- Home
- Conferences
- Conference Proceedings
- Conferences
12th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 14 Mar 1999 - 18 Mar 1999
- Location: Oakland, California, USA
- Published: 14 March 1999
61 - 80 of 108 results
-
-
Self Potential Monitoring Of Jet Fuel Air Sparging
Authors Yervant Vichabian and Frank Dale MorganIn recent years, several remediation methods have been developed based on in-situ
oxidation. However, there are not efficient ways to monitor the effectiveness of these
methods in enhancing oxygen levels or delineating their zone of influence. In this
presentation we study the use of self potential (SP) geophysics to monitor the air sparging
and soil vapor extraction system at FS-12 on the Massachusetts Military Reservation,
Cape Cod, Massachusetts. Data has been collected over a time period of two years using
the gradient SP method with 130 permanent measuring stations. We have observed a
large 800 to 1000 mV SP anomaly in the region where the remediation system is in
operation. Using the Nemst equation, we convert the SP anomaly to the partial pressure
of oxygen, from which a contour plot is generated showing the effective area of sparging.
In this paper, we show that SP can be used to monitor remediation methods, which rely
on increasing oxygen levels in the subsurface.
-
-
-
3-D Gpr Imaging Of Complex Fluvial Stratigraphy At The Boise Hydrogeophysical Research Site
Authors William R. Peretti, Michael D. Knoll, William P. Clement and Warren BarrashA series of three-dimensional (3-D) ground-penetrating radar (GPR) data sets were acquired
over the central wellfield area at the Boise Hydrogeophysical Research Site (BHRS). The survey
region is 30 m x 18 m and encompasses 13 wells. The goal of the surveys is to image the
complex fluvial (cobble-and-sand) stratigraphy around the wellfield. These images will be used
to construct 3-D models of the sedimentary architecture and to help constrain fine-scale models
of hydrologic and geophysical parameters at the site. The data sets were acquired using 25 MHz,
50 MHz, 100 MHz and 200 MHz antennas. Depth of penetration ranges from -9.6 m for the 200
MHz data to -22 m for the 25 MHz data. Processing significantly improves the reliability and
interpretability of the images. The images suggest that the deposit can be subdivided laterally
and vertically into several distinct units or radar architectural elements; these elements are
typically separated by erosional bounding surfaces. Horizontal bedding, cross-bedding and
channel structures are clearly evident in the 100 MHz and 200 MHz data, and a clay layer that
underlies the cobble-and-sand aquifer at -20 m depth is successfully imaged in the 25 MHz and
50 MHz data. The water table, at a depth of l-2 m, is imaged in the 100 MHz and 200 MHz data.
Time slices and vertical cuts through the data volumes are used to identify the shape and
orientation of the different architectural elements, and to accurately locate important
hydrostratigraphic boundaries. These data are being used to construct a 3-D model of the
hydrogeologic zonation of the aquifer. Hydrologic and geophysical parameter values associated
with each zone will be determined from additional field measurements (e.g., hydraulic tests in
wells, crosshole radar and seismic tomography, transient electromagnetics, and well logs). The
3-D GPR surveys provide valuable information about the location, scale and geometry of
different stratigraphic units at the BHRS.
-
-
-
An Imaging Algorithm For Gpr Data
Authors Yoshinori Sanada and Yuzuru AshidaThe finite difference time domain (FDTD) method is calculated by the explicit
finite approximation scheme of Maxwell’s curl equations. Since it allows arbitrary
electrical conductivity and permittivity variations within a model, the FDTD method
has become one of the powerful forward modeling methods for electromagnetic (EM)
phenomena. On the other hand, the reverse time migration is the imaging algorithms,
which is performed by inserting the recorded data as boundary conditions at each
recorder position in reverse time order. Due to the advantage of simple calculation
algorithm and applicability to arbitrary model, both methods are powerful tools for GPR.
