U.S. Department of the Interior

U.S. Geological Survey

Simulation of Ground-Water Flow and 

Delineation of Areas Contributing Recharge 

within the Mt. Simon-Hinckley Aquifer to Well 

Fields in the Prairie Island Indian Community, 

Minnesota 

By J.F. Ruhl 

Water-Resources Investigations Report 02-4155 

Prepared in cooperation with the Prairie Island Indian Community 
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. Geological Survey. 

Mounds View, Minnesota, 2002 

For additional information write to: 

U.S. Geological Survey 

District Chief 

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, MS 517 

Federal Center 

Denver, CO 80225 

Information regarding the USGS is available on the Internet via the World Wide Web. 


You may connect to the USGS Home Page using the Universal Resource Locator (URL) at http://www.rvares.er.usgs.gov 


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Water-Resources Investigations Report 02-4155

CONTENTS


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

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

Purpose and scope .......................................................................................................................................................... 3

Previous investigations................................................................................................................................................... 3

Hydrogeologic setting .................................................................................................................................................... 3

Simulation of ground-water flow.......................................................................................................................................... 4

Model design and discretization..................................................................................................................................... 4

Model geometry and hydraulic properties ..................................................................................................................... 4

Model boundary conditions............................................................................................................................................ 4

Inflows .....................................................................................................................................................................6

Outflows ..................................................................................................................................................................6

Model calibration ........................................................................................................................................................... 6

Model sensitivity ............................................................................................................................................................ 9

Delineation of recharge areas ............................................................................................................................................... 9

Model limitations.................................................................................................................................................................. 9

Summary............................................................................................................................................................................. 10

References........................................................................................................................................................................... 10

ILLUSTRATIONS 

Figures 1-3. Maps showing: 

1. Location map, study area, model grid boundaries, and two well fields, Prairie Island Indian Community, 

east-central Minnesota .......................................................................................................................................... 2

2. Model grid and simulated potentiometric surface for the Mt. Simon-Hinckley aquifer, Prairie Island Indian 

Community, east-central Minnesota..................................................................................................................... 5

3. Recharge areas for well fields A and B based on a rate of withdrawal of 625 cubic meters per day for 

each well field, Prairie Island Indian Community, east-central Minnesota.......................................................... 6

TABLES 

1. Simulated volumetric water budget for the steady-state ground-water flow model under non-pumping

and pumping conditions for the Prairie Island Indian Community, east-central Minnesota ................................. 7

2. Sensitivity analysis of calibrated ground-water flow model of the Mt. Simon-Hinckley aquifer in the 

Prairie Island Indian Community, east-central Minnesota .................................................................................... 8

CONVERSION FACTORS 

Multiply: By: To obtain: 

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

square meter per day (m2

/d) 10.76 square foot per day 

cubic meter per day (m3

/d) 35.3 cubic foot per day 

cubic meter per day per kilometer (m3

/d/km) 56.8 cubic foot per day per mile 

kilometer (km) .6215 mile 

Sea level: Vertical coordinate information is referenced to the North American Vertical Datum of 1988. 

iii 
iv
Simulation of Ground-Water Flow and 

Delineation of Areas Contributing Recharge 

within the Mt. Simon-Hinckley Aquifer to Well 

Fields in the Prairie Island Indian Community, 

Minnesota 

By James F. Ruhl 

ABSTRACT 

The Prairie Island Indian Community in east-central Minnesota uses ground water from the Mt. Simon-Hinckley aquifer 

as its source of water supply. Tribal officials implemented a Source Water Protection Program to protect the quality of this 

water. Areas of contributing recharge were delineated for two community well fields. At well field A are two wells 325 m 

apart, and at well field B are two wells 25 m apart. 

A steady state single layer, two-dimensional ground-water flow model constructed with the computer program MODFLOW, combined with the particle-tracking computer program MODPATH, was used to track water particles (upgradient) 

from the two well fields. A withdrawal rate of 625 m3/d was simulated for each well field. The ground-water flow paths 

delineated areas of contributing recharge that are 0.38 and 0.65 km2

 based on 10- and 50-year travel times, respectively. 

The flow paths that define these areas extend for maximum distances of about 350 and 450 m, respectively, from the wells. 

At well field A the area of contributing recharge was delineated for each well as separate withdrawal points. At well field B 

the area of contributing recharge was delineated for the two wells as a single withdrawal point. Delineation of areas of contributing recharge to the well fields from land surface would require construction of a multi-layer ground-water flow 

model. 

INTRODUCTION ground water to four community SWPP to assist State and local agenwells, two each located in separate cies and other entities in the developThe Prairie Island Indian Commu- well fields. At one of the well fields ment of strategies to protect areas that 

nity (hereinafter referred to as the (identified as A, fig. 1), the wells are surround water-supply wells against study area) is located along the Mis- about 325 m apart, and at the other infiltration, percolation, and transport sissippi River in Goodhue County, well field (identified as B, fig. 1), the of leachate to ground water. The gen- which is southeast of the seven- wells are about 25 m apart. These eral goals of the SWPP are to: (1) county Twin Cities metropolitan area wells are open to the Mt. Simon- delineate sensitive areas around pub- in east-central Minnesota (fig. 1). The Hinckley aquifer, a confined sedimencommunity is surrounded by rivers, tary bedrock aquifer. A priority water- lic water-supply wells for protection 

lakes, and wetlands and is underlain management goal of community offi- against potential contamination of 

by surficial (water-table) and buried cials is delineation of recharge areas source ground water to the wells; (2) 

(confined) aquifers. Ground water is around the two well fields for protec- identify within these areas potential 

the source of water supply in the tion against ground-water contamina- sources of contamination that may 

study area. tion. Water managers for the adversely affect the water supply produced by the wells; and (3) identify Protection of the quality of ground community have initiated a SWPP 

water is an important natural resource (Source Water Protection Program) to alternative water supplies for use in 

issue for community officials. Of par- satisfy this goal. the event that current supplies become 

ticular concern to these officials is The U.S. Environmental Protec- contaminated (U.S. Environmental 

potential contamination of sources of tion Agency (1987) designed the Protection Agency, 1987). 

