United States

Environmental Proection

Agency

Application of the

Electromagnetic

Borehole Flowmeter

Office of Research and

Development

Washington, DC 20460

EPA/600/R-98/058

August 1998
EPA/600/R-98/058

August 1998

Application of the

Electromagnetic

Borehole Flowmeter

by

Steven C. Young, Hank E. Julian, and Hubert S. Pearson

Tennessee Valley Authority

Engineering Laboratory

Norris, TN 37828

and

Fred J. Molz and Gerald K. Boman

Auburn University

Auburn, AL 36849

Interagency Agreement

DW64934812

Project Officer

Steven D. Acree

Subsurface Protection and Remediation Division

National Risk Management Research Laboratory

Ada, OK 74820

National Risk Management Research Laboratory

Office of Research and Development

U.S. Environmental Protection Agency

Cincinnati, OH 45268
ii

The U.S. Environmental Protection Agency, through its Office of Research and Development, partially funded and collaborated

in the research described here under Interagency Agreement DW64934812 to the Tennessee Valley Authority. It has been subjected

to the Agency’s peer and administrative review and has been approved for publication as an EPA document. Mention of trade names

or commercial products does not constitute endorsement or recommendation for use.

All research projects funded by the U.S. Environmental Protection Agency that make conclusions or recommendations based on

environmentally related measurements are required to participate in the Agency Quality Assurance Program. This project was

conducted under an approved Quality Assurance Project Plan and the procedures therein specified were used. Information on the

plan and documentation of the quality assurance activities and results are available from the Principal Investigator.

Notice
iii

Foreword

The U.S. Environmental Protection Agency is charged by Congress with protecting the Nation’s land, air, and water resources.

Under a mandate of national environmental laws, the Agency strives to formulate and implement actions leading to a compatible

balance between human activities and the ability of natural systems to support and nurture life. To meet these mandates, EPA’s

research program is providing data and technical support for solving environmental problems today and building a science knowledge

base necessary to manage our ecological resources wisely, understand how pollutants affect our health, and prevent or reduce

environmental risks in the future.

The National Risk Management Research Laboratory is the Agency’s center for investigation of technological and management

approaches for reducing risks from threats to human health and the environment. The focus of the Laboratory’s research program is

on methods for the prevention and control of pollution to air, land, water, and subsurface resources; protection of water quality in

public water systems; remediation of contaminated sites and ground water; and prevention and control of indoor air pollution. The

goal of this research effort is to catalyze development and implementation of innovative, cost-effective environmental technologies;

develop scientific and engineering information needed by EPA to support regulatory and policy decisions; and provide technical

support and information transfer to ensure effective implementation of environmental regulations and strategies.

This report presents a discussion of the applications of vertical-component borehole flowmeters to site characterization with an

emphasis on the design and use of a sensitive electromagnetic flowmeter partially developed under this project. The methodologies

discussed in this document provide cost-effective means for obtaining detailed definitions of hydrogeologic controls on groundwater flow and contaminant transport. Such information is often essential for evaluation of contaminant fate in the environment and

design of effective monitoring and remediation systems. It is published and made available by EPA’s Office of Research and

Development to assist the user community.

Clinton W. Hall, Director

Subsurface Protection and Remediation Division

National Risk Management Research Laboratory
iv

Abstract

A prerequisite for useful monitoring, modeling, and remedial design strategies is knowledge of the network of hydraulically

active fractures in bedrock aquifers and three-dimensional hydraulic conductivity fields in granular aquifers. Due to a relative lack

of practicable characterization technologies, many ground-water remediation strategies have been designed based on very little, if

any, detailed information regarding fracture or hydraulic conductivity distribution. As a result, the underestimation of aquifer

heterogeneity may contribute to inadequate conceptual models of contaminant transport/fate and inadequate design/performance of

many remediation systems.

Borehole flowmeters are effective tools for measuring vertical variations in the flow field of an aquifer. Although borehole

flowmeters have been used in the petroleum industry for decades, they are not common in ground-water studies due, in part, to the

lack of suitable meters. A vertical component electromagnetic (EM) borehole flowmeter with the versatility and sensitivity required

for application at most sites has been developed by the Tennessee Valley Authority (TVA). The prototype TVA EM flowmeters have

outer diameters of less than 5.25 cm, and inner diameters of either 2.54 cm or 1.27 cm. The detection limits for the 1.27-cm and 2.54-

cm flowmeters are near 0.005 L/min and 0.03 L/min, respectively. In addition to a low detection limit, attractive features of the

prototype and commercial versions of this EM flowmeter include a wide measurement range, durable construction, no moving parts,

and a design that facilitates use with packer assemblies.

This report describes the operation and application of the TVA prototype EM borehole flowmeters, including theory, design,

calibration, basic field applications, data analysis, and potential effects of various well construction and development procedures on

data. The majority of these results are also applicable to the commercial version of this meter and other vertical component borehole

flowmeters, including heat pulse and impeller tools. Several case studies illustrating specific uses of these tools are also discussed.
v

Contents

Section Page

Notice ........................................................................................................................................................................................... ii

Foreword .....................................................................................................................................................................................iii

Abstract ....................................................................................................................................................................................... iv

List of Figures ............................................................................................................................................................................ vii

List of Tables ............................................................................................................................................................................... ix

I. Theory and Application of the Electromagnetic Borehole Flowmeter ........................................................................................ 1

I-1. Overview ............................................................................................................................................................................ 1

I-2. Principles of Operation ....................................................................................................................................................... 2

I-3. Collection of Flowmeter Logs ............................................................................................................................................ 2

I-4. Analysis of Flowmeter Logs .............................................................................................................................................. 2

a. Flow Distribution Logs .............................................................................................................................................. 2

b. Hydraulic Conductivity Logs in Granular Aquifers ................................................................................................... 6

c. Data Analysis.............................................................................................................................................................. 7

I-5. Conclusions ........................................................................................................................................................................ 8

II. Electromagnetic Borehole Flowmeter System ............................................................................................................................. 9

II-1. Design and Construction .................................................................................................................................................... 9

II-2. Laboratory Calibration ..................................................................................................................................................... 10

III. Hydrogeologic Characterization Test Design ............................................................................................................................. 13

III-1. Overview .......................................................................................................................................................................... 13

III-2. Measurement Interval Selection ....................................................................................................................................... 13

III-3. Flowmeter Measurements ................................................................................................................................................ 13

III-4. Pumping Rate and Drawdown Measurements ................................................................................................................. 14

III-5. Selection of Pumps ........................................................................................................................................................... 14

III-6. Packer Selection ............................................................................................................................................................... 14

III-7. Method of Inflation .......................................................................................................................................................... 15

III-8. Issues Regarding Flowmeter Measurements in the Field ................................................................................................. 15

a. Well or Borehole Storage ......................................................................................................................................... 15

b. Selection of Pumping Rate ....................................................................................................................................... 15

c. Background Electromagnetic Currents .................................................................................................................... 16

d. Reproducibility of Flowmeter Data .......................................................................................................................... 16

III-9. Flowmeter Investigations in Consolidated Materials ....................................................................................................... 16

a. Introduction .............................................................................................................................................................. 16

b. Fractured Rock Applications .................................................................................................................................... 17

c. Conclusions .............................................................................................................................................................. 18

IV. Well Construction and Development ......................................................................................................................................... 19

IV-1. Background ...................................................................................................................................................................... 19

a. In-Situ Hydraulic Conductivity Estimates Using Wells ........................................................................................... 19

b. Formation Damages and Skin Effects ...................................................................................................................... 19

IV-2. Well Design ...................................................................................................................................................................... 19

IV-3. Well Installation Methods................................................................................................................................................. 20

a. Overview .................................................................................................................................................................. 20

b. Drilling Techniques and Hydraulic Conductivity Estimates .................................................................................... 20
vi

Contents

(continued)

Section Page

IV-4. Well Development Methods .......................................................................................................................................... 21

a. Overview ................................................................................................................................................................. 21

b. Development Methods and Hydraulic Conductivity Estimates .............................................................................. 21

V. Field Studies of Well Construction and Development at Columbus, Mississippi ...................................................................... 23

V-1. Description of Test Site.................................................................................................................................................. 23

a. Site Location ............................................................................................................................................................ 23

b. Aquifer Characteristics ............................................................................................................................................ 23

c. Previous Pumping Tests .......................................................................................................................................... 23

d. Monitoring Well Installation ................................................................................................................................... 24

V-2. Test Descriptions ........................................................................................................................................................... 25

V-3. Test Analyses and Results .............................................................................................................................................. 26

a. Ambient Flow Distributions .................................................................................................................................... 26

b. Induced Flow Distributions ..................................................................................................................................... 28

c. Specific Capacity Values ......................................................................................................................................... 28

d. Transmissivity Values .............................................................................................................................................. 28

V-4. Summary ........................................................................................................................................................................ 31

VI. Field Studies of Well Construction and Development at Mobile, Alabama............................................................................... 33

VI-1. Description of Test Site.................................................................................................................................................. 33

a. Site Location ............................................................................................................................................................ 33

b. Aquifer Characteristics ............................................................................................................................................ 33

c. Well Installation ....................................................................................................................................................... 33

VI-2. Test Description ............................................................................................................................................................. 34

VI-3. Test Results .................................................................................................................................................................... 35

a. Shallow Well A ........................................................................................................................................................ 35

b. Shallow Well B ........................................................................................................................................................ 36

c. Deep Well C ............................................................................................................................................................ 38

VI-4. Summary and Discussion .............................................................................................................................................. 40

VII. Case Studies ............................................................................................................................................................................... 43

VII-1. Field Applications .......................................................................................................................................................... 43

VII-2. Columbus AFB, Mississippi .......................................................................................................................................... 43

VII-3. Oak Ridge National Laboratory, Tennessee .................................................................................................................. 45

VII-4. The Oklahoma Refining Company Superfund Site, Oklahoma .................................................................................... 46

VII-5. Gilson Road Superfund Site, New Hampshire .............................................................................................................. 46

VII-6. Mirror Lake, New Hampshire........................................................................................................................................ 46

VII-7. Logan Martin Dam, Alabama ........................................................................................................................................ 48

VII-8. Cape Cod, Massachusetts .............................................................................................................................................. 50

VII-9. Summary ........................................................................................................................................................................ 51

VIII. References ............................................................................................................................................................................... 53

APPENDIX A. Field Data Sheets for Borehole Flowmeter Tests .................................................................................................... 57

APPENDIX B. Equipment Checklist ............................................................................................................................................... 59
vii

Figures

Number Page

I-1 Schematic diagram of the TVA electromagnetic borehole flowmeter .................................................................................. 3

I-2 Apparatus and geometry associated with a borehole flowmeter test .................................................................................... 3

I-3 Graphical illustration of the hypothetical case presented in Table I-1 .................................................................................. 4

I-4 Assumed layered geometry within which flowmeter data are collected and analyzed......................................................... 5

II-1 Mechanical packer (a) assembled on probe and (b) in schematic view ................................................................................ 9

II-2 Inflatable packer assembled on probe ................................................................................................................................. 10

II-3 Conceptual system for flowmeter calibration ..................................................................................................................... 10

II-4 Calibration data for the 1.27-cm ID flowmeter in 5.1-cm PVC pipe.................................................................................. 11

II-5 Frictional losses associated with the 1.27-cm and 2.54-cm ID flowmeters ........................................................................ 12

III-1 Acoustic-televiewer, caliper, single-point resistance, and flowmeter logs for borehole

DH-14 in northeastern Illinois (Paillet and Keys, 1984; Molz et al., 1990) ....................................................................... 17

V-1 Ox bow meander at the Columbus AFB site drawn from a 1956 aerial photograph .......................................................... 23

V-2 Well network at the 1-Ha test site ....................................................................................................................................... 24

V-3 Design of wells used to evaluate the effect of well development on flowmeter tests ........................................................ 25

V-4 Ambient flow profiles after successive well development ................................................................................................. 27

V-5 Induced flow profiles after successive well development................................................................................................... 29

V-6 Effect of well development on the drawdown values for pumping tests at the 38-39-40 well cluster ............................... 30

V-7 Comparison of specific capacities at different wells........................................................................................................... 31

V-8 Calculated transmissivities using early time data ............................................................................................................... 32

VI-1 Vertical cross-sectional illustration of the subsurface hydrologic system at the Mobile site.............................................. 33

VI-2 Schematic diagram providing the details of the shallow and deep wells constructed at the Mobile site.

Well casing and well screen are the same dimension and schedule. The only difference is the depth

dimensions of the casing and screen ................................................................................................................................... 34

VI-3 (Well A) (a) Ambient flow as measured by the EM flowmeter and (b) net flow (total flow -

ambient flow). Data were obtained after the 2nd and 3rd developments........................................................................... 36

VI-4 (Well A) Differential net flow obtained (a) after 2nd development, (b) after 2nd

development and an overnight waiting period, and (c) after 3rd development .................................................................. 37
viii

Figures

 (continued)

Number Page

VI-5 (Well B) (a) Ambient flow as measured by the EM flowmeter and (b) net flow (total flow - ambient flow).

Data sets were obtained prior to development and after 1st, 2nd, and 3rd developments .................................................. 38

VI-6 (Well B) Differential net flow obtained (a) prior to development, (b) after 1st development, (c) after 2nd

development, and (d) after 3rd development ...................................................................................................................... 39

VI-7 (Well B) Ambient flow after the first development and repeated after an overnight period............................................... 40

VI-8 (Well C) (a) Ambient flow as measured by the EM flowmeter and (b) net flow (total flow -

ambient flow). Data were obtained prior to development and after 1st, 2nd, and

3rd developments for the ambient flow and after 1st, 2nd, and 3rd developments for net flow ........................................ 40

VI-9 (Well C) Differential net flow obtained (a) after 1st development, (b) after 1st development and overnight

waiting period, (c) after 2nd development, and (d) after 3rd development ........................................................................ 41

VII-1 Vertical profile of hydraulic conductivity values along the longitudinal axis of the MADE tracer plume ........................ 44

VII-2 Depth-averaged hydraulic conductivity values for the lowermost 2 m (left) and the uppermost 2 m (right)

of the unconfined aquifer below the 1-Ha test site at Columbus AFB ............................................................................... 44

VII-3 (a) Ambient flow distribution in a well and (b) the flow distribution caused by constant-rate pumping ........................... 45

VII-4 Ambient and induced flow distributions for wells NE-2, SBB-36, and IBB-4 at the ORC Superfund Site ....................... 47

VII-5 Ambient and induced flow distributions for wells I, J, and K at the Gilson Road site ....................................................... 47

VII-6 Ambient and induced flow distributions for wells FSE-06, FSE-09, and FSE-10 at Mirror Lake,

New Hampshire................................................................................................................................................................... 49

VII-7 Substantial ambient flow moving from one stratum to another as detected by an impeller flowmeter. The

flow is moving under a dam, the base of which is at an elevation of about 140 m AMSL. Flowmeter

data were used to help select a geologic model for explaining the large amount of leakage of water low

in dissolved oxygen that was observed below the dam ..................................................................................................... .50
ix

Tables

Number Page

I-1 Hypothetical data and data analysis related to the application of a borehole flowmeter. ..................................................... 6

I-2 Results of the analysis of data from a borehole flowmeter test to estimate hydraulic conductivity distributions ................ 8

II-1 Sample calibration factors (liter/min/volt) from a linear regression of discharge versus voltage for

electromagnetic flowmeter data .......................................................................................................................................... 12

III-1 Generalized borehole flowmeter field test procedures........................................................................................................ 13

III-2 Problems that produce errors in EM flowmeter measurements .......................................................................................... 14

V-1 Testing sequence ................................................................................................................................................................. 26

V-2 Early-time CJSL transmissivity values ............................................................................................................................... 32

VI-1 Pump-induced flow and ambient flow tests performed on wells A, B, and C .................................................................... 35

VII-1 Characterization objectives for borehole flowmeter studies ............................................................................................... 43

VII-2 Summary statistics of hydraulic conductivity data obtained using a borehole flowmeter method

and a permeameter analysis method (Hess et al. (1992)).................................................................................................... 51
x
1

Chapter 1

Theory and Application of the

Electromagnetic Borehole Flowmeter

I-1 Overview

The underestimation of aquifer heterogeneity has significantly

contributed to the inefficient design and, consequently,

inadequate performance of many types of remediation systems

(Mercer et al., 1990; Haley et al., 1991). This is especially

true of pump-and-treat remediation systems. In many cases,

interpretation of hydraulic properties is limited by field

measurement capability. Characterization of a hydrogeologic

system requires an effective method for measuring vertical

variations in hydraulic properties. At least three research

teams (Boggs et al., 1989; Rehfeldt et al., 1989b; Molz et al.,

1989, 1990) have evaluated alternative methods for measuring

the vertical variation of hydraulic conductivity (K). These

methods included: small-scale tracer tests, multilevel slug

tests, laboratory permeameter tests, empirical equations based

on grain-size distributions, and borehole flowmeter tests.

These comparisons indicated that the borehole flowmeter test

is one of the most promising methods for measuring the

spatial variability of the hydraulic conductivity fields.

Various types of flowmeters based on impeller, thermal-pulse,

tracer-release or electromagnetic technologies have been

devised for measuring flow distribution along a borehole or

well screen. Impeller meters (also known as spinners) have

been used for several decades in the petroleum industry, and

such instruments suitable for some ground-water applications

are now available. A meter of this type was applied in the

field by Hufschmied (1983), Molz et al. (1990), and others.

Most impeller meters cannot operate at the lower flow ranges

often required for ground-water applications. Based on the

need to measure low flow velocities, the United States

Geological Survey (USGS) developed a thermal-pulse

flowmeter (Hess, 1982, 1986; Morin et al., 1988a; Paillet et

al., 1987). Such tools are quite sensitive to low flow

velocities. Electromagnetic flowmeters can also operate

within a relatively large range of flow rates suitable for most

ground-water investigations. Although this document focuses

on the design and application of the electromagnetic

flowmeter developed under this project for the measurement

of the vertical component of flow within a well, the data

collection and methods of analysis apply to other types of

vertical component flowmeters.

A sensitive, vertical-component borehole flowmeter enables

one to accomplish two basic tasks:

1. It allows one to measure the natural (ambient)

vertical flow that exists in many wells; and

2. If the well is pumped at a steady rate, it enables one

to determine the flow distribution that is entering the

well from the surrounding medium.

Ambient flow distributions provide information on the

direction of the vertical component of the hydraulic gradient,

and on the location of hydraulically active fractures in the case

of a fractured formation. If certain conditions are met, flow

distributions during pumping provide information on the

relative differences in the permeability of selected aquifer

zones or additional information on fracture hydraulic

characteristics.

Flowmeter measurements depend on factors such as skin

effects due to well construction and development and ambient

hydrologic conditions. Such factors may be variable within a

well and some may change with time. Also, it cannot be

overemphasized that a borehole flowmeter should be viewed

only as another tool available to ground-water hydrologists.

As expected, the best hydrogeologic characterizations are

achieved when this tool is used in combination with other

methods (e.g., geophysical measurements and traditional

aquifer tests). Application of several technologies that are

suitable for characterization of various aspects of site

hydrology on different scales are necessary for definition of

hydrogeologic controls on ground-water flow.

A sensitive borehole flowmeter, such as tools based on

thermal-pulse technology or the electromagnetic system

discussed in this report, is most applicable for characterization

objectives that require few assumptions regarding aquifer

properties or other complex variables. These tools are directly

applicable for such objectives as identifying transmissive

intervals in wells, evaluation of the effects and state of well

development, and identification of natural flow patterns within

conventional monitoring wells. Information regarding zones

where ground water enters and, in the case of ambient flow,

exits a well is often essential for detailed evaluation of

ground-water monitoring efforts. Studies (e.g., Church and

Granato, 1996; Collar and Mock, 1997; Martin-Hayden and

Robbins, 1997) have demonstrated the potential effects of the

mixing of waters with different chemistries within a

conventional monitoring well on contaminant transport

evaluations. Borehole flowmeters provide direct information

concerning the mix of water that enters a well under either

ambient or pumping conditions. In fractured rock settings,

where water may enter the well from only a few discrete

intervals, the flowmeter allows identification of those

intervals. Such intervals may then be individually targeted for
2

characterization of water chemistry. Direction of natural flow

within a well under ambient conditions is a direct means of

assessing vertical components of the hydraulic gradient at the

time of the study. This information is useful in conceptualization of the hydrologic setting in various parts of a site.

Such direct uses of these tools are readily apparent and not

discussed in detail in this report.

These tools may also provide data used in the estimation of

detailed profiles of the differences in hydraulic conductivity of

granular aquifer materials. However, many simplifying

assumptions are required in such analyses increasing

uncertainty in the results as is true for more traditional aquifer

tests. This indirect use of data obtained using these tools is

not readily apparent and is discussed in detail in this

document. As with any site characterization tool, study

objectives and site conditions must be critically evaluated

during test selection and design. Results obtained from

borehole flowmeter studies, such as investigations described

in this document, should be viewed as only one piece of

information used in the overall characterization of site

conditions.

I-2 Principles of Operation

An electromagnetic (EM) prototype flowmeter (Figure I-1)

was developed at the Tennessee Valley Authority (TVA)

Engineering Laboratory in Norris, Tennessee. It consists of an

electromagnet and two electrodes that are cast in a durable

epoxy. The epoxy is molded in a cylindrical shape to

minimize turbulence associated with channeling water past the

electrodes and electromagnet. Having no moving parts, the

flowmeter operates according to Faraday's Law of Induction,

which states that the voltage induced across a conductor

moving at right angles through a magnetic field is directly

proportional to the translational velocity of the conductor.

Flowing water is the conductor, the electromagnet generates a

magnetic field, and the electrodes are used to measure the

induced voltage. Electronics connected to the electrodes

transmit a voltage that is directly proportional to the velocity

of the water.

I-3 Collection of Flowmeter Logs

The concept of borehole flowmeter measurements using the

simplest test design is illustrated in Figure I-2. A flowmeter

log is recorded before pumping to measure any ambient flow

in the well. This step is very important, particularly in the

case of highly sensitive flowmeters and low permeability

formations, where the ambient flow may be a significant

fraction of the flow induced by pumping. Following the

ambient test, a pump is placed in the well and operated at a

constant flow rate, QP. After a steady flow field toward the

well is obtained, the flowmeter is positioned near the bottom

of the well and a measurement of discharge rate is obtained.

