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Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, South Dakota and Wyoming, 1931–2022

Colton J. Medler, Todd M. Anderson, William G. Eldridge, C.G. Bowles, W.A. Braddock, J.M. Carter · U.S. Geological Survey

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aquifers area availability hydrologic six south usgsscientificinvestigationsreport water

usgs, geological survey, united states, science, government publication, usgs scientific investigations report, 2025, 5067, hydrologic, budgets, water, availability, six, bedrock, aquifers, black, hills, area, south, dakota, wyoming, 1931, 2022

Prepared in cooperation with the Western Dakota Regional Water System

Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, South Dakota and Wyoming, 1931–2022

Scientific Investigations Report 2025–5067

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

Cover front and back. Photograph showing the confluence of Cleopatra Creek (left) with Spearfish Creek (right), taken in Spearfish Canyon, South Dakota, on May 11, 2024, by Colton Medler, U.S. Geological Survey.

Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, South Dakota and Wyoming, 1931–2022 By Colton J. Medler, Todd M. Anderson, and William G. Eldridge

Prepared in cooperation with the Western Dakota Regional Water System

Scientific Investigations Report 2025–5067

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

U.S. Geological Survey, Reston, Virginia: 2025

For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–392–8545. For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov/ or contact the store at 1–888–275–8747. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Medler, C.J., Anderson, T.M., and Eldridge, W.G., 2025, Hydrologic budgets and water availability of six bedrock aquifers in the Black Hills area, South Dakota and Wyoming, 1931–2022: U.S. Geological Survey Scientific Investigations Report 2025–5067, 87 p., https://doi.org/10.3133/sir20255067. Associated data for this publication: Medler, C.J., Anderson, T.M., and Eldridge, W.G., 2025, Datasets used in constructing hydrologic budgets for six bedrock aquifers in the Black Hills area of South Dakota and Wyoming, 1931–2022: U.S. Geological Survey data release, https://doi.org/10.5066/P1QWKUKP. ISSN 2328-0328 (online)

iii

Acknowledgments The authors would like to acknowledge the Western Dakota Regional Water System for its contributions to this study by providing guidance and opportunities to present this work to the community. The authors also want to thank the many water system managers in the Black Hills region for access to well withdrawal records and their water system histories. The authors acknowledge the South Dakota Department of Agriculture and Natural Resources staff for providing well withdrawal datasets and information about well withdrawal permitting in South Dakota. Daniel Driscoll and Janet Carter, both authors of the Black Hills hydrology study, were invaluable and provided insight to methodologies used in past studies that were the foundation of this work.

Contents Acknowledgments��iii Abstract��1 Introduction��1 Purposes and Scope��3 Study Area Description��4 Hydrogeologic Setting��4 Geology��4 Climate��8 Hydrology��8 Population��12 Previous Studies��13 Hydrologic Budgets��14 Inflows—Precipitation and Streamflow Recharge, 1931–2022��16 Precipitation Recharge��16 Streamflow Recharge��18 Methods for Quantifying Streamflow Recharge��18 Recharge From Streams with Continuous Records, 1950–2022��23 Recharge from Streams with Miscellaneous Records, Water Years 1992–2022��29 Recharge From Ungaged Streams, Water Years 1992–2022��32 Precipitation and Streamflow Recharge, 1931–2022��32 Outflows—Artesian Springflow and Well Withdrawals��39 Artesian Springflow��39 Well Withdrawals��39 Methods of Data Collection for Groundwater Permits and Well Withdrawals��39 Water Rights and Permit Information��39 Well Withdrawal Data Collection��42 Methods for Creating the Well Withdrawal Dataset for 2003–22��43 Artesian Springflow and Annual Well Withdrawals��44 Storage Considerations��48 Discussion of Groundwater Budget and Availability��54 Groundwater Budgets��54 Groundwater Availability��59 Limitations��63 Summary��66 References Cited��68 Appendix 1. Streamflow Recharge Extrapolation Methods��72 Appendix 2. Headwater Springflow Estimates, 1931–2022��83 Appendix 3. Artesian Springflow Estimates, 1931–2022��86

Figures 1. 2. 3. 4. 5. 6. 7. 8.

9. 10.

11. 12. 13. 14. 15. 16.

Map showing study area with subareas 1–9 and recharge areas of aquifers evaluated in this report��2 Schematic diagram illustrating hydrologic processes��5 Generalized stratigraphic column for the Black Hills of western South Dakota and eastern Wyoming��6 Graphs showing 30-year normal precipitation from 1991 to 2020 for different locations and elevations within the Black Hills region��9 Graphs showing mean annual precipitation totals for the Black Hills area, South Dakota for 1931–2022��10 Graphs showing 30-year normal temperature from 1991 to 2020 for different locations and elevations within the Black Hills��11 Map showing outcrop areas of geologic units containing aquifers in the study area used for estimating precipitation recharge in subareas 1–9��15 Map showing mean annual precipitation for the study area showing weather stations used for the inverse distance weighting interpolation for water years 1931–80 and weather stations used in the Daymet algorithm for water years 1981–2022��17 Map showing drainage basins used to estimate annual streamflow recharge in the Black Hills area, South Dakota��24 Graphs showing mean annual precipitation and streamflow recharge for the Deadwood, Madison, Minnelusa, Minnekahta, Sundance, and Inyan Kara aquifers in subareas 1–9��38 Map showing U.S. Geological Survey streamgages used for estimating artesian springflow��40 Graph showing total annual well withdrawals and annual well withdrawals for each aquifer for 2003–22��46 Graphs showing hydrographs for observation wells completed in the Deadwood, Madison, Minnelusa, Minnekahta, and Inyan Kara aquifers��53 Map showing generalized potentiometric contours of the Madison aquifer in the study area��57 Map showing generalized potentiometric contours of the Minnelusa aquifer in the study area��58 Graphs showing hydrographs of wells completed in the Madison and Minnelusa aquifers near Rapid City, South Dakota��60

Tables 1.

Estimated population by subarea and year in the study area from 1930 through 2022��12 2. Recharge factors and outcrop areas used in calculating precipitation recharge for the Deadwood, Madison, Minnelusa, Minnekahta, Sundance, and Inyan Kara aquifers��18 3. Selected site information for streamgages used in determining streamflow recharge��19 4. Loss thresholds and associated drainage areas of selected streams used to calculate streamflow recharge��21

vii

5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

20. 21.

Annual streamflow recharge for basins with continuous-record gages, water years 1950–2022, for the Madison and Minnelusa aquifers��25 Linear regression equations used to estimate annual streamflow recharge for streams with continuous, miscellaneous, and ungaged records��28 Selected information used to estimate recharge from streams with miscellaneous-record streamgages��29 Annual streamflow recharge for streams with miscellaneous measurements sites, water years 1992–2022��30 Summary of selected information used to estimate recharge from ungaged streams��32 Annual streamflow recharge from ungaged basins, water years 1992–2022, for the Madison and Minnelusa aquifers��33 Annual precipitation and streamflow recharge statistics for the Deadwood, Madison, Minnelusa, Minnekahta, Sundance, and Inyan Kara aquifers by subarea��34 Site information for streamgages and miscellaneous-record streamgages used for estimating mean annual artesian springflow��41 The total number of active permits and active appropriated annual volume by aquifer for water rights in the study area as of 2022��42 Summary of the methods used to construct the well withdrawal dataset for 2003–22 for subareas 1–9��43 Summary statistics of total annual well withdrawals for each aquifer for 2003–22��45 Summary statistics for annual well withdrawals by subarea and aquifer for 2003–22��47 Observation wells within the study area selected for analysis with site information, length of the water-level record, and Pearson correlation coefficient��50 Summary statistics of Pearson correlation coefficient calculations for the Deadwood, Madison, Minnelusa, Minnekahta, and Inyan Kara aquifers��52 Hydrologic budget including inflows from recharge and outflows from springs and well withdrawals for the Deadwood, Madison and Minnelusa, Minnekahta, Sundance, and Inyan Kara aquifers in subareas 1–9��55 Total mean annual recharge, mean annual well withdrawals, maximum annual well withdrawals, and total annual appropriations for aquifers in subareas 1–9��61 Aquifer characteristics, including area, maximum thickness, mean saturated thickness, and effective porosity, and the estimated total amount of recoverable water in storage��63

viii

Conversion Factors U.S. customary units to International System of Units

Multiply

To obtain

Length inch (in.)

2.54

centimeter (cm)

inch (in.)

25.4

millimeter (mm)

foot (ft)

0.3048

meter (m)

mile (mi)

1.609

kilometer (km)

Area acre

4,047

square meter (m2)

acre

0.4047

hectare (ha)

acre

0.4047

square hectometer (hm2)

acre

0.004047

square kilometer (km2)

square mile (mi2)

259.0

square mile (mi2)

2.590

hectare (ha) square kilometer (km2)

Volume gallon (gal)

3.785

liter (L)

gallon (gal)

0.003785

cubic meter (m3)

gallon (gal)

3.785

cubic decimeter (dm3)

acre-foot (acre-ft)

1,233

acre-foot (acre-ft)

0.001233

cubic meter (m3) cubic hectometer (hm3)

Flow rate acre-foot per year (acre-ft/yr)

1,233

cubic meter per year (m3/yr)

acre-foot per year (acre-ft/yr)

0.001233

cubic hectometer per year (hm3/yr)

cubic foot per second (ft3/s)

0.02832

cubic meter per second (m3/s)

gallon per minute (gal/min)

0.06309

liter per second (L/s)

25.4

millimeter per year (mm/yr)

inch per year (in/yr)

Transmissivity foot squared per day (ft2/d)

0.09290

meter squared per day (m2/d)

International System of Units to U.S. customary units

Multiply

To obtain

Length kilometer (km)

0.6214

mile (mi)

kilometer (km)

0.5400

mile, nautical (nmi)

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C = (°F – 32) / 1.8.

Datums Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Altitude, as used in this report, refers to distance above the vertical datum.

Abbreviations BFI

base flow index

BHHS

Black Hills hydrology study

groundwater

IDW

inverse distance weighting

NAD 83

North American Datum of 1983

NAVD 88

North American Vertical Datum of 1988

NGVD 29

National Geodetic Vertical Datum of 1929

NWIS

National Water Information System

coefficient of determination

SDDANR

South Dakota Department of Agriculture and Natural Resources

USGS

U.S. Geological Survey

WYSEO

Wyoming State Engineer’s Office

Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, South Dakota and Wyoming, 1931–2022 By Colton J. Medler, Todd M. Anderson, and William G. Eldridge

Abstract Population growth and recurring droughts in the Black Hills region raised interest in water resources and future availability. The Black Hills hydrology study (BHHS) was initiated in the early 1990s to address questions regarding water resources. Since completion of the BHHS in the early 2000s, the population of the Black Hills region increased by about 39 percent, which has renewed interest in water demand and availability in the Black Hills. The U.S. Geological Survey, in cooperation with the Western Dakota Regional Water System, completed a study to update hydrologic budgets from the BHHS for six of the most used aquifers in the Black Hills. Water availability was determined by comparing results from hydrologic budgets to modern well withdrawals (2003–22) and water rights information. Key updates to the BHHS budgets included adding available data from 1999 to 2022 and determining hydrologic budgets for six aquifers in nine smaller areas (called “subareas”). Inflows for the hydrologic budget included recharge from precipitation and streamflow losses to aquifers. Total mean annual recharge for the six aquifers in the study area was estimated at 278,900 acre-feet, with 205,100 acre-feet from precipitation recharge and 73,800 acre-feet from streamflow recharge. Mean annual precipitation recharge for the Madison and Minnelusa aquifers together accounted for 76 percent of the total mean annual precipitation recharge, with the Madison aquifer contributing 57,000 acre-feet and the Minnelusa aquifer contributing 98,100 acre-feet. Outflow components estimated for the hydrologic budget include artesian springflow and well withdrawals. Total mean annual artesian springflow in the study area was estimated as 166,100 acre-feet for the combined Madison and Minnelusa aquifers. Mean total annual well withdrawals for 2003–22 in the study area were about 50,000 acre-feet. No increased well withdrawal patterns corresponding to population increases were observed between 2003 and 2022. Water availability was determined by comparing total annual appropriations and mean and maximum annual well withdrawals for 2003–22 to mean annual recharge for 1931–2022 for each aquifer in subareas 1–9. Modern well

withdrawals (mean and maximum for 2003–22) exceeded mean annual recharge for only the Deadwood and Inyan Kara aquifers in subareas 9 and 4, respectively. Additionally, total annual appropriations did not exceed mean annual recharge in most subareas, except most notably in subarea 4 (Rapid City area) where appropriations exceeded recharge for the Madison, Minnelusa, and Inyan Kara aquifers. Total annual appropriations also exceeded mean annual recharge for the Inyan Kara aquifer in subareas 3 and 5. In addition to recharge, water availability includes the water stored in pore spaces of aquifer materials. Estimates of total volume of recoverable water in storage were updated as part of this study to include the portion of aquifers in Wyoming, which were omitted during the BHHS. In total, the estimated total amount of recoverable water in storage in the study area was 356.9 million acre-feet for six major aquifers in the Black Hills area of South Dakota and Wyoming.

Introduction The Black Hills are a mountainous region in western South Dakota and eastern Wyoming (fig. 1) with important natural resources, such as timber and minerals, and popular tourist locations, such as Mount Rushmore National Memorial, that historically have served as the economic base for local communities (Driscoll and Carter, 2001). Water resources also are important to the region because the Black Hills are the origin of many streams and are a major recharge area for many local and regional aquifers (fig. 1) that supply water to residents, industry, irrigation, and tourism. Population growth and recurring droughts in the Black Hills region can affect water resources and future availability. Between 1980 and 2022, the region’s population grew by about 73 percent, from about 124,000 to 214,100 (U.S. Census Bureau, 1983, 2024). Drought conditions in the late 1980s and the early 2000s stressed local water systems that relied heavily on surface water as the population of the region was increasing. Consequently, water managers began exploring alternative water supplies, primarily utilizing underdeveloped groundwater resources. Municipalities, like Rapid City,

2 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 104°30'

104°

103°30' BUTTE COUNTY

USC00390559

44° 30'

CROOK COUNTY

USC00397882

EXPLANATION

Fruitdale

Vale

Saint Onge

Spearfish

Sturgis

USC00394834

Central City

MEADE COUNTY

Tilford

Deadwood

Hereford

Lead LAWRENCE COUNTY

Piedmont

Lime

Osage

USC00393868

e Pla

Hill City

Newcastle Hill View Heights

Colonial Pine Hills

Rockerville Keystone

teau

WESTON COUNTY

Rapid Valley

PENNINGTON COUNTY

ston

44°

Caputa

Deadwood Formation National Oceanic and Atmospheric Administration climate stations

Map area

Hermosa

MT. RUSHMORE NATIONAL MEMORIAL

Custer

Madison Limestone

Rapid City

Jurassic units (undifferentiated)

Minnelusa Formation

USC00396947

Box Elder

Johnson Siding

Inyan Kara Group

Minnekahta Limestone

Summerset Blackhawk

Subareas from Carter and others (2001b)— Red number is the subarea number Tertiary intrusives and Precambrian crystalline rocks

Whitewood

USC00488705

Sundance

Newell

Nisland

Belle Fourche

Beulah

103°

SOUTH DAKOTA

WYOMING JEWEL CAVE NATIONAL MONUMENT

CUSTER COUNTY

Pringle

43° 30'

Fairburn

Black Hills physiographic province from Fenneman and Johnson (1946)

WIND CAVE NATIONAL PARK

7 Buffalo Gap

USC00394007

NIOBRARA COUNTY

WYOMING SOUTH DAKOTA

Hot Springs

8 Edgemont

Base modified from U.S. Geological Survey digital data, various scales Universal Transverse Mercator, zone 13 north North American Datum of 1983

FALL RIVER COUNTY

Oelrichs

0 0

5 5

20 MILES

20 KILOMETERS

Figure 1. Study area with subareas 1–9 and recharge areas of aquifers evaluated in this report. Madison Limestone and Minnelusa Formation and South Dakota geology modified from Strobel and others (1999) and DeWitt and others (1989); Wyoming geology of Minnekahta Limestone, Jurassic units (undivided), Inyan Kara Group modified from Wyoming Geologic Survey 1:100,000 quadrangle maps of the Devils Tower (Sutherland, 2008), Sundance (Sutherland, 2007), Newcastle (McLaughlin and Ver Ploeg, 2006), and Lance Creek (Johnson and Micale, 2008) quadrangles. Black Hills physiographic province (shown in inset map) from Fenneman and Johnson (1946).

Introduction 3 South Dakota, also began securing future use permits (South Dakota Department of Agriculture and Natural Resources [SDDANR], 2024a) for additional groundwater withdrawals and surface water from the Missouri River to ensure a reliable future water supply amid growing demand. The Black Hills hydrology study (BHHS) was initiated in the early 1990s to inventory and assess the region's water resources, focusing on the quantity, quality, and distribution of surface water and groundwater. The BHHS was a collection of work completed by the U.S. Geological Survey (USGS) and is described in greater detail in the “Previous Studies” section of this report. The population of the Black Hills region increased by about 39 percent since completion of the BHHS in 2000 compared to 2022 (U.S. Census Bureau, 2003, 2024), which has renewed interest in future water demand and availability in the Black Hills. Groundwater in the Black Hills region has been increasingly in demand since 2000 relative to surface water; water rights data from South Dakota (SDDANR, 2024a) showed nearly four times as many approved groundwater permits (302) than surface water permits (78). Historical well withdrawal patterns and availability estimates can inform effective resource management. The USGS has not comprehensively collected or analyzed detailed well withdrawal data and hydrologic budgets for aquifers in the Black Hills region since completion of the BHHS. The USGS, in cooperation with the Western Dakota Regional Water System, completed a study to (1) update hydrologic budgets from the BHHS for six of the most used aquifers in the Black Hills and (2) to evaluate water availability by comparing results from hydrologic budgets to modern (2003–22) well withdrawals and water rights information from State agencies and (or) water systems. Hydrologic budgets provide a means for evaluating the availability and sustainability of a water supply by accounting for each component of the water cycle and how each components interacts and contributes to the cycle. A hydrologic budget quantifies the rate of change in water stored in an area and balances it with the rate at which water flows either into or out of the area. Inflows to aquifers in this study included recharge, inflows of regional groundwater, and leakage between adjacent aquifers. Outflow components to the hydrologic budget included springflow, well withdrawals, regional groundwater outflow, and leakage between adjacent aquifers. Water availability was estimated by comparing long-term recharge conditions from updated hydrologic budgets to modern well withdrawals and the total amount of withdrawable water from water rights information. Evaluating water availability also included estimating the volume of water stored in each aquifer.

Purposes and Scope The purposes of this report are to (1) describe updates to hydrologic budgets from the BHHS for six regionally important aquifers in the Black Hills region for 1931–2022 and (2) estimate long-term water availability for each aquifer.

Hydrologic budgets were developed by estimating the inflow and outflow components for each aquifer, following methods established by the BHHS (Carter and others, 2001a, 2001b; Driscoll and Carter, 2001). This report summarizes the methods and results used to construct hydrologic budgets and estimate water availability for six bedrock aquifers. Surface water budgets and availability are outside the scope of this report and are not discussed. Hydrologic budgets were constructed for six aquifers in the Black Hills region in South Dakota and Wyoming (hereafter referred to as the “study area”; fig. 1) for the period 1931–2022. Key updates to the BHHS budgets include (1) adding available data from 1999 to 2022 and (2) dividing hydrologic budgets for each aquifer into smaller areas. Previous studies collected data up to 1998, and newer data had since become available. The study area was divided into nine separate areas (hereafter referred to as “subareas”), consistent with the delineation by Carter and others (2001b; fig. 1). Dividing the study area into subareas allowed for the development of local hydrologic budgets for each aquifer, which had previously been analyzed for only two aquifers (the Madison and Minnelusa aquifers). Subarea hydrologic budgets were useful because budget components and water availability can vary considerably throughout the study area. Hydrologic budgets developed in this study differed from previous studies in that budget components are presented by subarea for a different subset of aquifers for 1931–2022. Geologic units containing aquifers included in this study were the Deadwood Formation, Madison (Pahasapa) Limestone, Minnelusa Formation, Minnekahta Limestone, Sundance Formation, and Inyan Kara Group (fig. 1). Hydrologic budgets were not developed for aquifers within Tertiary and Precambrian igneous and metamorphic rocks, referred to as “crystalline core aquifers” by the BHHS, because these aquifers lack regional groundwater flow because of localized recharge (Driscoll and Carter, 2001). The Sundance aquifer, the saturated part of the Jurassic Sundance Formation, was the only Jurassic unit considered for recharge calculations by Driscoll and Carter (2001). The Sundance aquifer was termed the “Jurassic-sequence semiconfining unit” by Driscoll and Carter (2001) but was renamed to Sundance aquifer in this report for simplification. The Newcastle aquifer, the saturated part of the Cretaceous Newcastle Sandstone, was the only Cretaceous unit other than the Inyan Kara Group considered for recharge calculations by Driscoll and Carter (2001). The Newcastle aquifer was termed the “Cretaceous-sequence confining unit” but was renamed to Newcastle aquifer in this report for simplification. Additionally, after reviewing historical well withdrawals, the Newcastle aquifer was not included in this report because it was not considered a regionally important bedrock aquifer in the study area. The subset of aquifers and the time period for budget components varied and were determined based on assumptions from previous studies and objectives of this report. Precipitation recharge, defined as the infiltration of precipitation on outcrops of geological units, was estimated

4 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 for all six aquifers between 1931 and 2022. Streamflow recharge, which refers to water infiltrating geological units along streams, and springflow, characterized as water discharged from geological units to the land surface, were estimated exclusively for the Madison and Minnelusa aquifers (discussed in the “Hydrogeologic Setting” section of this report). Streamflow recharge was estimated between 1931 and 2022, whereas springflow estimates varied by site depending on the period of available data. Well withdrawals were estimated for all aquifers with available withdrawal data in the study area between 2003 and 2022. Although the authors acknowledge well withdrawals from aquifers other than the six analyzed in this report are an important source of water locally throughout the Black Hills, budgets were not estimated for these aquifers because they collectively represent a relatively small part of the groundwater resources used in the study area. Budgets were not created for aquifers other than the six regionally important aquifers because they were not considered regionally important based on available withdrawal data. Additionally, certain aquifers, including those within igneous, metamorphic, or alluvial materials, also were excluded from budget analyses because they received localized recharge and lacked regional groundwater flow.

Study Area Description The study area consists of the Black Hills of western South Dakota and eastern Wyoming (fig. 1). The hydrogeologic setting and population of the study area are described in the following sections. The hydrogeologic setting discussion includes descriptions of relevant geologic units present in the study area, the climatic conditions during the period of investigation (1931–2022), and the general hydrology of the Black Hills area.

Hydrogeologic Setting The hydrogeologic setting of the Black Hills includes the geology, climate, and hydrology of the region. In general, precipitation falls on the elevated terrain of the Black Hills where it infiltrates and recharges aquifers of permeable geologic materials or becomes streamflow in areas of low permeability. The geological conditions of the area create extensive surface-water and groundwater interactions including headwater springs that feed base streamflow, streamflow loss zones where water from streams recharges aquifers, and artesian springs that discharge groundwater from deep aquifers at the land surface (fig. 2).

Geology Uplift during the Late Cretaceous and early Tertiary, Tertiary intrusions, and subsequent erosion created the mountainous terrain of the Black Hills in western South Dakota and northeastern Wyoming (Carter and others, 2003). Darton and Paige (1925) described the general structure of the

Black Hills as a north-northwest trending, irregularly shaped, doubly plunging anticline with a length of 125 miles and a width of 60 miles. The Black Hills are generally defined as the area contained within the extent of the erosion-resistant, dipping Cretaceous sandstone formations that form a hogback that surrounds the central part of the uplift. The uplift exposed the Precambrian geologic units consisting of igneous and metasedimentary rocks in the central core of the Black Hills, with younger Paleozoic and Mesozoic geologic units consisting of sedimentary rocks dipping radially away from the central crystalline core. Tertiary laccoliths, dikes, and sills intruded the sedimentary rocks in the northern Black Hills and formed geologic features such as Bear Butte, Crow Peak, and Devils Tower (not shown in fig. 1). Structural features in the Black Hills formed from deformation during the uplift and intrusions include fractures, folds, and faults that occur throughout the Black Hills on local and regional scales (DeWitt and others, 1986). The Precambrian units of the crystalline core (fig. 3) are generally low permeability rocks and confining where overlain by Phanerozoic sedimentary rocks or sediment, but isolated local zones of highly fractured and weathered Precambrian rocks form important aquifers for communities in the central Black Hills, such as Custer, Keystone, and Hill City (fig. 1). Aquifers formed by the fractured zones of the Precambrian rocks are generally unconfined and are recharged where fractures are exposed at the land surface or are overlain by highly permeable unconsolidated material (Driscoll and others, 2002; Eldridge and others, 2021). Paleozoic and Mesozoic sedimentary rocks surround the crystalline core and constitute aquifers that receive recharge where outcropping. The oldest sedimentary unit in the Black Hills is the Cambrian and Ordovician Deadwood Formation. The Deadwood Formation ranges from 0 to 500 feet (ft) in thickness and consists of sandstone, glauconitic shale, and conglomerate locally at the base (fig. 3). The sandstone layers within the Deadwood Formation form the Deadwood aquifer and are confined below by Precambrian igneous and metamorphic rocks and above by shales and siltstones of the Ordovician Winnipeg Formation and the dolomite layers of the Ordovician Whitewood Limestone, where present (fig. 3). Groundwater from the Deadwood aquifer is used mostly by domestic users within and near outcrops (Carter and others, 2001b). Where the Winnipeg Formation and Whitewood Limestone are not present, the Devonian and Mississippian Englewood Limestone overlies the Deadwood Formation. The Englewood Formation is a 30-to-60-ft pinkish limestone with shale at its base (fig. 3) and was included in the Madison hydrologic unit by Strobel and others (1999) and is considered part of the Madison aquifer in this study. Overlying the Englewood Formation is the Mississippian Madison Limestone, also locally known as the Pahasapa Limestone, which consists of up to 1,000 ft of light-colored limestone and dolomite (fig. 3). The Madison Limestone has extensive secondary porosity in the upper 100 to 200 ft formed from fractures and solution features. The bottom

West E ON ST AU E E LIM LAT P

Minnelusa Formation

dison

od dwo Dea

Limestone

EXPLANATION

Headwater Springs

Major aquifer

Formation

Confining unit Spring

East Preca mb metam rian igneou s and orphic rocks

Alluvial aquifer

Water table

Artesian spring

ati

Flowing well

Spring conduit Cave

Dip of sedimentary rocks exaggerated. Relative thickness NOT to scale.

in n

elu sa

is o

M in

Sun da

neka hta

F o rm ation

Inyan Kara Group

nce Fo rmation

Potentiometric surface of the Madison aquifer

Limesto ne

Limes

tone

Figure 2. Schematic diagram illustrating hydrologic processes (modified from Driscoll and Carter, 2001; original fromAnderson and others, 1999).

Introduction 5

6 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 [--, not applicable; <, less than]

Cenozoic

Erathem

System

Stratigraphic unit

Quaternary & Tertiary (?)

Undifferentiated alluvium, terraces, and colluvium White River Group Intrusive igneous rocks

Tertiary

Pierre Shale

Paleozoic

Permian

Light colored clays with sandstone channel fillings and local limestone lenses. Includes rhyolite, latite, trachyte, and phonolite. Principal horizon of limestone lenses giving teepee buttes. Dark-gray shale containing scattered concretions. 1,200–2,700 Widely scattered limestone masses, giving small teepee buttes. Black fissile shale with concretions.

Niobrara Formation

Carlile Shale

80–300

225–380

Belle Fourche Shale

150–850

Mowry Shale Muddy Newcastle Sandstone Sandstone Skull Creek Shale

125–230 0–150

Brown to light-yellow and white sandstone.

150–270

Dark-gray to black siliceous shale.

Fall River Formation

10–200

Massive to thin-bedded, brown to reddish-brown sandstone.

35–700

Yellow, brown, and reddish-brown massive to thinly bedded sandstone, pebble conglomerate, silstone, and claystone. Local fine-grained limestone and coal.

Lakota Formation

350–750

Morrison Formation Unkpapa Sandstone

0–220 0–225

Sundance Formation

250–450

Gypsum Spring Formation

0–45

Spearfish Formation

375–800

Minnekahta Limestone

Opeche Shale

Mississippian

Madison (Pahasapa) Limestone

Devonian

Englewood Formation

Ordovician

Green to maroon shale. Thin sandstone. Massive fine-grained sandstone. Greenish-gray shale, thin limestone lenses. Glauconitic sandstone; red sandstone near middle Red siltstone, gypsum, and limestone. Red silty shale, soft red sandstone and siltstone with gypsum and thin limestone layers. Gypsum locally near base.

25–65

Thin to medium-bedded, fine grained, purplish-gray laminated limestone.

25–150

Red shale and sandstone. Yellow to red cross-bedded sandstone, limestone, and anhydrite locally at top. Interbedded sandstone, limestone, dolomite, shale, and anhydrite. Red shale with interbedded limestone and sandstone at base.

375–1,175

<200–1,000 Massive light-colored limestone. Dolomite in part. Cavernous in upper part. 30–60

Pink to buff limestone. Shale locally at base.

Whitewood (Red River) Limestone Winnipeg Formation

Deadwood Formation

Buff dolomite and limestone. Green shale with siltstone. Massive to thin-bedded brown to light-gray sandstone. Greenish glauconitic shale, flaggy dolomite, and flat-pebble limestone conglomerate. Sandstone, with conglomerate locally at the base. Schist, slate, quartzite, and arkosic grit. Intruded by diorite, metamorphosed to amphibolite, and by granite and pegmatite

Cambrian Precambrian 1

0–300 --

Minnelusa Formation

Pennslyvanian

Sand, gravel, boulders, and clay.

Greenhorn Formation

Inyan Kara Group

Mesozoic

Triassic

0–50

Description

Impure chalk and calcareous shale. Light-gray shale with numerous large concretions and sandy layers. Dark-gray shale. Impure slabby limestone. Weathers buff. Dark-gray calcareous shale, with thin Orman Lake limestone at base. Gray shale with scattered limestone concretions. Clay spur bentonite at base. Light-gray siliceous shale. Fish scales and thin layers of bentonite.

Cretaceous

Jurassic

Thickness, in feet

Undifferentiated igneous and metamorphic rocks

0–235 0–150 0–500 --

Modified based on drill-hole data.

Figure 3. Generalized stratigraphic column for the Black Hills of western South Dakota and eastern Wyoming. Modified from Carter and others (2003) and originally from information furnished by the Department of Geology and Geological Engineering, South Dakota School of Mines and Technology (written commun., January 1994).

Introduction 7 part of the Madison Limestone generally lacks the solution features and fractures of the upper part and has a larger component of dolomite than the upper portion (Greene, 1993). The Madison aquifer receives water from precipitation on outcrops, streamflow loss where streams cross outcrops, and leakage from adjacent aquifers. Hydraulic connection between the Deadwood and Madison aquifers likely occurs in areas where the potentiometric head of the groundwater in the Deadwood aquifer is above the bottom potentiometric head of the Madison aquifer and the confining layers are thin or absent (Strobel and others, 1999). The Madison aquifer is artesian where confined and flowing wells are common where the potentiometric contour elevation exceeds the elevation of the land surface. Losses from the Madison aquifer include evapotranspiration, headwater and artesian spring flow, leakage to adjacent aquifers, and pumping from wells. The Madison aquifer is confined from above by a red paleosol and shale from the basal unit of the Pennsylvanian and Permian Minnelusa Formation that is discontinuous in parts of the study area (Greene, 1993; Gries, 1996). The thickness of the Minnelusa Formation ranges from 375 to 1,175 ft, which generally increases to the south. Sequences of alternating deposits of sandstone, limestone, dolomite, and shale constitute the Minnelusa Formation (fig. 3), with the thick sandstone units in the upper 200 to 300 ft constituting most of the aquifer used for municipal and domestic use, although sandstone units in the middle and lower parts of the formation are used locally (Greene, 1993). Solution of anhydrite in the upper portions of the Minnelusa Formation caused collapse features such as breccia pipes, which are roughly funnel shaped cylindrical masses of angular blocks and fragments from overlying geologic materials that can be as much as 200 ft tall and 10 to several hundred feet in diameter (Bowles and Braddock, 1963). Leakage from the Madison aquifer into the overlying Minnelusa aquifer occurs in areas where the hydraulic gradient between the Madison and Minnelusa aquifers is large and the confining basal unit of the Minnelusa Formation does not exist or was deformed by tectonic stress (Rahn and Gries, 1973). The Minnelusa aquifer is confined from above by the Permian Opeche Shale, a 25- to 150-ft thick, red shale with sandstone (fig. 3) that separates the Minnelusa aquifer from overlying aquifers. Leakage between the Minnelusa aquifer into the Opeche Shale can occur where the Opeche Shale is fractured and faulted. Areas where the Minnelusa Formation collapsed into solution cavities from the solution of anhydrite also are areas where the Minnelusa aquifer could potentially lose water to overlying geologic units. The Permian Minnekahta Limestone overlies the confining Opeche Shale and is a 25- to 65-ft thick, thin to medium bedded, laminated limestone (fig. 3). Precipitation on the outcrops of the Minnekahta aquifer is the primary recharge mechanism, with only minor amounts of streamflow recharge occurring where streams flow over the outcrops. The Minnekahta Limestone is an aquifer with high permeability, but the thin nature of the aquifer limits well yields to volumes that can provide water for small, local users rather than large

developments or municipalities. The Minnekahta aquifer is confined from above by the Permian and Triassic Spearfish Formation, a 375- to 800-ft thick, red shale and siltstone unit with white gypsum and thin limestone beds (fig. 3; DeWitt and others, 1989). The “red valley” or “red racetrack” of the Black Hills is an area where the shale of the Spearfish Formation was eroded into an area of low topographical relief between the cliff forming Minnekahta Limestone and the Jurassic and Cretaceous sandstone units of the hogback. A 0- to 45-ft thick white gypsum layer of the Jurassic Gypsum Spring Formation (fig. 3) overlies the Spearfish Formation and forms white cliffs that cap the Spearfish Formation in some locations along the hogback of the Black Hills. The Jurassic Sundance Formation overlies the Gypsum Spring Formation where present or the Spearfish Formation where the Gypsum Spring Formation is absent. The Sundance Formation ranges from 250 to 450 ft in thickness and consists of siltstone, sandstone, limestone, and shale (fig. 3; DeWitt and others, 1989). The sandstone units within the Sundance Formation form a minor aquifer where saturated. Other Jurassic units overlying the Sundance Formation are the 0- to 225-ft thick Unkpapa Sandstone and the 0- to 220-ft thick silty shale and claystone units of the Morrison Formation (fig. 3). The Unkpapa Sandstone thins to the north and is not present on the western flank of the Black Hills, where it is replaced by the Morrison Formation completely (DeWitt and others, 1986). The Unkpapa Sandstone forms a minor aquifer where saturated (Driscoll and Carter, 2001). Jurassic geologic units (Sundance, Unkpapa, and Morrison Formations) were considered a semiconfining unit by Driscoll and Carter (2001) because of its interbedded shales, sandstones, and gypsum (Strobel and others, 1999). The sandstones within the Sundance Formation form an aquifer, the Sundance aquifer, where saturated. Aquifers in other Jurassic formations are used locally to lesser degrees than the Sundance aquifer and were not considered in recharge calculations in this report, which was consistent with Driscoll and Carter (2001). Lower Cretaceous sandstone units of the Inyan Kara Group overly the Morrison Formation. The Inyan Kara Group ranges from 135 to 900 ft in thickness and is comprised of the Lakota Formation at its base and Fall River Formation at its top (fig. 3). The Inyan Kara aquifer consists of saturated sandstone layers and is used extensively in the study area (Driscoll and Carter, 2001). Inflows to the Inyan Kara aquifer are primarily from precipitation on the outcrop but leakage from the underlying Jurassic units is possible (Gott and others, 1974). The Inyan Kara aquifer is confined from above by Cretaceous shales and below by the shales of the Morrison Formation (fig. 3) and is the youngest aquifer considered for the budget analysis in the present study. Other minor aquifers in the Cretaceous units surrounding the Black Hills, such as the Newcastle Sandstone (fig. 3), exist but are not extensively used in the study area and were not considered for the budget analysis.

