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Master's Theses Graduate College
6-1997
Geophysical Investigation of Anomalous Conductivity Associated Geophysical Investigation of Anomalous Conductivity Associated
with a Hydrocarbon Contamination Site with a Hydrocarbon Contamination Site
Mike S. Nash
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I
GEOPHYSICAL INVESTIGATION OF ANOMALOUS CONDUCTIVITY
ASSOCIATED WITH A HYDROCARBON CONTAMINATION SITE
by
Mike S. Nash
A Thesis
Submitted to the
Faculty of The Graduate College in partial fulfillment of the
requirements for the
Degree of Master of Science Department of Geology
Western Michigan University
Kalamazoo, Michigan
June 1997
ACKNOWLEDGMENTS
It is difficult to list all of the people and institutions that have assisted me in
this research project. First off, thanks to my committee, Dr. William Sauck, Dr.
Estella Atekwana, and Dr. Alan Kehew, who provided their total support to my work.
I am also indebted to the Society of Exploration Geophysicists ,Western Michigan
University, the Graduate College, and the Department of Geology, all of which
provided funds or equipment to assist me with the research.
Secondly, I thank my able and willing assistants Mr. Darin Meyer and Ms.
Beth Pelland, who helped with much of the field work. Also, a special thanks to Mr.
D. Dale Werkema, who assisted with the field studies and critiqued much of the
analysis. Additional thanks are due to Dr. Anthony Endres and Dr. John Greenhouse,
both formerly of the University of Waterloo who provided a needed critique of the
work in progress. Special thanks are due to SERDP and NCIBRD, especially Mark
Henry and Dr. Michael Barcelona for all of the generously provided information.
Finally, I thank my brother Matty, for demonstrating to me the value of
questioning everything and for telling me to do it: "my way".
Mike S. Nash
11
..
GEOPHYSICAL INVESTIGATION OF ANOMALOUS CONDUCTIVITY
ASSOCIATED WITH A HYDROCARBON CONTAMINATION SITE
Mike S. Nash, M.S.
Western Michigan University, 1997
The high electrical conductivity measured from chemical analyses from
ground water below a hydrocarbon contaminated site was the focus of this study.
Most theoretical studies have indicated that the electrical conductivity of hydrocarbon
contamination is lower than that of the surrounding medium. Geochemical studies at
other sites have shown that areas of dissolved fuel oil plume have a higher electrical
conductivity. Six methods: Self Potential, Mise-a-la-Masse, Vertical Electrical
Sounding, Dipole-Dipole Resistivity Profiling, Electromagnetic Induction, and
Ground Penetrating Radar were all used in an attempt to see which method( s) could
identify regions of high conductivity.
The findings of this study show that the Ground Penetrating Radar, Dipole
Dipole Resistivity Profiling and Self Potential identified conductive zones coincident
with the location of the dissolved plume. Vertical Electrical Soundings showed some
broad changes in anomalous areas, but not to high degree of resolution. The Mise-a
la-Masse and Electromagnetic Induction techniques, as applied to this site, did not
show a conductive anomaly in areas identified by geochemical studies.
TABLE OF CONTENTS
ACKNOWLEDGEMENTS.................................................................................... 11
LIST OF TABLES ........................................................ :......................................... Vl
LIST OF FIGURES ................................................................................................ vu
CHAPTER
I. INTRODUCTION ... .......................................................................... ....... .. 1
Statement of Problem......................................................................... 1
Purpose of Study................................................................................ 2
Site History . . . .. . . . . . . . .. . . . .. . . . . . . . . . . .. . . . .. . . . .. . . . .. .. . .. .. . . . .. . . . .. . . . . . . . .. . . . . . . . . . . .. . . . . 2
Site Geology . . . .. . . . . . .. . . . .. .. . . . .. . . . .. . . . . . . . . . . .. . . . .. . . . . . . . . .. .. . . . .. . . . . . .. . . . . . .. . . . . . .. . . 3
Site Geochemistry.............................................................................. 5
II. REVIEW OF RELEVANT LITERATURE ............................................... 11
Theoretical Models . . .. .. . .. .. . . . . . .. . .. .. . .. .. . . . .. . . . . . . . . . . .. . . . .. .. . . . .. .. . . . .. . . . . . .. . . . . . 11
Controlled Spill Studies..................................................................... 13
Field Studies ...................................................................................... 15
Geochemical Studies.......................................................................... 17
III. METHODOLOGY ..................................................................................... 20
Self Potential...................................................................................... 20
Mise-a-la-masse ................................................................................. 21
Electrical Resistivity.......................................................................... 24
lll
CHAPTER
Table of Contents -- Continued
Vertical Electrical Soundings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . 24
Dipole-Dipole Resistivity Profiling.......................................... 26
Electromagnetic Induction................................................................. 28
Ground Penetrating Radar . . .. . .. . . . .. . . . .. . . . .. . .. .. . .. .. . .. .. . .. .. . .. .. . . . .. .. . . . .. . . . .. . 30
IV. RESULTS................................................................................................... 32
Self Potential...................................................................................... 32
Mise-a-la-masse ................................................................................. 32
Electrical Resistivity.......................................................................... 35
Vertical Electrical Soundings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 5
Dipole-Dipole Resistivity Profiling.......................................... 39
Electromagnetic Induction................................................................. 45
Ground Penetrating Radar . . .. . . . .. . .. .. . .. .. . .. . . . .. . . . . . . .. . . . .. . . . . . . . . . . .. . . . .. . . . . ... . 45
V. INTERPRETATIONS ................................................................................ 50
Geophysical Results........................................................................... 50
Self Potential............................................................................. 50
Mise-a-la-masse ........................................................................ 51
Vertical Electrical Soundings .. .. ... . . ... .. ... . . .... .. .. .. ... .. ... . . .. .. . . . ... . . 52
Dipole-Dipole Resistivity Profiling.......................................... 55
Electromagnetic Induction........................................................ 59
IV
CHAPTER
Table of Contents -- Continued
Ground Penetrating Radar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
Performance of the Methods.............................................................. 62
Conclusions and Recommendations ...... .. ...... .. .. .. .... .. .. .. .... .. .. .. .. .. .... .. 65
APPENDICES
A. Organic Chemicals Detected in July 1996.... .... .. .. .. .... .. .. .. .... .. .. .. .. .... .. .. .. .. .. 67
B. Coincident EM-31 and EM-34 Profiles...................................................... 69
C. Permission to Use NCIBRD Files .............................................................. 73
BIBLIOGRAPHY................................................................................................... 75
V
LIST OF TABLES
1. Results ofNCIBRD Chemical Analyses of FT-02 Site From April 1996.. 8
2. Inverse Models for VES # 1 ............................ :........................................... 35
3. Inverse Models for VES # 2........................................................................ 37
4. Inverse and Forward Models for VES # 3 .................................................. 39
5. Inverse Models for Each VES..................................................................... 52
6. Forward Models for Electromagnetic Induction......................................... 60
7. Results ofElectomagnetic Induction Forward Models............................... 61
Vl
LIST OF FIGURES
1. FT-02 Site Map.............................................................................................. 4
2. Topographic Map ofFT-02 Site ........................ ."........................................... 6
3. FT-02 Site Plume With Well Locations......................................................... 7
4. Electrode Configurations for Mise-a-la-masse, Vertical ElectricalSoundings, and Dipole-Dipole Profiling........................................................ 22
5. Self Potential Contour Plot............................................................................ 3 3
6. Mise-a-la-masse Contour Plots...................................................................... 34
7. Field and Inverse Model Plot for VES # 1..................................................... 36
8. Field and Inverse Model Plot for VES # 2..................................................... 38
9. Field and Inverse Model Plot for VES # 3..... .. . . . .. . . . . . .. . . . . . .. . . . . . . . .. . . . . . . . . . . . . . . . . . . 40
10. Dipole-Dipole Resistivity Profile Along Line 305 m North,10 m Dipoles... 41
11. Dipole-Dipole Resistivity Profile Along Line 305 m North, 20 m Dipoles.. 4 3
12. Dipole-Dipole Resistivity Profile Along Line 275 m North, 15 m Dipoles.. 44
1 3. EM-31 and EM-34 Profiles Along Line 305 m North................................... 46
14. GPR Profile Along Line 305 m North........................................................... 47
15. GPR Spectral Analysis for 4 Traces Along Line 305 m North...................... 49
16. Dipole-Dipole Resistivity Forward Model Without Plume........................... 57
17. Dipole-Dipole Resistivity Forward Model With Plume................................ 58
vu ..
CHAPTER I
INTRODUCTION
Statement of Problem
Contamination of shallow aquifers by fuel oils is an increasing problem in the
United States. This contamination is commonly associated with leaks from petroleum
product storage tanks or spills that occur during the handling of the petroleum. This
contamination of the shallow aquifer can ruin a water supply and, in extreme cases,
endanger regions down gradient from the contamination site. It is in the best interest
of the public to develop techniques for determining the location of contamination and,
in some cases, the specific nature of the contamination.
The intuitive electrical model for fuel oil contamination treats the fuel oil as a
electrically resistive body in a more conductive host of groundwater (Monier
Williams, 1995). Laboratory experiments by Mazac and others (1990), DeRyck and
others (1993) and Gajdos and Kral (1995) have attempted to analyze the effect of fuel
oil contamination in the subsurface by measuring the physical properties of electrical
conductivity, electrical permittivity, and magnetic permeability. The conclusions of
most of the laboratory studies have corroborated the theoretical model. However,
field studies conducted by Western Michigan University have found instances where
1
the fuel oil contamination has appeared as an electrically conductive body (McNeil,
1994). Therefore, an analysis of the field results in comparison with the laboratory
studies must be conducted to determine the reasons for this serious discrepancy.
