VOLUME I
OCCURRENCE AND CHARACTERISTICS
OF GROUND WATER IN
THE GREAT PLAINS REGION, MONTANA
Roger A. Noble, Robert N
Brenda C. Sholes
Montana Bureau of
Bergantino, Tom Patton,
and Faith Daniel
Mines and Geology
Report to
U. S. ENVIRONMENTAL PROTECTION AGENCY
Contract Number GO-082-908-10
Project Officer
William E. Engle
January 1, 1982
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ii
PREFACE
This report, "Aquifer Characterization of Montana", is a two-volume
study; Volume I has been compiled for the Great Plains physiographic province
and Volume II for the Rocky Mountains physiographic province of Montana. The
division into two volumes was necessary in order to facilitate descriptions of
the various aquifers that occur in these two distinct topographic and structural
provinces. This report contains descriptions of thickness, potentiometric
surface, structural configuration and water-quality data for the major aquifers
within each province.
These two volumes contain a compilation of existing hydrogeologic informa-
tion for the State. Because state-wide hydrogeologic investigations have only
recently begun in Montana, there are many data gaps especially for the deeper
aquifers, and consequently some information is still conjectural. Demands on
Montana's ground water are expanding because of increasing energy development
and agricultural requirements (especially irrigation). For new developments,
ground water is the only alternative left, as most of Montana's surface waters
are already over-appropriated.
Montana is currently quantifying its water use and consumption through a
water-right adjudication program. This program is being implemented by the
Department of Natural Resources and Conservation through Senate Bill No. 76.
The completion date for the adjudication program is April 30, 1982; therefore,
quantitative statistics for Montana's ground-water use will not be available
until after this date. The ground-water use section is thus based on estimates
of current trends.
This study, "Aquifer Characterization of Montana", was funded by the U. S.
Environmental Protection Agency through Contract No. GO-082-908-10, for the
Underground Injection Control Program. The U. S. Congress enacted the Safe
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Drinking Water Act (Public Law 93-523) for the purpose of protecting under-
ground sources of water from contamination caused by well injection. This
act mandated the U. S. Environmental Protection Agency to establish the Under-
ground Injection Control Program for the purpose of preventing underground
injections that endanger ground-water resources. The Montana Bureau of Mines
and Geology's role in the Underground Injection Control Program is to identify
and characterize the aquifers in the State of Montana.
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TABLE OF CONTENTS
CHAPTER PACE
PREFACE
GENERAL STATEMENT 1
Purpose and Scope 1
Description of Montana 1
Previous Investigations 5
I. INTRODUCTION TO THE GREAT PLAINS REGION 6
Physiography 6
Topography 6
Surface Drainage 7
Climate 8
Cultural Geography 11
Population 11
Land Use and Ownership 17
Geology 18
Stratigraphy 18
Structure 18
II. HYDROGEOLOCY BY AQUIFERS 22
Unconsolidated Deposits 22
Lower Tertiary Formations 25
Fox Hills-Hell Creek Formations 26
Judith River Formation 27
Eagle Formation 29
Kootenai Formation 30
Swift Formation 31
Madison Group 32
III. GROUND-WATER USE 35
Municipal and Domestic 37
Agriculture 39
Industry 40
IV. WATER QUALITY 42
Data Sources 42
General Water Quality 43
Quaternary and Late Tertiary Rocks 43
Early Tertiary Fort Union Formation 44
Fox Hills-Hell Creek Aquifers 44
Judith River Aquifer 45
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TABLE OF CONTENTS
PAGE 2
Eagle Aquifer 48
Kootenai Aquifer 50
Jurassic Aquifer 51
Madison Aquifer 51
V. SUMMARY AND CONCLUSIONS 57
VI. REFERENCES 57
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LIST OF FIGURES
Figure Page
1-1. Major Drainage Basins 4
1-2. Mean Annual Runoff of Major Streams 9
1-3. County Census Subdivisions 16
1-4. Stratigraphic Column 19
1-5. Major Structural Features of the Montana Plains . 21
1-6. Frequency of Occurrence Compared to Dissolved
Solids' in Water from Unconsolidated Materials . .
1-7. Frequency of Occurrence Compared to Dissolved
Solids in Water from Early Tertiary Aquifers . .
1-8. Frequency of Occurrence Compared to Dissolved
Solids in Water from the Fox Hills and Hell
Creek Aquifers 46
1-9. Frequency of Occurrence Compared to Dissolved
Solids in Water from the Judith River
Formation 47
1-10. Frequency of Occurrence Compared to Dissolved
Solids in Water from the Eagle and Virgelle
Formations 49
1-11. Frequency of Occurrence Compared to Dissolved
Solids in Water from the Kootenai Formation ... 52
1-12. Frequency of Occurrence Compared to Dissolved
Solids in Water from Jurassic Formations .... 53
1-13. Frequency of Occurrence Compared to Dissolved
Solids in Water from Mississippian Formations . . 55
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LIST OF TABLES
TABLE PAGE
1-1. Drainage Area in Montana 3
I -2. River Basin Inflow and Outflow 8
I -3. Population of Counties and County Subdivisions . 12
I -k. Well Use by County 36
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LIST OF PLATES
Plate
TF 211.11 E Hell Creek and Fox Hills
TF 211.29 E-W Judith River Formation
TF 211.41 E-W Eagle and Telegraph Creek
TF 217.70 E-W Kootenai Formation
TF 221.47 E-W Swift Formation
TF 331.60 E-W Madison Group
AT 211.07 E Hell Creek Formation
AT 211.13 E Fox Hills-Hell Creek aquifer
AT 211.21 E Bearpaw Shale
AT 211.29 E-W Judith River Formation
AT 211.39 E-W Eagle Formation
AT 217.32 E-W Basal Colorado Sandstone
AT 217.70 E-W Kootenai Formation
AT 221.47 E-W Swift Formation
AT 331.60 E-W Madison Group
DS 100.10 E Quaternary and late Tertiary unconsolidated
DS 125.50 E Fort Union Formation
DS 211.11'E Fox Hills and Hell Creek
DS 211.29 E-W Judith River Formation
DS 211.39 E-W Eagle Formation
DS 217.70 E-W Kootenai Formation
DS 220.50 E-W Jurassic Formation
DS 331.60 E-W Madison Group
PS 331.60 E Madison Group
Legend
TF - Thickness of Formation
AT - Altitude of Formation
DS - Dissolved Solids
PS - Potentiometric Surface
211.11 - Formation Code
E - Eastern Half of Montana's 1:500,000 scale map
W - Western Half of Montana's 1:500,000 scale map
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GENERAL STATEMENT
A. Purpose and Scope
This report was prepared by the Montana Bureau of Mines and Geology in
order for the State of Montana to comply with federal requirements relating
to the Underground Injection Control Program. Existing hydrogeologic data
were used for the aquifer characterization maps and the descriptive narrative.
The aquifer characterization maps depict: (1) the area], and subareal extent;
(2) surface configuration; (3) thickness; (4) potentiometric surface; and
(5) water chemistry is expressed as dissolved solids for the major aquifers in
Montana. The narrative describes the lithology, general hydrogeologic parameters
and potential well yields for individual aquifers. The inventory of injection
wells was compiled from information obtained from the Montana Oil and Gas
Commission. The inventory provides a listing of injection wells with locations,
owners, affected aquifers and injection rates. The report also contains a
section delineating well use by county. While broad in scope, this report is
designed to meet the needs of federal regulatory agencies responsible for
writing and implementing regulations for underground injection.
B. Description of Montana
Montana, the third largest state of the forty-eight contiguous United States,
is vast and diverse. It has an area of 147,138 square miles and a population of
786,690 (U.S. Dept. of Commerce, 1980); the average population density is 5.4
people per square mile. Most Montanans live in the major cities that are geo-
graphically dispersed throughout the state. These cities are supported by the
surrounding rural communities. Although Montana is sparsely populated, it is
rich in natural resources and is a prime producer of agricultural staples for
the nation. Montana's abundant natural resources include fossil fuels, minerals,
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timber and water. These resources, however, are either fully appropriated or
are being exploited rapidly.
In 1980, Montana's low-sulfur coal reserves were estimated to be in excess
of 120 billion tons (U.S. "Bureau of Mines, 1980). These coal deposits of the
Fort Union Formation are easily accessible through strip-mining procedures and
supply a substantial part of needed energy for the nation. Total coal production
for 1980 was 29,905,627 tons (Cole and others, 1981), of which 90 percent was
exported to other states. Montana also has projected oil reserves of 248 trillion
barrels, an undetermined reserve of natural, gas and unknown potential for uranium
resources (Montana Dept. of Natural Resources and Conservation, 1980).
Montana's mineral resources are of great economic importance to the state.
Montana ranks among the top five states in the production of antimony, silver,
copper, talc, vermiculite and bentonite (U.S. Dept. of Interior, 1979). In
addition to these commodities, Montana has significant deposits of lead, zinc,
tungsten, chromium, manganese, nickel, titanium, vanadium, platinum-group metals,
molybdenum, arsenic, iron, antimony, thorium and other rare earths. Metallic
and non-metallic exploration activity in the state is increasing every year.
Most of western Montana is heavily forested and most of these forests lie
within designated state and national forests or parks. Timber harvesting occurs
on selected tracts within these forests and on privately-owned land. The volume
of timber harvested in Montana from 1976 to present (1982) has decreased because
high mortgage rates have substantially reduced the number of new buildings1 being
constructed.
Montana's water, both from ground-water reserves and surface-water flow,
is one of the state's most valuable resources because it is vital to agriculture,
mining and power production. More than forty-three million acre-feet of water
flow from the state each year; 65 percent of it originates in Montana (Montana
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Department of Natural Resources and Conservation, 1976). Three major river
basins, the Columbia, Upper Missouri and Yellowstone, account for 97 percent of
this flow. Statistics concerning the drainage areas of the major river basins
are presented in Table 1-1 with the major drainage basins displayed in Figure 1-1.