8 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Climate The abrupt rise in topography of the Black Hills from the surrounding plains creates an orographic effect that causes greater amounts of precipitation to fall in the higher elevations of the Black Hills than the lower elevations of the surrounding area (Driscoll and others, 2000). Precipitation is greatest in the northern Black Hills near Lead, S. Dak. (fig. 1), and lowest in the southern periphery of the Black Hills near Hot Springs, S. Dak. (fig. 1; Driscoll and others, 2000). Monthly precipitation varies across the different elevations and locations within the Black Hills. Precipitation in the Black Hills peaks in the late spring and early summer months of May and June, although a second peak in monthly precipitation occurs in the late fall as snow in the higher elevations (fig. 4). Precipitation records from the National Oceanic and Atmospheric Administration extending back to 1930 (Palecki and others, 2021) indicate precipitation fluctuates annually in the Black Hills region, with relatively long dry periods in the 1930s, the late 1940s through the mid-1960s, the late 1980s to the early 1990s, and the early to mid-2000s (fig. 5). Drought conditions during 1988–92 and 2002–07 in the Black Hills region caused reduced streamflow, declining reservoir and groundwater levels, increasing fire activity, and water supply shortages (South Dakota Drought Task Force, 2015; USGS, 2024a). Temperatures in the Black Hills peak in the summer months of July and August with mean monthly maximums of almost 90 degrees Fahrenheit (°F) and mean monthly minimums of approximately 55 °F (fig. 6; Palecki and others, 2021). Additionally, monthly normal temperatures are greater at lower elevations and generally increase to the south near Hot Springs, S. Dak. (fig. 6A). Greater monthly normal temperatures at lower elevations and in the southern part of the study area cause greater evaporation that leads to less precipitation recharge. The coldest months are December and January with mean monthly temperatures below freezing (32 °F) and mean minimum monthly temperatures near 10 °F (fig. 6). In general, colder temperatures during winter months occur at the higher elevations and in the northern part of the study area (fig. 6). Temperatures generally increase at lower elevations and in the southern part of the study area.

Hydrology The hydrology of the Black Hills region is characterized by interactions between climate, geology, and the landscape. Driscoll and others (2002) provide detailed descriptions of hydrologic processes occurring in the Black Hills region, which are discussed in general terms in this section. Precipitation falling on the landscape infiltrates into the soil horizon, becomes direct runoff if the soil is saturated or its infiltration capacity is exceeded, and (or) is returned to the land surface from the soil horizon through lateral movement within the soil layers (interflow). Where evaporation exceeds precipitation, most water is returned to the atmosphere through evapotranspiration. Water infiltrating past the soil

horizon can recharge groundwater systems; however, a component of groundwater is discharged at the land surface and may contribute to streamflow (base flow). Soil horizon characteristics, such as soil type or thickness, are an important aspect of the hydrologic cycle where soils are present in the Black Hills region and can greatly affect groundwater recharge rates. In areas where soils are thin or absent, recharge rates are affected by the characteristics of geologic units. Driscoll and Carter (2001) subdivided the hydrogeologic setting of the Black Hills in South Dakota into four areas: the crystalline core, the limestone headwater, the loss zone and artesian spring area, and the exterior. The crystalline core area is characterized by mostly impervious rocks of the Precambrian in the central part of the Black Hills. The limestone headwater area is the area of the western flank of the Black Hills where the Madison Limestone discharges groundwater as headwater springs that then flow away from the limestone as streamflow. The loss zone and artesian spring area encompasses the region where streamflow loss zones and artesian springs occur. Streams radiate outward from the elevated areas of the Black Hills and lose significant amounts of flow in regions where they intersect the fractured and permeable Madison Limestone and Minnelusa Formation. Water then reemerges as artesian springs that surround the Black Hills (Rahn and Gries, 1973). The loss zone and artesian spring area is bounded by the extent of the outcrops of the Inyan Kara Group (fig. 1), which is commonly considered the outer extent of the Black Hills. Areas outside of the extent of the Black Hills are in the exterior. Springs are a common hydrologic feature in the Black Hills and are culturally important for local Tribes. Rahn and Gries (1973) classified springs in the Black Hills into different types based on the geologic controls and amount of flow of the springs. Headwater springs originate in the Limestone Plateau area (fig. 1) on the western flank of the Black Hills (Rahn and Gries, 1973). Headwater springs form where water percolates vertically through outcrops of the Madison Limestone and then discharges at the base of the limestone where it overlies less permeable surfaces. Base flow of several streams originates at the headwater springs area before flowing eastward across the Precambrian core to loss zones in the Madison and Minnelusa aquifers where surface water becomes groundwater again. Artesian springs occur downstream from the loss zones where groundwater from aquifers in artesian conditions discharges at the land surface. Groundwater from aquifers in artesian conditions can be discharged through porous media or through structures, such as faults or breccia pipes, that extend to the land surface. Rahn and Gries (1973) classified artesian springs in the Black Hills as those that discharge groundwater from the Madison and Minnelusa aquifers at low elevations near the contact between the Minnekahta Limestone and Spearfish Formation or the contact between the Minnelusa Formation and Opeche Shale. Many of the artesian springs in the Black Hills discharge from the Madison and Minnelusa aquifers.

Introduction 9 5.0

5.0

Precipitation, in inches

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Precipitation, in inches

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Precipitation, in inches

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

4.5

0.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0.0

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

5.0

Precipitation, in inches

0.0

5.0

5.0 4.5

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

5.0

5.0 4.5

0.0

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Month

0.0

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Month

Figure 4. 30-year normal precipitation from 1991 to 2020 for different locations and elevations within the Black Hills region. Data from National Oceanic and Atmospheric Administration National Centers for Environmental Information (Palecki and others, 2021). A, Hot Springs, SD US (USC00394007). B, Belle Fourche, SD US (USC00390559). C, Spearfish, SD US (USC00397882). D, Sundance, WY US (USC00488705). E, Hill City, SD US (USC00393868). F, Lead, SD US (USC00394834). G, Rapid City 4 NW, SD US (USC00396947). H, Devil’s Tower Number 2, WY US (USC00482466).

10 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Annual precipitation, in inches

A. Annual precipitation for the study area 30.0 27.5 25.0 22.5 20.0 17.5 15.0 12.5 10.0

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

1980

1985

1990

1995

2000

2005

2010

2015

2020

1975

1980

1985

1990

1995

2000

2005

2010

2015

2020

1980

1985

1990

1995

2000

2005

2010

2015

2020

Year

B. Annual departure from long-term mean annual precipitation

Annual precipitation departure, in inches

10.0 7.5 5.0 2.5 0.0 −2.5 −5.0 −7.5 1930

1935

1940

1945

1950

1955

1960

1965

1970

Cumulative annual precipitation departure, in inches

C. Cumulative departure from long-term mean annual precipitation

Year

0 −10 −20 −30 −40 −50 −60 −70

1930

1935

1940

1945

1950

1955

1960

1965

1970

1975

Year

EXPLANATION Annual precipitation greater than long-term (1931–2022) average annual precipitation

Annual precipitation Long-term mean annual precipitation

Annual precipitation less than long-term (1931–2022) average annual precipitation

Figure 5. Mean annual precipitation totals for the Black Hills area, South Dakota for 1931–2022 using records from the climate stations in figure 4 (shown in fig. 1). A, Annual precipitation for the study area. B, Departure of annual precipitation from the long-term mean annual precipitation for the study area for water years 1931–2022. C, Cumulative departure of annual precipitation from the long-term mean annual precipitation for the study area for water years 1931–2022. Data from National Oceanic and Atmospheric Administration National Centers for Environmental Information (Palecki and others, 2021).

Temperature, in degrees Fahrenheit

Introduction 11

90 A

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

70 60

10 Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

90 G

80 70

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

90 C

Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec.

Month

Month EXPLANATION

Maximum temperature

Mean temperature

Minimum temperature

Figure 6. 30-year normal temperature from 1991 to 2020 for different locations and elevations within the Black Hills. A, Hot Springs, SD US (USC00394007). B, Belle Fourche, SD US (USC00390559). C, Spearfish, SD US (USC00397882). D, Sundance, WY US (USC00488705). E, Hill City, SD US (USC00393868). F, Lead, SD US (USC00394834). G, Rapid City 4 NW, SD US (USC00396947). H, Devil’s Tower Number 2, WY US (USC00482466). Data from Palecki and others (2021).

12 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 Surface water in the study area is present as streamflow and reservoirs. Streamflow follows precipitation patterns with high flows in the early spring months of June and July and lower flows in the fall (Driscoll and Carter, 2001). Streamflow is an important source of recharge to aquifers in the Black Hills area. During base flow conditions, most streams lose all or most of their flow as they cross loss zones of high permeability geologic materials. Each loss zone has a maximum streamflow (or threshold) that can recharge the aquifers. Hortness and Driscoll (1998) determined loss thresholds for 24 streams in the Black Hills area. The aquifers receiving relatively consistent recharge from streams flowing overtop outcrops are the Madison and Minnelusa aquifers. Other aquifers, such as the Deadwood and Minnekahta aquifers, also receive recharge from streams; however, streamflow losses to these aquifers are relatively small in comparison to the Madison and Minnelusa aquifers and often are difficult to quantify. Regulated releases from reservoirs can provide a constant source of water to loss zones, which are particularly important along Rapid and Spearfish Creeks (not shown).

Population Population in the study area is an important factor for hydrologic budgets, because growth can increase the demand for water resources. Population estimates for the overall study area and each of the nine subareas (fig. 1) were derived from decadal census data between 1930 and 2022 provided by the U.S. Census Bureau (1952, 1973, 1983, 1992, 2003, 2012, 2024). Populations were assigned to each subarea based on their geographical location; however, some populated areas, such as townships or counties, overlapped multiple subareas, necessitating additional steps to distribute the population among the subareas. For these overlapping areas, portions of the population were allocated to each subarea in proportion to their respective areas. For example, the population of Custer County (fig. 1) was divided among subareas 5, 6, 7, 8, and

9, with 20 percent of the population value allocated to each subarea for every census decade. This allocation method introduced uncertainty into the population estimates for each subarea. Population estimates for each subarea are in table 1. The population of the study area from 1930 to 2022 varied across subareas 1–9. Overall, the population increased from about 60,000 in 1930 to approximately 214,100 in 2022 (table 1). Generally, subareas in the northern Black Hills (subareas 1–4) had larger populations and greater annual growth rates compared to those in the southern Black Hills (subareas 5–9; table 1). Throughout every decadal census from 1930 to 2020, subarea 4 consistently recorded the largest population, because it includes Rapid City, S. Dak. (fig. 1), which is the largest city in the region. Notably, subarea 4 surpassed 100,000 residents in 2020, making it the only subarea with over 100,000 residents. By 2022, subarea 1, which includes Spearfish and Belle Fourche, S. Dak. (fig. 1), had the second-largest population at about 39,000—about 76,500 less than subarea 4 (table 1). The populations of subareas 2, 3, and 5–9 either slightly increased or decreased from 1930 to 2022, with subarea 8 being the only region with a population decline. Since completion of the BHHS, the population of the study area increased from 154,200 to 214,100, reflecting a 39-percent increase (table 1). The mean annual population growth rate for the study area from 2000 through 2022 was about 1.8 percent with the greatest mean annual growth rates for the same time observed for subareas 3 and 4 at 4.5 and 2.3 percent, respectively. In contrast, subareas 5 and 6 experienced the lowest growth rates during this time, with mean annual rates of −0.7 and 0.6 percent, respectively. The population of subareas 1–4 (northern Black Hills and Rapid City, S. Dak., area) grew by 58,428 between 2000 and 2022, with subarea 4 adding 39,206 residents. In comparison, the population in subareas 5–9 (southern Black Hills) increased by only 1,488 from 2000–22, with subarea 5 being the only subarea to report a population decline, losing an estimated 1,286 residents (table 1).

Table 1. Estimated population by subarea and year in the study area from 1930 through 2022. Population data were obtained from the U.S. Census Bureau (1952, 1973, 1983, 1992, 2003, 2012, 2024) and modified to estimate population in the study area (fig. 1). Subarea

1930

1940

1950

1960

1970

1980

1990

2000

2010

2020

2021

2022

10,520

11,547

12,863

14,660

18,047

23,507

28,723

32,149

32,853

37,044

37,657

38,993

14,050

18,048

16,598

17,528

18,820

19,217

17,760

18,381

19,916

24,159

24,409

24,878

2,983

2,331

2,502

2,384

2,389

2,421

5,329

5,941

7,488

11,451

11,592

11,822

15,790

19,471

30,353

51,039

56,356

60,797

70,791

76,298

89,315

110,726

112,918

115,504

878

1,005

905

584

4,346

5,007

5,444

7,997

8,623

6,503

6,593

6,711

2,044

2,849

2,879

2,610

2,179

2,490

2,576

2,876

3,238

3,117

3,169

3,250

933

1,066

968

797

773

1,020

1,042

1,234

1,324

1,392

1,460

1,542

11,984

11,686

15,454

9,680

7,856

8,756

8,071

8,380

8,165

9,485

9,837

10,127

9 Total

786

920

819

458

532

765

773

938

1,086

1,150

1,211

1,283

59,967

68,921

83,341

99,739

111,299

123,981

140,507

154,195

172,007

205,024

208,845

214,111

Introduction 13

Previous Studies Previous studies relevant to the scope of this research include numerous investigations from the BHHS—a long-term regional study initiated in 1990 focused on the quality, quantity, and distribution of surface water and groundwater resources in the Black Hills area. The BHHS consisted of two phases: data collection and interpretation. During the first phase, a network comprised of 71 observation wells, 94 precipitation gages, and 60 streamgages was established. Phase two produced various reports and products, including 21 reports and 11 maps. The objectives of the BHHS outlined in Driscoll (1992) were to (1) inventory and describe hydrologic data (precipitation, streamflow, groundwater levels, water-quality characteristics), (2) develop hydrologic budgets of selected watersheds, (3) describe the significance of bedrock aquifers in the Black Hills, and (4) develop conceptual models of the hydrogeologic system in the Black Hills area. Overviews of the BHHS are provided in Carter and others (2002) and Driscoll and others (2002). Driscoll and others (2000) provided monthly and annual precipitation totals for water years—beginning October 1 of the year prior and ending September 30—from 1931 to 1998 for 94 precipitation gages in the Black Hills area of South Dakota, evaluating spatial and temporal precipitation patterns. Generally, precipitation totals increased from south to north and from lower to higher elevations within the region, with mean annual precipitation ranging from 16 to 17 inches per year in Fall River County, S. Dak., to more than 29 inches per year in parts of Lawrence County, S. Dak. (fig. 1). Temporal analysis indicated sustained periods of precipitation deficit during 1931–40 and 1948–61, whereas surplus precipitation was observed during 1941–47, 1962–68, and 1991–98. Carter and others (2001a) estimated annual precipitation and streamflow recharge to the Madison and Minnelusa aquifers in the Black Hills area for water years 1931–98. Annual precipitation recharge was estimated by applying basin yield techniques to precipitation data from Driscoll and others (2000). Annual streamflow recharge for water years 1950–98 was computed using daily streamflow data and streamflow loss thresholds measured by Hortness and Driscoll (1998). Linear regression analyses were used to estimate streamflow recharge from 1931 to 1949 based on relations between precipitation and streamflow recharge from 1989 to 1998 when both datasets were most complete. Precipitation recharge averaged about 3.6 inches per year for the Madison aquifer and 2.6 inches per year for the Minnelusa aquifer during 1931–98. Streamflow recharge was not separated by aquifer; rather, the total combined annual streamflow recharge for the Madison and Minnelusa aquifers averaged about 93 cubic feet per second (ft3/s) for 1931–98. Mean annual combined precipitation and streamflow recharge to both aquifers for 1931–98 was 344 ft3/s. Carter and others (2001b) developed hydrologic budgets for the Madison and Minnelusa aquifers in the Black Hills area for water years 1987–96. Hydrologic budgets were

determined for two scenarios: the first scenario consisted of a general budget for the entire Black Hills area and the second scenario involved detailed budgets for nine subareas. Subarea boundaries were based on groundwater flow direction of the Madison and Minnelusa aquifers and were drawn to minimize groundwater flow across subarea boundaries. The period from 1987–96 was chosen because it represented a period of zero storage change because of offsetting wet and dry cycles. Inflow components included recharge (precipitation and streamflow), leakage from adjacent aquifers, and groundwater inflows across the study area boundaries. Outflow components were springflow (headwater and artesian), well withdrawals, leakage to adjacent aquifers, and groundwater outflows across study area boundaries. Leakage, groundwater inflows, and groundwater outflows were combined into net groundwater flow because all three components were difficult to quantify and could not be distinguished. Estimates of combined budget components from Carter and others (2001b) for the Madison and Minnelusa aquifers for 1987–96 include 395 ft3/s for recharge (precipitation and streamflow), 78 ft3/s for headwater springflow, 189 ft3/s for artesian springflow, and 28 ft3/s for well withdrawals. Net groundwater flow was calculated as difference between inflows and outflows, which was 100 ft3/s. Hydrologic budgets determined by Carter and others (2001b) for nine subareas consisted of the same inflow and outflow components as the overall budget but also considered net groundwater inflows or outflows between subareas to account for budget surpluses or deficits. The intent of selected subareas was to minimize flow across the boundaries; however, zero-flow boundaries could not be established for both aquifers along all subarea boundaries. Therefore, inflows and outflows to each subarea for both aquifers were estimated using budget surpluses or deficits. Because the storage change from 1987 to 1996 was near zero, the net inflow (negative net groundwater flow) or outflow (positive net groundwater flow) could be calculated by summing the inflows and outflows from 1987 to 1996 for each subarea and dividing the sum by the number of years (10) to calculate mean annual groundwater inflow or outflow. Net groundwater outflows exceeded inflows for seven subareas and values ranged from 5.9 to 48.6 ft3/s. Net groundwater inflows exceeded outflows for two subareas where artesian springflow was greater than recharge. Net groundwater flows also were used to determine hydrologic properties, such as transmissivity, for each subarea. Transmissivity values estimated for subareas ranged from 90 to 7,400 feet squared per day (Carter and others, 2001b). Driscoll and Carter (2001) developed mean hydrologic budgets for various bedrock aquifers and surface waters in the Black Hills area for water years 1950–98. The same methods used for calculating groundwater inflows (recharge) and outflows (springflow and well withdrawals) to the Madison and Minnelusa aquifers in Carter and others (2001a) and Carter and others (2001b) were used to develop budgets for other bedrock aquifers. Eight bedrock aquifers, some consisting of combinations of several geologic units, were investigated by Driscoll and Carter (2001), including

14 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 the crystalline core, Deadwood, Madison, Minnelusa, Minnekahta, Jurassic-sequence semiconfining unit (Sundance aquifer), Inyan Kara, and Cretaceous-sequence confining unit (Newcastle aquifer) aquifers. Outcrop areas for geologic units containing the bedrock aquifers evaluated are shown in figure 1 except for the Cretaceous-sequence confining unit (Newcastle aquifer) because it was not included in recharge calculations in this report. Surface water budgets were estimated by Driscoll and Carter (2001) but were not included in this study. The mean hydrologic budget for 1950–98 for all aquifers was summarized in Driscoll and Carter (2001). Annual total recharge for all eight aquifers was estimated as 348 ft3/s, of which 292 ft3/s was recharged to the Madison and Minnelusa aquifers. Precipitation and streamflow recharge accounted for 200 and 92 ft3/s, respectively. Outflows for all wells and springs were estimated as 259 ft3/s, of which the Madison and Minnelusa aquifers accounted for 206 ft3/s of total springflow and 28 ft3/s of well withdrawals. The Deadwood aquifer accounted for a total of 14 ft3/s, with springflow and well withdrawals of 12.6 and 1.4 ft3/s, respectively. Well withdrawals from other aquifers accounted for the remaining 11 ft3/s. Net groundwater outflow was calculated as 89 ft3/s by subtracting outflows from inflows in the study area.

Hydrologic Budgets Hydrologic budgets were updated for the Deadwood, Madison, Minnelusa, Minnekahta, Sundance, and Inyan Kara aquifers between 1931 and 2022 using methods from Carter and others (2001a), Carter and others (2001b), and Driscoll and Carter (2001). Hydrologic budgets for each aquifer were separated into subareas 1–9 from Carter and others (2001b) and consisted of various budget components including inflows and outflows. For some components, data were not available for the entire period of investigation and (or) methods from previous studies were modified so that budgets could be prepared. This section presents the methods and results for each budget component. All hydrologic budgets presented in this study were developed using the same basic continuity equation as Carter and others (2001b): ∑Inflows−∑Outflows=ΔStorage(1) where ∑Inflows

is the sum of inflows,

∑Outflows

is the sum of outflows, and

ΔStorage

is the change in storage (positive ΔStorage is when inflows exceed outflows).

Inflows included recharge, leakage from adjacent (underlying or overlying) aquifers, and groundwater inflows across the study area boundary (regional groundwater flow). Recharge included infiltration of precipitation on outcrops of geologic units and streamflow recharge where streams cross outcrops and lose all or part of their flow. The various methods used to estimate recharge from precipitation and streamflow losses are described in the following sections. Outflows included springflow, well withdrawals, leakage to adjacent aquifers, and regional groundwater flow out of the study area. Springflow consisted of two types: headwater and artesian. Headwater springs generally are at the base of the Madison Limestone near the headwaters of many streams in the Black Hills (fig. 2). Artesian springs are formed where water in aquifers under artesian pressure leaks upward through structures or porous material and discharge at the land surface typically downgradient of outcrops. Headwater springflow was not a component of the hydrologic budget because the outcrop areas for the Madison aquifer contributing to discharge at springs were removed from precipitation recharge calculations because the streamflow contributions from headwater springflow were already considered in gaged streamflow downstream. Outcrops contributing to headwater springflow (fig. 7) were mapped by Jarrell (2000) and modified by Carter and others (2001b). Headwater springflow estimates from Carter and others (2001b) for 1931–98 were updated as part of this study and are in appendix 2. Leakage to and from adjacent aquifers was difficult to quantify, so Carter and others (2001b) included leakage with groundwater flows for budgeting purposes. Net groundwater flow (groundwater outflow minus groundwater inflow) was determined using an assumption of zero storage change (discussed later in this section). When storage change is assumed equal to zero, the sum of inflows equals the sum of outflows, and the hydrologic budget equation can be rewritten as GWinflows−GWoutflows=Recharge−Springflow−Well Withdrawals(2) where GWinflows

is groundwater inflows, and

GWoutflows

is groundwater outflows.

Net groundwater flow (left side of eq. 2) is more difficult to quantify than the budget items on the right side of equation 2. Therefore, net groundwater flow can be calculated as the residual of budget items on the right side of equation 2. Net groundwater flow for aquifers in the study area is discussed in the “Groundwater Budgets” section later in this report. Groundwater budgets estimated in this study could not be directly compared to budgets from previous studies (Carter and others, 2001b; Driscoll and Carter, 2001) because of differences in study area boundaries and how budgets were

Hydrologic Budgets 15 104°30'

104°

103°30'

103°

BUTTE COUNTY

44° 30'

EXPLANATION

Newell

Nisland Belle Fourche

Fruitdale

Vale

Saint Onge

Spearfish

CROOK COUNTY

Sundance

Deadwood

Central City

Recharge area MEADE COUNTY

Sturgis

Hereford

Isolated outcrop Sundance Formation

Lead LAWRENCE COUNTY

Groundwater divide

Inyan Kara Group

Whitewood

Subareas from Carter and others (2001b)— Red number is the subarea number

Tilford

Recharge area

Piedmont

Isolated outcrop Minnekahta Limestone

Lime

Madison and Minnelusa formations and South Dakota geology Nemo Blackhawk Recharge area and DeWitt and others(1989); Wyoming geology of Inyan-Kara, Rochford Box Elder Minnekahta, and Jurassic units Isolated outcrop Rapid1:100,000 City Silver City from Hallberg andHeadwater Case, Wyoming Geologic Survey quadrangle maps of the springs (2001), Sundance (2001), Newcastle and Lance Creek (2001) quadrangles. Minnelusa Formation 4 (2000),Colonial area Pine Hills

PENNINGTON COUNTY

ston

44°

Caputa

Rockerville

e Pla

Hill City

teau

Keystone

Recharge area Hermosa

Isolated outcrop Deadwood Formation

Custer

WESTON COUNTY

Isolated outcrop Madison Limestone

Newcastle

Recharge area

CUSTER COUNTY

Recharge area

Fairburn

Isolated outcrop

Pringle

Dewey

Buffalo Gap

43° 30'

Burdock

NIOBRARA COUNTY

WYOMING SOUTH DAKOTA

Hot Springs

Oral

WYOMING

Edgemont

Subarea boundaries

Smithwick

FALL RIVER COUNTY

SOUTH DAKOTA

Igloo Provo

Oelrichs

Rumford Base modified from U.S. Geological Survey digital data, various scales Universal Transverse Mercator, zone 13 north North American Datum of 1983

0 0

5 5

20 MILES

20 KILOMETERS

Figure 7. Outcrop areas of geologic units containing aquifers in the study area used for estimating precipitation recharge in subareas 1–9. Outcrops east of the groundwater divide from Jarrell (2000) and modified by Carter and others (2001b) were excluded from calculations of precipitation recharge.

16 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 prepared. Budgets were not comparable for the Deadwood, Minnekahta, Sundance, and Inyan Kara aquifers because the study area of Driscoll and Carter (2001) did not include Wyoming, and budgets were not previously divided among the nine subareas. Instead, differences between budget components from previous studies and this study are discussed for the entire study area to provide readers with context of how the budget changed by including additional area in Wyoming. Budget estimates from Carter and others (2001b) could be compared directly for the Madison and Minnelusa aquifers because their study area was used in this study; however, these budgets were developed only for 1987–96 and are not representative of long-term conditions.

Inflows—Precipitation and Streamflow Recharge, 1931–2022 Inflows of the hydrologic budget consisted of recharge from precipitation and streamflow losses to aquifers. Recharge estimates were calculated by water year for 1931 to 2022. Recharge estimates for 1931–98 for the Madison and Minnelusa aquifers from Carter and others (2001a) were updated to include water years 1999 through 2022. Recharge estimates for 1999–2022 were calculated as part of this study using methods from Carter and others (2001a), Carter and others (2001b), and Driscoll and Carter (2001); however, some methods were modified and are discussed in “Precipitation Recharge” and “Streamflow Recharge” sections of this report and in appendix 1. The recharge results presented in this study were separated into the nine subareas delineated by Carter and others (2001b) for each aquifer. Additional information regarding recharge estimates is available in Carter and others (2001a), Carter and others (2001b), and Driscoll and others (2000). Complete data for precipitation and streamflow recharge are provided in the accompanying data release (Medler and others, 2025).

Precipitation Recharge Annual precipitation recharge was estimated for 1931–2022 by subarea for the aquifers in the Deadwood Formation, Madison Limestone, Minnelusa Formation, Minnekahta Limestone, Sundance Formation, and Inyan Kara Group in the study area (fig. 7). Precipitation recharge was calculated only for connected outcrops contributing to the regional groundwater flow system of each aquifer (fig. 7). Carter and others (2001a) noted recharge to disconnected (or isolated) outcrops surrounded by igneous and metamorphic rocks likely does not directly join the regional groundwater flow system and, therefore, should be excluded from calculations of precipitation recharge. Outcrop areas of the Madison aquifer on the Limestone Plateau east of the groundwater divide (Jarrell, 2000; fig. 7) contributing to headwater springflow also were excluded because recharge in this area was believed to contribute to springflow rather than the regional aquifer (Driscoll and Carter, 2001).

Precipitation recharge was estimated using the total yield equation developed by Carter and others (2001a) for outcrops contributing to the regional groundwater flow. The total yield equation (eq. 3) consists of variables for annual precipitation, average annual precipitation, and average yield efficiency.

Pannual   Y Emean   Q annual = [_ × _ × Pannual   Pmean   ] 100 1.6

where Qannual

(3)

is the annual yield,

Pannual

is the annual precipitation,

Pmean

is the mean annual precipitation, and

YEmean

is the mean annual yield efficiency.

Inverse distance weighting (IDW) interpolation was used to interpolate annual precipitation (Pannual) from 94 stations given in Driscoll and others (2000) to create annual precipitation 1-kilometer (km) grids for water years 1931–80. Settings used for the IDW interpolation tool in geographic information system software (ArcGIS Pro, Esri, 2024a) were the same as those used in the Driscoll and others (2000) report and were as follows: a power of 2, a maximum search area of 50 km, and a maximum number of points of 15. Gridded annual precipitation data for 1981–2022 were aggregated from Daymet daily climate data on a 1-km grid (Thornton and others, 2022). Daymet data are available for 1981 through present and use a workflow that processes weather station observations and gridded terrain data along with cross-validation statistics to produce a standardized gridded dataset of daily climate data on a 1-km grid on a national scale (Thornton and others, 2021). When possible, Daymet data were utilized for the standardized quality, ease-of-use, and public accessibility. The mean of the annual precipitation grids from 1931 to 2022 was calculated on a cell-by-cell basis (fig. 8) to create the mean annual precipitation (Pmean) grid used in the yield equation (eq. 3). Mean yield efficiency contours for the study area published by Carter and others (2001a) were gridded into a 1-km grid and used for the total yield calculation. Gridded annual recharge was calculated by multiplying the results from equation 3 by the recharge factor (table 2) of a given aquifer using the following equation: Rannual=Qannual×r(4) where Rannual

is the annual recharge,

Qannual

is the annual yield, and

is the recharge factor.

Hydrologic Budgets 17 104°30'

104°

103°30'

103°

EXPLANATION 1

1 44° 30'

20 21 22 23

21 20

Mean precipitation 1931–2022, in inches

27 26

25 24 17

44°

17 21

8 16

Precipitation contour— Contour interval is 1 inch

Stations used for inverse distance interpolation for water years 1931–80

WYOMING SOUTH DAKOTA

Stations used for Daymet algorithm

19 43° 30'

Subareas from Carter and others (2001b)— Red number is the subarea number

Base modified from U.S. Geological Survey digital data, various scales Universal Transverse Mercator, zone 13 north North American Datum of 1983

WYOMING

Subarea boundaries

0 0

5 5

SOUTH DAKOTA

20 MILES

20 KILOMETERS

Figure 8. Mean annual precipitation for the study area showing weather stations used for the inverse distance weighting interpolation for water years 1931–80 and weather stations used in the Daymet algorithm (Thornton and others, 2021) for water years 1981–2022.

18 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 Table 2. Recharge factors and outcrop areas used in calculating precipitation recharge for the Deadwood, Madison, Minnelusa, Minnekahta, Sundance, and Inyan Kara aquifers. Recharge factors were developed by Driscoll and Carter (2001). [NA, not applicable]

Area (acres) Deadwood

Madison

Minnelusa

Minnekahta

Sundance

Inyan Kara

Combined area (acres)1

8,450

48,556

150,465

61,089

107,768

59,597

432,557

4,246

13,719

18,912

6,596

9,845

20,773

74,091

10,128

11,700

4,134

2,847

2,795

12,988

34,938

8,146

21,141

19,925

5,204

4,979

7,031

66,425

3,421

7,013

11,183

2,556

5,014

11,674

40,860

1,012

2,848

3,849

921

3,241

7,499

19,369

1,545

5,378

8,751

4,627

4,244

13,419

37,964

3,414

25,211

67,074

23,934

27,629

109,131

256,394

113

86,169

142,652

32,989

10,978

25,694

298,595

221,735

426,945

140,764

Subarea 1

Recharge factor Total

0.8 40,475

0.4 176,493

0.8 267,806

NA 1,261,193

1Headwater spring areas not included in outcrop areas was 81,796 acres.

The recharge factor was developed by Driscoll and Carter (2001) to simulate the recharge fraction of total yield (sum of runoff plus recharge). The value of recharge factors was based on hydrologic properties of each aquifer and the extent of outcrop areas. Gridded recharge was clipped to the aquifer boundary and zonal statistics (ArcGIS Pro, Esri, 2024b) were calculated for each of the nine subareas (fig. 7). The annual precipitation recharge for each subarea, in inches, was converted to feet and then multiplied by the area, in acres, of the non-isolated outcrops of each aquifer in the subarea to calculate an annual volume of precipitation recharge in acre-feet. Outcrop areas for all Paleozoic geologic units identified by Carter and others (2001b) as contributing to headwater springs on the Limestone Plateau were excluded from subareas before calculating zonal statistics so that precipitation recharge estimates would not include outcrops recharging headwater springs. Additionally, 50 percent of the precipitation recharge calculated for the Deadwood aquifer in the Spearfish Creek, Little Elk Creek, and Meadow Creek drainages was excluded to be consistent with Driscoll and Carter (2001) in assuming that some fraction of precipitation recharge in those drainages contributes to headwater springflow.

Streamflow Recharge Streamflow recharge was estimated annually for 1931–2022 for the regional Madison and Minnelusa aquifers for the nine subareas delineated by Carter and others (2001b). The Madison and Minnelusa aquifers receive recharge from streams flowing overtop outcrop areas of both formations up to a certain threshold that is unique to each loss zone. Loss

thresholds for 24 streams in the Black Hills were determined by Hortness and Driscoll (1998). Streamflow losses to aquifers other than the Madison and Minnelusa were not calculated because recharge to other aquifers, such as the Deadwood and Minnekahta aquifers, was relatively small in comparison and often was difficult to distinguish from other aquifers. Streamflow recharge values for 1931–98 were originally estimated by Carter and others (2001b) but were recalculated using new information and were separated into nine subareas. Streamflow recharge was calculated for 1999–2022 using the methods outlined in Carter and others (2001b) and is discussed in the following sections. Extrapolation techniques used to extend streamflow recharge records differed from those in previous studies and are discussed in appendix 1.

