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17th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 22 Feb 2004 - 26 Feb 2004
- Location: Colorado Springs, Colorado, USA
- Published: 22 February 2004
1 - 100 of 165 results
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Gravimetry Of The Anderson Bedrock Valley Of Central Indiana
By R.M. RenéGravity was measured at 173 stations in 30 km of profiles near Middletown in central Indiana to
map the Anderson bedrock valley and direct test drilling to the deepest part of that valley. The valley fill
includes coarse-grained aquifers and fine-grained aquatards of lakebed sediments and tills that overlie
Silurian and Ordovician strata dominated by carbonate rocks. Available maps derived from seismic
refraction profiles and scattered water, oil, gas, and test wells have generally provided insufficient detail
to suitably locate test wells. Two test wells were recently drilled at sites adjacent to relative gravity
minima in the profiles of the present survey. These wells penetrated the bedrock surface near the
thalweg of the Anderson bedrock valley at elevations of 175 to 176 m above sea level or about 23 m
deeper than was previously penetrated by wells in the area. The maximum thickness of unconsolidated
strata is about 120 m. Seismic refraction records were reinterpreted using hidden layers and dipping
bedrock refractors.
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Soil Electrical Conductivity Variability In Irrigated Sandy Soils Of Colorado
Authors Hamid J. Farahani and Gerald. W. BuchleiterRecent advances in apparent soil electrical conductivity (ECa) sensor technology have provided
the opportunity to rapidly map the nature of soil spatial variability for purposes of agricultural sitespecific
management. A better understanding of the temporal and spatial variability of ECa is needed to
enhance its practical utility in agriculture. In this article, we summarize our recent studies that utilized
multi-year measurements of field-scale ECa and soil profile properties in three non-saline and irrigated
sandy fields in eastern Colorado. The objectives were to quantify the degree of temporal change in ECa
patterns across the fields and to identify the main soil properties that alter ECa values. Results show that
in the sandy and non-saline fields examined in this study, delineated ECa patterns into low, medium, and
high zones remained largely unchanged between 1998 and 2002, even though the absolute values of ECa
varied. When salt concentration and buildup is low (as was the case herein), results suggest single ECa
mapping should suffice to delineate stable ECa zones without a need for remapping. In all three fields,
ECa was found to be a strong linear function of soil water content, clay, CEC, and organic matter
contents with correlation coefficients ranging between 0.75 and 0.94. In spite of the strong correlations
between ECa and soil properties at each given measurement day, there was no single unique relationship
applicable across all measurement days.
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Cropand Soil Status As Indicated By Electrical Conductivity Surveys Ofa Field With Cover Cropand Manure Amendments
Authors Roger A. Eigenberg, John A. Nienaber and Richard B. FergusonAnimal manure can be an important resource in providing soil available N for crop plant needs.
Management of animal manure to match crop needs throughout the crop growing season is one
challenge for sustainable agriculture. This study was conducted to examine changes in electromagnetic
(EM) soil conductivity and available N levels over three growing seasons in relation to manure/compost
application and use of a green winter cover crop. A series (weekly surveys) of soil conductivity maps of
a research cornfield were generated using global positioning system (GPS) and EM induction methods
with simultaneous soil samples. The study site was treated over a ten-year period with a rye (Secale
cereale L.) winter cover crop and no-cover crop. The cornfield research site was split for sub-treatments
of manure and compost at rates matching either the P or the N requirements of silage corn (Zea mays
L.). Sequential measurement of profile weighted soil electrical conductivity (ECa) was effective in
identifying the dynamic changes in plant-available soil N, as affected by animal manure and N fertilizer
treatments, during three corn growing seasons. This method also clearly identified the effectiveness of
cover crops in minimizing levels of available soil N before and after the corn growing season, when
nitrate is most subject to loss. The EM method for assessing soil condition provides insights into the
dynamics of available N transformations that are supported by soil chemical analyses. This real-time
monitoring approach could also be useful to farmers in enhancing N use efficiencies of cropping
management systems, and in minimizing N losses to the environment.
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Characterizing Soil Spatial Variability For Precision Agriculture Using Geophysical Measurements
Authors Dennis L. Corwin, Scott M. Lesch, Peter J. Shouse, Richard Soppe and James E. AyarsKey components of precision agriculture are (i) identifying the site-specific factors that influence
within-field crop yield variation and (ii) spatially characterizing those factors. Geo-referenced
measurements of apparent soil electrical conductivity (ECa) provide a potential means of characterizing
the spatial variability of edaphic properties that influence crop yield. It is the objective (i) to utilize an
intensive ECa survey to direct soil sampling, (ii) to identify soil properties that influence cotton yield,
and (iii) to use this spatial information to make site-specific management recommendations to increase
cotton yield. A 32.4-ha field in California’s San Joaquin Valley was used as a study site. Cotton yield
monitoring data were collected in August 1999 followed by an intensive ECa survey of 4000+
measurements using electrical resistivity. Sixty soil sample sites were selected based upon a responsesurface
sampling design utilizing the spatial ECa measurements. Scatter plots were obtained and
correlation and regression analyses were performed to assess the relationship between cotton yield and
the properties of pH, boron (B), nitrate-nitrogen (NO3-N), chloride (Cl-), salinity (i.e., electrical
conductivity of the saturation extract; ECe), leaching fraction (LF), water content (θg), bulk density (ρb),
% clay, and saturation percentage (SP). Correlation coefficients of -0.01, 0.50, -0.03, 0.25, 0.53, -0.49,
0.42, -0.29, 0.36, and 0.38, respectively, were found. The correlation coefficient between yield and ECa
was 0.51. A site-specific response model of cotton yield based on ordinary least squares (OLS) and
adjusted for spatial autocorrelation using restricted maximum likelihood was developed. The response
model indicated that leaching fraction, salinity, water content, and pH were the most significant soil
properties influencing cotton yield: cotton yield (Mg ha-1) = 19.28 + 0.22 ECe – 0.02 ECe
2 – 4.42 LF2 –
1.99 pH + 6.93 θg. The spatial information and response model provide sufficient information to make
site-specific management recommendations to increase cotton yield.
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Golf Course Applications Of Near-Surface Geophysical Methods
Authors Barry J. Allred, Dave Redman and Edward L. McCoyAs of 2000, there were over 15,000 golf course facilities in the U.S.A. alone. The upkeep of
these facilities requires continual maintenance and occasional remodeling. The superintendents and
architects responsible for the maintenance and remodeling efforts need non-destructive tools for
obtaining information on subsurface features within golf course components such as greens and tees.
The subsurface features of importance include, but are not limited to, engineered soil layer
characteristics and drainage system infrastructure. Near-surface geophysical methods can potentially
provide a non-destructive means for golf course superintendents and architects to obtain the shallow
subsurface information required to address their maintenance and remodeling concerns.
Two near-surface geophysical methods, electromagnetic induction (EMI) and ground penetrating
radar (GPR), were assessed with respect to golf course applications. Investigations were conducted at
two sites. EMI and GPR were tested on a tee and a green at the Muirfield Village Golf Club in Dublin,
Ohio, U.S.A. GPR was also tested on a golf course green at the Guelph Turfgrass Institute &
Environmental Research Centre in Guelph, Ontario, Canada. Although the EMI apparent electrical
conductivity measurements showed substantial variation across the tee and green on which data were
collected, there was no apparent correspondence of these values with the engineered soil layer horizontal
boundaries or the drainage system infrastructure. GPR proved to be more capable of obtaining readily
useable information on the golf course tee and greens that were investigated, at least in regard to
engineered soil layer depths or horizontal boundaries and in locating the subsurface drainage systems
present. In addition, computer modeling of synthetic GPR profiles provided valuable insight and helped
considerably with data interpretation. While more research is certainly warranted, near-surface
geophysical methods, particularly GPR, appear to have the ability for obtaining the data needed in golf
course maintenance and remodeling applications.
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An Overview Of Agricultural Drainage Pipe Detection Using Ground Penetrating Radar
Enhancing the efficiency of soil water removal on land already containing a subsurface drainage
system typically involves installing new drain lines between the old ones. However, before this
approach can be attempted, the older drainage pipes need to be located. In ongoing research, ground
penetrating radar (GPR) has been successful in locating on average 72% of the total amount of drainage
pipe present at thirteen test plots in southwest, central, and northwest Ohio. The effective use of GPR
for drainage pipe detection requires careful consideration of computer processing procedures, equipment
parameters, and site conditions, all of which were thoroughly investigated in this study.
Application of a signal saturation correction filter along with a spreading and exponential
compensation gain function were the computer processing steps most helpful for enhancing the drainage
pipe response exhibited within GPR images of the soil profile. GPR amplitude maps that show the
overall subsurface drainage pipe system required additional computer processing, which included 2-D
migration, signal trace enveloping, and in some cases, a high frequency noise filter and a spatial
background subtraction filter. Equipment parameter test results indicate that a 250 MHz antenna
frequency worked best, and that data quality is good over a range of spatial sampling intervals and signal
trace stacking. In regard to the site conditions present, shallow hydrology, soil texture, and drainage
pipe orientation all substantially influence the GPR response. However, the fired clay or plastic material
of which the drainage pipe is comprised does not appear to have much of an impact. The information
supplied by this study can be employed to formulate guidelines that will enhance the potential of success
for using ground penetrating radar in locating buried agricultural drainage pipe.
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Uxo Time-Constant Estimation From Helicopter-Borne Tem Data
Oak Ridge National Laboratory, in cooperation with Geosensors Inc., has developed a family of
airborne sensor systems known collectively as the Oak Ridge Airborne Geophysical System, or
ORAGS. The principal focus of the ORAGS research program to date has been on airborne mapping
and detection of unexploded ordnance, initially through magnetometry, leading to the ORAGSArrowhead
system and its vertical gradiometer variant ORAGS-VG. More recently the ORAGS effort
has been extended to include transient electromagnetic (TEM) measurements performed by the ORAGSTEM
system. The ongoing TEM development effort has already achieved considerable success over
both prepared test grids (Beard et al, in press, Beard et al 2003) and a former bombing site (Doll et al,
2003) at the former Badlands Bombing Range (BBR) in South Dakota. Unexploded ordnance (UXO)
objects ranging in size from 250 pound bombs down to 61mm mortar rounds, 60 mm illumination shells
and 2.75 inch rocket components were detected by both magnetometer and transient electromagnetic
technologies during the BBR trials conducted in September, 2002.
The signal/noise ratio (SNR) observed in TEM measurements during these trials was high
enough to motivate investigation of the target decay information contained in the measured transients.
An improved transient analysis technique based on the Matrix Pencil Method was developed to improve
the accuracy of exponential decomposition of the observed transients. Where SNR was satisfactory, this
method yielded repeatable results that reliably distinguished compact, long-time-constant targets such as
bombs and artillery shells from short-time-constant targets such as thin-walled scrap from practice
bombs. This step marks another milestone toward the goal of rapid, detailed mapping and discrimination
of unexploded ordnance based on airborne surveys. As system sensitivity and resolution continues to
improve, target discrimination methods are expected to become standard data analysis tools.
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Magnetic Compensation Of Magnetic Noises Related To Aircraft’S Maneuvers In Airborne Survey
Authors R.W. Groom, Ruizhong Jia and Bob LoFor a variety of applications, magnetic data is collected from airborne platforms. Normally, this
data is collected with sensors that measure the total field or amplitude of the magnetic vector data. New
generations of optically pumped sensors are extremely sensitive with their sensitivity quoted often in
picoteslas. At present, some new instrumentation is also attempting to measure high accuracy vector
data. Despite the accuracy of modern sensors and data acquisition systems, the noise of the flying
platform is still one of the limiting factors in obtaining highly accurate data.
The aircraft or helicopter itself emanates magnetic signals. These signals are due to a number of
factors including induced fields due to magnetically susceptible materials and permanent magnetic
materials on the platforms as well as both induced electromagnetic signals and electromagnetic signals
generated either by electrical systems or moving parts such as rotors.
This subject of this paper are problems and techniques related to removing the effects of the
moving platform as well as attempts to study the subject with the use of simulated data.
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Skytem – Data Processing And A Survey
Authors Esben Auken, Max Halkjær and Kurt I. SørensenApproximately 50,000 ground based TEM soundings have been carried out in Denmark during
the last decade for groundwater investigations. This number will increase in the future and therefore we
have developed a new helicopter time-domain electromagnetic (TEM) system, SkyTEM.
In the development and design of the SkyTEM system it has been an unchangeable demand that
the data quality of the SkyTEM system should be the same or better than the data quality from ground
based systems obtained by e.g. the Protem 47 system (40 x 40 m central loop configuration). Because
the amounts of data produced from the system are very high, new concepts for the processing and
inversion of TEM data have been developed.
In this paper we discuss the processing of the data produced by the SkyTEM system – GPS data,
transmitter frame angle and altitude data, transmitter status parameters and the transient decays. We
conclude the paper by presenting the results from a 50 km2 large groundwater survey west of Århus
which demonstrates the high resolution capabilities of the SkyTEM system.
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Inferences From Repeated Airborne Magnetic Measurements On The Island Of Vulcano (Eolian Islands, Italy) For Volcanic Risk Mitigation
The Island of Vulcano belongs to the active Eolian volcanic arc. Recent events on Stromboli
have renewed public interest and consciousness about this type of natural hazard not only in Italy, but
almost in the whole of Europe. A strong need for a reliable method to recognise significant changes in
the internal state of a volcano has risen, because of the currently ongoing and permanently changing
activity of the Eolian volcanic system. The measurement of variations in the local total magnetic field
anomaly within repeated airborne surveys is a promising strategy since rocks loose their magnetisation
when they are heated to temperatures higher than the so-called Curie-point resulting in a decline within
anomalies in the local magnetic field. Thus, changes in the geomagnetic field can indicate changes in the
dynamical behaviour of the geothermal volcanic system. Two airborne magnetic surveys have been
conducted by the Geological Survey of Austria in 1999 and in 2002 in the area of Vulcano and over a
part of Lipari. The raw data have to be carefully processed in order to be comparable, since they have
been assembled at different altitudes. Sophisticated innovative field transformation algorithms had to be
developed, and the rough topography and high susceptibility of the island of Vulcano require a
topographic correction of the measured data. Preliminary results, however, exhibit some significant
changes in the magnetic anomaly field.
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Using Helicopter Tdem Surveys To Identify Flooded Workings In Underground Coal Mines; The First Attempt
Authors Richard W. Hammack, Ken Witherly, Mark S. Zellman, Brian A. Lipinski and Bill HarbertThe U.S. Department of Energy’s National Energy Technology Laboratory (NETL) has used
helicopter-mounted electromagnetic (HEM) surveys to identify mine pools within active and
abandoned underground coal mines in the eastern United States. Two types of HEM surveys have
been tested: frequency domain electromagnetic (FDEM) and time domain electromagnetic (TDEM).
Previous surveys have indicated that FDEM surveys can identify flooded mine workings in areas
where overburden is less than 50-m thick. However, most mines are deeper than 50 m. This survey
attempted to use helicopter TDEM to locate deep, flooded mine workings at challenging sites in
southwestern Virginia, an area containing multiple levels of mining, thin seams, and mine water of
relatively low conductivity. The rationale behind this choice of field sites was that if the technology
worked in this admittedly difficult region, it could be applied to any coalfield. However, the survey
was unsuccessful; mine workings known to be flooded were not detected. This paper discusses
problems that were encountered, particularly electromagnetic noise, which rendered 25-50 pct of
each flight line unusable.
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Helicopter Electromagnetic And Magnetic Survey Of The Upper Animas River Watershed; Application To Abandoned Mine Land Studies
A helicopter electromagnetic and magnetic (HEM) survey has been done as part of an abandoned
mine land study. An important aspect of this study is to estimate ground water flow paths in the surface
and subsurface (bedrock). The apparent conductivity and total field magnetic maps from the HEM
survey are used to identify geologic features that can influence ground water flow. The most easily
understood studied ground water flow paths are near surface streams and flow through alluvial or
colluvial deposits. The HEM data indicates parts of the upper Animas River where bedrock ground
water flow may be important. Interestingly the other two major drainages (Cement and Mineral Creek)
are not associated with geophysical responses that indicate deep structures. High apparent conductivities
near one mine waste pile suggest near surface flow paths and a source for high dissolved solids where
high sulfide mill tailings have been removed after the HEM survey. The youngest dacite-rhyolite
intrusives show different types of magnetic and electrical properties that may have implications for the
occurrence of acid generating lithologies. Apparent conductivity maps suggest a northwest trending
structural zone along Cement creek that may control ground water flow. Total field magnetic data
suggest northwest trending structures that cross the Silverton Caldera ring fracture system.