Gajdos and Kral, (1995) and others have also noticed conductive behavior.
Purpose of Study
Geophysical field surveys were deployed over an area of known fuel oil
contamination. Geochemical and geological background information exists for this
site, and the geophysical results can be compared to models based on the subsurface
conditions. The first objective was to determine if the dissolved fuel oil plume
contamination was electrically conductive or resistive. The second objective was to
evaluate the specific methods used in the surveys to see which are best suited for
determining contamination. This study is intended to provide a framework for
subsequent surveys to improve and supplement the various methods to a higher
degree of accuracy and precision with respect to the measurement of the physical
properties.
Site History
The site is located on the decommissioned Wurtsmith Air Force Base
(WAFB), in Oscoda, Michigan. The site itself was a former fire training facility, Fire
Training Area 02 (FT-02), used for weekly training exercises for a duration of almost
2
40 years (Barcelona, oral commun., 1996). The training exercises typically consisted
of the ignition of approximately 2000 gallons of JP-4 aviation fuel. Some but not all
of the JP-4 was consumed during the exercise, leaving the rest to either evaporate into
the air or seep into the ground below. Until the early 1980's the ground cover in the
site consisted only of grass. At that point a concrete fire pad was installed with a
drain. This drain was connected to a oil-water separator in an attempt to capture the
fuel before it seeped into the ground. Personal communications with engineers
working on the site have revealed that the drain often overflowed, leaving the JP-4
and fire fighting chemicals to seep into the ground (Barcelona, oral commun, 1996).
The FT-02 site is currently being studied under the auspices of the National Center for
Bioremediation Research and Development (NCIBRD), which is a partnership of the
Department of Defense, the Department of Energy, and the Environmental Protection
Agency. The FT-02 site is used to monitor natural changes in the JP-4 contamination
over time, and provides an opportunity to analyze a field site that has not been
impacted by various remediation technologies.
Site Geology
Wurtsmith Air Force Base is bordered by the Au Sable River to the south, and
by Van Etten Lake to the East. Both bodies of water discharge into Lake Huron,
which is located less than 2 miles from the southeastern boundary of WAFB. The
FT-02 site is located in the southwestern portion of the base (Figure 1 ), and is
3
Figure 1.
Source:
VAFB
0 0 0 0 0
.
0 0 0 0
. 0 0 0
. 0 0 0
�00
Meters
-e- V(s locat;on
61 0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 .
0 .
0 0
l?i;0 0
0
.
0�
0 0
0 0
• 0
0 0 0
0 0 0
GPR Survey l;nes and DDR Lnes where Marked=:::::::::: Grove,( Roads
o Survey Gr;d Node,sSP
FT-02 Site Map.
. . I . .
Modified from NCIBRD files. Used With permission ofM. Henry.
488
L . L ' L ' J J d';;\ 0 0 0 427
0
-A.
. . .
• • • . . . . . • . . . 0 . . . . . .
. . 0
. .
0DDR 0
DDR
. '•
. . . 0 0
0 0 0 0 0
0 0 0 0 0
Sur vey
MALM Survey
--
183
122 3
adjacent to a series of wetlands that are connected to the Au Sable River. A survey
grid of concrete benchmarks has been installed over the site, and all surveys were
located relative to a benchmark in the southwest comer of the site. For the purposes
of this study, all directions were set to align with their magnetic ordinal counterparts.
Changes in topography over the FT-02 site are very subdued, with elevations ranging
from 188 m to 192 m above mean sea level. Most of the topographic relief occurs in
two linear depressions that cross the middle of the site to the north and south of the
concrete fire pad and trend towards the east (Figure 2). The subsurface of the FT-02
site is comprised of glacial materials lying unconformably above the bedrock. The
glacial materials are composed of a flat lying glaciofluvial sand approximately 20 m
to 24 m thick and underlain by a 40 m to 76 m lacustrine silty clay. Depth to water
table in the unconfined aquifer of glaciofluvial sand ranges from 5 m to 7 m. The
direction of flow in the unconfined aquifer is from the northwest to the southeast, and
much of the flow discharges at the surface into the wetland complex located to the
south of the FT-02 site.
Site Geochemistry
Geochemical analyses of water samples have been run by NCIBRD on
samples from over 50 wells at the FT-02 site. The plume is comprised of several
distinct components (Figure 3). The JP-4 is comprised of aliphatic and aromatic
hydrocarbons, which exist either as a separate liquid phase above the ground water
5
�o 1'1E>ters
======= Grave/ Road
VArB
Q • �I.
0 0
0 0
0 0 0
0 0
0 0 0
0 0 0
FT-J◄ Mon;tor;ng w'el/ Loco t;on
Fig_ure 3.
0 1.2�
0 0
0 ••
.1�3.
0 0
0 0 0
. 3�6. 0 . 4?7•\\· 0
0 0 0 0 0 �\ 0
0 488
0 4 27
0 366
·305
0183
•0 122
PLUME0
0 0 0 0
0 0 0
Source:
FT-02 Site Plume With Well Locations.Modified fron, NCIBRD files. Used With permission ofM. Henry_
--
'-J
0
·o
table or as a dissolved phase within the saturated zone. There are also chlorinated
hydrocarbons such as 1,2-dichloroethene and vinyl chloride in low concentrations. A
complete list of the organic compounds tested for in July 1996 is listed in Appendix
A. In addition to the organic analyses, tests were run on water samples to determine
pH, dissolved oxygen (DO), specific conductance, and iron(II) concentration. Ground
water samples from uncontaminated areas have a low specific conductances of 180 to
240 microSiemenslcentimeter, DO values of greater than 2.48 ppm, and no detectable
iron(II) concentration. Ground water samples from areas contaminated by the
dissolved fuel plume show both an increased concentration of iron(II) ranging from 5
to 45 ppm, DO values less than 1.2 ppm and increased specific conductance
ranging from 400 to 575 microSiemenslcentimeter. Table 1 depicts the full range of
chemical data.
Table 1
Results ofNCIBRD Chemical Analyses ofFT-02 Site From April 1996
Well# (* - plume)
FT-1
FT-2*
FT-3*
FT-4S*
pH
7.13
7.05
6.95
8.37
DO (mg/L)
NIA
0.51
0.65
0.63
Fe2+
(mg/L)
NIA
4.69
6.06
6.24
Spec. Cond (µSiem)
290
348
444
517
Depth (m)
7.62
7.62
7.32
6.09
8
Table 1--Continued
Well# (* - plume)
FT-4D
FT-5D
FT-6S
FT-6D
FT-7S
FT-7D
FT-8S*
FT-8D
FT-9S*
FT-9D
FT-10S
FT-l0D
FT-11S
FT-1 lD
FT-12S
FT-12D
FT-13S*
FT-13D
pH
7.59
8.54
8.51
8.58
8.10
8.25
7.09
8.19
7.33
8.26
8.35
8.31
8.35
8.48
7.59
7.98
7.48
8.39
DO (mg/L)
0.55
2.18
>2.48
1.91
NIA
0.76
0.81
0.71
0.65
0.78
>2.48
>2.48
>2.48
>2.48
0.66
0.98
0.58
0.93
Fe2+
(mg/L)
0.03
<0.02
<0.02
<0.02
NIA
<0.02
13.74
<0.02
142
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
>7.6
0.14
Spec.Cond (µSiem)
227
253
225
225
136
182
502
117
455
117
243
274
300
247
431
282
574
216
Depth (m)
18.90
12.19
6.09
12.19
9.45
14.94
9.45
14.94
9.75
14.93
7.62
11.89
9.45
12.19
9.45
12.19
9.14
12.19
9
Table 1 -- Continued
Well#
(* - plume)
FT-14S
FT-14D
pH
7.95
8.38
DO
(mg/L)
1.54
2.47
Fe2+
(mg/L)
<0.02
<0.02
Spec. Cond
(µSiem)
301
232
Depth (m)
9.45
12.50
Overall, the chemical data show that there is a decrease in specific
conductance with depth, as the deeper wells (denoted with a D) have lower values
than their shallow counterparts ( denoted with a S). All but one of the pH values is
above 7.0, indicating that neutral to slightly alkaline conditions are present throughout
the site. There appears to be a good correlation between increased conductivity and
iron(II) concentration in areas affected by the dissolved plume. Other ions species
concentration were unavailable.
10
CHAPTER II
REVIEW OF RELEVANT LITERATURE
Theoretical Models
Several models have been developed to describe fuel oil contamination with
respect to the hydrogeologic parameters and the electrical parameters. The
hydro geologic parameters help describe the shape and concentration of the plume
after the contaminant has entered the subsurface (Fetter, 1994). At this particular site,
FT-02, the contaminant is a light non-aqueous phase liquid (LNAPL) which mixes
with the ground water to a limited extent. Some of the JP-4 will reside directly above
the capillary fringe in a pool that is called "free product". This free product can
diffuse into the vadose zone, but will not diffuse into the saturated zone. A smaller
portion of the JP-4 can dissolve into the ground water in the saturated zone, where it
can be advected (carried along with the flowing ground water) and diffused
(spreading due to variability in flow paths in a porous matrix) further into the
saturated zone.
