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10th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 23 Mar 1997 - 26 Mar 1997
- Location: Reno, Nevada, USA
- Published: 23 March 1997
1 - 100 of 106 results
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History Of Geophysical Studies At The Waste Isolation Pilot Plant (Wipp), Southeastern New Mexico*
More LessA variety of geophysical methods including the spectrum of seismic, electrical, electromagnetic and potential field
techniques have used support characterization, monitoring and experimental studies at the Waste Isolation Pilot
Plant (WIPP). The geophysical studies have provided significant understanding of the nature of site deformation,
tectonics and stability. Geophysical methods have delineated possible brine reservoirs beneath the underground
facility and have defined the disturbed rock zone that forms around underground excavations. The role of
geophysics in the WIPP project has evolved with the project. The early uses were for site characterization to satisfy
site selection criteria or factors. As the regulatory framework for WIPP grew since 1980, the geophysics program
was focused on support of experimental and field programs such as Salado hydrogeology and underground room
systems and excavations. In summary, the major types of issues that geophysical studies addressed for WIPP are:
l Issue I: Site Characterization
l Issue 2: Castile Brine Reservoirs
l Issue 3: Rustler /Dewey Lake Hydrogeology
l Issue 4: Salado Hydrogeology
l Issue 5: Excavation Effects
The nature of geophysics program for WIPP has been to support investigation rather than being the principal
investigation itself The geophysics program has been used to define conceptual models (e.g., the Disturbed Rock
Zone-DRZ) or to test conceptual models (e.g., high transmissivity zones in the Rustler Formation). An effect of
being a support program is that as new project priorities arose the funding for the geophysics program was limited
and withdrawn. An outcome is that much of the geophysics survey information resides in contractor reports since
final interpretation reports were not funded.
*This work was supported by the United States Department of Energy under contract DE-AC04-94AL85000
Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company for the United Sates Department of Energy
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Electrical Resistivity Monitoring Of The Thermomechanical Heater Test In Yucca Mountain
Authors A. Ramirez, W. Daily, M. Buettner and D. LaBrecqueA test is being conducted in the densely welded Jopopah Springs tuff
within Yucca Mountain, Nevada to study the thermomechanical and
hydrological behavior of this horizon when it is headed. A single 4 kW heater,
placed in a horizontal borehole, was turned on August, 1996 and will continue
to heat the rockmass until April 1997. Of the several thermal, mechanical and
hydrological measurements being used to monitor the rockmass response,
electrical resistance tomography (ERT) is being used to monitor the movement
of liquid water with a special interest in the movement of condensate out of the
system. Four boreholes, containing a total of 30 ERT electrodes, were drilled to
form the sides of a 30 foot square with the heater at the center and
perpendicular to the plane. Images of resistivity change were calculated using
data collected before and during the heating episode. The changes recovered
show a region of decreasing resistivity approximately centered around the
heater. The size this region grows with time and the resistivity decreases
become stronger. The changes in resistivity are caused by both temperature
and saturation changes. The observed resistivity changes suggest that the rock
adjacent to the heater dries as heating progresses. This dry region is
surrounded by a region of increased saturation where steam recondenses and
imbibes into the rock.
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Test Results Of Cpt-Deployed Vertical Electrode Arrays At The Doe Hanford Site
Authors S.M. Narbutovskih, W. Daily, A.L. Ramirez and R.M. MoreyField studies were conducted at the DOE Hanford Site to test cone penetrometer installation of
vertical electrode arrays (VEA) for use with Electrical Resistivity Tomography (ERT). Most
VEA installation methods in current use are not economic for environmental applications. The
cone penetrometer technology (CPT) can provide an economic and relatively non-intrusive
installation method. However, a VEA with deployable and properly functioning electrodes was
required. Results of the design, installation and testing of CPT VEAs are reported in this paper.
Several designs were developed and bench tested for use with the CPT. After initial field
installation studies, one design was chosen for further testing at the DOE Hanford Site. Four
VEAs were each pushed to 100 feet in 4 days. To test the CPT VEAs, an infiltration experiment
was conducted with cross VEA tomographic data collected for three vertical planes. These data
were processed using the electrical resistivity tomography code developed by Lawrence
I,ivermore National Laboratory (LLNL). Tomographic images for each vertical plane tracked
the subsurface resistivity changes associated with the migrating fluid.
It is concluded from these test results that the CPT is a viable method for installing VEAs. The
VEAs were rapidly and economically installed to the maximum depth required, data of adequate
quality were obtained and tomographic images from the infiltration experiment verified that the
CPT VEAs provide viable ERT data.
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Focusing Transformations - The Reliable Way To Search For Safe Location For Nuclear Waste Disposal
Authors V.A. Pozdniakov, V.A. Tcheverda and D.V. SafonovAt present pre-stack migration is widely used in seismic data processing in order to get wave image of
a medium under investigation. Of course it is rather time-consuming procedure but its application is
justified by necessity to deal with complicated geological structures and to recover them as completely
as possible. The paper is devoted to the approach to pre-stack migration of multicoverage seismic data
by means of diffraction and focusing transformation in application to the problem of careful geological
investigation of consolidated rocky blocks in order to choose as safety as possible location of nuclear waste
deposit. Results of some real seismic data processing gathered at Nijnekanskaja area near Krasnoyarsk
city, where a granite block is searching for as a suitable candidate for disposal of radioactive waste, are
presented and discussed.
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Locating Buried Trenches Using An Integrated Geophysical Study At The Parks Shallow Land Disposal Area
Authors Robert J. Withers, John E. Scaife and Steffan HelbigAt the Parks site, Western Pennsylvania, a geophysical survey was undertaken to
determine the size and location of buried trenches containing radiological waste. Several
geophysical techniques were used to non-intrusively locate the trench boundaries. The
trenches outlines could be mapped from surface conductivity profiles. Magnetometer
surveys identified much of the ferrous material buried within the trenches, and further
defined the location of the trenches.
Several vintages of ground penetrating radar were used, with the need for low frequency
antenna demonstrated by testing. A 50 MHz GPR antenna was elected for a series of
profiles across the trenches. By integrating interpretations from the total magnetic field,
magnetic gradients, conductivity data and radar profiles it was possible to provide an
accurate map of the trenches verified by subsequent drilling. Seismic and microgravity
techniques were not able to verify the location of mine workings beneath the area of
investigation.
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Practical Geophysical Applications For Everyday Operational And Engineering Problems At Newmont Gold Company
Authors Kevin Freeman, Jim Wright and Nigel PhillipsNewmont Exploration Limited’s Carlin based geophysics team primarily concerns itself with
gold exploration along the 101 Moz Carlin Trend. While most of this activity takes place off the
mine sites, occasions arise where the team is called upon or recognizes an opportunity to perform
tasks for mine operations and engineering.
Various electrical and potential field methods have been used in different applications with
mixed results. Past efforts have included electrical potential mapping for leak detection in leach
solution collection ponds and bio-leach culture tanks; time domain EM was utilized in leach pad
solution saturation studies; and highly detailed gravity has been used in void detection in the
Rain Pit. Brief case histories of each of these are presented. Included are logistical scenarios and
methodology of select applications and their results.
Results of past geophysical efforts by NEL have proved highly successful, resulting in quick,
inexpensive, and definitive answers for mine operations and engineering problems.
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The Development And Testing Of A Geophysical Blast Movement Measurement Technique For Surface Mines
Authors Geraint W. Harris, Pierre Mousset-Jones, Jaak Daemen and Robert KarlinIn order to minimize the ore dilution induced by blast movement in surface mines it is necessary to quantify
such movement. This will make it possible to more accurately locate the grade boundaries on the surface of a
blasted rockpile prior to excavation. This paper describes the development and testing of a method to accurately
measure the direction and magnitude of sub-surface blast movement. The technique involves the use of magnetic
gradiometry, using a cesium vapor gradiometer and real-time differentially corrected, GPS system, to locate the
post-blast position of magnetically enhanced target objects, whose pre-blast locations are known, without
disturbance of the blasted rock. The objective is to design an accurate and eflicient technique which can be
integrated into a mine’s production cycle.
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Case Histories Of Electrical And Electromagnetic Geophysics For Environmental Applications At Active Mines
Authors Norman R. Carlson and Kenneth L. ZongeAlthough some aspects of the environmental service industry appear to be leveling off or
declining, as a contractor primarily serving the minerals exploration industry, we continue to see
a slow but steady increase in the use of geophysics for enviromnental and engineering problems
at active mines. We attribute this to several factors. One reason is that mine geologists and
engineers are typically more familiar with geophysics (its applications and limitations) than
many of our environmental clients, and they are more familiar with a broader range of
geophysics. Other important factors are the technological advances (both hardware and
software) that allow data acquisition in mine enviromnents that were once too noisy or
complicated. In this paper, we discuss several examples of environmental and engineering
projects at active mines, with an emphasis on how these projects differ from our “normal”
enviromnental projects.
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Tests Of Ground Penetrating Radar And Induced Polarization For Mapping Flwial Mine Tailings On The Floor Of Coeur D’Alene River, Idaho
In order to investigate sequences of mine tailings that have settled in the bed of the Coeur
d’Alene River, we improvised ways to make geophysical measurements on the river floor. To
make ground penetrating radar (GPR) profiles, we mounted borehole antennas on a skid that was
towed along the river bottom. To make induced polarization (IP) profiles, we devised a bottom
streamer from a garden hose, Pb strips, and insulated wire. Both expedients worked well. GPR
showed shallow stratigraphy, but did not directly detect the presence of contaminating metals. IP
showed a zone of high chargeability that is probably due to pockets of relatively higher metal
content. Neither method was able to define the base of the fluvial tailings section.
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Downhole Ip Measurements Ulth A Piezocone At Mine Tailings Impoundment
Authors H. Kristiansen, R.G. Campanella, M.P. Davies and C. DanielThe last decade’s environmental concerns have resulted in additions to the Cone
Penetration Test piezocone making it capable of measuring geophysical parameters and therefore
effective at identifying anomalies. This paper describes one of the most recently developed
additions, which measures the induced polarization (IP) effects.
The testing site used to assess the capability of the IP-piezocone consisted of very
conductive mine tailings impoundments. The piezocone was used to study the detailed
stratigraphy, measure hydrogeological and geotechnical parameters and therefore provided
ground truthing.
The IP measuring system is described in detail. A typical IP trace is presented and
discussed in combination with the resistivity piezocone profiles and parameters.
Factors affecting results and application of IP measured with the piezocone are discussed.
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Surface And Downhole Em Investigations At Potash Mine Sites In Saskatchewan, Canada: Case Histories
Authors G. Phillips and H. MaathuisWaste products from the potash industry in Saskatchewan are stored in surface tailings
management areas (TMA) which commonly consist of a salt tailings pile and a brine pond,
surrounded by dykes. Because the fluid level within the TMA is higher than its surrounding, and
because of density effects, surface brine migration occurs in varying degrees.
The high electrical conductivity of the brine compared to normal groundwater make geo-electrical
methods well suited to measure and monitor both lateral and vertical brine migration originating
from TMA’s. Historically, shallow lateral brine migration was measured by monitor wells or soil extract
analyses, but in recent years surface EM measurements increasingly have been used for mapping,
and for monitoring of the rate of migration and impact of remedial measures.
Vertical brine migration occurs both within the TMA as well as outside the perimeter dykes, in
areas affected by shallow lateral brine migration. In the past, detailed data on vertical brine
migration could only be obtained by means of soil extract data. Downhole EM measurements
have shown that vertical brine migration occurs typically to depths of 5 to 10 m. The transition
zone from full brine concentration to background values commonly is in the order of 2 to 3 rn,
consistent with diffusion-controlled vertical brine migration.
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The Use Of Geophysical Methods For Assessment Of The Fracture Process Due To Mining Subsidence
More LessThe space distribution and time advance of subsidence of rock overburden in exploited
areas depends on the volume and shape of the exploited area.
Three causes of subsidence are discussed in the paper; tunnels with elliptical crosssection,
upward moving elongated disturbance of rock properties, and exploited areas beyond
long-wall exploitation. In each case, seismic and geoelectric methods may be used to assess
the fracture zone shape and location or predict the appearance of fracturing.
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Seismic Mapping Of An Abandoned Lead-Zinc Mine, Joplin, Missouri
More LessIn the mining of lead and zinc in the Joplin Missouri area, the open-pit method of mining was used if the ore extended
close to the surface or following the collapse of the underground operations. A regional hospital in Joplin Missouri
owns property in this mining region that in places overlies an infilled and abandoned open-pit lead-zinc mine. Much
of the infilled pit area has been covered by asphalt and is currently used as an open parking lot (about 62,500 ff). The
southern edge of the parking lot abuts a wing of the hospital complex; the eastern edge abuts a multi-storied parking
facility.
The hospital administration is considering erecting a multi-storied annex to the hospital wing on the asphalt parking lot
site. Recent subsidence of the asphalt paving occurred in parts of the parking lot which did not correlate with existing
maps that outlined the old open-pit mine location. To obtain a more detailed structural control at bedrock level, drilling
to bedrock and the acquisition of 25 parallel high-resolution reflection seismic profiles were undertaken. On the seismic
data, the bedrock reflector can be interpreted and spatially mapped across the parking lot from one line to the next. The
interpretation of the reflection seismic data was constrained and validated by the test boreholes within the parking lot
area.
This case study is presented as an example of the utility of the seismic technique for mapping bedrock in a structurally
complex area, and in a noisy urban environment with adverse surface conditions.
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Reflection Seismic Mapping Of An Abandoned Coal Mine, Belleville, Illinois
Authors Neil Anderson, Ronald Hinds, Doug Lambert, Mike Roark, Mike Shoemaker and Jesse BakerOld mine location maps (1958 vintage) indicate that the northwestern part of an undeveloped property near the town of
Belleville, St. Clair County, Illinois, is situated above an abandoned and now water-filled, room-and-pillar type coal mine.
The central and southeast parts of the Belleville property are shown as overlying intact (non-mined) coal. The coal unit
mined at the Belleville site, the Herrin #6 is Pennsylvanian in age and about 2.5 m thick at a depth of around 40 m.
The current owners of the BelleviIle property want to construct a large building on the central and southeast parts of the site,
but have been concerned about the accuracy of the old mine location maps because of recent mine-related surface subsidence
in areas designated on the maps as not mined. To ensure that the proposed new development is located on structurally stable
ground, a grid of ten high-resolution reflection seismic lines was acquired on-site. On these reflection seismic data, minedout
areas can be visually identitied and d&rentiated Tom non-mined areas. The interpretation of the reflection seismic data
was constrained and validated by 15 test boreholes. These seismic and borehole data confirm that the central and southeast
parts of the property have not been mined extensively. Development of the Belleville site has proceeded with confidence.
