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8th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 23 Apr 1995 - 26 Apr 1995
- Location: Orlando, Florida, Canada
- Published: 23 April 1995
61 - 80 of 104 results
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Processing A Shallow Seismic Cdp Survey: An Example From The Oak Ridges Moraine, Ontario, Canada
Authors David G. Schieck and Susan E. PullanShallow common depth point (CDP) seismic reflection techniques are now being used effectively to solve engineering,
geotechnical and hydrogeological problems. By using advanced data processing techniques previously developed for
petroleum exploration, excellent images of the subsurface can be made. These techniques address near-surface effects
such as ground coupling and statics, lateral velocity variations and image enhancements. The effectiveness of such data
processing techniques is discussed and demonstrated here, using shallow seismic reflection data acquired as part of a
hydrogeological investigation of the Oak Ridges Moraine in southern Ontario. Advanced data processing techniques
such as surface-consistent deconvolution, scaling and residual static analysis, structural modelling to enhance velocity
and static analysis, and migration have been applied to these data.
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Airborne Detection Of Magnetic Anomalies Associated With Soils On The Oak Ridge Reservation, Tennessee
Authors W.E. Doll, J.M. Helm and L.P. BeardReconnaissance airborne geophysical data acquired over the 35,000-acre (18,000 hectare) Oak Ridge Reservation
(ORR), Tennessee, between December, 1992 and February, 1993 (Doll and others, 1993) show several magnetic
anomalies over undisturbed areas mapped as Copper Ridge Dolomite (CRD). The CRD is exposed on three
ridges on the ORR. On Copper Ridge, near the southern border of the ORR, the exposure is widest (up to 1.25
mi, 2 km) because the dips approach horizontal. Figure 1 is a vertical magnetic gradient map of a portion of
Copper Ridge from the southwestern portion of the ORR. The anomalies of interest are most apparent in
magnetic gradient maps where they exceed 0.06 nT/m (Figure 1) and in some cases exceed 0.5 nT/m.
Anomalies as large as 25nT are seen on residual magnetic anomaly maps (Figure 2). Some of the anomalies
correlate with known or suspected karst, or with apparent conductivity anomalies calculated from
electromagnetic data acquired contemporaneously with the magnetic data (Beard and others, 1994).
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High Sensitivity Aeromagnetic Surveys For Environmental Hazard Detection In South Texas
Authors J.D. Phillips, J.E. Lundy, D.L. Carpenter, T.J. McConnell and G. KuhlmanThe recent availability of high resolution airborne surveying techniques employing supersensitive magnetometers
(-0.01 nanoTesla or gamma) and differential GPS has made it possible to detect and map the short wavelength,
weak magnetic anomalies caused by environmental hazards. These hazards include abandoned oil/gas wellheads
and buried steel barrel cache, chemical waste sites. With this environmental objective in mind, new high resolution,
low altitude aeromagnetic surveys have been flown over producing oil/gas fields and abandoned uranium mine pits
in Wilson and Karnes counties, Texas. This study clearly identified weak short wavelength anomalies associated
with abandoned wellheads, reclaimed uranium mining/ore milling equipment burial sites and a recently designated
Superfund (CERCLA, Comprehensive Environmental Response Compensation and Liability Act), chemical waste
disposal site consisting of only 158 steel barrels.
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High Resolution Airborne Geophysics At Hazardous Waste Disposal Sites
Authors L.P. Beard, J.E. Nyquist, W.E. Doll, M. Chong Foo and T. Jeffrey GameyIn 1994, a high resolution helicopter geophysical survey was conducted over portions of the Oak Ridge
Reservation, Tennessee. The 1800 line kilometer survey included multi-frequency electromagnetic and magnetic
sensors. The areas covered by the high resolution portion of the survey were selected on the basis of their
importance to the environmental restoration effort and on data obtained from the reconnaissance phase of the
airborne survey in which electromagnetic, magnetic, and radiometric data were collected over the entire Oak Ridge
Reservation in 1992-93 .
The high resolution phase had lower sensor heights, more and higher EM frequencies, and tighter line
spacings than did the reconnaissance survey. When flying over exceptionally clear areas, the high resolution bird
came within a few meters of the ground surface. Unfortunately, even sparse trees and power or phone lines could
prevent the bird from being towed safely at low altitudes, and over such areas it was more usual for it to be flown
at about the same altitude as the bird in the reconnaissance survey, about 30m. Even so, the magnetometers used
in the high resolution phase were 20m closer to the ground than in the reconnaissance phase because they were
mounted on the tail of the bird rather than on the tow cable above the bird. The EM frequencies used in the high
resolution survey ranged from 7400Hz to 67000Hz. Only the horizontal coplanar loop configuration was used in
the high resolution flyovers Flight line spacings in the high resolution flyover ranged from 46m over large treecovered
areas to about 1Om in cleared waste burial grounds.
