysis for Water Years 2001–10.........................................................................................22

Specific Conductance...............................................................................................................23

Sodium Adsorption Ratios........................................................................................................25

Trend Analysis for Water Years 2005–10.........................................................................................27

Specific Conductance...............................................................................................................27

Sodium Adsorption Ratios........................................................................................................30

Trend Analysis for Water Years 1991–2010.....................................................................................32

Specific Conductance...............................................................................................................32

Sodium Adsorption Ratios........................................................................................................32

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

References....................................................................................................................................................34

Appendix 1. Summary statistics for water-quality constituents for sites in the 

Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins, 

Wyoming and Montana, water years 2001–10.......................................................................40

Appendix 2. Trend results for selected water-quality constituents for selected 

sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 1991–2010....................................53
v

Figures

1. Map showing location of sampling sites in the Tongue, Powder, Cheyenne, 

and Belle Fourche River drainage basins, Wyoming and Montana, water 

years 2001–10 ................................................................................................................................3

2. Graph showing amount of produced water from coalbed-natural gas wells, 

Powder River structural basin, Wyoming, calendar years 1991–2010.................................4

3. Graph showing annual runoff for selected main-stem sampling sites in the 

Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins, 

Wyoming and Montana, water years 2001–10.......................................................................16

4. Graphs showing streamflow at sites in the Tongue, Powder, Cheyenne, and 

Belle Fourche River drainage basins, Wyoming and Montana, water 

years 2001–10 ..............................................................................................................................17

5. Graph showing statistical summary of specific conductance for site groups 

in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins, 

Wyoming and Montana, water years 2001–10.......................................................................18

6. Graphs showing specific conductance through time at sites in the Tongue, 

Powder, Cheyenne, and Belle Fourche River drainage basins, Wyoming and 

Montana, water years 2001–10 ................................................................................................19

7. Graph showing statistical summary of sodium adsorption ratios for site 

groups in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10........................................21

8. Graphs showing sodium adsorption ratios through time at sites in the 

Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins, 

Wyoming and Montana, water years 2001–10.......................................................................22

9. Map showing trend results for flow-adjusted specific conductance at sites 

in the Tongue, Powder, and Belle Fourche River drainage basins, Wyoming 

and Montana, water years 2001–10.........................................................................................24

10. Map showing trend results for flow-adjusted sodium adsorption ratios at 

sites in the Tongue, Powder, and Belle Fourche River drainage basins, 

Wyoming and Montana, water years 2001–10.......................................................................26

11. Map showing trend results for flow-adjusted specific conductance at sites 

in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins, 

Wyoming and Montana, water years 2005–10.......................................................................28

12. Map showing trend results for flow-adjusted sodium adsorption ratios at 

sites in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage 

basins, Wyoming and Montana, water years 2005–10.........................................................31

Tables

1. Selected characteristics for sampling sites in the Tongue, Powder, Cheyenne, 

and Belle Fourche River drainage basins, Wyoming and Montana.....................................7

2. Periods for which water-quality data were analyzed for sampling sites in 

the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins, 

Wyoming and Montana .............................................................................................................11

3. Quality-control summary for equipment blank samples and replicate samples 

collected at sampling sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 2001–10..............14
vi

Conversion Factors and Datums

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

cubic foot (ft3) 0.02832 cubic meter (m3) 

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

acre-foot (acre-ft) 0.001233 cubic hectometer (hm3) 

Flow rate

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

Mass

ton per day (ton/d) 0.9072 metric ton per day

ton per day (ton/d) 0.9072 megagram per day (Mg/d)

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

°F=(1.8×°C)+32

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

°C=(°F-32)/1.8

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

25°C). 

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

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

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

Water year is the 12-month period from October 1 through September 30 and is designated by 

the year in which it ends. For example, the water year ending September 30, 2001 is called water 

year 2001. 

Concentrations of chemical constituents in water in this report are given in milligrams per liter 

(mg/L).
vii

Abbreviated Water-Quality Units

mg/L milligrams per liter

μS/cm at 25°C microsiemens per centimeter at 25 degrees Celsius

Abbreviations

< less than

CBNG coalbed natural gas

ESTREND EStimate TREND 

NWIS National Water Information System

p p-value

RPD relative percent difference

SAR sodium adsorption ratio

USGS U.S. Geological Survey 

WDEQ Wyoming Department of Environmental Quality

Water-Quality Characteristics and Trend Analyses for 

the Tongue, Powder, Cheyenne, and Belle Fourche River 

Drainage Basins, Wyoming and Montana, for Selected 

Periods, Water Years 1991 through 2010

By Melanie L. Clark 

Abstract

The Powder River structural basin in northeastern Wyoming and southeastern Montana is an area of ongoing coalbed 

natural gas (CBNG) development. Waters produced during 

CBNG development are managed with a variety of techniques, 

including surface impoundments and discharges into stream 

drainages. The interaction of CBNG-produced waters with the 

atmosphere and the semiarid soils of the Powder River structural basin can affect water chemistry in several ways. Specific 

conductance and sodium adsorption ratios (SAR) of CBNGproduced waters that are discharged to streams have been of 

particular concern because they have the potential to affect 

the use of the water for irrigation. Water-quality monitoring 

has been conducted since 2001 at main-stem and tributary 

sites in the Tongue, Powder, Cheyenne, and Belle Fourche 

River drainage basins in response to concerns about CBNG 

effects. A study was conducted to summarize characteristics 

of stream-water quality for water years 2001–10 (October 1, 

2000, to September 30, 2010) and examine trends in specific 

conductance, SAR, and primary constituents that contribute 

to specific conductance and SAR for changes through time 

(water years 1991–2010) that may have occurred as a result 

of CBNG development. Specific conductance and SAR are 

the focus characteristics of this report. Dissolved calcium, 

magnesium, and sodium, which are primary contributors to 

specific conductance and SAR, as well as dissolved alkalinity, 

chloride, and sulfate, which are other primary contributors to 

specific conductance, also are described.

Stream-water quality in the Tongue, Powder, Cheyenne, 

and Belle Fourche River drainage basins was variable during water years 2001–10, in part because of variations in 

streamflow. In general, annual runoff was less than average 

during water years 2001–06 and near or above average during 

water years 2007–10. Stream water of the Tongue River had 

the smallest specific conductance values, sodium adsorption 

ratios, and major ion concentrations of the main-stem streams. 

Sites in the Tongue River drainage basin typically had the 

smallest range of specific conductance and SAR values. The 

water chemistry of sites in the Powder River drainage basin 

generally was the most variable as a result of diverse characteristics of that basin. Plains tributaries in the Powder River 

drainage basin had the largest range of specific conductance 

and SAR values, in part due to the many tributaries that 

receive CBNG-produced waters. 

Trends were analyzed using the seasonal Kendall test 

with flow-adjusted concentrations to determine changes to 

water quality through time at sites in the Tongue, Powder, 

Cheyenne, and Belle Fourche River drainage basins. Trends 

were evaluated for water years 2001–10 for 17 sites, which 

generally were on the main-stem streams and primary tributaries. Trends were evaluated for water years 2005–10 for 

26 sites to increase the spatial coverage of sites. Trends were 

evaluated for water years 1991–2010 for eight sites to include 

water-quality data collected prior to widespread CBNG development and expand the temporal context of trends.

Consistent patterns were not observed in trend results for 

water years 2001–10 for flow-adjusted specific conductance 

and SAR values in the Tongue, Powder, and Belle Fourche 

River drainage basins. Significant (p-values less than 0.05) 

upward trends in flow-adjusted specific conductance values 

were determined for 3 sites, a downward trend was determined for 1 site, and no significant (p-value greater than 

0.05) trends were determined for 13 sites. One of the sites 

with a significant upward trend was the Tongue River at the 

Wyoming-Montana State line. No trend in flow-adjusted 

specific conductance values was determined for the Powder River at Moorhead, Mont. Significant upward trends in 

flow-adjusted SAR values were determined for 2 sites and no 

significant trends were determined for 15 sites. No trends in 

flow-adjusted SAR values were determined for the Tongue 

River at the Wyoming-Montana State line or for the Powder 

River at Moorhead, Mont. One of the sites with a significant 

upward trend in flow-adjusted SAR values was the Powder 

River at Arvada, Wyo.

For water years 2005–10, significant upward trends in 

flow-adjusted specific conductance values were determined 
2 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

for 9 sites, downward trends were determined for 4 sites, and 

no significant trends were determined for 13 sites. A significant upward trend was determined for flow-adjusted specific 

conductance values for the Tongue River at the WyomingMontana State line. No trend in flow-adjusted specific 

conductance values was determined for the Powder River at 

Moorhead, Mont. Significant upward trends in flow-adjusted 

SAR values were determined for 4 sites, downward trends 

were determined for 5 sites, and no significant trend was determined for 17 sites. No trends in flow-adjusted SAR values 

were determined for the Tongue River at the Wyoming-Montana State line or for the Powder River at Moorhead, Mont.

Results of the seasonal Kendall test applied to flowadjusted specific conductance values for water years 

1991–2010 indicated no significant trend for eight sites in the 

Tongue, Powder, and Belle Fourche River drainage basins. No 

significant trend in flow-adjusted specific conductance was 

determined for the Tongue River at the Wyoming-Montana 

State line or the Powder River at Moorhead, Mont. Results of 

the seasonal Kendall test applied to flow-adjusted SAR values 

for water years 1991–2010 indicated an upward trend for one 

site and no significant trend for four sites in the Powder and 

Belle Fourche River drainage basins. The significant upward 

trend in flow-adjusted SAR values was determined for the 

Powder River at Arvada, Wyo., for water years 1991–2010. 

Results indicate that CBNG development in the Powder 

River structural basin may have contributed to some trends, 

such as the upward trend in flow-adjusted SAR for the Powder 

River at Arvada, Wyo., for water years 1991–2010. An upward 

trend in flow-adjusted alkalinity concentrations for water years 

2001–10 also was determined for the Powder River at Arvada, 

Wyo. Trend results are consistent with changes that can occur 

from the addition of sodium and bicarbonate associated with 

CBNG-produced waters to the Powder River. Upward trends 

in constituents at other sites, including the Belle Fourche 

River, may be the result of declining CBNG development, 

indicating that CBNG-produced waters may have had a dilution effect on some streams. The factors affecting other trends 

could not be determined because multiple factors could have 

been affecting the stream-water quality or because trends were 

observed at sites upstream from CBNG development that may 

have affected water-quality trends at sites downstream. 

Introduction

Coalbed natural gas (CBNG) has become an increasingly 

important resource for the United States. Energy production 

data for 2009 from the U.S. Energy Information Administration (2011) indicate that CBNG represents about 8 percent of 

the total United States natural gas production. Many of the 

States with CBNG development are in the western United 

States. During 2009, Wyoming had the largest CBNG production in the United States with an estimated production of about 

535 billion cubic feet (ft3), which accounted for 28 percent of 

the total CBNG production (U.S. Energy Information Administration, 2011). Production in other western States included 

498 billion ft3 in Colorado, 432 billion ft3 in New Mexico, and 

12 billion ft3 in Montana (U.S. Energy Information Administration, 2011).

The Powder River structural basin in northeastern Wyoming and southeastern Montana (fig. 1) is an area of ongoing 

CBNG development. The structural basin contains large 

deposits of Tertiary-age coalbeds. Methane, a major component of the natural gas, can form during coalification as a 

result of biogenic or thermogenic processes (DeBruin, 2010). 

During early stages of coalification, biogenic methane forms 

from anaerobic bacteria that produce methane through the 

consumption of carbon dioxide during anaerobic respiration. 

As coalification proceeds, temperatures tend to increase as a 

result of deep burial or increased geothermal gradients and 

eventually begin to exceed temperatures in which bacteria can 

survive. When temperatures reach about 120 degrees Celsius 

(°C), a thermogenic process favors the production of methane 

over carbon dioxide. Coalbeds of the Powder River structural 

basin, including those in the Tertiary-age Wasatch and Fort 

Union Formations, generally are subbituminous in rank and 

have not undergone substantial thermal alteration (DeBruin, 

2010). Deposits generally are thick, laterally continuous, 

relatively shallow, and contain a large resource of biogenic 

CBNG. The Powder River structural basin was estimated to 

contain nearly 14.3 trillion ft3 (mean estimate) of undiscovered 

CBNG when it was assessed by the U.S. Geological Survey 

(USGS) in 2001 (U.S. Geological Survey, 2002). 

During CBNG development, water is pumped from wells 

drilled into coalbeds, thus lowering the hydrostatic pressure 

in the coalbeds. This allows the natural gas that was confined 

and stored within the internal surfaces and voids of the coal to 

flow and be captured for use. The volume of water produced 

during CBNG development is largest during the early stages 

of development and decreases as production time proceeds 

(DeBruin and others, 2004). Although CBNG development in the Powder River structural basin began during the 

1980s, it was not widespread until the late 1990s. Information 

from the Wyoming Oil and Gas Conservation Commission 

(2011), which has compiled gas and water-production data 

by drainage, indicates produced waters were being generated in the four major surface drainage basins of the Powder 

River structural basin by 1999 (fig. 2). The Wyoming Oil and 

Gas Conservation Commission (2011) database is the most 

comprehensive public source of information available for 

CBNG development in Wyoming and was used as a source of 

information about produced waters for this study. Water-production data by drainage were summed by year and converted 

to acre-feet (acre-ft), but otherwise were accepted as presented 

in the Wyoming Oil and Gas Conservation Commission database. The cumulative volume of produced water from 1991 to 

2010 for the Tongue, Powder, Cheyenne, and Belle Fourche 

River drainage basins in Wyoming was about 844,000 acre-ft 

(based on compilation of data retrieved from the Wyoming 

Oil and Gas Conservation Commission, 2011). In contrast, 
Introduction 3

Figure 1. Location of sampling sites in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins, Wyoming and 

Montana, water years 2001–10.

Powder River

structural basin

MONTANA

WYOMING

Map area

Creek

River

River

Powder

River

River

Fourche

Belle

Creek Pumpkin

River

Little

Creek

Beaver

Pumpkin

Caballo

Creek

Donkey Creek

Cheyenne

Creek

Creek

Tongue

Little Go ose Creek

Prairie Dog Creek

Clear

Creek

Woman

Crazy

Creek

Willow

Salt

North

Platte River

Burger Draw

Goose

Keyhole

Reservoir

Van Houten Draw

Barber Creek

Barber Creek

River

Powder

Wild Horse Creek

Spotted Horse Creek

Creek

LX Bar

Creek

S A

Creek

Creek

Rawhide

Elk

Creek

Horse Creek

Creek

Dry

Rattlesnake

Creek

Double

Crossing Kumor Creek Draw

Cottonwood

Powder

Sussex

Arvada Hulett

Buffalo

Gillette

Moorhead

Newcastle

Sheridan

Moorcroft

Clearmont

Decker

Acme

SHERIDAN

CAMPBELL

JOHNSON

CROOK

NATRONA

CONVERSE

WESTON

NIOBRARA

BIG

HORN

W

ASH

A

KIE

CARTER

BIG HORN

POWDER

RIVER

Tongue River

B5

B4

B3

B2

B1

C2

C1

P9

P8 P7

P6

P5

P4

P3

P2

P1

T6

T5

T4 T3 T2

T1

P27

P26

P25

P24

P23

P22 P21

P20

P19

P18

P17 P16

P15

P14

P12

P13

P11

P10

Powder River structural basin

25

25

0

0 50 KILOMETERS

50 MILES

14

MONTANA

WYOMING

BLA

CK

HILLS

BIGHORN MOUNTAINS

107° 106° 105° 104°

45°

44°

43°

EXPLANATION

Powder River

Cheyenne River

Belle Fourche River

Drainage basin

Water-quality sampling site 

and map number

P13

SOUTH DAKOTA

Casper

Base from U.S. Geological Survey digital data,

variously dated, various scales

Transportation network from Federal Highway 

Administration, 2002, 1:100,000

Albers Equal-Area Conic projection

Standard parallels 41°N and 45°N

Central meridian 105°W

North American Datum of 1983 (NAD 83)

16

25

90

90

25

90

Piney

20

85

Lusk

Weston

Spencer

Dull Center

Wakely Siding
4 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

the cumulative volume of produced water in Montana, which 

is limited to a few operations in the Tongue River drainage 

basin, was about 19,200 acre-ft through 2008 (Peterson and 

others, 2010). During the 1990s and through 2001, the largest 

volumes of waters were produced in the Belle Fourche River 

drainage basin. As CBNG development continued, the largest 

volumes of produced waters were in the Powder River drainage basin. 

Produced waters associated with CBNG development can 

be managed with a variety of techniques—including surface 

impoundments, direct stream discharge, irrigation, and reinjection. In Wyoming, about 84 percent of the water produced 

during CBNG development in the Powder River structural 

basin is managed on the land surface, either as discharges into 

surface impoundments (64 percent), where it is allowed to 

evaporate or infiltrate into the subsurface, or as discharges into 

ephemeral or perennial drainages (20 percent), where it may 

infiltrate or become part of the streamflow (Wyoming Department of Environmental Quality, 2009). Water discharged to 

streams may be treated (9 percent) or untreated (11 percent) 

prior to being discharged, depending on the quality of the 

produced waters and requirements of the discharge permit. 

The remaining 16 percent of the water produced during CBNG 

development is used for other beneficial uses such as irrigation 

(8 percent) and subsurface irrigation (5 percent) or disposed of 

through deep-well injection (3 percent). In Montana, the primary method of management has been discharges to streams, 

which accounts for about 61–65 percent of produced water 

(National Research Council of the National Academies, 2010), 

and only about 5 percent of the water is disposed of using 

impoundments. Beneficial uses such as dust control (4–5 percent) and surface or subsurface irrigation (26–30 percent) 

account for the remainder. Since 2010, the State of Montana 

has required all discharges of CBNG-produced waters to Montana streams to undergo water treatment (Frost and Mailloux, 

2011). 

Because most waters produced during CBNG development in the Powder River structural basin are disposed of 

on the land surface, concerns have been raised regarding the 

effect CBNG-produced waters may have on water quality 

in the area. The quantity and quality of the produced waters 

vary depending on the coalbed source (Rice and others, 2000; 

Clarey and Stafford, 2008). The major ion composition of 

coalbed waters varies with depth. Shallow coalbed waters generally are dominated by mixed cations and sulfate compared 

to deep coalbed waters, which are dominated by sodium and 

bicarbonate as a result of ion exchange and sulfate reduction (Bartos and Ogle, 2002). Specific conductance, which 

is a measure of a substance’s ability to conduct an electrical 

current, is a general indicator of overall water quality that 

directly relates to the amount of dissolved ions (or dissolvedsolids concentrations) in solution. Specific conductance values 

ranged from 665 to 4,180 microsiemens per centimeter at 

25 degrees Celsius (μS/cm at 25°C) for coalbed waters in 

the eastern Powder River structural basin (Bartos and Ogle, 

2002). Sodium adsorption ratio (SAR) values, which indicate 

the quantity of sodium relative to calcium and magnesium, 

ranged from 5.0 to 26 for coalbed waters (Bartos and Ogle, 

Figure 2. Amount of produced water from coalbed-natural gas wells, Powder River structural basin, Wyoming, calendar years 

1991–2010 (Wyoming Oil and Gas Conservation Commission, 2011).

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

100,000

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Produced water, in acre-feet

Year

Tongue River

EXPLANATION

Powder River

Belle Fourche River

Cheyenne River

Drainage basin
Introduction 5

2002). Rice and others (2002) reported SAR values as large 

as 68.9 in waters produced from coalbeds of the Fort Union 

Formation. Coalbed waters generally have not been reported 

to have large trace element concentrations, with the exception of barium, iron, and manganese, which are soluble under 

reduced conditions (Rice and others, 2002). Elevated ammonia 

concentrations also were associated with the reduced coalbed 

waters (Rice and others, 2000). In general, concentrations of 

dissolved constituents are smallest near coalbed recharge areas 

and increase as water flows away from recharge areas, because 

the contact time with aquifer materials increases. Clinker, 

which is high permeability rock composed of burned coalbeds 

and baked sediments associated with the coalbeds, enhances 

groundwater recharge along the eastern margins of the Powder 

River structural basin (Heffern and Coates, 1999). Groundwater flow in coalbeds in the eastern part of the basin generally 

is from the southeast to the northwest (Daddow, 1986). As a 

result of groundwater flow patterns, dissolved-solids concentrations (or specific conductance) and SAR values of coalbed 

waters in the Powder River structural basin generally increase 

from east to west and from south to north (Rice and others, 

2002; Clarey and Stafford, 2008). 

The interaction of CBNG-produced waters with the 

atmosphere and the semiarid soils of the Powder River structural basin can affect water chemistry in several ways. When 

produced waters from the coalbeds interact with oxygen in 

the air and surface environment at outfalls, minerals such as 

calcite, iron hydroxide, and barite can precipitate, resulting 

in decreases in concentrations of calcium, iron, and barium 

from outfalls to surface waters, such as CBNG impoundments 

(Brinck and others, 2008). Concentrations of other constituents increase from outfalls to CBNG impoundments or stream 

channels as a result of dissolution and adsorption and desorption processes (Patz and others, 2006; Jackson and Reddy, 

2007a; Jackson and Reddy, 2010). For example, arsenic and 

selenium can be soluble and mobilize in semiarid alkaline 

environments like the Powder River structural basin; thus, 

increases in arsenic and selenium concentrations have been 

observed in stream channels and impoundments. Selenium has 

been a trace element of concern in surface disposal of CBNGproduced waters because of toxicity issues related to fish 

and aquatic birds (U.S. Fish and Wildlife Service, 2005). In 

general, concentrations of arsenic are small in streams and did 

not exceed any State of Wyoming aquatic-life criteria in the 

CBNG development area (Clark and Mason, 2007). Concentrations of selenium have exceeded chronic aquatic-life criteria 

in some samples (Clark and Mason, 2007). The potential 

increase of bicarbonate concentrations in stream waters from 

CBNG-produced waters also has been a concern for aquatic 

life. Elevated concentrations of sodium bicarbonate have been 

shown to be toxic to some species of larval fish and aquatic 

invertebrates (Skaar and others, 2006; Farag and others, 2010). 

Smith and others (2009) found that ammonia in discharged 

coalbed waters increases the dissolved inorganic nitrogen load 

to surface waters during certain times of the year. 

When produced waters infiltrate into the subsurface 

beneath CBNG impoundments, salts dissolve in the subsurface, resulting in increased concentrations of dissolved constituents in groundwater (Brinck and others, 2008; Healy and 

others, 2008). A study of groundwater quality in the Powder 

River drainage basin determined that CBNG-produced waters 

were not the primary source of solutes in the groundwater 

beneath a CBNG impoundment; rather, naturally occurring 

salts and minerals in the unsaturated zone that were mobilized by infiltrating CBNG-produced waters accounted for 

most of the solute mass (Healy and others, 2011). Tracking 

of solutes and water from subsurface drip irrigation that used 

CBNG-produced waters determined that the evaporation and 

dissolution of native salts in the vadose zone, not the CBNGproduced waters themselves, were the primary source of the 

solutes (Engle and others, 2011).

Specific conductance and SAR characteristics of CBNGproduced waters that are discharged to streams have been of 

particular concern because they have the potential to affect the 

use of the water for irrigation (Bureau of Land Management, 

2003, 2012). Irrigating with waters that have large specific 

conductance values can cause soil flocculation and aeration 

of the soil; however, irrigating with waters that have excessive dissolved salts can have a negative effect on plant health. 

Surface applications of waters that have large SAR values can 

result in the exchange of sodium ions for calcium and magnesium ions in clay particles of soils, which can induce swelling of clay particles (Hanson and others, 2006). The swelling 

of clay particles can cause soil dispersion, thereby reducing 

infiltration rates and increasing erosion. McBeth and others 

(2003) found that adding CBNG-produced waters to the soils 

of drainages in the eastern part of the Powder River structural 

basin caused precipitation of calcium carbonate in soils, which 

also may decrease infiltration rates. In general, for a given 

SAR, the potential for reductions to infiltration rates increases 

as specific conductance values decrease (Hanson and others, 

2006). Because the Tongue River is characterized by small 

specific conductance values, even small increases in SAR have 

potential to cause reductions in infiltration. A study conducted 

by Kinsey and Nimick (2011) determined that the Tongue 

River is particularly vulnerable to SAR increases from CBNG 

discharges during low-flow conditions. 

In response to concerns about effects of CBNG-produced 

waters on streams, the USGS, in cooperation with the Wyoming Department of Environmental Quality (WDEQ) and 

the Bureau of Land Management, began monitoring water 

quality during 2001 in the Tongue, Powder, Cheyenne, and 

Belle Fourche River drainage basins (table 1). Characteristics 

of field constituents, major ions, and trace elements collected 

during water years 2001–05 were summarized in Clark and 

Mason (2007). Data requirements for trend analysis, a statistical technique to examine whether data are changing through 

time, were met at a few of the sampling sites at the time of 

that report. Trend analysis for the period 1991–2005 indicated 

no significant trend for specific conductance values at eight 

sites when values were adjusted for streamflow variability 
6 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

(Clark and Mason, 2007); trends that were not significant for 

the Clark and Mason (2007) study were indicated by p-values 

greater than (>) 0.10. Significant upward trends in SAR values 

(adjusted for streamflow variability) were determined for two 

sites on the Powder River; however, one of the sites with the 

upward trend was upstream from CBNG development; trends 

that were significant for the Clark and Mason (2007) study 

were indicated by p-values less than (<) 0.10. Wang and others 

(2007) analyzed trends for four sites on the Powder River for 

pre- and post-CBNG development time periods. Those results 

also indicated that specific conductance values generally were 

unchanged and that SAR values showed upward trends on 

the Powder River during the post-CBNG development time 

period of 1991–2002. An upward trend was not determined 

for the Powder River upstream from CBNG development in 

the Wang and others (2007) study; however, the trend analysis 

periods differed between the two studies. Rank sum tests were 

conducted for pre- and post-CBNG development time periods 

by Dawson (2007) in the upper Tongue River drainage basin 

for water years 1967–2005. Results of those tests generally 

indicated that CBNG development did not substantially affect 

specific conductance and SAR in the upper Tongue River 

drainage basin; however, some increase in SAR values was 

observed in samples from the Tongue River at the WyomingMontana State line. The cause of the SAR increase was not 

determined, and additional monitoring and analysis through 

time was recommended. CBNG development and water-quality monitoring has continued in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins since these 

studies were completed.

Limited analysis has been conducted on stream monitoring data collected since 2005. Water year 2010 marked the 

completion of 10 years of monitoring at many stream sites. 

A study was conducted by the USGS, in cooperation with the 

WDEQ, to summarize stream-water quality for water years 

2001–10 and examine trends in specific conductance, SAR, 

and primary constituents that contribute to specific conductance and SAR for changes through time that may have 

occurred as a result of CBNG development. An additional 

study by the USGS, in cooperation with the Montana Department of Environmental Quality, currently (2012) is being 

conducted to examine long-term changes in water quality 

of the Tongue River and Powder River (Steven Sando, U.S. 

Geological Survey, written commun., 2011). The Montana 

study includes fewer sites in the upper basins in Wyoming and 

focuses more on water-quality trends in the lower Tongue and 

Powder River drainage basins of Montana compared to the 

WDEQ study.

Purpose and Scope

The purpose of this report is to summarize water quality of streams in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins through water year 2010. 

Specifically, this report presents (1) summaries of selected 

water-quality characteristics during water years 2001–10 and 

(2) summaries of trend analyses for selected sites and waterquality characteristics through water year 2010. Trend analyses were initially conducted for the 10-year period of water 

years 2001–10. Additional trend analyses were conducted for 

water years 2005–10, to expand the spatial coverage of sites, 

and for water years 1991–2010, to include water-quality data 

collected prior to widespread CBNG development and expand 

the temporal context of trends. Specific conductance and SAR 

are the focus characteristics of this report. Dissolved calcium, 

magnesium, and sodium, which are primary contributors to 

specific conductance and SAR, as well as dissolved alkalinity, 

chloride, and sulfate, which are other primary contributors to 

specific conductance, also are described. 

The site numbers given in table 1 and on figure 1 are 

used throughout the report for site identification; the formal 

USGS site-identification numbers and site names are given in 

table 1. The site numbers are composed of a letter followed by 

a number. The letter denotes the major drainage basin in which 

the site is located: T, Tongue River; P, Powder River; C, Cheyenne River; and B, Belle Fourche River. The number denotes 

the downstream order of the site or the downstream order in 

which streamflow from a tributary enters the main stem of the 

drainage. For example, site P1 is the farthest upstream site in 

the Powder River drainage basin, site P2 is the second farthest 

upstream site, and so on. For the sake of brevity, sites are 

referred to in the text by their abbreviated site names (table 1). 

Study Area Description

The study area for this report includes those parts of the 

Tongue, Powder, Cheyenne, and Belle Fourche River drainage 

basins within or near the southern two-thirds of the Powder 

River structural basin (fig. 1). Sampling sites in the Tongue, 

Powder, Cheyenne, and Belle Fourche River drainage basins 

are in Wyoming, with the exception of two sites in Montana that are near the Wyoming-Montana State line (Tongue 

River at State line, site T6, and Powder River at Moorhead, 

site P23). 

The study area includes parts of the Middle Rocky Mountains and Northwestern Great Plains ecoregions (Omernik, 

1987; Zelt and others, 1999). Altitudes in the study area range 

from about 3,350 feet (ft) above the National Geodetic Vertical 

Datum of 1929 (NGVD 29) at the streamgage at Moorhead 

(site P23) to more than 13,100 ft above NGVD 29 in the Bighorn Mountains. The dominant land cover in the mountainous 

areas, which includes the Bighorn Mountains and Black Hills, 

is evergreen forest and mixed forest (Homer and others, 2004). 

The dominant land cover in the plains is shrubland and herbaceous grassland. Agricultural land cover is sparse in the study 

area. The main areas with pasture/hay or cultivated crops are 

along the Tongue River and in the Goose Creek, Prairie Dog 

Creek, and Clear Creek drainage basins. Large coal mines are 

in the Little Powder River, Cheyenne River, and Belle Fourche 

River drainage basins near Gillette, Wyo. The largest city in 
Introduction 7

Table 1. Selected characteristics for sampling sites in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins, 

Wyoming and Montana.

[Shading indicates main-stem sites. USGS, U.S. Geological Survey; —, not determined. Vertical datum: National Geodetic Vertical Datum of 1929]

Site 

number 

(fig. 1)

USGS site 

identification 

number

USGS site name Abbreviated site name Site group

Drainage area, 

in square 

miles

Altitude, 

in feet above 

vertical datum

T1 06299980 Tongue River at Monarch, 

Wyo.

Tongue River at Monarch Tongue River 478 3,620

T2 06304500 Little Goose Creek at Sheridan, 

Wyo.

Little Goose Creek Tongue River 159 3,740

T3 06305500 Goose Creek below Sheridan, 

Wyo.

Goose Creek Tongue River 392 3,701

T4 06306200 Prairie Dog Creek at Wakeley 

Siding, near Sheridan, Wyo.

Prairie Dog Creek near 

Sheridan

Tongue River 88 3,695

T5 06306250 Prairie Dog Creek near Acme, 

Wyo.

Prairie Dog Creek near 

Acme

Tongue River 358 3,450

T6 06306300 Tongue River at State line, near 

Decker, Mont.

Tongue River at State line Tongue River 1,453 3,429

P1 06313400 Salt Creek near Sussex, Wyo. Salt Creek Powder River 

plains tributary

769 4,480

P2 06313500 Powder River at Sussex, Wyo. Powder River at Sussex Powder River 

main stem

3,090 4,362

P3 06313540 Willow Creek near mouth, near 

Sussex, Wyo. 

Willow Creek Powder River 

plains tributary

— 4,295

P4 06313560 Pumpkin Creek near mouth, 

near Sussex, Wyo.

Pumpkin Creek Powder River 

plains tributary

— 4,180

P5 06313585 Beaver Creek at mouth, near 

Sussex, Wyo.

Beaver Creek Powder River 

plains tributary

— 4,020

P6 06313590 Powder River above Burger 

Draw, near Buffalo, Wyo.

Powder River above 

Burger Draw

Powder River 

main stem

4,290 4,000

P7 06313604 Burger Draw at mouth, near 

Buffalo, Wyo.

Burger Draw Powder River 

plains tributary

— 3,990

P8 06313605 Powder River below Burger 

Draw, near Buffalo, Wyo.

Powder River below 

Burger Draw

Powder River 

main stem

— 3,990

P9 06313633 Van Houten Draw at mouth, 

near Buffalo, Wyo.

Van Houten Draw Powder River 

plains tributary

— 3,970

P10 06313750 Barber Creek at mouth, near 

Buffalo, Wyo.

Barber Creek Powder River 

plains tributary

— 3,875

P11 06316400 Crazy Woman Creek at Upper 

Station, near Arvada, Wyo. 

Crazy Woman Creek Powder River 

mountain 

tributary

937 3,780

P12 06316900 Cottonwood Creek at mouth, 

near Arvada, Wyo. 

