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9th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 28 Apr 1996 - 02 May 1996
- Location: Keystone, Colorado, USA
- Published: 28 April 1996
1 - 100 of 134 results
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Pulled Array Continuous Vertical Electrical Sounding (Pa-Cites) With An Additional Inductive Source.
Authors Niels B. Christensen and Kurt SørensenElectrical and electromagnetic profiling methods are used extensively in environmental
geophysical investigations for many different purposes. The PA-CVES method (Pulled-
Array Continuous Vertical Electrical Sounding), where a tail of electrodes is towed behind
a small vehicle while continuously measuring in many electrode configurations, has been
used extensively for mapping the vulnerabilty of aquifers. Measurements are done for
every 1 metre and lo-15 km of profile can be made in one day.
This paper presents a theoretical study of the resolution capabilities of PA-CVES
measurements, as they are now performed, and an experimental design study for
including an inductive source in the measuring equipment. The joint interpretation of the
galvanic data set of ordinary PA-CVES measuements and a small number of induc.tive
data from a horizontal magnetic dipole source will significantly enhance the resolution
capabilities of the data set.
The study is carried out by analyzing the uncertainty of the model parameters of a onedimensional
three layer model using the covariance matrix of the inversion problem.
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Development Of A Continuously Monitoring Resistivity Probe For Free-Phase Petroleum Hydrocarbons
More LessAn in-situ electrical resistivity probe was evaluated for use in monitoring the vertical distribution of petroleum
hydrocarbon in contaminated soil. By installing the probe to intersect the water table, it continuously monitors the
presence of free-phase hydrocarbons by detecting electrical resistivity changes corresponding to the degree of oil
saturation in the sediment pores. At a field site where diesel contamination occurs within a fine-grained sand, the
results from the probe were compared to chemical analysis of total petroleum hydrocarbons (TPH) of soil borings
and measured free product (light non-aqueous phase liquid-LNAPL) thickness and groundwater level in wells. The
resistivity probe was also used to study LNAPL behavior under fluctuating water table conditions in a controlled
laboratory environment. Results from the resistivity probe reflect the distribution of the contaminant within the
sediment on a continuous basis and more accurately than contaminant thickness measurements in wells.
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Seismoelectric Studies In An Outwash Plain
Authors Paul J. Wolfe, Jianming Yu and Naum GershenzonInitial studies of the seismoelectric effect in an outwash plain have been conducted near Yellow
Springs, Ohio. The purpose was to make seismoelectric measurements in a simple, well-understood
test site where the seismoelectric signals could be clearly recorded and theoretical predictions could
be calculated with as few assumptions as possible. Suppression of electrical noise was a major
concern because 60 Hz electromagnetic fields from the power grid system are unavoidable in most
parts of the United States.
The site was characterized by seismic refraction surveys, DC resistivity surveys, and two drill holes.
The site has a fairly uniform, 3 m thick unsaturated layer over a thick saturated sandy layer. The
water table was near the top of the outwash layer.
For the seismoelectric studies a sledgehammer source was used. Seismic signals and electrical signals
were recorded separately and jointly with a variety of electrode combinations. An engineering
seismograph was used to record both the seismic and electrical signals. The built-in 60 Hz and 180
Hz notch filters were effective in suppressing much of the power grid pickup.
Electrical signals were observed which were consistent in time and frequency with the expectation
of seismoelectric response due to the electrokinetic effect. The peak-to-peak electric field amplitude
was about 6 mV/m and the time delay corresponded with one-way seismic travel times to the water
table.
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The Electromagnetic Azimuthal Resistivity Method
Authors Stewart K. Sandberg and Donald L. JagelPumping ground water from a fractured rock aquifer commonly leads to preferential drawdown
controlled by bedrock fracture orientation. The azimuthal resistivity method has previously been used to detect
this fracture orientation in covered areas, which has led to a determination of the principal directions of
transmissivity by geophysical means. However, the azimuthal resistivity method often requires a large amount
of space, free from cultural interference. In additon, data collection can be both labor intensive and time
consuming.
In this paper, we describe the collection of azimuthal resistivity data using electromagnetic methods.
Commonly available terrain conductivity instruments can be used in the horizontal coplanar (vertical dipole)
configuration, and data collected in an azimuthal array. Field examples using this system are presented showing
empirical comparisons with azimuthal resistivity data, and both geologic and hydrogeologic data sets. Data
collection efficiency is increased six-fold by using electromagnetic methods in this application, compared to the
azimuthal resistivity method. Disadvantages of the resistivity method, such as high electrode contact resistance
and large spread lengths necessary for relatively shallow penetration, are avoided or lessened by the use of
electromagnetic methods.
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Determining Fracture Geometry From Azimuthal Resistivity Data
Authors John Jansen and Robert TaylorThis paper presents the results of a series of three-dimensional finite difference models conducted to
determine the response for Wenner array azimuthal resistivity surveys run over conductive fracture zones in resistive
bedrock beneath conductive overburden. Microanisotropic and macroanisotropic fracture systems with varying
overburden thicknesses were simulated. Microanisotropic models were simulated by applying a uniform anisotropy
factor to the bedrock layers. Macroanisotropic models were simulated by representing fracture zones as conductive
vertical dikes. The model results demonstrated that for both microanistropic and macroanistropic cases, the shape
and magnitude of the apparent resistivity ellipse varies significantly as a function of overburden and “a” spacing.
The magnitude of the variations is sufficient to cause significant misinterpretations of azimuthal resistivity field data.
Several important factors must be considered when interpreting fracture patterns from field data. In summary, these
are: 1) the choice of a macroanisotropic or microanisotropic conceptual model, 2) the thickness of overburden
relative to the “a” spacing, 3) the position of macroanisotropic fracture zones relative to the center of the array, 4)
the width of macroanisotropic fracture zone relative to the “a’ spacing and thickness of overburden, 5) the presence
of parallel or intersecting macroanisotropic fracture zones, and 6) the degree to which the field conditions are purely
microanisotropic or macroanisotropic, rather than a mixed model.
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Azimuthal Electrical Resistivity As A Tool For Determination Of The Orientation Of Preferred Hydraulic Transmissivity For A Dolomite Aquifer In Southeastern Wisconsin
Authors Douglas A. Carlson, Robert W. Taylor and Douglas S. CherkauerJoints in rock act as avenues for the flow of both electrical charge and water. Therefore methods which can efficiently map anisotropic distribution of electrical pathways should also provide
a good indication of hydraulic anisotropy. The azimuthal electrical resistivity survey method has been successfully used as a method for determining the trend(s) of generally local joint sets
in a variety of rock and soil types. This study, which is a regional study, demonstrates that the azimuthal resistivity method can be a reliable method for determining the trend of regional
joint sets within the Silurian-Devonian dolomite, a single rock type, in southeastern Wisconsin. In particular the study demonstrates on a regional scale the consistency of azimuthal
resistivity survey results with results from direct observation of joints and from the analysis of numerous multiple-well-aquifer tests conducted nearby. For this study, 26 azimuthal resistivity surveys were conducted at 17 sites scattered throughout the approximately 500 km2 area around Milwaukee, Wisconsin. Direct observation by previous workers have shown two major sets of joints within the dolomite at 24 sites throughout southeastern Wisconsin. Azimuthal resistivity surveys for this study have been able to reproduce the average observed joint trend to within 3 degrees. In addition, the transmissivity ellipses from 14 multiple-well-aquifer tests in nearby Mequon, Wisconsin are compared with the apparent resistivity ellipse results from azimuthal resistivity surveys. The average tend of maximum transmissivity obtained from this study's azimuthal resistivity surveys is within 6 degrees of the average trend of maximum transmissivity determined by multiple-well-aquifer tests. In addition, the azimuthal resistivity surveys may be can differentiated between which of the joints sets should dominate the flow of water.
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Very Low Frequency (Vlf) Geophysics: A Case Study On Locating Bedrock Wells In Water Bearing Fracture Zones For Use In Contaminant Migration Interception
Authors Christopher L. Covel, Darryn T. Kaymen, Ian M. Phillips and James C. HarrisonA Very Low Frequency (VLF) geophysical investigation was performed during June 1995 at an industrial facility in Waltham, MA. The VLF survey was used to locate ground water monitoring wells in water bearing bedrock fracture zones at the site to determine contaminate migration pathways and improve ongoing remediation of the ground water. The bedrock at the site consisted of Granodiorite and Gabbro-diorite and brittle fracture analysis indicated bedrock was permeable and highly fractured. Historical releases of chemicals have reportedly occurred at the site.
Previous investigations indicated contaminated ground water exists in the bedrock at the site. The objective of using VLF geophysics was to increase the likelihood that water bearing fractures in the bedrock were intercepted during drilling, and that the most conductive zones were intercepted. The VLF geophysical survey consisted of six days of field work by
two geophysicists, covering 5,290 meters of geophysical survey line, and nine days of data interpretation, to select the proper drill targets. Three separate VLF stations were used to collect
the data. The data was collected and interpreted using the ABEM WADIcTM' instrument and SECTOR software.
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The Very Early Time Electromagnetic (Vetem) System: First Field Test Results
Authors David L. Wright, Thomas P. Grover and Victor F. LabsonThe very early time electromagnetic (VETEM) system is a time-domain, surface-deployed system
that has potential applications to direct detection of non-aqueous phase liquids as well as to the
detection of buried objects. It is designed to operate in environments that are too conductive for
ground penetrating radar (GPR) to be effective, and too shallow for standard electromagnetic
systems. The VETEM system is a faster profiling complement to the frequency-domain high
frequency sounder (HFS).
First field tests of the VETEM were made at the Geophysics Performance Evaluation Range at
Rabbit Valley west of Grand Junction, Colorado in June and July, 1995. A number of well
defined targets of various types are buried there (Allen, 1995). The VETEM system was next
used as part of the Electromagnetics Integrated Demonstation (EMID) at the Cold Test Pit at the
Idaho National Engineering Laboratory (INEL) in November, 1995. The Cold Test Pit has a
number of subareas with buried objects of various types. For the EMID tests, VETEM was run
over three gridded areas: the Primary Grid (PG), the Large Object Pit (LOP), and the Calibration
Cell (CC). In this paper we display recorded lines from the LOP that show VETEM is
responding to electrical properties of the near surface and to buried objects.
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Vetem - A Very Early Time Electromagnetic System - Year 2
Authors Louise Pellerin, M. Cathy Pfeifer and Victor F. LabsonIn electrically conductive conditions common in environmental characterization studies the
minimum depth of investigation for traditional electromagnetic (EM) sounding techniques is
roughly 5 meters, while ground penetrating radar (GPR) systems often investigate no more than
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 between the lower limit of GPR and the upper limit of traditional
electromagnetics (EM). Bridging this gap is essential to the characterization of buried waste,
contaminant plumes, and other environmental and hydrogeological targets located in the shallow
subsurface. The Very Early Time Electromagnetic (VETEM) system is designed to ascertain the
conductivity and dielectric properties of the shallow subsurface in conductive terrain (Pellet-in et al.;
1994, 1995). Hence, the one-dimensional (1-D) and three-dimensional (3-D) numerical modeling
algorithms, developed in the first year of the project, contain the full solution to the EM problem
including both displacement and conduction currents.
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Resolution Of 3D Earth Structures - Detection And Measurement Configuration Using Different Sources.
Authors E. Auken and G.M. HoverstenIn this paper it is shown that a plane wave source, an infinite line source and a vertical magnetic dipole source
generate approximately equal peak responses from a thin three dimensional (3-D) conductor. The main difference between
source types come in the layered response. In general the plane wave source is greater than the infinite line source layered
response which in turn is larger than the dipole layered response. For the anomaly index, as measured by the ratio of
secondary to layered response, the magnetic field component is largest for the dipole source and smallest for the plane wave
source whereas for the electric field the magnetic dipole has the smallest anomaly index. This is true both when the dominant
mode of excitation is current gathered into the scatter from the surroundings (channeling currents) and current induced in
the scatter (vortex currents).
We consider large and small transmitter loops with in loop and out of loop receiver configuration in both the
frequency and the time domain, Most of the currently used prospecting system configurations in either mining or
environmental work are thus covered. In the time and the frequency domain we find that a system which measures the
horizontal magnetic field has a anomaly index one to two orders of magnitude larger than a system which measures the
vertical magnetic field. Furthermore, conclusions regarding the optimum source-receiver configuration are dependent on
the target orientation. In the time domain, for a vertical thin sheet, the anomaly index is largest when the loop size is of the
order of the depth to the conductor whereas in the frequency domain a much larger loop can be employed.
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The Quantitative Influence Of Sallnity On The Apparent Resistnity On A Physical Model Upon Saltnation
Authors Kamal Khair and Catherine SkokanThe excessive exploitation of groundwater aquifers leads to water table drawdown, and
subsequentfy to the contamination of these aquifers by the intrusion of sea water or other hazardous
sources. This wortdwide environmental problem is becoming increasingly critical in coastal agricultural
areas, where the fine grarned materials develop a thick fringe zone. By evapo-transpiration the moisture
of this zone pumps up the satt in the dry season, which cannot be efficiently washed away in the wet
season. Over the years the salt will accumulate at different rates for different terrarns and climates.
which will uttrmately cause the deterioration of the land Lebanon is not an exception and the moderate
precipitation rate together with a strong water flow in wmter cannot, in the long term, compensate for the
consequences of chaotrc and uncontrolled exploitation of coastal aquifers.
The current study investigates the possibility of an early detectron of salination. through
systematic observation of electrical resistivity in selected positions with fixed electrode arrays A direct
current electrtcal profiling system of Wenner configuration was tested in the laboratory using a physlcal
model. The model was constructed of wood and plastic filled with saturated sand and hawng a constant
water flow of 1.6 Vmn. The model size is 148 by 85 cm for lateral dimensions and 25 cm of sand
thickness. with a total porosity of 36%. Upon salination the salt was increasingly added to fhe system to
reach a concentration of 32 gn. Upon desalinahon satt water was replaced by fresh water to dilute the
water In the system to a concentration of 0.25 g/t. The results show that the relationship between
sallnrty and electrical resistivity is inversety proportional and characterized by linear loganthmlc function.
the velocity of water flow calculated by abrupt resistivity changes is tower than the hydraulic velocity; the
reslstivity values for low salinity upon desalination are much different (smaller) than those upon
salination of equivalent salt concentrations; the relative change of resistivity upon salination and
desatination involves almost equally all features of the tank that have distinctive resrstrvrty values.
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Mapping Of Impediments To Contamination Flow Using Multicomponent Reflection Seismology At The Savannah River Site
Authors Omar A. Dickenson, Gilein J. Steensma and Thomas M. BoydA major obstacle to the remediation of contaminated aquifers at the Savannah River Site in Aiken, South Carolina is
the presence of discontinuous sand and clay lenses that are difficult to map effectively using geologic and geophysical
well logs. In order to map these discontinuous sand and clay lenses we acquire two perpendicular nine-component
(9C) seismic lines, a 9C Vertical Seismic Profile, (VSP) and p-wave and s-wave sonic logs in a borehole south of the
Old Burial Ground at the Savannah River Site within which were available natural gamma ray and interpreted geology
logs. P-wave reflections are interpreted as originating from water table, the Tan Clay, the Green Clay, the top of
the Ellenton Clay, and a calcareous sediment layer within the Barnwell/McBean aquifer. Along the east-west trending
line, reflectors are generally continuous except for the occurrence of a discontinuity in the upper reflectors near the
east end of the line. This discontinuity could be interpreted as a sediment slump feature possibly related to the dissolution
of the calcareous sediment layer, or as the eastern terminus of a large scour feature. Along the north-south
trending line, reflectors are spatially less continuous and are interpreted as being cut by several channel/scour features.
The shear-wave stacks are interpreted as mapping the top of the Tan Clay and the calcareous sediment layer and show
evidence of azimuthal anisotropy. Using Alford rotations to maximize the energy in the fast and slow shear directions
gives a magnitude of anisotropy of 3% with a direction of anisotropy agreeing, near the center of the east-west trending
line, with the regional stress direction. Although the most consistent anisotropy is observed near the center of the
line, systematic variations along the line suggest that the observed anisotropy is not related solely to the regional
stress field. Other mechanisms that could be responsible include grain orientation, stacked stratigraphic features, and
depositional or erosional lineations. None of these mechanisms can be excluded until further analysis of the 9C VSP
and until laboratory measurements of core samples have been completed.
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Shallow Seismics When Access Across Contaminated Areas Is Prohibited
Authors James C. Hasbrouck and Rust GeotechBecause of health hazards and possible breach of contaminant caps, waste-site managers are
reluctant to grant permission to conduct geophysical surveys directly across repositories. Yet,
they need to know if the integrity of confined aquifers is being maintained beneath these sites
and if contaminant pathways may exist outward from these sites. One possible way to supply
these needed answers is the use of three-dimensional (3D) seismic reflection surveys. These
surveys can acquire data around the perimeter of a restricted-access area while lines that
traverse the area may be selected for processing and interpretation.