A comparison with ground conductivity and magnetic data from the WAG 11 area shows that the ground
survey provides much more detail than the high resolution aerial data, however the aerial survey of WAG 11
detected the major anomalous areas--buried processing equipment, buried drums, and an area of scattered debris.
Better resolution could have been obtained had the area been clear enough for the sensor to drop below treetop
level. Geologic structures and contacts appear to be as accurately mapped using a coil frequency of 7400Hz .
Apparent resistivity maps at the highest frequency--66000Hz--do not correspond well with bedrock geology, but
may be correlated with soil variations and the presence of buried metal.
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Airborne Electromagnetic Resistivity Mapping In Everglades National Park, Florida
More LessA helicopter electromagnetic (HEM) survey was flown over a portion of the Everglades
National Park to map conductivity variations associated with salt-water intrusion in the Biscayne
aquifer system and to monitor the effects of the South Florida Ecosystem restoration effort. Maps
from the HEM survey define a dramatic transition between a high resistivity region landward and
a low resistivity region toward the coastline. Based upon induction logs and water quality data
from wells, this transition zone is interpreted as the freshwater-saltwater interface. The HEM data
provide a rapid and efficient means of monitoring water quality changes in the surficial Biscayne
aquifer system caused by remediation activities intended to increase the supply of fresh water to
the Everglades.
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Real-Time Interpretation Of Em-31 And Gpr Data For Expedited Site Investigation
Authors Fred S. Stockbauer and James A. KalinecSmaller and faster computers with enhanced graphic software, now available,
allow real-time data processing and infield interpretation of results. The availability of these
resources and digitally collected electromagnetic (EM) and ground penetrating radar (GPR)
data allow for computer processing and final display with many off-the-shelf programs.
Furthermore, based upon the processed results, quick decisions are possible for
setting up subsequent work plans involving, as examples, tank removal, screening tests such
as soil sampling, soil gas testing, and installation of monitoring wells. Real-time
interpretation of data is especially beneficial in remote areas where mobilization costs can
become extreme.
Providing ease of use in the field was a special goal of this project and
numerous signal processing routines were written in such a fashion to allow field personnel
the ability to collect, process, and display data without large training expenses. Especially
with the GPR data sets, a number of sequential processing steps are necessary to extract the
maximum information from the raw data. Batch routines were written that allowed a
complete process sequence to run in the order selected without intervention from the analyst.
The resultant displays in a Microsoft Windows format allowed viewing of the
data at each processing step and, through color printer output, the reports were produced in
the field for sponsor review. The graphic representations of the processed data at this point
are used as inputs to commercial display software packages.
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Backus-Gilbert Inversion Of Electrical Resistivity Soundings And Its Application To Solid-Waste Landfills
Authors Lawrence J. Barrows and Mark E. EdwardsElectrical resistivity surveys are conducted by injecting a known current into the earth through
two electrodes and measuring the resulting voltage across two other electrodes. By varying the
locations of the electrodes and applying appropriate interpretation techniques, a three-dimensional
model of subsurface material resistivity can be developed. This material resistivity normally
reflects either the salinity of the contained fluids or the amount of disseminated clay minerals so
the electrical techniques have a broad range of applications in groundwater and environmental
investigations.
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Neural Network Interpretation With Electromagnetic And Magnetic Data For Envlronmental Site Investigations
Authors Marshall P. Brown and Mary M. PoultonA feasibility study for the application of neural networks to electromagnetic and magnetic data interpretation was
done. The scope of \vork cntailcd three major parts: classification of data as target or background; estimation of
depth of targets; classification of the conductivity of the targets. The purpose of the study was to determine if
neural networks could be trained to find the same anomalies as a skilled human interpreter and also give
quantitative information that a human interpreter may or may not be able to give. We found the neural networks
capable of classifying the majority of the targets in the data set. Respectable depth and conductivity estimates were
also able to be made on these same targets.
