Ground-Water Recharge and Flowpaths Near 

the Edge of the Decorah-Platteville-Glenwood 

Confining Unit, Rochester, Minnesota

		 

!"#"$%		

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U.S. Department of the Interior

U.S. Geological Survey

Ground-Water Recharge and Flowpaths Near 

the Edge of the Decorah-Platteville-Glenwood 

Confining Unit, Rochester, Minnesota

By Richard J. Lindgren

Water-Resources Investigations Report 00-4215

Prepared in cooperation with the City of Rochester, Minnesota
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

Use of trade, product, or firm names in this report is for identification purposes only and does not

constitute endorsement by the U.S. Government.

Mounds View, Minnesota, 2001

For additional information write to:

District Chief

U.S. Geological Survey, WRD

2280 Woodale Drive

Mounds View MN 55112

Copies of this report can be purchased from:

U.S. Geological Survey

Branch of Information Services

Box 25286

Federal Center

Denver CO 80225

For more information on the USGS in Minnesota, you may connect to the Minnesota District home page at

http://mn.water.usgs.gov

For more information n all USGS reports and products (including maps mages, and computerized data), call 1-888-ASK-USGS

Water-Resources Investigations Report 00-4215
1

CONTENTS

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

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

Purpose and Scope 4

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

Methods of Investigation.................................................................................................................................................. 7

Test Drilling and Well Installation ............................................................................................................................ 7

Water Levels and Stream Discharge.......................................................................................................................... 7

Hydrograph Analysis................................................................................................................................................. 8

Water Sampling and Analysis for Ground-Water Age Dating.................................................................................. 8

Modeling of Ground-Water Flow............................................................................................................................ 10

Acknowledgments.......................................................................................................................................................... 10

Hydrogeologic Setting .......................................................................................................................................................... 10

Hydrogeologic Units ...................................................................................................................................................... 10

Hydraulic Properties ....................................................................................................................................................... 11

Ground-Water Recharge ................................................................................................................................................ 14

Water-Level Fluctuations ........................................................................................................................................ 15

Stream-Aquifer Leakage ................................................................................................................................................ 15

Ground-Water Flow ....................................................................................................................................................... 15

Simulation of Ground-Water Flow....................................................................................................................................... 18

Numerical Model Description........................................................................................................................................ 18

Numerical Model Calibration......................................................................................................................................... 24

Sensitivity Analysis 25

Ground-Water Flowpaths and Travel Times.................................................................................................................. 28

Model Experiments ........................................................................................................................................................ 31

Results for the cross-sectional model experiments, Rochester area, Minnesota 36

Model Limitations.......................................................................................................................................................... 37

Discussion of Recharge and ground-water Flow.................................................................................................................. 37

Summary............................................................................................................................................................................... 38

References Cited................................................................................................................................................................... 40

ILLUSTRATIONS

Figure 1. Map showing location of study area, observation wells drilled for this study, biweekly observation wells, and 

bedrock hydrogeology, Rochester area, Minnesota ......................................................................................................................2

Figure 2. Diagram showing generalized hydrogeologic column of regional aquifers and confining units Olmsted 

County, Minnesota ........................................................................................................................................................................3

Figure 3. Map showing trace of hydrogeologic section A - A′, locations of wells along flowpath, stream stage and 

streamflow measurement sites, potentiometric surface of the St. Peter-Prairie du Chien-Jordan aquifer, February 

through March 1995, and ground-water divide, Rochester area, Minnesota................................................................................5

Figure 4. Hydrogeologic section A - A′ showing hydrogeologic units, measured hydraulic heads October and November 1998, 

equipotential lines, and direction of ground-water flow, Rochester area, Minnesota...................................................................6

Figure 5. Map showing bedrock hydrogeology and locations of wells sampled for chlorofluorocarbon analysis, Rochester

 area, Minnesota ............................................................................................................................................................................9

Figure 6. Water levels in observation wells during 1997–99in the St. Peter-Prairie du Chien-Jordan aquifer, Rochester area, Minnesota

12

Figures 7a–11. Hydrogeologic section showing: 

7a. Model layers, corresponding hydrogeologic units, and simulated areal recharge zones, Rochester area, Minnesota..........20

7b. Model layers, corresponding hydrogeologic units, and simulated areal recharge zones near edge of confining 

units, Rochester area, Minnesota ......................................................................................................................................... 21

Figures 8a-11. Hydrogeologic sections showing:

8a. Model layers, corresponding hydrogeologic units, and simulated equipotential lines, Rochester area, Minnesota............. 26

8b. Model layers, corresponding hydrogeologic units, and simulated equipotential lines near edge of confining units,

 Rochester area, Minnesota.................................................................................................................................................. 27
2

ILLUSTRATIONS--CONTINUED

9a. Hydrogeologic units and flowpath-line plot representing the movement of recharge water derived from infiltration 

of precipitation through the aquifer system, Rochester area, Minnesota............................................................................. 32

9b. Hydrogeologic units and flowpath-line plot representing the movement of recharge water derived from infiltration 

of precipitation through the aquifer system near edge of confining units, Rochester area, Minnesota.............................. 33

10. Hydrogeologic units and flowpath-line plot representing the movement of water originating near the eastern model 

boundary through the aquifer system, Rochester area, Minnesota ...................................................................................... 34

11. Hydrogeologic units and flowpath-line plot representing the movement of water originating near the top of layer 3 

through the aquifer system, Rochester area, Minnesota ...................................................................................................... 35

TABLES

Table 1. Estimated ground-water recharge rates to the aquifer system based on hydrograph analysis, Rochester area, Minnesota....... 16

Table 2. Comparison of ground-water recharge rates to the aquifer system derived from hydrograph analysis, 

chlorofluorocarbon age-dating, and numerical ground-water-flow model analysis, Rochester area, Minnesota............................... 17

Table 3. Initial and best-fit calibrated values of hydraulic properties used in the cross-sectional model of the aquifer system, 

Rochester area, Minnesota .................................................................................................................................................................. 22

Table 4. Initial and best-fit calibrated values of areal recharge rate used in the cross-sectional model of the aquifer system,

Rochester area, Minnesota .................................................................................................................................................................. 23

Table 5. Simulated water budget from the cross-sectional model of the aquifer system, Rochester area, Minnesota ............................ 28

Table 6. Simulated leakage between model layers from the cross-sectional model of the aquifer system, Rochester area, 

Minnesota............................................................................................................................................................................................ 29

Table 7. Sensitivity of simulated hydraulic heads and flows in the aquifer system to changes in values of hydrogeologic 

properties or conditions in steady-state simulation, Rochester area, Minnesota ................................................................................ 30

Table 8. Results for the cross-sectional model experiments, Rochester area, Minnesota......................................................................... 36
1

Ground-Water Recharge and Flowpaths Near 

the Edge of the Decorah-Platteville-Glenwood 

Confining Unit, Rochester, Minnesota

By Richard J. Lindgren

ABSTRACT ABSTRACT

The primary source of ground water for the city of Rochester, Olmsted County, southeastern Minnesota is the St. 

Peter-Prairie du Chien-Jordan aquifer. Based on results of a 

previous U.S. Geological Survey investigation in the Rochester area, relatively high rates of areal recharge to the St. 

Peter-Prairie du Chien-Jordan aquifer occur along the edge 

of the overlying Decorah-Platteville-Glenwood confining 

unit. The primary source of water to the zone of increased 

recharge along the edge of the confining unit is the upper 

carbonate aquifer. 

Ground-water recharge rates to the St. Peter-Prairie du 

Chien-Jordan aquifer during all of 1998 ranged from 1.9 to 

25.5 in./yr (inches per year). Recharge rates were greatest 

near the edge of the Decorah-Platteville-Glenwood confining unit and least where the confining unit is thick and is 

overlain by the upper carbonate aquifer (mean of 2.0 in./yr). 

Recharge rates downslope from the edge of the confining 

unit were greatest to the St. Peter on the slope entering the 

main South Fork Zumbro River Valley. Results of groundwater age dating using chlorofluorocarbons (CFCs) indicated recharge dates ranging from (1) the mid-1950’s to the 

early 1990’s for the St. Peter, (2) the late 1960’s to approximately 1990 for the Prairie du Chien, and (3) the early to 

mid-1950’s for the Jordan. 

Cross-sectional model simulations indicated that most of 

the areal recharge entering the aquifer system through the 

upper carbonate aquifer discharges from springs and seeps. 

Of the 2.28 ft3/s (cubic feet per second) of areal recharge 

that enters the upper carbonate aquifer, 2.23 ft3/s is discharged from the aquifer by springs and seeps. Results indicate that areal recharge to the upper Prairie du Chien moves 

primarily westward and discharges to Bear Creek. 

Areal recharge rates derived from hydrograph analysis, 

CFC age-dating, and cross-sectional model analysis were 

much greater to the St. Peter downslope from the edge of the 

Decorah-Platteville-Glenwood confining unit (25.5, 35.3, 

and 23.75 in./yr, respectively) than occurs to the Prairie du 

Chien in any hydrogeologic setting. The model-simulated 

discharge from springs and seeps in the lower part of the 

upper carbonate aquifer represents a potential source of 

water of 33 in./yr to the St. Peter unit, similar to the estimated areal recharge rates derived from hydrograph analysis and CFC age-dating. 

The water withdrawn by pumped wells or discharged to 

Bear Creek is derived predominantly from areal recharge 

near the edge of the Decorah-Platteville-Glenwood confining unit (0.47 ft3/s), rather than from water that has leaked 

downward through the Decorah unit (0.03 ft3

/s). Model simulated discharge through springs and seeps in the lower part 

of the upper carbonate aquifer (0.21 ft3/s) represents a 

potential source of water to the St. Peter-Prairie du ChienJordan aquifer.

INTRODUCTION

The primary source of ground 

water for the city of Rochester, Olmsted County, southeastern Minnesota 

(fig. 1), is the St. Peter-Prairie du 

Chien-Jordan aquifer. Based on results 

of a previous U.S. Geological Survey 

(USGS) investigation in the Rochester 

area (Delin, 1990), relatively high 

rates of recharge to the St. Peter-Prairie du Chien-Jordan aquifer from infiltration of precipitation and water 

discharged from springs and seeps, 

hereinafter termed areal recharge, 

occur along the edge of the overlying 

Decorah-Platteville-Glenwood confining unit (figs. 1 and 2). Increased areal 

recharge along the edge of the Decorah-Platteville-Glenwood confining 

unit is the likely cause of highs in the 

potentiometric surface of regional 

aquifers throughout southeastern Minnesota, which are displaced from topographic highs (Delin and Woodward, 

1984). Based on analysis by use of a 

numerical ground-water-flow model, 

areal recharge to the St. Peter-Prairie 

du Chien-Jordan aquifer near the edge 

of the Decorah-Platteville-Glenwood 

confining unit in the Rochester area is 

13 in./yr, compared to a rate as low as 

0.1 in./yr where the confining unit is 

present. A rate of 5 in./yr was determined where the confining unit is 

absent (Delin, 1990). 

The St. Peter-Prairie du Chien-Jordan aquifer is highly susceptible to 

contamination where the Decorah-
2

R14W R13W R12W R11W

T

107

N

T

106

N

T

105

N

Cascade

Creek

Silver

Creek

Bear

Creek

Badger Run

Willow

Creek

N.

B.

Root

Riv.

Middle

F. Whitewater R.

S. Fork

Zumbro

River

Zumbro

S. Fork

River

Rochester

43°55'

44°00'

44°05'

92°30' 92°25' 92°20' 92°15' 92°10'

Base from U.S. Geological Survey digital data 1:100,000 1972

U.S. Albers Equal Area Projection

standard parellels 29°30' and 45°30', central meridian -92°20'

Bedrock hydrogeology modified

0 1 2 3 4 5 MILES from N.H. Balaban, 1988.

0 1 2 3 4 5 KILOMETERS

Location of study area, observation wells drilled for this study, biweekly observation wells, and bedrock

hydrogeology, Rochester area, Minnesota.

Upper carbonate aquifer

Decorah-Platteville-Glenwood confining unit

St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer

Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan aquifer

Biweekly observation well. Number indicates Minnesota unique

number for wells with hydrographs shown in figure 6. Number

in parentheses indicates nested wells

Observation well drilled for this study. Number

for wells with hydrographs shown in figure 6.

Number in parentheses indicates nested wells

indicates Minnesota

unique number

EXPLANATION

160815

(2)

(2)

601283

River

Minnesota

River

Lake Superior

94°

92°

90°

96°

48°

46°

44°

0 50 100 MILES

0 50 100 KILOMETERS

Study

Area

LOCATION MAP

MINNESOTA

Mississippi

Olmsted

County

Minneapolis-St. Paul

Metropolitan Area

Figure 1.

(2)

601284

591905 601283

220772

446667

179232

227491

160815

148301

(2)(2)

(2)

(2)

(2)
3

Erathem

System

Formation

or Group

Thickness

(in feet)

Water-bearing characteristics General

lithology

--Glacial drift is generally a confining unit, but locally may supply water to

wells. Drift consists primarily of till and outwash. Drift is thin or absent throughout much of the

area.

--Used for domestic purposes in upland areas of Olmsted County.

Permeability is attributed to extensive karst development. The horizontal hydraulic conductivity

generally ranges from 3 to 40 feet per day. Well yields are from 200 to 500 gallons per minute, but

are highly variable because solution cavities and channels differ in size and distribution. For most

of the study area, the aquifer consists of an upper part, (the Prosser Limestone), and a lower part

with a higher shale content, (the Cummingsville) Formation.

--The vertical hydraulic conductivity ranges from

about 10 to 10 feet per day. -5 -4

--The most extensively used aquifer in Olmsted County.

Ground-water flow is through joints, fractures, and solution cavities in the Prairie du Chien and is

intergranular in the St. Peter and Jordan aquifers. Horizontal hydraulic conductivity generally

ranges from 1 to 40 feet per day, but can be greater than 1,000 feet per day locally. Yields to wells

commonly range from about 500 to 1,000 gallons per minute and can exceed 2,000 gallons per

minute. Upper part of Prairie du Chien has a higher density of fractures and solution features, and

a higher hydraulic conductivity than the lower part based on video logs and dye tracing. Horizontal

hydraulic conductivity in the upper part ranges from about 0.85 to 8,500 feet per day and in the lower

part may be substantially less than 0.85 feet per day.

--The base of St. Peter locally consists of shale, claystone, and siltstone

interlayered with fine-grained sandstone. The vertical hydraulic conductivity ranges from about

10 to 1.5x10 feet per day. -6 -3

--The vertical hydraulic conductivity ranges from about 10 to 10 feet

per day.

-5 -3

0-100

about

70

about

30

80

65

65

40

25

100

130

170

100

75

5

Generalized hydrogeologic column of regional aquifers and confining units Olmsted County, Minnesota (geology modified

from N.H. Balaban, 1988, water-bearing characteristics modified from G.N. Delin, 1990). P a l e o z o i c C a m b r i a n O r d o v i c i a n Cenozoic Quaternary Prairie du Chien Group

Undifferentiated

glacial drift

Maquoketa

Formation

Dubuque

Formation

Stewartville

Formation

Prosser

Limestone

Cummingsville

Formation

Galena Group

Decorah

Shale

Platteville

Formation

Glenwood

Formation

St. Peter

Sandstone

Jordan

Sandstone

St. Lawrence

Formation

Shakopee

Formation

Oneota

Dolomite

NOT EXPOSED IN OLMSTED

COUNTY

EXPLANATION

Till, sand, and gravel

Shale

Limestone/dolomite

Sandstone

Aquifer

Undifferentiated drift

Upper carbonate aquifer

Decorah-Platteville-Glenwood confining unit

St. Peter-Prairie du Chien-Jordan aquifer

Basal St. Peter confining bed

St. Lawrence confining unit

Figure 2.
4

Platteville-Glenwood confining unit is 

absent. Smith and Nemetz (1996) 

reported greater concentrations of 

nitrite-plus-nitrate nitrogen, chloride, 

and tritium in water from the St. PeterPrairie du Chien-Jordan aquifer in 

areas where the confining unit is 

absent compared to areas where the 

confining unit is present near Rochester. Nitrite-plus-nitrate nitrogen and 

chloride are commonly used as indicators of human activities that affect 

ground water. 

The primary source of water to the 

zone of increased areal recharge along 

the edge of the Decorah-PlattevilleGlenwood confining unit in the Rochester area is the upper carbonate aquifer, which underlies the uplands away 

from the stream valleys. The upper 

carbonate aquifer has large secondary 

permeability and has been affected by 

widespread contamination from agricultural chemicals. There is concern 

that water withdrawn from the deeper 

St. Peter-Prairie du Chien-Jordan 

aquifer may become contaminated by 

water that originated in the overlying 

upper carbonate aquifer. Ground water 

pumped from wells in the city of 

Rochester may obtain as much as 50 

percent of their water supplies from 

water entering the aquifer in the zone 

of increased areal recharge along the 

edge of the confining unit (Delin, 

1990). 

Management of ground-water 

resources is critical for Rochester Public Utilities (RPU), which regulates 

Rochester municipal ground-water 

use. In addition, the Minnesota 

Department of Natural Resources 

(MDNR) issues permits for groundwater use within the State and is promoting conservation and efficient use 

of water. Additional information is 

needed by the RPU and the MDNR on 

areal recharge rates, sources of water 

to the St. Peter-Prairie du Chien-Jordan aquifer, and flowpaths in the 

ground-water system to better manage 

ground-water resources in the Rochester area. 

