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11th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 22 Mar 1998 - 26 Mar 1998
- Location: Chicago, Illinois, USA
- Published: 22 March 1998
41 - 60 of 111 results
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Brownfield Site Investigation Using Geophysics: A Case History From East Chicago
More LessBrownfields are areas in cities that have been determined to have environmental problems
due to industry that once operated at those sites. At present, most of the areas are open tracts of
land and they cannot be used or cleaned up until the extent of contamination has been determined.
It has been suggested that geophysics be used to conduct non-invasive sit characterization. Urban
areas have additional problems associated with then, including power line, rebar in concrete, electrical
lines in buildings, and large metal objects near by that often interfere with electromagnetic
(EM) and magnetic measurements. All of these aspects must be taken into account in designing an
effective geophysical survey in an urban environment. A Brownfield site in East Chicago was used
to demonstrate the effectiveness of utilizing geophysics and to develop strategies for applying geophysics
to Brownfields. The site contained all of the problems listed above. Ground penetrating
radar (GPR), multi-frequency EM measurements, and vertical and horizontal gradient measurements
were made. Comparisons of the magnetic and EM measurements proved to make it easier to
evaluate the GPR measurements at this site. This is the most extensive study to date of a comparison
of geophysical methods in an urban setting. The comparison of methods indicate the following:
(1) there needs to be very close (one foot or less) line and station spacing, (2) instruments
should be run in orthogonal directions, and (3) multiple methods should be used for the best characterization
of the sites.
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Characterizatlon Of A Newly Discovered Lnapl Plume At Wurtsmith Afb, Oscoda, Michigan
Authors William A. Sauck, Estella A. Atekwana and Jose L. BermejoA Light Non-Aqueous Phase Liquid (LNAPL) ground water contaminant plume has been
discovered by purely geophysical means at the former Wurtsmith AFB near Oscoda, Michigan.
The plume was discovered by Ground Penetrating Radar (GPR) while extending a long line
horn another contaminated area (FT-02) to establish background variability around that plume.
The new plume was apparent because of a high-conductivity “shadow” or GPR reflection
attenuation, identical to the pattern observed at the FT-02 plume. The GPR survey was
supplemented by an electromagnetic (EM-31) survey which revealed a group of cables
crossing the area, but no anomalous regions associated with the presence of the plume. A
magnetometer survey was conducted to search for any buried steel objects which might not
have been detected by the EM survey. The results of these initial geophysical surveys were
used by the National Center for Integrated Bioremediation and Development (NCIBRD) staff
to guide subsurface soil and fluid sampling, which verified the presence of residual LNAPL
product and ground water with conductivities 2.5 to 3.3 times above background. Subsequent
surveys were conducted, including mise-a-la-masse (MALM), dipole-dipole resistivity/induced
polarization (IP) and vertical resistivity probe (VRP) measurements. The MALM survey
shows marked elongation along the plume axis, while the resistivity/IP showed two anomalous
regions coincident with buried utilities. In addition, the VRP revealed the presence of a
conductive zone at the top of the aquifer. This newly discovered LNAPL plume, along with
other “mature” plumes, fits an electrical model which predicts conductive ground water below
the decomposing LNAPLs.
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Comparison Of Magnetic And Electromagnetic Anomalies
Authors I.J. Won and Dean KeiswetterMagnetic and electromagnetic (EM) methods are perhaps the most convenient and popular
geophysical survey methods for detecting buried manmade objects. This is due to their nonintrusiveness,
light field logistics, high survey speed, and the high quality of information. Thus, they
should considered as precursors to additional geophysical surveys. Often, the information resulting
from the two methods are sufficient for characterizing buried objects. During the oral presentation, we
will present case history examples showing magnetic and EM data collected at sites that have a range of
environmental conditions and project objectives. We find through these and numerous other
comparisons that broadband EM data are usually superior to magnetic data in terms of the amount and
the quality of information. The monopolar EM anomaly is invariably easier to interpret, and thus can
locate a buried target more accurately than the dipolar magnetic anomaly. In addition, the EM method
senses both electrically conductive and magnetically permeable targets. In contrast, the magnetic
method responds only to permeable, or ferrous, metals. In that sense, the magnetic method should be
considered a subset of the EM method, or as a special “passive” EM method at zero frequency.
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Fractures In Limestone Imaged By Radar
More LessRadar data collected along profiles and in grids have assisted in identifying subsurface
pathways that might carry motor fuel known to be contaminating domestic water wells.
