Geophysical Methods for Geotechnical Site Investigations

STP 1101
GeophysicalApplicationsfor
GeotechnicalInvestigations
Frederick L. Paillet and Wayne R. Saunders, editors
As M
1916 Race Street
Philadelphia, PA 19103

Library of Congress Cataloging-in-PublicationData
Geophysical applications for geotechnical investigations / Frederick L. Paillet and Wayne
R. Saunders, editors.
p. cm.--(STP ; 1101)
Papers from the Symposium on Geophysical Methods for Geotechnical Investigations,
held in St. Louis, Mo., June 29, 1989, sponsored by ASTM Committee D-18 on Soil and
Rock.
"ASTM publication code number (PCN) 04-011010-38"--T.p. verso.
Includes bibliographical references and index.
ISBN 0-8031-1403-6
1. Engineering geology--Congresses, 2. Geophysics--Congresses. I. Paillet,
Frederick L., 1948- . II. Saunders, Wayne R., 1946- III. Symposium on
Geophysical Methods for Geotechnical Investigations (1989 : Si. Louis,
Mo.) IV. ASTM Committee D-18 on Soil and Rock. V. Series: ASTM special
technical publication ; 1101.
TA703.5.G45 1990
624.1 '51--dc20 90-40924
CIP
Copyright 9 by AMERICAN SOCIETY FOR TESTING AND MATERIALS 1990
NOTE
The Society is not responsible, as a body,
for the statements and opinions
advanced in this publication.
Peer Review Policy
Each paper published in this volume was evaluated by three peer reviewers. The authors
addressed all of the reviewers' comments to the satisfaction of both the technical editor(s)
and the ASTM Committee on Publications.
The quality of the papers in this publication reflects not only the obvious efforts of the
authors and the technical editor(s), but also the work of these peer reviewers. The ASTM
Committee on Publications acknowledges with appreciation their dedication and contribution
of time and effort on behalf of ASTM.
Printedin Baltimore
October 1990

Foreword
The symposium on Geophysical Methods for Geotechnical Investigations was presented
at St. Louis, Missouri, on 29 June 1989. ASTM Committee D-18 on Soil and Rock sponsored
the symposium. Frederick L. Paillet, U.S. Geological Survey, and Wayne R. Saunders,
ICF-Kaiser Inc., served as co-chairmen of the symposium and co-editors of the resulting
publication.

Contents
Overview 1
SURFACE GEOPHYSICS
Surface Geophysical Investigations for Hazardous Waste Sites--DAVID CUMMINGS 9
A Case Study of Geotomography Applied to a Detailed Investigation of a Highway
Bridge Foundation--HIDEKI SAITO, HIROMASA SHIMA, TETSUMA TOSHIOKA,
SHIN-ICHI KAINO, AND HIDEO OHTOMO 17
BOREHOLE GEOPHYSICS
Economic Considerations of Borehole Geophysics for Hazardous Waste Projects--
ROBERT E. CROWDER, LARRY A. IRONS, AND ELLIOT N. YEARSLEY 37
Estimating Water Quality from Geophysical Logs--DONALD G. JORGENSEN 47
Acoustic Waveform Logs and the In-Situ Measurement of Permeability--A
Review--DANIEL R. BURNS 65
Low-Frequency Shear Wave Logging in Unconsolidated Formations for Geotechnical
Applications--FUMIO KANEKO, TAKASHI KANEMORI, AND KEIJI TONOUCHI 79
Applications of the Thermal-Pulse Fiowmeter in the Hydraulic Characterization of
Fractured Rocks--ALFRED E. HESS AND FREDERICK L. PAILLET 99

STP1101-EB/Oct. 1990
Overview
The latest environmental concerns related to contamination from landfills and other dis-
posal sites, along with the need for improved evaluation of the mechanical properties of
soils and other geological substrates in civil engineering, have greatly increased the interest
in the application of geophysics in geotechnical investigations. Geophysics provides the
means to probe the properties of soils, sediments, and rock outcrops without costly exca-
vation. The nonintrusive sampling of geological formations is important because extensive
disturbance of these deposits could compromise the integrity of a natural geological migration
barrier or foundation site. Moreover, many physical properties of importance in engineering
such as density, porosity, permeability, and shear modulus are highly sensitive to in-situ
conditions. Relief of overburden stress, shearing, and desiccation associated with sample
retrieval can significantly alter the measured properties of sediments. On the other hand,
most geophysical methods involve the measurement of physical properties such as acoustic
velocity or electrical conductivity that are. different from those needed for engineering
studies. In the ideal situation, laboratory analysis of a finite number Of carefully extracted
samples can be used in conjunction with continuous geophysical surveys to produce a two-
or three-dimensional map of the area of interest.
More than 25 years ago, ASTM Committee D-18 on Soil and Rock indicated an interest
in geophysical methods by including several papers on both borehole and surface geophysical
applications in a symposium on Soil Exploration [1]. Even earlier (1951), ASTM Committee
D-18 sponsored a symposium on Surface and Subsurface Reconnaissance [2] in which the
subsequent STP contained 8 papers and a panel discussion related to surface geophysics
techniques and applications in engineering site investigations.
This present volume presents a series of papers originally given at the ASTM Symposium
on Geophysical Methods for Geotechnical Investigations held on 29 June 1989 in St. Louis,
Missouri. The papers were selected to provide a broad overview of the latest geophysical
techniques being applied to environmental and geotechnical engineering problems. Such
geophysical methods have traditionally been divided into those applied at the land surface
to generate two-dimensional maps of geophysical properties and those applied in boreholes
to generate one-dimensional maps, or "logs," of geophysical properties along the length of
the borehole. The two approaches yield complementary results because the geophysical well
logs provide much greater spatial resolution (usually on the order of a metre) in comparison
with the surface soundings (where resolution is on the order of 10 to 100 m). When surface
methods result in soundings plotted as a vertical cross section of the formation, geophysical
logs can be used to calibrate the depth scale in the surface-generated data section.
In the latest geophysical technology, the distinction between surface and borehole methods
has become somewhat blurred. Borehole-to-borehole and surface-to-borehole soundings are
now being used to generate three-dimensional images of the rock volume between boreholes
Copyright* 1990by ASTM International
1
www.astm.org

2 GEOPHYSICALAPPLICATIONS FOR GEOTECHNICAL INVESTIGATIONS
on spatial scales intermediate between those traditionally assigned to either surface geo-
physics or well logging. We can expect the scale disparities between surface and borehole
geophysics to become even more indistinct in the near future. The papers included in this
volume are but a sample of the many different kinds of investigations that may soon be
used to probe the properties of geological formations on scales ranging all the way from
small volumes immediately adjacent to individual boreholes to the entire rock mass con-
taining a potential repository site or building foundation.
Surface Geophysics
Surface geophysical methods provide valuable information in geotechnical studies in the
form of horizontal maps of subsurface properties or vertical profiles or "'soundings" along
sections of interest. The paper by Cummings in this volume gives a broad overview of the
various geophysical techniques applicable in studies at hazardous waste sites, but it also
serves as a useful sampling of the many techniques available for other applications. Saito
et al.'s paper gives an excellent example of the state of the art in application of both seismic
and electromagnetic (resistivity) methods to three-dimensional mapping (known in the lit-
erature as "tomography") of the properties of a volume of rock and sediment located beneath
a proposed bridge foundation.
Both of these papers demonstrate the importance of using different methods for the
investigation in that the seismic and electromagnetic methods respond to different properties
of geological formations. The seismic methods are closely tied to the compressional and
shear velocities, related in turn to rock bulk and shear moduli, whereas the electrical methods
are related to the degree of saturation, presence of clay minerals, and quality of saturating
fluids. The non-uniqueness associated with the interpretation of any given geophysical in-
vestigation is one of the most important issues in geophysical applications. The planning of
such investigation almost always prescribes the use of more than one technique or makes
provisions for other investigations such as drilling and sampling to calibrate the geophysical
interpretation or to verify the assumptions required to implement the interpretation.
Borehole Geophysics
Borehole geophysics or "well logging" was originally developed as a way to apply the
techniques of surface sounding to the volume of rock adjacent to the borehold. The log
consists of the continuous recording of a specific geophysical measurement such as electrical
resistivity or natural radioactivity along the length of the borehole. Although the measure-
ment is almost always related to a physicat property of the formation other than those of
direct interest to the hydrologist or civil engineer, the log has the advantage of providing a
single continuous measurement associated with a uniform depth scale. The advantages of
such a reliable depth scale become apparent when compared to a limited set of laboratory
tests performed on a few samples recovered during drilling, each a "part" measurement
associated with a certain finite depth error. In the ideal situation, the core sample analyses
can be used to calibrate the continuous logs in terms of parameters of interest, so that the
log is used to generate a vertical profile of the geological formation or the contaminated
ground water within the formation. This approach is evidently best suited for locating the
edges of plumes, geologic boundaries, or the local maxima or minima of specific properties
of interest.
Almost all of the earliest applications of well logging were developed for the petroleum
industry. After 1960, there were a number of programs designed to apply the petroleum-

