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7th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 27 Mar 1994 - 31 Mar 1994
- Location: Boston, Massachusetts, USA
- Published: 27 March 1994
41 - 60 of 76 results
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Evaluation Of High Resolution Seismic For Characterization Of The Owens Lake, California, Aquifer System
Authors Thomas A. Brooks and Kent R. JohnsonHigh resolution seismic reflection data are being used as part of an integrated program to characterize the ground water system of the Owens Lake, California, area. The feasibility study for the project consisted of acquiring data in both river delta and alluvial fan depositional settings. We performed a series of noise tests to determine the best seismic sources, receivers and
other acquisition parameters. Noise test data were evaluated using a field-based processing system. We acquired approximately two miles of Z4-fold high lbesolution seismic reflection data for evaluation. We simulated reduced fold geometries during processing to determine the optimal fold coverage for A large scale survey. Reflection data were acquired to 1/2 second (twoway
traveltime), representirlg a useful depth of investigation of roughly 1500 feet.
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Case History: Brine Inflow Beneath An Underground Alcove Floor, Alcove L-3, At The Waste Isolation Pilot Plant, Se New Mexico
Authors D.I. Neuman and H.T. AndersenAn underground alcove, Alcove L-3, at the Waste Isolation Pilot Plant in SE New Mexico, is part of a brine inflow investigation. The first indication of brine inflow was noted through the drilling of boreholes in the invert. Initial determinations of the extent of the brine inflow was accomplished through a modified mise-a-la-masse survey. Corrections were applied to account for the underground geometry. Modelling was also performed to study the sensitivity of the survey to its structural surroundings, such as neighboring alcoves and connecting driftways.
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Monitoring Of A Tracer Experiment With Electrical Resistivity At Haslemoen, Hedmark County, Norway
Authors J.S. Rønning, Marian Morris, N.O. Kitterød and O.B. LilePotential differences measured on the surface were used in an attempt to
monitor the movement of a low-volume tracer. The experiment was conducted
in the unconfined groundwater aquifer at Haslemoen, in Hedmark County,
Norway. 300 1 of NaCl solution were injected at a depth of 4.1-5 m. A pole-dipole
electrode configuration was used, with the near current electrode embedded in
the zone of injection. The direction of tracer movement was identified. The
measurements are affected both by the moving conductive zone and the changes
in electric current concentration.
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Mapping Of A Stratigraphic Boundary By Its Seismoelectric Respons
Authors K.E. Butler, R.D. Russell, A.W. Kepic and M. MaxwellExperiments carried out at our Haney test site near Vancouver, Canada, have shown that
some boundaries in unconsolidated sediments may be mapped on the basis of their seismoelectric
response. Using a sledgehammer source and electric field receivers, we have observed that an
electromagnetic signal is generated when a seismic wave impinges upon a boundary between
organic-rich fill and impermeable glacial till. The depth to the interface, verified by drilling,
ranges from about 1 to 3 m. The electrical response is believed to be a transient streaming
potential produced by a seismically-induced flow of pore water at the interface.
The seismoelectric response is linear in that its frequency content is comparable to that of
the seismic wave. Surface measurements exhibit radial symmetry about the shotpoint, and the
arrival time of the signal corresponds to the seismic traveltime from the shotpoint to the
subsurface boundary. The response cannot be attributed to seismic shaking of the dipole receivers
because it is observed simultaneously by receivers in different locations.
The maximum amplitude of the electrical response observed at the surface, following a
sledgehammer blow 2 m above the boundary, is about 1 mV/m. This is measured by a horizontal
dipole at an offset of 4 m from the shotpoint. At greater distances, the amplitude of the first
arrival decays rapidly with offset and the waveform broadens. The change in waveform with
dipole offset suggests that the effective area of the interface contributing to the response may be
greater at more distant observation points.
Measurements were also made by detonating blasting caps at various depths in boreholes
penetrating the geologic boundary. The results of these tests support the conclusion that it is the
boundary, rather than the water table, that is responsible for the seismoelectric conversion.
Although the scale of our experiments was relatively small, the results are significant in
that they suggest that the seismoelectric method may be used to map aquitards or the boundaries
of permeable formations.