Cottonwood Creek Powder River 

plains tributary

— 3,700

P13 06317000 Powder River at Arvada, Wyo. Powder River at Arvada Powder River 

main stem

6,050 3,620

P14 06317020 Wild Horse Creek near Arvada, 

Wyo.

Wild Horse Creek near 

Arvada

Powder River 

plains tributary

250 3,730

P15 06317030 Wild Horse Creek at mouth, at 

Arvada, Wyo.

Wild Horse Creek at 

mouth

Powder River 

plains tributary

— 3,630

P16 06317095 Spotted Horse Creek at mouth, 

near Arvada, Wyo.

Spotted Horse Creek Powder River 

plains tributary

— 3,530
8 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification 

number

USGS site name Abbreviated site name Site group

Drainage area, 

in square 

miles

Altitude, 

in feet above 

vertical datum

P17 06317100 Powder River above Clear 

Creek, near Arvada, Wyo.

Powder River above Clear 

Creek

Powder River 

main stem

— 3,495

P18 06320210 Clear Creek above Kumor 

Draw, near Buffalo, Wyo.

Clear Creek near Buffalo Powder River 

mountain 

tributary

— 4,410

P19 06323550 Clear Creek above Double 

Crossing Creek, near Clearmont, Wyo.

Clear Creek near ClearmontPowder River 

mountain 

tributary

— 3,970

P20 06324000 Clear Creek near Arvada, Wyo. Clear Creek near Arvada Powder River 

mountain 

tributary

1,110 3,507

P21 06324200 LX Bar Creek at mouth, near 

Moorhead, Mont.

LX Bar Creek Powder River 

plains tributary

— 3,480

P22 06324300 SA Creek at mouth, near Moorhead, Mont. SA Creek Powder River 

plains tributary

— 3,440

P23 06324500 Powder River at Moorhead, 

Mont. 

Powder River at Moorhead Powder River 

main stem

8,086 3,351

P24 06324870 Rawhide Creek at mouth, near 

Gillette, Wyo. 

Rawhide Creek Little Powder 

River

— 4,030

P25 06324940 Horse Creek at mouth, near 

Weston, Wyo.

Horse Creek Little Powder 

River

— 3,595

P26 06324950 Little Powder River below Elk 

Creek, near Weston, Wyo.

Little Powder River below 

Elk Creek

Little Powder 

River

— 3,500

P27 06324970 Little Powder River above Dry 

Creek, near Weston, Wyo.

Little Powder River above 

Dry Creek

Little Powder 

River

1,237 3,410

C1 06365900 Cheyenne River near Dull 

Center, Wyo.

Cheyenne River near Dull 

Center

Cheyenne River 1,527 4,310

C2 06386500 Cheyenne River near Spencer, 

Wyo.

Cheyenne River near 

Spencer

Cheyenne River 5,350 3,626

B1 06425720 Belle Fourche River below 

Rattlesnake Creek, near 

Piney, Wyo.

 Belle Fourche River near 

Piney

Belle Fourche 

River

495 4,535

B2 06425900 Caballo Creek at mouth, near 

Piney, Wyo.

Caballo Creek Belle Fourche 

River

260 —

B3 06426400 Donkey Creek near Moorcroft, 

Wyo.

Donkey Creek Belle Fourche 

River

246 —

B4 06426500 Belle Fourche River below 

Moorcroft, Wyo.

Belle Fourche River below 

Moorcroft

Belle Fourche 

River

1,690 4,110

B5 06428050 Belle Fourche River below 

Hulett, Wyo. 

Belle Fourche River below 

Hulett

Belle Fourche 

River

— —

Table 1. Selected characteristics for sampling sites in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins, 

Wyoming and Montana.—Continued

[Shading indicates main-stem sites. USGS, U.S. Geological Survey; —, not determined. Vertical datum: National Geodetic Vertical Datum of 1929]
Introduction 9

the study area is Gillette, Wyo., with a population of about 

29,100; followed by Sheridan, Wyo., with a population of 

about 17,400 (U.S. Census Bureau, 2011). Rural populations 

are dispersed throughout the study area.

The Powder River structural basin is an asymmetric 

syncline with a northwest-to-southeast trending axis along the 

western margin (Rice and others, 2002). The structural basin 

is flanked by uplifts, including the Bighorn Mountains to the 

west and the Black Hills on the east. The CBNG development is associated with coalbeds in both the Wasatch and 

the Fort Union Formations. In Wyoming, the central part of 

the structural basin is dominated by terrestrial sedimentary 

rocks of the Wasatch Formation from the Eocene epoch. The 

Wasatch Formation contains alluvial sediments consisting 

primarily of mudstone and sandstone, with minor amounts of 

conglomerate, carbonaceous shale, and coal. Terrestrial sedimentary rocks of the Fort Union Formation from the Paleocene epoch crop out along the margins of the sedimentary 

basin in Wyoming. In Montana, the Wasatch Formation largely 

has been eroded, and the Fort Union Formation is the nearsurface bedrock throughout the lower part of the basin. Sandy 

soils are associated with the Wasatch Formation in Wyoming 

in contrast to clayey soils that are associated with the Fort 

Union Formation in Montana. This difference in geology 

has increased concerns about the effects of CBNG-produced 

waters in Montana, because the high clay content of soils 

makes them susceptible to problems associated with sodium 

ion exchange in clay particles (Wheaton and Donato, 2004). 

The geologic characteristics of the four major drainage 

basins are diverse. Detailed geology for the State of Wyoming 

is presented by Love and Christiansen (1985). Generalized 

maps for the Tongue and Powder River drainage basins (Zelt 

and others, 1999) and the Powder River structural basin (Rice 

and others, 2002) describe the geology for the Montana part of 

the study area. The bedrock of the western edge of the Tongue 

and Powder River drainage basins includes metamorphic 

gneiss and plutonic igneous rocks from the Precambrian era, 

and sedimentary rocks of marine origin from the Paleozoic 

and Mesozoic eras compose the Bighorn Mountains (Love 

and Christiansen, 1985). The bedrock of the eastern part of 

the Tongue River drainage basin and a large part of the central 

Powder River drainage basin is underlain by the Wasatch 

Formation. The Fort Union Formation is prevalent in the 

lower drainage basins of the Tongue River, Clear Creek, the 

Powder River, and the Little Powder River. The upper parts 

of the Cheyenne and Belle Fourche River drainage basins 

are underlain by the Wasatch Formation, with Fort Union 

Formation in the lower reaches of those drainage basins that 

are still within the structural basin. Farther downstream and 

outside the boundary of the structural basin (fig. 1), bedrock 

geology includes sedimentary rocks of terrestrial and marine 

origin from the Cretaceous period. The lower part of the 

Belle Fourche River drainage basin (southeast of site B5) is 

underlain by rocks from the Paleozoic and Mesozoic era that 

compose part of the Black Hills. 

The Tongue, Powder, Cheyenne, and Belle Fourche 

Rivers are part of the Missouri River drainage basin. The 

Tongue and Powder Rivers generally flow northward toward 

the Missouri River, whereas the Cheyenne and Belle Fourche 

Rivers generally flow eastward toward the Missouri River. The 

Tongue River drainage basin is the smallest of the four drainage basins, with a drainage area of 1,453 square miles (mi2

) 

at the Tongue River at State line (site T6). The Powder River 

drainage basin is the largest of the four drainage basins, with a 

drainage area of 8,086 mi2 for the Powder River at Moorhead 

(site P23). The hydrologic characteristics vary among the 

drainage basins. Mean annual precipitation, which accounts 

for much of the difference, ranges from about 10 to 15 inches 

(in.) in the plains to nearly 40 in. at high altitudes in the Bighorn Mountains (PRISM Climate Group, 2006). The hydrograph for the Tongue River typically is dominated by a single 

peak of moderate duration from snowmelt in the Bighorn 

Mountains during late spring through early summer and generally has relatively low variability in streamflow throughout the 

remainder of the year (Clark and Mason, 2007). In contrast, 

streamflows of the Powder, Cheyenne, and Belle Fourche 

Rivers are more variable. The Powder River generally has an 

early spring peak in response to lowland snowmelt, followed 

by a higher peak from snowmelt in the Bighorn Mountains. 

Short duration peaks occur in response to rainfall, and periods 

of low flow or no flow are common in late summer. The Cheyenne and Belle Fourche Rivers generally have an increase in 

streamflow during spring in response to lowland snowmelt, 

intermittent peaks in response to rainstorms, and extended 

periods of low flow. For the Cheyenne River, extended periods 

of no flow are common.

The general stream-water chemistry of the Tongue, Powder, Cheyenne, and Belle Fourche Rivers varies because of 

differences in geologic and hydrologic characteristics. For the 

Tongue River at the State line (site T6), which integrates the 

upper basin, water type is magnesium-calcium bicarbonate. 

The Tongue River has the smallest specific conductance values, sodium adsorption ratios, and major ion concentrations, 

because it has the largest percentage of area underlain by older 

and more resistant rocks of the Bighorn Mountains (Clark and 

Mason, 2007) of the streams included in the study. In general, 

high annual precipitation and steep gradients for much of the 

Tongue River drainage basin produce relatively fast stream 

velocities, which result in a short contact time between stream 

waters and basin materials. The Powder River drainage basin 

has mixed characteristics. Water type is a sodium-sulfate, and 

dissolved constituents are concentrated in stream water in the 

upper and eastern part of the drainage basin that originates 

in the plains, including the Little Powder River, which drains 

into the Powder River downstream from Moorhead, Mont. 

Drainage basins in the plains have low precipitation, soluble 

geologic materials, and relatively low gradients that produce 

slow stream velocities and long contact times. Western tributaries of Crazy Woman Creek and Clear Creek that drain from 

the Bighorn Mountains have a dilution effect on dissolved 
10 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

constituents of the Powder River, and the water type of the 

Powder River in the lower basin changes to a mixed sodiummagnesium-calcium-sulfate type (Clark and Mason, 2007). 

Water type of the Cheyenne River, which lies entirely in the 

plains, is a sodium-sulfate type, and dissolved constituents 

are concentrated. The Belle Fourche River is characterized as 

a sodium-sulfate type, and dissolved constituents are concentrated in the upper basin. Cations are mixed, and dilution 

occurs in the lower Belle Fourche River drainage basin as a 

result of changes in geology and precipitation associated with 

the Black Hills. 

Data Collection and Analysis

Water-quality data for 40 sampling sites in the Tongue, 

Powder, Cheyenne, and Belle Fourche River drainage basins 

were compiled for this report (table 2). Sampling sites and 

water-quality characteristics monitored have varied slightly 

through the monitoring period. When monitoring for effects of 

CBNG development began in water year 2001, sites generally 

were established on the main-stem streams and their primary 

tributaries. Additional sites were established in the Powder 

River drainage basin during summer 2004, commonly on 

small tributaries that receive discharges of CBNG-produced 

waters. Water-quality sampling did not begin at some of these 

sites until after water year 2004 because some streams were 

not flowing during early visits. Sampling frequency generally was on a monthly basis; however, sampling frequency 

was substantially less at sites that did not have perennial flow. 

Sampling frequency was increased at a few sites, including 

the Tongue River at State line (site T6) and the Powder River 

at Moorhead (site P23). A few samples that were collected as 

part of other sampling programs, such as the USGS National 

Water-Quality Assessment Program and the Tongue River 

monitoring network (Nimick, 2004) were included in this 

report to supplement data at a few sites. Data collection methods and chemical analysis methods for those programs were 

similar to those used for this study. Sampling was discontinued at a few sites where monitoring needs changed or where 

monitoring could be more efficiently conducted at a different 

site. For example, monitoring in the Cheyenne River drainage 

basin initially was conducted at sampling sites on some small 

tributaries. A site was eventually established on the Cheyenne 

River near Dull Center (site C1) to integrate water quality 

in the upper part of the drainage basin. Data summaries for 

discontinued sites were not compiled for this report, but may 

be found in Clark and Mason (2007). 

Water-quality characteristics analyzed for this report 

varied by site because of differences in analytical services 

requests. For all sites, field measurements of streamflow, pH, 

and specific conductance are reported. The major ion concentrations and properties of calcium, magnesium, sodium, 

SAR, alkalinity, chloride, sulfate, and dissolved solids are 

summarized for sites where major ion analyses were requested 

(table 2). For other sites, major cations (calcium, magnesium, 

and sodium), SAR, and dissolved solids are summarized 

where abbreviated analytical services were requested. Additional constituents, such as potassium, fluoride, nutrients, or 

trace elements, were analyzed in some samples, but results are 

not included in this report because these constituents do not 

contribute substantially to specific conductance compared to 

other major ions. A description of all water-quality characteristics is beyond the scope of this report; however, all waterquality data are electronically stored in the USGS’s National 

Water Information System (NWIS) and are available to the 

public from NWISWeb (U.S. Geological Survey, 2011a) at 

http://waterdata.usgs.gov/nwis/. 

Field and Analytical Methods

Field measurements were made and samples were collected in accordance with methods established by the USGS 

(U.S. Geological Survey, variously dated). Instantaneous 

streamflow typically was measured using a current meter. For 

sampling sites where streamgages are operated, some instantaneous streamflow measurements were obtained by recording gage heights and determining the streamflow using the 

most current streamflow rating curve. Specific conductance 

and pH generally were measured in-stream using a multiparameter water-quality probe. For large streams during normal 

streamflow conditions, samples to be analyzed for major ion 

concentrations generally were collected using depth-integrated 

samplers and applying the equal-width-increment method 

described by Ward and Harr (1990). When samples were collected from large streams during extreme conditions, such as 

hazardous ice conditions and very low flows of shallow depth, 

traditional depth- and width-integrating techniques may not 

have been possible and multiple vertical or grab-sampling 

techniques were used. For small streams, streamflow conditions generally did not meet depth-integrated sampler requirements; therefore, grab-sampling techniques were used. 

Samples were processed onsite using standard methods 

and equipment described by the U.S. Geological Survey (variously dated). Subsamples analyzed for major ion concentrations were filtered in the field using a disposable filter with a 

pore size of 0.45 micrometer, and concentrations are reported 

as dissolved. Subsamples analyzed for major cation concentrations were acidified in the field with nitric acid. Samples 

were sent to the USGS National Water Quality Laboratory in 

Lakewood, Colo., for analysis using standard USGS methods 

(Fishman and Friedman, 1989; Fishman, 1993). Alkalinity 

values were determined in the laboratory using a fixed-end 

titration method and are reported as the equivalent amount of 

calcium carbonate. Alkalinity values represent the combined 

bicarbonate and carbonate concentrations, with bicarbonate 

being the primary contributor. Dissolved-solids concentrations 

were determined analytically for an aliquot of filtered water 

using a method for residue on evaporation at 180°C. The SAR 

values were calculated on the basis of laboratory results for 
Data Collection and Analysis 11

Table 2. Periods for which water-quality data were analyzed for sampling sites in the Tongue, Powder, Cheyenne, and Belle Fourche 

River drainage basins, Wyoming and Montana.

[Shading indicates main-stem sites. USGS, U.S. Geological Survey; F, field measurements of streamflow, pH, and specific conductance; M, analyses of major 

ions, sodium-adsorption ratio, and dissolved solids; C, analyses of cations, sodium adsoprtion ratio, and dissolved solids]

Site number 

(fig. 1)

USGS site 

identification 

number

Water-quality characteristics data summary 

period (water years)

Water-quality 

characteristics included 

in this report

Water year 

2001–10 trends

Water year 

2005–10 trends

Water year 

1991–2010 

trends

T1 06299980 2004–10 F, M No Yes No

T2 06304500 2001–10 F, M1 Yes No No

T3 06305500 2001–10 F, M1 Yes No Yes

T4 06306200 2004–10 F, M No Yes No

T5 06306250 2001–10 F, M Yes Yes No

T6 06306300 2001–10 F, M Yes Yes Yes

P1 06313400 2001–10 F, M Yes Yes Yes

P2 06313500 2001–10 F, M Yes Yes Yes

P3 06313540 2008–10 F, C2 No No No

P4 06313560 2005–10 F, C2 No Yes No

P5 06313585 2004–10 F, C2 No Yes No

P6 06313590 2003–10 F, M No Yes No

P7 06313604 2004–10 F, C2 No Yes No

P8 06313605 2001–10 F, M Yes Yes No

P9 06313633 2004–10 F, C2 No No No

P10 06313750 2005–10 F, C2 No No No

P11 06316400 2001–10 F, M Yes Yes No

P12 06316900 2004–10 F, C2 No No No

P13 06317000 2001–10 F, M Yes Yes Yes

P14 06317020 2001–10 F, M No No No

P15 06317030 2004–10 F, C2 No Yes No

P16 06317095 2004–10 F, C2 No No No

P17 06317100 2004–10 F, C No Yes No

P18 06320210 2001–10 F, M1 Yes Yes No

P19 06323550 2004–10 F, C2 No Yes No

P20 06324000 2001–10 F, M Yes Yes No

P21 06324200 2005–10 F, C2 No No No

P22 06324300 2004–10 F, C2 No Yes No

P23 06324500 2001–10 F, M Yes Yes Yes

P24 06324870 2007–10 F, C No No No

P25 06324940 2005–10 F, C No No No

P26 06324950 2004–10 F, C No Yes No

P27 06324970 2001–10 F, M Yes Yes Yes

C1 06365900 2004–10 F, M No No No

C2 06386500 2005–10 F, M No Yes No

B1 06425720 2001–10 F, M Yes Yes No

B2 06425900 2001–10 F, M No No No

B3 06426400 2001–10 F, M Yes Yes No

B4 06426500 2001–10 F, M Yes Yes Yes

B5 06428050 2001–10 F, M1 Yes No No

1

Major ions added in water year 2002.

2

Anions included in water year 2010.
12 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

discrete samples. The SAR values were calculated using the 

analytical results for dissolved calcium, dissolved magnesium, 

and dissolved sodium obtained for a discrete sample using the 

following equation:

SAR Na

Ca Mg

=

( ) + ( ) 

 

+

+ +

( )

1 2 2 2

(1)

where Na+, Ca2+, and Mg2+ represent concentrations expressed 

in milliequivalents per liter for sodium, calcium, and magnesium, respectively. 

Data Analysis Methods

Data for this report were analyzed using several statistical techniques. Descriptive summary statistics (minimum 

value, 25th percentile, median (50th percentile), 75th percentile, and maximum value) were compiled by site for selected 

water-quality characteristics of streamflow, pH, specific 

conductance, dissolved solids, instantaneous dissolved-solids 

loads, dissolved calcium, dissolved magnesium, SAR, dissolved sodium, alkalinity, dissolved chloride, and dissolved 

sulfate. Boxplots are used to graphically summarize specific 

conductance and SAR data by site group. Sites were grouped 

together for boxplots because of the large number of monitoring sites. Sites in the Tongue, Cheyenne, and Belle Fourche 

River drainage basins were grouped together by their major 

drainage basin because water-quality characteristics generally were similar in their range of values. Because of the wide 

range of water-quality characteristics and large number of 

sites in the Powder River drainage basin, sites were grouped 

as Powder River plains tributaries, Powder River mountain 

tributaries, Powder River main stem, and Little Powder River 

(table 1). For the boxplots, the lower and upper edges of the 

box indicate the 25th and 75th percentiles, respectively, and 

the median is a line within the box. The whiskers extend to the 

smallest value within 1.5 times the interquartile range below 

the 25th percentile and the largest value within 1.5 times the 

interquartile range above the 75th percentile. Values outside 

this range are shown as individual points. Scatter plots of 

specific conductance and SAR for selected main-stem sites are 

shown with a locally weighted, scatterplot smoothing curve, 

which is a nonparametric technique used to reduce apparent 

scatter in the overall pattern of data (TIBCO Software, Inc., 

2008). The curve does not necessarily correspond with a significant statistical trend through time when seasonal variation 

is taken into account.

Trend analysis techniques, which are used to determine 

if data have statistically changed through time, have been 

developed by the USGS and account for the inherent variability of water-quality data. Trend analysis techniques vary in 

their statistical strength and data requirements. For example, 

the water-quality model, QWTREND, is a robust parametric 

technique that evaluates data for nonmonotonic trends (trends 

that have one or more changes in slope during the period 

being evaluated); however, it requires a daily mean streamflow 

record and a water-quality record of at least 15 years (Vecchia, 2005). The EStimate TREND (ESTREND) statistical 

trend procedure uses the seasonal Kendall test, which is a 

nonparametric test to determine monotonic (single direction 

through the entire specified trend period) trends in waterquality data (Schertz and others, 1991). Data requirements 

for the ESTREND procedure are less restrictive than for the 

QWTREND model in that only instantaneous measurements 

of streamflow are required to be associated with water-quality 

data and recommended minimum data requirements include 

a 5-year period of water-quality record and at least 50 observations. The ESTREND procedure is less statistically robust 

than QWTREND; however, less rigid data requirements 

allows ESTREND to be applied to more sites. The ESTREND 

procedure was selected as the statistical procedure for this 

study because of the relatively short sampling period since 

2001 when the monitoring for CBNG development began and 

because daily mean streamflow records do not exist for many 

sites. 

The ESTREND procedure is contained as a program 

within the USGS library for S-PLUS for Windows, Release 

2.1 (Slack and others, 2003). The program divides the selected 

time period into a beginning-ending period that is about 

40 percent of the analysis period and a middle period that is 

about 60 percent of the analysis period. Seasonal definitions 

can range from 2 seasons per year to as many as 12 seasons 

per year. Minimum criteria were established for the percentage 

of possible comparisons within a season adequate to define 

a trend (50 percent) and the percentage of seasons that meet 

the criterion for seasonal definition (80 percent). The program computes a separate Mann-Kendall test for each of the 

defined seasons. By restricting the possible comparisons to 

water-quality values that are collected during the same season, 

the effect of seasonal variation is reduced (Hirsch and others, 

1982; Helsel and Hirsch, 1992). The null hypothesis for the 

Mann-Kendall test is that the probability distribution of the 

variable has not changed over time (Schertz and others, 1991). 

The test makes all possible pair-wise comparisons of timeordered water-quality values within the season and assigns a 

large value that is later in time a “plus” and a small value that 

is later in time a “minus.” The test statistic is computed as the 

difference between the total number of pluses and the total 

number of minuses; therefore, the more the test statistic deviates from zero, the more likely a trend exists. The ESTREND 

program computes the seasonal Kendall test by combining 

results of the Mann-Kendall tests. The p-value (p) is obtained 

from a standard normal distribution of the overall test statistic. 

The ESTREND program was used to compute a seasonal 

Kendall test on unadjusted concentrations and flow-adjusted 

concentrations. Trend results for unadjusted concentrations 

may be useful to water managers because unadjusted concentrations commonly are used for making water-quality 

assessments, such as comparisons to water-quality criteria. 

Otherwise, the usefulness of trend results for unadjusted concentrations is limited because concentrations of water-quality 
Data Collection and Analysis 13

constituents commonly are correlated with streamflow, which 

may change in response to seasonal and annual climatic variability. An apparent trend in unadjusted concentrations may 

simply be an artifact of streamflow conditions at the time of 

sampling. Flow-adjusting techniques increase the likelihood 

that a resulting trend is real and not an artifact of streamflow 

variability. Parametric models that use linear regression and 

nonparametric models that use locally weighted least-squares 

regression exist within the ESTREND program for filtering 

out streamflow-related variability before analyzing for constituent trends. 

The strength of relations between streamflow and waterquality data characteristics was variable among sites, particularly in some of the small tributary drainages. As a result, a 

nonparametric local regression model with base-10 logarithm 

transformation of streamflow was selected in the ESTREND 

program for flow adjustment. The residuals (estimated values 

minus measured values), which are called flow-adjusted 

concentrations, are then tested using the seasonal Kendall trend test (Schertz and others, 1991). Results from the 

seasonal Kendall test include tau, a rank-based correlation 

coefficient, which measures the strength of the monotonic 

relation between a water-quality variable and time, with values 

ranging from -1 to +1. Tau values greater than zero indicate 

the variable has a tendency to increase over time, and negative tau values indicate a tendency to decrease. As deviations 

of tau from zero increase, the strength of the correlation 

increases. The upward or downward direction of the trend is 

presented if the trend was significant, which was determined 

using a 95-percent confidence level (p<0.05). Slopes of trends 

also were calculated. For unadjusted trend tests, the slopes of 

trends reflect changes per year in original measurement units; 

for flow-adjusted trend tests, the slopes reflect relative changes 

in units after adjustment for streamflow variability. 

Sample size for the trend test is determined by both the 

length of the trend period and the seasonal period. Efforts 

were made to maximize the number of sites meeting the 

requirement of 50 observations by adjusting trend periods and 

seasonal definitions. Trend analysis initially was scoped for 

the 10-year period of water years 2001–10 to coincide with 

the data collection period for CBNG monitoring. Bimonthly 

seasonal periods were defined for the seasonal Kendall test as 

October through November, December through January, February through March, April through May, June through July, 

and August through September. Data from 17 of the 40 sites 

(table 2) met the trend test requirements for the period of 

water years 2001–10. In order to increase the spatial coverage 

of sites, trends were analyzed for the 6-year period of water 

years 2005–10 to include those sites added to the monitoring 

program during 2004. Data from 26 of the 40 sites (table 2) 

met the trend test requirements for the period of water years 

2005–10. Seasonal periods were defined for the seasonal Kendall test to correspond with the monthly sampling frequency. 

Data were not sufficient to meet trend test requirements for 

either the 2001–10 or 2005–10 trend periods at 11 sites that 

commonly were dry (table 2). To place the trends in a longer 

time frame and include data collected prior to widespread 

CBNG development, a 20-year trend period of water years 

1991–2010 was analyzed for eight sites that had historical data 

(table 2). Seasonal periods were defined as October through 

December, January through March, April through June, and 

July through September, to coincide with historical quarterly 

sampling frequencies. 

Quality Assurance

Quality assurance can be assessed using data-quality 

checks and quality-control samples. Data-quality checks routinely are conducted on laboratory results. Field and laboratory values are checked for compatibility; ion balances are 

calculated and percent differences are checked; and data ratios 

(such as dissolved solids to specific conductance) are checked 

against typical data ranges. For a few samples, constituent 

values were rejected during this review period and were not 

included in this report. Where a field specific conductance 

value was missing or rejected, a laboratory specific conductance value was used to complete the time-series record for 

this report. The median ion balance difference was 1.4 percent 

for 2,878 samples where an ion balance could be calculated. 

Less than 2 percent of samples had ion balance differences 

greater than the quality-check range of plus or minus 5.5 percent. Samples with ion balances outside this range were 

further evaluated. Ratios of dissolved-solids concentration to 

specific conductance typically are from 0.55 to 0.75 for natural 

waters, with the full range expected from 0.54 to 0.96 (Hem, 

1985). About 98 percent of samples were within this range. A 

few samples that had differences or ratios outside these ranges 

were samples with large dissolved-solids concentrations. 

Samples with large dissolved-solids concentrations typically 

had large sulfate concentrations that can cause large ratios of 

dissolved-solids concentration to specific conductance (Hem, 

1985). Also, samples with large dissolved-solids concentrations may require laboratory dilution, which can result in some 

additional analytical variability. 

Quality-control samples, including equipment blank samples and replicate samples, are collected to help estimate the 

bias and variability resulting from sample collection, processing, and chemical analysis. Equipment blank samples typically 

are collected and processed using inorganic-grade deionized 

water to demonstrate that field methods and laboratory analysis have not introduced contamination to the sample, thus providing a measure of bias (Mueller and others, 1997). Replicate 

samples are prepared by splitting the routine environmental 

sample into duplicate subsamples, which are considered to 

be identical in composition. Laboratory analyses of replicate 

samples provide a measure of variability (or reproducibility). 

Measurement variability for replicate samples was determined 

for constituents by calculating a relative percent difference 

(RPD) between concentrations in the paired replicate samples 

using the following equation:
14 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

RPD routine environment sample concentration replicat = × − 100 | e sample concentration

routine environment sample concent

 |

( ) ration r + eplicate s ample concentration  

 / 2 (2)

Analysis of quality-control samples for water years 

2001–05 (Clark and Mason, 2007) indicated contamination 

was not causing widespread bias and that laboratory reproducibility was good; therefore, an abbreviated summary of 

quality-control data collected during water years 2001–10 is 

provided in this report. The maximum concentration for major 

cation constituents of dissolved calcium, magnesium, and 

sodium was 0.2 mg/L or less in 165 equipment blank samples 

(table 3). The maximum concentration for major anion constituents of dissolved chloride and sulfate was 0.4 mg/L or 

less in 117 equipment blank samples. Alkalinity (as calcium 

carbonate) concentrations were less than the laboratory 

reporting level of 8 mg/L for 108 equipment blank samples. 

The median RPD was 1.6 percent or less for 173 samples for 

replicate measurements of dissolved calcium, magnesium, and 

sodium. The median RPD was 0.53 percent or less for 123 

samples for replicate measurements of alkalinity, dissolved 

chloride, and dissolved sulfate. Results for data-quality checks 

and quality-control samples for water years 2001–10 continue 

to support findings that field and laboratory procedures are not 

introducing bias and variability that affect the interpretation of 

environmental samples. 

Table 3. Quality-control summary for equipment blank samples and replicate samples collected at 

sampling sites in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins, Wyoming 

and Montana, water years 2001–10.

[<, less than]

Constituent

Number of 

equipment 

blank samples

Maximum concentration in equipment blank 

sample, in milligrams 

per liter

Number of 

replicate 

sample pairs

Median relative 

percent 

difference 

Calcium, dissolved 165 0.08 173 1.6

Magnesium, dissolved 165 0.04 173 1.4

Sodium, dissolved 165 0.2 173 1.6

Alkalinity, as calcium 

carbonate

108 <8.0 123 0.29

Chloride, dissolved 117 0.4 123 0.53

Sulfate, dissolved 117 0.4 123 0.28
Water-Quality Characteristics 15

Water-Quality Characteristics

Water-quality characteristics at 40 sampling sites in 

the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins were summarized for water years 2001–10 

(appendix 1). Statistical summaries include properties of 

streamflow, pH, specific conductance, and SAR and concentrations of selected constituents including dissolved solids, major 

ions, and alkalinity (appendix 1). The statistical summaries 

represent the range of conditions for a given site for the period 

of data collection (table 2). General patterns in the data for 

streamflow, specific conductance, and SAR are described in 

this section.

Streamflow

Hydrologic conditions are an important factor in waterquality variability and are described to provide perspective on 

differences in water quality that can occur annually. Annual 

runoff for selected main-stem sites on the Tongue, Powder, 

Cheyenne, and Belle Fourche Rivers varied substantially 

during water years 2001–10 (fig. 3). For comparison, average annual runoff for period of record (U.S. Geological 

Survey, 2011b) is 316,500 acre-ft (water years 1961–2010) 

for the Tongue River at State line (site T6); 319,100 acre-ft 

(water years 1930–2010, excluding 1973 and 1974) for the 

Powder River at Moorhead (site P23); 35,080 acre-ft (water 

years 1949–2010, excluding 1975–2003) for the Cheyenne 

River near Spencer (site C2); and 16,380 acre-ft (water years 

1944–2010, excluding 1971–75, 1984–85, and 1988–90) 

for the Belle Fourche River below Moorcroft (site B4). In 

general, annual runoff was less than average as a result of less 

than average precipitation during water years 2001–06 on the 

Tongue, Powder, and Belle Fourche Rivers (Natural Resources 

Conservation Service, 2011). Annual runoff was near or above 

average for sites on those rivers during water years 2007–10. 

Annual runoff for the Cheyenne River was less than average 

during water years 2004–10. 

Variability in streamflows primarily results from variability in the distribution of precipitation in these drainage basins. 

The magnitude of streamflow during a sampling event can 

affect stream-water quality in several ways. Large magnitude 

streamflows tend to have small concentrations of dissolved 

constituents as a result of dilution but commonly have large 

concentrations of suspended constituents. Streamflow at a site 

can vary by orders of magnitude; thus, it is important to collect water-quality samples throughout the year to adequately 

characterize extremes, seasonal differences, and average 

conditions. 

Streamflow measured during sampling events for the 

Tongue River at State line (site T6) ranged from 10 cubic feet 

per second (ft3/s) to 5,430 ft3/s during water years 2001–10 

(appendix 1) and generally covered the hydrograph for 

continuous streamflow data collected at the USGS streamgage 

at this site (fig. 4). Streamflow measured during sampling 

events for the Powder River at Moorhead (site P23) ranged 

from 0.57 to 5,220 ft3/s and generally covered the hydrograph for the USGS streamgage at this site (fig. 4). Because 

streamflow peaks on the Tongue and Powder Rivers generally 

are associated with snowmelt runoff and are sustained for a 

period of time, sampling events are able to capture nearly all 

of the full range of conditions. Streamflow measured during 

sampling events ranged from 0.01 to 121 ft3/s for the Cheyenne River near Spencer (site C2) during water years 2005–10 

and from 0.02 to 599 ft3/s for the Belle Fourche River below 

Moorcroft (site B4) during water years 2001–10. Peak streamflow events on the Cheyenne and Belle Fourche Rivers are 

difficult to capture during sampling events because they occur 

rapidly in response to rainfall. 

Streamflow varied substantially for tributaries in the 

drainage basins during water years 2001–10 (appendix 1). 