To evaluate the feasibility of this approach for an area where these problems exist, a threedimensional,
three-component (3D/3C) seismic survey was conducted at the U.S. Department
of Energy’s Savannah River Site (Figure 1) along the survey lines shown in Figure 2. Both
P- and S-wave seismic data were taken from a set of 13 source points along Line A at a
separation of 12 m into a spread of 24 three-component, 40-Hz geophones along Line C. The
geophones were set at a perpendicular offset of 36 to 105 m from the center of the source
point array (Figure 3). At each source point, a 9.1-kg hammer was repeatedly struck
vertically and then horizontally in four directions against a firmly embedded steel fixture.
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The Anomalous Behavior Of Sh-Waves Across The Water Table
Authors P. Michaels and W. BarrashMost theoretical studies of seismic wave propagation in a porous medium do not predict a significant
increase in SH-wave velocity with increasing water saturation. Although that type of behavior is commonly
predicted for P-waves (and confirmed by countless observations), the expectation for SH-waves is a slight
decrease in propagation velocity with increasing water saturations. While published measurements of SH-wave
velocity in laboratory studies have been supportive of such a slight decrease in velocity, the data have been
biased towards high pressures (typical of oil reservoirs at large depths of burial). On the other hand, the few
published low pressure laboratory measurements have revealed significantly different results.
The authors’ in-situ measurements of seismic wave velocities in a shallow, coarse grained, unconfined
alluvial aquifer document a significant SH-wave velocity increase in the transition from the vadose zone to the
water table. In one vertical seismic profile (VSP), the P-wave velocity increases by a factor of 4.2 and the SHwave
velocity increases by a factor of 2.6. What is not clear at this point is the true nature of the increase. Is
the velocity increase an expression of the presence of water in the pores, or does water alter the rigidity of the
soil matrix?
In addition to the broad-band velocity increase, we have also observed changes in the attenuation of SHwaves
across the water table. After correcting for geometric spreading, the amplitude decay observed in the
vadose zone has been found to be larger than that observed below the water table. However, the variation in
amplitude decay as a function of frequency and the measurements of body wave dispersion were found to be
larger below the water table than above. That is, the water saturated soil behavior is consistent with a Voigt
solid, but the dry material appears to follow a different model.
The authors will discuss these observations in the context of the current debate on Poisson’s ratio and the
Vp/Vs ratio.
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Multi-Component Seismic Acquisition In Engineering And Environmental Investigations
More LessShear waves and compressional waves are sensitive to different physical properties of earth materials. In addition
shear waves exhibit unique phenomena associated with anisotropic material which can be used to examine
variations in earth properties with direction. These facts have been exploited to advantage in the oil and gas
industry for over 10 years. In the engineering and environmental fields, similar advantages can be demonstrated.
The advanced utility of multi-component seismic will be illustrated using a number of examples from both the
shallow and deeper fields.
Fracture maDDin2. In bedrock controlled hydrology, fracture and shear zones often represent the dominant
pathways for groundwater flow and contaminant migration. On entering such anisotropic zones, shear waves split
into two distinct waves with different velocities and polarization directions. The split shear waves (s-wave
birefringence) can be used to determine not only the strike of fractured zone but can also be used as a tool to map
areas of increased fracturing.
ManDing stratiPraDhv in unconsolidated sediments. In unconsolidated sediment sequences, important objectives
often are mapping clay and sand strata. In particular, the continuity of clay layers as barriers or aquitards to
contaminant migration is a principal objective in characterization and remediation investigations. As noted by Clark
et al. (1994) and Dobecki (1995) shear wave reflection surveys can, for this purpose, under certain circumstances,
demonstrate significant advantages over compressional wave reflection surveys, such as; higher seismic impedance
contrasts at clay-sand interfaces, insensitivity to water table and better resolution for detecting “thin strata.
However, these benefits are not always realized.
In shallow investigations only a small part of the potential information available in shear wave investigations is
typically acquired and analyzed. The full amount of information available in multi-component data has been
illustrated by Crampin (1985) and by Hasbrouck (1987) for the shallow field. By recording a full nine component
(9C) data set or some subset thereof, properties associated with shear wave birefringence can be utilized. For
example, the difference between Sh, or cross line, and Sv, or inline, shear wave travel times at the far offsets on a
surface reflection survey can reveal the magnitude of the layer anisotropy in unconsolidated sediment sequences.
These additional properties and the information contained within them are reviewed in further detail.
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The Accuracy Of Shear Wave Velocity Measurements Taken Using The Seismic Cone Penetrometer
More LessThe purposeo f this study was to determinet he accuracy of shear wave velocity measurementsm ade using the seismic
cone penetrometer. The general framework for the performance of this test and the evaluation of the field data is from
the area of geophysical exploration, and is based on the premise that the first arrival time of a shear wave can be easily
deciphered from field seismic wave traces. However, when seismic wave traces are not clear, it is common to pick peak
arrival times for the calculation of interval shear wave velocities. Many of the important aspects of wave propagation
which can have an influence on the peak arrival times of the shear wave such as multiples, transmission effects, and
attenuation, are usually not corrected for, meaning that some amount of error may be introduced into the arrival times
used for calculating interval shear wave velocities.
Since development of the seismic cone, studies have been done to address this issue. However, they focused primarily
on using digital signal processing techniques to obtain more accurate arrival times from clear seismic cone wave trace
data whose first arriving shear wave times were distinct, rather than on accounting for the case where the first arrival
time could not be easily deciphered from the trace. For this research, we used acoustic modeling (SH wave equation) to
account for transmissione ffects, multiples, reflection, refraction, and ghosts. Using the acquisition geometry and the
velocities estimated from several seismic cone penetrometer test sites in the San Francisco bay area, we modeled the
theoretical seismic wave traces. We estimated the first arrival times of the theoretical seismic traces and then computed
interval shear wave velocities. We then compared these velocities to the field seismic cone velocities.
The results indicate that seismic cone velocities can be within *5% of theoretically derived velocities when the first
arrival time is used. When peak arrival times are used, seismic cone velocities, are approximately 20% higher than
theoretical velocities in soil with increasing density, and approximately 20% lower than theoretical velocities in soils
with decreasing density. At interfaces where there is a change in soil type, it is recommended that seismic cone
velocities not be used. Confidence in the resultso btained from seismicc one penetrometer test measurementsc an be
greatly increasedif knowledgeo f the specific soil types is available.
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High-Resolution Seismic Reflection Survey At Dover Afb: A Comparison Of Three Seismic Sources
More LessIn June of 1995, the Earth Sciences Division of the Air Force Phillips Lab, with survey equipment
from the University of Delaware and assisted by the Kansas Geological Survey and Elohi Geophysics,
conducted a geophysical site characterization of the SERDP-funded Groundwater Remediation Field
Lab (GRFL) located at Dover AFB, Delaware and administered by Applied Research Associates for
USAF Armstrong Lab. Seismic data were collected in order to 1) compare the results using three
different compressional sources and 2) cover the field site well enough to characterize the seismic
response of the shallow subsurface. This paper will focus primarily on the first of these two goals.
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A Vibratory Seismic System For High-Resolution Applications
Authors George W. Schneider and John VanderkooyA vibratory seismic system has been developed by the authors, utilizing an engineering seismograph a&
a low-cost vibratory source. The project was a collaboration between the Geophysics Group at the Waterloo Centre
for Groundwater Research (WCGR) and the Audio Research Group in the Department of Physics at the University
of Waterloo. The system was developed in the winter of 1995 and preliminary field work was completed in the
spring of 1995. The source consists of an electrodynamic vibrator driven by a portable car audio amplifier. Source
excitation signals are generated with a sound card for a personal computer (PC). Software was developed to
generate excitations and perform crosscorrelation on the data. The source was well instrumented during preliminary
field tests, with accelerometers on both the reaction mass and moving coil, and a strain gauge between the coupler
and the moving coil to monitor the force acting on the coupler. Three different coupling devices were tested: a
short auger, a long auger and a baseplate. The preliminary testing was done at the Bauer Warehouse area on the
University of Waterloo’s North Campus, where both surface and downhole data were acquired. Continuous core
from a drill hole at the site shows that the stratigraphy consists of a series of glacial tills and alluvium underlain
by limestone of Silurian age below 68 metres. The water table was about 1 metre below ground surface at the time
of the survey.
For the surface tests, 24-channel common shot records were recorded. Twenty-four 100 Hz geophones
were spaced 2 metres apart with a source offset of 2 metres from the end of the array. For the downhole tests, an
8-channel hydrophone array was used to acquire a vertical seismic profile (VSP) from ground surface to 70 metres
depth. Hydrophones were deployed every metre with a source offset of 20 metres from the borehole. A number
of acquisition parameters were used and compared: sweep range, sweep duration, sampling rate and stack count.
Cosine-tapered linear sweeps as wide band as 50-1000 Hz were used. As well, pseudo-random maximal length
sequences (MLS) were tested. The 14-bit sequence used was “clocked out” at rate of 5 kHz, then bandpass filtered
from 100-1000 Hz prior to being used as an excitation. The results have been very encouraging; the vibrator
compared favourably to both a 12-gauge shotgun and a hammer and plate as a source. The baseplate was found
to be the preferred coupler, although the long auger generated a correlation wavelet with a higher centre-frequency
than the baseplate on VSP recordings. The short auger produced relatively poor records. Analysis of the strain
gauge response suggests the short auger applied the least force to the earth. Very good correllograms were obtained
using: 8 second sweeps from 50-1000 Hz, stacked 16 times, and recorded at a sampling rate of 2 kHz. The filtered
MLS excitation was found to be just as effective as sweeps of similar duration, stack count and frequency content.
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High Resolution Seismic Reflection Profiling At Aberdeen Proving Grounds, Maryland
Authors Richard D. Miller, Jianghai Xia, Stanley Swartzel, Jose Llopis and Paul MillerThe effectiveness of shallow high resolution ‘seismic reflection (i.e., resolution potential) to image geologic
interfaces between about 70 and 750 ft at the Aberdeen Proving Grounds, Maryland (APG), appears to vary locally
with the geometric complexity of the unconsolidated sediments that overlay crystalline bedrock. The bedrock surface
(which represents the primary geologic target of this study) was imaged at each of three test areas on walkaway noise
tests and CDP (common depth point) stacked data. Proven high resolution techniques were used to design and acquire
data on this survey.
Feasibility of the technique and minimum acquisition requirements were determined through evaluation and
correlation of walkaway noise tests, CDP survey lines, and a downhole velocity check shot survey. Data processing
and analysis revealed several critical attributes of shallow seismic data from APG that need careful consideration and
compensation on reflection data sets. This survey determined: 1) the feasibility of the technique, 2) the resolution
potential (both horizontal and vertical) of the technique, 3) the optimum source for this site, 4) the optimum acquisition
geometries, 5) general processing flow, and 6) a basic idea of the acoustic variability across this site. Source
testing involved an accelerated weight drop, land air gun, downhole black powder charge, sledge hammer/plate, and
high frequency vibrator.
Shallow seismic reflection profiles provided for a more detailed picture of the geometric complexity and
variability of the distinct clay sequences (aquatards), previously inferred from drilling to be present, based on sparse
drill holes and basewide conceptual models. The seismic data also reveal a clear explanation for the difficulties previously
noted in correlating individual, borehole-identified sand or clay units over even short distances. Geologic
cross-sections derived from CDP stacked data and borehole logs suggest locally complex geometries and horizontally
variable geologic contacts.
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High Resolution Seismic Refection To Determine Thickness Of Alluvium And Faulting In Bedrock
Authors Bart Hoekstra, Gilein Steensma, Walt Grinyer and Norman HarthillA seismic reflection survey was conducted at March Air Force Base (MAFB) with the objective to map the depth to
bedrock, locate bedrock faulting and define the stratigraphy overlying bedrock. The survey was conducted for the
purpose of identifying possible groundwater and contaminant migration pathways or obstructions, as well as areas
of depressed basement where dense non-aqueous phase liquid (DNAPL) contaminants might concentrate. The
survey consisted of a coarse grid of seismic lines and was designed to get coverage over a large area in an attempt to
get a basewide basement picture and define potential fault systems crossing the base (Figure 1). The design has the
disadvantage that the data are aliased because the station spacing is much shorter than the line spacing. However,
the design allowed us to determine four very valuable pieces of information: a) anomalous trends in groundwater
movement, b) depth and general structure of the basement reflector, c) areas where more detailed work may be
necessary and d) input for the more judicious placement of future drilling locations.
Previous work conducted in specific areas of the base by Tetra Tech (1993) and IT (1994) indicated that it was
possible to delineate these targets with the seismic reflection method, by that the data quality was dependent on
local site conditions and survey design had to be adjusted for these conditions. The types of cultural noise present at
the site during the survey included aircraft and ground traffic, with the latter posing a particular challenge, and
being a significant contributor to the choice of source type, as discussed in the next section. Other sources of noise
included electrical noise and all motors, engines and other noise associated with normal base operations.
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High-Resolution Shallow Seismic Structure Imaging Using Grid-Based Nonlinear Refraction Traveltime Tomography
Authors Jie Zhang, Doria L. Kutrubes and M. Nafi ToksözWe develop a nonlinear refraction traveltime tomography technique that can rapidly reconstruct seismic
velocity distribution in a large 2-D gridded model. For the traveltime and raypath calculations, we improve
a graph-theoretical method by placing nodes on each grid boundary with an optimized distribution pattern.
This method greatly reduces errors in traveltime and raypath calculations for complex velocity models.
We pose a nonlinear objective function for inversion, which includes not only the traveltime misfit and
model curvature roughness norm, but also traveltime gradient misfit norm. Our numerical experiments show
that fitting the gradients of the traveltime curves in addition to the traveltime itself can better resolve the
velocity contrasts across interfaces. We apply Newton’s method to minimize the nonlinear objective function
iteratively. The use of Tikhonov regularization allows to perform a global inversion and reconstruct the whole
model with minimum model curvature roughness.
We apply this refraction traveltime tomography technique to image shallow bedrock topography at a
coastal site near Boston, Massachusetts. We will demonstrate that performing nonlinear tomography can
effectively reconstruct the subsurface image for complex velocity structure.
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The U.S. Forest Ser Vice Abandoned Mine Land Inventory In Colorado: Background, Progress, And Preliminary Findings
More LessThe U.S. Forest Service (USFS) and the Colorado Geological Survey (CGS) are continuing a cooperative agreement to identify sites
of environmental degradation associated with abandoned and inactive mines on Colorado’s USFS administered lands. The USFS
Abandoned Mine Land inventory Project is a “discovery” process and is a precursor to the Environmental Protection Agency’s
“Preliminary Assessment” process. identification of environmentally degraded sites may lead to a formal Preliminary Assessment.
The inventory process begins in the office and involves reviewing existing mining and geologic literature, previous mine inventory
work, current and historical maps, water quality information, and aerial photographs. During field investigation, each mine feature
is given a unique identification number. Field geologists collect data on the physical and geographic characteristics of the mine
features along with information on any water emanating from or interacting with the mine features. This information is used to assign
a qualitative environmental degradation rating to the individual mine feature. Guidelines for the rating system are given to field
personnel to facilitate consistency within the data set.
All data collected are entered into a computer database. From a computer perspective, both location and attribute data are being
collected. Therefore, the data are well suited for integration into a geographic information system (GIS) creating a geo-referenced
data set.
The USFS Abandoned Mine Land Inventory Project began in 1991 and is ongoing. To date, field inventories of the Arapaho,
Roosevelt, Pike, and Rio Grande National Forests have been completed. Work in the San Isabel, San Juan, White River, Gunnison,
Uncompahgre, and Grand Mesa National Forests is in progress. Through the 1994 field season approximately 9,667 mine features
(openings, dumps, tailings, highwalls, etc.) have been inventoried.
In the course of field investigations, evidence of naturally occuring water quality degradation has been found in various parts of the
state. The geology and hydrology of these areas are conducive to producing waters from springs and seeps with relatively high
concentrations of metals and low pH. These areas usually exhibit hydrothermal alteration of the country rock in addition to vein
mineralization. Many of these occurrences are in, or associated with, volcanic terranes. However, some occurrences are known
in areas of metamorphic, sedimentary, and igneous terranes.
As inventoried mine sites exhibiting environmental degradation progress from identification to site characterization and remediation,
it will be important to clearly identify the goals of remediation. Sites that occur in areas of naturally degraded water should, if
possible, have background conditions characterized in addition to mine site characterization. Remediation goals for minecontaminated
waters can then be set at realistic levels.
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Gis-Based Geoenvironmental Assessments Of Watersheds Affected By Metal-Mining Activity
The environmental effects of metal mining activity are receiving ever increasing
attention from the public, regulators, land managers, and the mining industry. There are
several issues currently of primary interest: (1) assessment and remediation of
environmental problems at abandoned metal-mine sites; (2) prediction and mitigation (or
prevention) of potential environmental effects from future mining activity; (3) determination
of baseline conditions that existed in mineralized areas prior to mining (conditions which in
many mineralized areas were naturally degraded) and; (4) development of effective,
scientifically-realistic regulations to govern past, present, and future mining activity.
