science for a changing world

U.S. Geological Survey Monitoring of Powder River Basin

Stream-Water Quantity and Quality

By Melanie L. Clark, Kirk A. Miller, and Myron H. Brooks

U.S. Department of the Interior

U.S. Geological Survey

Water-Resources Investigations Report 01-4279

Cheyenne, Wyoming, December 2001

Figure 1. Major-ion chemistry for samples from the

Powder River at Arvada, Wyo., July 21, 1999 (Swanson

and others, 2000b) and CBM well 441451105375501,

June 18, 1999 (Swanson and others, 2000a).

0 0

4 4

8 8

12 12

CONCENTRATION, IN

MILLIEQUIVALENTS PER LITER

SODIUM-ADSORPTION RATIO

MAJOR IONS AND

SODIUM-ADSORPTION RATIO (SAR)

16 16

20 20

Ca+2 Mg+2 Na+ Cl SO42 HCO3

Powder River

CBM 441451105375501

SAR

Streamflow-gaging

station 06317000,

Powder River at

Arvada, Wyo. (site 32)

1

INTRODUCTION

Ranchers, water managers, and others are concerned about

the quality of coalbed methane (CBM) discharge waters and

the effect they may have on stream-water quality in the

Powder River Basin. During the production of CBM, water

is pumped from wells, lowering hydrostatic pressure in the

coal beds and allowing the previously confined methane that

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

flow (DeBruin and others, 2000). Currently, most water

produced during CBM production in the Powder River Basin

is discharged into constructed reservoirs or into surface

drainages, where it may become part of the streamflow or

infiltrate into the ground. Proposed uses of CBM-produced

water include agriculture, domestic, industrial, and publicwater supply.

Understanding and predicting the effect of CBM-produced

water on stream-water quality is complicated by many factors

including local hydrology and geology, stream chemistry,

land use, and climate. The U.S. Geological Survey (USGS)

has been monitoring streamflow and stream-water quality at

sites in the Powder River Basin since 1900. The data can be

used to help understand

water-quality conditions in the basin and to

provide a useful

baseline against which

future changes can be

compared. This report

summarizes some of the

available monitoring

data and data relations

that may be useful for

assessing water-quality

changes, if any, that

CBM discharges may

have on stream-water

quality.

All natural waters contain dissolved chemicals. These are

introduced into the water from the atmosphere, soil, and rocks

that have come in contact with the water, and by human

activities. Water from different geologic settings commonly

will have distinctly different chemical signatures that can be

used to infer the source of water. This is the case when water

from streams in the Powder River Basin is compared to water

from CBM discharges. A comparison of the major chemical

constituents dissolved in a sample from the Powder River and

a sample of water obtained from a subsurface coal bed is

shown in figure 1. Although these samples are not representative of all surface- and ground-water samples in the basin,

they do illustrate some of the possible chemical differences.

Water from the Powder River is higher in dissolved calcium

(Ca ), magnesium (Mg ), chloride (Cl ) and sulfate (SO ),

whereas water from the coal bed is higher in dissolved

sodium (Na ) and bicarbonate (HCO ).

Chemical differences can be important when waters from

the different sources are mixed. For example, the ratio of

sodium ions to calcium and magnesium ions present in water,

in part, dictates the suitability of that water for crop irrigation.

This ratio is known as the sodium-adsorption ratio (SAR).

The higher the SAR value for a given water, the less suitable

it is for irrigation. SAR values for the sample from the

Powder River and a sample of water obtained from a

subsurface coal bed are shown at the far right in figure 1.

Elevated SAR values have been reported for some coalbed

waters (Rice and others, 2000). Introduction of higher SAR

water from CBM discharges into the Powder River has the

potential to affect the use of water by irrigators downstream

of those CBM discharges.

+2 +2

4

-2

+ 3




2

90

94

87

20 26

0

0 10 20 30 40 KILOMETERS

10 20 30 40 MILES

Figure 2. Location of streamflow-gaging stations and stream-water-quality sites in the Powder River Basin, Wyoming and Montana.

