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17th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 22 Feb 2004 - 26 Feb 2004
- Location: Colorado Springs, Colorado, USA
- Published: 22 February 2004
21 - 40 of 165 results
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Environmental Corrections In Shallow Borehole Resistivity Logging
Authors Ludovic Baron and Dominique-Marie ChapellierBorehole logging is more and more used in civil engineering, hydrogeology and environmental
studies. Simple logging equipment can be obtained at reasonable cost but most of the time the probes are
not correctly calibrated, standardized, and environmental corrections are not made. It is essential to
remember that only accurate logs will enable a correct formation evaluation.
In shallow borehole equipment, conventional resistivity measuring devices are generally “normal
devices” with several electrode spacing. “Old electric logs” were corrected by the past, for resistivity
contrast between mud and formation, borehole diameter etc., using charts. The equations corresponding
to the chart curves can nowadays be very easily programmed and so the corrections are simple to apply.
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An Automated Transmissivity Modeling Method For Use With Borehole Flowmeter Data
More LessMany different methods are available to model subsurface hydraulic properties using transient
measurements. An improved flow modeling technique for borehole measurements was formulated and
tested. In this technique (called the convolution-inversion method), the flow from a producing interval
is modeled as a confined aquifer intersecting a borehole. The produced flow is a function of the driving
head, and is independent of the storage in the borehole. By considering each flowing interval separately,
the more complicated simultaneous analysis of a multi flow unit system in a borehole is avoided. The
data required for the inversion are the drawdown (the driving force) and flow from each producing depth
interval, both of which are measured as a function of time. An automated computer program convolves
the drawdown transient with the characteristic confined aquifer function for a given transmissivity to
predict transient flow. An inversion algorithm finds the transmissivity that causes the predicted flow to
most closely match the measured flow. The method is applicable to any means used to stress a well, as
long as the water level in the well can be changed over time. The algorithm was applied to pump test
data from a clay capped alluvial aquifer. The results compare reasonably well to results from a previous
analysis. The convolution-inversion method provides increased utility in that tests can be performed
more quickly, with minimal control over pumping, and with inexpensive equipment.
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A New Casing Inspection Tool: Two Case Studies
Authors J.-L. Deltombe, R. Schepers and P. van EyllAn Acoustic Televiewer scans the borehole wall with a focussed acoustic beam. At each scan
point amplitude and traveltime of the reflected signal are recorded. The slim hole ABI40 Televiewer has
become a standard tool in geotechnical exploration, in mining exploration and in hydrological
applications including water well inspection. Until now, the inspection of steel casing for corrosion and
the determination of absolute casing thickness required complexe and expensive logging tools. The
newly developed ABI40 casing inspection tool offers an attractive and inexpensive alternative. The tool
with a length of 1.8m can be operated in a wide range of applications from shallow water wells to deep
oil or gas wells.
The hardware of the standard ABI40 Televiewer is used to realize a logging tool which is
capable of determining casing thickness. New software is all that has to be installed in the real-time
processing unit of the ABI40 Televiewer to upgrade the ABI40 tool to a casing thickness logging tool.
The ABI40 tool for casing inspection transmits four images to the surface unit:
1. Traveltime image of inner surface (Traveltime 1)
2. Amplitude image of inner surface (Amplitude 1)
3. Thickness Traveltime image
4. Thickness Amplitude image
Traveltime 1 is used to detect casing thickness changes due to variation of the inner casing radius.
Amplitude 1 is applied to distinguish between inner and outer corrosion. Thickness Traveltime gives the
remaining thickness of the casing wall and Thickness Amplitude helps to identify areas of casing wall
defects even if the correct casing thickness cannot be determined.
To verify the performance of the new tool a number of short casing samples with well-known
defects were examined in the laboratory. Finally a field test measurement was made in a cased well,
which has already been logged before by other casing inspection tools.
It could be demonstrated that the present ABI40 tool can operate in casings with an inner
diameter from 6 inch to 20 inch. A maximum of 72 casing thickness values can be determined per
revolution of the acoustical head. The reliability of the casing thickness determination could be
confirmed and its precision was found to be less than 10%.
