U.S. Department of the Interior

U.S. Geological Survey

Geochemistry of the Madison and

Minnelusa Aquifers in the

Black Hills Area, South Dakota

Prepared in cooperation with the

South Dakota Department of Environment and Natural Resources

and the West Dakota Water Development District

Water-Resources Investigations Report 01-4129

By Cheryl A. Naus, Daniel G. Driscoll, and Janet M. Carter
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and 

does not constitute endorsement by the U.S. Geological Survey.

Rapid City, South Dakota: 2001

For additional information write to:

District Chief

U.S. Geological Survey

1608 Mt. View Road

Rapid City, SD 57702

Copies of this report can be purchased from:

U.S. Geological Survey

Information Services

Building 810

Box 25286, Federal Center

Denver, CO 80225-0286
Contents III

CONTENTS

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

Introduction ........................................................................................................................................................................... 3

Purpose and Scope....................................................................................................................................................... 3

Previous Investigations ................................................................................................................................................ 3

Acknowledgments ....................................................................................................................................................... 4

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

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

Hydrologic Setting....................................................................................................................................................... 10

Regional Setting ................................................................................................................................................ 10

Local Setting...................................................................................................................................................... 12

Methods Used and Data Sets Considered.............................................................................................................................. 16

Geochemistry of Madison and Minnelusa Aquifers.............................................................................................................. 16

Major-Ion Chemistry ................................................................................................................................................... 16

Distribution of Major Ions................................................................................................................................. 17

Saturation State.................................................................................................................................................. 20

Evolutionary Processes...................................................................................................................................... 24

Isotope Chemistry........................................................................................................................................................ 26

Background Information and Isotopic Composition of Recharge Water .......................................................... 26

Stable Isotopes of Oxygen and Hydrogen ............................................................................................... 29

Tritium ..................................................................................................................................................... 32

Conceptual Mixing Models ............................................................................................................................... 36

Description of Models ............................................................................................................................. 36

Limitations of Models ............................................................................................................................. 40

Areal Flowpaths, Ages, and Mixing Conditions ............................................................................................... 41

Isotope Distributions and General Considerations .................................................................................. 41

Stable Isotopes............................................................................................................................... 41

Tritium ........................................................................................................................................... 46

Site-Specific Considerations.................................................................................................................... 51

Rapid City Area............................................................................................................................. 51

Headwater Springs......................................................................................................................... 54

Northern Black Hills Area............................................................................................................. 55

Southern Black Hills Area............................................................................................................. 56

Regional Flowpaths ............................................................................................................................................................... 56

Interactions Between Madison and Minnelusa Aquifers....................................................................................................... 60

Interactions at Well Pairs ............................................................................................................................................. 60

Hydraulic Considerations .................................................................................................................................. 60

Geochemical Considerations ............................................................................................................................. 61

Interactions at Artesian Springs................................................................................................................................... 63

Hydraulic Considerations .................................................................................................................................. 63

Geochemical Considerations ............................................................................................................................. 65

Synopsis of Interaction Processes................................................................................................................................ 67

Summary and Conclusions .................................................................................................................................................... 68

References ............................................................................................................................................................................. 72

Supplemental Information ..................................................................................................................................................... 77
IV Contents

FIGURES

1. Map showing generalized outcrops of Madison Limestone, Minnelusa Formation, and

outer extent of Inyan Kara Group within the study area for Black Hills Hydrology Study..................................... 5

2. Stratigraphic section for the Black Hills .................................................................................................................. 6

3. Map showing distribution of hydrogeologic units in the Black Hills area............................................................... 7

4. Geologic cross section A-A′..................................................................................................................................... 9

5. Schematic showing hydrogeologic setting of the Black Hills area.......................................................................... 10

6. Map showing general direction of ground-water flow in Paleozoic aquifers in the

northern Great Plains................................................................................................................................................ 11

7. Map showing potentiometric surface of the Madison aquifer and locations of major artesian springs................... 14

8. Map showing potentiometric surface of the Minnelusa aquifer and locations of major artesian springs................ 15

9. Trilinear diagrams showing proportional concentrations of major ions in the 

Madison and Minnelusa aquifers ............................................................................................................................. 17

10. Selected Stiff diagrams showing the distribution of major-ion chemistry in the Madison aquifer.......................... 18

11. Selected Stiff diagrams showing the distribution of major-ion chemistry in the Minnelusa aquifer....................... 19

12. Graph showing relation between gypsum saturation index and dissolved sulfate in the

Madison and Minnelusa aquifers ............................................................................................................................. 23

13. Boxplots showing calcite and dolomite saturation indices for selected samples from the

Madison and Minnelusa aquifers ............................................................................................................................. 23

14-17. Graphs showing:

14. Modeled relations between calcium and magnesium concentrations, pH, and dissolved sulfate..................... 25

15. Relations between dissolved calcium and magnesium concentrations and dissolved sulfate in

the Madison and Minnelusa aquifers ................................................................................................................ 27

16. Relation between pH and dissolved sulfate in the Madison and Minnelusa aquifers....................................... 28

17. Relation between dissolved oxygen and distance from outcrop in the Madison

and Minnelusa aquifers ..................................................................................................................................... 28

18. Schematic showing fractionation of stable oxygen and hydrogen isotopes during rainout ..................................... 29

19. Graph showing relation between δ18O and δD in Black Hills samples in comparison

to the Global Meteoric Water Line........................................................................................................................... 30

20. Map showing generalized distribution of δ18O in surface water and ground water in near-recharge areas ............ 31

21. Graphs showing temporal variation of δ18O for selected sites ................................................................................ 33

22. Map showing cumulative tritium deposition on the continental United States, 1953-83, 

and location of selected collection sites ................................................................................................................... 34

23. Graph showing monthly tritium concentrations in precipitation at Ottawa, Canada ............................................... 34

24. Graph showing weighted annual tritium concentrations in precipitation at selected locations ............................... 35

25. Schematic diagrams illustrating mixing models for age dating for various ground-water flow conditions ............ 37

26. Graph showing estimated tritium concentrations in precipitation for Black Hills area and

decay curves for selected years ................................................................................................................................ 39

27-32. Maps showing:

27. Distribution of δ18O in selected Madison and Minnelusa wells and springs in the

northern Black Hills area .................................................................................................................................. 42

28. Distribution of δ18O in selected Madison and Minnelusa wells and springs in the Rapid City area ............... 43

29. Distribution of δ18O in selected Madison and Minnelusa wells and springs in the southern

Black Hills area................................................................................................................................................. 44

30. Distribution of tritium for selected sites in the northern Black Hills................................................................ 47

31. Distribution of tritium for selected sites in the Rapid City area ....................................................................... 48

32. Distribution of tritium for selected sites in the southern Black Hills area........................................................ 49

33. Boxplots of tritium concentrations for selected ground-water and surface-water samples

collected during 1990-98 in the Black Hills area..................................................................................................... 50

34. Map showing distribution of δ18O in selected Madison wells and springs and generalized 

flowpaths in the Black Hills of South Dakota and Wyoming .................................................................................. 57

35. Selected Stiff diagrams showing the distribution of major-ion chemistry in selected well

pairs and artesian springs in the Black Hills area..................................................................................................... 59

36. Graphs showing decay-curve families for time-delay mixing model ...................................................................... 79

37. Hydrographs of selected well pairs .......................................................................................................................... 84
Contents V

TABLES

1. Saturation indices for selected samples from wells completed in the Madison and Minnelusa aquifers............... 21

2. Selected results of geochemical modeling.............................................................................................................. 25

3. Selected data for observation well pairs ................................................................................................................. 45

4. Tritium data for selected sites having data for 2000............................................................................................... 52

5. Generalized age estimates for headwater springs, derived using immediate-arrival mixing model....................... 54

6. Selected hydraulic and geochemical information for major artesian springs......................................................... 64

7. Selected site information and isotope data for sites used in report......................................................................... 87

8. Stable isotope data for sites with multiple samples................................................................................................ 103

9. Weighted annual tritium concentrations in precipitation for Black Hills area ....................................................... 114

10. Monthly estimated tritium concentrations in precipitation, monthly precipitation, and weighted

annual tritium concentrations in precipitation for Black Hills area........................................................................ 115

11. Estimated tritium concentrations in precipitation for Black Hills area, adjusted for decay................................... 117

CONVERSION FACTORS, ACRONYMS, AND ABBREVIATIONS

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F = (1.8 × °C) + 32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C = (°F - 32) / 1.8

Water year: Water year is the 12-month period, October 1 through September 30, and is designated

by the calendar year in which it ends. Thus, the water year ending September 30, 1998, is called the

“1998 water year.”

Per mil (‰): A unit expressing the ratio of stable-isotopic abundances of an element in a sample to those of a standard material. Per mil

units are equivalent to parts per thousand. Stable-isotopic ratios are computed as follows:

where

X is the heavier isotope and

R is the ratio of the heavier, less abundant stable isotope to the lighter, stable isotope in a sample or standard.

The δ values for oxygen and hydrogen stable isotopic ratios discussed in this report are referenced to the following standard material:

Multiply By To obtain

acre 4,047 square meter

acre 0.4047 hectare

acre-foot per year (acre-ft/yr) 1,233 cubic meter per year

acre-foot per year (acre-ft/yr) 0.001233 cubic hectometer per year

cubic foot per second (ft3

/s) 0.02832 cubic meter per second 

foot per year (ft/yr) 0.3048 meter per year

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

inch 2.54 centimeter

inch 25.4 millimeter

inch per year (in/yr) 25.4 millimeter per year

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

Ratio (R) Standard identity and reference

hydrogen-2:hydrogen-1 Vienna Standard Mean Ocean Water (VSMOW)

oxygen-18:oxygen-16 Vienna Standard Mean Ocean Water (VSMOW)

δX R sample ( )

R s dard ( ) tan

------------------------------- 1 –    = × 1 000 ,
Abstract 1

Geochemistry of the Madison and Minnelusa

Aquifers in the Black Hills Area, South Dakota

By Cheryl A. Naus, Daniel G. Driscoll, and Janet M. Carter

ABSTRACT

The Madison and Minnelusa aquifers are 

two of the most important aquifers in the Black 

Hills area because of utilization for water supplies 

and important influences on surface-water 

resources resulting from large springs and streamflow-loss zones. Examination of geochemical 

information provides a better understanding of the 

complex flow systems within these aquifers and 

interactions between the aquifers.

Major-ion chemistry in both aquifers is 

dominated by calcium and bicarbonate near outcrop areas, with basinward evolution towards 

various other water types. The most notable differences in major-ion chemistry between the 

Madison and Minnelusa aquifers are in concentrations of sulfate within the Minnelusa aquifer. 

Sulfate concentrations increase dramatically near 

a transition zone where dissolution of anhydrite is 

actively occurring. 

Water chemistry for the Madison and 

Minnelusa aquifers is controlled by reactions 

among calcite, dolomite, and anhydrite. Saturation indices for gypsum, calcite, and dolomite for 

most samples in both the Madison and Minnelusa 

aquifers are indicative of the occurrence of dedolomitization. Because water in the Madison 

aquifer remains undersaturated with respect to 

gypsum, even at the highest sulfate concentrations, upward leakage into the overlying 

Minnelusa aquifer has potential to drive increased 

dissolution of anhydrite in the Minnelusa 

Formation.

Isotopic information is used to evaluate 

ground-water flowpaths, ages, and mixing conditions for the Madison and Minnelusa aquifers. 

Distinctive patterns exist in the distribution of 

stable isotopes of oxygen and hydrogen in precipitation for the Black Hills area, with isotopically 

lighter precipitation generally occurring at higher 

elevations and latitudes. Distributions of δ18O in 

ground water are consistent with spatial patterns in 

recharge areas, with isotopically lighter δ18O 

values in the Madison aquifer resulting from 

generally higher elevation recharge sources, 

relative to the Minnelusa aquifer.

Three conceptual models, which are simplifications of lumped-parameter models, are considered for evaluation of mixing conditions and 

general ground-water ages. For a simple slug-flow 

model, which assumes no mixing, measured tritium concentrations in ground water can be related 

through a first-order decay equation to estimated 

concentrations at the time of recharge. Two simplified mixing models that assume equal proportions of annual recharge over a range of years also 

are considered. An “immediate-arrival” model is 

used to conceptually represent conditions in outcrop areas and a “time-delay” model is used for 

locations removed from outcrops, where delay 

times for earliest arrival of ground water generally 

would be expected. Because of limitations associated with estimating tritium input and gross simplifying assumptions of equal annual recharge and 

thorough mixing conditions, the conceptual 

models are used only for general evaluation of 

mixing conditions and approximation of age 

ranges. 
2 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Headwater springs, which are located in 

or near outcrop areas, have the highest tritium 

concentrations, which is consistent with the 

immediate-arrival mixing model. Tritium concentrations for many wells are very low, or nondetectable, indicating general applicability of the timedelay conceptual model for locations beyond outcrop areas, where artesian conditions generally 

occur. Concentrations for artesian springs generally are higher than for wells, which indicates 

generally shorter delay times resulting from preferential flowpaths that typically are associated 

with artesian springs.

In the Rapid City area, a distinct division of 

isotopic values for the Madison aquifer corresponds with distinguishing δ18O signatures for 

nearby streams, where large streamflow recharge 

occurs. Previous dye testing in this area documented rapid ground-water flow (timeframe of 

weeks) from a streamflow loss zone to sites 

located several miles away. These results are used 

to illustrate potential errors that may result from 

the simplified conceptualization of this complex 

ground-water setting with dual-porosity hydraulic 

characteristics. For Rapid City sites with timeseries data, minimal variability in δ18O values corresponded with tritium data indicative of dominant 

proportions of older water. Other sites showed 

response to temporal δ18O trends in streamflow 

recharge, with tritium data indicating larger proportions of modern recharge. Several large production wells located near the isotopic transition 

zone had changes in δ18O values indicative of 

changes in capture zones associated with recent 

production.

Evaluation of major-ion and isotope data 

indicates that regional flowpaths for the Madison 

aquifer are essentially deflected around the study 

area, with the possible exception of the southwestern and northwestern corners. Two wells just 

north of the study area clearly show influence of 

regional flow, and a well just within the study area 

shows possible influence. Large artesian springs 

near the northern axis of the uplift show no 

regional influence and are concluded to be 

recharged within the uplift area. Ion concentrations for wells west of the study area in Wyoming 

indicate deflection of regional flowpaths, with 

minor influence possible for several wells. The

δ18O values for large springs along the southern 

axis of the uplift essentially preclude regional 

influence, which also is supported by ion chemistry, and indicate potential recharge areas extending 

along the entire southwestern flank of the uplift. 

Low, but detectable, tritium concentrations in 

these springs along the southern axis confirm the 

influence of recharge from within the study area, 

but indicate relatively long traveltimes.

Hydrographs for 9 of 13 well pairs are fairly 

well separated and do not indicate direct hydraulic 

connection between the Madison and Minnelusa 

aquifers. Comparison of geochemical information 

provides no evidence of extensive mixing 

resulting from general, areal leakage between the 

aquifers.

Aquifer interactions can occur at artesian 

springs, which discharge about one-half of average recharge to the Madison and Minnelusa aquifers in the Black Hills area. Various investigators 

have hypothesized that the Madison aquifer is the 

primary source for many artesian springs, based on 

geochemical modeling. The Madison aquifer is 

inferred as the primary source for several springs 

where artesian conditions in the Minnelusa aquifer 

are precluded by nearby outcrop sections. For 

many springs, quantifying relative contributions 

from each aquifer is hampered by geochemical 

similarities between the Madison and Minnelusa 

aquifers, especially near recharge areas. For some 

springs, high sulfate concentrations indicate 

Minnelusa influence, but may result from dissolution of Minnelusa minerals by water from the 

Madison aquifer.

Generally higher hydraulic head in the 

Madison aquifer, in combination with gypsum 

undersaturation, is concluded to be a primary 

mechanism driving interactions with the 

Minnelusa aquifer, in areas where artesian conditions exist in the Madison aquifer. Upward leakage from the Madison aquifer probably contributes 

to general dissolution of anhydrite deposits in the 

Minnelusa aquifer and development of breccia 

pipes, which enhances vertical hydraulic conductivity. Breccia pipes are a likely mechanism for 
Introduction 3

upward movement of large quantities of water 

through the Minnelusa aquifer at artesian spring 

locations and many exposed breccia pipes of the 

upper Minnelusa Formation probably are the 

throats of abandoned artesian springs. Dissolution 

processes are an important factor in a selfperpetuating process associated with development 

of artesian springs and preferential flowpaths, 

which initially develop in locations with large 

secondary porosity and associated hydraulic conductivity, with ongoing enhancement resulting 

from dissolution activity.

Outward (downgradient) migration of the 

artesian springs probably occurs as upgradient 

spring-discharge points are abandoned and new 

ones are occupied, keeping pace with regional 

erosion over geologic time. In response, hydraulic 

heads in the Madison and Minnelusa aquifers also 

have declined over geologic time. Artesian 

springflow and general leakage are concluded to 

be important factors in governing water levels in 

the Madison and Minnelusa aquifers. Artesian 

springs are especially important in acting as a 

relief mechanism that provides an upper limit for 

hydraulic head, with springflow increasing in 

response to increasing water levels.

INTRODUCTION

The Madison and Minnelusa aquifers are two of 

the most important aquifers in the Black Hills area. 

These aquifers are used extensively for domestic, 

municipal, irrigation, and industrial uses and have a 

major influence on the surface-water resources because 

of large spring discharges and large streamflow losses 

that occur along many stream channels.

Population growth, resource development, and 

periodic droughts have the potential to affect the quantity, quality, and availability of water within the Black 

Hills area. Because of this concern, the Black Hills 

Hydrology Study was initiated in 1990 to assess the 

quantity, quality, and distribution of surface and ground 

water in the Black Hills area of South Dakota (Driscoll, 

1992). This long-term study is a cooperative effort 

between the U.S. Geological Survey, the South Dakota 

Department of Environment and Natural Resources, 

and the West Dakota Water Development District, 

which represents various local and county cooperators. 

The Madison and Minnelusa aquifers are the primary 

focus of the Black Hills Hydrology Study.

Ground-water conditions in the Madison and 

Minnelusa aquifers are extremely complex because of 

several factors. Water recharged in the uplifted Black 

Hills area mixes with the regional flow system at lower 

elevations; however, interfaces and mixing conditions 

are not well defined. Both aquifers are potential 

sources for numerous large springs in the Black Hills 

area, and hydraulic connections are possible in other 

locations because of large secondary porosity and permeability in both aquifers. Ground-water flowpaths 

and velocities in both aquifers are influenced by anisotropic and heterogeneous hydraulic properties caused 

by secondary porosity resulting from fractures, faults, 

and dissolution activity. Karst features, including sinkholes, collapse features, solution cavities, and caves, in 

the Madison aquifer, and collapse breccia associated 

with dissolution of interbedded evaporites in the 

Minnelusa aquifer, create the potential for the introduction and rapid transport of contaminants within the 

Madison and Minnelusa aquifers.

Geochemistry is a useful tool for better understanding the complex flow systems in the Madison and 

Minnelusa aquifers. The major-ion chemistry of water 

from these aquifers is an important water-quality consideration. Isotope information provides insights 

regarding recharge areas and traveltimes. Both majorion and isotope information provide insights regarding 

flowpaths within the Madison and Minnelusa aquifers 

and potential interconnections between them.

Purpose and Scope

The purpose of this report is to present geochemical information for the Madison and Minnelusa aquifers in the Black Hills area of South Dakota, with an 

emphasis on information relating to understanding the 

ground-water flow conditions in these aquifers. The 

report includes discussions of major-ion and isotope 

chemistry of the Madison and Minnelusa aquifers, possible influences from regional flowpaths, and interactions that may occur between the two aquifers. 

Previous Investigations

Previous investigations have provided various 

information regarding the geochemistry of the Madison 

and Minnelusa aquifers in the Black Hills area. The 

geochemical evolution of ground water in the Madison 
4 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

and Minnelusa aquifers has been studied by Bowles 

and Braddock (1963), Braddock and Bowles (1963), 

Back and others (1983), Busby and others (1983, 1991, 

1995), Plummer and others (1990), and Naus (1999). 

Potential source aquifers for springs in the Black Hills 

area were investigated by Alexander and others (1988, 

1989), Whalen (1994), Klemp (1995), and Wenker 

(1997). Browne (1992) studied water-quality characteristics and geochemical differentiation of the Madison and Minnelusa aquifers near Rapid City. 

Applications of oxygen and hydrogen isotopes to the 

study of ground-water source areas, flowpaths, and 

mixing in the Madison aquifer in the Black Hills area 

have been presented by Back and others (1983), Busby 

and others (1983), Greene (1997, 1999), and Anderson 

and others (1999).

Acknowledgments

The authors acknowledge the efforts of the West 

Dakota Water Development District for helping to 

develop and support the Black Hills Hydrology Study. 

West Dakota’s coordination of various local and county 

cooperators has been a key element in making this 

study possible. The authors also recognize the 

numerous local and county cooperators represented by 

West Dakota, as well as the numerous private citizens 

who have helped provide guidance and support for the 

Black Hills Hydrology Study. The South Dakota 

Department of Environment and Natural Resources has 

provided support and extensive technical assistance to 

the study. David Parkhurst, U.S. Geological Survey, 

provided extensive guidance and numerous insights 

regarding this report. In addition, the authors acknowledge technical assistance from many faculty and 

students at the South Dakota School of Mines and 

Technology.

DESCRIPTION OF STUDY AREA

The study area consists of the topographically 

defined Black Hills and adjacent areas located in 

western South Dakota (fig. 1). Outcrops of the 

Madison Limestone and Minnelusa Formation, as well 

as the generalized outer extent of the Inyan Kara 

Group, which approximates the outer extent of the 

Black Hills area, also are shown in figure 1. The study 

area includes most of the larger communities in 

western South Dakota and contains about one-fifth of 

the State’s population. 

The Black Hills are a dome-shaped uplift about 

125 miles long and 60 miles wide (Feldman and Heimlich, 1980). Land-surface elevations range from about 

7,200 ft at the highest peaks to about 3,000 ft in the 

surrounding plains. The overall climate of the study 

area is continental, with generally low precipitation 

amounts, hot summers, cold winters, and extreme variations in both precipitation and temperatures (Johnson, 

1933). Local climatic conditions are affected by topography, with generally lower temperatures and higher 

precipitation at the higher elevations.

The average annual precipitation for the study 

area (1931-98) is 18.61 inches, and has ranged from 

10.22 inches for water year 1936 to 27.39 inches for 

water year 1995 (Driscoll, Hamade, and Kenner, 2000). 

The largest precipitation amounts typically occur in the 

northern Black Hills near Lead, where average annual 

precipitation exceeds 29 inches. Annual averages 

(1931-98) for counties within the study area range from 

16.35 inches for Fall River County to 23.11 inches for 

Lawrence County. The average annual temperature is 

43.9°F (U.S. Department of Commerce, 1999) and 

ranges from 48.7°F at Hot Springs to approximately 

37°F near Deerfield Reservoir. Average annual evaporation generally exceeds average annual precipitation 

throughout the study area. Average pan evaporation for 

April through October is about 30 inches at Pactola 

Reservoir and about 50 inches at Oral.

Geologic Setting

The oldest geologic units in the study area are the 

Precambrian metamorphic and igneous rocks (fig. 2), 

which underlie the Paleozoic, Mesozoic, and Cenozoic 

rocks and sediments, except where exposed at the land 

surface. The Precambrian rocks range in age from 

about 1.7 to 2.5 billion years, and were eroded to a 

gentle undulating plain at the beginning of the Paleozoic era (Gries, 1996). The Paleozoic and Mesozoic 

rocks were deposited as nearly horizontal beds and 

were later uplifted during the rise of the Black Hills 

during the Laramide orogeny. Uplift during the Laramide orogeny and related erosion exposed the Precambrian rocks in the central core of the Black Hills with 

the Paleozoic and Mesozoic sedimentary rocks 

exposed in roughly concentric rings around the core. 

Deformation during the Laramide orogeny contributed 

to the numerous fractures, folds, and other features 

present throughout the Black Hills. Tertiary intrusive 

activity in the northern Black Hills (fig. 3) also contributed to rock fracturing.
Description of Study Area 5

N. Fork Rapid Cr

Belle Fourche

Reservoir

FOURCHE

Victoria

Spring

Rhoads Fork

Coolidge

Angostura

Reservoir

Castl e Cr

N. Fork Castle Cr

Canyon

Red

Bear

Gulch

Creek

Crow

Sheridan

Lake

Hot Brook Canyon

Deerfield

Reservoir

Pactola

Reservoir

Horse

Creek

Owl

Creek

Crow Creek

BELLE

RIVER

REDWATER

R I VER

Creek

Cr

Little Spearfish

Spearfish

Whitewood

Creek

Creek

Bear

Butte

Elk

Elk

Creek

Creek

Creek

Boxelder

Rapid

Rapid

Creek

Creek

Creek

Spring

Creek

French

Creek

Creek

Creek

Grace

Creek

Creek

S. Fork

S. Fork Rapid Cr

Battle

French

Beaver

Creek

Creek

Creek

Fall R

Hat

Creek

Creek

Horsehead

CHEYENNE

RIVER

Cottonwood

Hay Creek

Bottom

False

Creek

Lame

Johnny

Higgins

Beaver

Creek

Gulch

Castle

Castle

Creek

Creek

Meadow Cr

Creek

Pass

Hell

Canyon

Boles Canyon

Whitewood

Spearfish

Saint

Onge

DEADWOOD

Lead

BELLE FOURCHE

Newell

STURGIS

Blackhawk

Piedmont

Tilford

Box Elder 

RAPID CITY

Hill City

Hermosa

CUSTER

HOT SPRINGS

Edgemont

Minnekahta

Tinton

Maurice

Nemo

Hayward

Keystone

Rochford

Pringle

Fairburn

Buffalo Gap

Oral

Provo

Wind Cave National Park

Jewel Cave

National Monument

Mt. Rushmore National

Memorial

CUSTER

STATE

PARK

Wind

Cave

Ellsworth

Air Force

Base

BUTTE CO

LAWRENCE CO MEADE CO

PENNINGTON CO

CUSTER CO

FALL RIVER CO

WYOMING

SOUTH DAKOTA LIMESTONE

PLATEAU

Figure 1. Generalized outcrops of Madison Limestone, Minnelusa Formation, and outer extent of Inyan Kara Group

within the study area for Black Hills Hydrology Study.

0 10 20

0 10 20 MILES

KILOMETERS

OUTCROP OF MADISON

 LIMESTONE (from Strobel

 and others, 1999)

OUTCROP OF MINNELUSA

 FORMATION (from Strobel

 and others, 1999)

EXPLANATION

APPROXIMATE EXTENT OF

 THE BLACK HILLS AREA,

 REPRESENTED BY

 GENERALIZED OUTER

 EXTENT OF INYAN KARA

 GROUP (modified from

 Strobel and others, 1999)

SOUTH DAKOTA

Study

Area

Black

Hills

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13

104o 45' 103o

30'

15' 103o

30'

44o

45'

15'

44o

45'

30'

43o

15'
6 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Figure 2. Stratigraphic section for the Black Hills.

STRATIGRAPHIC UNIT DESCRIPTION THICKNESS IN FEET

ABBREVIATION

FOR

STRATIGRAPHIC

INTERVAL

SYSTEM ERATHEM

QUATERNARY

& TERTIARY (?)

UNDIFFERENTIATED SANDS AND GRAVELS 0-50 Alluvial and colluvial materials.

1,200-2,700

Light colored clays with sandstone channel fillings and local limestone lenses. WHITE RIVER GROUP Tw

TERTIARY

QTac

Principal horizon of limestone lenses giving teepee buttes. Dark-gray shale containing scattered concretions. Widely scattered limestone masses, giving small teepee buttes. Black fissile shale with concretions. 

PIERRE SHALENIOBRARA FORMATION 180-300 Impure chalk and calcareous shale.

CARLILE SHALE Turner Sandy Member

Wall Creek Member

1350-750 Light-gray shale with numerous large concretions and sandy layers.

Dark-gray shale.

GRANEROS GROUP

GREENHORN FORMATION

Kps

225-380 Impure slabby limestone. Weathers buff.

Dark-gray calcareous shale, with thin Orman Lake limestone at base.

BELLE FOURCHE SHALE

MOWRY SHALE

MUDDY

SANDSTONE

NEWCASTLESANDSTONE

SKULL CREEK SHALE

150-850

Gray shale with scattered limestone concretions.Clay spur bentonite at base.

125-230

0-150

Light-gray siliceous shale. Fish scales and thin layers of bentonite.Brown to light-yellow and white sandstone.

150-270 Dark-gray to black siliceous shale.

CRETACEOUS

FALL RIVER FORMATION

LAKOTA

FM

INYAN KARA

GROUPFuson Shale Minnewaste Limestone Chilson Member

10-200 Massive to slabby sandstone.

Coarse gray to buff cross-bedded conglomeratic sandstone, interbedded with buff, red, and gray clay, especially toward top. Local fine-grained limestone.

10-190

0-25

25-485

0-2200-225

Green to maroon shale. Thin sandstone.Massive fine-grained sandstone.

250-450

0-45

Greenish-gray shale, thin limestone lenses.Glauconitic sandstone; red sandstone near middle.Red siltstone, gypsum, and limestone.

MORRISON FORMATION

UNKPAPA SS Redwater Member

Lak MemberHulett MemberStockade Beaver Mem.Canyon Spr Member

SUNDANCEFORMATIONGYPSUM SPRING FORMATION

Kik

Ju JURASSIC

Goose Egg Equivalent

SPEARFISH FORMATION RT Ps TRIASSIC

MINNEKAHTA LIMESTONEOPECHE SHALE Po

Pmk

375-800

125-65

Red sandy shale, soft red sandstone and siltstone with gypsum and thin limestone layers.Gypsum locally near the base.Thin to medium-bedded fine-grained, purplish-gray laminated limestone.Red shale and sandstone. 125-150

1375-1,1751250-1,000

30-60

10-23510-15010-500

Yellow to red cross-bedded sandstone, limestone, and anhydrite locally at top.Red shale with interbedded limestone and sandstone at base.Massive light-colored limestone. Dolomite in part. Cavernous in upper part.Pink to buff limestone. Shale locally at base.Buff dolomite and limestone.Green shale with siltstone.Massive to thin-bedded buff to purple 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.

PERMIAN

PENNSYLVANIAN

MISSISSIPPIAN

P Pm MINNELUSA FORMATION

MADISON (PAHASAPA) LIMESTONEENGLEWOOD FORMATION

MDm

Ou

DEVONIAN

WHITEWOOD (RED RIVER) FORMATIONWINNIPEG FORMATIONDEADWOOD FORMATIONUNDIFFERENTIATED METAMORPHICAND IGNEOUS ROCKS

OCd

pCu

ORDOVICIAN

CAMBRIAN

PALEOZOIC MESOZOIC CENOZOIC

PRECAMBRIAN

Modified from information furnished by the Department of Geology and Geological Engineering,

South Dakota School of Mines and Technology (written commun., January 1994)

0-300

Includes rhyolite, latite, trachyte, and phonolite. INTRUSIVE IGNEOUS ROCKS Tui --

1Modified based on drill-hole data

Interbedded sandstone, limestone, dolomite, shale, and anhydrite.
Description of Study Area 7

Whitewood

Spearfish

Saint

Onge

DEADWOOD

Lead

BELLE FOURCHE

Newell

STURGIS

Blackhawk

Piedmont

Tilford

Box Elder 

RAPID CITY

Hill City

Hermosa

CUSTER

HOT SPRINGS

Edgemont

Minnekahta

Tinton

Maurice

Nemo

Hayward

Keystone

Rochford

Pringle

Fairburn

Buffalo Gap

Oral

Provo

Rhoads Fork

Hot Brook Canyon

Crow Creek

Meadow Cr

Creek

Pass

Hell

Canyon

Boles Canyon

N Fork Rapid Cr

Belle Fourche

Reservoir

FOURCHE

Victoria

Spring

Spring

Angostura

Reservoir

Castl e Cr

N Fork Castle Cr

Canyon Red

Bear

Gulch

Creek

Crow

Sheridan

Lake

Deerfield

Reservoir

Pactola

Reservoir

Indian

Cr

Horse

Creek

Owl

BELLE

Creek

RIVER

REDWATER

R I VER

Creek

Spearfish

Whitewood

Creek

Creek

Bear

Butte

Elk

Elk

Creek

Creek

Creek

Boxelder

Rapid

Rapid

Creek

Creek

Creek

Creek

Creek

Creek

Creek

Creek

Creek

S. Fork

S. Fork Rapid Cr

Battle

French

French

Beaver

Creek

Creek

Creek

Fall R

Hat

Creek

Creek

Horsehead

CHEYENNE

RIVER

Cottonwood

Hay Creek

Lame Johnny

Beaver

Creek

Gulch

Castle

Castle

H gi gins

Creek

Creek

Bottom False

Creek

Cr

Little Spearfish

Coolidge

Grace

Jewel Cave

National Monument

Mt. Rushmore National

Memorial

CUSTER

STATE

PARK

Wind

Cave

Ellsworth

Air Force

Base

Wind Cave National Park

BUTTE CO

LAWRENCE CO MEADE CO

PENNINGTON CO

CUSTER CO

FALL RIVER CO

WYOMING

SOUTH DAKOTA LIMESTONE

PLATEAU

QTac

Tw

Tui

Kps

Ju

TRPs

MDme

Kik

Pmk

Po

Ou

PPm

OCd

pCu

A

A'

Figure 3. Distribution of hydrogeologic units in the Black Hills area (modified from Strobel and others, 1999).

0 10 20

0 10 20 MILES

KILOMETERS

EXPLANATION

Alluvium and colluvium,

 undifferentiaed

Unconsolidated units

White River aquifer

Minnekahta aquifer

Minnelusa aquifer

Madison aquifer

Deadwood aquifer

Inyan Kara aquifer

Tertiary intrusive units

Spearfish confining

unit

Opeche confining unit

Cretaceoussequence

confining unit

Jurassic-sequence

semiconfining unit

Ordovician-sequence

semiconfining unit

Precambrian igneous

and

metamorphic units

White River Group

Undifferentiated intrusive

 igneous rocks

Pierre Shale to Skull Creek Shale,

 undifferentiated

Inyan Kara Group

Morrison Formation to Sundance

 Formation, undifferentiated

Spearfish Formation

Minnekahta Limestone

Opeche Shale

Minnelusa Formation

Madison (Pahasapa) Limestone

 and Englewood Formation

Whitewood Formation and

 Winnipeg Formation

Deadwood Formation

Undifferentiated metamorphic

 and igneous rocks

Stratigraphic

Units Map Units HydrogeologicUnits

A A' LINE OF GEOLOGIC SECTION

FAULT--Dashed where approximated.

 Bar and ball on downthrown side.

ANTICLINE--Showing trace of axial

 plane and direction of plunge.

 Dashed where approximated.

SYNCLINE--Showing trace of axial plane

 and direction of plunge. Dashed

 where approximated.

MONOCLINE--Showing trace of axial

 plane. Dashed where approximated.

DOME--Symbol size approximately pro-

 portional to size of dome. Dome

 asymmetry indicated by arrow length.

104o 45' 103o

30'

15' 103o

30'

44o

45'

15'

44o

45'

30'

43o

15'

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13
8 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Surrounding the central core is a layered series of 

sedimentary rocks including outcrops of the Madison 

Limestone (also locally known as the Pahasapa Limestone) and the Minnelusa Formation (fig. 3). The bedrock sedimentary units typically dip away from the 

uplifted Black Hills at angles that can approach or 

exceed 15 to 20 degrees near the outcrops, and 

decrease with distance from the uplift to less than 

1 degree (Carter and Redden, 1999a, 1999b, 1999c, 

1999d, 1999e) (fig. 4). Following are descriptions for 

selected bedrock formations from the Deadwood 

Formation through the Inyan Kara Group.

The oldest sedimentary unit in the study area is 

the Cambrian- and Ordovician-age Deadwood Formation, which is composed primarily of brown to lightgray glauconitic sandstone, shale, limestone, and local 

basal conglomerate (Strobel and others, 1999). These 

sediments were deposited on top of a generally horizontal plain of Precambrian rocks in a coastal to nearshore environment (Gries, 1975). The thickness of the 

Deadwood Formation increases from south to north in 

the study area and ranges from 0 to 500 ft (Carter and 

Redden, 1999e). In the northern and central Black 

Hills, the Deadwood Formation is disconformably 

overlain by Ordovician rocks, which include the 

Whitewood and Winnipeg Formations. The Winnipeg 

Formation is absent in the southern Black Hills, and the 

Whitewood Formation has eroded to the south and is 

not present south of the approximate latitude of Nemo 

(DeWitt and others, 1986). In the southern Black Hills, 

the Deadwood Formation is unconformably overlain 

by the Devonian- and Mississippian-age Englewood 

Formation because of the absence of the Ordovician 

sequence. 

The Mississippian-age Madison Limestone is a 

massive, gray to buff limestone that is locally dolomitic 

(Strobel and others, 1999). The Madison Limestone, 

which was deposited as a marine carbonate, was 

exposed at land surface for approximately 50 million 

years. During this period, significant erosion, soil 

development, and karstification occurred (Gries, 

1996). There are numerous caves and fractures within 

the upper part of the formation (Peter, 1985). The 

thickness of the Madison Limestone increases from 

south to north in the study area and ranges from almost 

zero in the southeast corner of the study area (Rahn, 

1985) to 1,000 ft east of Belle Fourche (Carter and 

Redden, 1999d). Local variations in thickness are due 

largely to the karst topography that developed before 

the deposition of the overlying formations (DeWitt and 

others, 1986). Because the surface of the Madison 

Limestone was exposed to weathering and karstification for millions of years, the formation is unconformably overlain by the Pennsylvanian- and Permian-age 

Minnelusa Formation. The Madison Limestone is 

underlain by the Englewood Formation, which Gries 

(1996) included as an impure basal phase of the Madison Limestone but Fahrenbach (1995) described as a 

separate unit from the Madison Limestone. The 

Madison Limestone and equivalent units are regionally 

extensive throughout the northern Great Plains area 

and pinch out in southern and eastern South Dakota. 

The Pennsylvanian- and Permian-age Minnelusa 

Formation consists mostly of yellow to red crossstratified sandstone, limestone, dolomite, and shale 

(Strobel and others, 1999). Anhydrite cements are 

prevalent in many layers within the subsurface, but 

generally have been removed by dissolution at or near 

outcrop areas (DeWitt and others, 1986). Collapse 

features filled with breccia (breccia pipes) occur within 

the upper part of the Minnelusa Formation in many 

locations (Braddock, 1963; Long and others, 1999; 

Epstein, 2000). The thickness of the Minnelusa Formation in the study area increases from north to south in 

the study area and ranges from about 375 ft near Belle 

Fourche to 1,175 ft near Edgemont (Carter and 

Redden, 1999c). The Minnelusa Formation was 

deposited in a coastal environment, and dune structures 

at the top of the formation may represent beach sediments (Gries, 1996). Along the northeastern flank of 

the Black Hills, there is little anhydrite in the subsurface due to a change in the depositional environment 

(Carter and Redden, 1999c). On the south and southwest side of the study area, there is a considerable 

increase in thickness of clastic units as well as a thick 

section of anhydrite. The Minnelusa Formation disconformably is overlain by the Permian-age Opeche 

Shale, which is overlain by the Minnekahta Limestone. 

The Minnelusa Formation and equivalent units are 

regionally extensive throughout the northern Great 

Plains area and pinch out in eastern South Dakota.

The Permian-age Minnekahta Limestone is a 

fine-grained, purple to gray laminated limestone 

(Strobel and others, 1999), which ranges in thickness 

from 25 to 65 ft in the study area. The Minnekahta 

Limestone is overlain by the Triassic- and Permian-age 

Spearfish Formation.
D

escriptionofStudyArea9

SEA

6,0005,0004,0003,0002,0001,000

LEVEL

SEA

LEVEL

FEET

7,0006,0005,0004,0003,0002,0001,000

A A'

FEET

7,000

MDme

MDme

Kps

Ju

Kik

PPm

PPm

OCd

OCd Pmk

Po QTac QTac

Rapid Creek Rapid Creek

South Fork Castle Creek

Rapid Creek

Rapid Creek

Rapid City

Rapid Creek

210

210 4 2

2 4 6 8 10 MILES

8 6 10 KILOMETERS

VERTICAL EXAGGERATION X5

T Ps R

Figure 4. Geologic cross section A-A' (Location of section is shown in figure 3. Abbreviations for stratigraphic intervals are explained in figure 2.).

Modified from Strobel and others, 1999

SOUTH DAKOTA

WYOMING

pCu pCu
10 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

The Spearfish Formation is a red, silty shale with 

interbedded red sandstone and siltstone, which ranges 

in thickness from about 375 to 800 ft (Strobel and 

others, 1999). The Spearfish Formation contains massive gypsum throughout. The overlying Mesozoic-age 

units are composed primarily of shale, siltstone, and 

sandstone deposits, and include the Cretaceous-age 

Inyan Kara Group. The thickness of the Inyan Kara 

Group ranges from about 135 to 900 ft in the study area 

(Carter and Redden, 1999a).

Hydrologic Setting

The hydrologic setting of the Black Hills area is 

schematically illustrated in figure 5, and the areal distribution of hydrogeologic units is shown in figure 3. 

Four of the major bedrock aquifers in the Black Hills 

area (Deadwood, Madison, Minnelusa, and Inyan Kara 

aquifers) are regionally extensive and are discussed in 

the following sections in the context of both regional 

and local hydrologic settings. A fifth major aquifer 

(Minnekahta) generally is used only locally, as are 

aquifers in the metamorphic and igneous rocks within 

the central core area.

Regional Setting

The Paleozoic aquifers underlie parts of 

Montana, North Dakota, South Dakota, Wyoming, and 

Canada (Downey, 1984). The Canadian part of the 

regional aquifer system is not described or shown in 

this report. For the description of the regional setting 

(a large part of the northern Great Plains), it is convenient to use aquifer names of Downey and Dinwiddie 

(1988) and Whitehead (1996). The Paleozoic aquifers 

include the Cambrian-Ordovician aquifer (or Deadwood aquifer in the Black Hills), Mississippian aquifer 

(or Madison aquifer in the Black Hills), and the Pennsylvanian aquifer (or Minnelusa aquifer in the Black 

Hills). The Paleozoic aquifers are recharged in outcrop 

areas around major uplifts (fig. 6).

Figure 5. Schematic showing hydrogeologic setting of the Black Hills area. Figure also shows caves and

breccia pipes, which contribute to secondary porosity in the Madison and Minnelusa aquifers. Breccia pipes

may result from upward leakage from the Madison aquifer, creating conduits for artesian springs. 

Potentiometric surface

of Madison aquifer

Alluvium

Dip of sedimentary rocks exaggerated

Precambrian metamorphic

and igneous rocks

Deadwood

Inyan Kara Group

Thicknesses not to scale

Madison Limestone

Minnelusa

Minnekahta

Limestone

CAVE

BRECCIA PIPE

CONFINING UNIT

EXPLANATION

Formation

Formation

Water

table

Artesian spring

OTHER AQUIFERS

MADISON AND MINNELUSA

 AQUIFERS
Description of Study Area 11

Approximate Boundary of

Williston Basin

Base modified from U.S. GeologicalSurvey digital data, 1:2,000,000, 1972

0 50 100 MILES

0 50 100 KILOMETERS

●

★

●

★

●

●

●

●

●

●

★

★

Casper

Cheyenne

Grand Forks

Bismarck

Helena

Great Falls

Butte

Billings

Rapid City

Pierre

Sioux

Falls

Fargo

100o 105o 110o

115o

48o

43o

N O R T H D A K O T A

M O N T A N A

S O U T H D A K O T A

W Y O M I N G

RECHARGE AREADISCHARGE AREA FOR THE MISSISSIPPIAN (MADISON) AQUIFER (via adjacent and overlying aquifers)DISCHARGE AREA FOR THE CAMBRIAN-ORDOVICIAN (DEADWOOD) AQUIFER (via adjacent aquifers, springs, and seeps)BODY OF WATER WITH DISSOLVED-SOLIDS CONCENTRATION GREATER THAN 100,000 MILLIGRAMS PER LITERLIMIT OF CAMBRIAN-ORDOVICIAN AQUIFER--Dashed where approximately locatedDIRECTION OF GROUND-WATER MOVEMENT

EXPLANATION

Figure 6. General direction of ground-water flow in Paleozoic aquifers in the northern Great Plains (modified from Downey and Dinwiddie, 1988 and Whitehead,

1996).
12 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

The Cambrian-Ordovician (or Deadwood) 

aquifer consists of sandstones of Cambrian age (Deadwood Formation and equivalents) and limestones of 

Ordovician age. The Cambrian-Ordovician aquifer 

contains freshwater, with dissolved solids concentrations less than 1,000 mg/L (milligrams per liter), only 

in an area surrounding the Black Hills and in a small 

area in north-central Wyoming (Whitehead, 1996).

The Mississippian (or Madison) aquifer is contained within the limestones, siltstones, sandstones, 

and dolomite of the Madison Limestone and equivalent 

units. Generally, water in the Mississippian aquifer 

is confined except in outcrop areas. Flow in the 

Mississippian aquifer generally is from the recharge 

areas to the northeast (fig. 6). Discharge from the 

Mississippian aquifer occurs by upward leakage to the 

lower Cretaceous aquifer in central South Dakota and 

eastern flow to the Cambrian-Ordovician aquifer in 

eastern North Dakota (Downey, 1984). Water in the 

Mississippian aquifer is fresh only in small areas near 

recharge areas and becomes slightly saline to saline as 

it moves downgradient. The water is a brine with 

dissolved solids concentrations greater than 

300,000 mg/L in the deep parts of the Williston basin 

(Whitehead, 1996).

