U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007-5001

Prepared in cooperation with the City of Spearfish and Lawrence County

Characterization of Ground-Water Flow and

Water Quality for the Madison and Minnelusa

Aquifers in Northern Lawrence County,

South Dakota
Cover:  Photograph of collecting a water sample from the bottom of Mirror Lake near spring opening T. 7 N., R. 1 E., section 17

(photograph by Larry D. Putnam, U.S. Geological Survey)
Characterization of Ground-Water Flow 

and Water Quality for the Madison and 

Minnelusa Aquifers in Northern Lawrence 

County, South Dakota

By Larry D. Putnam and Andrew J. Long

Prepared in cooperation with the City of Spearfish and Lawrence County

Scientific Investigations Report 2007–5001

U.S. Department of the Interior

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

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Putnam, L.D., and Long, A.J., 2007, Characterization of ground-water flow and water quality for the Madison and 

Minnelusa aquifers in northern Lawrence County, South Dakota: U.S. Geological Survey Scientific Investigations 

Report 2007–5001, 61 p.
iii

Contents

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

Introduction.....................................................................................................................................................2

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

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

Acknowledgments................................................................................................................................2

Hydrogeologic Setting...................................................................................................................................2

Methods...........................................................................................................................................................3

Mapping Potentiometric Surfaces.....................................................................................................3

Dye Tracing Tests................................................................................................................................10

Geochemical Tracers .........................................................................................................................10

Sample Collection and Analysis..............................................................................................10

Oxygen and Deuterium Isotopes.............................................................................................11

Chlorofluorocarbons .................................................................................................................11

Tritium .........................................................................................................................................11

Estimating Ground-Water Age from Chlorofluorocarbons .................................................12

Water Quality.......................................................................................................................................12

Characterization of Ground-Water Flow..................................................................................................13

Recharge..............................................................................................................................................13

Areal Recharge ..........................................................................................................................16

Streamflow Recharge ...............................................................................................................16

Spring Discharge ................................................................................................................................18

Potentiometric Surfaces....................................................................................................................19

Flow Paths and Flow Rates Based on Dye Tracing.......................................................................19

Fluorescein Injection.................................................................................................................24

Rhodamine WT Injection ..........................................................................................................26

Ground-Water Flow Paths, Ages, and Mixing Based on Geochemical Tracers ......................29

Oxygen and Deuterium Isotopes.............................................................................................29

Chlorofluorocarbons .................................................................................................................31

Ground-Water Age Distributions from Chlorofluorocarbon Data.............................33

Evidence for a Conduit Based on the Spatial Distribution of Apparent Ages ........33

Tritium ................................................................................................................................34

Synopsis of Results from Geochemical Tracers...................................................................35

Characterization of Water Quality.............................................................................................................36

Summary........................................................................................................................................................44

References....................................................................................................................................................45

Supplemental Information..........................................................................................................................49

Section A.  Additional data .............................................................................................................51

Section B.  Dye Tracing Methods ..................................................................................................58

Fluorescein..................................................................................................................................58

Rhodamine WT...........................................................................................................................58
iv

Section C.  Chlorofluorocarbon Age-Dating Methods and Background ................................60

Chlorofluorocarbons .................................................................................................................60

Dissolved Gas Data....................................................................................................................60

Figures

1.  Map showing location of study area.........................................................................................4

2.  Map showing hydrogeologic units of study area....................................................................6

3.  Chart showing stratigraphic section for study area...............................................................8

4.  Simplified hydrogeologic setting in the study area.................................................................9

5.  Graph showing estimated 6-month tritium concentration in precipitation for the

Black Hills, South Dakota ..........................................................................................................12

6.  Graphs showing water-level hydrographs for observation wells completed in the

Madison aquifer and the Minnelusa aquifer..........................................................................14

7.  Graph showing comparison of average annual streamflow and base flow for

Crow Creek ..................................................................................................................................18

8.  Map showing generalized potentiometric surface of the Madison aquifer

in 2004 ...........................................................................................................................................20

9.  Map showing generalized potentiometric surface of the Minnelusa aquifer

in 2004 ...........................................................................................................................................22

10–15.  Graphs showing

10.  Fluorescein breakthrough curves for wells where dye was detected,

March 2003–September 2004 ..........................................................................................24

11.  Rhodamine WT breakthrough curves for wells where dye may be present,

May 2003–September 2004 ..............................................................................................28

12.  Water level in the Madison aquifer for observation well LA–88C near

Spearfish during dye injections.......................................................................................29

13.  Relation between δ18O and δD in water samples collected from 1978 to

2005 from Madison and Minnelusa wells and springs, and surface water.............31

14.  Regression analysis of CFC–11 apparent age with distance to a possible

major conduit......................................................................................................................34

15.  Regression analysis of tritium concentration with distance to a possible

major conduit......................................................................................................................35

16.  Map showing specific conductance of water from the Madison aquifer........................38

17.  Map showing specific conductance of water from the Minnelusa aquifer. ....................40

18.  Boxplot showing comparison of background, blank, and replicate samples for

fluorescein dye analysis............................................................................................................58

19.  Graph showing comparison of initial fluorescein concentrations with

concentrations in samples that were stored for about 1 year............................................59

20.  Boxplot showing comparison of background, blank, and replicate samples for

Rhodamine WT dye analysis.....................................................................................................59

21.  Graph showing atmospheric concentrations of chlorofluorocarbons CFC–11,

CFC–12, and CFC–113 .................................................................................................................60
Tables

1.  Estimated average annual recharge to the Madison and Minnelusa aquifers in the

study area ....................................................................................................................................16

2.  Streamflow loss to the Madison aquifer in upper reach of loss zone along

Spearfish Creek...........................................................................................................................17

3.  Streamflow gains or losses for selected reaches of Spearfish Creek..............................17

4.  Streamflow losses to the Madison aquifer from Spearfish Creek .....................................18

5.  Summary of fluorometric analysis of water samples for fluorescein dye ........................25

6.  Summary of fluorometric analysis of water samples for Rhodamine WT dye.................27

7.  Oxygen- and deuterium-isotope data for wells and springs in the study area................30

8.  Chlorofluorocarbon and tritium data for wells and springs in the study area .................32

9.  Chemical analyses of selected ground-water samples from the Madison and

Minnelusa aquifers.....................................................................................................................42

10.  Observation wells used for monitoring water levels in the study area.............................51

11.  Water wells completed in the Madison aquifer and used for interpretation of

average potentiometric surface...............................................................................................52

12.  Water wells completed in the Minnelusa aquifer and used for interpretation of

average potentiometric surface...............................................................................................54

13.  Analysis of fluorescein standards for concentrations of Rhodamine WT........................59

14.  Dissolved-gas data for selected wells and springs in the study area...............................61

Conversion Factors

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

ounce, fluid (fl. oz) 0.02957 liter (L) 

pint (pt) 0.4732 liter (L) 

quart (qt) 0.9464 liter (L) 

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3) 

gallon (gal) 3.785 cubic decimeter (dm3) 

million gallons (Mgal) 3,785 cubic meter (m3)

cubic inch (in3) 16.39 cubic centimeter (cm3) 
vi

Multiply By To obtain

Flow rate

foot per day (ft/d) 0.3048 meter per day (m/d)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

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

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

Mass

pound, avoirdupois (lb) 0.4536 kilogram (kg) 

Pressure

pound per square inch (lb/in2) 6.895 kilopascal (kPa) 

Transmissivity*

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d) 

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

°F=(1.8×°C)+32

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

°C=(°F-32)/1.8

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929

(NGVD 29).

Horizontal coordinate information is referenced to the North American Datum of 1927 (NAD 27).

Altitude, as used in this report, refers to distance above the vertical datum.

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot

squared per day (ft2/d), is used for convenience.

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

at 25°C).

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L)

or micrograms per liter (μg/L).

Isotopic ratios are expressed in units of per mil (parts per thousand). Tritium concentrations are

expressed in units of picocuries per liter (pCi/L) or tritium units (TU).

Water year is the 12–month period, October 1 through September 30, and is designated by the

calendar year in which it ends. Thus, the water year ending September 30, 2003, is called

“water year 2003.”
vii

Acronyms and Abbreviations

‰ per mil

MCL Maximum Contaminant Level

CFC chlorofluorocarbon

pptv parts per trillion by volume

pCi/L picocuries per liter

SDDENR–WR Water Rights Program of the South Dakota Department of Environment

and Natural Resources

TU tritium units

USEPA U.S. Environmental Protection Agency

USGS U.S. Geological Survey

VSMOW Vienna Standard Mean Ocean Water

δD 2H/1H ratio compared to a reference composition

δ18O 18O/16O ratio compared to a reference composition

cm3/L cubic meters per liter
viii
Characterization of Ground-Water Flow and Water Quality 

for the Madison and Minnelusa Aquifers in Northern 

Lawrence County, South Dakota

By Larry D. Putnam and Andrew J. Long

originating from the outcrops of the Madison Limestone and 

Minnelusa Formation within the study area.

Concentrations of three chlorofluorocarbons (CFC–11, 

CFC–12, and CFC–113) were used to characterize groundwater residence times in the study area. For the four wells 

where dye was detected, CFC–11 apparent ages ranged from 

12 to 26 years, indicating that the wells contained months-old 

water mixed with years- to decades-old water. Logarithmic 

regression analysis of the CFC–11 apparent ages for water 

from 10 wells and distance to a possible conduit trending 

north through the area where dye was detected, yielded an r2

value of 0.71. Straight-line regression analysis of the CFC–11 

apparent ages for the six wells closest to the possible conduit 

had an r2 value of 0.96. Two wells located relatively close to 

the outcrop areas had no or very low tritium values indicating 

relatively long residence times and diffuse ground-water 

flow. The tritium value of 7.2 TU in water from well COL 

where dye was detected, indicated that the water probably 

is a bimodal mixture, with a substantial portion that is older 

than 50 years. Water from well ELL, where dye was detected, 

had a tritium value of 19.7 TU and a CFC apparent age of 

15 years, indicating that the sample from this well probably is 

a unimodal mixture with very little water older than 50 years. 

Comparison of the CFC apparent age for three spring sites 

(Cox Lake, 26 years; McNenny Pond, 26 years; Mirror Lake, 

13 years) also indicated that Mirror Lake spring probably has 

a component of local recharge from formations that overlie the 

Minnelusa Formation.

In the Madison aquifer, specific conductance ranges from 

18 to 945 microsiemens per centimeter. In the Minnelusa aquifer, specific conductance increases with distance from the outcrop and ranges from 2 to 3,000 microsiemens per centimeter. 

Water samples from two observation wells completed in the 

Madison and Minnelusa aquifers near Spearfish and two wells 

about 6 miles east of Spearfish were analyzed for physical 

properties, major ions, nutrients, trace elements, and radionuclides. U.S. Environmental Protection Agency Maximum 

Contaminant Levels were not exceeded for any of the constituents analyzed in water from the four wells. The U.S. Environmental Protection Agency Secondary Maximum Contaminant 

Level for sulfate (250 milligrams per liter) was exceeded in 

Abstract

The Madison and Minnelusa aquifers are used extensively 

for water supplies for the city of Spearfish and other users in 

northern Lawrence County, South Dakota. Ground water in the 

Madison and Minnelusa aquifers in the study area generally 

flows north from outcrop areas where recharge from sinking 

streams and infiltration of precipitation occurs. Ground water 

that moves northward and eastward around the Black Hills 

enters the study area from the west and results in hydraulic 

heads that are several hundred feet higher on the western 

side of the study area than on the eastern side. The estimated 

average recharge rate of 38 cubic feet per second (ft3/s) on 

outcrops of the Madison Limestone and Minnelusa Formation 

is less than the total estimated average spring discharge rate of 

51 ft3/s in the northwestern part of the study area.

Sixteen pounds of fluorescein dye were injected into 

Spearfish Creek on March 25, 2003, when streamflow was 

6.6 ft3/s. The dye was detected in water samples from four 

wells completed in the Madison aquifer ranging from 2.6 to 

4.5 miles north of the injection site. First arrival times ranged 

from 5 to 169 days, and ground-water velocities ranged from 

about 0.1 to 0.5 mile per day. Sixty-four pounds of Rhodamine 

WT was injected into Spearfish Creek at the same location on 

May 9, 2003, when streamflow was 5.6 ft3/s. Rhodamine WT 

dye concentrations measured in samples from the same four 

wells were about an order of magnitude less than measured 

fluorescein concentrations.

Oxygen- and deuterium-isotope values for samples from 

Cox Lake and McNenny Pond springs indicated a probable 

component of spring discharge that originates from outcrops 

of the Madison Limestone and Minnelusa Formation on the 

Limestone Plateau south of the study area. Oxygen- and 

deuterium-isotope values for samples from Mirror Lake spring 

indicated possible contributions from overlying aquifers and 

local recharge. Oxygen- and deuterium-isotope values for the 

combined springflow contributing to Crow Creek in the northwestern part of the study area indicated that the primary source 

of water is the Madison and Minnelusa aquifers. Oxygen- and 

deuterium-isotope values for Old Hatchery and Higgins Gulch 

springs, located north of Spearfish, indicated a source water 
water from the Minnelusa well located east of Spearfish, with 

a concentration of 392 milligrams per liter.

Introduction

The Madison and Minnelusa aquifers are used extensively for water supplies for the city of Spearfish and other 

users in northern Lawrence County, South Dakota, that include 

domestic, non-community, community, and irrigation users. 

A better understanding of ground-water flow in this complex 

hydrologic setting is needed to manage and protect these 

important water resources. The Madison Limestone and Minnelusa Formation have extensive fractures, solution-enhanced 

openings, and collapse features that result in large and variable 

secondary porosities and large heterogeneity in associated 

aquifer properties. For this reason, ground-water flow generally is complicated in these aquifers, and influences regarding 

water quality can be complex. A cooperative study between 

the U.S. Geological Survey (USGS), Lawrence County, and 

the city of Spearfish was initiated in 2000 to collect and analyze ground-water data to improve understanding of groundwater flow and water quality in these complex aquifers in 

northern Lawrence County.

Purpose and Scope

The purpose of this report is to present information 

that characterizes ground-water flow and water quality in 

the Madison and Minnelusa aquifers in northern Lawrence 

County. Most of the data included in this report were collected 

during 2000–2006. For the characterization of ground-water 

flow, this report includes estimates of recharge and spring 

discharge; potentiometric surfaces, flow paths and flow rates 

based on dye tracing; and ground-water flow paths, ages, 

and mixing based on geochemical tracing. The description of 

water quality for the Madison and Minnelusa aquifers focuses 

on selected wells and the general distribution of specific conductance.

Description of Study Area

The study area in northern Lawrence County consists of 

about 400 square miles (mi2) in the northwestern part of the 

topographically distinct Black Hills and adjacent foothills 

and plains to the north (fig. 1). Land-surface altitudes range 

from about 6,000 feet (ft) in the southwestern part of the study 

area to about 3,000–4,000 ft in the plains to the north, resulting in an orographically induced microclimate characterized 

generally by greater precipitation and lower temperatures at 

the higher altitudes. The lowest altitude is near 3,000 ft in the 

northeastern corner of the county. Average annual precipitation for 1961–1990 ranged from about 29 inches (in.) near 

Deadwood to about 18 in. in the northwestern part of the 

study area (Driscoll and others, 2000). The average 30-year 

annual temperature is 46.5oF at Spearfish and 41.8oF at Lead 

(National Oceanic and Atmospheric Administration, 1997), 

which is located about 1 mi southwest of Deadwood.

Acknowledgments

The authors thank the city of Spearfish and residents 

of Lawrence County for their cooperation with data collection associated with this study. The Water Rights Program of 

the South Dakota Department of Environment and Natural 

Resources (SDDENR–WR) provided water-level records 

for observation wells and access to the observation wells for 

water-quality sampling. South Dakota Game Fish and Parks 

allowed access to spring-fed ponds for sampling. Numerous 

private entities also allowed access to wells and springs for 

sampling. The city of Spearfish provided extensive assistance 

with the collection of samples from municipal production 

wells for fluorescent dye tracing. The city of Spearfish and 

Homestake Mining Company also provided assistance with the 

streamflow measurements for Spearfish Creek.

Hydrogeologic Setting

Geologic formations in the study area have been grouped 

into hydrogeologic units and mapped for the Black Hills 

area based on similarity in hydraulic properties (Strobel and 

others, 1999). A generalization of that map (fig. 2) shows the 

surface exposures of the hydrogeologic units for the study 

area, labeled with the stratigraphic unit abbreviations for the 

grouped geologic formations (fig. 3). Precambrian igneous 

and metamorphic rocks in the southern part of the study area 

represent the northern extent of the central core of the Black 

Hills where the sedimentary rocks have been removed by erosion. Various outcrops of Tertiary-age intrusive rocks exist in 

the southern part of the study area (Lisenbee, 1985) that may 

include shallowly emplaced sills, laccoliths, dikes, and plugs. 

North of the Precambrian rocks are exposures of overlying 

limestone, sandstone, and shale. These bedrock sedimentary 

formations typically dip away from the uplifted Black Hills 

at angles that approach 15 to 20 degrees near the outcrops 

(Carter and Redden, 1999a, 1999b, 1999c), and decrease with 

distance from the uplift to about 2 degrees in the northeastern 

part of the study area. Unconsolidated units of Quaternary age 

include alluvium, colluvium, and gravel deposits. Mapped 

alluvial deposits along streams generally are widest in the 

northern part of the study area, where stream gradients generally are lowest.

The Madison and Minnelusa aquifers are contained 

within the Paleozoic-age Madison Limestone and Minnelusa 

Formation, and their relation to other sedimentary units is 

schematically illustrated in figure 4. The Minnelusa Formation 

is overlain by the Opeche Shale, and the Madison Limestone 

is underlain by the Englewood Formation. The hydraulic 

 Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
connection between the Madison Limestone and Minnelusa 

Formation is spatially variable and probably results from 

faults, fractures, and breccia pipes. Collapse features resulting 

from the dissolution of anhydrite and gypsum in the Minnelusa Formation and from the dissolution of carbonates in the 

Madison Limestone may be pathways for vertical movement 

of water between these units. These features are described by 

several authors including Brobst and Epstein (1963), Bowles 

and Braddock (1963), Gott and others (1974), Hayes (1999), 

Greene (1999), and Long and Putnam (2002).

The Mississippian-age Madison Limestone is composed 

of limestone and dolomite, and thickness ranges from about 

350 to 1,000 ft in the study area (Putnam, 2000). Secondary 

permeability generally is greater in the upper part of the 

formation because of solution openings and fractures (Greene, 

1993). The upper surface of the formation is a weathered karst 

surface, unconformable with the overlying Minnelusa Formation (Cattermole, 1969). The aquifer is considered karstic 

because of the extensive solution enlargement of fractures that 

have resulted in a predominance of conduit flow. Secondary 

permeability in the lower part of the Madison Limestone generally is much smaller than in the upper part (Greene, 1993); 

however, the lower part of the unit can have greater permeability near outcrop areas, especially along stream channels. Well 

yields in the Madison aquifer are highly variable and most 

range from 10 to 200 gallons per minute (gal/min) with some 

yields ranging from 400 to 1,750 gal/min.

The Pennsylvanian- and Permian-age Minnelusa 

Formation is 350 to 650 ft thick in the study area. Bowles and 

Braddock (1963) describe the upper part as thick sandstone 

with thin limestone, dolomite, and mudstone, and the lower 

part as having less sandstone and more shale, limestone, and 

dolomite. Siltstone, gypsum, and anhydrite also can be present. At the base of the Minnelusa Formation is a red clay shale 

that ranges from 0 to 50 ft thick (Cattermole, 1969; Greene, 

1993). This shale is an ancient residual soil developed on the 

surface of the Madison Limestone (Gries, 1996). The upper 

200 to 300 ft of the Minnelusa Formation is more permeable 

than the lower part of the formation because of the coarser 

sandstone, solution openings, breccias, and other collapse 

features in the upper part (Peter and others, 1987; Greene, 

1993). The lower part of the formation generally impedes 

flow between the Minnelusa and Madison aquifers (Kyllonen 

and Peter, 1987; Peter and others, 1987; Greene, 1993). Near 

outcrop areas and structural features, the lower part of the 

Minnelusa Formation can have increased permeability due 

to weathering and fracturing. Well yields are highly variable; 

most of the wells yield between 10 and 200 gal/min, many 

wells yield between 200 and 700 gal/min, and a few wells 

yield as much as 1,700 gal/min.

The Madison and Minnelusa aquifers are unconfined in 

and near the outcrop areas and confined in the rest of the study 

area north of the outcrops. When the confined portions of an 

aquifer are penetrated by wells, the water level rises above 

the top of the respective formation. A well drilled into such 

an aquifer is often referred to as an artesian well. When the 

water in the well rises above the land surface, the well may 

be referred to as a flowing well. Also, springs that discharge 

to the land surface through openings in overlying confining 

layers often are referred to as artesian springs.

Transmissivity of the Madison and Minnelusa aquifers is 

very heterogeneous. Transmissivity values from aquifer tests 

that analyzed the formations at several different scales of area 

around a well stressed by aquifer tests (Greene and others, 

1998) ranged over several orders of magnitude. Transmissivity values from testing production wells at a scale of 1,000–

2,000 ft were about 10,000 feet squared per day (ft2/d) for 

the Minnelusa aquifer and about 40,000 ft2/d for the Madison 

aquifer. Confined storage coefficients ranged from 0.00007

to 0.0003. A summary of estimates of hydraulic conductivity, transmissivity, storage coefficient, and porosity for the 

Madison and Minnelusa aquifers in the Black Hills area is 

provided by Driscoll and others (2002, p. 27–28).

Methods

This section of the report describes methods used for 

mapping potentiometric surfaces, dye tracing tests, geochemical tracers, and water quality. Additional data for mapping 

potentiometric surfaces are provided in Supplemental Information Section A at the end of this report. Additional information 

regarding methods for dye tracing and chlorofluorocarbon 

(CFC) age-dating is provided in Supplemental Information 

Sections B and C, respectively, at the end of this report.

