- Home
- Conferences
- Conference Proceedings
- Conferences
11th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 22 Mar 1998 - 26 Mar 1998
- Location: Chicago, Illinois, USA
- Published: 22 March 1998
61 - 80 of 111 results
-
-
Dc Resistivity Monitoring Of Potassium Permanganate Injected To Oxidize Tce In Situ
Authors Jonathan E. Nyquist, Bradley J. Carr and R. Kim DavisThe X-70 1B Site at the Portsmouth Gaseous Diffusion Plant, Piketon, OH, was
selected by Department of Energy’s Office of Science and Technology for a
demonstration of in-situ groundwater treatment by chemical oxidation. The goal was to
oxidize trichloroethylene (TCE), present in both the soil and groundwater of the local
_ Gallia aquifer, by circulating a solution of potassium permanganate (KMnO4) between
two horizontal wells positioned to intercept contaminated groundwater migrating from a
nearby industrial waste holding pond. Potassium permanganate is a salt. Laboratory
measurements showed that the addition of 1 .O% of potassium permanganate increased the
fluid conductivity of a Portsmouth groundwater sample from 339 to 7250 mS/m, or
equivalently, decreased the electrical resistivity from 29 ohm-m to 1.4 ohm-m. Although
the contaminated Gallia aquifer is only about 1.5m thick at this site, and is overlain by
nearly 8m of Minford clay, geophysical modeling showed that the change in resistivity
would be detectable from the surface using DC electrical resistivity if the injection
flooded a sufficient portion of the aquifer. Field measurements made using a multielectrode
resistivity system along two lines - one parallel and one perpendicular to the
two horizontal wells - confirmed that the potassium permanganate injection was
detectable as a subtle change in the resistivity section. The change in resistivity is
apparent after the background resistivity information collected before the injection is
removed from the data. We conclude that geophysical monitoring of in situ chemical
oxidation is a feasible, and a could reduce reliance on monitoring wells.
-
-
-
3-D Ert Inversion Used To Monitor An Infiltration Experiment
Authors Melissa A. Stubben and Douglas J. LaBrecqueThe purpose of this project was to test the capability of 3-D electrical resistance
tomography (ERT) to monitor changes in vadose zone moisture content movement.
The infiltration took place on a 50 m x 50 m plot at the Maricopa Agricultural Center,
- located in Maricopa, Arizona. After background data was collected, the field was
infiltrated with water of low salt concentration. Data collection was frequent (bi-weekly)
during the beginning of infiltration and less frequent (weekly) towards the end of
infiltration and for several weeks after infiltration ceased. The ERT experiment consisted
of 12 boreholes, spaced 10 m apart, along two east-west lines. In each borehole, 15
electrodes were spaced 1 m apart vertically. Data was collected in 3-D blocks consisting
of planes of data between different pairs of boreholes. Data sets for each block were
inverted to get a 3-D image of resistivities. A variety of other hydrogeological and
geophysical methods used at this site provided ground truth for evaluation of the ERT
interpretation. The inverted ERT data corresponds closely with neutron probe and EM-39
data collected from 6 deep boreholes (-15 m deep) located near some of the ERT
boreholes. The 3-D ERT inversion technique was capable of monitoring vadose zone
moisture content movement and provided a realistic image of infiltration events.
-
-
-
3-D Ert Inversion Used To Monitor An Injection Experiment
Authors Melissa A. Stubben and Douglas J. LaBrecqueThe purpose of this project was to test the capability of three-dimensional (3-D) electrical
resistance tomography (ERT) to monitor changes in ground-water conductivity in a
saturated zone. This project is Phase I of a project funded by BHP Copper to monitor
injection of acid for in-situ leaching. Phase I of the BHP project was to inject the target
formation with a safe fluid consisting of natural ground water with a conductivity of about
double that of the target formation ground-water conductivity. This project was carried
out at a test site near Florence, Arizona. ERT was used to monitor the movement of the
injected fluid. Background ERT data was collected before injection began. The
conductive ground water was then injected into a well in the center of the test area. At
the same time, fluid was extracted from four wells, one at each corner of the test area.
This injection was continuous for about two months. Once injection started, ERT data
was collected bi-weekly for the first two weeks, weekly for the next two weeks, and every
two weeks for the next month. Data sets for a block were inverted to get a 3-D image of
resistivities. The 3-D ERT inversion technique was capable of detecting small changes in
electrical conductivity of the target formation due to the injected fluid, and provided a
realistic image of how the injected fluid moved through the formation with time.
