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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 - 20 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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