Methods for Quantifying Streamflow Recharge Methods and assumptions outlined in Carter and others (2001a) were used to quantify recharge from streamflow losses to the Madison and Minnelusa aquifers for 55 basins in the study area (fig. 9). In general, streamflow data from USGS streamgages (table 3) and loss threshold rates determined by Hortness and Driscoll (1998; table 4) were used to calculate streamflow recharge, when possible, from drainage basins upstream from loss zones delineated by Carter and others (2001a). Streamflow data were downloaded from the USGS National Water Information System (NWIS; USGS, 2024a). For basins without daily streamflow records, daily streamflow was synthesized using statistical relations between drainage areas of nearby basins. Loss threshold rates for streams were available either from Hortness and Driscoll (1998) for 24 streams in the study area or were selected from a representative nearby site. Loss threshold rates were quantified

Table 3. Selected site information for streamgages (shown in fig. 9) used in determining streamflow recharge from Carter and others (2001a). [C, continuous-record; M, miscellaneous-record]

Site number

Station identification number

Station name

Latitude (decimal degrees)

Longitude (decimal degrees)

Type of station

Drainage area (square miles)

06402430

Beaver Creek near Pringle, South Dakota

43.58137177

−103.4765835

45.8

433532103284800

Reaves Gulch above Madison outcrop near Pringle, South Dakota

43.5922053

−103.4804723

6.86

433745103261900

Highland Creek above Madison outcrop near Pringle, South Dakota

43.6291514

−103.4390833

8.69

433930103250000

South Fork Lame Johnny Creek above Madison outcrop near Fairburn, South Dakota

43.6583192

−103.4171386

4.34

433910103251000

Flynn Creek above Madison outcrop near Fairburn, South Dakota

43.65276346

−103.4199164

10.3

434105103240200

North Fork Lame Johnny Creek above Madison outcrop near Fairburn, South Dakota

43.68470906

−103.4010272

2.8

06403300

French Creek above Fairburn, South Dakota

43.7172105

−103.3679713

105

06404000

Battle Creek near Keystone, South Dakota

43.87164727

−103.3363029

58 178

06406000

Battle Creek at Hermosa, South Dakota

43.82804586

−103.1960211

06404998

Grace Coolidge Creek near Game Lodge near Custer, South Dakota

43.76110028

−103.3640816

25.2

06405800

Bear Gulch near Hayward, South Dakota

43.79193375

−103.3474139

4.23

434929103215700

Spokane Creek above Madison outcrop near Hayward, South Dakota

43.824711

−103.366302

4.92

434800103174400

Spokane Creek below Madison outcrop near Hayward, South Dakota

43.7999901

−103.2960243

3.76

06407500

Spring Creek near Keystone, South Dakota

43.97871038

−103.3460469

163

06408500

Spring Creek near Hermosa, South Dakota

43.9416695

−103.1591456

199 320

06411500

440105103230700

44.07665378

−103.482134

44.01804337

−103.385742

6.82

06422500

Boxelder Creek near Nemo, South Dakota

44.1443339

−103.4545385

06423010

Boxelder Creek near Rapid City, South Dakota

44.131654

−103.2987949

128

06424000

441614103253300

06425500

Elk Creek near Roubaix, South Dakota

44.2947073

−103.5968592

21.5

Elk Creek at Minnekahta outcrop, near Tilford, South Dakota

44.27054144

−103.4262985

23.8

Elk Creek near Elm Springs, South Dakota

44.24831768

−102.5032217

540

Hydrologic Budgets 19

Rapid Creek below Pactola Dam, South Dakota Victoria Creek below Victoria Dam near Rapid City, South Dakota

[C, continuous-record; M, miscellaneous-record]

Site number 23

Station identification number 441412103275600

Station name Little Elk Creek below Dalton Lake, near Piedmont, South Dakota

Latitude (decimal degrees)

Longitude (decimal degrees)

Type of station

Drainage area (square miles)

44.23665257

−103.4660218

11.39

06429920

Bear Gulch near Maurice, South Dakota

44.4205398

−104.0410442

6.17

06430520

Beaver Creek near Maurice, South Dakota

44.38248366

−104.0040983

6.86

442242103565400

Iron Creek below Sawmill Gulch, near Savoy, South Dakota

44.37831708

−103.948818

8.16

06430800

Annie Creek near Lead, South Dakota

44.32749778

−103.894532

3.55

06430898

Cleopatra Creek near Spearfish, South Dakota

44.40077556

−103.8939183

06430900

Spearfish Creek above Spearfish, South Dakota

44.40165056

−103.8949267

06430950

Spearfish Creek below Robison Gulch near Spearfish, South Dakota

44.4372061

−103.876037

06431500

Spearfish Creek at Spearfish, South Dakota

44.48248388

−103.861592

168

442754103565000

Higgins Gulch below East Fork, near Spearfish, South Dakota

44.46498387

−103.947707

12.55

442405103485100

False Bottom Creek above Madison outcrop, near Central City, South Dakota

44.4013729

−103.8146453

5.55

06432180

False Bottom Creek near Spearfish, South Dakota

44.4524839

−103.8065895

8.91 920

6.95 139 8.44

06433000

Redwater River above Belle Fourche, South Dakota

44.66720665

−103.8393696

06436170

Whitewood Creek at Deadwood, South Dakota

44.37994546

−103.724182

40.6

06437020

Bear Butte Creek near Deadwood, South Dakota

44.3355403

−103.6354716

16.6

442337103350600

Bear Butte Creek at Boulder Park, near Sturgis, South Dakota

44.3935957

−103.58547

32.23

442447103332800

Bear Butte Creek above Sturgis, South Dakota

44.41304015

−103.558247

5.59

1Continuous-record station used only for extension of streamflow records.

20 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Table 3. Selected site information for streamgages (shown in fig. 9) used in determining streamflow recharge from Carter and others (2001a).—Continued

Table 4. Loss thresholds and associated drainage areas of selected streams (shown in fig. 9) used to calculate streamflow recharge by Carter and others (2001a). [ft3/s, cubic feet per second; C, continuous-record; --, none used; M, miscellaneous-record; >, greater than; e, estimated; UG, ungaged; <, less than; ND, not determined; NA, not applicable]

Basin number

Stream name

Associated station type

Drainage area (square miles)

Adjusted drainage area (square miles)

Loss threshold (ft3/s)

Adjusted loss threshold (ft3/s)

Aquifers potentially receiving recharge

Beaver Creek

45.8

Madison, Minnelusa, Minnekahta

Reaves Gulch

6.86

>0.2

Madison

Highland Creek

8.69

e10

Madison, Minnelusa, Minnekahta

South Fork Lame Johnny Creek

4.34

1.4

Madison, Minnelusa

Flynn Creek

10.3

(3)

Madison, Minnelusa

North Fork Lame Johnny Creek

2.8

2.3

Deadwood, Madison

French Creek

Madison

Minnelusa

Madison

Battle Creek

105 58

Battle Creek tributary

6.59

5.33

(3)

Madison

Grace Coolidge Creek

25.2

Madison

Minnelusa

Bear Gulch

4.23

0.4

Deadwood, Madison, White River

Spokane Creek

4.92

2.2

3.7

Deadwood, Madison, Minnelusa, Minnekahta

Spokane Creek

3.76

2.52

(3)

Deadwood, Madison, Minnelusa, Minnekahta

Spring Creek

Madison

163

Minnelusa

3.5 Rapid Creek

320

Deadwood, Madison, Minnelusa

16A

Rapid Creek

33.33

(3)

Deadwood, Madison, Minnelusa

Victoria Creek

6.82

2.1

Deadwood, Madison

17A

Victoria Creek

5.33

4.27

(3)

Deadwood, Madison

Boxelder Creek

>25

---

Madison

<20

Minnelusa

18A

Boxelder Creek tributary

13.3

(3)

Madison, Minnelusa

Elk Creek

21.5

Madison

Minnelusa

Elk Creek

23.8

12.1

(3)

Madison, Minnelusa

Little Elk Creek

12.56

0.7

Madison

2.6

Minnelusa

Hydrologic Budgets 21

[ft3/s, cubic feet per second; C, continuous-record; --, none used; M, miscellaneous-record; >, greater than; e, estimated; UG, ungaged; <, less than; ND, not determined; NA, not applicable]

Basin number

Stream name

Associated station type

Drainage area (square miles)

Adjusted drainage area (square miles)

Loss threshold (ft3/s)

Adjusted loss threshold (ft3/s)

Aquifers potentially receiving recharge

Bear Gulch

6.17

Deadwood, Madison, Minnelusa

Beaver Creek

6.86

Deadwood, Madison, Minnelusa, Minnekahta

25A

Beaver Creek

2.9

2.15

Deadwood, Madison, Minnelusa, Minnekahta

Iron Creek

8.16

Spearfish Creek

Madison, Minnelusa

Spearfish Creek

8.44

521

Madison, Minnelusa

Higgins Gulch

12.55

False Bottom Creek

5.55

1.4

2.9

Madison

7.3

15.1

Minnelusa

139

8.91

4.92

Madison, Minnelusa

Whitewood Creek

40.6

Whitewood Creek

5.15

Bear Butte Creek

16.6

False Bottom Creek

36 36A 37

3.8

Madison

4.1

Minnelusa

Bear Butte Creek

32.23

19.2

Madison, Minnelusa

Bear Butte Creek

5.59

3.33

4.2

Minnelusa

1Outcrop areas of the Madison Limestone and Minnelusa Formation that are considered to contribute to the regional basin were subtracted. 2From Hortness and Driscoll, 1998. 3Basin has common loss zone with preceding basin; same loss thresholds and aquifers apply. 4Loss within diversion aqueduct. 5Threshold loss when flow in Spearfish Creek exceeds the estimated capacity of the diversion aqueduct (115 to 135 ft3/s).

22 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Table 4. Loss thresholds and associated drainage areas of selected streams (shown in fig. 9) used to calculate streamflow recharge by Carter and others (2001a).—Continued

Hydrologic Budgets 23 individually for the Madison and Minnelusa aquifers for some streams, which allowed for determination of individual and combined streamflow recharge. Combined recharge to the Madison and Minnelusa aquifers was calculated for streams where loss thresholds could not be differentiated between the aquifers. Additionally, loss threshold rates were adjusted by Carter and others (2001a) for some streams to account for unmeasured flow from additional minor drainage areas (table 4). Drainage basins were delineated based on the availability and distribution of USGS streamgages in the study area and adjusted using outcrop areas of the Madison Limestone and Minnelusa Formation. Streamgages (table 3) were used to delineate drainage basins using watershed boundaries downloaded from USGS StreamStats (USGS, 2024b). Adjustments to drainage basins involved removing areas of outcrop of the Madison and Minnelusa connected to the regional groundwater flow system of both aquifers. It was assumed by Carter and others (2001a) that precipitation on these outcrops of Madison and Minnelusa did not contribute to runoff. Isolated outcrops of the Madison and Minnelusa were not excluded from drainage basins because Carter and others (2001a) assumed these outcrops were disconnected from the regional groundwater flow system of both aquifers and contributed to streamflow. Additional adjustments were necessary to account for unmeasured streamflow from tributary basins upgradient of loss zones. Basins with unmeasured streamflow were delineated by including outcrop areas of geologic units older than the Madison and Minnelusa aquifers that were not within the boundaries of basins delineated using streamgages (fig. 9). In total, 55 drainage basins were delineated and closely resembled those of Carter and others (2001a; fig. 9). Drainage area adjustments are shown in table 4 for basins that required adjustment except for basins with unmeasured streamflow. Estimates of streamflow recharge were calculated for drainage basins using three types of streamflow records: (1) those with continuous records, (2) those with miscellaneous discrete measurements, and (3) those with no measurements (ungaged). All available streamflow data were downloaded for each streamgage from the USGS NWIS database (USGS, 2024a). Site information, drainage area, type of streamflow data available, and period of record for each site are summarized in table 3. Of the 55 drainage basins, 13 had continuous streamflow data, 19 had miscellaneous streamflow data, and 23 had no streamflow data (fig. 9). The drainage area for streamgages with continuous records accounted for about 78 percent of the total drainage area. The drainage area for streamgages with miscellaneous or no measurements accounted for 13 and 9 percent, respectively, of the total drainage area.

Recharge From Streams with Continuous Records, 1950–2022 Annual streamflow recharge was calculated for 11 of the 13 basins with continuous-record streamgages. The other two basins were either combined with another basin or excluded from the analysis based on assumptions by Carter and others (2001a). Basins 16 and 16A were combined for recharge calculations, and streamflow losses in basin 36 (Whitewood Creek) were considered negligible based on streamflow observations by Hortness and Driscoll (1998). Recharge calculations for five basins with continuous-record streamgages (Battle, Boxelder, Elk, Spearfish, and Bear Butte Creeks) involved consideration of four basins with miscellaneous-record streamgages (basins 21, 30, 38, and 39) and two ungaged basins (basins 8A and 18A). These six basins were included in calculations of streamflow recharge for basins with continuous-record streamgages and are not addressed in subsequent discussions of recharge for basins with miscellaneous-record streamgages or ungaged basins. Recharge calculations for basins with continuous-record streamgages involved comparing mean daily streamflow values to loss threshold rates. Loss threshold rates determined by Hortness and Driscoll (1998) or adjusted rates from Carter and others (2001a) were available for all 11 streams with continuous-record streamgages. Loss thresholds were applied to Madison aquifer first and Minnelusa aquifer second if loss thresholds were provided individually for both aquifers because streamflow typically flows overtop outcrops of the Madison Limestone before the Minnelusa Formation. If daily mean flows were less than the loss threshold rate, then daily recharge to the Madison and (or) Minnelusa aquifers was equal to the mean daily flow value. If daily mean flows were equal to or exceeded the loss threshold rate, then the daily recharge to the Madison and (or) Minnelusa aquifers was equal to the loss threshold rate. Calculated daily streamflow losses were aggregated to provide annual streamflow recharge for 1999–2022 and were combined with estimates from Carter and others (2001a) for 1950–98 (table 5). Estimation of annual streamflow recharge for basins involving continuous- and miscellaneous-record streamgages required adjustments to account for contributions from tributaries. Carter and others (2001a) provided detailed descriptions of considerations for each stream used to calculate annual streamflow recharge. For some basins with shared streams, miscellaneous-record streamgages were combined with basins with continuous-record streamgages to create a synthetic daily streamflow record that accounted for losses in ungaged tributaries. Drainage-area ratios and linear-regression analyses were used to create synthetic daily streamflow records. Drainage-area ratios were calculated by adding the drainage areas contributing to runoff for basins with continuous- and miscellaneous-record streamgages and dividing by the drainage area of the continuous-record streamgage. Drainage-area ratios were used for Battle Creek

24 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 104°

103°40'

103°20'

Spe arfi Cre sh ek

36A

Sturgis

Deadwood

06437020

06430800

Tilford Pl ea s

ld Sp

Slate

Cree

Spr

ing

Beaver

Stockade Beaver Creek Whoopup

Stockade

Map area

13 06406000

434800103174400

06405800

06425500

06405800

Dry

Streamgage not shown in main map

Creek

Fairburn

WYOMING

06404998

SOUTH DAKOTA

French Cr eek

434105103240200 433930103250000

47 433910103251000 46 433745103261900 45

Pringle

433532103284800

Cr ee

Bea

ver Buffalo Gap

06402430

Pas s

06408500

Creek

Cre

C Hermosa reek Battle

12 11

Miscellaneous-record streamgage and identifier

06404000

ing

Keystone

Spr

eek Cr

434929103215700

Rapid City

Continuous-record streamgage and identifier

Colonial Pine Hills 06407500

ek Cre Custer

06431500

06432180

17A

440105103230700

Hill City

Named stream in National Hydrography Dataset (U.S. Geological Survey, 2024c)

d Cree

nch

Ungaged basin—Number is basin number

06423010

ek Cre

Fre

Lake and reservoirs from National Hydrography Dataset (U.S. Geological Survey, 2024c)

Piedmont Summerset r e Blackhawk oxeld B

Hills View Heights k Cree

Basin with a miscellaneous-record streamgage—Number is basin number in table 4

16A

06411500

Cr ee

Creek

Cre

Basin with a continuous-record streamgage—Number is basin number in table 4

441412103275600

rin

Valley

18A

Creek

k Creek

tle

Madison Limestone outcrop from DeWitt and others (2004)

Cree

Cas

441614103253300

06422500

rris

18 Rap

0642400

Creek

43° 40'

urc

Alkali Creek

442337103350600

442242103565400

44°

Creek

r Whitewood 06432180 Bea 442405103485100 39 442447103332800

Minnelusa Formation outcrop from DeWitt and others (2004)

od tewo

But

Whi

Spearfish

06430898 Lead 06430900

lle

River

06430520

Creek

06431500

06430950

Vale

tom B ot

25A

sh reek arfi C Spe

442754103565000 06429920

ee Cr

Fal

River

ater

Redw

06433000

EXPLANATION

eek Cr

Fruitdale

Belle Fourche ek Hay Cre

Beulah

44° 20'

e re y C

WYOMING SOUTH DAKOTA

ee Cr

44° 40'

Newell Ho rse Cr Nisland ee

Willow

Cr M ow Cr Bel F idd le o le ee urc k he

Cr ee

Base map created from digital datasets Universal Transverse Mercator, zone 13 north American Datum of 1983 (2011)

0 0

5 5

k Cree

Hot Springs 10

20 KILOMETERS

20 MILES

Figure 9. Drainage basins used to estimate annual streamflow recharge in the Black Hills area, South Dakota.

Table 5. Annual streamflow recharge for basins with continuous-record gages, water years 1950–2022, for the Madison and Minnelusa aquifers. Daily streamflow data used in calculations were downloaded from the U.S. Geological Survey National Water Information System database (USGS, 2024a). [All cells contain values derived from extrapolation of streamflow recharge estimates unless otherwise noted]

Annual streamflow recharge (cubic feet per second) Water year 1950

Rapid Creek (basins 16 and 16A) 210

Spearfish Creek (basins 29 and 30)

Battle Creek (basins 8 and 8A)

Boxelder Creek (basins 18 and 18A)

Grace Coolidge Creek (basin 10)

French Creek (basin 7)

Spring Creek (basin 14)

Bear Butte Creek (basins 37, 38, 39)

Bear Gulch (basin 11)

Beaver Creek (basin 1)

Elk Creek (basins 20 and 21)

25.14

Subtotal

Total1

3.5

9.89

2.22

4.22

6.33

8.62

0.36

1.74

7.62

44.5

59.64

1951

29.96

24.65

3.36

8.14

2.34

3.87

5.91

7.72

0.35

1.22

7.06

39.96

54.57

1952

29.98

25.58

5.01

12.7

3.97

5.05

18.95

9.61

0.33

0.81

7.26

63.67

79.23

1953

210

25.83

3.84

11.46

2.27

4.33

11.93

8.79

0.36

1.81

7.72

52.51

68.34

1954

210

24.84

3.01

7.19

1.8

3.31

2.22

7.47

0.35

1.17

6.79

33.32

48.16

1955

210

25.48

2.87

7.28

1.71

3.53

7.8

0.36

1.51

7.15

32.21

47.69

1956

29.97

24.71

3.06

6.6

1.98

3.21

3.74

0.34

0.86

6.51

33.29

47.97

1957

29.02

24.95

5.5

12.9

4.98

5.64

19.99

10.15

0.31

0.39

7.19

67.05

81.02

1958

28.65

24.81

3.44

7.6

2.48

3.63

6.41

7.48

0.33

0.81

6.65

38.83

52.29

1959

29.45

24.38

3.01

5.39

1.93

2.64

4.74

6.21

0.32

0.29

5.82

30.35

44.18

1960

28.71

24.08

2.97

5.55

1.82

2.63

4.58

6.25

0.33

0.4

5.9

30.41

43.2

1961

29.67

23.7

2.87

4.39

1.72

2.14

4.7

5.56

0.31

5.34

27.04

40.41

1962

27.82

24.78

24.43

16.39

4.54

6.36

16.78

12.49

0.35

1.64

8.47

71.45

84.05

1963

27.78

26.45

26.61

13.56

4.1

6.07

4.94

12.21

0.35

1.8

8.47

58.12

72.35

1964

210

26.64

25.61

11.78

2.59

5.17

4.68

10.11

0.38

2.39

8.53

51.24

67.88

1965

210

28.19

25.79

21.06

5.53

8.58

7.59

17.16

0.38

3.07

10.53

79.7

97.89

1966

210

26.56

23.94

12.22

2.31

4.85

9.11

9.59

0.38

2.34

8.35

53.08

69.64

1967

210

26.44

25.18

218.13

4.33

7.05

11.54

11.91

0.35

1.72

7.75

67.97

84.41

1968

210

25.84

23.84

29.57

2.97

4.22

7.28

9.04

0.32

0.27

6.05

43.57

59.41

26.15

23.11

29.18

1969

29.99

3.81

6.21

7.47

0.32

0.2

5.12

37.76

53.9

210

28.26

23.89

216.76

3.18

6.14

9.45

9.14

0.35

1.49

6.11

56.5

74.76

1971

210

28.02

25.01

219.21

4.21

7.27

11.64

11.55

0.35

1.9

7.54

68.68

86.7

28.01

25.59

218.18

4.68

7.24

12.08

12.78

0.35

1.73

8.26

70.89

88.76

1973

210

28.72

25.56

216.79

4.63

6.86

11.64

12.73

0.35

1.49

8.23

68.29

87.01

1974

210

26.63

21.81

26.58

1.15

2.57

3.76

4.69

0.31

3.48

24.35

40.98

26.55

23.67

214.89

1972

1975

29.86

29.99

2.95

5.55

8.62

8.67

0.34

1.17

5.83

51.69

68.23

1976

210

26.59

25.16

215.18

4.25

6.27

10.65

11.87

0.34

1.22

7.73

62.67

79.26

1977

210

26.72

22.93

214.73

21.27

5.2

7.6

7.08

0.34

1.14

4.89

45.18

61.9

Hydrologic Budgets 25

2.33

1970

[All cells contain values derived from extrapolation of streamflow recharge estimates unless otherwise noted]

Annual streamflow recharge (cubic feet per second) Water year 1978

Rapid Creek (basins 16 and 16A)

Spearfish Creek (basins 29 and 30)

Battle Creek (basins 8 and 8A)

Boxelder Creek (basins 18 and 18A)

Grace Coolidge Creek (basin 10)

French Creek (basin 7)

Spring Creek (basin 14)

Bear Butte Creek (basins 37, 38, 39)

Bear Gulch (basin 11)

Beaver Creek (basin 1)

Elk Creek (basins 20 and 21)

Subtotal

Total1

29.99

27.67

24.46

215.84

23.9

6.14

9.93

10.37

0.34

1.33

6.83

59.14

76.8

1979

210

26.28

24.13

28.79

23.66

4.14

7.42

9.65

0.32

0.13

6.41

44.64

60.92

1980

210

25.59

22.72

25.94

21.17

2.79

4.76

6.65

0.31

4.63

28.98

44.57

1981

210

25.03

23.01

24.55

22.45

2.54

4.71

7.25

0.31

4.99

29.8

44.83

26.3

24.14

210.14

23.89

4.5

7.84

9.69

0.32

0.36

6.43

47.32

63.52

1983

210

27.82

23.81

221.64

22.48

27.05

10.78

8.97

0.36

2.31

6.01

63.42

81.24

1984

210

28.03

24.89

219.63

23.97

26.86

11.6

11.28

0.36

1.97

7.37

67.92

85.95

1985

210

25.48

21.22

27.17

20.82

23.53

3.16

3.42

0.31

2.73

22.36

37.84

1986

210

25.65

24.32

213.1

22.03

23.63

8.94

10.07

0.33

0.87

6.66

49.97

65.62

1987

210

24.83

26.22

210.92

23.49

25.5

210.64

14.15

0.33

0.5

9.07

60.82

75.65

1988

210

24.92

20.76

25.07

20.61

22.11

21.8

2.44

0.31

2.15

15.25

30.17

1989

210

25.03

20.89

24.19

21.2

21.02

20.98

25.56

0.3

2.31

16.46

31.49

1990

210

25.04

25.09

26.18

23.4

23.65

26.76

20.33

7.63

39.8

54.84

24.94

25.15

211.21

24.92

25.63

210.92

211.25

20.29

20.23

7.71

57.32

72.25

1992

210

24.78

23.72

27.57

22.98

24.48

27.46

25.03

20.32

20.33

24.67

236.55

251.33

1993

210

25.26

26.66

218.05

27.12

27.26

213.35

212.76

20.34

20.76

28.36

274.66

289.92

1994

210

26.78

25.21

217.53

23.27

26.02

211.63

214.24

20.35

21.35

29.15

268.75

285.53

1995

210

28.56

26.17

221.09

27.2

28.91

213.64

221.52

20.36

22.77

210.04

291.7

2110.26

1996

210

29.2

28.1

225.55

26.45

210.92

218.02

218.12

20.39

23.98

211.52

2103.07

2122.27

1997

210

210.92

210.5

234.08

29.31

213.07

222.15

225.6

20.39

23.89

213.91

2132.89

2153.81

1998

210

29.59

28.26

228.3

27.57

212.12

218.89

215.27

20.39

23.56

212.25

2106.61

2126.2

1999

210

210.82

211.68

236.47

212.67

214.86

224.00

223.41

0.41

24.56

215.79

143.86

164.69

2000

210

29.72

25.71

220.64

24.69

29.80

213.35

211.82

0.36

23.07

210.73

80.17

99.89

2001

210

28.08

26.35

213.82

23.59

27.55

212.21

29.64

0.34

21.39

27.98

62.85

80.93

2002

210

26.76

23.24

26.34

22.12

24.63

27.40

24.78

0.31

20.95

24.63

34.39

51.15

2003

210

26.89

23.55

29.76

22.67

24.89

28.73

27.62

0.32

20.76

26.85

45.15

62.04

2004

210

26.05

21.17

24.12

20.93

22.36

22.87

23.60

0.30

20.53

23.84

19.73

35.78

2005

210

25.86

22.53

23.80

21.05

22.11

22.74

25.06

0.30

20.42

24.00

22.02

37.88

1982

1991

29.9

29.99

26 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Table 5. Annual streamflow recharge for basins with continuous-record gages, water years 1950–2022, for the Madison and Minnelusa aquifers. Daily streamflow data used in calculations were downloaded from the U.S. Geological Survey National Water Information System database (USGS, 2024a).—Continued [All cells contain values derived from extrapolation of streamflow recharge estimates unless otherwise noted]

Annual streamflow recharge (cubic feet per second) Water year

Rapid Creek (basins 16 and 16A)

Spearfish Creek (basins 29 and 30)

Battle Creek (basins 8 and 8A)

Boxelder Creek (basins 18 and 18A)

Grace Coolidge Creek (basin 10)

French Creek (basin 7)

Spring Creek (basin 14)

Bear Butte Creek (basins 37, 38, 39)

Bear Gulch (basin 11)

Beaver Creek (basin 1)

Elk Creek (basins 20 and 21)

Subtotal

Total1

2006

210

26.42

22.10

28.66

21.19

22.22

22.85

211.98

0.32

20.37

26.93

36.62

53.04

2007

210

26.76

21.41

210.79

20.88

21.74

22.33

213.88

0.33

20.15

29.19

40.69

57.45

2008

210

28.49

23.76

220.66

23.22

25.03

27.78

218.43

0.36

20.22

29.47

68.92

87.41

2009

210

29.47

26.55

223.76

23.99

26.25

211.29

220.26

0.37

20.31

211.81

84.59

104.06

2010

210

29.97

26.64

223.87

26.33

28.58

214.35

218.77

0.37

21.79

211.63

92.32

112.29

2011

210

210.79

25.62

221.18

25.12

29.34

214.75

217.33

0.36

22.83

211.46

87.99

108.77

2012

210

29.04

22.16

28.83

21.42

24.89

27.26

25.39

0.32

21.41

26.66

38.34

57.37

2013

210

28.56

22.52

210.93

20.83

22.46

25.22

210.54

0.33

20.78

28.03

41.62

60.18

2014

210

211.54

28.77

234.18

25.29

29.71

219.96

229.84

0.40

22.18

215.49

125.80

147.34

2015

210

211.51

28.88

229.96

26.90

210.37

219.14

223.09

0.39

23.28

214.98

116.98

138.49

2016

210

29.60

25.84

212.69

22.80

27.42

212.80

27.57

0.33

22.57

29.80

61.83

81.43

2017

210

27.37

24.39

210.54

21.69

25.29

27.22

24.75

0.33

21.27

26.79

42.26

59.63

2018

210

26.92

26.73

216.81

25.14

28.59

213.58

29.92

0.35

22.03

29.49

72.64

89.56

2019

210

28.51

29.04

226.80

27.22

211.14

219.23

225.97

0.38

23.74

212.71

116.22

134.74

2020

210

29.13

27.66

225.49

24.54

210.88

219.98

218.50

0.38

24.13

215.35

106.91

126.04

2021

210

27.63

23.86

210.67

22.38

26.39

211.07

28.04

0.33

22.56

7.08

52.37

70.01

2022

210

27.41

23.09

211.38

21.66

25.12

28.21

210.77

0.33

21.96

7.32

49.84

67.25

1Individual estimates may not sum to total due to independent rounding. 2Calculated values for period of daily flow record.

Hydrologic Budgets 27

28 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 (basins 8 and 8A), Boxelder Creek (basins 18 and 18A), Elk Creek (basins 20 and 21), and Bear Butte Creek (basins 37, 38, and 39; fig. 9). Linear regression analyses were used to create synthetic daily streamflow for Spearfish Creek (basins 29, 30, and 31) by developing relations between continuous daily flows and miscellaneous flows. Other considerations discussed in Carter and others (2001a) involved accounting for aqueduct influences on recharge along Spearfish Creek, the effect of Pactola Dam on recharge along Rapid Creek (basins 16 and 16A), and the location of streamgages and outcrops of the Madison and Minnelusa aquifers along Bear Gulch (basin 11) and Bear Butte Creek (basins 37, 38, and 39). The same methods used by Carter and others (2001a) for basins with continuous and miscellaneous records were used in this study for consistency. Additional information on special considerations for each stream are provided in Carter and others (2001a) and are not further discussed in this report. Recharge estimates for 1999–2022 for basins requiring adjustments were combined with estimates from Carter and others (2001a) for 1950–98 (table 5). Annual recharge estimates for 1950–98 were estimated by Carter and others (2001a) using streamflow data and (or) statistical analyses. If available, mean daily streamflow data were used to calculate annual streamflow recharge; however, many sites had sparse streamflow records before the 1980s. Carter and others (2001a) provided annual streamflow recharge for 1950–98 despite only two of the streamgages used to calculate annual streamflow recharge

having streamflow records extending back to 1950. Single and multiple linear regression techniques were used by Carter and others (2001a) to extend the record of recharge estimates back to 1950. Streamflow data from Battle (site 9 in table 3; fig. 9) and Boxelder Creeks (site 18 in table 3; fig. 9) were used to extrapolate recharge estimates from 1967 to 1991. Four streamgages (sites 9, 15, 22, and 35 in table 3; fig. 9)—three of which are downstream from loss zones and were not used to calculate streamflow losses—were used as representative streamgages to estimate recharge from 1950 to 1966. Carter and others (2001a) performed a stepwise regression analysis using annual mean flow from the four representative streamgages to estimate recharge for sites without available streamflow data. Additional details regarding statistical analyses are provided in Carter and others (2001a). Statistical techniques also were used to estimate annual recharge for two sites because streamflow data were unavailable between 1999 and 2022. Streamgages along Bear Gulch (basin 11) and Elk Creek (basins 20 and 21) did not have complete streamflow records because streamgages were decommissioned before 2022. Linear regression equations were developed using the period of available data and a nearby representative streamgage. For Bear Gulch (basin 11) and Elk Creek (basins 20 and 21), the representative streamgage with the best coefficient of determination was Boxelder Creek (basin 18; table 6). Regression equations were used to estimate annual streamflow recharge during 1999–2022 for Bear Gulch (basin 11) and during 2021–22 for Elk Creek (basins 20 and 21) using relations with Boxelder Creek (basin 18; fig. 9).

Table 6. Linear regression equations used to estimate annual streamflow recharge for streams with continuous, miscellaneous, and ungaged records. [R 2, coefficient of determination]

Recharge regression equation

Years of estimated recharge

0.033

0.76

1999–2022

0.352

0.91

2021–22

−0.176

0.184

0.92

2019–22

1992–98

0.521

0.195

0.83

1999–2022

Miscellaneous

1992–98

0.542

0.247

0.83

1999–2022

Ungaged

1992–98

0.039

0.693

0.81

1999–2022

Representative stream or basin

Type

Span of regression

Intercept

Coefficient

Bear Gulch (basin 11)

Boxelder Creek (basin 18)

Elk Creek (basins 20 and 21)

Boxelder Creek (basin 18)

Continuous

1990–98

0.291

Continuous

1992–2020

3.324

Bear Gulch (basin 24)

Elk Creek (basins 20 and 21)

Miscellaneous

1992–2018

Beaver Creek (basin 25 and 25A)

Bear Butte Creek (basins 37, 38, and 39)

Miscellaneous

False Bottom Creek (basins 33 and 34)

Bear Butte Creek (basins 37, 38, and 39)

Basin 56

Basin 57

Stream or basin

R 2 for

Hydrologic Budgets 29

Recharge from Streams with Miscellaneous Records, Water Years 1992–2022 In total, 11 basins had miscellaneous-record streamgages (table 4). Four of the 11 basins were considered previously in calculations of recharge for basins with continuous-record streamgages and were not analyzed using methods for basins with miscellaneous-record streamgages. Additionally, two more basins, Iron Creek (basin 26) and Higgins Gulch (basin 32), were excluded from streamflow recharge calculations because Hortness and Driscoll (1998) determined streams in both basins gained flow across outcrops of the Madison and Minnelusa aquifers. Loss thresholds determined by Hortness and Driscoll (1998) or adjusted by Carter and others (2001a) were used for the remaining five basins. Loss thresholds for Victoria Creek (basin 17) and Beaver Creek (basin 25) included losses from drainage areas in ungaged basins 17A and 25A. Therefore, these two ungaged basins are included in analyses in this section and are not addressed in the subsequent section addressing ungaged streams. The methods used to quantify recharge for basins with continuous-record streamgages could not be used for basins with miscellaneous-record streamgages because mean daily streamflow data were unavailable. Instead, Carter and others (2001a) computed synthetic daily streamflow data for basins with miscellaneous-record streamgages using representative streamgages. A representative streamgage with continuous records was selected for each basin with a miscellaneous streamgage based on proximity, streamflow characteristics, and elevation. A drainage-area ratio was calculated for each basin pair by dividing the drainage area of the miscellaneous streamgage by the drainage area of the representative continuous streamgage (table 7). If applicable, adjusted drainage areas that excluded outcrops of the regional Madison and Minnelusa aquifers were used in drainage-area ratio calculations. Representative streamgages included French Creek (site 7), Battle Creek (site 8), Annie Creek (site 27), and

Cleopatra Creek (site 28; table 4). Mean daily streamflow data for two representative streamgages with continuous records were not available for all years from 1999 to 2022 because the streamgages were decommissioned. The streamgages along Annie Creek (site 27) and Cleopatra Creek were decommissioned in 2018 and 1998, respectively. Therefore, statistical regression techniques instead of drainage-area ratios were used to estimate recharge for years without streamflow data. Drainage-area ratios and (or) statistical regression techniques were used to estimate recharge for 1992–2022 for basins with miscellaneous-record streamgages depending on the availability of mean daily streamflow data. If mean daily streamflow data were available, then drainage-area ratios (table 7) were multiplied by mean daily streamflow data from the representative continuous-record streamgage to create a synthetic daily streamflow record for each basin with a miscellaneous-record streamgage. Loss thresholds (table 4) were applied to the synthetic daily streamflow record and aggregated by water year to calculate annual streamflow recharge. Noted recharge values in table 8 were calculated using synthetic daily streamflow data and loss thresholds. If mean daily streamflow were unavailable at representative continuous-record streamgages, then statistical regression techniques were used to estimate recharge. Linear regression equations were developed for Bear Gulch (basin 24), Beaver Creek (basins 25 and 25A), and False Bottom Creek (basins 33 and 34) using relations between annual recharge estimates for each of the three streams and streams with continuous records (table 6). Annual recharge estimates for Bear Gulch (basin 24), Beaver Creek (basins 25 and 25A), and False Bottom Creek (basins 33 and 34) were regressed with annual recharge estimates from representative continuous-record streamgages based on proximity, streamflow characteristics, and elevation. Spearfish Creek (basins 29 and 30) was excluded because it is controlled by

Table 7. Selected information used to estimate recharge from streams with miscellaneous-record streamgages. Drainage basins shown for streams shown in figure 9.