TABLE 1-1
DRAINAGE AREA IN MONTANA
River Basin Area (sq. mi.) Percentage of Percentage of
Montana's Area Montana's Water
Columbia 25,152 17% 59%
Upper Missouri 82,352 56% 17%
Yellowstone 35,890 24% 21%
Little Missouri 3,428 2% 1%
St. Mary 648 1% 2%
147,470 100% 100%
Of the fifteen million acres of cropland in production in the state, 12.5
million acres are dryland and the remainder are irrigated. Montana's major
water use is the irrigation of these 2.5 million acres of cropland from both
surface-water and ground-water diversions. Agricultural demands, hydro-electric
generating facilities and instream-flow reservations have already claimed most
of the surface water. This surface-water demand has resulted in over-appropria-
tion of these waters, placing additional demands on ground-water resources.
Sources of potable ground water in certain areas are now limited.
For the purpose of this report, the state has been divided into the Rocky
Mountains region and the Great Plains region. Because geology, climate and
aquifer characteristics of the Great Plains region are significantly different
from those of the Rocky Mountains region, this natural physiographic division
was used to facilitate the aquifer descriptions in this report. The line sep-
arating the two divisions is not precisely the same as that used by geographers
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MAJOR DRAINAGE BASINS
FIGURE 1-1
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- 5
because it follows the eastern edge of rocks that were severely disturbed by
the Laramide Orogeny rather than the actual mountain front except where the
two coincide. The following is a compilation of data for each of the major
aquifers of the Great Plains region.
C. Previous Investigations and Sources of Information
The collection of data for this report was made possible by the cooperation
of the U. S. Geological Survey, especially Richard D. Feltis and William R.
Hotchkiss, who furnished essential information on particular aquifer units.
Other data were compiled from oil well logs of the Montana Oil and Gas Commission,
various Montana Bureau of Mines and Geology and U. S. Geological Survey publica-
tions, numerous theses and dissertations and unpublished information generated
from water-well logs and records.
Water quality data in this report were obtained from Montana Bureau of Mines
and Geology files. Additional analyses were collected from the U. S. Geological
Survey.
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I. INTRODUCTION TO THE GREAT PLAINS REGION
The Great Plains region of Montana extends from the eastern base of the
Rocky Mountains between 45° and 49° north latitude to Montana's eastern border.
Nearly two-thirds of the state's 147,138 square miles lie within this region.
Along the western edge of the Great Plains is a zone, as much as 25 miles wide,
that was tectonically disturbed during the formation of the Rocky Mountains.
Although mountains did not develop in this zone, the structure is generally so
complex that meaningful structural contour, isopach or potentiometric surface
maps could not be produced. For this reason the Disturbed Belt has been in-
cluded with the Rocky Mountains region in Volume II of this report and the
western edge of the Great Plains region thus begins at the eastern edge of the
Disturbed Belt for this discussion.
Agricultural trade, based on livestock and grain production, is the main
economy of the region. Industry and retail marketing, however, are expanding
in importance. Oil well drilling and coal mining operations have grown rapidly
since 1974 when the need to develop additional domestic energy resources was
recognized. These operations are adding significant strength to the economic
base for the region, but are placing additional demands on the ground-water
resources of the region.
A. Physiography
1. Topography
The Great Plains region comprises almost two-thirds of Montana (roughly
92,400 square miles) east of the Disturbed Belt. This region is underlain by flat
to gently-dipping sedimentary rocks. The rocks that form the surface are generally
quite soft and have been eroded into open, rolling plains. Near some of the major
rivers and in areas of recent drainage changes, however, the plains have been
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sharply dissected into badlands and isolated, flat-topped buttes. Near the
western edge of the plains, especially in central Montana, igneous intrusions
and extrusions have formed minor mountain ranges such as the Sweetgrass Hills,
the Bearpaw Mountains, the Little Rocky Mountains, the Big Snowy Mountains,
the Bighorn Mountains and the Pryor Mountains. Although many of these folded
mountains are high and rugged, they generally are not severely disturbed by
faulting as are rocks in the Disturbed Belt. Because useful structural contour,
isopach and potentiometric surface maps can be made up to the bases of these
mountains, they are included in the Great Plains region. Altitudes within the
area designated as the Great Plains region range from 1,864 feet above sea level
at the Montana-North Dakota border where the Missouri River flows out of the
state to 11,214 feet above sea level at the summit of Crazy Peak in the Crazy
Mountains.
2. Surface Drainage
The Upper Missouri River, the Yellowstone River and the Little Missouri
River comprise the major drainage systems of Montana's Great Plains region. The
Upper Missouri River basin is the largest river basin in the state. It contains
approximately 56 percent of the land area, yet it discharges only 17 percent of
the water that annually leaves the state. Within the Upper Missouri basin there
are 38 reservoirs that have storage capacities of 5,000 acre-feet or more. Fort
Peck Reservoir on the main stem of the Missouri River is the largest of these,
having a storage capacity of 19,410,000 acre-feet. The net reservoir storage
for the basin is greater than 25,000,000 acre-feet.
The Yellowstone River basin in Montana includes 24 percent of the state's
area and annually discharges 21 percent of Montana's surface water. Yellowtail
Reservoir (1,375,000 acre-feet) is the largest of seven reservoirs that have a
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storage capacity of 5,000 acre-feet or more.
River basin inflow and outflow figures for drainages in the Great Plains
region of Montana are presented in Table 1-2. The mean annual runoff of the
major streams for this region is represented schematically in Figure 1-2.
TABLE 1-2
RIVER BASIN INFLOW AND OUTFLOW (IN ACRE-FEET)
Drainage Inflow Originating Leaving the Percentage Origin-
in the State State ating in the State
Upper Missouri 893,600 6,431,400 7,325,000 88
Yellowstone 6,227,000 3,126,000 9,353,000 33
Little Missouri 55,930 132,500 188,430 70
3. Climate
Warm-to-hot summers, cold winters and scant precipitation characterize
the Great Plains region of Montana. In the KBppen system, the climate of the
area is classed as "steppe" (BSk). In the Thornwaite system, the plains are
classed as "semiarid, microthermal, precipitation deficiency in all seasons",
(DC'd). Because Thornwaite's map is more detailed than most regional climate
maps, additional climate zones are shown within the region. The mountains
(based on the data available at the time of compilation) are shown as "subhumid,
microthermal, precipitation deficiency in all seasons", (CC'd). Had the data
been available, an additional class would have been added for the eastern
outliers of the Rocky Mountains and classified as "subhumid, microthermal,
adequate precipitation in all seasons", (CC'r). Also on the summit of the
Crazy Mountains additional classes of "humid, microthermal, precipitation
adequate in all seasons", (BC'r) and "taiga", (D1) would be shown. In the
Bighorn Basin, Thornwaite shows a small area where the climate is "arid, micro-
thermal, precipitation deficiency in all seasons", (EC'd).
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N
SOURCE
U.S G S Wall' Ratourcti Ooto For Wonioao Port I, 1969
Earfn 5ciinc«i Department, Montano S'o»« Univtrnty
MEAN ANNUAL RUNOFF OF MAJOR STREAMS
Width of stream line corresponds to top width of channel. Mean annual discharge, in
thousands of cubic feet per second, is represented by channel cross section.
FIGURE 1-2
-o
I
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The warmest average July temperatures occur along the Yellowstone and
Powder Rivers where July maximum temperatures exceed 90°F. The coldest average
January temperatures occur in extreme northeastern Montana where average
January minimums are approximately 0°F. The difference in temperature between
the average monthly maximum and the average monthly minimum is about 80°F.
Average temperatures moderate toward the western edge of the great Plains. The
summers are cooler because of the altitude, and the winters are warmer because
of the proximity of Pacific air masses and because of the occurrence of chinook
(foehn) winds.
Although precipitation averages about 14 inches per year throughout the
plains region, amounts as low as eight inches per year occur in some of the
low-lying valleys and in the rainshadows of mountains and amounts as much as
18 inches per year (enough to support the growth of coniferous trees) occur on
some of the higher hills and pleateaus. Most of the isolated mountain ranges
receive more than 20 inches of precipitation per year, thereby supporting
abundant conifers. Precipitation amounts of as much as 40 inches per year occur
on the summits of the Big Snowy, Little Belt and Bighorn Mountains and 60 inches
per year fall on the summit of the Crazy Mountains. Spring is the main season
of ground-water recharge because this is usually the only time when there is a
surplus of precipitation, cool weather and little evapotranspiration.
Snowfall is scant over most of the Montana plains; the average is about
40 inches per year. The average annual snowfall increases from east to west.
At the eastern border of the state the average is about 30 inches per year, but
at the western edge of the plains the average annual snowfall is about 50 inches
per year. The summits of the isolated mountain ranges of the plains receive
much more snowfall than the lower-lying plains: 100-200 inches per year on the
Little Rocky, Judith and Moccasin Mountains, 200-300 inches per year on the
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Bearpaw, Highwood and Bighorn Mountains and 300-500 inches per year on the Big
Snowy and Little Belt Mountains and Crazy Mountains. The moisture content of
a deep snowpack on these mountains helps assure abundant surface water during
warm, dry summers.
B. Cultural Geography
1. Population
Most of the Great Plains region is sparsely populated. The 1980 census
showed 393,063 persons living in this region. The average population density
of the region is 4.25 persons per square mile. Approximately AO percent of
these people reside in five cities of over 7,000 population: Billings, Great
Falls, Miles City, Havre and Lewistown. The population distribution is sum-
marized in Table 1-3, with the county census subdivisions represented in
Figure 1-3.
The largest city of the Montana plains region is Billings with a population
of 66,798 in 1980. Nearby subdivisions and towns raise the population of the
Billings marketing area to nearly double that figure. Billings is a home-base
for most of the coal and oil exploration activity in the Powder River and
Williston Basins, and is also a hub for livestock processing for south-central
and southeastern Montana.
Great Falls, in north-central Montana, closely follows Billings with a
population of 56,725 and is supported by surrounding subdivisions doubling its
population. Great Falls is primarily a marketing outlet for grain and livestock
production. The city also is the site for operations of Malmstrom Air Force
Base which contributes to the economy of the area.