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Borehole Engineering – A Proven Cost Effective Method For Determination Of Engineering Parameters
Authors Nathan O. Davis and Thomas M. StaatzFor years, engineers and geoscientists in Europe and Asia have used borehole engineering to
accurately acquire rock properties, structural stress-strain relationships, fracture statistics, and other insitu
properties for major tunneling and engineering projects. Geophysical methods have been shown to
dramatically reduce costs of rock quality analysis by increasing the sum of valuable information while
reducing the number of core samples that require laboratory analysis. Just as engineering companies
have embraced the use of engineering gauges, acquisition of borehole measurements can be streamlined
into an effective program. Engineers and geoscientists in North America are just beginning to expand
the use of borehole engineering.
The integration of acoustic or optical televiewer, full waveform sonic, calibrated formation
density, borehole caliper, natural gamma, and relative neutron porosity logs allows the engineer to
derive invaluable rock properties. Bulk density, bulk modulus, Young’s modulus, shear modulus,
Poisson’s ratio, fracture density, and dominant bedding and fracturing trends are all available without
expensive oriented core, and laboratory analysis of core can be significantly reduced.
A lag in North American acceptance may be a factor of poor interdisciplinary communication.
At present, many project managers are unaware of studies relating the accuracy of borehole engineering
to more traditional methods. Those engineers that are more informed may perceive regulatory blocks,
including radioactive source licensing and reciprocity, that can be intimidating, but with the right
information, the benefits, including significant time and cost savings, increased sample density, and
simplified data presentation far outweigh the minor expenses of geophysical engineering.
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Are Current Generation Climate Change Simulations Accurate Enough To Reliably Guide Mitigation Strategies?
Authors Thomas N. Chasel and Eungul LeeWe examine the utility of downscaling climate change information from coarse resolution
climate models to scales useful for operational decision making. For a variety of reasons
including poor simulation of recently observed climate changes we conclude that downscaling
using present climate change simulations should be approached very cautiously.
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Change And Variability In The Global Climate System: Past, Present, And Future
More LessGlobal Climate Change is an issue that has garnered tremendous public attention and captured
headlines. However, many people do not have a good understanding of what is natural, what is not, or
how climate variability differs from anthropogenic, greenhouse gas-induced climate change. This talk
will consider the instrumental data on changing climate and the current models of climate in the next
century, and will place them in the context of climate variability from the past 2000, and 500,000 years.
We will also consider the influence of some drivers of natural climate change and their role in forcing
today’s climate. The awareness of abrupt changes in the climate system, and the possibility that the
gradual changes being caused by human activities today may trigger an abrupt change similar to those
seen in the past has become a new and important concern. We will discuss climate change, climate
extremes, and abrupt change as seen in instrumental and paleoclimatic records and in models. This will
include comparisons of the magnitudes and rates of past changes compared with the magnitudes and
rates of change currently being seen and predicted.
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The Role Of Geophysics In Developing Strategies For Co2 Sequestration In Geologic Formations
Authors Scott M. Klara, Karen Cohen, Charles Byrer and Rameshwar D. SrivastavaGlobal Climate Change has been attributed to emissions to the atmosphere of
greenhouse gases (GHG), with a major constituent being anthropogenic CO2 emissions
from coal-fired power plants and the transportation sector. Many approaches have been
proposed to mitigate CO2 emissions. Among the most promising is capture and
sequestration in geologic formations. This option has the advantage of being able to cope
with the large volume of CO2 involved, which will continue to increase because of the
growing energy demand. Consequently, an important component of the United States
Department of Energy’s (DOE) research and development program is dedicated to
reducing CO2 emissions from power plants by developing technologies for capturing and
sequestering CO2 in geologic formations.
This paper presents an overview of DOE’s research program in the area of CO2
sequestration and storage in geologic formations. Geophysical field techniques are
playing a major role in current field demonstrations of CO2 sequestration and have the
potential to play an even greater role as geologic sequestration becomes a reality in a
future “carbon constrained world.” The role of geophysical techniques in studying the
processes involved in the CO2 geologic sequestration life cycle are discussed. These
processes include CO2 capture, transport, injection, and measurement, monitoring, and
verification (MMV) of the permanence of storage in a geologic reservoir with an
effective caprock seal. Techniques, including seismic surveys using a variety of data
acquisition and processing strategies (2D seismic surveys, seismic tomography, and
others), microseismic monitoring, microgravity surveys, electrical and electromagnetic
methods, and geophysical well logging all can, potentially, provide valuable subsurface
stratigraphic and structural imaging data, as well as information on subsurface properties
such as the location of fractures and faults that could serve as migratory pathways for
escape of injected CO2.