Stream name and basin number Reaves Gulch (2)

Representative continuousrecord streamgage French Creek (site 7)

Drainagearea ratio 0.065

Highland Creek (3)

0.083

South Fork Lame Johnny Creek and Flynn Creek (4 and 5)

0.139

North Fork Lame Johnny Creek (6)

0.027

Spokane Creek (12 and 13)

Battle Creek (site 8)

Victoria Creek (17 and 17A)

0.128 0.191

Little Elk Creek (23)

Boxelder Creek (site 18)

0.131

Bear Gulch (24)

Annie Creek (site 27)

1.74

Beaver Creek (25 and 25A)

Cleopatra Creek (site 28)

1.30

False Bottom Creek (33 and 34)

1.50

[All cells contain values derived from extrapolation of streamflow recharge estimates unless otherwise noted]

Annual streamflow recharge (cubic feet per second)

Reaves Gulch (basin 2)

Highland Creek (basin 3)

South Fork Lame Johnny Creek and Flynn Creek (basins 4 and 5)

1992

20.17

20.37

20.6

20.12

20.45

20.64

20.9

20.56

21.23

21.46

6.5

1993

20.15

20.96

20.79

20.3

21.14

21.06

21.69

21.36

23.16

23.88

14.49

1994

20.17

20.59

20.72

20.19

20.65

20.88

21.72

21.5

22.97

23.66

13.05

1995

20.19

22.27

20.95

20.63

21.24

21.13

21.96

22.27

25.07

26.27

21.98

1996

20.2

21.45

21.22

20.46

21.17

21.33

22.39

21.79

25.08

26.36

21.45

1997

20.2

22.01

21.34

20.64

21.79

21.67

22.89

22.13

24.75

25.92

23.36

1998

20.2

21.59

21.3

20.51

21.25

21.33

22.67

22.25

23.33

24.01

18.45

1999

20.20

22.68

21.40

20.87

22.26

21.82

23.09

22.87

5.09

6.33

26.61

2000

20.19

21.03

21.11

20.33

20.83

20.94

22.13

21.67

2.83

3.46

14.52

2001

20.20

20.75

20.88

20.24

20.87

21.04

21.60

21.20

2.40

2.92

12.11

2002

20.16

20.40

20.58

20.13

20.39

20.55

20.75

20.65

1.45

1.72

6.78

2003

20.15

20.45

20.60

20.15

20.51

20.59

21.11

21.22

2.01

2.42

9.20

2004

20.13

20.20

20.33

20.06

20.14

20.20

20.49

20.55

1.22

1.43

4.75

2005

20.11

20.18

20.29

20.06

20.31

20.43

20.45

20.72

1.51

1.79

5.85

2006

20.11

20.19

20.30

20.06

20.25

20.36

20.88

21.23

2.86

3.50

9.74

2007

20.09

20.16

20.23

20.05

20.18

20.24

21.14

21.67

3.23

3.97

10.96

2008

20.14

20.61

20.58

20.19

20.61

20.60

21.74

21.37

4.11

5.09

15.06

2009

20.18

20.62

20.73

20.20

21.09

21.04

22.33

21.79

4.47

5.55

18.00

2010

20.19

21.52

20.95

20.47

21.19

21.06

22.22

21.76

4.18

5.18

18.72

2011

20.20

21.34

21.05

20.41

20.93

20.92

22.11

21.96

3.90

4.82

17.64

2012

20.16

20.41

20.66

20.13

20.25

20.37

21.05

21.21

1.57

1.87

7.70

2013

20.12

20.20

20.34

20.07

20.35

20.42

21.20

21.17

2.58

3.14

9.58

2014

20.20

21.21

21.05

20.39

21.45

21.42

22.98

22.76

6.34

7.91

25.72

2015

20.20

22.18

21.15

20.64

21.64

21.41

22.85

22.72

5.02

6.25

24.06

2016

20.19

20.63

20.96

20.21

20.76

20.99

21.51

21.64

2.00

2.41

11.30

2017

20.18

20.45

20.68

20.15

20.56

20.72

21.25

20.81

1.45

1.72

7.96

Water year

North Fork Lame Johnny Creek (basin 6)

Spokane Creek (basins 12 and 13)

Victoria Creek (basins 17 and 17A)

Little Elk Creek (basin 23)

Bear Gulch (basin 24)

Beaver Creek (basins 25 and 25A)

False Bottom Creek (basins 33 and 34)

Total1

30 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Table 8. Annual streamflow recharge for streams with miscellaneous measurements sites, water years 1992–2022. Daily streamflow data used in calculations were synthesized from daily streamflow records downloaded from the U.S. Geological Survey National Water Information System database (U.S. Geological Survey, 2024a).

Annual streamflow recharge (cubic feet per second)

Reaves Gulch (basin 2)

Highland Creek (basin 3)

South Fork Lame Johnny Creek and Flynn Creek (basins 4 and 5)

2018

20.19

21.42

20.92

20.44

21.17

21.08

21.78

21.51

2.46

2.99

13.96

2019

20.20

22.60

21.15

20.78

21.59

21.43

22.26

2.16

5.59

6.96

24.72

2020

20.20

21.38

21.19

20.45

21.16

21.24

22.52

2.65

4.13

5.11

20.03

2021

20.18

20.62

20.75

20.20

20.48

20.66

21.26

1.13

2.09

2.53

9.93

2022

20.17

20.44

20.66

20.14

20.37

20.53

21.29

1.17

2.62

3.20

10.64

Water year

North Fork Lame Johnny Creek (basin 6)

Spokane Creek (basins 12 and 13)

Victoria Creek (basins 17 and 17A)

Little Elk Creek (basin 23)

Bear Gulch (basin 24)

Beaver Creek (basins 25 and 25A)

False Bottom Creek (basins 33 and 34)

Total1

1Individual estimates may not sum to total due to independent rounding. 2Calculated values for period of daily flow record.

Hydrologic Budgets 31

32 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 an aqueduct that alters the natural streamflow characteristics along the loss zone. Some of the annual streamflow recharge estimates in table 8 were estimated using linear regression. Carter and others (2001a) used statistical regression techniques to estimate annual streamflow recharge to the combined Madison and Minnelusa aquifers for 1950–91 for basins with miscellaneous-record streamgages. The techniques used in this study to estimate recharge deviated slightly from Carter and others (2001a) and are discussed in appendix 1.

Recharge From Ungaged Streams, Water Years 1992–2022 Ungaged basins were relatively small drainage areas (fig. 9) with undetermined loss thresholds. In total, 18 basins were ungaged and five of the ungaged basins were included in recharge calculations for basins with a continuous-record (8A, 18A, 36A) or miscellaneous-record (basins 17A and 25A) streamgage. Hortness and Driscoll (1998) did not determine loss thresholds for ungaged basins, so Carter and others (2001a) assumed 90 percent of streamflow generated within ungaged basins became recharge to the Madison and Minnelusa aquifers. The loss threshold of 90 percent of streamflow was considered appropriate because Carter and others (2001a) observed that streamflow seldom occurred downstream from loss zones in each basin. Drainage-area ratios and (or) statistical regression techniques were used to estimate recharge for water years 1992–2022 for ungaged basins, depending on the availability of mean daily streamflow data. Because mean daily streamflow data were unavailable for ungaged basins, a representative basin with a continuous-record streamgage was selected for each basin with an ungaged stream. Four basins with a continuous-record streamgage represented streamflow in 18 ungaged basins (table 9). Drainage-area ratios were calculated by Carter and others (2001a) by dividing the total drainage area of ungaged basins associated with each streamgage by the drainage area of the representative continuous-record streamgage (table 9). Mean annual daily streamflow for each water year from the representative continuous-record streamgage was multiplied by the drainage-area ratio and by 0.90 (90-percent loss threshold) to calculate annual streamflow recharge. Annual streamflow recharge for ungaged basins represents recharge to the

Madison and Minnelusa aquifers because individual recharge estimates could not be calculated. Annual streamflow recharge for basins in Wyoming were estimated using the same methods as Carter and others (2001a) by multiplying the combined recharge for Bear Gulch (basin 24) and Beaver Creek (basins 25 and 25A) in table 8 by a factor of 2. Mean daily streamflow data were available for 1999–2022 for representative streamgages along French Creek (site 7 in table 3), Battle Creek (site 8 in table 3), and Bear Butte Creek (site 37 in table 3). Synthetic mean daily streamflow records generated from representative streamgages and the loss threshold of 0.90 were used to calculate annual streamflow recharge estimates for basins 40–50, basins 51–55, and basin 56 (table 10). Mean daily streamflow data were unavailable for 1999–2022 for the representative streamgage along Cleopatra Creek because it was decommissioned in 1998. Instead, linear regression using relations among annual recharge estimates for basin 56 and basin 57 between 1992 and 1998 from Carter and others (2001a) was used to develop a regression equation for basin 57 (table 6). Annual streamflow recharge estimates from the linear regression equation for basin 57 are provided in table 10. Carter and others (2001a) used statistical regression techniques to estimate annual recharge to the combined Madison and Minnelusa aquifers for 1950–91 for ungaged basins. The techniques used to estimate recharge deviated slightly from Carter and others (2001a) and are discussed in the appendix 1.

Precipitation and Streamflow Recharge, 1931–2022 Summary statistics for precipitation and streamflow recharge were calculated by aquifer, if applicable, for the study area and by aquifer for subareas 1–9 (table 11) using annual recharge estimates from 1931 to 2022 in appendix 1. Statistics include minimum; maximum; mean; and the 25th, 50th (median), and 75th percentiles. Statistics were calculated for each aquifer for estimates of precipitation recharge. Streamflow recharge estimates were considered only for the Madison and Minnelusa aquifers and were combined because streamflow loss thresholds for some streams could not be

Table 9. Summary of selected information used to estimate recharge from ungaged streams.

Basin numbers

Drainage area, in square miles

Representative continuous-record streamgage (table 3)

Representative continuousrecord streamgage drainage area

Drainagearea ratio

40–50

51.47

French Creek (site 7)

105

0.49

51–55

12.41

Battle Creek (site 8)

163.33

0.20

10.55

Bear Butte Creek (site 37)

16.6

0.64

6.96

Cleopatra Creek (site 28)

6.95

1.00

1Adjusted drainage area from table 4.

Hydrologic Budgets 33 Table 10. Annual streamflow recharge from ungaged basins, water years 1992–2022, for the Madison and Minnelusa aquifers. Daily streamflow data used in calculations were synthesized from daily streamflow records downloaded from the U.S. Geological Survey National Water Information System database (U.S. Geological Survey, 2024a). [--, not determined]

Annual streamflow recharge (cubic feet per second) Water year

Ungaged basins and representative continuous-record stations Basins 40-50 (French Creek)

Basins 51-55 (Battle Creek)

Basin 56 (Bear Butte Creek)

Basin 57 (Cleopatra Creek)

Wyoming basins

Total1

1992

2.02

0.67

1.31

0.89

3.58

8.47

1993

5.29

2.91

4.36

2.83

9.04

24.42

1994

3.11

0.97

5.03

3.52

8.94

21.58

1995

15.3

5.33

8.41

7.6

14.68

51.33

1996

7.76

2.77

6.53

4.96

13.74

35.76

1997

10.89

4.56

9.79

5.38

13.76

44.38

1998

8.6

2.48

4.86

3.02

11.16

30.12

1999

14.42

5.30

8.40

5.86

15.91

49.90

2000

5.49

1.44

3.79

2.67

9.00

22.40

2001

3.96

1.50

2.90

2.05

7.20

17.62

2002

2.14

0.60

1.39

1.01

4.21

9.35

2003

2.42

0.84

2.22

1.58

6.45

13.51

2004

1.04

0.21

0.93

0.68

3.55

6.42

2005

0.94

0.48

1.41

1.02

4.46

8.31

2006

0.98

0.39

4.23

2.97

8.18

16.75

2007

0.83

0.28

4.65

3.26

9.79

18.81

2008

3.27

1.43

7.21

5.04

10.96

27.91

2009

3.27

1.82

7.19

5.02

12.53

29.83

2010

8.53

3.68

6.68

4.67

11.88

35.44

2011

7.69

2.73

6.23

4.36

11.72

32.73

2012

2.18

0.39

1.39

1.00

5.56

10.52

2013

1.08

0.58

3.71

2.61

7.49

15.47

2014

6.50

3.11

11.45

7.98

18.20

47.24

2015

12.51

6.81

8.77

6.12

15.49

49.69

2016

3.36

1.36

1.96

1.39

7.27

15.34

2017

2.41

0.88

1.22

0.88

4.51

9.91

2018

7.65

2.81

2.97

2.10

7.94

23.46

2019

16.05

4.63

10.51

7.32

15.50

54.01

2020

7.35

1.80

6.14

4.30

13.55

33.14

2021

3.30

0.75

2.12

1.51

6.43

14.19

2022

2.34

0.57

3.40

2.40

7.59

16.37

Combined area (square miles)

51.47

12.41

10.55

6.96

1Individual recharge estimates may not sum to total due to independent rounding.

Total mean annual recharge by subarea (acre-feet)

Recharge (acre-feet) Statistic Precipitation Deadwood

Madison

Minnelusa

Minnekahta

Sundance

Inyan Kara

Streamflow1

Precipitation recharge2

Total recharge3

113,946

127,178

13,803

28,047

5,817

12,237

Subarea 1 Mean

2,622

26,227

62,418

12,452

5,321

4,906

13,232

Standard deviation

1,650

14,587

33,760

6,845

2,962

2,865

4,743

301

3,064

8,975

2,311

1,141

1,008

5,880

25th percentile

1,370

14,458

36,348

7,348

3,141

2,661

9,176

Median

2,051

22,411

55,036

10,528

4,405

4,164

12,823

Minimum

75th percentile

3,565

35,832

85,416

17,012

7,104

6,790

15,397

Maximum

7,560

66,931

152,657

31,613

13,920

13,186

26,765

Mean

1,366

3,981

4,322

1,243

580

2,311

14,244

832

2,434

2,626

760

363

1,452

7,530

Subarea 2 Standard deviation Minimum

146

446

515

156

324

3,559

25th percentile

767

2,158

2,381

669

321

1,287

9,110

Median

1,113

3,277

3,621

1,042

485

1,950

12,849

75th percentile

1,952

5,447

6,109

1,650

758

3,033

16,460

Maximum

3,820

11,009

13,170

4,099

2,039

8,243

41,395

1,262

6,420

Subarea 3 Mean

1,276

2,142

601

395

Standard deviation

771

1,383

387

254

847

2,525

Minimum

125

241

159

1,826

25th percentile Median

141

739

1,212

327

208

701

4,795

1,051

1,700

479

327

114

1,011

6,123

75th percentile

1,656

2,819

777

536

183

1,648

7,375

Maximum

3,839

6,970

1,878

1,211

449

4,030

13,668

34 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Table 11. Annual precipitation and streamflow recharge statistics for the Deadwood, Madison, Minnelusa, Minnekahta, Sundance, and Inyan Kara aquifers by subarea. Streamflow recharge values are given only for the combined Madison and Minnelusa aquifers. Recharge values do not include inflows from aquifer exchange or regional groundwater flow.

Recharge (acre-feet) Statistic Precipitation Deadwood

Madison

Minnelusa

Minnekahta

Sundance

Inyan Kara

Streamflow1

Precipitation recharge2

Total recharge3

7,439

31,264

3,235

10,279

1,165

6,221

1,499

3,235

Subarea 4 Mean

999

2,750

2,318

569

211

592

23,825

Standard deviation

707

2,082

1,796

452

166

464

9,284

Minimum

101

262

222

10,450

25th percentile

558

1,477

1,263

304

111

308

16,156

Median

801

2,209

1,795

438

165

468

22,412

75th percentile

1,300

3,467

2,961

719

266

771

29,472

Maximum

4,143

12,460

11,299

3,050

1,118

3,073

52,430

Mean

293

718

1,089

227

169

739

7,044

Subarea 5 Standard deviation

216

526

784

158

118

512

3,913

Minimum

104

162

120

1,379

25th percentile

144

342

523

104

336

4,394

Median

230

569

873

186

143

627

6,068

75th percentile

373

924

1,423

296

213

957

8,629

Maximum

1,117

2,780

4,289

845

669

2,937

23,017

Subarea 6 Mean

235

292

407

5,056

Standard deviation

159

191

267

2,582

Minimum

1,056

120

145

193

3,231

194

243

341

4,584

75th percentile

302

383

124

555

6,288

Maximum

240

800

942

222

304

1,452

14,103

Mean

279

423

202

456

1,736

Standard deviation

189

282

133

305

1,225

Minimum

209

Subarea 7

Hydrologic Budgets 35

25th percentile Median

Total mean annual recharge by subarea (acre-feet)

Recharge (acre-feet) Statistic Precipitation Deadwood

Madison

Minnelusa

Minnekahta

Sundance

Inyan Kara

Streamflow1

Precipitation recharge2

Total recharge3

1,499

3,235

7,926

10,154

50,315

205,145

278,930

Subarea 7—Continued 25th percentile

151

224

103

234

891

Median

244

380

179

395

1,452

75th percentile

348

524

257

574

2,188

Maximum

247

1,048

1,480

668

240

1,500

5,996

Subarea 8 Mean

157

1,296

2,649

827

355

2,642

2,228

Standard deviation

106

854

1,641

505

212

1,567

1,663

Minimum

173

425

104

327

466

25th percentile

656

1,425

442

190

1,457

1,260

Median

132

1,082

2,331

731

318

2,292

1,839

75th percentile

189

1,542

3,346

1,070

456

3,326

2,457

Maximum

556

4,321

7,612

2,433

1,020

8,203

9,048

Mean

19,375

23,949

5,480

410

1,090

Standard deviation

11,657

13,804

2,744

225

617

Minimum

2,712

4,106

1,042

233

Subarea 9

25th percentile

10,478

12,884

3,301

241

646

Median

17,534

22,041

4,954

376

941

75th percentile

24,307

30,053

7,357

530

1,422

Maximum Total mean annual recharge

49,738

59,274

11,714

1,144

3,518

6,858

57,003

98,061

21,466

7,352

14,405

73,785

1Streamflow recharge considered only for the Madison and Minnelusa aquifers. Streamflow recharge in Subarea 9 was assumed to be zero based on assumptions by Carter and others (2001b). 2Total mean annual precipitation recharge by subarea was calculated as the sum of mean annual precipitation recharge for each aquifer within a subarea. 3Total mean annual recharge by subarea was calculated as the sum of mean annual precipitation and streamflow recharge for each aquifer within a subarea.

36 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Hydrologic Budgets 37 differentiated by aquifer. Recharge estimates from this study (table 11) also were compared, if appropriate, to estimates from Driscoll and Carter (2001) and Carter and others (2001a, 2001b). Total mean annual recharge for all aquifers in the study area for 1931–2022 was estimated as 278,900 acre-feet (acre-ft), with 205,100 acre-ft from precipitation recharge and 73,800 acre-ft from streamflow recharge (table 11). Mean annual precipitation recharge was greatest for the Madison (57,000 acre-ft) and Minnelusa (98,100 acre-ft) aquifers, which combined accounted for about 76 percent (or 155,100 acre-ft) of the total mean annual precipitation recharge (table 11). Mean annual precipitation recharge for the Deadwood, Minnekahta, Sundance, and Inyan Kara aquifers combined accounted for 24 percent (or 50,100 acre-ft) of the total mean annual precipitation recharge (table 11). Mean annual streamflow recharge, considered only for the Madison and Minnelusa aquifers, was about 73,800 acre-ft (table 11). Combined mean annual recharge was 228,900 for the Madison and Minnelusa aquifers (sum of mean annual precipitation and streamflow recharge in table 11), or about 82 percent of the total recharge in the study area. Total mean annual recharge for 1950–98 estimated by Driscoll and Carter (2001) could not be directly compared to results from this study because recharge to outcrops in Wyoming were excluded. Recharge estimates for the combined Madison and Minnelusa aquifers from this study were directly compared to estimates from Carter and others (2001a) and Driscoll and Carter (2001). Mean annual precipitation recharge for the Madison (57,000 acre-ft) and Minnelusa (98,100 acre-ft) aquifers for 1931–2022 from this study were 34 and 7 percent, respectively, greater than estimates from Carter and others (2001a). Driscoll and Carter (2001) estimated precipitation recharge to the combined Madison and Minnelusa aquifers as 144,500 acre-ft for the wetter period from 1950 to 1998, which was about 7 percent less than estimates of combined precipitation recharge in this study (155,100 acre-ft; table 11). Greater precipitation recharge estimates were expected for this study because the mean precipitation for 1999–2022 (21.16 inches; Palecki and others, 2021) was greater than the long-term mean precipitation from 1950 to 1998 presented in Driscoll and Carter (2001; 18.98 inches). Mean annual streamflow recharge for 1931–2022 was about 73,800 acre-ft (table 11), which was 9 percent greater than estimates by Carter and others (2001a; about

67,500 acre-ft) for 1931–98 and 4 percent greater than estimates by Driscoll and Carter (2001; 70,900 acre-ft) for 1950–98. Greater streamflow recharge was expected because streamflow increased in response to greater mean annual precipitation during 1999–2022. Carter and others (2001a) estimated mean annual recharge of 202,000 acre-ft for the combined Madison and Minnelusa aquifers, which was about 13 percent less than total recharge estimates in this study (228,900 acre-ft). Driscoll and Carter (2001) estimated combined recharge as 215,400 acre-ft or about 6 percent less than in this study. Precipitation and streamflow recharge varied among subareas 1–9 (fig. 10A; table 11) depending on the spatial variability of precipitation, outcrop surface area, and the distribution of streamflow loss zones. Precipitation recharge generally was greatest in the northern and western Black Hills (subareas 1–4 and 9; fig. 10A; table 11) where mean annual precipitation was relatively high (fig. 8) and outcrop areas were extensive for many aquifers (fig. 7). Mean annual precipitation recharge in subareas 1 (Spearfish area) and 9 (Jewel Cave area) combined accounted for 80 percent of the precipitation recharge in the study area. In contrast, precipitation recharge was lowest in the southern and eastern Black Hills (subareas 5–8; fig. 10A; table 11) because of lower mean annual precipitation (fig. 8) and, except for subarea 8 (Hot Springs area), limited outcrops of aquifers (fig. 7). Subarea 8 had extensive outcrops of the Madison and Minnelusa aquifers but received relatively little precipitation compared to subareas further north. Streamflow recharge also generally was greatest for subareas in the northern and western Black Hills (fig. 10A; table 11). Greater precipitation (fig. 8) and relatively high loss thresholds for many streams contributed to the relatively high streamflow recharge for subareas in the northern Black Hills. An exception was subarea 9 (Jewel Cave area) where Carter and others (2001b) noted precipitation predominantly infiltrates the extensive outcrops of the Madison and Minnelusa aquifers or evaporates before reaching any streams. Streamflow recharge was greatest in subarea 4 (Rapid City area; fig. 10A; table 11) and contributed to about 76 percent of total recharge in the subarea. Similarly, most of the total recharge was streamflow recharge for subareas along the eastern flank of the Black Hills (subareas 2–7). Streamflow recharge in subarea 1 also was relatively high but did not constitute most of the recharge in the subarea (fig. 10A).

38 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 A

Subarea 1: 127,178 acre-feet 4,906 2,622

Subarea 2: 28,047 acre-feet

5,321

580 2,311

13,232

Subarea 3: 12,237 acre-feet 141

1,243

395

1,262

12,452

601

26,227

4,322

14,244

6,420

62,418

2,142

3,981

1,276 1,366

Subarea 4: 31,264 acre-feet 211

592

Subarea 5: 10,279 acre-feet

569

169

227

739

2,318 2,749

Subarea 6: 6,221 acre-feet 71

407

292 235

1,089

999 718 7,044

23,825

Subarea 7: 3,235 acre-feet

5,056

293

Subarea 8: 10,154 acre-feet

Subarea 9: 50,315 acre-feet 11 (Deadwood)

456

410 5,480

2,228 202

1,736

1,090

2,642 19,375

157

423

355

1,296 2,649

279

23,949

827

EXPLANATION

Total mean annual recharge

Recharge, in acre-feet

Mean annual precipitation recharge, in acre-feet

Deadwood

Minnelusa

Sundance

Madison

Minnekahta

Inyan Kara

Mean annual streamflow recharge, in acre-feet

Subarea

Figure 10. Mean annual precipitation and streamflow recharge for the Deadwood, Madison, Minnelusa, Minnekahta, Sundance, and Inyan Kara aquifers in subareas 1–9. A, Pie charts showing the distribution of recharge in subareas 1–9 for each aquifer. Streamflow recharge was considered only for the Madison and Minnelusa aquifers and was separated from precipitation recharge for comparison. B, Mean total recharge (sum of precipitation and streamflow recharge) for subareas 1–9 on a logarithmic y-axis.

Hydrologic Budgets 39

Outflows—Artesian Springflow and Well Withdrawals Outflow components estimated for the hydrologic budget include artesian springflow and well withdrawals. Artesian springflow consists of springs discharging at the land surface from confined aquifers located downstream from loss zones, which are typically present at the periphery of the Black Hills. These springs are generally situated near or within outcrops of the Spearfish Formation and originate from the Madison or Minnelusa aquifers (Carter and others, 2001b). Some artesian springs, such as Cleghorn/Jackson Springs, are located within the outcrops of the Minnelusa Formation, where the Madison aquifer is confined by the Minnelusa Formation. Artesian springflow was estimated only for the Madison and Minnelusa aquifers. Well withdrawals include water pumped from wells, with water rights information gathered from the SDDANR (2024a) and Wyoming State Engineer’s Office (WYSEO, 2024a). These withdrawals were estimated by calendar year instead of water year, because most users report their water usage in calendar years.

Artesian Springflow Artesian springflow in the study area was estimated using similar methods as Carter and others (2001b) for the Madison and Minnelusa aquifers (appendix 3). Artesian springflow was assumed to be zero for all other aquifers. It is possible artesian springflow exists for one or more of the Deadwood, Minnekahta, Sundance, and Inyan Kara aquifers; however, information on possible springs and their discharge rates was unavailable and, therefore, was not estimated in this study. Mean annual springflow estimates were based on streamflow records from streamgages (fig. 11; table 12). The period of record and the methods used to estimate mean annual artesian springflow varied for each site and are discussed in appendix 3. Streamflow records at these streamgages were analyzed for the available period of record through 2022 using data from the USGS NWIS (USGS, 2024a). Annual streamflow and base flow estimates were determined using the USGS Groundwater Toolbox version 1.3.1 (Barlow and others, 2014; 2017). Base flow for this study was calculated using the base flow index (BFI) standard hydrograph-separation method (Barlow and others, 2014). Streamgages were assigned to a subarea based on location to estimate artesian springflow for each subarea budget (table 12).

Well Withdrawals Well withdrawals were determined for all aquifers monitored by State agencies in South Dakota and Wyoming, which included some aquifers that were not part of the hydrologic budget but were included to estimate the total mean annual well withdrawals in the study area. Regional

aquifers included in the hydrologic budget were the Deadwood, Madison, Minnelusa, Minnekahta, Sundance, and Inyan Kara. Additional aquifers for which well withdrawals were estimated include the crystalline core aquifer (consisting of Tertiary and Precambrian igneous and metamorphic rocks); an undifferentiated group of minor aquifers termed “other aquifers” within the Opeche Shale, Spearfish Formation, Unkpapa Sandstone, Newcastle Sandstone, and Pierre Shale; and Quaternary alluvial deposits. The following sections summarize the methods used to collect and analyze well withdrawal data for aquifers in the study area. Additionally, annual well withdrawal patterns from 2003 to 2022 in the study area and in each subarea are discussed.

Methods of Data Collection for Groundwater Permits and Well Withdrawals The process for estimating well withdrawals in the study area involved three steps. First, water rights from South Dakota and Wyoming were reviewed and downloaded to calculate the total annual volume of water allowed to be diverted from each aquifer in each subarea. Second, well withdrawal data were obtained from water systems, the SDDANR (2024a), and the WYSEO (2024a). In some instances, water users are not required to report well withdrawals and did not provide historical well withdrawal data; therefore, the third step was to synthesize well withdrawal data for these systems, which is described in the following sections. A well withdrawal dataset consisting of real and synthetic well withdrawal information was constructed from 2003 to 2022 using compiled well withdrawal datasets and synthetic data.

Water Rights and Permit Information Laws regarding water rights in South Dakota and Wyoming were reviewed before downloading permit information and estimating well withdrawals. A brief discussion of laws in each State is provided so that readers are aware of the uncertainty in well withdrawal estimates. In South Dakota, water users are required to obtain a water right permit for groundwater depending on the type of water use and if the requested maximum diversion rate exceeds a certain threshold. According to South Dakota Codified Law 46–1–6 (South Dakota State Legislature, 2024a), the only type of water use that does not require a permit is domestic, unless one of the following apply: the water use exceeds 18 gallons per minute (gal/min); irrigation of noncommercial land exceeds 1 acre in size; or the peak pumping rate exceeds 25 gal/min. Additionally, water distribution systems using 18 gal/min or less do not need to apply for a water right permit for groundwater. In Wyoming, all water users intending to utilize groundwater must obtain a permit from the State Engineer before construction and development (Wyoming Statutes Title 41, Chapter 3, Provision 930; Wyoming State Legislature, 2024). Well withdrawals for users in South Dakota with systems using 18 gal/min or less

40 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 103°20'

103°40'

104°

Nisland

06433000

Belle Fourche

Fruitdale

Spearfish

Whitewood

Sundance

Central City

44° 20'

Drainage basins used to estimate artesian springflow for the Deadwood aquifer

Sturgis

Deadwood

Tilford

Lead

Little Elk Creek basin

06424000

CROOK COUNTY

LAWRENCE COUNTY WESTON COUNTY

06423010

PENNINGTON COUNTY

44°

Rapid City Rapid 06413650 Valley

06412900

Colonial Pine Hills

Hill City

Keystone 06392950

06404000

Hill View Heights

Custer

CUSTER COUNTY

5 Hermosa 06406000

06404998

43° 40'

Box Elder

06413800

06412500

Fairburn

Pringle 06402470

43° 20'

WYOMING SOUTH DAKOTA

NIOBRARA COUNTY

Buffalo Gap

Hot Springs 06402000 432013103332200

432012103331100

06400497

Edgemont FALL RIVER COUNTY

Base modified from U.S. Geological Survey digital data, various scales Universal Transverse Mercator, zone 13 north North American Datum of 1983 (2011)

0 0

5 5

10 10

Meadow Creek basin Spearfish Creek basin Minnelusa Formation

Blackhawk

Johnson Siding 06413600

104°20'

06425100

Piedmont Summerset 06422500

Subareas from Carter and others (2001b)—Red number is the subarea number Headwater recharge area used to estimate headwater springflow

MEADE COUNTY

St. Onge 06431500

44° 40'

Vale

06432020

Beulah

EXPLANATION

Newell

BUTTE COUNTY

20 MILES

20 KILOMETERS

Figure 11. U.S. Geological Survey streamgages used for estimating artesian springflow.

Madison Limestone Deadwood Formation Reservoirs and lakes from National Hydrography Dataset (U.S. Geological Survey, 2024c) Streams from National Hydrography Dataset (U.S. Geological Survey, 2024c) U.S. Geological Survey streamgage—Number is the site identification number from the National Water Information System (U.S. Geological Survey, 2024)

Table 12. Site information for streamgages and miscellaneous-record streamgages used for estimating mean annual artesian springflow. [NWIS, National Water Information System; ID, identification; WY, water year; ft3/s, cubic feet per second; BFI, base flow index; --, not applicable or no data]

Name Redwater River

NWIS ID for site used in calculating springflow

Budget subarea

06431500 and 06433000

Period of record (WY) available and used for analysis 1947–2022

Mean BFI estimated base flow (ft3/s)

Mean BFI

Mean annual streamflow, if applicable (ft3/s)

Mean annual artesian springflow (ft3/s)

103.6

Mean annual artesian springflow (acre-ft) 75,002

Subarea mean annual artesian springflow (ft3/s) 2114.5

Spearfish Creek

06431500 and 06432020

1989–98

10.9

7,891

Elk Creek

06424000 and 06425100

1992–2020

6.1

4,416

6.1 229.5

Jackson and Cleghorn Springs

06412500 and 06412900

1988–94

23.6

17,085

Other Rapid City springs

06413600, 06413650, and 06413800

1991–96, 1988–2002, 1988–90, respectively

5.4

3,909

Boxelder Creek

06423010 and 06422500

1978–2010

0.47

0.15

0.5

362

Battle Creek

06404000, 06404998, and 06406000

1976–2022

8.2

0.78

17.4

8.2

5,936

8.2

Beaver Creek above Buffalo

06402470

1991–97

9.9

0.98

10.2

9.9

7,167

9.9

Cascade Springs

06400497

1976–95

19.4

0.99

19.5

19.4

14,045

248.1

Springs near Cascade1

432013103332200 and 432012103331100

September 12, 1996, and March 6, 2024

4.3

3,113

Fall River at Hot Springs

06402000

1939–46; 1948–2020

24.4

0.96

25.3

24.4

17,665

Stockade Beaver Creek, near Newcastle, Wyo.

06392950

1975–81; 1992–2019

13.2

0.9

14.1

13.2

9,556

13.2

229.5

166,149

Total

1Measurements from 1996 and 2024 were used for analysis because of the infrequent measurements, even though 2024 is outside the study period. 2Value indicates the total springflow within the subarea.

Hydrologic Budgets 41

42 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 were not included in analyses because no information was available on the number of active wells and most wells did not specify the aquifer in which it was completed. It is likely well withdrawals from smaller systems constitutes a relatively small proportion of the total well withdrawals but may be locally important in some areas of the Black Hills. Groundwater permit and license information were obtained from the SDDANR water rights database (SDDANR, 2024a) and the WYSEO permit database (WYSEO, 2024a). The criteria used for downloading water rights permit data include (1) permits with a priority date on or before December 31, 2022; (2) only permits from groundwater sources; (3) only permits within the study area; and (4) the status of the permit was “Licensed,” “Permitted,” or “Future use” in the SDDANR database and “Adjudicated” in the WYSEO database. Cancelled and unused water rights were not included, although it is acknowledged that some cancelled permits may have been active during the period of investigation. Location information provided in each permit was used to exclude those outside the study area and to separate water rights into the nine subareas constituting the study area. In total, the study area included 808 total active and future use permits (table 13), with 796 in South Dakota and 12 in Wyoming. Permits from SDDANR and WYSEO databases contain diversion rates (maximum pumping rate), and, if specified, the maximum annual diversion volume. The diversion rate, typically given in cubic feet per second or gallons per minute,

was used to calculate the maximum annual diversion volume for permits with unspecified annual diversion volumes by converting the given rate into an annual volume. For example, the maximum annual diversion volume of a water right with a maximum diversion rate of 1.0 ft3/s would equal about 724 acre-ft of water annually. The maximum annual diversion volume was summed for each aquifer in each subarea to obtain the total amount of appropriated water by aquifer in each subarea. The SDDANR and WYSEO permit data provide the type(s) of water use (municipal, irrigation, and so forth) for each permit. Types of water-use categories included commercial, domestic, fish and wildlife propagation, geothermal, groundwater remediation, industrial, institutional, irrigation, municipal, recreation, rural water system, suburban housing development, and water distribution system. Some permits had two or more types of water use that were revised to one type to simplify analyses that determined water use by category. The major use was selected by inspecting permit documentation to determine which type of use likely required the greatest annual volume. For example, if a groundwater permit for a year-round cattle operation listed “commercial” and “domestic” as types of water use, then it was assumed the cattle required most of the water use and the water-use type was simplified to “commercial.” In total, 104 of the 808 permits specified more than one type of use and were revised to one use type.

