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7th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 27 Mar 1994 - 31 Mar 1994
- Location: Boston, Massachusetts, USA
- Published: 27 March 1994
76 results
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Science The Law And Environmental Remediation
More LessModern science has evolved into the most powerful tool
ever developed by humans to understand the world in which
they live. That power has arisen by a unique combination of
success in making predictions, the ability to have its
conclusions falsified, and a public, peer reviewed system of
quality control. It is the public nature of science that
allows, indeed requires, the discovery of error to be used in
the search for truth. In the legal arena, the search for
truth takes on a different meaning.
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Pitfalls In Shallow Seismic Reflection
Authors Don W. Steeples and Richard D. MillerSubstantial progress has occurred during the past 15 years in development of shallow
CDP seismic-reflection techniques, but there are occasional interpretation problems with the
resulting data. We discuss examples of the pitfalls of the method, along with some procedures
to help avoid them. Problems that often occur include spatial aliasing of ground roll, interpreting
processed ground-coupled air waves as true seismic waves, misinterpreting refractions as
reflections on stacked CDP sections, and not recognizing processing artifacts. Aliasing occurs
when data are not sampled often enough in time and/or space. Decreasing the geophone interval
by a substantial amount (such as a factor of two) will improve coherency of a true reflector, but
will destroy coherency of spatially aliased ground roll. It is often difficult to separate shallow
reflections from shallow refractions during processing. Reflected energy from shallow depths
tends to have frequency content close to that of the direct wave and/or early refracted arrivals on
field seismograms. Refractions on a stacked section tend to be a bit lower in frequency because
the NM0 correction in a CDP stack assumes hyperbolic moveout, while refractions arrive as a
linear time-distance function. Hence, they don’t stack as coherently as reflections, which
decreases their frequency. Processing artifacts from inadequate velocity analysis and inaccurate
static corrections are at least as troublesome on shallow reflection sections as they are on classical
reflection surveys from petroleum exploration. It has been our experience that occasional field
records will display unusually good reflections. These field seismograms can be used to
correlate to the processed seismic sections. Unequivocally separating shallow reflections from
shallow refractions is clearly one of the major limitations of the shallow-seismic reflection
method at present.
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Assessing The Role Of Infield Resistivity Image Processing In Shallow Subsurface Investigations
By Max A. MejuReal-time image processing is desirable in any field survey as it enables the success of the
experiment to be assessed on the spot and leads to a cost-effective survey since the experimental
geometry may be changed to attain the desired goals or the optimum depth of exploration. The
specific roles played by a novel imaging algorithm in optimizing survey design parameters, data
quality control, target definition and increased productivity are emphasized using examples drawn
from shallow dc and TEM investigations of glacial overburden, an old landfill site, complex
bedrock topography and underground mine workings. The effectiveness of this imaging tool is
gauged by comparison with borehole data and suggestions are offered for optimizing shallowdepth
surveys.
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Use Of Fractal Dimension To Determine The Applicability Of Euler’S Homogeneity Equation For Finding Source Locations Of Gravity And Magnetic Anomalies
By D. RavatSelection of the proper anomaly attenuation rate (also known as the structural index) in the
Euler’s Homogeneity Equation (EHE) computations for determining source locations of potentialfield
anomalies is investigated using calculations of fractal dimension. Theoretical examples are
provided to show that the use of the EHE method is valid only when the anomaly attenuation rate
can be regarded as being nearly constant (in other words, when the anomaly has nearly constant
fractal dimension with respect to its source over the distance range of interest). When this condition
is satisfied, the EHE method can yield useful source locations from well-isolated potential-field
anomalies. Residual magnetic anomalies from 12 steel drums show that the anomaly attenuation
rates vary as a function of source-to-observation distance. With increasing source-to-observation
distance, attenuation rates of most of the investigated drums also show a strong tendency to reach a
value appropriate for a magnetized dipole (n = 3). This precludes the use of an identical attenuation
rate for all drums at all depths of interest.
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Site Characterization At The Rabbit Valley Geophysics Performance Evaluation Range
Authors Steven Koppenjan and Michael MartinezThe United States Department of Energy (U.S. DOE) is developing a Geophysics Performance Evaluation
Range (GPER) at Rabbit Valley located 30 miles west of Grand Junction, Colorado. The purpose of the range is
to provide a test area for geophysical instruments and survey procedures. Assessment of equipment accuracy and
resolution is accomplished through the use of static and dynamic physical models. These models include targets
with fixed configurations and targets that can be re-configured to simulate specific specifications. Initial testing
(199 1) combined with the current tests at the Rabbit Valley GPER will establish baseline data and will provide
performance criteria for the development of geophysical technologies and techniques.
The U.S. DOE’s Special Technologies Laboratory (STL) staff has conducted a ground penetrating radar
(GPR) survey of the site with its stepped FM-CW GPR. Additionally, STL contracted several other geophysical
tests. These include an airborne GPR survey incorporating a “chirped” FM-CW GPR system and a magnetic survey
with a surfaced-towed magnetometer array unit. Ground-based and aerial video and still frame pictures were also
acquired. STL compiled and analyzed all of the geophysical maps and created a site characterization database.
This paper discusses the results of the multi-sensor geophysical studies performed at Rabbit Valley and the
future plans for the site.
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Surface Wave Imaging Of Shallow Refraction Data In Mexico City Basin
A good knowledge of the elastic properties of shallow stratigraphy is fundamental to understand
and simulate the strong ground motion characteristics of recent earthquakes recorded by the
Mexico City accelerometric array. Accordingly, we are interested in determining shear (S) wave
velocities at some sites to correlate them with those of inhabited zones of the city. Despite
population density and paved surfaces, it is feasible to gather shallow refraction data and obtain
laterally homogeneous subsoil structures at some locations. We recorded Rayleigh and Love
surface waves using explosive and sledgehammer sources and low frequency vertical and
horizontal geophones, respectively. We focused our analysis in the Texcoco Lake region,
northeastern Mexico City basin. This area consists of unconsolidated clay sediments similar to the
ones of the lake bed zone in Mexico City, where ground motion amplifications and long durations
are commonly observed. We obtained phase velocity dispersion curves from ray parameterfrequency
domain analyses and inverted them for vertical distribution of S wave velocity. The
initial model was provided by standard first break refraction analyses. We obtained a very good
agreement between theoretical and observed dispersion curves for a two-layer model with
thicknesses of 18 and 46 m and S-wave velocities of 35 and 85 m/s, respectively, underlain by a
halfspace with S-wave of 200 m/s. Results compare well with tilt and cone resistance
measurements for the same area, emphasizing the importance of this kind of studies for
engineering purposes.
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The Use Of Shallow Seismic Techniques To Target Subsurface Mine Voids For Installation Of Monitoring Wells
Authors K.K. Cohen and J.G. DonahueA Superfund waste disposal site in western Pennsylvania was the location of a recent shallow seismic
survey conducted with the objective of detecting subsurface mine voids for the installation of
groundwater monitoring wells. Waste was disposed between 1950 and 1964 along benches of an
abandoned strip mine; the highwall of this mine also contained drift openings into an underground mine.
The waste contained mobile organic contaminants which entered the underground mine and migrated
down gradient from the disposal site. The remediation design for the site required the installation of
monitoring wells drilled to the underground mine voids; these wells would be used to determine the
extent of the organic contaminants and to monitor the efficacy of the cleanup efforts. Site stratigraphy
was determined from pre-existing monitoring wells and consists of 3-5.5 m (lo-15 ft) of unconsolidated
overburden overlying Pennsylvanian-aged interbedded shale, siltstone, sandstone, and coal. Although
mine maps were not available, information from the existing monitoring wells suggested the mine
workings in the Pittsburgh coal were at a depth of 35 m (100 ft). Excavation of a nearby underground
mine indicated that mine entries could be as little as 3.5 m (10 ft) wide and 1.5 m (5 ft) high. A seismic
survey conducted at the site used the common offset technique and a 24-channel seismograph.
Anomalies in the seismic records marked by loss of signal coherency were identified as representing
mine voids. On the basis of these results, seven target sites were selected. Three monitoring wells were
drilled at three of these sites and all wells encountered mine voids.
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A Detailed Ground Penetrating Radar Investigation Of A Coastal Barrier Spit, Long Beach, Washington, U.S.A.
Authors Harry M. Jol, Richard A. Meyers, Don C. Lawton and Derald G. SmithA regressive modern barrier spit at Willapa Bay, Washington (north of the
Columbia River mouth) is influenced by a 4 m tidal range (spring), high energy,
longshore transport and high wave energy depositional processes. The spit is 38 km
long, up to 5 km wide and is composed of medium-grained beach sand. The spit has
a freshwater aquifer recharged by rainfall. Results from a ground penetrating radar
(GPR) test indicate a shingle-like accretionary depositional pattern of beach and
upper shoreface reflections which dip towards the ocean at about one degree. The
loss of radar signal from below 7-11 m deep may indicate either a brackish/saline
water zone or a major lithofacies change.
PulseEKKO™ IV GPR reflection profiles, with antennae frequencies of 25, 50,
100 and 200 Mhz, were obtained along a main test line. Both 400 v and 1000 v
transmitters were used. In addition, 100 MHz antennae were used for collecting a
detailed grid of data (50 x 50 m, sampled every metre), a multifold dataset and
antennae orientation tests. The grid pattern data provides a detailed view of the
three-dimensional geometry of individual facies units.
Results from the present study demonstrate that the 200 MHz antennae
showed high resolution within the top 5-6 m, while the 25 and 50 MHz antennae
showed deeper penetration to 12-13 m. For this study site, the 100 MHz antennae
provided acceptable resolution, continuity of reflections and penetrated (7-8 m) to
the base of the dipping beach beds. The dip profiles show a shingle-like accretionary
depositional pattern while the strike profiles show a horizontal and subhorizontal,
nearly continuous reflection patterns.
The parallel broadside and perpendicular broadside antennae orientation tests
showed detailed stratigraphy, continuity, and depth of penetration, while cross
polarization tests exhibited reduced continuity of reflections and less depth of
penetration, but dipping reflections were apparent.
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Geophysical Observations Of Geological, Hydrological And Geochemical Heterogeneity
More LessThe single largest uncertainty in determining the success of remediating
environmental contamination problems results from inability to quantify and descrtbe the
natural variability within the earth --- geological, hydrological and geochemical
heterogeneity (Schwartz and others, 1990; Sudicky and Huyakorn, 1991). Heterogeneity IS
a natural result of the properties of geological materials and the processes that create and
modify them. It has been known for years that the single largest uncertainty in determining
the success of petroleum recovery is geological heterogeneity (Dickey, 1986), resulting in
increased emphasis on reservoir characterization (Lake and Carroll, 1986). Increased
emphasis on site characterization is the natural parallel attack on the problems caused by
heterogeneity in environmental remediation.