The meter is then raised a distance ∆z and another reading is

taken. As illustrated in Figure I-2, the result is a series of

measurements of cumulative vertical discharge, Q, within the

well screen as a function of vertical position, z. Just above the

top of the screen the meter reading should be equal to QP, the

steady pumping rate that is measured independently at the

surface. This procedure may be repeated several times to

ascertain that the readings are stable and flow to the well has

reached a steady-state condition. EM flowmeters are capable

of measuring upward or downward flow. Therefore, if the

selected pumping rate, QP, causes excessive drawdown or

there are concerns associated with disposal of contaminated

ground water, one can employ an injection procedure as an

alternative.

I-4 Analysis of Flowmeter Logs

a. Flow Distribution Logs

The basic data obtained in the field (Table I-1) are:

• Column (a) - the elevations where readings are

taken,

• Column (b) - the ambient flow log, and

• Column (d) - the total flow log, which is measured

flow under pumping conditions.

The following data are then calculated:

• Column (c) - differential ambient flow,

• Column (e) - the net flow log, and

• Column (f) - the differential net flow.

The data in Table I-1 are shown graphically in Figure I-3. The

aquifer base is located at z = 0, and the water table or upper

confining layer is located at z = 20 m.

Measurements and calculations are made based on the

assumed layered geometry illustrated in Figure I-4. Flow to

the well is assumed to be horizontal. The basic flow logs,

Columns (b) and (d) represent upward (positive) or downward

(negative) vertical flow within the well itself; while the

differential flow logs represent horizontal flow in the assumed

layers to the well (positive) or from the well (negative). The

sign convention introduced herein is not universal. However,

the same sign convention should be followed for any

particular application.

For the example of Table I-1 and Figure I-3, the ambient flow

is upward. The differential ambient flow log, obtained by

taking differences between adjacent values of ambient flow in

the well, indicates that water enters the well at varying rates

from the bottom half of the aquifer and exits the well at

varying rates in the top half of the aquifer.

At this stage in the data analysis, a distinction must be made.

The drawdown that is measured while recording the total flow

log is due only to pumping. However, the measured flow log

is due to a superposition of the ambient flow and the pumping

flow. Therefore, to be consistent one must subtract the

ambient flow log from the total flow log to obtain the net flow

log, which is that portion of the total flow due to the measured

drawdown. If this subtraction is not made, the results could be

ambiguous.
3

Figure I-1. Schematic diagram of the TVA electromagnetic borehole flowmeter.

Figure I-2. Apparatus and geometry associated with a borehole flowmeter test.

QP

To Flowmeter Logger (Q)

Pump

Casing

Borehole

Flowmeter

Screen

or

Borehole

Flow (Q)

Data

(Discharge from Pump)

Elevation (z)

Amplifier

Electromagnet

Electrodes

Iron Core

Magnet

Wire

Plastic

Tube

Top View

Section AA

A A B B

E

B

( = x )

EpoxyEpoxy

E V

Metal

Core

Magnet

Wire

Magnetic Field

Induced EM Field

Velocity of Fluid

Side View

Section BB

E

V

B

E V B
4

Figure I-3. Graphical illustration of the hypothetical case presented in Table I-1.

0 0.2 0.4 0.6 0.8 1

8

4

0

20

16

12

Ambient Flow - Column (b) Data

Flow (L/min)

Elevation (m)

-0.4 -0.2 0 0.2 0.4

Flow (L/min)

Differential Ambient Flow - Column (c) Data

01234 6

84

0

20

16

12

Column (d) Data

 Flow (L/min)

Elevation (m)

Flow (L/min)

Differential Net Flow - Column (f) Data

Total Flow

Ambient Flow

5

01234 6

8

4

0

20

16

12

Net Flow - Column (e) Data

Flow (L/min)

Elevation (m)

5 0 0.2 0.4 0.6 0.8 1.2

8

4

0

20

16

12

1
5

Figure I-4. Assumed layered geometry within which flowmeter data are collected and analyzed.

n

n-1n-2n-3

i+1

i

3210

ScreenSegment

Q(zi+1)

Q(zi)

∆Qi = Q(zi+1) - Q(zi)

z = zi

z = zi+1

z

Well

. . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . .
6

Table I-1. Hypothetical Data and Data Analysis Related to the Application of a Borehole Flowmeter

Elevation Ambient Flow ∆ Ambient Flow Total Flow Net Flow ∆Net Flow

(m) (L/min) (L/min) (L/min) (L/min) (L/min)

(a) (b) (c) (d) (e) (f)

20 0.0 -.07 6.0 6.0 0.87

18 0.07 -0.10 5.2 5.13 0.70

16 0.17 -0.16 4.6 4.43 1.16

14 0.33 -0.37 3.6 3.27 1.27

12 0.70 -0.05 2.7 2.00 0.25

10 0.75 +0.15 2.5 1.75 0.55

8 0.60 +0.21 1.8 1.20 0.19

6 0.39 +0.21 1.4 1.01 0.19

4 0.18 +0.13 1.0 0.82 0.57

2 0.05 +0.05 0.3 0.25 0.25

0 0.00 -- 0.0 0.00 --

The final column in Table I-1, the differential net flow, is

obtained by calculating the difference between adjacent values

in the net flow log. This yields the horizontal flow that is

entering the well from each interval due to pumping. Under

conditions of steady, horizontal flow into the well, this flow is

proportional to the vertical distribution of horizontal hydraulic

conductivity in the vicinity of the test well (Molz et al., 1988;

1989).

b. Hydraulic Conductivity Logs in Granular

Aquifers

For purposes of these analyses, the aquifer is assumed to be

composed of a series of n horizontal layers (Figure I-4). In

practice, hydrogeologic information, such as data available

from cores and geophysical logs, may be used to

conceptualize potential geologic layers and choose appropriate

intervals for measurements during the flowmeter study. The

difference between two successive flowmeter readings

obtained under pumping conditions yields the flow, ∆Qi,

entering a well screen between the elevations where the

readings are taken, which are assumed to bound layer i (i =

1,2,...,n). The ∆qi from the ambient flow log are computed in

an identical manner. Most, aquifers are not composed of

horizontal, homogeneous layers. However, the n-layer case at

this scale is more realistic than the single-layer case of

classical pumping test analyses.

To calculate a hydraulic conductivity profile, three methods

have been detailed in the literature. The first is based on the

Cooper-Jacob equation relating drawdown to a constant

pumping rate in a fully penetrating well (Cooper and Jacob,

1946). The second is based on the numerical results by

Javandel and Witherspoon (1969). Molz and Young (1993)

provided an overview of these methods. A third method is the

two-step procedure described by Kabala (1994), which yields

an Si

 as well as a K distribution. Drawdown data collected at

different times and flowmeter data are used to estimate the

vertical distribution of hydraulic parameters. Such a

procedure does not require knowledge or estimation of

specific storage (Ss) and may have advantages in certain

situations where Ss is expected to vary greatly. Only the first

two methods are discussed herein. Xiang (1995), Hanson and

Nishikawa (1996), and Ruud and Kabala (1996) provide

additional discussion on numerical evaluation of flowmeter

tests.

In the Cooper-Jacob method, the assumed horizontal flow in

each layer is treated as if it was from an aquifer of infinite

horizontal extent and thickness, ∆zi

. Then for each layer, i,

one can write

 ∆ H i ( r 

w , t ) = á ∆ Q i − ∆ q i é 

2 π K i ∆ z i 

 ln 1 . 5 

r 

w 

 K i ∆ z i t 

S i 

(I-1)

where:

∆Hi = drawdown in ith layer

∆Qi = induced flow from ith layer

∆qi = ambient flow from ith layer

Ki = horizontal hydraulic conductivity of the ith

layer

∆zi = ith layer thickness

rw = effective well radius

t = time since pumping started

Si = storage coefficient for the ith layer.

If one assumes that head losses associated with flow within

the well are negligible, then all the ∆Hi are equal to ∆H, the

measured drawdown in the test well. If such an assumption

cannot be made, then one must measure the head loss opposite

each layer associated with pumping the test well. Rehfeldt et

al. (1989b) provide further discussion of various possible head

losses.
7

Often, a value for the storativity of the aquifer being studied

will be estimated, and the question becomes how to use this

information to obtain Si

 for each layer. In previous studies,

two assumptions have been made. The most basic assumption

is to assume that Ss

, the specific storage, is constant, in which

case Si = Ss∆zi (Morin et al., 1988a; Molz et al., 1989). An

alternate assumption used by Rehfeldt et al. (1989b) is that Ss

varies in such a way that the hydraulic diffusivity of each

layer, Ki∆zi/Si, remains constant and equal to the hydraulic

diffusivity (T/S) for the aquifer, where T is transmissivity and

S is the storage coefficient. If the latter assumption is made,

Equation (I-1) may be solved for Ki

 yielding

K i = á ∆ Q i − ∆ q i é 

2 π ∆ H i ∆ z i 

 ln 1 . 5 

r w 

 T t 

S . (I-2)

If the constant Ss assumption is made, one can solve Equation

(I-1) for Ki outside the logarithmic term to yield

K i = á ∆ Q i − ∆ q i é 

2 π ∆ H i ∆ z i 

 ln 1 . 5 

r 

w 

 K i ∆ z i t 

S i 

(I-3)

which can be solved iteratively to obtain a value for Ki.

Further details may be found in Morin et al. (1988a), Molz et

al. (1989), or Rehfeldt et al. (1989b).

Javandel and Witherspoon (1969) showed that, in idealized

layered aquifers, flow at the well-bore radius, rw, rapidly

becomes horizontal even for relatively large permeability

contrasts between layers. Under such conditions the radial

gradients along the wellbore are constant and uniform, and

flow into the well from a given layer, due to pumping, is

proportional to the transmissivity of that layer, that is:

á ∆ Q i − ∆ q i é = α ∆ z i K i (I-4)

where α is a constant of proportionality. This condition occurs

when the dimensionless variable t D = K t / á S s r 2 

w é is $ 100. 

In this expression, K is the average or bulk horizontal

hydraulic conductivity defined as ∑Ki

∆zi/b, where b is the

aquifer thickness, Ss is the aquifer specific storage, t is time

since pumping started, and rw is the wellbore radius.

To solve for α, sum the (∆Qi-∆qi) over the aquifer thickness,

to obtain

n 

3 

i = 1 

á ∆ Q i − ∆ q i é = QP = α 

n 

3 

i = 1 

 ∆ z i K i . (I-5)

Multiplying the right-hand side of Equation (I-5) by b/b and

solving for α yields

 α = QP

b K . (I-6)

Finally, substitutingfor α in Equation (I-4) and solving for

K i / K gives

 K i 

K = á ∆ Q i − ∆ q i é / ∆ z i 

QP/ b ; i = 1,2,...n . (I-7)

To obtain Equation (I-7), it was assumed that ∆Qi and QP do

not change with time and pseudo-steady-state conditions were

reached. Thus, a plot of K i / K versus elevation may be

obtained from the basic data. If one then has an estimate of

K from a conventional aquifer test (e.g., fully-penetrating

pumping test), dimensional values for Ki

 can easily be

calculated by taking the product of K and the flowmeter test

result.

In situations where the inherent assumptions are valid, the

K i / K approach has practical appeal because the values for rw

and Si, which are difficult to estimate, are not required. Also,

errors in flowmeter readings involving constant multipliers are

canceled out, and the meter calibration is not critical as long as

its response is linear. However, a reliable aquifer test must be

performed to estimate K . A detailed example of data analysis,

including head loss measurements for each layer, is presented

in the following section.

c. Data Analysis

The data presented in this section were obtained from a

borehole flowmeter test conducted in a fully-penetrating well

in a confined aquifer located 40 m to 61 m below ground. The

well screen was 10.2-cm diameter slotted PVC pipe (0.025-cm

slots). Testing began with mild redevelopment and cleaning of

the test well screen using injected air.

Prior to the flowmeter survey, caliper and ambient pressure

logs were run. Data obtained from the caliper logs were used

to verify and compute the cross-sectional area of the well, and

the hydraulic head distribution derived from the pressure logs

served as calibration references for evaluating ∆Hi

 produced

by pumping. No ambient flow was detected. Subsequently, a

pressure transducer and a flowmeter with centralizer were

lowered into the well, followed by a submersible pump. The

pump was started and allowed to run for about 50 minutes

prior to taking pressure and impeller meter readings.

Listed in the first three columns of Table I-2 are corresponding

values of depth, head change, and discharge associated with

pumping. This constitutes the basic data resulting from the

flowmeter test. The discharge measured at the 40-m depth

(0.24 m3/min) was taken as the pumping rate QP.

Additional hydraulic information about the aquifer in the

vicinity of the test well was obtained from small-scale

pumping tests. A standard Cooper-Jacob (1946) analysis

resulted in a transmissivity of 0.83 m2/min, a K of 0.039 m/

min, a storage coefficient of 4.5 x 10-3, and a specific storage

of 2.1 x 10-4 m-1. Data analysis proceeds by subtracting
8

neighboring Q values to get the ∆Qi for each of the 13 layers

(Column 4, Table I-2), noting that layer 1 is 3.05-m thick and

succeeding layers are 1.52-m thick. Listed in the last three

columns of Table I-2 are K distributions denoted by K2, K3,

and K7. These were calculated based on Equations (I-2),

(I-3), and (I-7), respectively. In order to account for the small

change in pressure head between the bottom and top of the

screen, Equation (I-7) was modified to read

 K i 

K = 

∆ H á ∆ Q i − ∆ q i é / ∆ z i 

∆ H i QP/ b ; i = 1, 2, ...n. (I-8)

Equation (I-8) is a good approximation when the ∆Hi

 are close

to ∆H, the average change in pressure head. When the

aquifer/well hydraulic data, including rw = 0.0634 m and

t = 60 min, are substituted in Equations (I-2), (I-3), and (I-8),

one arrives at (meter, minute units)

K 2 i = 

0 . 8176 ∆ Q i 

∆ H i 

;

K 3 i = 

0 . 1044 ∆ Q i ln á12, 677 K 3 i é

∆ H i 

; and

K 7 i = 

0 . 8031 ∆ Q i 

∆ H i 

(I-9)

with the exception of the bottom layer where ∆z1 = 3.05 m

rather than 1.52 m. The results show that there are no

significant differences between the three alternate hydraulic

conductivity calculations using data from this flowmeter test.

Table I-2. Results of the Analysis of Data from a Borehole Flowmeter Test to Estimate Hydraulic Conductivity Distributions

z(m) ∆Hi

(m) Q(m3/min) ∆Qi(m3/min) K2i(m/min)* K3i(m/min)* K7i(m/min)* Interval (i)

39.6 0.371 0.240 0.0062 0.014 0.013 0.014 13

41.1 0.366 0.234 0.0057 0.013 0.012 0.012 12

42.7 0.362 0.229 0.0147 0.034 0.033 0.033 11

44.2 0.359 0.214 0.0071 0.016 0.015 0.016 10

45.7 0.355 0.207 0.0119 0.027 0.027 0.027 9

47.2 0.353 0.195 0.0057 0.013 0.012 0.013 8

48.8 0.350 0.189 0.0113 0.027 0.026 0.026 7

50.3 0.348 0.178 0.0422 0.099 0.105 0.098 6

51.8 0.347 0.136 0.0153 0.036 0.036 0.035 5

53.3 0.347 0.120 0.0099 0.023 0.023 0.023 4

54.9 0.347 0.110 0.0331 0.078 0.082 0.077 3

56.4 0.347 0.077 0.0436 0.103 0.109 0.101 2

57.9 0.347 0.034 0.0337 0.040 0.042 0.039 1

61.0 0.347 0

*Based on Equations I-2, I-3, and I-7, respectively.

I.5 Conclusions

Presented in this chapter is an overview of vertical-component

flowmeter operation, application, and data analysis. While the

EM flowmeter was emphasized, the data collection and

analysis procedures apply to many types of flowmeters. A

flowmeter of this design measures only one thing directly:

upward or downward water velocity in a borehole, screen, or

casing due to natural head differences (ambient flow) or to

artificial head differences (pumping-induced flow). By

calibrating the meter for volumetric flowrate and taking

differences between two vertical flow measurements at known

elevations, assuming that no undetected flow is leaking past

the meter, it is possible to calculate the incremental horizontal

flow in the aquifer to or from the well. It is the horizontal

flow distribution over the vertical extent of the well that

enables one to calculate a horizontal hydraulic conductivity

distribution as a function of position in the vertical, K(z). The

calculated K distribution may be absolute, K(z), or relative,

K ( z ) / K . Alternate formulas are given for both quantities.

The advantage of the K ( z ) / K calculation [Equation (I-7)] is

that well radius and storativity do not have to be known or

estimated.
9

Chapter II

Electromagnetic Borehole

Flowmeter System

II-1 Design and Construction

The electromagnetic borehole flowmeter system discussed in

this report can measure vertical flow in various types of wells

and boreholes. The flowmeter system has three main

components: downhole flowmeter, packer assembly, and

above-ground electronics. The flowmeter provides accurate

flow measurements across a four order-of-magnitude range

and fits snugly in wells with casing diameters as small as

5.1 cm (standard 2-inch schedule-40 PVC pipe). A packer

assembly may be attached to the flowmeter to direct flow

through the meter in larger diameter wells. The above-ground

electronics package provides the magnetic drive and converts

the flowmeter signal to a discharge reading.

Two of the major components of the meter are an

electromagnet and a pair of silver chloride electrodes mounted

at right angles to the pole pieces of the electromagnet (Figure

I-1). During operation, the electromagnet creates a strong

magnetic field across the flow passage. As water (the

conductor) flows through the magnetic field, a voltage

gradient is generated. The voltage is proportional to the

average velocity of the water across the magnetic field and is

detected by the electrodes. The magnitude of the voltage is

unaffected by the electrical conductivity of ground water

under normal conditions. The polarity of the generated

voltage is dependent on the direction of flow. Upward flow is

generally designated as a positive voltage and downward flow

as a negative voltage.

Flowmeters of this design can be built to any outer diameter

greater than 4.8 cm. As flow is channeled through this meter,

the applicable flow range is a function of the inner diameter of

the open probe core. Flowmeters with inner diameters (IDs)

of 1.27 cm or 2.54 cm have been produced. The length of the

current prototype flowmeter is 30 cm, but flowmeters as short

as 10 cm have been used successfully. The 1.27-cm and 2.54-

cm ID flowmeters are typically used to measure low and high

flow rates, respectively. In wells or boreholes with relatively

large diameters, the effectiveness of the flowmeter diminishes

unless a packer assembly is used to direct flow through the

flowmeter. Both mechanical (Figure II-1) and inflatable

(Figure II-2) packers have been developed.

The mechanical packer assembly used with prototype meters

was a collar consisting of a rubber gasket sandwiched between

two plexiglass or stainless steel rings that slipped over the

flowmeter and was held in place with set screws. The rubber

gasket was sized to insure a tight seal between the probe and

the inner surface of the well. The mechanical packer was

easily used, but its application was tedious because the friction

between the collar and well made lowering of the flowmeter

Figure II-1. Mechanical packer (a) assembled on probe and (b) in schematic view.

Retaining Ring

Rubber Gasket

Retaining Ring

Bolts

Downhole

Probe

(a)

Bolts (4)

Retaining

Rings (2)

Rubber Gasket

(b)
10

more difficult. In situations where the screen or borehole was

uneven, the collar design may not have provided an adequate

seal and was not used.

The inflatable packer for the prototype system consisted of a

rubber sleeve attached to a stainless steel assembly. The

packer assembly easily slipped onto the flowmeter and sealed

with “O” rings. This assembled unit had a diameter of 8.9 cm.

If the rubber sleeve was slipped directly onto the flowmeter,

the flowmeter and sleeve had a combined diameter of 8.7 cm.

Approximately 103 kPa (15 psi) and 172 kPa (25 psi) of

pressure was needed to inflate the rubber sleeve to diameters

of 10 cm and 20 cm, respectively. Inflation was achieved by

injecting water into the rubber sleeve through a tube in the

packer assembly. Both a pressurized chamber at the ground

surface and a submersible pump have been used to inject

water into the sleeve. For most applications, the submersible

pump was the method of choice. However, at shallow depths

(<20 meters) where only a few flowmeter measurements were

desired, the pressurized chamber had an advantage in its

simplicity and relatively short set-up time. The seal provided

by a properly inflated packer was such that the flowmeter

could not be moved by pulling the cable and rope.

The above-ground electronics includes an electromagnet drive,

power supplies, amplifiers, and synchronous demodulator for

converting the voltage from the probe’s electrodes to flow

rate. The probe’s signal is in the microvolt range and is

typically several orders-of-magnitude less than background

noise. Synchronous demodulation is used to extract the signal

and has the effect of canceling noise out of phase with the

electromagnetic drive. With additional amplification and

filtering, a DC signal proportional to water velocity through

the flowmeter is generated. The electronics package collects

and processes signals from the flowmeter every second. At

the end of a pre-set time interval or upon keyboard command,

the signals are averaged and the standard deviation is calculated. This average and standard deviation are displayed,

stored on disk, and printed to a hardcopy device.

II-2 Laboratory Calibration

Calibration of the prototype flowmeter was performed in a

facility located at the TVA Engineering Laboratory, Norris,

Tennessee. The apparatus included standard 5.1-cm, 10.2-cm,

and 15.2-cm schedule-40 flush-joint PVC pipes. Before and

after any field measurements, calibration checks were

performed at a range of flow rates using the same flowmeter

system (above-ground electronics, cable, and flowmeter) used

in the field. Calibrations were simple and consisted primarily

of establishing a constant uniform flow through a vertical PVC

pipe and comparing the flowmeter measurements to other flow

measurements at the intake and/or the outlet of the PVC pipe

(Figure II-3). Flow rates were maintained by throttling a

pressure valve on the public waterline and measuring the

generated flow rate near the PVC pipe intake with an in-line

commercial flowmeter. For all flows, the baseline rate was

determined by measuring the time required for the discharge

to fill a calibrated container. At lower flow rates (< 30 ml/

min), the discharge volume was determined by dividing the

weight of water by the temperature corrected density of water.

Electromagnetic flowmeter calibrations are similar to those for

other flowmeter types and require: (1) the use of proper and

certified measuring devices for volume, time, length, weight,

and temperature; and (2) the documentation of calibration

conditions including personnel, date and time, and equipment

set-up. Instructions and guidelines for performing flow

Figure II-2. Inflatable packer assembled on probe.

Air or

Water

Inflation

Tubing

Inflatable

Rubber

Bladder

Clamps

Downhole

Probe

Figure II-3. Conceptual system for flowmeter calibration.

