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12th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 14 Mar 1999 - 18 Mar 1999
- Location: Oakland, California, USA
- Published: 14 March 1999
51 - 100 of 108 results
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Ultrasonic Characterization Of Synthetic Soils For Application To Near Surface Geophysics
Authors B.P. Bonner, P. Berge, C. Aracne-Ruddle, C. Bore, E. Hardy and C. TrombinoEffective seismic interrogation of the near subsurface requires that measured parameters, such as
compressional and shear velocities and attenuation, be related to important soil properties. Porosity,
composition (clay content), and fluid content and identification are of particular interest. The
ultrasonic (100-500 kHz) pulse transmission technique was used to collect data for highly attenuating
materials appropriate to the vadose zone. Up to several meters of overburden was simulated by
applying low uniaxial stress of 0.1 MPa to the sample. The approach has been to make baseline
measurements for pure quartz sand, because the elastic properties are relatively well known except at
the lowest pressures. Second phases are then added to modify the sample microstructure and
ultrasonic measurements are made to characterize the effect of the admixed second phase. Samples are
fabricated from Ottawa sand mixed with a swelling clay (Wyoming bentonite), and with a common
organic soil amendment, peat. Compressional (P) velocities are low, ranging from 169 to 360 m/s for
the mixtures at low stress. Shear (S) velocities are about half of the compressional velocity, but show
different sensitivity to microstructure. Adding clay increases the shear amplitude dramatically with
respect to P, and also changes the sensitivity of the velocities to load. These experiments demonstrate
that P and S velocities are sensitive to the amount and type of admixed second phase, even at low
concentrations. Other properties of the transmitted signals which include the ratio of S and P
amplitudes, velocity gradient with depth, and the frequency content of transmitted pulses, provide
additional information and are not now used in near-surface surveys.
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Comparing Geophysical Measurements To Theoretical Estimates For Soil Mixtures At Low Pressures
Authors P.A. Berge, J.G. Berryman, B.P. Bonner, J.J. Roberts and D. WildenschildRelationships between geophysical and hydrogeological properties are needed for
improving characterization of the subsurface at contaminated sites using geophysical
methods. As part of an on-going project with the goal of improving underground imaging,
we are developing rock physics theories for relating elastic wave velocities to soil
composition and fluid-flow parameters. Here we use effective medium theories to estimate
velocities of unconsolidated sand-peat moss mixtures and compare the estimates to
measured compressional and shear velocities from low-pressure laboratory experiments.
We found that a self-consistent effective medium theory model using sand and porous peat
as the constituents provides estimated velocities that are in good agreement with measured
velocities. Understanding the microstructural assumptions inherent in various mixture
theories guides the selection of appropriate theories for modeling velocities in soils.
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Saturation And Contamination Dependence Of Electrical Properties In The Mhz Range
Authors Andreas Weller, Claus Urban and Joachim SchonartA Dielectric Measurement System is used to investigate the influence of pore filling and
saturation on electrical permittivity and conductivity in a frequency range from 2 MHz to 1.3
GHz. The small size of the sample holder requires a special preparation method of the samples.
The influence of the geometry of the sample holder was investigated with synthetic samples of
known permittivity.
Only the experiments with glass beads and pure sand verified the validity of known mixing laws.
Samples with varying clay content reveal the dominant influence of clay minerals on electrical
permittivity. The large specific internal surface of clay minerals requires the consideration of
surface effects. Mixing laws considering only the volume fraction of the components fail to
describe the electrical properties of samples with strong surface effects. Temporal variation of
electrical properties are observed which are caused by the imbibition process after the injection.
The intrusion of hydrocarbon contaminants into the pore space resulted only in small changes of
electrical permittivity compared to significant changes due to varying water and clay content.
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Large-Scale Geophysical Mapping And Its Application For Ground Water Protection In Urban Areas.
Authors Kurt I. Sørensen and Verner H. SøndergaardThe water supply in Denmark strongly relies on ground water, but pure water may soon be in
short supply. The Danish Parliament has therefore decided, that protection of ground water
against polution should be intensified by means of protection zones and area1 planning activities,
which means that for instance urban expansion will be under stronger control.
In order to act on a proper basis the knowledge about the geological and hydrogeological
situation has to be considerably improved. Over the next 10 years some 140 million US dollars
will be spent to obtain a better geological mapping of recharge areas with great drinking
water interests. These areas add up to a total of some 15.000 km2 in Denmark.
Geophysical methods, especially electrical and electromagnetic methods, are expected to
play an important role, accounting for more than half of the 140 million dollar mapping
expenses.
A large scale mapping project around the City of Aarhus has provided good experiences
about using high density geophysical measurements combined with drillings covering large
areas.
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Geophysical Imaging Of A Former Landfill And Its Associated Leachate Plume
An integrated geophysical investigation was conducted at a closed landfill site
(LF-30) at the decommissioned Wurtsmith Air Force Base (WAFB), Oscoda, MI in May
and June of 1998. Frequency domain horizontal loop electromagnetic (HLEM),
magnetic, self-potential (SP), electrical resistivity (ER), and ground penetrating radar
(GPR) methods were used. The site is nearly flat topographically, with less than two
meters of local relief, and is covered by dense tree growth approximately 23 years old.
Previous hydrogeologic investigations show PCE, TCE, DCE, vinyl chloride, and BTEX
are the main constituents of a leachate plume emanating from the landfill. Additionally,
the landfill plume contains elevated levels of total dissloved solids(TDS) leached from
the fill material, causing groundwater plume conductivities three times background
values. Groundwater flow in the area is toward the northeast and discharges into Van
Etten Lake.
All of the methods utilized in this study were successful in delineating the landfill.
The electromagnetic and magnetic data suggest the existence of eight separate clustered
burial cells (and one outlier) containing significant amounts of metal within the landfill.
Additionally, areas of fill are characterized by attenuated GPR signals and very low
apparent resistivities compared to background. Furthermore, the EM and SP surveys
were most effective in delineating an anomalous zone approximately 1600 R wide, where
boundaries are coincident with the lateral boundaries of the BTEX plume as determined
by scattered monitor wells. The difference in size between the small LF-30 landfill and
the much larger associated plume width, suggest the possibility of an additional source.
Therefore, it is likely that another landfill (LF-3 l), located up gradient from LF-30, is a
major contributor to this contaminant plume.
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The Temporal Variation Of A Saltwater Contaminant Plume As Evidenced Through Long-Term Resistivity Monitoring
Authors Gail Lipfert, Stewart Sandberg, Lee Slater, Andrew Reeve and Marc LoiselleThe site of a formerly uncovered sand/salt pile in Verona, Maine was used to investigate
the changes in resistivity over time of a fractured bedrock ground-water system. Terrain
conductivity of the area immediately down-slope from the site of the former sand/salt pile was
measured using a small horizontal loop electromagnetic (EM) profiling technique. High terrain
conductivity measurements delineate the contaminant plume. In areas where overburden is
shallow, anomalies in terrain conductivity along traverses indicated fracture locations. The angular
shape of the plume of high terrain conductivity represents the orientations of regional and local
bedrock fractures and indicates fracture control of the ground-water flow. A permanent array of
electrodes was established along six of the EM traverses and electrical resistivity measurements
were taken every one to two weeks over a five-month period. A correlation of rain events to
apparent resistivity changes are attributed to the migration of the plume.