Advanced field operations and field studies sponsored by DOE are utilizing a
variety of geophysics in the life cycle of CO2 geologic sequestration. Examples include
the Sleipner field operations in the North Sea, the Canadian Weyburn Enhanced Oil
Field, the pilot CO2 injection into the Texas Frio Formation saline aquifer, the pilot CO2
injection in the West Pearl Queen depleted oil reservoir in New Mexico, and the
characterization of potential reservoirs for the Ohio River Valley at the AEP Mountaineer
Power Plant in Virginia. Geophysics is also important relative to the President’s
initiative for a ten year, $1billion dollar FutureGen project to develop a power plant with
“zero emissions.” This may be achieved, in part, by geologic sequestration of CO2.
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The Climate Temperature Cycles Of The Earth And What Drives Them (Part 1)
More LessThe surface materials of the earth comprise the Atmosphere, Lithosphere, and
Hydrosphere; their physical properties along with solar energy determine the climate.
The changes in surface atmospheric temperature are referred to when discussing climate
changes. However, the Hydrosphere is the main heat source/sink of the surface materials.
The hydrosphere receives more energy and stores more energy from the sun than either
the atmosphere or lithosphere. Climate changes have been going on in the past and are
necessary to maintain the biodiversity that exists on the earth. Yesterday the climate was
different, it will be different tomorrow, to paraphrase a biblical phrase; “Climate
Changes, as it was in the past, is now, and ever shall be World Climate with change”. To
stop climate changes would be unnatural, illogical, and not in anyone’s best interest.
The Total Solar irradiance S that reaches the earth has a large positive correlation
coefficient to the surface temperature. Since the irradiance S is totally a function of solar
activity, the surface temperature must be a function of the solar irradiance S. Changes in
Solar irradiance S can be easily explained by changes in the Sun-Earth geometric
relationship, similar to what is proposed in the 1940’s by the Milankovitch Cycle Theory.
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The Climate Temperature Cycles Of The Earth And What Drives Them (Part 2)
More LessThe paleo-temperature records are an important source of information with which
to study paleo-climates. One such record is the Western Pacific Sea Surface temperature.
It extends back some 60 million years before present. This temperature profile is
composed of a simple decay curve with a superimposed 5 million sinusoidal cycle. The
other record studies was the Vostok Ice Core data from NOAA. The Vostok ice core data
is composed of Temperature CO2 and CH4 and is in considerable more detail extending
back some 420,000 years.
Spectral analysis was run on the data and the primary components have some of
the same periods that were hypothesis by the Milankovitch Cycle Theory. The spectral
component of the Vostok temperature data and its correlation with the Western Pacific
Sea Surface data is extremely suggestive the origin of the cycles are from Solar
influences and the Sun-Earth Geometric relationships.
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Using Helicopter Fdem To Monitor The Fate Of Conductive Water Co-Produced With Methane In The Powder River Basin Of Wyoming
Authors Richard Hammack, James Sams, Garret Veloski, Brian Lipinski, Mark Zellman and Bill HarbertThe development of coalbed methane resources in the Powder River Basin of Wyoming
and Montana has produced more than 248,000 acre-ft of groundwater (produced water) that is
disposed on the surface by land application or returned to groundwater aquifers via infiltration
basins or injection wells. Because the chemistry of produced water differs from that of surface
waters, there is concern pertaining to the ultimate fate of the produced water. This paper
describes the use of airborne frequency domain electromagnetic (FDEM) surveys to trace the
movement of produced water away from infiltration basins and leaking containment basins.
