- Home
- Conferences
- Conference Proceedings
- Conferences
4th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 11 Mar 1991 - 14 Mar 1991
- Location: Knoxville, Tennessee, USA
- Published: 11 March 1991
21 - 30 of 30 results
-
-
Interactive Image Analysis Of Borehole Televiewer Data
Authors Colleen A. Barton, Lawrence G. Tesler and Mark D. ZobackThis chapter describes an interactive graphics system designed for borehole
televiewer (BHTV) image analysis. The software provides one of the fust comprehensive
tools for borehole image data analysis available to exploration and research scientists on a
low cost and easy-to-use personal computer, the Apple Macintosh II.
The program, called BHTVImage, provides an integrated environment for analyzing
borehole shape and features. Images of BHTV data are displayed in false color on a
graphics screen and are manipulated with a mouse pointing device. A variety of two and
three-dimensional displays of borehole radius and acoustic reflectivity are used to display
the data. Tens of meters of borehole wall can be rapidly viewed by scrolling through the
data within a graphics window. Interactive measuring tools are provided to quickly
measure and record wellbore features. The values of the scales, units, and grid intervals
can be modified interactively during program execution. Gross scale features can be easily
extracted from the images through interactive thresholding to produce a scaled comparison
with complementary log data such as resistivity or sonic recordings. Alternatively, fulI
resolution images can be analyzed to investigate the fme details of fractures or crossbedding
intersecting the well.
-
-
-
Geophysical Surveys For Underground Storage Tank Locations Hickam Air Force Base, Hawaii: A Case Study
Authors H.D. MacLean, J.W. Dickerson, J.C. Hasbrouck and E.T. CotterChem-Nuclear Geotech, Inc. (Geotech), personnel performed geophysical surveys
at Hickam Air Force Base (HAFB), Hawaii, to determine the presence or
absence of underground storage tanks. Geophysical survey techniques included
magnetic total field, magnetic gradient, and horizontal-loop electromagnetic
methods. This case study presents validated data from five sites.
Twenty-three sites at Hickam Air Force Base were designated for investigation
following interviews with HAFB personnel and examination of base records and
historical land use. Geophysical investigations were conducted at 10 sites to
confirm the removal of tanks and at 3 sites to establish the location of tanks
presumed abandoned in place. Tests were conducted at an additional 10 sites,
for which no historical tank disposition records were available, to determine
whether tanks were present.
Magnetic and electromagnetic (EM) instruments respond characteristically
to steel underground storage tanks because the tanks are ferromagnetic
and good electrical conductors. Determinations were made of an equivalent
magnetic susceptibility and a conductor EM-response parameter range
characteristic of steel storage tanks. The presence of other metal objects
within the surveyed areas affected the instrument readings, but these objects
usually produced significantly different response parameters.
In six areas, our interpretation of the geophysical data confirmed the
presence of 14 tanks and the probability of an additional 5 tanks.
Interpretation of the data indicated that no tanks were present at 16 of the
investigated areas. Survey results from one area were indeterminant because
of the limited scope of the measurements.
Exploratory excavations and augering were conducted at 9 of the 23 sites to
provide ground-truth for the geophysical interpretation of the collected
survey data. Conclusions derived from the geophysical data were validated at
eight of the nine sites.
This case study presents data from five of the investigated sites.
Underground storage tanks were uncovered at three of the sites, and the
absence of storage tanks was verified at one site. The fifth site illustrates
the need for an integrated, multiple-method approach for proper geophysical
investigations.
-
-
-
Geophysical Methods Used To Investigate A &Jdioac!I’Ivb Waste Burial Site
Authors Jo-Ann Sherwin and Alan WittenA suspected radioactive waste burial site was investigated using geophysical
surveys, performed in sequence to learn about the site without intruding into it. The
site is described as active in the 1950s and the location where low-level
radioactive materials such as cathode ray tubes, scopes and radium dials were
disposed of in a 15-foot deep trench approximately forty feet in length. The waste
materials were covered with general refuse and local soil material. Examination of 1988 aerial photographs detected a 4-acre scar of disturbed earth that may be the location of the burial site.
