•. 

Prepared in cooperation with the University of Minnesota and the Minnesota Geological Survey 

Cyclic Injection, Storage, and Withdrawal of Heated Water in a Sandstone Aquifer at 

St. Paul, Minnesota 

Analysis of Thermal Data and Non isothermal Modeling 

of Long-Term Test Cycles 1 and 2 

U.S. Geological Survey Professional Paper 1530-C 

U.S. Department of the Interior 

U.S. Geological Survey 

J 

,. . ' 

~... 

. ... 

Cyclic Injection, Storage, and Withdrawal of Heated Water in a Sandstone Aquifer at 

St. Paul, Minnesota 

By G.N. DEILN1

, M.C. HOYER2, T.A. WINTERSTEIN1 andR.T. MILLER3 

Analysis of Thermal Data and Non isothermal Modeling 

of Long-Term Test Cycles 1 and 2 

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1530-C 

Prepared in cooperation with the University of Minnesota 

and the Minnesota Geological Survey 

1 U.S. Geological Surrvey, Mounds View, Minnesota 2 University of Minnesota, Underground Space Center, Department of Civil Engineering, Minneapolis, Minnesota 

3 Groundwater Investigations, Inc., Pine Bush, New York 
U.S. DEPARTMENT OF THE INTERIOR 

Gale A. Norton, Secretary 

U.S. GEOLOGICAL SURVEY 

Charles G. Groat, Director 

Use of brand names in this report is for identification purposes only and does not 

constitute endorsement by the U.S. Geological Survey. 

Mound View, Minnesota, 2002 

Library of Congress Cataloging in Publications Data 

Delin, G.N., Hoyer, M.C., Winterstein, T.A., and Miller, R.T 

Cyclic injection, storage, and withdrawal of heated water in a sandstone aquifer at St. Paul, Minnesota I G.N. Delin, M.C. Hoyer, T.A. 

Winterstein, and R.T. Miller. 

80 p., 28 em.- (Analysis of thermal data and nonisothermal modeling of long-term test cycles 1 and 2) (U.S. Geological Survey 

Professional Paper; 1530-C) 

"Prepared in cooperation wth the University of Minnesota and the Minnesota Geological Survey." 

Includes bibliographic references (p. 79). 

ISBN 0-607-99152-6 

Supt. of Docs. no.: 119.16: 1530-C 

1. Hot-air heating. 2. Hot water. 3. Water-storage-Minnesota-St. Paul. 4. Aquifers-Minnesota-St. Paul. I. Univesity of Minnesota. 

II. Minnesota Geological Survey. Ill. Title. IV. Series. V. Series: U.S. Geological Survey professional paper; 1530-C. 

TH7602.M55 2002 

697'.4-dc20 

For sale by U.S. Geological Survey, Information Services, 

Box 25286, Federal Center, 

Denver, CO 80225 

92-23497 

CIP 
CONTENTS 

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

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

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

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

Aquifer selection .......................................................................................................................................................... 4 

Description of test facility . . . . .. .. .... . . . . .. .. . .. . . . . .. .. .. .. . . . .. .. .. .. .. .. . . . . .... .. . .. . . . .. ... .... . . . .. .. .. .. . . . . .. .. .... .. .. .. .. .. .. .. . . . . . .. .. .... . . . .. .. .. .. .. . 5 

Long-term test cycles 1 and 2 ................................................................................................................................................ 7 

Analysis of thermal data for long-term test cycles I and 2 ................................................................................................... 11 

Temperature as a function of time ............................................................................................................................... II 

Temperature profiles .................................................................................................................................................... 3 8 

Discussion of thermal data .......................................................................................................................................... 45 

Nonisothermal modeling of long-term test cycles I and 2 .................................................................................................... 45 

Simulation of model anisotropy .................................................................................................................................. 4 7 

Discretization of aquifer system .................................................................. : ............................................................... 47 

Boundary and initial conditions ................................................................................................................................... 48 

Model calibration ......................................................................................................................................................... 48 

Analysis of simulations ............................................................................................................................................... 52 

Summary ................................................................................................................................................................................ 78 

References ............................................................................................................................................................................. 79 

Illustrations 

Figure I. Map and block diagram showing location and generalized schematic diagram of hydrogeology of the 

Aquifer Thermal-Energy Storage site ................................................................................................................... 2 

2. Map showing plan view of the Aquifer Thermal Energy Storage site ................................................................... 6 

3. Schematic diagram of sites A and Bat the Aquifer Thermal-Energy Storage site ................................................ 7 

4. Schematic section showing depths of screened intervals of observation wells, stratigraphy, and location of 

measurement points of the Aquifer Thermal-Energy Storage site ........................................................................ 8 

5. Diagram showing model grid and position of observation wells at various depths .............................................. I 0 

Figures 6-22. Graphs showing: 

6. Temperatures at the wellhead in production well A during long-term test cycle I, November I984 through 

May I985 ............................................................................................................................................................... I2 

7. Temperatures in observation well AMI during long-term test cycle I, November I984 through May I985 ...... I4 

8. Temperatures in observation well ASI during long-term test cycle I, November I984 through May I985 ........ I6 

9. Temperatures in observation well AM2 during long-term test cycle I, November I984 through May I985 ....... 18 

IO. Temperatures in observation well AM3 during long-term test cycle I, November I984 through May I985 ..... 20 

Il. Temperatures in observation well AM4 during long-term test cycle I, November I984 through May I985 ..... 22 

I2. Temperatures in production well A during long-term test cycle 2, October I986 through Aprili987 ............... 24 

13. Temperatures in observation well AMI during long-term test cycle 2, October I986 through Aprill987 ........ 26 

14. Temperatures in observation well AS 1 during long-term test cycle 2, October 1986 through April 1987 ......... 28 

15. Temperatures in observation well AM2 during long-term test cycle 2, October 1986 through April1987 ........ 30 

16. Temperatures in observation well AM3 during long-term test cycle 2, October 1986 through April1987 ........ 32 

I7. Temperatures in observation well AM4 during long-term test cycle 2, October 1986 through Aprili987 ........ 34 

I8. Temperatures measured in observation well AMI at the beginning of injection and at the end of injection, 

storage, and withdrawal for long-term test cycles 1 and 2 .................................................................................... 40 

I9. Temperatures measured in observation well AS I at the beginning of injection and at the end of injection, 

storage, and withdrawal for long-term test cycles 1 and 2 .................................................................................... 41 

III 
Illustrations-Continued 

20. Temperatures measured in observation well AM2 at the beginning of injection and at the end of injection, 

storage, and withdrawal for long-term test cycles 1 and 2 .................................................................................... 42 

21. Temperatures measured in observation well AM3 at the beginning of injection and at the end of injection, 

storage, and withdrawal for long-term test cycles 1 and 2 .................................................................................... 43 

22. Temperatures measured in observation well AM4 at the beginning of injection and at the end of injection, 

storage, and withdrawal for long-term test cycles 1 and 2 .................................................................................... 44 

Figures 23-24. Diagrams showing: 

23. Model grid and flow net for the Ironton and Galesville Sandstones near production well A for the 

long-term test cycles ............................................................................................................................................. 49 

24. Model grid and flow net for the upper part of the Franconia Formation near production well A for the 

long-term test cycles ............................................................................................................................................. 50 

Figures 25-36. Graphs showing: 

25. Model-computed and measured temperatures at production well A during long-term test cycle 1 .................... 54 

26. Model-computed and average measured temperatures in observation well AMl during long-term 

test cycle 1 ............................................................................................................................................................. 56 

27. Model-computed and average measured temperatures in observation well AS 1 during long-term 

test cycle 1 ............................................................................................................................................................. 58 

28. Model-computed and average measured temperatures in observation well AM2 during long-term 

test cycle 1 ............................................................................................................................................................. 60 

29. Model-computed and average measured temperatures in observation well AM3 during long-term 

test cycle 1 ............................................................................................................................................................. 62 

30. Model-computed and averaged measured temperatures in observation well AM4 during long-term 

test cycle 1 ............................................................................................................................................................. 64 

31. Model-computed and measured temperatures in production well A during long-term test cycle 2 ................... 66 

32. Model-computed and averaged measured temperatures in observation well AMl during long-term 

test cycle 2 ............................................................................................................................................................. 68 

33. Model-computed and average measured temperatures in observation well ASl during long-term 

test cycle 2 ............................................................................................................................................................. 70 

34. Model-computed and average measured temperatures in observation well AM2 during long-term 

test cycle 2 ............................................................................................................................................................. 72 

35. Model-computed and average measured temperatures in observation well AM3 during long-term 

test cycle 2 ............................................................................................................................................................. 7 4 

36.Model-computed and average measured temperatures in observation well AM4 during long-term 

test cycle 2 ............................................................................................................................................................. 76 

Tables 

Table 1. Summary of duration, average rates of injection and withdrawal, and average temperatures of injection, 

IV 

storage, and withdrawal for long-term test cycles 1 and 2 ..................................................................................... 11 

2. Temperature front arrival time at measurement points in the upper part of the Franconia Formation 

and in the Ironton and Galesville Sandstones for long term test cyclfs 1 and 2 ................................................... 36 

3. Comparison of model-computed thermal efficiencies of the aquifer and final withdrawal-water 

temperatures at production well A with corresponding calculated and measured values for long-term 

test cycles 1 and 2 .................................................................................................................................................. 46 

4. Layer number, thickness, and corresponding stratigraphic/hydrogeologic unit for the three-dimensional 

model ..................................................................................................................................................................... 51 

5. Thermal properties used for simulation of the long-term test cycles 1 and 2 ........................................................ 51 

6. Hydraulic properties used for simulation of the long-term test cycles ................................................................... 52 

7. Summary of long-term test cycles 1 and 2 simulation times, durations, flow rates, and temperatures ............... 53 

8. Altitudes of measurement points where temperatures were averaged to correspond with model layers ............... 78 
CONVERSION FACTORS, VERTICAL DATUM, AND ABBREVIATIONS 

Multiply 

meter (m) 

square meter (m2) 

cubic meter (m3) 

meter per day (m/d)) 

cubic meter per second (m3 /s) 

liter per second (Lis) 

cubic meter per day (m3/d) 

kilogram (kg) 

kilopascal (kPa) 

kilogram per cubic meter (kg/m3) 

joule 

watt per square meter (W/m2) 

watt per cubic meter (W/m3) 

By 

Length 

3.281 

Area 

0.0002471 

Volume 

6.290 

Flow rate 

3.281 

35.31 

15.85 

264.2 

Mass 

2.205 

Pressure 

0.1450 

Density 

0.06242 

Energy 

0.0000002 

8.804 x w-5 

2.684 x w-5 

To obtain 

foot 

acre 

barrel (petroleum, 1 barrel=42 gal) 

foot per day 

cubic foot per second 

gallon per minute 

gallon per day 

pound avoirdupois 

pound-force per inch 

pound per cubic foot 

kilowatt -hour 

British thermal unit per square foot per second 

British thermal unit per cubic foot per second 

British thermal unit per foot Celsius per day per 

joule per meter per day per degree [((J/m)/d)/ degree Fahrenheit 0 C] 

joule per cubic meter per degree [(J/m3)/°C] 

joule per kilogram per degree [(J/kg)/0

C] 

1.605 x w-4 

1.491 x w-5 

2.388 x w-4 

Hydraulic conductivity 

3.281 

British thermal unit per cubic pound avoirdupois per 

British thermal unit per pound avoirdupois per degree 

Fahrenheit 

meter per day (m/d) 

meter per kilometer (m/km) 

meter squared per day (m2/d) 

Hydraulic gradient 

5.27983 

Transmissivity 

10.76 

foot per day 

foot per mile 

foot squared per day 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows: °F = (1.8 X °C) + 32 

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum of 1929 (NGVD of 1929)-a geodetic datum 

derived from a general adjustment of the first-order level nets of both the United States and Canada, formerly called Sea Level 

Datum of 1929. 

Altitude, as used in this report, refers to distance above or below sea level. 

Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times foot of aquifer thickness [(ft3

d)/ 

ft2]ft. In this report, the mathematically reduced form, foot squared per day (ft2/d), is used for convenience. 

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (j..LS/cm at 

25 °C). 

Concentrations of chemical constituents in water are given either in milligrams per liter (mg/L) or micrograms per liter (J..lg/L). 

NOTE TO USGS USERS: Use of hectare (ha) as an alternative name for square hectometer (hm2) is restricted to the measurement of small land or water areas. Use of liter (L) as a special name for cubic decimeter ( dm3) is restricted to the measurement of liquids and gases. No prefix other than milli should be used with liter. Metric ton (t) as a name for megagram (Mg) 

should be restricted to commercial usage, and no prefixes should be used with it. 

v 

Cyclic Injection, Storage, and Withdrawal of Heated Water in a Sandstone Aquifer at St. 

Paul, Minnesota 

Analysis of Thermal Data and Non isothermal 

Modeling of Long-Term Test Cycles 1 and 2 

By G.N. Delin1, M.C. Moyer2, T.A. Winterstein1, and R.T. Miller3 

ABSTRACT 

In May 1980, the University of Minnesota began a 

project to evaluate the feasibility of storing heated water 

(150 degrees Celsius) in the Franconia-IrontonGalesville aquifer (183 to 245 meters below land 

surface) and later recovering it for space heating. The 

University's steam-generation facilities supplied hightemperature water for injection. This Aquifer ThermalEnergy Storage system had a doublet-well design in 

which the injection and withdrawal wells were spaced 

approximately 250 meters apart. Water was pumped 

from one of the wells through a heat exchanger, where 

heat was added or removed. This water was then 

injected back into the aquifer through the other well. 

Two long-term test cycles, consisting of 

approximately equal durations of injection, storage and 

withdrawal of about 59 days, were completed. Rates of 

injection and withdrawal of about 18 liters per second 

were maintained for each long-term test cycle. Injection 

temperatures averaged about 108.5 and 117.7 degrees 

Celsius for long-term test cycles 1 and 2, respectively. 

Withdrawal temperatures averaged about 75 and 85 

degrees Celsius, respectively. 

Temperature graphs for selected depths at individual 

observation wells indicate that the Ironton and 

Galesville Sandstones received, stored, and yielded 

more thermal energy than the upper part of the 

Franconia Formation. Vertical-profile plots and timegraphs during storage indicate that the effects of 

buoyancy flow were minimal within the aquifer. 

A three-dimensional, anisotropic, nonisothermal 

ground-water-flow and thermal-energy-transport 

1 U.S. Geological Survey, Mounds View, Minnesota 

2University of Minnesota, Underground Space Center, 

Depa1tment of Civil Engineering, Minneapolis, Minnesota 

3Groundwater Investigations, Inc. , Pine Bush, New York 

model was constructed to simulate the two long-term 

test cycles. The only model properties varied during 

model calibration were longitudinal and transverse 

thermal dispersivities, which, for final calibration, were 

simulated as 3.3 and 0.33 meters, respectively. The 

model was calibrated by comparing model-computed 

results to: (1) measured temperatures at selected 

altitudes in five observation wells, (2) measured 

temperatures at the production well, and (3) calculated 

thermal efficiencies of the aquifer. Model-computed 

withdrawal-water temperatures were within about 3 

percent of measured values and model-computed 

aquifer-thermal efficiencies were within about 1 

percent of calculated values for the long-term test 

cycles. On the basis of these data, the model accurately 

simulates aquifer thermal-energy storage within the 

Franconia-Ironton-Galesville aquifer. 

INTRODUCTION 

The University of Minnesota started a project in May 

1980 to evaluate use of a confined, sedimentarybedrock (sandstone) aquifer [about 183 m beneath the 

St. Paul campus] for thermal-energy storage (fig. 1). 

The project was funded by the U.S. Department of 

Energy through Battelle Pacific Northwest 

Laboratories. Other participants in the project include 

the Minnesota Energy Agency, the Minnesota 

Geological Survey, National Biocentrics, Inc., OrrSchelen-Mayeron and Associates, and the U.S. 

Geological Survey. The project was designed to 

evaluate the feasibility and effects of storing hightemperature (150°C) water in the Franconia-IrontonGalesville aquifer beneath the St. Paul campus and later 

recovering the heat for water and space heating. 

The specific objectives of the U.S. Geological Survey 

in evaluating Aquifer Thermal-Energy Storage (ATES) 

were to: (1) develop an understanding of the groundwater-flow system near the site, (2) identify the 

Cl 
Building 

Gtac · - IEJf Pt.8 ;: - _ drift - '<8•·. - aq/J. --- •If/e.G-- ''er -- lenw -- -- oodc--- - - - O/Jffnin- - - St. p - - - g /JJ)it - eter a - qiJJfer 

LOCATION MAP 

C2 

Figure 1. Location and generalized schematic diagram of hydrogeology 

of the Aquifer Thermal-Energy Storage (ATES) site. 
hydraulic properties of the ground-water-flow system 

that are most important with respect to thermal-energy 

storage and identify data-collection needs for 

monitoring and evaluating aquifer-system 

performance, (3) develop a method to evaluate flow and 

thermal-energy transport for various cyclic injection 

and withdrawal schemes and aid in selection of an 

efficient well-system design, and (4) assist in the 

collection of hydraulic and thermal data during 

injection-withdrawal tests and design a data-processing 

system that will facilitate entry of the data into computer 

storage. Miller (1984 and 1985) described the 

anisotropy of the Franconia-Ironton -Gales ville aquifer, 

and preliminary modeling at the ATES site, 

respectively. Miller and Voss (1986) described the 

design of the finite-difference grid at the ATES site. 

