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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 - 50 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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