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Applications Of Some New Techniques To Detect Groundwater Contamination At Mine Tailings Dams
Authors G. Buselli and K. LuWe have recently applied electrical and electromagnetic methods to two
environmental problems at minesites: firstly, to an acid mine drainage problem at the
tailings dam of a disused pyrite mine at Brukunga, South Australia, and secondly, to
the detection of any seepage from a tailings dam at the operating Ranger minesite,
Northern Territory, Australia. Using these examples, we stress the importance of the
use of combined methods for both measurement and interpretation of data.
At the first minesite, we used a combination of direct current (DC), transient
electromagnetic (TEM) and self-potential (SP) surveys to locate the source of
groundwater entering the tailings dam and to map the depth to water-table over the site.
At the second minesite, more extensive experimental surveys have been made with
these and the induced polarization (IP) method. The surveys include the use of a 2D
array of electrodes and measurements with a multichannel data acquisition system.
Results of a previous airborne electromagnetic survey have been interpreted using
newly-developed conductivity-depth imaging software.
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A Mise A La Masse Survey To Track Ground Water Cokduits In Weathered Bedrock Near A Salvage Yard
Authors John Jansen, Phillip Osborn and Michael WilsonA series of monitoring wells were installed as part of a ground water investigation around
a salvage yard. Most of the wells encountered relatively dense silty clay deposits and
shale. A few wells hit voids related to a paleochannel system filled with high TDS
ground water. A mise a la masse survey was conducted to map the trend of the
paleochanneis by placing a current electrode inside a monitoring well completed in a
channel feature. The survey identified the area of highest hydraulic conductivity and the
trend of the major channel system. The survey also appears to have mapped individual
minor channel features. The survey results were used to predict the trend of the
paleochannel system to the east of the site. The predicted location of the paleochannels
was confirmed by a test drilling program.
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An Integrated Approach To Monitoring A Field Test Of In Situ Contaminant Destruction
The development of in situ thermal remediation techniques requires parallel development
of techniques capable of monitoring the physical and chemical changes for purposes of
process control. Recent research indicates that many common contaminants can be
destroyed in situ by hydrous pyrolysis/oxidation (HPO), eliminating the need for costly
surface treatment and disposal. Steam injection, combined with supplemental air, can
create the conditions in which HP0 occurs. Field testing of this process, conducted in the
summer of 1997, indicates rapid destruction of polycyclic aromatic hydrocarbons (PAHs).
Previous work established a suite of underground geophysical imaging techniques capable
of providing sufficient knowledge of the physical changes in the subsurface during thermal
treatment at sufficient frequencies to be used to monitor and guide the heating and
extraction processes. In this field test, electrical resistance tomography (ERT) and
temperature measurements provided the primary information regarding the temporal and
spatial distribution of the heated zones.
Verifying the in situ chemical destruction posed new challenges. We developed field
methods for sampling and analyzing hot water for contaminants, oxygen, intermediates
and products of reaction. Since the addition of air or oxygen to the contaminated region is
a critical aspect of HPO, noble gas tracers were used to identify fluids from different
sources. The combination of physical monitoring with noble gas identification of the native
and injected fluids and accurate fluid sampling resulted in an excellent temporal and spatial
evaluation of the subsurface processes, from which the amount of in situ destruction
occurring in the treated region could be quantified. The experimental field results
constrain the destruction rates throughout the site, and enable site management to make
accurate estimates of total in situ destruction based on the recovered carbon. As of
October, 1998, over 400,000 kg (900,000 lb) of contaminant have been removed from the
site; about 18% of this has been destroyed in situ.
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Induced Polariza Tion Imaging Of A Jet Fuel Plume
Time-domain induced polarization data has been collected and analyzed for a site at the
Otis ANGB, Massachusetts Military Reservation, Cape Cod, Massachusetts. The
specific plume is designated FS- 12 and is due to break in the subsurface fuel transport
pipeline. Approximately 70,000 gallons of jet fuel were spilled in the early 1970’s. The
predominant contaminants are benzene and ethyl dibromide (EDB).
The data have been inverted to give resistivity and chargeability tomograms to depths of
300 feet and 1400 feet in extent. We also processed the IP time domain signals for short
and long times separately and produced a time domain gross spectral chargeability
difference. Both the chargeability and spectral chargeability difference show good
agreement with the known location of the plume from sampling wells.
The IP mapping provides detailed information that cannot otherwise be obtained from the
sparse borehole distribution.
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Self Potential Monitoring Of Jet Fuel Air Sparging
Authors Yervant Vichabian and Frank Dale MorganIn recent years, several remediation methods have been developed based on in-situ
oxidation. However, there are not efficient ways to monitor the effectiveness of these
methods in enhancing oxygen levels or delineating their zone of influence. In this
presentation we study the use of self potential (SP) geophysics to monitor the air sparging
and soil vapor extraction system at FS-12 on the Massachusetts Military Reservation,
Cape Cod, Massachusetts. Data has been collected over a time period of two years using
the gradient SP method with 130 permanent measuring stations. We have observed a
large 800 to 1000 mV SP anomaly in the region where the remediation system is in
operation. Using the Nemst equation, we convert the SP anomaly to the partial pressure
of oxygen, from which a contour plot is generated showing the effective area of sparging.
In this paper, we show that SP can be used to monitor remediation methods, which rely
on increasing oxygen levels in the subsurface.
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3-D Gpr Imaging Of Complex Fluvial Stratigraphy At The Boise Hydrogeophysical Research Site
Authors William R. Peretti, Michael D. Knoll, William P. Clement and Warren BarrashA series of three-dimensional (3-D) ground-penetrating radar (GPR) data sets were acquired
over the central wellfield area at the Boise Hydrogeophysical Research Site (BHRS). The survey
region is 30 m x 18 m and encompasses 13 wells. The goal of the surveys is to image the
complex fluvial (cobble-and-sand) stratigraphy around the wellfield. These images will be used
to construct 3-D models of the sedimentary architecture and to help constrain fine-scale models
of hydrologic and geophysical parameters at the site. The data sets were acquired using 25 MHz,
50 MHz, 100 MHz and 200 MHz antennas. Depth of penetration ranges from -9.6 m for the 200
MHz data to -22 m for the 25 MHz data. Processing significantly improves the reliability and
interpretability of the images. The images suggest that the deposit can be subdivided laterally
and vertically into several distinct units or radar architectural elements; these elements are
typically separated by erosional bounding surfaces. Horizontal bedding, cross-bedding and
channel structures are clearly evident in the 100 MHz and 200 MHz data, and a clay layer that
underlies the cobble-and-sand aquifer at -20 m depth is successfully imaged in the 25 MHz and
50 MHz data. The water table, at a depth of l-2 m, is imaged in the 100 MHz and 200 MHz data.
Time slices and vertical cuts through the data volumes are used to identify the shape and
orientation of the different architectural elements, and to accurately locate important
hydrostratigraphic boundaries. These data are being used to construct a 3-D model of the
hydrogeologic zonation of the aquifer. Hydrologic and geophysical parameter values associated
with each zone will be determined from additional field measurements (e.g., hydraulic tests in
wells, crosshole radar and seismic tomography, transient electromagnetics, and well logs). The
3-D GPR surveys provide valuable information about the location, scale and geometry of
different stratigraphic units at the BHRS.
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An Imaging Algorithm For Gpr Data
Authors Yoshinori Sanada and Yuzuru AshidaThe finite difference time domain (FDTD) method is calculated by the explicit
finite approximation scheme of Maxwell’s curl equations. Since it allows arbitrary
electrical conductivity and permittivity variations within a model, the FDTD method
has become one of the powerful forward modeling methods for electromagnetic (EM)
phenomena. On the other hand, the reverse time migration is the imaging algorithms,
which is performed by inserting the recorded data as boundary conditions at each
recorder position in reverse time order. Due to the advantage of simple calculation
algorithm and applicability to arbitrary model, both methods are powerful tools for GPR.
