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3rd EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 12 Mar 1990 - 15 Mar 1990
- Location: Golden, Colorado, USA
- Published: 12 March 1990
21 - 31 of 31 results
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Geographic Information System Analysis Applied To Mapping Subsurface Brine, Brookhaven Oil Field, Mississippi
Authors Bruce D. Smith, Joseph L. Plesha and Robert J. BisdorfOil and brine production from deep horizons (1 km) in the Brookhaven oil field in southern Mississippi
has caused brine contamination of shallow (400 m) ground water. In order to evaluate the use of airborne
geophysical methods to map the extent of subsurface brine contamination, the U.S.Geological Survey, with
research funding from the Environmental Protection Agency, contracted a helicopter electromagnetic (HEM)
survey of the oil field area. The speciiic objectives of this research are to (1) evaluate the application of
airborne geophysical methods in an area of many cultural features that can interfere with these measurements,
and (2) interpret the subsurface distriiution of brine and fresh water. We applied a particular Geographic
Information System (GIS) can be to address these objectives.
The GRASS (Geographical Resource Analysis Support System) program developed and distriiuted
in the public domain by the Army Corps of Engineers Research Laboratory (CERL) has been adapted by the
USGS for use on a networked system of Hewlett Packard 9000 series 300 computers. Many other GIS software
packages available both commercially and in the public domain could be used to perform tasks similar to those
described here.
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Transient Electromawetic Imaginq Of A Basin Margin Underneath The Savannah River Site, Aiken, South Canolina
Authors Bryan James, Van Price and Jim HildAn experimental transient electromagnetic (TEM) survey was performed at
the Savannah River Site (SRS) near Alken, South Carolina, to assess the
viability of a subsurface imaging method. The goal of the survey was to
improve resolution of mapping the margln of a buried Triassic basin partially
underlying SRS. A high data density survey was conducted utiiizing multiple
large loop transmitters with overlapping profiles of measurements from each
transmitter. Any attempt to image subsurface structure requires such data density.
A gap in interpretation tools exists in all electrical methods between
layered earth inversion and numerical modeling of two-dimensional (20) or
three-dimensional (3D) structures. Recent TEM research has focused on
development of methods to image subsurface geoelectric structure without
resorting to numerical modeling. The method described here constructs a
subsurface geoeiectric image by a novel means of stacking TEM data in both
time and space.
The stacking procedure is based on knowledge of where currents are
flowing in the subsurface of an approximate background model. Weights for
stacking of the TEM data into estimates of anomalous current flow on a
subsurface grid are calculated from these known current flow patterns as a
function of time, measurement position and subsurface grid element position
using Biot-Savart’s Law.
Thus, for the SRS survey, a 2D structure is imaged built on knowledge
of the fleids of an approximate one-dimensional (1D) model. The basin margin
under SRS is successfully resolved by the imaging method. The imaging
result provldes better resolution than obtained by splicing together layered
earth inversion models.
Various pros and cons of this imaging method are discussed to indicate
future directions for TEM imaging.
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We Don't Get No Respect / Perceptions Of Engineering And Environmental Geophysics
More LessThe lament in the title is familiar to every geophysicist in this audience. For at least the last
twenty-five years that I have been in the business, geophysicists in every industry except oil have been
complaining that our clients neither understand what we do nor appreciate what we have to offer. For the
most part we have blamed everyone but ourselves:
Geologists call us “geomagicians”; they don’t comprehend our technology.
Engineers want answers with too many significant figures; they don’t understand the uncertainties
in our measurements. Environmental geoscientists won’t listen; they need to learn how we can help them.
Mining engineers don’t trust us. Clients never want to pay what it takes for good results; they don’t appreciate the complexities of
our business. Regulators have unrealistic qualitycontrol expectations; they don’t realize that every project is
inherently research. Politicians want to register us. Charlatans give us a bad name. SAGEEP was one of the first serious attempts to admit that we have a responsibility to
communicate with and sell ourselves to industries such as mining, groundwater, civil/geotechnlcal
engineering, and environmental management. The attendance at these symposia and the national
recognition they’ve received are testimony to the insight, hard work and success of a small group of
geophysicists who conceived and organized SAGEEP. Now it is time to recognize that all of us have a
responsibility to build on their beginning.