In the Tongue River drainage basin, Goose Creek has a 

large part of its drainage area in the Bighorn Mountains and 

contributes substantial flow to the Tongue River, particularly 

during snowmelt runoff. Instantaneous streamflow during 

sampling events for Goose Creek (site T3) ranged from 3.8 

to 1,790 ft3/s. In contrast, streamflow for Prairie Dog Creek 

near Acme (site T5), which has most of its drainage area in the 

plains, ranged from 0.21 to 127 ft3/s. Streamflows in Prairie 

Dog Creek are augmented by transbasin diversions for irrigation in the summer and are larger than would naturally occur 

(Sheridan County Conservation District, 2011). In the Powder 

River drainage basin, the range of instantaneous streamflow 

measured for plains tributaries in the eastern part of the basin 

generally is small; for example, streamflow ranged from 0.06 

to 1.6 ft3/s for Willow Creek (site P3); from 0.04 to 2.8 ft3/s 

for Burger Draw (site P7); and from 0.03 to 3.6 ft3/s for Van 

Houten Draw (site P9). Streamflow in these small drainages 

responds very quickly to precipitation events, and runoff 

events, if they occur at all during the year, rarely coincided 

with sampling events. Discharges of CBNG-produced 

waters can sustain flows in some of these small drainages for 

extended periods; however, tributaries were completely dry 

during some site visits. In contrast to the eastern tributaries, 

instantaneous streamflow for sampling events ranged from 

0.01 to 422 ft3/s on Crazy Woman Creek (site P11) and from 

0.24 to 2,230 ft3/s on Clear Creek near Arvada (site P20) 

because snowmelt from the Bighorn Mountains contributes to 

streamflows in the spring. In the Belle Fourche River drainage 

basin, instantaneous streamflow values measured on Donkey 

Creek (site B3) ranged from 0.05 to 46 ft3/s and were larger 

than streamflows measured on Caballo Creek (site B2), which 

ranged from 0.02 to 7.4 ft3/s. Flows on Donkey Creek generally are sustained from discharges of CBNG-produced water, 

discharges from coal mines, and discharges from the City of 

Gillette (Wyoming Department of Environmental Quality, 

2010). 
16 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Figure 3. Annual runoff for selected main-stem sampling sites in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage 

basins, Wyoming and Montana, water years 2001–10.

B

A

Annual runoff, in acre-feet

0

5,000

10,000

15,000

20,000

25,000

30,000

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

0

100,000

200,000

300,000

400,000

500,000

600,000

Water year

T6

EXPLANATION

P23

Site number (table 1)

EXPLANATION

B4

C2

Site number (table 1)
Figure 4. Streamflow at sites in the A, Tongue; B, Powder; C, Cheyenne; and D, Belle Fourche River drainage basins, Wyoming and Montana, water years 2001–10.

10

100

1,000

Streamflow, in cubic feet per second

A Tongue River (site T6)

1.00.1

10

100

1,000

10,000 B Powder River (site P23)

0.01

0.1

1

10

100

1,000

C Cheyenne River (site C2)

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

0.01

0.1

1

10

100

1,000

D Belle Fourche River (site B4)

Water year

Water-Quality Characteristics 17
18 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Specific Conductance

Field measurements of specific conductance in streams 

varied among site groups for the four major drainage basins. 

Stream water in the Tongue River drainage basin had the 

smallest median specific conductance values of the four drainage basins, indicating that concentrations are diluted by large 

runoff in this drainage basin. Water concentrations are largest, 

as indicated by the largest median specific conductance, in the 

Cheyenne River drainage basin. Specific conductance values 

were most variable for plains tributaries to the Powder River 

(fig. 5). 

For selected Tongue, Powder, Cheyenne, and Belle 

Fourche River main-stem sites, specific conductance values 

were examined through time (fig. 6). The range of specific 

conductance values measured on the main stem of the Tongue 

River (site T6) is substantially smaller and the least variable through time compared to specific conductance values 

measured on the Powder River (site P23), Cheyenne River 

(site C2), and Belle Fourche River (site B4). Specific conductance values measured on the Cheyenne River (site C2) were 

highly variable through time. The curve (fig. 6) smoothes 

the overall pattern of data with time; however, it may not 

necessarily correspond with a significant trend through time 

when seasonal variation is taken into account. 

Median specific conductance values at sites in the Tongue 

River drainage basin ranged from 411 μS/cm at 25°C for the 

Tongue River at Monarch (site T1) to 1,460 μS/cm at 25°C 

for Prairie Dog Creek near Acme (site T5) during water 

years 2001–10 (appendix 1). Median specific conductance is 

substantially smaller (936 μS/cm at 25°C) upstream on Prairie 

Dog Creek near Sheridan (site T4) compared to near Acme 

(site T5), which is downstream from much of the CBNG 

development (based on compilation of data retrieved from 

Wyoming Oil and Gas Conservation Commission, 2011). 

Irrigated areas occur throughout the Prairie Creek drainage 

basin (Sheridan County Conservation District, 2011). Overall, 

specific conductance values are smaller for Prairie Dog Creek 

compared to other plains tributaries because transbasin diversions, which are contributed from tributaries that originate in 

the Bighorn Mountains and receive snowmelt runoff, likely 

have a dilution effect on specific conductance. Although the 

Prairie Dog Creek drainage basin has the most CBNG production in the Tongue River drainage basin (based on compilation 

of data retrieved from Wyoming Oil and Gas Conservation 

Commission, 2011), CBNG-produced waters generally are 

Figure 5. Statistical summary of specific conductance for site groups in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.

0

2,000

4,000

6,000

8,000

10,000

12,000

Specific conductance, in microsiemens per centimeter at 25 degrees Celsius

Tongue

River

Powder River

plains

tributaries

Powder River

mountain

tributaries

Powder River

main stem

Little Powder

River 

Cheyenne

River

Belle

Fourche

River

663

770

585

871

256

103

500

Site group

EXPLANATION

Number of values 

75th percentile

50th percentile

(median)

25th percentile

Interquartile range

500

Largest value within 1.5 times 

interquartile range above 

the 75th percentile

Smallest value within 1.5 times 

interquartile range below the 

25th percentile

Value is greater than 1.5 times the 

interquartile range beyond either 

end of box
Water-Quality Characteristics 19

not discharged directly into Prairie Dog Creek. Most produced 

waters are discharged into on- and off-channel impoundments 

in unnamed draws or small streams that drain into Prairie 

Dog Creek (Sheridan County Conservation District, 2011). 

Quillinan and others (2012) identified a small tributary that 

originates in the plains and flows into Prairie Dog Creek 

between sites T4 and T5 as a major contributor to the specific 

conductance of lower Prairie Dog Creek. Specific conductance 

increased on the main stem of the Tongue River from the 

upstream site at Monarch (site T1) to downstream at State line 

(site T6), where the median value was 636 μS/cm at 25°C, in 

part because of inflows from Prairie Dog Creek. 

 The Powder River drainage basin has the largest drainage area and most diverse site conditions among the four 

major drainage basins resulting in the most variable specific 

conductance values (fig. 5). Median specific conductance 

values in the basin ranged from 672 μS/cm at 25°C for Clear 

Creek near Buffalo (site P18) during water years 2001–10 to 

7,350 μS/cm at 25°C for SA Creek (site P22) during water 

years 2004–10 (appendix 1). Salt Creek (site P1) had the 

second largest median specific conductance of 5,950 μS/cm 

at 25°C during water years 2001–10. Salt Creek contributes 

the largest dissolved-solids load to the Powder River of any 

plains tributary because of its larger streamflows. Salt Creek 

is upstream from any CBNG development in the Powder 

River drainage basin; however, it receives discharges of saline 

groundwaters that are associated with conventional gas and 

oil production in that basin (RETEC Group, Inc., 2004). In 

the upper part of the Powder River drainage basin, eastern 

drainages such as Willow Creek (site P3), Pumpkin Creek 

(site P4), and Burger Draw (site P7) receive discharges of 

CBNG-produced waters and generally have larger specific 

conductance values than the main-stem sites on the Powder 

River (appendix 1). In the lower part of the Powder River 

drainage basin downstream from Arvada, Wyo., eastern drainages receiving CBNG-produced waters with large specific 

conductance values include Wild Horse Creek (site P14 and 

site P15) and Spotted Horse Creek (site P16). The largest 

specific conductance measured for any sampling event was 

11,200 μS/cm at 25°C on LX Bar Creek (site P21). LX Bar 

Creek and SA Creek (site P22) are eastern plains drainage 

basins with CBNG development that drain into the Powder 

Figure 6. Specific conductance through time at sites in the A, Tongue; B, Powder; C, Cheyenne; and D, Belle Fourche River drainage 

basins, Wyoming and Montana, water years 2001–10.

0

2,000

4,000

6,000

Specific conductance, in microsiemens

per centimeter at 25 degrees Celsius

Specific conductance, in microsiemens

per centimeter at 25 degrees Celsius

A Tongue River (site T6) B Powder River (site P23)

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Water year

0

2,000

4,000

6,000

C Cheyenne River (site C2)

D Belle Fourche River (site B4)

Locally weighted, scatterplot 

smoothing curve

EXPLANATION

Sample
20 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

River downstream from Clear Creek and upstream from 

the Powder River at Moorhead (site P23). Median specific 

conductance (1,820 μS/cm at 25°C) at Moorhead (site P23) 

is smaller than median specific conductance (2,200 μS/cm at 

25°C) upstream at the Powder River above Clear Creek (site 

P17) because of the dilution effects from Clear Creek.

Median specific conductance values for the Cheyenne 

River were 3,645 μS/cm at 25°C near Dull Center (site C1) 

during water years 2004–10 and 4,900 μS/cm at 25°C near 

Spencer (site C2) during water years 2005–10 (appendix 1). 

The entire Cheyenne River drainage basin is in the plains, 

where low precipitation and relatively low land-surface 

gradients produce slow stream velocities and long contact 

times with soluble geologic materials, resulting in large 

amounts of dissolved solids. Water quality for the Cheyenne 

River near Dull Center (site C1) generally is representative 

of groundwater, because flow at site C1 issues from nearby 

groundwater seeps. The Cheyenne River channel typically is 

completely dry upstream from the seeps at site C1. Fogg and 

others (1991) reported groundwater in the local flow system in 

the upper Cheyenne River drainage basin may be discharged 

by springs and flowing wells. The Cheyenne River near Dull 

Center (site C1) has the smallest median pH (7.8) compared to 

all other sampling sites, which is consistent with a groundwater source. Springs sampled in the study by Bartos and Ogle 

(2002) had pH values that were similar to pH values measured 

at site C1. Specific conductance and major ion concentrations 

at site C1 during water years 2004–10 generally were larger 

than historical data collected prior to CBNG development 

(Peterson, 1988); however, streamflows were much smaller 

during water years 2004–10 as a result of drought conditions 

compared to historical values reported by Peterson (1988). 

In the Belle Fourche River drainage basin, median 

specific conductance was largest (2,860 μS/cm at 25°C) 

for the Belle Fourche River near Piney (site B1). Specific 

conductance decreases in the downstream direction on the 

Belle Fourche River and is smallest (median of 1,900 μS/

cm at 25°C) below Hulett (site B5). The upper part of the 

Belle Fourche River drainage basin lies in the plains; however, downstream near Hulett, Wyo., dilution occurs as a 

result of changes in geology and precipitation associated with 

the Black Hills. A reservoir between site B4 and site B5 on 

the Belle Fourche River also may affect the water quality 

at site B5. Median specific conductance values for tributaries were 1,920 μS/cm at 25°C for Caballo Creek (site B2) 

and 2,780 μS/cm at 25°C for Donkey Creek (site B3). Specific conductance values reported by Rice and others (2000) 

for coalbed waters in the eastern part of the Powder River 

structural basin generally were less than specific conductance 

values for sites in the Belle Fourche River drainage basin. 

Median specific conductance values were smaller for the Belle 

Fourche River near Piney (site B1), Caballo Creek (site B2), 

and Donkey Creek (site B3) compared to historical data collected prior to CBNG development (Peterson, 1988), indicating that CBNG-produced waters may have a dilution effect on 

these streams. 

Sodium Adsorption Ratios

The SAR values for samples collected from streams 

varied among site groups for the four major drainage basins 

(fig. 7). The SAR values were most variable in the Powder 

River drainage basin. Plains tributaries and Powder River 

main-stem site groups had large ranges of SAR values. In 

contrast, the mountain tributaries to the Powder River had a 

small range of SAR values. The Tongue River had the smallest 

median value and range of SAR values of the site groups. 

For selected main-stem sites, the range of SAR values in 

samples collected from the Tongue River (site T6) is substantially smaller and less variable through time (fig. 8) compared 

to SAR values for samples collected from the Powder River 

(site P23), Cheyenne River (site C2), and Belle Fourche River 

(site B4). The SAR values were most variable in samples collected from the Cheyenne River. The curve (fig. 8) smoothes 

the overall pattern of data with time; however, it may not necessarily correspond with a significant trend through time when 

seasonal variation is taken into account.

Median SAR values in the Tongue River drainage basin 

ranged from 0.32 for the Tongue River at Monarch (site T1) 

during water years 2004–10 to 1.3 for Prairie Dog Creek near 

Acme (site T5) during water years 2001–10 (appendix 1) . 

The median SAR was 0.73 for the Tongue River at State line 

(site T6) during water years 2001–10.

Sites in the Powder River drainage basin had the largest range of median SAR values, from 0.87 (sites P18 and 

P19) on Clear Creek to 32.8 on Cottonwood Creek (site P12) 

during water years 2001–10 (appendix 1). Large median SAR 

values generally were for sites on eastern plains tributaries that 

receive discharges of CBNG-produced waters, such as 19.1 for 

Pumpkin Creek (site P4), 16.0 for Beaver Creek (site P5), 29.8 

for Burger Draw (site P7), 15.8 for Barber Creek (site P10), 

and 15.3 for LX Bar Creek (site P21). Cottonwood Creek 

(site P12), which is a plains tributary with CBNG development that drains the western side of the Powder River, had 

the largest SAR value (46.7) reported for any sample as well 

as the largest median value. Coalbeds in the Powder River 

structural basin near Cottonwood Creek are deeper than coalbeds in the eastern part of the basin. The quality of coalbed 

waters generally decreases, in terms of increasing concentrations of sodium, as the depth to the coal increases (Rice and 

others, 2002). Salt Creek, which receives discharges from 

conventional oil and gas development, also had a large median 

SAR value of 18.0. For the Powder River main-stem sites, 

samples collected from the Powder River below Burger Draw 

(site P8) had a median SAR value of 5.6 and ranged from 

1.9 to 26.7. Large SAR values in samples from site P8 were 

observed when flows were small and Burger Draw (site P7) 

substantially contributed to the streamflow of the Powder 

River. The SAR values for samples from the Powder River 

generally were smallest at Moorhead (site P23), which had 

a median SAR value of 4.1 and ranged from 1.1 to 9.0. The 

median SAR value for Clear Creek near Arvada (site P20) was 

1.2. Similar to specific conductance, median SAR values are 
Water-Quality Characteristics 21

affected by dilution by tributary inflow from Clear Creek as 

observed in the decrease in median SAR values from 5.6 for 

the Powder River above Clear Creek (site P17) to 4.1 for the 

Powder River at Moorhead (site P23). 

Median SAR values for the Cheyenne River were 4.8 

at the upstream site (site C1) during water years 2004–10 

and 10.4 at the downstream site (site C2) during water years 

2005–10. The SAR values for samples collected at site C1 

likely are representative of groundwater because of flow 

conditions previously described for site C1. The CBNG 

development occurs in tributary basins upstream from site C1; 

however, discharges of CBNG-produced waters do not directly 

contribute to streamflow in the Cheyenne River upstream from 

site C1 because the site generally is dry just upstream from 

the sampling location. The CBNG development also occurs in 

tributary drainages between site C1 and site C2; however, the 

Cheyenne River may go dry between these sites. 

The SAR values for samples from the Belle Fourche 

River generally are largest at the farthest upstream site near 

Piney (site B1) and smallest below Hulett (site B5). The 

median SAR value on the Belle Fourche River decreased from 

5.6 near Piney (site B1) to 1.3 below Hulett (site B5) during water years 2001–10 (appendix 1). Substantially larger 

calcium concentrations and smaller sodium concentrations 

occur below Hulett (site B5) compared to upstream sites on 

the Belle Fourche River (sites B1 and site B4), likely as a 

result of changes in geology. Although Caballo Creek and 

Donkey Creek (sites B2 and B3) receive discharges of CBNGproduced waters, median SAR values for samples from these 

tributaries (4.9 and 4.1) are much smaller than tributaries that 

receive CBNG-produced waters in the Powder River drainage 

basin. The SAR values reported by Rice and others (2000) for 

coalbed waters in the southeastern part of the Powder River 

structural basin near Gillette, Wyo., generally were less than 

9.0. Although specific conductance values generally were 

smaller in the Belle Fourche River drainage basin during 

water years 2001–10 compared to historical values (Peterson, 

1988), some mixed geochemical changes may have occurred 

in stream waters. For example, SAR values for Caballo Creek 

(site B2) generally increased compared to historical data 

collected prior to CBNG development (Peterson, 1988). The 

change in SAR values coincides with smaller calcium concentrations at site B2 during water years 2001–10. In contrast, 

SAR values for Donkey Creek (site B3) generally decreased 

compared to historical values owing to smaller sodium concentrations during water years 2001–10.

Figure 7. Statistical summary of sodium adsorption ratios for site groups in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.

Tongue

River

Powder River

plains

tributaries

Powder River

mountain

tributaries

Powder River

main stem

Little Powder

River 

Cheyenne

River

Belle

Fourche

River

Site group

493

0

10

20

30

40

50

Sodium adsorption ratio, unitless

653

760

579

867

256

103

493

EXPLANATION

Number of values 

75th percentile

50th percentile

(median)

25th percentile

Interquartile range

Largest value within 1.5 times 

interquartile range above 

the 75th percentile

Smallest value within 1.5 times 

interquartile range below the 

25th percentile

Value is greater than 1.5 times the 

interquartile range beyond either 

end of box
22 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Trend Analyses of Selected WaterQuality Characteristics

Trends were analyzed for selected sites to help evaluate 

whether changes in water-quality characteristics have occurred 

through time. Increases in specific conductance and SAR as a 

result of CBNG development could affect water use for irrigation. Trends were evaluated for unadjusted and flow-adjusted 

specific conductance and SAR values using the seasonal Kendall test. Results for the various trend analyses are presented 

in appendix 2. Because streamflow typically has a relation 

with specific conductance and SAR for sites in the study area 

and was variable during the study period, it is difficult to 

determine cause and effect relations for unadjusted values. 

The description of trends in the following sections is limited 

to results of the seasonal Kendall test applied to flow-adjusted 

values, because they are more useful for determining potential 

factors affecting trends. 

Trend Analysis for Water Years 2001–10

Trends were evaluated for the 10-year period of 

water years 2001–10 at sites in the Tongue River drainage 

basin (4 sites); Powder River drainage basin (9 sites); and 

the Belle Fourche River drainage basin (4 sites). Most of the 

sites evaluated for trends for water years 2001–10 are on the 

main-stem rivers or on primary tributaries in those drainages 

(table 2). In addition to specific conductance and SAR, trends 

were evaluated for dissolved concentrations of calcium, magnesium, sodium, alkalinity, chloride, and sulfate to determine 

which of the primary components may be contributing to a 

trend in specific conductance or SAR.

Figure 8. Graphs showing sodium adsorption ratios through time at sites in the A, Tongue; B, Powder; C, Cheyenne; and D, Belle 

Fourche River drainage basins, Wyoming and Montana, water years 2001–10.

2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Water year

Locally weighted, scatterplot 

smoothing curve

EXPLANATION

Sample

0.0

2.5

5.0

7.5

10.0

12.5

Sodium adsorption ratio, unitless

A Tongue River (site T6) B Powder River (site P23)

0.0

2.5

5.0

7.5

10.0

12.5

Sodium adsorption ratio, unitless

C Cheyenne River (site C2) D Belle Fourche River (site B4)
Trend Analyses of Selected Water-Quality Characteristics 23

Specific Conductance

Consistent basinwide patterns were not observed in trend 

results for specific conductance for water years 2001–10 in 

the Tongue, Powder, and Belle Fourche River drainage basins 

(fig. 9). Significant (p<0.05) upward trends in flow-adjusted 

specific conductance values were determined for 3 sites, a 

downward trend was determined for 1 site, and no significant 

(p>0.05) trends were determined for 13 sites. 

In the Tongue River drainage basin, results of the seasonal Kendall test applied to flow-adjusted specific conductance values for water years 2001–10 indicated significant 

(p<0.05) upward trend on the Tongue River at Stateline 

(site T6). No significant (p>0.05) trends were determined for 

flow-adjusted specific conductance values on Little Goose 

Creek (site T2), Goose Creek (site T3), and Prairie Dog Creek 

near Acme (site T5).

Significant (p<0.05) upward trends also were determined 

for flow-adjusted concentrations of calcium, chloride, and 

sulfate on the Tongue River at Stateline (site T6), which would 

contribute to the upward trend in specific conductance. A significant upward trend in flow-adjusted chloride concentrations 

was determined for Prairie Dog Creek near Acme (site T5), 

which may have contributed to increasing chloride concentrations of the Tongue River. Determining the source of trends 

for the Tongue River at State line (site T6) for water years 

2001–10 is complicated by several factors. Large concentrations of calcium, chloride, and sulfate are not directly associated with coalbed waters. The subsurface movement of major 

ions dissolved from soils as a result of infiltrating CBNGproduced waters is one potential source of calcium, chloride, 

or sulfate to streams; however, other land uses also may have 

contributed to trends in major ions. Irrigation, which occurs 

in the Tongue River drainage basin, can increase concentrations of dissolved constituents in the soil profile or in return 

flows as a result of evaporation and transpiration (Hanson and 

others, 2006). Rural septic systems in the drainage basin may 

also contribute to dissolved solids (Canter and Knox, 1984), 

as well as the city of Sheridan. Drought conditions that persisted in the Tongue River drainage basin during water years 

2001–06 may have produced an accumulation of salts at the 

surface and in the near subsurface through evaporation. When 

precipitation returned to normal (Natural Resources Conservation Service, 2011), some of these accumulated salts may have 

been flushed to streams. Quillinan and others (2012) reported 

that increased dissolved solids observed in the Tongue River 

during early spring runoff are likely the result of soluble salts 

being mobilized from the soil profile in the basin interior. 

In the Powder River drainage basin, results of the seasonal Kendall test applied to flow-adjusted specific conductance values for water years 2001–10 indicated a significant 

(p<0.05) upward trend on Clear Creek near Buffalo (site 

P18). A significant downward trend in flow-adjusted specific 

conductance values was determined for the Powder River 

below Burger Draw (site P8). No significant (p>0.05) trend in 

flow-adjusted specific conductance values were determined 

for Salt Creek (site P1), Powder River at Sussex (site P2), 

Crazy Woman Creek (site P11), the Powder River at Arvada 

(site P13), Clear Creek near Arvada (site P20), the Powder 

River at Moorhead (site P23), and the Little Powder River 

above Dry Creek (site P27).

Results of the seasonal Kendall test applied to major ion 

concentrations indicated significant (p<0.05) upward trends 

in flow-adjusted concentrations of calcium, magnesium, and 

alkalinity contributed to the upward trend in specific conductance for Clear Creek near Buffalo (site P18). Calcium, 

magnesium, and alkalinity commonly are associated with 

carbonate rocks, which are present in the upper basin. Trends 

in these constituents may indicate that groundwater composed 

a relatively larger part of the streamflow as a result of drought 

conditions, because concentrations of calcium, magnesium, 

and alkalinity typically are larger under base-flow conditions 

compared to surface runoff. Sparse CBNG development has 

occurred in the upper Clear Creek drainage basin upstream 

from site P18 (based on compilation of data retrieved from 

Wyoming Oil and Gas Conservation Commission, 2011). 

Results of the seasonal Kendall test applied to major ion 

constituents indicated a significant (p<0.05) downward trend 

for flow-adjusted sulfate concentrations contributed to the 

downward trend in specific conductance for the Powder River 

below Burger Draw (site P8). The CBNG production occurs in 

drainages upstream from site P8 on the Powder River, including the Burger Draw drainage basin, which is immediately 

upstream from site P8. Because coalbed waters typically do 

not contain large sulfate concentrations, discharges of CBNGproduced waters in the Burger Draw drainage basin may dilute 

sulfate concentrations in the Powder River below Burger Draw 

(site P8), particularly during low flows. Because flow is occurring more regularly in some of the plains ephemeral drainages, some flushing of surficial sulfate salts also may have 

occurred, which may decrease sulfate concentrations through 

time. Precipitation of barium sulfate also may contribute to 

the downward trend in flow-adjusted sulfate concentrations. 

Barium is a constituent commonly associated with CBNGproduced waters that will precipitate when mixed with sulfate 

in drainages (Wyoming Department of Environmental Quality, 

2000; Brinck and others, 2008). 

The seasonal Kendall test applied to major ion constituents indicated significant (p<0.05) downward trends in flowadjusted sulfate concentrations downstream on the Powder 

River at Arvada (site P13) and at Moorhead (site P23), as well 

as on Clear Creek near Arvada (site P20); however, no trends 

were determined for flow-adjusted specific conductance values 

for these sites. Significant upward trends in flow-adjusted 

alkalinity concentrations were determined for the Powder 

River at Arvada (site P13) and at Moorhead (site P23). The 

CBNG-produced waters that typically have bicarbonate as 

their dominant anion may be the source affecting the upward 

trend in alkalinity on the Powder River at sites P13 and P23. 

Multiple approaches for assessing water quality indicate that 

some reaches of the Powder River may have been affected by 

CBNG-produced waters. Sharma and Frost (2008) used stable 
24 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Figure 9. Trend results for flow-adjusted specific conductance at sites in the Tongue, Powder, and Belle Fourche River drainage 

basins, Wyoming and Montana, water years 2001–10.

MONTANA

WYOMING

Map area

Powder River

structural basin

Creek

River

River

Powder

River

River

Fourche

Belle

Creek Pumpkin

River

Little

Creek

Beaver

Pumpkin

Caballo

Creek

Donkey Creek

Cheyenne

Creek

Creek

Tongue

Little Go ose Creek

Prairie Dog Creek

Clear

Creek

Woman

Crazy

Creek

Willow

Salt

North

Platte River

Burger Draw

Goose

Keyhole

Reservoir

Van Houten Draw

Barber Creek

Barber Creek

River

Powder

Wild Horse Creek

Spotted Horse Creek

Creek

LX Bar

Creek

S A

Creek

Creek

Rawhide

Elk

Creek

Horse Creek

Creek

Dry

Rattlesnake

Creek

Double

Crossing Kumor Creek Draw

Cottonwood

Powder

Sussex

Arvada Hulett

Buffalo

Gillette

Moorhead

Newcastle

Sheridan

Moorcroft

Clearmont

Wakely Siding

SHERIDAN

CAMPBELL

JOHNSON

CROOK

NATRONA

CONVERSE

WESTON

NIOBRARA

BIG

HORN

W

ASH

A

KIE

CARTER

BIG HORN

POWDER

RIVER

B3 B4

B1

P8

P2

P1

T6

T5

T3

T2

P27

P23

P20

P18

P13

P11

B5

Powder River structural basin

Sampling site map number

Upward trend

Downward trend

No trend

25

25

0

0 50 KILOMETERS

50 MILES

14

MONTANA

WYOMING

BLA

CK

HILLS

BIGHORN MOUNTAINS

107° 106° 105° 104°

45°

44°

43°

EXPLANATION

Powder River

Drainage basin

P1

SOUTH DAKOTA

Casper

Base from U.S. Geological Survey digital data,

variously dated, various scales

Transportation network from Federal Highway 

Administration, 2002, 1:100,000

Albers Equal-Area Conic projection

Standard parallels 41°N and 45°N

Central meridian 105°W

North American Datum of 1983 (NAD 83)

16

25

90

90

25

90

Piney

20

85

Lusk

Weston

Spencer

Dull Center

Tongue River

Decker

Acme

Cheyenne River

Belle Fourche River
Trend Analyses of Selected Water-Quality Characteristics 25

isotopes of carbon as a tracer to determine that the reach of the 

Powder River downstream from Beaver Creek to near Moorhead, Mont., was affected by CBNG-produced waters. Isotope 

analysis results for the Powder River farther downstream in 

Montana generally reflected ambient conditions, indicating 

that waters were not affected by CBNG-produced waters. 

Peterson and others (2011) reported a decline in biological 

conditions in reaches of the Powder River between Barber 

Creek and Wild Horse Creek that may indicate cumulative 

effects from CBNG-produced waters, including effects from 

alkalinity. Barber Creek is one of the plains tributaries where 

CBNG-produced waters receive treatment to reduce concentrations of some of the dissolved constituents (Wyoming 

Department of Environmental Quality, 2011). Median dissolved sodium concentrations were substantially smaller for 

Barber Creek (site P10) compared to other drainages with 

CBNG development, such as Pumpkin Creek (site P4) and 

Burger Draw (site P7); however, median alkalinity concentrations were similar, although few samples from these sites were 

analyzed for anions (appendix 1).

In the Belle Fourche River drainage basin, a significant 

(p<0.05) upward trend in flow-adjusted specific conductance 

values was determined for the Belle Fourche River near Piney 

(site B1). No significant (p>0.05) trend in flow-adjusted specific conductance was determined for Donkey Creek (site B3) 

or for two sites downstream on the Belle Fourche River 

(sites B4 and B5).

Results of the seasonal Kendall test applied to major ion 

constituents indicated a significant (p<0.05) upward trend 

in flow-adjusted sodium concentrations contributed to the 

upward trend in specific conductance on the Belle Fourche 

River near Piney (site B1). Water production associated with 

CBNG development has been declining in the upper Belle 

Fourche River drainage basin since 2003 when it was at its 

peak (based on compilation of data retrieved from Wyoming 

and Gas Conservation Commission, 2011). Specific conductance values and sodium concentrations generally were 

smaller during water years 2001–10 compared to values 

reported by Peterson (1988) for water years 1975–81 for 

site B1. This indicates that CBNG-produced waters may have 

had a dilution effect on the water quality of the Belle Fourche 

River near Piney and as a result of declining CBNG production, concentrations are returning to larger levels that occurred 

prior to CBNG development.

Although no corresponding trends were determined for 

flow-adjusted specific conductance values, the seasonal Kendall test applied to major ion constituents indicated a significant 

(p<0.05) downward trend in flow-adjusted alkalinity concentrations on the Belle Fourche River below Moorcroft (site B4). 

Significant upward trends in flow-adjusted concentrations of 

calcium, magnesium, and chloride concentrations also were 

determined for Belle Fourche River below Moorcroft (site 

B4). Increases in chloride have been reported for Donkey 

Creek, and the Belle Fourche River downstream from Donkey Creek has been listed as impaired for chloride (Wyoming 

Department of Environmental Quality, 2010). One source 

potentially contributing to the upward trend in flow-adjusted 

magnesium and chloride concentrations may be magnesium 

chloride, which is used throughout the year in the Belle 

Fourche River drainage basin (Tetra Tech, Inc., 2011). During 

the winter, magnesium chloride is used as a de-icing agent for 

roads, and from May to October, as a dust suppressant applied 

to haul roads used to transport materials from extraction 

facilities.

Sodium Adsorption Ratios

Consistent basinwide patterns were not observed in trend 

results for SAR values for water years 2001–10 in the Tongue, 

Powder, and Belle Fourche River drainages basins (fig. 10). 

Significant (p<0.05) upward trends in flow-adjusted SAR 

values were determined at 2 sites and no significant (p>0.05) 

trends were determined for 15 sites. 

In the Tongue River drainage basin, results of the seasonal Kendall test applied to flow-adjusted SAR values for 

water years 2001–10 indicated no significant (p>0.05) trends 

for Little Goose Creek (site T2), Goose Creek (site T3), Prairie 

Dog Creek near Acme (site T5), and the Tongue River at State 

line (site T6). As previously described for specific conductance 

trends, a significant (p<0.05) upward trend in flow-adjusted 

calcium was determined for site T6; however, a corresponding 

downward trend in flow-adjusted SAR was not determined. A 

downward trend was significant for unadjusted SAR values at 

site T6 (appendix 2). 

In the Powder River drainage basin, results of the seasonal Kendall test applied to flow-adjusted SAR values for 

water years 2001–10 indicated a significant (p<0.05) upward 

trend on the Powder River at Arvada (site P13). The trend in 

flow-adjusted SAR values was not significant (p>0.05) for 

other sites on the Powder River, including at Sussex (site P2), 

below Burger Draw (site P8), and at Moorhead (site P23). No 

significant trends in flow-adjusted SAR values were determined for tributary sites in the Powder River drainage basin, 

including Salt Creek (site P1), Crazy Woman Creek (site P11), 

Clear Creek (site P18 and site P20), and the Little Powder 

River (site P27). 

No significant trends (p>0.05) were determined for flowadjusted concentrations of calcium, magnesium, and sodium 

for the Powder River at Arvada (site 13). Flow-adjusted 

calcium concentrations, which have an inverse relation with 

SAR, had a larger test statistic (tau = -0.310) than sodium 

(tau = 0.034) or magnesium (tau = -0.073) for the trend 

period, indicating the trend in flow-adjusted SAR values may 

be primarily the result of decreasing calcium concentrations. 