Mapping Potentiometric Surfaces

The potentiometric surface of an aquifer is equal to the 

altitude at which water will rise in tightly cased wells open to 

that aquifer (Lohman and others, 1972). In unconfined areas, 

such as outcrops of water-bearing rocks, this surface is equal 

to the water-table altitude. Potentiometric surfaces of the 

Madison and Minnelusa aquifers were defined based on water 

levels or pressures measured in public and private wells. For 

wells under pressure, pressure measurements were converted 

to equivalent feet of water above the land surface. The potentiometric surfaces represent water-level altitudes, which are 

referred to as hydraulic heads.

Water levels in wells were measured on various dates 

between 1905 and 2002 by the drillers at the time of well 

installation or by USGS personnel during previous studies. 

Because of difficulties related to access of private or publicsupply wells, water levels were not measured as part of this 

study. Wells constructed since about 1993, when the last well 

inventory was completed, were site visited and locations and 

land-surface altitudes were determined. The static water level 

reported in the well completion report was used in addition 

to previous water-level measurements in creating the potentiometric maps. An attempt was made to adjust for low water 

levels that were measured during dry conditions and for high 

Methods 
Figure 1.  Location of study area.

Spearfish

Beaver

Beaver

Bear

Iron

Creek

False

Robison

Gulch

Bottom

Creek

Spearfish

Creek

Creek

Creek

Crow

Creek

Creek

Gulch

Gulch

Higgins

Red

Water

River

14A

385

14

90

14

85

85

34

Spearfish

Maurice

Deadwood

LaFlamme

anticline

!?

#

#

#

#

#

#

#

#

#

Streamflow

loss zone

MDme

MDme

MDme

MDme

MDme

PPm

PPm

PPm

PPm

06430950

06431500

06430532

442637103521100

06430900

442757103510600

442649103520200

442433103534400

442835103510501

06430950

06430900

06431500

442757103510600

442835103510501

442649103520200

442433103534400

06430532

442637103521100

MIT 

SAL COL

DIC

ELL

MP2

PT

GC

KYT

NEV

JEF

MP3

VIG

PT

GC

KYT

NEV

JEF

MP3

VIG

Cox Lake

Mirror Lake

McNenny Pond

Old Hatchery

Higgins Gulch

LA-95C

LA-87A

LA-87B

LA-96B

LA-96C

LA-88A

LA-95A

LA-86A

LA-62A

LA-88B

LA-88C

LA-95C

LA-87A

LA-87B

LA-96B

LA-96C

LA-88A

LA-95A

LA-86A

LA-62A

LA-88B

LA-88C

Split Rock

Limestone Plateau

Planimetric base from U.S. Geological Survey digital data: 1:100,000, 1977, 1983

Universal Transverse Mercator projections, zone 13

104°0'

103°50'

44°35'

44°30'

44°25'

R. 1 E. R. 2 E. R. 3 E. 

 Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Study

area

South Dakota

Madison

Limestone

outcrop in

Black Hills

area

Creek

Whitewood

90 14

14

34

Whitewood

!?

#

MDme

MDme

MDme

MDme

PPm

PPm

PPm

PPm PPm

0643053206430532

MIT

ELL

VIGVIG

LA-96D

LA-86C

LA-90A

LA-63A

LA-96D

LA-86C

LA-90A

LA-63A

LA-88A

0 1 2 3 4 5

0 1 2 3 4 5

MILES

KILOMETERS

Fault—Bar on downthrown side

Anticline—Showing trace of axial plane and direction 

 of plunge

Syncline—Showing trace of axial plane and direction 

 of plunge. Dashed where approximate

Monocline—Showing trace of axial plane

Dome—Symbol size approximately proportional to size 

 of dome. Dome asymmetry indicated by arrow length

EXPLANATION

USGS stream gaging station—Number is station identification 

 number

Possible conduit location

Outcrop of Madison Limestone ( )— Includes areas 

 overlain by surficial deposits (modified from Strobel and 

 others, 1999)

Outcrop of Minnelusa Formation ( )—Includes areas 

 overlain by surficial deposits (modified from Strobel and 

 others, 1999)

Streamflow diversion intake at Maurice

Structural features (from Strobel and others, 1999)

Water well where tracer dye was detected—Label is well 

 identification

Water well where tracer dye was not detected—Label is well 

 identification

Water well where tracer dye was not sampled—Label is well 

 identification

Continuous-record observation well—Label is well 

 identification

Spring sampled for tracer dye (not detected)—Tail indicates

 direction of flow

Spring—Tail indicates direction of flow

103°40'

T. 7 N.

T. 6 N.

T. 5 N.

R. 4 E.

Methods 
Figure 2.  Hydrogeologic units of study area (modified from Strobel and others, 1999).

Spearfish

Beaver

Bear

Gulch

Beaver

Creek

False

Bottom

Creek

Spearfish

Creek

Creek

Creek

Crow

Red

Water

River

Gulch

Higgins

Iron

Creek

14A

385

14

90

14

85

85

34

Spearfish

Maurice

Deadwood

LaFlamme

anticline

Kik

Kik

Qa

Qa

Qa

Qa

Qa

Qa

Qa

Pmk Pmk

Qa

Tui

MDme

TrPs

Po

Po

Po

Po

Ju

Ju

Tui

Tw

Tw

Tw

Qg

Pmk

Tui

Qa

Tui

MDme

Qg

Ju

Ju

Tui 

Tui

Qg

Qg

Tui

Qg

Tui

Qg

Qa

Qa

Tui

Qg

Ou

Ou

Kps

Qg

Qg

MDme

Ou

Qc

Qc

Qg

Tw

Pmk

Po

Qg

Ou

Ou

Ou

Po

Ju

Ju

Tw

Kik

Qa

pCu

pCu

OCd OCd

OCd

OCd

OCd

PPm

PPm

PPm PPm

PPm

TRPs

TRPs

TRPs TRPs

TRPs

TRPs

TRPs

Split Rock

Limestone Plateau

Planimetric base from U.S. Geological Survey digital data: 1:100,000, 1977, 1983

Universal Transverse Mercator projections, zone 13

104°

103°50'

44°35'

44°30'

44°25'

R. 1 E. R. 2 E. R. 3 E. 

 Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Creek

Whitewood

90 14

14

34

Whitewood

Qa

Qc

Qg

Tw

Tui

Kps

Ju

TRPs

MDm

Kik

Pmk

Po

Ou

PPm

OCd

pCu

Kps

Qa

Qa

Kik

Kik

Tw

Tw

Kik

Ju

Tui

Qg

Qg

Qg

Kps

Kps

Tui

Pmk

Ju

Pmk

Qg

Qa

Qa

Qa

Qa

Qa

MDme

MDme

Ju

Ou

Tw

Qc

g

Qg

Qg

Qa

Po

Tui

Qg

Qg

Qa

Tui

OCd

OCd

PPm

PPm

PPm

PPm

PPm

PPm

TRPs

TRPs

0 1 2 3 4 5

0 1 2 3 4 5

MILES

KILOMETERS

EXPLANATION

Alluvium

Colluvium

Gravel deposits

White River aquifer

Tertiary intrusive units

Cretaceous-sequence confining unit

Inyan Kara aquifer

Jurassic-sequence semiconfining unit

Spearfish confining unit

Minnekahta aquifer

Opeche confining unit

Minnelusa aquifer

Madison aquifer

Ordovician-sequence semiconfining unit

Deadwood aquifer

Precambrian igneous and metamorphic units

Hydrogeologic Units

Water body

103°40'

T. 7 N.

T. 6 N.

T. 5 N.

R. 4 E.

Fault—Bar on downthrown side

Anticline—Showing trace of axial plane and direction 

 of plunge

Syncline—Showing trace of axial plane and direction 

 of plunge. Dashed where approximate

Monocline—Showing trace of axial plane

Dome—Symbol size approximately proportional to size 

 of dome. Dome asymmetry indicated by arrow length

Structural features (from Strobel and others, 1999)

Methods 
Figure 3.  Stratigraphic section for study area.

GEOLOGIC FORMATION DESCRIPTION

SUBSURFACE

THICKNESS,

IN FEET1

ABBREVIATION

FOR

STRATIGRAPHIC

INTERVAL

SYSTEM ERATHEM

QUATERNARY

& TERTIARY (?)

UNDIFFERENTIATED SANDS AND GRAVELS 20-60 Sand, gravel, and boulders

Light colored clays with sandstone channel fillings and local limestone lenses. WHITE RIVER GROUPIncludes rhyolite, latite, trachyte, and phonolite. INTRUSIVE IGNEOUS ROCKS

TwTui TERTIARY

Qa, Qc, Qg

GRANEROS GROUP Kps BELLE FOURCHE SHALE MOWRY SHALE MUDDY SANDSTONE DYNNESON NEWCASTLE

SKULL CREEK SHALE

2150-850

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

2125-230

20-100

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

2150-270 Dark gray to black siliceous shale.

CRETACEOUS

FALL RIVER FORMATION

LAKOTA

FM

INYAN KARA

GROUPFuson Shale Minnewaste Limestone

410-200 Massive to slabby sandstone.

Coarse gray to buff cross-bedded conglomeratic sandstone, interbedded with buff, red, and gray clay, especially toward top. Local fine-grained limestone. 430-300

20-15020-275

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

2250-475

20-125

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

MORRISON FORMATION

UNKPAPA SS Redwater Member

Lak MemberHulett MemberStockade Beaver Mem.Canyon Spr Member

SUNDANCEFORMATIONGYPSUM SPRING FORMATION

Kik

Ju JURASSIC

Goose Egg Equivalent

SPEARFISH FORMATION T Ps R TRIASSICMINNEKAHTA LIMESTONEOPECHE SHALE Po

Pmk

2375-800

335-50

Red sandy shale, soft red sandstone and siltstone with gypsum and thin limestone layers.Gypsum locally near the base.Thin to medium-bedded finely-crystalline, purplish gray laminated limestone.Red shale and sandstone. 225-150

5350-650

6350-1000

440-7520-15020-110

3300-500

Yellow to red cross-bedded sandstone, limestone, mudstone, and anhydrite locally at top.Red shale with interbedded limestone and sandstone at base.Massive light-colored limestone. Dolomite in part. Cavernous in upper part.Pink to buff limestone. Shale locally at base.Buff dolomite and limestone.Green shale with siltstone.Massive to thin-bedded buff to purple sandstone. Greenish glauconitic shale, flaggy dolomite, and flatpebble limestone conglomerate. Sandstone, with conglomerate locally at the base.Schist, slate, quartzite, and arkosic grit. Intruded by diorite, metamorphosed to amphibolite, and by granite and pegmatite.

PERMIAN

PENNSYLVANIAN

MISSISSIPPIAN

P Pm MINNELUSA FORMATION

MADISON (PAHASAPA) LIMESTONEENGLEWOOD FORMATION

MDm

Ou

DEVONIAN

WHITEWOOD (RED RIVER) FORMATIONWINNIPEG FORMATIONDEADWOOD FORMATIONUNDIFFERENTIATED METAMORPHICAND IGNEOUS ROCKS

OCd

pCu

ORDOVICIAN

CAMBRIAN

CENOZOIC MESOZOIC PALEOZOIC

PRECAMBRIAN

Modified from information furnished by the Department of Geology and

Geological Engineering, South Dakota School of Mines and Technology

(written commun., January 1994)

30-150

---

1 The subsurface thickness was modified from several references to provide

a range that was the most specific to the study area.

2 DeWitt and others, 1989.3 Robinson and others, 1964.4 Kyllonen and Peter, 1987.5 Thickness estimated from subtracting surfaces created from structure contours

of the tops of Madison Limestone and Minnelusa Formation (Carter and Redden, 1999b; 1999a).

6 Thickness estimated from subtracting surfaces created from structure contours

of the tops of Deadwood Formation and Madison Limestone (Carter and Redden, 1999c; 1999b). The subsurface thicknesses of the Madison Limestone greater than 700 feet are in the northeast part of the study area.

Interbedded sandstone, limestone, dolomite, shale, gypsum, and anhydrite.

 Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Precambrian metamorphic

and igneous rocks

Deadwood

Madison

Inyan Kara

Group Formation

Limestone

Limestone

Minnekahta Minnelusa

Madison

Limestone

Formation

Minnelusa

Formation

Deadwood

Formation

Alluvial

aquifer

Potentiometric

surface of

Madison

aquifer

Spring

conduit

Water

table

Cave

Flowing well

LIMESTONE

PLATEAU

Headwater

springs

Artesian

springs

Dip of sedimentary rocks exaggerated

Relative thickness NOT TO SCALE

Major aquifers

Confining unit

EXPLANATION

South North

Figure 4.  Simplified hydrogeologic setting in the study area.

water levels measured during wet conditions. To create a contemporaneous potentiometric surface, it was necessary to estimate water levels that represent current conditions. Therefore, 

measured water levels were adjusted based on records from 

continuous water-level observation wells in the study area 

to approximate potentiometric surfaces representing current 

conditions. The similarity of water level records for observation wells at various locations (as described in the “Characterization of Ground-Water Flow” section) indicates that water 

levels in nearby wells with single measurements probably also 

changed similarly to water levels in the observation wells.

September 15, 2004, was selected as the date for which 

potentiometric surfaces would be estimated. Thus, measured 

water levels were adjusted to a water level that was estimated 

for each well based on the nearest observation well open to 

the same aquifer (table 10 in Supplemental Information Section A). If the date of measurement was prior to the measured 

period of record for the nearest observation well, the adjustment was made on the basis of well LA–63A, which had the 

longest water-level record in the study area (1969–2006) and 

is open to the Minnelusa aquifer. The magnitude and sign of 

each adjustment was equal to the difference in hydraulic head 

in the observation well between September 15, 2004, and the 

measurement date. For example, if the water level in the nearest observation well declined 12 ft between the date at which a 

private well was measured and September 15, 2004, then 12 ft 

were subtracted from the measured water level for the private 

well.

For the Minnelusa aquifer, seven wells had water-level 

measurements prior to the period of record for LA–63A, and 

thus these water levels could not be adjusted. Although some 

error is accepted, the adjustments were considered an improvement over no adjustment. The mean and standard deviation for 

the absolute values of the adjustments were 16.9 ft and 1.6 ft, 

respectively, for the Madison aquifer and 9.5 ft and 0.9 ft, 

respectively, for the Minnelusa aquifer. Considering the total 

relief in the potentiometric surfaces (2,200 ft and 2,000 ft, 

respectively), the adjustments are relatively small and thus did 

not substantially effect the overall potentiometric surface.

Only sites where the location has been verified were used 

in constructing potentiometric-surface maps. In some locations, the data indicate excessive spatial variability in hydraulic head at local scales, which probably does not represent 

the potentiometric surface. This variability may result from 

measurement errors or errors in estimating the land-surface 

altitude at the well. One-hundred-foot contour intervals were 

constructed with the intent of showing the smoothest potentiometric surface possible within the constraints of the data. 

Therefore, local hydraulic-head variability within contour 

intervals sometimes was ignored by assuming the strict 

Methods 
linear interpolation between contour lines need not necessarily apply to each data point. In addition, about 9 percent of 

these data points did not reasonably fit between appropriate 

contours without introducing improbable bends or unlikely 

closed contours. These data points were assumed to be in 

error, were not used in constructing the potentiometric surface, 

and are not shown on the potentiometric surface. Data for all 

site-visited wells in the study area used for interpretation of 

average potentiometric surfaces and those not used are listed 

in Supplemental Information Section A (tables 10–12).

The land-surface altitude of a spring in an outcrop area 

is approximately equal to the water-table altitude at that 

location, and thus selected springs were used in constructing 

potentiometric-surface maps. However, some springs may 

discharge from perched aquifers and thus do not represent the 

main water-table altitude. Springs at unusually high altitudes 

were assumed to discharge perched water and therefore were 

not used in constructing potentiometric-surface maps. Artesian 

springs discharging water into Cox Lake, Mirror Lake, and 

the McNenny Fish Hatchery rearing pond probably flow 

from the Madison and Minnelusa aquifers (Klemp, 1995). 

Because these aquifers are buried at these locations, hydraulic 

head must be above the land surface to compensate for head 

losses incurred as water is forced to the land surface. It was 

assumed that hydraulic head was at least within 100 ft of the 

land surface at these springs. This situation may be similar to 

Jackson-Cleghorn Springs in Rapid City, South Dakota, which 

is a large relatively steady spring discharging primarily from 

the Madison aquifer with a hydraulic head about 20 ft above 

the land surface (Long and Putnam, 2002).

Dye Tracing Tests

Two fluorescent dye injections into the Madison 

aquifer were accomplished during spring 2003 by injecting 

dye into Spearfish Creek in a “streamflow loss zone” within 

the outcrop of the Madison Limestone. Streamflow entering 

the loss zone was about 6 ft3

/s and extended about 0.75 mile 

(mi) south of station 06430950 (fig. 1) before disappearing. 

Fluorescein—a yellow green dye—was used for the first 

injection, and Rhodamine WT—a red dye—was used for the 

second injection. The first injection was intended as a reconnaissance injection to be followed by an injection of a larger 

amount of Rhodamine WT, which can be detected at lower 

concentrations than fluorescein.

One method of dye injection is to introduce a slug of dye 

instantaneously in a swallow hole and trace the concentrations 

with a time series of samples from wells and springs located 

downgradient. No specific swallow holes were readily identifiable in Spearfish Creek because of alluvial deposits that were 

thick enough to obscure individual swallow holes. Thus, dye 

was injected into Spearfish Creek upstream from the loss zone 

over a period of about 1 hour. The dye was assumed to be thoroughly mixed with the water below the injection point because 

of the turbulence in the stream. This allowed dye to enter the 

aquifer at all locations where streamflow losses were occurring. A small amount of dye dispersion may have occurred as 

the stream water moved through the alluvium to the underlying Madison Limestone. Fluorescein dye is photochemically 

unstable (Jones, 1984); therefore, the fluorescein dye injection 

was initiated at dusk. Periodic water samples were collected 

from wells and springs for about 18 months after injection and 

were stored in opaque plastic bottles to minimize degradation 

of dye from sunlight exposure.

The methods used for the fluorometric analysis of water 

samples and quality-control data are described in Supplemental Information Section B. Natural waters often have some 

fluorescent characteristics that need to be established before 

dye is injected; therefore, samples were collected prior to 

dye injection to quantify background fluorescence. Replicate 

samples were used to test the effects of storing samples and 

instrument variability.

Geochemical Tracers

For this study, several geochemical tracers were used as 

tools to improve understanding of ground-water flow in the 

Madison aquifer in the study area. In addition to data available 

from previous studies, samples from selected wells and springs 

were collected and analyzed for stable isotopes of oxygen and 

deuterium, CFCs, other dissolved gases, and tritium.

Sample Collection and Analysis

Samples for analysis of stable isotopes of oxygen and 

deuterium were collected during the inventory of private wells 

in the study area. A grab sample of raw water was collected 

as close as possible to the pumping well in 60-milliliter (mL) 

glass bottles with polyseal caps. Samples were analyzed at 

the USGS Reston Stable Isotope Laboratory. A description 

of the analytical method is available at http://isotopes.usgs.

gov/Quality.htm#samples.Two replicate samples analyzed 

for delta (δ)18O had a difference of less than 1 percent. Two 

replicate samples analyzed for δD had a difference of less than 

2 percent.

CFC samples were collected from wells and springs 

by sequentially filling five welded glass ampoules for each 

sample. The method for filling and welding the glass ampoules 

is described at http://water.usgs.gov/lab/chlorofluorocarbons/

sampling/ampoules. Refrigeration grade copper tubing 

and a Bennet pump were used for sampling to avoid contact with materials that can contaminate CFC samples. The 

spring samples were collected by placing the Bennet pump 

in the spring-fed lakes near the openings where the springs 

entered the bottom of the lakes to prevent any contact with 

the atmosphere. Three of the five ampoules for each sample 

set were analyzed at the USGS Reston Chlorofluorocarbon 

Laboratory by methods described at http://water.usgs.gov/

lab/chlorofluorocarbons/lab/analytical_procedures. The CFC 

concentrations used in this report are an average of these three 

10 Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
values. For 11 of the 13 sample sets, the difference between 

the average of the three samples in the set and the individual 

samples was less than 20 percent, with an average difference 

of 2.2 percent. The percent difference for two samples was as 

high as 50 percent, with an average difference of 12.7 percent. 

These two samples had very low concentrations of CFCs; 

therefore, a small difference between samples resulted in a 

large difference when described as a percentage.

The dissolved gas data were collected with the same 

equipment and materials as used for CFCs. Two 150-mL 

septum bottles were filled for each sample by submerging 

the bottles in a beaker of the sample of water and inserting 

the sample tube into the bottle. A stopper was inserted in the 

bottles after filling while submerged to prevent exposure of the 

sample to the atmosphere. More details on the method of collecting the dissolved gas samples are available at http://water.

usgs.gov/lab/dissolved-gas/sampling. Both samples were analyzed at the USGS Reston Chlorofluorocarbon Laboratory by 

methods described at http://water.usgs.gov/lab/dissolved-gas/

lab/analytical_procedures. For dissolved gases, the difference 

between the values for the duplicate samples was less that 

29 percent with an average difference of 2.0 percent.

Oxygen and Deuterium Isotopes

Stable isotopes of oxygen and hydrogen have more neutrons and thus greater atomic weight than typical oxygen and 

hydrogen atoms. Meteorological processes result in isotopic 

fractionation that may impart a unique signature in space and 

time to water that recharges aquifers. Delta (δ)18O is a measure of the 18O/16O ratio compared to a reference composition 

expressed in parts per thousand or per mil (‰) and is given by 

the following equation:

( ) 



















δ O = - 1 × 1000 ‰ VSMOW 18

O18

O16

sample

sample

( ) O18

O16

reference

where VSMOW is the Vienna Standard Mean Ocean Water, 

which is used as the reference composition (Clark and Fritz, 

1997). Similarly, the delta notation for deuterium (δD) is a 

metric describing the 2H/1H ratio compared to a reference 

composition. Thus, δ values are expressed as a difference from 

the value of the reference composition. For example, a sample 

with a value of -20 ‰ is isotopically depleted by 20 parts per 

thousand (2 percent) relative to the reference composition. 

Isotope values in δ notation are commonly described as light 

(more negative) or heavy (more positive), which is analogous 

to low or high for concentration.