In the present paper, the synthetic GPR data are calculated by using of the FDTD
method with the exploding reflector method. The reverse time migration is formulated
using FDTD scheme and applied to model with lossless and lossy media. In lossless
media, the forward and reverse time schemes are expressed by the completely same
scheme. The proposed method is successfully applied to synthetic data for two models,
these are steeply dipping structure and point diffractors model. In lossy media, the
forward scheme includes diffusion term, while the reverse time scheme includes
divergence term. In such a case, we show the condition that the EM wave velocity is
regarded as constant, then this methodology is applicable successively. We also discuss
the reverse time migration for the lossy media after the amplitude recovery under the
lossless media condition.
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Terrain- Permittivity Mapping: Gpr Measurements Of Near-Surface Soil Moisture
Authors David P. Lesmes, Robert J. Herbstzuber and David WertzGPR can be used to rapidly and non-intrusively measure soil moisture content
over spatial scales that are intermediate between the point measurement techniques (e.g.
TDR and neutron probes) and remotely sensed soil moisture measurements which are
made at the regional scale (e.g. airborne SAR measurements). In bi-static GPR surveys
the direct ground wave passes from the transmitter to the receiver through the nearsurface
soil. The GPR ground wave velocity can therefore be used to determine the
permittivity (or dielectric constant) of the near-surface soil. Estimates of soil moisture
content can be obtained using dielectric mixing equations. Variance in the velocity of the
ground wave can largely be attributed to variance in the level of soil moisture. We are
using GPR ground wave velocity measurements, with a constant antenna off-set, to map
lateral variations in terrain permittivity and to estimate near-surface soil moisture content.
Experiments have been conducted to determine the effects of frequency, antenna spacing,
and soil type on the soil moisture estimates and the effective depth of penetration.
Furthermore, we have used this methodology to monitor changes in soil moisture during
controlled spill experiments. Ongoing experiments include the monitoring of seasonal
fluctuations in soil moisture over a grass covered field at the Weston Geophysical
Observatory in Weston, Massachusetts.
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An Investigation Of Cross-Borehole Ground Penetrating Radar Measurements For Characterizing The 2D Moisture Content Distribution In The Vadose Zone
Authors Lee Paprocki and David AlumbaughThe use of cross-borehole ground penetrating radar (GPR) imaging for determining the two dimensional (2D) in situ moisture content distribution within the vadose zone is being investigated. The ultimate goal is to use the GPR images as input to a 2D hydrologic inversion scheme for recovering the van Genuchten parameters governing unsaturated hydraulic flow. Initial experiments conducted on synthetic data have shown that at least in theory, cross-borehole GPR measurements can provide realistic estimates of the spatial variation in moisture content that are needed for this type of hydrologic inversion scheme. However, the method can not recover exact values of moisture content due to 1) the break down of the empirical expression often employed to convert GPR velocity images to moisture content, and 2) the smearing nature of the imaging algorithm. To test the applicability of this method in a real world environment, crossborehole GPR measurements were made at a hydrologic/ geophysical vadose zone test site in Socorro, New Mexico. Results show that the GPR images compare well with the
uncalibrated borehole neutron log data. GPR data acquisition will continue once an infiltration test has started, and the results from these measurements will be employed in a 2D hydrologic inverse scheme.
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Ground Penetrating Radar & Avo
Authors Philip M. Reppert, Frank Dale Morgan and M. Nafi ToksozThis presentation concerns the use of Amplitude Versus Offset (AVO) with ground
penetrating radar (GPR) data. We demonstrate that AVO may have possible uses with
GPR. Theory is presented in this paper on the principle of AVO as applied to
electromagnetic (EM) waves. The theory is demonstrated on field data obtained over a
drain field in Massachusetts.
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Conversion Of Hydraulic Conductivity To Synthetic Radar Traces
More LessIn the interest of interpreting radar data and establishing a empirical correspondence between
hydraulic conductivity and ground penetrating radar data, hydraulic conductivity logs have
been converted to synthetic radar traces. The assumption in the computation is that hydraulic
conductivity is closely related to porosity and thus water content and dielectric constant.
The synthetic radar traces have been used to interpret the radar cross section in terms of
zones of hydraulic conductivity.
In the absence of a deterministic model between radar waveforms and hydraulic conductivity
empirical relations are sought. Radar data have been acquired at the MADE site near Columbus,
Mississippi. Hydraulic conductivities measured in wells have been converted to dielectric
constant using a simple empirical relationship and used to compute the radar traces that
would be obtained at the borehole. The comparisons with the field radar traces are encouraging.
Key words: radar, hydraulic conductivity, synthetic radargram
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Investigation Of Mountainous Rock Destruction: A New Physicothematical Conception
Authors A.L. Aleinikov, V.T. Belikov and L.V. EppelbaumInvestigation of mountainous rock destruction under different thermodynamic conditions
is one of the most important problems of the engineering hazard. It was earlier considered
that this destruction is taking place when at least one component of the stress tensor
reaches some critical value called as a material strength. However, conducted analysis
allowed us to conclude that such a notion is correct only for a relatively short-term action
and is unsuitable by a prolonged stress to target. On the basis of the detail theoretical
analysis we propose a new physico-mathematical conception describing the destruction
process as a phase transition. From this viewpoint, generation of microfault is an initiation
of a new phase. Such a generation causes emission of a definite number of seismo-acoustical
impulses. Quantity of the impulses during the time unit shows an intensity of process
destruction and frequency of oscillation indicates dimension of the microfaults forming.
Thus, the suggested conception allows to develop procedures for monitoring of durability
of different artificial underground constructions: mines, reservoirs and military objects as
well as other artificial and natural structures.
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Use Of Vsp Techniques To View, In 3D, Partially Saturated Layers In The Shallow Subsurface At Lawrence Livermore National Laboratory, California
Authors Paul A. Milligan, James W. Rector III and Robert BainerA multi-offset VSP (vertical seismic profiling) method was developed to help define aquifer boundaries and below
water table partially saturated zones at the Lawrence Livermore National Laboratory, Livermore Site, California.
The VSP method consisted of using a multilevel hydrophone array giving 48 channels of recorded seismic data per
shot. Hydrophone spacing was 0.5 m, with anti-tubewave baffling devices inserted between each phone, and at each
end of the array to slow down and attenuate tube wave noise contaminating the desired data signals. The seismic
source consisted of an impact weight-drop machine.
The VSP data was processed, and inverted to produce 2D p-wave interval velocity sections with up to 0.5 m of vertical
resolution in the unconsolidated sediments below the water table. Multiple 2D velocity sections were created,
corresponding to radial arms of walk-away shot point records from multiple wells. These 2D velocity sections were
then visually projected into the 3D survey volume, together with well locations, predefined hydrostratigraphic unit
(HSU) layer boundaries, and the interpreted isopach map of a major HSU of interest. The interactive graphical display
of all these data in 3D allowed correlations to be made between the VSP velocity images and the pre-existing data.
The discovery of several low velocity zones below the water table was attributed to partially saturated pore spaces.
