- Home
- Conferences
- Conference Proceedings
- Conferences
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
1 - 50 of 104 results
-
-
Properties Of Light Non-Aqueous Phase Liquids And Detection Using Commonly Applied Shallow Sensing Geophysical Techniques
More LessProperties of light non-aqueous phase liquids (LNAPLs) and their interaction with the unsaturated, shallow
subsurface provide a variety of detection criteria for commonly applied geophysical mapping techniques including
electromagnetic induction (terrain apparent conductivity) and galvanic resistivity (terrain apparent resistivity) and
ground penetrating radar for profiling discrete horizons in the sub-surface. These physio-chemical phenomena in
the unsaturated zone may include: aqueous phase dynamic displacement due to downward migration of the
immiscible phase, alteration of interfacial tension effects if the immiscible phase replaces air as the wetting fluid
to the aqueous phase or if the immiscible phase is partially soluble or is volatile, capillary fringe collapse and
restructuring of the effective geophysical water table due to free product buoyancy, and additives to the non-aqueous
phase which may promote the formation of emulsions and provide surface conductance effects. Early literature on
direct geophysical detection of shallow organic contaminants has provided a simplistic approach. Simply stated,
the presence of LNAPLs in the subsurface with apparent conductivities orders of magnitude less than natural
groundwater, should produce measurable anomalies by acting as an insulating layer. It has become apparent that
the “insulating layer” concept is inadequate to explain mapped geophysical anomalies over and about LNAPL spills.
Considerable effort has been devoted to studying geophysical detection of pooled hydrocarbons but this has generally
been restricted to immiscible/miscible organic contaminant interactions with groundwater in controlled field or
column experiments. It is common to apply geophysical techniques at sites where multiple immiscible contaminants,
exhibiting a variety of properties, may exist in a complex subsurface. This paper provides insight into some of the
resultant geophysical detection criteria for these immiscible contaminants.
-
-
-
Detection And Mapping Of An Lnapl Plume Using Gpr: A Case Study
Authors Michael Maxwell and Jeffrey SchmokGround penetrating radar was used to delineate a gasoline (LNAPL) plume at the site of a
former gasoline station. Monitoring wells indicated the approximate location of the plume
and a free product thickness of up to 1.7 m above a water table typically 3-4 m below ground
surface. Anomalous GPR responses were detected well above the expected depth of mobile
LNAPL. The shallow depths of anomalous responses indicates that a residual or possibly
vapour contaminant found in the non-saturated zone produces the characteristic GPR
anomaly detected during this survey.
-
-
-
Can Accurate Estimates Of Permeability Be Obtained From Measurements Of Dielectric Properties?
Authors Michael D. Knoll, Rosemary Knight and Elizabeth BrownA laboratory study was conducted to investigate relationships between dielectric properties and hydraulic
permeability of sand-clay mixtures. The mixtures were generated in such a way as to vary systematically parameters
such as porosity, clay volume fraction and specific surface. Each of these parameters affects both dielectric properties
and permeability. For each mixture, measurements were made of porosity, clay content, permeability and dielectric
constant at two levels of water saturation (room dry and fully saturated). For the suite of mixtures generated,
porosity ranges from 0.240 to 0.605, clay content ranges from 0.000 to 1.000, and permeability ranges from
5.3~10~‘~ to 2.7~10~~ cm2. At a frequency of 1 MHz, the dielectric constant ranges from 3.54 (dry quartz sand) to
49.4 (saturated kaolinite clay). Crossplots are used to investigate relationships between various parameters. Results
show that many relationships such as porosity-permeability and dielectric constant-permeability are multivalued and
involve critical points or minima in some parameter. In addition, the experimental data are compared to predictions
from three interrelated petrophysical models: (1) a microgeometrical model which describes the relationship between
porosity and clay content in sand-clay mixtures, (2) a permeability model based on the Kozeny-Carmen equation, and
(3) a dielectric model which incorporates geometric information through the use of wetted matrix parameters.
Results show excellent agreement between predicted and observed data. At least for these mixtures, permeability
estimates accurate to within an order of magnitude may indeed be derived from dielectric measurements. Such
petrophysical relationships can be used in ground penetrating radar and very early time electromagnetic surveys to
estimate permeability values and connectivity functions in the field.
-
-
-
Dual Geophysical Data Set Interpretation For Landfill Plume Delineation
Authors T.H. Rowley, Paul R. Donaldson, James L. Osiensky and J. Carlton ParkerA contaminant plume containing high concentrations of Dense Non-Aqueous Phase Liquids (DNAPLs) and
inorganic contaminants emanates from the Bannock County Landfill, in Fort Hall Canyon, Idaho. These DNAPLs
and inorganics have been detected in nearby domestic and municipal water supply wells in an alluvial fan aquifer.
The alluvial fan aquifer is underlain by cemented, fluvial gravels. A surface electrical field survey was conducted
down gradient from the Bannock County Landfill to help delineate the extent of the plume. The field site is
relatively free of cultural interference that would adversely affect electrical-potential fields. Data collected during
the survey were correlated with seismic refraction data.
The mise-a-la-masse method for plume delineation was utilized for this investigation. The method is much easier to
use and data interpretation is less subjective than other electrical methods; however, it does not yield depth
information. The mise-a-la-masse method was used successfully to identify electrical-field anomalies near the
Bannock County Landfill. The seismic refraction method was used to determine depth to the subsurface structure.
The seismic refraction survey suggested that three buried channels exist beneath the site.
The electrical-field map correlates very well with the seismic data in those areas where the data sets coincide. Most
electrical-field highs are located above areas interpreted seismically as buried channels or basins. These features
may provide preferential flow paths for the contaminated groundwater and DNAPLs.
-
-
-
Ultrasonic Crosshole And Crossmedium Tomography For The Detection Of Defects In Structural Concrete
Authors Farrokh Jalinoos, Larry D. Olson and Marwan F. AouadThe use of ultrasonic crossmedium and crosshole tomography is described as a means for nondestructive
evaluation (NDE) of flaws or imperfections in structural concrete. Tomography is an inversion procedure that can
provide for ultrasonic images of a concrete specimen from the observation of transmitted compressional or shear first
arrival energy. Two applications for ultrasonic tomographic imaging are presented here. Crossmedium tomographic
images are obtained from concrete walls or columns with two-sided access. Crosshole tomographic images are acquired
from drilled shafts or slurry walls containing steel or PVC access tubes set in place during the concrete placement.
In order to study the application of crossmedium tomography for imaging flaws in concrete, four concrete
walls containing simulated flaws or defects were cast-in-place in the laboratory as part of a 1993 National Science
Foundation (NSF) SBIR study. A new specialized rolling ultrasonic scanner source was developed for this testing and
was used for rapid scanning of structural concrete with two-sided access. Using the new scanner, a typical 116 cm (45.5
in) survey line for 1764 different source-receiver combinations was acquired in 1% hours. A comparable tomographic
test line, performed on a single source-receiver measurement basis, takes approximately 40-60 hours. Therefore, the
scanner source now makes locating and imaging flaws in critical concrete structures practical. Tomographic analysis
was performed using two series expansion algorithms from geotomography: Simultaneous Iterative Reconstruction
Technique (SIRT) and a least square matrix inversion approach using an optimized Conjugate Gradient (CG) approach.
The results of this study indicated that travel time tomography was most successful in locating simulated voids in
concrete. The crossmedium tomography was also used to locate and image simulated honeycombs, simulated open
cracks, microcracks, and weak concrete.
-
-
-
Three Dimensional Visualization Of Concrete Structures
Authors D. Wiese, M. Thomas and H. CaratinThis paper describes the application of geophysical tomography and scientific visualization techniques for
evaluating the internal condition of massive concrete structure. The resulting output is a three dimensional
representation of the structure showing the spatiai distribution of ultrasound data. As various aspects of ultrasound
data (e.g. velocity and attenuation) are related to concrete quality, the location and orientation of areas of inferior
material or discontinuities can be identified. In addition, specific features within the image can be highlighted and
quantified.
There are several nondestructive, noninvasive techniques for determining various in-situ properties of concrete.
Most of these techniques only measure properties of the concrete at, or close to, the concrete surface. However,
geophysical techniques such as ultrasound or seismic velocity measurements taken across a section give an
indication of the quality of concrete between the points of transmission and reception at the concrete surface.