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Using Modflow As An Interpretive Tool For Several Geophysical Methods
Authors John Jansen and Dr. Robert TaylorGround water flow models have received considerable development
over the last decade. One finite difference model, MODFLOW, has
developed into a versatile program capable of simulating a variety
of three-dimensional problems. Unfortunately, solutions for most
geophysical methods have limited ability to describe threedimensional
problems. Many physical phenomenon obey the same
governing equation as ground water flow. If a geophysical method
is governed by an equation that is analogous to the ground water
equation, MODFLOW can be used to produce solutions for complex site
geometries. This paper illustrates the use of MODFLOW to solve
complex electrical resistivity, heat flow, and spontaneous
potential problems.
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Dc-Resistivity Array To Monitor Fluid Flow At The Inel Infiltration Test
Authors M.C. Pfeifer and H.T. AndersenDuring 1994 a semi-permanent DC-resistivity array of nearly 2600 electrodes was installed to monitor
vadose zone fluid flow as part of a Large Scale Infiltration Test carried out at the Idaho National Engineering
Laboratory (INEL) to determine contaminant transport properties for the highly heterogeneous subsurface
at the INEL. The infiltration test consisted of an integration of hydrologic, geochemical, and
geophysical techniques used to monitor the migration of tracer-spiked water through the subsurface. Most of
the sensors used were down-hole monitoring sensors which have limited spatial coverage. To augment the
borehole monitoring, a surface DC-resistivity array was deployed to obtain additional information in the
regions between the boreholes. The DC-resistivity array was located in the area external to the infiltration
basin :o monitor lateral fluid flow along barriers to vertical flow.
The array of electrodes was installed in a pattern of four radial arms and three concentric circles about the
infiltration basin. Groups of 120 to 200 electrodes were connected to a set of 22 seismic cables and brought
to 8 common points for recording. A PC field computer and a multiplexing system was used to record the
array. The array was installed on a semipermanent basis, and remained in place throughout the duration of
the Large Scale Infiltration Test, so that small changes in the subsurface resistivity over time could be monitored
and related to the vadose zone fluid flow.
Data was acquired using multiple current sources and was interpreted to obtain an overall geoelectric structure
of the infiltration test site. The DC resistivity data was used lo delineate preferred flow paths in the
vadose zone. These zones of preferred fluid flow are seen in features interpreted from the multi-source resistivity
data and also from well log data obtained from the monitoring wells situated around the monitoring
basin.
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Ultra Wide Band Radar Holographic Imaging Of Buried Waste At Doe Sites
Authors H.D. Collins, R.P. Gribble, T.E. Hall and W.M. LecheltUltra wideband linear array holography is a unique real-time imaging technique for in-situ inspection of buried
waste at various DOE sites. The array can be mounted on various platforms such as crane booms, pickup trucks,
ATVs, and scanned generating “3-D” subsurface images in real time. Inspection speeds are approximately 0.5 to
2 meters/set, if the image is viewed in real time, greater for off-line processing.
The Ground Penetrating Holographic (GPH) system developed for inspection of DOE sites employs two 32-
element arrays of tapered-slot antenna operating at 5-GHz and 2.5-GHz center frequencies. The GPH system,
which is mounted on a small trailer with a computer image processor, display, and power supply, is capable of
imaging a wide swath (1 to 2 meters) with its linear arrays. The lower frequency array will be used at INEL
(for greater depth penetration) because of high soil attenuation.
Recent holographic “3-D” images of buried waste container lids and dielectrics obtained in Hanford sand and
INEL soils at various depths graphically illustrate the unique image resolution capabilities of the system.
Experimental results using the 5-GHz array will be presented showing the excellent holographic image quality of
various subsurface targets in sand and INEL soil.
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Vetem - A Very Early Time Electromagnetic System - The First Year
Authors Louise Pellerin, Victor F. Labson and M. Cathy PfeiferIn electrically conductive conditions common in environmental studies the minimum depth of
investigation for traditional electromagnetic (EM) sounding techniques is roughly 5 meters, while
ground penetrating radar (GPR) systems can typically investigate only the top meter or so when
clay minerals are present in the soil. Hence, in many cases, there is a gap in our detection
capability between the lower limit of GPR and the upper limit of traditional electromagnetics (EM).
Bridging this gap is essential to the characterization of buried waste, non-aqueous phase liquids
(NAPL) plumes, and other environmental and hydrogeological targets located in the shallow
subsurface. The Very Early Time Electromagnetic (VETEM) system, which includes modeling
and interpretational software along with frequency and time domain instrumentation, is designed to
ascertain the conductivity and dielectric properties of the shallow subsurface in conductive terrain.