The Pennsylvanian (or Minnelusa) aquifer is 

comprised of sandstones and limestones of the 

Minnelusa Formation and equivalent units of Pennsylvanian age. Water in the Pennsylvanian aquifer moves 

from recharge areas to discharge areas in eastern South 

Dakota (Downey and Dinwiddie, 1988). Some water 

discharges by upward leakage to the lower Cretaceous 

aquifer (Swenson, 1968; Gott and others, 1974).

Several sandstone units compose the lower 

Cretaceous aquifer, which generally is known as the 

Inyan Kara aquifer in South Dakota and the Dakota 

aquifer in North Dakota. Generally, water in the lower 

Cretaceous aquifer is confined by several thick shale 

layers except in aquifer outcrop areas around structural 

uplifts, such as the Black Hills. Water in the lower 

Cretaceous aquifer generally moves northeasterly from 

high-elevation recharge areas to discharge areas in 

eastern North Dakota and South Dakota (Whitehead, 

1996). Although the aquifer is widespread, it contains 

little freshwater. Much of the saline water is believed 

to be from upward leakage of mineralized water from 

the Paleozoic aquifers (Whitehead, 1996).

Local Setting

Many of the sedimentary units in the Black Hills 

area contain aquifers, both within and beyond the study 

area. Within the Paleozoic rock interval, aquifers in the 

Deadwood Formation, Madison Limestone, Minnelusa 

Formation, and Minnekahta Limestone are used extensively. These aquifers are collectively confined by the 

underlying Precambrian rocks (fig. 5) and the overlying Spearfish Formation (fig. 2). Individually, these 

aquifers are separated by minor confining units or by 

relatively impermeable layers within the individual 

units. Extremely variable leakage can occur between 

these aquifers (Peter, 1985; Greene, 1993).

Artesian (confined) conditions generally exist 

within the sedimentary aquifers where an upper confining unit is present. Under artesian conditions, water 

in a well will rise above the top of the aquifer in which 

it is completed. Flowing wells will result when drilled 

in areas where the potentiometric surface is above the 

land surface. Flowing wells and artesian springs that 

originate from confined aquifers are common around 

the periphery of the Black Hills.

Numerous headwater springs from the Paleozoic 

units on the western side of the study area (fig. 3) provide base flow for many streams. These streams flow 

across the central core of the Black Hills, and most 

Black Hills streams lose all or part of their flow as 

they cross outcrops of the Madison Limestone and 

Minnelusa Formation (Hortness and Driscoll, 1998). 

Karst features of the Madison Limestone, including 

sinkholes, collapse features, solution cavities, and 

caves are responsible for the Madison aquifer’s 

capacity to accept streamflow recharge. Large streamflow losses also occur in many locations within the outcrop of the Minnelusa Formation (Hortness and 

Driscoll, 1998). Large artesian springs occur in many 

locations downgradient from these loss zones, most 

commonly within or near the outcrop of the Spearfish 

Formation, providing an important source of base flow 

in many streams beyond the periphery of the Black 

Hills (Rahn and Gries, 1973; Miller and Driscoll, 

1998).

Although the Precambrian basement rocks 

generally have low permeability and form the lower 

confining unit for the series of overlying aquifers, 

localized aquifers occur in many locations in the central core of the Black Hills, where enhanced secondary 

permeability has resulted from weathering and fracturing. Where the Precambrian-rock aquifers are saturated, water-table (unconfined) conditions generally 

occur and land-surface topography can strongly control 

ground-water flow directions.
Description of Study Area 13

Overlying the Precambrian rocks is the Deadwood aquifer, which is contained within the Deadwood 

Formation and is utilized primarily near its outcrop 

area. Regionally, the Precambrian rocks act as a lower 

confining unit to the Deadwood aquifer, and the 

Whitewood and Winnipeg Formations, where present, 

act as overlying semiconfining units (Strobel and 

others, 1999). Where the Whitewood and Winnipeg 

Formations are absent, the Deadwood aquifer is overlain by the Englewood Formation, which Strobel and 

others (1999) included as part of the Madison aquifer.

The Madison aquifer generally is considered to 

consist primarily of the karstic upper part of the 

Madison Limestone, where numerous fractures and 

solution openings provide extensive secondary 

porosity. Strobel and others (1999) included the entire 

Madison Limestone and the Englewood Formation in 

their delineation of the Madison aquifer, which 

receives recharge from streamflow losses and precipitation on its outcrop. In this report, outcrops of the 

Madison Limestone and Englewood Formation (fig. 3) 

are referred to as the outcrop of the Madison Limestone 

for simplicity. Low-permeability layers in the lower 

part of the Minnelusa Formation generally act as an 

upper confining unit to the Madison aquifer. However, 

karst features in the top of the Madison Limestone may 

contribute to reduced competency of the overlying 

confining unit in some locations.

The potentiometric surface of the Madison 

aquifer is shown in figure 7. In many locations, 

ground-water flow in the Madison aquifer follows the 

bedding dip, which generally is radially away from the 

central core of the Black Hills. Ground-water flowpaths and velocities also are heavily influenced by 

anisotropic and heterogeneous hydraulic properties of 

the Madison aquifer. Flowpaths are not necessarily 

orthogonal to potentiometric contours because of 

highly variable directional transmissivities and may be 

further influenced by vertical flow components 

between the Madison and Minnelusa aquifers. Long 

(2000) described anisotropy in the Madison aquifer in 

the Rapid City area that causes ground-water flow to be 

nearly parallel to the potentiometric contours in some 

cases. Regional ground-water flow from the west may 

influence the potentiometric surface in the northern and 

southwestern parts of the study area. 

The Minnelusa aquifer is contained within the 

thin layers of sandstone, dolomite, and anhydrite in the 

lower portion of the Minnelusa Formation and within 

sandstone and anhydrite in the upper portion. Shales in 

the lower portion of the Minnelusa Formation act as a 

confining unit to the underlying Madison aquifer; 

however, the extent of hydraulic separation is spatially 

variable and is not well defined, as discussed in a subsequent section of this report. The Minnelusa aquifer 

may have enhanced vertical hydraulic conductivity in 

areas of collapse breccia (breccia pipes in fig. 5) associated with dissolution of interbedded evaporites (Long 

and others, 1999). Hayes (1999) concluded that 

upward leakage of relatively fresh water from the 

Madison aquifer is a probable agent for dissolution of 

anhydrite within the Minnelusa Formation, which is a 

likely mechanism for development of breccia pipes 

within the Minnelusa Formation. Exposed breccia 

pipes, which are common in many areas, were hypothesized to be conduits for abandoned springs, which 

migrate outwards from the flanks of the Black Hills 

over geologic time, keeping pace with regional erosion.

The Minnelusa aquifer receives recharge from 

streamflow losses and precipitation on its outcrop. 

Streamflow losses to the Minnelusa aquifer generally 

are less than to the Madison aquifer (Carter, Driscoll, 

and Hamade, 2001) because most of the flow is lost to 

the Madison aquifer before reaching the outcrop of the 

Minnelusa Formation. The Minnelusa aquifer is confined by the overlying Opeche Shale.

The potentiometric surface of the Minnelusa 

aquifer is shown in figure 8. Ground-water flow in the 

Minnelusa aquifer in the study area generally follows 

the bedding dip, but may be affected by structural 

features. Regional ground-water flow from the west 

may influence the potentiometric surface in the 

northern and southwestern parts of the study area.

The Minnekahta aquifer, which overlies the 

Opeche Shale, is contained within the Minnekahta 

Limestone. The Minnekahta aquifer typically is very 

permeable, but well yields are limited by the aquifer 

thickness. The overlying Spearfish Formation acts as a 

confining unit to the Minnekahta aquifer. 

Within the Mesozoic rock interval, the Inyan 

Kara aquifer is used extensively and various other 

aquifers are used locally to lesser degrees. The Inyan 

Kara aquifer receives recharge primarily from precipitation on its outcrop and also may receive recharge 

from leakage from the underlying Paleozoic aquifers 

(Swenson, 1968; Gott and others, 1974). As much as 

4,000 ft of Cretaceous strata (primarily shales) act as 

the upper confining unit to aquifers in the Mesozoic 

rock interval.
14 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Whitewood

Spearfish

Saint

Onge

DEADWOOD

Lead

BELLE FOURCHE

Newell

STURGIS

Blackhawk

Piedmont

Tilford

Box Elder 

RAPID CITY

Hill City

Hermosa

CUSTER

HOT SPRINGS

Edgemont

Minnekahta

Tinton

Maurice

Nemo

Hayward

Keystone

Rochford

Pringle

Fairburn

Buffalo Gap

Oral

Provo

N. Fork Rapid Cr

Belle Fourche Reservoir

FOURCHE

Victoria

Spring

Rhoads Fork

Coolidge

Angostura

Reservoir

Castl e Cr

N. Fork Castle Cr

Canyon

Red

Bear

Gulch

Creek

Crow

Sheridan

Lake

Hot Brook Canyon

Deerfield

Reservoir

Pactola

Reservoir

Horse

Creek

Owl

Creek

Crow Creek

BELLE

RIVER

REDWATER

R I VER

Creek

Cr

Little Spearfish

Spearfish

Whitewood

Creek

Creek

Bear

Butte

Elk

Elk

Creek

Creek

Creek

Boxelder

Rapid

Rapid

Creek

Creek

Creek

Spring

Creek

French

Creek

Creek

Creek

Grace

Creek

Creek

S. Fork

S. Fork Rapid Cr

Battle

French

Beaver

Creek

Creek

Creek

Fall R

Hat

Creek

Creek

Horsehead

CHEYENNE

RIVER

Cottonwood

Hay Creek

Bottom

False

Creek

Lame Johnny

Higgins

Beaver

Creek

Gulch

Castle

Castle

Creek

Creek

Meadow Cr

Creek

Pass

Hell

Canyon

Boles Canyon

Wind Cave National Park

Jewel Cave

National Monument

Mt. Rushmore National

Memorial

CUSTER

STATE

PARK

Wind

Cave

Ellsworth

Air Force

Base

BUTTE CO

LAWRENCE CO MEADE CO

PENNINGTON CO

CUSTER CO

FALL RIVER CO

WYOMING

SOUTH DAKOTA LIMESTONE

PLATEAU 3700

3600

5800

4800

4400

6600

3600

6400

3500

3400

3800

4000

4200

4400

5000 5200

4800

3200

5400

5600

4600

6000

6200

4200

6400

4000

4400

6400

3400

36003800

4200

2600

4000

2800

2800

3000

3000

6600

6600

6000

6400

6200

5500

5000

4500

3600

4000

3900

3700

3200

3600

3500

4600

3400

3400

3800

3900

3800

3700

Fall River gage

Crow

Creek

gage

Elk

Creek

gage

Cool Spring

Hot Brook Spring

Cascade

Springs

Beaver

Creek

Spring

Battle

Creek

Spring

Evans Plunge Spring

Elk Creek

Springs

Cleghorn/

Jackson

Springs

City

Springs

Higgins Gulch

Spring

Old Spearfish

Hatchery Cox

Lake

Mirror

Lake

and

McNenny

Rearing

Pond

Grace

Coolidge

Creek

Spring

Figure 7. Potentiometric surface of the Madison aquifer and locations of major artesian springs.

0 10 20

0 10 20 MILES

KILOMETERS

EXPLANATION

OUTCROP OF MADISON

 LIMESTONE (from Strobel

 and others, 1999)

MADISON LIMESTONE ABSENT

 (from Carter and Redden, 1999d)

POTENTIOMETRIC CONTOUR--

 Shows altitude at which water

 would have stood in tightly cased,

 nonpumping wells (modified from

 Strobel and others, 2000a).

 Contour interval 100, 200, or

 500 feet, where appropriate.

 Dashed where inferred. Datum

 is sea level

MADISON LIMESTONE PRESENT,

 BUT OVERLAIN BY SURFICIAL

 DEPOSITS (from Carter and

 Redden, 1999d)

FAULT--Dashed where approxi-

 mated. Bar and ball on down-

 thrown side

ANTICLINE--Showing trace of axial

 plane and direction of plunge.

 Dashed where approximated

SYNCLINE--Showing trace of axial

 plane and direction of plunge.

 Dashed where approximated

MONOCLINE--Showing trace of

 axial plane. Dashed where

 approximated

DOME--Symbol size approximately

 proportional to size of dome.

 Dome asymmetry indicated by

 arrow length

ARTESIAN SPRING

STREAMFLOW-GAGING STATION

 FOR SPRING REACH

3000

104o 45' 103o

30'

15' 103o

30'

44o

45'

15'

44o

45'

30'

43o

15'

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13
Description of Study Area 15

Whitewood

Spearfish

Saint

Onge

DEADWOOD

Lead

BELLE FOURCHE

Newell

STURGIS

Blackhawk

Piedmont

Tilford

Box Elder 

RAPID CITY

Hill City

Hermosa

CUSTER

HOT SPRINGS

Edgemont

Minnekahta

Tinton

Maurice

Nemo

Hayward

Keystone

Rochford

Pringle

Fairburn

Buffalo Gap

Oral

Provo

N. Fork Rapid Cr

Belle Fourche Reservoir

FOURCHE

Victoria

Spring

Rhoads Fork

Coolidge

Angostura

Reservoir

Castl e Cr

N. Fork Castle Cr

Canyon

Red

Bear

Gulch

Creek

Crow

Sheridan

Lake

Hot Brook Canyon

Deerfield

Reservoir

Pactola

Reservoir

Horse

Creek

Owl

Creek

Crow Creek

BELLE

RIVER

REDWATER

R I VER

Creek

Cr

Little Spearfish

Spearfish

Whitewood

Creek

Creek

Bear

Butte

Elk

Elk

Creek

Creek

Creek

Boxelder

Rapid

Rapid

Creek

Creek

Creek

Spring

Creek

French

Creek

Creek

Creek

Grace

Creek

Creek

S. Fork

S. Fork Rapid Cr

Battle

French

Beaver

Creek

Creek

Creek

Fall R

Hat

Creek

Creek

Horsehead

CHEYENNE

RIVER

Cottonwood

Hay Creek

Bottom

False

Creek

Lame Johnny

Higgins

Beaver

Creek

Gulch

Castle

Castle

Creek

Creek

Meadow Cr

Creek

Pass

Hell

Canyon

Boles Canyon

Wind Cave

National Park

Jewel Cave

National Monument

Mt. Rushmore National

Memorial

CUSTER

STATE

PARK

Wind

Cave

Ellsworth

Air Force

Base

BUTTE CO

LAWRENCE CO MEADE CO

PENNINGTON CO

CUSTER CO

FALL RIVER CO

WYOMING

SOUTH DAKOTA LIMESTONE

PLATEAU

3000

4000 4200

6600

6200

3400

6000

5400

5800

5000

5200

4400 4200

2800

3600

3600

3400

4000

3200

3000

4400

4600

3800

4800

4200

5000

4000

3800

3600

6000

6200

6400

6400

3800

6800

6600

3800

6000

6400

6200 6200

5600

5800

6000

2800

3000

3200

5400

3800

3800

4800

4600

4800

3600

4600

3400

4200

4400

4000

3600

2600

3000

2800

3200

3400

Fall River gage

Crow

Creek

gage

Elk

Creek

gage

Cool Spring

Hot Brook Spring

Cascade

Springs

Beaver

Creek

Spring

Battle

Creek

Spring Grace

Coolidge

Creek

Spring

Evans Plunge Spring

Higgins Gulch

Spring

Old Spearfish

Hatchery

Mirror

Lake

and

McNenny

Rearing

Pond

Elk Creek

Springs

City

Springs

Cox

Lake

Cleghorn/

Jackson

Springs

Figure 8. Potentiometric surface of the Minnelusa aquifer and locations of major artesian springs.

0 10 20

0 10 20 MILES

KILOMETERS

EXPLANATION

OUTCROP OF MINNELUSA

 FORMATION (from Strobel

 and others, 1999)

MINNELUSA FORMATION

 ABSENT (from Carter and

 Redden, 1999c)

MINNELUSA FORMATION

 PRESENT, BUT OVERLAIN

 BY SURFICIAL DEPOSITS

 (from Carter and Redden, 1999c)

POTENTIOMETRIC CONTOUR--

 Shows altitude at which water

 would have stood in tightly

 cased, nonpumping wells

 (modified from Strobel and

 others, 2000b). Contour

 interval 200 feet. Dashed where

 inferred. Datum is sea level 

FAULT--Dashed where approxi-

 mated. Bar and ball on down-

 thrown side

ANTICLINE--Showing trace of axial

 plane and direction of plunge.

 Dashed where approximated

SYNCLINE--Showing trace of axial

 plane and direction of plunge.

 Dashed where approximated

MONOCLINE--Showing trace of

 axial plane. Dashed where

 approximated

DOME--Symbol size approximately

 proportional to size of dome.

 Dome asymmetry indicated by

 arrow length

ARTESIAN SPRING

STREAMFLOW-GAGING STATION

 FOR SPRING REACH

104o 45' 103o

30'

15' 103o

30'

44o

45'

15'

44o

45'

30'

43o

15'

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13
16 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

METHODS USED AND DATA SETS

CONSIDERED

Most of the data used in this study were collected 

as part of the U.S. Geological Survey Regional Aquifer 

System Analysis Program (Busby and others, 1983, 

1991) or the Black Hills Hydrology Study, using applicable methods and protocols. Data sets considered 

primarily include samples collected prior to the end of 

water year 1998, when data collection for the Black 

Hills Hydrology Study was completed. However, 

several isotope samples collected during water year 

2000 also are considered. Additional chemical data for 

precipitation in Newcastle, Wyoming, were obtained 

from the National Atmospheric Deposition 

Program/National Trends Network (1999).

For geochemical analyses involving major ions, 

a cation/anion balance within 10 percent was used as a 

general sample selection criterion. For some selected 

single constituents, all applicable data were used. For 

geochemical analyses based on pH or results of speciation calculations, only samples collected specifically 

for the Black Hills Hydrology Study were used because 

these samples were collected using a closed-system 

device, thereby avoiding reaction with the atmosphere 

during sampling. Field measurement of pH values 

included temperature compensation to correct for the 

effect of temperature on electrode response.

For some samples used in speciation calculations, an estimated temperature was calculated from a 

linear regression of temperature with distance from 

outcrop area. The geochemical program PHREEQC 

(Parkhurst and Appelo, 1999) was used for speciation 

calculations and for conducting forward geochemical 

modeling to illustrate relations among chemical parameters that would be expected for certain chemical 

reactions.

Selected site information for all samples considered in this report is presented in table 7 in the Supplemental Information section at the end of this report. 

The same site numbers are used consistently 

throughout the report.

GEOCHEMISTRY OF MADISON AND

MINNELUSA AQUIFERS

The major-ion and isotope chemistry of the 

Madison and Minnelusa aquifers are discussed in the 

following sections. The discussion of major-ion 

chemistry includes information regarding distribution 

of major ions, saturation state, and evolutionary 

processes. Stable isotopes of oxygen and hydrogen are 

used to evaluate ground-water recharge areas and flowpaths. Tritium, which is an unstable hydrogen isotope, 

is used for analysis of ground-water ages. 

Major-Ion Chemistry

Major reactive minerals in the Madison and 

Minnelusa aquifers are calcite (CaCO3), dolomite 

(CaMg(CO3)2), and anhydrite (CaSO4). The interactions of these minerals with water and dissolved 

gases, to a large extent, defines the chemical composition of ground water in the two aquifers. An important 

consequence of the presence of both calcite and anhydrite in the Madison and Minnelusa aquifers is the 

potential for precipitation of calcite by the common-ion 

effect, which can be represented as 

CaSO4 + 2HCO3

- → CaCO3 + SO42- + CO2

(Langmuir, 1997). (1)

In partially dolomitized limestone, dolomite dissolution also can lead to precipitation of calcite:

CaMg(CO3)2 → CaCO3 + Mg2+ + CO3

2- 

(Krauskopf and Bird, 1995). (2)

The term “dedolomite” was originally used to 

describe the replacement of dolomite by calcite during 

near-surface chemical weathering (von Morlot, 1847). 

Strictly speaking, “dedolomitization” describes the formation of the mineral phase dedolomite, which is 

calcite pseudomorphous after dolomite. In this report, 

“dedolomitization” is used to describe a combination 

of the above two reactions (eqs. 1 and 2), in which the 

irreversible dissolution of anhydrite in waters saturated 

with calcite and dolomite drives additional dissolution 

of dolomite and concurrent precipitation of calcite 

(Back and others, 1983). The dedolomitization 

reaction can be represented as:

CaSO4 + 1/2 CaMg(CO3)2 → CaCO3

+ 1/2 Ca2++ 1/2 Mg2+ + SO4

2-. (3)

The extent to which dedolomitization occurs in the 

Madison and Minnelusa aquifers can be illustrated 

through the major-ion chemistry and saturation indices 

of the ground water as well as through identification of 

trends in pH and calcium, magnesium, and sulfate 

concentrations. 
Major-Ion Chemistry 17

Distribution of Major Ions 

The major-ion chemistry of water in the Madison 

and Minnelusa aquifers can be illustrated with trilinear 

and Stiff (1951) diagrams, which show spatial variations and possible trends in the major-ion chemistry of 

the waters. In constructing Stiff diagrams, the average 

milliequivalent value was used where more than one 

sample existed for a site. For clarity, not all diagrams 

were plotted on the maps, but an effort was made to 

include diagrams representative of the water chemistry 

in a particular area. 

A trilinear diagram showing percentages of 

major ions in the Madison aquifer is shown in figure 9, 

and the distribution of major-ion chemistry in the 

Madison aquifer throughout the study area is shown in 

figure 10. Figure 9 shows two main types of water in 

the Madison aquifer: calcium magnesium bicarbonate 

type and calcium sodium chloride sulfate type. 

Figure 10 shows that water in the Madison aquifer is 

dominated by calcium, magnesium, and bicarbonate 

ions throughout most of the study area. The high concentrations of chloride, sulfate, and sodium in the 

southwestern part of the study area relative to the 

rest of the study area probably reflect the presence of 

more evolved ground water and regional flow, or 

greater amounts of evaporite minerals available for 

dissolution. Ion chemistry is somewhat anomalous for 

site 188 (Rapid City area), which has high chloride 

with calcium and magnesium, rather than sodium. 

A trilinear diagram showing percentages of 

major ions in the Minnelusa aquifer is shown in 

figure 9, and Stiff diagrams representative of the 

major-ion chemistry in water from Minnelusa wells are 

shown in figure 11. Figure 9 illustrates three main 

types of water in the Minnelusa aquifer: calcium magnesium bicarbonate type, calcium magnesium sulfate 

type, and calcium magnesium bicarbonate sulfate chloride type. Figure 11 shows that water in the Minnelusa 

aquifer generally evolves downgradient from a calcium 

magnesium bicarbonate type to a calcium magnesium 

sulfate type due to dissolution of anhydrite. In the Hot 

Springs area, ground water in the Minnelusa aquifer is 

characterized by higher concentrations of sodium and 

chloride. Because chloride is conservative in water, it 

can be used to identify leakage between aquifers 

(Busby and others, 1995). The high chloride concentrations in this area in both the Madison and Minnelusa 

aquifers could reflect hydraulic connection between the 

aquifers. The dissolution of evaporite minerals and the 

presence of more evolved ground water contributed by 

regional flow also are possible explanations for the 

occurrence of this water type in the Minnelusa aquifer.

Figure 9. Trilinear diagrams showing proportional concentrations of major ions in the Madison and Minnelusa

aquifers.

Calcium + Magnesium

Sulfate

Sodium + Potassium

Chloride + Fluoride + Sulfate

Chloride + Fluoride + Sulfate

Bicarbonate + Carbonate

Magnesium

Calcium Chloride + Fluoride Chloride + Fluoride

PERCENT OF REACTING VALUES PERCENT OF REACTING VALUES

80

60

40

20

80

80

60

40

20

20

20

40

60

80

40

60

80

60

40

20

20

80

6040

20

40

60

80

80

60

40

20

Number of samples = 127

Calcium + Magnesium

Sulfate

Sodium + Potassium

Bicarbonate + Carbonate

Magnesium

Calcium

80

60

40

20

80

80

60

40

20

20

20

40

60

80

40

60

80

60

40

20

20

80

60

40

20

40

60

80

80

60

40

20

Number of samples = 241

Madison Aquifer Minnelusa Aquifer
18 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Whitewood

Spearfish

Saint

Onge

DEADWOOD

Lead

BELLE FOURCHE

Newell

STURGIS

Blackhawk

Piedmont

Tilford

Box Elder 

RAPID CITY

Hill City

Hermosa

CUSTER

HOT SPRINGS

Edgemont

Minnekahta

Tinton

Maurice

Nemo

Hayward

Keystone

Rochford

Pringle

Fairburn

Buffalo Gap

Oral

Provo

N. Fork Rapid Cr

Belle Fourche

Reservoir

FOURCHE

Victoria

Spring

Rhoads Fork

Coolidge

Angostura

Reservoir

Castl e Cr

N. Fork Castle Cr

Canyon

Red

Bear

Gulch

Creek

Crow

Sheridan

Lake

Hot Brook Canyon

Deerfield

Reservoir

Pactola

Reservoir

Horse

Creek

Owl

Creek

Crow Creek

BELLE

RIVER

REDWATER

R I VER

Creek

Cr

Little Spearfish

Spearfish

Whitewood

Creek

Creek

Bear

Butte

Elk

Elk

Creek

Creek

Creek

Boxelder

Rapid

Rapid

Creek

Creek

Creek

Spring

Creek

French

Creek

Creek

Creek

Grace

Creek

Creek

S. Fork

S. Fork Rapid Cr

Battle

French

Beaver

Creek

Creek

Creek

Fall R

Hat

Creek

Creek

Horsehead

CHEYENNE

RIVER

Cottonwood

Hay Creek

Bottom

False

Creek

Lame Johnny

Higgins

Beaver

Creek

Gulch

Castle

Castle

Creek

Creek

Meadow Cr

Creek

Pass

Hell

Canyon

Boles Canyon

Wind Cave National Park

Jewel Cave

National Monument

Mt. Rushmore National

Memorial

CUSTER

STATE

PARK

Wind

Cave

Ellsworth

Air Force

Base

BUTTE CO

LAWRENCE CO MEADE CO

PENNINGTON CO

CUSTER CO

FALL RIVER CO

WYOMING

SOUTH DAKOTA LIMESTONE

PLATEAU

282

284

286

283

278

4

6

8

12

17 20

36

39

47

58 59 61

69

73

82 83

85 89

90

95

100

104

106

107

108 110

117 123 124

126 138

140

143

145

150

164

172 182

188

189

195 191

201

203

206 210

215

217

220

221

222

231 233

237 238

242

253

256

257

258

260

262 261

197

247

108

Figure 10. Selected Stiff diagrams showing the distribution of major-ion chemistry in the Madison aquifer.

0 10 20

0 10 20 MILES

KILOMETERS

EXPLANATION

OUTCROP OF MADISON LIME-

 STONE (from Strobel and others,

 1999)

MADISON LIMESTONE ABSENT

 (from Carter and Redden, 1999d)

STIFF DIAGRAM--

WELL COMPLETED IN THE 

 MADISON AQUIFER--Number is

 site number from table 7

Sodium + Potassium

Calcium

Magnesium

Chloride + Fluoride

Bicarbonate + Carbonate

Sulfate

10 10 0

CONCENTRATION, IN MILLIEQUIVALENTS PER LITER

SPRING--Number is site number

 from table 7 276

104o 45' 103o

30'

15' 103o

30'

44o

45'

15'

44o

45'

30'

43o

15'

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13
Major-Ion Chemistry 19

BUTTE CO

LAWRENCE CO MEADE CO

PENNINGTON CO

CUSTER CO

FALL RIVER CO

WYOMING

SOUTH DAKOTA LIMESTONE

PLATEAU

N. Fork Rapid Cr

Belle Fourche

Reservoir

FOURCHE

Victoria

Spring

Rhoads Fork

Coolidge

Angostura

Reservoir

Castl e Cr

N. Fork Castle Cr

Canyon

Red

Bear

Gulch

Creek

Crow

Sheridan

Lake

Hot Brook Canyon

Deerfield

Reservoir

Pactola

Reservoir

Horse

Creek

Owl

Creek

Crow Creek

BELLE

RIVER

REDWATER

R I VER

Creek

Cr

Little Spearfish

Spearfish

Whitewood

Creek

Creek

Bear

Butte

Elk

Elk

Creek

Creek

Creek

Boxelder

Rapid

Rapid

Creek

Creek

Creek

Spring

Creek

French

Creek

Creek

Creek

Grace

Creek

Creek

S. Fork

S. Fork Rapid Cr

Battle

French

Beaver

Creek

Creek

Creek

Fall R

Hat

Creek

Creek

Horsehead

CHEYENNE

RIVER

Cottonwood

Hay Creek

Bottom

False

Creek

Lame Johnny

Higgins

Beaver

Creek

Gulch

Castle

Castle

Creek

Creek

Meadow Cr

Creek

Pass

Hell

Canyon

Boles Canyon

Whitewood

Spearfish

Saint

Onge

DEADWOOD

Lead

BELLE FOURCHE

Newell

STURGIS

Blackhawk

Piedmont

Tilford

Box Elder 

RAPID CITY

Hill City

Hermosa

CUSTER

HOT SPRINGS

Edgemont

Minnekahta

Tinton

Maurice

Nemo

Hayward

Keystone

Rochford

Pringle

Fairburn

Buffalo Gap

Oral

Provo

Wind Cave

National Park

Jewel Cave

National Monument

Mt. Rushmore National

Memorial

CUSTER

STATE

PARK

Wind

Cave

Ellsworth

Air Force

Base

287

289

288

276

3

9

11

13

14

15 16

22

29

32

33

35

41 43

44

48

49 51

52

53

54 55

5764 62

68

76 72 79

80 81

86

88

97

98

105

101

109 113

119

125

129

139

155 157

179

183

192

194

198

199

200

204 205

207 208

209

211

212

213

214

216

218

219

223

227

228

230 234

235

236

239

243

244

245 250 249 248

251

252

254

202

0 10 20

0 10 20 MILES

KILOMETERS

Less than 250 milligrams per liter

ESTIMATED SULFATE CONCEN-

 TRATIONS IN MINNELUSA

 AQUIFER

Between 250 and 1,000 milligrams

 per liter

Greater than 1,000 milligrams per

 liter

EXPLANATION

OUTCROP OF MINNELUSA

 FORMATION (from Strobel

 and others, 1999)

MINNELUSA FORMATION ABSENT

 (from Carter and Redden, 1999c)

Figure 11. Selected Stiff diagrams showing the distribution of major-ion chemistry in the Minnelusa aquifer.

Approximate location of anhydrite dissolution front showing transition between low and high sulfate concentrations

also is shown.

STIFF DIAGRAM--

WELL COMPLETED IN THE 

 MINNELUSA AQUIFER--Number

 is site number from table 7

Sodium + Potassium

Calcium

Magnesium

Chloride + Fluoride

Bicarbonate + Carbonate

Sulfate

10 10 0

CONCENTRATION, IN MILLIEQUIVALENTS PER LITER

204

SPRING--Number is site number

 from table 7 276

104o 45' 103o

30'

15' 103o

30'

44o

45'

15'

44o

45'

30'

43o

15'

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13
20 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Sulfate concentrations in the Madison aquifer 

generally are low and increase slightly with increasing 

distance from outcrop areas (fig. 10). In contrast, an 

extremely sharp gradation in sulfate concentrations 

occurs in the Minnelusa aquifer, such as near sites 22, 

29, 32, and 33 in the northern part of the study area. 

Sulfate concentrations in the Minnelusa aquifer are 

dependent on the amount of anhydrite present in the 

Minnelusa Formation. Thick anhydrite beds were 

observed in cores from Minnelusa Formation drill 

holes in the southern Black Hills (Braddock and 

Bowles, 1963; Brobst and Epstein, 1963). These thick 

anhydrite deposits are mostly absent in and near outcrops because of earlier removal by dissolution in the 

subsurface (Epstein, 2000).

Where dissolution of anhydrite currently is 

taking place (Epstein, 2000), a transition zone from low 

to high sulfate concentrations is postulated, as shown in 

figure 11. Sulfate concentrations less than 250 mg/L 

delineate a zone in which anhydrite probably has been 

largely removed by dissolution. The zone in which 

sulfate concentrations are between 250 and 1,000 mg/L 

marks the position of the “anhydrite dissolution front,”

an area of active removal of anhydrite by dissolution. 

Downgradient from the anhydrite dissolution front, 

sulfate concentrations are greater than 1,000 mg/L, 

which delineates a zone in which thick anhydrite beds 

remain in the formation. A similar approach was presented by Klemp (1995), who used specific conductance of ground-water samples from the Minnelusa 

aquifer to identify a line of dissolution of anhydrite. 

Brobst and Epstein (1963), Gott and others (1974), 

Kyllonen and Peter (1987), and Epstein (2000) also 

presented models of this anhydrite dissolution front, 

wherein the Minnelusa Formation is thinner near the 

outcrop area because of removal of the anhydrite and 

thicker where the anhydrite still remains. Epstein 

(2000) proposed that sinkholes in overlying formations 

are caused by collapses in the Minnelusa Formation 

because of removal of anhydrite, and that the sinkholes 

mark the zone of active dissolution of anhydrite. 

Dissolution of anhydrite cements could increase 

hydraulic conductivity and secondary porosity in the 

Minnelusa aquifer; thus, low sulfate concentrations 

may indicate areas of greater hydraulic conductivity 

and enhanced secondary porosity where anhydrite has 

been removed from the aquifer. The anhydrite dissolution front in the northern Black Hills generally is 

located farther from outcrop areas than in other locations, although basinward deflections of the front also 

are apparent in the Rapid City area and along the southeastern flank of the uplift. In some areas, basinward 

deflections may correspond with structural features 

where enhanced hydraulic conductivity can occur; 

however, available data are insufficient for conclusive 

determinations.

Saturation State

Saturation indices measure departures from 

thermodynamic equilibrium and can be used to develop 

hypotheses related to the reactivity of minerals in an 

aquifer. The saturation index (SI) for a particular 

mineral generally indicates whether the ground water is 

undersaturated (SI < 0), at equilibrium (SI = 0), or 

supersaturated (SI > 0) with respect to that particular 

mineral. If ground water is undersaturated with respect 

to a mineral, as indicated by a negative SI, the ground 

water would theoretically dissolve the mineral if 

present. Conversely, if ground water is supersaturated 

with respect to a mineral, then the mineral would theoretically precipitate from the ground water. There is 

some uncertainty associated with the range in SI values 

that indicates equilibrium because of uncertainties in 

field-measured pH, laboratory-analyzed concentrations, and ionic strength and equilibrium constants 

involved in calculations of SI values (Langmuir, 1997).

The geochemical program PHREEQC 

(Parkhurst and Appelo, 1999) was used to calculate SI 

values for 41 samples (35 wells) from the Madison 

aquifer and 25 samples (24 wells) from the Minnelusa 

aquifer (table 1). The default thermodynamic database, phreeqc.dat (Parkhurst, 1995), provided the thermodynamic data for calculations. Although anhydrite 

is more common than gypsum in the Madison and 

Minnelusa aquifers, gypsum (CaSO4•2H2O) is the 

more stable phase. Therefore, SIgypsum is used as an 

indicator for both anhydrite and gypsum throughout the 

remainder of this report.

Calculated SI values show that water in the 

Madison aquifer is greatly undersaturated with respect 

to halite (NaCl) and, to a lesser extent, with respect to 

gypsum. These minerals should, if present, continue to 

dissolve in the Madison aquifer. However, ground 

water in the Madison aquifer remains undersaturated 

with respect to gypsum even at the highest sulfate concentrations (fig. 12). Figure 13 shows that most waters 

in the Madison aquifer are in equilibrium with respect 

to calcite and are slightly undersaturated with respect to 

dolomite.
Major-Ion Chemistry 21

 Table 1. Saturation indices for selected samples from wells completed in the Madison and Minnelusa aquifers

[SIcalcite, calcite saturation index; SIdolomite, dolomite saturation index; SIgypsum, gypsum saturation index; SIhalite, halite saturation index;

e, estimated; --, no data]

Site

number

Station identification 

number

Temperature

(degrees Celsius)

pH

(standard

units)

SIcalcite SIdolomite SIgypsum SIhalite

Madison Aquifer

6 444129103514801 29.4 7.2 0.0 0.0 -1.6 -10.2

36 443100104002001 11.3 7.4 .1 -.3 -1.3 -10.3

58 442802103544601 11.3 7.3 .1 -.1 -1.8 -7.7

59 442919103511601 12.3 7.4 -.1 -.4 -2.3 -9.6

61 442842103505501 7.8 7.6 -.1 -.4 -2.4 -9.4

83 442435103571101 e10.9 7.2 .0 -.4 -3.1 -10.5

85 441759103261202 11.5 7.5 -.1 -.4 -2.1 -10.6

95 441055103230501 13.8 7.4 .1 .2 -3.2 -11.0

100 441337103225002 12.5 7.3 -.1 -.3 -2.7 -10.5

106 440629103040901 47.5 6.9 -.2 -.3 -1.5 -9.9

112 440519103160701 20.6 7.7 .1 .2 -2.8 -10.2

116 440526103173001 13.6 7.7 .0 -.1 -2.7 -9.7

116 440526103173001 13.2 7.6 .0 -.2 -2.6 -9.2

121 440500103193601 13.8 7.6 .0 -.1 -2.5 -9.4

123 440612103152001 15.3 7.5 -.2 -.4 -2.7 -10.1

123 440612103152001 15.2 7.5 -.1 -.3 -2.6 -8.9

124 440655103140501 20.0 7.5 -.1 -.1 -2.7 -9.4

138 440931103141401 20.3 7.3 -.1 .0 -2.7 -10.4

145 440811103222201 16.8 7.3 -.1 -.1 -3.0 -10.2

161 440205103172001 13.7 7.6 -.1 -.5 -2.4 -8.9

164 440308103184601 7.0 7.6 -.2 -.8 -2.3 -9.0

168 440300103173501 e12.7 7.0 -.7 -1.7 -2.4 -9.1

168 440300103173501 18.4 7.7 .1 .0 -2.3 -8.9

169 440220103164001 15.2 7.7 .0 -.2 -2.3 -9.2

169 440220103164001 16.0 7.6 -.1 -.4 -2.4 -9.1

172 440342103160701 16.5 7.6 -.1 -.2 -2.3 -9.1

172 440342103160701 17.8 7.7 .1 .1 -2.0 -9.4

176 440310103173802 14.8 7.7 -.1 -.2 -2.0 -9.2

178 440338103173302 12.0 7.7 .0 -.2 -2.3 -9.3

182 440430103160202 15.5 7.7 .0 .0 -2.5 -9.6

185 440443103161301 16.2 7.7 .1 .0 -2.7 -9.7

186 440446103161701 e16.3 7.4 -.3 -.6 -2.7 -10.2

186 440446103161701 16.4 7.7 .1 .0 -2.7 -10.4

188 440427103131701 26.4 6.1 -.3 -.8 -2.1 -6.9
22 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Madison Aquifer—Continued

195 435851103143501 13.3 7.5 -0.3 -0.8 -2.4 -8.7

201 434700104021401 10.1 8.1 .6 1.0 -2.7 -9.8

210 434350103201901 14.5 7.9 .2 .3 -2.4 -9.6

215 433517103534201 14.5 8.3 .6 .6 -1.4 -7.9

238 433115103251401 17.2 7.7 .1 .0 -2.4 -8.6

242 432548103414801 21.0 7.5 .2 .3 -2.0 -8.7

253 432136103321001 21.3 7.3 .2 .0 -1.0 -6.5

Minnelusa Aquifer

29 443515103513901 13.4 7.3 .4 .3 -.1 -9.8

35 443100104002002 10.4 7.4 .0 -.4 -1.7 -10.6

44 443320104004501 11.5 7.4 .1 -.2 -1.4 -10.3

48 443515103572501 18.3 7.1 .2 -.1 .0 -9.7

65 443100103543001 13.0 8.6 1.3 2.1 -2.5 -10.4

81 442545103343701 12.5 8.6 1.2 2.0 -2.2 -10.3

86 441759103261201 11.2 7.5 -.1 -.4 -2.7 -10.3

113 440528103155201 15.2 7.5 -.1 -.3 -2.4 -10.3

118 440544103180001 10.8 7.9 .2 .1 -2.3 -9.1

119 440516103194001 19.6 7.6 .2 .3 -2.4 -9.2

129 440818103180801 18.5 7.6 .2 .2 -2.5 -10.3

177 440310103173801 12.6 7.8 .1 .0 -2.3 -9.4

179 440338103173301 12.0 7.8 .2 .1 -2.4 -9.8

181 440414103164601 16.1 7.5 .1 .0 -1.6 -9.2

183 440430103160201 11.7 7.7 .0 -.2 -2.6 --

183 440430103160201 14.2 7.7 .1 .1 -2.2 -9.6

187 440452103155301 14.8 7.7 .1 .2 -2.2 --

192 435916103161802 12.4 7.2 -.4 -1.1 -2.5 -9.7

199 435018103155801 12.8 7.7 -.2 -.7 -2.7 -9.6

211 434350103201902 e11.5 7.7 .0 -.3 -2.1 -9.0

216 433517103534202 13.6 7.4 .3 .0 -.7 -8.7

227 433003103420701 13.8 7.5 .1 -.1 -2.5 -9.5

239 433115103251402 14.2 7.8 .1 .0 -2.3 -8.8

243 432548103414802 17.2 7.3 .2 .0 .0 -7.8

254 432127103325601 19.6 7.0 .2 .0 .0 -7.4

Table 1. Saturation indices for selected samples from wells completed in the Madison and Minnelusa aquifers—Continued

[SIcalcite, calcite saturation index; SIdolomite, dolomite saturation index; SIgypsum, gypsum saturation index; SIhalite, halite saturation index;

e, estimated; --, no data]

Site

number

Station identification 

number

Temperature

(degrees Celsius)

pH

(standard

units)

SIcalcite SIdolomite SIgypsum SIhalite
Major-Ion Chemistry 23

0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 20 50 100

DISSOLVED SULFATE, IN MILLIMOLES PER LITER

-4

1

-3

-2

-1

0

GYPSUM SATURATION INDEX

Madison aquifer

Minnelusa aquifer

Figure 12. Relation between gypsum saturation index and dissolved sulfate in the Madison and Minnelusa

aquifers.

41 25

Madison Minnelusa

AQUIFER

-1.0

1.5

-0.5

0

0.5

1.0

CALCITE SATURATION INDEX

Figure 13. Boxplots showing calcite and dolomite saturation indices for selected samples from the Madison and

Minnelusa aquifers.

41 25

Madison Minnelusa

AQUIFER

-2

3

-1

0

1

2

DOLOMITE SATURATION INDEX

25th percentile

Median

75th percentile

Data value less than or equal to 1.5 times

the interquartile range outside the quartile

Outlier data value less than or equal to 3

and more than 1.5 times the

interquartile range outside the quartile

Outlier data value more than 3 times the

interquartile range outside the quartile

41 Number of samples

X

X

X

X X

EXPLANATION
24 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

All samples from the Minnelusa aquifer are 

undersaturated with respect to halite, and most are 

undersaturated with respect to gypsum. In some samples, SI values for gypsum approach zero, indicating 

near equilibrium with respect to gypsum at high sulfate 

concentrations (fig. 12). Most samples in the Minnelusa aquifer are near equilibrium to slightly supersaturated with respect to calcite and are saturated with 

respect to dolomite (fig. 13).

 For most samples in both the Madison and 

Minnelusa aquifers, SI values for gypsum, calcite, and 

dolomite are indicative of the occurrence of dedolomitization. Busby and others (1983) noted that conditions consistent with the dedolomitization process 

generally include waters that are in equilibrium with 

respect to calcite, undersaturated but approaching saturation with respect to dolomite, and undersaturated 

with respect to gypsum. Samples that are undersaturated with respect to gypsum, calcite, or dolomite may 

be indicative of large hydraulic conductivity, especially 

in the Madison aquifer, where fast flow velocities and 

short ground-water residence times in karst conduits 

may limit the extent of mineral dissolution. Undersaturation with respect to these minerals also could result 

from the influence of streamflow recharge for samples 

collected near loss zones in outcrops of the Madison 

Limestone and Minnelusa Formation. The contribution of calcium from anhydrite dissolution could cause 

slight supersaturation with respect to calcite or dolomite due to the common-ion effect. Samples with high 

SI values for calcite and dolomite may reflect errors in 

pH measurements, which are not uncommon primarily 

because of instrumentation problems. All of the positive outlier values in figure 13 are associated with pH 

values greater than 8 (table 1), which may be of 

questionable validity.

The saturation state with respect to gypsum of 

water in the Madison and Minnelusa aquifers may provide insight into mechanisms controlling hydraulic 

connection between the aquifers. Because water in the 

Madison aquifer remains undersaturated with respect 

to gypsum even at the highest sulfate concentrations 

(fig. 12), upward leakage could drive increased dissolution of anhydrite in the Minnelusa Formation, 

especially where Minnelusa aquifer water is nearly 

saturated with respect to gypsum.

Evolutionary Processes

As shown in figures 10 and 11, dissolved sulfate 

concentrations generally increase with distance from 

outcrops in the Madison and Minnelusa aquifers, indicating that sulfate can be used as a measure of the reaction progress. Variations in pH and concentrations of 

calcium and magnesium as a function of dissolved 

sulfate can be used to evaluate chemical processes 

occurring in the aquifers. 

