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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 - 100 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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Polarization And Kinematic Effects In Azimuthal Investigations Of Linear Structures With Ground-Penetrating Radar
Authors M. Pipan, L. Baradello, E. Forte and A. PrizzonAzimuthal variations of the GPR response may be diagnostic of elongated subsurface targets.
We performed tests on two classes of targets of interest in archaeological and engineering
applications: walls (archaeological remains) and underground utilities (plastic and
metallic pipes). The objective of the study is the implementation and test of a procedure
for the identification of elongated subsurface targets by means of GPR which may
provide information on the properties of the materials and may be an effective alternative
at sites where logistic constraints prevent from the acquisition of conventional grids. We
analyzed the response of targets buried at different depths in soils ranging from clays to
coarse sands, to compare the performance of azimuthal Multi-Fold and conventional GPR
techniques. A 3-D azimuthal Multi-Fold (MF) G round Penetrating Radar (GPR) data acquisition
and processing scheme was implemented and tested. Bi-static co-polarized and
cross-polarized 200 MHz and 400 MHz antennas were rotated around a Common Mid Point
in steps of 10’ and 30”. We obtained an average 6000% fold at each azimuth by varying the
source-receiver offset in steps of 10 cm. The amplitude of the radar response and the radar
velocities measured by means of Common Mid Point analysis exhibit sinusoidal variations.
The range of amplitude and velocity can be effectively used to discriminate among targets
of different characteristics. The location of maxima and minima in the (a) amplitude and
(b) amplitude-velocity responses can be used to evaluate the strike of the subsurface targets
in case of small and large radar cross-section respectively.
KEYWORDS
Ground Penetrating Radar - Multi-azimuth - Multi-fold - Velocity analysis - Amplitude analysis
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Detection Of Buried Steel Drums From Magnetic Anomaly Data Using Neural Networks
Authors Ahmed Salem, Keisuke Ushijima, Dhananjay Ravat and Ross JohnsonMagnetic detection to locate buried ferro-metallic objects has become one of the
standard methods in environmental investigation. However, geophysical measurements need
to be interpreted and this can be time consuming. As a result, shallow sources are usually
investigated by heavy machinery without the knowledge of their depth. This practice may
risk contamination by damaging the containers with hazardous materials. Therefore, there is a
need for an interpretation technique that could make rapid decisions in the field in real-time.
Conventional inversion methods cannot meet this need because they depend on initial models
that are nearly correct. In this paper, we have investigated the ability of neural network
processing method to estimate the location of steel drums. Back propagation neural network
was trained to estimate the spatial location of steel drums using theoretical magnetic
signatures of equivalent dipole source. The performance of the neural network was tested
using theoretical and field data. The neural network could estimate the location of drums
from theoretical data with maximum error 0.03 m for depth and 0.24 m for horizontal
location. The neural network also showed a potential to estimate the depths in the presence of
noise. The accuracy of the estimated depth from real magnetic data is greater than 80% when
regional can be adequately removed beforehand. The neural network system has proven to be
fast, accurate, and objective for detection of steel drums.
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Magnetic And Gpr Surveys Of A Former Munitions Foundry Site At The Denver Federal Center
Authors David L. Campbell, Shay Beanland, Jeffrey E. Lucius and Michael H. PowersWe made magnetometer and ground penetrating radar (GPR) surveys over part of
the foundation of a World War II-era foundry located on the Denver Federal Center. The
site-contains a number of highly magnetic source bodies, concrete foundation walls, and
underground openings, buried under a clay cap. The cap is several feet thick and has a
conductivity of about 35 mS/m, making the features underneath it a poor target for
conventional GPR. Indeed, the raw data look unlike typical GPR data, but rather show
reverberation (?) bands under sidewalks and other shallow buried sources. Using a
newly-written computer package, we made plan maps of the GPR response at different
time slices. The sliced GPR data did not outline buried foundry foundations, as we had
hoped it might. The resulting plan maps of the sliced data show sidewalks and other
blobby features, some of which correspond to magnetometer highs.
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A Vetem Survey Of A Former Munitions Foundry Site At The Denver Federal Center
Authors David L. Wright, David V. Smith and Jared D. AbrahamThe present Denver Federal Center in Lakewood, Colorado, was a center for production of small
arms and artillery ammunition during World War II and was then known as the Denver
Ordnance Plant. When munitions manufacturing ended, some of the buildings were converted to
other uses and some were removed, A massive building, thought to be a foundry, just east of
Building 20 at the Denver Federal Center, was removed just before the end of the war.
Remaining subsurface parts of the building are buried under a clayey loam soil. High-resolution
images we recently made using data recorded by the very early time electromagnetic (VETEM)
system clearly show some buried parts of the building or objects that were in the building. Many
of the subsurface structures produced exceptionally strong signatures that we think were caused
by large, relatively shallow buried electrically conductive objects. We find, however, that the
correlation between the VETEM images and magnetic data is not high, suggesting that some of
the highly conducting objects may not have metal in them. The former foundry site affords an
excellent opportunity to evaluate the performance of the VETEM system and other geophysical
instruments because of the location and conditions.
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Advances In Very Early Time Electromagnetic (Vetem) System Data Analysis And Image Processing
Authors David vonG. Smith, David L. Wright and Jared D. AbrahamThe Very Early Time Electromagnetic (VETEM) system operates in a frequency band
between electromagnetic (EM) conductivity systems and ground penetrating radar (GPR).
VETEM survey data exhibit higher resolution than EM methods and better detection
depth than GPR. A single computer application performs data analysis and image
processing, yielding detailed images of transient response over the survey area, with the
ability to discriminate between metallic and nonmetallic buried objects using a method
based on the persistence of the received signal. Processing steps of field data from the
Idaho National Engineering and Environmental Laboratory (INEEL) are presented, and
data processing methods are discussed.
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Optimized Model Resolution Using Low Pass Filters In Tdem Soundings
Authors E. Auken, K.I. Sørensen, P. Thomsen and F. EffersøIn the time domain electromagnetic (TDEM) method it has been common practice to model the
current waveform of the transmitted signal, but the effect of the instrument transfer function has
been neglected. In Effersar et al. (1999) it was shown that inverting TDEM data without taking
into account the system transfer function in the forward modeling scheme lead to an erroneous
description of the shallow part on the geophysical/geological model. The degree of error is very
dependent of the near-surface resistivity of the model. High resistivity models leads to distinct
but localized errors at very early time gates, whereas the effect from models with low to
intermediate resistivities is “smeared” out over a larger time interval.
The system transfer function can be described as a combination of one or several low-pass (LP)
filters in the TDEM receiver. In this abstract we describe some side effects of having a bandlimited
receiver. It turns out that it is possible to actually enhance the model resolution to some
degree by band-limiting the receiver. This means that not only do the low-pass filters in the
receiver system suppress coherent noise from power lines etc., but they also enhance the model
resolution if the filters are of optimal designed.