OVERVIEW 3
orientated logging technology to environmental and hydrological studies. A decade later
the accelerating interest in environmental issues and radioactive waste disposal prompted
interest in designing logging equipment for various specific environmental and engineering
applications. The recent proliferation of microprocessors and solid state electronics has
further increased the flexibility available in logging for geotechnical applications. Today,
geotechnical logging equipment includes sources and transducers designed to measure prop-
erties of interest in engineering and hydrology, compensated probe configurations equivalent
to the most sophisticated used in the petroleum industry, downhole digitization of geophysical
measurements, and uphole processing of log data. All of these trends indicate that in the
future geophysical logging will become an important tool in many kinds of geotechnical
studies in which logging has not usually been considered relevant in the past.
The papers included in this volume were selected to give a representative cross section
of the latest equipment designs and data analysis techniques being made available to the
hydrologist and civil engineer. The overview of logging logistics and economics by Crowder
provides an instructive introduction into the role of borehole geophysics in environmental
studies. One of the most important issues is related to time and efficiency. Complete coring
provides a direct sampling of formations, but simple drilling and logging provides most of
the information in a fraction of the time and at substantially reduced costs. A carefully
thought-out combination of sampling, drilling, and logging clearly has an important role in
such studies and may sometimes be the only way in which a study can be completed to meet
schedules imposed by legal and operational constraints.
The papers by Jorgensen and Burns describe some of the most recent developments in
relating geophysical measurements in boreholes to the specific sediments properties of in-
terest in engineering and hydrology. Burns describes the information that can be derived
from the most advanced acoustic logging techniques. Not only are the seismic velocities of
sediments directly related to the mechanical properties (dynamic rather than static), but
acoustic measurements can sometimes be related to formation permeability. The latest
acoustic studies show that new transducer designs may greatly improve the ability to make
mechanical property and permeability measurements in situ. The paper by Jorgensen pre-
sents a review of the methods which may be used to infer the quality of water present in
the formation. In many situations, these methods can be used to produce a qualitative or
semi-quantitative profile of contaminant distribution adjacent to the borehole. If additional
information is available under the proper circumstances, these qualitative measurements
can be turned into estimates of solute content. The interested reader can consult the ref-
erences listed by these papers, especially the earlier review by Alger [3], the case study by
Dyck et al. [4], or the recent review by Alger and Harrison [5].
The papers by Kaneko et al. and Hess and Paillet each present a specific logging tool
developed to address geotechnical applications. Hess and Paillet describe a recently devel-
oped flowmeter logging system capable of measuring vertical flows in boreholes with much
greater resolution than available by means of conventional spinner flowmeters. This device
has important applications in identifying the location of inflows and exit flows in boreholes
under stressed and unstressed conditions, providing useful information on the source of
waters sampled from test wells and on the distribution of permeability in tight or fractured
formations. The significance of high-resolution flowmeter data in identifying the movement
of water in fractured crystalline rocks is indicated by such studies as Hess [6], Paillet et al.
[7], and Paillet [8].
The paper by Kaneko et al. emphasizes the interpretation of the shear modulus of soils
in situ by what appears to be standard geophysical logging methods. However, the approach
is based on a relatively new transducer design [9] developed especially for such engineering

4 GEOPHYSICALAPPLICATIONSFOR GEOTECHNICALINVESTIGATIONS
applications. This source configuration was but the first of many such applications of acoustic
logging with nonaxisymmetric sources [10,11]. The paper in this volume indicates the use
of these low-frequency shear measurements in boreholes; some of the future applications
for this developing method are also mentioned by Burns.
The five papers on borehole geophysics applications in geotechnical studies included in
this volume are but a small sample of the proliferating technologies becoming available to
modern geoscientists and engineers. Additional information on geotechnical applications of
logging can be found in the two recent monographs by Keys [12] and Hearst and Nelson
[13] and in the paper by Keys [14]. We hope that these four papers in this volume serve as
examples indicating a number of important ways in which borehole geophysics can contribute
to geotechnical studies, and that they stimulate the reader to investigate the broader pos-
sibilities of geophysical logging in the future.
Contributions made by the authors and technical reviewers are gratefully acknowledged.
The editors also express appreciation to the ASTM staff and officers of ASTM Committee
D-18 for their assistance and support in organizing and publishing these papers resulting
from the symposium.
Frederick L. Paillet
U.S. Geological Survey
Denver, CO; symposium
co-chairman and co-editor
Wayne R. Saunders
ICF-Kaiser Inc.
Fairfax, VA; symposium
co-chairman and co-editor
References
[1] Gnaedinger, G. P. and Johnson, A. I., Eds., Symposium on Soil Exploration, ASTM STP 351,
American Society for Testing and Materials, Philadelphia, 1964.
[2] McAlpin, G. W. and Gregg, L. E., Eds., Symposium on Surface and Subsurface Reconnaissance,
ASTM STP 122, American Society for Testing and Materials, Philadelphia, 1951.
[3] Alger, REP., "Interpretationof Electric Logs inFresh Water Wellsin Unconsolidated Formation,"
Society of Professional Well Log Analysts 7th Annual Logging Symposium, Transactions, Tulsa,
OK, 1966, pp. CC1-CC25.
[4] Dyck, J. H., Keys, W. S., and Meneley, W. A., "Application of Geophysical Loggingto Ground-
water Studies in Southern Saskatchewan," Canadian Journal of Earth Sciences, Vol. 9, No. 1,
1972, pp. 78-94.
[5] Alger, REP. and Harrison, C. W., "Improved Fresh Water Assessment in Sand Aquifers Utilizing
Geophysical Well Logs," The Log Analyst, Vol. 30, No. 1, 1989, pp. 31-44.
[61 Hess, A. E., "Identifying Hydraulically-Conductive Fractures with a Low-VelocityBorehole Flow-
meter," Canadian Geotechnical Journal, Vol. 23, 1986, pp. 69-78.
[7] Paillet, F. L., Hess, A. E., Cheng, C. H., and Hardin, E. L., "Characterization of Fracture
Permeabilitywith High-ResolutionVerticalFlowMeasurements during Borehole Pumping," Ground
Water, Vol. 25, No. 1, 1987, pp. 28-40.
[8] Paillet, F. L., "Analysis of Geophysical Well Logs and Flowmeter Measurements in Boreholes
Penetrating Subhorizontal Fracture Zones: Lac Du Bonnet Batholith, Manitoba, Canada," Water
Resources Investigations Report 89-4211, U.S. Geological Survey, Denver, CO, 1990, in press.
[9] Kitsunesaki, C., "A New Method for Shear Wave Logging," Geophysics, Vol. 45, 1980,pp. 1489-
1506.

OVERVIEW 5
[10] Winbow, G. A., "Compressional and Shear Arrivals in a Multiple Sonic Log," Geophysics, Vol.
50, 1985, pp. 119-126.
[11] Chen, S. T., "Shear-Wave Logging with Dipole Sources," Geophysics, Vol. 53, No. 5, 1988,
pp. 659-667.
[12] Keys, S. W., Borehole Geophysics Applied to Ground-Water Investigations, National Water Well
Association, Dublin, OH, 1990.
[13] Hearst, J. R. and Nelson, P. M., Well Logging for Physical Properties, McGraw-Hill, New York,
1985.
[14] Keys, S. W., "Analysis of Geophysical Logs of Water Wells with a Microcomputer," Ground
Water, Vol. 24, No. 3, 1986, pp. 750-760.

David Cummings 1
Surface Geophysical Investigations
Hazardous Waste Sites
for
REFERENCE: Cummings, D., "Surface GeophysicalInvestigationsfor HazardousWaste Sites,"
GeophysicalApplications for GeotechnicalInvestigations, ASTM STP 1101,Frederick L. Paillet
and Wayne R. Saunders, Eds., American Society for Testing and Materials, Philadelphia,
1990, pp. 9-16.
ABSTRACT: Surface geophysical surveys provide regional and site-specificsubsurface infor-
mation for hazardous waste investigations. The surveys can be used: (1) during the recon-
naissance phase of an investigation, (2) for obtaining detailed site-specific information, and
(3) for monitoring purposes after detailed investigations have been completed.
The choice of the geophysical method used in a survey depends on: (1) a knowledge of the
geologic and hydrologic conditions and (2) the type of contaminant and its suspected depth.
The different methods measure different physical properties which can be interpreted as
geologic features or, if the target is man-made, as cultural features. The ambiguity inherent
in geophysical methods can be reduced by conducting two or more surveys that measure
different physical properties.
KEY WORDS: geophysics, hazardous waste, surveys, physical properties
The purpose of this paper is to provide some general information on the use of surface
geophysical methods for hazardous waste investigations. Although borehole and airborne
methods may be used, they are not discussed here because they are beyond the scope of
this paper.
Geophysical surveys are a cost-effective way of providing regional and site-specific sub-
surface information for hazardous waste investigations. Geophysical methods measure phys-
ical properties of the subsurface and can distinguish between layers of sand and clay, alluvium
and bedrock, saturated and unsaturated soil, and contaminated and uncontaminated soils
and can locate underground tanks and pipes. The surveys can be used: (1) during the
reconnaissance phase of an investigation, (2) for obtaining detailed site-specific information,
and (3) for monitoring purposes after detailed investigations have been completed. A major
advantage of geophysical surveys is that they are nondestructive.
Typical assignments for geophysical surveys include:
9 determining subsurface geology;
9 determining depth to the water table and its gradient;
9 locating buried metal drums, canisters, and metal or plastic pipes;
9 defining boundaries of landfills; and
9 outlining the three-dimensional configuration of a contaminant plume as well as its
direction and rate of migration.
aSenior geophysicist, Science Applications International Corp., Inc., 3351 S. Highland Dr.,
Suite 206, Las Vegas, NV 89109.
9
Copyright91990byASTMInternational www.astm.org

Hazardous Materials
Generalized Classification
Hazardous materials can be classified according to their chemical group (organic, inor-
ganic, metallic, nonmetallic) and their physical state (solid, liquid, gas) (Table 1). The
chemical groups can occur in each physical state. Radioactive materials are a special case
because it is the radiation emitted during radioactive decay that is the hazardous material.
Occurrence
Hazardous materials are generated from two sources: natural and man-made. Examples
of natural sources include natural hydrocarbon seeps, brackish water in the subsurface,
uranium-bearing shales, and radon. Examples of man-made sources include landfills, in-
dustrial plants, and agricultural fields.
Migration
Although hazardous substances can occur almost anywhere, it is their relative abundance
and proximity to people that usually dictates a need for an investigation. Important infor-
mation for any investigation includes three items: (1) the horizontal and vertical extent as
well as concentration of contamination, (2) the physical state and chemical group of the
substance, and (3) how and in what direction the substance migrates through the subsurface.
The source of the contamination may be: (1) at the surface, from accidental spills; (2) in
the near surface soils or rocks, from landfills and leaking tanks or pipelines; or (3) in deep
rock, from oil and gas fields, or deep-well disposal of industrial wastes. Additional sources
of contaminants include septic systems; leach field leaks; sewage systems; saltwater intrusion
of aquifers; salt accumulation from irrigation systems; and agricultural contamination with
pesticides, fertilizers, and manure.
Migration of a contaminant from a source at or near the surface is generally downward
with some lateral spreading. Downward migration can be retarded or diverted laterally by
silt and clay layers in the soils. Contaminationfrom a leaking tank or pipeline can be retarded
or even restricted to the trench that contains the tank or pipeline. Migration of contaminants
TABLE I--Generalized classification of hazardous materials.
Physical States
Chemical Group Solid Liquid Gas and Vapors
Organic plastics hydrocarbons and de- hydrocarbons and
rivatives, phenola derivatives
Inorganic
Metallic iron, copper cadmium sulfateb mercury, carbonyls
Nonmetallic asbestos arsenic (in solution) halogens
Radioactive uranium, thorium, radon
MaterialsC strontium com-
pounds
aOrganic substances may occur as solutions or as emulsions.
bInorganic substances are commonly dissolved in the liquid, but can occur as discrete
particles.
CRadioactivedecays occur in both organic and inorganic elements.

