U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2009–5168

Prepared in cooperation with the Bureau of Land Management and the Wyoming Department of 

Environmental Quality

Specific Conductance and Dissolved-Solids Characteristics 

for the Green River and Muddy Creek, Wyoming, Water Years 

1999–2008
Cover. The banks of the Green River, Wyoming. Photograph by Kirk A. Miller, U.S. Geological Survey, taken March 22, 2007.
Specific Conductance and DissolvedSolids Characteristics for the Green River 

and Muddy Creek, Wyoming, 

Water Years 1999–2008

By Melanie L. Clark and Seth L. Davidson

Prepared in cooperation with the Bureau of Land Management and the 

Wyoming Department of Environmental Quality

Scientific Investigations Report 2009–5168

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Clark, M.L., and Davidson, S.L., 2009, Specific conductance and dissolved-solids characteristics for the Green 

River and Muddy Creek, Wyoming, water years 1999–2008: U.S. Geological Survey Scientific Investigations 

Report 2009–5168, 18 p.
iii

Contents

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

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

Purpose and Scope ..............................................................................................................................4

Description of Drainage Basins .........................................................................................................4

Green River Drainage Basin ......................................................................................................4

Muddy Creek Drainage Basin....................................................................................................5

Methods...........................................................................................................................................................5

Data Collection......................................................................................................................................6

Data Analysis.........................................................................................................................................6

Specific Conductance and Dissolved-Solids Characteristics ...............................................................7

Streamflow Conditions and Influence...............................................................................................7

Specific Conductance Characteristics ...........................................................................................10

Dissolved-Solids Characteristics.....................................................................................................10

Regression Equations for Estimating Dissolved Solids ................................................................12

Summary........................................................................................................................................................16

References....................................................................................................................................................17

Figures

1. Map showing locations of selected streamflow-gaging stations and 

water-quality sampling sites in the Green River and Muddy Creek 

drainage basins, Wyoming..........................................................................................................2

2–8. Graphs showing:

2. Annual runoff for the Green River (site 09217000) and Muddy 

Creek (site 09258980), Wyoming, water years 1999–2008 .............................................8

3. Daily mean streamflow and instantaneous streamflow during 

water-quality sampling at the Green River (site 09217000) and 

Muddy Creek (site 09258980), Wyoming, water years 1999–2008................................9

4. Daily mean and discrete values of specific conductance during 

water-quality sampling at the Green River (site 09217000) and 

Muddy Creek (site 09258980), Wyoming, water years 1999–2008..............................11

5. Specific conductance during water-quality sampling at the 

Green River (site 09217000), water years 1999–2008, and 

Muddy Creek (site 09258980), water years 2006–08, Wyoming..................................12

6. Dissolved-solids concentrations for samples collected during 

water-quality sampling at the Green River (site 09217000), water 

years 1999–2008, and Muddy Creek (site 09258980), water 

years 2006–08, Wyoming ..................................................................................................13

7. Relations between specific conductance and dissolved-solids 

concentration for the Green River (site 09217000), water 

years 1999–2008, and Muddy Creek (site 09258980), water 

years 2006–08, Wyoming ..................................................................................................14

8. Measured and estimated dissolved-solids concentrations for the 

Green River (site 09217000) and Muddy Creek (site 09258980), 

Wyoming, water years 1999–2008...................................................................................15
iv

Tables

1. Summary of site information for streamflow-gaging stations and 

water-quality sampling sites on the Green River and Muddy Creek, 

Wyoming, used in this report......................................................................................................3

2. Regression equations for estimates of dissolved-solids concentration 

for the Green River (site 09217000) and Muddy Creek (site 09258980), 

Wyoming.......................................................................................................................................15

Conversion Factors and Datums

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

acre 4,047 square meter (m2

)

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)

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

°F=(1.8×°C)+32

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.

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

25°C).

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

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, 2008, is called 

water year 2008. 
v

Abbreviations and Symbols

< less than

mg/L milligrams per liter

μS/cm microsiemens per centimeter at 25 degrees Celsius

BLM Bureau of Land Management

CRBSCF Colorado River Basin Salinity Control Forum

JIDPA Jonah Infill Drilling Project Area

MSE mean square error

NWIS National Water Information System

PAPA Pinedale Anticline Project Area

IQR interquartile range

p-value significance level

R2 coefficient of determination

USGS U.S. Geological Survey 

WDEQ Wyoming Department of Environmental Quality

WLCI Wyoming Landscape Conservation Initiative

Specific Conductance and Dissolved-Solids 

Characteristics for the Green River and Muddy Creek, 

Wyoming, Water Years 1999–2008

By Melanie L. Clark and Seth L. Davidson

Abstract

Southwestern Wyoming is an area of diverse scenery, 

wildlife, and natural resources that is actively undergoing 

energy development. The U.S. Department of the Interior’s 

Wyoming Landscape Conservation Initiative is a long-term 

science-based effort to assess and enhance aquatic and terrestrial habitats at a landscape scale, while facilitating responsible 

energy development through local collaboration and partnerships. Water-quality monitoring has been conducted by the 

U.S. Geological Survey on the Green River near Green River, 

Wyoming, and Muddy Creek near Baggs, Wyoming. This 

monitoring, which is being conducted in cooperation with 

State and other Federal agencies and as part of the Wyoming 

Landscape Conservation Initiative, is in response to concerns 

about potentially increased dissolved solids in the Colorado 

River Basin as a result of energy development. Because of 

the need to provide real-time dissolved-solids concentrations for the Green River and Muddy Creek on the World 

Wide Web, the U.S. Geological Survey developed regression equations to estimate dissolved-solids concentrations on 

the basis of continuous specific conductance using relations 

between measured specific conductance and dissolved-solids 

concentrations. 

Specific conductance and dissolved-solids concentrations were less varied and generally lower for the Green 

River than for Muddy Creek. The median dissolved-solids 

concentration for the site on the Green River was 318 milligrams per liter, and the median concentration for the site on 

Muddy Creek was 943 milligrams per liter. Dissolved-solids 

concentrations ranged from 187 to 594 milligrams per liter 

in samples collected from the Green River during water 

years 1999–2008. Dissolved-solids concentrations ranged 

from 293 to 2,485 milligrams per liter in samples collected 

from Muddy Creek during water years 2006–08. The differences in dissolved-solids concentrations in samples collected 

from the Green River compared to samples collected from 

Muddy Creek reflect the different basin characteristics.

Relations between specific conductance and dissolvedsolids concentrations were statistically significant for the 

Green River (p-value less than 0.001) and Muddy Creek 

(p-value less than 0.001); therefore, specific conductance can 

be used to estimate dissolved-solids concentrations. Using 

continuous specific conductance values to estimate dissolved 

solids in real-time on the World Wide Web increases the 

amount and improves the timeliness of data available to water 

managers for assessing dissolved-solids concentrations in the 

Colorado River Basin. 