Generally, higher velocities are indicative of good quality concrete.
In the current study, a large number of measurements (ultrasonic pulse velocity) are taken to provide a network of
velocities across a section, algebraic tomographic techniques are then applied to reconstruct a two dimensional
image. By taking a series of contiguous sections and stacking them together, a three dimensional model of the
sample or structure is created. FinaIly the three dimensional data set is visualized using advanced graphics
techniques such as volume rendering. Scientific visualization gives form and shape to numerical data that may be
abstract and difficult to interpret. Direct volume rendering in particular is appropriate for tomographic images
because it enhances the detailed spatial distribution of heterogeneous information without distortion or smoothing.
Results will be presented from a preliminary study carried out to assess the potential application of this technique
for evaluating the internal condition of large concrete elements. Measurements were made on a large concrete
block constructed with a number of internal defects such as cracks, areas of poorly compacted concrete and
uncemented aggregate, and large voids (polystyrene blocks). Overall, the initial results were promising, indicated
that the presence and location of internal defects can be determined and visualized using this technique. The
successful development of a technique for determining and visualizing the internal condition of large concrete
structures would be a significant advance in the area of concrete inspection and maintenance.
-
-
-
Ground Penetrating Radar Technique In Monitoring Defects In Roads And Highways
Authors Tom Scullion and Timo SaarenketoIn recent years the trend in the highway industry has been on maintaining and rehabilitating existing
structures rather than building new ones. In this area the use of nondestructive testing techniques
particularly Ground Penetrating Radar has been growing in importance. Before planning major
improvements to any highway it is essential to detect any major defects in the structure. Traditional
methods include expensive coring and boring which have limited success at detecting random subsurface
defects. GPR offers much potential in providing a cost effective and relatively rapid procedure for
nondestructive testing of pavements.
The main focus of the paper will be to present a series of case studies in which GPR techniques have
been used to tackle a variety of highway related problems. These case studies involve studies undertaken
in both Finland and Texas, two completely different environments.
-
-
-
The Use Of Dielectric And Electrical Conductivity Measurements And Ground Penetrating Radar For Frost Susceptibility Evaluations Of Subgrade Soils
More LessIn this study several tests have been made to evaluate, if in situ dielectric value and electrical conductivity
measurements together with ground penetrating radar survey (GPR) results could be used to estimate frost
susceptibility of subgrade soils in Finnish Lapland. Dielectric value and electrical conductivity were measured in
situ from the soil beside the road with a Dielectric Constant & Conductivity Meter made by Adek Ltd, Estonia
and GPR surveys were performed with 500 MHz ground coupled antenna. GPR measurements were performed
both in winter when the ground was frozen and in summer when it was totally thawed. The test site on highway
21 at Pello was selected as it exhibited variations of frost heave damages and a section with no frost heave was
also surveyed. The measurement results were compared with the frost heave measurements and the visual frost
damage mapping on the road surface.
The study results showed good correlation between frost heave and dielectric constant. If the dielectric value was
less than 8, no frost heave could been found. The highest frost heave values were achieved with the dielectric
constant between 15 and 22 in the case of glacial till and 20 and 30 in the case of silt. With higher dielectric
values frost heave started to decrease. Electric conductivity measurements gave information about the soil type
and compressibility.
With Ground Penetrating Radar it is possible to measure the frost depth and estimate the presence of unfrozen
water in road structures and subgrade soils. This is based on the fact that the dielectric value of ice is 3.6-4.0
and the presence of unfrozen water can be seen as major reflectors in GPR data. GPR results gave also the total
thickness of road structures, which is needed for dimensioning road structures against frost heave. Other
valuable information gained from the radar results were the presence of bedrock, presence of boulders and
information about the quality of the existing road structure.
As a result of this study a method of classifying the frost susceptibility of subgrade soils was proposed. This
classification is based upon the in situ measurements of dielectric value and electrical conductivity.
-
-
-
Correlating Gpr And Resistivity Surveys With Cone Penetrometer And Shallow Coring Studies Along The Aberjona River.
Authors David B. Cistt, Randall L. Mackie, Peter J. Zeeb and M. Nafi TöksozA multi-modality survey using 3-D GPR and Resistivity techniques was performed to
assist hydrologists in characterizing groundwater flow near the Well-H region of the
Aberjona river in Woburn, Massachusetts. Concurrent cone penetrometer and coring
studies provided “ground truth” data about the stratigraphy, soil chemistry and
composition of the first ten meters of peat and sand. What remained for GPR and
resistivity was to extend such point-source ground truth information into a 3-D map of
the stratigraphy of the entire region by inferring soil properties from the electrical
measurements.
Electrical conductivity values were measured at some of the same points where coring
and cone penetrometer measurements had been made, to physically correlate electrical
properties with structural data collected at the same location. Conductivities at these
locations were also estimated independently using GPR and resistivity and then compared
to probe measurements.
EM wave velocity estimates were determined by CMP gathers which were used to infer
the depth to the reflective layers. A synthesis of the conductivity changes was then
compared to the stratigraphic surfaces detected by the resistivity and GPR surveys as well
as the penetrometer data. Finally, an empirical relationship between soil stratigraphy and
attenuation of the radar signal at these isolated locations was assembled.
Cone penetrometer measurements were made along two orthogonal lines against which
GPR surveys along the same profiles could be compared. The results show a strong
correlation between the probe data and the electrical measurements. By combining the
probe data that had been collected along these profiles with the GPR and resistivity data
of the area, we were then able to create a 3-D map of the subsurface properties and to
generate a structural interpretation of the entire region.
-
-
-
Geophysical Investigations Of A Waste Deposit In Southern Sweden
Authors Torleif Dahlin and Hans JeppssonGeophysical surveying was performed in order to investigate the existence and location of
buried metal waste, which might be drums containing hazardous waste. Three methods were
used: magnetometry, slingram (dual loop EM) and electrical resistivity. The magnetic and
slingram surveys were carried out manually, whereas a computer controlled data acquisition
system was used for the resistivity surveying.
The magnetic profiles show the presence of object with high magnetic susceptibility. The
anomalies can be joined together and lie parallel to extension of the valley. Magnetic
modelling shows that the anomalies fit well with metallic objects in the bottom of the original
valley.
The slingram results indicate objects with high electrical conductivity. The anomalies are
more point shaped than the magnetic ones, but correspond well in location.
The resistivity data were measured and interpreted as two-dimensional sections, using the
Wenner array, which were merged to form a three-dimensional model. A number of low
resistive objects can be identified in the images, which agree with the magnetic as well as the
slingram results.
Excavation revealed many metal objects, including a large number flattened metal drums,
corresponding to the geophysical anomalies. However, no hazardous waste was found.
-
-
-
High Resolution Magnetic Characterization In Complex Settings: Two Case Studies
More LessThis paper describes the results of two separate deployments of the GPS navigated, high density magnetic
characterization system, STOLS. In both cases, complex cultural signatures from nearby structures contaminated
the magnetic field data and obscured the magnetic signatures of the buried targets. Specialized processing
techniques were required to determine the location and size of each target. The high density of the survey data (-25
samples I m* ) and the high quality of the sensor positioning via GPS allowed for the application of image and data
processing techniques. The first case comes from the Department of Energy Project Office in Grand Junction,
Colorado, where the location of buried 55 gallon drums was in question. The site was a small sensor test facility
adjacent to several buildings, powerlines and fences. Data was collected and filtered to produce a high spatial
frequency map of the facility. A 2D spatial correlation filter was applied to statistically rank all likely targets. The
second case comes from the Chocolate Mountain Aerial Gunnery Range, in southeastern California, where STOLS
was deployed to quickly and accurately detect and characterize, in terms of position, depth and size, all buried
unexploded ordnance. At Chocolate Mountain an 18 mile gas pipeline easement within the Aerial Gunnery Range
was successfully surveyed. The magnetic anomaly data collected along the easement were severely contaminated
by two existing pipelines, A new processing technique which isolates the signatures of ordnance items was
developed and applied to the data to remove the pipeline effect and reveal anomalies adjacent to the pipeline. This
technique enabled STOLS to detect and locate all UXO in the easement.