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Shallow Geophysics In A Hydrogeological Investigation Of The Oak Ridges Moraine, Ontario
Authors S.E. Pullan, A. Pugin, L.D. Dyke, J.A. Hunter, J.A. Pilon, B.J. Todd, V.S. Allen and P.J. BarnettIn 1993, the Geological Survey of Canada launched a three year program to investigate the
hydrogeology of the Oak Ridges Moraine. This feature is a major recharge/aquifer system
affecting over 3 million residents in the greater Toronto area. The moraine is on the order of
160 km in length, covers approximately 1500 square kilometres, and in places the thickness of
overburden exceeds 200 metres. Because of the size of the feature, three type areas have been
selected for investigation. Extensive use of shallow geophysical surveys is planned before
deciding on the most strategic locations for drilling a number of boreholes.
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Integrated Use Of Electromagnetic Methods For Hydrogeological Investigations
Authors Niels B. Christensen and Kurt I. SørensenThe widespread problems with the quality of ground water call for a much more detailed and
regional covering with geophysical data when performing a hydrogeological investigation. This demands
that efficient methods for measurement and for interpretation are developed, and the strategic aspects of
data collection and interpretation become important. We present two novel electromagnetic methods:
the pulled array continuous electrical profiling and the Ellog auger drilling method, which together with
traditional transient electromagnetic soundings and geoelectrical soundings can be combined into an
efficient scheme for hydrogeological investigations. It is shown how the dense data coverage obtainable
with the combined methods can deliver the detailed knowledge desired, and how the quality and the
dependability of the data are much improved.
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Geophysical Well Logging And Pumping Water Column Sampling For Radionuclide Reduction Studies In Municlpal Wells
By John JansenSeveral hundred municipal wells producing from the Cambro-Ordovician aquifer in the upper
midwest exceed the USEPA interim standard of 5 pCi/l for combined Ra(226) and Ra(228).
Numerous geophysical logging studies were performed to determine if the Radium
concentration could be reduced in these wells by isolating discrete portions of the aquifer with
casings or liners. This paper presents the results of a study of two municipal wells in Ottawa,
Illinois that demonstrate some of the methods tested.
Well 12 was drilled in 1989 to a depth of 1200 feet with surface casing to 427 feet. The
well was initially tested at 1200 gpm with 7.1 pCi/l of total Radium. A suite of well logs,
consisting of dual induction, neutron density, gamma density, and spectral gamma logs, was
run to identify water bearing formations which may contain high levels of Uranium or Thorium,
the precursors of Ra(226) and Ra(228). A zone of the Oneota Dolomite between 530 to 580
feet was found to have relatively high effective porosity with moderately elevated levels of
Uranium and Thorium. A surface casing with packer was installed to a depth of 600 feet to
isolate the unit. The well was test pumped at 500 gpm for 20 hours with a 4% reduction in
specific capacity and a total Radium level of 4.8 pCi/l, a reduction of 32%.
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Using Geophysical Techniques To Control In Situ Thermal Remediation
More LessMonitoring the thermal and hydrologic processes that occur during
thermal environmental remediation programs in near real-time provides
essential information for controlling the process. Geophysical techniques
played a crucial role in process control as well as for characterization during
the recent Dynamic Underground Stripping Project demonstration in which
several thousand gallons of gasoline were removed from heterogeneous soils
both above and below the water table. Dynamic Underground Stripping
combines steam injection and electrical heating for thermal enhancement
with ground water pumping and vacuum extraction for contaminant
removal. These processes produce rapid changes in the subsurface properties,
including changes in temperature, fluid saturation, pressure and chemistry.
Subsurface imaging methods are used to map the heated zones and control
the thermal process.
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Monitoring Of Deep Well Injection Of Hazardous Material
Authors Robert J. Withers and Richard G. KeckIn the fall of 1993 ARC0 performed a field demonstration of technology to
predict and monitor hydrofracture injection of industrial waste solids and liquids.
Results of this test show it is feasible to inject large quantities of simulated waste
at pressures above those required to fracture the formation, while
simultaneously verifying containment within sealing horizons. This application
of hydraulic fracturing may provide an alternative to existing methods of waste
disposal.
Three wells were drilled and instrumented with geophones along one wing of
the predicted fracture wing at an East Texas site. A total of 4 million lbs of solid
and 2.1 million gallons of inert nonhazardous material was injected over a 5 day
period. The fracture growth was monitored using a variety of diagnostic
techniques: passive borehole seismic monitoring, an active surface seismic
technique, surface tiltmeters, and routine logging techniques, The fracture
height, a critical parameter for disposal applications, was monitored by
triangulation, noise logs and minimum time analysis of the acoustic emissions in
near real-time at the well site. The results analyzed to date convincingly showed
containment within the bounding shale layers.
The purpose of the program was to verify that ARCO’s state-of-the-art fracture
models successfully predict the containment parameters of a proposed fracture.
This paper will present the results of the program to design the wells and to
monitor the fracture evolution with the various seismic techniques. Analysis of
the numerous phases observed in the fracture process will also be presented.
The process to obtain regulatory approval of fracturing for waste disposal
applications is ongoing, based in part on the success of this carefully documented
test.
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The Application Of High Resolution Shear Wave Seismic Reflection Surveying To Hxdrogeological And Geotechnical Investigations
Authors John C. Clark, William J. Johnson and William A. MillerThe seismic reflection technique is the mainstay of oil and gas exploration, but has seen to date
relatively few engineering and environmental applications. The high cost of achieving high
resolution in the shallow subsurface and relatively low borehole costs (when compared to oil and
gas wells), restricts the seismic reflection technique from being a more widely used exploration
tool.
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Use Of Geophysical Methods To Refine Geological Site Characterization At An Eastern Nebraska Landfill - A Case History
Authors Edward P. Pedersen and David ButlerThe goal of this project was geological site characterization of a closed landfill in eastern
Nebraska. Geologic characterization is essential to the interpretation of the spatial
distribution of aquifer characteristics. The desired final result of the geological
characterization was collection of sufficient data to locate monitoring wells for long-term
study of ground water quality.
A phased approach of geological characterization was conducted at the site. The first phase
consisted of a detailed review of the existing geologic data. Included in this review were
regional geologic references, data from geotechnical borings in and adjacent to the landfill
area, driller’s logs and water level data from nearby irrigation and water wells, and limited
surface exposures. This review resulted in the development of a preliminary five-layer
geologic model and identification of obvious data gaps.
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Ground Penetrating Radar Surveys Over An Alluvial Dnapl Site, Paducah Gaseous Diffusion Plant, Kentucky
Authors P.J. Carpenter, W.E. Doll and B.E. PhillipsGround penetrating radar (GPR) surveys were used to map shallow sands and gravels which are
DNAPL migration pathways at the Paducah Gaseous Diffusion Plant in western Kentucky. The
sands and gravels occur as paleochannel deposits, at depths of 17-25 A, embedded in Pleistocene
lacustrine clays. More than 30 GPR profiles were completed over the Drop Test Area (DTA) to
map the top and base of the paleochannel deposits, and to assess their lateral continuity. A
bistatic radar system was used with antenna frequencies of 25 and 50 MHz. An average velocity
of 0.25 ft/ns for silty and clayey materials above the paleochannel deposits was established from
radar walkaway tests, profiles over culverts of known depth, and comparison of radar sections
with borings. In the south portion of the DTA, strong reflections corresponded to the water table
at approximately 9-10 ft, the top of the paleochannel deposits at approximately 18 ft, and to
gravel horizons within these deposits. The base of these deposits was not visible on the radar
sections. Depth estimates for the top of the paleochannel deposits (from 50 MHz records) were
accurate to within 2 ft across the southern portion of the DTA. Continuity of these sands and
gravels could not be assessed due to interference from air-wave reflections and lateral changes in
signal penetration depth. However, the sands and gravels appear to extend across the entire
southern portion of the DTA, at depths as shallow as 17 ft. Ringing, air-wave reflections and
diffractions from powerlines, vehicles, well casings, and metal equipment severly degraded GPR
profiles in the northern portion of the DTA; depths computed from reflection times (where
visible) were accurate to within 4 ft in this area. The paleochannel deposits are deeper to the north
and northeast where DNAPL has apparently pooled (DNAPL was not directly imaged by the
GPR, however). Existing hydrogeological models of the DTA will be revised with the newly
defined extent and depth of these sands and gravels.
Note: The submitted manuscript has been authored by a contractor of the U.S. Government
under contract No. DE-ACO584OR21400. Accordingly, the U.S. Government retains a
nonexclusive, royalty-free license to publish or reproduce the published form of this
contribution, or allows others to do so, for U.S. Government purposes.
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Earthquake Ground Motions For Application In Landfill Design
Authors George C. Klimkiewicz and R. NewmarkThe U.S. Environmental Protection Agency (EPA) recently established revised
minimum national criteria for seismic design of municipal solid waste landfills.
Specifically, Title 40 of the Code of Federal Regulations, Part 258, requires
as of October 9, 1993 that all landfills be designed to withstand the impact of
earthquake ground motions for the case that the containment structures are
located in a seismic impact zone, In $258.14, a seismic impact zone is defined
as “an area with a 10% or greater probability that the maximum horizontal
acceleration in lithified earth material, expressed as a percentage of the
earth’s gravitational pull (g) will exceed O.lOg in 250 years.” Location of the
landfill site in a seismic impact zone can be established from a published
seismic hazard map, or through a site-specific seismic hazard assessment.
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Borehole Induction Logging For The Dynamic Underground Stripping Project Llnl Gasoline Spill Site
By S. BoydBorehole induction logs were acquired for the purpose of characterizing
subsurface physical properties and monitoring steam clean up activities at the
Lawrence Livermore National Laboratory. This work was part of the Dynamic
Underground Stripping Project’s demonstrated clean up of a gasoline spill. The
site is composed of unconsolidated clays, sands and gravels which contain
gasoline both above and below the water table. Induction logs were used to
characterize lithology, to provide “ground truth’ resistivity values for electrical
resistance tomography (ERT), and to monitor the movement of an underground
steam plume used to heat the soil and drive volatile organic compounds (VOCs)
to the extraction wells.
Induction logs collected before steaming show close correlation with
lithology and are useful for identifying the more permeable zones. The sands and
gravels are readily identified by a relatively high resistivity as compared to the
silts and clays. During the steam injection phase, subsurface temperatures were
monitored and induction logs were obtained periodically. The resistivity
decreases throughout the heated zone. Subsurface resistivities typically dropped
by a factor of two or more as the subsurface temperature increased to more than
1OOoC. Contour plots of the induction data from several of the monitoring wells
also indicate regions and depths of low resistivities corresponding with the
steam saturated gravels. In the fine-grained silts and clays, the decrease in
resistivity is primarily a result of temperature effects; in the coarser-grained
sediments, both the fluid saturation and chemistry change as well as the
temperature, resulting in lower resistivities (Newmark and Wilt, 1992).