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Tdem In Groundwater Mapping - A Continuous Approach
Authors K.I. Sørensen, E. Auken and P. ThomsenCulturally developed areas provide a challenge when applying the transient electromagnetic
(TDEM) method, for mapping valley aquifers in inhomogeneous glacial geologies.
Magnetic coupling between the transmitter coil and cultural conductors such as power lines,
metal fences, metal pipes, etc. distort the measurements of the earth responses and generate
datasets that in many cases will yield erroneous interpretations. Furthermore, as TDEM
soundings are routinely interpreted with one-dimensional (1 -D) inversion schemes (Christensen
and Sorensen, 1995), perturbations in data originating from two- and three-dimensional (2-D, 3-
D) geological structures have to be revealed in order to ensure reliable 1-D interpretations
(Auken, 1995).
In Denmark it has become a common practice to perform 16 - 25 soundings/km2. In many cases
this number provides basis for estimating the data and interpretation quality. However, much
denser data coverage is generally required to discover distorted data and to resolve the multidimensional
geology of the valley aquifers. Due to the expense involved in acquiring dense
datasets, coverage is unfortunately seldom attained.
In order to meet the demands of dense spatial sampling a new method, the Pulled Array
Transient Electromagnetic Method (PATEM) has been developed. With the PATEM method a
transmitter and a receiver coil system is towed along profile lines while measuring. Obviously
this technique generates dense data sets and reduces the cost of the fieldwork drastically.
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Variable Frequency Monopole-Dipole Sonic Logging For Mechanical And Hydrogeologic Properties
Authors Charles P. Oden and James J. LoCocoMost traditional sonic logging tools operate at a single frequency. Usually this frequency
is a relatively high frequency, which in turn excites many unwanted modes that can make
waveform interpretation difficult (Paillet and Cheng, 1991). If the survey frequency is too low,
fixed frequency tools may not excite the desired modes in fast rocks or small boreholes. A
variable frequency sonic tool can minimize these problems.
Low frequency tools can provide waveforms from which it is easy to pick shear wave
arrivals in real time. By selecting a proper survey frequency, compressional head wave
amplitude can be reduced, and the first high amplitude head wave is the shear wave. Low
frequency dipole logging can be used to find shear velocities for soft formations (Chen, 1988).
Mechanical properties are readily calculated from compressional and shear velocities.
Many authors relate Stoneley wave amplitude (or Stoneley index) to permeability (Tang,
et al., 1996). Stoneley waves are easily interpreted from low frequency surveys when the
amplitude of other modes are reduced. Stoneley index can be directly generated while logging
from this type of survey.
A prototype variable frequency tool was tested in soft shale, mudstone, and concrete
boreholes. By varying the source frequencies, the modal content of the received waveforms was
controlled. The tool can be configured so that the first high amplitude arrival is a shear wave or a
Stoneley wave. We conclude that a variable tool exhibits greater versatility than conventional
tools by being able to provide good shear wave and Stoneley wave data in real time.
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Physical Modeling Of A Prototype Slim-Hole Time-Domain Dielectric Logging Tool
More LessDielectric logging tools were originally developed by the oil industry to determine oil saturation in highly
resistive environments. Conventional resistivity and induction tools are insensitive to the oil/water interface within
fresh water formations. Recently dielectric logging tools have found potential uses in environmental applications to
estimate porosity, to distinguish between water and organic-solvents, estimate water content, and to provide velocity
information for surface radar and boundary constraints for radar tomography. A prototype slim-hole time-domain
dielectric logging tool was developed at the U.S. Geological Survey. This tool was designed to utilize a broadband
EM-pulse to determine the frequency dependent dielectric properties of the surrounding geologic medium. In an
attempt to understand and characterize the tool, physical modeling experiments were conducted using a 100 gallon
polyethylene barrel filled with dry silica sand, deionized water saturated silica sand, and deionized water.
Examination of the results indicated that the borehole has a strong influence on the dielectric logging tool.
We have found that the travel time and amplitude are not monotonic with dielectric properties. The likely
explanation of the observed effect is that wave guides are being set up within the borehole and/or the tool.
Reflections and resonances internal and external to the tool produce a frequency-dependent tool response. Favorable
results from the physical modeling and field tests indicate that the tool is highly sensitive to changes in the dielectric
permittivity of the surrounding geologic media, particularly to thin layers perpendicular to the borehole.
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Incorporating Size Scaling As A Modelling Parameter For Estimating The Dielectric And Electrical Properties Of Porous Rocks And Soils
More LessThe solid components and pore spaces in rocks and soils have a spectrum of size scales,
ranging from clay platelets and intergranular cracks to vugs and boulder size grains. While the
size scale of structural features has been recognized as a factor in determining the physical
properties of porous media, it is rarely an explicit modelling parameter.
The differential effective medium approximation (DEMA) is used to estimate the dielectric
and electrical properties of porous rocks and soils. This approximation employs a sequential
embedding process that implies a progressive size scale increase as it proceeds. This feature of
DEMA is used to explicitly incorporate size scale relationships that occur in porous rocks and
soils into estimates of their dielectric and electrical response. The effects of size scaling are
investigated using a model where the pore space is divided into microscopic porosity (e.g.,
intergranular cracks), mesoscopic porosity (e.g., main pore volumes) and macroscopic porosity
(e.g., vugs and fractures). Modelling results demonstrate that the dielectric and electrical
properties of porous rocks and soils are very sensitive to the range of porosity size scales present.
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Dielectric Permittivity Of Clay-Water Mixture: Frequency Dependency And Volumetric Mixing Model
By Birsen CananThe dielectric permittivities of Na- and Ca- montmorillonite-water mixtures were
measured with respect to frequency (0.03-300 MHz), and two different inorganic salts (NaCl,
and CaC12). For the volumetric mixing model of the clay-water mixtures, the model suggested by
Schwarz (1962) was investigated and with slight modification, this model was applied to
calculate dielectric permittiviy of clay-water mixture.
It is seen from the measured dielectric permittivity values and frequency spectra analysis
that polarization of ions in the electrical double layer plays an important role in the high values
of dielectric pemittivities of clay-water mixtures even at higher frequencies. A comparison of the
frequency response signature of these materials suggest the possibility of material identification
based on measurements made over a wide frequency bandwidth.
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A Physiochemical Interpretation Of The Cole-Cole Dielectric Model
Authors David Lesmes, John Sturrock and Kevin FryeThe Cole-Cole dielectric model has been extensively used to fit the observed broadband
electrical properties of water-saturated rocks and soils as well as many other types of ionically
conducting solids (e.g. colloid suspensions, porous glasses, and biological tissues). The Cole-
Cole model was empirically derived and consists of three fitting parameters: the dielectric
increment (AZ), a major relaxation time (TO>, and a dispersion parameter (a). In addition to these
three parameters it is common to include frequency independent terms for the low-frequency
conductivity (oslatic) and the high-frequency permittivity (cm> of the sample. Although the Cole-
Cole model has been extensively used for the interpretation of both low-frequency spectral
induced-polarization data and high frequency dielectric data, the significance of the model
parameters is still not well understood. In this paper we present a physicochemical interpretation
of the Cole-Cole dielectric model. It is shown that the Cole-Cole parameters r and a can be
related to the mean and variance of the grain size distribution and & is a weighted product of the
specific surface area and the surface charge density.