Although the population of the Great Plains region of Montana has increased
by only 3.7 percent from 1970 to 1980, the population of Richland and Rosebud
Counties has increased 24.5 and 64.1 percent, respectively. The population
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TABLE 1-3
POPULATION OF COUNTIES AND COUNTY SUBDIVISIONS
OF THE GREAT PLAINS REGION, MONTANA
County/County Subdivision
1980
1970
% Change
Big Horn County
Crow Reservation Division
Hardin Division
Northern Cheyenne Division
Tongue River Division
11,096
5,645
4,249
1,013
189
10,057
10.3
Blaine County
Chinook Division
Fort Belknap Division
Harlem Division
6,999
3,172
1,854
1.973
6,727
3,263
1,312
4.0
- 2.8
41.3
Carbon County
Carbon East Division
Fromberg-Bridger Division
Joliet Division
Red Lodge Division
Roberts Division
8,099
658
1,753
1,782
3,082
824
7,080
1,613
1,384
753
14.4
8.7
28.8
9.4
Carter County
Ekalaka Division
Little Missouri Division
1,799
1,100
699
1,956
1,135
821
- 8.0
- 3.1
-14.9
Cascade County
Belt Division
Cascade Division
Eden-Stockett Division
Great Falls Division
Great Falls North Division
Monarch-Neihart Division
80,696
1,626
1,559
862
70,600
2,514
277
81,804
1,406
1,354
866
260
- 1.4
15.6
15.1
- 0.5
6.5
Choteau County
Big Sandy Division
Fort Benton Division
Geraldine Division
6,092
9.998
2,866
1,228
6,473
2,127
3,066
5.9
6.1
6.5
Custer County
Miles City Division
Mizpah-Pumpkin Division
North Custer Division
Shirley-Ismay Division
13,109
11,846
511
383
369
12,174
7.7
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TABLE 1-3
(CONTINUED)
County/County Subdivision 1980 1970 % Change
Daniels County
Daniels North Division
Fort Peck Division
2,835
2,709
126
3,083
- 8.0
Dawson County
Dawson North Division
Glendive Division
11,805
1,552
10,253
11,269
4.8
Fallon County
Baker Division
Plevna Division
3,763
3,235
528
4,050
3,471
579
7.1
6.8
Fergus County
Denton Division
Grass Range Division
Hanover Division
Lewis town Division
Roy Division
Winifred Division
13,076
820
617
765
10,046
405
423
12,611
977
721
899
437
492
3.7
-16.1
-14.4
-14.9
- 7.3
-14.0
Garfield County
North Garfield Division
South Garfield Division
1,656
1,204
452
1,796
1,309
487
7.8
8.0
7.2
Glacier County
Cut Bank Division
10,628
4,540
10,783
- 1.4
Golden Valley County
Lavina Division
Ryegate Division
1,026
438
588
931
10.2
Hill County
Gildford Division
Havre Division
Rocky Boy Division
Rudyard Division
Wild Horse Lake Division
17,985
910
13,738
1,778
998
561
17,358
3.6
Judith Basin County
Geyser Division
Hobson Division
Stanford Division
2,646
542
920
1,184
2,667
644
960
1,063
- 0.8
-15.8
- 4.2
11.4
Liberty County
Chester Division
Joplin Division
2,329
1,839
490
2,359
1,851
508
1.3
0.6
3.5
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TABLE 1-3
(CONTINUED)
County/County Subdivision 1980 1970 % Change
McCone County
2,702
2,875
- 6.0
Circle Division
1,766
North McCone Division
936
Musselshell County
4,428
3,734
18.6
Klein Division
988
411
140.4
Melstone Division
656
623
5.3
Roundup Division
2,784
Petroleum County
655
675
- 3.0
Winnett North Division
189
457
-58.6
Winnett South Division
466
218
113.8
Phillips County
5,367
5,386
- 0.4
Belknap Division
206
Malta Division
4,242
Phillips South Division
390
Whitewater Division
529
Pondera County
6,731
6,611
1.8
Blackfeet East Division
148
Conrad Division
4,522
Valier-Dupuyer Division
1,588
2,080
-23.7
Powder River County
2,520
2,862
-11.9
Broadus Division
1,321
1,442
- 8.4
East Powder River Division
725
928
-21.9
Otter Division
474
Prairie County
1,836
1,752
4.8
Terry North Division
270
259
4.2
Terry South Division
1,566
1,493
4.9
Richland County
12,243
9,837
24.5
Fairview Division
2,267
Lambert Division
753
Savage-Crane Division
1,341
Sidney Division
7,882
Roosevelt County
10,467
10,365
1.0
East Roosevelt Division
2,134
Fort Peck Division
8,333
Rosebud County
9,899
6,032
64.1
Ashland Division
564
Forsyth Division
3,516
Northern Cheyenne Division
2,651
Rosebud Division
3,168
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TABLE 1-3
(CONTINUED)
County/County Subdivision 1980 1970 % Change
Sheridan County
Fort Peck Division
Medicine Lake Division
Plentywood Division
Westby Division
Stillwater County
Columbus Division
Park City Division
Stillwater North Division
Sweet Grass.County
North of Yellowstone Division
South of Yellowstone Division
Teton County
Choteau Division
Dutton-Power Division
Fairfield Division
Treasure County
North Treasure Division
South Treasure Division
Valley County
Fort Peck Reservation Division
Glasgow Division
Wheatland County
Harlowton Division
Judith Gap-Shawmut Division
Wibaux County
Pine Hills-St. Phillips Division
Wibaux Division
Yellowstone County
Billings Division
Buffalo Creek Division
Huntley Project Division
Laurel Division
Northwest Yellowstone Division
Shepherd Division
South Yellowstone Division
Yellowstone National Park Division 275
5,414
179
1,040
3,562
633
5,598
2,387
1,223
581
3,216
675
2,541
6,491
3,481
1,198
1,812
981
288
693
10,250
1,283
6 ,636
2,359
1,821
538
1,476
347
1,129
108,035
86,493
191
2,905
10,086
1,669
2,550
4,141
5,779
721
4,632
822
2,980
678
2,302
6,116
1,298
1,719
1,049
427
642
11,471
2,529
1,465
459
1,006
87,367
156
2,179
1,226
1,320
64
- 6.3
-12.2
20.9
48.8
7.9
- 0.4
10.4
6.1
- 7.7
5.4
- 8.2
-32.6
7.9
-10.6
- 6.7
0.8
-24.4
12.2
23.7
22.4
33.3
108.0
213.7
329.7
-------
COUNTY CENSUS SUBDIVISIONS
-------
- 17 -
growth in these counties can be attributed dominantly to oil exploration in
Richland County and coal strip-mining in Rosebud County. This rapid growth
usually produces a "boom" for the area and increases construction activity.
2. Land Use and Ownership
Roughly 60 percent of Montana's Great Plains region is used as pasture and
range for livestock grazing (this includes the open woodland areas used as
summer pasture as well as for timber operation). Twenty-five percent of the
pasture and less than one percent of the range are irrigated. The Great Plains
region has 13,138,066 acres that are classified as cropland, accounting for 22
percent of the land use in the region. According to the 1974 Census of Agriculture,
54 percent of those 13,138,066 acres are classified as harvested and five percent
are used as pasture (not included in the above class). Other activities such as
mining and petroleum operations, human habitations and recreational areas
account for the small remainder of land use.
About 60 percent of the Great Plains region of Montana are privately owned,
but state and federal agencies administer large portions of certain counties.
The federally administered lands include game ranges, national forests, Indian
Reservations and lands that were either never homesteaded or were withdrawn from
homesteading at a later time. The state-owned lands include two sections (school
sections) out of nearly every township and school sections that were traded out
of Indian Reservations, national forests, etc. The state land is administered
by the Department of State Lands, whereas federal land dominantly falls under
the jurisdiction of either the Bureau of Land Management or the U. S. Forest
Service.
-------
18 -
C. Geology
1. Stratigraphy
Sedimentary rocks of all geologic ages, from Precambrian to Quaternary,
underlie parts of the Great Plains region of Montana. The seas that repeatedly
covered Montana in the geologic past were comparatively shallow, but gradual
subsidence of the region allowed a great thickness of sediments to accumulate.
The thickness of sedimentary rock over Precambrian crystalline basement ranges
from 4,000 feet along the Sweetgrass Arch in west-central Montana to 15,000
feet in the Montana portion of the Williston Basin.
The Precambrian sedimentary rocks are predominantly quartzite and argillite,
belonging to the Belt Group. The Paleozoic sedimentary rocks are mainly lime-
stone and dolomite, but shale is abundant also. Many of the Paleozoic units,
especially the Madison Group, are the targets of oil exploration in the Great
Plains region or Big Horn, Powder River and Sweetgrass Arch. The Madison Group
is also one of the most productive deep aquifers in eastern Montana. Mesozoic
sedimentary rocks are dominantly shale but there are also several sandstone
units of great areal extent which are generally good aquifers. The Fort Union
Formation and Wasatch Formation are Cenozoic sedimentary units that contain
abundant coal. Other important Cenozoic sedimentary formations are the Flaxville
gravel, glacial deposits and alluvium. Almost all of the Cenozoic formations are
used for water supplies because they are at or near the surface. Glacial deposits
sometimes yield as little as two gallons per minute, whereas alluvium may yield
more than 1,000 gpm. The various stratigraphic units and their time relation-
ship are shown in Figure 1-4.
2. Structure
Most of the Great Plains region of Montana is underlain by sedimentary
-------
MILLIONS
VCftHJ
AGO
Holotwf "1 . ,
QUATlRNftftY,. PkisJ-ouni J Pl,ot'ne
wanted
Ftrt Union PormoAfon
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tr
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FIGURE 1-4
fttlfc Greuf>
-------
- 20 -
rocks that have eastward dips usually less than 5°. Reversals of this dip occurs
only in open anticlines, synclines and domes. Near the mountains and adjacent
to the Porcupine Dome and the western flank of the Cedar Creek Anticline, dips
exceed 30° for a few miles. The major structural features of the Montana plains
are shown in Figure 1-5.