Two thin (less than 1 m thick) layers with p-wave velocities as low as 500 m/s appeared to be perched on top of major
aquifers undergoing pump extraction and treatment. Gas analysis from water samples taken from one of the aquifers
indicated normal atmospheric air as a probable gas source. High pumping flow rates (20 to 30 gal/min) may
help to explain how venturi action could be responsible for the intake of air from the vadose zone into porous but
less permeable silty-sand units overlying sand-gravel aquifers. Possible uses for this VSP technique would be to delineate
the zone of pumping influence, and help in the choice of suitable new well locations for either pumping or
monitoring.
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Hydrogeological Property Estimation Using Tomographic Data At The Boise Hydrogeophysical Research Site
Authors John E. Peterson, Ernest L. Majer and Michael D. KnollCrosswell seismic and radar data were acquired at the Boise Hydrogeophysical Research
Site (BHRS) as part of an effort to characterize the hydrological property distribution in a
heterogeneous alluvial aquifer. The dielectric constant and amplitude attenuation values
obtained from inversion of the radar data, as well as the seismic P-wave velocity values
obtained from inversion of the seismic data, reveal similar spatial patterns. Comparison of
this tomographic information with coincident wellbore logs suggest that the geophysical
attributes are sensitive to hydrogeological variations. Information obtained from the radar
tomography data were used to produce 2-D, high-resolution images of porosity and electrical
conductivity. Comparison of these images with coincident log data reveal that these estimates
are reasonable and suggests that the tomography data will be useful at this site for delineating
variations in hydrological parameters.
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Dielectric Dependence On Salinity And Probe Length In Tdr-Measurements
Authors Sari Penttinen, Pekka Hanninen and Raimo SutinenTime domain reflectometry (TDR) is widely used in soil sciences and forestry to determine soil
dielectric properties and water content. The effects of TDR probe length, geometry and water
electrical conductivity (%) on dielectric values were studied. The three-prong TRD probes, 0.06
m in diameter and lenght varying from 0.035 to 0.15 m with varying the spacing of the probes
tested in water, whose electrical conductivity (%) varied from 0.6 mS/m to 700 mS/m. The
scattering in dielectric values increased significantly, when the probe lengt was 0.035 m or
shorter. However, the scatter level was minor with probes bend outward or inward. Probe
spacing greater than 0.06 m resulted in unreliable readings. The increase of electrical
conductivity of water with %> 200 mS/m resulted in scattered data, particularly with the 0.035-
m-long probes. Dielectric data for all probe lenghts were scattered with water electrical
conductivity with oW> 500 mS/m.
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Field Investigation Of Salt Transport Processes Using .Resistivity/Ip Imaging
Authors Lee Slater and Stewart K. SandbergTwo examples of the use of combined resistivity/induced polarization (IP) monitoring of salt
transport under natural hydraulic loads are presented. Previous workers have performed electrical
monitoring of the transport of a tracer artificially injected into the subsurface. The detection of
tracer transport due to natural hydraulic processes is a more difficult goal as neither the hydraulic
load nor the resistivity contrast can be controlled. Tide-induced salt transport at the saltwaterfreshwater
interface was investigated in the first study. 2D resistivity and IP models resolved the
structure of the interface. The IP modeling provided greater clarity of the subsurface
hydrology/geology than the resistivity modeling alone. Modeling of electrical changes over a
tidal cycle revealed resistivity increases in the near surface and at depth, 5-l 5 m up-beach of the
high tide mark. The results indicate a phase lag between the subsurface hydrological response
and the tidal cycle. In the second study, salt transport from the site of an old road-salt storage pile
was investigated. The hydraulic mechanism was natural recharge events that occurred over a
four-month period. 2D conductivity and IP models resolved the subsurface distribution of salt,
initially identified from an EM3 1 survey. Modeling of resistivity change on lines spaced 33.5 m
apart revealed changes at the location of salt contamination. The changes on each line appear
closely coupled and correlate with the recharge pattern over the monitoring period. The studies
indicate that salt transport occurring under natural hydraulic conditions can be detected with
resistivity, and to some extent, IP.
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Self Potential Mapping Of Contaminants
Authors Yervant Vichabian, Philip Reppert and Frank Dale MorganVarious geophysical techniques are useful for detection and mapping of subsurface
contamination plumes. Self potential seems to be a particularly promising technique due
to its cost effectiveness and speed of acquisition and processing. The electrochemical
phenomena of organic contaminants and their interactions with microorganisms in the
subsurface provide a detection method for self potential (SP) geophysics. In this
presentation, we couple biodegradation with several examples of SP detecting
contaminant plumes.
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An Electromagnetic Induction Tomography Field Experiment At Lost Hills, Ca
Authors H. Michael Buettner and James G. BerrymanWe have collected borehole to surface electromagnetic induction field data for a shallow steam
injection that is underway at Mobil Oil’s Lost Hills-3 field in San Joaquin Valley. Earlier
work had been done at the same site by Wilt et al. (1996). This site is an interesting test
for techniques under development for environmental engineering, because it can be viewed as
an excellent analog of a shallow environmental remediation using steam injection. Surface
magnetic field data (vertical and radial fields, magnitude and phase) were collected using 18
receiver stations along two profiles which ran radially from the EM transmitter well from 5
m to 120 m. The data at each surface station were collected while the EM transmitter was
raised slowly from a depth of 120 m to a final depth of 20 m. As part of this experiment, a
calibration of the EM transmitter was also performed. Magnetic field data from Lost Hills were
successfully collected, including both vertical and horizontal (surface radial) magnitude and
phase data along a northerly profile and along a westerly profile. We have observed that the
radial receiver data appear to be better behaved than the vertical receiver data, suggesting that
these data may be less sensitive to environmental clutter (numerous metallic pipes crisscrossing
the site at the surface) than are the vertical data. Some simple 1-D modeling has been done to
confirm that the expected conductivity change in the steam zone should produce an observable
anomaly in the measured data when comparing the pre-steam to the post-steam conditions.
Results of this test were positive. Further analyses of these data making use of a new code
developed in a companion paper are in progress and will presented separately.
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High-Performance Computational And Geostatistical Experiments For Testing The Capabilities Of 3-D Electrical Resis’Iiance Tomography
Authors Steven Carle, Abelardo Rarnirez, William Daily, Robin Newmark and Andrew TompsonThis project explores the feasibility of combining geologic insight, geostatistics, and high-performance
computing to analyze the capabilities of 3-D electrical resistance tomography (ERT), Geostatistical
methods are used to characterize the spatial variability of geologic facies that control subsurface
variability of permeability and electrical resistivity. Synthetic ERT data sets are generated
from geostatistical realizations of alluvial facies architecture. The synthetic data sets enable comparison
of the “truth” to inversion results, quantification of the ability to detect particular facies at
particular locations, and sensitivity studies on inversion parameters.
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Electrical Imaging Of Engineered Hydraulic Barriers
Authors William Daily and Abelardo RamirezElectrical resistance tomography (ERT) was used to image the full scale test
emplacement of a thin-wall grout barrier installed by high pressure jetting. ERT was also
used to monitor the waterflood of a thin-wall grout barrier to vertfy its hydraulic integrety.
Both case studies were done by comparing images of electrical resistivity before and after a
change was induced in the subsurhace. Barrier materials or flood water were imaged as
anomalies which were more electrically conducting than the native sandy soils at the test
sites. Although the spatial resolution of the ERT was not sufficient to resolve flaws in the
barrier under construction smaller than a reconstruction voxel(50 cm on a side), the images
did show the spatial extent of the barrier materials and therefore the general shape of the
structure.