1 
A D 

Clear Lake 

North 

Lake 

Sturgeon Lake 

Vermillion 

River 

Mississippi River 

Goose Lake 

Cannon 

River 

Lock and 

Dam No. 3 

Specified head

model boundary 

No-flow model boundary 

No-flow model boundary 

GOODHUE CO. 

PIERCE CO. 

WISCONSIN 

D 

D 

D 

See Figure 3 

Inset A 

See Figure 3 

Inset B 

2 4 

0 2 4 6 KILOMETERS

0 

A 

B 

C 

Reservation lands 

(Coincident with subcrop of Mt. Simonunconsolidated valley sediments) 

(Coincident with subcrop of Eau Claire 

confining unit, which separates the 

Mt. Simon-Hinckley aquifer from overlying 

unconsolidated valley sediments) 

MINNESO

River

Minnesota 

River 

Lake Superior 

94° 

92° 

90° 

96° 

48° 

46° 

44° 

0 50 

0 50 

Study 

Area 

Location Map 

Mississippi 

Seven County Twin Cities

Metropolitan Area 

Upstream Downstream 

92o45' 

92o40' 

92o35' 

44o35' 

44o40' 

DAKOTA CO.

MINNESOTA 

6 MILES 

High-conductance river model boundary. 

Hinckley aquifer, which directly underlies 

Low-conductance river model boundary. 

Well field. (Letter is field identifier) 

EXPLANATION 

TA 

100 MILES 

100 KILOMETERS 

Figure 1. Location map, study area model grid boundaries, and two well fields, Prairie Island Indian Community, 

east-central Minnesota. 

 The SWPP categorizes sensitive 

areas around public water-supply 

wells into the following three types of 

zones: (1) contribution zones; (2) 

influence zones; and (3) capture zones 

(U.S. Environmental Protection 

Agency, 1987). The contribution zone 

is the area from where ground-water 

flow is diverted to a supply well. This 

area can be thought of as the area 

bounded by lines of infinite travel 

time. The influence zone is the area 

where water levels are perceptibly 

lowered by withdrawals from a supply 

well. This area is commonly called 

the cone of depression. The capture 

zone is the area around a supply well 

bounded by lines of equal groundwater travel time. Thus, a capture 

zone typically is associated with a 

specified period of years that commonly ranges from 10 to 100 years or 

greater. In this study capture zones are 

considered to represent areas of contributing recharge to supply wells. 

The methods used to delineate 

recharge areas around supply wells 

range from simple techniques, such as 

specification of a radius around the 

well of interest, to construction of 

complex ground-water flow models 

combined with particle-tracking programs (U.S. Environmental Protection 

Agency, 1987). Studies for a wide 

variety of hydrogeologic settings have 

been done that document approaches 

to delineation of capture zones around 

supply wells (Bailey, 1993; Zarriello, 

1993; Landmeyer, 1994; Sheets, 

1994; Misut and Feldman, 1996; Barlow, 1997; Franke and others, 1998; 

Masterson and others, 1998; Nicholson and Watt, 1998). 

The U.S. Geological Survey 

(USGS), in cooperation with the Prai2
rie Island Indian Community, delineated areas of contributing recharge 

within the Mt. Simon-Hinckley aquifer to two well fields based on a 

ground-water flow model and particle 

tracking program. Construction of the 

ground-water flow model improved 

the understanding of the effects of 

stresses imposed on the hydrogeologic system of the study area by 

withdrawals from these well fields. 

PURPOSE AND SCOPE 

The purpose of this report is: (1) to 

describe the development, construction, and application of a groundwater flow model of the Mt. SimonHinckley aquifer in the study area 

(fig. 1); and (2) to use the flow simulation results for delineation of 10- 

and 50-year areas within the aquifer 

that contribute recharge to two community well fields. A calibrated 

numerical ground-water flow model 

of the Mt. Simon-Hinckley aquifer 

combined with a particle-tracking 

program provided the basis for delineation of the recharge areas. The particle tracking program used hydraulic 

heads and flow-distribution output 

from the ground-water flow model 

and assumed pumping conditions 

based on recent water-use records 

from one of the well fields (water-use 

records were not available for the 

other well field, which was not yet 

operational). 

PREVIOUS INVESTIGATIONS 

Two site-specific studies present 

water-quality data and describe water 

resources in the study area. Winterstein (2000) presents water-quality 

data collected during 1998-99 from 

the northern portion of the study area. 

These data were based on water samples collected from 17 wells completed in surficial aquifers. These data 

included physical and chemical properties such as specific conductance, 

pH, temperature, dissolved oxygen, 

alkalinity, and concentrations of 

chemical constituents such as major 

ions, nutrients, and iron and manganese. Water from two wells were analyzed for common agricultural 

pesticides. 

Cowdery (1999) described the 

water resources of the study area 

based on water-quality data collected 

from 8 surface-water sites and 22 

wells completed in surficial aquifers 

during 1994-97 and historical data. 