The 3-dimensional electrical properties of resistivity and electric permittivity
are highly variable between the vadose zone, the saturated zone and the contaminated
areas. Resistivity is defined as the inverse of the ability to transmit current; materials
11
with a high resistivity require more potential to transmit a given amount of current
than materials with a low resistivity (Telford and others, 1990). The bulk resistivity
of a granular rock or unconsolidated sediment can be modeled by the parameters of
porosity, fluid resistivity, degree of saturation and a cementation factor by using
Archie's Law (Archie, 1942). Archie's law is an empirical relationship that links the
various parameters to the bulk resistivity. Soil and glacial material can be modeled
by
where Pb is the bulk resistivity; a, m, and n are empirically derived constants; S is the
fraction of the pores containing the fluid, and Pf is the fluid resistivity. The bulk
resistivity of a soil is highly dependent on the resistivity and degree of saturation of
the fluids in the pore spaces. The resistivity of the matrix materials ranges from
4E+10 Ohm-meters for pure quartz to 20 Ohm-meters for an unconsolidated wet clay
(Telford and others, 1990). Theoretical models by Endres and Redman (1993)
demonstrate that as hydrocarbon saturation in porous media increases, the bulk
resistivity increases as well. Endres and Redman (1993) also demonstrated that the
relative electrical permittivity can change from 20 for a mixture of uncontaminated
ground water and sand, to 4 for a mixture of petroleum hydrocarbons and sand.
A survey of the properties ofLNAPLs by Monier-Williams (1995)
summarizes some possible mechanisms for an increase in resistivity and some
12
,1,.•ms•n Pb== a'!' Pf
possible mechanisms for a decrease in resistivity of a LNAPL plume. The
mechanisms for an increase in resistivity involve the dynamic displacement of the
water by the LNAPL resulting in depletion of the aqueous phase, a loss of the
capillary fringe and depression of the water table, reduction in connectivity of the
aqueous phase, and a change in the wetting phase of the aquifer solids (Monier
Williams, 1995). The mechanisms for a decrease in resistivity involve alternate
changes in the wetting phase of the aquifer solids, the formation of emulsions
increasing the water/LNAPL surface contact area, enhanced aqueous phase
connectivity due to changes in the gas phase, and additives in the original LNAPL that
would enhance current flow (Monier-Williams, 1995)
Controlled Spill Studies
Several experiments have been undertaken in the laboratory in order to test the
hypotheses developed from the theoretical models. These experiments were run in a
tank or column constructed to model a glacial aquifer. Typically, a model was
injected with a known amount of hydrocarbons, and monitored with geophysical and
geochemical analyses over time to see what the effect of injection would be. A tank
model developed by DeRyck and others (1993) showed a strong increase in resistivity
in the capillary fringe as the hydrocarbon (kerosene) displaced the water in a portion
of the capillary fringe.
A column experiment by Gajdos and Kral (1995) indicated that at low
concentrations of hydrocarbons (less than 5% by liquid phase volume), a decrease in
13
resistivity in the saturated zone can be measured of up to 20% of the original bulk
resistivity. This decrease was attributed to a non-equilibrium state in the wetting
phase that preferentially channelled current through the pores. The authors noted an
increase in resistivity as concentrations increased past ten percent of the starting
volume.
A tank experiment by Grumman and Daniels (1995) simulated a kerosene spill
in a sand matrix in order to test the electrical behavior by adding the kerosene into
ports that connected with the aquifer. The electrical properties were measured
indirectly with a ground penetrating radar (GPR) unit, and demonstrated that a GPR
signal can be attenuated slightly by the presence of kerosene in the vadose zone and
the capillary fringe. This is attributed to either a redistribution of soil moisture or
contaminant vapor effects (Grumman and Daniels, 1995).
The results of the controlled spill studies show that the apparent resistivity
increases as the kerosene or other light hydrocarbon displaces the water in the
capillary fringe and in the water table below. Occasionally, a decrease in resistivity is
measured, which has been attributed to current channeling due to a change in the
wetting phase of the grains. This change involves replacement of water by LNAPL as
the wetting fluid on the grain surface. This will restrict the water to the middle of the
pore space, and the effective cross section of the water in the pore space is reduced as
well. This reduction in cross section will allow current to pass easily through a layer
that appears to be mostly hydrocarbon. As the hydrocarbon concentration increases in
14
the pores, this decrease in resistivity declines and then switches back to an increase in
resisitivity.
Field Studies
Several field studies have been conducted over known hydrocarbon
contamination plumes to test whether the phenomena observed in the laboratory
studies can be duplicated by actual spills. The field studies range in age from less
than 1 week, to some more than 10 years.
Daniels and Vendl (1992) found a decrease in GPR amplitude which they
interpreted as being due to the contaminant vapor phase in the capillary fringe. The
study found a correlation between the decrease of the GPR signal amplitude in the
vicinity of the gasoline concentration and the presence of gasoline. The decrease in
amplitude was determined to be located in the vadose zone, and is attributed to the
contaminant vapor phase.
Mazac and others (1990) found that a very young (less than 1 week) spill had
a high electrical resistivity in contaminated areas. The survey was conducted in
Quaternary sands and gravels, with a free product plume 0.2 m thick. Vertical
electrical soundings (VES) and a modified mise-a-la-masse (MALM) survey were
used to measure the electrical resistivity over the contamination. The high electrical
resistivity was attributed to the insulating properties of the fuel oil contaminant.
A case history by Maxwell and Schmok (1995) shows an anomalous region of
decreased GPR amplitude over a hydrocarbon plume, but based their depth estimate
15
of the plume on fully saturated conditions. This is contradictory to their assertion that
the decreased GPR amplitude is due to the contaminant vapor phase, which would be
located in the vadose zone. Also, the anomalous GPR amplitude has a signature that
is more indicative of conductive surficial fill in a trench.
A case history by Monier-Williams ( 1995) found low electrical resistivity in
areas with significant free product thickness around a landfill. The low electrical
resistivity was measured with a frequency domain electromagnetic induction
instrument. The reason for the low electrical resistivity was attributed to either an
emulsion or enhanced surface conductance at the fuel oil-aqueous contact. A good
statistical correlation between maximum free product thickness and low electrical
resistivity was seen, however, no chemical basis for the theorized emulsion was
shown.
A similar case history by Gajdos and Kral (1995) also measured a low
electrical resistivity over areas associated with fuel oil pollution. The low electrical
resistivity was measured with a frequency domain electromagnetic induction
instrument. The low resistivity was attributed to the increase of free ion density due
to a change in the wetting phase.
A study of a gas station tank leak by Grumman and Daniels (1995) found GPR
signal attenuation in areas of hydrocarbon contamination above the interpreted water
table. The site cover is glacio-lacustrine soil, with strong contaminant vapors present
in the vadose zone. The GPR signal attenuation is attributed to the contaminant vapor
phase in the vadose zone causing loss of signal.
16
There are three classes of results from the field studies. First, electrical
resistivity highs are measured over very young spills in the capillary fringe. Second, a
decrease in GPR amplitude can be measured over contaminated areas in either the
capillary fringe or in the saturated zone. Third, low electrical resistivity is measured
in contaminated areas that are of an older age.
Geochemical Studies
There are several papers dealing with the geochemistry of a hydrocarbon
contamination plume. A series of papers was based on analyses of a pipeline spill
near Bemidji, Minnesota. The spill was monitored over time to see how the plume
evolved chemically. The first paper, by Bennett and others (1993), discussed how the
dissolved portion of the hydrocarbon plume was degraded naturally by microbes
present in the soil. This degradation, also known as natural bioattenuation, showed
that several distinct chemical zones developed in the regions down gradient and
within the dissolved plume. These zones were dependent on the specific
electrochemical makeup of the ground water, and followed a regular pattern (Bennett
and others, 1993).
The second paper, by Eganhouse and others (1993), discussed the amount and
type of hydrocarbons present in each zone. In addition, the authors established the
particular type of hydrocarbon that was most likely to degrade in each zone. All types
of hydrocarbons were found to degrade in oxic zones, but the rates varied
17
significantly (Eganhouse and others, 1993). Overall, the results of the second paper
supported the degradation zones established by the authors of the first paper.
The third paper, by Baedecker and others (1993), dealt with the specific
reactions that occur in each zone that lead to the degradation of the hydrocarbon. The
products of the bioremediation include: soluble iron(II) and manganese(II),
production of organic acids in anoxic zones, CO2 and CH4 (Baedecker and others,
1993 ). The presence of CO2 and organic acids can lower the pH of the ground water,
and bring more ions into solution (Bennett and others 1993). In addition to the
chemical studies, physical measurements on the fluid resistivities of uncontaminated
and contaminated regions of the dissolved plume at Bemidji have shown a 3 to 5 fold
decrease in resistivity when comparing ground waters from contaminated regions to
uncontaminated regions.
The fourth and final paper, by Cozzarelli and others (1994), discussed the
evolution of organic acids from the degradation of the hydrocarbon. The authors
concluded that location of the production of organic acids varied over time, as the
chemical zones shifted location. Organic acids were found to accumulate in anoxic
groundwater, and when oxygen is present, the acids are degraded as well.
The conclusion of the geochemical literature is that hydrocarbons will degrade
over time, if the terminal electron acceptors ( oxygen, nitrate, ferric iron and others)
are present. These degradation reactions will evolve CO2 and will increase the
acidity of the ground water. This increase in acidity can aid in the dissolution of
aquifer solids, which will increase the ionic content of the ground water. The end
18
result of these reactions can bring about a decrease in apparent resistivity. This is in
disagreement with the earlier intuitive geophysical models, which theorize that
electrical resistivity increases over hydrocarbon contamination, but does provide a
plausible explanation for why many field studies have shown decreased electrical
resistivity over hydrocarbon contaminated sites around the dissolved plume.