Disruptions of reflections were visible in conventional radar profiles were interpreted as
fractures zone in limestone bedrock. Radar data acquired in a grid over zones where
these fractures were the most dense are presented as a three dimensional display,
facilitating the visualization of the extension of these fractures across the survey areas
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Characterization Of A Complex Refinery Groundwater Contamination Plume Using Multiple Geoelectric Methods
Authors Estella A. Atekwana, William A. Sauck and Douglas D. WerkemaThe geoelectric properties of hydrocarbon contaminant plumes vary and their geophysical
responses suggest that the ‘insulating layer’ model cannot be uniformly applied to all hydrocarbon
contaminated sites. Changes in the aquifer pore fluids chemistry, causes the variability of the
geoelectrical signature. In this study, we investigate the electrical properties of a complex hydrocarbon
plume resulting t?om 50 years of leakage into a glacio-fluvial geologic setting using ground penetrating
radar (GPR) and electrical resistivity methods. The results show the following: (1) regions of low
apparent resistivities are coincident with attenuated GPR reflections (shadow zones) but are limited to
the edges of the surveyed areas; (2) a central region of high apparent resistivities with bright GPR
reflections below the water table; (3) an upper GPR reflector subparallel to the water table, several feet
above the current free product level and coincident with the top of an gray, oil-stained layer, and (4) the
existence of a thin conductive layer coincident with a dark gray to black layer saturated with free
product occupying a zone immediately above the water table. These results suggest that the light
hydrocarbon free-product, and associated dissolved plumes are dynamic systems whose chemistry is
changing in time and position within the plume. As a result, this influences the variability of the
geoelectrical signature. Therefore, geophysical results must be interpreted in the light of a coherent
model based upon combined geological, geochemical, and geophysical understanding of the evolution
of these systems.
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Composite Landfill Characterization: An Integrated Geophysical Study
Authors Eva Lanz, Hansruedi Maurer, David E. Boemer, Heinrich Horstmeyer and Alan G. GreenGeophysical methods provide non-invasive means of probing buried waste disposal sites.
Using a small composite waste site in northern Switzerland as an example, we obtain accurate
images of the host sedimentary succession and structure from 3-D seismic reflection and ground
penetrating radar (GPR) surveys. Lateral boundaries of the disposal site are clearly visible in
detailed images of the magnetic gradient field and in various maps constructed from conductivity
data. Tomographic inversion techniques applied to seismic refraction data provide information on
waste pit thickness variations. While individual geophysical methods are quite powerful for
mapping aspects of the shallow subsurface, our study highlights the need to acquire diverse data
sets. Only with independent subsurface constraints is it possible to obtain reliable models of the
earth so essential for environmental and engineering studies.
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Application Of Magnetic And Multi-Frequency Em Techniques For Landfill Investigations: Case Histories
Authors Craig Murray and Dean KeiswetterMagnetic and electromagnetic techniques were used in the investigation of three landfill sites.
Historical records of the content and location of buried waste in all three landfills were poor.
The geophysical surveys were conducted to map the trenched areas or locate buried drums and
other metal objects within the landfill. Waste filled trenches exhibit a higher conductivity than
the surrounding undisturbed materials. Drum burial areas have a higher apparent conductivity
and also produce significant magnetic anomalies.
These geophysical surveys provided accurate locations of the trenches and drum caches in all
three cases. When used together, the magnetic and electromagnetic data could be used to
differentiate between ferrous and non-ferrous metallic waste. Modern equipment measures and
logs EM and magnetic data efficiently, allowing surveys to have high spatial density. This
increase in data density provides more precise delineation of trenched areas and more accurate
location of buried objects such as drums. The increased efficiency of the modern instruments,
computers, and techniques enables the user to complete high quality surveys in hours or days and
present the environmental investigator with understandable maps in the field.
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How Important Is The Orientation Of A Horizontal Loop Em System? Examples From A Leachate Plume And A Fault Zone
More LessThe coupling between a horizontal loop EM (HLEM) system such as the Geonics EM31@,
and a buried object, e.g., a buried pipe, is well-established. The response from a buried pipe or
from a vertical lamp-post will depend on the orientation of the transmitter-receiver loop system
relative to the object in question. However, diffuse boundaries do not respond like discrete buried
objects. In particular, evidence from a survey of a landfill leachate plume and from two lines
across the Alpine Fault of the Southern Alps of New Zealand illustrates that the difference is
generally negligible. The leachate survey was carried out in an area of heavily-vegetated coastal
dunes adjacent to a landfill site. Survey lines criss-crossed the area, using cut trails for access. The
line crossings were used for analysis, and the net difference was 0.30 + 0.55 mS/m (less than
2.5% on average). The Alpine Fault EM surveys were carried out in advance of and in support of
a ground penetrating radar survey. The survey line followed a 6 m wide farm access road that was
bordered on both sides by wire fences. The EM survey was completed twice, using two
orientations - one parallel to the road (and fences) and the other perpendicular to the road. The
results indicate that the response differed by only 0.14 f 0.03 mS/rn, except for the gates and
fence corners where different responses would be expected. Therefore, the HLEM system
orientation is not significant when surveying features that are not sharp, discrete objects.
