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11th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 22 Mar 1998 - 26 Mar 1998
- Location: Chicago, Illinois, USA
- Published: 22 March 1998
1 - 50 of 111 results
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Enviro-Core - A Dual-Tube Direct Push System For Rapid Site Characterization
Authors Murray D. Einarson, Michael B. Casef, Donald L. Winglewich and Mary I. MorkinEnviro-Core® is a patented dual-tube or “cased” soil coring system that uses small-diameter
temporary drive casing to prevent the probe hole from collapsing between sampling runs. The
small-diameter drive casing and inner sample barrel are simultaneously pushed, pounded, or
vibrated into the ground. Soil cores are collected in liners inside the sample barrel. After being
advanced, the sample barrel is retrieved, while the drive casing is left in place to prevent the
borehole from collapsing. The drive casing ensures that subsequent samples are collected from the
targeted interval, rather than potentially contaminated slough from higher up in the probe hole. The
Enviro-Core system is most commonly used with portable sampling rigs that combine percussion
hammer and high-frequency vibration to advance the tool, although the system can be used with any
direct push (DP) sampling vehicle or conventional drilling rig. The design of the dual-tube
sampling system allows consultants to collect depth-discrete soil gas samples, groundwater samples,
and install small-diameter temporary or permanent monitoring wells. The system facilitates
retraction grouting, the most effective method of sealing DP probe holes.
The Enviro-Core® system was used during an accelerated environmental site investigation at
Alameda Naval Air Station in Alameda, California. The site geology and contaminant plume were
quickly defined in three dimensions, providing the design data necessary to install an experimental
in situ funnel-and-gate remediation system.
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The Use Of Time Domain Reflectometry For Vertically Profiling The Water Content Through The Unsaturated Zone
Authors P.A. Ferre and D.L. RudolphStandard, continuous-rod time domain reflectometry (TDR) probes, installed
vertically at the ground surface, measure the average water content from the ground
surface to the ends of the rods. Alternative probes have been described that allow for
vertical profiling of the water content beneath a single surface point. However, no single
probe design is optimal for all measurement needs Based on analyses of the properties of
published TDR probe designs, we make suggestions regarding the conditions for which
several probes are best suited. We suggest the use of two-rod, standard probes wherever
possible. Often, interval differencing of the responses of a series of vertically installed
probes of different lengths can provide an approximate measure of the water content
profile in a relatively homogeneous medium. Horizontally installed standard probes can be
used to improve the resolution of the water content profile if the disturbance caused by
their placement is acceptable. Two surface probe designs have been presented that can
measure the water content very near the ground surface. Two access tube designs have
been presented that can measure the water content over several preselected depth
intervals. However, probes with coated rods and probes that place the rods entirely within
an access tube will underestimate the water content if the water content varies along the
rods. In addition, the sample volume of these probes will vary with the water content of
the medium, becoming restricted to a region immediately adjacent to the coatings or
access tubes in higher water content conditions.
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Status Of Astm Standardization Activities On Direct Push Technology
More LessThe American Society for Testing and Materials (ASTM) has an active program on developing
standards for use of direct push technology for environmental sites characterization. Numerous
ASTM subcommittees are working on standards for environmental site characterization. ASTM
committee D-l 8 on Soil and Rock developed subcommittee D-18.21 to develop standards on
ground water and vadose zone investigations. Direct push technology is focused in
subcommittee section D-l 8.21 .O 1 on direct push technology. Standard guides have been
published on direct push soil and water sampling. Standards on use of the electronic cone
penetrometer and the use of laser induced fluorescence have been completed. A general guide on
different induced fluorescence techniques are under development. Standards are needed for
resistivity/conductivity penetrometers. There are new penetrometer sensors being developed
which will eventually require standardization. The approach has been to generate general
information guides and then to develop more specific operations techniques for specific sampling
systems. Contrary to claims of ASFE and NGWA our guides do not restrict the use of
engineering judgement or development of new technologies. ASTM standards will evolve to
include new technologies as they are developed. However, monetary support from government is
now gone, the process is time consuming, and many participants find it hard to generate the
needed standards. It is doubtful the section will generate specific operations guides for
individual equipments.
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Innovative Site Characterization And Analysis Penetrometer System (Scaps): In-Situ Sensor And Sampling Technologies
Authors John H. Ballard and M. John CullinaneThe U.S. Army Engineer Waterways Experiment Station (WES), sponsored by the U.S. Army
Environmental Center (AEC), developed the Site Characterization and Analysis Penetrometer
System (SCAPS) in response to a critical need of the U.S. Government to characterize soil and
groundwater conditions on military installations. A cooperative, partnered effort was instituted
between Tri-Service (Army, Navy, and Air Force) and Department of Energy (DOE) research
laboratories to accelerate the development, demonstration, and transition of contaminant sensor
and sampler technologies. This effort has produced a suite of cost-effective, in-situ, sensing and
sampling technologies under the SCAPS umbrella that are capable of rapidly detecting,
discriminating, and quantifying subsurface physical characteristics and a wide variety of soil and
groundwater contaminants.
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Cone Penetrometer Testing And Discrete-Depth Groundwater Sampling Techniques: A Cost-Effective Method Of Site Characterization In A Multiple-Aquifer Setting
Authors Dawn A. Zemo, Yvonne G. Pierce and John D. GallinattiCone penetrometer testing (CPT), combined with discrete-depth groundwater sampling methods, can
reduce significantly the time and expense required to characterize large sites that have multiple aquifers,
especially compared to the more common practice of installing monitoring wells. Results from the
screening site characterization then can be used to design and install a cost-effective monitoring well
network. At a site in northern California, it was necessary to characterize the stratigraphy and the
distribution of volatile organic compounds (VOCs) to a depth of 80 feet within a %-mile-by-%-mile
residential and commercial area in a complex alluvial fan setting. To expedite characterization, a tiveweek
field screening program was implemented that consisted of a shallow groundwater survey, CPT
soundings and pore-pressure measurements, and discrete-depth groundwater sampling. Based on
continuous lithologic information provided by the CPT soundings, four predominantly coarse-grained,
water-yielding stratigraphic packages were identified. Individual coarse-grained units within each
package are discontinuous, as they coalesce and pinch out in longitudinal and transverse directions.
Seventy-nine discrete-depth groundwater samples were collected using either shallow groundwater
survey techniques, the BAT Enviroprobe, or the QED HydroPunch I, depending on subsurface
conditions.
Using results from these efforts, a 20-well monitoring network was designed and installed to monitor
critical points within each stratigraphic package. Good correlation was found for hydraulic head and
chemical results between discrete-depth screening data and monitoring well data. Understanding the
vertical VOC distribution and concentrations produced substantial time and cost savings by minimizing
the number of permanent monitoring wells and reducing the number of costly conductor casings that had
to be installed. Additionally, significant long-term cost savings will result from reduced sampling costs,
because fewer wells comprise the monitoring network. We estimate these savings to be 50 percent for site
characterization costs, 65 percent for site characterization time, and 60 percent for long-term monitoring
costs.
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Detailed Subsurface Characterization Using The Waterloo Profiler
More LessGroundwater contaminant plumes are often very complex, exhibiting sharp concentration gradients, complex source
geometries and transport pathways and variability in the conditions affecting the fate of the contaminants. Failure to
understand these complexities can lead to the failure of the chosen remedy. Rapid adaptive site characterization
(RASC) is a new approach to site investigation in which a conceptual model is developed, resources are mobilized to
the site and data are produced and interpreted on site in near real time. The data interpretations are used to revise the
conceptual model and revise the site investigation in response to site conditions. The Waterloo Profiler is a new tool
which is an integral part of RASC on suitable porous media sites. The Waterloo Profiler was developed at the
University of Waterloo in 1992 and has undergone extensive testing and development since then. This tool is
uniquely suited to resolving the spatial structure of contaminant distributions, hydraulic head and hydraulic
conductivity as well as physico-chemical properties such as pH, dissolved oxygen, oxidation/reduction potential,
specific conductance and turbidity. This ability leads to enhanced understandings of source geometries, travel
pathways and contaminant fate which are essential to making sound decisions about plume management.