Well Withdrawal Data Collection Table 13. The total number of active permits and active appropriated annual volume by aquifer for water rights in the study area as of 2022. Aquifer (fig. 1) Crystalline

Number of permits1 182

Appropriated volume1 (acre-feet) 14,788

Deadwood

3,203

Madison2

165

72,000

Minnelusa

191

31,285

Minnekahta

3,826

Inyan Kara

112

12,074

Sundance

185

Alluvial

33,833

Other3

5,584

Total

808

176,777

1Includes future use permits and values are rounded to the nearest whole number. 2Appropriated volume specified separately for the Madison and Minnelusa aquifers for permit 1709-1. The permit was counted with the Minnelusa aquifer because the permit specified more appropriated volume for the Minnelusa aquifer than the Madison aquifer. 3Includes minor aquifers within the Opeche Shale, Spearfish Formation, Unkpapa Sandstone, Newcastle Sandstone, and Pierre Shale.

Well withdrawal data were obtained from water systems, the SDDANR (Adam Mathiowetz, SDDANR, written commun., 2024), and the WYSEO (WYSEO, 2024b). USGS staff contacted operators of water systems in the Black Hills area inquiring about obtaining withdrawal records spanning as far back as possible. Most system operators provided either monthly or annual withdrawal data for the last 5 to 10 years; however, some water users provided withdrawal records into the 1980s and 1990s. The most complete withdrawal record was provided by Rapid City, the largest city and greatest water user in the Black Hills, which provided annual consumption back to 1950. The SDDANR provided annual well withdrawal data from 2003 to 2022 for nonirrigation purposes from certain water systems and individual users (Adam Mathiowetz, SDDANR, written commun., 2024). Additionally, the SDDANR provided annual well withdrawal data from 1994 to 2022 for irrigation purposes (Nakaila Steen, SDDANR, written commun., 2024). Well withdrawal data for water users in Wyoming were downloaded from WYSEO Water Usage Data Across Wyoming database (WYSEO, 2024b). The timeframe for well withdrawal data collected for Wyoming was from 2016 to 2022. All available annual well withdrawal data are provided in the data release accompanying this report (Medler and others, 2025).

Hydrologic Budgets 43

Methods for Creating the Well Withdrawal Dataset for 2003–22 The well withdrawal dataset for 2003–22 was generated using annual well withdrawal data and by synthesizing annual well withdrawals for permits. Annual well withdrawal data provided by water systems, SDDANR, and WYSEO were applied to their respective permits to inventory how many permits would require synthetic data and to help calculate a multiplier that will be discussed later in this section. The year of the priority date—the date an application was filed— provided in each permit was used to determine the starting year each permit became active regardless of the month and day. In total, partial or complete well withdrawal records were provided for 298 of 808 permits (about 37 percent; table 14). Permits with partial well withdrawal records accounted for 35 of those 298 permits and the years with missing data were estimated as the mean annual well withdrawals only if 3 or more years of data were available. Synthetic annual well withdrawal data were generated for the remaining 510 permits using three methods. The well withdrawal dataset, including both data collected from users or State agencies and synthetic data for 2003–22, is provided in the data release accompanying this report (Medler and others, 2025).

The first method involved inspecting water permit documentation (SDDANR, 2024a) and well withdrawal records from SDDANR (Adam Mathiowetz, SDDANR, written commun., 2024) to determine if permits were actively diverting water. Annual well withdrawals for 2003–22 were excluded for permits meeting specified criteria. The criteria included (1) a type of “future use,” (2) standby wells only used for emergency purposes, (3) permits that added an additional diversion point but no increase of the diversion rate or volume, and (4) permits with well withdrawals that were combined with or indistinguishable from other permits. Future use permits were excluded because the permits do not become consumptive until the permittee receives approval from the SDDANR. Standby wells used for emergency purposes were excluded because annual well withdrawals for 2003–22 averaged to nearly zero for water systems that provided well withdrawal data for standby wells. Permits for adding an additional point of diversion or changing a point of diversion were excluded only if the diversion rate or volume of the original permit did not change. Well withdrawal data provided by some water users and the SDDANR grouped well withdrawals from multiple permits into a single permit. In these instances, the well withdrawals were either assigned to the permit with the greatest diversion rate or volume if

Table 14. Summary of the methods used to construct the well withdrawal dataset for 2003–22 for subareas 1–9 from Carter and others (2001b). Number of permits Partial or complete records

Percent of total

Extrapolated values4

Multiplier5

Total by subarea

Percent of partial or complete records6

Partial1

Complete2

Inactive (zero well withdrawals)3

167

122

124

241

Total

263

400

808

Subarea

Percent of synthetic records7

1Missing data for partial records were synthesized by replacing missing values with the mean annual use only if three of more years of data were available. 2Complete well withdrawal records with no synthetic data. 3Water permits or well withdrawal records indicated the well either has not yet been drilled or used during 2003–2022. 4Well withdrawal values were extrapolated to annual well withdrawal estimates using daily withdrawal estimates provided in drinking water quality records

from the South Dakota Department of Agriculture and Natural Resources (2024b). 5A multiplier of 0.5 was multiplied by the maximum annual appropriated volume of each permit. The value of 0.50 was the mean ratio of mean annual well

withdrawals for 2003–2022 to the maximum appropriated volume for 44 permits within the study area. 6Sum of partial or complete records and inactive records in each subarea divided by the total permits in each subarea. 7Sum of permits with extrapolated values and permits for which the multiplier was used in each subarea divided by the total permits of each subarea.

44 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 the aquifer for all grouped permits was the same; otherwise, if the aquifer was different among the permit, then the well withdrawals were divided evenly among each permit. In total, 42 of the 510 permits (about 8 percent) met the criteria for exclusion (table 14). The second method involved estimating mean annual well withdrawals for public water systems from mean daily well withdrawal rates provided in drinking water quality reports (SDDANR, 2024b). Mean daily well withdrawal rates in drinking water quality reports were calculated by the SDDANR using annual well withdrawal totals provided by the water system (Mark McIntire, SDDANR, written commun., 2024). The mean annual well withdrawal estimated from daily rates was applied to each year from 2003 to 2022. The year of the priority date in each permit was used to determine the length of the annual well withdrawal record for each permit. In total, synthetic well withdrawal data were generated for 68 of 510 permits (about 13 percent) using the mean daily rate from drinking water quality reports (table 14). The third method was applied to permits for water users not required to report well withdrawal data to the SDDANR or to publish drinking water quality reports. The third method involved multiplying the maximum annual diversion volume either specified in permits or calculated using maximum diversion rates by a multiplier. The SDDANR uses a multiplier of 0.6 (60 percent) to estimate well withdrawals for permits not required to report withdrawals as part of the approval process for new permits (Adam Mathiowetz, SDDANR, written commun., 2024). However, a new multiplier of 0.5 was calculated using annual well withdrawal data and maximum annual appropriated volumes for selected water permits. Permits were selected if they were within the study area and had at least 3 years of annual well withdrawal data. In total, 44 permits met the specified criteria. The multiplier was calculated by dividing the mean annual withdrawal of each permit from 2003 to 2022 by the maximum appropriated annual volume specified by each permit. The water use type of permits used in calculating the new multiplier included 15 commercial, 10 municipal, 6 suburban housing development, 6 water distribution system, 5 rural water system, 1 domestic, and 1 industrial. It is possible the new multiplier may not accurately calculate the fraction of actual well withdrawals by permitted volume for certain water use type categories that were underrepresented in calculations. In total, synthetic well withdrawal data were generated for 400 of the 510 permits (about 78 percent) using the multiplier of 0.5 (table 14).

Artesian Springflow and Annual Well Withdrawals Artesian springflow and annual well withdrawals were estimated for the study area and for subareas 1–9. Summary statistics were not calculated for artesian springflow because the period of record was inconsistent between sites (table 12). Summary statistics were calculated for annual well

withdrawals by subarea and aquifer. Statistical calculations included values of zero annual well withdrawals and synthetic withdrawal estimates. Zero values were included in statistical calculations because they represent true well withdrawals. Synthetic withdrawal estimates were included to provide the best estimate possible; however, statistical estimates of annual withdrawals may not represent the true withdrawals. Total mean annual artesian springflow in the study area was estimated as 229 ft3/s (or 166,100 acre-ft) for the Madison and Minnelusa aquifers (table 12). Artesian springflow ranged from 0.5 ft3/s (360 acre-ft) along Boxelder Creek to 103.6 ft3/s (75,000 acre-ft) along the Redwater River (table 12). Artesian springflow and well withdrawals estimated for this study were compared to results from Carter and others (2001b) and Driscoll and Carter (2001). Artesian springflow estimated in this study (166,100 acre-ft) was about 21 and 36 percent greater than mean annual artesian springflow estimated by Carter and others (2001b; 136,800 acre-ft) and Driscoll and Carter (2001; 122,400 acre-ft), respectively. Greater artesian springflow was expected because the precipitation totals were relatively high for the 23 years of additional data added for 1999–2022. Additionally, estimates of artesian springflow for this study likely were biased to wetter conditions because calculations generally included years with relatively high precipitation from the 1970s to 2022 and did not capture the drier conditions from the 1930s to the 1960s. Therefore, artesian springflow may be overestimated compared to other budget components. Artesian springflow also was estimated for each subarea. Artesian springflow was observed in all subareas except subarea 2 (Sturgis area; table 12). For subareas containing artesian springs, springflow ranged from 6.1 ft3/s in subarea 3 (Piedmont area) to 114.5 ft3/s in subarea 1 (Spearfish area; table 12). Mean annual artesian springflow was highest in subareas 1, 4, and 8 (table 12) where large artesian springs, such as those along Spearfish Creek and Redwater River (subarea 1; Spearfish area), Jackson and Cleghorn Springs (subarea 4; Rapid City area), and Cascade Springs (subarea 8; Hot Springs area), contribute to streamflow in the study area’s largest perennial streams (Spearfish Creek, Redwater River, Rapid Creek, and Fall River). Mean annual artesian springflow was lowest in subareas 3, 5 (Hermosa area), and 7 (Wind Cave area) where springs contribute to relatively small streams (Elk Creek, Battle Creek, and Beaver Creek). Total annual well withdrawals (sum of well withdrawals for all aquifers) varied annually but no long-term patterns were observed (fig. 12). Mean total annual well withdrawals for 2003–22 in the study area were about 50,000 acre-ft, which was about 33 percent higher than groundwater-withdrawal estimates from 1995 and 2000 (Amundson, 1998, 2002) during the BHHS. Annual well withdrawal estimates ranged from about 45,100 acre-ft in 2019 to about 52,800 acre-ft in 2017 (fig. 12; table 15). Variability of the total annual well withdrawals was attributed to climate conditions, which were evaluated by determining annual precipitation totals for climate stations in the study area (National Oceanic and

Hydrologic Budgets 45 Table 15. Summary statistics of total annual well withdrawals for each aquifer for 2003–22. Aquifer Crystalline

Mean

Standard deviation

Minimum

25th percentile

Median

75th percentile

Maximum

4,949

151

4,621

4,902

4,944

5,071

5,153

Deadwood

1,311

1,230

1,254

1,305

1,340

1,444

Madison

16,534

2,292

12,139

14,720

16,651

18,289

20,047

Minnelusa

9,137

984

7,188

8,515

8,940

9,865

10,618

Minnekahta

1,268

1,136

1,230

1,280

1,308

1,384

Sundance

Inyan Kara

3,137

2,983

3,100

3,139

3,187

3,301

Other1

2,462

115

2,265

2,386

2,457

2,518

2,737

Alluvial

11,184

2,701

7,644

7,960

12,646

12,970

15,232

Total

49,982

2,124

45,128

48,389

50,137

51,620

52,837

1Includes minor aquifers within the Opeche Shale, Spearfish Formation, Unkpapa Sandstone, Newcastle Sandstone, and Pierre Shale.

Atmospheric Administration, 2024; fig. 12). Total annual well withdrawals generally increased during dry conditions (below normal precipitation) and decreased during wet conditions (above normal precipitation; fig. 12). For example, the lowest annual well withdrawals occurred during 2019, which was the wettest year on record (National Oceanic and Atmospheric Administration, 2024). Conversely, the greatest annual well withdrawals occurred during periods of below normal precipitation from 2003 to 2005 and 2016 to 2017 (fig. 12). Other than annual variations from precipitation variations, no long-term patterns corresponding to population increases were observed (fig. 12) despite the study area population increasing by about 39 percent from 2000 to 2022 (table 1). Annual well withdrawal variations and mean annual withdrawals were greatest for the Madison, Minnelusa, and alluvial aquifers (fig. 12; table 15). Annual withdrawal variations for the Madison and Minnelusa aquifers generally correlated with total annual withdrawals and annual climate variations except for a period of abnormally high withdrawals from the Madison aquifer from 2006 to 2012 (fig. 12). This period coincided with abnormally low withdrawals from alluvial aquifers (fig. 12). Water system operators for Rapid City, S. Dak., were performing maintenance on their system that withdraws water from an alluvial aquifer and were supplementing by withdrawing water from wells completed in the Madison aquifer (City of Rapid City, written commun., 2024). Other than 2006 to 2012, annual well withdrawals were relatively consistent for alluvial aquifers (fig. 12). Mean annual withdrawals for the Madison and Minnelusa aquifers for 2003–22 were 16,500 and 9,100 acre-ft, respectively (table 15). Combined mean annual well withdrawals for the Madison and Minnelusa aquifers (25,600 acre-ft) accounted for 51 percent of the total mean annual withdrawals for aquifers in table 15. Carter and others (2001b) and Driscoll and Carter (2001) estimated well withdrawals totaling about 20,300 acre-feet per year from the Madison and Minnelusa aquifers, which was 5,300 acre-ft (or

about 26 percent) less than estimates provided in this study (table 15). Mean annual withdrawals for alluvial aquifers were 11,200 acre-ft between 2003 and 2022 (table 15). Well withdrawals for alluvial aquifers were not previously estimated by the BHHS and, therefore, were not comparable to previous estimates. Annual well withdrawals for the crystalline core, Deadwood, Minnekahta, Sundance, Inyan Kara, and “other” aquifers were relatively consistent from 2003 to 2022 (fig. 12). Withdrawals for these aquifers did not correlate with precipitation patterns or population increases in the study area because synthetic well withdrawal data were generated for more than one-half of the permits used to estimate well withdrawals. Mean annual well withdrawals for each of these aquifers were less than 5,000 acre-ft each (table 15). Well withdrawals in this study were 1.4, 1.3, 1.8, and 2.2 greater than withdrawals in Driscoll and Carter (2001) for the crystalline core, Deadwood, Minnekahta, and Inyan Kara aquifers, respectively. Withdrawals for the Sundance aquifer were 10.6 times smaller in this study than in Driscoll and Carter (2001). Annual well withdrawal statistics also were computed for each aquifer in subareas 1–9 (table 16). Mean annual well withdrawals in subareas 1–9 ranged from about 600 acre-ft in subarea 9 (Jewel Cave area) to about 19,900 acre-ft in subarea 4 (Rapid City area; table 16). Generally, subareas 1–4, located in the northern and northeastern parts of the Black Hills, had the highest well withdrawals, whereas subareas 5–9 in the southern and southeastern Black Hills had the lowest well withdrawals. Mean annual well withdrawals were greatest in subareas 1 (Spearfish area) and 4 (Rapid City area), which corresponds with the relatively large population in both subareas (table 1). In contrast, rural subareas with smaller populations, such as subareas 6 (Custer area) and 9 (Jewel Cave area; table 1) reported the least annual well withdrawals.

46 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 55,000

27,500

Total

50,000

Total annual well withdrawals, in acre-feet

45,000

Madison 17,500

40,000

Alluvial

35,000

12,500

Minnelusa 7,500

Crystalline 30,000

Inyan Kara 2,500

Deadwood Minnekahta

2022

2021

2020

2019

2018

2017

2016

2015

2014

0 2013

2012

2010

2009

2008

2007

2006

2005

2004

2003

2011

Sundance

25,000

Year

EXPLANATION Precipitation below annual normal Precipitation exceeding annual normal

Total withdrawals

Madison aquifer

Inyan Kara aquifer

Crystalline aquifer

Minnelusa aquifer

Sundance aquifer

Deadwood aquifer

Minnekahta aquifer

Alluvial aquifers

Figure 12. Total annual well withdrawals and annual well withdrawals for each aquifer for 2003–22.

Annual well withdrawals by aquifer, in acre-feet

22,500

Hydrologic Budgets 47 Table 16. Summary statistics for annual well withdrawals by subarea and aquifer for 2003–22. Summary statistic (acre-feet) Subarea

Aquifer

Mean

Standard deviation

Minimum

25th percentile

Median

75th percentile

Maximum

Subarea total mean annual well withdrawals 14,549

Crystalline

239

Deadwood

497

484

515

540

Madison

5,240

334

4,641

5,022

5,265

5,483

5,770

Minnelusa

3,043

666

1,771

2,675

2,920

3,702

4,275

Minnekahta

965

843

938

975

993

1,091

Sundance

Inyan Kara

854

848

852

856

887

Other1

2,226

127

2,065

2,134

2,217

2,279

2,538

Alluvial

1,475

1,373

1,459

1,466

1,482

1,642

Crystalline

927

887

921

931

940

965

Deadwood

138

Madison

1,591

196

1,233

1,462

1,575

1,718

1,996

Minnelusa

796

110

585

714

785

878

953

Minnekahta

Sundance

Inyan Kara

518

456

500

513

529

592

Other1

Alluvial

138

132

133

138

191

Madison

192

126

147

161

195

366

Minnelusa

1,216

1,106

1,200

1,206

1,221

1,327

Minnekahta

Inyan Kara

383

214

384

398

411

447

Other1

115

159

Alluvial

134

135

Crystalline

1,996

1,862

1,938

1,970

2,060

2,200

Deadwood

681

621

645

691

699

769

Madison

8,053

2,164

4,339

6,477

7,538

10,201

11,499

Minnelusa

3,879

352

3,433

3,576

3,831

4,133

4,600

Minnekahta

227

223

224

227

229

233

Inyan Kara

647

616

625

637

654

718

Other1

Alluvial

4,407

2,813

807

819

5,956

6,383

8,258

Crystalline

707

668

696

710

721

752

Deadwood

Madison

340

206

326

358

378

404

Minnelusa

Inyan Kara

211

178

187

189

209

339

Crystalline

877

801

854

871

912

960

Madison

Minnelusa

Inyan Kara

4,157

2,084

19,912

1,343

877

Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Table 16. Summary statistics for annual well withdrawals by subarea and aquifer for 2003–22.—Continued Summary statistic (acre-feet) Subarea

Aquifer

Mean

Standard deviation

Minimum

25th percentile

Median

75th percentile

Maximum

Subarea total mean annual well withdrawals 4,300

Crystalline

150

136

154

Madison

342

Minnelusa

Inyan Kara

Alluvial

4,014

3,982

4,012

4,043

4,086

Crystalline

Madison

598

173

433

449

495

737

963

Minnelusa

136

107

116

131

147

197

Minnekahta

Inyan Kara

366

354

370

455

Other1

Alluvial

1,015

225

653

830

1,052

1,150

1,375

Deadwood

Madison

468

130

287

301

464

556

715

Inyan Kara

2,185

572

1Includes minor aquifers within the Opeche Shale, Spearfish Formation, Unkpapa Sandstone, Newcastle Sandstone, and Pierre Shale.

The amount of water withdrawn from each aquifer varied by subarea but generally was highest for the crystalline core, Madison, Minnelusa, and alluvial aquifers (table 16). The crystalline core aquifer was most used in subareas 2 (Sturgis area) and 4 (Rapid City area), with mean annual withdrawals of about 900 and 2,000 acre-ft, respectively. The crystalline core aquifer contributed to about 53 and nearly 100 percent of the total withdrawals of all aquifers in subareas 5 (Keystone area) and 6 (Custer area; table 16). The Madison and Minnelusa aquifers were the most used in subarea 4, with mean annual withdrawals of about 8,100 acre-ft and 3,900 acre-ft, respectively (table 16). Well withdrawals also were relatively high for the Madison and Minnelusa aquifers in subarea 1, with mean withdrawals of about 5,200 and 3,000 acre-ft, respectively (table 16). Alluvial aquifers were most used in subareas 4 and 7 (Buffalo Gap area) with mean withdrawals of 4,400 and 4,000 acre-ft, respectively.

Storage Considerations To calculate net groundwater outflow (inflows minus outflows) in equation 2 like Carter and others (2001b), the assumption of a net zero change of storage was needed for the period of investigation from 1931 to 2022. Carter and others (2001b) used hydrographs of the Madison and Minnelusa aquifers and recharge estimates to assume zero storage change for their selected period of investigation from 1987 to 1996. Water-level datasets for hydrographs of the Madison and

Minnelusa were not available before the 1960s and generally the datasets were most complete for 1990–2022; therefore, a different technique was needed to simulate water levels before the 1960s. Annual precipitation data for the study area was used to construct a curve representing the cumulative difference between each year’s annual precipitation value and the long-term mean annual precipitation from 1931 to 2022 (departure from mean annual precipitation; fig. 5). This curve can be used as a proxy for water-level changes in aquifers if correlation exists with hydrographs. Storage considerations were evaluated by comparing hydrographs to the cumulative departure from long-term mean annual precipitation curve (hereafter referred to as “cumulative departure curve”). Additionally, the cumulative departure curve was used to identify three time periods when recharge estimates were either decreasing, constant, or increasing that were evaluated to verify comparisons of hydrographs and the cumulative departure curve. Observation wells used to evaluate correlation between water-level changes and the cumulative departure curve were selected based on several criteria. Observation well data were downloaded from the SDDANR (2024c) observation well database and the USGS NWIS database (USGS, 2024a). Wells were selected only if they were within subareas 1–9 and completed in the Deadwood, Madison, Minnelusa, Minnekahta, and Inyan Kara aquifers. Additionally, water-level records had to be 20 years or greater so that long-term comparisons could be made. In total, 72 observation

Hydrologic Budgets 49 wells met the selection criteria (table 17). Each observation well had continuous and (or) discrete water-level records with varying periods of record that ranged from 20 to 65 years (table 17). The oldest water-level records were from the 1960s; however, the completeness of water-level records varied by well. The mean annual water level (mean of water levels within a calendar year) was calculated for each observation well to show annual patterns that were compared to annual patterns for the cumulative departure curve. The Pearson correlation coefficient was calculated to evaluate the linear relation between each hydrograph and the cumulative departure curve. Additional information on the Pearson correlation coefficient, including mathematical derivations and descriptions of the method, are summarized in Helsel and others (2020). Correlation coefficients range from −1 (perfect negative correlation) to 1 (perfect positive correlation), where negative values indicate negative correlation, a value equal to 0 indicates no correlation, and positive values indicate positive correlation. Additionally, larger absolute values indicate stronger correlation and smaller absolute values indicate weaker correlation. Correlation was considered weak if correlation coefficients were less than 0.4 and moderate to strong if correlation coefficients were greater than or equal to 0.4. The mean correlation coefficient was greater than zero for all aquifers and ranged from 0.38 for the Deadwood aquifer to 0.64 for the Minnelusa aquifer (table 18). Correlation was moderate to strong for the Madison, Minnelusa, and Minnekahta aquifers and weak for the Deadwood and Inyan Kara aquifers (table 18). Hydrographs displaying the best correlation with the cumulative departure curve were selected for each aquifer to discuss general patterns for various timescales (fig. 13). Water-level records for most wells were most complete for 1990–2022 when water levels in all aquifers generally increased because of above normal precipitation. Similar patterns were observed for all aquifers—water levels increased during the 1990s, decreased during the early 2000s, and increased during the 2010s and 2020s (fig. 13). These patterns resembled the cumulative departure curve, which was expected because of the strong correlation coefficients (fig. 13). Some wells, such as LA–63A for the Minnelusa aquifer, had water-level records back to the 1960s, which were useful for determining patterns before 1990. Between 1969 and 1990 water levels at well LA–63A followed patterns of increasing and decreasing precipitation values from the cumulative departure curve (fig. 13C). Of the 72 total wells evaluated, negative correlation coefficients were observed for 5 wells and weak correlation coefficients (values less than 0.4) were observed for 13 wells (table 18). Negative correlation was observed for wells with decreasing water levels during the 2010s and 2020s when

the cumulative departure curve increased. It is possible water-level decreases were caused by nearby pumping wells, which was true for at least one well (PE–65A) completed in Madison aquifer that was within 1 mile of an active pumping well in Rapid City, S. Dak. Hydrographs for wells with weak correlation followed the same general increasing and decreasing patterns as the cumulative departure curve; however, the maximum water level for 11 of the 13 wells was greater in the early 2000s than in 2022, which did not match the cumulative departure curve. It is possible varying recharge mechanisms may be responsible for the discrepancy, such as a greater percentage of recharge coming from streamflow rather than precipitation or greater influences from regional groundwater flow. Correlation between hydrographs and the cumulative departure curve were verified using combined recharge estimates for 1931–2022 (fig. 13). The cumulative departure curve was used to identify a period of decreasing water levels (decreasing storage) from 1931 to 1964, a period of relatively stable water levels (zero storage change) from 1965 to 1986, and a period of increasing water levels (increasing storage) from 1987 to 2022 (fig. 13). Recharge mechanisms likely have not changed since the 1930s, so it was assumed that recharge estimates for each period were comparable. The period from 1931 to 1964 was considered a deficit for recharge because the cumulative departure curve decreased throughout nearly the entire period (fig. 13). Near zero storage change was considered for the period from 1965 to 1986 when the cumulative departure curve was relatively stable with no long-term increasing or decreasing precipitation patterns. A surplus of recharge was observed for the period from 1987 to 2022, which was confirmed by hydrographs (fig. 13). Combined mean annual recharge was calculated for each period and compared to combined mean annual recharge for 1931–2022. Combined mean annual recharge for 1965–86 was 220,861 acre-ft, which was about 7,890 acre-ft (or 3.5 percent) less than the combined mean annual recharge for 1931–2022 (228,751 acre-ft; table 1.3). The relatively small difference between the combined mean annual recharge for 1931–2022 and combined mean annual recharge for 1965–86 was expected because hydrographs showed that storage change was minimal. The absolute difference between combined mean annual recharge for 1931–2022 and combined mean annual recharge for 1931–64 (171,576 acre-ft) and 1987–2022 (287,571 acre-ft) were approximately equal at about 57,175 (deficit) and 58,820 (surplus) acre-ft, respectively. The combined mean annual recharge values for 1931–64 and 1987–2022 verified that storage change was minimal between 1931 and 2022 because their recharge values were nearly equal in magnitude but opposite in sign (negative for 1931–64 and positive for 1987–2022).

50 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 Table 17. Observation wells within the study area selected for analysis with site information, length of the water-level record, and Pearson correlation coefficient. [NAVD88; North American Vertical Datum of 1988; SDDANR, South Dakota Department of Agriculture and Natural Resources; USGS, U.S. Geological Survey]

Agency

Aquifer

Latitude (decimal degrees)

Longitude (decimal degrees)

Elevation (feet above NAVD88)

CU–83A

SDDANR

Minnelusa

43.838849

−103.266754

CU–83B

SDDANR

Inyan Kara

43.829935

CU–83C

SDDANR

Inyan Kara

CU–91A

SDDANR

CU–91B

SDDANR

CU–93A CU–93B

Well name or site number

Period of record

Correlation coefficient

3,478.36

1983–84; 1990–2022

0.46

−103.238026

3,368.43

1983–85; 1989–2022

−0.18

43.781713

−103.218623

3,507.15

1983–84; 1990–2022

0.31

Madison

43.520900

−103.421078

3,647.14

1991–2022

0.86

Minnelusa

43.520850

−103.421038

3,647.00

1991–2022

0.60

SDDANR

Madison

43.730877

−103.339034

3,860.00

1993–2022

0.26

SDDANR

Minnelusa

43.730869

−103.339038

3,860.00

1993–2022

0.24

CU–93C

SDDANR

Madison

43.781386

−104.039946

4,660.00

1994–2008; 2014–22

0.81

CU–93D

SDDANR

Minnelusa

43.783763

−104.037716

4,660.00

1994–2007; 2014–22

0.13

CU–95A

SDDANR

Madison

43.588131

−103.895091

4,250.00

1995–2022

0.78

CU–95B

SDDANR

Minnelusa

43.588133

−103.895094

4,250.00

1995–2022

0.80

CU–96A

SDDANR

Minnekahta

43.520924

−103.421046

3,640.00

1997–2022

0.50

FR–92A

SDDANR

Madison

43.447585

−103.642425

4,175.55

1992–2022

0.82

FR–94A

SDDANR

Minnelusa

43.429354

−103.697793

4,172.00

1995–2022

0.75

FR–95A

SDDANR

Madison

43.434152

−103.499670

3,730.00

1996–2022

0.76

FR–95B

SDDANR

Minnelusa

43.434153

−103.499660

3,730.00

1996–2022

0.86

FR–95C

SDDANR

Inyan Kara

43.298523

−103.392596

3,220.00

1995–2022

0.45

LA–62A

SDDANR

Minnelusa

44.574649

−103.846960

3,210.00

1962–2015; 2018–22

0.46

LA–63A

SDDANR

Minnelusa

44.395107

−103.587671

3,880.00

1963; 1969–2022

0.94

LA–86A

SDDANR

Minnelusa

44.518018

−103.910283

3,676.92

1990–2022

0.90

LA–86B

SDDANR

Minnekahta

44.518021

−103.910285

3,676.20

1990–2022

0.44

LA–86C

SDDANR

Minnelusa

44.429055

−103.577191

3,629.31

1990–2022

0.88

LA–87A

SDDANR

Madison

44.517789

−104.007069

3,669.68

1990–2022

0.73

LA–87B

SDDANR

Minnelusa

44.517778

−104.007103

3,668.50

1990–2022

0.55

LA–88A

SDDANR

Minnelusa

44.476353

−103.729516

3,678.00

1990–2022

0.90

LA–88B

SDDANR

Minnelusa

44.481719

−103.848504

3,725.00

1990–2022

0.81

LA–88C

SDDANR

Madison

44.481703

−103.848508

3,725.00

1990–2022

0.88

LA–90A

SDDANR

Madison

44.429052

−103.577190

3,630.00

1990–2022

0.88

LA–90B

SDDANR

Inyan Kara

44.553044

−103.729622

3,415.00

1991–2022

0.22

LA–94A

SDDANR

Minnekahta

44.517786

−104.007075

3,666.00

1994–2022

0.57

LA–94B

SDDANR

Deadwood

44.176096

−103.879654

6,460.00

1995–2022

0.62

LA–95A

SDDANR

Madison

44.476335

−103.729516

3,780.00

1995–2022

0.82

LA–95B

SDDANR

Madison

44.299234

−103.912716

6,180.00

1996–2022

0.26

LA–95C

SDDANR

Madison

44.409624

−103.953039

5,520.00

1995–2022

0.24

Hydrologic Budgets 51 Table 17. Observation wells within the study area selected for analysis with site information, length of the water-level record, and Pearson correlation coefficient.—Continued [NAVD88; North American Vertical Datum of 1988; SDDANR, South Dakota Department of Agriculture and Natural Resources; USGS, U.S. Geological Survey]

Agency

Aquifer

Latitude (decimal degrees)

Longitude (decimal degrees)

Elevation (feet above NAVD88)

Period of record

Correlation coefficient

LA–96A

SDDANR

Deadwood

44.299235

−103.912718

6,180.00

1997–2022

0.74

LA–96B

SDDANR

Madison

44.466631

−103.913848

4,580.00

1997–2009; 2011–17

0.89

LA–96C

SDDANR

Minnelusa

44.475149

−103.913011

4,580.00

1997–2022

0.48

LA–96D

SDDANR

Madison

44.383554

−103.615573

4,080.00

1998–2022

0.73

MD–84A

SDDANR

Minnelusa

44.226481

−103.380910

3,480.00

1984; 1990–2022

0.79

MD–84B

SDDANR

Minnelusa

44.299947

−103.436731

3,638.00

1984–85; 1990–91; 1996–2009; 2013–22

0.51

MD–86A

SDDANR

Madison

44.393583

−103.519428

3,606.71

1991–2022

0.73

MD–89A

SDDANR

Inyan Kara

44.474240

−103.523069

3,265.00

1990–2022

−0.38

MD–90A

SDDANR

Madison

44.299922

−103.436723

3,630.00

1991; 1995–2010; 2013–22

0.43

MD–94A

SDDANR

Madison

44.226475

−103.380882

3,480.00

1994–2022

0.42

MD–95A

SDDANR

Minnekahta

44.299938

−103.436719

3,630.00

1995–2009; 2014–22

0.38

PE–64A

SDDANR

Minnelusa

44.092862

−103.271643

3,330.00

1990–2022

0.18

PE–64B

SDDANR

Minnelusa

44.061879

−103.255953

3,300.00

1964; 1966–77; 1990–2022

0.82

PE–65A

SDDANR

Madison

44.074475

−103.267973

3,300.00

1966–99; 2002–22

−0.25

PE–84A

SDDANR

Deadwood

44.014890

−103.302898

3,880.00

1984–2022

0.55

PE–84B

SDDANR

Minnelusa

44.138848

−103.302945

3,500.00

1984–2022

0.56

PE–86A

SDDANR

Madison

36.656291

−86.060500

3,510.00

1993–2022

0.41

PE–89A

SDDANR

Madison

44.060942

−103.292905

3,372.90

1990–2022

0.35

PE–89B

SDDANR

Minnelusa

44.060943

−103.292920

3,372.50

1989–91; 1994–2022

0.71

PE–89C

SDDANR

Madison

44.095436

−103.301466

3,493.70

1989–2022

0.62

PE–89D

SDDANR

Minnelusa

44.095446

−103.301469

3,493.94

1989–2003; 2005–11; 2013–22

0.67

PE–91A

SDDANR

Deadwood

44.107588

−103.976560

6,890.00

1991–2015

0.68

PE–94A

SDDANR

Minnelusa

43.987487

−103.272406

3,515.00

1994–2022

0.08

PE–95A

SDDANR

Madison

43.871888

−103.314595

3,928.00

1995–2022

0.48

PE–95B

SDDANR

Inyan Kara

44.056833

−103.210687

3,225.00

1996–2022

0.92

PE–95C

SDDANR

Madison

44.136349

−103.372684

4,050.00

1996–2022

0.42

PE–95E

SDDANR

Inyan Kara

44.129743

−103.211839

3,235.00

1995–2022

−0.13

PE–96A

SDDANR

Madison

44.052220

−103.313042

3,420.00

1996–2022

0.26

PE–96B

SDDANR

Deadwood

44.125971

−103.355294

4,050.00

1996–2022

−0.67

Well name or site number

52 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 Table 17. Observation wells within the study area selected for analysis with site information, length of the water-level record, and Pearson correlation coefficient.—Continued [NAVD88; North American Vertical Datum of 1988; SDDANR, South Dakota Department of Agriculture and Natural Resources; USGS, U.S. Geological Survey]

Agency

Aquifer

Latitude (decimal degrees)

Longitude (decimal degrees)

Elevation (feet above NAVD88)

Period of record

Correlation coefficient

PE–96C

SDDANR

Madison

43.920836

−103.838597

6,696.28

1997–2022

0.38

440149103164901

USGS

Minnelusa

44.03026577

−103.2807385

3,676.60

1996–2022

0.87

440326103180702

USGS

Madison

44.05720999

−103.3024059

3,389.52

1999–2022

0.86

440430103160202

USGS

Madison

44.07422220

−103.26805560

3,352.93

1990–2012; 2014–22

0.92

440544103180001

USGS

Minnelusa

44.09544444

−103.30144440

3,493.78

1990–2022

0.92

440544103180002

USGS

Madison

44.09544444

−103.30144440

3,493.78

1990–2022

0.92

441759103261201

USGS

Minnelusa

44.30002778

−103.43677780

3,638.00

2000–2002; 2004–22

0.89

441759103261202

USGS

Madison

44.29991667

−103.43672220

3,639.10

1991–2022

0.92

441759103261203

USGS

Minnekahta

44.29997220

−103.43675000

3,639.20

1999–2022

0.86

440427103131701

USGS

Madison

44.07405556

−103.22166670

3,397.44

1990–2022

0.92

Well name or site number

Table 18. Summary statistics of Pearson correlation coefficient calculations for the Deadwood, Madison, Minnelusa, Minnekahta, and Inyan Kara aquifers. Wells with negative correlation coefficients

Wells with weak correlation (coefficients less than 0.4)

0.74

0.86

0.92

0.86

0.94

0.50

0.57

0.86

0.22

0.38

0.92

Summary statistic, unitless Pearson correlation coefficient Aquifer

Number of wells

Mean

Standard deviation

Minimum

25th percentile

Median

75th percentile

Maximum

Deadwood

0.38

0.59

−0.67

0.55

0.62

0.68

Madison

0.61

0.29

−0.25

0.41

0.73

Minnelusa

0.64

0.26

0.08

0.49

0.73

Minnekahta

0.55

0.19

0.38

0.44

Inyan Kara

0.17

0.44

−0.38

−0.15

Hydrologic Budgets 53

–410

–30

–420

–40

–430

–50

–440

–60

–450

–70

10 C

–140

–10 –160

–20

–180

–30 –40

–200

–50 –220

1931 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

–240

–40

–200

–50

–220

–60

–240

–160 –165

10 D

0 –10

–170

–20

–175

–30

–180

–40

–185

–50

–60

–190

–60

–70

–195

–70

Year

0 –10

–20

–30

–40

–50

–60

–5

–70

Cumulative departure from mean annual precipitation, in inches

–70

Year

1931 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

Water level, in feet

–30

–180

Year 30

–20

1931 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

–120

–160

1931 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

–20

–10

Water level, in feet

–400

–140

Water level, in feet

–10

Year

Water level, in feet

Cumulative departure from mean annual precipitation, in inches

–390

–120

1931 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

Water level, in feet

–380

10 A

EXPLANATION Mean annual water level relative to land surface for observation well—Negative values indicate the water level is below land surface and positive values indicate above land surface Cumulative departure from long-term mean annual precipitation curve from figure 4C.