Chlorofluorocarbons

CFCs are tracers that can be used to characterize groundwater residence times. The atmospheric concentrations of 

three CFCs (CFC–11, CFC–12, and CFC–113) have been 

changing over time, generally increasing from small concentrations in the 1960s and peaking in the 1990s. Residence 

times or ages of ground water often are estimated by comparing concentrations in ground-water samples to historical 

atmospheric concentrations. The three CFCs have different 

atmospheric concentrations, and examining all three of these 

tracers in conjunction with tritium can be helpful when characterizing ground-water mixtures. Because CFCs are dissolved 

gases, the results are expressed as parts per trillion by volume 

(pptv). This volumetric ratio is a function of the pressure 

and temperature at which recharge occurred, and dissolved 

gas data were used to estimate these parameters. Additional 

background information on CFC and dissolved gas analyses is 

described in Supplemental Information Section C.

Tritium

Tritium, a radioactive isotope with a half-life of 

12.5 years, also can be helpful in characterizing ground-water 

age. Naturally occurring background concentrations of tritium 

in continental precipitation are estimated to range from 1 to 

20 tritium units (TU), depending on location (Michel, 1989). 

One TU is defined as 1 3H atom per 1,180 atoms of hydrogen, 

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

water (International Atomic Energy Agency, 1981). Because 

of nuclear testing during the 1950s and 1960s and a subsequent treaty limiting such tests, tritium concentrations in 

atmospheric water increased sharply in 1953, peaked in 1963, 

and since then have been declining.

Naus and others (2001) compiled estimates of annual 

average tritium concentrations for precipitation recharge for 

the Black Hills area for 1953–1998. These estimates were 

weighted by monthly precipitation rates for the Black Hills. 

By using a method similar to that used by Naus and others 

(2001), average 6-month tritium concentrations in precipitation were estimated for the Black Hills for 1953–2002. The 

estimated record for the Black Hills was based on four stations 

with long-term tritium data (Bismarck, North Dakota; Lincoln, 

Nebraska; Ottawa, Quebec; and Albuquerque, New Mexico) 

and was not weighted by precipitation (fig. 5).

The Bismarck record (1963–1984) and the Lincoln record 

(1962–1986) were selected because of proximity to the Black 

Hills and because the Black Hills is located approximately 

equidistant and between these two stations. For the Bismarck 

and Lincoln records, data prior to 1962 or 1963 were estimated 

based on linear regression with the Ottawa station (1953–

2002), and data after 1984 or 1986 were estimated based on 

Methods 11
3,500 10,000

Linear scale

Log scale

1,000

100

10

1

3,000

2,500

TRITIUM CONCENTRATION, IN TRITIUM UNITSTRITIUM CONCENTRATION, IN TRITIUM UNITS

2,000

1,500

1,000

500

0

1950 1955 1960 1965 1970 1975

YEAR

1980 1985 1990 1995 2000 2005

Figure 5.  Estimated 6-month tritium concentration in precipitation for the Black Hills, South Dakota.

linear regression with the Albuquerque station (1962–2002). 

The Ottawa and Albuquerque stations were selected because 

of their record lengths and because they had tritium concentrations similar to the Bismarck and Lincoln stations. Although 

the Ottawa station could have been used to estimate all of the 

missing data, tritium concentrations for this station deviate 

upward beginning in about 1984 in comparison to most other 

stations in North America that have data after 1984. This may 

have resulted from a local source of tritium near the Ottawa 

station in recent years (Naus and others, 2001). Therefore, the 

Albuquerque station was used to estimate the recent data for 

Bismarck and Lincoln. The Ottawa and Albuquerque records 

also were used to estimate any missing data within the periods 

of record for Bismarck and Lincoln. The record for the Black 

Hills (1953–2002) was estimated by averaging the measured 

or estimated data for the Bismarck and Lincoln stations. 

Finally, 6-month averages were calculated from the estimated 

monthly record for the Black Hills.

Estimating Ground-Water Age from

Chlorofluorocarbons

One way to get a general sense of relative ground-water 

age is to apply a simple piston-flow model, in which all of the 

water in a sample is assumed to have the same transit time 

with no dispersion (Maloszewski and Zuber, 1982; Plummer 

and Busenberg, 2005). The piston date is the date at which 

the historical concentration in precipitation was equal to that 

of the sample, for example, the date that a hypothetical nondispersive piston of water would have entered the aquifer. The 

apparent age (piston-flow age) is equal to the date sampled 

minus the piston date. Because the apparent age is not necessarily equal to the mean transit time, the apparent age for any 

single location is not particularly meaningful. Furthermore, the 

piston-flow model is inadequate to describe the range of ages 

in a sample, especially for karst aquifers, where the velocities 

in conduits can be orders of magnitude faster than in other 

parts of the aquifer, and a sample may contain a mixture of 

fast and slow moving ground water. However, the apparent 

age can be useful when assessing the relative ages for different 

sites. As the fraction of water less than 1 year old increases, 

the apparent age generally decreases, which indicates fast flow 

and possibly the presence of a major karst conduit.

Water Quality

Water-quality samples from two observation wells in 

the Madison aquifer and two in the Minnelusa aquifer were 

col­lected in August 2005 and processed using standard USGS 

techniques (U.S. Geological Survey, 1997–2006). The observation wells are 5-in. steel cased wells with open hole in the 

Madison Limestone or Minnelusa Formation. The depth of the 

12  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
wells ranged from 220 to 780 ft, and the pumping rate ranged 

from 3 to 10 gal/min. Polyethylene tubing and a pump with 

brass components were used to extract water from the wells. 

Field parameters for these samples were determined with a 

YSI multiparameter monitoring system. Specific conductance 

values were determined with a specific conductance meter 

in the field for water samples collected from wells during 

the well inventory for this study. Also, specific conductance 

values determined in previous studies with collection dates 

that ranged from 1956 to 1998 were used in describing the 

distribution of specific conductance for the aquifers. Historical 

specific conductance data were retrieved from the USGS 

National Water Information System.

Analyses for major ions, trace elements, and low-level 

nutrients were done at the USGS National Water Quality 

Laboratory (NWQL) in Denver, Colorado, by methods 

described by Fishman (1993) and Faires (1993). Analyses for 

mercury were done at the NWQL in Denver, Colorado, by 

cold vapor–atomic fluorescence spectrometry (Garbarino and 

Damrau, 2001). Analyses for gross alpha and beta radioactivity were performed at Eberline Services in Richmond, 

California, using U.S. Environmental Protection Agency 

(USEPA) approved methods for drinking water (http://www.

epa.gov/OGWDW/methods/methods.html). For a replicate sample set, the difference between the replicate and the reported 

value for all constituents was less than 50 percent with an 

average difference of 1.8 percent. The constituents that had 

differences between reported and replicate values greater than 

10 percent were near the reporting limit for the constituent.

Characterization of Ground-Water Flow

Ground water in the Madison and Minnelusa aquifers in 

the study area generally flows north from the outcrop areas 

(fig. 1) where ground-water recharge from sinking streams 

(streamflow recharge) and infiltration of precipitation (areal 

recharge) occurs. Outcrops of the Madison Limestone and 

Minnelusa Formation extend south beyond the study area 

along the western flank of the Black Hills (Strobel and others, 

1999), which is referred to as the Limestone Plateau (fig. 1). 

Recharge to the Madison and Minnelusa aquifers on the 

Limestone Plateau west of a ground-water flow divide (Carter, 

Driscoll, Hamade, and Jarrell, 2001) flows west into Wyoming where it merges with regional ground-water flow. The 

general direction of this regional flow in Paleozoic aquifers 

in the northern Great Plains is to the northeast (Downey and 

Dinwiddie, 1988; Whitehead, 1996). Ground water originating as recharge in the northern part of the Limestone Plateau 

moves northward where it encounters regional flow, then 

moves eastward around the northern flank of the Black Hills. 

Based on an analysis of regional flow paths using geochemical information, Naus and others (2001) concluded that water 

in the Madison and Minnelusa aquifers in the study area 

originates from the central Black Hills area and does not 

include recharge from areas west of the Black Hills. Regional 

hydraulic heads, however, probably influence hydraulic heads 

in the study area. For purposes of discussion, ground-water 

movement around the northern flank of the Black Hills is 

referred to as the eastern flow component, and ground water 

originating from recharge within the study area is referred 

to as the northern flow component. The eastern and northern 

flow components merge in the northwestern part of the study 

area, the hydraulics of which are influenced by large spring 

discharges.

Generalized potentiometric surfaces for the Madison and 

Minnelusa aquifers in the Black Hills area (Strobel and others, 

2000a, 2000b) show that hydraulic heads are several hundred 

feet lower on the eastern side of the study area than on the 

western side. Spring discharges in the northwestern part of the 

study area, which are discussed in more detail in the “Spring 

Discharge” section, are very steady, indicating relatively small 

changes in hydraulic heads over time in this area. Recharge, 

which is discussed in more detail in the “Recharge” section, 

on average is less than total spring discharge in the study area. 

Transient changes in recharge are substantial between wet 

periods and dry periods (Carter, Driscoll, Hamade, and Jarrell, 

2001).

Water-level hydrographs for SDDENR–WR observation 

wells in the study area (fig. 6) show the response of Madison 

and Minnelusa aquifer hydraulic heads to dry and wet periods 

from 1990 to 2005. The wells are located in the study area 

(fig. 1) with the label beginning with LA–xx. The early 1990s 

were dry followed by a wet period in the late 1990s followed 

by another dry period beginning in 2000. Hydraulic-head 

changes in wells LA–87A and LA–88B on the western side 

of the study area were substantially less than changes in wells 

LA–90A and LA–86C on the eastern side of the study area.

Recharge

Recharge to the Madison and Minnelusa aquifers occurs 

as areal recharge (infiltration of precipitation on outcrop 

areas) and streamflow recharge (infiltration of streamflow as 

streams cross outcrops). Carter, Driscoll, and Hamade (2001) 

estimated an average annual recharge rate of 334 ft3/s for 

the Madison and Minnelusa aquifers in the Black Hills for 

the period 1931–1998, with a minimum rate of 61 ft3/s and a 

maximum rate of 847 ft3/s. This relatively large difference in 

recharge between dry and wet periods could result in considerable differences in how the northern and eastern flow components interact. The length of the flow paths, the storage capacity of rocks in the Limestone Plateau area, and the influence of 

gradual changes in flow in the regional system probably buffer 

the transient changes in the eastern flow component. The 

northern flow component probably is more responsive than the 

eastern flow component to changes in recharge associated with 

dry and wet cycles. Estimated average annual recharge rate to 

the Madison and Minnelusa aquifers in the study area is about 

38 ft3/s (table 1).

Characterization of Ground-Water Flow 13
Spearfish GC Mdsn LA-88C

Tinton Road Mdsn LA-96B

State Line Mdsn LA-87A

Boulder Canyon Mdsn LA-96D

Whitewood Mdsn LA-90A

Frawley Ranch Mdsn LA-95A

3,800

3,750

3,700

3,650

3,600

3,550

3,500

3,450

3,400

3,350

1990 1991 1992 1993 1994 1995 1996 1997

YEAR

1998 1999 2000 2001 2002 2003 2004 2005

HYDRAULIC HEAD, IN FEET ABOVE LAND SURFACE

A. Madison aquifer

Figure 6.  Water-level hydrographs for observation wells completed in (A) the Madison (MDSN) aquifer and (B) the Minnelusa

(MNLS) aquifer.

14  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Figure 6.  Water-level hydrographs for observation wells completed in (A) the Madison (MDSN) aquifer and (B) the Minnelusa

(MNLS) aquifer.—Continued

Spearfish W Mnls LA-86A

Fawley Ranch Mnls LA-88A

Spearfish GC Mnls LA-88B

Boulder Canyon Mnls LA-63A

State line Mnls LA-87B

Redwater LA-62A

Whitewood Mnls LA-86C

3,800

3,750

3,700

3,650

3,600

3,550

3,500

3,450

3,400

3,350

1990 1991 1992 1993 1994 1995 1996 1997

YEAR

1998 1999 2000 2001 2002 2003 2004 2005

B. Minnelusa aquifer

HYDRAULIC HEAD, IN FEET ABOVE LAND SURFACE

Characterization of Ground-Water Flow 15
Table 1.  Estimated average annual recharge to the Madison and

Minnelusa aquifers in the study area.

[--, not determined]

Recharge component

Average annual recharge rate

(cubic feet per second)

Madison 

aquifer 

Minnelusa 

aquifer

Combined 

Madison and 

Minnelusa 

aquifers

Areal recharge 8.0 12.6 20.6

Streamflow recharge

Bear Gulch -- -- 2.0

Beaver Creek -- -- 4.0

Spearfish Creek 6.5 .5 7.0

False Bottom Creek 2.0 2.5 4.5

Total -- -- 38.1

Areal Recharge

The average annual areal recharge rate for the Madison 

and Minnelusa aquifers ranges from about 6 inches per year 

(in/yr) in the southwestern part of study area to less than 

3 in/yr for the northern and western outcrop areas (Carter, 

Driscoll, and Hamade, 2001). Areal extent of the Madison 

Limestone outcrop in the study area, including overlying 

surficial deposits and intrusive rocks within outcrops, was 

estimated to be 28.6 mi2. Infiltration occurring on the Madison 

Limestone outcrop south of Iron Creek and adjacent to 

Spearfish Creek upstream from the loss zone was assumed to 

discharge as base flow to Spearfish Creek and thus was not 

included in the estimated 28.6 mi2 recharge area. The area 

of the Minnelusa Formation outcrop contributing to areal 

recharge in the study area was 57.7 mi2. A discretized grid of 

spatially variable recharge rates (Carter, Driscoll, and Hamade, 

2001) on the outcrop areas was used to calculate volumetric 

areal recharge rates of 8.0 and 12.6 ft3/s for the Madison and 

Minnelusa aquifers, respectively.

Streamflow Recharge

An important source of recharge to the Madison and 

Minnelusa aquifers is streamflow loss that occurs as streams 

cross outcrops of the Madison Limestone and Minnelusa 

Formation. Streamflow recharge occurs from Bear Gulch, 

Beaver Creek, Spearfish Creek, and False Bottom Creek 

(fig. 1). On the basis of annual streamflow recharge estimates 

for 1992–1998 for Bear Gulch, Beaver Creek, and False 

Bottom Creek, and for 1950–1998 for Spearfish Creek (Carter, 

Driscoll, and Hamade, 2001), an average annual recharge rate 

was estimated for each of the four streams (table 1). The combined annual streamflow recharge rate in the study area was 

estimated to be about 17.5 ft3/s.

Streamflow in Spearfish Creek upstream from outcrops 

of the Madison Limestone and Minnelusa Formation usually 

is diverted around these outcrops at the Spearfish diversion 

intake at Maurice (fig. 1) through an aqueduct to a power plant 

located near Spearfish. This diversion intake is located about 

2 mi upstream from the Madison Limestone outcrop. When 

streamflow in Spearfish Creek is greater than about 115 ft3/s 

(Hortness and Driscoll, 1998), water flows over the diversion 

structure, and usually disappears in the reach that crosses the 

Madison Limestone outcrop except during high-flow conditions when flow in the creek is sustained downstream from 

the outcrop. An analysis of streamflow for Spearfish Creek 

at USGS gaging station 06431500 (fig. 1) indicates that 

streamflow exceeds 94 ft3/s only 5 percent of the time (Miller 

and Driscoll, 1998). Therefore, opportunities to characterize 

streamflow recharge to the Madison and Minnelusa aquifers 

from Spearfish Creek are limited. In addition, before streamflow measurements can be made to estimate loss, the unsaturated alluvium overlying the bedrock formations needs to be 

saturated. Hortness and Driscoll (1998) estimated a streamflow 

loss threshold of about 21 ft3/s for the Madison Limestone 

on the basis of four streamflow measurements upstream and 

downstream from the outcrop. The streamflow loss threshold 

is the maximum rate of streamflow loss that occurs when flow 

is sustained through the loss zone.

In October 2000, streamflow measurements were made 

within an upper reach of the Madison Limestone loss zone 

to quantify loss characteristics. Streamflow measurements 

and computations were made with a current meter in downstream sequence using USGS standard methods described by 

Rantz and others (1982). Streamflow was allowed to bypass 

the diversion structure in conjunction with tunnel maintenance and assistance from Barrick Corporation. Streamflow 

bypass began the morning of October 2, 2000, and lasted until 

October 7, 2000. The bypass flow rate was increased each 

morning during this period, and streamflow measurements 

were made each morning after the bypass flow rate had been 

constant for about 24 hours (fig. 1 and table 2) so that streamflow would be approaching equilibrium conditions. A rise 

in stream stage causes an increased amount of storage in the 

alluvium. When the stage stabilizes for a sufficient amount of 

time and equilibrium conditions are met, the difference in flow 

between an upstream and downstream location would be equal 

to the loss rate if evapotranspiration is assumed negligible. 

No tributaries were contributing flow within the intervening 

reach. Although it is uncertain whether 24 hours was sufficient 

time to attain equilibrium, a longer period of bypass flow was 

not possible. Rantz and others (1982) describe the potential 

sources of error in streamflow measurements with a current 

meter. A measurement rated as good has a cumulative measurement error of ±5 percent. To provide a range of potential 

errors associated with the estimated streamflow loss, the sum 

of a 5-percent error for each measurement involved in the 

calculated loss is listed in table 2. Under these limitations and 

assumptions, the estimated streamflow loss rate for this stream 

reach on Spearfish Creek most likely is between 4 and 8 ft3/s.

16  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Table 2.  Streamflow loss to the Madison aquifer in upper reach of loss zone along Spearfish Creek.

[ft3/s, cubic feet per second]

Date of 

measurement

Streamflow (ft3/s) Streamflow 

loss

(ft3/s)

Potential 

measurement 

error in 

calculated loss

(ft3/s)

Station 06430950 

(upstream)

Station 

442637103521100 

(downstream)

10–03–2000 3.26 0.00 3.26 0.2

10–04–2000 6.92 2.18 4.74 .5

10–05–2000 14.1 7.72 6.38 1.1

10–06–2000 26.7 17.9 8.80 2.2

10–07–2000 48.2 39.2 9.00 4.4

During spring 2006, runoff following a large snowfall 

event created streamflow in Spearfish Creek that was able to 

saturate the alluvium and sustain flow through the loss zone 

for several days. The USGS, in cooperation with the city of 

Spearfish, conducted a series of streamflow measurements at 

five sites on Spearfish Creek between the diversion intake and 

Table 3.  Streamflow gains or losses for selected reaches of Spearfish Creek.

[ft3/s, cubic feet per second; e, estimated value; --, not applicable]

Description of stream 

reach Date Streamflow at gaging station (ft3

/s) Streamflow gain 

or loss (ft3/s)

Potential 

measurement 

error in 

calculated gain 

or loss (ft3/s)

442433103534400 06430950 Gain

Diversion intake to above 

Madison Limestone 

outcrop

05–05–2006 41.2 51.6 10.4 4.6

05–07–2006 27.4 40.2 12.8 3.4

05–12–2006 32.0 37.7 5.7 3.5

06–08–2006 .4 4.6 4.2 .2

06430950 442649103520200 Loss

Above Madison Limestone 

outcrop to Split Rock

05–05–2006 51.6 43.4 8.2 4.8

05–07–2006 40.2 32.7 7.5 3.6

05–12–2006 37.7 34.3 3.4 3.6

05–18–2006 24.3 18.9 5.4 2.2

06–08–2006 4.6 .0 4.6 .2

442649103520200 442757103510600 Loss

Split Rock to below 

Madison Limestone 

outcrop

05–05–2006 43.4 27.4 16.0 3.5

05–07–2006 32.7 14.5 18.2 2.4

05–12–2006 34.3 15.7 18.6 2.5

05–18–2006 18.9 5.2 13.7 1.2

06–08–2006 .0 .0 -- --

442757103510600 442835103510501 Loss

Below Madison Limestone 

outcrop to above Power 

Plant

05–12–2006 15.7 e5 10.7 --

05–17–2006 12.2 4.2 8.0 0.8

05–18–2006 5.2 e.2 5.0 --

Spearfish (fig. 1 and table 3). Gains or losses were calculated 

for each set of measurements for the four reaches between 

these gaging sites (table 3). The measurements were made 

in downstream order to minimize the effects that changes in 

streamflow during the measurements would have on calculated 

gains and losses.

Characterization of Ground-Water Flow 17
Crow Creek (station 06430532)

0

5

10

15

20

25

30

35

40

45

50

WATER YEAR

FLOW, IN CUBIC FEET PER SECOND

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

Average annual streamflow

Average annual base flow

Figure 7.  Comparison of average annual streamflow and base

flow for Crow Creek.

for station 06430532 (fig. 1) for water years 1994–2004 was 

estimated using a hydrograph separation program (Sloto and 

Crouse, 1996), and the fixed interval method using an interval 

of 11 days, which was selected to minimize the influence of 

alluvial bank storage. Comparison of base flow to streamflow 

for Crow Creek (fig. 7) indicates a consistently large contribution of springflow with an average base flow of 36.0 ft3

/s. 

During the relatively dry years during 2002–2004, base flow 

declined slightly to about 33 ft3/s. A similar analysis for Cox 

Lake for water years 1992–1995 indicated base flow was very 

steady at 4.2 ft3/s.

The reach between the diversion intake and the Madison 

Limestone outcrop was always a gaining stream and the 

reaches that overlie the Madison Limestone outcrop were 

always losing reaches. The measurements made above and 

below the Madison Limestone outcrop are compared in 

table 4. The streamflow losses to the Madison Limestone 

below Split Rock generally are about twice the loss that occurs 

above Split Rock. The measured losses are very close to 

the streamflow loss threshold of 21 ft3/s that was previously 

estimated by Hortness and Driscoll (1998). Some unexplainable variability is inherent in estimation of streamflow losses. 

On the basis of previous and more recent measurements, it 

is concluded that the streamflow loss threshold for Spearfish 

Creek probably is in the range of 20–25 ft3/s. On the basis of 

three measurements above the Power Plant, additional substantial losses probably occur downstream from the Madison 

Limestone outcrop.