Well Casing

Flowmeter

Water Supply

Calibrated Vessel

Electronics
11

calibrations can be found in standard texts such as Ferson

(1983) and Liptak and Venczel (1982). Besides standard

flowmeter calibrations, similar equipment has been used to

investigate phenomena such as turbulence, frictional losses,

and flow around the probe. The three main PVC pipes used in

the calibration facility are transparent to permit visual

monitoring of dye releases so that turbulence and flow around

the probe can be evaluated. One of the PVC pipes is fitted

with manometers to measure head losses within the pipe and

flowmeter. All of the PVC pipes possess side ports to permit

the introduction of flow. This allows monitoring of the

flowmeter response as it approaches and passes a horizontal

inlet source. Horizontal inflows may be large enough to

produce turbulence effects, and gauging the sensitivity of the

flowmeter to these inflows was important. Testing indicates

that the electromagnetic flowmeter is insensitive to the

proximity of horizontal inflows.

Figure II-4 provides a sample calibration data set associated

with field testing of the EM flowmeter. The figure shows the

calibration data on both linear and logarithmic scales. The

linear scale illustrates the linear response between volts

(flowmeter signal) and flow. The logarithmic scale shows the

sensitivity of the meter at lower flow ranges. The 2.54-cm ID

flowmeter exhibits good repeatability and linearity from about

100 ml/min to 40 L/min. The 1.27-cm ID flowmeter exhibits

good repeatability and linearity from 30 ml/min to 10 L/min.

Below 30 ml/min, the repeatability and linearity of the

Figure II-4. Calibration data for the 1.27-cm ID flowmeter in 5.1-cm PVC pipe.

0.01

0.02

0.05

0.1

0.2

0.5

1

2

5

10

0.01 0.1 1 10

Discharge (L/min)

0

2

4

6

8

10

0 2 4 6 8 10 12 14

Discharge (L/min)

1.27-cm ID Flowmeter in 5.1-cm PVC Pipe

Calibration

 - 7-10-92

 - 7-08-92

 - 6-29-92

 - 5-27-92

 - 5-13-92

 - 1 Standard

Deviation

+_

 - 7-10-92

 - 7-08-92

 - 6-29-92

 - 5-27-92

 - 5-13-92

 - 1 Standard

Deviation

+_

Volts Volts
12

Figure II-5. Frictional losses associated with the 1.27-cm and

2.54-cm ID flowmeters.

Table II-1. Sample Calibration Factors (Liter/Min/Volt) from a

Linear Regression of Discharge Versus Voltage for

Electromagnetic Flowmeter Data

1.27-cm ID 2.54-cm ID

EM Flowmeter EM Flowmeter

Flowmeter in a 5.1-cm pipe* 1.46 3.99

Flowmeter with a mechanical

 collar in a 10.2-cm pipe* 1.38 3.95

Flowmeter with an inflatable

 packer in a 15.4-cm pipe* 1.32 3.94

* pipe is schedule-40 PVC

1.27-cm ID flowmeter drops significantly. Deviation from

linearity at these low flows may be a result of shifts in the

flowmeter response over time, or problems/uncertainties

associated with maintaining and measuring low flows during

calibration.

In Figure II-4, each calibration point is the mean of sixty

readings taken over a one minute period. For the majority of

the flow measurements, the relative standard deviation is less

than 2 percent of the average flow rate. Significantly lower

percentages occur at the higher flow rates and slightly higher

percentages occur at the lower flow rates. Calibration data

show that the sensitivity and low end accuracy (below 50 ml/

min) of the 1.27-cm ID flowmeter is less in a 5.1-cm pipe

without a packer assembly, than in larger diameter pipes with

a packer assembly. For the 5.1-cm pipe, the calibration plot is

essentially linear up to 6 L/min. Above 6 L/min, the

flowmeter signal becomes slightly nonlinear. As no packer

assembly was used in the 5.1-cm application, the nonlinearity

is probably the result of water flow around the probe.

Flowmeter sensitivity can be expressed in a calibration factor.

Calibration factors are used to convert voltage from the probe

electrodes to flow and have the units of volume per time per

volt (e.g., liter/minute/volt). Table II-1 provides example

calibration factors calculated for different combinations of

flowmeter sizes, packer types, and well diameters. Greater

sensitivity is achieved with a packer because less water flows

around the exterior of the flowmeter. The flowmeter should

be calibrated using the same equipment and in the same type

of casing as the wells to be surveyed prior to use.

At flow rates above 10 L/min, two concerns exist with use of

the 1.27-cm ID flowmeter: high frictional losses through the

orifice, and an electrode voltage that will exceed the capacity

of the above-ground electronics. High frictional losses (Figure

II-5) affect the hydraulic head distribution and, consequently,

the distribution of flow in the well and through the meter. In

selecting between electromagnetic flowmeters with different

orifice diameters, the trade-offs associated with decreases in

the detection limit and increases in frictional losses should be

considered. As a general rule, the frictional losses should be a

concern if they exceed 10 percent of the total drawdown in a

well or borehole for cases where the data will be used to

calculate a hydraulic conductivity profile.

2.54-cm ID (10-cm length)

2.54-cm ID (25-cm length)

1.27-cm ID (25-cm length)

25

20

15

10

5

0

0 5 10 15 20 25 30 35

Flow (L/min)

Frictional Loss (cm of water)
13

Chapter III

Hydrogeologic Characterization Test Design

III-1 Overview

The primary objective of an electromagnetic borehole

flowmeter test is to measure the profile of horizontal flow into

or out of designated aquifer intervals during ambient and/or

pumping conditions. These profiles are used to identify the

zones of relatively high and low permeability. Combined with

a transmissivity measurement or the proper drawdown data at

the tested well, the flowmeter data may be used to calculate a

vertical profile of horizontal hydraulic conductivity. In many

situations, the pumping tests performed concurrently with

such flowmeter tests will provide the drawdown data

necessary to calculate a transmissivity value.

Table III-1 lists the general procedures which were used in

these studies to perform borehole flowmeter tests. Detailed

descriptions of these procedures and associated equipment are

contained in the following sections. Appendix A provides the

forms used to record the field data and Appendix B provides

an equipment checklist.

III-2 Measurement Interval Selection

Selection of appropriate intervals for obtaining flowmeter

measurements in porous media involves consideration of site

stratigraphy interpreted from geologic and geophysical logs.

However, such logs generally provide only enough

information to determine the basic hydrogeologic framework

and not the detailed variability within geologic units.

Although, these logs may provide constraints for specifying

measurement intervals, the scale on which measurements are

ultimately obtained will usually be based on other factors.

Such factors include the pumping rate to be used during the

test. Constraints on pumping rate, such as limitations related

to water storage, treatment, and disposal, may necessitate

increased interval size to provide meaningful data. The

thickness of the disturbed zone surrounding the well screen is

also a factor that affects interval selection. Results of studies

by Ruud and Kabala (1997) indicate that skin effects bias the

distribution of flow to a well. As the ratio of the flowmeter

measurement interval thickness to the thickness of the

disturbed zone decreases, the bias in the test results increases.

In general, local deviations from horizontal flow will occur

during most tests. Errors associated with these deviations will

increase as the size of the measurement interval decreases.

III-3 Flowmeter Measurements

Prior to testing, the flowmeter is connected to the electronics

and permitted to warm up. This warm-up period was

approximately 30 min for the prototype electromagnetic

system. Well construction logs, including a caliper log of the

test well, are reviewed if there is any doubt about the screen or

borehole diameter. Field testing has shown that the calibration

of the prototype electromagnetic flowmeter may drift up to

10 millivolts (0.1 percent full scale) over several hours if large

temperature changes (> 10°C) occur. In many instances, this

temperature sensitivity is not a concern because of the

relatively short time needed to obtain a flow log. However,

flowmeter calibration at zero flow is checked prior to initiation

of the test and at the end of each test. This is accomplished by

positioning the flowmeter at a location in the well where no

Table III-1. Generalized Borehole Flowmeter Field Test Procedures

1. Measure ground-water elevation in the well relative to a fixed datum (such as top of well casing) and total well depth. Examine well

construction, geologic, and geophysical logs to determine measurement intervals.

2. Zero flowmeter under no-flow conditions. Measure the ambient vertical flow profile. In these studies, this profile typically consisted of a

minimum of ten measurements. Obtain flowmeter reading under no-flow conditions to evaluate baseline drift.

3. Install equipment as for a single-well pumping test, including pressure transducer, data logger, and pump. Place intake hose or pump

above the pressure transducer and within the well casing above the screen, if possible. Measure ground-water elevation to insure static

conditions are attained.

4. Start constant-rate pumping test. Accurately measure pump discharge rate on a routine basis. Record drawdown. Verify that wellbore

storage effects have dissipated and estimate transmissivity based on drawdown data.

5. After pseudo-steady-state conditions have been achieved, obtain flowmeter measurements at the same elevations as the ambient

measurements. Repeat flowmeter measurements to demonstrate a stable flow profile has been achieved. Shut system down and obtain

flowmeter reading under no-flow conditions.
14

ambient flow exists. In a well, no ambient flow should exist

above or below the screened interval. In a borehole, no

ambient flow should occur in the cased interval. If there is

doubt about the location of a no-flow zone, the problem is

resolved by manually plugging the flowmeter and lowering it

into the well. Plugging may be accomplished by securely

fastening a cork in the lower orifice of the flowmeter.

Lowering or raising the flowmeter induces water movement in

a wellbore and it may require several minutes to regain

quiescent conditions in low permeability aquifers. After

moving the flowmeter, measurements should not begin until

the flowmeter signals have stabilized. If the readings do not

stabilize, and/or if the standard deviation is approximately ten

times greater than observed in the calibration data for the

measured flow, then reject the reading and attempt to diagnose

the problem. Table III-2 lists problems that have been

encountered in the field. Problems 3 and 4 can often be

remedied by rapidly moving the flowmeter up and down the

well or borehole several times.

Table III-2. Problems that Produce Errors in EM Flowmeter

Measurements

1. Insufficient time to regain quiescent conditions in well after

flowmeter movement.

2. High ground currents (above- or below-ground power lines or

power sources in vicinity of well or boreholes.)

3. Coating on the electrodes such as mud or oil.

4. Blockage of signal path to electrodes by gas bubbles.

5. High flow rate entering well near location of flowmeter.

III-4 Pumping Rate and Drawdown

Measurements

One of the most important aspects of the pumping test is the

pumping rate, which should be high enough to achieve a

measurable drawdown, if analyses of time/drawdown data are

desired. The rate should also be low enough to support the

assumption of negligible head loss within the well, if head loss

across each interval is not measured. Additional

considerations include methods for maintaining a constant

flow rate throughout the test and constraints due to

containment, treatment, and disposal requirements for

contaminated water. In practice, it is often necessary to set the

pumping rate by trial and error. After each trial start,

sufficient time should be allowed for the well to recover

before beginning a subsequent pumping test.

Constant flow rates are important for two reasons. First, a

constant flow rate permits calculation of horizontal inflow

from aquifer intervals by subtracting the cumulative flow rates

at different elevations. Second, a constant flow rate permits

the use of conventional pumping test analytical solutions to

calculate a transmissivity value at a well location.

Problems associated with maintaining a constant flow rate are

greatest where large drawdowns occur and the lift requirements of a pump are affected. If no adjustments are made to

the pump as the drawdown increases, the pumping rate will

decrease until the drawdown stabilizes. In regions of low

transmissivity, the problems associated with a constant flow

rate can be severe because of large drawdowns. Although data

analysis methods can be adjusted to compensate for changes in

the pumping rate, these changes are not desirable. Injection

tests may be considered instead of pumping tests if large

drawdowns are expected.

Accurate measurement of drawdown response during the

pumping test generally requires a pressure transducer and data

logger to record data at frequent intervals. As any movement

in the well has the potential to alter the water level or the

position of the transducer, sufficient drawdown data for

calculating transmissivity should be collected before

flowmeter testing begins.

III-5 Selection of Pumps

The type of pump used for the test depends on site conditions,

well construction, and available power. If the depth of the

water from the top of casing will not exceed approximately 7

m, then a surface pump may be used. For flows greater than 4

L/min, centrifugal surface pumps have proven to be reliable.

This type of pump is tolerant of suspended solids and high or

blocked discharge pressures, has good lift, and can provide an

order-of-magnitude flow range by manually adjusting the back

pressure. A disadvantage of this pump is the difficulty of

presetting the pump to a known rate. A peristaltic pump is

often a good choice for flows less than 4 L/min. It is easy to

use, there is no contamination of the pump itself, and it may

be preset within reasonable tolerances.

Dissolved gases may be a problem with surface pumps when

air bubbles accumulate in the intake line. The intake line

pressure will be lowest near the surface pump. In some cases,

the pressure may be sufficiently low to cause the water to

degas. If sufficient gas accumulates in the intake line, then

flow will be restricted to the pump and the pumping rate will

decrease. In situations where degassing is a concern, the

pump should be located above the well head to allow gas

movement upward and through the pump.

If the depth to water exceeds approximately 7 m, then

submersible pumps are required. In general, submersible

pumps present less operational problems than surface pumps.

However, their use is often limited to wells with an ID greater

than 5.1 cm due to the size of most pumps and the induced

flow test design. If a submersible pump is used, it should be

small enough to fit into the well and allow passage of

flowmeter and pressure transducer cables.

III-6 Packer Selection

For wells greater than 5.1 cm in diameter, a packer may be

needed to channel water through the flowmeter. If the

velocities are sufficiently high, and the well has a constant
15

diameter, the flowmeter may be operated as a velocity meter

without a packer. When used as a velocity meter, flow occurs

around, as well as through, the EM flowmeter. Hence, a

different set of calibration data is required in lieu of that

obtained under conditions where packer assemblies are used.

Where low flows are of concern and/or the well or borehole is

not of constant diameter, a packer generally is required.

Packer systems of different designs may be appropriate for

these investigations.

III-7 Method of Inflation

Two methods generally were used for inflating/deflating the

prototype inflatable packer assembly. One method

incorporated an above-ground pressure chamber and the other

used a submersible pump positioned above the flowmeter.

Inflation using the pressure chamber was relatively slow and

use was limited to sites where the water table was relatively

shallow. The submersible pump has the advantage of rapid

inflation and operates at wide ranges of depth to water and

pressure heads. At Oak Ridge National Laboratory, Oak

Ridge, Tennessee, submersible pump inflation has been

successful at depths below 300 m, and depths-to-water of

greater than 15 m.

Installation using the above-ground pressure chamber was

relatively simple. The pressure chamber has a fill port, a vent

port, a pressure gauge, and a discharge port attached to a tube

that inflates the packer. The most common setup involved

filling the chamber 75 % full with water. The pressure

chamber was charged to the required pressure with an air

compressor or air tank. When the discharge valve was

opened, the packer assembly inflated. Packer inflation was

monitored by observing the decline in water level in the

chamber. Adequate inflation was checked by tugging on a

rope connected to the flowmeter. Packer deflation was usually

accomplished by venting only the connection hose.

In situations where the packer was inflated at large depths, or

inflated and deflated relatively quickly, a submersible pump

was used with the packer assembly. Several alternative and

equally viable submersible pump configurations exist. A small

ground-water sampling pump located approximately 0.3 m

above the packer was used in these studies. The pump

discharge was connected to the packer via a tube and integral

solenoid valve. The assembly was wired such that the valve

could not be closed when the pump was operating. In

operation, the pump was turned on and the valve was opened

to inflate the packer. Once the packer was inflated, the pump

was stopped and the valve closed simultaneously. For

deflation, the valve was opened, allowing the relatively highpressure water inside the packer to flow back through the

pump. Operation was reasonably fail safe as the pump could

not operate against a closed valve, and the valve would open

and deflate the packer upon power failure.

Inflation times ranged from approximately 10 s to 15 s for a

10.2-cm well to greater than 3 min for a 17.8-cm well. At

shallow depths, packer inflation was checked by pulling the

cable to determine if the flowmeter was firmly in place.

However, at depths of 500 ft and greater the weight of the

cable makes it difficult to check for inflation. At these depths,

rapid increase in the electrical current drawn by the pump was

monitored as an indicator of inflation.

III-8 Issues Regarding Flowmeter

Measurements in the Field

Successful performance of investigations using the procedures

described in this document requires knowledge of the

mechanics of single-well pumping tests. This understanding

provides the framework necessary to designate appropriate

pumping rates, ascertain that flow conditions have stabilized,

and select elevations for flowmeter measurements. In

addition, familiarity with local geology, analytical solutions

for pumping tests, and issues such as those listed below is

necessary.

a. Well or Borehole Storage

During a pumping test, a common assumption is that the

pumping rate equals the discharge from the aquifer. This

assumption is acceptable only as long as a small percentage of

discharge originates from within the well or borehole. In any

large diameter well, borehole storage is a potential concern. If

borehole storage dominates the response of a single-well

pumping test, the time/drawdown data will appear as a straight

line on a log-log plot with a slope of one. During a pumping

test, the effects of borehole storage diminish with time and

may be ignored at late times. Until storage effects dissipate,

the drawdown will be less than if storage effects were not

present.

Two problems exist if flowmeter measurements are made

before borehole storage dissipates. One problem is that the

total flow into the well from the aquifer is increasing with

time. Hence, the flow distribution to the well will be changing

with time. Another problem is that calculated transmissivity

values will be too high unless the drawdown values are

corrected for wellbore storage. When performing a flowmeter

test of this design, borehole storage should be considered in

the analyses, especially in low permeability aquifers or in

boreholes of large diameters.

b. Selection of Pumping Rate

Factors affected by the pumping rate include the magnitude of

the total discharge, the drawdown response, and friction

losses. In situations where ground-water contamination is of

concern and discharged water may require treatment, a lower

pumping rate is beneficial. Minimizing the drawdown also

reduces the importance of vertical flow in unconfined aquifers.

As discussed in Chapter I, horizontal flow is an assumption in

the data analysis. For large drawdowns, horizontal groundwater flow is not a valid assumption for unconfined aquifers.

During any flowmeter test, frictional losses occur through the

well screen, well casing, and flowmeter. Because they are
16

difficult to measure in the field and can complicate the

analysis of flowmeter data, these losses should be minimized.

Conditions for which frictional losses may be of concern

include heterogeneous highly transmissive aquifers and deep

boreholes. In the former case, frictional losses associated with

high flows entering the well through a narrow interval may be

a problem if the total drawdown is small (e.g., < 25 cm) as the

well loss becomes a significant fraction of the drawdown. In

deep boreholes, cumulative friction losses associated with

flow through a well pipe or borehole may be significant.

Concerns associated with low pumping rates include:

possible reduced sensitivity of the electromagnetic flowmeter,

difficulty in monitoring the drawdown response, and

adequately stressing the aquifer. Hence, although low

pumping rates might be desirable, they should be high enough

to ensure that the aquifer and well responses can be

accurately measured with the available equipment.

c. Background Electromagnetic Currents

The flowmeter shell and telemetry cables are shielded

against ground currents, but the inlet and outlet of the

prototype flowmeter are not shielded. As a result, large

background voltage gradients may influence the circuitry.

Although the flowmeter is designed to reject such noise, its

signal is in the micro-volt range and large voltage

gradients may produce masking effects. Several wells

where instabilities occurred in the flowmeter readings have

been observed during development and use of the

flowmeter. In such cases, the problems were believed to

be caused by background currents. One of these wells,

located near a building with large machinery, was surveyed

twice. The first survey occurred with the machinery

operating. During this survey, unstable flowmeter readings

were recorded. The second survey occurred when the

machinery was turned off. Stable, reproducible flowmeter

readings were recorded.

Due to the uncertainties associated with field testing, some

simple laboratory tests were performed to better identify

the problem. The tests involved inducing a voltage

gradient across a pipe in the calibration facility and

recording flowmeter responses. As long as the induced

gradient was a sine wave synchronized with the power

line, no instabilities were observed. However, once the

voltage gradient varied in both amplitude and frequency,

instabilities occurred. To shield the flowmeter from the

voltage gradient, a metal screen was placed across the

flowmeter's outlet and inlet. This modification reduced the

sensitivity of the flowmeter's response, but appeared to

eliminate the instabilities induced by background currents.

In situations where electromagnetic background currents

are large, problems may occur with the performance of the

electromagnetic flowmeter. Preliminary investigations

indicate these problems may be overcome by providing

additional shielding for the flowmeter. However,

additional testing is required before appropriate shielding

can be developed.

d. Reproducibility of Flowmeter Data

A concern with any test is the reproducibility of the data.

During a borehole flowmeter test, it is a good practice to

repeat several flowmeter measurements without changing

flowmeter position. If two measurements produce similar

means and standard deviations, then the flowmeter system is

assumed to be functioning properly. As standard practice, the

flowmeter was considered to be performing adequately if two

successive measurements produced mean values that

overlapped in the range of their standard deviations.

In developing a quality assurance plan for field testing, two

types of duplicate measurements should be taken. The first

type involves two successive measurements without moving

the flowmeter. An assumption in comparing these values is

that flow conditions in the aquifer have remained constant

between measurements so that any differences reflect the

uncertainties associated with the measurement technique. The

second type involves measurements at the same location but at

different times. Over periods of minutes and/or hours, the

flow conditions in the aquifer may change. Differences in

flow measurements would be primarily produced by variations

in the saturated thickness of an unconfined aquifer in response

to a pumping test, variations in the pumping rate caused by

fluctuations in the performance of the pump, and inability to

exactly reoccupy the same elevation in the well. The second

type of duplicate measurement reflects the error associated

with assuming that the flow conditions are at steady-state.

III-9 Flowmeter Investigations in Consolidated

Materials

a. Introduction

Many of the most intractable ground-water contamination

problems occur in consolidated rocks and sediments where

transport is dominated by flow through fractures or solution

features. In systems where flow is dominated by secondary

porosity (fractures, conduits, etc.), the identification of

fractures that are hydraulically active and how they are

interconnected is often important. This task may be

complicated by the general observation that many fractures are

inactive. Therefore, identifying fracture distributions using

only a caliper log or a televiewer log provides limited

information on the actual flow distribution that exists (Paillet

et al., 1987; Paillet and Hess, 1987; Molz et al., 1990).

Characterization of ground-water flow in fractured media will

often involve measurements of flow to or from individual

fractures or fracture zones. Over the past decade, researchers

at the U.S. Geological Survey (USGS) have been refining

procedures developed using a sensitive heat-pulse flowmeter

(Hess, 1982, 1986; Paillet et al., 1987; Paillet and Hess, 1987;

Hess and Paillet, 1990; Paillet and Kapucu, 1989; Paillet,

1991a, 1991b, 1991c; Paillet et al., 1992). It is mainly their

contributions that will be reviewed in the remainder of this

section. The applications described below illustrate the need to

incorporate a variety of geological, hydrogeological, and
17

geophysical tools in the investigation of site hydrology.