-
-
-
Using High-Density Magnetic And Electromagnetic Data For Waste Site Characterization A Case Study
Authors John R. Cochran and Kim E. DaltonMagnetometers are frequently used to characterize hazardous waste sites. Due to cost and time
considerations, data are typically collected on a coarse grid with nodes on 3 to 6 meter (ml
centers. Hardware and software are now available which allow the rapid and cost effective
collection of information on a much finer sampling grid. In this paper we present and compare total
field magnetometery data collected on 3 m centers to total field magnetometery data collected on a
grid with centers of 0.5 m or less. We also compare the magnetometery data to time-domain
electromagnetic (EM) data collected on a 1 m by 0.2 m grid using the recently introduced Geonics
Ltd. EM61 metal detector. All three data sets were collected at an abandoned landfill.
-
-
-
Interpretation Of Hybrid Data For Characterization Of Shallow Landfills
Authors Edward Hensel and Kim E. DaltonNew Mexico State University has been actively developing a pre-commercial public domain software
package for analyzing and interpreting the data which arises from site surveys that can be performed with
field survey systems. The Multi-sensor Analysis Program for Environmental Restoration, MAPER, allows
analysis of multiple data types, and yields an optimal estimate of the distribution of subsurface materials
at a site. Researchers at New Mexico State University analyze data acquired by public and private sector
collaborators to determine the subsurface distribution of buried waste in landfills. A central aspect of the
effort is to achieve sensor data fusion, by taking data available from multiple sensing technologies and using
it to provide a comprehensive characterization of a buried waste site. The MAPER software modules have
recently been used in the analysis of geomagnetic anomaly detection (GAD) and ground penetrating radar
(GPR) data obtained at several DOE waste sites.
In this article, we review the mathematical approach that is being used in the current development of
the MAPER software, present some preliminary results that have been obtained with a research version of
the software, and discuss our plans for converting MAPER from an academic research tool into a suite of
analysis programs and modules available for public and private sector use. The development of the MAPER
concept has proceeded from the very beginning with the understanding that the ultimate goal of the research
program was to eventually arrive at a set of routines appropriate for field application.
-
-
-
3D Diagnosis Of A Tunnel Through Infrared Thermography Combined With Ground Penetrating Radar
Authors Jean Christophe Gourry, Colette Sirieix, Lucien Bertrand and Francis MathieuIn 1994, BRGM began a research project based on the combined use of infrared thermography and ground
penetrating radar (GPR) for the non-destructive testing of civil engineering works. This project aims to
combine these two techniques to enable: a). a more-precise knowledge of the nature and three-dimensional
extension of each anomaly, and b). a reduction in time spent on the measurement stage, and c). a better
interpretation.
The first measurements were taken during the survey of a railway tunnel, 1601 m long, in the east of France in
August 1994. The two entrances to the tunnel were tested over a distance of a few hundred metres.
A thermal imaging radiometer was used to take infrared scenes, 4 m wide and positioned by thermal markers,
whilst six parallel radar profiles (or radargrams) were recorded at three different frequencies.
A large amount of anomalies are detected when both techniques are combined, with correlation between the
total anomalies located during the present survey being 55%. In addition, this high level of correlation between
anomalies confirms both their existence and dimension. GPR systematically detects voids in masonry and
country rock whereas the depth penetration of infrared thermography is 1 m. On the other hand, the latter
technique is far more sensitive to problems of spoiled subsurface areas and humidity.
Finally, combined use of the two techniques provides a much clearer picture of the extension of each anomaly
in three-dimensions. Much work remains to be done however, specifically the calibration of radar profiles by
systematic velocity analysis. In addition, a better understanding of the ditTusion effect of each thermal anomaly
is required for a more precise estimation of the true extension.
-
-
-
An Investigation Of Cracks In Rock Slope Using Ground Penetrating Radar
Authors Katsuo Sasahara, I. Asahi, Tsuneo Tsuchida, Tsuyoshi Kobayashi and Thomas J. FennerRock slope collapse is an important problem in road maintenance works. Earlier investigations in collapsed
rock slope suggest that the internal structures of the cracks are important in forecasting rock collapses. Various
geophysical exploration methods may be applied in cases when visual inspection alone dose not provide sufficient
information. Recognizing the high resolution capability of ground penetrating radar (GPR), a site experiment was
conducted on a vertical wall of welded tuff in order to determine the applicability of GP to substance crack investigations.
-
-
-
Multiple Geophysical Studies At The Urban Central Environment Of Athens In Connection With The Construction Of The Metro’S Main Station
Authors St.P. Papamarinopoulos, M.G. Papaioannou, X. Kappopoulos and Y. BalatsasTwo main objectives were set to the personnel of the Laboratory of Geophysics of Patras University
and of the company Geome Ltd. by the scientists of the consortium of companies who were interested
in exploring a ten hectare area in the most central part of Athens. The objectives were, the location
of public utility networks unknown to the archives of the city and possible geological unconformities.
The case of the public networks was twofold. Firstly, it was important to know in advance of any
engineering and /or excavation procedure, the location of any network of pipes in order to avoid
damages which could raise the cost of the venture but they would not have consequences on the
public. Secondly, and more important, it was absolutely necessary to locate forgotten fragments of
gas pipes which have been installed in the past and which probably had trapped gas for ages. It is
understood that this case could be extremely dangerous for anybody who would operate for whatever
reason in close distance in connection with these buried pipes. In order to answer these questions a
magnetic gradiometer, a conductivity meter and a ground penetrating radar were utilized. The study
of the site for locating possible geological unconformities, involved resistivity measurements with
Schlumberger soundings, from which vertical parallel geoelectric sections could be produced, along
the main axis of the main avenue. On the same transects the antenna of the 80 MHz of the ground
penetrating radar was utilized.. The geophysical approach was fruitful by pin pointing a variety of
ferro-mettalic objects, geological contacts and a sub-terranean river.
-
-
-
Piezocone Technology: Downhole Geophysics For The Geoenvironmental Characterization Of Soil
Authors Michael P. Davies and Richard G. CampanellaThe electronic cone penetration test with pore pressure measurement, commonly referred to as the piezocone test or
CPTU, has been established by the worldwide geotechnical community as the premier stratigraphic logging tool for
most soil conditions. Besides stratigraphic information, the piezocone also provides accurate estimates of key
geotechnical parameters and yields extensive information on the physical groundwater regime. Groundwater
parameters assessed include accurate location of the phreatic surface, determination of in-situ gradients, and estimates
of hydraulic conductivities.
In recent years, additional geophysical measurement capabilities have been added to the standard piezocone. These
additions have included seismic pick-ups (geophone or accelerometer) for downhole and/or cross-hole seismic wave
measurements and resistivity modules which can be modified to include induced-polarization measurements. With
these additions, current piezocone technology represents an unparalleled means of accurately, rapidly ti
economically geoenvironmentally characterizing most natural and man-made soil deposits.
This paper introduces traditional piezocone technology and summarizes recent key advances with this geophysical
logging tool. A brief case study is presented to demonstrate the technological and economical advantages of the
piezocone over more traditional site characterization methods.
-
-
-
Application Of Geophysical Methods To The Detection And Monitoring Of Acid Mine Drainage
More LessThe application of geophysical methods to the detection and monitoring of acid mine drainage is beyond
the experimental stage and is being applied in the management of waste from a number of producing and
abandoned mines. Experimental studies, mainly in North America and Australia, have shown that non-invasive
measurements by airborne, ground and waterborne platforms can be used effectively in recognising and mapping
the movement of acid effluents in and around mine workings. Some methods can only recognise changes in the
first metre or so of the ground surface; others are limited to depths of one to five meters; others are capable
of detecting plumes at depths of several tens or even hundreds of metres. Some methods are qualitative in
nature while others can provide quantitative answers within various degrees of accuracy and reliability. Studies,
mainly sponsored by government agencies, but supported in many cases by industry, are attempting to establish
the effectiveness of a wide variety of methods and techniques, mainly by conducting test surveys and examining
available data in the vicinity of abandoned mines. One of the more ambitious of these studies was carried out
recently in the Sudbury area, Ontario, under the MEND2 program by INCO Exploration and Technical Services
Limited, (Ring, 1994). This study establishes useful parameters for applications of specific techniques in a
specific geological environment. A more comprehensive study (Paterson et al, 1994), was commissioned by
MEND in 1993, and is the basis for following paper. The project involved a review of available literature, an
information survey of users and suppliers, and discussions with experts in a variety of disciplines.