19
CHAPTER III
METHODOLOGY
Self Potential
The self potential (SP) method was developed in mining exploration, and also
applied to well logging for petroleum exploration (Telford and others, 1990). There
have been several attempts at applying the SP method to water resource evaluation,
with varying degrees of success (Corwin, 1990). The self potential is a natural
potential present beneath the Earth's surface that is generated by several physical and
chemical mechanisms. The mechanisms that can cause the self potential are: the
streaming potential, the diffusion potential, the Nemst potential, and the electrolytic
contact potential (Telford and others, 1990). An in-depth analysis of the various
mechanisms that comprise the self potential can be found in Telford and others (1990)
or Corwin (1990). Although it is nearly impossible to determine the amount each self
potential mechanism adds to the self potential, qualitative estimates of the
contribution by each mechanism can be evaluated based on the geologic conditions at
a particular site.
The data were acquired using non-polarizing electrodes and a high input
impedance voltmeter. The non-polarizing electrodes consisted of a PVC housing and
a porous plug (a wooden dowel) in contact with a saturated solution of copper sulfate.
20
This solution was placed in contact with a copper wire to act as an electrode, with the
copper sulfate solution making the connection between the subsurface and the
voltmeter. The use of the non-polarizing electrodes allowed for the exclusion of
electrolytic contact potentials at the metallic electrodes. The high input impedance
voltmeter was used so that the measurement of potentials between two electrodes
would not be interfered with by current leakage through the voltmeter.
The survey was conducted over the southern portion of the site utilizing a
fixed reference electrode at 305 m North and 472 m East. Potentials were measured
at 15.24 m intervals along east-west lines, and the mobile electrode was returned to
the reference electrode position to measure drift after 4 east-west lines had been
surveyed. The data were plotted in SURFER, using the kriging option for generating
the contour plot.
Mise-a-la-masse
The mise-a-la-masse (MALM) method was developed in the mining industry
in order to roughly determine the boundaries of an ore body after one borehole had
been drilled into a conductive sulfide mineral deposit. The method makes use of a 4
electrode system, 2 current electrodes and 2 potential electrodes. One current
electrode is placed down the borehole into the ore body, and the other current
electrode is placed very far away from the borehole on the ground surface (Figure 4).
One of the potential electrodes is placed on the ground surface very far away from
21
B@ CO·�'------,L
Figure 4.
A M N B
t J l t-�tlW I�
�---A�---
Dif
,o\t - D,pole. R.es 1s+;0i+y Pro911, tlj A ·e M N
+ i l t.I I <'-- (l - ->!.---(\a_---:,;<:--<.\.-') : I
Electrode Configurations for Mise-a-la-masse, Vertical Electrical
Soudings, and Dipole-Dipole Resistivity Profiling.
22
either the downhole or surface current electrodes. The other potential electrode is
used to measure the potential difference on the surface around the borehole electrode.
It can be demonstrated from electrical theory that the potential around the downhole
electrode will appear as a radially concentric pattern, with the largest potential
difference located near the downhole electrode (Telford and others, 1990). This
radially concentric pattern will only appear in a homogenous subsurface with no
variations in the electrical resistivity. In the presence of a conductive ore body, or
conductive contaminant plume, the radially concentric pattern will distort to roughly
follow the boundaries of the conductive body (Telford and others, 1990). This is due
to the increased density of current in the conductive region, which leads to a higher
potential difference relative to the distant potential electrode. The conductive
subsurface body acts as an extended electrode of constant potential.
In this study, for lack of a better access point to the plume, the "downhole"
current electrode was attached to the steel casing of the cable tool drilled well FT-4D
located at 311 m North, 309 m East. The surface return current electrode was placed
at 335 m North, 76 m East and the surface potential reference electrode was placed at
274 m North, 503 m East. The potential drop was measured using the BISON 2390
resistivity meter, which used a constant current source of 100 mA, allowing all
potentials to be plotted without normalization. The potential differences were
corrected for the minor influences of the distant surface current and potential the
electrodes not being located at infinity, and were contoured using the kriging option
23
on SURFER.
Electrical Resistivity
Vertical Electrical Soundin� (VES)
Vertical electrical sounding is a resistivity measurement using a four electrode
system similar to the one described in the mise-a-la-masse section. In this case, all
four electrodes are located in a line on the surface. The two current electrodes are
placed outside of the two potential electrodes. In Figure 4, the current electrodes are
labeled A and B, with AB equal to the distance between the current electrodes. The
potential electrodes are labeled M and N, with MN equal to the distance between the
potential electrodes. An expression can be used to calculate the apparent resistivity of
the earth based on the input current, measured potential difference, and the surface
geometry of the electrodes by the equation:
Pa = (1t/4) * [ ((AB)2 - (MN)2)/(MN)] * (VII)
where V = potential difference in Volts, I = input current in Amperes and Pa =
apparent resistivity in Ohm-meters.
Apparent resistivity is a field measured quantity that gives relative information
about the resistance to current flow in a particular volume of the subsurface (Telford
�d others, 1990). In the case of a homogeneous isotropic earth, the apparent
resistivity will remain constant for all electrode configurations, and over any range of
24
input currents. By measuring the changes in terms of apparent resistivity, it is
possible to infer vertical and lateral changes in electrical resistivity over a particular
area. The VES method determines the change in apparent resistivity with depth, by
expanding the current electrode spacing AB and keeping the potential electrode
spacing MN constant around a fixed center. The data are plotted on a log-log graph
with apparent resistivity on the vertical axis and AB/2 on the horizontal axis. The
apparent resistivity curve was inverted in an iterative I-dimensional computer
program which finds the best statistical fit to a measured field curve starting with an
operator-supplied resistivity versus depth model. There is a great deal of uncertainty
in the results, due to the Principle of Equivalence, as a layer of a given thickness and
resistivity can be modeled as a thicker and less resistive layer to give the same effect
on a maximum portion of a VES curve and the expression of thickness divided by
resistivity is constant for the minima of the VES curve (Telford and others, 1990).
However, by matching the resistivity layer thicknesses to known geological controls
such as topsoil, vadose zone, and saturated zone thickness at a control well, a good
estimate of the true resistivity of layers and thicknesses elsewhere can be determined.
For this study, several model resistivity values were calculated to estimate the effect
of the Principle of Equivalence and the Principle of Suppression.
Three soundings were measured over the FT-02 site, each using six steps per
decade of AB/2, and stopping at AB/2 = 100 meters. VES # 1 was measured 259 m
North, 351 m East; VES # 2 was measured at152 m North, 396 m East; and VES # 3
25
was measured at 107 m North, 448 m East. VES # 1 located within the dissolved
plume, used the BISON 2390 resistivity meter. VES # 2 located on the border of the
dissolved plume, used the SYSCAL R-2 resistivity meter. VES # 3 located outside of
the boundaries of the dissolved plume, used the SYSCAL R-2 resistivity meter.
Dipole-Dipole Resistivity Profilin2
Dipole-Dipole resistivity profiling (DDR) is another in-line resistivity
measurement like the VES method. The DDR method combines elements of
profiling, the measurement of lateral changes in apparent resistivity, and sounding, the
measurement of vertical changes in apparent resistivity. In the field array the
potential electrodes are closely spaced and remote from the current electrodes, which
are also closely spaced (Telford and others, 1990). The close spacing between the
pairs of the current and the potential electrodes is held constant, and the separation
between these dipoles is an integer multiple of the constant spacing. A general
schematic of the field layout is shown in Figure 4, with the equation for the apparent
resistivity given by:
Pa= 7t *a* n * (n+l) * (n+2) * (VII)
where a = electrode dipole spacing in meters , n = integer spacing in meters, V =
potential difference in Volts, I = input current in Amperes, and Pa = apparent
resistivity in Ohm-meters. The data were collected at regularly spaced intervals by
26
holding the centerpoint between the groups fixed and expanding the distance between
the groups out to n=4. The centerpoint was then shifted along the line by the "a"
spacing and the dipole separation was again expanded from n= l to 4. After all the
data have been collected and all the apparent resistivities calculated, the data are
presented in a pseudosection format as described in Telford and others (1990).
Three dipole-dipole surveys were measured over the FT-02 site. The first
survey was collected along line 305 m North with 10 meter dipole spacings using the
SYSCAL R-2 resistivity meter. The second survey was collected along line 274 m
North with 15 meter dipole spacings using the SYSCAL R-2 resistivity meter. The
third survey was collected along line 305 m North with 20 meter dipole spacings
using the SYSCAL R-2 resistivity meter.
This pseudosection apparent resistivity data are then inverted using an
iterative 2-dimensional computer program which generates theoretical earth models
that would give the measured pseudosection values. The particular program used in
this study was RES2DINV, a quasi-Newton solving method designed to invert
measured DDR profile data into a theoretical earth model (Loke and Barker, 1995).
As in the VES computer inversions, there is a great deal of uncertainty in the results,
again due to the Principle of Equivalence. This uncertainty is present both in the
vertical and lateral positions of the apparent resistivity structures, as they are
determined from the apparent resistivity parameter. The apparent resistivity
parameter is simply a ratio that reflects the effect of potential drop, current, and the
27
/
geometry of an array (Telford and others, 1990), and is not simply related to the true
resistivity structures which lie beneath the surface. For this site, the inverse model
resistivity depths from this program for the various "n" values were divided by two in
order to better fit known depth to a principal resistivity boundary, the vadose zone -
saturated zone interface. In addition to the inverse models, 2 forward models were
developed in order to estimate the effects of the water saturated zone and the clay
layer have on the measured resistivity pseudosection.