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A Permeable Membrane Sensor For The Detection Of Volatile Compounds In Soil
More LessThe large volume of site investigation workbeing performed since 1980 has spurred numerous attempts to improve
field methods of data collection. As part of this effort, GeoProbe Systems has developed two soil logging tools
which can be driven into soil to determine either lithology or contaminant concentration. These two tools are the
soil conductivity logging tool and the membrane interface probe. Both of these methods can be combined into the
same probe giving the site investigator a powerful means of collecting subsurface information. The soil conductivity
log of this probing tool is used to interpret lithology while the membrane interface probe is used to determine the
position and approximate concentration of volatile organic compounds (VOCs).
This paper will describe the principle of operation of the combined soil conductivity (SC) and membrane interface
probe (MIP). Data is presented in this paper from actual field use of
the MIP/SC logging system on fuel hydrocarbon and chlorinated
solvent contamination and comparisons are made to soil core analyses.
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Delineation Of A Chlorinated-Solvents Plume In Complex Stratigraphy Using The Waterloo (Ingleton) Prof’Iler
Authors Scott A. MacFabe, Dr. David Rudolph and Carol J. SchollDuring site-characterization activities at a former waste-disposal structure in Illinois, chlorinated solvents
including trichloroethene (PCE) and related degradation products were found in shallow soils and ground water.
The nature of the contaminants that were released, combined with the complicated alluvial stratigraphy presented
a relatively common but problematic setting with regard to characterization and remediation of the site. The
preliminary investigation involved conventional field methods including geophysical surveys, GeoProbe@
borings, and conventional drilling and monitoring using an auger rig and monitoring wells. This preliminary
assessmenpt rovided a coarse outline of the plume emanating from the source area, but more detailed delineation
of the comam.ination and site lithology was required to confidently define the plume comiguration.
A review of alternative technologies identified a newly developed direct-push profiling device designed by Bob
Ingleton at the University of Waterloo to facilitate detailed, depth-discrete ground water sampling. This device
has the following advantages: eliminates generation of contaminated drill spoil, greatly reduces volume of
dewntamination water required, provides qualitative determinations of hydraulic conductivity and lithology,
enables multiple sample wllection at various depths without need for retracting device between samples and no
permanent wells are left behind At the Illinois site, application of the Profiler provided an inexpensive and rapid
method of developing vertical profiles of ground water quality, resulting in a more comprehensive delineation
of wmammation as well as evidence supporting the intrinsic remedial capabilities of the subsurface. The results
of the investigation show that the Waterloo Profiler produces superior results in settings requiring detailed
analysis, minimal waste generation, and temporary sampling locations.
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Use Of Scaps Suite Of Tools To Rapidly Delineate A Large Mtbe Plume
Authors Mark Kram and Ernest LoryThe Navy Site Characterization and Analysis Penetrometer System (SCAPS) was used to
rapidly delineate the extent of a dissolved Methyl Tertiary Butyl Ether (MTBE) plume
resulting from an underground storage tank system petroleum release. Records indicated
that approximately 11,000 gallons (42 cubic meters) of leaded and unleaded gasoline
were released from the tank system between September 1984 and March 1985. MTBE
was identified in the most downgradient monitoring wells present at the site in the Fall of
1996. These wells were beyond the extent of the delineated benzene plume, but
contained MTBE levels exceeding 10 parts per million (ppm). A combination of
innovative water sampling, rapid turn around chemical analyses, near real-time plume
mapping, and geophysical methods were used to delineate the extent of the MTBE plume
to 35 parts per billion (ppb) concentration levels, install longitudinal and sentry wells in
the most appropriate locations, and conduct the site characterization efforts in an
expedient fashion. During the 15 field days it was determined that the dissolved MTBE
plume extends approximately 4,100 feet (1,250 meters) in length, approximately 500 feet
(150 meters) in width through the widest segment, and approximately 33 acres (133,55 1
m”) in map view. Assuming that contaminants were first introduced into the aquifer in
September 1984, the calculated linear contaminant velocity for dissolved MTBE at the
downgradient edge of the plume is approximately 342 feet (104 meters) per year for this
site.
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Optimizing 3D Refraction And Reflection Survey Design
Authors Jie Zhang and Eugene LavelyA useful approach to optimal seismic survey design is to simulate the seismic response for a suite
of a priori subsurface models and shot-receiver templates. We present a method for estimating an
effective source-receiver distribution for resolving an assumed 3D structure. To design the receiver
distribution, we calculate continuous traveltime slices at the surface from a given source template
and plot the RMS curvatures of the wavefronts. The spatial density of the receiver coverage should
be in proportion to the locally varying magnitude of the RMS curvature. Similarly, to determine
the optimal source distribution, we sum the RMS curvatures of the wavefront traveltimes due to
each source in the entire survey area. In the same way, the magnitude of the curvatures suggest
the most important areas for source locations.
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True Topographic 2-D Migration Of Georadar Data
Authors Frank Lehmann, Daniel Vonder Mühll, Michiel van der Veen, Peter Wild and Alan G. GreenThe principal goal of georadar investigations is to determine the geometries of fine
structures in the shallow subsurface. If strongly dipping reflections or diffraction
hyperbolas are present in the georadar data, migration is a necessary processing step.
Classical migration routines normally employed in seismic data processing may not be
suitable for georadar data collected across regions of moderate to high topographic relief.
To address this problem, we have written a modified Kirchhoff migration program that
accounts automatically for antenna separation and topographic variations.
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Introduction To A Model Based Inversion Algorithm For Gpr Signal Processing
Authors Dr. Mark D. Patz and Dr. Madjid A. BelkerdidThis paper describes a non-intrusive buried object classifier for a ground penetration
radar (GPR) system. Various GPR data sets and the implemented processing are described. A
model based inversion algorithm that utilizes correlation methodology for target classification is
introduced. Real data was collected with a continuous wave GPR. Synthetic data was generated
with a new software package that implements mathematical models to predict the
electromagnetic returns from an underground object. Sample targets and geometries were
chosen to produce two experimental scenarios.
Each of-the real measurements and their matching simulated data set were imaged with
the same signal processing algorithms. The imaged results were correlated amongst each other
to produce a performance measurement for each combination. Thus producing a confusion
matrix from which the real data can be analytically compared to the simulated. This final result
was used to determine the effectiveness of this technique to determine the real object’s identity.
The synthetic data images exhibited similar traits as present in the real data, however, good
correlation results were not observed.
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Interpretation Of Shallow Stratigraphic Facies Using Artificial Neural Networks And Borehole Geophysical Data
Authors Curtis A. Link and Stuart BlundellA study has recently been conducted to assess the extent of hydrocarbon impacts to groundwater
and soil resources at a petroleum refinery site in Billings, Montana. To accomplish the study,
forty-six groundwater monitoring wells were installed at the site. Data collected from the wells
included detailed lithologic descriptions from split-spoon samples, cutting returns from air rotary
drilling, and suites of geophysical well logs. Because the quality of the lithologic descriptions
from the borings was erratic, our approach was to produce lithofacies interpretations based on
gamma ray logs input into a neural network classifier system.
The type of neural network used was a self-organizing map. This type of network does not
require user interpretations, instead, the network categorizes each input vector into a class based
on similarity to other input vectors. The number of output classes is determined by the user. The
output classifications were then plotted as ‘pseudo-logs’ and correlation performed using these
pseudo-logs.