-
-
-
Seismic Field Investigation At A Subsidence Site In The Anthracite Fields Of Eastern Pennsylvania: Tools To Aid Multiple Phases Of Characterization And Remediation
Authors K. Kluger Cohen, M.A. Trevits and J. PweedleThis study used several seismic techniques to aid different phases of a subsidence investigation at an
abandoned coal mine subsidence site in a community located in the anthracite fields of eastern
Pennsylvania. Two surface collapse features, each about 3-5 m (lo-l.5 ft) in diameter, developed on
an athletic field underlain by an abandoned room-and-pillar mine 20 m (60 ft) deep. In a multiphase
investigation, surface seismic techniques were utilized to characterize mine level and overburden
conditions, and to design an effective drilling pattern for the remediation phase. Subsequently,
borehole pressure grouting techniques were used as an abatement procedure to stabilize the ground.
During this phase, borehole seismic techniques were used to further characterize subsurface
conditions as more than 680 stere (890 cubic yards) of grout was injected. The surface seismic study
included walkaway tests followed by a series of common offset lines that traversed the athletic field.
A signal enhancement seismograph, lOO-Hz geophones, and a sledge hammer were used for data
acquisition. The seismic data combined with information from a mine map and several borehole logs
suggested that the athletic field was divided into two zones: the western portion of the field
characterized by open mine voids, and the eastern portion of the field characterized by mine voids
more likely to be ftied with collapsed rubble. Using these results, a drilling pattern was
recommended and more than 20 boreholes were drilled in preparation for the remediation phase.
Borehole logs corroborated the predicted trends. All boreholes that would allow placement of grout
were selected for the grouting operations and the borehole seismic study was conducted concurrently
with grouting. One shot hole and three receiver holes were selected. An air gun served as an energy
source and downhole receivers consisted of 4O-Hz geophones arranged in a triaxial configuration.
Shot-receiver crosshole traveltimes were acquired for selected depths and these were used to
determine crosshole velocity distributions prior to and during injection. Preliminary analyses of the
crosshole data indicated a correlation between high velocities and competent mine overburden. In
contrast, velocities tended to decrease as the mine level was reached. Both the surface seismic and
the crosshole seismic studies provided valuable data and additional subsurface constraints for the
characterization and remediation of this abandoned coal mine site.
-
-
-
Detection Of Abandoned Mine Hazards On Government Lands Using Geophysical Methods
Authors Ken Hauser and James A. JessopSubsurface hazards are numerous in the United States, and are cause for increasing concern. The number of
hazardous sites related to previous mining activity on public lands is particularly alarming, and Congress has
stated that the problem must be addressed. Specifically, the proclivity of abandoned mine sites on government
lands has created dangerous situations in many of our nation’s National Forests, National Park Lands, and on a
variety of lands overseen by the Department of the Interior. The affects of subsidence due to historical mining
activity can be a long-term economic drain on the limited resources available to maintain roads and trails
through these areas. Catastrophic failure and collapse of the ground above old mine workings carries the
implication of severe health and safety hazards for hikers, bicyclists, horseback riders and recreational vehicle
users. In response to these issues, the U. S. Bureau of Mines has been successful in addressing the problem of
subsurface hazard detection and characterization on public lands using geophysical technologies in several recent
projects. At the Shawnee National Forest in southern Illinois, in addition to creating dangerous conditions for
recreational land users, poorly mapped abandoned tripoli mines pose a potential problem for future logging
operations. Old mine workings have been collapsing in certain areas on the property and introduction of the
heavy equipment associated with logging may be dangerous. An integrated geophysical investigation, including
ground penetrating radar, common offset seismic reflection profiling and magnetic gradient surveying was
implemented in attempts to remotely identify the subsurface workings. At the Prince William Forest Park in
Virginia, speculation regarding both the location and structural integrity of the main shaft of an abandoned
pyrite mine required that some investigation be made. Electrical and magnetic geophysical methods were used
to locate the shaft and to assess shaft conditions.
-
-
-
Three-Dimensional Imaging Of Underground Mine Structures Using Seismic Tomography
Authors M.J. Jackson, M.J. Friedel, D.R. Tweeton, D.F. Scott and T. WilliamsThree-dimensional seismic imaging has a number of important advantages over two-dimensional tomography, in artifact suppression and selfconsistency. However, the underdetermined or illconditioned nature of the inversion is typically more severe in three dimensions than in two. Methods for characterizing resolution and robustness are concomitantly more important for three-dimensional studies. Checkerboard resolution tests and robustness tests based on multiple inversion with different starting models provide means of evaluating the results of
travel-time inversions for two underground mine sites.
-
-
-
Saltwater Intrusion: Concepts For Measurements And A Regional Characterization For Broward County, Florida
Authors Lynn Yuhr and Richard C. BensonFour basic components are necessary to properly manage our groundwater resources against saltwater intrusion;
measurement, monitoring, modeling and modification. While a discussion of the saltwater interface is presented to
provide an understanding of the hydrologic problems, this paper focuses on the first two steps in the process of
characterization; the measurements to define existing conditions of the saltwater interface and techniques for
monitoring changes in the saltwater interface over time.
A variety of techniques to measure the saltwater interface (both traditional and contemporary) are presented along
the their advantages and disadvantages. Two contemporary techniques are highlighted because of their dramatic
improvement in information which they provide: surface time domain electromagnetics (TDEM) and borehole
induction logging.
A county-wide case study is presented which utilized these contemporary techniques in Broward County, Florida.
The results of this study were used to map the saltwater interface, and identify anomalous conditions caused by
effects of head differences due to pumping, irrigation and saltwater recharge from canals as well as the presence of
“connate” saltwater in the aquifer. This regional characterization of the salhvater intrusion will be used to assess
the existing county-wide saltwater monitoring network and identify locations for future monitoring wells. The
approach for characterizing the extent of saltwater intrusion was unique and provided solid technical information
on the groundwater resources in which planning and development of the county can be based.
-
-
-
Hydrogeological Investigations Of Minor Islands In Denmark
Authors K.I. Sørensen and J.P. JensenDenmark is a kingdom of islands. Denmark consists of more than 500 islands,
200 of which are inhabited, though many are smaller than 10 km2. Supplying good
quality drinking water for the inhabitants often presents major problems, some of
which are specific for the islands.
For geometrical reasons the coast-near regions of an island are a relatively larger
proportion of the total area, the smaller the island is. This means that the area, where
the proximity of the sea presents problems of salt water intrusion in the aquifers, is
relatively large, and abstraction of fresh ground water is most often precluded in these
parts, On the other hand, farming is the main occupation and means of living on the
smaller islands, so the problems with infiltration of nitrate from excess fertiliser and
pesticides related to agricultural use are very acute. For these reasons’ reports of
deteriorating water quality have appeared from many of the smaller islands.
There are many good reasons why the problem should be solved locally. The
Department of Earth Sciences has been involved in co-operative research projects with
several municipal water supplies in Denmark to find strategies for the application of
geophysical methods to solve the specific hydrogeological problems of the minor
islands, all of which are characterised by a Quatemary sedimentary geology.
An integrated use of geophysical methods has proven ifself to be very applicable
in the type of detailed hydrogeophysical investigations, which must be carried out to
provide the necessary insight into the hydrogeology of an island. This demands that
efficient and detailed methods for measurements and interpretations are developed,
and the strategic aspects of data collection and interpretation become important.
In this context we present results from the PA-CEP electrical profiling method
and the Ellog auger drilling method with undisturbed water sampling which, together
with transient electromagnetic soundings and geoelectrical soundings, can be
combined into an efficient scheme for detailed hydrogeological investigations. The
results of these investigations are the foundation for decisions on remediating
measures, sitings of new abstraction wells, and possible restrictions on the land use.
-
-
-
A Comparison Of Electromagnetic Techniques Used In A Reconnaissance Of The Ground-Water Resources Under The Coastal Plain Of Isla De Mona, Puerto Rico
Authors Ronald T. Richards, Joseph W. Troester and Myrna I. MartinezAn electromagnetic reconnaissance of the ground-water resources of the coastal plain of Isla de Mona, Puerto Rico
was conducted with both terrain conductivity (TC) and transient electromagnetic (TEM) geophysical techniques.