This paper summarizes a GIS-based approach developed to help address these issues.
Continually in refinement, our approach uses geologic and geochemical data layers to help
estimate potential environmental impacts of metal-mining activities on surrounding
watersheds. The approach is based on the fact that mineral-deposit geology as well as
geochemical processes exert fundamental and predictable controls on the environmental
conditions in mineralized areas prior to mining, and environmental conditions that result
from mining and mineral processing (Smith et al., 1994; Plumlee, in press). Similarly, the
geologic and geochemical characteristics of the rock units in the watersheds surrounding
mining districts and unmined mineralized areas can strongly influence the spatial extent and
magnitude of environmental impacts on the surrounding watersheds.
Results of prototype work in the State of Colorado are presented here with a focus on
environmental effects on surface-water quality; however, the techniques are generally
applicable, with appropriate changes in complexity of scale, for areas ranging in size from a
single watershed to a large state and for other environmental effects such as smelter
emissions and windblown solid contaminants. A second prototype for the State of
Montana is currently under development (S. Marsh, oral comm., 1995).
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Aml Inventory And Characterization Upper Animas Watershed, Colorado Bureau Of Land Management
Authors Barbara J. Hite and Robert H. RobinsonIn 1993, the Bureau of Land Management (BLM) implemented a nationwide program to
inventory abandoned mine lands (AML) on public lands managed by the Bureau. The
inventory is expected to be complete by the end of 1997. The US Bureau of Mines
(USBM) provided extensive technical expertise and field crews for implementing
the AML inventory. In large part due to the USBM support, the AML inventory in
Colorado has progressed ahead of schedule, and is expected to be substantially
complete by the end of 1996. At the request of the Colorado Department of Public
Health and Environment (CDPHE), the upper Animas River watershed above Silverton,
Colorado was inventoried first as part of a group effort led by the Animas
Stakeholder Group. The upper Animas inventory was completed in 1994 followed by
detailed characterization of high priority AML sites initiated in 1995.
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A Collaborative Approach For Mine Waste Cleanup -- The Animas River Experience
Authors Gary Broetzman and Greg ParsonsAn innovative, collaborative approach is underway in the Animas River Basin for
addressing a myriad of inactive mine waste sites using a watershed framework. A group
composed of all vested interest in the Basin, including the regulatory agencies, are
evaluating all sites. Their intent is to select those sites that will lead to a cost-effective
attainment of State-defined water quality improvements in the Animas River. This paper
will address process, methodology, regulatory, and related issues associated with this
overall effort.
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Indicators And Discriminators Used To Separate Metal Sources From Contrasting Upstream Mining Districts
By S.E. ChurchMining has played an important role in the development of the western U.S. Mineral extraction and
production is a wealth creating endeavor that provides jobs and supplies raw materials needed to sustain an
industrial economy. Increased use of public lands resulting from a growing population has increased public
awareness of the effect of mining activities on the environment. Today, mining practices of many companies
are closely regulated to reduce these effects, but unfortunately, mining practices of the past have resulted in
substantially increased concentrations of many metals associated with sulfide ore deposits in both soils and
stream sediments. The U.S. Geological Survey has adapted geochemical and isotopic tracer methods,
originally developed for mineral-resource assessment, to delineate the extent of metal contamination from
mineral extraction and mineral processing in the environment. Our goal is to use these scientific methods to
define the extent of the area affected by mining and to advise the public and private industry on the
effectiveness of mitigation strategies. Application of these methods to drainage basins in the western U.S.,
where land-management and trust-resource agencies have particular concerns about the effects of mining
on human health and aquatic and riparian habitats has resulted in delineation of discrete areas affected by
mineral-resource extraction activities.
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Characterization Of Heavy Metals Pollution Sources Associated Witi-I The Inactive Wellington-Or0 Mine Complex, Summit County Colorado
By B.K. StoverToxic concentrations of heavy metals have contaminated waters of French Gulch and several
miles of the Blue River below the Wellington-Oro mine complex, near Breckenridge,
Colorado. The Wellington-Oro mines and mill operated from 1887 until the early 1950’s,
developing rich lead-zinc-silver sulphide ores from an extensive underground network of
tunnels and drifts on at least eight levels. Five levels below the alluvial gravel aquifer in
French Gulch are now flooded. Stream sampling showed water quality meeting class one
cold water standards for aquatic life upstream from the mine site, and that toxic amounts
of zinc, cadmium, manganese, iron, and copper below the mine site greatly exceed state
chronic standards for aquatic life in French Gulch and the receiving Blue River. In an effort
to design a Non-Point Source reclamation and water quality improvement project under
section 319 of the Clean Water Act, it was necessary to characterize the geologic and
hydrologic systems present at the site, as well as identify and quantify the sources of metals
contamination emanating from the mine complex. A ground and surface water sampling
program was initiated in 1991, followed by detailed site mapping, geophysical surveys, and
investigation of historic mine maps and subsurface data. Continued drilling, ground water
sampling, mine waste analysis, and interpretation of the bedrock and mine geology
eventually revealed the site was far more complex than originally anticipated. Ultimately,
four separate sources of metals contamination were identified: 1) Discharge of the mine
pool from abandoned shafts constructed through the alluvial aquifer to the stopes and drifts
below; 2) Discharge of the mine pool through faults and fractures in the bedrock which are
in communication with the mine workings and valley floor of French Gulch; 3) Leaching of
metals from mill tailings and roaster waste heaps dumped in and on the gravel aquifer of
the valley floor, which are periodically saturated during spring high flow period, then
drained during dryer seasons; 4) Storm water runoff from the waste piles, tailings, and
roaster heaps which runs directly into the creek. This paper describes key elements
necessary to characterize inactive/abandoned mine sites for potential water quality
remediation work, illustrating the dangers of plunging ahead with pre-conceived or “off-theshelf’
abatement strategies before an understanding of the geologic, hydrologic, and physical
systems governing metals contaminant sources at the site is developed.
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Geologic And Vegetation Mapping Using Aviris Data At Summitville, Colorado And In The Adjacent San Juan Mountains And San Luis Valley
Authors Trude V.V. King, Roger N. Clark and Gregg A. SwayzeFrom 1985 through 1992, the Summitville open-pit mine produced gold from low-grade ore using cyanide
heap-leach techniques, a method to extract gold whereby the ore pile is sprayed with water containing cyanide,
which dissolves the minute gold grains. Environmental problems at Summitville include significant increases in
acidic and metal-rich drainage from the site, leakage of cyanide-bearing solutions from the heap-leach pad into
an underdrain system and several surface leaks of cyanide-bearing solutions into the Wightman Fork of the
Alamosa River. The mine’s operator had ceased active mining and begun environmental remediation, including
treatment of the heap-leach pile and installation of a water-treatment facility when it declared bankruptcy in
December 1992 and abandoned the mine site. The EPA immediately took over the Summitville site under EPA
Superfund Emergency Response authority. Summitville was added to the EPA National Priorities List in late
May 1994.
Summitville has focused public attention on the environmental effects of modern mineral-resource
development. Soon after the mine was abandoned, Federal, State, and local agencies, along with Alamosa River
water users and private companies, began extensive studies at the mine site and surrounding areas. These studies
included analysis of water, soil, livestock and vegetation. The role of the U.S. Geological Survey (USGS) was
to provide geologic, hydrologic and agricultural information about the mine and surrounding area and to
describe and evaluate the environmental condition of the Summitville mine and the downstream effects of the
mine on the San Luis Valley. The environmental condition of the Summitville area is a result of the geologic
evolution of this area that culminated in the formation of precious-metal mineral deposits and a result of the
mining activity. Understanding the geologic and hydrologic history of this area is a critical piece to
understanding the environmental puzzle at Summitville.
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The Control Of Acid Mine Drainage At The S-Le Mine Superfund Site
Authors Victor L. Ketellapper and Laura O. WilliamsThe Summitville Mine Superfund Site is located about 25 miles south of Del Norte, Colorado, in Rio Grande County. Occurring at an average elevation of 11,500 feet in the San Juan Mountain Range, the mine site is located two miles east of the Continental Divide. Mining at Summitville has occurred since 1870. The mine was most recently operated by Summitville Consolidated Mining Company, Inc. (SCMCI) as an open pit gold mine with extraction by means of a cyanide leaching process. In December of 1992, SCMCI declared bankruptcy and vacated the mine site. At that time, the US Environmental Protection Agency (EPA) took over operations of the water treatment facilities to prevent a catastrophic release of cyanide and metal-laden water from the mine site. Due to high operational costs of water treatment (approximately $50,000 per day), EPA established a goal to minimize active water treatment by reducing or eliminating acid
mine drainage @MD). All of the sources of AMD generation on the mine site were evaluated and prioritized. Of the twelve areas identified as sources of AMD, the Cropsy Waste Pile, the Summitville Dam Impoundment, the Beaver Mud Dump, the Reynolds and Chandler adits, and the Mine Pits were consider to be the most significant contributors to the generation of metal-laden acidic (low pH) water. A two part plan was developed to control AMD from the most significant sources. The first part was initiated immediately to control AMD being released from the Site. This part focused on improving the efficiency of the water treatment facilities and controlling the AMD discharges from the mine drainage adits. The discharges from the adits was
accomplished by plugging the Reynolds and Chandler adits. The second part of the plan was aimed at reducing the AMD generated in groundwater and surface water runoff from the mine wastes. A lined and capped repository located in the mine pits for acid generating mining waste and water treatment plant sludge was found to be the most feasible alternative. Beginning in 1993, mining wastes which were the most significant sources of AMD were being excavated and placed in the Mine Pits. In November 1995, all of the waste from these sources had been excavated and placed in the the Mine Pits. This paper discusses EPA’s overall approach to stabilize on-site sources sufficiently such that aquatic, agricultural, and drinking water uses in the Alamosa watershed are restored and/or maintained with minimal water treatment.
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Acid Mine Drainage On Public And Private Lands, The Walker Mine Experience, Plumas County, California
Authors William A. Croyle and Steve E. RosenbaumA widespread environmental problem associated with abandoned mines and their tailings is acid mine
drainage @MD). AMD typically has low pH and elevated metal concentrations that are toxic to
aquatic life. In Northern California, Iron Mountain and other mines in the Shasta mining districts are
the largest sources of AMD. Additional sources lie to the south along a discontinuous belt of copper
and zinc mineralization in the western Sierra foothills. Between these areas lies a remote group of
copper mines in northeastern Plumas County including the Walker, Engels and Superior mines. Of
this group, AMD from Walker Mine has caused the most severe water quality impairment.
This paper describes the history and environmental setting of Walker Mine and the approaches used
by the Central Valley Regional Water Quality Control Board, a state regulatory agency, to improve
water quality at the site. Both the mine and its tailings contribute pollutants to the watershed. The
mine has a portal discharge with depressed pH and high copper concentrations. The tailings add fine
grained sediment to the creek and generate low but significant concentrations of dissolved copper.
The mine is on private property and the tailings are on land managed by the U. S. Forest Service.
Because of these differences in pollution problems and ownership, the methods employed by the
Regional Board to improve conditions at the mine and tailings have been on different, but parallel
tracks. Monitoring shows these efforts have significantly improved water quality in the watershed
over the last 10 years.
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Bonanza Mining Area - South Central Colorado Status Report On Voluntary Cercla Removal Actions
By Tim BuxtonThe Bonanza Mining District is located in the northern end of the San Luis
Valley of south-central Colorado, centered around upper Kerber Creek and its
tributaries and the old mining town of Bonanza.
Rich silver ore was first discovered in the Kerber Creek drainage in
approximately 1880; hundreds of claims were soon staked and the town of Bonanza
was established. Productive early strikes included the Rawley lode in Rawley
Gulch, two miles upstream from the town of Bonanza, and the Bonanza mine,
located a mile upstream of town in upper Kerber Creek.
The initial boom was short-lived, however, as the rich surface ores were
rapidly depleted. The twin problems of discontinuous, generally low-grade
sulfide ores at depth, requiring more sophisticated milling, and a 16-mile
wagon trip from Bonanza to the railhead at Villa Grove, soon emerged.
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A Comparison Of Natural Acid Rock Drainage Occurrences In Colorado
Authors Wendy A. Meyer, Randall K. Streufer and Mark A. WilliamsonA difficult question that arises in matters related to metal mining concerns the
background concentration of elements in natural waters prior to mining. The answer to this
question speaks to both regulatory limits for operating facilities as well as cleanup and
remediation practices for abandoned mines. This study characterizes the aqueous geochemistry
of naturally-occurring acid rock drainage (ARD) for three historic mining districts of Colorado
and considers the magnitude of the initial impact as well as natural amelioration processes.
Water quality data are reported for seeps and streams in drainage basins with weathering
sulfides hosted in metasediments, metamorphic terrain, and highly altered volcanics. Water
samples and field parameters were collected from both natural ARD seeps, and from within
natural ARD streams. Water samples were analyzed at the Colorado Department of Health for
dissolved Al, Ca, Cu, Fe, Mg, Mn, K, Na, SO4, and Zn. Additionally, select samples were
analyzed for dissolved As, Cd, Cr, Co, Pb, Hg, MO, Ni and Se. Results indicate that two types of
water contribute to natural ARD: 1) dilute ARD, influenced by storm events; and 2) concentrated
seeps. The naturally-occurring ARD from concentrated seeps showed a range in pH from 2.39 to
4.49 and TDS from 1890 mg/L to 2 18 mg/L. The naturally-occurring ARD from stream samples
showed a similar range in pH, but with TDS measurements as low as 18.3 mg/L.
Naturally-occurring ARD is observed to be attenuated by precipitation of secondary
solid phases and simple dilution. The precipitation of ferrihydrite and other minerals, as
determined by extraction analysis and equilibrium modeling, accumulate to create ferricrete
mounds. This process removes iron and trace metals from ARD solutions. The concentrated
ARD seeps negatively impact the water quality in receiving streams, but are quickly diluted by
the primary stream flow and/or storm events. This is evident by low flow volumes having high
concentrations, and high flow volumes having low concentrations. The combination of
precipitation and dilution is observed to restore the water quality of one stream within 12
kilometers.
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Geophysical Surveys For Ground Water Exploration In Northern Guam
Authors James F. Hild, Richard J. Blohm, Raye M. Lahti and Mark W. BlohmThe general geology of northern Guam consists of reef limestones overlying altered volcanic pyroclastics. The
limestones are highly porous and permeable which make them excellent aquifers. The volcanics which underlie the
limestones consist primarily of pyroclastic volcanics which were transported to their present location by a gravity
slide from the side of a submarine volcano, which was located west of the island of Guam. The volcanics are highly
deformed as a result of the sliding. These originally glass-rich (no crystalline structure) pyroclastics were
diagenetically altered at low temperature to a clay-rich rock. The permeability of the altered pyroclastics is very
low and the unit acts as an aquitard, consequently, very little water can be produced from the volcanics.
The fresh ground water in this portion of the island occurs in the limestones in two modes:
. parabasal - lying on top of the impermeable volcanics; and, l basal - a lens of fresh water floating on denser salt water.
In the basal mode, the ground water approximately follows the Ghyben-Herzberg principle which states that the salt
water/fresh water interface occurs below sea level at a depth 40 times the elevation of the top of fresh water. For
example, a head of 2 ft above sea level for fresh ground water in the basal mode means the salt water/fresh water
interface is at an elevation of 80 ft below sea level. Heads of 2.5 to 3.0 ft above sea level are typical for fresh water
occurrences in the basal mode in northern Guam, which places the elevation of the fresh water/salt water interface
between 100 ft and 120 ft below sea level. Therefore, most ground water occurs below sea level, although some
ground water resources perched on volcanics may exist at higher elevations.
The limestone/volcanic and fresh water/saline water interfaces are important components in the ground water
regime of northern Guam. Thus, it is necessary to map these interfaces to explore for ground water resources, and
to understand how the ground water regime will be affected by pumping of ground water.
Time Domain Electromagnetic (TDEM) soundings were employed in the surveys because the three units to be
delineated (limestones saturated with fresh water; limestones saturated with salt water; and, volcanics) have
characteristic ranges of electrical resistivity. The boundaries of these units can be inferred from the geoelectric
section. Sample case histories of TDEM surveys in northern Guam will be shown.
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Detailed Regional Hydrogeophysical Investigations - The Solbjerg Case
More LessIn cultivated areas with growing ground water abstraction there is an increasing need to map the vulnerability
of the aquifers and to delineate the aquifer systems circumstantially in order to obtain sufficient detailed and
reliable hydrogeological models. These models are demanded for the set-up of hydraulic frameworks used to
estimate the effects of abstractions on drawdown, on surface waters and on mobilization of unwanted ground
water qualities. These initiatives are required to ensure that future water supply can provide the same good
quality of drinking water as today.