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Geophysical Techniques For Maritime Archaeological Surveys
Authors Mark Lawrence, Ian Oxley and C. Richard BatesOver the last ten years, the high-resolution marine geophysical survey field has witnessed
significant advances in survey investigation equipment. New equipment is based on acoustic,
optical, electrical, and magnetic sensors. This paper will focus on the use of quantitative acoustic
methods for the high-resolution mapping of the seafloor for archaeological heritage management. In
particular multibeam sonar and acoustic ground discrimination sonar (agds) were tested at two
historic wreck sites on the UK shelf, namely the Stirling Castle, Goodwin Sands, England and the
SMS Cöln, Scapa Flow, Scotland. At both sites, acoustic reflection amplitude values were mapped
using the single beam sonar over each wreck site and in the immediate wreck vicinity. The
amplitude values were analysed with respect to the 3D topography of the site obtained mapped from
very high resolution bathymetric surveying using the multibeam sonar. Subsequent ground truth
inspection based on the maps produced from the agds and multibeam sonar was carried out using
both diver and ROV observations. Correlations obtained between the remote geophysical surveying
and the ground truth observations provided new insight into the current state of the wrecks and the
wreck site stability. With increasing pressure on the near shore zone from leisure activities, the
extraction industry and environmental changes, there is a great need for rapid mapping and
evaluation techniques. Thus the information provided by remote geophysics can be of great benefit
not only for mapping what is in these zones today but also for future long-term management of the
archaeological heritage.
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Archaeological Reconnaissance At Tel Yavne, Israel: 2-D Electrical Imaging And Low Altitude Aerial Photography
Authors Paul C. Bauman, Dan Parker, Avner Goren, Richard Freund and Phillip ReederTel Yavne in Israel is the site of the ancient city of Yavne. Located about 20 kilometers south of
Tel Aviv, and about 8 km inland from the ancient seaport of Yavne Yam (meaning Yavne by the Sea), it
is believed that underneath the tel (an archaeological mound) are the remains of more than 3,000 years
of continuous occupation. The tel, at 4 hectares in area and approximately 30 m in elevation, is
relatively large in comparison to other ancient sites in Israel. To date, no excavations have been carried
out at the site. In preparation for excavation work at a later date, electrical resistivity tomography (ERT)
surveys, ground penetrating radar surveys, and low altitude photography from kites and balloons were
carried out at the site. This paper will discuss the ERT and photographic surveys. The objectives of
these two surveys were to delineate the plan view and vertical extent of accumulated cultural debris, and
to identify particular areas for initial test pitting by archaeologists. Eight ERT cross-sections were
imaged, ranging in length from 80 to 140 m. Approximately 500 low altitude photographs were shot.
Specific features possibly identified include a 9th century B.C.E. (before the common era) water system,
the Philistine city wall dating from 790 B.C.E., the ruins of a 12th century C.E. Crusader castle, and
numerous architectural features from the Mameluke, Ottoman, and Palestinian periods of habitation.
This is the first time that non-destructive techniques have been used in the first phase of an
archaeological exploration program in Israel at such an important, well recognised ancient site.
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Use Of Multi-Tool Geophysics Surveys To Identify Structures Of A 2Nd To 4Th Century Roman Fort, Humayma, Jordan
Previous seasons of excavation at the site of Humayma in southern Jordan have revealed an
important Roman fort, dating from the early 2nd century to the late 4th century AD, which is the earliest
known Roman fort in Jordan. Several other settlement areas were found at the site covering an
occupation span of almost 900 years. Three geophysical tools -- ground-penetrating radar, electrical
resistivity, and magnetic gradiometry -- were used to conduct a geophysical survey of the Roman fort, in
order to verify the layout of the many well preserved interior and exterior structures. The survey
focused mainly on the areas inside and immediately surrounding the exterior walls of the fort. The 200
m by 150 m structure was surveyed inside using eleven small sized zones with a 1 m profile spacing and
outside using five larger sized zones with a 2.5 m profile spacing. The survey has revealed several
internal structures of the fort, as well as some major features outside the fort, such as a possible semicircular
defense structure and sections of the site’s water supply system.
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Characterization Of Complex Archaeological Sites Using 3D Electrical Resistivity Tomography
Several types of circular burial tombs, built by different populations in different ages, can be
discovered in Europe and have in common only their location inside small hills in the countryside.
These mounds have lateral dimensions varying from few meters to tens of meters, and heights around 5-
10 meters. Since the standard geophysical mapping measurements used by archaeologists are not well
suited for such targets under complex topography, a method that allows accurate image reconstructions
in 3D is required.
Different kind of mounds have been analyzed in this work: Etruscan (pre-Roman) burial sites,
very common in central Italy, and Celtic "Princes Age" (VI century b. C.) tombs in the Western Alps,
similar to sites excavated in the ’70s in southern Germany, that provide a good experimental set for the
variety of dimensions and materials used. The wood posts and stone walls surrounded by clay trenches
used in Celtic tombs create strong resistivity contrasts, while weaker anomalies are found over Etruscan
tombs.
The paper describes the development of a specific DC measurements on electrode grids placed
over the whole surface of the mounds, that provide realistic 3D pictures meant to guide drilling or
excavation and avoid collaptions. The use of fast multi-channel instruments allows the collection of
many data points in different array configurations, while data is processed using a 3D FEM modelling
and inversion routine that allows to input complex topographic information.
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An Assessment Of Seismic And Thermal Imaging Techniques For Archaeological Applications
MSE, in cooperation with the Department of Defense (DOD) United States Army Construction
Engineering Research Laboratory (CERL), Geoscan Research/Archaeo-Physics, and Montana Tech of
the University of Montana, investigated the applicability of both a towed array of geophones acquiring
diving wave seismic tomography data and a handheld thermal imager to collect data for archaeological
investigations. Currently, neither archaeologists nor geophysicists use these techniques very often for
archaeology. The driver for this work was the need to reduce the cost and improve the reliability of
traditional archaeological strategies widely used to assess the significance of the thousands of sites
located on Department of Defense managed lands.
Field tests were conducted at two locations: an 18th century mission in California and Cahokia,
the largest and most complex late prehistoric mound site in the U.S. The tests compared the seismic
results and thermal sensor output to results from electrical resistivity, magnetic field gradiometry, and
ground penetrating radar. The seismic technique was effective at locating buried historic era
foundations; however, better areal coverage would improve the results. This was possible because the
towed geophone array provides rapid high-density data acquisition. Thermal imaging was problematic
due to weather conditions, but the results suggested that with further refinement, it might be useful for
archaeology.
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Locating Buried Earthquake-Induced Liquefaction Deposits At Native American Cultural Sites Using Non-Invasive Geophysical Surveys
Authors Lorraine W. Wolf, Stephanie Park, Sharon Browning and Martitia TuttleGeophysical surveys were conducted at culturally sensitive sites in the New Madrid seismic zone
(NMSZ) of the central United States to locate buried earthquake-induced liquefaction deposits for
paleoseismic study. Although recent seismicity of the zone is of low to moderate magnitude, studies of
prehistoric earthquake sequences suggest that very large earthquakes occurred in A.D. 900 ± 100 years
and A.D. 1450 ± 150 years, in addition to the well-known historic events of 1811-1812 that caused
widespread soil liquefaction in Mississippi Valley alluvial deposits. Dates for the prehistoric
earthquakes are derived from radiocarbon dating of charcoal and from the presence of Native American
cultural features and artifacts of distinct periods that are collocated with buried liquefaction features,
such as sand fissures and sand blows. Trench excavations are often necessary to establish stratigraphic
and structural relationships critical for determining the timing of these paleoliquefaction events. Because
many sites are located in culturally sensitive or federally protected areas, non-invasive methods that can
increase the likelihood of identifying potential excavation sites while minimizing destruction of the site
are highly desirable. Geophysical surveys conducted at numerous sites in the NMSZ demonstrate that
subsurface imaging techniques can be useful for siting trenches for paleoseismic study and for
identifying areas susceptible to liquefaction.
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Gpr Surveys At Some 700 Years-Old Structures In The Old City Of Cairo, Egypt
More LessRemediation and restoration plans of the Ancient Egyptian Heritage are currently taking
much attention from local governmental and international organizations. Khan El-Khalily
region, which is located in Al Azhr area, is one of the important archeological places in the old
city of Cairo. It contains several famous structures (such as palaces, schools, graves, houses, and
fountains) that had been built seven centuries ago. Such constructions are now suffering from
fluctuations of groundwater and increasing ambient vibrations due to daily human activities as
well as traffics. Several incidents for wall-collapse, ground subsidence, buildings differential
settlement, and elevated groundwater were reported in Khan El-Khalily region. Information on
subsurface conditions, such as presence of voids, water tanks, foundations, and antiquities, at
these structures are considered valuable for the designed remediation and restoration plans.
The non-destructive GPR-surveys, using 500 MHz antenna, were performed at three
selected sites in Khan El-Khalily region. At each site, a CMP-survey was conducted to
determine the radar-wave velocity. The interpreted radar records of the first site, which
represented by a palace, could differentiate between subsurface fill-materials (silt and rock
fragments) and cement fill that found at depth interval of 1.0-2.0m. Remains of buried
foundations could also be mapped at depth of 2.7m. The second site is a conference hall that
contains ancient fountain in its center. The fountain itself was surveyed by using flat wooden
sheets. GPR-records showed the pipe that had been used to supply water to the fountain. The
third site is an ancient grave of important value to the Middle Egyptian History. Several
supporting pillars and even the stairs leading to the grave entrance could be mapped from GPRrecords.
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Borehole Ground Penetrating Radar Surveys Of Fractured Limestone
Authors E. Jorgen Bergstrom and Kathleen McKinleyTwo Borehole Ground Penetrating Radar (GPR) surveys were conducted to evaluate
fractured limestone bedrock formations. One survey was conducted at the proposed location for
a bridge pylon and one at a limestone quarry. The objective for both surveys was to identify
small voids and fractures in the limestone. At the proposed pylon site, the voids and fractures
were mapped to evaluate the limestone’s bearing capacity and to design a grouting program. At
the quarry site, the voids and fractures were mapped to help identifying permeable layers.
Borehole GPR is the only geophysical technique capable of imaging individual small voids and
fractures that do not intersect a borehole. A MALA Geoscience borehole GPR tool configured
with 250 and 100 MHz antennas was employed for these investigations.
Nine boreholes were drilled into the limestone formation at the footprint of the proposed
pylon. All nine boreholes were surveyed in reflection mode using 100 MHz and 250 MHz
borehole GPR antennas. Two cross-hole tomographic surveys were also conducted at the site.
The reflection surveys identified multiple layers that indicated voids and fractures of varying intensity.
The tomography data provided information regarding the bulk characteristics of geological units
and identified smaller areas with anomalous high porosity that could indicate high density of voids or
fractures.
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Environmental Corrections In Shallow Borehole Resistivity Logging
Authors Ludovic Baron and Dominique-Marie ChapellierBorehole logging is more and more used in civil engineering, hydrogeology and environmental
studies. Simple logging equipment can be obtained at reasonable cost but most of the time the probes are
not correctly calibrated, standardized, and environmental corrections are not made. It is essential to
remember that only accurate logs will enable a correct formation evaluation.
In shallow borehole equipment, conventional resistivity measuring devices are generally “normal
devices” with several electrode spacing. “Old electric logs” were corrected by the past, for resistivity
contrast between mud and formation, borehole diameter etc., using charts. The equations corresponding
to the chart curves can nowadays be very easily programmed and so the corrections are simple to apply.
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An Automated Transmissivity Modeling Method For Use With Borehole Flowmeter Data
More LessMany different methods are available to model subsurface hydraulic properties using transient
measurements. An improved flow modeling technique for borehole measurements was formulated and
tested. In this technique (called the convolution-inversion method), the flow from a producing interval
is modeled as a confined aquifer intersecting a borehole. The produced flow is a function of the driving
head, and is independent of the storage in the borehole. By considering each flowing interval separately,
the more complicated simultaneous analysis of a multi flow unit system in a borehole is avoided. The
data required for the inversion are the drawdown (the driving force) and flow from each producing depth
interval, both of which are measured as a function of time. An automated computer program convolves
the drawdown transient with the characteristic confined aquifer function for a given transmissivity to
predict transient flow. An inversion algorithm finds the transmissivity that causes the predicted flow to
most closely match the measured flow. The method is applicable to any means used to stress a well, as
long as the water level in the well can be changed over time. The algorithm was applied to pump test
data from a clay capped alluvial aquifer. The results compare reasonably well to results from a previous
analysis. The convolution-inversion method provides increased utility in that tests can be performed
more quickly, with minimal control over pumping, and with inexpensive equipment.
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A New Casing Inspection Tool: Two Case Studies
Authors J.-L. Deltombe, R. Schepers and P. van EyllAn Acoustic Televiewer scans the borehole wall with a focussed acoustic beam. At each scan
point amplitude and traveltime of the reflected signal are recorded. The slim hole ABI40 Televiewer has
become a standard tool in geotechnical exploration, in mining exploration and in hydrological
applications including water well inspection. Until now, the inspection of steel casing for corrosion and
the determination of absolute casing thickness required complexe and expensive logging tools. The
newly developed ABI40 casing inspection tool offers an attractive and inexpensive alternative. The tool
with a length of 1.8m can be operated in a wide range of applications from shallow water wells to deep
oil or gas wells.
The hardware of the standard ABI40 Televiewer is used to realize a logging tool which is
capable of determining casing thickness. New software is all that has to be installed in the real-time
processing unit of the ABI40 Televiewer to upgrade the ABI40 tool to a casing thickness logging tool.
The ABI40 tool for casing inspection transmits four images to the surface unit:
1. Traveltime image of inner surface (Traveltime 1)
2. Amplitude image of inner surface (Amplitude 1)
3. Thickness Traveltime image
4. Thickness Amplitude image
Traveltime 1 is used to detect casing thickness changes due to variation of the inner casing radius.
Amplitude 1 is applied to distinguish between inner and outer corrosion. Thickness Traveltime gives the
remaining thickness of the casing wall and Thickness Amplitude helps to identify areas of casing wall
defects even if the correct casing thickness cannot be determined.
To verify the performance of the new tool a number of short casing samples with well-known
defects were examined in the laboratory. Finally a field test measurement was made in a cased well,
which has already been logged before by other casing inspection tools.
It could be demonstrated that the present ABI40 tool can operate in casings with an inner
diameter from 6 inch to 20 inch. A maximum of 72 casing thickness values can be determined per
revolution of the acoustical head. The reliability of the casing thickness determination could be
confirmed and its precision was found to be less than 10%.
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Borehole Engineering – A Proven Cost Effective Method For Determination Of Engineering Parameters
Authors Nathan O. Davis and Thomas M. StaatzFor years, engineers and geoscientists in Europe and Asia have used borehole engineering to
accurately acquire rock properties, structural stress-strain relationships, fracture statistics, and other insitu
properties for major tunneling and engineering projects. Geophysical methods have been shown to
dramatically reduce costs of rock quality analysis by increasing the sum of valuable information while
reducing the number of core samples that require laboratory analysis. Just as engineering companies
have embraced the use of engineering gauges, acquisition of borehole measurements can be streamlined
into an effective program. Engineers and geoscientists in North America are just beginning to expand
the use of borehole engineering.
The integration of acoustic or optical televiewer, full waveform sonic, calibrated formation
density, borehole caliper, natural gamma, and relative neutron porosity logs allows the engineer to
derive invaluable rock properties. Bulk density, bulk modulus, Young’s modulus, shear modulus,
Poisson’s ratio, fracture density, and dominant bedding and fracturing trends are all available without
expensive oriented core, and laboratory analysis of core can be significantly reduced.
A lag in North American acceptance may be a factor of poor interdisciplinary communication.
At present, many project managers are unaware of studies relating the accuracy of borehole engineering
to more traditional methods. Those engineers that are more informed may perceive regulatory blocks,
including radioactive source licensing and reciprocity, that can be intimidating, but with the right
information, the benefits, including significant time and cost savings, increased sample density, and
simplified data presentation far outweigh the minor expenses of geophysical engineering.
