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13th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 20 Feb 2000 - 24 Feb 2000
- Location: Arlington, Virginia, USA
- Published: 20 February 2000
1 - 50 of 140 results
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Detection Of Higher Mode Surface Waves Over Unconsolidated Sediments By The Mx4 Wmethod
Authors Choon Byong Park, Richard D. Miller and Jianghai XiaIn engineering application of surface waves it is critically important to accurately extract the
fundamental mode dispersion curve. Among several factors that may adversely affect the
extraction is the existence of higher modes with significant amount of energy. A calculated
phase velocity can be an average of the fundamental and the higher-modes phase velocities or it
can be the phase velocity of a specific higher mode, depending upon the specific method used for
the application, unless the higher modes are properly handled during the data acquisition and
processing steps. Therefore, it will have a practical value to observe the higher mode generation
through field experiments and examine for any parameter that can be controlled during data
acquisition.
A higher mode (the first overtone) of high frequency (5-30 Hz) surface waves was observed by
using the multi-channel analysis of surface waves (MASW) method at three boreholes located in
unconsolidated sediments in the Fraser River Delta, near Vancouver, British Columbia. Each
site has a unique near-surface shear (S)-wave velocity (Vs) structure as verified from downhole
Ys measurements. The relative dominance of higher mode energy is examined in association
with source distance as well as Ys structure. Our examination indicates that energy of higher
modes tends to become more significant as the source distance becomes greater. It also reveals
that the dominance may be related to a Vs structure: a greater dominance as fi changes little
with depth, or fi has an overall low value, or a combination. The dependency on the source distance
is observed to be stronger than that on the Vs structure. Attempts are made to explain the
dependency by referring to one or a combination of three factors: attenuation, the near-field
effects, and the intrinsic nature of surface waves. Inclusion of higher mode during a surface
wave measurement for near-surface (~30 m) application can be either an advantage or a-disadvantage,
depending on the specific type of application and the method used during the data
acquisition and processing steps. It is, therefore, important to recognize through field
observations those conditions both favorable and unfavorable to the generation of higher modes
of high-frequency surface waves.
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Mapping Poisson’S Ratio Of Unconsolidated Materials From A Joint Analysis Of Surface-Wave And Refraction Events
Authors Julian Ivanov, Choon B. Park, Richard D. Miller and Jianghai XiaPoisson’s ratio (°) of the near-surface materials is one of the key parameters in various types of
geotechnical projects. It is usually associated with the integrity of the materials from the
engineering perspectives. A two-dimensional (2-D) distribution map of °, therefore, would have
an invaluable value.
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Fluid-Induced Changes In Shear Velocity From Surface Waves
Authors Michael West and William MenkeSeismic methods can monitor transient ground water by detecting changes in seismic velocity.
Compressional and shear wave velocities respond to changes in the bulk modulus, shear modulus
and density caused by the presence of water. We present three methods that allow these small
perturbations in seismic velocities to be tracked through time in a field setting. Compressional
velocities are tracked using differences in first arrival traveltimes. Shear velocities and
subsequent perturbations are calculated from surface wave frequency components. A simple
inversion scheme allows these velocities to be tracked as a function of depth below the surface.
Using these strategies, several observations are made addressing how fluid saturation can be
derived from seismic properties. We confirm prior observations of a large compressional velocity
change associated with full saturation. Contrary to prior lab studies, we find shear velocities in an
unconsolidated sandy environment to be quite sensitive to moisture content. Partial saturation can
be detected from increased shear velocities resulting from greater cohesion between grains. We
also observe the influence of pore pressure changes below the water table. This suggests that
shear velocities might be used to monitor pressure changes in a fluid reservoir.
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Detection Of Underground Voids With Surface Waves
Authors Christopher Phillips, Giovanni Cascante and Jean HutchinsonThe conventional approach to the detection of underground voids by the Spectral Analysis of
Surface Waves (SASW) method is through analysis of the phase difference between two
transducers. This approach requires lengthy field testing and complex data manipulation,
including filtering and unwrapping of the phase function. In the frequency domain two properties
are measured for each frequency, its amplitude and wrapped phase value. This study proposes a
method for the detection of underground voids by analyzing the measured power spectral
density, a function related to the amplitude of the frequency. The proposed method does not
require complex data manipulation since the power spectral density is directly measured and
testing can be completed with an oscilliscope, decreasing the time required to conduct a seismic
survey.
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Shallow S-Wave Structure Can Be Interpreted From Surfacewave Group-Velocity Tomography
Authors L.T. Long, A.H. Kocaoglu and J. MartinSurface-wave group-velocity tomography provides an efficient way to measure
the shallow S-wave structure at waste sites and other areas where measurements are not
advisable directly above the structure. In this technique, measurements are made only on
the boundary of a test area. The wavelength and area dimensions determine the depth of
resolution. For example, structures in the depth range of 1 to 8 m may be interpreted
from 16 to 48 Hz surface waves traversing a 30 m square. Given sufficiently dense
record traces, the horizontal resolution is limited principally by wavelength. A 40 Hz
wave will resolve structures less than 2 m in diameter near the surface. Unlike phase
velocity measurements (e.g. SASW) corrections for energy delays introduced by the
instrument response and geophone ground coupling are required for accurate velocity
determination. The multiple filter technique is used to determine group arrival times and
their uncertainties at individual frequencies. The SIRT algorithm is used to obtain a
tomographic image of the group velocity at each frequency. The images for individual
frequencies can be used to interpret geologic structure, or they can be combined to
generate group-velocity dispersion curves and their associated S-wave structure for any
position in the test area.
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Mapping Conductivity With Helicopter Electromagnetic Surveys As An Aid To Planning And Monitoring Pipeline Construction
Authors Greg Hodges, Jonathan Rudd and Dominique BoitierHelicopter EM surveys have been used to map apparent conductivity as an aid to
characterizing ground conditions in advance of pipeline construction. The cost of pipeline
construction is strongly dependent on the ground conditions encountered, and accurate
prediction of these conditions can reduce the planning risk considerably.
A DIGHEMV conductivity survey was used to map ground conditions along
approximately 130km of prospective pipeline corridor, 400m in width. The survey took
four days to complete, providing a map of apparent conductivity with a resolution of
approximately 10m. The results are interpreted to determine the extent of shallow
bedrock (which would require blasting) and deeper overburden which could be trenched
to the depth necessary for the pipeline. Over much of the survey area it is possible to
define a single apparent conductivity value as the borderline between soils, which could
be trenched, and rock which would have to be blasted. The data can be mathematically
inverted to produce maps of the depth to bedrock.
The airborne EM survey reduced the time and cost associated with gaining land
access and permission for drilling. The survey also served as a check for buried, unknown
power lines and pipelines. Airborne EM surveys have also been used to map ground
conductivity after the pipelines have been constructed to detect areas of high ground
conductivity due to clays or saline soils. These soils can create conditions in which
pipeline corrosion is accelerated.
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Evaluation Of Improved Airborne Techniques For Detection Of Uxo
Authors T.J. Gamey, W.E. Doll, D.T. Bell, A. Duffy and S.D. MillhouseRecent development of helicopter boom-mounted magnetic detection systems (Gamey and
Mahler, 1999) have made it possible to detect much smaller objects than could be detected with
conventional towed systems. Data acquired with the HM3TM system in June 1999 at the
Badlands Bombing Range (BBR) in South Dakota indicate sensitivity to ordnance and buried
metals that have a mass of less than 1Okg. This is significantly better than was observed in an
earlier test with the HM3TM system at Edwards Air Force Base (EAFB) in California (Doll et. al.,
1999). This paper presents an overview of the project and initial results.
