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11th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 22 Mar 1998 - 26 Mar 1998
- Location: Chicago, Illinois, USA
- Published: 22 March 1998
21 - 40 of 111 results
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Geophysical Surveys For Mapping Brine Contamination Resulting From Oil And Gas Production
More LessWith the production of oil and gas, brines with high concentration of dissolved solids (TDS) are
also brought to the surface. In processing plants, the hydrocarbon and water are separated. In
modern disposal practices, the brines are injected in deep formations. Occurrences of brine
contamination are mainly the result of disposal practices from the early days of production. The
lateral and vertical extent of brine contamination can often be inferred from measurements of the
geoelectric section. Frequency and time domain electromagnetic methods have proven good
tools for determining the geoelectric section, and three case histories will illustrate the use of
these methods. In two case histories, the brine contamination resulted from disposal in unlined
surface ponds. In one case history, an improperly abandoned well is likely cause of
contamination.
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Use Of Terrain Electromagnetic Geophysical Methods To Map Saline-Water Contamination, East Poplar Oil Field, Northeastern Montana
Authors Joanna N. Thamke, Steven D. Craigg and Thomas M. MendesQuaternary deposits, comprised of the Poplar River alluvium and glacial deposits, are the sole
developed source of ground water for residents in and near the East Poplar oil field. The extent of
saline-water contamination in Quaternary deposits in and near the East Poplar oil field may be as
much as 12.4 square miles. The probable source of saline-water contamination in the Quaternary
deposits is brine that is a byproduct of the production of crude oil in the East Poplar oil field study area.
Terrain electromagnetic apparent conductivity data collected in an area of about 21.6 square
miles correlate well with ground-water quality. These data were collected and interpreted in conjunction
with water-quality data from existing water wells to delineate possible saline-water contamination
plumes. Monitoring wells were subsequently drilled in some areas that lacked existing
water wells to confirm most of the delineated saline-water plumes. Analysis of ground-water samples
from both existing and newly drilled monitoring wells confirms the presence of 7.3 square
miles of contamination, as much as 2.0 square miles of which are considerably contaminated. Terrain
electromagnetic apparent conductivity data in areas with no wells delineate an additional 5.1
square miles of possible contamination, 3.2 square miles of which might be considerably contaminated.
Brine-injection wells, oil wells, pipelines, and storage-tank facilities appear to be probable
sources of the saline-water contamination in many of the plumes.
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Brine In The Near-Surface Environment: Determining Salinization Extent, Identifying Sources, And Estimating Chloride Mass Using Surface, Borehole, And Airborne Em
Authors J.G. Paine, A.R. Dutton, S.D. Hovorka, M.U. Bltim, M.P. Mahoney and E.J. SullivanElectromagnetic (EM) methods can be used to locate salinized soil and water, identify likely
salinity sources, and estimate the total chloride mass in the saturated and unsaturated zone. Groundbased
EM measurements can be used to establish boundaries of the salinized area and determine the
range of electrical conductivity, borehole measurements and time-domain EM soundings can determine
the vertical extent of salinization and establish the relationship between ground conductivity
and chloride content, and airborne measurements can establish the lateral extent of salinization and
locate potential salinity sources. Total chloride mass in a salt-water plume can be estimated from
airborne EM data and the empirical chloride-conductivity relationship.
EM methods employed in geophysical studies of near-surface salinization owe their success
to the increase in electrical conductivity that occurs where saline water infiltrates saturated or unsaturated
geologic materials. EM data can also be combined with information on soil type, moisture
content, and water chemical composition to help identify geophysical signatures that distinguish
important causes of salinization such as natural saline seeps and springs, oil-field sources such as
brine-disposal pits and leaking oil or gas wells, and agricultural activities.
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Stochastic Inversion Of 3D Ert Data
Authors Xianj in Yang and Doug J. LaBrecqueA new stochastic inversion algorithm to invert three-dimensional (3D) electrical resistivity
tomography (ERT) data has been implemented. The statistical information about the correlation
among the model parameters and the correlation among observed data was employed to stabilize
the ill-posed 3D ERT inverse problem. The data noise covariance matrix was diagonal based on
the assumption of uncorrelated data noises. The model parameter covariance matrix, however,
could be a full matrix depending on the correlation length between the model parameters. The
resulting unsymmetric linear system was solved by bi-conjugate gradient (BICG) methods, such
as BICGSTAB, a stabilized variant of BICG algorithm, and TFQMR, a transpose-free quasiminimal
residual algorithm.