Forward geochemical modeling was used in this 

study to illustrate trends in pH and calcium and magnesium concentrations with increasing dissolution of 

anhydrite. It is assumed in the modeling that the 

aquifer contains calcite, dolomite, and anhydrite and is 

recharged by rainwater. Hypothetical recharge water 

was created by defining water with a temperature of 

15°C and a pH of 5.4, which was the average pH of 

rainwater at Newcastle, Wyoming, from August 1981 

through December 1998 (National Atmospheric Deposition Program/National Trends Network, 1999). The 

recharge water was allowed to equilibrate with calcite 

and dolomite at a of 10-2 bar, typical of values in 

the soil zone (Freeze and Cherry, 1979). Conceptually, 

the recharge water then moved into a saturated zone 

containing calcite, dolomite, and anhydrite. The saturation index of dolomite was fixed at -0.2 to represent 

slight undersaturation with respect to dolomite, and the 

saturation index of calcite was fixed at 0 to represent 

equilibrium conditions. These values are consistent 

with the dedolomitization process and reflect median 

SI values in the Madison aquifer (fig. 13). Dissolution 

of anhydrite occurred incrementally and was limited 

not to exceed gypsum equilibrium. Reactions were 

carried out at a constant temperature of 15°C, which is 

representative of average temperatures in the Madison 

and Minnelusa aquifers in the study area (table 1). 

For the simulated reactions occurring in the 

saturated zone, changes in modeled pH values and 

concentrations of calcium and magnesium, relative 

to increasing sulfate concentrations, are summarized 

in table 2 and figure 14. Table 2 shows the pH; 

molality of calcium (mCa), magnesium (mMg), and 

sulfate (mSO4) in solution; number of moles of anhydrite (∆manhydrite), calcite (∆mcalcite), and dolomite 

(∆mdolomite) dissolved or precipitated (negative values 

indicate precipitation); and saturation index for 

gypsum (SIgypsum) for each reaction step. Figure 14 

shows how the modeled pH, calcium molality, and 

magnesium molality change with reaction progress. 

Calcite precipitated while dolomite dissolved, pH 

decreased, and concentrations of dissolved magnesium 

and sulfate increased during reaction with anhydrite. 

In the ninth model reaction step, the solution reached 

saturation with respect to gypsum.

PCO2
Major-Ion Chemistry 25

Table 2. Selected results of geochemical modeling

[°C, degrees Celsius; mCa, calcium molality; mMg, magnesium molality; mSO4, sulfate molality; ∆manhydrite, number of moles of anhydrite dissolved or 

precipitated (negative values indicate precipitation); ∆mcalcite, number of moles of calcite dissolved or precipitated (negative values indicate precipitation); 

∆mdolomite, number of moles of dolomite dissolved or precipitated (negative values indicate precipitation); SIgypsum, gypsum saturation index] 

Temperature

(°C)

pH

(standard

units)

mCa mMg mSO4 ∆manhydrite ∆mcalcite ∆mdolomite SIgypsum

15 7.20 0.0029 0.0019 0.0025 0.0025 -0.0010 0.0006 -1.1316

15 7.11 .0044 .0028 .0050 .0050 -.0030 .0015 -.7708

15 7.05 .0059 .0038 .0075 .0075 -.0050 .0025 -.5555

15 7.01 .0074 .0047 .0100 .0100 -.0070 .0034 -.4020

15 6.98 .0089 .0057 .0125 .0125 -.0090 .0044 -.2830

15 6.95 .0104 .0066 .0150 .0150 -.0110 .0053 -.1859

15 6.92 .0119 .0076 .0175 .0175 -.0130 .0063 -.1041

15 6.90 .0135 .0085 .0200 .0200 -.0150 .0073 -.0334

15 6.89 .0143 .0090 .0213 .0225 -.0160 .0078 .0000

15 6.89 .0143 .0090 .0213 .0250 -.0160 .0078 .0000

Figure 14. Modeled relations between calcium and magnesium concentrations, pH, and dissolved sulfate.

CALCIUM

MAGNESIUM

pH

DISSOLVED SULFATE, IN MILLIMOLES PER LITER

DISSOLVED CALCIUM OR MAGNESIUM, 

IN MILLIMOLES PER LITER

pH, IN STANDARD UNITS

EXPLANATION

2 4 6 8 10 12 14 16 18 20 22

0

16

2

4

6

8

10

12

14

6.8

7.3

6.9

7.0

7.1

7.2

7.3
26 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

The forward modeling results indicate that the 

incongruent dissolution of dolomite occurring in conjunction with anhydrite dissolution should result in 

increases in calcium and magnesium concentrations 

and a decrease in pH. Figure 15 shows the relation 

between dissolved calcium and magnesium concentrations and dissolved sulfate in the Madison and 

Minnelusa aquifers. To show only data reflecting significant reaction progress, only samples with sulfate 

concentrations greater than 1 millimole per liter are 

included. The variations of dissolved calcium and 

magnesium concentrations with dissolved sulfate 

shown in figure 15 for the Madison and Minnelusa 

aquifers are similar to those resulting from the 

geochemical modeling shown in figure 14 in that both 

calcium and magnesium concentrations increase with 

increasing sulfate concentrations, with calcium 

increasing at a greater rate. However, the modeled 

calcium/magnesium ratio is lower than observed in the 

Madison and Minnelusa aquifers. The relative rates of 

increase of calcium and magnesium concentrations are 

affected by the equilibrium constants (K) as well as 

temperature. Comparison of actual calcium and magnesium concentrations to model results indicates that if 

dedolomitization is occurring in both the Madison and 

Minnelusa aquifers, conditions in the aquifers (temperature, Kdolomite) are similar but not identical to those 

that were modeled.

Figure 16 shows the relation between pH and 

dissolved sulfate in the Madison and Minnelusa 

aquifers. In the Minnelusa aquifer, pH generally is 

lower at high sulfate concentrations, which supports 

the occurrence of dedolomitization. In the Madison 

aquifer, the data are consistent with dedolomitization, 

but pH trends are limited by the extent of anhydrite 

dissolution.

Other processes that could cause a decrease in 

pH along a flowpath include nitrate reduction, denitrification, and sulfate reduction. These reactions 

become important in environments in which the 

oxygen introduced by ground-water recharge has been 

depleted (Langmuir, 1997). Oxygen is supplied to 

ground water by the movement of air through unsaturated material above the water table as well as by 

recharge (Hem, 1992). This oxygen is consumed by 

reaction with organic materials and reduced inorganic 

minerals such as pyrite and siderite. Well-oxygenated 

ground water may persist for long distances along a 

flowpath if little reactive material is available. In both 

the Madison and Minnelusa aquifers, most samples 

have dissolved oxygen concentrations greater than 

2 mg/L (fig. 17), which indicates that the aquifers are 

well oxygenated, even at considerable distances from 

the outcrops. Much of the recharge to the aquifers is

from streamflow losses or through outcrop areas with 

limited soil development. Thus, recharge has limited 

interaction with organic materials in the soil horizon 

and consumption of oxygen is incomplete. Reduction 

of sulfate, nitrate, and ferric iron minerals, methane 

fermentation, and anaerobic decay of organic matter, 

therefore, are not likely in the Madison and Minnelusa 

aquifers in the study area. 

Isotope Chemistry

This section presents information regarding the 

isotope chemistry of the Madison and Minnelusa aquifers in the Black Hills area. Stable isotopes of oxygen 

(

18O and 16O) and hydrogen (2H, deuterium; and 1H) 

are used to evaluate ground-water flowpaths, recharge 

areas, and mixing conditions. The radioisotope tritium 

(

3H) provides additional information for evaluation of 

mixing conditions and ground-water ages.

Isotope data for selected sampling sites are presented in tables 7 and 8 in the Supplemental Information section. The majority of sampling sites are 

ground-water sites, including wells (or caves) and 

springs. Spring samples are categorized as either headwater springs (generally located upgradient of streamflow loss zones) or downgradient springs (within or 

downgradient of loss zones). Two of the downgradient 

springs (sites 291 and 299) are perched springs that are 

located along stream channels where streamflow losses 

occur. The remainder of the downgradient springs are 

located downgradient of loss zones and are presumed 

to be artesian springs. Data also are included for 14 

surface-water sites, all of which are located immediately upgradient from loss zones where recharge occurs 

to the Madison or Minnelusa aquifers. Data for three 

meteorological sites also are provided.

Background Information and Isotopic 

Composition of Recharge Water

This section provides background information 

regarding stable isotopes and tritium. Because of spatial variations in isotopic signatures for precipitation in 

the Black Hills area, stable isotopes can be used for 

identification of potential recharge areas and evaluation of ground-water flowpaths. Tritium is useful for 

evaluation of ground-water ages because large temporal variations of concentrations in precipitation have 

resulted from atmospheric testing of thermonuclear 

bombs during the 1950’s and 1960’s.
Isotope Chemistry 27

Figure 15. Relations between dissolved calcium and magnesium concentrations and dissolved sulfate in the

Madison and Minnelusa aquifers.

CALCIUM

MAGNESIUM

DISSOLVED SULFATE, IN MILLIMOLES PER LITER

DISSOLVED CALCIUM OR MAGNESIUM, IN MILLIMOLES PER LITER

EXPLANATION

0

5

1

2

3

4

0 5 10 15 20 25

0

20

5

10

15

MADISON AQUIFER

MINNELUSA AQUIFER
28 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Figure 16. Relation between pH and dissolved sulfate in the Madison and Minnelusa aquifers.

DISSOLVED SULFATE, IN MILLIMOLES PER LITER

pH, IN STANDARD UNITS

0 2 4 6 8 10 12 14 16 18 20

6.0

9.0

6.5

7.0

7.5

8.0

8.5

Madison aquifer

Minnelusa aquifer

DISTANCE FROM OUTCROP, IN MILES

DISSOLVED OXYGEN, IN MILLIGRAMS PER LITER

Madison aquifer

Minnelusa aquifer

Figure 17. Relation between dissolved oxygen and distance from outcrop in the Madison and Minnelusa

aquifers.

0 2 4 6 8 10 12 14 16 18 20 22

0

16

2

4

6

8

10

12

14
Isotope Chemistry 29

Stable Isotopes of Oxygen and Hydrogen

Stable isotopes, unlike radioisotopes, do not 

decay by any known mechanisms. Stable isotopes of 

oxygen are ideal indicators of ground-water flowpaths 

because the ratios of these isotopes in water are 

affected by meteorological processes but generally not 

by interactions between minerals and ground water at 

temperatures less than about 100°C.

Stable isotope values are given in “delta notation,” which compares the ratio between heavy and 

light isotopes of a sample to that of a reference standard. Delta values are expressed as a difference, in 

parts per thousand, or per mil (‰), from value reference standard. For example, the oxygen isotope ratio 

of a sample written in delta notation is:

A sample with a δ value of -20 ‰ is depleted by 

20 parts per thousand (2 percent) in the heavier isotope 

of the element relative to the standard. In this report, 

δ18O (18O/16O) and δD (deuterium/hydrogen) values 

are reported in per mil relative to Vienna Standard 

Mean Ocean Water (VSMOW) and are described as 

lighter and heavier in relation to each other. The lighter 

values are more negative relative to the heavier values, 

which are less negative.

Distinct isotopic signatures can result from isotope fractionation, which occurs during “rainout,” a 

term used to describe the loss of water vapor from a 

cooling air mass as it passes from its oceanic source 

over continents (fig. 18). As air masses rise to higher 

elevations, lower temperatures and the subsequent formation of precipitation cause fractionation to occur 

within the cloud, and 18O and D are partitioned preferentially into the rain or snow. The heavy isotopes thus 

are distilled from the vapor, which is progressively 

depleted in 18O and D (Clark and Fritz, 1997).

δ

18Osample

O/ 18 16Osample O/ 18 16Ostandard –

O/ 18 16Ostandard

= ------------------------------------------------------------------------

× 1,000 ‰ VSMOW.

Figure 18. Schematic showing fractionation of stable oxygen and hydrogen isotopes during rainout. Stable

isotope values, which compare isotopic ratios relative to ocean water, are expressed in per mil (‰).

Rain

Ocean

Mountain

δ18Ο = -13‰

δD = -94‰

δ18Ο = 0‰

δD = 0‰

δ18Ο = -22‰

δD = -166‰

δ18Ο = -12‰

δD = -86‰

δ18Ο = -4‰

δD = -22‰
30 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Data for Black Hills sites include both δ18O and 

δD values (table 7). For sites with more than one set of 

δ18O and δD values, a mean value is listed in table 7, 

and individual values are listed in table 8. A linear 

relation exists between δ18O and δD (fig. 19); thus, 

subsequent discussions and illustrations generally refer 

only to δ18O for simplicity. Most samples for the Black 

Hills area fall along or slightly below Craig’s (1961) 

global meteoric water line.

Precipitation in the northern Black Hills generally is isotopically lighter than in the south because of 

relatively high elevations and the influence of Pacific 

storms that are isotopically depleted due to rainout in 

crossing the Rocky Mountains. The generally lower 

elevations in the southern Black Hills, combined with 

warm, moist weather patterns from the south, result in 

precipitation that is isotopically heavier than in the 

north (Back and others, 1983; Busby and others, 1983; 

Greene, 1997). The resulting distribution of isotopes in 

near-recharge areas of the Black Hills serves as a 

natural tracer for ground-water flowpaths. A generalized distribution of δ18O values in near-recharge areas 

of the study area is presented in figure 20, which is 

derived using samples from headwater springs with 

localized recharge areas, selected (Minnekahta) wells 

and caves in outcrop areas, and streams upstream from 

loss zones. The approximate centroids of drainage 

basins were used to represent stream sampling locations for contouring purposes; thus, gaging stations 

shown in figure 20 do not necessarily fall within the 

respective contours.

δ18O, IN PER MIL (‰)

δD, IN PER MIL (

‰)

EXPLANATION

Figure 19. Relation between δ18O and δD in Black Hills samples in comparison to the global meteoric water

line (Craig, 1961).

-19 -18 -17 -16 -15 -14 -13 -12 -11 -10

-150

-80

-140

-130

-120

-110

-100

-90

Global meteoric water line:

 δD = 8δ18O + 10

Downgradient springs

Headwater springs - Deadwood aquifer

Headwater springs - Madison aquifer

Headwater springs - Minnelusa aquifer

Surface water - loss zone

Well - Deadwood aquifer

Well - Madison aquifer

Well - Minnekahta aquifer

Well - Minnelusa aquifer

#

#

#

#

#

#

#

#

# ##### #

##

###

##

## ##

# ##

#

#

#

# #

#

#

##

# #

#

#

###

#
Isotope Chemistry 31

 

BUTTE CO

LAWRENCE CO MEADE CO

PENNINGTON CO

CUSTER CO

FALL RIVER CO

WYOMING

SOUTH DAKOTA LIMESTONE

PLATEAU

N. Fork Rapid Cr

Belle Fourche

Reservoir

FOURCHE

Victoria

Spring

Rhoads Fork

Coolidge

Angostura

Reservoir

Castl e Cr

N. Fork Castle Cr

Canyon

Red

Bear

Gulch

Creek

Crow

Sheridan

Lake

Hot Brook Canyon

Deerfield

Reservoir

Pactola

Reservoir

Horse

Creek

Owl

Creek

Crow Creek

BELLE

RIVER

REDWATER

R I VER

Creek

Cr

Little Spearfish

Spearfish

Whitewood

Creek

Creek

Bear

Butte

Elk

Elk

Creek

Creek

Creek

Boxelder

Rapid

Rapid

Creek

Creek

Creek

Spring

Creek

French

Creek

Creek

Creek

Grace

Creek

Creek

S. Fork

S. Fork Rapid Cr

Battle

French

Beaver

Creek

Creek

Creek

Fall R

Hat

Creek

Creek

Horsehead

CHEYENNE

RIVER

Cottonwood

Hay Creek

Bottom

False

Creek

Lame

Johnny

Higgins

Beaver

Creek

Gulch

Castle

Castle

Creek

Creek

Meadow Cr

Creek

Pass

Hell

Canyon

Boles Canyon

Whitewood

Spearfish

Saint

Onge

DEADWOOD

Lead

BELLE FOURCHE

Newell

STURGIS

Blackhawk

Piedmont

Tilford

Box Elder 

RAPID CITY

Hill City

Hermosa

CUSTER

HOT SPRINGS

Edgemont

Minnekahta

Tinton

Maurice

Nemo

Hayward

Keystone

Rochford

Pringle

Fairburn

Buffalo Gap

Oral

Provo

Wind Cave National Park

Jewel Cave

National Monument

Mt. Rushmore National

Memorial

CUSTER

STATE

PARK

Wind

Cave

Ellsworth

Air Force

Base

-13

-14

-15

-16

-17

-12

240 -12.44

84 -14.63

34

-15.58

240

-12.44

84

-14.63

34

-15.58

322 -12.28

317 -13.49

318 -12.59

319 -11.51

320 -11.58

321 -11.58

312

-16.01 313 -16.24

314 -15.74

315 -15.35

309 -16.96

310

-16.59

311 -16.93

322

-12.28

317

-13.49

318

-12.59

319

-11.51

320

-11.58

321

-11.58

312

-16.01 313

-16.24

314

-15.74

315

-15.35

309

-16.96

310

-16.59

311

-16.93

288

289 -14.27

-13.41

277 -14.61

279 -14.06

280

-13.96

281 -16.56

283 -16.96

285

-16.41

276

-16.91

282 -17.59

287

-14.60

288

289 -14.27

-13.41

277

-14.61

279

-14.06

280

-13.96

281

-16.56

283

-16.96

285

-16.41

276

-16.91

282

-17.59

287

-14.60

232 -12.25

190

-13.33

0 10 20

0 10 20 MILES

KILOMETERS

Figure 20. Generalized distribution of δ18O in surface water and ground water in near-recharge areas.

EXPLANATION

OUTCROP OF MINNELUSA

 FORMATION (from Strobel and

 others, 1999)

OUTCROP OF MADISON

 LIMESTONE (from Strobel and

 others, 1999)

HEADWATER SPRING--Numbers

 indicate site number from table 7

 and δ18O value in per mil

WELL COMPLETED IN THE

 MINNEKAHTA AQUIFER--

 Numbers indicate site number

 from table 7 and δ18O value in

 per mil

CAVE--Numbers indicate site

 number from table 7 and δ18O

 value in per mil

LINE OF EQUAL δ18O VALUE--

 Interval 1 per mil

STREAMFLOW GAGING

 STATION--Numbers indicate

 site number from table 7 and

 δ18O value in per mil. The δ18O

 values are contoured using the

 approximate centroid of the

 basin

-15

277

-14.61

190

-13.33

318

-12.59

84

-14.63

104o 45' 103o

30'

15' 103o

30'

44o

45'

15'

44o

45'

30'

43o

15'

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13
32 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Many of the data points used to develop 

figure 20 are ground-water samples, which generally 

have small temporal variability in δ18O values relative 

to surface-water samples. A perspective on temporal 

variability in precipitation is presented in figure 21A, 

which shows δ18O values for selected loss-zone 

streams and headwater springs. Some temporal variability in loss-zone streams (Spring Creek, Rapid 

Creek, and Boxelder Creek) is due to seasonal variability in isotopic composition of precipitation. Data 

sets for Rhoads Fork and Castle Creek are somewhat 

limited, but indicate less variability because of mixing 

associated with ground-water storage. Thus, for the 

wells and headwater springs shown in figure 20, 

variability in δ18O is assumed to be small and values 

are considered representative of average isotopic 

composition in near-recharge areas.

Temporal variability of δ18O is shown in 

figures 21B and 21C for selected wells and downgradient springs for which time-series data are available. Temporal variability for these sites is magnified 

somewhat by use of different Y-axis scales, but is much 

smaller than for the surface-water samples (fig. 21A). 

Temporal variability for some sites is influenced by 

ground-water mixing conditions, as discussed in 

subsequent sections.

Tritium

 Tritium (3H), which beta-decays to 3He with a 

half-life of 12.43 years (Clark and Fritz, 1997), is 

produced naturally in small concentrations by cosmic 

radiation in the stratosphere. Naturally occurring background concentrations of tritium in continental precipitation are estimated to range from 1 to 20 TU (tritium 

units), depending on location (Michel, 1989). One TU 

is defined as one 3

H atom per 1018 atoms of hydrogen, 

which is equivalent to 3.19 pCi/L (picocuries per liter) 

in water (International Atomic Energy Agency, 1981). 

Because of nuclear testing during the 1950’s and 

1960’s and a subsequent treaty limiting such tests, 

tritium concentrations in atmospheric water increased 

sharply in 1953, peaked in 1963, and then declined. 

Current sources of tritium, such as nuclear power 

production, contribute to atmospheric tritium concentrations that are slightly higher than background 

concentrations prior to nuclear testing.

Tritium concentrations in precipitation have 

been collected at numerous locations around the world 

(International Atomic Energy Agency, 1999). Locations of collection sites in and near the United States 

that are considered for this report are shown in 

figure 22, which shows estimated cumulative deposition of tritium (weighted average concentration multiplied by precipitation depth) for 1953-83 (Michel, 

1989). Tritium concentrations are low in oceans; thus, 

concentrations in precipitation generally are low in 

coastal areas but tend to increase in inland areas 

because of increasing stratospheric influence.

Monthly tritium concentrations in precipitation 

are shown in figure 23 for Ottawa, Canada, which has 

the longest available period of record. Three precipitation samples collected in the Black Hills area during 

the late 1990’s (table 7) also are shown. Figure 23 

shows that in addition to the long-term trends, there is 

considerable seasonal variability in tritium concentrations, with highest concentrations generally in the 

spring.

Tritium concentrations in ground water can be 

related through a first-order decay equation to estimated concentrations at the time of recharge. Because 

recharge to the Madison and Minnelusa aquifers occurs 

from infiltration of precipitation on outcrops and from 

streamflow losses, tritium input from both sources 

must be considered.

A combination of methods has been used to estimate annual tritium concentrations for precipitation 

recharge for the Black Hills area. Annual estimates are 

presented in table 9 in the Supplemental Information 

section and are shown by dashed lines in figure 24, 

which also shows the three actual samples for the Black 

Hills area.

Estimates of tritium concentrations from Michel 

(1989) for 2- by 5-degree blocks were used for the 

period 1953-83. These estimates are based on interpolations between stations with relatively long periods of 

record. Michel (1989) extended station records, for 

periods prior to initiation of data collection, using 

regression coefficients developed by the International 

Atomic Energy Agency (1981) for correlations with 

long-term records for Ottawa, Canada.
Isotope Chemistry 33

Figure 21. Temporal variation of δ18O for selected sites. Graph A shows selected loss-zone streams and

headwater springs. Graphs B and C show selected wells and artesian springs.

1986 1988 1990 1992 1994 1996 1998

A

B

C

YEAR

-18

-10

-17

-15

-13

-11

-16

-14

-12

δ18O, IN PER MIL (

‰)

x x xxxxxx

-15.0

-12.5

-14.5

-14.0

-13.5

-13.0

-14.0

-11.5

-13.5

-13.0

-12.5

-12.0

x x x x

+

+

+ ++ + +

x

x

x x

x xx x

xx x x

x x

++

++ +

+

+

+

+++

Spring Creek (site 318)

Rhoads Fork (site 283)

x Castle Creek (site 285)

Rapid Creek (site 316)

Boxelder Creek (site 315)

x

+

x

+

Black Hills Power & Light (site 112)

Rapid City No. 6 (site 116)

Westberry Trails - Madison (site 121)

Rapid City No. 10 (site 123)

Rapid City No. 8 (site 124)

Rapid City No. 9 (site 172)

Rapid City No. 5 (site 185)

City Springs (site 298)

Highland Hills (site 149)

Carriage Hills Main Well (site 165)

Chapel Lane Madison (site 168)

Rapid City No. 11 (site 169)

Hart Ranch (site 195)

Pine Grove (site 196)

Cleghorn Springs (site 300)
34 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Figure 22. Cumulative tritium deposition on the continental United States, 1953-83, and location of selected

collection sites (modified from Michel, 1989).

Salt

Lake

City

Portland

Bismarck Ottawa

Denver

Lincoln

500 MILES

0 500 KILOMETERS

0

EXPLANATION

LINE OF EQUAL TRITIUM DEPOSITION

 IN TRITIUM-UNIT-METERS

Black Hills

Hydrology

Study Area

1000

1000

2000

3000

4000

3000

2000

5000 6000

5000

6000

7000

1000

YEAR

OTTAWA, CANADA

BLACK HILLS AREA

Figure 23. Monthly tritium concentrations in precipitation at Ottawa, Canada. Samples collected in Black Hills

area of South Dakota also are shown.

1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000

10

10,000

20

30

40

50

70

100

200

300

400

500

700

1,000

2,000

3,000

4,000

5,000

7,000

TRITIUM, IN TRITIUM UNITS
Isotope Chemistry 35

For 1984, monthly tritium concentrations in 

precipitation for the Black Hills area were estimated by 

averaging data for Bismarck, North Dakota, and 

Lincoln, Nebraska. For 1985-98, estimates for the 

Black Hills area were derived by averaging forward 

extensions of data for Bismarck and Lincoln, based on 

least-squares linear regression with monthly data for 

Ottawa. The regression equation is of the form: 

TU = a TUOTTAWA + b; where: TU is tritium in 

precipitation (for either Bismarck or Lincoln), and 

TUOTTAWA is tritium in precipitation at Ottawa. The 

coefficients a and b are obtained from regression 

analysis using all available months of data from 

January 1979 through July 1984 for Bismarck, and 

from January 1970 through May 1986 for Lincoln. 

During these periods, annual concentrations for 

Bismarck and Lincoln were consistently less than 

concentrations for Ottawa (fig. 24), which recently has 

been affected by localized tritium sources (Bob Michel, 

U.S. Geological Survey, oral commun., 2000). For 

Bismarck, the resulting coefficients for a and b are 

0.483 and 0.732, respectively, and for Lincoln, the 

coefficients are 0.881 and 0.028.

For 1984-98, annual weighted tritium concentrations were calculated from the reconstructed monthly 

data (table 9) and Black Hills precipitation records 

(Driscoll, Hamade, and Kenner, 2000) as follows: 

(4)

YEAR

Figure 24. Weighted annual tritium concentrations in precipitation at selected locations. Estimated input and

samples for Black Hills area of South Dakota also are shown.

1950 1960 1970 1980 1990 2000

1

10,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

TRITIUM CONCENTRATION, IN TRITIUM UNITS

Bismarck, North Dakota

Portland, Oregon

Ottawa, Ontario

Lincoln, Nebraska

Salt Lake City, Utah

Denver, Colorado

Michel (1989) estimates for

 Black Hills (1953-83)

Regression estimates for

 Black Hills (1984-98)

EXPLANATION

WEIGHTED ANNUAL TRITIUM

 CONCENTRATIONS

TRITIUM CONCENTRATION FOR

 SINGLE SAMPLES IN THE BLACK

 HILLS AREA

TUweighted

PrecipiTUi

i = 1

12



Precipi

i = 1

12



= --------------------------------------
36 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

where Precipi and TUi denote monthly precipitation 

and tritium concentrations, respectively.

Estimated monthly and weighted annual tritium 

concentrations in precipitation for the Black Hills area 

for 1984-98 are presented in table 10 in the Supplemental Information section. Estimates for 1985-98 

have larger uncertainty than for previous periods 

because of discontinuation of data collection at 

Bismarck and Lincoln. All concentrations prior to 

1953 are assumed equal to 15.0 TU. Actual background concentrations probably were slightly lower 

(Bob Michel, U.S. Geological Survey, written 

commun., 2000); however, estimated input of 15 TU 

results in essentially negligible decayed tritium 

concentrations for the primary sampling period 

(1990-98).

Additional inferences regarding recent tritium 

concentrations in precipitation are available from 

examination of tritium concentrations in samples collected from 14 streams (table 7) where streamflow 

recharge occurs. These streams generally are relatively 

responsive to short-term precipitation influences 

(Miller and Driscoll, 1998); however, the range of 

tritium values indicates considerable variability in tritium concentrations in precipitation and streamflow 

responses. The lowest concentrations are near 15 TU, 

which probably is representative of the lower end of the 

range of average tritium concentrations in recent (since 

about 1992) precipitation. The upper end of the range 

for stream samples (25 to 40 TU) is considerably 

higher, however, than estimated concentrations in precipitation during the mid-1990's (fig. 24), which may 

indicate slight underestimation of precipitation input 

during this period or large seasonal variability.

The streams with higher tritium concentrations 

generally have larger influence from ground-water discharge than streams with lower tritium concentrations. 

This observation is consistent with the work of Rose 

(1993), who investigated tritium systematics of base 

flow and effects on tritium concentrations in streams.

Conceptual Mixing Models

Complex ground-water flow conditions within 

the Madison and Minnelusa aquifers necessitate formulation of conceptual models for evaluation of mixing 

conditions and ground-water ages. Within this section, 

three conceptual mixing models are described and 

limitations of the models are discussed.

Description of Models

Within the Madison aquifer, primary porosity 

and hydraulic conductivity generally are small and 

hydraulic properties are dominated by fractures and 

solution openings, which range in size from microfractures to massive caverns. In this dual-porosity system 

(Long, 2000), a large part of ground-water flow may 

occur in preferential flowpaths within openings, with 

smaller influence from the low-porosity matrix. A significant amount of ground-water storage, however, 

may occur in dead-end or poorly connected openings. 

Within some water-bearing layers of the Minnelusa 

aquifer, relatively homogenous aquifer characteristics 

probably occur; however, extensive fracturing and 

solution activity also contribute to dual-porosity characteristics in many locations. Overall, the Minnelusa 

aquifer generally is heterogeneous across the Black 

Hills area.

Three conceptual models (fig. 25) are considered 

for general evaluation of mixing conditions and 

ground-water ages within the Madison and Minnelusa 

aquifers. Given the large range of hydraulic characteristics within these aquifers, the simplified models 

cannot address all of the complex mixing and flow 

conditions that occur. Under the best conditions, none 

of these simplified models would be expected to 

exactly represent complicated ground-water flow conditions that occur. Under the worst conditions, large 

errors in estimated ages can occur. The conceptual 

models do, however, provide a mechanism by which 

finite numerical age estimates can be derived for water 

samples.

Mathematically, the three conceptual models 

illustrated in figure 25 belong to a general group of 

models known as lumped-parameter models (Yurtsever 

and Payne, 1986), where the system description 

(relating tracer input to tracer output) is attained by 

assuming a system response function (transit-time 

distribution function). Models of this type often are 

used to interpret radioisotope tracer data in groundwater studies (Katz and others, 1999; Manga, 1999). 

Although this approach is simplistic in that the aquifer 

is assumed to be homogeneous (detailed spatial variations are not represented), it is appropriate when the 

available data are limited to temporal observations at 

the input and output of the system (Yurtsever and 

Payne, 1986; Manga, 1999) and may be particularly 

useful for karst and fractured-rock systems (Zuber, 

1986).
Isotope Chemistry 37

Figure 25. Schematic diagrams illustrating mixing models for age dating for various ground-water flow

conditions.

A. Slug flow or pipe flow - negligible mixing with delayed arival

B. Hypothetical water-table spring with maximum traveltime of 10 years - thorough mixing

with immediate arrival

C. Well completed in artesian aquifer at considerable distance from recharge area - thorough

mixing with delayed arrival

1998

1998

1997 1996 1995 1994 1993 etc. Flow

direction

Water table Potentiometric surface

Spring

Aquifer

outcrop

Aquifer

10% in storage

90% discharged

Confining unit

1997

1996

1995

1994

1993

1992

1991

1990

1998 Precipitation

1998 Precipitation

1989

1998

1988

1978

1968

1958

1948

1938

1928

Aquifer outcrop/recharge area

Well

Confining unit

Confining unit

Stream

channel

90% in storage

10% discharged

Water table
38 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

For a lumped-parameter model, the relation 

between time-variable tracer input and output concentrations (Zuber, 1986) can be expressed as:

 (5)

where, and are the output and input 

concentrations, t is the calendar time at which the output is to be evaluated, is the traveltime of the tracer, 

 is the radioactive decay constant, and is a 

system response, or weighting, function. The three 

models shown in figure 25 are represented mathematically by using different system response functions in 

equation 5. 

Figure 25A depicts slug flow (often termed pipe 

or piston flow), which is a common assumption in 

tracer-based dating of ground water. In slug flow, a 

given water front advances with a uniform velocity and 

little dispersion or mixing. Existing water is completely, immiscibly displaced by the advancing water. 

The slug-flow model often is applied to the percolation 

of water through the unsaturated zone and also may be 

appropriate for isotropic, confined aquifers (Zuber, 

1986; Gonfiantini and others, 1998) as well as unconfined, surficial aquifers (Reilly and others, 1994). For 

the Madison and Minnelusa aquifers, a slug-flow 

model could approximate ground-water flow conditions in dual-porosity settings if the dominant flow proportions are in fractures and solution openings, with 

minimal contributions from the low-porosity matrix.

For slug flow, the system response function is 

described by a mathematical function called the Dirac 

delta function (sometimes called the unit impulse 

function), , where τ is the turnover time or 

mean transit time of water (τ = volume of water in the 

system/volumetric flow rate through the system). In 

this case, the traveltime of the tracer is equivalent to the 

turnover time; in all other cases, the two differ considerably (Maloszewski and Zuber, 1982). Use of this 

system response function reduces equation 5 to:

 (Zuber, 1986). (6)

Equation 6 describes the decrease in concentration due 

to decay during the time span of a tracer that entered 

the system at time and exited the system at 

time . 

Tritium concentrations remaining in ground 

water after decaying to a particular sample-collection 

date can be computed for a given recharge year using 

the weighted annual tritium concentration (table 9) as 

the initial concentration in equation 6. Estimated tritium concentrations in precipitation for recharge years 

through 1998 and decay-corrected tritium concentrations for sample-collection dates ranging from 1978 

through 1998 are included as table 11 in the Supplemental Information section.

Figure 26 shows estimated concentrations of 

tritium in precipitation for the Black Hills area for 

1940-98 and decay curves in 5-year increments 

between 1978 and 1998, which covers the primary

period for which samples are available. For slug-flow 

conditions, a recharge date (or range of dates) for any 

sample can be estimated by selecting the appropriate 

decay curve for the year of sample collection (or interpolating between curves) and identifying the point(s) 

on the curve that are equal to the measured tritium concentration. As an example, for a sample collected 

during 1993 with a concentration of 5 TU, the estimated recharge date for slug-flow conditions is about 

1953. Two or more recharge dates are possible for 

many samples. Numerous solutions are possible for a 

1993 sample with a concentration of 20 TU. For this 

example, recharge may have occurred anytime in the 

range of about 1954-57 or 1980-93, considering 

within-year variability in tritium concentrations in precipitation and uncertainty in estimating tritium input 

for the Black Hills area.

Figure 25B depicts a simplified mixing model 

that generally is applicable for locations where watertable conditions exist within outcrop areas, such as 

headwater springs. For this “immediate-arrival” 

model, it is assumed that some percentage of the water 

recharged during a given year is discharged during that 

same year; in other words, the minimum traveltime for 

a portion of the water is zero. For this scenario, water 

recharged during a given year is mixed with equal 

proportions of water recharged during previous years. 

For the hypothetical water-table spring with a maximum traveltime of about 10 years that is shown in 

figure 25B, 10 percent of the water recharged during 

the current year is discharged as springflow during that 

same year. The remaining 90 percent of the water 

discharged is composed of equal proportions of water 

recharged during each of the previous 9 years. Thus, 

tritium composition for this scenario can be represented as the average of decay-corrected tritium input 

concentrations over the previous 10 years.

Cout( )t Cin( )e t t – ′ –λt′

g( ) t′ dt′

0

∞

 =

Cout( )t Cin( ) t t – ′

t′

λ g( ) t′

δ( ) t – τ

Cout( )t Cin( )e t t – ′ –λt′ =

t′

( ) t t – ′

t
Isotope Chemistry 39

The mathematical expression for this immediatearrival mixing model utilizes a simple system response 

function such that the observed output concentration is 

represented as a mix of equal proportions of decaycorrected tritium input concentrations for all years 

between the minimum (0 years for immediate arrival) 

and maximum traveltimes:

(7)

Equation 7 is identical to the example of a simple 

lumped-parameter model given by Zuber (1986, p. 12) 

except that all input concentrations for the range of 

years between the minimum and maximum traveltimes 

are weighted equally in equation 7. Here, is the 

mixing time period, computed as the difference 

between the maximum and minimum 

traveltimes in the system.

For the hypothetical water-table spring shown

in figure 25B, the summation is calculated using 

decay-corrected tritium input concentrations for 

recharge years 1998 ( ) through 1989 

( ). With the equal-weight system 

response function, equal proportions of water are contributed each year; in this case the proportion is

 = 10 percent.

Figure 25C depicts a conceptual model that 

assumes a delay time before any recharge water 

reaches a discharge point. Use of this model requires a 

minimum delay time of 1 year because annual input is 

used for calculation purposes. This “time-delay”

mixing model is appropriate where an upper confining 

unit is present and wells or springs are located some 

distance from outcrop areas, which is applicable for 

many locations around the periphery of the Black Hills, 

especially where artesian conditions occur. For 

example, the hypothetical artesian well shown in 

figure 25C withdraws a mixture of water that was 

recharged during a 50-year period from 1929 to 1978. 

The minimum traveltime (delay time) in this case is 

20 years; in other words, the earliest arrival of recharge 

water is delayed by about 20 years before reaching the 

discharge point. The maximum traveltime is 70 years. 

In this case, the summation (eq. 7) is calculated using 

decay-corrected tritium input concentrations for 

recharge years 1978 ( ) through 1929 

YEAR

Figure 26. Estimated tritium concentrations in precipitation for Black Hills area and decay curves for selected years.

Decay curves depict decayed tritium concentrations for selected sampling years.

1

10,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000

TRITIUM CONCENTRATION, IN TRITIUM UNITS

TRITIUM INPUT

1978

1983

1988

1993

1998

1940 1950 1960 1970 1980 1990 2000

Cout( )t

1

T

-- Cin( )e t t – ′ –λt′

t′

min

t′

max – 1

= 

T

t′max ( ) t′min ( )

Cin( ) 1998 0 –

Cin( ) 1998 9 –

1

t′max t′min ( ) – ---------------------------------

Cin( ) 1998 20 –
40 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

( ). The equal-weight system response 

function in this case results in a mix consisting of contributions of 2 percent, ( ) for each 

input year.

Curves for estimating ages for both immediatearrival and time-delay mixing models (figs. 25B 

and C) are presented in figure 36 in the Supplemental 

Information section. Each graph includes a family of 

curves depicting minimum traveltimes, or delay times, 

in 4-year increments. The 0-year delay curve in each 

curve family is applicable for the immediate-arrival 

mixing model (fig. 25B), and the other curves are 

applicable for time-delay mixing scenarios. Individual 

curves in each family were constructed from output 

concentrations calculated for ranges of input years 

using equation 7. Curve families are presented for 

sampling years 1978 and 1989-97, which cover the 

majority of samples considered. Calculations should 

theoretically be carried out for all possible traveltimes, 

from zero to infinity (Zuber, 1986); however, the 

curves are arbitrarily extended only to possible 

recharge years through 1800.

Using a 1993 sample (fig. 36F) with a concentration of 30 TU as an example, if an immediate-arrival 

mixing model is considered appropriate, the estimated 

maximum traveltime is either 23 years (earliest

recharge occurring about 1970) or 130 years (earliest

recharge occurring about 1863). For this example, no 

solutions exist for time-delay mixing scenarios with 

delay times exceeding about 36 years, and only one 

possible solution exists for delay times in the range of 

about 20 to 36 years. Two solutions are possible for 

each of the delay times up to about 20 years.

Limitations of Models

As discussed, the three simplified, conceptual 

models that are considered cannot address all of the 

complex mixing and flow conditions that occur within 

the Madison and Minnelusa aquifers within the study 

area. The conceptual models do, however, provide a 

mechanism by which finite numerical age estimates 

can be derived for water samples. Readers are cautioned that accurate age dating is not possible because 

of large potential errors resulting from numerous limitations associated with the simplified models, which 

are intended only for general evaluation of mixing conditions and approximate age ranges. Sources of potential error are associated primarily with estimation of 

tritium concentrations in recharge and with assumptions regarding the mixing models that are considered.

Estimates of tritium concentrations in precipitation are subject to large potential error because of the 

sparsity of data-collection points near the Black Hills 

area, especially since discontinuation of data collection 

at Bismarck and Lincoln. Age estimates for recent 

years have progressively increasing sensitivity to errors 

in estimated tritium concentrations in precipitation 

because atmospheric tritium has progressively 

decreased since 1963.

The use of annual averages for tritium in precipitation is another source of potential error because of 

the episodic nature of recharge; however, some withinyear proportioning is obtained because monthly concentrations are precipitation weighted. The immediateand delayed-arrival mixing models are based on an 

implicit assumption of equal recharge each year; however, recharge may vary by as much as an order of 

magnitude from one year to the next (Carter, Driscoll, 

and Hamade, 2001).

Variability of tritium concentrations in streamflow creates an additional complication for areas influenced by streamflow recharge. The age of water in a 

stream always lags that of precipitation, whether by 

minutes, days, or many years. The extent of this effect 

is highly variable and depends on the lag time associated with a particular stream, the degree of variability 

of tritium concentrations in the base-flow component 

of streamflow (Rose, 1993), and the proportion of 

ground-water recharge resulting from streamflow 

losses relative to direct precipitation on aquifer outcrops. Although stream water is inherently older than 

precipitation, systematic influences on age dating 

probably are overshadowed, in most cases, by seasonal 

variability in tritium input and by other sources of 

uncertainty.

Various hydrologic and hydraulic factors also 

complicate the paramount assumption that samples 

contain a mix of equal proportions of water from 

various years. Variability in recharge rates probably 

causes temporal variability in ground-water traveltimes 

and flowpaths from recharge areas to discharge areas. 

Variable residence times in the unsaturated zone in 

recharge areas and in confining units also may be complicating factors. For applications of the immediatearrival model in unconfined headwater settings, the 

effects of the shape of a contributing ground-water 

basin on the relative contributions of recharge from 

different parts of the basin also could seriously violate 

this assumption.

Cin( ) 1998 69 –

1 t′max t′min ⁄ ( ) –
Isotope Chemistry 41

The cumulative effects of all of the aforementioned factors probably are small, relative to error 

potential associated with the spatial variability in 

hydraulic properties of the aquifers. Dual-porosity 

hydraulic characteristics contribute to large variability 

in ground-water flow and mixing conditions, which 

cannot be generically accommodated by the conceptual 

mixing models. Actual conditions may be more accurately represented as a combination of mixing models, 

with influence from slug-flow effects in fractures and 

solution features. Even in cases where one conceptual 

model may be appropriate, there are important limitations. In settings where ground-water flow is predominantly in fractures and solution openings, which may 

be approximated by the slug-flow model, some mixing 

of ground water occurs during convergence upon the 

screened interval of wells (Reilly and others, 1994). A 

limitation of the immediate- and delayed-arrival 

mixing models is the assumption of thorough groundwater mixing. Specific examples and additional details 

regarding model limitations are provided in subsequent 

sections of this report.

As discussed, two or more age estimates are 

possible for many samples, depending on the tritium 

concentration and the mixing model that is considered 

most applicable. Multiple samples for any site improve 

the ability to make credible age estimates; however, 

effects of large well withdrawals at a site could change 

the age characteristics between successive samples.

Areal Flowpaths, Ages, and Mixing Conditions

Within this section, isotopic interpretations are 

used to evaluate areal flowpaths, ages, and mixing 

conditions for the Madison and Minnelusa aquifers in 

the Black Hills area. General considerations regarding 

isotope distributions are discussed first, after which 

various site-specific considerations are addressed. 

Potential influences of regional flow from the west are 

discussed in a subsequent section.

Isotope Distributions and General Considerations

Distributions for stable isotopes and tritium are 

presented in this section. Various general considerations associated with the isotope distributions also are 

discussed.

Stable Isotopes

Distributions of δ18O values in Madison and 

Minnelusa wells and selected springs are shown in 

figures 27, 28, and 29. Mean values are shown for sites 

with multiple samples. Figures 27 and 29 show the 

northern and southern Black Hills, respectively, and 

figure 28 shows the Rapid City area. These figures 

generally include sites near or downgradient from the 

Madison and Minnelusa outcrops, which probably are 

influenced primarily by recharge originating from 

within the study area. Sites considered representative 

of the isotopic composition of recharge in the study 

area were presented earlier in figure 20 and are 

excluded from figures 27-29.

Distributions of stable isotopes generally are 

consistent with spatial patterns in recharge areas

(fig. 20), with isotopically lighter precipitation

generally occurring at higher elevations and latitudes. 

Effects of recharge elevation are examined in table 3, 

which shows that δ18O values are lighter in the 

Madison aquifer than in the Minnelusa aquifer for 10 of 

13 well pairs. An example is provided by sites 35 and 

36 (State Line wells, fig. 27), along with a co-located 

Minnekahta well (site 34, fig. 20), which show the 

typical progression of isotopically lighter water 

associated with progressively higher elevation 

recharge sources. The Madison aquifer also is influenced by preferentially larger volumes of isotopically 

light streamflow recharge, relative to the Minnelusa 

aquifer.

