U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2012–5209

Prepared in cooperation with the Northern Cheyenne Tribe

Estimates of the Volume of Water in Five Coal 

Aquifers, Northern Cheyenne Indian Reservation, 

Southeastern Montana

THE GREAT SEAL OF THE

NORTHERN CHEYENNE TRIBE

THE GREAT SEAL OF THE

NORTHERN CHEYENNE TRIBE
Front cover. Outcrop of Tertiary Fort Union Formation, Tongue River Member along U.S. Route 212 east of Lame Deer, Mont.

Back cover. Drill core from well NC05-2 showing cleats in coal.

 Drill core from NC05-2 showing fractures in coal.

 U.S. Geological Survey observation well NC97-3.

 All photographs by M.R. Cannon, U.S. Geological Survey (retired), various dates, 1997 and 2005.
Estimates of the Volume of Water in Five 

Coal Aquifers, Northern Cheyenne Indian 

Reservation, Southeastern Montana

By L.K. Tuck, Daniel K. Pearson, M.R. Cannon, and DeAnn M. Dutton

Prepared in cooperation with the Northern Cheyenne Tribe

Scientific Investigations Report 2012–5209

U.S. Department of the Interior

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

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

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

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Suggested citation:

Tuck, L.K., Pearson, D.K., Cannon, M.R., and Dutton, D.M., 2013, Estimates of the volume of water in five coal 

aquifers, Northern Cheyenne Indian Reservation, southeastern Montana: U.S. Geological Survey Scientific 

Investigations Report 2012–5209, 26 p., http://pubs.usgs.gov/sir/2012/5209/.
iii

Acknowledgments

The Northern Cheyenne Tribe is gratefully acknowledged for field assistance and information 

about the study area. We also gratefully acknowledge the invaluable contribution of Edward L. 

Heffern, Bureau of Land Management (retired), who provided personal observations about the 

geology and coal stratigraphy of the study area.
iv

Contents

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

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

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

Description of Study Area ...................................................................................................................4

Geohydrologic Framework..................................................................................................................4

Geologic Setting...........................................................................................................................4

Hydrologic Setting .......................................................................................................................6

Previous Investigations........................................................................................................................7

Location-Numbering System ..............................................................................................................7

Methods of Investigation..............................................................................................................................8

Estimation of Extent, Thickness, and Volume of Coal Beds...........................................................8

Estimation of the Volume of Water in Aquifers................................................................................9

Aquifer Characteristics...............................................................................................................9

Storage .................................................................................................................................9

Hydraulic Conductivity and Transmissivity...................................................................12

Water-Level Data.......................................................................................................................12

Estimates of the Volume of Water in Five Coal Aquifers.......................................................................13

Canyon Coal.........................................................................................................................................13

Wall Coal ..............................................................................................................................................13

Pawnee Coal........................................................................................................................................15

Knobloch Coal......................................................................................................................................15

Flowers-Goodale Coal........................................................................................................................15

Reliability and Uncertainty of Volume Estimates....................................................................................18

Summary........................................................................................................................................................23

References Cited..........................................................................................................................................24

Figures

1. Map showing location of the study area, southeastern Montana.......................................3

2. Diagram of idealized stratigraphic section of the Tongue River Member 

of the Fort Union Formation from the Rosebud Creek–Tongue River divide 

eastward to the Tongue River.....................................................................................................5

3. Diagram of location-numbering system and site number for wells in and 

near the study area, southeastern Montana ...........................................................................7

4. Diagram of conceptual model of complex thinning, splitting, merging, and 

pinching out of coal beds ...........................................................................................................9

5. Map of generalized subsurface extent and thickness of the Canyon coal 

in the study area, southeastern Montana ..............................................................................14

6. Generalized geologic section of the Tongue River Member of the Tertiary 

Fort Union Formation along the southern part of the Northern Cheyenne 

Indian Reservation, southeastern Montana...........................................................................16
v

7. Map of generalized subsurface extent and thickness of the Wall coal in 

the study area, southeastern Montana...................................................................................19

8. Map of generalized subsurface extent and thickness of the Pawnee coal 

in the study area, southeastern Montana ..............................................................................20

9. Map of generalized subsurface extent and thickness of the Knobloch coal 

in the study area, southeastern Montana ..............................................................................21

10. Map of generalized subsurface extent and thickness of the Flowers-Goodale 

coal in the study area, southeastern Montana......................................................................22

Tables

1. Hydrogeologic data for selected wells completed in five coal beds in and 

near the study area, southeastern Montana .........................................................................10

2. Range of estimates of the volume of water in five coal aquifers in the study 

area, Northern Cheyenne Indian Reservation, southeastern Montana............................18

Conversion Factors, Datum, Transmissivity, 

Water-Year Definition, and Abbreviations

Multiply By To obtain

acre 4,047 square meter (m2)

acre 0.004047 square kilometer (km2)

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

cubic foot 0.02832 cubic meter (m3)

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

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

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

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d)

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

mile (mi) 1.609 kilometer (km)

square mile (mi2) 2.590 square kilometer (km2)

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 North American Vertical Datum of 1988 

(NAVD 88) and the National Geodetic Vertical Datum of 1929 (NGVD 29). Horizontal coordinate 

information is referenced to the North American Datum of 1983 (NAD 83) and the North 

American Datum of 1927 (NAD 27).

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

Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

Water-year definition: Water year is the 12-month period from October 1 through September 30 

of the following calendar year. The water year is designated by the calendar year in which it ends. 

For example, water year 2010 is the period from October 1, 2009, through September 30, 2010.
vi

Abbreviations Used in This Report:

BLM Bureau of Land Management

CBM coal-bed methane

CD–ROM compact disc—read-only memory

DEM digital-elevation model

ESRI Environmental Systems Research Institute

GIS geographic information system

GWIC Ground Water Information Center, Montana Bureau of Mines and Geology

(database)

IDW inverse distance weighting

MBMG Montana Bureau of Mines and Geology

NWIS National Water Information System, Groundwater Information and Data

(database), U.S. Geological Survey

USGS U.S. Geological Survey
Estimates of the Volume of Water in Five Coal 

Aquifers, Northern Cheyenne Indian Reservation, 

Southeastern Montana

By L.K. Tuck, Daniel K. Pearson, M.R. Cannon,1 and DeAnn M. Dutton

indicate that the Wall coal was both unconfined and confined 

within and near the study area. Thus, the estimates of the 

volume of water in the Wall coal probably are reasonable.

The volume of water in the Pawnee coal was estimated 

to range from about 9,440 acre-feet (100 percent saturated) to 

2,360 acre-feet (25 percent saturated). Water-level data from 

one well and information from one geologist’s log indicated that 

the Pawnee coal probably was fully saturated and might have 

been under confined conditions in the study area. However, 

estimates of the volume of water in the Pawnee coal might 

have large errors and need to be used with caution because the 

water-level data needed to define the volume of water were 

largely unavailable.

The volume of water in the Knobloch coal was estimated to range from about 38,700 acre-feet (100 percent 

saturated) to 9,680 acre-feet (25 percent saturated). Waterlevel data indicate that the Knobloch coal was both unconfined 

and confined within and near the study area. Thus, the 

estimates of the volume of water in the Knobloch coal 

probably are reasonable.

The volume of water in the Flowers-Goodale coal was 

estimated to be about 35,800 acre-feet (100 percent saturated). 

Water-level data and information from one geologist’s log 

indicate that the Flowers-Goodale coal was confined at these 

wells. Also, because this coal generally is deeply buried in 

the study area, the Flowers-Goodale coal was assumed to be 

confined throughout its extent in the study area. Thus, the 

estimates of the volume of water in the Flowers-Goodale coal 

probably are reasonable.

Sufficient data are needed to accurately characterize 

coal-bed horizontal and vertical variability, which is highly 

complex both locally and regionally. Where data points are 

widely spaced, the reliability of estimates of the volume of 

coal beds is decreased. Additionally, reliable estimates of 

the volume of water in coal aquifers depend heavily on data 

about water levels and data about coal-aquifer characteristics. 

Because the data needed to define the volume of water were 

sparse, only conservative estimates of the volume of water 

in the five coal aquifers are presented in this report. These 

estimates need to be used with caution and mindfulness of 

the uncertainty associated with these estimates.

Abstract

Water is one of the Northern Cheyenne Tribe’s most 

valuable natural resources—vital to the health and economic 

welfare of the Northern Cheyenne people. The Tongue River 

Member of the Tertiary Fort Union Formation is the primary 

source of groundwater in the Northern Cheyenne Indian 

Reservation in southeastern Montana. Coal beds within this 

formation generally contain the most laterally extensive 

aquifers in much of the reservation. The U.S. Geological 

Survey, in cooperation with the Northern Cheyenne Tribe, 

conducted a study to estimate the volume of water in five 

coal aquifers.

This report presents estimates of the volume of water 

in five coal aquifers in the eastern and southern parts of the 

Northern Cheyenne Indian Reservation. The Canyon, Wall, 

Pawnee, Knobloch, and Flowers-Goodale coal beds in the 

Tongue River Member of the Tertiary Fort Union Formation 

were investigated. Only conservative estimates of the volume 

of water in the Canyon, Wall, Pawnee, Knobloch, and 

Flowers-Goodale coal aquifers are presented because (1) the 

subsurface extent of the coal beds are not well defined, (2) in 

some instances, well and drill-hole data were widely spaced 

and not well distributed, (3) of the possibility that some coal 

beds split, merge, or pinch out laterally, and (4) water-level 

data for the five aquifers were scarce.

The volume of water in the Canyon coal was estimated 

to range from about 10,400 acre-feet (75 percent saturated) to 

3,450 acre-feet (25 percent saturated). The smaller estimates 

of water in the Canyon coal (75 to 25 percent saturation) are 

considered more reasonable; 100 percent saturation was not 

considered probable within the study area. However, estimates 

of the volume of water in the Canyon coal might have large 

errors and need to be used with caution because the water-level 

data needed to define the volume of water were unavailable.

The volume of water in the Wall coal was estimated to 

range from about 14,200 acre-feet (100 percent saturated) 

to 3,560 acre-feet (25 percent saturated). Water-level data 

1

U.S. Geological Survey, retired.
2 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana

Introduction

Water is one of the Northern Cheyenne Tribe’s most 

valuable natural resources—vital to the health and economic 

welfare of the Northern Cheyenne people. Except for the 

Tongue River and Rosebud Creek (fig. 1), surface water in 

many parts of the Northern Cheyenne Indian Reservation 

is not available for use. Although small ephemeral streams 

can provide water for livestock and some agriculture, most 

water for domestic, livestock, and municipal use is obtained 

from wells (Matson and Blumer, 1973; Barbara A. Burkland, 

U.S. Environmental Protection Agency, oral commun., 

2010). The Tongue River Member of the Tertiary Fort Union 

Formation is the primary source of groundwater in the 

Northern Cheyenne Indian Reservation, in southeastern 

Montana. Coal beds within this formation generally contain 

the most laterally extensive aquifers; coal aquifers are readily 

used and can provide abundant water to wells and springs 

(Woessner and others, 1981). In much of the reservation, a 

practical alternative to groundwater from the Tongue River 

Member does not exist.