An advantage of this algorithm is that any prior knowledge about the model parameters
can be easily incorporated in the inversion process in the form of covariance model type and
correlation length. This is the basis for our future implementation of a joint hydrologicalgeophysical
inversion. This stochastic inverse technique will be used for characterizing,
monitoring, and predicting fluid movement in heterogeneous vadose zone.
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3-D Characterization Of An Alluvial Aquifer System: A Case Study Using Borehole Data And Indicator Geostatistics
More LessThe three-dimensional characterization of a complex, alluvial aquifer system in the
West Alberta Plains was made possible by using indicator geostatistics to interpolate
between borehole log interpretations. Gamma-ray logs, induction logs, and lithology
determined from cuttings were used to assign indicators (categories) of sandstone and till
aquifers, and mudstone/ siltstone aquitards. The indicators in ninety well columns were
then used to compute variograms and create a 3-D, anisotropic variogram model. The
variogram model and the vertical proportions of sandstone and non-sandstone were used to
constrain the indicator simulation of the sandstone and non-sandstone indicators. Then,
using sequential gaussian simulation, the thickness of the till was simulated and added to
the sandstone and non-sandstone models. The resulting 3-D geologic models will be used
for groundwater flow and chemical transport modeling.
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Improved Detection Performance Using A Bayesian Decisiontheoretic Approach
Authors Leslie Collins, Dean Keiswette, Lawrence Carin and I.J. WonThe fundamental goal of target identification using geophysical methods is to achieve a
high detection rate along with a low false alarm rate. While many electromagnetic (EM)
and magnetic detectors achieve the first of these goals, it is often at the cost of a
prohibitively high false alarm rate. In this paper, we present a Bayesian decisiontheoretic
approach to target identification using EM data. This approach provides both an
improved detection scheme and performance evaluation in the form of ROC curves
plotting probability of detection versus false alarm rate. In addition to detailing the
Bayesian-based approach, we present selected case studies that utilize broadband
electromagnetic data acquired with the GEM-3 sensor. We compare the survey results
obtained with standard thresholding analyses to survey results obtained using statistically
based signal detection theory. Our preliminary results indicate that the detector derived
using signal detection theory is superior to the standard detection schemes that utilize
contour plots and thresholding. The results also indicate that detection performance is
dramatically improved when multi-frequency data is utilized. Furthermore, since
detection performance is observed to be a function of frequency, careful selection of the
EM frequencies at which data is recorded may result in further improvements.
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Optimal 3-D Geophysical Tomography
Authors Margaret J. Eppstein and David E. DoughertyAcoustic and electromagnetic tomographic methods attempt to provide accurate and
highly resolved estimates of spatially varying parameters. High resolution is obtained by
discretizing the domain into a large number of parameters to be estimated. Because the
resulting problem size is large, most implementations rely on iterative methods that attempt
to minimize the output least-squares criterion through the repetitive application of relatively
simple parameter updates. The accuracy and efficiency of such methods depends on the
quality of the initial estimates and the parameterization employed, as well as on the update
mechanism. Conversely, optimal filtering methods enable the computation of non-iterative,
minimum-variance updates and can be used to yield estimates of both parameter values and
covariances. Despite the statistical superiority of optimal methods, they have seldom been
exploited in geophysical applications due to their computational demands for large systems.
We have devised an approximate extended Kalman filter, which is a recursive, Bayesian,
minimum variance estimator for nonlinear dynamic systems. The inverse of an a priori
estimate of the parameter covariance matrix is used to damp the system and the weighting
matrix includes the inverse of the measurement error covariance matrix. While the recursive
nature of the filter is designed to handle time-series data, it can also be exploited to assimilate
batch data iteratively and/or recursively in smaller batches.
We have built efficient approximations into the filter that, in conjunction with our
domain-decomposition strategy and dynamic parameterization scheme, enable application
of the method to very large domains. The integrated method simultaneously estimates
the number, geometry, value, and covariance of spatially distributed parameters. Threedimensional
tomographic results are presented.
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A Geostatistical Analysis Of Gold Mineralisation In Oakley’S Reef, Hutti Gold Mines, Karnataka, India
By D.D. SarmaA geostatistical analysis of gold mineralisation process. characterised by discrete regular
samples drawn in respect of Oakley’s reef of Hutti gold fields and based on a segment of the
lode comprising level 10 (305 m in depth) to level 20 (620 m in depth) is presented. As the
stationary phenomena was observed to hold good for each level (local stationarity) but not for
the segment of the reef as a whole (global stationarity), geostatistical modeling was carried out
by processing each level data separately. In addition, the data of two vertical profiles were also
analysed geostatistically for a study of depth-wise variation and possible continuity of
mineralisation etc.
