U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2011–5235

Prepared in cooperation with the National Park Service

Groundwater Flow, Quality (2007–10), and Mixing in the 

Wind Cave National Park Area, South Dakota
Front cover. Fluorescein dye in Wind Cave in Windy City Lake, a lake that merged with Calcite Lake before the end of 1999. Dye was 

injected by National Park Service staff into What the Hell Lake in February 2008 and was detected in Windy City Lake 2 

months later. This photograph was taken November 2008 by Peter Sprouse, National Park Service.

Back cover. Upper left: Measuring the physical properties of water from Stairway Spring. 

Upper right: Leading us to the water in Wind Cave! Photograph by Jason Walz, National Park Service. 

Lower left: Squeezing through a narrow place above What the Hell Lake in Wind Cave. Photograph by Jason Walz, 

National Park Service.

Lower right: Downloading temperature data collected from Highland Creek. Photograph by Jason Walz, National Park 

Service.
Groundwater Flow, Quality (2007–10), and 

Mixing in the Wind Cave National Park 

Area, South Dakota

By Andrew J. Long, Marc J. Ohms, and Jonathan D.R.G. McKaskey

Prepared in cooperation with the National Park Service

Scientific Investigations Report 2011–5235

U.S. Department of the Interior

U.S. Geological Survey
ISBN 978-1-4113-3320-8

U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2012

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Long, A.J., Ohms, M.J., McKaskey, J.D.R.G., 2012, Groundwater flow, quality (2007–10), and mixing in the Wind Cave 

National Park area, South Dakota: U.S. Geological Survey Scientific Investigations Report 2011–5235, 50 p.
iii

Acknowledgments

The authors would like to thank Jennifer Back, Jeff Hughes, Jason Walz, and Steve Schrempp of 

the National Park Service for assistance in sample collection. Jennifer Back assisted in planning 

the study and making other helpful suggestions for data collection and interpretation. 

Joel Petersen of the U.S. Geological Survey assisted in installing water-level transducers and 

data loggers for wells. 
iv

Figures

1. Map of study area showing hydrogeologic units and potentiometric 

surface of the Madison aquifer..................................................................................................3

2. Map showing mapped passages of Wind Cave and sampled sites 

shown in plan view and as a generalized hydrogeologic cross-section 

projected onto a single vertical plane.......................................................................................5

3. Graph showing chlorofluorocarbon and tritium concentrations in the 

atmosphere..................................................................................................................................12

4. Map showing potentiometric surface of the Minnelusa aquifer........................................13

5. Graph showing water-level hydrographs for Windy City Lake (site WCL) 

and well Md7–11.........................................................................................................................14

Contents

Acknowledgments........................................................................................................................................iii

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

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Description of Study Area ...................................................................................................................2

Methods...........................................................................................................................................................7

Sample Collection and Hydrochemical Data ...................................................................................7

Principal Component and Cluster Analyses...................................................................................11

End-Member Mixing...........................................................................................................................11

Groundwater Age Dating...................................................................................................................11

Groundwater Flow, Quality, and Mixing Assessments ..........................................................................12

Groundwater Flow ..............................................................................................................................12

Groundwater Gradients and Flow Directions .......................................................................12

Dye Tracing .................................................................................................................................16

Groundwater Quality ..........................................................................................................................17

Specific Conductance...............................................................................................................17

Arsenic.........................................................................................................................................17

Nitrate Plus Nitrite.....................................................................................................................24

Trace Metals...............................................................................................................................24

Groundwater Mixing...........................................................................................................................24

Principal Component and Cluster Analyses..........................................................................26

End-Member Mixing..................................................................................................................30

End-Member Mixing Evaluation..............................................................................................31

Groundwater Age Dating..........................................................................................................33

Summary and Conclusions.........................................................................................................................37

References Cited..........................................................................................................................................38

Supplemental Tables ...................................................................................................................................43
v

Tables

1. Description of hydrogeologic units............................................................................................4

2. Sampled cave sites and springs ................................................................................................6

3. Water-quality sampling sites and constituents analyzed in samples..................................8

4. Chlorofluorocarbon (CFC) and tritium data.............................................................................18

5. Results of laboratory analyses of the presence of fluorescein dye in 

charcoal dye receptors that were placed in Wind Cave water bodies 

and two wells ..............................................................................................................................20

6. Trace-metal data for water samples from selected sites within 

Wind Cave National Park ..........................................................................................................21

7. Physical interpretation of end-member waters.....................................................................31

8. End-member contributions as an average to each cluster area........................................31

9. End-member contributions for Wind Cave sites....................................................................32

10. Temperature, specific conductance, and calcium plus sulfate in 

water samples from artesian springs......................................................................................33

11. Dissolved gas data for water samples....................................................................................34

12. Hydrochemical data for water samples..................................................................................44

13. Summary of hydrochemical data for the five hydrogeologic domains..............................50

6. Map showing difference in hydraulic head between the Madison and 

Minnelusa aquifers.....................................................................................................................15

7. Geologic cross section A–A′ shown on figure 1 ...................................................................16

8. Map showing geospatial distribution of specific conductance for the 

Minnelusa, Madison, and Precambrian aquifers in the study area...................................22

9. Map showing geospatial distribution of arsenic concentrations for the 

Minnelusa, Madison, and Precambrian aquifers in the study area...................................23

10. Boxplots of arsenic concentrations in the Minnelusa and Madison 

aquifers.........................................................................................................................................24

11. Map showing geospatial distribution of arsenic concentrations for all 

groundwater and surface-water samples in and near the study area..............................25

12. Scatter plot of arsenic concentrations in the Minnelusa aquifer and 

sampling depth from the top of the aquifer............................................................................26

13. Map showing geospatial distribution of nitrate plus nitrite for the 

Minnelusa and Madison aquifers in the study area.............................................................27

14. Graph showing results of principal component analysis and cluster 

analysis for site-averaged data plotted on the first two principal 

component axes..........................................................................................................................28

15. Map showing results of cluster analysis showing the geographic 

locations of cluster areas..........................................................................................................29

16. Graph showing principal component analysis biplot ...........................................................30

17. Map showing geospatial distribution of apparent groundwater ages 

for the Madison aquifer estimated from CFC–12...................................................................36
vi

Conversion Factors

SI to Inch/Pound

Multiply By To obtain

Length

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

Volume

liter (L) 33.82 ounce, fluid (fl. oz)

liter (L) 2.113 pint (pt)

liter (L) 1.057 quart (qt)

liter (L) 0.2642 gallon (gal)

liter (L) 61.02 cubic inch (in3) 

Flow rate

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

meter per day (m/d) 3.281 foot per day (ft/d)

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

°F=(1.8×°C)+32

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88). 

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). 

Altitude, as used in this report, refers to distance above the North American Vertical Datum of 

1988 (NAVD 88) unless otherwise specified. 

Water year (WY) 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, 2006, is called the 

“2006” water year.

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25°C).

Concentrations of chemical constituents in water in this report are given in milligrams per liter 

(mg/L) or micrograms per liter (μg/L).

Abbreviations and Acronyms

δ2H stable isotope of hydrogen

δ18O stable isotope of oxygen

CFC chlorofluorocarbon

3

H tritium

PCA principal components analysis

RPD relative percent difference

USEPA U.S. Environmental Protection Agency
Groundwater Flow, Quality (2007–10), and Mixing in the 

Wind Cave National Park Area, South Dakota

By Andrew J. Long,1 Marc J. Ohms,2 and Jonathan D.R.G. McKaskey1

1

 U.S. Geological Survey.

2

 National Park Service.

Abstract

A study of groundwater flow, quality, and mixing in relation to Wind Cave National Park in western South Dakota was 

conducted during 2007–11 by the U.S. Geological Survey in 

cooperation with the National Park Service because of waterquality concerns and to determine possible sources of groundwater contamination in the Wind Cave National Park area. A 

large area surrounding Wind Cave National Park was included 

in this study because to understand groundwater in the park, 

a general understanding of groundwater in the surrounding 

southern Black Hills is necessary. Three aquifers are of particular importance for this purpose: the Minnelusa, Madison, 

and Precambrian aquifers. Multivariate methods applied to 

hydrochemical data, consisting of principal component analysis (PCA), cluster analysis, and an end-member mixing model, 

were applied to characterize groundwater flow and mixing. 

This provided a way to assess characteristics important for 

groundwater quality, including the differentiation of hydrogeologic domains within the study area, sources of groundwater to 

these domains, and groundwater mixing within these domains. 

Groundwater and surface-water samples collected for this 

study were analyzed for common ions (calcium, magnesium, 

sodium, bicarbonate, chloride, silica, and sulfate), arsenic, 

stable isotopes of oxygen and hydrogen, specific conductance, 

and pH. These 12 variables were used in all multivariate methods. A total of 100 samples were collected from 60 sites from 

2007 to 2010 and included stream sinks, cave drip, cave water 

bodies, springs, and wells.

In previous approaches that combined PCA with endmember mixing, extreme-value samples identified by PCA 

typically were assumed to represent end members. In this 

study, end members were not assumed to have been sampled 

but rather were estimated and constrained by prior hydrologic 

knowledge. Also, the end-member mixing model was quantified in relation to hydrogeologic domains, which focuses 

model results on major hydrologic processes. Finally, conservative tracers were weighted preferentially in model calibration, which distributed model errors of optimized values, or 

residuals, more appropriately than would otherwise be the 

case. The latter item also provides an estimate of the relative 

effect of geochemical evolution along flow paths in comparison to mixing. The end-member mixing model estimated that 

Wind Cave sites received 38 percent of their groundwater 

inflow from local surface recharge, 34 percent from the upgradient Precambrian aquifer, 26 percent from surface recharge 

to the west, and 2 percent from regional flow. Artesian springs 

primarily received water from end members assumed to represent regional groundwater flow.

Groundwater samples were collected and analyzed for 

chlorofluorocarbons, dissolved gasses (argon, carbon dioxide, methane, nitrogen, and oxygen), and tritium at selected 

sites and used to estimate groundwater age. Apparent ages, or 

model ages, for the Madison aquifer in the study area indicate 

that groundwater closest to surface recharge areas is youngest, 

with increasing age in a downgradient direction toward deeper 

parts of the aquifer. Arsenic concentrations in samples collected for this study ranged from 0.28 to 37.1 micrograms per 

liter (μg/L) with a median value of 6.4 μg/L, and 32 percent of 

these exceeded 10 μg/L. The highest arsenic concentrations in 

and near the study area are approximately coincident with the 

outcrop of the Minnelusa Formation and likely originated from 

arsenic in shale layers in this formation. Sample concentrations of nitrate plus nitrite were less than 2 milligrams per liter 

for 92 percent of samples collected, which is not a concern for 

drinking-water quality. Water samples were collected in the 

park and analyzed for five trace metals (chromium, copper, 

lithium, vanadium, and zinc), the concentrations of which did 

not correlate with arsenic. Dye tracing indicated hydraulic 

connection between three water bodies in Wind Cave. 

Introduction

Established in 1903, Wind Cave and the surrounding land 

became the eighth national park in the United States and the 

first one created to protect a cave (Wind Cave National Park, 

2008). Wind Cave is located in western South Dakota (fig. 1) 

and is the fifth longest cave in the world with 218 kilometers 

(km) of accessible passages (Gulden, 2011). Groundwater 

is an important resource for the park and, in particular, for 
2 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

Wind Cave. Groundwater drips from the ceiling of the cave at 

numerous locations and exists in ponds, lakes, and streams on 

the cave floor. The water table of the Madison aquifer is accessible at the deepest part of this cave, where subterranean lakes 

exist. These lakes are in hydraulic connection with the regionally extensive Madison aquifer, which exists in the northern 

Great Plains in several States, including South Dakota, North 

Dakota, Montana, Wyoming, Saskatchewan, and Manitoba. To 

understand the hydrology and hydrochemistry of Wind Cave, 

it is essential to understand the surrounding Madison aquifer 

within which the cave exists. 

The National Park Service is concerned about water 

quality and possible sources of current (2011) or future 

groundwater contamination in Wind Cave National Park. 

To address these concerns, the U.S. Geological Survey in 

cooperation with the National Park Service conducted a study 

during 2007–11. The objective of this study was to characterize groundwater flow, quality, and mixing in the Wind Cave 

National Park area (fig. 1). This objective was carried out 

by assessing or estimating (1) groundwater gradients, flow 

directions, and transit times; (2) the occurrence and geospatial 

distributions of arsenic and nitrate and possible associations 

with trace metals; (3) groundwater sources for Wind Cave and 

sources of arsenic in the park, and (4) the relative proportions 

of different source waters contributing to Wind Cave and other 

areas of interest.

Purpose and Scope

The purpose of this report is to document results of a 

4-year study of groundwater flow, quality, and mixing within 

and surrounding Wind Cave National Park in western South 

Dakota. Analytical results from a total of 100 samples collected from 2007 to 2010 from 60 selected sites including 

stream sinks, cave drip, cave water bodies, artesian and 

shallow springs, and wells are presented. Samples collected 

for this study were analyzed for common ions, arsenic, stable 

isotopes of oxygen and hydrogen, specific conductance, and 

pH. Data from these samples were used in principal component analysis (PCA), cluster analysis, and end-member mixing, which are described in this report. Samples from selected 

sites also were analyzed for nitrate plus nitrite to determine if 

concentrations were of concern and for trace metals to assess 

possible existence of unusually high concentrations or correlations of these metals with arsenic. Samples were analyzed for 

chlorofluorocarbons (CFCs), dissolved gasses, and tritium for 

the purpose of estimating groundwater age, or residence time. 

Dye tracing using a fluorescent dye was used to determine the 

hydraulic connectivity between water bodies in Wind Cave.

This report provides information that is useful for 

understanding sources of groundwater to the park and the 

hydrologic interactions between the park’s groundwater and 

surrounding groundwater. This report will be useful for identifying possible sources of contamination if such events occur in 

the future. Water-quality concerns, primarily related to arsenic, 

are addressed, and possible sources are described. 

Description of Study Area

The study area is located in the southern part of the Black 

Hills of western South Dakota, which is a dome-type structure 

with sedimentary layers of Paleozoic age dipping radially 

outward on the flanks (fig. 1, table 1). Detailed geologic and 

hydrogeologic descriptions can be found in Gries and Martin 

(1981), Strobel and others (1999), and Redden and DeWitt 

(2008). Hydrochemical groundwater and cave studies in the 

Black Hills area include Back and others (1983), Bakalowicz and others (1987), Alexander and Davis (1989), Palmer 

and Palmer (1989), Ford and others (1993), Naus and others 

(2001), and Heakin (2004). Back (2011) investigated the 

hydrochemistry of Wind Cave National Park and interpreted 

data collected during 2007; these 2007 data are included in the 

analyses described in this report.

Underlying Paleozoic sedimentary layers and exposed 

at the central core of the Black Hills are Precambrian-age 

fractured metamorphic and igneous rocks, within which the 

Precambrian aquifer is contained (unit =; fig. 1, table 1). The 

Paleozoic Formations overlie the Precambrian rocks and are 

exposed in roughly concentric rings surrounding the central 

core of the Black Hills. The Cambrian- and Ordovician-age 

Deadwood Formation is the lowermost Paleozoic Formation 

and contains the Deadwood aquifer (unit O_d; fig. 1). The 

Devonian-age Englewood Limestone and Mississippian-age 

Madison Limestone overlie the Deadwood Formation. The 

Madison aquifer (unit MDme; fig. 1) is a mature karst aquifer 

contained within the regionally extensive Madison Limestone 

(locally called the Pahasapa Limestone) and the Englewood 

Limestone, which are referred to as the Madison Limestone 

for the remainder of this report. The Madison aquifer contains 

fractures and solution-enlarged caves, and at least 15 large 

Black Hills caves are contained within this formation (Greene 

and Rahn, 1995). Wind Cave National Park maintains a database of more than 250 caves in the Black Hills that are more 

than 8 meters (m) in length. The lower part of the Madison 

Limestone and the underlying Englewood Limestone generally 

have lower permeability than the upper part of the Madison 

aquifer in the Black Hills (Greene, 1993). Overlying the 

Madison Limestone is the Pennsylvanian- and Permian-age 

Minnelusa Formation (fig. 1), which contains the Minnelusa 

aquifer. The Minnelusa Formation is composed of interbedded sandstone, limestone, dolostone, and shale, with solution openings in carbonate layers including caves as much as 

1,500 m in length (table 1). At the base of the Minnelusa Formation is a red clay shale that varies between 0 and 15 m thick 

in some areas of the Black Hills and is a residual weathered 

soil developed on the surface of the Madison Limestone (Cattermole, 1969; Gries, 1996). Overlying the Minnelusa Formation is the Permian-age Opeche Shale, which is a confining 

unit that underlies the Permian-age Minnekahta Limestone and 

the Permian- and Triassic-age Spearfish Formation (fig. 1). 

Overlying the Spearfish Formation are formations described in 

table 1, including the Tertiary-age White River Group, which 

contains the White River aquifer that overlies the Madison 
Figure 1. Study area showing hydrogeologic units and potentiometric surface of the Madison aquifer (geology modified from Strobel 

and others, 1999).

Study area

SOUTH DAKOTA

Madison Limestone outcrop

Study area

Rapid City

Approximate areal extent of 

Madison Limestone in United States 

(Downey, 1986)

Canyon

Creek

Beaver

Creek

Fall

River

Cheyenne

River

Creek

Highland

Angostura

Reservoir

Red

A

A′

Po

QT

QT

QT

KJ

KJ

KJ

Pmk

MDme

MDme

^Ps

^Ps

P*m

P*m

P*m

=

O_d

WIND CAVE

NATIONAL PARK

RR

PP

WOO

SZE

MOR

GRE

WIL

PEK

PAL

MYR

MEY LEF

INM

HUN

HAL

FRA

CRA

COL

BOW

PW1

WCL

SVE

STR

PW2

MIL

KAI

DP3

BOG

CON

SWsp

BRsp

SLsp

KIR1

MILN

KIR2

NCsp HSsp

BCsp

WTHL

HBsp

EPsp

CBsp

RGPsp

IRIsp

BEVcr

BRNsp

WITsp

MNKsp

KIDsp

HSIsp

COOsp

CASsp

HIGHcr

Md7–11

WCsp

EMsp

DUR

FER

DP2

DP1

1,050

1,450

1,250

1,400

1,300

1,350

1,500

1,550

1,000

1,600

1,200

1,150

1,100

1,250

1,200

1,150

1,100

PARsp

Wind Cave National Park boundary

Hydrologic features with site labels

Springs—Tail indicates direction

Madison aquifer potentiometric contour—Shows altitude of flow

at which water level would have stood in tightly cased 

wells (1956–2009). Dashed where approximately 

located. Contour interval 50 meters. Datum is North 

American Vertical Datum of 1988

Line of geologic cross section

Apparent groundwater-flow direction in Madison aquifer

0 2.5 5 MILES

0 2.5 5 KILOMETERS

103°40’ 103°30’ 103°20’

43°40’

43°30’

43°20’

KJ

MDme

Pmk

Po

QT

Cretaceous-age and Jurassic-age formations

Madison (Pahasapa) and Englewood Limestones

Deadwood Formation

Precambrian rocks

Minnelusa Formation

Minnekahta Limestone

Opeche Shale

Quaternary-age and Tertiary-age formations

Spearfish Formation

EXPLANATION

Base from U.S. Geological Survey 

digital data, 1997,1:100,000

Universal Transverse Mercator projection, 

Zone 13 

Stuctural features

Hydrogeologic units

Geology modified from Strobel and others, 1999

1,100

A A′

MIL

INM

WOO

CASsp

WCsp

WCL

BEVcr

Anticline—Showing trace of axial plane

Syncline—Showing trace of axial plane

Cave site

Stream sink

Area shown on figure 2 and approximate location of 

Wind Cave

QT

KJ

Pmk

Wells

Artesian spring

Possible artesian spring

Shallow or unknown 

spring type

Madison aquifer

Minnelusa aquifer

Precambrian aquifer

CBsp

P*m

^Ps

=

O_d

O_d

^Ps

Introduction 3
Table 1. Description of hydrogeologic units.

[Summarized from Strobel and others, 1999; Redden and DeWitt, 2008]

Unit label 

(fig. 1) Formation and description

Aquifer name or 

hydrogeologic 

description

Pore water type Thickness 

(meters) Age

Qt Alluvium, colluvium, gravel, claystone, 

poorly indurated sandstone, conglomerate

Unconsolidated 

aquifers

Intergranular 0–140 Quaternary and 

Tertiary.