Coal-bed methane (CBM) production is an important 

industry in southeastern Montana. Potential reserves of CBM 

might exist in the southern and eastern parts of the Northern 

Cheyenne Indian Reservation and in adjacent areas where 

some of the same coal aquifers in the Tongue River Member 

extend beyond the boundaries of the reservation (Biewick 

and McLellan, 1990). To extract this methane, groundwater 

is pumped from the coal aquifer so that water levels in wells 

(hydraulic head) are reduced sufficiently to release methane 

stored in the coal aquifer; the methane is in solution in the 

water (Wo and others, 2004). The extraction and subsequent 

management of CBM-produced water has raised concerns 

about the potential reduction of groundwater supplies caused by 

lowering of water levels and the potential effects of the disposal 

of produced water on surface water and soils. After 10 years 

of CBM production in coal fields near Decker, Mont. (fig. 1), 

Meredith and others (2010) reported that water levels in some 

of the coal aquifers in the production field decreased 150 to 

600 feet (ft), and that as far as 1.0 to 1.5 miles (mi) beyond the 

boundaries of the production field, water levels had decreased 

by 20 ft. Likewise, flow from springs and water available in 

wells might be diminished proportionally to the decrease in 

hydraulic head in the aquifer (Wheaton and Donato, 2004). 

Where pumping has lowered water levels below the top of a 

confined coal aquifer (below the base of a confining or leakyconfining layer), the coal aquifer then becomes unconfined 

and dewatering of the aquifer occurs. Dewatering reduces the 

saturated thickness of an aquifer and can affect the productivity 

of the aquifer (Slagle and others, 1985).

Additionally, in 2010, the State of Montana approved 

the lease of coal resources of about 8,300 acres that are 

approximately 3 mi east of the Tongue River (Montana 

Department of Natural Resources, 2002). The Tongue River 

is the eastern boundary of the Northern Cheyenne Indian 

Reservation. Some of the coal beds targeted for that development 

under this lease might be contiguous with those in the eastern 

part of the reservation (Heffern and others, 1993).

Information about the volume of water in coal aquifers 

in the reservation was needed because possible development 

of coal and CBM could deplete the Tribe’s groundwater 

resources by lowering water levels. This potential depletion 

also raised concerns about groundwater rights and that 

loss of water from coal aquifers would affect traditional 

land and water uses. To enable the Northern Cheyenne 

Tribe to manage its groundwater resources, the amount of 

groundwater in the coal aquifers underlying the reservation 

needed to be estimated. Consequently, the U.S. Geological 

Survey (USGS), in cooperation with the Northern Cheyenne 

Tribe, conducted a study to estimate the volume of water 

in five coal aquifers. The eastern and southern parts of 

the reservation were selected for study because some coal 

aquifers in this area might be more likely to be affected by 

CBM development.

Purpose and Scope

This report presents estimates of the volume of water 

in five coal aquifers in the eastern and southern parts of the 

Northern Cheyenne Indian Reservation. The Canyon, Wall, 

Pawnee, Knobloch, and Flowers-Goodale coal beds in the 

Tongue River Member of the Tertiary Fort Union Formation 

were investigated (stratigraphic nomenclature from Flores 

and others, 2010). These five coal beds are known to yield 

water in the study area; thus, coal aquifers contained in these 

coal beds are the focus of this report. Other coal beds within 

the Tongue River Member in the study area also probably 

yield water in usable quantities. However, these other coal 

beds were not investigated and their water-yielding properties 

are unknown.

To define the volume of water in each coal aquifer, 

existing data from lithologic logs from various sources, 

along with geologic maps of the study area, were compiled. 

Extent and thickness data for each coal bed were then used 

to estimate the volume of coal for each of the five coal beds 

by using computer interpolation methods. The volume of 

water in each of the five coal aquifers was estimated by 

assuming that each coal bed was fully saturated (thickness 

of the coal bed was equal to the thickness of the coal aquifer, 

except for the Canyon coal). Estimates of the volume of 

water in these coal aquifers were determined from existing 

data about hydraulic properties of coal beds in areas of 

Montana, North Dakota, and Wyoming. Existing water-level 

data measured from wells in the study area and from nearby 

areas were used to determine if coal beds were unconfined or 

confined and also to evaluate the percentage of saturation for 

each coal bed and, thus, to estimate the volume of water in 

each coal aquifer.
Introduction 3

Figure 1. Location of the study area, southeastern Montana.

Rosebud

Creek

Indian

Coulee

Lynch Creek

Teeth Creek

Lame

Deer

Creek

Coal

Creek

South

Fork

East Fork

Alderson Creek

Creek Reservation

Creek

Stebbins

Creek

Logging

Creek

Kelty

Tie Creek

Cook Creek

Creek

Muddy

Fork

West

Fork

East

Fork

North

Fork

South

Creek

Dry

Trail

Creek

Busby

Creek

r C kee besoR ud

Tongue

River

Bull

Cr

Black

Eagle

Fork

Pawnee

Creek

Fork Middle

Prairie

Dog Creek

eek

06307616

06295113

Birney Day

School

Lame Deer 3W

Ashland

Lame Deer

Busby

Birney

S-314

212 212

39

Busby

ROSEBUD

COUNTY

BIG HORN

COUNTY

NORTHERN CHEYENNE

INDIAN RESERVATION

Base modified from U.S. Geological Survey

1° × 2° quadrangle, Hardin, Montana, 1954

North American Datum of 1927 (NAD 27)

06307616

EXPLANATION

Study area

U.S. Geological Survey streamflow-

 gaging station and number

Well or drill hole

Weather station

T. 2 S.

T. 3 S.

T. 4 S.

T. 5 S.

R. 38 E. R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 43 E. R. 44 E.

45°40'

45°30'

45°20'

107°00' 106°30'

0 5 MILES

0 5 KILOMETERS

NEBRASKA

Decker

WYOMING

MONTANA NORTH

DAKOTA

SOUTH

DAKOTA Powder

River

Basin

NORTHERN

CHEYENNE

INDIAN RESERVATION

TONGUE RIVER DAM

06307500

Helena

Billings

Kirby 1S

MONTANA

Missouri

Yellowstone

River

R i ver
4 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana

Description of Study Area

The Northern Cheyenne Indian Reservation (fig. 1) 

encompasses about 445,000 acres in Big Horn and Rosebud 

Counties in southeastern Montana (Wo and others, 2004). 

The reservation lies on an unglaciated, semiarid, rolling plain 

that is underlain by the Tertiary Fort Union Formation and is 

dissected by many small ephemeral or intermittent streams. 

Grass-covered rangeland used to raise cattle is interspersed 

with farmland (Woods and others, 2002); hay is raised as the 

principal crop along the valley bottoms of the Tongue River 

and Rosebud and Lame Deer Creeks. Native grasslands are 

extensive, especially in areas of steep or rugged terrain. Pine 

and juniper forests predominate in upland areas; grazing in 

these areas can be limited because of rough terrain and lack 

of water (Woods and others, 2002).

The Tongue River is an important source of surface 

water in this part of southeastern Montana. Streamflow in 

the Tongue River is regulated by the Tongue River Dam 

(fig. 1), about 73 river miles upstream from Ashland (Montana 

Department of Natural Resources and Conservation, 1976). 

For water years 1939–2010, the annual mean streamflow 

at Tongue River at Tongue River Dam, near Decker, Mont. 

(streamflow-gaging station 06307500), was 430 cubic feet per 

second (ft3/s). For water years 1980–2010 the mean annual 

streamflow at Tongue River at Birney Day School Bridge, 

near Birney, Mont. (streamflow-gaging station 06307616), 

was 380 ft3/s (U.S. Geological Survey, 2010a).

Rosebud Creek, also an important source of surface 

water, flows across the western and northern parts of the 

reservation. For water years 1980–2010, the mean annual 

streamflow of Rosebud Creek at reservation boundary, near 

Kirby, Mont. (streamflow-gaging station 06295113), was 

6.29 ft3/s (U.S. Geological Survey, 2010a).

 The climate of the study area is characterized by cold, 

dry winters and hot, moderately dry summers. December and 

January typically are the coldest months, whereas July and 

August typically are the warmest months. At Busby, Kirby 1S, 

and Lame Deer 3W weather stations (fig. 1), the mean 

monthly minimum temperature in December and January 

ranged from about 4 to 10°F and the mean monthly maximum 

temperature in July and August ranged from about 86 to 88°F. 

Mean annual precipitation at these three stations ranged from 

about 14 to 19 inches (in.); about 45 to 55 percent of the 

mean precipitation falls in April, May, June, and July (various 

periods of record from 1907 to 2010; Western Regional 

Climate Center, 2010).

Geohydrologic Framework

Geologic Setting

The Northern Cheyenne Indian Reservation is located 

in the northwestern part of the Powder River Basin (fig. 1), 

which is an asymmetrical structural basin. Within Montana, 

the axis of the Powder River Basin trends northeast-southwest, 

approximately along the valley of the Tongue River. Along 

the northwestern margin of the basin, rocks of the Fort 

Union Formation dip less than 1 degree to the southeast. The 

Powder River Basin covers more than 21,600 square miles 

(mi2) in Montana and Wyoming (Heffern and others, 2007). 

A shallow syncline plunges to the south through the center 

of the reservation (Wo and others, 2004), and a system of 

northeast-trending normal faults in the northeastern part of the 

reservation formed as a result of strike-slip movements along 

the boundaries of basement rocks (Culberson and Saperstone, 

1987a, b; Wo and others, 2004). In places, faults can offset 

strata by as much as 60 to 160 ft (Heffern, 1980; Woessner 

and others, 1981).

The Fort Union Formation of Tertiary age consists 

of three members—the Tullock, Lebo Shale, and Tongue 

River Members; the Lebo Shale and Tullock Members 

underlie the Tongue River Member. Generally, the Tullock 

Member consists mostly of thin-bedded siltstone and 

sandstone and only local stringers of coal (Hansen and 

Culbertson, 1985; Culbertson, 1987). The Lebo Shale member 

consists mostly of dark shale and mudstone and contains a few 

thin beds of sandstone and coal, whereas the Tongue River 

Member consists of interbedded sandstone, siltstone, shale, 

coal, and a few lenses of limestone. The Fort Union Formation 

can be as much as 3,900 ft thick in the Powder River Basin 

(Lewis and Roberts, 1978) but ranges from about 800 to 

1,700 ft thick in the reservation (Hopkins, 1973; Vuke and 

others, 2001a, b).

Sedimentary rocks of the Tongue River Member 

(fig. 2) are exposed at the surface in most of the study area 

and underlie the entire study area. These rocks were deposited 

in the Powder River Basin, which formed as a result of 

intermittent crustal movements throughout Late Cretaceous 

and Tertiary time. The depositional environments were mainly 

fluvial systems consisting of braided and meandering streams 

in the center of the basin and alluvial fans along the western 

basin margin. Coals formed in numerous and extensive peat 

mires or swamps in fluvial flood plains, abandoned fluvial 

channels, and interchannel environments (Flores and Ethridge, 

1985; Flores, 1986; Heffern and others, 2007; Flores and 

others, 2010).

In the Birney-Decker area (fig. 1), the Tongue River 

Member can locally contain as many as 20 coal beds. 

However, the beds split, merge, or pinch out laterally within 

relatively short distances (about 3 to 5 mi), which complicates 

correlation throughout this part of Montana (Culbertson and 

Saperstone, 1987a, b; Culbertson, 1987). The interval of the 

Tongue River Member present on the reservation contains 

about 15 informally named coal beds (Woessner and others, 

1981; Culbertson, 1987; Wo and others, 2004) and several 

local unnamed coal beds. Some of the coal beds are quite 

laterally extensive. For example, east of the reservation, the 

Knobloch coal, which represents a long period of continued 

peat deposition, underlies an area of 270 mi2 (Culbertson and 

Saperstone, 1987b; McLellan and others, 1990).
Introduction 5

Figure 2. Idealized stratigraphic section of the Tongue River Member of the Fort Union Formation from 

the Rosebud Creek–Tongue River divide eastward to the Tongue River (thickness and extent information 

modified from Woessner and others, 1981; Culbertson, 1987).