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Laboratory Scale Tests Of Electrical Impedance Tomography
Authors Abelardo Ramirez, William Daily, Andrew Binley and Douglas LaBrecqueElectrical impedance tomographs (magnitude and phase) of known, laboratory-scale
targets are reported. Three methods are used to invert electrical impedance data and their
tomographs compared. The first method uses an electrical resistance tomography (ERT)
algorithm (designed for DC resistivity inversion) to perform impedance magnitude
inversion and a linearized perturbation approach (PA) to invert the imaginary part. The
second approximate method compares ERT magnitude inversions at two frequencies and
uses the frequency effect (FE) to compute phase tomographs. The third approach,
electrical impedance tomography (EIT), employs fully complex algebra to account for
the real and imaginary components of electrical impedance data. The EIT approach
provided useful magnitude and phase images for the frequency range of 0.0625 to 64 Hz;
images for higher frequencies were not reliable. Comparisons of the ERT and EIT
magnitude images show that both methods provided equivalent results for the water
blank, copper rod and PVC rod targets. The EIT magnitude images showed better spatial
resolution for a sand-lead mixture target. Phase images located anomalies of both high
and low contrast IP and provided better spatial resolution than the magnitude images.
When IP was absent from the data, the EIT algorithm reconstructed phase values
consistent with the data noise levels.
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Simultaneous Acquisition Of P- And S-Wave Crosswell Seismic Profiles In A Contaminated Basalt Aquifer
Authors Thomas M. Daley, John E. Peterson and Ernest L. MajerMultiple seismic crosswell surveys have been acquired by LBNL in a fractured basalt aquifer
at Idaho National Engineering and Environmental Laboratory (INEEL). Most of these surveys
used a high frequency piezoelectric seismic source to obtain P-wave velocity tomograms.
Additionally, we deployed a new type of borehole seismic source, know as an orbital vibrator, in
a crosswell seismic survey as part of the subsurface characterization program at this
contaminated groundwater site. This source, know as an orbital vibrator, allows simultaneous
acquisition of P- and S-waves. The orbital vibrator was developed for oil field applications and,
to our knowledge, this is the first environmental scale crosswell application. Both velocity and
attenuation tomograms have been calculated. The velocity tomograms show a relationship to
contaminant propagation in the groundwater (as measured by logs and cores). Zones of high
contaminant flow are consistent with zones of low velocity (both P- and S-wave) and high
attenuation. We believe horizontal fracture zones at the boundaries of basalt flows are
controlling the contaminant flow and the seismic properties. Additionally, high amplitude guided
waves are observed and we believe these waves delineate thin (l-2 m) zones of velocity contrast
which relate to fracturing and, in some instances, coincide with contaminate flow.
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Reverse Vsps And Crosshole Seismic Tomography While Coring
Authors William P. Clement, Lee M. Liberty and Michael D. KnollAt the Boise Hydrogeophysical Research Site, numerous 20 m deep wells were continuously
cored with a split spoon sampler to detail geologic changes beneath the site. During the coring of
one of these wells, we recorded the energy radiating from the drill stem using a combination of
downhole hydrophones and surface geophones. The hydrophone strings were located in a pair of
adjacent wells and the geophones were located along the surface between these wells and the
well being cored. The experiment’s geometry provides a series of reverse VSPs and crosshole
tomographic data sets that can help distinguish P-wave velocity changes in the subsurface.
Energy from the core tip is not necessarily the first arrival. However, the near continuous
recording of the source as it penetrates the ground enables us to locate the energy from the core
tip. We also record energy when the source is in the vadose zone. Comparing the seismic while
coring results with a similar experiment using a borehole sparker source confirms the reliability
of recording seismic energy generated by the split spoon sampler. Core tip recording is an
inexpensive seismic method that has great potential for borehole-to-surface and crosshole
tomographic imaging at relatively large offsets in near-surface environments.
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Surface And Borehole Seismic Characterization Of The Boise Hydrogeophysical Research Site
Authors Lee M. Liberty, William P. Clement and Michael D. KnollWe conducted borehole to borehole, borehole to surface, and surface seismic experiments
to optimize data acquisition parameters, obtain a seismic velocity model, and to characterize seismic
stratigraphic units in a shallow aquifer at the Boise Hydrogeophysical Research Site. The
aquifer consists of coarse (cobble-and-sand) fluvial deposits underlain by clay at 18-2 1.5 m depth.
We acquired data with a downhole seismic source (sparker), a sledge hammer source, a hydrophone
string, a borehole geophone, and a surface geophone array to compare seismic signal quality
and to place limitations on each seismic method. To fully characterize seismic reflections, the
source-receiver geometry is an important parameter for both borehole and surface experiments.
Direct arrivals and the presence of seismic reflections suggest a correlation between porosity
changes and seismic velocities at the site. We have defined four seismic stratigraphic horizons
that correlate with surface and borehole ground penetrating radar results, geophysical logs, and
lithologic logs. These results provide an initial framework for hydrologic modeling.
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Characterization Of Shear-Wave Velocity Anisotropy In The Upper 33 M Of A Dipping, Consolidated Sandstone
Authors Gilein J. Steensma, Paul E. Murray, Michael L. Batzle and Thomas M. BoydThe extraction of groundwater or hydrocarbons from the subsurface and the effective remediation
of contaminated sites depend upon knowledge of preferential fluid migration. Shear-waves (s-waves)
have proven to be an effective tool to ascertain fracture orientation and the stress regimes responsible for
fractures. Grain and void alignment due to stratigraphy, rock texture and intergranular pore space can
cause s-waves velocity anisotropy, or variations in velocity with direction. S-waves with particle motion
parallel to the stiffer direction of the medium propagate faster than those parallel to the more compliant
direction of the medium.
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Object Identification Using Multifrequency Emi Data
Authors Dean Keiswetter, I.J. Won, Bruce Barrow and Tom BellUnexploded ordnance (UXO) cleanup is the number one priority Army Cleanup Problem
requirement and is identified as a major problem throughout the Department of Defense (DOD).
A recent SERDP technical report summarizes the status of capability for buried UXO detection,
discrimination, and identification as follows: (a) can detect UXO, within definable limits; (b)
cannot effectively discriminate UXO anomalies from ‘false alarm’ anomalies; and (c) cannot
identify UXO. False alarm anomalies are defined here as geophysical anomalies caused by
buried UXO debris, other metallic objects, gravel and cobbles, soil heterogeneities, tree roots,
and other natural and cultural features. False alarm anomalies significantly contribute to the cost
of UXO remediation due to the large number of unnecessary excavations, A major initiative in
the research and development community, therefore, is to develop discrimination (target
identification) capabilities. One potential methodology for target identification involves utilizing
the broadband scattered electromagnetic induction response. This technique, which is known as
Electromagnetic Induction Spectroscopy (EMIS), h as recently become feasible due to the
development of the GEM-3 sensor. The GEM-3 is an efficient, broadband, handheld EMI sensor
than employs a unique monostatic coil design. Analyzing the EMI spectral content for target
identification is not new. In fact, elementary EM theory states that an object must exhibit
different responses at different frequencies. All fundamental EM equations involving a timevarying
source testify as such. By fully characterizing and identifying an object without
excavation, we should be able to significantly reduce the number of false targets. EMIS should
be fully applicable to many other problems where target identification and recognition (without
intrusive search) are important.