Electromagnetic Induction
The electromagnetic induction method was originally developed for the
detection of conductive ore bodies in the mining industry. There are two major types
of electromagnetic induction equipment, frequency domain and time domain. The
two instruments used in this study are frequency domain units. The theory of
electromagnetic induction can be found in many texts, such as Telford and others
(1990) or Dobrin and Savit (1990). The underlying principle of frequency domain
electromagnetic induction is as follows. A primary electromagnetic (EM) signal of
constant frequency and power is sent out from a transmitter coil. This primary EM
signal travels into the subsurface and interacts with conductors that are present. The
interaction of the primary EM signal and the subsurface conductors induce a circular
current flow in the subsurface conductor. This "eddy" current flow, in turn, creates a
secondary EM signal. The secondary EM signal, along with the primary EM signal
28
that travels through the air, is measured at a receiver coil. The secondary signal
properties are dependent on the electrical resistivity, relative electrical permittivity,
and the magnetic permeability of the subsurface. Since the operating frequency of the
measurements is low with respect to the electromagnetic spectrum, the relative
permittivity has an insignificant effect on the secondary signal (McNeill, 1980). The
relationship between the primary and secondary signal is expressed as the amount of
secondary in-phase with the primary, and the amount of signal 90 degrees out-of
phase from the primary is measured as well. The out-of-phase ratio can then be
converted into an apparent conductivity, using the assumptions developed by McNeill
(1980). This apparent conductivity shares the same characteristics as the apparent
resistivity parameter discussed previously, as the apparent conductivity is the inverse
of the apparent resistivity.
The two units used in this study were the Geonics EM-31 and EM-34. Both
were employed in the horizontal loop configuration, which provided the maximum
depth penetration of which the unit is capable of (McN eill, 1980). The EM-31 data
were collected along numerous EW and NS trending lines, while the EM-34 data
were collected along several EW trending lines only using the 20 meter coil spacing.
In addition, forward models were run on a generalized resistivity structure to estimate
the expected values of ground conductivity off and on the plume.
29
.
Ground Penetrating Radar
The principles and theory of GPR are based on the wave equation which is
derived from Maxwell's equations, a succinct summary of which can be found in
Daniels (1989). The parameters that affect GPR are co�ductivity (cr), magnetic
permeability(µ), and electric permittivity (t). The paramter of magnetic permeability
was not considered in this study because the concentration very low in common earth
materials. The two properties that affect attenuation and propagation of
electromagnetic waves are cr and t (Daniels, 1989). The velocity of the GPR signal is
approximated by:
where V m = velocity in the medium in meters per second, V c
= velocity of light in a
vacuum (3 E+08 mis), tr= relative electrical permittivity, which is unitless. The
attenuation of the GPR signal is governed both by tr and cr, with the cr term
dominating the attenuation factor at cr = 5.6 mS/m or greater for a 100 MHz radar
signal in a saturated aquifer (tr= 20) (Daniels, 1989).
GPR data were collected along north-south and east-west lines, with 30.5
meters between lines. The gain function of the amplifier was set in an area known to
be free of contamination and set such that later signals had approximately the same
amplitude as the early signals. Bistatic 100 MHz antennae were used with the GSSI
30
SIR-10 GPR system. The scan length of all records was 400 nanoseconds, with a
sample digitization rate of 512 samples/scan. Scans were generated at 40
scans/second. Acquisition filters used were 3-stage Instantaneous Impulse Response
(IIR) with low-pass set at 80 cycles/scan and high-pass at 10 cycles/scan. Horizontal
smoothing was accomplished with a 5-scan running average filter. Field data were
down loaded to a personal computer for data processing.
Data processing consisted of rectifying the horizontal scale to approximately
15 scans/meter to account for variances in the towing speed of the antennae. GPR
lines were also corrected for changes in topography by applying static shifts based on
ground elevation. No post-processing filters were applied to this data set.
31
CHAPTER IV
RESULTS
Self Potential
The drift corrected data from the self potential survey were plotted and
contoured in SURFER, utilizing the kriging option to interpolate values between
measured points. The data are presented in Figure 5. There is high positive trend
passing through the center of the surveyed region, oriented around N 30 W. The
positive trend has a value ranging from 10 to 20 mV, with background values in the
region ranging around -5 mV to +5 mV. There is a secondary positive trend to the
east of the major trend, with a value ranging from 10 to 16 m V.
Mise-a-la-masse
The normalized potential data from the mise-a-la-masse survey were plotted
and contoured in SURFER, utilizing the kriging option to interpolate values between
the measured points. The map results of the raw and processed data are presented in
Figure 6. There is an circular trend passing through the surveyed area, with higher
potential differences nearest to the location of the downhole current electrode, and the
lowest potential differences furthest from the downhole current electrode. There is
slight deviation from the circular trend around the point 260 m North 411 m East
32
,-... 2
0 2 z
1
1
200 250 300 350
Easting (m)
Figure 5. Self Potential Contour Plot.
400 450 500
22
19
4
1
-2
-5
-8
-11
-14
-17
-20
33
SP (mV)
E .._, O> C
€
34
MALM Field Data - Contour Interval 10 mV
fvlagnetic Easting (m)
MALM Processed Data - Contour Interval 4 mV
fvlagnetic Easting (m)
Figure 6. Mise-a-la-masse Contour Plots.
Mag
netic
Nor
thing
(m)
Mag
netic
Nor
thing
(m)
oo·o
0 8
that has a lower negative potential than the circular trend.
Electrical Resistivity
Vertical Electrical Soundin�
The 3 vertical electrical soundings were plotted and inverted on the SCHLINV
program, with the field data and inversion results plotted on the graph. The first
sounding (VES # 1) at 259 m North, 351 m East, which is located within the region of
the plume, had the best statistical fit with a 4 layer model. Two inversion attempts
were run on this VES, in order to evaluate the effect of suppression and equivalence.
The inversion results are shown below in Figure 7, the models are in Table 2 below.
Table 2
Inverse Models for VES # 1
Inverse Model 1 Inverse Model 2
Layer 1 98nm 0.24m 97 nm 0.25 m
Layer 2 1113 nm 6m* 1103 nm 6m*
Layer 3 120nm 15.36 m 89nm 12 m *
Layer 4 32nm 33nm
RMS error 16.823 % 12.832 %
* - denotes parameter was held constant during inversion
35
-
E
E
� ·5
c � ro
Figure 7.
1000
� � 0
100
0
□
6
1
0
0 0 � ij
�
Curve
Field Data
Inverse Model 1
Inverse Model 2
10
AB/2 (m)
Field and Inverse Model Plot for VES # 1.
36
§
D
D 0
0 6
@
100
10
The second sounding (VES # 2) at 152 m North, 396 m East, which is located on the
border of the plume, had the best statistical fit with a 5 layer model. Due to the
extreme decrease in resistivity with depth, no forward models were attempted on this
model. The resultant inverse model is shown below, the plot of field and model
values are on Figure 8 with the inverse model shown below in Table 3.
Table 3
Inverse Model for VES #2
Inverse Model
Layer 1 3632 nm 0.14 m
Layer 2 33000 nm 0.89 m
Layer 3 5600 nm 7.27 m
Layer 4 800nm 10.0 m *
Layer 5 27nm
RMS error 11.223 %
* - denotes parameter was held constant during inversion
The third sounding (VES # 3) at 107 m North, 488 m East, which is located in an area
well outside of the plume, had the best statistical fit with a 5 layer model. In addition
to the inverse model, two forward models were run in order to evaluate the effects of
equivalence and suppression on layer 4. The models are shown below, and plots of
37
38
100000
10000 0 8 0 □ �
8 §---�
0
·5
1000
.... Curve C
8 � □ Field Dataro 100
0 Inverse Model
8
10
1 10 100
AB/2 (m)
Figure 8. Field and Inverse Model Plot for VES # 2.
-E E
• 1n B
0
the field and model resistivities are shown in Figure 9 and the inverse and forward
models are shown in Table 4.
Table 4
Inverse and Forward Models for VES # 3
Apparent Resistivity and Thickness of Layer
Inverse Model Forward Model 1 Forward Model 2
Layer 1 3631 nm 0.1 m* 3632 nm 0.14m 3632 nm 0.14m
Layer 2 33086 nm 1.14 m 33000 nm 0.89m 33000 nm 0.89m
Layer 3 6970 nm 6.84m 5600 nm 7.27 m 5600 nm 7.27m
Layer 4 4200nm 3.67m 400nm 10.0m 1600 nm 10.0m
Layer 5 42nm 27nm 27nm
RMS 6.27 % NIA NIA
error
* - denotes parameter was held constant during inversion
Dipole-Dipole Resistivity Profilin2
Three dipole-dipole resistivity soundings were deployed across the plume . The
first and second profiles were extended along line 305 m North . The first profile,
measured with a 10 meter dipole, is shown in Figure 10 along with the associated
inverse model, and the tabular data for the field data are in Appendix B. In Figure 10,
39
40
100000
Qi � li]
E 10000 �
8 e
� � ">
1000 6.
� Curve �
0
◊ Field Data 6.
□ Inverse l\t1odel 8co 100 0 Forward fvlodel 1 6.
� 6 Forward�2 8
10
1 10 100
AB/2 (m)
Figure 9. Field and Inverse Model Plots for VES # 3.