In the present paper, the synthetic GPR data are calculated by using of the FDTD
method with the exploding reflector method. The reverse time migration is formulated
using FDTD scheme and applied to model with lossless and lossy media. In lossless
media, the forward and reverse time schemes are expressed by the completely same
scheme. The proposed method is successfully applied to synthetic data for two models,
these are steeply dipping structure and point diffractors model. In lossy media, the
forward scheme includes diffusion term, while the reverse time scheme includes
divergence term. In such a case, we show the condition that the EM wave velocity is
regarded as constant, then this methodology is applicable successively. We also discuss
the reverse time migration for the lossy media after the amplitude recovery under the
lossless media condition.
-
-
-
Terrain- Permittivity Mapping: Gpr Measurements Of Near-Surface Soil Moisture
Authors David P. Lesmes, Robert J. Herbstzuber and David WertzGPR can be used to rapidly and non-intrusively measure soil moisture content
over spatial scales that are intermediate between the point measurement techniques (e.g.
TDR and neutron probes) and remotely sensed soil moisture measurements which are
made at the regional scale (e.g. airborne SAR measurements). In bi-static GPR surveys
the direct ground wave passes from the transmitter to the receiver through the nearsurface
soil. The GPR ground wave velocity can therefore be used to determine the
permittivity (or dielectric constant) of the near-surface soil. Estimates of soil moisture
content can be obtained using dielectric mixing equations. Variance in the velocity of the
ground wave can largely be attributed to variance in the level of soil moisture. We are
using GPR ground wave velocity measurements, with a constant antenna off-set, to map
lateral variations in terrain permittivity and to estimate near-surface soil moisture content.
Experiments have been conducted to determine the effects of frequency, antenna spacing,
and soil type on the soil moisture estimates and the effective depth of penetration.
Furthermore, we have used this methodology to monitor changes in soil moisture during
controlled spill experiments. Ongoing experiments include the monitoring of seasonal
fluctuations in soil moisture over a grass covered field at the Weston Geophysical
Observatory in Weston, Massachusetts.
-
-
-
An Investigation Of Cross-Borehole Ground Penetrating Radar Measurements For Characterizing The 2D Moisture Content Distribution In The Vadose Zone
Authors Lee Paprocki and David AlumbaughThe use of cross-borehole ground penetrating radar (GPR) imaging for determining the two dimensional (2D) in situ moisture content distribution within the vadose zone is being investigated. The ultimate goal is to use the GPR images as input to a 2D hydrologic inversion scheme for recovering the van Genuchten parameters governing unsaturated hydraulic flow. Initial experiments conducted on synthetic data have shown that at least in theory, cross-borehole GPR measurements can provide realistic estimates of the spatial variation in moisture content that are needed for this type of hydrologic inversion scheme. However, the method can not recover exact values of moisture content due to 1) the break down of the empirical expression often employed to convert GPR velocity images to moisture content, and 2) the smearing nature of the imaging algorithm. To test the applicability of this method in a real world environment, crossborehole GPR measurements were made at a hydrologic/ geophysical vadose zone test site in Socorro, New Mexico. Results show that the GPR images compare well with the
uncalibrated borehole neutron log data. GPR data acquisition will continue once an infiltration test has started, and the results from these measurements will be employed in a 2D hydrologic inverse scheme.
-
-
-
Ground Penetrating Radar & Avo
Authors Philip M. Reppert, Frank Dale Morgan and M. Nafi ToksozThis presentation concerns the use of Amplitude Versus Offset (AVO) with ground
penetrating radar (GPR) data. We demonstrate that AVO may have possible uses with
GPR. Theory is presented in this paper on the principle of AVO as applied to
electromagnetic (EM) waves. The theory is demonstrated on field data obtained over a
drain field in Massachusetts.
-
-
-
Conversion Of Hydraulic Conductivity To Synthetic Radar Traces
More LessIn the interest of interpreting radar data and establishing a empirical correspondence between
hydraulic conductivity and ground penetrating radar data, hydraulic conductivity logs have
been converted to synthetic radar traces. The assumption in the computation is that hydraulic
conductivity is closely related to porosity and thus water content and dielectric constant.