Miller and Delin (1993) described (1) analysis of field 

observations for aquifer characterization and 

observation-network design, (2) preliminary model 

analysis to determine model sensitivity to hydraulic and 

thermal characteristics and to facilitate final model 

design, and (3) model simulations of the aquifer's 

thermal efficiency. Miller and De lin ( 1994) described 

analysis of the thermal data and nonisothermal 

modeling for the short-term test cycles. Walton and 

others ( 1991) described the geologic and hydrologic 

setting of the ATES site, the ATES system and its 

operation during the short-term test cycles, and 

presented the water chemistry, system flow, and 

temperature results for the short-term test cycles. Hoyer 

and others (1991 a and 1991 b) describe additions to and 

operation of the ATES system during the first and 

second long-term test cycles, and present the water 

chemistry, system flow, and temperature results for the 

first and second long-term test cycles. 

Purpose and Scope 

This report describes (1) the collection of hydraulic 

and thermal data for two long-term test cycles of heatedwater injection, storage, and withdrawal; and (2) the 

analysis and nonisothermal modeling for the two 

cycles. This report is one in a series that describes the 

potential for thermal-energy storage within the 

Franconia-Ironton-Galesville aquifer beneath the St. 

Paul campus of the University of Minnesota. 

Hydrogeologic Setting 

The St. Paul metropolitan area is underlain by a 

stratified sequence of Proterozoic and early Paleozoic 

sedimentary formations consisting of porous sandstone 

and fractured dolomite, which can be grouped into four 

major regional aquifers. The aquifers generally are 

separated by semipermeable sandstone, siltstone, or 

shale formations. The major aquifers are the St. Peter, 

Prairie du Chien-Jordan, Franconia-Ironton-Galesville, 

and Mount Simon-Hinckley-Fond duLac (fig. 1). 

The St. Peter aquifer consists of the St. Peter 

Sandstone, which is composed of a light-yellow or 

white, massive, quartzose, fine- to medium-grained, 

well-sorted, and friable sandstone. Thin beds of 

siltstone and shale near the base of the St. Peter 

Sandstone form a lower confining layer. The upper 

confining layer, consisting of the Platteville and 

Glenwood Formations, overlies the St. Peter Sandstone 

and is in contact with glacial drift. At the test site, the 

St. Peter aquifer is approximately 57 m below land 

surface and is 50 m thick. Transmissivity ranges from 

220 to 280 m2/d and the storage coefficient ranges from 

9.0 x 105 to 9.75 x 103. Porosity ranges from 0.28 to 

0.30. The hydraulic gradient was estimated to be 0.006 

and the pore velocity was estimated to be 0.18 m/d by 

Norvitch and others (1973). 

The Prairie du Chien-Jordan aquifer consists of the 

Prairie du Chien Group and the Jordan Sandstone (fig. 

1 ). The Prairie du Chien Group is predominantly a light 

brownish-gray or buff, sandy, thin- to thick-bedded 

dolomite that is vuggy and fractured and contains thin 

layers of interbedded grayish-green shale. The 

underlying Jordan Sandstone is a white to yellow, 

quartzose, fine-to coarse-grained sandstone that is 

massive or thick to thin bedded and varies from friable 

to well cemented. Despite the differing lithologies, the 

Prairie du Chien Group and Jordan Sandstone function 

as one aquifer because there is no regional confining 

unit between them. At the test site the aquifer is 

approximately 107 m below land surface and is 69 m 

thick. The average transmissivity is approximately 

1,235 m2/d, with a porosity of 0.30. The hydraulic 

gradient was estimated to be approximately 0.005 and 

the pore velocity was estimated to be 0.30 m/d by 

Norvitch and Walton (1979). 

The St. Lawrence Formation acts as a confining layer 

between the Prairie du Chien-Jordan and the FranconiaIronton Galesville aquifers. The St. Lawrence 

Formation is about 176m below land surface and is 

approximately 7 m thick at the test site. It is a gray and 

greenish-gray, laminated, thin-bedded, dolomite 

siltstone, silty dolomite, and shale. The porosity ranges 

from 0.15 to 0.20 and transmissivities range from 1 to 10 

n12/d. 

C3 
The Franconia-Ironton-Galesville aquifer consists of 

the Franconia Formation, and the Ironton and Galesville 

Sandstones. The Franconia Formation is divided into 

four members: Reno, Mazomanie, Tomah, and 

Birkmose (Walton and others, 1991). The Reno 

Member in the upper part of the Franconia is a fine- to 

very fine-grained, quartz, and glauconitic sandstone. 

The Reno is divided into two sections and is located 

approximately between 180 and 183 m and between 193 

and 206 m below land surface. The Mazomanie 

member is in the upper part of the Franconia between 

the depths of 186-193 m. The Mazomanie also is a fineto very-fine grained, quartz sandstone, but has minor 

glauconite content. The Tomah Member in the lower 

part of the Franconia is an interbedded sequence of fineto very fine-grained, silty sandstone with interbedded 

siltstone or shale. The Tomah is located between 206 

and 219 m below land surface. The Birkmose Member 

in the lower part of the Franconia is a dolomitic siltstone 

with some shale and fine- to very fine-grained 

glauconitic sandstone interbedded. Based on laboratory 

permeability tests (Walton and others, 1991), the 

horizontal hydraulic conductivity of the upper part of 

the Franconia is about 158 times greater than the 

hydraulic conductivity of the lower part of the 

Franconia. Analysis of results of packer tests indicate 

two hydraulic zones within the Franconia Formation 

(Miller and Delin, 1993). Based on the distinct 

differences in grain size, geophysical logs, and 

hydraulic properties between the upper and lower parts 

of the Franconia Formation, the upper 14 m of the 

Franconia was considered an aquifer and the lower 25 m 

of the Franconia was considered a confining unit. The 

Ironton Sandstone is white, medium-grained, 

moderately well-sorted quartz arenite that contains 

some silt -sized material. The Galesville Sandstone 

consists of a white to light-gray slightly glauconitic, 

well- to moderately well-sorted, mostly mediumgrained quartzose sandstone. The depth of the 

Franconia-Ironton -Galesville aquifer beneath the site is 

about 183 m and its thickness is about 62 m. The total 

transmissivity is 97.5 m2 /d and the storage coefficient is 

2.75 x 10-5. Transmissivity of the Franconia-IrontonGalesville aquifer is anisotropic, with the principal axis 

of transmissivity oriented about 30 degrees east of 

north. Average porosity ranges from 0.25 to 0.31 with 

a hydraulic gradient of 0.002 and an estimated pore 

velocity of 0.05 m/d. The ambient temperature of the 

ground-water system is typically about 11 °C. 

C4 

The Eau Claire Formation is a confining layer 

between the Franconia-Ironton Galesville and the 

Mount Simon-Hinckley-Fond duLac aquifers. The Eau 

Claire Formation consists of interbedded siltstone, 

shale, and fine silty sandstone with a few thin layers of 

dolomite. The depth of the formation beneath the site is 

about 245 m and its thickness is about 29 m. 

Transmissivity ranges from 0.5 to 5 m2

/d and porosity 

ranges from 0.28 to 0.35 (Norvitch and others, 1973). 

The Mount Simon-Hinckley-Fond duLac aquifer 

consists of the Mount Simon and Hinckley Sandstones 

and the Fond du Lac Formation. The Mount Simon 

Sandstone is fine- to coarse-grained, contains very thin 

beds of shale, and commonly is gray, white, or pink. 

The Hinckley Sandstone is fine- to coarse-grained and 

pale red to light pink. The Fond du Lac Formation 

contains lenticular beds of fine- to medium-grained 

arkosic sandstone interbedded with mudstone and is 

dark red to pink. The top of the aquifer is approximately 

274m below land surface and the aquifer is 

approximately 60 m thick. The transmissivity is 

approximately 250 m2

/d and the storage coefficient is 

about 6 x 105 (Norvitch and others, 1973). The porosity 

averages 0.25, the hydraulic gradient is 0.0025, and the 

pore velocity is approximately 0.03 m/d (Norvitch and 

others, 1973). 

Aquifer Selection 

The selection of an aquifer for thermal-energy testing 

was based on the following criteria: (1) minimal use of 

water from the aquifer in the Twin Cities area, (2) ability 

of the confining units above and below the aquifer to 

contain the injected heated water, and (3) the 

hydrogeologic properties and natural gradients within· 

the aquifer and their effect on the transfer of heat. 

Description of Test Facility 

The University of Minnesota test facility was a 

doublet well system in which production wells A and B 

were spaced approximately 250m apart (fig. 2). During 

heat injection, water was pumped from the FranconiaIronton-Galesville aquifer through production well B 

(fig. 2), transported through the ion-exchange water 

softener where hardness was reduced, passed through a 

heat exchanger where the water was heated, and 

injected back into the Franconia-Ironton-Galesville 

aquifer through production well A (fig. 3). During heat 

withdrawal, water was pumped from the FranconiaIronton-Galesville aquifer through production well A 

(fig. 2), transported through a radiator where the water 
AC1 

AM3 

Site A 

(See Insert) 

U) 

ffi 

1--

UJ 

::;;; 

Production well B 

BS1 _j• ~ BC1 

Site B 

Site C 

CM1 

N 

A 

0 100 200 300 FEET 

0 20 40 60 80 1 00 METERS 

EXPLANATION 

• AM2 Observation well and identifier 

Figure 2. Plan view of the Aquifer Thermal-Energy Storage (ATES) sites. 

cs 
was cooled, and then injected back into the aquifer 

through production well B (fig. 3). The system also 

included piping between the production wells, steam 

and condensate piping to the campus steam plant, heat 

exchangers, water treatment facility, observation wells, 

and instrumentation (fig. 3). The production wells were 

screened from about 40 to 61 m (Ironton and Galesville 

Sandstones) and from about 90 to 104m (upper part of 

the Franconia Formation) above sea level, respectively 

(fig. 4; Miller and Delio, 1993). For the long-term test 

cycles an ion-exchange water softener was added to the 

system (fig. 3). 

The ion-exchange water softener was added to the 

ATES system to prevent calcium carbonate 

precipitation in the storage well and aquifer, replacing 

the above-ground precipitation filters that had been 

used during the short-term cycles (Walton and others, 

1991 ; Miller and De lin, 1994 ). l'he ion-exchange water 

softener reduced the hardness of the ground water 

before it was heated, reducing the degree of scaling in 

the heat exchangers and in the storage well (Hoyer and 

others, 199la and 199lb). Use of the water softener 

allowed the uninterrupted operation of the ATES system 

during heat injection (Hoyer and others, 1991 a and 

1991 b). During the short-term test cycles, the 

precipitation filters and the heat exchangers required 

cleaning after one or two days of injection (Walton and 

others, 1991; Miller and Delio, 1994). 

Temperature and pressure measurements were made 

in observation wells AMI, AM2, AM3, AM4, and AS I 

(figs. 2 and 3). Observation well AM4 was installed 

30.5 meters from production well A before the longterm test cycles began to record temperatures near the 

anticipated maximum extent of the thennal front for the 

long-term test cycles. Separate wells were installed for 

temperature and pressure measurements at each 

location (fig. 4). The altitudes of individual 

measurement points for the observation wells are also 

shown in figure 4. 

Temperature measurements at production well A 

were made by use of a type-T (copper-constantan) 

thermocouple installed within the injection/discharge 

pipe at the wellhead. Temperature measurements 

within each of the observation wells (fig. 4) were made 

by use of as many as 12 type-T thermocouples as 

described in detail by Miller and Del in (1993). The 

thermocouples were in 1 or 2 manufactured strings (one 

containing 8 thermocouples and one containing 4) in 

protective 3.2-cm- or 5.1-cm- diameter steel casings 

within the observation wells at the altitudes shown in 

C6 

figure 4. Individual thermocouples were coated with 

Teflon for resistance to heat, and each 4 or 8 

thermocouple string was covered with a stainless steel 

overbraid to add rigidity and to protect each string as it 

was lowered into the steel casing. During installation, 

however, the overbraid tended to twist and kink causing 

excessive wear to the thermocouple wire where the 

kinks rubbed on the side of the well casing. Several 

thermocouples failed because of electrical shorts in 

thermocouple wires at these points of excessive wear. 

Temperatures measured by the thermocouples probably 

were slightly less than the actual temperatures in the 

aquifer because of conductive heat losses to the well 

casing; however, these temperature losses were 

minimal and measured temperatures were considered 

representative of temperatures in the aquifer. 

Submersible pressure transducers were installed to 

measure pressures in the observation wells. Pressures 

from 0 to 1,724 kPa could be measured in a temperature 

range of 1 0-121 °C. Measurement accuracy was ±2 

percent of the full-scale output over the compensated 

temperature range, or a maximum of ±34 kPa at 121 °C. 

The pressure transducers in most observation wells 

failed shortly after being installed. Several pressure 

transducers were replaced more than once, only to fail 

again. Only one pressure transducer functioned during 

long-term test cycle 1 and none functioned during longterm test cycle 2. Consequently, water levels were 

measured periodically in the observation wells during 

the long-term test cycles. Water-level data are reported 

in Hoyer and others (1991a and 199lb). 

All temperature and pressure-transducer data were 

transmitted through buried cables to a central data 

logger that measured data on electrostatic paper and 

nine-track computer tape. The operation of the data 

logger and the computer programs written to reduce the 

stored data are described in detail by Czarnecki (1983). 

Minor modification of the data-logger entries and the 

data-reduction program were required with the addition 

of observation well AM4 for the long-term test cycles. 

Some data were lost during the test cycles as a result of 

occasional failure of individual data-logger channels. 

Individual data-collection points will be referred to in 

this report by their observation-well location with 

respect to production well A and by their vertical 

position within each observation well as referenced to 

sea level. Reference to sea level as a datum is justified 

because over the very small area of the site, the 

formations are essentially flat-lying. 
..;, 

v 

SITE A 

AMl• 

(/) 

cc 

Production LJ.J 

r-LJ.J 

Well A :;',! 

14 METERS >0. ..... 

AM21< 

• <---- <---- ')~ 

~> ~1 ~ U' r- - ,-----c:j" LJ.J f\ :;',! 1 CJ2 

(/) 

ACl ,_ ASl cc <(O LJ.J 

g~ f-C!l 

<(Z • r-~ LJ.J<( 

<(CJ :I: :I: LJ.J<( u (/) 

:I:~ X cc LJ.J LJ.J 

r-

~ LJ.J 

- :;',! 

-it 1' ..... 

~ AM3 

Water "' • 

Softener "' c:: 

Q) 

"0 

If\ c:: 

0 ~Steam To Site B via 

I u~ steam tunnel 

Tunnel 

----> Aquifer Water ----> ~ 

0 10 20 30 

0 

EXPLANATION 

• AM2 Observation well and identifier 

Value 

Aquifer water movement direction 

----> Withdrawal step, from production 

well A to B 

Injection step, from production 

well B to A 

40 

10 

TRAILER 

Data recording, 

field laboratory, 

and field office 

Jos 

. lt-?f'}'-6 

;9s 

50 FEET 

SITE B 

To Site A via 

steam tunnel 

20 METERS 

LO~ 

~Production we ll B 

BSl BCl 

• • 

Figure 3. Schematic diagram of sites A and Bat the Aquifer Thermal-Energy 

Storage (ATES) site. (Modified from Walton and others, 1991). 

AM4• 

horizontal deviations were considered during 

interpretation of temperature data. 

LONG-TERM TEST CYCLES 1 AND 2 

Downhole gyroscopic surveys were conducted in 

several observation wells to determine deviations of 

each well bore with respect to land surface position 

(Hoyer and others, 199la; Miller and De lin, 1993). The 

bottoms of some wells deviate from their land-surface 

locations by as much as 8 m horizontally (fig. 5). These 

Following completion of the ATES short-term test 

cycles (Walton and others, 1991; Miller and Delin, 

C7 
Glacial 

Drift 

Pfatteville Formation 

Glenwood ~ormation 

St. Peter 

Sandstone .....1 

L.U 

> L.U 

.....1 

<( 

L.U 

U) 

Prairie du s 

Chien 0 

.....1 

L.U 

Group r:D 

0 

z 

<( 

L.U 

Jordan > 

0 

Sandstone r:D 

<( 

U) 

a: St. Lawrence Formation L.U 

fL.U 

2 

Franconia z 

Formation L.U' 

Cl 

:::::l 

fi= 

.....1 

Ironton and <( 

Galesville 

Sandstones 

Eau Claire 

Formation 

Mount Simon 

Sandstone 

C8 

225 

200 

175 

125 

100 

75 

50 

25 

-25 

PRODUCTION ACl 

WELL A 

~~~ ~~~~ 

!:!~~ Q:IQ)Q)Q) 

"'"'"' QJ~QJQ) 

E E E EEEE ",P"+J".t=i ·.;::; ·+=i·.;::;·.;::; c::c::c:: c::c::c:c:: 

~~~ Cl,)Q)Q)Q) 

uuuu 

~~"! Ll':ILnN.-

MMM NNMLri 

ASl AMl AM2 AM3 AM4 

SITE A 

EXPLANATION 

Screened interval in production well 

• Altitude range of screened interval, in meters 49.7-48.8 

f- 110 Temperature measurement point and altitude, in meters 

(refer to well AM3 for measurement altitudes) 

Figure 4. Depths of screened intervals of observation wells, 

Thermal-Energy Storage (ATES) site. (Horizontal 
Glacial 

Drift 

Platteville Formation 

Glenwood Formation 

St. Peter 

Sandstone 

Prairie du 

Chien 

Group 

Jordan 

Sandstone 

St. lawrence Formation 

Franconia 

Formation 

Ironton and 

Galesville 

Sandstones 

Eau Claire 

Formation 

Mount Simon 

Sandstone 

-182 

65 

4if.5:-4f6 41 I 

36.3-35.4 

~ 1 L3-10.4 

BCl 

111-4-1_11.3 

BSl 

SITE 8 

stratigraphy, and location of measurement points of the Aquifer 

arrangement of wells is arbitrary and not to scale.) 