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Seismic Measurements Of Ground Displacements At The Superconducting Super Collider Site
Authors Dale Morgan and David LesmesIn November 1993 the United States Congress ordered the Department of Energy to halt
construction on the muti-billion dollar superconducting super collider (SSC) which was being built
in the state of Texas. The SSC is an oval shaped ring, which is 53 miles in circumference. The ring
is centered upon the town of Waxahachie, which is located approximately 30 miles south of Dallas
A design limit of the SSC is that the ground vibrations must be less than 5.0 x 10e4 inches. As part
of a preliminary site investigation, the Department of Geophysics at Texas A&M University was
contracted by the State of Texas to measure near surface ground displacements at the proposed
SSC site. Seismic measurements of ground velocity were made, both at the surface and within
boreholes, at several sites within the survey area Through a series of data processing steps the
ground velocity measurements were transformed into ground displacements. Results from this
study show that the primary sources of ground vibrations in the area are blasts at a nearby quarry
and vibrations caused by trains at railroad crossings. Both of these noise sources posed potential
problems which would have to be addressed in the construction of the SSC.
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Digital Impulse Radar And Sonic Testing Of Bridges
Authors M.C. Forde and A.J. BatchelorDigital non-destructive testing techniques available in both the time and frequency domains
are outlined: including digital sonic echo testing, digital sonic frequency domain testing
and digital time domain radar testing. The new non-destructive evaluation techniques are
described in relation to applications to concrete foundation piles and masonry bridges. A
comparison of the techniques with those applied to concrete structures is made.
Case studies are used to illustrate that the techniques of digital sonic impulse hammer
testing and digital impulse radar testing are complementary in nature and can be used to
cost effectively identify the geometries of piles and masonry bridges in addition to fault
detection and location.
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Unconventional Applications Of Terrain Conductivity Logging To Groundwater Investigations
Authors Paul Bauman, Janan Sallomy, Mike Brewster and Anthony BrownConventionally, terrain conductivity logging is used in hydrogeologic studies to map groundwater
contaminant plumes of elevated total dissolved solids (TDS). While well-suited to this
application, terrain conductivity logging is also a tool useful for approaching a wide variety of
other groundwater studies. In this paper, four case studies illustrate the application of borehole
electromagnetic (EM) logging to four different problems. The first case study of EM logging iS
used to identify fractured zones in an otherwise homogeneous cemented sandstone aquifer. The
second case study uses EM logging to establish the connectedness of a fracture or fractures
between two monitoring wells. In the third study, multiple aquifers overlooked during drilling are
clearly delineated by terrain conductivity logging. In the final study, EM logging is used to
describe and delineate paleochannel deposits which are controlling contaminant migration. All
of the above studies are related to light non-aqueous phase liquid (LNAPL) remediation projects.
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High Resolution Flowbeter Lqgging - A Unique Cobbination Of Borehole Geophysks And Hydraulics; Part I: Flwbetrr Techniques And Equipment Deveu)Phent
Authors Robert Crowder, Frederick Paillet and Alfred HessHigh resolution flow logging has the potential to significantly improve
geophysical interpretations in ground-water studies. Surface geophysical
soundings, borehole-to-borehole tomography, and conventional geophysical
logs all provide techniques for the non-invasive characterization of
aquifers on different scales. These techniques generally characterize
aquifers in terms of physical properties such as electrical conductivity or
seismic attenuation that are only indirectly related to hydraulic
parameters. However, borehole flowmetering is a technique included in the
standard suite of well logs that can provide a direct measurement of the
hydraulic properties of sediments and'fractured rocks adjacent to boreholes.
For many years the resolution of available flowmeters severely limited the
application of flowmeter logs in aquifer studies. As a result of recent
emphasis on the application of well logging techniques to aquifer
contamination and remediation projects, a number of different flowmeters
with the potential for making much more accurate flow measurements than
previously possible have been produced. These include techniques based on
laser and acoustic Doppler, electromagnetic, heat-pulse, fluid conductivity
profile, and acoustic scattering measurements.
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High-Resolution Flowmeter Logging - A Unique Combination Of Borehole Geophysics And Hydraulics: Part Ii - Borehole Applications With The Heat-Pulse Flowmeter
Authors Frederick Paillet, Robert Crowder and Alfred HessA number of recently-developed high-resolution flowmeter logging
techniques are described in the well logging literature. These techniques are
now or soon will be capable of measuring flows corresponding to less than 0.01
gallons per minute of borehole discharge. Such measurements have the
potential to significantly improve the interpretation of geophysical logs in
ground water studies by showing how geological structure indicated on logs and
tomographs is related to hydraulic properties of beds, solution openings and
fractures. The potential benefits of such borehole measurements are
illustrated by the results obtained with the U.S. Geological Survey heat-pulse
flowmeter. One of the most potentially useful applications of high-resolution
borehole flow measurements is associated with the disturbance to aquifer
hydraulics induced by the presence of an open borehole. This effect can be
modeled and analyzed to provide a controlled test of aquifer response to
disturbance. Flow measurements can also indicate ground water flow in the
vicinity of the well bore during short, low-capacity aquifer tests. A number
of researchers have shown how such flowmeter profiles can be analyzed to give
rigorous profiles of permeability and specific storage in situ. At the same
time, monitoring of flow transients in cross-borehole pumping tests may be
formulated as a hydraulic tomography study. One useful application of flow
logging is the quick and definitive assessment of flow connections between and
around boreholes within hours after the completion of drilling. Such
measurements could greatly reduce the time and effort involved in the
otherwise expensive and labor intensive procedures of conventional hydraulic
testing and tracer studies.
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Monitoring Well Completion Evaluation With Borehole Geophysical Methods
Authors Robert Crowder and William HenrichGeophysical logs amenable to the evaluation of well completion features in monitoring wells
have included acoustic, gamma-gamma dual density, natural gamma, caliper and video. Well
completion features surveyed have consisted of validation the vertical position and physical
integrity of slotted micro screen and the identification and extent of annular materials behind casing
such as sand pack, bentonite seals and sanitary cement grout seals.
Traditional oil field logging methods of well evaluation such as the Cement Bond Log
(acoustic) can be used under certain conditions in PVC cased monitoring wells, however the
interpretation emphasis is placed on acoustic velocity as a diagnostic means to identify various
annular materials. This is in contrast to oil field cement bond log methodology which focuses on
amplitude reduction in the first sonic wave arrivals as a measure of 1) the presence of cement
grout and 2) subjective estimate of the degree of bond (e.g. casing to cement, cement to
formation). These interpretation disparities are primarily the result of differences in construction
materials, geologic setting and construction procedures between oil & gas well and environmental
monitoring wells.
A number of case histories utilizing acoustic, gamma-gamma dual density and natural
gamma logs are presented to show well completion aspects of polyvinyl chloride cased monitoring
wells in a variety of shallow geologic settings. The case histories show the importance of
combining complementary logging techniques to help validate final interpretation and demonstrate
certain limitations and constraints characteristic of geophysical methods in general.
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Modeling Borehole Stoneley Wave Propagation Across Permeable In-Situ Fractures
Authors C.H. Cheng and X.M. TangThe characterization of the hydraulic transmissivity of permeable fractures is a very important
task in the study of ground water flow in basement rocks. Previous studies that model the permeable
structure as a single fluid-filled fracture failed to explain the observed significant Stoneley
wave attenuation across the permeable structure. In this paper, the structure is modeled as a
permeable fracture zone. The results show that Stoneley waves can be strongly attenuated or
even eliminated without significant reflection, because of the dissipation of wave energy into the
permeable zone. Three field cases are modeled and the theoretical results are compared with
the field data. It is shown that low- and medium-frequency Stoneley waves (1 - 5 kHz) are very
sensitive to the permeability of the fractures and can be used to assess permeability from in-situ
logging data, if the fracture porosity and zone thickness can be measured. At higher frequencies,
however, Stoneley waves are not very sensitive to permeability but are mainly affected by the sum
of the fracture openings expressed as the product of fracture zone thickness and porosity in the
fracture zone. This finding is demonstrated by a logging data set obtained using high-frequency
Stoneley waves at 34 kHz.
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Use Of Borehole Electromagnetic-Induction And Natural-Gamma Logs To Delineate A Contaminant Plume In Ground Water
More LessElectromagnetic-induction and natural-gamma borehole logs were used to delineate the
vertical extent of contamination in ground water at a former plating facility. The facility
discharged plating wastes, including volatile organic compounds and numerous metals, into
unlined lagoons. These wastes leached into an unconsolidated glacial aquifer and formed an
electrically conductive contaminant plume that is flowing towards surface-water bodies.
Electromagnetic-induction and natural-gamma borehole surveys were conducted in eight
monitoring wells to delineate zones of electrically conductive ground water indicative of the
contaminant plume. Three contaminated zones delineated at two wells immediately
downgradient of the plating facility were 5 to 15 ft thick. At monitoring wells farther
downgradient from the site, contaminant zones were more than 20 ft thick in places.
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Analysis Of Wellbore Image Data Applied To Environmental And Geotechnical Case Studies
Authors Colleen A. Barton and Jerry WrightThe application of borehole televiewer (BHTV) data analyses recorded in the shallow crust
to environmental and hydrological investigations is fourfold: 1) fracture characterization, 2) in-situ
stress measurement, 3) providing site geologic and lithologic constraints, and 4) geotechnical
monitoring. One of the primary uses of the borehole televiewer data since the tool became
operational in geophysical logging has been measurement of the orientation and distribution of
planar features in a drillhole. The resolution of the borehole televiewer is capable of detecting a
wide range of fracture sizes and these data can provide a wealth of information pertinent to
understanding the mechanical behavior of the Earths crust at a drillsite. Fractures provide
permeable pathways for fluids and affect rock properties by chemical alteration of the surrounding
rock mass. Fracture geometry is therefore important to fluid flow and permeability in reservoirs
and waste disposal sites and to the safety of groundwater aquifers. In situ stresses play a major
role in the stability of natural and man made structures. The measurement of stress orientation and
magnitude, possible through the analysis of BHTV image data, can provide information about the
ambient tectonic stresses and information crucial to the design, construction and monitoring of
dams, tunnels or aqueducts. Stress orientation and magnitude also has a major impact on the
development of natural fractures and subsequent movement along preexisting fault surfaces. In
shallow crustal wells the constraints placed on in-situ stress from the analysis of BHTV data are
important to interpreting the interaction between pore pressure and hydrostatic pressure in a well
and subsequent wellbore stability.
Case studies from wells that exemplify the application of BHTV data analysis to
geotechnical and environmental issues are presented. The first study involved in the siting and
construction of a major aqueduct/tunnel in central Utah. The objectives of this study were to
characterize the natural fractures within the shallow crust at the drillsite and to determine the
orientation of in-situ stresses. A second study, conducted in two phases, concerned the analysis of
fractures developed in a concrete dam abutment in Colorado. Detailed measurements of the aperture
of fractures detected by BHTV imaging were made at a ten month interval to help establish the
integrity of the dam. Finally, a study of wellbore image data recorded at county landfill in Oregon
was performed to measure the orientation, aperture and depth distribution of fractures at the site.