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Crosswell Seismic Reflection Imaging Of A Shallow Cobble-Andsand Aquifer: An Example From The Boise Hydrogeophysical Research Site
Authors Lee M. Liberty, William P. Clement and Michael D. KnollCrosswell seismic data contain first-arrival information for velocity inversion and reflections
for seismic stratigraphic analysis. Seismic velocity information is useful for directly comparing
to, and inverting for, physical properties such as porosity. Reflections within the data are
often under utilized, but can help map the subsurface structural architecture that often define
hydrostratigraphic bounding surfaces between sedimentary units. We have acquired numerous
crosswell data sets from the Boise Hydrogeophysical Research Site (BHRS), a shallow (less than
20 m depth) cobble-and-sand unconfined aquifer. Preliminary crosswell seismic reflection results
show meter-scale structure that can help constrain our velocity model and define seismic boundaries
that first arrival tomograms cannot provide. Both crosswell reflection and velocity information
can help constrain hydrostratigraphic parameters that may be used to model groundwater
flow.
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Tomographic Inversion Of Crosshole Radar Data: Confidence In Results
Authors William P. Clement and Michael D. KnollCrosshole radar tomography is increasingly being used to characterize the shallow subsurface
and to monitor hydrologic processes. Although tomographic inversion provides a subsurface
model, confidently interpreting the resulting image can be challenging. We conducted a simple
modeling study to better understand the capabilities and limitations of tomographic inversion. We
start with a known earth model, simulate a tomography experiment, and invert the synthetic data.
We investigate the effects of straight and curved ray approximations to wave propagation, regularization,
grid size, and starting model. We also investigate the effects of limited ray coverage
through the earth model and noise in the data. Understanding the effects of these different methods
and parameterizations will help us place confidence limits on modeled features to more accurately
reflect our knowledge of the subsurface.
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Borehole Geophysics As An Aid To Kimberlite Exploration In The Canadian Prairie Region
Authors Paul Bauman, Richard Kellett, Russ Pagulayan and Andrew HinnellThis paper examines various suites of logs from a number of kimberlite fields in the Western
Canadian Sedimentary Basin. It is observed that while the physical properties of kimberlite may
vary widely, even within a single borehole or pipe, borehole geophysical logs do effectively
distinguish kimberlite from the host rock. Ranges of physical properties, including magnetic
susceptibility and formation resistivity, can be identified and used in forward magnetic and
geoelectrical modeling. Airborne data can thus be modeled with greater confidence, while the
effectiveness of various ground based techniques can be predicted in advance of field programs.
In addition, logging programs have been useful in identifying kimberlitic material that may have
been bypassed in the drilling progam, in locating offhole bodies, and in sterilizing prospects
identified from incorrectly modeled surface magnetic data.
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Borehole Geophysical Characterization Of Hydraulic Stimulation Of Fractured Bedrock Aquifers
Authors Frederick L. Paillet and Harry HanscombChanges induced by typical hydraulic stimulation procedures were monitored in two
adjacent boreholes at a site in northeastern Maine by comparing geophysical well logs run before
and alter stimulation. Caliper and acoustic televiewer logs run before stimulation indicated a
few faint, impermeable-looking horizontal and vertical fractures, but inflow before treatment was
too weak to detect with a heat-pulse flowmeter. Caliper and televiewer logs run after stimulation
showed no significant differences compared to the pre-stimulation logs. Flow logs run after
stimulation demonstrate that inflow in both boreholes is associated with a faint horizontal
fracture on the televiewer logs near 60 m in depth, which appears no different from several other
similar fractures. A cross-borehole flow experiment confirms that the stimulated zone is a single
horizontal fracture connecting the two boreholes. These results demonstrate that the hydraulic
stimulation produced at least a IO-fold increase in well capacity from less than 0.5 to more than
5.0 liters per minute. The results also agree with previous studies where fractures affected by
stimulation: 1) were present before treatment; 2) showed no obvious changes in the immediate
vicinity of the borehole after stimulation; and 3) experienced a 10 to 20 fold increase in
permeability attributed to the treatment.
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Ground Penetrating Radar Survey Of Interstate 70 Across Missouri
Authors Steve Cardimona, Brent Willeford, Doyle Webb, Todd Lippincott, John Wenzlick and Neil AndersonThis study summarizes a ground penetrating radar survey along Interstate 70 across the state of
Missouri. Goals of this survey were threefold: 1) determine asphalt and concrete layer thickness
every tenth mile; 2) update history information related to types of pavements that make up 170
across Missouri; and 3) note regions where the radar signal appears anomalous. Goals (1) and (2)
are related and were the primary goals. Goal (3) required visually interpreting the full data set and
was done as a guide for further investigation. The result is an extensive data set allowing the user
to visualize the east and westbound pavement profiles in comparison to design history information,
view a table of surface types and anomalous regions associated with those profiles, and crossreference
this information with the radar-interpreted layer data at 0.1 mile marks in spreadsheet
form.
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Geophysical Site Characterization In Support Of Highway Expansion Project
Authors Todd Lippincott, Steve Cardimona, Neil Anderson, Shane Hickman and Tim NewtonWe performed an integrated survey using ground penetrating radar (GPR), shallow highresolution
reflection seismic and dipole-dipole electrical resistivity methods in order to
characterize a site slated for roadway development. The intent of this project was to investigate
the subsurface and determine the structure of the dolomite bedrock along a proposed expansion
area for Highway 63, near Cabool, Missouri. We acquired a total of 68 GPR profiles to cover the
area of highest interest, including a sinkhole visible at the time of the survey. Five highresolution
seismic reflection profiles and four multi-channel resistivity lines were positioned
along key GPR survey lines. The soil to weathered bedrock interface appears as high amplitude
disturbed reflections and diffractions on the GPR profiles. The seismic images contain
anomalous sections of bedrock represented by diffractions and missing or offset reflections.
Pseudo-section resistivity data indicates highly resistive regions within the subsurface that
correlate with areas of concern on both the seismic and GPR data. We ranked areas based on
whether one, two, or all three of the methods indicated anomalies. The correlation of anomalous
areas across data from all three geophysical methods provides the spatial information necessary
for further geotechnical investigation prior to construction.