Year

Figure 13. Hydrographs for observation wells completed in the Deadwood, Madison, Minnelusa, Minnekahta, and Inyan Kara aquifers. A, Deadwood aquifer (observation well PE–84A). B, Madison aquifer (observation well LA–90A). C, Minnelusa aquifer (observation well LA–63A). D, Minnekahta aquifer (observation well CU–96A). E, Inyan Kara aquifer (observation well PE–95B). Observation well data were from the South Dakota Department of Agriculture and Natural Resources (2024c).

Cumulative departure from mean annual precipitation, in inches

–370

54 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Discussion of Groundwater Budget and Availability Groundwater budgets and availability are discussed for the Deadwood, Madison, Minnelusa, Minnekahta, Sundance, and Inyan Kara aquifers in subareas 1–9. Budget items for the Madison and Minnelusa aquifers were combined because streamflow recharge could not be differentiated for loss zones in many basins. Groundwater budgets were evaluated by calculating net groundwater flow (inflows minus outflows) for each aquifer in subareas 1–9. Net groundwater flow values are discussed by aquifer and subarea. Water availability is discussed by comparing inflows (recharge) to well withdrawals and total appropriations from water permits and by updating the volume of extractable water in storage for aquifers in the Black Hills region. Mean values were used for inflows and outflows in the groundwater budget to calculate net groundwater flow. The time span from which mean values were calculated varied by budget item. Mean values were chosen so that budget estimates were as unbiased as possible to wet or dry periods that may skew long-term mean values. Mean precipitation and streamflow recharge were calculated for 1931–2022 using recharge estimates in table 19. The period of available data used for calculating artesian springflow varied by spring (table 12) but generally was from wetter periods from the 1970s to the 2020s. Therefore, the artesian springflow estimates provided in the groundwater budget (table 19) may be more biased toward wetter periods than other budget items. Mean well withdrawals were calculated for the shortest period (2003–22) but were considered adequate because the purpose of this study was to compare long-term budgets to modern well withdrawals. Mean values used for budget items were considered adequate representations of the long-term mean because storage change was estimated to be near zero with the study area experiencing both wet and dry periods.

Groundwater Budgets Net groundwater flow was calculated using equation 2 for each aquifer in subareas 1–9 based on the assumption of zero storage change for aquifers in the study area (table 19). Net groundwater flow included inflows and outflows from regional groundwater in and out of subarea boundaries and for leakage between adjacent aquifers occurring within subareas. Vertical leakage to and from adjacent aquifers could not be distinguished from groundwater inflow or outflows. Driscoll and Carter (2001) considered vertical leakage a relatively small component of the budget and, therefore, included it with net groundwater flow. Aquifers with positive net groundwater flow values (inflows greater than outflows) likely had a surplus of groundwater that contributed to regional groundwater flow out of a subarea. Aquifers with negative net groundwater flow values (outflows greater than inflows) likely had a deficit of

groundwater and relied on inflows from regional groundwater flow to account for the deficit. Carter and others (2001b) used potentiometric contours of the Madison and Minnelusa aquifers to determine the direction of regional groundwater flow in and out of subareas. Potentiometric contours for the study area were available only for the Madison and Minnelusa aquifers, and, therefore, are not discussed for other aquifers. Net groundwater flow was positive for most aquifers in subareas 1–9 with exceptions for the Madison and Minnelusa aquifers in subareas 4, 7, and 8 and for the Deadwood and Inyan Kara aquifers in subareas 9 and 4 respectively (table 19). Negative net groundwater flow for the Madison and Minnelusa aquifers in subareas 7 and 8 can be accounted for by inflows from regional groundwater flow across subarea boundaries and from outside the study area. Based on generalized potentiometric contours of the Madison and Minnelusa aquifers from Carter and others (2001b; figs. 14 and 15), subarea 8 receives regional groundwater flow from subarea 9 and from outside the study area, which then flows into subarea 7. The groundwater deficit for the Madison and Minnelusa aquifers in subarea 8 (about −29,400 acre-ft; table 19) was accounted for by the surplus in subarea 9 (about 33,300 acre-ft); however, it is possible subarea 8 also receives additional inflows from regional groundwater flow of the Madison and Minnelusa aquifers that is recharged outside of the study area. The Madison and Minnelusa aquifers in subarea 7 also had a groundwater deficit (−4,800 acre-ft) but likely received inflows from subareas 6 and 8 based on potentiometric contours of the Madison and Minnelusa aquifers (figs. 14 and 15; table 19). The combined surplus of groundwater for the Madison and Minnelusa aquifers in subareas 6 (5,600 acre-ft) and 8 after receiving inflows from subarea 9 (3,900 acre-ft; totaling 9,500 acre-ft; table 19) accounted for the groundwater deficit in subarea 7 (about −4,800 acre-ft) and likely contributed to regional groundwater flow east of the study area. Negative net groundwater flow in subarea 9 was −3 acre-ft, which was within the margin of error for estimates of inflows and outflows and, therefore, may not actually be negative. In subarea 4, the net groundwater flow for the Madison and Minnelusa aquifers was negative (about −4,400 acre-ft; table 19). Based on potentiometric contours of the Madison and Minnelusa aquifers (figs. 14 and 15), relatively large inflows from other subareas and (or) regional groundwater flow were unlikely; however, potentiometric contours are generalized and may not accurately represent localized flow across subarea boundaries. It is also possible that leakage from adjacent aquifers, such as the Deadwood aquifer, may contribute water that was not accounted for in the hydrologic budget. Aquifer exchange is difficult to quantify and, therefore, was included in net groundwater flow. Budget uncertainty also may be a factor when considering net groundwater flow because outflows (artesian springflow and well withdrawals) could be overestimated, or inflows (recharge from precipitation and streamflow losses) could

Discussion of Groundwater Budget and Availability 55 Table 19. Hydrologic budget including inflows from recharge and outflows from springs and well withdrawals for the Deadwood, Madison and Minnelusa, Minnekahta, Sundance, and Inyan Kara aquifers in subareas 1–9. Inflows (acre-feet) Subarea

Aquifer

Precipitation

Streamflow

Outflows (acre-feet)

Total

Artesian springflow

Well withdrawals

Net groundwater flow (inflows− outflows) (acre-feet)

Total

Deadwood

2,622

497

2,125

Madison and Minnelusa

88,645

13,232

101,877

82,822

8,283

91,105

10,772

Minnekahta

12,452

965

11,487

Sundance

5,321

5,312

Inyan Kara

4,906

854

4,052

Deadwood

1,366

1,282

Madison and Minnelusa

8,303

14,244

22,547

2,387

20,160

Minnekahta

1,243

1,227

Sundance

580

522

Inyan Kara

2,311

518

1,793

Deadwood

1,276

Madison and Minnelusa

2,743

6,420

9,163

4,416

1,408

5,824

3,339

Minnekahta

395

351

Sundance

141

Inyan Kara

1,262

383

879

Deadwood

999

681

318

Madison and Minnelusa

5,069

23,825

28,894

21,357

11,932

33,289

−4,395

Minnekahta

569

227

342

Sundance

211

188

Inyan Kara

592

647

−55

Deadwood

293

258

Madison and Minnelusa

1,807

7,044

8,851

5,937

390

6,327

2,524

Minnekahta

227

Sundance

169

Inyan Kara

739

211

528

Deadwood

Madison and Minnelusa

527

5,056

5,583

Minnekahta

Sundance

Inyan Kara

407

56 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 Table 19. Hydrologic budget including inflows from recharge and outflows from springs and well withdrawals for the Deadwood, Madison and Minnelusa, Minnekahta, Sundance, and Inyan Kara aquifers in subareas 1–9.—Continued Inflows (acre-feet) Subarea

Total for study area

Aquifer

Outflows (acre-feet)

Net groundwater flow (inflows− outflows) (acre-feet)

Precipitation

Streamflow

Total

Artesian springflow

Well withdrawals

Total

Deadwood

Madison and Minnelusa

702

1,736

2,438

7,167

7,234

−4,797

Minnekahta

202

Sundance

Inyan Kara

456

387

Deadwood

157

Madison and Minnelusa

3,945

2,228

6,173

34,823

734

35,557

−29,384

Minnekahta

827

811

Sundance

355

Inyan Kara

2,642

366

2,276

Deadwood

−3

Madison and Minnelusa

43,324

9,556

468

10,024

33,299

Minnekahta

5,480

Sundance

410

Inyan Kara

1,090

1,000

Deadwood

6,858

1,311

5,547

Madison and Minnelusa

155,064

73,785

228,849

166,078

25,669

191,747

37,102

Minnekahta

21,466

1,268

20,198

Sundance

7,353

7,263

Inyan Kara

14,406

3,138

11,268

Discussion of Groundwater Budget and Availability 57

Whitewood

Deadwood Central City

5,4 5,600 00 5,800

4,2

3 Piedmont Summerset

4,20

6 6,200,000

00 5,0

Johnson Siding

4 00

5 Hermosa

4,00

6,0

Custer

CUSTER COUNTY

Hill View Heights

PE-89A

3,4

Keystone

6,40

Newcastle

5,00

Fairburn

Base modified from U.S. Geological Survey digital data, various scales Universal Transverse Mercator, zone 13 north North American Datum of 1983 (2011)

4,0

Hot Springs

0 ,60

Buffalo Gap

FALL RIVER COUNTY

Edgemont

Observation wells—Wells are from the South Dakota Department of Agriculture and Natural Resources (2024c) and (or) the National Water Information System (NWIS; U.S. Geological Survey, 2024a); label is the name of the well or the site number

Pringle

Potentiometric contours of the Madison aquifer— Shows altitude at which water would have stood in tightly cased, nonpumping wells (modified from Strobel and others, 2000a; Rahn, 1995; and Carter and others, 2001b). Contour interval 200 feet. Datum is sea level

3,40

WYOMING SOUTH DAKOTA

NIOBRARA COUNTY

43° 20'

3,80

43° 40' 4,0 3,8 00 00

Subareas from Carter and others (2001b)—Red number is the subarea number

General direction of groundwater flow based on potentiometric contours

440427103131701

Colonial Pine Hills

Hill City

6,2

Box Elder

Rapid City Rapid Valley

PE-89A

PENNINGTON COUNTY

6,6

44°

Blackhawk 440430103160202

3,200

4,00

4,000

Tilford

LAWRENCE COUNTY

104°20' Osage

Madison Limestone

00 3,6

WESTON COUNTY

EXPLANATION

Sturgis

Lead

6,400

44° 40'

MEADE COUNTY

0 4,000 3,800

3,8 00

Spearfish

0 4,20 4,4000 4,800 0 4,6 5,200

CROOK COUNTY

Vale

00 0 3,6 3,80

44° 20'

0 3,4

St. Onge

1 Sundance

3,2 00

Fruitdale

2,800

3,6 00

Nisland

Belle Fourche

Beulah

3,000

Newell

BUTTE COUNTY

2,600

103°20'

103°40'

104°

0 0

5 5

20 MILES

20 KILOMETERS

Figure 14. Generalized potentiometric contours of the Madison aquifer in the study area from Strobel and others (2000a) and modified by Carter and others (2001b).

58 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

3,400 3,800

Vale

Spearfish

Whitewood

4,000

Tilford

Deadwood Lead

6,000 6,200 6,400

WESTON COUNTY

6,000

PENNINGTON COUNTY Hill City

3,800

Custer

CUSTER COUNTY

5,4

5,200

43° 40'

WYOMING SOUTH DAKOTA

NIOBRARA COUNTY

4,0

43° 20'

Buffalo Gap

8 Edgemont

Base modified from U.S. Geological Survey digital data, various scales Universal Transverse Mercator, zone 13 north North American Datum of 1983 (2011)

Fairburn

4,8

3,600

Hermosa

Pringle

5,0

4,6

2,800

5,6

2,600

6,000 ,800

5 Hill View Heights

Newcastle

Potentiometric contours of the Minnelusa aquifer— Shows altitude at which water would have stood in tightly cased, nonpumping wells (modified from Strobel and others, 2000b; Rahn, 1995; and Carter and others, 2001b). Contour interval 200 feet. Datum is sea level General direction of groundwater flow based on potentiometric contours

PE-64A

Keystone

3,000

6,400 6,200

4,2

Colonial Pine Hills

3,200

PE-64B

Rapid City Rapid Valley

3,600

4,0

Box Elder PE-64A

Johnson Siding

44°

Blackhawk

6,800 6,600

5,000

4,800

Osage

4,60

104°20' 4,4 00

Piedmont Summerset

LAWRENCE COUNTY

6,600

3,40

CROOK COUNTY

Subareas from Carter and others (2001b)—Red number is the subarea number Minnelusa Formation

Sturgis

4,800 Central City

4,2

4,200

44° 20'

EXPLANATION

MEADE COUNTY

St. Onge

0 4,00

44° 40'

2 ,8

3,600

Nisland

Belle Fourche

Fruitdale

2,6

Newell

3 ,0 0

0 3,20

BUTTE COUNTY

Beulah

Sundance

103°20'

103°40'

104°

3,80

FALL RIVER COUNTY

Hot Springs

3,400

0 0

10 10

20 MILES

20 KILOMETERS

Figure 15. Generalized potentiometric contours of the Minnelusa aquifer in the study area from Strobel and others (2000b) and modified by Carter and others (2001b).

Discussion of Groundwater Budget and Availability 59 be underestimated. It is likely that one or more of the possible explanations discussed contribute to the negative net groundwater flow calculated for subarea 4 (table 19). Hydrographs for wells completed in the Madison and Minnelusa aquifers in subarea 4 were evaluated to determine if storage in both aquifers was decreasing near Rapid City, S. Dak., because it was the largest water user in subarea 4 and, on average, accounted for about 49 percent of the mean annual well withdrawals from the Madison and Minnelusa aquifers. In total, five wells completed in the Madison or Minnelusa aquifers near Rapid City, S. Dak., with greater than 20 years of water-level data were evaluated (fig. 16). Hydrographs for observation wells near or downgradient of pumping wells in Rapid City, S. Dak., generally show similar annual water-level increases and decreases as other wells in the study area that correlate with precipitation patterns (fig. 13); however, water levels in 2022 were similar or lower than water levels in the late 1990s for wells near and downgradient of pumping wells (fig. 16). Water levels were greater in 2022 than in the late 1990s for most observation wells away from pumping, which correlated with the cumulative departure curve for precipitation (fig. 13). Well withdrawals at pumping wells may be responsible for water-level discrepancies and it is possible that pumping may have reduced the amount of water added to storage in the Madison aquifer in subarea 4. Additional observation wells downgradient of pumping wells in subarea 4 could help further determine the influence of pumping wells on the aquifers, such as the Madison aquifer.

Groundwater Availability Groundwater availability in the study area is affected by many factors and varies spatially. Aquifer-related factors affecting groundwater availability include location, local recharge, groundwater flow conditions, historical well withdrawals, and structural features (Carter and others, 2003). Other factors affecting groundwater availability are the laws governing entities use to issue water rights or manage aquifers and the water quality of groundwater resources. Previous sections of this report discussed aquifer-related factors affecting groundwater availability, but not State laws or groundwater quality. Therefore, discussions of groundwater availability in this section are focused on relevant State laws and groundwater quality. Carter and others (2003) provide a detailed summary of groundwater availability in the Black Hills area of South Dakota and some parts of their analysis are either used or updated in this section. Water availability for aquifers in the study area was evaluated for subareas 1–9 by comparing estimated mean annual recharge to estimated mean annual well withdrawals. According to South Dakota State Codified Law 46–6–3.1 (South Dakota State Legislature, 2024b), applications to appropriate groundwater cannot be approved if the proposed quantity of water withdrawn annually would exceed the quantity of estimated mean annual recharge to an aquifer;

however, applications can be approved for instances where appropriations exceed mean annual recharge for withdrawals from formations older than or stratigraphically lower than the Cretaceous Greenhorn Formation for water distribution systems, such as municipalities or rural water systems. The State codified law does not divide mean annual recharge into the subareas used in this report, so water availability estimates (“Total annual appropriations as a percentage of mean annual recharge” in table 20) do not indicate compliance or noncompliance with codified laws. Annual appropriations generally are greater than actual well withdrawals because most water users do not use the total annual amount appropriated by permits. Total annual appropriations (excluding appropriations for future use) and mean and maximum annual well withdrawals for 2003–22 are included in table 20 for comparison with mean annual recharge for 1931–2022 for each aquifer in subareas 1–9. It should be noted that artesian springflow was the greatest outflow component for Madison and Minnelusa aquifers but was not included as an outflow in table 20. Mean annual recharge was not exceeded by mean annual well withdrawals, maximum annual well withdrawals, or total annual appropriations in subareas 1, 2, and 6–8 for all aquifers. Total annual appropriations as a percentage of mean annual recharge was calculated for each aquifer to assess the approximate availability of each aquifer in subareas 1–9 by dividing mean annual recharge by total annual appropriations (as of 2022). More than 50 percent was available for all aquifers in subareas 1 and 2 except for the Inyan Kara aquifer (table 20). In subarea 6 (Custer area), the percentage of mean annual recharge was near zero for all aquifers except for the Madison and Minnelusa aquifers. Percentage of mean annual recharge was greater than 30 percent for the Madison and Minnelusa and Inyan Kara aquifers in subarea 7 (Wind Cave area) but was near zero for other aquifers. Total appropriations in subarea 8 (Hot Springs area) were less than 50 percent for all aquifers except for the Madison and Minnelusa aquifers, which were nearly equal to the total recharge and differed by about 100 acre-ft (table 20). As stated previously, subarea 8 receives regional groundwater flow from subarea 9 (Jewel Cave area) and, therefore, availability may be slightly underestimated in subarea 8. Total annual appropriations, mean annual well withdrawals, and (or) maximum annual well withdrawals exceeded mean annual recharge for various aquifers in 4 of the 9 subareas (table 20). In subarea 3 (Piedmont area), total annual appropriations for the Inyan Kara aquifer exceeded mean annual recharge by about 200 acre-ft. Mean and maximum well withdrawals, however, did not exceed mean annual recharge for the Inyan Kara aquifer in subarea 3. Mean annual recharge was exceeded by total appropriations in subarea 4 for the Madison and Minnelusa aquifers and the Inyan Kara aquifer (table 20). Total appropriations for the Madison and Minnelusa aquifers exceeded mean annual recharge by about 3,600 acre-ft. Mean and maximum annual well withdrawals for the Madison and Minnelusa aquifers

60 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

–40

–30

–50 –60

1931 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

–10

–70

Year 10

–120 –140

0 –10

–160

–20 –30

–180

–40

–200

–50 –220

1931 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

–240

–20

–180

–30 –40

–200

–50 –60

–240

–70

Year

–160 –165

0 –10

–170

–20

–175

–30

–180

–40

–185

–50

–60

–190

–60

–70

–195

–70

Year 10

0 –10

–110

–20

–100

–30 –40

–90

–50 –80

–60

1931 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

–70

Cumulative departure from mean annual precipitation, in inches

Water level, in feet

–120

–10 –160

–220

Year –130

1931 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

–30

1931 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

–40

Water level, in feet

–20

Water level, in feet

–10 –50

–20

Water level, in feet

–140

Cumulative departure from mean annual precipitation, in inches

Water level, in feet

–60

–120

Cumulative departure from mean annual precipitation, in inches

–70

Year

Figure 16. Hydrographs of wells completed in the Madison and Minnelusa aquifers near Rapid City, South Dakota (shown in figs. 14 and 15). A, Madison aquifer (observation well PE–89A). B, Madison aquifer (observation well 440430103160202). C, Madison aquifer (observation well 440427103131701). D, Minnelusa aquifer (observation well PE–64A). E, Minnelusa aquifer (observation well PE–64B).

Discussion of Groundwater Budget and Availability 61 Table 20. Total mean annual recharge (table 11), mean annual well withdrawals (table 15), maximum annual well withdrawals (table 15), and total annual appropriations (as of 2022) for aquifers in subareas 1–9.

Subarea 1

Total mean annual recharge, in acre-ft (1931–2022)1

Mean annual well withdrawals, in acre-ft (2003–22; table 16)

Maximum annual well withdrawals, in acre-ft (year varies; table 16)

Total annual appropriated volume as of 2022, in acre-ft2

Deadwood

2,622

497

540

1,014

38.7

Madison and Minnelusa

101,877

8,283

10,045

34,536

33.9

Minnekahta

12,452

965

1,091

3,219

25.9

Aquifer

Total annual appropriations as a percentage of mean annual recharge3

Sundance

5,321

1.3

Inyan Kara

4,906

854

887

2,862

58.3

Deadwood

1,366

138

263

19.2

Madison and Minnelusa

22,547

2,387

2,949

9,298

41.2

Minnekahta

1,243

2.7

Sundance

580

116

20.0

Inyan Kara

2,311

518

592

1,869

80.9

Deadwood

1,276

0.0

Madison and Minnelusa

9,163

1,408

1,693

5,722

62.4

Minnekahta

395

22.3

Sundance

141

0.0

Inyan Kara

1,262

383

447

1,473

116.7

Deadwood

999

681

769

1,826

182.8

Madison and Minnelusa

28,894

11,932

16,099

32,480

112.4

Minnekahta

569

227

233

470

82.6

Sundance

211

0.0

Inyan Kara

592

647

718

2,828

477.5

Deadwood

293

24.2

Madison and Minnelusa

8,851

390

472

1,465

16.6

Minnekahta

227

0.0

Sundance

169

0.0

Inyan Kara

739

211

339

1,533

207.3

Deadwood

0.0

Madison and Minnelusa

5,583

618

11.1

Minnekahta

0.0

Sundance

0.0

Inyan Kara

407

0.0

Deadwood

0.0

Madison and Minnelusa

2,438

378

790

32.4

Minnekahta

202

0.0

Sundance

0.0

Inyan Kara

456

138

30.2

62 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 Table 20. Total mean annual recharge (table 11), mean annual well withdrawals (table 15), maximum annual well withdrawals (table 15), and total annual appropriations (as of 2022) for aquifers in subareas 1–9.—Continued

Subarea

Total mean annual recharge, in acre-ft (1931–2022)1

Mean annual well withdrawals, in acre-ft (2003–22; table 16)

Maximum annual well withdrawals, in acre-ft (year varies; table 16)

Total annual appropriated volume as of 2022, in acre-ft2

Deadwood

157

0.0

Madison and Minnelusa

6,173

734

1,160

6,065

98.3

Minnekahta

827

1.8

Aquifer

Total annual appropriations as a percentage of mean annual recharge3

Sundance

355

0.0

Inyan Kara

2,642

366

455

1,191

45.1

261.5

Madison and Minnelusa

Deadwood

43,324

468

715

2,400

5.5

Minnekahta

5,480

0.0

Sundance

410

0.0

Inyan Kara

1,090

180

16.5

1Includes precipitation and streamflow recharge for the Madison and Minnelusa aquifers. 2Excludes future use appropriations. 3Calculated by dividing the total annual appropriations by the mean annual recharge for each aquifer.

were about 41 and 56 percent, respectively, of mean annual recharge in subarea 4. Total appropriations, mean annual well withdrawals, and maximum annual well withdrawals all exceeded mean annual recharge for the Inyan Kara aquifer in subarea 4 (Rapid City area; table 20). In subarea 5 (Hermosa area), mean annual recharge for the Inyan Kara aquifer was nearly two times less than total annual appropriations but was greater than mean and maximum well withdrawals. Total annual appropriations for the Deadwood aquifer were more than two times greater than mean annual recharge in subarea 9 (Jewel Cave area) and mean and maximum annual well withdrawals were nearly equal to recharge. In addition to recharge, water availability also includes the water stored in pore spaces of aquifer materials. It is important to note that not all water stored in aquifers can be removed, so Carter and others (2003) used effective porosity values for each aquifer from Rahn (1985) to estimate the volume of recoverable water in six major aquifers in the Black Hills area (table 21). Effective porosity was multiplied by the area encompassed by each aquifer and the mean or maximum saturated thickness of each aquifer depending on whether the aquifers were unconfined or confined to calculate the volume of recoverable water. Estimates of total volume of recoverable water were updated as part of this study to include areas in Wyoming and used the same saturated thickness and effective porosity estimates as Carter and others (2003). Estimates of total recoverable volume were not provided by Carter and others (2003) for the Sundance aquifer and the total volume of recoverable water was not calculated in this report because the information needed for calculations was unavailable.

In total, the estimated total amount of recoverable water in storage in the study area was 356.9 million acre-ft for six major aquifers in the Black Hills area of South Dakota and Wyoming (table 21), which is more than 15 times greater than the maximum storage capacity of Oahe Reservoir on the Missouri River (23,137,000 acre-ft; U.S. Army Corps of Engineers, 2012) east of the Black Hills in South Dakota (not shown). Estimates provided in this study were about 40 percent greater than in Carter and others (2003) because of the additional area added in Wyoming. The largest storage volume was for the Inyan Kara aquifer (127.2 million acre-ft) because of its relatively large effective porosity (0.17). Estimated storage volumes for the Madison (83.6 million acre-ft) and Minnelusa (96.9 million acre-ft) aquifers were the third and second largest, respectively, because of the relatively large saturated thickness of both aquifers (table 21). The Precambrian, Deadwood, and Minnekahta aquifers had the smallest estimated storage volumes of all major aquifers because of relatively small areas, saturated thicknesses, and (or) low effective porosity. The estimated volume of recoverable water in storage in the study area was large; however, water quality varies throughout the study area and, in some areas, may not be suitable for all types of water use. Water quality is an important consideration because the desired quality varies depending on the type of use. For example, water systems supplying drinking water require greater water quality than systems used for industrial and irrigation purposes. Groundwater quality can be affected by many factors and can contain numerous constituents from natural and (or)

Limitations 63 Table 21. Aquifer characteristics, including area, maximum thickness, mean saturated thickness, and effective porosity, and the estimated total amount of recoverable water in storage. [--, not applicable]

Aquifer

Area (square miles)

Maximum formation thickness (feet)

Mean saturated thickness (feet)

Effective porosity1

1500

0.01

Estimated amount of recoverable water in storage2 (million acre-feet)

Precambrian

35,041

Deadwood

4,216

500

226

0.05

39.6

0.05

583.6

0.05

596.9

Madison

4,113

1,000

4521

Minnelusa

3,623

1,175

6736

2.6

Minnekahta

3,082

0.05

6.9

Inyan Kara

2,512

900

310

0.17

127.2

356.9

Combined storage for major aquifers 1From Rahn (1985).

2Storage estimated by multiplying area times mean saturated thicknesses times effective porosity. 3The area used in storage calculation was the area of the exposed Precambrian rocks, which is 825 square miles. 4Mean saturated thickness of the confined area of the Madison aquifer. The unconfined area had a mean saturated thickness of 300 feet. 5Storage values are the summation of storage in the confined and unconfined areas. 6Mean saturated thickness of the confined area of the Minnelusa aquifer. The unconfined area had a mean saturated thickness of 142 feet.

human sources. Natural sources primarily are introduced from the geologic materials within aquifers and the length of time water is in contact with geological materials, which can increase the concentration of constituents (Winter and others, 1998). Human-related constituents can be introduced to groundwater from many sources, such as chemicals used in agricultural practices leaching into the groundwater table or biologic constituents leaking into aquifers from septic tanks or sewer systems. In the Black Hills area, groundwater quality is affected by natural and human sources and heavily affected by interactions between groundwater and surface water. Williamson and Carter (2001) provide a detailed overview of groundwater quality for aquifers in the Black Hills area. Carter and others (2003) evaluated the spatial variability of groundwater quality in the Black Hills area of South Dakota. In general, water quality was best within and near outcrop areas of aquifers and decreased downgradient of outcrop areas as aquifer depth increased. Groundwater quality varied by aquifer but in most cases physical properties (temperature, specific conductance, and hardness) and chemical constituents (arsenic, iron, manganese, sodium, sulfate) that could require water treatment increased downgradient. Radionuclide concentrations also were relatively high for some aquifers, such as the Deadwood and Inyan Kara aquifers, and exceeded U.S. Environmental Protection Agency standards in some areas (Carter and others, 2003). Municipal pumping wells completed in the Madison aquifer for the cities of Hot Springs, Rapid City, Spearfish, Sturgis, and Whitewood generally were within 20 miles of

outcrops and had adequate groundwater quality for drinking water. Conversely, water was relatively hot and salty for municipal wells completed in the Madison aquifer for the cities of Box Elder and Edgemont, which were farther than 20 miles from outcrops. Therefore, the amount of recoverable water in storage adequate for drinking water systems without treatment likely is considerably less than estimates provided in table 21.

Limitations Limitations affecting the datasets and methods used in this study were identified and are discussed in this section. Limitations are discussed for the various inflow and outflows of the hydrologic budget and groundwater availability. Carter and others (2001a), Carter and others (2001b), and Driscoll and Carter (2001) each provide discussions of limitations and uncertainty for their studies, which also apply to this study because many of the same methods and datasets were used. Uncertainty was not quantified for any of the results presented in this study but is discussed in general terms by evaluating datasets and methods used to construct hydrologic budgets and estimate water availability. Precipitation recharge estimates were limited by the data and methods used to estimate recharge. Older precipitation datasets, especially records before the 1950s, have greater uncertainty than more recent datasets because fewer climate

64 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 stations were available with complete records (Driscoll and others, 2000). Uncertainty was also introduced by interpolation of precipitation data between climate station locations. Inherently, precipitation data for areas with sparse climate stations have higher uncertainty than areas with dense climate station distributions. The recharge calculation for this study simplified a complex system of evapotranspiration and precipitation infiltration that is affected by many variables including land cover, soil permeability and thicknesses, temperature, soil saturation, precipitation intensities, and so forth, into a simple equation with annual precipitation, mean annual precipitation, and mean annual yield efficiency as the only variables. The use of the annual yield equation (eq. 3) was based on multiple assumptions that make the quantification of uncertainty difficult. The assumption that equation 3 was sufficient in estimating annual yield efficiency was based on regressions between yield efficiency and precipitation from different streamgages with varying amounts of data (Carter and others, 2001a). The recharge factor used to estimate how much precipitation from the yield equation becomes groundwater recharge was also a simplifying factor that increased uncertainty of the recharge estimates. The infiltration rates of soil horizons and hydrologic units of the study area likely vary spatially with higher infiltration rates in some areas. Although many assumptions and simplifications were made, the general estimates of the groundwater recharge were reasonable and close to estimates made in previous studies. Streamflow recharge estimates had fewer limitations and less uncertainty than precipitation recharge because estimates were based on measured values of streamflow and loss thresholds for most basins; however, the data and methods used to calculate streamflow recharge presented limitations that varied by site. Streamflow records and loss thresholds were available for most basins in the study area, but the length and completeness of streamflow records varied by streamgage. In general, streamflow records were sparse before 1990 for most streamgages and only a few streamgages had records back to the 1950s. Some streamgages had relatively long streamflow records but were not complete because streamflow was not measured for some years. The period from 1990 to 2022 had the most complete streamflow records and the least uncertainty. Streamgages with relatively long streamflow records had the least uncertainty, whereas sites with short streamflow records and (or) no measured loss thresholds presented the greatest uncertainty and required additional methods to estimate streamflow recharge. The synthetically generated streamflow records and loss thresholds from representative basins used to estimate recharge for some basins may not accurately represent true basin conditions; however, no additional information was available and, therefore, these estimates were considered adequate for calculating streamflow recharge. Statistical linear regression techniques were used to lengthen streamflow records and (or) estimate annual recharge for various basins and time periods, such as 1931–50

when almost no streamflow records were available. Linear regression techniques inherently introduced uncertainty because relations among sites were not perfect, and the variability of natural systems, such as streams, cannot be captured by linear regression. The best regression equation with the highest coefficient of determination value was used to reduce uncertainty as much as possible. Uncertainty in estimates of headwater and artesian springflow were from the method used to estimate precipitation recharge, which was used to estimate headwater springflow, and the varying data available for estimating artesian springflow. Headwater springflow was assumed to equal the recharge from infiltration of precipitation in the part of the Limestone Plateau east of the groundwater divide. The accuracy of the estimates depends on the accuracy of the yield efficiencies used to estimate precipitation recharge, which was discussed earlier in this section. Jarrell (2000) compared headwater springflow estimates using yield efficiency to the measured runoff or base flow at several springs with multiple years of discharge records. Differences in the annual values for the period of record between the estimated basin yield and the measured discharge ranged from 1 percent to about 70 percent of the measured discharge (Carter and others, 2001b). However, all but one site had differences less than 22 percent. This range of differences likely represents the uncertainty of headwater springflow estimates. Uncertainty for artesian springflow estimates varied for each site based on the availability of discharge measurements at each site. Sites with more discharge data had more accurate annual mean estimates; however, sites with few discharge measurements, such as the springs near Cascade Springs (432013103332200 and 432012103331100) in the southern Black Hills had more uncertainty and less accurate annual mean estimates. The data and methods used to estimate well withdrawals had several limitations. The water rights dataset (SDDANR, 2024a) used in this study likely was not complete for 1931–2022. Only water rights active as of 2022 were included in the dataset and all cancelled permits were excluded. It is probable that some permits cancelled before 2022 were active for some time between 1931 and 2022 and exclusions of these permits would underestimate the true number of permits and appropriations for years spanning the active period of cancelled permits. Another limitation was that some permits were for two or more aquifers, which made differentiating appropriations difficult for each aquifer. Only one permit for multiple aquifers was identified, so this limitation likely did not have a large effect on the results of this study; however, it is possible more permits with two or more aquifers were missed. In addition to multiple aquifers, some permits specified one or more types of water use. Permits with several water-use types were simplified to one type—the inferred major type of water use—to evaluate how water was used in the study area because permits do not specify appropriations for each type of water use. The simplification likely either underestimated or overestimated the number of permits and (or) appropriations for the various water use types.