The plains region has not undergone appreciable deformation since the end
of the Laramide in Eocene times. Small-scale, open folds occur in Oligocene
and Miocene formations of southeastern Montana. This deformation may be evidence
of small-scale compression or tectonism since these sediments were deposited.
Epeirogenic uplift of 1,500 feet has occurred in extreme eastern Montana and
4,000 feet of uplift has occurred near the Rocky Mountains. This uplift is
thought to have occurred since mid- or late-Pliocene, and may have been accompanied
by regional tectonic deformation.
There have been few recorded seismic events in eastern Montana since the
days of organized records in 1805. The absence of seismic events, however, does
not necessarily imply tectonic quiescence. A fault-zone extending from Froid,
in northeastern Montana, through Brockton, on the Missouri River, to south of
Weldon in McCone County (a distance of more than 100 miles) seems to have had
displacement of several tens of feet since the Wisconsin glaciation. The recency
of this faulting is suggested by the glacial deposits preserved in the central
graben of the fault but eroded from its flanks.
-------
MAJOR FOLD TRENDS
NORMAL FAULT
•Y- HIGH-ANGLE REVERSE FAULT
SHOWING DIP
STRUCTURE CONTOURS ON BASE
OF COLORADO SHALE
I
N
I
FIGURE 1-5
O
I )
50
1
75
1
100 MILES
TECTONIC MAP OF THE GREAT PLAINS REGION
-------
- 22 -
II. HYDROCEOLOCY BY AQUIFERS
A. Unconsolidated Deposits
Above the Mesozoic and early Tertiary formations are several types of un-
consolidated deposits from which ground water may be derived. These unconsoli-
dated aquifers include: alluvium, colluvium, terrace deposits, eolian deposits,
glacial deposits, high-level gravels and the deeply weathered surface of some
sandstone formations.
Alluvium and terrace deposits are sinuous, river-lain sands, silts, gravels
and clays within or adjacent to present-day drainage systems. Alluvium and
terrace deposits are generally less than 30 feet thick along most drainages,
but may be as much as 200 feet thick along some of the major rivers. Colluvium
exists nearly everywhere, but it is rarely thicker than 15 feet except near the
base of slopes undergoing active erosion. Eolian deposits are quite thin also
(usually less than 10 feet thick) and sometimes are hard to distinguish from
colluvium unless good exposures are available. Eolian deposits are commonly
found on the lee side of sandy hills and on the top of high river terraces.
Extensive areas of eolian deposits occur in glaciated northern Montana, but the
material does not resemble typical loess. Glacial deposits are found primarily
north of the Missouri River. The deposits left behind by the ice that advanced
as much as 50 miles south of the Missouri River have been largely removed by
post-glacial erosion. Glacial deposits are usually less than 50 feet thick but
thicknesses greater than 100 feet occur in the Havre-Great Falls-Shelby area, in
the extreme northeastern corner of Montana and where extensive terminal or
recessional moraines developed. High-level gravels are unconsolidated to semi-
consolidated, Miocene and younger fluvial deposits. High-level gravels adjacent
to the isolated mountains of central Montana and those extending from the Bear-
tooth and Bighorn Mountains may have developed either as a result of recent
-------
- 23 -
uplift of these mountains or from climatic change. The high-level gravels 700
to 1,400 feet above the Missouri and Yellowstone Rivers were deposited by river
systems ancestral to these two rivers. Differential uplift, glacial diversion
and stream piracy have left many of these deposits as much as 75 miles from the
present-day rivers. High-level gravels are generally less than 50 feet thick,
but may be as much as 100 feet thick.
Although well yields of 1,000 gallons per minute or more have been obtained
from high-level gravels, terrace deposits, reworked glacial deposits and some
bedrock aquifers, alluvium typically yields more water to a well than any other
aquifer. The certainty of obtaining water from alluvium and the shallowness of
a well necessary to reach this water make alluvium the most used aquifer in the
Great Plains region of Montana. This high usage of alluvium for wells occurs
because alluvial valleys contain the best farmland and have the greatest
population density.
Terrace deposits within major river valleys adjacent to alluvium generally
yield more water than terrace deposits outside the main valley or where isolated
from alluvium. This difference in yield is largely a result of less ground-
water recharge to the higher or more isolated deposits.
Colluvium and eolain deposits are generally thin and rarely yield more than
10 gpm to a well. These aquifers were used mainly during the "Homestead Days"
when dug wells were common. Despite the low yield of water from these deposits,
the water was often satisfactory in quantity and quality to provide domestic
and stockwater."to the homesteader.
Well yields from glacial deposits are highly variable. Where the glacial
deposits are mainly heterogeneous silt, clay and sand (till), water is rarely
obtained, but where glacial deposits have been reworked by running water (glacio-
fluvial deposits, ice-marginal stream deposits, etc.) yields of more than 1,000
gpm have been obtained. Generally, however, a yield of 5 to 10 gpm may be
-------
- 24 -
expected from glacial deposits.
The quality of water from unconsolidated deposits is as variable as the
nature of the deposits themselves. Water from alluvium normally ranges from
300 mg/L to 2,500 mg/L. The dissolved solids content increases where alluvial
deposits are in contact with Cretaceous shale or is influenced by salt migration
from irrigated areas.
Water from colluvium or weathered bedrock contains few dissolved solids if
the parent material is a sandstone, but contains a large amount of dissolved
solids if the parent material is a siltstone or contains much shale.
Water from terrace deposits generally contains more dissolved solids than
does water from alluvium. These higher concentrations of dissolved solids
probably occur because there is less flushing of the terrace deposits by ground-
water movement. Terrace deposits that have been cultivated for many years or
overlie shale also seem to contain water with higher concentrations of dissolved
solids.
High-level gravels often yield water with a low dissolved solids content.
Because areas underlain by these gravels are often quite flat and cultivated,
water from these gravels is in demand for irrigation.
Glacial deposits usually contain water with higher than average concentra-
tion of dissolved solids. This condition probably results from the admixture of
Cretaceous shale into much of the glacial till. Glaciofluvial deposits, on the
other hand, often contain water with few dissolved solids.
Few chemical analyses are available for water from eolian aquifers and,
considering the size and distribution of these deposits, the water quality is
probably variable.
Unconsolidated deposits are widely used as aquifers throughout the Great
Plains region of Montana. The first well in the state was probably an alluvium
well because the water table in alluvium is usually close to the ground surface
-------
- 25 -
and the probability of obtaining water is very good—a strong consideration
when a well was made with the pickax and shovel. More water is probably with-
drawn from unconsolidated deposits (especially alluvium) than any of the other
aquifers. These shallow ground-water systems are highly susceptible to con-
tamination and over-use.
B. Lower Tertiary Formations
Only a few small patches of the Eocene Wasatch Formation are present in
Montana, and the Cretaceous-Paleocene Willow Creek Formation of the northwestern
Great Plains region has been little studied. For these reasons, the main forma-
tion addressed is the Fort Union Formation.
Continuous outcropping and maximum areal extent of the Fort Union Formation
occur primarily in the eastern third of Montana. A large area of Fort Union
Formation that is separated from the main body lies in the Bighorn Basin-Reedpoint
Syncline area of south-central Montana. Small isolated patches, often less than
one square mile in extent, occur adjacent to the Bearpaw Mountains in north-
central Montana.
Erosion has removed the lower Tertiary deposits from much of Montana east
of the Disturbed Belt and has beveled much, if not all, of these formations even
where they are preserved. The lower Tertiary formations were not deposited as
a uniform, continuous blanket as were most of the previously deposited formations.
Tectonic activity of the Laramide Orogeny was already producing major folds in
the nearly horizontal strata of the Great Plains region and these lower Tertiary
deposits are accordingly thick or thin depending upon the tectonic pattern that
was then current in their area of deposition. Over much of the Great Plains of
Montana, restored thickness of lower Tertiary deposits indicates an accumulation
of less than 1,500 feet. In the Bighorn and Powder River Basins, however, lower
Tertiary formations are more than 8,000 feet thick.
-------
- 26 -
The lower Tertiary formations in Montana were deposited entirely by fluvial
systems. Channel sandstones are common in the Tullock and Tongue River Members
of the Fort Union formation, and overbank siltstones and shales occur. Back-
water swamps in which lush, subtropical vegetation grew were plentiful and of
long duration in southern Montana—especially during Tongue River time. Thick,
extensive coal beds attest to the presence of these swamps. Because lower
Tertiary sediments were deposited by fluvial systems, lithologic changes often
occur rapidly in short distances.
Ground water from lower Tertiary formations is obtained mainly from the
sandstone units and from the coal beds, but some water is obtained from clinker.
The water from the lower Tertiary formations is usually a calcium or magnesium
bicarbonate type and dissolved solids concentrations range from about 500 mg/L
to more than 5,000 mg/L. The water quality and chemistry often reflect the
lithologic changes that are the result of fluvial deposition. Yields of water
from wells completed in lower Tertiary formations are typically less than 15
gallons per minute, but wells yielding as much as 50 gpm have been reported.
The Fort Union Formation is the most widely used aquifer in eastern Montana.
This usage is because of the great areal extent of the formation and because
water is often available from it within 250 feet of the ground surface.
C. Fox Hills-Hell Creek Formations
These uppermost Cretaceous formations once extended from western Montana
into the eastern Dakotas. Although erosion has removed much of the formations,
they still are present in eastern Montana. These formations also occur just
east of the Disturbed Belt where they are referred to as the Horsethief Sand-
stone and St. Mary's River Formation. Throughout most of its extent, the Fox
Hills Sandstone is usually about 300 feet thick. In parts of east-central
Montana, however, it was eroded and often completely removed during Hell Creek
-------
- 27 -
time. The Hell Creek Formation ranges in thickness from 500 to 1,100 feet. The
Fox Hills Sandstone was the last marine formation to have developed in Montana.
