sUSGS

science for a changing world

HYDROGEOLOGIC CHARACTERIZATION OF SIX SITES IN 

SOUTHEASTERN MINNESOTA USING BOREHOLE 

FLOWMETERS AND OTHER GEOPHYSICAL LOGS

Water-Resources Investigation Report 00-4142

\ MINNESOTA

U.S. Department of the Interior 

U.S. Geological Survey
Cover: Location of six boreholes in southeastern Minnesota.
U.S. Department of the Interior 

U.S. Geological Survey

HYDROGEOLOGIC CHARACTERIZATION OF SIX 

SITES IN SOUTHEASTERN MINNESOTA USING 

BOREHOLE FLOWMETERS AND OTHER 

GEOPHYSICAL LOGS

By F.L. Paillet1 , James Lundy2, Robert Tipping3, Anthony Runkel3, Laurel Reeves4 

and Jeffrey Green4

Water-Resources Investigations Report 00-4142

Denver, Colorado 

2000

1 U.S. Geological Survey, Denver, Colorado

2 Minnesota Pollution Control Agency, St. Paul, Minnesota

3 Minnesota Geological Survey, St. Paul, Minnesota

4 Minnesota Department of Natural Resources, St. Paul, Minnesota
U.S. Department of the Interior

Bruce Babbitt, Secretary

U.S. Geological Survey

Charles G. Groat, Director

The use of brand, firm, or trade names is for identification purposes only and does not constitute endorsement by the U.S. Geological 

Survey.

For additional information write to:

Chief, Branch of Regional Research 

U.S. Geological Survey 

Box 25046, MS 418 

Denver Federal Center 

Denver, CO 80225

Copies of this report can be purchased from:

U.S. Geological Survey 

Earth Science Information Center 

Open-Files Reports Section 

Box 25286, MS 517 

Denver Federal Center 

Denver, CO 80225
CONTENTS

ABSTRACT.............................................................................:...................,...................................... 1

INTRODUCTION..................................................................................................................^

Purpose............................................................................................................................................ 1

Scope ............................................................................................................................................... 2

REGIONAL HYDROGEOLOGY...................................................................................................... 2

METHODS.........................................................................................................^^

Geophysical Logs in Consolidated Sedimentary Aquifers.............................................................. 2

Borehole Flowmeter Interpretation ................................................................................................. 4

RESULTS....................................................................:....................................................................... 6

Savage Site...................................................................................................................................... 6

Faribault Site.................................................................................................................................... 7

Pine Island Site................................................................................................................................ 8

Rochester Site.................................................................................................................................. 8

Austin Site....................................................................................................................................... 9

Winona Site..................................................................................................................................... 9

CONCLUSIONS................................^

REFERENCES..............................................................................................^

APPENDIX 1. Faribault flow log interpretation.............................................................................. 32

FIGURES

1. Location of the six boreholes in southeastern Minnesota ..................................................................... 18

2A. Regional stratigraphic column divided into A) upper and

B) lower sections, showing the gamma logs from the six

study boreholes for comparison with the typical gamma

signatures given by Mossier (1998)................................................................................................... 19

2B. Regional stratigraphic column divided into A) upper and

B) lower sections, showing the gamma logs from the six

study boreholes for comparison with the typical gamma

signatures given by Mossier (1998)................................................................................................... 20

3. Explanation of graphical representation of televiewer logs

used in figures 4-7 and figures 9-13 ................................................................................................... 21

4. Electromagnetic flowmeter profiles obtained under ambient 

(stationary) and injection (stationary and trolling) conditions 

compared to other geophysical logs for the Savage borehole ............................................................ 22

5. Stationary electromagnetic flowmeter data obtained under

ambient and pumping conditions compared to other geophysical

logs for the Faribault borehole ........................................................................................................... 23

6. Electromagnetic flowmeter profiles obtained in the Faribault 

borehole while trolling upward at about 10 ft per minute under 

ambient and steady pumping conditions; the flow scale represents 

the flow through the probe measurement section while trolling 

and not true borehole discharge, and the dashed line represents 

the response equivalent to no net borehole flow ................................................................................ 24

7. Trolled electromagnetic flowmeter profile interpretation for 

the Faribault borehole calibrated to produce a true borehole

Contents
discharge scale by shifting the profiles to fit the stationary flow data ............................................... 25

8. Borehole flow model computations fit to trolled electromagnetic 

flowmeter profiles for the Faribault borehole; model parameters 

are listed in table 4 ............................................................................................................................. 26

9. Geophysical logs for the Pine Island borehole ...................................................................................... 27

10. Stationary heat-pulse flowmeter data obtained under ambient 

and pumping conditions compared to other geophysical logs for 

the Rochester borehole ....................................................................................................................... 28

11. Borehole flow model computations fit to the stationary heat-pulse

flowmeter data for the Rochester site ................................................................................................. 29

12. Stationary heat-pulse flowmeter profiles obtained under ambient 

and pumping conditions compared to other geophysical logs for the 

Austin borehole.................................................................................................................................. 30

13. Stationary heat-pulse flowmeter data obtained under ambient 

conditions compared to other geophysical logs for the Winona 

borehole.............................................................................................................................................. 31

TABLES

1. Summary of geophysical logs run in southeastern Minnesota .............................................................. 12

2. Summary of boreholes logged in southeastern Minnesota .................................................................... 13

3. Summary of relative transmissivity profiles expressed as percent of total 

borehole transmissivity for the four boreholes where paired ambient and 

pumped or injection flow profiles were obtained .................................................................................. 15

4. Relative transmissivity of water-producing zones in the Faribault 

borehole expressed as percent of total borehole transmissivity 

computed by the subtraction of inflows method and based on trolled 

electromagnetic flowmeter data in figure 7 ........................................................................................... 16

5A. Estimated transmissivity and hydraulic-head values for the seven 

water-producing zones in the Faribault borehole based on flow 

model matching.................................................................................................................................. 17

5B. Estimated transmissivity and hydraulic-head values for the seven 

water-producing zones in the Rochester borehole based on flow 

model matching.................................................................................................................................. 17

IV Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
CONVERSION FACTORS AND ABBREVIATIONS

Multiply

foot (ft)

inch (in.)

mile (mi)

gallon (gal)

gallon per minute (gal/min)

By

0.3048

25.4

1.609

3.785

0.06309

To obtain

meter

millimeter

kilometer

liter

liter per second

The following terms and abbreviations also are used in this report:

ohm-meters (ohm-m)

transmissivity (T)

hydraulic head(H)

heat-pulse flowmeter (HPFM)

electromagnetic flowmeter (EMFM)

number of zones (N)

measured ambient flow entering the borehole from zone with index k(Q£) 

measured pumping/injection flow entering the borehole from zone with index k(Qkb )

difference of Qk a and Qk b for borehole zone with index k (<2°) 

transmissivity of borehole zone with Index k(Tk )

gallons per minute (gpm) 

borehole televiewer (BHTV)

resistivity (R) [in Table 1] 

temperature (T) [in Table 1]

Contents V

HYDROGEOLOGIC CHARACTERIZATION OF SIX SITES IN 

SOUTHEASTERN MINNESOTA USING BOREHOLE 

FLOWMETERS AND OTHER GEOPHYSICAL LOGS

By Frederick Paillet, James Lundy, Robert Tipping, Anthony Runkel, Laurel Reeves, and Jeffrey Green

ABSTRACT

Caliper, gamma, normal resistivity, fluid column temperature and resistivity, and televiewer logs were 

combined with borehole flow logs to infer the nature of water-producing intervals in six observation 

boreholes at sites in southeastern Minnesota. Row profiles were obtained with either the electromagnetic or 

heat-pulse flowmeters, depending upon equipment availability at the time of logging. Gamma and resistivity 

logs were used to determine the stratigraphic position of open intervals in each of the boreholes. Waterproducing intervals identified using the flowmeter logs were characterized as permeable coarse-clastic beds, 

solution openings along bedding planes, fractures, or karstic horizons on the basis of gamma, caliper, and 

televiewer logs. Flow log interpretation theory demonstrates that the hydraulic head and transmissivity of 

water-producing intervals intersecting an open borehole can be estimated if flow logs are obtained under two 

different quasi-steady conditions, and if the difference in open-borehole water level between the two 

conditions can be measured. If logistical conditions prevent flow logging under more than one condition, 

water-producing zones can be identified, but relative transmissivity values cannot be estimated. If flow logs 

are obtained under two different flow conditions, but the drawdown between the two conditions cannot be 

measured, relative transmissivity can be estimated where the zone transmissivity values are given in percent 

of total borehole transmissivity. Of the six boreholes logged in this study, two different flow logs could be 

obtained at four sites, and drawdown could be measured at two sites. Thus, quantitative estimates of zone 

transmissivity and hydraulic head were obtained at the Faribault and Rochester sites, relative permeability 

profiles were obtained at the Savage and Austin sites, and limited information about water-producing zones 

were obtained at the Pine Island and Winona sites. Model results indicate that there are seven waterproducing zones in the Faribault borehole, with transmissivity values ranging from about 100 to about 1000 

ft2/day, and with hydraulic-head variations of about 2.4 feet within the open borehole interval. The model 

results indicate four water-producing zones in the Rochester borehole, with transmissivity values ranging 

from about 10 to almost 500 ft2/day, and with head variations of about 2.0 feet in the open borehole interval.