The image data was used in conjunction with geophysical logs to discriminate between bedding
plane fractures and through-going fractures in siltstone units and fractures in basalt units.
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Downhole Shearwave Studies Enhanced By Gamma Log Litholocic Interpretations
Authors Alan C. Samuelson, Donald L. Eggert and William R. EckhoffOver the past fifteen years the Indiana Geological Survey has routinely used gamma logs in
its investigations of unconsolidated sediments: These logs have become powerful tools that allow
interpretation of the distribution of particle sizes in a sedimentary column. Thus, interpretations of
the depositional setting and correlations of Quaternary deposits have been improved.
In 1990 the Indiana Geological Survey began investigation of the particle and shearwave
velocity of Quaternary deposits in Indiana as part of the Survey’s seismic hazards reduction program.
Over a hundred downhole velocity records from southern and central Indiana have been recorded
and analyzed over the past three years. Each of these holes have been gamma logged. Based on
sample description and log signatures; eolian, Iacustrine, fluvial, and glacial till deposition have been
recognized.
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Preliminary Results Of A Seismic Borehole Test Using Downhgle Shaped Charges At The Doe Hanford Site
Authors Susan Narbutovskih and Finn MichelsenGeophysical site characterization studies can be important steps in the process of designing and
monitoring remediation at hazardous waste storage facilities. However, use of seismic techniques for
subsurface characterization at the DOE Hanford Site has been limited for several reasons. One reason
is the lack of borehole velocity control, which is valuable to the development of initial geologic
models and seismic data processing. Current drilling procedures result in steel-cased boreholes which
are poorly coupled to the surrounding sediments. In addition, these low-velocity sediments are highly
attenuative. Consequently, standard techniques to provide velocity control are not adequate. Both
Vertical Seismic Profiling (VSP) and reversed VSP (RVSP) surveys are currently being investigated
to provide velocity control and for subsurface imaging capabilities.
Recently a jet perforating gun was used to perforate a double-cased borehole in the 200 West Area.
During this operation, acoustic emissions were recorded from numerous depths to obtain velocity
control for a previous surface survey conducted in the same area. Both P- and S-wave data were
recorded simultaneously from multiple horizons using the DAS-1 seismograph and 3-component
geophones. The data were analyzed for a variety of uses besides velocity control. Signal attenuation
was studied as a function of source depth and offset distance to evaluate formation absorption while
vertical resolution was determined from the frequency spectrum.
Preliminary results indicate that adequate P-wave velocity control can be obtained even though the
near-surface sediments are very attenuative. However, we conclude that the perforating gun produces
little SH energy. Preliminary velocities indicate that reflection coefficients should be great enough to
use surface techniques. Results from the frequency study suggest that a swept source for both surface
and borehole surveys may be necessary to obtain required resolutions. Finally, signal attenuation as a
function of formation facies suggest that seismic techniques may be useful in mapping perched water
zones and for long term vadose zone monitoring.
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Resistivity Surveying For Planning Of Infrastructure
Authors Torleif Dahlin, Sam Johansson and Ola LandinResistivity surveying can play an important role for providing a geotechnical planning basis
for infrastructure projects if used in an early stage of the pre-investigations. The result can
then guide the selection of geotechnical drilling and sounding points, to ensure that the
selected points are representative. It can also decrease the total number of drilling points
needed. In order to be an attractive method which complements the traditional geotechnical
methods resistivity surveying has to give an area1 cover, be economically efficient and provide
easily accessible presentations. This in turn makes it necessary to automate data collection,
interpretation and presentation as far as possible, and an approach for this is presented
together with results from two field sites.
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Urban Geophysics - Seeking The Difficult And Hidden
Authors P.J. Fenning, D. McCann and K. VenessEnvironmental Geophysics is defined by Steeples and Miller
(1993) as the use of geophysical measurements of part of the
earth to evaluate or remediate problems in the earth's
environment. A reveiw of environmental geophysical literature
shows a substantial pre-occupation with localities or targets
that will require future remediation. Greenhouse (1992)
comments that the term environmental geophysics is "not
descriptive so much of methodology or target as it is of a
context. It is usually practiced in association with
hydrogeology and hydrogeologists.
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Sasw & Gpr To Detect Buried Objects
Authors Naser Al-Shayea, Richard Woods and Park GilmoreThe spectral-analysis-of-surface-waves (SASW) technique is compared with the ground
penetration radar (GPR) method for detection of buried objects. Tests were performed in a 7 m
diameter by 2 m deep sand bin in the G. G. Brown Lab of the University of Michigan. The bin is
filled with uniform silica sand compacted to a uniform density of about 16 kN/m³. During the
filling process, a three-cell void was buried at a depth of 305 mm to the top in the center of the bin.
SASW and GPR tests were performed with all three cells empty, one cell (center cell) empty, and
all cells full of sand. The two experimental techniques are being compared with each other for
eflicacy of void detection.
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Locating Railroad Track Bed Subsurface Defects Utilizing Nondestructive Remote Sensing Technologies
Authors Richard J. Graf, Leann M. Forister and Gary J. WeilThe railroad is a vital transportation link with tracks traversing thousands of miles throughout the United States.
When this link fails, the resultant damage costs millions of dollars. Track failure, attributed to moisture trails and
erosion voids in the rock ballast and subsoils that support the tracks, slowly deteriorate the railbed to a critical
point in which iron rail shifts occur. All railroad lines experience failures on a regular basis, but the recent Flood
of ‘93, that inundated thousands of square miles of land and hundreds of miles of railroad tracks in the midwestem
United States, brought a new impetus to quickly locate and repair these hidden subsurface defect areas.
This paper illustrates a new technology combination of nondestructive, remote sensing Computer Enhanced
Infrared llennography and Ground Penetrating Ruder that was used to detect buried moisture trails and erosion
voids of railroad track beds. This technology combination is described in theory and by discussion of a case study
based upon a successful project, conducted immediately following the flood, for Burlington Northern Railroad.
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Automated, Rapid, Comprehensive Non-Destructive Tunnel Testing
Authors P. Fisk, R. Holt, H. Russell and B. BohlkeAutomated seismic/sonic wave velocity, frequency and reflection measurements and radar profiling
measurements are obtained to provide a rapid, comprehensive and efficient non-destructive
evaluation of tunnel liner conditions. The automated seismic/sonic system acquires overlapping
(continuous data) at 6,18, and 30 inch intervals at a rate of 500 to 2,000 feet per hour. Radar profiling
data are acquired simultaneously to provide a complete suite of non-destructive data to evaluate the
following critical tunnel parameters:
. strength of the tunnel liner;
. identification and mapping of weak, deteriorated, cracked, delaminated tunnel liner;
. identification of metal structural or functional members such as rebars, pipes, ribs etc.;
. identification of thinner tunnel liner areas;
. identification and mapping of voiding behind the liner.
All data are displayed in the field for quality and recorded on digital disks for future analysis,
processing and playback on analog chart recordings for on-site interpretation.
The seismic/sonic/ultrasonic measurements provide data to calculate the moduli values (Young’s, bulk
and shear) and an evaluation of the strength/mechanical properties of tunnel liner materials (concrete
and masonry). The seismic/sonic/ultrasonic results identify and quantify areas of interior
deterioration, as well as liner thinning and voiding behind the liner. Radar profiling is used to
identify metal within the liner, areas of increased moisture or water infiltration, as well as water filled
void conditions behind the liner.
This system has been utilized on a number of projects throughout the United States and abroad
including: rapid transit, water supply, railway, automobile, and hydroelectric tunnels as well as
pipelines.
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Inspection Of Cast-In-Place Piles By Ultrasonic And Radiometric Testing
By Olli T. OkkoThe possible existence of casting defects in cast-in-place piles in Finland has been
systematically inspected by ultrasonic cross-hole testing in tubes installed beforehand in the
pile. In order to analyze the accuracy of the method a test pile was built up. The internal
structure of the pile was tested also by nuclear logging and water injection tests carried out in
the PVC-sleeve tubes installed in the pile.
Small cracks in the concrete pile were clearly detected on the analog sonograms of the
ultrasonic cross-hole records. On the other hand the largest casting defect was not well
identified, probably due to the homogeneity of the weak concrete. The density and the water
content in the large volume of concrete was measured by back-scattering techniques of
gamma rays and thermal neutrons. By means of these methods casting defects thicker than 5
cm were detected. After the pile was grouted, only the nuclear methods could be used to
inspect the quality of the grouted pile. The sonograms were similar to those obtained before
the grouting.
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The Use Of Geophysical Techniques For The Detection Of - Partially Collapsed - Mine Shafts
Authors Jan Brouwer and Vincent NijhofDuring the past centuries the Southernmost part of the Netherlands has been known for
extensive marl recovery. Systems of galleries and mine shafts exist over - assumed - areas
of several hundred km2. At some locations mine galleries have recently collapsed causing
severe damage to the roads and buildings in the surrounding urban areas. Due to these
collapsed galleries parts of the system of mining shafts have become unreachable making it
but impossible to determine the exact lateral extent of the collapse features and the galleries
from within the mining system and leaving only surface methods to locate the shafts and to
determine the potential hazard for similar collapse features.
In this paper we present a feasibility study that addresses the use of three surface geophysical
investigation techniques - Resistivity Image Profiling (RIP), Ground Probing Radar (GPR),
and Reflection Seismic Profiling - to locate the mine shafts and to determine whether the
shafts are collapsed or intact.
Although all three techniques gave at least some indication to the location of the shafts, the
RIP was found to be superior to both other methods since it did not merely prove to correctly
reveal the location of the mine-shafts, it also gave some indication to whether the shafts were
collapsed or not.
GPR measurements clearly showed diffracted energy in areas where shafts were expected. The
use of GPR methods, however, was limited to it’s application on roads and other areas of
relatively flat surface conditions.
Seismic measurements highly suffered from low-velocity layer effects. Although diffracted
energy could be noticed that possibly correlates to some of the mine-shafts, data were
obscured by the occurrence of strong refraction multiples.
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The Integration Of Imaging And Parameter Estimation In Shallow Geophysics
Authors Alan Witten and Stephen NortonThis paper presents two related approaches to signal processing of shallow geophysical
data based on the concept of geophysical diffraction tomography. While both methods can be
considered imaging, one is imaging in the traditional sense where images of spatial variations
in subsurface physical properties are reconstructed. The second method is one of parameter
estimation based upon known characteristics of targets of interest. This technique yields a
reconstruction of the spa.tial variations in the likelihood of a specified target being present,
the log likelihood function, and, consequently, this method can also be considered an imaging
procedure. Several examples are given of the results of selected signal processing algorithms
applied to actual data.