In some areas, effects of streamflow recharge on 

isotopic composition can be identified. For example, 

the δ18O values (by aquifer) for sites 35 and 36 (State 

Line wells, fig. 27) are distinctly lighter than values for 

sites 57 and 58 (Tinton Road wells), which probably 

results from the influence of streamflow recharge from 

Beaver Creek or Bear Gulch. The Tinton Road wells 

probably are recharged primarily by precipitation on 

outcrops because no major streamflow loss zones are 

nearby. Similarly, values for sites 85 and 86 (Tilford 

wells) are nearly identical (fig. 27) and are somewhat 

lighter than in nearby outcrop areas (fig. 20), where 

δ18O values are predominantly in the range of -14 to 

-15 ‰, indicating that these wells probably are heavily 

influenced by streamflow recharge from Elk Creek. In 

contrast, Madison and Minnelusa wells at Piedmont 

(sites 100 and 101) and springflow along Elk Creek 

(site 297) probably are influenced primarily by precipitation recharge on large outcrop areas southwest of 

Piedmont.
42 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Cr

Little Spearfish

N Fork

Rapid

Cr Belle Fourche

Reservoir

FOURCHE

Victoria

N Fork Castle Cr

Bear

Gulch

Creek

Crow

Deerfield

Reservoir

Pactola

Reservoir

Indian Cr

Horse

Creek

Owl

BELLE

Creek

RIVER

REDWATER

R I VER

Creek

Spearfish

Whitewood

Creek

Creek

Bear

Butte

Elk

Creek

Creek

Boxelder

Rapid

Rapid

Creek

Creek

Creek

S. Fork Rapid Cr

Hay Creek

Crow

Creek

Beaver

Creek

Gulch

Castle

Castle

Higgins

Creek

Cr e ek

Bottom

False

Creek

Meadow C r

Rhoads Fork

Whitewood

Spearfish

Maurice

Saint

Onge

DEADWOOD

Lead

Nemo

BELLE FOURCHE

Newell

STURGIS

Blackhawk

Piedmont

Tilford

Box Elder 

RAPID CITY

Rochford

Ellsworth

Air Force

Base

104o 45' 103o

30'

15' 103o

30'

44o

45'

15'

44o

BUTTE CO

LAWRENCE CO MEADE CO

WYOMING

SOUTH DAKOTA

LIMESTONE

PLATEAU

290 -16.36

291 -16.75

292

-16.71

293 -17.19

294 -15.34

295 -16.95 296 -16.67

297 -13.79

297 -13.79

290

-16.36

291

-16.75

292

-16.71

293

-17.19

294

-15.34

295

-16.95

296

-16.67

297

-13.79

297

-13.79

36 -17.28

58 -16.66

59 -16.65

61 -16.84

69 -15.04

73

-15.11

82 -16.13

83 -17.19

85 -15.61

95 -13.90

100 -13.68

106 -14.15

107

-14.13

148 -12.55

148 -12.55

36 -17.28

58 -16.66

59 -16.65

61 -16.84

69 -15.04

73

-15.11

82 -16.13

83 -17.19

85 -15.61

95 -13.90

100

-13.68

106

-14.15

107

-14.13

148

-12.55

148

-12.55

4 -17.80 6 -17.07

29 -16.88

35

-16.98

43 -17.43 44 -17.07

48

-17.46

57 -15.90

86 -15.52

101

-13.61

101

-13.61

29 -16.88

35

-16.98

43 -17.43 44 -17.07

48

-17.46

57 -15.90

86 -15.52

101

-13.61

101

-13.61

Figure 27. Distribution of δ18O in selected Madison and Minnelusa wells and springs in the northern Black Hills

area. Sampling dates are through 1998, with mean values shown for sites with multiple samples.

OUTCROP OF MINNELUSA FORMATION (from Strobel and others, 1999)

WELL COMPLETED IN MADISON AQUIFER--Numbers indicate site

 number and δ18O value in per mil

WELL COMPLETED IN MINNELUSA AQUIFER--Numbers indicate site

 number and δ18O value in per mil

DOWNGRADIENT SPRING--Numbers indicate site number and δ18O

 value in per mil

EXPLANATION

0 10

0 10 MILES

KILOMETERS

OUTCROP OF MADISON LIMESTONE (from Strobel and others, 1999)

DAKOTA

SOUTH

Study

Area

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13

Area

Shown
Isotope Chemistry 43

103o22'30" 20' 17'30" 15' 103o12'30"

44o

10'

7'30"

5'

2'30"

44o

City Springs

Cleghorn/

Jackson

Springs

Tittle

Springs

Canyon

Lake

Creek

Creek

Creek

Creek

Creek

Spring

Creek

Rapid

Rapid

Victoria

Lime

MEADE COUNTY

PENNINGT PENNINGTON COUNTY ON COUNTY

RAPID CITY

Boxelder

151

-12.26

123 -14.38

124

-14.40

126

-14.18

130

-13.66

138

-13.45

142

-14.43

145 -13.25

121

-13.94

180

-13.69

117

-14.35

116 -14.28 112 -14.30

188 -14.40

165

-12.13 169 -12.09

168 -12.05

167 -12.09

164

-12.44

176 -12.35

172

-12.77

178 -12.70

182 -14.16

186 -14.38

151 -12.26

149

-12.66

154 -12.44

191

-12.78

193

-12.36

195

-12.27

185 -14.23

123

-14.38

124

-14.40

126

-14.18

130

-13.66

138

-13.45

142

-14.43

145

-13.25

121

-13.94

180

-13.69

117

-14.35

116

-14.28 112 -14.30

188

-14.40

165

-12.13 169

-12.09

168

-12.05

167

-12.09

164

-12.44

176

-12.35

172

-12.77

178

-12.70

182

-14.16

186

-14.38

151

-12.26

149

-12.66

154

-12.44

191

-12.78

193

-12.36

195

-12.27

185

-14.23

129

-13.40

119 -13.65

118 -14.25

113

-13.95

177

-12.90

179 -13.90

175

-13.11

181

-13.83

183 -14.38

187 -13.70

129

-13.40

119

-13.65

118

-14.25

113

-13.95

177

-12.90

179

-13.90

175

-13.11

181

-13.83

183

-14.38

187

-13.70

192

-12.51

192

-12.51

299

-14.45

298 -14.37

299 -14.45

300 -12.92

298

-14.37

299

-14.45

300

-12.92

Figure 28. Distribution of δ18O in selected Madison and Minnelusa wells and springs in the Rapid City area.

Sampling dates are through 1998, with mean values shown for sites with multiple samples.

OUTCROP OF MADISON LIMESTONE (from Strobel and others, 1999)

OUTCROP OF MINNELUSA FORMATION (from Strobel and others, 1999)

EXPLANATION

WELL COMPLETED IN MADISON AQUIFER--Numbers indicate site number and δ18O value in per mil

WELL COMPLETED IN MINNELUSA AQUIFER--Numbers indicate site number and δ18O value in per mil

DOWNGRADIENT SPRING--Numbers indicate site number and δ18O value in per mil

1 2 MILES

0 1 KILOMETERS 2

Base from U.S. Geological Survey digital line graph, 1:100,000, 0

Rapid City, Office of City Engineer map, 1:18,000, 1996

DAKOTA

SOUTH

Study

Area

Area

Shown
44 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Creek

Pass

Hell

Canyon

Bole Canyo

Hot Brook Canyon

Spring

Grace Cooli d ge

Angostura

Reservoir

Castl e Cr

Canyon

Red

Sheridan

Lake

Creek

Creek

Creek

Creek

Creek

S. Fork

Battle

French

Beaver

Creek

Creek

Creek

Fall R

Hat

Creek

Creek

Horsehead

CHEYENNE

RIVER

Cottonwood

Spokane

Lame

Johnny

Bear Gulch

Hill City

Hermosa

CUSTER

HOT SPRINGS

Edgemont

Keystone

Hayward

Fairburn

Buffalo

Gap

Pringle

Oral

Provo

Minnekahta

Wind Cave

National Park

CUSTER

STATE

PARK

Wind

Cave

Jewel Cave

National Monument

Mt. Rushmore

National

Memorial

PENNINGTON CO

CUSTER CO

FALL RIVER CO

WYOMING

SOUTH DAKOTA

45'

30'

43o

15'

104o 45' 30' 15' 103o

44o

297

-13.79

301

-11.62

302 -11.68

303 -14.10

304 -14.86 305 -16.71

306 -15.43

307 -15.23 308 -15.40

301

-11.62

302

-11.68

303

-14.10

304

-14.86 305

-16.71

306

-15.43

307

-15.23 308

-15.40

148

-12.55

196 -11.89

197 -12.06

210 -11.75

237 -11.96

233 -12.13

238 -11.93

247 -15.97

253 -16.59

242 -14.88

215 -17.23

201 -16.32

196

-11.89

197

-12.06

210

-11.75

237

-11.96

233

-12.13

238

-11.93

247 -15.97

253

-16.59

242 -14.88

215

-17.23

201

-16.32

263 -17.09

101

-13.61

199 -11.98

211 -11.50

239 -12.38

254 -15.15

243 -13.87

227 -14.27

216 -14.21

202 -15.88

199

-11.98

211 -11.50

239

-12.38

254

-15.15

243

-13.87

227 -14.27

216

-14.21

202

-15.88

0 10

0 10 MILES

KILOMETERS

OUTCROP OF MINNELUSA FORMATION (from Strobel and others, 1999)

WELL COMPLETED IN MADISON AQUIFER--Numbers indicate site

 number and δ18O value in per mil

WELL COMPLETED IN MINNELUSA AQUIFER--Numbers indicate site

 number and δ18O value in per mil

DOWNGRADIENT SPRING--Numbers indicate site number and δ18O

 value in per mil

EXPLANATION

Figure 29. Distribution of δ18O in selected Madison and Minnelusa wells and springs in the southern Black Hills area.

Sampling dates are through 1998, with mean values shown for sites with multiple samples.

OUTCROP OF MADISON LIMESTONE (from Strobel and others, 1999)

DAKOTA

SOUTH

Study

Area

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13

Area

Shown
Isotope Chemistry 45

Table 3. Selected data for observation well pairs[S, similar; SS, somewhat similar; DS, dissimilar; H, higher or heavier; L, lower or lighter. mg/L, milligrams per liter; pCi/L, picocuries per liter; TU, tritium units; <, less than; --, no data or not shown]

Site

number Name Aquifer

δ18O Tritium Hydraulic head Sulfate

(mg/L)

Chloride

(mg/L) Per mil Heavier/ lighter S/DS1 Date pCi/L TU Higher/ lower S/DS Higher/ lower

36 State Line Madison -17.28 L SS 04-11-94 61.0 19.1 H DS H 150 0.735 State Line Minnelusa -16.98 H SS 04-11-94 <1.0 <.3 L DS L 73 .558 Tinton Road Madison -16.66 L DS 09-08-98 30.4 9.5 L DS L 58 3057 Tinton Road Minnelusa -15.90 H DS 09-08-98 78.4 24.6 H DS H 3.8 1.285 Tilford Madison -15.61 L S 09-03-96 4.0 1.3 L SS H 38 .586 Tilford Minnelusa -15.52 H S 08-27-96 100.0 31.3 H SS L 8.4 .9

100 Piedmont Madison -13.68 L S 09-04-96 <1.0 <.3 L DS H 9.3 .7101 Piedmont Minnelusa -13.61 H S 09-04-96 3.0 .9 H DS L 4.2 1.0117 City Quarry Madison -14.35 L S 05-13-92 96.0 30.1 H S H 20 27118 City Quarry Minnelusa -14.25 H S 05-12-92 2.0 .6 L S L 27 6.0178 Canyon Lake Madison 2-12.70 H DS 09-28-93 75.9 23.8 H DS H 25 3.2

179 Canyon Lake Minnelusa -13.90 L DS 05-14-92 22.0 6.9 L DS L 22 1.4182 Sioux Park Madison 2-14.16 H S -- -- -- -- DS H 20 1.6183 Sioux Park Minnelusa 2-14.38 L S -- -- -- -- DS L 22 1.7191 Reptile Gardens Madison -12.78 L SS 07-29-96 15.0 4.7 H SS H 20 1.5192 Reptile Gardens Minnelusa -12.51 H SS 07-30-96 4.0 1.3 L SS L 14 1.5201 Boles Canyon Madison -16.32 L DS 03-22-94 9.0 2.8 H DS L 8.3 1.1202 Boles Canyon Minnelusa -15.88 H DS 12-17-97 3.2 1.0 L DS H 26 5.9210 CSP Airport Madison -11.75 L SS 09-06-95 <1.0 <.3 L S Same 22 1.4211 CSP Airport Minnelusa -11.50 H SS 08-31-95 3.0 .9 H S Same 38 2.7215 Hell Canyon Madison -17.23 L DS 11-05-97 1.9 .6 H DS H 230 4.3216 Hell Canyon Minnelusa -14.21 H DS 11-03-97 <1.0 <.3 L DS L 470 4.0238 7-11 Ranch Madison -11.93 H DS 03-31-94 <1.0 <.3 -- DS H 24 6.4239 7-11 Ranch Minnelusa -12.38 L DS 04-05-94 <1.0 <.3 -- DS L 32 4.3242 Minnekahta Jnct Madison -14.88 L DS 03-24-94 <1.0 <.3 -- DS H 37 5.2243 Minnekahta Jnct Minnelusa -13.87 H DS 09-11-95 <1.0 <.3 -- DS L 1,800 12

1Comparison between δ18O values for each well pair using criteria of <0.25 per mil for similar, between 0.25 and 0.30 per mil for somewhat similar, and >0.30 per mil for dissimilar.2Mean value for multiple sampling dates.
46 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

In the Rapid City area (fig. 28), recharge probably is dominated by large streamflow losses from 

Boxelder, Rapid, and Spring Creeks, rather than from 

precipitation on the relatively small outcrop areas. In 

western Rapid City, a distinct division of lighter δ18O 

values to the north and heavier values to the south is 

apparent for the Madison aquifer along Rapid Creek. 

Areas south of Rapid Creek apparently are isotopically 

similar to Spring Creek (fig. 20) and sites north of 

Rapid Creek generally reflect isotopically lighter composition similar to that of Rapid Creek and Boxelder 

Creek.

The δ18O values for sites near Battle, Grace 

Coolidge, and French Creeks (fig. 29) are isotopically 

heavier than for any other part of the Black Hills area. 

Values in this area generally are in the range of about 

-11.5 to -12.0 ‰ and are very similar to values for the 

nearby streamflow loss zones. These values probably 

indicate a substantial influence from streamflow 

recharge; however, information is not available for 

evaluation of isotopic composition in the outcrop areas. 

Along the southern and southwestern flanks of the 

uplift, δ18O values for most wells and springs (fig. 29) 

are much lighter than estimated values for nearrecharge areas immediately nearby (fig. 20), indicating 

either recharge areas to the northwest or possible influence of regional flow from the west, as discussed in 

subsequent sections of this report.

Tritium

Tritium data for Black Hills sites are presented in 

table 7. Most sites include data collected only through 

water year 1998. Additional tritium data collected 

during water year 2000 are included for six selected 

sites that are relevant to site-specific discussions of 

isotope geochemistry for the Rapid City area, which 

are presented in a subsequent section.

Spatial distributions of tritium concentrations for 

wells, headwater springs, and downgradient springs in 

the Black Hills area are shown in figures 30, 31, 

and 32. The sites shown include a limited number of 

samples available for the Deadwood and Minnekahta 

aquifers. For sites with more than one tritium sample, 

the most recent concentration (through water year 

1998) is shown.

Various observations can be made from examination of the tritium distributions (figs. 30-32). Large 

spatial variability in concentrations occurs near outcrop 

areas, which reflects large variability in mixing conditions and aquifer characteristics (heterogeneity). Most 

of the wells that are far removed from outcrop areas 

have low, or nondetectable (<0.3 TU) tritium concentrations, which generally supports the use of the timedelay mixing model for artesian areas. Concentrations 

noted as <0.3 TU are equivalent to about <1.0 pCi/L, 

which is the method reporting limit (MRL) for most of 

the laboratory analyses that have been performed. The 

“2 sigma” value is reported as 1.0 pCi/L for most 

samples with concentrations at or near the MRL 

(table 7). The true concentration is expected to be 

within 2 sigma of the reported concentration about 

95 percent of the time (Bob Michel, U.S. Geological 

Survey, oral commun., 2000). Thus, based on estimated tritium concentrations in precipitation (table 11), 

samples reported as <0.3 TU are assumed to be composed primarily of water recharged prior to initial 

influence of nuclear testing in 1953 (pre-bomb water), 

regardless of sampling date or mixing conditions 

(figs. 26 and 36).

Samples with tritium concentrations that equal 

or slightly exceed the MRL also are dominated by prebomb water, but probably are showing the presence of 

some proportion of modern tritium (tritium produced 

during 1953 or later). For concentrations between 0.3 

and 1.0 TU, the detection of modern tritium is fairly 

certain, from an analytical standpoint, and would indicate either: (1) the initial arrival of modern water for 

slug-flow conditions; or (2) at least some proportion of 

modern water for all mixing conditions.

Given the uncertainty in estimation of tritium 

concentrations in recent precipitation (since about 

1992) for the Black Hills area, concentrations as low as 

10 TU (fig. 23) may be possible for recently recharged 

water. Thus, for samples with tritium concentrations 

between about 1 and 5 TU, dominant proportions of 

pre-bomb water generally can be assumed. For concentrations greater than about 5 TU, it is difficult to 

make generalizations because of numerous possible 

mixing scenarios; however, for all mixing conditions, 

the probability of dominant proportions of modern 

water increases with increasing tritium concentrations.
Isotope Chemistry 47

Rhoads Fork

N Fork

Rapid

Cr Belle Fourche

Reservoir

FOURCHE

Victoria

N Fork Castle Cr

Bear

Gulch

Creek

Crow

Deerfield

Reservoir

Pactola

Reservoir

Indian Cr

Horse

Creek

Owl

BELLE

Creek

RIVER

REDWATER

R I VER

Creek

Spearfish

Whitewood

Creek

Creek

Bear

Butte

Elk

Creek

Creek

Boxelder

Rapid

Rapid

Creek

Creek

Creek

S. Fork Rapid Cr

Hay Creek

Beaver

Creek

Gulch

Castle

Castle

Higgins

Creek

Cr e ek

Bottom

False

Creek

Crow

Creek

Cr

Little Spearfish

Meadow C r

Whitewood

Spearfish

Maurice

Savoy

Saint

Onge

DEADWOOD

Lead

Nemo

BELLE FOURCHE

Newell

STURGIS

Blackhawk

Piedmont

Tilford

Box Elder 

RAPID CITY

Rochford

Ellsworth

Air Force

Base

104o 45' 103o

30'

15' 103o

30'

44o

45'

15'

44o

BUTTE CO

LAWRENCE CO MEADE CO

WYOMING

SOUTH DAKOTA

LIMESTONE

PLATEAU

297

 30.1

290

 28.1

291

 24.0

292

293 13.4

 20.7

294

 16.9

295

 21.0

296

 19.1

297

 30.1

297

 30.1

290

 28.1

291

 24.0

292

293 13.4

 20.7

294

 16.9

295

 21.0

296

 19.1

276

 40.8

281

 53.3

282

 31.3

283

 43.9

277

 276.0

279

 40.8

280

 53.3

276

 40.8

281

 53.3

281

 53.3

282

 31.3

283

 43.9

277

 276.0

279

 40.8

280

 53.3

106

<0.3

148

<0.3

95

<0.3

100

<0.3

85

 1.3

73

 0.3

82 65.6

36 19.1

58

 9.5

59 19.7

61 27.3

83 33.0

6 <0.3

106

<0.3

106

<0.3

148

<0.3

95

<0.3

100

<0.3

85

 1.3

73

 0.3

82 65.6

36 19.1

58

 9.5

59 19.7

61 27.3

83 33.0

6 <0.3

101

 0.9

86 31.3

57 24.6

35

<0.3

44 19.4

29

 0.9

48

 0.6

43 11.4

101

 0.9

86 31.3

86 31.3

57 24.6

35

<0.3

44 19.4

29

 0.9

48

 0.6

43 11.4

84

43.9

34

7.5

84

43.9

84

43.9

Figure 30. Distribution of tritium for selected sites in the northern Black Hills area. Sampling dates are through

1998, with the most recent concentration shown for sites with multiple samples.

OUTCROP OF MINNELUSA FORMATION (from Strobel and others, 1999)

WELL COMPLETED IN MADISON AQUIFER--Numbers indicate site

 number and tritium concentration in tritium units

WELL COMPLETED IN MINNELUSA AQUIFER--Numbers indicate site

 number and tritium concentration in tritium units

WELL COMPLETED IN MINNEKAHTA AQUIFER--Numbers indicate site

 number and tritium concentration in tritium units

HEADWATER SPRING--Numbers indicate site number and tritium

 concentration in tritium units

DOWNGRADIENT SPRING--Numbers indicate site number and tritium

 concentration in tritium units

EXPLANATION

0 10

0 10 MILES

KILOMETERS

OUTCROP OF MADISON LIMESTONE (from Strobel and others, 1999)

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13

DAKOTA

SOUTH

Study

Area

Area

Shown
48 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

103o22'30" 20' 17'30" 15' 103o12'30"

44o

10'

7'30"

5'

2'30"

44o

City Springs

Cleghorn/

Jackson

Springs

Tittle

Springs

Canyon

Lake

Creek

Creek

Creek

Creek

Spring

Creek

Rapid

Rapid

Victoria

Lime

MEADE COUNTY

PENNINGT PENNINGTON COUNTY ON COUNTY

RAPID CITY

Creek

Boxelder

126 145 16.6 8.1

138

<0.3

117

 26.3

123

 4.7

124

<0.3

116

 14.5 112

 3.7

121

 31.0

185

 4.3

186

<0.3

164

 25.7

165

 22.9 169

 16.0

172

 22.3

176

 2.2

178

 23.8

149

 22.3

191

 4.7 195

 21.6

168

 27.5

188

<0.3

126

145 16.6

 8.1

138

<0.3

117

 26.3

123

 4.7

124

<0.3

116

 14.5 112

 3.7

121

 31.0

185

 4.3

186

<0.3

164

 25.7

165

 22.9 169

 16.0

172

 22.3

176

 2.2

178

 23.8

149

 22.3

191

 4.7 195

 21.6

195

 21.6

168

 27.5

188

<0.3

187

<0.3

129

<0.3

118

 0.6

177

 20.1

192

 1.3

179

 6.9

187

<0.3

129

<0.3

118

 0.6

177

 20.1

192

 1.3

192

 1.3

179

 6.9

144

 43.5

144

 43.5

298

 40.8

299

 28.8

300

 30.2

298

 40.8

299

 28.8

299

 28.8

300

 30.2

Figure 31. Distribution of tritium for selected sites in the Rapid City area. Sampling dates are through 1998,

with the most recent concentration shown for sites with multiple samples.

OUTCROP OF MADISON LIMESTONE (from Strobel and others, 1999)

OUTCROP OF MINNELUSA FORMATION (from Strobel and others, 1999)

EXPLANATION

WELL COMPLETED IN MADISON AQUIFER--Numbers indicate site number and tritium concentration in tritium units

WELL COMPLETED IN MINNELUSA AQUIFER--Numbers indicate site number and tritium concentration in tritium units

WELL COMPLETED IN DEADWOOD AQUIFER--Numbers indicate site number and tritium concentration in tritium units

DOWNGRADIENT SPRING--Numbers indicate site number and tritium concentration in tritium units

1 2 MILES

0 1 KILOMETERS 2

0

SOUTH

DAKOTA

Study

Area

Area

Shown

Base from U.S. Geological Survey digital line graph, 1:100,000,

and Office of City Engineer, Rapid City, 1:18,000, 1996
Isotope Chemistry 49

Creek

Pass

Hell

Canyon

Bole Canyo

Spring

Grace Cooli d ge

Angostura

Reservoir

Castl e Cr

Canyon

Red

Sheridan

Lake

Creek

Creek

Creek

Creek

Creek

S. Fork

Battle

French

Beaver

Creek

Creek

Creek

Fall R

Hat

Creek

Creek

Horsehead

CHEYENNE

RIVER

Cottonwood

Spokane

Lame

Johnny

Bear Gulch

Hot Brook Canyon

Hill City

Hermosa

CUSTER

HOT SPRINGS

Edgemont

Keystone

Hayward

Fairburn

Buffalo Gap

Pringle

Oral

Provo

Minnekahta

Wind Cave

National Park

CUSTER

STATE

PARK

Wind

Cave

Jewel Cave

National Monument

Mt. Rushmore

National

Memorial

PENNINGTON CO

CUSTER CO

FALL RIVER CO

WYOMING

SOUTH DAKOTA

45'

30'

43o

15'

104o 45' 30' 15' 103o

44o

301

 20.4

302

 17.2

303

 6.0

304

 3.8 305

 0.6

306

 2.5

307

 2.5 308

 2.2

301

 20.4

302

 17.2

303

 6.0

304

 3.8 305

 0.6

306

 2.5

307

 2.5 308

 2.2

308

 2.2

288

 12.9

287

 18.5

288

 12.9

289

 8.2

287

 18.5

288

 12.9

289

 8.2

242

<0.3

196

 25.9

197

 18.7

210

<0.3

238

<0.3

233

 27.7

237

 11.7

247

<0.3

242

<0.3

253

<0.3

215

 0.6

201

 2.8

196

 25.9

197

 18.7

210

<0.3

238

<0.3

233

 27.7

237

 11.7

247

<0.3

242

<0.3

253

<0.3

215

 0.6

201

 2.8

254

<0.3

199

<0.3

211

 0.9

239

<0.3

243

<0.3

254

<0.3

227

<0.3

241

<0.7

216

<0.3

202

 1.0

199

<0.3

211

 0.9

239

<0.3

243

<0.3

254

<0.3

227

<0.3

241

<0.7

216

<0.3

202

 1.0

240

 24.8

240

 24.8

0 10

0 10 MILES

KILOMETERS

Figure 32. Distribution of tritium for selected sites in the southern Black Hills area. Sampling dates are through 1998,

with the most recent concentration shown for sites with multiple samples.

OUTCROP OF MINNELUSA FORMATION (from Strobel and others, 1999)

WELL COMPLETED IN MADISON AQUIFER--Numbers indicate site number and tritium concentration in tritium units

WELL COMPLETED IN MINNELUSA AQUIFER--Numbers indicate site number and tritium concentration in tritium units

WELL COMPLETED IN MINNEKAHTA AQUIFER--Numbers indicate site number and tritium concentration in tritium units

HEADWATER SPRING--Numbers indicate site number and tritium concentration in tritium units

DOWNGRADIENT SPRING--Numbers indicate site number and tritium concentration in tritium units

EXPLANATION

OUTCROP OF MADISON LIMESTONE (from Strobel and others, 1999)

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13

DAKOTA

SOUTH

Study

Area

Area

Shown
50 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Boxplots showing the most recent tritium concentrations for 96 ground-water samples collected 

during 1990-98 from wells, headwater springs, and 

downgradient springs, and 12 samples from streams 

upstream from loss zones are presented in figure 33. 

These plots provide evidence that the mixing models 

illustrated in figure 25 have general applicability. The 

lower end of the range of tritium concentrations for 

headwater springs is much higher than for the wells and 

downgradient springs, which is consistent with the concept of an immediate-arrival mixing model in outcrop 

areas for the Madison and Minnelusa aquifers. The 

lower end of the range of tritium concentrations for 

both wells and downgradient springs is near zero, 

which indicates that the time-delay mixing model 

generally is applicable for artesian conditions, where 

an upper confining unit is present and recharge water 

must travel a substantial lateral distance before 

reaching a discharge point. 

Delay times for wells generally are longer than 

for downgradient springs, which probably tend to 

develop near preferential flowpaths that may be further 

enhanced by dissolution activity. This dual-porosity 

setting is conceptually inconsistent with the assumption of thorough mixing; however, extensive mixing 

may be approximated by springs with large discharges, 

which can capture water from large recharge areas.

It can be demonstrated that effects of dilution 

from mixing have a major influence on tritium concentrations in the Madison and Minnelusa aquifers. For 

slug-flow conditions, water recharged between about 

1962 and 1970 would have tritium concentrations of 

about 70 TU to as much as several hundred TU for all 

sample dates prior to 1998 (fig. 26). Tritium concentrations for the 96 ground-water samples collected 

since 1990, however, are uniformly less than 70 TU 

(fig. 33), indicating a conspicuous absence of values 

reflecting slug-flow conditions for recharge during this 

period. Concentrations indicative of “pulses” consisting of several consecutive years of recharge during 

this peak-tritium period also are absent from the sample 

set. Dual-porosity flow conditions consisting of a 

combination of near-slug flow scenarios (which may 

include recently recharged water) and general mixing 

with older water, however, are entirely plausible and 

are consistent with the range of sampled values 

(fig. 33).

SITE TYPES

TRITIUM CONCENTRATION, IN TRITIUM UNITS

EXPLANATION

10th percentile

25th percentile

Median

75th percentile

90th percentile

68 Number of samples

Figure 33. Boxplots of tritium concentrations for selected ground-water and surface-water samples

collected during 1990-98 in the Black Hills area.

Minimum

Maximum

68 9 19 12

Wells Headwater

springs

Downgradient

springs

Streams

upstream from

loss zones

0

70

10

20

30

40

50

60
Isotope Chemistry 51

Sophisticated methods are available to address 

the numerous mixing possibilities in complex hydrologic settings. Combinations of lumped-parameter 

models have been used, for example, to represent settings where both slug-flow and mixed-reservoir effects 

are important (Maloszewski and Zuber, 1982; Zuber, 

1986; Richter and others, 1993). Compartmental 

mixing models (Yurtsever and Payne, 1986) and 

combinations of environmental tracer techniques with 

numerical ground-water flow models (Reilly and 

others, 1994) also have been used to address complicated hydraulic settings. These methods, however, 

require more extensive data sets than those that are 

currently available. Future collection of time-series 

tracer data in the Black Hills area would facilitate more 

sophisticated evaluations of mixing conditions and 

ground-water ages. The tritium data and conceptual 

models presented in this report, in conjunction with 

stable-isotope and major-ion data, can be used to draw 

various conclusions about flowpaths and mixing conditions in the Black Hills area, as discussed in subsequent 

sections.

Site-Specific Considerations

Site-specific discussions of isotopic interpretations regarding areal flowpaths, ages, and mixing conditions for the Madison and Minnelusa aquifers in the 

Black Hills area are presented in this section. The 

Rapid City area is discussed first because detailed data 

sets are available for this area. Discussions of headwater springs and northern and southern Black Hills 

areas also are included. Previous discussions of 

general considerations for stable isotopes included 

various interpretations regarding recharge areas and 

general flowpaths for several example sites along the 

northern and northeastern flanks of the uplift; these 

examples are not repeated herein.

Rapid City Area

A large data set is available for the Rapid City 

area for stable isotopes (fig. 28) and tritium (fig. 31), 

with multiple samples available for many sites (tables 7 

and 8). Evaluation of flowpaths and mixing conditions 

for the Rapid City area is especially complicated 

because: (1) recharge generally is dominated by 

streamflow losses, rather than precipitation on outcrop 

areas (Carter, Driscoll, and Hamade, 2001); and (2) 

large and variable withdrawals from the Madison and 

Minnelusa aquifers have occurred. Municipal production from the Madison aquifer has increased substantially since about 1990 (Anderson and others, 1999).

As previously discussed, a distinct division of 

stable isotope values is apparent for the Madison 

aquifer along Rapid Creek. Areas south of Rapid 

Creek reflect isotopic composition similar to Spring 

Creek, which is isotopically heavier than Rapid Creek 

and Boxelder Creek (fig. 21). Sites north of Rapid 

Creek generally reflect isotopically lighter composition 

similar to that of Rapid Creek and Boxelder Creek. 

Isotopic composition of precipitation on outcrops in the 

Rapid City area is heavier than in Rapid and Boxelder 

Creeks and averages about -13 to -14 ‰ (fig. 20). The 

δ18O values for several Madison wells north of Rapid 

City (sites 130, 138, and 145) reflect this heavier 

isotopic composition (fig. 28), which probably indicates larger influence from precipitation recharge. The 

δ18O values for Minnelusa wells in the Rapid City area 

show a general gradation from north to south of lighter 

to heavier values, with no distinct division, which 

probably indicates larger influence from precipitation 

recharge, than for the Madison aquifer in this area.

The δ18O values for the Madison wells south of 

Rapid Creek probably indicate a northerly flow component for recharge in the Spring Creek area. The δ18O 

values for springs along Rapid Creek, however, indicate flow from different sources. Cleghorn (site 300) 

and Jackson Springs are large springs with combined 

discharge in excess of 20 ft3/s, which probably are 

recharged primarily by Spring Creek, Rapid Creek, and 

precipitation on outcrop areas to the southwest and 

west (Anderson and others, 1999). Dye testing has 

confirmed rapid movement of water from a loss zone in 

Boxelder Creek to City Springs (site 298) and several 

wells in northwestern Rapid City; however, detectable 

dye concentrations have not been recovered in 

Cleghorn Springs (Rahn, 1971; Greene, 1999). The 

δ18O value for Tittle Springs (site 299) is notably 

lighter than for precipitation in the outcrop area, which 

probably indicates recharge from Rapid Creek.

Results of dye testing in the Rapid City area 

(Greene, 1999), in combination with tritium samples, 

provides relatively definitive age-dating information 

for several sites. Dye was injected in the loss zone of 

Boxelder Creek (site 315) during August 1993. A tritium concentration of 58.1 TU was measured in Boxelder Creek one month later (table 7). Greene (1999) 

reported dye recovery at several sampling locations, 

including site 112 (Black Hills Power and Light) and 

site 123 (Rapid City No. 10), with dye arrival times of 

41 and 49 days, respectively, and tritium concentrations of 3.7 and 4.7 TU.
52 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

The conceptual mixing models, which are based 

on an assumption of equal annual recharge proportions, 

are unable to provide age estimates that are compatible 

with dye results. Using a 0-year delay curve for 1993 

(fig. 36F), which is consistent with prompt dye arrival, 

maximum traveltimes dating back hundreds of years 

are indicated for the sample concentrations of 3.7 and 

4.7 TU. Dye concentrations in the resulting mix would 

be much lower than reported by Greene (1999) and 

probably would be undetectable. Unequal mixing of 

about 5 to 10 percent very recent water (tritium concentration of about 58 TU) with 90 to 95 percent 

pre-bomb water (0 TU) would produce a viable mix. 

Intermediate-age water (with high tritium concentrations) probably is not entirely absent; however, the proportion contributed to the mix must be extremely small. 

This scenario is a noteworthy example of unequal 

mixing conditions that can occur in a dual-porosity 

system.

Greene (1999) also reported dye recovery at 

sites 116 (Rapid City No. 6), 121 (Westberry Trails), 

and 298 (City Springs), with dye arrival times of 30, 

26, and 30 days, respectively, and tritium concentrations of 14.5, 31.0, and 40.8 TU. Dye also was recovered at site 117 (City Quarry Madison), which had a 

tritium concentration of 26.3 TU; however, an arrival 

time was not reported. Viable estimates of maximum 

traveltime can be made for these samples using a 0-

year delay mixing model; however, the resulting mixes 

again are not compatible with reported dye concentrations. Unequal mixes of very recent and older water 

again provide more plausible explanations.

Subsequent samples collected during 2000 from 

Boxelder Creek, Rapid City No. 10, and City Springs 

had tritium concentrations of 15.9, 7.3, and 25.7 TU, 

respectively (table 4). The increased tritium concentration in the sample from Rapid City No. 10 probably 

indicates an increased proportion of recent water (perhaps approaching 50 percent), which is attributed primarily to effects of pumping during the interim years. 

The well was constructed during 1991 and produces 

about 1,800 gal/min (Anderson and others, 1999). The 

tritium concentration of the 2000 sample for City 

Springs is higher than the corresponding Boxelder 

Creek sample, whereas the concentration of the 1993 

sample was lower, which may be indicative of transient 

flow and mixing conditions associated with changing 

recharge and discharge conditions.

Additional insights are obtained from examination of temporal variability in stable isotope values for 

ground-water sites. Data for sites with multiple samples are listed in table 8 and selected sites are shown in 

figure 21B, which was presented earlier. The four 

wells in which dye was recovered (Black Hills Power 

and Light, Rapid City Nos. 6 and 10, and Westberry 

Trails) and City Springs show only minor variability in 

δ18O values. This dampened response to relatively 

large variability in δ18O values recharged by Boxelder 

Creek is consistent with the traveltime analysis, which 

indicates relatively small proportions of recent water.

Table 4. Tritium data for selected sites having data for 2000

[Data are included in table 7; --, no data available]

Site

number Name

Tritium, in tritium units

1991 1993 1996 1997 2000

123 Rapid City No. 10 -- 4.7 -- -- 7.3

169 Rapid City No. 11 10.7 16.6 16.0 -- 12.0

172 Rapid City No. 9 21.0 24.3 -- 22.3 18.2

195 Hart Ranch -- 23.5 21.6 -- 17.7

298 City Springs -- 40.8 -- -- 25.7

315 Boxelder Creek near Nemo -- 58.1 -- 26.8 15.9
Isotope Chemistry 53

Cleghorn Springs (site 300) provides an example 

of ground-water flow and mixing conditions that may 

be reasonably represented by the time-delay mixing 

model. The δ18O values (fig. 21C) for 1986-95 have 

only minor variability (-12.80 to -12.95 ‰) and values 

for 11 samples collected between January 1999 and 

May 2000 range only from -13.09 to -13.19 ‰ (L.D. 

Putnam, U.S. Geological Survey, written commun., 

2000). Thus, a delayed and dampened response to the 

temporal trends in Spring and Rapid Creeks is indicated (fig. 21A). Tritium concentrations in Cleghorn 

Springs (table 7) from 1978 (182 TU) and 1993 

(30.2 TU) indicate dominant proportions of water 

recharged within a timeframe of about 10 to 20 years 

(fig. 36, graphs A and F). Estimates of older age also 

are possible for each sample, but probably can be 

discounted because of the response of δ18O values to 

recharge conditions.

Temporal changes in mixing conditions and age 

characteristics probably have occurred in the vicinity 

of several high-production wells in the Rapid City area 

that have been completed since about 1990 (Anderson 

and others, 1999). Potential changes for site 123 

(Rapid City No. 10) were discussed previously. An 

initial (1991) δ18O sample for site 172 (Rapid City 

No. 9) is notably lighter than later samples, which 

show negligible variability during subsequent years 

(table 8, fig. 21B). Tritium concentrations (table 4) 

increased from 21.0 to 24.3 TU (1991 to 1993), which 

probably indicates a larger component of more modern 

water in an altered mix. Steadily decreasing tritium 

concentrations measured in 1997 and 2000 may be 

indicative of progressive decay of a relatively longterm mix, which is consistent with stabilized δ18O 

values. The decay-curve families for 1993 and 1997 

(fig. 36, graphs F and J) show a variety of plausible age 

estimates.

Tritium concentrations for site 169 (Rapid City 

No. 11) also increased between 1991 and 1993 

(table 4), which may indicate a response to initial 

production. Subsequent tritium samples for 1996 and 

2000 have smaller concentrations. The δ18O values 

(fig. 21C) trend towards progressively lighter values, 

which probably reflects a response to the Spring Creek 

trend. The tritium decay-curve families for 1991, 

1993, and 1996 (fig. 36, graphs D, F, and I) generally 

provide no solutions for mixes involving water recently 

recharged (within several years), which is indicated by 

the δ18O values. Thus, unequal mixing of recent and 

pre-bomb water is a likely scenario at this site.

The δ18O values for site 185 (Rapid City No. 5) 

show a trend towards progressively heavier water 

(fig. 21B), which is opposite to the trend in streamflow 

recharge. The single available tritium concentration of 

4.3 TU in 1993 indicates probable dominance by old 

water, which would tend to dampen δ18O variability. A 

plausible explanation is increased proportions of isotopically heavier water from the south-southwest or from 

the overlying Minnelusa aquifer (fig. 28), induced 

from recent production. Either source would be consistent with aquifer test results (Greene, 1993) that 

showed strongly directional transmissivities and leaky 

confinement at this site. Tritium concentrations of 

<0.3 TU were measured in 1990 and 1993 from the 

Lime Creek observation well (site 186), which is 

located about 700 ft away from Rapid City No. 5. 

Rapid City No. 5 produces about 1,700 gal/min, which 

indicates that the well is located in a transmissive part 

of the aquifer. The low tritium concentrations in both 

wells, however, may indicate that: (1) the matrix is not 

exchanging much water with preferential flowpaths; or 

(2) preferential flowpaths are not well connected to 

modern recharge sources.

Variability in δ18O values for site 195 (Hart 

Ranch) is the largest of any ground-water site for which 

temporal data are available (fig. 21C). Variability 

during 1986-95 appears to be small; however, data for 

1987-93 are absent. Values for 1996-98 are notably 

lighter than for previous periods, which again is consistent with the trend for Spring Creek. Tritium concentrations decreased steadily for samples from 1993, 

1996, and 2000 (table 4), which can be indicative of 

long-term mixes. However, this mixing condition contradicts the δ18O data, which indicate a relatively large 

response to recent recharge.

Tritium data for sites 168 and 176 (Chapel Lane 

Madison wells), which are located within 1,000 ft of 

each other (fig. 31), provide an example of large differences in ground-water ages and mixing conditions 

resulting from aquifer heterogeneity. Low tritium concentrations for site 176 for 1991 and 1993 samples (1.9 

and 2.2 TU, respectively) indicate production primarily from the aquifer matrix. A much higher tritium 

concentration from 1993 (27.5 TU) for site 168 indicates production primarily from preferential flowpaths, 

which is supported by variability in δ18O values 

(fig. 21C). Another example of aquifer heterogeneity 

is provided by the low tritium concentration for 

site 191 (Reptile Gardens Madison well) that is located 

generally upgradient from site 195 (Hart Ranch), 

which has a much higher tritium concentration.
54 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

A low (undetectable) tritium value for site 124 

(Rapid City No. 8) is consistent with small δ18O variability (fig. 21B) and with large distance from the outcrop (fig. 31). The δ18O values (fig. 21C) for site 149 

(Highland Hills) show large variability, which is consistent with relatively high and variable tritium concentrations (table 4). The δ18O values (fig. 21C) for 

site 165 (Carriage Hills) show less variability than 

Highland Hills, but trend more steadily towards lighter 

values, which may indicate more dampened response 

to recent recharge. The single tritium sample 

(22.9 TU) for site 165 provides no information beyond 

confirming the presence of modern water. For the Pine 

Grove well (site 196), which is located just south of the 

Rapid City area (fig. 29), moderate variability in δ18O 

values (fig. 21C) is consistent with the tritium concentration of 25.9 TU (fig. 32).

Headwater Springs

The stable isotope values for headwater springs 

were used in developing the map of generalized spatial 

distribution for δ18O for the Black Hills area (fig. 20). 

Temporal variability in δ18O values is small for headwater springs (table 8), which supports the use of the 

immediate-arrival mixing model (fig. 25B) for general 

evaluation of ground-water ages in this hydrologic setting. The use of the immediate-arrival model is further 

supported by the distribution of tritium concentrations 

for headwater springs, relative to wells and downgradient springs, as discussed previously (fig. 33). All 

of the headwater springs are located within or near 

aquifer outcrops, with some recharge presumably 

occurring in the immediate proximity of springs. 

Generalized age estimates for headwater springs are 

presented in table 5.

The age estimates in table 5 are derived using the 

0-year delay curves (fig. 36) for the appropriate date of 

sample collection. A mix of equal proportions from all 

years between the minimum (0 years for immediate 

arrival) and maximum traveltimes is assumed for this 

mixing model. Two possible estimates for the maximum traveltime exist for most samples; thus, “young”

and “old” estimates are provided for each sample.

Table 5. Generalized age estimates for headwater springs, derived using immediate-arrival mixing model1

[--, unnamed)

Site

number

Spring

name

Sample

date

Tritium concentration

(tritium 

units)

Minimum

traveltime1

(years)

Maximum traveltimes1 (years)

Young estimate Old estimate

Year range2 Average

of range Year range2 Averageof range

276 Knight 08-04-95 40.8 0 1965-67 30 1900-20 80

277 Jones 01-01-78 276.0 0 1963-65 14 1948-54 27

279 -- 3

07-18-96 40.8 0 1964-66 31 1915-25 76

280 -- 08-08-95 53.3 0 1964-65 30 1930-40 60

281 JHD 09-13-95 53.3 0 1964-65 30 1930-40 60

282 Intake Gulch 08-03-95 31.3 0 1967-69 27 1875-95 110

283 Rhoads Fork 4

01-01-78

08-07-95

62.2

43.9

0

0

1972-78

1965-66

3

30

1840-60

1910-30

130

75

287 Barrel 07-25-95 18.5 0 1975-95 0-20 1800-30 160

288 Water Draw 09-14-95 12.9 0 (5) (5) pre 1800 >200

289 McKenna 09-14-95 8.2 0 (5

) (5) pre 1700 >300

1

For immediate arrival model, a mix of equal proportions from all years between minimum and maximum traveltimes is assumed. Two solutions for 

the maximum traveltime are possible for most samples. 2Range of years for maximum traveltimes.

3

Exact sample date unknown (see table 7).

4Location for the 1978 sample is unknown and probably does not exactly coincide with the 1995 sampling location. Exact sample date also 

unknown (see table 7). 5

No mixing solution available for younger estimate using immediate-arrival model; however, plausible solutions for unequal mixing are possible.
Isotope Chemistry 55

Two of the springs (Jones and Rhoads Fork) 

were sampled during 1978. The tritium concentration 

for Jones Spring (276 TU) is very high and shows a 

substantial proportion of water recharged near the 1963 

peak (figs. 26 and 36A). The concentration for 

Rhoads Fork (62.2 TU) is much lower, indicating 

either: (1) dominance by recharge after 1972; or (2) 

maximum traveltimes exceeding about 100 years. In 

deriving the young estimate, it was necessary to 

assume a slightly higher tritium concentration (about 

80-100 TU) in order to obtain a viable solution. An 

additional (1995) sample for Rhoads Fork provides a 

conflicting age estimate; however, the precise location 

of the 1978 sample is not known and is presumed to be 

different.

The young estimates for many of the springs 

indicate maximum traveltimes dating to the mid 1960’s 

(just subsequent to the tritium peak of 1963). The old 

estimates for most springs indicate maximum traveltimes approaching or exceeding 100 years. Notable 

exceptions are the last three springs listed in table 5, for 

which old estimates are much older than for other headwater springs. Viable solutions for young estimates for 

these springs cannot be obtained using the immediate 

arrival mixing model (fig. 36H); however, unequal 

mixing conditions involving recently recharged water 

are plausible.

Continuous records of daily discharge for 

site 283 (Rhoads Fork) indicate dominance by groundwater discharge, with virtually no short-term variability in streamflow. Annual streamflow, however, 

correlates strongly with 9-year moving average precipitation (Driscoll and Carter, in press). Flow characteristics are similar for a gaging station downstream from 

site 282 (Intake Gulch). The thickness of the Madison 

Limestone near these two sites (Carter and Redden, 

1999e) is insufficient to accommodate storage volumes 

associated with the old estimates. Thus, the old 

estimates for Rhoads Fork and Intake Gulch are not 

considered plausible. 