Quantitative interpretation of the data was done using forward and inverse modeling with various starting geoelectric
models. The final geoelectric models produced by the two techniques are similar. Neither method was able to provide
useful information about the water table. The freshwater lens under the coastal plain was found to have a maximum
thickness of about 10 m near the center of the coastal plain. The lens thins toward the ocean and also thins toward the
interior of the island. This finding was not expected and indicates that the flow paths in the aquifer are not radially
symmetrical from the center of the island to the ocean. At least some of the ground water flows to the ocean by a more
circuitous and longer path. The asymmetry of the flow paths indicate that differences in hydraulic conductivity are
controlling the shape of the freshwater lens.
-
-
-
Salinity And Hydrodynamics Of The Holocene And Upper Pleistocene Beneath The Louisiana Wetlands From Electrical Measurements
Authors L.D. McGinnis, M.D. Thompson, G.J. Kuecher, P.L. Wilkey and H.R. IsaacsonA conceptual hydrodynamic model in the Holocene and upper Pleistocene beneath the
Louisiana wetlands is described in terms of salinity distributions. Porewater salinity is calculated
from electrical measurements, including resistivity soundings, electric logs, and electromagnetic
profiling. Electrical measurements support the primary, basin-wide groundwater flow model;
however, the data also indicate secondary contributions from expulsion of fluids under geopressure
along active growth faults and from original waters of deposition. Expulsion of water from
growth faults has been described previously for deeper sections of the Pleistocene, but has not been
reported for the Holocene or upper Pleistocene beneath the Louisiana wetlands. Porewater
chemistry variations beneath the coastal wetlands are a consequence of the following (in order of
importance): (1) environment of deposition; (2) a basin-wide, regional flow system; (3) expulsion
from deep-seated growth faults; and (4) pore water extrusion due to compaction. Water chemistry
in Holocene clays and muds is influenced primarily by the deposition environment. In Pleistocene
sands, the chemistry is a function of the other three factors.
-
-
-
Saltmap - High Resolution Airborne Em For Electrical Conductivity Profiling
Authors G.J. Street and G.P. RobertsShallow conductivity mapping using airborne electromagnetic systems has been used extensively in
Australia for environmental applications. The aim of such surveys is to define near surface
conductivity variations which can be related to dissolved salts in the groundwater. In most parts of
Australia the principal salt is naturally occurring sodium chloride (NaCl) and in many cases salt
deposits are concentrated or remobilised by the effects of man’s interaction with the environment.
To understand how these deposits are moving in the ground it is necessary to map the conductivity
variations in the near surface in three dimensions. The airborne electromagnetic system employed
must measure both at high frequency and at high sampling rates to achieve this aim. To resolve
conductivity structures at high resolution in the ground’s near surface is in some ways a more
difficult problem than to detect anomalies at great depth. A wider system bandwidth and superior
noise immunity are required and consequently greater real-time computing power. Results from the
initial surveys using SALTMAP show that most of the planned specifications of the system have
been met. The challenge for the future is to utilise the data generated in remedial environmental
work.
-
-
-
The Use Of Ground Penetrating Radar For Aquifer Characterization: An Example From Southwestern British Columbia
Authors Jane Rea and Rosemary KnightTwelve kilometers of ground penetrating radar (GPR) data have been collected over the Brookswood
aquifer in southwestern British Columbia. The data have been analyzed to assess how GPR can be used to
characterize the distribution and connectivity of hydraulic units.
We have used GPR to locate the aquifer/aquitard boundary at several locations in the study area. The
electrical contrast between these two materials makes the aquifer/aquitard boundary an excellent target for GPR
surveys.
GPR was also used to reconstruct the paleo-environment of one area of the Brookswood aquifer. This was
accomplished by using a modification of the concept of architectural element analysis. Radar elements were
identified in the survey and were assigned sedimentary parameters using data from trenching and drilling in the area.
These elements were used to develop an interpretation of the paleo-environment that provides information about the
spatial distribution of hydraulic units.
-
-
-
Hydrogeophysical Characterization Of Water Wells Through Geophysical Logs In Deccan Trap Of M.P., India
Authors Subhash C. Singh and G. SuryanaraynaThe western part of Madhya Pradesh particularly, Malwa
plateau region is most extensively occupied by dark greenish
black to grey, apparentlyhomogeneous looking basaltic rocks of
either A, or Paaboe type. Each flow comprises either zeolitic
vesicular basalt followed by hard massive/j.ointed fractured
basalt. Groundwater occurs in weathered mantle: joints and
fractures. Identification of hydrogeological units forming the
complex frame-work of basaltic aquifer system has been
cunsiderably made easier through the use of multi-parameter
geophysical devices of sub-surface horehole logging. The
massive part of basaltic flow which is hard and compact shows
very high resistivity (300 ohm-m to 5000 ohm-m) and low natural
gamma counts (15 cps to 40 cps) whereas t-he ves.icular part
which is filled with secondary minerals (amygdules) and the
fractured basalt show intermediate resistivity (50 ohm-m to 300
ohm-m) and natural gamma counts (40 cps to 100 cps). The inter
- trappean flow shows very low resistivity (6 to 50 ohm-m) and
very high gamma counts (100 cps to 300 cps).
The synergistic study of multi-parameter logs and .its
cross plotting followed by statistical techniques of filtering
and deconvolution have been used in the present study and
useful correlation and inferences for precise zoning of even
thin layers like redbole at deeper depths could be drawn up.
The paper h.ighlights the effective correlation between
resistivity logs and natural gamma logs so as to work out the
probable sub-surface configuration of aquifer system which will
have a major bearing on the safe and sustainable design of
groundwater abstraction structures.
-
-
-
Application Of New Data Processing Techniques To Hydrogeophysical Survey Data From The Netherlands
Authors M.A. Meju and J.A.C. MeekesThe determination of aquifer characteristics from surface geoelectrical measurements is a difficult nonlinear
inverse problem. In routine data analysis, this problem can be addressed by time-consuming forward
modelling and automated iterative inversion or recently by the faster approach of direct inversion. A major
draw-back of these standard approaches is that in the absence of accurate a priori information, there is no
guarantee that the constructed model represents the true subsurface structure. A simple and effective
alternative scheme for approximate direct resistivity-depth transformation of geoelectrical data is combined
with standard numerical modelling techniques and applied to well-known transient electromagnetic and dc
resistivity survey data from the Netherlands in order to evaluate its usefulness in this geological setting.
The resulting models of the subsurface are found to be in excellent agreement with borehole lithological and
permeability distribution data and demonstrate that dc resistivity and TEM methods are an essential
combination for accurate geoelectrostratigraphic characterisation. The results also suggest that the rapid
scheme for simultaneous TEM and dc resistivity data analysis is a powerful tool for hydrogeophysical
studies in the region.
-
-
-
Vertical Profiling Of Aquifer Flow Characteristics And Water Quality Parameters Using Hydrophysical’” Logging
HvdroPhvsical™ ( HpL) logging technology is a revolutionarv advancement in aquifer characterization that was
recently applied at Schofield Army Barracks, Oahu, Hawaii. The purpose of using this innovative technology was to
assess the aquifer permeability and groundwater quality to gain a quantitative understanding of groundwater flow
conditions and potential contaminant pathways. Fractured and caved zones within the boreholes precluded the use
of other techniques (e.g., inflatable packers) to obtain these data. The versatile and time saving benefits of HpL
logging provided hydrogeologic understanding of the aquifer at a cost savings from other available technologies.
-
-
-
Simulation Of Airborne Electromagnetic Measurements In Three Dimensional Environments
Authors David L. Alumbaugh and Gregory A. NewmanA 3-D frequency domain EM modeling code has been implemented for helicopter
electromagnetic (HEM) simulations. A vector Helmholtz formulation for the electric fields is
employed to avoid problems associated with the first order Maxwell’s equations numerically
decoupling in the air. Additional stability is introduced by formulating the problem in terms of the
scattered electric fields which replaces an impressed dipole source with an equivalent source that
possesses a much smoother spatial dependence and is easier to model. In order to compute this
equivalent source, a primary field arising from dipole sources in a whole space must be calculated
where ever the conductivity is different than that of the background.