It was deposited as forest beds in a -wide-spread delta that formed as the
Bearpaw Sea withdrew. Sandstone is its most abundant component, but siltstone
and shale units are also present. The Hell Creek Formation is the uppermost
Cretaceous formation to be deposited in Montana. It is a fluvial deposit that
contains lenticular sandstone bodies and overbank silt and clay. Carbonaceous
shale lenses provide evidence that swampy conditions existed during the deposition
of the Hell Creek Formation. Although the structural configuration of the surface
of these formations was formed by the end of the Laramide orogeny, their present
altitude was attained only during early Pleistocene as the result of epeirogenic
uplift.
In eastern Montana these uppermost Cretaceous formations are sought as a
preferred source of water. Wells often penetrate several other water-bearing
zones that are close to the surface, but that water is cased off in order to
obtain the softer water contained in the Fox Hills and Hell Creek formations.
Total dissolved solids in these aquifers typically range from 500 mg/L to 1,100
mg/L. Yields of water from wells completed in these aquifers are also somewhat
higher than those from aquifers nearer the surface. In many p]aces, especially
in southeastern Montana, wells penetrating Fox Hills-Hell Creek Formations will
have static water levels above that of the ground surface. Because many people
like to have flowing artesian wells as their water sources, these aquifers are
often preferred over shallower aquifers.
D. Judith River Formation
The Judith River Formation is a wedge of sandstone, siltstone and silty
shale overlying the Claggett Shale and underlying the Bearpaw Shale; all these
-------
- 28 -
units are Cretaceous in age. Near the western margin of the Great Plains, the
Judith River Formation grades into the Two Medicine Formation and is more than
700 feet thick. Near the eastern border of Montana the Judith River Formation
has thinned to usually less than 50 feet, and is dominantly a silty shale. In
much of north-central Montana, the lower part of the Judith River Formation is
a fluvial, continental deposit, and includes coal seams as much as five feet
thick. In south-central Montana, the lower part of the Judith River Formation
is a marine sandstone and is often designated as the Parlcman Sandstone or Park-
man Member of the Judith River Formation. Although the Judith River Formation
thins eastward, east-west zones occur where the formation is considerably thicker
than it is either to the north or south. These east-west zones probably mark
the location of fluvial distributary channels or major near-shore submarine
channels that were later filled with sand transported by longshore currents.
The present structural configuration of the Judith River Formation was essentially
attained at the close of the Laramide orogeny. At that time, however, the top
surface of the formation was generally well below sea level except along the
major uplifts. The Judith River Formation was raised to its present altitude
during the early Pleistocene as a result of regional epeirogenic uplift.
Well yields from the Judith River Formation range up to approximately 100
gallons per minute. There is usually a good correlation between yield and total
sandstone thickness for wells that fully penetrate an aquifer. Unfortunately,
most wells completed in the Judith River Formation do not fully penetrate it,
but stop when enough water for household or stock use has been obtained. Thus,
the yields from this aquifer usually reflect water needs rather than true
capacity of the aquifer. High drilling costs and low well yields have combined
to prevent development of this aquifer where it is substantially beyond 500 feet
below ground surface. Consequently, little is known about its water-yielding
-------
- 29 -
capabilities or potentiometric surface of few tens of miles east of its outcrop
areas.
Water from the Judith River Formation is under sufficient pressure to cause
it to rise in the well considerably above the level at which it enters the well.
Flowing wells occur along the Missouri River between Little Rocky Mountans and
Larb Creek and along the Musselshell River (and its preglacial course) from
about Mosby to Beaver Creek.
The quality of water from the Judith River Formation can range up to
5,000 mg/L dissolved solids. The water with the fewest dissolved solids is
found close to recharge areas and the more saline water is found in the eastern
part of the state where the formation contains more shale. Ground water that
stays in contact with salt-containing formations leaches the salts by solution.
In structurally low areas this water rarely moves laterally and the dissolved
solids concentration of the water increases greatly. Wide ranges in water
quality occur even near the outcrops. These quality variations may reflect
lithologic differences.
E. Eagle Formation
The Eagle Formation is one of the main aquifers in the northwestern part of
the Great Plains region of Montana. It is also commonly used in southern Montana
west of 108° west longitude. The areas in which this aquifer is highly used
correspond to the area of its outcrop and where the formation is less than 300
feet below the ground surface. The Eagle Formation is rarely more than 400 feet
thick; its thickest section is near the western limit of the Great Plains region
where the formation is predominantly sandstone. Siltstone and shale become
dominant in the Eagle Formation with distance eastward from the disturbed Belt.
East of 107° west longitude, the Eagle Formation contains so much shale that it
is often called the Gammon Formation or Gammon Shale and includes the equally
-------
- 30 -
shaley Telegraph Creek Formation. The Gammon Shale is exposed in the Black Hills
uplift of southeastern Montana, but contains so much shale that only about five
wells are known to obtain water from it. The yields from these wells average
less than 3 gpm and the water can be used only for stock watering. The Eagle
Formation receives little use as an aquifer in northeastern Montana because of
its great depth below surface and scant yield of water. In northwestern Montana
and near the Bowdoin Dome, water from the Eagle Formation may contain natural gas.
Cattle will drink this water after some of the gas has escaped, but humans who
try to use this water complain of a sulfur taste.
In the areas where the Eagle Formation is highly used as a source of water,
the quality of its water is generally good. Dissolved solids content of the
water is usually less than 1,500 mg/L and often less than 1,000 mg/L. Yields of
500 gpm have been reported from the Cut Bank area, but yields generally average
less than 50 gpm.
F. Kootenai Formation
In latest Jurassic time, mountain uplift began in extreme western Montana
and eastern Idaho with the primary intrusion of the Idaho Batholith. The inten-
sive mountain building of the Laramide Orogeny was millions of years in the
future, but the steepened gradients formed by these newly emergent hills pro-
duced streams that flowed eastward across swampy deposits that were to become
the Morrison Formation. At first the streams cut into the eroded Morrison
deposits but, as uplift ceased or was reduced in the west, the streams began
to deposit sand along their channels. In time, the channels coalesced and
migrated laterally. Eventually, sand blanketed most of eastern Montana to a
depth of as much as 100 feet. This sand now forms the basal unit of the
Kootenai Formation and is referred to as: the Sunburst Sandstone, Cutbank
Sandstone, the Third Cat Creek Sandstone, the Pryor Conglomerate or the Lakota
Sandstone. Following the deposition of this basal unit, crustal subsidence of
-------
- 31 -
the continental interior allowed the Cretaceous sea to enter eastern Montana.
In this sea, the upper part of the Kootenai Formation was deposited. It consists
of maroon or red and green shale with local bodies of sandstone. Locally, fresh-
water limestone was deposited.
The basal sandstone unit of the Kootenai Formation is the main aquifer but,
in many places the upper sandstone units and the limestone unit produce enough
water for stock or domestic use. Throughout most of the central and western
Montana plains, where the Kootenai Formation is within 500 feet of the surface,
the Kootenai Formation is sought for its ground water. Although yields as low
as ten gallons per minute are sometimes obtained from the upper part of this
formation, yields of 300 gpm have been obtained from the basal sandstone. In
many places a well tapping the basal sandstone will produce flowing water.
Chemical analyses of water from the Kootenai Formation show dissolved
solids ranging from less than 500 mg/L near outcrop areas in the Little Belt
Mountains to more than 14,000 mg/L in the Sweetgrass Arch near Cutbank.
G. Swift Formation
The only Jurassic formation known to have sufficient water-bearing potential
to be considered an aquifer is the Swift Formation. This formation is present
throughout the Great Plains region of Montana except in the central areas of
the plains mountains from where it has been eroded. The Swift Formation gen-
erally thickens from west to east. It is about 100 feet thick along the east
edge of the Disturbed Belt and 400 to 600 feet thick along Montana's eastern
border. This greater thickness is caused by shale units which are more abundant
in the east than in the west. Throughout most of central and western Montana
the Swift Formation contains a total sandstone thickness of 40 to 150 feet. In
eastern Montana, however, the total sandstone thickness is commonly less than
50 feet and in many places is less than 25 feet.
-------
- 32 -
Because the Swift Formation is at a considerable depth below land surface,
few wells have been drilled into it solely to obtain water, thus, most informa-
tion on its water-bearing characteristics comes from oil wells. This information
indicates that where total sandstone thickness is more than 100 feet (western
and central Great Plains region), wells will generally yield 50 gallons of water
per minute. In eastern Montana, where the Swift Formation is much deeper below
land surface and where the total thickness of sandstone is less, data are in-
sufficient to evaluate its aquifer characteristics.
Almost all chemical analyses of water from the Swift Formation are from
western and north-central Montana. These analyses show that water from the
Swift Formation commonly contains less than 500 mg/L dissolved solids within ten
miles of the outcrop, but dissolved solids increase rapidly with increasing dis-
tance from the outcrop. Water with a dissolved solids content of more than
A,000 mg/L is found in many places along the axis of the Sweetgrass Arch.
II. Madison Group
The Madison Group aquifer extends across the entire Great Plains region.
It is absent only in a few small areas at the center of mountain uplifts where
it has been removed by emplacement of igneous rocks or by erosion. The Madison
Group is dominantly limestone, but its uppermost unit, the Charles Formation,
becomes increasingly an anhydrite with proximity to the center of the Williston
Basin. In some places the limestone has been largely dolomitized. Throughout
most of eastern Montana, the Madison Group is more than 600 feet thick. A
maximum thickness of more than 1,000 feet occurs along a trough that extends
from the Big Snowy Mountains to the center of the Williston Basin. Because of
its great potential as an aquifer, the Madison Group has been the object of an
extensive drilling and investigation program throughout the northern Great
Plains. Data are currently becoming available to make a reasonably detailed
-------
- 33 -
evaluation of this aquifer.
The test wells drilled through the Madison Group showed a great degree of
variability in yield of water from this aquifer. The yield was highly dependent
on fracture porosity, initial porosity and degree of dolomitization. Well
yields ranged from 20 gpm to more than 1,000 gpm. Data from oil well drill-stem
tests are currently being compiled to determine the spatial variation in water
yield. Because the Madison Group is recharged with ground water in the central
areas of mountain uplifts, water in this aquifer is commonly under enough pressure
to flow at the surface from any well that penetrates the aquifer. In some places
the pressure is great enough to produce a static water leve] several hundred
feet above the land surface.