Introduction 

Southwestern Wyoming is an area of diverse scenery, 

wildlife, and natural resources. It provides crucial habitat 

for deer, elk, pronghorn antelope, greater sage-grouse, and 

other nongame species. It also is actively undergoing energy 

development. The U.S. Geological Survey (USGS) recently 

completed a geology-based assessment of energy resources for 

southwestern Wyoming that reported a mean of 84.6 trillion 

cubic feet of undiscovered natural gas, a mean of 131 million 

barrels of undiscovered oil, and a mean of 2.6 billion barrels 

of undiscovered natural gas liquids in nine total petroleum 

systems defined for the Southwestern Wyoming Province 

(U.S. Geological Survey, 2002). To ensure Wyoming’s wildlife 

and habitat remain viable in areas with energy development, 

the U.S. Department of the Interior implemented the Wyoming 

Landscape Conservation Initiative (WLCI) in cooperation with 

local, State, and Federal agencies. The WLCI is a long-term 

science-based effort to assess and enhance aquatic and terrestrial habitats at a landscape scale, while facilitating responsible energy development through local collaboration and 

partnerships (D’Erchia, 2008). The WLCI study area includes 

15 million acres in southwestern Wyoming (fig. 1).

Assessments of water quality are important components 

of the WLCI objectives because energy development has the 

potential to affect water resources and aquatic environments. 

Dissolved-solids concentrations have been identified as a 

water-quality concern for streams in the WLCI study area. 

Dissolved solids primarily are composed of major cations 

(dissolved calcium, magnesium, potassium, and sodium), 

major anions (dissolved carbonate species, chloride, fluoride, 

and sulfate), and nonionic silica (Hem, 1985, p. 157). Specific 
Figure 1. Locations of selected streamflow-gaging stations and water-quality sampling sites in the Green River and Muddy Creek drainage basins, W

Wind

River

Win

Li

d

ttle

R

River

S

weetwater

Popo Agie River

Creek

Cr

Creek

Muddy

Wells Salt

Slate

Snake

River

Hoback

River

River

R

R

River

River

S andy

Big

Fork

East

Fork

New

Green

Green

River

Greys

Bear

Salt

River

River

Ham s

Smiths Fork

Fork

Fork

Creek

Muddy

Fk

Green River

River

R

River Platte

North

Encam pm ent

River

Elk

Snake

Little

Fk

Sm it s h

Black s

River

River Uinta

R

L o ak e F kr

River

Weber

Bear

Henrys

R

Fork

Powder

South

River

Platte N

Bear Lake

Fontenelle

 Reservoir

Flaming Gorge Reservoir

WoodruffNarrowsReservoir

Palisades Reservoir

BlackfootReservoir

GraysLake

Boysen

Reservoir

BullLake Ocean Lake

 PathfinderReservoir

AlcovaRes

SeminoeReservoir

FremontLake

Creek

Bitter

Creek

Vermillion

PineCr

FREMONT 

CARBON 

SWEETWATER 

TETON 

NATRONA 

SUBLETTE 

LINCOLN 

MOFFAT 

UINTA 

SUMMIT 

RICH 

ROUTT 

UINTAH 

JACKSON 

CARIBOU 

BEAR 

LAKE 

DUCHESNE 

DAGGETT 

CACHE 

WASATCH

MORGAN

BONNEVILLE 

WYO

MING

COLORAD

O

UTAH IDAHO

Lander

Casper

Rawlins

Craig

Kemmerer

Riverton

Evanston

Coalville

Green

River

RockSprings

Baggs

111° 110° 109° 108° 107° 

41° 42° 43° 

0 20 40 60 80 MILES 

0 20 40 60 80 KILOMETERS 

287 

40 

191 

20 

26 

26 

287 

189 

30 

26 

89 

191 

189 

89 

80

25

80

Base modified from U.S. Bureau of the Census digital data, 1990 and 2000Hydrography modified from USGS National Hydrography Dataset (NHD) digital data, 1999,and U.S. Geological Survey digital data, Enhanced River Reach File, 1999Albers Equal-area Conic projection, Standard parallels 29°30′N and 45°30′N, central meridian 107°30′W 

30

09258980

09217000

WYOMING RANGE

WIND RIVER RANGE 

0000

09211200

09216050

ATLANTIC

RIM

UTAH 

IDAHO
Introduction 3

conductance, which can be measured in the field, is a measure 

of water’s ability to conduct an electrical current at 25 degrees 

Celsius (°C) and is a useful indicator of dissolved solids. 

Natural processes, such as contributions from saline springs 

and groundwater discharge, erosion and dissolution of sediments, and concentration effects from evaporation and transpiration, can contribute dissolved solids to streams. Activities, 

such as irrigation, livestock grazing, energy development, 

road building, urbanization, and wildlife management, also 

can contribute to the movement of dissolved solids to streams 

(Colorado River Basin Salinity Control Forum, 2008).

Most of the surface-water drainage from the WLCI study 

area is to the Colorado River Basin, where dissolved-solids 

concentrations are administered under the Salinity Control 

Act (Public Law 93–320). The Colorado River Basin Salinity Control Forum (CRBSCF), which is a cooperative effort 

among State and Federal agencies to manage dissolved solids 

in the Colorado River Basin, has identified rapidly expanding 

energy development in the Upper Colorado River Basin as a 

high priority issue because energy development has potential to increase dissolved-solids concentrations (Bureau of 

Land Management, 2008a). The Green River drainage basin 

and the Muddy Creek drainage basin (fig. 1), which are both 

part of the Colorado River Basin, are two areas experiencing 

energy development in the WLCI study area. An increase in 

dissolved-solids concentrations can adversely affect the ability 

to meet water-quality standards established for the Colorado 

River Basin and potentially affect water uses in the basin 

(Colorado River Basin Salinity Control Forum, 2008). 

The Bureau of Land Management (BLM) administers 

millions of acres of public land and Federal surface and 

mineral estates in the WLCI study area. Energy development 

in the WLCI study area largely is on BLM-administered lands, 

including lands in the Green River drainage basin and the 

Muddy Creek drainage basin. The BLM coordinates salinity 

control efforts for the lands that it manages with the CRBSCF, 

with the goal of reducing the contribution of dissolved 

solids from lands that it administers. As part of its overall 

land management efforts, the BLM has developed management plans for much of the land in the WLCI study area. The 

Pinedale Field Office of the BLM has developed the Pinedale 

Resource Management Plan (Bureau of Land Management, 

2008a) and the Rawlins Field Office of the BLM has developed the Rawlins Resource Management Plan (Bureau of 

Land Management, 2008b) to establish guidance, objectives, 

policies, and management actions for addressing a variety of 

issues on a broad scale, including energy development and 

water quality. 

The CRBSCF has encouraged the implementation of 

water-quality monitoring to help assess the effectiveness of 

management practices. Water-quality monitoring has been 

conducted for decades on the Green River near Green River, 

Wyoming (site 09217000), by the USGS in cooperation with 

the Bureau of Reclamation (table 1). Historically, the monitoring was related to irrigation projects in the Green River 

drainage basin; however, additional current (2009) monitoring efforts have been implemented as part of the WLCI to 

monitor potential effects from energy development projects. 

Water-quality monitoring was implemented on Muddy Creek 

below Young Draw near Baggs, Wyoming (site 09258980), 

hereafter referred to as Muddy Creek near Baggs, Wyoming, 

during 2005 and 2006 by the USGS, in cooperation with the 

BLM and the Wyoming Department of Environmental Quality 

(WDEQ), in response to concerns about energy development in that basin (table 1). Water-quality monitoring for the 

Green River and Muddy Creek includes measurements of 

streamflow, measurements of specific conductance, and the 

collection of samples for laboratory analysis of dissolvedsolids concentrations. Data from these measurements and 

analyses are electronically stored in the USGS National 

Water Information System (NWIS) and are available to the 

public from NWISWeb (U.S. Geological Survey, 2009a) 

at http://waterdata.usgs.gov/nwis/. Because of the need to 

provide real-time dissolved-solids concentrations for the 

Green River and Muddy Creek on the World Wide Web, the 

USGS developed regression equations to estimate dissolvedsolids concentrations on the basis of continuous specific 

conductance using relations between measured specific 

conductance and dissolved-solids concentrations. 