Spring Discharge

Total artesian springflow for the Redwater River above 

Belle Fourche, which flows along the northwestern part of 

the study area (fig. 1), has been estimated to be about 94 ft3/s 

(Carter, Driscoll, Hamade, and Jarrell, 2001). Sources in 

the northwestern part of the study area that include springflow contributing to Crow Creek and discharge from Cox 

Lake accounted for about 41 ft3/s of that total. Artesian 

springs contributing to Spearfish Creek accounted for about 

10 ft3/s of that total. On the basis of streamflow measurements 

(U.S. Geological Survey, 1977–2003), Higgins Gulch and Old 

Hatchery springs make up most of this spring discharge to 

Spearfish Creek. The combined total of this estimated spring 

discharge rate (51 ft3/s) is more than the estimated average 

recharge rate (38 ft3/s) in the study area.

The relatively steady spring discharge in the northwestern part of the study area is illustrated by analysis of the base 

flow for Crow Creek and Cox Lake. Average annual base flow 

Table 4.  Streamflow losses to the Madison aquifer from Spearfish Creek.

[ft3/s, cubic feet per second]

Description of stream 

reach Date Streamflow at gaging station (ft3

/s) Streamflow loss 

(ft3/s)

Potential measurement 

error in calculated 

loss (ft3/s)

06430950 442757103510600

Above Madison 

Limestone outcrop 

to below Madison 

Limestone outcrop

05–05–2006 51.6 27.4 24.2 3.9

05–07–2006 40.2 14.5 25.7 2.7

05–12–2006 37.7 15.7 22.0 2.7

05–18–2006 24.3 5.2 19.1 1.5

06–08–2006 4.6 .0 14.6 .2

1

Insufficient flow for inclusion in loss threshold estimate

18  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
On the basis of geochemical modeling (Klemp, 1995), 

the source of the spring discharge was presumed to originate 

primarily from the Madison and Minnelusa aquifers. An 

analysis of oxygen and deuterium isotope data described in 

a subsequent section generally agrees with this assumption, 

except that additional data indicate possible small contributions from other sources.

Potentiometric Surfaces

Generalized potentiometric surfaces of the Madison and 

Minnelusa aquifers are shown in figures 8 and 9, respectively. 

The potentiometric contours near the perimeter of the study 

area where there are no control points were estimated on the 

basis of potentiometric maps for the Black Hills area (Strobel 

and others, 2000a; 2000b). Ground-water flow in the Madison 

and Minnelusa aquifers in the study area generally is toward 

the northeast. In isotropic aquifers, the direction of flow is 

perpendicular to potentiometric contour lines. However, in an 

aquifer with possible anisotropic transmissivity, such as the 

Madison aquifer, flow direction can deviate from that perpendicular direction. Therefore, the potentiometric surface of 

the Madison aquifer does not indicate precise flow directions. 

Flow directions in the Minnelusa aquifer, however, probably 

are approximately perpendicular to the potentiometric contours in most locations.

Hydraulic gradients become progressively less steep with 

distance from outcrops for both aquifers and is indicated by 

the decreasing density of the potentiometric contours to the 

north (figs. 8 and 9). Steeper hydraulic gradients near recharge 

areas are expected; however, recharge alone probably does not 

explain the large change in gradient. Another factor that can 

cause steeper gradients is lower relative transmissivity. On 

the eastern flank of the Black Hills, however, transmissivity 

in the Madison aquifer generally is higher near outcrops than 

with distance from the outcrops (Long and Putnam, 2002). 

Ground-water flow that moves northward and eastward around 

the Black Hills in the study area might contribute to anomalies 

in the hydraulic gradient because of converging flow paths; 

however, the specific boundary conditions and structural 

features that could explain the changes in gradient are not well 

understood. The large discharge from artesian springs, which 

is greater than the estimated recharge in the study area, as 

discussed previously, probably influences hydraulic gradients 

to a large degree. Spring discharge in the northwestern part 

of the study area probably contributes to lowered hydraulic 

heads in the Minnelusa aquifer (fig. 8). Near observation well 

LA–62A (fig. 9), there is a confirmed hydraulic gradient that 

decreases to the west toward the springs. Hydraulic head at 

well LA–62A was 3,500 ft on December 1, 1999, and the 

closest well to the west (7N 2E18ABBA) had a shut-in pressure of 32 pounds per square inch (lb/in2

) reported by the 

driller 2 days earlier, which is equivalent to a hydraulic head 

of 3,464 ft. Although data are sparse for the Madison aquifer 

in the northern part of the study area, it is assumed that the 

potentiometric surface is similar to that of the Minnelusa 

aquifer near the springs because the springs discharge from 

both aquifers. Geochemical modeling has indicated that the 

predominant source of spring discharge at Cox Lake and 

McNenny Pond is the Madison aquifer, whereas the spring 

source of Mirror Lake is a 1:1 ratio of water from the Madison 

and Minnelusa aquifers (Klemp, 1995). Because the majority of the spring discharge probably originates from the 

Madison aquifer, hydraulic head was assumed to be higher for 

the Madison aquifer than for the Minnelusa aquifer near the 

springs.

Higher relative transmissivity near the springs than near 

outcrop areas might explain the lower hydraulic gradient in 

the northwestern part of the study area. Long and Putnam 

(2002) concluded that the area surrounding Jackson-Cleghorn 

Springs, a large spring discharging from the Madison aquifer 

in the east-central part of the Black Hills, had high relative 

transmissivity as a result of enhanced ground-water circulation, which resulted from greater karst development than in 

surrounding areas. Total artesian springflow for the study area 

was estimated to be about 51 ft3/s (see “Spring Discharge” section), which is substantially larger than the estimated discharge 

of 22 ft3/s for Jackson-Cleghorn Springs (Long and Putnam, 

2002). Thus, potential for karst development in the northwestern part of Lawrence County is large.

Flow Paths and Flow Rates Based on Dye 

Tracing

Dye tracing is a useful tool that has been widely used 

to describe ground-water flow in formations with enlarged 

openings or conduits that result from dissolution of limestone. 

Ground-water flow paths in the Madison Limestone that 

extend for several miles with velocities as high as 1,000 feet 

per day (ft/d) have been documented by dye tracing in the 

Black Hills area (Rahn, 1971; Greene, 1993). These previous 

tracer studies involved injecting dye in swallow holes associated with sinking streamflow. Characterizing these major flow 

paths can be a useful starting point in understanding groundwater flow in karst aquifers.

Spearfish Creek, the largest stream in the study area, 

was selected as a site for injecting dye because the maximum 

streamflow recharge rate for the Madison and Minnelusa 

aquifers south of Spearfish (fig. 1) is about 21 ft3/s (Hortness 

and Driscoll, 1998), which is the largest streamflow recharge 

rate in the northern Black Hills. This focused recharge often 

is associated with enlarged openings or conduits in the aquifer 

that can rapidly move water downgradient.

Two fluorescent dye injections into the Madison aquifer 

were made during spring 2003. Fluorescein—a green dye—

was used for the first injection, and Rhodamine WT—a red 

dye—was used for the second injection.

Characterization of Ground-Water Flow 19
Figure 8.  Generalized potentiometric surface of the Madison aquifer in 2004.

Spearfish

Beaver

Beaver

Creek

False

Bottom

Creek

Spearfish

Creek

Creek

Crow

Creek

Creek

Gulch

Bear

Gulch

Higgins

Red

Water

River

Iron

Creek

14A

385

14

90

14

85

85

34

Planimetric base from U.S. Geological Survey digital data: 1:100,000, 1977, 1983

Universal Transverse Mercator projections, zone 13

3,600

3,700

3,900

3,800

4,100

4,000

4,200

4,300

4,500

4,400

5,100

4,900

4,900

5,000

5,100

5,200

5,300

5,200

5,000

4,600

4,500

4,400

4,300 4,200

4,100

4,800

4,800

4,700

4,700

4,600

4,600

5,300

5,400

5,500

5,900

5,600

5,400

5,500

6,000

5,300

5,700

3,500

5,800

Maurice

Deadwood

Spearfish

LaFlamme

anticline

5,260

3,675

GC

3,681

PT

3,681

MP3

3,619

3,666 JEF

MP2

3,657

MP1 3,561

VIG

3,663

NEV

3,669

ELL 3,643

KYT

3,645

COL 3,665

SAL

3,653

MIT 

4,019 

5,946

4,047 4,197

4,020

4,021

4,062 4,011 3,563 3,527 3,790

3,576

3,677 3,

3,737 3,710

3,538 3,518 3,697 3,530

3,525

3,592

3,609

3,535

3,534

3,683 4,105

3,757 3,561

3,788 3,691 3,837

3,722 3,663

3,702

3,651

LA-96B

4,881

LA-95C

3,520

LA-95A

3,641

LA-88C

3,736

LA-87A

5,260

3,675

GC

3,681

PT

3,681

MP3

3,619

3,666 JEF

MP2

3,657

MP1 3,561

VIG

3,663

NEV

3,669

ELL 3,643

KYT

3,645

COL 3,665

SAL

3,653

MIT 

4,019 

5,946

4,047 4,197

4,020

4,021

4,062 4,011 3,563 3,527 3,790

3,576

3,677 3,

3,737 3,710

3,538 3,518 3,697 3,530

3,525

3,592

3,609

3,535

3,534

3,683 4,105

3,757 3,561

3,788 3,691 3,837

3,722 3,663

3,702

3,651

LA-96B

4,881

LA-95C

3,520

LA-95A

3,641

LA-88C

3,736

LA-87A

Split Rock

Limestone Plateau

Cox Lake

Mirror Lake

McNenny Pond

Old Hatchery

Higgins Gulch

104°

103°50'

44°35'

44°30'

44°25'

R. 1 E. R. 2 E. R. 3 E. 

Eastern

Northern

20 Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Creek

Whitewood

90 14

14

34

0 1 2 3 4 5

0 1 2 3 4 5

MILES

KILOMETERS

3,700

3,800

3,900

4,000

3,500

3,600

3,400

4,100

4,200

3,300

3,200

4,300

4,400

4,500

4,600

3,100

5,000

Whitewood

3,653

MIT

4,620

3,613 4,501

3,640

4,036

3,563

558

3,520

LA-95A

3,443

LA-90A

3,642

LA-96D

3,653

MIT

4,620

3,613 4,501

3,640

4,036

3,563

558

3,520

LA-95A

3,443

LA-90A

3,642

LA-96D

103°40'

T. 7 N.

T. 6 N.

T. 5 N.

R. 4 E.

EXPLANATION

Outcrop of Madison Limestone— Includes areas 

 overlain by surficial deposits (modified from Strobel 

 and others, 1999)

Potentiometric contour— Shows altitude at which 

 water would have stood in tightly cased, nonpumping 

 wells. Contour interval 100 feet. Dashed where 

 inferred. Datum is National Geodetic Vertical Datum 

 of 1929 (NGVD 29)

Continuous-record observation well— Top number 

 shows hydraulic head for September 2004, in feet 

 above NGVD 29. Bottom label is well identification

Water well— Top number shows estimated hydraulic 

 head for September 2004, in feet above NGVD 29. 

 Bottom label, if given, is well identification

Fault—Bar on downthrown side

Anticline—Showing trace of axial plane and direction 

 of plunge

Syncline—Showing trace of axial plane and direction 

 of plunge. Dashed where approximate

Monocline—Showing trace of axial plane

Dome—Symbol size approximately proportional to size 

 of dome. Dome asymmetry indicated by arrow length

Structural features (from Strobel and others 1999)

Spring sampled for tracer dye (not detected)—Tail 

 indicates direction of flow

Spring—Tail indicates direction of flow

Approximate direction of ground-water flow

Flow component

Characterization of Ground-Water Flow  21
Figure 9.  Generalized potentiometric surface of the Minnelusa aquifer in 2004.

Spearfish

Beaver

Beaver

Creek

False

Bottom

Creek

Spearfish

Creek

Creek

Crow

Creek

Creek

Gulch

Bear

Gulch

Higgins

Red

Water

River

Iron

Creek

14A

385

14

90 14

85

85

34

3,500

3,400

3,700

3,600

3,800

3,900

4,000

4,100

4,500

4,500

4,600

4,600

4,700

4,300

4,200

4,100

4,000

4,400

5,000

4,800

4,900

5,100

4,300

3,700

4,800

3,500

3,500

4,400

4,100

3,900

3,900

4,100

4,000

3,800

4,200

4,300

Maurice

Deadwood

Spearfish

LaFlamme

anticline

Cox Lake

Mirror Lake

McNenny Pond

Old Hatchery

Higgins Gulch

3,550

LA-88A

3,653

LA-88B

4,313

LA-96C

3,543

LA-86A

3,484

LA-62A

3,644

LA-87B

3,550

LA-88A

3,653

LA-88B

4,313

LA-96C

3,543

LA-86A

3,484

LA-62A

3,644

LA-87B

3,940

4,240

4,640

4,640 4,720

5,190

3,446

3,449

3,457

3,475

3,480

3,481

3,489 3,491

3,496

3,497

3,500

3,504

3,507

3,511

3,515

3,520

3,524

3,526

3,527

3,528

3,531

3,533

3,539

3,540

3,543 3,543

3550

3,552

3,556 3,561

3,563

3,577

3,577 3,579

3,584

3,588

3,590

3,593

3,598

3,603

3,608

3,615

3,620

3,621

3,621

3,622

3,642

3,699 3,647

3,653

3,656

3,660

3,661

3,661

3,666

3,660

3,688

3,666

3,667

3,668

3,675 3,680

3,684

3,684

3,689

3,698

3,698

3,716

3,717

3,736

3,738

3,752

3,754

3,755

3,764 3,775

3,832

3,910

3,941

4,131 4,040

4,172

4,209

4,244

4,329

3,940

4,240

4,640

4,640 4,720

5,190

3,446

3,449

3,457

3,475

3,480

3,481

3,489 3,491

3,496

3,497

3,500

3,504

3,507

3,511

3,515

3,520

3,524

3,526

3,527

3,528

3,531

3,533

3,539

3,540

3,543 3,543

3550

3,552

3,556 3,561

3,563

3,577

3,577 3,579

3,584

3,588

3,590

3,593

3,598

3,603

3,608

3,615

3,620

3,621

3,621

3,622

3,642

3,699 3,647

3,653

3,656

3,660

3,661

3,661

3,666

3,660

3,688

3,666

3,667

3,668

3,675 3,680

3,684

3,684

3,689

3,698

3,698

3,716

3,717

3,736

3,738

3,752

3,754

3,755

3,764 3,775

3,832

3,910

3,941

4,131 4,040

4,172

4,209

4,244

4,329

Split Rock

Limestone Plateau

104°

103°50'

44°35'

44°30'

44°25'

R. 1 E. R. 2 E. R. 3 E. 

Planimetric base from U.S. Geological Survey digital data: 1:100,000, 1977, 1983

Universal Transverse Mercator projections, zone 13

22  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Creek

Whitewood

90 14

14

34

3,600

3,500

3,400

3,300

3,200

3,100

4,000

4,100

4,100

3,700

3,900

3,800

Whitewood

3,520

LA-95A

3,675

LA-63A

3,453

LA-86C

3,675

LA-63A

3,453

LA-86C

3,442

3,454

3,471

3,475

3,488

3,489

3,494

3,498

3,507

3,508

3,510

3,542

3,622

3,631

3,632

3,660

3,735

3,749

4,447

3,442

3,454

3,471

3,475

3,488

3,489

3,494

3,498

3,507

3,508

3,510

3,542

3,622

3,631

3,632

3,660

3,735

3,749

4,447

103°40'

T. 7 N.

T. 6 N.

T. 5 N.

R. 4 E.

EXPLANATION

Outcrop of Minnelusa Formation— Includes areas 

 overlain by surficial deposits (modified from Strobel 

 and others, 1999)

Potentiometric contour— Shows altitude at which 

 water would have stood in tightly cased, nonpumping 

 wells. Contour interval 100 feet. Dashed where 

 inferred. Datum is National Geodetic Vertical Datum 

 of 1929 (NGVD 29)

Continuous-record observation well— Top number 

 shows hydraulic head for September 2004, in feet 

 above NGVD 29. Bottom number is well identification

Water well— Top number shows estimated hydraulic 

 head for September 2004, in feet above NGVD 29. 

 Bottom label, if given, is well identification

4,000

0 1 2 3 4 5

0 1 2 3 4 5

MILES

KILOMETERS

3,669

ELL

Fault—Bar on downthrown side

Anticline—Showing trace of axial plane and direction 

 of plunge

Syncline—Showing trace of axial plane and direction 

 of plunge. Dashed where approximate

Monocline—Showing trace of axial plane

Dome—Symbol size approximately proportional to size 

 of dome. Dome asymmetry indicated by arrow length

Structural features (from Strobel and others, 1999)

Spring sampled for tracer dye (not detected)—Tail 

 indicates direction of flow

Spring—Tail indicates direction of flow

Approximate direction of ground-water flow

Characterization of Ground-Water Flow  23
442757103512901 (MP2)

0

5

10

15

20

25

FLUORESCEIN CONCENTRATION, IN MICROGRAMS PER LITER

442950103521501 (COL)

0

1

2

3

4

5

0 100 200 300 400 500 600

DAYS AFTER DYE INJECTION

442919103511601901 (DIC)

0

1

2

3

4

5

44442906103510501 (ELL)

0

1

2

3

4

5

0 100 200 300 400 500 600

DAYS AFTER DYE INJECTION

Figure 10.  Fluorescein breakthrough curves for wells where dye was detected, March 2003–September 2004.

Fluorescein Injection

Sixteen pounds (lb) (dry weight) of fluorescein dye were 

injected in Spearfish Creek during the evening of March 25, 

2003. Measured streamflow was 6.6 ft3/s at the time of injection. Periodic water samples were collected from 10 wells 

and 2 springs (table 5 and fig. 10) and analyzed for dye with 

a Turner Model TD700 filter fluorometer. Samples were collected daily at the beginning of the injection, and the interval 

was increased to several days for some wells and springs as 

the dye study progressed.

Fluorescein dye was detected in water samples from four 

wells ranging in distance from 2.6 to 4.5 mi from the injection 

point (table 5). Dye breakthrough curves for the four wells 

(fig. 10) indicate first arrival times that ranged from 5 to 169 

days. Some gaps in the dye breakthrough curve were the result 

of well operation and maintenance issues. During the periods 

when the concentrations for well MP2 drop to background 

levels (fig. 10), water was being supplied to the sampling 

point by a different well connected to the distribution system. 

Sampling from well DIC was discontinued 154 days after the 

injection because of well repair work.

24  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Table 5.  Summary of fluorometric analysis of water samples for fluorescein dye.

[--, no data]

Station number Other Identifier

Beginning 

date of 

 sampling 

period

Ending date 

of sampling 

period

Number 

of samples

Concentration 

(micrograms per liter)

Distance from 

injection point 

(miles)

Days to first 

arrival of dye

Days to peak 

dye 

concentration Maximum Minimum1

442748103524501 MP3 03–24–2003 10–15–2003 116 0.25 -0.04 2.3 -- --442757103512901 MP2 03–24–2003 05–12–2004 322 22.77 -.16 2.6 5 15442752103501901 JEF 03–20–2003 205–13–2003 81 .30 -.02 2.9 -- --442842103505501 NEV 03–25–2003 05–03–2004 236 .32 -.12 3.5 -- --442906103510501 ELL 03–20–2003 09–07–2004 293 1.35 -.06 3.8 169 301442919103511601 DIC 03–20–2003 309–07–2004 154 1.39 -.06 3.9 109 --

442855103503501 GC 03–20–2003 07–21–2003 29 .23 -.20 4.0 -- --442936103530001 PT 03–25–2003 05–03–2004 202 .15 -.08 4.3 -- --442815103481701 VIG 407–09–2003 09–07–2004 133 .32 -.07 4.4 -- --442950103521501 COL 03–26–2003 09–07–2004 295 .69 -.08 4.5 130 153443309103532401 OH (Old 

Hatchery Spring)

05–13–2003 02–27–2004 28 .32 .02 8.1 -- --

443237103525801 HG (Higgins 

Gulch Spring)

05–13–2003 11–19–2003 23 .35 .05 7.8 -- --

1Negative concentrations are not possible and represent instrument noise. 2Well not sampled from May 10, 2003, to July 8, 2003.3Well not sampled from August 16, 2003, to August 17, 2004, because of well repairs.4Well not sampled until July 9, 2003, because of well repairs. 

Characterization of Ground-Water Flow  25
On the basis of first arrival times, ground-water velocities 

ranged from about 0.1 mi/d for the three wells downgradient 

to about 0.5 mi/d for well MP2. The peak concentration of 

about 23 μg/L for the closest well (MP2) occurred 15 days 

after injection, then gradually decreased; however, concentrations greater than 1 μg/L were still measured about 9 months 

later. First arrival for wells DIC, COL, and ELL was interpreted to range from 109 to 169 days. The observed concentrations for wells COL and ELL intermittently decreased to near 

background (natural fluorescence) levels. A possible explanation for this could be that the dye was being drawn toward the 

wells by pumping. When the wells were only pumped briefly 

to collect a sample, the drawdown created by pumping may 

not have been large enough to intersect the conduits of the 

main flow path that was transporting the dye.

Detectable dye concentrations for well ELL were 

observed for about 400 days compared to about 100 days for 

well COL. The detection of dye in both wells DIC and ELL 

could be the result of pumping and anastomosis of conduits 

along the approximate location of a possible main conduit 

as shown in figure 1. Assuming such a conduit exists, it may 

trend in the direction of Old Hatchery (OH) and Higgins 

Gulch (HG) springs. Conduits in karst aquifers typically 

propagate downgradient from swallow holes and upgradient 

from springs (Clemens and others, 1997). Although detectable 

dye concentrations were not observed for springs OH and HG, 

the location of the springs several miles farther downgradient 

could have resulted in dilution of the dye beyond the point of 

detection. Spearfish Creek streamflow of about 5 ft3/s at the 

time of injection was small in relation to the loss threshold 

of about 21 ft3/s. Streamflow entering the loss zone probably 

decreased during the summer; therefore, the flow velocity in 

conduits associated with the Spearfish Creek loss zone also 

may have slowed as the dye test progressed.

 A comparison of dye breakthrough curves, apparent 

age of water samples from wells on the basis of CFCs, and 

the distance of the wells from a possible conduit indicate that 

the generalized location of the conduit may be plausible. A 

least-squares, straight-line regression analysis of apparent age 

and distance for the six closest wells had an r2 value of 0.96 

(see “Ground-Water Flow Paths, Ages, and Mixing Based on 

Geochemical Tracers” section).