The quality of water in the Madison Group is highly dependent on the com-
position of the Madison Group and the distance the water has traveled from area
of recharge or, more specifically, the amount of time it has spent within the
aquifer. Adjacent to the mountains, where the aquifer is recharged and where
the Madison Group is dominantly limestone, dissolved solids content of the water
within the Madison Group is commonly less than 500 mg/L. Dissolved solids con-
tent of the water increases within a few miles of the 500 mg/L isoline to more
than 1,000 mg/L and then increases more slowly. Near the periphery of the
Williston Basin, where the Charles Formation is largely an anhydrite, dissolved
solids again rapidly increase from 4,000-5,000 mg/L to more than 15,000 mg/L
within about ten miles. The dissolved solids content of water from the Madison
Group near the center of the Williston Basin is greater than 300,000 mg/L or
about ten times that of seawater.
Water-bearing formations occur below the base of the Madison Group. Some
of these formations have great potential as aquifers. The well depth required
to obtain water from these formations exceeds 6,000 feet throughout most of
-------
- 34 -
eastern Montana. Well depth's of 16,000 feet are necessary to reach the base of
these formations in the Williston Basin. Because of these extreme drilling
depths and the sparse data on aquifer characteristics, these pre-Madison Group
formations are not included as aquifers in this report.
-------
- 35 -
III. GROUND-WATER USE
Information on water use in Montana prior to 1980 is extremely limited
because of a lack of accurate withdrawal rate data. While communities have
the best opportunity to record water use, in most instances only new delivery
systems are equipped to measure discharge. Similarly, rural, agricultural
and industrial water users often have no means of measurement and only
estimates can be made for these values. However, Montana is presently
quantifying its water use and consumption through a water-right adjudication
program. This program is being implemented through the Department of Natural
Resources and Conservation under Senate Bill No. 76. All water-use applications
are to be filed by April 30, 1982 and then will be reviewed and summarized.
Better estimates of precise ground-water and surface-water use will become
available after that date.
Major uses of ground water in the Great Plains region are for irrigation,
municipalities, industry, rural domestic use, and livestock. Table 1-4 is a
summary by county of the various well uses in this region. Most of these
wells are completed in the Quaternary alluvium or Tertiary and Cretaceous
aquifers, although deeper aquifers are exploited locally. The cumulative
total of ground water withdrawn from the Great Plains region is approximately
114.41 million gallons per day (mgd) or 56.68 acre-feet per day. This value
for ground water represents about two percent of the total amount of water
diverted within the Great Plains region, a value much lower than for most other
Western states. Even though two percent is a small percentage, ground
water is the only viable source of potable water that can and will be further
developed now that surface-water supplies are over-appropriated in this region.
-------
- 36 -
table
1 -
4
WELL USE
BY COUNTY IN
THE
GREAT
PLAINS
REGION
COUNTY
COM
noM
1)+S
1KR
I NO
PUB
STK
MU
0T1I
NOT
RPT
TOTAL
B ighorn
3
199
180
7
18
10
377
39
41
13
887
Blaine
1
109
233
2 3
6
8
374
14
10
8
786
Ca rbon
1
61 1
269
13
2
1 3
202
55
63
8
1237
Ca r ler
0
65
no
0
0
2
648
13
6
0
CO
Cascade
22
904
417
14
5
1 1
233
62
53
1
1722
Chou-au
0
96
395
6
0
28
338
82
34
5
984
Cus tcr
12
22 5
2 IB
19
3
9
685
92
22
8
1293
Dame I s
1 35
126
2
2
6
191
74
1 1
6
554
Onwyon
1 i
36 2
J 38
17
1 7
14
693
89
30
U
1577
Fallon
0
62
235
3
8
7
568
28
8
6
925
Fergus
1
301
4 24
10
13
7
449
1 10
52
3
1370
Ca r f ield
0
63
153
4
2
2
685
25
15
0
951
Golden V,i 1 luy
0
50
1 15
1
0
0
276
1 7
3
0
4 64
Mil 1
0
345
119
12
9
21
226
70
25
4
1031
Jud i Lh It a s l n
2
175
1 50
1 5
3
8
308
60
1 5
1
737
I.ibei ty
0
66
102
2
0
3
lift
33
7
1
330
McCone
2
133
16 7
10
0
7
4S6
25
12
851
Musselshel 1
0
235
31 1
6
2
9
823
33
14
21
1454
Petrol cum
i
15
56
4
4 7
1
189
22
7
1
34 3
I'hi 11 1 p s
2
162
'.3 5
20
a
7
4 76
29
21
t,i
1 164
Pondera
0
36
148
2
0
13
8 3
2 1
6
1
310
Po«der River
1
226
216
28
3
9
1577
i 1
15
1
2087
!'ra i i 1 e
U
109
1 02
10
9
5
580
14
10
1
844
Richland
1
3 34
281
1 7
2 1
20
817
4 8
17
8
1536
Roosevelt
1
19 1
2 1 2
4 1
1 i
10
331
4 8
10
9
868
Rosebud
0
1 64
1 52
9
1 7
21
66 3
21
32
9
1088
Sheridan
0
1 2
224
5
6
1 2
185
26
19
4
593
Stillwator
3
4 5 J
215
7
5
r»
394
4 0
30
1
1 1 54
Sweuigrnss
0
185
156
5
2
2
175
22
11
1
559
Teton
5
368
390
4 3
?
10
257
79
14
u
11 72
Tool e
0
23
88
i,
1
1 1
12 3
4 7
14
2
313
Treasure
0
11
A /.
2
0
2
22 1
9
0
1
306
Val ley
0
27 3
4 35
21
6
24
553
99
29
21
1461
Wheatland
1
6'.
57
8
2
2
288
26
10
0
458
Wibaux
0
51
1HS
5
2
7
4 05
23
12
1
694
Yellovstone
u
1711
54 4
J_52_
_]7
|_8
7 17
219
54
8
3464
Tocal
81
8666
82 1 5
549
253
345
1 57 32
1 725
732
175
364 7 1
COM- Community; DOM-Domcsi lr , !HS-l)onu*s L i c .nul SiockuMter; I RU-I rr Ignl Lon ; 1ND- 1 nclusir i n 1 ; PbK-Public, STK-
S Lockwn lor only, MU-Mu It I use-; OTll-Oihcr, NOT KPT- No i Koporu-d.
-------
- 37 -
A. Municipal and Domestic
A computer listing produced by the Montana Department of Health and
Environmental Sciences (1980) shows that there are 89 communities in the
Great Plains region of Montana that have a municipal water-supply system.
The total number of public supply systems exceeds 250, if including trailer
courts, nursing homes and other institutions. Of the 89 communities, 13 rely
exclusively on surface water, another 8 use both surface and ground water
and the remaining 68 communities depend solely on wells or springs for their
water supply. Of the 393,063 people who reside within the Great Plains
region of Montana, approximately 264,300 live in municipalities. Of these,
91,400 (35%) depend exclusively upon ground water for their drinking and
household needs; they withdraw a total of about 19.06 million gallons of
ground water per day. Only a small percentage of this total is used to
satisfy industrial or commercial needs.
Although several different aquifers are used throughout the Montana
plains for municipal water, no study or examination has been made to determine
which aquifers are used. A cursory examination of the.relationship of
towns in the plains to geology indicates that, perhaps, as many as 90% of
these water supplies derive their water from alluvium or other unconsolidated
deposits. At least two towns (Broadus and Ekalaka) obtain water from either
the Foxhills or Hell Creek Formations, several may obtain water from the
Eagle and Kootenai Formations and Lewistown obtains its water supply from a
spring that emerges from a limestone formation of the Madison Group.
The quality of water used by many of the communities in the Montana
plains region often exceeds the EPA's maximum recommended limits for dissolved
solids. Several systems distribute water that contains more than 1500 mg/L
-------
- 38 -
and the well supplying the town of Jordan has dissolved solids of about 1800
mg/L. Although these values greatly exceed the 500 mg/L recommended maximum,
most communities have no other source.
Iron is a problem for many community water systems. Most systems distribute
water that contains less than the recommended maximum of 0.3 mg/L for iron,
but others greatly exceed it. Four community systems that distribute water
exceeding 4.0 mg/L in 1980 were North Harlem Colony, Wibaux, Wolf Point and
Wyola. Nitrates in water are a problem in some farming communities both from
application of fertilizers and from degradation of water supplies caused by
saline seeps. The following community systems in 1980 delivered water with
exceptionally high nitrate values: North Turner Colony (35 mg/L), Flaxville
(28 mg/L), Conrad (21 mg/L), Coffee Creek (14 mg/L) and Denton (13 mg/L).
In addition, the water from several trailer courts was analyzed to contain
more than 7 mg/L. These latter high nitrate values may result from septic
system effluent or related pollution. Fluoride values are generally well
below the EPA recommended maximum. Community systems that distributed water
high in fluorides in 1980 were: Sidney (5.1 mg/L), Circle (4.7 mg/L),
Richey (4.2 mg/L) and Lambert (4.0 mg/L). Several trailer courts also
distributed water in 1980 that exceeded 2.0 mg/L. Trace metals in water
from public supply systems were all usually within the recommended maximum.
One exception was Wyola with 0.805 mg/L of lead.
Domestic water is that which is used by all persons not served by a
municipal or community water system. For the most part, domestic wells
primarily belong to rural residents, although some subdivisions have
individual wells. There are approximately 17,000 domestic and stockwater
wells in the Great Plains region. Ground water from these wells provides
95% of the rural population with a potable supply. Rural inhabitants withdraw
-------
- 39 -
25.85 million gallons per day, most of which is consumed.
Domestic wells are commonly drilled until sufficient amounts of relatively
good quality water are reached, and for this reason, well yields are generally -
small. For most rural inhabitants of the Great Plains region, ground water
is essential for their well being and livelihood.
B. Agriculture
Agriculture is the largest ground-water user in the Great Plains region.