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Large Scale Hydrogeological Investigation In The Beder Area - A Case Study
Authors Esben Auken, Niels B. Christensen, Kurt I. Sørensen and Flemming EffersøBy the integrated use of geophysical methods a ltydrogeological investigation with a very
high r~~solution of the geology has heen carried out in Denmark. llsing newly developed
methods such as auger Ellog drilling with levrl specific Water sampling and pulled array
contitttlous electric profiling together along with more Ouniliar techniques such as transient
electromagnetic sounding we have perfortned a general exantinatiott of the vulnerability,
the volumetric extent and the chemical properties of the aquifer itt the area. The
protection of the aquifer was less than expected. There was a rorrelation between the water
quality and the lithology of the aquifer.
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Use Of Ground-Penetrating Radar To Determine The Depositional Environment Of Glacial Deposits In Southern New Hampshire
More LessGround-penetrating-radar (GPR) surveys were made along more than 8 miles of land and
water within the Flints Pond and Lyle Reed Brook areas in southern New Hampshire. The GPR
data revealed thick sequences of continuous reflectors that represent stratified drift. Surficial
geologic mapping of the area indicates that the stratified-drift deposits are graded to the various
levels of glacial Lake Nashua. Four distinct signatures were apparent on the GPR profiles and
were correlated with various glacial depositional environments: (1) thin, relatively flat-lying,
continuous reflectors draped over the underlying till or bedrock topography, which represent
fine-grained lacustrine sediment; (2) medium-grained, subparallel to slightly chaotic, continuous
reflectors, steeply dipping in places, which represent predominantly medium- to coarse-grained
sands deposited as deltaic sediments in a lacustrine environment; (3) subparallel to hummocky,
chaotic, coarse-grained reflectors, steeply dipping in places, which represent coarse-grained icecontact
deposits, such as eskers or crevasse fillings; and (4) sharply diffracted, fine-grained,
chaotic reflectors, which represent till and (or) till over bedrock. The signatures were correlated
with geologic structures by comparing the radar records to analyses of undisturbed sediment
samples collected at six test-boring sites in the area. Correlation of radar signatures with
geologic structures can be used to indicate the depositional environment of the structure.
Land and water surveys using GPR detected glacially scoured valleys in bedrock that have
been subsequently filled with stratified drift. Geologic structures are visible in greater detail
from GPR surveys on land than on water. Penetration depths of greater than 80 feet (800
nanoseconds) were common on land surveys done over stratified drift. Penetration depths of
approximately 45 feet (400 nanoseconds) were common on water surveys as a result of the
attenuation of the radar signal by the water column.
GPR also was used to delineate the surface contact between stratified drift and the adjacent
till and (or) bedrock. Typically, the signal was attenuated as the survey passed from the
stratified-drift surface to the till surface because of the increased electrical conductivity of the till.
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Evaluation Of High Resolution Seismic For Characterization Of The Owens Lake, California, Aquifer System
Authors Thomas A. Brooks and Kent R. JohnsonHigh resolution seismic reflection data are being used as part of an integrated program to characterize the ground water system of the Owens Lake, California, area. The feasibility study for the project consisted of acquiring data in both river delta and alluvial fan depositional settings. We performed a series of noise tests to determine the best seismic sources, receivers and
other acquisition parameters. Noise test data were evaluated using a field-based processing system. We acquired approximately two miles of Z4-fold high lbesolution seismic reflection data for evaluation. We simulated reduced fold geometries during processing to determine the optimal fold coverage for A large scale survey. Reflection data were acquired to 1/2 second (twoway
traveltime), representirlg a useful depth of investigation of roughly 1500 feet.
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Case History: Brine Inflow Beneath An Underground Alcove Floor, Alcove L-3, At The Waste Isolation Pilot Plant, Se New Mexico
Authors D.I. Neuman and H.T. AndersenAn underground alcove, Alcove L-3, at the Waste Isolation Pilot Plant in SE New Mexico, is part of a brine inflow investigation. The first indication of brine inflow was noted through the drilling of boreholes in the invert. Initial determinations of the extent of the brine inflow was accomplished through a modified mise-a-la-masse survey. Corrections were applied to account for the underground geometry. Modelling was also performed to study the sensitivity of the survey to its structural surroundings, such as neighboring alcoves and connecting driftways.
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Monitoring Of A Tracer Experiment With Electrical Resistivity At Haslemoen, Hedmark County, Norway
Authors J.S. Rønning, Marian Morris, N.O. Kitterød and O.B. LilePotential differences measured on the surface were used in an attempt to
monitor the movement of a low-volume tracer. The experiment was conducted
in the unconfined groundwater aquifer at Haslemoen, in Hedmark County,
Norway. 300 1 of NaCl solution were injected at a depth of 4.1-5 m. A pole-dipole
electrode configuration was used, with the near current electrode embedded in
the zone of injection. The direction of tracer movement was identified. The
measurements are affected both by the moving conductive zone and the changes
in electric current concentration.
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Mapping Of A Stratigraphic Boundary By Its Seismoelectric Respons
Authors K.E. Butler, R.D. Russell, A.W. Kepic and M. MaxwellExperiments carried out at our Haney test site near Vancouver, Canada, have shown that
some boundaries in unconsolidated sediments may be mapped on the basis of their seismoelectric
response. Using a sledgehammer source and electric field receivers, we have observed that an
electromagnetic signal is generated when a seismic wave impinges upon a boundary between
organic-rich fill and impermeable glacial till. The depth to the interface, verified by drilling,
ranges from about 1 to 3 m. The electrical response is believed to be a transient streaming
potential produced by a seismically-induced flow of pore water at the interface.
The seismoelectric response is linear in that its frequency content is comparable to that of
the seismic wave. Surface measurements exhibit radial symmetry about the shotpoint, and the
arrival time of the signal corresponds to the seismic traveltime from the shotpoint to the
subsurface boundary. The response cannot be attributed to seismic shaking of the dipole receivers
because it is observed simultaneously by receivers in different locations.
The maximum amplitude of the electrical response observed at the surface, following a
sledgehammer blow 2 m above the boundary, is about 1 mV/m. This is measured by a horizontal
dipole at an offset of 4 m from the shotpoint. At greater distances, the amplitude of the first
arrival decays rapidly with offset and the waveform broadens. The change in waveform with
dipole offset suggests that the effective area of the interface contributing to the response may be
greater at more distant observation points.
Measurements were also made by detonating blasting caps at various depths in boreholes
penetrating the geologic boundary. The results of these tests support the conclusion that it is the
boundary, rather than the water table, that is responsible for the seismoelectric conversion.
Although the scale of our experiments was relatively small, the results are significant in
that they suggest that the seismoelectric method may be used to map aquitards or the boundaries
of permeable formations.
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A New Ground Resistivity Method For Engineering And Environmental Geophysics
Authors V.M. Timofeev, A.W. Rogozinski, J.A. Hunter and M. DoumaSeveral years ago, a capacitive-coupled resistivity system was developed in Russia by one of us
(V.M.T.), for engineering geophysical applications in permafrost areas of Siberia. This system,
called VCHEP (cyrillic acronym for high frequency capacitive-coupled resistivity) uses both
transmitter and receiver antennas operating in the range of several kilohertz. Measurements of
applied current and received voltage potential are converted to apparent resistivity using a
geometrical factor related to the antenna array. The transmitter and receiver type and geometry
can be varied depending upon a particular application; however, the most cost-effective array
is the in-line double dipole line antenna configuration. Using such a, drag-cable design of
antennas, data acquisition rates may far exceed those techniques requiring galvanic electrode
contact. Considerable experience with this method has been obtained in northern areas of
Siberia; and as part of the Canada/Russia Northern Scientific Exchange Program, testing has also
been conducted in the Canadian western arctic.
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Surface Nuclear Magnetic Resonance Experiments To Detect Subsurface Water At Haddam Meadows, Connecticut
Authors D.A. Lieblich, A. Legchenko, F.P. Haeni and A. PortselanNuclear magnetic resonance (NMR) techniques have been adapted to surface
geophysical prospecting by scientists at the Institute of Chemical Kinetics and Combustion,
Novosibirsk, in Russia. The first tests of this method in the U.S. were conducted in the summer
of 1993 through a joint collaboration between the U.S. Geological Survey; the U.S.
Environmental Protection Agency; the Institute of Chemical Kinetics and Combustion,
Novosibirsk, Russia; and Firm Hydrogeotom, Moscow, Russia. NMR “soundings” were
conducted at 10 sites throughout the U.S. The results from Haddam Meadows State Park,
Connecticut, are reported here. They are of interest, in part, because Haddam Meadows was
found to be a “high noise” site for the NMR soundings but is considered to be a fairly typical
site; in terms of noise, for urban and many rural areas.
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Simulation Of Em Wave Propagation In Three-Dimensional Structures By A Finite-Difference Method
Authors Tsili Wang and Alan C. TrippWe have developed a finite-difference time-domain solution to Maxwell’s equations for
simulating electromagnetic wave propagation in three-dimensional media. The algorithm
allows arbitrary variations of electrical conductivity and permittivity within a model. It
uses the Yee’s staggered grid technique to discretize the model and approximates spatial
derivatives with optimized second-order, finite differences everywhere except close to the
computational domain boundary where it uses conventional central differences. The pointwise
computational time of the optimized second-order difference scheme is the same as
that of the conventional fourth-order difference scheme, but the former has better dispersion
characteristics. Although the optimized difference scheme imposes stricter limitations
on the size of time steps allowed for an explicit time-marching scheme, a simple calculation
shows that this scheme is more cost-effective, due to its lower required spatial sampling rate,
than the conventional second- or fourth-order difference scheme. The temporal derivatives
are approximated by second-order central differences throughout.
We used the Liao transmitting boundary conditions to truncate an open problem. A
reflection coefficient analysis shows that this transmitting boundary condition works very
well. However, it is subject to instability. We propose a method which stabilizes the
boundary condition and which can be easily implemented.
The finite-difference solution was compared to closed-form solutions for both conducting
and non-conducting whole spaces and for a non-conducting half-space. In all cases, the
finite-difference results are in good agreement with the closed-form solutions.
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Using Resistivity Tomography To Monitor Air Sparging
Authors Susan Schima, Douglas J. LaBrecque and Paul LundegardAir sparging is a relatively new technique for remediation of
ground water contaminated with petroleum hydrocarbons. In this
technique, air is injected below the water table. The air is usually
removed by vacuum extraction in the vadose zone. Remediation
occurs through a combination of contaminant partitioning into the
vapor and enhanced biodegradation.
Although remedial efficiency is strongly a function of the
pattern of air flow, the distribution of the injected air in space and
time is poorly understood. Cross-borehole resistivity surveys were
carried out at an air sparging site to address these unknowns. The
site is a former service station in Florence, Oregon. Resistivity
measurements were made using six 40 ft deep wells, one of which
was the air sparge (air injection) well. Data were collected over a two
week period during and after several sparge events. Tomographic
resistivity reconstructions were generated between wells using an
algorithm that assumes axially symmetric structures. The movement
of air throughout time is clearly defined by high resistivity regions.