PRODUCTION 

WELL B 

42 

275 

250 

225 

200 u::l 

> w 

_J 

<( 

w 

175 C/') 

5 

Cl 

_J 

w 

co 

150 ~ 

<( 

w 

> 

75 

Cl 

co 

<( 

C/') 

r:r: 

w 

fw 

:a:: 

z 

------- 25 

CMl -25 

SITE C 

C9 
Production well A 

0 10 20 30 40 50 60 70 80 90 100 FEET 

0 10 20 30 40 METERS 

EXPLANATION 

Position of observation well 

AM4 ~ Land surface and we ll number 

I Model-layer 1 (St. Lawrence Formation) 

Model-layer 6 (Eau Claire Formation) 

Figure 5. Model grid and position of observation wells at various depths. 

1994), addition of an ion-exchange water softener, and 

addition of observation well AM4, testing of the ATES 

system continued with two long-term test cycles of 

heated-water injection, storage, and withdrawal. Each 

cycle was planned to be approximately 180 days long; 

the injection, storage, and withdrawal periods for each 

cycle each were to be approximately 60 days in duration. 

ClO 

The first long-term test cycle was conducted from 

November 1984 through May 1985; the second longterm test cycle from October 1986 through April 1987. 

The duration, average rate of injection and withdrawal, 

and average temperature of injection and withdrawal for 

long -term test cycles 1 and 2 are shown in table 1. A third 

long-term test cycle, not described in this report, during 
which recovered water was sent to a heat exchanger in 

a campus building for use, was conducted from October 

1989 through March 1990 (Hoyer and others, 1994 ). 

Table 1. Summary of duration, average rates of injection and 

withdrawal, and average temperatures of injection, storage, and 

withdrawal for long-term test cycles 1 and 2 

Average flow 

Phase duration rate (liters per 

(days) second) 

Long-term test cycle 1 

Injection 1

59.1 18.0 

Storage 61.0 

Withdrawal 2

58.0 18.4 

Long-term test cycle 2 

Injection 3

59.3 

Storage 59.1 

Withdrawal 4

59.7 

1

0ver a period of 76 days. 2

0ver a period of 58.8 days. 

3

0ver a period of 65.0 days. 

40ver a period of 59.8 days. 

18.3 

17.9 

Average 

temperature 

(degrees Celsius) 

108.5 

74.7 

117.7 

85.1 

Operation of the ATES system during long-term test 

cycles 1 and 2 was relatively trouble free. Unlike the 

short-term test cycles, when injection was interrupted to 

clean the filters after 1 or 2 days, flow was maintained for 

many days at relatively constant temperatures during the 

long-term test cycles with few interruptions. The source 

water temperature varied smoothly and the temperature 

of the injected water was controlled by the temperature 

controller, or varied as a response to the capacity of the 

heat exchanger (Hoyer and others, 1991a and 1991b). 

Injection was interrupted eight times during long-term 

test cycle 1, and five times during long -term test cycle 2. 

Withdrawal was interrupted once during each cycle by 

an electrical outage. Interruptions during the injection 

phases resulted from malfunctioning of the ionexchange water softener, freezing of pressure shutoff 

valves, and shutdowns for repairs. A detailed 

description of the operation of the long-term test cycles 

is given in Hoyer and others (1991a and 1991b). 

ANALYSIS OF THERMAL DATA FOR LONGTERM TEST CYCLES 1 AND 2 

The following sections of the report summarize and 

interpret the thermal data for the long-term test cycles 

and describe the movement of heat and the changes in 

temperature in relation to the hydraulic and thermal 

properties of the aquifer and confining units. Thermal 

data are presented in graphs having temperature plotted 

as a function of time and in graphs of temperature 

profiles of observation wells at the start and end of each 

phase of the cycles. Discussion and possible 

explanations are given for measured trends at individual 

observation wells and measurement points. 

Temperature as a Function of Time 

Graphs of temperature as a function of time since each 

test cycle began were used to evaluate temperature front 

arrivals, temperature trends, maximum temperatures, 

and transient thermal effects at specific points within the 

aquifer. These graphs were particularly useful at points 

where aquifer properties change between measuring 

points. Temperatures measured at the wellhead in 

production well A and in observation wells AM 1, AS 1, 

AM2, AM3, and AM 4 are presented. Figures 6 through 

11 present temperatures for periods of injection, storage, 

and withdrawal for long-term test cycle 1; figures 12 

through 17 present temperatures for injection, storage, 

and withdrawal periods for long-term test cycle 2. 

Relatively small temperature fluctuations, which 

represent intermittent failure of thermocouples due to 

insulation wear at kinks in the thermocouple wires or 

electronic noise in the data logger, are evident in some of 

the graphs for the observation wells and should be 

ignored. An example of this type of noise is evident in 

the graph of the 73.1-m thermocouple between days 3 

and 10. Temperatures are not plotted for thermocouples 

that failed during the long-term test cycles. 

Temperatures for production well A were measured at 

the wellhead, not within the Franconia-IrontonGalesville aquifer. Therefore, temperatures for 

production well A indicate when injection or withdrawal 

of heated water took place, and when injection or 

withdrawal was interrupted (figs. 6 and 12). When water 

was not flowing through the wellhead, as during periods 

of storage and during interruptions to injection or 

withdrawal, temperatures in production well A rapidly 

decreased to the air temperature at the time, below 50°C. 

Temperatures measured during storage periods, 

therefore, represent air temperatures and are not 

representative of temperatures in the Franconia-IrontonGalesville aquifer. 

A temperature front is hereinafter defined as the first 

temperature increase or decrease measured at a 

thermocouple, which defines the beginning of a trend of 

increasing or decreasing temperatures. Identifying the 

first arrival time of a temperature front was imprecise 

when the temperature changes were small and when the 

Cll 
Cl) 

::::> 

Cl) 

.....1 

w 

u 80 Cl) 

w 

w 

a: 

(!) 

w 

Cl 

~ 70 

w~ 

a: 

::::> 

I-

<( 

a: 

w 60 a.. 

2: 

w 

I50 l Injection 

temporarily 

stopped 

40 

10 

C12 

~ \ Injection J 

temporarily 

stopped 

20 30 40 50 60 

DAYS FROM BEGINNING OF INJECTION 

70 80 90 100 

Figure 6. Temperatures at the wellhead in production well A 
100 110 

Injection J 

temporarily 

started 

120 130 140 150 160 

DAYS FROM BEGINNING OF INJECTION 

during long-term test cycle 1, November 1984 through May 1985. 

170 180 190 200 

Cl3 
100 

St. Lawrence Formation 

80 

60 

40 

20 

0 

140 

Upper part of Franconia Formation 

120 

100 

80 

60 

40 

20 

(I) 

::> 0 (I) 

~ 

L.LJ 100 u 

(I) 

L.LJ 80 L.LJ 

a: 

(.!) 

L.LJ 

Cl 60 

z 

L.LJ- 40 

a: 

::> 

f- 20 

<! 

a: 

L.LJ 

a... 0 

~ 140 L.LJ 

f120 

100 

80 

60 

40 -

20 

0 

100 

80 

60 

40 

20 

00 10 20 

C l4 

30 

INJECTION STORAGE 

40 50 60 70 80 90 

DAYS FROM BEGINNING OF INJECTION 

' _j 

_j 

I 

- 1 

---1 

_j 

-1 

_j 

I 

- 1 

-1 

_j 

I 

- 1 

-1 

_j 

I 

I 

I 

- 1 

-1 

_j 

I 

- 1 

-1 

_j 

I 

- 1 

-1 

_j 

100 

Figure 7. Temperatures in observation well AM1 during 
I 

1-

tL 

r 

L 

tL 

I 

r 

tL 

r 

I 

1-

tL 

I 

1-

r 

L 

I 

I 

I 

1-

tL 

STORAGE 

I 

-~ I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

WITHDRAWAL --- Temperature at 109.7 meter altitude 

--- Temperature at 104.2 meter altitude 

--- Temperature at 93.0 meter altitude 

--- Temperature at 88.4 meter altitude 

: Temperature at 73.1 meter altitude I 

r= F.==========-----====:--======~ Temperature at 65.5 meter altitude 

L jl -= ~::::::==~~~~~~~= I I ----==- : = 1- I 

I t- I 

L I 

I I 

I 

I 

1-

tL 

tL 

I 

1-

tL 

I 

1-

tL 

I 

1-

I 

1-

tL 

I 

tL 

I 

1-

tL 

100 110 120 130 140 150 160 170 180 190 

DAYS FROM BEGINNING OF INJECTION 

long-term test cycle 1, November 1984 through May 1985. 

200 

CIS 
100 I 

-I 

80 ---j 

_j 

60 I 

- I 

-; 

40 _j 

20 _j 

0 

140 I 

- 1 

120 ---j 

_j 

100 

-; 

80 _j 

/ I 

~'\ - I 

60 ---j 

_j 

40 

Pump I 

temporarily - 1 

stopped -; 

20 _j 

I U) I ::l 0 U) 

-' 

LLJ 100 

Lower pa ~ of Franconia

1 

Formation 

I I I I I I I I u I 

U) - 1 

LLJ 80 - ---j 

LLJ 

0: _j 

(.!) _ I LLJ 60 -

Cl I 

z -"' 

40 - _j 

0: 

uJ 

~ ~ ~ 

::l 

t- 20 =- / ---j 

<t _j 

0: 

LLJ I I I I I I I I l a... 0 

::::!: 140 LLJ 

t- I 

- 1 

120 ---j 

_j 

100 

80 _j 

I 

- 1 

60 ---j 

_j 

40 - 1 

-; 

20 _j 

I 

I 

0 

100 I 

- 1 

80 ---j 

_j 

60 _ I 

-; 

40 _j 

20 ---j 

_j 

10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 8. Temperatures in observation well AS1 during 

CJ6 
I 

1- STORAGE rL 

I 

-

I 

rL 

I 

1-

L 

I 

I 

1-

r--

L 

rL 

I 

1-

rL 

I 

1-

rL 

I 

1-

I 

1-

r--

L 

I 

I 

I 

I 

I 

WITHDRAWAL 

I 

1-

1-" 

L 

L 

r-

----------------------------------~ 

I 

1-

r--

L 

--- Temperature at 109.7 meter altitude 

--- Temperature at 104.2 meter altitude 

--- Temperature at 99.1 meter altitude 

- -- Temperature at 93.0 meter altitude 

--- Temperature at 88.4 meter altitude 

Temperature at 73.1 meter altitude 

Temperature at 65.5 meter altitude 

------ Temperature at 58.2 meter altitude } 

Ironton ----- Temperature at 51 .5 meter altitude 

jeo==================±==::=-------------...... ------ Temperature at 44.8 meter altitude } Galesville 

L 

I 

1-

r--

L 

I 

1-

rL 

I 

1-

I 

1-

rL 

rL 

I 

1-

rL 

100 110 120 130 140 150 160 170 180 190 

DAYS FROM BEGINNING OF INJECTION 

long-term test cycle 1, November 1984 through May 1985. 

200 

C I7 
St. Lawrence Formation 

80 

60 

40 

120 

100 

80 

60 

40 

(I) 

INJECTION l STORAGE I 

I 

I I I -

- 1 

---1 

- I 

_J 

I 

- 1 

---1 

...J 

I 

- 1 

4 

_j 

I 

- 1 

~ 100 r---,----,----,---,----,----,----,---,----,----,----r---.----,----,---,---,----,----,---.-----I u 

(I) 

w 

w 

a: 

(!) 

w 

Cl 

z 

80 

60 

80 

60 

40 

20 

I 

I 

I 

I 

I 

I 

I 

---------+--- I 

I 

I 

I 

- 1 

---1 

...J 

I -

4 

_j 

_I 

---1 

...J 

I 

- 1 

---1 

...J 

I 

- 1 

4 

_j 

-I 

---1 

...J 

I 

- 1 

4 

_j 

I 

I oL---~--~--~--~---L __ _L __ _L __ _L __ ~--~--~--__j ____ L-__ L_ __ il_ __ L_ __ ~--~--~---

10or---.---,----r---,---,----,---~--~---.---.---.----.---~--.---~---r---,---,----,----

I 

- 1 

80 ---1 

...J 

I 

60 -1 

4 

_j 

40~-------------------------------------------+------------~ 20 ---1 

...J 

10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 9. Temperatures in observation well AM2 during 

CI S 
I 

1-

tL 

I 

c ~ 

r 

L 

I 

I 

tL 

I 

1-

tI 

1-

L 

I 

1-

tL 

I 

I 

r 

L 

I 

1-

I 

1-

tL 

I_ 

r 

L 

tL 

I 

1-

tI 

1-

r 

L 

I 

1-

tL 

I 

1-

r 

L 

I 

I 

I 

1-

tL 

I 

1-

r 

L 

I 

I 

tL 

100 110 120 

STORAGE I WITHDRAWAL I 

I 

I 

I 

I 

- - - Temperature at 109.7 meter altitude 

--- Temperature at 104.2 meter altitude 

~----~-~~·---- I ---- --~ 

130 

I 

I 

I 

140 150 160 

DAYS FROM BEGINNING OF INJECTION 

--- Temperature at 93.0 meter altitude 

--- Temperature at 88.4 meter altitude 

170 

Temperature at 73.1 meter altitude 

Temperature at 65.5 meter altitude 

180 190 

long-term test cycle 1, November 1984 through May 1985. 

200 

Cl9 
100 

80 

60 

40 

20 

0 

140 

120 

100 

80 

60 

40 

20 

(/) 

::::> 0 (/) 

...J 

LU 100 u I . I . 

(/) Lower part of Franconia Formation LU 80 1- LU 

0: 

~ 

LU 60 1- Cl 

z 

LU• 40 1-

0: 

::::> 20 1- 1-

<! iol 1~. 0: r T1 LU llr 1 I a... 0 ~ 140 LU 

1- Ironton and Galesville Sandstones 

120 

100 

80 

60 

40 

20 

0 

100 

80 

60 

40 

20 

0 

0 10 20 

C20 

I 

I 

30 

I I I I 

I I I I 

40 50 60 70 

DAYS FROM BEGINNING OF INJECTION 

l I I 

! 

i I l 

80 90 

_j 

-' 

I 

_j 

_j 

100 

Figure 10. Temperatures in observation well AM3 during 
L 

I 

rI 

I 

rL 

I 

1-

r 

L 

I 

I 

rL 

I_ 

I 

1-

rL 

STORAGE WITHDRAWAL --- Temperature at 109.7 meter altitude 

- -- Temperature at 104.2 meter altitude 

--- Temperature at 93.0 meter altitude 

--- Temperature at 88.4 meter altitude 

--- Temperature at 58.2 meter altitude } Ironton --- Temperature at 51.5 meter altitude 

r 

L 

I 

;=======================f:::::====:::::::-Temperature at 44.8 meter altitude } Galesville 

1-

rL 

I 

1-

r 

L 

I 

1-

I 

1-

rL 

1-

r 

L 

I 

1-

rL 

100 110 120 130 140 150 160 170 180 190 

DAYS FROM BEGINNING OF INJECTION 

long-term test cycle 1, November 1984 through May 1985. 

200 

C21 
20 

I 

- 1 

-I 

_I 

100 I 

- 1 

-; 

80 _j 

I 

- 1 

60 -I 

_j 

40 _ I 

20 _j 

Cl') 

:=J 0 Cl') 

-' 

UJ 100 u 

Cl') - I 

UJ -I UJ 

c: _I 

(.!) I UJ 60 - 1 Cl 

z -; 

UJ- 40 

- --- --"'-- - --"'-- - I c: - 1 :=J 

f- 20 -I 

<( 

c: 

UJ 

c... 0 

2 

UJ 140 f- I 

- I 

120 -I 

_I 

I 100 - 1 

-; 

80 _j 

----- - - - I 

~--- - 1 

60 -I 

_j 

40 I 

- I 

-; 

_j 

I 

- 1 

0 

100 I 

- 1 

80 -I 

_j 

60 - I 

-; 

40 _j 

I 

- 1 

20 _j 

00 10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 11. Temperatures in observation well AM4 during 

C22 
I 

I STORAGE WITHDRAWAL --- Temperature at 109.7 meter altitude 

L 

L 

L 

I 

I _ ----- -- ~---.,.,-- 1 

I 

1-

tL 

I 

1-

tL 

I 

1-

tL 

I 

I 

tL 

I 

I 

I 

1-

tL 

I 

1-

tL 

L 

100 110 

I 

I 

I _J..---

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

-~-

--- Temperature at 104.2 meter altitude 

--- Temperature at 93.0 meter altitude 

Temperature at 88.4 meter altitude 

Temperature at 73.1 meter altitude 

Temperature at 65.5 meter altitude 

--- Temperature at 58.2 meter altitude } 

Ironton --- Temperature at 51.5 meter altitude 

Temperature at 44.8 meter altitude } Galesville 

140 150 160 170 

DAYS FROM BEGINNING OF INJECTION 

long-term test cycle 1, November 1984 through May 1985. 

200 

C23 
Cl) 

:::1 

Cl) 

--' UJ 

u 

Cl) 

UJ 

UJ 

a: 

~ 

UJ 

Cl 

z 

w' 

a: 

:::1 

f-

<( 

a: 

UJ 

c... 

::2! 

UJ 

f60 

50 

40 

30 

20 

10 

'In)ectlon ·. 

temporarily 

stopped 

~ Injection ....---"? 

temporarily 

stopped 

~--~--~--~--~--~---'----L---L--~--~--~--~--~~LuL-WLL-~C---~--~~~~~ 

10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 12. Temperatures in production well A during 

C24 
100 110 120 130 140 150 160 170 

DAYS FROM BEGINNING OF INJECTION 

long-term test cycle 2, October 1986 through April1987. 

