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10th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 23 Mar 1997 - 26 Mar 1997
- Location: Reno, Nevada, USA
- Published: 23 March 1997
61 - 80 of 106 results
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Electromagnetic Investigation At The Combat Maneuver Training Center, Hohenfels, Germany
Authors Mike D. Thompson, M.A. Benson, L.D. McGinnis, M.A. Glennon, C.A. Padar, S.F. Miller, P.C. Heigold and Albert BöhmElectromagnetic surveys were conducted at the Combat Maneuver Training
Center (CMTC), Hohenfels, Germany to detect zones where solution cavities develop
within lowland areas of the karst valley systems. Geologic models indicate that solution
activity occurs at the loess-bedrock interface, and is concentrated along loess-filled
fracture trends within the underlying carbonate bedrock. Soil arches that develop along
these fracture trends have the potential to fail catastrophically, posing a considerable
degree of danger to current training activities. Rapid, continuously recording
electromagnetic instruments provide an economical solution for locating zones of high
conductivity associated with loess-filled fractures.
The electromagnetic surveys delineated high-conductivity trends interpreted to be
fracture-controlled. In many instances dolines were observed either along or immediately
adjacent to these conductivity lineaments. Analysis of anomaly maps indicate that highconductivity
lineaments are aligned subparallel to fracture and joint orientations
measured in nearby outcrops. These associations are the basis for predicting locations
where solution cavity collapse and doline development will occur in the future.
Information derived from the EM data can be extended directly to hydrologic modeling
and to safety programs for military training at the CMTC.
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Delineation Of Voided And Hydrocarbon Contaminated Regions With Rdem And Sti
By Bob WhiteleyUndetected voids and cavernous regions at shallow depth are a significant geotechnical and environmental hazard ifthey
are filled or act as conduits for pollutants, particularly for LNAPL and DNAPL contaminants. Such features are often
difticult to locate with drilling and conventional geophysical methods including resistivity, electromagnetics,
microgravity, seismic and ground penetrating radar when they occur in industrial or urban areas where electrical and
vibrational interference can combine with subsurface complexity due to human action to severely degrade geophysical
data quality.
A new geophysical method called Radiowave D&-action Electromagnetics (RDEM) has proved successful for rapid
screening of difficult sites and for the delineation of buried sinkholes, cavities and hydrocarbon plumes. RDEM operates
with a null coupled coil configuration at about 1.6 MHZ and is relatively insensitive to electrical interference and
surrounding metal objects. It responds to subsurface variations in both conductivity and dielectric constant,
Voided and contaminated regions can be more fully detailed when RDEM is combined with Seismic Tomographic
Imaging (STI) horn follow-up boreholes. Case studies from sites in Australia and South East Asia demonstrate the
application of RDEM and ST1 and the value in combining both methods.
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Hydraulic Testing Of A Single Screened Well To Implement A Multi-Level Purge And Sampling Design
Authors Keith S. Caplan, Timothy J. Peck, Ian D. MacFarlane and Joy E. LigéVertical flowmeter testing of a fully penetrating well, screened in a confined sand and gravel
aquifer, was performed to characterize the vertical variation of aquifer hydraulic conductivity.
Acquired data were used to design multi-level sampling without the use of packers or nested wells.
While slow pumping the well from above the screened interval, a Mount Sopris Instrument
Company, Inc. Heat Pulse vertical flowmeter was used to log the cumulative contribution to
vertical flow in the well at I-ft intervals. An impeller flowmeter was also tested at higher purge
rates, but could not measure low flows near the bottom of the well. An equation derived by Molz,
et al. (1989) was applied to the data to solve for hydraulic conductivity at each interval using an
average hydraulic conductivity calculated from slug tests. Variations of hydraulic conductivity
correlated closely with sedimentary strata.
Changes in the rate of cumulative flow versus depth were used to select discrete well sampling
intervals for simultaneous, multi-level sampling of the well without causing in-well mixing.
Peristaltic pumps and stainless steel tubing were used. Ground-water samples were analyzed for
organic compounds to evaluate if contaminant concentrations resulted either from the dissolution
of a bottom dense non-aqueous phase liquid (DNAPL) layer or preferential flow of contaminants
from a distal DNAPL source through coarser sediment layers.