One of the geochemical effects of adding sodium bicarbonate produced waters to streams is the precipitation of calcium 

carbonate. This results in a decrease in calcium concentrations 

and a corresponding increase in SAR (Patz and others, 2004). 

Decreases in calcium concentrations in CBNG impoundments 

compared to CBNG outfalls also have been attributed to the 

precipitation of calcite (Jackson and Reddy, 2007b). The 

SAR trend, combined with the upward trend in flow-adjusted 
26 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Figure 10. Trend results for flow-adjusted sodium adsorption ratios at sites in the Tongue, Powder, and Belle Fourche River drainage 

basins, Wyoming and Montana, water years 2001–10.

MONTANA

WYOMING

Map area

Powder River

structural basin

Creek

River

River

Powder

River

River

Fourche

Belle

Creek Pumpkin

River

Little

Creek

Beaver

Caballo

Creek

Donkey Creek

Cheyenne

Creek

Creek

Tongue

Little Go ose Creek

Prairie Dog Creek

Clear

Creek

Woman

Crazy

Creek

Willow

Salt

North

Platte River

Goose

Keyhole

Reservoir Barber Creek

Barber Creek

River

Powder

Wild Horse Creek

Spotted Horse Creek

Creek

LX Bar

Creek

S A

Creek

Creek

Rawhide

Elk

Creek

Horse Creek

Creek

Dry

Rattlesnake

Creek

Double

Crossing Kumor Creek Draw

Cottonwood

Powder

Beaver

Burger Draw

Van Houten Draw

Sussex

Arvada Hulett

Buffalo

Gillette

Moorhead

Newcastle

Sheridan

Moorcroft

Clearmont

Decker

Acme

SHERIDAN

CAMPBELL

JOHNSON

CROOK

NATRONA

CONVERSE

WESTON

NIOBRARA

BIG

HORN

W

ASH

A

KIE

CARTER

BIG HORN

POWDER

RIVER

B5

B4

B3

B1

P8

P2

P1

T6

T5

T3 T2

P23

P20

P18

P13

P11

P27

25

25

0

0 50 KILOMETERS

50 MILES

14

MONTANA

WYOMING

BLA

CK

HILLS

BIGHORN MOUNTAINS

107° 106° 105° 104°

45°

44°

43°

SOUTH DAKOTA

Casper

Base from U.S. Geological Survey digital data,

variously dated, various scales

Transportation network from Federal Highway 

Administration, 2002, 1:100,000

Albers Equal-Area Conic projection

Standard parallels 41°N and 45°N

Central meridian 105°W

North American Datum of 1983 (NAD 83)

16

25

90

90

25

90

Piney

20

85

Lusk

Weston

Spencer

Dull Center

Wakely Siding

Powder River structural basin

Sampling site map number

Upward trend

Downward trend

No trend

EXPLANATION

Powder River

Drainage basin

P1 Tongue River

Cheyenne River

Belle Fourche River
Trend Analyses of Selected Water-Quality Characteristics 27

alkalinity concentration, is additional evidence that CBNGproduced waters may be causing the water-quality changes 

to the Powder River at Arvada (site P13) during water years 

2001–10. Frost and others (2010) used strontium isotopes and 

mixing models to show that CBNG-produced waters account 

for less than 1 percent of the flow of the Powder River, but 

that it is possible for even a small amount of CBNG-produced 

waters to affect SAR values of the Powder River. 

In the Belle Fourche River drainage basin, results of the 

seasonal Kendall test applied to flow-adjusted SAR values for 

water years 2001–10 indicated a significant (p<0.05) upward 

trend on the Belle Fourche River near Piney (site B1). Trends 

in flow-adjusted SAR values were not significant (p>0.05) for 

Donkey Creek (site B3) or downstream on the Belle Fourche 

River (site B4 and site B5). The upward SAR trend for site B1 

corresponded with a significant upward trend in flow-adjusted 

sodium concentrations at that site. Because trends in flowadjusted concentrations of calcium or magnesium were not 

significant, the increase in sodium, which is directly related to 

SAR, likely is the primary factor affecting the upward trend in 

SAR for the Belle Fourche River near Piney (site B1). 

Trend Analysis for Water Years 2005–10

Trends were evaluated for the 6-year period of water 

years 2005–10 at sites in the Tongue River drainage basin 

(4 sites), the Powder River drainage basin (18 sites), the 

Cheyenne River drainage basin (1 site), and the Belle Fourche 

River drainage basin (3 sites). Sites that met data requirements for trend analyses for water years 2005–10 varied 

slightly compared to water years 2001–10 (table 2). Sampling 

frequency was decreased on Little Goose Creek (site T2), 

Goose Creek (site T3), and the Belle Fourche River below 

Hulett (site B5) and as a result, the number of observations 

in the ending period for those sites was not adequate to 

meet the trend test requirements. Two additional sites in the 

Tongue River drainage basin that were added to the monitoring network during water year 2004 (site T1 and site T4) were 

included in the trend analysis. Nine additional sites in the 

Powder River drainage basin (sites P4, P5 P6, P7, P15, P17, 

P19, P22, and P26) that were added to the monitoring network 

during water year 2004 were included in the trend analysis. 

One site in the Cheyenne River drainage basin that was added 

to the monitoring network during water year 2005 (site C2) 

was included in the trend analysis.

Trends were evaluated for specific conductance and SAR. 

In addition, trends were evaluated for dissolved concentrations of calcium, magnesium, sodium, alkalinity, chloride, and 

sulfate to determine which of the primary components may be 

contributing to a trend in specific conductance or SAR. For 

some sites, samples were analyzed only for cations (table 2); 

thus, trends in anions that may contribute to trends in specific 

conductance could not be evaluated for these sites. 

Specific Conductance

Consistent basinwide patterns were not observed in trend 

results for specific conductance for water years 2005–10 in the 

Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins (fig. 11). Significant (p<0.05) upward trends in 

flow-adjusted specific conductance values were determined 

at 9 sites, downward trends were determined at 4 sites, and 

no significant (p>0.05) trends were determined for 13 sites 

(appendix 2). 

In the Tongue River drainage basin, results of the seasonal Kendall test applied to flow-adjusted specific conductance values for water years 2005–10 indicated significant 

(p<0.05) upward trends on the Tongue River at Monarch 

(site T1), Prairie Dog Creek near Acme (site T5), and the 

Tongue River at State line (site T6). No significant (p>0.05) 

trend in flow-adjusted specific conductance values was determined for Prairie Dog Creek near Sheridan (site T4). 

Results of the seasonal Kendall test applied to major ion 

constituents indicated upward trends for several constituents 

contributed to the upward trends in specific conductance. 

Significant (p<0.05) upward trends in flow-adjusted concentrations of magnesium, alkalinity, chloride, and sulfate 

were determined for the Tongue River at Monarch (site T1). 

Significant upward trends were determined in flow-adjusted 

concentrations of magnesium, sodium, alkalinity, chloride, and 

sulfate for Prairie Dog Creek near Acme (site T5). Upward 

trends in flow-adjusted concentrations of calcium, magnesium, 

alkalinity, chloride, and sulfate were significant for the Tongue 

River at State line (site T6). An upward trend in flow-adjusted 

chloride concentrations also was determined for Prairie Dog 

Creek near Sheridan (site T4), although no corresponding 

trend in flow-adjusted specific conductance was determined.

Determining the factors affecting trends in the Tongue 

River drainage basin for water years 2005–10 is complicated 

by several factors as previously described for water years 

2001–10. Large concentrations of sodium and alkalinity typically are associated with coalbed waters; however, calcium, 

magnesium, chloride, and sulfate typically are not. In addition, 

the Tongue River at Monarch (site T1), which is upstream 

from CBNG development, generally had the same trends 

as downstream sites (T5 and T6). Studies that used other 

approaches to determine effects from CBNG developments in 

the Tongue River drainage basin were inconclusive. A study 

that used major ion composition and carbon isotopes to differentiate water sources found that surface waters were geochemically and isotopically distinct from CBNG-produced waters, 

particularly in the Prairie Dog Creek drainage basin where 

most of the development occurs (Quillinan and others, 2012). 

In addition, Peterson and others (2011) did not find substantial 

changes in biological conditions between sites upstream and 

downstream from CBNG development on the Tongue River 

and Prairie Dog Creek.
28 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Figure 11. Trend results for flow-adjusted specific conductance at sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2005–10.

MONTANA

WYOMING

Map area

Powder River

structural basin

Creek

River

River

Powder

River

River

Fourche

Belle

Creek Pumpkin

River

Little

Creek

Beaver

Pumpkin

Caballo

Creek

Donkey Creek

Cheyenne

Creek

Creek

Tongue

Little Go ose Creek

Prairie Dog Creek

Clear

Creek

Woman

Crazy

Creek

Willow

Salt

North

Platte River

Burger Draw

Goose

Keyhole

Reservoir

Van Houten Draw

Barber Creek

Barber Creek

River

Powder

Wild Horse Creek

Spotted Horse Creek

Creek

LX Bar

Creek

S A

Creek

Creek

Rawhide

Elk

Creek

Horse Creek

Creek

Dry

Rattlesnake

Creek

Double

Crossing Kumor Creek Draw

Cottonwood

Powder

Sussex

Arvada Hulett

Buffalo

Gillette

Moorhead

Newcastle

Sheridan

Moorcroft

Clearmont

Decker

Acme

SHERIDAN

CAMPBELL

JOHNSON

CROOK

NATRONA

CONVERSE

WESTON

NIOBRARA

BIG

HORN

W

ASH

A

KIE

CARTER

BIG HORN

POWDER

RIVER

B4

B3

B1

C2

P8 P7

P6

P5

P4

P2

P1

T6

T5

T4

T1 P27

P26

P23

P22

P19

P18

P15

P13

P11

25

25

0

0 50 KILOMETERS

50 MILES

14

MONTANA

WYOMING

BLA

CK

HILLS

BIGHORN MOUNTAINS

107° 106° 105° 104°

45°

44°

43°

SOUTH DAKOTA

Casper

Base from U.S. Geological Survey digital data,

variously dated, various scales

Transportation network from Federal Highway 

Administration, 2002, 1:100,000

Albers Equal-Area Conic projection

Standard parallels 41°N and 45°N

Central meridian 105°W

North American Datum of 1983 (NAD 83)

16

25

90

90

25

90

Piney

20

85

Lusk

Weston

Spencer

Dull Center

Wakely Siding

Powder River structural basin

Sampling site map number

Upward trend

Downward trend

No trend

EXPLANATION

Powder River

Drainage basin

P1 Tongue River

Cheyenne River

Belle Fourche River

P20

P17
Trend Analyses of Selected Water-Quality Characteristics 29

In the Powder River drainage basin, results of the seasonal Kendall test applied to flow-adjusted specific conductance values for water years 2005–10 indicated significant 

(p<0.05) downward trends on Salt Creek (site P1), Pumpkin 

Creek (site P4), Burger Draw (site P7), and the Powder River 

below Burger Draw (site P8). Significant upward trends in 

flow-adjusted specific conductance were determined for Wild 

Horse Creek at mouth (site P15) and for two sites on the Little 

Powder River (sites P26 and P27). No significant (p>0.05) 

trends in flow-adjusted specific conductance values were 

determined for other sites on the Powder River (sites P2, P6, 

P13, P17, and P23), Beaver Creek (site P5), Crazy Woman 

Creek (site P11), Clear Creek (sites P18, P19, and P20), and 

SA Creek (site P22). 

Results of the seasonal Kendall test applied to major ion 

constituents indicated significant (p<0.05) downward trends 

in flow-adjusted concentrations of sodium, alkalinity, and 

chloride contributed to the downward trend in flow-adjusted 

specific conductance for Salt Creek (site P1), despite upward 

trends in flow-adjusted concentrations of calcium and sulfate. 

Changes to traditional oil and gas development practices, such 

as decreased discharges of saline groundwaters that are associated with conventional gas and oil production, have historically affected water quality in the Salt Creek drainage basin 

(RETEC Group, Inc., 2004) and may be the cause of recent 

trends in Salt Creek; CBNG development likely is not the 

cause. Although no significant trend in flow-adjusted specific 

conductance was determined downstream from Salt Creek 

on the Powder River at Sussex (site P2), major ion trends for 

site P2 were similar to trends for site P1. Major ion trends 

included downward trends in flow-adjusted concentrations of 

sodium and chloride and an upward trend in flow-adjusted calcium concentrations, which illustrates the substantial effects 

that Salt Creek has on the water quality of the Powder River. 

An understanding of water-quality trends at sites upstream 

from CBNG development, including Salt Creek, is critical 

for defining constituent inputs to the Powder River; without 

an understanding of these trends, potential causes of waterquality trends at the Powder River main-stem sites that are 

downstream from Salt Creek could be misinterpreted. 

Results of the seasonal Kendall test applied to major ion 

constituents indicated significant (p<0.05) downward trends 

in flow-adjusted sodium concentrations contributed to the 

downward trend in specific conductance for Burger Draw 

(site P7) and the Powder River below Burger Draw (site P8) 

for water years 2005–10. A significant downward trend in 

flow-adjusted magnesium concentrations also was determined 

at Burger Draw (site P7), and a significant downward trend 

in flow-adjusted alkalinity concentrations was determined for 

the Powder River below Burger Draw (site P8). Downward 

trends in sodium (sites P7 and P8) and alkalinity (site P8) are 

consistent with a decline in CBNG production in the Burger 

Draw drainage basin. Data retrieved and compiled from the 

Wyoming Oil and Gas Conservation Commission (2011) 

indicate that CBNG production in the Burger Draw drainage 

basin generally decreased after 2006 when production was at 

its peak. Changes to conventional oil and gas production in the 

Salt Creek drainage basin also may have affected sodium concentrations for the Powder River below Burger Draw (site P8). 

Significant (p<0.05) upward trends in flow-adjusted 

calcium and magnesium contributed to the upward trend in 

specific conductance on Wild Horse Creek at mouth (site 

P15) and the Little Powder River below Elk Creek (site P26). 

Significant upward trends in flow-adjusted concentrations 

of calcium, magnesium, sodium, alkalinity, and sulfate were 

determined downstream for the Little Powder River above 

Dry Creek (site P27). Nearly all of the CBNG development 

during the 1990s in the Powder River drainage basin was 

in the Little Powder River drainage basin. In contrast, the 

volume of produced water in the Little Powder drainage basin 

during 2010 represented only 6 percent of the total volume 

of produced water for the Powder River drainage basin as a 

result of declining production in the Little Powder drainage 

basin during 2003—10 (based on compilation of data retrieved 

from Wyoming Oil and Gas Conservation Commission, 2011). 

CBNG-produced waters discharged in the Little Powder River 

drainage basin likely have relatively small dissolved solids 

because of the water quality of coalbeds in the eastern part of 

the structural basin (Rice and others, 2000); however, waterquality characteristics and determining the source of trends for 

the Little Powder River are complicated by coal-mine dewatering and streamflow contributions from groundwater, including groundwater that is affected by clinker deposits (Miller 

and others, 2005). 

Although no corresponding trend in flow-adjusted 

specific conductance was determined for these sites, trends in 

major ion constituents were determined for some sites. Significant (p<0.05) downward trends in flow-adjusted concentrations of magnesium and sodium were determined for Beaver 

Creek (site P5). Significant upward trends in flow-adjusted 

concentrations of alkalinity and chloride were determined 

for Crazy Woman Creek (site P11). Upward trends in flowadjusted alkalinity were determined for Clear Creek (sites 

P18 and P20) and the Powder River at Moorhead (site P23). A 

downward trend in flow-adjusted calcium concentrations was 

determined for Clear Creek near Clearmont (site P19). 

In the Cheyenne River drainage basin, a significant 

(p<0.05) upward trend in flow-adjusted specific conductance values was determined for water years 2005–10 for the 

Cheyenne River near Spencer (site C2). Significant upward 

trends in flow-adjusted concentrations of calcium, magnesium, 

sodium, and sulfate contributed to the upward trend in specific 

conductance at that site. Because coalbeds in the eastern part 

of the Powder River structural basin generally have relatively 

small dissolved-solids concentrations, CBNG-produced waters 

can have a dilution effect on some streams with naturally large 

dissolved solids concentrations, like the Cheyenne River. The 

upward trend in flow-adjusted specific conductance and major 

ion constituents may reflect the decrease in CBNG production in this drainage basin during water years 2005–10 (based 

on compilation of data retrieved from Wyoming Oil and Gas 

Conservation Commission, 2011), although persistent drought 
30 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

conditions, which tend to increase salts at the surface, also 

have occurred in the basin. 

In the Belle Fourche River drainage basin, significant 

(p<0.05) upward trends in flow-adjusted specific conductance 

values were determined for Donkey Creek (site B3) and the 

Belle Fourche River below Moorcroft (site B4). Significant 

upward trends in flow-adjusted concentrations of magnesium 

and sulfate were determined for Donkey Creek (site B3) during water years 2005–10. Significant upward trends in flowadjusted concentrations of magnesium, sodium, and sulfate 

were determined for the Belle Fourche River below Moorcroft 

(site B4) for water years 2005–10. Like the Cheyenne River, 

CBNG-produced waters may have a dilution effect in the Belle 

Fourche River drainage basin. Upward trends in flow-adjusted 

concentrations of sodium and sulfate, in particular, may reflect 

the decrease in CBNG production in the Belle Fourche River 

drainage basins (based on compilation of data retrieved from 

Wyoming Oil and Gas Conservation Commission, 2011). As 

previously described in the “Trend Analysis for Water Years 

2001–10” section, the use of magnesium chloride for de-icing 

and dust suppression may contribute to the upward trends in 

flow-adjusted magnesium concentrations in Donkey Creek and 

the Belle Fourche River.

Sodium Adsorption Ratios

Consistent basinwide patterns were not observed in trend 

results for SAR values for water years 2005–10 in the Tongue, 

Powder, Cheyenne, and Belle Fourche River drainage basins 

(fig. 12). Significant (p<0.05) upward trends in flow-adjusted 

SAR values were determined at 4 sites, downward trends were 

determined at 5 sites, and no significant (p>0.05) trends were 

determined for 17 sites. 

In the Tongue River drainage basin, results of the 

seasonal Kendall test applied to flow-adjusted SAR values 

for water years 2005–10 indicated that upward trends were 

significant (p<0.05) for Prairie Dog Creek (sites T4 and T5). 

The cation affecting the SAR trend for Prairie Dog Creek 

near Sheridan (site T4) was not isolated, because no significant trends (p>0.05) were determined for flow-adjusted 

calcium, magnesium, and sodium concentrations for water 

years 2005–10, although the trend for flow-adjusted sodium 

concentrations was nearly significant (p=0.077). Also, SAR 

is a computed constituent, and the relative proportions of 

cations may have varied slightly through time even though the 

magnitude of concentrations of individual cations did not significantly increase or decrease. Significant upward trends were 

determined for flow-adjusted magnesium and sodium concentrations for Prairie Dog Creek near Acme (site T5), indicating 

increases in sodium had a larger effect on increasing SAR values than increases in magnesium had in decreasing SAR values. As described for specific conductance trends, the factors 

affecting trends in the Tongue River drainage basin is difficult 

to isolate for several reasons. Most of the CBNG development 

in the Prairie Dog Creek drainage basin occurs downstream 

from site T4. Infiltration of CBNG-produced waters, as well 

as other land uses and drought conditions, could contribute to 

sodium concentrations. Continued monitoring for SAR and 

related constituents is important given the assimilative capacity for sodium is small for the Tongue River.

In the Powder River drainage basin, results of the 

seasonal Kendall test applied to flow-adjusted SAR values 

for water years 2005–10 indicated downward trends were significant (p<0.05) for Salt Creek (site P1), the Powder River at 

Sussex (site P2), Pumpkin Creek (site P4), the Powder River 

below Burger Draw (site P8), and Wild Horse Creek at mouth 

(site P15). Results of the seasonal Kendall test applied to 

flow-adjusted SAR values for water years 2005–10 indicated 

a significant upward trend for the Little Powder River above 

Dry Creek (site P27). No significant (p>0.05) trends in flowadjusted SAR values were determined for Beaver Creek (site 

P5), Burger Draw (site P7), Crazy Woman Creek (site P11), 

Clear Creek (sites P18, P19, and P20), SA Creek (site P22), 

the Powder River at several sites (sites P6, P13, P17, and P23), 

and the Little Powder River below Elk Creek (site P26). 

Significant (p<0.05) downward trends in flow-adjusted 

sodium concentrations contribute to downward trends in SAR 

for Salt Creek (site P1), the Powder River at Sussex (site P2), 

and the Powder River below Burger Draw (site P8). Significant upward trends in flow-adjusted calcium concentrations 

for Salt Creek (site P1) and the Powder River at Sussex (site 

P2) are consistent with the downward SAR trends. The trend 

in SAR values was not significant (p>0.05) farther downstream on the Powder River at Arvada (site P13) for water 

years 2005–10. Because an upward trend in flow-adjusted 

SAR values for the Powder River at Arvada (site P13) was significant for water years 2001–10 and not significant for water 

years 2005–10, the increase in flow-adjusted SAR values 

may have largely occurred before water year 2005. This may 

indicate that changes to Salt Creek could have an effect on 

the Powder River as far downstream as Arvada. For Pumpkin 

Creek (site P4), no significant trends were observed in flowadjusted calcium, magnesium, or sodium. For Wild Horse 

Creek at mouth (site P15), significant upward trends in flowadjusted concentrations of calcium and magnesium would 

both contribute to the downward trend in SAR at that site. The 

volume of CBNG-produced waters declined in the Wild Horse 

Creek drainage basin during 2008–10 (based on compilation 

of data retrieved from Wyoming Oil and Gas Conservation 

Commission, 2011). Significant upward trends in flowadjusted concentrations of calcium, magnesium, and sodium 

were determined for the Little Powder River below Dry Creek 

(site P27). The tau test statistic (0.389) was largest for flowadjusted sodium concentrations, indicating that the increase 

in sodium affected SAR values more than did increases in 

calcium and magnesium. As previously described for specific 

conductance, CBNG development decreased in the Little Powder River drainage basin during water years 2005–10 (based 

on compilation of data retrieved from Wyoming Oil and Gas 

Conservation Commission, 2011).

In the Cheyenne River drainage basin, results of the 

seasonal Kendall test applied to flow-adjusted SAR values 
Trend Analyses of Selected Water-Quality Characteristics 31

Figure 12. Trend results for flow-adjusted sodium adsorption ratios at sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2005–10.

MONTANA

WYOMING

Map area

Powder River

structural basin

Creek

River

River

Powder

River

River

Fourche

Belle

Creek Pumpkin

River

Little

Creek

Beaver

Pumpkin

Caballo

Creek

Donkey Creek

Cheyenne

Creek

Creek

Tongue

Little Go ose Creek

Prairie Dog Creek

Clear

Creek

Woman

Crazy

Creek

Willow

Salt

North

Platte River

Burger Draw

Goose

Keyhole

Reservoir

Van Houten Draw

Barber Creek

Barber Creek

River

Powder

Wild Horse Creek

Spotted Horse Creek

Creek

LX Bar

Creek

S A

Creek

Creek

Rawhide

Elk

Creek

Horse Creek

Creek

Dry

Rattlesnake

Creek

Double

Crossing Kumor Creek Draw

Cottonwood

Powder

Sussex

Arvada Hulett

Buffalo

Gillette

Moorhead

Newcastle

Sheridan

Moorcroft

Clearmont

Decker

Acme

SHERIDAN

CAMPBELL

JOHNSON

CROOK

NATRONA

CONVERSE

WESTON

NIOBRARA

BIG

HORN

W

ASH

A

KIE

CARTER

BIG HORN

POWDER

RIVER

B4

B3

B1

C2

P8 P7

P6

P5 P4

P2

P1

T6

T5

T4

T1 P27

P26

P23

P22

P20

P19

P18

P17

P15

P13

P11

25

25

0

0 50 KILOMETERS

50 MILES

14

MONTANA

WYOMING

BLA

CK

HILLS

BIGHORN MOUNTAINS

107° 106° 105° 104°

45°

44°

43°

SOUTH DAKOTA

Casper

Base from U.S. Geological Survey digital data,

variously dated, various scales

Transportation network from Federal Highway 

Administration, 2002, 1:100,000

Albers Equal-Area Conic projection

Standard parallels 41°N and 45°N

Central meridian 105°W

North American Datum of 1983 (NAD 83)

16

25

90

90

25

90

Piney

20

85

Lusk

Weston

Spencer

Dull Center

Wakely Siding

Powder River structural basin

Sampling site map number

Upward trend

Downward trend

No trend

EXPLANATION

Powder River

Drainage basin

P1 Tongue River

Cheyenne River

Belle Fourche River
32 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

for water years 2005–10 indicated no significant (p>0.05) 

trend for the Cheyenne River near Spencer (site C2). Significant (p<0.05) upward trends in flow-adjusted concentrations 

of calcium, magnesium, and sodium were determined at 

site C2, indicating that increases in sodium were coupled with 

increases in calcium and magnesium such that no increase in 

SAR occurred. 

In the Belle Fourche River drainage basin, results of the 

seasonal Kendall test applied to flow-adjusted SAR values 

for water years 2005–10 indicated a significant (p<0.05) 

upward trend for the Belle Fourche River near Piney (site B1). 

No significant (p>0.05) trends for flow-adjusted SAR were 

determined for Donkey Creek (site B3) and the Belle Fourche 

River below Moorcroft (site B4). A significant upward trend in 

flow-adjusted sodium concentrations was determined for the 

Belle Fourche River near Piney (site B1), and no significant 

trends were determined for flow-adjusted concentrations of 

calcium and magnesium at site B1, indicating the increase in 

sodium likely caused the upward trend in SAR. 

Trend Analysis for Water Years 1991–2010

The CBNG development was occurring in the Tongue, 

Powder, Cheyenne, and Belle Fourche River drainage basins 

by 1999. Because CBNG development began before establishment of monitoring for CBNG effects in 2001, data for 

samples collected as part of other monitoring programs during 

1991–2000 for selected sites were compiled to expand the 

temporal context of trends. 

The suitability of the Powder River and its tributaries 

for irrigation water use was a concern prior to CBNG development. Upward trends in dissolved solids and SAR were 

reported by Cary (1991) for the Powder River at Arvada 

(site P13) for water years 1968–88 and 1975–88. To aid in 

water-management decisions for the Powder River, simulations using a computer model showed that removing oil and 

gas production water from Salt Creek had a positive effect 

on decreasing dissolved-solids concentrations in the Powder 

River (Lindner-Lunsford and others, 1992). During 1990, 

disposal of some of the saline groundwaters associated with 

conventional oil and gas production in the Salt Creek drainage 

basin was modified to include subsurface injection (RETEC 

Group, Inc., 2004). The change to subsurface injection substantially reduced the inputs from Salt Creek to the Powder 

River and decreased specific conductance in the Powder River 

as far downstream as Arvada, Wyo. (Clark and others, 2001). 

As a result of this time-specific change to the water quality 

in the Powder River drainage basin, water years 1991–2010 

were selected as the long-term trend analysis period to exclude 

pre-1991 characteristics of water quality from Salt Creek on 

the Powder River that were related to conventional oil and gas 

production. 

Many of the monitoring sites either did not have available data for water years 1991–2000, or data collection was 

inconsistent, thus making the sites ineligible for the trend 

analysis. Because of inconsistencies in data collection, trends 

were evaluated for a subset of constituents, including specific 

conductance, SAR, and the primary contributors to SAR (calcium, magnesium, and sodium). For some sites, only specific 

conductance was available for water years 1991–2000. Longterm trends in flow-adjusted specific conductance values were 

evaluated at 8 sites, and long-term trends in flow-adjusted 

SAR values were evaluated at 5 sites in the study area. 

Specific Conductance

Sites analyzed for the trend period of 1991–2010 for 

specific conductance included 2 sites in the Tongue River 

drainage basin, 5 sites in the Powder River drainage basin, 

and 1 site on the Belle Fourche River (appendix 2). Results 

of the seasonal Kendall test applied to flow-adjusted specific 

conductance values for water years 1991–2010 indicated no 

significant (p>0.05) trends were determined for Goose Creek 

(site T3) and the Tongue River at the Stateline (site T6) in the 

Tongue River drainage basin. In the Powder River drainage 

basin, no significant trends in flow-adjusted specific conductance values were determined for Salt Creek (site P1), the 

Powder River at Sussex (site P2), the Powder River at Arvada 

(site P13), the Powder River at Moorhead (site P23), and the 

Little Powder River (site P27). No significant trend in flowadjusted specific conductance values was determined for the 

Belle Fourche River below Moorcroft (site B4). 

Sodium Adsorption Ratios

Sites analyzed for the trend period of 1991–2010 for 

SAR included four sites in the Powder River drainage basin 

and one site on the Belle Fourche River (appendix 2). In the 

Powder River drainage basin, results of the seasonal Kendall 

test applied to flow-adjusted SAR values indicated a significant (p<0.05) upward trend for the Powder River at Arvada 

(site P13) for water years 1991–2010. No significant (p>0.05) 

trend was determined for flow-adjusted SAR values for Salt 

Creek (site P1), the Powder River at Sussex (site P2), and the 

Little Powder River above Dry Creek (site P27). No significant trend was determined for flow-adjusted SAR values for 

the Belle Fourche River below Moorcroft (site B4) for water 

years 1991–2010.

Results of the seasonal Kendall test applied to flowadjusted calcium and magnesium concentrations, which have 

an inverse relation with SAR, indicated significant (p<0.05) 

downward trends for the Powder River at Arvada (site P13) 

for water years 1991–2010. Results of the seasonal Kendall 

test applied to flow-adjusted sodium concentrations, which 

have a direct relation with SAR, indicated a significant upward 

trend for the Powder River at Arvada (site P13). Downward 

trends in calcium and magnesium concentrations may indicate 

precipitation of carbonate minerals, such as calcite and dolomite, as a result of CBNG development. Jackson and Reddy 

(2007b) observed a decrease in calcium concentrations, but 
Summary 33

not in magnesium concentrations, as a result of precipitation 

from CBNG outfalls to impoundments; however, their study 

was focused on geochemical reactions in ponds, which may 

have different chemistry and saturation characteristics than the 

Powder River at Arvada (site P13). The source of increased 

sodium likely is CBNG-produced waters that are discharged 

into tributary drainages of the Powder River upstream from 

Arvada, Wyo. Continued water-quality monitoring of the Powder River is important for determining whether these apparent 

CBNG effects will be relatively persistent or if other waterquality changes will occur as CBNG production declines, as 

well as whether changes in the water quality of Salt Creek 

during water years 2005–2010 will affect the Powder River at 

Arvada with the passage of additional time. 

Although no significant (p>0.05) trend was determined 

for flow-adjusted SAR values for the Belle Fourche River 

below Moorcroft (site B4), an upward trend in flow-adjusted 

magnesium concentrations was significant (p<0.05) for water 

years 1991–2010. Trends in magnesium concentrations were 

significant for all three trend periods. As previously described, 

the source affecting the upward trend in flow-adjusted 

magnesium concentrations may be magnesium chloride, 

which is used throughout the year in the Belle Fourche River 

drainage basin (Tetra Tech, Inc., 2011) for de-icing and dust 

suppression. 

Summary

The Powder River structural basin in northeastern Wyoming and southeastern Montana is an area of ongoing coalbed 

natural gas (CBNG) development. Produced waters associated 

with CBNG development in Wyoming are managed with a 

variety of techniques, including surface impoundments and 

discharges into stream drainages. The interaction of CBNGproduced waters with the atmosphere and the semiarid soils of 

the Powder River structural basin can affect water chemistry 

in several ways. Specific conductance and sodium adsorption 

ratios (SAR) of CBNG-produced waters that are discharged 

to streams have been of particular concern because they 

have the potential to affect the use of the water for irrigation. 

Water-quality monitoring has been conducted since 2001 at 

main-stem and tributary sites in the Tongue, Powder, Cheyenne, and Belle Fourche River drainage basins in response 

to concerns about CBNG effects. A study was conducted to 

summarize characteristics for stream-water quality for water 

years 2001–10 (October 1, 2000, to September 30, 2010), and 

examine trends in specific conductance, SAR, and primary 

constituents that contribute to specific conductance and SAR 

for changes through time (water years 1991–2010) that may 

have occurred as a result of CBNG development. Specific 

conductance and SAR are the focus characteristics of this 

report. Dissolved calcium, magnesium, and sodium, which 

are primary contributors to specific conductance and SAR, as 

well as dissolved alkalinity, chloride, and sulfate, which are 

other primary contributors to specific conductance, also are 

described.

Stream-water quality in the Tongue, Powder, Cheyenne, 

and Belle Fourche River drainage basins was variable during 

water years 2001–10, in part because of variations in streamflow. In general, annual runoff was less than average during 

water years 2001–06 and near or above average during water 

years 2007–10. Streamflow measured during sampling events 

for the Tongue River near the Wyoming-Montana State line 

ranged from 10 cubic feet per second (ft3/s) to 5,430 ft3/s 

during water years 2001–10. Streamflow measured during 

sampling events for the Powder River at Moorhead, Mont., 

ranged from 0.57 to 5,220 ft3/s. Streamflow ranged from 0.01 

to 121 ft3/s during sampling events for the Cheyenne River 

near Spencer, Wyo., during water years 2005–10 and from 

0.02 to 599 ft3/s for the Belle Fourche River downstream from 

Moorcroft, Wyo., during water years 2001–10.