A large number of the aquifers in Denmark are composed of Quaternary sand and gravel deposited in deep
valleys eroded in Tertiary clays and covered by an inhomogeneous moraine clay cap. It is generally observed
that variations of hydraulic conductivity of these formations are closely related to variations of electrical
formation resistivity.
In recent years the application of geophysical mapping of aquifers using electrical methods has increased
significantly in Denmark. By joint interpretation of spatially dense measured data a detailed and reliable
delineation of aquifers and their vulnerability is carried out.
The Municipal Water Supply of Aarhus has performed investigations to increase the number of abstraction
sites to provide supplementary capacity. A large area at the village of Solbjerg south of Aarhus has been
investigated using detailed geophysical mapping. The methods applied are the transient electromagnetic
method, and PA-CEP electrical profiling. The presented case demonstrates how the aquifer systems are
delineated and the vulnerability estimated from the results of the investigation.
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An Investigation Of A Dry Water-Well Near Floriano In Northeast Brazil Using Combined Vestem-Emap Techniques
Authors Max A. Meju and Sergio L. FontesCombined dc resistivity (VES), transient electromagnetic (TEM) and high resolution
continuous electromagnetic array profiling (EMAP) techniques have been applied to
the determination of the subsurface structure across part of the Mato Gross0 Farm (a
small settlement located about 25km east of Floriano city in Piaui State of Brazil) in
order to ascertain any structural influence on the cessation in water supply when an
original 13m deep, water-bearing, hand-dug well was excavated to a depth of 23m in
1988. Droughts are frequent in this semi-arid region but nearby wells in the same
geological formation have good yields. TEM and VES measurements were made on
four sides of the dry well enabling a clear assessment of the aquifer geometry at the
survey site. Two orthogonal lines of continuous electromagnetic array profiling
(EMAP), with five contiguous electric field stations (each having a dipole length of
50m) for good lateral resolution, enabled the local structure to be tied into a preexisting
regional model and the rejection of cavernous structures as the possible cause
of water loss at the farm site. The results suggest that another uncompleted, hand-dug
lm-diameter shallow well, 50m east of the dry well, will not be productive and should
be aborted. It is shown that deep-lying regional aquifers underlie the survey site and
we suggest that these can be developed at the dry well location or further west by a
machine-drilled borehole.
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The Exploration For A Deep Aquifer In The Hadhramaut, Yemen
Authors Paul Bauman, Dr. Janan Sallomy, Lucien Lyness, Tom Parker, John Watson, Steve Ross and Mike LockhardThe Hadhramaut province of Yemen, an area with a population of more than half a million inhabitants, is
presently facing a serious water crisis. A groundwater exploration project is presently drilling 23 exploration wells
widely spaced over the Masila Block, an oil exploration lease are within the province. The main target is the
Cretaceous Mukalla Formation, a 300 m thick highly permeable sandstone. Field reconnaissance was integrated
with satellite images; geologic, hydrogeologic, geophysical, topographic maps; and local socioeconomic and
political information to choose the well locations. Studying available seismic reflection data was particularly
useful for choosing drilling locations over grabens buried in wadi fill. The various pieces of information were
integrated in a geographic information system (GIS). To date, eight wells have been drilled and completed.
Borehole geophysical logging has played an important role in all phases of well completion. All completed
boreholes have tested from 200 to over 1,000 imperial gallons per minute.
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Clay Thickness Mapping For Irrigation Canals Using Airborne Electromagnetics
Authors T. Jeffrey Gamey, J. Scott Holladay, Richard Lewis and Dennis AbernathyThe farmland in Arkansas near the Mississippi River is famous as the principal rice growing region of the United States. This form of agriculture requires considerable amounts of water to flood the fields for long periods of time. Irrigation canals have been built to provide fresh water from nearby rivers as a supplement to ground water wells. An expansion of the irrigation system is planned, and an airborne electromagnetic investigation was undertaken by Aerodat under contract to the US Army Corps of Engineers Waterways Experimental Station to support this expansion.
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Seepage Detection Along The Chicago Sanitary And Ship Canal Near Lockport, Illinois
Authors Keith J. Sjostrom and Glenn HotchkissWater leakage between the Chicago Sanitary and Ship Canal and an adjacent stream,
Deep Run Creek, has been detected and monitored by personnel of the U.S. Army Engineer
District, Rock Island (CENCR) at a location situated approximately 1.1 miles upstream of the
Lockport Lock (see Figure 1). The area of seepage outflow is located at the base of the 16th
Street Bridge in Lockport, Illinois as illustrated in Figure 2. The seepage area consists of
three primary outflow points each located approximately five to ten feet apart. CENCR
engineers are interested in delineating seepage paths between the canal and outflow area and
locating points of water inflow along the canal wall such that this information can be applied
to any monitoring or remediation efforts necessary to control the water leakage. Waterborne
self-potential (SP) surveys and dye tracing tests were conducted along a 900 ft section of the
southeastern retaining wall to locate any seepage paths and/or points of water inflow along the
canal wall. The results of this survey will supplement previous monitoring information
acquired by CENCR personnel and facilitate the accurate positioning of any borings or
corrective measures as may be required to monitor or remediate the water leakage.
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Definition Of A Critical Confining Zone Using Surface Geophysical Methods
Authors Carol A. Eddy-Dilek, Pieter Hoekstra, Norman Harthill, Mark Blohm and David R. PhillipsDefinition of the hydrogeologic framework in layered sediments of fluvial and deltaic origin is a difficult challenge
for environmental characterization and remediation programs due to the lithologic and stratigraphic heterogeneities
inherent in these settings. These heterogeneties often control contaminant transport ,and the effectiveness of
remediation alternatives. Surface geophysical surveys can be cost-effective methods for characterization, but
individual methods have inherent limitations in resolution and sensitivity. A synergistic approach, utilizing two
geophysical survey methods was applied, to define and examine the nature and extent of a deep confining zone of
reguiatory importance, the Crouch Branch Confining Unit, in Coastal Plain sediments at the Savannah River Site.
TDEM accurately maps the overall conductance (product of thickness and electrical conductivity) of a confining
zone clay facies; from variation in conductance, changes in lithology of the confining zone can be inferred.. Shear
wave seismic reflection surveys map the depth to the clay layers, and the clay layer thickness, but provides little
information on the lithologic nature of the confining zone. Integrated interpretation of the combined data set
(including all available borehole logs) allows for delineation of the lateral and vertical extent of clay-dominated
zones, sand-dominated zones, key stratigraphic horizons, and erosional features associated with unconformities.
This approach has resulted in the collection of critical information that will be used to optimize remedial system
design, representing a significant cost savings to environmental restoration programs at the Savannah River Site.
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Rectangular Schlumberger Resistivity Arrays For Delineating Vadose Zone Clay-Lined Fractures In Shallow Tuff
Authors Martin Miele, Doug Laymon, Robert Gilkeson and Roy MichelottiRectangular Schlumberger arrays can be used for 2-dimensional lateral profiling of apparent
resistivity at a unique current electrode separation, hence single depth of penetration. Numerous
apparent resistivity measurements are collected moving the potential electrodes (fixed MN spacing)
within a rectangle of defined dimensions. The method provides a fast, cost-effective means for the
collection of dense resistivity data to provide high-resolution information on subsurface hydeogeologic
conditions.
Several rectangular Schlumberger resistivity arrays were employed at Los Alamos National
Laboratory (LANL) from 1989 through 1995 in an area adjacent to and downhill from an outfall pipe,
septic tank, septic drainfield, and sump. Six rectangular arrays with 2 AB spacings were used to
delineate lateral low resistivity anomalies that may be related to fractures that contain clay and/or
vadose zone water. Duplicate arrays collected over a three year time period exhibited very good data
repeatability.
The properties of tritium make it an excellent groundwater tracer. Because tritium was present
in discharged water from all of the anthropogenic sources in the vicinity it was used for this purpose.
One major low resistivity anomaly correlates with relatively high tritium concentrations in the tuff. This
was determined from borehole samples collected within and outside of the anomalous zone. The
anomaly is interpreted to be due to fractures that contain clay from the soil profile. The clay was
deposited in the fractures by aeolian processes and by surface water infiltration. The fractures likely
served as a shallow vadose zone groundwater pathway.
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Monitoring Dnapl Pumping Using Integrated Geophysical Techniques
Authors Robin L. Newmark, William D. Daily, Kevin R. Kyle and Abelardo L. RamirezThe removal of DNAPL during pumping has been monitored using integrated in situ
geophysical techniques. At Hill Air Force Base in Utah, a free-product DNAPL plume
(consisting predominantly of TCE) is pooled in water-wet soil on a thick clay aquitard.
Groundwater pumping at Operable Unit 2 (OU 2) began in 1994; to date, nearly 30,000
gallons of DNAPL have been recovered from the site. From September, 1994 through
September, 1995, changes in the basin during DNAPL pumping were monitored using an
integrated geophysical system. Fiber optic sensors and neutron logs verify the presence of
DNAPL in the vicinity of three boreholes which form a cross section from the perimeter of
the basin to its center. Cross borehole electrical resistance tomography (ERT) images the
changes in formation electrical properties due to the removal of DNAPL, extending the
understanding of DNAPL removal between the boreholes. During pumping, electrical
resistivities decreased; we suggest that these decreases are directly caused by the reduction
in DNAPL. During ground water pumping, water with relatively low resistivity replaces
some of the DNAPL pockets as the highly insulating DNAPL is removed. The results
suggest that, as DNAPL is pumped from a nearby well, product slowly drains along the
top of an aquitard and into the pump well, where it collects.
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Fractures, Fluid Flow And In Situ Stress Indicators In Shallow Sedimentary Rocks At The Proposed Wake/Chatham Low Level Nuclear Waste Disposal Site, North Carolina
Authors Colleen A. Barton and Colleen A. BartonRecent analyses of borehole data recorded in relatively deep crystalline rock show a significant
correlation between critically-stressed fractures (that is, fractures optimally-oriented to the stress
field for frictional failure) and hydraulic conductivity (Barton et al. 1995). In this study, we
examine the relationship between fracture orientation, fluid flow and in situ stress using data from
detailed analyses of fracture geometry, precision temperature logs that indicate localized fluid flow
and in-situ stress indicators recorded in sediments at relatively shallow depths. We have conducted
this study to determine if a correlation exists between in situ stress and fluid flow in the shallow
crust similar to that found at depth in crystalline rock.
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Geophysical Characterization Of A Fractured-Bedrock Aquifer And Blast-Fractured Contaminant-Recovery Trench
Authors J.W. Lane, F.P. Haeni, Susan Soloyanis, Gary Placzek, J.H. Williams, C.D. Johnson, M.L. Buursink, P.K. Joesten and K.D. KnutsonBorehole- and surface-geophysical methods were used to characterize the hydrogeology and the effects of
blast fracturing an in-situ recovery trench in a contaminated fractured-bedrock aquifer. The recovery trench is located
at the former fire-training area of Loring Air Force Base in Aroostook County, Maine. Borehole-geophysical
methods, used in six wells at the site, included video, acoustic televiewer, heat-pulse flowmeter under nonpumping
and low-rate pumping conditions, natural gamma, electromagnetic induction, tluid temperature and conductivity,
caliper, deviation, and borehole radar. Borehole radar was used in a single-hole reflection configuration with
directional and non-directional 60-MHz (megahertz) antennas and in a cross-hole tomography configuration with 22-
MHz antennas. One surface-geophysical method, azimuthal square-array direct-current resistivity, also was used.
Geophysical surveys were conducted before and after blast fracturin, 0 the recovery trench. Integrated
interpretation of the geophysical data collected before blasting indicates that most transmissive fractures are steeply
dipping and are oriented northeast and southwest. Analysis of azimuthal square-array-resistivity data indicates that
the secondary porosity of the fractured-bedrock aquifer is about I percent. The borehole-geophysical data and crosshole
radar tomography data indicate that more fractures are present in the upper 20 to 25 m (meters) of bedrock than
in bedrock below this depth. Interpretation of the geophysical data collected after blast fracturing the recovery trench
indicates that the blast created an intensely fractured zone about 3 m wide, 26 m deep, along the 50-m length of the
recovery trench. Blast-induced porosity in the recovery trench is estimated from the borehole-radar data to be 13.5+ 5
percent at the midpoint of the trench, decreasin, u to 7.3+ 6 percent at the northwestern end. Post-blast effects on the
hydrology of the area adjacent to the recovery trench include (1) a decline in static water levels, (2) order-ofmagnitude
increases in upward flow in two wells, (3) reversal of flow directions in two wells, (4) order-of-magnitude
increases in the estimated transmissivity of three wells, and (5) an estimated increase in aquifer secondary porosity to
2 percent near the trench. The increase in secondary porosity is estimated on the basis of azimuthal square-array
resistivity data collected over the recovery trench and cross-hole tomography collected parallel to but outside the
trench. These effects are consistent with increased porosity and permeability in the blast-fractured recovery trench
and with increased fracture transmissivity near the recovery trench. The increased fracture transmissivity resulted
from an apparent hydraulic cleaning that occurred when water was ejected out of wells near the trench during the
blast.
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Subsurface Utility Engineering: Utility Detection Methods And Applications
More LessThe nation’s infrastructure continues to grow as a result of population growth and the proliferation of new
technologies. New technologies include the replacement of copper communication cables with fiber optics. In
addition, the deterioration and replacement of existing structures have expanded activity in the infrastructure industry.
The “footprint” of new construction often conflicts with existing infrastructure. When this existiug infrastructure is
hidden from view (e.g., buried), it is often discovered in the construction phase of a project. During this phase, the
costs of con&t resolution and the potential for catastrophic damages are the highest.
Existing underground utilities and then related structures constitute a significant portion of this infrastructure. They
create inefficiencies and risks on projects. The majority of these inefIicieucies and risks result from inaccurate,
incomplete, and/or out-of-date information on the existence and location of existing subsurface utilities, In the past,
utilities were rarely a high priority. However, the costs of these risks are becoming high enough that priorities are
changing.
Many surface geophysical methods exist that are useful in identifying and characterizing underground utilities.
Utilities as near surface structures often interfere with the interpretation of data for deeper structures, soils,
contaminants, and so forth. Therefore. in cases such as brown field sites, military bases, etc., it becomes necessary to
first apply appropriate surface methods to identify and characterize the existing utilities so that then influence on
other data can be ascertained. Subsequent mapping and data management accrues other benefits. This practice is
gaining momentum in a field called subsurface utility engineering.
Subsurface Utility Engineering has been a program focus for federal agencies such as the IJSDOT. DOE, NSF,
NTSB and others. Additionally, professional organizations such as AXE and SAME are educating their members
about how the application of surface geophysics can reap benefits in identifying and mapping utilities for engineering
and environmental purposes.
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Sensor Evaluation Study For Use With Towed Arrays For Uxo Site Characterization
Authors J.R. McDonald and Richard RobertsonThe Naval Research Laboratory is developing a Multi-sensor Towed Array Detection System
(MTADS) with support from the DOD Environmental Security Technology Certification Program (ESTCP).
In this effort we seek to extend and refine ordnance detection technology to more efficiently characterize OEW
sites, identifying nonferrous and smaller items, distinguishing ordnance from clutter and analyzing clustered
targets to identify and locate individual targets within complex target fields. Our evaluation shows that these
goals are best met by combining magnetic and electromagnetic sensors. We report on field studies at a prepared
test range of commercial sensors in arrays in various configurations and including; Cesium vapor
magnetometers in single sensor and gradiometric configurations, fluxgate gradiometers, proton procession
magnetometers, and electromagnetic pulsed induction sensors. The advantages and disadvantages of each
technology and their applicability based upon survey requirements is discussed. We also discuss recommended
data densities including horizontal sensor spacings, survey speeds, sensor heights and make recommendations
about the appropriate use of gradiometers and active sensors.
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The Probability Of Magnetic Or Electromagnetic Detection Of A X+-Gallon Drum As A Function Of Line And Station Spacing
By David ButlerA simplified elliptical footprint of a %-gallon drum for electromagnetic and magnetic detection as a function
of depth is defined. The signal-to-noise ratio for field measurements is used to scale this ellipse. For a given
ellipse, the probability of detection at various line and station spacings is calculated.
Representative numbers indicate that with a line spacing equal to the major axis of the ellipse and a station
spacing equal to the minor axis, the probability of detection of a 1:2 (minor:major axis) ellipse by at least one
station is 0.66, but only 0.12 for the recording of two anomalous values.
Compound probability enters the problem if more than one target is present. If location rather than detection
is the goal, more that one anomalous station is required. If the number of stations is proportional to cost,
location or characterization will certainly increase the costs. This paper provides information to disqualify
specifications tendered by procurement departments who often request badly aliased surveys.
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The Combined Use Of Magnetic And Electromagnetic Sensors For Detection And Characterization Of Uxo
Authors Bruce Barrow, Nagi Khadr, Robert DiMarco and Herbert H. NelsonData has been collected on a test field of inert UXO with both a Geometries 822A total field
magnetometer and a Geonics EM61 pulsed, electromagnetic induction sensor. This study
allows comparison of the two instrument’s detection capabilities. While the EM61 as
currently configured is not as sensitive as the 822A in terms of depth of detection, it does
detect objects of interest down to IO-l.5 feet, as well as detecting non-ferrous materials.