Shale and sandstone

Coal—Queried where uncertain

Interbedded sandstone, siltstone,

 and shale 

Shale and mudstone

Tongue River

WASATCH

FORMATION

(EOCENE)

TONGUE RIVER MEMBER OF FORT UNION FORMATION 

(PALEOCENE)

LEBO SHALE MEMBER OF

FORT UNION FORMATION

(PALEOCENE)

Roland coal (5–15 feet thick)

Anderson coal (20–65 feet thick)

Dietz coal (6–8 feet thick)

Canyon coal (10–33 feet thick)

Cook coal (6–20 feet thick)

Wall coal (28–55 feet thick)

Pawnee coal (4–27 feet thick)

Brewster-Arnold coal (8–13 feet thick)

Sawyer coal (2–6 feet thick)

Knobloch coal (0–68 feet thick)

Flowers-Goodale coal (0

Nance coal (3–12 feet thick)

Flowers-Goodale coal (0–28 feet thick)

Rosebud Creek–Tongue River divide

?

Alluvium

TERTIARY

?

?

?

EXPLANATION

Terret coal (0–7 feet thick)

?

?

Sawyer coal (2–6 feet thick)

Nance coal (3–12 feet thick)

Flowers-Goodale coal (0–28 feet thick)

?

?

?

?

Terret coal (0–7 feet thick)

?

?

Smith coal (less than 10 feet thick)
6 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana

Along the valleys of Rosebud Creek and the Tongue 

River, much of the Tongue River Member has been removed 

by erosion. Because the reservation is highly dissected by 

ephemeral and perennial streams, many coal beds crop out 

only as erosional remnants along some of the ridges and 

higher plateaus.

 Overlying the Tongue River Member, along the 

drainage divide between Rosebud Creek and the Tongue River, 

Tertiary-aged sedimentary rocks of the Wasatch Formation 

cap some of the higher buttes and ridges (fig. 2). The Wasatch 

Formation, which can be as much as 500 ft thick, consists of 

grayish-brown and gray shale, some carbonaceous shale, and 

thin beds of brown calcareous sandstone. The contact of the 

Fort Union and Wasatch Formations is placed at the top of the 

Roland coal (Hopkins, 1973; Matson and Blumer, 1973).

Thick beds of red clinker—formed by the burning, 

welding, and melting of sedimentary rock above and below 

coal beds—are present where coal beds have burned along 

their outcrops. Most coal beds have burned in place and, 

consequently, formed distinctive red, erosion-resistant clinker 

(Woessner and others, 1981; Heffern and others, 2007). 

Generally, clinker erodes more slowly than other rocks of 

the Tongue River Member and Wasatch Formation and, thus, 

tends to control topography by capping plateaus and hilltops 

to form escarpments (Heffern and Coates, 2004). About 7 

percent of the Powder River Basin and about 30 percent of the 

reservation is covered by outcrops of clinker (Heffern, 1980; 

Heffern and others, 2007).

The valleys of Rosebud Creek, Tongue River, and 

some of their larger tributaries contain Quaternary alluvium 

derived from sandstone, shale, and clinker of the Fort Union 

and Wasatch Formations. Alluvium underlying these stream 

valleys consists of gravel, sand, silt, and clay; in some areas, 

the alluvium can be thick. These streams have eroded through 

parts of Tongue River Member and exposed coal along valleys 

and in coulees (Woessner and others, 1981; Wheaton and 

Donato, 2004).

Hydrologic Setting

Principal aquifers in the study area include alluvium, 

clinker, and sandstone and coal. Alluvium, which can be as 

much as 80 ft thick, is primarily located in the valleys of the 

Tongue River and Rosebud and Lame Deer Creeks (Hopkins, 

1973); alluvium also extends along the channels of smaller 

intermittent streams. Locally, alluvium can contain sufficient 

saturated sand and gravel to be an important source of water 

for domestic and livestock use and limited irrigation. Wells 

completed in alluvium typically yield 10 to 20 gallons per 

minute (gal/min) (Hopkins, 1973; Woessner and others, 1981).

Clinker is highly fractured, porous, and permeable; these 

characteristics allow infiltration of precipitation and percolation 

of water and flow to springs, which typically can be found 

along the base of clinker outcrops. Lateral flow from adjacent 

coal beds also recharges clinker (Hopkins, 1973; Woessner 

and others, 1981; Cannon, 1982). Conversely, clinker can form 

discontinuous, generally perched aquifers because underlying 

and overlying sandstone and shale typically were altered 

(hardened and perhaps melted by baking) and now can be less 

permeable than the fractured clinker (Woessner and others, 

1981). Few wells are completed in clinker because of the 

extreme difficulty of drilling and because of its small saturated 

thickness. In many areas, water in clinker can move through 

talus or colluvium into adjacent alluvium without reaching land 

surface to issue as a spring. Clinker can be a reliable source 

of water for domestic and livestock use (Woessner and others, 

1981; Cannon, 1982; McClymonds, 1982).

Sandstone and coal aquifers of the Tongue River Member 

are present throughout the reservation and collectively compose 

the most laterally extensive hydrogeologic units used for 

domestic and livestock wells (Woessner and others, 1981). 

Sandstone beds generally are lenticular and interbedded with 

shale, which can result in discontinuous aquifers. However, 

the many lenticular sandstone beds, combined with the many 

coal beds, create hydrogeologic units where water supplies 

can be obtained (Woessner and others, 1981). Some of the 

sandstone beds can be as much as 100 ft thick with porosities 

as much as 30 percent (Wo and others, 2004). Yields of wells 

in sandstone and coal aquifers generally range from about 2 

to 50 gal/min (Hopkins, 1973: Woessner and others, 1981; 

McClymonds, 1982). Conversely, some sandstone can be 

relatively impermeable (probably leaky-confining layers), 

and both the sandstone and coal can be dry depending on the 

location of the beds (Hopkins, 1973; Woessner and others, 

1981; McClymonds, 1982).

Coal beds are important aquifers in southeastern Montana 

because generally the beds can be more laterally continuous 

than sandstone. Thus, domestic and livestock wells typically 

are completed in coal. Springs that issue from coal aquifers in 

outcrop and subcrop areas can provide water for livestock and 

wildlife and base flow to streams (Woessner and others, 1981; 

McClymonds, 1982; Wheaton and Donato, 2004). Springs are 

present throughout the Powder River Basin but are particularly 

abundant along contacts at the base of clinker zones and 

coal outcrops. In the Powder River Basin, springs have an 

average density of at least one spring per 5 mi2 (Kennelly and 

Donato, 2001).

Between each of the five coal aquifers examined for 

this study, stratigraphic intervals of less permeable interbedded 

sandstone, siltstone, shale, and coal (fig. 2) can range from 

about 30 to as much as 400 ft thick. Because these intervals 

can be less permeable, they probably act, to some extent, as 

confining or leaky-confining layers depending on the location 

and permeability of the beds (Woessner and others, 1981). 

The underlying Lebo Shale Member is reported to be a limited 

source of water in the Powder River Basin but only where 

local coarse-grained channel sandstones also are found (Lewis 

and Roberts, 1978).
Introduction 7

Previous Investigations

The most comprehensive reports on the hydrology and 

coal resources of the Northern Cheyenne Indian Reservation 

were the product of a 3-year research project that assessed 

the potential effects of surface mining of coal on groundwater 

and surface-water resources (Woessner and others, 1981; and 

the companion data report by Andrews and others, 1981). The 

researchers collected and published a large variety and volume 

of data, including information about the extent and thickness 

of coal beds; water-level and water-quality data from test 

holes, monitoring wells, and domestic wells; and hydraulic 

properties of coal, clinker, and sandstone aquifers.

Notable reports containing general information on 

geology or hydrology of the reservation include a report 

on geology and groundwater resources of Rosebud County 

(Renick, 1929), a report on geology and water-yielding 

characteristics of rocks in the northern Powder River 

Basin (Lewis and Roberts, 1978), and a map of geology 

and distribution of clinker in the northern Powder River 

Basin (Heffern and others, 1993). A report on the general 

geology, water quality, and occurrence of groundwater 

in the reservation was published by Hopkins (1973). The 

Montana Bureau of Mines and Geology (MBMG) published 

geologic maps of the Lame Deer 30×60 minute quadrangle 

(Vuke and others, 2001a) and the Birney 30×60 minute 

quadrangle (Vuke and others, 2001b), which encompass the 

entire study area.

Many reports by the USGS, Bureau of Land Management 

(BLM), and the MBMG contain detailed information about 

coal deposits on lands adjacent to the reservation and much 

of the Powder River Basin of southeastern Montana (Baker, 

1929; Bass, 1932; Warren, 1960; Matson and Blumer, 1973; 

Mapel, 1976; Robinson and Culbertson, 1984; Derkey, 1986; 

Culbertson and Saperstone, 1987a, b; Biewick and McLellan, 

1990, and Gruber, 1990). Coal data from wells and drill holes 

in the area were published in several reports (U.S. Geological 

Survey and Montana Bureau of Mines and Geology, 1980; 

Hansen and Culbertson, 1985; Culbertson, 1987; Wheaton and 

Donato, 2004).

Location-Numbering System

For this report, location numbers are used to identify 

wells according to their geographic position within the 

rectangular grid system used for the subdivision of lands 

(fig. 3). The location number consists of as many as 14 

characters and is assigned according to the location of a well 

within a given township, range, and section. The first three 

characters (for example, 05S) specify the position of a well 

in a township south (S) of the Montana Base Line, whereas 

the next three characters (40E) specify its position east (E) 

of the Montana Principal Meridian. The next two characters 

(31) are the section number; the next three to four characters 

(here, BDCC) designate the quarter section (160-acre tract), 

the quarter-quarter section (40-acre tract), the quarter-quarterquarter section (10-acre tract), and the quarter-quarter-quarterquarter section (2.5-acre tract), respectively, in which the 

well is located. These four subdivisions of the section are 

designated A, B, C, and D in a counter-clockwise direction, 

beginning in the northeastern quadrant. The last two characters 

(01) specify a sequence number to distinguish between 

multiple wells in a single tract. For example, as shown in 

figure 3, well 05S40E31BDCC01 is the first well inventoried 

in the SW1⁄4 of the SW1⁄4 of the SE1⁄4 of the NW1⁄4 of sec. 31, 

T. 1 S., R. 40 E.

Wells have been assigned other identifiers because data 

from these sites have been used in other investigations. For 

clarity and continuity, these site numbers are presented in this 

report as well.

6

 39 40 41

43 42

38

3 2 1E 1W 2 3

45 44

2

1S

29

30

31

32

3

4

5

5

4

3

2

1

7

18

8

10

11

12

13

14

15

16

18

19

21 22

20

28 27 26 25

24 23

29

30

34 35 36

32 33

17

1N

9

TOWNSHIP

RANGE

RANGE 40 EAST

TOWNSHIP 5 SOUTH

Location number for

well 05S40E31BDCC01

(NC02–1) 

A

A

A

A

A

D

D

B

B

B

B

C

C

C

C

D

D

D

31

SECTION 31

D

B

 Base line

Principal meridian

Figure 3. Location-numbering system and site number for wells 

in and near the study area, southeastern Montana.
8 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana

Methods of Investigation

Hydrogeologic data were compiled from various 

sources including the USGS National Water Information 

System—Groundwater Information and Data (NWIS) database, 

MBMG Ground-Water Information Center (GWIC) database, 

Woessner and others, (1981), and various coal-resource 

investigations of areas primarily outside the reservation. 