Cross sections constructed using conventional well log interpretation and the neural network
classifications show good, general agreement. A significant advantage of the neural network
approach over a conventional interpretation approach is that all of the well log data are analyzed
concurrently preventing inconsistencies that frequently occur with conventional methods.
Another major benefit to the neural network approach is the choice of the number of classes
which correlates with the level of lithologic detail that can be resolved.
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The Determination Of Electrical Anisotropy Using Surface Electric And Electromagnetic Methods
More LessThe concepts of homogeneity and isotropy play an important role in electromagnetic
modeling. Usually we consider models to be composed of elements that are homogeneous and
isotropic, whether the models be one-, two-, or three-dimensional. However, real geological
formations may exhibit anisotropy in two ways. Firstly, the formation may be intrinsically
anisotropic because of the micro-structure of the formation. In this category we find clays that
because of the elongated shape of the individual mineral grains and the processes of deposition
can have a better conductivity in the direction parallel to the grain planes. Secondly, surface
electric and electromagnetic methods have a limited resolution of the conductivity structure of
the subsurface, and in one-dimensional modeling we shall often have to consider the collection
of many thin layers as one composite layer, which will then be macro-anisotropic. In both cases it
is most often assumed in one-dimensional modeling that the conductivity is the same in all
horizontal directions, but different from the vertical conductivity.
Neither galvanic nor inductive methods alone can resolve the anisotropy of the ground.
However, a joint inversion of galvanic and inductive data requires that anisotropy be taken into
account and can also resolve the coefficient of anisotropy and thereby contribute to a more
detailed description of the subsurface resistivity structure (Jupp and Vozoff 1977).
The determination of electrical anisotropy is desirable as it may serve as an indicative
parameter for the presence of otherwise unresolved thin layers. From a hydrogeological point of
view these may severely influence the hydraulic flow pattern in the ground. Thin clay layers in an
otherwise sandy formation will lower the vertical hydraulic conductivity considerably, and the
presence of thin sand and gravel layers in an otherwise clayey formation may serve as fast
hydraulic conduction channels for polluted water. In connection with mapping of raw materials
anisotropy indicates that the material under investigation is not homogeneous throughout and
may thus be of inferior quality.
In the following an analysis of the importance of taking anisotropy into account in inverse
modeling will be presented, and it is shown how the combined use of geoelectrical and transient
soundings can resolve the coefficient of anisotropy of a subsurface layer. It is found that the
coefficient of anisotropy is only well resolved for layers which are many times thicker than the
overburden.
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An Approximate Inversion Procedure For Lines/Grids/Collections Of Time-Domain Electromagnetic Soundings
Authors Colin G. Farquharson, Douglas W. Oldenburg and Yaoguo LiTime-domain electromagnetic surveys typically comprise numerous soundings. Any
useful interpretation procedure must be rapid enough to cope with these large amounts
of data. Even though the geological target invariably displays a degree of three-dimensionality,
it is often possible to obtain information about its structure from an Earth model
constructed from the results of one-dimensional inversions of each sounding. We derive
from this process an approximate inversion procedure. The observations from all soundings
are averaged to generate a representative data-set which is then inverted using a rigorous
one-dimensional algorithm to produce a layered background model. As by-products of the
inversion, the sensitivities for the background model are available, as well as the value of
the trade-off parameter in the objective function being minimized. Approximate inversion
steps, which do not involve re-calculating the full sensitivities, are then carried out for
each sounding. Each step requires only the solution of a small matrix equation, and a
few forward modellings. Two or three steps generally result in a marked decrease in the
objective function, and hence an improvement in the model for that sounding.
The technique is illustrated with synthetic data generated from a three-dimensional
model, and with field data collected in Venezuela. The inversion procedures are tailored
to produce piecewise-constant models, and use a robust measure of data misfit. For the
field example, rigorous one-dimensional inversions provide the model for comparison. The
approximate inversion is shown to provide much of the same information, but in a substantially
reduced amount of time.
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Electromagnetic Induction Spectroscopy
Authors I.J. Won, Dean Keiswetter and Elena NovikovaAn object, made partly or wholly of metals, has a distinct combination of electrical conductivity,
magnetic permeability, and geometrical shape and size. When the object is exposed to a low-frequency
electromagnetic field, it produces a secondary magnetic field. By measuring the secondary field in a
broadband spectrum, we obtain a distinct spectral signature that may uniquely identify the object. Based
on the response spectrum, we attempt to “fingerprint” the object. This is the basic concept of
Electromagnetic Induction Spectroscopy (EMIS). EMIS technology may be particularly useful for
detecting and characterizing buried landmines and unexploded ordnance. EMIS should be fully
applicable to many other problems where target identification and recognition (without intrusive search)
are important. Potential applications may include industrial sorting processes and robotics.
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Man Portable Gps/Geophysical Instrument Interface (A Practical Case Study)
Authors R.J. Bowers and W.R. SaundersIn the past few years the emphasis for research in the geophysics,
unexploded ordnance detection arena has been towards remote
pilotless vehicles to collect data or knowledge base software.
Although promising, both of these technologies are either
prohibitively expensive in the competitive environment of UXO
remediation, or time intensive. Both technologies tend to take the
operator out of the equation. Unfortunately, many if not most UXO
jobs take place in areas where a vehicle cannot operate or a
canned knowledge base will tend to pick unacceptable quantities of
false targets.
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Continuous Transient Electromagnetic Sounding
More LessThe mapping of subsurface resistivity structures using transient electromagnetic soundings,
TEM, has gained an important role in hydrogeological investigations in Denmark. Regional
mapping with TEM have produced results, which leaves no doubt as to the ability of the
method to delineate freshwater sandy aquifers in well conducting hosts of Tertiary clays,
These results have been achieved measuring in a dense grid and do demonstrated the necessity
of estimating the data quality and variation by correlating adjecent data sets to reveal
distortion and multidimensionality of the measurements. The fact that these investigations are
often carried out in densely populated areas, where the cultural noise level is high, accentuates
this necessity even more (Christensen and Sorensen, 1994).
In this context a new method, the Pulled Array Transient Electromagnetic Method, PATEM,
is developed. The method applies a transmitter and a receiver coil system which are towed
along profile lines while measuring. With this method the cost of the field work is drastically
reduced. Furthermore, as the measurements are recorded very densely, adjacent data sets can
be correlated to ensure good data quality, and distortion from cultural effect from powerlines,
fences, etc. of the data sets is more easily revealed. Finally the necessary density of the data
sets for multidimensional interpretation can be provided (Auken, 1995).
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Improvement In The Azimuthal Em Method - The Value Of Signal Processing
Authors Lee Slater, Stewart Sandberg and Mariusz JankowskiThe azimuthal EM method has recently been proposed as an alternative to the well-applied azimuthal
resistivity survey, primarily for the investigation of fracture-induced electrical anisotropy. The advantages
of the EM approach include (1) reduced data acquisition time, (2) simple field acquisition procedure, and
(3) a reduced data acquisition area. In addition, the problem of electrode contact resistance is overcome
with the EM method.
Signal processing techniques were developed to assist quantification of noise in azimuthal EM datasets and
to enable noise reduction. Comparison of the energy in the even and odd coefficients of the frequency
spectra of azimuthal EM datasets allows the signal-to-noise ratio to be identified. Convolution of the
azimuthal data with linear phase low pass filters allows for significant noise removal. These processing
techniques were applied to azimuthal EM datasets collected at two study sites. Following data processing,
the EM datasets revealed apparent resistivity lobes consistent with the orientation of fracture strike mapped
at these locations. These results suggest that, with the application of data processing, structural information
obtained from an azimuthal EM survey is likely to be comparable to that obtained from an azimuthal
resistivity survey.