A zone of increased areal recharge 

along the edge of the Decorah-Platteville-Glenwood confining unit is 

likely in many areas in southeastern 

Minnesota. In addition, the topography and structure of the Ordovicianage rocks in southeastern Minnesota 

make this a favorable location to estimate varying areal recharge rates 

across a broad spectrum of hydrogeologic settings. The distribution and 

rates of areal recharge along the edge 

of confining units is poorly understood. 

The USGS, in cooperation with the 

city of Rochester, conducted a 3-year 

study (October 1996–September 

1999) to quantify areal recharge rates 

along the edge of the Decorah-Platteville-Glenwood confining unit in the 

Rochester area. The study also 

included an analysis of areal recharge 

rates in areas where the confining unit 

is thick and where the confining unit is 

absent. A numerical steady-state 

cross-sectional ground-water-flow 

model of the ground-water system in 

the Rochester area was constructed to 

test concepts of increased areal 

recharge and to evaluate ground-water 

flowpaths along the edge of the confining unit. 

PURPOSE AND SCOPE

This report describes results of 

field data collection during 1996–99, 

sources and types of data used in constructing a numerical cross-sectional 

ground-water-flow model, the model 

calibration process, and results of 

model simulations. Areal recharge 

rates were estimated for three hydrogeologic settings where differing rates 

of areal recharge were expected. The 

three hydrogeologic settings were (1) 

near the edge of the Decorah-Platteville-Glenwood confining unit, (2) 

where the confining unit is thick and is 

overlain by the upper carbonate aquifer, and (3) where the confining unit is 

absent and the Prairie du Chien unit of 

the St. Peter-Prairie du Chien-Jordan 

aquifer is the uppermost bedrock unit 

(fig. 1). The scope of the report 

includes a discussion of estimated 

ground-water recharge rates for the 

three hydrogeologic settings using 

hydrograph analysis and chlorofluorocarbon (CFC) age-dating methods. 

Areal recharge, ground-water flow, 

and discharge along a ground-water 

flowpath are analyzed, using a numerical cross-sectional ground-waterflow model. The trace of section and 

hydrogeologic section A-A', representing the hydrogeology along a 

flowpath from the regional groundwater divide for the St. Peter-Prairie 

du Chien-Jordan aquifer, located east 

of Rochester, westward to the South 

Fork Zumbro River, are shown in figures 3 and 4, respectively.

The term ground-water system, as 

used in this report, refers to the 

sequence of hydrogeologic units 

shown in figure 4 from land surface to 

the St. Lawrence confining unit. For 

the purposes of this report, the St. 

Peter-Prairie du Chien-Jordan aquifer 

is composed of three distinct units. 

Similarly, the Decorah-PlattevilleGlenwood confining unit is composed 

of three distinct units. Throughout the 

report, the individual units of the aquifer (St. Peter, Prairie du Chien, and 

Jordan) or the confining unit (Decorah, Platteville, and Glenwood) are 

referred to, as well as the entire aquifer 

or confining unit.

DESCRIPTION OF STUDY 

AREA

The study area includes approximately 325 mi2 in Olmsted County in 

southeastern Minnesota (fig. 1). The 

study area is drained by the South Fork 

Zumbro, Whitewater, and Root Rivers, which are tributaries of the Mississippi River. Topography is rolling to 

undulating in upland areas and steep 

near streams and drainage ways. Land 

use is primarily for agriculture, including dairy farming, hog production, and 

corn and soybean cropping. The City 

of Rochester is growing rapidly over 

the zone along the edge of the Deco-
5

R14W R13W R12W R11W

T

107

N

T

106

N

T

105

N

Cascade

Creek S. fork

Zumbro

River

Zumbro

S. Fork

River

Silver

Creek

Bear

Creek

Badger Run

Willow

Creek

N.

B.

Root

Riv.

Middle

F. Whitewater R.

Rochester

43°55'

44°00'

44°05'

92°30' 92°25' 92°20' 92°15' 92°10'

A A' (2)

Base from U.S. Geological Survey digital data 1:100,000 1972

U.S. Albers Equal Area Projection

standard parellels 29°30' and 45°30', central meridian -92°20'

Reference (Lindgren, 1997)

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

Trace of hydrogeologic section A - A', locations of wells along flowpath, stream stage and streamflow measurement

sites, potentiometric surface of the St. Peter-Prairie du Chien-Jordan aquifer, February through March 1995, and ground-water

divide, Rochester area, Minnesota.

See

Inset

Inset

0 1 MILE

0 1 KILOMETER

SilverLake

Silver

Creek

Bear

Creek

South

Fork

Zumbro

ROCHESTER River

44°

44°01'

44°02'

92°28' 92°27'

EXPLANATION

Trace of hydrogeologic section

Boundary of flowpath

Ground-water divide

Potentiometric contour. Interval,

in feet, is variable.

Datum is

sea level

Biweekly observation well

Observation well installed for this

study. Number in parentheses

indicates nested wells

Dashed

where inferred.

A A' Domestic or commercial well

Streamflow only measurement site

Stream stage only measurement site

Both stream stage and

streamflow measurement

site

Generalized direction of

ground-water flow

Figure 3.
6

2 3 4 5 6 1 2 3 4 5 6 1 2 1

R14W R13W R12W

VERTICAL EXAGGERATION X 46

DATUM IS SEA LEVEL

Trace of section shown on figure 3

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(7)

(1)

(9)

(8)

(9)

(10)

(10)

(11)

(11)

(12)

(12)

Hydrogeologic

units

Section Section

961.9

1003.6

1032.1

1035.4

1057.4 1035.8 1045.6 1062.6

1044.1 1055.2

1062.4

1056.5

1058.0

1230.5

1063.6

1062.8

1067.1

1068.9

1070.5

1073.0

1079.3

1074.5

Water table based on well WLS and Balaban (1988) in

the upper carbonate aquifer. Dashed where inferred

Generalized direction of ground-water flow

Equipotential line. Interval varies. Dashed

where approximate

Screened intervals of wells. Number indicates

measured hydraulic head

1068.9

Aquifer

Confining unit

EXPLANATION

Hydrogeologic section A-A' showing hydrogeologic units, measured hydraulic heads in October and November 1998,

equipotential lines, and direction of ground-water flow, Rochester area, Minnesota.

Contact. Dashed where approximate

Nested observation wells

601284 and 591905

Figure 4.

Hydrogeologic units

Upper carbonate aquifer

Glacial drift

Lower part of the upper carbonate aquifer

Upper part of the upper carbonate aquifer

Decorah-Plattevills-Glenwood confining unit

Glenwood unit of the Decorah-Platteville-Glenwood confining unit

Platteville unit of the Decorah-Plateville-Glenwood confining unit

Decorah unit of the Decorah-Platteville-Glenwood confining unit

St. Peter-Prairie du Chien-Jordan aquifer

St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer

Upper Prairie du Chien unit of the St. Peter

Basal St. Peter confining bed

-Prairie du Chien-Jordan aquifer

Lower Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan aquifer

Jordan unit of the St. Peter-Prairie du Chien-Jordan aquifer

St. Lawrence confining unit

(9)

(8)

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(12)

(11)

(10)

1000

1100

1200

1300

1400

500

600

700

800

900

FEET

WEST

A A'

EAST

South Fork Zumbro River

Bear Creek

Middle Fork

Whitewater River

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS
7

rah-Platteville-Glenwood confining 

unit where increased recharge is 

thought to occur. Mean annual precipitation is 27.5 in. (Baker and Kuehnast, 1978). 

METHODS OF 

INVESTIGATION

Previously collected data on the 

hydrogeology and hydraulic properties of the aquifer system near Rochester were compiled from a variety of 

sources including water-well logs, 

geologic maps, State and Federal data 

bases, and published reports. The 

results of recent work investigating the 

hydraulic properties of the Prairie du 

Chien in southeastern Minnesota were 

obtained from Tony Runkel of the 

Minnesota Geological Survey (MGS). 

Additional test drilling and well installation, measurements of water levels 

and stream discharge, and water sampling for ground-water age-dating 

were done for this study. A numerical 

cross-sectional ground-water-flow 

model was constructed using information from water-well logs and geologic 

maps along a selected flowpath. 

Test Drilling and Well Installation

Water-well and test-hole logs were 

obtained from the MGS County Well 

Index for Olmsted County and from 

the U.S. Geological Survey GroundWater Site Inventory data base. 

Hydrogeologic information was compiled from Balaban (1988), Delin 

(1990), and recent unpublished work 

in southeastern Minnesota (Tony 

Runkel, Minnesota Geological Survey, written commun., 1999). 

Four, 2-inch-diameter, observation 

wells were installed during November 

1997 at three sites (fig. 1). Three of the 

wells were screened in the Prairie du 

Chien. The fourth well, screened in the 

St. Peter, was installed near one of the 

other wells, creating a nested pair of 

wells. The hydrogeologic setting for 

two of the sites was at the edge of the 

Decorah-Platteville-Glenwood confining unit and for the third site was in 

Rochester where the confining unit is 

absent and the Prairie du Chien is the 

uppermost bedrock unit. The site with 

the pair of nested wells (wells 601284 

and 591905) is located where the St. 

Peter is the uppermost unit and downslope from the edge of the Decorah unit 

of the Decorah-Platteville-Glenwood 

confining unit in the zone of increased 

recharge. The nested wells were used 

to determine differences in hydraulic 

heads between the St. Peter and Prairie 

du Chien units of the St. Peter-Prairie 

du Chien-Jordan aquifer. 

Water Levels and Stream 

Discharge

The four observation wells 

installed for this study were instrumented with pressure transducers to 

provide hourly water-level measurements. Domestic and commercial 

wells completed in the bedrock aquifers were also used extensively for 

water-level measurements. Water levels were measured biweekly, or 

monthly during the winter months, in 

35 domestic and commercial supply 

wells and 7 industrial, 2-inch-diameter, observation wells (fig. 1). There 

are 42 biweekly observation wells. 

The biweekly observation wells are 

located predominantly near the edge 

of the Decorah-Platteville-Glenwood 

confining unit in differing hydrogeologic settings (fig. 1). Three of the 42 

wells are located near the edge of the 

confining unit on slopes entering the 

main South Fork Zumbro River Valley. Nineteen of the wells are located 

on side slopes entering tributary valleys to the South Fork Zumbro River 

Valley. Five of the wells are located in 

the Marion area near the head of a tributary valley. Seven of the wells are 

located east of the edge of the confining unit, where the confining unit is 

thick and is overlain by the upper carbonate aquifer. Eight of the wells, 

including the seven industrial observation wells, are located west of the edge 

of the confining unit in the city of 

Rochester where the Prairie du Chien 

is the uppermost bedrock unit. 

The biweekly observation wells are 

open to differing units of the St. PeterPrairie du Chien-Jordan aquifer. Seven 

of the 39 wells are screened in the St. 

Peter, 24 in the Prairie du Chien, 7 in 

the Jordan, and 1 in both the Prairie du 

Chien and the Jordan. The water-level 

information was used to calculate 

areal recharge rates to the aquifers 

using hydrograph analysis and to 

quantify differences in areal recharge 

rates in different hydrogeologic settings near and distant from the edge of 

the Decorah-Platteville-Glenwood 

confining unit. 

Water levels were measured in 29 

domestic and commercial supply 

wells during October and November 

1998, in addition to the biweekly 

observation wells. The wells were 

located within a 3-mi wide area representing a flowpath from the regional 

ground-water divide for the St. PeterPrairie du Chien-Jordan aquifer east of 

Rochester westward to the South Fork 

Zumbro River (fig. 3). The 29 domestic and commercial supply wells, 12 

biweekly observation wells, and 4 

observation wells installed for this 

study are included in this set of 45 

wells, hereinafter termed flowpath 

wells. The flowpath wells included 

wells near and distant from the edge of 

the confining unit in different hydrogeologic settings. The flowpath wells 

are screened in the glacial drift (2 

wells), in the upper carbonate aquifer 

(2 wells), in the St. Peter (9 wells), in 

the Prairie du Chien (24 wells), in the 

Jordan (7 wells), and in both the Prairie du Chien and the Jordan (1 well) . 

Few domestic or commercial wells 

completed in the upper carbonate 

aquifer were available for water-level 

measurements. New supply wells are 

prohibited from being completed in 

this aquifer due to concerns about contamination from land and surfacewater sources, and many have been 

abandoned and sealed (Terry Lee, 
8

Olmsted County Environmental 

Resource Services, oral commun., 

1997). Water-level data from 22 of the 

flowpath wells were used to calibrate a 

numerical cross-sectional model. 

Stream-stage measurements were 

made during November 1998 at five 

sites on the South Fork Zumbro River 

and two sites on Bear Creek at the 

western end of the flowpath. Streamflow measurements were also made 

during November 1998 at three sites 

on the South Fork Zumbro River and 

at two sites on Bear Creek. The 

streamflow measurements were used 

to derive estimates of stream-aquifer 

leakage. The streamflow measurements made on the South Fork Zumbro River, however, were not 

sufficiently accurate to estimate 

stream-aquifer leakage and could not 

be used. The stream stages, and 

streamflow measurements made on 

Bear Creek, were used in the construction and calibration of a numerical 

cross-sectional ground-water-flow 

model. 

The altitudes of all water-level 

measurement points were determined 

by surveying done by the USGS (Greg 

Payne, written commun., 1998). Altitudes of measuring points were measured with a precision of ±0.1 ft. 

Hydrograph Analysis

Ground-water recharge rates to the 

three units comprising the St. PeterPrairie du Chien-Jordan aquifer were 

estimated from water-level measurements of the biweekly observation 

wells and the four observation wells 

installed for this study. Areal recharge 

to the St. Peter and Prairie du Chien 

occurs where the Decorah-PlattevilleGlenwood confining unit is absent and 

the St. Peter and Prairie du Chien units 

are the uppermost bedrock units. 

Ground-water recharge rates were 

estimated using the method of 

hydrograph analysis described by Rasmussen and Andreasen (1959). The 

method assumes that all water-level 

rises in the well result from areal 

recharge from infiltration of precipitation or from leakage through overlying 

hydrogeologic units. Recharge is 

equivalent to the water-level rise over 

a given period of time multiplied by 

the aquifer specific yield. Specific 

yield was assumed to be approximately equal to porosity. Porosity values of 0.25 for the St. Peter and 0.1 for 

the Prairie du Chien and Jordan were 

used in the recharge calculations. The 

porosity value used for the Jordan was 

less than that for the St. Peter because 

in the Rochester area the Jordan 

includes a feldspathic facies of much 

lower hydraulic conductivity and 

porosity than the quartzose facies 

(Runkel, 1996). Recharge to all three 

units of the St. Peter-Prairie du ChienJordan aquifer occurs by leakage 

through the Decorah-Platteville-Glenwood confining unit where it overlies 

the aquifer. 

Water Sampling and Analysis for 

Ground-Water Age Dating 

Ground-water samples were collected during October 1997 from 34 

wells screened in the St. Peter-Prairie 

du Chien-Jordan aquifer. Water samples were collected from most of the 

biweekly observation wells and a few 

other wells. The water samples were 

analyzed for tritium concentrations to 

determine the approximate age of the 

water to determine which wells to 

sample for analysis of CFC concentrations. 

The CFC age-dating technique for 

ground water as described by Busenberg and Plummer (1992) and Dunkle 

and others (1993) was used to estimate 

ground-water recharge rates. Groundwater samples were collected during 

May 1998 from six of the biweekly 

observation wells and from three of 

the four observation wells installed for 

this study (fig. 5). All the wells were 

open to the St. Peter-Prairie du ChienJordan aquifer. Recharge dates of 

ground water at screened depths below 

the water table were estimated from 

measured concentrations of CFCs 

(CFC-11, CFC-12, and CFC-13) in the 

ground-water samples collected during May 1998. The year of recharge 

for each sample was determined by 

matching the measured CFC concentration in the sample, converted to an 

equivalent partial pressure, with the 

appropriate year in the historical 

record of CFC partial pressure in the 

atmosphere (Busenberg and others, 

1993). Overall uncertainties in estimated recharge dates between 1960 

and 1990 caused by uncertainties in 

recharge temperatures, and by analytical uncertainties, are estimated to be 

on the order of ± 2 years. Recharge 

dates before 1960 and after 1990 have 

larger uncertainties. For this study, the 

best results were obtained using the 

CFC-12 concentrations. 

The downward vertical groundwater velocity gradient at each sampled well was estimated as a function 

of the recharge date of the ground 

water and the depth of the screened 

interval below the water table. Ideally, 

water samples from multiple nested 

wells at a site are used to determine 

ground-water age-depth profiles to 

estimate the ground-water velocity 

gradient. For this study, however, 

nested wells were available at only one 

site. The average porosity of the 

screened aquifer unit was then multiplied by the ground-water velocity 

gradient to determine the groundwater recharge rate. The method is 

limited in spatial resolution because 

deeper water represents water 

recharged at increasingly greater distances upgradient from the well site.

Tritium concentrations in groundwater samples were determined using 

the enriched tritium technique at the 

Environmental Isotope Laboratory, 

University of Waterloo, Waterloo, 

Ontario, Canada. Concentrations of 

dissolved gases and CFCs in groundwater samples were analyzed at the 

USGS CFC Laboratory in Reston, Virginia, and the ground-water ages estimated using procedures described by 

Busenburg and Plummer (1992). 
9

T

106

N

T

107

N

Willow

Creek

Cascade

Creek

Fork

Zumbro

South

South

Fork

Zumbro

River

River

Silver

Creek

Bear

Creek

Badger

Run

Silver

Lake

Rochester

Chester

Golden Hill

Marion

43°56'

44°00'

44°04'

92°30' 92°25' 92°20'

R 14 W R 13 W

012345 MILES

012345 KILOMETERS

Base from U.S. Geological Survey digital data 1:100,000 1972

U.S. Albers Equal Area Projection

standard parellels 29°30' and 45°30', central meridian -92°20'

Bedrock hydrogeology and locations of wells sampled for chlorofluorocarbon analysis, Rochester area, Minnesota.