C25 
100 I 

St. Lawrence Formation INJECTION STORAGE - 1 

80 ---j 

60 I 

- 1 

"1 

40 _j 

I 

- 1 

20 ---j 

_j 

0 I 

140 I 

- 1 

120 ---j 

_j 

100 - I 

"1 

80 _j 

I 

- 1 

60 ---j 

_j 

40 I - I 

"1 

20 _j 

I (I') - 1 

::> 0 Ci3 

--' w 100 u I 

(I') - 1 

w 80 ---j 

w 

c::: _j 

(!) 

w 

0 60 

z "1 

40 _j 

w· 

c::: 

::> 

I- 20 ---j 

<( _j 

c::: 

w 

c... 0 

w 

~ 140 I- I 

- 1 

120 ---j 

100 - I 

"1 

80 _j 

I 

-I 

60 ---j 

_j 

40 I -1 

"1 

20 _j 

I 

- 1 

0 

100 I 

- 1 

80 _j 

60 I 

- 1 

"1 

40 _j 

I 

- 1 

20 -, 

_j 

00 10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 13. Temperatures in observation well AM1 during 

C26 
STORAGE 

r 

L 

rL 

I 

1-

rL 

1-

r 

L 

I 

1-

rL 

I 

1-

r 

L 

I 

1-

I 

1-

rI 

I 

WITHDRAWAL --- Temperature at 109.7 meter altitude 

--- Temperature at 104.2 meter altitude 

--- Temperature at 93.0 meter altitude 

--- Temperature at 88.4 meter altitude 

I Temperature at 73.1 meter altitude L 

- -= r 

L 

~~~~~~-~ ~= ~~ ~~~~~~~~~~ ~~~~~~~Te at ~6~5mMera~rude i 

I 

I 

I 

I 

I 

I 

I 

I 

I 

rL 

I 

1-

tI 

=--- I 

r 

L 

I 

1-

tL 

I_ 

I 

r 

L 

I 

I 

I 

1-

L 

r 

L 

I 

1-

rL 

100 110 

I 

-----r----

120 

1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

130 

--- Temperature at 58.2 meter altitude } Ironton --- Temperatu re at 51.5 meter altitude 

Temperature at 44.8 meter altitude } Galesville 

140 150 160 170 180 190 

DAYS FROM BEGINNING OF INJECTION 

long-term test cycle 2. October 1986 through April1987. 

200 

C27 
100 

80 

60 

40 

20 

0 

140 

120 

100 

80 

60 

40 

20 

(/) 

:=! 0 (/) 

...J 

w 100 u 

(/) 

w 80 w 

a: 

(.!J 

w 60 Cl 

z 

u1 40 

a: 

:=! 

f- 20 

<! 

a: 

w 

a.. 0 

w 

~ 140 f120 

100 

80 

60 

40 

20 

0 

100 

80 

60 

40 

20 

10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 14. Temperatures in observation well AS1 during 

C28 
L 

I_ 

rL 

STORAGE WITHDRAWAL --- Temperature at 109.7 meter altitude 

--- Temperature at 104.2 meter altitude 

--- Temperature at 93.0 meter altitude 

--- Temperature at 88.4 meter altitude 

Temperature at 73.1 meter altitude 

t: 

~ 

~~~~~ ~~~~~~~~~~~~~~~~~~~~ ~~ ~~ em pe tu eu~.5m~eraH~de 

~ : r- I 

L : 

I 

1-

rL 

I 

1-

r 

L 

I 

I 

I 

1-

rL 

1-

r 

L 

I 

1-

rL 

100 110 120 130 

--- Temperature at 58.2 meter altitude } Ironton --- Temperature at 51.5 meter altitude 

--- Temperature at 44.8 meter altitude } Galesville 

140 150 160 170 180 190 

DAYS FROM BEGINNING OF INJECTION 

long-term test cycle 2, October 1986 through April1987. 

200 

C29 
100 

80 

60 

40 

20 

0 

140 

120 

100 

80 Water sampling 

60 

40 

20 

U) 

::l 0 U) 

-' 

UJ 100 u 

U) 

UJ 80 UJ 

c: 

Lower pa ~ of Fran conia

1 

Formation 

I I I I I I I I 

t.::" Water sampling - 1 

- event -1 

_J 

~ 

UJ 60 Cl 

z 

w· 40 

c: 

::l 

1- 20 

I - I 

rtl'--1"-1'-- A.-._... ~ -; 

_j 

PC:=J"='"'= '="'=\A: I 

- -1 

<! 

c: 

UJ 

a... 0 

_J 

I I I I I I I I I I 

UJ 

~ 140 1- I 

- 1 

120 _J 

100 I 

- 1 

-; 

80 _j 

I 

- 1 

60 -1 

_J 

40 I 

- 1 

-; 

20 _j 

I 

- 1 

0 

100 I 

- 1 

80 -1 

_J 

60 

Data lost because of equipment malfunction I 

- 1 

-; 

40 _j 

I 

- I 

20 -1 

_J 

I 

10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 15. Temperatures in observation well AM2 during 

C30 
1-

rL 

I 

-

L - - ~ 

I - 1-

rL 

I 

1-

r 

L 

I 

I 

I 

1-

rL 

I 

1-

r 

L 

rL 

I 

1-

L 

I 

1-

r 

L 

I 

1-

rL 

I 

1-

r 

L 

I 

1-

I 

1-

rL 

I 

1-

r 

L 

I 

1-

rL 

100 110 

--- Temperature at 93.0 meter altitude 

-- Temperature at 88.4 meter altitude 

Temperature at 80.8 meter altitude 

Temperature at 73.1 meter altitude 

----r--_,..----~-----------~-----__:_::_: em pe .::tu:.:_ re::__-:at 65.5 meter altitude 

--- Temperature at 58.2 meter altitude } Ironton 

--- Temperature at 44.8 meter altitude } Galesville 

Data lost because of equipment malfunction 

120 130 140 150 160 170 180 190 

DAYS FROM BEGINNING OF INJECTION 

long-term test cycle 2, October 1986 through April1987. 

200 

C3 1 
100 

80 

60 

40 

20 _J 

a 

140 

Upper part of Franconia Formation 

120 

100 

80 

60 

40 

20 

C/) 

:::::l a C/) 

_J 

UJ 100 u 

C/) 

UJ 80 UJ 

a: 

Lower part of Franconia Formation I 

- 1 

_, 

_J 

~ 

UJ 60 Cl 

z 

UJ- 40 

a: 

""1 

__J 

_I 

:::::l 

I- 20 _, <! _J 

a: 

L.LJ 

a... a 

UJ 

~ 140 I- - I 

120 _, 

100 - I 

""1 

80 _I 

I 

- I 

60 _, 

_J 

40 - I 

""1 

20 __J 

I 

-1 

a 

100 I 

- 1 

80 _, 

60 I 

- 1 

""1 

40 __J 

I 

I 

20 _, 

_J 

a 

a 10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 16. Temperatures in observation well AM3 during 

C32 
I 

1- STORAGE WITHDRAWAL tL 

I_ 

I 

' L 

1-

L 

I 

I 

1-

tL 

I_ 

' 

I 

1-

tL 

I 

I 

L 

I 

1-

I 

1-

tL 

' L 

I 

-

tL 

I 

1-

tL 

1-

' L 

I 

1-

tL 

I 

1-

' L 

I 

1-

I 

1-

t-

' L 

I 

1-

tL 

100 110 130 140 150 160 

DAYS FROM BEGINNING OF INJECTION 

long-term test cycle 2, October 1986 through April1987. 

--- Temperature at 109.7 meter altitude 

--- Temperature at 104.2 meter altitude 

--- Temperature at 93.0 meter altitude 

--- Temperature at 88.4 meter altitude 

170 

Temperature at 73.1 meter altitude 

Temperature at 65.5 meter altitude 

: 

190 200 

C33 
100 

80 

60 

40 

20 

0 

140 

120 

100 

80 

60 . / Water sampling 

1::: event _j 

40 

20 :: _J 

(/) 

:::l 0 (/) 

-' UJ 100 u 

(/) 

I I I I I I I I I I 

Lower part of Franconia Formation - 1 

UJ 80 UJ 1- -j 

cr: _j 

(!) 

UJ 60 Cl 

I 1- - 1 

z 

UJ- 40 

cr: 

:::l 

f- 20 

<l: 

cr: 

UJ 

Cl.. 0 

- l'i-- _J 

I I 

~~ I 

I _j 

I I I j I I I I I I I 

~ 140 UJ 

f- Ironton and Galesville Sandstones I 

- 1 

120 -j 

100 I 

- 1 

-1 

80 :=J 

- I 

60 -j 

_j 

40 I 

- 1 

-1 

20 _J 

I 

- 1 

0 

100 I 

- 1 

80 -j 

_j 

60 _ I 

I 

-1 

40 _J 

20 -j 

_j 

20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 17. Temperatures in observation well AM4 during 

C34 
I 

1- STORAGE WITHDRAWAL - - - Temperature at 109.7 meter altitude 

t- --- Temperature at 104.2 meter altitude L 

I 

1-

r 

L 

~ 

I 

1-

t- --- Temperature at 93.0 meter altitude L 

I --- Temperature at 88.4 meter altitude 1-

r 

L 

I 

1-

t-

~ : : l I 

1-

I 

1-

t- Temperature at 73.1 meter altitude L 

I Temperature at 65.5 meter altitude 1-

tl :: ::...:..:. k L 

1-

--- Temperature at 58.2 meter altitude } t- Ironton - -- Temperature at 51 .5 meter altitude I 

1- --- Temperature at 44.8 meter altitude } Galesville 

r 

I 

1-

tL 

I 

1-

r 

L 

I 

1-

I 

1-

tL 

I 

1-

r 

L 

tL 

100 110 120 130 140 150 160 170 180 190 200 

DAYS FROM BEGINNING OF INJECTION 

long-term test cycle 2, October 1986 through April1987. 

C35 
measured temperatures were fluctuating. The arrival of 

temperature fronts at the observation wells can be seen 

in the graphs for the observation wells. Figure 8, for 

example, shows the arrival of a temperature front in 

observation well AS 1 less than 1 day into the injection 

phase of long-term test cycle 1 in the Ironton and 

Galesville Sandstones part of the aquifer. A 

temperature front arrived in the upper part of the 

Franconia Formation in observation well AS 1 after 

about 3.5 days (fig. 8). 

For the Ironton and Galesville Sandstones, the 

earliest arrival times for the temperature front in all 

wells for both cycles typically were at the 58.2-m 

altitude in the upper part of the Ironton Sandstone (figs. 

7-11 and 13-17; table 2). The second measured arrival 

times typically were at the 51.5-m altitude, although the 

second arrival time occurred at the 44.8-m altitude for 

well AS 1 (fig. 8). The rate of temperature rise was 

greatest at the 52.8-m altitude. For observation AM4 

during the second cycle (fig. 17), the temperature 

change initially was very slow; about 4 days into the 

cycle the rate of temperature change suddenly 

increased. The initial arrival may have been residual 

heat from the previous cycle; the increase in rate may 

Table 2. Temperature front arrival time at measurement points in the upper part of the Franconia Formation and in the Ironton and 

Galesville Sandstones for long term test cycles I and 2 

Well number and 

distance from injection 

well 

C36 

AMI 

7m 

ASl 

7m 

AM2 

14m 

AM3 

14m 

AM4 

30m 

[m, meters; --, no data or temperature front not detected; do., ditto] 

Altitude of measurement 

point (meters above sea 

Stratigraphic unit level) 

Upper part of the Franconia Form. 99.1 

do. 93.0 

do. 88.4 

Ironton and Galesville Sandstones 58.2 

do. 51.5 

do. 44.8 

Upper part of the Franconia Form. 99.1 

do. 93.0 

do. 88.4 

Ironton and Galesville Sandstones 58.2 

do. 51.5 

do. 44.8 

Upper part of the Franconia Form. 99.1 

do. 93.0 

do. 88.4 

Ironton and Galesville Sandstones 58.2 

do. 51.5 

do. 44.8 

Upper part of the Franconia Form. 99.1 

do. 93.0 

do. 88.4 

Ironton and Galesville Sandstones 58.2 

do. 51.5 

do. 44.8 

Upper part of the Franconia Form. 99.1 

do. 93.0 

do. 88.4 

Ironton and Galesville Sandstones 58.2 

do. 51.5 

do. 44.8 

Time of temperature front 

arrival (days since start of 

injection) 

Cycle 1 Cycle2 

3.1 1.7 

3.1 1.7 

4.7 1.7 

0.1 0.2 

0.1 0.8 

1.6 2.7 

5.0 3.5 

3.9 3.0 

3.9 3.0 

0.6 0.4 

1.5 1.2 

1.3 1.0 

9.5 10.0 

9.5 10.0 

4.5 2.0 

3.6 1.5 

4.8 4.0 

12.0 10.0 

11.3 8.7 

3.2 1.5 

5.0 3.2 

5.8 4.4 

50.0 45.0 

40.0 35.0 

55.0 50.0 

7.0 4.5 

8.0 8.5 

12.0 12.5 
have been the actual arrival from the second cycle. 

Multiple cycles somewhat complicate data 

interpretation. 

For the upper part of the Franconia, temperature front 

arrival times were considerably slower than in the 

Ironton and Galesville Sandstones (figs. 7-11 and 13-

17; table 2). This delay is not surprising because the 

permeability of the upper part of the Franconia 

Formation is about one-half that of the Ironton and 

Galesville Sandstones. The earliest arrival times for the 

temperature front at observation well AM 1 were at the 

93.0-m and the 99.1-m altitudes during the first longterm test cycle (fig. 7), and at all three thermocouples 

(88.4-m, 93.0-m, 99.1-m) during the second long-term 

test cycle (fig. 13). The temperature front reached 

observation well AS 1 in the upper part of the Franconia 

Formation first at the 93.0-m and 88.4-m, and last at the 

99.1-m altitudes (figs. 8 and 14). The first arrivals at 

well AM2 were at the 88.4-m altitude (figs. 9 and 15). 

The first arrivals at wells AM3 (figs. 10 and 16) and 

AM4 (figs. 11 and 17) were at the 93.0-m altitude. The 

initial arrival may have been residual heat from the 

previous cycle; the increase in rate may have been the 

actual arrival from the second cycle. 

The highest temperatures measured during both 

cycles in every observation well were at either the 51.5 

or 58.2 m altitudes, corresponding to the Ironton 

Sandstone, which is the most permeable part of the 

Franconia-Ironton-Galesville aquifer (Walton and 

others, 1991; Miller and Delin, 1993). The Ironton 

Sandstone part of the aquifer is approximately four 

times as permeable as the Galesville Sandstone part of 

the aquifer, represented by the 44.8-m thermocouple. 

Highest temperatures measured at the 44.8, 51.5, and 

58.2-m thermocouples were measured during the 

injection phase. At all observation wells, the maximum 

temperatures in the Ironton and Galesville Sandstones 

were reached before the end of the injection phase, 

probably due to the temperature of the injected water 

being lower toward the end of the injection phase (figs. 

6 and 12). After reaching their maximums, 

temperatures in the Ironton and Galesville Sandstones 

at observation wells AM 1, AS 1, AM2, and AM3 

decreased similar to the trend of the injected-water 

temperatures. 

The highest temperatures in the upper part of the 

Franconia Formation at observation wells AM 1, AS 1, 

AM2, and AM3 during the second cycle were only a few 

degrees lower than those measured in the Ironton and 

Galesville Sandstones. However, the highest 

temperature was reached at the end of the injection 

phase. Similar observations were made for the first 

cycle except at wells AS1 and AMl. For well AM4, a 

high temperature of between 40 and 50°C was reached 

at the end of the injection phases of both test cycles. 

Temperatures measured at several thermocouples 

changed immediately at the end of injection periods and 

at the beginning of withdrawal periods. These 

temperature changes of generally less than 5°C, some 

incteases and some decreases, may be attributed to the 

pressure changes caused by interruptions or startups. 

The changes caused water in the piezometer tubes 

adjacent to the thermocouples to move past the 

thermocouples, moving water of a different temperature 

to the level of the thermocouple. 

Some of the temperature-versus-time graphs for 

observation wells AM2 (fig. 15) and AM4 (fig. 17) 

show the effect of sampling the wells during the test 

cycles. These sampling periods are evident as sharp 

vertical spikes in the graphs, such as those for the upper 

part of the Franconia Formation at AM2 during the first 

13 days of cycle 2 (fig. 15). Water samples were 

obtained by pumping water from the observation wells 

at a rate of approximately 0.06 L/s. The effect is shown 

most frequently during the second long-term test cycle 

atwellAM2(fig.15). Thepumpingcausedthesampled 

water to flow past thermocouples at all overlying 

temperature measurement points. When the sampled 

water had a temperature greater (or less) than the 

temperature detected by the thermocouples, a sudden 

increase (or decrease) was measured. When sampling 

was completed, temperatures measured at the affected 

thermocouples returned to pre-sampling temperatures. 

During storage periods, when water was not added to 

or removed from the storage zone around production 

well A, temperatures in the observation wells changed 

slowly. In most wells, temperature changes at the same 

altitudes were generally in the same direction, either 

decreasing or increasing, and of similar magnitude 

during both test cycles. 

During storage periods, heat was conducted from the 

upper part of the Franconia Formation both into the St. 

Lawrence Formation and into the lower part of the 

Franconia Formation. Heat was also conducted from 

the Ironton and Galesville Sandstones both into the 

lower part of the Franconia Formation and into the Eau 

Claire Formation. Temperatures for the beginning of 

withdrawal periods generally were lower than the 

temperatures at the end of the injection periods at all 

C37 
temperature measurement points opposite the screened 

intervals of production well A. The greatest drop in 

temperature was measured at the lowest thermocouple 

in the upper part of the Franconia Formation (88.4-m 

altitude) and the thermocouple in the Galesville 

Sandstone (44.8-m altitude). Thermally-induced 

convection during storage periods may have caused 

some of the measured temperature changes. 

In addition to the heat conduction described above, 

heat was also transported down the well bore of 

production well A from the upper part of the Franconia 

Formation to the Ironton and Galesville Sandstones 

during storage periods. This heat transport occurred 

because production well A was open to both formations 

and because hydraulic heads decreased with depth, 

allowing ground water to flow down and out of the well 

bore during storage periods. Thus, heat was transported 

from the Franconia Formation to the Ironton and 

Galesville Sandstones because of the convective flow of 

heated water through the well bore of production well 

A. 