-
-
-
Electrical Resistivity Tomography Monitoring For Process Control In Environmental Remediation
Authors Douglas LaBrecque, Jesse Bennett, Gail Heath, Susan Schima and Hank SowersThis paper discusses the adaptation of electrical resistivity tomography (ERT) for near-real time
monitoring of steam injection during Dynamic Underground Stripping for Environmental
Remedition. This application required very large data sets to be collected, processed and imaged
in less than 24 hours and still produce reliable, high quality images. The paper describes and
automated data processing system to reduce and image data sets collected with an automated
collection system. Data quality is assessed by collecting a reciprical measurement for every data
point. A variety of errors can be detected by errors in reciprical measurements. On one site, it
was found that a number of electrode strings were defective and were replaced. Replacing the
electrode strings dramatically improved the quality of the images. It was also found to be
necessary to use a fully three-dimensional interpretation routine which allowed for the modeling
of metal well casings near the image planes. Finally, an example shows the ability of ERT to
track the advance of a complex, rapidly changing steam front.
-
-
-
In Situ Verification And Monitoring Of Stabilized Trwmixed Waste
Authors Mark Ewanic, David Reichhardt and M. Cathy PfeiferDuring 1997, MSE Technology Applications, Inc. (MSE) in cooperation with the U.S. Department of Energy
(DOE) Office of Science and Technology, Subsurface Contaminants Focus Area and the Idaho National
Engineering and Environmental Laboratory (INEEL) tested the feasibility of in situ waste stabilization for either
encapsulating waste for in situ disposal or as a step in the process of contaminated retrieval with improved
contamination control. In situ stabilization was accomplished by encapsulating the waste in a monolith constructed
by injecting grout at high pressure into the subsurface. A vital part of this test was the confirmation that the
monolith had encapsulated the waste and evaluate the internal integrity of the monolith (detect voids, poorly grouted
zones, fractures, . ..).
Verifying the internal integrity of the emplaced monolith can be accomplished any number of ways, including
destructive examination of the monolith (i.e., coring and excavating). Although effective, these methods are not
often preferred, as the spread of contamination may be significant. As a result, a method to nondestructively
examine these monoliths was investigated.
Monoliths were emplaced at the INEEL Radioactive Waste Management Complex (RWMC) as part of an In Situ
Stabilization Treatability Study. Cold and Hot Demonstration sites were nondestructively examined using seismic
geophysical methods. These methods require limited access to the monoliths. Data obtained from the seismic
measurements were used to generate 3-dimensional models of the grout monoliths. Results, presented in this paper,
are expected to show that borehole seismic methods are an effective means of nondestructively imaging the grout
monoliths.
-
-
-
Verification Of Subsurface Barriers Using Integrated Geophysical Techniques
During 1997 a suite of borehole geophysical surveys were completed at the Dover National Test
Site (DNTS), Dover Air Force Base (DAFB) to demonstrate the efficiency and accuracy of
geophysical methods in determining the areal extent of cement bentonite subsurface barriers. Two
barriers were emplaced as vertical walls keyed into a clay aquitard with a modified jetting
technique. These barriers are denoted as the ‘shallow’ active’ and ‘deep passive’ barriers extending
to 5 and 13 m, respectively. The active and passive descriptors refer to the hydraulic and gaseous
tracer work performed at the sites. Demonstrated methodologies included electromagnetic
induction logging (EM), ground penetrating radar (GPR), electrical resistivity (ER), and borehole
seismic. The geophysical instruments were deployed from boreholes or permanently emplaced
vertical electrode arrays (VEAs).
The purpose of the work was to develop a robust methodology for the verification and monitoring
of a subsurface barrier. Site characterization data were used to estimate the physical properties of
the background host and laboratory measurements were performed to estimate the properties of the
grout. Based on these data numerical models were computed for survey design and interpretation.
Representative data and discussion for each of the methods are presented. Additionally, a brief
discussion is presented on the site preparation activities. Preliminary results indicate that the GPR
and ER methods are successful at imaging the area1 extent of the barrier and assist with leak
detection through ER monitoring of a salt water flood test. Future work will combine the
information obtained from the geophysical measurements with the hydraulic and gaseous tracer
results to produce a comprehensive understanding of the quality and performance of the barrier.