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Are Current Generation Climate Change Simulations Accurate Enough To Reliably Guide Mitigation Strategies?
Authors Thomas N. Chasel and Eungul LeeWe examine the utility of downscaling climate change information from coarse resolution
climate models to scales useful for operational decision making. For a variety of reasons
including poor simulation of recently observed climate changes we conclude that downscaling
using present climate change simulations should be approached very cautiously.
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Change And Variability In The Global Climate System: Past, Present, And Future
More LessGlobal Climate Change is an issue that has garnered tremendous public attention and captured
headlines. However, many people do not have a good understanding of what is natural, what is not, or
how climate variability differs from anthropogenic, greenhouse gas-induced climate change. This talk
will consider the instrumental data on changing climate and the current models of climate in the next
century, and will place them in the context of climate variability from the past 2000, and 500,000 years.
We will also consider the influence of some drivers of natural climate change and their role in forcing
today’s climate. The awareness of abrupt changes in the climate system, and the possibility that the
gradual changes being caused by human activities today may trigger an abrupt change similar to those
seen in the past has become a new and important concern. We will discuss climate change, climate
extremes, and abrupt change as seen in instrumental and paleoclimatic records and in models. This will
include comparisons of the magnitudes and rates of past changes compared with the magnitudes and
rates of change currently being seen and predicted.
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The Role Of Geophysics In Developing Strategies For Co2 Sequestration In Geologic Formations
Authors Scott M. Klara, Karen Cohen, Charles Byrer and Rameshwar D. SrivastavaGlobal Climate Change has been attributed to emissions to the atmosphere of
greenhouse gases (GHG), with a major constituent being anthropogenic CO2 emissions
from coal-fired power plants and the transportation sector. Many approaches have been
proposed to mitigate CO2 emissions. Among the most promising is capture and
sequestration in geologic formations. This option has the advantage of being able to cope
with the large volume of CO2 involved, which will continue to increase because of the
growing energy demand. Consequently, an important component of the United States
Department of Energy’s (DOE) research and development program is dedicated to
reducing CO2 emissions from power plants by developing technologies for capturing and
sequestering CO2 in geologic formations.
This paper presents an overview of DOE’s research program in the area of CO2
sequestration and storage in geologic formations. Geophysical field techniques are
playing a major role in current field demonstrations of CO2 sequestration and have the
potential to play an even greater role as geologic sequestration becomes a reality in a
future “carbon constrained world.” The role of geophysical techniques in studying the
processes involved in the CO2 geologic sequestration life cycle are discussed. These
processes include CO2 capture, transport, injection, and measurement, monitoring, and
verification (MMV) of the permanence of storage in a geologic reservoir with an
effective caprock seal. Techniques, including seismic surveys using a variety of data
acquisition and processing strategies (2D seismic surveys, seismic tomography, and
others), microseismic monitoring, microgravity surveys, electrical and electromagnetic
methods, and geophysical well logging all can, potentially, provide valuable subsurface
stratigraphic and structural imaging data, as well as information on subsurface properties
such as the location of fractures and faults that could serve as migratory pathways for
escape of injected CO2.
Advanced field operations and field studies sponsored by DOE are utilizing a
variety of geophysics in the life cycle of CO2 geologic sequestration. Examples include
the Sleipner field operations in the North Sea, the Canadian Weyburn Enhanced Oil
Field, the pilot CO2 injection into the Texas Frio Formation saline aquifer, the pilot CO2
injection in the West Pearl Queen depleted oil reservoir in New Mexico, and the
characterization of potential reservoirs for the Ohio River Valley at the AEP Mountaineer
Power Plant in Virginia. Geophysics is also important relative to the President’s
initiative for a ten year, $1billion dollar FutureGen project to develop a power plant with
“zero emissions.” This may be achieved, in part, by geologic sequestration of CO2.
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The Climate Temperature Cycles Of The Earth And What Drives Them (Part 1)
More LessThe surface materials of the earth comprise the Atmosphere, Lithosphere, and
Hydrosphere; their physical properties along with solar energy determine the climate.
The changes in surface atmospheric temperature are referred to when discussing climate
changes. However, the Hydrosphere is the main heat source/sink of the surface materials.
The hydrosphere receives more energy and stores more energy from the sun than either
the atmosphere or lithosphere. Climate changes have been going on in the past and are
necessary to maintain the biodiversity that exists on the earth. Yesterday the climate was
different, it will be different tomorrow, to paraphrase a biblical phrase; “Climate
Changes, as it was in the past, is now, and ever shall be World Climate with change”. To
stop climate changes would be unnatural, illogical, and not in anyone’s best interest.
The Total Solar irradiance S that reaches the earth has a large positive correlation
coefficient to the surface temperature. Since the irradiance S is totally a function of solar
activity, the surface temperature must be a function of the solar irradiance S. Changes in
Solar irradiance S can be easily explained by changes in the Sun-Earth geometric
relationship, similar to what is proposed in the 1940’s by the Milankovitch Cycle Theory.
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The Climate Temperature Cycles Of The Earth And What Drives Them (Part 2)
More LessThe paleo-temperature records are an important source of information with which
to study paleo-climates. One such record is the Western Pacific Sea Surface temperature.
It extends back some 60 million years before present. This temperature profile is
composed of a simple decay curve with a superimposed 5 million sinusoidal cycle. The
other record studies was the Vostok Ice Core data from NOAA. The Vostok ice core data
is composed of Temperature CO2 and CH4 and is in considerable more detail extending
back some 420,000 years.
Spectral analysis was run on the data and the primary components have some of
the same periods that were hypothesis by the Milankovitch Cycle Theory. The spectral
component of the Vostok temperature data and its correlation with the Western Pacific
Sea Surface data is extremely suggestive the origin of the cycles are from Solar
influences and the Sun-Earth Geometric relationships.
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Using Helicopter Fdem To Monitor The Fate Of Conductive Water Co-Produced With Methane In The Powder River Basin Of Wyoming
Authors Richard Hammack, James Sams, Garret Veloski, Brian Lipinski, Mark Zellman and Bill HarbertThe development of coalbed methane resources in the Powder River Basin of Wyoming
and Montana has produced more than 248,000 acre-ft of groundwater (produced water) that is
disposed on the surface by land application or returned to groundwater aquifers via infiltration
basins or injection wells. Because the chemistry of produced water differs from that of surface
waters, there is concern pertaining to the ultimate fate of the produced water. This paper
describes the use of airborne frequency domain electromagnetic (FDEM) surveys to trace the
movement of produced water away from infiltration basins and leaking containment basins.
Three sites are described: 1) a leaking containment basin, 2) a dilution anomaly at an infiltration
basin, and 3) a dilution anomaly at a flowing well. The FDEM survey identified leaks at two
containment basins before down-slope seeps were observed at ground level. Also, the survey
identified a dilution zone on the Powder River floodplain where produced water from an
infiltration basin was diluting more conductive groundwater in a shallow aquifer. The long-term
effect of deep groundwater being applied to the surface and infiltrating into near-surface aquifers
was observed at a flowing well, where groundwater from a coalbed aquifer has been flowing
onto the surface for almost 50 years. The hydrology of the flowing well site may be indicative of
the future hydrology at infiltration impoundment sites.
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3D Electrical Imaging Of Contaminated Soil Near A Gas Station At Brugelette, Belgium
Authors Olivier Kaufmann and John DeceusterA field experiment was conducted over a contaminated site located near a gas station where tank
leakage has been pointed. In this area, a dolomitic bedrock is overlaid with 5 to 8 meters of clayey
sands. In order to delineate the plume and measure piezometric heads and depths to bedrock, ten
boreholes were drilled and four cone penetrometer tests were conducted. Soil and water samples were
collected and analysed. Although these samplings highlight the presence of hydrocarbons in some
boreholes, the plume is poorly outlined due to the small number of drillings.
To assess the contribution of geophysical investigations in delineating contaminated areas, a 3-D
cross-diagonal resistivity survey was performed using roll-along technique and a seismic refraction
profile was conducted. The electrical dataset was inverted with Res3DInv to build a resistivity-depth
model of the ground. High resistivities suggest a bedrock geometry which is consistent with the drilling
results. However a finer analysis reveals that the resistivities at the top of the bedrock tend to be
significantly higher in areas where gas was detected than in uncontaminated areas. This increase in
resistivities is interpreted as an effect of the presence of fresh hydrocarbons. Confronting boreholes and
geophysical investigations could therefore lead to better estimations of the spill extent.
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Quantitative Imaging Of 3D Solute Transport Using 2D Time-Lapse Ert: A Synthetic Feasibility Study
Authors Andreas Kemna, Jan Vanderborght, Horst Hardelauf and Harry VereeckenTime-lapse electrical resistance tomography (ERT) has proven significant potential to monitor
solute plumes in the subsurface. However, the ultimate value of ERT for quantitative imaging of solute
transport, for example in heterogeneous aquifers, is still under dispute. Here, difficulties may be
expected to arise particularly from the fact that ERT data acquisition and interpretation is often limited
to 2D image planes, while aquifers are generally characterized by a 3D structure involving considerable
variability of flow and transport properties. The potential of time-lapse ERT in such a situation is
investigated by means of a synthetic tracer experiment. For this purpose, 3D solute transport in a
heterogeneous hydraulic conductivity field, characterized by an exponential covariance function, is
simulated. Assuming that solute concentration is linearly related to electrical conductivity, the spatiotemporal
evolution of the tracer plume is imaged in a transect spanned by a set of fictive boreholes using
2D time-lapse ERT. Although the 3D process is imaged using a 2D inversion approach, the recovered
electrical conductivity distributions coincide well with the input distributions. The obtained images are
interpreted as concentration maps and then analyzed in terms of transport properties. By adopting a
stream-tube model, an equivalent advection velocity and longitudinal dispersivity can be quantified for
each pixel in the ERT image plane. The recovered equivalent advection velocities exhibit fair agreement
with those obtained from the original model. The results of the synthetic study demonstrate that
quantitative imaging of 3D solute transport by means of time-lapse ERT is feasible. Importantly,
systematic errors associated with the 2D representation of a 3D model are found to play an insignificant
role concerning the quantification of transport properties, justifying the use of simple 2D imaging, for
instance if equipment, time, and/or budget is limited.
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Relationship Between Biodegradation And Bulk Electrical Conductivity
Geochemical and stable carbon isotope data obtained at closely spaced intervals within a
hydrocarbon impacted aquifer were used to assess the relationship between high bulk conductivity
zones and biodegradation of hydrocarbon. Biodegradation was verified using terminal electron
acceptors (nitrate, sulfate, and iron), dissolved inorganic carbon (DIC), and the isotope ratio of DIC
(δ13CDIC). The bulk conductivity was measured using in situ vertical resistivity probes. The results
show that peak values in the bulk conductivity occurred in zones in the aquifer where total petroleum
hydrocarbon were high and nitrate, sulfate and iron reduction were occurring. Also in the zones where
bulk conductivity was higher, DIC was higher and δ13CDIC was either more negative or more positive
while the major cations were elevated compared to uncontaminated locations. These results suggest
that the higher bulk conductivities were related to microbial redox processes. It appears that the bulk
conductivity measured in hydrocarbon impacted portions of the aquifer is the result of an integrated
process-driven biogeochemical changes reflected in the redox zonation in the aquifer. Hence, higher
bulk conductivity zones may be explained by enhanced mineral weathering within zones of higher
biological activity stimulated by the presence of hydrocarbon and available terminal electron
acceptors. Our results suggest a qualitative interrelationship between redox processes,
biomineralization of hydrocarbons, and high bulk conductivities, and argue for the need to incorporate
geophysical investigations as part of natural attenuation assessment programs.
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Laboratory And Field Results Linking High Bulk Conductivities To The Microbial Degradation Of Petroleum Hydrocarbons
The results of a field and laboratory investigation of unconsolidated sediments contaminated by
petroleum hydrocarbons and undergoing natural biodegradation are presented. Fundamental to
geophysical investigations of hydrocarbon impacted sediments is the assessment of how microbial
degradational processes affect their geoelectrical response. Therefore, the primary goal of this study
was to understand how microbially mediated processes in hydrocarbon impacted sediments influence the
geoelectrical response of this impacted zone. The field and laboratory results showed higher bulk
conductivity in sediments impacted by petroleum hydrocarbons. The impacted sediments also showed
increased populations of alkane degrading microbes and elevated dissolved cations (e.g. Ca2+). The
elevated cations in the contaminated sediments relative to uncontaminated sediments suggest enhanced
mineral dissolution related to the microbial degradation of the hydrocarbon. Both the laboratory and
field data showed the highest bulk conductivities occurring within zones impacted with the free-phase
and residual phase hydrocarbon and not within the water saturated zone. A model using a simplified
form of Archie's Law suggests highly elevated estimated pore water conductivities within this
conductive zone (~4 to 6 times background bulk conductivity) for both the laboratory and field data.
The similar results for hydrocarbon contaminated sediments in laboratory experiments and field settings
suggest that the mechanism for the high bulk conductivity in the contaminated zone is related to the
microbial metabolism of the hydrocarbon and the resulting geochemical alterations within the
contaminated zone. This study demonstrates that the higher bulk conductivity measured by geoelectrical
methods at hydrocarbon impacted sites may be in part related to the microbial mineralization of the
hydrocarbon.
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Wurtsmith Air Force Base Revisited
Authors Laura A. Smart, Mike Nash and William A. SauckBioremediation at hydrocarbon contaminated sites has been known to change the pore water
chemistry in such a manner that the conductivity increase due to the bioremediation is visible through
geophysical imaging. Geophysical techniques are often considered only upon initial site investigation as
a method of determining the extent of contamination and to map the boundaries of the contaminant
plume(s). However, this paper presents another aspect of the geophysical survey methods. The FT-02
plume at Wurtsmith Air Force Base contains both hydrocarbon and chlorinated contaminants. It was
surveyed extensively during the summer of 1996 with ground penetrating radar and electrical resistivity
(dipole-dipole). These surveys distinctly imaged the lateral and vertical extents of the higherconductivity
plume, correlating with the available hydrochemical data from well samples. The area was
revisited during the summer of 2003 to resurvey the original profiles. The purpose of this paper is to
report the changes that occurred to the geophysical signature of this well-known plume which has
undergone initial passive bioremediation and subsequent active remediation. The plume appeared to
undergo some lateral movement as well as significant changes in conductivity. The latter appear clearly
as attenuated zones on the GPR sections.
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Effect Of Different Phases Of Diesel Biodegradation On Low Frequency Electrical Properties Of Unconsolidated Sediments
Authors Gamal Z. Abdel Aal, Estella A. Atekwana, Lee D. Slater and Eliot A. AtekwanaLow frequency electrical measurements were made in laboratory sand columns contaminated
with different phases of hydrocarbon and undergoing biodegradation. The objectives of the study were
to 1) investigate the effect of microbial processes on the low frequency electrical properties and 2)
determine if the phase of hydrocarbon (dissolved or residual) contamination showed measurable
differences in the electrical properties of the sediments during biodegradation. The experimental sand
columns were constructed with the following treatments: uncontaminated (control) column with
nutrients (25% Bushnell Hass medium); column with nutrients + dissolved phase of diesel + bacteria;
and column with nutrients + residual phase of diesel + bacteria. Electrical measurements were made in
the frequency range of 0.1 to 1000 Hz biweekly for the first twenty weeks and monthly for the duration
of the experiments (36 weeks).
The diesel contaminated columns showed a steady increase in microbial population numbers and
a concurrent decrease in nitrate, sulfate, and benzene, toluene, ethylbenzene and xylene (BTEX)
concentrations compared to the control column. These results indicate microbial mineralization of the
diesel in the contaminated columns. Furthermore, the contaminated columns showed temporal increase
in dissolved inorganic carbon (DIC) and decrease in pH concomitant with increase in the fluid
conductivity and calcium ion concentration relative to the control column. Such changes suggest
microbial enhanced mineral weathering possibly by carbonic acid that resulted in higher fluid
conductivity in the contaminated columns. The contaminated columns also showed temporal increase in
the real and imaginary conductivity relative to the control column. The electrical data showed a higher
relative increase in the surface conductivity component in the contaminated columns compared to the
control column. Finally, we observed that the magnitude of the changes for all measured
biogeochemical and electrical parameters was greater (10-30%) in the sand column contaminated with
residual phase of diesel compared to the column contaminated with dissolved phase diesel. The results
are consistent with models that suggest that residual hydrocarbons trapped in the pore sediments are
more freely available for degradation by bacteria than in the dissolved phase. This resulted in the
relatively higher rate of biodegradation and accompanying biogeochemical alterations reflected in the
electrical measurements. We infer from these results of this study that microbial processes can impact
electrical properties and the accompanying physicochemical alterations at the mineral-fluid interface are
readily detectable using low frequency electrical measurements.
