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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 - 20 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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