Upper carbonate aquifer

Decorah-Platteville-Glenwood

confining unit

St. Peter unit of the St. Peter-Prairie

du Chien-Jordan aquifer

Prairie du Chien unit of the St. PeterPrairie du Chien-Jordan aquifer

EXPLANATION

Observation well drilled for this

study and sampled for

chlorofluorocarbon analysis.

Number indicates Minnesota unique

well number. Number in parentheses

indicates nested wells

Well sampled for chlorofluorocarbon

analysis. Number indicates Minnesota

unique well number

Rochester

Study Area

Inset Area (2)

160815

601284

Figure 5.

241037

601284, 591905

(2)

233030

220773

220770 220772

160815

601283
10

Modeling of Ground-Water Flow

A numerical cross-sectional 

ground-water-flow model of the aquifer system in the Rochester area, hereinafter termed the cross-sectional 

model, was constructed to test concepts of increased areal recharge and 

to evaluate ground-water flowpaths 

near the edge of the Decorah-Platteville-Glenwood confining unit. 

Water-level measurements for the 

flowpath wells were used to determine 

a trace of section for the cross-sectional model and to verify that the 

direction of horizontal ground-water 

flow along the flowpath is predominantly east-to-west with no appreciable components of flow in other 

directions. The influence of tributary 

valleys on flow within the flowpath 

was also evaluated. Tributary valleys 

are distant enough to minimize the 

effects of horizontal components of 

lateral flow near the valleys not 

aligned with the regional east-to-west 

flowpath. 

The cross-sectional model used 

was the USGS modular three-dimensional, finite-difference ground-waterflow model developed by McDonald 

and Harbaugh (1988) (MODFLOW). 

The cross-sectional model was calibrated for steady-state conditions 

using (1) water levels measured during 

October and November 1998 in 22 

observation wells, and (2) streamflow 

measurements made on Bear Creek at 

two sites during November 1998. Estimates of stream-aquifer leakage 

derived from the streamflow measurements were compared to simulated 

values. Visual MODFLOW (Guiguer 

and Franz, 1994) was used as a preprocessor to input the required data, to run 

the MODFLOW simulations, and as a 

post-processor to visualize and analyze the results of the simulations. 

The particle-tracking post-processing package MODPATH (Pollock, 

1989) was used to compute groundwater flowpath lines based on output 

from the calibrated steady-state simulation obtained with MODFLOW. 

MODPATH also computes the position of particles at specified points in 

time and the total time of travel for 

each particle. The particle-tracking 

program was used by specifying starting locations for hypothetical water 

particles and then tracking the particles forward in time through the flow 

field until they reached a sink. The 

sinks simulated in the cross-sectional 

model were rivers, drains, and a simulated pumped well. All water particles 

entering a cell containing a river, 

drain, or a simulated pumped well 

were assumed to discharge to these 

sinks. The particle-tracking program 

was also used to track water particles 

backward in time until they reached an 

inflow boundary. Travel times of 

water particles from the inflow boundaries of the simulated aquifer system 

to the sinks where they discharged 

were also computed using MODPATH. 

ACKNOWLEDGMENTS

The author is grateful to Rochester 

Public Utilities for performing waterlevel measurements for this study and 

to Tony Runkel of the Minnesota Geological Survey for providing information on the hydrogeology of the 

aquifer system in the Rochester area. 

The author is also grateful to land 

owners who allowed the installation of 

observation wells on their property 

and to well owners who permitted 

measurement of water levels in their 

wells. Thanks also are given to 

employees of the U.S. Geological Survey for their assistance with this study, 

particularly Michael Menheer, Abdul 

Mohammad, Robert Borgstede, and 

Christopher Sanocki. 

HYDROGEOLOGIC SETTING

The sequence of sedimentary rocks 

in the Rochester area (fig. 2) has been 

divided into hydrogeologic units of 

regional aquifers and regional confining units (Delin and Woodward, 1984; 

Balaban, 1988). Regional bedrock 

aquifers discussed in this report, in 

descending order, are the upper carbonate aquifer and the St. Peter-Prairie 

du Chien-Jordan aquifer (fig. 2). Glacial deposits in the Rochester area 

locally confine the underlying bedrock 

aquifers. The reader is referred to Balaban (1988), Delin (1990), and Runkel 

(1994a, 1994b, and 1996) for a 

detailed description of the lithology 

and hydraulic characteristics of the 

hydrogeologic units in the Rochester 

area. 

HYDROGEOLOGIC UNITS

The hydrogeologic units in the 

Rochester area of importance for this 

report are discussed below in descending order from land surface. Glacial 

drift overlying bedrock is as much as 

100 ft thick in the Rochester area, and 

locally is thin or absent (Balaban, 

1988). Glacial drift includes till and 

outwash. Till, an unsorted, unstratified 

sediment deposited directly by glacial 

ice, contains a high percentage of clay 

and silt. Outwash is sorted and stratified sand and gravel deposited by 

water from melting glacier ice. For 

simplification, post-glacial alluvium 

composed of silt, sand, and gravel is 

included with the glacial drift. Sand 

and gravel lenses in glacial till and the 

terrace deposits along streams are a 

source of water for domestic use. 

The upper carbonate aquifer is 

composed of the Galena Group, and is 

as much as 210-ft thick (Balaban, 

1988). The aquifer underlies areas 

west, south, and east of Rochester (fig. 

1). For most of the study area, the 

Galena Group includes only the 

Prosser Limestone and the Cummingsville Formation (fig. 2). The 

Prosser is a very fine-grained, thinbedded limestone that becomes dolomitic near the top. The Cummingsville 

is a very fine-grained limestone and 

interbedded calcareous shale, with the 

shale content decreasing upward, and 

is less permeable than the overlying 

Prosser. A third member of the Galena 

Group, the Stewartville, is present in 
11

the southern part of the study area. The 

Stewartville is a fine-grained dolomite 

and dolomitic limestone. The upper 

carbonate aquifer supplies water to 

domestic and farm wells, but is not 

used for high-capacity wells. 

The Decorah-Platteville-Glenwood confining unit hydraulically 

separates the upper carbonate aquifer 

from the underlying St. Peter-Prairie 

du Chien-Jordan aquifer. The confining unit underlies areas west, south, 

and east of Rochester (fig. 1), with an 

average thickness of about 70 ft (Balaban, 1988). The Decorah, a blocky, 

bluish-green to bluish-gray shale, has 

a very low hydraulic conductivity and 

is the principal confining unit. The 

Platteville is a gray to buff, thin-tomedium bedded dolomitic limestone 

and dolomite with some shale partings. The Glenwood, a plastic to 

slightly fissile, green to buff shale and 

claystone, has a low hydraulic conductivity and is a confining unit, and is 5 

to 10 ft thick in the Rochester area 

(Balaban, 1988). Although the Platteville has generally been lumped with 

the Decorah and Glenwood as a confining unit, it is karsted limestone and 

will yield some water to wells. 

Lindgren (1995) simulated the Platteville as a separate aquifer in a 

numerical cross-sectional groundwater-flow model of the aquifer system in the St. Louis Park area of the 

Minneapolis-St. Paul metropolitan 

area, east-central Minnesota (fig. 1). 

The St. Peter-Prairie du Chien-Jordan aquifer consists of the St. Peter, 

Prairie du Chien, and Jordan units (fig. 

2). The St. Peter is a fine- to mediumgrained sandstone, well sorted and 

poorly cemented; its average thickness 

is approximately 100 ft (Balaban, 

1988). The St. Peter underlies areas 

west, south, and east of Rochester (fig. 

1). The Prairie du Chien is composed 

of the Shakopee Formation, a sandy, 

shaley, thin-bedded dolomite, and the 

underlying thick-bedded Oneota 

Dolomite. Average thickness of the 

Prairie du Chien is approximately 300 

ft (Balaban, 1988). The Prairie du 

Chien is generally the uppermost bedrock unit beneath the city of Rochester. The Jordan is a friable to wellcemented, fine- to coarse-grained 

sandstone with an average thickness of 

about 100 ft (Balaban, 1988). The 

Prairie du Chien and Jordan underlie 

the entire study area. 

Hydraulic information indicates 

that the basal part of the St. Peter 

impedes the flow of ground water 

between the St. Peter and the Prairie 

du Chien units of the aquifer. Measured water-level differences were as 

much as 7.2 ft (fig. 6) between these 

two units. 

The Prairie du Chien was considered as consisting of two distinct layers for this study. Previous studies in 

the Rochester area have assumed that 

the entire Prairie du Chien has more or 

less uniform hydraulic conductivity 

and is hydraulically connected to the 

underlying Jordan. However, recent 

work conducted in southeastern Minnesota indicates that the lower part of 

the Prairie du Chien has a reduced 

hydraulic conductivity compared to 

the upper part of the Prairie du Chien. 

Vertical variations in the density of 

fractures and solution features indicate 

that the lower part of the Oneota Dolomite within the Prairie du Chien has 

the lowest density of fractures and 

solution features, based on video logs 

and dye tracing (Tony Runkel, Minnesota Geological Survey, written commun., 1999). 

The St. Lawrence Formation is a 

confining unit and is composed of 

dolomitic siltstone. The confining unit 

is about 75 ft thick (Balaban, 1988). It 

is present throughout the study area 

and immediately underlies the St. 

Peter-Prairie du Chien-Jordan aquifer. 

HYDRAULIC PROPERTIES

Hydraulic-conductivity data are 

sparse for the aquifers and confining 

units, other than for the units of the St. 

Peter-Prairie du Chien-Jordan aquifer. 

Data are insufficient to accurately map 

areal variations in the hydraulic properties of the hydrogeologic units. The 

hydraulic properties of the aquifer 

units are discussed first, followed by a 

discussion of the hydraulic properties 

of the confining units.

Hydraulic properties of the glacial 

drift are variable, primarily because of 

the wide range in composition and 

sorting of the material. Consequently, 

glacial drift can be either an aquifer or 

a confining unit. Where drift consisting mostly of till is relatively thick 

(greater than 50 ft), it is a confining 

unit for the underlying bedrock aquifers. The vertical hydraulic conductivity of till typically ranges from 10-6 to 

1 ft/d (Freeze and Cherry, 1979, p. 29). 

Movement of water in the drift is primarily intergranular. Horizontal 

hydraulic conductivities for glacial 

aquifers typically range from 101

 to 

104

 ft/d (Freeze and Cherry, 1979, p. 

29). 

The upper carbonate aquifer yields 

water primarily to wells that intersect 

fractures, joints, and solution channels 

in the carbonate rocks. Transmissivity 

of the upper carbonate aquifer generally ranges from 300 to 8,400 ft2

/d on 

the basis of horizontal hydraulic conductivities of 3–40 ft/d (Kanivetsky 

and Walton, 1979). 

Movement of water in the St. Peter 

unit is primarily intergranular. Transmissivity of the St. Peter ranges from 

200 to 3,000 ft2/d, but may be greater 

than 30,000 ft2/d locally, based on the 

results of 58 specific-capacity tests in 

Olmsted County (Delin, 1990) and on 

the results of laboratory analyses of 

rocks from the Minneapolis-St. Paul 

metropolitan area (Norvitch and others, 1974, p. 114–115). 

Transmissivity of the Prairie du 

Chien unit is highly variable due to 

secondary permeability caused by 

fractures and solution cavities. The 

Prairie du Chien transmits water primarily through fractures, joints, and 

solution channels. The transmissivity 
12

Water levels in observation wells during 1997-99 in the St.

WATER LEVEL, IN FEET ABOVE SEA LEVEL WATER LEVEL, IN FEET ABOVE SEA LEVEL WATER LEVEL, IN FEET ABOVE SEA LEVEL WATER LEVEL, IN FEET ABOVE SEA LEVEL

M AM J J A S ON D J F M AMJ J A S O ND J F MAMJ J A

1997 1998 1999

1,070

1,068

1,066

1,064

1,062

1,060

1,058

1,056

1,054

1,052

Observation well 160815

St. Peter

972

970

968

966

964

962

960

958

956

1,066.0

1,065.5

1,065.0

1,064.5

1,064.0

1,073.5

1,073.0

1,072.5

1,072.0

1,071.5

1,071.0

1,070.5

1,070.0

1,069.5

1,069.0

Observation wells 601284 and 591905

Observation well 601283

St. Peter

Prairie du Chien

Prairie du Chien

St. Peter

Observation well 148301

Figure 6.
13

WATER LEVEL, IN FEET ABOVE SEA LEVEL WATER LEVEL, IN FEET ABOVE SEA LEVEL WATER LEVEL, IN FEET ABOVE SEA LEVEL WATER LEVEL, IN FEET ABOVE SEA LEVEL

M AM J J A S ON D J F M AMJ J A S O ND J F MAMJ J A

1997 1998 1999

Observation well 179232

Prairie du Chien

Observation well 220772

Observation well 227491

Prairie du Chien

Prairie du Chien

Jordan

Observation well 446667

1,070.0

1,069.5

1,069.0

1,068.5

1,068.0

1,067.5

1,067.0

1,066.5

1,066.0

1,065.5

1,065.0

1,064.5

1,064.0

1,065.5

1,065.0

1,064.5

1,064.0

1,063.5

1,063.0

1,064.0

1,063.5

1,063.0

1,062.5

1,062.0

1,061.5

1,061.0

1,055.5

1,055.0

1,054.5

1,054.0

1,053.5

Peter-Prairie du Chien-Jordan aquifer, Rochester area, Minnesota.
14

of the Prairie du Chien is from 300 to 

1,000 ft2/d (Delin, 1990). Transmissivities greater than 100,000 ft2

/d 

were calculated at some wells. Norvitch and others (1974) reported a 

maximum horizontal hydraulic conductivity of approximately 50 ft/d for 

the Prairie du Chien. There is a range 

in horizontal hydraulic conductivity of 

at least three orders of magnitude in 

the upper part of the Prairie du Chien, 

from as low as 0.85 ft/d to as high as 

8,500 ft/d, based on recent testing of 

discrete intervals in southeastern Minnesota (Tony Runkel, Minnesota Geological Survey, written commun., 

1999). The greatest values of hydraulic conductivity are for wells that 

intersected well-connected fractures. 

The lowest values are for wells in 

comparatively less-fractured parts of 

the Prairie du Chien. The horizontal 

hydraulic conductivity of the lower 

part of the Prairie du Chien may be 

substantially less than 0.85 ft/d, based 

on video logs that show thick unfractured intervals of the Oneota Dolomite 

that have no intergranular permeability (Tony Runkel, Minnesota Geological Survey, written commun., 1999). 

However, hydraulic tests are unavailable to substantiate this hypothesis.

Movement of water in the Jordan 

unit is predominantly intergranular. 

Based on the results of aquifer tests at 

four municipal wells in Rochester, 

transmissivity of the Jordan ranged 

from 100 to 1,700 ft2

/d (Delin, 1990). 

Transmissivities ranging from 100 to 

5,000 ft2

/d were calculated from 54 

specific-capacity tests in Olmsted 

County (Delin, 1990).

Results of aquifer tests for seven 

Rochester municipal wells open to 

both the Prairie du Chien and Jordan 

units of the aquifer indicated that 

transmissivities were less than 10,000 

ft2

/d for much of the aquifer underlying the central part of the city of Rochester (Lindgren, 1997). Results of 

aquifer tests for four of the seven wells 

indicated transmissivities less than 

5,000 ft2

/d. The horizontal hydraulic 

conductivity for each unit of the aquifer ranges from 1 to 35 ft/d (Delin, 

1990). The best-fit calibrated value for 

vertical hydraulic conductivity was 1 

ft/d for each unit. Freeze and Cherry 

(1979) indicate a range in porosity of 

0 to 20 percent for limestone and dolomite and 5 to 30 percent for sandstone. 

In the Rochester area, Delin and 

Almendinger (1991) reported porosities of 10 percent for the Prairie du 

Chien and 25 percent for the St. Peter 

and Jordan, based on published data 

by Norvitch and others (1974). 

A vertical hydraulic conductivity 

of 10-4 ft/d was estimated for the Decorah-Platteville-Glenwood confining 

unit from numerical ground-waterflow model analysis in the Minneapolis-St. Paul metropolitan area (Schoenberg, 1990). Delin (1990) reported a 

value of 10-5 ft/d in the Rochester 

area, based on Darcy’s Law calculations. Specific capacities of wells 

screened in the Platteville unit of the 

confining unit in the St. Louis Park 

area, Minnesota generally are between 

10 and 100 gal/min per foot of drawdown (Stark and Hult, 1985). Results 

from one aquifer test indicate the 

transmissivity of the Platteville in the 

St. Louis Park area is about 9,000 ft2/d 

(Stark and Hult, 1985). Rocks with 

secondary solution cavity and fracture 

permeability, such as the Platteville, 

often have heterogeneous hydraulic 

properties. Liesch (1973) documented 

large local differences in the transmissivity and storage coefficient of the 

Platteville in Minneapolis, Minnesota. 

The vertical hydraulic conductivity of 

the Glenwood unit of the confining 

unit was estimated to be 9 x 10-6 ft/d 

in the St. Louis Park area, Minnesota, 

based on laboratory measurements of 

core samples (Hult and Schoenberg, 

1984). 

Stark and Hult (1985) reported a 

vertical hydraulic conductivity of 9 x 

10-4 ft/d for the basal St. Peter confining bed in the St. Louis Park area. 