While the location, depth, and size of single UXO targets are readily estimated from
magnetic measurements, it is not as clear what can be done with an electromagnetic sensor
that will synergistically add to the capability of the magnetic sensor. Based on laboratory
measurements, electromagnetic sensors may be capable of size estimation based on their
temporal response. For frequency domain instruments such as the EM31, this involves
measuring the phase angle response. For time domain instruments such as the EM61, this
mvolves recording the time decaying response. This size estimation is not affected by
remnant magnetization and also reflects the size of individual objects in a collection of
obiects. Because the spatial response of an electromagnetic sensor involves the relative
geometry of the transmitter, the object, and the receiver, it is expected to be sensitive to
obiect orientation. Measurements made on large elongated UXO in different orientations
confirm this.
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Delineation Of Pipeline River Crossing Using Cable And Pipe Locator With Real-Time Differential Gps
Authors B.S. Waddington and M. MaxwellThe location and depth of cover over pipeline river crossings must be checked periodically to ascertain that
the pipeline remains undisturbed and adequately covered. We have developed a technique to determine
pipeline plan location and depth of cover utilizin, Q a combination of electromagnetic detection and
echosounding with real-time navigation, in this case differential GPS. The technique offers an alternative
to acoustic location methods where small pipe size or the presence of acoustically opaque sediments
prevent pipe detection. In addition, the technique can be used in fast-flowing rivers or in heavy marine
traffic where anchoring is an unlikely option. We have successfully applied the method to locate and
profile a 168 mm steel pipeline crossing under the Fraser River, near Vancouver, Canada.
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Sasw Test In Location Of Buried Objects
Authors Nenad Gucunski, Vahid Ganji and Mohamad H. MaherThe ability to detect underground objects is of significant importance in certain aspects of civil
(geotechnical) and environmental engineering. A number of geophysical techniques have shown excellent
results in location of certain types underground obstacles (anomalies). The Spectral-Analysis-of-Surface-
Waves (SASW) method is a seismic nondestructive technique, that has so far been typically used in the
evaluation of elastic moduli and layer thicknesses of layered systems, like soils and pavements. One of
the assumptions of the test is that the system tested consists of infinite homogeneous layers of a constant
thickness. This assumption is violated whenever heterogeneity of the system exists due presence of buried
objects and cavities, presence of discontinuities, like pavement edges [Sheu et al. (1988)], variation of
layer thicknesses, etc. The problem is of special importance in SASW testing of pavements in an urban
environment, where obstacles like utility conduits, subways, and foundation structures cause wave
reflections that can affect significantly test results.
The effects of anomalies on propagation of elastic waves have been examined by a number of
authors. Cooper and Ballard (1988) reported a distinct travel time increase during refraction surveying in
soil with voids present close to the surface. Belesky and Hardy (1986) report successful implementation
of reflection survey in deep cavity detection, but significant difficulties in identification of shallow
cavities. On the other hand, Haupt (1977), Dravinsky (1983) and Curro (1983) demonstrated numerically
and experimentally that surface waves are sensitive to anomalies close to the surface. Recently Al-Shayea
et al. (1994) demonstrated experimentally that results of the SASW test are affected by underground
objects. They showed that an underground cavity artificially created in a homogeneous sand layer can
cause significant decrease in the phase velocity of the Rayleigh wave in a broad frequency range. Later,
numerical simulations by Gucunski et al. (1996a and 1996b) confirmed findings of Al-Shayea et al.
(1994). The following paragraphs discuss the most important findings on the effects of underground
obstacles on the Rayleigh wave dispersion obtained from the SASW test, and the application of the test
in detection of buried objects.
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Gpr In Forensic And Archeological Work: Hits And Misses
More LessGround-penetrating radar has been used successfully in the location of human
remains, both at archeological sites and in forensic work involving the discovery of I
clandestine graves. Forensic searches have occurred in subsoil burials, as well as burials
under concrete floor slabs. Not all investigations yield buried remains, however, and we
must separate out cases where bodies are not found because none is buried there, and
cases where the radar fails to detect the buried remains.
Witnesses can give faulty or misleading testimony leading to wild gooses chases in
otherwise credible cases. Investigators not familiar with the availability of noninvasive
geophysical search methods may try massive excavations that seriously disturb the
ground surface, and then call in someone to do GPR.
Physico-chemical characteristics of the subsoil can dramatically influence the length
of time skeletal remains persist in the ground, acid, well drained soils will cause loss of
identifiable remains over decades to centuries. At other sites, circulating mineral-rich
groundwater can impregnate the bony remains, yielding a more solid GPR target. Most
New England burials were made in deposits of stratified drift, which is a resistive and
almost ideal GPR medium; on the other hand it is an acid, well drained environment.
Burials using stone crypts (e.g., some 18th and 19th century US burials) will be
easily detected because the stone cover and an underlying air space will provide
dielectric contrasts recognizable on a GPR scan. Articles of clothing may also provide a
good GPR target when a body search is being conducted.
Recent clandestine burials yield near surface conductive anomalies that prevent radar
depth penetration below the body and appear as a signal loss whiteout. Once conductive
body fluids begin diffusing away, the skeleton and clothing articles provide point targets
that can be detected with radar.
Key words: ground-penetrating radar, human remains,
archaeology, forensics.
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Location Of Mohegan Burial Grounds Using Gpr
Authors Roelof Versteeg, Jeffrey Bendremer and John LaneFort Shantok is a national Historic Landmark and one of the most important and sacred historical sites d
the Mohegan Tribe, which recently repossessed the site. While the Mohegan Tribe is strongly interested in
a detailed characterization of the site, there is a strong pi&em for using non invasive tools. One of the
parts of the sites that needed to be characterized was a small cemetery. On this cemetery (where the gmve
markers have been removed and whem no surface indications of the graves remain) a pseudo 3D radar set
was collected. The time slices generated from this dataset give signatures which are strongly suggestive cf
time which can be expected from graves. The results from this data (and from follow up work) will be used
to remark the graves and the cemetery.
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Magnetic Viscosity Of Baked Clays And The Possibility Of Its Use In The Location Of Buried Ceramic Objects
Authors N.O. Kozhevnikov and S.P. NikiforovElectromagnetic (EM) methods have been used in archaeology since about 1960. The
study of soil electrical conductivity plays a significant part in archaeological surveying, as in
the case for any superficial exploration. That is why one of the most useful prospection
instrument still in use today is the inductive soil conductivity meter: surveys can be carried out
almost as fast as the operator can walk, making this among the fastest ground geophysical
methods now available. Metal detectors. which work on a similar principle. are frequently used
to search for ancient metallic objects not yet completely oxidized and to sort out modern cultural
pollution from magnetic anomalies deriving from older sources such as hearths (Wynn, 1986).
I_Jse of Slingram EM systems with carefully designed spatial and frequency parameters
now permits archaeologists to obtain both electrical conductivity and magnetic susceptibility
data at the same time without having to establish physical contact with the ground (Tabbagh, 1986).
As EM techniques were becoming more and more sophisticated, it has been found that
secondary magnetic field is affected not only by conductivity and susceptibility but by magnetic
viscosity of earth’s upper layers as well. C. Colani and M.J. Aitken studying archaeological
sites in England revealed that magnetic viscosity of soil influences substantially EM data
obtained with pulse metal detector ( 1966). The effects of soil magnetic viscosity on transient
electromagnetic methods (TEM) were also observed and reported by Buselli ( 1982). In 1985 the
soil magnetic viscosity has been found to produce TEM anomalies measured at some sites in
Western Pri bai kalje (Vakhromeev and Kozhevni kov, 1988).
Being measured in the time domain magnetic viscosity manifests itself in the slowly
decaying transients (Colani and Aitken, 1966: Buselli, 1982: Vakhromeev and Kozhevnikov,
1988). In frequency domain magnetic viscosity gives rise to the imaginary part of magnetic
susceptibility and to the dependence of its real part on frequency (Tabbagh, 1986:
Kozhevnikov and Snopkov, 1990). In either case the interpretation of EM data without
regard for magnetic viscosity results in soil conductivities too high when compared to actual.
If an object to be investigated is well conductive. magnetic viscosity effects are small as compared
with those produced by eddy currents. However, when studying resistive media magnetic
viscosity effects become dominant.
It has been found that for the most part the magnetic viscosity of soils is caused by
relaxation of superparamagnetic (SPM) particles (Buselli, 1982). Recall that superparamagnetlsm
is a property exhibited by single domain (SD) particles of ferro - and ferrimagnetic materials. In
contrast to large particles which consist of many domains, in the small one a multidomain
structure is impossible and thus the whole particle is a single domain. In SD particles the
response to an applied field is a rotation of the magnetization rather than domain wall
movement (Parkinson. 1983 ).
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Recommendations For A The Creation Of A National Organization Of Geophysicists Dedicated To Providing Assistance To The Law Enforcement Community
By John R. DewInvestigations requiring the location of human remains or underground caches are rare on a state or local level. Crime scenes requiring a search for human remains are complex and especially of great media interest. Because of infrequent need, however, most law enforcement organizations do not maintain a state of readiness enabling them to provide an adequate response to process these crime scenes.
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The Scientist As An Expert Witness
Authors G. Clark Davenport and Miles MadorinThe work environment of a scientist is characterized by orderliness and control. A scientist is
trained to think reflectively and in logical sequences; his or her success as a professional is
measured by the rigor with which he or she follows methodological processes to gather and
evaluate data. But how well do these skills translate to other, less well controlled, work
environments where the scientist may be called upon to provide technical expertise?
One such environment is the courtroom, where a scientist may be called upon to assist the court,
counsel and fact-finder by way of expert testimony or other assistance. In this instance, a scientist
is faced with a work environment characterized by seemingly random events, which follow a
course of Byzantine rules and procedures which defy common sense. Witness questioning does
not allow the luxury of thoughtful consideration, but demands immediate responses and facilitates
spontaneous dialogs. And while science is an objective assessment of data, a trial is an adversary
proceeding, where each side is motivated by subjective considerations. not necessarily in a
collegial fashion.
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Monitoring Of A Controlled Lnapl Spill Using Ground-Penetrating Radar
Authors David L. Campbell, Jeffrey E. Lucius, Karl J. Ellefsen and Maryla Deszcz-PanUsing ground penetrating radar (GPR), we monitored a controlled low-density non-aqueous
phase liquid (LNAPL) gasoline spill at a test facility at Oregon Graduate Institute, near Portland OR. The
results were different from some reported for uncontrolled gasoline spills, in which the gasoline apparently
blurs the contrast in dielectric permittivity that usually exists at the top of the saturated zone (SZ), so that
GPR reflections from the SZ are subdued. Instead, at OGI we saw a SZ reflection almost everywhere, but
this reflection was brighter (higher amplitude) under the spill. The bright spots grew and spread as the spill
progressed. We explain this effect by noting that sand grains above the SZ were quite moist, so that values
of relative dielectric permittivity (RDP) were relatively high there. As the spilled gasoline displaced this
interstitial moisture, RDP values dropped, leading to a GPR high velocity layer and concomitant bright spots.
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Imaging Pvc Gas Pipes Using 3-D Gpr
Authors J. Bradford, M. Ramaswamy and C. PeddyOver the years, many enhancements have been made by the oil and gas industry to improve the quality of seismic
images. The GPR project at GTRI borrows heavily from these technologies in order to produce 3-D GPR images of PVC
gas pipes. As will be demonstrated, improvements in GPR data acquisition, 3-D processing and visualization schemes yield
good images of PVC pipes in the subsurface.
Data have been collected in cooperation with the local gas company and at a test facility in Texas. Surveys were
conducted over both a metal pipe and PVC pipes of diameters ranging from i/z in. to 4 in. at depths from 1 ft to 3 ft in
different soil conditions. The metal pipe produced very good reflections and was used to fine tune and optimize the
processing run stream. It was found that the following steps significantly improve the overall image:
1) Statics for drift and topography compensation
2) Deconvolution
3) Filtering and automatic gain control
4) Migration for focusing and resolution
5) Visualization optimization
The processing flow implemented is relatively straightforward, simple to execute and robust under varying
conditions. Future work will include testing resolution limits, effects of soil conditions, and leak detection.
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Modeling The Gpr Response Of Leaking, Buried Pipes
Authors Michael H. Powers and Gary R. OlhoeftUsing a 2SD, dispersive, full waveform GPR modeling program that generates complete GPR response
profiles in minutes on a Pentium PC, the effects of leaking versus non-leaking buried pipes are examined. The
program accounts for the dispersive, lossy nature of subsurface materials to GPR wave propagation, and accepts
complex functions of dielectric permittivity and magnetic permeability versus frequency through Cole-Cole
parameters fit to laboratory data. Steel and plastic pipes containing a DNAPL chlorinated solvent, an LNAPL
hydrocarbon, and natural gas are modeled in a surrounding medium of wet, moist, and dry sand. Leaking fluids are
found to be more detectable when the sand around the pipes is fully water saturated. The short runtimes of the
modeling program and its execution on a PC make it a useful tool for exploring various subsurface models.
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Recent Improvements In Ground Penetrating Radar Antenna Design
Authors Paul R. Hague and Eugene BogatyrevGeophysical Survey Systems, Inc.(GSSI) has developed several new antenna designs to expand and improve its
subsurface investigation capabilities. These antennas operate in the 16 - 80 MHz range, and at center frequencies of
200 MHz, 400 MHz, 1 GHz and 2 GHz. These new antennas significantly expand the range of available
frequencies with which we can profile the near-subsurface.
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Near Surface Applications Of Borehole Radar
Authors E.W. Gilson, J.D. Redman, J. Pilon and A.P. AnnanBorehole radar (BHR) measurements, collected adjacent to a landfill site, demonstrate the useful
application of this technique in understanding the near surface (upper 30m) hydrogeological conditions.
The stratigraphy consists of relatively uniform ice-contact sand deposits, with the water table at a depth
of 16.5 m. Zero offset gathers provide a simple technique for defining stratigraphy, water content and
contaminate delineation, Multiple offset gathers, before and during a water injection experiment,
demonstrate that velocity tomograms can image water content changes on the order of 0.5 percent.
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Radar Tomography For Cavities Detection
Authors Stefano Valle and Luigi ZanziPreliminary tests on laboratory models have enabled us to provide some guidelines for traveltime ray
tomography with GPR applied to civil engineering problems, specifically to find voids in pillars, walls and
structures. The width of the Fresnel zone and the source and receiver locations are the limits to resolution
capability. For crosshole geometry a criterion to know resolution capability, based on detectable wavenumbers,
is analytically derived.
Acquisition and reconstruction parameters (source and receiver location, operating frequency, measurement
number, acquisition time, slowness grid) are discussed and optimized with tomographic experiments on some
models drilled expressly to produce voids. Tomography is solved by SVD, experimenting both regular and
irregular gridding. An iterative procedure for noise reduction is proposed to improve the solution. A sort of
black and white tomography is also applied to explore the actual limits of straight ray approximation. For
crosshole geometry a wavenumber decomposition of the problem is proposed and the benefits discussed.
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Radar Tomograms At Mirror Lake, New Hampshire: 3-D Visualization And A Brine Tracer Experiment
Authors David L. Wright, Thomas P. Grover, Karl J. Ellefsen, John W. Lane and Paul G. KaseIn this paper we examine radar tomograms produced from data acquired in the FSE well field
at the fractured rock hydrology site at Mirror Lake, Grafton County, New Hampshire. We first
show an example of 3-dimensional tomogram visualization with superimposed projections of
hydraulically significant fractures. We find a generally good, but not one-to-one, correlation
between electromagnetic velocity tomograms and fracture projections from individual wells. One
reason why the velocity tomograms do not always provide unambiguous indications of flow paths
is that the tomograms reflect rock electrical properties which vary because of lithologic
heterogeneity at the site. Another is that hydraulic permeability in fractured media may be
controlled by small-aperture “choke points” that are probably not well imaged by the tomograms.
In addition, hydraulic flow may be through a network of interconnected fractures, many of which
may be oriented differently from any particular fracture observed at a borehole.
We then show a difference attenuation tomogram produced from a brine tracer experiment carried
out at the Mirror Lake site in 1995. An objective of this experiment was to distinguish between
the mere presence of water and hydraulic permeability. When interpreting tomograms between
two hydraulically connected wells, an unrecognized assumption is often made that hydraulic flow
paths are in the plane of the wells. This assumption may be invalid, especially in crystalline rock
where flow is dominantly through fractures, rather than through the rock matrix. Our difference
attenuation tomogram shows that the primary flow path left the plane of the injection and pumped
wells.