Table 1. Summary of site information for streamflow-gaging stations and water-quality sampling sites on the Green River and Muddy 

Creek, Wyoming, used in this report. 

U.S. Geological 

Survey site number

(fig. 1)

Site name Drainage area 

(square miles)

Continuous 

streamflow data 

(water years)

Continuous 

specific conductance 

data 

(water years)

Discrete waterquality data 

(water years)

09217000 Green River near Green River, 

Wyoming

14,000 1999–2008 2007–08 1999–2008

09258980 Muddy Creek below Young 

Draw near Baggs, Wyoming

1,200 2005–08 2005–08 2006–08
4 Specific Conductance and Dissolved-Solids Characteristics for the Green River and Muddy Creek, Wyoming

Purpose and Scope

The purpose of this report is to describe specific conductance and dissolved-solids characteristics for two streams in 

the WLCI study area in Wyoming. Specifically, this report 

presents characteristics for the Green River near Green River, 

Wyoming, and for Muddy Creek near Baggs, Wyoming, 

including (1) a summary of streamflow data, (2) a summary of 

specific conductance data, (3) a summary of dissolved-solids 

concentrations, and (4) regression relations between specific 

conductance and dissolved solids. The scope includes data 

for water years 1999–2008 for the Green River and for water 

years 2005–08 for Muddy Creek. 

Description of Drainage Basins

The Green River and Muddy Creek drainage basins are 

located in southwestern Wyoming (fig. 1). The drainage basins 

of the Green River and Muddy Creek (table 1) have different 

characteristics, as described in this section of the report.

Green River Drainage Basin

 The Green River is one of the major river basins in 

Wyoming and drains the central part of the WLCI study area. 

The Green River near Green River, Wyoming (site 09217000, 

fig. 1), has a drainage area of about 14,000 square miles (about 

9,740 square miles of contributing drainage area) and drains 

a diverse landscape. Altitudes in the drainage basin range 

from about 6,060 feet above the National Geodetic Vertical 

Datum of 1929 (NGVD 29) at the sampling site to more than 

13,800 feet above NGVD 29 in the Wind River Range. The 

Green River in Wyoming is classified by the WDEQ as class 1 

waters upstream from the New Fork River and as class 2AB 

waters downstream to Flaming Gorge Reservoir (Wyoming 

Department of Environmental Quality, 2001). Designated 

uses of the Green River include drinking water, game fish, 

non-game fish, fish consumption, other aquatic life, recreation, 

wildlife, agriculture, industry, and scenic value. The New 

Fork River, which is a major tributary in the eastern part of 

the upper basin, drains much of the Wind River Range. The 

western part of the upper basin drains the Wyoming Range. 

The Big Sandy River and Bitter Creek drain most of the basin 

between Fontenelle Reservoir and Green River, Wyoming. 

The high-altitude areas of the Green River drainage basin 

are part of the Middle Rockies ecoregion. These areas have 

open forests and foothills that are partly wooded or shrub- and 

grass-covered (Omernick, 1987). The low-altitude areas of the 

Green River drainage basin are part of the Wyoming Basin 

ecoregion, which is largely a broad intermontane basin that is 

covered by arid grasslands and shrublands, supporting bunchgrasses and sagebrush (Omernick, 1987). Annual precipitation in the Green River drainage basin ranges from less than 

8 inches at low altitudes to more than 40 inches in the mountainous areas (Daly and others, 1994). Annual precipitation at 

the climate station at Green River, Wyoming, is 8.11 inches 

for the period of record from 1915–2005 (Western Regional 

Climate Center, 2009). Average monthly maximum temperatures at Green River range from 30.8°C during July to 0.0°C 

during January (Western Regional Climate Center, 2009).

The geology of the Green River drainage basin is diverse. 

The oldest rocks in the basin are Precambrian-era igneous 

and metamorphic rocks that form the core of the Wind River 

Range (Love and Christiansen, 1985). Rock types include 

granite, granodiorite, granite gneiss, and schist. Paleozoicand Mesozoic-era sedimentary rocks, including limestone, 

dolomite, and sandstone, occur in the mountainous areas in 

the northern and western parts of the upper basin. Tertiaryage sedimentary rocks of the Wasatch Formation and the 

Green River Formation, including shale, mudstone, marlstone, siltstone, sandstone, and limestone, underlie much of 

the intermontane basin upstream from Fontenelle Reservoir. 

Downstream from Fontenelle Reservoir, another unit of the 

Green River Formation, the Laney Member, which is an oil 

shale and marlstone, underlies most of the eastern part of the 

basin, and the Bridger Formation, which is a sandstone and 

claystone, underlies much of the western part of the basin. 

Quaternary-age alluvium and colluvium occur in and adjacent 

to stream channels. 

Energy development in the upper Green River drainage basin primarily is associated with two large projects, the 

Pinedale Anticline Oil and Gas Exploration and Development 

Project (Bureau of Land Management, 2000a, 2008c) and 

the Jonah Infill Drilling Project (Bureau of Land Management, 2006a). The Pinedale Anticline Project Area (PAPA) 

encompasses more than 197,000 acres in Sublette County, 

Wyoming, in the eastern part of the Green River drainage 

basin upstream from Fontenelle Reservoir (Bureau of Land 

Management, 2000a). Drainage from the PAPA primarily is 

to the New Fork River and to the Green River. The approved 

project components included 700 producing wells or well pads 

and about 276 miles of access roads (Bureau of Land Management, 2000b). As of November 2006, the PAPA included more 

than 642 producing wells on 340 well pads, and the project 

was revised to include as many as 4,399 additional wells on 

no more than 600 total well pads, construction of new roads, 

and a pipeline corridor (Bureau of Land Management, 2008c, 

2008d). Produced waters from the PAPA generally are used for 

industrial purposes, are treated and used for drilling and dust 

control, or are reinjected. Increased dissolved-solids concentrations in streams as a result of soil disturbance and increased 

dissolved-solids concentrations in shallow aquifers that are in 

connection with streams were identified as potential waterquality concerns (Bureau of Land Management, 2008c). 

The Jonah Infill Drilling Project Area (JIDPA) encompasses about 30,500 acres in Sublette County, Wyoming 

(Bureau of Land Management, 2006a). The JIDPA is drained 

by intermittent and ephemeral streams that are tributaries 

of the New Fork River and the Green River upstream from 

Fontenelle Reservoir and of the Big Sandy River downstream 

from Fontenelle Reservoir. The project components for the 
Methods 5

JIDPA includes drilling as many as 3,100 additional oil and 

gas wells within the existing JIDPA area and limits surface 

disturbance to a maximum of 14,030 acres (Bureau of Land 

Management, 2006b). Salt-loading to streams was identified 

as a concern because of potential disturbance of saline soils in 

the project area; however, salinity models predicted that this 

disturbance would not increase dissolved solids to the Colorado River from the Green River or Big Sandy River (Bureau 

of Land Management, 2006a). 