Three sites are described: 1) a leaking containment basin, 2) a dilution anomaly at an infiltration
basin, and 3) a dilution anomaly at a flowing well. The FDEM survey identified leaks at two
containment basins before down-slope seeps were observed at ground level. Also, the survey
identified a dilution zone on the Powder River floodplain where produced water from an
infiltration basin was diluting more conductive groundwater in a shallow aquifer. The long-term
effect of deep groundwater being applied to the surface and infiltrating into near-surface aquifers
was observed at a flowing well, where groundwater from a coalbed aquifer has been flowing
onto the surface for almost 50 years. The hydrology of the flowing well site may be indicative of
the future hydrology at infiltration impoundment sites.
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3D Electrical Imaging Of Contaminated Soil Near A Gas Station At Brugelette, Belgium
Authors Olivier Kaufmann and John DeceusterA field experiment was conducted over a contaminated site located near a gas station where tank
leakage has been pointed. In this area, a dolomitic bedrock is overlaid with 5 to 8 meters of clayey
sands. In order to delineate the plume and measure piezometric heads and depths to bedrock, ten
boreholes were drilled and four cone penetrometer tests were conducted. Soil and water samples were
collected and analysed. Although these samplings highlight the presence of hydrocarbons in some
boreholes, the plume is poorly outlined due to the small number of drillings.
To assess the contribution of geophysical investigations in delineating contaminated areas, a 3-D
cross-diagonal resistivity survey was performed using roll-along technique and a seismic refraction
profile was conducted. The electrical dataset was inverted with Res3DInv to build a resistivity-depth
model of the ground. High resistivities suggest a bedrock geometry which is consistent with the drilling
results. However a finer analysis reveals that the resistivities at the top of the bedrock tend to be
significantly higher in areas where gas was detected than in uncontaminated areas. This increase in
resistivities is interpreted as an effect of the presence of fresh hydrocarbons. Confronting boreholes and
geophysical investigations could therefore lead to better estimations of the spill extent.
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Quantitative Imaging Of 3D Solute Transport Using 2D Time-Lapse Ert: A Synthetic Feasibility Study
Authors Andreas Kemna, Jan Vanderborght, Horst Hardelauf and Harry VereeckenTime-lapse electrical resistance tomography (ERT) has proven significant potential to monitor
solute plumes in the subsurface. However, the ultimate value of ERT for quantitative imaging of solute
transport, for example in heterogeneous aquifers, is still under dispute. Here, difficulties may be
expected to arise particularly from the fact that ERT data acquisition and interpretation is often limited
to 2D image planes, while aquifers are generally characterized by a 3D structure involving considerable
variability of flow and transport properties. The potential of time-lapse ERT in such a situation is
investigated by means of a synthetic tracer experiment. For this purpose, 3D solute transport in a
heterogeneous hydraulic conductivity field, characterized by an exponential covariance function, is
simulated. Assuming that solute concentration is linearly related to electrical conductivity, the spatiotemporal
evolution of the tracer plume is imaged in a transect spanned by a set of fictive boreholes using
2D time-lapse ERT. Although the 3D process is imaged using a 2D inversion approach, the recovered
electrical conductivity distributions coincide well with the input distributions. The obtained images are
interpreted as concentration maps and then analyzed in terms of transport properties. By adopting a
stream-tube model, an equivalent advection velocity and longitudinal dispersivity can be quantified for
each pixel in the ERT image plane. The recovered equivalent advection velocities exhibit fair agreement
with those obtained from the original model. The results of the synthetic study demonstrate that
quantitative imaging of 3D solute transport by means of time-lapse ERT is feasible. Importantly,
systematic errors associated with the 2D representation of a 3D model are found to play an insignificant
role concerning the quantification of transport properties, justifying the use of simple 2D imaging, for
instance if equipment, time, and/or budget is limited.