Rhodamine WT Injection

The fluorescein injection was followed by an injection of 

64 lb (dry weight) of Rhodamine WT dye on May 9, 2003, at 

the same location. Measured streamflow was 5.6 ft3/s or about 

1 ft3/s less than during the fluorescein injection. Periodic water 

samples were collected from 10 wells and 2 springs (table 6 

and fig. 11) and analyzed for dye with a Turner Model TD700 

filter fluorometer. Samples were collected daily at the beginning of the injection, and the interval was increased to several 

days for some wells and springs as the dye study progressed.

Because streamflow conditions were similar to those of 

the first injection, it was assumed that injecting about four 

times the amount of injected fluorescein dye would cause the 

Rhodamine WT concentrations in wells to be greater than the 

fluorescein concentrations; however, the measured Rhodamine 

WT concentrations were about an order of magnitude less 

than the measured fluorescein concentrations. First arrival and 

peak concentrations were not estimated for well MP2 because 

the well was not in operation during a brief period when the 

first arrival and peak probably would have occurred. The 

Rhodamine WT concentrations in wells ELL, DIC, and COL 

were near background levels, and thus there is uncertainty 

in estimating dye arrival or peak traveltimes for these wells. 

However, the general shape and magnitude of the concentration breakthrough curves were similar to those for fluorescein, 

except with a dilution of more than an order of magnitude. In 

the analysis of samples with a filter fluorometer, some overlap 

in the fluorescent bandwidths of fluorescein and Rhodamine 

WT can occur (Jones, 1984). An evaluation of samples with 

standard concentrations of fluorescein (Supplemental Information Section B) indicated that any overlap between fluorescein 

and Rhodamine WT in the analysis was small.

The small change in streamflow between the fluorescein 

and Rhodamine WT injections does not explain the degree 

of dilution in measured Rhodamine WT dye concentrations 

in comparison to the measured fluorescein concentrations. 

Greater absorption of Rhodamine WT or other degradation 

of the dye in the alluvium in Spearfish Creek compared to 

fluorescein dye may be possible. However, the large difference 

in concentrations cannot be explained by absorption or 

degradation alone.

Examination of the hydraulic head in the area (fig. 8) provides some insight on dilution possibilities. The relatively flat 

gradient in hydraulic head in the area where dye was detected 

probably is the result of solution-enlarged openings associated 

with recharge in the Spearfish Creek loss zone and indicates 

an area of high transmissivity. This high transmissivity would 

result in ground water moving easily to the north. Because 

of the current diversion of water around the loss zone, there 

is less streamflow recharge than before water was diverted 

around the loss zone. Water levels in the Madison aquifer have 

been estimated to have decreased about 100 ft as the result of 

the diversion (Greene and others, 1998).

A large proportion of recharge on the outcrop of the 

Madison Limestone occurs when snowmelt and spring precipitation infiltrate and fill cave-like openings in the unconfined 

area with water. As these openings fill with water, additional 

openings are utilized in the downgradient movement of ground 

water. Part of this water probably moves toward the highly 

conductive conduits underlying the streamflow loss zone. 

Water-level response in Madison aquifer observation well 

LA–88C located about 1 mi north of the loss zone (fig. 1) is 

consistent with this flow mechanism. Water levels generally 

rise quickly in early spring and then decline gradually through 

the summer and winter (Driscoll and others, 2000) (fig. 12). 

The injection of fluorescein on March 25, 2003, was near the 

beginning of this typical water-level rise, whereas when the 

Rhodamine WT was injected on May 9, 2003, water levels 

26  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Table 6. Summary of fluorometric analysis of water samples for Rhodamine WT dye.

[--, no data]

Station number Other identifier Beginning of sample period End of sample period Number of samples

Concentration

 (micrograms per liter)

Distance 

from 

injection 

point 

(miles)

Days to 

first 

arrival 

of dye

Days to peak 

dye

 concentration Maximum Minimum1

442748103524501 MP3 03–24–2003 10–15–2003 116 0.25 -0.04 2.3 -- --

442757103512901 MP2 05–07–2003 01–28–2004 239 1.02 -.02 2.6 (2) (2)442752103501901 JEF 03–20–2003 305–13–2003 81 .30 -.02 2.9 -- --

442842103505501 NEV 03–25–2003 05–03–2004 236 .32 -.12 3.5 -- --442906103510501 ELL 03–20–2003 09–07–2004 273 .27 -.07 3.8 (4) (4)

442919103511601 DIC 03–20–2003 509–07–2004 111 .13 -.02 3.9 (4) (4)

442855103503501 GC 03–20–2003 07–21–2003 29 .23 -.20 4.0 -- --442936103530001 PT 03–25–2003 05–03–2004 202 .15 -.08 4.3 -- --

442815103481701 VIG 07–09–2003 609–07–2004 133 .32 -.07 4.4 -- --442950103521501 COL 03–26–2003 09–07–2004 248 .09 -.05 4.5 (4) (4)

443309103532401 OH (Old 

Hatchery spring)

05–13–2003 02–27–2004 28 .32 .02 8.1 -- --

443237103525801 HG (Higgins 

Gulch spring)

05–13–2003 11–19–2003 23 .35 .05 7.8 -- --

1Negative concentrations are not possible and represent instrument noise.2First arrival and peak probably occurred when pump was out of service.3Well not sampled from May 10, 2003, to July 8, 2003.4First arrival and peak not determined because concentrations are too close to background and instrument noise.5Well not sampled from August 16, 2003, to August 17, 2004, because of well repairs.6Well not sampled until July 9, 2003, because of well repairs.

Characterization of Ground-Water Flow  27
442757103512901 (MP2)

RHODAMINE WT CONCENTRATION, IN MICROGRAMS PER LITER

442950103521501 (COL)

0

0.2

0.4

0.6

0.8

1.0

0

0.2

0.4

0.6

0.8

1.0

0

0.5

1.0

1.5

2.0

0

0.2

0.4

0.6

0.8

1.0

0 100 200 300 400 500

DAYS AFTER DYE INJECTION

442919103511601901 (DIC)

44442906103510501 (ELL)

DAYS AFTER DYE INJECTION

0 100 200 300 400 500

Figure 11.  Rhodamine WT breakthrough curves for wells where dye may be present, May 2003–September 2004.

28  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
442854103505601 (LA-88C)

80

82

84

86

88

90

92

94

Mar Apr May Jun Jul Aug Sep Oct Nov

2003

WATER LEVEL, IN FEET BELOW LAND SURFACE

Figure 12.  Water level in the Madison aquifer for observation

well LA–88C near Spearfish during dye injections.

Oxygen and Deuterium Isotopes

Meteorological processes that affect stable-isotope distributions for the Black Hills area and the generalized distribution of oxygen and deuterium isotopes were described in Naus 

and others (2001). Water recharging the Madison and Minnelusa aquifers in the northern Black Hills generally has δ18O 

values lighter than -16 ‰, with values becoming heavier in 

an outward direction from the central part of the Black Hills. 

Oxygen- and deuterium-isotope values for samples collected 

for this study are listed in table 7. Additional oxygen- and 

deuterium-isotope values reported in Naus and others (2001) 

were used in the interpretation of ground-water flow in the 

study area.

were rising rapidly and had already risen about 5 ft. A combination of this water-level rise, the diversion of streamflow 

around the loss zone, and the highly transmissive conduits 

associated with streamflow loss may explain the transient differences in dilution of dye concentrations.

Ground-Water Flow Paths, Ages, and Mixing 

Based on Geochemical Tracers

Geochemical tracers used in previous studies to characterize ground-water flow in the Black Hills area (Naus and 

others, 2001) include stable isotopes of oxygen and hydrogen 

(deuterium) and the radioisotope tritium. For this study, several geochemical tracers were used as tools to better understand ground-water flow in the Madison aquifer in the study 

area. In addition to the data available from previous studies, 

samples from selected wells and springs were collected and 

analyzed for oxygen and deuterium isotopes, tritium, CFCs, 

and dissolved gases that included nitrogen, argon, oxygen, carbon dioxide, and methane. CFCs are young age-dating tracers, 

and the dissolved-gas analyses provide additional information 

that is useful in interpreting CFC data. These tracers provide 

insights on ground-water flow paths, ages, and mixing, which 

are described in the following sections. Conjunctive analysis 

of several tracers was useful in understanding ground-water 

flow in selected locations as described in the “Synopsis of 

Results from Geochemical Tracers” section.

Comparison of δ18O and δD values for water from 

Madison and Minnelusa wells and springs (fig. 13) 

provides information that is relevant to ground-water flow 

interpretations. On the basis of the generalized distribution of 

δ18O for the Black Hills (Naus and others, 2001), ground water 

moving around the northern flank of the Black Hills from the 

Limestone Plateau probably would have lighter isotope values 

than the recharge from outcrops in the study area. Values from 

samples from Cox Lake (COX) and McNenny Pond (McNEN) 

springs plot with the lightest isotope values observed for wells, 

which is consistent with the interpretation of a component of 

spring discharge originating from outcrops of the Madison 

Limestone and Minnelusa Formation in the Limestone Plateau 

area. Values for the three isotope samples from Mirror Lake 

(MIR) spring are heavier and more variable than values from 

springs COX and McNEN, indicating possible contributions 

from overlying formations and local recharge. The overlying 

Minnekahta aquifer is a potential source of water to MIR 

spring discharge. An observation well completed in the 

Minnekahta aquifer about 2 mi southwest of Mirror Lake had 

a δ18O value of -15.6 ‰ (Naus and others, 2001).

The oxygen- and deuterium-isotope values for surfacewater samples collected at station 06430532 (Naus and others, 

2001), which represents the combined springflow contributing to Crow Creek, were more similar to springs COX and 

McNEN than to spring MIR. Geochemical modeling by 

Klemp (1995) indicated that McNenny Pond primarily was 

little-evolved Madison aquifer water, Cox Lake was Madison 

aquifer water with influence from the Minnelusa aquifer, 

and Mirror Lake was a mixture of water from the Madison 

and Minnelusa aquifers. The geologic processes involved in 

the formation of these springs are complex and include karst 

development in gypsum layers as well as limestone units and 

collapse features associated with these dissolution processes 

(Epstein and Putnam, 2005). The general location of the 

LaFlamme anticline (Strobel and others, 1999) in relation to 

Crow Creek and Cox Lake indicates that structural features 

also influence the development of ground-water flow paths 

to springs. Although movement of water in overlying formations contributes to spring discharge, isotope data indicate that 

Characterization of Ground-Water Flow  29
Table 7.  Oxygen- and deuterium-isotope data for wells and springs in the study area.

[Mdsn, Madison; Mnls, Minnelusa; --, none]

Station 

identification number Local number Other identifier Name Site type Sample date δ18

O

(per mil)

δD

(per mil)

443237103525801 7N 2E28BACD HG Higgins Gulch 

below I-90

Spring 09–10–2001 -16.46 -124

443012103544700 -- -- Higgins Gulch 

above 

Spearfish

Spring 09–10–2001 -16.25 -122

443309103532401 7N 2E20DAAD OH Old Hatchery Spring 09–10–2001 -16.57 -126

443330104003401 7N 1E21BBCD McNEN McNenny Pond Spring 11–05–2001 -17.04 -131

443335104010001 7N 1E20AABC MIR Mirror Lake Spring 11–06–2001 -16.17 -126

443335104010001 7N 1E20AABC MIR Mirror Lake Spring 09–10–2001 -14.02 -115

443356103593701 7N 1E16DADC COX Cox Lake Spring 11–05–2001 -17.06 -131

443356103593701 7N 1E16DADC COX Cox Lake Spring 09–10–2001 -16.99 -129

442752103501901 6N 2E23DBCA JEF -- Mdsn well 10–31–2001 -16.74 -128

442752103501901 6N 2E23DBCA JEF -- Mdsn well 08–16–2001 -16.74 -126

442826103503801 6N 2E23BABB -- -- Mnls well 06–13–2001 -16.78 -127

442757103512901 6N 2E22CBAB MP2 -- Mdsn well 06–13–2001 -16.71 -124

442822103514001 6N 2E22BADB -- -- Mnls well 08–16–2001 -16.12 -123

442823103514301 6N 2E22BAAC -- -- Mnls well 08–16–2001 -16.35 -124

442918103523001 6N 2E16AAB KYT -- Mdsn well 10–30–2001 -16.46 -126

442918103523001 6N 2E16AAB KYT -- Mdsn well 06–14–2001 -16.66 -126

442918103523001 6N 2E16AAB KYT -- Mdsn well 06–14–2001 -16.68 -125

442919103511601 6N 2E15BBBB DIC -- Mdsn well 10–19–2001 -16.72 -126

442906103510501 6N 2E15AADC ELL -- Mdsn well 05–29–2001 -16.78 -127

442842103505501 6N 2E14CBCC NEV -- Mdsn well 10–30–2001 -16.71 -128

442842103505501 6N 2E14CBCC NEV -- Mdsn well 06–14–2001 -16.68 -126

442855103503501 6N 2E14ACDC GC -- Mdsn well 11–01–2001 -16.78 -126

442950103521501 6N 2E 9ADDB COL -- Mdsn well 05–29–2001 -16.76 -128

442956103542701 6N 2E 8CCDA -- -- Mnls well 08–16–2001 -15.32 -116

442953103551801 6N 2E 7BDDA -- -- Mnls well 08–15–2001 -16.31 -122

443005103553801 6N 2E 7BBDB SAL -- Mdsn well 10–22–2001 -16.24 -123

443005103553801 6N 2E 7BBDB SAL -- Mdsn well 08–14–2001 -16.23 -123

443011103552101 6N 2E 7BAAB -- -- Mnls well 08–14–2001 -16.14 -120

443012103550601 6N 2E 7ABBA -- -- Mnls well 08–14–2001 -16.03 -121

443021103544801 6N 2E 6DDBD -- -- Mnls well 08–15–2001 -16.05 -123

443016103545801 6N 2E 6DCDA -- -- Mnls well 08–15–2001 -16.29 -122

443017103553601 6N 2E 6CCDA MIT -- Mdsn well 11–01–2001 -16.18 -122

443017103553601 6N 2E 6CCDA MIT -- Mdsn well 06–07–2001 -16.14 -122

443013103542301 6N 2E 5CCDC -- -- Mnls well 08–16–2001 -15.79 -120

30 Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Figure 13.  Relation between δ18O and δD in water samples collected from 1978 to 2005 from Madison and Minnelusa wells and

springs, and surface water (data prior to 2001 from Naus and others, 2001).

-135

-130

-125

-120

-115

-110

-18 -17.5 -17 -16.5 -16 -15.5 -15 -14.5 -14

Madison aquifer well

Minnelusa aquifer well

Mirror Lake spring

Cox Lake spring

McNenny Pond spring

Crow Creek (station 06430532)

Old Hatchery spring

Higgins Gulch spring

D18O, IN PER MIL

DD, IN PER MIL

the primary sources of water for these spring inflows to Crow 

Creek are the Madison and Minnelusa aquifers.

Oxygen- and deuterium-isotope values for samples from 

springs OH and HG were heavier than values for springs 

COX and McNEN in the northwestern part of the study area. 

This heavier isotope signature is consistent with source water 

originating from outcrops of the Madison Limestone and 

Minnelusa Formation primarily within the study area rather 

than from ground-water flow originating in the Limestone 

Plateau area and entering the study area along the eastern flow 

component that was described earlier (fig. 8). Oxygen- and 

deuterium-isotope values for spring OH were lighter than 

values for spring HG, which is located about 1 mi southeast 

of spring OH and closer to the outcrops in the study area. This 

could indicate a small fraction of water from the eastern flow 

component contributing to spring OH.

Chlorofluorocarbons

Concentrations of three CFCs (CFC–11, CFC–12, and 

CFC–113) were used to characterize ground-water residence 

times in the study area. Ten wells completed in the Madison 

aquifer and three springs were sampled for CFCs (fig. 1 and 

table 8). For the four wells where dye was detected, at least 

part of the mixture contains water that is less than 1 year old 

because dye reached these wells within 1 year. For these four 

wells, the apparent age ranged from 12 to 26 years, indicating 

that the samples contained months-old water mixed with 

years- to decades-old water. The following section summarizes 

a method described in Long and Putnam (2006) and used to 

model ground-water age distributions for the data shown in 

table 8.

Characterization of Ground-Water Flow  31
Table 8.  Chlorofluorocarbon and tritium data for wells and springs in the study area.

[CFC, chlorofluorocarbon; pptv; parts per trillion by volume; pCi/L, picocuries per liter; TU, tritium units; Mdsn, Madison; Mnls, Minnelusa; --, none or no data]

Site identification 

number Local number Other identifier Other identifier Site type Sample date

CFC concentration 

(pptv)

Apparent age 

(years) Tritium 

(pCi/L)

Tritium 2-

sigma 

(pCi/L)

Tritium 

(TU) CFC–

12

CFC–

11

CFC–

113

CFC–

12

CFC–

11

CFC–

113 Mean

443017103553601 6N 2E 6CCDA MIT -- Mdsn well 11–01–2001 49.7 14.2 0.0 39.2 40.2 -- 40 -- -- --443005103553801 6N 2E 7BBDB SAL -- Mdsn well 10–22–2001 5.3 .2 .0 53.1 54.1 -- 54 0.0 1 0442950103521501 6N 2E 9ADDB COL -- Mdsn well 05–29–2001 201.3 74.0 21.2 27.7 29.7 21.7 26 23 1.6 7.2442855103503501 6N 2E14ACDC GC -- Mdsn well 11–01–2001 -- -- -- -- -- -- -- 48 3.2 15.0

442854103505601 6N 2E14BCCC LA–88B Spearfish GC 

Mnls

Mnls well 08–18–2005 -- -- -- -- -- -- -- 61.4 3.8 19.2

442854103505602 6N 2E14BCCC2 LA–88C Spearfish GC 

Mdsn

Mdsn well 08–17–2005 -- -- -- -- -- -- -- 13.8 1 4.3

442842103505501 6N 2E14CBCC NEV -- Mdsn well 10–30–2001 398.1 165.2 47.9 16.7 22.2 16.2 18 -- -- --

442842103505501 6N 2E14CBCC NEV -- Mdsn well 06–14–2001 -- -- -- -- -- -- -- 68 4.5 21.3442906103510501 6N 2E15AADC ELL -- Mdsn well 05–29–2001 480.5 201.0 57.9 12.2 17.7 13.7 15 63 3.8 19.7

442919103511601 6N 2E15BBBB DIC -- Mdsn well 10–19–2001 445.9 164.3 47.9 14.6 22.1 16.1 18 -- -- --

442918103523001 6N 2E16AAB KYT -- Mdsn well 10–30–2001 18.3 46.4 .0 39.7 38.7 -- 39 1 1 .3442918103523001 6N 2E16AAB KYT -- Mdsn well 06–14–2001 -- -- -- -- -- -- -- 34 2.6 10.7

442757103512901 6N 2E22CBAB MP2 -- Mdsn well 06–13–2001 (

1

) 254.5 78.0 -- 13.3 11.2 12 72 4.5 22.6

442752103501901 6N 2E23DBCA JEF -- Mdsn well 10–31–2001 421.3 169.5 50.8 15.7 21.7 15.7 18 -- -- --442833103434601 6N 3E15DDDA LA–88A Frawley Ranch 

Mnls

Mnls well 08–17–2005 -- -- -- -- -- -- -- 106.9 6.4 33.5

442833103434602 6N 3E15DDDA2 LA–95A Frawley Ranch 

Mdsn

Mdsn well 08–16–2005 -- -- -- -- -- -- -- .3 .6 .1

442815103481701 6N 3E19BBDC VIG -- Mdsn well 08–24–2005 48.1 264.2 3.5 43.5 35.4 39.5 39 21.8 1.6 6.8

443356103593701 7N 1E16DADC COX Cox Lake Spring 11–05–2001 255.0 82.3 18.8 25.2 29.7 23.2 26 -- -- --

443356103593701 7N 1E16DADC COX Cox Lake Spring 09–10–2001 -- -- -- -- -- -- -- 43 2.6 13.5443335104010001 7N 1E20AABC MIR Mirror Lake Spring 11–06–2001 524.6 217.6 65.5 8.7 16.2 13.2 13 -- -- --

443335104010001 7N 1E20AABC MIR Mirror Lake Spring 09–10–2001 -- -- -- -- -- -- -- 35 2.6 11.0443330104003401 7N 1E21BBCD McNEN McNenny 

Pond

Spring 11–05–2001 232.7 93.4 25.1 26.7 28.7 21.2 26 -- -- --

443309103532401 7N 2E20DAAD OH Old Spearfish 

Hatchery

Spring 09–10–2001 -- -- -- -- -- -- -- 42 2.6 13.2

443012103544700 -- -- Higgins Gulch 

above Spearfish

Spring 09–10–2001 -- -- -- -- -- -- -- 55 3.2 17.2

443237103525801 7N 2E28BACD HG Higgins Gulch 

below I–90

Spring 09–10–2001 -- -- -- -- -- -- -- 73 4.5 22.9

1CFC-12 for samples was contaminated.2CFC-11 value is average of two samples because one of three samples was contaminated. All other values are the average of three samples.

32  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Ground-Water Age Distributions from Chlorofluorocarbon

data

The mixture of young and old ground water in a sample 

can be described quantitatively by a ground-water age distribution. The type and shape of the age distribution provides 

important information related to ground-water mixing and the 

complex nature of flow networks in karst aquifers. Long and 

Putnam (2006) used CFC concentrations to evaluate various 

age distributions for different areas of the Madison aquifer. 

One type of age distribution was classified as bimodal because 

the age categories were separated into two distinct groups that 

were separated by as much as two decades. For example, a 

bimodal age distribution could indicate that 30 percent of the 

water in a sample is less than 2 years old and 40 percent is 

from 20 to 40 years old. This distribution also might indicate 

that water from 3 to 19 years old and from 41 to 50 years is 

not present or negligible. Because CFCs only can be used 

to estimate ground-water age less than about 50 years old, 

the remaining 30 percent would be of an unknown age that 

is older than 50 years. Another type of age distribution was 

classified as unimodal, which had one age category where 

100 percent of the water was young, generally less than a few 

years old.