Muddy Creek Drainage Basin

The Muddy Creek drainage basin is a much smaller 

basin and generally is physiographically and geologically 

less diverse than the Green River drainage basin. Muddy 

Creek is a tributary of the Little Snake River and drains about 

1,200 square miles at site 09258980 near Baggs, Wyoming, 

in the southeastern part of the WLCI study area (fig. 1). 

Altitudes in the drainage basin range from about 6,270 feet 

above NGVD 29 at the sampling site to more than 8,300 feet 

above NGVD 29 in the upland area. The northern border of 

the drainage basin is part of the boundary of the Great Divide 

Basin and includes an upland area called the Atlantic Rim. 

The Sierra Madre and Continental Divide form the northeast boundary of the drainage basin. The western part of the 

Muddy Creek drainage basin is part of the Washakie structural 

basin (Bartos and others, 2006). Muddy Creek is classified 

by the WDEQ as class 2AB waters (Wyoming Department 

of Environmental Quality, 2001). Designated uses include 

drinking water, game fish, non-game fish, fish consumption, 

other aquatic life, recreation, wildlife, agriculture, industry, 

and scenic value. The WDEQ has listed the use support of 

Muddy Creek as “threatened” since 1996 because of habitat 

degradation associated with grazing (Wyoming Department 

of Environmental Quality, 2008). The Little Snake Resource 

Conservation District, the BLM, land owners, and other 

stakeholders have been involved in a Coordinated Resource 

Management process in the basin to improve water quality and 

riparian habitat problems (Ellison and others, 2008; Wyoming 

Department of Environmental Quality, 2008). Colorado River 

cutthroat trout have been reintroduced in the upper part of the 

Muddy Creek drainage basin as part of the process (Wyoming 

Department of Environmental Quality, 2008).

The entire Muddy Creek drainage basin is part of the 

Wyoming Basin ecoregion and is mostly covered by arid 

grasslands and shrublands (Omernick, 1987). Annual precipitation in the Muddy Creek drainage basin ranges from about 8 

to 10 inches at low altitudes to more than 20 inches in upland 

areas (Daly and others, 1994). Muddy Creek is perennial in 

the upper part of the drainage basin near the upland areas 

and flows intermittently downstream where groundwater 

discharge sometimes is not sufficient to sustain streamflow. 

Annual precipitation at the climate station at Baggs, Wyoming, 

is 10.72 inches for the period of record from 1979–2005 

(Western Regional Climate Center, 2009). Average monthly 

maximum temperatures at Baggs range from 30.2°C during 

July to 0.6°C during January (Western Regional Climate 

Center, 2009).

The bedrock geology of the Muddy Creek drainage basin 

is dominated by Cretaceous-age and Tertiary-age sedimentary 

rocks (Love and Christiansen, 1985). The bedrock geology of 

the eastern part of the Muddy Creek drainage basin is predominantly Cretaceous-age sedimentary rocks including the Steele 

Shale, Mesaverde Formation, and Lewis Shale of marine 

origin, and the Lance Formation of fluvial origin (Bartos and 

others, 2006). The bedrock geology immediately adjacent to 

Muddy Creek includes Tertiary-age sedimentary rocks of the 

Fort Union and Wasatch Formations. The Fort Union Formation includes sandstone, shale, and thin coal beds (Love and 

Christiansen, 1985). The Wasatch Formation is composed 

primarily of mudstone and sandstone. The Green River Formation, which is composed primarily of shale, mudstones, and 

sandstone, occurs in the western part of the drainage basin. 

Quaternary-age alluvium and colluvium occur in and adjacent 

to stream channels.

Energy development projects in the Muddy Creek drainage basin include the Continental Divide-Creston Natural 

Gas Development Project, which is mostly in the western 

part of the drainage basin (Bureau of Land Management, 

2006c), and the Atlantic Rim Natural Gas Field Development 

Project, which is mostly in the eastern part of the drainage 

basin (Bureau of Land Management, 2006d). The Continental Divide-Creston Natural Gas Development Project 

encompasses about 1,100,000 acres and involves drilling and 

developing as many as 8,950 wells and constructing associated facilities, such as roads and compressor stations. Shortterm surface disturbance areas associated with well pads, road 

building, pipelines, and other facilities are estimated to be 

about 47,060 acres for the entire project area (Bureau of Land 

Management, 2006c). Reinjection of water produced during 

gas development is proposed, and surface discharges are not 

planned. The Atlantic Rim Project Area encompasses about 

270,080 acres, of which about 69 percent is in the Muddy 

Creek drainage basin (Bureau of Land Management, 2006d). 

The project components include drilling about 2,000 gas wells 

and limiting surface disturbance to a maximum of 7,600 acres 

at any given time (Bureau of Land Management, 2007). Gas 

development in the Muddy Creek drainage basin includes 

drilling conventional natural gas wells and coalbed natural 

gas wells. Dissolved-solids loading from surface discharges of 

produced waters is not anticipated because most of the water 

is reinjected, with the exception of small amounts of surface 

discharges that are allowed under existing permits. 

Methods

Methods are described for collection of continuous 

and discrete streamflow and specific conductance data 

and for collection of discrete water-quality samples for 

dissolved solids determination. The data-analysis methods 
6 Specific Conductance and Dissolved-Solids Characteristics for the Green River and Muddy Creek, Wyoming

for statistically summarizing data and determining relations 

between specific conductance and dissolved solids also are 

described. 

Data Collection

Data collection at the sampling sites on the Green River 

(site 09217000) and Muddy Creek (site 09258980) included 

continuous and discrete measurements of streamflow, continuous and discrete measurements of specific conductance, and 

discrete collection of water-quality samples. Methods for the 

collection and analysis of streamflow data are described in 

Rantz and others (1982). Continuous streamflow data used 

in this report were collected during water years 1999–2008 

on the Green River (site 09217000) and during water years 

2005–08 on Muddy Creek (site 09258980). Although some 

streamflow data were collected during water year 2004 at 

site 09258980, these data are not included in this report 

because a complete water year record was not available. 

Instantaneous streamflow generally was measured when 

water-quality samples were collected. Instantaneous streamflow is reported as cubic feet per second (ft3

/s) and total annual 

streamflow, or annual runoff, is reported in acre-feet (acre-ft). 

Instruments for continuous measurement of specific 

conductance were installed during water year 2007 on the 

Green River (site 09217000) and during water year 2005 on 

Muddy Creek (site 09258980). Operation of the instruments 

is described in Wagner and others (2006). Continuous specific 

conductance was measured only during ice-free periods, 

which generally were from about March or April to October or 

November, and the data are summarized in this report as daily 

mean values. Discrete measurements of specific conductance 

were made throughout the water year when water-quality 

samples were collected and followed methods described in 

the National Field Manual for the Collection of Water-Quality 

Data (U.S. Geological Survey, 1997–2009). Discrete measurements either were made instream by using a multiprobe meter 

or were made by using a probe in an aliquot of water that was 

composited in a churn for water-quality samples. Daily mean 

and discrete values of specific conductance are reported in 

microsiemens per centimeter at 25°C (μS/cm). 