Temperatures measured during withdrawal periods 

support the concept that transport of heat within the 

aquifer was a function of permeability; the maximum 

decrease [cooling] of aquifer temperature occurred in 

the Ironton and Galesville Sandstones. At the start of 

withdrawal periods, temperatures in the Ironton and 

Galesville Sandstones and in the upper part of the 

Franconia Formation were somewhat lower than at the 

beginning of storage periods. Temperatures measured 

in the lower part of the Franconia Formation and in the 

St. Lawrence Formation and Eau Claire Formation were 

somewhat higher than at the beginning of storage 

periods. During withdrawal periods, temperatures 

initially decreased rapidly in the upper part of the 

Franconia Formation, then decreased more slowly. 

During withdrawal periods, temperatures in the Ironton 

and Galesville Sandstones decreased slowly. 

Temperatures of the withdrawal water more closely 

resembled the temperatures in the Ironton and 

Galesville Sandstones than in the upper part of the 

Franconia Formation. Thus, the Ironton and Galesville 

Sandstones contributed a majority of the water and heat 

during withdrawal periods. The withdrawal plots (figs. 

7-17) illustrate that, as expected, the injected heat was 

not fully recovered by the end of the withdrawal 

periods. 

Water temperatures reached a maximum at 

production well A about 12 to 24 hours after withdrawal 

began (figs. 6 and 12), likely because the well was 

C38 

completed in two different units. Intra-aquifer 

[interformational] flow during storage periods, 

described earlier, resulted in a slight cooling of water in 

the well bore as it flowed from the upper part of the 

Franconia Formation into the Ironton and Galesville 

Sandstones. At the beginning of withdrawal periods, 

the water withdrawn from the Ironton and Galesville 

Sandstones was cooled further as it traveled up the well 

bore past the unscreened lower part of the Franconia 

Formation. The water also lost heat through conduction 

to the well bore and casing at the beginning of 

withdrawal periods that also caused an initial warming 

of the lower part of the Franconia Formation in the 

vicinity of the well bore. Consequently, thermal 

equilibrium at the wellhead, and thus the highest 

temperatures, were not reached until12 to 24 hours into 

each withdrawal period (figs. 6 and 12). 

Temperature Profiles 

Temperature profiles as a function of depth at 

individual observations wells are useful in: ( 1) 

determining whether density-driven buoyancy flow of 

heated water occurs (Miller and Delin, 1994), (2) 

examining temperature variations in relation to 

hydraulic and thermal properties of the aquifer, and (3) 

determining possible long-term trends of vertical heat 

loss from the aquifer. Temperature profiles are 

presented for the beginning and the end of each injection 

period, and for the end of each storage and recovery 

period for each cycle at each observation well (figs. 18 

through 22). The temperature-measurement altitudes 

for each of the observation wells are shown in figure 4. 

The temperature profiles were constructed by 

connecting the successive temperature-measurement 

values with straight lines. Where thermocouples failed, 

successive operating temperature-measurement values 

were connected with straight lines. This linear 

interpolation may not accurately represent temperatures 

between the temperature-measurement points, 

especially where temperatures are interpolated across a 

major hydraulic or thermal boundary such as near 

confining layers or the unscreened lower part of the 

Franconia Formation. Contrasts in temperatures across 

major hydraulic boundaries were large (about 20 to 

40°C) following injection. The contrast in the advective 

heat-transport rate in the most permeable part of the 

aquifer and the conductive heat-transport rate in the 

least permeable parts of the aquifer and in the confining 

layers was noticeable at all wells. The contrast in 

temperatures across major hydraulic boundaries is best 
illustrated by the thermal separation, both in time and 

space, measured at well AM4, the most distant well 

from production well A (figs. 11, 17, and 22). Although 

detail is lacking for temperature variation at the 

hydraulic and thermal boundaries, the linearinterpolation method did not serious! y hinder use of the 

temperature profiles in describing the energy-transfer 

processes within the aquifer and confining units. 

The shape of the temperature profiles in figures 18 

through 22 generally reflects the permeability 

distribution described by Miller and Delin (1993) for 

the Franconia-Ironton-Galesville aquifer. Highest 

temperatures were measured in the Ironton and 

Galesville Sandstones and in the upper part of the 

Franconia Formation, the most permeable parts of the 

aquifer. Lowest temperatures were measured in the 

lower part of the Franconia Formation, the least 

permeable part of the aquifer. Maximum temperatures 

in the Ironton and Galesville Sandstones and in the 

upper part of the Franconia Formation at radial 

distances of 7 m and 14 m from production well A, as 

expected, were similar to the injected water 

temperatures of 1 08.5°C (cycle 1) and 117. 7°C (cycle 2) 

(figs. 18 through 22). The lowest temperatures were 

measured in the lower part of the Franconia Formation, 

the St. Lawrence Formation, and in the Eau Claire 

Formation, which are confining units. By the end of the 

withdrawal periods, temperatures in all formations were 

within about l5°C of each other. 

The convection of ground water created by 

differences in density between the ambient-temperature 

aquifer water and the warmer injected water is termed 

buoyancy flow (Hellstrom and others, 1979). 

Buoyancy flow causes thermal stratification and tilting 

of the thermal front (Miller and De lin, 1994 ). If 

buoyancy flow occurred it would be most readily 

observed near the top of an aquifer at the end of storage 

periods. 

The effects of buoyancy flow were not readily 

noticeable in the temperature profiles at the test facility 

(figs. 18 through 22). The effects of buoyancy flow 

were most noticeable in the Ironton and Galesville 

Sandstones in observation well AM4 at the end of 

injection and storage periods for cycle 2 (fig. 22). The 

measured buoyancy flow was small in comparison to 

the buoyancy flow as described by the sensitivity 

analysis for the Franconia-Ironton-Galesville aquifer 

(Miller and Delin, 1993). Although the magnitude of 

buoyancy flow was small, it was likely realistic for an 

operational thermal-energy storage system and, 

perhaps, accurately represents the potential long-term 

effects of buoyancy flow for the Franconia-IrontonGalesville aquifer at the end of injection and storage 

periods (fig. 22). The general lack of noticeable 

buoyancy flow in the test results probably was due to (1) 

an insufficient density of temperature-measurement 

locations, and (2) vertical changes in hydraulic 

properties caused by the presence of generally 

continuous, thin, horizontally bedded silt, shale, and 

clay stringers within the Franconia-Ironton-Galesville 

aquifer (Walton and others, 1991; Miller and Delin, 

1994 ). These stringers could have reduced the effects of 

buoyancy flow by acting as barriers to convective flow 

induced by density differences in the water. 

Earlier model-sensitivity analyses (Miller and Delin, 

1993) indicated that the decreases in temperature within 

the upper part of the Franconia Formation near 

production well A could be due to interformation flow 

within the well bore of production well A. Similar 

decreases were observed during the storage periods of 

cycles 1 and 2 (figs. 18 through 22). Temperatures in the 

Ironton and Galesville Sandstones and the upper part of 

the Franconia Formation decreased at most observation 

points in all observation wells. The decrease in 

temperature in the upper part of the Franconia 

Formation at the observation wells likely resulted from 

both conduction of heat to the St. Lawrence Formation 

and the lower part of the Franconia Formation and from 

interformation flow through production well A. The 

decrease in temperature in the Ironton and Galesville 

Sandstones likely resulted from conduction of heat to 

the Eau Claire Formation and to the lower part of the 

Franconia Formation. 

The above-described interformation flow, which was 

confirmed by use of a flow meter, resulted from a 

natural downward vertical gradient between the upper 

part of the Franconia Formation and the Ironton and 

Galesville Sandstones during periods of storage. This 

interformation flow caused advective flow of water in 

the upper part of the Franconia Formation past the 

observation wells toward production well A. Water 

from the upper part of the Franconia Formation was 

cooled as it traveled down production well A past the 

cooler, unscreened lower part of the Franconia 

Formation. This cooled water mixed with warmer water 

in the Ironton and Galesville Sandstones and 

maintained a positive advective flow outward into the 

sandstones. This flow of water into the Ironton and 

Galesville Sandstones tended to increase, or maintain, 

C39 
115 

110 

105 

100 

95 

90 

_, 

w 

> w 

_, 85 

<! 

w 

(/) 

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> 80 Cl 

co 

<! 

(/) 

a: 75 w 

fw 

~ 

z 70 

w· 

D 

:::> 

f- 65 ~ <! 

60 

55 

50 

45 

40 

C40 

I 

I 

I -------+--------- 1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I ------------1---

I 

I 

I 

I 

I 

I 

I 

I 

I 

-- --- --------- ----------- -------- - ------- ----------------- ----- -------

1 

I 

I 

I 

I 

I 

I 

I 

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I 

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I 

\ --------- ~- ------ -----------

\ 

\ 

I 

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I 

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I 

I 

I 

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1 

I 

I 

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I 

I 

I 

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I 

I 

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I -- -- ------------ ---------- - - ------------------- ----------- ·-- ----------- --

1 

20 40 60 80 

CYCLE 1 

1 

100 120 140 0 20 40 

TEMPERATURE, IN DEGREES CELSIUS 

EXPLANATION 

60 80 

CYCLE 2 

---- Temperature at beginning of injection 

--- Temperature at end of injection 

--- Temperature at end of storage 

- - - Temperature at end of withdrawal 

100 120 

Figure 18. Temperatures measured in observation well AM1 at the beginning of injection 

and at the end of injection, storage, and withdrawal for long-term test cycles 1 and 2. 

140 

"' (,) c:: c:: 0 "' ·- ~ 10 _, "'..... E 

0 ._;L.L 

(/) 

c:: 

0 

0 ~ 

t:: E "' O.l.L 0 

..... "' 

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E 

l.L 

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0 

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t::~ 

0 =-= ..... > 

- "' "' 

(.!) "' 

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u -"' E ::l ..... 

w "' 0 l.L 
115 

110 

105 

100 

95 

90 

-' w 

> 

w 85 -' 

<t 

w 

(/) 

w 

> 80 0 

Cl) 

<t 

(/) 

a: 75 w 

1-

w 

~ 

z 70 

w' 

0 

::;) 

1- 65 ~ <t 

60 

55 

50 

45 

40 

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I -----r -----------

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\ 

l 

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I 

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I 

20 40 60 80 

CYCLE 1 

1 

100 120 140 a 20 40 

TEMPERATURE, IN DEGREES CELSIUS 

EXPLANATION 

60 80 

CYCLE 2 

---- Temperature at beginning of injection 

--- Temperature at end of injection 

- -- Temperature at end of storage 

- --Temperature at end of withdrawa l 

100 120 

Figure 19. Temperatures measured in observation well AS1 at the beginning of injection 

and at the end of injection, storage, and withdrawal for long-term test cycles 1 and 2. 

140 

"' u c c 0 "' ·- ~ ~ "' E -' ~ 0 .... ~ 

(/) 

c 

0 -·;::; 

0 "' t: § "' 

c.~ 0 

~ "' ~ ·g 0 u -' c 

..I: "' 

en 

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0 

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u -"' E ::l ~ 

w "' ~ 

0 

C4 1 
115 

110 

105 

100 

95 

90 

-' w 

> w 85 -' 

<! 

w 

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w 

> 80 a 

co 

<! 

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cr: 75 w 

fw 

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z 70 

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=> 

f- 65 i= 

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60 

55 

50 

45 

40 

C42 

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I 

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I 

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20 40 60 80 

CYCLE 1 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

I 

~ ~ ~~ ~ ~ ~ ~~~ ~ ~ ~ ~ ~ 

100 120 140 0 20 40 

TEMPERATURE, IN DEGREES CELSIUS 

EXPLANATION 

60 80 

CYCLE 2 

- --- Temperature at beginning of injection 

--- Temperature at end of injection 

--- Temperature at end of storage 

--- Temperature at end of withdrawal 

100 120 

Figure 20. Temperatures measured in observation well AM2 at the beginning of injection 

and at the end of injection, storage, and withdrawal for long-term test cycles 1 and 2. 

140 

Q) 

u c c 0 Q) · -

~ to ro E -' ~ 0 ,._;U.. 

C/) 

(I) 

Q) 

c 

0 

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a: 

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115 

110 

105 

100 

95 

90 

85 

80 

75 

70 

65 

60 

55 

50 

45 

40 

I 

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1 

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1 

35~~~~~~~~~~--~~~~~~ 

0 20 40 60 80 100 120 140 0 20 40 60 80 100 120 

TEMPERATURE, IN DEGREES CELSIUS 

CYCLE 1 CYCLE 2 

EXPLANATION 

---- Temperature at beginning of injection 

----- Temperature at end of injection 

---- Temperature at end of storage 

----- Temperature at end of withdrawal 

Figure 21. Temperatures measured in observation well AM3 at the beginning of injection 

and at the end of injection, storage, and withdrawal for long-term test cycles 1 and 2. 

140 

"' u c c 0 "' ·- ~ ~ _J "' E ~ 

0 ,._;U... 

C/l 

(/) 

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0 

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wu... "' 0 

C43 
115 

110 

105 

100 

95 

90 

--' 

UJ 

> UJ 85 --' 

<{ 

UJ 

Cl) 

UJ 

> 80 0 

CD 

<{ 

Cl) 

a: 75 UJ 

tUJ 

~ 

z 70 

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t- 65 i= 

--' 

<{ 

60 

55 

50 

45 

40 

35 0 

C44 

20 40 60 80 

CYCLE 1 

100 120 140 0 20 40 

TEMPERATURE, IN DEGREES CELSIUS 

EXPLANATION 

60 80 

CYCLE 2 

---- Temperature at beginning of injection 

--- Temperature at end of injection 

--- Temperature at end of storage 

--- Temperature at end of withdrawal 

100 120 

Figure 22. Temperatures measured in observation well AM4 at the beginning of injection 

and at the end of injection, storage, and withdrawal for long-term test cycles 1 and 2. 

140 

Q) 

u c c 0 Q) · -

~ ~ 

--' "' E ~ 0 ._;L.L 

Cl) 

c 

0 

·.;::: 

o E t ~ 

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~ "' ~·c 

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E 

L.L 

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0 

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t=~ 

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u -"' E ::::J ~ 

UJ "' 0 L.L 
the temperatures measured at the observation wells 

completed in these formations. 

Discussion of Thermal Data 

Temperatures should have been similar at the same 

depths and radial distances from production well A if 

the hydraulic and thermal properties were similar in all 

directions. Although observation wells AM2 and AM3 

were both 14 m from production well A at land surface 

(fig. 2), the temperatures at well AM2 were noticeably 

greater than temperatures at well AM3 (figs. 9, 10, 15, 

and 16). Although temperatures in the Ironton and 

Galesville Sandstones were similar in both wells, 

temperatures in the upper part of the Franconia 

Formation were 10°C to 75°C less in well AM3 than in 

well AM2. The measured ten1perature differences 

likely resulted from (1) the bottom of observation well 

AM2 being about 16 m from production well A and the 

bottom of observation well AM3 being about 19m from 

production well A, and (2) anisotropy of the aquifer. 

Observation well AM2 was aligned more closely with 

the axis of maximum transmissivity than was 

observation well AM3 (Miller, 1984). Increased 

ground-water flow and heat transport likely occmTed in 

association with the axis of maximum transmissivity, 

therefore resulting in higher temperatures at well AM2 

than at well AM3. 

Although observation wells AM 1 and AS 1 were both 

7 m from production well A at land surface (fig. 2), 

arrival times for well AM1 were earlier than for well 

AS 1. Earlier arrival times at well AM 1 were probably 

due to the bottom of well AS 1 being about 7 m farther 

from production well A (fig. 5). 

Interpretation of the temperature graphs indicates 

that significant heat loss occurred through conduction 

from the injection zones to the overlying St. Lawrence 

confining unit (altitude 109.7 m), the underlying Eau 

Claire confining unit (altitude 38.1 m), and the 

unscreened lower part of the Franconia Formation 

(altitudes 8 to 65.5 m). Heat-conduction losses were 

greatest to the lower part of the Franconia Formation 

and the Eau Claire confining unit. Some of the 

temperature increases measured in well AM1 may have 

been due to horizontal heat convection, because the 

screened interval of production well A extended into the 

top 1.5 m of the Eau Claire Formation (Miller and Delin, 

1993). Although observation wellsAM1 andAS1 were 

both 7 m from production well A at land surface, heatconduction losses were greater for well AM1. These 

greater heat losses probably were due to the bottom of 

well AM 1 being 7 m closer to production well A than 

the bottom of well AS 1 (fig. 5). Because water 

temperatures were greater at well AM1, greater heatconduction losses to the Eau Claire confining unit 

probably occurred at that well. 

Time-lag heat conduction was not as apparent during 

the long-term test cycles as it was in the short-term test 

cycles (Miller and Delin, 1994). The relatively long 

injection periods with few interruptions likely limited 

time-lag heat conduction during the long-term test 

cycles. 

Temperatures in the Ironton and Galesville 

Sandstones generally followed the trend of the injected 

water temperatures. Injected water temperatures were 

highest during the early part of the injection periods. 

Therefore, maximum temperatures occurred early in the 

injection periods in the Ironton and Galesville 

Sandstones at wells 7 and 14m from production well A. 

Conversely, maximum temperatures occurred at the end 

of the injection periods in the upper part of the 

Franconia Formation at all observation wells, and in the 

Ironton and Galesville Sandstones at well AM4, located 

30.5 m from production well A. Results of the longterm test cycles suggest that aquifer clogging either did 

not occur or was insignificant. 

A significant amount of heat remained both in the 

aquifer and in the confining units when the long-term 

test cycles ended. Temperatures at the end of the first 

long-term cycle averaged about 40°C at the upper part 

of the Franconia Formation and about 45°C at the 

Ironton and Galesville Sandstones in observation wells, 

similar to temperatures of water withdrawn at the end of 

storage. Temperatures in the immediately overlying 

and underlying confining units were greater than those 

in the permeable part of the aquifer. A similar picture 

emerged at the end of the second long-term cycle, at 

somewhat higher temperatures. About 62 percent of the 

heat stored in the aquifer was recovered during each of 

the two long-term cycles (table 3). 