-
-
-
Cavern Detection In The Presence Of A High-Contrast Surface Layer
More LessVarious geophysical methods for cavern detection were tested over a known shallow
cavern (Cave of the Mounds in S. Central WI) where the geologic section was particularly
problematic for geophysical work. The physical properties contrasts of the weathered
shale/shale, and massive dolomite section were so great that the conventional use of several
geophysical methods failed. Seismic refraction, however, was useful for defining the shale
thickness and also showed that the shale-dolomite contact was irregular, with several meters
of local relief. A detailed gravity survey showed numerous small features which were
apparently due to the variability in the thickness of the low-density surface layer. No seismic
Head waves passed through the cave level because the cave is located well within the thick
dolomite unit; hence arrival time delays were not significant. Shallow reflection records
were overwhelmed by reverberations due to the 1:10 velocity contrast. GPR was unable to
reach the dolomite because of the 20 Ohm-m surface resistivity. Slant resistivity soundings
using the Bristow technique (pole-dipole array) was the only technique which showed the
presence of the 30 foot deep cave, but even this required drastic modification of the
reduction and plotting methods to accommodate the 1:40 contrast in layer resistivities. This
example illustrates how crucial it is to obtain physical properties information early, to assist
in the choice of the appropriate geophysical techniques or their modifications.
-
-
-
Environmental Geophysics - Breaking The Cost Barrier
Authors James R. Rossiter and J. Les DavisThe number of environmental site assessmentsc onducted in North America has grown rapidly
over the past decade. This growth is expected to continue, driven by tighter environmental
regulations in almost all jurisdictions and concerns about environmental liability. However, the
use of non-invasive, geophysical techniques for environmental work has not kept pace with this
growth generally. We find this relative reluctance to use geophysics for environmental
investigation curious, particularly since it would appear that there is a need for the kind of rapid,
non-invasive information that geophysics has been providing steadily to the explorationist for
several decades (Barinaga, 1990; Won, 1990).
-
-
-
Electromagnetic-Terrain-Conductive And Ground-Penetrating-Radar Investigation At And Near The Ciba-Geigy Superfund Site, Ocean County, New Jersey: Quality Controland Quality Assurance Plan And Results
Authors Gary J. Barton and Tamara IvahnenkoGround water is the principal source of drinking water in the
vicinity of the Ciba-Geigy Superfund site near Toms River, Ocean County,
New Jersey. The presence of earlier identified point sources of
organic-compound and, to a lesser extent, metals contamination dt the
Ciba-Geigy Toms River Chemical Company Plant has resulted-in severe
degradation of ground-water quality and has increased the potentiil for
water-supply problems (NUS Corporation, 1988). The point sources of
contamination include a manufacturing area, a backfilled-lagoons area, a
former fire-prevention training area, several sludge-disposal areas, and
a drum-disposal area. A borrow area also is considered a potential
source of contamination (Camp Dresser 6 McKee, Inc., 1989).
The U.S. Environmental Protection Agency requested that the U.S.
Geological Survey evaluate the hydrogeologic conditions in the Kirkwood-
Cohansey aquifer system (Zapecza, 1989) and the extent of ground-water
contamination on the property of the plant (which includes the Superfund
site) and in Winding River Park, which borders the Toms River
immediately to the east of the Superfund site (Barton, 1989). This
investigation included an electromagnetic-induction survey covering
45 line miles throughout the site and a ground-penetrating-radar survey
in part of the borrow area.
The quality assurance/quality control plan (QA/QC) for the
electromagnetic-induction survey established guidelines for performance,
system audits, and data validation, and set control limits for
instrument and procedural precision. The QA/QC plan for the groundpenetrating-
radar survey sets guidelines for performance and system
audits.
-
-
-
Low And High Frequency Electromagnetics In Landfill Investigations
More LessLow frequency induced electromagnetic (EM) fields (< 1 megahertz (MHz)) primarily respond to
the earth’s conductivity, whereas high frequency EM fields (propagated as in ground penetrating
radar (GPR)) are a complex function of the earth’s dielectric permittivity, conductivity and
magnetic permeability.
Low frequency (c 40 kilohertz &Hz)) EM data can be utilized to approximate a shallow (< 6
meters (m)) multi-layered earth model provided different instruments and intercoil spacings are
used. The constructed model can be used as a starting model for higher frequency EM
techniques such as GPR, which operate at radio frequencies and provide increased resolution of
the geologic system.
-
-
-
The Determination Of Physical Properties Of Groundwater Aquifers Using Shallow Seismic Reflection Methods
Authors P.T. Miller, J.A. Madsen and S. McGearyA land-based shallow seismic reflection data set was
acquired along the barrier island complex of coastal New Jersey
for the purpose of understanding the physical properties and two
dimensional organization of four Tertiary hydrogeologic units:
the Kirkwood-Cohansey Aquifer System, the Rio Grande Water
Bearing Zone, the Atlantic City 800 Foot Sand, and the Piney
Point Aquifer. A series of 6-fold common depth point seismic
sections covering 5.0 km. was obtained. Data were acquired on
sandy beach areas, oceanward of the central island axis, to
depths of 600 feet. A detailed velocity analysis (5 m intervals)
revealed subtle vertical and lateral velocity variations
(detectable to 10 m/s) within the sediments. Dominant reflector
frequencies of ,200-250 Hz were observed leading to a theoretical
vertical resolution of 1.0 to 2.0 m. The seismic results were
combined with local well log information to make important
inferences regarding porosity, permeability, and aquifer
geometry. A synthetic seismogram generated from the Island Beach
State Park Test Well No.1 (sonic log) correlates well with field
sections, enabling a more precise definition of bed boundaries
and aquifer wavelet responses.