Azimuthal resistivity surveys have been previously performed with array configurations that allow for
misinterpretation of apparent resistivity variability caused by lateral heterogeneity as evidence for the
presence of anisotropy. Use of an asymmetric azimuthal EM array, combined with analysis of the energy of
the even and odd coefficients of the frequency spectra, provides a means to differentiate heterogeneity from
anisotropy. The value of this approach is described and the results of a test at a site of known lateral
heterogeneity are presented. Analysis of the frequency spectrum for an asymmetric array allowed
identification of the lateral heterogeneity at this site.
These examples illustrate that analysis of the frequency spectra of azimuthal EM data greatly assists
interpretation. The ability to (1) characterize and reduce noise, and (2) differentiate lateral heterogeneity
from anisotropy, significantly improves the value of the azimuthal EM technique in site characterization.
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Water Produced With Oil And Gas -- A Concern For Production And Development Of Petroleum Resources
Authors G.N. Breit, B.D. Smith, M.J. McCormick, R.A. Zielinski and J.K. OttonWater produced with oil and gas can affect petroleum resource development and, if improperly
handled, adversely impact the environment. Dissolved salts, organic compounds, trace metals and
radionuclides in the 20 billion barrels of produced water handled annually in the U.S., limit
methods of disposal. Inadvertent discharge of this water and historic practices of water disposal
have resulted in contamination of production sites by substances dissolved and suspended in the
water as well as solids that precipitated from the water. Investigations related to produced water
underway at the USGS are focused on understanding geochemical and hydrologic processes and
applications of geophysics. Understanding the processes that affect the accumulation and
dispersion of substances contained in produced water will refine site assessment techniques and
provide additional tools to evaluate the impact of produced water on soil and water quality.
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Geophysical Surveys For Mapping Brine Contamination Resulting From Oil And Gas Production
More LessWith the production of oil and gas, brines with high concentration of dissolved solids (TDS) are
also brought to the surface. In processing plants, the hydrocarbon and water are separated. In
modern disposal practices, the brines are injected in deep formations. Occurrences of brine
contamination are mainly the result of disposal practices from the early days of production. The
lateral and vertical extent of brine contamination can often be inferred from measurements of the
geoelectric section. Frequency and time domain electromagnetic methods have proven good
tools for determining the geoelectric section, and three case histories will illustrate the use of
these methods. In two case histories, the brine contamination resulted from disposal in unlined
surface ponds. In one case history, an improperly abandoned well is likely cause of
contamination.
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Use Of Terrain Electromagnetic Geophysical Methods To Map Saline-Water Contamination, East Poplar Oil Field, Northeastern Montana
Authors Joanna N. Thamke, Steven D. Craigg and Thomas M. MendesQuaternary deposits, comprised of the Poplar River alluvium and glacial deposits, are the sole
developed source of ground water for residents in and near the East Poplar oil field. The extent of
saline-water contamination in Quaternary deposits in and near the East Poplar oil field may be as
much as 12.4 square miles. The probable source of saline-water contamination in the Quaternary
deposits is brine that is a byproduct of the production of crude oil in the East Poplar oil field study area.
Terrain electromagnetic apparent conductivity data collected in an area of about 21.6 square
miles correlate well with ground-water quality. These data were collected and interpreted in conjunction
with water-quality data from existing water wells to delineate possible saline-water contamination
plumes. Monitoring wells were subsequently drilled in some areas that lacked existing
water wells to confirm most of the delineated saline-water plumes. Analysis of ground-water samples
from both existing and newly drilled monitoring wells confirms the presence of 7.3 square
miles of contamination, as much as 2.0 square miles of which are considerably contaminated. Terrain
electromagnetic apparent conductivity data in areas with no wells delineate an additional 5.1
square miles of possible contamination, 3.2 square miles of which might be considerably contaminated.
Brine-injection wells, oil wells, pipelines, and storage-tank facilities appear to be probable
sources of the saline-water contamination in many of the plumes.
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Brine In The Near-Surface Environment: Determining Salinization Extent, Identifying Sources, And Estimating Chloride Mass Using Surface, Borehole, And Airborne Em
Authors J.G. Paine, A.R. Dutton, S.D. Hovorka, M.U. Bltim, M.P. Mahoney and E.J. SullivanElectromagnetic (EM) methods can be used to locate salinized soil and water, identify likely
salinity sources, and estimate the total chloride mass in the saturated and unsaturated zone. Groundbased
EM measurements can be used to establish boundaries of the salinized area and determine the
range of electrical conductivity, borehole measurements and time-domain EM soundings can determine
the vertical extent of salinization and establish the relationship between ground conductivity
and chloride content, and airborne measurements can establish the lateral extent of salinization and
locate potential salinity sources. Total chloride mass in a salt-water plume can be estimated from
airborne EM data and the empirical chloride-conductivity relationship.
EM methods employed in geophysical studies of near-surface salinization owe their success
to the increase in electrical conductivity that occurs where saline water infiltrates saturated or unsaturated
geologic materials. EM data can also be combined with information on soil type, moisture
content, and water chemical composition to help identify geophysical signatures that distinguish
important causes of salinization such as natural saline seeps and springs, oil-field sources such as
brine-disposal pits and leaking oil or gas wells, and agricultural activities.
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Stochastic Inversion Of 3D Ert Data
Authors Xianj in Yang and Doug J. LaBrecqueA new stochastic inversion algorithm to invert three-dimensional (3D) electrical resistivity
tomography (ERT) data has been implemented. The statistical information about the correlation
among the model parameters and the correlation among observed data was employed to stabilize
the ill-posed 3D ERT inverse problem. The data noise covariance matrix was diagonal based on
the assumption of uncorrelated data noises. The model parameter covariance matrix, however,
could be a full matrix depending on the correlation length between the model parameters. The
resulting unsymmetric linear system was solved by bi-conjugate gradient (BICG) methods, such
as BICGSTAB, a stabilized variant of BICG algorithm, and TFQMR, a transpose-free quasiminimal
residual algorithm.
An advantage of this algorithm is that any prior knowledge about the model parameters
can be easily incorporated in the inversion process in the form of covariance model type and
correlation length. This is the basis for our future implementation of a joint hydrologicalgeophysical
inversion. This stochastic inverse technique will be used for characterizing,
monitoring, and predicting fluid movement in heterogeneous vadose zone.
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3-D Characterization Of An Alluvial Aquifer System: A Case Study Using Borehole Data And Indicator Geostatistics
More LessThe three-dimensional characterization of a complex, alluvial aquifer system in the
West Alberta Plains was made possible by using indicator geostatistics to interpolate
between borehole log interpretations. Gamma-ray logs, induction logs, and lithology
determined from cuttings were used to assign indicators (categories) of sandstone and till
aquifers, and mudstone/ siltstone aquitards. The indicators in ninety well columns were
then used to compute variograms and create a 3-D, anisotropic variogram model. The
variogram model and the vertical proportions of sandstone and non-sandstone were used to
constrain the indicator simulation of the sandstone and non-sandstone indicators. Then,
using sequential gaussian simulation, the thickness of the till was simulated and added to
the sandstone and non-sandstone models. The resulting 3-D geologic models will be used
for groundwater flow and chemical transport modeling.