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Nondestructive Assessment Of Pile Tip Elevation Using Flexural Waves
Authors Glenn J. Rix, Laurence J. Jacobs, Raymond Q. Raparelli and Patrick B. RhodesFor approximately 6000 of Georgia’s 14,500 bridges, pile tip elevations are unknown because design and
construction records no longer exist. This lack of information is critical because it is diEcult to determine the
capacity of these piles - particuhuly in the presence of scour. The unknown bridge foundation problem is an
important problem for federal and state agencies and has been the focus of several studies (Olson et al., 1995;
Douglas and Halt, 1993) The unknown bridge foundation problem is one in which either the type and depth of
foundation is unknown, or the type of foundation is known but the depth is unknown. Although soil borings and
other intrusive tests are capable of determining pile tip elevations, the time and cost of performing these tests on a
large number of bridges is prohibitive. Nondestructive tests are an effective alternative for assessing pile tip
elevations.
This study focuses on bridges which are supported by exposed pile foundations that have unknown lengths. The
purpose of this study is to evaluate the nondestructive use of flexural waves to determine the length of these bridge
pile foundations. Many nondestructive test methods rely on the use of longitudinal waves excited axially down a
pile. This type of testing is not feasible since the bridge superstructure prevents access to the top of a pile. Although
the theory behind flexural wave testing is more complicated than that of the traditional longitudinal wave testing,
flexural or bending waves can be excited laterally on the side of the pile with no physical interference from the
bridge superstructure. The pile in most cases can be modeled as a long slender member since its ratio of length to
section depth ratio is large. The propagation of the flexural waves within the beam is a function of its length, mass
density, moment of inertia, elastic modulus and end conditions. When dealing with bridge piles, the primary
unknown is the embedment length since all of the other variables can be assumed or measured.
The nondestructive test method developed in this study uses modal analysis techniques to interpret the pile length.
A three-step approach is used. First, the response model of the pile is determined by measuring a set of frequency
response functions for the pile. Second, the modal model consisting of the natural frequencies, modal damping
parameters, and mode shapes is calculated from the response model. Finally, the spatial model is determined from
which the embedded length of the pile can be obtained.
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Determination Of Unknown Depth Of Bridge Foundations Using Two Nondestructive Seismic Methods
Authors Farrokh Jalinoos, Larry D. Olson and Marwan F. AouadThis paper presents the test results of a research study on two nondestructive test (NDT) methods used for
determining the unknown depths of bridge foundations. Of the over 580,000 highway bridges in the National Bridge
Inventory, 106,000 (over-the-water) bridges have unknown foundation characteristics because no design plans are
available. Consequently, it is difficult for the state transportation departments (DOTS) to assess their susceptibility
to scour. Nondestructive and non-invasive test methods are needed to evaluate unknown foundation depth and
geometries.
This study documents the results for two acoustic NDT methods of Ultraseismic (a proposed new test
method), and the Parallel Seismic test method which were found to have the broadest application to the investigated
concrete, timber, and steel bridge substructures.
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Imaging And Characterizing Fractures Ahead Of Tunnel Face Using In-Tunnel Hsp Method
Authors Tomio Inazaki and Toshiyuki KurahashiA new method for imaging and characterizing fractures ahead of a tunnel face has been
developed and successfully applied to field measurements. The fundamental technique of the
method, we named in-tunnel HSP ( Horizontal Seismic Profiling ), is featured as an
combination of that being employed in VSP and reflection seismic method. The measuring
process of in-tunnel HSP is basically the same as refraction seismic survey. In-tunnel HSP can
provide 2-D sections for in-line and backward portions as well as the portion ahead of a tunnel
face, which enables us to verily the certainty of seismic events in the 2-D sections by
correlating them with actual fractures cropped out in a tunnel and characterize them
geotechnically prior to the prediction of undriven section.
We have applied in-tunnel HSP to 29 survey lines in 15 tunnels in Japan until now.
Field application of the method and engineering evaluation of the results has proved in-tunnel
HSP is quite practical to delineate and characterize fractures ahead of tunnel face and to
ensure the safety through the focused tunneling based on the prediction.
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Analysis Of Possible Relationships Between Seismic Properties And Some Of Rock Mass Geomechanic Properties Of The Outcropping Carbonate Rock Masses In Wad1 El-Kaffrien Dam Site (Jordan)
Authors Nasser Abu-Zeid and Fiorenzo VuillerminA seismic refraction and a geomechanic surveys were employed in the investigation of possible
relationships that may exist between elastic and geomechanic parameters of a number of outcropping carbonate
rock masses in the Wadi El-Kaffrein dam site, western Jordan. Seventeen seismic profiles were conducted
across the top of vertical exposures where the underlying geologic and structural conditions are quite visible to
be studied in detail. Therefore, the correlations could thus be correctly assessed.
The above mentioned prospections were completed on limestones, marly- and dolomitic limestones of the
Upper Cretaceous age. The seismic survey enabled the determination of the P- and S-wave velocities, the
dynamic elastic moduli, in addition, to a number of seismic ratios. While the geomechanic survey resulted in
the quantification of some of the geomechanic characteristics of the discontinuities present in the rock masses,
in addition, to the assessment of their overall qualities through the employment of two of the widely used
classification systems, namely, RMR and Q.
The obtained data were subjected to a bi-variate and multi-variate statistical analyses, so that possible
correlations could be evidenced. Such analyses considered eighteen seismic and geomechanic properties. The
analysis procedure started by investigating the seismic parameters themselves: Vp, Vs and the dynamic elastic
moduli, then these latter parameters were correlated to some of the geomechanical properties. Such
correlations led to the development of a preliminary classification system for the assessment of rock mass
quality, based upon seismically derived parameters as well as Jf and Jn. The system divides the rock mass in
five classes of quality.
Concerning the correlations conducted between the RMR- and Qquality indices and the geoseismic
parameters, it resulted that the RMR-indices correlate better to the seismic parameters.
Results of the multi-variate regression analysis show that the following geomechanic properties could be
estimated with a good approximation: Jn, Jf and RMR, while the prediction of RQD and Q indices can’t be
predicted from seismic parameters.
The study resulted in the individuation of zones or sectors that present a high grade of fracturing and/or
lithologic heterogeneity. More in detail, such sectors are located on the left abutment of the dam, where further
works should take place if the dam’s height will be increased. Moreover, the obtained bi-variate and multivariate
regression equations furnish a wealth of information upon which extrapolation of geomechanic
properties to other areas can be based.
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Shear Wave Velocities Of Gulf Coast Soils Determined From Crosshole And Seismic Cone Penetration
Authors Tracy Brettmann, Robert C. Gauer and Recep YilmazThis paper provides a summary of shear wave velocity data obtained from Texas and Louisiana Gulf
Coast soils using both crosshole test (CHT) and seismic cone penetration test (SCPT) methods. Both
methods are described and a side-by-side comparison of the results from several sites where both
methods were used is presented. The data collected were evaluated based on both soil type and geologic
formation. Best-fit equations are listed for each material type relating shear wave velocity to various
parameters.
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Optimization Of Geophysical Survey Design
More LessWe discuss the general problem of geophysical survey design, and present criteria that can be used to evaluate the
efficiency of a given survey. The survey design can be adjusted until an objective function defined by the criteria is
maximized. This process depends on the ability to compute the forward and inverse solutions. In addition, since the
objective function may be topologically complex, it is necessary to use an optimization technique capable of
locating the globally optimum solution. In this paper we show that the smallest singular value of the design matrix
constitutes a useful objective function, and we suggest that genetic algorithms are well-suited for discovering the
optimal solution.
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Robust Scheme For Ert Inverse Modeling
Authors Gianfranco Morelli and Douglas J. LaBrecqueImprovements in the automated interpretation of cross-borehole electrical resistivity measurements are presented
comparing results from both simulations and recent field surveys. Improvements were achieved by means of a
statistically robust inversion scheme and include faster convergence, availability of a stopping criterion, and
decreased dependence on data quality. The theoretical basis for the new method is explained concisely to concentrate
on its main features and capabilities that arise from the analysis of the results. Particularly, the effect of standard
noise and systematic errors present in the data on the reconstructed resistivity images are discussed. The aim is to
provide a simple guide for the correct choice of the parameters that characterize an inversion, as for a correct
understanding of the images obtained.
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Magaid: Pc-Based Target Characterization Software For Use With Total Field Magnetometer Survey Data
Authors Thomas Bell, Thomas Bell and Mark ProutyMagAID is a PC software application designed for use in interpreting the results of magnetic
surveys conducted for environmental cleanup and unexploded ordnance (UXO) clearance operations.
It employs a Windows-based graphical user interface, and accepts gridded and contoured data from
commercial mapping software. MagAID allows users to work with a contoured survey map,
interactively using the cursor to select magnetic anomalies visible in the survey map. Once an
anomaly has been selected, MagAID invokes a dipole-based Maximum Likelihood Estimation
algorithm to automatically determine the location (x, y, depth) and apparent size of the object
which caused the anomaly. This paper describes the target characterization procedure used in
MagAID and presents results of tests of the algorithm and the software’s performance using data
from controlled magnetic surveys at test sites containing buried inert ordnance and metal drums.
Typical estimation accuracies are of order fifteen to twenty percent in size and depth for compact
objects.
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Progress In Interpretation Of Transient Electromagnetic Data In Terms Of Subsurface Permeability
Authors M.E. Everett, C.N. Burden, K. Sananikone and B.E. HerbertThe relative importance of nonpoint-source (NPS) pollution in the degradation of water quality has
increased in the last two decades due to the control of pollutant releases from point sources (Sharpley and
Meyer 1994). The most important source of NPS pollutants are agriculture and urban areas, which impact
water quality in rivers, lakes, estuaries and groundwaters through the release of eroded sediments, fertilizers,
pesticides, and municipal sewage sludge. Because of this, NPS pollution is an important environmental
concern at state and national levels.
Several transport processes control the dispersal of NPS pollutants, including leaching to groundwater,
surface runoff (Pereira and Rostad 1990), and aerial transport and deposition (Glotfelty et al. 1984). Once
in groundwater, these contaminants can impact surface water during stream recharge. While the losses of
NPS pollutants from agricultural fields or urban areas can be small as a percentage of the total amount
released, the cumulative additions to river systems from large drainage areas can be significant.
The development of a reliable contaminant transport model for tracing the dispersal of NPS pollutants
through a heterogeneous aquifer requires knowledge of the spatial distribution of hydrologic parameters such
as hydraulic conductivity or permeability (Zheng and Bennett 1995). In the commonly used stochastic
approach (Dagan 1989), these distributions are treated as spatial random functions whose variance and
correlation length scale are determined from hydrological information collected by head measurements, pump
and tracer tests, and soil core analyses. Point estimates of the hydraulic conductivity or permeability are
determined by kriging, a geostatistical interpolation procedure which estimates unknown random functions
based on spatial correlations between point observations.
Noninvasive geophysical techniques are becoming an increasingly popular component of hydrogeological
studies since many geophysical data are sensitive to spatial variations in hydraulic conductivity and permeability.
In addition, the cost of surface exploration is only a fraction of the cost of drilling and a wide area1
coverage is readily obtained. Controlled source electromagnetic (CSEM) methods provide maps of electrical
conductivity and are an appropriate choice if the depth scale of investigation is on the order of 10 m-l km.
We are investigating the possibility of placing electrical constraints on the subsurface permeability as
part of a larger, integrated study to determine the fate of agricultural chemicals introduced at a research
site near the Brazos River. The research involves a joint analysis of the electrical conductivity structure, the
available soil cores, and other hydrologic data. A Bayesian approach is taken, following Copty et al. (1993),
in which geophysical data are used to update the variance and correlation length scale of a hydrologicallyderived,
random permeability field. In this paper we will describe the underlying theory and demonstrate an example using synthetic CSEM data that have been generated from a simulated geoelectrical section of our study site.
The incorporation of CSEM data into a determination of subsurface permeability is made more difficult
by the presence of man-made electrical conductors at the site. These include an aluminum pipeline and an
overhead power line. Such artifacts are characteristic of the human impact at many environmental sites. We
are presently applying the integral equation code of Qian and Boerner (1995) to account for the effect of the
aluminum pipeline on the CSEM data.
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Rapid 2D Inversion By Multichannel Deconvolution Of Geophysical Profile Data
More LessHigh resolution geophysical data are now often acquired in regular profile geometries, where pseudo
section display modes give very useful qualitative insight. For a more quantitative foundation on which to
base decisions we need a proper data inversion approach. These years the growth in airborne and surface
based acquisition power more than matches the growth in computer power. This has accentuated the need
for inversion methods that are rapid and yet safe and easy to use for non-specialists.
Approximate inversion methods based on the Born approximation are well suited for this purpose as
shown by Loke and Barker (1995) for the case of DC geoelectrical multi-offset profiling. Their approach is
adequate for relatively short, detailed profiles. In a similar study Li and Oldenburg (1992, 1994) show
how to solve the approximate inversion of DC data in the Fourier domain, thereby gaining an important
speed-up when data profiles are long and densely sampled. Meller et al. (1996a) test this method both
numerically and on densely sampled field data acquired with the Pulled Array Continuous Electrical
Profiling technology (Sorensen, 1995, 1996).
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Teaching The Practice Of Geophysics: A Prototype World Wide Web Environment For Conceptual Learning
Authors Thomas M. Boyd and Phillip R. RomigThe history of the United States has been driven by a surplus of resources (energy, materials, air,
water, open space). Today we are entering an era when there will no longer be more resources
than people. This transition from a resource-rich to a resource-limited environment is responsible
for many of the changes occurring within our society today, including the restructuring of industry
and government.
With regard to the earth sciences, one of the dominant issues of the 21st century will be how to
use a finite earth to support a burgeoning global population. We must continue to provide the raw
materials needed to feed, clothe, house, and provide a reasonable standard of living for all humans
on earth. We must learn to extract and use resources and dispose of the waste products of that
activity without poisoning the air we breathe and the water we drink. The quality of life of future
generations depends on the earth sciences being equal to this challenge.
A major impediment to the successful execution of these tasks is the fact that earth science has
evolved as a collection of loosely-related, poorly-coordinated specialties with little communication
or interaction between them. This has made it difficult for earth-scientists to provide the public
with a coherent education in the fundamentals of earth science so that they can make informed
choices. More importantly, it has discouraged the development of a common foundation for all
earth-science specialists, thus inhibiting our ability to work together to effectively solve the
important challenges facing us.
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A New Approach To Interpretation Of Airborne Magnetic And Electromagnetic Data.
Authors P. Traynin, M. Zhdanov, J. Nyquist, L. Beard and W. DollWe present a new technique for underground imaging based on the idea of space-frequency filtering and
downward continuation of the observed airborne magnetic and electromagnetic data. The technique
includes two major methods. The first method is related to the downward analytical continuation and
is based on the calculation of the total normalized gradient of the observed field. The second method
is based on Wiener filtering and takes into account a priori information about typical AEM anomaly
shape from a possible target.
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Regularization In 3-D Dc Resistivity Tomography
Authors Jie Zhang, William Rodi, Randall L. Mackie and Weiqun ShiWe demonstrate that the solution of 3-D DC resistivity tomography has strong numerical artifacts if the inverse
problem is not properly regularized. With only few data points but a large number of model parameters
(unknowns), the nonlinear inverse problem is ill-posed. Many studies have shown that some kind of model
correlation must be constructed to stabilize the inversion. Among those, Tikhonov regularization takes a
more explicit approach by damping spatial derivatives of the model function as opposed to applying ,ad hoc
smoothing. However, we show evidence that not all smoothness criteria in the class of Tikhonov methods
are well-posed for 3-D DC resistivity inversion. In fact, only under the second- or higher-order derivative
regularization, 3-D DC resistivity tomography can produce a physically meaningful solution which has no
dependence on the model discretization. In adopting effective smoothness criteria, the solution approximates
a continuous function with no more structure than is necessary to fit the data. Further, we demonstrate
that using Tikhonov method to regularize the model stepsize rather than the model itself does not improve
the ill-posedness of the inverse problem. As the result, only the data misfit has been minimized and model
correlation is not constrained. Finally, we apply our tomography approach to model real data collected at the
Mojave Generating Station in Laughlin, Nevada. For different model discretization, our approach prbduces
similar subsurface image.
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Magnetic Interpretation By Scanning Multiple Models For Best Least Squares Fit
Authors G. Hunter Ware and Hunter Andreas WareMagnetic interpretation is generally accomplished by comparing discrete anomalies in the
residual field with theoretical profiles of reasonable models. Simplified ‘rules of thumb”
based upon sets of model curves are also employed. Direct analytical inversion of field
data is impractical due to non-uniqueness and computational difficulties. The problem is
that even the simplest models may be adjusted in depth, horizontal position, and
orientation. More complicated models may also be varied in two- or three-dimensional
shape, and may involve multiple bodies. It is therefore very difficult to optimize model
parameters and measure the degree of fit or agreement with field data.
We have developed a procedure called MAGFIT for automatically comparing actual and
model profiles, and calculating a best least squares fit. With our algorithm, it is possible to
rapidly scan a simple set of models (such as dipoles) over many locations and orientations,
and determine the best fit as a function of position (and/or other model variables). “Best
fit” plots generally show closed contours around a best tit of 60% to 90%, identifying the
likely locations of magnetic bodies.