Norvitch and others (1974) reported 

vertical hydraulic conductivities as 

low as 10-6 ft/d for the basal St. Peter 

confining bed and Lindgren (1990) 

reported a value of 1.5 x 10-3 ft/d, 

based on numerical ground-waterflow model analysis, in the Minneapolis-St. Paul metropolitan area. 

Packer-test data in the St. Paul area 

reported by Miller (1984) indicated a 

vertical hydraulic conductivity of 10-3 

ft/d for the St. Lawrence confining 

unit,whereas a value of 10-5 ft/d was 

estimated from numerical groundwater-flow model analysis for the 

Minneapolis-St. Paul metropolitan 

area (Schoenberg, 1990). Freeze and 

Cherry (1979) indicate a range in 

porosity of from less than 20 to less 

than 5 percent for shale. 

GROUND-WATER RECHARGE

Ground-water recharge occurs primarily by infiltration of precipitation 

to the saturated zone (areal recharge). 

Recharge as used in this report also 

includes water that leaks downward 

through the confining units to underlying aquifers. Recharge to the uppermost bedrock unit occurs through a 

thin (generally less than 50-ft thick) 

layer of glacial drift. 

Hydrograph analysis was used to 

estimate ground-water recharge rates 

to the St. Peter-Prairie du Chien-Jordan aquifer for 42 wells. The wells 

were located in the following hydrogeologic settings: (1a) along the edge 

of the Decorah-Platteville-Glenwood 

confining unit on slopes of the South 

Fork Zumbro River Valley, (1b) along 

the edge of the confining unit on side 

slopes of tributary valleys to the South 

Fork Zumbro River, (1c) along the 

edge of the confining unit near the 

head of a tributary valley in the Marion area, (2) where the Decorah-Platteville-Glenwood confining unit is 

thick and overlain by the upper carbonate aquifer, and (3) in the city of 

Rochester where the Prairie du Chien 

is the uppermost bedrock unit. 

Recharge decreased with depth of well 
15

completion beneath each of these 

hydrogeologic settings and ranged 

from 1.9 to 25.5 in. during all of 1998 

(table 1). Recharge was greatest near 

the edge of the confining unit, with 

means of as great as 13.8 in./yr, similar 

to results of Delin (1990) who 

reported a rate of 13 in./yr along the 

edge based on model analyses. The 

maximum recharge rate of 25.5 in./yr 

was for a St. Peter well (601284, 

table 2) located downslope from the 

edge of the confining unit and on the 

slope of the South Fork Zumbro River 

Valley. Recharge was least (2.0 in./yr) 

where the confining unit is thick and 

overlain by the upper carbonate aquifer. Mean recharge where the Prairie 

du Chien is the uppermost bedrock 

unit ranged from 4.8 to 6.2 in./yr during all of 1998 (table 1), similar to the 

value of 5 in./yr reported by Delin 

(1990). 

Ground-water age dating based on 

CFC concentrations was used at nine 

wells to estimate recharge rates to the 

St. Peter-Prairie du Chien-Jordan 

aquifer (fig. 5). Recharge rates ranged 

from 3.0 to 9.7 in./yr in most hydrogeologic settings (table 2). Recharge 

was greatest (35.3 in./yr) for the St. 

Peter well (601284) mentioned in the 

previous paragraph. Recharge dates 

ranged from: (1) the mid-1950’s to the 

early 1990’s for wells in the St. Peter 

unit, (2) the late 1960’s to approximately 1990 for wells in the Prairie du 

Chien, and (3) the early to mid-1950’s 

for wells in the Jordan.

Water-Level Fluctuations

Ground-water levels in the Rochester area during 1997–99 fluctuated 

seasonally in response to variations in 

recharge and discharge from the aquifer system (fig. 6). Spring peaks in 

ground-water levels occurred during 

April 1998 and May 1999 because of 

snowmelt, spring rain, and minimal 

evapotranspiration losses (fig. 6). At 

the time of the last water-level measurements during May 1999, water 

levels were still rising in most wells, 

but were likely near spring peak levels. Ground-water levels generally 

decline in summer due to evapotranspiration, ground-water discharge to 

streams, and ground-water withdrawals. However, a rise in water levels 

occurred during July 1998 due to a 

major storm that resulted in net 

recharge to the aquifer. Similarly, net 

recharge also occurred in September 

1998 due to rainfall and low evapotranspiration rates. 

Hydrographs for the nested observation wells (601284 and 591905) 

located down slope from the DecorahPlatteville-Glenwood confining unit 

indicate that water-level fluctuations 

in the Prairie du Chien and St. Peter 

units are similar (fig. 6). Fluctuations 

in the St. Peter were generally of lesser 

magnitude where the confining unit is 

thick (well 148301), due to reduced 

leakage. The comparatively large fluctuations observed in well 148301 during 1997 were due to pumpage. The 

largest fluctuations in water levels 

were observed in Prairie du Chien well 

601283 because it is within about 

1,000 ft of three high-capacity industrial supply wells. 

STREAM-AQUIFER LEAKAGE

Ground-water leakage to streams 

in the Rochester area generally is 

greater than leakage from streams to 

the underlying aquifer, and the streams 

are therefore gaining streams overall. 

A gain in streamflow of 0.5 ft3/s was 

measured for Bear Creek from US 

Highway 14 to near its confluence 

with the South Fork Zumbro River, a 

distance of approximately one river 

mile. However, the measured gain in 

streamflow was approximately 1.3 

percent of the flow in the stream 

(38 ft3/s), less than the assumed accuracy of plus or minus 5 percent for current-meter measurements. 

Delin (1990) reported that streamflow increased in about three-fourths 

of the stream reaches measured for the 

South Fork Zumbro River, Bear 

Creek, and Cascade Creek during two 

synoptic measurement periods during 

March and August 1987. Estimated 

stream-aquifer leakage rates were generally less than 5 ft3

/s/mi (cubic feet 

per second per stream mile) during the 

two measurement periods. 

The South Fork Zumbro River and 

Bear Creek flow on top of the Prairie 

du Chien unit of the St. Peter-Prairie 

du Chien-Jordan aquifer near the western end of hydrogeologic section A-A' 

(fig. 4; trace of section shown on figure 3). Streamflow in a reach of the 

South Fork Zumbro River immediately north of US Highway 14 and 

adjacent to the western end of hydrogeologic section A-A′ decreased during August 1987 by approximately 

1 ft3

/s/mi (Delin, 1990). The measured decrease occurred in a reach 

near the center of the cone of depression in the potentiometric surface of 

the St. Peter-Prairie du Chien-Jordan 

aquifer in Rochester caused by pumpage from high-capacity supply wells 

(Lindgren, 1997, figs. 6 and 9). Three 

industrial supply wells are located 

within 500 ft of two observation wells 

near the western end of hydrogeologic 

section A-A' and are also in close 

proximity to the losing river reach. 

Water-level measurements in one 

observation well located near the three 

industrial supply wells indicated that 

hydraulic heads in the Prairie du Chien 

were consistently lower than the stage 

in the South Fork Zumbro River at a 

site approximately 1,000 ft from the 

observation well. The lower hydraulic 

head in the Prairie du Chien compared 

to the nearby river stage indicates that 

movement of stream water into the 

aquifer was likely. 

GROUND-WATER FLOW

Ground water in the upper carbonate aquifer moves rapidly through 

solution-widened fractures and caverns. Where the upper carbonate rock 

is less affected by karst development, 

ground water moves slowly through 

much narrower fractures. Balaban 

(1988, plate 5) mapped a radial distri-
16

 Table 1. Estimated ground-water recharge rates to the aquifer system based on hydrograph analysis, Rochester area, Minnesota

[in., inches; in./yr, inches per year; --, no estimate or one value only; number in parentheses is number of wells with an estimate for the specified time period; confined, 

where Decorah-Platteville-Glenwood confining unit is thick]

Time period of estimate

Spring 1998 All of 1998 Spring 1999

Hydrogeologic setting, unit of the 

St. Peter-Prairie du Chien-Jordan 

aquifer [uppermost bedrock unit]

Number of 

wells

Value or range 

(in.) Mean (in.) Value or range (in./yr) Mean (in./yr) Value or range (in.) Mean (in.)

Confined

St. Peter 

 [Galena Group] 2 1.8–2.4 2.1 -- -- 1.9–1.9 1.9

Prairie du Chien 

 [Galena Group] 3 1.7–2.4 2.1 -- -- 1.0–1.0 (2) 1.0 (2)

Jordan 

 [Galena Group] 1 1.2 -- -- -- 1.3 --

Mean for hydrogeologic setting 2.0 (6) -- 1.4 (5)

Edge (slope of main valley)

St. Peter 

[Platteville Formation] 1 16.8 -- 25.5 -- 22.5 --

[Decorah Shale] 1 6.2 -- 7.8 -- 10.7 --

Prairie du Chien 

[Platteville Formation] 3 3.2–5.5 4.1 8.0 -- 3.6–5.3 4.3

Jordan 0 -- -- -- -- -- --

Mean for hydrogeologic setting 7.0 (5) 13.8 (3) 9.2 (5)

Edge (side slope of tributary valley)

Prairie du Chien 

[Prairie du Chien Group] 4 2.8–4.1 3.5 3.8–9.5 6.2 3.2–4.0 3.6

[St. Peter Sandstone] 4 2.1–2.7 (3) 2.4 (3) 2.6–3.2 (3) 2.9 (3) 2.1–2.9 (3) 2.4 (3)

[Platteville Formation] 3 2.3–3.9 2.8 2.6–4.7 3.3 2.7–4.2 3.3

[Decorah Shale] 2 3.3–3.6 3.4 6.4 (1) -- 3.0–5.8 4.4

Jordan 

[Prairie du Chien Group] 2 2.8–3.4 3.1 4.3–5.2 4.8 2.6–4.0 3.3

[Galena Group] 1 2.0 -- 2.8 -- 2.2 --

[Decorah Shale] 2 1.2 -- 1.9 (1) -- 1.3–1.6 1.4

[Platteville Formation] 1 4.1 -- 4.8 -- 2.6 --

Mean for hydrogeologic setting 2.9 (17) 4.3 (16) 3.0 (18)

Edge (head of tributary valley)

St. Peter 

[Decorah Shale] 1 5.4 -- -- -- 3.3 --

[Platteville Formation] 3 4.8–9.3 6.5 5.9–10.1 7.4 4.4–5.8 5.1

Prairie du Chien 

[Platteville Formation] 1 2.2 -- 2.4 -- 1.6 --

Mean for hydrogeologic setting 5.4 (5) 6.2 (4) 4.0 (5)

Absent

Glacial drift 3 5.3–10.4 8.6 19.0 -- 4.8–16.8 10.7

Prairie du Chien 

[Prairie du Chien Group] 4 1.1–5.8 3.4 2.6–9.6 (4) 5.9 (4) 1.8–7.0 4.4

Mean for hydrogeologic setting 5.4 (8) 8.5 (5) 6.8 (8)
17

bution pattern of potentiometric contours from the centers of the large 

remnants of the upper carbonate aquifer in Olmsted County. This pattern is 

evident in hydrogeologic section A-A′ 

(fig. 4), with flow outward from a high 

in the potentiometric surface of the 

upper carbonate aquifer located near 

the center of R12W toward the South 

Fork Zumbro River Valley to the west 

and toward the Middle Fork Whitewater River Valley to the east. Discharge 

into local stream drainages also occurs 

where the streams have cut into the 

aquifer, and local stream valleys are 

the main influence on the volume of 

water in the aquifer (Balaban, 1988). 

Many springs occur where the base of 

the aquifer is exposed or is near the 

land surface, due to the underlying 

low-permeability Decorah-PlattevilleGlenwood confining unit that greatly 

impedes the downward movement of 

water. 

Hydraulic heads in the upper carbonate aquifer are approximately 

200 ft higher than in the St. Peter-Prairie du Chien-Jordan aquifer (fig. 4). 

The difference in heads decreases near 

the South Fork Zumbro and Middle 

Fork Whitewater River Valleys due to 

discharge of water from the upper carbonate aquifer into the river valleys. 

 Table 2. Comparison of ground-water recharge rates to the aquifer system derived from hydrograph analysis, chlorofluorocarbon agedating, and numerical ground-water-flow model analysis, Rochester area, Minnesota

[in., inches; in./yr, inches per year; --no estimate; edge, near edge of confining unit; absent, where confining unit is absent and Prairie du Chien Group is uppermost 

bedrock unit; CFC, chlorofluorocarbon]

Hydrograph analysis

CFC

analysis

(in./yr)

Numerical

model

analysis

(in./yr)

Time period of estimate

Hydrogeologic setting, unit of the St. Peter-Prairie du Chien-Jordan aquifer, uppermost bedrock 

unit [in brackets], and Minnesota unique well 

number

Spring 1998

Mean

(in.)

All of 1998

Mean

(in./yr)

Spring 1999

Mean

(in.)

Edge (Slope of main valley)

St. Peter 23.75

[Platteville Formation]

601284 16.8 25.5 22.5 35.3 --

Prairie du Chien 

[Platteville Formation]

591905 5.5 8.0 5.3 6.4 --

Edge (side slope of tributary valley)

Prairie du Chien 

[Prairie du Chien Group]

220770 3.3 9.5 3.2 6.8 --

220772 4.1 7.0 3.8 4.0 --

241037 3.7 4.7 4.0 5.3 --

[Decorah Shale]

220773 3.6 6.4 3.0 9.7 --

Edge (head of tributary)

St. Peter 

[Platteville Formation]

160815 5.4 6.1 4.4 4.3 --

Absent

Prairie du Chien 5.1

[Prairie du Chien Group]

601283 5.8 9.6 6.9 6.5 --

Prairie du Chien-Jordan 

[Prairie du Chien Group]

233030 -- -- -- 3.0 --
18

The large vertical gradients indicate 

that water from the upper carbonate 

aquifer moves vertically downward 

through joints or other pathways in the 

Decorah-Platteville-Glenwood confining unit to the St. Peter-Prairie du 

Chien-Jordan aquifer. The amount of 

this vertical leakage, and the areas 

where it is most likely to occur, are not 

known. Improper well construction 

also may add to interaquifer connection. 

Horizontal and vertical directions 

of flow in the aquifer system may be 

illustrated using hydrogeologic sections and equipotential lines (fig. 4). 

Figure 4 illustrates predominantly horizontal flow in the upper carbonate and 

St. Peter-Prairie du Chien-Jordan 

aquifers and predominantly vertical 

flow through the Decorah-PlattevilleGlenwood confining unit separating 

the aquifers. The hydraulic conductivity of the Platteville is appreciably 

greater than the Decorah and Glenwood, but because it is relatively thin 

and is bounded by the two confining 

units it likely has limited affect on 

flow through the Decorah-PlattevilleGlenwood confining unit. No data are 

available for hydraulic heads in the 

Platteville in the Rochester area. The 

comparatively small variations in 

hydraulic head vertically within the 

aquifer units reflect the predominantly 

horizontal flow in the aquifers (fig. 4). 

An exception to this generalization 

within the St. Peter-Prairie du ChienJordan aquifer occurs in the vicinity of 

the pair of nested observation wells 

installed for this study in T106N, 

R13W, section 3, where the measured 

hydraulic head difference between the 

St. Peter and Prairie du Chien units is 

7.2 ft (fig. 4). The difference in 

hydraulic heads is partially due to 

increased ground-water recharge to 

the St. Peter near the edge of the Decorah unit of the Decorah-PlattevilleGlenwood confining unit, creating a 

mounding effect and altering the equipotential lines (fig. 4). A further cause 

may be the localized presence of the 

basal St. Peter confining bed, although 

it is not recorded in water-well logs in 

the Rochester area. Localized confining units within the St. Peter-Prairie du 

Chien-Jordan aquifer can produce 

large vertical hydraulic gradients 

(Delin, 1990). 

Regional flow in the St. Peter-Prairie du Chien-Jordan aquifer generally 

is from a ground-water divide in the 

potentiometric surface, west, south, 

and east of Rochester, toward the 

South Fork Zumbro River (fig. 3). The 

divide bisects highs in the potentiometric surface, separating groundwater flow toward and away from 

Rochester. The ground-water divide 

moves in response to seasonal fluctuations in recharge to and discharge from 

the aquifer system. Lindgren (1997) 

reported that there were no appreciable changes in the location of the 

ground-water divide, however, from 

1988 to 1995. The regional hydraulic 

gradient is approximately 3 to 

20 ft/mi, and increases near the South 

Fork Zumbro River. Ground-water 

discharge from the aquifer is to 

streams, to supply wells completed in 

the aquifer, and possibly to underlying 

units as leakage, based on downward 

vertical gradients in hydraulic heads 

between units at some locations. 

Hydraulic head generally increases 

with depth near streams in the Rochester area, indicating that the vertical 

component of flow is upward, as is 

illustrated in hydrogeologic section AA′ (fig. 4) east of Bear Creek. The 

lowering of the potentiometric surface 

in the aquifer due to pumpage by supply wells results in locally downward 

flow in the area underlying the South 

Fork Zumbro River (fig. 4). 

SIMULATION OF GROUNDWATER FLOW

A conceptual model was formulated for the selected flowpath in the 

Rochester area, from knowledge of the 

hydrogeologic setting, aquifer characteristics, distribution and amount of 

recharge and discharge, and aquifer 

boundaries. A numerical model of 

ground-water flow was constructed 

based on the conceptual model of the 

aquifer system. 

A cross-sectional ground-waterflow model was constructed and calibrated for steady-state (equilibrium) 

conditions. No storage terms are 

included in the steady-state simulations. The cross-sectional model was 

used to test concepts of increased 

ground-water recharge near the edge 

of the Decorah-Platteville-Glenwood 

confining unit and to evaluate groundwater flowpaths in the aquifer system, 

particularly near the edge of the confining unit. 