INTRODUCTION

A single geologic core or set of well logs 

serves to define the hydrostratigraphy of 

homogeneous, stratified aquifers. Aquifers 

characterized by a heterogeneous distribution of 

permeability in the form of vugs, fractures, and 

solution openings are more difficult to describe. 

Aquifer heterogeneity also introduces scale effects 

in predicting the performance of production and 

observation wells constructed at specific 

locations. A single local sample of aquifer 

hydraulic properties derived from a flowmeter log 

may not provide a useful description of aquifer 

properties in such situations.

Purpose

In this study, a combination of geophysical 

logs are used to define local aquifer geometry 

within heterogeneous sedimentary aquifers at six 

study sites in southeastern Minnesota using a 

technique described by Paillet (1998) for the 

characterization of fractured heterogeneous 

aquifers. The study was designed to identify the 

water-producing intervals within observation or 

pilot production wells, and to identify where those 

zones fit into the regional stratigraphic column. 

The method is based on quantifying the effects of 

aquifer drawdown measured in observation wells 

under the influences of steady pumping from

Introduction 1
adjacent production wells. It is hoped that this 

information will result in an improved 

understanding of aquifer dynamics in the vicinity 

of production well intakes, and will allow 

improved monitoring well installation and more 

effective interpretation of aquifer performance.

Scope

The geophysical well logs described in 

this report were obtained in six different boreholes 

at representative locations in southeastern 

Minnesota (fig. 1). Boreholes were selected as 

representative of observation or pilot production 

boreholes completed in various sections of the 

regional stratigraphic column. The intent was to 

demonstrate the technique at representative sites 

where open observation wells and the ability to 

control well field operations provided suitable 

conditions for borehole flow logging. The logs 

were obtained over the period from May 5 to May 

10, 1999. A summary of the logs run during this 

period is listed in table 1. Details concerning the 

construction, depth, and formations intersected by 

each borehole are listed in table 2. A list of the 

water-producing intervals identified in these 

boreholes is given in table 3.

REGIONAL HYDROGEOLOGY

Regional stratigraphy of southeastern 

Minnesota is illustrated in figure 2. The 

sedimentary rocks in this interval are consolidated 

Paleozoic sandstones, carbonates, and shales 

ranging in age from Upper Cambrian to Upper 

Ordovician (Mossier, 1998). These rocks can 

generally be divided into three classes: coarse 

elastics, fine elastics, and carbonate rocks 

(Runkel, 1996, 1998; Setterholm and others, 

1991). Core plugs from the coarse elastics 

suggest poor to moderate cementation, primary 

porosity from 15 to more than 30 percent, and 

permeability ranging from 1.0 to as much as 10.0 

ft/day (Miller and Delin, 1993). Core plugs from 

fine elastics indicate variable cementation, total 

porosity (combined effective and non-effective) 

from 10 to 30 percent, and horizontal permeability 

from less than 10"4 to 10" 1 ft/day (Miller and 

Delin, 1993; Wenck and Associates, 1997). Fine 

elastics are also characterized by anisotropy

caused by bedding, such that horizontal 

permeability is usually 10 to 100 times greater 

than vertical permeability in these siliclastic rocks 

(Miller, 1984; Miller and Delin, 1993). Carbonate 

rocks are generally strongly cemented, have 

various degrees of anisotropy attributed to 

bedding, and core plugs have permeabilities 

similar to those of the fine elastics (Minnesota 

Geological Survey, unpub. data).

In addition to the primary porosity and 

permeability of the three classes of consolidated 

sedimentary rocks, the carbonate rocks contain 

secondary permeability in the form of fractures, 

solution openings along bedding planes, and other 

paleo-karst features (Gianniny and others, 1996; 

Libra and Hallenberg, 1985). There are numerous 

fractures and solution openings in the uppermost 

interval of bedrock. Intervals characterized by 

shallow bedrock conditions have intervalaveraged permeability values one or more orders 

of magnitude greater than that of unfractured 

rocks in those intervals (Wenck and Associates, 

1997; Gianniny and others, 1996). The lower 

limit of the shallow bedrock conditions appears to 

occur at about 100 ft in depth, because borehole 

image logs and cores indicate open fractures and 

dissolution features are uncommon below that 

depth. Information on deep bedrock conditions is 

relatively limited. On the basis of the limited 

information available from locations in Minnesota 

and adjacent states, the secondary permeability of 

deep bedrock occurs mostly in the form of 

solution openings along bedding planes and paleokarst intervals in carbonate rocks below the lower 

limit of shallow borehole conditions.

METHODS

Geophysical Logs in Consolidated 

Sedimentary Aquifers

Geophysical well logs are routinely used to 

characterize the lithology and hydraulic properties 

of sedimentary rocks (Paillet and Crowder; 1996; 

Keys, 1990). A suite of gamma and electric logs 

is often sufficient to determine lithology. Neutron 

porosity and gamma-gamma density logs in 

combination with gamma and electric logs can be 

used to determine primary porosity in coarse 

elastics, and to separate effective from non2 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
effective porosity in fine elastics, but those logs 

were not used in this study for logistical reasons. 

Instead, a combination of acoustic televiewer (a 

borehole wall imaging device) and flow logs were 

used to infer the combination of primary and 

secondary permeability in each interval. The 

flowmeter logs are used to identify permeable 

intervals (Paillet and others, 1996). The 

televiewer log is used to determine the character 

of the water-producing intervals. When the 

flowmeter log indicates a discrete "jump" in a 

flow profile and the televiewer log indicates an 

associated fracture, bedding plane, or other 

solution opening, the permeability is assumed to 

be secondary permeability. When inflow is 

distributed over a wider interval, and no potential 

fractures or solution openings are present, the 

inflow is attributed to primary permeability. In 

addition, intervals of primary permeability are 

expected to coincide with intervals of coarse 

elastics, as indicated by relatively low gamma log 

counts and relatively high formation resistivity, 

which are characterized by significant effective 

primary porosity.

One of the most important considerations in 

geophysical logging is depth control (Paillet and 

Crowder, 1996). Quantitative measurements in 

boreholes consist of two values: the geophysical 

measurement and the depth measurement. Depth 

control is a minor issue with most logs, where 

measurements are made in one continuous run 

from the bottom to the top of the borehole, and 

where the logging cable is always under tension. 

If there is a zero point offset at the completion of 

the logging run, the discrepancy can be assumed 

to have occurred during the lowering of the probe, 

when logging cable tension may have been 

decreased below the minimum required to turn the 

measuring wheel used to drive the depth encoding 

system. In that case, the measured depth offset at 

the end of logging can simply be added to the 

entire log.

Depth errors are likely to be more 

significant in flow logging with the 

electromagnetic and heat-pulse flowmeters for 

two reasons: 1) the flowmeter probes are equipped 

with centralizers and diverters (flexible disks to 

block flow in the annulus around the probe) that 

are likely to "catch" on borehole irregularities; and 

2) flowmeters are often run in the stationary mode 

where they are moved up and down between

discrete measurement stations. Thus, the 

flowmeters are especially prone to depth errors 

when being moved down the borehole, and the 

stationary mode of measurement involves 

frequent reversals of probe movement which also 

can cause depth errors. For these reasons, flow 

measurements usually have more reliable depth 

scales when made in the trolling mode. 

Otherwise, there is a trade-off in accuracy 

between the spatial resolution of the trolled logs 

and the flow resolution of the stationary data 

points. Stationary measurements can be 

calibrated directly in units of borehole flow, but 

are prone to depth errors because of the reversal 

of probe movement, and because inflow zones are 

only defined to within the spacing of ^ 

measurements. Trolling measurements are less 

prone to depth errors, and show the precise depth 

where flow enters the borehole, but the flow 

values given while trolling are offset by the 

trolling speed. In addition, trolling measurements 

are usually made with a diverter that provides a 

relatively poor fit to the borehole in order to allow 

the probe to move smoothly. Stationary 

measurements can be made at depth locations 

where borehole conditions are likely to allow 

effective operation of diverters. In contrast, 

trolling measurements will include data points 

where diameter effects influence the operation of 

diverters or when trolling speed is interrupted by 

the logging probe temporarily "sticking" on a 

ledge or other obstruction, causing considerable 

"noise" to be added to the flow profile.