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Soil Resistivity Measurements For Clay Content Estimation And Its Application For Petroleum Contamination Study
Authors Vladimir Shevnin, Omar Delgado Rodríguez, Aleksandr Mousatov and Albert RyjovInformation about clay content is useful at contamination study because clay influences on
position and movements of contaminants by means of soil permeability and adsorption. Technology for
clay content estimation is based on soil resistivity measurements as function of water salinity at full
saturation of soil samples and data interpretation (or inversion) to find clay content and porosity of the
sample. Together with water resistivity estimation for an investigated site this information permits
characterizing uncontaminated soil and estimating boundary conditions for separating uncontaminated
and contaminated zones. This information helps in geological interpretation of vertical electrical
sounding data. Soil resistivity is determined by pore water resistivity, porosity, clay content and
humidity. To reduce number of unknown factors influencing on resistivity, we measure both soil and
water resistivity in the survey area. Soils below a groundwater level have humidity 100 % of pore space
that allows not taking this factor into account. Measurements of water and soil resistivity can be
performed with different types of resistivimeters and field resistivity meter. Estimating soil parameters is
performed with the help of forward and inverse petrophysical calculation.
Measurements of petrophysical parameters on calibrated sand and clay samples and on their
mixtures showed good accuracy of clay content estimation.
We studied sensitivity of petrophysical algorithm to principal soil parameters and estimated
errors of interpretation depending on input error.
Practical examples from different contaminated sites are presented. These demonstrate good
correspondence between vertical electrical sounding data, water and soil resistivity measurements, and
petrophysical estimations.
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Application Of A New Monte Carlo Approach To Calibrating Rock Physics Relationships: Examples Using Electrical Resistivity And Ground Penetrating Radar Tomography
Authors Kamini Singha and Stephen MoyseyIn applying geophysics to problems in hydrology, a relationship must exist
between the geophysical response from the subsurface and the hydrologic variable of
concern. In this paper we discuss the estimation of aquifer tracer concentrations using
electrical resistivity tomography and the determination of subsurface water content from
cross-borehole radar. Obtaining site-specific relationships between geophysical and
hydrologic parameters traditionally entails empirical calibration based on reconstructed
geophysical images and small-scale lab measurements or in-situ well logs. This direct
approach to calibration, however, can become biased in several ways: reconstructed
tomograms are often highly uncertain and subject to inversion artifacts, the range of
subsurface conditions represented by calibration data sets can be incomplete due to the
sparsity of collocated well or core data and aquifer heterogeneity, and the discrepancy in
scale between different measurements is not accounted for. We use Full Inverse
Statistical (FISt) calibration, a new Monte Carlo approach to calibration, to address these
problems. FISt calibration integrates all available data; e.g., aquifer geostatistics, pointscale
measurements, and physically based relationships, to obtain the best possible
relationship between the geophysical and hydrologic variables. We have found that
concentration and water content estimates obtained using FISt calibration are typically
significantly better than those obtained using traditional empirical calibrations.
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Application Of Cross-Borehole Radar To Monitor Fieldscale Vegetable Oil Injection Experiments For Biostimulation
Cross-borehole radar methods were used to monitor a field-scale biostimulation pilot project at
the Anoka County Riverfront Park (ACP), located downgradient of the Naval Industrial Reserve
Ordnance Plant, in Fridley, Minnesota. The goal of the pilot project is to evaluate biostimulation using
emulsified vegetable oil to treat ground water contaminated with chlorinated hydrocarbons. Vegetable
oil is intended to serve as substrate to naturally occurring microbes, which ultimately break down
chlorinated hydrocarbons into chloride, carbon dioxide, and water through oxidation-reduction
reactions. In support of this effort, cross-borehole radar data were acquired by the U.S Geological
Survey in five site visits over 1.5 years. This paper presents level-run (zero-offset profile) and time-lapse
radar tomography data collected in multiple planes. Comparison of pre- and post-injection data sets
provides valuable insights into the spatial and temporal distribution of both emulsified vegetable oil and
also the extent of ground water with altered chemistry resulting from injections—information important
for understanding microbial degradation of chlorinated hydrocarbons at the site.
In order to facilitate data interpretation and test the effectiveness of radar for monitoring oilemulsion
placement and movement, three injection mixtures with different radar signatures were used:
(1) vegetable oil emulsion, (2) vegetable oil emulsion with a colloidal iron tracer, and (3) vegetable oil
emulsion with a magnetite tracer. Based on petrophysical modeling, mixture (1) is expected to increase
radar velocity and decrease radar attenuation relative to background—a water-saturated porous medium;
mixtures (2) and (3) are expected to increase radar velocity and also increase radar attenuation due to
their greater electrical conductivity compared to native ground water.
Radar slowness (inverse radar velocity) tomograms and level-run profiles show decreases in
slowness in the vicinity of injection wells. Slowness anomalies are observed only in planes connected to
injection wells, indicating that the emplaced emulsified vegetable oil does not migrate far after injection.
In contrast to the localization of slowness anomalies, attenuation anomalies are observed in all level-run
profiles, particularly those downgradient of the injection wells. Despite the expected signatures of
different tracers, increases in attenuation are observed downgradient of all three injections; thus, we
infer that the attenuation changes do not result from the iron tracers. One viable explanation for the
observed attenuation changes is that products of oil-enhanced biodegradation (for example, ferrous iron)
increase electrical conductivity of ground water and thus radar attenuation.
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Electrical Impedance Tomography For Detection Of Dnapl Contamina
Authors William Daily and Abelardo RamirezMapping the distribution of dense non-aqueous phase liquid (DNAPL) contaminants in
subsurface soils and ground water at a site is an important task before remedial action can
be intelligently planned. Recently laboratory studies (e.g., McKinley, 2003) has shown
that the low frequency electrical properties of a soil from the Savannah River Site (SRS)
containing certain clay and contaminated by perchloroethane (PEC) may be sufficiently
unique to make it possible to use electrical impedance tomography (EIT) to differentiate
normal electrical heterogeneities of the subsurface from parts of the subsurface
containing DNAPL contamination.
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Cross-Hole Complex Resistivity Survey For Pce At The Srs A-014 Outfall
Authors Robert E. Grimm and Gary R. OlhoeftCross-hole complex-resistivity imaging of the vadose zone was performed at the A-014
Outfall at the Savannah River Site, Aiken, SC. Five vertical electrode arrays (VEAs) were
installed with ~15-ft separations in and around a suspected DNAPL source zone to depths of 72
feet. Amplitude and phase data were edited for quality and then inverted to form threedimensional
(3D) images of the target volume. The comparatively small magnitude of the
nonlinear resistivity Hilbert distortion allowed approximate linearized imaging of the 3D
distribution of these effects. Laboratory analysis of nearby soil contaminated in situ indicated
that the CR response to the PCE-clay reaction was maximized near 50 mHz. PCE occurrence
was predicted to track phase and Hilbert-distortion indicators. PCE concentrations were
measured at three drilling locations and were compared to predictions a receiver-operating
characteristic analysis. The optimum performance at 1000 mg/kg in situ PCE was >80%
detection (true positives) with <30% false alarms (false positives) at an effective resolution of 4
ft, ~1/3 of the interwell separation. The CR survey successfully predicted the general distribution
of PCE at parts-per-thousand concentrations, specifically widespread near-surface contamination
and a zone of discontinuous pods or stringers immediately below the source.
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Three Dimensional Self-Potential Inversion For Subsurface Contaminant Detection And Mapping At The Doe Savannah River Site, South Carolina
Self-potential (SP) data are collected using a 3D array of non-polarizing electrodes, consisting of
a surface grid and four borehole arrays, over an area known to be contaminated with DNAPLs (Dense
Non-Aqueous Phase Liquids). The self-potential method is commonly used to measure the electric field
produced by electrokinetic, thermoelectric, or electrochemical coupling processes that take place in the
subsurface. DNAPLs are known to undergo oxidation-reduction (redox) reactions in the environment,
and are proposed as an electrochemical source for this investigation. Electrical currents that exist due to
the redox reactions at depth traverse the resistive Earth materials and are manifested as a potential field
that is measured at the surface and borehole locations. A 3D inversion algorithm is used to find the
electrical current source model that supports the measured data, taking into account the resistivity
structure derived from an induced polarization survey at the same field location. The sources and sinks
of electrical current are related to the zones of redox activity, and therefore to the areas of
contamination. These results are correlated with chemical concentration data obtained from a series of
ground-truth well measurements taken at the site.
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Mapping Of Tce And Pce Contaminant Plumes Using A 3-D Induced Polarization Borehole Data
In-situ complex resistivity (CR) or Induced Polarization (IP) data are collected using a 3D array
of surface and borehole electrodes, over an area known to be contaminated with DNAPLs (Dense Non-
Aqueous Phase Liquids). The contaminants include Tetrachloroethylene (TCE) and Trichloroethylene
(PCE), which, until recent years have been disposed of directly into the environment. The design of the
surface and cross-borehole array allows for a 3D IP inversion. Data are measured at two frequencies (1/4
and 1/16 Hz), and are inverted for resistivity magnitude and phase. The inversion results are compared
with PCE and TCE contaminant concentrations measured from core samples taken from three ground
truthing wells drilled within the region of interest. The phase and imaginary resistivity are shown to be
well correlated with the concentration data from two of the three ground truthing boreholes where the
TCE and PCE concentrations are above 1mg/kg.
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Sediment Sampling At The A-014 Outfall For Comparison With Complex Resistivity Measurements
Authors Joseph Rossabi, Brian D. Riha and Dennis G. JacksonChlorinated solvents were usually released as dense non-aqueous phase liquids (DNAPLs) to the
subsurface where they move in an unstable fashion driven by gravitational and capillary forces. They are
often retained in small discrete blobs (<< 1 m3) in fine grain materials particularly in the vadose zone
and contaminate ground water by slow continuous release through dissolution and diffusion. Locating
these small sources is a difficult but crucial part of remediating a contaminated site. Several methods
have been developed for subsurface DNAPL location but nearly all are intrusive and can only identify
DNAPL in close proximity to the access hole. Minimally invasive geophysical methods to locate
residual DNAPL have been proposed and developed but few methods are capable of the spatial
resolution required. Complex resistivity measurements sensitive to DNAPL (tetrachloroethylene)
interactions with clay (smectite) have recently been shown to have promise in laboratory experiments.
Based on these laboratory results, field tests of the complex resistivity technique were performed at the
A-014 outfall of the Savannah River Site.
The Savannah River Site (SRS) continues to use both innovative and baseline methods to
characterize sites including DNAPL contaminated areas. To support the field testing of complex
resistivity techniques an area (approximately 10m x 15m) was selected with residual DNAPL confirmed
by both the NAPL FLUTe (Ribbon NAPL Sampler) and cone penetrometer soil sampling and analysis.
After complex resistivity measurements were made, approximately 400 depth-discrete soil samples at 5
selected locations within the test area were collected and analyzed to compare with the geophysical
results. Despite inherent differences in spatial resolution and coverage, and the limited number of
baseline samples this comparison can be used to provide some measure of performance of the
geophysical technique.
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Geophysical Characterization Of The Fuel Producing Zones Near The Bedrock At Campbell Army Airfield, Fort Campbell, Ky
Authors M.D. Thompson, Wayne Mandell, Bill Davies, Steve Miller and Pat WilkeyFuel leakage adjacent to the Campbell Army Airfield, Fort Campbell, Kentucky has
introduced jet fuel (JP-4), a light, non-aqueous phase liquid, into soils and possibly the underlying
karst system where it poses a threat to the ground water supply. Previous geotechnical
investigations conducted over a 15-year period using traditional drilling and sampling methods
showed varied success in locating the presence of LNAPL contamination. Two contaminated
regimes were identified from this effort; a shallow zone that corresponds to perched water intervals,
and a deeper zone within the epikarst where free product is currently being recovered.
Surface geophysical data (seismic and electrical) were used to augment the established
network of wells by identifying changes in bedrock topography and overburden character likely to
be associated with the contamination regimes. A mapped bedrock depression appears to control the
spatial extent of the deeper contaminated zone, as extraction rates are greatest within the vicinity of
the rim of this depression. A weak correlation between fuel producing areas and zones of lowresistivity
(higher electrical-conductivity) can be established at this site. If true, this would imply
that active degradation of the fuel is occurring and producing an electrically conductive pore fluid.
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Reprocessing Gpr Data From The Cfb Borden Experiment Using Apvo/Gpr Techniques
Authors Thomas E. Jordan and Gregory S. BakerThis paper presents reprocessed GPR data from a 1991 Canadian Forces Base (CFB) Borden
experiment conducted by Brewster and Annan (1994). The purpose of our research is to
determine if a modified amplitude and phase variation with offset analysis of the ground
penetrating radar (APVO/GPR) data is a feasible technique for monitoring a dense non-aqueous
phase liquid (DNAPL) release. Forward models using the Fresnel reflection coefficient equation
accounting for low loss conditions indicate that conductivity is inversely related to the maximum
absolute value reflection coefficient max R observed for incidence angles of 0 through 89
degrees. The injection of a low conductivity DNAPL into a saturated sand decreases
conductivity by displacing some ground water. Conductivity values then increase as the DNAPL
migrates vertically downward. It is anticipated that values of max R increase as DNAPL is
injected followed by a decrease as the DNAPL drains. The ability to detect changes in the
amplitude of reflectors due to zones of anomalously conductive liquids may be an additional
method for monitoring NAPL releases. The APVO/GPR technique may also be useful for
determining the conductivity of subsurface reflectors.
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3D Multi-Offset, Multi-Polarization Acquisition And Processing Of Gpr Data: A Controlled Dnapl Spill Experiment
More LessDense non-aqueous phase liquid contaminants (DNAPL) typically have much lower electric
conductivity and electric permittivity than water. The bulk electric properties of the subsurface can be
significantly altered when these contaminants replace water in the pore space. Ground-penetrating radar
(GPR) is sensitive to permittivity contrasts and provides the potential to identify zones of low permittivity
associated with the presence of DNAPL. To test 3D multi-fold GPR techniques for quantifying DNAPL
induced permittivity anomalies, my research team conducted a small (107 cm x 122 cm), controlled DNAPL
spill experiment. The model was confined within a cylindrical polyethylene tank; model material consisted
of medium to coarse grained sand with a thin gravel layer near the base. My team injected twenty liters of
a chlorinated solvent solution into the vadose zone just below the surface, and monitored contaminant
migration into and through the water saturated zone to the bottom of the tank. I compiled a comprehensive
dataset for testing a variety of data processing and analysis techniques including 900 MHz, multi-offset, 3D
surface datasets in both TE and TM polarizations, 2D GPR transmission data, downhole TDR probe data,
and post-injection soil samples for chemical analysis. Both reflection tomography from TE polarized surface
data and crosswell tomography from transmission data reveal significant velocity anomalies associated with
pooled DNAPL that approaches a saturation of 40%. Further, thinbed offset-dependent reflectivity analysis
of TM surface data suggests the formation of a thin, highly saturated (80-100%) DNAPL zone at the top of
the main DNAPL pool. This work demonstrates that detailed analysis of multi-offset, multi-polarization GPR
data can significantly improve our ability to quantify subsurface permittivity anomalies.
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A Laboratory Study Of The Complex Electrical Resistivity Response Of Soils
Authors Stephen R. Brown, Jason R. Sorenson and Thackery I. BrownThere is an increasing need for new non-invasive geophysical techniques to locate DNAPLs in the
subsurface. G. Olhoeft and colleagues have published several reports which indicate that organic solvents,
notably toluene, PCE, and TCE, residing in clay-bearing soils have distinctive electrical signatures. These
results suggest a new measurement technique for remote characterization of DNAPL pollution.