Proprietary drill-hole data from coal, oil, and gas wells were 

obtained from the Northern Cheyenne Tribe.

Estimation of Extent, Thickness, 

and Volume of Coal Beds

For each of the five coal beds evaluated in this study, 

the extent, thickness, and volume of the coal beds were 

estimated by using available well, drill-hole, and outcrop 

data in the reservation and nearby areas (fig. 1). Coal beds 

throughout the study area were indentified manually by 

considering correlations determined in previous studies, 

structural relations, and observations of geologists and Tribal 

officials. Altitude of the top and bottom of each coal bed 

then was used for correlation, to the extent possible, across 

the study area. Coal-bed thickness could be determined only 

from well and drill-hole data. In some instances, thickness 

data were not available where coal beds crop out; these 

outcrops typically are obscured by clinker and overlying 

sediments that have subsided into the burned area that formed 

the clinker (Heffern and Coates, 2004; Heffern and others, 

2007). Geologic information and correlation of coal beds in 

the study area relied primarily on geologic information from 

McKay (1976a, b), Woessner and others (1981), Andrews and 

others (1981), Culbertson (1987), Culbertson and Saperstone 

(1987a, b), Biewick and McLellan (1990), McLellan and 

others (1990), and Heffern and others (1993), and from 

proprietary data. Additionally, to estimate the volume of the 

Flowers-Goodale coal, thickness information from Biewick 

and McLellan (1990) were used to supplement other data 

compiled for this report.

Data for each well and drill hole included location 

(latitude and longitude), altitude of tops and bottoms, and 

thickness (in feet) for each of the five coal beds. These data 

were compiled into a single geodatabase and processed by 

computer interpolation methods to estimate the volume of 

each coal bed. This geodatabase stored both tabular and spatial 

data in a format that was used internally and externally with 

software applications for a geographic information system 

(GIS). This approach provided a flexible platform for querying 

information about data in the geodatabase in multiple software 

platforms. ArcGIS, ArcScene 9.3.1 [Environmental Systems 

Research Institute (ESRI), 2010], and Microsoft Access 2007 

(Microsoft Corporation, 2010) were used to manage data and 

estimate the volume of each coal bed.

By using ArcGIS 9.3.1 tools, the top surface of each 

coal bed was interpolated between data points by using an 

inverse distance weighting (IDW) method. This method 

of interpolation estimates and assigns thickness values to 

locations (cells) by averaging the weighted values of known 

thickness at a data point (well and drill-hole data) near each 

processing cell. The closer a data point is to the center of the 

cell being estimated, the more influence, or weight, it has 

in the averaging process (Environmental Systems Research 

Institute, 2010).

Raster-based surfaces representing the thickness of 

each coal bed were developed from point data and manually 

contoured lines of equal thickness (4-ft contour intervals); 

the contour data were subsequently digitized and used as 

input data. Raster-based surfaces representing the coal 

thickness were created by using the “Topo to Raster” tool 

in ArcGIS 9.3.1, which is an interpolation method specifically designed to create raster surfaces and hydrologically 

corrected digital-elevation models (DEMs). The interpolation procedure uses commonly available data, such as point, 

line, and polygon features and the known characteristics 

of altitude of the raster-based surfaces. The method uses 

iterative, finite-difference interpolation that is optimized 

to have the computational efficiency of local interpolation methods (such as IDW interpolation) without losing 

the surface continuity of other interpolation methods, such 

as kriging and spline (Environmental Systems Research 

Institute, 2010).

By using both of the raster-based surfaces created for 

the top elevation and the thickness for each of the five coal 

beds, the additive “Map Algebra” functions in ArcGIS 9.3.1 

were then used to calculate the bottom altitude for each coal 

bed. All of the surfaces created (top, bottom, and thickness) 

were reviewed, inconsistencies and errors were identified, 

and surfaces were re-created through an iterative process.

Last, by using the raster-based thickness surface for 

each coal bed, volume estimates were calculated by using 

the “3D Analyst” extension in ArcGIS 9.3.1. The “Surface 

Volume” tool was used to calculate the volume of the rasterbased surface relative to a given base height or reference 

plane. The tool was used to calculate the volume as cubic 

meters (subsequently calculated as acre-feet) between the 

plane and the top of the surface. Data were reviewed and 

stored in the final geodatabase.

The results of the computer interpolations used for 

this study are simplified representations of very complex 

physical conditions. One important assumption used to estimate the volume of the coal beds was that each coal was laterally continuous for an arbitrary distance of 1,320 ft (0.25 mi) 

beyond each data point. Additionally, the volume of each coal 

bed was only estimated to 1,320 ft beyond the 4-ft contour 

because it was assumed that coal aquifers that were less than 

4 ft thick were unlikely to yield substantial amounts of water. 

Furthermore, another important assumption used to estimate 
Methods of Investigation 9

the volume of each coal bed was that the coal beds were 

presumed to be continuous and uniform between data points 

where the volume was estimated. However, these coals are not 

necessarily continuous and uniform (fig. 4). Typically, coal 

beds can change in relatively short distances by (1) splitting, 

(2) merging, (3) pinching out, (4) differential compaction, and 

(5) fault displacement (Flores and others, 2010). For example, 

Woessner and others (1981, fig. 5. 13) report that in the western part of T. 3 S., R. 43 E., the Knobloch coal bed splits to 

form the upper Sawyer and lower Knobloch coal beds. These 

researchers also report many other instances in which this and 

other coal beds split, merge, or pinch out in the reservation 

and, thus, most likely in the study area.

Estimation of the Volume of Water in Aquifers

The volume of water in each of the five coal aquifers was 

estimated by assuming that each coal bed was fully saturated 

(thickness of the coal bed was equal to thickness of the coal 

aquifer) and by using reported aquifer characteristics for coal 

beds in areas of Montana, North Dakota, and Wyoming. Waterlevel data (period of record from 1976–2009, table 1) also were 

compiled to determine whether coal beds were unconfined or 

confined and to determine the percentage of saturation of each 

coal bed. Based on the compilation, estimates of the volume 

of water in the aquifers were determined for 25, 50, 75, or 

100 percent saturation of the coal bed when possible.

Aquifer Characteristics

Storage

The ability of unconfined coal aquifers to store water 

largely is related to the network of natural fractures (cleats) 

within the coal aquifer. Additionally, coal aquifers in the study 

area were determined to have a fracture system controlled by 

bedding properties and perhaps to crustal movements (Morin, 

2005). When an unconfined coal aquifer is dewatered, water 

stored within the cleats is drained by gravity; cleats within 

coal aquifers provide the permeability for fluid flow (Purl 

and others, 1991). The volume of water derived by gravity 

drainage of a saturated coal aquifer (specific yield or effective 

porosity) is no larger than the fracture porosity of the coal 

aquifer (Rehm and others, 1980).

In an unconfined aquifer, the volume of water derived 

from the expansion of water and the compression of the 

aquifer is negligible (Heath, 1983). Thus, for unconfined coal 

aquifers in the study area, the volume of water that can be 

obtained by gravity drainage can be estimated by using the 

equation (modified from Heath 1983):

Vw = Sy × Va, (1)

where

Vw is the volume of water drained from the coal 

aquifer by gravity, in acre-feet;

Sy is the specific yield, dimensionless;

Va is the volume of the aquifer, in acre-feet.

Various researchers have examined the hydraulic 

properties of coal aquifers in areas of Montana, North Dakota, 

and Wyoming and have measured or estimated the specific 

yield of coal aquifers to range from about 0.3 to 3 percent 

(Groenewold and others, 1979; Rehm and others, 1980; 

Woessner and others, 1981; Davis, 1984). Thus, fracture 

porosity in the coal aquifers investigated in this study was 

assumed to range from 0.3 to 3 percent and average about 

1 percent by volume (specific yield of 0.01). A specific yield 

of 0.01 was used to estimate the volume of water in each of 

the five coal aquifers where the volume of bed was estimated 

by computer interpolation.

Figure 4. Conceptual model showing complex thinning, splitting, merging, and pinching out of coal beds (modifed from Flores and 

others, 2010). 

Split Split

Split

Pinchout

Partings

Pinchout

Merge

Merge

Coal

Interbedded sandstone, 

 siltstone, and shale

Clinker

EXPLANATION
10 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana

Table 1. Hydrogeologic data for selected wells completed in five coal beds in and near the study area, southeastern Montana.

[Location-numbering system described in text. Latitude and longitude are referenced to the North American Datum of 1983 (NAD 83). All altitudes are reported 

in feet above National Geodetic Vertical Datum of 1929 (NGVD 29). Altitudes of static-water levels are rounded to the nearest foot. Abbreviations: CBM, coal-bed 

methane; C, confined; E, electric tape; ft, feet; gal/min, gallons per minute; GWIC, Ground Water Information Center (Montana Bureau of Mines and Geology); 

M or MBMG, Montana Bureau of Mines and Geology; S, source of data, U.S. Geological Survey; SO, sounder; TOC; top of casing; UC, unconfined; USGS, 

U.S. Geological Survey; W, data from Woesnner and others (1981). Symbol: – –, no data or no remarks]

Location

number1

Site

number

Latitude Longitude Altitude of 

land surface 

or top of 

the casing2

Well depth, 

in feet, below 

land surface

Static-water level, 

in feet, below land 

surface or top of 

the casing2

Altitude of 

static-water 

level, below 

measuring point2

Altitude of top 

coal aquifer, 

below land 

surface 

Percent saturation 

of coal bed the at 

the time of waterlevel measurement

in degrees, 

minutes, seconds

Canyon coal

05S40E13ADAB01 NC02–4 452429 1064354 3,940 326 – – – – 43,916 – –

05S40E31BDCC01 NC02–1 452139 1065049 4,440 655 – – – – 4,079 0

Wall coal

05S40E13ADAB01 NC02–4 452429 1064354 3,940 326 200.07 3,740 3,636 C 100

05S40E31BDCC01 NC02–1 452139 1065049 4,440 655 624.7 3,815 3,828 UC 76

06S40E01CDDC01 PDC–33 452021 1064652 3,940 250 96.15 3,844 3,702 C 100

06S40E02DBDA01 PDC–6 452040 1064744 4,030 278 270.32 3,760 3,803 UC 6

06S41E06ABBC01 DH79–108 452101 1064526 4,020 348 273.29 3,747 3,681 C 100

Pawnee coal

05S41E14BDCD01 NC02–6 452408 1063833 3,510 356 – – – – 53,402 C 5,100

05S41E17ADBD01 NC02–3 452416 1064132 3,740 348 182.25 3,558 3,418 C 100

Knobloch coal

02S43E35CBC01 NCRP 27 453702 1061630 3,380 283 254.04 3,126 3,183 UC 28

03S43E01BDAA01 NCRP 31C 453134 1062245 3,220 176 126.38 3,094 3,106 UC 73

03S43E15AAAA01 NCRP 29A 453457 1062401 3,275 260 38.90 3,236 3,097 C 100

03S43E23BCC01 NCRP 30A 453342 1062009 3,080 124 85.15 2,995 2,989 C 100

04S42E36BDAA01 NCRP 11A 452707 1062931 3,302 265 138.08 3,164 3,052 C 100

05S41E14BDCD01 NC02–6 452408 1063824 3,510 356 238.94 3,271 3,174 C 100

05S42E14ADDC01 NC02–2 452412 1063018 3,220 394 – – – – 3,075 UC – –

05S42E16CCAB01 NC02–5 452355 1063339 3,400 370 262.58 3,137 3,055 C 100

05S42E28DDAC02 CBM01–8KC 452208 1063252 3,262 208 158.00 3,104 3,070 C 100

05S43E07DBBA01 NC97–3 452500 1062812 3,115 240 – – – – – – – –

Flowers-Goodale coal

05S42E14ADDC02 NC02–2 452412 1063018 3,220 394 107.40 3,113 2,856 C 100

05S42E28DDAC01 CBM02–8FG 452208 1063252 3,261 480 101.59 3,159 2,801 C 100

05S43E07CCDC01 NC05–1 452438 1062839 3,170 750 Flowing; staticwater level not 

available

– – 2,856 C 100

05S43E07CCDC02 NC05–2 452438 1062840 3,170 348 49.25 3,121 2,865 C 100
Methods of Investigation 11