The stream water of the Tongue River drainage basin had 

the smallest specific conductance values, sodium adsorption 

ratios, and major ion concentrations. Sites in the Tongue River 

drainage basin typically had the smallest range of specific 

conductance and SAR values. Median specific conductance 

values at sites in the Tongue River drainage basin ranged from 

411 microsiemens per centimeter at 25°C (μS/cm at 25°C) 

for the Tongue River at Monarch, Wyo., during water years 

2004–10 to 1,460 μS/cm at 25°C for Prairie Dog Creek near 

Acme, Wyo., during water years 2001–10. Median SAR values for sites in the Tongue River drainage basin ranged from 

0.32 to 1.3. The Powder River drainage basin has the largest 

drainage area and most diverse site conditions among the four 

major drainage basins. Median specific conductance values in 

the basin ranged from 672 μS/cm at 25°C for Clear Creek near 

Buffalo, Wyo., during water years 2001–10 to 7,350 μS/cm at 

25°C for SA Creek near Moorhead, Mont., during water years 

2004–10. Sites in the Powder River drainage basin had the 

largest range of median SAR values (0.87 to 32.8) during 

water years 2001–10. 

Trend analyses using the seasonal Kendall test with 

flow-adjusted concentrations were conducted to determine 

changes to water quality through time in sites in the Tongue, 

Powder, Cheyenne, and Belle Fourche River drainage basins. 

Trends were evaluated for water years 2001–10 for 17 sites, 

which generally were on the main-stem streams and primary 

tributaries. Trends were evaluated for water years 2005–10 for 

26 sites to increase the spatial coverage of sites. Trends were 

evaluated for water years 1991–2010 for eight sites to include 

water-quality data collected prior to widespread CBNG development and expand the temporal context of trends.

Consistent patterns were not observed in trend results for 

water years 2001–10 for flow-adjusted specific conductance 

and SAR values in the Tongue, Powder, and Belle Fourche 

River drainage basins. Significant (p-values less than 0.05) 

upward trends in flow-adjusted specific conductance values 

were determined for 3 sites, a downward trend was determined for 1 site, and no significant (p-value greater than 0.05) 

trends were determined for 13 sites. One of the sites with a 
34 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

significant upward trend in flow-adjusted specific conductance 

was the Tongue River at the Wyoming-Montana State line. 

Trend results for flow-adjusted concentrations of individual 

constituents indicated calcium, chloride, and sulfate contributed to the upward trend. Large concentrations of calcium, 

chloride, and sulfate typically are not associated with coalbed 

waters. Although no corresponding trends were determined 

for flow-adjusted specific conductance values, significant 

upward trends in flow-adjusted alkalinity concentrations 

were determined for the Powder River at Arvada, Wyo., and 

at Moorhead, Mont. Discharges of CBNG-produced waters, 

which typically are dominated by sodium and bicarbonate, 

likely are the sources affecting the upward trend in alkalinity; 

however, no corresponding upward trends in flow-adjusted 

sodium concentrations were determined. Significant (p-values 

less than 0.05) upward trends for water years 2001–10 in 

flow-adjusted SAR values were determined for 2 sites and no 

significant (p-value greater than 0.05) trends were determined 

for 15 sites. No trends in flow-adjusted SAR values were 

determined for the Tongue River at the Wyoming-Montana 

State line or for the Powder River at Moorhead, Mont. One of 

the sites with a significant upward trend in flow-adjusted SAR 

values was the Powder River at Arvada, Wyo.; however, no 

significant trends were determined for flow-adjusted concentrations of calcium, magnesium, and sodium.

For water years 2005–10, significant upward trends in 

flow-adjusted specific conductance values were determined 

for 9 sites, downward trends were determined for 4 sites, and 

no significant trends were determined for 13 sites. A significant upward trend was determined for flow-adjusted specific 

conductance values for the Tongue River at the WyomingMontana State line; however, a significant upward trend also 

was determined at a site on the Tongue River at Monarch, 

Wyo., which is upstream from CBNG development. Salt 

Creek, which has had a substantial effect on the water quality of the Powder River through time, had a downward trend 

in flow-adjusted specific conductance. Significant downward 

trends in flow-adjusted concentrations of sodium, alkalinity, 

and chloride contributed to the downward trend in specific 

conductance for Salt Creek. Several of the sites with upward 

trends in flow-adjusted specific conductance, including the 

Little Powder River, were in the plains in the eastern part of 

the study area. Significant upward trends in flow-adjusted 

SAR values for water years 2005–10 were determined for 

4 sites, downward trends were determined for 5 sites, and no 

significant trends were determined for 17 sites. No trends in 

flow-adjusted SAR values were determined for the Tongue 

River at the Wyoming-Montana State line or for the Powder 

River at Moorhead, Mont.

Results of the seasonal Kendall test applied to flowadjusted specific conductance values for water years 

1991–2010 indicated no significant trend for eight sites in the 

Tongue, Powder, and Belle Fourche River drainage basins. No 

significant trend in flow-adjusted specific conductance was 

determined for the Tongue River at the Wyoming-Montana 

State line and the Powder River at Moorhead, Mont. Results of 

the seasonal Kendall test applied to flow-adjusted SAR values 

for water years 1991–2010 indicated an upward trend for one 

site and no significant trend for four sites in the Powder and 

Belle Fourche River drainage basins. The significant upward 

trend in flow-adjusted SAR values was determined for the 

Powder River at Arvada, Wyo., during water years 1991–2010. 

A significant upward trend in flow-adjusted sodium concentrations and significant downward trends in flow-adjusted concentrations of calcium and magnesium also were determined. 

Results indicate that CBNG development in the Powder 

River structural basin may have contributed to some trends, 

such as the upward trend in flow-adjusted SAR for the Powder 

River at Arvada, Wyo., for water years 1991–2010. An upward 

trend in flow-adjusted alkalinity concentrations for water years 

2001–10 also was determined for the Powder River at Arvada, 

Wyo. Trend results are consistent with changes that can occur 

from the addition of sodium and bicarbonate associated with 

CBNG-produced waters to the Powder River. Upward trends 

in constituents at other sites, including the Belle Fourche 

River, may be the result of declining CBNG development, 

indicating that CBNG-produced waters may have had a dilution effect on some streams. The factors affecting other trends 

could not be determined because multiple factors could have 

been affecting the stream-water quality or because trends were 

observed at sites upstream from CBNG development that may 

have affected water-quality trends at sites downstream from 

CBNG development.

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Appendixes
40 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

T1 06299980 Streamflow, instantaneous, ft3/s 90 30 71 99 183 2,520

T1 06299980 pH, in standard units 89 7.7 8.1 8.3 8.5 8.8

T1 06299980 Specific conductance, in μS/cm 90 177 316 411 443 545

T1 06299980 Dissolved solids, in mg/L 90 106 187 243 271 337

T1 06299980 Dissolved solids, in tons per day 90 24.3 50.2 68.8 102 1,144

T1 06299980 Calcium, dissolved, in mg/L 90 22.1 36.2 46.7 50.2 67.7

T1 06299980 Magnesium, dissolved, in mg/L 90 6.67 15.0 20.1 22.2 30.8

T1 06299980 Sodium adsorption ratio (unitless) 90 0.12 0.26 0.32 0.38 0.79

T1 06299980 Sodium, dissolved, in mg/L 90 2.45 7.69 10.4 12.8 26.8

T1 06299980 Alkalinity, in mg/L as calcium 

carbonate

90 80.8 139 177 189 235

T1 06299980 Chloride, dissolved, in mg/L 90 0.54 1.21 1.51 1.86 3.60

T1 06299980 Sulfate, dissolved, in mg/L 90 8.26 28.8 44.3 54.3 110

T2 06304500 Streamflow, instantaneous, ft3/s 103 2.1 20 31 44 1,180

T2 06304500 pH, in standard units 103 7.7 8.1 8.3 8.5 8.7

T2 06304500 Specific conductance, in μS/cm 103 124 553 643 690 984

T2 06304500 Dissolved solids, in mg/L 99 69.3 341 395 427 640

T2 06304500 Dissolved solids, in tons per day 99 3.70 23.2 31.9 44.5 593

T2 06304500 Calcium, dissolved, in mg/L 98 12.0 51.4 61.2 65.4 87.9

T2 06304500 Magnesium, dissolved, in mg/L 98 5.50 33.9 39.6 44.7 67.7

T2 06304500 Sodium adsorption ratio (unitless) 98 0.19 0.43 0.47 0.52 2.2

T2 06304500 Sodium, dissolved, in mg/L 98 3.16 16.5 19.5 22.2 89.4

T2 06304500 Alkalinity, in mg/L as calcium 

carbonate

99 52.2 206 246 268 318

T2 06304500 Chloride, dissolved, in mg/L 99 0.75 3.60 4.48 5.27 117

T2 06304500 Sulfate, dissolved, in mg/L 99 9.08 74.5 90.1 109 270

T3 06305500 Streamflow, instantaneous, ft3/s 103 3.8 46 66 98 1,790

T3 06305500 pH, in standard units 103 7.8 8.1 8.3 8.5 8.9

T3 06305500 Specific conductance, in μS/cm 103 110 540 639 690 868

T3 06305500 Dissolved solids, in mg/L 98 75.4 347 410 448 571

T3 06305500 Dissolved solids, in tons per day 98 4.63 52.4 72.1 90.1 891

T3 06305500 Calcium, dissolved, in mg/L 98 10.5 50.6 59.4 64.0 75.8

T3 06305500 Magnesium, dissolved, in mg/L 98 4.39 30.9 37.1 42.1 49.6

T3 06305500 Sodium adsorption ratio (unitless) 98 0.19 0.51 0.57 0.63 1.0

T3 06305500 Sodium, dissolved, in mg/L 98 2.93 19.0 23.6 25.8 42.3

T3 06305500 Alkalinity, in mg/L as calcium 

carbonate

97 43.0 200 229 246 292

T3 06305500 Chloride, dissolved, in mg/L 98 0.71 4.97 6.27 8.06 20.7

T3 06305500 Sulfate, dissolved, in mg/L 98 10.4 91.6 110 125 190

T4 06306200 Streamflow, instantaneous, ft3/s 87 0.53 9.0 13 29 116

T4 06306200 pH, in standard units 87 7.7 8.1 8.2 8.3 8.5
Appendix 1 41

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

T4 06306200 Specific conductance, in μS/cm 87 425 670 936 1,030 1,240

T4 06306200 Dissolved solids, in mg/L 87 275 448 622 705 891

T4 06306200 Dissolved solids, in tons per day 87 1.27 17.8 22.8 36.7 177

T4 06306200 Calcium, dissolved, in mg/L 87 42.8 72.7 98.1 114 145

T4 06306200 Magnesium, dissolved, in mg/L 87 21.2 37.6 56.7 62.7 77.1

T4 06306200 Sodium adsorption ratio (unitless) 87 0.32 0.41 0.50 0.58 0.89

T4 06306200 Sodium, dissolved, in mg/L 87 10.7 17.2 26.3 31.4 44.8

T4 06306200 Alkalinity, in mg/L as calcium 

carbonate

86 118 214 286 321 423

T4 06306200 Chloride, dissolved, in mg/L 87 1.20 2.25 3.27 4.39 7.86

T4 06306200 Sulfate, dissolved, in mg/L 87 80.3 159 223 248 368

T5 06306250 Streamflow, instantaneous, ft3/s 131 0.21 11 18 36 127

T5 06306250 pH, in standard units 129 7.6 8.0 8.2 8.3 8.5

T5 06306250 Specific conductance, in μS/cm 131 642 1,240 1,460 1,670 2,510

T5 06306250 Dissolved solids, in mg/L 131 427 912 1,089 1,301 2,157

T5 06306250 Dissolved solids, in tons per day 131 1.01 34.3 50.3 76.7 398

T5 06306250 Calcium, dissolved, in mg/L 131 37.5 111 135 152 209

T5 06306250 Magnesium, dissolved, in mg/L 131 20.5 71.1 88.2 105 167

T5 06306250 Sodium adsorption ratio (unitless) 131 0.57 1.1 1.3 1.6 3.6

T5 06306250 Sodium, dissolved, in mg/L 131 22.9 63.6 76.0 105 216

T5 06306250 Alkalinity, in mg/L as calcium 

carbonate

131 155 275 317 361 488

T5 06306250 Chloride, dissolved, in mg/L 131 1.93 3.94 4.79 5.95 9.03

T5 06306250 Sulfate, dissolved, in mg/L 131 163 406 506 639 1,156

T6 06306300 Streamflow, instantaneous, ft3/s 149 10 131 181 310 5,430

T6 06306300 pH, in standard units 147 7.7 8.2 8.3 8.5 8.8

T6 06306300 Specific conductance, in μS/cm 149 186 488 636 725 1,280

T6 06306300 Dissolved solids, in mg/L 149 108 302 399 466 776

T6 06306300 Dissolved solids, in tons per day 149 21.0 151 186 297 3,580

T6 06306300 Calcium, dissolved, in mg/L 149 20.1 45.9 57.0 63.1 78.9

T6 06306300 Magnesium, dissolved, in mg/L 149 7.83 24.2 34.2 39.5 63.2

T6 06306300 Sodium adsorption ratio (unitless) 149 0.23 0.60 0.73 0.86 2.8

T6 06306300 Sodium, dissolved, in mg/L 149 4.97 20.4 28.2 35.4 124

T6 06306300 Alkalinity, in mg/L as calcium 

carbonate

149 73.1 170 214 239 356

T6 06306300 Chloride, dissolved, in mg/L 149 0.83 3.04 4.11 5.19 7.93

T6 06306300 Sulfate, dissolved, in mg/L 149 20.5 82.3 123 151 302

P1 06313400 Streamflow, instantaneous, ft3/s 110 4.5 12 15 18 384

P1 06313400 pH, in standard units 110 7.7 8.1 8.2 8.4 8.9

P1 06313400 Specific conductance, in μS/cm 110 1,110 5,490 5,950 6,480 8,460

P1 06313400 Dissolved solids, in mg/L 110 792 3,720 3,948 4,276 5,529

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
42 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

P1 06313400 Dissolved solids, in tons per day 110 48.4 125 162 203 1,580

P1 06313400 Calcium, dissolved, in mg/L 110 50.2 119 154 203 287

P1 06313400 Magnesium, dissolved, in mg/L 110 21.3 56.0 64.8 73.9 144

P1 06313400 Sodium adsorption ratio (unitless) 110 4.9 14.2 18.0 20.8 30.0

P1 06313400 Sodium, dissolved, in mg/L 110 164 938 1,078 1,192 1,488

P1 06313400 Alkalinity, in mg/L as calcium 

carbonate

110 75.7 236 310 365 640

P1 06313400 Chloride, dissolved, in mg/L 110 39.2 890 1,046 1,203 1,646

P1 06313400 Sulfate, dissolved, in mg/L 110 341 1,093 1,222 1,425 2,325

P2 06313500 Streamflow, instantaneous, ft3/s 195 3.7 53 110 160 1,410

P2 06313500 pH, in standard units 194 7.6 8.1 8.2 8.3 8.6

P2 06313500 Specific conductance, in μS/cm 195 545 1,960 2,270 2,940 6,240

P2 06313500 Dissolved solids, in mg/L 195 338 1,360 1,589 2,046 4,075

P2 06313500 Dissolved solids, in tons per day 195 40.7 264 428 603 5,924

P2 06313500 Calcium, dissolved, in mg/L 194 41.8 122 141 156 288

P2 06313500 Magnesium, dissolved, in mg/L 195 13.2 45.9 52.0 58.9 103

P2 06313500 Sodium adsorption ratio (unitless) 194 1.5 4.3 5.1 7.4 21.1

P2 06313500 Sodium, dissolved, in mg/L 195 43.3 220 281 423 1,128

P2 06313500 Alkalinity, in mg/L as calcium 

carbonate

195 82.9 183 213 236 330

P2 06313500 Chloride, dissolved, in mg/L 195 28.0 156 214 336 1,186

P2 06313500 Sulfate, dissolved, in mg/L 195 134 556 663 869 1,634

P3 06313540 Streamflow, instantaneous, ft3/s 21 0.06 0.20 0.26 0.55 1.6

P3 06313540 pH, in standard units 21 7.9 8.1 8.2 8.4 8.7

P3 06313540 Specific conductance, in μS/cm 21 3,140 3,480 3,640 3,820 4,700

P3 06313540 Dissolved solids, in mg/L 21 2,215 2,534 2,592 2,718 3,429

P3 06313540 Dissolved solids, in tons per day 21 0.59 1.45 1.85 3.74 11.1

P3 06313540 Calcium, dissolved, in mg/L 21 17.5 57.6 86.4 152 271

P3 06313540 Magnesium, dissolved, in mg/L 21 32.1 65.6 69.3 77.5 117

P3 06313540 Sodium adsorption ratio (unitless) 21 8.5 11.0 13.0 16.1 25.3

P3 06313540 Sodium, dissolved, in mg/L 21 521 639 719 767 859

P3 06313540 Alkalinity, in mg/L as calcium 

carbonate

3 412 — 578 — 651

P3 06313540 Chloride, dissolved, in mg/L 3 18.3 — 26.7 — 26.9

P3 06313540 Sulfate, dissolved, in mg/L 3 1,319 — 1,827 — 2,035

P4 06313560 Streamflow, instantaneous, ft3/s 63 0.10 1.6 3.5 4.6 14

P4 06313560 pH, in standard units 63 8.1 8.3 8.4 8.6 9.1

P4 06313560 Specific conductance, in μS/cm 63 2,010 3,220 3,600 3,850 5,250

P4 06313560 Dissolved solids, in mg/L 63 1,401 2,145 2,479 2,591 4,224

P4 06313560 Dissolved solids, in tons per day 63 0.60 12.3 21.7 28.2 56.2

P4 06313560 Calcium, dissolved, in mg/L 61 8.07 27.0 32.5 41.5 161

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
Appendix 1 43

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

P4 06313560 Magnesium, dissolved, in mg/L 63 30.8 38.2 45.8 65.8 174

P4 06313560 Sodium adsorption ratio (unitless) 61 9.4 15.5 19.1 24.5 27.8

P4 06313560 Sodium, dissolved, in mg/L 63 390 687 774 871 1,037

P4 06313560 Alkalinity, in mg/L as calcium 

carbonate

4 385 — 1,245 — 1,548

P4 06313560 Chloride, dissolved, in mg/L 4 21.9 — 23.7 — 30.7

P4 06313560 Sulfate, dissolved, in mg/L 4 566 — 895 — 1,780

P5 06313585 Streamflow, instantaneous, ft3/s 75 0.45 1.3 2.8 6.0 16

P5 06313585 pH, in standard units 75 8.2 8.6 8.7 8.8 9.1

P5 06313585 Specific conductance, in μS/cm 75 1,180 1,590 2,560 2,840 3,820

P5 06313585 Dissolved solids, in mg/L 75 766 1,019 1,710 1,904 2,563

P5 06313585 Dissolved solids, in tons per day 75 2.30 6.89 12.3 16.2 35.5

P5 06313585 Calcium, dissolved, in mg/L 73 8.02 15.3 22.2 32.2 68.4

P5 06313585 Magnesium, dissolved, in mg/L 75 11.4 22.9 31.1 37.6 86.5

P5 06313585 Sodium adsorption ratio (unitless) 73 5.9 11.9 16.0 19.0 26.1

P5 06313585 Sodium, dissolved, in mg/L 75 201 336 560 634 774

P5 06313585 Alkalinity, in mg/L as calcium 

carbonate

6 469 502 621 642 816

P5 06313585 Chloride, dissolved, in mg/L 6 23.9 25.6 28.5 31.8 40.5

P5 06313585 Sulfate, dissolved, in mg/L 6 54.1 76.4 173 287 434

P6 06313590 Streamflow, instantaneous, ft3/s 88 0.07 41 115 186 761

P6 06313590 pH, in standard units 88 7.8 8.2 8.3 8.4 8.8

P6 06313590 Specific conductance, in μS/cm 88 723 1,995 2,340 2,935 5,310

P6 06313590 Dissolved solids, in mg/L 88 462 1,395 1,597 2,030 4,093

P6 06313590 Dissolved solids, in tons per day 88 0.77 230 483 722 2,858

P6 06313590 Calcium, dissolved, in mg/L 88 17.2 118 130 147 291

P6 06313590 Magnesium, dissolved, in mg/L 88 20.7 46.0 52.0 63.8 124

P6 06313590 Sodium adsorption ratio (unitless) 88 1.9 4.9 5.6 7.0 21.7

P6 06313590 Sodium, dissolved, in mg/L 88 66.5 256 303 410 770

P6 06313590 Alkalinity, in mg/L as calcium 

carbonate

88 122 188 227 275 1,158

P6 06313590 Chloride, dissolved, in mg/L 88 32.6 146 198 286 565

P6 06313590 Sulfate, dissolved, in mg/L 88 204 559 692 890 1,973

P7 06313604 Streamflow, instantaneous, ft3/s 71 0.04 0.53 0.99 1.8 2.8

P7 06313604 pH, in standard units 71 8.3 8.6 8.7 8.8 9.5

P7 06313604 Specific conductance, in μS/cm 71 1,940 3,260 3,430 3,740 3,900

P7 06313604 Dissolved solids, in mg/L 71 1,430 2,154 2,255 2,445 2,537

P7 06313604 Dissolved solids, in tons per day 71 0.22 3.14 6.40 11.6 18.9

P7 06313604 Calcium, dissolved, in mg/L 71 10.3 14.5 16.7 19.3 31.5

P7 06313604 Magnesium, dissolved, in mg/L 71 14.9 19.3 22.1 26.6 32.4

P7 06313604 Sodium adsorption ratio (unitless) 71 18.2 28.4 29.8 31.7 37.1

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
44 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

P7 06313604 Sodium, dissolved, in mg/L 71 446 772 813 851 1,007

P7 06313604 Alkalinity, in mg/L as calcium 

carbonate

4 1,037 — 1,486 — 1,955

P7 06313604 Chloride, dissolved, in mg/L 4 22.9 — 32.8 — 34.5

P7 06313604 Sulfate, dissolved, in mg/L 4 27.5 — 49.0 — 110

P8 06313605 Streamflow, instantaneous, ft3/s 114 1.4 52 110 172 1,030

P8 06313605 pH, in standard units 114 7.6 8.2 8.3 8.4 9.1

P8 06313605 Specific conductance, in μS/cm 114 726 2,050 2,375 2,870 5,790

P8 06313605 Dissolved solids, in mg/L 114 469 1,405 1,649 2,031 3,830

P8 06313605 Dissolved solids, in tons per day 114 9.64 277 441 676 5,796

P8 06313605 Calcium, dissolved, in mg/L 114 15.6 113 130 148 223

P8 06313605 Magnesium, dissolved, in mg/L 114 20.4 45.5 52.4 62.8 108

P8 06313605 Sodium adsorption ratio (unitless) 114 1.9 5.0 5.6 7.2 26.7

P8 06313605 Sodium, dissolved, in mg/L 114 67.5 259 307 404 1,037

P8 06313605 Alkalinity, in mg/L as calcium 

carbonate

114 103 210 248 304 2,091

P8 06313605 Chloride, dissolved, in mg/L 114 32.6 146 198 258 926

P8 06313605 Sulfate, dissolved, in mg/L 114 116 553 686 863 1,665

P9 06313633 Streamflow, instantaneous, ft3/s 46 0.03 0.20 1.2 1.9 3.6

P9 06313633 pH, in standard units 46 7.6 8.8 8.9 9.0 9.4

P9 06313633 Specific conductance, in μS/cm 46 1,050 1,310 1,370 1,650 4,840

P9 06313633 Dissolved solids, in mg/L 46 635 803 871 1,172 3,201

P9 06313633 Dissolved solids, in tons per day 46 0.05 1.04 2.70 4.33 9.28

P9 06313633 Calcium, dissolved, in mg/L 45 6.96 12.4 16.2 21.8 92.0

P9 06313633 Magnesium, dissolved, in mg/L 46 8.07 11.1 14.5 24.9 70.6

P9 06313633 Sodium adsorption ratio (unitless) 45 4.8 10.9 12.7 14.9 37.7

P9 06313633 Sodium, dissolved, in mg/L 46 196 271 291 325 1,160

P9 06313633 Alkalinity, in mg/L as calcium 

carbonate

3 175 — 475 — 484

P9 06313633 Chloride, dissolved, in mg/L 3 22.9 — 38.9 — 46.3

P9 06313633 Sulfate, dissolved, in mg/L 3 44.6 — 66.6 — 881

P10 06313750 Streamflow, instantaneous, ft3/s 52 0.03 0.32 0.66 1.6 15

P10 06313750 pH, in standard units 52 7.5 8.3 8.6 8.8 9.3

P10 06313750 Specific conductance, in μS/cm 52 776 1,220 1,635 2,160 3,690

P10 06313750 Dissolved solids, in mg/L 52 505 721 1,060 1,469 2,824

P10 06313750 Dissolved solids, in tons per day 52 0.11 0.67 1.94 6.51 35.0

P10 06313750 Calcium, dissolved, in mg/L 52 5.89 13.1 17.0 32.5 234

P10 06313750 Magnesium, dissolved, in mg/L 52 2.87 6.05 8.97 18.0 150

P10 06313750 Sodium adsorption ratio (unitless) 52 2.8 9.8 15.8 24.6 33.8

P10 06313750 Sodium, dissolved, in mg/L 52 115 238 327 500 768

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
Appendix 1 45

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

P10 06313750 Alkalinity, in mg/L as calcium 

carbonate

5 923 — 1,188 — 1,283

P10 06313750 Chloride, dissolved, in mg/L 5 14.0 — 16.9 — 28.3

P10 06313750 Sulfate, dissolved, in mg/L 5 0.50 — 5.63 — 34.0

P11 06316400 Streamflow, instantaneous, ft3/s 193 0.01 5.1 11 21 422

P11 06316400 pH, in standard units 193 7.4 8.0 8.1 8.3 8.6

P11 06316400 Specific conductance, in μS/cm 193 335 1,280 1,630 2,140 3,660

P11 06316400 Dissolved solids, in mg/L 193 245 1,028 1,316 1,834 3,363

P11 06316400 Dissolved solids, in tons per day 193 0.06 20.9 38.9 64.6 343

P11 06316400 Calcium, dissolved, in mg/L 193 32.2 121 150 192 336

P11 06316400 Magnesium, dissolved, in mg/L 193 12.8 62.3 80.0 107 207

P11 06316400 Sodium adsorption ratio (unitless) 193 0.45 1.6 1.9 2.5 5.7

P11 06316400 Sodium, dissolved, in mg/L 193 17.9 87.3 115 178 476

P11 06316400 Alkalinity, in mg/L as calcium 

carbonate

192 70.0 180 215 244 468

P11 06316400 Chloride, dissolved, in mg/L 193 1.69 6.12 8.26 10.5 61.0

P11 06316400 Sulfate, dissolved, in mg/L 193 94.3 531 702 1,009 1,948

P12 06316900 Streamflow, instantaneous, ft3/s 40 0.01 0.01 0.03 0.06 7.1

P12 06316900 pH, in standard units 40 7.6 8.6 8.9 9.0 9.3

P12 06316900 Specific conductance, in μS/cm 40 1,150 2,080 2,740 3,085 4,110

P12 06316900 Dissolved solids, in mg/L 40 743 1,414 1,851 2,065 2,755

P12 06316900 Dissolved solids, in tons per day 40 0.02 0.06 0.15 0.28 20.8

P12 06316900 Calcium, dissolved, in mg/L 40 4.16 9.38 10.4 16.2 275

P12 06316900 Magnesium, dissolved, in mg/L 40 3.77 8.31 11.1 17.2 125

P12 06316900 Sodium adsorption ratio (unitless) 40 1.0 22.1 32.8 39.3 46.7

P12 06316900 Sodium, dissolved, in mg/L 40 57.3 410 640 729 1,009

P12 06316900 Alkalinity, in mg/L as calcium 

carbonate

1 — — — — 140

P12 06316900 Chloride, dissolved, in mg/L 1 — — — — 6.09

P12 06316900 Sulfate, dissolved, in mg/L 1 — — — — 1,254

P13 06317000 Streamflow, instantaneous, ft3/s 193 0.08 70 118 213 2,260

P13 06317000 pH, in standard units 193 7.3 8.1 8.3 8.4 8.9

P13 06317000 Specific conductance, in μS/cm 193 651 1,990 2,270 2,610 5,170

P13 06317000 Dissolved solids, in mg/L 193 412 1,398 1,595 1,874 4,101

P13 06317000 Dissolved solids, in tons per day 193 0.89 332 494 828 9,775

P13 06317000 Calcium, dissolved, in mg/L 191 40.8 105 126 149 307

P13 06317000 Magnesium, dissolved, in mg/L 193 18.0 45.7 54.8 63.9 133

P13 06317000 Sodium adsorption ratio (unitless) 191 1.9 4.7 5.5 6.5 11.8

P13 06317000 Sodium, dissolved, in mg/L 193 61.6 245 295 367 752

P13 06317000 Alkalinity, in mg/L as calcium 

carbonate

193 76.8 194 225 271 521

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
46 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