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Shear Wave Velocity Measurements For Earthquake Hazards Studies, Fraser River Delta, British Columbia
By J.A. HunterShear wave velocity-depth information in thick unconsolidated overburden is one of the fundamental
requirements for estimation of seismic site responses such as liquefaction potential and ground motion
amplification in an earthquake-prone area such as the Fraser River delta. The delta area (approximately 600 km*)
was surveyed in a reconnaissancem anner using direct shearw ave (S-wave) measurement methods such as surface
refraction, seismic cone penetrometer, and downhole logging. In addition, S-wave velocities of the entire
overburden thickness have been estimated from conventional exploration seismic reflection velocity analyses.
In all, S-wave velocitydepths have been obtained for over 400 sites where unconsolidated overburden thicknesses
range from ~5 m near the delta edges to > 1000 m in the south central region. Results indicate:
1) large S-wave velocity-depth gradients within the unconsolidated overburden which can give rise to
amplification effects for simple elastic models; confiiation of such amplifications are given from observations
of local earthquakes;
2) large S-wave velocity contrasts within the overburden sequence associated with the Holocene-Pleistocene
boundary; such contrasts can give rise to considerable lateral variation in site period response to earthquake
shaking;
3) widespread occurrence of low S-wave velocities in the near surface materials (mainly fine sands), suggesting
that the seismic liquefaction potential may be relatively high
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Geotechnical Use Of A Shear-Wave Vibrator: In-Situ Measurement Of Nonlinear Properties Of The Ground Surface
More LessA new method is proposed for evaluating non-linear properties or strong motion
responses of the soIt ground directly in the field. The method utilizes a shear-wave
vibrator, which has been conventionally used for the reflection survey in the resources
exploration, as an artificial strong motion source. Various types of cones, such as
seismic cones and electrical cones, penetrated into the near surface are used to monitor
the ground response to the vibration. Field tests for the method were performed at the
Tone River Site near Sawara City, approximately 60km northeast of Tokyo. The tests
showed the shear-wave vibrator had a power to oscillate the ground with lOOgal or
more at 5m from the vibrator baseplate. Decrease in shear wave velocity was clearly
observed with increasing vibration level, which means non-linearity of the shear
modulus of the ground is detectable in place by this method.
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Shallow Reflection Seismic Study Of Recent Faulting In The Benton Hills, Southeastern Missouri
Authors Anthony E. Shaw, N. Anderson, M. Shoemaker, G. Adams, S. Oppert, D. Webb and S. CardimonaDuring the summer of 1997, the Department of Geology and Geophysics at the University
of Missouri-Rolla conducted a high resolution shallow @IRS) reflection seismic study of the
Commerce Geophysical Lineament (CGL) both within and adjacent to the Benton Hills, southeast
Missouri. Our primary objective was to determine whether the CGL constitutes part of a late
Quaternary fault system located outside of the New Madrid area of active micro-seismicity. A
secondary objective was to demonstrate that the reflection seismic technique can be used to map the
shallow subsurface in an intensely faulted environment.
The reflection seismic study was successful. Our interpreted data demonstrate that the CGL
zone (both within and adjacent to the Benton Hills) is structurally complex - reflection seismic and
geologic data indicate extensive and episodic faulting of Paleozoic, Cretaceous, Tertiary, and
Quaternary strata. The individual faults exhibit significant near-vertical displacements, and appear
to be oriented north-northeast essentially paralleling the CGL.
These observations support the argument that the southeastern escarpment of the Benton
Hills is tectonic in origin, and indicate that the CGL constitutes part of a late Quaternary fault system
located outside of the New Madrid area of active micro-seismicity. This implies that earthquake risk
in southeast Missouri is greater than generally thought. This conclusion has important implications
for earthquake hazard assessment in the mid-west.