The data included concentrations of 

major ions, nutrients, coliform and 

streptococci bacteria, volatile organic 

compounds, and triazine herbicides 

and their degradation products. 

HYDROGEOLOGIC SETTING 

Surficial geologic and hydrologic 

features of the study area include glacial outwash, post-glacial alluvium 

and terrace deposits, lakes, and wetlands in the Mississippi River Valley 

(Hobbs and Setterholm, 1998). The 

Mississippi River Valley in this area 

generally ranges from 1.5 to 5 km in 

width. The valley is bounded on each 

side by bluffs 90-120 m in height that 

expose flat-lying bedrock formations. 

Ground water in the study area is 

available from unconsolidated alluvium, terrace deposits, and outwash, 

and from consolidated bedrock units. 

The alluvium, terrace deposits, and 

outwash consist primarily of sand and 

gravel. Cowdery (1999) describes the 

hydrogeologic characteristics of these 

deposits in detail. The bedrock units 

consist of alternating layers of predominantly sandstone and shale, 

which in descending order are the 

Paleozoic-age Franconia Formation, 

Ironton and Galesville Sandstones, 

Eau Claire Formation, Mt. Simon 

Sandstone, and Proterozoic-age 

Hinckley Sandstone. Delin and Woodward (1984) and Mossler and Tipping 

(2000) describe the hydrogeologic 

characteristics of these units in detail. 

The Franconia Formation (50-53 

m thick), which consists primarily of 

sandstone with lesser amounts of 

dolostone, siltstone, and shale, is considered to be an aquifer. The Ironton 

and Galesville Sandstones (15-20 m 

thick), which consist of very coarse to 

fine-grained quartzose sandstone, 

jointly form an aquifer. The Eau 

Claire Formation (36-43 m thick), 

which consists of interbedded layers 

of sandstone, siltstone, and shale, acts 

as a confining unit. The Mt. Simon 

Sandstone (as thick as 75 m) consists 

of coarse-grained quartzose sandstone. The Mt. Simon Sandstone and 

underlying Hinckley Sandstone comprise the deepest aquifer in the study 

area. 

The Mississippi River Valley 

along the study area boundary has 

eroded through the Prairie du ChienJordan aquifer, the St. Lawrence confining unit, and about 100 ft into the 

Franconia aquifer (Cowdery, 1999). 

Ground-water discharge from the 

Prairie du Chien-Jordan aquifer, and 

to a lesser extent from the Franconia 

aquifer, is from upland areas away 

from the valley to springs in exposed 

outcrops along the bluffs of the Mississippi River Valley. Ground-water 

discharge from the Franconia and 

underlying aquifers is predominantly 

upward flow through the unconsolidated valley sediments into the Mississippi River (Cowdery, 1999). 

The Mt. Simon-Hinckley aquifer, 

which is confined by the overlying 

Eau Claire Formation, discharges into 

overlying bedrock units and unconsolidated sediments within the Mississippi River Valley. This upward 

discharge contributes baseflow gain to 

the Mississippi River (Cowdery, 

1999). The Mt. Simon-Hinckley aquifer is a source of ground water for two 

community well fields (identified as 

A and B, on fig. 1). (The two wells at 

well field A are open to only the Mt. 

Simon Sandstone (Thomas Winterstein, U.S. Geological Survey, oral 

commun., 2001)). 

3 
SIMULATION OF GROUNDWATER FLOW 

The USGS modular, finite-difference computer code, MODFLOW 

(McDonald and Harbaugh, 1988), was 

used to simulate ground-water flow in 

the Mt. Simon-Hinckley aquifer. The 

governing partial differential groundwater flow equation solved by MODFLOW is: 

-----⎛Kxx∂h⎞ + -----⎛Kyy ∂ ∂h ----- ∂ -----⎞ = 0 ∂x⎝ ∂x⎠ ∂y⎝ ∂y⎠

where; 

Kxx, and Kyy = hydraulic conductivity along x and y coordinate axes, 

assumed to be parallel to the major 

axes of hydraulic conductivity (L/T); 

and 

h = hydraulic head (L). 

The model formulates the equation 

as sets of simultaneous algebraic 

equations that are solved by an iterative, finite-difference method of computation. The equations 

mathematically represent modeled 

aquifers as a grid of homogeneous 

blocks or cells with specified hydraulic properties. Boundary conditions 

are specified for the model grid that 

are based on the conceptual framework of the hydrologic system. 

MODEL DESIGN AND 

DISCRETIZATION 

Ground-water flow in the Mt. 

Simon-Hinckley aquifer was simulated as a two-dimensional, steadystate, single-layer, confined system. A 

variably-spaced model grid was 

defined for an approximately 135-

km2

 area that encompasses the study 

area, including the two community 

well fields (fig. 2). Orientation of the 

model grid is such that the rows are 

parallel to the Mississippi River, 

which represents the northeast boundary of the modeled area. The dimensions and numbers of rows and 

columns of the model grid result from 

the following considerations: (1) adequate representation of aquifer geometry and hydraulic properties and 

stresses; (2) minimization of computation time; and (3) suitability of the 

grid spacing for application of the particle-tracking program. 

Grid cell dimensions range from 

about 50 m on a side at each of the 

two well fields to nearly 300 m on a 

side along the boundaries of the modeled area farthest from the well fields. 

Grid cell size increases as distance 

from the well fields increases because 

the level of detail in the simulation of 

ground-water flow for these more distant cells was not needed and the 

available hydrogeologic data were 

insufficient to support finer grid spacing. 