Data were acquired in six areas at BBR. These included two trench areas, two bombing targets,
a controlled test site, and an undiscovered bombing target. The first two bombing targets had
previously been surveyed with the MTADS system (McDonald and Robertson, 1996). The third
bombing target was discovered in the course of a blind survey of a “clean” part of the range.
The controlled test site consisted of 24 holes in which deactivated ordnance, fragments of
ordnance, simulants, plumbing pipes, and known metallic objects (e.g. segments of reinforcing
rods and I-beams) were placed at depths ranging from 0 to lm. The smallest objects at the test
site were approximately 5kg.
The improved sensitivity at BBR is attributed to: 1) higher data sampling rates, 2) elimination of
a low pass filter that was used at EAFB, 3) improved techniques for removal of geologic noise,
4) lower instrument altitude in flatter terrain, and 5) more favorable geologic background
conditions. These results indicate that airborne magnetic methods are an appropriate tool for
detection of ordnance, and for screening or characterizing large areas of suspected
contamination. This is particularly true at sites where low survey altitudes are possible,
background geologic response is low, and expected target size is within range.
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Gem-2A Broadband Airborne Em System
Authors David Wright, I.J. Won and Neil GoodeyA helicopter towed broadband EM system capable of simultaneously transmitting and
receiving at several user-selected frequencies has been developed and is currently
operational in mineral and environmental programs. The system employs advanced
digitally controlled transmitter electronics providing flexible user selections for current
waveforms, as well as advanced built-in digital signal acquisition and processing
including real-time sine/cosine correlation for spectral analysis of the data. The system
architecture and performance are discussed in the context of conventional EM mapping,
advanced product derivations and the facilitation of new methodological approaches in
the application of airborne EM techniques.
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The Use Of Airborne Electromagnetic Systems For Hydrogeological Investigations
Traditionally, airborne frequency and time domain electromagnetic systems have been used for mineral prospecting, often in parts of the world with little environmental electromagnetic
disturbance. However, the increased focus on hydrogeological investigations in many parts of the world has led to a growing interest in the possibility of using airborne systems for such purposes, also in densely populated areas (Sengpiel and Siemon 1998). This raises many interesting questions as to the resolution capabilities of AEM systems and their sensitivity to disturbing influence from ambient electromagnetic noise, and the presence of man-made structures such as power lines, buried cables, and fences. The data quality of earlier AEM systems was such that they were mainly used as “bump detectors” capable of indicating the presence of good conductors. Quantitative interpretation of the data was often not warranted (Huang and Fraser 1999), but with the improvement of AEM systems in general new possibilities of quantitative interpretation have appeared (Macnae et al. 1991). Compared with ground systems, AEM systems have a larger footprint giving rise to reduced horizontal resolution, and a more narrow bandwidth resulting in inferior vertical resolution. Furthermore, it is often very difficult to estimate the system noise, especially that due to the motion of the aircraft, and not very much is known about the coupling effects to man-made structures in developed areas. On the positive side, the density of AEM measurements far exceeds the density of traditional ground surveys and the production rate is more than 1000 km per day. This paper presents analyses of the resolution capabilities of present-day transient electromagnetic (TEM) systems and makes comparisons between airborne and the corresponding ground systems for a number of hydrogeologically relevant models.
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Identifying And Assessing Ground Water In The Lower Rio Grande Valley, Texas, Using Airborne Electromagnetic Induction
Authors Jeffrey G. Paine, Edward S. Angle and Rima PetrossianWe are applying airborne and ground-based geophysical methods to identify potential groundwater
resources and assess their quality in two 260-km2 areas in the Lower Rio Grande Valley,
Texas. In this drought-prone and rapidly growing region, heavy agricultural, municipal, and industrial
demand for fresh water overburdens limited surface water supplied by the Rio Grande. Primary
data for this study are two electromagnetic induction surveys flown using time-domain instruments
carried by fixed-wing aircraft. Supporting data used to help interpret the geophysical
data include ground-based geophysical measurements, water quality data from existing wells, geophysical
well logs, and geologic maps and cross sections showing the lateral and vertical distribution
of hydrologic and stratigraphic units in this coastal plain setting. We are analyzing these data
within a geographic information system to interpret late Cenozoic geologic environments, analyze
the relationship between water quality and ground conductivity, and display subsurface images
showing likely availability and suitability of ground water at various depths. If successful, state and
local agencies will use results from this study to guide development of supplemental ground-water
resources.
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Airborne Em As A 3-D Aquifer-Mapping Tool
Authors Jeff Wynn, Don Pool, Mark Bultman, Mark Gettings and Jean LemieuxThe San Pedro River in southeastern Arizona hosts a major migratory bird flyway, and
was declared a Riparian Conservation Area by Congress in 1988. Recharge of the adjacent Upper
San Pedro Valley aquifer was thought to come primarily from the Huachuca Mountains, but the
US Army Garrison of Fort Huachuca and neighboring city of Sierra Vista have been tapping this
aquifer for many decades, giving rise to claims that they jointly threatened the integrity of the
Riparian Conservation Area. For this reason, the US Army funded two airborne geophysical
surveys over the Upper San Pedro Valley, and these have provided us valuable information on the
aquifer and the complex basement structure underlying the modern San Pedro Valley.
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Visualisation Of Sub-Surface Condljctivlty Derived From Airborne Em
Authors Richard Lane and Gabriella PracilioThe quality of predicted subsurface conductivity from airborne electromagnetic (AEM) data has
improved by bringing together three elements: calibrated broadband ground response
information from new AEM hardware, a practical method of transforming the ground response
data into 1D conductivity models, and visualisation routines to display and communicate
significant model features in 3D. TEMPEST is the new AEM system. It is distinguished from
other AEM systems by its greater bandwidth (25-37500 Hz), monitoring of transmitter loop -
ground - receiver coil geometry variations and advanced processing routines to extract calibrated
ground response data. Conductivity depth images (CDI’s) were derived from TEMPEST data
using EMFlow software. The CDl’s were validated against ground data to illustrate the quality of
the predicted sub surface data. A groundwater case study was used to present a range of displays
developed to enhance the information content from AEM data, illustrating that much can be
learnt by viewing the 1 D models gridded as 3D volumes.
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Environmental Geophysics At The U.S. Epa
By Mark VendlThe U.S. Environmental Protection Agency (U.S. EPA) has been involved in promoting
the use of environmental geophysics since the early 1980’s. The application of geophysical
surveys for site characterization began with one of the first Super-fund sites in the country - Love
CanaI. At the same time, the Office of Research and Development published the book
“Geophysical Techniques for Sensing Buried Wastes and Waste Migration” by Richard Benson,
Robert Glaccum ,and Michael Noel which was one of the first publications on environmental
geophysics.
There are three groups in the U.S. EPA that are currently active in promoting geophysics:
1) Technology Innovation Office (TIO), Headquarters, Washington, D.C.; Environmental
Monitoring Systems Laboratory (EMSL), Office of Research and Development, Las Vegas,
Nevada; and 3) Field Services Section (FSS), Superfund Division, Region 5, Chicago, Illinois.
TIO has two major ongoing projects which concern geophysics. The first is the
publication of a series of case studies which use innovative geophysical methods for site
characterization, The second project is a joint field study between the U.S. EPA, U.S.
Geological Survey (USGS), and New York State Electricity and Gas Co. (NYSEG) in which
several geophysical methods are used to the characterize a manufactured gas plant site in the
State of New York.