KJ Undifferentiated shale, limestone, 

sandstone, conglomerate, siltstone, 

claystone, gypsum

Aquifers and confining unitsIntergranular, fractures 800–2,300 Cretaceous and 

Jurrassic.

^` Spearfish Formation - shale with interbedded sandstone, siltstone, and 

gypsum

Low permeability in 

generala

Fractures, intergranular, 

dissolved gypsum

110–240 Triassic and Permian.

Pmk Minnekahta Limestone Minnekahta aquifer Fractures, solution 

openings

10–20 Permian.

Po Opeche Shale Confining unit Intergranular 10–50 Permian.

P*m Minnesula Formation - interbedded sandstone, limestone, dolostone, and shale

Minnelusa aquifer Fractures, intergranular, 

solution openings

110–360 Permian and Pennsylvanian.

MDme Madison (Pahasapa) and Englewood 

Limestones - also contains dolostone

Madison aquifer, 

mainly in upper 

part

Solution openings, 

fractures

90–320 Mississippian and 

Devonian.

O_d Deadwood Formation - glauconitic sandstone, shale, siltstone, and conglomerate

Deadwood aquifer Fractures, intergranular 0–150 Ordovician and 

Cambrian.

= Fractured metamorphosed quartzite and 

metagraywacke with isolated areas of 

granite and pegmatite

Precambrian aquifer Fractures Unknown Precambrian.

a

 Except for fractured areas and areas of dissolved gypsum cavities.

4 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

and Minnelusa aquifers in some areas and might contribute 

recharge to these aquifers. 

Wind Cave is located in the southeastern Black Hills, 

where sampled cave sites consist of cave drip (sites DP1, DP2, 

DP3) and subterranean water bodies (sites WCL, WTHL, 

PP, and RR; figs. 1 and 2, table 2). Land-surface altitudes in 

the study area range from about 1,700 m above the North 

American Vertical Datum of 1988 (NAVD 88) in the northwest to about 1,000 m in the southeast, and streams generally 

flow to the south and southeast (fig. 1). Surface recharge to 

the Minnelusa and Madison aquifers (units P*m and MDme; 

fig. 1) occurs on outcrop areas of the Minnelusa and Madison Formations. Additionally, streams flowing across these 

outcrop areas sink, fully or partially, into solution openings 

and fractures, primarily into the Madison aquifer and secondarily into the Minnelusa aquifer. Highland Creek flow rates 

at site HIGHcr (fig. 1) ranged from 0.02 to 0.05 cubic meters 

per second (m3/s) from 2002 to 2010 [30 measurements during this time; Wind Cave National Park written commun., 

(2010)]. Daily streamflow measurements for Beaver Creek at 

station BEVcr from 1990 to 2009 ranged from 0 to 2.4 m3/s 

with a mean of 0.06 m3/s (U.S. Geological Survey, 2011). The 

watersheds upstream from the Beaver Creek and Highland 

Creek (site HIGHcr) sites are almost entirely within Precambrian rocks. 

Collectively, artesian springs are a large source of 

groundwater discharge in the study area. Eight artesian springs 

are located in the southeast part of the study area (fig. 1, 

table 2), including five along the Fall River (sites HBsp, 

HSIsp, KIDsp, MNKsp, EPsp), two near the southern boundary of the study area (sites CASsp and COOsp), and one 

near Beaver Creek (site BCsp) at the eastern boundary. 

Flow from Cascade Springs (site CASsp) ranged from 0.37 

to 0.71 m3/s with a mean of 0.55 m3/s from 1976 to 1995 

(station 06400497; U.S. Geological Survey, 2011). 

Artesian springs generally emerge from or near outcrop 

areas of the Spearfish Formation (fig. 1), which generally 

has low permeability because of high shale content but also 

has flowing groundwater in fractures, cavities created by 

dissolved gypsum, and vertical breccia pipes. According to 

Hayes (1999), the throats of artesian springs in the southern 

Black Hills probably are breccia pipes that allow groundwater from deep bedrock aquifers to emerge from overlying 

formations. Cascade Springs (site CASsp), Cool Spring (site 
Paleo karst surface

Water table 

Altitude above North American Vertical Datum of 1988

METERS

NORTHWEST SOUTHEAST

VERTICAL EXAGGERATION X0

DP3 PP DP1 DP2 WTHL RR WCL

B

1,000

1,100

1,200

1,300

Land surface

MDme

P*m

103°29’30” 103°29’ 103°28’30”

43°33’30”

43°33’

43°32’30”

0 250 500 METERS

0 1,000 2,000 FEET

A

EXPLANATION

Quaternary-age and Tertiary-age 

formations

Minnelusa Formation

Madison (Pahasapa) and 

Englewood Limestones

Mapped cave passage 

(Horrocks, 2009)

Cave sampling site and label 

(table 2)

MDme

QT

RR

PP

WCL

DP2

DP1

WTHL

WCL

Madison aquifer potentiometric 

contour—Shows altitude at 

which water level would 

have stood in tightly cased 

wells (1956–2009). Contour 

interval 10 meters. Datum is 

North American Vertical 

Datum of 1988

1,110

1,150

1,140

1,160

1,130

1,170

1,120

1,180

MDme

QT

QT

DP3

1,110

0 250 500 METERS

0 1,000 2,000 FEET

Hydrogeologic units

Geology modified from Strobel

and others, 1999

P*m

P*m

P*m

P*m

Figure 2. Mapped passages of Wind Cave and sampled sites shown in (A) plan view and (B) as a generalized hydrogeologic crosssection projected onto a single vertical plane (modified from Horrocks, 2009).

Introduction 5
Table 2. Sampled cave sites and springs.

[∆h, estimated height in meters (m) of the Madison aquifer hydraulic head above (positive values) that of the Minnelusa aquifer; NAVD 88, North American 

Vertical Datum of 1988; --, not applicable]

Site name Descriptive name Source of flow Hydrogeologic 

domain ∆h (m) Altitude of site, in meters above NAVD 88

Cave drip sites

DP1 Cave drip 1 (C53) Madison aquifer East -- --

DP2 Cave drip 2 (UD17) Madison aquifer East -- --

DP3 Cave drip 3 (NP38A) Madison aquifer East -- --

Cave water body sites

WCL Windy City Lake Madison aquifer East -- 1,105a

WTHL What the Hell Lake Madison aquifer East -- 1,127

PP Petey’s puddle Madison aquifer East -- --

RR Rebel River Madison aquifer East -- 1,118

Artesian spring sites

HBsp Hot Brook Spring Minnelusa aquiferb Artesian 1 -20 1,106

HSIsp Hot Springs Intake Spring Madison aquiferc Artesian 1 10 1,065

KIDsp Kidney Spring Madison aquiferc Artesian 1 20 1,066

MNKsp Minnekahta Spring Madison aquiferc Artesian 1 20 1,079

EPsp Evans Plunge Springd Madison aquiferc Artesian 1 10 1,063

BCsp Beaver Creek Spring Madison aquiferc Artesian 2 50 1,260

CASsp Cascade Springs Madison aquiferc Artesian 2 10 1,049

COOsp Cool Spring Madison aquiferc Artesian 2 20 1,052

BRsp Boland Ridge Spring Unknowne Artesian 2 40 1,127

SWsp Stairway Spring Unknowne Artesian 2 10 1,143

CBsp Cold Brook Spring Unknowne Artesian 2 -20 1,127

Shallow spring sites

PARsp Parker Spring White River aquifer East 30 1,269

HSsp Horse Shelter Spring Minnelusa aquifer East -60 1,207

NCsp Negro Canyon Spring Minnelusa aquifer East -40 1,184

BRNsp Brown Spring Minnelusa aquifer West -170 1,378

EMsp Elk Mountain Spring Minnelusa aquifer West -110 1,330

WCsp Woodcock Spring Minnelusa aquifer West -140 1,293

WITsp Witch Spring Minnelusa aquifer West -90 1,409

IRIsp Irish Spring Precambrian aquifer PC -- 1,645

RGPsp RG Pegmatite Spring Precambrian aquifer PC -- 1,351

SLsp Southerland Spring Precambrian aquifer PC -- 1,621

a

 Altitude at which staff gage equals zero (surveyed May 28, 2008).

b

 Assumed to flow primarily from Minnelusa aquifer but could include water from other aquifers.

c

 Assumed to flow primarily from Madison aquifer but could include water from other aquifers.

d

 No sample available.

e

 Possibly artesian flowing from Madison or Minnelusa aquifer or both.

6 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota
Methods 7

COOsp), Hot Brook Spring (site HBsp), Evans Plunge Spring 

(site EPsp), and Beaver Creek Spring (site BCsp) are considered artesian and probably flow primarily from the Madison 

aquifer (Rahn and Gries, 1973; Back and others, 1983; Hayes, 

1999; Naus and others, 2001; Driscoll and others, 2002). 

Consistent with these previous studies identifying the Madison 

aquifer as the primary source of artesian springs is an assessment of vertical hydraulic-head gradients described in this 

report, where the Madison aquifer was estimated to be higher 

than in the Minnelusa aquifer for all artesian springs except 

Hot Brook Spring (table 2).

In addition to the previously classified springs, Hot 

Springs Intake Spring (site HSIsp) and Kidney Spring 

(site KIDsp) were classified in this study as artesian (previously unclassified) because of similarity in temperature and 

hydrochemistry to those of the other artesian springs near 

the Fall River (fig. 1). Three springs (sites BRsp, SWsp, and 

CBsp) are not known to be artesian but are hydrochemically 

and geologically similar to known artesian springs, and thus 

the Madison aquifer and possibly the Minnelusa aquifer might 

be a source of flow for these springs (table 2). Also, breccia 

pipes that do not extend to the land surface probably exist in 

the study area and facilitate groundwater exchange between 

the Madison, Minnelusa, and possibly other overlying aquifers 

(Brobst and Epstein, 1963; Hayes, 1999). 

Methods

Assessment of hydraulic gradients and flow direction 

were used in interpreting hydrochemical analyses. Plotting 

the geospatial distributions of arsenic concentrations, nitrate 

plus nitrite concentrations, specific conductance values, and 

groundwater age were useful for characterizing hydrochemical 

differences and gradients across the study area and provided 

supplemental information for assessing groundwater flow. 

Multivariate methods to estimate groundwater mixing consisted of principal component analysis (PCA), cluster analysis, 

and end-member mixing applied to hydrochemical data. Application of these multivariate methods presented in this report is 

a summary of results described by Long and Valder (2011).

Sample Collection and Hydrochemical Data

Sites that were sampled for this study include stream 

sinks; cave drip; cave water bodies; artesian springs primarily 

flowing from the Madison aquifer; shallow springs flowing 

from the White River, Minnelusa, and Precambrian aquifers; 

and wells open to the Minnelusa, Madison, and Precambrian 

aquifers (fig. 1, table 3). A total of 100 samples were collected 

from 60 sites from 2007 to 2010, and 93 percent of the sites 

were sampled at least once during 2009 and 2010. Multiple 

samples were collected during different months or years for 

19 sites, with as many as 5 samples per site from 2007 to 

2010, and were used to assess seasonal and annual variability. Five samples were collected from 5 of the 19 sites (four 

samples during 2007 and one during 2009), and 2 to 4 samples 

were collected from 2007 to 2009 for the other 14 sites. 

Samples collected for this study were analyzed for common ions (calcium, magnesium, sodium, bicarbonate, chloride, silica, and sulfate), arsenic, stable isotopes of oxygen 

(δ18O) and hydrogen (δ2H), specific conductance, and pH. 

These 12 variables were used in principal component analysis (PCA), cluster analysis, and end-member mixing. Also, 

samples collected during 2007 were analyzed for nitrate plus 

nitrite (table 3). Samples analyzed for chlorofluorocarbons 

(CFCs), dissolved gasses (argon, carbon dioxide, nitrogen, and 

oxygen), and tritium (3H) were collected at selected sites in 

the study area (table 3) for the purpose of estimating groundwater age, or residence time. Hydrochemical data for all sites 

described in this report as well as other sites in the study area, 

including historical data, are available from the National Water 

Information System (U.S. Geological Survey, 2011). 

Samples were collected according to methods described 

in U.S. Geological Survey (variously dated). Samples were 

analyzed for common ions and arsenic by the U.S. Geological Survey National Water Quality Laboratory in Lakewood, 

Colorado, using methods described by Fishman and Friedman 

(1989), Fishman (1993), and Garbarino and others (2006). 

Values of δ18O and δ2H were determined by the U.S. Geological Survey Reston Isotope Laboratory in Reston, Virginia, 

using a gaseous hydrogen equilibration procedure described 

by Révész and Coplen (2008a, 2008b). Samples were analyzed 

for CFCs and dissolved gasses at the Reston Chlorofluorocarbon Laboratory in Reston, Virginia. CFCs were analyzed using 

a purge-and-trap gas chromatography procedure (Shimadzu 

GC-8AIE) with an electron capture detector, and dissolved 

gases (argon, carbon dioxide, nitrogen, and oxygen) were 

determined by gas chromatography (Hewlett Packard model 

5890; http://water.usgs.gov/lab/). Samples were analyzed for 

tritium at the Tritium Laboratory in Menlo Park, California, by 

electrolytic enrichment and liquid scintillation (Thatcher and 

others, 1977).

Quality-control samples consisted of 12 pairs of replicate 

samples and 5 field-equipment blank samples. The relative 

percent difference (RPD) is defined as the difference between 

the replicate and sample values divided by the sample value 

times 100. The RPDs for each variable for each replicate pair 

was 6 percent or less for 96 percent of the data. Larger RPD 

values resulted from one sodium pair (14 percent RPD), one 

silica pair (9 percent RPD), and two arsenic pairs (11 and 

23 percent RPDs). The largest RPD (23 percent) was for a 

replicate pair with low arsenic concentrations of 0.25 and 0.28 

μg/L. The conservative tracers, chloride, δ18O, and δ2H, had 

RPDs of less than 3, 1, and 1 percent, respectively. Laboratory analyses of all field-equipment blank samples were below 

detection limits.
Table 3. Water-quality sampling sites and constituents analyzed in samples. [SC, specific conductance; CFC, chlorofluorocarbons; --, not applicable or not analyzed] Site name Descriptive name Station number Station name Source aquifer Number of samplesa Constituents analyzed in sampl

Common ions, arsenic, stable iso- topes, SC, pH Nitrate plus nitrite Trace metals Tritium C

Stream sink sites BevCr Beaver Creek sink 06402430 Beaver Creek near Pringle, S. Dak. -- 3 Yes Yes Yes Yes 

HIGHcr Highland Creek sink 433745103261900 Highland Creek above Madison outcrop near Pringle, S. Dak. -- 5 Yes Yes -- -- 

Cave drip sites DP1 Cave drip 1 (C53) 433302103281507 6S 5E12DBAB7 Madison 2 Yes Yes -- -- 

DP2 Cave drip 2 (UD17) 433302103281508 6S 5E12DBAB8 Madison 3 Yes Yes Yes -- DP3 Cave drip 3 (NP38A) 433302103281509 6S 5E12DBAB9 Madison 3 Yes Yes Yes Yes 

Cave water body sites PP Petey’s puddle 433302103281504 6S 5E12DBAB4 Madison 1 Yes Yes -- -- 

RR Rebel River 433302103281506 6S 5E12DBAB6 Madison 1 Yes Yes -- -- WCL Windy City Lake 433302103281501 6S 5E12DBAB Madison 2 Yes Yes -- -- WTHL What the Hell Lake 433302103281502 6S 5E12DBAB2 Madison 2 Yes Yes -- Yes Y

Artesian spring sites HBsp Hot Brook Spring 432703103302801 7S 5E10DCBA Minnelusab 5 Yes Yes Yes Yes Y

BCsp Beaver Creek Spring 433128103223401 6S 6E14CDB Madisonc 5 Yes Yes -- Yes YCASsp Cascade Springs 432006103330501 8S 5E20CDAB Madisonc 3 Yes -- -- Yes YCOOsp Cool Spring 432028103331601 8S 5E20BDCB Madisonc 1 Yes -- -- Yes YHSIsp Hot Springs Intake Spring 432632103285302 7S 5E14DDDA Madisonc 5 Yes Yes -- -- YKIDsp Kidney Spring 432605103285401 7S 5E14DDD Madisonc 1 Yes -- -- Yes YMNKsp Minnekahta Spring 432605103290901 7S 5E14DCD Madisonc 1 Yes -- -- Yes YBRsp Boland Ridge Spring 433525103224401 5S 6E26BBCD Unknownd 1 Yes -- Yes -- CBsp Cold Brook Spring 432744103293401 7S 5E11BAAB Unknownd 1 Yes -- -- -- SWsp Stairway Spring 432849103283201 6S 5E36CDBB Unknownd 1 Yes -- -- -- 
Site 

name Descriptive name Station number Station name Source aquifer Number of samplesa

Constituents analyzed in sampl

Common ions, 

arsenic, 

stable isotopes, 

SC, pH

Nitrate 

plus nitrite

Trace 

metals Tritium C

Shallow spring sites

PARsp Parker Spring 433717103235401 5S 6E15BBAC White River 1 Yes -- Yes -- BRNsp Brown Spring 433137103342101 6S 5E18CABD Minnelusa 1 Yes -- -- -- EMsp Elk Mountain Spring 433332103291801 6S 5E 2ACBD Minnelusa 1 Yes -- Yes -- HSsp Horse Shelter Spring 433258103270801 6S 6E 7BAAC Minnelusa 1 Yes -- -- -- IRIsp Irish Spring 434249103370401 4S 4E11CCBB Minnelusa 1 Yes -- -- -- NCsp Negro Canyon Spring 433312103264701 6S 6E 6DCAA Minnelusa 1 Yes -- Yes -- WCsp Woodcock Spring 433056103322201 6S 5E21BCBC Minnelusa 1 Yes -- -- -- WITsp Witch Spring 433611103335801 5S 4E35DDBC Minnelusa 1 Yes -- -- -- RGPsp RG Pegmatite Spring 433551103291901 5S 5E23DBCD Precambrian 1 Yes -- Yes -- SLsp Southerland Spring 434020103350101 4S 4E25DB Precambrian 1 Yes -- -- -- 

Well sites

BOW -- 432555103323201 7S 5E20AACA Minnelusa 1 Yes -- -- -- COL -- 432727103390201 7S 4E 9BACA Minnelusa 1 Yes -- -- -- CRA -- 432846103280501 6S 5E36DCBC Minnelusa 1 Yes -- -- -- FER -- 432437103305701 7S 5E27CCCD Minnelusa 1 Yes -- -- -- FRA -- 432437103305701 7S 5E27CCCD Minnelusa 1 Yes -- -- -- HAL -- 432720103303701 7S 5E15BABB Minnelusa 1 Yes -- -- -- HUN -- 433034103284701 6S 5E23DB Minnelusa 4 Yes Yes -- Yes YINM -- 432332103314801 7S 5E33ABDD Minnelusa 1 Yes -- -- -- KIR2 -- 433420103374901 5S 4E34BDDB Minnelusa 1 Yes -- -- -- LEF -- 433215103464401 6S 3E 5CCD Minnelusa 1 Yes -- -- -- MEY -- 433215103365801 6S 4E11CCDB Minnelusa 1 Yes -- -- -- MILN -- 432806103330801 8S 5E 5CADD Minnelusa 1 Yes -- -- -- MYR -- 433003103420701 7S 3E36CBCC Minnelusa 1 Yes -- -- -- PAL -- 432806103284101 7S 5E 1CBCC Minnelusa 1 Yes -- -- -- PEK -- 432852103264401 6S 6E31DBDA Minnelusa 1 Yes -- -- -- 

Table 3. Water-quality sampling sites and constituents analyzed in samples.—Continued[SC, specific conductance; CFC, chlorofluorocarbons; --, not applicable or not analyzed]
Site name Descriptive name Station number Station name Source aquifer Number of samplesa Constituents analyzed in sampl

Common ions, arsenic, stable iso- topes, SC, pH Nitrate plus nitrite Trace metals Tritium C

Well sites—Continued WIL -- 433141103390901 6S 4E16CABB Minnelusa 1 Yes -- -- -- 

BOG -- 432858103334201 6S 5E31DA Madison 2 Yes Yes -- Yes YCON -- 433326103352001 6S 4E 1DB Madison 2 Yes Yes -- Yes YKAI -- 433114103281601 6S 5E24BAAA Madison 2 Yes Yes -- -- Md7–11 -- 433115103251401 6S 6E21BBBB (CU91A) Madison 1 Yes Yes -- Yes YMIL -- 432340103421501 7S 3E36CBDC Madison 2 Yes Yes -- -- YPW1 -- 433311103263101 6S 6E 6DDA Madison 2 Yes Yes -- Yes YPW2 -- 433311103263102 6S 6E 6DDA2 Madison 2 Yes Yes -- Yes YSTR -- 433150103230501 6S 6E15ABDD Madison 5 Yes Yes -- Yes YSVE -- 432825103391201 7S 4E 4BAC Madison 1 Yes Yes -- Yes YDUR -- 433658103332301 5S 5E17BCDB Precambrian 1 Yes -- -- -- GRE -- 433701103323401 5S 5E17ACDD Precambrian 1 Yes -- -- -- KIR1 -- 433821103360901 5S 4E 2DDBD Precambrian 1 Yes -- -- -- MOR -- 433635103354301 5S 4E13CCAC Precambrian 1 Yes -- -- -- SZE -- 433718103333101 5S 5E17BBBA Precambrian 1 Yes -- -- -- WOO -- 433636103343901 5S 5E18CCAC Precambrian 1 Yes -- -- -- 

a Not including quality-control replicate samples. b Assumed to flow primarily from Minnelusa aquifer but could include water from other aquifers. c Assumed to flow primarily from Madison aquifer but could include water from other aquifers. d Possibly artesian flowing from Madison or Minnelusa aquifer or both. Table 3. Water-quality sampling sites and constituents analyzed in samples.—Continued [SC, specific conductance; CFC, chlorofluorocarbons; --, not applicable or not analyzed]
Methods 11

Principal Component and Cluster Analyses

Principal component analysis (PCA) is a linear transformation of data in multidimensional space, where the transformed axes, or principal components, align with the greatest 

variances in the data (Davis, 2002). Each principal component 

is a newly created variable, which is a linear combination of 

all original variables. PCA is a method that is used to graphically plot complex multivariate datasets and elucidate data patterns that otherwise might not be noticed. The term “scores” 

refers to the values of the new variables in the transformed 

space, and by plotting the data points as scores in this space, 

sample relations and groupings may become evident. PCA 

commonly is used to identify extreme-value points, which 

might be considered as possible end members (Davis, 2002).