Information from only one tool, such as a borehole flowmeter,

will generally be insufficient to evaluate ground-water flow

and contaminant transport and fate issues. This integrated

characterization approach is necessary for investigations in

porous media as well as fractured rock settings.

b. Fractured Rock Applications

Some of the most direct uses of a sensitive borehole flowmeter

are in fractured rock investigations. These applications

demonstrate the advantages in combining flowmeter

information with other types of geophysical data. Perhaps the

best way to describe this process is to present an example

application in fractured dolomite in northeastern Illinois. This

study was performed by the USGS (Molz et al., 1990).

Acoustic-televiewer, caliper, single-point-resistance, and

flowmeter logs were obtained in a 64-m deep borehole (DH14) in the northeastern Illinois area as part of a study of

ground-water flow and transport in fractured dolomite (Figure

III-1). The acoustic-televiewer log is a magnetically

orientated, television-like image of the borehole wall which is

produced with a short-range sonar probe (Zemanek et al.,

1970). Irregularities in the borehole wall, such as fractures

and vugular openings, absorb or scatter the incident acoustic

energy, and result in dark features on the recorded image.

Such televiewer logs may be used to determine the strike and

dip of observed features. The acoustic-televiewer and caliper

logs for borehole DH-14 (Figure III-1) indicate a number of

nearly horizontal fractures that seem to be associated with

bedding planes. The larger of these fractures are designated A,

B, C, and D, respectively. The caliper log indicates that the

major planar features on the televiewer log are large fractures

or solution openings associated with substantial borehole

diameter enlargements. The large but irregular features on the

televiewer log between fractures B and C also are associated

with borehole enlargements, but these are interpreted as

vugular cavities within the dolomite rather than fractures. The

Figure III-1. Acoustic-televiewer, caliper, single-point resistance, and flowmeter logs for borehole DH-14 in northeastern Illinois (Paillet

and Keys, 1984; Molz et al., 1990).

Caliper Log

DIAMETER, IN INCHES

ACOUSTIC

TELEVIEWER LOG

5 6 7 8 9 10

A

B

C

D

RELATIVE SINGLE-POINT

RESISTANCE LOG

INCREASING

RESISTANCE

Flowmeter Log

DOWNFLOW, IN GALLONS

PER MINUTE

DEPTH, IN METERS BELOW LAND SURFACE

DOWNFLOW, IN LITERS

PER MINUTE

23.0 0.5 0.0

60

50

40

30

6.0 5.8 0.2 0.0

INFLOW

OUTFLOW

INFLOW

OUTFLOW

22.0
18

single-point-resistance log indicates abrupt shifts in resistance,

at depths of about 40 m and 56 m. These shifts may reflect

differences in the dissolved-solids concentration of the water

in the borehole.

The pattern of vertical flow determined by the flowmeter

measurements indicates the probable origin for the inferred

water quality contrasts in the borehole (Figure III-1). The

flowmeter log indicated downflow, which probably was

associated with naturally occurring hydraulic-head differences,

causing water to enter at the uppermost fracture, A, and exit at

fracture B. A much smaller flow of water with the same

electrical conductivity and dissolved-solids concentration

continued down the borehole to fracture C. At this fracture,

the downflow increased and the water inflow apparently

contained a greater concentration of dissolved solids, which

accounts for the shift to greater electrical conductivity. This

increased downflow exited the borehole at fracture D, where

there was another, somewhat smaller, shift in single-pointresistance. Although not rigorously proven from the

geophysical logs, the second shift in resistance appears to be

associated with the dissolved-solids concentration of the water

entering at fracture C.

Subsequent water sampling confirmed that there were

differences in the dissolved-solids concentration of the water

at the different depths. Sample analysis indicated that the

water entering at fracture A had a dissolved-solids

concentration of about 750 mg/L; and the water entering at

fracture C had a dissolved-solids concentration of about 1,800

mg/L. In this instance, the geophysical data, especially the

thermal-pulse flowmeter data, were useful in planning

subsequent packer testing of the aquifer and in interpreting

water quality measurements. Identification of substantial

natural differences in background water quality was useful in

conceptualization prior to modeling of conservative solute

transport. At the same time, measurements of vertical velocity

distributions in the borehole provided useful indications of

hydraulic head differences between different depth intervals.

This information could not be obtained from conventional

water level measurements without the time-consuming

installation of packers at multiple levels in all of the boreholes

at the site.

Paillet et al. (1992) consider the application of borehole

flowmeters to measure flow transients in pumped boreholes

and in adjacent observation boreholes. Their approach is

based on the theoretical observation by Long et al. (1982) that

fracture connections are more important than local fracture

aperture in controlling the rate of flow through random

distributions of finite fractures. Thus, their technique is

designed to identify fracture connections. Paillet et al. (1992)

also consider approaches to the problem at different scales of

measurement which begins to attack the question of how

individual fractures and fracture sets are integrated into largerscale flow systems.

c. Conclusions

The previous study illustrates potential applications and

integration of borehole flowmeters with other geophysical

tools in the interpretation of flow in fractured aquifers. The

relative ease and simplicity of flowmeter measurements

permits reconnaissance of naturally occurring flows prior to

hydraulic testing and identification of transient pumping

effects. Flowmeter surveys may provide a valuable means by

which to identify fracture interconnections and solute transport

pathways during planning for much more time-consuming

packer and solute studies. The borehole flowmeter is

especially useful at sites where boreholes are intersected by

permeable horizontal fractures or bedding planes. The simple

and direct measurements of vertical flows provided

information pertaining to the relative magnitude and vertical

extent of naturally occurring hydraulic-head differences in a

few hours of measurement. While the studies described in this

section did not involve contaminated ground water, the

potential application to contaminant migration problems and

monitoring well screen location is obvious.
19

Chapter IV

Well Construction and Development

IV-1 Background

a. In-Situ Hydraulic Conductivity Estimates

Using Wells

Well installation results in disturbance of aquifer materials.

This immediately raises the question of what effects, if any,

well construction and development techniques have on

hydraulic conductivity measurements? There are many

considerations that contribute to the answer of this question.

Such considerations include the following.

1. Is the subsurface material consolidated or

unconsolidated?

2. What is the relative importance of primary versus

secondary porosity?

3. What drilling technique is selected?

4. Is the well constructed with an artificial filter pack?

5. What drilling fluid, if any, is used?

6. How is the finished well developed?

7. What scale does the hydraulic conductivity

measurement represent?

It is beyond the scope of this report to provide a comprehensive answer to the question of how well construction and

development affects hydraulic conductivity measurements.

Especially for small-scale measurements, this potential

problem is neither well-documented nor understood. The

approach herein will be to discuss the various drilling and

development methodologies, review previous studies, discuss

problems, and present test results concerning the sensitivity of

borehole flowmeter measurements to well development and

construction from two test sites.

b. Formation Damages and Skin Effects

All drilling methods alter the hydraulic characteristics of an

aquifer near the wellbore. The impairment may be caused by

the physical rearrangement of the matrix of aquifer material,

by the smearing of silt and/or clay particles across the

borehole face, or by invasion of drilling fluids or solids into

aquifer formations. The amount of damage that occurs is

related to the drilling method used for well construction and

subsurface geology. The changes in hydraulic conductivity

resulting from formation damage can produce skin effects in

the near-well aquifer formations.

The term “skin effect” was introduced by van Everdingen and

Hurst (1949) when they discovered mismatches between

analytical solutions and field data from well tests. The skin

effect was caused by mud particle invasion into aquifer

formations during well installation producing a decrease in

hydraulic conductivity. Skin effects can be either negative or

positive and represent increases or decreases, respectively, of

hydraulic conductivity near the wellbore. Negative skin

effects can be created at wellbores where drilling causes

fractures in the aquifer and/or development causes excessive

removal of fines from aquifer sediments. Negative skin

effects may also result from well construction using an

artificial filter pack that is significantly coarser than aquifer

material. Positive skin effects can result from compaction,

invasion of drilling fluids, smearing of clays, etc.

Skin effects influence the flow distribution along the well. In

single-well pressure transient tests, wellbore damage has been

recognized (Dudgeon and Huyakorn, 1976; Chu et al., 1980;

Moench and Hsieh, 1985) as adversely affecting the tests.

Analysis of the test data can result in large errors in estimates

of storativity and transmissivity if skin effects and wellbore

storage are not properly delineated. There are solutions

available that account for both wellbore storage and

infinitesimally thin skin in the pumping well (Sandal et al.,

1978; Chu et al., 1980) and both the pumping and observation

wells (Tongpenyai and Raghaven, 1981; Ogbe, 1984; Ogbe

and Brigham, 1984). The mathematical treatment used in

these models to account for the skin region, however, is only

an approximation and the hydraulic head drop across the skin

is presumed to occur under steady flow conditions.

Well development can reduce positive skin effects by repairing

damage to the aquifer formations so that natural hydraulic

properties are partially restored. For production wells,

development comprises the systematic procedures followed to

ensure the maximum discharge rate at the highest specific

capacity with minimum production of particulate matter (Moss

and Moss, 1990). More specific construction and

development considerations are necessary for wells that are to

be used to obtain geohydrologic data for aquifer

characterization.

IV-2 Well Design

Ideally, wells designed for characterization using techniques

described in this document should be fully screened across the

interval of interest, such as the contaminant plume, be

constructed without an artificial filter pack, and be screened

such that the top of the screen is far enough below the water

table to allow placement of the pump intake in the well casing
20

during the test. Boman et al. (1997) discuss the potential

influence of an artificial filter pack on flowmeter results. A

coarse-grained gravel or sand pack may result in significant

vertical flow through the pack prior to entering the screen.

This phenomena is enhanced by use of high flow rates that

result in resistance to flow through the downhole probe of the

electromagnetic flowmeter. In this situation, the measured

flow distribution is skewed with a high influx of water near

the top of the screen. For this reason, use of a borehole

flowmeter in wells constructed with a filter pack of gravelsized material may not provide meaningful data and generally

should be avoided. It is also possible to observe some effects

in wells with filter packs constructed of coarse-grained sand if

the hydraulic conductivity of the pack material is significantly

greater than aquifer materials. However, use of a natural

collapse well construction is not always feasible. For

example, formations with a significant fraction of fine-grained

materials or units may not be appropriate for natural collapse

construction and may result in void space within the annulus

that affects test results. Results of field applications of the

borehole flowmeter indicate that it is possible to obtain

representative flowmeter measurements in many wells

constructed using an artificial pack. In general, wells

specifically constructed for these tests should avoid use of

artificial filter packs, where possible. If an artificial pack is

used, the data should be carefully examined for evidence of

bias in the flow distribution.

Wells that are screened across the water table may be subject

to increased head loss near the pump intake. This is

particularly true for wells constructed with an artificial filter

pack that is significantly more conductive than surrounding

aquifer materials (Boman et al., 1997). This situation may

result in a nonuniform head distribution in the well and an

increased influx of water near the pump intake. Such a

situation would also bias flowmeter test results.

Presence of a low permeability skin (i.e., positive skin effect)

adjacent to the well may also significantly bias flowmeter

results by affecting the distribution of flow to the well.

Studies by Ruud and Kabala (1997) indicate that the presence

of a low permeability skin adjacent to the well may have a

much greater effect than the presence of a zone of increased

permeability. As previously noted, the bias in the flowmeter

measurements increases with increasing thickness of the

disturbed zone and increasing difference between the

permeability of the disturbed zone and the formation

materials.

These studies imply that wells should be designed and

constructed to minimize the size of disturbed zones and the

degree of disturbance. In general, formation of a higher

permeability disturbed zone would be preferable to the

presence of a lower permeability zone. The results also imply

that the minimum size of measurement intervals deserves

careful consideration in test design. Potential effects of well

design and construction on the representativeness of the data

obtained from these investigations should be carefully

considered prior to well installation. Many of these questions

are still areas for continuing research.

IV-3 Well Installation Methods

a. Overview

Drilling methods chosen for construction of test wells should

be those techniques that result in the least possible disturbance

to the formation surrounding the well and result in a minimum

annular space between the well screen and the borehole wall.

The most appropriate method will depend on site-specific

conditions. A number of references have appeared during the

past decade regarding well drilling techniques, technologies,

and related subject matter (e.g., Driscoll, 1986; Aller et al.,

1989; Harlan et al., 1989; and Moss and Moss, 1990).

b. Drilling Techniques and Hydraulic

Conductivity Estimates

There are many possible interactions between the various

drilling methods and the types of subsurface media at a

particular site. Optimum methods depend on site conditions.

In addition, the various studies that have dealt with the

interaction of well drilling and hydrogeologic measurements

have focused more on chemical measurements than on

hydraulic measurements. Prominent studies during the past

decade include Minning (1982), Barcelona and Helfrich

(1986), Hackett (1987, 1988), Keely and Boateng (1987a,b),

Paul et al. (1988), and Strauss et al. (1989).

Keely and Boateng (1987a,b) present an illuminating

discussion of various options and trade-offs when constructing

monitoring wells. Much of the following discussion is based

on those two references. Mud rotary has been a relatively

common drilling technique for water supply wells because it is

rapid, economical, and essential to the performance of certain

geophysical logs. However, the technique has the

disadvantage that the potential exists for large volumes of

drilling fluids to enter the formation resulting in formation of a

low permeability skin. Subsequent development sufficient to

remove this skin effect is usually difficult or impossible.

Improvements to this technology include driving a temporary

casing while drilling or use of dual-wall reverse circulation

drilling. In the dual-wall method, mud travels down a

cylindrical annulus that is bounded by the outer drill pipe and

an internal, rotating drill stem connected to the bit. Mud is

ejected just above the bit, picks up cuttings, and is pumped up

the inner drill stem to the surface. This technique limits

exposure of the borehole wall to drilling fluids and decreases

mud invasion into the formation.

Many of the problems associated with introduction of drilling

fluids using mud rotary techniques are also common to air

rotary methods. These problems can be minimized by driving

a temporary casing flush with the borehole wall. In fact, this

is often necessary to prevent caving of the borehole walls

when drilling in unconsolidated materials. However,

compressed air can still enter the formation, and “air binding”

is a well-known phenomenon that decreases the apparent

hydraulic conductivity of porous materials. Just as with mud
21

invasion, air invasion would be expected to be particle-size

dependent.

According to Keely and Boateng (1987a), the cable tool

method appears to have several advantages when used to

construct monitoring wells, although it is rarely used for this

purpose. In cable tool drilling, no drilling fluids are necessary.

A temporary casing is driven as the drilling proceeds. Water

may be added to the hole to aid bailing, but it is not under

pressure. Driving and removing the temporary casing may not

disturb the borehole wall significantly because there is a sharp

drive shoe at the bottom, the casing is smooth, the annular

spacing between the casing and the borehole wall is

sufficiently small that material is not dragged along with the

moving casing, and the casing is slowly moved up and down.

This method may produce a well that is exceptionally wellsuited for hydraulic conductivity and other measurements.

The hollow-stem augering method is relatively fast, does not

involve addition of drilling fluid, and formation samples may

be obtained easily during the course of drilling. A major

disadvantage, however, especially from the viewpoint of

estimating hydraulic conductivity, is that the augering process

causes wet clay and silt material to be smeared along the

borehole wall. In certain types of soils such as clayey

saprolites, the smearing and destruction of the open pore

structure of the soil can be so severe that the resulting well is

not suitable for hydraulic conductivity tests. Another potential

disadvantage is that the annular space between a well screen

installed through the hollow-stem auger and the borehole wall

can be relatively large. Thus, if one does not wish to install a

sand pack, there would be a relatively large volume into which

the surrounding formation would collapse, further disrupting

the structure of the natural formation. If collapse of cohesive

soils was not complete, channels for vertical water movement

would be formed.

Much of the available literature contains information

concerning well construction and measurements of various

types in a variety of subsurface environments. This

information is usually in the form of case histories, descriptions of problems that arose on particular projects, and the

manner in which these problems were addressed. There have

been relatively few investigations performed to study the

effects of well construction on hydraulic conductivity and

other measurements in a systematic fashion. One exception to

this is the work of Morin et al. (1988b). In this study,

epithermal neutron and natural gamma logs were used to

measure the formation disturbance caused by three different

well drilling techniques: hollow-stem augering; mud rotary;

and hammer-driven, flush-jointed, temporary casing within

which a permanent casing and screen were installed. Each

type of construction was utilized for a number of wells so that

a statistically significant set of logs could be obtained for each

method.

The study was conducted in a glacial outwash plane deposited

in a braided stream environment. The study aquifer was

composed of coarse sand and gravel in horizontal lenses and

layers with silt and clay comprising less than five percent of

the formation. This resulted in significant verticallydistributed heterogeneity that was reflected in the geophysical

logs. The basic concept of the study was to associate an

increase in formation disturbance due to well construction

with a decrease in the degree of heterogeneity (more

homogeneous appearance) observed in the well logs. Using

this criterion, the order of increasing disturbance was: driven

casing, mud rotary, and augering.

IV-4 Well Development Methods

a. Overview

Well development includes a broad spectrum of techniques,

procedures, and tools for applying some form of energy to the

well screen and adjacent formation. Historically, several

development methods that have been used following well

installation include: overpumping, backwashing, mechanical

surging, air development, and high-velocity jetting. Well

development methods such as chemical treatment, hydraulic

fracturing, and use of explosives to maximize the water yield

in production wells are not applicable to these studies.

Discussion in this text is restricted to aquifer characterization

wells and development methods that assist in restoring the

undisturbed hydraulic characteristics of aquifer formations.

Determining which development methods are most

appropriate for any given well requires an understanding of

available methods, a knowledge of the aquifer formations

present at the well location, and particulars of the well design.

In some cases, a single method might be effective for

development. However, in many instances, the use of more

than one development method will yield much better results.

Driscoll (1986), Moss and Moss (1990), and Harlan et al.

(1989) explain the mechanics of the different well

development methods.

b. Development Methods and Hydraulic

Conductivity Estimates

The literature offers little guidance on the selection of an

optimum method of well development for any particular site.

Much of the former work related to well development has

concentrated on maximizing water yield in production wells.

In general, these types of studies (National Ground Water

Association, 1989) provide evaluations of different well

drilling and development techniques based upon specific

capacity measurements. This is a measure of the reduction in

positive skin effects produced by well development.

Although the influence of skin effects on pumping tests has

long been recognized in the petroleum industry (e.g., van

Everdingen and Hurst, 1949; Hawkins, 1956) and by groundwater scientists (e.g., Moench and Hsieh, 1985), very few

studies provide comparisons of different development methods

using explicit hydrogeologic measurement techniques.

Rehfeldt et al. (1989b) provide results from experiments that

were undertaken using an impeller flowmeter to investigate

well installation and development methods on flowmeter
22

discharge profiles. The test site was a heterogeneous sand and

gravel aquifer located at the MacroDispersion Experiment

(MADE) site on the Columbus Air Force Base, Columbus,

Mississippi. One of the major objectives of the study was to

determine the most appropriate well installation and

development method that would minimally disturb the aquifer

and allow accurate estimates of hydraulic conductivity at the

test site. Wells evaluated in the experiment included a driven

steel well screen, drive-and-wash wells using compressed air,

and hollow-stem auger wells, constructed with both natural

and artificial filter packs. The wells were developed in three

stages; first by cyclic overpumping and backwashing, then

with a surge block attached to the drill rig, and finally using a

hand-drawn swab. Hydraulic conductivity profiles were

determined from impeller flowmeter measurements after each

stage of development. When hydraulic conductivity estimates

were reproducible, well development was considered

complete.

The study indicated that a large diameter (30 cm) hollow-stem

auger method of well installation was the least satisfactory of

the test methods because of the degree of disturbance

associated with auger drilling and the fact that more annular

space exists between the wellbore and screen. Although the

driven steel well screen was installed to represent a well with

no open annular space, it was substantially more expensive

than other methods because of material costs. The internal

vertical rods that support the steel screen also presented

problems with well development since the surge block and

swabbing tool could not develop a good seal along the inside

of the screen. Rehfeldt et al. (1989b) provide the following

observations based on their testing.

1. Well development caused changes in the aquifer

material adjacent to the wellbore and altered the

hydraulic conductivity profiles.

2. Overpumping and backwashing development

produced changes in the profiles of both the augered

well and the well installed using drive-and-wash

methods. Order-of-magnitude increases in hydraulic

conductivity were observed at a minimum of five

locations for the augered well, but were never that

large for the drive-and-wash well. Additionally, the

trends in the profiles after overpumping and

backwashing development were generally similar in

the drive-and-wash well but not in the augered well.

3. After swabbing, the augered well again showed

significant differences in the profiles, although less

than for the first two development cycles. The profile

for the drive-and-wash well after swabbing was

relatively consistent.

4. The profile for the driven steel screen generally had

lower values than the profile for both the augered and

drive-and-wash wells. The lower hydraulic

conductivity values may have been partly caused by

compressed aquifer material near the well, the

adherence of fine-grained material to the well screen,

or incomplete development of the well.
23

Chapter V

Field Studies of Well Construction and

Development at Columbus, Mississippi

V-1 Description of Test Site

a. Site Location

The test site occupies one of twenty-five hectares (Ha) in the

northeastern corner of Columbus Air Force Base (CAFB),

Columbus, Mississippi, leased from the U.S. Air Force for the

MacroDispersion Experiment (MADE). The site is

approximately 6 km east of the Tombigbee River and 2.5 km

south of the Buttahatchee River, and lies above the 100-yr

floodplain of both rivers. The site is situated on the youngest

terrace deposits associated with the Buttahatchee River.

b. Aquifer Characteristics

Young (1991b) describes the Columbus Aquifer as being

composed of approximately 10 m of Pleistocene and Holocene

fluvial deposits. The aquifer overlies the Eutaw formation that

consists primarily of marine clay and serves as an aquitard. In

addition to numerous samples from boreholes, a geological

investigation of the aquifer included mapped geological facies

at a gravel pit and an aerial photography survey that indicated

an abandoned river meander crossing the northern region of

the 1-Ha test site and passing through the middle of the

MADE test site (Figure V-1).

The aquifer at the site is composed of poorly-sorted to wellsorted sandy gravel and gravelly sand with minor amounts of

silt and clay. Sediments are generally unconsolidated and

cohesionless below the water table. The upper portion of the

aquifer is generally composed of coarse-grained sediments and

bar deposits from a meandering river system (Kaye, 1955;

Rehfeldt et al., 1989b). The abrupt changes in vertical

sequences and coarse texture suggest that the pointbar

sediments were deposited during catastrophic flooding events.