CUMMINGS ON HAZARDOUS WASTE SITES 11
from deep sources is generally upward, but the contaminants also spread laterally when
they come in contact with the impermeable layer.
The interaction of the contaminant with ground water is a major concern because of the
value of the water. To understand this interaction, it is necessary to determine: (1) how
water moves through the ground and (2) how the contaminants occur in the ground water.
Using simplifying assumptions, ground-water flow is considered to be laminar and, with
distance from its source, the contaminant becomes diluted. Dilution occurs by physical
process (for example, hydrodynamic dispersion) or chemical process (adsorption or cation
exchange) or both. Physical dispersion occurs by both mechanical mixing and molecular
diffusion. As the contaminant moves through the soil or rock, the chemical process of
adsorption or cation exchange occurs, thus retarding its migration.
The velocity of gasses through the unsaturated soil and rock depend primarily on: (1) the
density of the gas and (2) the vertical and horizontal hydraulic conductivity of the soil or
rock. Methane, generated from decaying organic matter in a landfill or from thermogenic
processes related to oil and gas fields, is lighter than air and migrates both laterally and
upward through the soils and rocks. If an impermeable barrier to the upward migration of
the gas does not exist, then the gas escapes at ground surface. But, if a barrier exists, then
the gas accumulates at the base of the barrier, migrates laterally, and updips along the base
of the barrier. Because methane is potentially explosive, drilling through this barrier and
into a pocket of unsuspected methane can be dangerous. If methane occurs below or in the
water table, some of this gas is dissolved in the water and migrates in the same direction
as the hydraulic gradient. However, some of the gas molecules are adsorbed on the soil or
rock particles. Because methane is reactive with the soils, it generally travels at a slower
rate than the water.
Liquid contaminants entering the soil from the ground surface (or slightly below) migrate
downward provided the soil has a high value of vertical hydraulic conductivity. Sands and
gravels are examples of such soils. If an impermeable layer, such as clay, impedes the
downward migration, then the liquid migrates laterally on the layer and downdips. A high
viscosity liquid, such as heavy crude oil, migrates only a few feet from the source because
of the adsorptive capacity and capillary attraction related to the soils. On the other hand,
gasoline can migrate relatively long distances underground. If the liquid contaminant reaches
the water table, the contaminant can either float on, sink in, or form a solution or an
emulsion with the water. Migration of the contaminant is in the same direction as the flow
of water.
By understanding the types of contaminants in the subsurface, how they occur, and how
they migrate, a geophysical program can be developed to locate the contaminants and
determine their three-dimensional configuration. Maximum benefits from a geophysical
program are obtained through continuous communication among all participants: the client,
the geologist, the engineer, and the geophysicist.
Surface Geophysical Method
Phases of GeophysicalSurveys
Geophysical methods are used for hazardous waste investigations in three phases:
(1) during the reconnaissance phase to obtain the general and detailed site characteristics
of geology and hydrogeology, (2) during the detailed site investigation phase to obtain the
three-dimensional configuration of the contaminant and the direction and rate of its migra-
tion, and (3) during the post-site investigation phase and for monitoring purposes. In general,
geophysical surveys must be a part of an overall investigation program which includes drilling.
Borings are generally needed to provide definitive information about contaminants; the

geophysical surveys are used to interpolate between the drill holes and extrapolate beyond
the drilled areas. The interpretations of the geophysical data provide insight into the limits
and three-dimensional configuration of contamination.
Reconnaissance
Geophysical surveys are commonly used in the reconnaissance phase to provide sufficient
general information so that more detailed investigations can be adequately planned. Re-
connaissance surveys are used to optimize drilling programs, either for detailed investigations
or to locate extraction wells. During the reconnaissance phase, the geophysical surveys can
be used to locate underground utilities for avoidance during drilling or trenching.
Detailed Site Investigation
During the detailed site investigation phase, the geophysical information from the recon-
naissance phase is integrated and correlated with site-specific geologic and drill hole infor-
mation. Using the geologic information, the reconnaissance geophysical interpretations are
modified where appropriate. Other geophysical surveys may then be conducted between
drill holes to obtain additional subsurface information at the site. The type of subsurface
information commonly required in the detailed investigation is: (1) continuity of soil or rock
layers, (2) three-dimensional configuration of contaminant plume, and (3) changes in hy-
draulic gradient and the existence of barriers in the path of contaminant migrations.
Monitoring
After the detailed site investigation has been completed, geophysical investigations are
used to monitor the area for the purposes of assessing the effectiveness of cleanup and to
act as an early warning system for future contamination.
Application of Geophysical Methods
The use of geophysical methods to hazardous waste investigations is summarized in Ta-
ble 2. The choice of the appropriate method depends on: (1) a general knowledge of the
geologic conditions, (2) the hydrogeologic conditions, (3) the type of the contaminant, and
(4) the suspected depth of the contaminant. Some of this information is generally available
before the investigation begins and is used to design the geophysical program.
Because of the inherent ambiguities in interpreting geophysical data, several different but
complementary geophysical methods are used to reduce the ambiguities and provide more
reliable information. The increase in reliability is related to the types and combinations of
methods used and their abilities to detect changes in physical properties at specific sites and
for specific targets.
The following is a brief discussion of the applications of geophysical methods commonly
used in hazardous waste investigations. A summary of the methods is listed in Table 3 along
with the physical properties measured and the potential sources of interference that may
cause spurious data. The theory and field operations of the methods are beyond the scope
of this paper and are given in standard textbooks on geophysics and in technical manuals.
Electrical Methods
Electrical methods are commonly used to locate lateral and vertical discontinuities in the
electrical properties of earth materials. The methods typically are used to determine depth to

CUMMINGS ON HAZARDOUS WASTE SITES
TABLE 2--Appfication of geophysical methods for hazardous waste
investigations.
13
Investigative Phase
Reconnaissance Detailed Site Monitoring
Method Surveys Surveys Surveys
Electrical
Resistivity
Vertical electrical sounding x" x x
Constant electrode spacing x x x
Induced polarization x x x
Self potential x x x
Seismic
Refraction x x _ b
Reflection x x -
Electromagnetic
Phase/amplitude x x x
Transient x x x
"Metal detectors" x x -
Ground Penetrating
Radar x x x
Magnetic
Magnetometer x x -
Gradiometer x x -
"x = applicable method.
b_ = not generally appropriate.
perched water, water table, boundaries between sand and clay, the edges of landfills, burial
sites, trenches, changes in water quality, and the two-dimensional and three-dimensional
configurations of contaminant plumes. The methods are also used to monitor the three-
dimensional configuration of contaminant plumes, their velocity, and direction of flow.
The methods use direct current or low-frequency alternating current to determine the
earth's electric properties. The current is put into the ground and the resulting differences
in electrical potential of the earth materials are measured. The deviation from the potential
difference of an assumed homogeneous medium provides a measure of the inhomogeneities
in the medium. For example, the inhomogeneities can occur at the upper and lower bound-
aries of a contaminant or at the distal edge of a contaminant plume. The common field
method for determining changes in vertical electrica! properties is vertical electrical sounding
(VES). The common field method for determining lateral variations is constant electrode
spacing (CES).
The methods have had mixed success in detecting petroleum contaminants that float on
the water table, primarily because the petroleum forms a relatively thin film.
The methods generally are not sufficiently sensitive to measure and resolve thin layers,
even though such layers may have a large resistivity contrast between the contaminant and
the surrounding earth materials and water.
Seismic Methods
Seismic refraction and reflection methods are commonly used to determine vertical and
lateral variations in the seismic velocity of earth materials. Seismic methods typically are
used to determine the depth to the soil-bedrock interface, thickness of alluvium, depth to
the water table, relative frequency and orientation of fractures in rock (which would be
applicable for inferring preferred direction of water flow in rock), and thickness of landfills.

TABLE 3--Summary of commonly used geophysicalmethods.
Physical Property
To Which Method Property
Method Is Sensitive Measured
Potential
Sources of
Interference
Electrical
Resistivity
Vertical electrical
sounding/constant
electrode spacing
electrical conductivity earth resistance
Induced polarization electrical capacitance frequency or time-
dependent earth
resistance
Self potential electrical conductivity electrical potential
Seismic
Refraction/Reflection elastic moduli, density travel time of re-
fracted/reflected
seismic waves
electrical conductivity electromagnetic
and inductance radiation
Electromagnetic
Phase/amplitude
Transient (TDEM) same same
Metal detector/ electric conductivity electromagnetic
"pipe locator" radiation
Ground Penetrating dielectric and electri- high frequency radio
Radar cal conductivity waves
Magnetic
Magnetometer/ magnetic susceptibility magnetic field
gradiometer and remnance
electric power lines:
electric storms;
buried metallic
metal
same
same
electric power lines;
buried metallic
pipe lines, metal;
ground vibrations
(automobile,
heavy equipment,
wind)
electric storms;
buried metal;
magnetic storms
same
electric power lines
electric storms;
magnetic storms
The methods use an energy source (hammer, explosive) to generate the seismic waves.
The seismic waves move through the ground and are detected by motion-sensitive transducers
(geophones).
Several differences exist between reflection and refraction surveys ranging from the path
that the seismic rays take from the energy source to the sensors, the field operations, and
the collection of data to the computer processing of data. One of the reasons that seismic
refraction surveys are more commonly used in hazardous waste investigation is that they
are less expensive to run than are reflection surveys.
The seismic refraction method has some inherent limitations for hazardous waste inves-
tigations. For example, the method is not sensitive to detecting low-velocity rocks sandwiched
between two higher velocity rocks, although analytical methods may be used to identify the
presence of the low-velocity layers. An example would be a shale sandwiched between two
sandstone layers where the shale acts as an impermeable barrier. Another example of the
method's limitation is when the velocity contrast is not large enough between a contaminant
plume in the ground water; the plume will not be detected.