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A New Ground Resistivity Method For Engineering And Environmental Geophysics
Authors V.M. Timofeev, A.W. Rogozinski, J.A. Hunter and M. DoumaSeveral years ago, a capacitive-coupled resistivity system was developed in Russia by one of us
(V.M.T.), for engineering geophysical applications in permafrost areas of Siberia. This system,
called VCHEP (cyrillic acronym for high frequency capacitive-coupled resistivity) uses both
transmitter and receiver antennas operating in the range of several kilohertz. Measurements of
applied current and received voltage potential are converted to apparent resistivity using a
geometrical factor related to the antenna array. The transmitter and receiver type and geometry
can be varied depending upon a particular application; however, the most cost-effective array
is the in-line double dipole line antenna configuration. Using such a, drag-cable design of
antennas, data acquisition rates may far exceed those techniques requiring galvanic electrode
contact. Considerable experience with this method has been obtained in northern areas of
Siberia; and as part of the Canada/Russia Northern Scientific Exchange Program, testing has also
been conducted in the Canadian western arctic.
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Surface Nuclear Magnetic Resonance Experiments To Detect Subsurface Water At Haddam Meadows, Connecticut
Authors D.A. Lieblich, A. Legchenko, F.P. Haeni and A. PortselanNuclear magnetic resonance (NMR) techniques have been adapted to surface
geophysical prospecting by scientists at the Institute of Chemical Kinetics and Combustion,
Novosibirsk, in Russia. The first tests of this method in the U.S. were conducted in the summer
of 1993 through a joint collaboration between the U.S. Geological Survey; the U.S.
Environmental Protection Agency; the Institute of Chemical Kinetics and Combustion,
Novosibirsk, Russia; and Firm Hydrogeotom, Moscow, Russia. NMR “soundings” were
conducted at 10 sites throughout the U.S. The results from Haddam Meadows State Park,
Connecticut, are reported here. They are of interest, in part, because Haddam Meadows was
found to be a “high noise” site for the NMR soundings but is considered to be a fairly typical
site; in terms of noise, for urban and many rural areas.
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Simulation Of Em Wave Propagation In Three-Dimensional Structures By A Finite-Difference Method
Authors Tsili Wang and Alan C. TrippWe have developed a finite-difference time-domain solution to Maxwell’s equations for
simulating electromagnetic wave propagation in three-dimensional media. The algorithm
allows arbitrary variations of electrical conductivity and permittivity within a model. It
uses the Yee’s staggered grid technique to discretize the model and approximates spatial
derivatives with optimized second-order, finite differences everywhere except close to the
computational domain boundary where it uses conventional central differences. The pointwise
computational time of the optimized second-order difference scheme is the same as
that of the conventional fourth-order difference scheme, but the former has better dispersion
characteristics. Although the optimized difference scheme imposes stricter limitations
on the size of time steps allowed for an explicit time-marching scheme, a simple calculation
shows that this scheme is more cost-effective, due to its lower required spatial sampling rate,
than the conventional second- or fourth-order difference scheme. The temporal derivatives
are approximated by second-order central differences throughout.
We used the Liao transmitting boundary conditions to truncate an open problem. A
reflection coefficient analysis shows that this transmitting boundary condition works very
well. However, it is subject to instability. We propose a method which stabilizes the
boundary condition and which can be easily implemented.
The finite-difference solution was compared to closed-form solutions for both conducting
and non-conducting whole spaces and for a non-conducting half-space. In all cases, the
finite-difference results are in good agreement with the closed-form solutions.
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Using Resistivity Tomography To Monitor Air Sparging
Authors Susan Schima, Douglas J. LaBrecque and Paul LundegardAir sparging is a relatively new technique for remediation of
ground water contaminated with petroleum hydrocarbons. In this
technique, air is injected below the water table. The air is usually
removed by vacuum extraction in the vadose zone. Remediation
occurs through a combination of contaminant partitioning into the
vapor and enhanced biodegradation.
Although remedial efficiency is strongly a function of the
pattern of air flow, the distribution of the injected air in space and
time is poorly understood. Cross-borehole resistivity surveys were
carried out at an air sparging site to address these unknowns. The
site is a former service station in Florence, Oregon. Resistivity
measurements were made using six 40 ft deep wells, one of which
was the air sparge (air injection) well. Data were collected over a two
week period during and after several sparge events. Tomographic
resistivity reconstructions were generated between wells using an
algorithm that assumes axially symmetric structures. The movement
of air throughout time is clearly defined by high resistivity regions.