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Application Of Multiple Geophysical Methods To Hydrologic And Environmental Investigations At U.S. Marine Corps Installations In North Carolina
Authors Alex P. Cardinell and Charles C. DanielHydrologic information for ongoing environmental studies at two U.S. Marine Corps Bases in the
Coastal Plain Province of North Carolina was obtained by using a combination of high-resolution land
seismic reflection, continuous marine seismic profiling, and borehole geophysics, that included vertical
seismic profiling. The geometry of areas of missing confining units at the southern end of Cherry Point
Marine Corps Air Station was mapped by using land seismic-reflection compressional (P) waves, marine
seismic profiling, and borehole-geophysical and -1ithologic data from more than 100 water-supply and
monitoring wells. The hydrogeologic framework at Camp Lejeune was mapped by using 100 miles of
continuous single-channel, marine seismic-profiling data that were correlated with land-based borehole
geophysical and lithologic data from 180 water-supply, monitoring, and stratigraphic test wells. These data
are being used by both Marine Corps Bases to manage drinking-water supplies and plan investigations of
hazardous-waste sites.
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Thie Application Of Surficial Geophysics To Well Site Exploration And Wellhead Protection In Fracture Controlled Aquifers
Authors John Jansen and Patrick JurcekSiting high capacity wells in fractured controlled aquifers is difficult due to the
unpredictable distribution of relatively narrow fracture zones. Geophysical methods can
be used to locate fracture zones and select favorable test well locations. Due to the
expense of rock drilling, it is common to estimate the parameters of fractured aquifers
without monitoring wells. Under these conditions, most interpreters assume an isotropic
porous media equivalent. This can lead to serious errors in defining the ground water flow
system.
This paper presents two case histories that illustrate how surficial geophysical
methods can be used to locate high capacity wells in fracture controlled areas. The cases
also demonstrate how the properties of fractured aquifers can grossly deviate from
isotropic porous media and the errors that can result from ignoring this fact. Geophysical
methods can be used to predict the trend of the axis of maximum transmissivity in the
aquifer, which can be used to efficiently site monitoring wells to accurately measure
aquifer properties. Accurate measurements of anisotropy are critical for defining
reasonable wellhead protection zones in fracture controlled aquifers.
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Resistivity, Oolites And A Fresh Water Lens
Authors Paul J. Wolfe, Lisa Jacob, Sara Hodl and Cindy CarneyWe have conducted a series of resistivity soundings and azimuthal resistivity surveys
across North Andros Island, Bahamas. The fresh water lens was mapped from a
combination of well data and resistivity soundings. The carbonate aquifer is dominated by
oolitic limestone and is known to have extensive karst development as evidenced by the
existence of blue holes. Charlies Blue Hole, which is several kilometers from the ocean, as
well as boreholes, exhibit clearly recognizable tidal fluctuations with small time lags
suggesting subsurface connection to the ocean, perhaps via fractures. Azimuthal resistivity
surveys allow us to evaluate the effects of preferred orientation of fractures.
Borings and surface sampling revealed changes in depositional environments across the
island. The resistivity surveys coupled with lithologic information from various locations,
allow us to draw a clearer picture of how the island geology is linked to the island
hydrology.
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Electrical Geophysical Study Over The Norman Landfill, Near Norman, Oklahoma
More LessIn 1995 and 1996 the US Geological Survey ma& 40 Schlumberger dc electrical resistivity soundings at the
Norman Landtill, near Norman, Oklahoma. Interpretation of the resistivity data indicates that high resistivities
(>300 ohm-m) are related to dry sand, intermediate resistivities (45-300 ohm-m) are related to freshwater saturated
sand, and low resistivities (~45 ohm-m) are related to fine-grained materials or materials saturated with the
conductive fluids. Interpreted resistivity maps show a low resistivity anomaly that extends from under the landfill to
just past a nearby slough. This anomaly corresponds to known areas of ground water contamination. A resistivity
cross section, constructed from interpreted Schlumberger soundings, shows that this low resistivity anomaly is about
5 m deep and up to 9 m thick.
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Geophysical And Geotechnical Site Characterization Data At The Groundwater Remediation Field Laboratory, Dover Air Force Base, Dover, Delaware
Authors William P. Clement, Steve Cardimona and Katharine Kadinsky-CadeSite characterization for environmental cleanup provides the information needed to
determine the extent and scope of a specific problem and to adequately design remediation
strategies. Site characterization can be expensive when based primarily on in situ sampling by
invasive techniques to sufficiently describe the subsurface. Closely spaced probes are necessary to
insure that important features are not overlooked. Additionally, drill holes are conduits to the
aquifer that potentially may lead to further contamination. To reduce costs and to provide
characterization of a wider area, geophysical methods are often used to supplement drilling.