MODEL GEOMETRY AND 

HYDRAULIC PROPERTIES 

A thickness of 72 m and a horizontal hydraulic conductivity of 1.35 m/d 

were specified as model inputs for the 

Mt. Simon-Hinckley aquifer. Geologic data from well logs and results 

of an aquifer test conducted at well 

field site A (fig. 1) provided the basis 

for these inputs. The aquifer test used 

two newly installed wells. One of 

these wells was installed to serve as a 

community supply well (identified as 

A-1, fig. 3), and the other well (identified as A-3, fig. 3) was installed as an 

observation well for the test. Results 

of the test indicated a transmissivity 

of 97.2 m2

/day (Thomas Winterstein, 

U.S. Geological Survey, oral commun., 2001). 

MODEL BOUNDARY 

CONDITIONS 

The northeastern side of the model 

grid, representing the Mississippi 

River Valley, is a head-dependent flux 

boundary. This boundary simulates 

outflow from the model as discharge 

to the Mississippi River Valley, 

which, except for withdrawals from 

wells, is considered to be the only 

mechanism of discharge from the Mt. 

Simon-Hinckley aquifer. The southwestern side of the model grid is a 

specified head boundary (fig. 1). This 

boundary simulates inflow to the 

model as lateral flow in the Mt. 

Simon-Hinckley aquifer from upgradient recharge areas described by 

Delin and Woodward (1984). The 

other two sides of the model grid are 

no-flow boundaries. These boundaries 

are aligned approximately parallel to 

regional flow paths through the Mt. 

Simon-Hinckley aquifer within the 

study area (Delin and Woodward, 

1984). 

Riverbed conductance values were 

specified for the head dependent flux 

boundaries. These values indicate the 

effectiveness of the hydraulic connection between the Mississippi River 

and the Mt. Simon-Hinckley aquifer. 

A relatively large conductance 

(1.5x10-4/d) was specified for the portion of the head-dependent flux 

boundary that coincides with the subcrop of the Mt. Simon-Hinckley aquifer (fig. 1), where unconsolidated 

valley sediments directly overlie the 

aquifer. A smaller conductance (1.5 

x10-6/d) was specified for the remaining portion of this boundary, where 

the Eau Claire confining unit separates the aquifer from the overlying 

unconsolidated valley sediments. 

The river stage specified for the 

head-dependent flux boundary 

upstream of the U.S. Army Corps of 

Engineers Lock and Dam No. 3 (fig. 

1) was 205.7 m above sea level. This 

stage is shown on the Red Wing topographic USGS 1:24,000 quadrangle as 

the normal pool elevation maintained 

by the lock and dam. The river stage 

specified for this boundary downstream of the dam was specified to be 

2.4 m lower than the upstream stage 

(based on the Red Wing topographic 

USGS 1:24,000 quadrangle). 

The initial hydraulic head value of 

223 m above sea level used for the 

specified head boundary was based on 

4 
5 

208

210

212

214 

216

218

220

222 

210

212

214 

216

218

220

222 

208 

216

1 

1 

10 

10 

20 

20 

30 

30 

40 

40 

50 

50 

54 

54 

ROWS 

ROWS 

1 

1 

10 

10 

20 

20 

30 

30 

40 

40 

50 

50 

60 

60 

70 

70 

80 

80 

90 

90 

100 

100 

108 

108 

COLUMNS 

COLUMNS 

D 

D 

D 

D 

A 

B 

A 

B 

2 4 6 MILES 

0 2 4 6 KILOMETERS

0 

Simulation based on withdrawal 

rate of 625 meters per day 

each for well fields A and B. 

cubic 

Simulation based on no withdrawals 

from well fields A and B. 

Model grid and simulated potentiometric surface for the 

Mt. Simon-Hinckley aquifer, Prairie Island Indian Community, 

east-central Minnesota. 

Potentiometric contour. Interval is 

2 meters. Datum is sea level 

Approximate ground-water 

flow direction 

Well field. Letter is field identifier 

218

A D 

EXPLANATION 

Figure 2. 
92o43'30" 92o43' 92o42'30" 92o39'30" 92o39' 92o38'30" 

T 

114 

N 

T 

113 

N 

44o38' 

44o37'30" 

North 

Lake 

15 14

22 23 

T 

114 

N 

44o40'30" 

44o40' 

A-1 

A-3 

A-2 

D 

D 

D 

B-1 B-2 

DD 

Inset A R 16 W R 15 W Inset B 0 0.25 0.50 KILOMETERS 

0 0.25 0.50 MILES 

EXPLANATION 

Outer extent of 10-year recharge area Reservation lands 

within the Mt. Simon-Hinckley aquifer 

Outer extent of 50-year recharge area A-1 D Well symbol and identifier 

within the Mt. Simon-Hinckley aquifer 

Figure 3. Recharge areas within the Mt. Simon-Hinckley aquifer to well fields A and B based on a rate of withdrawal of 625 

cubic meters per day for each well field, Prairie Island Indian Community, east-central Minnesota. 

the study by Delin and Woodward 7.0x10-8 m/d. This rate is based on Hinckley aquifer (table 1). Under 

(1984). That study mapped on a estimates of leakage to confined bed- pumping conditions, 64 percent of 

regional scale potentiometric surfaces rock aquifers in the Twin Cities met- outflow from the model is through the 

of aquifers that included the Mt. ropolitan area (Ruhl, 2002). The head-dependent flux boundary, and 