P13 06317000 Chloride, dissolved, in mg/L 193 22.5 130 175 221 514

P13 06317000 Sulfate, dissolved, in mg/L 193 179 557 689 823 2,010

P14 06317020 Streamflow, instantaneous, ft3/s 71 0.01 0.76 2.8 5.0 43

P14 06317020 pH, in standard units 71 7.6 8.0 8.3 8.4 9.0

P14 06317020 Specific conductance, in μS/cm 71 252 2,180 2,680 3,270 4,580

P14 06317020 Dissolved solids, in mg/L 71 218 1,569 2,024 2,512 4,013

P14 06317020 Dissolved solids, in tons per day 71 0.08 3.62 13.8 24.7 181

P14 06317020 Calcium, dissolved, in mg/L 70 19.6 63.0 104 153 253

P14 06317020 Magnesium, dissolved, in mg/L 71 6.80 57.6 90.9 124 236

P14 06317020 Sodium adsorption ratio (unitless) 70 1.3 6.3 7.2 7.9 12.3

P14 06317020 Sodium, dissolved, in mg/L 71 25.4 348 410 475 808

P14 06317020 Alkalinity, in mg/L as calcium 

carbonate

71 44.1 441 529 615 1,009

P14 06317020 Chloride, dissolved, in mg/L 71 2.76 15.6 17.5 19.9 40.6

P14 06317020 Sulfate, dissolved, in mg/L 71 84.3 600 1,033 1,346 2,256

P15 06317030 Streamflow, instantaneous, ft3/s 75 0.002 0.37 2.6 5.4 82

P15 06317030 pH, in standard units 75 7.6 8.3 8.4 8.5 8.9

P15 06317030 Specific conductance, in μS/cm 75 1,090 2,690 3,440 4,320 7,410

P15 06317030 Dissolved solids, in mg/L 75 749 1,983 2,597 3,561 7,139

P15 06317030 Dissolved solids, in tons per day 75 0.02 3.40 14.2 26.8 326

P15 06317030 Calcium, dissolved, in mg/L 74 33.0 71.4 101 146 343

P15 06317030 Magnesium, dissolved, in mg/L 75 27.6 86.9 130 174 507

P15 06317030 Sodium adsorption ratio (unitless) 74 4.3 7.2 8.0 10.2 17.7

P15 06317030 Sodium, dissolved, in mg/L 75 152 412 505 713 1,229

P15 06317030 Alkalinity, in mg/L as calcium 

carbonate

6 126 371 418 449 509

P15 06317030 Chloride, dissolved, in mg/L 6 6.07 15.1 23.4 27.0 32.5

P15 06317030 Sulfate, dissolved, in mg/L 6 547 1,942 2,433 3,132 3,510

P16 06317095 Streamflow, instantaneous, ft3/s 29 0.001 0.01 0.10 0.43 42

P16 06317095 pH, in standard units 29 8.0 8.3 8.4 8.5 8.8

P16 06317095 Specific conductance, in μS/cm 29 1,730 1,900 4,000 5,290 7,950

P16 06317095 Dissolved solids, in mg/L 29 1,121 1,277 2,920 4,866 8,313

P16 06317095 Dissolved solids, in tons per day 29 0.01 0.06 0.66 6.41 146

P16 06317095 Calcium, dissolved, in mg/L 29 7.65 11.1 72.6 199 356

P16 06317095 Magnesium, dissolved, in mg/L 29 5.74 10.5 97.8 328 628

P16 06317095 Sodium adsorption ratio (unitless) 29 3.4 8.9 11.8 22.8 31.6

P16 06317095 Sodium, dissolved, in mg/L 29 187 451 657 909 1,416

P16 06317095 Alkalinity, in mg/L as calcium 

carbonate

1 — — — — 338

P16 06317095 Chloride, dissolved, in mg/L 1 — — — — 19.9

P16 06317095 Sulfate, dissolved, in mg/L 1 — — — — 3,146

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
Appendix 1 47

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

P17 06317100 Streamflow, instantaneous, ft3/s 73 2.8 70 135 231 1,660

P17 06317100 pH, in standard units 75 7.2 8.2 8.3 8.4 8.6

P17 06317100 Specific conductance, in μS/cm 75 741 1,710 2,200 2,540 3,560

P17 06317100 Dissolved solids, in mg/L 75 485 1,365 1,591 1,794 2,616

P17 06317100 Dissolved solids, in tons per day 73 12.7 327 544 928 2,982

P17 06317100 Calcium, dissolved, in mg/L 74 52.2 101 119 136 210

P17 06317100 Magnesium, dissolved, in mg/L 74 20.2 46.9 56.6 65.5 101

P17 06317100 Sodium adsorption ratio (unitless) 74 1.5 4.4 5.6 6.4 8.8

P17 06317100 Sodium, dissolved, in mg/L 74 70.0 209 302 343 506

P18 06320210 Streamflow, instantaneous, ft3/s 113 4.4 28 42 67 2,340

P18 06320210 pH, in standard units 113 7.5 7.9 8.2 8.4 9.2

P18 06320210 Specific conductance, in μS/cm 113 104 470 672 783 1,010

P18 06320210 Dissolved solids, in mg/L 108 85.2 316 466 549 717

P18 06320210 Dissolved solids, in tons per day 108 7.29 39.6 50.5 65.9 938

P18 06320210 Calcium, dissolved, in mg/L 108 9.54 46.3 67.4 80.5 98.3

P18 06320210 Magnesium, dissolved, in mg/L 108 3.37 19.4 27.9 32.9 45.1

P18 06320210 Sodium adsorption ratio (unitless) 108 0.30 0.73 0.87 1.0 1.4

P18 06320210 Sodium, dissolved, in mg/L 108 4.24 23.0 33.6 41.4 62.6

P18 06320210 Alkalinity, in mg/L as calcium 

carbonate

107 29.0 106 142 168 233

P18 06320210 Chloride, dissolved, in mg/L 107 0.87 2.86 3.79 4.97 13.6

P18 06320210 Sulfate, dissolved, in mg/L 107 20.3 139 206 245 331

P19 06323550 Streamflow, instantaneous, ft3/s 75 27 55 90 142 2,045

P19 06323550 pH, in standard units 75 7.4 7.9 8.2 8.4 8.7

P19 06323550 Specific conductance, in μS/cm 75 136 658 725 789 972

P19 06323550 Dissolved solids, in mg/L 75 99.2 449 502 561 725

P19 06323550 Dissolved solids, in tons per day 75 44.2 83.1 116 166 548

P19 06323550 Calcium, dissolved, in mg/L 75 14.4 64.7 75.3 82.4 110

P19 06323550 Magnesium, dissolved, in mg/L 75 4.13 25.3 30.1 33.8 46.3

P19 06323550 Sodium adsorption ratio (unitless) 75 0.30 0.77 0.87 0.92 1.1

P19 06323550 Sodium, dissolved, in mg/L 75 4.99 29.4 35.2 38.5 52.4

P19 06323550 Alkalinity, in mg/L as calcium 

carbonate

1 — — — — 180

P19 06323550 Chloride, dissolved, in mg/L 1 — — — — 5.45

P19 06323550 Sulfate, dissolved, in mg/L 1 — — — — 319

P20 06324000 Streamflow, instantaneous, ft3/s 204 0.24 43 70 103 2,230

P20 06324000 pH, in standard units 204 7.6 8.0 8.2 8.4 8.8

P20 06324000 Specific conductance, in μS/cm 204 175 914 1,060 1,240 2,020

P20 06324000 Dissolved solids, in mg/L 203 90.3 654 787 940 1,663

P20 06324000 Dissolved solids, in tons per day 203 1.04 109 143 194 1,327

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
48 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

P20 06324000 Calcium, dissolved, in mg/L 203 17.7 90.3 108 127 189

P20 06324000 Magnesium, dissolved, in mg/L 203 5.49 39.3 48.0 56.8 105

P20 06324000 Sodium adsorption ratio (unitless) 203 0.33 1.1 1.2 1.3 2.6

P20 06324000 Sodium, dissolved, in mg/L 203 6.53 48.6 59.2 70.2 169

P20 06324000 Alkalinity, in mg/L as calcium 

carbonate

203 48.3 165 195 223 321

P20 06324000 Chloride, dissolved, in mg/L 203 0.69 3.10 3.72 4.31 6.82

P20 06324000 Sulfate, dissolved, in mg/L 203 32.9 297 372 455 878

P21 06324200 Streamflow, instantaneous, ft3/s 52 0.01 0.33 0.73 1.2 17

P21 06324200 pH, in standard units 52 8.1 8.5 8.6 8.7 9.0

P21 06324200 Specific conductance, in μS/cm 52 1,700 2,785 3,185 3,910 11,200

P21 06324200 Dissolved solids, in mg/L 52 1,284 1,917 2,171 2,981 11,310

P21 06324200 Dissolved solids, in tons per day 52 0.31 2.07 4.04 7.07 88.8

P21 06324200 Calcium, dissolved, in mg/L 50 9.58 22.6 36.9 85.2 366

P21 06324200 Magnesium, dissolved, in mg/L 51 8.51 34.6 57.0 139 788

P21 06324200 Sodium adsorption ratio (unitless) 50 4.6 12.4 15.3 20.4 32.6

P21 06324200 Sodium, dissolved, in mg/L 51 223 626 659 730 2,458

P21 06324200 Alkalinity, in mg/L as calcium 

carbonate

4 333 — 690 — 1,275

P21 06324200 Chloride, dissolved, in mg/L 4 8.51 — 18.0 — 22.5

P21 06324200 Sulfate, dissolved, in mg/L 4 195 — 1,135 — 2,050

P22 06324300 Streamflow, instantaneous, ft3/s 65 0.001 0.01 0.04 0.35 52

P22 06324300 pH, in standard units 65 6.6 7.8 7.9 8.1 8.6

P22 06324300 Specific conductance, in μS/cm 65 1,710 6,600 7,350 7,810 8,630

P22 06324300 Dissolved solids, in mg/L 65 1,286 5,895 7,194 7,676 8,741

P22 06324300 Dissolved solids, in tons per day 65 0.02 0.22 0.84 4.67 201

P22 06324300 Calcium, dissolved, in mg/L 65 63.7 251 286 322 369

P22 06324300 Magnesium, dissolved, in mg/L 65 70.2 363 416 446 540

P22 06324300 Sodium adsorption ratio (unitless) 64 4.3 9.9 10.5 11.1 13.1

P22 06324300 Sodium, dissolved, in mg/L 64 212 1,060 1,159 1,291 1,498

P22 06324300 Alkalinity, in mg/L as calcium 

carbonate

6 353 373 467 552 659

P22 06324300 Chloride, dissolved, in mg/L 6 12.2 16.6 33.4 39.0 41.9

P22 06324300 Sulfate, dissolved, in mg/L 6 1,906 2,651 4,780 5,405 5,423

P23 06324500 Streamflow, instantaneous, ft3/s 206 0.57 94 200 329 5,220

P23 06324500 pH, in standard units 202 7.6 8.2 8.3 8.4 8.7

P23 06324500 Specific conductance, in μS/cm 206 356 1,560 1,820 2,100 3,660

P23 06324500 Dissolved solids, in mg/L 206 231 1,132 1,313 1,556 2,817

P23 06324500 Dissolved solids, in tons per day 206 4.29 379 687 1,105 8,882

P23 06324500 Calcium, dissolved, in mg/L 206 30.9 97.8 117 137 295

P23 06324500 Magnesium, dissolved, in mg/L 206 10.1 45.1 54.0 65.1 160

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
Appendix 1 49

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

P23 06324500 Sodium adsorption ratio (unitless) 206 1.1 3.4 4.1 4.5 9.0

P23 06324500 Sodium, dissolved, in mg/L 206 27.2 164 214 250 520

P23 06324500 Alkalinity, in mg/L as calcium 

carbonate

206 78.4 169 203 244 458

P23 06324500 Chloride, dissolved, in mg/L 206 5.67 62.3 97.5 121 307

P23 06324500 Sulfate, dissolved, in mg/L 206 80.3 487 577 730 1,770

P24 06324870 Streamflow, instantaneous, ft3/s 34 0.07 0.35 0.75 2.4 7.2

P24 06324870 pH, in standard units 34 7.1 7.9 8.1 8.2 8.4

P24 06324870 Specific conductance, in μS/cm 34 2,130 3,210 3,850 4,420 5,410

P24 06324870 Dissolved solids, in mg/L 34 1,769 3,002 3,682 4,371 5,472

P24 06324870 Dissolved solids, in tons per day 34 1.03 4.28 8.21 19.9 65.5

P24 06324870 Calcium, dissolved, in mg/L 34 127 231 301 396 507

P24 06324870 Magnesium, dissolved, in mg/L 34 121 234 264 322 503

P24 06324870 Sodium adsorption ratio (unitless) 34 1.4 2.5 3.0 3.6 4.6

P24 06324870 Sodium, dissolved, in mg/L 34 138 213 292 370 586

P25 06324940 Streamflow, instantaneous, ft3/s 24 0.03 1.5 3.9 7.5 50

P25 06324940 pH, in standard units 24 7.6 8.0 8.1 8.2 8.4

P25 06324940 Specific conductance, in μS/cm 24 648 2,015 2,980 3,578 5,600

P25 06324940 Dissolved solids, in mg/L 24 478 1,604 2,507 3,204 5,363

P25 06324940 Dissolved solids, in tons per day 24 0.25 9.50 16.7 51.2 289

P25 06324940 Calcium, dissolved, in mg/L 24 32.9 94.6 147 199 350

P25 06324940 Magnesium, dissolved, in mg/L 24 24.1 92.3 143 207 396

P25 06324940 Sodium adsorption ratio (unitless) 24 1.9 3.8 4.7 5.6 7.6

P25 06324940 Sodium, dissolved, in mg/L 24 58.0 236 342 486 868

P26 06324950 Streamflow, instantaneous, ft3/s 75 0.01 1.5 3.2 13 130

P26 06324950 pH, in standard units 75 7.6 8.0 8.2 8.3 8.4

P26 06324950 Specific conductance, in μS/cm 75 588 2,160 3,070 3,640 4,600

P26 06324950 Dissolved solids, in mg/L 75 404 1,716 2,463 3,049 4,017

P26 06324950 Dissolved solids, in tons per day 75 0.09 9.71 22.2 56.6 479

P26 06324950 Calcium, dissolved, in mg/L 75 23.4 114 155 188 313

P26 06324950 Magnesium, dissolved, in mg/L 75 10.8 73.8 108 127 230

P26 06324950 Sodium adsorption ratio (unitless) 75 1.7 4.4 6.1 7.7 11.2

P26 06324950 Sodium, dissolved, in mg/L 75 49.6 249 434 543 672

P27 06324970 Streamflow, instantaneous, ft3/s 123 0.01 1.0 3.1 9.9 314

P27 06324970 pH, in standard units 123 7.4 7.9 8.1 8.2 8.5

P27 06324970 Specific conductance, in μS/cm 123 358 2,470 3,330 3,770 5,250

P27 06324970 Dissolved solids, in mg/L 123 225 1,868 2,716 3,136 4,585

P27 06324970 Dissolved solids, in tons per day 123 0.07 6.77 24.1 62.1 671

P27 06324970 Calcium, dissolved, in mg/L 123 17.6 119 163 189 313

P27 06324970 Magnesium, dissolved, in mg/L 123 7.38 78.8 111 129 211

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
50 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

P27 06324970 Sodium adsorption ratio (unitless) 123 1.9 5.6 6.9 7.9 10.6

P27 06324970 Sodium, dissolved, in mg/L 123 39.2 337 480 569 977

P27 06324970 Alkalinity, in mg/L as calcium 

carbonate

123 72.5 269 354 403 734

P27 06324970 Chloride, dissolved, in mg/L 123 6.09 38.8 55.7 90.2 298

P27 06324970 Sulfate, dissolved, in mg/L 123 75.9 986 1,436 1,726 2,555

C1 06365900 Streamflow, instantaneous, ft3/s 48 0.002 0.02 0.03 0.06 4.3

C1 06365900 pH, in standard units 48 7.0 7.5 7.8 7.9 8.1

C1 06365900 Specific conductance, in μS/cm 48 263 3,170 3,645 4,085 5,590

C1 06365900 Dissolved solids, in mg/L 48 175 2,789 3,299 3,750 5,178

C1 06365900 Dissolved solids, in tons per day 48 0.02 0.13 0.32 0.51 2.05

C1 06365900 Calcium, dissolved, in mg/L 48 16.2 266 303 368 479

C1 06365900 Magnesium, dissolved, in mg/L 48 6.01 132 154 176 226

C1 06365900 Sodium adsorption ratio (unitless) 48 0.92 4.4 4.8 5.2 7.1

C1 06365900 Sodium, dissolved, in mg/L 48 17.1 357 410 490 732

C1 06365900 Alkalinity, in mg/L as calcium 

carbonate

48 46.0 301 348 386 465

C1 06365900 Chloride, dissolved, in mg/L 48 3.28 24.9 28.2 30.9 39.9

C1 06365900 Sulfate, dissolved, in mg/L 48 64.4 1,634 1,906 2,184 3,100

C2 06386500 Streamflow, instantaneous, ft3/s 55 0.01 0.10 0.57 5.4 121

C2 06386500 pH, in standard units 54 7.6 8.0 8.2 8.4 8.4

C2 06386500 Specific conductance, in μS/cm 55 541 3,200 4,900 5,420 6,720

C2 06386500 Dissolved solids, in mg/L 55 363 2,607 4,093 4,597 5,986

C2 06386500 Dissolved solids, in tons per day 55 0.11 1.23 7.61 34.6 291

C2 06386500 Calcium, dissolved, in mg/L 55 31.2 149 243 307 407

C2 06386500 Magnesium, dissolved, in mg/L 55 10.7 71.0 110 132 174

C2 06386500 Sodium adsorption ratio (unitless) 55 2.3 7.3 10.4 11.5 13.7

C2 06386500 Sodium, dissolved, in mg/L 55 59.1 454 815 921 1,188

C2 06386500 Alkalinity, in mg/L as calcium 

carbonate

55 86.8 239 263 289 418

C2 06386500 Chloride, dissolved, in mg/L 55 5.27 65.3 97.1 113 148

C2 06386500 Sulfate, dissolved, in mg/L 55 150 1,508 2,467 2,809 3,491

B1 06425720 Streamflow, instantaneous, ft3/s 87 0.02 0.50 1.5 2.8 23

B1 06425720 pH, in standard units 87 7.5 7.8 8.1 8.2 9.2

B1 06425720 Specific conductance, in μS/cm 87 1,680 2,570 2,860 3,260 6,210

B1 06425720 Dissolved solids, in mg/L 86 1,320 2,071 2,330 2,680 5,718

B1 06425720 Dissolved solids, in tons per day 86 0.18 3.72 8.93 15.5 108

B1 06425720 Calcium, dissolved, in mg/L 86 65.3 118 148 172 394

B1 06425720 Magnesium, dissolved, in mg/L 86 53.6 99.5 116 134 300

B1 06425720 Sodium adsorption ratio (unitless) 86 3.1 4.8 5.6 6.4 8.5

B1 06425720 Sodium, dissolved, in mg/L 86 173 312 372 438 825

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
Appendix 1 51

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

B1 06425720 Alkalinity, in mg/L as calcium 

carbonate

80 90.1 243 300 366 778

B1 06425720 Chloride, dissolved, in mg/L 80 9.55 16.3 19.4 26.0 62.1

B1 06425720 Sulfate, dissolved, in mg/L 80 677 1,144 1,325 1,554 3,182

B2 06425900 Streamflow, instantaneous, ft3/s 74 0.02 0.59 1.8 2.8 7.4

B2 06425900 pH, in standard units 74 7.4 8.1 8.2 8.3 8.8

B2 06425900 Specific conductance, in μS/cm 74 772 1,560 1,920 2,530 5,370

B2 06425900 Dissolved solids, in mg/L 74 511 1,096 1,400 2,033 5,383

B2 06425900 Dissolved solids, in tons per day 74 0.28 3.01 6.03 9.61 35.8

B2 06425900 Calcium, dissolved, in mg/L 74 27.2 64.2 93.9 148 392

B2 06425900 Magnesium, dissolved, in mg/L 74 19.9 44.8 71.2 109 335

B2 06425900 Sodium adsorption ratio (unitless) 74 1.8 4.0 4.9 5.7 7.5

B2 06425900 Sodium, dissolved, in mg/L 74 79.1 217 249 314 641

B2 06425900 Alkalinity, in mg/L as calcium 

carbonate

74 107 267 342 400 778

B2 06425900 Chloride, dissolved, in mg/L 74 10.9 16.8 24.5 46.9 121

B2 06425900 Sulfate, dissolved, in mg/L 74 234 429 684 1,109 3,215

B3 06426400 Streamflow, instantaneous, ft3/s 115 0.05 1.6 3.1 7.6 46

B3 06426400 pH, in standard units 115 7.3 7.9 8.3 8.6 9.3

B3 06426400 Specific conductance, in μS/cm 115 1,020 2,440 2,780 2,990 4,540

B3 06426400 Dissolved solids, in mg/L 115 690 1,812 2,067 2,370 3,708

B3 06426400 Dissolved solids, in tons per day 115 0.40 8.15 17.1 39.1 179

B3 06426400 Calcium, dissolved, in mg/L 115 51.0 117 140 164 210

B3 06426400 Magnesium, dissolved, in mg/L 115 38.0 105 125 143 190

B3 06426400 Sodium adsorption ratio (unitless) 115 2.3 3.5 4.1 5.1 11.8

B3 06426400 Sodium, dissolved, in mg/L 115 88.0 244 281 337 798

B3 06426400 Alkalinity, in mg/L as calcium 

carbonate

115 98.9 226 286 341 626

B3 06426400 Chloride, dissolved, in mg/L 115 50.8 157 198 228 529

B3 06426400 Sulfate, dissolved, in mg/L 115 286 767 934 1,072 1,941

B4 06426500 Streamflow, instantaneous, ft3/s 120 0.02 3.0 5.7 12 599

B4 06426500 pH, in standard units 120 7.3 8.0 8.3 8.6 9.2

B4 06426500 Specific conductance, in μS/cm 120 300 2,210 2,640 2,975 4,590

B4 06426500 Dissolved solids, in mg/L 120 203 1,617 1,983 2,334 3,784

B4 06426500 Dissolved solids, in tons per day 120 0.14 18.8 31.7 67.7 342

B4 06426500 Calcium, dissolved, in mg/L 119 21.4 102 120 143 266

B4 06426500 Magnesium, dissolved, in mg/L 119 8.76 83.3 105 131 178

B4 06426500 Sodium adsorption ratio (unitless) 119 1.2 4.0 5.1 5.8 8.7

B4 06426500 Sodium, dissolved, in mg/L 119 25.7 234 325 389 595

B4 06426500 Alkalinity, in mg/L as calcium 

carbonate

120 63.2 217 281 374 714

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
52 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification 

number

Property or constituent Sample 

size Minimum 25th percentile Median 75th percentile Maximum

B4 06426500 Chloride, dissolved, in mg/L 120 3.42 98.3 138 184 414

B4 06426500 Sulfate, dissolved, in mg/L 120 70.6 729 945 1,148 1,738

B5 06428050 Streamflow, instantaneous, ft3/s 104 3.4 9.7 20 55 245

B5 06428050 pH, in standard units 104 7.4 7.9 8.1 8.4 8.8

B5 06428050 Specific conductance, in μS/cm 104 646 1,640 1,900 2,040 2,490

B5 06428050 Dissolved solids, in mg/L 100 459 1,219 1,605 1,721 2,225

B5 06428050 Dissolved solids, in tons per day 100 20.4 44.5 79.5 187 638

B5 06428050 Calcium, dissolved, in mg/L 99 53.9 161 238 288 369

B5 06428050 Magnesium, dissolved, in mg/L 99 17.1 58.7 71.3 78.0 92.2

B5 06428050 Sodium adsorption ratio (unitless) 99 0.50 1.0 1.3 2.0 4.8

B5 06428050 Sodium, dissolved, in mg/L 99 24.1 69.6 92.2 136 258

B5 06428050 Alkalinity, in mg/L as calcium 

carbonate

100 72.7 156 177 204 276

B5 06428050 Chloride, dissolved, in mg/L 100 3.26 11.4 19.2 30.0 62.4

B5 06428050 Sulfate, dissolved, in mg/L 100 231 692 912 993 1,218

Appendix 1. Summary statistics for water-quality constituents for sites in the Tongue, Powder, Cheyenne, and Belle Fourche River 

drainage basins, Wyoming and Montana, water years 2001–10.—Continued

[USGS, U.S. Geological Survey; ft3/s, cubic feet per second; μS/cm, microsiemens per centimeter at 25 degrees Celsius, mg/L, milligrams per liter; —, not 

calculated]
Appendix 2 53

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

T1 06299980 Unadjusted 2005–10 Specific conductance 63 0.085 0.495 2.21 No trend.

T1 06299980 Flow adjusted 2005–10 Specific conductance 63 0.324 0.005 0.022 Upward.

T1 06299980 Unadjusted 2005–10 Calcium 63 0.070 0.576 0.292 No trend.

T1 06299980 Flow adjusted 2005–10 Calcium 63 0.113 0.352 0.550 No trend.

T1 06299980 Unadjusted 2005–10 Magnesium 63 -0.028 0.852 -0.055 No trend.

T1 06299980 Flow adjusted 2005–10 Magnesium 63 0.268 0.022 0.326 Upward.

T1 06299980 Unadjusted 2005–10 Sodium adsorption ratio 63 -0.021 0.901 -0.001 No trend.

T1 06299980 Flow adjusted 2005–10 Sodium adsorption ratio 63 0.155 0.192 0.006 No trend.

T1 06299980 Unadjusted 2005–10 Sodium 63 -0.014 0.950 -0.018 No trend.

T1 06299980 Flow adjusted 2005–10 Sodium 63 0.155 0.192 0.272 No trend.

T1 06299980 Unadjusted 2005–10 Alkalinity 63 0.134 0.263 1.22 No trend.

T1 06299980 Flow adjusted 2005–10 Alkalinity 63 0.282 0.015 2.50 Upward.

T1 06299980 Unadjusted 2005–10 Chloride 63 0.282 0.015 0.040 Upward.

T1 06299980 Flow adjusted 2005–10 Chloride 63 0.296 0.011 0.065 Upward.

T1 06299980 Unadjusted 2005–10 Sulfate 63 0.028 0.852 0.261 No trend.

T1 06299980 Flow adjusted 2005–10 Sulfate 63 0.239 0.040 1.22 Upward.

T2 06304500 Unadjusted 2001–10 Specific conductance 56 -0.251 0.011 -9.75 Downward.

T2 06304500 Flow adjusted 2001–10 Specific conductance 56 0.064 0.523 1.97 No trend.

T2 06304500 Unadjusted 2001–10 Calcium 52 -0.220 0.073 -0.727 No trend.

T2 06304500 Flow adjusted 2001–10 Calcium 52 0.150 0.149 0.455 No trend.

T2 06304500 Unadjusted 2001–10 Magnesium 52 -0.130 0.341 -0.260 No trend.

T2 06304500 Flow adjusted 2001–10 Magnesium 52 0.120 0.371 0.223 No trend.

T2 06304500 Unadjusted 2001–10 Sodium adsorption ratio 52 -0.175 0.159 -0.004 No trend.

T2 06304500 Flow adjusted 2001–10 Sodium adsorption ratio 52 0.020 0.893 0.001 No trend.

T2 06304500 Unadjusted 2001–10 Sodium 52 -0.220 0.069 -0.287 No trend.

T2 06304500 Flow adjusted 2001–10 Sodium 52 0.030 0.787 0.059 No trend.

T2 06304500 Unadjusted 2001–10 Alkalinity 52 -0.020 0.872 -0.552 No trend.

T2 06304500 Flow adjusted 2001–10 Alkalinity 52 0.160 0.221 3.02 No trend.

T2 06304500 Unadjusted 2001–10 Chloride 52 -0.110 0.468 -0.042 No trend.

T2 06304500 Flow adjusted 2001–10 Chloride 52 0.220 0.163 0.060 No trend.

T2 06304500 Unadjusted 2001–10 Sulfate 52 -0.240 0.030 -2.83 Downward.

T2 06304500 Flow adjusted 2001–10 Sulfate 52 0.090 0.471 0.612 No trend.

T3 06305500 Unadjusted 1991–2010 Specific conductance 80 0.151 0.116 3.71 No trend.

T3 06305500 Flow adjusted 1991–2010 Specific conductance 80 -0.176 0.080 -2.56 No trend.

T3 06305500 Unadjusted 2001–10 Specific conductance 56 -0.277 0.039 -10.5 Downward.

T3 06305500 Flow adjusted 2001–10 Specific conductance 56 0.098 0.320 1.96 No trend.

T3 06305500 Unadjusted 2001–10 Calcium 52 -0.260 0.093 -0.946 No trend.

T3 06305500 Flow adjusted 2001–10 Calcium 52 -0.020 0.914 -0.093 No trend.

T3 06305500 Unadjusted 2001–10 Magnesium 52 -0.280 0.143 -0.771 No trend.
54 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

T3 06305500 Flow adjusted 2001–10 Magnesium 52 0.030 0.878 0.063 No trend.

T3 06305500 Unadjusted 2001–10 Sodium adsorption ratio 52 -0.345 0.017 -0.011 Downward.

T3 06305500 Flow adjusted 2001–10 Sodium adsorption ratio 52 0.050 0.534 0.002 No trend.

T3 06305500 Unadjusted 2001–10 Sodium 52 -0.340 0.020 -0.653 Downward.

T3 06305500 Flow adjusted 2001–10 Sodium 52 0.030 0.765 0.019 No trend.

T3 06305500 Unadjusted 2001–10 Alkalinity 52 -0.290 0.101 -3.69 No trend.

T3 06305500 Flow adjusted 2001–10 Alkalinity 52 -0.060 0.665 -0.390 No trend.

T3 06305500 Unadjusted 2001–10 Chloride 52 -0.080 0.431 -0.062 No trend.

T3 06305500 Flow adjusted 2001–10 Chloride 52 0.190 0.071 0.131 No trend.

T3 06305500 Unadjusted 2001–10 Sulfate 52 -0.440 0.008 -4.00 Downward.

T3 06305500 Flow adjusted 2001–10 Sulfate 52 -0.070 0.596 -0.387 No trend.

T4 06306200 Unadjusted 2005–10 Specific conductance 71 0.046 0.699 3.50 No trend.

T4 06306200 Flow adjusted 2005–10 Specific conductance 71 0.097 0.377 0.008 No trend.

T4 06306200 Unadjusted 2005–10 Calcium 71 -0.017 0.912 -0.377 No trend.

T4 06306200 Flow adjusted 2005–10 Calcium 71 0.029 0.825 0.404 No trend.

T4 06306200 Unadjusted 2005–10 Magnesium 71 -0.074 0.508 -0.470 No trend.

T4 06306200 Flow adjusted 2005–10 Magnesium 71 0.109 0.321 0.518 No trend.

T4 06306200 Unadjusted 2005–10 Sodium adsorption ratio 71 0.189 0.076 0.008 No trend.

T4 06306200 Flow adjusted 2005–10 Sodium adsorption ratio 71 0.234 0.027 0.008 Upward.

T4 06306200 Unadjusted 2005–10 Sodium 71 0.086 0.440 0.345 No trend.

T4 06306200 Flow adjusted 2005–10 Sodium 71 0.189 0.077 0.470 No trend.

T4 06306200 Unadjusted 2005–10 Alkalinity 70 -0.071 0.536 -1.32 No trend.

T4 06306200 Flow adjusted 2005–10 Alkalinity 70 0.129 0.238 2.74 No trend.

T4 06306200 Unadjusted 2005–10 Chloride 71 0.554 <0.001 0.366 Upward.

T4 06306200 Flow adjusted 2005–10 Chloride 71 0.497 <0.001 0.327 Upward.

T4 06306200 Unadjusted 2005–10 Sulfate 71 0.109 0.321 2.80 No trend.

T4 06306200 Flow adjusted 2005–10 Sulfate 71 0.189 0.077 4.09 No trend.

T5 06306250 Unadjusted 2001–10 Specific conductance 60 -0.059 0.585 -8.17 No trend.

T5 06306250 Flow adjusted 2001–10 Specific conductance 60 0.081 0.366 6.24 No trend.

T5 06306250 Unadjusted 2001–10 Calcium 60 -0.007 0.970 -0.182 No trend.

T5 06306250 Flow adjusted 2001–10 Calcium 60 0.015 0.836 0.465 No trend.

T5 06306250 Unadjusted 2001–10 Magnesium 60 -0.007 0.972 -0.405 No trend.

T5 06306250 Flow adjusted 2001–10 Magnesium 60 0.126 0.127 0.797 No trend.

T5 06306250 Unadjusted 2001–10 Sodium adsorption ratio 60 0.100 0.353 0.007 No trend.

T5 06306250 Flow adjusted 2001–10 Sodium adsorption ratio 60 0.178 0.065 0.008 No trend.

T5 06306250 Unadjusted 2001–10 Sodium 60 0.037 0.727 0.737 No trend.

T5 06306250 Flow adjusted 2001–10 Sodium 60 0.148 0.081 1.00 No trend.

T5 06306250 Unadjusted 2001–10 Alkalinity 60 0.007 0.970 0.378 No trend.

T5 06306250 Flow adjusted 2001–10 Alkalinity 60 0.133 0.337 2.99 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
Appendix 2 55

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

T5 06306250 Unadjusted 2001–10 Chloride 60 0.293 0.051 0.199 No trend.

T5 06306250 Flow adjusted 2001–10 Chloride 60 0.348 0.017 0.223 Upward.

T5 06306250 Unadjusted 2001–10 Sulfate 60 -0.081 0.490 -3.70 No trend.

T5 06306250 Flow adjusted 2001–10 Sulfate 60 0.074 0.419 3.17 No trend.

T5 06306250 Unadjusted 2005–10 Specific conductance 66 0.138 0.229 21.7 No trend.

T5 06306250 Flow adjusted 2005–10 Specific conductance 66 0.316 0.005 0.041 Upward.

T5 06306250 Unadjusted 2005–10 Calcium 66 -0.092 0.435 -1.42 No trend.

T5 06306250 Flow adjusted 2005–10 Calcium 66 0.092 0.435 1.28 No trend.

T5 06306250 Unadjusted 2005–10 Magnesium 66 0.092 0.435 1.74 No trend.

T5 06306250 Flow adjusted 2005–10 Magnesium 66 0.250 0.026 3.49 Upward.

T5 06306250 Unadjusted 2005–10 Sodium adsorption ratio 66 0.388 <0.001 0.050 Upward.

T5 06306250 Flow adjusted 2005–10 Sodium adsorption ratio 66 0.447 <0.001 0.069 Upward.

T5 06306250 Unadjusted 2005–10 Sodium 66 0.224 0.048 2.91 Upward.

T5 06306250 Flow adjusted 2005–10 Sodium 66 0.395 <0.001 5.63 Upward.

T5 06306250 Unadjusted 2005–10 Alkalinity 66 0.237 0.036 6.05 Upward.

T5 06306250 Flow adjusted 2005–10 Alkalinity 66 0.250 0.026 6.70 Upward.

T5 06306250 Unadjusted 2005–10 Chloride 66 0.579 <0.001 0.507 Upward.

T5 06306250 Flow adjusted 2005–10 Chloride 66 0.553 <0.001 0.511 Upward.

T5 06306250 Unadjusted 2005–10 Sulfate 66 0.184 0.105 18.9 No trend.

T5 06306250 Flow adjusted 2005–10 Sulfate 66 0.421 <0.001 33.4 Upward.

T6 06306300 Unadjusted 1991–2010 Specific conductance 78 0.253 0.006 5.40 Upward.

T6 06306300 Flow adjusted 1991–2010 Specific conductance 78 0.044 0.637 0.690 No trend.

T6 06306300 Unadjusted 2001–10 Specific conductance 58 -0.071 0.264 -4.33 No trend.

T6 06306300 Flow adjusted 2001–10 Specific conductance 58 0.233 0.040 9.24 Upward.

T6 06306300 Unadjusted 2001–10 Calcium 58 0.059 0.531 0.260 No trend.

T6 06306300 Flow adjusted 2001–10 Calcium 58 0.383 0.006 1.21 Upward.

T6 06306300 Unadjusted 2001–10 Magnesium 58 -0.036 0.613 -0.200 No trend.

T6 06306300 Flow adjusted 2001–10 Magnesium 58 0.233 0.051 0.650 No trend.

T6 06306300 Unadjusted 2001–10 Sodium adsorption ratio 58 -0.217 0.039 -0.014 Downward.

T6 06306300 Flow adjusted 2001–10 Sodium adsorption ratio 58 0.051 0.609 0.005 No trend.

T6 06306300 Unadjusted 2001–10 Sodium 58 -0.146 0.063 -0.503 No trend.