In general, most effective flow logging 

results when both trolled and stationary data are 

available. In situations where other logs limit 

potential inflow zones to a few specific bedding 

planes or fractures, the stationary measurements 

provide the best quantitative measurements of 

flow, and the spacing of water-producing zones 

can accommodate depth errors of as much as a 

few feet. When there are many potential inflow 

points, trolling measurements provide the best 

indication of inflow locations, but diameter 

variations and the borehole conditions, along with 

the operational problems in maintaining a steady 

trolling speed can significantly affect the quality 

of the logs.

Quantitative calibration of flow data is 

given in units of borehole flow (gallons per 

minute) by regressing probe output against known

Methods 3
flow rates in laboratory flow columns. These 

calibrated discharge values are the data recorded 

by either the heat-pulse or electromagnetic 

flowmeter systems. In the calibration set-up, all 

flow is forced to pass through the measurement 

section or "throat" of the logging probe. In the 

field, there is some bypass of flow around the 

flexible disk or diverter used to block the annulus 

between logging probe and the borehole wall. 

Field measurements are multiplied by a correction 

factor to compensate for the additional flow 

bypassing the measurement section. The 

correction factor is estimated in the field by 

comparing measured flow with known flow 

values at one or more control points. Such control 

points are most often found at the top of an open 

borehole section or in the lower part of casing, 

when water is being pumped or injected at a 

known rate. Changes in borehole diameter such 

as those indicated by the caliper log, or the effects 

of borehole irregularities on the efficiency of the 

diverter, can sometimes introduce significant 

scatter in the flow measurements.

Borehole Flowmeter Interpretation

High-resolution borehole flowmeters, such 

as the heat-pulse (HPFM; Hess, 1986; Paillet and 

Crowder, 1996) and the electromagnetic 

flowmeter (EMFM; Molz and Young, 1993; Molz 

and others, 1994), can be used to determine the 

permeability of intervals intersecting open 

intervals of boreholes. In the simplest situations, 

flow profiles indicate intervals where flow enters 

the borehole under a given hydraulic condition. 

The main advantage of high-resolution flow 

logging is that aquifer tests can be run under lowflow conditions. When boreholes are pumped at 

rates of a few gallons per minute, drawdown 

stabilizes quickly, and inlet losses in screens and 

pipe flow losses in the well bore can be neglected. 

Disposal of produced water at contaminated sites 

also poses problems, so that flowmeter 

experiments conducted at low discharges 

minimize the amount of water for disposal.

The one significant limitation on highresolution flow logging at low production rates is 

that the drawdown produced by pumping may be 

smaller than ambient hydraulic-head differences 

within the borehole. In such situations, the 

relative proportion of inflow in a given waterproducing interval may be very different from the 

relative transmissivity of that interval. The 

relative amount of inflow to the borehole, 

calculated from the difference in rate of flow 

above and below and inflow interval, is used to 

estimate inflow zone transmissivity (Molz et al., 

1989). The inflow under quasi-steady conditions 

is proportional to the product of transmissivity 

and hydraulic-head difference driving the flow. 

Since the head differences may be significantly 

different for each zone, the relative inflows are 

often not proportional to interval transmissivity. 

In fact, it is not uncommon to observe downflow 

between producing zones under ambient 

conditions. A small amount of pumping may not 

be enough to reverse this downflow. In such 

situations, there is outflow in some zones even 

during pumping. Acceptance of this outflow at 

face value would indicate negative transmissivity, 

which is clearly not possible.

The interpretation of vertical flow profiles 

in open boreholes where there is a vertical 

hydraulic-head gradient involves the analysis of 

flow data sets for both transmissivity and 

hydraulic head in each water-producing zone. 

Flow into or out of the borehole is assumed to 

occur through porous beds or fractures that can be 

modeled as ideal confined aquifers in the 

immediate vicinity of the borehole. If data are 

obtained under steady or quasi-steady conditions, 

aquifer storage coefficient can be ignored, but two 

such flow profiles are needed to solve for the 

double set of parameters, transmissivity (T) and 

zone hydraulic head (H). Considering the number 

of unknown variables to be determined, there are 

2N values of T and H for N water-producing 

intervals. There will be 2(N-1) values of 

measured flow in the borehole intervals between 

the N zones. In addition, there will be two other 

data points: the drawdown between ambient and 

pumping conditions, and the pumping rate. Thus, 

a combination of flow profiles under ambient and 

steady pumping conditions provide the 2N data 

points needed to "solve" for the 2N values of T 

and H. The general numerical formulation of the 

flow equations used to solve the flow equations 

for the T and H values are given by Molz et al. 

(1989) and Paillet (1998).

In the simplest flow logging situation, flow 

is obtained under only a single hydraulic 

condition, which is usually ambient flow. Such

4 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
limited flow logging situations arise when 

pumping or injection is not possible. There are 

also situations where hydraulic conditions are 

changing during the flow measurement period, so 

that steady flow profiles cannot be made. In these 

cases, flow logs can be used to identify the 

"hydraulically active" zones within a borehole. 

No other interpretation is possible under these 

circumstances.

In fact, the amplitude of inflow or outflow 

under even steady ambient conditions can be 

misleading. The water level in an open borehole 

represents the transmissivity-weighted average of 

the water levels in the individual zones connected 

to the borehole. In other words, the zone with 

lowest T controls flow between borehole 

intervals. Thus, the hydraulic conditions in the 

borehole act to minimize the hydraulic gradient 

driving flow from the most permeable zones into 

or out of the borehole. This, in turn, causes the 

inflow or outflow from the most transmissive 

zones to appear no different from the inflow or 

outflow from one or more of the other zones. 

Thus, relatively low transmissivity zones may 

have a negligible effect on the borehole water 

level, but a major or even dominant effect on the 

measured borehole flow.

A qualitative transmissivity profile can be 

obtained from a pair of flow profiles if drawdown 

cannot be measured. This condition applies to 

two common situations: 1) water level change 

cannot be measured because there is cascading 

water when "pumping" is performed by injection; 

and 2) the formation is so permeable that 

drawdown is too small to measure. In such 

situations, there are only 2N-1 data points with 

which to solve for the 2N hydraulic parameters. 

The best we can do is to eliminate the effects of 

H, and then solve for all of the T values as 

multiples of one. This gives a qualitative 

transmissivity profile. A quantitative scale may 

be added at a later time when well tests give an 

estimate for total well transmissivity - usually 

performed at a pumping rate high enough that 

head differences between the producing zones can 

be neglected. The head values are eliminated 

from the analysis by subtracting the data from the 

two flow profiles according to the equation 

(subtraction of inflows method; Paillet, 1998):

<&

; EC?

where Qk a and Qk b are the measured inflow for the

zone k (obtained by subtracting the flow below 

the fracture from that above the fracture in the 

profile) obtained under flow conditions "a" 

(usually ambient) or "b" (pumping or injection). 

Outflow is expressed as negative inflow. The 

relative transmissivity for zone k is then expressed

as the ratio of the <2° for zone k with the total of

all the Q° values. An important part of this

analysis is that the signs on the right hand side of 

the first of these two equations should be 

consistent, either positive for pumping (where 

there is net inflow), or negative for injection 

(where there is net outflow). If the difference for 

one such zone has the "wrong" sign, this indicates 

a condition that is hydraulically impossible. 

Small values with the wrong sign result from 

measurement errors, indicating that the relative 

transmissivity of a zone is effectively too small to 

estimate. A large value with the wrong sign 

indicates there is a major problem with the data 

set.

When two steady flow profiles are 

obtained and the change in water level between 

these two conditions can be measured, then the 

full set of T and H values can be estimated by 

modeling the flow data. This is a simple forwardmodeling problem, where the borehole flow is 

predicted for a given set of values for T and H 

values until the model predictions lie within an 

acceptable limit of the measured flow (Paillet, 

2000). Iterative methods, where the mean square 

difference between model and data are used to 

converge on the model fit, have not proven 

effective. This result is attributed to the strong 

non-linearity of the model, where predicted flows 

are determined by the product of the T and H 

values. However, flow model analysis confirms 

that there is a single, unique set of T and H values 

which allows an acceptable fit of the model to the 

two steady flow profiles whenever the drawdown 

between ambient and pumping or injection is 

known.