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Seismic Exploration For Cretaceous Kaolin Deposits In Glaciated Terrains: Example From Nova Scotia, Canada
Authors S.E. Pullan, R.R. Stea, P.W. Finck, R.A. Bums, M. Douma and R.L. GoodThe Geological Survey of Canada and the Nova Scotia Department of Natural Resources have
recently completed a joint project which has led to a major discovery of commercially viable
deposits of kaolin in the Shubenacadie and Musquodoboit Valleys in central Nova Scotia. The aim
of the project was to delineate the three-dimensional distribution of Cretaceous and Quatemary
unconsolidated sediments in the study area using shallow seismic reflection surveys, drilling, and
borehole geophysical logging. During the three year project a total of 65 shallow seismic test sites
and 10 line-km of CDP (12-fold) shallow seismic reflection profiles were acquired, and over 20 new
boreholes were drilled within the survey area. Initial seismic test results suggested that there were
areas in the Shubenacadie basin where bedrock was at depths greater than 100 m below surface.
This was subsequently confirmed by NSDNR drilling. The test sites were used to determine the
optimum locations for followup seismic profiling in the Shubenacadie valley (1994) and the
Musquodoboit valley (1995). The seismic sections and drilling results have clearly delineated
Cretaceous sediments in basins buried beneath glacial cover and have substantially increased the
known area1 extent of buried Cretaceous basins (from ~1 km2 to >57 km* in the Shubenacadie and
Musquodoboit valleys alone). Analyses of core samples have shown that these basins may harbour
economic quantities of kaolin suitable for use in the paper industry. Presentation of preliminary
results of the work in November 1995 resulted in the immediate staking of over 80,000 acres (2,000
claims) in the Shubenacadie, Musquodoboit and Antigonish valleys.
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Borehole Vector Magnetics: The Mcconnell Deposit, Sudbury, Canada
Authors Edna L. Mueller, William A. Morris, W. Hamilton, Patrick G. Killeen and Steve BalchIn this paper we investigate the potential advantages of employing vector, or 3-component
magnetic data. Vector magnetics have been applied in previous studies in a variety of
scenarios: land-based, borehole, and marine. The present study focuses upon vector
magnetic data from a series of boreholes around the McConnell nickel deposit located
within the Sudbury Basin, Canada.
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Borehole Correlation In Mineral Deposits Using Geophysical Parameters: Duck Pond, Newfoundland
Authors William A. Morris and Sean E. WalkerCorrelation of geophysical well logs is an exploration technique that has been employed
for many years in oil exploration. Over the past decade, a number of new slimline tools
have been introduced advancing the application of logging to the smaller diameter mineral
exploration boreholes. Interpretation of this data may follow a number of paths. Through
the collaborative use of procedures such as: a) univariate, bivariate, or multivariate
statistical methods it is often possible to characterize some lithologies that are defined by
distinctive physical property signatures; and b) the correlation of distinctive geophysical
signatures between adjacent boreholes can be used to establish structural features of the
subsurface. In this paper we show that gridding of geophysical parameters as
conventionally applied to both ground and airborne surveys can also be applied to a suite
of borehole data to produce an image of the subsurface which contains information on
both structure and lithology. In this example we present results from a multi-well and
multi-parameter survey of the volcanogenic massive sulphide deposit from Duck Pond,
Newfoundland.
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The Application Of Borehole Geophysics To The Delineation Of Leachate Contamination At The Trail Road Landfill Site: Nepean, Ontario
Authors Daron G. Abbey, C. Jonathan Mwenifumbo and Patrick G. KilleenThe sanitary landfill site poses many monitoring problems for the environmental scientist. An understanding of
the materials and processes controlling the distribution of leachate in the groundwater at a landfill site is an
essential component of landfill management. The Trail Road landfill site in Nepean, Ontario, is perched upon a
sand and gravel ridge which is part of a lacustrine silty clay plain. The delineation and monitoring of leachate
contamination, created by the decomposing municipal solid waste mixing with groundwater, is presently carried
out through chemical sampling of monitoring wells. Such monitoring of a complex and hydraulically conductive
environment, is expensive and time consuming because water samples must be analyzed in a laboratory.
Borehole geophysical logging of eight of these monitoring wells showed that the delineation of leachate plumes
could be accomplished through a full suite of borehole geophysical logs. The logs acquired included: natural
gamma ray, density, total magnetic field, magnetic susceptibility, electrical conductivity, and temperature. The
use of a full suite of logs provided a measure of the in-situ physical properties of all the components of the
subsurface, including air, water, and sediments. Chemical sampling provided only an inventory of ions present in
the groundwater. The geophysical logs in this study were acquired, processed and interpreted, in a shorter period
than the chemical sampling, and provided information allowing for a more refined geological interpretation, than
from drilling alone. Anomalous physical properties, interpreted to be the result of the presence of leachate
contamination, correlated well with data from chemical sampling which showed elevated levels of leachate
indicator ions, such as, calcium, magnesium, chloride, sulphate, potassium, ammonia, dissolved organic carbon
(DOC), phenols and iron. It was concluded that an interpretation of borehole geophysical logs produced a more
accurate delineation of areas of leachate contamination at the Trail Road landfill site, more directly (i.e. in situ).
and with greater efficiency and simplicity than chemical sampling.
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Geophysical Borehole Logging In Massive Carbonates Whitmoyer Laboratories Superfund Site Meyerstown, Pa
Authors Bill Bour and Craig B. ClemensCorrelation within massive carbonate sequences like those present in central Petmsylvania’s
Lebanon Valley is often difficult because the units contain few distinct marker beds and the
contacts between units are frequently gradational. This project demonstrated that correlations
among boreholes can successfully be made using a combination of geophysical logs,
particularly natural gamma, high resolution density and sonic. The technique involves
positioning logs from several of the deepest holes on cross sections at the best estimated
structural elevation (correcting for regional dip), comparing the general shape of the natural
gamma curve and adjusting the logs positions for a best fit. Once a datum has been
hypothesized, (all) the logs are examined for anomalies that might be traced through. The high
resolution density proved capable of identifying small fractures which appeared to correlate
along strata lines with the gamma. These hypothetical “marker beds” are projected onto as
many logs as possible to verify the anomaly. Once an anomaly (bed) is identitied on several
logs over a sutXciently wide area, three point strike and dip calculations are performed to verify
that the correlations fit the regional pattern.
This technique is not particularly new, it has been used in subsurface investigations for
decades. The application to massive units with only the most subtle marker beds, however, has
not been particularly successful. It proved successful at this site because of the use of sensitive
gamma and density sondes, and by a large number (62) of boreholes, a third of which penetrate
over 400 feet of section. (Although only two wells intersected the Ontelaunee-Amiville contact.)
Only very slight density (lower) and velocity (faster) differences were noted between the
dolomitic limestone (bioherm) of the Ontelaunee Formation and the limestones of the Amwille
and Epler Formations. These differences were so slight as to not be noticed until the logs were
positioned correctly on the sections by gamma and density log correlations.
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Borehole Geophysics Used To Characterize Vertical Fractures And Their Connections To Bedding Plane Aquifers In Dolomite
More LessGeophysical logs in an array of six boreholes in argillaceous dolomite at a contamination site in northern Illinois
intersect four aquifers: a shallow bedding plane fracture, a vertical fracture, and two deeper permeable beds. The
vertical fracture aquifer appears to be representative of a set of such fractures dipping at about 85 degrees and
striking approximately northeast. Cross-borehole flow measurement techniques are used to investigate the
properties of the three horizontal aquifers, and to infer the character of the connection between the vertical fracture
and the deeper horizontal aquifers. The data indicate that the vertical fracture and the shallow bedding plane have
transmissivities nearly an order of magnitude greater than those of the two deeper horizontal aquifers in the
vicinity of the point where they intersect boreholes. The data also indicate that the deeper aquifers are
characterized by a storage coefficient of about 2x10”. The bedding plane and vertical fracture aquifers cannot be
modeled as confined aquifers, although relatively large storage coefficient values characterize models that most
closely approximate the variation of flow in the shallow bedding plane aquifer. The cross-borehole flow
experiments suggest that the vertical fracture is hydraulically connected with the deeper horizontal fractures, but
that fracture aperture decreases somewhat with depth.
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Deconvolution Of High Density Electrical Well Logs
Authors Flemming Effersø and Bo Holm JacobsenDetailed information on vertical resistivity variations is relevant as an indicator of change in
lithology, porefluid chemistry, porosity and permeability. Traditionally the formation resistivity
is estimated solely on curves of the observed data, which are plotted as apparent resistivity data.
Apparent resistivity data may be a poor approximation to the local formation resistivity, and it
can be impossible to determine the resistivity levels and the location of the layer-interfaces. Jn
this paper we will present results of deconvolution of normal log apparent resistivity data.
Deconvolution of data using dual electrode offsets gives a significantly enhanced resolution of
the formation resistivity when moderate resistivity contrasts are considered.
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Advances In Instrumentation And Data Processing For Multi-Spaced Resistmty Measurements: Hydrogeologic P Arameters And Lithostratigraphic Delineation
By Charles OdenRecent advances in portable borehole geophysical instrumentation and processing
software allow hydrogeologic characterization of sandstone aquifers. Lithostratigraphic
delineation is also performed. A slimline logging probe allows logging of 4 normal
resistivity measurements (8, 16, 32, and 64 inch), as well as single point resistance,
spontaneous potential, natural gamma, fluid temperature and fluid resistivity. The data
can be quickly and easily processed on site to provide derived parameters and properties.
Hydrogeologic information can be easily calculated using processing software. Water
resistivity is indicated using shallow and deep resistivity measurements along with the
resistivity of the mud filtrate. Total dissolved solids can be found fi-om the water
resistivity. Porosity can be determined from Archie’s Law if a fresh water correction is
used. Hydraulic conductivity is indicated using depth of mud filtrate invasion. Examples
illustrate that calculated parameters agree with measured or otherwise indicated values.
Lithostratigraphic units can be delineated by synthesizing an approximated Laterolog7 log.
The synthesized focusing currents provide good a indication of bed boundaries. The
models generated from data sets obtained with the new multi-spaced normal resistivity
probe provides better vertical resolution due to the 8 inch normal resistivity measurement.
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Neural Network Interpretation Of Em39 Well Log Data
Authors Lin Zhang and Mary M. PoultonWe used a Modular Neural Network(MNN) to invert well logging curves from a Geonics EM39
induction logger In the interpretation scheme, there are several subsets of networks that depend on the
relative resistivities of adjacent layers, e.g. Rl>R2, RlR3, etc. The well logging curves are
subdivided into several pieces and run through each sub-network. The results are estimates of resistivity
and thickness of every layer. Using synthetic data, several training sets were made. The networks were
also tested on field data. The networks were examined for their ability to compute the right output patterns
for the corresponding input patterns of the training set and the ability to interpret the new patterns that are
not present in the training sets.
The results show that neural networks do facilitate interpretation of well logging data. When tested on
data from shallow wells 4-5m deep representing uniform material, the trained networks had an overall
accuracy of about 90% for both resistivity and thickness. When tested on a multi-layer case, the networks
gave reasonable estimates for each layer’s thickness and resistivity, although a shift in depth was
observed for some layers. Recently, we generated more training patterns for thinner layers and
incorporated a new way to pick data points for the input patterns. We found the results more satisfactory.
For two complicated multi-layer field cases, the networks had an overall accuracy of 92.1% for the
resistivity and thicknesses of the layers.
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The Interest Of Geophysical Methods For Locating Hydromorphic Horizons In Acid Pedological Systems
Authors V. Chaplot, P. Curmi, A. Hollier-Larousse, J. Pellerin and C. WalterThe aim of this study is to determine the interest of some geophysical methods, in particular Radio&IT in
locating hydromorphic horizons for acid pedological systems. Two areas were studied, one under forest, another in
an intensive agricultural site. A direct relationship between apparent resistivity and horizon type distribution was
established on the first site with a relative uniform soil depth. On the second site, soil depth and topsoil water
content explained most of the variations of the apparent resistivity, the influence of which was modelized by
multiple regression. Deviations from the regression model were then interpreted by taking into account the
succession of soil horizons. Results of Ground Penetrating Radar and Electrostatic Quadripole confirmed the
position of some of the limits between soils suspected by Radio-MT data. Finally, the prediction of hydromorphic
soil systems with the help of geophysical techniques is discussed.
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Gpr Attenuation Tomography For Detecting Dnapls
Authors Lanbo Liu and Youli QuanUsing the ground penetrating radar (GPR) to detect organic contaminants in the geological
formations is a relatively new technique for environmental site characterization. We present here an
attenuation tomography method that could be used to image subsurface organic contaminants like
DNAPLs. This method is based on centroid frequency shift when the electromagnetic (EM) waves
propagate in subsurface media. In most natural materials, EM wave attenuation increases with
frequency. As a result, the centroid of the signal’s spectrum experiences a downshift during
propagation. This downshift is proportional to a path integral through the attenuation distribution
and can be applied to the GPR data to tomographically reconstruct the attenuation distribution. The
frequency shift method is applicable to any data when the signal bandwidth is broad enough and
the attenuation is high enough to cause noticeable losses of high frequencies during propagation. In
comparison to some other methods of estimating attenuation, the frequency shift method is
relatively insensitive to geometric spreading, reflection effect, source and receiver coupling,
radiation patterns, and instrument responses. High attenuation has been regarded as the major
hurdle for using GPR in areas with high electric conductivity, this method provides an alternative
view to the attenuation.
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An Evaluation Of Geophysical Techniques To Measure Sub-Surface Hydrocarbon Contamination At A Disused Fuel Distribution Depot
Authors V.T. Nguyen, M.J. Quick, A.S. Eriksen, S. Booth, D. van der Roest, A. Wagebert, W. Al-Nuamy, M. Nakhkash, D. Zhang and Y. HuangAs part of a continuing programme to evaluate the potentials of non-invasive methods for rapid site assessment,
measurements have been made at a disused fuel distribution depot using geophysics techniques with particular
emphasis on the detection of sub-surface contamination. These include GPR, EM conductivity and 2D resistivity
imaging. The data have been analysed by a number of approaches and the results are compared with traditionally
acquired and chemically analysed soil samples.
The analysis of the data highlights the need for more work to be directed to the understanding of the physical processes
that give rise to the observed features, but encouragingly the comparison between the interpreted geophysics results
and the soil analysis has indicated that the non-invasive methods have potential to be developed into useful cost
effective screening tools. The direction for future work is discussed.