Unfortunately, the scarcity of subsurface samples can make it difficult to relate the images from
surface geophysical methods to relevant physical properties in the ground. The Groundwater
Remediation Field Laboratory in Dover, Delaware provides an opportunity to study the relationship
between in situ geotechnical measurements of physical properties with a variety of geophysical
data. We determine the ability of the geophysical techniques to image three targets beneath the
Groundwater Remediation Field Laboratory, and we compare the geophysical images with
subsurface properties inferred from extensive cone penetrometer data. Having in situ
measurements of the subsurface and a variety of geophysical data at one site enables us to correlate
geotechnical and geophysical methods to determine the subsurface character.
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Geophysical Investigation Of Anomalous Conductivity At A Hydrocarbon Contaminated Site
Authors Mike S. Nash, Estella Atekwana and William A. SauckThe intuitive geoelectric model for hydrocarbon light non-aqueous phase liquid (LNAPL)
plumes treats the plume as a resistive body in the subsurface. Results of field studies have
shown that plume bodies can develop conductive attributes over time, and that this dichotomous
nature of electrical conductivity varies over time. A comprehensive geophysical survey was
undertaken to evaluate the electrical nature of an older plume as well as to evaluate the methods
best suited for characterization. Dipole-dipole resistivity profiling, self potential,
electromagnetic induction, and ground penetrating radar were all used to characterize the
conductive plume. Ground penetrating radar located conductive plume boundaries best, while
the dipole-dipole resistivity and self potential methods located the plume but did not resolve the
boundaries of the plume.
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Evaluation Of Electromagnetic Mapping Methods To Delineate Subsurface Saline Waters In The Brookhaven Oil Field, Mississippi
Authors Bruce D. Smith, Robert Bisdorf, Larry J. Slack and Aldo MazzellaHydrologic and geophysical studies of saline waters at the Brookhaven oil field (Mississippi) began in 1985.
Past and present practices to dispose of brines produced with oil and gas poise an environmental risk to ground water
resources, agriculture, and other land uses. At Brookhaven, there is an elevated total chloride content in shallow
((mg/L), which is exceptionally fresh water in comparison to other oil producing areas, particularly in the western United
States. Contamination in the oil field at some sites is several hundred mg5 chloride as determined from water well
samples taken in the mid-1980s. The EPA funded a feasibility study that included a dc resistivity survey which showed
low resistivities in one area of known saline water contamination. Detailed electrical geophysical surveys are not
possible due to numerous metallic features associated with oil production. In 1988 a helicopter electromagnetic (HEM)
survey of the oil field was flown under contract to the USGS as part of an EPA funded research project. An interpreted
resistivity map for a depth of 30m showed low resistivities associated with clays, shales, and saline waters near some
of the abandoned brine disposal pits. In 1995 water wells were re-sampled and two areas of high changes in chloride
content were found. Also in 1995, a new HEM survey was flown and new dc resistivity soundings were made.
Comparison of the ground and airborne survey along a profile where there has been a high change in chloride content
shows good agreement for interpreted subsurface resistivities. The HEM survey shows greater detail than the ground
measurements and suggests there may be local vertical migration of saline waters in areas where there has been a large
increase in ground water chloride content.
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Multiple Views Of A Leachate Plume
Authors Seth R. Lemke, Micki M. Maki and Charles T. YoungResistivity, VLF, and radar were used to image a leachate plume emanating from a landfill
in northern Michigan. The resistivity arrays were dipole-monopole and mise-a-la-masse.
VLF data were enhanced and interpreted using linear filters to convert the data to subsurface
electric current densities and to apparent resistivities. The general agreement of these
methods provide confidence as to the extent of the plume and the direction of groundwater
flow.
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The Use Of Giant Magnetoresistance Technology In Electromagnetic Geophysical Exploration
More LessDiscovered in 1988 (Baibach, et al, 1988) in France during research into superconducting, ultrathin
films, the giant magneto-resistance (GMR) effect is similar to the Hall effect in that a change
in magnetic field strength causes a corresponding change in resistance in the GMR structure. The
differences occur in the underlying physics and the resulting increase in resistance change for a
given change of magnetic field strength. The vector sensitivity of the GMR structure combined
with the advantages of integrated circuit manufacturing techniques make this a very promising
technology for advanced electromagnetic geophysical exploration.