Methods 5
RESULTS

The flowmeter profiles and geophysical 

logs from the six Minnesota sites provided various 

levels of information about hydraulic conditions at 

each location. Fully successful characterization 

was achieved at two of the six sites, where site 

conditions and equipment logistics allowed 

unambiguous formulation of a flow log 

interpretation. The results obtained at each of the 

sites, and the degree of interpretation possible 

with the given geophysical log data are presented 

in the following subsections of this report. In 

representing the flowmeter data for the boreholes 

at each site, the figures plotting that data use a 

consistent notation throughout. Stationary flow 

measurements are given as solid dots for ambient 

flow data, and as open dots for flow data obtained 

under pumping or injection conditions. Trolled 

flowmeter profiles are given as light continuous 

lines. Interpretation of both stationary and trolled 

flow data are given as heavy solid lines 

superimposed on the flow plots. The 

interpretation lines are vertical over those 

intervals where flow is assumed to be constant. 

The interpretation lines shift either to the left or 

right over those intervals where inflow or outflow 

is assumed to occur. The size of the shift and the 

depth interval over which that shift occurs are 

clearly shown in each figure. In those situations 

where a model is fit to either data or 

interpretations of the data, the predictions of the 

flow model are superimposed as heavy dashed 

lines on the flow data plots. Original televiewer 

log images cannot be readily displayed with the 

flow log data because of the great difference in 

scale between the two classes of data. Televiewer 

log results are summarized in the geophysical and 

flowmeter data composite figures using the 

conventions presented in figure 3.

Savage Site

Although the Savage borehole is open to the 

520-680 ft interval, all of the inflow to this 

borehole is confined to the 580-660 ft interval 

(fig. 4). Flow was measured with the EMFM with 

a flexible diyerter to funnel flow into the 

measurement throat. The EMFM output gives 

flow in gpm through the measurement throat. A

field calibration was obtained by measuring the 

downflow in the casing during the 9 gpm 

injection. This calibration showed that the 

nominal flows given by the EMFM had to be 

multiplied by a factor of 6.0 to give true flow for 

measurements in the Savage borehole. This 

multiplication factor is similar to values obtained 

under similar conditions at other sites. A short 

interval of steady upflow was detected under 

ambient conditions. Thus, an aquitard is present 

at about 595 ft, separating the aquifer into upper 

and lower zones (table 3). Most of the outflow 

under injection occurs in the lowermost zone. 

When the subtraction of inflows method is used to 

compensate for the effects of hydraulic-head 

difference between the zones, the lower zone 

accounts for 82 percent of the water production 

from this well. The other 18 percent appears to 

originate from a thin zone a few feet above. Both 

zones appear to be permeable beds, since they are 

not associated with fractures, bedding planes, or 

solution openings on the borehole televiewer 

(BHTV) log. The aquitard may be associated 

with a series of faint shale beds or partings 

indicated on the BHTV log.

The logs and cuttings recovered during 

drilling indicate that the Savage borehole is open 

to the lower part of the Franconia Formation, all 

of the Ironton and Galesville Sandstones, and the 

upper part of the Eau Claire Formation (fig. 2). 

The flowmeter log indicates that most of the 

inflow to the borehole is derived from the 

distributed primary permeability of the coarse 

clastic rocks in the Galesville and Ironton 

Sandstones. The water-producing zone correlates 

with an interval of low gamma activity (590-640 

ft) that probably indicates a clean sandstone. Both 

trolling and stationary flow measurements were 

made with the EMFM. The trolled data confirm 

that inflow in this interval is not concentrated near 

bedding plane openings, but is evenly distributed 

over the entire interval.

The flow logs also indicate a small inflow 

coming from a thin interval just above 590 ft in 

depth. This zone is hydraulically isolated from 

the water-producing zone below because there is a 

small amount of ambient flow between zones. 

This water-producing zone is apparently in the 

lower part of a fine clastic interval in the lower 

part of the Franconia Formation extending from 

570 to 590 ft. Because there is no obvious

6 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
bedding plane or fracture indicated on the BHTV 

log, this inflow may be associated with either thin 

beds of medium to coarse-grained sand within the 

fine clastic rocks, or bedding plane openings that 

do not show up very well on the BHTV image 

log.

Faribault Site

The BHTV log for the Faribault borehole 

shows numerous bedding planes and karst 

horizons, as well as a few near-vertical fractures 

(fig. 5). These fractures strike about N60E, but do 

not seem to be associated with inflow to or 

outflow from the borehole. Flow logging was 

begun by taking stationary flow measurements 

with the EMFM. The flowmeter was used 

without diverter, because there was a relatively 

small annulus between probe and borehole wall, 

and because initial attempts to use the EMFM 

with diverter showed that the diverter interfered 

with movement of the probe in the rough 

borehole. Probe response was calibrated in casing 

while pumping at 2.0 gpm. Nominal flow 

measurements had to be multiplied by a factor of 

about 15.0 in a 4-in diameter borehole to give 

total borehole flow. Stationary EMFM 

measurements give accurate flow values, but are 

not very efficient at defining the exact depths of 

inflow or outflow in aquifers where other logs 

show many possible inflow depths. The EMFM 

data show there was a complex downflow profile 

in the Faribault borehole, which was only slightly 

suppressed during pumping at 2.0 gpm (fig. 5). 

Thus, the only place where the measured flow 

during pumping was upwards was above the 

bottom of casing. Everywhere else, the pumping 

only served to slow the ambient downflow rather 

than turn it around into upflow.

Although the stationary flow values give 

accurate measurements at a single point, they do 

not very effectively indicate exactly where flow 

enters the borehole between measurement 

stations. This was a problem in the Faribault 

borehole, because there were so many possible 

entry points. The repeated movement of the probe 

up and down to identify inflow points also 

increased the likelihood that depth errors would 

build up over time. Seven possible flow zones 

were inferred from the limited flow data. One 

clear diagnostic that there are problems with the

interpretation in figure 5 is given by the 

subtraction of inflow method to infer relative flow 

zone transmissivity (table 3). The subtractions 

produce negative numbers, indicating that one or 

both flow profiles inferred from the flow data 

points in figure 5 may be in error.

Possible depth errors in the flow profile 

inferred from the data in figure 5 can be addressed 

by comparing these results with flow logs 

obtained while trolling the EMFM at a constant 

speed. The trolled logs (fig. 6) have significant 

diameter effects and the trolling speed (which 

may vary slightly) is superimposed on the 

borehole flow. Some of the noise in the data may 

have been caused by the probe catching on 

bedding planes during the logging. The moving 

probe measures the difference of water movement 

due to borehole flow and the movement of the 

probe itself, and not just borehole flow. But the 

trolled logs do clearly show the precise depths 

where flow shifts in response to exit or entry. The 

two sets of flow data (stationary and trolled; fig. 

7) are combined to identify the exact inflow 

points, and to assign numerical flow values to 

"plateaus" on the trolled logs. There are several 

intervals near the bottom of the well where there 

are just not enough stationary values to adequately 

fix the flow "steps" in figure 7. This is now 

identified as the source of our problem in 

analyzing the data in figure 5. The combined data 

sets give a set of zone values that now make sense 

(table 4). The one zone where there is a small 

negative value of -0.1 can be attributed to 

measurement scatter where the difference is too 

small to measure, and can be effectively assigned 

a relative transmissivity value of 0.0. A numerical 

model fit (Paillet, 1998) to the flow data (fig. 8) is 

used to estimate the T and H values for the waterproducing zones indicated in figure 6. A detailed 

discussion of the analysis of the flow data from 

the Faribault borehole is given in Appendix 1.

Based on this information, three of the 

water-producing zones in the Faribault borehole 

are karstic horizons at about 115, 172, and 182 ft 

in depth. All of the these zones are located in the 

Shakopee Formation of the Prairie du Chien 

Group. Although some minor intervals of primary 

porosity are known to occur in this interval, 

essentially all of the water-production from the 

Faribault borehole is associated with bedding 

planes or other karstic features. The most

Results 7
permeable zone is a series of bedding planes right 

at the bottom of casing. These may be closely 

connected to the overburden. The zone at about 

208 ft may be a weaker karstic zone. The zone 

near 80 ft is apparently a bedding plane, but the 

response here is complex, because the televiewer 

and gamma together show there is a shale here, 

too. So the zone may be a bedding plane just 

above or below a shale bed. The major waterproducing zone at the very bottom of the borehole 

.may be below televiewer coverage, and appears to 

be a paleo-karst horizon developed along the 

regional unconformity at the contact between the 

Shakopee Formation and the underlying Oneota 

Dolomite.