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Neural Network Classification Techniques For Uxo Applications
Authors Matthew Gifford and John E. FoleyA neural network was used to predict the mass of shallow subsurface conductive objects. The field data was from
an unexploded ordnance (UXO) survey conducted at Camp Simms, Washington DC. The survey instrument was the
Geonics EM-6 1 pulsed induction sensor. The purpose of the study was to develop a neural network architecture
that could be fielded at numerous sites under the US Army Corps of Engineer’s Ordnance and Explosives
Knowledgebase (OE-KB) program. The neural network was successful in predicting masses and depths. This
paper presents the results of a single training session and is also intended as a short tutorial in how to prepare and
present geophysical field data for analysis by a neural network.
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A New Interpretation Technique Of Surface Wave Measurements For Geotechnical Profiling
Authors Chaim J. Poran, Jorge A. Rodriguez-Ordonez and Takenori SatohNon-invasive shear wave velocity (SWV) profiling of soil deposits has long been
recognized as a cost-effective approach to obtain SWV data essential for seismic response
analysis including site amplification and liquefaction. The controlled-source
measurement of surface wave dispersion (CXW) is a relatively new non-invasive method
that is used for site characterization in the USA, Japan, and other countries. The CXW
method uses harmonic controlled sources to produce steady state Rayleigh waves in order
to measure the dispersion characteristics of soil and rock. Several interpretation
techniques may be used to obtain SWV structure from Rayleigh waves dispersion data
(in a process that is referred to as the Vf-Vs method). CXW measurement data from
more than 200 soil and rock sites were analyzed. These results were used to formulate
a new approach for the Vf-Vs interpretation method based on the new concept of
reference profiles that describes the average dispersion curve and SWV structure. The
reference profile is based on SWV dependency on confining pressure (depth) in soils.
Simple equations were developed for direct inversion of the reference profile. The new
procedure is completed by considering the effects of single layers with properties that are
different than the reference profile. This new interpretation procedure is rapid and
computationally efficient and its results are more representative of actual soil structure
than results obtained from other non-invasive methods. This paper shows that inversion
based on surface waves dispersion can provide a good estimate of average SWV
variation.
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3-D Electrical Resistivity Tomography For Environmental Monitoring
Authors Douglas J. LaBrecque, Gianfranco Morelli and Paul LundegardElectrical Resistance Tomography (ERT) images the electrical properties of the subsurface using crosshole
resistivity measurements. Interpretation of ERT data requires multi-dimensional inverse modeling. We discuss a 3-
D Occam’s inversion routine. The routine uses a finite-element forward solution and a conjugate gradient based
inverse routine. The algorithm finds the smoothest possible model that fits the data to a given a-priori level. In
general, the 3-D algorithm takes 10 to 20 iterations to converge to a final solution. However, the 3-D algorithm
requires only a single forward solution per iteration and does not require direct solution of a large system of
equations. Instead, it requires only the multiplication of a vector times the sensitivity matrix or its transpose. This is
accomplished without creating or storing the full sensitivity matrix.
A field example is shown in which ERT was used to monitor the injection of air from a vertical well at a shallow
petroleum remediation site in California. Data was interpreted using both 3-D and 2-D methods. Air injection
caused large changes in resistivity. At early times these were confined to an area near the injection point. Later the
changes were along a dipping, tabular region. At the latest times there is evidence of mixing of brackish water at
the depth of the injection point with fresh water in a shallower aquifer on the site. This mixing would have
decreased the resistivity and thus the apparent the size and magnitude of the zone of influence of sparging.
Results of 3-D and 2-D inversion agreed well when the regions of interest were approximately 2-D.
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Monitoring Air Sparging In Complex Aquifers
Authors Douglas J. LaBrecque, Gianfranco Morelli and Paul LundegardThe success of air sparging depends on the size and geometry of the region of air flow. The purpose of this study
was to use BRT surveys to observe changes in saturation, and thus air flow in a complex aquifer.
This paper describes the results of ERT surveys to monitor air flow in a heterogeneous acquifer in glacial till in
Washington State. Most of the air flow was confined a single, thin layer. Within this layer, the flow was not
uniform but moved preferentially in one direction. Some flow also occurred in a shallower layer but there is little
evidence of leakage into the upper part of the aquifer. After sparging there was a great deal of air trapped within the
layers.
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A Unique Data Acquisition System For Electrical Resistance Tomography
Authors William Daily, Abelardo Ramirez and Ken ZongeUnique capabilities are needed in instrumentation used
for acquiring data to do electrical resistance tomography (ERT) . A
data acquisition system is described which has a good combination of
the required capabilities and yet is rugged and user friendly. The
system has a multichannel detector for high data rates, can operate
over a wide range of load conditions, and will measure both inphase
and quadrature resistance at frequencies between 0.0007 Hz and 8
kHz. The system has been used in both the field and laboratory to
collect data with a typical accuracy between 1 and 10%.
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Complex Electrical Resistance Tomography Of A Subsurface Pce Plume
Authors Abelardo Ramirez, William Daily and Douglas LaBrecqueA controlled experiment was conducted to evaluate the performance of complex electrical
resistivity tomography (CERT) for detecting and delineating free product dense non
aqueous phase liquid (DNAPL) in the subsurface. One hundred ninety liters of PCE were
released at a rate of 2 liters per hour from a point 0.5 m below ground surface. The spill
was conducted within a double walled tank where saturated layers of sand, bentonite and
a sand/bentonite mixture were installed. Complex electrical resistance measurements
were performed from 4 vertical electrode arrays, each with 10 electrodes spaced between
3 m and 0.5 m depth. Data were taken before the release, several times during, and then
after the PCE was released. Magnitude and phase were measured at 1 and 64 Hz. Data
from before the release were compared with those during the release for the purpose of
imaging the changes in conductivity resulting from the plume. Conductivity difference
tomographs showed a decrease in electrical conductivity as the DNAPL penetrated the
soil. A pancake-shaped anomaly developed on the top of a bentonite layer at 2 m depth.
The anomaly grew in magnitude and extent during the release and borehole television
surveys data confirmed the anomaly to be free-product PCE whose downward migration
was stopped by the low permeability clay. The tomographs clearly delineated the plume
as a resistive anomaly. Images showing phase changes caused by the spill are also
presented. The phase changes at 64 Hz suggest that the DNAPL spill increased the
induced polarization (IP) effect of the clay layers.
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Tank Leak Detection Using Electrical Resistance Methods
Authors Abelardo Ramirez, William Daily, Andrew Binley and Douglas LaBrecqueTwo field experiments were performed to evaluate the performance of electrical
resistance tomography (ERT) as a leak detection method under metal underground
storage tanks (UST). This paper provides a summary of the field experiments performed
under a 15 m diameter steel tank mockup located at the Hanford Reservation,
Washington. Two different leak events were created. About 3800 liters of saline solution
were first released along a portion of the tank’s edge and another 1900 liters were later
released near the tank’s center. The release rate averaged about 26 liters/hour for the leak
on the tank’s side and about 3.0 liters/hour for the center leak. Two and three
dimensional tomographs were calculated using data collected before, during and after
each spill. The tomographs show that, as the solution penetrated the soil, readily
detectable resistivity decreases appeared where the associated plume was expected. The
results indicate that the plume associated with these releases could be reliably detected
after approximately 190 liters were released. Results are also shown where the metal
tank is used as a large electrode.
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Electrical Resistivity Tomography At The Doe Hanford Site
Authors S.M. Narbutovskih, W. Daily, A.L. Ramirez, T.D. Halter and M.D. SweeneyRecent work at the DOE Hanford site has established the potential of applying Electrical Resistivity Tomography
(ERT) for early leak detection under hazardous waste storage facilities. Several studies have been concluded to test
the capabilities and limitations of ERT for two different applications. First, field experiments have been conducted
to determine the utility of ERT to detect and map leaks from underground storage tanks during waste removal
processes. Second, the use of ERT for long term vadose zone monitoring has been tested under different field
conditions of depth, installation design, acquisition mode/equipment and infiltration chemistry. This work involves
transferring the technology from Lawrence Livermore National Laboratory (LLNL) to the Resource Conservation
and Recovery Act (RCRA) program at the DOE Hanford Site. This paper covers field training studies relevant to
the second application for long term vadose zone monitoring.
Electrical resistivity tomography is a cross-borehole, imaging technique for mapping subsurface resistivity
variations. Electrodes are placed at predetermined depths in an array of boreholes. Electrical current is introduced
into one electrode pair located in one borehole while the resulting voltage change is detected between electrode
pairs in other boreholes similar to a surface dipole-dipole array. These data are tomographically inverted to image
temporal resistivity contrasts associated with an infiltration event. Thus a dynamic plume is spatially mapped as a
function of time.
As a long-term vadose zone monitoring method, different field conditions and performance requirements exist than
those for short term tank leak detection. To test ERT under these conditions, two vertical electrode arrays were
constructed to a depth of 160 feet with a linear surface array between boreholes. The fielding was used to facilitate
the technology transfer from LLNL to the Hanford RCRA program. Installation methods, commercial equipment
and acquisition mode were evaluated to determine economic and technical feasibility to assist design of long-term
monitoring networks. Preliminary results of the training test are presented.
Until recently, vadose zone monitoring techniques could provide only local point or linear coverage for leak
detection and thus, are used primarily under liquid collection systems at land disposal units. As developed by
LLNL, ERT can provide area1 coverage under waste treatment and storage facilities given the right conditions.
Advantages of ERT to groundwater protection programs are explored along with suggestions for future uses where
ERT can be employed today.
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Applications Of Geophysical Logging For Dilution Control In Mining
Authors Richard G. McCreary and Stefan WänstedtIn mining, waste rock dilution occurs when uneconomic rock is mined and processed with economic mineralized
ore. A survey of selected stopes from various Noranda Group mines estimated that aggregate dilution and oreloss
stood at 20% and 8% respectively in 1994. Various technologies are being investigated by Noranda Group mines
in an ongoing effort to minimize dilution and oreloss. The following three potential applications of geophysical
logging have been identified for dilution and oreloss reduction through improved orebody delineation.
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Assessment Of Geotechnical Features Of Miocene Volcaniclastics Using Integrated Logging
Authors Toshiyuki Kurahashi, Tomio Inazaki and Yasuo NakamuraThis paper describes that integrated logging evaluates geotechnical conditions of fractures in Miocene
volcaniclastics, where the damsites are for proposed. The purpose of this study was to detect fractures for
seepage contols along borehole wall and characterize its geotechnical features by integrated logging. It is
first step to evaluate the continuity and permeability of fractures.
Integrated logging comprises of caliper, acoustic borehole televiewer, full-wave sonic, temperature,
borehole video logging, natural gamma spectrum, and magnetic loggings. Natural gamma spectrum and
magnetic logs would characterize litholofacies. Caliper, acoustic borehole televiewer and borehole video
loggings would identify the depth, the dip and the azimuth of fractures. Besides temperature logging would
determine the groudwater flow and suggest the permeable fracture.
Integrated loggings were performed at damsites for proposed in northern Kanto district, middle part
of Japan, where Miocene volcaniclastics are widely exposed. In Yunishigawa site, thermal jump was
remarkaby observed at 84 meters in depth from temperature logging. Its thermal gradient, differntiation of
temperature, was 30 “C/m. The farcture causing it was recognized by the borehole enlargemnts from caliper
logging, and had low slowness of full-wave sonic logging.
Integrated logging enabled us to identify the fractures in the order of a dozen centimeters along a
borehole wall. The identification would be useful for the geotechnical evaluation. Especially Differentiation
of temperature revealed the fracture for seepage controls and classified the fractures into three types, which
are (1) the permeable fracture circulating the runoff, (2) the permeable one controlling the groundwater
from the deep, (3) the non-permeable fracture. As the first and the second are fractures for the seepage
controls, they would involve the geotechnical problems.
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Application Of Borehole Geophysics At The Retsof Salt-Mine Collapse Site, Western New York
More LessBorehole-geophysical methods were used in the hydrogeologic characterization of the valley fill and bedrock
at the site of the 1994 Retsof salt-mine collapse in western New York. Collapse of the mine roof and fracturing
of the overlying bedrock in the southern downdip section of the IO-square-mile salt mine resulted in flow of
ground water into the historically dry mine at a rate of more than 15,000 gallons per minute. A suite ofboreholegeophysical
logs, including caliper, gamma, electromagnetic induction, specific conductance, temperature,
acoustic televiewer, video camera, and impeller flowmeter, was collected from 17 test wells. Most of the logged
test wells were 700 to 850 feet deep and were completed with steel casing through the valley fill and finished as
open hole in the bedrock.
The valley-till sequence at the mine-collapse site was about 500 feet thick and the bedrock sequence, from
top of bedrock to the salt mine, was about 600 feet thick. Analysis of the borehole-geophysical logs and correlation
with reported drilling logs delineated (1) glaciolacustrine fine-grained sediments that restricted downward
flow of surface water and ground water from the overlying alluvium; and (2) ground-water flow zones in
glaciofluvial sand and gravel in the mixed deposits of the lower valley fill, near the top of bedrock, and in fracture
zones at the limestone-dolomite contact and in the lower part of the dolomite. Fractures that provided the vertical
hydraulic connection between the ground-water flow system and the mine were penetrated by several test wells
drilled within the collapse.
Borehole geophysics proved to be a highly efficient method for obtaining information on the hydrogeology
of the valley fill and bedrock at the Retsof salt-mine collapse site. This information was critical in evaluating
potential remedial actions at the site and developing a plan of study to assess the effects of the mine collapse on
the water resources of the area.
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The Synthetic Roadcut -- A Nuherical Technique For The Multiple-Scale Integration Of Surface And Borebole Data
Authors Frederick Paillet and Colleen BartonIntegration of geophysical soundings or tomograms with geophysical logs
and hydraulic test data from boreholes is complicated by the very different
scales of investigation of each of these techniques. We present a numerical
approach designed to optimize the comparison of large-scale geophysical
measurements with data from borehole arrays. This technique addresses four
important requirements: 1) borehole data are projected into a single vertical
plane or “synthetic roadcut”; 2) projections between boreholes are adjusted in
the representation plane within specified limits to improve spatial
correlations between boreholes; 3) borehole data are subjected to a range of
spatial averaging and smoothing techniques; and 4) soundings or tomograms and
borehole data sets are kept rigorously separate until the processed data are
formally compared. The technique is illustrated using data from the FSE
borehole array at the Mirror Lake, New Hampshire fractured rock hydrology
research site. The Mirror Lake data show that comparisons of borehole logs
and borehole packer test data with tomograms can indicate how discontinuous
fractures are organized into larger scale conductive zones, and how the
distribution of those zones may be related to the lithologic fabric of the
bedrock.
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Use Of Directional Borehole Radar And Azimuthal Square-Array D.C. Resistivity Methods To Characterize A Crystalline-Bedrock Aquifer
Authors Melinda J. Chapman and John W. LaneDirectional borehole radar and azimuthal square-array resistivity surveys were used to determine
orientations of fracture zones in a crystalline-rock aquifer in the Piedmont Province of northern Georgia. The aquifer
media is a sheared and highly jointed amphibolite that is overlain by about 25 feet (ft) of regolith. A production well
tapping fracture zones in this aquifer supplies ground water to the City of Lawrenceville, Ga., at an average rate of
about 230 gallons per minute (gal/min). Four bedrock observation wells near the production well yield more than
100 galimin each, and respond quickly when the production well is pumped. An integrated suite of borehole
geophysical logs, including caliper, focused resistivity, long- and short-normal resistivity, gamma, acoustic
televiewer and velocity, temperature, spontaneous potential, fluid resistivity, deviation, heat-pulse flowmeter, and
video camera, and single-hole directional radar, were collected in the four observation wells to delineate and
characterize zones of fracture permeability. Orientations of highly permeable zones were determined by correlating
results from directional borehole radar with surface azimuthal square-array resistivity, standard borehole geophysics
data, and detailed surface geologic structural mapping.
Single-hole borehole radar reflection surveys were conducted using a 60-megahertz (MHz) directional
antenna that allowed interpretation of the orientation and projected borehole intersection depth of reflectors as far as
115 ft from the borehole. The borehole radar data include many reflectors; however, only reflectors that could be
correlated with other geophysical anomalies and production zones reported in drilling logs were selected for further
reflector orientation analyses. Stikes of many reflectors near production zones were determined to be NlO-20W, N40-
5OW, and E-W (N80E to N80W), dipping 24-88 degrees. Depths of these fracture zones ranged from about 30 to 290
ft below land surface. Caliper, video camera, and acoustic televiewer logs indicate that productive fracture zones are
associated with zones of borehole enlargement and intense fracturing. Anomalies interpreted from focused resistivity
and acoustic velocity logs also were associated with borehole fracturing.
Surface azimuthal square-array resistivity surveys were used to provide estimates of the orientation of
areally extensive fractures. Results of azimuthal square-array resistivity soundings indicated fractures oriented at
N30-60W, N15E, and E-W. Apparent resistivities of the bedrock are low, ranging from about 55 to 450 ohm-meters.