Limitations 65 Well withdrawal estimates for 2003–22 were affected by the same limitations as water rights data but also by inherent uncertainty of well withdrawal datasets and the methods used to estimate well withdrawals if well withdrawal data were unavailable. Estimating annual well withdrawals involved matching reported annual water-use data from the SDDANR (Adam Mathiowetz, SDDANR, written commun., 2024), WYSEO (2024b), or provided by water users to permit information. Therefore, the same limitations regarding cancelled permits, permits with two or more aquifers, and simplification of water use types for permits apply to the spatial and temporal evaluations of groundwater. Well withdrawal datasets were provided by either State agencies in South Dakota and Wyoming or from individual water users. Water users are responsible for tracking and reporting well withdrawals, which involves installing devices that measure withdrawals. The devices used by water users to track water usage can break, causing a data gap, or can give erroneous readings that may underestimate or overestimate withdrawals. The uncertainty of well withdrawals measured by these devices was acknowledged but likely was relatively small compared to other sources of uncertainty in the following paragraphs. Annual well withdrawal data were unavailable for many permits because State agencies in South Dakota and Wyoming did not require water users to report their withdrawals until the 2000s. Water users for some permits still are not required to report their use as of 2022 and some users did not report withdrawals despite requirements. Additionally, well withdrawal estimates for certain types of water use were more uncertain than others. For example, many commercial and industrial permits did not require users to report water usage, whereas most municipal and irrigation permits required annual reporting. The most complete dataset was for 2003–22 when the greatest number of permits had available well withdrawal data. Before 2003, annual well withdrawal data were sparse and, therefore, withdrawals were not estimated. The scope of this study was to compare modern well withdrawals to long-term recharge, so the lack of well withdrawal data before 2003 did not affect the objectives of this study. Missing well withdrawal data between 2003 and 2022 were estimated using three methods that all introduced various degrees of uncertainty. The first method involved determining permits with zero well withdrawals based on information provided in permits and (or) by water users. Many water systems have backup systems that are used when a primary system goes offline or when water demand exceeds the maximum capacity of the primary system. Unless well withdrawal data were provided by water systems, well

withdrawals for permits for backup systems were assumed to be zero, which may have underestimated the true withdrawals. The second method consisted of calculating annual well withdrawals using mean daily withdrawal rates. Daily rates were calculated from annual well withdrawal data collected by State agencies for an unspecified year. The mean daily withdrawal rate represents well withdrawals for only 1 year and likely either underestimates or overestimates well withdrawals for a different year. The third method involved multiplying maximum annual diversion volumes by a ratio of 0.5 to determine annual well withdrawals, which was based on permits that were required to report withdrawals. Estimates derived using the third method (ratio) had the greatest uncertainty and estimated the same annual well withdrawals every year, which is not realistic because well withdrawals vary annually. In general, well withdrawal data had the least uncertainty relative to other budget items because the data were based on recorded numbers provided by water users. Additionally, most of the largest water users in the study area, such as municipalities, were required to report water usage, which made estimates of annual well withdrawals more accurate. Domestic well withdrawals for smaller users were not considered and, therefore, the annual total well withdrawal estimates provided in this study may be slightly underestimated for each aquifer. Domestic well withdrawals are difficult to quantify because users are not required to report withdrawals and the true number of wells actively being used is unknown. Groundwater availability presented in this report included discussion of the volume of recoverable water in storage for major bedrock aquifers. The data and methods used to estimate the volume of recoverable water in storage had several limitations. Storage calculations were based on generalized aquifer properties that may not accurately represent true conditions throughout the study area. The area encompassed by aquifers in the study area is not known and the estimates provided in this study were derived from spatial datasets of bedrock geology covering a large area. The uncertainty of geologic maps generally increases as the size of the mapped area increases. Despite the uncertainty associated with geologic maps, the size of each aquifer relative to one another likely was adequate for calculations. Greater uncertainty for storage calculations was from the other aquifer properties used in storage calculations—including maximum aquifer thickness, mean saturated thickness, and effective porosity values. Aquifer properties are known to vary considerably over short distances in the study area based on well drilling logs and aquifer tests (Carter and others, 2003).

66 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Summary Population growth and recurring droughts in the Black Hills region can affect water resources and future availability. Drought conditions in the late 1980s and the early 2000s stressed local water systems that relied heavily on surface water as the population of the region was increasing. The Black Hills hydrology study (BHHS) was initiated in the early 1990s to inventory and assess the region's water resources, focusing on the quantity, quality, and distribution of surface water and groundwater. The population of the Black Hills region increased by about 39 percent since completion of the BHHS in 2000 compared to 2022, which has renewed interest in future water demand and availability in the Black Hills. Historical well withdrawal patterns and availability estimates can inform effective resource management. The U.S. Geological Survey (USGS) has not comprehensively collected or analyzed detailed well withdrawal data and hydrologic budgets for aquifers in the Black Hills region since completion of the BHHS. The USGS, in cooperation with the Western Dakota Regional Water System, completed a study to (1) update hydrologic budgets from the BHHS for six of the most used aquifers in the Black Hills and (2) to evaluate water availability by comparing results from hydrologic budgets to modern well withdrawals and water rights information from State agencies and (or) water systems. Key updates to the BHHS budgets include (1) adding available data from 1999 to 2022 and (2) dividing hydrologic budgets for each aquifer into subareas. The aquifers included in this study were the Deadwood, Madison, Minnelusa, Minnekahta, Sundance, and Inyan Kara. Hydrologic budgets consisted of various budget components including inflows and outflows. Inflows included recharge, leakage from adjacent (underlying or overlying) aquifers, and groundwater inflows across the study area boundary (regional groundwater flow). Outflows included springflow, well withdrawals, leakage to adjacent aquifers, and regional groundwater flow out of the study area. Leakage to and from adjacent aquifers was difficult to quantify, so previous studies and this study included leakage with groundwater flows for budgeting purposes. Recharge included infiltration of precipitation on outcrops of geologic units and streamflow recharge where streams cross outcrops and lose all or part of their flow. Total mean annual recharge for all aquifers in the study area was estimated at 278,900 acre-feet (acre-ft), with 205,100 acre-ft from precipitation recharge and 73,800 acre-ft from streamflow recharge. Mean annual precipitation recharge for the Madison and Minnelusa aquifers together accounted for 76 percent of the total mean annual precipitation recharge, with the Madison aquifer contributing 57,000 acre-ft and the Minnelusa aquifer contributing 98,100 acre-ft. Mean annual precipitation recharge for the Madison (57,000 acre-ft) and Minnelusa (98,100 acre-ft) aquifers for 1931–2022 from this study were 34 and 7 percent, respectively, greater than estimates from Carter and others (2001a). Mean annual

streamflow recharge for 1931–2022 was about 73,800 acre-ft, which was 9 percent greater than estimates for 1931–98 (67,500 acre-ft) and 4 percent greater than estimates for 1950–98 (70,900 acre-ft). Mean annual precipitation recharge for the Deadwood, Minnekahta, Sundance, and Inyan Kara aquifers combined accounted for 24 percent (or 50,100 acre-ft) of the total mean annual precipitation recharge. Precipitation recharge generally was greatest in the northern and western Black Hills (subareas 1–4 and 9) where mean annual precipitation was relatively high and outcrop areas were extensive for many aquifers. Mean annual precipitation recharge in subareas 1 (Spearfish area) and 9 (Jewel Cave area) combined accounted for about 80 percent of the precipitation recharge in the study area. In contrast, precipitation recharge was lowest in the southern and eastern Black Hills (subareas 5–8) because of lower mean annual precipitation and, except for subarea 8 (Hot Springs area), limited outcrops of aquifers. Streamflow recharge also generally was greatest for subareas in the northern and western Black Hills except in subarea 9 (Jewel Cave area) where a previous study noted precipitation predominantly infiltrates the extensive outcrops of the Madison and Minnelusa aquifers or evaporates before reaching any streams. Streamflow recharge was greatest in subarea 4 (Rapid City area) and contributed to about 76 percent of total recharge in the subarea. Similarly, most of the total recharge was streamflow recharge for subareas along the eastern flank of the Black Hills (subareas 2–7). Outflow components estimated for the hydrologic budget include artesian springflow and well withdrawals. Artesian springflow was estimated only for the Madison and Minnelusa aquifers. Total mean annual artesian springflow in the study area was estimated as 229 cubic feet per second (ft3/s; or 166,100 acre-ft) for the Madison and Minnelusa aquifers. Artesian springflow estimated in this study (166,100 acre-ft) was about 21 and 36 percent greater than mean annual artesian springflow estimated for 1987–96 (136,800 acre-ft) and 1950–98 (122,400 acre-ft), respectively. Outflows from artesian springflow also were estimated for each subarea. Artesian springflow was observed in all subareas except subarea 2 (Sturgis area). Springflow ranged from 6.1 ft3/s in subarea 3 (Piedmont area) to 114.5 ft3/s in subarea 1 (Spearfish area). Mean annual artesian springflow was highest in subareas 1 (Spearfish area), 4 (Rapid City area), and 8 (Hot Springs area) where large artesian springs contribute to streamflow in the largest perennial streams in the study area. Mean annual artesian springflow was lowest in subareas 3 (Piedmont area), 5 (Hermosa area), and 7 (Wind Cave area) where springs contribute to relatively small streams. Mean total annual well withdrawals for 2003–22 in the study area were about 50,000 acre-ft, which was about 33 percent higher than groundwater-withdrawal estimates from 1995 and 2000 during the BHHS. Annual well withdrawal estimates ranged from about 45,100 acre-ft in 2019 to about 52,800 acre-ft in 2017. No increased well withdrawal patterns corresponding to population increases were observed

Summary 67 between 2003 and 2022 despite the study area population increasing by about 39 percent from 2000 to 2022. Mean annual withdrawals for the Madison and Minnelusa aquifers for 2003–22 were 16,500 and 9,100 acre-ft, respectively. Mean annual withdrawals for alluvial aquifers were 11,200 acre-ft. Annual well withdrawals for the crystalline core, Deadwood, Minnekahta, Sundance, Inyan Kara, and “other” aquifers were each less than 5,000 acre-ft. Mean annual well withdrawals in subareas 1–9 ranged from about 600 acre-ft in subarea 9 (Jewel Cave area) to about 19,900 acre-ft in subarea 4 (Rapid City area). Generally, subareas 1–4, located in the northern and northeastern parts of the Black Hills, had the highest well withdrawals, whereas subareas 5–9 in the southern and southeastern Black Hills had lower withdrawals. Well withdrawals were greatest in subareas 1 and 4 because of the relatively large municipal use for the cities of Rapid City and Spearfish, South Dakota, respectively. The amount of water withdrawn from each aquifer varied by subarea but generally was highest for the crystalline core, Madison, Minnelusa, and alluvial aquifers. The crystalline core aquifer contributed to about 53 and nearly 100 percent of the total withdrawals of all aquifers in subareas 5 (Keystone area) and 6 (Custer area). The Madison and Minnelusa aquifers were the most used in subarea 4, with mean annual withdrawals of about 8,100 acre-ft and 3,900 acre-ft, respectively. Well withdrawals also were relatively high for the Madison and Minnelusa aquifers in subarea 1, with mean withdrawals of about 5,200 and 3,000 acre-ft, respectively. Alluvial aquifers were most used in subareas 4 and 7 (Buffalo Gap area) with mean withdrawals of 4,400 and 4,000 acre-ft, respectively. Net groundwater flow included inflows and outflows from regional groundwater in and out of subarea boundaries and for leakage between adjacent aquifers occurring within subareas. Net groundwater was positive for most aquifers in subareas 1–9 with exceptions for the Madison and Minnelusa aquifers in subareas 4, 7, and 8 and for the Deadwood and Inyan Kara aquifers in subareas 9 and 1, respectively. Negative net groundwater flow for the Madison and Minnelusa aquifers in subareas 7 and 8 can be accounted for by inflows from regional groundwater flow across subarea boundaries and from outside the study area. Negative net groundwater flow in subarea 9 was −3 acre-ft, which was within the margin of error for estimates of inflows and outflows and, therefore, may not actually be negative. Based on potentiometric contours of the Madison and Minnelusa aquifers in subarea 4, relatively large inflows from other subareas and (or) regional groundwater flow were unlikely; however, potentiometric contours are generalized and may not accurately represent localized flow across subarea boundaries. It is also possible that leakage from adjacent aquifers in subarea 4, such as the Deadwood aquifer, may contribute water that was not accounted for in the hydrologic budget. Hydrographs for wells completed in the Madison and Minnelusa aquifers in subarea 4 were evaluated to determine if storage in both aquifers was decreasing near Rapid City,

S. Dak., because it was the largest water user in subarea 4 and, on average, accounted for about 49 percent of the mean annual well withdrawals from the Madison and Minnelusa aquifers. Hydrographs for observation wells near or downgradient of pumping wells in Rapid City, S. Dak., generally show similar annual water-level increases and decreases as other wells in the study area that correlate with precipitation patterns; however, water levels in 2022 were similar or lower than water levels in the late 1990s for wells near and downgradient of pumping wells. Water levels were greater in 2022 than in the late 1990s for most observation wells away from pumping, which correlated with the cumulative departure curve for precipitation. Well withdrawals at pumping wells may be responsible for water-level discrepancies and it is possible that pumping may have reduced the amount of water added to storage in the Madison aquifer in subarea 4. Aquifer-related factors affecting groundwater availability include location, local recharge, groundwater flow conditions, historical well withdrawals, and structural features. Other factors affecting groundwater availability are the laws governing entities’ use to issue water rights or manage aquifers and the water quality of groundwater resources. Total annual appropriations (excluding appropriations for future use) and mean and maximum annual well withdrawals for 2003–22 were compared to mean annual recharge for 1931–2022 for each aquifer in subareas 1–9. Mean annual recharge was not exceeded by mean annual well withdrawals, maximum annual well withdrawals, and total annual appropriations in subareas 1, 2, and 6–8 for all aquifers. In subarea 3 (Piedmont area), total annual appropriations for the Inyan Kara aquifer exceeded mean annual recharge by about 200 acre-ft. Mean and maximum well withdrawals, however, did not exceed mean annual recharge for the Inyan Kara aquifer in subarea 3. Mean annual recharge was exceeded by total appropriations in subarea 4 for the Madison and Minnelusa aquifers and the Inyan Kara aquifer. Total appropriations for the Madison and Minnelusa aquifers exceeded mean annual recharge by about 3,600 acre-ft. Mean and maximum annual well withdrawals for the Madison and Minnelusa aquifers were about 41 and 56 percent, respectively, of mean annual recharge in subarea 4. Total appropriations, mean annual well withdrawals, and maximum annual well withdrawals all exceeded mean annual recharge for the Inyan Kara aquifer in subarea 4 (Rapid City area). In subarea 5 (Hermosa area), mean annual recharge for the Inyan Kara aquifer was nearly two times less than total annual appropriations but was greater than mean and maximum well withdrawals. Total annual appropriations for the Deadwood aquifer were more than two times greater than mean annual recharge in subarea 9 (Jewel Cave area) and mean and maximum annual well withdrawals were nearly equal to recharge. In addition to recharge, water availability also includes the water stored in pore spaces of aquifer materials. Estimates of total volume of recoverable water were updated as part of this study to include areas in Wyoming and used the

68 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 same saturated thickness and effective porosity estimates as a previous study. In total, the estimated total amount of recoverable water in storage in the study area was 356.9 million acre-ft for six major aquifers in the Black Hills area of South Dakota. The largest storage volume was for the Inyan Kara aquifer (127.2 million acre-ft) because of its relatively large effective porosity (0.17). Estimated storage volumes for the Madison (83.6 million acre-ft) and Minnelusa (96.9 million acre-ft) aquifers were the third and second largest, respectively, because of the relatively large saturated thickness of both aquifers. The Precambrian, Deadwood, and Minnekahta aquifers had the smallest estimated storage volumes of all major aquifers because of relatively small areas, saturated thicknesses, and (or) low effective porosity. The estimated volume of recoverable groundwater in storage in the study area was large; however, water quality varies throughout the study area and, in some areas, may not be suitable for all types of water use. In the Black Hills area, groundwater quality is affected by natural and human sources and heavily affected by interactions between groundwater and surface water. In general, water quality was best within and near outcrop areas of aquifers and decreased downgradient of outcrop areas as aquifer depth increased. Therefore, the amount of recoverable water in storage adequate for drinking water systems without treatment likely is considerably less than estimates provided in this study.

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U.S. Geological Survey [USGS], 2024b, StreamStats: U.S. Geological Survey digital data, accessed August 2024 at https://streamstats.usgs.gov/ss/. U.S. Geological Survey [USGS], 2024c, National Hydrography Dataset (ver. USGS National Hydrography Dataset Plus High Resolution (NHDPlus HR) for 4-digit Hydrologic Unit - 1012 (published 20180503)): accessed January 2024 at https://www.usgs.gov/national- hydrography/access-national-hydrography-products. Williamson, J.E., and Carter, J.M., 2001, Water-quality characteristics in the Black Hills area, South Dakota: U.S. Geological Survey Water-Resources Investigations Report 2001–4194, 196 p., accessed August 2024 at https://doi.org/10.3133/wri20014194. Winter, T.C., Harvey, J.W., Franke, O.L., and Alley, W.M., 1998, Groundwater and surface water—A single resource: U.S. Geological Survey Circular 1139, 79 p., accessed August 2024 at https://doi.org/10.3133/cir1139. Wyoming State Engineer’s Office [WYSEO], 2024a, e-Permit and Instructions: Wyoming State Engineer’s Office, accessed August 2024 at https://seo.wyo.gov/home/e- permit-and-instructions. Wyoming State Engineer’s Office [WYSEO], 2024b, Water usage data across Wyoming: Wyoming State Engineer’s Office, accessed August 2024 at https:// lookerstudio.google.com/reporting/dcd8ee98-02fa-4718- b2cc-b0e87d0928e5/page/43OhB. Wyoming State Legislature, 2024, Chapter 1—General provisions: Wyoming State Legislature, Title 41—Water, accessed August 2024 at https://wyoleg.gov/statutes/ compress/title41.pdf.

72 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Appendix 1. Streamflow Recharge Extrapolation Methods Additional methods were needed to extrapolate streamflow recharge estimates. Carter and others (2001) extrapolated recharge estimates for streams with miscellaneous-record streamgages and ungaged streams for water years 1950–91 using available data, which was updated in this study using additional data for water years 1999–2022. The percentage of combined recharge for each type of basin (continuous, miscellaneous, ungaged) was calculated by Carter and others (2001) for each year from 1992 to 1998 by dividing the subtotal for each type of basin by the total combined recharge of all basins. Streamflow recharge estimates for water years 1999–2022 were combined with estimates for 1992–98 and mean annual percentages were recalculated. The updated percentages for water years 1992–2022 (table 1.1) for each type of basin rounded to the same values reported by Carter and others (2001) and, therefore, estimates for water years 1950–91 for basins with miscellaneous-record streamgages and ungaged basins were unchanged. Additional details regarding calculation of recharge estimates for water years 1950–91 for basins with miscellaneous-record streamgages and ungaged basins are provided in Carter and others (2001) and are not further discussed. Annual recharge for 1950–2022 for continuous-record, miscellaneous-record, and ungaged streams are provided in table 1.2. Carter and others (2001) also extrapolated annual streamflow recharge estimates for water years 1931–49 using statistical regression techniques. Linear regression of annual precipitation and streamflow recharge estimates from 1989 through 1998 from Carter and others (2001) yielded a coefficient of determination value of 0.81 and the regression equation: Streamflow Recharge=(0.294 × Precipitation Recharge)+21.319. As part of this study, linear regression was updated to include additional years of precipitation and streamflow data collection. Linear regression was performed using annual precipitation recharge and annual streamflow recharge for water years 1989 through 2022. The resulting equation yielded a coefficient of determination value of 0.57 and the regression equation: Streamflow Recharge=(0.327 × Precipitation Recharge)+33.791. Additional data for water years 1999–2022 lowered the coefficient of determination value of the linear regression; however, this result was expected because the updated regression consisted of climatic conditions with a greater range of annual precipitation and streamflow recharge values than those in Carter and others (2001). Additionally, streamflow data were scarce before the 1980s except for a few major streams, which made estimating streamflow recharge difficult. The updated regression equation was chosen to recalculate annual streamflow recharge estimates for 1931–49 (table 1.3). Updated annual streamflow recharge estimates generally were greater than estimates from

Carter and others (2001) but the differences varied by year. Percent difference of estimates from Carter and others (2001) and the result computed in this study ranged from −17.3 to 44.0 percent, with a mean of 9.3 percent. Combined annual streamflow recharge estimates in table 1.3 were used to determine streamflow recharge for each basin or group of basins for 1931–2022 so that streamflow recharge estimates could be calculated for subareas 1–9. Streamflow recharge values were determined for 1931–49 for basins with continuous-record streamgages and for 1931–91 for basins with miscellaneous-record streamgages and ungaged basins. In some instances, two or more basins were combined for streamflow recharge estimates, which were kept for extrapolation recharge estimates for consistency with previous calculations. Most drainage basins were completely within subarea boundaries with some exceptions. Parts of basins 14 and 16 west of the subarea 4 boundary were in subareas 1 and 9, but all recharge estimates were assumed to be within subarea 4. This assumption was considered valid because the major loss zones for both basins were within subarea 4 (Hortness and Driscoll, 1998) and recharge occurring in basins 14 and 16 east of subarea 4 mostly were east of the groundwater divide, which discharged at headwater springs that supplied base flow to Rapid and Spring Creeks. Recharge from streamflow losses in basins 14 and 16 west of the groundwater divide was likely but was considered negligible compared to the total streamflow recharge occurring in subarea 4 and, therefore, was not calculated. Groups of ungaged basins in table 10 (in main report; basins 40–50; basins 51–55) also crossed two or more subarea boundaries. Recharge estimates were determined for the larger group and then scaled using drainage areas so that recharge estimates could be determined for the subarea containing each basin. Annual streamflow recharge values for 1950–2022 in table 1.2 were used to determine the mean annual percent contribution for basins with continuous-record streamgages, basins with miscellaneous-record streamgages, and ungaged basins. Percent contribution was calculated for each year from 1950 to 2022 by dividing the annual streamflow recharge for each dataset (continuous, miscellaneous, ungaged) by the total annual streamflow recharge of all datasets. For example, in 1950, the annual streamflow recharge for basins with continuous-record streamgages was 59.64 cubic feet per second (ft3/s; table 5 in main report) and the total annual streamflow for all basins was 79.5 ft3/s. Dividing 59.64 ft3/s by 79.5 ft3/s yielded a percent contribution of 75 percent for basins with continuous-record streamgages. Mean percent contribution was calculated for 1950–2022 and was 71.3 percent for basins with continuous-record streamgages, 10.7 percent for basins with miscellaneousrecord streamgages, and 18.0 percent for ungaged basins.

Appendix 1. Streamflow Recharge Extrapolation Methods 73 Table 1.1. Estimated streamflow recharge for selected continuous-record, miscellaneous-record, and ungaged basins, water years 1992–2022. [ft3/s, cubic feet per second]

Continuous record1 Water year

Annual recharge (ft3/s)

Percent of combined recharge2

Miscellaneous record Annual recharge (ft3/s)

Percent of combined recharge2

Ungaged Annual recharge (ft3/s)

Percent of combined recharge2

Combined recharge (ft3/s)

1992

36.55

70.95

6.5

12.62

8.47

16.44

51.52

1993

74.66

65.74

14.49

12.76

24.42

21.5

113.57

1994

68.75

66.5

13.05

12.62

21.58

20.88

103.38

1995

91.7

55.57

21.98

13.32

51.33

31.11

165.01

1996

103.07

64.31

21.45

13.38

35.76

22.31

160.28

1997

132.89

66.24

23.36

11.64

44.38

22.12

200.63

1998

106.61

68.7

18.45

11.89

30.12

19.41

155.18

1999

143.86

65.28

26.61

12.07

49.90

22.64

220.37

2000

80.17

68.47

14.52

12.4

22.40

19.13

117.09

2001

62.85

67.89

12.11

13.08

17.62

19.03

92.58

2002

34.39

68.07

6.78

13.43

9.35

18.5

50.52

2003

45.15

66.53

9.20

13.56

13.51

19.9

67.86

2004

19.73

63.85

4.75

15.38

6.42

20.77

30.90

2005

22.02

60.86

5.85

16.17

8.31

22.98

36.18

2006

36.62

58.02

9.74

15.44

16.75

26.54

63.12

2007

40.69

57.76

10.96

15.55

18.81

26.69

70.46

2008

68.92

61.6

15.06

13.46

27.91

24.94

111.89

2009

84.59

63.88

18.00

13.59

29.83

22.53

132.42

2010

92.32

63.03

18.72

12.78

35.44

24.19

146.48

2011

87.99

63.59

17.64

12.75

32.73

23.66

138.37

2012

38.34

67.79

7.70

13.61

10.52

18.6

56.55

2013

41.62

62.43

9.58

14.37

15.47

23.2

66.67

2014

125.80

63.29

25.72

12.94

47.24

23.77

198.76

2015

116.98

61.33

24.06

12.61

49.69

26.05

190.72

2016

61.83

69.89

11.30

12.77

15.34

17.34

88.47

2017

42.26

70.28

7.96

13.24

9.91

16.48

60.13

2018

72.64

13.96

12.68

23.46

21.32

110.07

2019

116.22

59.62

24.72

12.68

54.01

27.7

194.95

2020

106.91

66.79

20.03

12.51

33.14

20.7

160.08

2021

52.37

68.57

9.89

12.95

14.12

18.48

76.37

2022

49.84

64.95

10.60

13.82

16.29

21.23

76.74

Mean3

87.75

65.43

17.04

12.6

30.87

21.97

135.66

Mean

72.85

64.77

14.67

13.29

25.62

21.94

113.14

1Excludes recharge from Rapid Creek and Spearfish Creek. 2Individual values may not sum to 100 percent because of independent rounding. 3Mean from Carter and others (2001).

[--, not computed]

Annual recharge Water year

Continuous-record streams

Moving means for total streamflow recharge

Rapid Creek

Spearfish Creek

Others1

Miscellaneousrecord streams

1950

5.14

44.5

9.59

10.27

1951

9.96

4.65

39.96

7.99

13.53

76.09

1952

9.98

5.58

63.67

12.73

21.55

113.52

89.7

1953

5.83

52.51

10.5

17.77

96.62

95.41

1954

4.84

33.32

6.66

11.28

66.1

92.08

86.37

1955

5.48

32.21

6.44

10.9

65.04

75.92

83.47

1956

9.97

4.71

33.29

6.66

11.27

65.9

65.68

81.43

1957

9.02

4.95

67.05

13.41

22.69

117.12

82.68

82.15

1958

8.65

4.81

38.83

7.77

13.14

73.2

85.41

77.47

1959

9.45

4.38

30.35

6.07

10.27

60.53

83.61

76.36

81.36

Ungaged streams

Total2

3-year mean

5-year mean

10-year mean

79.5

1960

8.71

4.08

30.41

6.08

10.29

59.57

64.43

75.26

79.37

1961

9.67

3.7

27.04

5.41

9.15

54.97

58.36

73.08

77.26

1962

7.82

4.78

71.45

14.29

24.18

122.52

79.02

74.16

78.16

1963

7.78

6.45

58.12

11.62

19.67

103.64

93.71

80.25

78.86

1964

6.64

51.24

10.25

17.34

95.48

107.21

87.24

81.8

1965

8.19

79.7

15.94

26.97

140.8

113.31

103.48

89.37

1966

6.56

53.08

10.62

17.97

98.23

111.5

112.13

92.61

1967

6.44

67.97

13.59

121

120.01

111.83

92.99

1968

5.84

43.57

8.71

14.75

82.87

100.7

107.68

93.96

1969

9.99

6.15

37.76

7.55

12.78

74.24

92.7

103.43

95.33

1970

8.26

56.5

11.3

19.12

105.19

87.43

96.31

99.89

1971

8.02

68.68

13.74

23.24

123.68

101.03

101.4

106.76

1972

9.86

8.01

70.89

14.18

23.99

126.93

118.6

102.58

107.2

1973

8.72

68.29

13.66

23.11

123.78

124.79

110.76

109.22

1974

6.63

24.35

4.87

8.24

54.09

101.6

106.73

105.08

1975

9.99

6.55

51.69

10.34

17.5

96.06

91.31

104.91

100.61

1976

6.59

62.67

12.53

21.21

113.01

87.72

102.77

102.08

1977

6.72

45.18

9.04

15.29

86.23

98.43

94.63

98.61

1978

9.99

7.67

59.14

11.83

20.02

108.65

102.63

91.61

101.19

74 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Table 1.2. Estimated total streamflow recharge, in cubic feet per second, from all sources, water years 1950–2022.

Table 1.2. Estimated total streamflow recharge, in cubic feet per second, from all sources, water years 1950–2022.—Continued [--, not computed]

Annual recharge Continuous-record streams

Moving means for total streamflow recharge

Spearfish Creek

Others1

1979

6.28

44.64

8.93

1980

5.59

28.98

5.8

9.81

60.17

84.59

90.6

97.76

1981

5.03

29.8

5.96

10.09

60.88

68.67

80.18

91.48

1982

9.9

6.3

47.32

9.46

16.02

70.02

80.73

87.68

1983

7.82

63.42

12.68

21.46

115.39

88.42

82.08

86.84

1984

8.03

67.92

13.58

22.99

122.53

108.97

89.59

93.69

1985

5.48

22.36

4.47

7.57

49.88

95.93

87.54

89.07

1986

5.65

49.97

9.99

16.91

92.52

88.31

93.86

87.02

1987

4.83

60.82

12.16

20.59

108.41

83.6

97.74

89.24

1988

4.92

15.25

3.05

5.16

38.38

79.77

82.34

82.21

1989

5.03

16.46

3.29

5.57

40.36

62.38

65.91

77.75

1990

5.04

39.8

7.96

13.47

76.27

51.67

71.19

79.36

Ungaged streams

Total2

3-year mean

5-year mean

10-year mean

15.11

84.96

93.28

97.78

102.26

1991

9.99

4.94

57.32

11.46

19.4

103.11

73.25

73.3

83.58

1992

4.78

36.55

6.5

8.47

66.3

81.89

64.88

81.31

1993

5.26

74.66

14.49

24.42

128.83

99.42

82.97

82.66

1994

6.78

68.75

13.05

21.58

120.16

105.1

98.93

82.42

1995

8.56

91.7

21.98

51.33

183.57

144.18

120.39

95.79

1996

9.2

103.07

21.45

35.76

179.48

161.07

135.67

104.49

1997

10.92

132.89

23.36

44.38

221.55

194.87

166.72

115.8

1998

9.59

106.61

18.45

30.12

174.77

191.93

175.9

129.44

1999

10.82

143.86

26.61

49.90

241.19

212.5

200.11

149.52

2000

9.72

80.17

14.52

22.40

136.81

184.26

190.76

155.58

2001

8.08

62.85

12.11

17.62

110.66

162.89

177

156.33

2002

6.76

34.39

6.78

9.35

67.28

104.92

146.14

156.43

2003

6.89

45.15

9.20

13.51

84.75

87.56

128.14

152.02

2004

6.05

19.73

4.75

6.42

46.95

66.33

89.29

144.7

2005

5.86

22.02

5.85

8.31

52.04

61.25

72.34

131.55

2006

6.42

36.62

9.74

16.75

79.53

59.51

66.11

121.55

2007

6.76

40.69

10.96

18.81

87.22

72.93

70.1

108.12

Appendix 1. Streamflow Recharge Extrapolation Methods 75

Rapid Creek

Miscellaneousrecord streams

Water year

[--, not computed]

Annual recharge Continuous-record streams

Moving means for total streamflow recharge

Rapid Creek

Spearfish Creek

Others1

Miscellaneousrecord streams

2008

8.49

68.92

15.06

27.91

130.38

99.04

79.22

103.68

2009

9.47

84.59

18.00

29.83

151.89

123.16

100.21

94.75

2010

9.97

92.32

18.72

35.44

166.45

149.57

123.09

97.72

2011

10.79

87.99

17.64

32.73

159.15

159.16

139.02

102.56

2012

9.04

38.34

7.70

10.52

75.60

133.73

136.69

103.4

2013

8.56

41.62

9.58

15.47

85.23

106.66

127.66

103.44

2014

11.54

125.80

25.72

47.24

220.30

127.04

141.35

120.78

2015

11.51

116.98

24.06

49.69

212.24

172.59

150.5

136.8

2016

9.6

61.83

11.30

15.34

108.07

180.2

140.29

139.65

2017

7.37

42.26

7.96

9.91

77.50

132.6

140.67

138.68

2018

6.92

72.64

13.96

23.46

126.98

104.18

149.02

138.34

2019

8.51

116.22

24.72

54.01

213.46

139.31

147.65

144.5

2020

9.13

106.91

20.03

33.14

179.21

173.22

141.04

145.77

2021

7.63

52.37

9.89

14.12

94.01

162.23

138.23

139.26

2022

7.41

49.84

10.60

16.29

94.14

122.45

141.56

141.11

Mean (1950–1998)3

9.81

6.25

53.5

10.64

18.18

98.39

Mean (1950–2022)

9.87

6.98

58.44

11.74

20.12

107.15

Water year

Ungaged streams

Total2

3-year mean

5-year mean

10-year mean

1Other streams with minimal regulation, including Battle Creek, Boxelder Creek, Grace Coolidge Creek, French Creek, Spring Creek, Bear Butte Creek, Bear Gulch, Beaver Creek, and Elk Creek. 2Values may not exactly sum to total due to independent rounding. 3Mean from Carter and others (2001).