The flow profiles given in figure 6 for the 

two steady flow profiles in the Faribault borehole 

were modeled using the numerical technique of 

Paillet (1998), and an acceptable fit to the profiles 

and the measured drawdown of 0.1 ft was found 

with the flow model predictions within the ±0.5 

1/min of the measured flow (fig. 8). The details of 

this analysis and the resolution of the 

inconsistencies in the subtraction of inflow results 

(table 3) based on stationary flow data for this site 

(fig. 5) are discussed in Appendix 1. The revised 

zone flows and subtraction of inflow estimates of 

relative zone T based on the flow data in figure 7 

are listed in table 4. The estimates for the T and 

H values for the seven water-producing zones in 

the Faribault borehole are listed in table 5A. The 

results indicate that the uppermost three zones 

have the same hydraulic head, and probably 

represent a single aquifer sub-unit. The hydraulic 

head is lowest in the 170-190 ft interval, and 

increases again between 190 ft and the bottom of 

the borehole. Although three of the zones appear 

to have about the same transmissivity (800-1000 

ft2/day), the 172 ft zone appears to be drawn down 

by pumping from the Faribault wellfield more 

than the other zones on the basis of the aquifer 

hydraulic heads given by the model fit. The sum 

of all of the transmissivity values of the seven 

zones (about 4000 ft2/day) can be used to 

estimated the productivity of a production well 

screened over the open-borehole interval (48-230 

ft) in the Faribault wellfield.

Pine Island Site

No meaningful flowmeter logs were

obtained at this site for logistical reasons related 

to scheduling use of a production well 

immediately adjacent to the Pine Island borehole 

(fig. 9). The other gamma logs show that the open 

borehole is divided into two sand (coarse clastic) 

intervals separated by a 20-ft-thick fine clastic bed 

(380-405 ft), where the gamma response is related 

to the presence of fine-grained, feldspathic sand 

with relatively little shale. All of these units are 

within the Jordan sandstone (fig. 2). The BHTV 

log shows a prominent bedding plane at the top of 

the fine clastic bed near 380 ft in depth, and a 

single steeply dipping fracture striking about 

N60E in the 360-370 ft depth interval. When the 

adjacent city supply well was turned on, the water 

level in this observation well dropped almost 

immediately from above 15 ft below land surface 

down to almost 100 ft below land surface. During 

limited EMFM measurements, oscillating flow 

was observed in the casing which was interpreted 

as the harmonic oscillation of the water column in 

response to the sudden lowering of water level 

when the adjacent production well was put into 

operation.

Rochester Site

The Rochester borehole is open to the 

Shakopee Formation under shallow bedrock 

conditions, characterized by a relatively high 

density of fractures and dissolution features. This 

borehole contained weak ambient upflow 

measured with the HPFM at the time of logging 

(fig. 10). The EMFM could not be used because 

of equipment failure. The BHTV log shows there 

are two sets of fractures: a set of N60E striking 

near-vertical fractures (for example, near 125 ft in 

depth), and shallow dipping (20-40 degrees) 

fractures striking roughly north-south (for 

example, the fractures in the 90-105 ft depth 

interval). HPFM flow log data show inflow at the 

time of logging was associated with shallow 

dipping fractures and/or bedding planes near the 

bottom of casing (90-95 ft), and in the 122-130 ft 

and 165-170 ft intervals. Another inflow zone 

appears to be associated with karst-like features 

on the televiewer log near 205 ft in depth. 

However, the subtraction of inflows method (table 

2) shows that the upper two zones are much more 

permeable than the lower two zones, which 

together account for less than five percent of the

8 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
ground water production from this borehole.

The flow profiles given in figure 10 for 

the two steady flow profiles in the Rochester 

borehole were modeled, and an acceptable fit to 

the profiles and the measured drawdown of 0.48 ft 

was found (fig. 11). The zone flows and 

subtraction of inflow estimates of relative zone T 

based on the flow data in figure 10 are listed in 

table 2. The estimates for the T and H values for 

the seven water-producing zones in the Rochester 

borehole are listed in table 5B. The results 

indicate that the two uppermost zones are much 

more permeable than the two lower zones. There 

is a small head difference driving flow up from 

the. 130 ft zone. The small ambient upflow from 

the 167 and 205-210 ft zones is hardly affected by 

the pumping because that upflow is driven by a 

head difference that is larger than the drawdown 

produced by the pumping. The sum of all of the 

transmissivity values of the seven zones (about 

250 ft2/day) can be used to estimate the 

productivity of a production well screened over 

the open-borehole interval (90-210 ft) at the 

Rochester site.

Austin Site

The Austin borehole is exposed to the 

Spillville Formation under shallow bedrock 

conditions as described in the regional 

hydrogeology section of this report, with a high 

density of interconnected fractures and karstic 

features, and with negligible primary 

permeability. The BHTV log for this borehole 

shows that there is a major karst zone between 85 

and 90 ft. Although this highly permeable zone 

probably originated as dissolution along one or 

more bedding planes, the dissolution has removed 

so much rock in the vicinity of the borehole that 

no definite interpretation can be made from the 

BHTV log. There is downflow from this zone 

into more karst and possible fractures only a few 

feet below this zone (fig. 12). Pumping at 2 gpm 

had hardly any effect at all on the downflow, and 

no measurable difference between water levels 

under ambient and pumping conditions could be 

detected. Thus, flow log analysis was limited to 

the estimation of relative zone transmissivity 

using the subtraction of inflow method (table 3). 

The analysis shows that more than 90 percent of 

the open borehole production is associated with

the large solution opening near 86 ft in depth. 

Winona Site

The suite of logs run in the Winona 

borehole was limited to caliper, natural gamma, 

normal resistivity logs, and the HPFM run under 

ambient conditions only because of the great 

depth to static water level and the large diameter 

of this borehole (fig. 13). The borehole is open to 

a long interval including the Oneota Dolomite, 

Jordan Sandstone, St. Lawrence Formation, 

Franconia Formation, and the Ironton and 

Galesville Sandstones (fig. 2). The BHTV log 

could not be obtained because of the large 

diameter of the open borehole. Weak downflow 

was present in the well. The flow might have 

been present over the whole column, but at the 

time of logging was only large enough to detect 

over the 300 - 440 ft interval.

Measurable inflow is associated with coarse 

elastics in the lower part of the Jordan Sandstone, 

and with the entire thickness of the St. Lawrence 

Formation. There are some intervals of coarse 

clastic rocks in the St. Lawrence Formation, but 

inflow is also probably associated with bedding 

plane openings in fine clastic rocks. The 

maximum downflow in the 350-380 ft interval 

separates the overlying zone of inflow from the 

underlying zone of outflow. Therefore, the 

gamma high at 380 ft may be an aquitard. This 

gamma peak corresponds with a fine clastic zone 

at the base of the St. Lawrence Formation. Most 

of the outflow on the HPFM profile occurs in the 

380-440 ft interval, corresponding to the coarsest 

and most permeable part of the Franconia 

Formation. The downflow indicated by the 

HPFM data has decreased below detectable levels 

at 440 ft in depth, where the gamma log indicates 

a sharp transition to fine elastics.

CONCLUSIONS

Geophysical logs were combined with flow 

profiles obtained using either the electromagnetic 

or heat-pulse flowmeters under ambient and 

pumped conditions (where possible) to identify 

the depth and character of water-producing zones 

in six observation boreholes in southeastern 

Minnesota. Flow logs were analyzed to identify

Conclusions 9
the specific zones contributing inflow or outflow 

to boreholes under ambient hydraulic-head 

conditions. The character of each producing zone 

was determined by comparing water-producing 

intervals with borehole images obtained with the 

televiewer to identify possible fractures, bedding 

planes, and solution openings serving as the 

source of inflow, and by correlating permeable 

coarse clastic intervals in the regional 

stratigraphic column with gamma and electric log 

signatures indicative of such lithology in the log 

composites. Ambient flow log data also indicate 

the presence of regional aquitards because 

ambient flow would not exist in the absence of 

such barriers to vertical flow within the formation 

surrounding the borehole.

At four of the six Minnesota sites, the flow 

log data could be used to generate a qualitative 

permeability profile. This analysis is important, 

because drawdown produced by pumping may be 

of the same order of magnitude as the naturallyoccurring hydraulic-head differences within 

different aquifer zones. If such hydraulic-head 

differences occur, they can strongly bias relative 

permeability estimates based on the percent of 

production from each zone. The subtraction of 

inflow method effectively removes that bias, but 

cannot give a precise, quantitative estimate of 

zone hydraulic head or transmissivity. In two of 

the boreholes (Faribault and Rochester sites), 

reliable flow profiles were obtained under both 

ambient and pumping conditions, and an accurate 

measurement of the difference in open borehole 

water levels between these two conditions could 

be made. For those two sites, the flow profiles 

could be uniquely fit to a steady-flow model. 

Model results indicate that there are seven 

different water-producing zones in the Faribault 

borehole, with transmissivity values ranging from 

about 100 to slightly more than 1000 ft2/day. The 

model also gives hydraulic-head estimates, 

showing there is a maximum head difference of 

about 2.4 ft within the open borehole section. 

Hydraulic head is lowest in the central part of the 

open borehole, and increases both above and 

below that central interval. For the Rochester site, 

the flow model fit to the data indicates four waterproducing zones, with the two upper zones being 

much more permeable than the two lower zones. 