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Applications Of Multi-Offset Ground Penetrating Radar
Authors Robert J. Greaves and M. Nafi ToksözThe estimation of propagation velocity is important for the correct processing and
interpretation of ground penetrating radar (GPR) reflection data. Most, if not all,
GPR surveys, are very limited in spatial extent and the common perception is that
within the survey range, radar propagation velocity in the shallow subsurface has very
slow or no lateral variation. Therefore, a single (1-D) velocity function is considered
adequate to describe the subsurface. In this study it is shown that, in fact, lateral
variation in radar velocity can be quite significant. An effective means of determining
velocity is based on normal moveout velocity analysis of common midpoint multi-offset
data. Applying this technique at many locations along a GPR survey provides a more
accurate description of the actual 2-D velocity distribution.
When the multi-offset acquisition geometry necessary for normal moveout velocity
analysis is applied continuously in the GPR survey, an improved radar reflection image
is attained by stacking traces at common midpoints. The 2-D normal moveout velocity
description is used to make necessary adjustments to the data before the stack. The
velocity analysis and common midpoint stack techniques are applied to an example
of GPR data acquired using the multi-offset geometry at every survey station. The
results show that reflection signal-to-noise and effective depth of penetration of stacked
multi-offset data are improved, as compared to standard single-offset GPR data. It
is also shown that, the stacked multi-offset data is itself improved as the number of
velocity analysis locations is increased, up to some practical limit.
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Vetem - A Very Early Time Electromagnetic System
Authors Louise Pellerin, Victor F. Labson and M. Cathy PfeiferThe Very Early Time Electromagnetic (VETEM) system is designed to investigate the
conductivity and dielectric properties of the shallow region of the geoelectrical section where
most buried waste is located. In the electrically conductive conditions (20-30 ohm-m) common
throughout the Department of Energy complex, the minimum depth of investigation for diffusive
electromagnetic (EM) sounding techniques is roughly 5 meters. At the other end of the
spectrum, ground penetrating radar (GPR) systems typically investigate only the top meter or so
when clay minerals are present in the soil. Hence, in many cases there is a gap in our detection
capability of the geoelectrical section between the lower limit of GPR and the upper limit of
traditional EM. Bridging this gap is essential to the characterization of buried waste sites.
For the successful development and deployment of the VETEM system three important
interconnected elements are necessary: (1) forward modeling, using multi-dimensional numerical
algorithms and physical modeling results to optimize instrument and survey design, and to test
and refine interpretational software; (2) instrumentation designed for rapid, high-resolution
mapping of conductive and dielectric targets in a conductive host; and (3) interpretational
schemes that are rapid for real-time imaging and rigorous enough to provide quantitative results.
All three elements are being developed simultaneously over a period of several years. In the first
year, the focus has been placed on the use of the USGS-developed prototype frequency-domain
slingram system, operating in the frequency range of 300 kHz to 30 MHz with intercoil spacing
of 1 to 4 meters; development of the time-domain transmitter; one- and three-dimensional
modeling software; and the adaptation of existing quasi-static interpretational software to
shallow targets. This poster highlights the data collected at INEL and the status of the modeling
and interpretational software.
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Investigating The Resolution Of Resistivity Arrays Using Inverse Theory
Authors L.P. Beard and A.C. TrippWe used a fast 2-D minimum structure inverse solution to examine the ability of different
resistivity arrays to resolve structures given noisy synthetic data. We found that the resistivity
models obtained from inversion of the dipole-dipole data were usually very similar to the estimated
models from pole-dipole data, and both were superior to estimated models from pole-pole data.
This is because noisy dipole-dipole or pole-dipole data define geoelectric structures much more
precisely than an equivalent set of noisy pole-pole data. One structure where the dipole-dipole
array appeared decidedly superior was the prism beneath a conductive overburden. The final
estimated models from the pole-pole data were more poorly resolved than the final models from the
other arrays. Our results show that the pole-pole data is a poor choice if vertical resolution of a
geoelectric structure is crucial. Furthermore, if pole-pole data contains even a fraction of a percent
of noise, the transformation of such data through superposition to equivalent data of other array
types is virtually impossible, and significant information is lost.
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A “Model” Geophysics Program
More LessIn 1993, I tested a radio-controlled airplane designed by Jim Walker of Brigham
Young University for low-elevation aerial photography. Model-air photography retains
most of the advantages of standard aerial photography --- the photographs can be
used to detect lineaments, to map roads and buildings, and to construct stereo pairs
to measure topography --- and it is far less expensive. Proven applications on the
Oak Ridge Reservation include: updating older aerial records to document new
construction; using repeated overflights of the same area to capture seasonal changes
in vegetation and the effects of major storms; and detecting waste trench boundaries
from the color and character of the overlying grass.
Aerial photography is only one of many possible applications of radio-controlled
aircraft. Currently, I am funded by the Department of Energy’s Office of Technology
Development to review the state of the art in microavionics, both military and civilian,
to determine ways this emerging technology can be used for environmental site
characterization. Being particularly interested in geophysical applications, I am also
collaborating with electrical engineers at Oak Ridge National Laboratory to design a
model plane that will carry a 3-component flux-gate magnetometer and a global
positioning system, which I hope to test in the spring of 1994.
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Inel Cold Test Pit Demonstration Of Improvements In Information Derived From Non-Intrusive Geophysical Methods Over Buried Waste Sites
Authors Bart Hoekstra and Raye LahtiA high density, multiple sensor geophysical survey was conducted at the Idaho National Engineering Laboratory
(INEL), a Department of Energy test facility, at its Cold Simulated Waste Demonstration Pit (CTP). The CTP site
was specifically prepared for testing and evaluation of remediation technologies, including geophysical surveys.
The INEL has been involved in the testing and development of nuclear power production since the early 1950’s. A
variety of waste products from nuclear processes on and off-site have been disposed of, primarily at the
Radioactive Waste Management Complex (RWMC). Included are waste products from the Rocky Flats Plant
(RFP) in Colorado. The simulated waste forms constructed for the CTP were formulated from 1971 to 1973
records of waste shipments from RFP, and deposited in a similar fashion as described in the records.
The objectives of the geophysical demonstration were to reduce risk, and improve the technologies that help to
meet DOE’s cleanup goals by providing a foundation for further advancing the use of geophysical methods for the
detection of buried waste. In this demonstration, the use of high density, multiple sensor data sets, advanced data
processing techniques, and the testing of an innovative time domain electromagnetic instrument were conducted.
Other instrumentation used included frequency domain electromagnetic conductivity profiling, total field
magnetics and vertical magnetic gradient, time domain electromagnetic profiling, and ground penetrating radar.
The geophysical field survey was conducted over a 15 day period on a grid over the CTP of about 300 feet by 140
feet. For most geophysical measurements a 2.5 foot grid was used.
The TDEM metal detector and the in-phase component of the FDEM conductivity surveys provided good
resolution of the CTP boundaries, berms and contents. The results over the CTP provide good illustrations of the
influence of the local geologic setting to sensor behavior. The GPR data was ineffective in providing any
information about the contents of the CTP. EM conductivity and magnetic data were influenced by variations in
thickness of surface sediments and basalt bedrock. These factors provide evidence of the necessity of using
multiple sensors for buried waste delineation. A combined interpretation using all available data was successful in
defining the CTP.
In addition, methods were developed to display the locations of the identified targets in a 3-D which can be
manipulated in real-time on a graphics workstation. Forward models were developed for the EM61 and used to
evaluate the resulting data.
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Success Criteria And Reasons For Failure Of Ground-Penetrating Radar Studies
Authors W.M. Roggenthen and D.K. ParrishThe literature is replete with examples of successful ground-penetrating radar (GPR)
investigations. Documentation of the failures, however, is not as well reported, although
cautionary notes are also abundant regarding the misuse and misapplication of the technique.
Such deficiencies in reporting are common artifacts in scientific and engineering literature in
that interest is generally greater in successful studies, but discussion of the failures is important
because it provides an understanding of the limitations of the method. Examination of the
types of surveys that have proven to offer a measure of success suggests a number of themes,
the most obvious of which is the presence of host materials with low conductivities and a
relative lack of mineralogic clays.
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High-Resolution Subsurface Imaging And Neural Network Recognition
Authors Ben K. Sternberg and Mary M. PoultonA high-frequency, high-resolution electromagnetic (EM) imaging system is being
developed for environmental geophysics surveys. Some key features of this system
include: (1) rapid surveying to allow dense spatial sampling over a large area, (2)
high-accuracy measurements which will be used to produce a high-resolution image
of the subsurface, (3) measurements which have excellent signal-to-noise ratio over a
wide bandwidth (32 kHz to 32 MHz), (4) large-scale physical modeling to produce
accurate theoretical responses over targets of interest in environmental geophysics
surveys, (5) rapid neural network interpretation at the field site, and (6) visualization of
complex structures during the survey.
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Integrated Geophysical Characterization Of Mine-Waste Sites In The Coeur D’Alene Mining District, Idaho
Authors Phillip R. Moyle, Jody M. Fay and Michael J. FriedelAs part of a study aimed at testing and developing effective and thorough
characterization procedures, the U.S. Bureau of Mines (USBM) Mine Site
Characterization Program is assessing the application of several surface
geophysical techniques to characterize heavy-metal mine wastes in northern Idaho.
Site characterization is fundamental to conducting accurate risk assessments and
for subsequent remediation plans, if proven necessary. Integrating geophysics
with the application of geology, metallurgy, physical chemistry, surface and
ground water hydrology, environmental science, geostatistics, and other
appropriate disciplines produces an interdisciplinary or “holistic” approach which
can significantly improve the quality and accuracy of characterization.
Furthermore, it is believed that selective application of minimally invasive,
integrated geophysical techniques will reduce disturbance of potentially hazardous
materials while decreasing the time and cost of the investigation. This paper
briefly describes the purpose, scope, and current status of an ongoing project.
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A Reconnaissance Gpr Investigation At Chichén Itzá, Yucatan, Mexico
A Ground Penetrating Radar survey was done over selected areas of the Great Plaza and
the Ball Court at the Mayan archaeological site of Chichen Itz& Yucatan, Mexico. The purpose
of the work was to test the GPR technology for the first time at this site; to map the bedrock
surface beneath the extensive artificial fill which was used to elevate the Plaza; to search for
buried structures; and if depth penetration allowed, to search for caverns within the limestone
bedrock. Geologically, the site is underlain by Tertiary limestone which forms a smooth plain
having approximately 5 meters of local relief, broken by occasional sinkholes. Water table was
at about 20 - 25 meters depth. The GPR study was done partly because physical properties
measurements on limestone samples done 9 years ago by Dolphin and Vickers of SRI showed
very low attenuation of radio waves. A GSSI SIR-10 with bistatic 500 MHz and monostatic 100
MHz antennae was used, with most work done at the lower frequency. Penetration was not as
great as was anticipated because the plaza fill includes appreciable amounts of residual clay soil
mixed with the limestone blocks and cobbles. Hence, cavern features were not within the range
of the instrument. However, penetration was sufficient to map relief of the “bedrock” surface,
to reflection times as great as 125 nsec. A number of bedrock knolls were found below the NE
part of the Plaza. At shallower levels, sub-horizontal reflections are probably derived from
earlier plaza levels. Internal structures within the fill give an indication of the direction in which
the plaza filling took place. Occasional hyperbolic reflectors at and above the bedrock surface
hint at large discrete blocks or similar structures. These await excavation by our colleagues at
INAH, to whom we are also grateful for on-site support during the field work. The success of
this test has led to a recommendation to cover the entire site in detail with GPR.