Simon-Hinckley aquifer. resulting volumetric rate of recharge the remainder is withdrawals from 

to the model is 9.1 m3/d (table 1). wells. The simulated withdrawals repInflows Under pumping conditions, inflows to resent pumpage from the pairs of 

the model increase to 3,460 m3

/d from community wells at well fields A and Under nonpumping conditions, the specified head boundary and are B (fig. 1). A withdrawal rate of 625 simulated total inflow to the model is assumed to remain the same from m3

/d was simulated for each well 

2,609.1 m3/d. The source of nearly all recharge (table 1). field. This rate of withdrawal is equiv- of this inflow is the specified head alent to the reported combined annual boundary, which accounts for 99.65 Outflows rate of withdrawal during 2000 for the percent of this total (table 1). Areal two community wells at well field B recharge to the model is the only other Under nonpumping conditions, (Sara Moore, Prairie Island Indian source of inflow to the model. This total simulated outflow (2,610 m3

/d) Community, written commun., 2001). recharge, which represents water that from the model is through the headenters the aquifer as leakage through dependent flux boundary, and nearly MODEL CALIBRATION 

the overlying Eau Claire confining all of that outflow is through the porunit, is uniformly distributed to the tion of the boundary that coincides Calibration of the model was done 

active cells of the model at a rate of with the subcrop of the Mt. Simon- primarily by comparison of simulated 

6 
-- -- --

-- -- --

Table 1. Simulated volumetric water budget for the steady-state ground-water flow model under nonpumping and pumping conditions for the 

Prairie Island Indian Community, east-central Minnesota

 [flow rates in cubic meters per day; --, no data] 

Nonpumping Conditions 

Inflow Outflow 

Source Rate Percent Source Rate Percent 

Specified head boundary 2,600 99.65 Head-dependent flux boundary (coincident with Eau Claire confining unit subcrop) 92 4 

Recharge 9.1 0.35 Head-dependent flux boundary (coincident with Mt. Simon-Hinckley 

aquifer subcrop) 2,518 96 

Withdrawals from wells 0 0 

Total 2,609.1 100 2,610 100 

Pumping Conditions 

Inflow Outflow 

Source Rate Percent Source Rate Percent 

Specifiedhead boundary 3,460 99.74 Head-dependent flux boundary (coincident with Eau Claire confining 

unit subcrop) 76 2 

Recharge 9.1 .26 Head-dependent flux boundary (coincident with Mt. Simon-Hinckley 

aquifer subcrop) 2,143 62 

Withdrawals from wells 1,250 36 

Total 3,469.1 100 3,469 100 

to observed ground-water levels for 

wells A-3, B-2, and C during the summer of 2001. The observed water levels for these wells are assumed to 

represent nonpumping, steady-state 

conditions for the Mt. Simon-Hinckley aquifer. Comparisons also were 

made of simulated head-dependent 

boundary outflows to the estimated 

gain in baseflow in the Mississippi 

River. Outflow from the head-dependent flux boundary would be expected 

to represent a significant portion of 

the gain in baseflow to the Mississippi 

River (the Franconia-Ironton-Galesville aquifer and unconsolidated valley sediments would also be expected 

to be sources of baseflow gain). The 

estimated gain in baseflow was based 

on a study by Payne (1995) of baseflow gains to the Mississippi River for 

six subreaches between the headwaters in northern Minnesota and the 

Twin Cities metropolitan area. 

The model was calibrated by 

adjustment of the hydraulic head 

value at the specified head boundary 

and riverbed conductance value at the 

head-dependent flux boundary. The 

initial values used for these model 

inputs were considered to have been 

less precise estimates of their true values than was the case for the other 

model inputs, which included horizontal hydraulic conductivity, 

recharge rate, and river stage of the 

head-dependent flux boundary. 

The model was calibrated to produce residual (observed minus simulated) hydraulic heads of -0.1, 0.0, and 

0.1 m for the wells at sites A-3, B-2, 

and C, respectively. Simulated outflow from the portion of the headdependent flux boundary where the 

Eau Claire confining unit separates 

the Mt. Simon-Hinckley aquifer from 

overlying unconsolidated valley sediments was 92 m3/d (table 1). Simulated outflow from the portion of the 

head-dependent flux boundary where 

the overlying unconsolidated valley 

sediments directly overlie the Mt. 

Simon-Hinckley aquifer was 2,518 

m3

/d (table 1). These outflows— 

expressed per lineal unit of distance of 

river—were 13 and 425 m3/d/km, 

respectively. These outflows are 

assumed to represent one-half the 

total gain in baseflow (ground-water 

discharge) to the Mississippi River 

(the other one-half from the Wisconsin side of the river). 

The total simulated rate of baseflow gain from the Mt. Simon-Hinckley portion of the head-dependent flux 

boundary would be equivalent to 850 

m3

/d/km (425 m3/d/km multiplied by 

2). This figure is in the lower part of 

the range (0 - 6,000 m3/d/km) 

reported by Payne (1995), which 

would be reasonable for two reasons. 

First, some of the six subreaches in 

Payne’s study flow through transmissive unconsolidated alluvial sediments similar to those in the study 

area, where the gain in baseflow 

would be expected to be similar to 

that for the study area. In the study 

area, however, ground-water discharge from the Mt. Simon-Hinckley 

aquifer to the river must pass through 

as much as 60 m of unconsolidated 

valley sediments (Cowdery, 1999), 

whereas in the upstream reaches studied by Payne (1995) some of the baseflow gain would have been direct 

discharge from surficial aquifers. Second, a portion of the gain in baseflow 

would include contributions from the 

Ironton-Galesville aquifer and the 

unconsolidated valley sediments, 

which were not simulated in the 

model. 