The synthetic radar traces have been used to interpret the radar cross section in terms of
zones of hydraulic conductivity.
In the absence of a deterministic model between radar waveforms and hydraulic conductivity
empirical relations are sought. Radar data have been acquired at the MADE site near Columbus,
Mississippi. Hydraulic conductivities measured in wells have been converted to dielectric
constant using a simple empirical relationship and used to compute the radar traces that
would be obtained at the borehole. The comparisons with the field radar traces are encouraging.
Key words: radar, hydraulic conductivity, synthetic radargram
-
-
-
Investigation Of Mountainous Rock Destruction: A New Physicothematical Conception
Authors A.L. Aleinikov, V.T. Belikov and L.V. EppelbaumInvestigation of mountainous rock destruction under different thermodynamic conditions
is one of the most important problems of the engineering hazard. It was earlier considered
that this destruction is taking place when at least one component of the stress tensor
reaches some critical value called as a material strength. However, conducted analysis
allowed us to conclude that such a notion is correct only for a relatively short-term action
and is unsuitable by a prolonged stress to target. On the basis of the detail theoretical
analysis we propose a new physico-mathematical conception describing the destruction
process as a phase transition. From this viewpoint, generation of microfault is an initiation
of a new phase. Such a generation causes emission of a definite number of seismo-acoustical
impulses. Quantity of the impulses during the time unit shows an intensity of process
destruction and frequency of oscillation indicates dimension of the microfaults forming.
Thus, the suggested conception allows to develop procedures for monitoring of durability
of different artificial underground constructions: mines, reservoirs and military objects as
well as other artificial and natural structures.
-
-
-
Use Of Vsp Techniques To View, In 3D, Partially Saturated Layers In The Shallow Subsurface At Lawrence Livermore National Laboratory, California
Authors Paul A. Milligan, James W. Rector III and Robert BainerA multi-offset VSP (vertical seismic profiling) method was developed to help define aquifer boundaries and below
water table partially saturated zones at the Lawrence Livermore National Laboratory, Livermore Site, California.
The VSP method consisted of using a multilevel hydrophone array giving 48 channels of recorded seismic data per
shot. Hydrophone spacing was 0.5 m, with anti-tubewave baffling devices inserted between each phone, and at each
end of the array to slow down and attenuate tube wave noise contaminating the desired data signals. The seismic
source consisted of an impact weight-drop machine.
The VSP data was processed, and inverted to produce 2D p-wave interval velocity sections with up to 0.5 m of vertical
resolution in the unconsolidated sediments below the water table. Multiple 2D velocity sections were created,
corresponding to radial arms of walk-away shot point records from multiple wells. These 2D velocity sections were
then visually projected into the 3D survey volume, together with well locations, predefined hydrostratigraphic unit
(HSU) layer boundaries, and the interpreted isopach map of a major HSU of interest. The interactive graphical display
of all these data in 3D allowed correlations to be made between the VSP velocity images and the pre-existing data.
The discovery of several low velocity zones below the water table was attributed to partially saturated pore spaces.
Two thin (less than 1 m thick) layers with p-wave velocities as low as 500 m/s appeared to be perched on top of major
aquifers undergoing pump extraction and treatment. Gas analysis from water samples taken from one of the aquifers
indicated normal atmospheric air as a probable gas source. High pumping flow rates (20 to 30 gal/min) may
help to explain how venturi action could be responsible for the intake of air from the vadose zone into porous but
less permeable silty-sand units overlying sand-gravel aquifers. Possible uses for this VSP technique would be to delineate
the zone of pumping influence, and help in the choice of suitable new well locations for either pumping or
monitoring.