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Application Of Multifocusing Seismic Processing To Gpr Data Analysis
Authors A. Berkovitch, L. Eppelbaum and U. BassonA multifocusing seismic processing (MFSP) is based on the homeomorphic imaging
theory and consists of stacking seismic data with arbitrary source-receiver distribution
according to a new local moveout correction. Three-parameter travel time representation
allows to obtain a precise approximation not only for the CMP travel time curves, but
also for the full multi-coverage travel time surfaces. In MFSP observed data are stacked
along a full travel time surface whereas in the CMP are used only hyperbolas. MFSP does
not require any knowledge of the subsurface model and produces an accurate zero offset
section, even in the cases of complicated geological structure and low relation
signal/noise. The optimal sets of parameters obtaining in MFSP (emergence angle of
normal rays and two fundamental solutions of differential equations of wavefront) play
an important role in the analysis of wavefield distribution. These parameters can be used
as initial ones for inverse problem solution and construction of velocity model. MFSP
with some modification may be applied for the ground penetrating radar data processing.
We illustrate application of MFSP technique to GPR profile aimed to map stratigraphy at
quarry “Nesher” in the Central Israel. The obtained results show that the presented
method may be effectively used together with conventional procedures.
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The Signal Of Gpr At A Hydrocarbon Contaminated Site
Authors Jamile Dehaini, Wagner Franca Aquino and Jose Milton Benetti MendesThis paper presents part of a case study of contamination by a leak in a of gasoline tank,
carried out at a gas station, in the city of Sso Paulo, Brazil. The GPR method was applied to
evaluate the quantitative behavior of the signal (velocity, spectral and amplitude analysis,
and instantaneous attributes) related to contamination. This analysis intends to establish a
more objective tool for the interpretation of contaminated areas compared with that
available in the literature. Thus, its application could be extended to provide a more reliable
diagnosis of the contaminant plume in subsurface. The field survey was performed in two
phases: before and after pumping the total free phase of the contaminant both comprised of
reflection profiling and CMP’s.
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Sub-Bottom Gpr For Mapping Lithology And Structure Of Lake Michigan Glacial Drift Deposits, Offshore Manistee, Mi
Authors Matthew VanderEide and William A. SauckThe WMU underwater GPR antenna has been applied to problems in mapping
structures and lithologies of glacially deposited sediments and younger fluvial and
lacustrine sediments in the near offshore of a part of the east-central shoreline of Lake
Michigan. Nearly 19 km of ground-penetrating radar lines have been profiled along the
reach beginning at Manistee and extending northward 7.5 km. The boat-towed bottom
sled contained a dipole antenna transmitting at about 145 MHz. Concurrent SONAR
tracks were recorded, and navigation was by differential GPS. The Lake Michigan basin
has had a complicated Pleistocene history. The rising water from a low stage 10,000
years BP have planed off and inundated a great variety of subaerial and fluvial features,
as well as deposits left by earlier glacial cycles. A large dune field was found, and using
orthogonal transects we were able to determine the strike of the slip faces, and hence the
paleo wind direction (NW to SE). Cobble and boulder tills could be recognized by the
poor radar penetration and frequent hyperbolae from individual boulders. Filled fluvial
channel-forms were found near Manistee. A sequence of at least eight layers of gently
shoreward-dipping sand beds was found. These thicken towards shore and are truncated
at the lake bottom in the offshore, updip direction, and remain an enigma. There are a
number of advantages of doing the GPR under the lake rather than onshore. At the lake
bottom, coupling is constant, topography is very smooth and predictable, and access is
unlimited. The 20 km surveyed for this project required only two (long) field days.
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Earthquake Occurrence Disclosure In Historical Environmental Site Assessments Performed In New England
More LessThe New England Seismic Network (NESN) operated by Boston College and MIT with funding
from the United State Geological Survey (USGS) has documented approximately 1000
earthquakes in the six New England states of Connecticut, Massachusetts, Rhode Island, New
Hampshire, Vermont, and Maine between late 1600’s to the 1990’s. Compared to other regions
of the United States, the apparent large number and frequency of reported earthquakes in New
England are low.
Disclosure of the potential for an earthquake to occur in New England is frequently absent in a
Historical Environmental Site Assessment (HESA) for commercial/industrial properties. Likely
reasons for this omission are the low frequency of occurrence and magnitude of earthquakes and
the public’s perspective of “there are no earthquakes in New England”. Examination of
earthquake occurrence data reported on the NESN website for the years between the late 1600’s
to 1990’s relative to the frequency and intensity of reported earthquake occurrence is evaluated
from an environmental consultant’s perspective. This information is readily accessible and
should be incorporated into HESA reports as useful information to a client even after completing
a New England HESA.
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The Electrical Resistivity - Acoustic Velocity Relationship: A Method For Constraining Porosity
Authors Wendy Wempe and Gary MavkoWe present a method for bounding the relationship between formation resistivity factor and
compressional velocity, which not only constrains possible data pairs, but also constrains
porosity. The technique involves simply combining the well-known Hashin-Shtrikman bounds
for electrical conductivity and acoustic velocity. The significance of this procedure is in it’s
potential for using relationships between formation factor and material properties in sediments
and rocks to explain velocity trends and vice versa.
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Downhole Seismic Logging Techniques In A Regional Hydrogeology Study, Oak Ridges Moraine, Southern Ontario
Authors S.E. Pullan, J.A. Hunter, A. Pugin, R.A. Burns and M.J. HintonDownhole seismic logging surveys have been carried out in plastic-cased, continuously-logged
boreholes drilled in the Oak Ridges Moraine (ORM) area in support of a regional hydrogeology study.
Compressional-wave logs were obtained using a multi-channel hydrophone array with 0.5 m detector
spacings and a surface in-hole shotgun source. These data provide detailed and accurate velocity
profiles down the hole. In this area, high velocities (>2500 m/s) are associated with the Newmarket Till,
a regionally significant aquitard. These velocities are significantly higher than those associated with
adjacent stratigraphic units, and more clearly delineate the Newmarket Till than other borehole logs
(natural gamma, conductivity or magnetic susceptibility). These data show that the Newmarket Till is
a thick (10’s of metres) unit that can be traced regionally beneath the Oak Ridges Moraine. The
downhole seismic data also provide a direct correlation between reflection events and depths which
improves the calibration and interpretation of surface seismic reflection data. Shear-wave logs have
been obtained in one ORM borehole using a compass-oriented, S-component, well-locked geophone.
In this borehole, preliminary correlations have been made between seismic velocities (both
compressional and shear) and porosity measurements obtained from the core.
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Integration Of A Seismic Reflection Survey With Traditional Geological Techniques To Site Monitoring Wells In An Unexploded Ordnance Area
Authors Melinda G. Truskowski, Mary Jane Stell and Bart HoekstraThe complex geological setting of the open burning/ open detonation (OB/OD) area of a former
demilitarization facility made conceptual hydrogeologic model development problematic. The
OB/OD area is located on the flank of a regional uplift where geologic strata transition from
nearly flat lying to dips of nearly 50 degrees. OB/OD operations as well as cutting and deposition
by an arroyo located through the center of the area have obscured the surface geology. Explosive
constituents have been detected in both the soil and ground water. A seismic reflection survey
was performed in the OB/OD area to better define the subsurface geological relationships, and
structural features within the area that could be influencing ground water flow. Since the
underlying geology strongly influences ground water occurrence and flow, a depth of
investigation exceeding 500 feet was necessary to achieve the project objectives. The seismic
source for this survey was the iVi Minibuggy vibrator, which is capable of maneuvering in the
steep and rugged terrain encountered at this site. One hundred twenty receiver channels were
recorded for this survey. To correlate the seismic reflectors to geologic horizons, two borings
were installed on one of the seismic lines. Coring and downhole logging were performed to
better characterize the geology at those points. Following interpretation of the seismic data, the
results were incorporated with traditional sources of geological data such as surface geologic
mapping and boring logs. This integrated approach provided an understanding of the site
hydrogeology to select monitoring well locations.