Water-quality samples were collected and processed by 

using methods described in the National Field Manual for the 

Collection of Water-Quality Data (U.S. Geological Survey, 

1997–2009). An equal-width-increment sampling technique 

with depth-integrating samplers was used when flow conditions were adequate. A hand-dip method at the centroid of 

flow was used for collecting samples on Muddy Creek when 

stream conditions were too shallow for a sampler. Samples 

for dissolved-solids analyses were filtered onsite by using a 

0.45-micron pore-size filter and were shipped to the USGS 

National Water Quality Laboratory in Denver, Colorado, for 

analysis. Dissolved-solids concentrations can be determined 

by a sum-of-constituents method, in which a value is calculated by summing the concentrations of individual dissolved 

constituents, including major cations, major anions, nonionic 

silica, and selected trace elements. Dissolved-solids concentrations can be directly measured by a residue-on-evaporation 

method at 180°C (Fishman and Friedman, 1989). Because 

most of the dissolved solids in stream waters are the major 

ions and nonionic silica, the two methods generally produce 

comparable results; however, the residue-on-evaporation 

method may produce slightly higher concentrations than the 

sum-of-constituents method because all the dissolved solids 

present in the water are part of the residue-on-evaporation 

analysis. The residue-on-evaporation method was used for 

samples collected from the Green River (site 09217000) 

during water years 2001–08. The sum-of-constituents method 

was used for samples collected during 1999–2000 because 

residue-on-evaporation analyses were not available. The 

residue-on-evaporation method was used for all samples 

collected from Muddy Creek (site 09258980) during water 

years 2006–08. Dissolved-solids concentrations are reported in 

milligrams per liter (mg/L).

Data Analysis

Data for this report were summarized by using several 

statistical techniques. Descriptive summary statistics were 

computed for specific conductance and for dissolved-solids 

concentrations, and are displayed as boxplots. The lower and 

upper edges of the box indicate the 25th and 75th percentiles, 

respectively, and the median (50th percentile) is a line within 

the box. The whiskers extend from the first quartile to the 

minimum value and from the third quartile to the maximum 

value, unless the minimum or maximum value is more than 

1.5 times the interquartile range (IQR) from that quartile. In 

that case, the whiskers extend to the lowest or highest value 

within 1.5 times the IQR. Values outside of this range are 

called outliers and are shown as individual points. 

Linear regression is a statistical technique that can be 

used to determine the relation between two constituents. The 

use of this relation can be helpful in estimating data where 

one constituent is measured (continuous specific conductance, 

in this case) but the other (continuous dissolved solids) is not 

(Helsel and Hirsch, 1992). The simple linear regression equation can be expressed as

yi = mxi + b + ei i = 1,2,....n, (1)

where

yi is the ith observation of the dependent 

variable; 

m is the slope;

xi is the ith observation of the independent, or 

explanatory, variable;

b is the y-axis intercept;

ei is the random error for the ith observation; 

and

n is the sample size. 
Specific Conductance and Dissolved-Solids Characteristics 7

The terms m and b are the parameters that need to be estimated from the data. The most common estimation technique 

is called ordinary least squares. S-PLUS statistical software 

(TIBCO Software Inc., 2008) was used to generate the 

regression equations in this report. Plots of the residuals from 

the regression equations were inspected for normality. The 

parameters displayed in this report for the regression equations include the mean square error (MSE), which is a measure 

of the variance between estimated and observed values; the 

coefficient of determination (R2

), which is the fraction of the 

variance explained by the regression; and the p-value, which is 

the probability that the slope is zero, indicating that there is no 

correlation between the two variables. The smaller the p-value 

is, the larger the probability that the two variables are related. 

For this report, a relation was determined to be statistically 

significant at the 95-percent confidence level. Therefore, if 

the calculated p-value was less than (<) 0.05, the relation is 

significant. Prediction intervals were determined to evaluate 

uncertainty of the estimated values by using the regression 

equation for the sites with continuous specific conductance 

monitors (Helsel and Hirsch, 1992). For this report, the 

95-percent prediction intervals were determined for the regression equation for each site. For a given specific conductance 

value, the 95-percent prediction interval represents the range 

of dissolved-solids concentrations that is expected to occur 

95 percent of the time for a given specific conductance value.

Specific Conductance and DissolvedSolids Characteristics

Specific conductance and dissolved-solids characteristics 

are summarized in the following sections. Linear regression 

relations between specific conductance and dissolved solids 

also are presented. Streamflow conditions are summarized in 

the following section to provide context for the water-quality 

data. 

Streamflow Conditions and Influence

Hydrologic conditions are important factors in waterquality variability and are described here to provide perspective on the potential annual and seasonal differences in water 

quality. Annual runoff for the Green River near Green River, 

Wyoming (site 09217000), ranged from about 417,100 acre-ft 

during water year 2002 to about 1,718,000 acre-ft during water 

year 1999 (fig. 2). Annual runoff for the Green River during 

the study period (water years 1999–2008) generally was less 

than the long-term period-of-record mean annual runoff; 

mean annual runoff was about 900,000 acre-ft for the study 

period and 1,160,000 acre-ft for the period of record (water 

years 1952–2008). Mean annual runoff of 1,133,000 acre-feet 

for USGS streamflow-gaging station 09211200 (fig. 1) on 

the Green River immediately downstream from Fontenelle 

Reservoir (for the period of record, water years 1964–2008; 

U.S. Geological Survey, 2009b) accounts for about 98 percent 

of the streamflow of Green River near Green River, Wyoming 

(site 09217000); however, the upper part of the drainage 

basin accounts for only about 31 percent of the total drainage 

area at site 09217000. The upper part of the drainage basin 

includes the high-altitude area in the mountain ranges, which 

have higher precipitation and lower evapotranspiration than 

the low-altitude parts of the drainage basin. Although the Big 

Sandy River and Bitter Creek drain much of the low-altitude 

parts of the basin, their combined annual runoff generally 

accounts for only about 2 percent of the annual runoff of the 

Green River near Green River, Wyoming (site 09217000). 

Irrigation is a consumptive use of part of the streamflow in the 

Big Sandy River drainage basin. 

Muddy Creek is a much smaller drainage basin and has 

substantially less annual runoff compared to the Green River. 

Annual runoff for Muddy Creek (site 09258980) ranged 

from about 4,510 acre-ft during water year 2006 to about 

18,830 acre-ft during water year 2008 (fig. 2). Comparisons 

to historical mean annual runoff cannot be made for Muddy 

Creek because the period of record is limited to water years 

2005–08; however, precipitation was less than average for that 

same period at a climate station in Baggs, Wyoming (Western 

Regional Climate Center, 2009). Because Muddy Creek drains 

mostly low- to mid-altitude areas, which generally have low 

annual precipitation, the annual runoff per unit area for the 

Muddy Creek drainage basin (0.20 inch at site 09258980) is 

substantially less than that for the Green River drainage basin 

(1.55 inches at site 09217000). 

Instantaneous streamflow can vary by orders of magnitude during a given year; thus, it is important to collect 

water-quality samples throughout the entire range of streamflows during a water year to adequately characterize extremes, 

seasonal differences, and average conditions. Instantaneous 

streamflow measurements during sample collection were 

compared with daily mean streamflow for selected sampling 

sites to illustrate the range of hydrologic conditions sampled at 

each site during the study period (fig. 3). 

Daily mean streamflow for the Green River 

(site 09217000), which is largely controlled by releases 

from Fontenelle Reservoir, ranged from 390 to 9,220 ft3/s 

(U.S. Geological Survey, 2009a). Instantaneous streamflows 

measured during sampling events at this site varied widely 

from 279 ft3

/s to 3,880 ft3/s. The highest streamflows measured 

for the Green River generally were in late spring or early 

summer as a result of runoff from melting snow in the mountainous parts of the upper basin. 