E
-
188
n
2
3
4
Depth 188
0.9
2.6
4.4
meters
6.4
0.5
228 268
Eosting nlong line 305 m North 308 348 388 428 468
Dipole Length= 10.0 meters
RMS error = 2.410
m.
-I
228 268 308 348 388 428 468 m.
c=J C=:J c::=J EiIJl 1-·-·-·-•.-4 mml mm mim l:liil.W 11111111 -123 ?35 451
hwerse Model nesisliuily Section
Ofifi 1661 0hm-mP.tcrs
Figure 10. Dipole-Dipole Resisitivity Profile Along Line 305 m North, 10 m Dipoles.
Field Data
there is an overall decrease in resistivity with depth with values ranging from 1600
nm to 2500 nm at the first datum level down to 100 nm and less at the fourth datum
level. Superimposed on top of this sharp decrease in resistivity with depth is a lateral
decrease in resistivity. The decrease occurs in 3 symmetrical peaks, with the center of
the middle peak around 318 m East. Overall, the 3 peaks are spread out from 288 m
East to 348 m East, and appear to be measurable at the first datum level in the field
pseudosection.
The second profile, measured with 20 meter dipoles, is shown in Figure 11,
and the tabular data are in Appendix B. As in the first profile there is sharp decrease
in resistivity with depth, with values at the first datum level ranging from 5100 nm to
500 nm, and values at the fourth datum level ranging from 30 nm to 200 nm. Along
with this sharp change in resistivity with depth, there are lower resistivities in the
center of the pseudosection for a given datum level. Unlike in Figure 10, this low
resistivity region has only 1 peak, centered around 325 m East.
The third profile, measured along line 275 m North with 15 meter dipoles, is
shown in Figure 12, and the tabular data are in Appendix B. There is a sharp decrease
in resistivity with depth, with values at the first datum level ranging from 4200 nm to
2000 nm, and values at the fourth datum level ranging from 40 nm to 200 nm.
Superimposed upon the sharp vertical change in resistivity is a lateral change in
resistivity. Values on a given datum level are much lower in the center region around
330 m East than those values in the distal regions of the pseudosection.
42
1.'l.'l
n
2
3
1
Depth 133
1.7
S.2
8.7
meters
12.7
17.0
21.'l Easling along line .'l05 m Nocth
293 .'l7.'l
. ii.I H: H: U IHI::: Ii! IJ}!.j;->>�·J5>·�sc�.[f Ii Ii Ii rf_�:.:�;�\�>-�-�,ij Hi:: iii i ifffiTfllii I ii I it, l: :,1 J.11 !,.I l.l,IJ..111(�•.l):-))):•:❖:-:•>fli' f
l I I I I I I I I I l I I I lip-(':•:•:-:-:-:-:-� .. 111111111111111 I fl 1111111
-it·�:1n�?'?�-?�\�:r�rtnff}rr{fi'"fi'"i111:.11: 1 u.1 t I � 1� 1i111 :n-� .. ;i•;=-
r���f�:�gtggff½tsr-, 1 !I !l ! lll!l In I !I (1/lili I! I! l!l !l l l!JJJlU !l!I. t :·.::::::.::::: :-,J_.q: t:J l ! :! J!: f IJ nr1�nrirrqrir
_'�� � :·� :� :� :': :� '.��JJ}J_ll)J_J.J_J)_J..i_�:� :� :�:::::: :·�:::::::::::::::::::::: . : :):':1t�� �'='}J_lJ)J)1)J)J)1) 1
. . . . . . . . . . . . . . . . . . . . . . .
·:��HHlHHfi!f=•·:::�.-
· · · · · · · ·.·.·.·.:.·.·.·.·.·.·.·.·.·: :·· Field Doto Dipole Lengt11 = 28 meters
213
RMS error = 7.8% 293 373
45.'l m .
'153 m.
c:::J c:::J G:=J [!lill) � !!!!!] - IBH8 llm!il - -17.1 152 189 1571 5017 Ohm-meters
lnuene Model Resistiuity Section
Figure 11. Dipole-Dipole Resisitivity Profile Along Line 305 m North, 20 m Dipoles. +:>, w
' / lXQ#IQ,X
\·•:•·•:•·········::::::,::i:i:i~::;:,._:,.:;:;:;:;:_·~·:: :::::::::.·:, ;,::) <,>.,:.>.:,::,::_::,:~:~:/
202
n
2
3
4
Depth 202
1.3
3.9
6.6 meters
9.5
12.0
262
262
[osllng olong line 274 m North 322
RMS Error = 14.3'1.
322
� C=:J c:=J Dill Ez:l I"""' mm! CBBB � 11Z1Z11 -
182
382
7.2 33.1 151 600 3139 Ohm-meters
lni•er\e Model Resi�tiuilu Section
442 IT'.
442 m.
Figure 12. Dipole-Dipole Resisitivity Profile Along Line 275 m North, 15 m Dipoles. .l:,. .l:,.
Field Oata Oipole Length = 15.0 metcn
Overall, each resistivity pseudosection shows a sharp decrease in resistivity
with depth. Along with this sharp vertical change, each pseudosection shows lower
resistivity values in the center region along a given datum level. The apparent
resistivity values change from survey to survey, but generally values on the first
datum level range in 1 000s of nm and values on the fourth datum level typically
range in the 1 Os of nm to the 1 00s of nm.
Electromagnetic Induction
The EM-31 and EM-34 profiles along Line 305 m North are shown in Figure
13. The coincident EM-31 and EM-34 profiles for several other lines are shown in
Appendix B. In the EM-34 profile there are two major spike anomalies near the ends
of the profile, with a minor drop in apparent conductivity around 325 m East. The
EM-31 profile shows several spike anomalies at the western edge of the profile, and a
slight high in apparent conductivity centered around 350 m East. There are no spike
anomalies at the eastern edge of the EM-31 profile. A line by line comparison of the
spike anomalies revealed several linear trends over the FT-02 site.
Ground Penetrating Radar
The GPR profile for line 305 m North is shown in Figure 14. The line for 305
m North shows a strong reflection doublet at approximately 80 nanoseconds into the
record. The amplitude of the record below the doublet around 80 nanoseconds varies
45
-. 40 E
� --
� ·5
g 0 "'O C
8 C
-�Q)� -40
-. 40 E
� --
� ·5
g 0 "'O C
8 C
-�
EM-34
EM-31
Q)� -40___._-----,---------,-----r-------.--
200 400 Easting (m)
Figure 13. EM-31 and EM-34 Profiles Along Line 305 m North.
46
w
200
300
Figure 14.
Legend:
IS
A
ISA
,� 321
Shadow Zone
GPR Profile Along Line 305 m North.
9.19m
;-------· I 13.98 m
SA denotes spectral analysis location; depth scales approximate based on tr= 8.3 in vadose zone and tr= 20
in saturated zone.
+>--..J
138 Thne 0
(RS
100
1.99 260 382
!SA E 443 488 Ill
4. m
across the radar record. There are strong amplitudes in the distal regions of the radar
record below 80 nanoseconds, and a marked decrease in amplitude in the central
region from 259 m East to 305 m East.
In order to evaluate the possible changes in reflection frequency along the line,
a spectral analysis was completed for 4 stacked traces located at 199 m East, 321 m
East, 352 m East, and 482 m East. The spectral analysis was computed over the entire
vertical length of the scan using RAD AN III and does not appear to have energy
normalization from scan to scan. The results of the spectral analysis of the stacked
traces are shown in Figure 15. Each spectral analysis shows similar results, with the
traces at 321 m East, 352 m East, and 428 m East showing more low frequency
content than that of the trace at 199 m East. For reference, the traces at 321 m East
and 352 m East are located within the plume region, and the traces at 199 m East and
428 m East are located outside of the plume region.
48
,
IIACNITUl)I
1.11
.. ,
II.II I-'.._,.-
IIACNITUDI 1.11
.. ,
Figure 15.
Legend:
35
33
50
y� -; bn
75 11111 CYCLES/ICIIN
,a 73 11111 CYCLES/ICIIN
GPR Sp�ctral Analysis Along Line 305 m North.
IIACNITUH 1..11
,.,
I � 8,8 r' V
IIACNITDH 1,1
1;,
35 50 75 lBB CYCLES/ICIIN
1,1f"Y !1 , ' � :p I
33 38 75 11111 CYCLES/I CAN
Clockwise from top left: 199 m East, 321 m East, 352 m East, 452 m East .i::,. '-0
.. A . - ~ 8 I
. --- ' CM -- -•
CHAPTER V
INTERPRETATIONS
Geophysical Results
Six different geophysical methods were used in an attempt to identify the
nature and location of a contaminant plume associated with hydrocarbon
contamination. Each method was first evaluated separately and then a final joint
interpretation was developed. All interpretations were based on the assumption that
there is a conductive plume associated with the dissolved hydrocarbon plume in the
ground water.
Self Potential
The self potential contour plot (Fig. 5) had a high positive anomaly running
through the center of the survey area. Based on the facts that non-polarizing
electrodes were used, and that there are no known mineral deposits underlying the
site, the SP anomaly is due to one of the hydrochemical potential mechanisms. A
likely source for this potential could be the presence of a conductive plume in ground
water. The conductive plume has a different concentration of ions and different
electrochemistry from that of the uncontaminated areas. When the two regions are
50
measured relative to one another, an anomaly can result due to the concentration
potential and the diffusion potential (Corwin, 1990). The maximum magnitude of the
potential is + 16 m V above background, which would indicate a change in ground
water conductance. This change in ground water conductance is based on the Nemst
potential, which is generated from two fluids at different concentrations, and can be
positive, unlike mineralization potentials. The cause of the secondary anomaly to the
east of the NW-SE trending anomaly is unknown. The dissolved plume boundaries
defined by the chemical surveys by the NCIBRD are located to the west of this
anomaly. A possible mechanism for this anomaly is the presence of a drain or utility
pipe. If the pipe is constructed of steel, it will oxidize in the ground and produce a SP
anomaly that is similar in magnitude to that seen in the contour plot.
