GEOLOGICAL SURVEY CIRCULAR 743

**9»V '

Land and Natural Resource Information 

and Some Potential Environmental 

Effects of Surface Mining of Coal 

in the Gillette Area, Wyoming
LAND AND NATURAL

RESOURCE INFORMATION AND

SOME POTENTIAL ENVIRONMENTAL

EFFECTS OF SURFACE MINING OF

COAL IN THE GILLETTE AREA, WYOMING
Wyodak-Anderson coal bed exposed in south pit of Wyodak mine, about 5 miles (8 km) east of Gillette, Wyo. The coal is about 90 feet (27 

m) thick, and the overburden is less than 50 feet (15 m) thick. View is to the south. Photograph by D. W. Moore.
Land and Natural Resource Information 

and Some Potential Environmental 

Effects of Surface Mining of Coal 

in the Gillette Area, Wyoming

By W. R. Keefer and R. F. Hadley

GEOLOGICAL SURVEY CIRCULAR 743

1976
United States Department of the Interior

THOMAS S. KLEPPE, Secretary

Geological Survey

V. E. McKelvey, Director

Free on application to the Branch of Distribution, Eastern Region, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304
CONTENTS

Abstract...................................................

In tioduction............................................

Acknowledgments...................................

Land and natural resource information.

Topography and landforms............

Geology............................................

Coal Resources.................................

Geochemical data............................

Land and coal ownership................

Current land use..............................

Surface water....................................

Page 

1

1

Page 

Land and natural resource information Con.

Ground water........................................................ 8

Erosion and sediment yield.................................. 15

Some environmental impacts of surface mining........ 15

Land disturbance and topographic changes........ 15

Potential effects on ground-water levels.............. 20

Potential changes in surface-drainage patterns... 23 

Potential geochemical changes ............................ 23

Reclamation potential of surface-mined lands ........... 26

Summary...................................................................... 26

References cited............................................................ 27

ILLUSTRATIONS

FRONTISPIECE. Photograph of Wyodak-Anderson coal bed, Wyodak mine, east of Gillette, Wyo.

FIGURE 1. Index map of Powdei River Basin and adjacent areas...............................................................................................

2. Index to 7'2-minute topographic quadrangle maps....................................................................................................

3. Map showing landforms, Gillette and vicinity...........................................................................................................

4. Map of Gillette study area, showing combined thickness of all coal beds in Fort LTnion and Wasatch Formations .

5. Stratigiaphic section coal beds penetrated by well.....................................................................................................

6-13. Maps of Gillette, Wyo., and vicinity showing:

6. Structure contours drawn on base of Wvodak-Anderson coal......................................................................

7. Area of strippable coal zone, W>odak-Anderson coal deposit......................................................................

8. Land and coal ownership..............................................................................................................................

9. Land use.........................................................................................................................................................

10. Ground-water levels and direction of movement..........................................................................................

11. Water quality in wells and springs ...............................................................................................................

12. Estimated annual source-area sediment \ields, 1975.....................................................................................

13. Extent of land disturbance invoked in surface mining................................................................................

14. Cross section showing potential changes in topography...........................................................................................

15. Block diagrams showing potential effects of mining on shallow aquifers................................................................

16-18. Maps of Gillette, Wyo., and vicinit\ showing:

16. Potential effects of surface mining on ground water....................................................................................

17. Present surface drainage.................................................................................................................................

18. Potential changes in surface diainage patterns after surface mining...........................................................

Page

9

10

12

13

14

16

17

18

19

21

22

24

25

TABLE

Page 

TABLE 1. Concentration of trace elements in Wyodak-Anderson coal, surface soils, near-surface soils and rocks, oveiburden

rocks, and sagebrush.............................................................................................................................................. 11
CONVERSION FACTORS

Factors for converting English units to metric units are shown to four significant figures. However, in 

the text the metric equivalents are shown only to the nearest whole number consistent with the 

values for the English units.

To convert ,, , . , , To obtain

,.,,., . Multiply by ,, English units ^ J J Metric units

acres 4.047 X 10"3 square kilometers (km2 )

acre-feet (acre-ftj 1.233 X 10"3 cubic hectometers (hm3 )

feet (ft) 3.048 X 10' 1 meters (m)

gallons (gal) 3.785 liters (1)

inches (in.) 2.54 centimeters (cm)

miles (mi) 1.609 kilometers (km)

square miles (mi 2 ) 2.590 square kilometers (km2 )

pounds (Ibs) 2.2046 kilograms (kg)

tons (short) 9.072 X 10" 1 metric tons or tonnes (t)

VI
Land and Natural Resource Information and

Some Potential Environmental Effects of Surf ace Mining

of Coal in the Gillette Area, Wyoming

By W. R. Keefer and R. F. Hadley

ABSTRACT

Campbell County, along the east margin of the Powder River 

Basin in northeastern Wyoming, contains more coal than any 

other county in the United States. The principal deposit is the 

Wyodak-Anderson coal bed. The bed is 50-100 feet (15-30 meters) 

thick over large areas, lies less than 200 feet (60 meters) deep in a 

north-south trending strip nearly 100 miles (161 kilometers) long 

and 2-3 miles (3-5 kilometers) wide, and contains an estimated 15 

billion tons (13.6 billion metric tons) of subbiluminous, lowsulfur coal that is presently considered to be accessible to surface 

mining. Extensive mining of this deposit has the potential for 

causing a variety of environmental impacts and has been a matter 

of much public concern and debate in recent years.

An integrated program of geologic, hydrologic, geochemical, 

and related studies by the U.S. Geological Survey in central 

Campbell County provides basic information about the land and 

its resources, including (1) characteristics of the landscape, (2) 

properties of rocks and surface materials, (3) depth and thickness 

of coal, (4) streamflow, (5) depth to ground water, (6) quality of 

ground water, (7) sediment yield, (8) concentrations of trace 

elements in soils, rocks, coal, vegetation, and water, and (9) 

current land use. The data are used to analyze and predict some of 

the potential environmental effects of surface mining, such as the 

extent of land distrubance, nature and degree of landscape 

modification, and disruption of surface-water and ground-water 

systems. Advance knowledge and understanding of these and 

other problems are useful in the planning and regulation of future 

leasing, mining, reclamation, and related activities.

INTRODUCTION

One of the principal areas being considered for 

significantly expanded coal production in the 

Western United States is the eastern Powder River 

Basin in northeastern Wyoming (fig. 1 ). Campbell 

County, for which the city of Gillette is the county 

seat, contains more coal than any other county in the 

nation. Although development in the area has been 

minimal to date, current proposals call for the 

opening of several large new surface mines. These 

proposed activities, which have the potential for

causing a variety of environmental impacts, clearly 

indicate the need for sound land-use planning, 

resource management, and environmental controls 

if the projected new development of coal is to 

proceed in the best public interest. Accordingly, 

many Federal, State, and local government agencies, 

as well as private organizations and institutions, are 

focusing considerable attention on Campbell 

County and adjacent areas in efforts to achieve this 

important goal. (For example, see Breckenridge and 

others, 1974.) Because the Federal Government is 

involved in many of the proposed actions, an 

environmental-impact statement has been prepared 

and issued on the eastern Powder River Basin (U.S. 

Department of the Interior, 1974).

A series of maps and other reports, published 

during the period 1973-76, presents some of the 

results of a broad program of integrated geologic, 

hydrologic, geochemical, and related studies being 

conducted by the U.S. Geological Survey in a 1,500- 

mi2 (3,900-km2) area surrounding the city of 

Gillette (Shown, 1973; U.S. Geological Survey, 1973, 

1974, 1975; Denson and others, 1973; Keefer and 

Schmidt, 1973; Denson and Keefer, 1974; King, 1974; 

Frickel and Shown, 1974; Hadley and Keefer, 1975; 

Connor and others, 1976). Preliminary results of 

some of the Gillette area studies are also 

incorporated in the environmental-impact statement on the eastern Powder River Basin (U.S. 

Department of the Interior, 1974; see, for example, 

pages 1-224, 1-471, VI-66, and VI-72). Each of the 

published items contains an important element of 

information about the land, water, and (or) coal 

resources. The purposes of the present report are to 

summarize the data shown in the published maps 

and reports, as well as unpublished data from
108° 106' 104° 102°

Approximate outline of 

Powder River Basin

100 MILES

_I

0

I 

100 KILOMETERS

FIGURE 1. Index map of the Powder River Basin and adjacent 

areas, showing location of the Gillette study area (cross 

hatched) and the four-township area (solid square) used 

to illustrate several sections of this report.

investigations still in progress, and to demonstrate 

how the different elements of information, used 

singly or in various combinations, can be applied to 

evaluations of some of the environmental effects of 

large-scale surface mining as related to land and 

water. Major emphasis is given to providing advance 

knowledge and understanding of potential problems 

that should be taken into account in the planning 

and regulation of future leasing, mining, and 

reclamation activities.