-
-
-
A Wire Net Design For Electrical Monitoring Of Environmental Barriers
Authors Christian Bernstone, Torleif Dahlin, Peter Ulriksen and Johan ClaessonA wire net concept for monitoring of environmental barriers is described and tested
in a laboratory model. The system is aimed for permanent installations and a pilotscale
version has been constructed below a brine pond mineral liner at the Filborna
landfill in Southern Sweden. The presentation includes the results from the
laboratory study and show some initial results from Filborna.
-
-
-
Monitoring Of Groundwater Pump Tests Using Gpr And Electrical Resistivity
Authors John Dolynchuk, David Lesmes, Alfredo Urzua and Chris KilbridgeGround-penetrating radar (GPR) and electrical resistivity surveys were used to monitor
two aquifer pump tests conducted at a test site near Boston, Massachusetts. Measurements of
drawdown were made both during and after each pumping test. Distance-drawdown experiments
were conducted in which GPR profiles and electrical resistivity pseudo-sections were used in an
attempt to image the depth to the water table (or the top of the capillary fringe). Although
differences could be observed between the profiles collected at maximum drawdown and at full
recovery, we have not yet been able to uniquely identify the phreatic surface and map the cone of
depression. Time-drawdown experiments using both electrical resistivity soundings and
stationary GPR measurements have proven to be more effective in directly imaging the depth to
the “water table”. In particular, we have been able to use GPR measurements made as a function
of time at a fixed location to estimate the conductivity of the aquifer. Increased processing and
inversion of the GPR profiles and resistivity pseudo-sections may enhance the analysis of the
distance-drawdown data. It may also be possible to use the time-drawdown data to facilitate the
location of the “water table” in the distance-drawdown measurements.
-
-
-
Monitoring Air Sparging In The Cfb Borden Aquifer Using Gpr Reflection Surveys, Borehole Gpr And Geophysical Well Logging
Authors J. David Redman, J. Brant Gill, Derek W. Tomlinson and Neil ThomsonAir sparging is a groundwater remediation technique that introduces air into the subsurface to
enhance the removal of contaminants. The effective application of this technique requires a
knowledge of the spatial distribution and magnitude of air saturation achieved during the sparging
process. This paper discusses the use of ground penetrating radar (GPR) reflection surveys,
borehole GPR, and geophysical well logging techniques to determine the steady state air
saturation distribution within a sandy aquifer during an air sparging experiment performed at
Canadian Forces Base (CFB), Borden, Ontario. Air was injected at a depth of 3 m below the
water table using a flow rate of 200 m3/day (5 scfm). Surface GPR reflection surveys, borehole
GPR surveys and geophysical well logs were acquired prior to the injection of air, and after the
eighth day of sparging.
GPR reflection surveys, sensitive to changes in air saturation with depth, mapped large flat lying
pockets of trapped air, that had moved to, and presumably past, the edges of the test site.
Borehole GPR surveys and neutron logging provided quantitative estimates of air saturation
throughout the test cell, giving maximum air saturations of 60% near the centre of the test area
and 20% at the edges. Electromagnetic (EM) induction logs indicated that as a result of surface
water pumping, more conductive water from a deeper inorganic plume moved into the zone being
sparged, but could not be used to determine air saturation.
-
-
-
Statics Applied To Shallow Seismic Reflection Data
Authors A. Pugin and S.E. PullanThe proper handling of static corrections is an issue that is of critical importance to shallow
seismic reflection surveys because of the high frequencies used, the large velocity variations that
frequently exist in the near surface, and the shallow depths of investigation. The adaptation of
conventional methods of determining static corrections is often inadequate for shallow seismic
reflection data. This paper presents a method of handling static corrections which addresses the
problem in terms of long-, medium-, and short-wavelength variations in topography and nearsurface
velocity variations. An analysis of first-arrival data at intervals along the survey line is
used to estimate a layered, near-surface, velocity structure. First-break picking is then used to
align the first arrivals to a laterally-interpolated, near-surface, velocity function. This process
corrects for medium- (i.e. within spread length), and long-wavelength (>spread length), nearsurface
velocity variations, as well as most of the static contributions related to individual
geophone locations and elevations (i.e. short-wavelength corrections). Accurate residual statics
correct any remaining short-wavelength errors. Finally, topographic variations (longwavelength)
are corrected post-stack. Both model results and application of this method to actual
shallow seismic reflection data show this to be a robust and effective method of correcting for
statics.