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Relationship Between Biodegradation And Bulk Electrical Conductivity
Geochemical and stable carbon isotope data obtained at closely spaced intervals within a
hydrocarbon impacted aquifer were used to assess the relationship between high bulk conductivity
zones and biodegradation of hydrocarbon. Biodegradation was verified using terminal electron
acceptors (nitrate, sulfate, and iron), dissolved inorganic carbon (DIC), and the isotope ratio of DIC
(δ13CDIC). The bulk conductivity was measured using in situ vertical resistivity probes. The results
show that peak values in the bulk conductivity occurred in zones in the aquifer where total petroleum
hydrocarbon were high and nitrate, sulfate and iron reduction were occurring. Also in the zones where
bulk conductivity was higher, DIC was higher and δ13CDIC was either more negative or more positive
while the major cations were elevated compared to uncontaminated locations. These results suggest
that the higher bulk conductivities were related to microbial redox processes. It appears that the bulk
conductivity measured in hydrocarbon impacted portions of the aquifer is the result of an integrated
process-driven biogeochemical changes reflected in the redox zonation in the aquifer. Hence, higher
bulk conductivity zones may be explained by enhanced mineral weathering within zones of higher
biological activity stimulated by the presence of hydrocarbon and available terminal electron
acceptors. Our results suggest a qualitative interrelationship between redox processes,
biomineralization of hydrocarbons, and high bulk conductivities, and argue for the need to incorporate
geophysical investigations as part of natural attenuation assessment programs.
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Laboratory And Field Results Linking High Bulk Conductivities To The Microbial Degradation Of Petroleum Hydrocarbons
The results of a field and laboratory investigation of unconsolidated sediments contaminated by
petroleum hydrocarbons and undergoing natural biodegradation are presented. Fundamental to
geophysical investigations of hydrocarbon impacted sediments is the assessment of how microbial
degradational processes affect their geoelectrical response. Therefore, the primary goal of this study
was to understand how microbially mediated processes in hydrocarbon impacted sediments influence the
geoelectrical response of this impacted zone. The field and laboratory results showed higher bulk
conductivity in sediments impacted by petroleum hydrocarbons. The impacted sediments also showed
increased populations of alkane degrading microbes and elevated dissolved cations (e.g. Ca2+). The
elevated cations in the contaminated sediments relative to uncontaminated sediments suggest enhanced
mineral dissolution related to the microbial degradation of the hydrocarbon. Both the laboratory and
field data showed the highest bulk conductivities occurring within zones impacted with the free-phase
and residual phase hydrocarbon and not within the water saturated zone. A model using a simplified
form of Archie's Law suggests highly elevated estimated pore water conductivities within this
conductive zone (~4 to 6 times background bulk conductivity) for both the laboratory and field data.
The similar results for hydrocarbon contaminated sediments in laboratory experiments and field settings
suggest that the mechanism for the high bulk conductivity in the contaminated zone is related to the
microbial metabolism of the hydrocarbon and the resulting geochemical alterations within the
contaminated zone. This study demonstrates that the higher bulk conductivity measured by geoelectrical
methods at hydrocarbon impacted sites may be in part related to the microbial mineralization of the
hydrocarbon.
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Wurtsmith Air Force Base Revisited
Authors Laura A. Smart, Mike Nash and William A. SauckBioremediation at hydrocarbon contaminated sites has been known to change the pore water
chemistry in such a manner that the conductivity increase due to the bioremediation is visible through
geophysical imaging. Geophysical techniques are often considered only upon initial site investigation as
a method of determining the extent of contamination and to map the boundaries of the contaminant
plume(s). However, this paper presents another aspect of the geophysical survey methods. The FT-02
plume at Wurtsmith Air Force Base contains both hydrocarbon and chlorinated contaminants. It was
surveyed extensively during the summer of 1996 with ground penetrating radar and electrical resistivity
(dipole-dipole). These surveys distinctly imaged the lateral and vertical extents of the higherconductivity
plume, correlating with the available hydrochemical data from well samples. The area was
revisited during the summer of 2003 to resurvey the original profiles. The purpose of this paper is to
report the changes that occurred to the geophysical signature of this well-known plume which has
undergone initial passive bioremediation and subsequent active remediation. The plume appeared to
undergo some lateral movement as well as significant changes in conductivity. The latter appear clearly
as attenuated zones on the GPR sections.