Chute bars and channels with clay drapes were also deposited

during flood stage. Such events result in an uneven sand

distribution and a seemingly chaotic occurrence of gravel

lenses and clay drapes (Collinson and Thompson, 1989).

The lower portion of the aquifer is composed of sediments

from a braided river system. This model implies an irregular

pattern of coarse gravelly lenses deposited as longitudinal and

transverse bars at high flow stage, alternating laterally and

vertically with finer sand and silt deposited in channels at low

flow stage. As these depositional bodies were formed by

short-lived branching and rejoining shallow channels, and

subsequent partial truncation by secondary stream channels,

a large range of shapes and sizes exist for the depositional

bodies. The shapes might best be described as irregular

tongues, shoestrings, wedges, and pods.

c. Previous Pumping Tests

A series of single-well pumping tests, slug tests, and

electromagnetic borehole flowmeter tests were conducted at

the original thirty-seven wells located across the 1-Ha test site.

The results of these tests indicate that a zone of interconnected

high-K deposits exists at elevations of 59 m to 62 m above

mean sea level (AMSL) within boundaries mapped by the

former meander shown in Figure V-1. These results also

indicated that positive (low-K) skin effects exist at most, if not

all, of the wells. Young (1991a,b) provides an analysis of the

pumping test data using the Cooper-Jacob equation and the

Cooper-Jacob Straight-Line (CJSL) method (Cooper and

Jacob, 1946). The analysis indicates that the two approaches

provide significantly different transmissivity values.

Considering that poorly-sorted coarse-grain sediments often

lie adjacent to well-sorted fine-grain sediments, and that

highly permeable lenses can dominate ground-water flow at

Columbus, significant skin effects were considered probable.

The following are potential causes of positive skin effects:

Figure V-1. Ox bow meander at the Columbus AFB site drawn

from a 1956 aerial photograph.
24

(1) smearing of silt and clay particles into and across highpermeability zones; (2) compaction of aquifer material by

methods that include advancement of a protective casing; and

(3) alignment of blank (i.e., nonslotted) sections of well casing

with aquifer zones of high permeability.

d. Monitoring Well Installation

For the purposes of this study, two clusters of three wells each

were added to an existing network of thirty-seven wells at the

1-Ha test site (Figure V-2). The drilling and development

methods used to install the first thirty-seven wells at the 1-Ha

test site are described by Young (1991a). The six new wells

are numbered 38 through 43. The well clusters were

configured as equilateral triangles with individual wells being

separated by distances of two meters so that aquifer

conditions near each well would be similar. The two well

clusters are separated by a distance of about 60 m. Well

cluster 38-39-40 resides on the southern side of the 1-Ha test

site within possible pointbar deposits in the upper aquifer and

possible braided river deposits in the lower aquifer. Well

cluster 41-42-43 is located in the northern portion of the test

site, within possible channel sediments from a meandering

river system and with possible channel sediments at depth

from a braided river system.

Each well is approximately 11 m deep and consists of 5.1-cm

(inside diameter), schedule-40 PVC casing and screen (Figure

V-3). The screen for each well is 9.14 m in length and

machine-slotted with 0.25-mm slots spaced at 3.18-mm

intervals. The following three drilling methods were used for

wells at each well cluster:

1. 19.4-cm hollow-stem auger - natural filter pack

2. 27.0-cm hollow-stem auger - artificial filter pack

3. 11.4-cm drive-and-wash - natural filter pack

Wells 39 and 43 were installed using a 19.4-cm (outside

diameter) hollow-stem auger. The aquifer material was

allowed to collapse around the screen and casing, and auger

cuttings were used to backfill approximately the top two

meters of borehole. Wells 38 and 41 were installed using a 27-

cm (outside diameter) hollow-stem auger with artificial filter

packs. The filter pack was comprised of 1.6 mm to 3.2 mm,

subangular to angular, quartz sand. A disadvantage of the

larger auger is the size of the annulus created.

Wells 40 and 42 were installed using a modified rotary wash

method. The method involved driving an 11.4-cm steel outercasing ahead of the rotary bit and then washing the cuttings

out of the casing with water. The well screen and casing were

lowered into place, and the outer steel casing was removed

allowing formation material to collapse around the well. The

modification minimizes both the wash into undisturbed aquifer

sediments and the amount of formation material removed.

In unconsolidated aquifer materials, the driving of casing

generally creates a region of compacted aquifer material

around the casing. Pulling the outside casing and allowing

aquifer material to collapse on the inner well screen and

casing may relieve this compression. Based upon studies by

Figure V-2. Well network at the 1-Ha test site.

10 20 30 40 50 60 70 80 90 100 110

10

20

30

40

50

60

70

80

90

100

110

1

2

3

4

5

6

7

8

9

10

11

12

13

14 15 16

17

18 19

20

21

22

23

24 25

26

27

28

29

30

31

32

33

34

35

36

37

Meters

40 39

38 2 meters

41

43 42

2 meters

2 meters

Well 38 - Artificial Pack

Well 39 - Auger Hole

Well 40 - Rotary Wash

Well 41 - Artificial Pack

Well 42 - Rotary Wash

Well 43 - Auger Hole

Well Locations

Meters
25

Rehfeldt et al. (1989a) at CAFB, this was expected to be the

preferred method of installation as the extent of aquifer

disturbance is much less than in auger drilling. The annular

space surrounding the well into which the aquifer material

must collapse is also effectively reduced from about 6.7 cm

for small (19.4-cm) diameter auger wells to 2.7 cm for the

driven wells. Hence, the in-situ hydraulic conductivity

estimated from a well installed by drive-and-wash methods is

more likely to be representative of the true aquifer hydraulic

conductivity.

V-2 Test Descriptions

This study consisted of a series of single-well pumping tests

conducted at six wells. Between pumping tests, additional

well development was performed. During each pumping test,

drawdown and electromagnetic flowmeter data were collected.

Testing at each of the two well clusters was conducted

concurrently using two teams outfitted with flowmeters,

pressure transducers, data loggers, lap-top computers, and

other equipment required for monitoring and testing. The

flowmeters were calibrated against known flows prior to, and

after, their use in the field. Both 1.27-cm and 2.54-cm (orifice

diameters) electromagnetic flowmeters were used during

testing.

The procedure for sequential development and testing of the

monitoring wells consisted of the following steps:

1. Ambient flowmeter tests were conducted at each

well.

2. Pumping tests and flowmeter tests were

performed.

3. Wells were developed according to prescribed

methods.

4. Retesting and development sequence was completed

for three development cycles.

5. Injection tests and high-rate pumping tests were

performed.

Ambient flowmeter tests were conducted to measure natural

(background) ground-water flow within each well. The type

of well installed, the aquifer formations present, and the

degree of formation damage from drilling have differing

effects on ambient flows. Ambient measurements were taken

at 30.5-cm increments beginning at the bottom of the well and

advancing upwards until the water table was reached. The

ambient measurements were taken after the test wells had

sufficient time to return to a quiescent state from development

activities and pumping tests, which was usually overnight.

Single-well pumping tests and borehole flowmeter tests were

completed at each well following ambient flowmeter testing.

Discharge measurements were made several times during each

test. The flowmeters were used to obtain a profile of the flow

distribution after a steady flow field was achieved in the

vicinity of the well, which generally occurred after 20 min to

Figure V-3. Design of wells used to evaluate the effect of well development on flowmeter tests.

Threaded

Joints

Borehole by

10.8-cm ID,

19.4-cm OD

Hollow Stem

Auger

5.1-cm

Schedule-40

PVC Slotted

Screen,

.25mm Slots

Solid Casing

Non-Shrink

Cap Grout

(b)

WELLS 39 & 43

Bottom Cap

Screen

9.14m(30 ft)

Screen

9.14m(30 ft)

2.3m (43)2.1m (40)2.3m (42)

Solid

Solid

2.7m (38)2.5m (41)2.6m (39)

Threaded

Joints

Borehole by

11.4-cm OD

Casing and

Rotary Wash

5.1-cm

Schedule-40

PVC Slotted

Screen,

.25mm Slots

Solid Casing

Non-Shrink

Cap Grout

(c)

WELLS 40 & 42

ROTARY WASH

Bottom Cap

(NOT TO SCALE)

Threaded

Joints

5.1-cm

Schedule-40

PVC Slotted

Screen,

.25mm Slots

Solid Casing

Non-Shrink

Cap Grout

(a)

WELLS 38 & 41

ARTIFICIAL FILTER PACK

Bottom Cap

Borehole by

15.9-cm ID,

27-cm OD

Hollow Stem

Auger

Artificial

Filter

Pack
26

30 min of pumping. Flowmeter readings were obtained at

30.5-cm increments as in ambient testing. Flow distribution

profiles were compared in the field after progressive well

development. Test wells were allowed to fully recover before

proceeding with each stage of development, usually overnight.

A total of six pumping and flowmeter tests were completed for

each well (Table V-1). The first four tests were conducted

prior to and after each development cycle. The last two tests

were injection and high-rate pumping tests. The first method

used for well development was overpumping and

backwashing. Initially, the well was pumped until the water

began to clear. Development was then completed by pumping

water through a discharge hose several feet above the top of

the well, and then allowing it to flow back through the pump

and out through the well screen. Water was occasionally

discharged to remove the fine-grained materials. Several

pumping cycles were completed until the discharge was clear.

The second development consisted of a modified swabbing

method that was alternated with overpumping and

backwashing. This method is similar to the procedure used

by Rehfeldt et al. (1989b). A section of galvanized pipe was

added to weight the swab and increase its rate of fall. The

swab and galvanized pipe had a combined weight of over 2.9

kg. Beginning at the bottom of the well, the swab was

manually raised with force over a 1-meter increment of the

well screen and then allowed to fall back to its original

position to provide a surging action. This swabbing

movement was repeated for a total of four repetitions, until

the water table was reached. Water was then pumped to

remove fines liberated during development and overpumping/

backwashing was conducted. The entire cycle was repeated

using three swabbing repetitions. The third and final

development was a reiteration of the alternating modified

swabbing and overpump/backwash method that was identical

to that used in the second development.

V-3 Test Analyses and Results

a. Ambient Flow Distributions

Ambient flow measurements collected after each successive

phase of well development (Figure V-4) varied from -0.34 L/

min to 0.04 L/min for well cluster 38-39-40, and from -0.06 L/

min to 0.29 L/min for well cluster 41-42-43. The sign

convention is positive for upward flow and negative for

downward flow. The initial development, if properly

conducted, should displace extraneous fines from the

wellbore. From observation of the flowmeter plots, it is

apparent that the initial development (overpumping and

backwashing in this case) is important. A relatively large

change in ambient flow is displayed after the first

development by all wells except wells 42 and 43. The

magnitude of the changes in ambient flows decrease with

ensuing stages of development. Following the first stage of

development, the changes that occur in the ambient flows also

vary according to well type and differences in aquifer

materials. The modified rotary wash wells (40 and 42) exhibit

ambient flow profiles that were essentially reproducible after

the first stage of development.

The ambient flow profiles for the wells constructed with an

artificial filter pack (38 and 41) show differing responses after

the second and third development (Figure V-4). The ambient

Table V-1. Testing Sequence

Test

No. Test Type Development Cycle Development Method

1 Ambient Borehole Flowmeter (BHFM) Tests Pre-development None

Constant Discharge Pumping Tests

BHFM Tests During Pumping

2 Ambient BHFM Tests After 1st development Overpump/Backwash (15 minutes)

Constant Discharge Pumping Tests

BHFM Tests During Pumping

3 Ambient BHFM Tests After 2nd development Alternating Modified Swabbing and

Constant Discharge Pumping Tests Overpump/Backwash (60 minutes)

BHFM Tests During Pumping

4 Ambient BHFM Tests After 3rd development Alternating Modified Swabbing and

Constant Discharge Pumping Tests Overpump/Backwash (60 minutes)

BHFM Tests During Pumping

5 Ambient BHFM Tests Development complete None

Constant-Rate Injection Tests

BHFM Tests During Injection

6 Ambient BHFM Tests Development complete None

Constant Discharge Pumping Tests

BHFM Tests During High-Rate Pumping
27

Figure V-4. Ambient flow profiles after successive well development.

WELL 38 - ARTIFICIAL FILTER PACK

-0.4 -0.3 -0.2 -0.1 0 0.1

525456586062

ELEVATION (m-msl)

WELL 39 - AUGER HOLE

-0.4 -0.3 -0.2 -0.1 0 0.1

WELL 40 - ROTA

-0.4 -0.3 -0.2 -0

WELL 41 - ARTIFICIAL FILTER PACK

-0.1 0 0.1 0.2 0.3 0.4

525456586062

FLOW (L/min)

ELEVATION (m-msl)

WELL 43 - AUGER HOLE

-0.1 0 0.1 0.2 0.3 0.4

FLOW (L/min)

WELL 42 - ROTAR

-0.1 0 0.1 0.2 

FLOW (L/min)

WELL SCREENSOLID CASING

AT JOINT

PRE-DEVELOPMENT AFTER 1st DEVELOPMENT

AFTER 2nd DEVELOPMENT AFTER 3rd DEVELOPMENT

downward flow

upward flow
28

flows at well 41 increase incrementally with diminishing

differences between development cycles. Well 38, on the

other hand, exhibits some irregularities in ambient flow

profiles. Below about 56 m, the first development of well 38

produces the highest ambient flows with succeeding

development resulting in reductions of ambient flow. Above

about 56 m, the second development of well 38 produces the

highest ambient flows with ambient flows being reduced

following the third development. These responses may simply

be due to stabilization of the filter pack or to effects of minor

temporal changes in local hydrology.

The augered wells with natural filter packs (39 and 43) display

ambient flow profiles that are quite variable (Figure V-4). For

both wells, the ambient flows measured following the second

stage of development are greater than those of the third stage of

development. The two wells also show the largest differences in

their ambient profiles between the second and third development

cycles. These results suggest that the material around the

augered wells was the most sensitive to well development.

Several shifts and peaks in the ambient flow profiles were

observed through the first two stages of well development for

both well clusters. These phenomena are attributed to

inadequate collapse and stabilization of aquifer material

around the screens for the auger hole wells, and to incomplete

grading and stabilization of aquifer and filter pack materials

for the wells with artificial filter packs. Very little deviation in

the ambient flow profiles are shown by the modified rotary

wash wells after initial development. By the third stage of

development, the shifts and peaks in all the ambient flow

profiles had decreased to the point that wellbore material was

stabilized and development was deemed complete.

Well cluster 38-39-40 shows good correlation between wells

for the final profiles of ambient flow. The profiles indicate

that most of the water is entering between about 57 m and 58

m AMSL and leaving between 54 m and 55 m AMSL, with

little ambient flow above 58 m AMSL. These two high

ambient flow zones suggest that sequences of high hydraulic

conductivity sediments may intersect the wells at these

horizons. For well cluster 41-42-43, there is less similarity

among the ambient flow plots. All three wells have upward

ambient flow but there is considerable variability in the source

and magnitude of the flow.

b. Induced Flow Distributions

The flow distributions measured under pumping conditions

(Figure V-5) represent the results from flowmeter testing during

steady-state flow conditions. The mean flow rates used for

pumping tests were 8.0 L/min and 13.4 L/min for well clusters

38-39-40 and 41-42-43, respectively. The pumping rates used

for the tests were fairly constant and had variances of only 0.015

L/min and 0.076 L/min for well clusters 38-39-40 and 41-42-43,

respectively. The cumulative flows were adjusted by taking the

net difference between the measured flows under pumping and

ambient conditions, and then normalizing the result to the

pumping rate.

The induced flow distributions for wells 41 and 43 show

changes after the initial development that are relatively large

in comparison to succeeding development cycles. The

magnitude of the changes in flow decreases incrementally

with ensuing stages of development for the well with the

artificial filter pack (well 41). Observation of the induced

flow distributions for well cluster 38-39-40 does not indicate a

large change in the profiles of wells 38 and 40 between preand initial development. The greatest change in the flow

profiles for these two wells occurs after the second

development, indicating that the modified swabbing method

was necessary to effectively develop the wells. The induced

flow profiles for well 39 indicate that it is experiencing a

moderate degree of formation stabilization during later stages

of development.

c. Specific Capacity Values

Drawdown data (Figure V-6) were used to calculate specific

capacity (Figure V-7) for each well based on the drawdown

responses at 1500 s after initiation of extraction. In general,

the greatest increases in specific capacity occur after the initial

development. Except for well 41, specific capacity values

stabilized after the second development. Well 41 has an

artificial filter pack and is located in a region where highly

transmissive aquifer zones exist near the top of the well

screen. The different response at well 41 may be caused by

spatial variability within the aquifer and the possible

intersection of a highly permeable lens that is not

interconnected with the neighboring wells.

d. Transmissivity Values

The single-well test drawdown curves (Figure V-6) were

analyzed using the Cooper-Jacob straight line (CJSL) method

(Cooper and Jacob, 1946) to calculate transmissivity. The

semilog plots of drawdown data are characterized by an early

slope that is about five to twenty-five times steeper than the

late slope (after 100 s). For comparison purposes,

transmissivities were calculated for both early and late times.

Typically, the late-time portion of the curve used for the CJSL

analysis began between 100 s and 300 s and ended between

900 s and 1,000 s. Late-time average transmissivities were

calculated using the data from all four pumping tests at each

cluster. The average transmissivities for well clusters 38-39-

40 and 41-42-43 are 19.8 cm2/s and 34.0 cm2/s, respectively.

At every well, the ratio of the transmissivity after each well

development to the average transmissivity were within a factor

of two. The results indicate increases and decreases in

transmissivity with additional well development. However, no

consistent trends are evident in the data. It is possible that the

changes in the calculated transmissivity values were caused

more by the differences in the testing and analyses procedures

than the aquifer conditions. In order to minimize recovery

time between pumping tests, low pumping rates were used.

As a result, trends in the drawdown curves are difficult to

define because the aquifer was not adequately stressed.

The CJSL analysis for the early-time portion of the semilog

drawdown curves typically began near 20 s and ended at about
29

Figure V-5. Induced flow profiles after successive well development.

WELL 38 - ARTIFICIAL FILTER PACK

ELEVATION (m-msl)

WELL 39 - AUGER HOLE WELL 40 - RO

WELL 41 - ARTIFICIAL FILTER PACK

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

NORMALIZED FLOW

ELEVATION (m-msl)

WELL 43 - AUGER HOLE

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

NORMALIZED FLOW

WELL 42 - RO

0 0.1 0.2 0.3 0.4 0.5 

NORMALIZE

525456586062

525456586062

WELL SCREEN

SOLID CASING

AT JOINT

PRE-DEVELOPMENT AFTER 1st DEVELOPMENT

AFTER 2nd DEVELOPMENT AFTER 3rd DEVELOPMENT
30

Figure V-6. Effect of well development on the drawdown values for pumping tests at the 38-39-40 well cluster.

PUMPED WELL

PUMPED WELL

OBSERVATION WELL

DRAWDOWN (m)

TIME (seconds)

Q = 8.0 L/min

TIME (seconds) TIME (seconds)

Q = 7.7 L/min

TIME (seconds)

Q = 8.3

L/min

WELL 39 - AUGER HOLE

Q = 7.8 L/min

WELL 39

OBSERVATION WELL

WELL 38 WELL 40

0

0.1

0.2

0.3

0.4

1 2 10 20 100 200 1,000 1 2 10 20 100 200 1,000 1 2 10 20 100 200 1,000 1 2 10 20 100 200 1,000

DRAWDOWN (m)

TIME (seconds)

Q = 8.1 L/min

TIME (seconds) TIME (seconds) TIME (seconds)

Q = 8.3 L/min

WELL 38 - ARTIFICIAL FILTER PACK

Q = 7.8 L/min

PUMPED WELL

WELL 38 WELL 39 WELL 40

1 2 10 20 100 200 1,000 0

0.1

0.2

0.3

1 2 10 20 100 200 1,000 1 2 10 20 100 200 1,000 1 2 10 20 100 200 1,000

Q = 7.8 L/min

PRE-DEVELOPMENT AFTER FIRST

DEVELOPMENT

AFTER SECOND

DEVELOPMENT

AFTER THIRD

DEVELOPMENT

DRAWDOWN (m)

TIME (seconds)

Q = 8.1 L/min

TIME (seconds) TIME (seconds) TIME (seconds)

Q = 8.3 L/min

WELL 40 - ROTARY WASH

Q = 7.8 L/min

WELL 40

OBSERVATION WELL

WELL 38 WELL 39

0

0.1

0.2

0.3

1 2 10 20 100 200 1,000 1 2 10 20 100 200 1,000 1 2 10 20 100 200 1,000 1 2 10 20 100 200 1,000

Q = 7.8 L/min

PRE-DEVELOPMENT AFTER FIRST

DEVELOPMENT

AFTER SECOND

DEVELOPMENT

AFTER THIRD

DEVELOPMENT

PREDEVELOPMENT

AFTER FIRST

DEVELOPMENT

AFTER SECOND

DEVELOPMENT

AFTER THIRD

DEVELOPMENT
31

Figure V-7. Comparison of specific capacities at different wells.

80 s. Values of early-time transmissivity (Figure V-8, Table

V-2) only increased with successive well development. These

increases are interpreted as reductions in positive skin effects.

There are no similarities evident for early-time transmissivity

increases among wells of a particular construction type.

However, well cluster 38-39-40 exhibits increases in earlytime transmissivity values that are up to an order-of-magnitude

less than estimates for well cluster 41-42-43. This appears to

be a reflection of the low transmissivity region in which

cluster 38-39-40 resides. The geometric means for early-time

transmissivity values were 1.6 cm2/s and 3.2 cm2/s for well

clusters 38-39-40 and 41-42-43, respectively. These averages

are approximately ten times lower than the transmissivity

values measured at late times, and are in good agreement with

that of 3.6 cm2/s calculated by Young (1991a,b) for early-time

slopes from fifty-seven single-well pumping tests and thirtyone slug tests at the 1-Ha test site.

V-4. Summary

A series of flowmeter tests were conducted at Columbus Air

Force Base to investigate the effects of well construction and

development methods on flow distributions and drawdown

responses in a highly heterogeneous aquifer. Two well

clusters were installed 60 m apart. Each well cluster included

three 5.1-cm diameter PVC wells installed using different

drilling techniques. The three installation techniques included

a modified rotary wash method, a 19.4-cm hollow-stem auger

method, and a 27.0-cm hollow-stem auger method using an

artificial filter pack in well construction. Differences in localscale geohydrology are immediately apparent from

observation of the ambient flow profiles. At one well cluster,

all three wells exhibit only downward ambient flow. At the

other well cluster, upward ambient flow was measured.