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Improved Detection Performance Using A Bayesian Decisiontheoretic Approach
Authors Leslie Collins, Dean Keiswette, Lawrence Carin and I.J. WonThe fundamental goal of target identification using geophysical methods is to achieve a
high detection rate along with a low false alarm rate. While many electromagnetic (EM)
and magnetic detectors achieve the first of these goals, it is often at the cost of a
prohibitively high false alarm rate. In this paper, we present a Bayesian decisiontheoretic
approach to target identification using EM data. This approach provides both an
improved detection scheme and performance evaluation in the form of ROC curves
plotting probability of detection versus false alarm rate. In addition to detailing the
Bayesian-based approach, we present selected case studies that utilize broadband
electromagnetic data acquired with the GEM-3 sensor. We compare the survey results
obtained with standard thresholding analyses to survey results obtained using statistically
based signal detection theory. Our preliminary results indicate that the detector derived
using signal detection theory is superior to the standard detection schemes that utilize
contour plots and thresholding. The results also indicate that detection performance is
dramatically improved when multi-frequency data is utilized. Furthermore, since
detection performance is observed to be a function of frequency, careful selection of the
EM frequencies at which data is recorded may result in further improvements.
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Optimal 3-D Geophysical Tomography
Authors Margaret J. Eppstein and David E. DoughertyAcoustic and electromagnetic tomographic methods attempt to provide accurate and
highly resolved estimates of spatially varying parameters. High resolution is obtained by
discretizing the domain into a large number of parameters to be estimated. Because the
resulting problem size is large, most implementations rely on iterative methods that attempt
to minimize the output least-squares criterion through the repetitive application of relatively
simple parameter updates. The accuracy and efficiency of such methods depends on the
quality of the initial estimates and the parameterization employed, as well as on the update
mechanism. Conversely, optimal filtering methods enable the computation of non-iterative,
minimum-variance updates and can be used to yield estimates of both parameter values and
covariances. Despite the statistical superiority of optimal methods, they have seldom been
exploited in geophysical applications due to their computational demands for large systems.
We have devised an approximate extended Kalman filter, which is a recursive, Bayesian,
minimum variance estimator for nonlinear dynamic systems. The inverse of an a priori
estimate of the parameter covariance matrix is used to damp the system and the weighting
matrix includes the inverse of the measurement error covariance matrix. While the recursive
nature of the filter is designed to handle time-series data, it can also be exploited to assimilate
batch data iteratively and/or recursively in smaller batches.
We have built efficient approximations into the filter that, in conjunction with our
domain-decomposition strategy and dynamic parameterization scheme, enable application
of the method to very large domains. The integrated method simultaneously estimates
the number, geometry, value, and covariance of spatially distributed parameters. Threedimensional
tomographic results are presented.
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A Geostatistical Analysis Of Gold Mineralisation In Oakley’S Reef, Hutti Gold Mines, Karnataka, India
By D.D. SarmaA geostatistical analysis of gold mineralisation process. characterised by discrete regular
samples drawn in respect of Oakley’s reef of Hutti gold fields and based on a segment of the
lode comprising level 10 (305 m in depth) to level 20 (620 m in depth) is presented. As the
stationary phenomena was observed to hold good for each level (local stationarity) but not for
the segment of the reef as a whole (global stationarity), geostatistical modeling was carried out
by processing each level data separately. In addition, the data of two vertical profiles were also
analysed geostatistically for a study of depth-wise variation and possible continuity of
mineralisation etc.
Variographic analysis revealed that the experimental variograms for each of the levels and
two vertical profiles could be represented by spherical model. However, the values for the
parameters C, (nugget effect), C (Sill) and a (range) of the model varied significantly from level
to level. High values were observed for the 16th level which is at a depth of 5 10 m. Using the
model parameters for each of these levels, kriging for 324 blocks of ore, each of size 30m x
width between one level and another, was carried out. A sample set of kriged estimates
together with kriged standard errors is presented. On the basis of variographic analysis it has
been inferred that the sample size can be reduced to half the present size without loss of
accuracy in the estimates for grade. This would result in substantial savings to the industry.
In order to quantify the chances of continuity of the mineralisation beyond the known
workings, Maximum Entropy Method (MEM) of spectral analysis and Markovian models were
found to be highly rewarding. MEM spectrum analysis revealed significant spectral spikes in
some of the deeper levels indicating periodicities in mineralisation ranging from
approximately 40 td 100 m in distance,, , and at approximately 50 m along the vertical profiles. In
respect of block data the estimated periodicity is from 130 to 230m along the strike and 100 to
300 m along the vertical profiles. Since the discrete gold assay values followed a Markovian
sequence, Markovian model analysis was carried out to quantify the extent(s) upto which
the present mineralisation pattern is likely to persist in the immediate unexplored area under
the assumption that the same geological conditions hold good in this area also. The likely
extents of gold mineralisation together with the respective probabilities of occurrence of grade >
2 .5 gms and > 3gms are presented.
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The Relevance Of Seismic Reflection Polarity To Dredging Performance - A Case Study
More LessIt is common knowledge that a discontinuous increase in seismic impedance produces a
reflection of positive polarity and a discontinuous decrease produces a reflection of negative
polarity. That knowledge seldom is applied in engineering contexts, however, because the
polarity of seismic reflections is not always obvious. That is particularly true in the case of
single-channel marine data when signal amplitude is displayed on paper as shades of grey. This
contribution documents a case in which reflection polarity was critical not only to the
interpretation of the seismic data but also to the client’s profit margin.
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High-Frequency Acoustic Imaging Of L Lake, Savannah River Site, South Carolina
Authors Keith J. Sjostrom and Rodney L. LeistA side scan sonar and seismic reflection study of L Lake, Savannah River Site, South
Carolina, was performed in June 1996. The geophysical investigation was conducted to
determine the location, distribution, and depth of existing burial pits and mounds within the
reservoir for incorporation into an Environmental Impact Statement. The results are also
intended to supplement previous scientific information obtained from soil samples, aerial
photography, and radiometric studies. Interpretation of the sonar data revealed numerous
mounds along the reservoir bottom that appear to have been constructed by pushing nearby
material into a heap to cover either the contaminated vegetative material, its ashes, or
contaminated sediments. The mounds do not cover any burial trenches or pits although some
small depressions are detected underneath the mounded material.
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Land-Based High-Resolution Seismic Reflection Image Of A Karst Sinkhole And Solution Pipe On Fort George Island, Duval County, Northeastern Florida
Monitoring of the drinking-water wells that tap the upper Floridan aquifer, indicate
increases in chloride concentration at some wells while at other nearby wells chloride
concentration are unchanged. One explanation for this is that geologic features (fracture zones,
joints, solution channels, and paleosinkholes) in the underlying carbonate strata of the Floridan
aquifer system have breached the semi-confining units, thus allowing warmer and more saline
water to flow upward and mix with fresh water production aquifers. A reconnaissance seismic
reflection survey was conducted at Fort George Island, Duval County, Florida, to determine if a
modified Mini-Sosie high-resolution seismic reflection technique, which has been successfully
used to image near-surface faults in urban areas, could be used to image karst hydrogeologic
features in this area.
We acquired good quality data in this survey within a depth range of 30-400 m. The
interpreted profiles of two perpendicular lines provide a clear image of geologic-karst
deformation in the form of a solution pipe and overlying buried sinkhole feature.
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Relating Cone Penetrometer Test Information To Geophysical Data: A Case Study
Authors Anthony L. Endres and William P. ClementAn analysis of data from a recent experiment at Dover Air Force Base (AFB)
has revealed a relationship between soil types determined from the mechanical
properties measured by cone penetrometer tests (CPT) and the electrical properties that
influence geophysical methods. This correlation connects two distinctly different types
of physical properties and provides a petrophysical basis for combining information
obtained from CPT and geophysical techniques governed by electrical properties. We
observed this relationship through the use of semi-logarithmic crossplots of dielectric
permittivity versus electrical resistivity where it was found that CPT soil types cluster in
a systematic manner to form a linear trend from clay-prone to sand-prone lithologies.
We obtained improved segregation of soil types when other factors, such as location
relative to the water table and stratigraphy, were used to refine the analyses of these
data. In addition, our results indicate that the ratio of permittivity to the logarithm of
resistivity is a good geophysical discriminator of the engineering soil classification.