The assignment of data points to a specified number of 

groups, or clusters, based on similarity of data is referred to as 

cluster analysis. The method described in this report partitions 

the data points by iteratively assigning each data point to a 

cluster that minimizes the sum of Euclidian distances between 

data points and the nearest cluster centroid (Seber, 1984; 

Spath, 1985). The scores from the PCA were used as the data 

from which clusters were generated to reduce the clustering 

error caused by data error or multicollinearity (Suk and Lee, 

1999).

End-Member Mixing

For an end-member mixing analysis, it is assumed that 

each water sample consists of water from one or more end 

members in varying proportions. An end member is defined 

as water having a characteristic geochemical signature that 

best represents a source of groundwater inflow to the system. 

An end member represents the hydrochemistry of a particular source of groundwater inflow, such as recharge within 

the study area or groundwater flowing into the study area. In 

some cases, an end member might be a point source of inflow, 

such as a sinking stream; in other cases, it might represent the 

integration, or characteristic hydrochemical signature, of a distributed source, such as areally distributed recharge or regional 

groundwater inflow. A two end-member model adapted from 

Fritz and others (1976) is described as

c=f1E1+f2E2 ˆ , (1) 

where cˆ is the concentration of a mixed water sample, f

1

 and f

2

are the fractions, or mixing proportions, of end-members 1 and 

2, respectively, and E1 and E2 are the respective end-member 

concentrations. 

A common approach in applying an end-member mixing 

model is to collect samples from assumed end-member waters 

and to then determine the mixing proportion, or contribution, 

of each end member in samples assumed to contain mixed 

water. In this study, it was not assumed that end members 

had been sampled, but rather these were estimated by inverse 

modeling using a generalized form of equation 1 that allows 

for any number of end members and variables:

ci,j= ∑ f

i,k

Ej,k

n

k=1

, (2)

where ci,j is the concentration of variable j for site i; f

i,k is the 

fraction, or mixing proportion, of end-member k that is associated with site i; and Ej,k is the end-member concentration for 

variable j and end-member k. Equation 2 was programmed 

in Fortran, and the mixing proportions f

i,k and end-member 

hydrochemical values Ej,k were estimated by inverse modeling 

using the parameter optimization software, PEST (Doherty, 

2005), which uses optimization methods described by Levenberg (1944) and Marquardt (1963). This process began with 

user-specified initial estimates for the values of f

i,k and Ej,k. 

Then, the calculated concentrations cˆ

i,j

 were compared to 

observed values ci,j, and the differences, or residuals, between 

calculated and observed values ci,j −ci,j ˆ were minimized by 

optimizing the values of f

i,k and Ej,k iteratively. New residuals were calculated for each iteration, and f

i,k and Ej,k were 

adjusted for the next iteration until no further reduction of 

residuals occurred.

The primary limitation of this model is that hydrochemical evolution of groundwater along a flow path is neglected. 

For the current study, this limitation was diminished by 

weighting the calibration data for conservative tracers more 

heavily than for other variables during inverse modeling. 

Groundwater Age Dating

Samples were collected and analyzed for CFCs and 

tritium for the purpose of estimating groundwater age, or the 

amount of time that a sampled groundwater has been out of 

contact with the atmosphere. This also is known as groundwater residence time and is important because it provides 

estimates of groundwater transit times, if greater than about 

5 to 10 years. The CFCs are anthropogenic tracers that are 

present in the atmosphere and have become assimilated with 

rainwater and surface water (Cook and others, 1996; Oster and 

others, 1996; Plummer and Busenberg, 2000). The CFCs then 

enter groundwater with infiltrating precipitation or sinking 

streams. Groundwater age can be estimated by comparing concentrations in groundwater samples to historical atmospheric 

concentrations for different CFC species, including CFC–11, 

CFC–12, and CFC–113. The CFCs in water exposed to the 

atmosphere become equilibrated with atmospheric concentrations, but in groundwater that is not in contact with the open 

atmosphere, CFCs generally remain at the concentration of 

recharge water, except in reducing environments. Atmospheric 

tritium concentrations in past decades were elevated when 

CFC concentrations were relatively low, and both of these 

were at low concentrations or not present in the atmosphere 

before about 1950 (fig. 3). 
12 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

Groundwater Flow, Quality, and Mixing 

Assessments

Results of this study are described first in relation to 

general groundwater flow, the understanding of which is necessary for interpreting the results of methods applied to hydrochemical data. This assessment consists of a description of 

groundwater hydraulic gradients and flow directions, sources 

and flow rates of springs, and dye tracing. Potentiometric 

maps of the Madison and Minnelusa aquifers (figs. 1 and 4, 

respectively) were constructed and used to estimate general 

groundwater-flow directions, horizontal hydraulic gradients 

in the Madison and Minnelusa aquifers, and vertical hydraulic 

gradients between these two aquifers. Next, the geospatial distributions and other relations of water-quality constituents in 

the study area are described. Geospatial distributions of hydrochemical data primarily indicated differences between surface 

recharge areas with young groundwater and deep aquifer areas 

with older groundwater. Finally, an assessment of groundwater 

mixing is described, where five hydrogeologic domains and 

groundwater flow between these domains were characterized 

on the basis of multivariate analyses of hydrochemical data. 

Groundwater Flow

The mapped passages of Wind Cave are almost entirely 

within the Madison aquifer’s unsaturated zone and below an 

unsaturated part of the Minnelusa aquifer (fig. 2). Infiltration 

of precipitation on the outcrop of the Minnelusa Formation 

seeps downward, enters unsaturated parts of the Madison 

aquifer, and drips from the ceiling of Wind Cave at numerous 

sites. Similarly, this type of recharge to the Madison aquifer 

from the Minnelusa aquifer is assumed also to occur elsewhere 

in the study area. Windy City Lake (site WCL; figs. 1 and 2) 

is a body of water at the deepest part of the cave and exists 

because of this hydrologic connection between the Madison 

Figure 3. Chlorofluorocarbon (CFC) and tritium concentrations in 

the atmosphere.

1940 1950 1960 1970

Year

1980 1990 2000 2010

Atmospheric chlorofluorocarbon mixing ratios

for North America (International Atomic Energy

Agency, 2006), in parts per trillion by volume

0

100

200

300

400

500

600

Tritium concentrations in precipitation in

the Black Hills, South Dakota (Putnam

and Long, 2007), in tritium units

0

10

100

1,000

10,000

CFC–12 

CFC–11 

CFC–113 

Tritium

and Minnelusa aquifers. Windy City Lake rises and declines 

with the surrounding water table as indicated by a comparison 

of water levels in the lake and well Md7–11 (fig. 5). Before 

1999, another similar lake existed in proximity to Wind City 

Lake called Calcite Lake. Sometime before the end of 2000, 

the Madison aquifer water table and the levels of both lakes 

increased in altitude, which resulted in the merging of the two 

lakes. 

What the Hell Lake (site WTHL; figs. 1 and 2) was filled 

unexpectedly in 1996 after being dry for decades (Shouse, 

2004). Wind Cave National Park staff observed this water 

body on July 18, 1996, and stated that a new pool had formed, 

which did not exist during a previous visit to the same site on 

June 12, 1996, and this site has contained water continuously 

from that time until the present (Wind Cave National Park, 

written commun., 2011). The filling of site WTHL might have 

been the result of perched groundwater in caverns above this 

site that emptied rapidly. Perched water frequently is observed 

in Black Hills caves and results from areas of impermeable 

limestone or the accumulation of clay sediments on cave floors 

(Long, 2009). Rapid outflow from a perched water body might 

have been the result of spillover through an outlet as water 

levels were rising or from the dislodgement of clay that had 

filled an outlet. Years 1995–2000 was a period in which the 

water level at site WCL was rising (fig. 5), which indicates 

relatively high recharge and infiltration rates. Groundwater in 

a karst aquifer unsaturated zone can be decades old in some 

cases (Even and others, 1986), and if perched groundwater 

above site WTHL had been in storage for decades and then 

released, this could explain why site WTHL was dry for 

decades before filling.

Groundwater Gradients and Flow Directions

A potentiometric-surface map of the Madison aquifer was 

constructed on the basis of water-level data available from 

the U.S. Geological Survey (2011) and helps to characterize 

groundwater flow (fig. 1). Apparent groundwater-flow directions are perpendicular to potentiometric contours, but these 

might not be the actual flow directions because of possible 

anisotropic permeability resulting from cave and fracture 

orientations (Greene and Rahn, 1995). Anisotropic permeability can cause flow to deviate from the apparent flow direction 

(Freeze and Cherry, 1979). Back and others (1983) described 

the general groundwater flow in the Madison aquifer for the 

Black Hills and surrounding area, indicating that groundwater 

flows from the surface recharge area in the northwestern part 

of study area to the southwest, then sweeps east and then 

northeast around the southern end of the Black Hills. This 

description generally is consistent with the apparent flow 

directions indicated by the potentiometric contours shown on 

figure 1. These apparent flow directions provide a generalization of groundwater flow in the study area and are not necessarily accurate. A low hydraulic gradient in the area of Wind 

Cave, as indicated by widely spaced contours (1,150-m to 
1,100

1,150

1,050

1,200

1,250

1,000

1,300

1,350

1,400

1,450

1,500

1,550

1,100

1,150

1,200

WIND CAVE

NATIONAL PARK

Canyon

Creek

Beaver

Creek

Fall

River

Cheyenne

River

Creek

Highland

Angostura

Reservoir

Red

Wind Cave National Park boundary

Hydrologic features

Minnelusa aquifer potentiometric 

contour—Shows altitude at which water 

level would have stood in tightly cased wells 

(1956–2009). Dashed where approximately 

located. Contour interval 50 meters. Datum 

is North American Vertical Datum of 1988

0 2.5 5 MILES

0 2.5 5 KILOMETERS

103°40’ 103°30’ 103°20’

43°40’

43°30’

43°20’

Cretaceous-age and Jurassic-age formations

Madison (Pahasapa) and Englewood Limestones

Deadwood Formation

Precambrian rocks

Minnelusa Formation

Minnekahta Limestone

Opeche Shale

Quaternary-age and Tertiary-age formations

Spearfish Formation

EXPLANATION

Hydrogeologic units

Geology modified from Strobel and others, 1999

1,100

Stream sink

Apparent groundwater-flow direction in 

Madison aquifer

Stuctural features

Anticline—Showing trace of axial plane

Syncline—Showing trace of axial plane

Area shown on figure 2 and approximate 

location of Wind Cave

QT

KJ

Pmk

Po

QT

QT

QT

KJ

KJ

KJ

Pmk

MDme

MDme

Base from U.S. Geological Survey digital data, 1997,

1:100,000

Universal Transverse Mercator projection, Zone 13 

Cave site

Springs—Tail indicates 

direction of flow

Wells

Artesian spring

Possible artesian spring

Shallow or unknown 

spring type

Madison aquifer

Minnelusa aquifer

Precambrian aquifer

KJ

MDme

Pmk

Po

QT

P*m

^Ps

=

O_d

^Ps

^Ps

^Ps

P*m

P*m

P*m O_d

O_d

=

Po

Pmk

Figure 4. Potentiometric surface of the Minnelusa aquifer.

Groundwater Flow, Quality, and Mixing Assessments 13
WCL staff gage (data from Wind Cave National Park, written commun., 2011)

WCL (U.S. Geological Survey, 2011)

Md7–11 (data from South Dakota Department of Environment and Natural Resources, 

written commun., 2011)

EXPLANATION

-4

-3

-2

-1

0

1

2

3

4

5

6

-157

-156

-155

-154

-153

-152

-151

-150

-149

-148

-147

Windy City Lake water level, in meters above land surface

7-11 MDSN water level, in meters above land surface

Year

198619871988198919901993199219911994199519961997199919982000200120022003200420052007200620082009201020112012

Figure 5. Water-level hydrographs for Windy City Lake (site WCL) and well Md7–11.

14 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

1,100-m contours; fig. 1), likely indicates anomalously high 

permeability resulting from extensive karst development.

A potentiometric-surface map of the Minnelusa aquifer 

also was constructed on the basis of water-level data available from the U.S. Geological Survey (2011). In general, the 

apparent groundwater-flow directions in the Minnelusa aquifer 

are similar to those in the Madison aquifer, except that in the 

western part of the study area the apparent flow direction is 

more westerly than in the Madison aquifer (figs. 1 and 4). The 

potentiometric surface of the Minnelusa aquifer (fig. 4) was 

subtracted from that of the Madison aquifer (fig. 1) to determine the direction and magnitude of the vertical hydraulic 

gradient (fig. 6). The resulting difference in hydraulic heads 

between the aquifers was used to estimate sources of spring 

flow. The Minnelusa aquifer has a potentiometric surface that 

is higher than that of the Madison aquifer within and near the 

outcrop of the Minnelusa Formation; farther from this outcrop, 

the Madison aquifer has the higher potentiometric surface 

(fig. 6). In places where the Madison and Minnelusa aquifers 

are connected hydraulically, groundwater flows from the 

aquifer with the higher hydraulic head into the aquifer with the 

lower hydraulic head. If breccia pipes are the throats of artesian springs as described by Hayes (1999), and if these throats 

hydraulically connect the Madison and Minnelusa aquifers, 

then the primary source of a spring would be the aquifer with 

the highest hydraulic head of the two. Artesian springs generally are located in areas where the Madison aquifer has the 

higher potentiometric surface of the two aquifers, which indicates that the Madison aquifer probably is the primary source 

of these springs.

Land-surface altitudes where Precambrian rocks are 

exposed generally are higher than within the outcrop of the 

Madison Limestone in the study area (figs. 1 and 7). Groundwater levels in the Precambrian aquifer generally are near 

the land surface and higher than in the Madison aquifer (U.S. 

Geological Survey, 2011), and this groundwater gradient indicates a possibility that groundwater might flow from the Precambrian aquifer through the Deadwood aquifer and into the 

Madison aquifer. Evidence for this includes apparent groundwater ages estimated from the CFC data for CFC–12 for sites 

CON and WTHL (table 4). The apparent age is an estimate of 

age where the entire sample is assumed to contain water of a 

single age. Well CON is located near the southwestern edge 

of the Madison Limestone outcrop (fig. 1) and penetrates the 

aquifer by about 15 m. If not for an apparent groundwater age 

of 22–26 years (table 4), groundwater at this well might be 

assumed to represent almost entirely surface recharge because 

of its location. However, the apparent age indicates that a 

large fraction of this water did not result from recent precipitation but might have originated in the upgradient Precambrian 
Canyon

Creek

Beaver

Creek

Fall

River

Cheyenne

River

Creek

Highland

Angostura

Reservoir

Red

WIND CAVE

NATIONAL PARK

RR

PP

WIL

MEY WCL

PW2

DP3

BOG

CON

MILN

KIR2

WTHL

BRNsp

WITsp

WCsp

EMsp DP2

DP1

RR

PP

WIL

MEY

INM

HAL

PW1

WCL

PW2

KAI

DP3

BOG

CON

MILN

KIR2

WTHL

HBsp EPsp

BRNsp

WITsp

MNKsp KIDsp

COOsp

CASsp

WCsp

EMsp

FER

DP2

DP1

BRsp

PARsp

NCsp STR

HSsp

BCsp

Md7–11

HUN

PEK

PAL

FRA

CRA

SWsp

CBsp

HSIsp

BOW

MYR

COL

SVE

MIL

LEF

SLsp

IRIsp

RGPsp

Wind Cave National Park 

boundary

Hydrologic features with 

site labels

Hydrogeologic units

0 2.5 5 MILES

0 2.5 5 KILOMETERS

103°40’ 103°30’ 103°20’

43°40’

43°30’

43°20’

EXPLANATION

Hydraulic head difference in meters, between the 

Madison and Minnelusa aquifers

Geology modified from Strobel and others, 1999

MIL

INM

CASsp

CBsp

WCsp

WCL Cave site

Area shown on figure 2 and 

approximate location 

of Wind Cave

Hydraulic head higher in 

Minnelusa aquifer than 

Madison aquifer

Hydraulic head higher in 

Madison aquifer than 

Minnelusa aquifer

Minnelusa Formation

Madison (Pahasapa) and 

Englewood Limestones

Less than -200

Greater than -200 to -140

Greater than -140 to -120

Greater than -120 to -60

Greater than -60 to 0

Greater than 0 to 60

Greater than 60 to 120

Base from U.S. Geological Survey digital data, 1997,

1:100,000

Universal Transverse Mercator projection, Zone 13 

Springs—Tail indicates direction

of flow

Wells

Artesian spring

Possible artesian spring

Shallow or unknown 

spring type

Madison aquifer

Minnelusa aquifer

Figure 6. Difference in hydraulic head between the Madison and Minnelusa aquifers.

Groundwater Flow, Quality, and Mixing Assessments 15
QT

Po Pmk

EXPLANATION

MDme

KJ

? ?

0

500

1,000

1,500

2,000

KJ

Pmk MDme

Po

QT

Cretaceous-age and Jurassic-age formations

Madison (Pahasapa) and Englewood Limestones

Deadwood Formation

Minnelusa Formation Precambrian rocks

Minnekahta Limestone

Opeche Shale

Quaternary-age and Tertiary-age formations

Spearfish Formation

Hydrogeologic units

Altitude above North American Vertical Datum of 1988

METERS

NORTH SOUTH

VERTICAL EXAGGERATION X5

A A′

0 2.5 5 KILOMETERS

0 2.5 5 MILES

^Ps

^Ps

P*m

P*m

O_d

O_d

=

=

Figure 7. Geologic cross section A–A′ shown on figure 1.

16 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

aquifer. Site WTHL, also located near the Madison Limestone 

outcrop, is a water body in Wind Cave (fig. 1) that is fed by 

groundwater emerging from the cave floor with an apparent 

age of 20–27 years (table 4), which also indicates the possible 

presence of water originating from the Precambrian aquifer. 

Dye Tracing

Dye tracing was conducted to determine the connectivity 

and transit times between different groundwater sites in and 

near Wind Cave. Fluorescein dye was injected into What the 

Hell Lake (site WTHL), and charcoal dye receptors and water 

samples were collected and analyzed to determine the presence and concentration of dye in Rebel River (site RR; fig. 1), 

Windy City Lake (site WCL; fig. 1), and two wells in the park 

(wells PW1 and PW2; fig. 1), all of which are hydraulically 

downgradient from site WTHL (fig. 1). A dye receptor is a 

packet of charcoal, which adsorbs fluorescent dyes in water. 

These receptors were deployed at sites and submerged in 

water for at least one month. After receptors were retrieved, 

the dye was removed by an eluent, which was then analyzed 

for the presence of dye, the concentration of which is affected 

by the dye concentration in the water during deployment and 

the duration of deployment. 