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Application Of Geotomography To Rock Investigations
Authors Hideki Saito, Hiromasa Shima and Tetsuma ToshiokaThree types of geotomography, namely, seismic, radar and resistivity tomographies were
developed and applied to investigating the rock foundation for a planned bridge pier.
These techniques made it possible to reconstruct distribution images of seismic wave velocity,
electromagnetic ( EM ) wave velocity and resistivity, respectively. Therefore, if we want to
know the rock conditions totally, it is very effective to apply these three kinds of geotomography
jointly, and to interpret the results consistently.
In this paper, the methods of these tomography techniques developed by the authors were
reviewed briefly and a field example of applications of these techniques to site investigations
was demonstrated. We obtained three kinds of tomograms and identified fracture zones as
the low seismic velocity, low EM wave velocity and low resistivity zones. In addition, from
the interpretation results of these tomograms, we could not only map the fracture zones, but
could also estimate the rock conditions in detail. The results were confirmed by geological and
geotechnical investigations conducted after the excavation for the construction of the bridge pier.
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A Case Study Of Rock Investigation Using Resistivity Image Profiling
Authors Hiromasa Shima and Hideki KamiyaThe authors have developed an electrical exploration
technology, called "Resistivity Image Profiling", which has
since been applied to many sites in Japan. In this method, a
two-dimensional or a three-dimensional underground resitivity
distribution is analyzed. This method combines an accurate
in-situ measurement technique and automatic computer analysis to
obtain more detailed and reliable results than conventional
electrical methods. The analyzed results are displayed as a
color profile which shows the resistivity structures more clearly.
2-D "Resistivity Image Profiling" was applied in a mountainous area where construction of a highway tunnel was
planned. The final analysis results show a complicated
resistivity distribution having a range from less than 50 Ω ·m
to more than 5000 Ω ·m. Using the resistivity values, we
classified the rock properties into four general categories:
fresh rock, relatively fresh rock that includes many joints,
weathered or altered rock, and fracture zone with clayey
materials. Further, we estimated both underground water levels
and locations of faults to identify the most likely area where
water burst out could occur. The tunnel is now under construction and the excavation
results are confirming our interpretations of fault locations
and rock properties. The actual locations of water burst out
also have shown good agreement with our predictions.
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Delineation Of Buried Valleys Using Integrated Geophysical Techniques
Authors Steven R. Becker, Benjamin H. Richard and Paul J. WolfeIn northeastern Greene County, Ohio, Beaver Creek (a very small
stream) flows through a valley whose width exceeds a mile in some places.
Orton (1874) recognized that this valley was once the site of a much
larger river. Kulibert (1979) established that during early Wisconsin
glaciation the valley was occupied by the much larger Mad River. The
valley is also partly superimposed on the preglacial Hamilton River Valley
(Norris et al., 1950). Both valleys, the ancestral Beaver Creek and
Hamilton River, are currently filled with sediments. This study is a
detailed multi-faceted geophysical profile study of the ancestral Beaver
Creek Valley where it exists cut into the west side of the Hamilton River
Valley (Figure 1).
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The Use Of Geophysics In Preacquisition Site Assessments (Psa’S) A Case History
Authors Don Kleinfelder, Todd Croft, Rich Fink and Bill GatesEnvironmental consultants must occasionally perform environmental audits on parcels that
have little or no known historic records. In such cases, the accurate evaluation of
geophysical data can be invaluable.
This paper presents a case study in which a magnetometer survey was used to evaluate a
vacant parcel that formerly contained six military helicopter pads and gotentiallg still
contained associated underground storage tanks. An in-depth records searc reveale little
-about the site, but evaluation of proton magnetometer data indicated a dense, potentially
vertical object approximately 15 to 20 feet below the surface near the pad locations.
Excavation of the anomaly revealed a concrete vault and a redwood vault connected by a
10’ long, 6” diameter metal pipe. The pad and vault were both filled with an assortment of
military porcelain, glassware and scrap metal. Unconvinced that such debris caused the
anomaly, we scanned the excavation with a metal detector and located an object beneath
the concrete pad. Further dewatering and excavation uncovered an 8-inch diameter, 40-
foot deep irrigation well remnant of pre-military ranching operations. We concluded that
this casing produced the magnetometer anomaly.