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Comparison Of Sonic Log Data For 4 Types Of Acoustic Tools
Authors Tomio Inazaki, Toshiyuki Kurahashi and Shiro WatanabeFour types of sonic log tools were tested in the same borehole drilled in a hard formation. One is the
suspension type P-S logging tool with a dipole source and two receivers. Second one is a conventional full
wave sonic tool with two monopole transmitters and three receivers. The third is a newly developed full
wave digital sonic tool with two monopole sources and two receivers, and the fourth is an array sonic tool
with two transmitters and twelve receivers. The former two tools transmit analog signals through the
cable and convert the data digitally in the surface equipment, whereas the latter two transmit digital data
converted using 12 bit A/D boards incorporated in the probe to the surface unit. All tools are available in
the slim hole with diameter from 66mm to 120mm. The result of field measurement showed the obtained
Vp profiles coincided well with each other, and careful discrimination of waveform taking account the
tool characteristics is important for the precise analysis. Obvious attenuation of the Stoneley wave was
observed at fracture zone recognized with a borehole video image tool.
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Geophysical Well Logging And Discrete Depth Water Sampling Methods To Identify Sources Of Elevated Barium In A Water Well In Northern Illinois
By John JansenA geophysical logging study was conducted on a municipal water well in the City of
Sycamore, Illinois. The purpose of the study was to identify the source of elevated barium
levels in the well and determine if the well could be reconstructed to reduce barium
concentrations without significant loss in production. The geophysical logging suite
included a downhole televising log, four arm caliper log, gamma ray log, dual induction
log, gamma density log, and neutron density log. In addition, a spinner flow meter log
was conducted while pumping and water samples were collected from the pumping water
column at discrete depths. The results of the logging study indicated that the majority of
the barium was entering the borehole from the lower portion of the well which appeared
to be producing only about 15 to 30% of the total water production. The lower portion of
the well was sealed off with a neat cement grout plug. Barium concentration was reduced
by over 50 % with a reduction in specific capacity of about 30 to 40%. While the logging
study was successful at identifying the high barium interval, the longevity of the barium
reduction is a function of the vertical isolation provided by the confining units in the
aquifer.
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Use Of Borehole-Radar Methods To Monitor The Movement Of A Saline Tracer In Carbonate Rock At Belvidere, Illinois
Authors J.W. Lane, P.K. Joesten, F.P. Haeni, Mark Vendl and Doug YeskiCommon-depth (CD) radar surveys and cross-hole radar tomography methods were used to
monitor the movement of a saline tracer in a dual-porosity dolomite aquifer at Belvidere, Illinois. The
tracer test was conducted using an array of six open-hole bedrock wells at the Parson’s Casket Hardware
Superfund site. The injection and recovery boreholes were about 20 m (meters) apart, and the imaging
boreholes were arranged to provide planar coverage across and along the anticipated tracer path. A
hydraulically conductive zone identified during previous investigations was isolated using straddle
packers and pumped to establish a hydraulic gradient between the injection and recovery wells. A sodium
chloride (NaCl) solution was continuously injected into this zone to move the tracer across the
tomographic image plane.
CD cross-hole radar surveys and cross-hole tomography surveys were conducted before and
periodically during the tracer injection. Background tomograms contain similar radar velocity and
attenuation changes with depth, consistent with a layered dolomite that has variable porosity and
electrical conductivity. Slow changes in attenuation associated with low tracer velocity permitted the
acquisition of multiple CD surveys and two cross-hole tomography surveys during injection. CD surveys
were used to rapidly identify the presence of tracer between wells. Attenuation-difference tomograms
contain attenuation increases that delineate the spatial distribution with time of the saline tracer and show
the progressive movement of the tracer within the tomographic image plane. Formation porosity and
resistivities calculated from radar velocity and attenuation tomograms were used to estimate changes in
fluid resistivity and tracer concentration in the tomographic image plane.
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The Application Of Very Low Frequency Electromagnetics And Downhole Geophysical Techniques To An Island Hydrogeologic Study: Rhode Island Formation, Narragansett Basin
Authors Scott C. Michaud and Christopher L. CovelVery Low Frequency (VLF) geophysics has been utilized to supplement data collected using
downhole geophysical techniques for the purpose of studying a fractured bedrock aquifer on
Conanicut Island in Narragansett Bay, Rhode Island. Other components of a larger ongoing study
include the modeling of groundwater flow, the study of the aquifer’s natural hydrogeochemistry,
and the anthropogenic impact on the aquifer. The aquifer is comprised of a portion of the Rhode
Island Formation, which ranges from a micaceous schist to a meta-sandstone and
meta-conglomerate. Geophysical and outcrop measurements reveal five fracture orientations
through which groundwater is expected to flow. These correspond to the bedrock’s dominant
foliation as well as numerous fracture surfaces apparently related to post-Carboniferous tectonics.
The groundwater model is being developed to evaluate the suitability of treating the aquifer as
an equivalent porous medium. Downhole geophysical investigations conducted on Conanicut
Island by the United States Geological Survey (USGS) yielded data which appear to suggest a
predictable trend in the flow of groundwater into a bedrock well with depth. Based on data
collected at the time of this publication, groundwater flow to the well is observed to decrease
exponentially with depth. The location of these fractures and their orientations provided the
impetus for the VLF application. Linear filtering of VLF measurements (after Karous and Hjelt,
1983) has provided for the modeling of the positions and orientations of large water-bearing
fracture zones. Fracture orientations based on VLF geophysical interpretations appear to
correspond to borehole televiewer images and orientations measured at formation outcrops on the
island.
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Integrating Surface And Borehole Geophysics In Ground Water Studies - An Example Using Electromagnetic Soundings In South Florida
Authors Frederick Paillet, Laura Hite and Matt CarlsonBorehole induction logs are used to calibrate surface induction soundings in units of pore water
salinity. This is accomplished by correlating water sample conductivity with the electrical
conductivity of the formation over the sampled interval. In addition to the hydraulic calibration of
the surface induction data, the analysis shows geophysical logs contribute to the interpretation of
the surface induction soundings in two other ways: 1) logs show that the constant conductivity
layer model most often used to analyze induction soundings is appropriate for the south Florida
study; and 2) several physically independent log measurements can be used to uncouple the
dependence of formation electrical conductivity on such parameters as salinity, permeability, and
clay mineral fraction. We conclude that geophysical logs have important applications in
formulating geophysical inversion problems and in defining quantitative relations between
geophysical measurements and hydraulic or water quality parameters of interest.
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Use Of A Multi-Offset Borehole-Radar Reflection Method In Fractured Crystalline Bedrock At Mirror Lake, Grafton County, New Hampshire
Authors J.W. Lane, F.P. Haeni and Roelof VersteegMulti-offset, single-hole, borehole-radar reflection surveys were conducted at the U.S.
Geological Survey Fractured Rock Research Site at Mirror Lake, in Grafton County, New
Hampshire. The study was conducted to evaluate the benefits of applying multi-offset seismic
processing techniques to borehole-radar reflection surveys in fractured rock.
The multi-offset reflection surveys were conducted in conjunction with a saline tracerinjection
experiment. During injection, a sodium chloride (NaCl) solution was continuously
pumped into a hydraulically conductive zone that was isolated by specially constructed, reusable,
PVC straddle packers suspended from PVC casing. Eight common-offset borehole reflection
profiles were collected within the PVC-sleeved portion of the borehole before and during the
tracer injection. The offset between the transmitter and receiver antennas ranged from 6.4 to 9.9
m (meters). The common offset data were filtered, sorted into common distance-point (CDP)
gathers, normal move-out (NMO) corrected, and stacked to produce a zero-offset borehole CDP
profile.