Wind Cave National Park staff deployed and collected the dye receptors and water samples and sent them to 

the Crawford Hydrology Laboratory at Western Kentucky 

University for analysis (table 5). The initial set of dye receptors were deployed on December 3, 2007. Dye receptors 

were replaced each time they were retrieved. Analyses of dye 

receptors and water samples were conducted at Crawford 

Hydrology Laboratory with a Shimadzu Model RF-5301PC 

Synchronously Scanning Spectrofluorophotometer, which can 

detect dye concentrations as low as 5 parts per trillion (http://

www.dyetracing.com). Four liters of liquid fluorescein dye 

(40-percent fluorescein by weight) were injected into What the 

Hell Lake (site WTHL) in Wind Cave on February 26, 2008. 

Visual dye was present in the water at WTHL and RR during 

a site visit on March 25, 2008. Visual dye was present in the 

water at WCL during a site visit on May 28, 2008. 

Dye tracing indicated that groundwater reached sites 

WCL and RR from the injection site (WTHL) in 28 days 

or less (table 5). Dye was detected in every dye receptor or 

sample from site WCL from March 2008 to August 2011, 

or 42 months. Assuming a straight-line flow path from site 

WTHL to site WCL (265 m), which is nearly perpendicular 

to potentiometric contours (fig. 2), the groundwater velocity 

was at least 9 meters per day (m/d), but might have been faster 

because the first sample collected from site WCL after injection was 28 days later. Residence time for dye at site WCL and 

this flow path combined was at least 42 months. Residence 

time at site WCL alone might be shorter than 42 months 

because of possible groundwater retention along the flow path, 

which could have been a source of ongoing input to this site. 

The last dye receptor retrieved from site RR was 92 days after 

injection and had an eluent concentration that was more than 

200 times higher than in eluent from any receptors retrieved 

from site WCL (table 5). Dye was not detected with certainty 
Groundwater Flow, Quality, and Mixing Assessments 17

for any of the five samples collected from wells PW1 and 

PW2 (table 5). 

Groundwater Quality

Hydrochemical data for samples collected from 60 sites 

are presented in table 12 in the “Supplemental Tables” section. 

Hydrochemical data presented in table 12 include pH, specific conductance, common ions, nitrate plus nitrite, arsenic, 

and stable isotopes of oxygen and hydrogen. Water samples 

from selected sites were analyzed for trace metals, and the 

analytical results are presented in table 6. The occurrence and 

geospatial distributions of specific conductance, nitrate plus 

nitrite, arsenic, and trace metals were assessed. Arsenic is a 

particular concern because of concentrations within the park 

that were higher than desirable for drinking-water quality. 

Specific Conductance

Specific conductance is a measure of the electrical 

conductivity of water and indicates relative dissolved-solid 

content (Hem, 1985). The geospatial distribution of specific 

conductance in groundwater samples provides a general 

overview of water quality and hydrochemical differences in 

the study area. Specific conductance was interpolated between 

sampled sites and is shown as ranges of values in the study 

area (fig. 8). Specific conductance generally is lowest in 

recharge areas for the Madison, Minnelusa, and Precambrian 

aquifers and highest in the southern part of the study area, distant from recharge areas (fig. 8). The highest specific conductance values might indicate long residence times because time 

is required to dissolve minerals in aquifer media. A correlation 

between apparent groundwater age and specific conductance 

in the Madison aquifer exists in the Rapid City area (Long and 

others, 2008; South Dakota inset map on fig. 1). The southern 

part of the study area probably represents a mixture of groundwater that originated as surface recharge within the study area 

and as regional flow from the west and northwest. 

Arsenic

Arsenic concentrations in samples collected for this 

study ranged from 0.28 to 37.1 mg/L with a median value 

of 6.4 mg/L (table 12), and 32 percent of these exceeded 

10 mg/L, which is the Maximum Contaminant Level (MCL) 

for drinking water in the United States (U.S. Environmental Protection Agency, 2010). The geospatial distribution of 

arsenic in groundwater samples for the Madison, Minnelusa, 

and Precambrian aquifers indicates that the highest arsenic 

concentrations in and near the study area are approximately 

coincident with the outcrop of the Minnelusa Formation as 

shown in figure 9, which indicates an arsenic anomaly in this 

area. Figure 9 was based on samples collected for this study 

(table 12) plus data for all other water samples available in the 

National Water Information System (U.S. Geological Survey, 

2011). The median arsenic concentration is about equal for 

the Madison and Minnelusa aquifers (fig. 10). Overall, the 

Minnelusa aquifer has slightly larger arsenic concentrations 

than the Madison aquifer (fig. 10). Where sampling sites for 

the Madison and Minnelusa aquifers are proximal, arsenic 

concentrations generally are similar (fig. 9), so the concentration differences indicated by figure 10 might result partly from 

geospatial differences in sample locations between the two 

aquifers. 

The exceptions to the association of arsenic with the outcrop of the Minnelusa Formation are samples from two wells 

open to the Precambrian aquifer (well MOR and WOO; fig. 9), 

which had arsenic concentrations of 35.2 and 12.7 mg/L, 

respectively. These concentrations, which are high relative 

to other Precambrian aquifer samples, might be the result of 

previous industrial activities in the town of Pringle (located 

at well MOR), which were the focus of U.S. Environmental 

Protection Agency (USEPA) investigations from 1991 to 2001 

(Hayhurst, 2002), and included wood preservative treatment 

with chromated copper arsenate. Soil in the Pringle area was 

contaminated with arsenic, chromium, copper, zinc, pentachlorophenol, polycyclic aromatic hydrocarbons, dioxins, and 

furans. Dioxins and furans were detected in Beaver Creek 

and its sediments downstream from the former industrial site, 

with decreasing concentrations in a downstream direction 

(Hayhurst, 2002). Heakin (2004) documented the presence 

of phenol in Beaver Creek in 2002 and 2003 in the park and 

about 2 km upstream from the western park boundary. 

The arsenic anomaly coincident with the outcrop of the 

Minnelusa Formation also exists when all groundwater and 

surface-water samples available from the National Water 

Information System (U.S. Geological Survey, 2011) in and 

near the study area are plotted (fig. 11). The area shown in 

figure 11 extends beyond the study area to show a larger 

representation of the arsenic anomaly and indicates that the 

Minnelusa and Madison aquifers have the highest arsenic 

concentrations when compared with other groundwater and 

surface-water sites in and near the southern Black Hills.

The geographic association of the arsenic anomaly with 

the Minnelusa Formation outcrop (excluding the Pringle area) 

indicates that arsenic in groundwater probably results from 

naturally occurring minerals in the marine shales of this formation. Marine shales commonly contain high concentrations 

of arsenic, which is released into the aqueous phase in aquifers 

as a result of oxidative weathering of iron-sulfide minerals, mainly pyrite (FeS2

) and arsenopyrite (FeAsS; Muloin 

and Dudas, 2005). During sulfide mineral formation, arsenic 

precipitates with iron and sulfide and is incorporated into the 

mineral structure (Muloin and Dudas, 2005). Zhu and others 

(2008) concluded that microbial sulfide production enhances 

arsenic mobilization in pyrite-bearing black shale formations. 

Solid-phase arsenic concentration was analyzed in clay, sand 

and gravel, shales, and limestones in aquifers of the Lower 

Illinois River Basin (not shown in report), where arsenic 

concentrations in groundwater were as high as 110 mg/L, and 

the highest solid-phase concentrations were in shales (Warner, 

2001). This author concluded that dark shales in the bedrock 
18 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota Groundwater Flow, Quality, and Mixing Assessments 19

Table 4. Chlorofluorocarbon (CFC) and tritium data.

[n, number of CFC samples; pptv, parts per trillion by volume; pCi/L, picocuries per liter; --, could not be estimated by this method]

Site 

name

Station number Station name Date n

Calculated atmospheric mixing 

ratio, in pptva

Apparent groundwater age, 

in yearsa Results of binary mixing modelb

Tritium, 

in pCi/L

Tritium, 

2-sigma, 

CFC– 11 CFC–12 CFC– 113 CFC–11 CFC–12 CFC–113 in pCi/L

CFC–11/CFC–

12 ratio age, 

in yearsa

Percent 

young 

water in 

mixturea,c

Number 

of samples 

used

CFC–113/

CFC–12 

ratio age, 

in yearsa

Percent 

young 

water in 

mixturea,c

Number 

of samples 

used

CFC–11/

CFC–11 

ratio age, 

in yearsa

Percent 

young 

water in 

mixturea,c

Number of 

samples 

used

Stream sink site Stream sink site

BevCr 06402430 Beaver Creek near 

Pringle, S. Dak.

04/16/2007 0 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 50.2 3.0

Cave drip site Cave drip site

DP3 433302103281509 6S 5E12DBAB9 04/25/2007 0 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 29.4 1.9

Cave water body sites Cave water body sites

WTHL 433302103281502 6S 5E12DBAB2 04/18/2007 2 196.8 439.8 55.0 24 20 20 -- -- -- -- -- -- 18 72 2 15.7 1.3

WTHL 433302103281502 6S 5E12DBAB2 07/16/2009 2 190.3 445.2 53.0 27 23 23 -- -- -- -- -- -- 20 75 2 -- --

Artesian spring sites Artesian spring sites

HBsp 432703103302801 7S 5E10DCBA 04/20/2007 2 44.3 107.3 12.3 39 39 32 -- -- -- 22 26 2 15 68 2 3.8 1.0

HBsp 432703103302801 7S 5E10DCBA 05/28/2009 2 35.5 104.9 11.1 43 41 35 -- -- -- 25 28 2 15 13 2 5.7 --

BCsp 433128103223401 6S 6E14CDB 04/17/2007 3 31.9 82.7 10.3 41 41 33 -- -- -- 21 20 3 19 63 2 4.5 1.0

BCsp 433128103223401 6S 6E14CDB 05/28/2009 2 30.2 91.7 8.6 44 42 37 -- -- -- 26 25 2 20 12 2 6.0 --

CASsp 432006103330501 8S 5E20CDAB 06/19/2009 3 24.6 60.6 6.9 45 46 38 38 36 2 24 15 3 20 10 3 4.0 --

COOsp 432028103331601 8S 5E20BDCB 06/19/2009 3 38.4 103.9 13.0 42 41 34 41 89 1 22 25 3 12 15 1 3.9 --

HSIsp 432632103285302 7S 5E14DDDA 05/21/2009 2 42.2 157.5 11.8 42 38 34 -- -- -- 29 52 2 20 16 2 -- --

KIDsp 432605103285401 7S 5E14DDD 06/19/2009 3 28.8 169.9 13.0 44 37 34 -- -- -- 29 55 3 -- -- -- .9 --

MIL 432340103421501 7S 3E36CBDC 04/08/2010 3 21.0 3.1 .0 47 64 57 -- -- -- -- -- -- -- -- -- -- --

MNKsp 432605103290901 7S 5E14DCD 05/28/2009 2 25.6 171.3 3.4 45 37 44 -- -- -- -- -- -- 30 16 2 .5 --

Well sites Well sites

HUN 433034103284701 6S 5E23DB 04/17/2007 3 129.4 283.2 35.6 31 29 24 -- -- -- 20 67 3 18 71 3 26.9 1.9

BOG 432858103334201 6S 5E31DA 04/26/2007 3 96.5 170.2 23.9 34 35 27 30 66 1 19 37 3 18 63 3 1.6 1.0

BOG 432858103334201 6S 5E31DA 07/15/2009 3 28.7 99.3 9.4 44 42 36 -- -- -- 26 28 3 13 11 2 .6 --

CON 433326103352001 6S 4E 1DB 07/15/2009 3 220.7 388.0 61.7 24 26 22 -- -- -- 18 76 2 20 86 3 29.3 --

Md7–11d 433115103251401 6S 6E21BBBB 

(CU91A)

04/20/2007 2 4.6 3.0 .0 52 61 54 -- -- -- -- -- -- -- -- -- .6 .6

PW1 433311103263101 6S 6E 6DDA 07/29/2009 2 147.3 316.1 38.3 32 29 26 -- -- -- 23 77 2 21 -- 2 21.4 --

PW2 433311103263102 6S 6E 6DDA2 07/29/2009 3 182.3 115.8 13.7 27 41 34 -- -- -- 24 29 3 21 20 1 9.2 --

STR 433150103230501 6S 6E15ABDD 04/17/2007 3 70.6 152.5 17.9 36 36 29 36 97 1 21 38 3 19 62 3 16.6 1.3

STR 433150103230501 6S 6E15ABDD 05/22/2009 2 66.0 162.2 19.3 39 38 31 -- -- -- 23 40 2 19 25 2 17.4 --

SVE 432825103391201 7S 4E 4BAC 09/02/2009 3 191.6 80.4 8.2 27 44 38 -- -- -- 26 21 3 -- -- -- 3.4 --

a

 Average of multiple samples. Age is the apparent age of the young fraction.

b

 Plummer and Busenberg (2000).

c

 Percentage younger than about 60 years.

d

 Methane present. Apparent ages represents the minimum apparent age.
Table 5. Results of laboratory analyses of the presence of fluorescein dye in charcoal dye receptors that were placed in Wind Cave 

water bodies and two wells. Dye was injected on February 26, 2008.

[ppb, parts per billion; B, background concentration; --, no sample; ND, nondetection]

Date collected Days since

 injection

Years since 

injection

Windy City Lake (WCL) Rebel River 

(RR), 

in ppb

Dye receptor eluent, Well PW1 Well PW2

in ppb

Water sample, 

in ppb

02/26/2008 0 0.0 B -- ND -- --

03/20/2008 23 .1 -- -- -- ND ND

03/25/2008 28 .1 0.85 -- 249,000 -- --

05/28/2008 92 .3 59.4 -- 93,000 -- --

07/09/2008 134 .4 168 -- -- -- --

08/04/2008 160 .4 -- -- -- B ND

09/11/2008 198 .5 -- -- -- -- ND

11/13/2008 261 .7 376 -- -- -- --

01/07/2009 316 .9 96.3 -- -- -- --

06/30/2009 490 1.3 -- -- -- -- B

05/03/2010 797 2.2 302 -- -- -- --

07/16/2010 871 2.4 261 -- -- -- --

04/25/2011 1,154 3.2 -- .52 -- -- --

06/08/2011 1,198 3.3 21.4 -- -- -- --

08/18/2011 1,269 3.5 101.5 -- -- -- --

20 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

aquifer were the likely source of arsenic in the overlying and 

adjacent glacial drift aquifer. In groundwater of the Piedmont Province of Pennsylvania (not shown in report), arsenic 

concentrations higher than 10 mg/L were the result of arsenic 

mobilization from shales, whereas the arsenic concentrations 

in the pore water of igneous, crystalline, and calcareous rocks 

typically were lower (Serfes and others, 2006; Peters and 

Burkert, 2008; Rhine and others, 2008). 

It is most likely that arsenic in the Minnelusa and Madison aquifers originates in shale layers of the Minnelusa aquifer 

and is transported downward into the Madison aquifer by 

advective flow. This is possible in areas where the hydraulic 

head in the Minnelusa aquifer is higher than in the Madison 

aquifer (fig. 6), which also is approximately coincident with 

the arsenic anomaly (fig. 9). This downward seepage is known 

to occur in the area of Wind Cave, where groundwater in the 

unsaturated zone of the Minnelusa aquifer seeps downward 

into the Madison aquifer and drips from the ceiling of the cave 

at numerous locations. Arsenic concentrations in sampled drip 

water (table 12) ranged from 24.3 to 34.2 mg/L (sites DP1, 

DP2, and DP3) and from 12.6 to 16.4 mg/L for water bodies 

in the cave (sites WCL, WTHL, PP, and RR). This indicates 

that arsenic concentrations in Wind Cave were highest for 

water that is known to originate in the Minnelusa aquifer. 

Cave drip probably contributes to cave water bodies, which 

also may receive contributions from the Precambrian aquifer 

as previously described in the “Groundwater Gradients and 

Flow Directions” section. If so, this would result in a mixture 

in the cave water bodies of groundwater from the Minnelusa 

aquifer (cave drip) and the Precambrian aquifer. The sampling site closest to the cave for the Precambrian aquifer was 

a spring (RGPsp; fig. 1), which had an arsenic concentration 

of 2.0 mg/L (table 12). Therefore, mixing could have affected 

the observed arsenic concentrations in the cave water bodies, 

which had concentrations between those of cave drip and the 

Precambrian aquifer.

It is uncertain why the arsenic anomaly is coincident 

with the Minnelusa Formation outcrop rather than confined 

aquifer areas, but might be related to weathering of shales in 

the outcrop. As Muloin and Dudas (2005) stated, weathering 

of marine shales releases arsenic into groundwater. Further, as 

described by Tuttle and others (2009), during oxidative weathering of iron-sulfide minerals in marine shales, arsenic and 

other trace elements are dispersed or redistributed in the environment by aqueous and mechanical transport. The decrease in 

arsenic concentration downgradient from the outcrop areas of 

the Minnelusa and Madison Formations indicates that mobilized arsenic is not transported large distances in the Minnelusa and Madison aquifers. The reason for this is unclear, 

and arsenic concentrations did not correlate with either pH or 

dissolved oxygen. It is possible that dissolved arsenic originates from particular shale layers in the Minnelusa Formation, 
Table 6. Trace-metal data for water samples from selected sites within Wind Cave National Park.

[μg/L, micrograms per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius; <, less than; E, estimated valuea; --, not applicable]

Site name Station number Station name Date

Arsenic, 

dissolved 

(μg/L)

Chromium, 

dissolved 

(μg/L)

Copper, 

dissolved 

(μg/L)

Lithium, 

dissolved 

(μg/L)

Vanadium, 

dissolved 

(μg/L)

Stream sink site

BevCr 06402430 Beaver Creek near 

Pringle, S. Dak.

06/25/2008 4.4 <0.12 <1 34 2.7 

Cave drip sites

DP2 433302103281508 6S 5E12DBAB8 06/26/2008 24.4 0.12 E 0.99 6 6.6 DP3 433302103281509 6S 5E12DBAB9 06/26/2008 23.8 <.12 E .54 2 6.5 

Artesian spring site

BRsp 433525103224401 5S 6E26BBCD 06/25/2008 5.6 0.38 2.4 422 19.6 

Shallow spring sites

PARsp 433717103235401 5S 6E15BBAC 06/25/2008 12.2 0.12 1.5 28 6.4 Emsp 433332103291801 6S 5E 2ACBD 06/25/2008 12 E .08 1.1 10 16.6 HSsp 433258103270801 6S 6E 7BAAC 06/26/2008 25.9 E .07 1.6 7 4.4 NCsp 433312103264701 6S 6E 6DCAA 06/26/2008 16.7 <.12 E .92 7 6 NCsp 433312103264701 6S 6E 6DCAA 06/26/2008 16.7 <.12 E .57 7 6 RGPsp 433551103291901 5S 5E23DBCD 06/25/2008 1.7 <.12 <1 37 .72 Maximum Contaminant Level (MCL), in μg/Lb 10 100 1,300 -- -- 

a Value less than the lowest calibration standard (Childress and others, 1999).b From U.S. Environmental Protection Agency (2010).
Canyon

Creek

Beaver

Creek

Fall

River

Cheyenne

River

Creek

Highland

Beaver

Creek

Highland

Angostura

Reservoir

Red Canyon

Creek

WIND CAVE

NATIONAL PARK

Hydrologic features

0 2.5 5 MILES

0 2.5 5 KILOMETERS

103°40’ 103°30’ 103°20’

43°40’

43°30’

43°20’

Geology modified from Strobel and others, 1999

Cave site

Stream sink

Wind Cave National Park 

boundary

Specific conductance, in microsiemens Hydrogeologic units

per centimeter at 25 degrees Celsius

Area shown on figure 2 and 

approximate location 

of Wind Cave

Minnelusa Formation

Madison (Pahasapa) and 

Englewood Limestones

Precambrian rocks and

Deadwood Formation

EXPLANATION

Less than or equal to 500

Greater than 500 to 1,000

Greater than 1,000 to 1,500

Greater than 1,500 to 2,000

Greater than 2,000 to 2,500

Greater than 2,500 to 3,000

Base from U.S. Geological Survey digital data, 1997,

1:100,000

Universal Transverse Mercator projection, Zone 13 

Springs—Tail indicates direction of flow

Wells

Artesian spring

Possible artesian spring

Shallow or unknown 

spring type

Madison aquifer

Minnelusa aquifer

Precambrian aquifer

Figure 8. Geospatial distribution of specific conductance for the Minnelusa, Madison, and Precambrian 

aquifers in the study area. (All relevant sites with specific conductance data available from the National Water 

Information System [U.S. Geological Survey, 2011] are included in map.)

