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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
1 - 20 of 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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