Water Availability and Use Science Program

Williston Basin Groundwater Availability, United States and Canada

The Williston Basin contains important oil and gas resources for the Nation. Freshwater supplies are limited in this 

semiarid area, and oil and gas development can require large volumes of freshwater. Groundwater is the primary source 

of water for many water users in the Williston Basin, so to better understand these resources, the U.S. Geological Survey 

(USGS) assessed the groundwater availability in this area. The final phase of this assessment included a computer model 

that simulates how groundwater flows in the aquifer systems and simulates how changes in water use and natural conditions may affect the water resources. These results provide a tool for land and water-resource managers to determine how 

water can be used for multiple purposes in the Williston Basin. For additional information about this assessment and more 

in-depth descriptions and results, see Long and others (2018).

Assessing Groundwater Availability on 

a National Scale

The USGS’s Water Availability and Use 

Science Program (formerly the Groundwater 

Resources Program) is assessing groundwater 

availability throughout the United States to 

gain a better understanding of the status of 

the Nation’s groundwater resources and how 

changes in land use, water use, and climate may 

affect those resources. The goal of this national 

assessment is to improve our ability to forecast 

water availability to meet human and ecological needs. Assessments will be completed for 

the Nation’s principal aquifer systems (large 

regional systems of multiple geologic units that 

can provide substantial quantities of water) to 

help characterize how much water is currently 

available, how water availability is changing, 

and how much water we can expect to have in 

the future (Reilly and others, 2008).

The primary objective of the Williston 

Basin groundwater availability study is to identify spatial and temporal changes in the overall 

water budget by more fully determining the 

processes that control how water enters, moves 

through, and leaves the groundwater system. 

Development of tools such as computer models 

can help hydrologists to better understand this 

groundwater system, to analyze forecasts about 

this system from natural and human stresses, 

and to analyze water quality and ecosystem 

health throughout the region.

The Importance of Groundwater and 

Energy Reserves in the Williston Basin

The Williston Basin (fig. 1) is a shallow 

and wide basin that underlies a land area of 

about 135,000 square miles beneath Montana, 

Jame sRiver

Little Missouri River

Missouri River

Cedar Creek

Big Muddy Creek

Cheyenne River

O'FallonCreek

Boxelder Creek

Rosebud Creek

Grand River

Cedar Creek

Knife River

Tong ue River

Souris River

HeartRiver

Moreau River

MilkRiver

Cannonball River

PowderRiver

Yellowstone River

Littl e Missouri River Redwater Rive r

Yellow stone River

South S askatchewan River

Frenchma n River

Big MuddyC reek

Bighorn River

Big Coulee

Little Muddy River

Moose Mountain Creek

Moose Jaw River Souris River

SourisRiver

A s s i niboineRiver

Qu'Appelle River

Jame sRiver

Little Missouri River

Missouri River

Cedar Creek

Cheyenne River

O'FallonCreek

Boxelder Creek

Rosebud Creek

Grand River

Cedar Creek

Knife River

Tong ue River

Souris River

HeartRiver

Moreau River

MilkRiver

Cannonball River

PowderRiver

Yellowstone River

Big Coulee

Missouri Riv e r

South S askatchewan River

Frenchma n River

Bighorn River

Moose Mountain Creek

Moose Jaw River Souris River

SourisRiver

A s s i niboineRiver

Qu'Appelle River

Lake Oahe

Lake Fort

Peck

Lake

Sakakawea

Old

Wives

Lake

F

F

Miles City arch

Cedar Creek anticline

UFU

LFU

MFU

FH

FH

UFU

FH

UFU

MFU

LHC

LFU

LFU

LHC

UHC

MFU

UHC

UFU

LFU

CANADA

UNITED STATES

MANITOBA

SASKATCHEWAN

NORTH DAKOTA

SOUTH DAKOTA

MONTANA

WYOMING

WILLISTON

BASIN

POWDER

RIVER

BASIN

Miles City

Regina

Williston

Bismarck

CANADA

UNITED STATES

Lower Tertiary and

Upper Cretaceous 

aquifer systems

Map area

Williston Basin

(Hamke and 

others, 1966)

EXPLANATION

 Anticline or arch

Area for numerical model

Geologic structure F Glacial aquifer system

UFU

MFU

LFU

UHC

LHC

FH

Hydrogeologic units—modified from 

 Thamke and others (2014)

Upper Fort Union aquifer

Middle Fort Union hydrogeologic unit

Lower Fort Union aquifer

Upper Hell Creek hydrogeologic unit

Lower Hell Creek aquifer

Fox Hills aquifer

Lower

Tertiary

aquifer

system

Upper

Cretaceous

aquifer

system

Base modified from U.S. Geological Survey and other Federal digital data, various scales

108° 106° 104° 102° 100°

50°

48°

46°

0 30 60 90 120MILES

0 30 60 90 120 KILOMETERS

F Nesson anticline

Figure 1. The three uppermost aquifer systems in the Williston Basin comprise 

seven hydrogeologic units. These three aquifer systems are the most accessible and 

primary sources of groundwater because they overlie as much as 3,000 feet of shale. 