22 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota
Figure 9. Geospatial distribution of arsenic concentrations for the Minnelusa, Madison, and Precambrian 

aquifers in the study area. (All relevant sites with arsenic data available from the National Water Information 

System [U.S. Geological Survey, 2011] are included in map.)

Springs—Tail indicates direction of flow

Wells

Artesian spring

Possible artesian spring

Shallow or unknown spring type

Madison aquifer

Minnelusa aquifer

Precambrian aquifer

Canyon

Creek

Beaver

Creek

Fall

River

Cheyenne

River

Creek

Highland

Angostura

Reservoir

Red

WIND CAVE

NATIONAL PARK

0 2.5 5 MILES

0 2.5 5 KILOMETERS

103°40’ 103°30’ 103°20’

43°40’

43°30’

43°20’

Geology modified from Strobel and others, 1999

Arsenic concentration, in 

micrograms per liter

EXPLANATION

Hydrologic features and site labels

Cave site

Stream sink

Less than or equal to 2.5

Greater than 2.5 to 5

Greater than 5 to 10

Greater than 10 to 15

Greater than 15 to 20

Greater than 20 to 35

Base from U.S. Geological Survey digital data, 1997,

1:100,000

Universal Transverse Mercator projection, Zone 13 

Wind Cave National Park 

boundary

Hydrogeologic units

Area shown on figure 2 and 

approximate location 

of Wind Cave

Minnelusa Formation

Madison (Pahasapa) and 

Englewood Limestones

Precambrian rocks and

Deadwood Formation

MOR WOO

WOO

Groundwater Flow, Quality, and Mixing Assessments 23
Figure 10. Boxplots of arsenic concentrations in the Minnelusa 

and Madison aquifers.

0

5

10

15

20

25

30

35

Madison

aquifer

Minnelusa

aquifer

40

n=23 n=22

Dissolved arsenic concentration, in micrograms per liter

n Number of values

EXPLANATION

Outlier—Individual observation outside of upper or lower whiskers

Upper whisker—Data value less than or equal to the 75th percentile plus 

1.5 times the interquartile range

75th percentile

Median, 50th percentile 

25th percentile

Lower whisker—Data value greater than or equal to the 25th percentile 

minus 1.5 times the interquartile range Interquartile range

24 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

which was assessed by considering a possible correlation 

between arsenic concentrations and the sampling depth from 

the top of the Minnelusa aquifer; however, no such correlation 

is apparent on a scatter plot (fig. 12). 

Nitrate Plus Nitrite

Potential sources of nitrate in groundwater include 

nitrogen fertilizer, mining, landfills, atmospheric deposition, 

and human or animal waste (Meyer, 1987; Taylor, 2003; Katz, 

2004; Rahn, 2006). Concentrations of nitrate plus nitrite in 

samples collected for this study are presented in table 12 and 

were less than 2 milligrams per liter (mg/L) for 92 percent of 

these samples and ranged from 0.13 to 2.38 mg/L. Concentrations in this range are not a concern for drinking-water quality 

because the MCL for nitrate drinking water is 10 mg/L (U.S. 

Environmental Protection Agency, 2010). The area with the 

highest nitrate plus nitrite concentrations is on the western side 

of the outcrop areas of the Madison and Minnelusa aquifers 

with concentrations decreasing to the south and east (fig. 13). 

The reason for this geospatial distribution is unclear and unaccounted for by land-use differences. Grazing of domestic stock 

occurs in many areas outside of Wind Cave National Park, and 

wildlife grazing occurs inside the park. Wind Cave National 

Park monitors nitrate concentrations in precipitation for the 

park and reports a 10-year average of 1.4 mg/L (Wind Cave 

National Park, written commun., 2011).

Site WCL in Wind Cave had a concentration of nitrate 

plus nitrite of 2.38 mg/L, which is not visible in the interpolated shaded areas on figure 13 because other proximal cave 

sites had lower concentrations ranging from 0.5 to 1.6 mg/L. 

Cave sites had a median concentration of 1.3 mg/L, and 

other sampled sites in the park had a median concentration of 

0.2 mg/L. The two wells within the park (sites PW1 and PW2) 

had concentrations of 0.6 and 0.2 mg/L, respectively. 

Trace Metals

Exploratory sampling of trace metals (chromium, copper, 

lithium, vanadium, and zinc) for selected sites in the park was 

conducted to assess possible existence of unusually high concentrations or correlations of these metals with arsenic. The 

USEPA regulates arsenic, chromium, and copper with MCLs 

of 10, 100, and 1,300 μg/L, respectively (U.S. Environmental 

Protection Agency, 2010). The highest concentrations for chromium and copper were 0.38 and 2.4 μg/L, respectively, or less 

than 1 percent of the MCL (table 6). The concentration of lithium for spring BRsp was 422 μg/L, which was much higher 

than the other sites, and specific conductance for this site also 

was much higher than the other sites (table 6). Although the 

USEPA has not set an MCL for drinking water for lithium, it 

can be toxic to plants. For example, injury to some crops from 

lithium in irrigation water occurred at concentrations as low as 

50 μg/L, but in other cases, injury was not observed at concentrations lower than 5,000 μg/L (Bingham and others, 1964). 

Lithium concentrations of 600 micrograms per gram (μg/g) in 

the leaves of Bush bean plants resulted in severe toxicity, and 

lithium accumulates in plant tissue (Wallace and others, 1977). 

Based on all samples collected in the park, arsenic indicated 

no apparent correlation with any of the five other trace metals 

when observed on scatter plots. Because of the generally low 

concentrations of trace metals and the lack of correlation with 

arsenic, additional sampling was not conducted. 

Groundwater Mixing

All variables used in PCA were log transformed, which 

resulted in datasets that approximated normal distributions, 

and all variables were then standardized to a mean of zero and 

standard deviation of one. Stable-isotope values (table 12), all 
Figure 11. Geospatial distribution of arsenic concentrations for all groundwater and surface-water samples in and 

near the study area. (All relevant sites with arsenic data available from the National Water Information System [U.S. 

Geological Survey, 2011] are included in map.)

Study area boundary

0 5 10 MILES

0 5 10 KILOMETERS

103°50’ 103°40’ 103°30’ 103°20’ 103°10’

43°50’

43°40’

43°30’

43°20’

Geology modified from Strobel and others, 1999

Arsenic concentration, in 

micrograms per liter

EXPLANATION

Hydrologic features

Cave site

Stream sink

Less than or equal to 2.5 Other surface-water site

Greater than 2.5 to 5

Greater than 5 to 10

Greater than 10 to 15

Greater than 15 to 20

Greater than 20 to 35

Base from U.S. Geological Survey digital data, 1997,

1:100,000

Universal Transverse Mercator projection, Zone 13 

Springs—Tail indicates direction of flow

Wells

Artesian spring

Possible artesian spring

Shallow or unknown spring type

Madison aquifer

Minnelusa aquifer

Precambrian aquifer

Other aquifer

WOO

Wind Cave National Park 

boundary

Hydrogeologic units

Area shown on figure 2 and 

approximate location 

of Wind Cave

Minnelusa Formation

Madison (Pahasapa) and 

Englewood Limestones

Precambrian rocks and

Deadwood Formation

Groundwater Flow, Quality, and Mixing Assessments 25
Figure 12. Scatter plot of arsenic concentrations in the 

Minnelusa aquifer and sampling depth from the top of the 

aquifer.

Arsenic concentration, in micrograms per liter

Effective sampling depth from top of aquifer, in meters

0

5

10

15

20

25

30

35

40

0 50 100 150 200 250 300 350

26 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

of which were negative, were multiplied by -1 for log transformation, then multiplied by -1 after transformation for consistency with the original sign. Values of pH were converted to 

hydrogen ion activity prior to normalization and standardization. To avoid giving disproportionate weight to any site, data 

for each site with multiple samples (excluding quality-control 

replicate samples) were averaged for PCA and end-member 

mixing so that each site had only one value per variable. Ten 

sites had missing data for one variable, and one site had missing data for four variables (1.2 percent of the dataset). However, because multiple samples were available for all of these 

sites, no values were missing in the site-averaged dataset. 

For end-member mixing, data were standardized to equalize 

variable weights and were not log transformed. The following 

results of PCA, cluster analysis, and end-member mixing are 

summarized from Long and Valder (2011).

Principal Component and Cluster Analyses

Results of PCA are shown as sampling sites plotted on 

the first two principal components, which explain 65 percent 

of the total variance of the data (fig. 14). Principal components 

1, 2, and 3 represented 48, 17, and 11 percent, respectively, of 

the total variance, with higher order principal components representing fractions of the total variance that ranged from 0.03 

to 7.9 percent. For cluster analysis, the number of clusters is 

specified by the user. Different numbers of clusters were tested 

with a maximum of six clusters. Five clusters were chosen 

because the five clusters that formed were separated by divisions that could be explained hydrogeologically and thus also 

would work well as a basis for an end-member mixing model 

(fig. 15). The PC cluster consists mainly of Precambrian aquifer sites. The West cluster consists of Minnelusa and Madison 

aquifer sites mainly located near or within the western surface 

recharge area of these aquifers. The East cluster is similar to 

the West cluster, except it includes all cave sites and the two 

stream sinks. The Artesian 1 cluster consists of all artesian 

springs near the Fall River and wells open to the Madison and 

Minnelusa aquifers in that general area, and the Artesian 2 

cluster consists of the remaining artesian springs, which are 

all located within or near the outcrop of the Spearfish Formation. Because these cluster areas could be interpreted and 

differentiated hydrogeologically, these geospatial areas of the 

groundwater-flow system are referred to as “hydrogeologic 

domains.” Hydrochemical data for these domains are summarized in table 13.

The relative influences of principal components 1 and 

2 on the five clusters are shown in figure 14. Principal component 1 separates the Artesian 1 and 2 clusters from the 

three clusters to the north and thus distinguishes groundwater 

affected by regional flow from that affected by local recharge. 

Hydrochemical differences between the Artesian 1 and 2 clusters account for the greatest variability in the dataset, which 

is indicated by the distances between clusters on figure 14. 

The PC, East, and West clusters all are separated from each 

other on principal component 2, which therefore distinguishes 

groundwater affected by different local recharge sources. 

Also, differentiation of the East cluster from the PC and West 

clusters is associated with principal component 1. The Artesian 1 and 2 clusters are separated on principal component 2 

and account for the largest variability of this principal component (fig. 14). Therefore, in addition to distinguishing local 

recharge, principal component 2 describes differences between 

artesian springs.

Similarly to the way scores determine the plotting 

positions for sites (fig. 14), the term “loadings” refers to the 

plotting positions of the original variables (Davis, 2002). Sites 

and variables are plotted together and used to assess relations 

of variables and clusters (fig. 16). Because of the different 

ranges of the values of scores and loadings, these values were 

scaled to range from -1 to 1 so that sites and variables could be 

plotted together (fig. 16). The vector lengths of the variables 

indicate their respective relative influences, and all variables 

except arsenic, pH, and bicarbonate have similar influence. 

Calcium, magnesium, sulfate, and specific conductance plot 

in the Artesian 2 cluster indicating a strong influence of these 

variables with this cluster, whereas the Artesian 1 cluster 

is influenced by sodium and chloride. Stable isotopes δ18O 

and δ2H plot near the East and West clusters and thus might 

help distinguish between these clusters, which is consistent 

with a gradient in these isotope values from east to west in 

the study area (Naus and others, 2001). The variables silica 

and magnesium are heavily loaded on principal component 2 

and therefore are important in distinguishing clusters that are 

separated on that principal component. Most of the remaining variables mainly are loaded on principal component 1 and 
Figure 13. Geospatial distribution of nitrate plus nitrite for the Minnelusa and Madison aquifers in the study 

area. [All relevant sites with nitrate plus nitrite data available from the National Water Information System (U.S. 

Geological Survey, 2011) are included in the map]. Canyon

Creek

Beaver

Creek

Fall

River

Cheyenne

River

Creek

Highland

Angostura

Reservoir

Red

WIND CAVE

NATIONAL PARK

Hydrologic features

0 2.5 5 MILES

0 2.5 5 KILOMETERS

103°40’ 103°30’ 103°20’

43°40’

43°30’

43°20’

Wells

Geology modified from Strobel and others, 1999

Cave site

Artesian spring—Tail indicates

direction of flow

Stream sink

Madison aquifer

Minnelusa aquifer Wind Cave National Park 

boundary

Nitrate plus nitrite concentration, Hydrogeologic units

in milligrams per liter

Area shown on figure 2 and 

approximate location 

of Wind Cave

Minnelusa Formation

Madison (Pahasapa) and 

Englewood Limestones

EXPLANATION

Less than or equal to 0.25

Greater than 0.25 to 0.5

Greater than 0.5 to 0.75

Greater than 0.75 to 1.0

Greater than 1.0 to 1.25

Greater than 1.25 to 1.5

Greater than 1.5 to 1.75

Greater than 1.75 to 2.0

Greater than 2.0 to 16

Base from U.S. Geological Survey digital data, 1997,

1:100,000

Universal Transverse Mercator projection, Zone 13 

Groundwater Flow, Quality, and Mixing Assessments 27
-5 -4 -3 -2 -1 0 1 2 3 4 5

-5

-4

-3

-2

-1

0

1

2

3

BEVcr

CASsp

COOsp

INM

MIL

FER

BOW

KIDsp

MNKsp

HSIsp

HBsp

HAL

COL

CBsp

PAL

MILN

SVE

CRA

SWsp

PEK

BOG

FRA

MYR

HUN

WCsp

KAI Md7-11

BRNsp BCsp

WIL

STR

MEY

LEF WCL HSsp

WTHL

PP

RR

DP1

DP2

DP3

PW1

NCsp PW2

CON

EMsp

KIR2

BRsp

RGPsp

WITsp MOR

WOO

DUR

GRE

PARsp

SZE

HIGHcr

KIR1

SLsp

IRIsp

Principal component 1 (score values, dimensionless)

Princpal component 2 (score values, dimensionless)

EXPLANATION

Cluster with name

Sampling site with site label

Sampling site from which hydrochemical data were 

used as initial values of estimated end members,

with site label

SWsp

East

West

Artesian 2

Artesian 1

PC

BRsp

West

Figure 14. Results of principal component analysis (PCA) and cluster analysis for site-averaged data plotted on the first two principal 

component axes. The scores are the plotting positions for sites sampled.

28 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

thus primarily distinguish the Artesian 1 and 2 clusters from 

the three clusters to the north and secondarily distinguish 

clusters that are separated on principal component 2. Variables 

that plot proximally on figure 16 indicate correlation (Davis, 

2002). For example, the conservative tracers δ18O and δ2H 

are correlated with each other and inversely correlated with 

sodium and chloride. The variables calcium, sulfate, and specific conductance also are correlated. 
Figure 15. Results of cluster analysis showing the geographic locations of cluster areas. Results of endmember mixing are shown as the largest end-member contribution for each site in relation to the clusters. Canyon

Creek

Beaver

Creek

Fall

River

Cheyenne

River

Creek

Beaver

Creek

HighlandHighland

Angostura

Reservoir

Red

WIND CAVE

NATIONAL PARK

0 2.5 5 MILES

0 2.5 5 KILOMETERS

103°40’ 103°30’ 103°20’

43°40’

43°30’

43°20’

EXPLANATION

Geology modified from Strobel and others, 1999

PC EM

West EM

East EM

Artesian 2 EM

Artesian 1 EM

Largest end-member (EM) 

contribution 

Wind Cave National Park 

boundary

Hydrogeologic units

Area shown on figure 2 and 

approximate location 

of Wind Cave

Minnelusa Formation

Madison (Pahasapa) and 

Englewood Limestones

Precambrian rocks

ARTESIAN 1

ARTESIAN 2

PC

WEST

EAST

ARTESIAN 2

ARTESIAN 2

ARTESIAN 2

Base from U.S. Geological Survey digital data, 1997,

1:100,000

Universal Transverse Mercator projection, Zone 13 

Groundwater Flow, Quality, and Mixing Assessments 29
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

Principal component 1 scaled, dimensionless

Principal component 2 scaled, dimensionless

East

West Artesian 2

Artesian 1

PC

As

HCO3

Mg

Ca SC

SO4

Na

Cl

pH

SiO2

δ2H

δ18O

EXPLANATION

Cluster with name

Sampling site—Scaled scores (score/scoremax) are the 

plotting positions

Original variables—Scaled loadings (loading/loadingmax) 

are the plotting positions

Vector—Length indicates relative influence of variable 

within cluster

West

Mg

Abbreviations:

Silica

Chloride

Sodium

Sulfate

Specific conductance

Calcium

Magnesium

Bicarbonate

Arsenic

Stable isotope of hydrogen

Stable isotope of oxygen

SiO2

Cl

Na

SO4

SC

Ca

Mg

HCO3

As

δ2

H

δ18O

Figure 16. Principal component analysis biplot. 

Scores and loadings were scaled to range 

from -1 to 1 to show sites sampled and original 

variables on similar scales.

30 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

End-Member Mixing

For inverse modeling, initial values of f

i,k and Ej,k (equation 2) that are proximal to optimized values are desirable; 

otherwise these parameter values might be optimized to satisfy 

local minima of residuals, rather than the true minimum 

(Doherty, 2005). Initial values for estimated end-member concentrations Ej,k were determined by PCA and cluster analysis 

by using the hydrochemistry of the site within each cluster that 

is farthest from the origin on figure 14. Such extreme-value 

points commonly are assumed to be end members (Christophersen and Hooper, 1992; Laaksoharju and others, 1999). 

During inverse modeling, end-member values were constrained to within 10 percent (plus or minus) of the total range 

of observation data for all sites.

As stated previously in the “Sample Collection and 

Hydrochemical Data” section, 12 variables were used in the 

PCA and end-member mixing: calcium, magnesium, sodium, 

bicarbonate, chloride, silica, sulfate, arsenic, δ18O, δ2H, specific conductance, and pH. Model error in end-member mixing 

is introduced by neglecting geochemical evolution along 

flow paths from the interaction of rocks and water. If only the 

conservative tracers (δ18O, δ2H, and chloride) are included in 

end-member mixing, then geochemical evolution need not be 

considered, but the model would be poorly constrained with 

only three variables for observation data. The model would be 

better constrained with 12 variables but would neglect geochemical evolution for 9 of the 12 variables. As a compromise, 

all 12 variables were used, but larger residuals were allowed 

for nonconservative variables than for conservative tracers. This was accomplished by preferentially weighting the 

calibration data (observed values) of conservative tracers by a 

factor of 2.0 for inverse modeling.

Water contributions from the Precambrian aquifer to 

the Madison and Minnelusa aquifers result from streams that 

drain Precambrian rocks, receive base flow from the Precambrian aquifer, and then sink into the Madison and Minnelusa aquifers. Precambrian aquifer contributions also might 

occur by direct groundwater underflow. However, flow in the 

opposite direction is not possible. Therefore, the end-member 

mixing model was constrained so that Precambrian aquifer 

sites could have contributions only from the PC end member, 

but that this end member could contribute to all sites. Mixing 

proportions for Precambrian aquifer sites were not estimated 

by inverse modeling but were set as fixed values, where the 

PC end-member proportion was set to 100 percent and other 

end-member contributions to zero. Also, it was assumed that 

the unsaturated part of the Minnelusa aquifer at this location 

could receive water only from proximal sources; that is, the 

East, West, or PC end members. Therefore, constraints were 

placed on mixing proportions for cave drip sites to satisfy this 

assumption. 

Model constraints, such as this, based on hydrologic 

information are known as “prior information” in inverse modeling. This reduced the number of parameter values to optimize from 300 to 255 and resulted in a well constrained model 
Table 7. Physical interpretation of end-member waters.

End member Description of end member

PC Precambrian aquifer.

East Recharge to exposed areas of Madison and 

Minnelusa aquifers on the eastern side of the 

Black Hills.

West Recharge to exposed areas of Madison and 

Minnelusa aquifers on the western side of the 

Black Hills.

Artesian 1 Regional Madison aquifer groundwater primarily 

contributing to the Artesian 1 domain.

Artesian 2 Regional Madison aquifer groundwater primarily 

contributing to the Artesian 2 domain.

Table 8. End-member contributions as an average to each 

cluster area.

[Shaded areas indicate the largest end-member contribution to each domain. 