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The Dahlonega Test Site: Test Bed For Evaluation Of Shallow Subsurface Geophysical Exploration Techniques
Authors Robert C. Kemerait, Douglas Baumgardt and Suzanne LeonardThe Dahlonega test site is located in the eastern foothills of the Appalachians in
Georgia. Dahlonega, Georgia marks the southern end of the Appalachian trail at the
base of the Blue Ridge in northern Georgia. Founded as a gold mining town in the early
1800’s, Dahlonega is now primarily a historical attraction setting in the foothills among
abandoned gold mines and works. A facility for testing shallow subsurface geophysical
exploration techniques is under construction near the Chestatee River approximately 4
miles to the east-southeast of the town of Dahlonega. The test facility is labeled the
Dahlonega Test Site (DTS).
Geological characteristics in the immediate vicinity of the DTS favor a highly
weathered clayey mica schist with abundant quartz veins. The quartz veins are fairly
substantial, in some areas up to 3-4” in thickness. The veined schist formation is
overburdened by a clayey reddish soil. From the drilling operation there is observable
evidence of layering. At approximately 20 feet the medium changes from a reddish
material to the darker schistose material. The water table appears at approximately 50
feet. Data recorded from borehole deviation measurements made with an Owl tool
indicate that the boreholes are straight until reaching a depth of approximately 75-80
feet where they began to deviate. This deviation suggests the presence of more
competent rock appearing at this depth.
An air filled tunnel with an axis that is nearly perpendicular to the test site is
present at a depth of approximately 42 feet.
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Stols™ Magnetic Survey At Sandia National Laboratory Technical Area 2
More LessTechnical Area 2 (TA2), a 45 acre site located at Kirtland AFB in Albuquerque NM, was run by
Sandia National Laboratory (SNL) as a nuclear weapons assembly facility from 1948 to the mid
1950’s, and as an explosive device development facility since the mid 1950’s. Presently, SNL
is developing an environmental remediation plan for TA2 which will allow for the safe closure
of the facility. One main concern of SNL is the location of underground burial containers, such
as 55 gallon drums, which may contain radioactive or chemical waste products.
In order to create a maps of buried ferromagnetic objects located at TA2, the Surface Towed
Ordnance Location System (STOLS™) was deployed by GEO-CENTERS, INC. at this site. This
survey, which covered over approximately 20 acres, was performed in September, 1993. Total
field magnetic data was recorded on seven separate magnetometers at a rate of 20 samples per
second per sensor. The magnetometers were mounted on a sensor platform which is towed by
a low magnetic signature vehicle and positioned with a GPS navigation system. Concurrent with
the survey a reference magnetometer was deployed in an adjacent area to record the low
frequency variations in the Earth’s ambient field. These reference data were later subtracted from
the survey data to produce a total field magnetic anomaly map of the site. Data was collected
at sufficient density to allow for final interpolation onto a 10 cm grid. All data were collected,
processed and analyzed in the field, on the same day of the survey.
The STOLS™ magnetometer surveys at TA2 resulted in very dense and highly accurate magnetic
anomaly maps of the facilities. The magnetic anomalies detected in the data were modeled to
produce a catalog of buried ferromagnetic objects at the sites. Buried objects are described in
terms of latitude, longitude, depth and size. Detected objects included fence posts, roadbeds,
buried pipes and barrels.
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Efficient, Cost Effective Waste Site Characterization Utilizing Complementary Non-Intrusive Geophysical Techniques: A Case Study Of 2-D And 3-D Ground Penetrating Radar And Magnetometer Surveys
Authors W.R. Sims, G.G. Rucker, R.A. Plunkett, K.M. Wise and H.M. HickeyThe Savannah River Site (SRS) has implemented a comprehensive environmental program to mitigate
impacts to the environment while maintaining compliance with environmental regulations. An element of
the environmental program is the investigation of over 100 waste sites - some of which include buried
hazardous waste materials. The SRS has effectively conducted subsurface field investigations at waste sites
suspected of containing buried wastes by utilizing non-intrusive geophysical techniques as opposed to
traditional intrusive techniques. Depending on the site specific conditions and objectives of the
investigation, multiple geophysical techniques often yield a more comprehensive conceptual model of the
site versus a single geophysical survey. Although multiple surveys are seemingly cost prohibitive early in
a waste site characterization history, the information obtained usually leads to a more efficient and cost
effective characterization or remediation design. In addition, the complementary data increases the level of
confidence in the investigating team, helps reduce the anxiety associated with contamination exposure, and
contributes to client and regulatory approvals.
Two and three-dimensional ground-penetrating radar and magnetometer surveys were conducted at the D-Area
Oil Seepage Basin, a waste site “suspected” of containing buried drums. The data from the integrated
geophysical investigations complemented one another, successfully delineating the lateral and vertical
dimensions of the waste site and detecting buried metal objects. This extended abstract compares the
application, results, and advantages of the individual geophysical techniques used at the waste site.
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High-Resolution Marine Seismic Reflection Data Acquisition Using An Engineering Seismograph
Authors Jeffrey S. Waldner, Robert E. Sheridan, David W. Hall and Gail M. AshleyA digital single-channel seismic reflection system was developed to acquire continuous
profiling data by interfacing a conventional analog system with a land-based digital signalenhancement
engineering seismograph. Digital profiles are enhanced by trace static correction,
deconvolution, automatic gain scaling, weighted horizontal stacking and digital filtering.
Problems common to analog data, such as wave-motion effects of surface sources, waterbottom
reverberation, multiple reflections, and bubble-pulse width can be addressed by the
processing. The fast firing rate for analog records is maintained while a trigger-divider sends a
slower trigger rate to the digital seismograph. An auto-save feature with an automatic rollalong
switch groups adjacent traces to files, eliminating system limitations of the mass-storage device.
The digital data were collected to map sand ridges of the inner continental shelf off New
Jersey for beach sand replenishment surveys. The seismic tracklines are correlated to
vibracores and known geologic stratigraphy. The digital data exhibit reflections from layers
less than 1 meter thick. Synthetic seismograms constructed from the vibracore information
show these internal reflectors are caused by shelly gravel/medium sand interfaces. Global
Positioning System (GPS) was used to plot real-time position as well as obtain a navigational
accuracy within 10 meters. The combination of the analog system with the land-based seismograph
offers a less expensive technique for digital acquisition and processing. This provides
improved results over older analog data.
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Ground Penetrating Radar Survey Of A Waste Disposal Area At The Site Of A Former Lumber Mill
Authors J.R. Pelton, L.M. Liberty, M.W. Lyle, M.E. Dougherty, D.D. Crowther, R.D. Bolger, P.J. Gallaway and M.P. PetteysApproximately 1.5 km of 200-MHz fixed-offset ground penetrating radar (GPR) profiles acquired
at the site of a former lumber mill are dominated by two different reflection configurations: (1) a
chaotic pattern consisting of laterally discontinuous reflections and/or overlapping diffraction
hyperbolas; and (2) a more uniform pattern that is characterized by mostly continuous reflections
with smooth lateral variations suggestive of natural sedimentary features. Comparison of the
GPR profiles with geologic logs of nearby trenches indicates that the chaotic pattern is associated
with disturbed areas where near-surface burial of up to 3 m of mill waste (i.e., fill material composed
of woody or organic matter intermixed with sediments and minor metal, rubber, and plastic)
has resulted in strong lateral variations in subsurface dielectric or conductivity properties; the
chaotic pattern is distinctive and is not likely to be caused by natural sedimentary features. In
contrast, trench logs indicate that the more uniform pattern is associated with undisturbed areas
where native sedimentary materials are still in place, or with disturbed areas characterized by laterally
uniform fill material and no diffraction-producing trash zones. This ambiguity can be
resolved by directly mapping the base of the fill material (i.e., the contact between the fill material
and the underlying native sediments), but an easily recognizable radar reflection from that interface
is not consistently observed at the site. Although interpretation of the radar profiles is therefore
subject to some limitations, an overall evaluation concludes that the data are very useful for
reconnaissance, for supporting and extending the results of the site trenching program, and for
outlining the waste disposal area.
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A Preliminary Geophysical Survey Of An Inactive Landfill Scheduled For Reclamatio
Authors E. Jay Knopf and John E. McCallenLandfill reclamation can provide a cost effective alternative to traditional landfill closures. Reclamation may emerge as a viable option to help extend the life of a landfill, to recover soil for use as cover and other purposes, to reclaim certain recyclable material such as white goods, tires, metals, and wood wastes and for energy recovery. In 1990 the New York State Energy Research and Development Authority (NYSERDA) initiated, and in 1993 has provided majority funding for a number of research and demonstration reclamation projects in New York State.
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Gamma Logging To Define The Stratigraphy In A Buried-Valley Aquifer System
Authors David F. Dominic, Benjamin H. Richard, Paul J. Wolfe and Songlin ChengA number of methods were employed to determine the stratigraphy, bedrock topography, and
regional ground water flow system within a bedrock valley filled with Pleistocene sediments. A
proposed highway extension within the valley will pass within one mile of Cedar Bog, a relict
boreal fen; we are evaluating the potential for construction to disrupt the ground water supply to
the fen. Seismic refraction and gravity surveys were used to delineate water table and bedrock
depths along the eight miles of proposed highway routes. Drilling along the survey lines
verified the geophysical interpretation that several tributary valleys join the main bedrock valley.
Several previous studies have suggested that such valleys connect recharge areas (to the north
and east) to observed discharge areas in and near the fen. Critical to evaluating this hypothesis
is the stratigraphy within the main and tributary valleys.
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Identification Of Hydraulically Conductive Fractures From The Analysis Of Localized Stress Perturbations And Thermal Anomalies
Authors Colleen A. Barton, Mark D. Zoback and Daniel MoosA number of key questions need to be addressed before the relationship between stress and
fluid flow in the Earths crust can be understood. First, how is fluid flow related to the current
stress field in highly fractured crystalline rock? Second, is enhanced permeability and permeability
anisotropy principally the result of flow along joints (Mode I failure) or shear faults (Mode II
failure) or both? Is it possible that answer is neither - that in highly fractured crystalline rock,
flow is dominated by the orientation of faults and fractures introduced into the rock mass during its
long geologic history and the orientation of these structures bears no strong relation to the current
stress field?