The principal use of ground water is for cropland irrigation with a secondary
use for livestock consumption.
1. Irrigation
There are about 1,347,740 acres of irrigated land in the Great Plains
region. However, the percentage of this acreage that is irrigated in any
given year is uncertain. Roughly 5.62 billion gallons per day (bgd) are
applied to this acreage of which 1% is withdrawn from ground-water sources.
Almost all of these irrigation wells are completed in the unconsolidated
alluvial aquifer. The Madison aquifer is also receiving renewed interest as
a deeper source of good quality water.
Requirements for diversion are more than double consumptive use, resulting
in a return flow of 53% of the total diversion (DNRC, 1975). Consumptive use
varies with irrigation efficiency, rates of application and other factors
such as the crop, soil, precipitation, growing season and temperature.
Nearly all irrigation is used to raise crops and feed to support the live-
stock industry.
2. Livestock
Stock consumptive use of ground water in the Great Plains is estimated
to be 19.71 million gallons per day of which 50% is withdrawn from ground-
-------
- AO -
water sources. Cattle and sheep account for the majority of the water being
consumed, with average daily consumption values of 15 and 3 gallons per head
per day, respectively. Pigs, horses and other livestock make up the remainder
of stock water consumed.
Stock water wells comprise the largest single category of permitted
wells in this region; roughly 43 percent of the wells in the Great Plains
region are used solely for stock watering purposes. These wells tap all the
aquifers within the region and are usually completed when a sufficient yield
is obtained. In many cases these wells are the only viable source of water
in the area for livestock ranchers.
C. Industry
Ground-water withdrawals by industry are separated into two distinct
constituents: (1) the petroleum industry which uses the largest quantity;
and (2) self-supplied industry which withdraws only a minor amount.
Ground-water withdrawals by the petroleum industry fall into two
major categories—fresh water, which is developed solely for use in the
secondary recovery of crude oil; and produced water, which is withdrawn as
a byproduct of primary and secondary oil recovery. Estimates of the total
petroleum ground water withdrawn are highly variable and for this reason an
accurate value could not be predicted. However, records show that there are
659 injection wells reinjecting water for secondary recovery in the Great
Plains region. According to Montana's Oil and Gas Conservation Division
(1980), these wells have an average daily injection rate of 15.06 million
gallons per day.
Major aquifers used to produce water for secondary oil recovery include
the Fox Hills, Judith River, Eagle and Kootenai Formations and the Madison
-------
- 41 -
Group. The Madison aquifer has been the principle source of secondary
recovery water for most oil fields in this region.
Future projections of oil production within the Big Horn Basin cannot
be made reliably. Much oil remains to be produced by secondary and tertiary
recovery methods, but economics will play a major role in whether or not this
oil is produced. It seems likely that with rising prices oil production in
the basin, especially the percentage produced by secondary recovery methods,
will continue to grow, as will petroleum industry water consumption.
The Montana Department of Natural Resources and Conservation defines
self-supplied industrial water as that which is obtained from a source of
supply by industry as opposed to that provided by a municipality. An
industry is also considered to be self-supplied if any of the water it uses
is obtained from its privately owned water supply facilities. The primary
industrial use of water is for condenser cooling, while smaller amounts are
used for processing, washing, conveying, air conditioning, boiler feeding
and sanitation. Ground water accounts for about 10.5 percent of the total
water used by industry in the Great Plains region. Approximately 3.47
million gallons of ground water are used daily as self-supplied industrial
water. A large percentage of this water is consumed by industry. Examples
of consumptive use are water, canned or bottled in foods or beverages, and
water absorbed or chemically combined into a manufactured product.
-------
- 42 -
IV. WATER QUALITY
A. DATA SOURCES
More than 3,600 water quality analyses contained in the computer files
at the Montana Bureau of Mines and Geology (MEMG) were reviewed for the
Underground Injection Control project, with approximately 3,100 of these
analyses from the Great Plains region. Additional analyses were located
and reviewed from MBMG and U. S. Geological Survey (USGS) publications
including: bulletins, memoirs, open-file reports, professional papers,
hydrologic atlas maps, and unpublished reports. USGS Open-File Report 76-40
by William Hopkins provided much data relating to deeper aquifers in eastern
Montana.
The MBMG water-quality file contains water-quality analyses generated
by the MBMC Analytical Division. Primary customers of this Division are
the MBMG Hydrology Division, the USGS Water Resources Division and the U. S.
Forest Service (USFS). The USGS Water Resources Division and the MBMG
Hydrology Division furnish water samples taken from ground-water sources
within the state of Montana to the MBMG laboratory for analysis, and the
results of these analyses become part of an integrated data bank. Approximately
2,000 ground-water analyses were completed and entered into computer's storage
during the USGS's Northern Great Plains project of recent years. Additionally,
the computer files contain data extracted from selected USGS and MBMG
publications which existed prior to the creation of the data bank. Documents
such as USGS Water Supply Papers 599 and 600, covering ground-water resources
for Rosebud, Treasure, and Yellowstone Counties, have been coded and included
in the file. Many similar publications are yet to be included.
Appendix V. contains a tabulation of those analyses in the ground-water
quality system selected for this project. These analyses have been sorted by
-------
- 43 -
aquifer and according to township, range, and section within the aquifer.
Many of these have been plotted on the Dissolved Solids Map series included
with this report. Occasionally, points will appear on the listings that
have not been plotted on the maps and, conversely, points will appear on
the maps which are not contained in the tabulation. This has occurred because
much of the previously published data are not computerized and because the
listings may include data created since the compilation of the maps.
B. General Water Quality
Ground-water quality data for eight aquifers or aquifer groups in the
Great Plains region were compiled. These aquifers included the:
1. Quaternary and late Tertiary (Flaxville
Formation) unconsolidated materials
2. Fort Union and Wasatch Formations
3. Foxhills and Hell Creek Formations
4. Judith River (Parkman) Formation
5. Eagle (Virgelle) Formation
6. Kootenai Formation and equivalents
7. Jurassic Age Formations
8. Madison Group and other formations of
Mississippian age
The next sections will discuss the water quality of these eight groups
in terms of their dissolved solids (DS) expressed as milligrams per liter (mg/L)
and dominant cation and anion.
1. Quaternary and Late Tertiary Unconsolidated Rocks
(Add description of unconsolidated materials when available)
-------
- 44 -
The late Tertiary unconsolidated rocks of the Great Plains regions
consist principally of the Flaxville Formation and its equivalents. Only
four analyses for waters from these materials are in the data bank..
Dissolved solids for these analyses range from 250 to 900 mg/L. Of these,
three analyses reported magnesium as being the dominant cation and all four
reported bicarbonate as the dominant anion. The fourth analysis had calcium
as the dominant cation. Zimmerman (1960) reports four additional analyses
from northern Blaine County, Montana. These analyses ranged in dissolved
solids from 300 to 1,430 mg/L. Two of these waters were sodium bicarbonate
while the others were sodium sulfate and magnesium bicarbonate waters.
The Flaxville Formation gravels underlie approximately 37 townships in
northeastern and eastern Montana. The formation generally occurs in isolated
patches except on the Big Flat north of Harlem and in the Plentywood-Scobey
area of northeastern Montana. In these latter areas the Flaxville Formation
is an important water source often providing the best quality water available
in the area, but elsewhere it finds relatively minor use as an aquifer.
2. Early Tertiary Fort Union and Wasatch Formations
(Add early Tertiary when available)
3. Foxhills and Hell Creek Aquifers
The regional Foxhills and Hell Creek aquifers in eastern Montana are
represented by 276 water-quality analyses in the MBMG's water quality files.
Ground water from these formations is generally soft and is of good quality
ranging in dissolved solids from 107 to 4,400 mg/L. The lowest dissolved
solids value reported is from an 80~l;oot-deep well in Sweetgrass County which
-------
_ 45 -
is completed in the Hell Creek Formation. The water is used for domestic
purposes and is a sodium bicarbonate type. The highest dissolved solids
value of 4,421 mg/L was measured in water from a 350 foot deep stock well
in Musselshell County and the water is a sodium sulfate type.
Figure 1-8 is a histogram of the number of analyses of waters versus
dissolved solids for the Foxhills and Hell Creek aquifers. This histogram
shows that 223 of the 276 samples (81%) were for waters with less than
2,000 mg/L dissolved solids. There are no reports of waters containing more
than 10,000 mg/L of dissolved solids in these aquifers. The frequency of
higher dissolved solids in waters tails off rapidly as values for dissolved
solids increases The chart also shows that ground water with less than
1,000 mg/L of dissolved solids from the Foxhills and Hell Creek Formations is
more often a sodium bicarbonate type with sodium sulfate becoming predominant
as values above 1,000 mg/L occur.
4. Judith River Aquifer
MBMG's data file contains 220 analyses of Judith River Formation waters.
Measurements range from a low dissolved solids value of 161 mg/L for water
from a 203 foot deep well in Wheatland County, to a high value of 27,500 mg/L
for ground water from a 200 foot deep well in Liberty County. The low value
represents a calcium bicarbonate type that is used for stock water. The
high dissolved solids value is a sodium sulfate type that is unused.
Figure 1-9 is a histogram showing the number of analyses and dominant
water type plotted against values for dissolved solids. The three most common
water types in descending order are: sodium sulfate, sodium bicarbonate and
sodium chloride. Other water types reported include: magnesium sulfate
(8 occurrences), magnesium bicarbonate (2 occurrences), and calcium bicarbonate
(5 occurrences). The histogram shows that analyses with dissolved solids of
-------
- 46 -
FREQUENCY OF OCCURRENCE COMPARED TO DISSOLVED SOLIDS IN WATER FROM THE
FOX HILLS AND HELL CREEK AQUIFERS
FIGURE 1-8
-------
- 47 -
FREQUENCY OF OCCURRENCE COMPARED TO DISSOLVED SOLIDS IN WATER FROM THE
JUDITH RIVER FORMATION
(TOO MEDICINE FORMATION AND PARKMAN SANDSTONE INCLUDED)
FIGURE 1-9
-------
- 48 -
less than 2,000 mg/L are dominantly sodium bicarbonate waters with sodium
sulfate becoming more common as dissolved solids increase. Variability
in water types appears to decrease as values of dissolved solids increase.