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Applications Of Multi-Offset Ground Penetrating Radar
Authors Robert J. Greaves and M. Nafi ToksözThe estimation of propagation velocity is important for the correct processing and
interpretation of ground penetrating radar (GPR) reflection data. Most, if not all,
GPR surveys, are very limited in spatial extent and the common perception is that
within the survey range, radar propagation velocity in the shallow subsurface has very
slow or no lateral variation. Therefore, a single (1-D) velocity function is considered
adequate to describe the subsurface. In this study it is shown that, in fact, lateral
variation in radar velocity can be quite significant. An effective means of determining
velocity is based on normal moveout velocity analysis of common midpoint multi-offset
data. Applying this technique at many locations along a GPR survey provides a more
accurate description of the actual 2-D velocity distribution.
When the multi-offset acquisition geometry necessary for normal moveout velocity
analysis is applied continuously in the GPR survey, an improved radar reflection image
is attained by stacking traces at common midpoints. The 2-D normal moveout velocity
description is used to make necessary adjustments to the data before the stack. The
velocity analysis and common midpoint stack techniques are applied to an example
of GPR data acquired using the multi-offset geometry at every survey station. The
results show that reflection signal-to-noise and effective depth of penetration of stacked
multi-offset data are improved, as compared to standard single-offset GPR data. It
is also shown that, the stacked multi-offset data is itself improved as the number of
velocity analysis locations is increased, up to some practical limit.
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Vetem - A Very Early Time Electromagnetic System
Authors Louise Pellerin, Victor F. Labson and M. Cathy PfeiferThe Very Early Time Electromagnetic (VETEM) system is designed to investigate the
conductivity and dielectric properties of the shallow region of the geoelectrical section where
most buried waste is located. In the electrically conductive conditions (20-30 ohm-m) common
throughout the Department of Energy complex, the minimum depth of investigation for diffusive
electromagnetic (EM) sounding techniques is roughly 5 meters. At the other end of the
spectrum, ground penetrating radar (GPR) systems typically investigate only the top meter or so
when clay minerals are present in the soil. Hence, in many cases there is a gap in our detection
capability of the geoelectrical section between the lower limit of GPR and the upper limit of
traditional EM. Bridging this gap is essential to the characterization of buried waste sites.
For the successful development and deployment of the VETEM system three important
interconnected elements are necessary: (1) forward modeling, using multi-dimensional numerical
algorithms and physical modeling results to optimize instrument and survey design, and to test
and refine interpretational software; (2) instrumentation designed for rapid, high-resolution
mapping of conductive and dielectric targets in a conductive host; and (3) interpretational
schemes that are rapid for real-time imaging and rigorous enough to provide quantitative results.
All three elements are being developed simultaneously over a period of several years. In the first
year, the focus has been placed on the use of the USGS-developed prototype frequency-domain
slingram system, operating in the frequency range of 300 kHz to 30 MHz with intercoil spacing
of 1 to 4 meters; development of the time-domain transmitter; one- and three-dimensional
modeling software; and the adaptation of existing quasi-static interpretational software to
shallow targets. This poster highlights the data collected at INEL and the status of the modeling
and interpretational software.
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Investigating The Resolution Of Resistivity Arrays Using Inverse Theory
Authors L.P. Beard and A.C. TrippWe used a fast 2-D minimum structure inverse solution to examine the ability of different
resistivity arrays to resolve structures given noisy synthetic data. We found that the resistivity
models obtained from inversion of the dipole-dipole data were usually very similar to the estimated
models from pole-dipole data, and both were superior to estimated models from pole-pole data.
This is because noisy dipole-dipole or pole-dipole data define geoelectric structures much more
precisely than an equivalent set of noisy pole-pole data. One structure where the dipole-dipole
array appeared decidedly superior was the prism beneath a conductive overburden. The final
estimated models from the pole-pole data were more poorly resolved than the final models from the
other arrays. Our results show that the pole-pole data is a poor choice if vertical resolution of a
geoelectric structure is crucial. Furthermore, if pole-pole data contains even a fraction of a percent
of noise, the transformation of such data through superposition to equivalent data of other array
types is virtually impossible, and significant information is lost.