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Case Studies Of 2D Resistivity Surveying For Soils, Waste Management, Geotechnical, And Groundwater Contaminant Investigations
Authors Paul D. Bauman, Mike Lockhard, Anil Sharma and Richard KellettThe direct-current (DC) resistivity method has seen wide use in mining, groundwater, contaminant, and
geotechnical applications since its first use in the early 1920’s. More recently, however, fixed frequency and
transient electromagnetic (EM) methods have supplanted many applications traditionally addressed by resistivity
techniques. In particular, the application of resistivity profiling and sounding has suffered from the time intensive
nature of these surveys as compared to using EM equipment.
The advent of the automation of 2D resistivity surveys (Dahlin. 1993) and the ability to quickly invert relatively
large 2D data sets (Loke and Barker, 1996) promises to re-introduce the DC resistivity method into a wide variety
of applications in the geosciences. This paper presents four case studies where 2D resistivity surveying was
applied. The technique was used in various geological terrains, extremes of weather, studies requiring varying
depths of investigation, and with varying degrees of cultural interference. The accuracy of the method is evaluated.
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Electromagnetic Terrain Conductivity Surveys Used To Screen Swine Confinement Facilities For Groundwater Contamination
Authors T.H. Larson, I.G. Krapac, W.S. Dey and C.J. SuchomskiElectromagnetic terrain conductivity (EM) surveys were conducted at two swine confinement
facilities in Illinois to assess the presence and extent of groundwater contamination and to guide
the installation of monitoring wells. At Site A, the waste lagoon was on a glacial outwash terrace
near an alluvial valley. At Site C, the waste lagoon was on glacial till overlying shale bedrock.
Measurements were made with a GEONICS EM-34 terrain conductivity meter on 10-m grids
surrounding the waste lagoons. Wells were installed in areas where EM surveys suggested that
contamination may and may not be occurring. Two shallow wells at Site A and one well at Site
C yielded water samples with electrical conductivity values 6 times higher than background,
suggesting contamination. Each of these wells was in areas of high EM conductivity. None of the
deep wells in areas of high EM conductivity or shallow wells in areas of low EM conductivity at
Site A or Site C yielded water samples with electrical conductivity values much higher than
background. It appeared that a terrain conductivity survey is a useful tool for for delineating
areas of groundwater contamination.
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High Resolution Seismic Reflection Survey To Map Bedrock And Glacial/Fluvial Layers In Fridley, Minnesota
Authors Richard D. Miller and Jianghai XiaShallow seismic reflection in conjunction with uphole velocity profiles and local borehole
data allowed delineation of discrete laying within the alluvial materials and glacial drift overlying
the St. Peters Sandstone and/or the Prairie du Chien dolomites at an average depth of around 120 ft
along the western perimeter of the Naval Industrial Reserve Ordnance Plant (NIROP) in Fridley,
Minnesota. The primary goals of this study were to determine the feasibility and limitations of the
technique and develop a continuous subsurface image of as many geologic/hydrologic contrasts as
possible that can be characterized by changes in acoustic impedance. Establishing feasibility includes
determining the horizontal and vertical resolution potential, optimum acquisition geometries
and parameters, best suited equipment for surface and subsurface conditions, level of effort necessary
to delineate the geologic/hydrologic features of interest, and to establish a reasonable set of
expectations for the technique at various unique near-surface settings across the entire facility.
Shallow seismic reflection profiles allowed delineation of potentially discontinuous confining units
within the glacial drift at this site. Incorporation of a high confidence reflection profile with existing
hydrologic models should greatly improve the understanding and therefore prediction of contaminant
transport and fate models in areas with significant lateral variability. The glacial drift that
covers the entire site consists of till, outwash, valley train, and lake deposits.
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Seismic Reflection Processing For Characterization Of A Hazardous Waste Site
Authors Zhi-Ming Liu and William E. DollSeismic reflection data have been acquired by the Kansas Geological Survey near the Oak Ridge
K-25 Plant on the Oak Ridge Reservation, Tennessee, to assist in the selection of ground water
monitoring well locations. The data were recorded in uncorrelated format to allow flexibility in
enhancement of stacked images.
During the summer of 1996, five of the thirteen seismic reflection lines acquired were
processed. An unconventional correlation procedure, “Vibroseis Whitening” (VSW) (Coruh and
Costain, 1983) has been applied to produce improved seismic sections. Refraction statics
corrections, which remove the detrimental effect of an irregular weathered layer, have also been
utilized to improve the seismic sections. The seismic data were stacked using the velocities
obtained from a standard semblance velocity analysis tool. Locations and orientations of faults
or fault zones can be interpreted from these stacked sections, and they are in agreement with the
interpretations of the surface mapping in the area.
This paper concludes that VSW and refraction statics can be important to near-surface
swept source seismic data processing.
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Dynamic Properties Of Municipal Solid Waste Landfills From Surface Wave Tests
Authors Christopher D. Haker, Glenn J. Rix and Carlo G. LaiThe seismic stability of municipal solid waste (MSW) landfills is often a significant consideration in landfill
design. However, until recently, the dynamic properties of the waste material itself, which govern the seismic
response of MSW landfills, have often been approximated or assumed. Tests to determine the dynamic properties
of the material directly have been limited. Measurements of seismic surface waves were used to determine the
dynamic properties of MSW, which are the initial tangent shear modulus and low-strain hysteretic damping ratio.
Surface wave tests were performed at three MSW landfills to determine their shear modulus and damping ratio
profiles. Surface wave tests are ideal for measuring the near-surface shear modulus and damping profiles of MSW
landflls because the tests are non-invasive, an advantage for testing environmentally sensitive waste material.
Factors which influence the dynamic properties of waste including density, confinement, age, and placement
techniques are used to interpret the measured shear modulus and damping ratio profiles.
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Evaluation Of Earth-Fill Embankments In Romania Using Electrical Methods And Ground Penetrating Radar
Authors Jean Christophe Gourry and Traian MoldoveanuDuring the 1970s embankments were constructed along several hundred kilometres of
rivers in Romania In recent years, several leaks have developed along the berms.
The aim of this study is to check whether GPR and electrical methods are efficient for
characterizing anomalies above the known leaks and, if so, to extrapolate the results into
unknown areas for systematic surveillance. GPR revealed variations of 5 to 10% in the
apparent water level, whereas piezometric measurements showed variations of less than
5%. Such large variations in the apparent water level may be due to variations in EMwave
velocity. CMP results confirmed a lower EM-wave velocity in the landslip area than
in the safe zone. The apparent water level drops in the area affected by the landslip.
Electrical soundings revealed that resistivity is higher in the anomalous crest areas than in
the secure parts of the embankment. One striking feature recorded in the anomalous zones
was that resistivity anomalies were positive along the crest, yet negative along the berm,
i.e. high resistivity along the crest but low along the berm for the landslip area. One
explanation is that the weak crest areas are made up of porous material, whereas those
along the berm consist of saturated material.
This study has demonstrated the correlation between known leakage areas and geophysical
anomalies. Furthermore, the coupling of GPR and electrical soundings proved efficient
for detecting most of the known anomalies. Due to its good spatial resolution and high
acquisition speed, GPR is perfectly adapted to this type of application.
2-D GPR tomography along the dams also provided detailed and interesting results.
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Seepage Investigation Using Geophysical Techniques At Coursier Lake Dam, B.C., Canada
By Phil SirlesSubsurface seepage flow at Coursier Lake Dam was identified by onshore
and offshore self-potential surveys, and electrical resistivity
profiles and soundings during a Deficiency Investigation by BChydro.
For typical seepage investigations baseline geophysical data are
collected at @llow-pool I1 level and the measurements are repeated when
high hydraulic gradient conditions exist. At Coursier Lake Dam a
rather unanticipated outcome of the low-no01 surveys was that
significant seepage beneath the structure'was detected. The low-pool
results were conclusive enough that, when combined with visual
inspection and observation of sinkholes on the embankment, an
immediate restriction was placed on the pool elevation. Thus, because
of the identified potential hazard, the remaining geophysical
investigations were conducted under a "minimum-pool" reservoir level
in order to complete the comparative study. Therefore, the dam was
studied under low- and minimum-pool reservoir conditions in the spring
and fall of 1993, respectively.
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Seepage Characterization During Dewatering Activities - Bradbury Dam, California
Authors Robert Furgerson, Robert Corwin and Jerry WrightA geophysical investigations program was performed at Bradbury Dam near Santa Ynez, California. The purpose of
the investigation was to 1) provide data on possible seepage paths into the dewatering area downstream of Bradbury
Dam, and 2) determine lithologies and stratigraphic correlation within the alluvium. The geophysical investigations
included surface self potential (SP) surveys along the centerline and offsets right and left of the newly constructed
cutoff wall, SP surveys within the dewatering area and stilling basin, borehole induction conductivity, borehole
temperature logs and other borehole geophysical logging.
Anomalies from the SP data were indicated along the downstream cutoff wall at several wall stations . SP data
collected within the dewatering area confirmed these anomalies No significant SP anomalies were noted in the
spillway stilling basin.
Correlation of borehole induction conductivity logs run in 34 observation wells and 8 geophysical shear wave holes
indicated the existence of two correlatable main units and four sub-units within the foundation alluvium. Lithologic
descriptions of these units are based on variations in electrical conductivity with supporting data Ii-om SPT samples,
core samples, grab samples, and corrected Becker blow counts. These lithologic units were used to aid in the
interpretation of the borehole temperature data, SPT and Becker results.
Borehole temperature logging was conducted on four separate dates in the observation wells. Temperatures in the
spillway stilling basin were also measured. Average temperatures in each borehole were calculated at the water
table, the base of the alluvium, and within bedrock where available. In addition the maximum variation of
temperature within the alluvium was also calculated.
A geologic model was constructed from correlation of induction conductivity logs , Becker blows, and analysis of
grab samples obtained during excavation of the downstream cutoff wall. SP and temperature data provided seepage
and hydrologic information within the dewatering area.
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Seismic Refraction And Downhole Velocity Surveys For Investigation Of The Tinemaha Dam Inyo County, California
Authors Mark Olson, Yogesh Prashar and Sinan InelSeismic refraction and downhole velocity surveys were conducted as part of a
geotechnical investigation of the Tinemaha Dam. Thirteen P and S-wave velocity surveys
were conducted concurrently with cone penetration testing along the crest and
downstream toe of this dam. One additional velocity survey was conducted from a
borehole on the crest of the dam using a downhole geophone array. The shear wave
velocities estimated for the dam and its underlying alluvium ranged from 345 to 2008
ft/sec. A depth profile of these velocities indicates areas within the dam and its
foundation where the shear wave velocities are less than 600 ft/sec. These velocity
estimates were used with other geotechnical data, to calculate the dynamic elastic moduli
for the dam and its foundation, to evaluate the stability of the dam in the event of a local
earthquake on the Owens Valley fault. To further investigate the location of this active
strike-slip fault, seismic refraction surveys were conducted at two locations. The first
refraction survey was positioned south of the dam across the expected trend of the Owens
Valley fault. A velocity analysis of the upper refracting horizon was conducted using the
generalized reciprocal method. This revealed changes in lateral velocity that were
interpreted as due to a fault-transition from saturated alluvium to volcanic bedrock. The
second survey was positioned along the dam’s crest at the west abutment to help locate a
possible fault beneath this area. The interpreted depth section from this survey locates a
point where the deeper bedrock unit appears to be truncated by faulting. This information
will help locate additional boreholes to evaluate lithologic conditions.
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Multi-Frequency Gpr Surveys
Authors Jeffrey E. Lucius and Michael H. PowersGround penetrating radar (GPR) antenna selection must be based on specific survey objectives. The choice of
antenna is primarily a compromise between resolution and depth of penetration. This paper briefly presents three
case histories of multi-frequency GPR surveys that explain and illustrate how the antenna and the electromagnetic
(EM) properties of the ground affect wavelength, loss mechanisms, far-field radiation, and the near-field. Changes in
these parameters are important because they affect vertical and horizontal resolution, and depth of penetration. In
general, when the depth of penetration is limited by conductive losses instead of scattering losses, changing to a
lower-frequency antenna will not help in detecting shallow features, and may not help in detecting deeper features.
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Locating Salinity Sources In West Texas With Airborne And Ground-Based Geophysical Methods And Gis
Authors Jeffrey G. Paine, Erika M. Boghici, Alan R. Dutton and Steven W. TweedySalinization of soil, surface water, and ground water is a chronic environmental and
agricultural concern in the southwestern U.S. In this study of a 91 km2 area near Ballinger in
Runnels County, Texas, we used a geographic information system (GIS) to integrate results from
airborne and ground-based geophysical surveys, water and soil sampling, and chemical analyses
to locate areas of brine concentration and determine their origin. Potential salinity sources in this
area are (a) subsurface brine moving upward along natural conduits (faults, fractures, joints, and
permeable stratigraphic units), (b) brine migrating downward from surface disposal pits,
(c) leaking oil and gas wells, and (d) evaporating shallow ground water as a result of agricultural
landscaping. A prime goal of the study was to determine the effectiveness of the method in
distinguishing potentially leaking wells from other salinity sources.
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Mapping Bedrock Topography With Seismic Refraction At An Oil And Gas Field: A Comparison Of Engineering And Petroleum Exploration Methods At A Site In The Wind River Basin Of Wyoming.
Authors David Phillips, Robert Grimm and Bart Hoekstra“Weathered-layer” corrections to seismic-reflection travel times for deep hydrocarbon exploration are often made
using shallow refracted arrivals on the reflection records. There has been recent interest in using these “refractionstatics”
solutions to provide depth-to-bedrock maps for environmental or engineering applications as a by-product of
the deep seismic survey. We show that the depth to bedrock and bedrock velocities produced by automatic
refraction-statics processing of a three-dimensional seismic survey of a gas field in Wyoming differ significantly
from those determined from an engineering survey. Manual reprocessing of the refraction statics produced some
improvement, but is still inferior to refraction data taken for the specific purpose of determining depth to bedrock.
Automatic refraction statics provide adequate travel-time adjustments to reflection records due to a shallow lowvelocity
layer, but such solutions should not be taken to represent explicit depth to bedrock.
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Neural Network Interpretation Of High-Frequency Electromagnetic Ellipticity Data
Authors RaIf A. Birken and Mary M. PoultonThis paper focuses on the detection of three dimensional (3D) small conductive targets from high-frequency
electromagnetic elliptic@ data using neural networks. For environmental investigations it is necessary to provide
as much information on the location of shallow buried conductive objects or the electrical properties of possible
contaminants. The networks are trained with one-dimensional (ID) forward models to estimate the resistivity and
dielectric constant structure of the ground. The input is given by elliptic@ sounding curves from eleven discrete
frequencies in binary steps in a range from 32 kHz to 32 MHz. Halfspace and layered earth neural networks will
provide reasonable fit to sounding curves even if they are influenced by shallow conductive 3D objects. We show
that a detailed inspection of elliptic@ profiles over targets such as a 5 m by 3 m aluminum sheet (depth of 1 m), a
5%gallon barrel (depth of 0.63 m), and two metal desk (depth of approximately 1 m) can help to detect these
anomalies. Piecewise halfspace neural network are capable of enhancing the anomalies in resistivity depth sections
and provide additional information for the detection and possible localization of the object. The visualization of
the results is very important since small targets will show up as subtle anomalies. Based on observations of
elliptic@ sounding curves and profiles we can train a neural network to classify target responses versus
background responses for specific sites, assuming that enough soundings are available to train the neural networks.