7 
8

Table 2. Sensitivity analysis of calibrated ground-water flow model of the Mt. Simon-Hinckley aquifer in the Prairie Island Indian Community, east-central Minnesota

[m3/d, cubic meters per day] 

Multiplication Change in headModel input tested Final values used in calibrated model factor used to dependent boundary Change in simulated hydraulic heads for wells used in model calibration change value outflow 

Well A-3 Well B-2 Well C 

Absolute 

Percent value Percent 

(m3/d) 

Absolute Absolute Absolute 

value Percent value Percent value 

(meters) (meters) (meters) 

Specifie head 223 0.99 -12 -310 -0.8 -1.7 -0.5 -1.1 -0.4 -0.8 

 (meters) 1.01 10 268 0.8 1.7 0.5 1.1 0.4 0.8 

River stage 203.3 205.7 0.90 114 3000 -1.7 -3.8 -4.3 -9.3 -5.6 -11.9 

(meters) below lock and dam above lock and dam 0.99 10 274 -0.2 -0.4 -0.4 -0.8 -0.6 -1.2 

1.01 -12 -309 0.0 0.1 0.5 1.0 0.4 0.9 1.10 -113 -2978 0.0 0.1 0.5 1.0 0.4 0.9 

Hydraulic conductivity 1.35 0.10 -84 -2210 -1.5 -3.4 -1.8 -3.8 -1.6 -3.4 

(meters/day) 0.99 -1 -17 0.0 -0.1 0.0 0.0 0.0 0.0 

1.01 1 17 0.0 -0.1 0.0 0.0 0.0 0.0 

10.00 153 4035 1.1 2.4 2.8 5.9 3.6 7.7 

Riverbed conductance 1.5000E-06 1.5000E-04 0.01 -97 -2550 1.4 3.0 3.6 7.7 5.0 10.5 

(1/days) no aquifer subcrop aquifer subcrop 0.10 -75 -1961 1.1 2.4 2.8 5.9 3.6 7.7 

0.99 0 -10 0.0 -0.1 0.0 0.0 0.0 0.0 1.01 0 9 0.0 -0.1 0.0 0.0 0.0 0.0 

10.00 63 1645 -1.8 -3.9 -1.8 -3.8 -1.6 -3.4 

100.00 102 2678 -3.5 -7.6 -2.1 -4.5 -1.9 -4.0 

Recharge 7.00E-08 0.01 -0.9 -23 0.0 0.0 0.0 0.0 0.0 0.0 

(meter/day) 0.10 -0.9 -23 0.0 0.0 0.0 0.0 0.0 0.0 

0.99 0.0 0 0.0 -0.1 0.0 0.0 0.0 0.0 1.01 0.0 0 0.0 -0.1 0.0 0.0 0.0 0.0 

10.00 -0.1 -2 0.0 0.1 0.0 0.0 0.0 0.0 

100.00 7.0 185 0.5 1.1 0.3 0.6 0.3 0.5 
MODEL SENSITIVITY 

A sensitivity analysis of the calibrated model was done based on 

changes in model-computed hydraulic 

heads at three wells identified as A-3, 

B-2, and C, and the head-dependent 

boundary outflow. Well A-3 (fig. 3) 

was used as the observation well for 

the aquifer test conducted at well field 

A, well B-2 (fig. 3) is one of two community wells at well field B, and well 

C (fig. 1) is the drinking-water supply 

well at the U.S. Army Corps of Engineers Lock and Dam No. 3. 

The hydraulic heads and outflow 

were most sensitive to changes in the 

specified head boundary and river 

stage of the head-dependent flux 

boundary. A change in the specified 

head and river stage of 1 percent 

resulted in changes of 10-12 percent 

in outflow, but considerably smaller 

changes of less than 1 percent in 

hydraulic heads (table 2). The model 

was much less sensitive to horizontal 

hydraulic conductivity. A change in 

horizontal hydraulic conductivity of 1 

percent resulted in changes of 1 percent in outflow and changes of 0 percent in hydraulic heads. A change in 

hydraulic conductivity of one order of 

magnitude resulted in changes of -84 

and 153 percent in outflow and 

changes of -1.8 to 3.6 percent in 

hydraulic heads. The model was least 

sensitive to riverbed conductance and 

recharge. Changes of 1 percent in 

riverbed conductance and recharge 

resulted in changes of 0 percent for 

both head-dependent boundary outflow and hydraulic heads. 

DELINEATION OF RECHARGE 

AREAS 

The USGS developed a particletracking program, MODPATH (Pollock, 1989), to simulate groundwater-flow paths for specified advective travel times that may range from 

one to many years. MODPATH uses 

the hydraulic heads and flow distribution computed by MODFLOW to 

determine these flow paths. The flow 

paths are computed by a semi-analytical particle-tracking scheme based on 

the assumption that the directional 

ground-water velocity components 

within a model vary linearly. The 

velocity components are based on the 

intercell flow rates computed by 

MODFLOW. The particle tracking 

done by MODPATH assumes that 

transport is by advection only and that 

other factors, such as chemical and 

biological attenuation, solid-phase 

partitioning, dispersion, and diffusion, 

are insignificant. MODPATH can 

track hypothetical particles of water 

up or down the hydraulic gradient 

(backward or forward) within the 

computed flow field. In this study 

backward tracking from two community well fields was done for advective travel times of 10 and 50 years. 