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A “Model” Geophysics Program
More LessIn 1993, I tested a radio-controlled airplane designed by Jim Walker of Brigham
Young University for low-elevation aerial photography. Model-air photography retains
most of the advantages of standard aerial photography --- the photographs can be
used to detect lineaments, to map roads and buildings, and to construct stereo pairs
to measure topography --- and it is far less expensive. Proven applications on the
Oak Ridge Reservation include: updating older aerial records to document new
construction; using repeated overflights of the same area to capture seasonal changes
in vegetation and the effects of major storms; and detecting waste trench boundaries
from the color and character of the overlying grass.
Aerial photography is only one of many possible applications of radio-controlled
aircraft. Currently, I am funded by the Department of Energy’s Office of Technology
Development to review the state of the art in microavionics, both military and civilian,
to determine ways this emerging technology can be used for environmental site
characterization. Being particularly interested in geophysical applications, I am also
collaborating with electrical engineers at Oak Ridge National Laboratory to design a
model plane that will carry a 3-component flux-gate magnetometer and a global
positioning system, which I hope to test in the spring of 1994.
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Inel Cold Test Pit Demonstration Of Improvements In Information Derived From Non-Intrusive Geophysical Methods Over Buried Waste Sites
Authors Bart Hoekstra and Raye LahtiA high density, multiple sensor geophysical survey was conducted at the Idaho National Engineering Laboratory
(INEL), a Department of Energy test facility, at its Cold Simulated Waste Demonstration Pit (CTP). The CTP site
was specifically prepared for testing and evaluation of remediation technologies, including geophysical surveys.
The INEL has been involved in the testing and development of nuclear power production since the early 1950’s. A
variety of waste products from nuclear processes on and off-site have been disposed of, primarily at the
Radioactive Waste Management Complex (RWMC). Included are waste products from the Rocky Flats Plant
(RFP) in Colorado. The simulated waste forms constructed for the CTP were formulated from 1971 to 1973
records of waste shipments from RFP, and deposited in a similar fashion as described in the records.
The objectives of the geophysical demonstration were to reduce risk, and improve the technologies that help to
meet DOE’s cleanup goals by providing a foundation for further advancing the use of geophysical methods for the
detection of buried waste. In this demonstration, the use of high density, multiple sensor data sets, advanced data
processing techniques, and the testing of an innovative time domain electromagnetic instrument were conducted.
Other instrumentation used included frequency domain electromagnetic conductivity profiling, total field
magnetics and vertical magnetic gradient, time domain electromagnetic profiling, and ground penetrating radar.
The geophysical field survey was conducted over a 15 day period on a grid over the CTP of about 300 feet by 140
feet. For most geophysical measurements a 2.5 foot grid was used.
The TDEM metal detector and the in-phase component of the FDEM conductivity surveys provided good
resolution of the CTP boundaries, berms and contents. The results over the CTP provide good illustrations of the
influence of the local geologic setting to sensor behavior. The GPR data was ineffective in providing any
information about the contents of the CTP. EM conductivity and magnetic data were influenced by variations in
thickness of surface sediments and basalt bedrock. These factors provide evidence of the necessity of using
multiple sensors for buried waste delineation. A combined interpretation using all available data was successful in
defining the CTP.
In addition, methods were developed to display the locations of the identified targets in a 3-D which can be
manipulated in real-time on a graphics workstation. Forward models were developed for the EM61 and used to
evaluate the resulting data.
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Success Criteria And Reasons For Failure Of Ground-Penetrating Radar Studies
Authors W.M. Roggenthen and D.K. ParrishThe literature is replete with examples of successful ground-penetrating radar (GPR)
investigations. Documentation of the failures, however, is not as well reported, although
cautionary notes are also abundant regarding the misuse and misapplication of the technique.
Such deficiencies in reporting are common artifacts in scientific and engineering literature in
that interest is generally greater in successful studies, but discussion of the failures is important
because it provides an understanding of the limitations of the method. Examination of the
types of surveys that have proven to offer a measure of success suggests a number of themes,
the most obvious of which is the presence of host materials with low conductivities and a
relative lack of mineralogic clays.