Results of the Long and Putnam (2006) study indicated 

that water sampled near presumed conduits with generally 

younger ages probably are unimodal and dominated by conduit flow, possibly mixed with intermediate flow. Water from 

wells near the possible conduit (fig. 1) was better characterized by the unimodal distribution than the bimodal distribution. For some of the wells where dye was detected and whose 

water was characterized by unimodal distributions, mixing 

with intermediate flow could explain apparent ages of 12 to 26 

years. Bimodal distributions were determined to be generally 

more applicable to areas farther from conduits that have older 

ground-water ages. The two components of a bimodal age 

distribution are interpreted as representing two components 

of flow (or storage) such as conduit and diffuse flow, and as 

much as two decades may separate the impulse responses of 

these components. Results of the Long and Putnam (2006) 

study indicated that bimodal distributions with a large age gap 

similar to this might characterize water sampled from many 

sites in the study area. Wells in these areas probably have 

good hydraulic connection to both diffuse and conduit flow. 

The large age gap between flow components may indicate that 

little mixing of components occurs naturally; however, mixing 

of these distinct flow components probably occurs at the well 

during pumping, which induces flow from both components.

Evidence for a Conduit Based on the Spatial Distribution

of Apparent Ages

An analysis was conducted to provide possible evidence 

for the existence of a major conduit, which could be useful 

for describing a physical basis for the different types of age 

distributions, especially the bimodal distribution. The objective of this analysis was to show that the spatial distribution 

of apparent ages may provide evidence for the presence of a 

conduit, but not to locate a conduit precisely. The spatial variability of apparent ages provides evidence that different flow 

components exist, such as conduit and diffuse flow.

Water supplied by major conduits is assumed to represent 

the youngest water in the Madison aquifer, and thus a relation 

may exist between apparent age and proximity to conduits. 

A north-trending line, which is centered on the four wells 

in which tracer dyes were detected, represents the possible 

location of a major conduit (fig. 1). The southern end of this 

line trends toward the dye injection point, and the northern 

end points toward springs OH and HG, for which the primary 

source is the Madison aquifer (Klemp, 1995). Because dye 

was not detected at springs OH and HG, orienting the conduit 

toward the springs is somewhat speculative; however, springs 

are a common discharge point for conduit flow (Clemens and 

others, 1997). Springs OH and HG emerge from streambeds 

and could not be located precisely, so dye samples were collected downstream from the springs. Possible tracer dye in 

these samples would have been diluted with small amounts 

of runoff and may have been degraded by organic matter in 

the stream and sunlight. Therefore, tracer dye probably would 

have been detected only with relatively high concentrations. In 

addition, if the conduit is assumed to be not farther from well 

COL than from the other wells where dye was detected, then 

the conduit near well COL would trend slightly toward the 

west, orienting it approximately toward the springs. The exact 

position chosen for this conduit was, to some extent, arbitrary, 

and alternative positions may result in equally good or better 

relations of apparent age and conduit proximity.

Dye tracers injected into Spearfish Creek were transported mainly toward the north but also were dispersed in an 

east-west transverse direction, as detection locations indicate 

(fig. 1). All wells where dye was detected are large production wells, which are more likely to draw water from a nearby 

conduit than are wells having smaller zones of influence. In 

addition, transverse flow could be the result of an anastomosing conduit network near a major central conduit or possibly 

from flushing of dye into the matrix (along fractures or bedding planes) especially during high flow.

To test the hypothesis that ground-water age is related to 

its proximity to a conduit, apparent age was used as a metric 

to assess relative age and was plotted in relation to distance to 

the possible conduit shown in figure 1. Three of the CFC–113 

samples from wells had concentrations of 0, which prevented 

an age estimate from that tracer, other than the knowledge 

that the water was more than about 50 years old. For CFC–12, 

one of the samples was contaminated, which prevented an 

age estimate from that tracer. For CFC–11, however, apparent ages were determined for all sites sampled for CFCs, and 

for consistency, only these apparent ages were included in the 

analysis of spatial distribution. In addition, the three springs in 

the northwest corner of the study area near Crow Creek were 

not included because the hydraulic gradient in this area slopes 

toward the northeast, and thus the source of water to these 

springs is unlikely to be a conduit near the city of Spearfish.

Characterization of Ground-Water Flow  33
60

CFC–11 APPARENT AGE, IN YEARS

DISTANCE TO POSSIBLE MAJOR CONDUIT, IN MILES

All 10 wells

Regression line for 10 wells

The 6 closest wells

Regression line for 6 wells 50

40

30

20

10

0 1 2 3 4

r2 = 0.71

r2 = 0.96

KYT

COL

NEV

DIC

ELL

MP2

JEF

VIG

MIT

SAL

Figure 14.  Regression analysis of CFC–11 apparent age with distance to a possible major conduit.

Figure 14 shows the results of a least-squares regression 

analysis of apparent age and distance to the possible conduit 

for the 10 wells with CFC–11 apparent ages. A logarithmic 

curve fit the 10 data points with an r2 value of 0.71. For only 

the six closest wells to the conduit (fig. 1) (wells MP2, ELL, 

DIC, NEV, COL, and KYT), a straight-line regression had an 

r

2

 value of 0.96. Because the six closest wells also are large 

production wells, the better fit for these data could result from 

either closer proximity to the conduit or from having larger 

zones of influence. Because the conduit is hypothetical, its 

location is approximate, and thus the regression analysis indicates that a plausible relation exists between apparent age and 

an approximate conduit location. Although this spatial analysis 

of age alone is not conclusive for the existence of a conduit, it 

provides additional evidence when considered in conjunction 

with other information such as locations of swallow holes and 

springs and other tracer data.

Tritium

Tritium values for samples collected for this study ranged 

from 0 to 33.5 TU (table 8). With complex mixtures a possibility, characterizing residence time from tritium data alone 

is often difficult; however, low values can indicate that a large 

portion of water is greater than 50 years old. This can be 

useful in understanding ground-water flow especially in the 

Madison aquifer. Two wells completed in the Madison aquifer 

had nondetectable (well SAL) or very low tritium concentrations (well LA–95A, 0.1 TU) (table 8). These wells are located 

about the same distance or closer to the outcrop areas than 

many wells (fig. 1) that have higher tritium concentrations, 

indicating that they are not located near a conduit and that 

water is largely derived from storage in the surrounding matrix 

(diffuse flow). Two tritium samples were collected from well 

KYT and had tritium concentrations of 0.3 and 10.1 TU. A 

possible explanation for the large difference is that the well 

may be drawing water from the Minnelusa aquifer in addition 

to the Madison aquifer, with pumping changing the mixture.

Tritium was used as a metric to characterize groundwater age in the area near a possible conduit. A straight line 

fit by linear regression between tritium concentration and 

distance to the possible conduit shown in figure 1 for the six 

wells closest to the conduit shows an inverse relation between 

these two parameters (fig. 15). As distance from the conduit 

increases, samples may contain larger fractions of pre-1950 

water that would not have detectable tritium concentrations 

34  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
25

TRITIUM CONCENTRATION, IN TRITIUM UNITS

DISTANCE TO POSSIBLE MAJOR CONDUIT, IN MILES

20

15

10

5

0

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

r2 = 0.68

MP2

ELL

NEV

KYT (1)

COL

KYT (2)

Figure 15.  Regression analysis of tritium concentration with distance to a possible major conduit.

because of low concentrations in precipitation for that period 

and subsequent radioactive decay. The correlation coefficient 

for the tritium regression (r2 = 0.68) is lower than that of the 

CFC–11 apparent-age regression (fig. 14). Tritium may be a 

less reliable age indicator than are CFCs because tritium concentrations in precipitation have risen and declined over time 

in contrast to CFCs, which have risen steadily up until about 

2000.

Synopsis of Results from Geochemical Tracers

Water from wells VIG, LA88C, and COL (fig. 1 and 

table 8) had low tritium concentrations indicating that a portion of the water probably is older than 50 years. Comparison 

of the tritium concentration of 7.2 TU for the Madison production well COL (fig. 1) to the tritium concentration in precipitation (fig. 5) indicates that even though dye was detected, a 

substantial portion of the water probably is older than 50 years 

when CFC data also are considered. Water from well ELL 

(fig. 1), in which dye also was detected, had a CFC apparent age of 15 years and a tritium concentration of 19.7 TU, 

which is about the same concentration as a unimodal mixture 

of water from precipitation averaged over the last 20 years 

with very little water older than 50 years. Comparison of 

CFC apparent ages for these two wells (COL, 26 years; ELL, 

15 years) is consistent with two different mixing scenarios, 

bimodal and unimodal, respectively, as described previously.

Age-dating parameters also can be useful in conjunction 

with other tracers in characterizing source waters. Comparison of the CFC apparent age for the three spring sites (COX, 

26 years; McNEN, 26 years; and MIR, 13 years) located in 

the northwest part of study area (fig. 1) is consistent with 

the interpretation from oxygen- and deuterium-isotope data 

that spring MIR probably has a local source of recharge from 

formations that overly the Madison Limestone and Minnelusa 

Formation. Analysis of potential mixing models (Long and 

Putnam, 2006) indicated that a bimodal distribution of a young 

fraction mixed with an older fraction is probable for springs 

COX and McNEN. This is consistent with the interpretation 

that spring flow from the Madison and Minnelusa aquifers 

in the northwest part of the study area represents a mixture 

of water with different flow paths and residence times. The 

relatively steady base flow in Crow Creek probably is related 

to this mixture of source waters with different hydraulic 

responses to stress over time.

Characterization of Ground-Water Flow  35
Characterization of Water Quality

Specific conductance is a measure of electrical 

conductivity, which is in general directly proportional to 

the concentration of dissolved solids in water. The general 

distributions of specific conductance for the Madison and 

Minnelusa aquifers are shown in figures 16 and 17. In 

addition to specific conductance values determined for 

this study, values in the USGS National Water Information 

System database with collection dates that ranged from 1956 

to 1998 were used to describe the distribution of specific 

conductance. In the Madison aquifer, specific conductance 

ranges from 18 to 945 microsiemens per centimeter. In the 

Minnelusa aquifer, specific conductance ranges from 2 to 

3,000 microsiemens per centimeter. In the Minnelusa aquifer, 

specific conductance increases with distance from the outcrop 

(downgradient) and probably is proportional to the amount of 

time that ground water is in contact with aquifer material. The 

spatial distribution of specific conductance in the Madison 

aquifer is less ordered than in the Minnelusa aquifer and is 

not necessarily related to distance from the outcrop. This may 

result from the greater heterogeneity of the Madison aquifer. 

The existence of fast flow paths, such as conduits, probably 

has a large influence on the spatial distribution of groundwater residence times and thus specific-conductance values. 

The mixing of young and old ground water at well intakes 

(see “Ground-Water Flow Paths, Ages, and Mixing Based on 

Geochemical Tracers” section) also could be a factor in the 

distribution of specific conductance.

Water samples from four observation wells completed 

in the Madison and Minnelusa aquifers in Spearfish (wells 

LA–88B and LA–88C) and about 6 mi east of Spearfish (wells 

LA–88A and LA–95A) (fig. 1) were analyzed for physical 

properties, major ions, nutrients, trace elements, and radionuclides (table 9). A description of water-quality characteristics 

for these constituent groups in ground water in the Black Hills 

area is available in Williamson and Carter (2001), which also 

describes water-quality criteria, standards or recommended 

limits, and general significance for selected properties.

USEPA Maximum Contaminant Levels (MCLs) are 

established for contaminants that, if present in drinking water, 

may cause adverse human-health effects; MCLs are enforceable health-based standards (U.S. Environmental Protection 

Agency, 2006a). USEPA Secondary Maximum Contaminant 

Levels (SMCLs) are established for contaminants that can 

adversely affect the taste, odor, or appearance of water and 

may result in discontinuation of use of the water; SMCLs are 

nonenforceable, generally non-health-based standards that 

are related to the aesthetics of water use (U.S. Environmental 

Protection Agency, 2006b).

No MCLs were exceeded for any of the constituents 

analyzed for samples from the four wells. The SMCL of 

250 mg/L for sulfate (U.S. Environmental Protection Agency, 

2006b) was exceeded in samples from the Minnelusa well 

LA–88A, with a concentration of 392 mg/L. Sulfates of 

calcium and magnesium form hard scale. Large concentrations of sulfate also have a laxative effect on some people 

and in combination with other ions give water a bitter taste. 

A potential source of the sulfates in the Minnelusa Formation 

are anhydrite and gypsum lenses (both minerals composed of 

calcium sulfate). A calcium concentration of 194 mg/L for this 

well sample also was relatively high compared to the median 

value of 68 mg/L for 250 Minnelusa aquifer well samples in 

the Black Hills area (Williamson and Carter, 2001).

Calcium and magnesium cause most of the hardness 

and scale forming properties in water. Hardness greater 

than 180 mg/L (as CaCO3) is considered very hard (Heath, 

1983). Hardness was 631 mg/L in water from Minnelusa 

well LA–88A and 263 mg/L in water from Minnelusa well 

LA–88B.

The major species of nitrogen usually found in ground 

water is nitrate. Nitrate is very mobile in ground water and 

moves with little or no retardation (Freeze and Cherry, 1979). 

Concentrations greater than local background levels may 

indicate pollution by feedlot runoff, sewage, or fertilizer. For 

samples from Minnelusa wells LA–88A and LA–88B, nitrite 

plus nitrate values of 2.41 mg/L and 0.58 mg/L, respectively, 

were relatively high compared to the median value of 0.2 mg/L 

for 157 Minnelusa aquifer well samples in the Black Hills area 

(Williamson and Carter, 2001).

36  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
This page intentionally left blank.

Characterization of Water Quality  37
Figure 16.  Specific conductance of water from the Madison aquifer (data from U.S. Geological Survey National Water Information

System, 1956–2005).

Spearfish

Beaver

Beaver

Creek

False

Bottom

Creek

Spearfish

Creek

Creek

Crow

Creek

Creek

Gulch

Bear

Gulch

Higgins

Red

Water

River

Iron

Creek

14A

385

14

90

14

85

85

34

Maurice

Deadwood

Spearfish

LaFlamme

anticline

Split Rock

Limestone Plateau

25

31

18

24

35

528

945

481

705

361

355

331 366

180

229

439

473

359 342

275

403

348

379

312

510 305 325

221

760

385

360

432

314 294 333 235

205

241

231 191

327 227

519

25

31

18

24

35

528

945

481

705

361

355

331 366

180

229

439

473

359 342

275

403

348

379

312

510 305 325

221

760

385

360

432

314 294 333 235

205

241

231 191

327 227

519

Planimetric base from U.S. Geological Survey digital data: 1:100,000, 1977, 1983

Universal Transverse Mercator projections, zone 13

104°

103°50'

44°35'

44°30'

44°25'

R. 1 E. R. 2 E. R. 3 E. 

38  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Creek

Whitewood

90 14

14

34

Whitewood

8

848

368

350

8

848

368

350

481

275

0 1 2 3 4 5

0 1 2 3 4 5

MILES

KILOMETERS

18 to less than 350

350 to 945

EXPLANATION

Outcrop of Madison Limestone— Includes areas 

 overlain by surficial deposits (modified from 

 Strobel and others, 1999)

Water wells open to the Madison aquifer—Specific 

 conductance, in microsiemens per centimeter 

103°40'

T. 7 N.

T. 6 N.

T. 5 N.

R. 4 E.

Fault—Bar on downthrown side

Anticline—Showing trace of axial plane and direction 

 of plunge

Syncline—Showing trace of axial plane and direction 

 of plunge. Dashed where approximate

Monocline—Showing trace of axial plane

Dome—Symbol size approximately proportional to size 

 of dome. Dome asymmetry indicated by arrow length

Structural features (from Strobel and others, 1999)

Characterization of Water Quality  39
Figure 17.  Specific conductance of water from the Minnelusa aquifer (data from U.S. Geological Survey National Water Information

System, 1956–2005).

Spearfish

Beaver

Beaver

Creek

False

Bottom

Creek

Spearfish

Creek

Creek

Crow

Creek

Creek

Gulch

Bear

Gulch

Higgins

Red

Water

River

Iron

Creek

14A

385

14

90

14

85

85

34

Maurice

Deadwood

Spearfish

LaFlamme

anticline

Split Rock

Limestone Plateau

Planimetric base from U.S. Geological Survey digital data: 1:100,000, 1977, 1983

Universal Transverse Mercator projections, zone 13

104°

103°50'

44°35'

44°30'

44°25'

R. 1 E. R. 2 E. R. 3 E. 

2

650 748

580

426

140 376 519 601

603

518

524

938

530

440 563

440

554 457

607 506

605 557

361

340 345

369

349

342 385

329 328

366

451

318 326 343 375

343 332

229 860 897

328 530

330

496

468

343

375

349

543 

455

660

165

2,480

2,210

1,380

1,120

2,250

2,410 1,580

1,960 1,800

1,350 1,790

2,810

1,500

1,140 1,005 1,670

1,070

2,340

40 Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Creek

Whitewood

90 14

14

34

Whitewood

748

650

0 1 2 3 4 5

0 1 2 3 4 5

MILES

KILOMETERS

2 to less than 700

700 to 3,000

EXPLANATION

Water wells open to the Minnelusa aquifer—Specific 

 conductance, in microsiemens per centimeter 

103°40'

T. 7 N.

T. 6 N.

T. 5 N.

R. 4 E.

Outcrop of Minnelusa Formation—Includes areas 

 overlain by surficial deposits (modified from 

 Strobel and others, 1999)

Fault—Bar on downthrown side

Anticline—Showing trace of axial plane and direction 

 of plunge

Syncline—Showing trace of axial plane and direction 

 of plunge. Dashed where approximate

Monocline—Showing trace of axial plane

Dome—Symbol size approximately proportional to size 

 of dome. Dome asymmetry indicated by arrow length

Structural features (from Strobel and others, 1999)

503

440

208

290

650

280

Characterization of Water Quality  41
Table 9.  Chemical analyses of selected ground-water samples from the Madison and Minnelusa aquifers.

[Number in parentheses below constituent is U.S. Geological Survey National Water Information System parameter code. FET, fixed end point titration; IT, 

incremental titration; gal/min, gallons per minute; μS/cm, microsiemens per centimeter; deg C, degrees Celsius; mm of Hg, millimeters of mercury; mg/L, 

milligrams per liter; μg/L, micrograms per liter; pCi/L, picocuries per liter; Mdsn, Madison aquifer; Mnls, Minnelusa aquifer; e, estimated; <, less than]

Station number Local number Other identifier Sample date

Flow rate 

(gal/min)

(00059)

Specific conductance 

(μS/cm) 

(000950)

pH, water 

whole, field 

(standard 

units)

(00400)

442833103434602 6N 3E15DDDA2 Frawley Ranch Mdsn 

(LA–95A)

08–16–2005 7.5 312 6.7

442833103434601 6N 3E15DDDA Frawley Ranch Mnls 

(LA–88A)

08–17–2005 6.0 1,070 6.8

442854103505602 6N 2E14BCCC2 Spearfish GC Mdsn 

(LA–88C)

08–17–2005 3.0 348 8.7

442854103505601 6N 2E14BCCC Spearfish GC Mnls 

(LA–88B)

08–18–2005 10.0 468 6.6

Other 

identifier

Temperature, air

 (deg C) 

(00020)

Temperature, 

water

(deg C) 

(00010)

Barometric 

pressure 

(mm of Hg) 

(00025)

Oxygen, 

dissolved 

(mg/L) 

(00300)

Oxygen, 

dissolved 

(percent 

saturation) 

(00301)

Hardness 

total

 (mg/L as 

CaCO3) 

(00900)

Alkalinity, 

filtered, 

IT field, 

(mg/L as 

CaCO3) 

(00410)

Calcium, 

dissolved 

(mg/L as 

Ca)

(00915)

Magnesium, 

dissolved 

(mg/L as 

Mg) 

(00925)

LA–95A 32.2 13.2 672 5.0 54 175 156 37.1 19.2

LA–88A 26.7 13.1 665 8.3 91 631 200 194 35.4

LA–88C 26.7 9.1 665 .7 6 84 1e33 7.1 16.2

LA–88B 23.9 9.2 670 11.3 97 263 221 64.2 24.9

Other 

identifier

Sodium, 

dissolved 

(mg/L as Na)

(00930)

Potassium, 

dissolved 

(mg/L as K)

 (00935)

Bicarbonate, 

dissolved, 

IT, field

 (mg/L as 

HCO3)

(00453)

Carbonate, 

dissolved, 

IT, field

 (mg/L as 

CO3)

(00452)

Sulfate, 

dissolved 

(mg/L as 

SO4) 

(00945)

Chloride, 

dissolved 

(mg/L as 

Cl) 

(00940)

Fluoride, 

dissolved 

(mg/L as F) 

(00950)

Silica, 

dissolved 

(mg/L as 

SiO2) 

(00955)

LA–95A 2.47 1.47 189 0 6.3 0.40 0.3 12.0

LA–88A 5.92 2.86 242 5 392 3.36 .2 11.9

LA–88C 19.5 22.4 1e22 1e8 4.0 67.5 .2 .2

LA–88B 3.22 .98 268 0 25.0 2.80 .2 12.8

42  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Table 9.  Chemical analyses of selected ground-water samples from the Madison and Minnelusa aquifers.—Continued

[Number in parentheses below constituent is U.S. Geological Survey National Water Information System parameter code. FET, fixed end point titration; IT, 

incremental titration; gal/min, gallons per minute; μS/cm, microsiemens per centimeter; deg C, degrees Celsius; mm of Hg, millimeters of mercury; mg/L, 

milligrams per liter; μg/L, micrograms per liter; pCi/L, picocuries per liter; Mdsn, Madison aquifer; Mnls, Minnelusa aquifer; e, estimated; <, less than]

Other 

identifier

Nitrogen, 

ammonia 

dissolved 

(mg/L as N)

(00608)

Nitrogen, 

nitrite 

dissolved 

(mg/L as N)

 (00613)

Nitrogen, 

NO2+NO3

dissolved 

(mg/L as N)

 (00631)

Phosphorus, 

dissolved 

(mg/L as P)

 (00666)

Phosphorus 

ortho, 

dissolved 

(mg/L as P)

(00671)

Aluminum, 

dissolved 

(μg/L as Al)

 (01106)

Antimony, 

dissolved 

(μg/L as Sb)

 (01095)

Arsenic, 

dissolved 

(μg/L as As)

(01000)

LA–95A <0.010 <0.002 0.1 0.008 e0.005 <2 <0.20 2.5

LA–88A .016 <.002 2.41 .021 .017 <2 <.20 3.8

LA–88C .063 <.002 <.016 .041 e.004 <2 <.20 <.2

LA–88B <.010 <.002 .579 .021 .016 <2 <.20 2.6

Other 

identifier

Barium, 

dissolved 

(μg/L as Ba) 

(01005)

Beryllium, 

dissolved 

(μg/L as Be) 

(01010)

Boron, 

dissolved 

(μg/L as B) 

(01020)

Cadmium 

dissolved 

(μg/L as Cd) 

(01025)

Chromium, 

dissolved 

(μg/L as Cr) 

(01030)

Cobalt, 

dissolved 

(μg/L as Co)

(01035)

Copper, 

dissolved 

(μg/L as Cu)

(01040)

Iron, 

dissolved 

(μg/L as Fe) 

(01046)

LA–95A 157 <0.06 9 <0.04 <0.8 0.307 <0.4 85

LA–88A 13 <.06 91 <.04 <.8 .418 3.7 30

LA–88C 15 <.06 11 e.03 <.8 .016 .4 17

LA–88B 277 <.06 9 <.04 <.8 .502 .8 e5

Other 

identifier

Lead, 

dissolved 

(μg/L as Pb)

(01049)

Lithium, 

dissolved 

(μg/L as Li) 

(01130)

Manganese, 

dissolved 

(μg/L as Mn) 

(01056)

Mercury, 

dissolved 

(μg/L as Hg) 

(71890)

Molybdenum, 

dissolved 

(μg/L as Mo) 

(01060)

Nickel, 

dissolved 

(μg/L as Ni)

 (01065)

Selenium, 

dissolved 

(μg/L as Se)

 (01145)

Silver, 

dissolved 

(μg/L as Ag) 

(01075)

LA–95A <0.08 5.0 40.7 <0.01 1.8 4.68 1.6 <0.2

LA–88A <.08 13.6 1.9 <.01 1.9 7.79 1.5 <.2

LA–88C <.08 56.2 16.8 <.01 10.8 .39 <.4 <.2

LA–88B <.08 3.0 .5 <.01 .5 2.77 .7 <.2

Other 

identifier

Strontium, 

dissolved 

(μg/L as Sr) 

(01080)

Thallium, 

dissolved 

(μg/L as Tl) 

(01057)

Vanadium, 

dissolved 

(μg/L as V) 

(01085)

Zinc, 

dissolved 

(μg/L as Zn) 

(01090)

Alpha 

radioactivity

(pCi/L) 

(04126)

Gross beta 

radioactivity 

(pCi/L) 

(03515)

Tritium 

(pCi/L) 

(07000)

Tritium 2–

sigma 

(pCi/L) 

(75985)

Uranium 

natural, 

dissolved 

(μg/L as U)

 (22703)

LA–95A 189 e0.02 2.0 0.7 0.9 1.2 0.3 0.60 1.50

LA–88A 2,610 <.04 3.1 3.4 4.4 1.3 107 6.4 2.77

LA–88C 174 <.04 <.1 1.1 -.2 13.5 13.8 1.0 <.04

LA–88B 222 <.04 2.8 2.2 2.4 1.4 61.4 3.8 1.13

1

Carbonate endpoint and theoretical titration curve did not fit data well.