-
-
-
Seismic Detection Of Viscous Contaminent Using Shallow Seismic Reflection
Authors Ran Bachrach, Amos Nur and James RickettWe conducted a high resolution very shallow seismic experiment in order to image
the effect of viscous fluids on signal attenuation in surface acquired seismic data. We
mixed 20 liters of honey with 200 liters of beach sand. Then we buried the mixture in a
pit at depth of 1 m in the center of the seismic line. We collected two CDP seismic
. sections, the first one with a dry pit, and the second with the honey sand mixture in the
pit, and analyzed the effect of the pore fluid on reflection strength. The spatial location of
the honey could be determined by the attenuated water table reflection, precisely in the
place where the honey was buried. The attenuation was higher in the 700Hz CDP stacked
section than in the 350Hz CDP stacked section. In this paper we discuss three aspects of
the problem: 1) Simplified assumption for attenuation mechanism and a methodology to
estimate the location of viscous pore fluid and its viscosity. 2) The experimental
description and 3) Seismic data processing issues, with application to fluid monitoring.
We show that given sufficient bandwidth, viscous contamination can be imaged from the
surface.
-
-
-
3-D High-Resolution Reflection Seismic Imaging Of Unconsolidated Glacial Sediments
Authors F. Büker, H. Horstmeyer and A.G. GreenShallow 3-D reflection seismic techniques have been used to map glacial deposits overlying the
Swiss Molasse Basin. A dense distribution of source and receiver positions resulted in a small CMP
bin size of 1.5 m x 1.5 m and a high fold >40. Common processing operations such as
deconvolution and bandpass filtering successfully enhanced shallow reflections relative to sourcegenerated
noise. Erroneous stacking of refracted and guided waves was avoided by careful selection
of top mutes. Three-dimensional migration of the stacked data yielded a reliable high-resolution
image of the shallow subsurface (cl50 m). Based on borehole information a continuous reflection
at 20 to 40 ms (-14 to -35 m) can be correlated with an interface between near-surface lacustrine
deposits and underlying glacial tills. A total of five major subsurface units can be distinguished on
the basis of their characteristic seismic facies.
-
-
-
Reprocessing Of Shallow Seismic Reflection Data To Image Faults Near A Hazardous Waste Site On The Oak Ridge Reservation, Tennessee
More LessShallow seismic reflection data from Bear Creek Valley on the Oak Ridge Reservation
demonstrates that spectral balancing and tomographic refraction statics can be
important processing tools for shallow seismic data. At this site, reprocessing of data
which had previously yielded no useable CMP stacked sections was successful after
application of these processing techniques.
-
-
-
Seismic Reflection Survey For Mapping Groundwater Migration Pathways At Tinker Air Force Base, Oklahoma
Authors Jeffrey B. Hackworth, Sara Sayler, Gilein J. Steensma and David W. MarcumOptimal placement of groundwater recovery wells in complex geologic environments often requires more subsurface
information than is available from boring log data, typically from widely spaced wells. A two-dimensional (2-D)
seismic reflection survey was conducted in the area of a planned groundwater recovery wellfield in the southwest
quadrant of Tinker Air Force Base (AFB) to help identify and map possible conduits for preferential groundwater flow
in the shallow subsurface. The primary targets of interest were near-surface sand channels and lenses within the upper
portion of the Permian-age Garber Formation, although the dataset also provided significant information on deeper
layers. The seismic data were acquired along eight survey lines totaling 17,510 linear feet.
The geophysical investigation at Tinker AFB included evaluating shear-wave (s-wave) and compressional wave (pwave)
seismic techniques along a short portion of one line to determine the best approach for the entire survey. Based
on the processed test sections, and consideration of s-wave data acquisition and processing costs, it was decided the pwave
survey offered an acceptable approach. The investigation also included acquisition of vertical seismic profile
(VSP) data, generating a synthetic seismogram from an existing sonic log, and collecting EM-3 1 data along each line to
assess the effect changes in near-surface soils, buried debris, and utilities had on the seismic data.
Seismic data were interpreted with the aid of PC-based software. To better understand the geometry and amplitudes of
some of the features observed in the site data, seismic models were generated with different combinations of velocity
and layer thickness. The interpreted seismic data indicate several locations where the potential for drilling into
significant sand lenses in the target zone is believed to be high. Deeper sand channel complexes cutting through the
target zone and extending to much greater depths are also interpreted. The results of Phase I groundwater recovery well
yield tests indicate good correlation with several of the seismic anomalies identified in the target zone.