EMSL has provided, for the past fifteen years, funding in the form of grants and
cooperative agreements to research institutions for basic research in the application of
geophysics to environmental problems. Recently, EMSL has been involved with research in the
use of geophysics for detecting Light Non-Aqueous Phase Liquids (LNAPLs).
FSS has been conducting geophysical surveys at Superfund sites since 1985. In support
of this field work, FSS has worked closely with The Ohio State University; the USGS Branch of
Geophysical Applications and Support; and the USGS Geologic Division in Denver to develop
new data acquisition and interpretation techniques particularly in the areas of ground-penetrating
radar (GPR) and borehole geophysics. Some of these techniques were recently applied to the
mapping of creosote at a site in Ohio using GPR.
In addition to field surveys, FSS has been conducting geophysics training courses for
Super-fund and the Oil Program first starting with the Superfund OSC/RPM Training Academy,
and currently with the four day Introduction to Environmental Geophysics course offered
several times a year through the Environmental Response Training Program. FSS is also
involved in the development of ASTM standard guides for both surface and borehole
geophysics.
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Characterization Of Dnapls At The Cape Canaveral Interagency Project
Authors Skip Chamberlain and Mary Cobb NeighborsNational Aeronautical Space Administration, Environmental Protection Agency and U.S.
Air Force, is sponsoring a project at Cape Canaveral, Florida to test subsurface
characterization and remediation technologies. Upon completion of the project we will
publish cost and performance data gleaned from these subsurface demonstrations. The
characterization program utilized various types of tools to define the area of
contamination and to determine the volume of contamination in the subsurface. Predemonstration
sampling, monitoring and analysis of soil and groundwater samples was
performed from June 1999 to August 1999, in three test plots located at Launch Complex
34 (LC34), Cape Canaveral, FL. Initial evaluations indicate the site contains 17,000 kg of
trichloroethylene (TCE) from the Apollo space program. Three remediation technologies
were selected to perform side by side demonstration in-situ oxidation, steam stripping
and Six-Phase HeatingrM (SPH). Vendors with geophysical tools are requesting to use the
Cape Canaveral site to test their characterization technologies and compare the results to
the intrusive techniques that were utilized. The tools are being tested for contaminant
location and to extend the understanding of DNAPL movement in the subsurface for
future federal and private sites.
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Performance Evaluations At The Moffett Field And Department Of Defense Permeable Barrier Sites
Authors Charles Reeter, Arun Gavaskar, Neeraj Gupta and Bruce SassA pilot scale permeable reactive barrier (PRB) demonstration project was initiated by the
US Navy Engineering Field Activity (EFA) West at the former Naval Air Station (NAS) Moffett
Field site in Mountain View, California in late 1995. Performance evaluations and cost-benefit
analyses were performed by US Naval Facilities Engineering Service Center (NFESC) at the
Moffett Field site, which were sponsored by the Department of Defense (DOD) Environmental
Security Technology Certification Program (ESTCP). The Moffett Field PRB uses a funnel-andgate
system design. The funnel is made of interlocking steel sheet piles and the gate consists of a
reactive cell filled with zero-valent granular iron. Performance monitoring was conducted at the
site to demonstrate the effectiveness of the PRB technology in capturing and remediating ground
water that contained dissolved chlorinated hydrocarbon compounds. The primary contaminants
of concern at Moffett Field in the vicinity of the PRB were trichloroethene (TCE), cis-1,2
dichloroethene (cDCE), and perchloroethene (PCE) at upgradient concentrations of about 2,900
micrograms per liter tug/L), 280 ug/L, and 26 ug/L, respectively. Monitoring events included
measuring water levels, testing field parameters, and ground-water quality sampling at about 75
monitoring points. Tracer tests using bromide solutions and flow-velocity meter testing were
also completed in April and August 1997. Iron cell coring samples were collected and analyzed
in December 1997 for early indications of chemical precipitation. The iron cell coring analyses
and geochemical modeling from Moffett Field indicated that changes in inorganic chemistry may
be caused by precipitation of calcium carbonates, iron-sulfide, and hydroxide compounds.
Chemical precipitates are of significant concern because of the potential loss of reactivity and
permeability in the iron cell. Long-term performance and life-expectancies of PRBs are generally
unknown. The DOD ESTCP, Environmental Protection Agency (EPA), and Department of
Energy (DOE) are sponsoring additional performance evaluations at several PRB sites to help
find answers to the longevity concerns. In the meantime, these agencies are also attempting to
help gain widespread regulatory acceptance and user confidence in implementing the PRB
technology.
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Seismic Applications For Detecting Preferential Pathways At Tinker Air Force Base, Oklahoma
By Sara SaylerTinker Air Force Base has been in operation since 1942, and serves as an international
repair depot for a variety of aircraft, weapons and engines. Past disposal practices of various
waste materials have caused contaminated soil and groundwater at many sites on the Base.
As part of the DNAPL plume delineation and remediation effort at Tinker Air Force
Base, various types of geophysical methods have been utilized. One that has proven successful
at Tinker is seismic. Two-dimensional seismic data has been acquired at three sites on Base.
Interpretation results are being used to help identify preferential pathways, such as subsurface
sand channels, low porosity zones and ‘holes’ located in the confining layer, that might
contribute to current plume configurations and locations. Once these pathways are identified,
their locations will be used to optimize future remediation systems.
The first 2D survey was successful in identifying subsurface sand channeling and will be
used to help locate future groundwater extraction wells for an existing pump and treat system.
At the second site, 2D seismic data is being used to identify pathways that are creating a plume
configuration which is oriented perpendicular to the groundwater flow direction. The third 2D
survey is being used to identify ‘holes’ in the confining layer, which are allowing contamination
to migrate vertically. In all cases, the seismic data, combined with monitor well data, is used to
identify ‘lows’ in the confining layer that might cause DNAPLs to pool.
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Uxocoe Master Plan For Quantitative Testing Of Uxo Sensor Technologies
Authors Richard Weaver and Denis Michael ReidyFairly comparing the detection and discrimination performance of sensors or systems is
always difficult. A useful comparison is nearly impossible in uncontrolled test situations.
The Unexploded Ordnance Center of Excellence (UXOCOE) proposes measuring
performance using a set of standard test locations, targets, and protocols that are
administered by an impartial entity. This paper briefly outlines a master plan to establish
standard test sites, protocols, and procedures for Unexploded Ordnance (UXO) sensors.
Since the 1990’s, significant investments by both the government and private industry
have produced an exciting array of promising developments in sensors for detection of
buried munitions, both ordnance and mines. Geophysical technologies such as ground
penetrating radar (GPR), magnetometry, electro-magnetic induction (EMI) and synthetic
aperture radar (SAR) are just a few examples that form the basis for many UXO detection
sensors under development. Within each of these technology categories of UXO sensors,
there are a number of different technical approaches being sold as the “best” way to
exploit the respective technology. In addition, sensor fusion concepts (i.e. using more
than one sensor technology) are being explored in an effort to bring the best of each
technology to bear in solving the UXO problem. The UXO industry (both military and
civilian) cannot reasonably equally support every technology and sensor type being
explored and promoted today. Rather, a tradeoff must occur in which only those
technologies that are the most superior (both technically and economically) will become
the de facto industry standards. Since it is unclear at this point which technologies and
sensors types are superior, deciding how to wisely invest scarce R&D funds in this
environment is complex.