NUMERICAL MODEL 

DESCRIPTION

The flowpath along the trace of 

hydrogeologic section A-A′ (fig. 3) 

was chosen as representative of the 

aquifer system and was used to investigate concepts of ground-water flow 

using the numerical cross-sectional 

model. Hydrogeologic section A-A′

represents a generalized compilation 

of hydrogeologic information within a 

3-mile-wide flowpath area (fig. 3). 

The trace of the section is aligned with 

a horizontal flowpath in the St. PeterPrairie du Chien-Jordan aquifer from 

the ground-water divide east of Rochester westward to the South Fork Zumbro River. There are no significant 

horizontal flows normal to the flowpath along the hydrogeologic section, 

except at the western end of the flowpath. 

In the cross-sectional model, the 

flowpath is represented by rectangular 

finite-difference grid cells within 

which the properties of the hydrogeologic unit represented are assumed to 

be uniform. The variably-spaced 

finite-difference grid used to spatially 

discretize the model area has 3 rows 

and 135 columns (figs. 7a and 7b). 

Although three rows are simulated in 
19

the model, it is cross sectional in 

nature because the hydraulic properties and flows simulated in each row 

are identical. The simulated hydraulic 

heads for a given column are the same 

for each row, except at the western end 

of the model (columns 1 and 2), where 

high-capacity supply wells are simulated. Three rows are included in the 

model to minimize boundary effects at 

the western end of the model. Notation 

of the form (3,2,120), where the first 

number in parentheses indicates the 

layer, the second number indicates the 

row, and the third number represents 

the column, is used to refer to the location of an individual cell within the 

grid. The dimensions of the grid cells 

are 880 ft along rows and range from 

100 to 1,000 ft along columns. The 

smallest cells are near the edge of the 

Decorah-Platteville-Glenwood confining unit, where the most detail is 

needed. 

The aquifer system along the flowpath was subdivided into 11 layers, 

corresponding to the generally horizontal hydrogeologic units (fig. 7a, 

and table 3). The glacial drift was 

included in the model as layer 1, but 

was designated as inactive for the simulations because it is generally thin 

(less than 50 ft thick) and unsaturated 

along the simulated flowpath. The 

lower part of the upper carbonate aquifer has a greater shale content, and presumably a lower hydraulic 

conductivity, than the upper part. The 

individual units of the Decorah-Platteville-Glenwood confining unit and 

the St. Peter-Prairie du Chien-Jordan 

aquifer were simulated as separate layers in the cross-sectional model due to 

the detailed nature of the model and to 

allow for an investigation of the simulated effects of variations in confining 

unit and aquifer structure. Layer 8, 

representing the basal St. Peter confining bed, was not initially included in 

the model, as discussed later in the 

Numerical Model Calibration section. 

Layer 9, representing the upper part of 

the Prairie du Chien unit of the St. 

Peter-Prairie du Chien-Jordan aquifer 

was assigned a greater hydraulic conductivity because it contains a greater 

density of fractures and solution features than for the lower part (represented by layer 10). 

The altitudes of the layer tops and 

bottoms were specified for each model 

cell for the 11 model layers. The thickness of a cell representing a hydrogeologic unit is incorporated in the 

transmissivity term for the cell. The 

transmissivities of layers 4, 5, 6, 8, 10, 

and 11 are constant in time for any 

individual model cell. The units are 

under confined conditions so their 

model-calculated saturated thicknesses do not vary. Layers 2, 3, 7, and 

9 are unconfined or confined along 

different parts of the modeled flowpath. The transmissivities of cells representing these units vary where the 

units are under unconfined conditions 

and are constant in time where the 

units are under confined conditions. 

Ideally, all model boundaries 

should be located at the physical limits 

of the aquifer system or at other hydrologic boundaries, such as a major river. 

The lateral boundaries for all layers in 

the cross-sectional model represent 

natural no-flow boundaries of the 

aquifer system. The lateral boundaries 

for layers 2–6 are located where the 

hydrogeologic units they represent are 

fully incised by the South Fork Zumbro River Valley on the west and by 

the Middle Fork Whitewater River 

Valley on the east. These units are 

truncated by the river valleys and there 

is no ground-water flow across the 

boundaries, other than from springs 

and seeps. The western boundaries of 

layers 7 and 8 are also located where 

the units are fully incised by the South 

Fork Zumbro River Valley, with no 

ground-water flow across the boundaries. 

The eastern boundaries of layers 7–

11 are located at the ground-water 

divide of the St. Peter-Prairie du 

Chien-Jordan aquifer located east of 

Rochester (fig. 3). This ground-water 

divide represents a plane of highest 

hydraulic head in the aquifer that generally separates flow westward toward 

and eastward away from Rochester. 

The western boundaries of layers 9–11 

are located at the South Fork Zumbro 

River. These boundaries are simulated 

as no-flow boundaries because the 

potentiometric contours indicate that 

the flow direction in that area is predominantly south to north, normal to 

the line of section. 

The effects of the component of 

flow normal to the line of section at the 

western end of the simulated flowpath, 

and the exclusion from the model of 

this potential source of water due to 

the use of no-flow boundaries, was 

evaluated. A simulation was done 

specifying a constant head with an altitude of 975 ft for layer 9, at the western end of the simulated flowpath (cell 

9,3,1) (fig. 3). The constant head 

allowed water to move into the cell, 

simulating the potential source of 

water derived from the indicated 

south-to-north ground-water flow. The 

effects of the constant head on hydraulic heads and flows in the simulated 

aquifer system were minimal. The 

simulated flow into the constant-head 

cell was 0.06 ft3/s. The simulated 

hydraulic head changes were less than 

0.1 ft, with simulated heads being 

unchanged in most cells. The simulated leakage from the South Fork 

Zumbro River to the upper Prairie du 

Chien was reduced by 0.05 ft3

/s, indicating that the primary effect of the 

source of water from the south not 

simulated in the cross-sectional model 

would be to lessen leakage from the 

South Fork Zumbro River into the 

upper Prairie du Chien. The leakage 

from the South Fork Zumbro River 

into the upper Prairie du Chien is 

caused by pumpage from a highcapacity well simulated in cell 

(11,2,1). The small magnitude of the 

simulated boundary inflow and result-
20

AREA NOT PART OF MODEL

5 10

15 25

50

75

95

100

105

110 115 125

130

1

120

135SEE FIGURE 7b

1000

1100

1200

1300

1400

500

600

700

800

900

FEET

WEST

A A'

EAST

South Fork Zumbro River

Bear Creek

Middle Fork

Whitewater River

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

RECHARGE

ZONE 1

RECHARGE

ZONE 5

COLUMNS

For zones 2, 3, 4

see Figure 7b

VERTICAL EXAGGERATION X 46

DATUM IS SEA LEVEL

Trace of section shown on figure 3

River cell

Drain cell

Zone 5--Columns 90-135; 7.0 in./yr

Zone 1--Columns 1-28; 5.1 in./yr

Recharge zone

Inactive cell

Model layer boundary

No-flow boundary

EXPLANATION

Model layers, corresponding hydrogeologic units, and simulated areal recharge zones, Rochester area, Minnesota.

of supply wells

Screened interval Screened interval

of supply wells of supply wells

Screened interval

Figure 7a.

Upper carbonate aquifer

Glacial drift

Lower part of the upper carbonate aquifer

Upper part of the upper carbonate aquifer

Decorah-Plattevills-Glenwood confining unit

Glenwood unit of the Decorah-Platteville-Glenwood confining unit

Platteville unit of the Decorah-Plateville-Glenwood confining unit

Decorah unit of the Decorah-Platteville-Glenwood confining unit

St. Peter-Prairie du Chien-Jordan aquifer

St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer

Upper Prairie du Chien unit of the St. Peter

Basal St. Peter confining bed

-Prairie du Chien-Jordan aquifer

Lower Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan aquifer

Jordan unit of the St. Peter-Prairie du Chien-Jordan aquifer

St. Lawrence confining unit

(9)

(8)

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(12)

(11)

(10)

Model layers

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(1)

(9)

(8)

(9)

(10)

(10)

(11)

(11)

(12)

(12)

Model layers
21

Drain cell

Inactive cell

Recharge zone

Zone 1--Columns 1-28; 5.10 in./yr

Zone 2--Columns 29-44, 47-53; 23.75 in./yr

Zone 3--Columns 45-46, 54-62; 0.00 in./yr

Zone 4--Columns 63-89; 7.50 in./yr

Zone 5--Columns 90-135; 7.00 in./yr

Model layer boundary

EXPLANATION

Glacial drift

Upper part of the

upper carbonate

aquifer

Lower part of the upper carbonate aquifer

Decorah unit of the

Decorah-Platteville-Gleenwood

confining unit

Platteville unit of the Decorah-Platteville-Glenwood

confining unit

Glenwood unit of the DecorahPlatteville-Glenwood

confining unit

St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer

Basal St. Peter confining bed

Upper Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan aquifer

FEET

1,200

1,180

1,160

1,140

1,120

1,100

1,080

1,060

1,040

1,020

1,000

980

25

30

35

40

45

50

55

60

65

70

75

80

85

90

20

RECHARGE

ZONE 1

RECHARGE

ZONE 3

RECHARGE

ZONE 4

RECHARGE

ZONE 5

COLUMNS

Model layers, corresponding hydrogeologic units, and simulated areal recharge zones near edge of confining

units, Rochester area, Minnesota.

0 1 MILE

0 1 KILOMETER

DATUM IS SEA LEVEL

VERTICAL EXAGGERATION X 46

Figure 7b.

RECHARGE

ZONE 2
22

ing change in stream-aquifer leakage, 

however, indicates that the effects are 

minimal for the purposes of this 

steady-state model. 

Simulation of leakage of water 

between model layers is dependent on 

the thicknesses and vertical hydraulic 

conductivities between adjacent layers. A more detailed discussion of 

leakage of water between model layers 

can be found in McDonald and Harbaugh (1988). Layer 11 is underlain by 

the St. Lawrence confining unit. The 

volume vertical flow across the base of 

layer 11 is small compared to the horizontal flow in the unit, and the base 

can be treated as a no-flow boundary. 

A specified-flux boundary was 

used to represent areal recharge to the 

uppermost active layer for each model 

column.Where a confining unit is the 

uppermost bedrock unit, no areal 

recharge was simulated. The crosssectional model was not used to simulate ground-water losses to evapotranspiration because these losses 

occur in only a small percentage of the 

flowpath area, primarily in the immediate vicinity of streams, where the 

water table is less than 5 ft below land 

surface. 

Areal recharge rates were assigned 

to five zones (figs. 7a and 7b; table 4). 

The initial simulated areal recharge 

rates for the five zones (table 4) were 

based on recharge rates reported by 

Delin (1990) in the Rochester area for 

zones 1 and 2 and on ranges of areal 

recharge reported elsewhere in Minnesota for zones 3, 4, and 5. 

Stream-aquifer leakage was simulated with head-dependent flux nodes 

(McDonald and Harbaugh, 1988). 

Stream-aquifer leakage through a 

reach of streambed is approximated by 

Darcy’s Law as:

QRIV = (KLW/M) (HRIV-HAQ), 

where:

QRIV = stream-aquifer leakage 

through the reach of the streambed 

(L3

/T),

K = vertical hydraulic conductivity 

of the streambed (L/T),

L = length of the reach (L),

W = width of the stream (L),

M = thickness of the streambed 

(L),

HAQ = head in the aquifer (L), and

HRIV = head in the stream (L). 

The length of the streambed in each 

river cell was measured from USGS 

7.5-minute-quadrangle topographic 

maps. The average width of the South 

 Table 3. Initial and best-fit calibrated values of hydraulic properties used in the cross-sectional model of the aquifer system, Rochester 

area, Minnesota

 [ft/d, feet per day; NA, model layer is inactive and no hydraulic properties were assigned]

Horizontal hydraulic 

conductivity (ft/d)

Vertical hydraulic 

conductivity (ft/d)

Hydrogeologic unit Model layer Model columns Initial Calibrated Initial Calibrated Porosity

Glacial drift 1 Inactive NA NA NA NA NA

Upper part of the upper carbonate aquifer 2 87–129 1

35

1

Kanivetsky and Walton (1979)

20 2

1.0

2Assumed to be the same as for upper Prairie du Chien, which is of similar composition

2.0 2

0.10

Lower part of the upper carbonate aquifer 3 63–134 125 10 21.0 1.0 20.10

Decorah unit of the Decorah-PlattevilleGlenwood confining unit 4 54–134 30.00001

3Delin (1990)

0.00001 30.00001 0.00001 4

0.05

4

Freeze and Cherry (1979)

Platteville unit of the Decorah-PlattevilleGlenwood confining unit 5 47–134 235 1.0 21.0 1.0 20.10

Glenwood unit of the Decorah-Platteville-Glenwood confining unit 6 44–134 30.00001 0.00001 30.00001 0.00001 40.05

St. Peter unit of the St. Peter-Prairie du 

Chien-Jordan aquifer 7 21–135 335 25 31.0 1.0 50.25

5Delin and Almendinger (1991)

Basal St. Peter confining bed 8 21–135 60.0015

6Lindgren (1990)

0.0015 60.0015 0.0015 40.05

Upper Prairie du Chien unit of the St. 

Peter-Prairie du Chien-Jordan aquifer 9 1–135 335 12.5 3

1.0 1.0 50.10

Lower Prairie du Chien unit of the St. 

Peter-Prairie du Chien-Jordan aquifer 10 1–135 70.85

7Tony Runkel, Minnesota Geological Survey, written commun., 1999

0.85 70.05 0.05 70.075

Jordan unit of the St. Peter-Prairie du 

Chien-Jordan aquifer 11 1–135 335 45 31.0 1.0 40.10
23

Fork Zumbro River and Bear Creek 

streambeds, measured at stream discharge measurement sites at the west 

end of the flowpath, is about 60 ft. 

Average streambed width for the Middle Fork Whitewater River was estimated to be about the same. The 

thickness of the streambed was 

assumed to be 1 ft for the model, as for 

other studies (Yager, 1993; Lindgren, 

1990). The lower limit of the streambed is poorly defined and not easily 

measurable. The initial value used in 

the cross-sectional model for vertical 

hydraulic conductivity of the South 

Fork Zumbro, Bear Creek, and Middle 

Fork Whitewater streambeds was 0.1 

ft/d, based on values reported by Delin 

(1990). 

Discharge from layer 2 by springs 

and seeps into local stream drainages 

occurring where streams have cut into 

the aquifer was simulated using the 

drain package of MODFLOW 

(McDonald and Harbaugh, 1988). 

Discharge by springs and seeps from 

layer 3 into the Middle Fork Whitewater River drainage at the eastern end of 

the simulated flowpath and at the edge 

of the Decorah unit of the confining 

unit was also simulated using the drain 

package. Seven drain cells were simulated in layer 2 and nine drain cells 

were simulated in layer 3 (figs. 7a and 

7b). 

Discharge from the model cell into 

the drain is calculated as:

QD = CD (H-D), where:

QD = discharge to the drain (L3/T), 

CD = conductance (L2/T),

H = head in the aquifer (L), and

D = altitude of the drain (L). 

The conductance was assumed to be 

proportional to the area of the drain 

and the hydraulic conductivity of the 

aquifer material. The altitude of the 

streambed dissecting the aquifer, 

determined from USGS 7.5-minutequadrangle topographic maps, was 

specified as the drain altitude. The altitude of the bottom of layer 3 was specified as the altitude of the drain at the 

edge of the Decorah unit of the confining unit. 

Ground water is withdrawn by 

three high-capacity industrial supply 

wells located near the South Fork 

Zumbro River at the western end of 

the simulated flowpath. A total of 

230.6 million gallons of water was 

pumped from the three wells during 

1998 (Harry Root, Associated Milk 

Producers, Inc., Plant Engineer, written commun., 1999). Two of the supply wells are open to the Jordan unit of 

the aquifer (layer 11). A third supply 

well is open to the Jordan and both the 

upper and lower Prairie du Chien units 

of the aquifer, but pumped only 0.1 

percent of the water withdrawn during 

1998. All of the water withdrawn by 

the supply wells was simulated as 

being pumped from the Jordan from 

cell (11,2,1) in the cross-sectional 

model. The effects of the lateral noflow boundaries on drawdowns due to 

the simulated pumpage are less than 

0.1 ft.

The initial and best-fit calibrated 

values of hydraulic properties represented in the cross-sectional model are 

listed in table 3 and the values for areal 

recharge are listed in table 4. Initial 

values for horizontal and vertical 

hydraulic conductivities and porosity 

for each hydrogeologic unit were 

based on previous studies in the Roch-

 Table 4. Initial and best-fit calibrated values of areal recharge rate used in the cross-sectional model of the aquifer system, Rochester 

area, Minnesota 

[All recharge rates are in inches per year]

Areal recharge 

zone Model columns Model layer Hydrogeologic unit

Areal recharge rate

Initial Calibrated

1 1–20 9 Upper Prairie du Chien unit of the St. Peter-Prairie du ChienJordan aquifer

5.0 5.1

21–28 7 St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer

2 29–44 7 St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer 13.0 23.75

47–53 5 Platteville unit of the Decorah-Platteville-Glenwood confining unit

3 45–46 6 Glenwood unit of the Decorah-Platteville-Glenwood confining unit

0.0 0.0

54–62 4 Decorah unit of the Decorah-Platteville-Glenwood confining 

unit 

4 63–86 3 Lower part of the upper carbonate aquifer 7.0 7.5

87–89 2 Upper part of the upper carbonate aquifer

5 90–129 2 Upper part of the upper carbonate aquifer 7.0 7.0

130–134 3 Lower part of the upper carbonate aquifer

135 7 St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer
24

ester area, published values for other 

areas in Minnesota, and unpublished 

information from previous work in the 

Rochester area (Tony Runkel, Minnesota Geological Survey, written commun., 1999). 