As with any new research result we note the importance of reproducing the work of previous researchers
to ensure that any effects observed are due to the physical phenomena occurring in the specimen
and not due to the particular experimental apparatus or method used. To this end, we independently
designed and built a laboratory system for the measurement of the complex electrical resistivity properties
of contaminated soil. After careful characterization and calibration of our equipment, we attempted
numerous times to reproduce the seminal results of Olhoeft and Sadowski on the response of toluenecontaminated
clay-rich samples. While we observe similar responses to theirs for plain clays with brine,
the addition of toluene does not produce the effects they described.
Our results indicate, at best, a low sensitivity of the complex electrical resistivity method to organic
contamination in rocks and soils.
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Using The Depth Of Investigation Index Method In 2D Resistivity Imaging For Civil Engineering Surveys
Authors Laurent Marescot and Meng Heng LokeTo assess whether features in 2D imaging results are demanded by the data or are artefacts of the
inversion process, a special inversion algorithm was applied to process DOI (Depth Of Investigation)
index maps. This method carries out two inversions of the same data set using different values of the
reference resistivity. The two inversions reproduce the same resistivity values in areas where the data
contain information about the resistivity of the subsurface whereas the final result depends on the
reference resistivity in areas where the data do not constrain the model. This calculation can be also
performed for borehole-to-borehole or borehole-to-surface surveys. In this case, regions of investigation
can be outlined. Without DOI maps, interpretation of models can be sometimes difficult, nonrepresentative
and dangerous. As can be inferred from field examples, the DOI maps prevent overinterpretation
or misinterpretation of inversion results in electrical imaging studies. The DOI map helps
explaining the occurrence of erratic and non-geologic structures at depth. It also says how deep we can
see into an inverted resistivity profile. In this paper, the implementation of the algorithm is first
described and the methodology is then illustrated with 2D surface and borehole electrical resistivity
imaging applied to civil engineering and hydrogeological surveys.
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Comparision Of Different 2D And 3D Geoelectric Survey Layouts For Detection Of Saltwater Convection Cells In The Okavango Delta (Botswana)
Authors R. Supper, P. Bauer, W. Kinzelbach and S. ZimmermannThe Okavango Delta is a huge wetland ecosystem in northwestern Botswana, Southern
Africa. Water from the moist tropical highlands of southern Angola flows down the Okavango
river, spills into the Kalahari basin and forms an alluvial fan of the size of approximately 30 000
km2. Some 6000 km2 of permanent swamps form the core of the Delta and towards the fringes,
the environment is gradually becoming drier.
Although the delta has no outflow, the swamps sill consist of fresh water with low
salinity. Density driven convection is regarded to be the phenomenon responsible for that. The
goal of the field campaign was to determine the salinity distribution below selected islands in the
Okavango Delta to verify this theory. We have tested and compared different geoelectrical
configurations (2d, 3d, borehole to surface) to resolve the phenomenon of density fingering under
such unfavourable situation of a full 3d problem and a very low resistive top layer covering high
resistive structures.
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New Achievements In Developing A High Speed Geoelectrical Monitoring System For Landslide Monitoring (Geomonitor2D)
More LessLandslides are one of the major threats to human settlements and infrastructure, causing over time enormous human suffering and property losses than any other geological hazard. Therefore much effort has to be centred on risk detection, risk reduction and development of timely warning systems to prevent future loss of life and property. During recent years the dc-geoelectric method has been used widely to investigate the structure of landslide areas, thus gaining the status of a state-of-the-art-method in civil engineering for this. However so far the dc-geoelectric method was hardly used to detect structural changes with time in active landslide areas. Within this talk we present the development of an innovative, high speed geoelectrical monitoring system, which allows remote controlled automatic measurements of geoelectric pseudo-sections. Each section, using a new kind of configuration, consists of 3000 single measurements, each one sampled for 1000 times. The acquisition time for such a section is about 30 minutes thus allowing to derive a point shot of the subsurface structure. This system was installed on an active landslide area. Within a period of two years, 6 pseudosections were measured each day. The results within this monitoring period will be discussed.
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Applications For Capacitively Coupled Resistivity Suvreys In Florida
Authors K. Michael Garman and Scott F. PurcellThe use of capacitively coupled resistivity (CCR) as a geophysical method has historically been of
limited use in Florida due to the shallow water table and the time necessary to make multiple passes to
collect resistivity data at depth. The induced current used by CCR instruments is stronger and can
penetrate to greater depth if the surface materials are resistive, because the voltage measured at the
receiver equals the current in the transmitter multiplied by the resistivity of the earth materials. The
presence of shallow groundwater increases conductivity thereby reducing the CCR signal strength. The
availability of a multi-channel CCR instrument, the Ohm-Mapper by Geometrics, Inc. has eliminated the
need for multiple passes for a study. Subsurface Evaluations, Inc. has investigated two applications for
multi-channel CCR surveys in Florida:
1. CCR has been successfully used to delineate buried depressions in sandy upland areas producing
results remarkably similar to ground penetrating radar (GPR) data but easier to interpret; and
2. CCR has been successfully tested on road projects for identifying shallow deleterious soil
conditions such as clay and peat lenses that might be missed by a standard drilling program and
that are not readily detectable by GPR.
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Comparison Of Different Electrode Materials For Induced Polarization Measurements
Authors Gareth Morris, Andrew M. Binley and Richard D. OgilvyIn recent years, there has been a marked increase in the use of the induced polarization (IP) and
spectral induced polarization (SIP) techniques in environmental surveys. As a result, the required
measurement sensitivity of this method has increased significantly from their original application in
mineral exploration. In order to obtain the best results from IP and SIP data, considerable work has been
done on the data inversion procedures whilst the field procedure has remained essentially the same.
Standard IP survey practice is to record data using non-polarizing electrodes. However, recent work has
concentrated on the use of different materials as potential electrodes. Of particular interest has been the
use of standard metal electrodes in the place of non-polarizing electrodes since this would greatly
improve the speed and ease of field surveys. Here we focus on the initial results of trials assessing the
use of different electrode materials in both laboratory and field-analogue environments. The
experiments compare and contrast the use of a range of electrode materials, including non-polarizing, for
IP measurements. Electrode performance assessment focussed on the strength, stability, noise levels,
and frequency response of the signal recorded with each material. The results have implications on the
design of future electrode arrays and field surveys.
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Forward And Inverse Resistivity Modelling On Complex Three Dimensional Structures Using The Finite Element Method
The finite element method has been used by several authors in the context of direct current
forward and inverse modelling. This versatile numerical method is particularly useful for engineering
applications in which very varied structures (e.g. walls, dams, concrete piles) can be modelled for nondestructive
investigations. Nevertheless, there is currently a need in developing forward and inverse
resistivity modelling codes that are better suited for imaging structures with complex geometries.
Therefore, various original approaches must be used to create a well-adapted program. This paper
presents the adaptation and the use of the CESAR-LCPC finite element code for the forward and inverse
modelling of 3D resistivity data. Firstly, the forward modelling code uses an electrode-independent
mesh that allows to place the electrodes at their exact locations and to use a coarse mesh at the same
time. To calculate apparent resistivity values, a normalisation approach is used that gives significantly
better results than the use of the geometrical factor and allows the modelling of any kind of complex 3D
structure. An inversion code was also implemented for the processing of resistivity tomographies on
complex 3D structures using any electrode arrangement. This algorithm uses an original strategy to
avoid high-computation costs since it does not involve the explicit calculation of a sensitivity (Jacobian)
matrix. Synthetic results are presented to illustrate the efficiency of these forward and inverse modelling
codes.
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A Fast Forward Modeling Algorithm For Ert Inversion
Authors Shan Wei and Roelof VersteegThe standard approach in electrical resistivity tomography (ERT) forward modeling is to find the
potentials resulting from a current dipole by solving a set of linear equations for this dipole. For N
electrodes, the number of sets of linear equations to solve can be as large as N*(N-1)/2. For large
numbers of current dipoles this approach is prohibitively inefficient. By first computing only single
current source (pole) data, then combining these data into dipole-dipole data, the maximum number of
sets of linear equations is N. Compared to conventional methods, this approach is much more efficient in
cases where we have large numbers of dipole current sources. Examples using this approach are given to
show that there is no loss of accuracy and it greatly reduces the computation cost.
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Ert Inversion On Sharp Contrast Boundaries
Authors Shan Wei and Roelof VersteegSmoothness constraint is one of commonly used regularization terms during the geophysical
inversion process to find a possible model fitting the data. However, if sharp contrasts boundaries exist
within the earth, inversions using smoothness constraints may fail to converge or yield suboptimal
results. As presence or location of sharp contrast boundaries is normally unknown, it is hard to apply the
corresponding constraints prior to the inversion. An algorithm to locate the possible sharp contrast
boundaries as part of the inversion through an iterative update of the smoothness constraints allows
significant improvement of the final image of subsurface properties. To demonstrate this algorithm,
electrical resistivity tomography (ERT) examples are given.
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Non-Invasive 3D Conductivity Measurements During Flow Experiments In Columns With Merit
Authors Axel Tillmann, Roy Kasteel, Arre Verweerd, Egon Zimmermann, Andreas Kemna and Harry VereeckenThe non-invasive measurement of physical parameters in soils is an important tool for observation and sustainable management of soils and aquifers so as to preserve or to restore groundwater quantity and quality from natural or anthropogeneous e ects. We present the Magneto-Electrical Resistivity Imaging Technique (MERIT) in theory and application to investigate the variation of the three-dimensional distribution of the electrical conductivity during fluid flow. Numerical experiments were performed to simulate water flow in cylindrical soil columns, the effect of saturation changes on electrical conductivity, and the changes in the resulting electrical potential and magnetic field due to current injection. As result we can state that MERIT is a non-invasive method that is capable of monitoring fluid flow and solute transport processes in soils, if the accuracy of the magnetic eld measurements is 0:1% and the resolution is 50 pT minimum.
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Towards Three And Four Dimensional Data Collection For Electrical Resistivity Data
Authors Douglas LaBrecque, Roger Sharpe and Melissa StubbenAdvances in hardware and software have made the collection of fully three-dimensional and four
dimensional resistivity data not only possible but practical. To fully utilize these new capabilities
requires new approaches to collecting data. This paper shows both theoretical and field comparisons of
data collection schemes comparing more traditional one- and two- dimensional data collection strategies
with fully three-dimensional strategies. These new approaches include array patterns, such as horizontal
subsurface dipoles, that were not possible in older schemes. Finding optimal arrays requires tradeoffs in
resolution, acquisition time, and signal levels. A new statistical based approach is shown that can be
used to determine optimal array types under various constraints. Tests of these new array types show
that they can provide substantial improvements in the resolution of subsurface resistivity and the change
in resistivity with time.
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Transient Audio-Magnetotelluric Imaging Of A Buried Valley
Authors David K. Goldak and Shawn M. GoldakThunderstorm activity produces large amounts of electromagnetic energy which is
trapped within the earth-ionosphere waveguide. The random sum of energy from activity
on a near global scale produces a low-level quasi-continuous source field. Very large, or
equivalently, relatively nearby lightning discharges produce individual transient events whose
amplitude are significantly larger than that of the low-level background field. Therefore, the
best possible signal-to-noise ratio is realized by recording exclusively sources of a transient
nature. However, the transient events are strongly linearly polarized, the polarization diversity
of which can affect the estimation of earth response curves.
It has been shown that an adaptive time domain averaging of the transient waveforms
results in earth response curves whose bias converges to zero super-exponentially in
stacked signal-to-noise ratio (Goldak et al., 2001). The efficacy of the algorithm is shown
in the results of a transient audio-magnetotelluric (TAMT) survey conducted over a buried
valley system in southern Manitoba, Canada. Twenty three sites at 200 m spacing were
collected with the impedance tensor ˜Z and the magnetic field tipper ˜T estimated over the
bandwidth 8 Hz - 32 kHz.
The results of the TAMT survey agree very well with those of a time domain
electromagnetic (TEM) survey conducted by the Saskatchewan Research Council with a
Geonics EM-47 over nearly the same profile.
Two dimensional OCCAM inversion of the TAMT data reveal the buried valley
to be approximately 1 km wide, 70 m deep with a resistivity of approximately 12 ¡ m,
incised into Cretaceous sediments of approximately 4 ¡ m resistivity.
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Depth Of Investigation For Small Broadband Electromagnetic Sensors
More LessThe depth of investigation (DI) in electromagnetic (EM) soundings is related to many factors
such as the sensor sensitivity, resolution, coil configuration, ambient noise level, and the techniques used
in data processing and interpretation. Quantitative understanding of the relationships between the DI and
these factors will help the users to meet their geological objectives, avoid unnecessary survey expense, and
display meaningful geologic features.
Simple equations to calculate the DI for hand-held EM sensors have been derived from the analysis
of the EM response based on layered models. The DI is proportional to the target conductivity and
inversely to the frequency, overburden conductivity, and detection threshold. We present field examples
to illustrate how to use the DI in data interpretation.
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Electromagnetic Smoke Rings Diffusion In A Horizontally Anisotropic Conducting Half-Space
More LessThe electromagnetic smoke ring provides an intuitive basis for qualitative interpretation of electromagnetic data.
Anisotropy in Earth materials often leads to unexpected geophysical responses that cannot be
anticipated from simple isotropic models. In this paper, I investigate the effect of lateral anisotropy on
the smoke ring diffusion in a conducting half-space excited by a horizontal loop.
Forward modeling computer program has been developed to investigate the effect of fractures on
the elliptic-like smoke ring diffusion in a horizontally anisotropic half-space to a sudden step-on of
electric current excited by the horizontal loop. Modeling of elliptic-like smoke ring diffusion is done for
two cases, namely σ (fractures are more conductive than the matrix) and σ (fractures are more
resistive than the matrix). It is observed that for a horizontal loop source in a horizontally anisotropic
medium the smoke ring becomes elliptic-like, with the long axis parallel to the direction of more
conductivity and short axis parallel to the direction of less conductivity and this shows the paradox of
anisotropy. Smoke rings in a horizontally anisotropic medium diffuse downward and outward as the
time elapses. The short axis and the long axis and the depth of smoke ring change their behavior
depending on their evaluating time. When σ , the short axis depends on parallel conductivity at
early time and perpendicular conductivity at later time and the long axis depends on perpendicular
conductivity at earlier time and combination of both conductivities at later time. When σ , the
short axis depends on perpendicular conductivity at earlier time and on parallel conductivity at later
time; the long axis depends on the parallel conductivity at earlier time and combination of both
conductivitities at later time. Accurate interpretation of electromagnetic data over a fractured medium
depends on the ability of the geophysicists to recognize the effect of anisotropy.
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Skytem – New High Resolution Helicopter Tem System
Authors Kurt I. Sørensen, Max Halkjær and Esben AukenDuring the last decade, approximately 60,000 ground-based, single-site TEM soundings have
been carried out for detailed groundwater investigations in Denmark -an areas of 42,000 km2-. In future
the investigations will be even more intensified.
Detailed groundwater investigation in Denmark calls for high-resolution, continuous off-time
TEM measurements in the decay time interval from approximately 10 microseconds. to 10 milliseconds,
providing resolution of the protective clay caps and the aquifer layers down to 200 – 250 meters.
To meet these requirements, a new airborne TEM system, SkyTEM, has been developed. The
transmitter coil, together with the Rx coil, is mounted on a 12.5 x 12.5 m frame carried by a helicopter at
an altitude of 15 to 25 meters above ground and with a speed of 20 to 30 km/hr.
The transmitter current has a square waveform with a 50% duty cycle with a fast turnoff and the
transmitted moment pattern is segmented with the highest moment reaching 45,000 Am2. The
transmitter waveform, together with other controlling parameters, is measured “on the fly” to ensure
high data quality. Off-time decay signals are measured in the time interval of 15 microseconds to 10
milliseconds in digital controlled analog gates to ensure maximum noise rejection. The data quality of
the SkyTEM system is equal to – and in many cases higher than - the data quality obtained by
conventional ground-based systems.
The total weight including power supply of the SkyTEM system is approx. 300 kg. SkyTEM
operates automatically without operator in the helicopter and transmits measured data to a ground base
for further “on the fly” processing and interpretation allowing ground personal to maximize the positions
of the profiles.
Interpretation programs optimized for the SkyTEM data sets are developed in order to get a fast
and efficient operating system.