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Joint Seismic And Electrical Tomography
Authors Jie Zhang and F. Dale MorganSeismic and electrical properties in the earth are not directly associated with each other. If a large seismic
velocity contrast occurs across a geological interface, certain change of the corresponding electrical properties
may also take place, but not necessarily. To seek solutions with maximum structure coherency between
the two physical parameters in the earth, we develop a joint seismic and electrical tomography method
that simultaneously reconstructs seismic velocities and electrical resistivities with cross constraints on the
normalized structure curvatures.
The joint approach applies a 2D nonlinear refraction traveltime tomography method and a 2.5D d.c.
resistivity tomography method in a joint process. It includes a wavefront raytracing method for rapid
traveltime calculation, and a transmission-network method for electrical potential calculation. A Conjugate
Gradient (CG) approach is applied to solve an inverse problem that minimizes the seismic traveltime and
the electrical potential misfits, and meanwhile maximizes coherency of their normalized structure curvatures
by the way of Tikhonov regularization.
We demonstrate the performance of the joint tomography technique with a numerical example. A geological
structure is characterized with three zones in terms of seismic and electrical properties. Applying
the joint inversion method takes advantages of both geophysical approaches and automatically reconstructs
consistent structures.
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Two-Dimensional Imaging Of Transient Electromagnetic Soundings
More LessTransient electromagnetic (TEM) soundings have been used extensively in geophysical
investigations in connection with environmental problems (Christensen and Sørensen 1994, 1995).
Within the geophysical community there is a growing realization that dense measurements
over large areas are needed to produce the reliability and detail demanded by the severity of many
of the problems addressed in environmental geophysics (Sørensen et al 1995, Sørensen 1996).
This calls for new efficient methods of data collection and fast interpretation procedures.
Consequently much interest has been directed towards rapid approximate interpretation
algorithms - imaging procedures - which will allow a quick overview of the data collected and
provide good starting models for rigorous, iterative inversion procedures.
A number of imaging methods for transient electromagnetic soundings have been suggested
based on the variation of the diffusion velocity with conductivity, e.g. Eaton and Hohmann (1989).
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3D Electromagnetic Inversion For Environmental Site Characterization
Authors David L. Alumbaugh and Gregory A. NewmanA 3-D non-linear electromagnetic inversion scheme has been developed to produce images
of subsurface conductivity structure from electromagnetic geophysical data. The solution is
obtained by successive linearized model updates where full forward modeling is employed
at each iteration to compute model sensitivities and predicted data. Regularization is applied
to the problem to provide stability. Because the inverse part of the problem requires the
solution of 10’s to 100’s of thousands of unknowns, and because each inverse iteration
requires many forward models to be computed, the code has been implemented on
massively parallel computer platforms. The use of the inversion code to image
environmental sites is demonstrated on a data set collected with the Apex Parametrics
‘MaxMin 1-8s’ over a section of stacked barrels and metal filled boxes at the Idaho
National Laboratory’s ‘Cold Test Pit’. The MaxMin is a loop-loop frequency domain
system which operates from 440 Hz up to 56 kHz using various coil separations; for this
survey coil separations of 15, 30 and 60 feet were employed. The out-of phase data are
shown to be of very good quality while the in-phase am rather noisy due to slight
mispositioning errors which cause improper cancellation of the primary free space field in
the receiver. Weighting the data appropriately by the estimated noise and applying the
inversion scheme is demonstrated to better define the structure of the pit. In addition,
comparisons are given for single coil separations and multiple separations to show the
benefits of using multiple offset data.
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3D Ert Applied To The Monitoring Of Joule Heating
More LessThis paper describes the application of three-dimensional Electrical Resistivity Tomography (ERT) to monitor
in-situ soil six-phase ohmic-heating (SPOH) at the Integrated Demonstration for VOCs in Soils and Groundwater at
Non Arid Sites. The ERT data sets, collected between five pairs of adjacent wells using an array of electrodes
located in 4 boreholes, have been previously interpreted with a 2D algorithm (Ramirez and Daily, 1994) to map the
changes in conductivity in a clay layer located in the vadose zone over a period of approximately 2 months (before,
during and after electrical heating). The objective of this work is to show the usefulness of a new 3D ERT
interpretation technique for a complete monitoring of a real 3D underground process. Heating causes moisture
content, temperature, and fluid conductivity changes, all of which affect electrical resistivity, and the successful
application of ERT provides a three-dimensional view of the subsurface resistivity or conductivity distribution.
This information helps us to understand the interaction between heating and the heterogeneous subsurface, the
effects of heating on fluid flow and on contaminant removal. The reconstruction of both the background resistivity
and of the changes over time, caused by the combined effects of moisture redistribution and heating caused by
SPOH and vapor extraction, is enhanced by the 3D interpretation.
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Effective Design Of A Horizontal Air Sparging Well
Authors Doug LaBrecque, Gianfranco Morelli and Paul D. LundegardIn air sparging, in-situ remediation is accelerated by injecting air in the saturated zone. The
success of air sparging depends on the size and geometry of the region of air flow. This study
used ERT surveys to observe changes in saturation, and thus air flow for a horizontal sparge
well. The site is in relatively homogeneous, well sorted fine to medium grained dune sands at
the Guadalupe Gil field. The horizontal sparge well was 4.7 m below the surface. The well was
constructed of stainless steel and perforated along 15 m interval. ERT images were made along
a pair of east-west trending planes near the north and south ends the well.
ERT images showed that the zone of influence of the horizontal sparge well is relatively small.
During the early times, the width of the zone of influence is between 1.5 and 2.5 m. Later, the
width expands slightly but never exceeds 3.3 m.
There were some differences between the north and south planes. The north plane had a slightly
narrower zone of influence but a higher peak saturation, exceeding 50% during the test. An
increase in pressure created a small increase in the saturation and size of the zone of influence.
The ERT images could not be reconstructed until the metal well was included in the FEM mesh.
The well was found to be located slightly further from the center ERT cables than expected.
The background resistivities are consistent with those of clean sands. Although there is some
variability in the resistivity of the background, it is small compared to the variability of the
image reconstructions and can be ignored.
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Three-Dimensional Georadar Studies Of Deformation In Deltaic Sediments
Authors Milan Beres, Andre Pugin and Alan GreenThree-dimensional ground-penetrating radar (georadar) data collected across a 4-m-high hill in the Rhone
River delta (western Switzerland) contain prominent reflections from faulted and folded bedding. Crosssections
and time slices extracted from the georadar data reveal a number of faults that strike parallel to the hill
slopes. Several circular-shaped uplifted blocks together with intervening graben-like features are observed at
various depths. A similar-sized graben-like structure with step faults that converge with depth has been mapped
at a nearby outcrop. Thin layers of silt and fine sand that were intersected in boreholes correlate with strong
georadar reflections and are interpreted as elastic intrusions. Our results are consistent with the hypothesis that
the hill and its internal structures were formed by a large rockfall.
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High Resolution 3-D Seismic Experiment Across The Oquirrh Fault
Authors David M. Morey, Chengjun Wu, Yue Wang, Zhaojun Liu, Jing Chen and Jerry SchusterA 3-D seismic data set was recorded across the Oquirrh fault in May of 1996
by University of Utah personnel. The data (112,896 traces) were collected on a
fine grid in order to image the shallow (SO’-100’) detailed features of this fault.
Previous trenching studies to a depth of about 20 feet along this fault reveal
offset bedding caused by large magnitude earthquakes. The goal of this study is
to explore the potential for complementing trenching studies with 3-D seismic
imaging, with the hope of correlating earthquake recurrence intervals to bed
offsets in the seismic image.
The processing of this data set includes 3-D tomography and 3-D prestack
migration. Results from 2-D tomography show a clear imaging of the shallow
subsurface fault to a resolution of about 10 feet.
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Characterization Of The Hydrogeologic Framework At Aberdeen Proving Ground, Maryland, Using Marine Seismic Reflection Profiling
More LessHigh-resolution, single-channel, marine seismic reflection profiles were collected in the shallow waters of
the Chesapeake Bay estuarine system surrounding the Edgewood Area of Aberdeen Proving Ground, MD. This
data set furthers our understanding of the hydrogeologic framework by identifying paleochannel locations,
delineating paleochannel geometries, and characterizing relationships between multiple generations of
paleochannels.
Fine-grained bottom sediment resting in deeper, low-energy waters were found to block high-frequency
acoustic wave transmission; therefore, data acquisition is limited to areas near-shore were water depths are less
than three meters. Approximately 120 km of shoreline were surveyed yielding 50 km of high quality data. Three
major reflectors are identified as erosional unconformities, and are interpreted to be Pleistocene paleochannel
surfaces. Paleochannels are found to be spatially and physiographically associated with all modern subaerial
lowlands and their local drainage systems. The marine seismic reflection data provide strong evidence that
present-day lowlands are underlain by an aquifer dominated by paleochannels. Paleochannel configurations,
together with paleochannel-fill models, indicate these paleochannels have the potential support vertical and
horizontal contaminant migration.
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Mapping A Near Surface Variable Geologic Regime Using An Integrated Geophysical Approach
Authors Noel T. Rogers, Stewart K. Sandberg, Peter Miller and Greg PowellAn integrated geophysical approach involving seismic, electromagnetic, and electrical methods was employed to
map fluvial, colluvial and bedrock geology, to delineate bedrock channels, and to determine fracture and joint
orientations that may influence migration of petroleum hydrocarbons at the Glenrock Oil Seep. Both P (primary)-
wave and S (shear)-wave seismic refraction techniques were used to map the bedrock surface topography, bedrock
minima, stratigraphic boundaries, and possible structure. S-wave data were preferred because of better vertical
resolution due to the combination of slower velocities and lower frequency wave train. Azimuthal resistivity/IP
(induced polarization) and azimuthal electromagnetics were used to determine fracture orientations and
groundwater flow directions. Terrain conductivity was used to map the fluvial sedimentary sequences (e.g.,
paleochannel and overbank deposits) in the North Platte River floodplain. Conductivity measurements were also
used to estimate bedrock depth and to assist in the placement and recording parameters of the azimuthal
soundings.
The geophysical investigation indicated that groundwater flow pathways were controlled by the fluvial
paleochannels and bedrock erosional features. Primary groundwater flow direction in the bedrock and collwial
sediments was determined from the azimuthal measurements and confirmed by drilling to be N20-4OW along the
measured strike of the bedrock and joint orientations. Joint/fracture orientations were measured at N20-4OW and NlO-
30E from the azimuthal data and confirmed from measurements at a bedrock outcrop south of the site. The bedrock has
an apparent NlOE anisotropy in the seismic velocity profiles on the old refinery property that closely match that of
measured joint/fracture orientations and may have a minor effect on groundwater flow.
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Application Of Electromagnetic Methods To Locate Shallow Water Well Sites In A Fractured Aquifer
Authors Kendrick Taylor, Matt Chesley, Korblaah Matanawi and Tim MinorLow permeability fractured bedrock makes it difficult to select productive locations
for shallow water wells in the Atebubu district of Ghana, West Africa. Drilling has
demonstrated that productive and nonproductive sites are frequently separated by less than
50 meters. The drilling success rate is approximately 25 percent when experienced
hydrogeologists use only surface visual observations to select drilling sites. A combination
of remote sensing and geophysics was used to improve the success rate. SPOT satellite
imagery and stereo aerial photography were used to identify areas where suspected
fractures cross drainages. These areas were typically 100 to 150 meters in diameter. The
frequency domain electromagnetic method was used to locate zones in these areas where
the electrical conductivity increased with depth. These were interpreted as zones of deeper
weathering and fractured bedrock, and were selected as favorable drill sites. Use of this
exploration strategy increased the success rate 35 f 10 percent when the best site within
2 kilometers of the target community was selected. This doubled the success rate and
reduced the number of holes drilled to provide wells to these community by more than a
factor of two. When SPOT satellite imagery and aerial photography were used without the
frequency domain electromagnetics, the success rate only increased 8 f 8 percent. The
methods are cost effective when they are implemented by Ghanaian personnel and in areas
that have a low drilling success rate.
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Monitoring Of A Pumping Test In An Unconfined Aquifer With Ground Penetrating Radar
Authors Anthony L. Endres, David L. Rudolph and William P. ClementThe temporal and spatial response of an unconfined aquifer at CFB Borden to a pumping
test was monitored by means of ground-penetrating radar (GPR) profiling. The reflection
caused by changing water content in the transition zone between the overlying residually
saturated material and the water saturated aquifer below was used to estimate the location of
the top of the water saturated zone (TWSZ). Observed depth variations in the TWSZ
reflection differed significantly from the water table drawdown measured in the piezometers.
The GPR results are consistent with the in-situ water content measurements of Nwankwor et
al. (1992) and support their proposed delayed drainage mechanism. Diffractions along the
TWSZ reflection indicate that differential drainage due to small scale variations in aquifer
properties occurs. Arrival time variations of reflections from underlying stratigraphic
horizons are accounted for by changes in the overlying velocity structure caused by the
lowering of the TWSZ.
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Geophysical Monitoring Of A Groundwater Tracer In The Gray Delta, Maine
Authors Stewart K. Sandberg, Charles R. Fitts and Roelof VersteegSurface geophysical measurements were successful in monitoring a groundwater tracer
experiment within the municipality of Gray, Maine. Low levels of volatile organic compounds
have been detected in the town’s water-supply well field, which is located 900 meters away from
the municipal landfii. In order to discover the relationship between the well field and la&ii, a
tracer experiment was conducted at an accessible location between them. The tracer, consisting of
minor amounts of salt mixed with water recovered from each injection point, was injected at two
locations 10 meters apart within a sand pit; one injection was in a monitoring well screened from
3.4 to 6.4 m below ground surface, and the other was a surficial injection, within a pit dug into the
saturated zone of the aquifer approximately 1 m below ground surface.
Geophysical methods tested included spontaneous polarization (SP), resistivity, induced
polarization (IF’), frequency- and time-domain electromagnetics (EM), and ground-penetrating
radar (GPR). Resistivity methods included the dipole-dipole array, radial array, and mise-a-lamasse.