CUMMINGSON HAZARDOUSWASTE SITES 15
As with the electrical methods, the field design of the seismic survey can provide infor-
mation on both vertical and horizontal variations of the physical properties. Conventional
refraction and reflection surveys can provide information on both vertical and horizontal
variations, but if lateral (horizontal) variations are of primary interest, the common offset
method (constant spacing) in both types of surveys is likely to provide greater sensitivity to
detect lateral variations.
Electromagnetic Methods
Electromagnetic (EM) methods are used to determine vertical and lateral variations in
the earth's electromagnetic radiation and can detect edges of a contaminant plume in ground
water, buried metal pipes and metal drums, the depth to water table, and boundary between
soil and bedrock.
The EM method puts a primary electromagnetic field both into the ground and directly
to the receiver. Inhomogeneities in the ground cause electrical eddy currents to be generated
which produce a secondary electromagnetic field. This secondary field is detected by the
receiver. The receiver resolves both the phase and amplitude produced by both the primary
and secondary electromagnetic fields. The difference between the primary and secondary
fields detected is a measure of both the geometry and electrical properties of the subsurface.
Both the phase and amplitude portions of the fields can be analyzed and interpreted sep-
arately; each portion provides different information about the subsurface. Most available
standard electromagnetic instruments are generally not able to obtain information deeper
than 30 m.
For greater depths, the transient or time-domain electromagnetic method (TDEM) is
used. This method is based on the principle that the earth has the electrical property of a
capacitor. A current is put through a wire coil lying on the surface; the electric charge is
stored in the earth. After a few moments, the current is turned off. The transient decay of
the residual voltage in the ground is a function of the electrical conductivity with depth.
Early arrival times at the receiver correspond to near-surface materials; later arrival times
correspond to materials at greater depths.
Metal detectors are commonly based on electromagnetic principles. Surveys are rapid and
generally inexpensive. In general, the depth of penetration is limited to about 5 m. Metal
detectors are commonly used to locate the underground metallic pipes, drums, and tanks.
Ground-Penetrating Radar Methods
Ground-penetrating radar (GPR) methods are used primarily to detect lateral and vertical
dielectric and electrical conductivity of the near-surface soils (upper 15 m) and man-made
objects contained in these soils such as boundaries of trenches and ditches; buried drums
and pipes, either metallic, concrete, or plastic; reinforcing steel bars in concrete slabs; and
voids beneath concrete or asphalt slabs.
The GPR method puts high-frequency radio waves into the ground and the reflected wave
is detected at the receiver. The method is somewhat analogous to seismic reflection except
for the energy source.
The method has some limitations in that the depth of penetration of the signal is hindered
by pore water and by thick clays. Interpretation of the records requires considerable skill
because spurious reflections occur. Misidentifying spurious reflections as real reflections
results in errors in interpretations.

16 GEOPHYSICAL APPLICATIONS FOR GEOTECHNICAL INVESTIGATIONS
Magnetic Methods
Magnetic methods are used to detect magnetic targets such as steel drums, iron pipes,
boundaries of landfills, and trenches containing ferrous materials.
The method measures the variations in the magnetic field caused by local sources super-
imposed on the earth's magnetic field. Although magnetometers have been used in hazardous
waste investigations, the magnetic gradiometer is a more sensitive instrument because: (1)
it eliminates most of the corrections necessary to reduce the raw data associated with standard
magnetometers and (2) it is more sensitive to near-surface magnetic targets than the standard
magnetometer. The gradiometer has two sensors vertically separated in a staff. The instru-
ment reads both sensors simultaneously, resulting in a measure of the magnetic gradient at
that station.
Other Methods
Gravimetric methods are occasionally used. The method measures the earth's gravitational
field. Local variations in the field are produced by local changes in density. Microgravity
surveys are used to locate voids in the subsurface, such as solution cavities and caverns in
limestone, lava tubes in volcanic areas, and shafts and tunnels in mining areas.
Thermal methods measure the thermal field and variations in temperature. Thermal
methods are used to map flow directions of ground water, underground fires in coal mines,
and leaks from ponds.
Scintillation counters or similar tools measure the rate of radioactive emission. Such tools
are used to determine the level of radioactivity on a regional scale or at a site. The simplest
and least expensive survey is to determine the total gamma radiation. For more detailed
information, the total radiation can be separated and identified as being caused by potassium,
uranium, or thorium. Radiation surveys are sometimes used to locate faults or fractures
that allow some radioactive gasses to reach the ground surface.
Summary
Geophysical surveys provide cost-effective and nondestructive means for obtaining sub-
surface ~eologic information and details of hazardous waste geometry, as well as the rate
and direction of contaminant migration. For the geophysical methods to provide the best
possible results, the investigators should have a general knowledge of the geology, the
characteristics of the contaminant,its occurrence, and migration. Surveyscan be used throughout
the duration of a site investigation, from the reconnaissance phase through the detailed site-
specific investigative phase to post-closure monitoring. Many methods are available; each
method measures a different property. Several methods should be run at a site to benefit
by the relative advantages of each method and to minimize the disadvantages.
Acknowledgment
A draft of this paper has been reviewed by Forrest D. Peters and his help is appreciated.
Bibliography
Keary, P. and Brooks, M., An Introduction to GeophysicalExploration, Blackwel[ Scientific Publica-
tions, Oxford, England, 1984.

Hideki Saito, 1 Hiromasa Shima, 2 Tetsuma Toshioka, 3 Shin-ichi
Kaino, 4 and Hideo Ohtomo 5
A Case Study of Geotomography Applied to
a Detailed Investigation of a Highway Bridge
Foundation
REFERENCE: Saito, H., Shima, H., Toshioka, T., Kaino, S., and Ohtomo, H., "A Case
Study of Geotomography Applied to a Detailed Investigation of a Highway Bridge Foundation,"
GeophysicalApplications for GeotechnicalInvestigations, ASTM STP 1101,Frederick L. Paillet
and Wayne R. Saunders, Eds., American Society for Testing and Materials, Philadelphia,
1990, pp. 17-34.
ABSTRACT: Three types of geotomographic surveys (seismic tomography, resistivity tomog-
raphy, and radar tomography) were conducted at a highway bridge pier construction site to
investigate rock characteristics. After the geophysicalinvestigation, bedrock was excavated to
construct the bridge foundation. Geological surveys and plate-loading tests were carried out
on the excavated surface. The geophysical and geological results were generally in good
agreement.
Seismic tomography can distinguish highly fractured rock from unfractured rock, and re-
sistivity tomography and radar tomography can classify rock according to different water
contents. The combined use of these three geotomographic surveys made it possible to detect
the anomalous zone whichwas highly fractured and saturated.
KEY WORDS: geotomography, seismic tomography, resistivity tomography, radar tomogra-
phy, bridge pier, fracture zone, geotechnical investigation, rock quality
A geological survey and drilling at a proposed highway bridge pier indicated that a vertical
fault existed at this site and that the rhyolite bedrock contained a fracture zone associated
with the fault. The fracture zone was not a desirable foundation for the bridge pier, but it
was difficult to change the proposed site of the pier because of topographic conditions and
the existence of other structures (a pier of another bridge, houses, and so forth) around the
site.
To design and construct the foundation of the bridge pier properly, the fracture zone had
to be located precisely and the in-situ mechanical strength of the surrounding rock had to
be obtained. Three types of geotomography, seismic tomography, resistivity tomography,
1Geophysicist, Geotechnical Institute, OYO Corp., c/o Earth Resources Lab., M.I.T., E34-408, 42
Carleton St., Cambridge, MA 02142. Member of SEG, EAEG, IEEE, SEG Japan.
2Geophysicist, Geotechnical Institute, OYO Corp., 2-2-19Daitakubo, Urawa, Saitama 336, Japan.
Member of SEG, EAEG, SSJ, SEG Japan.
3Geophysicist, Geotechnical Institute, OYO Corp., 2-2-19Daitakubo, Urawa, Saitama 336, Japan.
Member of SSJ, SEG Japan, IEICE.
4Geologist, Kansai Branch Office, OYO Corp., 2-36-27Tarumicho, Suita, Osaka 564, Japan.
5Senior geophysicist, Head Office, OYO Corp., 4-2-6 Kudankita, Chiyoda-ku, Tokyo 102, Japan.
Member of SEG, IEEE, SEG Japan, JSSMFE, JSCE.
17
Copyright91990byASTMInternational www.astm.org

and radar tomography, were conducted to obtain information on the physical properties
and distribution of the fracture zones. These methods were adequate to obtain information
about rock quality.
This paper describes the features of geotomography, presents results of the investigation,
and indicates the applicability of geotomography to rock investigations.
Features of Geotomography
Geotomography has attracted a great deal of attention as a method of investigating in
detail the distribution of underground physical properties [1]. Geotomography reconstructs
images of underground structures using a large data set. For this reason, geotomography
provides more information than surface geophysical survey methods. The three specific
advantages of geotomography over conventional surface surveys are: (1) the target area is
illuminated from several different angles, (2) the application of source transducers at points
in boreholes near the target allow for increased spatial resolution, and (3) the application
of sources in boreholes means that measurements are not degraded by propagation through
the shallow, extensively weathered zone.
Three kinds of geotomographic methods were used: (1) seismic tomography, (2) resistivity
tomography, and (3) radar tomography. The seismic wave velocity, the resistivity, or the
electromagnetic wave velocity are influenced by physical (rock) properties such as hardness,
condition of cracks, water content, or clay content. Because the response obtained by one
method may not be adequate to characterize all physical properties, it is effective to combine
different geotomographic methods to obtain a good image of the ground structure.
Characteristics of each geotomographic method are as follows.
Seismic Tornography
Seismic tomography reconstructs the seismic wave velocity distribution in the ground.
Seismic wave velocity varies according to rock type, degree of weathering, degree of meta-
morphism, number of cracks, and so forth. In this survey, the fracture zones are expected
to have lower seismic velocities than unfractured rock.
Resistivity Tomography
Resistivity tomography obtains the distribution of resistivity in the ground. Resistivity in
the ground changes according to rock type, mineral content, porosity, degree of saturation,
and the resistivity of water contained in the rock. In this survey, faults or fracture zones
are expected to have lower resistivity values than unfractured rock.
Radar Tomography
Radar tomography obtains the distribution of the propagation velocity of electromagnetic
waves in the ground. The propagation velocity of electromagnetic waves changes mainly
according to the water content of the rock. In this survey, the fracture zones are expected
to have lower velocities than unfractured rock.
Field Measurements and Results
Borehole Arrangernent
The previous geological survey indicated that the dip angle of the fracture zone was almost
vertical. When the predominant direction of the geological structure is nearly vertical,