45 00 ° ′

44 00 ° ′

44 30 ° ′ 44 30 ° ′

43 30 ° ′ 43 30 ° ′

43 00 ° ′

106 00 ° ′

105 30 ° ′

106 30 ° ′

106 30 ° ′

107 00 ° ′

45 30 ° ′ 45 30 ° ′

46 00 ° ′ 46 00 ° ′

46 30 ° ′

105 00 ° ′

105 00 ° ′

106 00 ° ′

105 30 ° ′

Lake

De Smet

Creek

Cr

Cr

Timber

Hay

East

Ranch

Creek

Fork

Spotted

Powder

River

Salt

Dry Cr

Creek

Cr

Dugout

Creek

Cr

Clear

Clear Cr

Crazy

North

Middle

Beaver

Buffalo

Middle

Cr

Fork

Fk

Fork

No

Rock

Piney

Cr

Cr

Fork

South

So Fork

Wallace Cr

Fork

Cr

River

Powder

Woman

Little

HorseCr

River

Powder

Mizpah

Cr

Locate

Miles City Locate

Mizpah

Moorhead

Arvada Weston

Ucross

Buffalo

Kaycee

Midwest

Sussex

Broadus

Powderville

Gillette

MONTANA

WYOMING

Powder River

County

Custer County

Campbell

County Sheridan

County

Johnson

County

Natrona

County

Carter

County

Base modified from Digital Chart of the World

digital data, 1:1,000,000, 1993

Albers Equal-area Conic projection

Standard parallels 43 00 and 47 00 ,

central meridian -106 00

°′ °′

° ′

B I G

H

O

R

N

M

O

U

N

T A I N

S

44 00 ° ′

2

3

4

5

6

7 8

9

16

15

14

10

26

22 24

34

35

37

38

39

44

40 41

42

43

52

32 33

30 31

21

57 56

58

59

60

61

62

55

65

63

66

67

68

64

53

54

20

51

49

46 45

5047

48

36

29

23

2728

25

11

13

12

19 18

17

1

Cottonwood Cr

25

16

90

59

56

16

14

212

Helena

Powder

River

structural

basin

Powder

River

drainage

basin

Cheyenne

Buffalo

Miles

City

INDEX MAP

MONTANA

WYOMING

19

18

Streamflow-gaging station

and reference number--

Color of symbol represents

number of years of record

Stream-water-quality

sampling site and

reference number--

Color of symbol represents

number of SAR analyses

EXPLANATION

Fewer than 10

Fewer than 10

10 50 

10 50 

More than 50

More than 50

Available Data

The USGS, in cooperation with Federal, State, and local agencies, has

been monitoring streamflow and stream-water quality in the Powder River

Basin for more than a century. The number and location of sites where

streamflow and water quality have been monitored have changed over time

as various study objectives, land-use patterns, and available funding have

varied. A summary of the historical period of record for streamflow-gaging

stations and the number of historical SAR analyses for water-quality sites

in the Powder River Basin through water year 2000 is shown in figure 2

and table 1. Readers should be aware that there could be gaps in the

records at streamflow-gaging stations. Therefore, an entry in table 1 that

indicates operation from 1921-1950 may or may not correspond to a

continuous 30-year record of streamflow at that site. The streamflowgaging station with the longest continuous record (78 years) is Piney

Creek at Kearny, Wyo. (site 51). The water-quality monitoring site with

the greatest number of SAR values measured (498) is Powder River near

Locate, Mont. (site 68). Because monitoring needs are changing quickly

as CBM production proceeds, there are additional monitoring sites in

the Powder River Basin that have been added since water year 2000

that may not be shown in figure 2 and table 1.

