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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 - 50 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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