T6 06306300 Flow adjusted 2001–10 Sodium 58 0.075 0.390 0.289 No trend.

T6 06306300 Unadjusted 2001–10 Alkalinity 58 -0.130 0.156 -2.10 No trend.

T6 06306300 Flow adjusted 2001–10 Alkalinity 58 0.186 0.138 2.42 No trend.

T6 06306300 Unadjusted 2001–10 Chloride 58 0.059 0.633 0.041 No trend.

T6 06306300 Flow adjusted 2001–10 Chloride 58 0.375 0.020 0.135 Upward.

T6 06306300 Unadjusted 2001–10 Sulfate 58 0.020 0.808 0.335 No trend.

T6 06306300 Flow adjusted 2001–10 Sulfate 58 0.257 0.042 4.08 Upward.

T6 06306300 Unadjusted 2005–10 Specific conductance 59 0.000 1.000 0.000 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
56 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

T6 06306300 Flow adjusted 2005–10 Specific conductance 59 0.354 0.003 16.1 Upward.

T6 06306300 Unadjusted 2005–10 Calcium 59 -0.062 0.649 -0.517 No trend.

T6 06306300 Flow adjusted 2005–10 Calcium 59 0.262 0.032 0.933 Upward.

T6 06306300 Unadjusted 2005–10 Magnesium 59 -0.046 0.745 -0.182 No trend.

T6 06306300 Flow adjusted 2005–10 Magnesium 59 0.308 0.011 0.689 Upward.

T6 06306300 Unadjusted 2005–10 Sodium adsorption ratio 59 -0.223 0.068 -0.022 No trend.

T6 06306300 Flow adjusted 2005–10 Sodium adsorption ratio 59 0.185 0.134 0.007 No trend.

T6 06306300 Unadjusted 2005–10 Sodium 59 -0.169 0.172 -0.780 No trend.

T6 06306300 Flow adjusted 2005–10 Sodium 59 0.154 0.216 0.864 No trend.

T6 06306300 Unadjusted 2005–10 Alkalinity 59 0.015 0.948 0.550 No trend.

T6 06306300 Flow adjusted 2005–10 Alkalinity 59 0.308 0.011 5.06 Upward.

T6 06306300 Unadjusted 2005–10 Chloride 59 0.062 0.649 0.080 No trend.

T6 06306300 Flow adjusted 2005–10 Chloride 59 0.308 0.011 0.232 Upward.

T6 06306300 Unadjusted 2005–10 Sulfate 59 0.031 0.845 0.314 No trend.

T6 06306300 Flow adjusted 2005–10 Sulfate 59 0.338 0.005 5.80 Upward.

P1 06313400 Unadjusted 1991–2010 Specific conductance 75 -0.073 0.517 -13.3 No trend.

P1 06313400 Flow adjusted 1991–2010 Specific conductance 75 -0.057 0.529 -8.36 No trend.

P1 06313400 Unadjusted 1991–2010 Calcium 76 -0.130 0.291 -1.41 No trend.

P1 06313400 Flow adjusted 1991–2010 Calcium 76 -0.188 0.131 -2.91 No trend.

P1 06313400 Unadjusted 1991–2010 Magnesium 76 -0.192 0.134 -1.11 No trend.

P1 06313400 Flow adjusted 1991–2010 Magnesium 76 -0.243 0.062 -1.12 No trend.

P1 06313400 Unadjusted 1991–2010 Sodium adsorption ratio 76 0.141 0.272 0.175 No trend.

P1 06313400 Flow adjusted 1991–2010 Sodium adsorption ratio 76 0.140 0.207 0.157 No trend.

P1 06313400 Unadjusted 1991–2010 Sodium 76 0.010 0.942 — No trend.

P1 06313400 Flow adjusted 1991–2010 Sodium 76 0.020 0.853 1.36 No trend.

P1 06313400 Unadjusted 2001–10 Specific conductance 58 -0.079 0.567 -48.3 No trend.

P1 06313400 Flow adjusted 2001–10 Specific conductance 58 -0.087 0.416 -39.1 No trend.

P1 06313400 Unadjusted 2001–10 Calcium 58 0.429 0.027 8.68 Upward.

P1 06313400 Flow adjusted 2001–10 Calcium 58 0.286 0.097 6.53 No trend.

P1 06313400 Unadjusted 2001–10 Magnesium 58 0.254 0.071 1.05 No trend.

P1 06313400 Flow adjusted 2001–10 Magnesium 58 0.159 0.234 0.857 No trend.

P1 06313400 Unadjusted 2001–10 Sodium adsorption ratio 58 -0.294 0.094 -0.727 No trend.

P1 06313400 Flow adjusted 2001–10 Sodium adsorption ratio 58 -0.214 0.158 -0.380 No trend.

P1 06313400 Unadjusted 2001–10 Sodium 58 -0.087 0.545 -13.5 No trend.

P1 06313400 Flow adjusted 2001–10 Sodium 58 -0.119 0.360 -10.8 No trend.

P1 06313400 Unadjusted 2001–10 Alkalinity 58 -0.056 0.698 -1.70 No trend.

P1 06313400 Flow adjusted 2001–10 Alkalinity 58 -0.159 0.243 -4.40 No trend.

P1 06313400 Unadjusted 2001–10 Chloride 58 -0.111 0.494 -19.4 No trend.

P1 06313400 Flow adjusted 2001–10 Chloride 58 -0.032 0.848 -2.23 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
Appendix 2 57

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

P1 06313400 Unadjusted 2001–10 Sulfate 58 0.143 0.332 18.7 No trend.

P1 06313400 Flow adjusted 2001–10 Sulfate 58 0.127 0.406 13.8 No trend.

P1 06313400 Unadjusted 2005–10 Specific conductance 72 -0.367 <0.001 -192 Downward.

P1 06313400 Flow adjusted 2005–10 Specific conductance 72 -0.322 0.002 -0.021 Downward.

P1 06313400 Unadjusted 2005–10 Calcium 72 0.544 <0.001 15.3 Upward.

P1 06313400 Flow adjusted 2005–10 Calcium 72 0.489 <0.001 14.3 Upward.

P1 06313400 Unadjusted 2005–10 Magnesium 72 0.300 0.004 1.78 Upward.

P1 06313400 Flow adjusted 2005–10 Magnesium 72 0.122 0.255 1.04 No trend.

P1 06313400 Unadjusted 2005–10 Sodium adsorption ratio 72 -0.544 <0.001 -1.83 Downward.

P1 06313400 Flow adjusted 2005–10 Sodium adsorption ratio 72 -0.433 <0.001 -1.55 Downward.

P1 06313400 Unadjusted 2005–10 Sodium 72 -0.439 <0.001 -64.4 Downward.

P1 06313400 Flow adjusted 2005–10 Sodium 72 -0.356 0.001 -50.8 Downward.

P1 06313400 Unadjusted 2005–10 Alkalinity 72 -0.311 0.003 -21.7 Downward.

P1 06313400 Flow adjusted 2005–10 Alkalinity 72 -0.389 <0.001 -16.4 Downward.

P1 06313400 Unadjusted 2005–10 Chloride 72 -0.367 <0.001 -56.2 Downward.

P1 06313400 Flow adjusted 2005–10 Chloride 72 -0.289 0.006 -34.2 Downward.

P1 06313400 Unadjusted 2005–10 Sulfate 72 0.411 <0.001 55.8 Upward.

P1 06313400 Flow adjusted 2005–10 Sulfate 72 0.233 0.026 41.7 Upward.

P2 06313500 Unadjusted 1991–2010 Specific conductance 80 0.079 0.425 8.54 No trend.

P2 06313500 Flow adjusted 1991–2010 Specific conductance 80 0.013 0.898 0.693 No trend.

P2 06313500 Unadjusted 1991–2010 Calcium 80 0.017 0.850 — No trend.

P2 06313500 Flow adjusted 1991–2010 Calcium 80 -0.120 0.247 -0.674 No trend.

P2 06313500 Unadjusted 1991–2010 Magnesium 80 -0.018 0.871 -0.025 No trend.

P2 06313500 Flow adjusted 1991–2010 Magnesium 80 -0.108 0.326 -0.152 No trend.

P2 06313500 Unadjusted 1991–2010 Sodium adsorption ratio 80 0.157 0.163 0.047 No trend.

P2 06313500 Flow adjusted 1991–2010 Sodium adsorption ratio 80 0.111 0.294 0.037 No trend.

P2 06313500 Unadjusted 1991–2010 Sodium 80 0.121 0.273 2.31 No trend.

P2 06313500 Flow adjusted 1991–2010 Sodium 80 0.066 0.528 1.21 No trend.

P2 06313500 Unadjusted 2001–10 Specific conductance 58 -0.024 0.749 -4.76 No trend.

P2 06313500 Flow adjusted 2001–10 Specific conductance 58 0.079 0.540 15.8 No trend.

P2 06313500 Unadjusted 2001–10 Calcium 58 0.063 0.620 0.506 No trend.

P2 06313500 Flow adjusted 2001–10 Calcium 58 0.175 0.221 1.80 No trend.

P2 06313500 Unadjusted 2001–10 Magnesium 58 -0.048 0.630 -0.118 No trend.

P2 06313500 Flow adjusted 2001–10 Magnesium 58 0.183 0.141 0.553 No trend.

P2 06313500 Unadjusted 2001–10 Sodium adsorption ratio 58 -0.063 0.570 -0.034 No trend.

P2 06313500 Flow adjusted 2001–10 Sodium adsorption ratio 58 -0.056 0.670 -0.034 No trend.

P2 06313500 Unadjusted 2001–10 Sodium 58 -0.008 0.960 -0.692 No trend.

P2 06313500 Flow adjusted 2001–10 Sodium 58 0.024 0.872 0.907 No trend.

P2 06313500 Unadjusted 2001–10 Alkalinity 58 0.063 0.539 1.36 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
58 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

P2 06313500 Flow adjusted 2001–10 Alkalinity 58 0.270 0.073 2.96 No trend.

P2 06313500 Unadjusted 2001–10 Chloride 58 -0.048 0.720 -1.65 No trend.

P2 06313500 Flow adjusted 2001–10 Chloride 58 0.063 0.600 1.78 No trend.

P2 06313500 Unadjusted 2001–10 Sulfate 58 -0.040 0.637 -2.62 No trend.

P2 06313500 Flow adjusted 2001–10 Sulfate 58 0.095 0.421 4.20 No trend.

P2 06313500 Unadjusted 2005–10 Specific conductance 72 -0.211 0.044 -90.6 Downward.

P2 06313500 Flow adjusted 2005–10 Specific conductance 72 -0.156 0.143 -0.018 No trend.

P2 06313500 Unadjusted 2005–10 Calcium 72 0.067 0.551 1.24 No trend.

P2 06313500 Flow adjusted 2005–10 Calcium 72 0.233 0.026 2.53 Upward.

P2 06313500 Unadjusted 2005–10 Magnesium 72 -0.100 0.357 -0.752 No trend.

P2 06313500 Flow adjusted 2005–10 Magnesium 72 0.122 0.255 0.770 No trend.

P2 06313500 Unadjusted 2005–10 Sodium adsorption ratio 72 -0.256 0.015 -0.281 Downward.

P2 06313500 Flow adjusted 2005–10 Sodium adsorption ratio 72 -0.222 0.034 -0.237 Downward.

P2 06313500 Unadjusted 2005–10 Sodium 72 -0.300 0.004 -14.7 Downward.

P2 06313500 Flow adjusted 2005–10 Sodium 72 -0.244 0.020 -9.53 Downward.

P2 06313500 Unadjusted 2005–10 Alkalinity 72 -0.156 0.143 -5.14 No trend.

P2 06313500 Flow adjusted 2005–10 Alkalinity 72 0.056 0.625 1.23 No trend.

P2 06313500 Unadjusted 2005–10 Chloride 72 -0.344 0.001 -18.0 Downward.

P2 06313500 Flow adjusted 2005–10 Chloride 72 -0.256 0.015 -7.00 Downward.

P2 06313500 Unadjusted 2005–10 Sulfate 72 -0.011 0.957 -1.08 No trend.

P2 06313500 Flow adjusted 2005–10 Sulfate 72 0.133 0.212 6.90 No trend.

P4 06313560 Unadjusted 2005–10 Specific conductance 63 -0.386 0.001 -103 Downward.

P4 06313560 Flow adjusted 2005–10 Specific conductance 63 -0.241 0.038 -0.015 Downward.

P4 06313560 Unadjusted 2005–10 Calcium 61 0.215 0.074 2.18 No trend.

P4 06313560 Flow adjusted 2005–10 Calcium 61 0.067 0.609 0.656 No trend.

P4 06313560 Unadjusted 2005–10 Magnesium 63 0.352 0.002 2.73 Upward.

P4 06313560 Flow adjusted 2005–10 Magnesium 63 0.214 0.067 2.55 No trend.

P4 06313560 Unadjusted 2005–10 Sodium adsorption ratio 61 -0.452 <0.001 -1.35 Downward.

P4 06313560 Flow adjusted 2005–10 Sodium adsorption ratio 61 -0.304 0.011 -0.834 Downward.

P4 06313560 Unadjusted 2005–10 Sodium 63 -0.379 0.001 -32.8 Downward.

P4 06313560 Flow adjusted 2005–10 Sodium 63 -0.186 0.112 -17.5 No trend.

P5 06313585 Unadjusted 2005–10 Specific conductance 72 -0.761 <0.001 -326 Downward.

P5 06313585 Flow adjusted 2005–10 Specific conductance 72 -0.189 0.074 -0.014 No trend.

P5 06313585 Unadjusted 2005–10 Calcium 70 -0.141 0.196 -1.00 No trend.

P5 06313585 Flow adjusted 2005–10 Calcium 70 -0.094 0.399 -1.07 No trend.

P5 06313585 Unadjusted 2005–10 Magnesium 72 -0.744 <0.001 -5.45 Downward.

P5 06313585 Flow adjusted 2005–10 Magnesium 72 -0.322 0.002 -1.39 Downward.

P5 06313585 Unadjusted 2005–10 Sodium adsorption ratio 70 -0.529 <0.001 -1.79 Downward.

P5 06313585 Flow adjusted 2005–10 Sodium adsorption ratio 70 -0.071 0.536 -0.157 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
Appendix 2 59

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

P5 06313585 Unadjusted 2005–10 Sodium 72 -0.744 <0.001 -76.0 Downward.

P5 06313585 Flow adjusted 2005–10 Sodium 72 -0.211 0.045 -8.93 Downward.

P6 06313590 Unadjusted 2005–10 Specific conductance 71 -0.269 0.011 -70.0 Downward.

P6 06313590 Flow adjusted 2005–10 Specific conductance 71 -0.143 0.185 -0.013 No trend.

P6 06313590 Unadjusted 2005–10 Calcium 71 -0.097 0.377 -2.32 No trend.

P6 06313590 Flow adjusted 2005–10 Calcium 71 -0.029 0.825 -0.175 No trend.

P6 06313590 Unadjusted 2005–10 Magnesium 71 -0.211 0.047 -1.73 Downward.

P6 06313590 Flow adjusted 2005–10 Magnesium 71 -0.109 0.321 -0.585 No trend.

P6 06313590 Unadjusted 2005–10 Sodium adsorption ratio 71 -0.280 0.008 -0.250 Downward.

P6 06313590 Flow adjusted 2005–10 Sodium adsorption ratio 71 -0.143 0.185 -0.150 No trend.

P6 06313590 Unadjusted 2005–10 Sodium 71 -0.269 0.011 -16.3 Downward.

P6 06313590 Flow adjusted 2005–10 Sodium 71 -0.189 0.077 -9.72 No trend.

P6 06313590 Unadjusted 2005–10 Alkalinity 71 -0.114 0.294 -5.35 No trend.

P6 06313590 Flow adjusted 2005–10 Alkalinity 71 0.040 0.741 2.31 No trend.

P6 06313590 Unadjusted 2005–10 Chloride 71 -0.314 0.003 -15.7 Downward.

P6 06313590 Flow adjusted 2005–10 Chloride 71 -0.177 0.098 -6.09 No trend.

P6 06313590 Unadjusted 2005–10 Sulfate 71 -0.166 0.122 -18.4 No trend.

P6 06313590 Flow adjusted 2005–10 Sulfate 71 -0.051 0.659 -6.24 No trend.

P7 06313604 Unadjusted 2005–10 Specific conductance 68 -0.809 <0.001 -130 Downward.

P7 06313604 Flow adjusted 2005–10 Specific conductance 68 -0.630 <0.001 -0.024 Downward.

P7 06313604 Unadjusted 2005–10 Calcium 68 -0.160 0.149 -0.645 No trend.

P7 06313604 Flow adjusted 2005–10 Calcium 68 -0.210 0.057 -0.600 No trend.

P7 06313604 Unadjusted 2005–10 Magnesium 68 -0.679 <0.001 -2.40 Downward.

P7 06313604 Flow adjusted 2005–10 Magnesium 68 -0.568 <0.001 -1.54 Downward.

P7 06313604 Unadjusted 2005–10 Sodium adsorption ratio 68 0.160 0.149 0.274 No trend.

P7 06313604 Flow adjusted 2005–10 Sodium adsorption ratio 68 0.111 0.327 0.146 No trend.

P7 06313604 Unadjusted 2005–10 Sodium 68 -0.383 <0.001 -22.8 Downward.

P7 06313604 Flow adjusted 2005–10 Sodium 68 -0.284 0.009 -15.7 Downward.

P8 06313605 Unadjusted 2001–10 Specific conductance 59 -0.307 0.030 -67.0 Downward.

P8 06313605 Flow adjusted 2001–10 Specific conductance 59 -0.203 0.034 -36.9 Downward.

P8 06313605 Unadjusted 2001–10 Calcium 59 -0.303 0.049 -4.13 Downward.

P8 06313605 Flow adjusted 2001–10 Calcium 59 -0.211 0.131 -2.66 No trend.

P8 06313605 Unadjusted 2001–10 Magnesium 59 -0.272 0.036 -1.56 Downward.

P8 06313605 Flow adjusted 2001–10 Magnesium 59 -0.126 0.244 -0.521 No trend.

P8 06313605 Unadjusted 2001–10 Sodium adsorption ratio 59 -0.126 0.313 -0.043 No trend.

P8 06313605 Flow adjusted 2001–10 Sodium adsorption ratio 59 -0.004 1.000 -0.001 No trend.

P8 06313605 Unadjusted 2001–10 Sodium 59 -0.264 0.045 -9.46 Downward.

P8 06313605 Flow adjusted 2001–10 Sodium 59 -0.119 0.122 -4.58 No trend.

P8 06313605 Unadjusted 2001–10 Alkalinity 59 0.042 0.732 1.05 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
60 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

P8 06313605 Flow adjusted 2001–10 Alkalinity 59 0.310 0.067 6.30 No trend.

P8 06313605 Unadjusted 2001–10 Chloride 59 -0.211 0.129 -4.74 No trend.

P8 06313605 Flow adjusted 2001–10 Chloride 59 0.027 0.811 0.788 No trend.

P8 06313605 Unadjusted 2001–10 Sulfate 59 -0.379 0.007 -24.9 Downward.

P8 06313605 Flow adjusted 2001–10 Sulfate 59 -0.218 0.038 -12.0 Downward.

P8 06313605 Unadjusted 2005–10 Specific conductance 72 -0.333 0.001 -78.8 Downward.

P8 06313605 Flow adjusted 2005–10 Specific conductance 72 -0.267 0.011 -0.025 Downward.

P8 06313605 Unadjusted 2005–10 Calcium 72 -0.033 0.786 -0.775 No trend.

P8 06313605 Flow adjusted 2005–10 Calcium 72 0.089 0.416 0.759 No trend.

P8 06313605 Unadjusted 2005–10 Magnesium 72 -0.189 0.074 -1.32 No trend.

P8 06313605 Flow adjusted 2005–10 Magnesium 72 -0.067 0.551 -0.603 No trend.

P8 06313605 Unadjusted 2005–10 Sodium adsorption ratio 72 -0.378 <0.001 -0.296 Downward.

P8 06313605 Flow adjusted 2005–10 Sodium adsorption ratio 72 -0.344 0.001 -0.222 Downward.

P8 06313605 Unadjusted 2005–10 Sodium 72 -0.311 0.003 -16.1 Downward.

P8 06313605 Flow adjusted 2005–10 Sodium 72 -0.256 0.015 -12.4 Downward.

P8 06313605 Unadjusted 2005–10 Alkalinity 72 -0.278 0.008 -10.5 Downward.

P8 06313605 Flow adjusted 2005–10 Alkalinity 72 -0.211 0.045 -5.50 Downward.

P8 06313605 Unadjusted 2005–10 Chloride 72 -0.322 0.002 -12.4 Downward.

P8 06313605 Flow adjusted 2005–10 Chloride 72 -0.200 0.058 -4.98 No trend.

P8 06313605 Unadjusted 2005–10 Sulfate 72 -0.167 0.116 -13.9 No trend.

P8 06313605 Flow adjusted 2005–10 Sulfate 72 -0.078 0.481 -6.02 No trend.

P11 06316400 Unadjusted 2001–10 Specific conductance 58 -0.349 0.017 -63.1 Downward.

P11 06316400 Flow adjusted 2001–10 Specific conductance 58 -0.048 0.698 -4.76 No trend.

P11 06316400 Unadjusted 2001–10 Calcium 58 -0.377 0.014 -5.76 Downward.

P11 06316400 Flow adjusted 2001–10 Calcium 58 -0.167 0.293 -1.23 No trend.

P11 06316400 Unadjusted 2001–10 Magnesium 58 -0.310 0.012 -3.05 Downward.

P11 06316400 Flow adjusted 2001–10 Magnesium 58 -0.087 0.536 -0.427 No trend.

P11 06316400 Unadjusted 2001–10 Sodium adsorption ratio 58 -0.179 0.126 -0.040 No trend.

P11 06316400 Flow adjusted 2001–10 Sodium adsorption ratio 58 -0.008 0.970 -0.001 No trend.

P11 06316400 Unadjusted 2001–10 Sodium 58 -0.262 0.041 -4.27 Downward.

P11 06316400 Flow adjusted 2001–10 Sodium 58 -0.048 0.696 -0.238 No trend.

P11 06316400 Unadjusted 2001–10 Alkalinity 58 -0.159 0.191 -3.28 No trend.

P11 06316400 Flow adjusted 2001–10 Alkalinity 58 0.087 0.460 0.571 No trend.

P11 06316400 Unadjusted 2001–10 Chloride 58 -0.230 0.068 -0.209 No trend.

P11 06316400 Flow adjusted 2001–10 Chloride 58 -0.079 0.488 -0.044 No trend.

P11 06316400 Unadjusted 2001–10 Sulfate 58 -0.341 0.024 -31.9 Downward.

P11 06316400 Flow adjusted 2001–10 Sulfate 58 -0.095 0.432 -4.41 No trend.

P11 06316400 Unadjusted 2005–10 Specific conductance 71 -0.120 0.270 -36.0 No trend.

P11 06316400 Flow adjusted 2005–10 Specific conductance 71 0.154 0.151 0.014 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
Appendix 2 61

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

P11 06316400 Unadjusted 2005–10 Calcium 71 -0.211 0.047 -5.22 Downward.

P11 06316400 Flow adjusted 2005–10 Calcium 71 0.120 0.270 2.02 No trend.

P11 06316400 Unadjusted 2005–10 Magnesium 71 -0.154 0.151 -2.31 No trend.

P11 06316400 Flow adjusted 2005–10 Magnesium 71 0.177 0.098 1.10 No trend.

P11 06316400 Unadjusted 2005–10 Sodium adsorption ratio 71 -0.046 0.699 -0.014 No trend.

P11 06316400 Flow adjusted 2005–10 Sodium adsorption ratio 71 0.143 0.185 0.026 No trend.

P11 06316400 Unadjusted 2005–10 Sodium 71 -0.109 0.321 -2.93 No trend.

P11 06316400 Flow adjusted 2005–10 Sodium 71 0.143 0.185 2.79 No trend.

P11 06316400 Unadjusted 2005–10 Alkalinity 71 -0.097 0.377 -3.77 No trend.

P11 06316400 Flow adjusted 2005–10 Alkalinity 71 0.223 0.036 2.70 Upward.

P11 06316400 Unadjusted 2005–10 Chloride 71 -0.006 1.000 -0.004 No trend.

P11 06316400 Flow adjusted 2005–10 Chloride 71 0.291 0.006 0.271 Upward.

P11 06316400 Unadjusted 2005–10 Sulfate 71 -0.074 0.508 -9.28 No trend.

P11 06316400 Flow adjusted 2005–10 Sulfate 71 0.154 0.151 11.2 No trend.

P13 06317000 Unadjusted 1991–2010 Specific conductance 79 0.007 0.954 — No trend.

P13 06317000 Flow adjusted 1991–2010 Specific conductance 79 -0.004 0.970 -1.03 No trend.

P13 06317000 Unadjusted 1991–2010 Calcium 79 -0.364 <0.001 -2.64 Downward.

P13 06317000 Flow adjusted 1991–2010 Calcium 79 -0.457 <0.001 -2.75 Downward.

P13 06317000 Unadjusted 1991–2010 Magnesium 79 -0.286 0.007 -0.769 Downward.

P13 06317000 Flow adjusted 1991–2010 Magnesium 79 -0.412 <0.001 -0.896 Downward.

P13 06317000 Unadjusted 1991–2010 Sodium adsorption ratio 79 0.335 0.002 0.100 Upward.

P13 06317000 Flow adjusted 1991–2010 Sodium adsorption ratio 79 0.317 <0.001 0.085 Upward.

P13 06317000 Unadjusted 1991–2010 Sodium 79 0.161 0.092 3.00 No trend.

P13 06317000 Flow adjusted 1991–2010 Sodium 79 0.198 0.005 2.56 Upward.

P13 06317000 Unadjusted 2001–10 Specific conductance 59 -0.153 0.317 -36.7 No trend.

P13 06317000 Flow adjusted 2001–10 Specific conductance 59 -0.073 0.493 -19.8 No trend.

P13 06317000 Unadjusted 2001–10 Calcium 59 -0.379 0.054 -4.76 No trend.

P13 06317000 Flow adjusted 2001–10 Calcium 59 -0.310 0.056 -2.96 No trend.

P13 06317000 Unadjusted 2001–10 Magnesium 59 -0.195 0.205 -1.13 No trend.

P13 06317000 Flow adjusted 2001–10 Magnesium 59 -0.073 0.578 -0.391 No trend.

P13 06317000 Unadjusted 2001–10 Sodium adsorption ratio 59 0.011 0.948 0.006 No trend.

P13 06317000 Flow adjusted 2001–10 Sodium adsorption ratio 59 0.172 0.036 0.088 Upward.

P13 06317000 Unadjusted 2001–10 Sodium 59 -0.119 0.432 -3.42 No trend.

P13 06317000 Flow adjusted 2001–10 Sodium 59 0.034 0.726 0.935 No trend.

P13 06317000 Unadjusted 2001–10 Alkalinity 59 0.387 0.010 7.41 Upward.

P13 06317000 Flow adjusted 2001–10 Alkalinity 59 0.402 0.010 8.86 Upward.

P13 06317000 Unadjusted 2001–10 Chloride 59 -0.165 0.308 -5.50 No trend.

P13 06317000 Flow adjusted 2001–10 Chloride 59 -0.057 0.661 -0.895 No trend.

P13 06317000 Unadjusted 2001–10 Sulfate 59 -0.349 0.042 -21.2 Downward.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
62 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

P13 06317000 Flow adjusted 2001–10 Sulfate 59 -0.272 0.031 -16.5 Downward.

P13 06317000 Unadjusted 2005–10 Specific conductance 71 -0.251 0.017 -90.0 Downward.

P13 06317000 Flow adjusted 2005–10 Specific conductance 71 -0.017 0.912 -0.003 No trend.

P13 06317000 Unadjusted 2005–10 Calcium 71 -0.154 0.151 -2.61 No trend.

P13 06317000 Flow adjusted 2005–10 Calcium 71 -0.029 0.825 -0.326 No trend.

P13 06317000 Unadjusted 2005–10 Magnesium 71 -0.234 0.027 -1.54 Downward.

P13 06317000 Flow adjusted 2005–10 Magnesium 71 -0.086 0.440 -0.251 No trend.

P13 06317000 Unadjusted 2005–10 Sodium adsorption ratio 71 -0.217 0.041 -0.182 Downward.

P13 06317000 Flow adjusted 2005–10 Sodium adsorption ratio 71 -0.074 0.508 -0.039 No trend.

P13 06317000 Unadjusted 2005–10 Sodium 71 -0.280 0.008 -12.2 Downward.

P13 06317000 Flow adjusted 2005–10 Sodium 71 -0.006 1.000 -0.588 No trend.

P13 06317000 Unadjusted 2005–10 Alkalinity 71 0.017 0.912 0.645 No trend.

P13 06317000 Flow adjusted 2005–10 Alkalinity 71 0.189 0.077 4.68 No trend.

P13 06317000 Unadjusted 2005–10 Chloride 71 -0.383 <0.001 -13.9 Downward.

P13 06317000 Flow adjusted 2005–10 Chloride 71 -0.189 0.077 -3.73 No trend.

P13 06317000 Unadjusted 2005–10 Sulfate 71 -0.143 0.185 -19.7 No trend.

P13 06317000 Flow adjusted 2005–10 Sulfate 71 0.006 1.000 0.959 No trend.

P15 06317030 Unadjusted 2005–10 Specific conductance 72 0.078 0.481 56.7 No trend.

P15 06317030 Flow adjusted 2005–10 Specific conductance 72 0.211 0.045 0.042 Upward.

P15 06317030 Unadjusted 2005–10 Calcium 71 0.326 0.002 12.3 Upward.

P15 06317030 Flow adjusted 2005–10 Calcium 71 0.394 <0.001 11.5 Upward.

P15 06317030 Unadjusted 2005–10 Magnesium 72 0.111 0.303 8.11 No trend.

P15 06317030 Flow adjusted 2005–10 Magnesium 72 0.289 0.006 11.1 Upward.

P15 06317030 Unadjusted 2005–10 Sodium adsorption ratio 71 -0.291 0.006 -0.416 Downward.

P15 06317030 Flow adjusted 2005–10 Sodium adsorption ratio 71 -0.371 <0.001 -0.275 Downward.

P15 06317030 Unadjusted 2005–10 Sodium 72 0.000 1.000 0.000 No trend.

P15 06317030 Flow adjusted 2005–10 Sodium 72 0.144 0.175 11.3 No trend.

P17 06317100 Unadjusted 2005–10 Specific conductance 72 -0.189 0.074 -43.3 No trend.

P17 06317100 Flow adjusted 2005–10 Specific conductance 70 0.053 0.655 0.005 No trend.

P17 06317100 Unadjusted 2005–10 Calcium 71 -0.246 0.020 -2.85 Downward.

P17 06317100 Flow adjusted 2005–10 Calcium 69 0.048 0.690 0.430 No trend.

P17 06317100 Unadjusted 2005–10 Magnesium 71 -0.211 0.047 -1.48 Downward.

P17 06317100 Flow adjusted 2005–10 Magnesium 69 0.108 0.333 0.556 No trend.

P17 06317100 Unadjusted 2005–10 Sodium adsorption ratio 71 -0.074 0.508 -0.033 No trend.

P17 06317100 Flow adjusted 2005–10 Sodium adsorption ratio 69 0.133 0.232 0.053 No trend.

P17 06317100 Unadjusted 2005–10 Sodium 71 -0.120 0.270 -5.03 No trend.

P17 06317100 Flow adjusted 2005–10 Sodium 69 0.096 0.393 3.52 No trend.

P18 06320210 Unadjusted 2001–10 Specific conductance 58 -0.103 0.477 -6.83 No trend.

P18 06320210 Flow adjusted 2001–10 Specific conductance 58 0.310 0.032 12.7 Upward.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
Appendix 2 63

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

P18 06320210 Unadjusted 2001–10 Calcium 54 -0.056 0.731 -0.537 No trend.

P18 06320210 Flow adjusted 2001–10 Calcium 54 0.324 0.032 1.24 Upward.

P18 06320210 Unadjusted 2001–10 Magnesium 54 0.028 0.895 0.054 No trend.

P18 06320210 Flow adjusted 2001–10 Magnesium 54 0.343 0.039 0.657 Upward.

P18 06320210 Unadjusted 2001–10 Sodium adsorption ratio 54 -0.093 0.606 -0.007 No trend.

P18 06320210 Flow adjusted 2001–10 Sodium adsorption ratio 54 0.306 0.067 0.010 No trend.

P18 06320210 Unadjusted 2001–10 Sodium 54 -0.065 0.723 -0.439 No trend.

P18 06320210 Flow adjusted 2001–10 Sodium 54 0.333 0.069 0.702 No trend.

P18 06320210 Unadjusted 2001–10 Alkalinity 54 -0.083 0.599 -0.798 No trend.

P18 06320210 Flow adjusted 2001–10 Alkalinity 54 0.398 0.024 2.96 Upward.

P18 06320210 Unadjusted 2001–10 Chloride 54 -0.074 0.699 -0.027 No trend.