Readers interested in examining the available data for any of

the sites listed in table 1 are referred to the USGS Internet

database. This database, which houses data from about 21,200

streamflow-gaging stations and water-quality data from about

338,000 sites nationwide, can be accessed at URL

http://water.usgs.gov/nwis/.
3

1

2

3

6

9

10

4

5

7

8

12

14

15

11

13

16

17

18

19

20

51

52

53

54

55

56

57

58

59

60

61

62

63

64

65

66

67

68

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45

46

47

48

49

50

21

22

23

24

25

26

27

28

29

30

06309200

06309260

06309270

06309280

06309450

06309460

06309500

06310000

06310500

06311000

06311060

06311400

06311500

06312000

06312500

06313000

06313180

06313400

06313500

06313665

06313700

06313950

06314000

06314500

06315000

06315480

06315490

06315500

06316000

06316400

06316500

06317000

06317020

06317300

06317340

06317500

06318500

06319470

06319480

06319500

06320000

06320200

06320400

06320500

06321000

06321020

06321040

06321100

06321500

06321800

06323000

06323500

06324000

06324500

06324710

06324890

06324925

06324970

06325000

06325500

06326000

06326300

06326500

06324830

06325550

06325650

06326050

06326200

1961-2000

1975-79

1975-79

1975-79

1975-89

1975-89

1949-92

1929-53

1911-32

1946-2000

1975-92

1974-2000

1941-73

1929-32

1939-80

1939-84

1975-83

1976-93

1938-98

--

1972-90

1974-84

1944-84

1949-72

1950-68

1975-77

1975-76

1942-72

1929-32

1963-81

1940-64

1931-2000

2000

1985-90

1985-88

1950-68

1917-92

1975-76

1975-76

1951-54

1945-2000

1976-81

1976-81

1947-2000

1951-80

1975-79

1975-79

1975-79

1952-82

1975-79

1903-2000

1900-1982

1915-82

1929-2000

1976-92

--

1977-83

1977-81

1973-2000

1938-43

1947-72

--

--

1928-33

--

--

1975-86

1938-2000

--

--

--

--

--

--

62

--

--

--

--

--

--

--

217

196

--

170

83

2

1

--

--

--

--

--

--

--

--

172

--

242

--

--

--

--

--

--

--

--

--

74

65

--

--

--

--

--

--

--

3

64

177

111

2

5

41

52

129

--

--

2

2

--

28

19

54

498

Table 1. Streamflow-gaging stations and stream-water-quality sampling sites in the Powder River Basin, Wyoming

and Montana, 1900-2000

[SAR, sodium-adsorption ratio; --, no data]

Site name

Reference

number

(fig. 2)

Site

number

Period of record

for streamflow1

Number of

SAR

analyses

1

Period of record is based on water year. A water year runs from October 1 of the previous year to September 30 of the indicated year. Streamflow record

may or may not be continuous for the period of record shown.

Middle Fork Powder River near Barnum, Wyo.

Buffalo Creek above North Fork Buffalo Creek near Arminto, Wyo.

Buffalo Creek below

Beaver Bayer Creek

B above White Panther Ditch

Red Fork near Barnum, Wyo.

M Kaycee, Wyo.

South

Dugout Creek tributary near Midwest, Wyo.

Salt Sussex, Wyo.

Dead Horse Buffalo, Wyo.

Poison Creek below Tetley Spring

Wildhorse C

Sourdough o.

Little

South Rock Creek at forest boundary

S Piney Creek at Willow Park, Wyo.

Mead-Coffeen Ditch above fish hatchery

North

Spring Creek

P at Kearny, Wyo.

P at Ucross, Wyo.

Powder River at Moorhead, Mont.

Powder River at Broadus, Mont.

Little below Corral Creek near Weston, Wyo.

Little Powder River at Biddle, Mont.

Little Powder River near Broadus, Mont.

Powder River near Mizpah, Mont.

Mizpah Creek near Mizpah, Mont.

Powder River near Locate, Mont.

North Fork Buffalo Creek near Arminto, Wyo.

North Fork Buffalo Creek near Arminto, Wyo.

Creek below near Barnum, Wyo.

eaver Creek near Barnum, Wyo.

Middle Fork Powder River above Kaycee, Wyo.

iddle Fork Powder River at

North Fork Powder River near Hazelton, Wyo.

North Fork Powder River below Bull Creek near Hazelton, Wyo.