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High-Resolution Subsurface Imaging And Neural Network Recognition
Authors Ben K. Sternberg and Mary M. PoultonA high-frequency, high-resolution electromagnetic (EM) imaging system is being
developed for environmental geophysics surveys. Some key features of this system
include: (1) rapid surveying to allow dense spatial sampling over a large area, (2)
high-accuracy measurements which will be used to produce a high-resolution image
of the subsurface, (3) measurements which have excellent signal-to-noise ratio over a
wide bandwidth (32 kHz to 32 MHz), (4) large-scale physical modeling to produce
accurate theoretical responses over targets of interest in environmental geophysics
surveys, (5) rapid neural network interpretation at the field site, and (6) visualization of
complex structures during the survey.
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Integrated Geophysical Characterization Of Mine-Waste Sites In The Coeur D’Alene Mining District, Idaho
Authors Phillip R. Moyle, Jody M. Fay and Michael J. FriedelAs part of a study aimed at testing and developing effective and thorough
characterization procedures, the U.S. Bureau of Mines (USBM) Mine Site
Characterization Program is assessing the application of several surface
geophysical techniques to characterize heavy-metal mine wastes in northern Idaho.
Site characterization is fundamental to conducting accurate risk assessments and
for subsequent remediation plans, if proven necessary. Integrating geophysics
with the application of geology, metallurgy, physical chemistry, surface and
ground water hydrology, environmental science, geostatistics, and other
appropriate disciplines produces an interdisciplinary or “holistic” approach which
can significantly improve the quality and accuracy of characterization.
Furthermore, it is believed that selective application of minimally invasive,
integrated geophysical techniques will reduce disturbance of potentially hazardous
materials while decreasing the time and cost of the investigation. This paper
briefly describes the purpose, scope, and current status of an ongoing project.
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A Reconnaissance Gpr Investigation At Chichén Itzá, Yucatan, Mexico
A Ground Penetrating Radar survey was done over selected areas of the Great Plaza and
the Ball Court at the Mayan archaeological site of Chichen Itz& Yucatan, Mexico. The purpose
of the work was to test the GPR technology for the first time at this site; to map the bedrock
surface beneath the extensive artificial fill which was used to elevate the Plaza; to search for
buried structures; and if depth penetration allowed, to search for caverns within the limestone
bedrock. Geologically, the site is underlain by Tertiary limestone which forms a smooth plain
having approximately 5 meters of local relief, broken by occasional sinkholes. Water table was
at about 20 - 25 meters depth. The GPR study was done partly because physical properties
measurements on limestone samples done 9 years ago by Dolphin and Vickers of SRI showed
very low attenuation of radio waves. A GSSI SIR-10 with bistatic 500 MHz and monostatic 100
MHz antennae was used, with most work done at the lower frequency. Penetration was not as
great as was anticipated because the plaza fill includes appreciable amounts of residual clay soil
mixed with the limestone blocks and cobbles. Hence, cavern features were not within the range
of the instrument. However, penetration was sufficient to map relief of the “bedrock” surface,
to reflection times as great as 125 nsec. A number of bedrock knolls were found below the NE
part of the Plaza. At shallower levels, sub-horizontal reflections are probably derived from
earlier plaza levels. Internal structures within the fill give an indication of the direction in which
the plaza filling took place. Occasional hyperbolic reflectors at and above the bedrock surface
hint at large discrete blocks or similar structures. These await excavation by our colleagues at
INAH, to whom we are also grateful for on-site support during the field work. The success of
this test has led to a recommendation to cover the entire site in detail with GPR.
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The Dahlonega Test Site: Test Bed For Evaluation Of Shallow Subsurface Geophysical Exploration Techniques
Authors Robert C. Kemerait, Douglas Baumgardt and Suzanne LeonardThe Dahlonega test site is located in the eastern foothills of the Appalachians in
Georgia. Dahlonega, Georgia marks the southern end of the Appalachian trail at the
base of the Blue Ridge in northern Georgia. Founded as a gold mining town in the early
1800’s, Dahlonega is now primarily a historical attraction setting in the foothills among
abandoned gold mines and works. A facility for testing shallow subsurface geophysical
exploration techniques is under construction near the Chestatee River approximately 4
miles to the east-southeast of the town of Dahlonega. The test facility is labeled the
Dahlonega Test Site (DTS).