SAITO ET AL. ON HIGHWAY BRIDGEFOUNDATION 19
tomography using only vertical boreholes cannot provide a good reconstruction image [2].
Therefore, four boreholes were drilled as shown in Figs. 1 and 2. Boreholes B1 and B2
were drilled at 45~ down from the horizontal and were 40 m long. Boreholes B3 and B4
were drilled at 10~ and were 30 m long.
Seismic Tomography
The measurements for seismic tomography were conducted by surrounding the objective
section with source points and receiver points placed in boreholes and on the ground surface
between boreholes. Both source and receiver intervals were 2 m. About 50 g of dynamite
was used as the seismic source. Three sets of twelve-channel borehole geophones and eleven
geophones on the ground surface were used for measurements. A forty-eight-channel digital
data acquisition system (OYO's McSEIS 1600 System) was used.
The objective area was divided into a number of rectangular cells, and the velocity value
for each cell was obtained by an iterative method. In the iterative method, the velocity
(value) for each cell was corrected to minimize the root mean squares of residuals between
calculated and observed travel times. To prevent the divergence of the correction values,
the damped least squares technique was used [3]. The damping parameters were determined
by taking account of the number and directionality of seismic rays passing through each
cell [4].
The measurements were conducted at two vertical sections (B1-B3 and B2-B4), a 10~
section (B3-B4), and a 45~section (B1-B2). The results for the two vertical sections and the
10~ section are compared with the results of another tomographic techniques. Figures 3
through 5 show source-receiver geometries, ray diagrams, and reconstructed velocity dis-
tribution images for each section.
B1-B3 Section (Fig. 3)--The P-wave velocity distribution of the B1-B3 section is shown
in Fig. 3b. Velocity values are indicated by shades of gray. Low velocity zones occur closer
to the surface-and between 8 to 19 m in Section B1 and 5 to 22 m in Section B3.
B2-B4 Section (Fig. 4)--Low velocity zones are found near the tops of the boreholes and
around the center of the area vertically. Between these low velocity zones, there is an
extremely high velocity zone.
B3-B4 Section (Fig. 5)--Nearly half of this section is a low velocity area with a velocity
of 2.5 km/s or lower.
Resistivity Tomography
Resistivity tomography is a two-dimensional resistivity exploration method having higher
resolution than the conventional resistivity exploration method [5].
Electrodes were placed at 2-m intervals in the borehol.es and on the ground surface between
boreholes surrounding the objective area. Electric potential was measured by the pole-pole
array method using OYO's McOHM resistivity meter.
Analysis was conducted by a combination of the alpha centers method and the nonlinear
least squares method [5]. The electric potential at each potential electrode was theoretically
calculated by the alpha centers method. The resistivity distribution was corrected to minimize
the root mean squares of the residuals between calculated and observed electric potentials
by the nonlinear least squares method.
The objective sections for resistivity tomography were two vertical sections (B1-B3 and

2. 5~
/
98 7 . 5
Excavated Area
5 0 ~
BI: 0 = 45 ~
= 40 m
0 : down from horizontal
@
B3: e = 10 ~ 9
= 30 m I /
/
B2: 9 = 45*
= 40 m
4Y2
[ B4 e = ' $
9~= 30 m
@ ..........
),.....,-- , , ,
......" /.
~ I(m )
FIG. 1--Plane view of investigation area and borehole arrangement.

SAITO ET AL. ON HIGHWAY BRIDGE FOUNDATION 21
B3
c
(a)
B4
s
(b)
FIG. 2--Vertical section of investigation area and borehole arrangement." (a) BI-B3 section and (b)
B2-B4 section.

FIG. 3--Seismic tomography at B1-B3 section: (a) source-receiver geometry and ray diagram and (b)
reconstructed velocity distribution image.

B2-B4) and the 10° section (B3-B4). Figures 6 through 8 show the electrode combinations
and the reconstructed images for each section. Resistivity values in each section were from
50 to 1000 f~ • m.
B1-B3 Section (Fig. 6)--Resistivity values between a depth of 8 to 22 m in B1 and a
depth of 5 to 19 m in B3 are lower than 120 f~ • m. Another low resistivity area is found
below 34 m in B 1.

FIG. 6--Resistivity tomography at B1-B3 section: (a) electrode combinations and (b) reconstructed
resistivity distribution image.
B2-B4 Section (Fig. 7)--A low resistivity area, in which resistivity is 160 ~ - m or lower,
is found at a depth of 19 m and below in B2 and at 11 to 21 m in B4.
B3-B4 Section (Fig. 8)--There is a low resistivity area of 150 ~ - m or lower at 7 to 26
m in B3 and at 15 to 21 m in B4.

FIG. 7--Resistivity tomography at B2-B4 section. (a) electrode combinations and (b) reconstructed

SA,ITO ET AL. ON HIGHWAY BRIDGE FOUNDATION 27
FIG. 8--Resistivity tomography at B3-B4 section." (a) electrode combinations and (b) reco~lstructed

Radar Tomography
In radar tomography, electromagnetic pulse waves are transmitted from one antenna
located in a borehole to a receiving antenna in another borehole. Each antenna was moved
at 2-m intervals. The measurement system used was OYO's YL-R2 Georadar system. The
borehole antennas were especially constructed for experimental use. The center frequency
of the antennas was about 100 MHz and transmitted power was 50 W [6]. The same analysis
procedure as that used in seismic tomography was used in radar tomography.
Attenuation of electromagnetic waves at this site was so high that significant signals could
not be received in horizontal sections. Therefore. the measurements were conducted only
at two vertical sections. Figures 9 and 10 show the transmitting and receiving points, ray
diagrams, and the electromagnetic wave velocity distribution.
B1-B3 Section (Fig. 9)--Electromagnetic wave velocity is relatively lower than the velocity
values in the B2-B4 section. It is estimated, therefore, that water content in the bedrock at
the B1-B3 section is rather high. The area at the depth of 7 m or below has low velocity
and is estimated to be a fracture zone having high water content.
B2-B4 Section (Fig. lO)--The zone, below 16 m in B2 and from 13 to 21 m in B4, is a
low velocity zone that continues vertically and is considered to be bedrock having high water
content.
Consideration
Based on the results of geotomography, we conducted an analysis of rock quality in the
B3-B4 section. We tried to classify the rock according to the values of seismic wave velocities
as shown in Fig. 11a and Table 1.
Since the seismic wave velocity is closely related to the mechanical strength of rock, it
can be said that this figure shows the distribution of mechanical properties of rock.
In this investigation site, the relative variation of resistivity depends mainly on water
content and the quantity of clay that was formed through alteration or fracturing. We tried
to classify the rock according to resistivity values, as shown in Fig. llb and Table 2.
Next, we tried to analyze the rock quality by using the results of seismic tomography
along with the results of resistivity tomography. The final analysis result of tomographic
investigations is shown in Fig. 12a.
Zone A was considered to be the surface soil layer having low seismic wave velocity and
high resistivity. Zones B, C, and D were each divided into two areas of high resistivity or
low resistivity. Zone Ba was considered to be weathered but unsaturated rock distributed
near the surface which had low seismic wave velocity and relatively high resistivity. Zone
Bb was considered to be a highly fractured zone of high water content which had low seismic
wave velocity and low resistivity. Both Zones Ca and Cb were considered to be a little
fractured, but the water content differed from each other. Zone Ca was considered to have
rather low water content which had rather low seismic wave velocity and a little low resistivity.
Zone Cb was considered to have high water content which had rather low seismic wave
velocity and low resistivity. Both Zones Da and Db were relatively fresh and sound rock,
however, Zone Db had rather high water content.
Consequently, it can be said that Zones Bb, Ca, and Cb correspond to fracture zones.
In particular, Zone Bb is considered to correspond to the most highly fractured zone having
high water content. The results mentioned above are shown in the left half of Table 3.
Excavation for the construction of the bridge pier foundation was carried out after the

SAITO ET AL. ON HIGHWAYBRIDGEFOUNDATION 29
FIG. 9--Radar tomography at B1-B3 section: (a) transmitter-receiver geometry and ray diagram and
(b) reconstructed velocity distribution image.

FIG. lO--Radar tomography at B2-B4 section: (a) transmitter-receiver geometry and ray diagram and
(b) reconstructed velocity distribution image.

.5kra/s B~
/ i
Ca)
EM velor "
I B4
' ~ / ,o--140-600(2 'm
p=200-400ff2,m / r t20 200" - ~ ~ ~
(b)
FIG. 11--Rock classification resultfront geotomography: (a) zoning resultfrom seismic tomography
~nd (b) zoning resultfrom resistivity and radar tomography.