-
-
-
Investigating Alpine Valley Fill With Reflection Seismics (2-D) And Georadar (2-D & 3-D)
Authors Heinrich Horstmeyer, Frank Büker, Patrick Geissmann, Lori Keller and Alan G. GreenThe internal structures of Alpine valleys have been of particular interest to Swiss society since
it was first recognised that more than two-thirds of the country’s fresh water supplies are
contained in the unconsolidated sedimentary fill. Since most of the valleys are also densely
populated and industrialized, there is a high risk of ground-water contamination. In the Reuss
Delta near the shore of Lake Lucerne, several profiles have been surveyed with high-resolution
reflection seismic and/or georadar techniques. In one region, where the character of the georadar
images changed significantly, a 3-D georadar survey (40 x 80 m*) was also conducted. The
uniformly high quality of both the seismic and georadar data seems to have been influenced by
the presence of near-surface saturated gravels and sands. Dense geophone spacing (1.5 m) and
careful processing has enabled seismic reflections as shallow as - 15 m to be imaged. The deepest
seismic reflections image the dipping contact between unconsolidated sediments and the
underlying basement at 200 - 525 m depth. Distinctive reflection patterns in the georadar data
volume have enabled us to determine the local conditions of sedimentation in the upper -12 m of
the subsurface. For example, a distinctive ancient river channel has been identified overlying a
strongly reflective clay/silt layer deposited during a major flooding event.
-
-
-
Time-Varying Fold In High-Resolution Seismic Reflection Data: A Recipe For Optimized Acquisition And Quality Control Processing And Interpretation
Authors Lee M. Liberty and Michael KnollA simple technique is presented to optimize seismic reflection acquisition and processing
parameters using the results of walkaway tests, time-varying trace fold, and geologic target
weighting. Fold varies significantly with travel-time on shallow seismic reflection surveys due to
mute operations and normal moveout (NMO) corrections. In the absence of well control,
increased fold may provide the only confidence measure that primary reflection energy is present,
based on stacking velocities. The recipe to optimize a seismic survey involves acquiring walkaway
tests (oversampling in space and time) at suspected end-member geologic targets. All mutes
and stacking NMO velocities are then applied to the walkaway gathers to calculate the optimum
window for maximum coherence for primary reflection energy. With the optimum window
derived from each walkaway gather, the operator can then calculate the acquisition parameters
needed to best image each target of interest, based on the number of seismograph channels available.
If the number of channels in shot space for a given target (in travel-time) falls below a
threshold (we recommend 6-channel coverage), then the operator must decide either to sacrifice a
depth range to image (define a no confidence or low confidence zone), employ more seismograph
channels to image all desired targets, or modify the acquisition experiment. If the above recipe is
followed, a contour map of the fold (which is one measure of reflector confidence) can also be
generated and displayed with the final stacked section as an overlay. To obtain this map, the operator
sorts a copy of the shot data into common midpoint (CMP) gathers, sets all amplitude values
to unity, applies mutes (zeroing those samples excluded from the processed seismic data), corrects
for NMO, and sums the data (as opposed to stacking or averaging the data). The result for both
acquisition and processing phases is a record of true fold as a function of time for all locations.
True fold displays are useful for quantifying the confidence of primary reflectors for geologic
interpretation or subsequent attribute analysis, and also for measuring the uncertainty of seismic
velocity estimates which, in turn, can affect seismic inversion-results and petrophysical parameter
estimates.
-
-
-
High-Frequency Sources In Shallow Seismic Experiments
Authors Michiel van der Veen, Hermann Buness, Frank Nitsche, Frank Biiker, Frank Lehmann and Alan GreenWe have compared the energy, frequency and noise characteristics of six highfrequency
seismic sources: 12-gauge pipegun, Seismic Impulse Source System (SISSY),
5-kg sledge hammer, an accelerated weight dropper, and the mini-vibrator from NLFB.
Seismic measurements were undertaken in the Reuss Delta (central Switzerland), which
is characterized by shallow reflection energy arriving at -50-200 ms, and the Suhre
Valley (Northern Switzerland), which is dominated by reflections from -20-200 ms. The
pipegun and SISSY sources have similar signal and field handling characteristics and are
suitable for imaging reflections from ultra-shallow to intermediate depths. A sledge
hammer generates less energy, but is relatively rich in higher frequencies. It is, therefore,
a good source for imaging ultra-shallow reflections. The accelerated weight dropper
generates a strong airwave that may mask early reflections, making it more suitable for
shallow to intermediate depth reflection surveying. Both vibratory sources have the
advantage of controlled bandwidth, determining the resolution and to some extent the
penetration. The resolution and penetration depth of the NLFB mini-vibrator is
comparable to that obtained with the shotgun. However, the relatively strong airwave
suggests it is best suited for imaging shallow to intermediate reflections.