Variographic analysis revealed that the experimental variograms for each of the levels and
two vertical profiles could be represented by spherical model. However, the values for the
parameters C, (nugget effect), C (Sill) and a (range) of the model varied significantly from level
to level. High values were observed for the 16th level which is at a depth of 5 10 m. Using the
model parameters for each of these levels, kriging for 324 blocks of ore, each of size 30m x
width between one level and another, was carried out. A sample set of kriged estimates
together with kriged standard errors is presented. On the basis of variographic analysis it has
been inferred that the sample size can be reduced to half the present size without loss of
accuracy in the estimates for grade. This would result in substantial savings to the industry.
In order to quantify the chances of continuity of the mineralisation beyond the known
workings, Maximum Entropy Method (MEM) of spectral analysis and Markovian models were
found to be highly rewarding. MEM spectrum analysis revealed significant spectral spikes in
some of the deeper levels indicating periodicities in mineralisation ranging from
approximately 40 td 100 m in distance,, , and at approximately 50 m along the vertical profiles. In
respect of block data the estimated periodicity is from 130 to 230m along the strike and 100 to
300 m along the vertical profiles. Since the discrete gold assay values followed a Markovian
sequence, Markovian model analysis was carried out to quantify the extent(s) upto which
the present mineralisation pattern is likely to persist in the immediate unexplored area under
the assumption that the same geological conditions hold good in this area also. The likely
extents of gold mineralisation together with the respective probabilities of occurrence of grade >
2 .5 gms and > 3gms are presented.
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The Relevance Of Seismic Reflection Polarity To Dredging Performance - A Case Study
More LessIt is common knowledge that a discontinuous increase in seismic impedance produces a
reflection of positive polarity and a discontinuous decrease produces a reflection of negative
polarity. That knowledge seldom is applied in engineering contexts, however, because the
polarity of seismic reflections is not always obvious. That is particularly true in the case of
single-channel marine data when signal amplitude is displayed on paper as shades of grey. This
contribution documents a case in which reflection polarity was critical not only to the
interpretation of the seismic data but also to the client’s profit margin.
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High-Frequency Acoustic Imaging Of L Lake, Savannah River Site, South Carolina
Authors Keith J. Sjostrom and Rodney L. LeistA side scan sonar and seismic reflection study of L Lake, Savannah River Site, South
Carolina, was performed in June 1996. The geophysical investigation was conducted to
determine the location, distribution, and depth of existing burial pits and mounds within the
reservoir for incorporation into an Environmental Impact Statement. The results are also
intended to supplement previous scientific information obtained from soil samples, aerial
photography, and radiometric studies. Interpretation of the sonar data revealed numerous
mounds along the reservoir bottom that appear to have been constructed by pushing nearby
material into a heap to cover either the contaminated vegetative material, its ashes, or
contaminated sediments. The mounds do not cover any burial trenches or pits although some
small depressions are detected underneath the mounded material.
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Land-Based High-Resolution Seismic Reflection Image Of A Karst Sinkhole And Solution Pipe On Fort George Island, Duval County, Northeastern Florida
Monitoring of the drinking-water wells that tap the upper Floridan aquifer, indicate
increases in chloride concentration at some wells while at other nearby wells chloride
concentration are unchanged. One explanation for this is that geologic features (fracture zones,
joints, solution channels, and paleosinkholes) in the underlying carbonate strata of the Floridan
aquifer system have breached the semi-confining units, thus allowing warmer and more saline
water to flow upward and mix with fresh water production aquifers. A reconnaissance seismic
reflection survey was conducted at Fort George Island, Duval County, Florida, to determine if a
modified Mini-Sosie high-resolution seismic reflection technique, which has been successfully
used to image near-surface faults in urban areas, could be used to image karst hydrogeologic
features in this area.
We acquired good quality data in this survey within a depth range of 30-400 m. The
interpreted profiles of two perpendicular lines provide a clear image of geologic-karst
deformation in the form of a solution pipe and overlying buried sinkhole feature.