PC, Precambrian aquifer]

Hydrogeologic 

domain

End-member (EM) contributions, in percent

PC 

EM

East 

EM

West 

EM

Artesian 1 

EM

Artesian 2 

EM

PC 95 3 2 0 1

East 39 33 25 1 3

West 34 21 34 4 7

Artesian 1 13 9 19 56 4

Artesian 2 10 9 15 14 53

Groundwater Flow, Quality, and Mixing Assessments 31

with 2.8 times as many observed values (720) as parameter 

values to be optimized. This effectively forced the PC end 

member to have final estimated values that are approximately 

the average of observed values for Precambrian aquifer samples. Also, this forced all simulated Precambrian aquifer sites 

to have exactly the same values as this end member, which 

was not desirable but was considered the best of all options. 

After inverse modeling, the coefficient of determination 

(R2) from a linear regression model (Davis, 2002) of observed 

and calculated values was 0.94 for conservative tracers and 

0.74 for the other nine variables. Differences, or residuals, 

from the regression lines are interpreted as resulting from four 

sources of errors: data errors, model errors, temporal variability, or processes other than pure mixing (that is, geochemical evolution along flow paths). Conservative tracers were 

assumed to be unaffected by geochemical evolution, and thus 

regression residuals for these tracers represent the former 

three sources of error only, whereas residuals for nonconservative variables represent all four sources of error. Therefore, 

the reduction in the R2 value for nonconservative variables 

(21 percent smaller than for conservative tracers) is a model 

estimate of the effect of geochemical evolution relative to 

that of mixing. Grouping the sites by the largest end-member 

contribution resulted in 65 percent similarity to the clusteranalysis groupings (fig. 15), which indicates that 35 percent of 

the sites received their largest contribution from end members 

outside of their corresponding clusters.

End-Member Mixing Evaluation

Each end member was assumed to represent a different hydrogeologic domain, and thus, PCA was used to 

determine how each estimated end member paired with each 

cluster (table 7). The proximity of end members to clusters in principal-component space was the criterion. For all 

hydrogeologic domains except East, the largest end-member 

contribution was from its own end member. The largest contribution to the East domain was from the PC end member, and 

the West domain received equal amounts from the West and 

PC end members (table 8). The East and West end members 

are interpreted to represent surface recharge to the Madison and Minnelusa aquifers (table 7), and thus end-member 

mixing estimated that the Precambrian aquifer contribution 

is larger than that from local surface recharge for the East 

domain and about equal for the West domain. The Artesian 1 

and 2 end members combined (or regional groundwater flow) 

contributed 60 and 67 percent to the Artesian 1 and 2 domains, 

respectively (table 8). 

The Artesian 1 and 2 end members are interpreted to represent regional groundwater flow, primarily from the Madison 

aquifer, because they primarily contribute to artesian springs 

that have relatively large discharge rates (tables 7 and 8). The 

Artesian 1 and 2 end members contributed from 1 to 7 percent 

to the East and West domains (table 8), which is consistent 

with the interpretation that artesian springs discharge regional 

groundwater flow that probably has little effect on the East 

and West domains. The West end member contributed about 

1.5 times as much as the East end member to the Artesian 1 

and 2 domains (table 8), which is consistent with general 

southward and eastward groundwater flow in the study area 

(fig. 1). 

Mean end-member contributions for Wind Cave sites 

(table 9) are similar to those of the entire East domain 

(table 8), except that the largest contribution for the cave sites 

was from the East end member, or local surface recharge 

(38 percent), and the second largest was from the PC end 

member (34 percent). This analysis indicates that contamination to the Precambrian aquifer has potential to affect 

groundwater in Wind Cave. The West end member, or surface 

recharge from the west, contributed 26 percent. The Artesian 1 

and 2 end-member contributions were 0 and 4 percent, respectively, to cave water bodies and 0 percent to cave drip sites 
Table 9. End-member contributions for Wind Cave sites.

[PC, Precambrian aquifer]

Site name Site type

End-member (EM) contributions, in percent

PC EM East EM West EM Artesian 1 EM Artesian 2 EM

DP1 Cave drip 27 41 30 0 0

DP2 Cave drip 32 44 23 0 0

DP3 Cave drip 45 39 17 0 0

Drip mean 35 41 24 0 0

PP Cave water body 33 34 30 0 3

RR Cave water body 34 33 28 0 5

WCL Cave water body 32 35 29 1 3

WTHL Cave water body 30 34 31 0 5

Water-body mean 32 34 29 0 4

Overall mean 34 38 26 0 2

32 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

because of model constraints (table 9). This small contribution 

from the Artesian 2 end member to cave water bodies is possible because it represents regional flow from the west, which 

might contribute a small amount to the cave depending on 

anisotropic permeability.

Artesian springs were separated into two clusters because 

of differences in hydrochemistry, but the hydrogeologic distinction between these two groups of springs is not obvious. 

Values of temperature, specific conductance, and calcium plus 

sulfate for artesian springs were distinctly different between 

the two hydrogeologic domains (table 10). The reason for the 

differences in temperature is uncertain but might result from a 

geothermal anomaly in deep rocks near the Artesian 1 springs 

that affected upwelling water discharging from these springs. 

Geographically, the Artesian 1 domain is distinct from the 

Artesian 2 domain because it contains all springs near the Fall 

River in a small area, which combined with hydrochemical 

and thermal data, provides a basis for assuming that different 

hydrogeologic processes are occurring in these two areas. The 

Artesian 1 and 2 clusters are separated on principal component 2 and account for the largest variability of this principal 

component (fig. 14).

Back (2011) estimated that Beaver Creek Spring 

(site BCsp) had a contribution of 55–58 percent regional flow 

by using geochemical modeling and assuming that the spring 

was a mixture of regional flow, represented by well MIL, and 

local recharge, represented by Wind Cave water bodies. The 

end-member mixing model in the current study described 

in this report resulted in an estimate of 74 percent regional 

flow as a combination of the two regional-flow end members 

(Artesian 1 and 2) and 26 percent local recharge as a combination of the other three end members. The estimates from these 

two methods did not differ greatly, especially considering 

differences in the two methods, both of which have strengths 

and limitations. The approach used by Back (2011) simulated 

geochemical evolution by physical processes along two flow 

paths originating from two end members that were assumed 

to be represented by the samples selected. In contrast, the 

approach described in this report allowed for as many as five 

end members, which were estimated and not assumed to have 

been sampled, but did not simulate geochemical evolution by 

physical processes. 

The separation on figure 14 of the Artesian 1 and 2 

clusters from the other three clusters indicates distinct hydrochemical differences; this does not, however, indicate hydraulic separation between the different hydrogeologic domains. 

Although the primary sources of groundwater and the groundwater flow paths to the different hydrogeologic domains may 

differ, the hydraulic head within any of these domains could 

affect the hydraulic head in the other domains. Results of the 

end-member mixing model indicate that all hydrogeologic 

domains (excluding Precambrian aquifer sites) received water 

from all upgradient end members (table 8), which indicates 

that the five domains all are hydraulically connected to some 

extent. For example, the Artesian 2 domain received 34 percent of its contribution from a combination of the PC, East, 

and West end members (table 8). This is consistent with the 

conclusions of Back (2011), which indicate that Beaver Creek 

Spring (site BCsp) is a mixture of local recharge and regional 

groundwater flow. Beaver Creek Spring and well STR have a 

spatial separation of only 1.2 km (fig. 1) but are within different hydrogeologic domains (Artesian 2 and East, respectively) 

and are hydrochemically dissimilar, as indicated on figure 14 

by their distant plotting positions. Despite these hydrochemical differences, some degree of hydraulic connection between 

these two sites probably exists because of similar contributing 

end members indicated by the end-member mixing model: 

Beaver Creek Spring received 24 percent of its contribution 
Table 10. Temperature, specific conductance, and calcium plus 

sulfate in water samples from artesian springs.

[°C, degrees Celsius; μS/cm, microsiemens per centimeter at 25°C; mg/L, 

milligrams per liter]

Constituent Mean Minimum Maximum

Artesian 1 hydrogeologic domaina

Temperature, °C 26 24 32

Specific conductance, 

μS/cm 961 672 1,580

Calcium plus sulfate, 

mg/L 254 131 660

Artesian 2 hydrogeologic domainb

Temperature, °C 19 18 19

Specific conductance, 

μS/cm 2,315 1,960 2,560

Calcium plus sulfate, 

mg/L 1,738 1,302 2,108

a

 4 springs, 12 samples.

b

 3 springs, 7 samples.

Groundwater Flow, Quality, and Mixing Assessments 33

from the PC and West end members combined, and well STR 

received 74 percent from these same end members.

Groundwater Age Dating

Age dating was useful for additional evaluation of endmember mixing results. Sample concentrations of the dissolved gasses argon, carbon dioxide, methane, nitrogen, and 

oxygen (table 11) were used to estimate the temperature of 

recharge water to improve the estimates of CFC-based groundwater age (table 4) and to assess possible CFC degradation 

by applying methods described by Plummer and Busenberg 

(2000). Groundwater samples commonly contain a mixture of 

water of different ages. The apparent age is an estimate of age 

that is based on the assumption that the sample contains water 

of a single age. Because any single sample from the Madison 

aquifer generally contains a mixture of ages ranging from 1 

to more than 60 years (Long and Putnam, 2006), the apparent 

age is not useful for describing groundwater flow to a single 

well or spring. However, the apparent age is useful because it 

is assumed to be proportional to the average age of a groundwater sample, and thus, the apparent age is useful for assessing 

the general geospatial distribution of groundwater age. 

Apparent ages for the Madison aquifer in the study area 

indicate that groundwater closest to surface recharge areas 

has the youngest apparent ages, with increasing apparent ages 

in deeper parts of the Madison and Minnelusa aquifers to the 

south (fig. 17). The geospatial distribution of apparent ages 

is consistent with that of specific conductance (fig. 8), where 

specific conductance generally is proportional to apparent 

age. Specific conductance increases with residence time in 

carbonate aquifers because of the dissolution of aquifer rocks 

with time. Apparent ages generally are consistent with results 

of end-member mixing. Sites within the East and West hydrogeologic domains have the youngest apparent ages, and these 

domains were estimated to receive 90–100 percent of their 

contributions from local surface recharge or from the shallow Precambrian aquifer (table 8). Sites within the Artesian 1 

and 2 hydrogeologic domains have the oldest apparent ages, 

and these domains were estimated to receive 60–67 percent 

of their water from end members representing regional flow 

(table 8). Apparent groundwater ages for Wind Cave are more 

than 20 years, which might be a result of partial groundwater 

inflow from the Precambrian aquifer and is consistent with 

results of the end-member mixing model. 

Water from well MIL had the oldest apparent age of all 

samples, which indicates a regional source for this well and 

is consistent with end-member mixing results. Based on flow 

directions indicated by Back and others (1983), the regional 

source for this well probably is groundwater recharge in the 

northwestern part of the study area and also areas outside of 

the study area to the northwest. Also indicated by Back and 

others (1983), this regional flow sweeps around the southern 

end of the Black Hills and flows to the east, which would indicate that Cascade and Cool Springs (sites CASsp and COOsp) 

probably receive water from this regional source. The younger 

groundwater age for these springs relative to well MIL 

indicates that the springs also have contributions from water 

recharged at a nearer source, from faster flow paths, or both. A 

possible explanation for this difference in water sources might 

be karst conduits in the Madison aquifer that connect springs 

to local recharge areas. The Artesian 1 and 2 hydrogeologic 

domains each were estimated to receive 41 and 34 percent, 

respectively, of their water from the PC, East, and West clusters combined (table 8).

The apparent age for water from well Md7–11 was 

61 years for CFC–12, which was much older than that of other 

proximal sites (table 4). An apparent age of 30 to 40 years 

might be expected for well Md7–11 based on apparent ages 

for proximal sites and its location near the Madison Limestone outcrop. This difference might be because this well is an 

observation well and not used for water production. Wells used 

for water production commonly are developed for maximum 

yield during installation. In a karst aquifer, this might result in 

the ability of the well to reach faster groundwater flow paths, 

such as conduits, than otherwise would be the case. Such well 

development is not necessary for an observation well that is 

used only to measure water levels. Therefore, water sampled 

from an observation well might represent water moving in a 

slower flow path with an older apparent age than for a production well. All wells other than Md7–11 were pumped regularly. 

Therefore, the apparent age for well Md7–11 was not plotted 

on figure 17 because it would result in a potentially misleading 

anomaly. 

Methane was present in the samples from well Md7–11, 

which could cause degradation of CFCs resulting in a lowering of the concentration, particularly for CFC–11 (Plummer 
Table 11. Dissolved gas data for water samples. [°C, degrees Celsius; mg/L, milligrams per liter; m, meters] Site name Station number Station name Date Time Sample temperature (°C) Argon (mg/L) Carbon dioxide (mg/L) Methane (mg/L) Nitrogen (mg/L) Oxygen (mg/L) A

CASsp 432006103330501 8S 5E20CDAB 06/19/2009 1135 19.31 0.58 38.53 0.00 16.12 3.38 CASsp 432006103330501 8S 5E20CDAB 06/19/2009 1135 19.31 .57 38.28 .00 15.92 3.28 COOsp 432028103331601 8S 5E20BDCB 06/19/2009 1438 17.78 .56 31.78 .00 15.28 4.51 COOsp 432028103331601 8S 5E20BDCB 06/19/2009 1438 17.78 .56 31.71 .00 15.20 4.60 KIDsp 432605103285401 7S 5E14DDD 06/19/2009 1645 27.77 .47 30.47 .00 12.31 3.90 KIDsp 432605103285401 7S 5E14DDD 06/19/2009 1645 27.77 .47 29.85 .00 11.99 3.81 MNKsp 432605103290901 7S 5E14D 05/28/2009 1510 32.43 .56 27.92 .00 15.15 3.55 MNKsp 432605103290901 7S 5E14D 05/28/2009 1510 32.43 .55 27.88 .00 15.07 3.49 HSIsp 432632103285302 7S 5E14DDDA 05/21/2009 1602 27.38 .51 21.87 .00 13.48 4.25 HSIsp 432632103285302 7S 5E14DDDA 05/21/2009 1602 27.38 .51 21.30 .00 13.50 4.56 HBsp 432703103302801 7S 5E10DCBA 04/20/2007 1726 23.90 .55 18.14 .00 14.25 6.32 HBsp 432703103302801 7S 5E10DCBA 04/20/2007 1726 23.90 .54 18.17 .00 14.11 6.31 HBsp 432703103302801 7S 5E10DCBA 05/28/2009 1339 23.62 .57 18.60 .00 15.48 5.71 HBsp 432703103302801 7S 5E10DCBA 05/28/2009 1339 23.62 .57 18.57 .00 15.50 5.66 SVE 432825103391201 7S 4E 4BACA 09/02/2009 1040 18.12 .59 17.69 .00 16.03 7.39 SVE 432825103391201 7S 4E 4BACA 09/02/2009 1040 18.12 .59 17.91 .00 16.06 7.10 HUN 433034103284701 6S 5E23DBBB 04/17/2007 940 14.98 .62 10.20 .00 17.27 7.04 HUN 433034103284701 6S 5E23DBBB 04/17/2007 940 14.98 .61 10.11 .00 17.19 6.67 Md7–11 433115103251401 6S 6E21BBBB (CU91A) 04/20/2007 1350 13.40 .61 9.05 .01 17.10 1.93 Md7–11 433115103251401 6S 6E21BBBB (CU91A) 04/20/2007 1350 13.40 .60 8.80 .01 16.93 1.85 BCsp 433128103223401 6S 6E14CDB 04/17/2007 1230 19.12 .58 31.49 .00 16.04 3.07 BCsp 433128103223401 6S 6E14CDB 04/17/2007 1230 19.12 .57 31.81 .00 15.97 3.01 BCsp 433128103223401 6S 6E14CDB 05/28/2009 1020 18.48 .58 30.49 .00 16.05 3.04 BCsp 433128103223401 6S 6E14CDB 05/28/2009 1020 18.48 .58 30.72 .00 16.14 2.98 STR 433150103230501 6S 6E15ABDD 04/17/2007 1430 20.02 .61 6.91 .00 16.99 7.16 STR 433150103230501 6S 6E15ABDD 04/17/2007 1430 20.02 .61 6.62 .00 16.94 7.30 STR 433150103230501 6S 6E15ABDD 05/22/2009 1117 19.24 .61 8.50 .00 17.32 5.18 STR 433150103230501 6S 6E15ABDD 05/22/2009 1117 19.24 .61 8.56 .00 17.34 5.29 PW1 433311103263101 6S 6E 6DDAB 07/29/2009 1325 14.66 .61 9.14 .00 17.23 6.13 PW1 433311103263101 6S 6E 6DDAB 07/29/2009 1330 14.66 .61 9.15 .00 17.22 6.21 
Site 

name

Station number Station name Date Time

Sample 

temperature 

(°C)

Argon 

(mg/L)

Carbon 

dioxide 

(mg/L)

Methane

(mg/L)

Nitrogen

(mg/L)

Oxygen

(mg/L)

A

PW2 433311103263102 6S 6E 6DDAA 07/29/2009 1010 14.49 0.82 7.46 0.00 28.29 3.85 PW2 433311103263102 6S 6E 6DDAA 07/29/2009 1015 14.49 .82 7.45 .00 28.30 3.89 CON 433326103352001 6S 4E 1DBBB 07/15/2009 942 12.49 .63 41.14 .00 18.09 4.44 CON 433326103352001 6S 4E 1DBBB 07/15/2009 942 12.46 .63 41.95 .00 18.14 4.17 WOO 433636103343901 5S 5E18CCAC 04/26/2007 1730 15.22 .58 8.73 .00 15.86 8.76 WOO 433636103343901 5S 5E18CCAC 04/26/2007 1730 15.22 .58 8.71 .00 15.85 8.69 WOO 433636103343901 5S 5E18CCAC 07/15/2009 1422 15.90 .59 11.79 .00 16.26 9.06 WOO 433636103343901 5S 5E18CCAC 07/15/2009 1422 15.90 .59 11.68 .00 16.12 9.14 

a Determined by methods described by Plummer and Busenberg (2000).

Table 11. Dissolved gas data for water samples.—Continued[°C, degrees Celsius; mg/L, milligrams per liter; m, meters]
Canyon

Creek

Beaver

Creek

Fall

River

Cheyenne

River

Creek

Highland

Angostura

Reservoir

Red

WIND CAVE

NATIONAL PARK

0 2.5 5 MILES

0 2.5 5 KILOMETERS

103°40’ 103°30’ 103°20’

43°40’

43°30’

Geology modified from Strobel and others, 1999

Hydrologic features with site labels

Wells with site labels

Cave site

Artesian spring—Tail indicates 

direction of flow

Madison aquifer

Minnelusa aquifer

Wind Cave National Park 

boundary

Apparent groundwater age, Hydrogeologic units

in years

Area shown on figure 2 and 

approximate location 

of Wind Cave

Minnelusa Formation

Madison (Pahasapa) and 

Englewood Limestones

EXPLANATION

20 to 25

Greater than 25 to 30

Greater than 30 to 35

Greater than 35 to 40

Greater than 40 to 45

Greater than 45 to 50

Greater than 50 to 55

Greater than 55 to 60

Greater than 60 to 65

SVE

CON

PW2 STR

BCsp

BOG

HUN

PW1

MIL

WTHL

HBsp

HSIsp

MNKsp KIDsp

CASsp

COOsp

CASsp

MIL

HUN

WTHL

Base from U.S. Geological Survey digital data, 1997,

1:100,000

Universal Transverse Mercator projection, Zone 13 

Figure 17. Geospatial distribution of apparent groundwater ages for the Madison aquifer estimated from 

CFC–12.

36 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota
Summary and Conclusions 37

and Busenberg, 2000). This would result in an apparent age 

that is older than for the case of no CFC degradation, and the 

apparent ages for Md7–11 are, therefore, considered to be 

the minimum apparent ages. Well Md7–11 is under hydraulic 

pressure at the land surface and sealed at the wellhead. To 

prevent freezing of the wellhead during winter, an antifreeze 

solution that is lighter than water is kept inside the top several 

feet of the well casing. Although the antifreeze solution was 

removed, and the well was allowed to flow overnight to clear 

the well before sampling, it is possible that the methane was a 

result of this antifreeze solution. 