Table 1. Hydrogeologic data for selected wells completed in five coal beds in and near the study area, southeastern Montana.—Continued

[Location-numbering system described in text. Latitude and longitude are referenced to the North American Datum of 1983 (NAD 83). All altitudes are reported 

in feet above National Geodetic Vertical Datum of 1929 (NGVD 29). Altitudes of static-water levels are rounded to the nearest foot. Abbreviations: CBM, coal-bed 

methane; C, confined; E, electric tape; ft, feet; gal/min, gallons per minute; GWIC, Ground Water Information Center (Montana Bureau of Mines and Geology); 

M or MBMG, Montana Bureau of Mines and Geology; S, source of data, U.S. Geological Survey; SO, sounder; TOC, top of casing; UC, unconfined; USGS, 

U.S. Geological Survey; W, data from Woesnner and others (1981). Symbol: – –, no data or no remarks]

Location

number1

Method 

of water-level

measurement

Date 

of water-level

measurement

Source

of data Remarks3

Canyon coal

05S40E13ADAB01 – – – – S Geologist’s log reported “from 24–44 ft, Coal (Canyon).” Well was completed in Wall coal.

05S40E31BDCC01 – – – – S USGS geologist’s log reported “from 361–382 ft, Coal, black, dry (Canyon).”

Wall coal

05S40E13ADAB01 E 11/03/09 S – –

05S40E31BDCC01 E 06/06/05 S – –

06S40E01CDDC01 S 03/06/82 S Geologist’s log reported 7 ft of parting between the upper Wall coal (47 ft thick) and lower 

Wall coal (10 ft thick). The packer was set at the top of the lower Wall coal and the well 

was perforated in this same bed.

06S40E02DBDA01 E 03/06/82 S Geologist’s log reported 46 ft of Wall coal.

06S41E06ABBC01 E 03/06/82 S Most likely completed in the upper Wall coal.

Pawnee coal

05S41E14BDCD01 – – – – S Geologist’s log reported “from 108–130, Coal (producing 15 gal/min, Pawnee).” Well 

was completed in Knobloch coal. Nearby test hole drilled to 740 ft. Combined depth 

shown on fig. 6 for NC02–6. Drilled to top of Lebo Shale Member of the Tertiary 

Fort Union Formation.

05S41E17ADBD01 E 11/03/09 S Geologist’s log reported “from 322–346, Coal (Pawnee); hole producing more than 20 gal/min.”

Knobloch coal

02S43E35CBC01 W 10/20/76 W – –

03S43E01BDAA01 W 10/20/76 W – –

03S43E15AAAA01 E 11/02/09 S – –

03S43E23BCC01 W 10/20/76 W – –

04S42E36BDAA01 W 10/20/76 W – –

05S41E14BDCD01 E 11/03/09 S Nearby test hole drilled to 740 ft. Combined depth shown on fig. 6 for NC02–6. Drilled to 

top of Lebo Shale Member.

05S42E14ADDC01 – – – – Geologist’s log reported “145–166 ft, coal, black moist (upper Knobloch), saturated in 

lower part.” Drilled to Flowers-Goodale coal.

05S42E16CCAB01 E 11/03/09 S – –

05S42E28DDAC02 SO 08/28/09 M MBMG other identifier: GWIC 203697

05S43E07DBBA01 – – – – S Well not completed in Knobloch coal; geologist’s log used for correlation (fig. 6).

Flowers-Goodale coal

05S42E14ADDC02 E 11/03/09 S – –

05S42E28DDAC01 SO 08/28/09 M MBMG CBM monitoring well and other identifier: GWIC 203701; MBMG geologist’s log 

reported “Brewster-Arnold damp at base.”

05S43E07CCDC01 – – – – S Geologist’s log reported “314–340 ft, coal (Flowers-Goodale); hole producing about 30 gal/min.” 

Drilled to determine top of Lebo Shale Member of the Tertiary Fort Union Formation.

05S43E07CCDC02 E 11/03/09 S – –

1

Some locations from Woessner and others (1981) were not field checked by the USGS. For these sites, latitude and longitudes were estimated from the 

Montana State Library—Natural Resouce Information Sysytem (http://maps2.nris.mt.gov/topofinder1/subsection.asp) that converts public-land survey information 

to latitude and longitude. Some of these wells were field checked in summer 2010 and were then assigned more accurate latitudes and longitudes.

2

Static-water level data from Woessner and others (1981) are reported from the top of the casing; all other static-water level data are reported from land surface.

3

All logs are from the USGS (unless noted otherwise) and on file at USGS Montana Water Science Center, Helena, Mont.

4

The Canyon coal at this well was assumed to be dry because the top of the coal was only 24 ft below land surface, and the same coal was dry at nearby 

well NC02–1.

5

The Pawnee coal at this well was assumed to be fully saturated and under confined conditions because a geologist’s log reported that the well was producing 

15 gal/min at that interval; the same aquifer was under confined conditions at nearby well NC02–3.
12 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana

Water storage in confined coal aquifers (storage 

coefficient or storativity, Freeze and Cherry, 1979) is related 

to properties of both cleats and compressible storage in the 

unfractured coal matrix. When hydraulic head is reduced in 

a confined coal aquifer, some water is released from storage 

through the expansion of water and compression of the aquifer 

material. Release of water from the cleat system is much faster 

than from the coal matrix because of the large difference in 

hydraulic conductivity between the cleats and coal matrix. 

However, compressible storage in the coal matrix is generally 

substantially greater than that in the cleats (Weeks, 2005). A 

storage coefficient calculated from a multiple-well aquifer 

test in the Flowers-Goodale coal (25 ft thick) near Birney 

Day School was 1.4×10–4 (Weeks, 2005). The corresponding 

specific storage (defined as the volume of water that a unit 

volume of confined aquifer releases from storage under a unit 

decrease in hydraulic head, Freeze and Cherry, 1979) was 

5.6×10–6/ft. The specific storage of the Flowers-Goodale coal 

compares favorably with a specific storage of 8×10–6/ft for 

the Anderson coal and 2×10–5/ft for the Sawyer-A coal in the 

Powder River Basin of Montana (Stoner, 1981). Additionally 

storage coefficients for coal aquifers in the Decker area [the 

Anderson, Dietz 1, and Dietz 2 coal beds of Baker (1929 

)] ranged from about 1.0×10–5 and 3.0×10–5 (Van Voast and 

Hedges, 1975). The storage coefficients of most confined 

aquifers range from 1.0×10–3 to 1.0×10–5 and is about 1.0×10–6

per foot of thickness (Lohman, 1979).

If the water level in a confined coal aquifer decreases 

below the top of the bed, then the aquifer becomes unconfined 

and the volume of water is then derived by gravity drainage; 

the volume of water can then be estimated by using 

equation 1. For example, by using a specific yield of 0.01, a 

coal aquifer that was 10-ft thick when dewatered by gravity 

drainage, would yield 0.1 acre-feet (acre-ft) of water per 

acre from a 10-ft decrease in hydraulic head. With a specific 

storage of 1.0×10–6/ft, a confined coal aquifer that was 10-ft 

thick would yield 0.0001 acre-ft of water per acre from a 

10-ft decrease in hydraulic head. This calculation shows 

that the volume of water stored in confined coal aquifers by 

compressible storage in the unfractured coal matrix typically 

would be at least three orders of magnitude smaller than the 

volume of water derived by gravity drainage of saturated coal. 

However, Freeze and Cherry (1979) and Lohman (1979) noted 

that large hydraulic head changes over extensive areas can 

produce substantial volumes of water from confined aquifers.

For this report, the estimated volume of water released 

from confined storage from coal aquifers also was assumed to 

be small when compared with the estimated volume of water 

derived by gravity drainage. Therefore, despite the fact that all 

five coal aquifers may exist in both unconfined and confined 

conditions in the study area, only the volume of water that 

could be drained by gravity from storage under unconfined 

conditions was included in estimates of the volume of water 

in each coal aquifer.

Hydraulic Conductivity and Transmissivity

The hydraulic conductivity of rock or soil is a measure 

of its ability to transmit water and typically is reported in 

units of foot per day (ft/d). Transmissivity also is used as a 

measure of how rock or soil can transmit water and is reported 

in feet squared per day (ft2/d). Hydraulic conductivity values 

of coal, sandstone, and interbedded siltstone, clay, and shale

of the Fort Union Formation are described here to show the 

relatively large hydraulic conductivity and transmissivity 

of the coal aquifers as compared with the other sedimentary 

rocks that make up the formation. The larger hydraulic 

conductivity and transmissivity of the laterally extensive 

coal aquifers makes these aquifers favorable conduits for 

groundwater flow.

The hydraulic conductivity of the Flowers-Goodale coal 

near Birney Day School was 4.3 ft/d (Weeks, 2005). Slagle 

and others (1985) reported that hydraulic conductivity for the 

Anderson coal ranged from 0.34 to 6.5 ft/d and transmissivity 

ranged from 11 to 223 ft2/d. McClymonds (1982) reported 

that hydraulic conductivity for the Wall coal (just south of the 

study area) ranged from 0.05 to 2.4 ft/d and transmissivity 

from the same aquifer tests ranged from 2.5 to 65 ft2/d. 

Woessner and others (1981) reported that hydraulic 

conductivity for the Knobloch coal ranged from 0.9 to 2.9 ft/d. 

Last, Van Voast and Hedges (1975) reported that hydraulic 

conductivity for coal beds in the Decker area ranged from 0.5 

to 19 ft/d and transmissivity ranged from 5 to 270 ft2/d.

For hydraulic conductivity, Wheaton and Metesh 

(2002) determined a geometric mean value of 1.1 ft/d (from 

370 values) for coal aquifers in the Powder River Basin of 

Montana, with standard deviations of 13 and 0.098 ft/d (plus 

or minus one standard deviation, respectively). The values 

of hydraulic conductivity for coal aquifers in the study area 

and in the Powder River Basin are somewhat larger than the 

geometric mean of hydraulic conductivity of 0.18 ft/d, with 

standard deviations of 2.1 and 0.015 ft/d (plus or minus one 

standard deviation, respectively) reported for sandstone in the 

Powder River Basin of Montana (Wheaton and Metesh, 2002). 

In contrast, Rehm and others (1980) determined a geometric 

mean for hydraulic conductivity of 0.007 ft/d (from 63 values) 

for Paleocene silt, clay, and shale in Montana, Wyoming, and 

North Dakota.