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Relating Cone Penetrometer Test Information To Geophysical Data: A Case Study
Authors Anthony L. Endres and William P. ClementAn analysis of data from a recent experiment at Dover Air Force Base (AFB)
has revealed a relationship between soil types determined from the mechanical
properties measured by cone penetrometer tests (CPT) and the electrical properties that
influence geophysical methods. This correlation connects two distinctly different types
of physical properties and provides a petrophysical basis for combining information
obtained from CPT and geophysical techniques governed by electrical properties. We
observed this relationship through the use of semi-logarithmic crossplots of dielectric
permittivity versus electrical resistivity where it was found that CPT soil types cluster in
a systematic manner to form a linear trend from clay-prone to sand-prone lithologies.
We obtained improved segregation of soil types when other factors, such as location
relative to the water table and stratigraphy, were used to refine the analyses of these
data. In addition, our results indicate that the ratio of permittivity to the logarithm of
resistivity is a good geophysical discriminator of the engineering soil classification.
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Comparison Of Sonic Log Data For 4 Types Of Acoustic Tools
Authors Tomio Inazaki, Toshiyuki Kurahashi and Shiro WatanabeFour types of sonic log tools were tested in the same borehole drilled in a hard formation. One is the
suspension type P-S logging tool with a dipole source and two receivers. Second one is a conventional full
wave sonic tool with two monopole transmitters and three receivers. The third is a newly developed full
wave digital sonic tool with two monopole sources and two receivers, and the fourth is an array sonic tool
with two transmitters and twelve receivers. The former two tools transmit analog signals through the
cable and convert the data digitally in the surface equipment, whereas the latter two transmit digital data
converted using 12 bit A/D boards incorporated in the probe to the surface unit. All tools are available in
the slim hole with diameter from 66mm to 120mm. The result of field measurement showed the obtained
Vp profiles coincided well with each other, and careful discrimination of waveform taking account the
tool characteristics is important for the precise analysis. Obvious attenuation of the Stoneley wave was
observed at fracture zone recognized with a borehole video image tool.
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Geophysical Well Logging And Discrete Depth Water Sampling Methods To Identify Sources Of Elevated Barium In A Water Well In Northern Illinois
By John JansenA geophysical logging study was conducted on a municipal water well in the City of
Sycamore, Illinois. The purpose of the study was to identify the source of elevated barium
levels in the well and determine if the well could be reconstructed to reduce barium
concentrations without significant loss in production. The geophysical logging suite
included a downhole televising log, four arm caliper log, gamma ray log, dual induction
log, gamma density log, and neutron density log. In addition, a spinner flow meter log
was conducted while pumping and water samples were collected from the pumping water
column at discrete depths. The results of the logging study indicated that the majority of
the barium was entering the borehole from the lower portion of the well which appeared
to be producing only about 15 to 30% of the total water production. The lower portion of
the well was sealed off with a neat cement grout plug. Barium concentration was reduced
by over 50 % with a reduction in specific capacity of about 30 to 40%. While the logging
study was successful at identifying the high barium interval, the longevity of the barium
reduction is a function of the vertical isolation provided by the confining units in the
aquifer.
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Use Of Borehole-Radar Methods To Monitor The Movement Of A Saline Tracer In Carbonate Rock At Belvidere, Illinois
Authors J.W. Lane, P.K. Joesten, F.P. Haeni, Mark Vendl and Doug YeskiCommon-depth (CD) radar surveys and cross-hole radar tomography methods were used to
monitor the movement of a saline tracer in a dual-porosity dolomite aquifer at Belvidere, Illinois. The
tracer test was conducted using an array of six open-hole bedrock wells at the Parson’s Casket Hardware
Superfund site. The injection and recovery boreholes were about 20 m (meters) apart, and the imaging
boreholes were arranged to provide planar coverage across and along the anticipated tracer path. A
hydraulically conductive zone identified during previous investigations was isolated using straddle
packers and pumped to establish a hydraulic gradient between the injection and recovery wells. A sodium
chloride (NaCl) solution was continuously injected into this zone to move the tracer across the
tomographic image plane.
CD cross-hole radar surveys and cross-hole tomography surveys were conducted before and
periodically during the tracer injection. Background tomograms contain similar radar velocity and
attenuation changes with depth, consistent with a layered dolomite that has variable porosity and
electrical conductivity. Slow changes in attenuation associated with low tracer velocity permitted the
acquisition of multiple CD surveys and two cross-hole tomography surveys during injection. CD surveys
were used to rapidly identify the presence of tracer between wells. Attenuation-difference tomograms
contain attenuation increases that delineate the spatial distribution with time of the saline tracer and show
the progressive movement of the tracer within the tomographic image plane. Formation porosity and
resistivities calculated from radar velocity and attenuation tomograms were used to estimate changes in
fluid resistivity and tracer concentration in the tomographic image plane.