Map modified from Long and others, 2018.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2018–3046

September 2018
North Dakota, and South Dakota in 

the United States and Manitoba and 

Saskatchewan in Canada. In this basin, 

the three uppermost aquifer systems—

the glacial, lower Tertiary, and Upper 

Cretaceous aquifer systems—are as 

much as 3,000 feet (ft) thick and overlie 

shale that serves as a barrier to underlying saline aquifers. Within the study 

area, the climate is semiarid, is driest in 

the southwest (6 inches per year [in/yr] 

of precipitation), and is wettest in the 

east (greater than 30 in/yr of precipitation). The recharge to groundwater is 

about 10 percent of the precipitation. 

Water from streams and rivers (surface 

water) is heavily appropriated in most 

of the study area (Schuh, 2010) and is 

not always a dependable water supply in 

stream reaches that may flow intermittently. Groundwater levels have declined 

markedly in parts of the study area, resulting in a need for users to obtain water 

from other sources (North Dakota State 

Water Commission, 2015) and resulting 

in development of recommendations for 

conservation measures (Montana Department of Natural Resources and Conservation, 2014).

The Williston Basin has been an 

important domestic oil and natural gas 

producing region since the 1950s. Previously inaccessible formations, such as 

the Bakken and Three Forks Formations, 

have been developed substantially since 

the mid-2000s because of improved 

precision horizontal drilling and hydraulic 

fracturing methods. These development 

methods require considerable volumes of 

freshwater, mostly from shallow aquifers 

or surface waters. Water use per oil well 

for hydraulic fracturing increased by 

about six times from 2005 to 2014 and 

averaged about 2.4 million gallons per 

well in 2014 (Scanlon and others, 2016). 

There were 3.7 million hydraulic fracturing treatments (sometimes called “frac 

jobs”) reported during 2000–15 in and 

near the Williston Basin (Barnhart and 

others, 2018). As the demand for energy 

increases in the United States, so does the 

demand for water used to produce many 

forms of that energy. Fortunately, one of 

the wettest periods of precipitation was 

during 2007–14 (Long and others, 2018), 

which was concurrent with substantial 

energy development in the area.

Understanding Groundwater 

Availability in the Williston Basin

The concept of groundwater availability is more than just how much water 

can be pumped from any given aquifer. 

Groundwater availability is a complex 

topic that is dependent on many factors, 

including the quantity and quality of 

water, climate variability, human use, 

aquifer characteristics, changes in 

groundwater storage, and changes in 

the ease of extracting groundwater. 

Initial steps to understand and assess 

the groundwater availability of the three 

uppermost principal aquifer systems in 

the Williston Basin included development of a three-dimensional framework 

of the geology and hydrology that defined 

characteristics such as aquifer thickness 

and depth to water (Thamke and others, 

2014), and development of a conceptual 

model that defined groundwater-flow 

directions and amounts of surface water 

and groundwater (Long and others, 2014). 

Using this information, a computer model 

of groundwater flow was developed 

to help assess changes in groundwater 

storage and groundwater levels that potentially would result from human activity 

and climate variability (Davis and Long, 

2018a; Davis and Long, 2018b; Davis and 

Long, 2018c). This model is a mathematical representation of groundwater flow 

through the three aquifer systems using 

information about aquifer properties and 

groundwater recharge, discharge, and 

levels, and physical processes governing groundwater flow. Models are useful 

tools for investigating how the complex 

groundwater system is affected by the 

interconnected variations in water supply, 

water demand, management strategies, 

exchange of groundwater and surfacewater, and climatic variation on the 

groundwater system.

A few key findings from this study 

include the following:

• The groundwater table in aquifers near 

the land surface closely resembles the 

undulating land topography, and flow 

directions are from upland areas toward 

streams (fig. 2).

• In the deeper aquifers, groundwaterflow directions follow a regional 

pattern from southwest to northeast, 

and minimal influence is from the land 

surface (fig. 2).

• The main components of recharge 

to groundwater are precipitation and 

infiltration from streams and reservoirs. 

Irrigation recharge and groundwater 

inflow from outside the Williston Basin 

were determined to be only a small part 

of total groundwater recharge.

• The deepest aquifer system has the 

smallest water budget—less than onethird as large as each of the other two 

shallower systems—yet accounts for 

about 70 percent of the total well withdrawals in the basin.