North Fork Powder River below Pass Creek near Mayoworth, Wyo.

North Fork Powder River near Mayoworth, Wyo.

North Fork Powder River near Kaycee, Wyo.

Powder River near Kaycee, Wyo.

Fork Powder River near Kaycee, Wyo.

Creek near

Powder River at Sussex, Wyo.

Powder River above Dead Horse Creek near Buffalo, Wyo.

Creek near

North Fork Crazy Woman Creek below Pole Creek near Buffalo, Wyo.

North Fork Crazy Woman Creek near Buffalo, Wyo.

North Fork Crazy Woman Creek below Spring Draw near Buffalo, Wyo.

North Fork Crazy Woman Creek near Greub, Wyo.

near Mayoworth, Wyo.

Poison Creek near Mayoworth, Wyo.

Middle Fork Crazy Woman Creek near Greub, Wyo.

Crazy Woman Creek near Buffalo, Wyo.

Crazy Woman Creek at upper station near Arvada, Wyo.

Crazy Woman Creek near Arvada, Wyo.

Powder River at Arvada, Wyo.

reek near Arvada, Wyo.

Creek near Buffalo, Wy

Sourdough Creek near Buffalo, Wyo.

North Fork Clear Creek near Buffalo, Wyo.

Clear Creek near Buffalo, Wyo.

near Buffalo, Wyo.

South Rock Creek above Red Canyon Creek near Buffalo, Wyo.

South Fork Rock Creek near Buffalo, Wyo.

Rock Creek near Buffalo, Wyo.

Clear Creek below Rock Creek near Buffalo, Wyo.

Clear Creek at Ucross, Wyo.

outh

South Piney Creek near Story, Wyo.

near Story, Wyo.

Mead-Coffeen Ditch below fish hatchery near Story, Wyo.

South Piney Creek below Mead-Coffeen Ditch near Story, Wyo.

Piney Creek near Story, Wyo.

near Story, Wyo.

iney Creek

iney Creek

Clear Creek near Arvada, Wyo.

Rawhide Creek at US Highway 14-16 near Gillette, Wyo.

Powder River

Little Powder River near Weston, Wyo.

Little Powder River above Dry Creek near Weston, Wyo.

Little Powder River at mouth near Broadus, Mont.

Powder River near Powderville, Mont.

Mizpah Creek at Olive, Mont.

Mizpah Creek near Volberg, Mont.
4

Site 59 (06324970)

Site 7 (06309500)

Site 32 (06317000)

SPECIFIC CONDUCTANCE, IN

MICROSIEMENS PER CENTIMETER

AT 25 DEGREES CELSIUS

SPECIFIC CONDUCTANCE, IN

MICROSIEMENS PER CENTIMETER

AT 25 DEGREES CELSIUS

SPECIFIC CONDUCTANCE, IN

MICROSIEMENS PER CENTIMETER

AT 25 DEGREES CELSIUS

STREAMFLOW, IN CUBIC FEET PER SECOND

STREAMFLOW, IN CUBIC FEET PER SECOND

STREAMFLOW, IN CUBIC FEET PER SECOND

2,000

1,500

6,000

8,000

1,000

4,000

6,000

4,000

500

2,000

2,000

0

0

0

10

0.001

0.1

20

0.01

1

50

0.1

10

100 200

1

100

500

10

1,000

1,000

100 1,000

10,000

Figure 4. Streamflow and specific-conductance relations at selected sites in the Powder River Basin, Wyoming

and Montana.

Figure 3. Statistical summary of daily mean streamflow for period of record at selected streamflow-gaging

stations, Powder River Basin, Wyoming and Montana.

1

1,000

100

10

Site 7 (06309500)

3

3,000

10

100

1,000

0.3

300

1

10

100

75th percentile

Mean

Median

25th percentile

10th percentile

EXPLANATION

Reference number (fig. 2)

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

MONTH OF WATER YEAR MONTH OF WATER YEAR

DAILY MEAN STREAMFLOW, IN CUBIC FEET PER SECOND

90th percentile

Streamflow-gaging

station number

Site 32 (06317000) Site 59 (06324970)

Site 59 (06324970)
5

Data from Selected Sites

Eight sites, which are a subset of the monitoring sites

shown in figure 2 and table 1, were selected for further

examination. These sites were selected because of their

hydrologic significance or regulatory interest in relation to

CBM development. Data examined from these sites were

restricted to those collected during water years 1981-2000.