The Helmholtz equation is approximated using finite differences on a staggered grid. After
finite differencing, a complex-symmetric matrix system of equations is assembled and
preconditioned using Jacobi scaling before it is solved using the quasi-minimum residual (QMR)
method. In order to both speed up the solution and allow for larger, more realistic models to be
simulated, the scheme has been modified to run on massively parallel architectures. The solution
has been compared against other 1-D and 3-D numerical models and is found to produce results in
good agreement. The versatility of the scheme is demonstrated by simulating a survey over a salt
water intrusion zone in the Florida Everglades.
-
-
-
1D Time Domain Electromagnetic Interpretations Over 2D / 3D Structures
By Esben AukenTime domain electromagnetic soundings have been calculated over 2D / 3D structures in a layered halfspace and
hereafter inverted using a 1D least squares time domain code. The forward calculations are done in the frequency domain
and the subsequent transform to time domain is performed using fast digital filters. The study focuses on typical
hydrogeological models. The investigated models include a resistive dyke, a resistive beam and resistive block structure with
edges with varying slopes in a conductive layered halfspace with an overburden. The 1D interpretations of the 2D / 3D
responses show that the vertical resolution is reduced and the resistivities are smeared out. The 2D / 3D responses over
models with a resistive body in a conductive host is easily fitted with the 1D models whereas it is not possible to fit the
responses from good conductors in a resistive host very well.
-
-
-
Characterization And In-Field Suppression Of Noise In Hydrogeophysics.
Authors Mette S. Munkholm, Kurt I. Sørensen and Bo H. JacobsenPresent developements of hydrogeophysical methods provide us with hitherto unseen sampling density in profiling and
sounding. Transient electromagnetic sounding (TEM) data and pulled array continuous electrical profiling, PA-CEP
(Sorensen and Christensen, 1994) are among these. Common to these types of data is the possibility of simple stacking or
moving averaging to increase the signal to noise ratio due to the data redundency. Moreover, due to the volume of the raw
data the stacking must be done in the held. However, only for white Gaussian noise is simple stacking optimal. Studies have
shown that it is critical to characterize the noise with respect to frequency spectrum and statistical distribution as a design
basis for more adaptive noise suppression procedures in order to achieve reliable results.
Flexible stacking schemes for the data types are presented and we demonstrate their adaptation based on studies of the noise
characteristics for each type. Also, the special problems arising in online processing for the different stacking schemes are
addressed. The large data volume involved calls for in-field reduction of the data. This study is aimed at designing the online
processing required.
-
-
-
Neural Network Interpretation Scheme For A Frequency-Domain Electromagnetic Ellipticity Surveys
Authors Ralf A. Birken and Mary M. PoultonA system of neural networks is used for the interpretation of electromagnetic ellipticity data from a frequencydomain
electromagnetic system developed at the Laboratory for Advanced Subsurface Imaging. The in-field data
interpretation consists of networks operating in mapping mode (1D) and object mode (3D, not yet implemented).
The purpose of the interpretation system is to provide a fast, approximate yet reasonable interpretation in the field
during a survey. Our approach to the neural network processing is to divide the interpretation into many parts
using several small networks. Three network paradigms were used for training, a backpropagation algorithm,
radial basis functions, and modular neural networks. We have tested the networks for a frequency range of 1kHz
to 1MHz with synthetic data and from a field survey in Wyoming.
-
-
-
The Application Of Geophysics To Archaeologic Mapping Of Prehistoric, Protohistoric And Historic Sites In Western Canada
Authors Paul Bauman, Rod Heitzmann and Jack PorterIn 1799, the site of Rocky Mountain House, Alberta, stood at the southwestern corner of the
northern fur empires of the North West Company and their competition, the Hudson’s Bay
Company. It marked the endpoint of a yearly journey of up to 3,000 kilometers for the traders who
inhabited the site. Between 1799 and 1875, four forts were constructed by the two fur trade
companies. The third of these forts, which stood from 1835 until 1861, has not been excavated.
As these forts were almost entirely constructed of wood, with very little metal or stone, their
surface remains are meager. The goal of this investigation was to evaluate the utility of
geophysics as an archaeological aid in studying such historic sites in Western Canada.
Specifically, the objectives were to identify the position of the rooms and palisades of the 1835
1861 fort, and to locate burial sites associated with this and other forts. An additional objective
was to explore for prehistoric and protohistoric native campsites in the vicinity of the fort. A
challenging obstacle in describing the 1835-1861 fort using geophysics is the fact that in 1861,
the Blackfoot peoples burned the fort to the ground.
Four geophysical methods were used. Ground penetrating radar data provided the greatest detail
in describing fort construction and burial locations. The GPR data, however, would have been
of limited use if not viewed in conjunction with the information provided by total magnetic field,
magnetic gradient, and terrain conductivity plots of the particular sites. The integration of the
various methods provided an overall plan of the original construction of the 1835 fort, including
some unexpected insights into the building techniques of the period. While GPR most clearly
pinpointed several burial sites, the use of multiple instruments provided greatly increased certainty
and an increased understanding of the nature of the identified graves. Beyond being a good
example of an archaeogeophysical data set, the significance of this paper is the clarity with which
it is shown the need to integrate a number of geophysical techniques at investigations of historic
sites in Western Canada. In addition, it is evident that the spatial relationships of buildings,
burials, and palisades provided by a detailed geophysical data set can greatly enhance the overall
understanding of the activity and history of a fur trade post during its active life.
-
-
-
The Geophysical Discovery Of A Second World War Battlefield In Central Crete During Construction Activities By A Building Company. The Solution To A Major Environmental Problem.
Authors St.P. Papamarinopoulos, M.G. Papaioannou, P. Stefanopoulos and X. BafitisDuring the initial steps of preparation of a ten hectares piece of land for building purposes in central
Crete a bomb was discovered accidentally. The Laboratory of Geophysics accepted a request by the
company and carried out differential magnetic, and ground penetrating radar measurements.
In spite of the environmental noise produced by the tratIic and the function of nearby radio station
emitting at 80 MHz, it became possible to apply a normalization and filtering technique in the
instruments and successfully locate a large variety of war remains from 1 to 4m depths. Depth
estimates of the explosives were obtained by modeling with 2-112 D theoretical bodies and later by
object delineation using Euler’s homogeneity equation.
-
-
-
Geophysical Investigation For The Location Of A Historic Heiau Kawaihae, Hawaii
Authors Jose L. Llopis and Michael K. SharpThere currently is an awareness in Hawaii to preserve historic sites and the culture of ancient Hawaii.
One area of cultural significance, Pu’ukohola Heiau National Historic Site, is located in Kawaihae on the
northwest coast of Hawaii (Figure 1). The site is administered by the U.S. Department of the Interior’s
National Park Service (NPS). A heiau is a massive stone structure which was used as a temple by the ancient
Hawaiians.
The Pu’ukohola Heiau is the primary structure associated with the founding of the Kingdom of Hawaii.
The last major heiau was built in 1791 by Kamehameha the Great to honor, regain the favor, and enlist the
services of his family war-god, Ku-ka-ili-moku. An Englishman, John Young, reported that Kamehameha
offered 11 human sacrifices at the dedication of the heiau. The principal offering was the body of Keoua Kuahu’ula,
Kamehameha’s only serious rival for the control of the island of Hawaii. With his war temple built
and acceptable to the war-god, Kamehameha conquered Maui, Lanai, and Molokai islands in 1794 and Oahu in
1795. With the successful conquest of Oahu, Kamehameha founded the Kingdom of Hawaii. Kauai remained
independent until 1810, when it joined the Kingdom by mutual consent to forestall invasion by Kamehameha.
Following the death of Kamehameha in 1819, the traditional religion was abandoned. The carved
wooden images of Pu’ukohola Heiau were discarded and its thatched temple houses, prayer tower and altar
destroyed. Today, there are two intact stone structures, or heiaus, that can be visited at the Pu’ukohola Heiau
National Historic Site. One structure is about 200 ft long and 100 ft wide and the other about 275 ft long and
50 ft wide. A third, smaller structure, measuring approximately 10 ft by 10 ft, has historically been reported to
exist at the site but its exact location is unknown. Some local residents claim that the missing heiau is located
in the bay just a few tens of yards offshore from the site while others maintain that it is buried somewhere
onshore near the shoreline.