Northern Black Hills Area

Several large artesian springs are located along 

the northern axis of the Black Hills uplift, all of which 

are presumed to originate primarily from the Madison 

and/or Minnelusa aquifers, based on the work of 

Klemp (1995), who evaluated source aquifers using 

geochemical modeling. These springs are a major 

discharge area for these aquifers, with cumulative 

discharge of all artesian springs along the northern 

flank estimated as 90 ft3

/s for 1987-96 (Carter, 

Driscoll, Hamade, and Jarrell, 2001). The potentiometric-surface maps for the Madison and Minnelusa 

aquifers (figs. 7 and 8) indicate primary flow components to these springs from the south and west. The 

possible contribution of regional flow components 

from the west (fig. 6) is evaluated in a subsequent 

section.

A substantial component of recharge from the 

Black Hills area is indicated for these artesian springs 

by the δ18O values (fig. 27), which are similar to values 

in large recharge areas to the south and west (fig. 20), 

which may extend to the Limestone Plateau. With the 

exception of site 294 (Mirror Lake), the δ18O values 

for these springs are very similar, which probably indicates generally thorough mixing conditions associated 

with large discharges and associated large recharge 

areas. The δ18O values for springs also are very similar 

to those for Madison and Minnelusa wells in this area. 

Values for wells generally grade to slightly heavier 

values in a southeasterly direction, reflecting more 

localized flowpaths (figs. 7 and 8) with isotopically 

heavier composition (fig. 20).

The δ18O value for site 294 (Mirror Lake) is similar to that for site 34 (fig. 20, State Line Minnekahta 

well), which may indicate a recharge contribution from 

the Minnekahta aquifer or localized recharge from 

other low-elevation outcrop areas. The tritium concentration for site 294 (fig. 30) also is notably lower than 

for three other springs in close proximity, which also 

may indicate a different recharge source. The relatively high tritium concentrations for the artesian 

springs do not necessarily preclude regional flow contributions, but indicate a substantial recharge contribution from areas within the Black Hills area.

The similarities in isotope values in the vicinity 

of the large springs probably indicates generally 

uniform mixing conditions, which is consistent with 

the physical setting (major discharge area with large 

recharge area) and supports the general applicability of 

the time-delay mixing model for general evaluation of 

ground-water ages. Tritium samples for two wells that 

are located about one-quarter mile apart along Crow 

Creek (fig. 30) provide a useful starting point for evaluation of ground-water ages. Site 43 (McNenny well 

No. 1) was sampled in 1978 (11.4 TU) and site 44 

(McNenny well No. 2) was sampled in 1994 (19.4 TU). 

Applying the time-delay mixing model for the earlier 
56 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

sample (fig. 36A) indicates viable solutions only for 

delay times in the range of about 16 to 24 years. Considering both samples, a common solution with a maximum traveltime of about 175 years can be obtained 

using a delay time of 16 years. Viable solutions with 

similar delay times and maximum traveltimes exist for 

site 293 (McNenny Rearing Pond) and site 296, which 

consists of the cumulative discharge of numerous 

springs along Crow Creek, as well as for site 295 (Cox 

Lake), which is located about 1 mi farther east. The 

theoretical solutions for these samples are relatively 

insensitive to changes in delay time, for delay times up 

to about 28 years.

Tritium samples from 1994 and 1997 are available (table 7) for sites 290 (Higgins Gulch) and 292 

(Old Spearfish Hatchery) located northwest of 

Spearfish (fig. 30). For site 290, the tritium concentrations are 31.3 and 28.1 TU, respectively, for which 

numerous combinations of delay times and residence 

times provide comparable solutions. Two δ18O values 

for the same years (-16.47 and -16.25 ‰, respectively) 

may be sufficiently different to indicate relatively 

short-term response to transient recharge conditions. 

For site 292, a large difference in tritium concentrations exists between the 1994 sample (26.0 TU) and the 

1997 sample (13.4 TU), strongly indicating short-term 

response to transient recharge conditions.

A single 1978 tritium sample for site 82 

(65.6 TU) is nearly identical to estimated concentrations in precipitation for that period (fig. 26). The 

immediate-arrival mixing model may be applicable 

because this Madison well is located within the outcrop 

area. In contrast, tritium was not detected for site 95, 

which also is located within the Madison outcrop near 

Blackhawk. Tritium also was not detected for sites 6, 

106, and 148, all of which are very remote from outcrop areas. Large variability in traveltimes is apparent 

for other wells along the northeastern flank. Substantial influence of modern recharge is apparent for 

springflow along Elk Creek (site 297), which is 

consistent with general characteristics for artesian 

springs.

Southern Black Hills Area

The δ18O values for sites near Battle, Grace 

Coolidge, and French Creeks are in the range of about 

-11.5 to -12.0 ‰ (fig. 29) and are very similar to values 

for the nearby streamflow loss zones (fig. 20). 

Recharge in this area is dominated by streamflow 

recharge (Carter, Driscoll, Hamade, and Jarrell, 2001) 

because of larger drainage areas for contributing 

streams, relative to outcrop areas of the Madison and 

Minnelusa Formations. Tritium concentrations for 

artesian springs along Battle and Grace Coolidge 

Creeks (sites 301 and 302) indicate younger water than 

for several nearby wells (fig. 32), which is consistent 

with mixing conditions associated with the development of artesian springs along preferential flowpaths.

The δ18O values for sites in recharge areas 

(fig. 20) along the southwestern flank of the uplift are 

isotopically lighter than for sites along the southeastern 

flank, which probably reflects larger influence from 

storms of Pacific origin along the western flank. 

Downgradient sites along the southwestern flank 

(fig. 29) reflect this lighter isotopic composition, with 

δ18O values that generally are even lighter than those in 

nearby outcrop areas. This pattern indicates generally 

southeasterly flowpaths originating in higher elevation 

areas to the north. This conclusion is supported by 

tritium concentrations for downgradient wells in this 

area (fig. 32), which generally are dominated by prebomb water, indicating generally long traveltimes and 

flowpaths. The possible influence of regional flowpaths from the west is discussed in the following section. Complex flowpaths in the southern Black Hills 

also may be influenced by interactions between the 

Madison and Minnelusa aquifers, which also are 

discussed in subsequent sections.

REGIONAL FLOWPATHS

Regional flow characteristics (fig. 6) are an 

important consideration in evaluating flowpaths, especially near the northern and southern axes of the uplift. 

Generalized regional flowpaths for the Madison 

aquifer near the study area, which are based on the 

following discussions, are presented in figure 34, along 

with δ18O values for samples from selected artesian 

springs and Madison wells. The artesian springs 

shown are major discharge points for the Madison 

and/or Minnelusa aquifers and do not necessarily consist entirely of flow from the Madison aquifer. Information is not available for evaluation of possible 

regional influences for the Minnelusa aquifer.
Regional Flowpaths 57

Hulett

Sundance

Upton

Newcastle

Whitewood

Spearfish

Saint

Onge

DEADWOOD

Lead

BELLE FOURCHE

Newell

STURGIS

Blackhawk

Piedmont

Tilford

Box Elder 

RAPID CITY

Hill City

Hermosa

CUSTER

HOT SPRINGS

Edgemont

Minnekahta

Tinton

Maurice

Nemo

Hayward

Keystone

Rochford

Pringle

Fairburn

Buffalo Gap

Oral

Provo

BELLE

RIVER

FOURCHE

Redwater

CreekSand

Creek

Cold

Springs

Inyan

Kara

Creek

Creek

Creek

Stockade

Beaver

Beaver

CHEYENNE

RIVER

Creek

Lance

Creek

Crow

Horse

BELLE

Cr

Whoopup

N. Fork Rapid Cr

Belle Fourche

Reservoir

FOURCHE

Victoria

Spring

Rhoads Fork

Coolidge

Angostura

Reservoir

Castle Cr

N. Fork Castle Cr

Canyon

Red

Bear

Gulch

Creek

Crow

Sheridan

Lake

H ot Brook Canyon

Deerfield

Reservoir

Pactola

Reservoir

Creek

Owl

Creek

Creek

RIVER

REDWATER

R I VER

Creek Cr

Little Spearfish

Spearfish

Whitewood

Creek

Creek Bear

Butte

Elk

Elk

Creek

Creek

Creek

Boxelder

Rapid

Rapid

Creek

Creek

Creek

Spring

Creek

French

Creek

Creek

Creek

Grace

Creek

Creek

S. Fork

S. Fork Rapid Cr

Battle

French

Beaver

Creek

Creek

Creek

Fall R

Hat

Creek

Creek

Horsehead

CHEYENNE

RIVER

Cottonwood

Hay Creek

Bottom

False

Creek

Lame Johnny

Higgins

Beaver

Creek

Gulch

Castle

Castle

Creek

Creek

Meadow Cr

Boles Canyon

Creek

Pass

Hell Canyon

Wind Cave National Park

Jewel Cave National Monument

Mt. Rushmore

National

Memorial

CUSTER

STATE

PARK

Wind

Cave

Ellsworth Air Force

CROOK CO Base

WESTON CO

NIOBRARA CO

104o 104o30' 103o30'

103o

44o30'

45o

44o

43o30'

BUTTE CO

LAWRENCE CO MEADE CO

PENNINGTON CO

CUSTER CO

FALL RIVER CO

WYOMING

SOUTH DAKOTA LIMESTONE

PLATEAU

306 -15.43

308 -15.40

293 -17.19

294 -15.34

295 -16.95

296 -16.67

306

-15.43

303

-14.10

308

-15.40

293

-17.19

294

-15.34

295

-16.95

296

-16.67

308

-15.40

1 -18.13

2 -19.66

4 -17.80 6 -17.07

263 -17.09

265 -17.85

266 -17.49

267

-18.18

268 -17.60

269

-18.15

270 -17.75 271

-17.45

272 -17.60

273 -17.40

274

-17.66

275 -17.95

1 -18.13

2 -19.66

4 -17.80 6 -17.07

263

-17.09

265

-17.85

266

-17.49

267

-18.18

268

-17.60

269

-18.15

270

-17.75 271

-17.45

272 -17.60

273

-17.40

274

-17.66

275

-17.95

263

-17.09

Figure 34. Distribution of δ18O in selected Madison wells and springs and generalized flowpaths, based on δ18O

values, in the Black Hills of South Dakota and Wyoming.

0 10 20

0 10 20 MILES

KILOMETERS

EXPLANATION

SOUTH DAKOTA

WYOMING

Study Area Area Shown

Black

Hills

OUTCROP OF MADISON LIMESTONE (from

 Strobel and others, 1999; DeWitt and others,

 1989)

OUTCROP OF MINNELUSA FORMATION

 (from Strobel and others, 1999; DeWitt and

 others, 1989)

GENERALIZED FLOWPATH

WELL COMPLETED IN MADISON AQUIFER--

 Numbers indicate site number and δ18O value

 in per mil

DOWNGRADIENT SPRING--Numbers indicate

 site number and δ18O value in per mil

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13
58 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

 The δ18O values for sites 1 and 2 (north of the 

study area) are -18.13 ‰ and -19.66 ‰, respectively 

(fig. 34), which are much lighter than any of the values 

in Black Hills recharge areas (fig. 20). Busby and 

others (1983) and Plummer and others (1990) note 

Madison wells near recharge areas in Wyoming near 

the Bighorn Mountains with δ18O values as light as 

-18.5 ‰ and near the Laramie Mountains as light as 

-19.25 ‰. In addition, concentrations of sodium (45 

and 36 mg/L, respectively), chloride (67 and 25 mg/L), 

and sulfate (1,700 and 1,600 mg/L) for sites 1 and 2 

(Busby and others, 1991) are approximately an order of 

magnitude higher than for wells along the northwestern 

flank of the Black Hills (fig. 10) and are consistent with 

a regional flowpath trending northeasterly from the 

Bighorn Mountains in Wyoming. This information 

provides strong evidence of a regional flow component 

from the west, just north of the study area.

The δ18O values for sites 4 and 6 (near Belle 

Fourche) and large artesian springs on the northwestern 

flank of the uplift (sites 293- 296) are consistent with 

values in Black Hills recharge areas (fig. 20). Majorion concentrations for site 6 (fig. 10) also are consistent 

with values near the uplift and show no influence from 

regional flowpaths. Major-ion concentrations for site 4 

are slightly higher than site 6, and the δ18O value is 

more similar to site 1 than site 6, indicating more 

evolved ground water at this well and perhaps a slight 

regional influence. However, south of site 4, the 

Madison aquifer probably is not influenced by regional 

flow from the west. Relatively high calcium and 

sulfate concentrations for some of the springs (fig. 35) 

are similar to many Minnelusa wells (fig. 11) and 

probably are influenced by dissolution of anhydrite in 

the Minnelusa aquifer, as discussed later. Relatively 

high tritium concentrations for the springs (fig. 30) 

indicate substantial influence from modern recharge 

and support the conclusion that flow near the northern 

flank of the uplift is dominated by Black Hills 

recharge.

The δ18O values for sites 271- 274, just west of 

the South Dakota/Wyoming border (fig. 34) are similar 

to, but slightly lighter than, the estimated isotopic composition in nearby recharge areas (fig. 20). The δ18O 

values for sites farther west are somewhat lighter and 

provide an indication of possible influence from 

regional flow from the west. Busby and others (1991) 

reported sodium, chloride, and sulfate concentrations 

for site 275 of 11.0, 7.6, and 200 mg/L, respectively, 

which also could indicate influence from regional flow. 

The reported sulfate concentration for site 265 

(210 mg/L) is similar; however, sodium (3.7 mg/L) and 

chloride (2.6 mg/L) concentrations show little, if any, 

influence of regional flow. Reported major-ion concentrations for all other sites in Wyoming are much 

lower and essentially preclude possible influence from 

regional flow.

For site 263 near Provo, sodium (200 mg/L) and 

chloride (270 mg/L) concentrations are high and may 

indicate influence of regional flow or the presence of 

evaporites. The sulfate concentration (310 mg/L) is 

similar to some regional values reported by Busby and 

others (1991), but is lower than values for sites 1 and 2 

north of the study area, which are influenced by 

regional flow. Thus, increasing constituent concentrations resulting from basinward evolutionary processes 

cannot be distinguished from a potential regional flow 

component. The δ18O value of -17.09 ‰ for site 263 

(fig. 34) does not preclude a regional flow component, 

but probably does preclude recharge originating south 

of about Pennington County (fig. 20). 

Sodium and chloride concentrations for large 

springs near the southern axis of the uplift (fig. 35) are 

sufficiently high to indicate possible influence of 

regional flow. Anomalously high sodium and chloride 

concentrations in this area (Whalen, 1994) are indicated by Stiff diagrams for various Madison and 

Minnelusa wells (figs. 10 and 11). Chloride concentrations also are comparable with those for several other 

wells (table 3) that have no possible influence from 

regional flow. Examples include the Tinton Road 

(site 36) and City Quarry (site 117) Madison wells. 

High calcium and sulfate concentrations for sites 307 

(Cool Spring), 308 (Cascade Springs), and other 

springs in this area probably are influenced by dissolution of anhydrite in the Minnelusa aquifer, as discussed 

in a subsequent section. The δ18O values for large 

springs northeast of Provo (fig. 34) are much heavier 

than for site 263 and for sites in Wyoming, which indicates dominant recharge from within the study area, 

including influence of isotopically heavy recharge 

along the southwestern flank of the uplift, within 

Custer County (fig. 20). Low, but detectable, tritium 

concentrations in these springs (fig. 32) indicate relatively long traveltimes, but confirm the influence of 

recharge from within the study area.
Regional Flowpaths 59

BUTTE CO

LAWRENCE CO MEADE CO

PENNINGTON CO

CUSTER CO

FALL RIVER CO

WYOMING

SOUTH DAKOTA LIMESTONE

PLATEAU

N. Fork Rapid Cr

Belle Fourche

Reservoir

FOURCHE

Victoria

Spring

Rhoads Fork

Coolidge

Angostura

Reservoir

Castl e Cr

N. Fork Castle Cr

Canyon

Red

Bear

Gulch

Creek

Crow

Sheridan

Lake

Hot Brook Canyon

Deerfield

Reservoir

Pactola

Reservoir

Horse

Creek

Owl

Creek

Crow Creek

BELLE

RIVER

REDWATER

R I VER

Creek

Cr

Little Spearfish

Spearfish

Whitewood

Creek

Creek

Bear

Butte

Elk

Elk

Creek

Creek

Creek

Boxelder

Rapid

Rapid

Creek

Creek

Creek

Spring

Creek

French

Creek

Creek

Creek

Grace

Creek

Creek

S. Fork

S. Fork Rapid Cr

Battle

French

Beaver

Creek

Creek

Creek

Fall R

Hat

Creek

Creek

Horsehead

CHEYENNE

RIVER

Cottonwood

Hay Creek

Bottom

False

Creek

Lame

Johnny

Higgins

Beaver

Creek

Gulch

Castle

Castle

Creek

Creek

Meadow Cr

Creek

Pass

Hell

Canyon

Boles Canyon

Whitewood

Spearfish

Saint

Onge

DEADWOOD

Lead

BELLE FOURCHE

Newell

STURGIS

Blackhawk

Piedmont

Tilford

Box Elder 

RAPID CITY

Hill City

Hermosa

CUSTER

HOT SPRINGS

Edgemont

Minnekahta

Tinton

Maurice

Nemo

Hayward

Keystone

Rochford

Pringle

Fairburn

Buffalo Gap

Oral

Provo

Wind Cave National Park

Jewel Cave

National Monument

Mt. Rushmore National

Memorial

CUSTER

STATE

PARK

Wind

Cave

Ellsworth

Air Force

Base

290

292

293

296 295

294

295

298

300

302

303

304 305

307

308

296

297

301

306

204

36

58

85

100

182

191 178

210

238

242

58

201

215

117

178

117

57

202

216

211

239

243

192

183

179

101

86

35

118

101

0 10 20

0 10 20 MILES

KILOMETERS

EXPLANATION

OUTCROP OF MINNELUSA

 FORMATION (from Strobel and

 others, 1999)

OUTCROP OF MADISON

 LIMESTONE (from Strobel and

 others, 1999)

Figure 35. Selected Stiff diagrams showing the distribution of major-ion chemistry in selected well pairs and artesian

springs in the Black Hills area.

STIFF DIAGRAM--

ARTESIAN SPRING--Number is

 site number on table 7

Sodium + Potassium

Calcium

Magnesium

Chloride + Fluoride

Bicarbonate + Carbonate

Sulfate

10 10 0

CONCENTRATION, IN MILLIEQUIVALENTS PER LITER

Less than 250 milligrams per liter

ESTIMATED SULFATE CONCEN-

 TRATIONS IN MINNELUSA

 AQUIFER

Between 250 and 1,000 milligrams

 per liter

Greater than 1,000 milligrams per

 liter

WELL COMPLETED IN THE 

 MADISON AQUIFER--Number

 is site number on table 7

WELL COMPLETED IN THE 

 MINNELUSA AQUIFER--

 Number is site number on

 table 7

Base modified from U.S. Geological Survey digital data, 1:100,000

Rapid City, Office of City Engineer map, 1:18,000, 1996

Universal Transverse Mercator projection, zone 13

104o 45' 103o

30'

15' 103o

30'

44o

45'

15'

44o

45'

30'

43o

15'
60 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

The δ18O value of -14.10 ‰ for Beaver Creek 

Spring (site 303) is much lighter than estimated values 

for nearby outcrop areas (fig. 20) and nearby wells 

(fig. 29), which indicates a possible flowpath 

extending from the general Hot Springs area. Such a 

flowpath would include a substantial component of isotopically light water recharged west of the uplift axis 

and would require ground-water flow nearly parallel to 

mapped potentiometric contours (figs. 7 and 8) in some 

areas. This hypothesis is possible, given the hydraulic 

characteristics of the Madison and Minnelusa aquifers 

(Long, 2000), a hydraulic gradient in that direction, and 

the accuracy of potentiometric-surface mapping, which 

is limited by sparsity of data points in the area (Strobel 

and others, 2000a, 2000b). A flowpath from the Hot 

Springs area to Beaver Creek Spring is supported by 

three general factors, including: (1) a low tritium concentration for site 303 (fig. 32) indicating generally 

long traveltimes; (2) the areal distribution of δ18O 

values (fig. 29) relative to recharge areas (fig. 20), indicating generally southeasterly (nonorthogonal) flowpaths along the southwestern flank; and (3) results of a 

water-budget analysis (Carter, Driscoll, Hamade, and 

Jarrell, 2001), which indicates a substantial flow component to Beaver Creek Springs from west of the uplift 

axis.

Evaluation of all available geochemical information indicates that regional flowpaths for the Madison 

aquifer are essentially deflected around the study area, 

with the possible exception of the southwestern and 

northwestern corners. Sites 1 and 2 (fig. 34) north of 

the study area show definite influence from regional 

flowpaths; however, areas south of site 4 are dominated 

by local recharge and probably have negligible regional 

influence. Major-ion chemistry for sites in the southwestern corner of the study area (fig. 10) indicate 

possible regional influence; however, north of this area 

regional influence probably is minor or negligible. The 

potentiometric-surface map for the Madison aquifer 

(fig. 7) neither confirms nor precludes a regional 

influence in these areas.

INTERACTIONS BETWEEN MADISON 

AND MINNELUSA AQUIFERS

Hydrographs for numerous well pairs indicate 

distinct hydraulic separation between the Madison and 

Minnelusa aquifers in many areas (Driscoll, Bradford, 

and Moran, 2000); however, possible hydraulic 

connection is indicated in other areas. Hydraulic connection probably occurs at various artesian springs 

around the periphery of the Black Hills, many of which 

are stratigraphically located within or slightly above 

the Minnelusa Formation. Previous investigators 

(Rahn, 1971; Whalen, 1994; Klemp, 1995; Hayes, 

1999) have identified the Madison and Minnelusa 

aquifers as potential sources for many artesian springs.

Geologic conditions facilitate hydraulic connection between the two aquifers. Confining layers in the 

lower portion of the Minnelusa Formation probably are 

influenced by paleo-karst features such as caverns and 

sinkholes in the upper Madison Limestone. Extensive 

fracturing and solution activity have contributed to 

extensive secondary porosity in both formations and 

decreased competency of the confining layers. Potential exists for downward leakage (from Minnelusa to 

Madison) in recharge areas where the aquifers are 

unconfined (water-table conditions), and for leakage in 

either direction, depending on direction of hydraulic 

gradient, where artesian conditions exist. In this section, potential interactions are evaluated through analysis of hydraulic and geochemical information for well 

pairs and artesian springs.

Interactions at Well Pairs

Potential interactions between the Madison and 

Minnelusa aquifers are evaluated through examination 

of hydraulic and geochemical information for well 

pairs. This section primarily addresses the potential for 

general, areal leakage between the aquifers.

Hydraulic Considerations

Hydrographs for 13 well pairs (26 wells), for 

which geochemical information is available, are presented as figure 37 in the Supplemental Information 

section. Locations of well pairs are shown in figure 35. 

A summary of hydraulic comparisons for these well 

pairs is included in table 3, which was presented previously.

Hydrographs for 9 of the 13 well pairs are fairly 

well separated and do not indicate direct hydraulic 

connection. Hydrographs are nearly identical in 

hydraulic head and shape for the City Quarry wells 

(fig. 37E) and the CSP Airport wells (fig. 37J). 

Hydrograph shapes for the Tilford wells (fig. 37C) are 

similar; however, hydraulic heads are slightly different. 

Hydrographs for the Reptile Gardens wells (fig. 37H) 
Interactions Between Madison and Minnelusa Aquifers 61

have some similarities; however, the period of record is 

insufficient to be definitive.

Similar hydrographs could result from similar 

hydraulic characteristics and recharge/discharge characteristics, rather than hydraulic connection. Of the 

four well pairs with similar hydrographs (table 3), 

hydraulic connection has been confirmed by aquifer 

testing (Greene, 1993) only for the City Quarry wells 

(fig. 37E). These wells are located about one-half mile 

from City Springs, which emerge through the Minnelusa Formation, but have been shown through dye 

testing to originate from the Madison aquifer (Greene, 

1997, 1999). Absence of effective hydraulic connection at some wells in the Rapid City area has been 

indicated by aquifer testing (Greene, 1993), as exemplified by the lack of response for the Sioux Park 

Minnelusa well (fig. 37G). Aquifer testing for two 

production wells in the Spearfish area also indicated no 

measurable hydraulic connection between the Madison 

and Minnelusa aquifers for the wells tested (Greene 

and others, 1999). Given the wide variety of hydrograph shapes, the striking similarities for the CSP 

Airport wells (fig. 37J) and Tilford wells (fig. 37C) 

probably result from hydraulic connection.

Conversely, hydraulic connection does not necessarily mean hydrographs will be similar. The Madison and Minnelusa aquifers probably are hydraulically 

connected at Cleghorn and Jackson Springs, which 

emerge through the Minnelusa Formation, but probably originate primarily from the Madison aquifer, as 

discussed later. The Canyon Lake wells (fig. 37F), 

which are located about one-fourth mile away, show no 

indication of connection, however.

Hydraulic head is higher in the Madison aquifer 

than in the Minnelusa aquifer for 10 of the 13 wells 

pairs considered (table 3, fig. 37). One exception is the 

CSP Airport wells (fig. 37J), where heads are nearly 

identical. The other exceptions are the Tinton Road 

wells (fig. 37B) and the Boles Canyon wells (fig. 37I), 

where water-table conditions occur in both aquifers. 

Paired wells are measured in five other locations where 

artesian conditions exist (Driscoll, Bradford, and 

Moran, 2000); however, paired geochemical data are 

not available. Hydraulic head in the Minnelusa aquifer 

consistently exceeds that of the Madison aquifer at only 

one of these locations. Thus, for areas near the outcrops with artesian conditions, the greatest leakage 

potential generally is from the Madison aquifer to the 

Minnelusa aquifer.

Geochemical Considerations

In this section, geochemical information for 

Madison/Minnelusa well pairs is examined for evidence of leakage between the two aquifers. Geochemical interpretations may be influenced by effects of well 

construction, especially for the Minnelusa aquifer, in 

which observation wells typically are completed only 

in the top of the aquifer (Driscoll, Bradford, and 

Moran, 2000).

Stiff diagrams (fig. 35) indicate major-ion chemistry is very similar for many well pairs, especially near 

outcrop areas. The most notable differences are in concentrations of sulfate, which increase with increasing 

distance from recharge areas in the Minnelusa aquifer. 

Comparisons of sulfate concentrations for well pairs 

are provided in table 3.

The distribution of δ18O values in the Black 

Hills area, including well pairs, was presented in 

figures 27-29. Values for δ18O for well pairs are summarized in table 3, with lighter values in the Madison 

aquifer for 10 of the 13 well pairs, which reflects 

generally higher recharge elevations than for the 

Minnelusa aquifer. Paired values also are categorized 

as similar, somewhat similar, or dissimilar, based on 

the difference in δ18O values, using criteria of less than 

0.25 ‰ for similar, greater than 0.30 ‰ for dissimilar, 

and within this range for somewhat similar. The δ18O 

values are categorized as dissimilar for six pairs 

(table 3), all of which also have dissimilar hydrographs.

All of the four pairs with similar or somewhat 

similar hydrographs (sites 85/86, 117/118, 191/192, 

and 210/211) have δ18O values that are similar or 

somewhat similar (table 3). These similarities are not 

necessarily indicative of extensive mixing because 

similarities in δ18O values may result from similarities 

in recharge characteristics. Hydraulic connection 

between the Madison and Minnelusa aquifers has been 

confirmed at the City Quarry wells (sites 117/118), 

however, by aquifer testing (Greene, 1993) and by dye 

testing (Greene, 1999). Although hydraulic connection 

has been confirmed at the City Quarry wells, tritium 

values indicate much longer traveltimes for the Minnelusa aquifer. 

Hydrographs are dissimilar (table 3) for the 

Sioux Park wells (sites 182/183); however, the δ18O 

values are quite similar. Furthermore, the δ18O value 

for the Minnelusa well (-14.38 ‰) is notably lighter 

than for several nearby Minnelusa wells (fig. 28) and 

closely resembles values for Madison wells to the 

northwest. Hydraulic head in the Madison aquifer 
62 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

generally exceeds that in the Minnelusa aquifer at the 

Sioux Park wells (fig. 37G); however, aquifer testing 

has indicated that direct hydraulic connection does not 

occur at this location. Thus, if the δ18O value for the 

Sioux Park Minnelusa well (site 183) is influenced by 

upward leakage from the Madison aquifer, the leakage 

probably occurs to the northwest, near where confirmed leakage occurs in the vicinity of the City Quarry 

wells (sites 117/118) and City Springs (site 298).

Geochemical comparisons for wells along the 

southwestern flank of the Black Hills provide useful 

information regarding complex flowpaths in this area. 

The δ18O value of -16.32 ‰ for the Boles Canyon 

Madison well (site 201) is somewhat heavier than for 

site 215 (fig. 29) and for wells to the northwest in 

Wyoming (fig. 34). The Madison aquifer is not fully 

saturated at site 201 and may be influenced by downward leakage from the overlying Minnelusa aquifer, 

where hydraulic head is about 500 ft higher (fig. 36I). 

The sulfate concentrations for sites 201 and 202 

(table 3) do not preclude this possibility.

The sulfate concentration for the Hell Canyon 

Madison well (site 215) is higher than for most other 

Madison wells (table 3, fig. 10), which could indicate 

downward leakage from the Minnelusa aquifer. The 

hydraulic gradient between aquifers is adverse 

(upward) at the well site (fig. 37K), but may be favorable at upgradient locations (such as Boles Canyon). 

The δ18O value for the Madison well (-17.23 ‰) is 

much lighter than for the Minnelusa well (site 216), 

however, which essentially precludes substantial influence from Minnelusa aquifer leakage. The δ18O value 

also is lighter than for nearby recharge areas (fig. 20), 

which could indicate a regional flow component. 

Overall major-ion chemistry (sodium sulfate) at this 

site is somewhat distinct (fig. 10), however, and a chloride deficiency (table 3) is not indicative of a regional 

flow component. The high sodium and sulfate concentrations probably are explained by generally increasing 

ion concentrations resulting from basinward evolutionary processes, which is consistent with the long 

flowpath indicated by the light δ18O value.

The δ18O values for both Minnekahta Junction 

wells (site 242 and 243) are notably heavier than for 

other nearby sites (fig. 29) and probably reflect 

recharge primarily near the southern end of the uplift. 

The relatively heavy δ18O values essentially preclude 

the influence of regional flow from the west at this 

location. The hydraulic head difference between the 

Madison and Minnelusa aquifers at this site is only 

about 5 to 15 ft (fig. 37M); thus, leakage in either 

direction might be possible in upgradient locations, 

depending on the hydraulic gradient. The large difference in sulfate concentrations (table 3) probably precludes substantial leakage from the Minnelusa to the 

Madison aquifer, however.

Tritium concentrations for well pairs also are 

summarized in table 3. Sample collection dates were 

comparable for most well pairs (table 7), with the 

exception of the Boles Canyon wells (sites 201/202), 

which were collected several years apart. Tritium 

concentrations cannot necessarily provide conclusive 

information regarding aquifer mixing. An example is 

the City Quarry wells (sites 117 and 118), where 

hydraulic connection between the aquifers has been 

confirmed by aquifer testing, and similar δ18O values 

indicate probable mixing. Without other information, 

the low tritium concentration for the Minnelusa well 

(0.6 TU), relative to the Madison well (30.1 TU), 

would indicate minimal mixing. With other information, the tritium concentrations indicate that a substantial traveltime occurs in the Minnelusa aquifer before 

arrival of any water originating as leakage from the 

Madison aquifer.

The greatest potential for extensive mixing probably exists near the other three well pairs with similar 

hydrographs. Tritium concentrations, however, do not 

provide additional insights regarding mixing at these 

sites. For the Reptile Gardens wells (sites 191 and 192) 

and the CSP Airport wells (sites 210 and 211), tritium 

concentrations are low and do not provide useful information. For the Tilford wells (sites 85 and 86), the 

hydraulic gradient is upward (Madison to Minnelusa) 

and small (fig. 37C). Tritium concentrations do not 

provide additional insights because the concentration 

for the Madison well (1.3 TU) is much lower than for 

the Minnelusa well (31.3 TU); thus, the only possible 

effect from upward leakage would be undiscernible 

dilution of concentrations in the Minnelusa aquifer. 

Tritium concentrations for the State Line Madison 

(19.1 TU) and Minnelusa (<0.3 TU) wells (sites 35 

and 36) indicate extensive mixing can be ruled out, in 

spite of a large hydraulic gradient from Madison to 

Minnelusa. Of the four well pairs with similar hydrographs, two pairs have notably different tritium concentrations (Tilford pair and City Quarry pair). Thus, 

extensive mixing near these two pairs probably does 

not occur. Tritium concentrations for the other two 

pairs (Reptile Gardens and CSP Airport) are very low 

and do not provide conclusive information.
Interactions Between Madison and Minnelusa Aquifers 63

The overall conclusion from comparison of 

hydraulic and geochemical information for well pairs is 

that general leakage between the Madison and 

Minnelusa aquifers probably does not result in areally 

extensive mixing in most locations. Comparisons of 

hydrographs for well pairs indicates the possibility of 

hydraulic connection in 4 of 13 locations. Geochemical information provides indications of mixing only in 

the general vicinity of City Springs in northwest Rapid 

City. Geochemical information for other areas is 

largely inconclusive and provides no definitive indications of extensive mixing. Interactions between the 

two aquifers in the vicinity of artesian springs are 

examined in the following section.

Interactions at Artesian Springs

Extensive interactions between the Madison and 

Minnelusa aquifers may occur at artesian springs, 

many of which have large discharges. Combined discharge of all artesian springs within the Black Hills 

area is estimated as 189 ft3/s for 1987-96, which represents about 48 percent of average recharge to the 

Madison and Minnelusa aquifers (Carter, Driscoll, 

Hamade, and Jarrell, 2001). Numerous investigators 

have identified the Madison and Minnelusa aquifers as 

probable sources for artesian springs in the Black Hills, 

based on hydraulic properties and geochemical characteristics. Extensive cavern development within the 

Madison aquifer creates potential for focused movement of large quantities of water. Breccia pipes within 

the Minnelusa Formation (Bowles and Braddock, 

1963) were identified by Hayes (1999) as a pathway for 

vertical movement of water from the Madison aquifer. 

The Minnekahta aquifer also may be a contributing 

source in locations where the Minnekahta Limestone is 

present. The underlying Deadwood aquifer also cannot 

be discounted as a possible source.

 Precise quantification of relative contributions 

from source aquifers to individual springs is not necessarily possible; however, geochemical information is 

useful for evaluating interactions between the Madison 

and Minnelusa aquifers at artesian springs. Hydraulic 

information also must be considered before geochemical information is addressed. 

Hydraulic Considerations

Locations of artesian springs are shown on 

potentiometric-surface maps of the Madison and 

Minnelusa aquifers (figs. 7 and 8). Hydraulic head in 

the Madison and Minnelusa aquifers at major spring 

locations is estimated from potentiometric-surface 

maps and is summarized in table 6, along with approximate land-surface elevations near the springs. Some 

of the springs considered in table 6 consist of a series 

of springs along stream reaches. For these cases, the 

elevations listed generally are for locations downstream from the individual discrete springs (sites 290, 

292, 296, 297, 301, 302, and 306).

Several hydraulic possibilities exist for interactions between the Madison and Minnelusa aquifers at 

spring locations, including: (1) water originates only 

from the Minnelusa aquifer, with no contribution from 

the underlying Madison aquifer; (2) water originates 

entirely from the Madison aquifer and passes through 

the Minnelusa Formation, with little interaction; 

(3) water originates entirely from the Madison aquifer, 

part of which discharges at the surface and part of 

which recharges the Minnelusa aquifer; and (4) water 

originating from both aquifers contributes to springflow. For cases where the Madison aquifer contributes 

to springflow, leakage to the Minnelusa aquifer could 

consist of either focused leakage in the immediate 

vicinity of the spring-discharge point or general 

leakage in upgradient directions.

The Minnelusa aquifer probably can be discounted as a primary source for springs located where 

the Minnelusa Formation is exposed, which generally 

precludes artesian conditions in the Minnelusa aquifer. 

One example is Cleghorn Springs (site 300) and 

Jackson Springs, which comprise a large spring complex in western Rapid City (fig. 35) adjacent to an 

outcrop section of the Minnelusa Formation, where 

several hundred feet of outcrop occurs in a cliff above 

the springs. Hydraulic head in the Madison aquifer is 

considerably above land surface at this location 

(table 6); however, hydraulic head in the Minnelusa 

aquifer is approximately at land surface, as indicated 

by water levels in a pair of observation wells (fig. 37F, 

sites 178 and 179) located about one-quarter mile east 

of the springs. The large and steady discharge of the 

springs (Anderson and others, 1999) also indicates a 

dominant contribution from the Madison aquifer. The 

spring complex probably serves as a relief mechanism 

for controlling hydraulic head in the Minnelusa 

aquifer; thus, a contribution to springflow from the 

Minnelusa aquifer cannot necessarily be excluded.
64 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota Table 6. Selected hydraulic and geochemical information for major artesian springs [ft3/s, cubic feet per second; MSL, mean sea level; mg/L, milligrams per liter; TU, tritium units; -- no information; %, percent; <, less than; ≈, approximately equal] Site number Name Approxi- mate discharge (ft3/s) Elevation of land surface (feet above MSL) Hydraulic head (feet above MSL) Sulfate (mg/L) Chloride (mg/L) Estimated spring source from previous studies Isotopes Madison aquifer Minnelusa aquifer Date δ18

O

(per mil)

Tritium

(TU)

290 Higgins Gulch 5-10 3,405 3,490 3,550 110 12 Mostly Madison1 09-26-94

10-10-97

mean

----

-16.36

31.328.1

--

292 Old Spearfish Hatchery ≈5 3,405 3,500 3,550 340 2.3 70% Madison,

30% Minnelusa1

09-26-9408-21-97

-16.71

--

26.013.4

293 NcNenny Rearing Pond

≈1 3,400 3,720 3,580 130 .8 Mostly Madison1 09-28-94 -17.19 20.7

294 Mirror Lake

≈1 3,410 3,720 3,580 1,600 2.7 50% Madison,

50% Minnelusa1

09-28-94 -15.34 16.9

295 Cox Lake

≈5 3,415 3,705 3,580 545 .7 Mostly Madison1 09-27-94 -16.95 21.0

296 Crow Creek 30-50 3,355 3,710 3,560 580 6.3 -- 08-30-96 -16.67 19.1297 Elk Creek 0-20 3,450 3,450 3,450 420 15 -- 09-05-96 -13.79 30.1298 City Springs 0-5 3,440 3,450 3,450 98 14 -- 06-26-93

mean

--

-14.37

40.8

--

300 Cleghorn Springs 20-25 3,380 3,420 3,380 25 6.5 -- 01-01-78

09-27-93

mean

----

-13.02

182.0

30.2

--

301 Battle Creek 1-10 3,540 3,540 3,540 19 5.4 -- 09-06-96 -11.62 20.4302 Grace Coolidge Creek 0-20 3,650 3,650 3,650 11 5.3 -- 09-10-96 -11.68 17.2303 Beaver Creek Spring 10-15 3,460 3,480 3,480 1,300 33 Mostly Madison with

dissolved Minnelusa minerals2

04-25-94

mean

--

-14.10

6.0

--

304 Hot Brook Spring <5 3,625 3,700 3,625 76 51 Mostly Madison2 04-21-94

10-03-94

--

-14.86

4.13.8

305 Evans Plunge Spring <5 3,465 3,610 3,420 540 110 Mostly Madison2 01-01-78

04-21-94

-16.71

--

--

0.6

306 Fall River 20-30 3,415 3,580 3,360 400 89 -- 09-11-96 -15.43 2.5307 Cool Spring

≈2 3,450 3,505 3,450 830 38 -- 09-12-96 -15.23 2.5

308 Cascade Spring 18-22 3,440 3,495 3,450 1,500 47 Mostly Madison with

dissolved Minnelusa minerals3

10-19-9509-12-96

mean

----

-15.40

2.22.2

--

1Estimated by Klemp (1995).2Estimated by Whalen (1994).3Estimated by Hayes (1999).
Interactions Between Madison and Minnelusa Aquifers 65

A similar setting exists for Hot Brook Spring 

(site 304) located just northwest of Hot Springs 

(fig. 35). This spring also is located within an outcrop 

section of the Minnelusa Formation, in an area where 

hydraulic head in the Madison aquifer is much higher 

than in the Minnelusa aquifer (table 6), as indicated by 

water levels in a pair of observation wells in Hot 

Springs (Driscoll, Bradford, and Moran, 2000). These 

wells are not included in figure 37 because geochemical data are not available for both wells.

All of the other artesian springs listed in table 6 

occur in locations where the Minnelusa Formation is 

confined by overlying units and artesian conditions are 

assumed for both the Madison and Minnelusa aquifers. 

Mapped hydraulic heads at other artesian spring locations generally are higher in the Madison aquifer than 

the Minnelusa aquifer (table 6, figs. 7 and 8), with the 

exception of sites 290 and 292 (just northwest of 

Spearfish) where mapped hydraulic heads may not be 

definitive because control points are sparse (Strobel 

and others, 2000a, 2000b). Hydraulic head is much 

higher in the Madison aquifer, relative to the Minnelusa 

aquifer, for spring areas along and near Crow Creek 

(sites 293-296) and in the Hot Springs area (sites 304-

306). Hydraulic head in the Madison aquifer is only 

slightly higher than in the Minnelusa aquifer in the 

vicinity of Cool Spring (site 307) and Cascade Springs 

(site 308).

The Madison aquifer generally has larger potential for higher hydraulic head because recharge areas 

occur at higher elevation than for the Minnelusa 

aquifer. Higher hydraulic head in the Madison aquifer 

could indicate higher potential for contributions to 

springflow, relative to contributions from the 

Minnelusa aquifer. An alternative line of reasoning 

may be plausible, however. Higher hydraulic head in 

the Madison aquifer also indicates relatively competent 

confinement by the overlying Minnelusa Formation, 

which could imply larger contributions from the 

Minnelusa aquifer. Thus, generalities regarding dominant contributions to artesian springflow cannot be 

inferred from comparisons of hydraulic head.

Discharge rates for artesian springs (table 6) also 

provide insights regarding hydraulic considerations. 

Flow variability is minimal for many artesian springs 

(Miller and Driscoll, 1998; Anderson and others, 1999; 

U.S. Geological Survey, 2000), including McNenny 

Rearing Pond, Cox Lake, Crow Creek, Cleghorn 

Springs, Beaver Creek Springs, Fall River, and 

Cascade Springs (sites 293, 295, 296, 300, 303, 306, 

308, respectively). Hydraulic heads at these sites 

generally are substantially above land surface for one 

or both of the two aquifers.

In contrast, discharge is much more variable for 

Elk Creek, City Springs, Battle Creek, and Grace 

Coolidge Creek (sites 297, 298, 301, and 302, respectively). At these sites, mapped hydraulic heads in both 

aquifers are approximately coincident with landsurface elevation; however, to some extent, landsurface elevations have been used to infer hydraulic 

heads for the two aquifers. This inference generally is 

validated, however, by hydrographs for observation 

wells in the vicinity of these springs (Driscoll, Bradford, and Moran, 2000). An example is City Springs 

(fig. 35, site 298), which is located about one-half mile 

downgradient from the City Quarry wells (sites 117 

and 118). The discharge of City Springs correlates 

strongly with hydraulic head, with flow occurring only 

when hydraulic head exceeds about 3,440 ft (fig. 37E).

The previous discussion supports a general conclusion that artesian springs are a relief mechanism that 

provide somewhat of an upper limit for hydraulic head 

in the Madison and Minnelusa aquifers. Artesian 

springflow increases in response to increasing recharge 

and increasing water levels. Springflow responds relatively slowly in locations where hydraulic head is substantially above land surface, with faster response in 

locations where hydraulic head is near land surface.

Geochemical Considerations

Previous investigators (Whalen, 1994; Klemp, 

1995; and Hayes, 1999) used geochemical modeling to 

estimate contributions of the Madison and Minnelusa 

aquifers to selected springs. Their methods considered 

major-ion chemistry and several isotopes that are 

influenced by rock/water interactions, including 

carbon, sulfur, and strontium isotopes. Results are not 

necessarily definitive because of: (1) uncertainties in 

selecting representative source and end-point waters 

along assumed flowpaths; (2) spatial variability in 

mineralogical characteristics within the two formations; and (3) potential geochemical influences from 

interactions with other aquifers or confining units. 

Generalized results of previous modeling efforts for 

selected artesian springs are summarized in table 6. 

The Madison aquifer generally was identified as the 

primary source, with variable contributions from the 

Minnelusa aquifer, or chemical influences resulting 

from residence time within the Minnelusa Formation.
66 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Stiff diagrams for artesian springs were presented in figure 35. Sulfate concentrations, which can 

be distinctly different for the Madison and Minnelusa 

aquifers, are listed in table 6 for large artesian springs. 

Springs with high sulfate concentrations have majorion chemistry similar to that of many Minnelusa wells 

(fig. 11), which generally indicates chemical influence 

from the Minnelusa aquifer (or from anhydrite dissolution in overlying confining units). High sulfate concentrations, however, may result from dissolution of 

Minnelusa minerals by water from the Madison aquifer 

and do not necessarily indicate a contribution of water 

from the Minnelusa aquifer. Springs with low sulfate 

concentrations have major-ion chemistry similar to that 

of many Madison and Minnelusa wells (figs. 10 

and 11) and are not necessarily indicative of a Madison 

aquifer source.