Transmissivity values range from about 10 to 

almost 500 ft /day. Ambient upflow is driven by

a head difference increasing from 0.5 to 2.0 feet 

with depth.

REFERENCES

Gianniny, G.L., Muldoon, M.A., Simo, J.A., and 

Bradbury, K.R., 1996, Correlation of high 

permeability zones with stratigraphic 

features in the Silurian dolomite, Sturgeon 

Bay, Wisconsin: Wisconsin Geological and 

Natural History Survey Open File Report, 

WOFR 1996-7, 102 p. and 1 plate.

Hess, A.E., 1986, Identifying hydraulically

conductive fractures with a slow-velocity 

borehole flowmeter: Canadian Geotechnical 

Journal, v. 23, no. 1, p. 69-78.

Keys, W.S., 1990, Borehole geophysics applied 

Survey Techniques of Water-Resources 

Investigations, book 2, chap. E2, 150 p.

Libra, R.D., and Hallberg, G.R., 1985,

Hydrogeologic observations from multiple 

core holes and piezometers in the Devoniancarbonate aquifers in Floyd and Mitchell 

Counties, Iowa: Iowa Geological Survey 

Open File Report 85-2, p. 1-20.

Miller, R.T., 1984, Anistropy in the Ironton and 

Galesville Sandstones near a thermal-energy 

storage well, St. Paul, Minnesota: Ground 

Water, v. 22, no. 5, p. 532-537.

Miller, R.T., and Delin, G.N., 1993, Field

observations, preliminary model analysis, 

and aquifer thermal efficiency: U.S. 

Geological Survey Professional Paper 1530- 

A, 55 p.

Molz, F.J., and Young, S.C., 1993, Development 

and application of borehole flowmeters for 

environmental assessment: Log Analyst, v. 

34, no. l,p. 13-23.

Molz, F.J., Bowman, G.K., Young, S.C., and 

Waldrop, W.R., 1994, Borehole 

flowmeters field application and data 

analysis: J. Hydrology, v. 163, p. 347-371.

Molz, F.J., Morin, R.H., Hess, A.E., Melville,

J.G., and Guven, Oktay, 1989, The impeller 

meter for measuring aquifer permeability 

variations evaluation and comparison with 

other tests: Water Resources Research, v. 

25, no. 7, p. 1677-1683.

Mossier, J.H., 1998, Bedrock geology, pi. 2 of 

Mossier, J.H., project manager, Geologic

10 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
atlas of Mower County, Minnesota: 

Minnesota Geological Survey County Atlas 

Series C-ll, Part A, scale 1:100,000.

Paillet, F.L., 2000, A field technique for

estimating aquifer parameters using flow 

log data: Ground Water, v. 38, no. 4, p. 510- 

521.

Paillet, F.L., 1998, Flow modeling and

permeability estimation using borehole flow 

logs in heterogeneous fractured formations: 

Water Resources Research, v. 34, no. 5, p. 

997-1010.

Paillet, F.L., and Crowder, R.E., 1996, A

generalized approach for the interpretation 

of geophysical well logs in ground water 

studies Theory and application: Ground 

Water, v. 34, no. 5, p. 883-898.

Paillet, F.L., Crowder, R.E., and Hess, A.E., 1996, 

High-resolution flowmeter logging 

applications with the heat-pulse flowmeter: 

Journal of Environmental and Engineering 

Geophysics, v. 1, no. 1., p. 1-14.

Runkel, A.C., 1996, Geologic investigations 

applicable to groundwater management, 

Rochester Metropolitan area, Minnesota: 

Minnesota Geological Survey Open File 

Report 96-1,27 p.

___1998, Bedrock Geology, Plate 2: Part A of 

Geologic Atlas of Goodhue County: 

Minnesota Geological Survey, scale 

1:100,000.

Setterholm, D.R., Runkel, A.C., Cleland, J.M., 

Tipping, R., Mossier, J.M., Kanivetsky, R., 

and Hobbs, H.C., 1991, Geologic factors 

affecting the sensitivity of the Prairie du 

Chien-Jordan aquifer: Minnesota 

Geological Survey Open File Report 91-5, 

18 p.

Wenck and Associates, Inc., 1997, Phase IIDetailed site investigation report and 

Phase II workplan for the hydrogeologic 

investigation of the proposed Red Wing 

ash disposal facility expansion: 36 p.

References 11
Table 1. Summary of geophysical logs run in southeastern Minnesota.

SITE PROBE LOGS AND COMMENTS

SAVAGE Caliper

Multi-function

Induction

BHTV

EMFM, stationary

EMFM, stationary

EMFM, 10fpm troll up

Multi-function

Borehole diameter

Gamma, Normal R, Fluid T, R

Gamma, Induction R

Borehole wall image

Ambient flow

Inject at 9 gpm

Inject at 9 gpm

Fluid R, T during injection

FARIBAULT Caliper

Multi-function

Induction

BHTV

EMFM, stationary

EMFM, 10fpm troll up

EMFM, stationary

EMFM, 10fpm troll up

Multi-function

EMFM, stationary

EMFM, stationary

EMFM, 10fpm troll up

Borehole diameter

Gamma, Normal R, Fluid T, R

Gamma, Induction R

Borehole wall image

Ambient flow

Ambient flow

Pump at 2 gpm

Pump at 2 gpm

Fluid R, T during pumping

Right after turn-on city well

Hour after turn-on city well

Hour after turn-on city well

PINE ISLAND Caliper 

Multi-function 

Induction 

BHTV

Borehole diameter 

Gamma, Normal R, Fluid T,R 

Gamma, Induction R 

Borehole wall image

ROCHESTER Caliper

Multi-function

Induction

BHTV

HPFM, stationary

HPFM, stationary

Borehole diameter 

Gamma, Normal R, Fluid T,R 

Gamma, Induction R 

Borehole wall image 

Ambient flow 

Pump at 2 gpm

AUSTIN Caliper

Multi-function

Induction

BHTV

HPFM, stationary

HPFM, stationary

EMFM, 10fpm troll up

EMFM, 10fpm troll up

Borehole diameter 

Gamma, Normal R, Fluid T, R 

Gamma, Induction R 

Borehole wall image 

Ambient flow 

Pump at 2 gpm 

Ambient flow 

Pump at 2 gpm

12 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
Table 1. Summary of geophysical logs run in southeastern Minnesota-Continued_______

SITE PROBE LOGS AND COMMENTS

WINONA Caliper Borehole diameter

Multi-function Gamma, Normal R, Fluid T, R

HPFM, stationary Ambient flow

Notes:

BHTV = Borehole televiewer 

EMFM = Electromagnetic flowmeter 

HPFM = Heat-pulse flowmeter 

R = Resistivity in ohm-meters 

T = Temperature, in degrees F

Tables 13
Table 2. Summary of boreholes logged in southeastern Minnesota.

SITE

SAVAGE

FARIBAULT

PINE ISLAND

ROCHESTER

AUSTIN

WINONA3

DATE NOMINAL TOTAL DEPTH DEPTH OPEN 

LOGGED DIAMETER DEPTH CASING WATER FORMATIONS 

(inches) (feet) 1 (feet) 1 LEVEL 

(feet)2

5/5/99 4 680 517 NM4 Franconia

Ironton/Galesville

Eau Claire

5/6/99 4 225 47 14.5 Shakopee

Oneota

5/7/99 4 452 344 14.3 Jordan

5/8/99 6 205 82 16.7 Shakopee

5/9/99 4 110 77 12.4 Spillville

5/10/99 8 600 70 232.0 Jordan

St. Lawrence

Franconia

Ironton/Galesville

Notes:

1. All depths given below reference point at top of casing.

2. Static water level at the start of logging.

3. Open formations include only formation below water level in Winona borehole.

4. NM indicates water level not measured at time of logging.

14 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
Table 3. Summary of relative transmissivity profiles expressed as percent of total borehole 

transmissivity for the four boreholes where paired ambient and pumped or injection flow profiles 

were obtained.