A geophysical investigation was performed at the Pu’ukohola Heiau National Historic Site during the
period 11-18 August 1993 in order to locate a purported “shark heiau” in the vicinity of the Kawaihae Boat
Harbor construction project, South Kohala, Island of Hawaii. This was performed as part of Section 106,
National Historic Preservation Act of 1966, as amended, compliance, pursuant to implementing regulations
contained in 36 CFR 800, for the proposed construction at Kawaihae Harbor. NPS persoMe desired to noninvasively
determine the location of the shark heiau; the heiau will then presumably be investigated and
protected. The geophysical investigation was conducted by personnel of the U.S. Army Engineer Waterways
Experiment Station (WES) at the request of the U.S. Army Engineer Division, Pacific Ocean.
-
-
-
Buried In The Basement - Geophysics Role In A Forensic Investigation
Authors Scott F. Calkin, Richard P. Allen and Michael P. HarrimanMrs. Pearl Bruns of South Portland, Maine was reported missing in August 199 1. The search for Mrs. Bruns
went on for thirteen months. Evidence from various forensic techniques and interviews suggested a remote
possibility that Mrs. Bruns may have been interred in the dirt basement (approximate 3.5 foot crawlspace) of her
residential home. In July 1992, the Maine State Police contacted ABB Environmental Services inquiring about
the use of geophysical methods which could detect shallow graves. Based on site conditions and law
enforcements’ desire not to tear the home from its foundation to dig up the cellar, ground-penetrating radar
(GPR) was chosen to screen for the presence of a shallow grave. Considering the target was approximately 5
feet long and 1.5 feet in width, a one by one foot survey grid was conducted in September 1992 using a GSSI
System III GPR unit equipped with a 500 MHz transducer. A strong reflector (approximately 3 feet below the
basement surface) was profiled throughout the survey area. A test pit revealed the reflector represented an
oxidized, cemented sand which could not be penetrated with hand tools. However, in one comer of the
basement next to a foundation wall, GPR data indicated the reflector was conspicuously absent. Mrs. Brims,
wrapped in plastic bags and bound by the wrists and ankles, was found buried 2.5 feet below the basement
surface at this location. Her husband, Mr. William Bruns was arrested and charged with murder. Mr. Bruns
plead guilty to manslaughter in April 1994 and is serving a twenty year prison sentence.
-
-
-
Use Of Bistatic Allofrequency Antennas In Ground-Penetrating Radar (Gpr) Investigations
More LessShielded monostatic transducers used in ground-penetrating radar investigations
(GPR) provide good results in probing subsurface features. Use of bistatic (paired) isofrequency
transducers can improve survey results. Bistatic antennas transmitting and receiving
at the same center frequency (iso-) can reduce ‘ringing” produced by initial contact
of a vertically incident radar pulse with highly conductive surface material. Selection
of a suitable antenna separation can improve capture of reflected pulses that would
be lost using a monostatic system. What is reported here is the use of a pair of antennas
having different center frequencies (allo-), with the higher frequency receiver serving as
a filter for the lower frequency transmitter. Impulse radar units transmit and receive
broad bandwidth pulses. Lower frequency antennas usually transmit pulses with higher
power, allowing specific frequencies to penetrate deeper into geologic media. In the
zone of frequency overlap, sufficient energy will be reflected back to the higher
frequency receiver to permit higher resolution of targets at greater depth.
-
-
-
Ultra-Wideband Antenna Design For Gpr Application
Authors Chris Thompson and Bibhas DeWe have been developing an ultra-wideband antenna design for use in Ground Penetrating Radar
applications. Adapted from a patented antenna intended for use in dielectric permittivity well logging (De
and Nelson (1992a)), the antenna is small (3cm by 3cm aperture) and has a wide bandwidth (10’s MHz to
1 Ghz useable range). Initial tests indicate that the basic antenna is compatible with current commercial
digital instruments, although relatively inefficient compared to conventional dipole antennae. Reasonable
quality field data were recorded which are comparable to dipole data but lower amplitude. Our ultimate
goal is to design a small, wideband antenna with superior insulation from the air half space. Such an
antenna is required for GPR site assessments at urban and culturally noisy sites.
-
-
-
3-D High-Resolution Seismic And Georadar Reflection Mapping Of Glacial, Glaciolacustrinel And Glaciofluvial Sediments In Switzerland
Authors A. Green, A. Pugin, M. Beres, E. Lanz, F. Bilker, P. Huggenberger, H. Horstmeyer, M. Grasmtick, R. De Iaco, K. Holliger and H.R. MaurerDuring the past decade significant progress has been made in the development of geophysical techniques designed
to resolve problems associated with the unconsolidated sedimentary layers of the shallow subsurface. Two of these
techniques, the high-resolution seismic reflection and the ground-penetrating radar (georadar) methods, have the
potential to define the character, size, and geometry of surficial sedimentary units. In an attempt to determine
optimum recording and processing strategies, seismic and gwradar reflection profiles have been recorded across
a variety of glacial, glaciolacustrine, and glaciofluvial deposits in Switzerland. At one test location we have also
conducted a pilot 3-D high-resolution seismic reflection survey and at another we have collected an experimental
3-D gwradar data set. Results of the 3-D surveys are striking images of the shallow subsurface that provide many
more details and much more reliable information on the 3-D heterogeneities of the shallow subsurface than are
afforded by conventional 2-D data sets; at both 3-D test sites critical geological features would have been misinterpreted
had only limited profile information been available.
-
-
-
3-D Gpr Imaging Of Complex Stratigraphy Within The Ferron Sandstone, Castle Valley, Utah
Authors Chris Thompson, George McMechan, Robert Szerbiak and Neil GaynorTwo detailed 3-D Ground Penetrating Radar surveys were recorded on outcrops of the Ferron Sandstone in Castle
Valley, Utah in an effort to image internal sedimentary structures. The Ferron Sandstone is a fluvial to proximal
marine sandstone which is considered to be a good analogue for some Gulf Coast oil and gas reservoirs. Because of
its excellent exposure in Castle Valley, the stratigraphy of the Ferron has been, and continues to be very extensively
studied to determine the relationships of bedforms to the distribution of reservoir properties. Our goal in imaging
these outcrops with 3-D GPR is to interpret reservoir heterogeneities at interwell scales. Correlation of these
heterogeneities to known porosity and permeability distributions from outcrop studies will be used to establish three
dimensional scales of reservoir flow behaviour. These data will subsequently be used to improve flow simulations
of analogous oil and gas reservoirs. Results of this study indicate that 3D GPR is indeed suitable for this application.
The first 3-D survey was recorded on a 15m by 15m grid with traces recorded every 25cm in both directions.
Adjacent outcrop showed the near-surface sandstones to be of a tidally reworked deltaic lithofacies, overlying lower
coastal plain carbonaceous siltstones. More than 4m of penetration and finer than 25cm resolution were achieved
using a PulseEKKO IV GPR system with 200 MHz antennae.
The second 3-D survey was recorded about 250m away from the first, over a stacked distributary channel to
nearshore sandstone lithofacies. 100 MHz antennae were used over a 25m by 25m grid, with 5Ocm spacing in both
directions. More than 8m of penetration and finer than 50cm resolution were observed.
A 2-D line with 50 MHz antennae and 1 .Om trace spacing was recorded to connect the two 3-D surveys and to
provide a more regional picture of stratigraphy. Reflections were recovered from as deep as 20m.
The data were processed both at Chevron, using the Promax seismic processing system, and at UT Dallas, using
in-house software. Data were flattened on the air arrival, gained, spatially smoothed and then migrated using a
fixed-offset prestack migration. Results were visualized with VoxelGeo, a software package which allows the user
to selectively render the volume with transparency to see the interior of the data cube in 3-D perspective.
Connectivity analysis within the cubes highlights discrete reflectors, and by implication, the main flow units of the
facies. Work is underway to correlate the vertical and horizontal scales of heterogeneity from the GPR data, with
the facies’ permeability distribution from outcrop studies.