The test results show that well development has a significant

impact on increasing the magnitude of ambient flows. At

several vertical zones, the directions of ambient flow changed

because of well development. The artificial filter packed and

rotary wash wells displayed the greatest changes in ambient

flow profiles following initial well development by

overpumping and backwashing. The largest changes for the

augered wells with a natural filter pack occurred after the

second well development, which included swabbing with a

surge block accompanied by overpumping and backwashing.

Among the ambient flow profiles, those from the rotary wash

wells had the least sensitivity to well development beyond the

initial development. At the two rotary wash wells, the ambient

flow profiles stabilized after the initial well development. At

the “19.4-cm augered” wells and one of the augered wells with

an artificial filter pack, the ambient profile patterns remained

similar after the initial well development, but the magnitude of

the flow rates differed. The data clearly indicate that some

type of well development is necessary to obtain useful

flowmeter data for ambient conditions, and suggests that the

amount and method of well development depends on the well

type and aquifer properties.

3

3.5

4

4.5

5

5.5

6

1234 2

4

6

8

10

12

14

16

Well 43-Auger Hole

Well 42-Rotary Wash

Well 41-Artificial Filter Pack

Pumping Test Number

Well 40-Rotary Wash

Well 39-Auger Hole

Well 38-Artificial Filter Pack

Specific Capacity @ 1500 S (cm2/s)
32

Figure V-8. Calculated transmissivities using early time data.

The flowmeter results for pumping conditions produced

conclusions similar to those obtained for the ambient flow

conditions. However, two differences were observed. The

first difference was a convergence to a stabilized flow profile

for all of the well types. The second was the effect of the well

cluster locations on the relative differences among the flow

profiles. One well cluster displayed the greatest flow profile

changes between the “pre-development” and “1st

development.” The other well cluster showed the greatest

differences between profiles for “1st development” and the

“2nd development.”

At several elevations in the “pre-development” profiles, a

decrease in net differential flow occurred with increasing

elevation. For this decrease to occur, vertical flow established

Table V-2. Early-Time CJSL Transmissivity Values

Initial T Final T Percent

Well No. (cm2/s) (cm2/s) Increase

38 1.2 1.7 42

39 1.7 2.1 25

40 1.6 1.9 18

41 3.8 8.8 129

42 1.4 4.9 242

43 0.9 5.6 494

within the well must temporarily exit the well. This might

occur near regions where voids existed in the well annulus

and/or the flowmeter caused significant blockage of incoming

flow. The flow bypass problem can be lessened by creating a

more uniform packing in the well annulus. In subsequent tests

after well development, the frequency and magnitude of the

flow bypass problems were greatly reduced.

For each flowmeter test, the drawdown data in the pumped

well were analyzed using the CJSL method to estimate

transmissivity. Typically, the drawdown response was

characterized by a linear slope at early times (<50 s) that was

about five to twenty-five times steeper than the late slope

(after 100 s). The early slope values are reflective of the

disturbed aquifer material near the well. The late-time values

better represent undisturbed aquifer material at radial distances

further away from the well. The CJSL analysis shows that the

transmissivity values calculated at early times only increased

with additional well development. Although positive skin

effects were not eliminated, these results indicate that the

effects were significantly reduced.

1

1.2

1.4

1.6

1.8

2

2.2

1 234 0

2

4

6

8

10

Well 40-Rotary Wash

Well 39-Auger Hole

Well 38-Artificial

 Filter Pack

Well 43-Auger Hole

Well 42-Rotary Wash

Well 41-Artificial Filter Pack

Pumping Test Number

Early-Time Transmissivity Values (cm2/s)
33

Chapter VI

Field Studies of Well Construction and

Development at Mobile, Alabama

VI-1 Description of Test Site

a. Site Location

The well field is located at the Barry Steam Plant, which is

owned and operated by the Alabama Power Company.

Geographically, it is approximately 32 km north of Mobile,

Alabama.

b. Aquifer Characteristics

The surface is composed of a low terrace deposit of

Quaternary age consisting of interbedded sands and clays that

have, in geologic time, been recently deposited along the

western edge of the Mobile River. The sand and clay deposits

(Figure VI-1) extend to a depth of 61 m where the contact

between the Quaternary and Tertiary formations is located.

Below the contact are deposits of the Miocene series that

consist of undifferentiated sands, silty clays, and thin-bedded

limestones extending to an approximate depth of 305 m.

The shallow subsurface consists of fluvial sediments with a

confined aquifer in the bottom 20 m of the Quaternary

sediments. The aquifer is confined above and below by clay

bearing strata that extend laterally for several thousands of

meters or more. The upper confining layer is located about

40 m deep, and the thickness of the aquifer is relatively

constant at about 20 m. The piezometric surface for the

confined aquifer ranges from land surface elevation to two or

three meters below land surface depending on seasonal and

climatic conditions. In general, the confined aquifer matrix may

be described as a medium sand with silt and clay fractions

ranging from one percent to fifteen percent by weight.

c. Well Installation

Four observation wells at the Mobile test site were designed to

provide two distinct environments for construction and

development studies. Two of the wells (Figure VI-2) were

deep wells and were installed to depths of 60 m, with fullypenetrating screens in the confined zone between 40 m and

60 m. The other two wells were shallow wells drilled in the

Figure VI-1. Vertical cross-sectional illustration of the subsurface hydrologic system at the Mobile site.
34

Figure VI-2. Schematic diagram providing the details of the shallow and deep wells constructed at the Mobile site. Well casing and well

screen are the same dimension and schedule. The only difference is the depth dimensions of the casing and screen.

sand, gravel, and clay strata (Figure VI-1) to a depth of 30 m

and screened between 4.5 m and 30 m. The layout of the

wells is in a 10 m x10 m square arrangement with a well

positioned at each corner. The designations for the wells are A

and B for the shallow wells, and C and D for the deep wells.

During construction, a portion of the installed casing of well D

was fractured allowing sediment to enter the well. Thus, well

D was then considered non-functional and removed from the

study. All wells were installed using the direct circulation

rotary drilling method. The shallow wells were drilled to

accommodate a 15.2-cm schedule-40 PVC casing from ground

surface to an approximate depth of 4.5 meters. The casing

was sealed in place by cement grout and left undisturbed for

12 hours. Following the 12-hour period, the well was drilled

to its final depth (30 m) to receive a 10.2-cm slotted schedule40 PVC screen. No artificial filter pack material was used in

the construction of these wells. A 3-m section of 10.2-cm

PVC pipe was attached to the screen and extended upward

approximately 3 m from the bottom of the casing. The annular

space between the pipe and the 15.2-cm casing was closed by

a packer. The deep well was constructed in the same manner

using the same size casing and screen. After completion, each

well was developed by forcing air into the casing to agitate,

surge, and lift the water; mildly cleaning the well of drilling

fluid, cuttings, and fines.

VI-2 Test Description

The direct rotary drilling method used a mud slurry as a

drilling fluid during the construction operation. Site

conditions necessitated use of this method. However, the mud

cake has a deleterious effect on the production capacity of the

well due to its very low hydraulic conductivity. Development

was necessary to remove the mud cake to the extent practical.

In this study, air development was used to surge compressed

air into the casing of each well for approximately fifteen

minutes. The key question, of course, was how much

development was necessary to remove the mud without

affecting the hydraulic properties of the aquifer materials

outside the well? This was the main question studied in the

field tests reported below.

The series of testing performed on wells A, B, and C were

identical with a few exceptions and consisted of four sets of

tests (Table VI-1). The first set consisted of an ambient flow

test and a pump-induced flow test which occurred before any

well development. The second, third, and fourth sets were

identical in procedure; air development, followed by an

ambient flow test, followed by a pump-induced flow test.

Some pump-induced flow tests were repeated following an

overnight rest period (without a repeat of the air development)

2.5-cm minimum

grout envelope

End Cap

10.2-cm schedule 40

slotted PVC screen

Surface

Packer

15.2-cm ID PVC casing

(Schedule 40)

1.5 m

Deep = 40 m Deep = 20 m

Shallow = 26 m

3 m

Shallow = 4.5 m

Well
35

to determine if the results were repeatable. The ambient and

pump-induced flow tests were conducted in the same manner

as far as flowmeter position was concerned. The

electromagnetic flowmeter was lowered to the bottom of the

borehole where the first measurement (zero reference) was

taken. Subsequent flow measurements were recorded as the

flowmeter was raised at 1.52-m increments until reaching the

top of the screen. The pump-induced flow was maintained at a

constant rate and averaged about 34 L/min for all tests.

VI-3 Test Results

a. Shallow Well A

Well A served as the standard for measurement procedures at

the remaining wells. Due to the experimental function of this

well, ambient testing was not performed until after the second

development. Pumping tests were completed from the predeveloped stage through the three stages of development. Net

flow and ambient flow plots (Figure VI-3), as well as

differential net flow charts (Figure VI-4) of the flow

distribution following the second and third developments, are

presented to illustrate the effects of a third air-development.

The ambient flow curve shown (Figure VI-3a) indicates that

either the natural vertical flow has been altered somewhat by

applying a third development, or the hydraulic conditions

causing the ambient flow have changed. The natural flow has

decreased by varying amounts at every measurement point

except the uppermost point, and the greater shifts occur

between depths of 15 m and 27 m. For example, at a depth of

18.3 m the ambient flow after the second development was 3.6

L/min, and at the same depth, after the third development it

was 2.9 L/min, an eighteen percent drop. It is possible that

variable hydraulic stresses on the aquifer resulted in the shifts

rather than changes in well development. Several chemical

processing plants and an electrical power plant, some of which

place huge water withdrawal demands on the aquifer, are

located within a 5-km radius of the testing site.

The net flow plot (Figure VI-3b) shows the pump-induced

flow data that have been corrected for the ambient flow

measurements. Both data plots begin at 27.4 m with nearly

the same nominal flow, and increase in tandem to about 15 m.

At this point, the plots indicate that at least some variable

development has occurred between depths of 6 m and 14 m.

The 4.2 L/min flow variation at 9.1 m is a seventeen percent

increase, but there is no clear evidence of its cause. This shift

Table VI-1. Pump-Induced Flow and Ambient Flow Tests Performed on Wells A, B, and C

Ambient Flow Tests Well A Well B Well C

Pre-development — X X

1st Development — X X

2nd Development X X X

3rd Development X X X

Pump-Induced Flow Tests

Pre-development X X —

1st Development X X X

2nd Development X X X

3rd Development X X X

Repeat Tests (Overnight)

Ambient Flow Test

1st Development — X —

Pump-Induced Flow Tests

1st Development — — X

2nd Development X — —
36

again may be attributable to external stresses placed on the

aquifer.

The differential net flow (DNF) logs (Figures VI-4) provide a

picture of successive development effects. Each bar

represents the amount of water released from the aquifer and

entering a segment of the screen. Adding the flow of each

segment should equal the net flow at the uppermost

measurement station. The screened segment in this case is the

length of the measurement interval. It is important to note that

a comparison of DNF charts at different stages of development

can be made only when the induced pumping rate Qp is

common among the tests.

Presumably, one would like to see a “shift and hold” pattern

occurring after the first or second development. Shown in

Figures VI-4a and 4b are the DNF measurements taken after

the second development for two time periods. There is not a

great deal of similarity in the two charts which indicates that

the well needs further development to stabilize, or there is

interference caused by stresses other than those produced by

the pumping test. In comparing the results of the second

development with the results obtained after the third development, there appears to be significant correlation. The upper

and lower segments have relatively low DNF with the bulk of

the DNF between 6.1 m and 21 m.

b. Shallow Well B

Well B is a shallow well having the same dimensions and

construction as well A and is located approximately 10 m

away. Each of the test series (pre-development through third

development) was performed on this well for ambient and

pump-induced flow. In addition, an ambient flow test after the

first development was repeated after an overnight waiting

period. The ambient flow data (Figure VI-5a) shows shifts in

the flow profile after successive developments. In measurements obtained prior to development, the ambient flows are

downward in the extreme lower and extreme upper sections of

the screen, and upward elsewhere. After the first development, the downward flows disappear except for the extreme

upward measurement point after the third development.

Noteworthy at this point are the relatively high ambient flows

in the mid-range of the screen when compared to the pumpinduced flow rate of 34 L/min. For example, after the third

development a measurement taken at a depth of 20 m

recorded a 7 L/min ambient flow; this is about twenty percent

of the pumping rate during the pump-induced flow test. The

“shift and hold” pattern is quite evident in the measurements

taken after the first and second development. Although a

further increase in ambient flow is observed after the third

development, this finding is not unusual considering the

aquifer character and the sensitivity of ambient flow to

external stresses. However, the cause of the large shift after

the third development is not certain.

The net flow curves (Figure VI-5b) indicate that successive

developments had a measurable effect on the well. Each

successive development showed slight decreases in net flows

while maintaining the profile. The net flow curves correlate well

with the ambient flow curves in that there were little changes in

the upper and lower segments of the screen, and much larger

Figure VI-3. (Well A) (a) Ambient flow as measured by the EM flowmeter and (b) net flow (total flow - ambient flow). Data sets were

obtained after the 2nd and 3rd developments.

0

-5

-10

-15

-20

-25

-30

0.0 1.0 2.0 3.0 4.0

2nd Development

3rd Development

Ambient Flow (L/min)

(a)

Depth (m)

0

-5

-10

-15

-20

-25

-30

0.0 10.0 20.0 30.0 40.0

2nd Development

3rd Development

Net Flow (L/min)

(b)

Depth (m)
37

Figure VI-4. (Well A) Differential net flow (a) obtained after 2nd development, (b) obtained after 2nd development and an overnight

waiting period, and (c) obtained after 3rd development.

-4.6

-6.1

-9.1

-12

-15

-18

-21

-24

-27

02468

Differential Net Flow (L/min)

Elevation (m)

2nd Development

(a)

-4.6

-6.1

-9.1

-12

-15

-18

-21

-24

-27

02468

Differential Net Flow (L/min)

Elevation (m)

2nd Development (overnight)

(b)

-4.6

-6.1

-9.1

-12

-15

-18

-21

-24

-27

02468

Differential Net Flow (L/min)

Elevation (m)

3rd Development

(c)
38

changes at the mid-screen level. It appears that for well B,

ambient flow varied more than net flow, as seen between predevelopment, first development, and third development.

The largest differences in the distribution of DNF (Figure

VI-6) occur between pre-development and first development,

while only minor differences occur after subsequent

developments. In addition, the large shift in ambient flow

occurring after the third development is not obvious in the

corresponding DNF chart. This result supports the conclusion

that the ambient flow variations must be removed from the

total flows to obtain consistent results. Since DNF reflects the

flow entering a screen segment due to pumping, it is logical

that pump-induced flow would be less responsive to

development than ambient flow.

For well B, an additional test was performed after the first

development to determine the effects of an overnight time

period on the ambient flows. No additional development was

performed between these tests. The results (Figure VI-7) are

quite similar to those obtained the previous day.

c. Deep Well C

The ambient flow in the confined aquifer screened by well C

would be expected to be much smaller than those in the

unconfined or semi-confined sediments above. It is known

also that local industries placed less external demand on this

aquifer than the shallow aquifers. The maximum ambient

flow (Figure VI-8a) was about 1.75 L/min and was recorded

prior to the first development. This flow is in contrast to 7 L/

min recorded as maximum ambient flow in shallow well B.

Development of well C resulted in irregular shifts of the ambient

flows, and the tendency was toward the aquifer having no natural

vertical flows. This result is clearly seen in the measurement

taken after the third development where the majority of ambient

flows are less than approximately 0.5 L/min.

Variability in the net flow curves following the first, second,

and third developments is generally small throughout the

range of measurements (Figure VI-8b). It appears that most

development took place in the upper three measurement

stations, which corresponds to the same area where the larger

shifts in the ambient flow occur.

The DNF profiles for well C are shown in Figure VI-9.

Although the pumping test data before the first development

were not available, the relevant sequential test data following

that stage are presented. A moderate change in the profile is

observed through the progression of developments. Some of

the flow in the upper half of the confined aquifer has shifted to

the bottom half, though most of the flow still remains in the

upper portion. The DNF chart displaying the pump-induced

flow test after an overnight period has the same general

distribution as the first development pump-induced flow test

performed the previous day.

Figure VI-5. (Well B) (a) Ambient flow as measured by the EM flowmeter and (b) net flow (total flow - ambient flow). Data sets were

obtained prior to development and after 1st, 2nd, and 3rd developments.

0

-5

-10

-15

-20

-25

-30

-35

-1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0

Pre-Development

1st Development

2nd Development

3rd Development

Depth (m)

Ambient Flow (L/min)

(a)

0

-5

-10

-15

-20

-25

-30

0.0 10.0 20.0 30.0 40.0

Depth (m)

Net Flow (L/min)

(b)

Pre-Development

1st Development

2nd Development

3rd Development
39

Figure VI-6. (Well B) Differential net flow obtained (a) prior to development, (b) after 1st development, (c) after 2nd development, and (d) after 3

-4.6-7.6

-11-14-17-20-23-26-29

01 3 6

Differential Net Flow (L/min)

Elevation (m)

Pre-Development

(a)

2 45

-4.6-7.6

-11-14-17-20-23-26-29

01 3 

Differential Net Flow (L/

Elevation (m)

1st Developmen

(b)

2 

-4.6-7.6

-11-14-17-20-23-26-29

01 3 6

Differential Net Flow (L/min)

Elevation (m)

2nd Development

(c)

2 45

-4.6-7.6

-11-14-17-20-23-26-29

01 3 

Differential Net Flow (L/m

Elevation (m)

3rd Developmen

(d)

2 
40

Figure VI-7. (Well B) Ambient flow obtained after the first

development and repeated after an overnight

period.

VI-4 Summary and Discussion

As noted earlier, the key question is how much development is

necessary to return disturbed porous media surrounding a well

to a near-natural state. This study has presented some initial

observations of the effects of successive developments on

three wells. Two wells were shallow and screened in phreatic

or semi-confined aquifers, and the third was a deeper, fullypenetrating well, screened through a confined aquifer.

The results of tests on well A were inconclusive, in part

because of a lack of ambient flow data from pre-development

and first development stages. In addition to the lack of data, a

good correlation between the flow distributions after second

and third development did not exist as shown by the

differential net flow charts. This was probably due, in part, to

the experimental technique used at this well. There was,

however, a similarity between a test repeated after the second

development and the test performed after the third

development. This similarity indicates that the first test may

have been influenced by factors other than those imposed by

the pump-induced flow.

The differential net flow charts for well B show that the first

development made a significant difference in the vertical

distribution of flow to the well. Tests after the first, second,

and third developments resulted in quite similar DNF profiles.

Figure VI-8. (Well C) (a) Ambient flow as measured by the EM flowmeter and (b) net flow (total flow - ambient flow). Data sets are

obtained prior to development and after the 1st, 2nd, and 3rd developments for the ambient flow and after the 1st, 2nd, and

3rd developments for net flow.

0

-5

-10

-15

-20

-25

-30

-35

-1.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0

1st Development

1st Development (overnight)

Depth (m)

Ambient Flow (L/min)

(a)

-35

-40

-45

-50

-55

-60

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0

Pre-Development

1st Development

2nd Development

3rd Development

Depth (m)

Ambient Flow (L/min)

(a)

-35

-40

-45

-50

-55

-60

0.0 10.0 20.0 30.0 40.0

1st Development

2nd Development

3rd Development

Depth (m)

Net Flow (L/min)

(b)
41

Figure VI-9. (Well C) Differential net flow obtained after (a) 1st development, (b) 1st development and an overnight period, (c) 2nd developmen

-40-43-46-49-52

0 2 4 6

Differential Net Flow (L/min)

Elevation (m)

1st Development

(a)

-55

1 5 3 0 2 

Differential Net Flow (L

Elevation (m)

1st Development (over

(b)

1 

3

0 2 4 6

Differential Net Flow (L/min)

Elevation (m)

2nd Development

(c)

1 5 3 0 2 

Differential Net Flow (L

Elevation (m)

3rd Developmen

(d)

1 

3

-40-43-46-49-52-55

-40-43-46-49-52-55

-40-43-46-49-52-55
42

However, as would be expected, the ambient flow data were

less stable. Part of the irregularity may be attributable to the

varying withdrawal demands placed on the aquifer by the local

industry.

The third well was screened in the confined aquifer,

presumably more shielded from the hydraulic stresses beyond

experimental control. The ambient flow in well C was small

compared to the other wells, although measurable shifts were

observed after each development. The irregularity of ambient

flows may be due more to experimental “noise” than to any

significant change in the natural flow. The differential net

flow charts were moderately dissimilar after each

development, indicating that slight adjustments were still

being made to the media even after the third development.

The results of the tests at the Mobile site were generally

similar to those obtained at the Columbus site. Ambient flow

profiles at both sites were more sensitive to effects such as the

state of well development and minor changes in hydraulic

stresses than induced flow profiles. In addition, the state of

well development appeared to vary with differences in aquifer

materials, as is expected.
43

Chapter VII

Case Studies

VII-1 Field Applications

Issues related to aquifer heterogeneity are particularly

important at sites where contaminant transport and fate will be

characterized or subsurface remediation will be performed. A

vertical-component borehole flowmeter may be used to

investigate several aspects of ground-water flow relevant to

monitoring and remedial design (Table VII-1). In order to

demonstrate the utility of flowmeter investigations for gaining

quantitative insight into aquifer characterization, results from

several borehole flowmeter applications are described.

Table VII-1. Characterization Objectives for Borehole Flowmeter

Studies

Measured

Flow Log Phenomena That Can Be Investigated

Ambient

Conditions • Direction of the vertical hydraulic gradient

• Cross-connection among geological units

intersected by a well

• Active fracture locations/zones in bedrock

Pumping

Conditions • Active fracture locations in bedrock

• Horizontal hydraulic conductivity distribution

• Identify zones of preferential flow and,

potentially, contaminant transport for design of

monitoring and remediation networks

VII-2 Columbus AFB, Mississippi

As discussed in Chapter V, borehole flowmeter tests were

performed at two sites on the Columbus Air Force Base

(CAFB). The two sites overlie a highly heterogeneous,

unconsolidated and unconfined fluvial aquifer, are about 60 m

apart, and are located approximately 6 km east of the

Tombigbee River and 2.5 km south of the Buttahatchee River.