-
-
-
Hydrogeological Property Estimation Using Tomographic Data At The Boise Hydrogeophysical Research Site
Authors John E. Peterson, Ernest L. Majer and Michael D. KnollCrosswell seismic and radar data were acquired at the Boise Hydrogeophysical Research
Site (BHRS) as part of an effort to characterize the hydrological property distribution in a
heterogeneous alluvial aquifer. The dielectric constant and amplitude attenuation values
obtained from inversion of the radar data, as well as the seismic P-wave velocity values
obtained from inversion of the seismic data, reveal similar spatial patterns. Comparison of
this tomographic information with coincident wellbore logs suggest that the geophysical
attributes are sensitive to hydrogeological variations. Information obtained from the radar
tomography data were used to produce 2-D, high-resolution images of porosity and electrical
conductivity. Comparison of these images with coincident log data reveal that these estimates
are reasonable and suggests that the tomography data will be useful at this site for delineating
variations in hydrological parameters.
-
-
-
Dielectric Dependence On Salinity And Probe Length In Tdr-Measurements
Authors Sari Penttinen, Pekka Hanninen and Raimo SutinenTime domain reflectometry (TDR) is widely used in soil sciences and forestry to determine soil
dielectric properties and water content. The effects of TDR probe length, geometry and water
electrical conductivity (%) on dielectric values were studied. The three-prong TRD probes, 0.06
m in diameter and lenght varying from 0.035 to 0.15 m with varying the spacing of the probes
tested in water, whose electrical conductivity (%) varied from 0.6 mS/m to 700 mS/m. The
scattering in dielectric values increased significantly, when the probe lengt was 0.035 m or
shorter. However, the scatter level was minor with probes bend outward or inward. Probe
spacing greater than 0.06 m resulted in unreliable readings. The increase of electrical
conductivity of water with %> 200 mS/m resulted in scattered data, particularly with the 0.035-
m-long probes. Dielectric data for all probe lenghts were scattered with water electrical
conductivity with oW> 500 mS/m.
-
-
-
Field Investigation Of Salt Transport Processes Using .Resistivity/Ip Imaging
Authors Lee Slater and Stewart K. SandbergTwo examples of the use of combined resistivity/induced polarization (IP) monitoring of salt
transport under natural hydraulic loads are presented. Previous workers have performed electrical
monitoring of the transport of a tracer artificially injected into the subsurface. The detection of
tracer transport due to natural hydraulic processes is a more difficult goal as neither the hydraulic
load nor the resistivity contrast can be controlled. Tide-induced salt transport at the saltwaterfreshwater
interface was investigated in the first study. 2D resistivity and IP models resolved the
structure of the interface. The IP modeling provided greater clarity of the subsurface
hydrology/geology than the resistivity modeling alone. Modeling of electrical changes over a
tidal cycle revealed resistivity increases in the near surface and at depth, 5-l 5 m up-beach of the
high tide mark. The results indicate a phase lag between the subsurface hydrological response
and the tidal cycle. In the second study, salt transport from the site of an old road-salt storage pile
was investigated. The hydraulic mechanism was natural recharge events that occurred over a
four-month period. 2D conductivity and IP models resolved the subsurface distribution of salt,
initially identified from an EM3 1 survey. Modeling of resistivity change on lines spaced 33.5 m
apart revealed changes at the location of salt contamination. The changes on each line appear
closely coupled and correlate with the recharge pattern over the monitoring period. The studies
indicate that salt transport occurring under natural hydraulic conditions can be detected with
resistivity, and to some extent, IP.
-
-
-
Self Potential Mapping Of Contaminants
Authors Yervant Vichabian, Philip Reppert and Frank Dale MorganVarious geophysical techniques are useful for detection and mapping of subsurface
contamination plumes. Self potential seems to be a particularly promising technique due
to its cost effectiveness and speed of acquisition and processing. The electrochemical
phenomena of organic contaminants and their interactions with microorganisms in the
subsurface provide a detection method for self potential (SP) geophysics. In this
presentation, we couple biodegradation with several examples of SP detecting
contaminant plumes.