Because of the large areal extent of the Gillette 

study, only a 144-mi2 (375-km2) four-township area 

surrounding the city of Gillette will be used to illustrate most sections of this report (solid square, fig. 1; 

fig. 3). The small scale of the maps (1:125,000; 1 inch 

equals approximately 2 miles; 1 cm equals 1.25 km) 

also has necessitated generalization of some of the 

data.

ACKNOWLEDGMENTS

The preparation of this report would not have 

been possible without the assistance and cooperation of many colleagues from the U.S. Geological 

Survey. Special thanks and acknowledgments are 

given the following individuals for contributions in 

advance of publication of the results of their own 

respective studies: F. R. Shawe (coal and postmining terrain data); L. M. Shown (sediment-yield 

data); D. A. Coates, D. S. Fullerton, and V. S. 

Williams (surficial sediments and landform data); 

and V. E. Swanson and J. R. Hatch (coal-chemistry 

data). In addition, the Gillette area investigation 

benefited materially from areal and regional 

geologic, hydrologic, coal resource, geochemical, 

and related studies in various parts of the Powder 

River Basin by B. M. Anderson, F. A. Branson, J. J. 

Connor, N. M. Denson, J. H. Dover, R. B. Ebens, J. 

A. Erdman, G. L. Feder, D. G. Frickel, G. L. 

Galyardt, S. L. Grazis, P. T. Hayes, G. H. Horn, J. R. 

Keith, B. H. Kent, N. J. King, E. R. Landis, B. E. 

Law, G. C. Lusby, H. E. Malde, W. J. Mapel, E. J. 

McKay, R. F. Miller, D. W. Moore, E. M. Schell, and 

R. R. Tidball. G. B. Glass, Wyoming Geological 

Survey, contributed several samples of coal, the 

analyses of which are incorporated in the 

appropriate section of this report.

LAND AND NATURAL RESOURCE 

INFORMATION

TOPOGRAPHY AND LANDFORMS

Topographic maps, in the form of 7%-minute 

quadrangles at a scale of 1:24,000 (1 inch equals 

2,000 feet; 1 cm equals 240 m), are available for all of 

the Gillette study area (fig. 2). These maps, showing 

detailed configuration and elevation of the land 

surface and cultural and surface-drainage features, 

are the principal base maps for compiling and 

recording land and resource information. Another 

series of topographic maps, at a scale of 1:100,000 (1 

inch equals approximately 1.57 miles; 1 cm equals 1 

km), are available for displaying regional information. The Gillette study area is included within 

the Gillette 1:100,000 quadrangle; the base map for 

the four-township area around the city of Gillette 

(fig. 3), at a scale of 1:125,000 (1 inch equals approximately 2 miles; 1 cm equals 1.25 km), was reduced 

from this 1:100,000 quadrangle map.

The terrain of the Gillette area is flat to moderately 

rolling. The most prominent topographic features 

are narrow isolated ridges, hills, and buttes, the tops
of which are capped by erosion-resistant red and 

purple clinker beds. (Clinker is the hard-baked and 

fused material from rocks that were directly above a 

burning coal bed, as well as the noncombustible 

materials within the coal.) Extensive burning of 

coal, triggered chiefly by natural causes during prehistoric times, has been a common occurrence in the 

Gillette area. The effects of this widespread burning 

have had a profound influence on the erosional 

history of the region, as is now evident in the appearance of the landscape. 

Figure 3 characterizes the landscape to be seen in

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QQ' R. 74 W. 73 72 71 70 R. 69 W.

20 KILOMETERS

EXPLANATION

Dr Gillette East

rtin Dr Law, 1974

Ro

Rozet SE

Scott Dam

Four Bar J Ranch

Appel Butte

The Gap, Galyardt, 1974a

Coyote Draw, Galyardt, 1974b

Coon Track Creek 

Whitetall Creek ME 

Double Tanks 

Pleasantdale, G

Wildcat, Kent, 1976

Calf Creek, McKay and Mapel, 

1973

Weston SW

Long Tree Creek

Adon

Flag Butte

Twentymile Butte

Oriva NW, geologic map called 

Townsend Spring, McLaughlin 

and Hayes, 1973 (1974)

Rawhide School, Mapel, 1973

Mover Springs

Green Hill

Rozet NW

Rozet NE

Jeffers Draw

Oriva, Law, 1975

Gillette West

FIGURE 2. Index to 7/^-minute topographic quadrangle maps 

and areas for which geologic maps have recently been published or released in open file. Letter(s) in lower right corner 

of each Quadrangle refers to list given above. Solid triangle 

in lower left indicates that geologic map is available (reference given in list).

the vicinity of Gillette. Such a landform map can be 

used for a variety of planning purposes. It shows the 

areal distribution of different types of terrain, 

indicates general slope conditions, and provides a 

measure of the amount of erosion that has presently 

taken place. Landscape characteristics are also an 

indication of the relative ease or difficulty involved 

in restoring mined lands to their approximate 

original contour that is, the pre-mining surface 

configuration of the land, not necessarily the premining elevation. Highly dissected badland topography, for example, could not be restored after 

mining to anything approaching its original shape, 

whereas gently rolling, moderately dissected terrain 

would be less difficult to duplicate. Surface-mine 

spoils in areas where the original slopes are other 

than flat or gentle would be especially susceptible to 

increased erosion unless careful terracing and 

revegetation measures are taken. The delineation of 

flood plains and adjacent low terraces along streams 

is of special importance because satisfactory restoration of these kinds of features and attendant hydrologic systems is particularly difficult to achieve 

(National Academy of Sciences, 1974, p. 44-45); for 

this reason, sponsors of Federal strip-mining legislation (for example, H. R. 25 in 1975 and H. R. 9725 in 

1976) have included provisions that seek to restrict 

mining on alluvial valley floors. Alluvial valley 

floors, as defined in general terms, are those features 

underlain by unconsolidated stream-laid deposits 

for which available water is sufficient for subirrigation or flood irrigation agricultural activities. The 

map unit labeled "stream terraces and flood plains" 

in figure 3 includes alluvial valley floors as thus 

defined.

GEOLOGY

The Fort Union Formation of Paleocene age (53 to 

65 million years ago) and the Wasatch Formation of 

Eocene age (38 to 53 million years ago) form the 

surface rocks throughout the Gillette study area. The 

areal distribution of these units over some parts of 

the area is shown on several recently published 

geologic quadrangle maps. (See fig. 2.) Both formations are characterized by interbedded soft sandstone, siltstone, shale, and carbonaceous shale in 

various shades of brown and gray. Both also contain 

coal beds, but the coal beds are notably thicker and 

more numerous in the Fort Union than in the 

Wasatch (figs. 4, 5). Disagreement exists as to the 

precise position of the contact between the two 

formations because of similar rock types and because 

a thick zone of clinker masks the contact in many
105° 22'30"

Base from U.S. Geological Survey 

1:100,000, 1972

I 1 I I I 

12345 KILOMETERS

CONTOUR INTERVAL 100 FEET 

DATUM IS MEAN SEA LEVEL

FIGURE 3. Map showing landforms, Gillette and vicinity four-township area. Generalized from written communication by D.

S. Fullerton and V. S. Williams, 1976.

places. In general, however, the formation boundary higher stratigraphic horizons in drill holes to the

is considered to lie at or somewhat above the top of west (perhaps above the Smith coal bed as shown in

the Wyodak-Anderson coal in surface exposures fig. 5).

(near line marking approximate eastern limit of Structurally, the Gillette study area lies along the

Wyodak-Anderson coal deposit in fig. 4), but lies at east margin of the Powder River Basin, where the
EXPLANATION

Stream terraces and floodplains Nearly level 

land formed by stream-deposited alluvium, 

and benches formed adjacent to streams by 

erosion

Playas Beds of ephemeral lakes and ponds

Flat lands Including alluvial plains formed from 

slopewash. Land with slopes generally less 

than 4 percent

Alluvial fans Fans or aprons of alluvium deposited by ephemeral streams; slopes generally 

3-15 percent

Dune fields Areas of hummocky, low-relief 

topography formed by deposition of windblown sand and silt. Dunes are now inactive

Rolling hills Lands formed by erosion but not 

deeply incised by streams; slopes greater than 

4 percent

Rough and broken terrain Lands moderately 

to highly dissected by stream erosion (some 

badlands); conical hills, mounds, knobs, knolls, 

buttes, and ridges formed primarily by erosion 

of resistant clinker beds; slopes 5-100 percent

Modified lands Land modified to the extent 

that its original form cannot be determined

rocks dip westward toward the basin interior at a very 

slight angle (commonly less than 1°). However, 

detailed mapping and plotting of coal beds indicate 

that the strata locally are folded into a series of gentle 

northwest-trending anticlines and synclines. (See 

figs. 6, 14.)