Backward particle tracking from 

well fields A and B was done to delineate areas within the Mt. SimonHinckley aquifer of contributing 

recharge based on ground-water flow 

paths determined for 10- and 50-year 

travel times (fig. 3). A withdrawal rate 

of 625 m3/d was simulated for each 

well field. This daily rate of withdrawal is equivalent to the reported 

combined annual rate of withdrawal 

during 2000 for the two community 

supply wells at well field B (Sara 

Moore, Prairie Island Indian Community, oral commun., 2001). 

At well field A, this rate of withdrawal, combined with backward particle tracking, was simulated as 

separate withdrawal points for community wells A-1 and A-2 because the 

distance between them (about 325 m) 

exceeds the model grid cell dimensions. At well field B, the two community wells were simulated as a 

single withdrawal point because the 

distance between them (about 25 m) 

is only about one-half the distance of 

the model grid cell dimensions. 

The 10- and 50-year recharge 

areas cover 0.38 and 0.65 km2

, 

respectively (fig. 3). These areas are 

shown separately for wells A-1 and 

A-2 because of the simulation as separate withdrawal points. The flow 

paths that define these areas extend 

for maximum distances of 350 and 

450 m, respectively, from the community supply wells used in the simulations. 

MODEL LIMITATIONS 

Only three hydraulic head values 

were available for model calibration. 

These hydraulic head values are considered to be accurate to within plus 

or minus 3 m. Baseflow gains for 

upstream subreaches of the Mississippi River (Payne, 1995) were used 

to evaluate the simulated head-dependent boundary outflows. The simulated outflows, however, are only a 

portion of the total baseflow gain. 

Precise estimation of the baseflow 

gain in the study area from the Mt. 

Simon-Hinckley aquifer would be difficult. 

Additional field data would be 

required to refine the calibration and 

thereby improve the accuracy of the 

model. More wells completed in the 

Mt. Simon-Hinckley aquifer would be 

needed to obtain additional hydraulic 

head data for the aquifer. More lowflow streamflow measurements would 

be needed to estimate the gain in 

baseflow to the Mississippi River. 

Ideally, streamflow measurements 

would be made during low-flow conditions at sites near the upstream and 

downstream ends of the study area. 

The downstream site should be 

upstream of Lock and Dam No. 3 (fig. 

1) because of potential effects on 

baseflow from the dam. Streamflow 

also would have to be measured in 

any in-flowing streams between the 

upstream and downstream measurement sites. 

The major limitation of the model 

is that the Mt. Simon-Hinckley aqui9 
fer is simulated as a 1-layer, 2-dimen- contaminant sources are likely to estimation of the general effects of 

sional system. A multi-layer occur. Acquisition of additional changes in hydraulic properties and 

simulation of the ground-water sys- hydrogeologic data would be needed boundary conditions of the Mt. 

tem would be required to delineate to construct a more complex multi- Simon-Hinckley aquifer on the size of 

contributing areas of recharge to the layer model. The model at its present the contributing recharge areas to the 

well fields from land surface where stage should be considered useful for well fields within the aquifer. 

SUMMARY	 three wells and outflows from the head-dependent flux 

boundary were sensitive to changes in the specified head 

The Prairie Island Indian Community in east-central boundary and river stage specified for the head-dependent 

Minnesota uses ground water from the Mt. Simon-Hinckley flux boundary. Calibration of the model was done by 

aquifer, a confined bedrock aquifer, for community water adjustment of the hydraulic head value at the specified head 

supply. Tribal officials regard protection of four community boundary and riverbed conductance value at the headsupply wells (two wells each in well fields A and B) that dependent flux boundary. 

are open to this aquifer to be an important natural resource 

management goal. To satisfy this goal tribal officials imple- The U.S. Geological Survey computer program MODmented a SWPP (Source Water Protection Program), which PATH was used to track water particles (upgradient) from 

specifies a strategy formulated by the U.S. Environmental well fields A and B to delineate areas of contributing 

Protection Agency to assist State and local agencies in the recharge based on a withdrawal rate of 625 m3

/d for each 

delineation of hydrogeologically sensitive areas around field. The flow paths defined areas of contributing recharge 

water-supply wells. Areas of contributing recharge, which for the two well fields that are 0.38 and 0.65 km2 in size for 

are defined by ground-water flow paths of equal travel time 10- and 50-year travel times, respectively. The flow paths 

represent these sensitive areas. that define these areas extend for maximum distances of 

A ground-water flow model combined with a particle- about 350 and 450 m, respectively. At well field A where 

tracking program was used to delineate areas of contribut- the wells are about 325 m apart, the areas of contributing 

ing recharge within the Mt. Simon-Hinckley aquifer to the recharge were delineated for each well as separate withtwo community well fields. At well field A the two wells drawal points. At well field B, where the wells are only 

are about 325 m apart, and at well field B the two wells are about 25 m apart, the area of contributing recharge was 

about 25 m apart. The U.S. Geological Survey modular, delineated for both wells as a single withdrawal point. 

finite-difference computer program MODFLOW was used The major limitation of the model is that delineation of 

to simulate ground-water flow in the Mt. Simon-Hinckley the areas of contributing recharge to the well fields are 

aquifer as a two-dimensional, steady-state, single-layer, based on a 2-dimensional, 1-layer simulation within the Mt. 

confined aquifer system. Simon-Hinckley aquifer. As a consequence the contributing 

A variably-spaced model grid was defined for an areas to the well fields are limited to within the Mt. Simonapproximately a 135-km2

 area. The grid was oriented such Hinckley aquifer. A more complex, multi-layer simulation 

that the rows are parallel with the Mississippi River, which of the ground-water flow system would be required to 

coincides with the northeast boundary of the grid. This grid delineate contributing areas of recharge to the aquifer from 

boundary was modeled as a head-dependent flux boundary. land surface. Construction of such a model would require 

The southwestern grid boundary was modeled as a speci- acquisition of additional hydrogeologic data not currently 

fied head boundary. Model-computed hydraulic heads at available. 