NONISOTHERMAL MODELING OF LONGTERM TEST CYCLES 1 AND 2 

A three-dimensional, anisotropic, nonisothermal, 

ground-water-flow and thermal-energy-transport 

model was used to simulate the two long-term test 

cycles. The model is similar to the three-dimensional, 

isothermal ground-water-flow model described by 

Miller and Delin (1993). Miller and Voss (1986) 

describe discretization of the model and the sensitivity 

C45 
of the lateral boundary conditions for various rates of 

heated-water injection. 

The finite-difference, ground-water-flow, and 

thermal-energy-transport model used in this study was 

developed for waste-injection problems (lntercomp 

Resources Development and Engineering, 1976) and 

will be referred to in this report as the Survey Waste 

Injection Program (SWIP) code. The SWIP code can be 

used to simulate ground-water flow and heat and solute 

transport in a liquid-saturated porous medium; it 

contains both reservoir and well-bore modeling 

capabilities. The major model assumptions are as 

follows: 

1. Ground-water flow is laminar (Darcian), three 

dimensional, and transient. 

2. Fluid density is a function of pressure, temperature, and 

concentration. 

3. Fluid viscosity is a function of temperature and 

concentration. 

4. The injected fluid is miscible with the in-place fluids. 

5. Aquifer properties vary with location. 

6. Hydrodynamic dispersion is a function of fluid 

velocity. 

7 .The energy equation can be described as: enthalpy in 

minus enthalpy out equals the change in internal 

energy of the system. 

8. Boundary conditions allow natural water movement in 

the aquifer and heat losses to adjacent formations. 

9. Thermal equilibrium exists within the simulated area. 

The basic equation describing single-phase flow in a 

porous medium is derived by combining the continuity 

equation and Darcy equation for three-dimensional 

flow (Intercomp Resources Development and 

Engineering, 1976, p. 3.4): 

V • [pk(Vp-pgVz)]-q' = i(q>p) ~ at 

where 

p =fluid density [M!L3] (kg/m3), 

~=fluid viscosity [M/(L-T)] (Pa-s), 

k = intrinsic permeability [L 2

] (m2), 

g =gravitational acceleration [L/T2] (m/s2), 

(1) 

z = spatial dimension in direction of gravity [L] (m), 

p =pressure [M/(L-T2)] (Pa), 

q'= mass rate of flow per unit volume from sources or 

sinks [M/(T-L3)] (kg/m3-s), 

t =time [T] (s), 

<1> =porosity [dimensionless], and 

V = gradient (for an axially symmetric cylindrical 

coordinate system, Vis 

a 1 a a 

-+--+- or rae az 

where r is the radial dimension). 

The energy-balance equation describing the 

transport of thermal energy in a ground-water system 

(lntercomp Resources Development and Engineering, 

1976, p.3.4) 

V • [P:H(Vp- pgVz)J + V • K • VT (2) 

a - qL- q'H = a/<1>PU + (1- <1>)(pCp)RT] 

where 

H = enthalpy per unit mass of fluid [ElM] (J/kg), 

K =hydrodynamic thermal dispersion plus convection 

[E/(T- L-t)] (W/m-°C), 

T =temperature [t] (°C), 

qL = heat loss across boundaries [EfT] (W), 

U =internal energy per unit mass of fluid [E/M](J/kg), 

(pCp)R =heat capacity of aquifer matrix [E!L3-T] (J/ 

m3-°C), and 

Cp = specific heat of aquifer matrix [ElM-T] ( J /kg- °C). 

(All other terms are previously defined.) 

Equations 1 and 2 are a nonlinear system of coupled 

partial-differential equations that are solved 

numerically by discretizing the aquifer into three 

dimensions (or two dimensions for radial flow) and 

developing finite-difference approximations. Finitedifference equations (lntercomp Resources 

Development and Engineering, 1976, p. 3.5) whose 

solutions closely approximate the solutions of equations 

1 and 2 are, for the basic flow equation: 

Table 3. Comparison of model-computed thermal efficiencies of the aquifer and final withdrawal-water temperatures at production well A 

with corresponding calculated and measured values for long-term test cycles 1 and 2 

C46 

Thermal efficiency of aquifer (percent) Long-term test-cycle --------------

number 

2 

Calculated 

62 

62 

Model computed 

61 

62 

Final withdrawal-water temperature, 

(degrees Celsius) 

Measured 

45.6 

55.4 

Model computed 

45.6 

59.5 
(3) 

and for the energy equation: 

11[TwH(!1p- pgl1z)] + 11(Tci1T)- qL (4) 

- (q'H) = ~8[<j>pU + (1- <j>)(pCp)RT] 

where 

q = mass rate of production or injection of liquid for a 

grid block units [L3

/t] (m3/s), 

V = volume of the grid block [L 3] (m3) 

kAp Tw = (5) I-ll 

T - cKA 

l (6) 

A= the area perpendicular to flow (that is, 11x/1y, 11xf1z, 

or11yf1z) [L2] (m2), 

1 =the distance between grid block centers [L] (m), and 

the temperature of the aquifer water (Tw) and the 

aquifer matrix (TJ are defined as 

(All other terms are previously defined.) 

The finite-difference operators are defined as: 

11(Twi1P) = (7) 

f1x(Twf1xp) + f1yCTwf1yp) + f1z(Twf1::P) 

with the terms: 

and 

where 

x, y, z =cartesian-space coordinates, 

i, j, k =grid-block indices, 

n = time level, t,1' 

(All other terms are previously defined.) 

(8) 

(9) 

Finally, the thermal-conductance term, K, in equation 

6 may be further defined as (Intercomp Resources 

Development and Engineering, 1976, p. 3.7): 

K = <i>(~u)(pCP)w + K, (10) 

where 

a= thermal dispersivity [L] (m), 

<1> =porosity [dimensionless], 

u =volumetric flux (Darcy velocity) [L/T] (m/s), 

(pCp)w =heat capacity of water [E/(L3-T)] (J/m3-°C), 

and 

Km =molecular heat conductivity of porous media [E/ 

(T-L-t)] (W/m-°C). 

Simulation of Model Anisotropy 

Analysis of aquifer-test data (Miller, 1984; Miller and 

De lin, 1993) indicates that the Ironton and Galesville 

Sandstones and the upper part of the Franconia 

Formation are areally anisotropic and that the angle 

between the major axis of transmissivity and the axis 

between production wells A and B is approximately 30 

degrees. Although the anisotropy may be considered 

small (less than 3: 1 ), its effect on the movement and 

direction of heat flow for the hydrologic conditions at 

the ATES site is not known. Use of a radial-flow 

equation would neglect the effect of anisotropy. The 

potential errors introduced in the radial-flow 

assumptions are discussed by Miller and De lin ( 1993) in 

the section of that report describing the radial-flow 

model. On the basis of their discussion, a threedimensional model was constructed to represent 

anisotropic conditions and to simulate the ATES shortterm test cycles (Miller and Delin 1994). This model 

was modified for simulation of the long -term test cycles 

and to accommodate movement of the thermal front 

past observation well AM4. 

Discretization of Aquifer System 

The area that can be modeled around the ATES 

doublet-well system is limited by (1) the constraint on 

the finite-difference grid spacings required by the 

model-solution techniques, (2) the lack of alignment of 

the axis of aquifer anisotropy and the axis on which the 

doublet wells are located, and (3) running the model for 

large three-dimensional problems exceeded allocated 

resources available at that time. Miller and Voss (1986) 

describe the construction of the finite-difference grid 

for the doublet-well system at the ATES site. Flow-net 

analysis (Miller and Voss, 1986) makes it possible to 

reduce the modeled area and to simulate flow only in the 

area around production well A, the flow region where 

energy transport is of greatest concern (figs. 23 and 24 ). 

The equipotentials and streamlines illustrated in figures 

23 and 24 are the steady-state solutions to twodimensional, isothermal flow in a homogeneous, 

confined, infinite, anisotropic aquifer that has no 

regional hydraulic gradient (Miller and Voss, 1986). 

Flow outside this modeled region is represented by a 

C47 
specified flux at model boundaries, as determined by 

flow-net analysis. 

The finite-difference grid for the ATES-site model 

was oriented such that the axis of maximum 

transmissivity was aligned with the horizontalcoordinate direction (figs. 23 and 24). The origin of the 

field-coordinate system shown in figures 23 and 24 was 

arbitrarily chosen to be halfway between production 

wells A and B. A variably-spaced grid was designed 

because of restrictions on grid size for solution accuracy 

and stability inherent to the difference approximation 

used in the SWIP code (Intercomp Resources 

Development and Engineering, 1976). Cell sizes range 

from 0.3 mona side at production well A to a maximum 

of 10.0 mona side at the periphery of the model. The 

grid had 6 layers with 806 cells per layer. Vertical grid 

spacings were selected to correspond with the four 

hydraulic zones in the Franconia-Ironton-Galesville 

aquifer and with the overlying and underlying confining 

units (table 4). The lateral boundaries of the model 

correspond to the 4.5-m equipotential for the Ironton 

and Galesville Sandstones (fig. 23) and for the upper 

part of the Franconia Formation (fig. 24 ). 

Boundary and Initial Conditions 

Flux rates were specified at the model boundaries 

such that the boundaries accurately represented groundwater flow and heat transport between the modeled area 

and the area outside the simulated region. The correct 

boundary fluxes were determined by analysis of the 

flow net for steady-state conditions (Miller and Voss, 

1986; Miller and Delin, 1993). The total flow crossing 

an equipotential (fig. 23 and 24) is equal to the injection 

rate and is thus known. In addition, an equal amount of 

flow is represented by each streamtube. Therefore, if 

quasi-steady-state flow is assumed, the distribution of 

fluxes along an equipotential is known for any injection 

rate. The locations of lateral-flux boundaries in the 

model are illustrated in figures 23 and 24. More detailed 

descriptions of the methods used to calculate the 

boundary fluxes for the model are provided by Miller 

and Voss (1986), and Miller and Delin (1993 and 1994). 

The following is a brief description of the thermal 

properties of the aquifer used as variables in the 

nonisothermal model. Heat capacity is the amount of 

heat required to raise the temperature of a material a 

specified amount. It is the product of density and 

specific heat and is a measure of the ability of a material 

to store heat. Values of 1.81 x 106 and 3.89 x 103 J/m3-

oc were used for heat capacity of rock and water, 

C48 

respectively (table 5). The value of rock heat capacity 

represents sandstones similar to those in the FranconiaIronton-Galesville aquifer. These values were based on 

data from Sommerton and others (1965), Clark (1966), 

Helgeson and others (1978), and Robie and others 

(1978). The values were calculated by use of methods 

described by Martin and Dew ( 1965). 

The constant of propmiionality between the heat flux 

and the temperature gradient is termed thermal 

conductivity. It is the quantity of heat transmitted in unit 

time through a unit cross-sectional area under a unit 

temperature gradient. For purposes of data analysis, 

thermal conductivity was assumed to be isotropic in the 

aquifer system. Values of thermal conductivity (table 5) 

were obtained from Clark (1966). 

Thermal diffusivity is defined as the transport of 

energy by conduction due to the exchange of kinetic 

energy between molecules. Molecular diffusion is 

independent of fluid velocities and is usually constant in 

saturated porous media. The value of 1.56 x 106 m2

/s 

(table 5) used for thermal diffusivity is representative of 

sandstones in the Franconia-Ironton-Galesville aquifer 

(Kappelmeyer and Haenel, 197 4). Thermal dispersion, 

resulting from fluctuations of velocity and temperature 

in the pore space, is similar to the more common term of 

mechanical hydrodynamic dispersion used in solute 

mass-transport problems. Hydrodynamic dispersion is 

the name for a group of mixing mechanisms that cause 

the spreading of a solute in a flow system (Bear, 1972). 

Values of dispersivity are dependent on the scale of 

model discretization. The values shown in table 5 were 

determined through calibration of the model. 

Model Calibration 

The model was calibrated to nonisothermal 

conditions to ensure that the hydraulic and thermal 

properties selected were reasonable for simulation of 

heat transport in the flow system. The relative 

importance of each property was evaluated during 

preliminary model analyses (Miller and Delin, 1993). 

Model sensitivity to changes in the hydraulic properties 

of hydraulic conductivity, porosity, and vertical 

anisotropy, plus model sensitivity to changes in the 

thermal properties of thermal conductivity of rock, heat 

capacity of rock, and thermal dispersivity, were tested 

during preliminary model analyses (Miller and Delin, 

1993). Based on results of these analyses, the model 

was most sensitive to changes in thermal dispersivity. 

The longitudinal thermal dispersivity was varied from 

1 to 6 m during the long-term nonisothermal model 
Flowline Model grid 4.5-meter equipotential 

110 

100 

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~ :;---... ....... < >< '\ ll A ~ ~ _...;.;--

' !--.' "" ·-, ' . .----

' ' '7"-, _,- K >< )<. f\ Vl '::t ..:.;; P->---- ·, ' ~ ' - -= ' ' ---:-- ~ ~· r--,.: _?'- .x ~:\ / [,.?' -..-- ·, 

' fz 

0 

0.... 

Cl 50 

~ 

' -;-. ~ Jflf - f::- I-<" f- ...... !"-. -.... "- r-

~ 

0 

a: 40 L.L.. 

LU 

u 

z 

<! 30 fCl) 

Cl 

20 

10 

[;...----\ -__.-->; v '.?' -0., ['X_ x :-,.:. ..__ --- -' h ~ '. ,.......:..:--- ·,_ ', )- ·-. v.: \ r'\. x "'). ~ [," r--..... : -----;k < \, .... -\ ·.. ·, V )' ·,< lf I \- 1\ '\ \-; ,X. "" \ t----. ~ "" 1- ~'' k '·,_ ''. > v / I I ·\ ·-\ k 'x ......._ 

r-, 'r·. ·/ .,../·r-7- '/ .. 1 

. -1 . - \ 

'\ .\ 

. -- . -- \ ~ ~ ' 

'x 

~ ,' 

'--> ~ 

~ ·--._ v..;x / ;·--I._ .J 1\ .-\ ""' ,' 

~ _,,' -

v .__ / ·- /- v ·- 1·-1-1 1-

1\ . -

~ ""' --, v -/ / 7 ! - .. \ 

~\ ---\ \ . -. . - 1- .. 1-- V - / _____ / f-- I ·--- /. ·-r-./1 - A I ---1 /-.---~ f. 

0 

50 

I I I I \.~--;---r ·\- 1 

60 70 80 90 100 110 120 130 140 150 

DISTANCE FROM MIDPOINT OF WELLS, IN METERS 

160 170 180 190 

EXPLANATION 

Ce ll in which heat transport was not simulated 

Streamtube 

---- Model flux boundary 

Figure 23. Model grid and flow net for the Ironton and Galesville Sandstones 

near production well A for the long-term test cycles. 

calibration and a value of 3.33 m most accurately 

duplicated the measured data (table 5). Field data have 

shown that transverse dispersivity usually is 0.1 to 0.3 

times the longitudinal dispersivity (Freeze and Cherry, 

1979, p. 396). Therefore, the transverse thermal 

dispersivity was varied from 0.1 to 0.6 m during the 

long-term non isothermal model calibration and a value 

of 0.33 m most accurately duplicated the measured data 

(table 5). The final thermal and hydraulic properties 

simulated in the model are listed in tables 5 and 6, 

respectively. Model accuracy perhaps could be 

improved by adjusting this long-term model following 

a rigorous sensitivity analysis; however, this was not 

deemed necessary based on the preliminary sensitivity 

analyses. The model necessarily is a simplification of 

the flow system, and accuracy of the model results is 

limited by the accuracy of the hydraulic and thermal 

input data on which the computations are based. In 

addition, different combinations of input data could 

C49 
Flowline Model grid 4.5-meter equipotential 

I I 110 .' x---~ ~~-1-~-----~---L- 1 

I I 7 /" ---.!,1-~-- I 

L' 

100 ~'-.._ "'-., <v K 

1- 1\ 1\ 1- -~I--

~ k -- 1- "! / '•, 

' "' . -- 1\ 

90 

C/) 

a:: 

lJj 

IlJj 80 

~ 

z 

K k' ~ . -

~ . - -- V-- k' > [7 -

f\ 

v--- ,' K . -K I- . - I v k-

~ ~ ;-...:. 1\: . - r\ 1/ -- t- 1/- v t ',' r--... - ' 

r--' .'~ ;--....... 

1"--- ..... ~ .- r\ 1\ ·-; --I :I )< --. C/)' 70 -' -' 

lJj 

s 

u.. 

0 60 Iz 

t- ' 

--.,._ r---.:' ~K I> [>._ ,:ll 1/ 1/- ·;-( > ', r- \ 

1-- ' ~ r-l. !;--. - "K K \ ' t-->-:.. I>< r- 1/ / , ..... v ~ 

--- ' ' I• "7"1--- K >< tx 1\ II ~/' .) ~ p f--. ·. t- . ; ~f---L. ~ > _>< ~[\ J ;;. -~ . = . 

. -;..... ~ ':2 . 0 

c... 

D 50 ~ ---== ~ 

~ 

0 

a:: 40 u.. 