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Synthetic Studies To Determine The Effects Of Anomalous Magnetic Permeability On A New Electrical Resistivity Tomography/Magnetometric Resistivity Survey System
Authors Matthew A. Ludwig, David Alumbaugh, Douglas LaBrecque, Roger Sharpe and Gail HeathThree-dimensional model studies are presented to determine the effects of electromagnetic
induction and magnetic permeability on magnetometric resistivity measurements, as well as on images
resulting from inversion of the data. This involves the use of two different forward modeling algorithms;
a full electromagnetic code that includes anomalous magnetic permeability, and a steady-state algorithm
that assumes free-space magnetic permeability. To determine the nature of problems caused by
electromagnetic induction in the presence of permeable materials, the two synthetic data sets are
compared directly, as well as inverted with a steady-state inversion algorithm. Including a magnetically
permeable target causes significant changes in the synthetic data and produces noticeable artifacts in the
inverted sections, especially at depth. However, despite the presence of artifacts, the images are still
dominated by the conductivity, and thus the extent of both conductive and resistive targets are well
defined.
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Use Of Geophysical Surveys For Fill Characterization And Quantity Estimation At Brownfield Sites – A Case History
Authors John A. Mundell and Gregory B. ByerNew building construction planning typically includes site characterization with standard
geotechnical drilling and sampling methods under the direction of a professional engineer. For project
sites with the potential for variable types and thicknesses of fill materials, including contaminated
wastes that pose a possible environmental hazard, this traditional site characterization approach can
result in under sampling and lead to an unrepresentative site characterization. This can also result in
significant cost overruns and other surprises. In recent years, as reuse of ‘brownfield’ properties has
increased, the need for better, more reliable site characterization methodologies has grown. The
combined use of geophysical surveys and standard drilling and sampling methods during the project
planning phase has been shown to be a valuable approach to meet these needs.
This paper presents a case history of an actual construction project in which geophysics was
combined with traditional drilling and sampling at a brownfield location where a 70,000 cubic yard
excavation for two commercial building basements was planned. Historical information combined with
the initial drilling results and geophysical testing revealed a potential two-dimensional bias to the fill
distribution. Closely-spaced, 2-dimensional resistivity profiles were independently acquired and
inverted, and then jointly interpolated in 3-dimensions to render a 3-dimensional image of the fill
materials. The 3-dimensional imaging allowed for the quantification of fill types and quantities for
proper management during excavation, and the development of estimates for transportation and disposal
of the materials. In addition, it also allowed the construction management team to plan for proper
segregation and handling of these materials to minimize total construction costs and schedule delays
while maintaining safe working conditions.
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Mapping An Industrial Landfill Area From Penetration Of Gpr Data
Authors Marica Calabrese, Luigi Zanzi and Maurizio LualdiThe investigation target is a landfill situated in Italy. The area covers a surface of about 7.000
m2. At the beginning the area was used for production of inert material. Later the area was used to
dispose the industrial waste of a company operating in the iron and steel field. In the eighties, the landfill
became exhausted and the activity for the rehabilitation of the site started. Within these activities an
electrical survey was performed. In this work, the GPR survey carried out in July 2003 is described. 250
MHz and 50 MHz antennas were used: the analysis of the profiles shows a strong difference in the
penetration between the landfill and the surrounding fields. Due to the high conductivity of the industrial
waste, the penetration in the landfill is very low while the penetration outside the landfill can reach a
depth of several meters. As a result, GPR is a successful method and was extensively applied for
accurate mapping the lateral extension of the landfill and for estimating possible variations of the
contamination level. Instead, the DC method is the most appropriate technique for an approximate
estimate of the landfill depth.
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Student Research Involving Shallow Geophysics In And Around Colorado Springs
More LessFour students taking an introductory geophysics course at Colorado College in October 2003
were responsible for running small research projects. Using the college’s geophysical equipment we (1)
investigated the stability of a dam at the Catamount Institute using resistivity and found low apparent
resistivities near the pond and a low-resistivity lens on the Eastern side of the dam; (2) surveyed a
magnetic profile across the college’s soccer field and modeled two anomalies, at 5 and 2 m depth,
respectively; (3) ran a gravity survey across a postulated fault on the West side of the Upper Arkansas
graben and obtained a gravity signature consistent with an East-dipping normal fault having ~180 m
vertical offset; (4) attempted to obtain seismic velocities across a known fault juxtaposing sediments
against crystalline rock on the East side of the Upper Arkansas graben but found only a shallow,
low–velocity overburden and no high velocities typical of crystalline rock; and (5) tested the feasibility
of using a resistivity survey to monitor septic systems and imaged a plume with low apparent resistivity
extending downhill from a septic leach field. Although the short amount of time allowed only for basic
data processing, centering the course on real problems was a rewarding experience for all involved.
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Delineation Of Subsurface Geometry By 2D And Joint Inversion Of Resistivity And Em Sounding Data From A Dam Site At Owena River Area South Western, Nigeria
More LessA total of twenty nine DC resistivity and several EM soundings were carried out along four
soundings profiles around river Owena, the area falls within the Basement Complex region predominant
in South Western Nigeria and is marked out for the construction of a multipurpose dam. The 1D
inversion of the sounding data, although satisfactory, revealed some complex, unresolved
geological/geometrical structures at some sounding stations. In light of this, the same data set was
reinterpreted using a 2D Inversion Scheme based on a modified form of the finite element method was
used to obtain a clearer image of the resistivity structure and geometry of the Owena river area, the
results obtained reveled sudden departures in the subsurface geometry between some sounding stations
and also between the profiles. The results presents a more clearer picture of the structure of the location
and compared with the inferred interpretation from 1D inversion reiterates the importance of carrying
out 2D inversion rather than the more common 1D inversion, the 2D inversion scheme used also makes
the inversion process less computationally expensive.
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Geophysics Applied To A Bioreactor During Leachate Recirculation And To Leachate Samples
Authors Solenne Grellier, Roger Guérin, Christophe Aran, Henri Robain and Gérard BellierThe bioreactor is a new concept of landfill where parameters of biodegradation can be controlled
in order to stabilize the waste mass. A high waste moisture, generally brought by leachate recirculation,
favours biodegradation and methanogenesis reactions.
This study conducted by CreeD, Paris 6 University and IRD aims to establish the validity of
geophysical measurement methods and the link between the geophysical measurements and the water
content variations in the waste mass. Electrical resistivity is mainly linked to water and ionic content.
This is the reason why geophysics methods measuring electrical resistivity are used in this study.
The originality of this study will consist in in situ and laboratory measurements:
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Waste Volume Estimation Using Geophysical Methods In A Complex Geologic Setting
Authors Mike Thompson, Drew Clemens, Steve Miller, John Tesner, Wayne Mandell, Phil Durgin, Bill Davies and Jim McKennaGeophysical surveys using electrical resistivity and seismic refraction profiling were used to
estimate the waste volume at Radford Army Ammunition Plant (RFAAP), Virginia. The Radford
area is underlain by a complex sequence of folded and faulted carbonate and clastic units, where
solution-enhanced fractures and sinkhole development is highly variable, depending on the
formation and degree of fracturing. This extremely heterogeneous and anisotropic environment
greatly complicates environmental characterization and evaluation of remedial action alternatives.
Complementary methods used in this effort increased the level of confidence in the resulting
models. 2D electrical resistivity imaging tended to overestimate the base of the waste area, but the
final interpretation was constrained using results from seismic refraction profiling and borehole
geophysical surveying.
The combined borehole and surface geophysical methods established a defensible, more
accurate estimate of waste boundaries and volumes. Because the waste base was much shallower
than originally thought, subsurface characterization was completed more quickly using less
expensive methods. The resulting conceptual site model provided a vastly improved assessment of
heterogeneities within the underlying hydrogeologic system. Borehole geophysics proved an
invaluable Quality Assurance tool for highlighting inconsistent interpretations and verifying
conceptual site models.
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Comparisons Of Ip And Resistivity Data At Several Old, Buried Landfills
Authors Norman R. Carlson and Scott A. UrquhartWhile resistivity and conductivity continue to be two of the most common methods used for
mapping old, buried landfills, we continue to encounter sites where the resistivity contrast between the
landfill and the background material is either non-existent or inconsistent. Several recent examples are
presented, including two landfill pits located just 2500 feet apart. Based on boring results, at one of the
landfills both resistivity and induced polarization (IP) data clearly delineated the waste boundaries, but
at the other landfill, in the same geological background material, resistivity (and conductivity) failed to
delineate the waste while there was a clear, well-defined correlation between IP effects and waste. The
location and volume of waste would have been severely misjudged had we relied on resistivity or
conductivity in advising the environmental firm tasked with evaluating the property.
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Design And Installation Of A Remotely Controllable Autonomous Resistivity Monitoring System At The Gilt Edge Mine Superfund Site, South Dakota
Authors Roelof Versteeg, Gail Heath, Clark Scott, Ken Wangerud and Dave PaulAcid mine site remediation is a significant problem in the U.S and globally. Due to the volume
of acid producing rock involved, the only practical solution is minimizing acid production by reducing
or eliminating water flow through the rock materials. One method to achieve this is utilizing a capping
system. Detailed monitoring information on cap and rock behavior allows for rapid and cost-effective
intervention in case of cap failure. A remotely controllable autonomous resistivity monitoring system
was integrated in the repository below the geo-membrane cap at the Gilt Edge Mine Superfund site. The
structure of this system allows users to have access to raw and processed data in real time.
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Integration Of Geophysics, Geologic Mapping And Water-Level Monitoring To Characterize The Hydrogeology Of A Fractured Bedrock Site In Berlin, New Hampshire
Authors James R. Degnan, Stewart F. Clark Jr. and Philip T. HarteElemental mercury is found in fractured depressions and potholes on the bedrock surface, in the
overburden, and is dissolved in ground water at the site of a former chlor-alkali plant (cell house) along
the bank of the Androscoggin River, in Berlin, N.H. The cell house has been demolished, ground-water
flow impeded by installation of an up-gradient-slurry wall, and capped with an impermeable geomembrane.
Mercury has been removed from fractures at the surface on the riverbank five times; however,
more continues to be found. Potential pathways for movement of mercury and ground water were indicated
with the results of a geohydrologic study. The study demonstrates the integration of geophysical
surveys, geologic mapping, and water-level monitoring in three areas: (1) the riverbank, (2) the site
perimeter, and (3) the capped area.
Results from ground-penetrating radar and two-dimensional-resistivity surveys along the riverbank
indicate electrically conductive zones that are interpreted as bedrock fractures, which are potential
ground-water-flow paths. Geologic mapping along the riverbank shows that bedrock fracturing is more
prevalent in gneiss than pegmatite and is associated with schist in shear zones that correspond to geophysical
anomalies. Nearly horizontal anomalies in ground-penetrating-radar survey results beneath
areas mapped as pegmatite may represent locations where vertical fractures in gneiss terminate on a horizontal
fractured contact between gneiss and pegmatite. Significant hydraulic connections were identified
by analysis of stage changes in the Androscoggin River and bedrock water levels. Assessment of hydraulic
heads in bedrock and overburden show vertical ground-water gradients in both directions. Resistivitysurvey
results along the site perimeter indicate fractures and overburden-filled bedrock troughs where
ground water may bypass a slurry wall. Overburden water levels and discharge from a drainage pipe suggest
that ground water is passing through or beneath the slurry wall. Response of overburden water levels
do not show connections with the river.
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Laboratory Determination Of Electric Properties Of Ornamental Stones In Georadar High Frequency Band
Authors Luigi Sambuelli, Paola Marini, Riccardo Tascone, Davide Vaccaneo and Francesca BrattaA new measurement system of dielectric permittivity and loss tangent of ornamental stones used
for example on historical buildings has been developed. Complex permittivity has been measured in the
frequency range 1.1 – 1.7 GHz on samples chosen between marbles, sandstones and limestones. The
values of dielectric parameters were measured experimentally by placing the sample in a resonant cavity
obtained from a waveguide. The research has been developed to define a laboratory testing method in
order to improve GPR interpretation by creating a data base of electromagnetic properties of the
analysed materials.
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Modeling Heterogeneity In Gpr Data
Authors Jennifer J. Holt and Jeffrey J. DanielsThe subsurface is rarely perfectly homogeneous due to different soil moisture levels, grain
packing, and soil types that all influence the ground properties. Ground Penetrating Radar (GPR)
is a common technique for investigating objects in the near surface. Physical properties play an
important role in GPR. Traditional geophysical models of GPR have not accounted for this
heterogeneity or its effect on spacial dispersion. This forward model incorporates heterogeneity
by replacing the traditional homogenous spatial regions with a distribution of physical properties.
The physical model values within each boundary were determined by a statistical distribution that
will more truly represent the physical properties of the earth than the traditional single value
approach. These statistical approximations to the physical properties are a better approximation
to the actual physical properties present that are beyond the resolution capabilities of the
instrumentation or the sampling procedures. This paper looks at heterogeneity, its influence on
spacial dispersion, and defining the response from a range of standard deviations.
Variations in soil properties should be taken into account when analyzing ground
properties while using GPR. This paper presented a theoretical analysis of random property
variations concentrating on a half space and a two layer earth model with a Ricker wavelet input.
At 9 ns and 12 ns, most of the visible dispersion in the electric field occurred in the near field.
However, the largest average difference occurred at 1.0 m distance from the dipole. Spacial
dispersion occurs when there is a standard deviation of 2.5% and a standard deviation of 25%
does not mask the response from a layer. The larger the area of the heterogeneity the more the
wave will reflect off that area.
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Application Of Ground Penetrating Radar To Assess Ground Control Problems In Two Underground Limestone Mines
Authors Michael A. Trevits, William D. Monaghan and Thomas P. MuchoIn this study we tested the ability of ground penetrating radar (GPR) to resolve ground conditions
in two underground limestone mines. The objective of our work was to determine if GPR signals could
be received from distant fractures in the limestone unit. At site A, located in western Pennsylvania, a
large fracture penetrated and crossed the mine workings and created mine roof problems. GPR was used
to evaluate the mine roof areas along the projection of the fracture. At site B, located in central
Pennsylvania, fracturing of the host limestone provided difficult water problems at the mine face. GPR
was used at this site to evaluate the conditions ahead of the mine face to determine if a significant jointbased
solution channel system existed that would signal a continuation of the water problems. We
conclude that at both sites, it was possible to utilize GPR to delineate potentially dangerous and
threatening ground conditions.
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Implementation Of Gps Navigation And 3D Volume Imaging Of Ground Penetrating Radar For Identification Of Subsurface Archaeology
The navigation of GPR equipment during surveys at archaeological sites has largely relied on the
time-consuming process of manually locating grid lines. When GPS has been available, positions are
generally only recorded at the ends of a GPR profile or at the corners of the survey grid. If the GPR
antenna deviates from individual grid lines during the field survey, or if the survey grid is inaccurately
established because of uneven terrain, targets of interest may be improperly located. In the summer and
fall of 2003, GPR data sets were recorded simultaneously with 1-second, real-time DGPS navigation at
several archaeological sites. The purpose of the GPR and DGPS integration is to automate the
collection of GPR data sets, particularly at sites where establishing grids would be problematic. In
addition, this integration allows for generation of accurate, geo-referenced time slice maps for
presentation or GIS purposes. Using the DGPS navigation at the archaeological sites, 3D volumes of
recorded energies were used to map subsurface archaeological structures. DGPS-navigated time slices
were compared with traditionally navigated time slices collected during an investigation at the Jena
Choctaw Tribal Cemetery in Louisiana. Results of this investigation indicate that DGPS navigation is
sufficient to map unmarked burials without sacrificing accuracy.
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Uncovering The Mysteries Of Gore Place: A Gpr Case History
Authors Ariane Heinz, Doria L. Kutrubes, Susanne M. Olson, Lana Lewis, Jeffrey Baker and John F. KickTheGore Place Estate, a historical landmark, was investigated using ground penetrating radar (GPR)
and total field magnetometry to identify any features of interest related to former ventilation, heating or
septic systems associated with the Revolutionary War era mansion.
GPR results from the north side of the building confirmed that a large buried structure is present
below the brick archways on the building north facade. Large reflectors indicating a collapse are also
observed in that area, and may correlate to the former building which burned in the 1790s.