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Field Verification Of Monitoring Wells Sited In An Unexploded Ordnance Area Using Seismic Reflection Survey And Traditional Geological Techniques
Authors Mary Jane Stell, Robert Gregory and Melinda G. TruskowskiBase Realignment and Closure of a former munition storage and demilitarization facility initiated
the closure of a RCRA permitted open burning/ open detonation (OB/OD) area. Explosive
constituents detected in soil and ground water necessitated an assessment to define impacts to
ground water and to design a monitoring well network, required during the post-closure care
period. The complex geological setting of the OB/OD area, located on the flank of a regional
uplift where geologic strata transition from nearly flat lying to dipping up to 60 degrees westward
with numerous faults, made development of a conceptual hydrogeologic model problematic. A
seismic reflection survey was performed to better define the surface and subsurface geological
relationships, and structural features within the area that could be influencing ground water flow.
Following interpretation of the seismic data, the results were incorporated with traditional
sources of geological data to select monitoring well locations.
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Vertical Distribution Of Microbial Abundances And Apparent Resistivity At An Lnapl Spill Site
Authors D. Dale Werkema, Estella Atekwana, William Sauck, Silvia Rossbach and Joe DurisIn an attempt to better understand the anomalously high conductivities in and below free
product/residual Light Non-Aqueous Phase Liquid (LNAPL) plumes, continuous soil
samples were obtained from four locations in the Carson City Park, which is located
adjacent to the former Crystal Refinery in Carson City, MI. The samples were taken
from borings next to monitoring wells, and Vertical Resistivity Probes (VRPs). Two of
the collection sites extended off the free product plume and include one site within the
dissolved product plume and another, considered the control, located outside of known
contamination. The two remaining locations occur within the LNAPL free product
plume. Sub-samples, used for counts of cultured bacteria, were removed from the sides
of the original cores at small vertical intervals. The bacterial counts were correlated with
the bulk apparent resistivities measured in the corresponding VRPs, and with the
sediment descriptions. In general, there is an orders-of magnitude increase in bacterial
abundance at the levels where the apparent resistivity is at a minimum. The control site
gave a good indication of natural vertical and lateral background variability in the
absence of LNAPL. The results indicate that apparent resistivity measurements can
provide a window into the biogeochemical processes ongoing at LNAPL-impacted sites.
The results continue to encourage the use of resistivity as an option to monitor the natural
or enhanced bioattenuation of such sites.
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Resistivity Imaging Of A Partially Reclaimed Coal Tailings Pile
Authors Mia A. Painter, Brett Laverty, Mary W. Stoertz and Douglas H. GreenAn electrical resistivity investigation was conducted at a partially reclaimed valleyfill
coal tailings pile in southeastern Ohio to determine the tailing thickness and to evaluate
the variation within the fill material. The study concentrated on a former slurry pond at the
Flint Run site. Dipole-dipole arrays were used to generate apparent resistivity
pseudosections with a station spacing of 5 m and a maximum dipole separation (n) of 6.
The pseudosections were inverted with a least squares method to produce resistivity
images of the pile to depths of 30 m along 870 m of profile lines. Comparison of the
images to data borehole lithology and conductivity logging shows strong correlation
between the occurrence of coal tailings and acid mine drainage (AMD) saturated waste
rock (as opposed to consolidated siltstone and sandstone) and resistivity lows. The
saturated coal and waste rock appear as resistivities below 20 Rm; consolidated siltstone
and sandstone appear as resistivities above 50 Rm. The slurry dam is seen in the images as
a resistivity high and the tailings in the former slurry pond are seen to increase in thickness
and/or depth consistent with the historical drainage.
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Location And Delineation Of Subsurface Tar Contamination Using Electrical Methods
Authors Elizabeth Granger and Samuel T. PeavyElectrical resistivity and induced polarization (IP) measurements were made to explore the
variability of electrical parameters within tar-contaminated soils at the site of a former shingle
manufacturing facility on the floodplain of the Oswego River in Fulton, NY. Degradation of the
buried shingles generated diapirs of tar, which extrude onto the surface, creating self-replenishing
“tar boils” at the site. Data from offset Wenner electrical resistivity surveys conducted in December
of 1997 and 1998 were used to delineate highly resistive areas believed to be associated with the tar.
Trenching and drilling after the 1997 effort revealed tar in some of the resistive zones; other
resistive zones contained large sandstone boulders believed to be associated with the building of the
Oswego River Barge Canal. Known and potential tar-contaminated zones were the focus of IP
surveys conducted in May through July of 1999. The field experiments conducted at this site were
designed to test the ability of IP parameters to distinguish between types of resistive zones in the
subsurface. Both dipole-dipole and gradient data were collected, targeting zones with the highest
resistivity and surface tar boils.
Results indicate that maps of chargeability at early times on the decay curve indicate the
presence of tar. In addition, Cole-Cole parameters calculated from the decay curve for exponent c =
0.25 were used to generate amplitude, phase and critical frequency values. Maps of these values
also separate zones of tar contamination from sandstone boulders and other resistive zones.
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A Regional Groundwater Evaluation Using Magnetotelluric Soundings For Monclova, Mexico
A regional groundwater evaluation and exploration project was completed for the city of Monclova, Mexico in
1998. Monclova is located in the desert (13.7 inches rainfall per year) and is dependent upon groundwater for its
municipal and industrial resources. Its population (332,000) is expected to grow to 1,200,OOO by 2046. The
municipal wells are completed in Cretaceous carbonate units up to 3,300 feet deep and 25 mgd of water is pumped
from the wells. Monclova has a deficiency of 9.4 mgd with a projected shortfall of 91 mgd in 50 years. In addition,
substantial dewatering of the aquifer is due to over pumpage.
The study began with an evaluation of regional water resources. Previous drilling programs encountered large
variations in production between closely spaced wells. The main aquifers are steeply dipping fractures and faults
generally located in the vicinity of the axis of large anticlinal structures forming the local mountain ranges in the
Coahuila folded belt of Northern Mexico.
A magnetotelhnic (MT) was conducted to assess new well sites to meet the long and short term shortfalls. A total of
77 MT soundings were conducted along nine profiles with the Stratagem system (Geometries). The profiles were
conducted to find favorable structural targets in the dolomite aquifer at depths up to 3,000 feet. The profiles were
located as the result of photo geologic interpretation of the structural geology of the area. Bostick transformations of
the profiles were constructed and the soundings were one-dimensional modeled and correlated into geologic crosssections.