TABLE 1--Rock classified according to the values
of seismic wave velocities.
Class Velocity, km/s Estimated Rock Quality
A - 1.5 surface soil
B -2.5 fractured or weathered
C -3.5 a little fractured
D 3.5- sound rock
TABLE 2--Rock classified according to resistivity
values.
Class Resistivity, fl 9m Estimated Rock Quality
a 140-600 surface soil
b 200-800 unsaturated or porous zone
c (80)-150 high water content
d 120-200 low water content
e 200-400 unsaturated or sound
geotomographic investigation. Geological and geotechnical investigations, which included
sketching, hammer-hitting tests, and plate-loading tests, were conducted on the excavated
surface. The results of these investigations are shown on the right half of Table 3 and the
geological section obtained is shown in Fig. 12b. The plate-loading tests were carried out
at five points indicated as No. 1 through No. 5 in Fig. 12b.
The results from geotomography (Fig. 12a) and those obtained after excavation (Fig. 12b)
are generally in good agreement. The "highly fractured" zone shown in Fig. 12b was regarded
as only one zone from the geotechnical point of view. However, we divided this zone into
two zones, Ba and Bb, according to differences in the resistivity values obtained from
geotomography. It must be said that Zone Bb with high water content is a highly fractured
zone, and Zone Ba is instead a weathered rock layer. Furthermore, each "a little fractured"
zone or "quartz porphyritic (fresh)" zone could be divided into two zones according to
differences in resistivity values obtained from geotomography.
In this way, the combined use of geotomography made it possible to obtain the distribution
of the most highly fractured zone at the pier foundation site.
Conclusion
Three kinds of geotomography were applied to rock investigation, and the results were
compared with those obtained by investigations after excavation.
As a result, both kinds of results were in good agreement. The combined use of three
kinds of geotomography made it possible to obtain more detailed and accurate characteristics
of the rock.

~ a4
Ba L
' g
I o
contens i
water [
c
-- 83
(a)
__ ~-- ...... B4
por i ~
, m
g
fai:e
Cb)
FIG. 12--Comparison of estimated rock quality by geotomography and investigation result after
excavation: (a) rock quality interpretation resultfrom geotomography and (b) result of geological survey
after excavation.

TABLE 3--Results from geotomography and investigationsafter excavation
Results from Geotomography
Results from Investigations after
Excavation
Seismic Deformation
Velocity, Resistivity, Estimated Constant,
Class km/s ~ 9m Quality Quality kgf/cmz
A -1.5 140-600 surface soil surface soil
weathered
Ba 200-800 (unsaturated)
-2.5 highly fractured
highly fractured
Bb 80-150 and high
water content
a little fractured
and rather
Ca 120~200
low water
content
-3.5 a little fractured
a little fractured
Cb 80-150 and high
water content
290
(No. 1 point)
160
(No. 2 point)
650
(No. 4 point)
quartz porphyry 1900
Da 200-400 sound or fresh (fresh) (No. 3 point)
3.5-
sound and rhyolite (fresh)
Db 80-150 rather high 840
water content (No. 5 point)
In the future, we intend to apply geotomography to many other sites having various
geological conditions and to conduct further studies on the applicability of geotomography
for civil engineering purposes.
References
[1] Sassa, K., "Suggested Methods for Seismic Testing Within and Between Boreholes,'" International
Journal of Rock Mechanic Sciences and Geomechanics Abstracts, Vol. 25, No. 6, 1988, pp. 447-
472.
[2] Sakayama, T., Ohtomo, H., Saito, H., and Shima. H., "Applicability and Some Problems Of
Geophysical Tomography Techniques in Estimation of Underground Structure and Physical Prop-
erties of Rock," presented at the 2nd International Symposium on Field Measurements in Geo-
mechanics, Kobe, Japan, April 1987.
[3] Aki, K. and Lee, W. H. K., "Determination of Three-Dimensional Velocity Anomalies Under a
Seismic Array Using First P Arrival Times from Local Earthquakes," Journal of Geophysical
Research, Vol. 81, 1976, pp. 4381-4399.
[4] Saito, H. and Ohtomo, H., "Seismic Ray Tomography Using the Method of Damped Least Squares,"
Exploration Geophysics. Vol. 19, Nos. 1/2, 1988. pp. 348-351.
[5} Shima, H. and Sakayama, T., "Resistivity Tomography: An Approach to 2-D Resistivity Inverse
Problems," presented at the 57th SEG Annual International Meeting, New Orleans, Oct. 1987.
[6] Toshioka, T. and Sakayama, T., "Preliminary Description of Borehole Radar and First Results,"
presented at the 76th SEGJ Conference, Tokyo, Japan, April 1987.

Robert E. Crowder, 1 Larry A. Irons, 2 and Elliot N. Yearsley ~
Economic Considerations of Borehole
Geophysics for Hazardous Waste Projects
REFERENCE: Crowder, R. E., Irons, L. A., and Yearsley, E. N., "Economic Considerations
of Borehole Geophysics for Hazardous Waste Projects," Geophysical Applications for Geo-
technical Investigations, ASTM STP 1101, Frederick L. Paillet and Wayne R. Saunders, Eds.,
American Society for Testing and Materials, Philadelphia, 1990, pp. 37-46.
ABSTRACT: In environmental or hazardous waste investigations, simple homogenous sub-
surface geologic conditions have historically been assumed. In reality, heterogeneous condi-
tions predominate. The costs of remediation and the consequences of incorrect remediation
are increasing rapidly. These investigations often require the collection of extensive amounts
of data to evaluate the problems sufficientlyto recommend and execute appropriate remedial
action.
Borehole geophysics can be used to obtain valuable data including information on geologic
conditions and in-situ physical parameters in drill holes. The amount and benefit of this
information is determined by the logging suite, borehole conditions, geologic parameters,
interpreter experience, and application of current technology.
Typical costs for drilling and geophysical logging associated with different types of environ-
mental investigations vary considerably. These costs are a function of the types and quantity
of the desired data, whether the geophysical logging and analysis will be performed in-house
or by an outside consultant, and the operational field environment.
Five case histories demonstrate the application of borehole geophysics to hazardous waste
investigations and provide qualitative evidence as to its cost-effectiveness. The primary con-
clusionsindicated by these case histories are that: (1) geophysical logs assist in well construction
efforts; (2) borehole geophysical logs provide in-situphysical measurements not available from
other methods; and (3) costs associated with borehole loggingcan be justified by consideration
of the total cost of drilling, completion, and monitoring and the implications of inadequate
understanding of the subsurface in a remediation program.
KEY WORDS: borehole geophysics, monitor well, cost, hazardous waste site investigations
In environmental investigations for ground-water contamination problems, simple, ho-
mogenous subsurface geologic conditions have historically been assumed. These site char-
acterizations are proving to be more difficult than originally anticipated, and a number of
prior investigations appear to be flawed. A U.S. Environmental Protection Agency (EPA)
study [1] of 22 Resource Conservation and Recovery Act (RCRA) sites showed problems
including:
(1) incorrect screening in 50% of the monitoring wells,
(2) incorrect placement of 30% of the wells, and
(3) on 10% of the sites, Wells were placed before determining the direction of ground-
water flow.
1President and geological engineer, respectively, Colog, Inc., 10198th St., Golden, CO 80401.
2Senior associate geophysicist, Ebasco/Envirosphere Co., 143 Union Blvd,, Suite 1010, Lakewood,
CO 80228.
37
Copyright91990by ASTM International www.astm.org

The geologic conditions encountered on most of these sites are complex and often require
collecting extensive amounts of data to evaluate the problems sufficiently to recommend
and execute the appropriate remedial action. The costs of remediation and the consequences
of incorrect remediation are increasing rapidly [2]. Each project is unique in certain respects
because the particular environment, potential contaminant, and goals will all be somewhat
different.
The purpose of this paper is to convey experience and information regarding the economic
considerations involved in obtaining subsurface data relevant to hazardous waste investi-
gations. Discussions contained herein outline the benefits of the application of borehole
geophysics to the problem of subsurface interpretation. These discussions provide guidelines
and considerations for geophysical logging operations and costs and review historical prac-
tices and costs of drilling, coring, testing, and geochemical analyses.
The common thread in these topics is their application toward the investigation and
characterization of hazardous (or potentially hazardous) waste sites. The relative cost-
effectiveness of borehole geophysics in these efforts is addressed. The thesis of this paper
is that borehole geophysics provides a cost-effective means for the subsurface investigations
of these sites. Furthermore, that the existential measurements provided by borehole geo-
physics complement core data, support surface geophysics, and offer geologic and hydro-
geologic information not otherwise available.
Borehole Geophysical Logging Considerations and Benefits
There is no uniform logging suite applicable to every project, and no unambiguous rules
for log interpretation exist. Most log analyses in ground-water investigations are based upon
techniques developed by the petroleum industry. These techniques may not be directly
applicable when applied to shallow ground-water investigations, and less experience and
scientific literature is available in this area. Many ground-water engineers and geologists
have no formal training in the use of borehole geophysics, whereas their counterparts in
the petroleum industry are well trained in the use of these logs.
Furthermore, logging tools developed for the petroleum industry are inadequate for the
shallow depth and small-diameter applications encountered in most environmental inves-
tigations. Many monitoring wells are drilled and completed with hollow-stem auger tech-
niques in the vadose zone. Logging in the vadose or unsaturated zone is feasible and provides
valuable information not available elsewhere, but disturbances to the formation from drilling
in this zone may produce large changes on the logs. Quantitative analysis usually requires
information from several types of logs. Sometimes the drill holes are not stable enough for
open-hole logging or to allow more than one open hole pass by a geophysical probe, and
the selection of probes for the initial pass requires careful consideration. Radioactive sources
required for some measurements are regulated, and the use of these sources may not be
feasible to use on some projects.
Many environmental projects are located in areas distant with respect to the historical
petroleum and mineral industry service companies, often requiring expensive mobilization.
Environmental projects frequently have a low production rate for drilling.new wells, both
in number and depth. The time lapse between wells may be several days. These factors
increase the logging costs. Health and safety training requirements can be a major burden
for many of the smaller slimhole logging contractors and may prevent them from entering
the environmental market.
Historically, only a few simple logs have been used in nonpetroleum applications. Many
people expect slimhole nonpetroleum logs for environmental applications to be inexpensive