UFU

MFU

LFU

UHC

LHC

FH

SOUTHWEST

NORTHEAST

Yellowstone River

Missouri River

Lake Sakakawea Souris River

 Nesson 

anticline

Basal confining unit

(thickness not to scale)

 Nesson 

anticline

Basal confining unit

(thickness not to scale)

 Cedar Creek anticline Cedar Creek anticline

Groundwater-flow direction

EXPLANATION

Glacial aquifer system, showing sand and 

gravel aquifers within large areas of till

UFU

MFU

LFU

UHC

LHC

FH

Upper Fort Union aquifer

Middle Fort Union hydrogeologic unit

Lower Fort Union aquifer

Upper Hell Creek hydrogeologic unit

Lower Hell Creek aquifer

Fox Hills aquifer

Lower Tertiary

aquifer system

Upper Cretaceous

aquifer system

Hydrogeologic units

Figure 2. Groundwater in the shallower aquifer systems generally flows towards rivers and 

streams, whereas groundwater in the deeper aquifer systems flows towards the northeastern 

part of the Williston Basin. Diagram modified from Long and others, 2018.
• Most groundwater discharge is to 

streams and reservoirs. Groundwater 

pumping is a small part (less than 

5 percent) of the total water budget; 

however, groundwater withdrawals 

from wells have increased from 1960 

to 2005 and have caused groundwater 

levels to drop locally.

In addition to the general understanding of the aquifer systems, specific 

scenarios were evaluated using the 

computer model. Key notable findings 

resulted from scenarios that include evaluating the following:

• Scenario 1.—Effects of flowing wells 

(wells that discharge water without a 

pump because the water in the well 

reaches the ground surface under the 

natural pressure of the aquifer) in the 

Fox Hills and Hell Creek aquifers. 

Model simulations of continuous flow 

from these wells during 1960–2035 

indicate the following:

• Groundwater levels would decline 

the most during 1960–2005; however, the area of drawdown would 

continue to enlarge after 2005.

• Areas with the largest groundwaterlevel declines (more than 100 ft) are 

near the Yellowstone, Missouri, and 

Little Missouri Rivers, where most 

flowing wells are located. However, 

groundwater-level declines would 

flatten after 2010 because modeled 

flow rates would decrease slightly in 

wells because of decreasing hydraulic pressures, and nearly one-quarter 

of the simulated wells would cease to 

flow by 2035 (fig. 3).

1960 1970 1980 1990 2000 2010 2020 2030 2040

0

10

20

30

40

50

60

70

1,940

1,960

1,980

2,000

2,020

2,040

2,060

2,080

Flow rate, in cubic feet per second 

Groundwater level elevation, in feet

above land surface 

Year

Simulated groundwater level for 

an example 

flowing well

Total flow from all 

simulated 

flowing wells

EXPLANATION

Figure 3. The computer model simulation demonstrates that as total flow from all simulated flowing wells (black line) in the Fox Hills and 

Hell Creek aquifers increased, the groundwater level (blue line) declined in response. Background photograph of Hell Creek Formation by 

Kevin Dennehy, U.S. Geological Survey.

• Modeled flow rates for flowing wells 

are much larger than actual flow 

rates, possibly because of inadequate 

sealing or corrosion of wells that 

could result in water leaking into the 

overlying aquifers and not discharging at the land surface.

• Scenario 2.— Effects of a 10-year 

study-area-wide drought. Groundwater 

declines are greatest (as much as 230 ft) 

in the climatically wet eastern part of 

the Williston Basin during drought conditions. Groundwater in the dry western 

areas of the Williston Basin was less 

susceptible to drought conditions.

• Scenario 3.—Effects of a 10-year 

drought with increased pumping for 

energy development during 2006–15.

• The reduced amount of groundwater 

recharge during drought conditions 

had a greater effect on the water 

budget than increased groundwater 

withdrawals because of energy 

development.

• The total effect to groundwater 

levels by adding pumping wells to 

support energy development is small 

regionally, but locally, the effects to 

groundwater levels can be substantial.

Groundwater is often the only 

water resource available in 

this drought-prone region. 

Photograph near Bainville, 

Montana, during a drought 

period; used with permission 

from Whitten Photography.

Large quantities of freshwater 

are needed year round for oil 

and gas development. Overall, 

groundwater use for oil and gas 

development has minimal effect 

on the basin; however, locally 

the effect can be substantial. 

The water stored in these tanks 

during the winter near Watford 

City, North Dakota, will be 

used as part of the hydraulic 

fracturing process. Photograph 

used with permission from 

Whitten Photography.
Where to Find More Information

For more information about this 

study, including downloadable data and 

publications, go to https://www.usgs.gov/

centers/wy-mt-water/science/willistonand-powder-river-basins-groundwateravailability-study.