Of the 220 analyses, 162 or 74% contained less than 3,000 mg/L of dissolved
solids and four analyses were for waters in excess of 10,000 mg/L. All
waters having dissolved solids values of more than 5,000 mg/L were sodium
sulfate waters.
5. Eagle (Virgelle) Formation
The Eagle Formation of north-central Montana has 93 analyses on file
in the water-quality data bank. Waters range from a low dissolved solids
value of 285 mg/L in a 91-foot-deep well in southern Blaine County on the
northwest flanks of the Little Rocky Mountains, to a high value of approximately
16,000 mg/L of a sodium sulfate water from a 91-foot-deep flowing well in
Toole County. A dissolved solids value of 13,000 mg/L of a sodium chloride
water recovered during a drill-stem test of the Shannon Sandstone in Bighorn
County was also reported. Both occurrences of dissolved solids in excess
of 10,000 mg/L are apparently related to oil and gas exploration work. The
Shannon test was from ground water between 2,300 and 2,350 feet below land
surface.
Copious data points appear on the Eagle Formation DS map from the Cut '.Bank
area; an area of primary use for this aquifer. Data for this region is
contained in MBMG Bulletin 60 by E. A. Zimmerman. Analyses in this report
are from water samples taken between T. 32 N. to T. 37 N. and between
R. 3 W. to R. 6 W. in Toole and Glacier Counties. Values of dissolved
solids in this area ranged from 384 mg/L in a 160-foot-deep well in T. 34 N.,
R. 5 W., Section 35DC to 5,210 mg/L in a 575-foot-deep well in T. 36 N.,
R. 6 W., 21CB. According to Zimmerman (1960) the quality of the water in
the Eagle Formation varies locally in this area, but sodium is normally the
-------
- 49 -
FREQUENCY OF OCCURRENCE COMPARED TO DISSOLVED SOLIDS IN WATER FROM THE
EAGLE AND VIRGELLE FORMATION
FIGURE 1-10
-------
- 50 -
predominant cation and bicarbonate or sulfate the predominate anions.
Figure 1-10 is a histogram showing the number of analyses versus
dissolved solids values for the Eagle aquifer. Of the samples in MBMG's
data files, 45 (58%) had dissolved solids values of less than 2,000 mg/L.
Most of these were sodium bicarbonate waters with the second most prevalent
type being sodium sulfate waters. Other ground water types represented were
calcium sulfate (2 occurrences), calcium bicarbonate (5 occurrences),
magnesium sulfate (2 occurrences), calcium bicarbonate (5 occurrences) and
magnesium sulfate (1 occurrence). Above the 2,000 mg/L level, sodium
bicarbonate waters become less common and sodium sulfate waters more prevalent.
Sodium chloride waters also become more common above this level.
6. Kootenai Formation
The water-quality data bank contains 130 analyses of Kootenai Formation
and Kootenai equivalent waters. Equivalent formations included are: the
Cloverly; the Fuson; the Lakota and the Second and Third Cat Creek Sandstones.
In addition to those analyses in MBMG's files, 20 analyses presented by
Hopkins in 1976 were reviewed. Of the 130 samples, 108 are from wells or
springs in an area bounded by T. 11 N. on the south side and T. 18 N. on
the north side and R. 9 E. and R. 35 E. on the west and east sides respectively,
in Judith Basin and Fergus Counties. Therefore, only a limited area extent
of these aquifers .is represented, although this is their primary-use area.
A low dissolved solids value of 204 mg/L was reported in water from a 690-
foot-deep well in Judith Basin County; this water is a calcium bicarbonate
type. A high dissolved solids value of 10,500 mg/L representing a sodium
chloride water was reported in drill-stem test water from an oil well
completed in the Third Cat Creek Formation in Stillwater County.
-------
- 51 -
The histogram of Figure I—11 shows that 121 (81%) of the 150 analyses
have dissolved solids values of less than 1,000 mg/L. These waters are
primarily sodium bicarbonate (32%) , calcium bicarbonate (37%), and calcium
sulfate (18%). So few samples exist in the higher values ranging between
1,000 and 5,000 mg/L that water-type breakdowns are not valid, however, it
does appear that sodium chloride type waters become more common. In the
Gut.'.Bank area, the lower Kootenai equivalent sands are oil and gas producers
and contain water-ranging from 4,000 to 13,000 mg/L of dissolved solids.
7. Jurassic Formations
Of the 35 (34 M$MG and 1 Hopkins) analyses reviewed for aquifers in
Jurassic-age rocks, one contained 36,100 mg/L of dissolved solids. This
water was a sodium chloride type from the Piper Formation and was obtained
during a drill-stem test at a well in eastern Valley County. In MBMG's
data bank, the highest value noted for dissolved solids was 4,245 mg/L from
a 4,702-foot-deep livestock well in northern Rosebud County; this is a
sodium sulfate type water. The lowest dissolved solids value was for a
calcium bicarbonate type water from a 249~foot~deep well finished in the
Morrison Formation in Judith Basin County.
Figure 1-12 is a histogram of water analyses plotted against values of
dissolved solids. There are too few analyses represented to distinguish
definite trends in water type. It does appear, however, that calcium
bicarbonate group waters predominate when dissolved solids values are less
than 1,000 mg/L.
8. Mississippian (Madison and equivalent)
MBMG's computer file contains 44 analyses from 37 different wells or
-------
- 52 -
FREQUENCY OF OCCURRENCE COMPARED TO DISSOLVED SOLIDS IN WATER FROM THE
KOOTENAI FORMATION
DISSOLVED SOL IDS (1^/0
FIGURE 1-11
-------
- 53 -
FREQUENCY OF OCCURRENCE COMPARED TO DISSOLVED SOLIDS IN HATER FROM THE
JURASSIC FORMATION
140-
130-
-140-
120 —
no —
100—
on 90-
>-u
uj
cc
QC
ZD
o
CJ
O
u_
O
Q£
Uj
OQ
2
80-
70-
feO-
50—
40-
30-
R0-
Zl
NaHC03
NaSO/
WO—
CaSO
h
80-
Others
(NaCl, MgS0A,
MgHC03, NaSO^)
w-
40—
20-
T~ 1 1—: 1
l iooi looi 3001 -tool 5001 tool 7001 8001 1 »ooi _
rc ro to r» to to to i» >;oool
10 O O 2000 JOOO 4000 SOOO feOOO 700O gOOO VOOO iOOOO
DISSOLVED SOLIDS H/l)
FIGURE 1-12
-------
- 54 -
springs producing water from Mississippian age rocks. These analyses
represent water sources in the western and central portions of the Great
Plains region. The water samples were obtained during research on warm water
wells and springs. Figure I-]3 is a comparison of dissolved solids values
to the number of analyses from waters from Mississippian age rocks. Hopkins
(1976) evaluated and classified an additional 75 waters from Mississippian
age rocks. Feltis (1980) mapped DS values, ratios of sulfate to total anions
and ratios of sodium plus potassium plus chloride to dissolved solids values
from Madison Group rocks in the Great Plains region. These references plus
others represent a wealth of information and data that has been gathered
for the Madison Group because of the high interest in the water-yielding and
water-quality characteristics of these rocks relative to their potential for
industrial water development.
The highest dissolved solids values reported occur in the extreme north-
eastern corner of Montana underlying portions of Sheridan, Richland and
eastern Roosevelt Counties. T.n this area, dissolved solids values of 100,000
mg/L are common and values approaching 300,000 mg/L are reported. These
waters are sodium chloride brines associated with evaporite deposits within
the Charles and Mission Canyon "Formations of this portion of the Williston
Basin. The highest dissolved solids value in MBMG's files is for water
from the Angela Hot Springs well in northeastern Rosebud County. This well
produces a sodium calcium chloride sulfate water from well perforations placed
between 8,152 and 8,183 feet below land surface.
Waters obtained from sources near the outcrops of Mississippian age
rocks represent the other extreme and are very much lower in dissolved solids.
The lowest dissolved solids value noted was from rocks of the Big Snowy
-------
- 55 -
FREQUENCY OF OCCURRENCE COMPARED TO DISSOLVED SOLIDS IN WATER FROM THE
M1SSISSIPPIAN FORMATIONS
|40 -
-140 —
130 —
120-
120—
110 -
100-
i/-i 90-
Ui
O
2 :
£ 80:
o 70-
O
O
QC
(?0—
03
§ »:
100—
NaHCO-
CaSO/
60-
Others
(MgHC03, MgSO^,
NaSO^, CaHCO^,
NaCl)
tc-
40-
40—
>ioooi
DISSOLVED SOLIDS H/O
FIGURE 1-13
-------
- 56 -
Group in Fergus County. A 225-foot-deep well completed in these rocks
produced a magnesium bicarbonate water of approximately 256 mg/L. This
water is used for domestic purposes. Figure 1-13 shows that 30 of the 37
analyses in this small group had dissolved solids values of less than
2,000 mg/L and calcium sulfate being'"the predominant, water; type.,. "Most of these
analyses represent waters in or relatively near the outcrop areas for
Mississippian age rocks.
According to Feltis (1980), anion trends closely follow increases in
dissolved solids values. Waters with low sulfate concentrations are generally
found near outcrops, but sulfate concentrations increase rapidly even a
short distance from the outcrop. Over most of the Great Plains region,
sulfate concentration is greater than 50% of the total anion content of the
water. In both the Williston Basin and Sweetgrass Arch areas, chloride
becomes the dominant anion. In these areas, Mississippian age rocks produce
oil and gas and have sodium plus potassium plus chloride ratios to dissolved
solids values of greater than 50 percent.
-------
- 57 -
SUMMARY AND CONCLUSIONS
(In Progress)
REFERENCES
Appendix A: System of Geographical Locations
Appendix B: Glossary
Appendix C: Montana Water Law
Appendix D: Printout of Injection Wells
Appendix E: Printout of Water Quality Analyses
(In Progress)
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