This 20-year period was selected as being representative of

the water-quality conditions prior to CBM development

little, if any, CBM discharge water streams

in the basin during this time period. As was mentioned

earlier, the sampling frequency and period of record varies at

each site. In addition, the data have not been adjusted to

account for natural climatic variability.

The Middle Fork Powder River above Kaycee, Wyo.

(site 7) originates from mountainous sources and is upstream

from the oil and methane development in the basin. Salt

Creek near Sussex, Wyo. (site 18) is a plains tributary of the

Powder River that receives saline oil-production water from

older, established oil fields and contributes to the salinity of

the Powder River (Lindner-Lunsford and others, 1992). The

Powder River at Sussex, Wyo. (site 19) is below Salt Creek

but above reaches of the Powder River where CBM development is occurring. Powder River at Arvada, Wyo. (site 32) is

the downstream-most site in Wyoming and is below areas of

CBM development. Powder River at Moorhead, Mont. (site

54) is near the Wyoming-Montana State line and will serve

as a point of compliance for the States. CBM development is

also occurring in the Arvada-Moorhead reach of the Powder

River (J. Smith, Wyoming Department of Environmental

Quality, oral commun., 2001). Clear Creek near Arvada,

Wyo. (site 53) contributes water from mountainous and

plains sources, and changes the water quality of the

mainstem Powder River between Arvada, Wyo. and

Moorhead, Mont. The Little Powder River above Dry Creek

near Weston, Wyo. (site 59) originates as a plains stream that

has received coal-mine discharges and is downstream of

CBM development. Powder River near Locate, Mont.

(site 68) is below inputs from the Little Powder River and

represents the cumulative effects on water quality from all

hydrologic sources and land uses within the watershed.

because entered

Powder River near Locate, Mont. near site 68

Streamflow Characteristics and Specific Conductance

Perhaps the single most important factor in determining the

effect of CBM discharges into Powder River Basin streams is the

amount of water flowing in the stream at the time the discharge

occurs. The amount of water flowing in streams in the Powder

River Basin varies by geographic location, climatic conditions,

time of year, and degree of human influence. For example,

precipitation is higher and evapotranspiration is lower in the

mountainous parts of the basin than in the plains (Marston, 1990).

Statistical summaries of daily mean streamflow measured at

selected streamflow-gaging stations illustrate these variations in

hydrologic settings (fig. 3). The graph for the Middle Fork

Powder River above Kaycee, Wyo., (site 7) is representative of

streams that originate in the mountainous areas of the basin.

Flows in these streams are perennial and dominated by a single

snowmelt peak of moderate duration in the late spring or early

summer. Low variability in streamflow exists during the rest of

the year as streamflow is generally sustained by discharge from

ground water. The graph for the Little Powder River above Dry

Creek near Weston, Wyo. (site 59) is representative of streams

that originate in the plains. Flows throughout the year in these

streams are much more variable than in mountain streams. These

plains streams may exhibit peak flows resulting from lowland

snowmelt during late winter or early spring as well as from

rainstorms throughout the remainder of the summer and fall.

More importantly, these streams are very likely to have little or no

flow for several months during the late summer through early

winter.

The Powder River has tributaries that are of both mountain

and plains origin. Consequently, the record from a gaging station

on the Powder River at Arvada, Wyo. (site 32) exhibits patterns

that are characteristic of both types of streams. Peaks in

streamflow occur from lowland snowmelt during late winter or

early spring and from mountain snowmelt during late spring or

early summer. Flow is more variable throughout the year than in

mountain streams, and periods of little or no flow still occur but

with less frequency than for plains streams. In addition to the

different hydrologic settings, irrigation withdrawals may affect

flows in some of the basins. In general, most of the water

withdrawn for irrigation in Wyoming is from the headwater and

tributary drainages, which may reduce flows to the Powder River.