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An Experiment At Inel Toanalyze Circular And Linear Polarization For Gpr Systems
More LessConventional commercial GPR systems utilize linear, horizontal dipole antennas. These
antennas transmit an electromagnetic wave that is linerally polarized, with a single electric field
component that is parallel to orientation of the dipole. A circularly polaized antenna system
transmits a wave with electric field intensities that are equal in orthogonal directions, and whose
direction vector is circular. Both systems offer particular advantages for detecting objects of
different shapes and sizes. For example, the reflected signal from a long linear object (e.g. a pipe)
will be oriented with a single direction of polarization parallel to the pipe if the signal from the
transmit antenna is circularily polarized, or if a linear transmit antenna is oriented parallel to the
direction of orientation of the pipe. No reflected signal will be received from a pipe whose
orientation is perpendicular to a lineraly polarized transmit antenna. Therefore, it is possible to
discern more infromation from GPR measurements when combinations of linear and circularily
polarized antennas are utilized.
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Electromagnetic Response Of Certain Layered Models To The Sixface To Downhole ‘Induction Profiling’ Coil Configuration
Authors G. Hunter Ware and G. Michael HoverstenSeveral contractors provide down-hole low- frequency electromagnetic (EM) surveys intended to delineate
resistive layers in the shallow subsurface. These surveys are called by various trade names and acronyms,
vve shall refer to them as ‘inductive profiling’ or ‘offset logging’ surveys. The coil geometry generally
consists of a horizontal loop transmitter (vertical magnetic dipole) on the surface. and a horizontal loop
receiv-er in a probe vyhich is lowered dew-n a nearby borehole. The open-ating frequenccy is usually 500 cps
or less. The method measures downhole profiles of the amplitude of the vertical component of the total
magnetic field intensity (evidently phase is not measured). This raw data profile is then processsed by an
undisclosed (proprietary) algorithm which is intended to calculate a resistivity (or ‘relative resistivity’)
profile beneath the transmitter coil. The coil arrangement is indicated in figure 1. Since details of the
instrumentation and the data processing procedures are not disclosed, the surveys provided by various
contractors may differ in some respects.
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Vertical Induction Profiling For Hydrocarbon Plumes
Authors Olaf Westphalen, Mark Peterson and David HeinsThe Unites States Army at Fort McPherson is managing the assessment and remediation of the
Building #105 leaking underground storage tank (UST) site at Fort McPherson, Georgia.
Traditional intrusive site assessment techniques have not been adequate to delineate the full
extent of subsurface hydrocarbon contamination at the site due to the possible presence of
contamination under buildings, the installation boundary, numerous overhead and subsurface
utilities, and an adjacent highway. The Directorate of Public Works at Fort McPherson has
commissioned the use of a non-intrusive geophysical site assessment technique to evaluate the
extent of hydrocarbons in the subsurface so that expeditious implementation of corrective actions
protective of human health and the environment can be completed in accordance with state
requirements.
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Borehole-To-Surface Electromagnetic Methods - System Design And Field Examples
Authors Lewis C. Bartel, Michael J. Wilt and Hung-Wen TsengBorehole-to-surface electromagnetic (EM) methods are an attractive alternative to surface-based EM
methods for a variety of environmental and engineering applications. They have improved sensitivity to the
subsurface resistivity distribution because of the closer proximity to the area of interest offered by the borehole
for the source or the receiver. For the borehole-to-surface measurements the source is in the borehole and the
receivers are on the surface. On the other hand, for the surface-to-borehole methods, the source is on the
surface and the receiver is in a borehole. The surface-to-borehole method has an added advantage since
measurements are often more accurate due to the lower noise environment for the receiver. For these methods,
the source can be a grounded electric dipole or a vertical magnetic dipole source. An added benefit of these
techniques is tield measurements are made using a variety of arrays where the system is tailored to the
application and where one can take advantage of some new imaging methods. In this short paper we describe
the application of the borehole-to-surface method, discuss benefits and shortcomings, and give two field
examples where they have been used for underground imaging.
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Influence Of Hydrocarbon Pollution To Soil Conductivity
Authors Vojtech Gajdoš and Vladimir KrálThe laboratory and field measurements show. that small contents of hydrocarbon pollution
increase soil conductivity and greater contents decrease soil conductivity (Fig. 1.). We tested some hydrocarbon
materials and all had this ability.