CROWDER ET AL. ON BOREHOLE GEOPHYSICS
TABLE 1--Direct benefits of borehole geophysics.
39
Broad Category Specific Aspects
Well construction
Physical properties
Stratigraphic
correlation
depth and identification of lithologicbeds, borehole size and volume,
water table
porosity, density, resistivity, temperature, fluid flow, water quality,
fracture identification, rock strength parameters
continuity of aquifers and confining beds based on cross-hole
correlation, facies changes
and accordingly do not budget for the necessary logs and interpretation. Many firms do not
have staff expertise to use much of the advanced geophysical information. For example,
knowledge may be limited to recognition of apparent sand-shale zones for screen selection
and may not include proper interpretation of the remaining data. The economics of running
a complex suite that cannot be properly used would appear questionable.
In spite of the above perceptions and hindrances to slimhole logging, borehole geophysics
has important benefits in hazardous waste investigations when interpreted properly [3].
These benefits can be classified as direct and indirect [4,5], as shown in Tables 1 and 2.
Borehole GeophysicalLogging Costs
Traditional logging costs were based upon a low service charge (base time rate), a footage
charge (based upon the types of probes and total project footage logged), and miscellaneous
expenses for such items as per diem and standby. Costs per foot were kept low by logging
high footages in many wells. Typically, the drill rig was not incurring standby charges on
energy/mineral exploration projects and the standby charges for the petroleum applications
were generally well understood by everyone involved with those projects.
The primary cost factor for most environmental logging programs is personnel and equip-
ment time. This time factor includes mobilization/demobilization to and from the project
area, standby waiting for a well to be finished, pre- and post-log calibration, data acquisition,
data processing, interpretation, and decontamination of personnel and equipment. For the
typical shallow wells encountered on most environmental investigations, actual data acqui-
sition time is the least significant aspect. Footage charges are difficult to compare to the
classical slimhole logging industry and tend to be a minor element in the overall cost. The
number and type of logs affect the overall costs in that it takes as long or longer to pre-
and post-calibrate, setup, and decontaminate on a shallow well as it does on a deep well.
However, on many projects, the cost to run one or several extra logs may be insignificant
TABLE 2--Indirect benefits of borehole geophysics.
1. Objective, repeatable data collected over a continuous vertical interval.
2. Digital data is conveniently stored, processed, and transmitted.
3. Log results are available at well site or shortly thereafter.
4. Borehole geophysical data is synergistic with core data, surface geophysics, and other
borehole geophysical data.
5. Borehole logs can be standardized to facilitate correlation between different phases of an
investigation by different firms.

to the overall logging costs. A detailed interpretation of log data requires at least 1 h/h of
data acquisition.
In an effort to minimize logging costs and to collect data inexpensively, many companies
are renting portable logging equipment. Rental equipment is available from several sources
for measurements such as natural gamma, spontaneous potential (SP), single-point resist-
ance, normal resistivity, induction, temperature, borehole video, fluid resistivity, flowmeter,
and caliper in both analog and digital mode. Normally, measurements requiring the use of
radioactive sources or more complex measurements such as sonic are not rented. Rental
costs start at less than $100 per day.
A number of companies with sufficient work load to maintain the necessary staff and
equipment have in-house logging capabilities. Unlike the conventional energy industry, it
is more difficult to schedule environmental drilling programs between different offices of a
company. These in-house logging capabilities tend either to be simple in nature with the
staff sharing other duties or are primarily available from only one base of operation. Logging
costs include the capitalization of the logging equipment (from $15 000 to hundreds of
thousands of dollars) including spares, maintenance costs, labor costs including training,
and benefits, such as vacation, insurance costs, and operational expenses.
Contract-logging costs range from less than $1000 per day to approximately $3500 or more
per day when logging. Standby time waiting for well or testhole availability is usually at a
lower rate. The number of logs, amount of decontamination, availability of wells, and access
affect the amount of logging that can be performed in one day. A simple suite of one to
two probes in Level D protective clothing with minimal decontamination may allow for a
number of 30- to 60-m (100- to 200-ft) wells or testholes to be logged in one day. Conversely,
it may be difficult to get even one 30- to 60-m (100- to 200-ft) testhole well logged in a day
on some projects.
Environmental Drilling and Testing Costs and Considerations
Sampling, drilling, and testing programs are necessary for every subsurface environmental
investigation. They are not without problems or concerns. For instance, sample descriptions
are subjective depending upon the experience and goals of the describing scientist. Core
samples are point measurements, hopefully representative of the zone of interest. Sample
recovery is not guaranteed, and the sample frequently is altered by the drilling process.
Sample and drilling problems are typified as follows:
(1) cross contamination from upper formations,
(2) contamination from drilling fluid,
(3) incorrect interval sampled as a result of inexperience or carelessness,
(4) no sample recovery and zones of loss circulation,
(5) chemical changes caused by oxidation when the sample is exposed to air and dehy-
dration of samples,
(6) errors in sample description and analysis, and
(7) lack of solid samples for petrophysical and geotechnical analysis.
While all of the aforementioned errors do not occur all of the time, they do happen often
enough to constitute significant problems with respect to quantitative interpretations. An-
other consideration is handling and storage of hazardous samples. The cost of treatment
and storage of these samples may limit the number of samples collected.
Aquifer tests provide information on the horizontal hydraulic conductivity and storage

CROWDER ET AL. ON BOREHOLE GEOPHYSICS 41
capacity of the aquifer. The hydraulic conductivity data obtained from aquifer testing may
be of limited value because of the spatial variability of aquifer properties that greatly affect
the transport of contaminants. Aquifer tests may also be of limited use as a result of vertical
variations because they produce hydraulic conductivity values that are integrated over the
vertical domain. Testing of individual strata can be done if the strata are horizontally
extensive, but this is usually not the case in shallow, unconsolidated sediments. Measurement
of the hydraulic conductivity tensor requires a minimum of three observation wells. The
aquifer must be homogeneous over the area of these observation wells, which is usually a
poor assumption for shallow, unconsolidated sediments.
Aquifer testing is often further complicated with the necessity of handling large quantities
of hazardous liquids. These liquids often must be treated, stored, and disposed offsite.
Under such conditions, most tests are made as simple as possible, and thus, the results may
be questionabl e at best.
A survey of some domestic engineering companies for average costs concerning the major
phases of drilling, well installation, and basic testing of commonly designed monitoring wells
was done informally. The diversity of environmental projects and the fact that different
costing methods were used by the various firms made this task difficult. Although every
project was unique, the following cost ranges are typical.
The costs for a 30-m (100-ft) deep well with Level D protective clothing, with a competent
borewall, completed with a single screen at the bottom of the well, and with a 10.8-cm (4.25-
in.) inner diameter (ID) hollow-stem auger with a 5.08-cm (2-in.) ID polyvinyl chloride
(PVC) well screen and riser averaged from $4500 to $5500. Split-spoon sampling added $500
to $1000 per well. Increasing the well diameter using a 21-cm (8.254-in.) ID hollow-stem
auger added $200 to $1000 per well. Changing from PVC to a stainless steel screen and riser
added $2000 to $3000 per well. Increasing the depth to 60 m (200 ft) nearly doubled the
costs. Going from Level D to Level C increased the costs by approximately 25%. Adverse
drilling conditions such as gravel or cobbles may increase the costs by 50% or more. Some-
times drilling conditions prevent completion of the well at all. The drive and wash (percussion
drilling) drilling method approximately doubles the costs over auger drilling. Typically, these
costs are roughly $1000 to $1500 more per 30-m (100-ft) well. The costs of a mud rotary
with a 15.24-cm (6-in.) hole are similar to those of a hollow-stem auger. Continuous-core
drilling can more than double the drilling costs on most projects.
The average 46-m (150-ft) well on eight large environmental investigations located on the
east and west coasts and in Colorado was $8500. The average for a 60-m (200-ft) well was
nearly $11 500. The high was for several 76-m (250-ft) wells with multiple completions in
difficult drilling conditions that cost up to approximately $25 000. None of these costs include
project management.
In-hole permeability testing costs are quite variable ranging from simple "slug" tests for
a single interval costing approximately $500 to $1000/test to drawdown tests ranging from
$4000 to $5000 minimum. One company constructed a special water treatment plant costing
$100 000 to handle the effluent from a number of long-term pump tests on one project.
Many environmental engineering firms try to perform all tasks possible in-house. This
frequently results in the specification of capabilities that are available within the company
as opposed to more suited measurements. Often these firms lack the experience to record
or interpret these measurements properly. Additionally, many of the engineering firms are
not accustomed to standard logging service contractor terms and conditions, especially
regarding liability for radioactive materials. As a result, they frequently have not included
the appropriate terms in their contracts with the primary client and cannot use measurements
that may be applicable for their project.

Geochemical Sample Analysis Cost Considerations
The economic implication of a poorly constructed monitoring well is not limited to the
cost of constructing this well. The costs related to the geochemical analysis of water samples
over the life of the well are much more significant expenses even though thev may come
from a different budget.
It is a general practice to sample each water-bearing zone on most hazardous waste
investigations quarterly until remediation is demonstrated after which time these wells are
usually sampled semiannually for another ten or more years to demonstrate that the problem
will not return. The cost of the analysis of these samples varies per project, but typically
ranges from $800 per sample for inorganic analysis to more than $1500 per sample for volatile
and organic analysis.
Considering the life of an average monitoring well may be 20 to 30 years or longer, the
cost of geochemical analysis for samples taken from this well may easily exceed $100 000
over its life. This does not include the cost to collect the sample, project management, and
so forth. Ideally, a poorly or incorrectly completed monitoring well will be identified early
in its life and corrected or abandoned. This process frequently takes a number of years, and
all too often these wells are not recognized ~t all. At one large site characterization project,
the addition of one sample analysis of each well cost $1 000 000. Geochemical sampling and
analysis over many years is very expensive: thus. the importance of using geophysical logs
to aid in design of a properly completed monitoring well cannot be overstated.
Design and Cost Analysis for Borehole Geophysical Surveys
The first step in design and analysis of a borehole-geophysical logging program is to
determine the short- and long-term goals for the project. The geophysical logs will be used
for one or more of the following:
(1) screen location and well construction;
(2) regulatory requirements;
(3) future integration and reinterpretation;
(4) lithologic data;
(5) in-situ parameter analysis needed for porosity, permeability, elastic moduli, fracture
evaluation, and so forth; and
(6) parameters for modeling surface geophysical methods.
The second step is to establish the options or techniques that exist for collection of the
required data. For instance:
(1) lithology information is available from drill samples including auger, rotary, and core,
as well as surface geophysics, and various well logs;
(2) porosity information can be obtained from laboratory testing of core samples, his-
torical data, and various logs;
(3) permeability information can be obtained for laboratory testing of core samples, pump
testing, and well logs; and
(4) fracture analysis is available from core data, borehole video, different well togs, pump
data, and so forth.