References Cited

Barnhart, T.B., Long, A.J., Haines, S.S., 

and Varela, B., 2018, Water use data 

for hydraulic fracturing treatments 

in the Williston Basin, United States, 

2000–2015: U.S. Geological Survey 

data release, accessed September 2018 

at https://doi.org/10.5066/F78P5ZDV.

Davis, K.W., and Long, A.J., 2018a, 

Construction and calibration of a 

groundwater-flow model to assess 

groundwater availability in the uppermost principal aquifer systems of 

the Williston Basin, United States 

and Canada: U.S. Geological Survey Scientific Investigations Report 

2017–5158, 70 p., accessed June 2018 

at https://doi.org/10.3133/sir20175158.

Davis, K.W., and Long, A.J., 2018b, 

MODFLOW-NWT model used to 

assess groundwater availability in the 

uppermost principal aquifer systems 

of the Williston structural basin, 

United States and Canada: U.S. Geological Survey data release, accessed 

June 2018 at https://doi.org/10.5066/

F75B01CZ.

Davis, K.W., and Long, A.J., 2018c, 

Predictive simulations of groundwater 

response to selected scenarios in the 

Williston Basin, United States and 

Canada: U.S. Geological Survey data 

release, accessed September 2018 at 

https://doi.org/10.5066/P9FACTT3.

Hamke, J.R., Marchant, L.C., and Cupps, 

C.Q., 1966, Oilfields in the Williston 

Basin in Montana, North Dakota, and 

South Dakota: U.S. Bureau of Mines 

Bulletin 629, 487 p.

Long, A.J., Aurand, K.R., Bednar, J.M., 

Davis, K.W., Mckaskey, J.D.R.G., 

and Thamke, J.N., 2014, Conceptual 

model of the uppermost principal 

aquifer systems in the Williston and 

Powder River structural basins, United 

States and Canada: U.S. Geological 

Survey Scientific Investigations Report 

2014–5055, 41 p., accessed June 2018 

at https://doi.org/10.3133/sir20145055.

Long, A.J., Thamke, J.N., Davis, K.W., 

and Bartos, T.T., 2018, Groundwater 

availability of the Williston Basin, 

United States and Canada: U.S. 

Geological Survey Professional Paper 

1841, 62 p., accessed September 2018 

at https://doi.org/10.3133/pp1841.

Montana Department of Natural 

Resources and Conservation, 2014, 

Montana State Water Plan—A watershed approach to the 2015 Montana 

State Water Plan: Helena, Mont., Montana Department of Natural Resources 

and Conservation, 81 p.

North Dakota State Water Commission, 

2015, 2015 North Dakota State Water 

Management Plan: Bismarck, N. Dak., 

North Dakota State Water Commission, 

119 p.

Reilly, T.E., Dennehy, K.F., Alley, W.M., 

and Cunningham, W.L., 2008, Groundwater availability in the United States: 

U.S. Geological Survey Circular 

1323, 70 p., accessed June 2018 at 

https://pubs.usgs.gov/circ/1323/.

Scanlon, B.R., Reedy, R.C., Male, F., and 

Hove, M., 2016, Managing the increasing water footprint of hydraulic fracturing in the Bakken Play, United States: 

Environmental Science & Technology, 

v. 50, no. 18, p. 10273–10281, accessed 

June 2018 at https://doi.org/10.1021/

acs.est.6b01375.

Schuh, W.M., 2010, Water appropriation 

requirements, current water use, and 

water availability for energy industries 

in North Dakota—A 2010 summary: 

North Dakota State Water Commission Water Resources Investigation 49, 415 p., accessed June 2018 at 

http://www.swc.state.nd.us/info_edu/

reports_and_publications/pdfs/wr_

investigations/wr49_report.pdf.

Thamke, J.N., LeCain, G.D., Ryter, 

D.W., Sando, R., and Long, A.J., 2014, 

Hydrogeologic framework of the 

uppermost principal aquifer systems 

in the Williston and Powder River 

structural basins, United States and 

Canada: U.S. Geological Survey Scientific Investigations Report 2014–5047, 

38 p., accessed June 2018 at 

By Joanna N. Thamke, Andrew J. Long, and Kyle W. Davis https://pubs.usgs.gov/sir/2014/5047/.

Photograph of lower Tertiary aquifer system, 8 miles south of Medora, North Dakota. Photograph by Whitten Photography, July 2012, used with permission.

ISSN 2327-6916 (print)

ISSN 2327-6932 (online)

https://doi.org/10.3133/fs20183046