Because of the generally soft, nonresistant 

character of the Fort Union and Wasatch strata and 

their ready susceptibility to weathering and erosion, 

large parts of the Gillette area are covered by a mantle 

of unconsolidated residuum and soil ranging in the 

thickness from a few inches to several feet. A 

mapping program was begun in 1975 to describe and 

classify these surficial deposits systematically. 

Primary emphasis is placed on the relation of active 

geologic processes to recent landforms. Interpretative studies of these processes may be used to predict 

how future mining, industrial, and agricultural 

activities may be affected by alteration or disturbance of the present landscape and, conversely, 

how the landscape may react to these modifications.

The mapping and related studies of surficial 

deposits are still in progress. Preliminary results, 

however, indicate that much of the landscape in the 

Gillette area especially in the uplands is 

relatively stable and that erosion is minimal. In an

environment that receives limited precipitation and 

has a short growing season, this natural balance may 

be difficult to maintain or restore if disrupted.

COAL RESOURCES

Detailed geologic mapping and the examination 

of records from numerous drill holes indicate that 

the Fort Union and Wasatch Formations in the 

eastern Powder River Basin locally contain a dozen 

or more coal beds of potential economic interest 

(Denson and others, 1973). The combined thickness 

of these beds is 100 feet (30 m) or more over large 

areas, and in several places exceeds 200 feet (60 m; fig. 

4). The sequence of coals penetrated by a well drilled 

about 6 miles (10 km) northwest of Gillette is shown 

in figure 5.

The bulk of the coal in the Gillette study area is too 

deeply buried to be considered for extraction by 

surface mining methods. However, across extensive 

tracts of land, a few beds are close enough to the 

ground surface to be reached by modern surface 

mining equipment. 1 One such bed is the WyodakAnderson2 , which, in terms of total volume, is the 

largest single coal deposit presently known in the 

United States and is a primary target for extensive 

exploitation in the coming years. (See frontispiece.)

The Wyodak-Anderson coal occurs either in a 

single layer, or in a group of closely spaced layers, 

and is 50-100 feet (15-30 m) thick over large areas of 

the eastern Powder River Basin (fig. 7; Denson and 

others, 1973; N. M. Denson, J. H. Dover, and L. M. 

Osmonson, oral commun., 1976). The potentially 

strippable tract, lying between the outcrop or "burn 

line"3 on the east and the 200-foot (60 m) overburden 

line on the west, occupies a strip nearly 100 miles 

(160 km) long and 2-3 miles (3-5 km) wide through 

Campbell County and northern Converse County 

(Keefer and Schmidt, 1973); it contains an estimated 

15 billion tons (13.6 billion metric tons) of subbituminous coal that is presently considered to be 

accessible to surface-mining. Specific delineation of 

this strippable tract (fig. 4) is an essential first step in

'For purposes of this report, coal beds less than 200 feet (60 m) below the land surface 

are arbitrarily placed in the strippable category; however, no economic limits with 

regard to depth have yet been established in the region. In the case of the WyodakAnderson bed, the strippable coal zone as outlined in figure 7 includes coal that in places 

lies at depths somewhat greater than 200 feet (60 m) because of local irregularities in 

topography.

2For purposes of this report, the Wyodak and Anderson coal beds are considered to 

form a single continuous coal unit, although the thick Wyodak bed, as exposed in the 

Wyodak mine, 5 miles (8 km) east of Gillette, may split westward into both the Anderson 

and Canyon beds (Denson and others, 1973).

'In many places the Wyodak-Anderson coal is not present in surface exposures, and 

the east edge of the strippable coal zone has been arbitrarily mapped as the boundary 

between clinkered rock and unclinkered rock. Scattered drill data indicate that some coal 

may be present locally beneath the clinker.
acquiring the necessary information for comprehensive resource evaluation, land-use planning, and 

environmental-impact analysis. The remainder of 

this report focuses primarily on that part of the tract 

that occurs within the four-township area surrounding the city of Gillette (figs. 6, 7).

Results of analyses performed by the U.S. Bureau 

of Mines, Forrest E. Walker, chemist-in-charge, 

Pittsburgh, Pa., on 10 samples collected from the 

Wyodak-Anderson coal bed within and adjacent to 

the Gillette study area are as follows (analyses reported as percentages on the as-received basis):

Proximate analyses I'llimale analyses

Mean Range Mean Range

Moisture..................24.7 10.4-29.9 Hydrogen..... 6.5 5.fi-fi.8

Volatile matter........ 33.5 31.5-40.9 Carbon......... 51.7 47.7-58.8

Fixed carbon ........... 36.2 31.2-40.3 Nitrogen ...... .9 .7-.9

Ash.......................... 4.6 4.2-9.0 Oxygen ........34.8 24.9-38.8

Sulfur........... .5 .3-.9

Ash............... 5.6 4.2-9.0

The average heat value of the 10 samples analyzed 

is 8,950 British Thermal Units (BTU) per pound 

(range 8,180=10,280 BTU), and the apparent rank of 

the coal is subbituminous B. Computations based 

on this value and the low average sulfur content (0.5 

percent) indicate that if all the sulfur in the average 

Wyodak-Anderson coal were converted to sulfur 

dioxide fumes upon combustion, 1.12 pounds (0.5 

kg) of sulfur dioxide would be created per million 

BTU (the maximum allowable by National Air 

Quality standards is 1 .2 pounds (0.54 kg) per million 

BTU). In practice, however, a certain proportion of 

the sulfur remains in the coal ash and does not become part of the stack effluent.

GEOCHEMICAL DATA

Knowledge of the distribution and concentration 

of chemical elements in the natural environment is 

of prime importance in efforts to predict, measure, 

and interpret changes in existing conditions. For 

example, redistribution of elements in landscape 

materials, which could result from coal exploitation and related industrialization could be detrimental, or in some instances beneficial, to future 

uses of the affected land and to the quality of ground 

water and surface water. Geochemical studies and 

sampling programs are being conducted in many 

parts of the Powder River Basin, and analyses are 

being made of soils, plants, rocks (including coal), 

and surface and ground water. The primary 

objective of these investigations is to determine the

geochemical properties of each of these materials, 

both locally and regionally, as a basis for establishing baselines in advance of the large-scale 

modifications that are now anticipated. Special 

attention is being given to concentrations of trace 

metals (such as arsenic, mercury, and selenium) and 

other potentially harmful substances that could 

cause problems if not detected and treated 

accordingly. Some of the results of the geochemical 

sampling and analytical program are given in table 

1.

As may be seen in table 1, few trace-element 

concentrations in the coal exceed the concentrations 

found in the surface and near-surface soil and rock 

materials of the Powder River Basin (mercury and 

selenium are exceptions), nor do they exceed the 

average concentrations found in rocks of the Earth's 

continental crust (boron, mercury, and selenium are 

exceptions). It should be noted that the coal may 

yield some, or all, of a few given elements to the 

atmosphere upon burning, whereas the other 

materials listed in table 1 are not likely to be burned. 

Also, surface and near-surface sandy materials to 

depths of 6.6 feet (2 m) show little significant variation in trace-element composition in the few localities that were sampled. Available geochemical data 

on overburden rocks, based on analyses of several 

different rock types, show a relatively wide range of 

concentrations for many elements, with the higher 

values for some elements noticeably exceeding those 

found either in the Wyodak-Anderson coal or in 

surface and near-surface materials.

Data on the concentrations of trace elements in 

ground water are still accumulating, and no reliable 

baselines have yet been established. However, the 

analysis of one sample of water from the WyodakAnderson coal bed, collected from the working face 

of the Belle Ayr mine (mine location in fig. 4), 

indicates that the chemical content is similar to that 

for ground water from noncoal aquifers in the Fort 

Union Formation (U.S. Geological Survey, 1974, p. 

34).