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Geophysical Investigations For Environmental Risk Assessments
Authors Thomas J. Nicholson and Jacob PhilipGeophysical techniques and surveys are useful for realistic site characterization, site monitoring
strategies, and/or detection and mapping of contaminant plumes for verification of environmental
risk assessments for nuclear waste facilities. The NRC staff has evaluated the role and
applicability of geophysical techniques at three research field locations involving unsaturated,
heterogeneous soils and fractured rock. The techniques evaluated included: (1) electroresistive
tomography (ERT) to assess water flow through unsaturated, heterogeneous soils and fractured
rock, to identify fracture aperture sizes that contribute to water migration and rapid fluxes, and to
image three-dimensional resistivity within the zone bounded by the boreholes; (2) surface
electromagnetic induction (EM) to detect changes in the apparent electrical conductivities from
which water content changes can be inferred; and (3) multi-sensor capacitance probes (MCP) to
determine temporal and spatial resolution of infiltration, deep percolation, and ground-water
recharge in shallow heterogeneous soils. Specifics of the geophysical techniques and surveys
used at the three sites are discussed and evaluated in the context of environmental risk
assessments involving radionuclide transport.
Key words: downhole geophysical methods, electromagnetic induction, electroresistive
borehole tomography, environmental risk assessment, geophysical investigations,
multi-sensor capacitance probe.
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Some Geophysical Work In The U.S. Geological Survey
Authors David L. Campbell, Victor F. Labson and V.J.S. GrauchWe summarize some recent examples of geophysical work in the Geologic
Division of USGS: aeromagnetic surveys of the Albuquerque Basin, NM; near surface
explosion seismic profiles to trace earthquake-generated faults in the alluvium in Los
Angeles County, CA; and complementary magnetic and EM signatures on a survey line
in Colorado.
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Water-Resource Related Geophysical Activities Of The U.S. Geological Survey: Mission Of The Branch Of Geophysical Applications And Support
By F.P. HaeniThe Branch of Geophysical Applications and Support (BGAS), serves as the focus point
for the water-resource related geophysical activities of the U.S. Geological Survey (USGS). The
mission of BGAS is to support the USGS and cooperating Federal, State, and local agencies by
providing technology transfer and training for the application and use of existing and newly
developed geophysical methods. The BGAS also carries out independent and cooperative
applied research on the use of geophysical methods in solving water-resource problems.
Most technology transfer and training activities of the USGS are conducted in support of
other Federal agencies, including the U.S. Environmental Protection Agency, Departments of
Defense and Energy, and Federal Highway Administration. Examples of technology that BGAS
has recently brought to the USGS include optical televiewer, borehole radar, borehole
electromagnetic flowmeter, two-dimensional resistivity, and continuous seismic profiling.
BGAS training programs emphasize a ‘tool-box’ approach that integrates the use of multiple
complementary geophysical methods and stresses the beneficial role of forward modeling for
geophysical method selection and study design.
Recent research activities include the integrated use of geophysics to: (1) define fracture
flow in boreholes that are equipped with innovative collapsible liners and packer assemblies, (2)
monitor ground-water tracer tests and remediation activities, and (3) characterize and map
sediments in shallow-water environments.
BGAS maintains a Website (http://water.usgs.gov/og;w/bgas) to provide information
about the mission and operational program of BGAS and to serve as a training tool. The Website
contains lists of available geophysical equipment and copies of recent publications, details
current research interests, and provides links to other Websites related to geophysics.
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Geophysics And Arms Control At The Defense Threat Reduction Agency
Authors Anton M. Dainty and Karl VeithOne of the missions of the Defense Threat Reduction Agency (DTRA) is arms control treaty
monitoring in accordance with the U.S. Department of Defense requirements. An example is the
Comprehensive Nuclear Test Ban Treaty (CTBT), which mandates hydroacoustic, infrasonic
(low frequency sound), radionuclide, and seismic monitoring to ensure compliance. An
International Monitoring System (IMS) of over 300 sensors distributed worldwide is currently
under construction; DTRA is responsible for the 38 stations and one laboratory that the United
States will contribute to the IMS. An International Data Centre (IDC) in Vienna, Austria will
process the data from the IMS. The United States has agreed to provide the initial software for
the IDC through DTRA contracts. This involves a large effort in the automatic processing of the
continuous data stream from the IMS using sound geophysical principles.
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Darpa Counter Underground Facilities Program: Interests In Selected Geophysical Technologies
By Dan CressDARPA is investing in the science and technologies applicable to characterizing
underground facilities (UGFs). Examples of characterization information include
orientation and depth of structure, operational tempo, locations of umbilicals and systems
(power, water, airflow-vents), and changes in activity levels. Geophysical exploration
techniques are among the areas of interest to DARPA, including both passive and actively
induced signals capable of extracting any portion of the characterization information.
Example geophysical observables of interest include seismic, acoustic, and
electromagnetic data. These observables have been evaluated for a number of
geophysical applications in the past.
The DARPA investment in this area is directed at defining the performance limits
for singular observables and evaluation of the information gain achievable by exploiting
the correlation among these observables. A number of questions need to be answered.
What are the maximum performance ranges? How can correlation among sensors be
used to enhance signal to noise ? What are the accuracy limits for source location? How
many sensors are required to achieve a given performance level in particular classes of
environments and backgrounds? Can reliable information be obtained for estimating
source depth? What are the source options for active seismic or active electromagnetic
techniques? How does grounding effect the electromagnetic response for operational
facilities?
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Changing Role Of Geophysics- U.S. Bureau Of Reclamation
By Jerry WrightIn response to decisions on dam safety issues being directed to a risk based process
requiring probability hazard assessments, geophysical applications strive for quantifiable results,
estimates of detection limits and accuracy. Many geophysical methods are employed for
evaluation of existing structures as well as soil and rock foundations, corrosion protection for
pipelines, environmental and stream restoration, seismic monitoring and seismic hazard
assessment. Methods include seismic refraction, high resolution reflection, multiple surface
resistivity and self potential methods, ground penetrating radar, gravity/magnetics, borehole
geophysical logging, cross hole and down hole shear wave velocity measurements, and cross
hole and surface to surface seismic tomography. Seismic monitoring for site ground motion is
used to determine site response characteristics, early warning and emergency action systems, and
deep brine injection monitoring. Utilizing existing oil and gas exploration data aids seismic
source characterization in blind thrust fault evaluation. Research activities include cooperative
efforts with the Canadian Electric Association on Internal Diagnostics for Embankment Dams,
focusing on quantification of seismic, self potential, temperature, and resistivity methods. Other
research includes development of seismo-electric measurements for seepage path identification
and seismic tomography for imaging internal quality of concrete and embankment dams. Public
safety and economic decisions are being based on geophysical results requiring well planned
surveys, sound interpretations, and clear presentations, incorporating engineering and geologic
properties.
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Laboratory Velocity Measurements Used For Recovering Soil Distributions From Field Seismic Data
Authors Patricia A. Berge and Hugo Bertete-AguirreRecent advances in field methods make it possible to obtain high quality compressional (P) and
shear (S) velocity data for the shallow subsurface. Environmental and engineering problems
require new methods for interpreting the velocity data in terms of sub-surface soil distribution.
Recent advances in laboratory measurement techniques have provided high quality velocity data
for soils at low pressures that can be used to improve interpretation of field data. We show how
laboratory data can be used to infer lithology from field data. We use laboratory ultrasonic
velocity measurements from artificial soils made by combining various amounts of sand and peat
moss.