Characterization of Water Quality  43
Summary

The Madison and Minnelusa aquifers are used extensively for water supplies for the city of Spearfish and other 

users in northern Lawrence County, South Dakota. The 

Madison and Minnelusa aquifers are contained within the 

Paleozoic-age Madison Limestone and Minnelusa Formation, 

and the hydraulic connection between the Madison and 

Minnelusa aquifers is spatially variable. Transmissivity of the 

Madison and Minnelusa aquifers is very heterogeneous with 

values determined from aquifer tests that range over several 

orders of magnitude.

Ground water in the Madison and Minnelusa aquifers in 

the study area generally flows north from outcrop areas where 

ground-water recharge from sinking streams and infiltration of 

precipitation occurs. Ground water that moves northward and 

eastward around the Black Hills enters the study area from the 

west and results in hydraulic heads that are several hundred 

feet higher on the western side of the study area than on the 

eastern side. The estimated average recharge rate of 38 cubic 

feet per second (ft3/s) on outcrops of the Madison Limestone 

and Minnelusa Formation is less than the total estimated average spring discharge rate of 51 ft3

/s in the northwestern part of 

the study area. Potentiometric contours for the Madison and 

Minnelusa aquifers show that the hydraulic gradient is steeper 

near outcrop areas than in the northern part of the study area.

The maximum potential streamflow recharge rate to 

Madison and Minnelusa aquifers along Spearfish Creek is 

about 21 ft3/s. Sixteen pounds of fluorescein dye were injected 

into Spearfish Creek on March 25, 2003, when streamflow 

was 6.6 ft3/s. The dye was detected in water samples from four 

wells completed in the Madison aquifer ranging from 2.6 to 

4.5 miles north of the injection site. First arrival times ranged 

from 5 to 169 days, and ground-water velocities ranged from 

about 0.1 to 0.5 mile per day. A peak concentration of about 

23 micrograms per liter (μg/L) at the nearest well occurred 

15 days after injection, then decreased gradually; however, 

concentrations greater than 1 μg/L were present about 

9 months later. Detectable dye concentrations were observed 

for as long as 400 days in a well farther downgradient. 

Sixty-four pounds of Rhodamine WT were injected into 

Spearfish Creek at the same location as the fluorescein dye 

injection on May 9, 2003, when streamflow was 5.6 ft3/s. 

Rhodamine WT dye concentrations measured in samples from 

the same four wells were about an order of magnitude less 

than measured fluorescein concentrations. A combination of 

recharge characteristics, the diversion of streamflow around 

the Spearfish Creek loss zone, and highly transmissive 

conduits associated with streamflow loss may explain transient 

differences in dye concentrations.

Samples from selected wells and springs in the study 

area were collected and analyzed for oxygen and deuterium 

isotopes, chlorofluorocarbons (CFCs), and tritium. Oxygenand deuterium-isotope distributions in precipitation for 

northern Lawrence County generally are lightest (more 

negative) in the southeast and become heavier (more positive) 

in an outward direction from the central part of the Black 

Hills. Oxygen- and deuterium-isotope values for samples 

from Cox Lake and McNenny Pond springs are similar to 

the lightest oxygen and deuterium values for water from 

wells, indicating a probable component of spring discharge 

that originates from outcrops of the Madison Limestone and 

Minnelusa Formation on the Limestone Plateau south of the 

study area. Oxygen- and deuterium-isotope values for three 

samples from Mirror Lake spring are heavier than values for 

Cox Lake and McNenny Pond springs, indicating possible 

contributions from overlying aquifers and local recharge. 

The oxygen- and deuterium-isotope values for the combined 

springflow contributing to Crow Creek in the northwestern 

part of the study area are similar to the values for Cox Lake 

and McNenny Pond springs indicating that the primary 

sources of water for the large spring discharge are the Madison 

and Minnelusa aquifers. Oxygen- and deuterium-isotope 

values for Old Hatchery and Higgins Gulch springs, located 

north of Spearfish, were heavier than values for Cox Lake and 

McNenny Pond springs, indicating a source water originating 

from the outcrops of the Madison Limestone and Minnelusa 

Formation within the study area rather than ground-water 

moving into the study area from the west.

Concentrations of three CFCs (CFC–11, CFC–12, and 

CFC–113) were used to characterize ground-water residence 

times in the study area. For the four wells where dye was 

detected, at least a portion of the water was less than 1 year 

old. CFC apparent ages ranged from 12 to 26 years, indicating 

that the wells contained months-old water mixed with yearsto decades-old water.

Logarithmic regression analysis of the CFC–11 apparent 

ages for water from 10 wells where dye was detected and 

distance to a possible conduit trending north through the area, 

yielded an r2 value of 0.71. Straight-line regression analysis 

of the CFC–11 apparent ages for the six wells closest to the 

possible conduit had an r2 value of 0.96. Although spatial 

analysis of age alone is not conclusive for the existence of a 

conduit, it provides additional evidence when considered in 

conjunction with other hydrologic and chemical data.

Two wells located relatively close to the outcrop areas 

had no or very low tritium values indicating relatively long 

residence times and diffuse ground-water flow. The low 

tritium value of 7.2 TU in water from well COL where dye 

was detected, indicates that the water probably is a bimodal 

mixture, with a substantial portion that is older than 50 years. 

Water from well ELL, in which dye also was detected, had a 

CFC apparent age of 15 years and a tritium concentration of 

19.7 TU, which is about the same concentration as a unimodal 

mixture of water from precipitation averaged over the last 

20 years with very little water older than 50 years. Comparison 

of the CFC apparent age for the three spring sites (Cox Lake, 

26 years; McNenny Pond, 26 years; Mirror Lake, 13 years) 

also indicates that Mirror Lake spring probably has a component of local recharge from aquifers that overlie the Minnelusa 

Formation.

44  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
In the Madison aquifer, specific conductance ranges from 

18 to 945 microsiemens per centimeter. In the Minnelusa 

aquifer, specific conductance ranges from 2 to 3,000 microsiemens per centimeter. The spatial distribution of specific 

conductance in the Madison aquifer is less ordered than in the 

Minnelusa aquifer and probably is the result of heterogeneity 

and the existence of solution conduits.

Water samples from two observation wells completed 

in the Madison and Minnelusa aquifers near Spearfish and 

two wells about 6 miles east of Spearfish were analyzed for 

physical properties, major ions, nutrients, trace elements, 

and radionuclides. U.S. Environmental Protection Agency 

Maximum Contaminant Levels were not exceeded for any of 

the constituents analyzed in water from the four wells. The 

U.S. Environmental Protection Agency Secondary Maximum 

Contaminant Level for sulfate (250 milligrams per liter) was 

exceeded in water from a Minnelusa well located east of 

Spearfish, with a value of 392 milligrams per liter.

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chaps. A1–A9, 2 v., variously paged. [Available online at 

http://pubs.water.usgs.gov/twri9A. Chapters were originally 

published from 1997–1999; updates and revisions are 

ongoing and are summarized at http://water.usgs.gov/owq/

FieldManual/mastererrata.html.]

References  47
Weiss, R.F., 1970, The solubility of nitrogen, oxygen, and 

argon in water and seawater: Deep Sea Research, v. 17, 

p. 721–735.

Whitehead, R.L., 1996, Ground water atlas of the United 

States—segment 8, Montana, North Dakota, South 

Dakota, Wyoming: U.S. Geological Survey Hydrologic 

Investigations Atlas 730–I, 24 p.

Williamson, J.E., and Carter, J.M., 2001, Water-quality 

characteristics in the Black Hills area, South Dakota: 

U.S. Geological Survey Water-Resources Investigations 

Report 01–4194, 196 p.

Wilson, J.F., Cobb, E.D., and Kilpatrick, F.A., 1986, 

Fluorometric procedures for dye tracing: U.S. Geological 

Survey Techniques of Water-Resources Investigations, 

book 3, chap. A12, 34 p.

48  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Supplemental Information

Section A. Additional data

Table 10.  Observation wells used for monitoring water levels in the study area.

[NGVD 29, National Geodetic Vertical Datum of 1929; Mdsn, Madison; Mnls, Minnelusa]

Station identification 

number Local number Other identifier

Other 

identifier Aquifer

Hydraulic head, 

September 2004

(feet above 

NGVD 29)

Land-surface 

altitude

(feet above 

NGVD 29) 

442435103571101 5N 1E11DABA Big Hill Trailhead 

Mdsn

LA–95C Mdsn 4,881 5,530

442545103343701 5N 4E 1ABBD Whitewood Mnls LA–86C Mnls 3,453 3,629

442545103343702 5N 4E 1ABBD2 Whitewood Mdsn LA–90A Mdsn 3,443 3,630

442344103253401 5N 4E14ADD Boulder Canyon 

Mnls

LA–63A Mnls 3,675 3,882

442301103365501 5N 4E22ADDA Boulder Canyon 

Mdsn

LA–96D Mdsn 3,642 4,062

443100103543001 6N 2E 5BBBB Spearfish W Mnls LA–86A Mnls 3,543 3,678

442854103505601 6N 2E14BCCC Spearfish GC Mnls LA–88B Mnls 3,653 3,734

442854103505602 6N 2E14BCCC2 Spearfish GC Mdsn LA–88C Mdsn 3,641 3,735

442802103544601 6N 2E19DABA Tinton Rd Mdsn LA–96B Mdsn 3,651 4,590

442802103544602 6N 2E19DABA2 Tinton Rd Mnls LA–96C Mnls 4,313 4,591

442833103434601 6N 3E15DDDA Fawley Ranch Mnls LA–88A Mnls 3,550 3,768

442833103434602 6N 3E15DDDA2 Frawley Ranch 

Mdsn

LA–95A Mdsn 3,520 3,768

443100104002001 7N 1E33CCDD State line Mdsn LA–87A Mdsn 3,736 3,667

443100104002002 7N 1E33CCDD2 State line Mnls LA–87B Mnls 3,644 3,668

443515103513901 7N 2E10BADC Redwater LA–62A Mnls 3,484 3,218

Section A. Additional data  51
Table 11.  Water wells completed in the Madison aquifer and used for interpretation of average potentiometric surface.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; --, none]

Station identification 

number Local number Other identifier

Adjusted 

hydraulic head

(feet above 

NGVD 29)

Observation 

well used for 

adjustment 

Land-surface 

altitude

 (feet above 

NGVD 29)

Well depth 

(feet)

441134103590301 3N 1E27DBAA -- 6,269 LA–63A 6,545 420

441700103535401 4N 2E29AACB -- 5,505 LA–63A 5,525 50

442113103524101 5N 2E33DCAA2 -- 5,946 LA–63A 6,040 480

442504103415301 5N 3E 1DCCB -- 4,036 LA–63A 4,360 550

442255103413401 5N 3E24ADCA -- 4,620 LA–63A 4,680 145

1

443146103362301 5N 4E14BBB -- 3,742 LA–63A 4,130 870

442358103370101 5N 4E15ABCA -- 3,640 LA–63A 4,260 900

442334103370501 5N 4E15DBCB -- 3,613 LA–63A 4,210 700

442344103405601 5N 4E18BDCD -- 4,501 LA–63A 4,800 540

442951103570701 6N 1E11ADDB -- 3,663 LA–63A 4,140 725

442925103573901 6N 1E11CDDD -- 3,837 LA–96B 4,340 962

442938103571801 6N 1E11DACB -- 3,722 LA–63A 4,175 680

442908103570701 6N 1E14AADC -- 3,757 LA–63A 4,330 750

442909103572601 6N 1E14ABDC -- 3,788 LA–63A 4,365 1,070

442900104014601 6N 1E17BCBC -- 4,105 LA–87A 4,285 760

443017103553601 6N 2E 6CCDA MIT 3,653 LA–63A 4,105 810

443005103553801 6N 2E 7BBDB SAL 3,665 LA–63A 4,155 1,262

442950103521501 6N 2E 9ADDB COL 3,645 LA–88C 3,640 741

442936103530001 6N 2E 9CAC2 PT 3,681 LA–63A 3,762 855

442855103503501 6N 2E14ACDC GC 3,675 LA–63A 3,805 1,180

442842103505501 6N 2E14CBCC NEV 3,663 LA–88C 3,760 842

1

442906103510501 6N 2E15AADC ELL 3,669 LA–88C 3,720 800

442918103523001 6N 2E16AAB KYT 3,643 LA–88C 3,840 925

442917103525601 6N 2E16BADD -- 3,548 LA–63A 3,900 760

442907103530801 6N 2E16BBBC -- 3,691 LA–63A 3,930 620

442853103530001 6N 2E16CBAB -- 3,683 LA–63A 4,020 600

442748103524501 6N 2E21DCBC MP3 3,681 LA–63A 4,230 965

442813103520501 6N 2E22BCCA MP1 3,657 LA–63A 4,220 1,140

442757103512901 6N 2E22CBAB MP2 3,666 LA–88C 4,240 870

442752103501901 6N 2E23DBCA JEF 3,619 LA–88C 4,020 720

442805103491801 6N 2E24BDCD -- 3,609 LA–88C 4,030 708

52  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Table 11.  Water wells completed in the Madison aquifer and used for interpretation of average potentiometric surface.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; --, none]

Station identification 

number Local number Other identifier

Adjusted 

hydraulic head

(feet above 

NGVD 29)

Observation 

well used for 

adjustment 

Land-surface 

altitude

 (feet above 

NGVD 29)

Well depth 

(feet)

442727103493701 6N 2E25BBCA -- 3,697 LA–63A 4,115 615

442636103480301 6N 2E31BADB -- 4,062 LA–88C 4,530 660

442627103530801 6N 2E33BCAC -- 4,197 LA–96B 4,835 1,285

442856103475701 6N 3E18BDAD -- 3,561 LA–63A 3,900 900

442818103472501 6N 3E19AACD -- 3,535 LA–63A 3,970 740

442815103481701 6N 3E19BBDC VIG 3,561 LA–88C 3,965 863

442823103465201 6N 3E20BAAC -- 3,534 LA–95A 3,940 902

442652103472801 6N 3E20DDAC -- 3,592 LA–63A 4,015 680

442742103462101 6N 3E20DDCA -- 3,525 LA–63A 4,025 820

1

442736103461401 6N 3E20DDDC -- 3,974 LA–63A 4,020 720

1

442715103432301 6N 3E26BDBD -- 3,727 LA–63A 3,898 880

442720103445501 6N 3E27BCBB -- 3,518 LA–95A 3,970 980

442727103451901 6N 3E28ABCA -- 3,530 LA–63A 3,970 950

442651103460401 6N 3E29DDDB -- 3,737 LA–63A 4,190 700

442714103480501 6N 3E30BDDB -- 3,538 LA–88C 4,160 980

442703103482401 6N 3E30CBDB -- 3,710 LA–88C 4,145 580

442631103480201 6N 3E31BADD -- 4,020 LA–88C 4,525 660

442632103481501 6N 3E31BBDD -- 4,011 LA–88C 4,440 640

442621103481901 6N 3E31BCDD -- 4,047 LA–88C 4,540 765

442623103485901 6N 3E31BDDA -- 4,021 LA–88C 4,500 760

442617103480901 6N 3E31CABB -- 4,019 LA–88C 4,500 700

442637103451501 6N 3E33AACB -- 3,576 LA–95A 4,220 894

442637103451901 6N 3E33BABC -- 3,677 LA–63A 4,190 760

442636103454901 6N 3E33BACB -- 3,790 LA–95A 4,220 660

442636103435601 6N 3E34AACA -- 3,527 LA–95A 4,055 820

442640103444501 6N 3E34BBCA -- 3,563 LA–63A 4,200 922

442640103425901 6N 3E35ABBA -- 3,558 LA–63A 4,035 1,140

442600103411301 6N 4E31CCBA -- 3,563 LA–63A 4,080 705

443204104001301 7N 1E28CDAC -- 3,702 LA–87A 3,535 1,530

1 The hydraulic head for this site displays excessive variability at the local scale and probably does not represent the potentiometric surface; therefore, the 

hydraulic head was not used in interpretation of the potentiometric surface.