In contrast, most of the water withdrawn for irrigation in Montana

is directly from the mainstem of the Powder River (LindnerLunsford and others, 1992).

Water quality in streams is a function of

streamflow. Consequently, the variations in streamflow that are

shown in figure 3 can influence water quality throughout the year.

One general indicator of water quality is specific conductance.

Specific conductance is a measure of the ability of water to

conduct an electrical current. Because this ability is related to the

quantity of chemical ions dissolved in water, specific conductance

can be used to estimate the salinity or dissolved solids present in

the stream (Hem, 1985). Streamflow and specific conductance

generally show an inverse relation, where specific conductance

decreases as flow increases (fig. 4). A typical relation is shown

for the Middle Fork Powder River above Kaycee, Wyo. (site 7).

High flows in the Middle Fork Powder River occur during

snowmelt runoff, which is characterized by low dissolved-solids

concentrations and a correspondingly low specific conductance.

A similar relation also exists for the Powder River at Arvada,

Wyo. (site 32), although the variance is somewhat greater. A

relation, if it exists, is much less evident for the Little Powder

River above Dry Creek near Weston, Wyo. (site 59). Possible

explanations for the lack of a strong relation include the

influence of coal-mine discharges in the basin and the evaporative accumulation of surface salts in plains watersheds that can

be flushed to the stream during rainfall events. Such short-lived

pulses of increased specific conductance during periods of

increasing flow can complicate the overall relation and result in

a wider scatter of data for a given flow.

commonly
Powder

River

Clear Creek

Salt Creek

Middle Fork

Powder River

Little Powder

River

6

1985 1990 1995

Site 19 (06313500)

WATER YEAR

0

2,000

4,000

6,000

8,000

10,000

SC

1985 1990 1995

Site 54 (06324500)

WATER YEAR

0

2,000

4,000

6,000

8,000

10,000

SC

WATER YEAR

1985 1990 1995

Site 53 (06324000)

0

2,000

4,000

6,000

8,000

10,000

SC

1985 1990 1995

Site 32 (06317000)

WATER YEAR

0

2,000

4,000

6,000

8,000

10,000

SC

1985 1990 1995

Site 59 (06324970)

WATER YEAR

0

2,000

4,000

6,000

8,000

10,000

SC

1985 1990 1995

Site 68 (06326500)

WATER YEAR

SC

0

2,000

4,000

6,000

8,000

10,000

SC

1985 1990 1995

Site 18 (06313400)

WATER YEAR

0

2,000

4,000

6,000

8,000

10,000

1985 1990 1995

Site 7 (06309500)

WATER YEAR

0

2,000

4,000

6,000

8,000

10,000

SC

Figure 5. Time-series plots of specific conductance for selected sites in the Powder River Basin, Wyoming and Montana,

1981-2000 (SC = specific conductance in microsiemens per centimeter at 25 degrees Celsius).

Specific-conductance values measured near Locate,

Mont. are similar to those measured at Moorhead,

Mont. (site 54), despite the fact that a large distance

separates the two sites. Streamflows measured

when the specific-conductance measurements were

made also did not vary substantially between the

sites. The median of 153 streamflow measurements

at site 54 was 305 cfs (cubic feet per second); the

median of 199 measurements at site 68 was 350 cfs.

Specific-conductance values

measured at the Middle Fork

Powder River site are consistently

low, reflecting the stream's

mountainous origins.

Specific conductance

values in the Powder

River increase

significantly below

the confluence of Salt

Creek.

Specific-conductance values in the

Little Powder River can be quite

high and variable owing to its plains

origin and discharges from coal

mines in the watershed.

Below the confluence of

Clear Creek, the Powder

River at Moorhead, Mont.

exhibits lower specificconductance values and

less variability compared

to upstream site 32.

Specific-conductance values in Clear

Creek, while relatively low, can be

twice those typically found at the

Middle Fork Powder River site

(site 7). This is because site 53 is

located far downstream from the

stream's mountainous headwaters.