-
-
-
Spectral Induced Polarization Studies Of Mine Dumps Near Silverton, Colorado
Authors David L. Campbell, David V. Fitterman, Andrew S. Hein and Daniel P. JonesAs part of a study of mechanisms that produce acid mine drainage, we made laboratory
and field studies of two mine dumps near Silver-ton, CO. Water that drains from both dumps
during spring to mid-summer had been found to be quite acidic. The dumps contained broken-up
material excavated from Pb-Zn-Ag prospects. In both laboratory and field measurements we
found that the resistivities of dump material varied substantially, while their spectral induced
polarization (SIP) characteristics were weaker than those expected for sulfides interacting with
porewaters. We speculate that after 40-plus years of residence in mine dumps, the grains of dump
material have become coated with oxidized minerals which inhibit the surface electrochemical
reactions that give rise to strong SIP response. If this is so, it implies that the mechanism for
generation of acid waters in the mine dumps we studied is probably not the oft-cited oxidation of
pyrite at grain surfaces, but rather some alternative process(es) such as those involving oxidized
minerals.
-
-
-
The Influence Of Pore Fluid Chemistry On The Induced Polarization Response Of Rocks And Soils
Authors Kevin M. Frye, David P. Lesmes and F. Dale MorganTo improve contaminant detection and monitoring, it is important to understand the role
of the bulk pore fluid chemistry on the induced polarization (IP) response of rocks and soils. IP
methods can be more effective than traditional resistivity surveys because they are more
sensitive to changes in electrochemistry at the mineral grain-pore fluid interface caused by small
amounts of dissolved contaminant. Clean and contaminated materials have been shown to have
comparatively different IP responses in both laboratory and field experiments. However,
electrochemical surface properties are also dependent on the bulk pore fluid chemistry and grain
microgeometry. The effect of contaminants on the IP response is superimposed upon these other
bulk fluid and microgeometry effects.
To document the influence of pore fluid chemistry on the IP response of earth materials,
experiments were performed to measure the complex conductivity and time domain IP of Berea
sandstone cores as a function of pore fluid pH, ionic strength, and cation type. A minimum in
surface conductivity and IP response is observed at pH 3, the approximate point of zero net
surface charge for quartz. While surface conductivity increases with ionic strength, the net IP
response, or phase angle, decreases with ionic strength. A suite of cores saturated with different
salt solutions of equal conductivity demonstrates significant variability in the IP response as a
function of cation type. These experiments are applicable to other quartz-dominated systems and
help to link field IP measurements to geochemical parameters, thus improving the IP
characterization of geochemical environments.
-
-
-
Experimental Use Of The Induced Polarization Method To Map And Characterize The Shallow Sea-Floor
Authors Jeff Wynn, Jack Kindinger and Dana WieseWe have developed a new high-resolution sea floor mapping system, based on the
induced polarization (IP) principle. This system uses a weighted streamer, designed to be towed
directly on the sea floor at speeds up to 3 knots. Signal injection is achieved by means of a pair
of titanium transmitter electrodes that force 2+ amps in the form of a 4 Hz square-wave into the
sediments. Two staggered receiver dipole arrays are used to detect polarizing materials in the top
5+ meters below the sediment-water interface. Using this system, we can continuously
characterize the sea floor at two different depths by means of a geophysical acquisition and
processing system (providing resistivity and phase for two different depths) and a GPS receiver
positioned on a ship. Data acquisition and control are via a laptop computer, and the entire
system is highly portable and battery-powered. We have demonstrated that the array can detect
ilmenite (a titanium-bearing heavy placer mineral) to concentrations at or below 1% by volume,
and can also characterize lithologic changes beneath an overlying veneer of sand. We believe
that the system has additional potential applications, including rapid characterization of
anthropogenic materials (including urban waste), identification and mapping of buried cables,
unexploded ordnance (UXO), and possibly even to map buried archeological sites. Theoretically
we can acquire more IP measurements in a week at sea than have been acquired historically on
land over the past 50 years.
-