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Effect Of Different Phases Of Diesel Biodegradation On Low Frequency Electrical Properties Of Unconsolidated Sediments
Authors Gamal Z. Abdel Aal, Estella A. Atekwana, Lee D. Slater and Eliot A. AtekwanaLow frequency electrical measurements were made in laboratory sand columns contaminated
with different phases of hydrocarbon and undergoing biodegradation. The objectives of the study were
to 1) investigate the effect of microbial processes on the low frequency electrical properties and 2)
determine if the phase of hydrocarbon (dissolved or residual) contamination showed measurable
differences in the electrical properties of the sediments during biodegradation. The experimental sand
columns were constructed with the following treatments: uncontaminated (control) column with
nutrients (25% Bushnell Hass medium); column with nutrients + dissolved phase of diesel + bacteria;
and column with nutrients + residual phase of diesel + bacteria. Electrical measurements were made in
the frequency range of 0.1 to 1000 Hz biweekly for the first twenty weeks and monthly for the duration
of the experiments (36 weeks).
The diesel contaminated columns showed a steady increase in microbial population numbers and
a concurrent decrease in nitrate, sulfate, and benzene, toluene, ethylbenzene and xylene (BTEX)
concentrations compared to the control column. These results indicate microbial mineralization of the
diesel in the contaminated columns. Furthermore, the contaminated columns showed temporal increase
in dissolved inorganic carbon (DIC) and decrease in pH concomitant with increase in the fluid
conductivity and calcium ion concentration relative to the control column. Such changes suggest
microbial enhanced mineral weathering possibly by carbonic acid that resulted in higher fluid
conductivity in the contaminated columns. The contaminated columns also showed temporal increase in
the real and imaginary conductivity relative to the control column. The electrical data showed a higher
relative increase in the surface conductivity component in the contaminated columns compared to the
control column. Finally, we observed that the magnitude of the changes for all measured
biogeochemical and electrical parameters was greater (10-30%) in the sand column contaminated with
residual phase of diesel compared to the column contaminated with dissolved phase diesel. The results
are consistent with models that suggest that residual hydrocarbons trapped in the pore sediments are
more freely available for degradation by bacteria than in the dissolved phase. This resulted in the
relatively higher rate of biodegradation and accompanying biogeochemical alterations reflected in the
electrical measurements. We infer from these results of this study that microbial processes can impact
electrical properties and the accompanying physicochemical alterations at the mineral-fluid interface are
readily detectable using low frequency electrical measurements.
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Soil Resistivity Measurements For Clay Content Estimation And Its Application For Petroleum Contamination Study
Authors Vladimir Shevnin, Omar Delgado Rodríguez, Aleksandr Mousatov and Albert RyjovInformation about clay content is useful at contamination study because clay influences on
position and movements of contaminants by means of soil permeability and adsorption. Technology for
clay content estimation is based on soil resistivity measurements as function of water salinity at full
saturation of soil samples and data interpretation (or inversion) to find clay content and porosity of the
sample. Together with water resistivity estimation for an investigated site this information permits
characterizing uncontaminated soil and estimating boundary conditions for separating uncontaminated
and contaminated zones. This information helps in geological interpretation of vertical electrical
sounding data. Soil resistivity is determined by pore water resistivity, porosity, clay content and
humidity. To reduce number of unknown factors influencing on resistivity, we measure both soil and
water resistivity in the survey area. Soils below a groundwater level have humidity 100 % of pore space
that allows not taking this factor into account. Measurements of water and soil resistivity can be
performed with different types of resistivimeters and field resistivity meter. Estimating soil parameters is
performed with the help of forward and inverse petrophysical calculation.
Measurements of petrophysical parameters on calibrated sand and clay samples and on their
mixtures showed good accuracy of clay content estimation.
We studied sensitivity of petrophysical algorithm to principal soil parameters and estimated
errors of interpretation depending on input error.
Practical examples from different contaminated sites are presented. These demonstrate good
correspondence between vertical electrical sounding data, water and soil resistivity measurements, and
petrophysical estimations.