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Geophysical Qa/Qc For A Uxo Eeka, Fort Ritchie Army Garrison, Md
Authors Kent Boler, Mike Ervine, Alex Smith, John Breznick and Chris EvansICF Kaiser, under contract to the US Army Corps of Engineers, Baltimore District
(CENAB) performed an engineering evaluation/cost analysis (EE/CA) in support of Base
Realignment and Closure (BRAC) to assess potential hazards due to unexploded
ordnance (UXO) in former and suspected range areas at Fort Ritchie Army Garrison, MD
(Fort Ritchie). EM61 geophysical surveys were conducted over portions of the now
developed cantonment area as part of a statistically based sampling plan to locate and dig
metallic anomalies potentially representing UXO. Select QA/QC aspects of the EM61
based ordnance location and sampling program are presented. Performance testing
documents a significant decrease in non-UXO anomalies vs mag-and-flag techniques at
this site. EM61 calibration pit results for simulated UXO items and analysis of 10%
replicate grid data show acceptable data accuracy, precision, and comparability.
Tracking of calibration pit test results show negligible variation of peak amplitudes
between instruments, or with variations in temperature and precipitation.
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Locating And Determining Dimensionality Of Uxos Using Time Domain Electromagnetic Induction
Authors Leonard R. Pasion and Douglas W. OldenburgIn this paper we assume that the Time Domain Electromagnetic (TEM) response of a buried
axisymmetric metallic object can be modelled as the sum of two dipoles centered at the midpoint of
the body. The strength of the dipoles depends upon the relative orientation between the object and
the source field, and also upon the shape and physical properties of the body. Upon termination of
the source field, each dipole is assumed to decay as k (t + a)-’ e-‘/y. The parameters k, LY, p and y
depend upon the conductivity, permeability, size and shape of the object, and these can be extracted
from field or laboratory measurements by using a nonlinear parametric inversion algorithm. Our
preliminary work, carried out using an analytic solution for a sphere and laboratory measurements
of steel plates, suggest the following methodology. The value of p might be used as a diagnostic
to assess whether the metallic object is non-magnetic or magnetic. If the object is thought to be
magnetic, then the ratios of ICI/k2 and pi//3 2 are diagnostic indicators as to whether the geometry
is plate-like (uninteresting) or rod-like (a high candidate for being a UXO).
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A Field Evaluation Of Airborne Techniques For Detection Of Unexploded Ordnance
Authors W.E. Doll, P. Hamlett, J. Smyre, D. Bell, T.J. Gamey and J.S. HolladayUnited States Defense Department estimates indicate that as many as 11 million acres of
government land in the U. S. may contain unexploded ordnance (UXO), with the cost of
identifying and disposing of this material estimated at nearly $500 billion. The size and
character of the ordnance, types of interference, vegetation, geology, and topography
vary from site to site. Because of size or composition, some ordnance is difficult to
detect with any geophysical method, even under favorable soil and cultural interference
conditions. For some sites, airborne methods may provide the most time and cost
effective means for detection of UXO. Airborne methods offer lower risk to field crews
from proximity to unstable ordnance, and less disturbance of sites that may be
environmentally sensitive.
Data were acquired over a test site at Edwards AFB, CA using airborne magnetic,
electromagnetic, multispectral and thermal sensors. Survey areas included sites where
trenches might occur, and a test site in which we placed deactivated ordnance, ranging in
size from small “bomblets” to large bombs. Magnetic data were then acquired with the
Aerodat HM-3 system, which consists of three cesium magnetometers within booms
extending to the front and sides of the helicopter, and mounted such that the helicopter
can be flown within 3m of the surface. Electromagnetic data were acquired with an
Aerodat 5 frequency coplanar induction system, deployed as a sling load from a
helicopter, with a sensor altitude of 15m. Surface data, acquired at selected sites,
provide a comparison with airborne data. Multispectral and thermal data were acquired
with a Daedelus AADS 1268 system. Preliminary analysis of the test data demonstrate the
value of airborne systems for UXO detection and provide insight into improvements that
might make the systems even more effective.
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A Comparison Of Towed And Mounted Helicopter Magnetometer Systems For Uxo Detection
Authors T. Jeffrey Gamey and Reinhold MahlerTraditional helicopter magnetic surveys have always utilised a towed platform, or bird, to
remove the need to compensate for the magnetic effects of the helicopter. Such platforms have
evolved to include total field, vertical gradient and triaxial gradient configurations. For detection
of small objects in the near surface, the principle limitation of towed systems is positional control
in three dimensions. In particular, the sensor height above the ground (Z) is critical for small
objects, and consistency as much as the actual altitude is an important consideration for
interpretation.
For environmental surveys with towed systems, nominal survey heights are reduced from 30 to 5
or 10 metres above ground level, tree cover permitting. In order to achieve these altitudes safely,
air speed is reduced which subsequently reduces aerodynamic stability. Speed changes also alter
the distance between helicopter and platform making control more difficult. Higher speeds drag
the bird back and upwards, and usually into a nose down orientation. Platform altitude is
monitored by laser altimeter and displayed to the pilot, but most pilots find this insufficient
warning, preferring direct visual observation. Depth perception from the top of a 30m cable is
still marginal, and minimum survey heights are limited by caution to 5m clearance under ideal
conditions (+/-3m) with 7-10m being more typical altitudes. For positioning in X&Y, lines can
theoretically be flown as close as the budget will allow. In practice, X&Y control is limited to
10m line spacing due to +/-5m of bird swing.
One solution to this problem is to mount sensors directly onto the helicopter in the tips of
stingers or booms. This provides a significant improvement in the pilot’s control, but requires a
more sophisticated data acquisition and processing system. When the mounting platform is a
direct extension of the helicopter and is placed at eye level for perspective, positional control can
be improved to +/-lm in any direction.
IABG in Germany has supported several years of airborne platform development through
European field projects. In 1997/98, the first phase of a research project consisted of comparison
surveys of Aerodat’s towed triaxial gradiometer and their boom mounted system. Tests were
conducted over a controlled test site, which included targets such as UXO, barrels, UST’s, pipes
and debris in varying amounts and configurations. This paper presents some of the results of
these comparative tests. Other tests by IABG at this site included multi-spectral and
photogrammetric surveys, but are not discussed within the scope of this paper.
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The Application Of An Integrated Magnetometer/Global Positioning System For An Unexploded Ordnance Investigation
More LessGeophysical techniques have been used for many years to detect unexploded
ordnance (UXO) buried in the subsurface. UXO detection can be performed by using
either “mag and flag” methods where anomalous metallic items are located without data
collection and flagged for excavation or dug immediately, or using a data collection
system where anomalous areas are selected from the data record and the positions are
reacquired for excavation. In recent years, recorded data surveys have begun to take
precedence over unrecorded surveys.
There are two elements to a successful recorded data geophysical survey:
1. Data collection (magnetic/electromagnetic field)
2. Location tracking.
Having only one of the above elements without the other yields nearly useless
information and certainly makes for an unsuccessful survey. Traditional methods of
tracking the location of data collected by the geophysical survey instrument have been to
use either a time/distance method or a mechanical measurement tool (i.e. wheel
odometer). Technological developments in survey equipment and the Global Positioning
System (GPS) have added a new way of tracking position during surveys in select
environments.
A geophysical investigation was conducted at a former military range in Mississippi
using an integrated magnetometer/GPS system. The use of the integrated system yielded
extremely good results in open areas but had limited use in areas under heavy tree
canopy. Results of the surveys performed indicate that the integration of GPS with
geophysical instruments is a viable tool and may become the standard operating
procedure in certain environments. The limitations of the integrated system primarily
stem from the ability of the GPS system to “speak” with satellites through tree cover.