LAND AND COAL OWNERSHIP

One of the most controversial issues involved in 

the expansion of coal development in the West is that 

dealing with the separation of surface ownership 

and mineral ownership. In many of the coal-rich 

areas of the Rocky Mountain and Northern Great 

Plains regions, much of the land surface is owned by 

private and State interests, whereas the mineral 

rights (including coal) are owned by the Federal
Government (that is, the general public). This 

circumstance, which has caused virtually irreconcilable conflicts in many cases, stems from the fact that 

by the year 1910 Federal statutes governing homesteading on the public lands had been modified to 

the extent that subsequen t homesteads would receive 

title to the surface but not to the underlying coal 

(U.S. Government, 1968). The modified statutes also 

reserved to the Federal Government the right to 

prospect for and mine the coal. In the Gillette area, as

elsewhere, much land was acquired by private 

interests as a result of the Stock Raising Homestead 

Act of 1916, giving rise to the present widespread 

separation of land and coal ownership. (See U.S. 

Geological Survey, 1973; Breckenridge and others, 

1974; and various land and mineral ownership maps 

issued by the U.S. Bureau of Land Management.)

Ownership patterns for the area surrounding the 

city of Gillette, typical for the eastern Powder River 

Basin, are shown in figure 8. The outlines of the zone

 Approximate east limftof 

Wyodak-Anderson coal

East margijn of coal beds 

in Fort Union and 

 Wasatch Formations

WYODAK 

MINE

'BELLE AYR

MINE

Approximate east limit of 

Wyodak-Anderson coal

R. 74 W, R.69 W.

10 20 MILES

0 10 20 KILOMETERS

FIGURE 4. Map of Gillette study area, showing areas where the Wyodak-Anderson coal bed lies less than 200 feet (60 

m) below the ground surface. Labeled lines indicate total thickness of all coal beds in the Fort Union and Wasatch 

Formations, in feet. Oil well symbol in T. 50 N., R. 73 W., is location of well shown in figure 5. Information is 

based on Denson and others, 1973; and Denson and Keefer, 1974 (modified by F. R. Shawe).
Depth below 

surface

METERS 0-rO FEET

-500

Coal bed and thickness, 

in feet

Felix 26'

220'

16'

-1000

-1500

128'

319'

157'

79'

80'

Smith 9'

Swartz 18' 

2 Anderson 62'

' Canyon 8'

Wall 10'

Upper Pawnee 4' 

Lower Pawnee 5'

Cache 8'

1 Contact between Wasatch

500 and Fort Union Formations 

probablv in lower part of 

this interval

2 Anderson and Canyon beds 

mav merge eastward to become 

the Wvodak-Anderson bed, 

as that term is used in this 

report

FIGURE 5. Coal beds penetrated by McCulloch Oil Corp. Fed 

eral No. 2-3 well, sec. 3, T. 50 N., R. 73 W. (location plotted 

in fig. 4). Based on information from Denson and others, 

1973.

underlain by strippable coal of the WyodakAnderson bed are drawn on this map to emphasize 

the problems inherent in separate ownership.

CURRENT LAND USE

Land in the Gillette area is used principally for 

agricultural purposes. Most of the acreage is occupied by rangeland; lesser amounts are utilized for the

cultivation of hay and small grains in support of 

ranching operations. Figure 9 shows current land 

uses in the four-township area surrounding the city 

of Gillette. Although the predominance of agriculture is illustrated in figure 9, agriculture is not entirely typical of the region because somewhat more 

than the usual amount of land near Gillette is given 

over to dryland farming and to urban and commercial development.

Surface mining of coal represents a land use that 

conflicts with the more traditional uses. The oudine 

of the strippable coal zone of the Wyodak-Anderson 

bed is superimposed on the current land-use map 

(fig. 9) to indicate where, and to what extent, conflicts may arise if the coal is extracted from this particular tract. The kinds of information shown on this 

map are especially important when advance 

decisions have to be made with regard to land-use 

priorities.

SURFACE WATER

Most of the streams in the Gillette study area (fig. 

17) are ephemeral, being dry much of the year and 

flowing only in response to spring snowmelt or rainstorms large enough to produce runoff. The average 

annual precipitation at Gillette is 14 inches (36 cm). 

One stream, Donkey Creek, exhibits characteristics 

of both ephemeral and perennial streams. It is 

perennial in the sense that parts of the channel 

contain water throughout the year in pools with 

little or no discernible flow. However, like that of 

ephemeral streams, most of the flow of Donkey Creek 

results from snowmelt or rainstorms.

The primary use of surface water in the study area 

is for flood irrigation of hayfields along valley floors. 

Small reservoirs for livestock water and erosion 

control also withhold significant amounts of.streamflow in some tributary basins. Surface water, 

however, does not make up a very large part of the 

total water available in the study area. The average 

annual runoff from the area is about 0.25 inches (0.63 

cm) or 13.3 acre-ft/mi2; in the four-township area 

surrounding Gillette, this amounts to approximately 2,000 acre-feet.

GROUND WATER

The aquifers considered in this report lie at depths 

less than 500 feet (153 m). Water from this shallow 

system, which includes both alluvial and bedrock 

aquifers, is used primarily for domestic and livestock use, whereas water for municipal or industrial 

use is derived from deeper aquifers. Ground water 

occurs under water-table conditions in the alluvial

8
aquifers but is generally under confined, or artesian, completed in the shallow ground-water aquifers in

conditions in most bedrock aquifers (King, 1974). the area surrounding the city of Gillette. Although

The map in figure 10 is based on measurements of the shallow ground-water system is a composite of

water-level elevations in wells that have been several aquifers, it is considered as a single inte105°22'30"

R. 72 W. R- 71 «-

Base from U.S. Geological Survey 

1:100,000, 1972

5 MILES

J

\ \ 

1234 2 3 5 KILOMETERS

CONTOUR INTERVAL 100 FEET 

DATUM IS MEAN SEA LEVEL

FIGURE 6. Structure contours drawn on base of Wyodak-Anderson coal, Gillette and vicinity (F. R. Shawe, written commun., 

1976). Contour interval is 50 feet (15 m); datum is mean sea level; hachures point toward areas of lower elevation. Strippable 

coal zone, Wyodak-Anderson coal deposit, is shown by shading.
EXPLANATION 

Coal thickness

Less than 25 ft (7.6 m)

25-50 ft (7.6-15.2m) 

50-75 ft (15.2-22.9 m) 

75-100 ft (22.9-30.5 m) 

100-125 ft (30.5-38 m) 

Greater than 125 ft (38 m)

 ''/// Overburden greater than 200 ft (61 m)

' R. 72 W. R, 71 W.

Base from U.S. Geological Survey 

1:100,000, 1972

3 1 2

1 1

1 1 1 3123

1 4

3 4 

1 1

1 5 KILOMETERS

5 MILES 

1

CONTOUR INTERVAL 100 FEET 

DATUM IS MEAN SEA LEVEL

FIGURE 7. Outline of strippable coal zone, Wyodak-Anderson coal deposit, showing thicknesses of coal (F. R. Shawe, written

commun., 1976).

grated system because most wells either are uncased the zone of saturation of the shallow ground water

or have been perforated to take advantage of ground- system (N. J. King, oral commun., 1976). In a later

water yields from most, if not all, of the aquifers section of this report which discusses the potential

penetrated. Hence, the water levels in these wells, as effects of surface mining on ground-water levels, a

contoured in figure 10, reflect the approximate top of distinction is made regarding the behavior of water

10
TABLE I . Concentrations of trace elements in Wyodak-Anderson coal, surface soils, near-surface soils and rocks, overburden rocks,

and sagebrush in the Powder River Basin

[Analyses performed in U.S. Geological Survey laboratories. Symbol < indicates concentration is less than the value shown. Leaders (...) indicate no available data. 