P18 06320210 Flow adjusted 2001–10 Chloride 54 0.269 0.083 0.101 No trend.

P18 06320210 Unadjusted 2001–10 Sulfate 54 -0.074 0.629 -1.53 No trend.

P18 06320210 Flow adjusted 2001–10 Sulfate 54 0.287 0.063 4.60 No trend.

P18 06320210 Unadjusted 2005–10 Specific conductance 72 -0.167 0.116 -15.2 No trend.

P18 06320210 Flow adjusted 2005–10 Specific conductance 72 0.078 0.481 0.003 No trend.

P18 06320210 Unadjusted 2005–10 Calcium 72 -0.178 0.093 -1.09 No trend.

P18 06320210 Flow adjusted 2005–10 Calcium 72 -0.033 0.786 -0.197 No trend.

P18 06320210 Unadjusted 2005–10 Magnesium 72 -0.178 0.093 -0.878 No trend.

P18 06320210 Flow adjusted 2005–10 Magnesium 72 -0.078 0.481 -0.133 No trend.

P18 06320210 Unadjusted 2005–10 Sodium adsorption ratio 72 -0.189 0.074 -0.014 No trend.

P18 06320210 Flow adjusted 2005–10 Sodium adsorption ratio 72 0.022 0.871 0.000 No trend.

P18 06320210 Unadjusted 2005–10 Sodium 72 -0.167 0.116 -1.00 No trend.

P18 06320210 Flow adjusted 2005–10 Sodium 72 -0.044 0.704 -0.142 No trend.

P18 06320210 Unadjusted 2005–10 Alkalinity 72 -0.056 0.625 -1.24 No trend.

P18 06320210 Flow adjusted 2005–10 Alkalinity 72 0.244 0.020 1.89 Upward.

P18 06320210 Unadjusted 2005–10 Chloride 72 -0.056 0.625 -0.030 No trend.

P18 06320210 Flow adjusted 2005–10 Chloride 72 0.144 0.175 0.059 No trend.

P18 06320210 Unadjusted 2005–10 Sulfate 72 -0.200 0.058 -4.87 No trend.

P18 06320210 Flow adjusted 2005–10 Sulfate 72 -0.067 0.551 -0.616 No trend.

P19 06323550 Unadjusted 2005–10 Specific conductance 72 -0.361 0.001 -29.5 Downward.

P19 06323550 Flow adjusted 2005–10 Specific conductance 72 -0.144 0.175 -0.010 No trend.

P19 06323550 Unadjusted 2005–10 Calcium 72 -0.400 <0.001 -3.26 Downward.

P19 06323550 Flow adjusted 2005–10 Calcium 72 -0.222 0.034 -1.22 Downward.

P19 06323550 Unadjusted 2005–10 Magnesium 72 -0.333 0.001 -1.30 Downward.

P19 06323550 Flow adjusted 2005–10 Magnesium 72 -0.100 0.357 -0.318 No trend.

P19 06323550 Unadjusted 2005–10 Sodium adsorption ratio 72 -0.322 0.002 -0.021 Downward.

P19 06323550 Flow adjusted 2005–10 Sodium adsorption ratio 72 -0.133 0.212 -0.009 No trend.

P19 06323550 Unadjusted 2005–10 Sodium 72 -0.389 <0.001 -1.48 Downward.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
64 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

P19 06323550 Flow adjusted 2005–10 Sodium 72 -0.200 0.058 -0.665 No trend.

P20 06324000 Unadjusted 2001–10 Specific conductance 60 -0.300 0.050 -38.0 No trend.

P20 06324000 Flow adjusted 2001–10 Specific conductance 60 -0.133 0.080 -8.01 No trend.

P20 06324000 Unadjusted 2001–10 Calcium 60 -0.333 0.038 -3.56 Downward.

P20 06324000 Flow adjusted 2001–10 Calcium 60 -0.074 0.416 -0.751 No trend.

P20 06324000 Unadjusted 2001–10 Magnesium 60 -0.311 0.044 -1.99 Downward.

P20 06324000 Flow adjusted 2001–10 Magnesium 60 -0.111 0.130 -0.526 No trend.

P20 06324000 Unadjusted 2001–10 Sodium adsorption ratio 60 -0.289 0.059 -0.024 No trend.

P20 06324000 Flow adjusted 2001–10 Sodium adsorption ratio 60 -0.022 0.830 -0.002 No trend.

P20 06324000 Unadjusted 2001–10 Sodium 60 -0.281 0.065 -2.30 No trend.

P20 06324000 Flow adjusted 2001–10 Sodium 60 -0.067 0.320 -0.618 No trend.

P20 06324000 Unadjusted 2001–10 Alkalinity 60 -0.148 0.167 -2.57 No trend.

P20 06324000 Flow adjusted 2001–10 Alkalinity 60 0.141 0.136 1.92 No trend.

P20 06324000 Unadjusted 2001–10 Chloride 60 -0.052 0.680 -0.019 No trend.

P20 06324000 Flow adjusted 2001–10 Chloride 60 0.104 0.450 0.036 No trend.

P20 06324000 Unadjusted 2001–10 Sulfate 60 -0.348 0.033 -17.6 Downward.

P20 06324000 Flow adjusted 2001–10 Sulfate 60 -0.193 0.034 -8.01 Downward.

P20 06324000 Unadjusted 2005–10 Specific conductance 72 -0.128 0.231 -14.2 No trend.

P20 06324000 Flow adjusted 2005–10 Specific conductance 72 0.022 0.871 0.004 No trend.

P20 06324000 Unadjusted 2005–10 Calcium 72 -0.244 0.020 -2.97 Downward.

P20 06324000 Flow adjusted 2005–10 Calcium 72 0.022 0.871 0.277 No trend.

P20 06324000 Unadjusted 2005–10 Magnesium 72 -0.178 0.093 -0.910 No trend.

P20 06324000 Flow adjusted 2005–10 Magnesium 72 -0.089 0.416 -0.299 No trend.

P20 06324000 Unadjusted 2005–10 Sodium adsorption ratio 72 -0.044 0.703 -0.007 No trend.

P20 06324000 Flow adjusted 2005–10 Sodium adsorption ratio 72 0.178 0.093 0.019 No trend.

P20 06324000 Unadjusted 2005–10 Sodium 72 -0.100 0.357 -0.747 No trend.

P20 06324000 Flow adjusted 2005–10 Sodium 72 0.056 0.625 0.769 No trend.

P20 06324000 Unadjusted 2005–10 Alkalinity 72 -0.022 0.871 -0.320 No trend.

P20 06324000 Flow adjusted 2005–10 Alkalinity 72 0.256 0.015 3.92 Upward.

P20 06324000 Unadjusted 2005–10 Chloride 72 0.133 0.212 0.082 No trend.

P20 06324000 Flow adjusted 2005–10 Chloride 72 0.200 0.058 0.130 No trend.

P20 06324000 Unadjusted 2005–10 Sulfate 72 -0.167 0.116 -9.20 No trend.

P20 06324000 Flow adjusted 2005–10 Sulfate 72 -0.100 0.357 -4.30 No trend.

P22 06324300 Unadjusted 2005–10 Specific conductance 62 0.224 0.060 68.3 No trend.

P22 06324300 Flow adjusted 2005–10 Specific conductance 62 -0.060 0.650 -0.005 No trend.

P22 06324300 Unadjusted 2005–10 Calcium 62 0.328 0.005 12.2 Upward.

P22 06324300 Flow adjusted 2005–10 Calcium 62 0.164 0.173 4.72 No trend.

P22 06324300 Unadjusted 2005–10 Magnesium 62 0.209 0.080 8.22 No trend.

P22 06324300 Flow adjusted 2005–10 Magnesium 62 0.045 0.746 1.73 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
Appendix 2 65

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

P22 06324300 Unadjusted 2005–10 Sodium adsorption ratio 61 0.054 0.690 0.012 No trend.

P22 06324300 Flow adjusted 2005–10 Sodium adsorption ratio 61 -0.194 0.110 -0.055 No trend.

P22 06324300 Unadjusted 2005–10 Sodium 61 0.295 0.014 23.3 Upward.

P22 06324300 Flow adjusted 2005–10 Sodium 61 0.039 0.790 3.01 No trend.

P23 06324500 Unadjusted 1991–2010 Specific conductance 76 0.070 0.516 4.29 No trend.

P23 06324500 Flow adjusted 1991–2010 Specific conductance 76 0.026 0.785 1.52 No trend.

P23 06324500 Unadjusted 2001–10 Specific conductance 57 -0.284 0.024 -53.7 Downward.

P23 06324500 Flow adjusted 2001–10 Specific conductance 57 -0.152 0.096 -14.8 No trend.

P23 06324500 Unadjusted 2001–10 Calcium 57 -0.510 0.008 -5.23 Downward.

P23 06324500 Flow adjusted 2001–10 Calcium 57 -0.267 0.096 -2.14 No trend.

P23 06324500 Unadjusted 2001–10 Magnesium 57 -0.358 0.014 -1.91 Downward.

P23 06324500 Flow adjusted 2001–10 Magnesium 57 -0.119 0.187 -0.552 No trend.

P23 06324500 Unadjusted 2001–10 Sodium adsorption ratio 57 -0.053 0.626 -0.017 No trend.

P23 06324500 Flow adjusted 2001–10 Sodium adsorption ratio 57 0.070 0.474 0.020 No trend.

P23 06324500 Unadjusted 2001–10 Sodium 57 -0.160 0.148 -4.32 No trend.

P23 06324500 Flow adjusted 2001–10 Sodium 57 -0.062 0.513 -1.79 No trend.

P23 06324500 Unadjusted 2001–10 Alkalinity 57 0.243 0.078 5.20 No trend.

P23 06324500 Flow adjusted 2001–10 Alkalinity 57 0.333 0.024 5.79 Upward.

P23 06324500 Unadjusted 2001–10 Chloride 57 -0.276 0.038 -4.97 Downward.

P23 06324500 Flow adjusted 2001–10 Chloride 57 -0.226 0.055 -3.04 No trend.

P23 06324500 Unadjusted 2001–10 Sulfate 57 -0.432 0.006 -26.7 Downward.

P23 06324500 Flow adjusted 2001–10 Sulfate 57 -0.317 0.006 -18.0 Downward.

P23 06324500 Unadjusted 2005–10 Specific conductance 71 -0.211 0.047 -29.2 Downward.

P23 06324500 Flow adjusted 2005–10 Specific conductance 71 0.086 0.440 16.6 No trend.

P23 06324500 Unadjusted 2005–10 Calcium 71 -0.291 0.006 -4.17 Downward.

P23 06324500 Flow adjusted 2005–10 Calcium 71 0.086 0.440 1.14 No trend.

P23 06324500 Unadjusted 2005–10 Magnesium 71 -0.280 0.008 -1.83 Downward.

P23 06324500 Flow adjusted 2005–10 Magnesium 71 0.051 0.659 0.214 No trend.

P23 06324500 Unadjusted 2005–10 Sodium adsorption ratio 71 -0.017 0.912 -0.009 No trend.

P23 06324500 Flow adjusted 2005–10 Sodium adsorption ratio 71 0.097 0.377 0.041 No trend.

P23 06324500 Unadjusted 2005–10 Sodium 71 -0.109 0.321 -2.73 No trend.

P23 06324500 Flow adjusted 2005–10 Sodium 71 0.097 0.377 4.02 No trend.

P23 06324500 Unadjusted 2005–10 Alkalinity 71 0.200 0.061 7.50 No trend.

P23 06324500 Flow adjusted 2005–10 Alkalinity 71 0.291 0.006 8.56 Upward.

P23 06324500 Unadjusted 2005–10 Chloride 71 -0.280 0.008 -6.61 Downward.

P23 06324500 Flow adjusted 2005–10 Chloride 71 -0.097 0.377 -2.04 No trend.

P23 06324500 Unadjusted 2005–10 Sulfate 71 -0.211 0.047 -16.8 Downward.

P23 06324500 Flow adjusted 2005–10 Sulfate 71 0.040 0.741 5.25 No trend.

P26 06324950 Unadjusted 2005–10 Specific conductance 72 0.206 0.051 113 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
66 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

P26 06324950 Flow adjusted 2005–10 Specific conductance 72 0.344 0.001 0.042 Upward.

P26 06324950 Unadjusted 2005–10 Calcium 72 0.333 0.001 8.14 Upward.

P26 06324950 Flow adjusted 2005–10 Calcium 72 0.444 <0.001 9.76 Upward.

P26 06324950 Unadjusted 2005–10 Magnesium 72 0.367 <0.001 8.80 Upward.

P26 06324950 Flow adjusted 2005–10 Magnesium 72 0.400 <0.001 9.54 Upward.

P26 06324950 Unadjusted 2005–10 Sodium adsorption ratio 72 -0.044 0.704 -0.061 No trend.

P26 06324950 Flow adjusted 2005–10 Sodium adsorption ratio 72 -0.011 0.957 -0.007 No trend.

P26 06324950 Unadjusted 2005–10 Sodium 72 0.106 0.328 6.60 No trend.

P26 06324950 Flow adjusted 2005–10 Sodium 72 0.200 0.058 15.2 No trend.

P27 06324970 Unadjusted 1991–2010 Specific conductance 80 0.057 0.528 13.9 No trend.

P27 06324970 Flow adjusted 1991–2010 Specific conductance 80 -0.039 0.688 -8.74 No trend.

P27 06324970 Unadjusted 1991–2010 Calcium 80 0.108 0.181 1.53 No trend.

P27 06324970 Flow adjusted 1991–2010 Calcium 80 0.055 0.483 0.404 No trend.

P27 06324970 Unadjusted 1991–2010 Magnesium 80 0.108 0.204 1.10 No trend.

P27 06324970 Flow adjusted 1991–2010 Magnesium 80 0.026 0.788 0.203 No trend.

P27 06324970 Unadjusted 1991–2010 Sodium adsorption ratio 80 -0.016 0.867 -0.015 No trend.

P27 06324970 Flow adjusted 1991–2010 Sodium adsorption ratio 80 -0.147 0.139 -0.037 No trend.

P27 06324970 Unadjusted 1991–2010 Sodium 80 0.037 0.675 1.54 No trend.

P27 06324970 Flow adjusted 1991–2010 Sodium 80 -0.055 0.578 -2.19 No trend.

P27 06324970 Unadjusted 2001–10 Specific conductance 60 0.030 0.821 12.8 No trend.

P27 06324970 Flow adjusted 2001–10 Specific conductance 60 0.215 0.096 69.4 No trend.

P27 06324970 Unadjusted 2001–10 Calcium 60 0.007 0.969 0.024 No trend.

P27 06324970 Flow adjusted 2001–10 Calcium 60 0.193 0.116 2.44 No trend.

P27 06324970 Unadjusted 2001–10 Magnesium 60 0.059 0.615 0.447 No trend.

P27 06324970 Flow adjusted 2001–10 Magnesium 60 0.230 0.082 2.84 No trend.

P27 06324970 Unadjusted 2001–10 Sodium adsorption ratio 60 0.000 1.000 0.000 No trend.

P27 06324970 Flow adjusted 2001–10 Sodium adsorption ratio 60 0.126 0.311 0.078 No trend.

P27 06324970 Unadjusted 2001–10 Sodium 60 0.022 0.866 1.52 No trend.

P27 06324970 Flow adjusted 2001–10 Sodium 60 0.207 0.108 8.77 No trend.

P27 06324970 Unadjusted 2001–10 Alkalinity 60 0.052 0.603 1.48 No trend.

P27 06324970 Flow adjusted 2001–10 Alkalinity 60 0.148 0.095 6.04 No trend.

P27 06324970 Unadjusted 2001–10 Chloride 60 0.037 0.767 0.786 No trend.

P27 06324970 Flow adjusted 2001–10 Chloride 60 0.193 0.131 2.27 No trend.

P27 06324970 Unadjusted 2001–10 Sulfate 60 -0.007 0.973 -1.82 No trend.

P27 06324970 Flow adjusted 2001–10 Sulfate 60 0.163 0.245 24.9 No trend.

P27 06324970 Unadjusted 2005–10 Specific conductance 72 0.111 0.303 85.8 No trend.

P27 06324970 Flow adjusted 2005–10 Specific conductance 72 0.289 0.006 0.062 Upward.

P27 06324970 Unadjusted 2005–10 Calcium 72 0.111 0.303 3.35 No trend.

P27 06324970 Flow adjusted 2005–10 Calcium 72 0.278 0.008 11.7 Upward.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
Appendix 2 67

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

P27 06324970 Unadjusted 2005–10 Magnesium 72 0.222 0.034 5.52 Upward.

P27 06324970 Flow adjusted 2005–10 Magnesium 72 0.333 0.001 9.15 Upward.

P27 06324970 Unadjusted 2005–10 Sodium adsorption ratio 72 0.067 0.551 0.063 No trend.

P27 06324970 Flow adjusted 2005–10 Sodium adsorption ratio 72 0.256 0.015 0.202 Upward.

P27 06324970 Unadjusted 2005–10 Sodium 72 0.144 0.175 15.2 No trend.

P27 06324970 Flow adjusted 2005–10 Sodium 72 0.389 <0.001 28.1 Upward.

P27 06324970 Unadjusted 2005–10 Alkalinity 72 0.100 0.357 7.64 No trend.

P27 06324970 Flow adjusted 2005–10 Alkalinity 72 0.278 0.008 13.3 Upward.

P27 06324970 Unadjusted 2005–10 Chloride 72 0.022 0.871 1.99 No trend.

P27 06324970 Flow adjusted 2005–10 Chloride 72 0.144 0.175 2.05 No trend.

P27 06324970 Unadjusted 2005–10 Sulfate 72 0.178 0.093 83.2 No trend.

P27 06324970 Flow adjusted 2005–10 Sulfate 72 0.333 0.001 130 Upward.

C2 06386500 Unadjusted 2005–10 Specific conductance 55 -0.124 0.362 -60.0 No trend.

C2 06386500 Flow adjusted 2005–10 Specific conductance 55 0.314 0.016 0.028 Upward.

C2 06386500 Unadjusted 2005–10 Calcium 55 -0.010 1.000 -0.200 No trend.

C2 06386500 Flow adjusted 2005–10 Calcium 55 0.333 0.010 11.6 Upward.

C2 06386500 Unadjusted 2005–10 Magnesium 55 0.000 1.000 0.000 No trend.

C2 06386500 Flow adjusted 2005–10 Magnesium 55 0.410 0.001 5.17 Upward.

C2 06386500 Unadjusted 2005–10 Sodium adsorption ratio 55 -0.162 0.226 -0.150 No trend.

C2 06386500 Flow adjusted 2005–10 Sodium adsorption ratio 55 0.200 0.131 0.270 No trend.

C2 06386500 Unadjusted 2005–10 Sodium 55 -0.048 0.762 -13.9 No trend.

C2 06386500 Flow adjusted 2005–10 Sodium 55 0.314 0.016 33.3 Upward.

C2 06386500 Unadjusted 2005–10 Alkalinity 55 0.238 0.070 4.95 No trend.

C2 06386500 Flow adjusted 2005–10 Alkalinity 55 0.219 0.096 3.43 No trend.

C2 06386500 Unadjusted 2005–10 Chloride 55 0.105 0.450 1.69 No trend.

C2 06386500 Flow adjusted 2005–10 Chloride 55 0.238 0.070 4.69 No trend.

C2 06386500 Unadjusted 2005–10 Sulfate 55 -0.048 0.762 -4.54 No trend.

C2 06386500 Flow adjusted 2005–10 Sulfate 55 0.352 0.007 98.3 Upward.

B1 06425720 Unadjusted 2001–10 Specific conductance 50 0.204 0.156 33.3 No trend.

B1 06425720 Flow adjusted 2001–10 Specific conductance 50 0.277 0.041 36.6 Upward.

B1 06425720 Unadjusted 2001–10 Calcium 50 -0.016 0.938 -0.180 No trend.

B1 06425720 Flow adjusted 2001–10 Calcium 50 0.016 0.937 0.133 No trend.

B1 06425720 Unadjusted 2001–10 Magnesium 50 -0.047 0.713 -0.445 No trend.

B1 06425720 Flow adjusted 2001–10 Magnesium 50 -0.026 0.872 -0.483 No trend.

B1 06425720 Unadjusted 2001–10 Sodium adsorption ratio 50 0.372 0.030 0.169 Upward.

B1 06425720 Flow adjusted 2001–10 Sodium adsorption ratio 50 0.455 0.020 0.149 Upward.

B1 06425720 Unadjusted 2001–10 Sodium 50 0.309 0.045 8.08 Upward.

B1 06425720 Flow adjusted 2001–10 Sodium 50 0.466 0.019 8.27 Upward.

B1 06425720 Unadjusted 2005–10 Specific conductance 57 0.047 0.744 10.0 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
68 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

B1 06425720 Flow adjusted 2005–10 Specific conductance 57 0.203 0.103 0.028 No trend.

B1 06425720 Unadjusted 2005–10 Calcium 57 -0.156 0.216 -4.76 No trend.

B1 06425720 Flow adjusted 2005–10 Calcium 57 -0.172 0.171 -4.86 No trend.

B1 06425720 Unadjusted 2005–10 Magnesium 57 -0.188 0.134 -3.60 No trend.

B1 06425720 Flow adjusted 2005–10 Magnesium 57 -0.078 0.557 -1.96 No trend.

B1 06425720 Unadjusted 2005–10 Sodium adsorption ratio 57 0.500 <0.001 0.256 Upward.

B1 06425720 Flow adjusted 2005–10 Sodium adsorption ratio 57 0.625 <0.001 0.343 Upward.

B1 06425720 Unadjusted 2005–10 Sodium 57 0.219 0.078 9.56 No trend.

B1 06425720 Flow adjusted 2005–10 Sodium 57 0.578 <0.001 19.7 Upward.

B3 06426400 Unadjusted 2001–10 Specific conductance 59 -0.038 0.636 -10.0 No trend.

B3 06426400 Flow adjusted 2001–10 Specific conductance 59 0.172 0.063 25.2 No trend.

B3 06426400 Unadjusted 2001–10 Calcium 59 0.218 0.007 2.70 Upward.

B3 06426400 Flow adjusted 2001–10 Calcium 59 0.157 0.062 2.18 No trend.

B3 06426400 Unadjusted 2001–10 Magnesium 59 0.234 0.020 2.35 Upward.

B3 06426400 Flow adjusted 2001–10 Magnesium 59 0.218 0.052 3.14 No trend.

B3 06426400 Unadjusted 2001–10 Sodium adsorption ratio 59 -0.318 0.025 -0.182 Downward.

B3 06426400 Flow adjusted 2001–10 Sodium adsorption ratio 59 -0.080 0.389 -0.013 No trend.

B3 06426400 Unadjusted 2001–10 Sodium 59 -0.241 0.052 -9.54 No trend.

B3 06426400 Flow adjusted 2001–10 Sodium 59 0.065 0.490 2.55 No trend.

B3 06426400 Unadjusted 2001–10 Alkalinity 59 -0.372 0.013 -12.5 Downward.

B3 06426400 Flow adjusted 2001–10 Alkalinity 59 -0.172 0.094 -4.08 No trend.

B3 06426400 Unadjusted 2001–10 Chloride 59 -0.065 0.557 -1.45 No trend.

B3 06426400 Flow adjusted 2001–10 Chloride 59 0.142 0.215 3.12 No trend.

B3 06426400 Unadjusted 2001–10 Sulfate 59 0.096 0.291 11.5 No trend.

B3 06426400 Flow adjusted 2001–10 Sulfate 59 0.165 0.119 20.7 No trend.

B3 06426400 Unadjusted 2005–10 Specific conductance 72 0.056 0.625 10.0 No trend.

B3 06426400 Flow adjusted 2005–10 Specific conductance 72 0.222 0.034 0.032 Upward.

B3 06426400 Unadjusted 2005–10 Calcium 72 0.261 0.012 4.68 Upward.

B3 06426400 Flow adjusted 2005–10 Calcium 72 0.200 0.058 4.46 No trend.

B3 06426400 Unadjusted 2005–10 Magnesium 72 0.311 0.003 6.50 Upward.

B3 06426400 Flow adjusted 2005–10 Magnesium 72 0.289 0.006 5.82 Upward.

B3 06426400 Unadjusted 2005–10 Sodium adsorption ratio 72 -0.344 0.001 -0.193 Downward.

B3 06426400 Flow adjusted 2005–10 Sodium adsorption ratio 72 0.100 0.357 0.018 No trend.

B3 06426400 Unadjusted 2005–10 Sodium 72 -0.178 0.093 -8.14 No trend.

B3 06426400 Flow adjusted 2005–10 Sodium 72 0.200 0.058 5.77 No trend.

B3 06426400 Unadjusted 2005–10 Alkalinity 72 -0.422 <0.001 -26.1 Downward.

B3 06426400 Flow adjusted 2005–10 Alkalinity 72 -0.178 0.093 -10.3 No trend.

B3 06426400 Unadjusted 2005–10 Chloride 72 -0.133 0.212 -4.32 No trend.

B3 06426400 Flow adjusted 2005–10 Chloride 72 0.089 0.416 3.00 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
Appendix 2 69

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

B3 06426400 Unadjusted 2005–10 Sulfate 72 0.333 0.001 59.0 Upward.

B3 06426400 Flow adjusted 2005–10 Sulfate 72 0.367 <0.001 61.7 Upward.

B4 06426500 Unadjusted 1991–2010 Specific conductance 76 0.118 0.167 22.9 No trend.

B4 06426500 Flow adjusted 1991–2010 Specific conductance 76 0.050 0.610 9.15 No trend.

B4 06426500 Unadjusted 1991–2010 Calcium 52 0.202 0.080 2.03 No trend.

B4 06426500 Flow adjusted 1991–2010 Calcium 52 0.205 0.075 1.29 No trend.

B4 06426500 Unadjusted 1991–2010 Magnesium 52 0.292 0.021 2.45 Upward.

B4 06426500 Flow adjusted 1991–2010 Magnesium 52 0.314 0.026 2.08 Upward.

B4 06426500 Unadjusted 1991–2010 Sodium adsorption ratio 52 -0.247 0.094 -0.086 No trend.

B4 06426500 Flow adjusted 1991–2010 Sodium adsorption ratio 52 -0.218 0.111 -0.039 No trend.

B4 06426500 Unadjusted 1991–2010 Sodium 52 -0.048 0.708 -2.02 No trend.

B4 06426500 Flow adjusted 1991–2010 Sodium 52 -0.006 0.979 -0.251 No trend.

B4 06426500 Unadjusted 2001–10 Specific conductance 60 0.048 0.573 9.17 No trend.

B4 06426500 Flow adjusted 2001–10 Specific conductance 60 0.170 0.212 34.9 No trend.

B4 06426500 Unadjusted 2001–10 Calcium 60 0.222 0.033 3.64 Upward.

B4 06426500 Flow adjusted 2001–10 Calcium 60 0.244 0.048 3.44 Upward.

B4 06426500 Unadjusted 2001–10 Magnesium 60 0.178 0.074 3.12 No trend.

B4 06426500 Flow adjusted 2001–10 Magnesium 60 0.356 0.021 3.82 Upward.

B4 06426500 Unadjusted 2001–10 Sodium adsorption ratio 60 -0.274 0.031 -0.135 Downward.

B4 06426500 Flow adjusted 2001–10 Sodium adsorption ratio 60 -0.052 0.669 -0.015 No trend.

B4 06426500 Unadjusted 2001–10 Sodium 60 -0.126 0.204 -6.97 No trend.

B4 06426500 Flow adjusted 2001–10 Sodium 60 0.089 0.500 2.30 No trend.

B4 06426500 Unadjusted 2001–10 Alkalinity 60 -0.333 0.014 -14.0 Downward.

B4 06426500 Flow adjusted 2001–10 Alkalinity 60 -0.267 0.033 -10.2 Downward.

B4 06426500 Unadjusted 2001–10 Chloride 60 0.141 0.267 6.07 No trend.

B4 06426500 Flow adjusted 2001–10 Chloride 60 0.481 0.005 7.39 Upward.

B4 06426500 Unadjusted 2001–10 Sulfate 60 0.096 0.425 17.5 No trend.

B4 06426500 Flow adjusted 2001–10 Sulfate 60 0.215 0.138 24.1 No trend.

B4 06426500 Unadjusted 2005–10 Specific conductance 72 0.022 0.871 25.0 No trend.

B4 06426500 Flow adjusted 2005–10 Specific conductance 72 0.222 0.034 0.031 Upward.

B4 06426500 Unadjusted 2005–10 Calcium 71 0.120 0.270 1.95 No trend.

B4 06426500 Flow adjusted 2005–10 Calcium 71 0.166 0.122 2.51 No trend.

B4 06426500 Unadjusted 2005–10 Magnesium 71 0.177 0.098 3.60 No trend.

B4 06426500 Flow adjusted 2005–10 Magnesium 71 0.406 <0.001 6.03 Upward.

B4 06426500 Unadjusted 2005–10 Sodium adsorption ratio 71 -0.097 0.377 -0.070 No trend.

B4 06426500 Flow adjusted 2005–10 Sodium adsorption ratio 71 0.177 0.098 0.058 No trend.

B4 06426500 Unadjusted 2005–10 Sodium 71 -0.051 0.659 -2.35 No trend.

B4 06426500 Flow adjusted 2005–10 Sodium 71 0.223 0.036 9.45 Upward.

B4 06426500 Unadjusted 2005–10 Alkalinity 72 -0.178 0.093 -5.76 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]
70 Water-Quality Characteristics, Tongue, Powder, Cheyenne, and Belle Fourche Rivers, Wyo. and Mont., 1991 through 2010

Site 

number 

(fig. 1)

USGS site 

identification number

Type of value 

used in trend 

test

Trend 

period 

(water 

years)

Property or 

constituent

Sample 

size

Tau 

value p-value Slope Trend direction

B4 06426500 Flow adjusted 2005–10 Alkalinity 72 0.033 0.786 1.91 No trend.

B4 06426500 Unadjusted 2005–10 Chloride 72 -0.233 0.026 -11.2 Downward.

B4 06426500 Flow adjusted 2005–10 Chloride 72 0.100 0.357 1.85 No trend.

B4 06426500 Unadjusted 2005–10 Sulfate 72 0.278 0.008 53.3 Upward.

B4 06426500 Flow adjusted 2005–10 Sulfate 72 0.444 <0.001 66.0 Upward.

B5 06428050 Unadjusted 2001–10 Specific conductance 56 -0.230 0.059 -28.0 No trend.

B5 06428050 Flow adjusted 2001–10 Specific conductance 56 -0.200 0.108 -20.1 No trend.

B5 06428050 Unadjusted 2001–10 Calcium 52 0.210 0.169 3.58 No trend.

B5 06428050 Flow adjusted 2001–10 Calcium 52 0.280 0.165 7.84 No trend.

B5 06428050 Unadjusted 2001–10 Magnesium 52 0.030 0.838 0.171 No trend.

B5 06428050 Flow adjusted 2001–10 Magnesium 52 0.030 0.792 0.235 No trend.

B5 06428050 Unadjusted 2001–10 Sodium adsorption ratio 52 -0.380 0.067 -0.103 No trend.

B5 06428050 Flow adjusted 2001–10 Sodium adsorption ratio 52 -0.380 0.097 -0.099 No trend.

B5 06428050 Unadjusted 2001–10 Sodium 52 -0.410 0.047 -7.69 Downward.

B5 06428050 Flow adjusted 2001–10 Sodium 52 -0.390 0.079 -6.39 No trend.

B5 06428050 Unadjusted 2001–10 Alkalinity 52 -0.130 0.369 -1.67 No trend.

B5 06428050 Flow adjusted 2001–10 Alkalinity 52 0.000 1.000 0.000 No trend.

B5 06428050 Unadjusted 2001–10 Chloride 52 -0.410 0.033 -1.92 Downward.

B5 06428050 Flow adjusted 2001–10 Chloride 52 -0.290 0.112 -1.69 No trend.

B5 06428050 Unadjusted 2001–10 Sulfate 52 0.030 0.811 1.76 No trend.

B5 06428050 Flow adjusted 2001–10 Sulfate 52 0.110 0.359 6.23 No trend.

Appendix 2. Trend results for selected water-quality constituents for selected sites in the Tongue, Powder, Cheyenne, and Belle 

Fourche River drainage basins, Wyoming and Montana, water years 1991–2010.—Continued

[USGS, U.S. Geological Survey; —, not calculated; <, less than. Slope for unadjusted trends is the change per year in original measurement units; for flowadjusted trends, the slopes reflect relative changes in units after adjustment for streamflow variability]

Publishing support provided by the: 

Columbus, Denver, and Rolla Publishing Service Centers

For more information concerning this publication, contact: 

Director, Wyoming Water Science Center 

U.S. Geological Survey 

521 Progress Circle, Suite 6 

Cheyenne, Wyoming 82007 

(307) 778-2931

Or visit the Wyoming Water Science Center Web site at: 

http://wy.water.usgs.gov/

Clark—Water Quality for the Tongue, Powder, Cheyenne, and Belle Fourche River Drainage Basins, Wyo. and Mont., 1991 through 2010—SIR 2012–5117

Printed on recycled paper

9 781411 334281

ISBN 978-1-4113-3428-1