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Physical-Scale And Numerical Modeling Of The Azimuthal Electromagnetic Response In The Macroanisotropic Case
Authors Kelly A. Rust, Stewart K. Sandberg and Esben AukenSince 1995, we have collected electromagnetic (EM) field data using a rotating azimuthal
geometry analogous to that described for resistivity surveys by other workers. These EM
azimuthal resistivity data are relatively easy to acquire and can be collected in areas with high
electrode contact resistance. As an aid to interpreting field results, including apparent paradox of
anisotropy conditions, we have used physical-scale modeling, and have run a suite of numerical
models.
Numerical and physical-scale modeling results indicate that the primary factor affecting the
orientation of the apparent resistivity ellipse relative to a macroanisotropic linear conductor is the
depth to the target (relative to the transmitter-receiver coil separation). At target depths less than
about 10% of the coil separation, an electromagnetic paradox of anisotropy is observed in the
modeling tank, in the numerical model, and in our field data (i.e., high values of apparent
resistivity along the strike of the target). While physical-scale modeling is limited by the
availability of materials of appropriate conductivity, numerical modeling provides a sufficiently
extended parameter space for these analyses. The numerical model also indicates that the
conductance of the target does not effect the orientation of the apparent resistivity ellipse.
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The Electromagnetic Integrated Demonstration At The Idaho National Engineering Laboratory Cold Test Pit
Authors Louise Pellerin, David L. Alumbaugh and M. Cathy PfeiferThe electromagnetic integrated demonstration (EMID) is a baseline study in electromagnetic (EM)
exploration of the shallow subsurface (c 10 m). Eleven distinct EM systems, covering the
geophysical spectrum, acquired data on a grid over the Idaho National Engineering Laboratory
(INEL) Cold Test Pit (CTP). The systems are investigated and evaluated for the purpose of
identifying and reviewing existing geophysical characterization instrumentation (commercial and
experimental), integrating those technologies with multi-dimensional interpretational algorithms,
and identifying gaps in shallow subsurface EM imaging technology. The EMID data, am valuable
for testing and evaluating new interpretational software, and developing techniques for integrating
multiple datasets. The experimental field techniques shows how the acquisition of data in a variety
of array configurations can considerably enhance interpretation. All data am available on the world
wide web (http://vetem.lbl.gov). Educators and students are encouraged to use the data for both
classroom and graduate studies. The purpose of this paper is to explain why, where, how and
what kind of data were collected. It is left to the reader to assess the value of a given system for
their particular application. Information about the EMID is organized into two general categories:
survey description and system evaluation.
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Inversion Of Airborne Electromagnetic Data Using An Occam Technique To Resolve A Variable Number Of Layers
Authors Wei Qian, T. Jeffrey Gamey, J. Scott Holladay, Richard Lewis and Dennis AbernathyDepth sections generated from multi-frequency helicopter electromagnetic (HEM) data have
become an important aspect of airborne surveys. Traditionally such depth sections are created by
an imaging approach, based on simplified physics or empirical relations (Macnae and
Lamontagne, 1987; Macnae et al., 1991; Sengpiel, 1988; Huang and Fraser, 1996; Bostick, 1977;
Nekut, 1987; Jones 1983 etc.). As computers become ever faster and cheaper, we are gradually
entering an era where inversion of HEM data in daily production is economically feasible.
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Monitoring Hydraulic Experimfnts By Complex Conductivity Tomography
Authors Andreas Weller, Mario Gruhne, Frank D. Borner and Matthias SeichterComplex electrical conductivity tomography has been applied to monitor hydraulic experiments
in a research facility for in-situ remediation of contaminated soils and aquifers.
Arrays of electrodes were installed in a flume where infiltration experiments with non-aqueous
phase liquids (NAPL) were performed. Data sets of about 500 configurations have been acquired
with a computer-controlled equipment for spectral induced polarization.
The tomographic algorithm used for interpretation is based on the simultaneous iterative
reconstruction technique (SIRT). As in other inversion techniques, the Jacobian or sensitivity
matrix has to be known. The three-dimensional forward modelling is performed by the ftite
difference method using complex values of conductivity and potential.
The resulting tomographic images show the distribution of complex conductivity inside the tanks.
They reflect both the spatial variability of soil and aquifer properties and changes between
different stages of the experiments. These images were successfully used to determine the state of
the multiphase system consisting of silicate matrix, water, NAPL and air.