Asterisk(*) indicates elements generally considered to be of environmental concern. All values are in ppm]

Wyodak-Anderson coal 1 Sagebrush ash 

(reported on whole- (Artemisia 

coal basis) tridentataT2

Element

Antimony* Arsenic* Beryllium 

Boron Cadmium* Chromium Cobalt ----- Copper* - Fluorine* 

Gallium - Lanthanum 

Lead* Lithium* 

Manganese 

Mercury* 

MolybdenumNiobium - Scandium 

Selenium* Silver ~

Strontium 

Thorium* Titanium 

Uranium* 

Vanadium Ytterbium--Yttrium - Zinc* 

Zirconium 

Mean

0.3

1.9 

300

.2

30

.1

5

2

13.2

47

25

4

2.5

50

.14.5

5 

1.5

2

1.5

70

1.5

500

.8

20

3

7.5

15

Range

<0.1-.7

<l-4 

150-500

<.15-.7

20-50

<.1-.12

1.5-50

<.5-3

3.3-51

30-200

1-20

<5-20

<1.5-8.2

<.5-49

10-200

.05-. 29

.3-1.5 

2-15

<1-20

.7-15.3-6.7

20-200

<1.5-7.9

150-5,000

<.2-3.2

5-150 __ <l-7

2.1-25

5-150

Mean

c on joU

280

6.8

21

2.6

~__65

12

530

~

11 

17 _ .68

700 _1,100

.72

39 __43064

Range _150-1,500

200-500

1.3-30

5-150

<l-6

~

<30-150

2-48

300-1,500

~

<7-30

<10-30 _.08-4.8

<1-1

150-1,500 _200-2,000

<.4-3.5<15-70

<2-3

<20-30200-800

20-150

Depth: 

(0-2,

Mean

1.2

7.2 

770

.96

3148

6.7

16

~

1318

22

280

.022

15

7.2

8.2

.20

180

9.6

3.1

80

1.9

17

62

160

Surface

0-1 inch 

.5 cm) 11

Range _500-3,000 

<1-1.5

<20-70

20-100<3-10

3-30

<400-2,200

7-20

10-3011-35

70-1,000

.01-. 04

<3-20

<5-30 

<10-10

<3-15

50-500

5.3-15

1.7-7

30-150

1-5

10-50

28-93

70-500

and near-surface materials 3

Depth: 6-8 inches 

(15-20 cm) 1*

Mean

1.1

8.2

760 

1.11

28

52

7.5

1814

34

18

25

250

.025

16

7.2

8.7

.14

180

9.83.2

92

1.9

18

64

150

Range __ 300-1,500 

<1-1.5

<20-70

20-100<5-20

5-50

<400-1,200

7-20

<30-70

10-100

24-47

100-700.01-. 04

<3-5 

<7-50

<10-10

<3-15

100-500

5.6-15

2.2-7

50-150

1-5

10-30

25-104

70-300

Depth: 

3.3 feet 

(1 m) 5

Range

0.4-.9

4-5 

500-700

<1-1

<20-20

20-30

<3-5

7

~

10

<30

15

9-15

30-200

.01-. 02

<3-5 

5-10

<10-10

3-5

<.l-.3

100-150

8.4-9.82.2-2.4

30-70

1

10

28-3570-150

Depth: 

6.6 feet 

(2 m) 6

Range

0.9-1.0

2.6-8.6 

700

<1

<20-20

20-30

57-20

10-15

<30-30

1512-21

100-150.02-. 03

<3-5 

7-10

<10

5-7

<.l

150

6.7-9.72.0-2.2

50-70

1

10

32-49

70-100

Overburden 

rocks 7

Depth: 

10-166 feet 

(3-35.5 m)

Range

1.6-2.9

3-70

300-1,000 

<2-3

<30-50

<l-2.530-100

<5-20

10-60

260-840

10-30

<50-70<25-30

11-50

~

.02-. 15

<5-7 

7-100

<10-15

<5-15

<.!-!. 4

70-200

7.3-18.3

2.3-6.9

30-150<2-3

15-30

30-37570-500

Average 

concentrationsin rocks 

of the 

Earth's 

conticrust 8

0.2

1.8 

425

2.8

10

.2

100

25

55

625

15

30

12.5

20

950

.08

1.5 

75

2022

.05

.07

375

9.6

5,700

2.7

135

3

33

70

165

ifiased on analyses of 15 samples from Wyodak mine and 11 samples from Belle Ayr mine. (See mine locations, figure 4.) Data compiled by 

J. R. Hatch and V. E. Swanson; analyses performed by Claude Huffman, Jr. (chemist-in-charge), A. J. Bartel, L. A. Bradley, G. T. Burrow, 

E. J. Fennelly, J. Gardner, W. D. Goss, P. Guest, J. C. Hamilton, A. W. Haubert, A. E. Hubert, R. E. McGregor, V. M. Merritt, Jr., H. G. 

Neiman, D. R. Norton, R. L. Rahill, F. N. Ward, and R. A. Zielinski (U.S. Geological Survey). For additional information, see Glass (1975).

2 Based on analyses of samples from 48 localities within the Powder River Basin. Data compiled from Connor, Keith, and Anderson (1976); U.S. 

Geological Survey (1974, 1975).

3 Data compiled from Connor, Keith, and Anderson (1976); U.S. Geological Survey (1974, 1975). 

''Based on analyses of samples from 48 localities within the Powder River Basin.

5 Based on analyses of samples of sand and clayey sand from three localities near Gillette. A single number indicates that the same value was 

obtained at each locality.

6 Based on analyses of samples of sandstone from two localities near Gillette. A single number indicates that the same value was obtained at 

each locality.

7 Based on analyses of 22 rock samples from 4 core holes in the eastern Powder River Basin; compiled from data in Department of Interior, 

1974, p. I-182c-I-182e.

8 From Taylor (1964).
105° 30' 105° 22'30"

R. 72 W. R. 71 VV.

Base from U.S. Geological Survey 

1:100,000, 1972

5 MILES 

J

CONTOUR INTERVAL 100 FEET 

DATUM IS MEAN SEA LEVEL

EXPLANATION 

Land and coal owned by

Private interests State of Wyoming Federal Government Coal owned by Federal 

Government; land 

owned by non-Federal 

interests

FIGURE 8. Land and coal ownership, Gillette and vicinity. From U.S. Geological Survey, 1973. Strippable coal zone, WyodakAnderson coal deposit, shown by shaded area.

12
105° 30' 105° 22'30"

R. 72 W. R. 71 W.

Base from U.S. Geological Survey 

1:100,000, 1972

I \ I I I I 

01234 5 KILOMETERS

CONTOUR INTERVAL 100 FEET 

DATUM IS MEAN SEA LEVEL

5 MILES

J

EXPLANATION 

Rangeland

Cropland, hayland, pasture 

Residential, commercial, services

Recreation 

Strip coal mine 

Airport

FIGURE 9. Land use map, Gillette and vicinity, 1970. (From Shown, 1973.) Strippable coal zone, Wyodak-Anderson coal deposit,

shown by shaded area.
105°22'30"

R, 72 VV. R. 71 W.

Base from U.S. Geological Survey 

1:100,000, 1972

I I I I I I 

012345 KILOMETERS

CONTOUR INTERVAL 100 FEET 

DATUM IS MEAN SEA LEVEL

5 MiLES

J

-4600 Ground-water-level contour in feet, 

1973 (1000 ft equal 305 m). 

Contour interval 50 feet. Datum 

is mean sea level

EXPLANATION

 >- Direction of ground-water movement 

 Water well

FIGURE 10. Level and direction of ground-water movement, Gillette and vicinity. (From King, 1974.) Strippable coal zone, WyodakAnderson coal deposit, shown by shaded area.

14
levels in tightly cased wells that bottom in different 

aquifers having different potentiometric surfaces. 

(See fig. 15.)

The bedrock aquifers in the shallow ground-water 

system generally exhibit similar water-bearing 

characteristics. All are composed largely of interbedded sandstone, siltstone, mudstone, and shale; all 

contain one or more coal layers. Sandstone generally 

yields water to wells in areas where the sandstone is 

saturated, with the water yield depending primarily 

on the permeability of the saturated rock. In contrast, 

siltstone, mudstone, and shale are relatively 

impermeable and yield little or no water to wells. 

Coal beds generally are sufficiently fractured to be 

good aquifers. Thin coal beds of limited areal extent 

will yield limited amounts of ground water; 

however, thick coal beds of broad areal extent may 

yield 10-100 gallons (38-380 liters) per minute.

In the central part of the four-township area 

surrounding the city of Gillette (fig. 10), ground 

water moves generally toward the channel of Donkey 

Creek. Ground-water divides occur near the south 

and north edges of this area. In the more permeable 

aquifers, the slope of the water level is generally 

about 10-25 feet per mile (2-5 m/km). In aquifers 

having low permeability, the slope may exceed 100 

feet per mile (19 m/km). The spacing of the contours 

in figure 10 provides some indication of the transmissivity of the shallow aquifers.

A generalized map of ground-water quality in 

shallow aquifers is shown in figure 11. This map was 

prepared from measurements of specific conductance (electrical conductivity) of water samples from 

wells (King, 1974). Specific conductance is controlled by, and is therefore an index of, the dissolvedsolids content of the water. Figure 11 shows 

comparatively well defined areal patterns of water 

quality at depths of 0-500 feet (0-153 m). These 

patterns probably reflect lithologic changes within 

the underlying bedrock units.