On the south side of the building, time-depth slices reveal a linear feature, presumably a shallow air
duct, trending from the center of the building towards the southwest. A brick-lined air duct was discovered
at ground surface, approximately 300 feet southwest of the building, following the same trend as the linear
feature detected with GPR. The purpose of the air duct was presumably to create a powerful draw for the
heating and ventilation system.
Amagnetic anomaly in excess of 2,000 gammaswasobserved coincident with thepresumed location
of a Revolutionary War era cistern. However, since the magnitude of the anomaly suggests the presence of
steel, not just brick, this structure, first believed to be the original cistern, must represent a more modern
structure.
Two ducts were detected using time-depth slice imaging within the Great Hall floor. The more
contemporary metal duct shows up clearly on the time-depth images, and connects two air vents located
south of the east and west chimneys. The older air duct, located just south of the chimneys centerline,
appears partially collapsed on the GPR records.
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Computer Assisted Radar Tomography – True Value Or Just Pretty Pictures
Authors Jorgen Bergstrom, Scott Smith and Kathleen McKinleyComputer Assisted Radar Tomography (CART) is a new technology that can deliver images of
the subsurface with an unparalleled level of accuracy and detail. Based on the physics of Ground
Penetrating Radar (GPR), CART can image objects of any material including metallic and non-metallic
utilities, valves, drums, trenches, underground storage tanks, paved over manholes and railroad tracks.
The CART system is tied to a total station with auto tracking capabilities for precise positioning. The
benefit of CART is that high density, accurately positioned data can be collected in a fairly short amount
of time. State-of-the art processing software is then used to create time slices and 3-D images of the
subsurface. Customers that are used to looking at wiggly GPR lines are often awed by the clarity and
the life likeness of CART images. But where is the true value for the customer? What problems can we
solve with CART that we cannot with GPR or can we do the same job quicker and cheaper with CART?
This paper will highlight our company’s experience with GPR and CART on a variety of projects and
discuss the strengths and limitations of both methods.
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The Capillary Rising Of Ground Water Monitored By Soil Dielectric Coefficient
The automatic monitoring station was established to the forested catchment in Eastern Finland. The
ground water level was situated approximately 0.5 m below the lowest one of the three dielectric
coefficient probe. There were three dielectric coefficient probes (CS615; Campbell Sci, UK) at three
different depths (0.25 m, 0.6 m, 0.8 m). Data collecting was happened with CR10X datalogger
(Campbell Sci, UK). The ground water level was measured by PDCR1830 (Druck, UK) from the nearest
ground water pipe.
The main aim of this study was to investigate how the rising ground water table effects to the measured
soil dielectric coefficients and how transpiration and evapotranspiration are seen in measured dielectric
coefficient and ground water level.
The main result was that how well dielectric coefficient follows changes of ground water level. The
transpiration of trees had an effect both dielectric coefficient (i.e. soil moisture) and ground water level.
It looked like that transpiration ends at the beginning of September; because of the pumping effect of
capillary increase disappear. And the ground water level is stable after the beginning of October, which
means that evapotranspiration have been ended in that time.
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Fracture Characterization Using Borehole Radar: The Link Of Geophysical And Hydrogeological Model
By Lanbo LiuPrecise characterization of subsurface fractures (their orientation, aperture, distribution,
hydraulic conductivity, etc.) is critical to many geoscience sub-disciplines such as water resources
exploration and management, contamination remediation, underground construction, as well as
subsurface energy resource (hydrocarbon, geothermal, etc.) exploration and management. This paper
presents the forward modeling results of borehole radar signature of fractures generated by the
hydrogeological model of a fractured rock aquifer environment. A fracture system consists of interconnected,
permeable fractures filled with either freshwater, air, or brine and the isolated, nonpermeable
ones filled with only freshwater forms hydrogeological test model. The fracture groups were
statistically generated with different and desired features in space density, length, orientation and
aperture. Electromagnetic (EM) wave was generated with the finite-difference time-domain (FDTD)
forward modeling technique and propagated through the fractured rock aquifer models to form the
synthetic radar data sets. The features in radar syntheses were then examined and corresponded to
predefined fracture models. Based on the comparison, it shows that (1) the amplitude of radar waves
was generally diminished when brine replacing freshwater in the permeable fractures; (2) replacing
freshwater with air significantly increases the fracture fluid property contrast and results in significant
changes in some time records at certain transmitter-receiver configurations, depending on their relative
position to the permeable fractures; (3) in general, radar syntheses in reflection mode contains more
information on fracture properties than its transmission counterpart; (4) it is easier to identify more
fractures when air replacing water than brine replacing water. Combination of computer forward
simulation and field data reduction bears the hope to successfully characterize fractures for various
scientific and engineering purposes.
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Rpm – Residual Potential Mapping; A New Approach To Mise-A-Lamasse
Authors Christopher A. Baldyga and James B. FinkBetter methods are needed for the detection and mapping of low-contrast hydrogeophysical
targets. Several publications within the last two decades show merit in the application of the mise-a-lamasse
method to hydrologic problems such as fracture flow, plume detection, and plume migration.
This presentation suggests a modification to the conventional approach that will enhance low contrast
targets.
The mise-a-la-masse method is a simple application of electrical methods where a buried
conductive feature is electrically energized and the resulting distorted electric field on the ground
surface is mapped. Mise-a-la-masse has been in use for decades in the mining industry on massive
sulfide orebodies, but, the requirement that the orebody be both massive and electrically contiguous has
limited the method’s application.
The normal interpretation of mise-a-la-masse data depend on the ability to observe the desired Efield
distortions caused by the energized target. In the case of low physical property contrasts,
distortions can be very difficult to see, if at all. The primary field observed in the proximity of the
energizing electrode dominates the response. Unless the target is particularly conductive and-or rather
shallow, it will not produce an E-field distortion distinct from the primary field. The observed E-field
consists of the superposition of several electrical responses.
The observed E-field at the ground surface is a combination of all of the effects created by the
energized target and various heterogeneities, conductive or resistive, that influence the distribution of
the current flux. These various effects may be due to geometry, such as layering; lateral paths, such as
fractures; and localized high-contrast features, such as culture.
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Complex Inversion Of Surface-Nmr Signals - Extending The Limits Of Model Resolution
Authors Martina Braun, Marian Hertrich and Ugur YaramanciThe technique of Surface Nuclear Magnetic Resonance (SNMR, also known as MRS - Magnetic
Resonance Sounding) is used for direct groundwater determination and aquifer characterization. Among
other influences, the electrical conductivity of the subsurface leads to a complex-valued signal. However,
the standard interpretation scheme uses only the amplitude of the signal for determining the water content.
But real and imaginary parts of the signal are sensitive to different depth volumes. Generally, the imaginary
part is more sensitive to deep structures than the real part of the signal, i.e. in conductive media, signals
arising from deep layers have a significantly greater imaginary part than an equivalent signal from shallow
depths. For real data, physical effects additionally to the electromagnetic phase delay have to be considered
and adequately quantified to use the phase information for an enhanced data interpretation. This study
assesses the complex inversion using real and imaginary parts of the signal. Analyzes of synthetic and real
data with sufficient data quality show that the complex inversion is more reliable in terms of determining
deep structures, equivalence errors are reduced, and the depth resolution is increased.
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Inversions Of Surface-Nmr Signals Using Complex Kernels1
Authors Martina Braun and Ugur YaramanciThe SNMR (Surface Nuclear Magnetic Resonance, also called MRS - Magnetic Resonance Sounding)
method is used for direct groundwater exploration and improved aquifer characterization with measurements
on the surface. Since the electrical conductivity of the subsurface alters the SNMR amplitude
and especially the phase, the conductivity structure must be known before the inversion of the SNMR
amplitudes. This study demonstrates the effect on the water content determination if the electrical conductivity
is not considered. Disregarding the electrical conductivity results into significant wrong water
content distributions even at moderate resistivities of 100 m. The conductivity must be taken into account
down to an appropriate depth, also structures below the assumed penetration depth of 100 m can
effect the water content determination. Non considering conductive structures above or in the aquifer results
into an underestimation and downward shift of the inverted water bearing layer; conductive media
below the aquifer lead to an overestimation of the water content. For real data, both amplitude and phase
values should agree with modeled data. Analyzing the SNMR phase values of real data provides additional
information for estimating the reliability of the inversion result.
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Assessing Groundwater Perching Horizons Using Synthetic, Ground, And Airborne Tdem Data At The Pantex Plant, Texas
Authors Jeffrey G. Paine, S. Todd Harris and James M. PhelanAt the U.S. Department of Energy's Pantex Plant near Amarillo, Texas, recharging groundwater
encounters a perching fine-grained zone (FGZ) above the main Ogallala (High Plains) aquifer, a critical
agricultural, municipal, and industrial water supply. We conducted modeling and ground-based timedomain
electromagnetic induction (TDEM) measurements to examine whether TDEM might help assess
the integrity of the FGZ and its ability to retard the flow of groundwater to the main aquifer. Conductivity
models based on well logs and representative TDEM soundings demonstrated that changes in thickness
of the FGZ and perched aquifer are detectable if changes in other stratigraphic horizons are minimal.
Based on these results, we conducted an airborne geophysical survey using Fugro's GEOTEM system.
Conductivity-depth transforms (CDTs) from airborne measurements matched the nearest ground-based
profiles reasonably well. Pseudo-depth slices constructed from CDTs depicted apparent conductivity at
critical depths, enabling refinement of borehole-based stratigraphic and hydrologic models. Elevated apparent
conductivities were observed where interpreted FGZ integrity was good and the saturated zone is relatively
thick; low apparent conductivities are interpreted to indicate areas where the FGZ and associated saturated
zone are thin or absent. Survey results are being used to support groundwater investigations, development
of fate and transport models, and upcoming corrective action decisions.
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Developing Recharge Reduction Strategies In The Tintinara Area Of South Australia Using Resolve Frequency Domain Helicopter Electromagnetic Data
Authors Tim J. Munday, Ross C. Brodie, Andy A. Green, Steve Barnett, Fred W. Leaney and K.P. TanIn the Tintinara area, located south-east South Australia, airborne geophysics was recognized as
having potential to provide valuable biophysical data relevant to the management of irrigation
development and groundwater recharge reduction in the area. The groundwater of the area sustains
irrigation and other dryland agriculture. However the lifetime of this resource is limited by the leaching
of salt that has accumulated in the soil prior to land clearing and agricultural development. For some
areas, the groundwater may be saline and unusable for irrigation within ten to twenty years. The
presence or absence of a near surface clay unit can have an important influence on the rate and timing of
this deterioration by slowing recharge. Forward modelling suggested that a frequency domain helicopter
electromagnetic (HEM) system could map spatial variability associated with this unit. A survey was
conducted using the RESOLVE® HEM system and demonstrated that, through the use of a constrained
inversion approach, this unit could be mapped. This was confirmed with shallow drilling. We have
generated a product, namely clay thickness, which is now being used as an input into a hydrogeological
model to help predict recharge rates and influence management decisions in the area.
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Constrained Inversion Of Helicopter Aem Data For Managing Irrigation Salinity
Authors Andy Green, Ross Brodie and Tim MundayThe RESOLVE frequency domain HEM system has been used to map the distribution of near-surface
clay-rich sediments in and around the Riverland irrigation districts of South Australia.
Approximately 12,000 line-km was surveyed at line spacings of 150 or 300 m. The data were
recalibrated with measurements from down-hole induction logs and then inverted using a 1-D layeredearth
model. In order to improve the sensitivity to the unknown aspects of the section, the inversion was
constrained with as much local geological and hydrologeological information as possible. These
constraints included information about the depth of the water table, the conductivity of the groundwater,
the variability of the conductivity and thickness of three sedimentary units, and the geomorphic history
of the area.
The resulting detailed map of the distribution of the Blanchetown Clay is being used to model the
recharge behavior of the area, which in turn can be used to help predict the future course of salinity
inflows to the River Murray. If more areas are to be released for irrigation, the map could be used to
select areas of thicker clay that are preferred locations for such developments.
The results of the inversion also allow us to reconstruct the strandline-dominated paleo-topography left
when the sea retreated from the Murray Basin in the Early Pliocene. The survey also revealed a hitherto
unsuspected, deeper variability in conductivity following the Pliocene strand line pattern. The cause of
this pattern is not clear. It could be due to variation in the porosity of Loxton Sands or to strandlinecorrelated
variability in the elevation of the contact between the Bookpurnong Beds and the Lower
Loxton sands.
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Bundaberg Groundwater Investigation, Australia – A Case For The Benefits Of Extensive Use Of Geophysics In Groundwater Investigations
Authors Geoff Pettifer and Warwick WoodIn 1998/99 the Department of Natural Resources (DNR) in Bundaberg, Queensland,
Australia contracted Geo-Eng Australia (now GHD Pty Ltd), to undertake a major joint study of the
coastal groundwater system of the Bundaberg Irrigation Area (BIA) which was experiencing
problems with the unregulated use of much of the aquifer and seawater intrusion problems. The
Bundaberg Groundwater Project is arguably the largest integrated geophysical, drilling and
hydrogeological project for water resources assessment undertaken in Australia.
The Project was a pre-cursor for a proposed new BIA groundwater model. One primary
project objective was to acquire sufficient data on the extent and properties of the groundwater
system to redefine the conceptual hydrogeological model. Another primary objective was to
systematically apply integrated geophysical, geological and hydrogeological techniques and gather
permeability data, directly and empirically, for identification of permeability trends.
The project provides a case study, showing the value of a strong commitment to the largescale
use of routine and innovative geophysics throughout a major groundwater investigation.
Firstly, the project budget allowed use of ground resistivity (of 702 kms of traversing and
273 soundings), seismic reflection soundings and multi-parameter geophysical logging (270
new/existing holes) on a scale generally not contemplated in groundwater studies. The extensive
geophysics guided a major drilling program of 130 new holes including 106 new piezometers
optimised in position and depth.
Secondly, it showed the value for groundwater management decision-making of an integrated
analysis of disparate datasets (airborne and ground geophysics, hydrogeological, topographic,
hydrochemistry and geophysical logs).
Thirdly the application of sequence stratigraphic analysis techniques, to geophysical log data
defined a new conceptual hydrogeological model and understanding of the hydrogeological context
and information value of each existing and new piezometer.
Finally, the geophysical logs assisted by the surface geophysics, proved useful in providing
an assessment of permeability trends for groundwater model building.
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Geophysical Methods Applied To Saltwater Intrusion In Antigua
Authors Stewart K. Sandberg and Hastin BarnesThe island of Antigua has been suffering from an acute shortage of potable water due largely to
drought conditions on the island. Because of the persistent drought conditions one of the island's
primary sources of potable water, the Potworks Dam, is dry. In addition to the Potworks Dam, the
nearby smaller Collins Dam is also dry. In addition to these dry surface impoundments, the problem is
further complicated by the fact that the reduced recharge has resulted in a lowering of the watertable in
the nearby Collins abstraction region. As a consequence, salinity levels in abstraction wells at Collins
have increased. In extreme cases, the watertable has declined below the depth of the abstraction pump.
A geophysical survey was conceived to generate information related to the hydrogeologic
framework of the area, while taking advantage of the simplified logistics resulting from the dry
conditions of Potworks reservoir. During the period from 14 April to 21 April, 2003, geophysical data
were acquired in the dry bed of the reservoir, and at two locations east toward the coastline.
Geophysical methods included EM-31, Schlumberger array resistivity soundings, and TEM central-loop
soundings.
Geophysical results show lateral variation in subsurface resistivity related to both lithologic
variation and groundwater salinity. Shallow resistivity variation, mapped with the EM-31 system, is
indicative of a channel system within the bed of the Potworks reservoir. Variation in resistivity mapped
using the TEM and resistivity soundings likely indicates structure of the Karst aquifer, which has
variable resistivity due to porosity/salinity variation.
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Seismic Anisotropy In The Edwards Formation: Government Canyon State Natural Area
More LessHigh resolution seismic data are acquired from the Edwards limestone formation in an area of
outcrop within the Government Canyon State Natural Area, to infer the local orientation of vertical
fracturing. The experiment consists of a single 3D seismic array of 16 3C recording stations. Seismic
sources are deployed around and within the array at short spacings resulting in 16 3C source gathers
(by reciprocity) with thousands of traces. A velocity-variation-with-azimuth trend is discernible in
the data attributable to azimuthal anisotropy due to vertical fracturing. A slow direction along
120 degrees from North is found, with a fast direction along 20 degrees from North. If vertical
fracturing and seismic anisotropy are correlated at this site, a fracture orientation along 20 degrees
from North is determined.