Four wells were drilled on the basis of the MT data. The wells were all excellent producers and make a combined
total of Smgd.
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Geophysical Surveying To Investigate Groundwater Contamination By A Cemetery
Electrical resistivity, electromagnetic, self potential methods and ground-penetrating radar were used to study the subsurface of a cemetery in Southeastern Brazil and to investigate the groundwater contamination by the leachate from the corpse decomposition. The cemetery sits on the top of a hill formed by heterogeneous sedimentary deposits underlain by crystalline rocks. Vertical electrical sounding suggests the presence of lenses of low-permeability materials forming perched aquifers in the study area. Some of the perched aquifers were confirmed by boreholes. Self-potential data were used to check the groundwater flow. The responses of the electromagnetic fields showed anomalous results of apparent conductivities in local areas corresponding to burial places. Water samples obtained by observation wells have shown electrical conductivity values seven times greater than background data. Analysis of the samples detected the presence of pathogenic bacteria. Ground-penetrating radar profiles also suggested the subsurface contamination.
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Tem Survey To Map Saline Ground Water In The Cambrianordovician Aquifer Of Eastern Wisconsin
Authors John Jansen, Patrick Jurcek and James VoigtThe sandstone aquifer is the major source for ground water in eastern Wisconsin. Over
the last decade, salinity has risen in several wells and several new wells have encountered
saline water in areas thought to contain fresh water. TEM surveys are being used to map
the location of saline water zones, as a tool to select new well locations, and to develop
better management methods for the aquifer. This paper presents a case history for a small
village which unexpectedly encountered poor water quality in a new municipal well. A
TEM survey suggested that the poor water quality was due to a stagnation zone behind a
previously unknown mound on the Precambrian surface. A new well location was
selected on the basis of the survey results. In addition, a regional TEM survey is being
completed for the western suburbs of Milwaukee to determine distribution of saline water
in that portion of the aquifer.
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Identification Of Sources Of Saline Water In A West Texas Tributary Using Electromagnetic Induction Methods.
Authors E.J. Sullivan and J.G. PaineElectromagnetic induction methods (EM) were used to identify the lateral and vertical extent of
salinization at a site in Howard County, Texas. Natural springs and water wells at the site
exhibited saline contamination from an unknown source. Several springs emanating from
Ogallala Fm. outcrops contribute to stream flow at the site. EM methods were used to bracket the
source area of saline water and help identify locations for monitoring wells. Six transects were
run in several locations and directions at the site from the ground surface at spacings of 10,20,
and 40 meters using the Geonics EM34-3 meter. Reconnaissance soundings were made at
multiple separations to screen individual borehole locations. Additional down-hole readings
were made using the Geonics EM39 meter to determine vertical changes in soil conductivity in
two contrasting zones. Transect data were used to produce simple models of vertical conductivity
changes. Over most of the site, the typical conductivity profile is that of a nonconductive surface
layer overlying a more conductive (saturated) layer. At the upland sites, the former represents
unsaturated Ogallala deposits, while the latter represents the top of the saturated zone, where
increases in modeled conductivity correlate to increases in water and chloride content.
Conductivities in the unsaturated Ogallala deposits were typically very low, less than 25 mS/m,
while conductivities in saturated soils in background locations varied from 50 to 80 mS/m. In
areas where saline contamination was found (and verified with later chemical analysis),
conductivities were very high, up to 300 mS/m. A distinct high-salinity source area was
identified in the oil field; further investigations of boreholes and wells in that area are ongoing.
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Uxo Geophysical Investigations Using Differential Gps Coupled With Real-Time Mapping And Database Management
Authors Jeff Baird, Beatrice Bidwell and Wendy JohnsonDeveloping technologies in UXO investigations requiring mapping, are utilizing Differential Global Positioning Satellite (DGPS) techniques to improve the quality of data collection. Additional benefits include accurate geographic referencing and anomaly re-acquisition during intrusive stages in the investigation. Until recently, differential GPS geographical referencing was typically merged with geophysical data during post processing allowing the user to view results without the capability to analyze the data with regard to Geographical Information Systems (GE) on larger scales. Recent developments to improve UXO geophysical investigations include multiple array sensors connected to real-time kinetic (RTK) GPS systems via a lap top computer. This method allows real-time data analysis, which reduces and/or eliminates much post processing stages of data analysis. The data collected by the RTWGPS and multiple array system is simultaneously imported into a spatial data collection and management product designed specifically to work with relational databases to support GIS applications. Since the goal of most UXO investigations involving map generation is to apply GIS techniques in risk assessment scenarios, rapidly created and adaptable databases are highly desirable. The integration of system components in real-time mode not only saves time in the analysis of the data, but also reduces the cost of the investigation and simultaneously enters data into a GIS database.
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Uxo Classification Using Characteristic Modes Of The Broadband Electromagnetic Induction Response
Authors D.D. Snyder, Scott MacInnes, Scott Urquhart and K.L. ZongeElectromagnetic induction methods are effective in locating unexploded ordnance (UXO).
However, the induction EM instruments that are used for UXO detection generally have limited
bandwidths and provide little, if any, information for UXO classification. It is well known that
the broadband induction EM response from confined conductors (such as UXO) can be
parameterized in the time-domain as a series of damped exponential decay curves, and in the
frequency domain as a set of discrete real first order poles and their residues. Characteristic
decay time or its equivalent real pole has been shown to be a function of characteristic target
dimensions, target conductivity, and relative magnetic permeability. Therefore,
parameterization of the broadband EM response in terms of these characteristic modes provides
a basis for the classification of UXO anomalies.
In this paper we have used a numerical method (Prony) to analyze TEM decay curves to obtain
a set of exponential decay time-constants and their corresponding residues. Using a
commercially available field data acquisition system, we have acquired fast transient TEM data
from UXO. We show that these data can be analyzed and displayed in a way that is simple to
understand and useful for classifying the TEM response.
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Modeling And Field Measurements Of The Seismic Response Of Shallow Unexploded Ordnance
Authors Jay J. Pulli, Peter J. Krumhansl and Carey BunksElectromagnetic methods provide a relatively quick way to survey a large area for UXO but
often suffer from a high rate of false detections due to clutter. Seismic methods detect the
mechanical properties of objects below the surface, providing an independent “look” and another
dimension in measurement space. The merging of the mechanical response with the
electromagnetic response may aid in target classification and a reduction in the number of
expensive excavations.
In this SERDP funded effort, we approach the problem from a systems point of view. The goal is
to estimate the excess SNR for a given target/environment combination, taking into account the
source characteristics, source coupling, forward propagation, target response, return propagation,
reverberation, and receiver array gain. Models and measurements of each of these factors aid in
the design of the prototype system. For example, finite element modeling of a 155~mm shell in a
realistic soil indicates a target resonance at about 1600 Hz. The target response characteristics, as
well as the target imaging, may thus be useful features, which can be merged with the EM data.