Seasonal water table fluctuations range from 2 m to 3 m. The

aquifer is composed of approximately 10 m of terrace deposits

consisting primarily of poorly- to well-sorted, sandy gravel

and gravelly sand that often occur in irregular lenses and

layers. Visual inspection of the facies exposed at a quarry

located a few kilometers from the site shows a complex series

of lenses with significantly different physical and hydrological

properties. The terrace aquifer is unconformably underlain by

the Cretaceous-age Eutaw Formation, an aquitard consisting

primarily of marine clay and silt.

The Electric Power Research Institute performed the MADE

study (Betson et al., 1985) at the first test site, which covers

about 8 Ha. The MADE experiment included a network of

258 multilevel sampling wells designed to monitor a 20-

month, rapid injection, natural gradient tracer study. Boggs et

al. (1992) provide a review of the tracer experiment. The

dominant feature of the tracer plume is a highly asymmetric

concentration distribution in the longitudinal direction. At the

conclusion of the experiment, the more concentrated region of

the plume remained within approximately 20 m of the

injection point, while a more dilute portion extended

downgradient a distance of more than 260 m. In certain

respects, the plume configuration would appear to be the result

of a continuous tracer injection rather than the rapid injection

that actually occurred.

One explanation for the skewed plume is that the tracer was

slowly bleeding from a zone of relatively low hydraulic

conductivity into relatively conductive zones, and thereafter

moved rapidly downgradient. This explanation is supported

by the hydraulic conductivity values from borehole flowmeter

tests performed by Boggs et al. (1989) and Rehfeldt et al.

(1989b). These particular flowmeter tests were performed

primarily with an impeller flowmeter. The electromagnetic

flowmeter was used only to supplement the basic data. Figure

VII-1 shows a vertical cross section of the spatially correlated

hydraulic conductivity profile along the longitudinal axis of

the plume. The profile shows that the tracer was injected into

a region of relatively low transmissivity and 25 m upgradient

of a large region of relatively high transmissivity that

contained several conductive lenses. Thus, the flowmeter

measurements provide the basis for understanding the major

characteristics of the tracer experiment.

The first major application of the electromagnetic flowmeter

in a granular aquifer was at the second CAFB site, which

covers about 1 Ha. This is the location of the tests described

in Chapter V. Numerous pumping, flowmeter, and

recirculating tracer tests were conducted using thirty-seven

fully-screened wells. Shown in Figure VII-2 are areal

distributions for the depth-averaged hydraulic conductivity

values for the uppermost and lowermost two meters of the
44

Distance (m)

-20 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280

Elevation (m)

46

48

50

52

54

56

58

60

62

64

FLOW

Injection

-0.2 < log K < 0.7

-0.9 < log K < -0.2

-1.6 < log K < -0.9

-2.3 < log K < -1.6

-3.0 < log K < -2.3

-3.7 < log K < -3.0

-4.4 < log K < -3.7

-5.1 < log K < -4.4

Figure VII-2. Depth-averaged hydraulic conductivity values for the lowermost 2 m (left) and the uppermost 2 m (right) of the unconfined

aquifer below the 1-Ha test site at Columbus AFB.

Figure VII-1. Vertical profile of hydraulic conductivity values along the longitudinal axis of the MADE tracer plume.

X (m)

20 40 60 80 100

Y (m)

20

40

60

80

100

-0.2 < log K < 0.7

-0.9 < log K < -0.2

-1.6 < log K < -0.9

-2.3 < log K < -1.6

-3.0 < log K < -2.3

-3.7 < log K < -3.0

-4.4 < log K < -3.7

-5.1 < log K < -4.4
45

Figure VII-3. (a) Ambient flow distribution in a well and (b) the flow distribution induced by constant-rate pumping.

0.04 0.03 0.02 0.01 0

0

50

100

150

200

250

Induced Flow (L/s)

(b)

0.012 0.008 0.004 0

0

20

40

60

80

100

120

Ambient Flow (L/s)

Depth (m)

(a)

saturated aquifer. In the upper portion of the aquifer, a band of

high hydraulic conductivity crosses the test site. The location

of this band matches the location of a former river meander

shown in a 1956 aerial photograph of the site (Figure V-1). In

the lower portion of the aquifer, the only non-clay material

occurs in a depression of the lower aquitard near the center of

the site. The S-shaped band of material with a relatively high

hydraulic conductivity in the central portion of the figure is

most likely sands and gravel deposited by an earlier river

system. Thus, flowmeter data at the 1-Ha test site provided

sufficient detail to delineate the sand and gravel beds of two

former river channels. Being able to observe correlations

between the hydraulic conductivity field and the geological/

depositional history of a study site provides the type of

detailed data required to understand flow and transport in

heterogeneous aquifers.

VII-3 Oak Ridge National Laboratory,

Tennessee

The electromagnetic borehole flowmeter has been used to

characterize the ground-water flow patterns in fractured

bedrock at the Oak Ridge National Laboratory (ORNL)

(Moore and Young, 1992; Young et al., 1991). The laboratory

is located in the Valley and Ridge physiographic province of

the Appalachian thrust belt of eastern Tennessee. The

geological units consist of fractured sequences of calcareous

shale, siltstone, shaley limestone, and limestone, which

typically dip at angles between 45° to 60° from horizontal.

Measurements at outcrops and on cores of the Conasauga

Group show a density of 10-15 joints per meter in shale and 6-

40 joints per meter in siltstone (Sledz and Huff, 1981). The

joints and fractures are oriented parallel to the bedding planes,

strikes, and dips of the lithologic units.

At ORNL, the electromagnetic flowmeter has been used in

open boreholes and in boreholes with sand-packed PVC

screens. In most of the deep boreholes, the measured ambient

flow profiles in the wells indicate that cross-communication

was occurring between different fracture zones. Figure VII-3

shows a profile of ambient flow where ground-water enters the

well at a depth of about 100 m and exits at a depth of 41 m.

The ambient flow is produced by natural upward hydraulic

gradients, along with hydraulically active fractures at depths

of 100 m and 41 m.

At most of the wells, the permeable vertical zones are

typically greater than 30 cm, which is the minimum vertical

distance required for a steeply dipping fracture (>60°) to cross

through a 17-cm OD borehole, the size of most of the

boreholes at ORNL. Analysis of flowmeter logs indicate that

the orthogonal spacing between fractures is about 0.15 m to

0.44 m in the shallow bedrock, and about 0.44 m to 0.73 m in

the deeper bedrock. Specific information regarding the

location of fractures assists in correlating lithologic structure

and hydraulically-significant fractures. Differences were

observed in the flow profiles between different strata and

regions. In some areas, a permeable flow zone is located near

the top of bedrock. This zone was likely produced by
46

weathering and serves as a pathway for significant shallow

ground-water flow toward valley streams.

At ORNL, newly drilled boreholes with depths near 500 m

penetrate several fracture zones. In some cases, the different

fracture zones contain ground waters of significantly different

chemistry and from different recharge zones. Among the

applications of the flowmeter data at ORNL is a refinement of

the monitoring program based on the location of hydraulically active fractures. Once the hydraulically active fractures

are located, specific borehole zones may be isolated so that

selective monitoring can include fluids from fractures or

fracture zones and matrix fluids with long residence times.

These data may be used to identify changes in water chemistry

with depth and water chemistry signatures associated with a

particular rock type.

VII-4 The Oklahoma Refining Company

Superfund Site, Oklahoma

The Oklahoma Refining Company (ORC) Superfund Site is

located in Caddo County on the eastern edge of Cyril,

Oklahoma. Site topography consists of low, rolling hills with

a deeply incised drainage system. Soils are characteristically

red silty clay loams with low to very low permeability.

Alluvium and terrace deposits are present in and around old

stream channel sediments. Soils are underlain by the

Weatherford Member of the Cloud Chief Formation (gypsum)

in the northwestern part of the ORC site, and the Rush Springs

Sandstone elsewhere. Ground water in the Weatherford

commingles with that of the Rush Springs Sandstone, which is

believed to act as an unconfined aquifer. The Rush Springs

Sandstone consists of even-bedded to highly cross-bedded,

very fine-grained, silty sandstone and outcrops on the eastern

side of the ORC site (Bechtel, 1991).

Electromagnetic flowmeter field demonstrations were

conducted at three pairs of ORC wells. One well pair

consisted of wells NE-2 and NE-3, which lies in a region

where gypsum overlies sandstone. Figure VII-4 shows the

flow distributions for ambient and induced-flow conditions at

well NE-2. The flow distributions for well NE-3 were very

similar. The profile of induced flow indicates that about

eighty percent of the total flow to the well originates from the

upper thirty percent of the well screen. This result suggests

that materials in the upper portion of the screened interval are

more permeable than those in the lower portion.

The downward ambient flows indicate downward vertical

hydraulic gradients and possible cross connection between

different hydrostratigraphic units. At wells NE-2 and NE-3,

about 0.2 L/min enters the well near the water table and

migrates down the well, where it flows into the aquifer. Of the

0.2 L/min, about half of it enters the sandstone at a depth 18 m

below the top of well casing (TOC). If the recharging ground

water was contaminated, ambient flows in the well would

accelerate the downward migration of ground-water

contamination. If the recharging ground water was clean but

the deeper ground water was contaminated, ambient flows in

the well could dilute ground-water contamination in the

vicinity of well and in samples, hindering characterization of

the ground-water contamination.

In the southeast quadrant of the site, flowmeter tests were

performed on a well pair consisting of wells IBB-4 and SBB36. The ambient flows at these wells (Figures VII-4) are

upward. Well IBB-4 was a flowing artesian well at the time of

the test. The flow profiles at well IBB-4 indicate that the

source of the artesian ground water is a narrow zone near a

depth of 36 m. Boring logs indicate that a 0.8-m thick

siltstone layer exists at the 36-m depth, which appears to be

the source of the artesian ground-water flow. Well SBB-36

shows two narrow zones of relatively high flow near depths of

13.5 m and 15.5 m. The limited flowmeter testing at the ORC

test site provided valuable information related to aquifer

heterogeneity and potential contaminant transport.

VII-5 Gilson Road Superfund Site,

New Hampshire

The Gilson Road site at Nashua, New Hampshire, was

originally a 2.4-Ha landfill for refuse and demolition material.

In 1979, it became a site for disposal of other wastes. Groundwater contamination formed a plume over 450 m wide and 33

m deep, which was estimated to be moving at a rate of 0.6 m/

day (Morrison, 1983). A bentonite slurry wall was constructed

to contain the plume and the surface was capped with a

synthetic membrane to prevent infiltration of rainfall. A

ground-water pump-and-treat system was in operation for

several years.

The Gilson Road site is underlain primarily by stratified,

unconsolidated sand and gravel deposits of glacial origin. The

permeable sand and gravel deposits are underlain by a thin,

discontinuous, low-permeability glacial till unit, that is up to

3-m thick. Bedrock underlying the till is biotite schist of the

Merrimack Group, which is differentially weathered and

fractured across the site (Morrison, 1983).

Electromagnetic flowmeter tests were conducted at four

monitoring wells and three recovery wells of the pump-andtreat remediation system. The recovery wells were designed

to fully penetrate the drift and till overburden. None of the

available well logs indicated intersection of the upper bedrock.

In all three recovery wells, the measured flow (Figure VII-5)

was significantly greater near the top of the well screen. These

results may be due to use of a coarse-grained filter pack in

well construction and may not be representative of actual site

conditions. However, if the results are representative of the

shallow hydraulic structure in this aquifer, they would indicate

potential inefficiencies in the recovery of ground water from

the lower portions of the overburden using these wells.

VII-6 Mirror Lake, New Hampshire

The Mirror Lake drainage basin is located in the Hubbard

Brook Experimental Forest in the White Mountains of central

New Hampshire. The drainage basin is a small, well-defined
47

Figure VII-4. Ambient and induced flow distributions for wells NE-2, SBB-36, and IBB-4 at the ORC Superfund Site.

01234

WELL NE-2

Pumping Rate = 3.8 L/min

Top of Screen

Bottom of Screen

Pumping Rate = 0.77 L/min

0 0.2 0.4 0.6 0.8

Pumping Rate = 0.88 L/min

0 0.2 0.4 0.6 0.8

Top of Screen

Bottom of Screen

Flow (L/min) Flow (L/min)

34

36

38

40

Depth Below TOC (m)

11

12

13

14

15

16

17

Depth Below TOC (m)

Flow (L/min)

WELL SBB-36 WELL IBB-4

a) b)

c) d)

-0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0.05

5

10

15

20

Flow (L/min)

WELL NE-2

Depth Below TOC (m)

Ambient Pumping

Figure VII-5. Ambient and induced flow distributions for wells I, J, and K at the Gilson Road site.

WELL K

Flow (L/min)

Top of Screen

Bottom of Screen

Depth Below TOC (m)

WELL J

Flow (L/min)

Depth Below TOC (m)

Top of Screen

Bottom of Screen

WELL I

Flow (L/min)

Depth Below TOC (m)

Top of Screen

Bottom of Screen

Ambient Pumping

0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35 0 5 10 15 20 25 30 35

14

10

11

12

13

15

16

17

18

10

11

12

13

14

15

16

17

18

10

11

12

13

14

15

16

17

18
48

hydrologic environment covering 85 Ha. A test site was

established in the southwest corner of the basin by the U.S.

Geological Survey for three primary purposes: long-term

monitoring of bedrock environments; maintenance of a controlled field-scale laboratory to test new equipment, methods,

and interpretive models; and characterization of fluid movement and solute transport in fractured rock (Winter, 1984).

Bedrock underlying the Mirror Lake drainage basin is

primarily composed of Silurian-age schist (Shapiro and Hsieh,

1991). The schist is intruded by granite, and less commonly

pegmatites and basalts. The rocks are extensively fractured

from folding and faulting during successive orogenies.

Overlying the bedrock is a layer of glacial drift, predominantly

till, which varies in thickness from zero to 49 m. At the test

site, bedrock is a granite dike, which is overlain by 12 m to 15

m of glacial drift.

Three existing wells, each drilled to a depth of 75 m, were

chosen for demonstration of the electromagnetic borehole

flowmeter. Well FSE-06 (Figure VII-6a) exhibited the largest

ambient flow at 0.3 L/min. The results indicate two zones of

significant transmissivity; an upper zone between 30 m and 35 m

below TOC and a lower zone around 57 m to 64 m. The two

zones are probably related to major rock fractures. Further

evidence of transmissive fractures can be seen in the flowmeter

profile obtained during pumping (Figure VII-6b). Ground water

predominantly enters the well from these two intervals.

Well FSE-09 exhibited much lower ambient flow (Figure

VII-6c) than that detected in FSE-06, but the flows are high

enough to indicate a hydraulically active fracture zone near a

depth of 42 m to 46 m. The presence of this fracture zone is

supported by the induced flow profile (Figure VII-6d). Very

low magnitude ambient flows (Figure VII-6e) were detected in

Well FSE-10. However, a large change in the ambient flow

around a depth of 30 m to 38 m suggests that a transmissive

fracture zone is present. Good correlation with the pumping

induced flow data (Figure VII-6f) verifies the fracture zone.

For comparison, results from acoustic televiewer surveys of

wells FSE-09 and FSE-10 were made available by the U.S.

Geological Survey. The televiewer images many linear

features in the walls of both holes, including a relatively large

feature at a depth of about 44 m in Well FSE-09. Similar

general correlations between televiewer features and the flow

profiles were observed in well FSE-10.

Collective interpretation of the flowmeter logs indicates that

there may be a network of hydraulically-active fractures at

approximately 40 m below the ground surface in this area of

the site. Data from these different logging methods are highly

complimentary. The acoustic televiewer may be used to estimate the density and orientation of linear features, including

fractures. The borehole flowmeter provides information to

identify which features or zones are hydraulically active.

VII-7 Logan Martin Dam, Alabama

Logan Martin Dam is located in east-central Alabama in a

complex geologic terrain. Situated on the lower Knox Group

of the Pell City Thrust Sheet, the dam rests on a bed

comprised of eighty percent to ninety percent dolomite which

ranges from fine- to coarse-grained. The remaining rock is

made up of a collection of cherts, shaley limestones, and finegrained silica. The rock is highly fractured and creates a

situation that is extremely conducive to diffuse ground-water

flow. The hydrogeology is complicated further by the fact that

certain layers of the underlying material are preferentially

solutioned. This solutioning has created areas of conduit flow

within the rock.

Logan Martin Dam has experienced extensive problems with

seepage and poor water quality downstream of the dam since

its completion in 1964. The rate of leakage under the dam

has increased from 168 m3/min in 1964 to approximately

1104 m3/min, with the flow rate increasing only 84 m3/min

since 1974. In 1968, it was observed that the flow rate at a

monitoring weir increased sharply from 0.6 m3/min to 10.2

m3/min. A steep-walled sinkhole then developed on the

downstream side of the earthworks. Subsequent

investigations revealed multiple sinkholes in the reservoir

upstream of the dam. Grouting the earthworks and filling the

sinkholes reduced the flow from the monitoring weir to the

original 0.6 m3/min.

Geologic mapping based on outcrops, lineaments, and core

analyses suggested that a zone of rocks within the Knox

Group, called Target Zone #1, was a major source of leakage

(Redwine et al., 1990). The geophysical/hydraulic procedure

to test this hypothesis was to use various existing wells and

coreholes to run a suite of caliper, temperature, and flowmeter

logs in an attempt to detect the vertical movement of water

within the target zone, thereby documenting the qualitative

information resulting from the earlier geologic study. Of the

wells that were tested, most were clogged with mud at various

depths, thus no substantive data were obtained from these

tests. However, two of the wells (Well 332 and Well 301)

were clear for logging.

At Well 332, upward flows of about 130 L/min were

encountered between 78 m and 110 m above mean sea level

(AMSL) (Figure VII-7). The natural flow entered the

borehole at 78 m to 80 m AMSL and flowed up the borehole

until reaching an exit point at about 110 m to 112 m AMSL.

These data were interpreted as indicative of large fractures or

conduits at these elevations.

Well 301 provided different results. At 1.5 m AMSL, a flow

of 51 L/min was measured entering the borehole. This flow

steadily decreased to 43.3 L/min at 29.5 m AMSL where the

flow then disappeared completely over a short section of the

borehole. The flow then resumed at 30.5 m AMSL and rose to

a maximum at about 33.5 m AMSL, then decreased, first

slowly and then rapidly, until 48 m AMSL, where flow was no

longer detected. The decrease of flow occurring between 29.5

m and 30.5 m AMSL was due to a large solution opening

where the cross-sectional area for flow was enlarged

dramatically, leading to a substantial decrease in flow velocity

in the wellbore. This expansion in the wellbore was shown on

a caliper log.
49

Figure VII-6. Ambient and induced flow distributions for wells FSE-06, FSE-09, and FSE-10 at Mirror Lake, New Hampshire.

Bottom of Casing

Bottom of Borehole

Bottom of Casing

Bottom of Borehole

-0.3 -0.25 -0.2 -0.15 -0.1 -0.05 0 0 2 4 6 8 10 12 14

10

20

30

40

50

60

70

80

02468

Bottom of Casing

Bottom of Borehole

-0.1 -0.05 0 0.05 0.1 0.15

10

20

30

40

50

60

70

80

Bottom of Casing

Bottom of Borehole

10

20

30

40

50

60

70

80

Bottom of Casing

Bottom of Borehole

Bottom of Casing

Bottom of Borehole

Flow (L/min) Flow (L/min)

-0.02 -0.015 -0.01 -0.005 0 0.005 0 0.5 1 1.5 2 2.5 3

Depth Below TOC (m) Depth Below TOC (m) Depth Below TOC (m)

Well FSE-10 Well FSE-10

Well FSE-09 Well FSE-09

a) b) Well FSE-06 Well FSE-06

c) d)

e) f)

Ambient Pumping
50

All detected flows were upward, indicating that water leakage

was from around and/or under the reservoir. It was concluded

that the borehole flowmeter was a valuable device for locating

transmissive features and directly measuring flows of ground

water in fractured rock systems.

VII-8 Cape Cod, Massachusetts

In a study by Hess et al. (1992), a comparison of the

variability of hydraulic conductivity was presented for in situ

borehole flowmeter measurements and lab permeameter

measurements. The theory and application pertaining to the

flowmeter data are those techniques given by Hufschmied

(1983, 1986) and Rehfeldt et al. (1989a, b). Much of what

follows comes directly from Hess et al. (1992).

Field studies into the characterization of aquifer heterogeneity

were conducted in an abandoned gravel pit south of Otis Air

Force Base at Cape Cod, Massachusetts. The unconfined

aquifer is located in a glacial outwash plain and is composed

of clean, medium-to-coarse sand and gravel, containing

typically less than one percent silt and clay. The aquifer is

about 30 m thick and is underlain by less permeable silty sand

and till deposits. The water table is about 14 m AMSL and

about 6 m below land surface. The hydraulic gradient is

approximately 0.0015 m/m and indicates a southward flow

direction. Ground-water seepage velocity averages 0.42 m/d

as calculated from average properties of the aquifer (LeBlanc

et al., 1991). Surface exposures of the outwash reveal

interbedded sand and gravel deposits. Crossbedded troughs up

to 1 m wide, but typically less than 0.5 m high, are observed in

exposures perpendicular to the hypothesized paleocurrent

direction, which is north to south. Parallel to this direction,

troughs exhibit a tubular form and are several meters long

(Hess and Wolf, 1991).

Sixteen wells were installed for flowmeter tests. Fifteen of the

wells were installed by a drive-and-wash technique to

minimize the disturbance of the aquifer region surrounding the

well. One well was installed using a hollow-stem auger so

that core material could be obtained for permeameter analysis,

which could then be directly compared to the flowmeter

analysis. In addition, core samples were taken from the upper

6 m of each of the boreholes. Each 5.1-cm diameter

flowmeter well was screened over the upper 12 m of the

saturated zone. Only the top 6 m to 7 m of the profiles were

used for comparisons. These intervals correspond to the core

sample zones, and also to the horizon of the aquifer through

which the tracers moved during an earlier tracer test.

Multiport, constant-head permeameter analysis of the core

samples was the second method used in this study to obtain a

measure of hydraulic conductivity. Measurements were taken

from each section of the core between adjacent manometer

probes inserted at 5-cm to 10-cm intervals along the core

sample length. Summary statistics, mean, variance, and range

for the hydraulic conductivity data sets from the two methods

are presented in Table VII-2. The flowmeter data have

significantly higher mean and variance values than do the

permeameter data. The flowmeter geometric mean of

0.11 cm/s lies within the range of values previously estimated

for this aquifer and is only slightly lower than the value

Figure VII-7. Substantial ambient flow moving from one stratum to another as detected by an impeller flowmeter. The flow is moving

under a dam, the base of which is at an elevation of about 140 m AMSL. Flowmeter data were used to help select a

geologic model for explaining the large leakage of water low in dissolved oxygen that was observed below the dam.