Mise-a-la-masse
The mise-a-la-masse contour plot showed very little deviation from the
circular trend (Fig. 6). The presence of the circular trend indicates that the down hole
current source did not act as a point but perhaps as a long vertical cylinder, primarily
contacting the vadose zone. This concept is reinforced when viewed in light of the
fact that the electrode was clipped to the casing of the cable tool drilled well FT-4D.
Assuming that the conductive plume should give an elongate anomaly with the
MALM data, the field data do not support the hypothesis. A likely reason for the lack
of any major trend over the plume is the use of the well casing as the current source.
51
The casing has rusted a great deal over the exposed length, and may not be
transmitting current below the first threaded joint. If this is the case, then the MALM
survey has simply measured potential drop in the vadose zone, which should not give
any deviation from concentric equipotential lines as no conductive plume is known to
reside in that region. The assumption that the current source was at the dissolved
plume depth is probably incorrect.
Vertical Electrical Soundin2s
The three VES surveys conducted over the area had many of the same
characteristics. Each showed a change from resistive layers near the surface to
conductive layers at depths. The inverse model for each VES is shown in Table 5.
The first 2 layers in VES # 1 and the first 3 layers in VES # 2 and VES # 3 are
interpreted to represent the vadose zone. There is a noticeable change from the
surface layer apparent resistivity from VES # 1, which is located above the plume,
and the surface layer and vadose zone apparent resistivities from the other two VES;
which are located off the plume. The lower surface layer and vadose zone apparent
resistivities over the plume indicate that some of the conductive ground water is
present in the vadose zone, and the degradation of the hydrocarbon is not limited
solely to the saturated zone. There is a great deal of variability in the saturated zone
apparent resistivities, which are represented by layer 3 for VES # 1, and layer 4 for
VES # 2 and VES # 3. The lowest apparent resistivity is from VES # 1, which is
52
Table 5
Inverse Models for Each VES
Apparent Resistivity and Thickness of Layer
VES# 1 VES# 2 VES#3
Layer 1 98nm 0.24m 363 2 nm 0.14m 363 1 nm 0.1 m*
Layer 2 1113 nm 6 m* 33000 nm 0.89m 330 86 nm 1.14 m
Layer 3 1 20nm 15.36*m 5600 nm 7.27m 6970 nm 6.84m
Layer 4 3 2nm 800nm 10.0 m* 4200nm 3.67m
Layer 5 not used 27nm 42nm
RMS error 16.8 23 % 11.2 23 % 6.27%
* - denotes parameter was held constant during inversion
located on the surface above the plume. The apparent resistivity for the saturated
zone in VES # 2 and VES # 3 is more than 25 times that of the VES # 1. This
indicates that there is a much more conductive ground water below VES # 1 than in
the other two. The lowest layer in each model represents the clay layer, with an
apparent resistivity ranging from 27 nm to 42 nm. The depth to the clay layer is
quite variable, in the inversion of VES # 3 the depth to clay was found to be less than
1 2 meters, which is highly unlikely. This anomalously shallow depth to clay is most
likely due to a problem of equivalence, as the apparent resistivity of 4200 nm for the
saturated zone is far too high for saturated aquifer sands. In order to evaluate the
53
effects of suppression and equivalence several models were run on VES # 1 and VES
# 3. Two inverse models were run on VES # 1, the results are shown below in Table
2. The results of the two inverse models are shown in Figure 8, and show that for the
electrically equivalent layer 3, the curves have a very similar appearance. Therefore
the values for the depth and resistivity of a given layer can be modified to give very
similar results. A similar set of forward models was run for VES # 3, and are shown
below in Table 4. The results of the varying the saturated zone apparent resistivity in
the two forward models for VES # 3 are shown in Figure 9. There are considerable
changes in the apparent resistivity with depth, but the two extremes for the model.
This example shows that by varying the apparent resistivity in a given layer can
produce similar results.
There are several problems associated with the VES surveys undertaken at the
FT-02 site. The VES method works best in an area that has horizontal layers of
uniform resistivity and thickness, and that have an infinite lateral extent. This is not
the case at the FT-02 site because the dissolved plume itself is not infinite in extent.
Also, the first two layers at the site were highly resistive, which has a degrading effect
on the measured potentials. A second problem is the presence of utilities and cables
within the subsurface. These bodies can provide an alternate path for the current, and
distort the VES curve. A third problem associated with this site is the number and
spacing between the VES surveys. If a series of VES surveys had been collected
along a line separated by a fixed difference, it may have been possible to identify
54
changes from contaminated and uncontaminated areas. The three surveys at this site
had different orientations and were located very far from one another.
Dipole-Dipole Resistivity Profilin�
The DDR profiles each show a shallow, low resistivity anomaly in the central
region of each survey. These anomalies had modified model depths of 2 to 4 meters,
indicating a conductive source in the vadose zone if the modified model depths are
correct. Also, there is no abrupt change at 6 meters, which is the depth to water table.
Since the water table should have a strong electrical contrast with the vadose zone, it
should appear distinctly on the model. The lack of this abrupt change indicates that
the inverse model generated by RES2DINV may not be well suited for accurately
determining horizontal layer thickness and resistivities using the DDR method due to
the Principle of Equivalence. The appearance of a conductive region in the vadose
zone cannot be corroborated by geochemical means, as all geochemical samples for
the FT-02 site are taken from the saturated zone. Overall, the field data show a
conductive anomaly, but the inversion model cannot uniquely determine the vertical
location of the conductive anomaly.
In light of the results from the inverse models, a series of forward models
were developed using RES2DMOD, a forward modeling program using the same
computer routines as RES2DINV. The model was run with and without a plume, and
included the vadose zone, the saturated zone and the silty clay layer. The result of the
55
model without the plume is shown in Figure 16, and the results of the model with the
plume are shown in Figure 17. The model without the plume has a sharp decrease in
apparent resistivity with depth, which is interpreted to be the program's representation
of the sharp contrast in apparent resistivity at the vadose zone - saturated zone
interface and the saturated zone - silty clay interface. It is interesting to note that even
at a 10 m dipole spacing, the silty clay layer has an effect on the measured
pseudosection. This is a good indication that the depths generated by the inverse
model are highly suspect, and may not represent the true depth. It is important to note
that the dome-shaped change in apparent resistivity at depth centered around 240 m is
an artifact of the modeling program, and does not represent any geological condition.
The model with the plume showed the same decrease in resistivity with depth, but
superimposed upon the sharp vertical gradient is a three peaked low resistivity zone
located over the area where the plume was modeled. This is the exact same signature
seen in the 10 meter dipole data from Line 305 m North, and is strong evidence for a
conductive plume. The larger dipole spacings over the plume showed a lesser effect
on the apparent resistivity pseudosections. Finally, the forward models were run
using different arrays at the surface, but there was no appreciable change from array
to array.
To briefly summarize, the two sharp resistivity interfaces appear to dominate
the pseudosection, creating a single zone of continuous steep gradient. The plume
56
in 0.0 8121.0
1
2
3
4
UAFB :ll.69
lF'r-�2 site 2:46
235 280
32� 40@1\1.
398 Apparent �esistivity CDipole-�ipoie) in OHH.� Unit Electrode Sp�cifig = 1G.@ �.
28 280 1itllili!l 1000
- - -
7. 0.�0.0
3.0
6.0
9.�
:ll.2
40.0 80.0 120 169 2010 240
Figure 16. Dipole-Dipole Resistivity Forward Model Without Plume.
280 320 360 4@@
v-,
---..)
ll1l 0.�
:ll.
2
3
4
8@.gJ l
Y�FB Ff-ij2 site l!.6� 241� 32®
- - lfflia limllll 11.11a - .mm mm Mm !ffl!lll!t!l - lll!IE
252 314 376 500
4\QIIBI M.
�P��lf'!?nt Resastnvnty <»a�ol�-�npoRe) im, OH�-� �mnt Eilectlt"Ode Sp�cn�� = :ll.0.9 M.
Figure 17.
30 280 10@11,J
- - -
ll.llill00 28 :ll.Sllill -
z ®·� 0.0
"ll0 .Ii!) 80 .0 1291 1691 290
3.0
6.0
'9J .0
l!..2
249
Dipole-Dipole Resistivity Forward Model With Plume.
280 320 360 <1100
V,
00
-.t28 :l9Q 438 -~ 562 -
produces a minor change superimposed on the sharp gradient. Several different
arrays were modeled over the site, but it appears that none of the models can
overcome the effect of the sharp interfaces. The dipole-dipole results are useful in
detecting the horizontal extent of the plume, but cannot resolve the depth effectively.
Electroma�netic Induction
The EM data (Fig. 13) show spike anomalies on both the EM-31 and EM-34
lines. These spike anomalies are interpreted to be utility pipes or cables in the
subsurface based on the strong conductivity and in-phase anomalies seen in the data.