-
-
-
An Electromagnetic Induction Tomography Field Experiment At Lost Hills, Ca
Authors H. Michael Buettner and James G. BerrymanWe have collected borehole to surface electromagnetic induction field data for a shallow steam
injection that is underway at Mobil Oil’s Lost Hills-3 field in San Joaquin Valley. Earlier
work had been done at the same site by Wilt et al. (1996). This site is an interesting test
for techniques under development for environmental engineering, because it can be viewed as
an excellent analog of a shallow environmental remediation using steam injection. Surface
magnetic field data (vertical and radial fields, magnitude and phase) were collected using 18
receiver stations along two profiles which ran radially from the EM transmitter well from 5
m to 120 m. The data at each surface station were collected while the EM transmitter was
raised slowly from a depth of 120 m to a final depth of 20 m. As part of this experiment, a
calibration of the EM transmitter was also performed. Magnetic field data from Lost Hills were
successfully collected, including both vertical and horizontal (surface radial) magnitude and
phase data along a northerly profile and along a westerly profile. We have observed that the
radial receiver data appear to be better behaved than the vertical receiver data, suggesting that
these data may be less sensitive to environmental clutter (numerous metallic pipes crisscrossing
the site at the surface) than are the vertical data. Some simple 1-D modeling has been done to
confirm that the expected conductivity change in the steam zone should produce an observable
anomaly in the measured data when comparing the pre-steam to the post-steam conditions.
Results of this test were positive. Further analyses of these data making use of a new code
developed in a companion paper are in progress and will presented separately.
-
-
-
High-Performance Computational And Geostatistical Experiments For Testing The Capabilities Of 3-D Electrical Resis’Iiance Tomography
Authors Steven Carle, Abelardo Rarnirez, William Daily, Robin Newmark and Andrew TompsonThis project explores the feasibility of combining geologic insight, geostatistics, and high-performance
computing to analyze the capabilities of 3-D electrical resistance tomography (ERT), Geostatistical
methods are used to characterize the spatial variability of geologic facies that control subsurface
variability of permeability and electrical resistivity. Synthetic ERT data sets are generated
from geostatistical realizations of alluvial facies architecture. The synthetic data sets enable comparison
of the “truth” to inversion results, quantification of the ability to detect particular facies at
particular locations, and sensitivity studies on inversion parameters.
-
-
-
Electrical Imaging Of Engineered Hydraulic Barriers
Authors William Daily and Abelardo RamirezElectrical resistance tomography (ERT) was used to image the full scale test
emplacement of a thin-wall grout barrier installed by high pressure jetting. ERT was also
used to monitor the waterflood of a thin-wall grout barrier to vertfy its hydraulic integrety.
Both case studies were done by comparing images of electrical resistivity before and after a
change was induced in the subsurhace. Barrier materials or flood water were imaged as
anomalies which were more electrically conducting than the native sandy soils at the test
sites. Although the spatial resolution of the ERT was not sufficient to resolve flaws in the
barrier under construction smaller than a reconstruction voxel(50 cm on a side), the images
did show the spatial extent of the barrier materials and therefore the general shape of the
structure.
-
-
-
Laboratory Scale Tests Of Electrical Impedance Tomography
Authors Abelardo Ramirez, William Daily, Andrew Binley and Douglas LaBrecqueElectrical impedance tomographs (magnitude and phase) of known, laboratory-scale
targets are reported. Three methods are used to invert electrical impedance data and their
tomographs compared. The first method uses an electrical resistance tomography (ERT)
algorithm (designed for DC resistivity inversion) to perform impedance magnitude
inversion and a linearized perturbation approach (PA) to invert the imaginary part. The
second approximate method compares ERT magnitude inversions at two frequencies and
uses the frequency effect (FE) to compute phase tomographs. The third approach,
electrical impedance tomography (EIT), employs fully complex algebra to account for
the real and imaginary components of electrical impedance data. The EIT approach
provided useful magnitude and phase images for the frequency range of 0.0625 to 64 Hz;
images for higher frequencies were not reliable. Comparisons of the ERT and EIT
magnitude images show that both methods provided equivalent results for the water
blank, copper rod and PVC rod targets. The EIT magnitude images showed better spatial
resolution for a sand-lead mixture target. Phase images located anomalies of both high
and low contrast IP and provided better spatial resolution than the magnitude images.