Daily mean streamflow for Muddy Creek (site 09258980) 

ranged from 0.07 to 499 ft3/s (fig. 3). Instantaneous streamflows measured during sampling events at this site varied 

widely from 0.09 to 124 ft3

/s. The highest streamflows 

measured for Muddy Creek generally were in late winter 

or early spring when streamflows are increased as a result 

of melting snow at low to middle altitudes. Streamflow for 

Muddy Creek also increases during summer in response 
8 Specific Conductance and Dissolved-Solids Characteristics for the Green River and Muddy Creek, Wyoming

to thunderstorms. The streamflow typically responds very 

quickly to precipitation events; thus, collection of samples 

associated with extreme high-flows is difficult. 

Streamflows at both sites tend to decrease in late summer 

through winter when groundwater discharge provides most 

of the base flow. Precipitation in fall and winter generally 

occurs in the form of snow, and surface-runoff events during 

this period are infrequent as a result of low temperatures 

(Mason and Miller, 2005). Water-quality samples collected 

from the two sites generally were representative of a wide 

variety of water-quality conditions because, with the exception of extreme high flows, a wide variety of streamflows were 

sampled. ANNUAL RUNOFF, IN ACRE-FEET

WATER YEAR

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Site 09217000

Site 09258980

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

0

200,000

400,000

600,000

800,000

1,000,000

1,200,000

1,400,000

1,600,000

1,800,000

2,000,000

Figure 2. Annual runoff for the Green River (site 09217000) and Muddy Creek (site 09258980), 

Wyoming, water years 1999–2008.
Specific Conductance and Dissolved-Solids Characteristics 9

2001 2005

STREAMFLOW, IN CUBIC FEET PER SECOND

100

200

500

1,000

2,000

5,000

10,000

15,000

O N D

2006

J F M A M J J A S O N D

2007

J F M A M J J A S O N D

2008

J F M A M J J A S

WATER YEAR

WATER YEAR

0.01

0.02

0.05

0.1

0.2

0.5

1

2

5

10

20

50

100

200

500

800

Daily mean streamflow

Instantaneous streamflow

EXPLANATION

Site 09217000

Site 09258980

1999 2000 2002 2003 2004 2006 2007 2008

Figure 3. Daily mean streamflow and instantaneous streamflow during water-quality sampling at the 

Green River (site 09217000) and Muddy Creek (site 09258980), Wyoming, water years 1999–2008.
10 Specific Conductance and Dissolved-Solids Characteristics for the Green River and Muddy Creek, Wyoming

Specific Conductance Characteristics

Specific conductance was measured by using continuous 

monitors during ice-free periods and by discrete measurements 

during water-quality sample collection throughout the water 

year (fig. 4). Daily mean specific conductance is summarized 

for water years 2007–08 for the Green River near Green River, 

Wyoming (site 09217000), and for water years 2005–08 for 

Muddy Creek near Baggs, Wyoming (site 09258980). Discrete 

specific conductance values were measured during water years 

1999–2008 at site 09217000 and during water years 2006–08 

at site 09258980. 

Specific conductance values (figs. 4 and 5) generally 

were less varied and lower for the Green River than for 

Muddy Creek. Daily mean specific conductance values for the 

Green River ranged from 316 to 779 μS/cm during water years 

2007–08 (fig. 4). Discrete values during this period ranged 

from 332 to 587 μS/cm. Discrete values for the entire study 

period (water years 1999–2008) for the Green River ranged 

from 330 to 862 μS/cm, with a median value of 492 μS/cm 

(fig. 5). Daily mean specific conductance values for Muddy 

Creek ranged from 370 to 4,340 μS/cm during water years 

2005–08 (fig. 4). Discrete values during water years 2006–08 

for Muddy Creek ranged from 448 to 3,640 μS/cm, with a 

median value of 1,445 μS/cm (fig. 5). Because of the greater 

measurement frequency with the use of continuous monitors, a 

wider variety of water-quality conditions can be characterized 

in streams than is possible with discrete sampling, especially 

for small streams that respond quickly to changing hydrologic 

conditions.

A general seasonal pattern is evident in the specific 

conductance data for both sites, particularly for discrete 

values, though daily mean values were not available for winter 

months. Specific conductance values tended to be low during 

periods of high streamflow in late spring to early summer 

when surface runoff, which has only brief contact with basin 

materials, composes a large part of the streamflow. In contrast, 

specific conductance values tended to be high in late summer 

through winter because groundwater, which has been in 

contact with basin materials for a long time and is typically 

higher in specific conductance than surface runoff, composes 

a large part of the streamflow. A longer term pattern between 

water years of increasing or decreasing specific conductance 

values was not observed for the Green River or Muddy Creek. 

Dissolved-Solids Characteristics

Samples were collected and analyzed for dissolvedsolids concentrations during water years 1999–2008 for the 

Green River near Green River, Wyoming (site 09217000), and 

during water years 2006–08 for Muddy Creek near Baggs, 

Wyoming (site 09258980). As with specific conductance, 

dissolved-solids concentrations were less varied and generally lower for Green River than for Muddy Creek (fig. 6). 

Dissolved-solids concentrations ranged from 187 to 594 mg/L 

in samples collected from the Green River during water years 

1999–2008. Dissolved-solids concentrations ranged from 293 

to 2,485 mg/L in samples collected from Muddy Creek during 

water years 2006–08. The median dissolved-solids concentration for the Green River was 318 mg/L, and the median 

concentration for Muddy Creek was 943 mg/L. 

The differences in dissolved-solids concentrations 

between samples collected from the Green River and samples 

collected from Muddy Creek reflect the different basin characteristics. As described in the section “Streamflow Conditions and Influence,” most of the streamflow in the Green 

River originates from the upper part of the drainage basin 

upstream from Fontenelle Reservoir; thus, the water quality 

at site 09217000 also is influenced by the upper basin. For 

example, dissolved-solids concentrations in samples collected 

from Pine Creek, which is a mountain headwater stream in 

the northern part of the basin, ranged from 9.0 to 15 mg/L 

during water year 2008 (U.S. Geological Survey, 2009b). 

Dissolved-solids concentrations in the upper part of the Green 

River drainage basin near the PAPA energy development area 

typically are less than 100 mg/L (Bureau of Land Management, 2008d). The low dissolved-solids concentrations in 

streams in the upper basin are a result, in part, of the rocks 

that constitute the mountainous parts of the basin, particularly 

the Precambrian-era rocks of the Wind River Range. A recent 

Colorado River Basin study determined that Precambrian-era 

and Paleozoic-era rocks, which are resistant to physical weathering and chemical dissolution, contribute about 8 percent of 

the dissolved solids to streams in the Green River drainage 

basin in Wyoming (Anning and others, 2007). In addition to 

the geology, the high annual precipitation and steep gradient 

in the upper basin produce relatively fast stream velocities, 

which result in a short contact time between stream waters and 

basin materials. 