The highest specific-conductance values

measured from the eight monitoring

sites are from Salt Creek.

Prior to 1990, oil-field brine was

discharged into Salt Creek. Since 1990,

this brine has been disposed by

subsurface injection. This change in

practice is evident in the Powder River

specific-conductance record as far

downstream as Arvada, Wyo.

Changes in Specific Conductance

with Time

Constituents of concern in CBM

discharge waters include the major ions

(sodium, for example), which comprise

most of the dissolved-solids concentration (salinity). Increases in the majorion concentrations in streams can be

indirectly measured as increases in

stream specific conductance.

Comparing patterns of specific conductance among sites and over a common period of time, such

as that shown in figure 5, is one strategy that regulators can

use to detect changes in water chemistry. These changes can

then be examined relative

to climatic patterns and

CBM or other activities

in the basin to evaluate

whether any cause-andeffect linkages can be

established. General

observations on patterns

in specific conductance

are provided with each

graph in figure 5.
Powder

River

Clear

Creek

Salt Creek

Middle Fork

Powder River

Little Powder

River

7

Figure 6. Specific conductance and sodium-adsorption ratio (SAR) for selected sites in the Powder River Basin, Wyoming

and Montana, 1981-2000 (SC = specific conductance in microsiemens per centimeter at 25 degrees Celsius).

Site 32 (06317000)

SC

SAR

0

30

20

10

0

2,000 4,000 6,000 8,000

Site 68 (06326500)

SC

SAR

0

100

20

50

10

5

2

1 2,000 4,000 6,000

Site 59 (06324970)

SC

SAR

0

15

10

0

5

2,000 4,000 6,000

Site 54 (06324500)

SC

SAR

0

100

20

50

10

5

2

1 2,000 4,000

Site 53 (06324000)

SC

SAR

0

3

1

0

2

1,000 2,000 3,000

SC

SAR

Site 18

(06313400)

0

60

20

40

1 5,000 10,000

Site 19 (06313500)

SC

SAR

0

60

40

20

1

2,000 6,000 8,000 4,000

Site 7 (06309500)

SC

SAR

0

1

0.7

0.5

0.4

0.3

0.1

0.2

500 1,000 1,500

1981 2000

Pre February 1990

Post February 1990







EXPLANATION

The relation between SAR and

specific conductance is different

for the pre- and post-February

1990 time periods for sites on

Salt Creek (site 18) and the

Powder River (sites 19 and 32).

Using pre-February 1990 data in

a regression to predict SAR from

specific-conductance measurements made today would most

likely over-predict SAR. This

observation indicates a notable

change in the ionic composition

of waters in Salt Creek,

presumably resulting from the

change to subsurface injection of

oil-field brine.

The Powder River near

Locate, Mont. represents the

cumulative mix of all the

basin's waters, and the

relation between SAR and

specific conductance at site

68 shows little difference

between pre- and postFebruary 1990 data.

SAR values for water from the Little

Powder River site range from about

2 to 13. A strong specific conductance-SAR relation is apparent at

this site.

SAR values are all less than 1 on

the Middle Fork Powder River.

A good mathematical relationship between SAR and specific

conductance is apparent.

Only pre-February 1990

SAR data are available

for the Powder River at

Moorhead, Mont.;

therefore, changes in the

relation resulting from

changes in the oil-field

brine discharges to Salt

Creek cannot be determined.

SAR values measured in Clear

Creek are generally less than 2

and correlate well with specific

conductance.

Relations between Specific Conductance and

Sodium-Adsorption Ratio

The combination of specific conductance and SAR is used

to determine the suitability of water for irrigation. The suitability is not a single number but rather a dynamic relation.