Water-Level Data

Water-level data were compiled to estimate the volume of 

water in each of the five coal beds and to determine whether 

these coal beds were unconfined or confined. Water-level data 

from wells completed in these coal beds were scarce (table 1); 

thus, in all instances, geologists’ logs were carefully reviewed 

to ensure that water-level data were determined for the specific 

coal bed for this study.
Estimates of the Volume of Water in Five Coal Aquifers 13

Estimates of the Volume of Water 

in Five Coal Aquifers

Estimates of the volume of water in the five coal aquifers 

were based on equation 1, a specific yield of 0.01, and the 

assumption that the five coal beds were unconfined. The 

volume of water was estimated by assuming that each coal 

bed was fully saturated (thickness of the coal bed was equal 

to the thickness of the coal aquifer, except for the Canyon 

coal). Additionally, estimates of the volume of water in 

the coal aquifers were determined only in areas where the 

volume of the coal beds could be estimated by computer 

interpolation. Woessner and others (1981) reported that the 

groundwater system within the Tongue River Member is 

complicated owing to complexly interstratified sandstone, 

shaley sandstone, siltstone, shale, and coal beds (figs. 2 and 

4). Only conservative estimates of the volume of water in the 

Canyon, Wall, Pawnee, Knobloch, and Flowers-Goodale coal 

beds are presented because (1) the subsurface extent of the 

coal beds are not well defined, (2) in some instances, well and 

drill-hole data were widely spaced and not well distributed, 

(3) of the possibility that some coal beds split, merge, or pinch 

out laterally, and (4) water-level data for wells completed in 

the five aquifers were scarce.

Canyon Coal

 The Canyon coal typically exists as erosional remnants 

in higher plateaus and can be highly dissected and, thus, has 

limited subsurface extent in the study area (figs. 5 and 6); the 

Canyon coal encompasses about 40,100 acres (about 63 mi2). 

Where the volume of this coal could be estimated by computer 

interpolation, the Canyon coal averages about 26 ft thick 

(table 2, fig. 5). This coal bed splits and thins just north and 

west of the study area boundary (Woessner and others, 1981).

For unconfined conditions, the volume of water in the 

Canyon coal was estimated to range from about 10,400 acre-ft 

(75 percent saturated) to 3,450 acre-ft (25 percent saturated, 

table 2). Water-level data for the Canyon coal were unavailable, 

but one geologist’s log (table 1) indicated that at well 

NC02–1 (fig. 5), the Canyon coal was dry. Because of its high 

topographic position (fig. 6), and because water-level data are 

unavailable to assess the amount of saturation of this coal, 

100 percent saturation was not considered probable within 

the study area. The smaller estimates of water in the Canyon 

coal (75 to 25 percent saturation, table 2) are considered more 

reasonable. However, estimates of the volume of water in the 

Canyon coal might have large errors and need to be used with 

caution because the water-level data needed to define the volume 

of water were unavailable.

Because the Canyon coal is highly dissected in the study 

area, this coal most likely is composed of local flow systems 

with variable amounts of recharge and discharge at different 

locations. For example, Woessner and others (1981) noted 

that in the southwest corner of the reservation, the base of 

the Canyon coal is the source of many springs. McClymonds 

(1982) also noted that just south of the study area near wells 

PDC–6 and PDC–33 (fig. 5), numerous seeps and springs 

issue from the Canyon coal. Additionally, McClymonds 

(1982) reported that this coal probably is a major contributor 

to increased streamflow in Prairie Dog Creek, which is a 

tributary to the Tongue River (fig. 1).

Wall Coal

The Wall coal, which has limited subsurface extent in 

the study area (fig. 7), encompasses about 54,800 acres (about 

86 mi2). Where the volume of this coal could be estimated by 

computer interpolation, the Wall coal averages about 44 ft thick 

(table 2, fig. 7). Near well NC02–1, the overlying Cook coal 

(fig. 2) was assumed to merge with the Wall coal (Woessner 

and others, 1981), which probably accounts for this coal’s 

greater thickness along part of the southern study area boundary 

(fig. 7). Conversely, splits of the upper and lower Wall coal 

were noted in the study area as far west as T. 5 S., R. 40 E. (drill 

holes A–12 and A–13 of Culbertson, 1987). The thickness of the 

Wall coal is unknown in the eastern part of the study area where 

it exists near Black Eagle Fork. Woessner and others (1981, 

fig. 5.15) reported that the Wall coal thins (not shown on fig. 7) 

and eventually disintegrates into thin clinker and white clayey 

zones near Pawnee and Kelty Creeks.

For unconfined conditions, the volume of water in the 

Wall coal was estimated to range from about 14,200 acre-ft 

(100 percent saturated) to 3,560 acre-ft (25 percent saturated, 

table 2). Water-level data from two wells (NC02–1 and 

PDC–6) indicate that the Wall coal at these wells was 

unconfined, and water-level data from three wells (NC02–4, 

PDC–33, and DH79–108) indicate that this coal at these 

wells was confined (table 1, fig. 7). Just south of the study 

area, McClymonds (1982) determined that the Wall coal is 

composed of two beds with a parting of about 7 ft. The upper 

bed can be unconfined or dry, whereas water levels in a well 

completed in the lower bed indicated confined conditions 

(PDC–33; table 1, fig. 7). Because the Wall coal exists under 

unconfined and confined conditions and can be 100 percent 

saturated, the estimates of the volume of water in the Wall 

coal probably are reasonable.

Periodic water-level data have been collected from two 

wells (figs. 6 and 7) completed in the Wall coal that are located 

in the study area. These data show that water levels in well 

NC02–4 fluctuated less than 1.5 ft (periodic measurements from 

December 2002 through November 2010), whereas water levels 

in well NC02–1 fluctuated about 53 ft (periodic measurements 

from December 2002 through June 2005; water-level data for 

both wells were accessed at http://nwis.waterdata.usgs.gov/mt/

nwis/gwlevels, April 11, 2011). The water level measured 

in well NC02–1 in December of 2002 (575.7 ft below land 

surface) is slightly higher than the rest of the measurements 

that ranged from 613.5 to 628.24 ft below land surface.
14 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana Figure 5. Generalized subsurface extent and thickness of the Canyon coal in the study area, southeastern Montana.

Dry

Cook

Logging

Tie

Kelty Creek

Pawnee Creek

Tongue

Creek

Creek

Fork

Black

Eagle

Creek

Creek

River

Cr

Prairie Dog

R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 44 E. R. 43 E.

T. 5 S.T. 4 S.T. 3 S.

0 3 6 MILES

0 3 6 KILOMETERS

106°22'30" 106°52'30"

45°35'

45°30'

45°22'30"

ROSEBUD COUNTY

Geology modified from 

Woessner and others (1981) and Heffern and others (1993) 

BIGHORN COUNTY

NC02–1

NC02–4

PDC–6

PDC–33

26

NC02–4

30

62

18

30

26

26

22

41

26

Base from U.S. Geological Survey digital-line graph data, 2010, 1:100,000; MontanaState Library, 1993–2003, 1:100,000; Montana Department of Administration, 2003, 1:24,000Albers Equal Area Conic projectionStandard parallels 29°30’ and 45°30’, central meridian 106°00’North American Datum of 1927 (NAD 27)

Birney Day

School

Well and site number (table 1)

EXPLAN

ATION

Canyon coal—Tongue River Member of the Tertiary  Fort Union Formation 

Generalized subsurface extentCoal volume estimated by computer interpolation  (table 2)

Line of equal thickness

—General thickness, in feet. 

 Contour interval is 4 feet. Dashed where approximately  located. Hachure indicates slight thinning of coal

MONTANA

Helena

Billings

Tongue River

NORTHERN

CHEYENNE

INDIAN

RESERVATION

Study

area

Yel ol wsto ne R vi er

Missouri R vi er
Estimates of the Volume of Water in Five Coal Aquifers 15

Pawnee Coal

The Pawnee coal, which is found in the subsurface 

throughout much of the study area (fig. 8), encompasses about 

73,600 acres (about 115 mi2). Where the volume of this coal 

could be estimated by computer interpolation, the Pawnee 

coal averages about 12 ft thick (table 2, fig. 8). This coal 

thins to the southwest and northeast and then thins and splits 

to the southeast (Woessner and others, 1981). Generally, the 

thickness of the Pawnee coal is unknown in the eastern part 

of the study area except near Pawnee and Kelty Creeks, where 

the coal ranges from about 6 to 10 ft thick.

For unconfined conditions, the volume of water in the 

Pawnee coal was estimated to range from about 9,440 acre-ft 

(100 percent saturated) to 2,360 acre-ft (25 percent saturated, 

table 2). Water-level data from one well (NC02–3, table 1, 

fig. 8) completed in the Pawnee coal indicated that the coal 

at this well was confined. Data from one geologist’s log 

indicated that at well NC02–6, the Pawnee coal probably was 

fully saturated and might have been confined (table 1, fig. 8). 

However, estimates of the volume of water in the Pawnee 

coal might have large errors and need to be used with caution 

because the water-level data needed to define the volume of 

water were largely unavailable.

 Periodic water-level data have been collected from 

one well (figs. 6 and 8) completed in the Pawnee coal that 

is located in the study area. These data show that water 

levels in well NC02–3 fluctuated less than 1.0 ft (periodic 

measurements from December 2002 through November 2010; 

http://nwis.waterdata.usgs.gov/mt/nwis/gwlevels, accessed 

April 11, 2011).

Knobloch Coal

The Knobloch coal, which is found in the subsurface 

throughout much of the study area (fig. 9), encompasses about 

75,200 acres (about 117 mi2). Where the volume of this coal 

could be estimated by computer interpolation, the Knobloch 

coal averages about 29 ft thick (table 2, fig. 9).

The Knobloch coal probably is one of the most 

complexly stratified geologic units in the study area. Heffern 

(1980), Woessner and others (1981), and Culbertson and 

Saperstone (1987b) reported that this coal is composed of a 

number of separate coal beds that merge near Ashland and can 

be as much as about 70 ft thick (McLellan and others, 1990). 

In the northeastern part of the study area near Logging Creek, 

part of the Knobloch coal is thought to split sharply from the 

main Knobloch coal bed to form the Sawyer coal (Woessner 

and others, 1981). North of Logging Creek, the Knobloch coal 

is composed of one main bed; south of Logging Creek, this 

coal bed splits into upper and lower beds. Near Birney Day 

School, the lower Knobloch bed splits again and the lower 

split is recognized as the Nance coal (Woessner and others, 

1981; Culbertson and Saperstone, 1987b). Farther south, the 

Knobloch coal splits and thins (Heffern, 1980) and to the west 

is either absent or splits and thins and (or) also pinches out to 

the west (Culbertson and Saperstone, 1987b). 

For unconfined conditions, the volume of water in 

the Knobloch coal was estimated to range from about 

38,700 acre-ft (100 percent saturated) to 9,680 acre-ft 

(25 percent saturated, table 2). Water-level data from two 

wells (NCRP 27 and NCRP 31C) and information from one 

geologist’s log (NC02–2) indicate that the Knobloch coal 

was unconfined at these wells, whereas water-level data from 

six wells (NCRP 29A, NCRP 30A, NCRP 11A, NC02–6, 

NC02–5, and CBM01–8KC) indicate this coal was confined 

at these wells (table 1, fig. 9). Water-levels in the two wells 

that indicate unconfined conditions show that this coal was at 

least 25 percent saturated when water levels were measured 

(table 1). Thus, estimates of the volume of water in the 

Knobloch coal probably are reasonable.

Water-level data have been collected in three wells 

(figs. 6 and 9) completed in the Knobloch coal that are 

located in the study area. Periodic water-level data indicate 

that water levels in well NCRP 29A fluctuated less than 11 ft 

(periodic measurements June 2007 through November 2010). 

By contrast, periodic water-level data indicate that water 

levels measured in wells NC02–5 and NC02–6 fluctuated less 

than about 2.5 ft (periodic measurements December 2002 

through November 2010; water-level data for both wells were 

accessed at http://nwis.waterdata.usgs.gov/mt/nwis/gwlevels, 

April 11, 2011).