Using calculated anisotropy ratios of 1.35 to 1.75, the interpreted secondary fracture porosity in the bedrock aquifer
ranges from 13 to 25 percent. These values of fracture porosity are extremely high and most likely reflect the
influence of foliation and (or) sulfide mineralization on bedrock anisotropy and apparent resistivity data.
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Comparison Of Heat-Pulse Flow Measurements And Vertical Gradients In A Fractured Limestone Aquifer
Authors Larry L. Dearborn, Scott F. Calkin, R. Henry Andolsek and William S. AllisonEstablishing a site-specific relationship between heat-pulse flowmeter (HPFM) data and corresponding
vertical gradient data may allow prediction of potential vertical gradients through HPFM logging alone.
Vertical gradient and corresponding HPFM rates were determined for 117 test intervals in a fractured
limestone bedrock aquifer. From these data, it appears that HPFM data can be used in place of more labor
intensive borehole packer testing to provide estimates of vertical gradients in this type of hydrogeologic
system.
Groundwater conditions in the fractured bedrock were investigated through testing of 66 open boreholes,
as part of the hazardous waste remedial investigation at the former Loring Air Force Base (LAFB) in
northern Maine, USA. Borehole geophysical logging tools, including HPFM and acoustic televiewer
(ATV), in conjunction with air hammer drilling logs, were used to target specific fracture(s) to test using
conventional straddle packers. HPFM and head data from 41 boreholes met general requirements for
comparison purposes, and a linear correlation trend was identified.
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Clean Enough For Industry? An Airborne Geophysical Case Study
Authors Jonathan E. Nyquist and Les P. BeardData from two airborne geophysical surveys of the Department of Energy’s Oak Ridge Reservation (ORR) were
extremely valuable in deciding whether a lOOO-acre (400 hectare) parcel of the ORR should be leased to the City of
Oak Ridge for industrial development. Our findings, based on electromagnetic and magnetic data, were
incorporated in the federally mandated Environmental Assessment Statement (EAS), and in general supported
claims that this land was never used as a hazardous waste disposal site. We estimated the amount of iron required
to produce each anomaly using a simple dipole model. All anomalies with equivalent sources greater than
approximately 1000 kg of iron were checked in the field, and the source of all but one identified as either a bridge,
reinforced concrete debris, or a similarly benign object. Additionally, some smaller anomalies (equivalent sources
of roughly 500 kg) have been checked; thus far, these also have innocuous sources. Airborne video proved
invaluable in identifying logging equipment as the source of some of these anomalies. Geologic noise may
account for some of the remaining anomalies. Naturally occurring accumulations of magnetic minerals in the soil
on the ORR have been shown to produce anomalies which, at a sensor height of 30 m, are comparable to the
anomaly produced by about 500 kg of iron. By comparison, the electronic noise of the magnetic gradiometer, O.Ol-
0.02 nT/m, is equivalent to only about 50-100 kg of iron at a 30 m sensor height. The electromagnetic data,
combined with field mapping of karst structures, provided evidence of a northeast-southwest striking conduit
spanning the parcel. The possible existence of a karst conduit led the EAS authors to conclude that this is a
“sensitive hydrologic setting.” We conclude that aerial geophysics is an extremely cost-effective, and efficient
technique for screening large tracts of land for environmental characterization.
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Integrated Environmental Site Characterization Involving Geochemistry, Geophysics, And Geology: A Shortcut To Remediation
Authors James Viellenave, Gerald Church, Mark Slatten and Mike AndersonEnvironmental site characterization processes have evolved from simple drill-and-sample routines into more
sophisticated evaluations of increasingly complex problems involving a variety of contaminants. Strategic
integration of several geoscience tools into a more holistic approach benefits the site owner/operator by developing
a synoptic perspective of the site at the earliest possible time, allowing for more selective and focused use of the
expensive and invasive technologies. The ultimate effect is a better site characterization. including attention to
difficult PRP issues, lower liability, fewer risks of bypassing potentially hazardous contaminant accumulations, and
a result that is more targeted to environmental and human health risks.
An integrated site investigation system requires good geology and hydrology, but is properly augmented by use of
modem and sophisticated geochemical and geophysical tools, Establishing characterization objectives is critical in
deciding what geoscience tool(s) to deploy in any given situation, For each tool, critical criteria are identified that
will enable the user to best decide which to use for what purposes.
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Integration Of Geochemical And Geophysical Data For The Montana Mineral-Environmental Study
Authors A.E. McCafferty, D.H. Knepper and H.V. AlminasAeromagnetic, Landsat multispectral scanner (MSS), radiometric, and geochemical data covering the state
of Montana were digitally integrated to identify areas that may be negatively affected from surface-water
contamination by metals and acid run-off due to mining activity and natural processes. Two mineralenvironmental
models were constructed using a variety of statistical, image processing, and frequency
filtering techniques. The first model is a combination of relative magnetizations (calculated from the
aeromagnetic data) and two suites of geochemical elements. The geochemical distributions include one
based on a lanthanide association, which characterizes intermediate and alkalic intrusives; another
association characterizes sulfide mineralization. The second model is a mathematical combination of
relative magnetizations, iron oxide data (calculated from MSS data), and apparent potassium
concentrations (derived from airborne gamma-ray data). This model is useful for locating areas of possible
potassic alteration and leaching or weathering of exposed and shallowly buried iron-rich igneous rocks.
Magnetization domains associated with iron oxide and relatively high potassium concentrations can be
indicative of hydrothermal alteration environments that host metal sulfides. Despite sedimentary cover in
eastern Montana, both models reveal areas where magnetization sources are at depths shallow enough to
permit leaching, possible alteration, and the presence of heavy metals at the surface. Follow-up studies
and integration of these results with geologic and hydrologic information will provide a clearer
understanding of the possible environmental effects within the identified areas.
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The Use Of Multiple Geophysical Techniques For Site Assessment In Mine Reclamation
Authors L.E. Dalverny, K. Kluger Cohen, G.L. Mowrey and A.G. KimSite assessment at a burning coal waste bank in Midvale, Ohio was conducted by the U.S. Bureau of
Mines with five different geophysical techniques. The geophysical study was the first phase of a
project to test a control method for subsurface fires. The site characterization was performed using
terrain conductivity, magnetometry, ground penetrating radar and seismic surveys, as well as infrared
imagery. Results from these five geophysical techniques were integrated to obtain information on
the subsurface structure of the bank, the probable location of combustion zones, and the presence of
underground water. Magnetometry measured magnetic anomalies due to changes in the magnetic
properties of materials exposed to elevated temperatures in combustion zones. Electrical terrain
conductivity identified changes in ground conductivity of the waste bank; anomalies were believed
to be related to the presence of mineral-bearing water in fracture zones beneath the surface of the
bank. Both ground penetrating radar and seismic methods determined waste bank structure and
interfaces between dissimilar materials. The ground penetrating radar was effective to a maximum
depth of approximately 3 m (10 ft); the seismic technique provided information to a depth of 8.3 m
(27 ft). Infrared imagery detected areas of elevated temperature near the surface of the waste bank.
These combined results indicated that the bank consisted of a surface layer of coal waste that was
underlain by a core of another material. Several high temperature areas were identified on the eastern
slope of the bank. Drilling and temperature surveys provide supplemental information and verified
the results obtained with geophysical techniques. Site characterization that integrated the data from
multiple geophysical techniques resolved uncertainties, with respect to subsurface conditions and the
locations of heated zones and water saturated areas, that could not have been adequately explained
with any single technique.
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Case Histories Of Buried Borehole Detection: An Exercise In Flexibility
Authors Norman R. Carlson and Kenneth L. ZongeIt is sometimes difficult to determine in advance exactly which equipment or technique is best suited to a given project. Although the response of a particular target may be predictable, the local background response may be more difficult to assess until field data have actually been gathered. This problem becomes economically significant when the job site is relatively remote, requiring downtime and/or additional airfreight expenses when the actual field results don't match expectations and a change in equipment systems becomes necessary. An example of this is a recent series of surveys in Indiana and Ohio, in which the goal was to ensure that no abandoned, buried oil wells were present within in a prescribed radius of proposed injection wells. After local tests, both the physical survey layout and the data processing techniques were varied in order to detect the various possible targets in the different environments.
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Demonstration Of Geophysical Methods For Burial Ground Geophysical Characterization Study At The Doe Savannah River Site
Authors James C. Hasbrouck and H. David Mac LeanRust Geotech, operating contractor at the U.S. Department of Energy Grand Junction Projects
Office (DOE-GJPO), conducted a demonstration of the trench boundary and large-object
location capabilities of five nonintrusive geophysical methods in the Low-Level Radioactive
Waste Disposal Facility (LLRWDF) at the DOE Savannah River Site (SRS). The plan for
Resource Conservation and Recovery Act (RCRA) closure of the SRS LLRWDF specifies inplace
compaction of “B-25” metal boxes containing low-level radioactive wastes. The boxes
are buried in Engineered Low-Level Trenches (ELLTs) at the facility. To properly guide and
control the compaction operation, the coordinates of the trench boundaries must be
determined to an accuracy within 5 feet and the outer edges of the metal boxes in the
trenches must be determined to within 2 feet.
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Application Of Surface Geophysical Methods To Delineate Fracture Zones Associated With Photolinear Features In West-Central Florida
More LessThis study was designed to investigate the geophysical characteristics of fracture zones associated with
photolinear features in West-central Florida and to determine the most effective geophysical profiling methods for
rapid field characterization. Multiple surface-geophysical techniques were employed to verify the geologic
significance of two photolinear features at the study site. Interpretation of the geophysical data was constrained by
using multiple geophysical methods, site lithologic data and information obtained in previous studies of photolinear
features in West-central Florida.
Closely spaced horizontal-loop electromagnetic (HLEM) and very low frequency electromagnetic (VLF)
tilt-angle data were used to locate geophysical anomalies associated with the fracture zone. Resistivity profiling
data correlate well with the results of the HLEM and VLF methods. The optimum-offset, seismic-reflection
technique accurately delineates the large-scale fracture zone; however resolution is insufficient for detailed
stratigraphic interpretation. Self-potential data show a negative-streaming potential associated with the center of the
fracture zone. Microgravity data along a section of the fracture zone indicate lateral variations in density that
correlate well with anomalies identified with the other geophysical methods. Future studies of photolinears in
West-central Florida should use high-density VLF and HLEM surveys as rapid reconnaissance techniques to locate
anomalies associated with photolinears. High-resolution, shallow, seismic reflection, resistivity, SP and gravity
methods can be used to provide additional correlation.
Geophysical and lithologic data from the study site are incorporated into a geologic model of the fracture
zone. Data suggest that the two photolinears are related to a large-scale fracture zone in the Floridan Aquifer. The
fracture zone appears to be greater than 700 m wide with a 100 m wide sand-filled bedrock low. The bedrock low is
flanked by zones of higher bulk density approximately 200-400 m wide. The zones of higher bulk density are
interpreted as zones of recrystallized limestone caused by the precipitation of calcite along the fracture zone. The
recrystallized limestone zones appear to host multiple limestone pinnacles and clay-tilled fractures. The observed
photolinears correspond to a sand-filled bedrock low and a zone of dense, recrystallized limestone adjacent to the
bedrock low.
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The Effective Use Of Electromagnetic Methods To Delineate A Fluvial Paleochannel System Controlling Oil Migration Near Glenrock, Wyoming
Authors Noel T. Rogers, Stewart K. Sandberg and Greg PowellA combination of three different electromagnetic methods was effectively used to map the shallow lithologic
variation interpreted to control the subsurface migration pattern of hydrocarbons near Glenrock, Wyoming.
Petroleum hydrocarbons were seeping from the south bank of the North Platte River approximately one-half mile
west of the Township of Glenrock, Wyoming. Product was moving along the top of the water table through coarse
grained sediments and discharging into the river. Initial investigations, resulting in the excavation of three trenches,
were unable to determine the source and migration pathways that the hydrocarbons were following. A geophysical
survey was performed that provided a map of the subsurface geology that controlled free and dissolved product
migration.
The geophysical methods used included terrain conductivity, using two instruments that allowed two different coil
separations (the Geonics EM-31 and EM-34), and transient electromagnetics (TEM). The portability and data
collection efficiency of the EM-31 guided its use as a reconnaissance tool. Data from the EM-31 provided a map of
near-surface conductivity patterns indicative of shallow lithologic variation between coarse-grained paleochannel
deposits and tine-grained fluvial overbank sediments. Correlation of the EM-31 response with known geology
observed in test pit excavations resulted in some concern as to whether the mapped lithologic variation was too
shallow to have controlled groundwater migration. To address this, the EM-31 was operated at ground, and at 3 and
7 feet (ft) heights above ground over a high conductivity zone (interpreted to be fine-grained material). Data
obtained indicated that the high conductivity material was not a thin surficial veneer, but instead represented finegrained
deposits at depths of 0 to greater than 10 ft. The EM-34 instrument was also used at a lo-meter coil
separation along selected traverses to confirm the vertical extent of the interpreted lithologic variation. In addition, a
profile of central loop TEM sounding provided enough information to allow one-dimensional computer modeling,
which provided a quantitative depth extent of fine-grained (fluvial overbank) deposits. Therefore, preferential
groundwater migration pathways (fluvial paleochannels) were not only detected, but quantitatively delineated using
this effective combination of electromagnetic methods.
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Orientation And Characteristics Of Fractures In Crystalline Bedrock Determined By Surface And Borehole Geophysical Surveys, Millville And Uxbridge, Massachusetts
Authors Bruce P. Hansen and John W. LaneFour geophysical techniques were used to determine bedrock fracture orientation and other site characteristics
that can be used to determine ground-water flow and contaminant transport at a study area underlain by fractured
crystalline bedrock in Millville and Uxbridge, Massachusetts. In the study area, azimuthal seismic-refraction and
azimuthal square-array direct-current resistivity surveys were conducted at three sites, borehole-radar surveys were
conducted in a cluster of three wells, and ground-penetrating radar surveys were conducted along roads.
Azimuthal seismic-refraction data indicated a primary fracture strike ranging from 56 to 101 degrees at the
three sites. Graphical and analytical analysis of azimuthal square-array resistivity data indicated a primary fracture
strike ranging from 45 to 90 degrees at the same three sites, Directional borehole-radar data from three wells
indicated 46 fractures or fracture zones located as far as 147 feet from the surveyed wells. Patterns of low radar-wave
velocity and high radar-wave attenuation from cross-hole radar surveys of two well pairs were interpreted as a planai
fracture zone that strikes 297 degrees and dips 55 degrees south. Ground-penetrating radar surveys with IOO-MHz
antennas penetrated 5 to 50 feet of unconsolidated overburden and as much as 60 feet of bedrock where the bedrock
surface was at or near land surface. Horizontal and subhorizontal fractures were observed on the ground-penetrating
radar records at numerous locations. Comparison of results from the various geophysical techniques indicates good
agreement and indicates primary high-angle fracturing striking east-northeast. Square-array resistivity data yielded an
average secondary bedrock porosity of 0.0044 and an average aperture of 0.007 1 foot for high-angle fractures.
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Geophysical Methods To Identify Underground Erosion In Lateritic Soil
Authors Augusto F. Mendonça and Augusto C.B. PiresUnderground erosion is a serious problem to development of urban areas in
the neighborhoods of Brasilia-Brazil. This problem was first identified in 1986, when the
occurrence of numerous pseudo-sinkholes condemned an area of 300,000 square meters,
causing the demolition of 52 houses. Occurrence of pseudo-sinkholes in other places
around Brasilia led the University of Brasilia Institute of Geology to investigate the
problem. The research focused on the determination of the factors that generate the
underground erosion, and analyzed the geological, hydrogeological, and geotechnical
characteristics of the areas where the pseudo-sinkholes were identified.
One of the most serious aspects of underground erosion is that it is only
detected at the surface, in advanced stages of evolution. When the pseudo-sinkholes start
to develop, the geotechnical conditions of the area are already jeopardized, implying huge
remediation costs. Therefore, the location of underground cavities in early stages of the
underground erosion process was considered a key issue, and the selection of geophysical
methodologies to locate the cavities were one of the focus of the research.
Eletroresistivity, microgravimetry, and the vertical gravimetric gradient were the
geophysical methodologies tested in the areas with underground erosion. The use of
geophysical methodologies proved to be of great value. The interpretation of geophysical
data, supported by geotechnical, geological, and hydrogeological studies, allowed the
identification of areas with potential risk for underground erosion. Geophysics
employment also permitted the precise location of the underground cavities.
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Microgravity Survey For Shallow Subsurface Investigations
Authors Kyozo Nozaki and Takashi KanemoriRecently, the portability, repeatability, and accuracy of gravity meter measurements have improved
enough to be useful for shallow applications for engineering purposes. The authors have performed microgravity
surveys in Japan for the last several years with successful results. In this paper, the authors present three case
histories of typical microgravity applications.
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