The radial array was a modified pole-dipole array where one transmitter electrode was
down the injection well at the screen and the other was some distance away. Potential measuring
points were located at n-spacings of 1,2,3, and 4, using an a-spacing of 5 m. IP data were also
acquired along with resistivity data. GPR data were collected using both 200 MHz and 100 MHz
antennas.
Initially, the most effective and efficient geophysical method for location of the tracer was
the SP method. Radial array resistivity, GPR, and n-&e-a-la-masse methods also proved effective
in detecting the tracer. Frequency-domain EM (terrain conductivity) measurements proved
excessively noisy. This paper describes SP, radial array resistivity, and GPR methods, since they
appear at this stage of our analysis to be the most informative.
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Resistivity Measurements And Modeling In The Vicinity Of A Trench Well
Authors Paul J. Wolfe and Sara B. HodlOn North Andros Island, Bahamas, an extensive array of trench wells has been dug to collect
fresh water from the surface (unconfined) aquifer for export to Nassau. There is concern that salt
water will upcone below the trenches if water is withdrawn too rapidly. Resistivity soundings are
a common method for determining depth to the fresh-salt water interface. Where the soundings
are most important, the normal assumptions of resistivity sounding interpretation methods fail
because of the presence of the open, water-filled trench.
To interpret the soundings in the vicinity of the trench, the finite differences ground water
modeling program, MODFLOW, was reinterpreted to model the electrical flow. The resulting
models and several forms of resistivity soundings are compared and evaluated to assess their
usefulness in this unusual setting.
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A Hydrogeologic Framework Of Washoe Valley, Nevada From Joint Gravity And Magnetic Modeling And Terrain Conductivity Data
Authors Ronald Petersen and Robert KarlinGravity, ground magnetic, and terrain conductivity surveys were conducted in Washoe
Valley, Nevada to define subsurface structure and lithology as part of an effort to assess
groundwater resources and model basin recharge in this rapidly growing commum ‘ty between
Reno and Carson City. The gravity results indicate the valley is an asymmetric fault-bounded
half-graben, backtilted to the west where it is filled with nearly 2000 feet of coarse-grained
sediments. A major fault runs beneath the axis of the valley, with considerably shallower
basement beneath the upthrown eastern side. A magnetic high immediately south of New
Washoe City suggests this shallower eastern basement is overlain by a volcanic unit. This unit
is in turn overlain by electrically conductive fine-grained sediments. Together, these results
suggest a more complex eastern subsurface with generally lower transmissivities relative to the
thicker section of coarser-grained sediments filling the western side of the valley and that the
locus of deposition has shifted eastward through time. These findings place important
constraints on ongoing efforts to model groundwater recharge and availability. This study
demonstrates the utility of using multiple geophysical surveys to map the spatial distribution of
interbasin lithologies and estimate their hydraulic properties.
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Hydraulic Modeling At Rokballe Test Site By Application Of Geophysical Data
Authors Dorte Dam, Steen Christensen and Niels B. ChristensenThe objective of the present study is to invistigate the by application of geophysical data in hydraulic modeling.
Numerical models have been developed for a 1 km2 Danish catchment using comprehensive field data. The
investigated area concerns a phreatic aquifer in a fluvioglacial formation. Three models are considered. The first is
based solely on bore hole informations and hydraulic head data. The remaining two include transient
electromagnetic data. The bottom of the aquifer is determined as the level of the good conductor, and the electrical
resistivity of the saturated zone provides qualitative information about the hydraulic conductivity.
Zonation of the aquifer based on the electrical resistivity, improves the estimation of the hydraulic conductivities.
The residual is slightly smaller even when only very little geophysical information has been implemented.
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Location Of Buried Valley Aquifers Applying Spatially Dense Transient Soundings
More LessThe water supply in Denmark is based solely on groundwater. The abstraction sites are often
located at the rim of the cities next to old dump sites posing a significant risk for
contaminating adjacent aquifers. Furthermore, the industrial development outside cities, and
agricultural activities form another substantial threat of leakage of unwanted substances down
to the aquifers.
It is a common problem that in cultivated areas there is an increasing need for mapping
ground water resources. This concerns the necessity to protect the ground water against
pollution from surface activities, to ensure that the effects of draw downs do not produce poor
water quality by sulfation, mobilisation of salt water or other unwanted water qualities, and to
make sure that the abstraction does not heavily influence on surface waters such as lakes,
rivers, streams etc. (Sorensen et al, 1995). In order to meet these demands it is necessary to
have sufficient detailed and reliable hydrological models from which an optimal strategy for
sustainable abstraction can be obtained. The set-up of these models calls for detailed and
reliable mapping of the aquifers.
In Denmark a considerable number of the aquifers are buried valley aquifers composed of
resistive Quatemary sand and gravel deposits laid down in deep valleys eroded in Tertiary
well conducting clays and covered by an inhomogeneous conductive Moraine clay cap.
Formerly the delineation of these aquifers has been based mainly on drilling information
and has provided a more regional understanding of the extent and interconnection of the
aquifer systems. It has been demonstrated that geophysical mapping in combination with
traditional geological mapping using drilling information and surface observations is a more
powerful and economical tool to achieve reliable mapping on a detailed scale. Within the last
decade the volume of geophysical investigations using electrical and electromagnetic
methods have increased substantially in Denmark. The main reasons for the successful
application of geophysical mapping are the use of newly developed field efficient methods
and the close relationship that exists between hydraulic conductivity’s and electrical
formation resistivities in the Danish buried valley aquifer systems.
This paper presents results from the geophysical mapping i.e. the application of the transient
electromagnetic method used for invastigating the interconnection of aquifers. and for
delineating the composition of the aquifers themselves.
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Reflection Seismic Mapping Of Caverns And Collapsed Caves, Carthage Missouri
Authors Jesse A. Baker, Mike L. Shoemaker, Mike Roark, Neil Anderson and Ron HindsInterest in locating a cave under the city of Carthage, Missouri was inspired by several pre- 1930 newspaper articles
wherein people claimed to have explored a large cavern system comprised of interconnected chambers, some with
lateral dimensions of 12Om x 60m and ceiling heights of 12m. One problem however, was the articles varied in their
descriptions of the entrances to this system and the subsurface location of the caverns.
Based on these historical accounts, the city of Carthage, in the interests of locating and developing a sizable cavern for
public use, asked the Department of Geology-Geophysics, University of Missouri-Rolla, to help locate the rumored
feature using the shallow reflection seismic technique. A total of twelve reflection seismic lines were acquired in the
northwest section of downtown Carthage and on city property near the eastern edge of town. Line locations were
selected based on the historic literature. Since the target feature was expected to be large and the city had a fixed budget
for exploration, a geophone spacing of twenty feet was used in the interest of maximizing coverage. Several prominent
hyperbolic ditEaction/reflected retraction patterns were imaged on the reflection seismic data, however none were as
laterally extensive as hoped. The city had also budgeted money for drilling, therefore test holes were drilled in order to
further investigate the findings of the reflection seismic data.
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Gravity Inversion Using A “Shape-Of-Anomaly” Mfxhod: Developments In Three-Dimensional Modeling And Application To Gravity Over An Abandoned Underground Limestone Mlne In Southeastern Indiana
By R.M. RenéA method is developed for threedimensional modeling of gravity measured at the earth’s surface. The model
is built of many rectangular parallelepipeds of constant horizontal dimensions. Each prism is assigned an allowed
density contrast; however, all density contrasts are of the same sign. An initial model of filled prisms, or “seed”,
is specified. Additional prisms are filled automatically, one for each pass through an algorithm that minimizes the
difference between the shapes of the modeled and observed gravity. This “shape-of-anomaly” criterion was
previously developed and applied to two-dimensional modeling of gravity profiles (Rene, 1986). Other criteria for
controlling the model’s compactness and depth to center of gravity are developed here. Applications are first
demonstrated using synthetic gravity. For the gravity of a buried sphere, the inverse model closely approximates
a sphere if the depth to center of gravity is unconstrained. Some models are generated by specifying allowed ranges
for depths to center of gravity. To treat random noise, including measurement errors and high spatial-frequency
“geologic” noise, a filter is applied to both the observed and modeled gravity. Effects of bias are also shown. An
inverse model is also derived from a negative 143-pgal gravity anomaly of the flooded underground Gheen’s Mill
Cementville Mine in southeastern Indiana. The anomaly is defined by gravity at 837 stations in nineteen profiles
with a 3-m (lo-foot) station spacing. The model is constrained by 17 boreholes that penetrated cavities and 39
boreholes that did not find cavities.
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A Ground-Penetrating Radar Study Of Karst Features In Soutekentral Missour
More LessKarst features (cavities and sinkholes) in south-central Missouri generally occur where the
Gasconade Dolomite and Roubidoux formations are exposed to a near-surface environment.
Karstic cavities develop as carbonic acid (derived from atmospheric carbon dioxide and rainwater)
percolates through these carbonate rocks along permeability pathways (e.g., fractures, faults, etc.)
from ground level to the water table. The carbonic acid gradually dissolves the carbonate country
rock and forms cavities. If the roof rock above a developing void becomes structurally unstable,
the cavity will collapse. Collapse features expressed at the surface are referred to as sinkholes. In
south-central Missouri, subsurface cavities and sinkholes are common and constitute a significant
engineering hazard.
To elucidate the internal structure of sinkholes in south-central Missouri, ground penetrating
radar surveys were conducted at eight sites on the Fort Leonard Wood Military Reservation. The
sinkholes studied developed in the upper Gasconade Dolomite and lower Roubidoux Formation.
Data were acquired with both a 500 MHZ antenna and a 120 MHZ antenna. The 500 MHZ data
proved to be most useful in terms of imaging the internal structure of the sinkholes. Depths of
investigation varied between one and four meters.
On the 500 MHZ radargrams, the internal collapse structure of the sinkholes is imaged by laterally
discontinuous events which reflect both the dip and dislocated nature of the collapsed strata.
These data are important because they demonstrate that ground-penetrating radar can be used to
map sinkhole features and potentially identify void space to a depth of 4m.
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New Wales Sinkhole Remediation
Authors Sam Sahebzamani and Vishwas SatheThis paper presents the Florida Department of Environmental Protection’s (FDEP) investigation of a sinkhole at the
IMC-Agrico Company (IMC) New Wales chemical plant, in Polk County, Florida.
In June 1994, a catastrophic condition occurred at the New Wales chemical plant. A sinkhole had opened under
their industrial waste storage area (phosphogypsum stack) creating a depression within it. The depression was
observed to be 185 feet deep and 120 feet wide, within the 200 foot tall phosphogypsum stack. Further investigation
revealed the existence of a 480 foot long conduit that extended from the top of the stack to the upper Floridan
aquifer system. Remedial alternatives for a sinkhole of such magnitude and potential harm to the potable water
source could not be determined without a thorough understanding of the extent of the sinkhole formation.
Exploratory work involved cross-hole seismic surveys together with the drilling of boreholes at strategic locations.
Remediation consisted of an extensive grouting program using angle drilling to gain safe access into the erosion
cavity. The Phosphate Management Program (PM) of FDEP was responsible for review, evaluation, and approval of
every technical aspect of the proposed exploratory and remedial activities, to ensure that an effective long term
solution was implemented. The Program also received valuable comments concerning this project from an
interdisciplinary technical advisory committee representing local, State, and Federal agencies.
IMC expended approximately $7 million toward sinkhole exploration and remediation, and is required to continue a
monitoring program to verify success of the remedial effort. The event made national headlines and was broadcast
over television networks such as CNN News. Inquiries were received from other countries on the technical aspects
of the remediation.
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Effectivenessofgroundpenetratingradarin Detectingcavesinkarstlimestoneofthe Yucatanpeninsula,Mexico
Authors Hans F. Schwaiger, Craig Murray and Larry BrownAlthough ground penetrating radar (GPR) is a promising technique in detecting subsurface cavities,
experience with this technique in limestone is still limited. To further evaluate the effectiveness of GPR
in detecting caves, several surveys were recently conducted in the karst terrane of the Yucatan Peninsula
in Mexico. The surveys were conducted near three cenotes (dolines), Kantun, Ponderosa, and Corral,
located approximately 1 mile inland from the Caribbean coast of the Yucatan Peninsula near Playa de1
Carmen. Cenotes expose the cave system and geometry of the cave roof, providing basic geometric control
for the GPR data. Most of the surveys were oriented radially with a typical length of 150 ft, beginning
at the cenote’s edge then traversing beyond the intersection of the roof of the cave with the water table.
One survey was conducted along a 1500 ft road connecting two cenotes and another conducted over a
passageway connecting Ponderosa cenote and Corral cenote.
A 100 MHz antenna was chosen to insure adequate penetration. The velocity in limestone was
determined from expanding spread CMP profiles to average 0.34 ft/ns, corresponding to a wavelength
of about 3.4 ft at this frequency. The limestone-to-air interface at the roof of the cave was expected
to produce strong reflections. Distinct reflections, however, at the expected times were rarely observed,
perhaps due to side scatter. A few surveys did provide a traceable reflection at the appropriate time
and with a dip that mimicked the shape of the roof of the cave. In addition, one survey also contained
a second reflection which, when depth corrected, revealed a flat horizon at a depth corresponding to the
water surface. These preliminary results suggest that, despite ambiguities, GPR profiling can be effective
for direct cave delineation in Yucatan karst.
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Electromagnetic Investigation At The Combat Maneuver Training Center, Hohenfels, Germany
Authors Mike D. Thompson, M.A. Benson, L.D. McGinnis, M.A. Glennon, C.A. Padar, S.F. Miller, P.C. Heigold and Albert BöhmElectromagnetic surveys were conducted at the Combat Maneuver Training
Center (CMTC), Hohenfels, Germany to detect zones where solution cavities develop
within lowland areas of the karst valley systems. Geologic models indicate that solution
activity occurs at the loess-bedrock interface, and is concentrated along loess-filled
fracture trends within the underlying carbonate bedrock. Soil arches that develop along
these fracture trends have the potential to fail catastrophically, posing a considerable
degree of danger to current training activities. Rapid, continuously recording
electromagnetic instruments provide an economical solution for locating zones of high
conductivity associated with loess-filled fractures.
The electromagnetic surveys delineated high-conductivity trends interpreted to be
fracture-controlled. In many instances dolines were observed either along or immediately
adjacent to these conductivity lineaments. Analysis of anomaly maps indicate that highconductivity
lineaments are aligned subparallel to fracture and joint orientations
measured in nearby outcrops. These associations are the basis for predicting locations
where solution cavity collapse and doline development will occur in the future.
Information derived from the EM data can be extended directly to hydrologic modeling
and to safety programs for military training at the CMTC.