Flowers-Goodale Coal

The Flowers-Goodale coal, which is found in the 

subsurface throughout most of the study area (fig. 10), 

extends west and north of the study area throughout the 

rest of the Northern Cheyenne Indian Reservation (Biewick 

and McLellan, 1990). Biewick and McLellan (1990) also 

showed that in the southern part of T. 5 S., R. 39 E. and 

T. 5 S., R. 40 E. this coal is missing (fig. 10). The FlowersGoodale coal encompasses about 132,400 acres (about 

207 mi2). Where the volume of this coal could be estimated 

by computer interpolation, the Flowers-Goodale coal averages 

about 17 ft thick (table 2, fig. 10) but is as much as 28 ft thick 

near Tie Creek (fig. 10). East and southeast of the Northern 

Cheyenne Indian Reservation, Biewick and McLellan (1990) 

showed that the Flowers-Goodale coal ranged from about 

3 to 20 ft in thick and also showed that the bed is laterally 

continuous across the reservation boundary.

For unconfined conditions, the volume of water 

in the Flowers-Goodale coal was estimated to be about 

35,800 acre-ft (100 percent saturated, table 2). Water-level 

data from three wells (NC02–2, CBM02–8FG, NC05–2) in 

and near the study area and information from one geologist’s 

log (NC05–1) indicate that the Flowers-Goodale coal was 

confined at these wells (table 1, fig. 10). Also, because this 
16 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana

?

?

?

?

?

?

? ? ?

?

?

Flowers-Goodale coal

?

?

Boundary of Northern Cheyenne Indian Reservation A

4,600

4,400

4,200

4,000

3,800

3,600

3,400

3,200

3,000

2,800

2,600

WEST

FEET

?

?

?

?

Apache Corp. 1–36 NC02–1

NC02–4

Cook Creek

NC02–3

Canyon coal

Canyon coal

Wall coal

Wall coal

Pawnee coal

BEND IN

SECTION

VERTICAL SCALE GREATLY EXAGGERATED

NATIONAL GEODETIC VERTICAL DATUM OF 1929 (NGVD 29)

Knobloch coal

Cook coal

Alluvium—Approximately located

Clinker—Approximately located

A A'

Coal—Dashed where inferred; queried where 

 extent or depth unknown

 Interbedded sandstone, siltstone, and shale

EXPLANATION

Quaternary

Tertiary—Tongue River Member, 

 Fort Union Formation

North Fork Bull Creek

Middle Fork Bull Creek

South Fork Bull Creek

Dietz 2 coal

Dietz 3 coal

0

0

1

1

2 KILOMETERS

2 MILES

Trace of section shown 

 on study-area map

Well and site number—

see table 1

NC02–1 NC02–1

Well and site number

MONTANA

Helena

Billings

Tongue River

NORTHERN

CHEYENNE

INDIAN RESERVATION

Study

area

Yellowsto ne River

Missouri River

Figure 6 (above and facing page). Generalized geologic section of the Tongue River Member of the Tertiary Fort Union Formation 

along the southern part of the Northern Cheyenne Indian Reservation, southeastern Montana.
Estimates of the Volume of Water in Five Coal Aquifers 17

4,600

4,400

4,200

4,000

3,800

3,600

3,400

3,200

3,000

2,800

2,600

EAST

FEET

NC02–6

Cook Creek

Cook Creek

Black Eagle Fork

NC02–5

NC02–2

Tongue River (Boundary of Northern Cheyenne Indian Reservation)

Pawnee coal

Knobloch coal

Flowers-Goodale coal

Nance coal

Pawnee coal

NC97–3

?

45°30'

106°30'

Birney Day

School

0 5 MILES

0 5 KILOMETERS

45°22’ 30”

106°52’30”

106°22'30"

Apache Corp. 1–36

NC02–1

NC02–4

NC02–3

NC02–6 NC02–2

NC02–5

A

׳A

Cook

Logging

Tongue

Creek

Creek

Pawnee Cr

River

Kelty Creek

Dry Creek

Bull Cr

Creek

Trail

Wall coal

Tie Cr

Black Eagle ForkBlack Eagle Fork

NC97–3

A'

South Fork

North Fork
18 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana

Table 2. Range of estimates of the volume of water in five coal aquifers in the study area, Northern Cheyenne Indian Reservation, 

southeastern Montana.

[Coal beds (aquifers) are within the Tongue River Member of the Tertiary Fort Union Formation. Areas where the volume of the five coal beds was estimated 

are shown in figures 5 and 7–10. Symbol: --, no estimate]

Estimated subsurface 

extent of coal bed,

in acres

Estimated subsurface

extent of coal bed used

for estimation of volume

Estimated average 

thickness of coal bed,

 in feet1

Estimated volume 

of coal bed,

 in acre-feet2

Estimated volume of water 

in coal aquifers, unconfined storage, 

in acre-feet3

Percent saturation

100 75 50 25

Canyon coal4

40,100 31,200 26 1,380,700 -- 10,400 6,900 3,450

Wall coal

54,800 36,800 44 1,422,900 14,200 10,700 7,110 3,560

Pawnee coal4

73,600 40,300 12 944,300 9,440 7,080 4,720 2,360

Knobloch coal 5

75,200 47,800 29 3,871,000 38,700 29,030 19,400 9,680

Flowers-Goodale coal

132,400 73,600 17 3,578,000 35,800 6-- 6-- 6--

1

Average thickness was calculated only for the area where the volume of the coal bed was estimated by computer interpolation.

2

Methods for estimating volume of coal beds are described in the section “Estimation of Extent, Thickness, and Volume of Coal Beds” of this report.

3

Methods for estimating volume of water in unconfined storage are described in the section “Storage” of this report. Estimated volumes are rounded to three 

significant figures.

4

Estimates might have large errors because water-level data needed to define the volume of water do not exist.

5

Generalized subsurface extent excludes that area where the extent of the Knobloch coal was uncertain (figure 9).

6

Flowers-Goodale coal was assumed to be confined throughout the study area; data indicate that water levels can be as much as about 350 feet above the top 

of this bed (table 1).

coal generally is deeply buried in the study area (about 200 ft 

or more, fig. 6), the Flowers-Goodale coal was assumed to 

be confined throughout its extent in the study area. Thus, the 

estimates of the volume of water in the Flowers-Goodale coal 

probably are reasonable.

Water-level data have been collected in two wells 

(figs. 6 and 10) completed in the Flowers-Goodale coal that are 

located in the study area. Periodic and continuous water-level 

data from wells NC02–2 (period of record September 2002 

through September 2010; U.S. Geological Survey, 2010b) and 

NC05–2 indicate that water levels in these wells have fluctuated 

less than about 2 ft (period of record June 2007 through 

November 2010, accessed at http://nwis.waterdata.usgs.gov/mt/

nwis/gwlevels, April 11, 2011).

Reliability and Uncertainty 

of Volume Estimates

As stated by Flores and others (2010), sufficient data 

are needed to accurately characterize coal-bed horizontal and 

vertical variability, which is highly complex both locally and 

regionally (fig. 4). Additionally, the distribution of wells or 

drill holes is important because data from these sites is the 

ultimate control governing the reliability and uncertainty of 

any estimate of the volume of coal (Wood and others, 1983). 

Splitting, merging, pinching out, differential compaction, 

and fault displacement can further complicate correlation of 

coal beds and also can affect the reliability of the estimates 

of the volume of the coal beds between data points. 

Variations of coal thickness presented in this report might 

reflect variations influenced by some or all of these factors. 

Where data points are widely spaced, the reliability of 

estimates of the volume of coal beds is decreased. Likewise, 

reliable estimates of the volume of water in coal aquifers 

depend heavily on reliable geologic information, such as 

subsurface extent and thickness and correlation of coal beds. 

Additionally, reliable estimates of the volume of water in 

coal aquifers depend heavily on data from wells, such as 

up-to-date water-level and well-completion data and data 

about coal-aquifer characteristics. Because the data needed 

to define the volume of water were sparse, only conservative 

estimates of the volume of water in the five coal aquifers are 

presented in this report. These estimates need to be used with 

caution and mindfulness of the uncertainty associated with 

these estimates.
Reliability and Uncertainty of Volume Estimates 19 Figure 7. Generalized subsurface extent and thickness of the Wall coal in the study area, southeastern Montana.

Well and site number—Upper letter(s) indicate whether coal at the well was unconfined (UC) or confined (C). Lower letters are site number (table 1)

EXPLAN

ATION

C

NC02–4

Wall coal—Tongue River Member of the Tertiary  Fort Union Formation 

Generalized subsurface extentArea where volume of coal was estimated by computer  interpolation (table 2) 

Line of equal thickness

—Shows general thickness, in feet. 

 Contour interval is 4 feet. Dashed where approximately  located. Hachure indicates slight thinning of aquifer 

36

0 3 6 MILES0 3 6 KILOMETERS

Geology modified from 

Woessner and others (1981) and Heffern and others (1993) Base from U.S. Geological Survey digital-line graph data, 2010, 1:100,000; Montana

State Library, 1993–2003, 1:100,000; Montana Department of Administration, 2003, 1:24,000Albers Equal Area Conic projectionStandard parallels 29°30' and 45°30', central meridian 106°00'North American Datum of 1927 (NAD 27)

R. 44 E. R. 43 E.

T. 4 S.T. 3 S.

R. 41 E. R. 42 E.

T. 5 S.

R. 39 E. R. 40 E.

106°22'30"

45°35'45°30'

106°52'30"

45°22'30"

ROSEBUD COUNTY

Logging

Creek

Tongue

River

Kelty Creek

Tie

Creek

Birney Day

School

Cook

Creek

C

PDC–33

C

DH79–108

BIGHORN

COUNTY

48

48

44

40

40

36

44

C

NC02–4

48 UC NC02–1

48

52

UC

PDC–6

40

48

44

44

Dry

Creek

Black

Eagle Fork

Pawnee Creek

MONTANA

Helena

Billings

Tongue River

NORTHERN

CHEYENNE

INDIAN

RESERVATION

Study

area

Yel ol wsto ne R vi er

Missouri R vi er

Prairie Dog Cr
20 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana Figure 8. Generalized subsurface extent and thickness of the Pawnee coal in the study area, southeastern Montana. 22

Well and site number

—Upper letter(s) indicate whether

 coal at the well was unconfined (UC) or confined (C). Lower letters are site number (table 1)

EXPLAN

ATION

C

NC02–3

Pawnee coal

—Tongue River Member of the Tertiary 

 Fort Union Formation

Generalized subsurface extentArea where volume of coal was estimated by computer  interpolation (table 2)

Line of equal thickness

—Shows general thickness, 

 in feet. Contour interval is 4 feet. Dashed where  approximately located

0 3 6 MILES0 3 6 KILOMETERS

Base from U.S. Geological Survey digital-line graph data, 2010, 1:100,000; MontanaState Library, 1993–2003, 1:100,000; Montana Department of Administration, 2003, 1:24,000Albers Equal Area Conic projectionStandard parallels 29°30' and 45°30', central meridian 106°00'North American Datum of 1927 (NAD 27)

Geology modified from 

Woessner and others (1981) and Heffern and others (1993) 

R. 44 E. R. 43 E.

T. 5 S.T. 4 S.T. 3 S.

R. 39 E. R. 40 E. R. 41 E. R. 42 E.

106°22'30"

45°35'45°30'

106°52'30"

45°22'30"

BIGHORN

COUNTY

Logging

Creek

ROSEBUD COUNTY

River

10

10

6

Tongue

Birney Day

School

14

C

NC02–3

C

NC02–6

18

22

22

26

26

14

18

22

6

10

22

Dry

Creek

10

6

Kelty

Creek

Pawnee Creek

TieCreekTieCreek

Black Eagle

Black Eagle

Cook

Creek

Cook

Creek

Fork

MONTANA

Helena

Billings

Tongue River

NORTHERN

CHEYENNE

INDIAN

RESERVATION

Study

area

Yel ol wsto ne R vi er

Missouri R vi er

Prairie Dog Creek
Reliability and Uncertainty of Volume Estimates 21 Figure 9. Generalized subsurface extent and thickness of the Knobloch coal in the study area, southeastern Montana. Base from U.S. Geological Survey digital-line graph data, 2010, 1:100,000; Montana State Library, 1993–2003, 1:100,000; Montana Department of Administration, 2003, 1:24,000 Albers Equal Area Conic projection Standard parallels 29°30' and 45°30', central meridian 106°00' North American Datum of 1927 (NAD 27) 

EXPLANATION

Knobloch coal

—Tongue River Member of the Tertiary 

 Fort Union Formation 

Generalized subsurface extent

Well and site name

—Upper letter(s) indicate whether

 coal at the well was unconfined (UC) or confined (C). Lower letters are site number (table 1)

Generalized area where subsurface extent uncertain.  Coal might have split, merged, or pinched outArea where volume of coal was estimated by computer  interpolation (table 2) 

Line of equal thickness

—Shows general thickness, in feet. 