After establishing the options that are available, consider which limitations and site con-
ditions may affect survey design:
(1) the need to standardize data;
(2) hole conditions--open, cased, dry, wet, type of casing, and so forth;
(3) level of interpreter/analyst's expertise;
(4) project time schedule; and
(5) project budget.
Talk with your client about your project goals and also with your logging group (in-house,
service company, consultant, and so forth) before starting your project. They can both
provide you with valuable information affecting your program.
After thinking through these steps, prioritize the different options and choose accordingly.
Remember that the money you are spending is no better than the results that you receive.
Try not to be "penny wise and pound foolish." The following brief case histories typify this
design and cost analysis procedure.
Case History l
This investigation involved a detailed lithologic and hydrogeologic characterization in-
cluding the planned continuous coring of five wells with subsequent observation well ficlds
around the core holes for aquifer testing and monitoring in the central United States. It was
decided before the start of the project to attempt to collect as much information as possible
from these wells. A borehole-geophysical logging program including compensated density,
full waveform sonic, focused resistivity, gamma, SP, normal resistivity, temperature, fluid
resistivity, caliper, and neutron was planned on the core holcs. This was significantly more
logs than had been used on previous work in the project arca.
As an immediate benefit, the log data were used to help construct the monitoring wells.
The log analyst recommended completion zones in several cases that were not evident in
the geologic descriptions. Over the longer term. this program helped determine in-situ
porosity and refined the lithology. For instance, it was difficult to classify many of the
carbonaceous units until a density log was made. Correlation was made in a complicated
stream channel sequence over 1 mile (1.6 km) in distance confirming what was previously
speculated. The data provided model parameters for several surfacc geophysical surveys
before expensive field testing. The core hole data were correlated to data from previous
monitoring wells that had been completed over the last 20 years and allowed for a better
understanding of the geologic setting.
Cost of the logging program was approximately 15% of the construction of the core holes.
The project was curtailed before completion of the subsequent aquifer testing. This project
demonstrated that borehole logging of rotary holes could replace continuous coring on many
wells in this area. Each of the 13 logs recorded on each boreholc were used in the final
interpretation.
Case History 2
This project involved a large hydrocarbon spill and investigation in a limestone environ-
ment in the eastern United States. Originally, the engineering company chose continuous
core drilling of approximately 35 holes with no well logging. After starting the project, it

became clear that the core drilling was going to take substantially longer than the allowable
term of the project and at a much higher cost. Therefore, the drilling technique was changed
to allow hammer drilling with a logging suite of gamma, SP, normal resistivity, single-point
resistance (SPR), temperature, fluid resistivity, and caliper using rental equipment. Not all
of the information desired was obtained from the well logs; however, correct screen place-
ment was determined on most wells, and the logs helped with the packer test locations. The
hammer-drilling costs with the logging costs were less than 50% of the core-drilling costs,
and the project was finished within the time constraint. The combination of drilling with
geophysical logging provided more information than from core drilling alone.
Log interpretation ability and the availability of additional log information were critical
limiting factors on this project. Several additional logs such as density and full waveform
acoustic would have provided valuable information to help understand some apparent am-
biguous conclusions. It may also be possible to use video or an acoustic televiewer successfully
on this project in the future. The heat-pulse flowmeter would have been desirable to dem-
onstrate on this project to evaluate permeable fractures.
Case History 3
This project involves the site characterization of a large hazardous waste site. Site char-
acterization has been ongoing on this project for several years, however, there is still not a
good understanding of the geologic environment, and therefore, more drilling and testing
are being performed. Well logging with a sophisticated logging suite (14 log parameters) in
rotary drilled holes was accepted instead of continuous core and split-spoon sampling. The
initial goal of the logging project was to aid in well construction by identifying the appropriate
screen intervals and provide additional lithologic information and well construction hazards
such as washouts and borehole constrictions.
The logging suite selected for this project was larger than absolutely necessary for these
goals. The selected logging suite provides additional information that allows for in-situ
parameter analysis. This comprehensive logging process is cheaper than the continuous
sampling log evaluation and much quicker, and the data are more objective. The logs allow
for team evaluation, interpretation, and well design immediately after logging and before
construction of the well. This program allows for optimization of the number of the wells
and the optimum placement of the monitoring wells.
Logging costs were 25 to 30% of the drilling and completion costs. Additionally, a surface-
geophysical program is being correlated to the well logs and thus increases the database. If
the additional information collected for in-situ parameter analysis is used over the long term,
the logging program will be even more cost-effective.
Case History 4
The objective of the drilling and logging program on this project was to find and evaluate
paleo-stream channels because they represent possible migration paths for a contaminate
plume. This project was the fourth phase of the drilling program but was the initial phase
of logging. Most of the earlier monitoring wells were of questionable value both in location
and in construction. For instance, one drilling phase had inadvertently used drilling water
from a nearby gravel quarry. This contaminated the installed monitoring wells. The drilling
plan for this phase consisted of 40 wells with predetermined inflexible drill locations and
depths.
A paleochannel sequence was interpreted from the geophysical log data early in this

drilling phase. The staked locations of most of the new monitoring wells were located outside
this channel. Unfortunately, the drilling program could not be changed on-site. This resulted
in wasting more than 50% of the monitoring wells on this phase and dictated an additional
phase of drilling at a later date.
The logs were used to select the screened interval of the monitoring wells and to design
the new drill program. Because the drilling program could not be changed once the project
was started, the most cost-effective contribution of the logging program was lost.
Case History 5
This project has not been started, but demonstrates the process of considering a borehole-
geophysical logging program. It is for remediation of a large hydraulic oil spill that had
occurred over a number of years at a manufacturing site. The spill is contained on and near
the water table at a depth of less than 15 ft (4.5 m) in a very permeable formation. Estimates
of the magnitude of the spill range from several hundred to 1 million gal (3.78 million L)
of oil. A number of conventional monitoring wells have been previously installed, yet it has
not been possible to determine in-situ porosity. Borehole geophysics is being considered for
this project for the single purpose of determining porosity across the project site. If the
porosity can be determined, and the hydrocarbon saturation determined from core samples,
then the volume bf the total spill can be more accurately estimated and the remediation can
be evaluated. The value of porosity information is considered enough to alter the drilling
methods for future monitoring wells to maximize the borehole geophysical log accuracy.
Conclusions
Table 3 places in perspective the relative cost of geophysical logs with respect to the total
cost of drilling, completing, and monitoring drill holes. This underscores a primary con-
clusion of this paper, which is that the costs of borehole geophysics are relatively minor
components in the total cost of subsurface investigations and monitoring.
Furthermore, it can be reiterated here that the direct and indirect benefits provided by
geophysical logs in terms of well construction, subsurface interpretation, and optimum
monitor well placement compare extremely well to the expense of acquisition and inter-
pretation of those logs.
The consequences of environmental investigations are becoming better known as the
remediation programs are coming under more scrutiny in terms of cost and scope, and the
need to collect as much information as possible early on in a project is increasingly apparent.
Companies are beginning to question the "we can engineer around anything" approach with
regard to remediation programs and the associated requirement for unlimited funds. Bore-
TABLE 3--Relative cost of geophysical logs with respect to the total cost of drilling, complet-
ing, and monitoring drill holes.
Average cost to drill and complete one 60-m well $11 500
Estimated cost to monitor over 25 years in 1989 dollarsa $53 000
Average cost for acquisition and interpretation of geophysical logs (per well) $1 350
Percent of total for geophysical logs 2%
"Average $5000/year, discounted 8% per year (without inflation).

hole geophysics is a tool that has been underused on many of these projects: however, it
can be cost-effective in site investigation and also in long-term monitoring.
Primary reasons for the lack of use of borehole geophysics include a lack of understanding
of the methods, the availability of the services, the availability of log interpreters/analysts,
and a lack of understanding of the goals of the projects. As these goals become better
defined, the value of more objective log data increases. Education and experience are starting
to overcome some of this lack of understanding, and regulations are now stipulating minimal
geophysical logs on many projects. A better understanding of the limitations of the log data,
especially during acquisition, also aids in evaluating the information effectively.
Acknowledgments
The authors of this paper wish to thank Mr. Larry Dearborn with CE Environmental,
Ebasco Services, Inc., and the other engineering companies contacted for the sharing of
cost information used in this paper.
References
[1] Wheatcraft, S. W.. Taylor, K. C., Hess, J. W.. and Morris, T. M., 'Borehole Sensing Methods
for Ground-Water Investigations at Hazardous Waste Sites." Water Resources Center, Desert
Research Institute, University of Nevada System. Cooperative Agreement CR 810t)52 for Envi-
ronmental Monitoring Systems Laboratory, Office of Research and Development. U.S. EPA, Las
Vegas, NV 89114, Dec. 1986. Reproduced bv U.S. Department of Commerce. National Technical
Information Service, Springfield, VA 22161.
[2] Crowder, R. E. and Irons, L., "Economic Considerations of Borehole Geophysics for Engineering
and EnvironmentalProjects," in Proceedings of the Symposium on the Application of Geophysics
to Engineeringand Environmental Problems. Colorado School of Mines, Golden, CO. 1989.
[3] Crowder, R. E., "Cost Effectiveness of Drill Hole Geophysical Logging For Coal Exploration,"
paper presented at the Third InternationalCoal Exploration Symposium,Calgary, Alberta, Canada,
1981.
[4] Keys, S., "Borehole GeophysicsApplied to Ground-WaterInvestigations,'"U.S. Geological Survey,
Open-File Report 87-539, Dec. 1988.
[5] Stegner, R. and Becker, A., "Borehole Geophysical Methodology: Analysis and Comparison of
New TechnologiesFor GroundWater Investigation," in Proceedingsof the Second National Outdoor
Action Conference and Aquifer Restoration, Ground Water Monitoring and Geophysical Methods,
Vol. II, 1988.

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