NUMERICAL MODEL 

CALIBRATION

Model calibration is the process in 

which initial estimates of aquifer properties and boundary conditions are 

adjusted until simulated hydraulic 

heads and flows acceptably match 

measured hydraulic heads and flows. 

For this study, aquifer properties and 

areal recharge were adjusted to produce an acceptable match between 

simulated and measured hydraulic 

heads and stream-aquifer leakage. 

Model-computed stream-aquifer leakage was compared to leakage between 

South Fork Zumbro River, Bear 

Creek, and the upper Prairie du Chien 

unit of the aquifer based on measured 

streamflows during November 1998 

and during 1987 (Delin, 1990). 

Water levels in 22 wells during 

October and November 1998 and 

streamflows at 2 sites on Bear Creek 

during November 1998 were used to 

calibrate the cross-sectional model 

under steady-state conditions. A map 

showing the potentiometric surface of 

the upper carbonate aquifer was published by Balaban (1988, plate 5). The 

locations of the 1,250-ft and 1,280-ft 

contours from that map along the modeled flowpath were also used to calibrate the model. Four hypothetical 

observation wells were simulated in 

the model at the locations of these contours and included in the calculations 

of average differences between simulated and measured hydraulic heads. 

The model was calibrated by varying the simulated values of (1) horizontal and vertical hydraulic 

conductivities of the hydrogeologic 

units, (2) hydraulic conductivity of the 

streambeds, and (3) areal recharge to 

the aquifers. The match between measured and simulated hydraulic heads 

and stream-aquifer leakage was 

improved by (1) reducing the horizontal hydraulic conductivities for layers 

2, 3, 5, 7, and 9, and (2) increasing the 

horizontal hydraulic conductivity for 

layer 11. The best-fit calibrated values 

are considered reasonable because 

they are all within previously reported 

values in the Rochester area and elsewhere in Minnesota. The initial values 

used for porosity for the hydrogeologic units were not varied because 

porosity is only used by the post-processing package MODPATH to determine average linear ground-water 

velocities for use in time-related capture zones and time markers along 

pathlines. The initial value for streambed hydraulic conductivity was varied 

by an order of magnitude during the 

calibration process, but the best-fit 

calibrated value was the same as the 

initial value of 0.1 ft/d. The conductance values specified for the drain 

package of MODFLOW were not varied during the calibration of the model 

because there were no data available to 

compare simulated and measured outflow from springs and seeps. 

The calibration was also improved 

by the addition of the basal St. Peter 

confining bed (layer 8). The confining 

bed was needed to acceptably simulate 

measured vertical hydraulic head differences between the aquifer units 

along the simulated flowpath, which 

are as much as 7.2 ft near the edge of 

the Decorah-Platteville-Glenwood 

confining bed. Without the inclusion 

of this confining unit, simulated 

hydraulic head differences between 

the two aquifer units within a column 

were approximately 0.5 ft or less. 

The best-fit calibrated areal 

recharge rates were greater than the 

initial values for three of the five simulated recharge zones (table 4). The 

increases for two of the three zones are 

minimal. It is reasonable that the simulated areal recharge rates to the aquifers are at the upper end of the range of 

values calculated using hydrograph 

analysis, considering that, at many of 

the wells included in the hydrographanalysis calculations the aquifer units 

were overlain by confining units of 

varying thicknesses. The best-fit calibrated areal recharge rate near the 

edge of the Decorah-Platteville-Glenwood confining unit, where recharge 

is greatest, is appreciably greater than 

the initial value of 13.0 in./yr (reported 

by Delin, 1990). The best-fit calibrated rate of 23.75 in./yr, however, is 

in good agreement with the calculated 

value from hydrograph analysis of 

25.5 in./yr for a well screened in the 

St. Peter unit. 

The calibrated cross-sectional 

model acceptably matches measured 

hydraulic heads, as indicated by the 

simulated equipotential lines shown in 

figures 8a and 8b. The best-fit calibrated hydraulic heads were within 4.3 

ft of measured water levels at all of the 

22 wells used to calibrate the model 

and within 1.7 ft of water levels in the 

four hypothetical observation wells 

based on the potentiometric contours 

reported by Balaban (1988). The differences between simulated and measured hydraulic heads were 2.0 ft or 

less in 17 of the 26 observation wells. 

The mean absolute difference between 

simulated and measured hydraulic 

heads is 1.80 ft. The mean algebraic 

difference between simulated and 

measured hydraulic heads is +0.04 ft, 

indicating that the positive differences 

were approximately balanced by the 

negative differences. 

Measured vertical differences in 

hydraulic heads between aquifer units 

were also acceptably simulated by the 

cross-sectional model. The measured 

difference in hydraulic heads between 

the St. Peter and upper Prairie du 

Chien units at a site with nested monitoring wells was 7.2 ft. The simulated 

difference between hydraulic heads in 

the St. Peter and upper Prairie du 

Chien at that location was 8.2 ft. The 

nested well site is located in 

T106N,R13W, section 3 (fig. 3). The 
25

measured difference in hydraulic 

heads for a pair of wells located 

approximately 150 ft apart in 

T106N,R13W, section 2, a monitoring 

well installed for this study screened in 

the upper Prairie du Chien and a 

domestic well open to the Jordan, was 

1.1 ft. The simulated difference 

between hydraulic heads in the upper 

Prairie du Chien and Jordan near that 

location was 0.5 ft. 

The model duplicated the correct 

direction and approximate amount of 

stream-aquifer leakage. The measured 

gain in streamflow during November 

1998 for an approximately 1 mile 

reach of Bear Creek, near the west end 

of the simulated flowpath, was 

0.5 ft3

/s, similar to the simulated leakage of water from the upper Prairie du 

Chien to Bear Creek of 0.64 ft3/s per 

river mile. The simulated leakage of 

water from the South Fork Zumbro 

River to the upper Prairie du Chien 

unit was 0.30 ft3

/s per river mile. 

A water budget is an accounting of 

inflow to, outflow from, and storage 

change in the aquifer system. For 

steady state, inflow (sources) to the 

aquifer equals outflow (discharges) 

from the aquifer (table 5) and storage 

change is zero. Along the simulated 

flowpath areal recharge accounts for 

93.7 percent of the sources of water to 

the aquifer system. Leakage from the 

South Fork Zumbro River to the upper 

Prairie du Chien unit of the aquifer 

(layer 9) (4.1 percent) and from the 

Middle Fork Whitewater River to the 

St. Peter unit of the aquifer (layer 7) 

(2.2 percent) are comparatively minor 

sources of water. Most of the areal 

recharge enters the aquifer system 

through the upper carbonate aquifer 

(layers 2 and 3) (66.5 percent) east of 

the edge of the Decorah-PlattevilleGlenwood confining unit and through 

the upper Prairie du Chien unit of the 

aquifer (layer 9) (19.9 percent) west of 

the edge of the confining unit. The 

amount of areal recharge entering the 

aquifer system near the edge of the 

Decorah unit (layer 4) through the 

Platteville unit (layer 5) (3.3 percent) 

and St. Peter unit of the aquifers in 

(layer 7) (9.5 percent) is much less 

than through the upper carbonate aquifer.

The largest simulated discharge 

from the aquifer system is outflow 

through springs and seeps from the 

upper carbonate aquifer (layers 2 and 

3) (61.0 percent). Of the 2.28 ft3

/s of 

areal recharge that enters the upper 

carbonate aquifer, 2.23 ft3

/s is discharged from the aquifer by springs 

and seeps, leaving only 0.05 ft3/s (2.2 

percent) to leak downward to the 

underlying part of the aquifer system. 

Excluding outflow through springs 

and seeps, the largest discharge from 

the aquifer system is by pumpage from 

the three industrial supply wells (layer 

11) simulated in cell (11,2,1), 

1.11 ft3

/s (30.3 percent). The sources 

of water withdrawn by the wells are 

(1) leakage of water from the South 

Fork Zumbro and Middle Fork Whitewater Rivers (0.23 ft3/s, 20.7 percent 

of pumpage), and (2) areal recharge 

(0.88 ft3

/s, 79.3 percent of pumpage) 

(fig. 9a). Some areal recharge entering 

the aquifer system through the upper 

Prairie du Chien, the Platteville, and 

the St. Peter discharges to Bear Creek 

(0.32 ft3

/s, 27.8 percent of that areal 

recharge). The small amount of water 

leaking downward from the upper carbonate aquifer to the underlying aquifer system is withdrawn by the supply 

wells or discharges to Bear Creek. 

Water flows vertically through the 

confining units in the aquifer system in 

both upward and downward directions 

(table 6). Table 6 summarizes simulated vertical leakage between model 

layers in the aquifer system. Much 

larger discharges occur through the 

lower boundary of a hydrogeologic 

unit (downward flow) than through the 

upper boundary (upward flow). The 

largest downward flows are for layers 

9 and 10, due to the greater areal 

extent of their simulated boundaries 

and the influence of the simulated 

pumpage in cell (11,2,1). 

SENSITIVITY ANALYSIS

A model-sensitivity analysis, 

wherein a single hydraulic property or 

flux is varied while all other properties 

and fluxes are held constant, was done 

to identify the relative effect of adjustments of hydraulic properties and 

fluxes on simulated hydraulic heads 

and stream-aquifer leakage. The 

degree to which the properties and 

fluxes were varied was related to the 

uncertainty associated with each. Variations were kept within reported or 

plausible ranges of values.

Simulated hydraulic heads for the 

cross-sectional steady-state model 

were most sensitive to variations in 

areal recharge, horizontal hydraulic 

conductivity of the Prairie du Chien 

and Jordan units of the St. Peter-Prairie du Chien-Jordan aquifer, and streambed hydraulic conductivity (table 

7). Increases in the areal recharge rate 

to zone 2 (zone of greatest simulated 

recharge downslope from the edge of 

the Decorah unit), and both increases 

and decreases in the horizontal 

hydraulic conductivity value for the 

Jordan unit, resulted in the greatest 

mean deviations in hydraulic heads. 

Varying the areal recharge rate to zone 

2 resulted in mean deviations similar 

to those resulting from changing the 

rates to the other four zones combined, 

although the land surface area of zone 

2 constitutes only about 3.5 percent of 

the total area. Varying the vertical 

hydraulic conductivities of the confining units by an order of magnitude had 

no discernible effect on simulated 

hydraulic heads in the aquifer system.

The greatest percent changes in 

stream-aquifer leakage resulted from 

variations in areal recharge and streambed hydraulic conductivity (table 

7). Variations in the horizontal hydraulic conductivity of the Jordan unit also 

resulted in appreciable changes in 

stream-aquifer leakage, particularly in 

leakage from the South Fork Zumbro 

River to the underlying St. Peter-Prairie du Chien-Jordan aquifer due to 
26

AREA NOT A PART OF MODEL

5 10

15 25

50

75

95 100

105

110 115 120 125

130

135

1

961.9

1003.6

1032.1

1035.4

1062.6

1044.1 1055.2

1062.4

1056.5

1058.0

1063.6

1062.8

1230.5

1250.0 1250.0 1280.0

1280.0

1067.1

1068.9

1070.5

1073.0

1079.3

1074.5

SEE FIGURE

8b

1057.4 1035.8 1045.6

1000

1100

1200

1300

1400

500

600

700

800

900

FEET

WEST

A A'

EAST

South Fork Zumbro River

Bear Creek

Middle Fork

Whitewater River

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

COLUMNS

VERTICAL EXAGGERATION X 46

DATUM IS SEA LEVEL

Trace of section shown on figure 3

Model layers, corresponding hydrogeologic units, and simulated equipotential lines, Rochester area, Minnesota.

Model layer boundary

Confining unit

Aquifer

EXPLANATION

Screened interval of well. Number indicates

Simulated equipotential line

measured hydraulic head

1068.9

Inactive

cells

Simulated water table Hypothetical observation well based on potentiometric

indicates mapped hydraulic head

surface contour (from Balaban, 1988). Number

1250.0

Model layers

Upper carbonate aquifer

Glacial drift

Lower part of the upper carbonate aquifer

Upper part of the upper carbonate aquifer

Decorah-Plattevills-Glenwood confining unit

Glenwood unit of the Decorah-Platteville-Glenwood confining unit

Platteville unit of the Decorah-Plateville-Glenwood confining unit

Decorah unit of the Decorah-Platteville-Glenwood confining unit

St. Peter-Prairie du Chien-Jordan aquifer

St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer

Upper Prairie du Chien unit of the St. Peter

Basal St. Peter confining bed

-Prairie du Chien-Jordan aquifer

Lower Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan aquifer

Jordan unit of the St. Peter-Prairie du Chien-Jordan aquifer

St. Lawrence confining unit

(9)

(8)

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(12)

(11)

(10)

Figure 8a.

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(1)

(9)

(8)

(9)

(10)

(10)

(11)

(11)

(12)

(12)

Model layers
27

FEET

1,200

1,180

1,160

1,140

1,120

1,100

1,080

1,060

1,040

1,020

1,000

980

25

30

35

40

45

50

55

60

65

70

75

80

85

90

20

1062.4

Model layers corresponding hydrogeologic units, and simulated equipotential lines near edge of confining

units, Rochester area, Minnesota.

Aquifer

Confining unit

Model layer boundary

EXPLANATION

Simulated equipotential line

Screened interval of well. Number indicates

measured hydraulic head

1062.4

Simulated water table

Glacial drift

COLUMNS

0 1 MILE

0 1 KILOMETER

DATUM IS SEA LEVEL

VERTICAL EXAGGERATION X 46

Upper part of the

upper carbonate

aquifer

Lower part of the upper carbonate aquifer

Decorah unit of the

Decorah-Platteville-Gleenwood

confining unit

Platteville unit of the Decorah-Platteville-Glenwood

confining unit

Glenwood unit of the DecorahPlatteville-Glenwood

confining unit

St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer

Basal St. Peter confining bed

Upper Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan aquifer

Figure 8b.
28

ground-water withdrawals by highcapacity wells. The horizontal hydraulic conductivity of the Jordan unit 

affects the amount of water available 

to the simulated pumped well, and 

therefore the amount of water induced 

to leak downward from the South Fork 

Zumbro River.

Discharge to springs and seeps is 

greatly affected by variations in simulated areal recharge rates to the upper 

carbonate aquifer (recharge zones 4 

and 5), but is minimally affected by 

the other variations. All but a small 

portion of the areal recharge that 

entered the aquifer is discharged 

through springs and seeps, rather than 

leaking downward through the underlying relatively impermeable Decorah 

unit. 

GROUND-WATER 

FLOWPATHS AND TRAVEL 

TIMES

The simulated flowpath lines (figs. 

9–11) indicate that nearly all of the 

areal recharge entering the aquifer system through the upper carbonate aquifer (layers 2 and 3) discharges by 

springs and seeps (represented as 

 Table 5. Simulated water budget from the cross-sectional model of the aquifer system, Rochester area, Minnesota

[Percent is percentage of total sources or of total discharges; --, no source or discharge for a budget component; ft3/s, cubic feet per second] 

Budget component and model layer Source (ft3/s)

Rate Percent

Areal recharge

 Layer 2 (Upper part of the upper carbonate aquifer) 1.90 51.9

 Layer 3 (Lower part of the upper carbonate aquifer) 0.38 10.4

 Layer 5 (Platteville unit of the Decorah-PlattevilleGlenwood confining unit)0.12 3.3

 Layer 7 (St. Peter unit of the St. Peter-Prairie du ChienJordan aquifer)0.35 9.5

 Layer 9 (Upper Prairie du Chien unit of the St. PeterPrairie du Chien-Jordan aquifer)0.68 18.6

 Subtotal 3.43 93.7

 Leakage from streams to the aquifer

 Layer 7 (St. Peter unit of the St. Peter-Prairie du ChienJordan aquifer)0.08 2.2

 Layer 9 (Upper Prairie du Chien unit of the St. PeterPrairie du Chien-Jordan aquifer)0.15 4.1

 Subtotal 0.23 6.3

Total 3.66 100.0

Budget component and model layer Discharge (ft3/s)

Rate Percent

Pumpage

 Layer 11 (Jordan unit of the St. Peter-Prairie du ChienJordan aquifer)1.11 30.3

Outflow through springs and seeps

 Layer 2 (Upper part of the upper carbonate aquifer) 1.50 41.0

 Layer 3 (Lower part of the upper carbonate aquifer) 0.73 20.0

 Subtotal 2.23 61.0

Leakage from the aquifer to streams

 Layer 9 (Upper Prairie du Chien unit of the St. PeterPrairie du Chien-Jordan aquifer)0.32 8.7

Total 3.66 100.0
29

drains in the cross-sectional model) 

into local stream drainages, the Middle Fork Whitewater River drainage, 

or at the edge of the Decorah unit 

(layer 4) (figs. 9a and 9b). The flowpath lines shown in figures 9a and 9b 

were generated with particles placed 

initially on the surface of the uppermost aquifer layer to represent the 

movement of water derived from infiltration of precipitation through the 

aquifer system. Particles were not 

placed in cells representing confining 

units because no areal recharge was 

simulated to confining units. These 

flowpath-line results support the conclusions indicated by the water budget. The simulated flowpath lines 

illustrate that the sources of water 

withdrawn by the simulated supply 

wells in cell (11,2,1) (fig. 9a) are: (1) 

leakage of water from the South Fork 

Zumbro River, (2) leakage from the 

Middle Fork Whitewater Rivers, (3) 

areal recharge through the upper Prairie du Chien unit (layer 9) west of the 

Decorah-Platteville-Glenwood confining unit, and (4) areal recharge 

through the Platteville unit (layer 5) 

and St. Peter unit (layer 7). Results 

indicate that areal recharge to the 

upper Prairie du Chien moves primarily westward and discharges to Bear 

Creek. 