Large spatial variability in sulfate concentrations 

occurs in the major artesian spring areas along the 

northern and southern axes of the Black Hills, which 

probably results from differences in availability of 

anhydrite within the Minnelusa Formation. Sulfate 

also could be derived from other potential sources, 

such as gypsum within the Spearfish Formation; however, many springs with low sulfate concentrations 

issue from the Spearfish Formation. Source aquifers 

cannot be determined from other major-ion constituents. High calcium and magnesium concentrations 

could be contributed by either aquifer (figs. 10 and 11). 

High concentrations of sodium/potassium occur only 

in several Madison wells in the southwestern corner of 

the study area (fig. 10); however, concentrations in 

downgradient springs are much smaller (fig. 35).

The large springs in the northwestern part of the 

study area have large spatial variability in major-ion 

chemistry (fig. 35). Sulfate concentrations among 

site 293 (McNenny Rearing Pond), site 294 (Mirror 

Lake), site 295 (Cox Lake), and site 296 (Crow Creek) 

range from 130 to 1,600 mg/L. The Madison aquifer 

was identified by Klemp (1995) as the primary source 

of McNenny Rearing Pond and Cox Lake (table 6), 

both of which had low sulfate concentrations. A mix of 

water from the Madison and Minnelusa aquifers was 

estimated for Mirror Lake (Klemp, 1995), which had 

the highest sulfate concentration. The large discharge 

of Crow Creek (table 6), which has an intermediate 

sulfate concentration (580 mg/L), is comprised of the 

cumulative flow of many artesian springs, including 

sites 293 and 294.

The δ18O value of -16.67 ‰ for Crow Creek 

(fig. 27) reflects the general isotopic composition for 

the Madison and Minnelusa aquifers in this large discharge area. Values for many other area springs are 

similar; however, the value for Mirror Lake (site 294) 

is notably heavier, as previously discussed. Modern 

tritium values for all springs in this large discharge 

area support the conclusion of small or negligible influence of regional flow from the west in this area, as 

previously discussed.

Three large spring discharge areas are located 

near the southern axis of the uplift (fig. 35), two of 

which consist of multiple springs. The discharge of 

Cascade Springs (site 308) is much larger than Cool 

Spring (site 307), and sulfate concentrations (1,500 and 

830 mg/L, respectively) are much different (table 6). 

The high sulfate concentrations resemble ion chemistry 

for Minnelusa wells and reflect influence from the sulfate dissolution front (fig. 35). Geochemical modeling 

of Cascade Springs water by Hayes (1999) indicated a 

primary component of relatively fresh water from the 

Madison aquifer as a dissolution agent for anhydrite 

within the Minnelusa Formation.

The δ18O values for Cascade (site 307) and Cool 

Springs (site 308) are notably lighter than for Madison 

and Minnelusa wells near the southern tip of the uplift 

and notably heavier than values further north (figs. 29 

and 34). This isotopic composition reflects a general 

mix from a large potential recharge area all along the 

western and southwestern flanks of the uplift, which 

may include contributions from the Minnelusa aquifer. 

This is consistent with tritium concentrations (fig. 32), 

which indicate a small proportion of modern water 

mixed with a dominant proportion of pre-bomb water, 

indicating generally long traveltimes. Upgradient 

wells all have even lower tritium concentrations, which 

illustrates the enhancement of preferential flowpaths 

near artesian springs. The combination of geochemical 

information generally excludes substantial contribution from regional flow from the west, as previously 

discussed.

Three closely spaced springs in the Hot Springs 

area (sites 304, 305, and 306) have large spatial variability in major-ion chemistry. The large flow (table 6) 

of Fall River (site 306) includes the discharge of 

sites 304 and 305, as well as various other individual 

springs (not shown), which have large spatial variability in ion chemistry (Alexander and others, 1989). 

Sulfate concentrations for the three sites considered 

range from 76 mg/L for site 304 (Hot Brook Spring) to 
Interactions Between Madison and Minnelusa Aquifers 67

540 mg/L for site 305 (Evans Plunge Spring). The 

Madison aquifer is the likely source of Hot Brook 

Spring, based on hydraulic head (table 6) and physical 

setting, as previously discussed; this conclusion is consistent with Whalen’s (1994) determination. Based on 

hydraulic head, the Madison aquifer also is the source 

of Evans Plunge Spring, but both aquifers could contribute to other springs along the Fall River. All three 

springs have relatively high sodium and chloride concentrations, which is consistent with localized conditions in the Madison and Minnelusa aquifers (Whalen, 

1994).

Springs that consist predominantly of pre-bomb 

water comprise the flow of Fall River (site 306), which 

has a tritium concentration of 2.5 TU. The youngest 

water is contributed by Hot Brook Spring (site 304, 

3.8 TU), with Evans Plunge Spring (site 305) contributing older water (0.6 TU). Water from the nearby Vets 

Home Madison well (site 247) is even older, with no 

detectable tritium.

As previously discussed, the recharge area for 

Beaver Creek Springs (site 303, fig. 34) probably 

extends to the west side of the uplift axis, based on the 

δ18O value, which is notably lighter than estimated 

values for nearby outcrop areas (fig. 20) and nearby 

wells (fig. 29). Relative contributions from the 

Madison and Minnelusa aquifers cannot be determined 

from the δ18O values; however, high sulfate concentrations (table 6, fig. 35) indicate substantial influence 

from the Minnelusa Formation (either flow contributions or rock/water interactions).

The tritium concentration (6.0 TU) for Beaver 

Creek Spring (fig. 32) is discernibly higher than for 

other artesian springs to the southwest, presumably 

from the influence of a localized recharge component 

from along the southeastern flank of the uplift. Tritium 

concentrations for wells near the spring indicate a wide 

range of traveltimes. Tritium was not detected in the 

7-11 Ranch Madison and Minnelusa wells (sites 238 

and 239, respectively); however, some proportion of 

modern water is apparent for other wells. A 1978 

sample (27.7 TU) for site 233 (Kaiser well) indicates 

some modern water, presumably mixed with pre-bomb 

water (fig. 36A). Site 237 (Streeter Ranch) has samples of 10.6 TU from 1977 and 11.7 TU from 1997 

(table 7). The time-delay mixing curves (fig. 36) 

generally indicate theoretical delay times of 10 or more 

years and mixing with substantial proportions of prebomb water. Unequal mixing conditions probably are 

more plausible, given the probable influence of preferential flowpaths associated with the nearby spring.

Synopsis of Interaction Processes

Consideration of both hydraulic and geochemical information is necessary to interpret complex interaction processes between the Madison and Minnelusa 

aquifers. A synopsis of interaction processes is provided in this section.

As previously discussed, various hydrogeologic 

factors such as paleo-karst features, fracturing, and 

solution activity facilitate hydraulic connections 

between the Madison and Minnelusa aquifers. The 

Madison aquifer has potential for higher hydraulic 

head than the Minnelusa aquifer because of higher elevation recharge areas. Hydrographs for paired observation wells indicate that higher hydraulic head in the 

Madison aquifer is maintained in most near-outcrop 

areas where artesian conditions exist, which indicates 

general competency of the confining layer between the 

two aquifers. This is consistent with a previous conclusion that general leakage between the Madison and 

Minnelusa aquifers probably does not result in areally 

extensive mixing.

Saturation indices indicate that the Madison 

aquifer is undersaturated with respect to gypsum, even 

at the highest sulfate concentrations. Thus, ongoing 

dissolution of Minnelusa Formation minerals probably 

occurs where the hydraulic gradient is favorable for 

upward leakage from the Madison aquifer, especially 

in areas where the competency of the confining layer 

has been substantially decreased.

Hayes (1999) hypothesized that upward leakage 

from the Madison aquifer was contributing to ongoing 

development of breccia pipes at Cascade Springs. 

Hayes (1999) noted that breccia pipes commonly occur 

in the upper Minnelusa Formation, but very few have 

been observed in the lower part of the formation. Networks of interbedded breccia layers and short, vertical 

breccia dikes do occur in the lower Minnelusa Formation, however, as schematically illustrated in figure 5. 

Paleo-karst features in the upper Madison Limestone 

have influenced the depositional environment of the 

overlying Minnelusa Formation. Deformation and 

fracturing associated with the subsequent uplift 

(Laramide Orogeny) also have contributed to 

decreased competency of the confining layer between 

the two aquifers.
68 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Hayes (1999) further hypothesized that many 

exposed breccia pipes of the upper Minnelusa Formation probably are the throats of abandoned artesian 

springs. An outward (downgradient) migration of 

artesian springs probably has occurred as upgradient 

spring-discharge points are abandoned and new ones 

are occupied, keeping pace with regional erosion over 

geologic time (Hayes, 1999). In response, hydraulic 

heads in the Madison and Minnelusa aquifers have 

declined over geologic time, as indicated by exposed 

breccia pipes located upgradient from Cascade Springs 

(Hayes, 1999). Further supporting evidence is provided by Ford and others (1993), who concluded that 

water-level declines of more than 300 ft have occurred 

in the Madison aquifer during the last 350,000 years, 

based on geochemical data for Wind Cave.

Ground water discharging from the Madison 

aquifer at artesian springs was referred to as “rejected 

recharge” by Huntoon (1985), who hypothesized that 

recharge is rejected as transmissivity decreases with 

distance from upgradient recharge areas. This hypothesis is consistent with decreasing potential for large 

secondary porosity with increasing distance from the 

uplift, which results from: (1) decreased deformation 

and associated fracturing of rocks; and (2) decreasing 

potential for dissolution enhancement associated with 

increasing basinward concentrations of dissolved 

constituents.

Artesian springflow, which represents about 

48 percent of average recharge to the Madison and 

Minnelusa aquifers (Carter, Driscoll, Hamade, and 

Jarrell, 2001), is an important factor in controlling 

water levels in these aquifers. Artesian springs are 

essentially a relief mechanism that provide an upper 

limit for hydraulic head. Springs located where 

hydraulic head is substantially above land surface 

generally have relatively stable discharge. In locations 

where hydraulic head is near land surface, however, 

discharge characteristics generally are more variable, 

with springflow increasing in response to increasing 

water levels.

The Madison aquifer is identified as the primary 

source for several large artesian springs located within 

outcrop sections of the Minnelusa Formation, which 

generally precludes artesian conditions within the 

Minnelusa aquifer. Precise quantification of relative 

contributions from the Madison and Minnelusa aquifers to artesian springs is complicated by numerous 

factors; however, geochemical modeling by various 

investigators has identified the Madison aquifer as the 

primary potential source for many springs.

Upward leakage from the Madison aquifer is 

concluded to be an important factor in development of 

artesian springs and probably contributes flow to most 

springs. This process is driven by the dissolution 

potential of water from the Madison aquifer, which is 

undersaturated with respect to gypsum. Upward 

leakage at artesian springs probably is a major factor in 

dissolution and transport of anhydrite cements, associated with ongoing development of the anhydrite dissolution front in the Minnelusa aquifer. Although 

conclusive geochemical evidence of extensive mixing 

is not apparent, general leakage from the Madison 

aquifer probably contributes to ongoing dissolution of 

anhydrite within the Minnelusa Formation.

Artesian spring development is further hypothesized to be a self-perpetuating process, with springs 

initially developing in locations with large secondary 

porosity and associated high hydraulic conductivity. 

Development of preferential flowpaths in these areas 

contributes to increased dissolution activity, which 

continually contributes to increased enhancement of 

hydraulic conductivity. Similar development of preferential flowpaths also can occur in locations without 

artesian springs.

Considering all available information, it is concluded that interactions between the Madison and 

Minnelusa aquifers are an important factor governing 

the hydraulic behavior of the two aquifers. The 

exchange of water resulting from general, areal leakage 

probably is small, relative to that which occurs near 

artesian springs; however, both processes probably 

contribute to the control of hydraulic heads in the Black 

Hills area.

SUMMARY AND CONCLUSIONS

The Madison and Minnelusa aquifers are two of 

the most important aquifers in the Black Hills area 

because of utilization for water supplies and important 

influences on surface-water resources resulting from 

large springs and streamflow-loss zones. Examination 

of geochemical information provides a better understanding of the complex flow systems within these 

aquifers and interactions between the aquifers.

Two main types of water exist within the 

Madison aquifer—calcium magnesium bicarbonate 

type, which is expected in a carbonate aquifer; and calcium sodium chloride sulfate type, which is present 

mainly in the southwestern part of the study area. This 
Summary and Conclusions 69

chemistry probably reflects the presence of more 

evolved ground water and regional flow, or greater 

amounts of evaporite minerals available for dissolution. 

Three main types of water exist within the 

Minnelusa aquifer—calcium magnesium bicarbonate 

type, calcium magnesium sulfate type, and calcium 

magnesium bicarbonate sulfate chloride type. Water in 

the Minnelusa aquifer generally evolves downgradient 

from a calcium magnesium bicarbonate type to a 

calcium magnesium sulfate type, due to dissolution of 

anhydrite. In the southern part of the study area, 

ground water in the Minnelusa aquifer is characterized 

by higher concentrations of sodium and chloride. The 

high chloride concentrations in this area could reflect 

leakage between the aquifers, the dissolution of 

evaporite minerals, or the presence of more evolved 

ground water contributed by regional flow. 

The most notable differences in major-ion chemistry between the Madison and Minnelusa aquifers are 

in concentrations of sulfate. Sulfate concentrations in 

the Minnelusa aquifer are dependent on the amount of 

anhydrite present in the Minnelusa Formation. A transition zone where dissolution of anhydrite is actively 

occurring was inferred from lines of equal sulfate concentrations in the range of 250 to 1,000 mg/L (milligrams per liter). Upgradient from this zone, the 

anhydrite generally is not present because of earlier 

removal from the formation by dissolution. Downgradient from this zone, thick anhydrite beds remain in 

the formation.

Water chemistry for the Madison and Minnelusa 

aquifers is controlled by reactions among calcite, dolomite, and anhydrite. Saturation indices for gypsum, 

calcite, and dolomite for most samples in both the 

Madison and Minnelusa aquifers are indicative of the 

occurrence of dedolomitization. Because water in the 

Madison aquifer remains undersaturated with respect 

to gypsum, even at the highest sulfate concentrations, 

upward leakage has potential to drive increased dissolution of anhydrite in the Minnelusa Formation, especially where Minnelusa aquifer water is nearly 

saturated with respect to gypsum.

Forward geochemical modeling is used to illustrate trends in pH and calcium and magnesium concentrations with increasing dissolution of anhydrite. 

Comparison of actual calcium and magnesium concentrations to model results indicates that if dedolomitization is occurring in both the Madison and Minnelusa 

aquifers, conditions in the aquifers (temperature, Kdolomite) are similar but not identical to modeled values. In 

the Minnelusa aquifer, pH generally is lower at high 

sulfate concentrations, which supports the occurrence 

of the dedolomitization reaction. In the Madison 

aquifer, the data are consistent with dedolomitization, 

but pH trends are limited by the extent of anhydrite 

dissolution.

Ground water in both aquifers generally is well 

oxygenated at considerable distances from the outcrop 

areas because little organic material or reduced inorganic minerals are available for oxidation reactions. 

Reduction of sulfate, nitrate, and ferric iron minerals, 

methane fermentation, and anaerobic decay of organic 

matter are therefore not likely in the Madison and 

Minnelusa aquifers in the study area.

Isotopic information is used to evaluate groundwater flowpaths, ages, and mixing conditions for the 

Madison and Minnelusa aquifers. Distinctive patterns 

exist in the distribution of stable isotopes of oxygen 

and hydrogen in precipitation for the Black Hills area, 

with isotopically lighter precipitation generally occurring at higher elevations and latitudes. A generalized 

distribution of δ18O (ratio of 18O/16O relative to a 

reference standard) for recharge areas is developed and 

used as a tracer for ground-water flowpaths. Distributions of δ18O in ground water are consistent with 

spatial patterns in recharge areas, with isotopically 

lighter δ18O values in the Madison aquifer resulting 

from generally higher elevation recharge sources, 

relative to the Minnelusa aquifer. For some areas, 

dominant proportions of isotopically light streamflow 

recharge are identified, relative to recharge from 

infiltration of precipitation on lower elevation outcrop 

areas. Both sources are important recharge mechanisms for the two aquifers.

The radioisotope tritium is used to evaluate 

mixing conditions and general ground-water ages. 

Estimates of annual tritium concentrations in precipitation for the Black Hills are based on long-term records 

for Ottawa, Canada, and shorter records for Bismarck, 

North Dakota, and Lincoln, Nebraska.

Three conceptual models, which are simplifications of lumped-parameter models, are considered for 

evaluation of ground-water flow and mixing conditions. For a simple slug-flow model, which assumes no 

mixing, tritium concentrations in ground water can be 

related through a first-order decay equation to estimated concentrations at the time of recharge. Two 

simplified mixing models that assume equal proportions of annual recharge over a range of years also are 

considered. An “immediate-arrival” model is used to 
70 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

conceptually represent conditions in outcrop areas and 

a “time-delay” model is used for locations removed 

from outcrops, where delay times for earliest arrival of 

ground water generally would be expected. Decay 

curve families with incremental delay times are used 

for evaluating approximate age ranges for these 

conceptual mixing applications.

Limitations for use of the simplified, conceptual 

models include uncertainties in estimated tritium input 

(which may include precipitation and streamflow 

recharge) and gross assumptions regarding equal 

annual recharge and thorough mixing conditions. A 

major limitation results from highly heterogeneous 

aquifer properties that commonly may be dominated by 

dual-porosity hydraulic characteristics, consisting of 

high-porosity secondary openings within a lowporosity aquifer matrix. For this setting, a wide variety 

of mixing conditions could occur, including relatively 

old water from the aquifer matrix mixing with various 

and transient proportions of modern water flowing in 

near slug-flow conditions. Because of these limitations, the conceptual models are used only for general 

evaluation of mixing conditions and approximation of 

age ranges.

Despite limitations, the general applicability of 

arrival times associated with the conceptual models is 

demonstrated by the distribution of tritium concentrations for several groupings of hydrogeologic situations. 

Headwater springs, which are located in or near outcrop areas, have the highest tritium concentrations, 

which is consistent with the immediate-arrival mixing 

model. Tritium concentrations for many wells are very 

low, or nondetectable, indicating general applicability 

of the time-delay conceptual model for locations 

beyond outcrop areas, where artesian conditions generally occur. Concentrations for artesian springs generally are higher than for wells, which indicates generally 

shorter delay times resulting from preferential flowpaths that typically are associated with artesian springs. 

The general applicability of mixing models is supported by the absence of extremely high tritium values, 

which would be indicative of near slug-flow conditions, with recharge centered around periods of high 

tritium concentrations that occurred near the 1963 

tritium peak. Exceptions to this generality cannot be 

discounted, however.

Extensive isotopic data sets are available for 

evaluation of mixing conditions and general groundwater ages in the Rapid City area, where large recharge 

occurs from streamflow losses along Boxelder, Rapid, 

and Spring Creeks, which have distinctively different 

δ18O signatures. A distinct division of lighter isotopic 

values to the north and heavier values to the south 

occurs in the Madison aquifer along Rapid Creek. A 

less distinctive gradation occurs for the Minnelusa 

aquifer, which probably reflects larger influence from 

precipitation recharge.

Dye testing has confirmed rapid ground-water 

flow (timeframe of weeks) from a loss zone in Boxelder Creek to City Springs and several wells located 

several miles downgradient in northwestern Rapid 

City. Tritium concentrations were very low (about 4 to 

5 tritium units) for two sites with prompt dye arrival, 

dramatically demonstrating the limitations of the conceptual mixing models, which were unable to provide 

compatible age estimates. The combination of tritium 

and dye data indicated unequal mixing of about 5 to 

10 percent very recent water and 90 to 95 percent prebomb water, which illustrates the complex mixing 

conditions that can occur in a dual-porosity system. 

Limited time-series δ18O data for these sites showed 

minimal response to temporal variations in Boxelder 

Creek, which is consistent with a dominant proportion 

of pre-bomb water. Several other sites with dye 

recovery had higher tritium concentrations, reflecting 

larger proportions of modern water, with δ18O data for 

these sites showing larger response to temporal variations in Boxelder Creek.

Time-series δ18O and tritium data provide useful 

information regarding mixing conditions and general 

ages for numerous other sampling sites in the Rapid 

City area. Sites with minimal variability in δ18O values 

generally have tritium data indicative of dominant 

proportions of pre-bomb water, reflecting generally 

thorough mixing conditions. A number of sites, however, showed response to temporal δ18O trends in 

streamflow recharge, with associated tritium data 

generally indicating relatively large proportions of 

modern recharge. Several large Madison production 

wells located near the Rapid Creek transition zone had 

changes in δ18O values indicative of changes in capture 

zones associated with recent production.

Evaluation of major-ion and isotope data indicates that regional flowpaths for the Madison aquifer 

are essentially deflected around the study area, with the 

possible exception of the southwestern and northwestern corners. Two wells just north of the study area 

clearly show influence of regional flow and a well just 

within the study area shows possible influence. Large 
Summary and Conclusions 71

artesian springs near the northern axis of the uplift 

show no regional influence and are concluded to be 

recharged within the uplift area.

Major-ion concentrations for wells just west of 

the study area in Wyoming indicate deflection of 

regional flowpaths; however, minor influence may be 

possible for the most westerly wells considered. High 

ion concentrations for several wells in the southwestern 

corner of the study area indicate possible regional 

influence, but cannot necessarily be distinguished from 

basinward increases in constituent concentrations. 

North of this area, regional influence probably is minor 

or negligible. The δ18O values for large springs along 

the southern axis of the uplift essentially preclude 

regional influence, which is supported by ion chemistry. Low, but detectable, tritium concentrations in 

these springs confirm the influence of recharge from 

within the study area, but indicate relatively long 

traveltimes. This is consistent with the δ18O values, 

which indicate potential recharge areas extending 

along the entire southwestern flank of the uplift. The 

δ18O value for Beaver Creek Spring is much lighter 

than estimated values for nearby outcrop areas and 

nearby wells, which indicates a possible flowpath 

extending from the general Hot Springs area. This 

flowpath to Beaver Creek Spring also is supported by a 

low tritium value indicating generally long traveltimes.

Potential interactions between the Madison and 

Minnelusa aquifer are examined using hydraulic and 

geochemical information for well pairs and artesian 

springs. Hydrographs for 9 of 13 well pairs are fairly 

well separated and do not indicate direct hydraulic 

connection between the aquifers. Although some 

exchange of water must occur in locations where 

hydraulic head differences occur, conclusive geochemical evidence of extensive mixing resulting from 

general, areal leakage between the aquifers is not 

apparent.

The Madison aquifer has been positively identified from dye testing/recovery as a source for City 

Springs and is concluded to be a primary source for 

several artesian springs (Cleghorn/Jackson and Hot 

Brook Springs) where artesian conditions in the 

Minnelusa aquifer are precluded by nearby outcrop 

sections. Contributions from these aquifers cannot 

necessarily be quantified for other artesian springs 

because of geochemical similarities between the 

Madison and Minnelusa aquifers. For some springs, 

high sulfate concentrations indicate Minnelusa influence, but may result from dissolution of Minnelusa 

minerals by water from the Madison aquifer. Various 

investigators have hypothesized that the Madison 

aquifer is the primary source for many artesian springs, 

based on geochemical modeling, which is consistent 

with generally higher hydraulic head in the Madison 

aquifer, relative to the Minnelusa aquifer.

Generally higher hydraulic head in the Madison 

aquifer, in combination with gypsum undersaturation, 

is concluded to be a primary mechanism driving interactions with the Minnelusa aquifer, in areas where 

artesian conditions exist. Upward leakage from the 

Madison aquifer probably contributes to general dissolution of anhydrite deposits and development of 

breccia pipes in the Minnelusa aquifer. Breccia development may be especially prevalent in locations where 

the competency of intervening confining layers has 

been decreased by fracturing or by depositional influences in the Minnelusa Formation resulting from 

paleo-karstification of the Madison Limestone.

Development of breccia pipes probably contributes to enhanced vertical hydraulic conductivity in the 

Minnelusa aquifer. Breccia pipes are a likely mechanism for upward movement of large quantities of water 

through the Minnelusa aquifer at artesian spring locations and many exposed breccia pipes of the upper 

Minnelusa Formation probably are the throats of abandoned artesian springs. Dissolution processes are an 

important factor in a self-perpetuating process associated with development of preferential flowpaths and 

artesian springs. Preferential flowpaths initially 

develop in locations with large secondary porosity and 

associated hydraulic conductivity, with ongoing 

enhancement resulting from dissolution activity.

Outward (downgradient) migration of the artesian springs probably occurs as upgradient springdischarge points are abandoned and new ones are occupied, keeping pace with regional erosion over geologic 

time. In response to this outward migration, hydraulic 

heads in the Madison and Minnelusa aquifers also have 

declined over geologic time.

Artesian springflow and general leakage are concluded to be important factors in governing hydraulic 

characteristics and water levels in the Madison and 

Minnelusa aquifers. Artesian springflow, which represents about one-half of average recharge to the 

Madison and Minnelusa aquifers, is especially important. Artesian springs act as a relief mechanism that 

provide an upper limit for hydraulic head, with springflow increasing in response to increasing water levels.
72 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

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U.S. Geological Survey Water-Resources Investigations Report 85-4022, 34 p.

Plummer, L.N., Busby, J.F., Lee, R.W., and Hanshaw, B.B., 

1990, Geochemical modeling of the Madison aquifer in 

parts of Montana, Wyoming, and South Dakota: Water 

Resources Research, v. 26, no. 9, p. 1981-2014.

Rahn, P.H., 1971, The hydrologic significance of the 

November 1968 dye test on Boxelder Creek, Black 

Hills, South Dakota: Proceedings of the South Dakota 

Academy of Science, v. 50, p. 52-56. 

———1985, Ground water stored in the rocks of western 

South Dakota, in Rich, F.J., ed., Geology of the Black 

Hills, South Dakota and Wyoming (2d ed.): Geological 

Society of America, Field Trip Guidebook, American 

Geological Institute, p. 154-174.

Rahn, P.H., and Gries, J.P., 1973, Large springs in the Black 

Hills, South Dakota and Wyoming: South Dakota 

Geological Survey Report of Investigations 107, 46 p.

Reilly, T.E., Plummer, L.N., Phillips, P.J., and Busenberg, 

E., 1994, The use of simulation and multiple environmental tracers to quantify groundwater flow in a shallow aquifer: Water Resources Research, v. 30, no. 2, 

p. 421-434.

Richter, J., Szymczak, P., Abrahan, T., and Jordan, H., 1993, 

Use of combinations of lumped-parameter models to 

interpret groundwater isotope data: Journal of Contaminant Hydrology, v. 14, p. 1-13.

Rose, S., 1993, Environmental tritium systematics of baseflow in Piedmont Province watersheds, Georgia: 

Journal of Hydrology, v. 143, p. 191-216.

Stiff, H.A., Jr., 1951, The interpretation of chemical water 

analysis by means of patterns: Journal of Petroleum 

Technology, v. 3, no. 10, p. 15-17.

Strobel, M.L., Galloway, J.M., Hamade, G.R., and Jarrell, 

G.J., 2000a, Potentiometric surface of the Madison 

aquifer, Black Hills area, South Dakota: U.S. Geological Survey Hydrologic Investigation Atlas 

HA-745-D, 2 sheets, scale 1:100,000.
References 75

———2000b, Potentiometric surface of the Minnelusa aquifer, Black Hills area, South Dakota: U.S. Geological 

Survey Hydrologic Investigation Atlas HA-745-C, 

2 sheets, scale 1:100,000.

Strobel, M.L., Jarrell, G.J., Sawyer, J.F., Schleicher, J.R., 

and Fahrenbach, M.D., 1999, Distribution of hydrogeologic units in the Black Hills area, South Dakota: U.S. 

Geological Survey Hydrologic Investigations Atlas 

HA-743, 3 sheets, scale 1:100,000.

Swenson, F.A., 1968, New theory of recharge to the artesian 

basin of the Dakotas: Geological Society of America 

Bulletin 1081-B, p. 163-182. 

U.S. Department of Commerce, 1999, Climatological data 

for South Dakota, annual summary: Asheville, N.C.

U.S. Geological Survey, 2000, Water resources data, South 

Dakota, water year 1999: U.S. Geological Survey 

Water-Data Report SD-99-1, 501 p.

von Morlot, A., 1847, Veber Dolomit und seine kunstliche 

Darstellung aus kalkstein: Naturwissenschaftliche 

Abhandlungenm, gesammelt und durch Subscription 

lursg, von Wilhelm Haidinger, v. 1, p. 305-315. 

Wenker, G.A., 1997, Geological setting and water quality of 

headwater springs in the Black Hills of South Dakota: 

Rapid City, South Dakota School of Mines and Technology, M.S. thesis, 101 p.

Whalen, P.J., 1994, Source aquifers for Cascade Springs, Hot 

Springs, and Beaver Creek Springs in the southern 

Black Hills of South Dakota: Rapid City, South Dakota 

School of Mines and Technology, unpublished M.S. 

thesis, 299 p.

Whitehead, R.L., 1996, Ground water atlas of the United 

States—segment 8, Montana, North Dakota, South 

Dakota, Wyoming: U.S. Geological Survey Hydrologic 

Investigations Atlas 730-I, 24 p.

Yurtsever, Y., and Payne, B.R., 1986, Mathematical models 

based on compartmental simulation approach for quantitative interpretation of tracer data in hydrological systems: Proceedings of the 5th International Symposium 

on Underground Water Tracing, v. 5, p. 341-353.

Zuber, 1986, Mathematical models for the interpretation of 

environmental radioisotopes in groundwater systems, 

in Fritz, P., and Fontes, J.C., eds., Handbook of Environmental Geochemistry, v. 2, The terrestrial environment: New York, Elsevier Publishing Company, 

p. 1-59.

SUPPLEMENTAL INFORMATION

Supplemental Information - Figure 36 79

1800 1850 1900 1950 2000

YEAR

TRITIUM CONCENTRATION, IN TRITIUM UNITS

0 year

4 year

8 year

12 year

16 year

20 year

24 year

GRAPH A - CURVES FOR 1978 SAMPLING DATE

1800 1850 1900 1950 2000

YEAR

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

TRITIUM CONCENTRATION, IN TRITIUM UNITS

0 year

4 year

8 year

12 year

16 year

20 year

24 year

28 year

32 year

36 year

GRAPH B - CURVES FOR 1989 SAMPLING DATE

28 year

Figure 36. Decay-curve families for time-delay mixing model. Each graph shows a family of curves for a given 

sampling year. Each curve shows average decayed tritium concentrations, for hypothetical mixes over time, for

specified delay times that are provided in 4-year increments.

1

10,000

2

5

10

20

50

100

200

500

1,000

2,000

5,000
80 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

1800 1850 1900 1950 2000

YEAR

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

TRITIUM CONCENTRATION, IN TRITIUM UNITS

0 year

4 year

8 year

12 year

16 year

20 year

24 year

28 year

32 year

36 year

GRAPH C - CURVES FOR 1990 SAMPLING DATE

1800 1850 1900 1950 2000

YEAR

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

TRITIUM CONCENTRATION, IN TRITIUM UNITS

0 year

4 year

8 year

12 year

16 year

20 year

24 year

28 year

32 year

36 year

GRAPH D - CURVES FOR 1991 SAMPLING DATE

40 year

40 year

Figure 36. Decay-curve families for time-delay mixing model. Each graph shows a family of curves for a given 

sampling year. Each curve shows average decayed tritium concentrations, for hypothetical mixes over time, for

specified delay times that are provided in 4-year increments.--Continued
Supplemental Information - Figure 36 81

1800 1850 1900 1950 2000

YEAR

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

TRITIUM CONCENTRATION, IN TRITIUM UNITS

0 year

4 year

8 year

12 year

16 year

20 year

24 year

28 year

32 year

36 year

40 year

GRAPH E - CURVES FOR 1992 SAMPLING DATE

1800 1850 1900 1950 2000

YEAR

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

TRITIUM CONCENTRATION, IN TRITIUM UNITS

0 year

4 year

8 year

12 year

16 year

20 year

24 year

28 year

32 year

36 year

40 year

GRAPH F - CURVES FOR 1993 SAMPLING DATE

Figure 36. Decay-curve families for time-delay mixing model. Each graph shows a family of curves for a given 

sampling year. Each curve shows average decayed tritium concentrations, for hypothetical mixes over time, for

specified delay times that are provided in 4-year increments.--Continued
82 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

1800 1850 1900 1950 2000

YEAR

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

TRITIUM CONCENTRATION, IN TRITIUM UNITS

0 year

4 year

8 year

12 year

16 year

20 year

24 year

28 year

32 year

36 year

40 year

GRAPH G - CURVES FOR 1994 SAMPLING DATE

1800 1850 1900 1950 2000

YEAR

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

TRITIUM CONCENTRATION, IN TRITIUM UNITS

0 year

4 year

8 year

12 year

16 year

20 year

24 year

28 year

32 year

36 year

40 year

GRAPH H - CURVES FOR 1995 SAMPLING DATE

Figure 36. Decay-curve families for time-delay mixing model. Each graph shows a family of curves for a given 

sampling year. Each curve shows average decayed tritium concentrations, for hypothetical mixes over time, for

specified delay times that are provided in 4-year increments.--Continued
Supplemental Information - Figure 36 83

1800 1850 1900 1950 2000

YEAR

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

TRITIUM CONCENTRATION, IN TRITIUM UNITS

0 year

4 year

8 year

12 year

16 year

20 year

24 year

28 year

32 year

36 year

40 year

GRAPH I - CURVES FOR 1996 SAMPLING DATE

1800 1850 1900 1950 2000

YEAR

1

1,000

2

3

4

5

7

10

20

30

40

50

70

100

200

300

400

500

700

TRITIUM CONCENTRATION, IN TRITIUM UNITS

0 year

4 year

8 year

12 year

16 year

20 year

24 year

28 year

32 year

36 year

40 year

GRAPH J - CURVES FOR 1997 SAMPLING DATE

44 year

Figure 36. Decay-curve families for time-delay mixing model. Each graph shows a family of curves for a given 

sampling year. Each curve shows average decayed tritium concentrations, for hypothetical mixes over time, for

specified delay times that are provided in 4-year increments.--Continued
84 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

3,600

3,800

3,650

3,700

3,750

WATER LEVEL, IN FEET ABOVE SEA LEVEL

State Line Madison, 7N 1E33CCDD (site 36)

State Line Minnelusa, 7N 1E33CCDD2 (site 35)

Figure 37. Hydrographs of selected well pairs.

3,600

4,400

3,800

4,000

4,200

Tinton Road Madison, 6N 2E19DABA (site 58)

Tinton Road Minnelusa, 6N 2E19DABA2 (site 57)

A

B

C

D

E

3,550

3,700

3,600

3,650

Tilford Madison, 4N 6E19AABA2 (site 85)

Tilford Minnelusa, 4N 6E19AABA (site 86)

1964 1968 1976 1972 1980

CALENDAR YEAR

1966 1970 1978 1974 1982 1986 1990 1994 1998 1984 1988 1992 1996

3,450

3,650

3,500

3,550

3,600

Piedmont Madison, 3N 6E15ABB2 (site 100)

Piedmont Minnelusa, 3N 6E15ABB (site 101)

3,420

3,500

3,440

3,460

3,480

City Quarry Madison, 2N 7E32ABBC2 (site 117)

City Quarry Minnelusa, 2N 7E32ABBC (site 118)
Supplemental Information - Figure 37 85

WATER LEVEL, IN FEET ABOVE SEA LEVEL

Figure 37. Hydrographs of selected well pairs.--Continued

F

G

H

I

J

1964 1968 1976 1972 1980

CALENDAR YEAR

1966 1970 1978 1974 1982 1986 1990 1994 1998 1984 1988 1992 1996

3,340

3,440

3,360

3,380

3,400

3,420 Canyon Lake Madison, 1N 7E 8ADDD2 (site 178)

Canyon Lake Minnelusa, 1N 7E 8ADDD (site 179)

3,340

3,460

3,360

3,380

3,400

3,420

3,440

Sioux Park Minnelusa, 1N 7E 3CBAA (site 183)

Sioux Park Madison, 1N 7E 3CBAA2 (site 182)

3,450

3,600

3,500

3,550

Reptile Gardens Madison, 1S 7E 3CDBD (site 191)

Reptile Gardens Minnelusa, 1S 7E 3CDBD2 (site 192)

3,600

4,400

3,800

4,000

4,200

Boles Canyon Madison, 3S 1E18DDDB (site 201)

Boles Canyon Minnelusa, 3S 1E18DDDB2 (site 202)

3,660

3,720

3,680

3,700

CSP Airport Madison, 4S 6E1DAAA (site 210)

CSP Airport Minnelusa, 4S 6E1DAAA2 (site 211)
86 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota WATER LEVEL, IN FEET ABOVE SEA LEVEL

Figure 37. Hydrographs of selected well pairs.--Continued

K

L

M

1964 1968 1976 1972 1980

CALENDAR YEAR

1966 1970 1978 1974 1982 1986 1990 1994 1998 1984 1988 1992 1996

3,700

3,740

3,710

3,720

3,730

Hell Canyon Madison, 5S 2E28BCCB (site 215)

Hell Canyon Minnelusa, 5S 2E28BCCB2 (site 216)

3,400

3,700

3,500

3,600

7-11 Ranch Madison, 6S 6E21BBBB (site 238)

7-11 Ranch Minnelusa, 6S 6E21BBBB2 (site 239)

3,635

3,655

3,640

3,645

3,650

Minnekahta Junction Madison, 7S 4E19BCCB (site 242)

Minnekahta Junction Minnelusa, 7S 4E19BCCB2 (site 243)
Supplemental Information - Table 7 87

Table 7. Selected site information and isotope data for sites used in report[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18O (per mil) δD (per mil) Tritium (pCi/L) Tritium 2-sigma (pCi/L) Tritium (TU)1

Wells or Caves

1 445739103465301 12N 3E32ACBC Delzer #2 445739 1034653 Mdsn NA 207-21-78 -18.13 -- <1.0 -- <0.3

2 445842103454301 12N 3E28ACBB2 Delzer #1 445842 1034543 Mdsn NA 208-11-78 -19.66 -- <1.0 -- <.33 444253103440001 9N 3E27ADBD NA 444253 1034359 Mnls NA -- -- -- -- -- --4 444312103465901 9N 3E20CDDD Bean 444313 1034653 Mdsn NA 208-23-78 -17.80 -- -- -- --5 444320103471801 9N 3E20CC NA 444320 1034718 Mdsn NA -- -- -- -- -- --6 444129103514801 9N 2E34CDDCA Belle Fourche Municipal 444129 1035148 Mdsn NA 08-17-94 -17.07 -131.0 <1.0 1 <.37 444128103514701 9N 2E34CDD NA 444128 1035147 Mdsn NA -- -- -- -- -- --8 444114103323901 8N 5E 5BCAB NA 444114 1033239 Mdsn NA -- -- -- -- -- --9 443627103460301 8N 3E33CCB NA 443625 1034555 Mnls NA -- -- -- -- -- --

10 443655103482001 8N 3E31ACA NA 443650 1034744 Mnls NA -- -- -- -- -- --11 444108103432201 8N 3E 2BDBC NA 444108 1034322 Mnls NA -- -- -- -- -- --12 443716103522501 8N 2E28DDCB NA 443716 1035225 Mdsn NA -- -- -- -- -- --13 443124103433401 7N 3E35CB NA 443124 1034334 Mnls NA -- -- -- -- -- --14 443515103473001 7N 3E 7AABA NA 443525 1034732 Mnls NA -- -- -- -- -- --15 443124103531601 7N 2E33CBCD2 NA 443124 1035316 Mnls NA -- -- -- -- -- --16 443117103541301 7N 2E32BAC NA 443147 1035413 Mnls NA -- -- -- -- -- --17 443148103534001 7N 2E32AACC NA 443148 1035340 Mdsn NA -- -- -- -- -- --18 443215103533001 7N 2E29D NA 443215 1035330 Mnls NA -- -- -- -- -- --19 443240103531002 7N 2E29AA2 NA 443240 1035310 Mnls NA -- -- -- -- -- --20 443227103503401 7N 2E26BDB NA 443227 1035034 Mdsn NA -- -- -- -- -- --21 443230103504101 7N 2E26BCDA NA 443230 1035041 Mnls NA -- -- -- -- -- --22 443255103502501 7N 2E23CDAB NA 443300 1035028 Mnls NA -- -- -- -- -- --23 443323103515501 7N 2E22BCA NA 443324 1035158 Mnls NA -- -- -- -- -- --24 443318103532701 7N 2E20ADD NA 443318 1035327 Mnls NA -- -- -- -- -- --25 443420103551001 7N 2E19CAAA NA 443315 1035514 Mnls NA -- -- -- -- -- --
88 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota Wells or Caves

—Continued

26 443355103553001 7N 2E18CA NA 443359 1035532 Mnls NA -- -- -- -- -- --27 443330103520301 7N 2E15CC NA 443348 1035203 Mnls NA -- -- -- -- -- --28 443423103510801 7N 2E15AADC NA 443423 1035108 Mnls NA -- -- -- -- -- --29 443515103513901 7N 2E10BADC LA-62A Redwater 443513 1035143 Mnls Obs 04-12-94 -16.88 -127.0 3.0 1 0.930 443010103523001 7N 2E 9ABAB NA 443010 1035230 Mnls NA -- -- -- -- -- --31 443108103530601 7N 2E 4BD NA 443108 1035306 Mnls NA -- -- -- -- -- --32 443553103502101 7N 2E 2CACA NA 443553 1035021 Mnls NA -- -- -- -- -- --33 443603103494001 7N 2E 1BBC NA 443603 1034940 Mnls NA -- -- -- -- -- --34 443100104002003 7N 1E33CCDD3 LA-94A State Line Minnekahta 443104 1040025 Mnkt Pair 08-18-94 -15.58 -121.0 24.0 2 7.535 443100104002002 7N 1E33CCDD2 LA-87B State Line Minnelusa 443104 1040025 Mnls Pair 04-11-94 -16.98 -128.0 <1.0 1 <.336 443100104002001 7N 1E33CCDD LA-87A State Line Madison 443104 1040025 Mdsn Pair 04-11-94 -17.28 -130.0 61.0 5 19.137 443153104015101 7N 1E32BBBB NA 443153 1040151 Mnls NA -- -- -- -- -- --38 443150104020001 7N 1E30DDDC NA 443156 1040205 Mnls NA -- -- -- -- -- --39 443210104021601 7N 1E30DDAB NA 443210 1040216 Mdsn NA -- -- -- -- -- --40 443330104024501 7N 1E30CADD NA 443230 1040241 Mnls NA -- -- -- -- -- --41 443240104024001 7N 1E30AAAD NA 443240 1040155 Mnls NA -- -- -- -- -- --42 443215103573001 7N 1E26ACD NA 443215 1035730 Mnls NA -- -- -- -- -- --43 443320104003501 7N 1E21BBC McNenny Well No. 1 443334 1040035 Mnls3 NA 201-01-78 -17.43 -127.0 36.4 -- 11.4

44 443320104004501 7N 1E20AAD McNenny Well No. 2 443328 1040045 Mnls3 NA 08-17-94 -17.07 -132.0 62.0 4 19.4

45 443355103574501 7N 1E14CCDD NA 443343 1035802 Mnls NA -- -- -- -- -- --46 443339103575701 7N 1E14CCD NA 443339 1035757 Mnls NA -- -- -- -- -- --47 443511103575801 7N 1E11BCAD NA 443511 1035758 Mdsn NA -- -- -- -- -- --48 443515103572501 7N 1E11ACAC Swanson Well 443508 1035730 Mnls NA 08-16-94 -- -- 2.0 1 .648 443515103572501 7N 1E11ACAC Swanson Well 443508 1035730 Mnls NA mean4 -17.46 -132.5 -- -- --

49 442754103220801 6N 6E22DABD NA 442754 1032208 Mnls NA -- -- -- -- -- --50 442901103281601 6N 5E14ADBD NA 442901 1032816 Mnls NA -- -- -- -- -- --

Table 7. Selected site information and isotope data for sites used in report

–Continued

[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18

O

(per mil)

δD

(per mil)

Tritium 

(pCi/L)

Tritium

2-sigma

(pCi/L)

Tritium 

(TU)1
Supplemental Information - Table 7 89

Wells or Caves—Continued

51 442749103381401 6N 4E21DBCD NA 442749 1033814 Mnls NA -- -- -- -- -- --52 442917103462901 6N 3E17ABAA NA 442917 1034629 Mnls NA -- -- -- -- -- --53 442721103493701 6N 2E25BBCB NA 442721 1034937 Mnls NA -- -- -- -- -- --54 442820103503501 6N 2E23BBBA NA 442820 1035035 Mnls NA -- -- -- -- -- --55 442857103513401 6N 2E22ABBB NA 442827 1035132 Mnls NA -- -- -- -- -- --56 442822103534501 6N 2E20ABAB2 NA 442822 1035345 Mdsn NA -- -- -- -- -- --57 442802103544602 6N 2E19DABA2 LA-96C Tinton Road Minnelusa 442759 1035449 Mnls Pair 09-08-98 -15.90 -119.5 78.4 5.1 24.658 442802103544601 6N 2E19DABA LA-96B Tinton Road Madison 442802 1035446 Mdsn Pair 09-08-98 -16.66 -124.8 30.4 2.6 9.559 442919103511601 6N 2E15BBBB City of Spearfish - Dickey Well 442917 1035206 Mdsn NA 08-06-96 -16.65 -126.0 63.0 4 19.760 442906103510501 6N 2E15AADC NA 442906 1035105 Mnls NA -- -- -- -- -- --61 442842103505501 6N 2E14CBCC City of Spearfish - Nevin Well 442842 1035055 Mdsn NA 08-06-96 -16.84 -128.0 87.0 5 27.362 442906103504201 6N 2E14BBCC NA 442906 1035042 Mnls NA -- -- -- -- -- --63 442937103511201 6N 2E10DACB NA 442937 1035112 Mnls NA -- -- -- -- -- --64 442930103522001 6N 2E 9D NA 442930 1035220 Mnls NA -- -- -- -- -- --65 443100103543001 6N 2E 5BBBB NA 443104 1035437 Mnls NA -- -- -- -- -- --66 443019103523101 6N 2E 4DCAD NA 443019 1035231 Mnls NA -- -- -- -- -- --67 443032103575001 6N 1E 2CABC NA 443032 1035750 Mnls NA -- -- -- -- -- --68 442111103265701 5N 5E36ADDA NA 442111 1032657 Mnls NA -- -- -- -- -- --69 442217103272201 5N 5E26ABDA Black Hills National Cemetery 442215 1032829 Mdsn NA 208-10-78 -15.04 -- -- -- --