Geological characteristics in the immediate vicinity of the DTS favor a highly
weathered clayey mica schist with abundant quartz veins. The quartz veins are fairly
substantial, in some areas up to 3-4” in thickness. The veined schist formation is
overburdened by a clayey reddish soil. From the drilling operation there is observable
evidence of layering. At approximately 20 feet the medium changes from a reddish
material to the darker schistose material. The water table appears at approximately 50
feet. Data recorded from borehole deviation measurements made with an Owl tool
indicate that the boreholes are straight until reaching a depth of approximately 75-80
feet where they began to deviate. This deviation suggests the presence of more
competent rock appearing at this depth.
An air filled tunnel with an axis that is nearly perpendicular to the test site is
present at a depth of approximately 42 feet.
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Stols™ Magnetic Survey At Sandia National Laboratory Technical Area 2
More LessTechnical Area 2 (TA2), a 45 acre site located at Kirtland AFB in Albuquerque NM, was run by
Sandia National Laboratory (SNL) as a nuclear weapons assembly facility from 1948 to the mid
1950’s, and as an explosive device development facility since the mid 1950’s. Presently, SNL
is developing an environmental remediation plan for TA2 which will allow for the safe closure
of the facility. One main concern of SNL is the location of underground burial containers, such
as 55 gallon drums, which may contain radioactive or chemical waste products.
In order to create a maps of buried ferromagnetic objects located at TA2, the Surface Towed
Ordnance Location System (STOLS™) was deployed by GEO-CENTERS, INC. at this site. This
survey, which covered over approximately 20 acres, was performed in September, 1993. Total
field magnetic data was recorded on seven separate magnetometers at a rate of 20 samples per
second per sensor. The magnetometers were mounted on a sensor platform which is towed by
a low magnetic signature vehicle and positioned with a GPS navigation system. Concurrent with
the survey a reference magnetometer was deployed in an adjacent area to record the low
frequency variations in the Earth’s ambient field. These reference data were later subtracted from
the survey data to produce a total field magnetic anomaly map of the site. Data was collected
at sufficient density to allow for final interpolation onto a 10 cm grid. All data were collected,
processed and analyzed in the field, on the same day of the survey.
The STOLS™ magnetometer surveys at TA2 resulted in very dense and highly accurate magnetic
anomaly maps of the facilities. The magnetic anomalies detected in the data were modeled to
produce a catalog of buried ferromagnetic objects at the sites. Buried objects are described in
terms of latitude, longitude, depth and size. Detected objects included fence posts, roadbeds,
buried pipes and barrels.
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Efficient, Cost Effective Waste Site Characterization Utilizing Complementary Non-Intrusive Geophysical Techniques: A Case Study Of 2-D And 3-D Ground Penetrating Radar And Magnetometer Surveys
Authors W.R. Sims, G.G. Rucker, R.A. Plunkett, K.M. Wise and H.M. HickeyThe Savannah River Site (SRS) has implemented a comprehensive environmental program to mitigate
impacts to the environment while maintaining compliance with environmental regulations. An element of
the environmental program is the investigation of over 100 waste sites - some of which include buried
hazardous waste materials. The SRS has effectively conducted subsurface field investigations at waste sites
suspected of containing buried wastes by utilizing non-intrusive geophysical techniques as opposed to
traditional intrusive techniques. Depending on the site specific conditions and objectives of the
investigation, multiple geophysical techniques often yield a more comprehensive conceptual model of the
site versus a single geophysical survey. Although multiple surveys are seemingly cost prohibitive early in
a waste site characterization history, the information obtained usually leads to a more efficient and cost
effective characterization or remediation design. In addition, the complementary data increases the level of
confidence in the investigating team, helps reduce the anxiety associated with contamination exposure, and
contributes to client and regulatory approvals.
Two and three-dimensional ground-penetrating radar and magnetometer surveys were conducted at the D-Area
Oil Seepage Basin, a waste site “suspected” of containing buried drums. The data from the integrated
geophysical investigations complemented one another, successfully delineating the lateral and vertical
dimensions of the waste site and detecting buried metal objects. This extended abstract compares the
application, results, and advantages of the individual geophysical techniques used at the waste site.
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