EROSION AND SEDIMENT YIELD

Upland erosion and stream-channel erosion 

generally are not serious problems in the Gillette 

study area, which lies astride a relatively undissected 

upland in the upper parts of the Little Powder and 

Belle Fourche River watersheds. The only major 

stream crossing the area is Donkey Creek, a tributary 

of the Belle Fourche River.

In order to estimate sediment yield on a regional 

basis under present land use, surveys were made of 

several small reservoirs of the type commonly used

for storing water for livestock. The sediment 

accumulations in these reservoirs are direct 

indicators of the erosion conditions and sediment 

yield from upland areas during the life of the 

structure, and the information can be used to 

establish reliable estimates of long-term sediment 

yield.

The study area was divided into four broad landform types based chiefly on interpretations of aerial 

photographs and on generalizations of landform 

information shown in figure 3; sediment-yield data 

from reservoirs were then extrapolated to areas 

exhibiting similar landform and erosion characteristics. The combined landform and sediment-yield 

information was used to construct the source-area 

sediment-yield map shown in figure 12.

Under present land use, most of the area underlain by strippable coal (fig. 12) has an estimated 

annual sediment yield of 0.05 to 0.25 acre-ft/mi2, and 

along the channel and flood plain of Donkey Creek it 

is probably less than 0.05 acre-ft/mi2 . These are low 

sediment yields for semiarid rangeland, but, as discussed earlier, most of the uplands in the Gillette 

area are undissected, and the vegetation cover is 

good. The potential for increased sediment yield is 

large if the vegetation cover is greatly reduced and 

slopes are steepened by surface disruptions 

associated with mining.

SOME ENVIRONMENTAL IMPACTS 

OF SURFACE MINING

LAND DISTURBANCE AND 

TOPOGRAPHIC CHANGES

Surface mining of coal cannot be accomplished 

without disturbing the land surface; the acreages involved depend primarily on the tonnages and thicknesses of the bed being mined. The following table 

shows the extent of land disturbance that will occur 

with the mining of different tonnages of coal from 

the Wyodak-Anderson deposit in the eastern Powder 

River Basin, assuming 90-percent recovery.4 The

Tonnage

(millions of 

short tons) /

1.. ...............

5.................

10.................

25

/ Extent of land disturbance (acres)

/ Average 

coal thickness....... 15

42

209

417

1 043

50

13 

63 

125 

313

100

6 

31 

63 

156

4The nationwide average for recovery of coal from surface mines is approximately 70 

percent. However, in many western surface mines recovery of thick coal beds may exceed 90 percent.

15
105° 30' 105° 22'30"

Base from U.S. Geological Survey 

1:100,000, 1972

D 1

I

I I 

) 1 2

2

I

I 

3

I

4

3 4 

I I

I 

5 KILOMETERS

5 MILES 

I

CONTOUR INTERVAL 100 FEET 

DATUM IS MEAN SEA LEVEL

EXPLANATION

Generally suited for most domestic uses

Marginal for most domestic uses and for 

lawn and garden irrigation; good for 

livestock use

Undesirable for most domestic uses; fair 

for livestock use

Unsuitable for most domestic uses; generally suitable for livestock use

Water well

FIGURE 11. Water quality in wells and springs, Gillette and vicinity. (From King, 1974.) Areal patterns of water quality based 

on approximate dissolved-solids content of water samples. Strippable coal zone, Wyodak-Anderson coal deposit, shown by 

shaded area.

16
105° 22'30"

^ ^^ x.x^^x^^

V ^\XxKx^x^X ^Xx^t1 ^xMSSI^k^Si^l

fc

Base from U.S. Geological Survey 

1:100,000, 1972

R. 72 .V. R. 71 W.

1 T I "1

2 3 4 5 KILOMETERS

CONTOUR INTERVAL 100 FEET 

DATUM IS MEAN SEA LEVEL

EXPLANATION 

Aere-ft/mi 2

5 MILES

J

FIGURE 12. Map of Gillette and vicinity showing estimated annual source-area sediment yields, 1975 (L. M. Shown, written 

commun., 1976). Strippable coal zone, Wyodak-Anderson coal deposit, shown by shaded area.

17
calculations are based on the fact that an acre-foot and a thickness of 1 foot) contains 1,770 short tons 

of subbituminous coal (a bed with an area of 1 acre (1.607 metric tons).

Average coal IgeWithickhess ' 

-.100 ft (30i5rtf)

Average coal bed thickness 

BOlftdSm) 1. 1 '!

Base from U.S. Geological Survey 

1:100,000, 1972 ^ r i n 

2345 KILOMETERS

CONTOUR INTERVAL 100 FEET 

DATUM IS MEAN SEA LEVEL

5 MILES

J

FIGURE 13. Map showing extent of land disturbance involved in surface mining of coal deposits that average 50 (15 m) 

and 100 (30 m) feet thick, assuming 90 percent recovery. Dark squares indicate acreages involved in mining 10 

million tons (9.1 million metric tons). Patterned areas (including dark squares) indicate tracts that would be disturbed in mining 350 million tons (320 million metric tons). Strippable coal zone, Wyodak-Anderson coal deposit, 

shown by shaded area. Line labeled A-A' shows location of cross section.

18
Relating the figures given in the above table to 

surface mining operations in the eastern Powder 

River Basin, it is assumed, for purposes of discussion, that a given mine has been designed to 

produce 10 million short tons (9.1 million metric 

tons) annually over a period of 35 years, for a total of 

350 million short tons (318 metric tons). If this 

amount were extracted from a tract where the underlying Wyodak-Anderson bed averages 100 feet (30 m) 

in thickness, the area involved, assuming 90 percent 

recovery, would be 2,188 acres (about 3.4 mi2 ). If the 

coal bed averages 50 feet (15.3 m) in thickness, the 

area of disturbance would be doubled. Map views of 

these two hypothetical mine areas, plotted with 

respect to assumed average coal thicknesses within 

the strippable coal zone of the Wyodak-Anderson 

bed, are shown in figure 13. It should be emphasized, 

however, that at no time would open pits probably 

occupy more than a small fraction of the areas of 

disturbed lands plotted in figure 13. At some predetermined stage in most surface mining operations, 

reclamation will begin, with spoil materials being 

graded and reclaimed at about the same rate as overburden is removed from new mining cuts. In addition to the acreages involved in actual mining 

operations, a few hundred adjacent acres will be 

occupied by associated surface facilities, including 

railroad trackage.

The degree to which the topography of an area 

will be altered by surface mining depends upon 

many factors; most important are the depth and 

thickness of the coal being mined (figs. 6, 7) and the 

manner in which the overburden is replaced in the 

mined-out pits. Overburden expands as the earth 

materials are broken up during mining; hence, overburden takes up more space where it is dumped than 

it did before being disturbed. The expansion factor 

("bulking") differs according to the kinds of rock 

involved, but it is common for soft sandstone and 

shale, as are found in the Gillette area, to increase 20 

to 25 percent in volume. Thus, where coal 20-25 feet 

(6-8 m) thick is overlain by 100 feet (30 m) of overburden, little change would occur in the average 

elevation of the land surface when the overburden 

has been returned to the mined-out pits. For the same 

amount of overburden, a lesser thickness of coal 

would result in a higher land surface, and a greater 

thickness of coal would result in a lower land 

surface. Figure 14 shows, in cross-sectional view, 

some of the changes in topography that might result 

from surface mining in areas where the WyodakAnderson bed is 100 feet (30 m) thick over a large part 

of the strippable coal zone. Note that the replaced 

overburden probably will undergo some compaction in ensuing years.

Advance knowledge of how the landscape will

Approximate east edge of 

strippable coal zone

o

o_

CD Final 

mining cut

Post-mining land surface. Average drop in ground 

elevation 60 ft (18 m) Present land surface

After mining

5000 FEET

0 1500 METERS 

VERTICAL EXAGGERATION X 5

FIGURE 14. Cross section showing potential changes in topography resulting from surface mining (location of section shown 

in fig. 13). Lower cross section is based on the assumption thai overburden is replaced on a cut-by-cut basis with 200- 

foot-wide (60-m-wide) cuts, spoils are smoothly graded, high walls are graded to 3:1 slopes, and overburden expands 20 

percent.