When IP was absent from the data, the EIT algorithm reconstructed phase values
consistent with the data noise levels.
-
-
-
Simultaneous Acquisition Of P- And S-Wave Crosswell Seismic Profiles In A Contaminated Basalt Aquifer
Authors Thomas M. Daley, John E. Peterson and Ernest L. MajerMultiple seismic crosswell surveys have been acquired by LBNL in a fractured basalt aquifer
at Idaho National Engineering and Environmental Laboratory (INEEL). Most of these surveys
used a high frequency piezoelectric seismic source to obtain P-wave velocity tomograms.
Additionally, we deployed a new type of borehole seismic source, know as an orbital vibrator, in
a crosswell seismic survey as part of the subsurface characterization program at this
contaminated groundwater site. This source, know as an orbital vibrator, allows simultaneous
acquisition of P- and S-waves. The orbital vibrator was developed for oil field applications and,
to our knowledge, this is the first environmental scale crosswell application. Both velocity and
attenuation tomograms have been calculated. The velocity tomograms show a relationship to
contaminant propagation in the groundwater (as measured by logs and cores). Zones of high
contaminant flow are consistent with zones of low velocity (both P- and S-wave) and high
attenuation. We believe horizontal fracture zones at the boundaries of basalt flows are
controlling the contaminant flow and the seismic properties. Additionally, high amplitude guided
waves are observed and we believe these waves delineate thin (l-2 m) zones of velocity contrast
which relate to fracturing and, in some instances, coincide with contaminate flow.
-
-
-
Reverse Vsps And Crosshole Seismic Tomography While Coring
Authors William P. Clement, Lee M. Liberty and Michael D. KnollAt the Boise Hydrogeophysical Research Site, numerous 20 m deep wells were continuously
cored with a split spoon sampler to detail geologic changes beneath the site. During the coring of
one of these wells, we recorded the energy radiating from the drill stem using a combination of
downhole hydrophones and surface geophones. The hydrophone strings were located in a pair of
adjacent wells and the geophones were located along the surface between these wells and the
well being cored. The experiment’s geometry provides a series of reverse VSPs and crosshole
tomographic data sets that can help distinguish P-wave velocity changes in the subsurface.
Energy from the core tip is not necessarily the first arrival. However, the near continuous
recording of the source as it penetrates the ground enables us to locate the energy from the core
tip. We also record energy when the source is in the vadose zone. Comparing the seismic while
coring results with a similar experiment using a borehole sparker source confirms the reliability
of recording seismic energy generated by the split spoon sampler. Core tip recording is an
inexpensive seismic method that has great potential for borehole-to-surface and crosshole
tomographic imaging at relatively large offsets in near-surface environments.
-
-
-
Surface And Borehole Seismic Characterization Of The Boise Hydrogeophysical Research Site
Authors Lee M. Liberty, William P. Clement and Michael D. KnollWe conducted borehole to borehole, borehole to surface, and surface seismic experiments
to optimize data acquisition parameters, obtain a seismic velocity model, and to characterize seismic
stratigraphic units in a shallow aquifer at the Boise Hydrogeophysical Research Site. The
aquifer consists of coarse (cobble-and-sand) fluvial deposits underlain by clay at 18-2 1.5 m depth.
We acquired data with a downhole seismic source (sparker), a sledge hammer source, a hydrophone
string, a borehole geophone, and a surface geophone array to compare seismic signal quality
and to place limitations on each seismic method. To fully characterize seismic reflections, the
source-receiver geometry is an important parameter for both borehole and surface experiments.
Direct arrivals and the presence of seismic reflections suggest a correlation between porosity
changes and seismic velocities at the site. We have defined four seismic stratigraphic horizons
that correlate with surface and borehole ground penetrating radar results, geophysical logs, and
lithologic logs. These results provide an initial framework for hydrologic modeling.
-