Section A. Additional data  53
Table 12.  Water wells completed in the Minnelusa aquifer and used for interpretation of average potentiometric surface.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; --, not applicable]

Station identification 

number Local number

Adjusted 

hydraulic head

(feet above 

NGVD 29)

Observation

well used for

 adjustment 

Land-surface 

altitude

(feet above 

NGVD 29)

Well depth

(feet)

442546103344101 5N 4E 1ABBC 3,454 LA–63A 3,618 310

442546103343301 5N 4E 1ABBD3 3,442 LA–63A 3,625 400

442337103350401 5N 4E13CCAC 3,735 LA–63A 3,870 315

442340103345001 5N 4E14ADA 3,660 -- 3,860 400

442400103362001 5N 4E14BBDA 3,622 LA–63A 4,030 620

442344103360601 5N 4E14BDCA 3,631 LA–63A 3,990 630

1

442347103364001 5N 4E15ADDA 3,655 LA–63A 4,075 560

442347103364002 5N 4E15ADDB2 3,749 LA–63A 4,175 560

442331103401401 5N 4E17CACB 4,447 LA–63A 4,480 70

443053103564301 6N 1E 1BAC 3,717 LA–63A 3,980 480

443036103575401 6N 1E 2CABB 3,910 LA–63A 3,930 160

443057104005001 6N 1E 5AADB 3,680 LA–87B 3,690 515

443049104024501 6N 1E 6BDAB 3,622 LA–63A 3,785 430

442952104015101 6N 1E 8BCBC 3,764 LA–63A 3,900 320

442953103595601 6N 1E 9ACBC 3,775 -- 3,840 189

1

442959103573201 6N 1E11ACBA 3,693 LA–87B 4,090 620

442859103571001 6N 1E14ADDB 4,329 LA–96C 4,415 752

442903103595601 6N 1E16ACBB 4,040 -- 4,180 263

442919104013301 6N 1E17BBA 3,832 LA–87B 4,140 402

442917104025801 6N 1E18BBAA 4,131 LA–63A 4,300 300

443101103530601 6N 2E 4BBAA 3,588 LA–63A 3,548 300

443028103522801 6N 2E 4DBCC 3,550 LA–63A 3,562 420

443029103542701 6N 2E 5CBBC 3,577 LA–86A 3,662 280

443035103543001 6N 2E 5CBDB 3,563 LA–86A 3,655 290

443013103542301 6N 2E 5CCDC 3,590 LA–86A 3,670 238

443020103525001 6N 2E 5DC2 3,579 LA–63A 3,625 285

443017103533801 6N 2E 5DDCB 3,577 LA–86A 3,615 300

443025103544501 6N 2E 6DACC 3,615 LA–63A 3,710 267

1

443016103545801 6N 2E 6DCDA 3,702 LA–86A 3,895 380

443019103551301 6N 2E 6DCDC 3,661 LA–86A 3,920 500

443021103544801 6N 2E 6DDBD 3,675 LA–86A 3,738 480

443008103544101 6N 2E 7AAAB 3,608 LA–86A 3,700 260

443001103544201 6N 2E 7AADC 3,656 LA–86A 3,795 240

443012103550601 6N 2E 7ABBA 3,698 LA–86A 3,965 480

54  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Table 12.  Water wells completed in the Minnelusa aquifer and used for interpretation of average potentiometric surface.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; --, not applicable]

Station identification 

number Local number

Adjusted 

hydraulic head

(feet above 

NGVD 29)

Observation

well used for

 adjustment 

Land-surface 

altitude

(feet above 

NGVD 29)

Well depth

(feet)

443011103552101 6N 2E 7BAAB 3,716 LA–86A 4,120 620

443012103554401 6N 2E 7BBBA 3,754 LA–86A 4,150 560

442953103553801 6N 2E 7BCBB 3,738 LA–86A 3,790 77

442953103553701 6N 2E 7BCBD 3,736 LA–86A 3,790 74

442953103551801 6N 2E 7BDDA 3,752 LA–86A 3,780 51

442946103543601 6N 2E 7DAAA 3,660 LA–86A 3,820 498

442942103545201 6N 2E 7DABC 3,621 LA–86A 3,838 320

443026103550401 6N 2E 7DCBA 3,941 LA–63A 4,080 220

442946103534401 6N 2E 8ACDD 3,661 LA–63A 3,700 180

1

442945103543201 6N 2E 8CBBB 3,706 LA–86A 3,807 440

442940103543401 6N 2E 8CBBC 3,666 LA–86A 3,840 472

442935103542201 6N 2E 8CBDD 3,666 LA–86A 3,822 540

442940103542801 6N 2E 8CBDD1 3,688 LA–86A 3,800 410

442921103463101 6N 3E 8DDAC 3,526 LA–88A 3,815 662

442935103530301 6N 2E 9CCB 3,653 LA–63A 3,820 205

442831103513501 6N 2E15CDDA 3,699 LA–63A 3,940 520

442903103530501 6N 2E16BCAD 3,684 LA–96C 3,970 440

442910103531001 6N 2E16BDBD 3,598 LA–96C 3,930 560

442901103530001 6N 2E16CBCB 3,755 LA–96C 4,110 500

442820103541001 6N 2E20BACA 4,209 LA–63A 4,280 200

442823103514301 6N 2E22BAAC 3,603 LA–88B 4,030 560

442822103514001 6N 2E22BADB 3,642 LA–88B 4,060 620

442825103520101 6N 2E22BBDC 3,698 LA–63A 4,000 520

442826103503801 6N 2E23BABB 3,647 LA–88B 3,790 180

442820103503501 6N 2E23BBBA 3,660 LA–88B 3,740 415

442741103495601 6N 2E23DD 3,668 LA–63A 4,042 540

1

442729103493601 6N 2E25BBDD 3,939 LA–63A 4,100 260

442630103485001 6N 2E36A 4,172 LA–63A 4,240 200

442636103491801 6N 2E36BACA 4,244 LA–63A 4,520 600

443006103431701 6N 3E11BAAC 3,527 LA–63A 3,665 775

442922103433301 6N 3E11CCDC 3,543 LA–88A 3,680 430

442923103431501 6N 3E11CDDC 3,543 LA–88A 3,660 430

1

442834103431501 6N 3E14CDA 3,715 LA–63A 3,750 100

442907103442301 6N 3E15BADD 3,515 LA–63A 3,840 598

Section A. Additional data  55
Table 12.  Water wells completed in the Minnelusa aquifer and used for interpretation of average potentiometric surface.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; --, not applicable]

Station identification 

number Local number

Adjusted 

hydraulic head

(feet above 

NGVD 29)

Observation

well used for

 adjustment 

Land-surface 

altitude

(feet above 

NGVD 29)

Well depth

(feet)

442844103434901 6N 3E15DAD 3,520 -- 3,740 300

442913103465401 6N 3E17ABAA2 3,552 LA–63A 3,830 700

1

442822103433501 6N 3E26BDBB 3,685 LA–63A 3,880 438

442708103432801 6N 3E26CBAA 3,539 LA–88A 3,950 560

1

442622103420601 6N 3E36DBBB 3,981 LA–63A 4,020 165

442950103374701 6N 4E 8DADD 3,632 LA–88A 3,680 242

442835103380101 6N 4E16DDBB 3,471 LA–63A 3,560 1,442

442749103381401 6N 4E21DBCD 3,507 LA–86C 3,620 630

442746103381301 6N 4E21DCBC 3,510 LA–86C 3,645 480

442728103381201 6N 4E28ABD 3,542 LA–63A 3,680 552

442610103401701 6N 4E31ADDD 3,508 LA–63A 4,040 700

1

442606103402301 6N 4E31DACD 3,462 LA–88A 3,970 730

1

442708103382001 6N 4E33ABDC 3,656 LA–86C 3,750 460

442624103353301 6N 4E35ADBC 3,489 LA–86C 3,560 315

442652103354201 6N 4E35BADA 3,488 LA–86C 3,583 495

442623103360401 6N 4E35BDCA 3,498 LA–63A 3,720 300

1

442610103345501 6N 4E36CACD 3,504 LA–63A 3,604 400

442610103350001 6N 4E36CBAA 3,475 LA–86C 3,595 460

442611103350301 6N 4E36CBDD 3,494 LA–86C 3,590 310

443536104004801 7N 1E 5DDAB 3,482 LA–87B 3,490 990

443355103574501 7N 1E14CCDD 3,496 -- 3,480 460

443355103574502 7N 1E14CCDD2 3,497 LA–63A 3,474 620

443320104030001 7N 1E19BCCC 3,524 LA–63A 3,520 825

443255104020301 7N 1E19DCCC 3,500 LA–63A 3,520 645

443320104004501 7N 1E20AAD 3,457 LA–63A 3,400 281

443320104003501 7N 1E21BBC 3,446 LA–63A 3,379 220

443202103581101 7N 1E25CCBC 3,528 LA–63A 3,620 240

443215103561501 7N 1E25DBDA 3,489 LA–86A 3,510 500

443215103573001 7N 1E26ACD 3,491 LA–87B 3,524 270

443231104004001 7N 1E28BCBC 3,620 LA–87B 3,485 740

443212104001601 7N 1E28CACD 3,684 LA–63A 3,535 1,530

443240104024001 7N 1E30AAAD 3,531 LA–63A 3,480 615

443150104020001 7N 1E30DDDC 3,584 LA–63A 3,510 985

443132103555501 7N 1E36ADDD 3,593 LA–86A 3,630 310

443141103562301 7N 1E36BDAA 3,511 LA–63A 3,655 240

443143103563001 7N 1E36BDAD 3,504 LA–86A 3,675 300

56  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Table 12.  Water wells completed in the Minnelusa aquifer and used for interpretation of average potentiometric surface.—Continued

[NGVD 29, National Geodetic Vertical Datum of 1929; --, not applicable]

Station identification 

number Local number

Adjusted 

hydraulic head

(feet above 

NGVD 29)

Observation

well used for

 adjustment 

Land-surface 

altitude

(feet above 

NGVD 29)

Well depth

(feet)

443105103563401 7N 1E36CDDC 3,689 LA–86A 3,930 480

443032103562501 7N 1E36CDDD 3,667 LA–63A 3,930 480

1

443117103560101 7N 1E36DCBC 3,716 LA–86A 3,890 500

443116103560801 7N 1E36DDBB 3,621 LA–86A 3,820 500

443430103550901 7N 2E18ABBA 3,449 LA–86A 3,390 1,076

443420103551001 7N 2E19CAAA 3,480 -- 3,405 700

443323103515501 7N 2E22BCA 3,481 -- 3,437 1,218

443230103504101 7N 2E26BCDA 3,540 LA–63A 3,400 825

443117103541301 7N 2E32BAC 3,561 LA–63A 3,570 500

443427103540201 7N 2E32BB 3,556 LA–63A 3,560 540

443115103540001 7N 2E32BDD 3,533 LA–63A 3,590 545

443117103501301 7N 2E35DCBA 3,475 LA–88B 3,545 717

443515103473001 7N 3E 7AABA 3,507 LA–63A 3,360 1,653

1

The hydraulic head for this site displays excessive variability at the local scale and probably does not represent the potentiometric surface; therefore, the 

hydraulic head was not used in interpretation of the potentiometric surface.

Section A. Additional data  57
Figure 18. Comparison of background, blank, and replicate

samples for fluorescein dye analysis.

Background

FLUORESCEIN CONCENTRATION, IN MICROGRAMS PER LITER

Blank Replicate

-0.2

-0.1

0

0.1

0.2

0.3

9 163 54

9

75th percentile

Number of samples

Replicate is a second analysis of the same sample

Data value less than or equal to 1.5 times the interquartile

 range outside the quartile

Median

25th percentile

Outlier data value less than or equal to 3 and more than 

 1.5 times the interquartile range outside the quartile

Outlier data value greater than 3 times the interquartile 

 range outside the quartile

EXPLANATION

Interquartile

range

Section B. Dye Tracing Methods

Fluorescent dyes can be detected at very low concentrations in water samples by analysis of glass ampoules containing the sample in a filter fluorometer. This instrument causes 

the dye in the sample to fluoresce when exposed to light of a 

particular bandwidth. The light emitted has a specific bandwidth that is characteristic for a particular dye. The fluorometer measures the relative magnitude of this emitted light, 

which is then calibrated to known standard concentrations of 

the dye in units of mass per volume. A Turner Designs Model 

TD–700 Laboratory fluorometer was used for the analyses in 

this study. Jones (1984) and Wilson and others (1986) provide 

more detailed technical information regarding operation of 

filter fluorometers.

Two types of tracer dyes were used in this study, fluorescein and Rhodamine WT. The two dyes emit fluorescence at 

different ranges of bandwidths with a small overlap; thus, a 

sample containing a mixture of the two dyes can be analyzed 

for each dye separately with little interference.

Fluorescein

Fluorescein is a green dye that can be detected at 

concentrations as low as 0.1 μg/L (Jones, 1984). Background 

water samples not containing dye often can have fluorometer 

readings at higher levels than this. Some constituents in 

natural waters, such as clay and organic substances such as 

humic acids have fluorescent properties, and instrument noise 

may be a factor. Boxplots of background concentrations for 

water samples collected prior to dye injection at selected wells 

and blank samples indicate that background concentrations 

generally were less than 0.2 μg/L (fig. 18). Variability in 

blank samples generally was less than ±0.1 μg/L, with some 

outliers of about 0.2 μg/L. The differences between sample 

concentrations and replicate analyses of the same samples 

were less than 0.1 μg/L for 75 percent of the samples. On 

the basis of this information, the calculated detectable dye 

concentrations at first arrival was estimated to be about 

0.35 μg/L. An isolated sample at this concentration may not 

indicate the presence of dye; however, an increasing trend 

beginning at this concentration was assumed to indicate the 

presence of fluorescein dye.

Because fluorescein concentrations are sensitive to 

sunlight exposure, samples were collected in opaque bottles. 

To test the loss of fluorescence, samples from well MP2 were 

stored for about 1 year and then reanalyzed and compared with 

the original analysis (fig. 19). The loss in dye concentration 

over this period averaged about 20 percent. Dye samples were 

usually collected over a several week period before analysis, 

and some loss of dye in sample storage is possible.

Rhodamine WT

Rhodamine WT is bright red at high concentrations and 

can be detected at concentrations as low as 0.01 μg/L with a 

fluorometer (Jones, 1984). The same considerations regarding background levels and instrument noise as described for 

fluorescein apply to Rhodamine WT except that the dye is 

58  Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
Figure 19.  Comparison of initial fluorescein concentrations with

concentrations in samples that were stored for about 1 year.

0

5

10

15

20

25

0 5 10 15 20 25

INITIAL FLUORESCEIN CONCENTRATION,

IN MICROGRAMS PER LITER 

REPLICATE FLUORESCEIN CONCENTRATION,

IN MICROGRAMS PER LITER

Figure 20. Comparison of background, blank, and replicate

samples for Rhodamine WT dye analysis.

Background

RHODAMINE WT CONCENTRATION, IN MICROGRAMS PER LITER

Blank Replicate

-0.1

0

0.1

0.2

0.3

0.4

9 83 166

9

75th percentile

Number of samples

Data value less than or equal to 1.5 times the interquartile

 range outside the quartile

Median

25th percentile

Outlier data value less than or equal to 3 and more than 

 1.5 times the interquartile range outside the quartile

Outlier data value greater than 3 times the interquartile 

 range outside the quartile

EXPLANATION

Interquartile

range

Replicate is a second analysis of the same sample

not as sensitive to sunlight exposure. Boxplots of background 

concentrations for water samples collected prior to dye injection at selected wells indicate that background concentrations 

generally were less than 0.03 μg/L (fig. 20). Variability in 

blank samples generally was less than ±0.10 μg/L. The differences between sample concentrations and replicate analyses 

of the same samples were less than 0.08 μg/L for 75 percent 

of the samples. On the basis of this information, the calculated 

detectable dye concentrations at first arrival was estimated to 

be about 0.10 μg/L. An isolated sample greater than this concentration may not indicate the presence of dye; however, an 

increasing trend beginning at this concentration was assumed 

to indicate the arrival of Rhodamine WT dye. Some isolated 

samples containing suspended sediment had concentrations 

greater than 0.10 μg/L.

In the analysis of samples with a filter fluorometer, there 

is a small area of overlap in the excitation wavelength between 

fluorescein and Rhodamine WT around 550 nanometers 

(Jones, 1984). Samples with standard concentrations of fluorescein were analyzed using the Rhodamine filters to quantify 

this potential overlap in wavelengths (table 13). The analysis 

of several different concentrations of fluorescein standards 

indicated that the presence of fluorescein dye would not interfere with the analysis of samples for Rhodamine WT.

Table 13.  Analysis of fluorescein standards for concentrations of

Rhodamine WT.

[μg/L, micrograms per liter]

Fluorescein

concentration

(μg/L)

Apparent

Rhodamine WT

concentration

(μg/L)

4 0.037

20 .074

100 .094

190 .023

Section B. Dye Tracing Methods  59
CHLOROFLUOROCARBON CONCENTRATION,

IN PARTS PER TRILLION BY VOLUME

0

100

200

300

400

500

600

1940 1950 1960 1970

YEAR

1980 1990 2000

CFC–12

CFC–113

CFC–11

Figure 21. Atmospheric concentrations of chlorofluorocarbons

CFC–11, CFC–12, and CFC–113 (Plummer and Busenberg, 2005).

Section C. Chlorofluorocarbon Age-Dating Methods and Background

Chlorofluorocarbons

Chlorofluorocarbons (CFCs) are anthropogenic tracers 

that are useful for estimating ground-water age (Busenberg 

and Plummer, 1992; Cook and others, 1996; Oster and others, 

1996; Szabo and others, 1996; Cook and Solomon, 1997; 

Plummer and Busenberg, 2005). These compounds have been 

used in a variety of industrial and refrigerant applications and 

are present in the atmosphere where they become assimilated 

into rain and snow as dissolved gases and infiltrate to ground 

water. Because atmospheric concentrations have been changing over time, the residence time or age of ground water often 

can be estimated by comparing concentrations in groundwater samples to historical atmospheric concentrations. Three 

species of CFCs that are used as tracers include CFC–11, 

CFC–12, and CFC–113. The atmospheric concentrations of 

these tracers (fig. 21) for Niwot Ridge, Colorado, increased 

between the 1940s and 1990s and recently (2002) began 

declining slightly (Plummer and Busenberg, 2005). Production 

and release of CFCs to the atmosphere rose rapidly during the 

1970s and 1980s (Alternative Fluorocarbons Environmental 

Acceptability Study, written commun., 2002).

In water that is exposed to the atmosphere, CFC concentrations become equilibrated with atmospheric concentrations; 

however, in ground water not in contact with the open 

atmosphere, CFC concentrations generally remain stable at 

the concentration of the recharge water. Shallow ground water 

remains closed to gas exchange because molecular diffusion 

coefficients of gases are about five orders of magnitude 

smaller in water than in air (Plummer and Busenberg, 2005). 

The gas concentration in water can be modified by gas 

exchange between the water at the water table and the 

unsaturated-zone atmosphere. Although the exchange can 

affect the concentration in the top few centimeters of this 

zone, the gases are confined below about 1 meter and do not 

exchange with the unsaturated zone atmosphere (Busenberg 

and others, 2001). For most dating applications, CFC 

confinement is thought to occur rapidly some time between 

the seasonal high and low water table (Cook and Solomon, 

1997).

In karstic aquifers, infiltrating rainwater and snowmelt 

can be stored above the confined part of the aquifer for years 

or decades in features such as perched caves or the epikarstic 

zone (Even and others, 1986). The water table may be in contact with the current atmosphere as caves and other openings 

breathe in and out due to changes in barometric pressure. As 

water levels change in these cave-like openings, some of the 

stored water could be re-exposed to the atmosphere during 

mixing as perched water spills and cascades downgradient. 

In the study area, water table conditions can exist in wells 

that are greater than 1,000 ft deep. Some resetting of the CFC 

clock may occur, and estimated ages may indicate a larger proportion of younger water than that indicated by tritium dating.

Henry’s Laws of solubilities of CFCs in water are known, 

and equilibration with atmospheric concentrations can be calculated with estimates of pressure and temperature. CFC–11, 

CFC–12, and CFC–113 all can be degraded under anaerobic 

conditions. Ground-water samples were analyzed for selected 

dissolved gases to assist with interpretation of CFC data.

Dissolved Gas Data

Dissolved gases including nitrogen, argon, oxygen, carbon dioxide, and methane (table 14) are useful in calculating 

recharge temperature and excess air, and in assessing potential 

degradation of CFCs. The ratio of nitrogen to argon can be 

used to calculate the temperature of the recharge water on 

the basis of the large differences in the solubility of nitrogen 

and argon at different temperatures (Weiss, 1970). Recharge 

temperature affects the solubility of CFCs and is used in determining the atmospheric mixing ratio in parts per trillion by 

volume (pptv). Recharge temperatures for 10 wells and springs 

60 Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota
ranged from 3.4 to 7.7°C, with an average of 6.2°C. A 1°C difference in the recharge temperature results in about a 5 percent 

difference in the calculated CFC mixing ratio; thus, calculating recharge temperatures from dissolved gases improves the 

accuracy of calculated CFC mixing ratios.

Excess air can be trapped in recharge water and dissolved 

under increased hydrostatic pressure resulting in increases 

in CFCs (Plummer and Busenberg, 2005). Excess air can be 

determined from nitrogen and argon ratios and generally is 

less than 6 cubic centimeters per liter (cm3/L). Calculated 

Table 14. Dissolved-gas data for selected wells and springs in the study area.

[NGVD 29, National Geodetic Vertical Datum of 1929; deg C, degrees Celsius, cm3/L, cubic centimeters per liter]

Station

Number

Other 

identifier

Sample 

date

Dissolved concentration (milligrams per liter) Estimated 

recharge 

altitude

(feet above 

NGVD 29)

Recharge 

temperature

(deg C)

Excess

air

(cm3/L) Nitrogen Argon Oxygen Carbon 

dioxide Methane

442752103501901 JEF 10–31–2001 22.043 0.7340 7.33 10.94 0.0000 5,000 5.7 5.1

442752103501901 JEF 10–31–2001 22.042 .7315 5.94 11.98 .0000 5,000 6.0 5.2

442815103481701 VIG 08–24–2005 18.671 .6774 7.52 5.63 .0000 5,000 3.8 1.3

442815103481701 VIG 08–24–2005 18.864 .6847 7.32 5.90 .0000 5,000 3.4 1.3

442842103505501 NEV 10–30–2001 23.684 .7732 8.00 10.10 .0000 5,000 3.7 6.4

442842103505501 NEV 10–30–2001 23.490 .7677 7.25 10.69 .0000 5,000 4.0 6.3

442918103523001 KYT 10–30–2001 20.462 .6841 3.04 23.24 .0000 5,000 7.4 4.6

442918103523001 KYT 10–30–2001 20.546 .6867 3.42 22.61 .0000 5,000 7.3 4.6

442919103511601 DIC 10–19–2001 20.663 .7052 6.25 13.41 .0000 5,000 5.4 4.0

442919103511601 DIC 10–19–2001 20.979 .7127 6.38 13.56 .0000 5,000 5.2 4.2

443005103553801 SAL 10–22–2001 17.852 .6439 3.93 16.05 .0000 5,000 6.9 1.7

443005103553801 SAL 10–22–2001 17.881 .6461 3.84 16.35 .0000 5,000 6.7 1.6

443017103553601 MIT 11–01–2001 18.091 .6511 3.92 16.40 .0000 5,000 6.6 1.8

443017103553601 MIT 11–01–2001 18.287 .6555 4.04 16.41 .0000 5,000 6.4 2.0

443330104003401 McNEN 11–05–2001 17.582 .6354 5.46 18.58 .0000 5,000 7.3 1.6

443330104003401 McNEN 11–05–2001 17.518 .6324 5.68 18.55 .0000 5,000 7.6 1.6

443335104010001 MIR 11–06–2001 16.990 .6360 6.54 6.89 .0010 4,000 7.6 .4

443335104010001 MIR 11–06–2001 17.078 .6387 7.75 6.45 .0010 4,000 7.4 .5

443356103593701 COX 11–05–2001 17.360 .6297 3.26 22.59 .0057 5,000 7.6 1.4

443356103593701 COX 11–05–2001 17.213 .6257 3.19 22.62 .0043 5,000 7.7 1.4

excess air for 10 sites ranged from 0.4 to 6.4 cm3/L, with an 

average of 2.8 cm3/L. When excess air is small as in this study, 

the effect on CFCs can be ignored in most ground-water cases 

(Busenberg and Plummer, 2005). Potential degradation of 

CFCs resulting from microbial processes and reducing conditions is indicated by the concentrations of carbon dioxide, dissolved oxygen, and methane. Dissolved oxygen was present at 

all sites, and methane concentrations were low, both indicating 

little potential for degradation of CFCs from reducing conditions for the samples collected for this study.

Section C. Chlorofluorocarbon Age-Dating Methods and Background  61
Manuscript approved for publication, January 2, 2007.

Prepared by the Helena Publishing Service Center.

For more information concerning the research in this report, contact:

U.S. Geological Survey

Director, South Dakota Water Science Center

1608 Mountain View Road

Rapid City, SD 57702

http://sd.water.usgs.gov/
Putnam and long—Characterization of Ground-Water Flow and Water Quality, Madison and Minnelusa Aquifers, South Dakota—SIR 2007-5001

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