76 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Table 1.2. Estimated total streamflow recharge, in cubic feet per second, from all sources, water years 1950–2022.—Continued

Appendix 1. Streamflow Recharge Extrapolation Methods 77 Table 1.3. Summary of streamflow, precipitation, and combined recharge, water years 1931–2022. [ft3/s, cubic feet per second; --, not applicable]

Water year

Streamflow recharge

Precipitation recharge

Total (ft3/s)

Total (acre-feet)

Rank

1931

250.99

236,915

1932

2102.66

274,322

1933

296.81

270,087

1934

249.71

235,988

1935

268.35

249,483

1936

243.84

1937

Total (ft3/s)

Combined recharge

Total (acre-feet)

Rank

52.61

38,091

210.66

152,512

192.78

139,563

48.69

35,250

105.71

76,534

231,739

30.73

22,247

263.5

245,972

90.88

65,791

1938

266.82

248,375

101.04

73,148

1939

266.66

248,260

100.56

72,802

1940

260.45

243,764

81.56

59,048

1941

2118.14

285,529

258.02

186,801

1942

298.81

271,535

198.89

1943

281.41

258,938

1944

276.84

255,630

1945

2115.04

283,285

1946

2156.75

2113,482

1947

289.81

1948 1949

Total1

Total (acre-feet)

Rank

103.60

75,007

313.32

226,835

289.59

209,651

98.40

71,238

174.06

126,017

74.57

53,985

154.38

111,763

167.86

121,524

167.22

121,062

142.01

102,812

376.16

272,331

143,991

297.70

215,527

145.67

105,459

227.08

164,398

131.70

95,348

208.54

150,978

248.53

179,929

363.57

263,215

376.14

272,313

532.89

385,795

265,019

171.35

124,052

261.16

189,072

281.89

259,286

147.15

106,532

229.04

165,818

265.84

247,666

98.03

70,970

163.87

118,636

(ft3/s)

1950

79.5

57,555

135.78

98,298

215.28

155,854

1951

76.09

55,087

126.71

91,737

202.80

146,824

1952

113.52

82,185

135.45

98,063

248.97

180,248

1953

96.62

69,950

135.43

98,047

232.05

167,997

1954

66.1

47,854

77.52

56,125

143.62

103,980

1955

65.04

47,087

192.71

139,515

257.75

186,602

1956

65.9

47,709

106.71

77,258

172.61

124,967

1957

117.12

84,791

201.42

145,825

318.54

230,616

1958

73.2

52,994

142.08

102,862

215.28

155,857

1959

60.53

43,822

110.35

79,886

170.88

123,708

1960

59.57

43,127

89.60

64,871

149.17

107,998

1961

54.97

39,796

60.24

43,614

115.21

83,410

1962

122.52

88,700

347.87

251,845

470.39

340,546

1963

103.64

75,032

290.45

210,274

394.09

285,307

1964

95.48

69,124

310.64

224,891

406.12

294,016

1965

140.8

101,934

354.36

256,546

495.16

358,481

1966

98.23

71,115

112.12

81,171

210.35

152,286

1967

121

87,600

230.01

166,516

351.01

254,117

1968

82.87

59,995

180.99

131,029

263.86

191,025

1969

74.24

53,747

159.11

115,187

233.35

168,935

1970

105.19

76,154

211.30

152,972

316.49

229,127

1971

123.68

89,540

258.15

186,891

381.83

276,432

78 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 Table 1.3. Summary of streamflow, precipitation, and combined recharge, water years 1931–2022.—Continued [ft3/s, cubic feet per second; --, not applicable]

Water year

Streamflow recharge

Precipitation recharge

Total (ft3/s)

Total (acre-feet)

Rank

Total (ft3/s)

1972

126.93

91,893

1973

123.78

89,613

1974

54.09

39,159

1975

96.06

69,544

1976

113.01

1977 1978 1979 1980

Total (acre-feet)

291.90 207.97

102.19

137.26

81,815

86.23

62,428

108.65

78,659

84.96 60.17

Combined recharge Rank

Total1 (ft3/s)

Total (acre-feet)

Rank

211,325

418.83

303,219

150,564

331.75

240,178

73,980

156.28

113,140

99,374

233.32

168,919

260.38

188,507

373.39

270,323

194.47

140,787

280.70

203,215

238.21

172,453

346.86

251,113

61,508

172.69

125,019

257.65

186,528

43,561

91.66

66,361

151.83

109,922

1981

60.88

44,075

156.05

112,974

216.93

157,049

1982

64,433

353.38

255,834

442.38

320,268

1983

115.39

83,538

198.15

143,451

313.54

226,990

1984

122.53

88,708

240.74

174,287

363.27

262,995

1985

49.88

36,111

59.84

43,319

109.72

79,430

1986

92.52

66,981

370.56

268,270

463.08

335,253

1987

108.41

78,485

134.34

97,256

242.75

175,741

1988

38.38

27,786

94.88

68,693

133.26

96,479

1989

40.36

29,219

131.00

94,840

171.36

124,060

1990

76.27

55,217

136.68

98,949

212.95

154,167

1991

103.11

74,648

304.27

220,282

407.38

294,931

1992

66.3

47,999

182.45

132,084

248.75

180,084

1993

128.83

93,269

429.40

310,873

558.23

404,143

1994

120.16

86,992

198.49

143,698

318.65

230,691

1995

183.57

132,898

426.87

309,039

610.44

441,938

1996

179.48

129,937

384.97

278,709

564.45

408,647

1997

221.55

160,395

437.89

317,017

659.44

477,413

1998

174.77

126,528

335.32

242,758

510.09

369,287

1999

241.19

174,613

478.18

346,183

719.37

520,797

2000

136.81

99,046

145.40

105,263

282.21

204,310

2001

110.66

80,114

177.96

128,837

288.62

208,952

2002

67.28

48,708

122.55

88,719

189.83

137,428

2003

84.75

61,356

208.65

151,058

293.40

212,415

2004

46.95

33,990

98.93

71,624

145.88

105,615

2005

52.04

37,675

158.04

114,413

210.08

152,088

2006

79.53

57,577

296.13

214,387

375.66

271,965

2007

87.22

63,144

189.72

137,354

276.94

200,499

2008

130.38

94,391

495.58

358,782

625.96

453,174

2009

151.89

109,963

303.07

219,409

454.96

329,373

2010

166.45

120,504

329.85

238,801

496.30

359,306

2011

159.15

115,219

486.87

352,481

646.02

467,701

2012

75.60

54,732

101.70

73,628

177.30

128,361

Appendix 1. Streamflow Recharge Extrapolation Methods 79 Table 1.3. Summary of streamflow, precipitation, and combined recharge, water years 1931–2022.—Continued [ft3/s, cubic feet per second; --, not applicable]

Water year

Streamflow recharge Total (ft3/s)

Precipitation recharge

Total (acre-feet)

Rank

Total (ft3/s)

Total (acre-feet)

Combined recharge Rank

Total1 (ft3/s)

Total (acre-feet)

Rank

2013

85.23

61,704

359.15

260,011

444.38

321,716

2014

220.30

159,490

500.43

362,294

720.73

521,785

2015

212.24

153,655

358.81

259,766

571.05

413,422

2016

108.07

78,239

166.04

120,206

274.11

198,446

2017

77.50

56,107

209.23

151,473

286.73

207,581

2018

126.98

91,929

389.67

282,111

516.65

374,041

2019

213.46

154,538

461.12

333,832

674.58

488,371

2020

179.21

129,742

196.66

142,377

375.87

272,120

2021

94.01

68,060

171.95

124,484

265.96

192,545

2022

94.14

68,154

254.63

184,344

348.77

252,499

Statistics for 1931–2022; includes updated annual streamflow recharge for 1931–49 Number

Minimum

38.38

27,786

30.73

22,247

74.57

53,985

Maximum

241.19

174,613

500.43

362,294

720.73

521,785

Mean

101.92

73,785

214.04

154,960

315.96

228,746

1Individual recharge estimates may not sum to total because of independent rounding. 2Updated annual streamflow recharge values differ from Carter and others (2001).

Mean percent contribution for each type of dataset was applied to annual streamflow recharge values for 1931–49 in table 1.3 to determine the total annual recharge for each type of dataset. Annual streamflow estimates were then calculated for each basin using the total annual recharge for each type of dataset for 1931–49. Percent contribution of each basin or group of basins within each type of dataset (continuous, miscellaneous, ungaged) was calculated by dividing available annual streamflow recharge values by the total streamflow recharge for each year. For example, the streamflow recharge for Rapid Creek in 1950 (10 ft3/s; table 1.2) was divided by

the total streamflow recharge of all basins with continuous record streamgages in 1950 (sum of Rapid Creek, Spearfish Creek and “Others” in table 1.2; 59.64 ft3/s), which yielded a percent contribution of about 16.8 percent. The mean percent contribution was then calculated for each basin or group of basins within each type of dataset and applied to the total annual recharge estimates for each type of dataset for 1931–49 to determine the recharge in each basin. Basins were then grouped into subareas and annual recharge values were summed by year for 1931–2022 (table 1.4).

80 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 Table 1.4. Extrapolated streamflow recharge to the Madison and Minnelusa aquifers for subareas 1–9 for 1931–2022 with minimum, maximum, mean, and median annual streamflow. Water year

Recharge, in cubic feet per second Subarea 1

Subarea 2

Subarea 3

Subarea 4

Subarea 5

Subarea 6

Subarea 7

Subarea 8

Subarea 9

Total

1931

9.42

9.61

4.52

16.74

4.72

3.42

1.12

1.44

0.00

50.99

1932

18.97

19.35

9.09

33.71

9.50

6.89

2.25

2.89

0.00

102.66

1933

17.89

18.24

8.58

31.79

8.96

6.50

2.13

2.73

0.00

96.81

1934

9.18

9.37

4.40

16.32

4.60

3.34

1.09

1.40

0.00

49.71

1935

12.63

12.88

6.06

22.44

6.33

4.59

1.50

1.93

0.00

68.35

1936

8.10

8.26

3.88

14.39

4.06

2.94

0.96

1.24

0.00

43.84

1937

11.73

11.97

5.63

20.85

5.88

4.26

1.39

1.79

0.00

63.50

1938

12.35

12.59

5.92

21.94

6.18

4.49

1.47

1.88

0.00

66.82

1939

12.32

12.56

5.91

21.89

6.17

4.48

1.46

1.88

0.00

66.66

1940

11.17

11.39

5.36

19.85

5.59

4.06

1.33

1.70

0.00

60.45

1941

21.83

22.26

10.47

38.79

10.93

7.93

2.59

3.33

0.00

118.14

1942

18.26

18.62

8.75

32.44

9.15

6.64

2.17

2.79

0.00

98.81

1943

15.04

15.34

7.21

26.73

7.53

5.47

1.79

2.30

0.00

81.41

1944

14.20

14.48

6.81

25.23

7.11

5.16

1.69

2.17

0.00

76.84

1945

21.25

21.68

10.19

37.77

10.65

7.72

2.53

3.24

0.00

115.04

1946

28.96

29.54

13.89

51.47

14.51

10.53

3.44

4.42

0.00

156.75

1947

16.59

16.92

7.96

29.49

8.31

6.03

1.97

2.53

0.00

89.81

1948

15.13

15.43

7.25

26.89

7.58

5.50

1.80

2.31

0.00

81.89

1949

12.16

12.41

5.83

21.62

6.09

4.42

1.45

1.86

0.00

65.84

1950

12.96

14.48

8.77

26.84

6.97

5.31

2.58

1.59

0.00

79.50

1951

13.27

14.18

8.02

24.53

7.09

4.94

1.97

2.10

0.00

76.10

1952

19.09

19.89

8.79

42.46

11.19

6.75

2.01

3.34

0.00

113.53

1953

17.06

17.27

8.98

34.08

7.93

5.73

2.80

2.76

0.00

96.61

1954

12.09

12.85

7.59

19.85

5.97

4.20

1.80

1.75

0.00

66.09

1955

12.51

13.00

7.92

17.70

5.70

4.39

2.12

1.69

0.00

65.03

1956

11.94

12.38

7.31

20.75

6.20

4.10

1.49

1.75

0.00

65.91

1957

19.14

20.98

8.80

42.79

12.81

7.43

1.66

3.52

0.00

117.12

1958

13.18

13.75

7.58

23.17

7.27

4.67

1.54

2.04

0.00

73.20

1959

10.98

11.11

6.55

19.98

5.99

3.45

0.86

1.59

0.00

60.52

1960

10.70

11.16

6.63

19.24

5.85

3.44

0.97

1.60

0.00

59.59

1961

9.61

9.93

5.99

19.11

5.53

2.86

0.51

1.42

0.00

54.96

1962

19.92

24.03

10.18

41.92

11.45

8.27

2.99

3.75

0.00

122.52

1963

18.83

21.60

9.86

27.04

12.73

7.62

2.90

3.05

0.00

103.63

1964

17.63

18.39

9.76

27.13

9.98

6.54

3.36

2.69

0.00

95.47

1965

25.07

30.03

12.44

39.69

14.09

10.71

4.58

4.18

0.00

140.79

1966

17.93

18.17

9.62

32.02

8.10

6.27

3.34

2.79

0.00

98.24

1967

20.86

22.89

9.38

40.56

11.87

8.86

3.00

3.57

0.00

120.99

1968

15.18

16.08

7.10

27.42

8.32

5.38

1.09

2.29

0.00

82.86

1969

14.29

13.57

6.03

25.87

6.75

4.82

0.91

1.98

0.00

74.22

1970

20.30

18.27

7.47

36.95

9.03

7.65

2.56

2.97

0.00

105.19

1971

22.59

22.64

9.19

41.75

11.61

9.10

3.20

3.61

0.00

123.68

1972

23.03

24.23

9.96

41.05

12.73

9.13

3.07

3.72

0.00

126.93

Appendix 1. Streamflow Recharge Extrapolation Methods 81 Table 1.4. Extrapolated streamflow recharge to the Madison and Minnelusa aquifers for subareas 1–9 for 1931–2022 with minimum, maximum, mean, and median annual streamflow.—Continued Water year

Recharge, in cubic feet per second Subarea 1

Subarea 2

Subarea 3

Subarea 4

Subarea 5

Subarea 6

Subarea 7

Subarea 8

Subarea 9

Total

1973

23.21

23.76

9.87

39.32

12.56

8.68

2.78

3.59

0.00

123.77

1974

11.98

8.62

4.06

20.66

3.81

3.22

0.46

1.28

0.00

54.09

1975

17.59

17.02

7.07

34.18

8.42

6.93

2.15

2.71

0.00

96.07

1976

19.90

21.99

9.23

36.65

11.59

7.94

2.40

3.29

0.00

113.00

1977

16.41

14.38

5.97

32.92

5.77

6.41

1.99

2.37

0.00

86.23

1978

20.25

19.92

8.25

36.53

10.42

7.72

2.45

3.11

0.00

108.65

1979

15.84

16.86

7.48

26.79

9.34

5.33

0.97

2.34

0.00

84.97

1980

11.90

11.33

5.33

21.08

4.90

3.56

0.55

1.52

0.00

60.17

1981

11.51

12.06

5.71

19.65

6.50

3.34

0.56

1.57

0.00

60.89

1982

16.42

17.33

7.57

28.50

9.67

5.76

1.25

2.49

0.00

88.99

1983

21.30

19.21

7.53

43.25

8.49

8.74

3.51

3.33

0.00

115.37

1984

22.45

22.25

9.00

42.12

11.22

8.67

3.25

3.57

0.00

122.53

1985

10.42

7.03

3.27

20.62

2.82

4.13

0.42

1.17

0.00

49.88

1986

16.32

18.14

7.86

32.69

8.09

4.96

1.81

2.62

0.00

92.50

1987

17.75

23.97

10.53

32.36

11.82

7.12

1.65

3.19

0.00

108.40

1988

8.39

4.90

2.52

17.07

1.90

2.52

0.29

0.80

0.00

38.38

1989

8.74

8.22

2.70

15.39

2.66

1.46

0.31

0.86

0.00

40.34

1990

13.61

13.19

8.59

23.46

9.87

4.71

0.75

2.09

0.00

76.27

1991

17.09

20.51

9.09

32.87

12.06

7.16

1.31

3.01

0.00

103.10

1992

10.47

8.69

5.57

25.69

7.80

5.53

0.99

1.57

0.00

66.31

1993

19.16

23.83

10.05

42.53

17.76

9.21

2.18

4.12

0.00

128.84

1994

20.54

26.45

10.87

40.06

10.08

7.44

2.29

2.42

0.00

120.15

1995

30.94

43.80

12.00

45.99

19.81

12.99

6.12

11.92

0.00

183.56

1996

30.20

35.97

13.91

54.97

18.42

13.87

6.08

6.04

0.00

179.46

1997

31.95

46.69

16.80

68.01

26.05

16.83

6.73

8.48

0.00

221.54

1998

26.72

27.16

14.92

58.58

19.50

15.33

5.85

6.70

0.00

174.76

1999

35.89

44.00

18.88

72.42

31.79

19.48

8.28

11.23

0.00

241.99

2000

24.96

21.74

12.86

44.96

12.64

12.14

4.61

4.28

0.00

138.19

2001

19.76

17.52

9.58

37.10

12.27

9.32

2.57

3.09

0.00

111.20

2002

13.96

8.90

5.38

24.31

6.33

5.69

1.63

1.67

0.00

67.86

2003

17.21

13.84

7.96

29.10

7.54

6.03

1.51

1.88

0.00

85.08

2004

12.17

6.65

4.33

17.20

2.43

2.92

0.92

0.81

0.00

47.43

2005

12.69

9.28

4.46

16.98

4.37

2.61

0.77

0.74

0.00

51.88

2006

17.36

22.69

7.81

21.88

3.92

2.74

0.72

0.77

0.00

77.88

2007

19.90

25.76

10.34

23.36

2.75

2.16

0.44

0.64

0.00

85.35

2008

24.10

35.77

11.21

39.07

8.99

6.34

1.16

2.54

0.00

129.19

2009

27.51

38.02

14.14

46.13

13.41

7.72

1.30

2.55

0.00

150.77

2010

27.64

35.30

13.85

49.37

17.74

11.39

4.00

6.64

0.00

165.92

2011

28.10

32.74

13.57

46.92

14.33

12.06

4.81

5.99

0.00

158.52

2012

18.66

9.65

7.71

26.47

4.21

6.03

2.11

1.70

0.00

76.55

2013

19.59

20.00

9.23

26.58

4.26

3.03

1.16

0.84

0.00

84.70

2014

36.97

57.18

18.47

65.63

18.54

12.22

3.96

5.07

0.00

218.03

82 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022 Table 1.4. Extrapolated streamflow recharge to the Madison and Minnelusa aquifers for subareas 1–9 for 1931–2022 with minimum, maximum, mean, and median annual streamflow.—Continued Water year

Recharge, in cubic feet per second Subarea 1

Subarea 2

Subarea 3

Subarea 4

Subarea 5

Subarea 6

Subarea 7

Subarea 8

Subarea 9

Total

2015

34.44

44.22

17.83

60.67

24.07

14.20

6.38

9.74

0.00

211.54

2016

21.91

13.33

11.31

36.51

10.73

9.14

3.59

2.62

0.00

109.13

2017

16.10

8.57

8.03

28.49

7.50

6.51

2.05

1.88

0.00

79.13

2018

20.35

17.98

11.28

41.54

15.78

11.20

4.08

5.96

0.00

128.16

2019

29.47

50.77

14.97

57.57

22.36

15.68

7.48

12.50

0.00

210.80

2020

28.62

34.05

17.86

56.76

15.12

13.72

6.13

5.72

0.00

177.99

2021

17.99

14.20

8.34

32.42

7.45

7.88

3.55

2.57

0.00

94.39

2022

18.61

19.77

8.61

30.13

5.67

6.31

2.71

1.83

0.00

93.63

Minimum

8.10

4.90

2.52

14.39

1.90

1.46

0.29

0.64

0.00

38.38

Maximum

36.97

57.18

18.88

72.42

31.79

19.48

8.28

12.50

0.00

241.99

Mean

18.26

19.66

8.86

32.89

9.72

6.98

2.40

3.08

0.00

101.85

Median

17.69

17.75

8.46

30.96

8.37

6.32

2.00

2.54

0.00

94.01

References Cited Carter, J.M., Driscoll, D.G., and Hamade, G.R., 2001, Estimated recharge to the Madison and Minnelusa aquifers in the Black Hills area, South Dakota and Wyoming, water years 1931–98: U.S. Geological Survey Water Resources Investigations Report 00–4278, 66 p., accessed August 2024 at https://doi.org/10.3133/wri004278.

Hortness, J.E., and Driscoll, D.G., 1998, Streamflow losses in the Black Hills of western South Dakota: U.S. Geological Survey Water-Resources Investigations Report 98–4116, 99 p., accessed August 2024 at https://doi.org/10.3133/wri984116.

Appendix 2. Headwater Springflow Estimates, 1931–2022 83

Appendix 2. Headwater Springflow Estimates, 1931–2022 Headwater springflow is discharged from aquifers to the land surface upstream from the aquifer loss zones in the Madison and Minnelusa outcrops (fig. 7 in main report). This type of springflow originates at the Limestone Plateau area of the western Black Hills (fig. 7 in main report), which is comprised of outcrops of the Deadwood Formation, Madison Limestone, and Minnelusa Formation. The Limestone Plateau is a significant recharge area because of its large relative size compared to other outcrop areas in the Black Hills and because of the relatively high permeability of the rock. Additionally, the plateau is the headwater origin of most major streams discharging from the Black Hills. A groundwater divide splits the direction of groundwater flow in the plateau (fig. 7 in main report). Precipitation on the east part of the divide infiltrates into the outcrops and recharges groundwater in the aquifers which then flows to the east. At the contact between the Madison Limestone and the underlying geologic units along the eastern fringe of the plateau, the groundwater discharges to the surface forming headwater springs. Springflow from individual headwater spring areas ranged from less than 1 to more than 30 cubic feet per second (ft3/s; Carter and others, 2001) and provided the headwaters for many of the streams flowing to the north and east in the Black Hills. Although the Limestone Plateau provides a source of groundwater for springflow, direct surface runoff from the outcrops of the plateau is rare and peak flows following heavy rain at streams in the plateau are subdued compared to other stream sites in the Black Hills (Bunkers and others, 2015). The absence of runoff is the basis of the assumption by Carter and others (2001) that the efficiency of recharge from

infiltration of precipitation approximates the yield efficiencies of nearby basins. The application of this assumption was used to estimate headwater springflow. Quantifying headwater springflow was accomplished using methods and assumptions described by Carter and others (2001) but with yield efficiency values gridded for the study area and updated precipitation data from 1981–2022. Assuming that direct surface runoff from outcrops of the Madison Limestone and Minnelusa Formation is uncommon (Miller and Driscoll, 1998), headwater springflow was assumed equal to the recharge from infiltration of precipitation in the part of the Limestone Plateau east of the groundwater divide (fig. 7 in main report). Recharge from precipitation infiltration was approximated by the yield equation (eq. 3 in main report), and yield was estimated as described in the “Precipitation Recharge” section in the main report. The gridded recharge resulting from equation 3 was clipped to the Madison Limestone and Minnelusa and Deadwood Formations outcrops east of the groundwater divide (fig. 7 in main report) in the Limestone Plateau. Estimated mean annual recharge to contributing areas for headwater springs for 1931–2022 is listed in table 2.1. Mean annual headwater springflow was 69.7 ft3/s for 1931–2002, the minimum was 8.4 ft3/s (1936), and the maximum was 191.6 ft3/s (2014). Carter and others (2001) estimated mean annual headwater springflow at 65.6 ft3/s for 1931–98, which was 6-percent less than estimates provided in this study. The higher mean annual headwater springflow estimate was expected because the mean annual precipitation was greater in this study for 1931–2022 than in Carter and others (2001) for 1931–98.

84 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Table 2.1. Estimated mean annual recharge to contributing areas for headwater springs, water years 1931–2022. [ft3/s, cubic feet per second]

Water year

Headwater springflow (ft3/s)

Water year

Headwater springflow (ft3/s)

Water year

Headwater springflow (ft3/s)

1931

14.1

1970

65.1

2009

102.6

1932

64.8

1971

77.1

2010

101.6

1933

56.6

1972

84.1

2011

160.4

1934

15.4

1973

59.7

2012

39.6

1935

36.4

1974

32.4

2013

127.2

1936

8.4

1975

42.8

2014

191.6

1937

26.0

1976

75.3

2015

132.4

1938

30.8

1977

61.9

2016

53.2

1939

33.3

1978

70.8

2017

68.1

1940

23.1

1979

53.2

2018

103.9

1941

73.8

1980

28.4

2019

123.5

1942

56.6

1981

46.5

2020

77.5

1943

51.2

1982

113.7

2021

65.5

1944

39.9

1983

77.4

2022

89.8

1945

77.5

1984

85.7

Mean annual

69.7

1946

117.0

1985

23.0

54.4

1986

118.3

Minimum (1936)

8.4

1947 1948

48.9

1987

50.4

191.6

1949

29.2

1988

38.4

Maximum (2014)

1950

44.7

1989

47.6

1951

36.9

1990

45.0

1952

46.4

1991

99.0

1953

49.5

1992

58.8

1954

27.3

1993

130.0

1955

63.6

1994

71.0

1956

34.0

1995

142.0

1957

62.1

1996

129.0

1958

43.8

1997

165.4

1959

34.7

1998

119.2

1960

36.0

1999

128.4

1961

18.4

2000

55.4

1962

101.1

2001

50.2

1963

92.5

2002

35.2

1964

109.1

2003

78.8

1965

103.8

2004

33.4

1966

29.6

2005

55.4

1967

67.7

2006

113.4

1968

57.9

2007

66.0

1969

51.3

2008

183.4

Appendix 2. Headwater Springflow Estimates, 1931–2022 85

References Cited Bunkers, M.J., Smith, M., Driscoll, D., and Hoogestraat, G., 2015, Hydrologic response for a high-elevation storm in the South Dakota Black Hills: Rapid City, South Dakota, National Oceanic and Atmospheric Administration/National Weather Service Internal Report 2015-01, 21 p., accessed September 2024 at www.weather.gov/media/unr/soo/ reports/2015-01/NWSUNR-Report-2015-01.pdf. Carter, J.M., Driscoll, D.G., Hamade, G.R., and Jarrell, G.J., 2001, Hydrologic budgets for the Madison and Minnelusa aquifers, Black Hills of South Dakota and Wyoming, water years 1987–96: U.S. Geological Survey Water-Resources Investigations Report 01–4119, 51 p., accessed August 2024 at https://doi.org/10.3133/wri014119.

Miller, L.D., and Driscoll, D.G., 1998, Streamflow characteristics for the Black Hills of South Dakota, through water year 1993: U.S. Geological Survey Water-Resources Investigations Report 97–4288, 322 p., accessed August 2024 at https://doi.org/10.3133/wri974288.

86 Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022

Appendix 3. Artesian Springflow Estimates, 1931–2022 Artesian springflow was estimated for several sites in the Black Hills area of South Dakota and Wyoming for 1931–2022. Artesian springflow was considered only for the Madison and Minnelusa aquifers. The period of record and method(s) used to estimate mean annual artesian springflow varied for each site (table 12 in main report). The mean annual artesian springflow estimates from this study also were compared to results from Carter and others (2001). The Redwater River, measured at streamgage 06433000 (table 12 in main report), often includes flow from several large artesian springs. Streamflow in the Redwater River also is influenced by surface runoff and diversions during irrigation seasons (Carter and others, 2001). Although continuous streamflow records exist for several spring areas contributing to the Redwater River, the records are insufficient to estimate all contributing artesian springflow. Annual total springflow contributing to the Redwater River was estimated by Carter and others (2001) using monthly differences in streamflow between sites 06431500 and 06433000 (table 12 in main report). Artesian springflow for each water year was assumed equal to the median of streamflow difference values from November through February when irrigation and surface runoff were minor. Estimates from Carter and others (2001) were updated by adding additional years of discharge measurements. Monthly differences in streamflow between sites 06431500 and 06433000 for water years 1947–2022 are provided in the data release accompanying this report (Medler and others, 2025). For water years 1947–2022, the mean annual artesian springflow contributing to the Redwater River was estimated at 103.6 cubic feet per second (ft3/s), which is about 15-percent higher than Carter and others (2001) estimate of 90.3 ft3/s that used data from 1987 to 1996. Mean annual artesian springflow along Spearfish Creek between sites 06431500 and 06432020 was estimated and included in the accompanying data release (Medler and others, 2025). Irrigation diversions also are part of the reach between the sites; therefore, a method like that used for the Redwater River was used to estimate artesian springflow. Artesian springflow was assumed equal to the median of monthly differences in measured streamflow between sites 06431500 and 06432020 from November through February. For 1989–98, the mean artesian springflow contribution to Spearfish Creek was estimated at 10.9 ft3/s, which is about 9-percent higher than Carter and others (2001) estimate of 10 ft3/s from 1989 to 1996. Artesian springflow along Elk Creek is variable and occurs mostly within a short reach upstream from the confluence with Little Elk Creek (Carter and others, 2001). Annual and mean annual artesian springflow was estimated from the available period of record (1992–2020) by using the daily base flow index (BFI) estimated flow for site 06425100

when streamflow at site 06424000 was less than the loss threshold of 19 ft3/s estimated by Hortness and Driscoll (1998). Daily BFI was aggregated into monthly values and then water years. The mean annual artesian springflow was estimated at 6.1 ft3/s, which is about 3.2 times greater than the Carter and others (2001) estimate of 1.9 ft3/s. Several artesian springs in the Rapid City area contribute to streamflow in Rapid Creek. The method used to estimate artesian springflow from Jackson and Cleghorn Springs was like that used by Anderson and others (1999) but updated to include data from additional water years that were not part of the original estimate. Anderson and others (1999) used a control volume analysis that included inflows and outflows in an area between streamgages 06412500 and 06412900. Inflows included streamflow from Rapid Creek at streamgage 06412500, tributary inflow, precipitation, and alluvial inflow. Mean annual inflow from streamflow was updated to include data from 1988 to 1994 (31.5 ft3/s), and annual precipitation was updated to 0.3 inch based on data from 1931 through 1994. Tributary and alluvial inflows remained the same as Anderson and others (1999). Outflows were updated to include annual mean data from streamgage 06412900 from 1988 through 1994 (47.2 ft3/s) and mean annual withdrawals from 1986 through 2006 and 2013 through 2022 (7.6 ft3/s). Evapotranspiration and alluvial outflows remained the same as the estimates from Anderson and others (1999). With updated data, the estimated Jackson and Cleghorn Spring artesian springflow was 23.6 ft3/s, which was a 9-percent increase from the original estimate of 21.6 ft3/s. Springflow from other Rapid City springs was estimated by adding the mean annual springflow at City Springs (06413600), Lime Creek (06413650), and Deadwood Avenue Spring (06413800). Additional data from water years not included in the estimate by Anderson and others (1999) were included. The total mean annual artesian springflow from these springs was 5.4 ft3/s, which was an increase of 26-percent from the estimate by Anderson and others (1999) of 4.3 ft3/s. Most of the reach of Boxelder Creek where stream losses occur are likely not in artesian conditions. However, artesian springflow could occur at the lower end of the reach upstream from site 06423010. Artesian springflow was estimated using the same method as Carter and others (2001) but with additional data from water years not included in the Carter and others (2001) study. Artesian springflow for Boxelder Creek was estimated by calculating the annual mean of base flow at site 06423010 using BFI only on days when the streamflow at site 06422500 was less than the loss threshold determined by Hortness and Driscoll (1998), which was assumed as 25 ft3/s. Artesian springflow was estimated as 0.5 ft3/s, which was a small increase from the Carter and others (2001) estimate of 0.3 ft3/s.

Appendix 3. Artesian Springflow Estimates, 1931–2022 87 The method for estimating artesian springflow at Battle Creek was like that used by Carter and others (2001) but with additional water years of data not included in the previous study. Artesian springflow at Battle Creek (site 06406000) was estimated by calculating the annual mean of base flow at the site using BFI only on days when the streamflow at Battle Creek (site 06404000) and Grace Coolidge Creek (site 06404998) were less than the loss thresholds determined by Hortness and Driscoll (1998), which were 14 ft3/s and 21 ft3/s, respectively. The daily BFI values were used to estimate the mean annual springflow of 8.2 ft3/s, which was about 17 percent higher than Carter and others (2001) estimate of 7 ft3/s. Streamflow at Beaver Creek above Buffalo Gap (06402470), Fall River at Hot Springs (06402000), and Stockade Beaver Creek near Newcastle, Wyoming (06392950) is dominated by artesian springflow (Carter and others, 2001). Artesian springflow was estimated using the same method as Carter and others (2001) by applying the BFI to measured daily flows but with additional daily values from years not included in the Carter and others (2001) study. The values were used to estimate annual mean BFI, which was then averaged to estimate the mean annual BFI for each site. Estimated mean annual artesian springflow was 9.9, 24.4, and 13.2 ft3/s for Beaver Creek above Buffalo Gap, Fall River at Hot Springs, and Stockade Beaver Creek near Newcastle, Wyoming, respectively (table 12 in main report). The values were about 3, 13, and 38 percent higher than values reported by Carter and others (2001) of 9.6, 21.5, and 9.6 ft3/s, respectively. Springflow at Cascade Springs (06400497) and nearby springs (between sites 432013103332200 and 432012103331100) were assumed to consist entirely of artesian springflow. Mean annual springflow at Cascade Springs was measured at 19.4 ft3/s (USGS, 2024) for the period of record in this study, which was 4 percent higher than the value reported by Carter and others (2001) of 18.7 ft3/s for water years 1987 through 1995. Artesian springflow from springs nearby Cascade Springs were estimated by the difference of measurements at sites 432013103332200 (Cascade Springs below Alabaugh Creek) and 432012103331100 (Cascade Springs above Alabaugh Creek). These two sites are between springs that provide tributary flow to Alabaugh Creek. Carter and others (2001) estimated springflow from the springs nearby to Cascade Springs with measurements in 1996 with a difference of 3.9 ft3/s. The measurements were completed again in 2024 with a difference of 4.3 ft3/s, or about a 10-percent increase.

References Cited Anderson, M.T., Driscoll, D.G., and Williamson, J.E., 1999, Ground-water and surface-water interactions along Rapid Creek near Rapid City, South Dakota: U.S. Geological Survey Water-Resources Investigations Report 98–4214, 99 p., accessed April 2025 at https://pubs. usgs.gov/publication/wri984214. Carter, J.M., Driscoll, D.G., Hamade, G.R., and Jarrell, G.J., 2001, Hydrologic budgets for the Madison and Minnelusa aquifers, Black Hills of South Dakota and Wyoming, water years 1987–96: U.S. Geological Survey Water-Resources Investigations Report 01–4119, 51 p., accessed August 2024 at https://doi.org/10.3133/wri014119. Hortness, J.E., and Driscoll, D.G., 1998, Streamflow losses in the Black Hills of western South Dakota: U.S. Geological Survey Water-Resources Investigations Report 98–4116, 99 p., accessed August 2024 at https://doi.org/10.3133/wri984116. Medler, C.J., Anderson, T.M., and Eldridge, W.G., 2025, Datasets used in constructing hydrologic budgets for six bedrock aquifers in the Black Hills area of South Dakota and Wyoming, 1931–2022: U.S. Geological Survey data release, https://doi.org/10.5066/P1QWKUKP. U.S. Geological Survey [USGS], 2024, USGS water data for the Nation: U.S. Geological Survey National Water Information System database, accessed August 2024 at https://doi.org/10.5066/F7P55KJN.

For more information about this publication, contact: Director, USGS Dakota Water Science Center 821 East Interstate Avenue, Bismarck, ND 58503 1608 Mountain View Road, Rapid City, SD 57702 605–394–3200 For additional information, visit: https://www.usgs.gov/centers/ dakota-water Publishing support provided by the Rolla and Sacramento Publishing Service Centers

Medler and others—Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, 1931–2022—SIR 2025–5067

ISSN 2328-0328 (online) https://doi.org/10.3133/sir20255067

Hydrologic Budgets and Water Availability of Six Bedrock Aquifers in the Black Hills Area, South Dakota and Wyoming, 1931–2022

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