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Mapping Buried Metallic Objects And Titaniferous Placers In The Mississippi Sound, Gulf Of Mexico
Authors Jeff Wynn and Kevin LaurentRecent experiments with a marine induced polarization (IP) streamer system have shown
that it can find and map titaniferous placers on and beneath the sea floor (Wynn and Laurent,
1998) and facies changes in the substrate beneath sandy shoals (Wymr and others, 1998). Close
examination of profile data acquired in the Mississippi Sound, however, shows that the system
can also detect certain conductive, polarizing objects that are buried beneath the sea floor and not
discernible with conventional bathymetry. The streamer system is designed to detect
polarizeable materials down to at least 6 meters below the sediment-water interface. The recent
data show broad phase-shift (IP) anomalies along the east side of Cat Island, off the coast of
Biloxi. MS. Dark, titaniferous sands can be seen in dissected benches and berms on the island’s
coastline, reinforcing the conclusion that the IP system is mapping the ilmenite-rich (FeTiO,)
sediments reported in shoals there (Foxworth, 1962). Interspersed in these data, however, are
several narrow electrical anomalies of two kinds: resistivity, and resistivity-IP anomalies. Both
kinds show pronounced drops in the already-low resistivity, and several of these also have
coincident phase-shift anomalies. The polarizing objects observed are -10 to 20 meters across,
but the IP anomalies can be seen - 20 to 40 meters laterally from their centers. The sources of
these anomalies are probably man-made in origin, buried under a veneer of modern sediments.
We speculate that these are shipwrecks, sunken buoys or parts thereof, lost and later buried (in
water now about 3 meters deep) by Hurricane Camille, which passed through the area in 1969.
We cannot, however, preclude emplacement and burial at an earlier time.
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New Field And Modeling Results From A Simulated Waste Pit Using The Enhanced Very Early Time Electromagnetic (Vetem) Prototype System
Tests in July, 1998, of an improved version of the prototype VETEM system demonstrated
improved depth of investigation at the Cold Test Pit (CTP) at the Idaho National Environmental
and Engineering Laboratory (INEEL). The improved depth of investigation is due primarily to
the development of larger loop antennas and a new transmitter capable of driving up to 30 times
more current than the original transmitter into the larger loop. An overlapped antenna
configuration was tried and proved effective in detecting buried objects. New display software
allows us, for the first time, to generate area1 time-slice displays of our data in the field for fast
qualitative evaluation. Comparisons of results using two different antenna configurations over
the Large Object Pit portion of the CTP show generally good agreement, but show an apparent
position offset of the two data sets from each other. The test over the Calibration Cell portion of
the CTP using the overlapped antenna configuration successfully located most of the indicated
targets in the cell. Results over both portions of the CTP suggest that the indicated locations of
some of the buried objects may not be completely accurate. New antenna and 3D forward
modeling codes run using an input waveform, antenna size and configuration, and system
bandwidth matching those of the VETEM system produce waveforms and show sensitivities
similar to those seen in recorded field data.
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Vertical Radar Profiling To Determine Dielectric Constant, Water Content And Porosity Values At Well Locations
Authors Michael D. Knoll and William P. ClementA vertical radar profiling (VRP) experiment was conducted at the Boise Hydrogeophysical
Research Site to determine if direct arrivals and reflections can be recorded using the surface-toborehole
survey geometry. The receiving antenna was deployed downhole to insulate it from
cultural noise. The transmitting antenna was located on the surface near the wellhead and
oriented radially to the well axis. Although the antenna polarizations are perpendicular, we were
able to record radar direct-arrivals and reflections. Picked first-arrival traveltimes were inverted
to determine layer interval velocities. The VRP-derived velocity estimates fall in the same range
as velocity estimates determined from crosshole radar tomography at the site; average velocities
for the unsaturated and saturated zones are 0.140 rn/ns and 0.080 m/ns, respectively. Resolution
of the VRP-derived velocity estimates is significantly better than the resolution of CMP-derived
velocity estimates. Dielectric constant and porosity estimates were also derived from the VRP
data using a simple petrophysical model, and compared to porosity estimates derived from
neutron logging. Correlation between the two porosity estimates is encouraging. While the VRP
method has not been widely used in site investigations to date, the results of this study suggest
that VRPs provide an accurate, high-resolution, and cost-effective means of obtaining dielectric
constant, EM velocity, volumetric moisture content and porosity values at well locations.
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Borehole Geophysics Applied To The Study Of Landfill Sites In Fractured Bedrock Terrains
Authors Horatio Ferriz and William PedlerGeotechnical and hydrogeologic studies for landfill sites in the fractured bedrock environment can
be a technically challenging prospect. Many of the problems involved in landfill construction in
fractured bedrock can be solved by detailed surface mapping of fracture density and orientation,
but ultimately data has to be collected from the subsurface via exploratory wellbores. Fracture
density and orientation can be obtained through acoustic televiewer logs or digital borehole
imaging logs, but identifying the fracture or fracture group that is water-bearing (hydraulically
conductive) is critical in characterizing the flow of water at the study site.
Hydrophysical logging and digital borehole imaging were used to log 13 wells to evaluate a
prospective canyon landfill site in weathered crystalline rocks. Hydrophysical cross-hole testing
was employed to evaluate hydraulic connections between wells and estimate medium scale
hydraulic conductivity. The results of this study found that: (1) For most wells, the more highly
transmissive intervals were within 30 feet of the piezometric level. This behavior is consistent
with the deeply weathered nature of the bedrock, which behaved in a manner hydraulically similar
to a silty sand. The hydraulically conductive intervals ranged in thickness between 2 and 8 feet,
and represented between 1% and 5% of the total length of the bedrock section, (2) In all but one
instance, the water bearing intervals were within 60 feet of the piezometric surface. In other
words, groundwater flow was largely concentrated in shallow fracture zones. (3) Based on the
hydrophysical logging results for ambient horizontal flow, a typical range of specific discharge
values for a discrete fractured interval between 0.3 and 0.02 A/day was observed at the study site.
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A Wireline-Operated Downhole Packer For Eiydraulic Measurements In Boreeoles
Authors F.L. Paillet, J.H. Williams and A.E. HessA wireline-operated packer was designed for reconnaissance logging in open boreholes and
field tested at a site in Belvidere, Illinois. Although the wireline packer uses a single downholeinflated
packer, analysis converts the wireline-packer data to estimates of hydraulic properties of
zones between adjacent packer measurement stations. A synthetic data example shows how the
single packer can be used to efficiently and effectively identify the depth intervals where
hydraulically active fractures or bedding planes intersect a borehole. Data analysis subsequently
provides estimates of the hydraulic head, transmissivity, and water quality for each of these zones.
Field tests of the wireline packer in Illinois produced estimates of zone hydraulic head and relative
transmissivity that agreed with values given by conventional straddle-packer hydraulic tests.
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Use, Comparison, Presentation, And Interpretation Of Borehole Image And Acoustic Televiewer Technology
By T.M. StaatzBorehole televiewers and image systems are used to accurately show sub surface
structural features. The borehole image system can show features not evident with the
acoustic televiewer under ideal conditions. Depending on the hole conditions, and the
data desired, either the image system or the televiewer may be the preferred instrument.
This paper will address:
1. General - The operation, calibration, survey setup, and complimentary logs to run
with each of these instrument types.
2. Comnarisons - The strengths, weaknesses, and similarities of the image system and
acoustic televiewer.