The slight high in conductivity in the EM-31 data along line 305 m North
is located directly above the plume and is probably the effect of the conductive
dissolved plume, which is approximately 6 meters deep, the effective range limit of
the EM-31 instrument. Line 305 m North is the only EM-31 profile that shows a rise
in conductivity over the dissolved plume, the rest of the profiles on other lines show
no change over the dissolved plume. Since the top of the dissolved plume is located
from 5.5 to 6 meters below the ground surface, it is very close to the effective range
limit of the EM-31 instrument.
The results of the EM-34 show similar results over the utilities identified from
the EM-31 instrument. The EM-34 instrument shows a terrain conductivity low over
the area associated with the dissolved plume, from 260 m East to 330 m East. This is
a region where a high terrain conductivity was expected, as the ground water
59
conductivities are higher in the center region of Line 305 m North than in the distal
regions. A possibility for the low terrain conductivity anomaly is a geometric
constraint on the method. The dissolved plume is only 60 meters wide at most points,
which is only 3 times the width of the coil spacing. It is possible that the EM-34 unit
will spatially alias the plume at this particular coil spacing and give an anomaly that
has a low centered around the dissolved plume.
In order to evaluate the effect of the plume at depth, a series of forward
models were developed for the EM-31 and EM-34 using PCLOOP, a forward model
designed to model EM data. Four models were run, two with a 0.5 m thick plume and
two without. The model data are shown in Table 6. Models 1 and 2 represent a plume
with a vadose zone apparent resistivity of 5000 nm and 1000 nm, respectively.
Models 3 and 4 represent clean areas with a vadose zone apparent resistivity of 5000
nm and 1000 nm, respectively. The results of terrain conductivity are shown below
for the horizontal loop configuration in Table 7. The forward model input parameters
are based on apparent resistivity values from the dipole-dipole and VES surveys, and
the resulting terrain conductivity is 3 to 4 times lower than what was measured in the
The values are assumed to be scaled to one another, and can represent the percent
change when comparing non-plume to plume areas. Overall, the change from non
plume to plume areas appears to have a significant effect on the measured terrain
conductivity. It appears to have the biggest change when measured with the EM-31,
and the lowest change when measured with the EM-34 at the 20 meter coil separation.
60
Table 6
Forward Models for Electromagnetic Induction
Apparent Resistivity and Thickness of Layer
Model 1 Model2 Model3
Layer 1 5000 Om 1000 Om 5000 Om
5.5 m thick 5.5 m thick 5.5 m thick
Layer 2 80Om 80Om 150Om
0.5 m thick 0.5 m thick very thick
Layer 3 150Om 150Om NIA
very thick very thick
Table 7
Results of Electromagnetic Induction Forward Models
Model 1
EM -31 1.83
EM-34 (10m) 3.68
EM -34 (20m) 4.98
Terrain Conductivity in mS/m
Model 2
2.36
3.86
5.09
Model3
1.71
3.51
4.87
Model 4
1000 Om
5.5 m thick
150Om
very thick
NIA
Model 4
2.25
3.79
4.99
61
This response is expected, as the EM-34 samples a much greater volume than the
EM-31, and the conductivity changes do not change as much as the volume. It cannot
be determined whether it is possible to detect the degrading plume, as the changes are
only 2 - 7% of the measured terrain conductivity.
Ground Penetratin� Radar
The two representative GPR profiles show very similar results. An area of
attenuation, or shadow zone, is coincident with the plume along all lines. The
attenuation is a direct result of the low electrical resistivity of the dissolved plume as
it is almost entirely below the water table. The transition to attenuated signal is very
sharp, and occurs regularly at or below the 80 nanosecond level on the time records.
A measurement of the average dielectric permittivity for the vadose zone by using the
radar travel time and the known depth to water table at a nearby well gives Er= 8.3
and resulting velocity of 0.104 m/ns, which correlates well with the vadose zone
velocities given by Daniels (1989).
Performance of the Methods
The mise-a-la-masse method had no success in detecting the conductive
anomaly because of errors in the setup of the MALM survey. A proper setup would
involve the direct placement of an electrode into the conductive plume by means of a
62
push tool. Also, a resistivity meter with a higher input current should be used in order
to survey further from the downhole electrode
The vertical electrical sounding method had a limited success in detecting the
anomaly. The method could detect an anomalous region, but could not assign a
proper depth to the anomaly which, due to the Principle of Equivalence, can only be
overcome by "calibrating" against coincident borehole conductivity logs or measured
depths to interfaces in a borehole. As mentioned earlier, a linear array of soundings
could provide a better picture of the contamination. Also, by deploying a row of
soundings with a fixed interval between them, a meaningful joint interpretation could
be calculated for the layers derived in the individual inversion models.
The dipole-dipole resistivity method had some success in detecting the
anomaly. The inverse models suffered from the same lack of absolute depth control
due to the Principle of Equivalence, but the raw data pseudosections themselves
showed the general region of contamination. The inverse models did locate the
horizontal boundaries of the conductive plume to the level of resolution possible in
dipole-dipole resistivity surveys. The use of forward models to depict the plume
boundaries showed that the sharp contrast in resistivity at the vadose zone - saturated
zone interface and the saturated zone - silty clay layer combined to produce a single
steep gradient zone which dominated a large portion of the pseudosection
measurements, and almost masked the conductive plume.
63
The electromagnetic induction method as applied did not have any success in
detecting the conductive plume. The method was well suited for locating utilities and
cables, but did not show a large increase in ground conductivity over the plume itself.
It is believed that the plume is located too deep to be resolved by the EM-31 unit, and
is not conductive nor thick enough to be resolved with the 20 meter coil spacing on
the EM-34 unit. There is a 10 meter coil spacing for the EM-34, so a survey run with
that particular coil spacing may show the anomalous conductive region.
The self potential and ground penetrating radar methods both were very
successful in detecting areas of known contamination. The SP plot had some features
extending beyond the known dissolved plume in the eastern edge of the site, perhaps
due to an interfering source, but the GPR method worked well at resolving the
vertical and lateral plume boundaries. The GPR method is highly sensitive to the
input parameters of record length and gain function. If the record length had been set
to 100 nanoseconds, the amplitude anomaly probably could not have been detected.
The GPR survey acquisition parameters must be inspected closely, and several
parameters should be adjusted to gauge the effect of the parameters on the detection.
The combination of results from the VES surveys into the forward models for
the dipole-dipole and EM surveys allowed for meaningful comparisons of the various
methods. Also, by measuring the expected response of a survey over a plume, the
surveys could then be evaluated based on the expected response. By integrating the
results from the GPR, SP, Dipole-Dipole, and VES surveys, a clear and consistent
64
picture of the plume was developed, and the specific shortcomings of each survey
could be overcome.
Conclusions and Recommendations
The conductivity of a hydrocarbon plume is highly dependent on which region
of the plume is being measured and the age of the plume. At the FT-02 site, a
conductive anomaly was found to be coincident with the dissolved plume. It may be
possible that a hydrocarbon plume undergoes a change from resistive to conductive
behavior over time, but that temporal progression was not evaluated at the FT-02 site.
Further geophysical studies on the evolution of a hydrocarbon plume from the start of
contamination could shed light on how a LNAPL plume changes over time.
There are several ways to improve the performance of the methods discussed
in this project. The YES method could be applied in a regular and repeated fashion to
investigate if changes over a site can be traced from the source of a plume to regions
down gradient. The dipole-dipole resistivity method could use shorter (5 meter)
dipoles in order to evaluate the depth resolution of the method at this site. New tools
and methods such as bore hole EM tools and the vertical resistivity probe can give
information about the vertical extent of the plume, which has not been unambiguously
established by the geophysical studies at FT-02.
Finally, a more in-depth analysis of the chemical data could yield information
about the specific zones of chemical alteration and biodegradation of the residual and
65
dissolved plume. It may be possible to detect and delimit the various zones, and the
amount and rate of plume degradation taking place. Very little chemical information
was made available for this project, but a more intensive study may lead to a better
understanding of the degradation and what methods are best suited to measure it.
The interpretation of the field studies has shown that a degrading hydrocarbon
plume shows a decrease in the electrical resistivity. This electrical resistivity low is
located in the top portion of the saturated zone, and is less than half the electrical
resistivity in the uncontaminated areas. This study clearly shows that a hydrocarbon
plume in the field can exhibit electrical resistivity that is the complete opposite of
theoretical models.
66
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72
ICIBRD ilifflffili � ••••···········
••••···········
•••............
•............. . . . ........
National Center for Integrated Bioremediation Research and Develop university of michigan • department of civil and environmental engineering • wurtsmith air force base • 4140 e. california street • oscoda, michigan 487'14
1 0/ 3 1/ 9 6telephone: 517-739-0185 • lax: 517-739-0186
Mike Nash
Dept. of GeologyCollege of Arts and SciencesWestern Michigan UniversityKalamazoo, MI 4 9 008
Dear Mr. Nash,
My staff and I have compiled most of the information that yourequested in your 9/4/96 letter. I have included: • well logs• water chemistry data• USGS geologic information• well information (NAD19 2 7, NAD19 83)• water levels • FTA-02/OT-16 grid node locations• volatile chemical information form NCIBRD and AF records
Some of this information is provided on disk and the rest 1s mhard copy. I have not yet compiled the sieve data that you requested, but I will send it to you at a later date. I you have anyquestions about this information, please call me at (517) 739 0185.
We would appreciate a copy of the final report that you produce from this information. Please include SERDP and NCIBRD inthe acknowledgments of any deliverables that utilize the informationthat we have provided to you.
cc. M Barcelona, NCIBRDP Laird, NCIBRD files
Sincerely, �/.-/�rk �ry
,·
BIBLIOGRAPHY
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