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Delineation Of Voided And Hydrocarbon Contaminated Regions With Rdem And Sti
By Bob WhiteleyUndetected voids and cavernous regions at shallow depth are a significant geotechnical and environmental hazard ifthey
are filled or act as conduits for pollutants, particularly for LNAPL and DNAPL contaminants. Such features are often
difticult to locate with drilling and conventional geophysical methods including resistivity, electromagnetics,
microgravity, seismic and ground penetrating radar when they occur in industrial or urban areas where electrical and
vibrational interference can combine with subsurface complexity due to human action to severely degrade geophysical
data quality.
A new geophysical method called Radiowave D&-action Electromagnetics (RDEM) has proved successful for rapid
screening of difficult sites and for the delineation of buried sinkholes, cavities and hydrocarbon plumes. RDEM operates
with a null coupled coil configuration at about 1.6 MHZ and is relatively insensitive to electrical interference and
surrounding metal objects. It responds to subsurface variations in both conductivity and dielectric constant,
Voided and contaminated regions can be more fully detailed when RDEM is combined with Seismic Tomographic
Imaging (STI) horn follow-up boreholes. Case studies from sites in Australia and South East Asia demonstrate the
application of RDEM and ST1 and the value in combining both methods.
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Hydraulic Testing Of A Single Screened Well To Implement A Multi-Level Purge And Sampling Design
Authors Keith S. Caplan, Timothy J. Peck, Ian D. MacFarlane and Joy E. LigéVertical flowmeter testing of a fully penetrating well, screened in a confined sand and gravel
aquifer, was performed to characterize the vertical variation of aquifer hydraulic conductivity.
Acquired data were used to design multi-level sampling without the use of packers or nested wells.
While slow pumping the well from above the screened interval, a Mount Sopris Instrument
Company, Inc. Heat Pulse vertical flowmeter was used to log the cumulative contribution to
vertical flow in the well at I-ft intervals. An impeller flowmeter was also tested at higher purge
rates, but could not measure low flows near the bottom of the well. An equation derived by Molz,
et al. (1989) was applied to the data to solve for hydraulic conductivity at each interval using an
average hydraulic conductivity calculated from slug tests. Variations of hydraulic conductivity
correlated closely with sedimentary strata.
Changes in the rate of cumulative flow versus depth were used to select discrete well sampling
intervals for simultaneous, multi-level sampling of the well without causing in-well mixing.
Peristaltic pumps and stainless steel tubing were used. Ground-water samples were analyzed for
organic compounds to evaluate if contaminant concentrations resulted either from the dissolution
of a bottom dense non-aqueous phase liquid (DNAPL) layer or preferential flow of contaminants
from a distal DNAPL source through coarser sediment layers.
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Application Of Multiple Geophysical Methods To Hydrologic And Environmental Investigations At U.S. Marine Corps Installations In North Carolina
Authors Alex P. Cardinell and Charles C. DanielHydrologic information for ongoing environmental studies at two U.S. Marine Corps Bases in the
Coastal Plain Province of North Carolina was obtained by using a combination of high-resolution land
seismic reflection, continuous marine seismic profiling, and borehole geophysics, that included vertical
seismic profiling. The geometry of areas of missing confining units at the southern end of Cherry Point
Marine Corps Air Station was mapped by using land seismic-reflection compressional (P) waves, marine
seismic profiling, and borehole-geophysical and -1ithologic data from more than 100 water-supply and
monitoring wells. The hydrogeologic framework at Camp Lejeune was mapped by using 100 miles of
continuous single-channel, marine seismic-profiling data that were correlated with land-based borehole
geophysical and lithologic data from 180 water-supply, monitoring, and stratigraphic test wells. These data
are being used by both Marine Corps Bases to manage drinking-water supplies and plan investigations of
hazardous-waste sites.
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Thie Application Of Surficial Geophysics To Well Site Exploration And Wellhead Protection In Fracture Controlled Aquifers
Authors John Jansen and Patrick JurcekSiting high capacity wells in fractured controlled aquifers is difficult due to the
unpredictable distribution of relatively narrow fracture zones. Geophysical methods can
be used to locate fracture zones and select favorable test well locations. Due to the
expense of rock drilling, it is common to estimate the parameters of fractured aquifers
without monitoring wells. Under these conditions, most interpreters assume an isotropic
porous media equivalent. This can lead to serious errors in defining the ground water flow
system.
This paper presents two case histories that illustrate how surficial geophysical
methods can be used to locate high capacity wells in fracture controlled areas. The cases
also demonstrate how the properties of fractured aquifers can grossly deviate from
isotropic porous media and the errors that can result from ignoring this fact. Geophysical
methods can be used to predict the trend of the axis of maximum transmissivity in the
aquifer, which can be used to efficiently site monitoring wells to accurately measure
aquifer properties. Accurate measurements of anisotropy are critical for defining
reasonable wellhead protection zones in fracture controlled aquifers.
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Resistivity, Oolites And A Fresh Water Lens
Authors Paul J. Wolfe, Lisa Jacob, Sara Hodl and Cindy CarneyWe have conducted a series of resistivity soundings and azimuthal resistivity surveys
across North Andros Island, Bahamas. The fresh water lens was mapped from a
combination of well data and resistivity soundings. The carbonate aquifer is dominated by
oolitic limestone and is known to have extensive karst development as evidenced by the
existence of blue holes. Charlies Blue Hole, which is several kilometers from the ocean, as
well as boreholes, exhibit clearly recognizable tidal fluctuations with small time lags
suggesting subsurface connection to the ocean, perhaps via fractures. Azimuthal resistivity
surveys allow us to evaluate the effects of preferred orientation of fractures.
Borings and surface sampling revealed changes in depositional environments across the
island. The resistivity surveys coupled with lithologic information from various locations,
allow us to draw a clearer picture of how the island geology is linked to the island
hydrology.
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Electrical Geophysical Study Over The Norman Landfill, Near Norman, Oklahoma
More LessIn 1995 and 1996 the US Geological Survey ma& 40 Schlumberger dc electrical resistivity soundings at the
Norman Landtill, near Norman, Oklahoma. Interpretation of the resistivity data indicates that high resistivities
(>300 ohm-m) are related to dry sand, intermediate resistivities (45-300 ohm-m) are related to freshwater saturated
sand, and low resistivities (~45 ohm-m) are related to fine-grained materials or materials saturated with the
conductive fluids. Interpreted resistivity maps show a low resistivity anomaly that extends from under the landfill to
just past a nearby slough. This anomaly corresponds to known areas of ground water contamination. A resistivity
cross section, constructed from interpreted Schlumberger soundings, shows that this low resistivity anomaly is about
5 m deep and up to 9 m thick.
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Geophysical And Geotechnical Site Characterization Data At The Groundwater Remediation Field Laboratory, Dover Air Force Base, Dover, Delaware
Authors William P. Clement, Steve Cardimona and Katharine Kadinsky-CadeSite characterization for environmental cleanup provides the information needed to
determine the extent and scope of a specific problem and to adequately design remediation
strategies. Site characterization can be expensive when based primarily on in situ sampling by
invasive techniques to sufficiently describe the subsurface. Closely spaced probes are necessary to
insure that important features are not overlooked. Additionally, drill holes are conduits to the
aquifer that potentially may lead to further contamination. To reduce costs and to provide
characterization of a wider area, geophysical methods are often used to supplement drilling.
Unfortunately, the scarcity of subsurface samples can make it difficult to relate the images from
surface geophysical methods to relevant physical properties in the ground. The Groundwater
Remediation Field Laboratory in Dover, Delaware provides an opportunity to study the relationship
between in situ geotechnical measurements of physical properties with a variety of geophysical
data. We determine the ability of the geophysical techniques to image three targets beneath the
Groundwater Remediation Field Laboratory, and we compare the geophysical images with
subsurface properties inferred from extensive cone penetrometer data. Having in situ
measurements of the subsurface and a variety of geophysical data at one site enables us to correlate
geotechnical and geophysical methods to determine the subsurface character.
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Geophysical Investigation Of Anomalous Conductivity At A Hydrocarbon Contaminated Site
Authors Mike S. Nash, Estella Atekwana and William A. SauckThe intuitive geoelectric model for hydrocarbon light non-aqueous phase liquid (LNAPL)
plumes treats the plume as a resistive body in the subsurface. Results of field studies have
shown that plume bodies can develop conductive attributes over time, and that this dichotomous
nature of electrical conductivity varies over time. A comprehensive geophysical survey was
undertaken to evaluate the electrical nature of an older plume as well as to evaluate the methods
best suited for characterization. Dipole-dipole resistivity profiling, self potential,
electromagnetic induction, and ground penetrating radar were all used to characterize the
conductive plume. Ground penetrating radar located conductive plume boundaries best, while
the dipole-dipole resistivity and self potential methods located the plume but did not resolve the
boundaries of the plume.
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Evaluation Of Electromagnetic Mapping Methods To Delineate Subsurface Saline Waters In The Brookhaven Oil Field, Mississippi
Authors Bruce D. Smith, Robert Bisdorf, Larry J. Slack and Aldo MazzellaHydrologic and geophysical studies of saline waters at the Brookhaven oil field (Mississippi) began in 1985.
Past and present practices to dispose of brines produced with oil and gas poise an environmental risk to ground water
resources, agriculture, and other land uses. At Brookhaven, there is an elevated total chloride content in shallow
((mg/L), which is exceptionally fresh water in comparison to other oil producing areas, particularly in the western United
States. Contamination in the oil field at some sites is several hundred mg5 chloride as determined from water well
samples taken in the mid-1980s. The EPA funded a feasibility study that included a dc resistivity survey which showed
low resistivities in one area of known saline water contamination. Detailed electrical geophysical surveys are not
possible due to numerous metallic features associated with oil production. In 1988 a helicopter electromagnetic (HEM)
survey of the oil field was flown under contract to the USGS as part of an EPA funded research project. An interpreted
resistivity map for a depth of 30m showed low resistivities associated with clays, shales, and saline waters near some
of the abandoned brine disposal pits. In 1995 water wells were re-sampled and two areas of high changes in chloride
content were found. Also in 1995, a new HEM survey was flown and new dc resistivity soundings were made.
Comparison of the ground and airborne survey along a profile where there has been a high change in chloride content
shows good agreement for interpreted subsurface resistivities. The HEM survey shows greater detail than the ground
measurements and suggests there may be local vertical migration of saline waters in areas where there has been a large
increase in ground water chloride content.
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Multiple Views Of A Leachate Plume
Authors Seth R. Lemke, Micki M. Maki and Charles T. YoungResistivity, VLF, and radar were used to image a leachate plume emanating from a landfill
in northern Michigan. The resistivity arrays were dipole-monopole and mise-a-la-masse.
VLF data were enhanced and interpreted using linear filters to convert the data to subsurface
electric current densities and to apparent resistivities. The general agreement of these
methods provide confidence as to the extent of the plume and the direction of groundwater
flow.
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The Use Of Giant Magnetoresistance Technology In Electromagnetic Geophysical Exploration
More LessDiscovered in 1988 (Baibach, et al, 1988) in France during research into superconducting, ultrathin
films, the giant magneto-resistance (GMR) effect is similar to the Hall effect in that a change
in magnetic field strength causes a corresponding change in resistance in the GMR structure. The
differences occur in the underlying physics and the resulting increase in resistance change for a
given change of magnetic field strength. The vector sensitivity of the GMR structure combined
with the advantages of integrated circuit manufacturing techniques make this a very promising
technology for advanced electromagnetic geophysical exploration.
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Physical-Scale And Numerical Modeling Of The Azimuthal Electromagnetic Response In The Macroanisotropic Case
Authors Kelly A. Rust, Stewart K. Sandberg and Esben AukenSince 1995, we have collected electromagnetic (EM) field data using a rotating azimuthal
geometry analogous to that described for resistivity surveys by other workers. These EM
azimuthal resistivity data are relatively easy to acquire and can be collected in areas with high
electrode contact resistance. As an aid to interpreting field results, including apparent paradox of
anisotropy conditions, we have used physical-scale modeling, and have run a suite of numerical
models.
Numerical and physical-scale modeling results indicate that the primary factor affecting the
orientation of the apparent resistivity ellipse relative to a macroanisotropic linear conductor is the
depth to the target (relative to the transmitter-receiver coil separation). At target depths less than
about 10% of the coil separation, an electromagnetic paradox of anisotropy is observed in the
modeling tank, in the numerical model, and in our field data (i.e., high values of apparent
resistivity along the strike of the target). While physical-scale modeling is limited by the
availability of materials of appropriate conductivity, numerical modeling provides a sufficiently
extended parameter space for these analyses. The numerical model also indicates that the
conductance of the target does not effect the orientation of the apparent resistivity ellipse.
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The Electromagnetic Integrated Demonstration At The Idaho National Engineering Laboratory Cold Test Pit
Authors Louise Pellerin, David L. Alumbaugh and M. Cathy PfeiferThe electromagnetic integrated demonstration (EMID) is a baseline study in electromagnetic (EM)
exploration of the shallow subsurface (c 10 m). Eleven distinct EM systems, covering the
geophysical spectrum, acquired data on a grid over the Idaho National Engineering Laboratory
(INEL) Cold Test Pit (CTP). The systems are investigated and evaluated for the purpose of
identifying and reviewing existing geophysical characterization instrumentation (commercial and
experimental), integrating those technologies with multi-dimensional interpretational algorithms,
and identifying gaps in shallow subsurface EM imaging technology. The EMID data, am valuable
for testing and evaluating new interpretational software, and developing techniques for integrating
multiple datasets. The experimental field techniques shows how the acquisition of data in a variety
of array configurations can considerably enhance interpretation. All data am available on the world
wide web (http://vetem.lbl.gov). Educators and students are encouraged to use the data for both
classroom and graduate studies. The purpose of this paper is to explain why, where, how and
what kind of data were collected. It is left to the reader to assess the value of a given system for
their particular application. Information about the EMID is organized into two general categories:
survey description and system evaluation.
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Inversion Of Airborne Electromagnetic Data Using An Occam Technique To Resolve A Variable Number Of Layers
Authors Wei Qian, T. Jeffrey Gamey, J. Scott Holladay, Richard Lewis and Dennis AbernathyDepth sections generated from multi-frequency helicopter electromagnetic (HEM) data have
become an important aspect of airborne surveys. Traditionally such depth sections are created by
an imaging approach, based on simplified physics or empirical relations (Macnae and
Lamontagne, 1987; Macnae et al., 1991; Sengpiel, 1988; Huang and Fraser, 1996; Bostick, 1977;
Nekut, 1987; Jones 1983 etc.). As computers become ever faster and cheaper, we are gradually
entering an era where inversion of HEM data in daily production is economically feasible.
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Monitoring Hydraulic Experimfnts By Complex Conductivity Tomography
Authors Andreas Weller, Mario Gruhne, Frank D. Borner and Matthias SeichterComplex electrical conductivity tomography has been applied to monitor hydraulic experiments
in a research facility for in-situ remediation of contaminated soils and aquifers.
