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6th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 18 Apr 1993 - 22 Apr 1993
- Location: San Diego, California, USA
- Published: 18 April 1993
61 - 65 of 65 results
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Two-Dimensional Subsurface Imaging With Transient Em For Mapping Of A Buried Dissolution Structure Near The Waste Isolation Pilot Plant
Authors Bryan A. James and David J. BornsA high density transient electromagnetic (TEM) survey carried out at the Waste
Isolation Pilot Plant (WIPP) has been interpreted using the TEM Two-Dimensional (2D)
Subsurface Imaging method. The purpose of the survey was to delineate a conductive zone
identified in the Rustler Formation, which overlies the waste storage panels and is thought
to coincide with a high hydraulic transmissivity zone indicated by hydrologic testing.
The TEM 2D Subsurface Imaging method is a new approach to TEM interpretation
that consists of two parts. First, the method interprets where distributed current flow, as a
function of time, is occurring in the subsurface. Secondly, an image resistivity section is
constructed from the interpreted current sections.
The interpretation of two high density data profiles identifies two conductive features
in the section overlying the Salado Formation, both trending roughly north-south. The
western anomaly lies in the lower half of the Dewey Lake Formation and is probably related
to perched water in the Dewey Lake. The eastern anomaly lies within the Rustler
Formation, probably the Culebra dolomite member, at a lateral offset to the east of the
storage facility of about 1500 meters, that is interpreted to be caused by active dissolution
processes in the Rustler. The Dewey Lake anomaly overlies the Rustler anomaly in part,
thus possibly suggesting a relationship between the two.
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Finding The Shallow West Valley Fault (Utah) By A Refraction Migration+Inversion Method
Authors Fuhao Qin, Wenying Cai and Gerard T. SchusterThe automated wavefront reconstruction method (Aldridge and Oldenburg, Geophysics
1992) uses a finite-difference solution to the eikonal equation (Vidale, Bull.
Seis. Sot. Am. 1988; Qin et al., Geophysics 1992) to downward extrapolate the
recorded refraction traveltimes from a forward and a reversed refraction shot gather.
The two extrapolated traveltime fields provide an image of the interface between the
overburden and the refractor based on a simple imaging condition. Another refractor
imaging method is refraction tomography, which inverts the refraction first arrival traveltimes
for the subsurface velocity. Both methods require the knowledge of the overburden
velocity distribution which can be obtained from the traveltime of near offset
direct waves. The velocity of the refractor can be found by inverting the backprojected
traveltime fields along the imaged interface.
The two methods are tested for several synthetic earth models, and results suggest
that both methods provide good 2-D images of the refractor. They also provide accurate
reconstructions of the refractor velocity. The advantage of the wavefront reconstruction
method is that it provides images with a higher signal to noise ratio, while
the advantage of the traveltime tomography method is that it is quite general and is not
restricted to a few homogeneous layers.
The wavefront reconstruction method and refraction traveltime tomography is tested
on refraction data from a shallow seismic survey conducted across the West Valley
Fault, Utah. The goal is to locate a shallow hidden normal fault (West Valley Fault,
Utah) by an inexpensive refraction survey. The reconstructed refraction image clearly
shows an interface discontinuity at the normal fault location. This conclusion is reinforced
by the consistent images for different combinations of migrated refraction and
traveltime tomograms from different reflection shot gathers.
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Modified Mise-A-La-Masse Measurements To Map Brine Invasion Beneath The Floor Of An Underground Excavation At The Wipp Site, Se New Mexico.
More LessAmodified mise-a-la-masse test survey was completed in Alcove
L-3 underground at the WIPP Site in SE New Mexico, to test whether
it is possible to map brine beneath the floor (invert). Two drill
holes into known brine pools were used as the local current source,
for two overlapping survey areas. Corrections were made for
variations in background noise and geometry.
The invaded brine appears to generally have accumulated to the
west of the center line of the Alcove. However, there seems to be
an influx of brine from a point on the east side of the Alcove. No
brine seems to have accumulated near the junction of the older main
access to the south end of the Alcove.
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Geophysical Investigation In Municipal Engineering
By Olli T. OkkoCombined resistivity and seismic soundings were applied very cost effectively to locate treatment
sites for municipal waste while enlarging the landfill area of the city of Hanko, which has been
founded on a very important ground water area at the most southern point of Finland on the Baltic
coast. The multielectrode resistivity scanner, which uses seismic cables with an electrode
separation of 2 men-es in the continuous vertical electrical sounding mode, was applied to correlate
the clay layers observed in several of the weight sounding tests drilled in a relative dense 50 m x
50 m grid. In the basically seismic refraction soundings, bedrock reflections were also analysed in
the digital records obtained from buffalo gun shots. The ground water table could be levelled
according to the shallow refractions. In the most effective field work mode the seismic surveys were
carried out while the scanner was obtaining the resistivity image. After this the electrodes were
replaced by geophones and the same seismic cables were connected to the resistivity scanner and
to the seismograph respectively in order to speed up the field work. On the basis of these
geophysical investigation results recommendations and instructions were given, including geoscientific
and environmental aspects of locating new facilities for waste management at the landfill area.
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Rapid Geophysical Surveyor
Authors L.G. Roybal, G.S. Carpenter and N.E. JostenThe Rapid Geophysical Surveyor (RGS) is a system designed to rapidly and economically collect
closely-spaced geophysical data used for characterization of Department of Energy (DOE) waste sites.
Geophysical surveys of waste sites are an important first step in the remediation and closure of these sites;
especially older sites where historical records are inaccurate and survey benchmarks have changed due to
refinements in coordinate controls and datum changes. Closely-spaced data am required to adequately
differentiate pits, trenches, and soil vault rows whose edges may be only a few feet from each other. A
prototype vehicle designed to collect magnetic field data was built at the Idaho National Engineering
Laboratory (INEL) during the summer of 1992. The RGS was one of several projects funded by the
Buried Waste Integrated Demonstration (BWID) program. This vehicle was demonstrated at the
Subsurface Disposal Area (SDA) within the Radioactive Waste Management Complex (RWMC) on the
INEL in September of 1992. Magnetic data were collected over two areas in the SDA, with a total survey
area of about 1.7 acres. Data were collected at a nominal density of 2!4 inches along survey lines spaced
1 foot apart. Over 350,000 data points were collected over a 6 day period corresponding to about 185
man-days using conventional ground survey techniques. This report documents the design and
demonstration of the RGS concept including the presentation of magnetic data collected at the SDA. The
surveys were able to show pit and trench boundaries and determine details of their spatial orientation never
before achieved.
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