Dissolved-solids concentrations generally increase 

downstream from Fontenelle Reservoir to Green River, 

Wyoming. Anning and others (2007) reported that the median 

concentration increased from 237 mg/L at a site downstream 

from Fontenelle Reservoir (site 09211200) to 359 mg/L near 

Green River, Wyoming (site 09217000). The Big Sandy River 

substantially contributes to the dissolved-solids concentration in the reach downstream from Fontenelle Reservoir 

and upstream from Green River, Wyoming (DeLong, 1977). 

Dissolved-solids concentrations for the Big Sandy River 

(site 09216050) upstream from its mouth at the Green River 

ranged from 187 to 7,840 mg/L during water years 1975–99 

(Anning and others, 2007). Much of the Big Sandy drainage basin is underlain by the Laney Member of the Green 

River Formation (Love and Christiansen, 1985). Groundwater 

associated with the Laney Member generally is of marginal to 

poor quality because of high sulfate concentrations and high 

dissolved-solids concentrations (Mason and Miller, 2005; 

Anning and others, 2007), and could affect the quality of the 

Big Sandy River, particularly during low-flow conditions. 

Soils associated with the Tertiary-age rocks that have naturally 

high salt content and with irrigated agriculture also have been 
Specific Conductance and Dissolved-Solids Characteristics 11

identified as sources of dissolved solids in the lower parts of 

the Green River drainage basin (Bureau of Land Management, 2000a). Anning and others (2007) determined that 

Tertiary-age rocks contribute about 56 percent of the dissolved 

solids in the Green River drainage basin in Wyoming. Salinity control measures have been implemented to reduce 

dissolved-solids concentrations in the Big Sandy drainage 

basin (Wyoming Department of Environmental Quality, 2008). 

Anning and others (2007) reported that dissolved-solids 

concentrations and adjusted annual dissolved-solids concentrations have decreased by 15 percent for the Big Sandy River 

(site 09216050) and by 25 percent for the Green River near 

Green River, Wyoming (site 09217000) for their study period 

of 1998–2003 when compared to a base period from 1974–79. 

Adjusted annual concentrations reported by Anning and others 

(2007) have undergone a statistical procedure to remove the 

variation in dissolved solids that is a function of streamflow. 

2006 2007

100

200

300

400

500

600

700

800

900

2005

J J A S O N D

2006

J F M A M J J A S O N D

2007

J F M A M J J A S O N D

2008

J F M A M J J A S

WATER YEAR

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

5,000

Site 09217000

Site 09258980

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER AT 25 DEGREES CELSIUS

1999 2000 2001 2002 2003 2004 2005 2008

Discrete value 

Daily mean value

Specific conductance 

EXPLANATION

Figure 4. Daily mean and discrete values of specific conductance during water-quality sampling at the Green River 

(site 09217000) and Muddy Creek (site 09258980), Wyoming, water years 1999–2008.
12 Specific Conductance and Dissolved-Solids Characteristics for the Green River and Muddy Creek, Wyoming

The Muddy Creek drainage basin is underlain entirely 

by Cretaceous-age and Tertiary-age sedimentary rocks, which 

are more soluble than the Precambrian-era rocks of the upper 

Green River drainage basin. In addition, the Muddy Creek 

drainage basin has lower annual precipitation and higher 

evapotransipration than much of the Green River drainage 

basin. These characteristics, combined with lower gradients 

that produce relatively slow stream velocities and longer 

contact times between stream waters and basin materials, 

result in high dissolved-solids concentrations in Muddy Creek. 

In contrast to the many perennial tributaries of the Green 

River, most tributaries of Muddy Creek are intermittent or 

ephemeral streams. The flow characteristics of intermittent and 

ephemeral streams affect the water quality of these streams. 

During periods of little to no precipitation and low runoff, 

salts tend to accumulate in channels and on other surfaces. 

As a result, dissolved solids can be flushed to streams during 

precipitation and increased runoff, enriching the dissolvedsolids concentrations of the stream (DeLong, 1986), rather 

than being diluted by the precipitation as typically occurs. 

Regression Equations for Estimating Dissolved 

Solids

Linear regression is a technique available for estimating one water-quality variable on the basis of another waterquality variable. Other studies have used specific conductance 

to estimate other water-quality constituents where water-quality concerns have been raised because of energy development. 

For example, sodium-adsorption ratios have been estimated 

from specific conductance values for sites in the Tongue River 

and Powder River drainage basins, where sodium concerns 

have been raised because of coalbed natural gas development 

(Clark and Mason, 2006; Cannon and others, 2007). Many 

water managers use dissolved-solids concentrations instead of 

specific conductance values because dissolved-solids concentrations are needed for calculating salt loads, which are a 

concern to water managers in the Colorado River Basin. 

The relations between specific conductance (independent variable) and dissolved-solids concentration (dependent 

Figure 5. Specific conductance during water-quality sampling at the Green River (site 09217000), water years 1999–2008, and Muddy 

Creek (site 09258980), water years 2006–08, Wyoming.

SITE

0

1,000

2,000

3,000

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER AT 25 DEGREES CELSIUS 

09217000 09258980

4,000 EXPLANATION

Number of samples 

75th percentile

Median

25th percentile

Outlier data value greater than 1.5 times the interquartile range

Value less than or equal to 1.5 times the interquartile range 

 from the third quartile

Value less than or equal to 1.5 times the interquartile range 

 from the first quartile

Interquartile range

(34) (34)

(60)
Specific Conductance and Dissolved-Solids Characteristics 13

variable) were graphically inspected for discrete samples 

collected from the Green River near Green River, Wyoming 

(site 09217000), and Muddy Creek near Baggs, Wyoming 

(site 09258980, fig. 7). As expected, strong linear relations 

exist between specific conductance and dissolved-solids 

concentration; thus, linear regression equations were developed for the sites (table 2). Relations between specific 

conductance and dissolved-solids concentration were statistically significant for the Green River (site 09217000, p-value 

<0.001) and Muddy Creek (site 09258980, p-value <0.001); 

therefore, specific conductance can be used as a surrogate to 

estimate the dissolved-solids concentration. About 95 percent 

of the variance in dissolved solids can be explained by the 

regression with specific conductance for the Green River 

(site 09217000), and more than 99 percent of the variance 

in dissolved solids can be explained by the regression with 

specific conductance for Muddy Creek (site 09258980). The 

larger MSE for Muddy Creek, relative to the Green River, 

is expected because of the larger variance of environmental 

concentrations in samples from Muddy Creek compared to 

those from the Green River.

Linear regression equations were used to estimate 

dissolved-solids concentrations for the periods when daily 

mean specific conductance values were available for the 

Green River and Muddy Creek. Estimated dissolved-solids 

concentrations from the regression equation were compared 

to the measured dissolved-solids concentrations in the 

discrete samples from both sites (fig. 8). For the Green River 

(site 09217000), measured concentrations for discrete samples 

generally covered the range of estimated concentrations during 

water year 2008. During water year 2007, measured concentrations from discrete samples were not available for some 

periods when high specific conductance was measured on 

the Green River, and correspondingly when high dissolvedsolids concentrations would have occurred; therefore, the 

discrete samples do not fully represent the range of concentrations that occurred during that water year. For Muddy Creek 

(site 09258980), measured dissolved-solids concentrations 

for discrete samples generally covered the range of estimated 

concentrations during water year 2006 and water year 2008; 

however, measured concentrations for discrete samples 

were not available for some periods when high specific 

Figure 6. Dissolved-solids concentrations for samples collected during water-quality sampling at the Green River (site 09217000), 

water years 1999–2008, and Muddy Creek (site 09258980), water years 2006–08, Wyoming.