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The Use Of Continuous Surface Wave Method To Determine In-Situ Stiffness Profiles Within A Natural Terrain Setting In Hong Kong
Authors Lung S. Chan and Julie D. BellA continuous surface wave survey was conducted in conjunction with geotechnical investigation
in a characterisation study of a hillslope in Hong Kong. Rayleigh waves with frequencies that
modulated incrementally from 2 to 100 Hz were used to reconstruct in-situ stiffness profiles
along designated traverses. The phase velocity and the stiffness modulus were computed based
on phase angles recorded for the different frequencies by geophones. The stiffness profiles were
then used to delineate the interface between the overlying colluvium and the weathered bedrock
at the site. The colluvium generally has a relatively low but highly varying shear modulus while
the shear modulus of the underlying weathered bedrock increases linearly with depth, The
colluvium isopachs reconstructed based on the CSW results were consistent with results from
drillhole and trial pit records. Variations in the penetration range and the shape of the stiffness
profiles at different locations are probably caused by the varying boulder-matrix ratio in the
colluvium. The study shows that the CSW method can be an important supplementary method
for engineering geology ground investigation.
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Borehole Techniques To Subsurface Water Flow Characterization
More LessThe Department of Applied Geophysics, Charles University, Prague, has contributed to the
solution of hydrogeologic tasks since the 1960s. At present, research on well log analysis
techniques is focused on providing a basis for protection and optimization of withdrawals
from both surface and ground waters. Well-logging methods applied to hydrogeologic
formation evaluation provide information on the reservoir properties of the penetrated rocks,
groundwater quality and groundwater flow. This manuscript presents a discussion of some
geophysical techniques used for logging fluid-movement. In addition, application and
verification of the methods under various geologic and hydrogeologic conditions are provided
to demonstrate the effectiveness of logging for hydrogeological investigations.
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Constraining Hydrogeologic Models Using Geophysical Techniques: Case Study Fortymile Wash And Amargosa Desert, Southern Nevada
Authors David A. Farrell, Peter La Femina, Amit Armstrong, Stewart Sandberg and Noel RogersFortymile Wash and the Amargosa Desert are located along the groundwater flow path from
Yucca Mountain, Nevada, site of a proposed high-level nuclear waste repository. Groundwater
flow models developed for .these regions are poorly constrained due to limited spatial information
on hydraulic head, hydraulic conductivity, and hydrostratigraphy. To overcome some of these
limitations, an integrated geophysical survey utilizing the time-domain electromagnetic method,
the induced polarization method, the Schlumberger resistivity method, and the magnetic method,
was used to map the spatial continuity of the hydrostratigraphy and watertable elevation between
point measurement locations in the region. Simultaneous inversion of the data from these surveys
identified several discontinuities that showed good correlation to stratigraphic units and
waterlevels identified at point measurement locations. In addition, several areas were identified
where units either thickened, terminated, or shallowed. The information obtained from these
surveys is currently being used to better constrain groundwater models for the region.
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Geophysical And Hydrogeological Studies In A Coastal Plain Affected By Salt Water Intrusion
Gravity, electrical and reflection seismic surveys, along with classical hydrogeological
investigations, were carried out in a coastal plain affected by salt water intrusion, within
the framework of a project aimed at constructing a structural and hydrogeological model
of the area. Hydrogeological investigations provide data necessary for characterizing the
aquifers at a depth of a few tens meters and show the zone of high contamination.
Gravity surveying allowed the depth to the basement to be estimated and hence the
thickness of sediments and alluvium. Electrical and seismic reflection surveys proved
to be effective tools for recognizing deep aquifer characteristics and the complex
stratigraphic structure of the plain.
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Geophysical Signature Of Moisture Distributions In The Vadose Zone
Authors Paula Hahesy, Graham Heinson, Anthony L. Endres and John L. HutsonGeophysicists commonly have a simplistic view of the watertable as a sharp interface
between the vadose zone (i.e., unsaturated region) and the phreatic zone (i.e., saturated
region). In reality, this boundary is a transition zone where moisture content continuously
varies with depth. Since geophysical methods respond to the depth variation in water
content, the use of this simplistic model could lead to significant errors in the interpretation
of geophysical data. An improved model for the moisture content profile that incorporates
different soil structures and types would allow better interpretation of near-surface
geophysical surveys. In addition, this model would permit the extraction of important near
surface hydrological information from geophysical data.
In this study, a systematic analysis of the relationship between moisture content profile and
the response of commonly used near surface geophysical methods (i.e., resistivity sounding,
ground penetrating radar, electromagnetic induction and refraction seismics) has been
performed. Using a computational model that considers the water and chemical regime in the
vadose zone, the water content profiles for various soil types (synthetic and field) were
generated. The corresponding geophysical profiles were constructed using petrophysical
relationships for electrical conductivity, dielectric permittivity and acoustic velocity. The
resulting surface geophysical responses were computed for these geophysical profiles.
Inversion of this data attempted to recover input soil profiles.
The results of the theoretical work have been compared with geophysical data from the North
Adelaide Plains, South Australia. The geophysical surveys were conducted in regions of soil
corresponding to established profiles. This field data has been analysed, establishing
common characteristics between models and observed data and providing insight into
inadequacies in the prediction models and near surface geophysical theory.
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Integrated Geophysical Study Of Near-Surface Faults In The Wilcox Group, Texas, With Application To Lignite Mining
Authors Sara A. Satti, Mark E. Everett and Richard L. Gibsonthe form of lignite, a soft coal found close to the surface. Since Texas gas reserves could
become exhausted by 2040, lignite mining will continue to play a major role in meeting
state energy requirements. Lignite can be mined only in opencast operations which
represents a serious incursion into the landscape. To open up or expand a mine costs tens
of millions of dollars. It is therefore important both economically and environmentally to
investigate subsurface geological structures before expanding mine operations.
This paper describes the results of near-surface geophysical studies conducted at the
Calvert Lignite Mine near Bremond, Texas. The research involved the coordinated use
of several geophysical methods to map near-surface faults within the host Wilcox Group
sedimentary formation. Several geophysical tools were used: magnetics, frequency and
time domain electromagnetic induction, and ground penetrating radar. We discuss how
these methods contribute to near-surface characterization, especially qualitative, rapid
mapping of faults.
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Integrating Geophysical And Geological Methods To Delineate Buried Paleochannels In The New Madrid Seismic Zone Of Southeastern Missouri
Authors Issa El-Hussain, John Holbrook and Clayton SneedBuried Mississippi River (MR) paleochannels within the New Madrid seismic zone
(NMSZ) were delineated using topographic, geological, satellite imagery, and electrical
conductivity data. Initially the abandoned paleochannels were delineated by using
topographic maps and satellite imagery to find associated ridges and swales. Boreholes were
used to collect sediment data to determine facies relationships and confirm the paleochannel
positions. The electromagnetic (EM) method was used to constrain the channel boundary,
confirm borehole data, and confirm topographic estimates of MR paleochannels. The Geonics
Em-3 1 was used to collect EM data and the Sting Rl was used to collect resistivity data at lofoot
intervals along protiles to measure the electrical conductivity of clay plugs filling two
abandoned paleochannels within the NMSZ near Portageville, Missouri. Conductivity
readings along the profiles were relatively high while resistivity readings were low above the
clay filled channel plugs. The conductivity values rapidly decline to relatively low values
when exiting the channel boundary while resistivity show opposite effect as expected. These
sharp declines in conductivities and increase in resistivities are indicative of the edge of the
channel plugs where they meet the paleobank. The EM/resistivity data, when compared to
topographic maps of the study area, shows a similarity of terrain to conductivityiresistivity
values. The data indicates that the clay plugs end well before the natural levee topographical
peak. When compared to a modern stream, the edge of clay fill channel indeed ends well
before the natural levee topographical peak. Comparison of this data to borehole data shows
that the scenario for the natural levee’s and the paleochannel are reasonable and conclusive.