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Practical Application Of Geophysical Mapping For Wellfield Exploration - Two Indiana Case Studies
Authors Gregory B. Byer and John VanderlaanMany communities in the State of Indiana rely on the availability of groundwater to sustain and
support population growth and new development. Although Indiana generally experiences plentiful
precipitation throughout the year, many communities were founded in localities where potential
groundwater production is limited by geologic factors. The northern two thirds of Indiana is covered by
glacial drift, which is often dominated by glacial till, a material that is generally unsuitable for
community water supply purposes due to both poor water quality and potential yield. At locations that
are both sited on glacial till and are not located near a significant source of surface water, the only other
alternative source of groundwater is fractured bedrock. And in fact many locations are able to utilize
fractured carbonate or sandstone aquifers.
However, some communities have no significant source of surface water and are underlain by
drift dominated by glacial till, which rests upon non-aquifer bedrock such as shale or siltstone. Few
good options remain in such a case, and some communities must import water from another location.
However, some of these communities do have isolated, coarse-grained water laid glacial outwash
deposits available to them, and due to the complexities of the glacial depositional environment, the
occurrences of these sand and gravel deposits are difficult to ascertain, and test drilling to find them
using a "hunt and peck" method can become cost prohibitive. In such cases geophysics can fill an
information gap. Two case histories in Indiana are presented here where terrain conductivity and
2-dimensional resistivity have been used to tackle this difficult problem in cooperation with both
municipal engineers and drilling contractors. Both examples illustrate the effectiveness and resulting
broad understanding and acceptance of these methods, and demonstrate the potential for the use of
geophysics to become the norm in wellfield exploration in these types of situations.
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Bedrock Water Supply Exploration Using Very Low Frequency Geophysics
Authors Christopher L. Covel and Darryn T. Kaymen-CovelVery Low Frequency (VLF) geophysics has consistently proven to be a successful method for
groundwater supply exploration in locating bedrock wells. The use of geophysics in solving difficult
and evolving water supply demands allows for the successful use of this technology to ever broadening
markets as restrictions and new requirements on water supply withdrawals increase. VLF geophysics is
a proven scientific technology used to locate the highest yielding bedrock water wells at a site by
identifying specific water bearing fractures before the actual drilling is performed. In this case study
VLF geophysics was applied at a site in central New Hampshire to locate a high yielding water supply
well for a golf course. For a proper VLF investigation to be performed a VLF transmitter must be
located approximately on strike or trend to the particular fractures or faults that are to be studied.
Knowing the bedrock fracture pattern is important, because the geophysical line must be laid out more
or less perpendicular to the VLF transmitter selected. This is critical for the collection of meaningful
data. The central New Hampshire site bedrock consisted of crystalline granite and metamorphic
bedrock which locally is known to produce low yielding wells. The investigation consisted of existing
data review, fracture trace/lineament analysis, bedrock mapping, line layout, collection of VLF data and
data interpretation. This bedrock well yielded 80+ gallons per minute (gpm). Alternatively, for the site
to withdraw 80 gpm from a local surface water source extensive permitting, construction and an
unpredictable amount of time would have been required. This example documents how VLF geophysics
is an accurate and cost effective solution to ever increasing water supply problems faced on the earth.
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An Overview Of The Inyo County’S 2003 Death Valley California Area Geophysical Program
Authors John R. Jansen, Michael J. King, Joy Loughry, Ted Powell and Doug LaymonThe relationship between carbonate waters from the Texas, Travertine, and Nevares springs in
Death Valley (within the Southern Funeral Mountain Range) and the groundwater flowing under Yucca
Mountain has yet to be conclusively demonstrated. Currently there is only one accessible monitoring
well that has penetrated the Lower Carbonate Aquifer near Yucca Mountain. There is only one
accessible well that penetrates the Lower Carbonate Aquifer down-gradient of Yucca Mountain.
The U.S. Department of Energy has awarded Inyo County grant funds for a geophysical and
drilling program to evaluate the connection between the Lower Carbonate Aquifer (LCA) in the
Amargosa Valley and the Southern Funeral Mountain Range. The program consists of a series of
geophysical surveys to characterize the geological structure of the LCA in the Southern Funeral
Mountain range, and the drilling of five monitoring wells into the LCA.
In FY2002 and FY2003, a total of 59 miles of gravity data were collected in the Armagosa
Valley near Bat Mountain in the Southern Funeral Mountains. The interpreted LCA surface shows a
complex topography with steep dips and several probable faults. The data was used to select drilling
locations for four monitoring wells to be drilled at depths of 1,000 to 4,000 feet.
Approximately 9 miles of continuous magnetic data and 8 TEM soundings were collected in the
Scotty’s Junction area of Sarcobatus Flats to map the Sarcobatus Fault as part of a water resources
investigation being conducted by the USGS on behalf of the National Park Service. Previous mapping
had indicated several possible locations of the fault. The magnetic data indicated the presence of a fault
system of at least three faults. The TEM soundings indicated that the faults were steeply dipping normal
faults.
This work is a continuation of surveys we conducted in previous years. The previous surveys
included TEM soundings at the Travertine, Texas, Nevares, and Grapevine Springs to determine the
hydrogeologic controls influencing the location of these springs. Future geophysical efforts will
concentrate on providing additional subsurface control to help quantify the groundwater discharge to the
saltpan of Death Valley.
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Groundwater Research Within The Estancia Basin, New Mexico
More LessGroundwater shortage is a serious issue within the Western United States. Controversies arise
when long-standing farmers and ranchers dispute with new residents moving in from suburban areas
concerning water rights. Vern Wood, resident and former member of the Edgewood Soil and Water
Conservation District brought his community’s concern to the Colorado School of Mines. Wood lives in
the Estancia Basin of New Mexico and identified three critical issues facing his community: the
characterization of the Estancia water aquifers, the quantification of the aquifers’ water volume, and the
recharge areas for the aquifers.
Mr. Wood prompted the 2003 Colorado School of Mines Field Camp to take place in Edgewood,
New Mexico in an effort to begin collecting data on the Estancia Basin. The intricacies of the
groundwater situation lent themselves well to a collaboration between ranchers, students, faculty, and
industry. Companies such as: Veritas, Sercel, Geonics, Newmont, and Zonge donated geophysical
equipment, giving Mines students and faculty the opportunity to work alongside local USGS experts,
professors, water groups, and residents using a wide array of geophysical methods. The geophysical
techniques employed to study the fracture system of the aquifers, included: surveying, deep seismic
reflection and refraction, well-logging, numerous DC resistivity methods, gravity, electromagnetic
induction (both time and frequency domain), VLFR, and shallow seismic reflection. The results of the
study included large amounts of data, and the opportunity to go back for further investigation.
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A Subway Project In Lausanne, Switzerland, As An Urban Microgravimetry Test Site: Acquisition, Correction Of Buildings Influence And Modeling
Authors Pier Vittorio Radogna, Raymond Olivier and Philippe LogeanA new subway will be constructed within the next decade in Lausanne. The geology involved
constitutes alpine molassic bedrock and an overlaying quaternary glacial fill. The choice of the subway
corridor (6 km) had to consider the exact thickness of these geological units. The availability of
mechanical logging data offered the opportunity for testing a microgravimetry survey. The distance from
nearby constructions determined whether corrections had to be made for these volumes or could be
omitted. We calculated, with an in house program, the effect of different buildings to choose
architectural styles with similar gravimetric responses. We are using then a geographic information
system (GIS) to group these buildings by typology based on cadastral records and correct all the
buildings with simplified architectural styles. The voids of the basements were included in the digital
elevation model to take account of the complexity of the Lausanne morphology. All these corrections
could be calculated before the acquisition in order to chose the best gravity stations location. The
residual gravity map is adjusted to only some drillings, in order to regionalize this punctual data and to
compare the results of the bedrock modeling with the drillings not taken into account.
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Locating Pipelines With A Broadband Electromagnetic Induction Array System
Authors Ralf Birken, Thorkild Hansen, Ross Deming and Michael OristaglioAn electromagnetic induction system for locating buried pipelines is being developed in
collaboration with utility companies under the United States Department of Transportation, Research
and Special Programs Administration’s Pipeline Safety Research and Development Program1. The
components of the system are (1) an array of broadband vector magnetic field (induction) sensors,
(2) transmitters at various (discrete) frequencies, (3) a laser positioning system, and (4) inversion
algorithms.
The system is designed to locate buried pipelines by creating a digital map of the vector
magnetic field generated by currents flowing along the pipelines (and in the surrounding soil). The
currents can be set up either by injecting current directly onto individual pipelines (where accessible)
with galvanic or toroidal current sources or by inducing currents remotely with a surface source. When
injecting currents directly to track several pipelines, each “clamp-on” source can inject current at a
different frequency within the spectral range of the broadband sensors (about 1 kHz to 50 kHz). In
principle, this allows tracking of individual pipelines by decomposing the recorded magnetic-field time
series into its frequency components. An inversion algorithm models the magnetic field with a system of
current filaments flowing along a network of underground pipelines. Current flowing along each
pipeline is represented by one or more (straight) line filaments, which can intersect with other lines; the
amount of current along the filament is allowed to vary linearly between its endpoints (nodes) to
simulate current leaking into the soil. Conservation of current is enforced at junctions between line
segments representing a pipeline (or at junctions between pipelines). The algorithm iteratively
determines the three-dimensional (3D) location of each current filament and the current at its nodes by
minimizing a cost function.
The system uses a self-tracking laser theodolite to monitor the position of the sensor array at
regular intervals during operations. The array can move along arbitrary paths (for example, in traffic) to
cover the area to be surveyed; special algorithms merge the data from different paths to create the
complete digital map of the surface magnetic field. Even without further processing, the digital map
itself shows useful information about the locations and shapes of underground features.
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Seismic Imaging To Accurately Characterize Subsurface Ground Conditions
More LessUnforeseen, variable subsurface ground conditions present serious challenges to the heavy
construction and civil engineering industry to design, construct, and maintain infrastructure.
Detailed, accurate knowledge of ground conditions reduces project risk, improves construction
performance and safety, prolongs structure life, and prevents waste in over-design. All forms of
major construction projects are impacted; including tunneling and microtunneling (transportation and
utility), foundations and structures (buildings, piers, runways, retaining walls), bridges and highways
(abutments, roadcuts, slopes), and dams and impoundments. Presently, site characterization and
geotechnical engineering, supporting these activities, are limited by the inability to adequately
describe these subsurface ground conditions.
NSA Geotechnical Services has successfully applied seismic tomography and holography
ground imaging technologies on tunneling and heavy civil construction projects worldwide. Seismic
signal waveforms traveling through a complex medium consist of various arrivals from refractions,
reflections, scattering, and dispersion. Tomography and holography are proven inversion
technologies for estimating location and extent of material property variations causing changes in
signal waveforms.
The basic principle behind RockVision3D™ is that seismic energy travels through different
material types with different attenuation rates and velocities. That is, seismic waves travel more
quickly, with less attenuation, in strong, competent material. Seismic waves travel more slowly,
with more attenuation, in weaker materials (e.g., voids, broken or weathered rock, soil).
The basic principle of TRT™ is that a portion of the seismic energy traveling through the
earth is reflected when it encounters an interface between ground zones possessing different seismic
properties. Most geologic structures, anomalies, and changes in lithology provide detectable seismic
reflections if they are within a reasonable distance of the seismic source.
This paper will present various applications of these technologies, illustrating how seismic
imaging can provide accurate information regarding ground conditions. With this information,
engineers can complete projects safely, within time and budget constraints.
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Data Collection, Processing And Analysis Challenges—Gpr Bridge Deck Deterioration Assessment Of Two Unique Bridge Deck Systems
Authors Francisco A. Romero and Roger L. RobertsBridge deck deterioration mapping using the top rebar reflection amplitude as a measure of
deterioration is a useful tool for rapid, non-invasive bridge deck condition assessment. Currently, the
technique is applied using either a dual-polarization horn antenna setup or a ground-coupled antenna.
Isolating the top rebar reflection in a bridge deck requires considerable planning and knowledge of the
bridge deck structure.
This paper presents the data collection, processing and analysis issues associated with the
deterioration assessment of two unique bridge deck systems located in Des Moines, Iowa. Some
considerations weighed during the selection of this GPR methodology will be discussed, with
comparisons made to other data collection/processing alternatives. Slight modification to the typical
analysis methodology was made to accommodate (a) a thick overlay (often greater than 4”) and (b) nonuniformity
of the reinforcement layout. On both decks, variability in reinforcement layout was a critical
analysis consideration.
Observations made during the analysis process suggest modification to a dual-polarization analysis
approach needs to be considered in special cases, particularly when both (a) longitudinal bars are tied on
top of transverse bars AND (b) longitudinal bar spacing is either fairly large (12” or greater) or very
small (less than 4” between bars). Other considerations will also be discussed.
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Application Of A Combined Nondestructive Evaluation Approach To Detecting Subgrade Voids Below A Dam Spillway
Authors David A. Hollema and Larry D. OlsonThe combination of Ground Penetrating Radar (GPR) and Slab Impulse Response (Slab IR)
nondestructive evaluation (NDE) methods can be used to improve detection of subgrade voids beneath
reinforced concrete slabs. Subgrade voids are typically created by the eroding action of flowing water
because of an elevation or otherwise caused pressure gradient. Voids promote cracking and potential for
major long-term damage resulting in expensive repairs or replacement. These methods were recently
utilized at an alpine dam spillway for detection of potential subgrade voids.
3-Dimensional (3-D) GPR data were analyzed in a “bright spot” fashion by looking for zones
where the slab bottom reflection was abnormally strong. The cause of this data signature was attributed
to a strong contrast in dielectric between that of wet concrete and that of air or water-filled voids. Slab
IR is a model vibration test method and measures the amplitude and frequency of the slab vibration
when impacted with an instrumented hammer. Slab areas overlying voids respond with higher
amplitudes and lower stiffnesses when impacted. The 3-D GPR and contoured Slab IR results correlated
well and the same anomalous areas were discovered in each data set. Coring and video borescope were
used for confirmation of NDE delineated voids and proved the success of the methods.
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Leonardo Da Vinci’S Channel System Of Milan: Preliminary Tests On The Side Walls For The Restoration Design Project
Authors P. Ronca, Giovanni Cascante, P. Crespi and G. FranchiThe network of channels called “Navigli” was mainly built in the surrounding country and
downtown Milan during the XVI century, according to the hydraulic and engineering designs made
by Leonardo da Vinci. Many of the main streets in downtown Milan lie nowadays on these
preexisting urban channels, some of them were covered during the first half of the XX century. The
current civic administration is facing the problem of saving what remains of these complex hydraulic
and historic structures.
This paper, after a short presentation and description of the Navigli channels, describes the
preliminary in-situ tests, as well as the calibration procedure for non-destructive sonic tests
performed in order to understand the actual hidden geometry and the material condition of the
remaining of this ancient masonry wall.
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Seismic Investigation Of A Sinkhole On Clearwater Dam
Authors Richard D. Miller, Julian Ivanov, Steve Hartung and Lisa BlockA 10 ft wide and 10 ft deep sinkhole that catastrophically formed approximately 120 ft upstream
of the crest of Clearwater Dam in southeastern Missouri was the target of a high-resolution seismic
imaging program including reflection, surface wave analysis, and crosshole tomography. The primary
goals were to determine the general subsidence geometry and integrity of the core and help ascertain the
involvement of bedrock and native alluvium beneath this earthen dam. Reflection data from this survey
possess excellent frequency content (dominant >150 Hz) and provide high-resolution images of layers
within the pervious shell. Using tightly spaced surface wave profiles, an elongated low shear-wave
velocity chimney-like feature was delineated and interpreted to represent the root of the sinkhole. Based
on seismic, construction, drill, and borehole tracer data, a borehole geophysics program was designed to
identify fractures/joints that might provide seepage pathways. Crosshole seismic data detected a large
low-velocity zone within the bedrock and an associated low-velocity zone within the pervious fill
consistent with the surface seismic interpretations. A comprehensive appraisal of the risk this disturbed
zone represents to the overall integrity of the dam and whether it is a symptom of a larger, yet
undetermined subsurface leaching problem is being developed.
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