Summary and Conclusions

A study of groundwater flow, quality, and mixing in 

relation to Wind Cave National Park in western South Dakota 

was conducted during 2007–10 by the U.S. Geological Survey 

in cooperation with the National Park Service because of 

water-quality concerns and to determine possible sources of 

groundwater contamination in the Wind Cave National Park 

area. Wind Cave is a primary natural resource for the park, and 

groundwater in the cave exists as cave drip at numerous locations and in underground streams, pools, and lakes. A large 

area surrounding the park was included in this study because 

to understand groundwater in the park, a general understanding of groundwater hydrochemistry and flow in the surrounding area of the southern Black Hills is necessary. Three 

primary aquifers interact with groundwater in Wind Cave: the 

Minnelusa, Madison and Precambrian aquifers. The Minnelusa aquifer is contained in the Minnelusa Formation, which 

is composed of interbedded limestone, dolostone, sandstone, 

and shale. The Madison Limestone and underlying Englewood 

Limestone contain Wind Cave and the Madison aquifer, which 

is a karstic aquifer. The Precambrian aquifer is contained in 

the underlying metamorphic and igneous fractured rocks of 

Precambrian age. 

Groundwater and surface-water samples collected for this 

study were analyzed for common ions (calcium, magnesium, 

sodium, bicarbonate, chloride, silica, and sulfate), arsenic, 

stable isotopes of oxygen and hydrogen, specific conductance, 

and pH. These 12 variables were used in all multivariate 

methods. A total of 100 samples were collected from 60 sites 

from 2007 to 2010 and included stream sinks, cave drip, 

cave water bodies, springs, and wells. Groundwater samples 

were collected and analyzed for chlorofluorocarbons (CFCs), 

dissolved gasses (argon, carbon dioxide, methane, nitrogen, 

and oxygen), and tritium at selected sites and used to estimate 

groundwater age.

Multivariate methods were applied to hydrochemical data 

to characterize groundwater flow and mixing for these three 

aquifers. The first of these methods is principal component 

analysis (PCA), which is used to graphically plot complex 

multivariate datasets and elucidate data patterns that otherwise 

might not be noticed. The second method is cluster analysis, 

which consists of the assignment of data points to a specified 

number of groups, or clusters, based on similarity of data. 

Finally, an end-member mixing model was used to estimate 

groundwater mixing and flow. This model is based on the 

assumption that each water sample consists of water originating from one or more end members, or sources of input, in 

varying proportions. Application of these methods provided 

a basis to assess characteristics important for groundwater 

quality, including the differentiation of hydrogeologic domains 

within the study area, sources of groundwater to these 

domains, and groundwater mixing within these domains. 

In general, groundwater flows from the surface recharge 

area in the northwestern part of study area to the southwest, 

then sweeps east and then northeast around the southern end 

of the Black Hills. A low area in the potentiometric surface 

in the area of Wind Cave likely indicates anomalously high 

permeability resulting from extensive karst development. Vertical hydraulic gradients between the Madison and Minnelusa 

aquifers indicates that the primary source of artesian spring 

flow is the Madison aquifer. Dye tracing indicated hydraulic 

connectivity of three water bodies in Wind Cave. Fluorescent 

dye injected into What the Hell Lake reached Rebel River and 

Windy City Lake with minimum velocities of 9 meters per 

day.

Specific conductance generally is lowest in recharge 

areas for the Minnelusa, Madison, and Precambrian aquifers 

and highest in the southern part of the study area, distant from 

aquifer recharge areas. Arsenic concentrations in samples 

collected for this study ranged from 0.28 to 37.1 micrograms per liter (mg/L) with a median value of 6.4 mg/L, and 

32 percent of these concentrations exceeded 10 mg/L, which 

is the Maximum Contaminant Level (MCL) established by the 

U.S. Environmental Protection Agency. The highest arsenic 

concentrations in and near the study area are approximately 

coincident with the outcrop of the Minnelusa Formation and 

likely originated from arsenic in shale layers in the Minnelusa 

aquifer. Sample concentrations of nitrate plus nitrite were less 

than 2 milligrams per liter for 92 percent of samples collected, 

which is not a concern for drinking-water quality. Water 

samples were collected in the park and analyzed for five trace 

metals (chromium, copper, lithium, vanadium, and zinc), the 

concentrations of which did not correlate with arsenic concentrations. Sample concentrations for chromium and copper were 

less than 1 percent of their respective MCLs established by the 

U.S. Environmental Protection Agency. 

For end-member mixing, end members were not assumed 

to have been sampled but rather were estimated and constrained by prior hydrologic knowledge in the end-member 

mixing model. This model was quantified in relation to the 

five hydrogeologic domains that were determined by PCA and 

cluster analysis, which focused model results on major hydrologic processes. Conservative tracers (chloride and stable isotopes of hydrogen and oxygen) were weighted preferentially in 

model calibration, which distributed model errors of optimized 

values, or residuals, more appropriately than would otherwise 

be the case. The smallest residuals were for conservative 
38 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

tracers, which is appropriate because geochemical evolution 

along groundwater flow paths for nonconservative variables 

was assumed to result in larger model residuals. The difference in residuals between conservative and nonconservative 

variables provided an estimate of the effect of geochemical 

evolution along flow paths relative to that of mixing, which 

was 21 percent.

Five hydrogeologic domains were distinguishable as 

a result of PCA, cluster analysis, and prior hydrogeologic 

knowledge. These are described as (1) the PC domain consisting mainly of Precambrian aquifer sites; (2) the West domain 

consisting of Madison and Minnelusa aquifer sites mainly 

located near or within the western surface recharge area of 

these aquifers; (3) the East domain, which is similar to the 

West domain, except it includes all cave sites and the two 

stream sinks; (4) the Artesian 1 domain consisting of all artesian springs near the Fall River and wells open to the Madison 

and Minnelusa aquifers in that general area; and (5) the Artesian 2 domain consisting of the remaining artesian springs, all 

of which are located within or near the outcrop of the Spearfish Formation. Each of the five end members estimated by the 

model were determined by PCA to be hydrochemically similar 

to one of the five domains. Thus, each domain included one 

estimated end member, and the end members were interpreted 

accordingly. The PC end member was interpreted to represent 

groundwater in the Precambrian aquifer; the East and West 

end members were interpreted to represent surface recharge 

in these domains; and the Artesian 1 and 2 end members were 

interpreted to represent regional groundwater flow contributing primarily to these domains. The end-member mixing 

model estimated that Wind Cave sites received 38 percent of 

their groundwater inflow from local surface recharge (East 

end member), 34 percent from the upgradient Precambrian 

aquifer, 26 percent originating from surface recharge to the 

west (West end member), and 2 percent from regional flow. 

The Artesian 1 and 2 end members combined contributed 60 

and 67 percent to the Artesian 1 and 2 domains, respectively. 

This analysis indicates that contamination to the Precambrian 

aquifer has potential to affect groundwater in Wind Cave. 

Flow from the Precambrian aquifer into Wind Cave might 

occur from sinking streams that drain Precambrian rocks and 

also from direct groundwater transfer from the Precambrian 

aquifer, through the Deadwood aquifer, and into the Madison 

aquifer.

Apparent ages, or model ages, for the Madison aquifer 

in the study area indicate that groundwater closest to surface 

recharge areas is youngest, with increasing age in a downgradient direction toward deeper parts of the aquifer. Apparent 

groundwater ages for Wind Cave are more than 20 years, 

which might be a result of partial groundwater inflow from the 

Precambrian aquifer and is consistent with results of the endmember mixing model. 

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Dakota: U.S. Geological Survey Scientific Investigations 

Report 2007–5001, 61 p. 

Rahn, P.H., 2006, Nitrate in Rapid City’s water supply: Proceedings of the South Dakota Academy of Science, v. 85, 

p. 31–42. 

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, 100 p. 

Redden, J.A., and DeWitt, Ed, 2008, Maps showing geology, 

structure, and geophysics of the central Black Hills, South 

Dakota: U.S. Geological Survey Scientific Investigations 

Map 2777, 44 p. pamphlet, 2 sheets.

Révész, K., and Coplen, T.B., 2008a, Determination of the 

δ(180/160) of water—RSIL lab code 489, in Révész, K., and 

Coplen, T.B., eds., Methods of the Reston Stable Isotope 

Laboratory: U.S. Geological Survey Techniques and Methods, book 10, chap. C2, p. 28. 

Révész, K., and Coplen, T.B., 2008b, Determination of the 

δ(2H/1H) of water: RSIL lab code 1574, in Révész, K., and 

Coplen, T.B., eds., Methods of the Reston Stable Isotope 

Laboratory: U.S. Geological Survey Techniques and Methods, book 10, chap. C1, p. 27. 

Rhine, E.D., Onesios, K.M., Serfes, M.E., Reinfelder, J.R., 

and Young, L.Y., 2008, Arsenic transformation and mobilization from minerals by the arsenite oxidizing strain 

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p. 1,423–1,429. 

Seber, G.A.F., 1984, Multivariate observations: Hoboken, 

New Jersey, John Wiley and Sons, Inc., 686 p. 

Serfes, M.E., Spayd, S.E., and Herman, G.C., 2006, Arsenic 

occurrence, sources, mobilization, and transport in groundwater in the Newark Basin of New Jersey: ACS Symposium 

Series, v. 915, p. 175–190. 

Shouse, Ben, 2004, Drought expands Wind Cave entry: Sioux 

Falls, South Dakota, Argus Leader, September 13, 2004.
References Cited 41

Spath, Helmuth, 1985, Cluster dissection and analysis—

Theory, FORTRAN programs, examples: New York, 

Halsted Press, 226 p. 

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–0743, 

3 sheets. 

Suk, H., and Lee, K., 1999, Characterization of a ground water 

hydrochemical system through multivariate analysis—Clustering into ground water zones: Ground Water, v. 37, no. 3, 

p. 358–366. 

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on-lot septic systems, a guidance model for land planning 

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Water-Resources Investigations, book 5, chap. A5, p. 79–81. 

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Weathering of the New Albany Shale, Kentucky—II. Redistribution of minor and trace elements: Applied Geochemistry, v. 24, no. 8, p. 1,565–1,578. 

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contaminants, accessed February 8, 2011, at http://water.

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U.S. Geological Survey, variously dated, National field manual for the collection of water-quality data: U.S. Geological Survey Techniques of Water-Resources Investigations, 

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Science and Plant Analysis, v. 8, no. 9, p. 773–780. 

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implication for drinking water—Lower Illinois River Basin: 

Ground Water, v. 39, no. 3, p. 433–442. 

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culture, accessed May 20, 2011, at http://www.nps.gov/wica/

historyculture/index.htm. 

Zhu, Wenyi, Young, L.Y., Yee, N., Serfes, M., Rhine, E.D., 

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et Cosmochimica Acta, v. 72, no. 21, p. 5,243–5,250.

Supplemental Tables
44 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota Supplemental Tables 45

Table 12. Hydrochemical data for water samples.

[mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius (°C); μg/L, micrograms per liter; ‰, per thousand; m, meters; --, no data 

or not applicable]

Site 

name

Station number Station name Source 

aquifer Date Time

Dissolved 

oxygen 

(mg/L)

pH

Specific 

conductance, 

unfiltered 

(μS/cm)

Temperature 

(°C)

Calcium, 

dissolved 

(mg/L)

Magnesium, 

dissolved 

(mg/L)

Sodium, 

dissolved 

(mg/L)

Nitrate + 

nitrite as 

nitrogen, 

dissolved 

(mg/L)

Acid neutralizing 

capacitya

(mg/L as 

CaCO3)

Alkalinityb

(mg/L as 

CaCO3)

Bicarbonatec

(mg/L)

Chloride, 

dissolved 

(mg/L)

Silica, 

dissolved 

(mg/L)

Sulfate, 

dissolved 

(mg/L)

Arsenic, 

dissolved 

(μg/L)

δ2H (‰) δ18O 

(‰)

Well 

depth 

below 

land 

surface 

(m)

Stream sink sites Stream sink sites

BEVcr 06402430 Beaver Creek sinkd -- 04/16/2007 1800 -- 8.1 538 -- 68.2 21.7 13.7 0.013 196 -- 236 14.3 14.8 39.7 3.7 -90.10 -11.92 --

BEVcr 06402430 Beaver Creek sinkd -- 06/25/2008 1120 -- 7.8 563 19.3 72.7 22.9 13.6 -- -- -- 278 25.6 16.5 65.6 4.4 -- -- --

BEVcr 06402430 Beaver Creek sinkd -- 05/22/2009 910 -- 7.9 559 11.1 77.6 26.6 13.6 -- -- 263 318 22.6 17.0 34.6 4.2 -89.41 -11.70 --

HIGHcr 433745103261900 Highland Creek sinke -- 03/15/2007 1230 10.4 8.8 286 11.4 38.9 7.25 7.93 .270 -- -- 149 3.06 19.2 14.5 3.3 -87.60 -11.95 --

HIGHcr 433745103261900 Highland Creek sinke -- 04/26/2007 1015 10.2 9.2 288 14.8 41.3 7.46 8.24 .161 131 -- 146 3.01 17.4 14.6 3.0 -87.70 -11.90 --

HIGHcr 433745103261900 Highland Creek sinke -- 07/09/2007 1600 2.8 8.0 315 27.2 43.7 7.80 8.97 .114 138 -- 163 3.04 22.4 13.7 3.9 -87.10 -11.78 --

HIGHcr 433745103261900 Highland Creek sinke -- 09/26/2007 1450 7.4 8.1 321 15.8 42.0 7.89 8.42 .111 138 -- 166 2.90 19.4 15.0 2.4 -88.30 -11.88 --

HIGHcr 433745103261900 Highland Creek sinke -- 05/14/2009 1345 9.5 9.2 280 20.4 40.1 7.63 8.39 -- -- 112 119 4.33 13.1 14.2 3.5 -87.30 -11.72 --

Cave drip sites Cave drip sites

DP1 433302103281507 6S 5E12DBAB7 Madison 04/27/2007 1400 9.5 8.3 385 -- 35.4 16.9 12.6 1.36 139 -- 167 13.2 17.6 21.3 34.2 -90.90 -12.42 --

DP1 433302103281507 6S 5E12DBAB7 Madison 07/29/2009 1130 12.9 7.8 348 -- 33.8 19.0 8.27 -- -- 146 177 7.25 16.0 22.6 32.4 -90.40 -12.15 --

DP2 433302103281508 6S 5E12DBAB8 Madison 04/25/2007 1200 9.6 8.4 339 -- 45.7 13.0 4.29 1.55 157 -- 188 3.88 17.5 10.7 29.3 -85.10 -11.69 --

DP2 433302103281508 6S 5E12DBAB8 Madison 05/22/2009 1515 -- -- 340 -- 47.3 13.1 4.28 -- -- 162 195 3.60 18.2 10.6 29.3 -83.90 -11.54 --

DP2 433302103281508 6S 5E12DBAB8 Madison 07/29/2009 1200 12.1 7.9 255 -- 50.1 13.3 4.40 -- -- 169 205 3.71 17.2 10.7 25.9 -82.20 -11.30 --

DP3 433302103281509 6S 5E12DBAB9 Madison 04/25/2007 1400 9.7 8.4 252 -- 37.2 8.19 .97 .455 120 -- 144 1.27 19.3 7.44 25.2 -84.40 -11.61 --

DP3 433302103281509 6S 5E12DBAB9 Madison 05/22/2009 1500 -- 7.3 255 -- 37.7 8.06 .96 -- -- 122 149 1.10 20.0 7.08 25.0 -84.00 -11.57 --

DP3 433302103281509 6S 5E12DBAB9 Madison 07/29/2009 1230 9.7 8.0 349 -- 38.2 8.04 .95 -- -- 125 151 1.17 19.0 7.79 24.3 -83.70 -11.54 --

Cave water body sites Cave water body sites

PP 433302103281504 6S 5E12DBAB4 Madison 04/27/2007 1200 9.4 8.1 331 -- 34.4 19.8 4.47 0.959 157 -- 189 3.07 12.6 6.62 13.1 -91.50 -12.25 --

RR 433302103281506 6S 5E12DBAB6 Madison 04/18/2007 1600 -- 7.8 435 13.8 43.2 25.1 4.86 1.29 182 -- 221 2.96 13.4 6.76 12.6 -90.70 -12.12 --

WCL 433302103281501 6S 5E12DBAB Madison 04/18/2007 1430 -- 8.0 335 14.8 35.7 19.4 7.67 2.38 149 -- 180 4.46 13.9 9.17 16.4 -90.50 -12.15 --

WCL 433302103281501 6S 5E12DBAB Madison 07/16/2009 1140 -- -- 362 14.0 35.8 19.6 7.21 -- -- 162 196 4.22 12.2 9.57 12.7 -91.60 -12.09 --

WTHL 433302103281502 6S 5E12DBAB2 Madison 04/18/2007 1230 -- 7.8 427 13.8 47.4 27.1 5.08 1.32 211 -- 255 3.02 13.2 6.91 12.8 -90.10 -12.11 --

WTHL 433302103281502 6S 5E12DBAB2 Madison 07/16/2009 1245 -- -- 411 12.5 43.3 24.1 4.63 -- -- 199 241 2.95 12.0 7.57 12.6 -92.50 -12.11 --

Artesian spring sites Artesian spring sites

HBsp 432703103302801 7S 5E10DCBA Minnelusaf 03/15/2007 1000 6.8 7.3 683 23.9 63.9 24.7 36.0 0.431 -- -- 256 45.6 18.2 69.3 6.6 -113 -15.05 --

HBsp 432703103302801 7S 5E10DCBA Minnelusaf 04/20/2007 1600 6.9 7.0 700 24.0 64.5 25.3 36.9 .417 208 -- 253 45.5 18.1 67.5 7.2 -113 -15.07 --

HBsp 432703103302801 7S 5E10DCBA Minnelusaf 07/09/2007 1215 5.2 7.1 718 23.9 64.6 25.5 35.6 .426 206 -- 251 45.8 18.9 68.7 4.7 -114 -15.08 --

HBsp 432703103302801 7S 5E10DCBA Minnelusaf 09/27/2007 1100 7.3 7.1 672 23.9 65.4 25.4 36.8 .430 211 -- 256 45.0 16.8 67.8 6.3 -115 -15.07 --

HBsp 432703103302801 7S 5E10DCBA Minnelusaf 05/28/2009 1330 -- 7.2 710 23.6 69.2 25.7 37.1 -- -- 217 264 44.7 18.7 68.9 7.0 -115 -15.03 --

BCsp 433128103223401 6S 6E14CDB Madisong 03/14/2007 1500 4.8 7.3 2,260 18.0 460 76.8 29.2 .409 -- -- 219 32.5 16.0 1,280 2.1 -110 -14.42 --

BCsp 433128103223401 6S 6E14CDB Madisong 04/17/2007 1230 6.2 7.1 2,390 19.1 443 73.3 27.4 .390 179 -- 217 32.9 14.9 1,290 2.1 -110 -14.40 --

BCsp 433128103223401 6S 6E14CDB Madisong 07/10/2007 1145 -- 7.0 -- 19.4 446 77.3 30.5 .490 177 -- 215 33.8 16.5 1,290 1.7 -110 -14.41 --

BCsp 433128103223401 6S 6E14CDB Madisong 09/26/2007 1320 5.2 6.9 2,350 18.9 478 79.4 30.8 .391 177 -- 215 33.1 14.3 1,280 2.0 -109 -14.42 --

BCsp 433128103223401 6S 6E14CDB Madisong 05/28/2009 945 -- 6.7 2,350 18.5 477 78.2 29.7 -- -- 186 227 34.5 16.6 1,310 1.0 -107 -14.00 --

CASsp 432006103330501 8S 5E20CDAB Madisong 06/19/2009 1100 -- 7.0 2,560 19.3 558 83.6 27.8 -- -- 190 231 29.3 13.7 1,550 1.2 -117 -15.09 --

COOsp 432028103331601 8S 5E20BDCB Madisong 06/19/2009 1425 -- 6.9 1,960 17.8 327 75.3 30.3 -- -- 193 235 33.1 14.5 975 2.3 -116 -15.01 --

HSIsp 432632103285302 7S 5E14DDDA Madisong 03/15/2007 1100 5.0 7.3 1,020 27.2 87.5 28.0 70.0 .450 -- -- 245 97.5 23.8 167 5.8 -120 -16.02 --

HSIsp 432632103285302 7S 5E14DDDA Madisong 04/17/2007 1630 5.4 7.2 1,030 27.3 89.2 29.1 71.9 .456 198 -- 240 99.1 22.7 168 5.7 -120 -16.13 --
46 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota Supplemental Tables 47

Site 

name

Station number Station name Source 

aquifer Date Time

Dissolved 

oxygen 

(mg/L)

pH

Specific 

conductance, 

unfiltered 

(μS/cm)

Temperature 

(°C)

Calcium, 

dissolved 

(mg/L)