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Gpr Attribute Analysis
Authors Seth R. Lemke and Leonard C. MankowskiInstantaneous amplitude, instantaneous phase, and instantaneous frequency were calculated
from a GPR data set acquired on St. Croix, U.S. Virgin Islands. The data was cross plotted to
search for any anomalous data clusters. These clusters were separated to determine their cause
and determine the implications of the clustering. This is the first step in an attempt to analyze
GPR data in terms of instantaneous amplitude, instantaneous frequency, and instantaneous phase
in order to more accurately determine the electrical properties of the subsurface.
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Monitoring Infiltration Within The Vadose Zone Using Cross Borehole Ground Penetrating Radar
Authors David Alumbaugh, Lee Paprocki, James Brainard and Christopher RautmanCross-borehole ground-penetrating radar (XBGPR) imaging has been employed to
monitor changes in moisture content within the vadose zone during an infiltration
experiment at a test site in Socorro, New Mexico. XBGPR data are being collected
between five wells located along a 1 l-m profile. The wells span a 3-by-3-m infiltrometer
which is producing a constant flux of 2.5 cm of water per day. This flux rate yields
unsaturated flow conditions within the sediments at the site. The XBCPR data are first
converted to velocity images via a non-linear travel time inversion scheme, next to
apparent dielectric constant, and finally to images of moisture content using an empirical
relationship derived from laboratory time domain reflectometry (TDR) measurements
made on samples collected at the site. This empirical relationship was employed rather
than Topp’s equation due to the presence of magnetic minerals in the soils. The results
indicate that the XBGPR images map the progress of the infiltration as it occurs. In
addition, although some lateral smearing is apparent in the images, the XBGPR derived
moisture contents compare well with calibrated borehole neutron-log data. XBGPR data
acquisition and imaging will continue until the hydrologic system is verified to have
reached steady state.
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Controlled Imaging Of Fluid Flow And A Saline Tracer Using Time Lapse Gpr And Electrical Resistivity Tomography
Authors Roelof Versteeg, Ralf Birken, Stewart Sandberg and Lee SlaterA controlled imaging facility was used to setup and execute a number of lD, 2D and 3D
time lapse experiments in which geophysical and direct measurements were used to
image fluid flow and a saline tracer. The resulting data definitely proves that geophysical
data can map 4D fluid flow, however it is imperative to have extremely high spatial and
temporal sampling in order to be able to see the processes.
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Determlning And Mapplng Dnapl Saturation Values From Nonlnvasive Gpr Measurements
Authors Kristen W. Sneddon, Gary R. Olhoeft and Michael H. PowersWith the possible application to fluid-flow modeling, saturation values of dense nonaqueous phase liquids
(DNAPLs) may be determined and mapped through the use of measurements acquited by noninvasive ground
penetrating radar (GPR). In 1991, a controlled injection of perchloroethylene @CE), a common DNAPL, was
performed by the University of Waterloo into an isolated, water-saturated, sandy aquifer at Canadian Forces Base
Borden. One of the geophysical techniques employed by the U. S. Geological Survey to monitor the location and
migration of the subsequent plume was 5OOMHz surface GPR acquited on a one meter grid spacing across the
nine meter by nine meter cell over a period of 340 hours. This paper describes how full-waveform GPR modeling
of these data for relative dielectric permittivity versus depth may be used to calculate and map spatial distributions of
DNAPL saturation over time using recursive solutions of the Bmggeman-Hark-Sen (BHS) mixing formula.
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A Physical Model Experiment Of The Gpr Response Over Gasoline
Authors Changryol Kim, Jeffrey J. Daniels, Jennifer J. Holt and Erich D. GuyAn experiment was conducted at the Ohio State University using a sand and gravel-filled tank
model, to investigate the influence on the GPR response of vadose zone gasoline vapor phase effects
and residual gasoline distributed by a fluctuating water table. After background GPR measurements
were made with only water in the tank, gasoline was injected into the bottom of the model to simulate
a subsurface discharge from a leaking pipe or tank. GPR measurements were made on a 3-D grid on
the surface of the tank for an extended period of time after the injection to monitor changes in a
vadose zone with no residual gasoline. Water was then introduced beneath this gasoline and the
water table was raised and lowered in stages with GPR measurements made at each liquid level.
Results from this experiment show the sensitivity of GPR to moisture content and it’s
effectiveness for monitoring changes in the water table. After the injection of gasoline into the tank
and prior to water table fluctuations, a decrease in reflection amplitudes within the vadose zone
occurred as a function of time. One interpretation of these results is that increasing hydrocarbon
vapor pressure displaced redistributed interstitial moisture in the vadose zone, which led to this
observed change in the GPR response. Additionally, data show that the GPR response can be
enhanced when residual gasoline is present in a water saturated system due to less attenuation through
the medium.
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Detectability Of Crude Oil In The Subsurface Near Bemid Ji, Minnesota, Using Ground Penetrating Radar
More LessNear Bemidji, Minnesota, where crude oil contaminates a glacial aquifer, ground
penetrating radar (GPR) data were collected to determine whether the subsurface distribution of
the crude oil could be detected using a geophysical technique. The crude oil, which is very
resistive (greater than lo7 Ohm-m), is in the fine-grained layers of the vadose zone and is pooled
near the water table. Geochemical analysis shows that biodegradation of the crude oil has
increased total dissolved solids in the ground water. Near the oil pools, the ground water
conductivity is three times higher than the background values. This increase in conductivity
causes attenuation of the radar signal, which is seen in both the cross-well borehole data and in
the surface data. However, the interpretation of the radar data is complicated by the fact that
signal attenuation also occurs in the saturated zone in uncontaminated areas.
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Gpr Jet Fuel Spill Investigation
Authors Mario Carnevale and Jutta HagerHager Geoscience, Inc. used ground penetrating radar as part of an integrated study to
investigate a jet fuel spill at Logan International Airport in Boston, Massachusetts. The
survey was performed at night on airport taxiways and runways. The primary objective was
to characterize soil stratigraphy and delineate trenches for utility conduits, areas of
excavation, and the boundary between granular till and the underlying native material that
could act as migration pathways for contaminants. Also considered was the response of GPR
signals to varying levels of sediment contamination.
In addition to GPR, several types of data were integrated to characterize the subsurface
conditions, including borehole and probe data regarding soil stratigraphy, water table
elevations, and measured VOC concentrations. Cross sections were constructed and used to
integrate all available data and characterize the effect of confined and unconfined
groundwater regimes on contaminant migration.
The cross sections and maps showing a series of horizontal slices of the subsurface were used
to decipher the spatial distribution of jet fuel at various depth intervals. The study showed
that an integrated geological and geophysical subsurface evaluation program is an effective
tool in deciphering contamination at complex sites.
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Seismic Mapping Of Subsurface Cavities
Authors Roland Gritto and Ernest L. MajerThe present numerical study investigates the possibility to invert seismic data
for the location and volume of a cavity. The data is generated using an exact solution
for the scattering of elastic waves by a sphere, whereas the inversion is based on the
low frequency Mie approximation to the exact solution. We use a correlation analysis
between these solutions to solve the inverse problem in two steps. First, the location
of the cavity is determined, before the volume is estimated in a second step. The
robustness of the results is tested by adding correlated and uncorrelated noise. We
find this method to be robust as long as the source receiver coverage is good enough
to reduce the noise level. The locations of the cavities are well determined while the
estimates of the radii are more susceptible to noise and the deviation between
approximation and exact solution.