Arrays of electrodes were installed in a flume where infiltration experiments with non-aqueous
phase liquids (NAPL) were performed. Data sets of about 500 configurations have been acquired
with a computer-controlled equipment for spectral induced polarization.
The tomographic algorithm used for interpretation is based on the simultaneous iterative
reconstruction technique (SIRT). As in other inversion techniques, the Jacobian or sensitivity
matrix has to be known. The three-dimensional forward modelling is performed by the ftite
difference method using complex values of conductivity and potential.
The resulting tomographic images show the distribution of complex conductivity inside the tanks.
They reflect both the spatial variability of soil and aquifer properties and changes between
different stages of the experiments. These images were successfully used to determine the state of
the multiphase system consisting of silicate matrix, water, NAPL and air.
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Refraction Traveltime Tomography Of Bala Kimberlite In Riley County, Kansas
Authors Jie Zhang and Brian K. MacyWe apply a nonlinear refraction traveltime tomography method to image the subsurface structure near the
Bala Kimberlite in Riley County, Kansas. The Bala Kimberlite is partially exposed at the surface near Bala,
Kansas in northwestern Riley County. Our fundamental goal of this study is to infer the structure of this
magma plug in the shallow structure. Applying the tomography approach to the data collected along two
perpendicular lines, we reconstruct a velocity structure corresponding to soil, weathered shale, limestone, and
shale, and the sharp discontinuity of the bedrock near the Bala Kimberlite. The imaging results supports the
hypothesis that the Bala Kimberlite might be emplaced into a fracture zone from the upper mantle during
major tectonic activity.
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High Frequency Electromagnetic Impedance For Subsurface Imaging
Authors Yoonho Song, H. Frank Morrison and Ki Ha LeeMost electromagnetic (EM) methods used for geophysical exploration are based on a low frequency, diffusion,
representation of fields in which displacement currents are negligible. If the ground is sufficiently resistive ground
penetrating radar (GPR) may be used and its interpretation usually relies on high frequency, wave field,
representation in which pulse transit time is measured and dielectric properties are recovered. We have
investigated the use of EM fields of intermediate frequency range, 1 to 100 MHz, where both diffusion and wave
fields must be considered and new measurement strategies must be used to recover both conductivity and electric
permittivity from the data.
We have chosen to analyze the ground response at these intermediate frequencies by way of the surface
impedance for plane waves. At these frequencies impedance measurements require scaling up the magnetic field
sensors used for low frequency EM and scaling down the dipole antennas used in radar. The impedance has a
distinct advantage in that coupling to the source is unnecessary, and the source can always be positioned far
enough away to yield plane waves at the receiver. This in turn permits the use of a wide range of fairly standard
imaging codes for interpreting the result.
The high-frequency EM impedance is shown to be very sensitive to ground electrical properties and strongly
dependent on the angle of incidence. In this paper we demonstrate methods for evaluating the incident angle,
correcting the impedance data for normal incidence, and finally imaging the electrical conductivity and
permittivity of simple layered earth models.
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Viability Of Using Seismic Data To Predict Hydrogeological Parameters
By Ken MelaDesign of modem contaminant mitigation and fluid extraction projects make use of
solutions from stochastic hydrogelogic models. These models rely heavily on the hydraulic
parameters of hydraulic conductivity and the correlation length of hydraulic conductivity.
Reliable values of these parameters must be acquired to successfully predict flow of fluids
through the aquifer of interest. An inexpensive method of acquiring these parameters by use of
seismic reflection surveying would be beneficial. Relationships between seismic velocity and
porosity together with empirical observations relating porosity to permeability may lead to a
method of extracting the correlation length of hydraulic conductivity from shallow high resolution
seismic data making the use of inexpensive high density data sets commonplace for these studies
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The Effects Of Sparging On P- And Sh- Vertical Seismic Profiles
Authors P. Michaels and W. BarrashWhile the introduction of pressurized air into an unconsolidated, coarse-grained fluvial aquifer might
well be expected to affect the P-wave velocity profile below the water table, we have found that S-waves are
also sensitive to changes induced by air sparging. In a study spanning over a year of sparging, observations of
both P- and S-waves were conducted by Vertical Seismic Profiling (VSP). While the primary objective was to
characterize the aquifer, we have found that air sparging has significantly affected both P- and S-wave
propagation. Below the water table we have observed as much as a 54% decrease in P-wave velocity, and as
much as a 31% increase in S-wave velocity after continued sparging. Above the water table, we observe only
small changes in both P- and S-wave velocities. This pattern of velocity change (decreasing P, increasing S)
may be due to an increase in the amount of trapped air below the water table.
Published laboratory studies in the small strain regime have shown P-wave velocities to be sensitive to
void ratio, fluid content, and confining stress. On the other hand, most similar studies of S-waves have only
been conducted on either dry or saturated samples. However, one recent laboratory study suggests that shear
modulus and shear velocity may increase significantly at partial water saturations (due to capillary forces). Data
from our in-situ survey supports this more recent lab work. We have observed that S-wave propagation may be
significantly altered by fluid content when soils are partially saturated with water (where trapped air may exist,
producing a 3-phase fluid-frame system). In addition, we have observed changes in the propagating wavelet.
This may be an indication that viscous damping is also affected by partial water saturation. We conclude by
observing that S-waves may prove to be an attractive alternative for mapping the effects of air sparging.
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Characterization Of The Electrical Structure Of An Agricultural Field In Burleson County, Tx
Authors K. Sananikone and M.E. EverettA transient, controlled-source electromagnetic survey has been performed at the Texas
A&M University Hydrogeologic Field Site adjacent to the Brazes River in Burleson County,
central Texas. The experiment is part of a larger, interdisciplinary effort to model the
fate of agricultural chemicals applied to river floodplains. A regularized inversion of the
electromagnetic data show that the sandy alluvial unit which constitutes the main aquifer
for subsurface transport of groundwater is apparent as a resistive zone at depths between
5-20 m. We observe effects in the transient electromagnetic responses that are indicative
of lateral heterogeneity and/or a polarizable Earth.
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Gravity Mapping Of Subsurface Structures In Batholithic Terrain
Authors Jeff S. Zawila, Brian N. Damiata, Shawn C. Biehler and Tien C. LeeA regional gravity survey was conducted in the vicinity of March Air Force Reserve,
southern California with the objective of mapping basement topography that may directly
influence groundwater flow. The data set consists of 3500 gravity stations that cover an area of
670 square kilometers. The raw gravity data were converted to complete Bouguer gravity values
by using standard techniques that included Digital Elevation Models to perform the necessary
terrain corrections. The complete Bouguer values were gridded using a kriging method while
spectral filtering techniques were employed to generate residual anomaly maps. The resulting
anomaly pattern reveals three mappable orders of subsurface structures. Inverse modeling, as
constrained by well-log data and seismic interpretations, indicates that the primary, secondary,
and tertiary structures have axial depths of 1000, 100 to 300, and less than 100 meters,
respectively. The primary structure is a tectonic trough while the secondary and tertiary
structures are erosional channels.
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Airborne Multispectral And Hyperspectral Remote Sensing: Examples Of Applications To The Study Of Environmental And Engineering Problems
Authors Remo Bianchi and Remo BianchiThe availability of a new aerial survey capability carried out by the CNR/LARA (National
Research Council - Airborne Laboratory for the Environmental Research) by a new
spectroradiometer AA5000 MIVIS (Multispectral Infrared and Visible Imaging Spectrometer) on
board a CASA 212/200 aircraft, enable the scientists to obtain innovative data sets, for different
approach to the definitions and the understanding of a variety of environmental and engineering
problems.
The 102 MIVIS channels spectral bandwidths are chosen to meet the needs of scientific research
for advaced applications of remote sensing data.
In such configuration MIVIS can offer significant contributions to problems solving in wide
sectors such as geologic exploration, agricultural crop studies, forestry, land use mapping,
idrogeology, oceanography and others.
LARA in 1994-96 has been active over different test-sites in joint-venture with JPL, Pasadena,
different European Institutions and Italian University and Research Institutes.
These aerial surveys allow the national and international scientific community to approach the use
of Hyperspectral Remote Sensing in environmental problems of very large interest.
The sites surveyed in Italy, France and Germany include a variety of targets such as quarries,
landfills, karst cavities areas, landslides, coastlines, geothermal areas, etc.
The deployments gathered up to now more than 300 GBytes of MIVIS data in more than 30 hours
of VLDS data recording.
The purpose of this work is to present and to comment the procedures and the results at reasearch
and at operational level of the past campaigns with special reference to the study of environmental
and engineering problems.
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Ip And Resistivity Survey At The Inel Cold Test Pit
More LessInduced polarization (IP) is a technique for detection of diffuse occurrences of
metallic material. The Idaho National Laboratory (INEL) Cold Test Pit (CTP) has been
carefully constructed to simulate stored hazardous waste occurrences. IP and resistivity
surveys of the CTP show a very strong IP response and a modest resistivity response
associated with the simulated waste. Several false positive resistivity anomalies are noted.
2-D inversion of the data accurately determine the lateral limits of the waste zone.
The depth of burial indicated is deeper than reported by the construction engineers.
Limited depth extent is recognized, in distinction to results from other, resistivity-based,
methods, but it also appears too deep. IP holds promise as a method for locating buried
waste.
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On The Application Of Radiomagnetotellurics To Waste Site Exploration In Germany
More LessSince several years, the environmental geophysics department of the University of Cologne
uses the radiomagnetotelluric method (RMT) extensively in connection with waste site
exploration successfully (Tezkan et al., 1996, Zacher et al., 1996, Dautel, 1995).
The RMT-method uses transmitters from powerful civilian and military radio stations in
the frequency range 10 to 240 kHz with possible extension to few Mhz. Horizontal
components of the magnetic field are measured by a coil and of the electric field by using
two grounded electrodes spaced 5 m apart. Apparent resistivity and phase data can be
derived from these data for several selected frequencies. These data are then interpreted by
using 2D conductivity models which give excellent information about the vertical and
lateral borders of the waste site and about the top layer.
Two case histories about waste site exploration from Germany will be demonstrated.
Depending on the accessability of the survey areas for geophysical measurements the
lateral borders of the waste sites are located in the field very accurately. They are
characterized by strongly decreasing apparent resistivities observed at nearly all
frequencies at the border between waste site and undisturbed geology. The information
about the thickness of the top layer and the resolution of the bottom of the waste site can
be obtained by 1D and 2D model calculations quantitatively. They give also information
about different areas of the waste site containing different materials.
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Geophysical Data Integration To Delineate Rupture Extension In A Urban Tunnel
São Paulo City, located in the southeast region of Brazil, is home to a population of 13 million
people and about 3 million vehicles. The megalopolis characteristic causes enormous traffic
problems, with combined daily average traffic jams of about 120 km.
One of the alternatives which has been adopted to minimize such a problem is the construction of
urban tunnels connecting important avenues of the city. One of these tunnels, which lies below
Ibirapuera Park (the city’s main park), links the Juscelino Kubitschek, Sena Madureira and 23 de
Maio Avenues.
During the construction of this tunnel, a roof rupture occurred involving an volume of about 20
m3. Despite the stabilization procedures taken by the contractors, there was doubt as to what
extent the massive had been compromised, giving rise to the need for more intensive support
treatment.
In an emergency character, a geophysical study was conducted with the aim of defining the
extension of the affected zone and, eventually, of helping in the proposition of recovering
solutions. Due to time constraints, limitation of surface space and mainly the scale and depth of
the rupture, high resolution seismic and detailed geoelectric mapping were carried out. To
overcome the natural noise of the city, the range of frequencies used by the seismic study was
between 200 Hz and 1,000 Hz, and a geophone spacing of 1 .O meter. Three profiles were taken,
one on the intact massive, the second on the known disturbed massive and the last crossing the
rupture zone.
The geoelectric studies encompassed time domain induced polarization (IP) - resistivity and
spontaneous potential (SP). A gradient array was utilized with an AB of 60 and 50 meters and
measurements were taken every 2 meters in a grid of 20 x 20 m.
The results allowed for the definition of a 3 m x 5 m zone in which the massive was disturbed,
consequently requiring treatment to improve the support. Boreholes confirmed the exactness of
the conclusions taken. AtIer the treatment and the reopening of the tunnel excavation, it was
possible to see that the rupture zone had been limited to about 3 x 3 m.
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Geophysical Imaging Of Transient Ground Water Flow In Partially Saturated Aquifers
Authors Ran Bachrach and Amos NurThe relation between the subsurface water table, saturation, and the hydraulic
conductivity is often used for estimating hydraulic conductivity by the use of
different inversion methods. We show that the ability to image the water table
and the saturation, using surface geophysical methods, together with flow
simulations, can significantly improve the characterization of a site. Our approach
also provides a useful tool for evaluating the performance of seismic and ground
penetrating radar (GPR) in different field conditions.
Elastic and electromagnetic wave velocities in porous media are sensitive to the
presence of fluids in the pore space. Consequently, monitoring velocity changes
in porous systems can serve to image time variations of saturation in the
subsurface, and to extract hydraulic transport properties. To investigate the
feasibility of monitoring we model the response of an unconfined aquifer to
shallow seismic and GPR surveys during pumping. We use a 3D radial flow
model to compute partial saturation profiles in a heterogeneous, unconfined
aquifer at different times of the pumping. We then compute the corresponding
time varying seismic and GPR images of the subsurface for these saturation
profiles. We use the Biot-Gassmann theory to extract the seismic velocity field of
the subsurface from the saturation. The electromagnetic response of the
subsurface is computed using an empirical regression relation between the
saturation and the dielectric constant of the medium. These are widely supported
by laboratory and field observations. The simulated results show that velocity
analysis of both the seismic and the GPR sections can be used for estimating the
saturation variations in an uncontined aquifer during pumping tests: High
permeability zones result in sharper images of the water table with both GPR and
seismic sections. Low permeability zones are detectable because of the relatively
high partial saturation values left behind the down drawn water table.
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Airborne Measured Analytic Signal For Uxo Detection
Authors T. Jeffrey Gamey, J. Scott Holladay and Reinhold MahlerThe Altmark Tank Training Range north of Haldensleben, Germany has been in
operation since WWI. Weapons training and testing has included cavalry, cannon,
small arms, rail guns, and tank battalions. Current plans are to convert the area to a
fully digital combat training facility. Instead of using blank or dummy ordnance, hits will
be registered with lasers and computers. Before this can happen, the 25,000 ha must
be cleared of old debris. In support of this cleanup operation, Aerodat Inc., in
conjunction with IABG of Germany, demonstrated a new high resolution magnetic
survey technique involving the measurement of 3-component magnetic gradient data.