UJ 

u 

z 

<! 30 IC/) 

D 

20 

10 

~ k _... 1-" ·, ~ K: r'-<' r-.... ,:.._ 

'----" ~ v ~ '><.. r-x: ~ --r-:.-. ' -I--_; 

~ N \_..... ~ ' ·, > ·-. \ ~- Lx. "';. 1>:. ......_ ,, . ; -- ~ 

------ v X / V- 1/ II '- \ 1'\ [\_ .>< X 

' -, ·,..:: 1\ 1'---..- 1'---. _,' ~ r-.. V. ·, ·, V ?< /f( V 1 ·\ ··\ ~ ~ -- --.. 1\ -· ~- ~ 

r-., ·, ', f/'r-,.,-V ·y. ~/ --, \ \ --- K !': . - ~ .- ~ --- xv l/ v~·-1/ -- 1-- v ', v ·, ;'··-1) . -

1- 1\ \ 1\ ""' .- ~ "" ---- - ·, ./ ', / -- ./. 1\ 1- .. \ 

~ .-- ---\ -,/ --- / f-- 1- . - -- - v/-/ -- -v J v 

-----./. ··r- /1 • A I ---i-1-.---~ / 

0 

50 

I I \ I \.~--~---~ ~ I 

60 70 80 90 100 110 120 130 140 150 

DISTANCE FROM MIDPOINT OF WELLS, IN METERS 

160 170 180 190 

EXPLANATION 

I Cell in which heat transport was not simulated 

[ Streamtube 

---- Model flux boundary 

Figure 24. Model grid and flow net for the upper part of the Franconia Formation 

near production well A for the long-term test cycles. 

conceivably yield the same results, particularly because 

only two variables were adjusted during calibration. 

The injection, storage, and withdrawal phases of the 

two long-term test cycles were simulated from the 

beginning of the first long-term test cycle to the end of 

the second long-term test cycle. Temperatures 

measured at observation wells in the aquifer at the start 

of the first long-term test cycle were used as initial 

temperatures for the simulation. Modeling the entire 

cso 

period of the two long-term test cycles allowed residual 

heat left in the aquifer at the storage site to be taken into 

account for the second cycle. The simulated injection 

was divided into periods of injection, flow-rate change, 

and injection-temperature change during each cycle 

(table 7). Simulated flow rates during periods of 

withdrawal were similarly divided. 

Calibration ofthe model to non isothermal conditions 

consisted of comparing model-computed thennal 
Table 4. Layer number, thickness, and corresponding stratigraphic/hydrogeologic unit for the three-dimensional model 

Model Thickness 

layer (meters) Stratigraphic/hydrogeologic unit 

7.6 St. Lawrence Formation (confining unit) 

2 13.7 Upper part of the Franconia Formation (aquifer) 

3 24.4 Lower part of the Franconia Formation (confining unit) 

4 15.2 Ironton Sandstone (aquifer) 

5 6.1 Galesville Sandstone (aquifer) 

6 30.5 Eau Claire Formation (confining unit) 

efficiencies and withdrawal-water temperatures to 

calculated and measured values (table 3). Thermal 

efficiency of the aquifer was computed by dividing the 

total energy injected into the aquifer system by the total 

energy withdrawn from the system. Calibration of the 

model also was achieved by comparing modelcomputed and average temperatures at the observation 

wells during the test cycles (figs. 25-36). The 

longitudinal and transverse dispersivities were varied 

during nonisothermal model calibration on the basis of 

relative hydraulic conductivities of the aquifer in the 

longitudinal and transverse directions (Miller, 1984 ). 

The longitudinal dispersivity was varied from 1.0 to 

30.0 m and the transverse dispersivity was varied from 

0.1 to 3.0 m, similar to calibration of the model for the 

short-term cycles (Miller and Delin, 1994). Values of 

3.33 and 0.33 m for longitudinal and transverse 

dispersivity, respectively, simulated aquifer thermal 

efficiencies, wellhead temperatures (table 5, and figs. 

25 and 31 ), and average temperatures (figs. 26-30, and 

32-36) close to measured values. 

Model-computed temperatures were compared to 

measured temperatures at each of the observation wells 

for each period of injection, storage, and withdrawal for 

the two long-term test cycles. Actual temperature 

measurements were averaged for all measurement 

points (which were operating) within each 

hydrogeologic unit in an attempt to make measured and 

model-computed data comparable. Table 8 lists the 

measurement-point altitudes for which data were 

averaged to compare with the model's vertical layering. 

Thermocouples that failed completely for a cycle phase 

were omitted from the temperature averages for 

comparison with model-computed temperatures. A 

factor that was considered when comparing modelcomputed temperatures with measured data is the radial 

distance of measurement points from production well 

A. Because of the limitations of finite-difference 

modeling, the actual location of measurement points 

may not be exactly simulated in the model at the correct 

radial distance (fig. 5). As described earlier, depthdeviation surveys indicate that some of the observation 

wells deviate as much as 7 m horizontally for depths 

ranging through the model's vertical-simulation region. 

Model-computed ten1peratures for each monitoring 

point at the site were correlated with measured values 

taking into account results of the deviation survey. 

Representation of variable pumping rates and 

injection temperatures must be considered when 

comparing model-con1puted and averaged 

temperatures. Variations in inputs are illustrated in 

figures 25 and 31, which show injection temperatures 

recorded at the wellhead and injection temperatures 

simulated with the model. During the long-term test 

cycles, the source-water temperature varied smoothly 

and the temperature of the injected water was controlled 

by the temperature controller, or varied as a response to 

Table 5. Them1al properties used for simulation of the long-term test cycles 1 and 2 

Thermal property 

Thermal conductivity, rock 

Thermal conductivity, aquifer water at 20 degrees Celsius 

Thermal diffusivity 

Heat capacity, rock 

Heat capacity, aquifer water 

Longitudinal dispersivity 

Transverse dispersivity 

Value and unit of measure 

= 2.20 watts per meter-degree Celsius 

= 0.60 watts per meter-degree Celsius 

= 1.56 x 106 square meter-second 

= 1.81 x 106 joules per cubic meter-degree Celsius 

= 3.89 x 103 joules per cubic meter-degree Celsius 

= 3.33 meters 

= 0.33 meters 

C51 
Table 6. Hydraulic properties used for simulation of the long-term test cycles 

Hydraulic conductivity 

(meters per day) 

Model layer Kx Ky 

0.003 0.003 

2 2.89 1.71 

3 .03 .03 

4 5.78 2.51 

5 1.45 .628 

6 .003 .003 

the capacity of the heat exchanger (Hoyer and others, 

1991a and 1991b). 

Analysis of Simulations 

A description of the differences between modelcomputed and averaged temperatures for long-term 

cycles 1 and 2 follows. Trends in the averaged 

temperatures will be discussed and related to model 

results to describe thermal processes that may explain 

the results. As described earlier, some thermocouples 

failed intermittently because of insulation wear at kinks 

in the wires or electronic noise in the data logger. These 

failures appear as small temperature fluctuations in 

figures 2S-36 and are not discussed further. 

The model accurately predicted thermal efficiencies 

of the aquifer to within about 1 percent of calculated 

values for the long-term test cycles (table 3). The model 

also accurately predicted the final withdrawal-water 

temperatures to within an average of about 3 percent of 

calculated values, or to within about 1 oc for the first 

long-term test cycle and to within about soc for the 

second long-term test cycle (table 3). 

Model-computed and measured temperatures at 

production well A compare closely (figs. 2S and 31 ). 

However, the model-computed temperatures are 

somewhat lower than measured temperatures 

throughout most of the withdrawal periods for both 

cycles (figs. 2S and 31 ). This deviation may be an 

indication that the model overestimated the down-well 

flow between the two screened intervals of production 

well A. 

The model closely matched both the trends in the 

averaged temperature profiles and the temperatures at 

the end of injection and withdrawal periods for cycles 1 

and 2. Overall, model-computed temperatures more 

closely matched averaged values for cycle 2 than for 

cycle 1. The close correspondence between modelC52 

Porosity 

Kz Kx:Ky (percent) 

0.00003 1.00 26.8 

.222 1.69 28.2 

.0003 1.00 27.3 

.380 2.30 25.2 

.095 2.30 25.6 

.00003 1.00 31.6 

computed and averaged temperatures for observation 

well AM 1 may be related to its short distance from 

production well A, compared to the other observation 

wells. Trends of the model-computed temperatures for 

observation wells AS 1 (figs. 27 and 33), AM2 (figs. 28 

and 34 ), and AM3 (figs. 29 and 3S) do not agree as well 

with averaged temperatures. The model did not 

duplicate the rapid rise in temperatures at all 

observation wells, and particularly in the Ironton and 

Galesville Sandstones that peaked about five days into 

both long-term tests. The model-computed and 

averaged temperatures differ by different amounts at 

different stages of the two cycles. For example, modelcomputed temperatures for observation well AM4 are 

too high for the upper part of the Franconia Formation, 

too low for the lower part of the Franconia Formation, 

and very close to measured values for the Ironton and 

Galesville Sandstones. The timing of the temperature 

changes for the Ironton and Galesville Sandstones is 

considerably behind the averaged temperature changes 

(figs. 30 and 36). 

For the upper part of the Franconia Formation, 

model-computed temperatures during injection were 

generally higher than average measured temperatures 

except at AS 1. Initial injection temperatures at wells 

AS1, AM1, and AM2 were also higher than measured 

values. By the end of injection, the model-computed 

temperatures were within Soc of the averaged 

temperatures at all wells except AM3 for both cycles 1 

and 2 and AM4 for cycle 2, which were within about 

10°C of the averaged values. By the end of withdrawal, 

model-computed temperatures in the upper part of the 

Franconia Formation were within about soc of 

averaged temperatures at all wells except AM3, which 

was 30°C higher than averaged values. Modelcomputed temperatures at AM2 cycle 2 were higher 

than averaged temperatures at all times. 
Table 7. Summary of long-term test cycles 1 and 2 simulation times, durations, flow rates, and temperatures 

[--,not applicable] 

Temperature at 

Simulation time Duration Flow rate wellhead 

(days) (days) (liters per second) (degrees Celsius) 

LONG-TERM TEST CYCLE 1 

Injection 0.0 1.6 284.0 234.0 

1.6 1.2 0 

2.8 6.9 282.7 235.0 

9.6 3.9 294.0 234.0 

13.6 5.4 296.0 234.0 

18.9 .9 0 

19.8 2.7 290.5 229.4 

22.5 .3 0 

22.8 2.7 286.6 238.3 

25.5 1.4 0 

26.8 9.8 286.6 233.8 

36.6 7.0 0 

43.6 3.4 287.8 230.5 

47.0 15.7 278.0 221.5 

62.7 7.3 280.0 220.0 

70.0 4.7 280.0 211.3 

Storage 74.7 64.0 0 

Withdrawal 138.7 1.1 297.2 156.0 

139.8 297.2 162.0 

140.8 2 297.2 169.0 

142.8 1 297.2 180.0 

143.8 3 296.1 185.0 

146.5 2 296.1 189.0 

148.8 4.1 296 190.0 

152.8 6.0 296 189.0 

158.8 1.1 293.3 181.0 

159.8 .8 0 170.0 

160.6 3.2 293.3 175.0 

163.8 5 291.8 177.0 

168.8 10 289.9 167.0 

178.8 5 289.9 149.0 

183.8 5 288.5 140.0 

188.8 5 288.3 132.0 

193.8 4 286.9 125.0 

197.8 0 0 120.0 

LONG-TERM TEST CYCLE 2 

Injection 685.8 8.3 291.7 244.6 

694.1 9.5 291.7 247.5 

713.7 4.1 0 

717.8 13.4 291.6 241.2 

731.1 8.5 291.6 243.9 

739.6 7.0 285.6 241.5 

746.6 3.1 285.6 237.3 

Storage 749.7 58.2 0 

Withdrawal 808.0 29.0 269.6 206.0 

837 10 269.6 187.0 

847 10 269.6 169.0 

857 10.2 269.6 153.0 

867.2 0 269.6 139.0 

C53 
130 

120 

110 

100 

90 

Cl) 

:::::> 

Cl) 

_J 

L..LJ 

u 80 Cl) 

L..LJ 

L..LJ 

a: 

c.!J 

L..LJ 

0 

z 70 

L..LJ' 

a: 

:::::> 

f-

<! 

a: 

L..LJ 60 a... 

~ L..LJ 

f50 

40 

30 

20 

10 

10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 25. Model-computed and measured temperatures 

C54 
- - - Model-computed temperature 

--- Measured temperature at wellhead 

100 110 120 130 140 150 160 170 180 190 200 

DAYS FROM BEGINNING OF INJECTION 

in production well A during long-term test cycle 1. 

css 
80 

60 

40 

20 

0 

100 

80 

Lower part of Franconia Formation 

60 (/) 

::> 40 U3 

-' 

l.U 

u 20 (/) 

l.U 

l.U 

cr: 0 ~ 

l.U 

Cl 

z 140 w· 

cr: 

::> 120 f-

<l: 

cr: 

l.U 100 ~ 

~ l.U 80 f60 

40 

20 

0 

140 

10 20 

C56 

30 40 50 60 70 80 90 

DAYS FROM BEGINNING OF INJECTION 

_j 

_I 

_j 

I 

- 1 

-I 

_j 

I 

- 1 

-; 

_j 

I 

I 

-I 

_j 

I 

- 1 

-; 

_j 

I 

I 

100 

Figure 26. Model-computed and average measured temperatures 
STORAGE WITHDRAWAL --- Model-computed temperature 

--- Average temperature at 88-, 

93-, and 99-meter altitudes 

L 

--- Model-computed temperature 

L --- Average temperature at 66-, 

73-, and 81 -meter altitudes 

L 

--- Model-computed temperature 

--- Average temperature at 52-, 

and 58-meter altitudes 

L 

L 

I 

1- --- Model-computed temperature 

tL 

I 

--- Measured temperature at 

45-meter altitude 

1-

r 

L 

I 

1-

tL 

I 

I 

r 

L 

I 

I 

100 110 120 130 140 150 160 170 180 190 200 

DAYS FROM BEGINNING OF INJECTION 

in observation well AM1 during long-term test cycle 1. 

C57 

STORAGE WITHDRAWAL - -- Model-computed temperature 

--- Average temperature at 88-, 

93-, and 99-meter altitudes 

L 

--- Model-computed temperature 

--- Average temperature at 66-, 

73-, and 81 -meter altitudes 

L 

--- Model-computed temperature 

--- Average temperature at 52-, 

and 58-meter altitudes 

L 

L 

I 

1- --- Model-computed temperature 

rL 

I 

--- Measured temperature at 

45-meter altitude -

r 

L 

I 

1-

rL 

I 

1-

r 

L 

I 

1-

100 110 120 130 140 150 160 170 180 190 200 

DAYS FROM BEGINNING OF INJECTION 

in observation well AS1 during long-term test cycle 1. 

C59 

I 

I 

1-

L 

L 

rL 

L 

I 

1-

1-

L 

r 

L 

I 

1-

1-

L 

I 

I 

r 

L 

I 

I 

100 110 120 130 140 150 160 

DAYS FROM BEGINNING OF INJECTION 

in observation well AM2 during long-term test cycle 1. 

--- Average temperature at 88-, 

93-, and 99-meter altitudes 

--- Model-computed temperature 

--- Average temperature at 66-, 

73-, and 81-meter altitudes 

--- Model-computed temperature 

--- Average temperature at 52-, 

and 58-meter altitudes 

--- Model-c omputed temperature 

--- Measured temperature at 

45-meter altitude 

170 180 190 200 

C61 
80 

60 ..J 

40 

4 

20 _j 

0 

100 

80 

60 Cl) 

::::> 40 Cl) 

-' 

UJ 

u 20 Cl) 

UJ _J 

UJ 

a: 0 (!) 

UJ 

0 

z 140 UJa: Ironton Sandstone ::::> 120 ..... 

<X: 

a: 

UJ 

a.. 100 

::2: 

UJ 80 ..... 

60 ..J 

40 

4 

20 _j 

0 

I 

Galesville Formation - I 

120 -I 

..J 

100 _ I 

4 

80 _j 

I 

- 1 

60 -I 

..J 

I 40 - 1 

4 

20 _j 

I 

- 1 

10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 29. Model-computed and average measured temperatures 

C62 
I 

r 

L 

rL 

L 

I_ 

I 

rL 

L 

L 

1-

rL 

I 

-

r 

L 

I 

I 

rL 

I_ 

I 

r 

L 

I 

I 

100 

STORAGE WITHDRAWAL 

110 120 130 140 150 160 

DAYS FROM BEGINNING OF INJECTION 

in observation well AM3 during long-term test cycle 1. 

--- Model-computed temperature 

---Average temperature at 88-, 

93-, and 99-meter altitudes 

--- Model-computed temperature 

--- Average temperature at 66-, 

73-, and 81 -meter altitudes 

--- Model-computed temperature 

--- Average temperature at 52-, 

and 58-meter altitudes 

--- Model-computed temperature 

--- Measured temperature at 

45-meter altitude 

170 180 190 200 

C63 
140 

120 _j 

100 

80 _j 

60 

40 

20 _j 

0 

100 

80 

60 (I) 

=:J 40 en 

--' 

UJ 

u 20 (I) 

UJ 

UJ 

a: 0 C!J 

UJ 

Cl 

z 140 UJa: Ironton Sandstone =:J 120 1-

<! _j 

a: 

UJ 100 a_ 

~ UJ 

1- 80 

60 _j 

40 

20 _J 

0 

140 I 

- 1 

120 -t 

_j 

100 I 

- 1 

, 80 _J 

I 

- 1 

60 -t 

_j 

40 I 

- 1 

, 20 _J 

I 

- I 

10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 30. Model-computed and average measured temperatures 

C64 
STORAGE WITHDRAWAL 

L 

tL 

L 

tL 

L 

L 

I 

1-

tL 

I 

1-

r 

L 

I 

1-

rL 

I 

I 

rL 

I 

I 

100 110 120 130 140 150 160 

DAYS FROM BEGINNING OF INJECTION 

in observation well AM4 during long-term test cycle 1. 