-
-
-
Location And Identification Of Compact Metallic Objects By Magnetics And Electromagnetic Induction
Authors John E. McFee and Yogadhish DasThis paper discusses methods of location and identification of compact metallic and ferrous objects
using magnetometers and electromagnetic pulse induction. To date, no commercially available systems
exist which can explicitly and accurately estimate the location of a compact ferrous or metallic object and
identify it reliably. Self-contained systems which could do so in real-time would represent a significant
advance in the state-of-the-art.
-
-
-
Detection Of Buried Contaminant Containers Using Gpr
Authors Leon Peters, Jonathan D. Young, Chi-Chih Chen and Jeffrey J. DanielsThe detection of buried containers is dependent on several factors including the GPR antenna properties,
the size, shape, material construction of the container, its contents and the physical and electrical properties
of the soil in which it is buried. These features will be discussed as will some target identification techniques.
-
-
-
An Integrated Approach For Measuring And Processing Geophysical Data For The Detection Of Unexploded Ordnance
Authors Jerzy Pawlowski, Dr. Richard Lewis, Tim Dobush and Nicholas ValleauLand and water borne electromagnetic and magnetic surveys were performed near
the old Lake Erie Ordnance depot in Ohio. The purpose of the study was to
determine the presence and subsurface density of unexploded ordnance (UXO).
Measurements were carried out within selected onshore and offshore areas using
instruments adapted for underwater investigations. A test site with known buried
ordnance was prepared in order to establish a base reference for conducting
detailed land surveys and transects for the underwater investigation.
The interpretation of magnetic field data for man-made metallic ordnance is often
difficult because of distortions to the observed field caused by permanent
magnetization. The interpretation of the electromagnetic data is dependent on the
condition of the metallic content of the object which will have an effect on the
electromagnetic field. Advanced data processing and presentation software
techniques were employed to determine the criteria for the plan and depth locations
of the buried ordnance.
The goal of the tests is to help to establish a baseline against which to evaluate
future changes in the rate of on-shore deposition of new ordnance. As the magnetic
results were limited for the Lake Erie site (low sampling density), magnetic data
from a Naval Research Laboratory (NRL) demonstration site at Fort Devens, MA
was utilized as a further example for this paper. The purpose was to examine the
relationship of higher sampling densities to the accuracy of the plan location and
depth calculations of magnetic data.
-
-
-
Army Research Laboratory Ultra-Wideband Crane Sar: System Overview And Results Of Early Ground Penetrating Radar Studies
Authors Keith A. Sturgess, Lam Nguyen, Marc Ressler, Tuan Ton and T.O. GroschArmy Research Laboratory (ARL) and Massachusetts Institute of Technology/Lincoln Laboratory (MIT/LL)
have been working in the field of ultra-wideband (UWB) synthetic aperture imaging radar (SAR) for foliage
penetration for a number of years. In 1993, ARL was appointed executing agent for a Defense Intelligence Agency
program to investigate ground penetrating radars on airborne platforms. In the summer of 1993 an experiment was
conducted at Yuma Proving Ground, Arizona involving many existing airborne radar sensors to assess GPR
potential. Data collected by Stanford Research Institute International on a minefield emplaced at Yuma is presented,
along with statistics of the targets and clutter as a function of frequency and depression angle, to show the current
capability and potential of improved sensors. An automatic group target detection algorithm designed to find
distributed targets is discussed and results of applying it to the minefield data are shown. Based on analysis of data
collected at Yuma and other research conducted, a new crane-based UWB SAR collection asset has been designed
and built at ARL that is fully polarimetric and covers a frequency range of 60 MHz to 1 GHz. This highly capable
radar system is described, and future data collection plans are discussed.
-
-
-
An Innovative And Cost Effective Approach For Uxo Detection Using Gis Is Setting A New Standard
Authors Charles Heaton, Robert Menke and Matthew GiffordFort Monroe is a 584-acre U.S. Army facility approximately ten miles north of Norfolk,
VA, near Hampton Roads, VA. Conventional OEW, some dating back to the 186Os, has been
found at many areas of Fort Monroe, and it is expected that much more remains. The ordnance
may represent a serious OEW safety hazard and a significant cost to remediate the site. The
1993 Base Realignment and Closure Commission Report recommended a comprehensive
investigation of UXO contamination at Fort Monroe.
-
-
-
Development And Testing Of A Tensor Magnetic Gradiometer
Authors D.D. Snyder and Robert BrackenMagnetic gradient measurementsp ossesss everal advantages compared with other magnetic field measurementsin
shallow-site investigations, hazardous-waste site characterization, and other investigations to locate buried ferromagnetic
objects. These advantages include (1) immunity from time-varying geomagnetic noise, (2) improved spatial resolution
because of the more rapid spatial attenuation of the gradient components compared with magnetic field components, and
(3) generally low-background gradient values from geological effects. For this reason, conventional magnetic surveys for
site investigations and for object detection routinely acquire the vertical gradient of the total magnetic field with a pair of
identical proton or alkali vapor (e.g., Cesium) magnetometers with spatial separations of a few feet.
Quantitative interpretation of magnetic gradient data requires the knowledge of several components of the gradient (Hood
1965; Reid et. al 1990). Theoretically, these gradients can be calculated from a properly sampled map of one of the
components of magnetic field (Nabighian 1984), but the advantage to their direct measurement is that interpretation can
be performed with data acquired at a few data points along a profile. Consequently, interpretation in near real time either
during acquisition or immediately after it is therefore quite feasible.
-
-
-
Time-Term Method With Tomographic Determination Of Refractor Velocities
Authors Masaya Yamauchi and Hideki SaitoThe authors applied time-term method in a seismic refraction survey to determine the variation of the
thickness of a gravel layer overlaying a weathered granite basement in a 100 x 400m area. The reason why we used
time-term method in this survey was that the ground surface at the site was covered with boulders as large as 1
meter in diameter, it was difficult to apply conventional refraction survey in which sources and receivers have to be
in a line. Before doing field measurements, it seemed that the velocity structure of the site satisfied all
requirements for the applicability of time-term method. However, when analyzing observed seismic refraction data,
we found that the structure was not satisfied one of the requirements that the basement had no lateral variation in
velocity. To determine the variation of basement velocities as well as the distribution of the thickness of gravel
layer, we incorporated a tomographic technique into a conventional method and successfully applied it to the survey
data.
-
-
-
Tomography Between Wells, A Transient Dielectric Logging Tool, And The Very Early Time Electromagnetic (Vetem) System
This paper reviews progress on three site characterization technologies we are developing
at the U.S. Geological Survey (USGS).
We produced hole-to-hole electromagnetic and seismic tomograms of fractured crystalline
rock at the Mirror Lake, New Hampshire, hydrology research site. Both electromagnetic
and seismic tomograms between well pairs correlate with zones of high hydraulic
conductivity. We processed the electromagnetic full wave recordings in a variety of ways
to produce velocity tomograms, attenuation tomograms, and dispersion tomograms. Since
tomograms image not only fracture zones, but lithology as well, it is important to examine
all additional available geological, hydrological, and geophysical information in order to
achieve the most accurate interpretation of the tomograms.
Dielectric single-hole tools should be useful for direct detection of non-aqueous phase
liquids. Borehole dielectric logging tools were developed by the petroleum industry for
measuring oil saturation in cases where electrical resistivity is too high for resistivity tools
to be effective. However, for many shallow environmental applications existing commercial
borehole tools are physically too large to be practical. Previous experience with single-hole
borehole radar suggested to us that a time-domain dielectric logging tool might be feasible.
An experiment in a laboratory sandpack confirmed that supposition. A further experiment
is in progress to assess resolution of such a tool and to measure the effects on the calculated
values of dielectric permittivity of borehole diameter and tool location in a borehole.
The very early time electromagnetic (VETEM) system is a time-domain, surface-deployed
system that has potential applications to direct detection of non-aqueous phase liquids as
well as to the detection of buried objects. It is designed to operate in environments that are
too conductive for ground penetrating radar to be effective, and too.shallow for standard
electromagnetic systems. The VETEM system provides a faster profiling alternative to the
frequency-domain high frequency sounder (HFS) we been built and successfully applied in
a number of field experiments. The VETEM system construction is essentially complete.
Laboratory system evaluation tests are in progress, and field tests will soon follow.
-