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Physical Ultrasonic Modeling Of Wave Scattering At Anisotropic Wave Barriers
Authors Elizabeth Its, Alexei Anisimov and Jong LeeIn this paper we report the results of 3D ultrasonic experiments on Rayleigh wave scattering
at a narrow vertical anisotropic slab. The experimental model was built from two rectangular
isotropic blocks and a narrow vertical anisotropic slab embedded between them. The slab
was made of woodfibre; the fibre was orilinted horizontally along the interfaces of the slab
(along the y-axis). As a result z+.a, long the y-axis wa.s about three times higher than along the
x-axis. Longitudinal and isochrone profiles were used for recording of the scattered surface
waves. In addition, several profiles were shot perpendicular to and along the slab in the
near-field zone. A scatterplot smoother (SPLUS ) was applied to construct the amplitude
curves of the Rayleigh waves. The results of the experiments are compared with the results
of calculation using the Green’s function technique.
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Formation Electrical Conductivity-Porewater Salinity Relationships In Quaternary Sediments From Two Canadian Sites
Authors C.S.B. Hyde and J.A. HunterBorehole and surface electromagnetic (EM) conductivity measurements have been made in
porous Quaternary sediments, both “Champlain Sea” sediments of Eastern Ontario and the Fraser
River Delta sediments of British Columbia. These silts, sands, gravels and coarse-grained
diamictons were deposited in marine or brackish-water environments. Post-depositional changes
in groundwater hydrogeological conditions have resulted in large vertical variations in porewater
salinities which are reflected in the measured formation electrical conductivities.
Salt leaching within cohesive sediments has resulted in “sensitive soil” conditions of
considerable geotechnical importance affecting slope stability. As well, vertical porewater salinity
gradients, both near-surface and at depth, have been associated with significant changes in subsurface
geological stratigraphy within the overburden.
Comparisons of measured porewater salinities to formation electrical conductivities have
yielded empirical relationships which are being used in regional geophysical studies to predict
occurrence of signiticant salinity anomalies associated with variations in sub-surface geological
structure and geotechnical properties.
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Locating Dangerous Historic Mine Workings In The Cresson Open-Pit Mine With The Aid Of Ground Penetrating Radar
Authors Robert A. Butts and Paul R. HagueThe Cresson open-pit mine is located in the Cripple Creek Mining District, a
region of concentrated historic underground mining activity. The area has been
worked extensively since the turn of the century and the activity has left the area honeycombed
with miles of subterranean tunnels. These cavities are continuously being intersected as the
working level of the Cresson open-pit mine progresses deeper, posing a hazard to men and
machines operating in the pit. Besides the obvious danger of the working surface collapsing into
one of these tunnels, blast efficiency is affected when these cavities occur within the blast
patterns.
Ground penetrating radar (GPR) is used in conjunction with historic underground workings
maps and a survey file of previously encountered workings to attempt to predict the location of
these dangerous subsurface cavities. Known workings are marked on the muck piles prior to
excavation and again on the pit floor after the muck face has progressed past these areas.
The blast-hole patterns are surveyed with the GPR prior to the blast-hole drills arrival because
they are most at risk. Voids found with the GPR are marked in the blast patterns and the areas
are drilled accordingly to minimize the possibilities of a catastrophe. The drill pattern and shot
loads are adjusted to account for the open areas that tend to absorb energy from the blasts
leaving “hard spots” in the muck.
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Acceptance Of The Expedited Site Characterization (Esc) Approach In Environmental Cleanups
Authors Caroline B. Purdy and Paul BeamIt has been several years since the Department of Energy (DOE) first started promoting a new
characterization approach for CERCLA/RCRA activities at DOE contaminated sites. This
approach, referred to as Expedited Site Characterization (ESC), has been demonstrated, reviewed
and observed by DOE and other agency program managers, and used in actual regulated site
activities at DOE’s Pantex Site, Savannah River Site, and the Nevada Test Site to confirm its cost
and schedule savings and, more importantly, its effectiveness. Since then, on a national level,
many new EPA policies and initiatives have been introduced for environmental activities in
general to speed up the cleanup process. State regulatory agencies are closely cooperating under
new programs to reduce the barriers for use of innovative approaches and technologies in
remediation programs. And several programs have emerged from federal agencies such as
Departments of Commerce and Defense and Energy, to assist the acceptance of new concepts
and approaches to environmental problems. The combination of these many changes and trends
in environmental policy and activities has an influence on the future use of ESC for site
characterization programs. The issues facing ESC acceptance are very similar to the issues
facing innovative technology acceptance. This paper will describe: the reason for DOE’s
original push to introduce ESC into environmental management programs, what ESC means,
what is its acceptance today in particular with respect to the changes occurring nationally in the
environmental business, and expected future use of this approach in both the private sector and
DOE. The emphasis in this paper is NOT so much on what ESC is but on how ESC gains
acceptance.