It is well known that relatively few fractures in fractured rock serve to conduct fluids
through the rock. The use of fracture geometry to predict hydrologic flow in the crust is therefore
severely limited by the lack of knowledge of which fractures measured in a given survey actually
provide conduits for fluid flow. This study examines the relationship between in situ stress and
fluid flow using data from detailed analyses of wellbore breakouts and fracture geometry in
conjunction with precision temperature logs.
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Seismic Refraction And Electromagnetic Methods For Mapping Confining Layer In Central New Jersey
More LessThe Woodbury clay is one of the major hydrogeologic confining
units in the New Jersey coastal plain. It separates two main
aquifer systems; the Englishtown and the Potomac-Raritan-Magothy
aquifers. Therefore, at a hazardous waste site, it is important
to map the surface of this confining layer to help define the
local hydrostratigraphy, ground water flow and possible contaminant
transport.
In a contaminated site in central New Jersey two wells were
drilled to determine the vertical extension of a contaminant and
the direction of groundwater flow. The drilling results show a
difference in the depth of the Woodbury clay between the two
wells and some thin clay beds. At this stage geophysical support
was requested to map the Woodbury clay between the two wells and
to determine the depth to the water table.
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When Is 1D 2D? Interpretation Of Geoelectrical Sections
Authors Peter M. Duch and Kurt I. SørensenSurface geoelectrical measurements are routinely used in environmental and mapping
geophysics. The methods are used for the investigation of waste deposits, detailed mapping
of aquifers in ground water source areas and mapping of raw materials. In Denmark, that
means gravel, sand and clay.
The geoelectrical data may be presented as apparent resistivity pseudosections for
interpretation by the geophysicist. A pseudosection shows an unfocused and distorted image
of the subsurface which can be a starting point for a qualitative interpretation.
Quantitative interpretation of geoelectrical data is done with the purpose of finding the
parameters of an assumed model. Model assumptions include layered (ID), horizontal
cylinders of arbitrary cross-section (20) or 3D bodies. Traditionally, geoelectrical soundings
are interpreted using 1D models and tools for such inversions are very well developed with
regard to speed and accuracy. Thus an initial interpretation can be accomplished quickly and
used for the planning of further field work.
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Pulled Array Continuous Electrical Profiling
More LessThe electrical profiling method is a powerful technique for mapping of the near
surface geology, and the method has been used for decades. With the increasing need for
detailed and fast mapping of the protective clay caps of the aquifers the method has
achieved renewed attention. In this context a new method for electrical profiling: Pulled
Array Continuous Electrical Profiling, PA-CEP, has been developed. Electrodes are
mounted on a tail pulled by a small vehicle, and inside the electrodes and on the vehicle
data processing electronics are mounted. Data from several arrays are measured
continuously and simultaneously while the tail is actively being towed. The PA-CEP
method has enabled fast and reliable mapping of large areas (lo-25 km2). With areas this
large, surprising insight into the morphogenesis of the survey areas has been obtained.
The density of the data reveals hitherto unseen geological details. The PA-CEP method
has been used intensively in hydrogeological investigations, in prospecting for raw
materials, and in the construction of highways and pipelines.
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The Ellog Auger Drilling Method
More LessWith the Ellog Auger Drilling Method a detailed electrical log and gammalog are
measured with tools integrated in the drilling stem while actively downward drilling, and
undisturbed level specific water samples are taken through inlets placed close to the
cutting head and pumped to the surface. The drilling stem is a hollow auger with
continuous flight, and no drilling mud is applied. Hence the measured logs are not
disturbed by mud or invasion zone, and the collected water samples have a chemical
composition that reflects the undisturbed conditions within a narrow depth interval. By
the new technique a detailed mapping of the lithology and a vertical chemical profile are
achieved with a resolution surpassing that of traditional techniques. The method provides
data which are essential for locating pollution plumes, chemical interfaces and mapping of
the variation in the water quality of aquifers. The combination of the chemical analysis of
the water samples and the hydrogeological conditions inferred from simultaneously
recorded geophysical logs opens up the possibility of understanding the relationship
between chemical and hydrogeological processes.
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Elastic Wave Equation Travel Time And Waveform Inversion Of Crosshole Seismic Data
Authors C. Zhou, G.T. Schuster and Sia HasanzadehAn acoustic wave equation traveltime and waveform (acoustic WTW)
inversion method was presented by Zhou et al. (1993) to invert for
the P-wave velocity distribution from crosshole seismic. data. The
acoustic WTW tomograms showed about 6 times better spatial resolution
relative to the associated travel time tomogram. In this
paper we present the elastic wave equation travel time and waveform
(elastic WTW) inversion method which inverts for the interwell
P-wave and S-wave velocity distributions. Comparison of the elastic
WTW tomograms with the acoustic WTW tomograms shows
that both methods can invert for the high resolution P-wave velocity
structure when the S-wave energy is very weak in the recorded
seismograms. Although the field data we used are dominated by unconverted
P-wave arrivals, the elastic waveform inversion can still
invert for the S-wave velocity structure. Results show that elastic
WTW inversion is superior to acoustic WTW inversion when there
are large amplitude converted S-waves in the recorded seismograms.
The disadvantage of elastic WTW inversion is that it requires about
3 times more CPU time compared to acoustic WTW inversion.
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Use Of I!Iigh Resolution Geomagnetic& 2D-Dc-Geoelectrics And Induced Polarisation In Environmental Investigations
More LessFor more then 10 years geophysical methods are used for environmental investigations in
Germany. Landfills and abandoned industrial sites are focal points.
Especially in urban areas High Resolution Geomagnetics has become an important tool. Up to
4 points/m2 are measured with Fluxgate Simultaneous Gradiometers. This leads to a horizontal
resolution and a signal/noise ratio not within reach with the conventional geomagnetic method.
Geoelectric methods are able to detect certain types of contaminations in the subsurface. But
the traditional kind of use (profiling, 1D soundings, pseudosections) often can’t describe the
structures exactly. Recently developed algorithms for 2D-inversion are showing us sharper
pictures of what’s going on under our feet.
In many cases measuring DC-resistivity is not enough. To distinguish between geological and
anthropogenuous features by registrating just this parameter sometimes is impossible.
Measuring Induced Polarisation can be a great help in delineating the boundaries of
contaminated soil.
Examples from landfills and an anbandoned gas works are presented.
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Enhancement Of Ground Penetrating Radar Data Through Signal Processing
Authors M.E. Dougherty, P. Michaels, J.R. Pelton and L.M. LibertyRecently collected ground penetrating radar (GPR) data from a former lumber mill waste site
near Boise, Idaho have proven to be a useful reconnaissance aid for delineating possible areas of
fill from surrounding fluvial sediments. Several lines of data were collected at coincident stations
using antennas with central frequencies of 50, 100, 200 MHz. Some ambiguities exist in the interpretation
of the original 200 MHz data due to lack of a distinct fill signature in the data processed
with standard seismic processing techniques. We present here an effort to enhance the original
GPR data through air wave removal, bandwidth enhancement, and cross-correlation analyses. In
general, these analyses appear to improve the usefulness of the data and in some environments
may become standard techniques for future GPR data collection and processing.
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Amplitude Control In Shallow Seismic Surveying
Authors Jan Brouwer, Peter Bakker and Klaus HelbigThe amplitude of seismic waves contains valuable information on sub-surface soil parameters. In order to extract this information from the seismic records we have to: 1) preserve seismic amplitudes during acquisition and subsequent (pre-) processing; 2) determine (preferably) absolute reflection strength-versus-offset distribution from the true amplitude data; 3) interpret reflection strength information in terms of sub-surface soil parameters. In this paper we deal with the implementation of amplitude-versus-offset analysis in shallow seismic exploration. We show that use of seismic amplitude information can be successful at the cost of extensive (quantitative) monitoring of, e.g., source-signature and geophoneresponse and compensation for any changes or differences observed. A method to determine absolute reflection strength as a function of offset followed by an estimation of soil parameters is presented. This method is based upon the interpretation of amplitude ratios in primary-multiple chains. Practical application of this method has been tested on several datasets, two of which are presented here.
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Electromagnetic Modeling Of Large Structures Using Integral Equations
Authors Zonghou Xiong and Alan C. TrippApplication of electromagnetic techniques to high resolution geotechnical problems will require
effective means of calculating the response of complex models having many cells of possibly
differing conductivity. To address this need, we have developed an electromagnetic modeling
algorithm for large conductivity structures based on the method of system iteration and spatial
symmetry reduction using integral equations.
Electromagnetic scattering of conductivity structures using the integral equation method has
been widely used in geophysical applications [l]-[8]. Recently, [9] introduced the method of
system iteration, where a scatterer is divided into substructures and the direct matrix inversion
is applied to each substructure only, while the mutual interactions among the substructures
introduce equivalent sources. This technique greatly reduces the matrix factorization time and
storage requirements. Using the lateral homogeneity of a layered earth, [lo] developed a spatial
symmetry reduction scheme which drastically reduces the computation time for forming the
scattering impedance matrix by identifying and reducing the redundancy of calculating the
scattering matrix elements. This scheme permits enhanced use of the method of system iteration.
The method of system iteration is applicable to arbitrary scatterers with arbitrary discretizations.
It divides a structure into many substructures and solves the resulting matrix equation
using a block iterative method. The block-submatrices usually need to be stored on disk in
order to save computer core memory. However, this requires a large disk for large structures. If
the body is discretized into equal size cells, it is possible to use the spatial symmetry relations
of the Green’s functions to re-generate the scattering matrix in each iteration, thus avoiding
the expensive disk storage. This will allow us to calculate the responese of models comprised
of tens of thousands of cells on workstation type of computers. Numerical tests show that the
algorithm effectively reduces the solution of the modeling problem to an order of O(N2), instead
of O(N³), as with direct solvers.
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Marine Sp Surveys For Dam Seepage Investigations; Evaluation Of Array Geometries Through Modeling And Field Trials
Authors John Jansen, Edward Billington, Frederic Snider and Patrick JurcekMarine SP surveys have been periodically used on reservoirs for several decades.
Most surveys have used gradient arrays towed at the surface or at some depth in the
water column. Water column gradient arrays are efficient, but at the cost of some
sensitivity. Some surveys have used a single fixed electrode and a roving electrode
dragged across the reservoir bottom. These surveys have typically been labor
intensive and logistically limited. The authors used finite difference models and field
trials to evaluate the sensitivity and field productivity of gradient arrays and roving
electrode arrays, in the water column and on the reservoir floor, for detecting narrow
seepage pathways in a large reservoir.
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Electrical Detection And Monitoring Of Leaks In Lined Waste Disposal Ponds
More LessWaste disposal ponds or landfills may be lined with
impermeable plastic liners to prevent escape of noxious or toxic
fluids into the environment. Verification of the integrity of the
liner is important, both to assure quality at time of installation
and to guard against damage during the life of the pond. Several
leak-detection techniques have been employed which exploit
similarities between fluid flow and electric current in such an
environment. In this work, I describe a method which overcomes the
short-comings suffered by previously described systems.
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