SITE

0

1,000

2,000

4,000

DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

09217000 09258980

3,000

EXPLANATION

Number of samples 

75th percentile

Median

25th percentile

Outlier data value greater than 1.5 times the interquartile range

Interquartile range

(34)

(34)

(60)

Value less than or equal to 1.5 times the interquartile range 

 from the third quartile

Value less than or equal to 1.5 times the interquartile range 

 from the first quartile
14 Specific Conductance and Dissolved-Solids Characteristics for the Green River and Muddy Creek, Wyoming

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900 1,000

DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

SPECIFIC CONDUCTANCE, IN MICROSIEMENS PER CENTIMETER AT 25 DEGREES CELSIUS

Site 09217000

95-percent prediction interval

Regression line

Sample

95-percent prediction interval

Regression line

Sample

DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

Site 09258980

0

400

800

1,200

1,600

2,000

2,400

2,800

0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000 2,200 2,400 2,600 2,800 3,000 3,200 3,400 3,600 3,800 4,000

Figure 7. Relations between specific conductance and dissolved-solids concentration for the Green River (site 09217000), water 

years 1999–2008, and Muddy Creek (site 09258980), water years 2006–08, Wyoming.
Specific Conductance and Dissolved-Solids Characteristics 15

DISSOLVED SOLIDS, IN MILLIGRAMS PER LITER

2004 2005 2006 2007 2008

100

150

200

250

300

350

400

450

500

550

600

650

2005

1999 2000 2001 2002 2003

J J A S O N D

2006

J F M A M J J A S O N D

2007

J F M A M J J A S O N D

2008

J F M A M J J A S

WATER YEAR

0

500

1,000

1,500

2,000

2,500

3,000

3,500

Measured dissolved-solids concentration for a discrete sample

Estimated dissolved-solids concentration from continuous 

 measurements of specific conductance

EXPLANATION

Site 09217000

Site 09258980

Figure 8. Measured and estimated dissolved-solids concentrations for the Green River (site 09217000) and Muddy Creek 

(site 09258980), Wyoming, water years 1999–2008.

Table 2. Regression equations for estimates of dissolved-solids concentration for the Green River 

(site 09217000) and Muddy Creek (site 09258980), Wyoming.

[DS, dissolved-solids concentration in milligrams per liter; SC, specific conductance in microsiemens per centimeter 

at 25 degrees Celsius; MSE, mean square error; R2, coefficient of determination; <, less than]

Site number

(fig. 1) Equation MSE R2 p-value

09217000 DS = 0.7057(SC) - 31.79 256 0.945 <0.001

09258980 DS = 0.6920(SC) - 30.24 1,292 .996 <.001
16 Specific Conductance and Dissolved-Solids Characteristics for the Green River and Muddy Creek, Wyoming

conductance was measured, and correspondingly when high 

dissolved-solids concentrations would have occurred, during 

water year 2007. Dissolved-solids concentrations analyzed 

in samples collected from Muddy Creek (site 09258980) 

during water year 2007 ranged from 293 to 1,870 mg/L, 

whereas estimated concentrations ranged from about 225 to 

2,970 mg/L. Using continuous specific conductance data to 

estimate dissolved-solids loads likely produces more accurate 

load values because loads computed using only measurements 

from discrete samples may underestimate (or overestimate) 

loads during certain periods. 

With the use of continuous-recording water-quality 

instruments that transmit data to satellites, specific conductance data are available in near real-time on NWISWeb (U.S. 

Geological Survey, 2009a). Regression equations (table 2) 

can be incorporated into the NWISWeb software to estimate dissolved-solids concentrations for site 09217000 and 

site 09258980. Using continuous specific conductance values 

to estimate dissolved-solids concentrations in real-time on 

the World Wide Web increases the amount and improves the 

timeliness of data available to water managers for assessing 

dissolved-solids concentrations in the Colorado River Basin.

between measured specific conductance and dissolved-solids 

concentrations. 

Instantaneous streamflows measured during sampling 

events were highly varied and ranged from 279 cubic feet 

per second (ft3/s) to 3,880 ft3/s for the Green River and from 

0.09 to 124 ft3/s for Muddy Creek. The highest streamflows 

measured for the Green River generally were in the late spring 

or early summer as a result of runoff from melting snow in 

the mountainous parts of the upper basin. The highest streamflows for Muddy Creek generally were during late-winter 

or early-spring sampling events as a result of the melting of 

snow at low to middle altitudes. Streamflows at both sites 

tend to decrease in late summer through winter when groundwater discharge provides most of the base flow. With the 

exception of extreme high flows, water-quality samples were 

collected from a wide range of streamflows at the two sites 

and thus were representative of a wide range of water-quality 

conditions.

Specific conductance and dissolved-solids concentrations were less varied and generally lower for the Green River 

than for Muddy Creek. The median specific conductance 

value for the Green River was 492 microsiemens per centimeter at 25 degrees Celsius (μS/cm), and the median value 

for Muddy Creek was 1,445 μS/cm. Discrete values for the 

entire study period (water years 1999–2008) ranged from 330 

to 862 μS/cm for the Green River, and discrete values during 

water years 2006–08 ranged from 448 to 3,640 μS/cm for 

Muddy Creek.

The median dissolved-solids concentration for the site 

on the Green River was 318 milligrams per liter (mg/L), and 

the median concentration for the site on Muddy Creek was 

943 mg/L. Dissolved-solids concentrations ranged from 187 

to 594 mg/L in samples collected from the Green River during 

water years 1999–2008. Dissolved-solids concentrations 

ranged from 293 to 2,485 mg/L in samples collected from 

Muddy Creek during water years 2006–08. The difference 

in dissolved-solids concentrations in samples collected from 

the Green River compared to samples collected from Muddy 

Creek reflect the different basin characteristics.

Relations between specific conductance and dissolvedsolids concentration were statistically significant for the Green 

River (p-value less than 0.001) and Muddy Creek (p-value 

less than 0.001); therefore, specific conductance can be used 

to estimate dissolved-solids concentration. Using continuous specific conductance values to estimate dissolved-solids 

concentrations in real-time on the World Wide Web increases 

the amount and improves the timeliness of data available to 

water managers for assessing dissolved-solids concentrations 

in the Colorado River Basin. 

Summary

Southwestern Wyoming is an area of diverse scenery, 

wildlife, and natural resources that is actively undergoing energy development. The Department of the Interior’s 

Wyoming Landscape Conservation Initiative is a long-term 

science-based effort to assess and enhance aquatic and terrestrial habitats at a landscape scale, while facilitating responsible 

energy development through local collaboration and partnerships. Water-quality monitoring (including streamflow, specific 

conductance, and dissolved solids) has been conducted by 

the U.S. Geological Survey on the Green River near Green 

River, Wyoming, and Muddy Creek near Baggs, Wyoming. 

This monitoring, which is being conducted in cooperation with 

State and other Federal agencies and as part of the Wyoming 

Landscape Conservation Initiative, is in response to concerns 

about potentially increased dissolved solids in the Colorado 

River Basin as a result of energy development. Because of 

the need to provide real-time dissolved-solids concentrations for the Green River and Muddy Creek on the World 

Wide Web, the U.S. Geological Survey developed regression equations to estimate dissolved-solids concentrations on 

the basis of continuous specific conductance using relations 
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