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Application Of A New Monte Carlo Approach To Calibrating Rock Physics Relationships: Examples Using Electrical Resistivity And Ground Penetrating Radar Tomography
Authors Kamini Singha and Stephen MoyseyIn applying geophysics to problems in hydrology, a relationship must exist
between the geophysical response from the subsurface and the hydrologic variable of
concern. In this paper we discuss the estimation of aquifer tracer concentrations using
electrical resistivity tomography and the determination of subsurface water content from
cross-borehole radar. Obtaining site-specific relationships between geophysical and
hydrologic parameters traditionally entails empirical calibration based on reconstructed
geophysical images and small-scale lab measurements or in-situ well logs. This direct
approach to calibration, however, can become biased in several ways: reconstructed
tomograms are often highly uncertain and subject to inversion artifacts, the range of
subsurface conditions represented by calibration data sets can be incomplete due to the
sparsity of collocated well or core data and aquifer heterogeneity, and the discrepancy in
scale between different measurements is not accounted for. We use Full Inverse
Statistical (FISt) calibration, a new Monte Carlo approach to calibration, to address these
problems. FISt calibration integrates all available data; e.g., aquifer geostatistics, pointscale
measurements, and physically based relationships, to obtain the best possible
relationship between the geophysical and hydrologic variables. We have found that
concentration and water content estimates obtained using FISt calibration are typically
significantly better than those obtained using traditional empirical calibrations.
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Application Of Cross-Borehole Radar To Monitor Fieldscale Vegetable Oil Injection Experiments For Biostimulation
Cross-borehole radar methods were used to monitor a field-scale biostimulation pilot project at
the Anoka County Riverfront Park (ACP), located downgradient of the Naval Industrial Reserve
Ordnance Plant, in Fridley, Minnesota. The goal of the pilot project is to evaluate biostimulation using
emulsified vegetable oil to treat ground water contaminated with chlorinated hydrocarbons. Vegetable
oil is intended to serve as substrate to naturally occurring microbes, which ultimately break down
chlorinated hydrocarbons into chloride, carbon dioxide, and water through oxidation-reduction
reactions. In support of this effort, cross-borehole radar data were acquired by the U.S Geological
Survey in five site visits over 1.5 years. This paper presents level-run (zero-offset profile) and time-lapse
radar tomography data collected in multiple planes. Comparison of pre- and post-injection data sets
provides valuable insights into the spatial and temporal distribution of both emulsified vegetable oil and
also the extent of ground water with altered chemistry resulting from injections—information important
for understanding microbial degradation of chlorinated hydrocarbons at the site.
In order to facilitate data interpretation and test the effectiveness of radar for monitoring oilemulsion
placement and movement, three injection mixtures with different radar signatures were used:
(1) vegetable oil emulsion, (2) vegetable oil emulsion with a colloidal iron tracer, and (3) vegetable oil
emulsion with a magnetite tracer. Based on petrophysical modeling, mixture (1) is expected to increase
radar velocity and decrease radar attenuation relative to background—a water-saturated porous medium;
mixtures (2) and (3) are expected to increase radar velocity and also increase radar attenuation due to
their greater electrical conductivity compared to native ground water.
Radar slowness (inverse radar velocity) tomograms and level-run profiles show decreases in
slowness in the vicinity of injection wells. Slowness anomalies are observed only in planes connected to
injection wells, indicating that the emplaced emulsified vegetable oil does not migrate far after injection.
In contrast to the localization of slowness anomalies, attenuation anomalies are observed in all level-run
profiles, particularly those downgradient of the injection wells. Despite the expected signatures of
different tracers, increases in attenuation are observed downgradient of all three injections; thus, we
infer that the attenuation changes do not result from the iron tracers. One viable explanation for the
observed attenuation changes is that products of oil-enhanced biodegradation (for example, ferrous iron)
increase electrical conductivity of ground water and thus radar attenuation.
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Electrical Impedance Tomography For Detection Of Dnapl Contamina
Authors William Daily and Abelardo RamirezMapping the distribution of dense non-aqueous phase liquid (DNAPL) contaminants in
subsurface soils and ground water at a site is an important task before remedial action can
be intelligently planned. Recently laboratory studies (e.g., McKinley, 2003) has shown
that the low frequency electrical properties of a soil from the Savannah River Site (SRS)
containing certain clay and contaminated by perchloroethane (PEC) may be sufficiently
unique to make it possible to use electrical impedance tomography (EIT) to differentiate
normal electrical heterogeneities of the subsurface from parts of the subsurface
containing DNAPL contamination.
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