DEPTH INTERVAL ZONE TYPE CONDITION CONDITION DIFFERENCE

(ft) A B (gpm) 

(gpm) (gpm)

Savage site - Observation well #593579

Ambient Injection

582-586 a orb -1.2 -2.8 1.6

605-640 a 1.2 -6.2 7.4

TOTAL 0.0 -9.0 9.0

Faribault site - Observation well #625327

Pumping Ambient

48 b 5.8 5.0 0.8

80 c 1.0 0.9 0.1

115 e 2.0 2.1 -0.1

172 e -4.5 -5.4 0.9

182 e -1.8 0.0 '1.8

208 b -0.5 -2.6 2.1

224 e 0.0 0.0 0.0

TOTAL 2.0 0.0 2.0

Rochester site - Observation well #48561 0

Pumping Ambient

87-92 b 0.55 -0.80 1.35

129-131 bandd 0.85 0.30 0.55

167 b 0.40 0.35 0.05

205-210 e 0.20 0.15 0.05

TOTAL 2.00 0.00 2.00

Austin site - Observation well #613746

Pumping Ambient

82-87 f 4.20 2.35 1.85

92-100 core -2.20 -2.35 0.15

TOTAL 2.00 0.00 2.00

ZONE DEFINITIONS

a Permeable bed without fractures or bedding planes 

b Bedding plane or set of planes with possible minor solution enlargements 

c Bedding plane or set of planes with significant enlargement by solutioning 

d Fracture or set of fractures, possibly enlarged by solutioning 

e Paleokarst horizon characterized by irregular solution openings 

f Cavernous zone possibly developed on bedding planes or paleokarst horizon

PERCENT

18

82

100

40

5

-5

45

-90

105

0

100

68

28

2

2

100

93

7

100

Tables 15
Table 4. Relative transmissivity of water-producing zones in the Faribault borehole expressed as 

percent of total borehole transmissivity computed by the subtraction of inflows method and based 

on trolled electromagnetic flowmeter data in figure 7.

ZONE NO. DEPTH 

(ft)

FLOW1

(gpm)

AMBIENT PUMPED

-

7

-

6

-

5

-

4

-

3

-

2

-

1

-

TOTAL

48

...

80

...

115

...

172

...

182

...

200

...

224

...

...

0.00

....

-5.50

....

-6.60

....

-8.00

....

-3.40

....

-1.10

....

-0.60

....

0.00

 

1.80

....

-4.50

....

-5.80

....

-7.00

....

-2.80

....

-0.50

....

0.00

....

0.00

INFLOW

(gpm)

2 DIFFERENCE PERCENT 

OF 

TOTAL!

AMBIENT PUMPED

....

5.50

 .

1.10

....

1.40

....

-4.60

....

-2.30

....

-0.50

....

-0.60

....

0.00

....

6.30

....

1.30

....

1.20

....

-4.20

....

-2.30

....

-0.50

....

0.00

....

1.80

....

0.80

....

0.20

....

-0.20

....

0.40

....

0.00

....

0.00

....

0.60

....

1.80

44.0

11.0

-11.0

22.0

0.0

0.0

33.0

100.0

NOTES:

1. Positive flow is upflow and negative flow is downflow. 

2. Negative inflow denotes outflow.

16 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
Table 5A. Estimated transmissivity and hydraulic-head values for the seven water-producing 

zones in the Faribault borehole based on flow model matching.

ZONE DEPTH

(ft)

7 48

6 80

5 115

4 172

3 182

2 208

1 224

COMPUTED STATIC WATER LEVEL 

COMPUTED PUMPED WATER LEVEL

DIFFERENCE (DRAWDOWN)

MEASURED DRAWDOWN

Hydraulic

head

(ft)

2.4

2.4

2.4

0.0

0.0

0.8

1.1

1.225ft 

1.107ft

0.118ft

0.12ft

Water level

(ft below TC)

11.2

11.2

11.2

13.6

13.6

12.8

12.5

Transmissivity

(ft2/day)

1023.00

140.00

140.00

837.00

279.00

93.00

837.00

Table 5B. Estimated transmissivity and hydraulic-head values for the seven water-producing 

zones in the Rochester borehole based on flow model matching.________________

ZONE DEPTH Hydraulic Water level Transmissivity

(ft) head (ft below TC) (ft2/day) 

(ft)

4 87-92 0.0 16.4 440.00

3 129-131 0.5 15.9 165.00

2 167 2.0 14.4 28.00

1 205-210 2.0 14.4 11.00

COMPUTED STATIC WATER LEVEL 0.299 ft

COMPUTED PUMPED WATER LEVEL -0.187 ft

DIFFERENCE (DRAWDOWN) 0.486 ft

MEASURED DRAWDOWN 0.48 ft

Tables 17
MINNESOTA

ROCHESTER 

 SITE

Olmsted

Figure 1. Location of the six boreholes in southeastern Minnesota.

18 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
(A)

STRATIGRAPHIC COLUMN

Natural 

Gamma Log 

Increasing 

9 *¥

API Gamma Units

GAMMA LOGS FROM MINNESOTA SITES, 

IN COUNTS PER SECOND

AUSTIN 

0 100 200

LIMESTONE

DOLOSTONE 

SANDY

SANDSTONE 

VERY FINE TO FINE 

FINE TO MEDIUM

MEDIUM TO COARSE 

SHALY 

SILTSTONE

« Vugs (commonly filled with 

coarse calcite)

 Chert

 "« K-bentonite bed (altered 

volcanic ash bed

 Oolites 

a Glauconite 

ft Iron stain

$> Goethite-hematite ore

pti Phosphate pellets

~~ Algal mats

 Algal domes; stromatolites

11 Fossiliferous; fossils (symbols not used 

in limestone and dolostone units)

T T Worm bored

. . Pebbles (gravel in

 unconsohdated units)

 - Flat-pebble conglomerate 

Cross-bedded (festoon) 

Cross-bedded (planar to tangential) 

Ripple, cross-laminations 

Dolomitic 

Calcareous

Contact marks a major erosional surface 

Facies change

Figure 2. Regional stratigraphic column divided into A) upper and B) lower sections, showing the 

gamma logs from the s\x study boreholes for comparison with the typical gamma signatures given 

by Mossier (1998).

Figures 19
(B)

-CONTINUEDSTRATIGRAPHIC COLUMN

GAMMA LOGS FROM MINNESOTA SITES, 

IN COUNTS PER SECOND

ROCHESTER FARIBAULT 

.0 50 100 0" ^ ^- 0 50 100

PINE ISLAND

Oi i i 0 50 100 100

WINONA

0 100 200 i i 100

100

200

-.300

 400

500

 600

200

300

400

200 -

100

200

200

300

400

500

600

SAVAGE

0 100 200

Figure 2. Regional stratigraphic column divided into A) upper and B) lower sections, showing the 

gamma logs from the six study boreholes for comparison with the typical gamma signatures given 

by Mossier (1998)-Continued

20 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
TELEVIEWER 

IMAGE

EXPLANATION

Uniform reflection from inside of steel 

casing

No televiewer data available from the open 

borehole

Uniformly reflective borehole wall without 

fractures or bedding planes

Minor bedding planes intersecting borehole

Major bedding planes possibly enlarged by 

solution opening

r

Minor, possibly permeable fracture cutting 

across bedding planes

\

Major, probably permeable fracture cutting 

across bedding planes

Subhorizontal zone of karst permeability, 

possibly defining a former erosion surface

NESWN

Image azimuth

Figure 3. Explanation of graphical representation of televiewer logs used in figures 4-7 and figures 

9-13.

Figures 21
GAMMA, IN 

COUNTS PER SECOND

SHORT-NORMAL

RESISTIVITY, 

IN OHM-METERS

CALIPER, 

IN INCHES

TELEVIEWER TROLLING FLOW, IN STATIONARY FLOW, IN 

GALLONS PER MINUf E GALLONS PER MINUTE

600 0 -10 -5 -15 -10 -5 0 5

1

INTERPRETATION

Figure 4. Electromagnetic flowmeter profiles obtained under ambient (stationary) and injection 

(stationary and trolling) conditions compared to other geophysical logs for the Savage borehole.

22 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
GAMMA, IN 

COUNTS PER SECOND

0 100 200

220 -

SHORT-NORMAL

RESISTIVITY, 

IN OHM-METERS

CALIPER, 

IN INCHES

1000 2000 0

STATIONARY FLOW, IN 

TELEVIEWER GALLONS PER MINUTE

-10 -5 0

AMBIENT 

FLOW

PUMPED _ 

FLOW

O

INTERPRETATION 

3

Figure 5. Stationary electromagnetic flowmeter data obtained under ambient and pumping 

conditions compared to other geophysical logs for the Faribault borehole.

Figures 23
APPARENT FLOW, IN GALLONS PER MINUTE 

AMBIENT PUMPING

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 

40

TELEVIEWER 

IMAGE

CALIPER, 

IN INCHES

CL

LU

O

INTERPRETATION

fl*

Figure 6. Electromagnetic flowmeter profiles obtained in the Faribault borehole while trolling 

upward at about 10 ft per minute under ambient and steady pumping conditions; the flow scale 

represents the flow through the probe measurement section while trolling and not true borehole 

discharge, and the dashed line represents the response equivalent to no net borehole flow.

24 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
610

FLOW, IN GALLONS PER MINUTE 

AMBIENT PUMPING 

-5 0 -10 -5 0

50

100

Q_ 

LU 

Q

150

200

STATIONARY 

FLOW 

1 DATA

TROLLING

"FLOW

INTERPRETATION

Figure 7. Trolled electromagnetic flowmeter profile interpretation for the Faribault borehole 

calibrated to produce a true borehole discharge scale by shifting the profiles to fit the stationary 

flow data.