REFERENCES complex flow systems, Cape Cod, 1984, Hydrogeologic setting and 

Massachusetts: U.S. Geological the potentiometric surfaces of Bailey, Z.C., 1993, Hydrology of the Survey Water-Supply Paper 2434, regional aquifers in the Hollandale Jackson, Tennessee, area and 66 p. Embayment, southeastern Minne- delineation of areas contributing 

ground water to the Jackson well Cowdery, T.K., 1999, Water sota, 1970-80: U.S. Geological 

fields: U.S. Geological Survey resources of the Prairie Island Survey Water-Supply Paper 2219, 

56 p. Water-Resources Investigations Indian Reservation, Minnesota, 

Report 92-4146, 54 p. 1994-97: U.S. Geological Survey Franke, O.L., Reilly, T.E., Pollock, 

Barlow, P.M., 1997, Particle-tracking Water-Resources Investigations D.W., and LaBaugh, J.W., 1998, 

analysis of contributing areas of Report 99-4069, 36 p. Estimating areas contributing 

public-supply wells in simple and Delin, G.N., and Woodward, D.G., recharge to wells, lessons from 

10 
previous studies: U.S. Geological 

Survey Circular 1174, 14 p. 

Hobbs, H.C., and Setterholm, D.R., 

1998, Geologic Atlas of Goodhue 

County, Minnesota: Minnesota 

Geological Survey, County Atlas 

Series, Map C-12, 6 plates, plate 

3--Surficial Geology and Thickness of Quaternary Sediments, 

scale 1:100,000. 

Landmeyer, J.E., 1994, Description 

and application of capture zone 

delineation for a wellfield at Hilton Head Island, South Carolina: 

U.S. Geological Survey WaterResources Investigations Report 

94-4012, 33 p. 

Masterson, J.P., Walter, D.A., and 

LeBlanc, D.R., 1998, Delineation 

of contributing areas to selected 

public-supply wells, western Cape 

Cod, Massachusetts: U.S. Geological Survey Water-Resources 

Investigations Report 98-4237, 45 

p. 

McDonald, M.G., and Harbaugh, 

A.W., 1988, A modular threedimensional finite-difference 

ground-water flow model: U.S. 

Geological Survey Techniques of 

Water-Resources Investigations, 

book 6, chap. A1, 586 p. 

Misut, P.E., and Feldman, S.M., 1996, 

Delineation of areas contributing 

recharge to wells in central Long 

Island, New York by particle 

tracking: U.S. Geological Survey 

Open-File Report 95-703, 47 p. 

Mossler, J.H., and Tipping, R.G., 

2000, Bedrock geology and structure of the seven-county Twin Cities metropolitan area, Minnesota: 

Minnesota Geological Survey, 

Miscellaneous Map Series M-104, 

1 plate, scale 1:125,000 

Nicholson, R.S., and Watt, M.K., 

1998, Simulation of ground-waterflow patterns and areas contributing recharge to streams and watersupply wells in a valley-fill and 

carbonate-rock aquifer system, 

southwestern Morris County, New 

Jersey: U.S. Geological Survey 

Water-Resources Investigations 

Report 97-4216, 40 p. 

Payne, G.A., 1995, Ground-water 

baseflow to the Upper Mississippi 

River upstream of the Minneapolis-St. Paul area, Minnesota during 

July 1988: U.S. Geological Survey 

Open-File Report 94-478, 28 p. 

Pollock, D.W., 1989, Documentation 

of computer programs to compute 

and display pathlines using results 

from the U.S. Geological Survey 

modular three-dimensional finitedifference ground-water flow 

model: U.S. Geological Survey 

Open-File Report 89-381, 188 p. 

Runkel, A.C., 1998, Geologic Atlas of 

Goodhue County, Minnesota: 

Minnesota Geological Survey, 

County Atlas Series, Map C-12, 6 

plates, plate 2--Bedrock Geology, 

scale 1:100,000. 

Ruhl, J.F., 2002, Estimates of 

recharge to unconfined aquifers 

and leakage to confined aquifers in 

the seven-county metropolitan 

area of Minneapolis-St. Paul, Minnesota: U.S. Geological Survey 

Water-Resources Investigations 

Report 02-4092, 32 p. 

Sheets, R.A., 1994, Contributing 

recharge areas of water-supply 

wells at Wright-Patterson Air 

Force Base, Ohio: U.S. Geological 

Survey Water-Resources Investigations Report 94-4231, 35 p. 

U.S. Environmental Protection 

Agency, 1987, Guidelines for 

delineation of wellhead protection 

areas: U.S. Environmental Protection Agency Office of GroundWater Protection, Washington, 

D.C., EPA 440/6-87-010, 189 p. 

Winterstein, T.A., 2000, Water-quality data collected on Prairie Island 

near Welch, Minnesota: U.S. Geological Survey Open-File Report 

00-78, 25 p. 

Zarriello, P.J., 1993, Determination of 

the contributing area to six municipal ground-water supplies in the 

Tug Hill glacial aquifer of northern New York, with emphasis on 

the Lacona-Sandy Creek well 

field: U.S. Geological Survey 

Water-Resources Investigations 

Report 90-4145, 51 p. 

11