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Kinematic Induction And Magnetic Survey System
Authors R. Josh Bowers and Michael GroundsUXB International, Inc. (UXB) has developed a flexible multi-sensor geophysical
mapping platform. This platform, known as the Kinematic Induction and Magnetic
Survey (KIMS) system, utilizes centimeter accuracy global positioning system (GPS)
equipment, laptop computing and geographic information system (GIS) technology to
perform geophysical mapping. The system is portable and allows for the rapid collection
andanalysis of geophysical and topographical data.
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Integrating Knowledge And Decisions Into The Uxo Risk Minimization Process
Authors Tim M. Dobush, Greg M. Hollyer and Troy WilsonThe objective of UXO investigations is to minimize risk related to the location,
characterization and removal of unexploded ordnance. Successful UXO remediation is a
function of two distinct processes - knowledge building and decision making - which in
turn, commonly rely on spatial data (i.e. located measurements) acquired from surface,
marine or airborne geophysical surveys.
Initially we rely on technical “knowledge experts” to acquire and transform spatial data,
such as magnetic or electromagnetic measurements, into information and combined with
their knowledge, be used for UXO decision-making and actions. From a risk
minimization perspective, the knowledge expert acts as the “custodian” for spatial data -
maintaining the integrity of original measurements, and recording all assumptions and
transformations from start to finish.
As projects advance, we rely on technical (or non-technical) “decision-makers” to review
results and recommendations, question their validity and direct actions. From a risk
minimization perspective, the decision-maker is the “arbitrator” over spatial data -
ensuring that all conclusions and recommendations are validated or at least understood in
the context of the original spatial observations.
In this paper, we examine the roles of spatial data, knowledge building and decisionmaking
in UXO risk minimization via the conceptual framework of the Integrated
Knowledge / Decision (IKD) model. The IKD model presented here describes knowledge
building and decision-making processes and the role of spatial data as the nucleus around
which all knowledge and decisions are formed.
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New Location And Geophysical Techniques For Uxo Identification In Wooded Terrains
Authors Wayne R. Saunders, Jeffrey Warren and Jeffrey LeberfingerMapping of Unexploded Ordnance (UXO) has been significantly improved by collecting high
resolution, position correlated survey data utilizing differential global positioning systems
(DGPS). Although the use of DPGS has been effective in open areas, it is inaccurate in
tree/vegetative canopied areas or near structures that attenuate and reflect the DPGS satellite
signals. A new positioning system utilizing ultrasonic technology has been developed the
UlTraB (Ultrasonic Tracking) and operator guided software, which allows for high resolution
(centimeter accuracy), positioned correlated data in areas where GPS systems are impractical.
Also, a modified EM61 has been designed by Science Application International Incorporated
which consists of a transmitter/receiver coil with the dimensions of 0.5 meters by 1 .O meter.
The internal wiring of the coil has also been modified, and the unit has the capability to measure
three (3) different time gates (as opposed to one (1) on a standard EM61). Tests have indicated
that the modified unit is able to discern buried targets at shallower depths at twice the resolution
as compared to the standard EM61. Overall depth of exploration of the modified EM61 is equal
to that of the standard EM61, but resolution is increased by about two-fold.
This paper presents the results of a test study to demonstrate a new location system and modified
geophysical techniques for UXO identification in wooded terrain. A test area was created with
buried dummy ordnance and surveyed utilizing the Ultra@ system and the modified EM-61 in a
wooded terrain.
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Imaging Uxo Using Electrical Impedance Tomography
Authors William Daily, Abelardo Ramirez, Robin Newmark, Victor George and John RandellWe report the results of tests where electrical impedance tomography (EIT) was used for
detecting and locating buried unexploded ordnance (UXO). The method relies on the
polarization induced at the boundary between soil and buried metal to produce a
measurable phase difference between the injected current and the measured voltage.
When natural sources of induced polarization are smaller than those due to buried metal
objects, then tomographs of impedance phase indicate regions were metal-soil
polarization may be present. Relatively large negative phases may indicate regions were
the buried UXO is located.
Unexploded ordnance is typically detected using magnetic surveys or conventional metal
detectors. These techniques provide limited information regarding the depth of burial of
potential targets and are adversely impacted by the presence of metal objects near the
surface, such as fences, building foundation, or buried utilities. The EIT method can
provide depth and position information on objects located below the surface, and can be
deployed around buildings, providing information regarding what lies beneath them.
Two controlled tests were performed at a field site containing UXO buried in known
locations. Both tests produced a phase anomaly of about 20 milliradians, which closely
matched the known location of buried UXO objects.
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Electromagnetic Induction Spectroscopy For Landmine Identification
Authors I.J. Won, Dean Keiswetter, Thomas H. Bell, Jonathan Miller and Bruce BarrowAn estimated 110 million landmines, mostly antipersonnel mines laid in over 60
countries, kill or maim over 26,000 people a year. One of the dilemmas for removing landmines
is the amount of false alarms in a typical minefield. Broadband electromagnetic induction
spectroscopy (EMIS), however, is a promising technology that can both detect and identify
buried objects as landmines. By reducing the number of false alarms, this approach significantly
reduces costs associated with landmine removal. Combining the EMIS technology and a
broadband EM1 sensor, the scientific phenomenology that has potential applications for
identifying landmines, unexploded ordnance, and hidden weapons at security checkpoints can
now be explored.
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Advances In Frequency Domain Electromagnetic Induction Techniques For Improved Discrimination And Identification Of Buried Unexploded Ordnance
Authors Dean Keiswetter, Stephen Norton, I.J. Won, Ernesto R. Cespedes and John C. MorganCost effective cleanup of lands contaminated with buried UXO requires significant advances
in our current capability to discriminate and identify UXO in cluttered environments.
Recently completed field tests have demonstrated that frequency domain sensors, such as
Geophex Ltd’s GEM-3, can reliably separate UXO targets from clutter objects based on their
complex broadband EM signatures. These field tests have also identified a number of areas
where improvements are needed before this technology is transitioned to full-scale UXO
cleanup applications. This paper describes our progress in addressing these needs, including
(a) improving our understanding of the GEM-3 phenomenology, (b) the development and
validation of physics-based analytical and numerical models of UXO target responses, and
(c) the development of improved multifrequency EM sensor prototypes. Recent
enhancements to our multifrequency EM data collection, visualization, and analysis systems
are described.