A linear multiple regression model was developed which
relates acoustic traveltime to relative gamma ray and relative
resistivity readings at the test well. The relation was then
applied to nearby wells possessing gamma ray and resistivity
logs, yet devoid of acoustic information. Pseudo-synthetic
seismograms were generated based upon the model and relative
gamma ray and relative resistivity readings from the new wells.
Comparison of the pseudo-synthetic seismograms with field seismic
sections shows good agreement, thereby enabling estimation of
lithology, velocity, and porosity. A characteristic seismic
signature for the aquifers of interest has been constructed from
the above information.
-
-
-
Shallow Seismic Reflection Applied To Quaternary Paleochannels
Authors R.B. Genau, J.A. Madsen and S. McGearyA high resolution seismic reflection survey was conducted
at Taylors Island, Maryland with the objective of identifing buried
paleochannels of the Susguehanna River. One 2.5 km six-fold CDP
reflection profile was acquired using a portable Bison 8012A
seismigraph, a 10 lb. sledge hammer/aluminum plate source, and 12
single accelerometers as receivers. Reflections from interfaces
to depths of 100 m were desired in order to observe the
relationship between incised Quaternary paleochannels and the
underlying Tertiary marine sediments. The data were collected
using an end-on spread configuration with a 25 m source to first
receiver offset and a 5 m receiver spacing. Profiles obtained from
processing of the data clearly indicate the presence of one or more
paleochannels in the subsurface that were cut during a low stand
of sea level. Channel margins are apparent due to the undulating
nature of the unconformable reflecting interface that is observed
to truncate older concordant sub-horizontal reflectors below.
Channel fill reflectors representing sediments deposited during a
subsequent high stand of sea level are generally horizontal and
concordant with underlying seismic reflectors except where they
onlap at the channel margins. The shallowest fill reflector
detected is at 10 m depth, whereas a channel depth of 53 m is
calculated assuming a velocity of 1420 m/s. A spectral analysis
of selected traces indicate a dominant frequency of approximately
125 Hz, with frequencies of up to 200 Hz not uncommon. The
theoretical vertical resolution of 1.8 m is possible using the l/4
wavelength criterion.
-
-
-
A Shallow Seismic Reflection Study Of The Water Table
Authors P.T. Miller and R.B. GenauA shallow seismic reflection survey was conducted
approximately one mile southeast of Newark, Delaware to determine
the depth and geometry of the water table. The site is located
0.25 miles from a landfill where this method may be used in a
pollution remediation effort. Of particular interest in this
study are the optimum in-field seismograph recording parameters
and geophone array spacings, the adequacy of a hammer/aluminum
plate seismic source in this environment, the vertical and
horizontal resolution of the water table reflector given an
unsaturated overburden, the seismic facies characteristics of the
water table reflector (reflector frequency, amplitude, coherency,
interval velocity, and configuration), and the three dimensional
geometry of the water table surface. A series of walkaway noise
tests were performed to (a) determine the feasibility of
accurately recording a reflection from the water table, (b)
define the ,low cut filter which maximizes the water table
reflection signal while simultaneously suppressing ground roll
effects, (c) to ascertain the nature of all coherent and
incoherent seismic noise (ground roll, ground coupled air wave,
multiple reflections, wind, and electrical), Cd) to observe
possible phase and amplitude distortions in the water table
reflector as predicted by the Zoeppritz equations, and (e) to
compare calculated reflection and refraction depth and velocity results.
All data were recorded with severe, low cut pre-emphasis
filters (350 Hz) to attenuate the high amplitude, low frequency
ground roll component which dominated the early portions of the
record. Reflection signals from the water table interface
exhibited dominant frequencies of loo-150 Hz and stacking
velocities of 1420 feet per second, leading to a theoretical
vertical resolution of 2.4 feet (based on l/4 wavelength
criterion). Reflection depths and velocities were 34.8 feet and
1420 feet per second as compared to refraction depths and
velocities of 35.5 feet and 1434 feet per second.
Two parallel six-fold common depth point seismic sections
and 5 common offset seismic sections comprised a three
dimensional seismic grid from which the geometry of the water
table was determined. The CDP seismic sections exhibited a
coherent, high amplitude reflection at 50 ms. Using a stacking
velocity of 1420 feet per second, a reflector depth of 35 feet
was calculated. Later drilling confirmed the water table depth at
35 feet.
-