The survey was conducted in May 1996, and covered 500 ha in two blocks. The
nominal line spacing was 10 m, and the average sensor altitude was 7 m. The geologic
column consisted of sands over a sedimentary basin. Topographic relief was generally
flat with approximately 3 m rolling dunes and occasional man-made features such as
fox holes, bunkers, tank traps and reviewing stands. Trees were sparse and short (2-3
metres) due to frequent burn off and tank activity. As such, this site was nearly ideal for
low altitude airborne surveying.
The geophysical sensors included four Cesium vapour magnetometers in a irregular
tetrahedron (Figure 1). The average spacing between sensors was 1.5 metres.
Reading from these sensors provided the basis for measuring three components of
gradient (G,, G,, G,). The vector sum of the gradients was calculated to create a
measured total gradient (G), or analytic signal (AS). A real time differentially corrected
Global Positioning System (RT-DGPS) was used to provide navigation and data
positioning information. A laser altimeter provided height control, and a multi-antenna
GPS unit monitored system attitude.
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Multi-Sensor Ordnance Signatures For Algorithm Development And Model Training
Authors H.H. Nelson, J.R. McDonald and Richard RobertsonThe Naval Research Laboratory is developing a Multi-Sensor Towed Array
Detection System, MEADS, for ordnance detection and site characterization, One
component of this task is construction and validation of algorithms for target
characterization and location for use in the data analysis system. In support of this
task, we have collected an extensive set of ordnance signatures using total field
magnetometers, total field magnetometers deployed as vertical gradiometers and
specially modified Geonics EM-61 pulsed induction sensors. The ordnance items
characterized range from Mk 42 submunitions to Mk 82, 500 lb bombs at depths
ranging from the surface to 20 ft. Where appropriate, signatures are recorded as a
function of azimuth and inclination. We discuss the details of the sensor systems and
the data collection methodologies. Typical signatures are presented and compared
to simple models. We anticipate that this data set will become one of the standards
for passive and active sensor algorithm development and training in the ordnance
detection community.
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Whole-Field Geophysical Measurements Using Coherent Optics
By Edgar ConleyThis paper describes powerful methods of optics and mechanics brought to bear on important geomechanical
problems. Whole-field surface glacier ice flow and mine-wall strains were mapped in two separate feasibility
studies using high-resolution photography and coherent light to interrogate the images. Young’s fringe patterns
result when a double-exposed transparency of a deforming surface is illuminated by a narrow beam of coherent
light. Geometry gives a relationship between the surface displacement vector and the interference fringe patterns.
The displacement occurring during the time-lapse interval is thus known. When applied to the surface of the
Nisqually Glacier, Mt Rainier National Park, WA, the speckle method yielded ice flow data that was compared with
similar flow data acquired by surveying techniques. In the areas for which results can be compared, our experiments
yield a flow of .6 meters/day where conventional methods yield about .4 meters/day. The same photographic
technique was applied to measure the visco-plastic deformation of a proposed nuclear waste repository carved into
bedded salt deep in the earth’s crust Data reduction concluded with the differentiation of the displacement vector
map to obtain the two-dimensional strain rate field which correlated well with extensometer-gathered data. The
research demonstrates the feasibility of using whole-field optical techniques to map ice flow and mine-wall strains,
and confirms certain, but not all, measurements of point-by-point instruments. Field work, data analysis, and
additional potential applications of the speckle photography method are indicated.
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Effective Electrical Resistivity Tomography Surveys For Environmental Monitoring
Authors Douglas J. LaBreque, Gianfianco Morelli and Paul LundegardThe paper emphasizes the need for careful design of ERT surveys for reliable, high resolution
imaging of subsurke processes. In this paper we discuss the use of the resolution radius matrix to
compare the resolution achieved with difkrent configurations of electrodes.
The most critical factor in designing ERT surveys is the aspect ratio of the image plane The aspect
ratio is the length of the boreholes fitted with electrodes divided by the separation of the boreholes.
With a large aspect ratios the resolution in the center of the image plane is about the same as the
resolution near the boreholes. As the aspect ratio decreases the resolution drops in the center of the
image plane but stays roughly the same near the edges. Data collected with ratios less than about
1.5: 1 have an unacceptably low resolution in the center of the images. This problem can be partly
offset by including surface electrodes as well as borehole electrodes.
The resolution does appear to improve with increased numbers of electrodes. However, using
large numbers of electrodes with large aspect ratios tends to produce only limited improvements in
resolution while greatly increasing the data acquisition time.
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Three-Dimensional Electrical Resistivity Tomography And Its Application To Larderello-Valle Secolo Geothermal Field In Tuscany, Italy
Authors Weiqun Shi, William Rodi, M. Nafi Toksoz, F. Dale Morgan, Adolfo Fiordelisi and G. Mauro CameliThe Valle Secolo region in the Larderello geothermal field in western Italy is a vapor-dominated
reservoir producing steam primarily from shallow, highly fractured Tuscan anhydrites. In this
area, water re-injection into various wells has been carried out for many years. During this period,
electrical resistivity surveys have been conducted for the purpose of monitoring distribution of
re-injected water and steam displacement through changes in subsurface electrical properties.
This paper describes a 3-D d.c. electrical resistivity inversion algorithm and its application to
data obtained from two surveys conducted in 1991 and 1993, respectively. The objective of this
effort is to relate the variations in resistivity with position and time to the injection history. Our
inversion models indicate that the primary resistivity variations in the Larderello geothermal field
are of structural origin, e.g., the variation of conductivity of the geologic section. However, the
models from both surveys contain a low resistivity anomaly at a depth of a few hundred meters that
does not correlate with structure. From its location relative to the injection wells, and from changes
in its properties between the two surveys, we infer that the anomaly is related to the injection and
is probably a zone of high permeability or high water saturation.
These preliminary results show that it is possible to detect and monitor the re-injection of fluid
through the systematic observation of electrical resistivity at the site. The method is also suitable
for the detection of environmental contaminant movement. However, field measurements must be
repeated using the same geometry and uniform calibration over time.
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Joint Refraction Traveltime Migration And Tomography
Authors Jie Zhang and M. Nafi ToksözMigration and tomography represent two major techniques in state-of-the-art seismic imaging technology.
Migration maps interfaces in the subsurface by reconstructing physical raypaths from a downward continuation
process, while tomography reconstructs a physical model by inverting recorded data. For interpreting
refraction traveltimes, we present two approaches that combine migration and tomography in one joint imaging
process in an iterative manner. The slowness parameters on a regular grid can be updated on the basis
of fitting traveltimes as well as defining interfaces associated with the migrated traveltime image. The first
method, model-interface method, assumes that the migration image corresponds to a slowness discontinuity
in the model. Therefore, an a priori curvature constraint is emplaced at the image location by way of
Tikhonov regularization. The second approach places a discontinuity in the regularization (Laplacian) operator
according to the location of the migration image, thus it is called derivative-interface method. The first
method gives a stronger model constraint, while the second one relies more on the data. We demonstrate
that both methods are capable of reconstructing a reliable velocity model with sharp features.
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Regularizing Data In 3D Dc Resistivity Tomography
By Jie ZhangBecause of the ill-posedness and high non-uniqueness of the 3D d.c. resistivity inverse problem, we cannot
find a stable and unique solution solely on the basis of fitting data. To stabilize the inverse problem and find a
minimum-structure solution, Tikhonov regularization is often applied. This usually involves the minimization
of the second-order model derivatives, which is equivalent to the application of nonlinear interpolation in
model space. For the same purpose, we propose to regularize data and invert a large number of interpolated
measurements with an estimated data covariance matrix. Because the potential field distribution is generally
smooth, interpolation can be an effective tool to fill in the missing data on the surface and construct 2D data
slices. Inverting 2D data slices along with the use of model regularization turns out to be more attractive,
because it can more tightly constrain the near-surface structure roughnesses. It also gives parameterization
for the model regularization more flexibility. In addition, inverting a large number of interpolated data with
an efficient algorithm does not require additional computational effort.
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3D Visualization Of A Resistivity Data Set - An Example From A Sludge Disposal Site
Authors Christian Bernstone, Torleif Dahlin and Peter JonssonA relatively large 2D inverted CVES resistivity data set from a waste pond area in southern Sweden was
visualized as an animated 3D model using state-of-the-art techniques and tools. The presentation includes a
description of the hardware and software used, outline of the case study and examples of scenes from the
animation’.
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A Roll-Along Technique For 3D Resistivity Data Acquisition With Multi-Electrode Arrays
Authors Torleif Dahlin and Christian BernstoneA roll-along technique for 3D data acquisition using standard multi electrode equipment, designed for
engineering and environmental applications, allow measurement of large true 3D resistivity data sets. Results
from a field test at a closed sludge disposal site display consistent data, with marked differences between
measurement directions. The data was inverted to form a resistivity-depth model of the ground using a 3D quasi-
Newton technique. The results achieved with the technique can be highly useful for engineering and
environmental applications, but would require the use of multi channel measurement to speed up the data
acquisition process for routine application.
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The Shallow Porosity Structure Of The Continental Shelf Off Humboldt Bay, California: Results Of A Towed Electromagnetic Survey
Authors Rob Evans, Lawrie Law, Benoit St Louis, Steve Cheesman and Khamla SananikoneWe have completed a towed electromagnetic survey, mapping the electrical resistivity of the seafloor across
an area of the Californian continental shelf. The area has been designated as a natural laboratory by the
Office of Naval Research as part of the STRATAFORM initiative. More than 120km of tow-lines were
completed, making measurements of resistivity over the top 20m of sediment every 20m or so along track
and from water depths of 1OOm to around 30m. We identify three distinct depositional environments based
on the resistivities recorded and the porosities inferred from them: one, a mid-shelf depo-center also
associated with recent flood deposits; another an uplifted, buried anticline system; and the third associated
with the Eel river delta.
We present the electromagnetic method used as a technique that can provide valuable information about
facies conditions across the littoral zone. Such information can be used for a variety of purposes, but from
an environmental perspective these include: identifying sand and gravel deposits; monitoring the effects of
storms on continental shelf erosion; finding suitable locations for the siting of offshore cables and pipelines;
quantifying the transport of material from river estuaries across and along the shelf; and mapping areas of
fine grained sediment that might preferentially scavenge pollutants from the water column.
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Borehole Velocity Logging For The Caltrans Bridge Retrofit Program
Authors William P. Owen and Darby K. VickeryThe influence of local soil conditions on ground shaking and the potential for resulting
structural damage has long been recognized. Two of the primary soil properties affecting the
intensity of ground motion are shear- and compressional-wave velocity. As part of a multidisciplinary
approach to the seismic retrofit of toll bridges, the California Department of
Transportation uses a suspended borehole probe to measure in situ compressional- and shearwave
velocity, both for onshore and offshore environments. These data are used as input for
ground-motion and foundation response analysis. The probe contains a dipole source that
directly produces compressional waves. Shear-wave velocity is measured via the low-frequency
component of the borehole flexural mode. A new empirical relationship between P-wave
velocity and density improves the fit to observed data. Experiments with logging through freehanging
plastic casing produced mixed results. Although resolution is low compared to
conventional sonic logs, the velocity data provide good delineation of gross stratigraphy (bed
thickness > 1 meter).
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Borehole Geophysics In Gold Exploration
Authors K.A. Pflug, P.G. Killeen and C.J. MwenifumboThe Borehole Geophysics Section of the Geological Survey of Canada has acquired
multiparameter borehole geophysical logs in several holes in gold deposits in Ontario. These
measurements were made to document the geophysical signatures of the ore zones and host rocks,
and to determine which physical properties may be used to outline zones favourable for gold
mineralization. The geophysical logs acquired include: spectral gamma-ray, density, spectral gammagamma
ratio (heavy element indicator), resistivity, induced polarization, self potential, magnetic
susceptibility, temperature and temperature gradient.
Although gold in economic quantities does not occur in high enough concentrations to be
directly detected by geophysical methods, geophysics may be used to delineate certain lithologic
units known to host the gold as well as structural features or alteration associated with gold
mineralization. In many gold deposits, an increase in the concentration of potassium is associated
with gold mineralization, due to sericite alteration. The potassium log (which is derived from the
spectral gamma-ray log) can be used to outline zones of potassium enrichment. The resistivity and
induced polarization logs also show characteristic responses to pyrite, which is frequently associated
with gold mineralization. Increases in other elements, such as the barium enrichment associated with
some of the Hemlo gold deposits, can also be detected by geophysical methods. Enrichment of
barium, which is a ‘heavy’ element, is detectable by the spectral gamma-gamma method. In areas
where gold is known to occur in certain lithologic units, the geophysical logs can be used to map
lithology. The use of multiparameter borehole geophysics to map lithology and to detect alteration
associated with gold mineralization is illustrated using examples from boreholes in the Kirkland
Lake and Hemlo mining areas.
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Towards Prediction Of Geological Drill Core Logs Using Geophysical Logs In Volcanic Stratigraphy
Authors P.G. Killeen, B.E. Elliott and C.J. MwenifumboIn base metal exploration projects in greenstone belts, geological logging of the drill core can be
difficult because different volcanic and volcaniclastic rocks are often visually similar. Geophysical
logging tools measure physical and chemical properties that are not visible and therefore complement
observations made in geological logs. The geophysical data can provide a more complete (e.g. no
missing drillcore) and objective geologically-related interpretation of the lithology intersected by the
drillholes and can be used as an aid to geological logging of the drill core.
The Borehole Geophysics Section of the Geological Survey of Canada has conducted multiparameter
geophysical logging in areas of massive sulphide exploration, for more than ten years. Excellent
correlation of geophysical logs with geological logs has been observed in boreholes associated with
volcanogenic massive sulphide deposits, at locations from Newfoundland to British Columbia. The
application of borehole geophysical logs to the problem of core logging in areas of volcanogenic
massive sulphide deposits, is illustrated with examples.
The first example is a geological hole-to-hole correlation problem at the McConnell Nickel Deposit
near Sudbury. A simple case of the obvious relation between geophysical logs and geological logs
at the Mudhole base metal prospect near Buchans, Newfoundland, is presented next. The third
example is from the Brazil Lake area of Nova Scotia, where the potential for development of a
pseudo-geological log based on the use of multiparameter logs is shown. In another example, in the
Kam-kotia Mine area near Timmins, Ontario, the pseudo-geological log was derived by using three
geophysical logs (gamma-ray, magnetic susceptibility and density). In all cases, the geological
interpretation from the geophysical logs was subjective, However, initial investigations suggest an
objective, computer-based method of deriving the pseudo-geological log, as a tool for the geologist,
is feasible. Some early trials of this semi-automated ‘pre-picking’ of the geology by computer, based
on the geophysical logs at the McConnell deposit, are presented, illustrating the difficulties and the
possibilities.
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