This study provides a lesson on the necessity of carefully evaluating excavated objects based
on the geophysical data before assuming that the objects represent the target anomaly.
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Case Eistory Of The Removal Of Lead Contaminated Soil Prom A Residential Area
More LessThe operation of a former battery processing facility from 1963
thru 1980 resulted in surface soil contamination of eighty homes
and nearby drainageways. Engineering plans were developed to
remove lead contaminated soil from the residential areas. The
plans defined area1 removal limits and depths based on a 500 parts
per million action level.
Soil removal plans were developed on a block by block basis.
Preliminary removal limits were established using the soil sampling
results performed an extent of contamination study. Removal limits
were verified with additional sampling prior to excavation.
Excavation sequences and methods were developed by the contractor
and engineers prior to removal activities to minimize unnecessary
inconveniences for the residents. Confirmatory samples taken after
the designed removal of contaminated soil were used to indicate the
need for additional excavation or the beginning of restoration.
A community relations program was instituted to provide residents
with a communication link to the client and engineers. The
community relations program promoted an atmosphere of open
communication which helped lead to a successful completion of the -
project. Periodic meetings between the residents and engineers
were set up during various project phases. These meetings often
provided valuable information explaining contamination patterns and
also allowed residents to express concerns and/or problems. This
program gave the residents a first hand knowledge of the project
and helped alleviate concern and worry.
This case history documents the procedures used to safely remove
lead contaminated soil from a residential area. Problems arising
from the removal action and restoration of properties were handled
on an individual basis. The open communications between the
engineers, the regulatory agency, and the residents resulted in a
successful remediation project.
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Use Of The Seismo-Electric Effect In Engineering Problems
Authors Catherine K. Skokan and Dong ChiThe seismo-electric effect is observed as the development of
potential between two points in a rock subjected to elastic
deformation. This effect is a function of physical properties
which are parameters desired in the collection of geotechnical
data relevant to the estimation of the effects of geologic site
conditions on the level of ground shaking. Standard, high
resolution reflection or refraction seismic measurement of both
shear and compressional waves provide values of elastic moduli.
Borehole information can be added to supplement these data.
These measurements, by their nature, are directionally dependent.
Of interest to the geotechnical engineer evaluating geologic site
conditions are also values of porosity, permeability, fluid
saturation, and fluid salinity. Seismo-electric measurements
could yield this information in situ and at the same time as the
standard seismic measurement. The seismo-electric effect is not
directionally dependent and will, therefore, yield information on
the bulk properties of the rock.
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Monitor Well Completion Evaluation With Geophysical Density Logging
Authors E.N. Yearsley, R.E. Crowder and L.A. IronsThe competency of monitor well completions with regard to grout
continuity and the presence of the bentonite seal and sand pack can be
uniquely evaluated with geophysical density logging. This method relies on
density contrasts among various completion conditions. The presence or lack
of particular completion materials results In differences measurable with
geophysical density probes.
Empirical measurements made in the laboratory with density probes
provide information on depths of investigation and probe response to specific
completion conditions. These measurements support interpretations made for
two geophysical log examples presented herein. The examples indicate
discontinuous grout Intermittent with alluvium and air voids.
The economics of the density evaluation method are advantageous,
particularly with respect to the implications of a poorly constructed monitor
well, which include possible contaminant cross-flow and misspent monitoring
expenses.
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Multi-Mode Seismic Imaging Of Forward And Back Scattered Seismic Waves In A Cross-Borehole Physical Model
Authors A.H. Balch, H. Chang, Gregg Hofland and Kurt RanzingerSeismic cross-borehole data are extremely complex because they usually
contain compressional, shear, and converted mode body waves, plus tube waves.
The complexity is compounded by the fact that many of the seismic events are
forward-reflected and forward-scattered, while conventional seismic
interpretation usually assumes back reflection.
At Colorado School of Mines, we have developed a cross-borehole
processing and interpretation system which: 1. Separates p-waves from swaves,
2, Compensates for travel time errors due to phase distortion, and then,
3. Converts the recorded data into images of the subsurface reflectors and
scatterers. Four image outputs are obtained, one each for p-p, p-s, s-p, and s-s
reflections/diffractions.
The examples shown will demonstrate that imaged cross-borehole data are
vastly easier to understand and interpret geologically than the original recordings.
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