For general reference, a specific conductance near 2,000

microsiemens per centimeter at 25 degrees Celsius, and an

SAR greater than 10 would represent a high sodium hazard

(Hem, 1985). Graphs shown in figure 6 depict the relations

between specific conductance and SAR at the eight selected

monitoring sites.

he linear patterns in the data

indicate that regression

equations can be

established for specific

conductance and SAR. A

regression equation is a

mathematical relation

between two constituents

where one measured

constituent is used to

predict another unmeasured constituent. This relation generally is site specific and can

change over time if stream chemistry changes. Because specific

conductance can be monitored remotely and instantaneously, regulators looking for changes in stream

SAR values have the option of monitoring

specific conductance as a surrogate for

SAR and having

nearly instantaneous, continuous

records of this

calculated SAR

approximation.

Sites potentially affected by oil-field brine

discharged into Salt Creek are plotted with two time periods:

pre- and post-February, 1990. T
8 Printed on recycled paper

Streamflow-gaging station 06324970,

Little Powder River above Dry Creek

near Weston, Wyo. (site 59)

For copies of this report or additional information,

contact:

U.S. Geological Survey, WRD

2617 E. Lincolnway, Suite B

Cheyenne, Wyoming 82001-5662

state_rep_wy@usgs.gov

District Chief

Email:

Internet: http://wy.water.usgs.gov/

Coalbed methane discharge point

in the Powder River Basin

Streamflow-gaging station

06315480 (discontinued),

Poison Creek below

Tetley Spring near

Mayoworth,

Wyo. (site 26)

Layout by Suzanne C. Roberts

Future Monitoring

The effect of CBM discharge waters on stream-water

quality in the Powder River Basin is still unknown. CBM

waters, which have a different ionic composition, could alter

the specific conductance and SAR relations in the drainages.

Specific conductance can be measured continuously with instream sensors, and the measurements can be transmitted via

satellite and displayed in near real time on the worldwide

web. This technology allows regulators the option of

monitoring changes in stream chemistry as they occur, as

indicated by surrogate measures of stream chemistry, rather

than waiting weeks to months for the results from analytical

laboratories. Site characteristics and seasonal variations in

streamflow, like ice cover, can affect accuracy of real-time

data, and routine visits are still required to check for sensor

accuracy. Other constituents of interest with regard to CBM

waters in the Powder River Basin include complete ion

analyses, particularly sodium and alkalinity, selected

nutrients, and trace metals (Montana Department of

Environmental Quality, written commun., 2001). Continued

monitoring at tributary and mainstem sites in the Powder

River Basin is important during the period of CBM

production to characterize the effects, if any, CBM discharges have on water resources.

References

DeBruin, R.H., Lyman, R.M., Jones, R.W., and Cook, L.W.,

2000, Coalbed methane in Wyoming: Wyoming State

Geological Survey Information Pamphlet 7, 15 p.

Hem, J.D., 1985, Study and interpretation of the chemical

characteristics of natural water, 3d ed.: U.S. Geological

Survey Water-Supply Paper 2254, 263 p.

Lindner-Lunsford, J.B., Parrett, Charles, Wilson, J.F., Jr.,

and Eddy-Miller, C.A., 1992, Chemical quality of

surface water and mathematical simulation of the

surface-water system, Powder River drainage basin,

northeastern Wyoming and southeastern Montana: U.S.

Geological Survey Water-Resources Investigations

Report 91-4199, 85 p.

Marston, R.A., 1990, Wyoming water atlas: Wyoming

Water Development Commission and University of

Wyoming, 124 p.

Rice, C.A., Ellis, M.S., and Bullock, J.H., Jr., 2000, Water

co-produced with coalbed methane in the Powder River

Basin, Wyoming: preliminary compositional data: U.S.

Geological Survey Open-File Report 00-372, 20 p.

Swanson, R.B., Mason, J.P., and Miller, D.T., 2000a, Water

resources data, Wyoming, Water Year 1999; volume 2,

ground water: U.S. Geological Survey Water-Data

Report WY-99-2, 125 p.

Swanson, R.B., Smalley, M.L., Woodruff, R.E., and Clark,

M.L., 2000b, Water resources data, Wyoming, Water

Year 1999; volume 1, surface water: U.S. Geological

Survey Water-Data Report WY-99-1, 484 p.