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Characterization Studies Of The Electromagnetic Induction Response Of Compact Metallic Objects For Improved Unexploded Ordnance / Clutter Discrimination
Authors Bruce Barrow, Thomas H. Bell and Jonathan MillerA simple induced dipole model has been found to effectively fit a large collection of measured
data over many compact metallic objects using several different types of EM1 sensors. The
induced moment is determined by a set of response coefficients that depend on the object’s size,
shape, and material properties. To the extent that these response coefficients differ between
ordnance and clutter, discrimination using EMI sensors may be possible. Observed differences in
the relative strength of these coefficients between flat and long objects have already been applied
as a means of shape discrimination. Presently, these coefficients are determined by direct
measurement with a given EM1 sensor. In an effort to empirically understand how these
coefficients depend on the object, careful measurements have been made as a function of
frequency over simple shapes like spheres and cylinders. A baseline model has been found that
fits most of the data, even UXO and clutter. To first order, the model parameters can be related
to physical parameters. For ferrous cylinders, the frequency response curves can be scaled to
cylinder diameter and aspect ratio. From this baseline model, future measurements will try to
understand the effects of tapering the cylinders to UXO-like shapes and then the effects of
adding fins and driving bands.
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Electromagnetic Induction Response Of Spherical Conductors Measured With The Gem-3 Sensor, And Compared To Analytic Models
Authors J. Miller, B. Barrow, T. Bell, D. Keiswetter and I.J. WonCurrently, most unexploded ordnance (UXO) remediation is carried out with magnetic and
electromagnetic induction (EMI) sensors. While highly effective in detecting metallic objects
such as UXO, present field techniques also result in many false targets from metallic scrap. To
reduce the cost of digging non-UXO, discrimination techniques are required. One approach to
UXO discrimination is to recognize features from broadband EM1 data that reflect the shape of
the target only, while filtering out other features which may relate to target depth, orientation,
sensor-dependent signals, or combinations of these factors. A thorough calibration of the sensor
against targets of known shape and material properties is required for proper interpretation of
field data. Toward this goal, controlled measurements were made using the GEM-3 (FDEM)
sensor on spherical conductors of various sizes at several distances. These data generally
compare very well against the analytic solution for a sphere in a spatially uniform, time varying
magnetic field, despite the fact that the GEM-3 sensor produces a primary field that is not
spatially uniform.
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The Need For A Methodology To Verify That Installed Soil-Cement Meets Design Requirements
Authors James Lambrechts and Alfredo UrzuaThe proof that installed soil-cement meets design requirements is difficult, and raises many
questions. There are many variables involved in making soil-cement, not the least of which are the
soil conditions which have significant impact on the final product. Furthermore, large areas or
volumes may be involved, and the confirmation testing needs to be quick, representative, and
reliable. Currently applied methods and their potential problems are discussed. The need for an
integrated approach is emphasized.
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Evaluation Of The Dynamic Properties Of Soil-Cement As They Relate To Unconfined Compressive Strength
Authors Johnston J. Huntress, Arthur D. Little, Alfredo Urzua and Vincent MurphyAlthough the concept and use of soil-cement for ground improvement, excavation
and liquefaction migitation has been available for several decades, a reliable, routinely applied
Non-Destructive Testing WT] method has yet to be defined. This thesis looks at two
approaches for examining the in-situ material as to its Unconfined Compressive Strength PCS].
The dynamic properties of the mixtures are examined by measuring shear wave velocity. Cored
samples were taken from the material at the 28-day mark for laboratory testing of UCS. These
results were correlated to the measurements made by the NDT device.
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In-Situ Verification Of Soil-Mix Ground Modification
Authors V.J. Murphy, E. Rostosky, P.B. Hubbard and A. UrzuaGround modification by “soil-mixing” is a relatively recent development of improving/stabilizing “soft” soils and re-constituting them effectively as “cemented” materials. In-situ seismic velocity measurements by cross-hole and down-hole procedures, and by clamped techniques for exposed materials such as walls and pits, have disclosed an “S” wave velocity increase from 800 to 2000 feet per second. For excavation stability, the required increase in unconfined compressive strength, to values in the range of 80 to 300 psi, is thus assured.
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Use Of A Ground-Coupled Monostatic Antenna For Determining Deterioration Of Concrete Structures
More LessA 1.5 GHz ground-coupled antenna was used with a digital ground penetrating radar system to
evaluate the amount of deterioration within an aboveground concrete holding tank. Because of
the corrosiveness of the solution held within and the structural design of the 72 year-old tank,
deterioration could manifest itself by delamination and/or by surface cracking. On the GPR
record, potential areas of deterioration appear as zones of attenuation. Delamination is most
likely to occur at the inner wall where the tile and concrete meet, but can also occur at either the
bottom or top rebar schedules within the concrete. Surface cracking can indicate both a suticial
stress problems, caused by the elliptical shape of the structure, as well as more severe
voiding/delamination problem. Over 50 vertical profiles were conducted on the 17-foot high
walls using GPR to more accurately assess the deterioration associated with failure of the
structure’s integrity.
Attenuation, measured as dB loss relative to the transmitted pulse when the antenna is coupled to
the concrete surface, was mapped and contoured for the tile/concrete boundary and the upper
rebar schedule. Deterioration at the concrete surface was achieved by calculating the real
concrete dielectric permittivity (i.e. dielectric “constant”) from the reflection coefficient of the
surface reflector when the antenna was mounted on a 12” thick foam block. Attenuation and
dielectric information were then compared with visual observations of the data to determine the
overall deterioration of the structure. Overall, the curved walls revealed more deterioration, over
25%, while the straight sections of wall had about 10 to 14% deterioration.
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Geophysical Surveys Across A Ground Subsidence Feature
Authors P.J. Fenning, A.J. Brown and D. NindIn many parts of Southern England the Cretaceous chalk formation exhibits solution features
which eventually lead to collapse and void formation. During early formation it is difficult to
decide when small subsidence features are due to either man-made industrial/archaeological
features or due to water ingress.
A case history of geophysical surveys is presented over a circular subsidence feature considered to
be of possible Iron Age origin and results are compared to similar surveys over known solution
voids.
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Use Of Marine Geophysical Methods To Guide Underwater Repairs To A Pumped Storage Plant Reservoir Foundation
More LessMarine geophysics has played an important role in a lo-year investigation and repair program at
the Ludington Pumped Storage Plant, an 1872 megawatt hydroelectric pumped storage facility
located on the eastern shore of Lake Michigan (Figure 1). The upper reservoir is 842 acres in size
and lined with clay on the bottom and lower inside slopes. Excessive seepage was noted in 1973
after the reservoir was filled for the first time. In 1975, trench-like features were first observed
extending through the clay liner. Geophysical and diver investigations later found that these
“trench features” ranged from four to ten feet in width, three to forty feet in depth, and hundreds
of feet in length (Figure 2). A geophysical testing program conducted in 1990 showed that sidescan
sonar and fathometer surveys combined with an accurate vessel positioning system were the
most effective methods to map the trench features. Annual side-scan sonar and fathometer
surveys have been performed since 1992 to assess the current status of the trench features and
provide a reliable map for diver inspections and underwater repairs. The digital trench feature
map is used as control for the real-time positioning of the boats and divers using differential GPS
and ultra-short baseline (USBL) tracking systems, respectively.
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