The travel times for particles 

derived from areal recharge to reach 

Table 6. Simulated leakage between model layers from the cross-sectional model of the aquifer system, Rochester area, Minnesota

[--, movement of water through the boundary was only downward, with no upward component of flow; ft3/s; cubic feet per second; <, less than]

Leakage between model layers

Source Discharge

(ft3/s) (ft3/s)

Layer 1 (Glacial drift)— Inactive none none

Layer 2 (Upper part of the upper carbonate aquifer)

 Through lower boundary 0.5919 0.9786

Layer 3 (Lower part of the upper carbonate aquifer)

 Through upper boundary 0.9786 0.5919

 Through lower boundary -- 0.0265

Layer 4 (Decorah unit of the Decorah-Platteville-Glenwood confining unit)

 Through upper boundary 0.0265 --

 Through lower boundary <0.0000 0.0572

Layer 5 (Platteville unit of the Decorah-Platteville-Glenwood confining unit)

 Through upper boundary 0.0572 <0.0000

 Through lower boundary 0.0013 0.1659

Layer 6 (Glenwood unit of the Decorah-Platteville-Glenwood confining unit)

 Through upper boundary 0.1659 0.0013

 Through lower boundary 0.0013 0.2119

Layer 7 (St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer)

 Through upper boundary 0.2119 0.0013

 Through lower boundary 0.0006 0.6189

Layer 8 (Basal St. Peter confining bed)

 Through upper boundary 0.6189 0.0006

 Through lower boundary 0.0006 0.6187

Layer 9 (Upper Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan 

aquifer)

 Through upper boundary 0.6187 0.0006

 Through lower boundary 0.0212 1.1301

Layer 10 (Lower Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan 

aquifer)

 Through upper boundary 1.1301 0.0212

 Through lower boundary 0.0084 1.1174

Layer 11 (Jordan unit of the St. Peter-Prairie du Chien-Jordan aquifer)

 Through upper boundary 1.1174 0.0084

Total 5.5505 5.5505
30

 Table 7. Sensitivity of simulated hydraulic heads and flows in the aquifer system to changes in values of hydrogeologic properties or co

Rochester area, Minnesota

[ft, feet; ft/d, feet per day; in./yr, inches per year; ft3/s, cubic feet per second; --, not applicable; NC, no change; <, less than. Mean deviations of hydraulic heads and ch

calculated by best-fit calibrated simulation. Number in parentheses is percent change in flow]

Hydrologic property 

or condition 

Hydrogeologic unit and 

model layer

Multiplied by 

factor of (or other 

specified 

variation)

Hydraulic heads (ft) Ch

Algebraic value 

of mean 

deviation

Absolute value of 

mean deviation Range Stream leakage to aquifer 

1Areal recharge to 

zones 1, 3, 4 and 5 (in./yr)

1Areal recharge zones shown in figures 7a and 7b.

-- 2.0 30.12 30.12 0.02 to 39.83 -.1743 (77.9) 

.5 -17.38 17.38 -23.93 to -0.02 .1172 (52.4) 

1Areal recharge to 

zone 2 (in./yr)

-- 2.0 31.89 31.89 0.00 to 54.12 -.1235 (55.2) 

.5 -16.7 16.7 -27.59 to 0.00 .0569 (25.4) 

Streambed hydraulic 

conductivity (ft/d)

-- 10.0 14.5 14.5 0.00 to 33.82 .1303 (58.2) 

.1 -5.46 5.55 -15.98 to 1.21 -.1802 (80.6) 

Horizontal hydraulic 

conductivity (ft/d)

Upper carbonate aquifer 240

2Upper limit of range of hydraulic conductivities reported by Kanivetsky and Walton (1979).

-3.03 3.03 -24.32 to -0.03 .0006 (0.3) 

(model layers 2 and 3) 33.0

3Lower limit of range of hydraulic conductivities reported by Kanivetsky and Walton (1979).

4.73 4.73 0.00 to 48.45 -.0018 (0.8) 

Platteville unit of the Decorah-Platteville-Glenwood confining unit 435

4Plausible upper limit in Rochester area.

0.17 0.3

-1.18 to 1.05 .0001 (<0.1) 

(model layer 5) 5.1

5Plausible lower limit in Rochester area.

-0.08 0.11 -0.24 to 0.35 NC 

St. Peter unit of the St. 

Peter-Prairie du ChienJordan aquifer

2.0 -0.71 0.76

-3.14 to 0.31 NC 

(model layer 7) .5 0.47 0.52 -0.30 to 2.19 NC Prairie du Chien unit of 

the St. Peter-Prairie du Chien-Jordan aquifer

2.0 -11.86 11.86

-18.29 to 0.00 .0166 (7.4) 

(model layers 9 and 10) .5 9.11 9.11 0.00 to 13.36 -.0249 (11.1) Jordan unit of the St. 

Peter-Prairie du ChienJordan aquifer

2.0 -29.91 30.37

-56.15 to 5.07 -.1451 (64.9) 

(model layer 11) .5 30.87 31.58 -9.16 to 45.01 .0940 (42.0) 

Vertical hydraulic 

conductivity (ft/d)

Decorah and Glenwood 

units of the DecorahPlatteville-Glenwood confining unit

10.0 0.00 0.00 NC NC 

.1 0.00 0.00

NC NC 

(model layers 4 and 6)Basal St. Peter confining 10.0 0.00 0.00 NC NC bed (model layer 8) .1 0.00 0.00 NC NC 
31

the three end points, or sinks, in the 

simulated aquifer system ranged from 

less than 1 year to as long as 400 years. 

The travel times for simulated water 

particles entering the upper carbonate 

aquifer (layers 2 and 3) to reach a drain 

cell ranged from 1 to 25 years, with 

most particles reaching a drain within 

5 to 10 years. Water particles derived 

from areal recharge to the upper Prairie du Chien unit (layer 9) had maximum simulated travel times of 60–70 

years before discharging to Bear 

Creek and from 50 to 200 years to 

reach the simulated supply well (fig. 

9a). Water particles derived from areal 

recharge to the Platteville unit (layer 

5) and St. Peter unit (layer 7) near the 

edge of the Decorah unit had simulated travel times of 125–400 years to 

reach the supply well. 

The flowpath lines in figure 10 represent the movement of water through 

the St. Peter-Prairie du Chien-Jordan 

aquifer from the eastern regional 

ground-water flow divide to the west. 

These flowpath lines were generated 

with particles placed initially on the 

eastern model boundary. The simulated flowpath lines indicate that flow 

is predominantly horizontal in the St. 

Peter and Jordan units. Flow is predominantly vertical in the lower Prairie du Chien unit because the 

horizontal hydraulic conductivity is an 

order of magnitude lower than for the 

other three aquifer units (table 3). The 

simulated flowpath lines indicate both 

vertical and horizontal components of 

flow for the upper Prairie du Chien 

unit, which has a horizontal hydraulic 

conductivity lower than the St. Peter 

and Jordan. All the simulated flowpath 

lines terminate at the simulated supply 

well with travel times of 1,500–1,750 

years. 

The flowpath lines shown in figure 

11 were generated with particles 

placed near the top of the lower part of 

the upper carbonate aquifer (layer 3). 

The simulated flowpath lines indicate 

that the particles flow toward and discharge to the simulated drains in the 

upper and lower parts of the upper carbonate aquifer (layers 2 and 3). 

MODEL EXPERIMENTS

The steady-state cross-sectional 

model was used to investigate hypothetical variations in the representation of selected hydrogeologic units, 

differing areal recharge distributions, 

and the effects of simulated pumpage. 

Results of the hypothetical simulations are summarized in table 8. 

The simulation of greater hydraulic 

conductivity values (scenario A) 

resulted (1) in much lower hydraulic 

heads in all model columns, except in 

column 1, (2) large increases in leakage from the South Fork Zumbro 

River to the combined Prairie du 

Chien unit (140 percent), and (3) large 

increases in leakage from the combined unit to Bear Creek (66 percent) 

(table 8). Vertical flows within the 

combined unit were also increased. 

These effects occur because the 

greater simulated hydraulic conductivities for the lower Prairie du Chien 

(compared to those for the calibrated 

simulation) result in more rapid movement of water through the unit from 

west to east and also vertically. 

Lesser hydraulic conductivity values (scenario B) conversely resulted in 

(1) much higher hydraulic heads, (2) 

large decreases in stream-aquifer leakage rates, and (3) somewhat reduced 

vertical flows within the combined 

unit of the upper Prairie du Chien. The 

results of scenario C are similar to 

those for scenario A, but the changes 

in hydraulic heads and rates of flow 

are of lesser magnitude. 

Combining the upper and lower 

parts of the upper carbonate aquifer 

(layers 2 and 3, respectively) in simulations D and E resulted in comparatively small changes in hydraulic 

heads (mean absolute difference of 

2.10 ft) and virtually no change in 

stream-aquifer leakage and flows 

through layer boundaries. The differences between the scenario D and calibrated discharge to drains for the 

upper and lower parts of the upper carbonate aquifer were less than 

0.01 ft3

/s. Scenario E eliminates vertical flow downward from the upper 

carbonate aquifer to the underlying 

part of the aquifer system. The results 

of scenario E indicate that although the 

rate of leakage of water downward is 

comparatively small (0.0265 ft3/s), the 

effects on hydraulic heads of eliminating this downward leakage are appreciable, with a lowering of hydraulic 

heads in all aquifer units by a mean of 

10.95 ft.

In scenario F, the Decorah, Platteville, and Glenwood units were combined to form a single confining unit, 

similar to other numerical groundwater flow models (Delin, 1990; 

Schoenberg, 1990). Results indicate 

that leakage from the South Fork Zumbro River to the upper Prairie du Chien 

unit (layer 9) increases and discharge 

from the upper Prairie du Chien to 

Bear Creek decreases. This is due to 

less water being available to move 

through the aquifer system from east 

to west and ultimately discharge to 

Bear Creek or be withdrawn by the 

simulated pumped well in cell 

(11,2,1). The change in the rate of flow 

downward is much greater for scenario F than for scenario E because no 

areal recharge to the Platteville (layer 

5) is simulated in scenario F. 

Scenarios G and H both indicate no 

change in stream-aquifer leakage due 

to the simulated absence of the Glenwood and basal St. Peter confining bed 

(table 8). Their presence has a large 

effect on the simulated vertical 

hydraulic gradient between the St. 

Peter unit (layer 7) and upper Prairie 

du Chien unit (layer 9). Scenario H 

indicated that the simulated difference 

in hydraulic heads between the two 

units at the nested well site located in 

T106NR13W, section 3 was only 0.2 

ft, whereas the measured difference in 

head was 7.2 ft. 

The results of Scenario I indicate 

that a reduction in recharge of about 70 

percent would result in a mean decline 
32

AREA NOT PART OF MODEL

5 10

15 25

50

75

95

100

105

110 115 120 125

130

135

1

of supply wells

Screened interval

Model layers

Upper carbonate aquifer

Glacial drift

Lower part of the upper carbonate aquifer

Upper part of the upper carbonate aquifer

Decorah-Plattevills-Glenwood confining unit

Glenwood unit of the Decorah-Platteville-Glenwood confining unit

Platteville unit of the Decorah-Plateville-Glenwood confining unit

Decorah unit of the Decorah-Platteville-Glenwood confining unit

St. Peter-Prairie du Chien-Jordan aquifer

St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer

Upper Prairie du Chien unit of the St. Peter

Basal St. Peter confining bed

-Prairie du Chien-Jordan aquifer

Lower Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan aquifer

Jordan unit of the St. Peter-Prairie du Chien-Jordan aquifer

St. Lawrence confining unit

(9)

(8)

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(12)

(11)

(10)

1000

1100

1200

1300

1400

500

600

700

800

900

FEET

WEST

A A'

EAST

South Fork Zumbro River

Bear Creek

Middle Fork

Whitewater River

SEE FIGURE

9b

0 1 2 3 4 5 MILES0 1 2 3 4 5 KILOMETERS

VERTICAL EXAGGERATION X 46

DATUM IS SEA LEVEL

Trace of section shown on figure 3

Hydrogeologic units and flowpath-line plot representing the movement of recharge water derived from infiltration of precipitation through the aquifer

system, Rochester area, Minnesota.

COLUMNS

Figure 9a.

River cell

Confining unit

Aquifer

Model layer boundary

Drain cell Particle flowpath line. Forward

direction of ground-water flow

surface. Arrow indicates

tracking from recharge

EXPLANATION

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(1)

(9)

(8)

(9)

(10)

(10)

(11)

(11)

(12)

(12)

Model layers
33

Aquifer

Confining unit

Drain cell

Model layer boundary

EXPLANATION

FEET

1,200

1,180

1,160

1,140

1,120

1,100

1,080

1,060

1,040

1,020

1,000

980

25

30

35

40

45

50

55

60

65

70

75

80

85

90

20

Hydrogeologic units and flowpath-line plot representing the movement of recharge water derived from infiltration

of precipitation through the aquifer system near edge of confining units, Rochester area, Minnesota.

COLUMNS

0 1 MILE

0 1 KILOMETER

DATUM IS SEA LEVEL

VERTICAL EXAGGERATION X 46

Glacial drift

Upper part of the

upper carbonate

aquifer

Lower part of the upper carbonate aquifer

Decorah unit of the

Decorah-Platteville-Gleenwood

confining unit

Platteville unit of the Decorah-Platteville-Glenwood

confining unit

Glenwood unit of the DecorahPlatteville-Glenwood

confining unit

St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer

Basal St. Peter confining bed

Upper Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan aquifer

Particle flowpath line. Forward tracking

from recharge surface. Arrow indicates

direction of ground-water flow

Figure 9b.
34

AREA NOT PART OF MODEL

5 10

15 25

50

75

95

100

105

110 115 120 125

130

135

1

of supply wells

Screened interval

1000

1100

1200

1300

1400

500

600

700

800

900

FEET

WEST

A A'

EAST

South Fork Zumbro River

Bear Creek

Middle Fork

Whitewater River

Hydrogeologic units and flowpath-line plot representing the movement of water originating near the eastern model boundary through the aquifer

system, Rochester area, Minnesota.

COLUMNS

Model layers

Upper carbonate aquifer

Glacial drift

Lower part of the upper carbonate aquifer

Upper part of the upper carbonate aquifer

Decorah-Plattevills-Glenwood confining unit

Glenwood unit of the Decorah-Platteville-Glenwood confining unit

Platteville unit of the Decorah-Plateville-Glenwood confining unit

Decorah unit of the Decorah-Platteville-Glenwood confining unit

St. Peter-Prairie du Chien-Jordan aquifer

St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer

Upper Prairie du Chien unit of the St. Peter

Basal St. Peter confining bed

-Prairie du Chien-Jordan aquifer

Lower Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan aquifer

Jordan unit of the St. Peter-Prairie du Chien-Jordan aquifer

St. Lawrence confining unit

(9)

(8)

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(12)

(11)

(10)

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

VERTICAL EXAGGERATION X 46

DATUM IS SEA LEVEL

Trace of section shown on figure 3

River cell

Confining unit

Aquifer

Model layer boundary

Drain cell Particle flowpath line. Forward

direction of ground-water flow

surface. Arrow indicates

tracking from recharge

EXPLANATION

Figure 10.

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(1)

(9)

(8)

(9)

(10)

(10)

(11)

(11)

(12)

(12)

Model layers
35

AREA NOT PART OF MODEL

5 10

15 25

50

75

95

100

105

110 115 120 125

130

135

1

of supply wells

Screened interval

1000

1100

1200

1300

1400

500

600

700

800

900

FEET

WEST

A A'

EAST

South Fork Zumbro River

Bear Creek

Middle Fork

Whitewater River

Hydrogeologic units and flowpath-line plot representing the movement of water originating near the top of layer 3 (lower part of upper carbonate

aquifer) through the aquifer system, Rochester area, Minnesota.

COLUMNS

Model layers

Upper carbonate aquifer

Glacial drift

Lower part of the upper carbonate aquifer

Upper part of the upper carbonate aquifer

Decorah-Plattevills-Glenwood confining unit

Glenwood unit of the Decorah-Platteville-Glenwood confining unit

Platteville unit of the Decorah-Plateville-Glenwood confining unit

Decorah unit of the Decorah-Platteville-Glenwood confining unit

St. Peter-Prairie du Chien-Jordan aquifer

St. Peter unit of the St. Peter-Prairie du Chien-Jordan aquifer

Upper Prairie du Chien unit of the St. Peter

Basal St. Peter confining bed

-Prairie du Chien-Jordan aquifer

Lower Prairie du Chien unit of the St. Peter-Prairie du Chien-Jordan aquifer

Jordan unit of the St. Peter-Prairie du Chien-Jordan aquifer

St. Lawrence confining unit

(9)

(8)

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(12)

(11)

(10)

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS

VERTICAL EXAGGERATION X 46

DATUM IS SEA LEVEL

Trace of section shown on figure 3

River cell

Confining unit

Aquifer

Model layer boundary

Drain cell Particle flowpath line. Forward

direction of ground-water flow

surface. Arrow indicates

tracking from recharge

EXPLANATION

Figure 11.