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Refraction Traveltime Tomography Of Bala Kimberlite In Riley County, Kansas
Authors Jie Zhang and Brian K. MacyWe apply a nonlinear refraction traveltime tomography method to image the subsurface structure near the
Bala Kimberlite in Riley County, Kansas. The Bala Kimberlite is partially exposed at the surface near Bala,
Kansas in northwestern Riley County. Our fundamental goal of this study is to infer the structure of this
magma plug in the shallow structure. Applying the tomography approach to the data collected along two
perpendicular lines, we reconstruct a velocity structure corresponding to soil, weathered shale, limestone, and
shale, and the sharp discontinuity of the bedrock near the Bala Kimberlite. The imaging results supports the
hypothesis that the Bala Kimberlite might be emplaced into a fracture zone from the upper mantle during
major tectonic activity.
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High Frequency Electromagnetic Impedance For Subsurface Imaging
Authors Yoonho Song, H. Frank Morrison and Ki Ha LeeMost electromagnetic (EM) methods used for geophysical exploration are based on a low frequency, diffusion,
representation of fields in which displacement currents are negligible. If the ground is sufficiently resistive ground
penetrating radar (GPR) may be used and its interpretation usually relies on high frequency, wave field,
representation in which pulse transit time is measured and dielectric properties are recovered. We have
investigated the use of EM fields of intermediate frequency range, 1 to 100 MHz, where both diffusion and wave
fields must be considered and new measurement strategies must be used to recover both conductivity and electric
permittivity from the data.
We have chosen to analyze the ground response at these intermediate frequencies by way of the surface
impedance for plane waves. At these frequencies impedance measurements require scaling up the magnetic field
sensors used for low frequency EM and scaling down the dipole antennas used in radar. The impedance has a
distinct advantage in that coupling to the source is unnecessary, and the source can always be positioned far
enough away to yield plane waves at the receiver. This in turn permits the use of a wide range of fairly standard
imaging codes for interpreting the result.
The high-frequency EM impedance is shown to be very sensitive to ground electrical properties and strongly
dependent on the angle of incidence. In this paper we demonstrate methods for evaluating the incident angle,
correcting the impedance data for normal incidence, and finally imaging the electrical conductivity and
permittivity of simple layered earth models.
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Viability Of Using Seismic Data To Predict Hydrogeological Parameters
By Ken MelaDesign of modem contaminant mitigation and fluid extraction projects make use of
solutions from stochastic hydrogelogic models. These models rely heavily on the hydraulic
parameters of hydraulic conductivity and the correlation length of hydraulic conductivity.
Reliable values of these parameters must be acquired to successfully predict flow of fluids
through the aquifer of interest. An inexpensive method of acquiring these parameters by use of
seismic reflection surveying would be beneficial. Relationships between seismic velocity and
porosity together with empirical observations relating porosity to permeability may lead to a
method of extracting the correlation length of hydraulic conductivity from shallow high resolution
seismic data making the use of inexpensive high density data sets commonplace for these studies
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The Effects Of Sparging On P- And Sh- Vertical Seismic Profiles
Authors P. Michaels and W. BarrashWhile the introduction of pressurized air into an unconsolidated, coarse-grained fluvial aquifer might
well be expected to affect the P-wave velocity profile below the water table, we have found that S-waves are
also sensitive to changes induced by air sparging. In a study spanning over a year of sparging, observations of
both P- and S-waves were conducted by Vertical Seismic Profiling (VSP). While the primary objective was to
characterize the aquifer, we have found that air sparging has significantly affected both P- and S-wave
propagation. Below the water table we have observed as much as a 54% decrease in P-wave velocity, and as
much as a 31% increase in S-wave velocity after continued sparging. Above the water table, we observe only
small changes in both P- and S-wave velocities. This pattern of velocity change (decreasing P, increasing S)
may be due to an increase in the amount of trapped air below the water table.
Published laboratory studies in the small strain regime have shown P-wave velocities to be sensitive to
void ratio, fluid content, and confining stress. On the other hand, most similar studies of S-waves have only
been conducted on either dry or saturated samples. However, one recent laboratory study suggests that shear
modulus and shear velocity may increase significantly at partial water saturations (due to capillary forces). Data
from our in-situ survey supports this more recent lab work. We have observed that S-wave propagation may be
significantly altered by fluid content when soils are partially saturated with water (where trapped air may exist,
producing a 3-phase fluid-frame system). In addition, we have observed changes in the propagating wavelet.
This may be an indication that viscous damping is also affected by partial water saturation. We conclude by
observing that S-waves may prove to be an attractive alternative for mapping the effects of air sparging.
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