Figures 25
FLOW, IN GALLONS PER MINUTE 

AMBIENT PUMPING

-10 -8 -6 -4-202 -10 -8 -6-4-2024

0

50

B 100

Q_ 

LU 

O

150

200

i I i i r i r

-MODEL

FLOW 

-DATA 

INTERPRETATION

Figure 8. Borehole flow model computations fit to trolled electromagnetic flowmeter profiles for the 

Faribault borehole; model parameters are listed in table 4.

26 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
SHORT-NORMAL

GAMMA, IN 

COUNTS PER SECOND

IE

Q_ 

LLJ 

Q

300

320

340

360

380

400

420

0 50 100 (

RESISTIVITY, 

IN OHM-METERS

) 1000 2000 I

i

-->

| .

i

CALIPER, 

IN INCHES TELEVIEV

3 3 6

-

~

-

-

'XX 

\X/'

"xx"

-i^

Mf '

^

- -

Figure 9. Geophysical logs for the Pine Island borehole.

Figures 27
GAMMA, IN 

COUNTS PER SECOND

50 100

SHORT-NORMAL

RESISTIVITY, 

IN OHM-METERS

1000 2000

CALIPER, 

IN INCHES TELEVIEWER

STATIONARY FLOW, IN 

GALLONS PER MINUTE

Figure 10. Stationary heat-pulse flowmeter data obtained under ambient and pumping conditions 

compared to other geophysical logs for the Rochester borehole.

28 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
-1

50

LLJ

Q_ 

LU 

Q

100

150

200

STATIONARY FLOW, IN 

GALLONS PER MINUTE

0 1

PUMPED 

FLOW

Figure 11. Borehole flow model computations fit to the stationary heat-pulse flowmeter data for the 

Rochester site.

Figures 29
GAMMA, IN 

COUNTS PER SECOND

60

70

80

90

100

no

50 100 0

BOTTOM' 

OF CASING

SHORT-NORMAL

RESISTIVITY, 

IN OHM-METERS

250

CALIPER, STATIONARY FLOW, IN 

IN INCHES TELEVIEWER GALLONS PER MINUTE

500

Figure 12. Stationary heat-pulse flowmeter profiles obtained under ambient and pumping 

conditions compared to other geophysical logs for the Austin borehole.

30 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
GAMMA, IN 

COUNTS PER SECOND

SHORT-NORMAL

RESISTIVITY, 

IN OHM-METERS

CALIPER, 

IN INCHES

STATIONARY FLOW, IN 

GALLONS PER MINUTE

0

AMBIENT 

FLOW

X

Figure 13. Stationary heat-pulse flowmeter data obtained under ambient conditions compared to 

other geophysical logs for the Winona borehole.

Figures 31
APPENDIX 1. Faribault flow log interpretation

The theory of flow log interpretation demonstrates that a unique Inversion exists if quasi-steady flow 

profiles can be obtained under two different conditions, and if a measurable difference in the open borehole 

water level is given between the two conditions. If there are N water-producing zones, the data set provides 

the 2N measurements needed to solve for the set of 2N variables (T, transmissivity, and H, hydraulic head) in 

each zone. Such a test was completed at Faribault, where one condition was ambient flow, and the other 

pumping at about 2 gpm. Measured drawdown stabilized within minutes at about 0.1 ft, and there were 

obvious differences in the flow regime between these two conditions. Thus, this set of flow log data 

provides the basis for quantitative analysis of aquifer properties.

A preliminary set of flow data was obtained by making stationary measurements at about ten 

representative depth stations (fig. 5). Complete flow profiles were then obtained under the two different flow 

conditions by trolling up at about 10 ft per minute "against the grain" of the predominantly downward flow. 

The nominal flow scale on these logs does not represent borehole flow. The scale gives the volume flux 

through the measurement throat of the logging tool while the probe is being trolled up the borehole. Thus, 

the "true" flow in the borehole (Q) is related to the measured flow (Qm) by the equation:

Q = AQm -B (1)

where A and B are constants that correct for the "leakage" of water around the probe, and for the trolling 

speed superimposed on the flow distribution.

Even before transforming the data, the flow logs in figure 5 indicate that there are seven different 

water-producing zones, each of which can be related to bedding planes or solution openings given by the 

televiewer log. The Qm data are converted to Q values by comparing the flow logs in figure 5 with a set of 

data obtained with the flowmeter held stationary at a series of points in the borehole (fig. 6). A few 

stationary points (10 points for the ambient flow profile and 15 for the flow profile made while pumping) are 

not sufficient to effectively characterize the complex distribution of flow. But these points do not have the 

effects of trolling added to the measurement. The stationary flow values (Qs) are related to total flow (Q) by 

a multiplication factor:

Q = CQS (2)

In this expression the constant C multiplies the fraction of the flow passing through the measurement throat 

to account for the additional flow bypassing the throat in the annulus around the probe. A value for C can be 

obtained by making measurements in the bottom of casing during pumping where the total borehole flow is 

known to be close to 2.0 gpm. The value of C is defined by measuring flow under the pump within the 

casing with the probe stationary. In this example, the scatter of about 0.3 gpm is greater than the typical 0.1 

gpm scatter because the flexible disk used to restrict flow in the annulus around the probe measurement 

section was removed at the beginning of logging. But even under the best of conditions, the "leakage" of 

flow around the probe introduces measurement error significantly greater than the nominal accuracy derived 

from flow column experiments.

When the stationary data points are converted to total borehole flow, these points do not effectively 

define the flow distribution. There are just not enough of these points to define the "true" flow profile in a 

situation where there are seven different inflow and outflow zones. The errors in estimating inflow or 

outflow at each zone account for the large negative values in the right-hand column for the Faribault 

borehole in table 2B. But the values of the constants A and B in equation (1) can be adjusted until the 

stationary flow points "pin down" the flow distributions. This is done in figure 6. In this way, the detailed 

flow distribution given by the trolled logs in figure 1 can be effectively calibrated. The resultant estimates of 

inflow and outflow at each of the seven zones (table 3) are derived from both stationary and trolled 

measurements, combining the vertical resolution of the trolled data with the flow measurement accuracy of

32 Hydrogeologic Characterization of Six Sites in Southeastern Minnesota
the stationary data.

A rough estimate of the relative transmissivity of each of the seven zones can be made by using the 

flow profiles in figure 6 to estimate the amount of water entering the borehole under the two flow conditions. 

In this analysis, negative inflow represents outflow. The amount of water entering under any condition 

depends on the product of the zone transmissivity and the difference between zone hydraulic head and open 

borehole water level. The open-borehole water level adjusts itself to approach the water level in the most 

permeable zone, so that the hydraulic gradient driving flow from that zone into the borehole is generally less 

than the gradient driving flow into or out of other zones. However, if the inflows under two different 

conditions are subtracted, the hydraulic head dependence factors out, and the differences are proportional to 

zone T. Doing this for the seven zones in figure 6, we get the results listed on the right hand side of table 3.

One test of consistency is that the total inflow under ambient conditions vanishes, and the total inflow 

under pumped conditions is 1.8 gpm (within measurement error of the known 2.0 gpm pumping rate where 

the magnitude of the measurement error of about ±0.30 gpm is estimated from the scatter in the flow log data 

between inflow zones). The data are inconsistent, in that the difference for zone 5 is negative, which is 

hydraulically impossible. We interpret this result as simply an artifact of the measurement error. The 

subtraction of two quantities which are determined from the differences of other quantities acts to amplify 

measurement error. Thus, the analysis suggests that zones 1,4, and 7 are an order of magnitude more 

permeable than the other zones. The percentages for the other four zones are effectively too small to 

quantify.

A more quantitative approach is to use a hydraulic model to predict the flow for the ambient and 

pumped conditions. With seven zones, this is a formidable problem. The idea is to find the one set of T and 

H values for the seven zones which gives the measured flow profiles at the measured drawdown. One has to 

guess 14 different parameters by trial and error to obtain the fit. This was accomplished by first ignoring all 

but the three main zones. When an approximate fit was obtained, the other four zones were added. A 

reasonable fit results with the parameters listed in table 4 and all flows predicted by the model fall within the 

±0.30 gpm measurement error. Note that the fit requires matching both flow profiles and the measured 0.1 ft 

drawdown, as indicated in table 4. These results indicate that the upper three water-producing zones are part 

of a single large-scale aquifer compartment. Drawdown is communicated to the aquifer via the 170-190 ft 

zone. Hydraulic-head gradients drive flow downward into that zone from above, and upward into that zone 

from below.

Appendix 33