Comparison of the common-offset and CDP profiles indicates that multi-offset data
acquisition and CDP processing; (1) increases the resolution of reflectors near the borehole, (2)
decreases the effects of direct wave coupling, antenna ringing, and system noise, and (3)
improves the clarity of difference images used to identify the effects of saline tracer on
reflections from transmissive fractures.
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Combination Of Downhole Gamma Logging And Soil Vapor Measurements To Track Low Level Chlorinated Solvent Contamination In The Deep Vadose Zone
Authors Rich Meixner, Dan Blout, Betsy Hovda, Bill Crawford, Duane Newell, Jim Viellenave and Richard HeibelDownhole gamma logging and a soil vapor investigation were used to identity an
unknown source and the subsurface pathway of chlorinated solvents migrating to ground
water at 110’ below ground surface (bgs). Thirty (30) borings were installed using Direct
Push Technology with 1.75” OD, 1 .OO” ID drive pipe to as deep as 67’ at a New Mexico
State Highway and Transportation Department Maintenance Yard in Deming, NM. While
the pipe was still in the ground, each hole was gamma logged to establish optimum
vertical locations for the installation of permanent soil vapor implant points. Two to four
points were then installed in 2-to-11 foot thick sand filter-pack beds, separated by granular
bentonite grout, in each boring. The borings were then completed as monitoring wells
with traffic covers. Soil gas samples were collected from each vapor implant point and
analyzed in a mobile environmental laboratory using EPA method 8010 (modified) for
chlorinated volatile organic compounds, including 1,l -dichloroethene (DCE), 1,l
dichloroethane (DCA), and 1 , 1, 1 trichloroethane (TCA). Confirmation analyses were run
by GC-MS onsite. The resulting three-dimensional representation clearly identified the
source area and a plume declining in concentration and descending in depth toward the
known area of ground water contamination. The gamma logging was instrumental in the
vertical placement of vapor implant points to obtain optimum gas samples, immediately
above potential low-permeability layers. Because the Direct Push borings were installed
without soil sampling or examination, the gamma logging was very useful in the
characterization of subsurface lithology for assessing source location and vapor plume
pathways.
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Mapping Hydraulically Permeable Fractures Using Directional Borehole Radar And Hole-To-Hole Tomography With A Saline Tracer
Authors David L. Wright and John W. LaneReflection-mode borehole radar and transmission-mode radar tomograms image heterogeneity in the
electromagnetic properties of rock. Heterogeneity may be produced by interfaces between different rock
types, foliation, and fracturing. In crystalline rock, hydraulic flow is primarily through fracture networks
rather than through the rock matrix. Borehole radar methods have been applied to help map flow paths
in crystalline rock. Correlation of features identified in borehole radar reflection records and tomograms
with hydraulic flow paths is generally uncertain because the records show responses to heterogeneity of
all- kinds, not just to hydraulically permeable fractures. Even in lithologically uniform rock, it is often
not possible to distinguish fractures of high hydraulic permeabilities from those with low permeabilities.
It is possible to “erase” signatures from lithologic interfaces and rock fabric to identify the signatures of
hydraulically permeable fractures by using a saline tracer in fractured crystalline rock because the
electrical properties of the rock, except for the fractures that are open to infiltration by the brine solution,
remain the same after the injection of the brine and may be removed by examining differences. Saline
tracer experiments were carried out in 1995, 1996, and 1997 in the FSE well field at the Mirror Lake
fractured-rock hydrology research site in Grafton County, New Hampshire. Comparisons of results from
directional radar reflection surveys to well-to-well difference attenuation tomography in the same pairs
of wells show generally good correspondence between the location of radar reflections and attenuation
anomalies. Our results demonstrate the advantage of using a saline tracer for before-and-after difference
mapping of hydraulically permeable fractures in lithologically heterogeneous rock and the utility of the
coordinated use of directional borehole radar and hole-to-hole radar tomography.
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Brownfield Site Investigation Using Geophysics: A Case History From East Chicago
More LessBrownfields are areas in cities that have been determined to have environmental problems
due to industry that once operated at those sites. At present, most of the areas are open tracts of
land and they cannot be used or cleaned up until the extent of contamination has been determined.
It has been suggested that geophysics be used to conduct non-invasive sit characterization. Urban
areas have additional problems associated with then, including power line, rebar in concrete, electrical
lines in buildings, and large metal objects near by that often interfere with electromagnetic
(EM) and magnetic measurements. All of these aspects must be taken into account in designing an
effective geophysical survey in an urban environment. A Brownfield site in East Chicago was used
to demonstrate the effectiveness of utilizing geophysics and to develop strategies for applying geophysics
to Brownfields. The site contained all of the problems listed above. Ground penetrating
radar (GPR), multi-frequency EM measurements, and vertical and horizontal gradient measurements
were made. Comparisons of the magnetic and EM measurements proved to make it easier to
evaluate the GPR measurements at this site. This is the most extensive study to date of a comparison
of geophysical methods in an urban setting. The comparison of methods indicate the following:
(1) there needs to be very close (one foot or less) line and station spacing, (2) instruments
should be run in orthogonal directions, and (3) multiple methods should be used for the best characterization
of the sites.
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Characterizatlon Of A Newly Discovered Lnapl Plume At Wurtsmith Afb, Oscoda, Michigan
Authors William A. Sauck, Estella A. Atekwana and Jose L. BermejoA Light Non-Aqueous Phase Liquid (LNAPL) ground water contaminant plume has been
discovered by purely geophysical means at the former Wurtsmith AFB near Oscoda, Michigan.
The plume was discovered by Ground Penetrating Radar (GPR) while extending a long line
horn another contaminated area (FT-02) to establish background variability around that plume.
The new plume was apparent because of a high-conductivity “shadow” or GPR reflection
attenuation, identical to the pattern observed at the FT-02 plume. The GPR survey was
supplemented by an electromagnetic (EM-31) survey which revealed a group of cables
crossing the area, but no anomalous regions associated with the presence of the plume. A
magnetometer survey was conducted to search for any buried steel objects which might not
have been detected by the EM survey. The results of these initial geophysical surveys were
used by the National Center for Integrated Bioremediation and Development (NCIBRD) staff
to guide subsurface soil and fluid sampling, which verified the presence of residual LNAPL
product and ground water with conductivities 2.5 to 3.3 times above background. Subsequent
surveys were conducted, including mise-a-la-masse (MALM), dipole-dipole resistivity/induced
polarization (IP) and vertical resistivity probe (VRP) measurements. The MALM survey
shows marked elongation along the plume axis, while the resistivity/IP showed two anomalous
regions coincident with buried utilities. In addition, the VRP revealed the presence of a
conductive zone at the top of the aquifer. This newly discovered LNAPL plume, along with
other “mature” plumes, fits an electrical model which predicts conductive ground water below
the decomposing LNAPLs.
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Comparison Of Magnetic And Electromagnetic Anomalies
Authors I.J. Won and Dean KeiswetterMagnetic and electromagnetic (EM) methods are perhaps the most convenient and popular
geophysical survey methods for detecting buried manmade objects. This is due to their nonintrusiveness,
light field logistics, high survey speed, and the high quality of information. Thus, they
should considered as precursors to additional geophysical surveys. Often, the information resulting
from the two methods are sufficient for characterizing buried objects. During the oral presentation, we
will present case history examples showing magnetic and EM data collected at sites that have a range of
environmental conditions and project objectives. We find through these and numerous other
comparisons that broadband EM data are usually superior to magnetic data in terms of the amount and
the quality of information. The monopolar EM anomaly is invariably easier to interpret, and thus can
locate a buried target more accurately than the dipolar magnetic anomaly. In addition, the EM method
senses both electrically conductive and magnetically permeable targets. In contrast, the magnetic
method responds only to permeable, or ferrous, metals. In that sense, the magnetic method should be
considered a subset of the EM method, or as a special “passive” EM method at zero frequency.