On the basis of laboratory measurements was developed the field method for mapping the hydrocarbon
pollution, The method includes resistivity profiling (with GEONICS EM-31) measurement of streaming
potentials and atmogeochemical measurements (with ECOPROBE 3M). For different sources of hydrocabon
pollutions the method has some modifications.
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Mapping Chloride Contamination From Salt Cake Fines With Transient Electromagnetics
More LessAluminum recycling is accomplished by smelting scrap aluminum using large quantities of sodium and
potassium chlorides as flux, then separating the aluminum concentrate from residual salts (known as salt
cake fines). In the past, salt cake fines were often stored in open landfills or in mounds. Salts mobilized
by rain can enter shallow groundwater via runoff or through downward flushing through the soils. From
a regulatory point of view, this poses two problems. First, chloride concentrations in groundwater may
exceed the secondary maximum contaminant level (SMCL) established by the EPA. Second, ammonia
gas is generated as a byproduct, posing a potential health concern.
Defining the three-dimensional extent of chloride contamination can be a difficult and costly process
in complex geology, where the size and shape of the contaminated zone can be unpredictable due to
unknown subsurface controls. This challenge becomes more complex when the contaminant has the
potential for transport to a deeper aquifer.
Electromagnetic geophysics techniques are available to improve sampling effectiveness (finding the
most contaminated zones) and reduce project cost (minimizing the number of wells needed to characterize
a site). Methods such as transient electromagnetics (TEM) and audio-frequency magnetotellurics (AMT)
are particularly effective in mapping electrically conductive chlorides beneath crowded industrial sites.
This paper describes TEM surveys designed to map chloride contamination and geology at two former
recycling plants. Drilling at both sites had not defined the horizontal or vertical extent of contamination.
TEM was selected to define these parameters and determine the best locations and screen depths of future
monitoring wells.
A central-loop configuration was employed at both sites, obtaining voltage data at 32 time windows
from 1.9 psec to 3,l msec, using a Zonge Engineering 16-bit receiver. Soundings were made at random
locations selected for minimal culture and optimum spatial coverage. Several quality control checks were
performed, including absolute repeatability and spatial aliasing. The data were modeled with a onedimensional
Inman-style ridge regression algorithm.
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Electromagnetic Terrain Conductivity Survey Methods For Detection Of Seepage Plumes From Animal Waste Lagoons
Authors R.L. Huffman and P.W. WestermanA four-year series of frequency-domain electromagnetic terrain conductivity surveys was used
to track the changes in ground-water contamination due to seepage from animal waste lagoons. The
survey data were compared with electrical conductivities of ground water samples from the same
period. Four instrument configurations were compared to determine which best reflected changes
in ground water conductivity.
Sequential surveys provide a good qualitative indicator of changing conditions. Increases in
ground water conductivity were reflected in simultaneous increases in the survey readings, but decreases
in the ground water conductivity produced somewhat smaller and less distinct changes in
survey readings, indicating a residual effect of the seepage.
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Geophysical And Geostatlstical Approach To Characixrization Of Contaminated Sediments In An Urban Waterway: Potential And Limitations
By Ken HauserThe detection and characterization of heavy metal contaminants in urban waterways at parts per million (ppm)
concentrations using standard geophysical techniques is a difficult undertaking. The essentially microscopic
nature of the target is outside the range of resolution available with typically employed geophysical tools.
Those methods which might produce useful results, such as electrical resistivity, electromagnetic, or magnetic
surveys are limited in their effectiveness by sources of interference generated by the urban environment. The
time and cost involved in sending samples to laboratories for analysis can be prohibitive, especially in view of
limited budgets for sediment sampling programs. In spite of these difficulties, there are geophysical
technologies which can contribute useful information to the problem of sediment characterization in urban
waterways. Methods such as side scan sonar and subbotom profiling cannot directly detect ppm concentrations
of metal contaminants, but they can provide useful information allowing for the most effective use of sampling
budgets. Modeling software can furnish indirect but useful secondary information by determining the type of
sediment on the river bottom from reflection data. Geotechnical properties such as density and porosity can be
estimated using the reflection data, and the relationship between particle size and the affinity for contaminants to
accumulate in sediments of a certain size may be exploited. Geostatistical analysis can be useful in determining
the minimum sample spacing necessary to adequately characterize the levels of pollutants in the river, using the
fact that samples taken too close together tend to spend sampling dollars inefficiently and those taken too far
apart are not representative of true conditions in the river bottom.
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