19
likely appear after being surface-mined is important 

for purposes of reclamation, land-use planning, and 

environmental-impact evaluation. This is especially 

true for the Gillette area, where the strippable coal is 

thick in comparison to overburden and where major 

modifications of the existing terrain are expected for 

large tracts of land (fig. 14). Maps showing simulated 

post-mining terrain in essence, maps depicting the 

shape of the land surface as it will look after mining 

and reclamation are being prepared for those parts 

of the Gillette study area that are underlain by 

strippable coal of the Wyodak-Anderson deposit. 

The maps are constructed by combining data on coal 

thickness, structure contours (figs. 6, 7), and presentday topography; they are based on assumptions that 

coal will be extracted and overburden replaced 

according to a specified set of mining and reclamation practices (such as those listed in the caption for 

fig. 18). These maps can be used to evaluate a variety 

of environmental impacts, such as determining the 

extent of potential disruption of the surfacedrainage system and predicting changes in erosion 

and sediment-yield patterns. (See, for example, fig. 

18 and the discussion on environmental impacts 

relating to surface drainage.) Identification of these 

and other problems will assist in all stages of 

planning of mining and reclamation activities.

POTENTIAL EFFECTS ON GROUND-WATER 

LEVELS

Some of the effects on ground-water levels that 

may result from surface mining of coal in the Gillette 

area can be inferred from the ground-water data 

shown in figure 10 and from the structure contour 

map (fig. 6). The combined information indicates 

that nearly everywhere along the strippable zone of 

the Wyodak-Anderson coal deposit the depth of 

mining will exceed the depth to ground water and 

thereby disrupt the shallow ground-water system. 

The potential effects are illustrated by the block 

diagrams in figure 15 and the map in figure 16.

On block diagram A (fig. 15), the ground-water 

level marked by the solid line (labeled "water table") 

represents the level of saturation, or potentiometric 

surface, in the discontinuous sandstone aquifers 

overlying the coal. The dashed line represents the 

potentiometric surface, or the level to which water 

will rise, in tightly cased wells that bottom in the 

coal-bed aquifer or deeper aquifers. Both water levels 

slope eastward to points of discharge along the 

stream that traverses the right (east) edge of the 

diagram.

Block diagram A (fig. 15) illustrates ground water 

conditions for an area where surface mining has not 

yet begun. Six water wells are shown that represent a 

variety of conditions based on well data collected 

throughout the Gillette study area (King, 1974). Well 

1 is completed in a discontinuous sandstone aquifer; 

the overburden above the Wyodak-Anderson coal is 

about 550 feet (170 m) thick. The well is 120 feet (37 

m) deep, and the water level is 60 feet (18 m) below 

the land surface. Well 2 is completed in the WyodakAnderson coal and is 520 feet (160 m) deep. The water 

level that is, the potentiometric surface of the coalbed aquifer stands 130 feet (40 m) below the land 

surface. Well 3 is completed in a discontinuous sandstone aquifer at a depth of 540 feet (165 m). This 

aquifer is partially confined and underlies the 

Wyodak-Anderson coal. Well 4 is completed at a 

depth of 200 feet (60 m) in a discontinuous sandstone aquifer above the coal. The water level stands 

40 feet (12 m) below the land surface. Well 5, 

completed in the same aquifer as well 4, is 120 feet (37 

m) deep, and the water level is 40 feet (12 m) below 

the land surface. The overburden above the WyodakAnderson coal at well 5 is only 140 feet (43 m) thick. 

Well 6 is east of the surface outcrop of the coal and is 

completed in a discontinuous sandstone aquifer. 

The well is 120 feet (37 m) deep, and the water level is 

10 feet (3 m) below the land surface. All these wells 

are used for domestic or livestock water and yield 

moderate amounts of water, generally less than 50 

gal/min (190 1/min).

In block diagram B, a hypothetical surface mining 

operation has been imposed on the ground-water 

system. The overburden has been removed to a depth 

of 200 feet (60 m) and the Wyodak-Anderson coal, 

having a thickness of 100 feet (30 m), has been mined. 

The inferred impact on the shallow aquifers after the 

removal of the overburden and coal is based on the 

assumptions that (1) the Wyodak-Anderson coal-bed 

aquifer will be dewatered to the level of the pit floor, 

and (2) the overlying aquifers will be drained to the 

lowest point on the high wall where they are 

exposed, instead of to the stream channel near the 

east edge of the block. As a consequence, the water 

table probably will be lowered appreciably near the 

open pit, and wells 4 and 5 will be dewatered. Well 1 

is far enough west of the mining operation that the 

water level probably will be lowered only slightly.

The potentiometric surface of the coal-bed aquifer 

will be lowered as in well 2 and graded to the bottom 

of the open pit. Because of the continuity and 

fracturing in the coal, however, the lowered poten20
tiometric surface should maintain a fairly constant aquifer below the coal bed, also will be affected, 

gradient to the east. Well 3, which is completed in an although to a lesser extent than well 2. Water could

FIGURE 15. Idealized block diagrams showing potential effects of mining on shallow aquifers. From 

Hadley and Keefer (1975). A, Ground-water levels before mining (water levels in numbered 

wells explained in text). B, Inferred changes in ground-water levels caused by removal of 

200 feet (60 m) of overburden and 100 feet (30 m) of coal. C, Inferred recovery of groundwater levels after completion of mining and rehabilitation of mined area.

21
105° 30'

 q

ft. 72 W. R. 71 W.

Base from U.S. Geological Survey 

1:100,000, 1972

D 1 

I

I I 

) 1 2

2

I

I 

3

I 

4

3 4 

I I

I 

5 KILOMETERS

5 

|

MILES

CONTOUR INTERVAL 100 FEET 

DATUM IS MEAN SEA LEVEL

EXPLANATION

Area where all aquifers above base of 

Wyodak-Anderson coal will be drained in the vicinity of mining operations

Areas where aquifers less than 200 ft 

(61 mldeep will be moderately affected; water levels may be lowered 

appreciably

Areas where wells in the Wyodak-Anderson coal will be 

moderately affected; shallower aquifers will not be 

affected appreciably

Areas where shallow aquifer system probably will be 

little affected by mining of the Wyodak-Anderson 

coal down to the 200-foot (61 m) overburden line

Water well

FIGURE 16. Potential effects of surface mining on ground water, Gillette and vicinity. (Modified from Hadley and Keefer, 1975.)

22
possibly move upward in well 3 and enter the coal 

bed because of the lowering of the point of discharge 

of the coal-bed aquifer to the base of the high wall, 

which, in turn, lowers the water level in this well.

Well 6, which is east of the coal outcrop, may be 

affected by the mining operation to a small extent. 

The stream channel to which the water level in this 

well is graded will be dewatered, and there will be a 

general lowering of the potentiometric surface that 

may also lower the water level in well 6.

The longevity of the described impacts on groundwater levels requires further study. However, 

inferences can be made as to what will happen if the 

overburden is returned to the mined-out pits and if 

the topography is properly reshaped. Block diagram 

C illustrates the topography as it may appear after 

rehabilitation of the mine shown in block diagram 

B. In time, the overburden will become saturated, the 

point of discharge of ground water will again rise to 

the stream-channel level on the east edge of the 

block, and water levels in the discontinuous sandstone aquifers and the coal-bed aquifer west of the 

mine will perhaps return nearly to pre-mining 

altitudes.

The map in figure 16 shows the strip in the 

Gillette study area that has potential for surface 

mining of coal and also the areas adjacent to this 

strip where shallow aquifers may be affected. 

However, it should be noted that the inferred 

impacts on shallow aquifers probably will be confined to areas that lie within only a few miles of an 

individual mine. Also, if water levels are lowered in 

domestic and livestock wells so that they are no 

longer productive, it may be feasible to deepen the 

wells either in the same aquifer or to a deeper 

aquifer.

POTENTIAL CHANGES IN 

SURFACE-DRAINAGE PATTERNS

The potnetial changes in topography, which were 

discussed in the section on land disturbance and 

topographic changes, will also cause disruption of 

surface drainage. Figure 17 shows the present 

drainage pattern in the four-township area surrounding Gillette; all streams are ephemeral except 

Donkey Creek. The ephemeral channels, however, 

also carry flood flows to the Belle Fourche and Little 

Powder Rivers.

Donkey Creek is the only stream that flows entirely 

through the Gillette area (fig. 17). It flows generally 

eastward across, and nearly perpendicular to, the 

strippable tract of the Wyodak-Anderson coal. At the

present time, there is only one surface mine the 

Wyodak mine about 5 miles (8 km) east of 

Gillette in the valley of Donkey Creek, but streamflow is not materially affected as a result of the stream 

being diverted around the mine pit.