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Fractures In Limestone Imaged By Radar
More LessRadar data collected along profiles and in grids have assisted in identifying subsurface
pathways that might carry motor fuel known to be contaminating domestic water wells.
Disruptions of reflections were visible in conventional radar profiles were interpreted as
fractures zone in limestone bedrock. Radar data acquired in a grid over zones where
these fractures were the most dense are presented as a three dimensional display,
facilitating the visualization of the extension of these fractures across the survey areas
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Characterization Of A Complex Refinery Groundwater Contamination Plume Using Multiple Geoelectric Methods
Authors Estella A. Atekwana, William A. Sauck and Douglas D. WerkemaThe geoelectric properties of hydrocarbon contaminant plumes vary and their geophysical
responses suggest that the ‘insulating layer’ model cannot be uniformly applied to all hydrocarbon
contaminated sites. Changes in the aquifer pore fluids chemistry, causes the variability of the
geoelectrical signature. In this study, we investigate the electrical properties of a complex hydrocarbon
plume resulting t?om 50 years of leakage into a glacio-fluvial geologic setting using ground penetrating
radar (GPR) and electrical resistivity methods. The results show the following: (1) regions of low
apparent resistivities are coincident with attenuated GPR reflections (shadow zones) but are limited to
the edges of the surveyed areas; (2) a central region of high apparent resistivities with bright GPR
reflections below the water table; (3) an upper GPR reflector subparallel to the water table, several feet
above the current free product level and coincident with the top of an gray, oil-stained layer, and (4) the
existence of a thin conductive layer coincident with a dark gray to black layer saturated with free
product occupying a zone immediately above the water table. These results suggest that the light
hydrocarbon free-product, and associated dissolved plumes are dynamic systems whose chemistry is
changing in time and position within the plume. As a result, this influences the variability of the
geoelectrical signature. Therefore, geophysical results must be interpreted in the light of a coherent
model based upon combined geological, geochemical, and geophysical understanding of the evolution
of these systems.
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Composite Landfill Characterization: An Integrated Geophysical Study
Authors Eva Lanz, Hansruedi Maurer, David E. Boemer, Heinrich Horstmeyer and Alan G. GreenGeophysical methods provide non-invasive means of probing buried waste disposal sites.
Using a small composite waste site in northern Switzerland as an example, we obtain accurate
images of the host sedimentary succession and structure from 3-D seismic reflection and ground
penetrating radar (GPR) surveys. Lateral boundaries of the disposal site are clearly visible in
detailed images of the magnetic gradient field and in various maps constructed from conductivity
data. Tomographic inversion techniques applied to seismic refraction data provide information on
waste pit thickness variations. While individual geophysical methods are quite powerful for
mapping aspects of the shallow subsurface, our study highlights the need to acquire diverse data
sets. Only with independent subsurface constraints is it possible to obtain reliable models of the
earth so essential for environmental and engineering studies.
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Application Of Magnetic And Multi-Frequency Em Techniques For Landfill Investigations: Case Histories
Authors Craig Murray and Dean KeiswetterMagnetic and electromagnetic techniques were used in the investigation of three landfill sites.
Historical records of the content and location of buried waste in all three landfills were poor.
The geophysical surveys were conducted to map the trenched areas or locate buried drums and
other metal objects within the landfill. Waste filled trenches exhibit a higher conductivity than
the surrounding undisturbed materials. Drum burial areas have a higher apparent conductivity
and also produce significant magnetic anomalies.
These geophysical surveys provided accurate locations of the trenches and drum caches in all
three cases. When used together, the magnetic and electromagnetic data could be used to
differentiate between ferrous and non-ferrous metallic waste. Modern equipment measures and
logs EM and magnetic data efficiently, allowing surveys to have high spatial density. This
increase in data density provides more precise delineation of trenched areas and more accurate
location of buried objects such as drums. The increased efficiency of the modern instruments,
computers, and techniques enables the user to complete high quality surveys in hours or days and
present the environmental investigator with understandable maps in the field.
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How Important Is The Orientation Of A Horizontal Loop Em System? Examples From A Leachate Plume And A Fault Zone
More LessThe coupling between a horizontal loop EM (HLEM) system such as the Geonics EM31@,
and a buried object, e.g., a buried pipe, is well-established. The response from a buried pipe or
from a vertical lamp-post will depend on the orientation of the transmitter-receiver loop system
relative to the object in question. However, diffuse boundaries do not respond like discrete buried
objects. In particular, evidence from a survey of a landfill leachate plume and from two lines
across the Alpine Fault of the Southern Alps of New Zealand illustrates that the difference is
generally negligible. The leachate survey was carried out in an area of heavily-vegetated coastal
dunes adjacent to a landfill site. Survey lines criss-crossed the area, using cut trails for access. The
line crossings were used for analysis, and the net difference was 0.30 + 0.55 mS/m (less than
2.5% on average). The Alpine Fault EM surveys were carried out in advance of and in support of
a ground penetrating radar survey. The survey line followed a 6 m wide farm access road that was
bordered on both sides by wire fences. The EM survey was completed twice, using two
orientations - one parallel to the road (and fences) and the other perpendicular to the road. The
results indicate that the response differed by only 0.14 f 0.03 mS/rn, except for the gates and
fence corners where different responses would be expected. Therefore, the HLEM system
orientation is not significant when surveying features that are not sharp, discrete objects.
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Shear Wave Velocity Measurements For Earthquake Hazards Studies, Fraser River Delta, British Columbia
By J.A. HunterShear wave velocity-depth information in thick unconsolidated overburden is one of the fundamental
requirements for estimation of seismic site responses such as liquefaction potential and ground motion
amplification in an earthquake-prone area such as the Fraser River delta. The delta area (approximately 600 km*)
was surveyed in a reconnaissancem anner using direct shearw ave (S-wave) measurement methods such as surface
refraction, seismic cone penetrometer, and downhole logging. In addition, S-wave velocities of the entire
overburden thickness have been estimated from conventional exploration seismic reflection velocity analyses.
In all, S-wave velocitydepths have been obtained for over 400 sites where unconsolidated overburden thicknesses
range from ~5 m near the delta edges to > 1000 m in the south central region. Results indicate:
1) large S-wave velocity-depth gradients within the unconsolidated overburden which can give rise to
amplification effects for simple elastic models; confiiation of such amplifications are given from observations
of local earthquakes;
2) large S-wave velocity contrasts within the overburden sequence associated with the Holocene-Pleistocene
boundary; such contrasts can give rise to considerable lateral variation in site period response to earthquake
shaking;
3) widespread occurrence of low S-wave velocities in the near surface materials (mainly fine sands), suggesting
that the seismic liquefaction potential may be relatively high
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Geotechnical Use Of A Shear-Wave Vibrator: In-Situ Measurement Of Nonlinear Properties Of The Ground Surface
More LessA new method is proposed for evaluating non-linear properties or strong motion
responses of the soIt ground directly in the field. The method utilizes a shear-wave
vibrator, which has been conventionally used for the reflection survey in the resources
exploration, as an artificial strong motion source. Various types of cones, such as
seismic cones and electrical cones, penetrated into the near surface are used to monitor
the ground response to the vibration. Field tests for the method were performed at the
Tone River Site near Sawara City, approximately 60km northeast of Tokyo. The tests
showed the shear-wave vibrator had a power to oscillate the ground with lOOgal or
more at 5m from the vibrator baseplate. Decrease in shear wave velocity was clearly
observed with increasing vibration level, which means non-linearity of the shear
modulus of the ground is detectable in place by this method.
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