Magnesium, 

dissolved 

(mg/L)

Sodium, 

dissolved 

(mg/L)

Nitrate + 

nitrite as 

nitrogen, 

dissolved 

(mg/L)

Acid neutralizing 

capacitya

(mg/L as 

CaCO3)

Alkalinityb

(mg/L as 

CaCO3)

Bicarbonatec

(mg/L)

Chloride, 

dissolved 

(mg/L)

Silica, 

dissolved 

(mg/L)

Sulfate, 

dissolved 

(mg/L)

Arsenic, 

dissolved 

(μg/L)

δ2H (‰) δ18O 

(‰)

Well 

depth 

below 

land 

surface 

(m)

Artesian spring sites—Continued Artesian spring sites—Continued

HSIsp 432632103285302 7S 5E14DDDA Madisong 07/09/2007 1350 5.7 7.0 1,040 27.6 92.2 29.3 71.2 0.487 198 -- 241 99.3 24.4 170 3.5 -120 -15.97 --

HSIsp 432632103285302 7S 5E14DDDA Madisong 09/27/2007 1320 5.5 6.8 1,050 27.6 94.1 30.1 74.4 .489 204 -- 248 94.0 21.9 174 5.8 -122 -15.91 --

HSIsp 432632103285302 7S 5E14DDDA Madisong 05/21/2009 1600 7.1 7.2 1,030 27.4 96.2 30.1 70.2 -- -- 206 251 96.4 25.0 187 6.3 -123 -15.88 --

KIDsp 432605103285401 7S 5E14DDD Madisong 06/19/2009 1630 -- 7.0 1,580 27.8 182 38.9 81.8 -- -- 180 219 117 22.4 478 3.5 -125 -16.31 --

MNKsp 432605103290901 7S 5E14D Madisong 05/28/2009 1450 -- 6.7 1,300 32.4 123 32.9 90.8 -- -- 195 238 125 27.4 275 5.2 -127 -16.44 --

BRsp 433525103224401 5S 6E26BBCD Unknownh 08/13/2009 1545 4.5 7.2 2,900 29.6 594 149 16.9 -- -- 134 163 3.21 13.8 1,940 2.2 -86.60 -11.11 --

CBsp 432744103293401 7S 5E 11BAAB Unknownh 08/21/2009 1445 9.1 7.0 1,130 14.6 168 49.2 15.1 -- -- 235 286 19.6 12.8 388 5.6 -101 -13.28 --

SWsp 432849103283201 6S 5E36CDBB Unknownh 06/17/2010 1600 11.8 7.4 2,500 15.7 502 107 6.78 -- -- 172 209 5.09 8.49 1,540 1.1 -90.80 -11.83 --

Shallow spring sites Shallow spring sites

BRNsp 433137103342101 6S 5E18CABD Minnelusaf 06/11/2010 1020 13.8 7.1 568 10.4 59.0 42.2 5.88 -- -- 295 359 3.64 11.4 20.5 16.9 -97.70 -12.73 --

EMsp 433332103291801 6S 5E 2ACBD Minnelusaf 08/13/2009 915 6.8 7.4 656 12.7 47.9 61.8 3.10 -- -- 358 436 2.04 11.2 20.4 15.3 -95.60 -12.48 --

HSsp 433258103270801 6S 6E 7BAAC Minnelusaf 08/13/2009 1100 4.9 7.1 575 14.8 72.8 11.8 3.98 -- -- 221 270 3.59 14.1 9.80 19.5 -95.90 -12.63 --

NCsp 433312103264701 6S 6E 6DCAA Minnelusaf 08/13/2009 1015 7.7 7.2 409 12.8 75.0 6.50 2.88 -- -- 210 256 2.40 12.3 7.12 16.9 -95.60 -12.55 --

WCsp 433056103322201 6S 5E21BCBC Minnelusaf 08/21/2009 945 1.5 7.1 689 15.0 67.8 53.9 5.27 -- -- 385 469 3.84 13.9 19.5 12.0 -95.20 -12.40 --

WITsp 433611103335801 5S 4E35DDBC Minnelusaf 08/22/2009 1230 10.4 7.2 528 11.6 55.4 23.4 10.2 -- -- 223 272 5.30 8.71 24.4 4.5 -90.90 -11.62 --

IRIsp 434249103370401 4S 4E11CCBB Precambrian 06/17/2010 1420 10.9 6.7 508 14.7 46.9 12.6 13.8 -- -- 156 190 10.5 21.2 19.2 2.7 -90.70 -12.06 --

RGPsp 433551103291901 5S 5E23DBCD Precambrian 08/13/2009 1300 7.0 6.5 372 9.1 55.3 11.9 6.67 -- -- 182 222 1.93 17.1 19.7 2.0 -89.50 -12.16 --

SLsp 434020103350101 4S 4E25DB Precambrian 03/17/2010 1135 7.6 6.5 319 2.1 44.8 8.47 5.62 -- -- 123 150 3.14 17.3 26.7 .82 -112 -14.91 --

PARsp 433717103235401 5S 6E15BBAC White River 08/13/2009 1415 .8 7.2 607 32.4 61.8 18.4 11.5 -- -- 258 314 5.15 21.0 8.38 11.1 -87.80 -11.10 --

Well sites Well sites

BOW 432555103323201 7S 5E20AACA Minnelusa 05/15/2009 1500 4.6 7.3 890 22.7 99.8 33.9 39.1 -- -- 208 253 48.6 18.1 198 3.3 -117 -15.28 152

COL 432727103390201 7S 4E 9BACA Minnelusa 05/07/2009 1200 6.1 7.2 760 7.9 99.2 41.5 6.49 -- -- 224 272 2.83 11.1 201 4.5 -101 -13.08 177

CRA 432846103280501 6S 5E36DCBC Minnelusa 05/14/2009 1615 8.6 7.4 809 12.8 101 46.9 9.76 -- -- 172 210 2.67 9.02 276 10.1 -93.20 -12.27 113

FER 432437103305701 7S 5E27CCCD Minnelusa 05/08/2009 1325 9.2 7.7 1,100 32.9 97.5 29.4 86.6 -- -- 185 224 123 27.5 207 5.6 -126 -16.26 107

FRA 432958103281401 6S 5E24CAAB Minnelusa 05/08/2009 1535 6.3 7.9 434 10.7 47.2 21.3 15.1 -- -- 200 242 3.32 9.00 32.9 37.1 -91.80 -12.08 128

HAL 432720103303701 7S 5E15BABB Minnelusa 05/08/2009 925 5.6 7.5 985 14.1 112 38.5 46.1 -- -- 243 295 67.3 14.4 210 4.0 -118 -15.40 43

HUN 433034103284701 6S 5E23DBBB Minnelusa 03/14/2007 1100 7.3 7.5 400 15.1 48.2 17.1 9.57 0.589 -- -- 235 5.88 15.5 17.3 7.9 -90.40 -12.17 250

HUN 433034103284701 6S 5E23DBBB Minnelusa 04/17/2007 940 -- 7.3 419 15.3 50.5 18.1 10.1 .608 190 -- 230 5.97 15.4 17.2 7.7 -92.40 -12.23 250

HUN 433034103284701 6S 5E23DBBB Minnelusa 09/27/2007 930 8.0 7.2 409 15.5 51.0 17.6 10.0 .596 192 -- 233 5.75 15.0 17.0 7.4 -91.10 -12.21 250

HUN 433034103284701 6S 5E23DBBB Minnelusa 05/21/2009 1510 7.6 7.3 414 13.9 51.1 17.9 9.32 -- -- 198 242 5.77 15.2 17.9 6.6 -92.20 -12.18 250

INM 432332103314801 7S 5E33ABDD Minnelusa 05/07/2009 1500 6.3 7.4 1,190 20.3 110 37.9 83.1 -- -- 209 255 119 23.9 247 4.4 -125 -16.22 147

KIR2 433420103374901 5S 4E34BDDB Minnelusa 06/11/2010 1340 9.3 7.2 771 8.3 107 30.9 13.4 -- -- 318 387 41.1 12.9 24.1 3.0 -97.00 -12.83 5

LEF 433215103464401 6S 3E 5CCD Minnelusa 05/14/2009 1110 6.5 7.5 467 13.2 48.0 26.1 9.70 -- -- 224 272 3.31 11.9 21.5 6.5 -106 -13.81 235

MEY 433215103365801 6S 4E11CCDB Minnelusa 06/11/2010 1510 39.0 7.4 495 10.5 55.8 30.9 6.69 -- -- 223 271 9.31 13.4 29.0 18.5 -99.30 -12.88 104

MILN 432806103330801 8S 5E 5CADD Minnelusa 05/07/2009 1650 4.8 7.0 1,490 23.1 179 52.6 75.1 -- -- 242 295 99.2 24.0 433 3.2 -122 -15.91 152

MYR 433003103420701 7S 3E36CBCC Minnelusa 05/08/2009 1110 12.0 7.5 444 11.2 59.0 20.2 5.27 -- -- 225 274 2.79 12.7 13.5 24.6 -109 -14.14 85

PAL 432806103284101 7S 5E 1CBCC Minnelusa 05/15/2009 1600 7.6 7.0 582 13.1 62.4 29.6 13.1 -- -- 222 270 15.9 10.3 61.4 10.6 -109 -14.30 168

PEK 432852103264401 6S 6E31DBDA Minnelusa 05/21/2009 1410 10.1 7.0 786 13.8 90.6 37.8 19.5 -- -- 203 248 16.0 12.5 198 6.1 -107 -14.16 187

WIL 433141103390901 6S 4E16CABB Minnelusa 06/25/2010 1030 10.5 7.2 479 11.8 53.0 29.8 8.07 -- -- 220 268 7.14 14.0 22.7 18.7 -104 -13.32 129

Table 12. Hydrochemical data for water samples.—Continued

[mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius (°C); μg/L, micrograms per liter; ‰, per thousand; m, meters; --, no data 

or not applicable]
48 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota Supplemental Tables 49

Site 

name

Station number Station name Source 

aquifer Date Time

Dissolved 

oxygen 

(mg/L)

pH

Specific 

conductance, 

unfiltered 

(μS/cm)

Temperature 

(°C)

Calcium, 

dissolved 

(mg/L)

Magnesium, 

dissolved 

(mg/L)

Sodium, 

dissolved 

(mg/L)

Nitrate + 

nitrite as 

nitrogen, 

dissolved 

(mg/L)

Acid neutralizing 

capacitya

 

(mg/L as 

CaCO )3

Alkalinityb 

(mg/L as 

CaCO )3

Bicarbonatec

 

(mg/L)

Chloride, 

dissolved 

(mg/L)

Silica, 

dissolved 

(mg/L)

Sulfate, 

dissolved 

(mg/L)

Arsenic, 

dissolved 

(μg/L)

δ2H (‰) δ18O 

(‰)

Well 

depth 

below 

land 

surface 

(m)

Well sites—Continued Well sites—Continued

BOG

BOG

CON

CON

KAI

KAI

Md7-11

MIL

MIL

PW1

PW1

PW2

PW2

STR

STR

STR

STR

STR

SVE

SVE

SVE

DUR

GRE

KIR1

MOR

SZE

WOO

432858103334201

432858103334201

433326103352001

433326103352001

433114103281601

433114103281601

433115103251401

432340103421501

432340103421501

433311103263101

433311103263101

433311103263102

433311103263102

433150103230501

433150103230501

433150103230501

433150103230501

433150103230501

432825103391201

432825103391201

432825103391201

433658103332301

433701103323401

433821103360901

433635103354301

433718103333101

433636103343901

6S 5E31DAAC

6S 5E31DAAC

6S 4E 1DBBB

6S 4E 1DBBB

6S 5E24BAAA

6S 5E24BAAA

6S 6E21BBBB 

(CU91A)

7S 3E36CBDC

7S 3E36CBDC

6S 6E 6DDAB

6S 6E 6DDAB

6S 6E 6DDAA

6S 6E 6DDAA

6S 6E15ABDD

6S 6E15ABDD

6S 6E15ABDD

6S 6E15ABDD

6S 6E15ABDD

7S 4E 4BACA

7S 4E 4BACA

7S 4E 4BACA

5S 5E17BCDB

5S 5E17ACDD

5S 4E 2DDBD

5S 4E13CCAC

5S 5E17BBBA

5S 5E18CCAC

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Madison

Precambrian

Precambrian

Precambrian

Precambrian

Precambrian

Precambrian

04/26/2007

07/15/2009

04/23/2007

07/15/2009

07/09/2007

09/26/2007

04/20/2007

04/23/2007

03/17/2010

05/24/2007

07/29/2009

05/24/2007

07/29/2009

03/14/2007

04/17/2007

07/10/2007

09/26/2007

05/22/2009

04/23/2007

06/26/2008

09/02/2009

06/17/2010

06/17/2010

06/17/2010

06/25/2010

06/03/2010

06/11/2010

1730

1415

1200

940

1000

1000

1150

1430

1500

1230

1245

1330

920

1400

1430

925

1130

1045

1800

1305

1000

1145

1325

1020

1200

1455

1215

8.4

--

8.6

--

6.8

8.4

4.0

3.9

8.3

7.5

13.7

3.9

7.4

6.7

7.4

--

.5

--

8.4

--

8.7

8.0

9.5

7.8

8.8

9.3

10.2

7.8

7.5

7.7

7.2

7.1

7.1

7.3

7.3

7.1

7.3

7.5

7.7

7.8

7.7

7.5

7.3

6.8

7.6

7.7

6.5

7.2

6.7

7.0

6.9

7.0

7.0

6.5

466

444

579

753

435

413

403

743

730

385

384

586

543

327

343

356

342

330

455

452

453

299

564

718

774

523

196

15.2

16.0

8.7

12.5

15.2

15.1

13.4

21.5

--

13.8

14.7

14.9

14.5

12.8

20.0

23.1

16.7

19.2

12.1

16.6

18.1

14.5

11.3

7.1

11.3

12.2

9.1

44.7

41.3

65.4

86.3

51.4

50.8

40.4

77.8

81.0

46.2

46.1

24.3

27.3

39.0

39.8

40.5

40.0

40.3

53.0

50.9

51.9

43.1

75.9

88.3

47.3

77.0

24.8

29.9

29.1

29.9

37.0

18.5

18.4

19.6

26.6

26.6

15.9

15.2

13.5

13.7

13.8

14.1

14.4

14.1

14.3

26.8

25.6

26.2

7.63

18.2

24.0

78.2

15.9

7.14

6.29

6.39

10.8

14.3

9.74

9.86

16.4

37.5

36.7

12.8

12.2

91.8

78.5

9.08

9.32

9.31

9.38

9.01

4.67

4.33

4.43

6.66

17.7

24.8

14.1

11.7

5.00

1.29

--

2.24

--

.616

.626

.310

.112

--

.569

--

.210

--

.511

.520

.516

.513

--

.451

--

--

--

--

--

--

--

--

217

--

240

--

188

188

170

212

--

178

--

223

--

--

157

142

158

--

231

--

--

--

--

--

--

--

--

--

216

--

316

--

--

--

--

213

--

185

--

223

--

--

--

--

166

--

--

241

130

208

252

424

217

62

262

263

292

385

229

228

206

257

259

217

225

270

271

189

190

172

192

201

281

288

294

158

253

307

517

265

76

2.63

2.24

8.10

17.5

5.74

5.52

5.95

48.0

48.4

5.10

5.33

20.2

17.4

2.48

2.55

2.56

2.47

2.57

1.86

1.82

1.93

3.82

28.8

53.8

8.07

15.1

4.57

12.7

11.8

12.6

13.0

16.3

14.9

12.8

22.1

24.3

16.1

16.0

11.1

11.5

16.3

16.4

17.2

15.8

17.0

12.6

11.6

12.0

22.9

19.7

19.3

18.8

19.4

17.3

10.5

10.0

28.9

34.3

16.4

16.4

23.5

110

98.3

17.9

18.3

43.8

38.4

11.2

11.0

10.9

11.3

11.4

8.61

8.81

9.11

14.4

36.7

40.6

22.1

40.5

27.1

15.8

10.2

6.4

3.6

6.8

7.1

.28

.99

.47

8.5

8.8

26.7

23.0

8.9

8.5

7.6

8.9

9.5

3.9

--

3.9

5.7

2.6

1.8

35.2

1.9

12.7

-99.00

-97.20

-98.60

-100

-90.10

-91.60

-89.70

-125

-128

-89.90

-90.00

-87.10

-88.30

-89.30

-88.20

-88.50

-87.10

-88.30

-114

--

-116

-87.80

-92.70

-97.80

-91.80

-94.20

-87.40

-12.90

-12.69

-12.86

-13.02

-12.24

-12.24

-11.98

-16.64

-16.54

-12.01

-11.94

-11.88

-11.83

-11.86

-11.87

-11.84

-11.82

-11.82

-15.14

--

-15.16

-12.00

-12.38

-12.84

-11.95

-12.63

-11.99

201

201

30

30

238

238

355

651

651

242

242

209

209

286

286

286

286

286

269

269

269

85

32

8

82

38

17

a

b

 Water, filtered, fixed endpoint (pH 4.5) titration, laboratory, milligrams per liter as calcium carbonate.

c

 Calculated from alkalinity by method of Eaton and others (1995).

d

 Beaver Creek near Pringle, South Dakota, station 06402430.

e

 Highland Creek above Madison outcrop, station 434249103370401.

f

 Assumed to flow primarily from Minnelusa aquifer but could include water from other aquifers.

g

 Assumed to flow primarily from Madison aquifer but could include water from other aquifers.

h

 Possibly artesian flowing from Madison or Minnelusa aquifer or both.

 Water, unfiltered, inflection-point titration method (incremental titration method), field, milligrams per liter as calcium carbonate.

Table 12. Hydrochemical data for water samples.—Continued

[mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius (°C); μg/L, micrograms per liter; ‰, per thousand; m, meters; --, no data 

or not applicable]
50 Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota

Table 13. Summary of hydrochemical data for the five hydrogeologic domains.

[PC, Precambrain aquifer; SD, standard deviation; mg/L, milligrams per liter; μS/cm, microsiemens per centimeter at 25 degrees Celsius (°C); μg/L, micrograms 

per liter; ‰, per thousand; m, meters; --, no data or not applicable]

Constituent Units

Artesian 1 Artesian 2 East West PC

Mean SD Mean SD Mean SD Mean SD Mean SD

Dissolved oxygen mg/L 6.1 1.4 6.9 2.9 7.8 3.1 10.4 7.8 8.3 2.1

pH 7.2 .2 7.1 .2 7.8 .5 7.2 .3 6.8 .3

Specific conductance μS/cm 981 271 2,268 495 395 94 605 137 434 160

Temperature °C 25.1 4.4 19.1 4.0 16.1 4.5 12.2 2.6 10.4 4.1

Calcium, dissolved mg/L 97.3 34.1 445.2 120.7 46.0 12.1 66.4 19.9 55.2 20.8

Magnesium, dissolved mg/L 31.1 6.9 84.9 26.4 16.2 6.2 36.8 14.7 13.9 5.9

Sodium, dissolved mg/L 58.8 21.1 24.4 8.4 11.6 16.9 8.9 4.4 12.0 6.8

Bicarbonatea mg/L 253 19 222 30 213 47 319 83 203 70

Chloride, dissolved mg/L 79.4 31.5 25.7 12.2 5.8 5.8 8.2 9.5 14.2 17.1

Silica, dissolved mg/L 21.7 3.6 14.2 2.4 15.6 2.9 12.3 2.1 18.6 2.9

Sulfate, dissolved mg/L 182.3 116.1 1,282.1 402.6 16.5 12.0 55.0 78.0 27.6 9.6

Arsenic, dissolved μg/L 4.7 1.9 2.1 1.3 13.9 9.7 11.4 8.8 3.4 3.8

δ2H ‰ -120.3 4.8 -105.8 10.0 -89.5 3.5 -101.4 7.5 -93.5 7.6

δ18O ‰ -15.80 .56 -13.80 1.34 -11.99 .36 -13.23 1.02 -12.55 .94

Well depth below land 

surface m 120 47 -- -- 120 107 128 81 36 30

a

 Calculated from alkalinity method of Eaton and others (1995).

Publishing support provided by:

Rolla Publishing Service Center

For additional information concerning this publication, contact:

Director, USGS South Dakota Water Science Center

1608 Mt. View Rd.

Rapid City, SD 57702

(605) 394-3200

Or visit the South Dakota Water Science Center Web site at:

http://sd.water.usgs.gov

Long and others—Groundwater Flow, Quality (2007–10), and Mixing in the Wind Cave National Park Area, South Dakota—SIR 2011–5235

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