70 442148103273801 5N 5E25CADB2 NA 442148 1032738 Mnls NA -- -- -- -- -- --71 442311103303501 5N 5E21AAA NA 442311 1033035 Mnls NA -- -- -- -- -- --72 442337103303501 5N 5E16DAA NA 442337 1033035 Mnls NA -- -- -- -- -- --73 442335103311001 5N 5E16CAAD MD-86A Sturgis 442336 1033111 Mdsn Obs 12-02-97 -15.11 -111.7 1.0 1 .374 442431103314101 5N 5E 9CBCC NA 442431 1033141 Mnls NA -- -- -- -- -- --75 442443103312701 5N 5E 9BCAA NA 442443 1033127 Mnls NA -- -- -- -- -- --76 442435103320301 5N 5E 8ACDD NA 442435 1033203 Mnls NA -- -- -- -- -- --

Table 7. Selected site information and isotope data for sites used in report–Continued[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18O (per mil) δD (per mil) Tritium (pCi/L) Tritium 2-sigma (pCi/L) Tritium (TU)1
90 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota Wells or Caves

—Continued

77 442502103325401 5N 5E 5CC NA 442511 1033238 Mnls NA -- -- -- -- -- --78 442533103324801 5N 5E 5BBCB NA 442533 1033248 Mnls NA -- -- -- -- -- --79 442306103352001 5N 4E23AAAD NA 442306 1033520 Mnls NA -- -- -- -- -- --80 442515103340401 5N 4E 1DAAD NA 442515 1033404 Mnls NA -- -- -- -- -- --81 442545103343701 5N 4E 1ABBD LA-86C Whitewood Minnelusa 442544 1033437 Mnls NA -- -- -- -- -- --82 442504103415301 5N 3E 1DCCB Fuhs 442504 1034153 Mdsn NA 207-21-78 -16.13 -- 209.3 -- 65.6

83 442435103571101 5N 1E11DABA LA-95C Big Hill Madison 442434 1035710 Mdsn Obs 10-29-97 -17.19 -128.9 105.3 6.4 33.084 441759103261203 4N 6E19AABA3 MD-95A Tilford Minnekahta 441759 1032612 Mnkt Pair 09-19-96 -14.63 -110.0 140.0 8 43.985 441759103261202 4N 6E19AABA2 MD-90A Tilford Madison 441759 1032612 Mdsn Pair 09-03-96 -15.61 -118.0 4.0 1 1.386 441759103261201 4N 6E19AABA MD-84B Tilford Minnelusa 441800 1032612 Mnls Pair 08-27-96 -15.52 -117.0 100.0 6 31.387 441812103230501 4N 6E16DCB NA 441812 1032405 Mnls NA -- -- -- -- -- --88 441807103235601 4N 6E16DCAC NA 441807 1032356 Mnls NA -- -- -- -- -- --89 441749103515701 4N 2E22BACB NA 441749 1035157 Mdsn NA -- -- -- -- -- --90 442024103545701 4N 2E 6AACD NA 442024 1035457 Mdsn NA -- -- -- -- -- --91 441023103194401 3N 7E31CBDD NA 441023 1031944 Mnls NA -- -- -- -- -- --92 441033103193001 3N 7E31CAA NA 441033 1031930 Mnls NA -- -- -- -- -- --93 441028103200401 3N 6E36DA NA 441028 1032004 Mnls NA -- -- -- -- -- --94 441033103210301 3N 6E35ADDA NA 441040 1032107 Mdsn NA -- -- -- -- -- --95 441055103230501 3N 6E34BA High Meadows 441055 1032305 Mdsn NA 12-18-91 -13.90 -103.0 <1.0 1 <.396 441130103205601 3N 6E25BCDC NA 441130 1032056 Mnls NA -- -- -- -- -- --97 441127103195801 3N 6E25ADDC NA 441127 1031958 Mnls NA -- -- -- -- -- --98 441318103221301 3N 6E24CADD NA 441207 1032033 Mnls NA -- -- -- -- -- --99 441208103205001 3N 6E24C NA 441208 1032050 Mnls NA -- -- -- -- -- --

100 441337103225002 3N 6E15ABB2 MD-94A Piedmont Madison 441335 1032250 Mdsn Pair 09-04-96 -13.68 -103.0 <1.0 1 <.3101 441337103225001 3N 6E15ABB MD-84A Piedmont Minnelusa 441335 1032250 Mnls Pair 09-04-96 -13.61 -100.0 3.0 1 .9102 441247103220701 3N 6E14CCDD NA 441247 1032207 Mnls NA -- -- -- -- -- --

Table 7. Selected site information and isotope data for sites used in report

–Continued

[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18

O

(per mil)

δD

(per mil)

Tritium 

(pCi/L)

Tritium

2-sigma

(pCi/L)

Tritium 

(TU)1
Supplemental Information - Table 7 91

Wells or Caves—Continued

103 441311103220801 3N 6E14CBAB NA 441311 1032208 Mnls NA -- -- -- -- -- --104 441355103230901 3N 6E10CDBB NA 441355 1032309 Mdsn NA -- -- -- -- -- --105 441303103232601 3N 6E10CBBA NA 441303 1032326 Mnls NA -- -- -- -- -- --106 440629103040901 2N 9E29BBCC City of Box Elder 440629 1030409 Mdsn NA 10-14-92 -14.15 -105.0 <1.0 1 <0.3106 440629103040901 2N 9E29BBCC City of Box Elder 440629 1030409 Mdsn NA 10-22-93 -- -- <1.0 -- <.3107 440851103044801 2N 9E 7CDCC Ellsworth AFB 440855 1030510 Mdsn NA 201-01-78 -14.13 -107.0 -- -- --

108 440650103110001 2N 8E20CCCD NA 440641 1031120 Mdsn NA -- -- -- -- -- --109 440730103112001 2N 8E17CCCD NA 440730 1031120 Mnls NA -- -- -- -- -- --110 440850103045001 2N 8E13BDC NA 440801 1030616 Mdsn NA -- -- -- -- -- --111 440504103161501 2N 7E34CCBC NA 440504 1031615 Mnls NA -- -- -- -- -- --112 440519103160701 2N 7E34CBAA Black Hills Power & Light 440523 1031557 Mdsn NA mean4 -14.30 -108.3 -- -- --

112 440519103160701 2N 7E34CBAA Black Hills Power & Light 440523 1031557 Mdsn NA 09-30-93 -- -- 11.7 -- 3.7113 440528103155201 2N 7E34BDAD Timberline 440528 1031552 Mnls NA 06-22-90 -13.95 -105.0 -- -- --114 440528103161001 2N 7E34BCCA NA 440528 1031610 Mnls NA -- -- -- -- -- --115 440538103161201 2N 7E34BBBC NA 440538 1031612 Mnls NA -- -- -- -- -- --116 440526103173001 2N 7E32ADDD Rapid City No. 6 440526 1031730 Mdsn NA 10-04-93 -- -- 46.3 -- 14.5116 440526103173001 2N 7E32ADDD Rapid City No. 6 440526 1031730 Mdsn NA mean4 -14.28 -107.2 -- -- --117 440544103180002 2N 7E32ABBD2 PE-89C City Quarry Madison 440543 1031805 Mdsn Pair 05-13-92 -14.35 -108.0 96.0 6 30.1117 440544103180002 2N 7E32ABBD2 PE-89C City Quarry Madison 440543 1031805 Mdsn Pair 10-13-93 -- -- 83.9 -- 26.3118 440544103180001 2N 7E32ABBD PE-89D City Quarry Minnelusa 440543 1031805 Mnls Pair 05-12-92 -14.25 -107.0 2.0 1 .6119 440516103194001 2N 7E31CDCB Westberry Trails - Minnelusa 440501 1031933 Mnls NA 08-15-90 -13.65 -101.0 -- -- --120 440500103195001 2N 7E31CCCA2 NA 440500 1031950 Mdsn NA -- -- -- -- -- --121 440500103193601 2N 7E31CCCA Westberry Trails - Madison 440458 1031950 Mdsn NA 09-30-93 -- -- 98.9 -- 31.0121 440500103193601 2N 7E31CCCA Westberry Trails - Madison 440458 1031950 Mdsn NA mean4 -13.94 -104.3 -- -- --122 440541103192301 2N 7E31BADA NA 440541 1031923 Mdsn NA -- -- -- -- -- --123 440612103152001 2N 7E27DABB Rapid City No. 10 440612 1031522 Mdsn NA 10-01-93 -- -- 14.9 -- 4.7

Table 7. Selected site information and isotope data for sites used in report–Continued[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18O (per mil) δD (per mil) Tritium (pCi/L) Tritium 2-sigma (pCi/L) Tritium (TU)1
92 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota Wells or Caves

—Continued

123 440612103152001 2N 7E27DABB Rapid City No. 10 440612 1031522 Mdsn NA 507-19-00 -- -- 23.4 1.6 7.3

123 440612103152001 2N 7E27DABB Rapid City No. 10 440612 1031522 Mdsn NA mean4 -14.38 -108.8 -- -- --

124 440655103140501 2N 7E23DACD Rapid City No. 8 440655 1031407 Mdsn NA 09-28-93 -- -- <1.0 -- <.3124 440655103140501 2N 7E23DACD Rapid City No. 8 440655 1031407 Mdsn NA mean4 -14.40 -108.5 -- -- --125 440647103183201 2N 7E20CCDB NA 440647 1031832 Mnls NA -- -- -- -- -- --126 440808103193701 2N 7E18BCA Lien 440808 1031937 Mdsn NA 207-20-78 -- -- 53.0 -- 16.6

126 440808103193701 2N 7E18BCA Lien 440808 1031937 Mdsn NA mean4 -14.18 -106.0 -- -- --

127 440738103173601 2N 7E17DDDB NA 440738 1031736 Mnls NA -- -- -- -- -- --128 440817103181701 2N 7E17BACA2 NA 440817 1031817 Mnls NA -- -- -- -- -- --129 440818103180801 2N 7E17BAAD PE-84B - Dog Track 440819 1031809 Mnls Obs 05-19-92 -13.40 -101.0 <1.0 1 <.3130 440823103162701 2N 7E16AAB Fischer Sand and Gravel 440823 1031627 Mdsn NA 09-18-96 -13.66 -102.0 -- -- --131 440832103160901 2N 7E10CDCA NA 440837 1031609 Mnls NA -- -- -- -- -- --132 440824103160401 2N 7E10CCDC NA 440824 1031604 Mnls NA -- -- -- -- -- --133 440826103174701 2N 7E 8DDCC2 NA 440826 1031747 Mnls NA -- -- -- -- -- --134 440833103184101 2N 7E 8CCBC NA 440833 1031841 Mnls NA -- -- -- -- -- --135 440907103183501 2N 7E 8BBCD NA 440907 1031835 Mnls NA -- -- -- -- -- --136 440901103184801 2N 7E 7ADAB NA 440901 1031848 Mnls NA -- -- -- -- -- --137 440919103170501 2N 7E 4CDCD NA 440920 1031658 Mnls NA -- -- -- -- -- --138 440931103141401 2N 7E 2DBDDC Weston Development 440931 1031414 Mdsn NA 10-08-92 -13.45 -100.0 <1.0 1 <.3138 440931103141401 2N 7E 2DBDDC Weston Development 440931 1031414 Mdsn NA 10-14-93 -- -- <1.0 -- <.3139 440939103142001 2N 7E 2DBDD NA 440939 1031420 Mnls NA -- -- -- -- -- --140 440527103220401 2N 6E35BCAB NA 440527 1032204 Mdsn NA -- -- -- -- -- --141 440541103211401 2N 6E35AADA NA 440541 1032114 Mdsn NA -- -- -- -- -- --142 440658103213001 2N 6E23DBAB Stanley 440704 1032132 Mdsn NA mean4 -14.43 -110.0 -- -- --143 440708103214301 2N 6E23BDD NA 440708 1032143 Mdsn NA -- -- -- -- -- --144 440811103222202 2N 6E15ADAA2 PE-96B Doty Deadwood 440811 1032221 Ddwd Pair 10-21-97 -13.07 -98.0 138.9 8.3 43.5

Table 7. Selected site information and isotope data for sites used in report

–Continued

[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18

O

(per mil)

δD

(per mil)

Tritium 

(pCi/L)

Tritium

2-sigma

(pCi/L)

Tritium 

(TU)1
Supplemental Information - Table 7 93

Wells or Caves—Continued

145 440811103222201 2N 6E15ADAA PE-95C Doty Madison 440811 1032221 Mdsn Pair 10-22-97 -13.25 -98.7 25.9 1.9 8.1146 440919103210201 2N 6E 1CCCD2 NA 440919 1032102 Mnls NA -- -- -- -- -- --147 440920103210401 2N 6E 1CCCD NA 440920 1032104 Mnls NA -- -- -- -- -- --148 440334103095601 1N 8E 9CAB2 Rapid Valley 440334 1030956 Mdsn NA 10-13-92 -12.55 -92.5 <1.0 1 <.3149 440004103174001 1N 7E32DABA Highland Hills 440006 1031742 Mdsn NA 07-25-96 -- -- 71.0 5 22.3149 440004103174001 1N 7E32DABA Highland Hills 440006 1031742 Mdsn NA mean4 -12.66 -96.7 -- -- --

150 440002103173901 1N 7E32DA2 NA 440002 1031739 Mdsn NA -- -- -- -- -- --151 440523103194201 1N 7E31BCAD Beardsley 440019 1031941 Mdsn NA 09-17-96 -12.26 -91.5 -- -- --152 440026103194001 1N 7E31BBDA NA 440026 1031940 Mdsn NA -- -- -- -- -- --153 440032103184601 1N 7E30DDDC NA 440032 1031846 Mdsn NA -- -- -- -- -- --154 440054103173801 1N 7E29DAAC Hamms Well A 440054 1031738 Mdsn NA mean4 -12.44 -92.8 -- -- --155 440148103150001 1N 7E23CBBA NA 440148 1031500 Mnls NA -- -- -- -- -- --156 440203103143601 1N 7E23BDAB NA 440203 1031436 Mnls NA -- -- -- -- -- --157 440140103152601 1N 7E22D NA 440140 1031526 Mnls NA -- -- -- -- -- --158 440213103153401 1N 7E22AB NA 440213 1031534 Mnls NA -- -- -- -- -- --159 440130103163401 1N 7E21DDC NA 440130 1031634 Mnls NA -- -- -- -- -- --160 440142103164301 1N 7E21DBDB NA 440142 1031643 Mnls NA -- -- -- -- -- --161 440223103173201 1N 7E21BCAB Carriage Hills 440205 1031720 Mdsn NA -- -- -- -- -- --162 440202103164101 1N 7E21ACA NA 440202 1031641 Mnls NA -- -- -- -- -- --163 440307103193001 1N 7E18BABB NA 440307 1031930 Mnls NA -- -- -- -- -- --164 440308103184601 1N 7E18AAAD Cleghorn Well 440308 1031847 Mdsn NA 11-13-96 -12.44 -96.8 82.0 5 25.7165 440223103173201 1N 7E17DDDA Carriage Hills Main Well 440225 1031734 Mdsn NA 07-24-96 -- -- 73.0 5 22.9165 440223103173201 1N 7E17DDDA Carriage Hills Main Well 440225 1031734 Mdsn NA mean4 -12.13 -92.8 -- -- --166 440237103173401 1N 7E17DADA NA 440237 1031734 Mnls NA -- -- -- -- -- --167 440308103180701 1N 7E17ABCC Steuerwald 440304 1031807 Mdsn NA 09-13-96 -12.09 -91.9 -- -- --168 440300103173501 1N 7E17AAAC2 Chapel Lane Madison (CHPLN-2) 440305 1031739 Mdsn NA 09-30-93 -- -- 87.7 -- 27.5

Table 7. Selected site information and isotope data for sites used in report–Continued[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18O (per mil) δD (per mil) Tritium (pCi/L) Tritium 2-sigma (pCi/L) Tritium (TU)1
94 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota Wells or Caves

—Continued

168 440300103173501 1N 7E17AAAC2 Chapel Lane Madison (CHPLN-2) 440305 1031739 Mdsn NA mean4 -12.05 -92.3 -- -- --

169 440220103164001 1N 7E16DCDC Rapid City No. 11 (Corral Drive) 440220 1031640 Mdsn NA 12-17-91 -- -- 34.0 3 10.7169 440220103164001 1N 7E16DCDC Rapid City No. 11 (Corral Drive) 440220 1031640 Mdsn NA 10-05-93 -- -- 53.0 -- 16.6169 440220103164001 1N 7E16DCDC Rapid City No. 11 (Corral Drive) 440220 1031640 Mdsn NA 07-24-96 -- -- 51.0 3 16.0169 440220103164001 1N 7E16DCDC Rapid City No. 11 (Corral Drive) 440220 1031640 Mdsn NA 507-19-00 -- -- 38.4 2.6 12.0

169 440220103164001 1N 7E16DCDC Rapid City No. 11 (Corral Drive) 440220 1031640 Mdsn NA mean4 -12.09 -91.5 -- -- --

170 440300103165801 1N 7E16BADB NA 440300 1031658 Mnls NA -- -- -- -- -- --171 440225103160801 1N 7E15CC NA 440225 1031608 Mnls NA -- -- -- -- -- --172 440342103160701 1N 7E10BCDB Rapid City No. 9 (Meadowbrook) 440342 1031609 Mdsn NA 05-08-91 -- -- 67.0 5 21.0172 440342103160701 1N 7E10BCDB Rapid City No. 9 (Meadowbrook) 440342 1031609 Mdsn NA 09-29-93 -- -- 77.5 -- 24.3172 440342103160701 1N 7E10BCDB Rapid City No. 9 (Meadowbrook) 440342 1031609 Mdsn NA 05-13-97 -- -- 71.0 4.5 22.3172 440342103160701 1N 7E10BCDB Rapid City No. 9 (Meadowbrook) 440342 1031609 Mdsn NA 507-19-00 -- -- 58.2 3.2 18.2

172 440342103160701 1N 7E10BCDB Rapid City No. 9 (Meadowbrook) 440342 1031609 Mdsn NA mean4 -12.77 -98.3 -- -- --

173 440331103171601 1N 7E 9CBAC NA 440331 1031716 Mnls NA -- -- -- -- -- --174 440338103171601 1N 7E 9BCDC NA 440338 1031716 Mnls NA -- -- -- -- -- --175 440351103171301 1N 7E 9BBCA Rapid City No. 3 440351 1031713 Mnls NA mean4 -13.11 -98.7 -- -- --176 440310103173802 1N 7E 8DDCD2 Chapel Lane-Madison (CHPLN-3) 440312 1031740 Mdsn Pair 12-11-91 -12.35 -92.0 6.0 1 1.9176 440310103173802 1N 7E 8DDCD2 Chapel Lane-Madison (CHPLN-3) 440312 1031740 Mdsn Pair 09-30-93 -- -- 6.9 -- 2.2177 440310103173801 1N 7E 8DDCD Chapel Lane-Minnelusa (CHPLN-1) 440312 1031741 Mnls Pair 05-20-92 -12.90 -96.5 64.0 4 20.1178 440338103173302 1N 7E 8ADDD2 PE-89A Canyon Lake Madison 440337 1031734 Mdsn Pair 09-28-93 -- -- 75.9 -- 23.8178 440338103173302 1N 7E 8ADDD2 PE-89A Canyon Lake Madison 440337 1031734 Mdsn Pair mean4 -12.70 -98.0 -- -- --179 440338103173301 1N 7E 8ADDD PE-89B Canyon Lake Minnelusa 440337 1031735 Mnls Pair 05-14-92 -13.90 -103.0 22.0 2 6.9180 440446103193201 1N 7E 6BACB Crosswaite 440446 1031932 Mdsn NA 09-16-96 -13.69 -104.0 -- -- --181 440414103164601 1N 7E 4DCBA Rapid City No. 4 440413 1031649 Mnls NA mean4 -13.83 -103.0 -- -- --182 440430103160202 1N 7E 3CBAA2 PE-65A Sioux Park 2 Madison 440427 1031605 Mdsn Pair mean4 -14.16 -105.7 -- -- --183 440430103160201 1N 7E 3CBAA PE-64B Sioux Park 1 Minnelusa 440427 1031605 Mnls Pair mean4 -14.38 -107.5 -- -- --

Table 7. Selected site information and isotope data for sites used in report

–Continued

[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18

O

(per mil)

δD

(per mil)

Tritium 

(pCi/L)

Tritium

2-sigma

(pCi/L)

Tritium 

(TU)1
Supplemental Information - Table 7 95

Wells or Caves—Continued

184 440436103161201 1N 7E 3BCBC NA 440436 1031612 Mnls NA -- -- -- -- -- --185 440443103161301 1N 7E 3BBCD Rapid City No. 5 440443 1031613 Mdsn NA 10-07-93 -- -- 13.7 -- 4.3185 440443103161301 1N 7E 3BBCD Rapid City No. 5 440443 1031613 Mdsn NA mean4 -14.23 -107.0 -- -- --

186 440446103161701 1N 7E 3BBCC PE-89E Lime Creek 440444 1031618 Mdsn NA 06-20-90 -- -- <1.0 1 <.3186 440446103161701 1N 7E 3BBCC PE-89E Lime Creek 440444 1031618 Mdsn NA 09-25-93 -- -- <1.0 -- <.3186 440446103161701 1N 7E 3BBCC PE-89E Lime Creek 440444 1031618 Mdsn NA mean4 -14.38 -109.0 -- -- --187 440452103155301 1N 7E 3BABD Camp Rapid 440452 1031553 Mnls NA 07-16-90 -13.70 -103.0 <1.0 1 <.3188 440427103131701 1N 7E 1DBBB Rapid City No. 7 (Star Village) 440426 1031318 Mdsn Obs 02-07-91 -14.40 -108.0 2.0 1 .6188 440427103131701 1N 7E 1DBBB Rapid City No. 7 (Star Village) 440426 1031318 Mdsn Obs 10-31-93 -- -- <1.0 -- <.3189 440032103195901 1N 6E36AAAB NA 440032 1031959 Mdsn NA -- -- -- -- -- --190 440224103195401 1N 6E13DDDD Brooks Cave 440224 1031954 Mdsn Cave 03-06-87 -13.40 -102.5 -- -- --191 435916103161801 1S 7E 3CDBD PE-86A Reptile Gardens Madison 435915 1031620 Mdsn Pair 10-30-93 -- -- 9.5 -- 3.0191 435916103161801 1S 7E 3CDBD PE-86A Reptile Gardens Madison 435915 1031620 Mdsn Pair 07-29-96 -12.78 -95.0 15.0 1 4.7192 435916103161802 1S 7E 3CDBD2 PE-94B Reptile Gardens Minnelusa 435915 1031620 Mnls Pair 07-30-96 -12.51 -90.7 4.0 1 1.3193 435937103184401 1S 7E 5BDCA Spring Canyon (Main Well) No. 1 435937 1031844 Mdsn NA 08-28-96 -12.36 -96.8 -- -- --194 435845103163401 1S 7E10BCAC NA 435845 1031634 Mnls NA -- -- -- -- -- --195 435851103143501 1S 7E11ACAB Hart Ranch 435848 1031445 Mdsn NA 10-19-93 -- -- 75.0 -- 23.5195 435851103143501 1S 7E11ACAB Hart Ranch 435848 1031445 Mdsn NA 07-23-96 -- -- 69.0 4 21.6195 435851103143501 1S 7E11ACAB Hart Ranch 435848 1031445 Mdsn NA 507-19-00 -- -- 56.6 3.2 17.7

195 435851103143501 1S 7E11ACAB Hart Ranch 435848 1031445 Mdsn NA mean4 -12.27 -93.3 -- -- --

196 435635103181401 1S 7E20CAD Pine Grove 435635 1031814 Mdsn NA 10-15-93 -- -- 82.6 -- 25.9196 435635103181401 1S 7E20CAD Pine Grove 435635 1031814 Mdsn NA mean4 -11.89 -88.1 -- -- --197 435227103185301 2S 7E17CCAA PE-95A Hayward 435227 1031852 Mdsn Obs 11-20-97 -12.06 -87.9 59.8 3.8 18.7198 435042103171101 2S 7E28DB NA 435042 1031711 Mnls NA -- -- -- -- -- --199 435018103155801 2S 7E34ABBA CU-83A Hermosa West 435020 1031600 Mnls Obs 10-28-97 -11.98 -87.3 <1.0 1 <.3200 435004103161301 2S 7E34BD NA 435004 1031613 Mnls NA -- -- -- -- -- --

Table 7. Selected site information and isotope data for sites used in report–Continued[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18O (per mil) δD (per mil) Tritium (pCi/L) Tritium 2-sigma (pCi/L) Tritium (TU)1
96 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota Wells or Caves

—Continued

201 434700104021401 3S 1E18DDDB CU-93C Boles Canyon Madison 434701 1040215 Mdsn Pair 03-22-94 -16.32 -125.0 9.0 1 2.8202 434700104021402 3S 1E18DDDB2 CU-93D Boles Canyon Minnelusa 434701 1040215 Mnls Pair 12-17-97 -15.88 -123.6 3.2 1 1.0203 434846103481801 3S 3E 6DCBB NA 434846 1034818 Mdsn NA -- -- -- -- -- --204 434503103183601 3S 7E32BABA NA 434503 1031836 Mnls NA -- -- -- -- -- --205 434502103165801 3S 7E33AACB NA 434502 1031658 Mnls NA -- -- -- -- -- --206 434402103502301 4S 2E 2ADB NA 434402 1035023 Mdsn NA -- -- -- -- -- --207 434326103555101 4S 2E 6CCDC NA 434326 1035551 Mnls NA -- -- -- -- -- --208 434351103461501 4S 3E 4BCDA NA 434351 1034615 Mnls NA -- -- -- -- -- --209 434218103463701 4S 3E17ADAB NA 434218 1034637 Mnls NA -- -- -- -- -- --210 434350103201901 4S 6E 1DAAA CU-93A CSP Airport Madison 434350 1032020 Mdsn Pair 09-06-95 -11.75 -87.6 <1.0 1 <.3211 434350103201902 4S 6E 1DAAA2 CU-93A CSP Airport Minnelusa 434350 1032020 Mnls Pair 08-31-95 -11.50 -84.9 3.0 1 .9212 434236103201601 4S 6E12DDAD NA 434236 1032016 Mnls NA -- -- -- -- -- --213 434001103131301 4S 7E25DDDB NA 434001 1031313 Mnls NA -- -- -- -- -- --214 433545103502701 5S 2E23DCAB NA 433545 1035027 Mnls NA -- -- -- -- -- --215 433517103534201 5S 2E28BCCB CU-95A Hell Canyon Madison 433517 1035342 Mdsn Pair 11-05-97 -17.23 -130.8 1.9 1 .6216 433517103534202 5S 2E28BCCB2 CU-95B Hell Canyon Minnelusa 433517 1035342 Mnls Pair 11-03-97 -14.21 -111.4 <1.0 1 <.3217 433849103442701 5S 3E 3ADBB NA 433849 1034427 Mdsn NA -- -- -- -- -- --218 433831103475201 5S 3E 6DAAC NA 433831 1034752 Mnls NA -- -- -- -- -- --219 433440103465501 5S 3E32ABAB NA 433440 1034655 Mnls NA -- -- -- -- -- --220 433852103384901 5S 4E 4ABCB NA 433852 1033849 Mdsn NA -- -- -- -- -- --221 433607103383401 5S 4E21ACAD NA 433607 1033834 Mdsn NA -- -- -- -- -- --222 433506103344001 5S 4E25DAAA NA 433510 1033445 Mdsn NA -- -- -- -- -- --223 433628103173801 5S 7E16CDCA NA 433628 1031738 Mnls NA -- -- -- -- -- --224 432927103520401 6S 2E34BA NA 432927 1035204 Mnls NA -- -- -- -- -- --225 432927103521001 6S 2E34BABC NA 432927 1035210 Mnls NA -- -- -- -- -- --226 432917103522101 6S 2E34BC NA 432917 1035221 Mnls NA -- -- -- -- -- --

Table 7. Selected site information and isotope data for sites used in report

–Continued

[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18

O

(per mil)

δD

(per mil)

Tritium 

(pCi/L)

Tritium

2-sigma

(pCi/L)

Tritium 

(TU)1
Supplemental Information - Table 7 97

Wells or Caves—Continued

227 433003103420701 6S 3E25ADDC Myrvik 433000 1034158 Mnls NA 05-04-94 -14.27 -109.0 <1.0 1 <0.3228 433347103385101 6S 4E 4BADA NA 433343 1033857 Mnls NA -- -- -- -- -- --229 433339103385601 6S 4E 4BADD NA 433339 1033856 Mnls NA -- -- -- -- -- --230 433119103360001 6S 4E14DDAC NA 433119 1033600 Mnls NA -- -- -- -- -- --231 433000103393901 6S 4E29ADCA NA 433000 1033939 Mdsn NA -- -- -- -- -- --232 433302103281501 6S 5E12DBAB Windy City Lake 433255 1032827 Mdsn Cave mean4 -12.25 -90.3 -- -- --

233 433114103281601 6S 5E24BAAA Kaiser 433114 1032816 Mdsn NA 207-19-78 -12.13 -- 88.4 -- 27.7

234 433021103273601 6S 5E24DDDD NA 433021 1032736 Mnls NA -- -- -- -- -- --235 432945103323801 6S 5E29DBDA NA 432945 1033238 Mnls NA -- -- -- -- -- --236 433303103225801 6S 6E 3DDCA NA 433303 1032258 Mnls NA -- -- -- -- -- --237 433150103230501 6S 6E15ABDD Streeter Ranch 433150 1032305 Mdsn NA 211-01-77 -- -- 33.8 -- 10.6237 433150103230501 6S 6E15ABDD Streeter Ranch 433150 1032305 Mdsn NA 03-11-97 -- -- 37.4 2.6 11.7237 433150103230501 6S 6E15ABDD Streeter Ranch 433150 1032305 Mdsn NA mean4 -11.96 -87.6 -- -- --

238 433115103251401 6S 6E21BBBB CU-91A (7-11 Ranch 1) Madison 433115 1032516 Mdsn Pair 03-31-94 -11.93 -88.7 <1.0 1 <.3239 433115103251402 6S 6E21BBBB2 CU-91B (7-11 Ranch 2) Minnelusa 433115 1032516 Mnls Pair 04-05-94 -12.38 -93.3 <1.0 1 <.3240 433115103251403 6S 6E21BBBB3 CU-96A (7-11 Ranch 3) Minnekahta 433115 1032516 Mnkt Pair 11-13-97 -12.44 -94.5 79.0 4.5 24.8241 432613103584001 7S 1E15DD Superior #1 Peterson 432613 1035840 Mnls NA 10-04-68 -- -- <2.3 -- <.7242 432548103414801 7S 4E19BCCB FR-92A Minnekahta Jnct Madison 432545 1034151 Mdsn Pair 03-24-94 -14.88 -114.0 <1.0 1 <.3243 432548103414802 7S 4E19BCCB2 FR-94A Minnekahta Jnct Minnelusa 432545 1034151 Mnls Pair 09-11-95 -13.87 -104.0 <1.0 1 <.3244 432808103294901 7S 5E 2CBAB NA 432808 1032949 Mnls NA -- -- -- -- -- --245 432616103294701 7S 5E14CBDD NA 432616 1032947 Mnls NA -- -- -- -- -- --246 432616103294702 7S 5E14CBDD2 NA 432616 1032947 Mnls NA -- -- -- -- -- --247 432603103295901 7S 5E14CCCC FR-95A Vets Home Madison 432602 1032958 Mdsn Obs 11-18-97 -15.97 -121.9 <1.0 1 <.3248 432622103291501 7S 5E14DBC NA 432622 1032915 Mnls NA -- -- -- -- -- --249 432537103301401 7S 5E22ADBC NA 432537 1033014 Mnls NA -- -- -- -- -- --250 432523103305401 7S 5E22CDCB NA 432523 1033054 Mnls NA -- -- -- -- -- --

Table 7. Selected site information and isotope data for sites used in report–Continued[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18O (per mil) δD (per mil) Tritium (pCi/L) Tritium 2-sigma (pCi/L) Tritium (TU)1
98 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota Wells or Caves

—Continued

251 432510103304801 7S 5E22CDCD NA 432510 1033048 Mnls NA -- -- -- -- -- --252 432459103290101 7S 5E26AACA NA 432459 1032901 Mnls NA -- -- -- -- -- --253 432136103321001 8S 5E16BBAD Fetters 432136 1033210 Mdsn NA 05-12-94 -16.59 -127.0 <1.0 1 <0.3254 432127103325601 8S 5E17ACBB Chiller 432127 1033256 Mnls NA 05-11-94 -15.15 -118.0 <1.0 1 <.3255 431810103491701 9S 2E 1AABC NA 431810 1034917 Mdsn NA -- -- -- -- -- --256 431804103492101 9S 2E 1ABDD NA 431804 1034921 Mdsn NA -- -- -- -- -- --257 431753103492601 9S 2E 1ACDB NA 431753 1034926 Mdsn NA -- -- -- -- -- --258 431750103500301 9S 2E 1BCDC NA 431750 1035003 Mdsn NA -- -- -- -- -- --259 431743103501501 9S 2E 2DAAA NA 431743 1035015 Mdsn NA -- -- -- -- -- --260 431232103513501 10S 2E 3DAA NA 431232 1035135 Mdsn NA -- -- -- -- -- --261 431218103512501 10S 2E 3DADD NA 431218 1035125 Mdsn NA -- -- -- -- -- --262 431220103514001 10S 2E 3DDAA NA 431220 1035140 Mdsn NA -- -- -- -- -- --263 431246103515901 10S 2E13ACBA Black Hills Army Depot #2 (Provo) 431105 1034935 Mdsn NA 201-01-78 -17.09 -131.0 -- -- --

264 445546104382701 57N 65W15DA - Wyo HTH No. 1 445546 1043827 Mdsn NA 201-01-78 -- -- 17.2 -- 5.4265 443458104425801 53N 65W18BBD - Wyo Devils Tower 443458 1044258 Mdsn NA 201-01-78 -17.85 -139.9 4.8 -- 1.5266 442930104063501 52N 60W18C - Wyo Ranch A 442930 1040635 Mdsn NA 201-01-78 -17.49 -- 132.7 -- 41.6267 440621104364301 48N 65W25CC - Wyo Upton 440621 1043643 Mdsn NA 201-01-78 -18.18 -133.0 -- -- --268 435740104294002 46N 64W13CC - Wyo Coronado No. 2 435740 1042940 Mdsn NA 201-01-78 -17.60 -133.3 <1.0 -- <.3269 435800104244001 46N 63W15BD - Wyo Osage 435800 1042440 Mdsn NA 201-01-78 -18.15 -135.0 1.6 -- .5270 435800104210001 46N 62W18BDC - Wyo Seeley 435800 1042100 Mdsn NA 201-01-78 -17.75 -133.5 2.6 -- .8271 435540104063001 46N 60W31BA - Wyo Martens 435540 1040630 Mdsn NA 201-01-78 -17.45 -130.9 -- -- --272 435030104110001 45N 61W33AB - Wyo Self 435030 1041100 Mdsn NA 201-01-78 -17.60 -131.8 <1.0 -- <.3273 435125104110502 45N 61W28AB - Wyo Voss 435125 1041105 Mdsn NA 201-01-78 -17.40 -130.6 7.3 -- 2.3274 435138104121101 45N 61W20DCA - Wyo Newcastle 435138 1041211 Mdsn NA 201-01-78 -17.66 -130.0 <1.0 -- <.3275 434700104230001 44N 63W26CAC - Wyo JBJ 434700 1042300 Mdsn NA 201-01-78 -17.95 -130.6 <1.0 -- <.3

Table 7. Selected site information and isotope data for sites used in report

–Continued

[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18

O

(per mil)

δD

(per mil)

Tritium 

(pCi/L)

Tritium

2-sigma

(pCi/L)

Tritium 

(TU)1
Supplemental Information - Table 7 99

Springs

276 442706104015401 6N 1E30DAAD Knight Spring 442706 1040154 Mnls HW 08-04-95 -- -- 130.0 7 40.8276 442706104015401 6N 1E30DAAD Knight Spring 442706 1040154 Mnls HW mean4 -16.91 -126.6 -- -- --

277 441726103285801 4N 5E23DBCB Jones Spring 441726 1032858 Mdsn HW 201-01-78 -14.61 -110.0 880.4 -- 276.0

278 441949103583201 4N 1E 3DD NA 441950 1035830 Mdsn HW -- -- -- -- -- --279 441232103264301 3N 6E19BDBA NA 441232 1032643 Mdsn HW 07-18-96 -14.06 -103.0 130.0 8 40.8280 441322103272801 3N 5E13ACAA NA 441322 1032728 Ddwd HW 08-08-95 -- -- 170.0 9 53.3280 441322103272801 3N 5E13ACAA NA 441322 1032728 Ddwd HW mean4 -13.96 -104.4 -- -- --

281 441310103435901 3N 3E14CBBB JHD Spring 441310 1034359 Ddwd HW 09-13-95 -- -- 170.0 9 53.3281 441310103435901 3N 3E14CBBB JHD Spring 441310 1034359 Ddwd HW mean4 -16.56 -126.8 -- -- --282 441434103560001 3N 2E 6CCCD Intake Gulch 441434 1035600 Mdsn HW 08-03-95 -- -- 100.0 6 31.3282 441434103560001 3N 2E 6CCCD Intake Gulch 441434 1035600 Mdsn HW mean4 -17.59 -133.7 -- -- --283 06408700 2N 2E15ADB Rhoads Fork near Rochford 440812 1035129 Mdsn HW 201-01-78 -- -- 198.4 -- 62.2

283 06408700 2N 2E15ADB Rhoads Fork near Rochford 440812 1035129 Mdsn HW 08-07-95 -- -- 140.0 8 43.9283 06408700 2N 2E15ADB Rhoads Fork near Rochford 440812 1035129 Mdsn HW mean4 -16.96 -127.1 -- -- --

284 440820104004000 2N 1E16BBD Cold Creek Springs 440820 1040040 Mdsn HW -- -- -- -- -- --285 06409000 1N 2E25CCA Castle Creek above Deerfield 440049 1034948 Mdsn HW mean4 -16.41 -123.7 -- -- --286 440415104014000 1N 1E 5CCA Beaver Creek Springs 440415 1040140 Mdsn HW -- -- -- -- -- --287 434953103585201 2S 1E34DBAC Barrel Spring 434953 1035852 Mnls HW 07-25-95 -- -- 59.0 4 18.5287 434953103585201 2S 1E34DBAC Barrel Spring 434953 1035852 Mnls HW mean4 -14.60 -113.6 -- -- --288 434045103502301 4S 2E26AABC Water Draw Spring 434045 1035023 Mnls HW 09-14-95 -- -- 41.0 3 12.9288 434045103502301 4S 2E26AABC Water Draw Spring 434045 1035023 Mnls HW mean4 -14.27 -112.5 -- -- --289 433944103521801 4S 2E34BCAB Mckenna Spring 433944 1035218 Mnls HW 09-14-95 -- -- 26.0 2 8.2289 433944103521801 4S 2E34BCAB Mckenna Spring 433944 1035218 Mnls HW mean4 -13.41 -103.6 -- -- --290 443237103525801 7N2E28BACD Higgins Gulch below I-90 443237 1035258 DG 09-26-94 -- -- 100.0 6 31.3290 443237103525801 7N2E28BACD Higgins Gulch below I-90 443237 1035258 DG 10-10-97 -- -- 89.6 5.1 28.1290 443237103525801 7N2E28BACD Higgins Gulch below I-90 443237 1035258 DG mean4 -16.36 -123.8 -- -- --

Table 7. Selected site information and isotope data for sites used in report–Continued[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18O (per mil) δD (per mil) Tritium (pCi/L) Tritium 2-sigma (pCi/L) Tritium (TU)1
100 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota Springs

—Continued

291 443012103544700 Higgins Gulch above Spearfish 443012 1035447 DG 08-21-97 -16.75 -126.2 76.5 4.5 24.0292 443309103532401 7N 2E20DAAD Old Spearfish Hatchery 443309 1035324 DG 09-26-94 -16.71 -128.0 83.0 5 26.0292 443309103532401 7N 2E20DAAD Old Spearfish Hatchery 443309 1035324 DG 08-21-97 -- -- 42.9 2.6 13.4293 443330104003401 7N 1E21BBCD NcNenny Rearing Pond 443330 1040034 DG 09-28-94 -17.19 -132.0 66.0 4 20.7294 443335104010001 7N 1E20AABC Mirror Lake 443335 1040100 DG 09-28-94 -15.34 -123.0 54.0 3 16.9295 443356103593701 7N 1E16DADC Cox Lake 443356 1035937 DG 09-27-94 -16.95 -129.0 67.0 4 21.0296 06430532 7N 1E16BDB Crow Creek near Beulah, WY 443414 1040019 DG 08-30-96 -16.67 -128.0 61.0 4 19.1297 06425100 3N 8E 9AA Elk Creek near Rapid City 441425 1030903 DG 09-05-96 -13.79 -106.0 96.0 6 30.1298 440525103173701 2N 7E32ADDA2 City Springs 440525 1031737 DG 09-26-93 -- -- 130.2 -- 40.8298 440525103173701 2N 7E32ADDA2 City Springs 440525 1031737 DG 506-06-00 -- -- 81.9 4.8 25.7

298 440525103173701 2N 7E32ADDA2 City Springs 440525 1031737 DG mean4 -14.37 -107.9 -- -- --

299 440243103193701 1N 7E18CBAA Tittle Spring 440243 1031937 DG 07-22-96 -14.45 -111.0 92.0 5 28.8300 440327103180503 1N 7E 8DBBD Cleghorn Springs 440331 1031801 DG 201-01-78 -- -- 580.6 -- 182.0

300 440327103180503 1N 7E 8DBBD Cleghorn Springs 440331 1031801 DG 09-27-93 -- -- 96.3 -- 30.2300 440327103180503 1N 7E 8DBBD Cleghorn Springs 440331 1031801 DG mean4 -12.92 -99.1 -- -- --

301 435013103162600 2S 7E34BBD Battle Creek bel. Minnelusa outcrop 435013 1031626 DG 09-06-96 -11.62 -85.9 65.0 4 20.4302 434655103181701 3S 7E17DCDD Grace Coolidge Creek 434655 1031817 DG 09-10-96 -11.68 -88.5 55.0 3 17.2303 433128103223401 6S 6E14CDB Beaver Creek Spring 433128 1032234 DG 04-25-94 -- -- 19.0 2 6.0303 433128103223401 6S 6E14CDB Beaver Creek Spring 433128 1032234 DG 10-03-94 -14.10 -108.0 -- -- --304 432703103302801 7S 5E10DCBA Hot Brook Spring 432703 1033028 DG 04-21-94 -- -- 13.0 1 4.1304 432703103302801 7S 5E10DCBA Hot Brook Spring 432703 1033028 DG 10-03-94 -14.86 -113.0 12.0 1 3.8305 432630103284701 7S 5E13BCCC Evans Plunge Spring 432630 1032847 DG 201-01-78 -16.71 -121.0 -- -- --

305 432630103284701 7S 5E13BCCC Evans Plunge Spring 432630 1032847 DG 04-21-94 -- -- 2.0 1 .6306 06402000 7S 5E24BB Fall River at Hot Springs 432550 1032833 DG 09-11-96 -15.43 -119.0 8.0 1 2.5307 432028103331601 8S 5E20BDCB Cool Spring 432028 1033316 DG 09-12-96 -15.23 -116.0 8.0 1 2.5308 432006103330501 8S 5E20CDAB Cascade Springs 432006 1033305 DG 10-19-95 -- -- 7.0 1 2.2

Table 7. Selected site information and isotope data for sites used in report

–Continued

[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18

O

(per mil)

δD

(per mil)

Tritium 

(pCi/L)

Tritium

2-sigma

(pCi/L)

Tritium 

(TU)1
Supplemental Information - Table 7 101

Springs—Continued

308 432006103330501 8S 5E20CDAB Cascade Springs 432006 1033305 DG 09-12-96 -- -- 7.0 1 2.2308 432006103330501 8S 5E20CDAB Cascade Springs 432006 1033305 DG mean4 -15.40 -118.5 -- -- --

Surface Water

309 06429920 Bear Gulch near Maurice 442514 1040226 NA LZ 10-10-96 -- -- 42.0 3 13.2309 06429920 Bear Gulch near Maurice 442514 1040226 NA LZ 09-11-97 -- -- 59.2 3.8 18.6309 06429920 Bear Gulch near Maurice 442514 1040226 NA LZ mean4 -16.96 -128.8 -- -- --

310 06430520 Beaver Creek near Maurice 442257 1040013 NA LZ 10-09-96 -- -- 75.0 5 23.5310 06430520 Beaver Creek near Maurice 442257 1040013 NA LZ 09-11-97 -- -- 68.8 4.5 21.6310 06430520 Beaver Creek near Maurice 442257 1040013 NA LZ mean4 -16.59 -127.4 -- -- --311 442405103485100 False Bottom Cr ab Madison outcrop 442405 1034851 NA LZ 08-21-97 -16.93 -127.7 43.5 2.6 13.6312 06437020 Bear Butte Creek near Deadwood 442008 1033806 NA LZ 10-09-96 -- -- 99.0 6 31.0312 06437020 Bear Butte Creek near Deadwood 442008 1033806 NA LZ 10-10-97 -- -- 81.9 5.1 25.7312 06437020 Bear Butte Creek near Deadwood 442008 1033806 NA LZ mean4 -16.01 -121.2 -- -- --313 441742103333300 Elk Creek above Meadow Creek 441742 1033333 NA LZ 09-20-96 -- -- 100.0 6 31.3313 441742103333300 Elk Creek above Meadow Creek 441742 1033333 NA LZ 10-09-97 -- -- 81.0 4.5 25.4313 441742103333300 Elk Creek above Meadow Creek 441742 1033333 NA LZ mean4 -16.24 -123.7 -- -- --314 441738103333400 Meadow Creek above Elk Creek 441738 1033334 NA LZ 09-20-96 -- -- 120.0 7 37.6314 441738103333400 Meadow Creek above Elk Creek 441738 1033334 NA LZ 10-09-97 -- -- 113.6 6.4 35.6314 441738103333400 Meadow Creek above Elk Creek 441738 1033334 NA LZ mean4 -15.74 -118.2 -- -- --315 06422500 Boxelder Creek near Nemo 440838 1032716 NA LZ 09-27-93 -- -- 185.3 -- 58.1315 06422500 Boxelder Creek near Nemo 440838 1032716 NA LZ 10-08-97 -- -- 85.4 5.1 26.8315 06422500 Boxelder Creek near Nemo 440838 1032716 NA LZ 506-06-00 -- -- 50.6 3.2 15.9

315 06422500 Boxelder Creek near Nemo 440838 1032716 NA LZ mean4 -15.35 -116.3 -- -- --

316 06412200 Rapid Creek above Victoria Creek 440248 1032106 NA LZ 09-27-93 -- -- 110.7 -- 34.7316 06412200 Rapid Creek above Victoria Creek 440248 1032106 NA LZ mean4 -14.18 -109.9 -- -- --317 440110103245101 Victoria Creek 440110 1032451 NA LZ mean4 -13.49 -99.7 -- -- --

Table 7. Selected site information and isotope data for sites used in report–Continued[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18O (per mil) δD (per mil) Tritium (pCi/L) Tritium 2-sigma (pCi/L) Tritium (TU)1
102 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota Surface Water

—Continued

318 06407500 Spring Creek near Keystone 435845 1032025 NA LZ 09-27-93 -- -- 94.7 -- 29.7318 06407500 Spring Creek near Keystone 435845 1032025 NA LZ 09-09-96 -- -- 80.0 5 25.1318 06407500 Spring Creek near Keystone 435845 1032025 NA LZ mean4 -12.59 -96.5 -- -- --

319 06404000 Battle Creek near Keystone 435221 1032010 NA LZ 09-06-96 -- -- 61.0 4 19.1319 06404000 Battle Creek near Keystone 435221 1032010 NA LZ 09-12-97 -- -- 61.1 3.8 19.2319 6404000 Battle Creek near Keystone 435221 1032010 NA LZ mean4 -11.51 -84.8 -- -- --320 06404998 Grace Coolidge Cr nr Game Lodge 434540 1032149 NA LZ 09-10-96 -- -- 51.0 3 16.0320 06404998 Grace Coolidge Cr nr Game Lodge 434540 1032149 NA LZ 09-12-97 -- -- 50.6 3.2 15.9320 06404998 Grace Coolidge Cr nr Game Lodge 434540 1032149 NA LZ mean4 -11.58 -85.8 -- -- --321 06403300 French Creek above Fairburn 434302 1032203 NA LZ 10-07-96 -- -- 65.0 4 20.4321 06403300 French Creek above Fairburn 434302 1032203 NA LZ 09-11-97 -- -- 57.6 3.8 18.1321 06403300 French Creek above Fairburn 434302 1032203 NA LZ mean4 -11.58 -89.5 -- -- --322 06402430 Beaver Creek near Pringle 433453 1032834 NA LZ 10-01-96 -- -- 83.0 5 26.0322 06402430 Beaver Creek near Pringle 433453 1032834 NA LZ 09-10-97 -- -- 73.3 4.5 23.0322 06402430 Beaver Creek near Pringle 433453 1032834 NA LZ mean4 -12.28 -92.2 -- -- --

Meteorological

323 441852103594800 Precip at Little Spearfish Cr 441852 1035948 NA NA 06-20-98 -- -- 40.3 2.6 12.6324 440415103151500 Precip at USGS at Rapid City 440415 1031515 NA NA 05-22-97 -- -- 45.8 3.2 14.4324 440415103151500 Precip at USGS at Rapid City 440415 1031515 NA NA 05-21-98 -- -- 66.9 3.8 21.0

11 TU = 3.19 pCi/L.2Data from Busby and others (1983, 1991). In some cases, exact sample dates are unknown but are listed as 01-01-78.3Recent drilling in the vicinity indicates that these may be Opeche or Minnekahta.4Mean values for individual samples listed in table 8.5Table includes only data collected through water year 1998, with exception of tritium data for six selected sites collected during water year 2000.