Figure 18 shows potential changes in surfacedrainage patterns near Gillette, based on the 

extraction of all coal from the Wyodak-Anderson 

deposit between the outcrop or burn line on the east 

and the 200-foot (60 m) overburden line on the west, 

according to the mining and reclamation practices 

outlined in the figure caption. Because the coal is 75 

to more than 100 feet (23 to more than 30 m) thick 

over much of this area (fig. 7), the ground surface 

will be lowered appreciably and extensive closed 

depressions may be created. Restoring and maintaining through-flowing drainage ways, therefore, 

will be difficult, and water flowing in stream 

channels that are intersected by mining may become 

permanently impounded, unless measures are taken 

to insure proper outflow. Other problems of equal 

importance are those relating to gullying along 

stream courses upstream from the high walls and to 

increased erosion and sediment yield both inside and 

outside the mined-out area. The potential for 

stream-channel disruption must therefore be 

recognized and planned for on a site-by-site basis, as 

well as regionally, in the pre-mining stages of 

surface mine development. The technology for 

stabilizing stream-gradient breaks by using engineering structures is available and should be applied 

wherever necessary in the reclamation planning.

POTENTIAL GEOCHEMICAL CHANGES

The greatest potential for change in the chemical 

makeup of surface materials stems from the substitution of overburden rocks for surface soils 

following strip mining (U.S. Geological Survey, 

1975, p. 5). This potential may be minimized by the 

removal, stockpiling, and subsequent return of 

existing surface and near-surface soils and rocks as 

topdressing on mine spoils. As indicated in table 1, 

the few localities in which these materials have been 

sampled show little change in geochemical 

properties from the surface downward to 6 to 7 feet 

(about 200 cm).

One inevitable result of surface mining, however, 

is that still more deeply buried, relatively unaltered 

rocks will be brought closer to the land surface in 

many places and subjected to the natural cycle of 

leaching, weathering, and erosion. Although available analyses on overburden rocks (table 1) indicate

23
higher concentrations of some trace elements as 

compared with concentrations in surface and nearsurface materials, conclusions have been reached 

(Department of the Interior, 1974, p. I-182b and 

I-182f) that (1) when the higher values for the 

samples that were analyzed are averaged with those

of other samples from the same core, their significance is minimal; (2) none of the elements occur in 

abnormally greater amounts than are present in 

similar rock types throughout the United States; and 

(3) the presence of toxic trace elements (those 

indicated with an asterisk in table 1) serves as a

12345 

i I I I r

KILOMETERS

5 MILES 

J

FIGURE 17. Present surface drainage, Gillette and vicinity. Closed topographic depressions shown by patterned areas. Strippable 

coal zone, Wyodak-Anderson coal deposit, shown by shaded area. All drainage is intermittent except part of Donkey Creek 

shown as heavy line.

24
warning of a potential pollutant or contaminant but 

does not necessarily indicate that toxic concentrations would result from the oxidation and leaching of overburden materials. Few oxidation

5 MILES

FIGURE 18. Reconstructed surface drainage, Gillette and vicinity, if all coal is extracted from the strippable zone of the 

Wyodak-Anderson deposit according to the following 

assumed methods of mining and reclamation: 1, Overburden is replaced on a cut-by-cut basis as mining proceeds 

from east to west on 200-foot-wide (60-m-wide) northsouth trending panels; 2, spoils are smoothly graded; 3, 

high walls are graded to 3:1 slopes; 4, overburden swells

\

5 KILOMETERS

20 percent; and 5, no attempt is made to reestablish throughflowing drainage. Topographic depressions marking areas 

of internal drainage within the mined-out tract are shown 

by pattern. Arrows indicate direction of streamflow. Based 

on a detailed reconstruction of the post-mining terrain by 

F. R. Shawe. All drainages are intermittent except parts 

of Donkey Creek shown as heavy line.

25
and leaching tests, however, have yet been conducted for overburden rocks in the eastern Powder 

River Basin.

Energy conversion plants especially those 

involving combusiton of coal, such as steampowered electrical generating plants may cause 

chemical changes in surface materials through 

fallout from stack emissions. Few generalizations, 

however, can be made with regard to emissions 

resulting from the burning of any given coal, such as 

the Wyodak-Anderson, because individual powerplants vary widely in their operating procedures. For 

example, coal may be burned at a higher temperature in one plant than in another, thereby 

producing a larger volume of volatile (gaseous) 

materials. Nevertheless, certain elements (such as 

arsenic, fluorine, mercury, and selenium) are highly 

volatile and may become parts of the stack effluent 

under a wide range of conditions, whereas other 

elements (such as uranium, barium, and zinc) are 

largely nonvolatile and concentrate in the remaining 

ash. Thus, it is necessary to sample and test each 

plant individually, even though the same source of 

fuel is being used.

Of interest to the present investigation are geocheinical studies conducted near the 750-megawatt 

Dave Johnston power-generating plant in the 

southern part of the Powder River Basin, approximately 100 miles (160 km) south of Gillette. The 

results of a sampling and analytical program there 

show that the concentrations of some trace elements 

(antimony, arsenic, selenium, strontium, vanadium, 

and uranium) in near-surface materials and sagebrush decrease significantly with distance downwind (eastward) from the plant. Although geochemical baseline data were not available prior to the 

construction and operation of the generating plant, 

the distribution pattern of these trace elements is 

believed to have been influenced by its presence, perhaps through stack emissions (Connor and others, 

1976, p. 56; U.S. Geological Survey, 1975, p. 57). 

Note, however, that the coal being used in the dave 

Johnston plant is not from the Wyodak-Anderson 

deposit.

At mine-mouth electrical generating plants, the 

captured bottom ash and fly ash are usually returned 

to the mined-out coal pits and buried. Such ash is 

generally less stable chemically than overburden 

rock and is subject to leaching by ground water. 

Studies therefore need to be made to determine the 

least environmentally damaging effects of ash 

disposal. In fact, the possible constructive use of this

ash for example, in manufacturing concrete blocks 

or for use as road metal should not be overlooked.

RECLAMATION POTENTIAL OF 

SURFACE-MINED LANDS

Today, surface mining is generally viewed as only 

a temporary use of the land; after that use the affected 

land is expected to be returned to some use 

commensurate with its former condition and 

productivity. Reclamation is now prescribed by laws 

and regulations in many States and by the Federal 

Government. (See Imhoff and others, 1976.) The 

degree to which a given tract can be reclaimed after 

surface mining, however, is difficult to determine 

except through observation of actual reclamation 

results. Although it is a common practice to think of 

reclamation primarily in terms of reestablishing soil 

and vegetation on mine spoils (for example, 

Department of Interior, 1974, p. I-78-I-79), this is 

only a part of the process. A complex array of many 

critical factors geologic, hydrologic, geochemical, 

topographic, biologic (in addition to re vegetation), 

climatic, economic, and social must be considered 

in comprehensive evaluations of reclamation 

potential and of procedures that are best to follow in 

achieving reclamation goals.

As part of its investigations in the Gillette area, the 

U.S. Geological Survey is studying the reclamation 

potential of lands across, and adjacent to, the 

strippable zone of the Wyodak-Anderson coal 

deposit. The inherent attributes of land and water 

are fundamental to a determination of reclamation 

potential, hence the need for many of the kinds of 

data and interpretations that are discussed in this 

report. The results of the reclamation-potential 

study are incomplete and are not summarized in the 

present report.

SUMMARY

Surface mining inevitably causes disturbances of 

natural land features and environmental conditions. In the foregoing pages we have presented a 

sequence of maps and descriptive materials that 

show existing conditions of land, water, and coal 

resources in a representative area of the eastern 

Powder River Basin, Wyo. These data have led to 

interpretations and predictions concerning some of 

the potential impacts of surface mining in that area, 

and to the recognition of certain problems that 

require special consideration in the planning and 

regulation of future leasing, mining, and reclamation activities. Further study is needed to determine

26
whether the identified impacts are long-term or only 

short-lived and the extent to which they may be 

mitigated by proper mining and reclamation 

practices. Nevertheless, the kinds of data assembled 

in this report emphasize the importance of 

evaluating all aspects of resource development as 

they relate to the protection of the environment.

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W. G., 1974, Campbell County, Wyoming, geologic map 

atlas and summary of land, water, and mineral resources: 

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Basin, Wyoming and Montana: U.S. Geol. Survey Jour. 

Research, v. 4, no. 1, p. 49-59.

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27