- - - Model-computed temperature 

---Average temperature at 88-, 93-, and 99-meter altitudes 

--- Model-computed temperature 

---Average temperature at 66-, 73-, and 81-meter altitudes 

---Average temperature at 52-, and 58-meter altitudes 

- - - Model-computed temperature 

--- Measured temperature at 

45-meter altitude 

170 180 190 200 

C65 
(/) 

:::;, 

Ci) 

....J 

UJ 

u 

(/) 

UJ 

UJ 

a: 

{!J 

UJ 

Cl 

z 

UJa: 

:::;, 

I-

<( 

a: 

UJ 

a... 60 ~ UJ 

I50 

OL---L---~--~--J---~---L __ _L __ _L __ _L __ ~-- --~--~~_u u_L_ -- --~~J_~ 

0 1 0 20 30 40 50 60 70 80 90 1 00 

DAYS FROM BEGINNING OF INJECTION 

Figure 31. Model-computed and measured temperatures 

C66 
--- Model-computed temperature 

--- Measured temperature at wellhead 

100 110 120 130 140 150 160 170 180 190 200 

DAYS FROM BEGINNING OF INJECTION 

in production well A during long-term test cycle 2. 

C67 
140 I 

Upper part of Franconia Formation INJECTION STORAGE - I 

120 ---j 

_j 

100 - 1 

"1 

80 __] 

I 

- 1 

60 ---j 

_j 

40 I 

- 1 

"1 

20 __] 

I 

I 

0 

100 I 

Lower part of Franconia Formation - 1 

80 ---j 

_j 

60 I 

(/) 

:::l 40 __] 

(/) 

--' 

LU 

u 20 (/) ---j 

LU _j 

LU 

a: 0 (!) 

LU 

Cl 

z 140 LUa: Ironton Sandstone I :::l 

1- 120 ---j 

<! 

a: I LU 100 I a... 

2 "1 

LU 80 __] 

1- I 

I 

60 ---j 

_j 

40 I 

I 

"1 

20 __] 

I 

I 

0 

140 I 

Galesville Formation - 1 

120 ---j 

_j 

100 - I 

"1 

80 __] 

I 

- 1 

60 ---j 

_j 

40 - I 

"1 

20 __] 

_I 

0 

0 10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 32. Model-computed and average measured temperatures 

C68 
STORAGE WITHDRAWAL --- Model-computed temperature 

--- Average temperature at 88-, 

93-, and 99-meter altitudes 

L 

L 

--- Model-computed temperature 

- --Average temperature at 66-, 

73-, and 81-meter altitudes 

I 

~~~~~~~==~~ 

I 

L 

I 

I 

I 

r 

L 

L 

I 

1-

r 

L 

1-

r 

L 

I 

1-

r 

L 

I 

1-

r 

L 

I 

1-

100 110 130 140 150 160 

DAYS FROM BEGINNING OF INJECTION 

in observation well AM1 during long-term test cycle 2. 

- -- Model-computed temperature 

--- Average temperature at 52-, 

and 58-meter altitudes 

--- Model-computed temperature 

--- Measured temperature at 

45-meter altitude 

170 180 200 

C69 
C/) 

:::> 

C/) 

-' UJ 

u 

C/) 

UJ 

UJ 

c:: 

(.!:) 

UJ 

0 

80 

60 

40 

20 

80 

60 

20 

...J 

I 

I 

-; 

_J 

I 

I 

...J 

z 140,---~--,----r---,---,---,,---,---.---,----.---,---.----.---~--,----r---,---,----,---- w· 

c:: 

:::> 120 

~ c:: 

UJ 100 a.. 

2 

UJ 

I- 80 

60 

40 

20 

120 

100 

80 

60 

40 

20 

C70 

Ironton Sandstone 

40 50 60 

DAYS FROM BEGINNING OF INJECTION 

I 

I 

...J 

I 

I 

_J 

Figure 33. Model-computed and average measured temperatures 
I 

rL 

L 

L 

I 

1-

rI 

1-

r 

L 

I_ 

I 

rL 

I 

1-

r 

L 

I 

I 

100 110 

STORAGE WITHDRAWAL 

120 130 140 150 160 

DAYS FROM BEGINNING OF INJECTION 

in observation well AS1 during long-term test cycle 2. 

--- Model-computed temperature 

---Average temperature at 88-, 

93-, and 99-meter altitudes 

- -- Model-computed temperature 

--- Average temperature at 66-, 

73-, and 81 -meter altitudes 

--- Model-computed temperature 

--- Average temperature at 52-, 

and 58-meter altitudes 

- -- Model-computed temperature 

--- Measured temperature at 

45-meter altitude 

170 180 190 200 

C7 l 
140 I 

Upper part of Franconia Formation INJECTION STORAGE - 1 

120 __, 

.J 

100 - 1 

80 _j 

I 

- 1 

60 __, 

.J 

40 I 

- 1 

; 

20 _j 

I 

- 1 

0 

100 I I I I I I I I I I 

Lower part of Franconia Formation - 1 

80 [- -; 

t:::" Water sampling .J 

60 : Jl '-\A event 

I 

- I 

(/) ; :::J 40 :.:.J (/) 

_J 

L.U 

u 20 [- I ...., (/) I L.U .J 

L.U I I I I I I ~ I I L I a: 0 (.!) 

L.U 

Cl 

z 140 w' I 

a: Ironton Sandstone I :::J 120 __, 1-

<{ 

a: 100 I L.U I a... 

~ ; 

L.U 80 _j 

1- I 

I 

60 __, 

.J 

40 I 

I 

; 

20 _j 

I 

I 

0 

140 I 

Galesville Formation - I 

120 __, 

.J 

100 I 

; 

80 _j 

I 

- 1 

60 __, 

.J 

I 40 I 

; 

20 _J 

I 

- 1 

0 

0 10 20 30 40 50 60 70 80 90 100 

DAYS FROM BEGINNING OF INJECTION 

Figure 34. Model-computed and average measured temperatures 

en 
L 

I 

IIL 

I 

I 

L 

L 

L 

I 

L 

1-

tL 

1-

r 

L 

I 

1-

1-

L 

I 

1-

r 

L 

I 

I 

100 

STORAGE WITHDRAWAL 

110 130 140 150 160 

DAYS FROM BEGINNING OF INJECTION 

in observation well AM2 during long-term test cycle 2. 

--- Model-computed temperature 

---Average temperature at 88-, 

93-, and 99-meter altitudes 

--- Model-computed temperature 

--- Average temperature at 66-, 

73-, and 81-meter altitudes 

--- Model-computed temperature 

---Average temperature at 52-, 

and 58-meter altitudes 

--- Model-computed temperature 

--- Measured temperature at 

45-meter altitude 

200 

C73 
140 

120 

100 

80 

60 

40 

20 

0 

100 

80 

60 U) 

:::> 40 U) 

-' UJ 

u 20 U) 

UJ 

UJ 

a: 0 C!l 

UJ 

Cl 

z 140 UJa: Ironton Sandstone :::> 120 f-

<! 

a: 

UJ 

a... 100 

2 

UJ 80 f60 

40 

20 

0 

Galesville Formation 

10 

C74 

20 30 40 50 60 70 80 90 

DAYS FROM BEGINNING OF INJECTION 

_j 

_j 

--; 

_j 

I 

I 

"1 

_j 

I 

I 

--; 

_j 

I 

I 

"1 

_j 

I 

I 

I 

- 1 

--; 

_j 

- 1 

"1 

_j 

I 

- 1 

--; 

_j 

I 

- 1 

"1 

_j 

I 

I 

100 

Figure 35. Model-computed and average measured temperatures 
L 

tL 

L 

tL 

I 

L 

1-

tL 

1-

r 

L 

I 

1-

tL 

I 

1-

r 

L 

I 

1-

100 110 

STORAGE WITHDRAWAL 

120 130 140 150 160 

DAYS FROM BEGINNING OF INJECTION 

in observation well AM3 during long-term test cycle 2. 

--- Model-computed temperature 

--- Average temperature at 88-, 

93-, and 99-meter altitudes 

--- Model-computed temperature 

--- Average temperature at 66-, 

73-, and 81 -meter altitudes 

--- Model-computed temperature 

--- Average temperature at 52-, 

and 58-meter altitudes 

--- Model-computed temperature 

--- Measured temperature at 

45-meter altitude 

170 180 190 200 

C75 
140 

120 

100 

80 

60 

40 

20 

0 

100 

80 

60 (/) 

::> 40 (/) 

....J 

UJ 

u 20 (/) 

UJ 

UJ 

0: 0 (.!) 

UJ 

Cl 

z 140 UJ0: Ironton Sa ndstone ::> 120 1-

<( 

0: 

UJ 100 c... 

~ UJ 

1- 80 

60 

40 

20 

0 

10 20 

C76 

30 40 50 60 70 80 90 

DAYS FROM BEGINNING OF INJECTION 

_ I 

_j 

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- 1 

_, 

_j 

_ I 

I 

_j ' 

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I 

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I 

I 

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100 

Figure 36. Model-computed and average measured temperatures 
STORAGE WITHDRAWAL - - - Model-computed temperature 

--- Average temperature at 88-, 

93-, and 99-meter altitudes 

L 

--- Model-computed temperature 

--- Average temperature at 66-, 

73-, and 81-meter altitudes 

L 

--- Model-computed temperature 

--- Average temperature at 52-, 

and 58-meter altitudes 

L 

I 

1- --- Model-computed temperature 

rL 

I 

--- Measured temperature at 

45-meter altitude 

1-

r 

I 

rL 

I_ 

I 

r 

L 

I 

1-

100 110 120 130 140 150 160 170 180 190 200 

DAYS FROM BEGINNING OF INJECTION 

in observation well AM4 during long-term test cycle 2. 

C77 
Table 8. Altitudes of measurement points where temperatures were averaged to correspond with model layers 

Altitude(s) of 

Model composited values 

layer Stratigraphic unit (meters) 

St. Lawrence Formation 110, 104 

2 Upper part of Franconia Formation 99,93,88 

3 Lower part of Franconia Formation 81,73,66 

4 Ironton Sandstone 

5 Galesville Sandstone 

6 Eau Claire Formation 

For the lower part of the Franconia Formation, 

model-computed temperatures were lower than 

averaged temperatures at all observation wells. The 

temperature differences were from less than 5 oc to as 

much as 30°C. This relatively poor approximation of 

the temperatures measured in the lower part of the 

Franconia Formation may have resulted from one or 

more of the following factors: (1) underestimation of 

the thermal conductivity of the unit or the pipe; (2) more 

convection transport of heat vertically within the 

observation well than is accounted for in the model; and 

(3) leakage between the upper part of the Franconia 

Formation and the Ironton and Galesville Sandstones, 

resulting in the transport of heat vertically within the 

observation well. 

The computed temperatures for the model increased 

more slowly than the averaged temperatures, but ended 

the injection phases at about the same temperature 

(within about 10°C). Model-computed temperatures 

during withdrawal typically were within 1 0°C of the 

averaged temperatures. Model-computed temperatures 

in the Ironton Sandstone were 20-40°C higher than 

averaged temperatures at well AM2. These averaged 

temperatures are anomalous in comparison to the 

averaged temperatures at well AM3, which is at 

approximately the same radial distance from production 

well A as well AM2. Well AM2 is on the axis of 

minimum transmissivity (Miller, 1984 ). Therefore, it is 

possible that the model did not accurately simulate the 

effects of lesser transmissivity near well AM2, causing 

higher model-computed temperatures. For the 

Galesville Sandstone, model-computed and averaged 

temperatures had the best match of all the simulated 

formations. The timing and magnitude of temperature 

changes were very close (less than 5°C). 

The calibrated nonisothermal model is a tool for 

evaluating aquifer thermal-energy storage. The model 

can be used to evaluate the optimum: ( 1) rates of 

injection and withdrawal, (2) injection temperature, and 

58,52 

45 

38 

(3) duration of injection, storage, withdrawal periods. 

The model should prove useful in estimating the 

recovery temperatures of heated-water injection in the 

Franconia-Ironton-Galesville aquifer and is a valuable 

tool in computing thermal efficiency of the aquifer. 

Results of simulating the long-term test-cycles 

suggest that the model closely estimated temperatures at 

the observation wells, except in the low permeability 

layers. Results of model analyses indicate that the 

model is accurate in predicting thermal efficiency of the 

aquifer and temperatures at production well A during 

periods of withdrawal. The model is less accurate in 

simulating temperatures at the observation wells 

because of the effects of aquifer anisotropy. Model 

accuracy in simulating temperatures at the observations 

wells could perhaps be improved by obtaining 

additional information on anisotropy of the FranconiaIronton-Galesville aquifer and studying its effect on the 

movement and direction of heat flow for the hydrologic 

conditions at the ATES site. 

SUMMARY 

In May 1980, the University of Minnesota began a 

project to evaluate the feasibility of storing heated water 

(150 degrees Celsius) in the Franconia-IrontonGalesville aquifer (183 to 245 meters below land 

surface) and later recovering it for space heating. The 

University's steam-generation facilities supplied hightemperature water for injection. This Aquifer ThermalEnergy Storage system had a doublet-well design in 

which the injection and withdrawal wells were spaced 

approximately 250 meters apart. Water was pumped 

from one of the wells through a heat exchanger, where 

heat was added or removed. This water was then 

injected back into the aquifer through the other well. 

Two long-term test cycles were conducted during 

which high-temperature water (at 108.5 degrees Celsius 

and 117.7 degrees Celsius, respectively) was injected 

for periods of about 59 days duration. Periods of storage 

C78 
were 61.0 and 59.1 days, and periods of withdrawal 

were 58.0 and 59.7 days, respectively. Approximately 

equal rates of injection and withdrawal of about 18 L/s 

were maintained for each test cycle. Withdrawal 

temperatures averaged about 75 and 85 degrees Celsius, 

respectively. 

Temperature graphs for selected depths at individual 

observation wells indicate that the Ironton and 

Galesville Sandstones received, stored, and yielded 

more thermal energy than the upper part of the 

Franconia Formation. Vertical-profile plots and timegraphs during storage indicate that the effects of 

buoyancy flow were minimal within the aquifer. 

Temperature graphs indicate that the shortest arrival 

times for temperature fronts, and the hottest 

temperatures measured at all observation wells, were in 

the Ironton and Galesville Sandstones. The next 

shortest arrival times, and somewhat cooler 

temperatures, were in the less permeable upper part of 

the Franconia Formation. The latest arrival times for 

temperature fronts were measured in the lower part of 

the Franconia Formation. Because the lower part of the 

Franconia Formation was not screened, heat within this 

part of the aquifer was transported by conduction. 

Significant heat was conducted into the lower part of the 

Franconia Formation. However, the percentage of total 

injected heat that remained in the lower part of the 

Franconia Formation after withdrawal was 

insignificant. Very little heat conduction was observed 

in the upper St. Lawrence Formation and Eau Claire 

Formation confining layers to the aquifer. Buoyancy 

flow within the aquifer was minimal, as evidenced by 

temperature profiles at individual observation wells 

during periods of injection, storage, and withdrawal. 

A three-dimensional, anisotropic, nonisothermal 

ground-water-flow and thermal-energy-transport 

model was used to simulate the two long-term test 

cycles. Calibration of the model to nonisothermal 

conditions consisted of comparing model-computed 

thermal efficiencies and withdrawal-water 

temperatures to calculated or measured values. The 

model was calibrated by comparing model-computed 

results to: (1) measured temperatures at selected 

altitudes in five observation wells, (2) measured 

temperatures at the production well, and (3) calculated 

thermal efficiencies of the aquifer. The only input 

properties varied during model calibration were the 

longitudinal and transverse thermal dispersivity, which 

were simulated at 3.3 and 0.33 m, respectively. The 

model accurately simulated aquifer thermal efficiencies 

C79 

to within about 1 percent of calculated values. The 

model accurately simulated withdrawal-water 

temperatures to within an average of about 3 percent of 

calculated values. Graphs of model-computed 

temperatures closely matched graphs of average 

measured temperatures in most cases. Results of model 

analyses indicate that the model is accurate in 

simulating thermal efficiency of the aquifer and 

temperatures of production well A during periods of 

withdrawal. The model is less accurate in simulating 

temperatures at the observation wells because of the 

effects of aquifer anisotropy. 

The calibrated nonisothermal model is a tool for 

evaluating aquifer thermal-energy storage. The model 

can be used to evaluate the optimum: (1) rates of 

injection and withdrawal, (2) injection temperature, and 

(3) duration of injection, storage, and withdrawal 

periods. The model should prove useful in estimating 

the recovery temperatures of heated-water injection in 

the Franconia-Ironton-Galesville aquifer and is a 

valuable tool in computing thermal efficiency of the 

aquifer. 

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Freeze, R.A., and Cherry, J.A., 1979, Groundwater: Englewood Cliffs, N.J., Prentice-Hall, Inc., 604 p. 

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__ 1985, Preliminary modeling of an aquifer thermalenergy storage system, in Subitzky, Seymour, eds., 

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aquifer at St. Paul, Minnesota-Field observations, preliminary model analysis, and aquifer thermal efficiency: U.S. Geological Survey Professional Paper 

1530-A, 55 p. 

__ 1994, Cyclic injection, storage, and withdrawal of 

heated water in a sandstone aquifer at St. Paul, Minnesota-Thermal data analysis and nonisothermal modeling of short-term test cycles: U.S. Geological Survey 

Open File Report 93-435, 70 p. 

Miller, R.T., and Voss, C.I., 1986, Design of a finite-difference grid for a doublet-well thermal-energy storage system in an anisotropic aquifer: Ground Water, v. 24, no. 

4, p. 490-496. 

Norvitch, R.F., Ross, T.G., and Brietkrietz, Alex, 1973, 

Water resources outlook for the Minneapolis-St. Paul 

Metropolitan Area, Minnesota: Metropolitan Council 

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hydrologic aspects of tunneling in the Twin Cities area, 

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Thermodynamic properties of minerals and substances 

at 298°K and 1 bar (1 05 pascals) pressure and at higher 

temperatures: U.S. Geological Survey Bulletin 1452, 

456p. 

Sommerton, W.H., Mehta, M.M., and Dean, G.W., 1965, 

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Walton, M., Hoyer, M.C., Eisenreich, S.J., Holm, N.L., 

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