 Contour interval is 4 feet. Dashed where approximately  located. Hachure indicates slight thinning of coal 

C

NC02–6

8

0 3 6 MILES0 3 6 KILOMETERS

Geology modified from Woessner and others (1981) and Heffern and others (1993) 

T. 3 S.T. 4 S.T. 5 S.

R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 44 E. R. 43 E.

45°22'30"

106°22'30" 106°52'30"

45°35'45°30'

ROSEBUD

COUNTY

BIGHORN COUNTY

C

NC02–6

20UC

NC02–2

C

NC02–5 C

CBM01–8KC

C

NCRP 11A

32

28

20

4

Birney Day

School

24

Tongue

28

36

36

40

40

44

48

44

River

44

52

56

C

NCRP 29A

52

48

48

UC

NCRP 27

64

64

60

60

68

C

NCRP 30A

UC

NCRP 31C

Dry

Creek

Loggin g Creek

Kelty C reek

Pawnee Cr Pawnee Cr

Cook

Creek

Cook

Creek

Black Eagle ForkBlack Eagle Fork

Tie Cr

16

12

8

MONTANA

Helena

Billings

Tongue River

NORTHERN

CHEYENNE

INDIAN

RESERVATION

Study

area

Yel ol wstone R vi er

Missouri R vi er

Prairie Dog

Creek
22 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana Figure 10. Generalized subsurface extent and thickness of the Flowers-Goodale coal in the study area, southeastern Montana.

Dry

Cook

Kelty Creek

Tongue

Creek

Creek

Fork

Creek

River

Creek

Birney Day

School

20

24

16

12

20

24

8

16

20

24

C

NC02–2

C

NC05–1, 2

28

C

CBM02–8FG

Black Eagle

Pawnee

Logging

4

0

20

Well and site number

—Upper letter(s) indicate whether

 coal at the well was unconfined (UC) or confined (C). Lower letters are site number (table 1)

EXPLAN

ATION

C

NC02–2

Flowers-Goodale coal—Tongue River Member of the  Tertiary Fort Union formation 

Generalized subsurface extentArea where volume of coal was estimated by computer  interpolation (table 2)

Line of equal thickness—Shows general thickness,  in feet. Contour interval is 4 feet. Dashed where  approximately located 

0 3 6 MILES

0 3 6 KILOMETERS

Geology modified from 

Woessner and others (1981) and Heffern and others (1993);

lines of equal thickness modified from Biewick and McLellan (1990) 

Base from U.S. Geological Survey digital-line graph data, 2010, 1:100,000; Montana State Library, 1993–2003, 1:100,000; Montana Department of Administration, 2003, 1:24,000Albers Equal Area Conic projectionStandard parallels 29°30' and 45°30', central meridian 106°00'

North American Datum of 1927 (NAD 27)

R. 39 E. R. 40 E. R. 41 E. R. 42 E. R. 44 E. R. 43 E.

T. 5 S.T. 4 S.T. 3 S.

106°22'30" 106°52'30"

45°35'45°30'

45°22'30"

ROSEBUD COUNTY

BIGHORN COUNTY

MONTANA

Helena

Billings

Tongue River

NORTHERN

CHEYENNE

INDIAN

RESERVATION

Study

area

Yel ol wsto ne R vi er

Missouri R vi er

Prairie Dog Creek
Summary 23

Summary

Water is one of the Northern Cheyenne Tribe’s most 

valuable natural resources—vital to the health and economic 

welfare of the Northern Cheyenne people. The Tongue River 

Member of the Tertiary Fort Union Formation is the primary 

source of groundwater in the Northern Cheyenne Indian 

Reservation, in southeastern Montana. Coal beds within 

this formation generally contain the most laterally extensive 

aquifers; in much of the reservation, a practical alternative to 

groundwater from the Tongue River Member does not exist.

Potential reserves of CBM might exist in the southern 

and eastern parts of the Northern Cheyenne Indian Reservation 

and in adjacent areas where some of the same coal aquifers in 

the Tongue River Member continue beyond the boundaries of 

the reservation. The extraction and subsequent management of 

CBM-produced water has raised concerns about the potential 

reduction of groundwater supplies caused by lowering of 

water levels and the potential effects of the disposal of 

produced water on surface water and soils. Consequently, 

the U.S. Geological Survey, in cooperation with the Northern 

Cheyenne Tribe, conducted a study to estimate the volume of 

in water in five coal aquifers. This report presents estimates 

of the volume of water in five coal aquifers in the eastern and 

southern parts of the Northern Cheyenne Indian Reservation. 

The Canyon, Wall, Pawnee, Knobloch, and Flowers-Goodale 

coal beds in the Tongue River Member of the Tertiary Fort 

Union Formation were investigated.

Estimates of the volume of water in the five coal aquifers 

were based on a specific yield of 0.01 and on the assumption 

that the five coal beds were unconfined. The volume of water 

was estimated by assuming that each coal bed was fully 

saturated (thickness of the coal bed was equal to the thickness 

of the coal aquifer, except for the Canyon coal). Estimates of 

the volume of water in the coal aquifers were determined only 

in areas where the volume of the coal beds could be estimated 

by computer interpolation. Only conservative estimates of 

the volume of water in the Canyon, Wall, Pawnee, Knobloch, 

and Flowers-Goodale coal aquifers are presented because 

(1) the subsurface extent of the coal beds are not well defined, 

(2) in some instances, well and drill-hole data were widely 

spaced and not well distributed, (3) of the possibility that coal 

beds split, merge, or pinch out laterally, and (4) water-level 

data for the five aquifers were scarce.

The Canyon coal encompasses about 40,100 acres 

(about 63 mi2). Where the volume of this coal could be 

estimated by computer interpolation, the Canyon coal averages 

about 26 ft thick. The volume of water in the Canyon coal 

was estimated to range from about 10,400 acre-ft (75 percent 

saturated) to 3,450 acre-ft (25 percent saturated). Because of 

its high topographic position and because water-level data are 

unavailable to assess the amount of saturation of this coal, 

100 percent saturation was not considered probable within the 

study area. The smaller estimates of water in the Canyon coal 

(75 to 25 percent saturation) are considered more reasonable. 

However, estimates of the volume of water in the Canyon 

coal might have large errors and need to be used with caution 

because the water-level data needed to define the volume of 

water were unavailable.

The Wall coal encompasses about 54,800 acres (about 

86 mi2). Where the volume of this coal could be estimated 

by computer interpolation, the Wall coal averages about 44 ft 

thick. The volume of water in the Wall coal was estimated to 

range from about 14,200 acre-ft (100 percent saturated) to 

3,560 acre-ft (25 percent saturated). Water-level data indicate 

that the Wall coal was both unconfined and confined within 

and near the study area. Thus, the estimates of the volume of 

water in the Wall coal probably are reasonable.

The Pawnee coal encompasses about 73,600 acres (about 

115 mi2). Where the volume of this coal could be estimated by 

computer interpolation, the Pawnee coal averages about 12 ft 

thick. The volume of water in the Pawnee coal was estimated 

to range from about 9,440 acre-ft (100 percent saturated) to 

2,360 acre-ft (25 percent saturated). Water-level data from 

one well and data from information from one geologist’s log 

indicated that the Pawnee coal probably was fully saturated 

and might have been under confined conditions in the study 

area. However, estimates of the volume of water in the Pawnee 

coal might have large errors and need to be used with caution 

because the water-level data needed to define the volume of 

water were largely unavailable.

The Knobloch coal encompasses about 75,200 acres

(about 117 mi2). Where the volume of this coal could 

be estimated by computer interpolation, the Knobloch 

coal averages about 29 ft thick. The volume of water in 

the Knobloch coal was estimated to range from about 

38,700 acre-ft (100 percent saturated) to 9,680 acre-ft 

(25 percent saturated). Water-level data indicate that the 

Knobloch coal was both unconfined and confined within and 

near the study area. Thus, the estimates of the volume of water 

in the Knobloch coal probably are reasonable.

The Flowers-Goodale coal encompasses about 

132,400 acres (about 207 mi2). Where the volume of this 

coal could be estimated by computer interpolation, the 

Flowers-Goodale coal averages about 17 ft. The volume of 

water in the Flowers-Goodale coal was estimated to be about 

35,800 acre-ft (100 percent saturated). Water-level data from 

three wells and information from one geologist’s log indicate 

that the Flowers-Goodale coal was confined at these wells. 

Also, because this coal generally is deeply buried in the study 

area, the Flowers-Goodale coal was assumed to be confined 

throughout its extent in the study area. Thus, the estimates 

of the volume of water in the Flowers-Goodale coal probably 

are reasonable.
24 Estimates of the Volume of Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana

Sufficient data are needed to accurately characterize 

coal-bed horizontal and vertical variability, which is highly 

complex both locally and regionally. Splitting, merging, 

pinching out, differential compaction, and fault displacement 

can further complicate correlation of coal beds and also can 

affect the reliability of the estimates of the volume of the 

coal beds between data points. Where data points are widely 

spaced, the reliability of estimates of the volume of coal beds 

is decreased. Likewise, reliable estimates of the volume of 

water in coal aquifers depend heavily on reliable geologic 

information, such as subsurface extent and thickness and 

correlation of coal beds. Additionally, reliable estimates of the 

volume of water in coal aquifers depend heavily on data from 

wells, such as up-to-date water-level and well-completion 

data and data about coal-aquifer characteristics. Because the 

data needed to define the volume of water were sparse, only 

conservative estimates of the volume of water in the five coal 

aquifers are presented in this report. These estimates need 

to be used with caution and mindfulness of the uncertainty 

associated with these estimates.

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Publishing support provided by:

Denver Publishing Service Center, Denver, Colorado

For more information concerning this publication, contact:

Director, Montana Water Science Center

U.S. Geological Survey

3162 Bozeman Avenue

Helena, MT 59601

(406) 457-5900

Or visit the Montana Water Science Center Web site at:

http://mt.water.usgs.gov/

This report is available at: http://pubs.usgs.gov/sir/2012/5209/
Tuck and others—Estimates, Water in Five Coal Aquifers, Northern Cheyenne Indian Reservation, Southeastern Montana—Scientific Investigations Report 2012– 5209