Table 7. Selected site information and isotope data for sites used in report

–Continued

[pCi/L, picocuries per liter; TU, tritium unit; Mdsn, Madison; Mnls, Minnelusa; Mnkt, Minnekahta; Ddwd, Deadwood; <, less than; NA, not applicable; Obs, observation; LZ, loss zone; --, no data. Site types: Obs, observation well; Pair, observation well pair; HW, headwater spring; DG, downgradient spring; LZ, stream above loss zone]

Site

number

Station

identification

number

Local number Name Latitude Longitude Aquifer Site type Date δ18

O

(per mil)

δD

(per mil)

Tritium 

(pCi/L)

Tritium

2-sigma

(pCi/L)

Tritium 

(TU)1
Supplemental Information - Table 8 103

 Table 8. Stable isotope data for sites with multiple samples

[--, no data]

Site

number Name Date δ18O

(per mil)

δD

(per mil)

48 Swanson Well 08-16-94 -17.45 -133.0

48 Swanson Well 08-30-96 -17.46 -132.0

112 Black Hills Power & Light 06-26-90 -14.30 -108.0

112 Black Hills Power & Light 09-30-93 -14.40 -108.0

112 Black Hills Power & Light 04-20-95 -14.20 -109.0

116 Rapid City No. 6 04-03-90 -14.15 -105.0

116 Rapid City No. 6 12-13-90 -14.45 -109.0

116 Rapid City No. 6 10-04-93 -14.40 -107.0

116 Rapid City No. 6 04-20-95 -14.20 -108.0

116 Rapid City No. 6 08-26-96 -14.22 -107.0

121 Westberry Trails - Madison 08-21-90 -14.00 -103.0

121 Westberry Trails - Madison 09-30-93 -14.00 -105.0

121 Westberry Trails - Madison 04-26-95 -13.80 -106.0

121 Westberry Trails - Madison 09-11-96 -13.96 -103.0

123 Rapid City No. 10 09-06-91 -14.35 -110.0

123 Rapid City No. 10 10-01-93 -14.40 -108.0

123 Rapid City No. 10 10-14-94 -14.40 -109.0

123 Rapid City No. 10 08-26-96 -14.36 -108.0

124 Rapid City No. 8 09-05-91 -14.30 -108.0

124 Rapid City No. 8 09-28-93 -14.50 -109.0

124 Rapid City No. 8 04-18-95 -14.40 -109.0

124 Rapid City No. 8 08-26-96 -14.41 -108.0

126 Lien 107-20-78 -14.19 --

126 Lien 09-10-96 -14.17 -106.0

142 Stanley 08-23-89 -14.36 -109.0

142 Stanley 09-10-96 -14.49 -111.0

149 Highland Hills 07-25-96 -12.53 -96.3

149 Highland Hills 11-18-96 -12.47 -94.8

149 Highland Hills 01-09-97 -12.50 -95.6

149 Highland Hills 03-03-97 -12.54 -94.9

149 Highland Hills 05-13-97 -12.72 -97.9

149 Highland Hills 07-14-97 -12.94 -100.3

149 Highland Hills 09-10-97 -12.79 -97.4

149 Highland Hills 12-05-97 -12.73 -96.4

149 Highland Hills 02-06-98 -12.63 -96.1
104 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

149 Highland Hills 05-11-98 -12.74 -95.9

149 Highland Hills 07-08-98 -12.73 -97.2

149 Highland Hills 09-30-98 -12.56 -98.0

154 Hamms Well A 12-04-86 -12.55 -93.0

154 Hamms Well A 02-06-87 -12.40 -93.0

154 Hamms Well A 04-09-87 -12.50 -92.0

154 Hamms Well A 06-04-87 -12.40 -94.0

154 Hamms Well A 07-02-87 -12.35 -91.0

154 Hamms Well A 08-11-87 -12.45 -93.5

165 Carriage Hills Main Well 07-24-96 -11.93 -91.3

165 Carriage Hills Main Well 11-18-96 -12.03 -90.6

165 Carriage Hills Main Well 01-07-97 -11.98 -91.0

165 Carriage Hills Main Well 03-03-97 -11.99 -90.7

165 Carriage Hills Main Well 05-13-97 -12.04 -93.4

165 Carriage Hills Main Well 07-11-97 -12.13 -92.9

165 Carriage Hills Main Well 09-10-97 -12.12 -94.3

165 Carriage Hills Main Well 12-05-97 -12.15 -91.8

165 Carriage Hills Main Well 02-06-98 -12.20 -94.7

165 Carriage Hills Main Well 05-07-98 -12.24 -93.9

165 Carriage Hills Main Well 07-08-98 -12.34 -94.6

165 Carriage Hills Main Well 09-29-98 -12.35 -93.8

168 Chapel Lane Madison (CHPLN-2) 04-09-87 -11.85 -90.5

168 Chapel Lane Madison (CHPLN-2) 05-07-87 -11.81 -90.5

168 Chapel Lane Madison (CHPLN-2) 08-21-87 -11.90 -91.5

168 Chapel Lane Madison (CHPLN-2) 01-21-88 -11.75 -89.8

168 Chapel Lane Madison (CHPLN-2) 03-22-88 -11.79 -91.0

168 Chapel Lane Madison (CHPLN-2) 05-17-88 -11.76 -90.3

168 Chapel Lane Madison (CHPLN-2) 06-24-88 -11.80 -90.0

168 Chapel Lane Madison (CHPLN-2) 07-22-88 -11.80 -91.7

168 Chapel Lane Madison (CHPLN-2) 08-19-88 -11.82 -92.3

168 Chapel Lane Madison (CHPLN-2) 01-19-90 -12.10 -94.5

168 Chapel Lane Madison (CHPLN-2) 07-23-90 -12.15 -92.5

168 Chapel Lane Madison (CHPLN-2) 09-30-93 -11.90 -91.0

168 Chapel Lane Madison (CHPLN-2) 04-25-95 -11.80 -92.0

168 Chapel Lane Madison (CHPLN-2) 09-13-96 -12.09 -92.5

Table 8. Stable isotope data for sites with multiple samples–Continued

[--, no data]

Site

number Name Date δ18O(per mil)

δD

(per mil)
Supplemental Information - Table 8 105

168 Chapel Lane Madison (CHPLN-2) 10-24-96 -12.07 -91.8

168 Chapel Lane Madison (CHPLN-2) 11-18-96 -12.04 -90.2

168 Chapel Lane Madison (CHPLN-2) 01-07-97 -12.11 -91.1

168 Chapel Lane Madison (CHPLN-2) 03-03-97 -12.16 -91.6

168 Chapel Lane Madison (CHPLN-2) 05-13-97 -12.16 -95.3

168 Chapel Lane Madison (CHPLN-2) 07-11-97 -12.20 -94.3

168 Chapel Lane Madison (CHPLN-2) 09-10-97 -12.29 -93.4

168 Chapel Lane Madison (CHPLN-2) 12-05-97 -12.36 -94.6

168 Chapel Lane Madison (CHPLN-2) 02-06-98 -12.39 -93.3

168 Chapel Lane Madison (CHPLN-2) 05-07-98 -12.36 -94.4

168 Chapel Lane Madison (CHPLN-2) 07-08-98 -12.34 -94.2

168 Chapel Lane Madison (CHPLN-2) 09-29-98 -12.39 -95.0

169 Rapid City No. 11 (Corral Drive) 12-17-91 -11.90 -90.5

169 Rapid City No. 11 (Corral Drive) 10-05-93 -12.20 -92.0

169 Rapid City No. 11 (Corral Drive) 04-21-95 -12.00 -91.0

169 Rapid City No. 11 (Corral Drive) 07-24-96 -12.07 -90.8

169 Rapid City No. 11 (Corral Drive) 08-26-96 -12.13 -92.5

169 Rapid City No. 11 (Corral Drive) 11-14-96 -12.07 -91.0

169 Rapid City No. 11 (Corral Drive) 01-07-97 -12.04 -90.8

169 Rapid City No. 11 (Corral Drive) 03-11-97 -12.00 -92.0

169 Rapid City No. 11 (Corral Drive) 05-13-97 -12.07 -92.1

169 Rapid City No. 11 (Corral Drive) 07-11-97 -12.13 -91.5

169 Rapid City No. 11 (Corral Drive) 09-10-97 -12.13 -92.6

169 Rapid City No. 11 (Corral Drive) 05-07-98 -12.13 -91.2

169 Rapid City No. 11 (Corral Drive) 07-08-98 -12.21 -90.8

169 Rapid City No. 11 (Corral Drive) 09-29-98 -12.21 -92.6

172 Rapid City No. 9 (Meadowbrook) 05-08-91 -13.40 -101.0

172 Rapid City No. 9 (Meadowbrook) 09-26-93 -12.70 -97.0

172 Rapid City No. 9 (Meadowbrook) 04-24-95 -12.60 -97.0

172 Rapid City No. 9 (Meadowbrook) 07-26-96 -12.65 -99.3

172 Rapid City No. 9 (Meadowbrook) 08-26-96 -12.69 -98.1

172 Rapid City No. 9 (Meadowbrook) 05-13-97 -12.68 -97.8

172 Rapid City No. 9 (Meadowbrook) 07-08-98 -12.70 -97.9

175 Rapid City No. 3 12-05-86 -13.30 -99.0

175 Rapid City No. 3 02-06-87 -13.25 -98.0

Table 8. Stable isotope data for sites with multiple samples–Continued

[--, no data]

Site

number Name Date δ18O(per mil)

δD

(per mil)
106 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

175 Rapid City No. 3 03-10-87 -13.10 --

175 Rapid City No. 3 04-10-87 -13.30 -98.5

175 Rapid City No. 3 06-16-87 -13.30 -99.0

175 Rapid City No. 3 07-02-87 -11.55 -95.5

175 Rapid City No. 3 08-20-87 -13.30 -97.9

175 Rapid City No. 3 09-01-87 -13.25 -98.5

175 Rapid City No. 3 03-17-88 -13.25 -99.5

175 Rapid City No. 3 05-17-88 -13.20 -98.5

175 Rapid City No. 3 07-19-88 -13.40 -102.5

178 PE-89A Canyon Lake Madison 12-06-89 -12.85 -100.0

178 PE-89A Canyon Lake Madison 09-28-93 -12.70 -98.0

178 PE-89A Canyon Lake Madison 04-19-95 -12.60 -97.0

178 PE-89A Canyon Lake Madison 10-10-96 -12.63 -97.1

181 Rapid City No. 4 12-05-86 -13.90 -104.5

181 Rapid City No. 4 02-06-87 -13.90 -102.0

181 Rapid City No. 4 03-10-87 -13.90 -102.0

181 Rapid City No. 4 04-10-87 -13.85 -102.5

181 Rapid City No. 4 06-16-87 -13.85 -105.0

181 Rapid City No. 4 07-02-87 -13.30 -102.5

181 Rapid City No. 4 08-07-87 -13.90 -103.0

181 Rapid City No. 4 09-01-87 -14.00 -103.5

181 Rapid City No. 4 03-22-88 -13.85 -102.5

181 Rapid City No. 4 05-17-88 -13.85 -103.0

181 Rapid City No. 4 07-15-88 -13.90 -103.0

181 Rapid City No. 4 07-18-90 -13.75 -101.0

181 Rapid City No. 4 08-26-96 -13.81 -104.0

182 PE-65A Sioux Park 2 Madison 03-14-90 -14.25 -105.0

182 PE-65A Sioux Park 2 Madison 08-30-90 -14.45 -108.0

182 PE-65A Sioux Park 2 Madison 10-10-96 -13.79 -104.0

183 PE-64B Sioux Park 1 Minnelusa 03-14-90 -14.50 -109.0

183 PE-64B Sioux Park 1 Minnelusa 08-29-90 -14.25 -106.0

185 Rapid City No. 5 04-25-90 -14.50 -108.0

185 Rapid City No. 5 10-07-93 -14.30 -107.0

185 Rapid City No. 5 10-13-94 -14.10 -106.0

185 Rapid City No. 5 08-26-96 -14.01 -107.0

Table 8. Stable isotope data for sites with multiple samples–Continued

[--, no data]

Site

number Name Date δ18O(per mil)

δD

(per mil)
Supplemental Information - Table 8 107

186 PE-89E Lime Creek 11-21-89 -14.45 -109.0

186 PE-89E Lime Creek 06-20-90 -14.30 -109.0

195 Hart Ranch 12-08-86 -11.70 -89.0

195 Hart Ranch 06-08-87 -11.70 -90.0

195 Hart Ranch 07-12-87 -11.70 -89.5

195 Hart Ranch 08-20-87 -11.70 -90.0

195 Hart Ranch 10-19-93 -11.70 -90.0

195 Hart Ranch 04-26-95 -11.80 -91.0

195 Hart Ranch 07-23-96 -12.37 -93.3

195 Hart Ranch 11-14-96 -12.38 -93.0

195 Hart Ranch 01-08-97 -12.41 -94.9

195 Hart Ranch 03-11-97 -12.36 -95.0

195 Hart Ranch 05-13-97 -12.47 -93.8

195 Hart Ranch 07-11-97 -12.54 -94.5

195 Hart Ranch 09-10-97 -12.70 -97.1

195 Hart Ranch 12-05-97 -12.73 -95.8

195 Hart Ranch 02-06-98 -12.68 -95.3

195 Hart Ranch 05-07-98 -12.53 -94.5

195 Hart Ranch 07-08-98 -12.69 -96.0

195 Hart Ranch 09-29-98 -12.65 -97.2

196 Pine Grove 12-09-86 -11.90 -87.5

196 Pine Grove 02-10-87 -11.85 -87.5

196 Pine Grove 03-10-87 -11.95 -87.0

196 Pine Grove 04-10-87 -11.95 -89.0

196 Pine Grove 07-13-87 -11.95 -87.0

196 Pine Grove 08-16-89 -11.76 -88.4

196 Pine Grove 10-15-93 -12.00 -89.0

196 Pine Grove 04-21-95 -11.80 -88.0

196 Pine Grove 11-18-96 -11.89 -88.6

196 Pine Grove 01-09-97 -11.86 -88.0

196 Pine Grove 03-05-97 -11.90 -88.5

232 Windy City Lake 03-10-87 -12.45 -91.0

232 Windy City Lake 05-17-88 -12.05 -89.5

237 Streeter Ranch 111-01-77 -12.05 -88.4

237 Streeter Ranch 03-11-97 -11.87 -86.8

Table 8. Stable isotope data for sites with multiple samples–Continued

[--, no data]

Site

number Name Date δ18O(per mil)

δD

(per mil)
108 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

276 Knight Spring 08-04-95 -16.85 -125.0

276 Knight Spring 08-28-96 -16.90 -127.0

276 Knight Spring 09-11-97 -16.98 -127.8

280 08-08-95 -13.86 -103.0

280 09-09-96 -13.97 -106.0

280 09-09-97 -14.04 -104.2

281 JHD Spring 09-13-95 -16.55 -128.0

281 JHD Spring 09-06-96 -16.61 -126.0

281 JHD Spring 09-09-97 -16.53 -126.4

282 Intake Gulch 08-03-95 -17.55 -135.0

282 Intake Gulch 08-28-96 -17.67 -133.0

282 Intake Gulch 09-09-97 -17.54 -133.0

283 Rhoads Fork near Rochford 1

01-01-78 -17.22 -125.0

283 Rhoads Fork near Rochford 12-05-86 -16.95 -126.5

283 Rhoads Fork near Rochford 04-14-87 -16.95 -127.5

283 Rhoads Fork near Rochford 06-12-87 -17.05 -128.0

283 Rhoads Fork near Rochford 07-06-87 -17.05 -127.5

283 Rhoads Fork near Rochford 08-11-87 -17.00 -129.0

283 Rhoads Fork near Rochford 08-07-95 -16.89 -125.0

283 Rhoads Fork near Rochford 08-28-96 -16.79 -127.0

283 Rhoads Fork near Rochford 09-09-97 -16.75 -128.5

285 Castle Creek above Deerfield 02-09-87 -16.45 -123.0

285 Castle Creek above Deerfield 04-14-87 -16.60 -124.0

285 Castle Creek above Deerfield 05-05-87 -16.50 -124.0

285 Castle Creek above Deerfield 06-12-87 -16.40 -123.5

285 Castle Creek above Deerfield 07-06-87 -16.35 -125.0

285 Castle Creek above Deerfield 08-11-87 -16.25 -122.5

285 Castle Creek above Deerfield 10-20-87 -16.35 -124.0

285 Castle Creek above Deerfield 07-14-88 -16.35 -123.5

287 Barrel Spring 07-25-95 -14.67 -115.0

287 Barrel Spring 09-13-96 -14.44 -112.0

287 Barrel Spring 09-08-97 -14.69 -113.8

288 Water Draw Spring 09-14-95 -14.34 -113.0

288 Water Draw Spring 09-13-96 -14.26 -113.0

288 Water Draw Spring 09-08-97 -14.22 -111.5

Table 8. Stable isotope data for sites with multiple samples–Continued

[--, no data]

Site

number Name Date δ18O(per mil)

δD

(per mil)
Supplemental Information - Table 8 109

289 Mckenna Spring 09-14-95 -13.46 -103.0

289 Mckenna Spring 09-13-96 -13.53 -106.0

289 Mckenna Spring 09-08-97 -13.24 -101.8

290 Higgins Gulch below I-90 09-26-94 -16.47 -126.0

290 Higgins Gulch below I-90 10-10-97 -16.25 -121.6

298 City Springs 12-04-86 -14.35 -107.0

298 City Springs 04-09-87 -14.20 -107.0

298 City Springs 05-12-87 -14.40 -107.5

298 City Springs 06-04-87 -14.40 -108.5

298 City Springs 09-29-87 -14.50 -109.0

298 City Springs 05-12-88 -14.50 -109.0

298 City Springs 09-26-93 -14.20 -106.0

298 City Springs 10-15-94 -14.40 -109.0

300 Cleghorn Springs 12-05-86 -12.95 -98.5

300 Cleghorn Springs 02-06-87 -12.95 -98.0

300 Cleghorn Springs 04-10-87 -12.90 -98.0

300 Cleghorn Springs 06-04-87 -12.85 -99.0

300 Cleghorn Springs 07-02-87 -12.90 -100.0

300 Cleghorn Springs 08-07-87 -12.90 -98.5

300 Cleghorn Springs 09-27-93 -12.80 -99.0

300 Cleghorn Springs 04-20-95 -12.80 -100.0

300 Cleghorn Springs 08-05-98 -13.26 -100.7

308 Cascade Spring 101-01-78 -15.48 -118.0

308 Cascade Spring 09-12-96 -15.32 -119.0

309 Bear Gulch near Maurice 10-10-96 -16.76 -127.0

309 Bear Gulch near Maurice 09-11-97 -17.16 -130.6

310 Beaver Creek near Maurice 10-09-96 -16.40 -126.0

310 Beaver Creek near Maurice 09-11-97 -16.77 -128.8

312 Bear Butte Creek near Deadwood 10-09-96 -16.03 -122.0

312 Bear Butte Creek near Deadwood 10-10-97 -15.98 -120.3

313 Elk Creek above Meadow Creek 09-20-96 -16.10 -123.0

313 Elk Creek above Meadow Creek 10-09-97 -16.37 -124.4

314 Meadow Creek above Elk Creek 09-20-96 -15.69 -119.0

314 Meadow Creek above Elk Creek 10-09-97 -15.78 -117.4

315 Boxelder Creek near Nemo 09-27-93 -14.70 -111.0

Table 8. Stable isotope data for sites with multiple samples–Continued

[--, no data]

Site

number Name Date δ18O(per mil)

δD

(per mil)
110 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

315 Boxelder Creek near Nemo 10-29-93 -14.70 -113.0

315 Boxelder Creek near Nemo 11-24-93 -15.00 -113.0

315 Boxelder Creek near Nemo 12-22-93 -15.10 -114.0

315 Boxelder Creek near Nemo 01-20-94 -15.20 -114.0

315 Boxelder Creek near Nemo 02-18-94 -17.10 -129.0

315 Boxelder Creek near Nemo 03-25-94 -16.10 -121.0

315 Boxelder Creek near Nemo 04-20-94 -16.30 -125.0

315 Boxelder Creek near Nemo 05-19-94 -15.60 -118.0

315 Boxelder Creek near Nemo 06-27-94 -14.70 -112.0

315 Boxelder Creek near Nemo 07-15-94 -14.80 -112.0

315 Boxelder Creek near Nemo 08-17-94 -14.30 -108.0

315 Boxelder Creek near Nemo 09-27-94 -14.60 -112.0

315 Boxelder Creek near Nemo 10-26-94 -15.10 -115.0

315 Boxelder Creek near Nemo 11-23-94 -15.40 -118.0

315 Boxelder Creek near Nemo 12-29-94 -15.40 -114.0

315 Boxelder Creek near Nemo 03-10-95 -16.10 -123.0

315 Boxelder Creek near Nemo 04-13-95 -15.50 -118.0

315 Boxelder Creek near Nemo 10-18-95 -14.91 -114.0

315 Boxelder Creek near Nemo 11-29-95 -15.33 -113.0

315 Boxelder Creek near Nemo 01-16-96 -15.23 -115.0

315 Boxelder Creek near Nemo 08-28-96 -14.77 -112.0

315 Boxelder Creek near Nemo 10-11-96 -14.97 -115.0

315 Boxelder Creek near Nemo 12-31-96 -16.04 -122.0

315 Boxelder Creek near Nemo 03-17-97 -15.92 -120.1

315 Boxelder Creek near Nemo 04-25-97 -16.45 -124.0

315 Boxelder Creek near Nemo 06-23-97 -15.36 -118.0

315 Boxelder Creek near Nemo 08-12-97 -15.17 -114.1

315 Boxelder Creek near Nemo 10-08-97 -14.76 -112.8

315 Boxelder Creek near Nemo 12-11-97 -15.12 -113.2

315 Boxelder Creek near Nemo 02-12-98 -15.29 -116.8

315 Boxelder Creek near Nemo 03-23-98 -16.27 -122.7

315 Boxelder Creek near Nemo 07-01-98 -15.53 -117.5

315 Boxelder Creek near Nemo 08-14-98 -15.06 -112.9

316 Rapid Creek above Victoria Creek 01-19-90 -13.30 -107.0

316 Rapid Creek above Victoria Creek 09-27-93 -13.70 -108.0

Table 8. Stable isotope data for sites with multiple samples–Continued

[--, no data]

Site

number Name Date δ18O(per mil)

δD

(per mil)
Supplemental Information - Table 8 111

316 Rapid Creek above Victoria Creek 10-29-93 -13.40 -103.0

316 Rapid Creek above Victoria Creek 11-24-93 -13.60 -106.0

316 Rapid Creek above Victoria Creek 12-22-93 -13.50 -106.0

316 Rapid Creek above Victoria Creek 01-20-94 -13.60 -105.0

316 Rapid Creek above Victoria Creek 02-18-94 -13.80 -108.0

316 Rapid Creek above Victoria Creek 03-25-94 -13.80 -103.0

316 Rapid Creek above Victoria Creek 04-20-94 -13.70 -108.0

316 Rapid Creek above Victoria Creek 05-19-94 -13.80 -107.0

316 Rapid Creek above Victoria Creek 06-27-94 -13.80 -109.0

316 Rapid Creek above Victoria Creek 07-15-94 -14.00 -109.0

316 Rapid Creek above Victoria Creek 08-17-94 -14.00 -109.0

316 Rapid Creek above Victoria Creek 09-27-94 -14.00 -109.0

316 Rapid Creek above Victoria Creek 10-26-94 -13.80 -108.0

316 Rapid Creek above Victoria Creek 11-23-94 -13.60 -107.0

316 Rapid Creek above Victoria Creek 12-29-94 -13.50 -108.0

316 Rapid Creek above Victoria Creek 03-10-95 -13.70 -109.0

316 Rapid Creek above Victoria Creek 04-13-95 -13.70 -107.0

316 Rapid Creek above Victoria Creek 10-18-95 -14.04 -109.0

316 Rapid Creek above Victoria Creek 11-30-95 -13.72 -105.0

316 Rapid Creek above Victoria Creek 01-16-96 -13.97 -107.0

316 Rapid Creek above Victoria Creek 08-28-96 -14.74 -113.0

316 Rapid Creek above Victoria Creek 10-11-96 -14.68 -113.0

316 Rapid Creek above Victoria Creek 11-04-96 -14.16 -109.0

316 Rapid Creek above Victoria Creek 12-05-96 -14.12 -109.0

316 Rapid Creek above Victoria Creek 01-08-97 -14.38 -109.0

316 Rapid Creek above Victoria Creek 02-13-97 -14.56 -111.9

316 Rapid Creek above Victoria Creek 03-20-97 -14.50 -113.3

316 Rapid Creek above Victoria Creek 04-29-97 -14.72 -116.1

316 Rapid Creek above Victoria Creek 05-29-97 -14.91 -114.5

316 Rapid Creek above Victoria Creek 07-10-97 -15.10 -115.5

316 Rapid Creek above Victoria Creek 08-21-97 -15.23 -116.2

316 Rapid Creek above Victoria Creek 10-03-97 -15.06 -114.3

316 Rapid Creek above Victoria Creek 11-12-97 -14.44 -110.7

316 Rapid Creek above Victoria Creek 12-16-97 -14.43 -110.4

316 Rapid Creek above Victoria Creek 01-26-98 -14.69 -114.1

Table 8. Stable isotope data for sites with multiple samples–Continued

[--, no data]

Site

number Name Date δ18O(per mil)

δD

(per mil)
112 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

316 Rapid Creek above Victoria Creek 03-02-98 -14.80 -113.1

316 Rapid Creek above Victoria Creek 04-14-98 -14.85 -115.5

316 Rapid Creek above Victoria Creek 06-30-98 -14.94 -115.1

316 Rapid Creek above Victoria Creek 09-08-98 -15.04 -113.9

317 Victoria Creek 04-09-87 -13.95 -102.5

317 Victoria Creek 06-09-87 -13.55 -100.0

317 Victoria Creek 07-06-87 -13.30 -98.4

317 Victoria Creek 08-13-87 -13.15 -98.0

318 Spring Creek near Keystone 12-04-86 -11.15 -89.5

318 Spring Creek near Keystone 09-27-93 -12.20 -93.0

318 Spring Creek near Keystone 10-29-93 -11.90 -91.0

318 Spring Creek near Keystone 11-24-93 -12.20 -93.0

318 Spring Creek near Keystone 12-22-93 -12.20 -92.0

318 Spring Creek near Keystone 01-20-94 -12.30 -94.0

318 Spring Creek near Keystone 02-18-94 -12.60 -96.0

318 Spring Creek near Keystone 03-25-94 -12.40 -93.0

318 Spring Creek near Keystone 04-20-94 -12.30 -93.0

318 Spring Creek near Keystone 05-19-94 -12.50 -96.0

318 Spring Creek near Keystone 06-27-94 -11.90 -93.0

318 Spring Creek near Keystone 07-15-94 -11.60 -90.0

318 Spring Creek near Keystone 08-17-94 -10.90 -88.0

318 Spring Creek near Keystone 09-27-94 -10.70 -87.0

318 Spring Creek near Keystone 10-26-94 -11.60 -91.0

318 Spring Creek near Keystone 11-23-94 -11.70 -93.0

318 Spring Creek near Keystone 12-29-94 -11.80 -93.0

318 Spring Creek near Keystone 03-10-95 -12.00 -93.0

318 Spring Creek near Keystone 04-13-95 -12.00 -95.0

318 Spring Creek near Keystone 10-18-95 -12.54 -96.1

318 Spring Creek near Keystone 11-29-95 -12.62 -96.4

318 Spring Creek near Keystone 01-16-96 -12.81 -96.9

318 Spring Creek near Keystone 08-28-96 -13.20 -101.0

318 Spring Creek near Keystone 09-09-96 -12.89 -98.9

318 Spring Creek near Keystone 10-14-96 -13.33 -102.0

318 Spring Creek near Keystone 11-06-96 -12.70 -95.8

318 Spring Creek near Keystone 12-06-96 -12.66 -96.6

Table 8. Stable isotope data for sites with multiple samples–Continued

[--, no data]

Site

number Name Date δ18O(per mil)

δD

(per mil)
Supplemental Information - Table 8 113

318 Spring Creek near Keystone 01-08-97 -12.93 -97.5

318 Spring Creek near Keystone 02-14-97 -13.01 -99.3

318 Spring Creek near Keystone 03-17-97 -13.11 -101.1

318 Spring Creek near Keystone 04-30-97 -13.54 -104.0

318 Spring Creek near Keystone 06-13-97 -14.10 -106.0

318 Spring Creek near Keystone 07-23-97 -13.66 -102.6

318 Spring Creek near Keystone 08-22-97 -13.53 -102.1

318 Spring Creek near Keystone 10-07-97 -13.24 -98.9

318 Spring Creek near Keystone 11-13-97 -13.05 -98.7

318 Spring Creek near Keystone 12-18-97 -13.10 -98.5

318 Spring Creek near Keystone 01-29-98 -13.11 -99.8

318 Spring Creek near Keystone 03-05-98 -13.19 -100.3

318 Spring Creek near Keystone 04-16-98 -13.37 -102.6

318 Spring Creek near Keystone 06-05-98 -13.18 -101.3

318 Spring Creek near Keystone 07-06-98 -13.53 -101.9

318 Spring Creek near Keystone 08-13-98 -12.88 -98.3

319 Battle Creek near Keystone 09-06-96 -11.09 -82.4

319 Battle Creek near Keystone 09-12-97 -11.92 -87.2

320 Grace Coolidge Cr nr Game Lodge 09-10-96 -11.33 -84.2

320 Grace Coolidge Cr nr Game Lodge 09-12-97 -11.82 -87.4

321 French Creek above Fairburn 10-07-96 -11.54 -89.8

321 French Creek above Fairburn 09-11-97 -11.62 -89.1

322 Beaver Creek near Pringle 10-01-96 -12.38 -92.4

322 Beaver Creek near Pringle 09-10-97 -12.18 -91.9

1

Data from Busby and others (1983, 1991). Sites for which exact sample date is unknown are 

listed as 01-01-78.

Table 8. Stable isotope data for sites with multiple samples–Continued

[--, no data]

Site

number Name Date δ18O(per mil)

δD

(per mil)
114 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota

Table 9. Weighted annual tritium concentrations in precipitation for Black Hills area

[TU-m, tritium-unit-meters; TU, tritium units; mm, millimeters; --, no data]

Year Deposition

(TU-m)

Precipitation

(mm)

Weighted tritium 

concentration 

(TU)

Assumed Values

1952 and prior -- -- 15.00

Data from Michel (1989)

1953 18 460 39.13

1954 190 420 452.38

1955 26 370 70.27

1956 77 330 233.33

1957 87 460 189.13

1958 320 410 780.49

1959 300 370 810.81

1960 85 390 217.95

1961 99 310 319.35

1962 960 600 1,600.00

1963 2,000 480 4,166.67

1964 1,200 360 3,333.33

1965 680 460 1,478.26

1966 470 500 940.00

1967 240 480 500.00

1968 180 490 367.35

1969 130 340 382.35

1970 140 400 350.00

1971 93.8 469 200.00

1972 53.4 445 120.00

1973 48.8 488 100.00

1974 27.4 249 110.04

1975 35.4 443 79.91

1976 27.0 396 68.18

1977 56.2 661 85.02

1978 39.5 395 100.00

1979 21.3 355 60.00

1980 19.6 436 44.95

1981 19.4 357 54.34

1982 23.0 660 34.85

1983 9.8 393 24.94

Regression Estimates from Table 10

1984 -- -- 23.75

1985 -- -- 25.31

1986 -- -- 31.72

1987 -- -- 29.14

1988 -- -- 28.83

1989 -- -- 30.14

1990 -- -- 27.46

1991 -- -- 27.07

1992 -- -- 19.66

1993 -- -- 19.37

1994 -- -- 19.52

1995 -- -- 16.61

1996 -- -- 16.72

1997 -- -- 20.48

1998 -- -- 20.76
Supplemental Information - Table 10 115

Table 10. Monthly estimated tritium concentrations in precipitation, monthly precipitation, and weighted annual tritium concentrations in precipitation for Black Hills area[Estimated tritium input based on average of extended records for Bismarck, North Dakota, and Lincoln, Nebraska. TU, tritium unit; mm, millimeter; --, no data]

Month

1984 1985 1986 1987 1988 1989 1990 1991

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

January 33.35 7 27.22 9 19.58 12 29.00 5 33.14 10 30.54 3 24.76 6 41.13 12February -- -- 25.66 5 23.73 26 32.62 41 26.92 11 38.97 14 43.42 15 35.71 26March 24.15 23 24.06 29 30.34 19 15.10 44 39.54 31 22.85 29 25.77 33 20.47 21April -- -- 26.19 28 -- -- 21.56 9 26.71 20 31.61 58 20.93 53 20.99 81May -- -- 39.54 31 32.71 44 29.05 104 25.82 81 29.50 49 25.40 100 24.92 144June 21.55 116 -- -- 34.55 124 35.98 22 28.30 57 28.25 45 26.92 35 35.02 94July 26.35 69 31.56 43 35.39 49 34.41 34 33.23 29 37.17 49 27.12 83 29.30 40August -- -- 29.90 28 39.81 32 34.36 57 32.42 51 41.69 44 33.75 31 28.30 32September -- -- 13.43 50 26.76 111 24.81 22 26.60 27 21.04 82 39.59 30 26.92 19October -- -- 29.90 19 36.44 54 42.26 13 23.51 16 20.17 37 23.57 21 24.38 29November -- -- 15.10 43 27.79 30 20.05 13 20.87 23 27.28 21 31.61 17 18.62 30December -- -- 29.70 23 19.10 3 26.76 13 26.92 11 47.08 26 20.17 16 31.46 2Weighted 

annual tritium input

23.75 25.31 31.72 29.14 28.83 30.14 27.46 27.07
116 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota Table 10. Monthly estimated tritium input concentrations, monthly precipitation, and weighted annual tritium input concentrations for Black Hills area

—Continued

[Estimated tritium input based on average of extended records for Bismarck, North Dakota, and Lincoln, Nebraska. TU, tritium unit; mm, millimeter; --, no data]

Month

1992 1993 1994 1995 1996 1997 1998

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

Tritium 

input

(TU)

Precipitation 

(mm)

January 18.00 7 14.48 20 17.50 24 12.55 8 17.19 30 -- -- 12.10 14February 22.91 12 21.62 25 21.90 19 20.70 19 13.21 6 20.81 22 19.22 31March 14.76 47 16.03 27 16.42 19 24.17 26 18.74 41 16.23 15 19.22 48April 16.36 37 16.03 66 17.88 52 18.62 56 17.13 60 20.76 75 25.19 20May 20.29 71 21.79 90 20.58 40 14.07 175 14.42 147 20.17 104 13.79 71June 20.99 82 19.94 147 20.87 38 14.96 118 19.70 46 18.43 70 18.98 148July 20.23 86 20.52 98 20.64 46 20.29 72 17.88 41 20.47 134 27.74 82August 23.51 34 22.57 54 20.58 31 19.70 26 20.41 77 22.96 51 27.48 83September 16.74 13 20.05 34 19.70 16 20.58 43 18.43 53 23.13 32 19.16 55October 24.55 16 17.75 36 21.04 117 13.50 71 14.21 90 23.24 27 21.33 129November 13.64 22 12.41 21 13.57 21 16.23 21 15.30 16 17.13 11 15.83 35December 22.74 27 17.13 25 13.36 14 14.62 34 17.50 12 17.19 8Weighted 

annual tritium input

19.66 19.37 19.52 16.61 16.72 20.48 20.76
Supplemental Information - Table 11 117

Table 11. Estimated tritium concentrations in precipitation for Black Hills area, adjusted for decay[TU, tritium units; --, not computed]

Recharge

year

Tritium 

input

(TU)

Sample collection date

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998

1951 and 

prior

15 4 3 3 3 3 3 2 2 2 2 2 2 2 2 2 1 1 1 1 1 1

1952 15 4 3 3 3 3 3 3 2 2 2 2 2 2 2 2 2 1 1 1 1 11953 39 10 9 9 8 8 7 7 7 6 6 6 5 5 5 4 4 4 4 4 3 31954 452 119 112 106 100 95 90 85 80 76 72 68 64 61 57 54 51 49 46 43 41 391955 70 19 18 17 16 16 15 14 13 12 12 11 11 10 9 9 8 8 8 7 7 61956 233 68 65 61 58 55 52 49 46 44 41 39 37 35 33 31 30 28 26 25 24 221957 189 59 55 52 50 47 44 42 40 38 35 34 32 30 28 27 25 24 23 21 20 191958 780 256 242 229 216 205 194 183 173 164 155 146 138 131 124 117 111 105 99 94 89 841959 811 281 266 251 238 225 213 201 190 180 170 161 152 144 136 129 122 115 109 103 97 921960 218 80 76 71 68 64 60 57 54 51 48 46 43 41 39 37 35 33 31 29 28 261961 319 124 117 111 105 99 94 88 84 79 75 71 67 63 60 57 54 51 48 45 43 411962 1,600 656 620 586 555 525 496 469 444 420 397 375 355 336 318 300 284 269 254 240 227 2151963 4,167 1,805 1,708 1,615 1,527 1,444 1,366 1,292 1,222 1,156 1,093 1,034 978 925 875 827 782 740 700 662 626 5921964 3,333 1,527 1,444 1,366 1,292 1,222 1,155 1,093 1,033 977 924 874 827 782 740 699 662 626 592 560 529 5011965 1,478 716 677 640 606 573 542 512 485 458 433 410 388 367 347 328 310 293 277 262 248 2351966 940 481 455 431 407 385 364 345 326 308 291 276 261 247 233 221 209 197 187 176 167 1581967 500 271 256 242 229 217 205 194 183 173 164 155 147 139 131 124 117 111 105 99 94 891968 367 210 199 188 178 168 159 150 142 135 127 120 114 108 102 96 91 86 81 77 73 691969 382 231 219 207 196 185 175 166 157 148 140 132 125 118 112 106 100 95 90 85 80 761970 350 224 212 200 190 179 170 160 152 143 136 128 121 115 109 103 97 92 87 82 78 731971 200 135 128 121 115 108 102 97 92 87 82 78 73 69 66 62 59 55 52 50 47 441972 120 86 81 77 73 69 65 61 58 55 52 49 47 44 42 39 37 35 33 31 30 281973 100 76 72 68 64 61 57 54 51 48 46 43 41 39 37 35 33 31 29 28 26 251974 110 88 83 79 74 70 67 63 60 56 53 50 48 45 43 40 38 36 34 32 31 29
118 Geochemistry of the Madison and Minnelusa Aquifers in the Black Hills Area, South Dakota Table 11 1975 80 68 64 61 57 54 51 48 46 43 41 39 37 35 33 31 29 28 26 25 23 22 1976 68 61 58 54 51 49 46 44 41 39 37 35 33 31 29 28 26 25 24 22 21 20 1977 85 80 76 72 68 64 61 58 54 51 49 46 44 41 39 37 35 33 31 29 28 26 1978 100 100 95 89 85 80 76 72 68 64 61 57 54 51 48 46 43 41 39 37 35 33 1979 60 -- 60 57 54 51 48 45 43 41 38 36 34 32 31 29 27 26 25 23 22 21 1980 45 -- -- 45 43 40 38 36 34 32 30 29 27 26 24 23 22 21 19 18 17 16 1981 54 -- -- -- 54 51 48 46 43 41 39 37 35 33 31 29 28 26 25 23 22 21 1982 35 -- -- -- -- 35 33 31 30 28 26 25 24 22 21 20 19 18 17 16 15 14 1983 25 -- -- -- -- -- 25 24 22 21 20 19 18 17 16 15 14 14 13 12 11 11 1984 24 -- -- -- -- -- -- 24 23 21 20 19 18 17 16 15 15 14 13 12 12 11 1985 25 -- -- -- -- -- -- -- 25 24 22 21 20 19 18 17 16 15 14 14 13 12 1986 32 -- -- -- -- -- -- -- -- 32 30 29 27 26 24 23 22 20 19 18 17 16 1987 29 -- -- -- -- -- -- -- -- -- 29 27 26 25 23 22 21 20 19 18 17 16 1988 29 -- -- -- -- -- -- -- -- -- -- 29 27 26 25 23 22 21 20 19 18 17 1989 30 -- -- -- -- -- -- -- -- -- -- -- 30 28 27 25 24 23 21 20 19 18 1990 27 -- -- -- -- -- -- -- -- -- -- -- -- 27 26 24 23 22 20 19 18 17 1991 27 -- -- -- -- -- -- -- -- -- -- -- -- -- 27 26 24 23 22 20 19 18 1992 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- 20 19 18 17 16 15 14 1993 19 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 19 18 17 16 15 14

1994 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 20 19 18 17 161995 17 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 17 16 15 141996 17 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 17 16 151997 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 20 191998 21 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 22 21

. Estimated tritium concentrations in precipitation for Black Hills area, adjusted for decay

–Continued

[TU, tritium units; --, not computed]

Recharge

year

Tritium 

input

(TU)

Sample collection date

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998