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Geophysical Surveys To Map The Vertical Extension Of A Sinkhole: A Comparison Study
Authors M.G. El-Behiry and S.M. HanafySinkholes are important near-surface indicators of active karst features at depth,
such as cavities and solutionally enlarged fractures. Geophysical surveys were made at
an engineered site in the lSth-May City, south of Cairo, Egypt, where excavations show
two openings (about 0.5 m2 each) in the limestone bedrock. Subsurface extension of the
two holes could not be revealed by visual inspection. This study compare between
different geophysical methods to map the vertical extension of a sinkhole as a means of
inferring the possible existence of this deeper hydraulically active karst feature.
The performed GPR profiles, with 200 & 500 MHz antennas, showed that the
two holes are a part of main sinkhole that extend l-2m deep, 6m length and about 4.5m
wide. Numerous subsurface voids and fractures could also be delineated with no
evidence of deep cavities.
Dipole-dipole resistivity survey was carried across the two holes using electrode
separation “a” of 5 and 1 Om. The 2D-inversion of resistivity profile with a=5m revealed
very high resistivity anomaly (20,000 Ohmm) at the location of the two holes and
extend to a depth of 6m. The inversion of the other profile (a=lOm) gave the vertical
extension of the same anomaly outlined above to a depth of 16m. This anomaly was
interpreted as due to highly fractured zone rather than cavity.
Seismic refraction data acquired at the location of the two holes show delayed
first breaks and wave attenuation. Low seismic velocity of 570 m/s was obtained for the
surface layer containing the two holes. A bedrock refractor (3800 m/s) was identified at
3m deep and considered as the base of the holes.
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Identifying Potential Collapse Zones Under Highways
Authors Paul J. Wolfe, Benjamin H. Richard, Ernest C. Hauser and James D. HicksSubsidence of abandoned coal mines is a problem in many places, e.g., the opening of a large hole in Interstate 70 in eastern Ohio. With the support of the Ohio DOT we are looking for geophysical methods to economically determine locations where potential coliapse may threaten highways. The goal is a reconnaissance survey method to identify areas that need detailed investigation. We have completed the first phase study at a site with collapsing coal mines. The techniques tested were:
1. P-wave refraction,
2. S-wave refraction,
3. Gravity,
4. 2D resistivity,
5. Ground penetrating radar (GPR),
6. Surface waves
a) spectral analysis (SASW)
b) profiling.
The data were acquired along a 480 ft (146 m) section of Ohio Route 32 in Jackson County. The data were interpreted and several test borings were made to verify the geophysical results. We found that P-wave refraction, 2D resistivity, and surface wave profiling provided the best correlation with the boring results. S-wave refraction was useful. Gravity and SASW did not have adequate horizontal resolution to be worthwhile additions to the interpretation. GPR signals were too attenuated by the clay-rich soil.
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Locating Subsurface Voids In Karst: A Comparison Of Multi-Electrode Earth Resistivity Testing And Gravity Testing
Authors M.J.S. Roth, J.E. Nyquist and B. GuzasIn this paper, the authors compare microgravity, multi-electrode resistivity, and boring data in
karst at a site in eastern Pennsylvania. The hypothesis being tested is that a comparison of
resistivity results and gravity results (both non-intrusive tests) can be used to provide information
concerning the location of voids at a site where the depth to bedrock is highly variable. The
authors conclude that while either resistivity or gravity can be used to predict bedrock depths,
fluctuations observed in the gravity data in areas without voids are of a similar magnitude to
those observed in areas with voids. Therefore, void locations cannot be reliably identified using
a combination of these two test methods.
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4-D Microgravity: A Method For Cave Detection And Monitoring
Authors M. Rybakov, V. Goldshmidt and L. Fleischer and Y. RotsteinSinkhole hazard is becoming an apparent problem in the Dead Sea area and a severe obstacle in future land use planning in the region. A feasibility study for the use of microgravity for cave
detection (3D) and monitoring the collapse development over time (4D) has been completed in the area. The microgravity was used with the assumption that it could detect subsurface cavities, regardless of their shape or filling material, as long as there is sufficient density contrast. 3-D modeling indicated that subsurface sinkholes could be detected at a depth of up to several times the diameter of the subsurface cavity. Detection was carried out microgravity mapping, using a 5x5-meter grid, with accurate geodetic control in real time. Accuracy is estimated to be in the range of 0.01 to 0.02 mGa1. The microgravity maps indicate the presence of large subsurface cavities underlying the areas where several open sinkholes are observed, suggesting that additional sinkhole development can be expected. Tracing the development of sinkholes, before their roof collapses and they become an apparent surface feature, was attempted by repeated measurements along a road, where such sinkholes were observed in the past. This 4D microgravity monitoring experiment lasted 4 months and revealed apparent changes in the gravity field in the order of 0.03 mGa1, which are thought to be associated with changes in the size of the cavity, probably as a result of roof collapse. The results suggest that microgravity can be an effective technique, not only for detecting and delineating subsurface cavities, but also in monitoring their development in time and prediction of collapse hazards.
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A Geophysical Investigation Of A Sugar Cane Plantation, St. Croix, U.S. Virgin Islands: Using Multiple Techniques To Assess A Complex Industrial Site
Authors Len Mankowski, Seth Lemke, Susan Martin, David Hayes, Pat Martin, Charles Young and Jimmy DiehlAn archaeological geophysical investigation was conducted at Estate Whim Plantation Museum
(Whim) February 25 to March 5, 1999. Whim is the only preserved and publicly open site
on St. Croix that offers a guided interpretation of lifeways and processes associated with the island’s
historical role in the sugar trade from the 1 sth to the early 20th centuries. During its operation
Whim was not only a plantation, but also housed a factory for on-site cane processing. The plantation
and factory were worked by slaves until 1848. While many features remain standing, the
original slave village and factory have been buried up to a depth of three meters.
Three geophysical techniques were used to assess potential excavation sites. These were:
Magnetics (Total field), DC resistivity (square array); and ground penetrating radar (GPR).
Ambient noise levels were high due to soil inhomogeneity. The industrial site also contained
a complex firebrick foundation with an extremely strong magnetic and resistivity signature which
masked more subtle structural features. Low amplitude boundary features were revealed by converting
measured resistances to transverse anisotropy plots. The magnetics data required more intensive
processing. Removal of an upward continued dataset served as a high pass filter. This was
reduced to the pole and converted to pseudogravity sections to perform a horizontal derivative.
The GPR survey was performed using 200 MHz antennas; lower than those typically used at archaeological
sites. Removal of the average trace from a line and band-pass filtering, indicated numerous
shallow diffraction events and discontinuous surfaces not apparent in the raw data.
The data from all three techniques were combined to produce maps to assess the site. Processing
did not appear to introduce significant artifacts. Interpretation of anomalies (e.g. foundations,
firebrick, etc.) proceeded with much greater confidence due to multiple technique results.
Several sites within the factory were chosen for excavation in August of 1999, based in-part on the
geophysical results. Compared to excavation results, transverse anisotropy and magnetics had
been reliable indicators of potential excavation sites. GPR’s service as an interpretive tool was
heightened after excavation.