3. Data acauisition - Data gleaned from surveys can include: fractures and fracture
orientation; lithology and lithlogic changes; strike and dips; bedding planes, joint
sets, and foliation; compressional, extensional and horizontal stress determination;
information on how the borehole was drilled; and orientation of core. Interpretation
of this data will be discussed.
4. Presentation and annlication - Real examples will be used to show how a geoprofessional
would apply this data to varying situations. Data from a range of diverse
environments will be included, and various data formats will be presented.
Applications for when and type of surveys to run will be investigated.
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Field Evaluation Of A New Borehole Resistivity Probe Using Capacitive Electrodes.
Authors C.J. Mwenifumbo and Q. BristowA prototype resistivity probe using capacitive electrodes has been built under a collaborative
project funded jointly by the Geological Survey of Canada (GSC) and IFG Corporation, a
Canadian manufacturer of borehole geophysical instrumentation. The GSC carried out field tests
at its borehole test facilities in Ottawa and at the New Calumet massive sulphide deposit in
Quebec. Results indicate that the capacitive technique is sensitive in the resistivity range 100-
10,000 ohm-m and compares well with galvanically and inductively measured resistivities. Field
tests were also carried out for several transmitter-receiver spacings and in plastic-cased fluidfilled
boreholes. Capacitive resistivity logs acquired in a plastic-cased borehole are almost
identical to those acquired in the same but uncased borehole. Therefore, capacitive resistivity
logs promise to be valuable for use in environmental applications where boreholes drilled in
unconsolidated sediments are often plastic-cased.
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Assessing Exploratory Borehole Seals With Electrical Geophysical Techniques
Authors Stanford A. Gibson, Craig H. Benson and Tuncer B. EdilThis paper describes how time domain reflectometry (TDR) and electrical resistivity
logging were used to examine the integrity of seals placed in exploratory boreholes. Laboratory
tests were conducted in PVC columns containing layers simulating sealants and defect materials.
TDR or resistivity probes were installed in the columns and used to log the materials in the
column. Column testing showed that the TDR method could be used to identify defect types and
sizes. However, conduction losses limited the useful length of the TDR probe to less than 3-m.
Resistivity logging proved more suitable and thus field tests were conducted with the resistivity
probes. Resistivity logs clearly delineated portions of a borehole seal that contained either
sealant or defect materials.
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Characterization Of Well Seals Using An Ultrasonic Method
Authors Martin C. Christman, Tuncer B. Edil and Craig H. BensonA downhole ultrasonic method was modified and used to test water well seals. The
method analyzes reflections of ultrasonic waves off interfaces to determine the presence of
different materials between the casing and formation. The method of waveform analysis was
modified for thicker well casings. Indices for characterizing waveforms were compared, and
delineation between water and bentonite grout was improved. Laboratory tests using sand as an
annular material also led to changes in the method of interpretation. Test results from two water
wells are presented. Bentonite grout and sand were detected in the armulus of both wells.
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A Three-Dimensional Interpretation Of An Aem Survey In The Upper San Pedro Basin, Arizona
Authors Mark W. Bultman, Mark E. Gettings and Jeff WynnIn March 1997, a time-domain Airborne ElectroMagnetic (AEM) survey was flown over the
upper San Pedro basin, Arizona, by Geoterrex-Dighem Ltd. of Ottawa, Canada. This survey was
contracted and analyzed by the U.S. Geological Survey Geologic Division. A mathematical
transformation of the AEM data, referred to as a conductivity depth transform or CDT, was used
to build a three-dimensional model of resistivity in the basin. Comparisons of the CDTs and
resistivity measured in electric well logs from nine Fort Huachuca test wells show that the CDTs
are a good representation of the electrical conductivity of basin sediments for the upper 150 m.
Below 150 m trends in conductivity systematically decrease with depth, and therefore conductors
deeper than 150 m represented on the CDTs are underestimated. The depth to the water table
generally corresponds to the uppermost maximum of conductivity, but there are many
exceptions. It is possible that the relationship is coincidental with those areas where the water
table happens to fall in a zone of (more conductive) silts and clays. The eastern half of the basin
near the Tombstone Hills contains an increasing proportion of silts and clays with depth. We
infer that this is due to weathering of the volcanic rocks off of the Tombstone Hills into a low
energy environment during the filling of the basin. This resulted in a southwestward extending
wedge of silt and clay which is most extensive at depth and least at the surface. The lower part of
this wedge may include outflow tuff from the Tombstone caldera. This material limits the
permeability of much of the aquifer and thus is hydrologically significant.
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A World Of Applications For Helicopter Electromagnetics To Environmental And Engineering Problems
By Greg HodgesThe variety of environmental and engineering applications for helicopter-borne
electromagnetic surveys has increased in recent years. Helicopter EM surveys
undertaken by Geoterrex-Dighem have been used for:
l measuring soil conductivity near oil pipelines to assess corrosion risk,
l estimating soil type and depth for pipeline planning,
l mapping sand and gravel deposits for aggregate resource exploration,
l measuring the extent of salt water invasion into the Florida Everglades,
l mapping soil salinity in Australian farmland, assessing groundwater resources,
l locating brine leaks from abandoned Texas oil wells,
l site characterization and detection of leaks in mine tailings dams,
l assessing land slumping hazards in Japan,
l measuring ocean bathymetry
l locating igneous dikes in coal mines.
Magnetic and radiometric data can be collected simultaneously, and have been used to
find buried metal structures, and illegally abandoned radioactive sources.
The major advantages of helicopter EM over ground EM surveys are the reduced cost for
surveys over large areas, the speed of surveying coverage (approx 1000 hectares/hour),
and the multiple frequency/multiple depth sample nature of the data, which render a 3-
dimensional conductivity image of the ground conditions.
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A Case History Of The Scintrex Helicopterborne Pds3M Pipeline Detection System To Aid In The Safety And Planning Of 3D Seismic Surveys
Authors Terry McConnell and Bob LoThe Scintrex PDS-3M Pipeline Detection System was engineered to detect steel pipelines as
small as 2 inches in diameter under favourable conditions. Using three Scintrex CS-2 cesium
vapour magnetometer sensors arranged in a triangular fashion in a helicopter towed bird, the
PDS-3 system measures all three components of the magnetic gradient and the total magnetic
intensity. The data is interpreted to yield the location, likely layout of the magnetic responses.
The combination of high sensitivity gradient measurements and data collection from an airborne
platform allows for rapid surveying over areas which are difficult to access, such as over
swamps. The PDS-3M survey yields a good infrastructure maps for the 3D seismic acquisition
companies to plan their survey. The presented case history is taken from a PDS-3M survey over
an oil field in Mexico. It shows that the existing infrastructure maps are often grossly simplified
- creating uncertainty in the “safe areas” for seismic shot point locations. With the increased
confidence of the pipeline locations due to a PDS-3M survey, the safe areas for shotpoints were
identified and gaps in the seismic coverage were tilled in.
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Gem-2A Broadband Airborne Em System
Authors Bill SanFilipo and I.J. WonA helicopter towed bistatic EM system capableofsimultaneously transmitting and receiving at
several user-selected frequencies has been developed, and is currently operational in mineral
exploration programs in Australia. This 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. A reference, or “bucking” coil is incorporated,
which is wired in reverse polarity to the primary receiver coil, thus removing the direct system
response as observed iq the absence of a conductive target (i.e. at high altitudes). This feature
is critical in maximizing the observability ofthe weaker response from currents induced in the
earth. A case study is presented with presentations of apparent conductivity maps for real
survey data.
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