(7)

(6)

(5)

(4)

(3)

(2)

(1)

(1)

(9)

(8)

(9)

(10)

(10)

(11)

(11)

(12)

(12)

Model layers
36

 Table 3. Results for the cross-sectional model experiments, Rochester area, Minnesota Table 3. Results for the cross-sectional model experiments, Rochester area, Minnesota 

[Kh, horizontal hydraulic conductivity; Kv, vertical hydraulic conductivity; ft, feet; ft/d, feet per day; ft3/d, cubic feet per day; ft3/s, cubic feet per second; in./yr, inches per y

as the algebraic sum of the differences between simulated hydraulic heads for the scenario and for the best-fit calibrated simulation divided by the number of wells; mean 

of the absolute values of the differences divided by the number of wells; change in flow is the difference in flow rate between the flow rate for the best-fit calibrated simul

tion; NC, no change in rate of flow]

Scenario Conditions of scenario

Changes in hydraulic 

heads (ft) Changes in flow 

Mean

 algebraic 

difference

Mean

 absolute 

difference

Leakage from South 

Fork Zumbro River to 

layer 9 (upper Prairie 

du Chien)

Leakage from layer 9 

(upper Prairie du Chien) 

to Bear Creek

Rate Percent Rate Percent 

A Upper and lower Prairie du Chien units of the St. Peter-Prairie 

du Chien-Jordan aquifer (layers 9 and 10) combined to form a single unit with a uniform Kh of 12.5 ft/d and Kv of 1.0 ft/d

-16.93 17.52 0.21 140 0.21 66 

B Upper and lower Prairie du Chien units of the St. Peter-Prairie 

du Chien-Jordan aquifer (layers 9 and 10) combined to form a single unit with a uniform Kh of 0.85 ft/d and Kv of 0.05 ft/d

20.41 20.82 -0.11 73 -0.11 34 

C Bottom boundary of upper Prairie du Chien unit of the St. 

Peter-Prairie du Chien-Jordan aquifer (layer 9) lowered by 100 ft, thereby increasing the thickness of the upper Prairie du Chien unit and decreasing the thickness of the lower Prairie du Chien unit

-9.60 10.65 0.08 44 0.08 25 

D Upper and lower parts of the upper carbonate aquifer (layers 2 

and 3) combined to form a single unit with a uniform Kh of 20 ft/d and a Kv of 2.0 ft/d

-0.48 2.10 NC NC 

2 

E Vertical flow downward from the upper carbonate aquifer 

eliminated by simulating layers 2 and 3 as inactive and assigning zero areal recharge to model columns 63–134 where layers 2 and 3 are uppermost bedrock units

-10.95 10.95 0.02 13 -0.06 19 

F Decorah, Platteville, and Glenwood units of the Decorah-Platteville-Glenwood confining unit (layers 4, 5, and 6) combined 

to form a single confining unit with a uniform Kh of 1.00E-05 and a Kv of 1.00E-05

-10.99 11.10 0.04 27 -0.10 31 

G Glenwood unit of the Decorah-Platteville-Glenwood confining unit (layer 6) eliminated by assigning cells representing it 

hydraulic properties of layer 5 (Platteville)

0.12 1.87 NC NC 

.

H Basal St. Peter confining bed (layer 8) eliminated by assigning 

cells representing it hydraulic properties of layer 7 (St. Peter)

-0.78 1.91 NC NC 

I Areal recharge in zone of highest rate near edge of the Decorah unit of Decorah-Platteville-Glenwood confining unit 

(model columns 29-44, 47–53) decreased from 23.75 in/yr to 7.5 in/yr

-21.88 21.99 0.07 47 -0.20 62 

J Pumpage eliminated from the simulation 16.83 17.24 -0.15 100 0.96 300 

K Pumpage rate increased by 50 percent, with a simulated total 

pumpage rate from layer 10 (lower Prairie du Chien) and layer 11 (Jordan) of 1.66 ft3/s in row 2,column 1

-9.28 9.39 0.24 160 -0.32 100 
37

in hydraulic heads in the aquifer system of 21.99 ft (table 8). The lower 

recharge rate near the edge of the Decorah resulted in less water available 

for discharge to Bear Creek and less 

water available for withdrawal by the 

simulated supply well. 

The results of Scenario J indicate 

that removal of pumpage from the well 

would cause (1) hydraulic heads to rise 

an average of about 17 ft, (2) a 300 

percent increase in ground-water discharge to Bear Creek, and (3) a reversal in flow directions for streamaquifer leakage for the South Fork 

Zumbro River (table 8). The simulated 

flow direction was from the upper 

Prairie du Chien unit to the river 

because ground-water pumpage was 

no longer lowering hydraulic heads 

near the river and thereby inducing 

downward leakage. 

Results of scenario K indicate that 

a 50 percent increase in pumpage 

would cause (1) large declines in 

hydraulic heads (mean difference of 

9.39 ft.), (2) large changes in streamaquifer leakage rates, and (3) large 

increases in rates of downward leakage through the lower boundaries of 

the upper and lower Prairie du Chien 

(layers 9 and 10, respectively) (table 

8). 

MODEL LIMITATIONS

A ground-water-flow model is a 

practical tool for simulating the 

response of the aquifer system to areal 

recharge and stresses (pumpage) on 

the system. A model is a simplification 

of a complex flow system. The accuracy of the simulations is limited by 

the accuracy of the data used to 

describe the properties of the aquifers 

and the confining units, areal recharge 

rates, pumpage, streambed-leakage 

coefficients, and boundary conditions. 

In addition, a combination of assigned 

inputs different from that used in a 

simulation could produce the same 

result. 

Improvements in the accuracy of 

the various inputs to the model could 

enhance model accuracy. Additional 

information that would be beneficial 

includes hydraulic conductivities for 

the Prairie du Chien unit, spatial distribution of and variations in hydraulic 

conductivity, and additional hydrogeologic data for the part of the aquifer 

system overlying the Prairie du Chien 

unit. 

DISCUSSION OF RECHARGE 

AND GROUND-WATER FLOW

The areal recharge rates derived 

from the three different methods of 

analysis are generally similar for a 

given aquifer unit and hydrogeologic 

setting (table 2). The differences in 

areal recharge rates for sites with estimated rates of less than 10 in./yr are all 

3.3 in./yr or less, and for the site on the 

slope of the main valley in the zone of 

greatest recharge is 9.8 in./yr. The estimate of areal recharge derived from 

hydrograph analysis is greater than the 

estimate derived from CFC age-dating 

in five of the eight wells. These estimates are reasonably similar, considering the hydrograph-analysis 

estimates are for one year (1998) and 

the CFC age-dating estimates represent an average recharge rate over the 

period of time that water had been in 

the saturated zone. Both methods of 

analysis indicated that a much greater 

rate of areal recharge occurs to the St. 

Peter unit downslope from the edge of 

the Decorah-Platteville-Glenwood 

confining unit than occurs to the Prairie du Chien unit in any hydrogeologic 

setting. 

The numerical-model analysis 

indicated that the zone of increased 

recharge near the edge of the DecorahPlatteville-Glenwood confining unit 

has an effect on flow in the aquifer 

system and constitutes an important 

source of water to high-capacity wells 

in the Rochester area and discharge to 

Bear Creek.The best-fit calibrated 

areal recharge value from the crosssectional model of 23.75 in./yr for the 

site downslope from the edge of the 

Decorah-Platteville-Glenwood confining unit (Minnesota unique well 

number 601284) is in close agreement 

with the estimate of 25.5 in./yr derived 

from hydrograph analysis The modelsimulated discharge from the lower 

part of the upper carbonate aquifer 

(layer 3) located upslope from the confining unit (fig. 9b) was 0.21 ft3/s. 

Based on the simulated area of the 

slope above the confining unit, this 

rate of discharge represents a potential 

source of water of 33 in./yr to the St. 

Peter, assuming a maximum groundwater evapotranspiration rate of 

27 in./yr (70 percent of the pan-evaporation rate). The rate of 33 in./yr is 

similar to the estimated areal recharge 

rates derived from hydrograph analysis and CFC age-dating in the zone of 

highest recharge. The best-fit calibrated recharge value of 5.1 in./yr for 

the zone west of the edge of the confining unit where the Prairie du Chien 

unit is the uppermost bedrock unit is 

similar to the mean value of 5.9 in./yr 

for that hydrogeologic setting derived 

from hydrograph analysis (table 1). 

The cross-sectional model simulated leakage rates of 0.5–1.0 in./yr 

where the aquifer is overlain by the 

Decorah-Platteville-Glenwood confining unit. By comparison, Delin 

(1990) calculated a rate of leakage of 

0.1 in./yr, using Darcy’s Law. The 

recharge estimates derived from 

hydrograph analysis were greater (as 

much as 2 in./yr), which may be due to 

pumpage effects. This leakage value 

may also be an order of magnitude or 

more too high because porosity was 

used in the hydrograph-analysis calculations rather than specific yield. 

The calibrated model results indicated that most of the areal recharge to 

the upper carbonate aquifer discharges 

to springs and seeps (drains), with 

minimal leakage downward through 

the Decorah. The effect of the zone of 

increased recharge is indicated by simulated leakage rates between the units 

of the St. Peter-Prairie du Chien-Jor-
38

dan aquifer that are approximately 10 

times greater near the edge of the Decorah than they are more distant from 

the edge. The amount of water withdrawn by pumped wells or discharged 

to Bear Creek is derived predominantly from areal recharge near the 

edge of the Decorah (0.47 ft3

/s), rather 

than from water that has leaked downward through the Decorah (0.03 ft3/s). 

Model results indicate that 0.21 ft3

/s 

discharges from the upper carbonate 

aquifer through springs and seeps and 

subsequently infiltrates into the St. 

Peter downslope from the Decorah. 

Decreasing the simulated areal 

recharge rate downslope from the 

Decorah (23.75 in./yr) to the same 

simulated rate as for upslope from the 

Decorah (7.5 in./yr) (scenario I) 

resulted in a 47 percent increase in 

leakage from the South Fork Zumbro 

River to the upper Prairie du Chien 

and a 62 percent decrease in leakage 

from the upper Prairie du Chien to 

Bear Creek. 

The hydraulic conductivities of the 

Prairie du Chien unit and the DecorahPlatteville-Glenwood confining unit 

affect flow in the aquifer system. Representing the upper and lower units of 

the Prairie du Chien as single unit 

with higher or lower uniform hydraulic conductivities resulted in appreciably higher or lower rates of streamaquifer leakage and vertical leakage 

between the units, respectively. Simulating the Platteville with a low 

hydraulic conductivity (scenario F) 

resulted in a reduction of 64 percent in 

flow downward through the lower 

boundary and less water available to 

the lower part of the aquifer system. 

The simulation that, in effect, eliminated the Glenwood unit of the Decorah-Platteville-Glenwood confining 

unit (scenario G) resulted in an 

increase of 43 percent in flow downward through the lower boundary, but 

virtually no change in simulated 

stream-aquifer leakage. The reason for 

the difference in stream-aquifer leakage between scenarios F and G is that 

for scenario F no areal recharge was 

simulated to the Platteville, further 

illustrating the appreciable effects of 

the zone of increased areal recharge on 

flow in the aquifer system. 

SUMMARY

The primary source of ground water for the city of Rochester, Olmsted County, southeastern Minnesota is the St. 

Peter-Prairie du Chien-Jordan aquifer. Based on results of a 

previous U.S. Geological Survey investigation in the Rochester area, relatively high rates of areal recharge to the St. 

Peter-Prairie du Chien-Jordan aquifer occur along the edge 

of the overlying Decorah-Platteville-Glenwood confining 

unit. The primary source of water to the zone of increased 

recharge along the edge of the confining unit is the upper 

carbonate aquifer. 

Ground-water recharge rates to the three units comprising the St. Peter-Prairie du Chien-Jordan aquifer were estimated from water-level measurements using the method of 

hydrograph analysis. The estimated ground-water recharge 

rates to the aquifer during all of 1998 ranged from 1.9 to 

25.5 in./yr. Recharge rates decreased with depth of the aquifer unit in a similar hydrogeologic setting. Recharge rates 

were greatest near the edge of the confining unit (with 

means as great as 13.8 in./yr) and least where the confining 

unit is thick and overlain by the upper carbonate aquifer 

(mean of 2.0 in./yr). Recharge rates downslope from the 

edge of the confining unit were greatest to the St. Peter on 

the slope of the South Fork Zumbro River Valley (as much 

as 25.5 in./yr). Results of ground-water age dating using 

chlorofluorocarbons (CFCs) indicated recharge dates ranging from (1) the mid-1950’s to the early 1990’s for the St. 

Peter, (2) the late 1960’s to approximately 1990 for the Prairie du Chien, and (3) the early to mid-1950’s for the Jordan. 

The estimated areal recharge rates derived from 

hydrograph analysis and from CFC age-dating were in good 

agreement. The differences in areal recharge rates for sites 

with estimated rates of less than 10 in./yr were all 3.3 in./yr 

or less, and for the site on the slope of the main valley in the 

zone of greatest recharge was 9.8 in./yr. The best-fit calibrated model areal recharge value of 23.75 in./yr is in close 

agreement with the estimate of 25.5 in./yr derived from 

hydrograph analysis for the site downslope from the edge of 

the Decorah-Platteville-Glenwood confining unit in the 

zone of increased areal recharge. The model-simulated discharge from springs and seeps in the lower part of the upper 

carbonate aquifer (0.21 ft3/s) located upslope from the confining unit represents a potential source of water of 33 in./yr 

to the St. Peter. The rate of 33 in./yr is similar to the estimated areal recharge rates derived from hydrograph analysis and CFC age-dating. 

Predominantly horizontal flow occurs in the upper carbonate and St. Peter-Prairie du Chien-Jordan aquifers and 

predominantly vertical flow occurs through the DecorahPlatteville-Glenwood confining unit separating the aquifers. 

Hydraulic heads in the upper carbonate aquifer are approximately 200 ft higher than in the St. Peter-Prairie du ChienJordan aquifer. The large vertical gradients indicate that 

water from the upper carbonate aquifer will move vertically 

downward where the Decorah-Platteville-Glenwood confining unit contains any joints or other pathways open to the 

St. Peter-Prairie du Chien-Jordan aquifer.

A numerical cross-sectional ground-water-flow model 

was constructed and calibrated for steady-state conditions. 

Along the flowpath, areal recharge accounts for 93.7 percent of the of the sources of water to the aquifer system. 

Most of the areal recharge enters the aquifer system through 
39

the upper carbonate aquifer (66.5 percent) and through the 

upper Prairie du Chien unit (19.9 percent). Although the 

amount of areal recharge entering the aquifer system near 

the edge of the Decorah unit through the Platteville (3.3 percent) and St. Peter (9.5 percent) is much less than through 

the upper carbonate aquifer, the recharge is occurring over a 

much smaller land surface area, and in that context is disproportionately large. 

The largest simulated discharge from the aquifer system 

is outflow through springs and seeps from the upper carbonate aquifer (61.0 percent). Of the 2.28 ft3/s of areal recharge 

that enters the upper carbonate aquifer, 2.23 ft3

/s is discharged from the aquifer by springs and seeps, leaving only 

0.05 ft3/s (2.2 percent) to leak downward to the underlying 

part of the aquifer system. 

A particle-tracking program MODPATH was used to 

compute ground-water flowpath lines based on output from 

the calibrated steady-state cross-sectional model. The simulated flowpath lines indicate that nearly all of the areal 

recharge entering the aquifer system through the upper carbonate aquifer discharges by springs and seeps into local 

stream drainages, the Middle Fork Whitewater River drain 

age, or at the edge of the Decorah unit. The simulated flowpath lines indicate that areal recharge entering the aquifer 

system through the Platteville and St. Peter near the edge of 

the Decorah moves primarily vertically downward to the 

Jordan and then horizontally to the simulated supply well.

The calibrated steady-state cross-sectional model was 

used to investigate hypothetical variations in the representation of selected hydrogeologic units, differing areal 

recharge distributions, and the effects of simulated pumpage. Combining the upper and lower parts of the upper carbonate aquifer (Scenario D) resulted in comparatively small 

changes in hydraulic heads (mean absolute difference of 

2.10 ft) and virtually no change in stream-aquifer leakage 

and flows through layer boundaries.

The hydraulic properties of the Decorah-PlattevilleGlenwood confining unit have an affect on flow in the aquifer system. Simulating the confining unit with uniform low 

hydraulic conductivities resulted in a reduction of 64 percent in leakage through the bottom of the confining unit. 

The simulation in effect eliminating the Glenwood part of 

the Decorah-Platteville-Glenwood confining unit resulted 

in a 43 percent increase in flow through the bottom of the 

layer. A simulated scenario indicated that although the basal 

St. Peter confining bed has minimal effect on flows in the 

aquifer system, the confining bed has a large effect on the 

simulated vertical hydraulic gradient between the St. Peter 

and upper Prairie du Chien units of the St. Peter-Prairie du 

Chien-Jordan aquifer.

The cross-sectional model simulations indicated that the 

amount of water withdrawn by pumped wells or discharged 

to Bear Creek is derived predominantly from areal recharge 

near the edge of the Decorah-Platteville-Glenwood confining unit (0.47 ft3

/s), rather than from water that has leaked 

downward through the unit (0.03 ft3/s). Decreasing the simulated areal recharge rate downslope from the Decorah 

(23.75 in./yr) to the same simulated rate as for upslope from 

the Decorah (7.5 in./yr) resulted in a 47 percent increase in 

leakage from the South Fork Zumbro River to the upper 

Prairie du Chien and a 62 percent decrease in leakage from 

the upper Prairie du Chien unit to Bear Creek. 
40

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