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Development Of The Initial Physico-Archaeological Model Of The Nahal Zehora Site (Central Israel) Using Modern Magnetic Data Interpretation
Authors Lev Eppelbaum, Sonya Itkis and Avi GopherMagnetic survey provides a ground plan of cultural remains before archaeological
excavations. In special cases it may even be used instead of excavations for understanding
the cultural environment in order to avoid the site destruction. For the first time a detail
magnetic survey was conducted in Israel at sufficiently large (60 x 80 m) area. This area
borders south the known Prehistoric Nahal Zehora site partially excavated during the
many year’s archaeological investigations. The total magnetic field was observed with a
step between points of 0.5 m, distance between investigated profiles was 10 m and the
total number of the observed points was about 5,200. Magnetic susceptibility of soil
was measured on 180 samples. At the studied area has been recognized 12 anomalies
apparently reflecting three types of archaeological remains: (1) local high-intensive
anomalies due iron-containing (we do not exclude an agricultural origin of these objects)
or fired structures, (2) negative anomalies caused by the ancient constructions made
from a non-magnetic material (limestone), (3) positive anomalies due to accumulation
of the ancient human habitation (repeated heating of the soil as well as accumulation of
organic debris, etc.). In parallel with the conventional procedures (removing temporal
magnetic variations, gridding magnetic data and qualitative interpretation) here were
applied improved methods for inverse problem solution and 3-D modeling of magnetic
field. The developed initial physico-archaeological model of the site shows ranging studied
targets, their exact location and calculated depth of the upper edge (for the model of thin
bed) and position of the center of anomalous body (for the model of horizontal circular
cylinder).
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Combined Shallow Seismic And Hydrogeological Investigation Of The Ancient Hierakonpolis Site In Southern Egypt
Authors S.S. Alexander, S.M. Brown, R.R. Parizek and D.P. GoldThe ancient temple-town of Hierakonpolis, and its surrounding area near Edfu in southern Egypt
has been investigated using shallow seismic observations and hydrologic field measurements.
This temple-town, now buried in Nile silts beneath a shallow water table produced by
surrounding irrigation canals, was continuously inhabited from at least 3200 B.C. through
Roman times and is believed to hold many important artifacts in addition to those found at the
turn of this century. Any future excavations will require continuous dewatering to a depth of at
least 5 m. Typically 24- or 36-channel profiles or arrays were run using shotgun shell shallow
sources placed off the ends and in the middle of each spread. The high-quality data collected has
been used together with shallow boreholes to map the depth of the water table (l-4 m) beneath ’
the site and in adjacent areas; to locate localized anomalies believed to be associated with burred
man-made structures or objects: to discover a major reflecting boundary, interpreted to be an
ancient channel of the Nile River. at a depth of approximately 100 m; to discover a prominent
deeper reflector at a depth of approximately 180 m; and to discover a prominent shallow reflector
at a depth of approximately 30 m, the origin and significance of which is unknown. The
water-table depth distribution over the site has been determined at approximately 60 borehole
locations. Some of these boreholes. co-located with seismic profiles, provide calibration data for
continuous seismic determinations of water depth as well as soil moisture and soil composition
that are very helpful in the seismic interpretation. Borehole temperature and salinity
measurements help to characterize the groundwater flow regime induced by nearby irrigation
canals. Examples of the field observations and their interpretation will illustrate each of these
major findings.
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Nondestructive Geophysical Surveys For Delineating Buried Tombs And Identifying Their Environmental Status
More LessA number of ring roads and highways surrounding the highly populated city of
Cairo, Egypt are currently under construction. To the south of Cairo, part of these roads is
planned to cross a graveyard of unknown layout. Site observation indicates that a
significant part of this site is a constant drain for sewage and household water. Due to the
sacred nature of the site, non-destructive, geophysical tools (Electromagnetic, electric
resistivity, and Ground Penetrating Radar”GPR”) were decided upon for delineating buried
tombs and identifying their environmental status.
An exhaustive sequence of 2-D data processing techniques was applied to the EMdata
to minimize the disturbed electrical conductivity pattern imposed by the infiltrated
wastewater. Observed and buried graveyard boundaries were delineated on the high-pass
(0.15 cycle/m) filtered conductivity map. Buried tombs (2.5m x 2m) were detected as high
conductivity anomalies indicating that tombs may be filled with soil and/or infiltrated
wastewater. EM-method succeeded in delineating the area1 extent of the buried graves; the
GPR-technique complemented this information by determining their depth of burial. .
A dc-resistivity profile was performed at an abnormally high EM-anomaly, using
dipole-dipole array, to delineate the extent of infiltrated sewage water and its spreading
direction. An 2-D inverse resistivity model revealed a very low resistivity (0.24-0.91
Ohmm) anomaly, indicating its saline sewage water, spreading at the shallow part of the
resistivity section and possessing the highest thickness, about 2.0m, at the northeastern part
of the section close to the nearby housing utilities.
GPR survey lines, at 500 MHz central frequency, was conducted at two selected
EM-anomalies to essentially map the depth of the buried graves. The graves are located
within the depth range of l-1.8m. The observed radar wave attenuation suggested soil
contamination with saline wastewater.
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Significance Of Crossed-Dipole Antennas For High Noise Environments
Authors Stanley J. Radzevicius, Jefhey J. Daniels, Erich D. Guy and Mark A. VendCrossed-dipole antennas can be used to reduce clutter and improve the signal-tonoise
ratio of ground penetrating radar (GPR) surveys, depending upon field conditions
and the targets of interest. The crossed-dipole antenna consists of transmit and receive
antennas oriented orthogonal to each other, and is sensitive to field components oriented
parallel to the long axis of the receive antenna. These cross-polarized components can be
introduced by scattering from subsurface targets or may be composed of scattered crosspolarized
components present in the field incident on the target. The physical shape and
composition of targets will influence the polarization of the scattered field, and this
enables cross-pole and co-pole antenna configurations to discriminate between different
classes of targets for clutter removal. The crossed-dipole antenna configuration also
improves isolation of the receive antenna from the direct arrival of the transmit antenna.
The improved isolation and ability to discriminate between different targets can therefore
result in an improved signal-to-noise ratio.
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Consideration Of Automatic Waveform Interpretation Of Gpr Data To Detect Void Space Beneath A Concrete Highway
More LessFor waveform interpretation of ground penetrating radar (GPR) data, one must compute
the response of the earth to a specific source wavelet. This is not commonly done, because it
requires either prior knowledge of the source wavelet shape, or a good understanding of the local
earth model. When waveform interpretation is possible, then certain steps in the interpretation
process can be automated. This paper describes a successful case history of GPR waveform
interpretation used to solve a problem of locating voids under a concrete highway. It worked in
this case because the earth model was well constrained according to design specifications and
core information. Automatic interpretation is really just the creation and use of a computer
algorithm to recognize specific features in the data. The human interpreter must still do the work
of determining what the diagnostic features are, and then do a good job of writing the program to
recognize them. This process is only cost-effective for large surveys or those where the
distinguishing data features are already known.
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3-D Imaging Of Subsurface Features Using Gpr Array Beam Imaging
Authors Jeffrey L. Orrey, Phil C. Sirles and Charles B. ArchambeauIn this paper, we provide a brief review of standard survey and analysis methods for ground
penetrating radar (GPR) and then introduce a new method for producing three-dimensional (3-D)
images of the subsurface using GPR. We outline the theory of the new imaging method, called
Array Beam Imaging ( ABI ), by way of a schematic description. We then show results from
application of the ABI imaging method to the characterization of a former manufactured gas
plant (MGP) site. The 3-D image results are examined using 3-D isosurfaces, 3-D and 2-D
volumetric projections, and 2-D tomographic slices. These techniques improve the interpretation
of the otherwise standard GPR survey of the relatively complex characteristics of the gas holder
and coal tar at the site. Finally, we discuss the relative advantages of the ABI method over
traditional methods and summarize some potential future applications of the method.
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