Well 332 Well 301

0 25 50 75 100 125 150

120

110

100

90

80

70

60

Flow (L/min)

0 10 20 30 40 50 60

60

50

40

30

20

10

0

Flow (L/min)

Elevation (m-AMSL)
51

Table VII-2. Summary Statistics of Hydraulic Conductivity Data

Obtained Using a Borehole Flowmeter Method and

a Permeameter Analysis Method (from Hess et al.

(1992))

Flowmeter Permeameter

Number of wells or coring locations 16 16

Number of hydraulic conductivity values (K) 668 825

Mean vertical spacing (cm) 15 7.3

Geometric mean of K (cm/s) 0.11 0.035

Variance of ln K (σf

2) 0.24 0.14

Range

 Minimum K (cm/s) 0.013 0.006

 Maximum K (cm/s) 0.37 0.14

Range in horizontal spacing (m) 0.9-24 0.9-24

estimated from the aquifer and tracer tests (0.13 cm/s). The

permeameter mean of 0.035 cm/s is significantly lower than

previously reported values. Several potential reasons for the

low permeameter calculations include: local-scale anisotropy,

nonrepresentative sampling techniques, and the influence of

compaction during the coring process. In comparison, the

flowmeter appears to supply more representative data, and is

an easier and cost-effective alternative to core sampling and

permeameter measurements.

VII-9 Summary

Sensitive borehole flowmeters, including the electromagnetic

flowmeter described in this report, are valuable tools for

detailed characterization of hydrogeology. In many cases,

these tools may be used in existing wells to obtain such

information as natural ground-water flow patterns within the

well, identification of hydraulically active fracture zones in

rock, and, potentially, estimates of the relative hydraulic

conductivities of materials adjacent to the well screen. In

conjunction with other data, including information from

geologic and geophysical logs, these results may be used to

define the hydrostratigraphy of aquifer formations and

evaluate such issues as contaminant transport and fate,

efficient design of extraction and injection systems for

subsurface remediation, and monitoring network design.
52
53

Chapter VIII

References

Aller, L., T. W. Bennett, G. Hackett, R. J. Petty, J. H. Lehr, H.

Sedoris, D. M. Nielsen, and J. E. Denne, 1989. Handbook

of Suggested Practices for the Design and Installation of

Ground-Water Monitoring Wells, National Ground Water

Association, Dublin, Ohio.

Barcelona, M. J., and J. A. Helfrich, 1986. Well construction

and purging effects on ground-water samples,

Environmental Science and Technology, 20:1179-1184.

Bechtel Environmental, Inc., 1991. Remedial investigation

report: Oklahoma Refining Company (ORC) Superfund

Site, Cyril, Oklahoma, Contract No. BP02358, Houston,

Texas.

Betson, R. P., J. M. Boggs, S. C. Young, and L. W. Gelhar,

1985. Macrodispersion Experiment (MADE): Design of a

field experiment to investigate transport processes in a

saturated groundwater zone, EPRI Interim Report, EA4082, Electric Power Research Institute, Palo Alto,

California.

Boggs, J. M., S. C. Young, D. J. Benton, and Y. C. Chung,

1989. Hydrogeologic characterization of the MADE site,

EPRI Interim Report, EN-6915, Electric Power Research

Institute, Palo Alto, California.

Boggs, J. M., S. C. Young, L. M. Beard, L. W. Gelhar, K. R.

Rehfeldt, and E. E. Adams, 1992. Field study of

dispersion in a heterogeneous aquifer, 1. Overview and

site description, Water Resources Research, 28:3281-

3292.

Boman, G.K., F.J. Molz, and K.D. Boone, 1997. Borehole

flowmeter application in fluvial sediments: Methodology,

results, and assessment, Ground Water, 35:443-450.

Chu, W. C., J. Garcia-Rivera, and R. Raghavan, 1980.

Analysis of interference test data influenced by wellbore

storage and skin at the flowing well, Journal of Petroleum

Technology, 32(1):171.

Church, P.E., and G.E. Granato, 1996. Bias in ground-water

data caused by well-bore flow in long-screen wells,

Ground Water, 34:262-273.

Collar, R.J., and P.A. Mock, 1997. Using water-supply wells to

investigate vertical ground-water quality, Ground Water,

35:743-750.

Collinson, J. D., and D. B. Thompson, 1989. Sedimentary

Structures, Routledge, Chapman & Hall, Inc., New York,

New York.

Cooper, Jr., H. H., and C. E. Jacob, 1946. A generalized

graphical method for evaluations of formation constants

and summarizing well-field history, Transactions of the

American Geophysical Union, 27:526-534.

Driscoll, F. G., 1986. Groundwater and Wells, Johnson

Filtration Systems, St. Paul, Minnesota.

Dudgeon, C. R., and P. S. Huyakorn, 1976. Effects of nearwell permeability variation on well performance,

Australian Water Resource Council Technical Paper No.

18, Canberra, Australia.

Ferson, L. M., ed., 1983. Standards and Practices for

Instrumentation, Instrument Society of America, Research

Triangle Park, North Carolina.

Hackett, G., 1987. Drilling and constructing monitoring wells

with hollow/stem augers. Part 1: Drilling considerations,

Ground Water Monitoring Review, 7:51-62.

Hackett, G., 1988. Drilling and constructing monitoring wells

with hollow/stem augers. Part 2: Monitoring well

installation, Ground Water Monitoring Review, 8:60-68.

Haley, J. L., B. Hanson, C. Enfield, and J. Glass, 1991.

Evaluating the effectiveness of ground-water extraction

systems, Ground Water Monitoring Review, 11:119-124.

Hanson, R.T., and T. Nishikawa, 1996. Combined use of

flowmeter and time-drawdown data to estimate hydraulic

conductivities in layered aquifer systems, Ground Water,

34:84-94.

Harlan, R. L., K. E. Kolm, and E. D. Gutentag, 1989. Water/Well

Design and Construction, Elsevier, New York, New York.

Hawkins, M. F., Jr., 1956. A note on the skin effect, Trans. Am.

Inst. Min. Metall. Pet. Eng., 207:356-367.

Hess, A. E., 1982. A heat-pulse flowmeter for measuring low

velocities in boreholes, U.S. Geological Survey Open-File

Report 82-699, U.S. Geological Survey, Reston, Virginia.

Hess, A. E., 1986. Identifying hydraulically conductive

fractures with a slow-velocity borehole flowmeter,

Canadian Geotechnical Journal, 23:69-78.
54

Hess, A. E., and F. L. Paillet, 1990. Applications of the

thermal-pulse flowmeter in the hydraulic characterization

of fractured rocks, in Geophysical Applications for

Geotechnical Investigations, Paillet and Saunders, ed.,

ASTM STP 1101, ASTM, Philadelphia, Pennsylvania, 99-

112.

Hess, K. M., and S. H. Wolf, 1991. Techniques to determine

spatial variations in hydraulic conductivity of sand and

gravel, EPA/600/2-91/006, U.S. Environmental Protection

Agency, Ada, Oklahoma.

Hess, K. M., S. H. Wolf, and M. A. Celia, 1992. Large-scale

natural gradient tracer test in sand and gravel, Cape Cod,

Massachusetts, 3. Hydraulic conductivity variability and

calculated macrodispersivities, Water Resources

Research, 8:2011-2027.

Hufschmied, P., 1983. Ermittlung der durchlassigkeit von

lockergesteins-grundwasserleitern, eine vergleichende

untersuchcung verschiednener feldmethoden, Ph.D.

Dissertation 7397, Eidgenossische Technische

Hochschule, Zurich, Switzerland.

Hufschmied, P., 1986. Estimation of three-dimensional

statistically anisotropic hydraulic conductivity field by

means of a single well pumping test combined with

flowmeter measurements, Hydrogeologie, 2:163-174.

Javandel, I., and P.A. Witherspoon, 1969. A method of

analyzing transient fluid flow in multilayered aquifers,

Water Resources Research, 5:856-869.

Kabala, Z.J., 1994. Measuring distributions of hydraulic

conductivity and specific storage by the double flowmeter

test, Water Resources Research, 30:685-690.

Kaye, J. M., 1955. Certain aspects of the geology of Lowndes

County, Mississippi, M. S. Thesis, Mississippi State

University.

Keely, J. F., and K. Boateng, 1987a. Monitoring well

installation, purging and sampling techniques - Part 1:

Conceptualizations, Ground Water, 25:300-314.

Keely, J. F., and K. Boateng, 1987b. Monitoring well

installation, purging and sampling techniques - Part 2:

Case histories, Ground Water, 25:427-439.

LeBlanc, D. R., S. R. Garabedian, K. M. Hess, L. W. Gelhar,

R. D. Quadri, K. G. Stollenwork, and W. W. Wood, 1991.

Large-scale natural gradient tracer test in sand and gravel,

Cape Cod, Massachusetts, 1. Experimental design and

observed tracer movement, Water Resources Research,

27:895-910.

Liptak, B. G., and L. Venczel, 1982. Instrument Engineers’

Handbook, Chilton Book Company, Radnor,

Pennsylvania.

Long, J.C.S., J. S. Remer, C. R. Wilson, and P. A.

Witherspoon, 1982. Porous media equivalents for

networks of discontinuous fractures, Water Resources

Research, 18:645-658.

Martin-Hayden, J.M., and G.A. Robbins, 1997. Plume

distortion and apparent attenuation due to concentration

averaging in monitoring wells, Ground Water, 35:339-

346.

Mercer, J.W., D.C. Skipp, and D. Griffin, 1990. Basics of

pump-and-treat remediation technology, EPA/600/8-90/

003, U.S. Environmental Protection Agency, Ada,

Oklahoma.

Minning, R. C., 1982. Monitoring well design and installation,

Proceedings of the Second National Symposium on

Aquifer Restoration and Ground Water Monitoring,

Columbus, Ohio, National Ground Water Association,

Dublin, Ohio, 194-197.

Moench, A. F., and P. A. Hsieh, 1985. Analysis of slug test

data in a well with finite thickness skin, in Memoirs of the

17th International Congress on the Hydrogeology of

Rocks of Low Permeability, 17(1):1729, Int. Assoc.

Hydrogeol., Tucson, Arizona.

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

application of borehole flow meters for environmental

assessment, The Log Analyst, 34:13-23.

Molz, F. J., O. Güven, J. G. Melville, J. S. Nohrstedt, and J. K.

Overholtzer, 1988. Forced-gradient tracer tests and

inferred hydraulic conductivity distributions at the Mobile

site, Ground Water, 26:570-579.

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

Güven, 1989. The impeller meter for measuring aquifer

permeability variations: Evaluations and comparison with

other tests, Water Resources Research, 25:1677-1683.

Molz, F. J., O. Güven, J. G. Melville, (with contributions by I.

Javandel, A. E. Hess, and F. L. Paillet), 1990. A new

approach and methodologies for characterizing the

hydrogeologic properties of aquifers, EPA/600/2-90/002,

U.S. Environmental Protection Agency, Ada, Oklahoma.

Moore, G. K., and S. C. Young, 1992. Borehole flowmeter

data and interpretation, Report ORNL/ER-91, Oak Ridge

National Laboratory, Oak Ridge, Tennessee.

Morin, R. H., A. E. Hess, and F. L. Paillet, 1988a. Determining

the distribution of hydraulic conductivity in fractured

limestone aquifers by simultaneous injection and

geophysical logging, Ground Water, 26:587-595.

Morin, R. H., D. R. LeBlanc, and W. E. Teasdale, 1988b. A

statistical evaluation of formation disturbance produced

by well/casing installation method, Ground Water,

26:207-217.
55

Morrison, A., 1983. Arresting a toxic plume, Civil

Engineering, ASCE, 53(8):35-37.

Moss, R., Jr., and G. E. Moss, 1990. Handbook for

Groundwater Development, John Wiley & Sons, New

York, New York.

National Ground Water Association, 1989. Development

methods for water wells - an anthology, National Ground

Water Association, Dublin, Ohio.

Ogbe, D.O., 1984. Pulse testing in the presence of wellbore

storage and skin effect, Ph.D. Dissertation, Stanford

University, Stanford, California.

Ogbe, D.O., and W. E. Brigham, 1984. A model for

interference testing with wellbore storage and skin effects

at both wells, Society of Petroleum Engineers 59th

Annual Technical Conference, Houston, Texas.

Paillet, F. L., 1991a. Use of geophysical well-logs in

evaluating crystalline rocks for siting of radioactive waste

repositories, The Log Analyst, 33:85-107.

Paillet, F. L., 1991b. High-resolution flow logging in

observation boreholes during hydraulic testing of

fractured-rock aquifers, Society of Professional Well Log

Analysts 32nd Annual Logging Symposium Transactions,

Midland, Texas, L1-L23.

Paillet, F. L., 1991c. The 1st core hole at Mirror Lake, New

Hampshire—Comparing geophysical logs to core and

cross-hole flow logging, U.S. Geological Survey Toxic

Substance Hydrology Conference, Monterrey, California,

Proceedings, Water Resources Investigations Report 91-

4034, U.S. Geological Survey, Reston, Virginia, 162-171.

Paillet, F. L., and A. E. Hess, 1987. Geophysical well log

analysis of fractured granitic rocks at Atikokan, Ontario,

Canada, U.S. Geological Survey Water Resources

Investigations Report 87-4154, U.S. Geological Survey,

Reston, Virginia.

Paillet, F. L., and K. Kapucu, 1989. Characterization of

fracture permeability and fracture flow modeling at

Mirror Lake, New Hampshire, U.S. Geological Survey

Water Resources Investigations Report 89-4058, U.S.

Geological Survey, Reston, Virginia.

Paillet, F. L., and W.S. Keys, 1984. Applications of borehole

geophysics in characterizing the hydrology of fractured

rocks, Proc. of NWWA/EPA Conference on Surface and

Borehole Geophysical Methods in Ground-Water

Investigations, San Antonio, TX, 743-761.

Paillet, F. L., A. E. Hess, C. H. Cheng, and E. L. Hardin, 1987.

Characterization of fracture permeability with highresolution vertical flow measurements during borehole

pumping, Ground Water, 25:28-40.

Paillet, F. L., K. Novakowski, and P. Lapcevic, 1992. Analysis of

transient flows in boreholes during pumping in fractured

formations, Society of Professional Well Log Analysts 33rd

Annual Logging Symposium Transactions, S1-S22.

Paul, D. G., C. D. Palmer, and D. S. Cherkauer, 1988. The

effect of construction, installation and development on the

turbidity of water in monitoring wells in fine-grained

glacial till, Ground Water Monitoring Review, 8:73-82.

Redwine, J. C., R. R. Parizek, and F. J. Molz, 1990. Controls

on porosity and permeability in fracture-flow/conduitflow rocks of the Knox Group, Southern Appalachian

Fold-and-Thrust Belt, U.S.A., Southern Company

Services, Birmingham, Alabama.

Rehfeldt, K. R., L. W. Gelhar, J. B. Southard, and A. M.

Dasinger, 1989a. Estimates of macrodispersivity based on

analysis of hydraulic conductivity variability at the

MADE site, EPRI Interim Report EN-6405, Electric

Power Research Institute, Palo Alto, California.

Rehfeldt, K. R., P. Hufschmied, L. W. Gelhar, and M. E.

Schaefer, 1989b. Measuring hydraulic conductivity with

the borehole flowmeter, EPRI Topical Report EN-6511,

Electric Power Research Institute, Palo Alto, California.

Ruud, N.C., and Z.J. Kabala, 1996. Numerical evaluation of

flowmeter test interpretation methodologies, Water

Resources Research, 32:845-852.

Ruud, N.C., and Z.J. Kabala, 1997. Numerical evaluation of

the flowmeter test in a layered aquifer with a skin zone,

Journal of Hydrology, 203:101-108.

Sandal, H. M., R. N. Horne, and H. J. Ramey, Jr., and J. W.

Williamson, 1978. Interference testing with wellbore

storage and skin effects at the produced well, Society of

Petroleum Engineers, 53rd Annual Technical Conference,

Houston, Texas.

Shapiro, A.M., and P.A. Hsieh, 1991. Research in fractured

rock hydrogeology: Characterizing fluid movement and

chemical transport in fractured rock at the Mirror Lake

Drainage Basin, New Hampshire, in U.S. Geological

Survey Open File Report, Proc. of USGS Toxic

Substances Hydrology Program Technical Meeting,

Monterey, California, March 1991, U.S. Geological

Survey, Reston, Virginia.

Sledz, J. J., and D. D. Huff, 1981. Computer model for

determining fracture porosity and permeability in the

Conasauga Group, Report ORNL/TM-7695, Oak Ridge

National Laboratory, Oak Ridge, Tennessee.

Strauss, M. F., S. L. Story, and N. E. Mehlhorn, 1989.

Applications of dual-wall reverse-circulation drilling in

ground-water exploration and monitoring, Ground Water

Monitoring Review, 9:63-71.
56

Tongpenyai, Y., and R. Raghaven, 1981. The effect of storage

and skin on interference test data, Journal of Petroleum

Technology, 33:151-160.

van Everdingen, A. F., and W. Hurst, 1949. The application of

Laplace transforms to flow problems in reservoirs,

Transactions of the American Institute for Min. Metall.

Pet. Eng., 186:305-320.

Winter, T. C., 1984. Geohydrologic setting of Mirror Lake,

West Thorton, New Hampshire, U.S. Geological Survey

Water Resources Investigations Report 84-4266, U.S.

Geological Survey, Reston, Virginia.

Xiang, J., 1995. The evaluation of the flowmeter test in threelayer aquifers and the influence of disturbed zones,

Journal of Hydrology, 166:127-145.

Young, S. C., 1991a. A site characterization methodology for

aquifers in support of bioreclamation activities, Vol. I:

Well network design, well equation, and aquifer multiwell and single-well tests, U.S. Air Force Engineering and

Services Center, Tyndall AFB, Florida.

Young, S. C., 1991b. A site characterization methodology for

aquifers in support of bioreclamation activities, Vol. II:

Borehole flowmeter technique, tracer tests, geostatistics,

and geology, U.S. Air Force Engineering and Services

Center, Tyndall AFB, Florida.

Young S. C., H. S. Pearson, G. K. Moore, and R. B. Clapp,

1991. Application of the electromagnetic borehole

flowmeter technique at the Oak Ridge National

Laboratory, Report WR28-1-900-247, Tennessee Valley

Authority, Norris, Tennessee.

Zemanek, J., E. E. Glenn, L. J. Norton, and R. L. Caldwell,

1970. Formation evaluation by inspection with the

borehole televiewer, Geophysics, 35:254-269.
57

Appendix A

Field Data Sheets for Borehole Flowmeter Tests

TVA ENGINEERING LABORATORY

EM FLOWMETER FIELD DATA SHEET

Project Name / Project Abbr. (xxx) QA Number (xxx....)

Date Start Time End Time Survey By

Pre-Calibration Ref No. Flowmeter Cal

LPM / Volt

Flowmeter Zero

Volts

Gain Switch Integration Switch Excitation Voltage

HI LOW 1s 10s 20s VRMS

Packer Collar (Serial #)

Yes No

Flowmeter Serial # Electronic Serial # Cable Serial #

Pump Injection Ambient Pump Intake Depth GW Temperature

Rate

Well Number:

Top of Reference Elevation:

Construction Type:

Pipe Size:

Screen Type:

Blank Sections in Screened Interval:

Depth to Water:

Depth to Top of Screen:

Depth of Bottom of Screen:

Depth to Bottom of Well:

Comments:

Yes No
58

Appendix A

Field Data Sheets for Borehole Flowmeter Tests (continued)

TVA ENGINEERING LABORATORY

SINGLE-WELL FIELD DATA SHEET

Project Name / Project Abbr. (xxx) QA Number (xxx....)

Well Number Survey By Date

Pump Type: Transducer Serial #

Comments:

Pump Serial # Transducer Type:

Flow Check

Time Volume Time to Fill Flow Rate Depth of Transducer:

Initial Transducer Reading:

Datalogger File Name:

Pumping Schedule

Time (hr, min) Rate (LPM)

1.

2.

3.

Drawdown Check

Time Electric Tape Datalogger

Depth Reading Depth
59

Appendix B

Equipment Checklist

__ Address & phone number of contact __ OSHA Training Card

__ Site maps __ Stop Watch

__ Well specifications __ 120 ACV generator

__ Calibration sheets __ 220 ACV generator

__ Test forms __ 50 ft 120 ACV extension cord

__ Equipment manuals __ 50 ft 220 ACV extension cord

__ 1/2-inch flowmeter __ 25 ft 120 ACV extension cord

__ 1-inch flowmeter __ Special extension cords

__ Flowmeter electronic system __ Ground fault box

__ Computer interface (6B12, HPIB) __ Power strip

__ Flowmeter spare parts __ Gas can

__ Flowmeter collar __ Weight for steel tape

__ Collar weight __ Engineering rule

__ Packer assembly __ Steel tape

__ Packer inflator __ Tools (electrical and mechanical)

__ Air compressor __ Hack saw

__ Air tank __ Drill and bits

__ Pressure inflator tank __ Tie wraps

__ Inflation tubing, fittings, and valves __ Electrical tape

__ Flowmeter cables __ Flashlight

__ 5 psi pressure transducer __ Electrical supplies (splicing kit, solder, wire, etc.)

__ 10 psi pressure transducer __ Misc hardware (screws, bolts, etc.)

__ 20 psi pressure transducer __ Marking tape

__ 30 psi pressure transducer __ Indelible pen

__ Flowmeter computer __ Rope

__ Electronic data logger __ Tarpaulins

__ Printer __ Canopy

__ Computer, printer, transducer, & electronics cables __ Tent

__ Cable for downloading data logger __ Spring clamps

__ Floppy disks __ Parachute cord

__ Application and operating software __ Multimeter

__ Flowmeter software __ Oscilloscope

__ Datalogger software __ Rain suit

__ Other software __ Boots

__ Peristaltic pump __ Cold weather gear

__ Submersible pump __ Sun screen

__ Centrifugal pump __ Insect repellent

__ Other pumps __ Cooler and drinking water

__ Valves __ Stools, chairs

__ Inlet hoses __ Portable table

__ Discharge hoses __ Cart

__ Checkvalve __ Decontamination supplies (buckets, water, soap, brushes)

__ Hose clamps and fittings __ Rubber gloves

__ Pump calibration containers __ Work gloves

__ Flowmeter calibration cylinder __ Rags, paper towels

__ Water containers __ First aid kit
60