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Esc: How It Differs From Current State Of The Practice
Authors Richard C. Benson, Al Bevolo and Paul BeamProblems with the current state of the practice in site characterization for both geotechnical and
environmental projects are abundant. The Expedited Site Characterization (ESC) strategy
developed by DOE provides a means for a major improvement in the statusquo. Unlike previous
EPA and DOE site characterization practices, ESC has elevated the experienced professional and
their quality of work, and re-identified hydrology and geology as critically important for site
characterization.
The ESC process can be applied to site characterization for either geotechnical investigations or
environmental assessment and remediation. The general ESC model as presented should be the
basis for planning any site characterization work. However, the model may be modified based
upon the specific project size, objectives, and the project’s status when beginning the ESC effort.
The purpose of this paper is to highlight the key elements of the ESC process and show how it is
a large improvement to the current state of the practice.
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Esc Phase I: Locating And Mapping Drilling Mud Pits At The Central Nevada Test Area
Authors Ronald D. Kaufmann, Lynn B. Yuhr and J. David WonderAn Expedited Site Characterization (ESC) was recently carried out at the Central Nevada Test
Area (CNTA) for the U.S. Department of Energy. The CNTA was the site of several deep well
drilling operations in the late 1960’s. One of these wells was the site of a nuclear detonation in
1968 (Project Faultless). The focus of the ESC was to locate and characterize contaminants
associated with drilling mud disposed of in pits. Most of these mud pits have been backfilled
and their exact locations were not known. The objective of Phase I was to locate the boundaries
of the mud pits using non-invasive and minimally invasive geophysical techniques. Accurate
site maps developed from existing data, observations and a topographic survey served as a
positional reference for all measurements and subsequent chemical sampling. The results from
Phase I provided a conceptual model of site conditions and guided the chemical sampling in
Phase II.
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Esc Demonstration D-Area Oil Seepage Basin - Savannah River Site A Case Study
Authors Steven B. Gelb and J. David WonderBetween June and September 1995, the Expedited Site Characterization (ESC) process was
demonstrated at a 4-acre site which contained buried waste trenches at the U.S. Department of
Energy’s Savannah River Site (SRS) in South Carolina. This demonstration project was sponsored
by the DOE Office of Environmental Management’s Office of Technology Development, and
implemented under the direction of the Ames Laboratory. The two-phased ESC program was
successful at accurately characterizing both geologic/hydrogeologic and environmental quality
conditions at the site in a compressed timeframe. Information obtained from this program resulted
in the identification of a discrete source area within the waste trenches, and quick delineation of the
vertical and horizontal extent of groundwater quality impacts with a high degree of resolution.
Consequently, the ESC program allowed the identified source area to be removed through the
implementation of a focused interim remedial measure in a timely manner, while providing the data
needed to conduct a risk assessment and achieve rapid site closure.
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Managing Data And Its Integrity In The Esc Process
By Lynn YuhrThe Expedited Site Characterization (ESC) process relies heavily upon the use of timely and
reliable data. The importance of data in any site characterization is paramount. The ESC process
strives to create a solid foundation of data by having appropriate, adequate and accurate data to
build upon which increases the confidence in all subsequent decisions and actions.
This paper focuses upon the critical review necessary in all aspects of data management to
include quality control, processing, interpretation and presentation. No guidelines, procedures or
software will substitute for the involvement of the professional staff who are able to focus upon
basics and are sensitive to the fact that errors and omissions can and do occur. The ESC strategy
addresses these issues by requiring a consistent team of hands-on professionals in the field as
well as throughout the project.
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Optimization Of Ert Surveys
Authors Emily Sullivan and Douglas J. LaBrecqueThe objective of this project was to determine the optimum array and electrode configurations to
produce the best resolution in ERT surveys. In this experiment, we considered the effects of
surface electrodes on resolution and the effects of different arrays on resolution. Experiments
were conducted at the University of Arizona Maricopa Field station using two rectangular ERT
cells equipped with surface and borehole electrodes. Data were collected with five different
arrays; pole-pole with and without surface electrodes and dipole-dipole arrays with 3 different
dipole lengths were conducted between boreholes and surface electrodes. Data have been
analyzed and inverted to get 3-D images of resistivities within a block of four boreholes.
Resolution steadily improved with distance in dipole length. The pole-pole surveys show much
more detail at lower depths. When augmented with surface electrodes, the pole-pole surveys
showed clearer resolution of layers.
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