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The Application Of Very Low Frequency Electromagnetics And Downhole Geophysical Techniques To An Island Hydrogeologic Study: Rhode Island Formation, Narragansett Basin
Authors Scott C. Michaud and Christopher L. CovelVery Low Frequency (VLF) geophysics has been utilized to supplement data collected using
downhole geophysical techniques for the purpose of studying a fractured bedrock aquifer on
Conanicut Island in Narragansett Bay, Rhode Island. Other components of a larger ongoing study
include the modeling of groundwater flow, the study of the aquifer’s natural hydrogeochemistry,
and the anthropogenic impact on the aquifer. The aquifer is comprised of a portion of the Rhode
Island Formation, which ranges from a micaceous schist to a meta-sandstone and
meta-conglomerate. Geophysical and outcrop measurements reveal five fracture orientations
through which groundwater is expected to flow. These correspond to the bedrock’s dominant
foliation as well as numerous fracture surfaces apparently related to post-Carboniferous tectonics.
The groundwater model is being developed to evaluate the suitability of treating the aquifer as
an equivalent porous medium. Downhole geophysical investigations conducted on Conanicut
Island by the United States Geological Survey (USGS) yielded data which appear to suggest a
predictable trend in the flow of groundwater into a bedrock well with depth. Based on data
collected at the time of this publication, groundwater flow to the well is observed to decrease
exponentially with depth. The location of these fractures and their orientations provided the
impetus for the VLF application. Linear filtering of VLF measurements (after Karous and Hjelt,
1983) has provided for the modeling of the positions and orientations of large water-bearing
fracture zones. Fracture orientations based on VLF geophysical interpretations appear to
correspond to borehole televiewer images and orientations measured at formation outcrops on the
island.
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Integrating Surface And Borehole Geophysics In Ground Water Studies - An Example Using Electromagnetic Soundings In South Florida
Authors Frederick Paillet, Laura Hite and Matt CarlsonBorehole induction logs are used to calibrate surface induction soundings in units of pore water
salinity. This is accomplished by correlating water sample conductivity with the electrical
conductivity of the formation over the sampled interval. In addition to the hydraulic calibration of
the surface induction data, the analysis shows geophysical logs contribute to the interpretation of
the surface induction soundings in two other ways: 1) logs show that the constant conductivity
layer model most often used to analyze induction soundings is appropriate for the south Florida
study; and 2) several physically independent log measurements can be used to uncouple the
dependence of formation electrical conductivity on such parameters as salinity, permeability, and
clay mineral fraction. We conclude that geophysical logs have important applications in
formulating geophysical inversion problems and in defining quantitative relations between
geophysical measurements and hydraulic or water quality parameters of interest.
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Use Of A Multi-Offset Borehole-Radar Reflection Method In Fractured Crystalline Bedrock At Mirror Lake, Grafton County, New Hampshire
Authors J.W. Lane, F.P. Haeni and Roelof VersteegMulti-offset, single-hole, borehole-radar reflection surveys were conducted at the U.S.
Geological Survey Fractured Rock Research Site at Mirror Lake, in Grafton County, New
Hampshire. The study was conducted to evaluate the benefits of applying multi-offset seismic
processing techniques to borehole-radar reflection surveys in fractured rock.
The multi-offset reflection surveys were conducted in conjunction with a saline tracerinjection
experiment. During injection, a sodium chloride (NaCl) solution was continuously
pumped into a hydraulically conductive zone that was isolated by specially constructed, reusable,
PVC straddle packers suspended from PVC casing. Eight common-offset borehole reflection
profiles were collected within the PVC-sleeved portion of the borehole before and during the
tracer injection. The offset between the transmitter and receiver antennas ranged from 6.4 to 9.9
m (meters). The common offset data were filtered, sorted into common distance-point (CDP)
gathers, normal move-out (NMO) corrected, and stacked to produce a zero-offset borehole CDP
profile.
Comparison of the common-offset and CDP profiles indicates that multi-offset data
acquisition and CDP processing; (1) increases the resolution of reflectors near the borehole, (2)
decreases the effects of direct wave coupling, antenna ringing, and system noise, and (3)
improves the clarity of difference images used to identify the effects of saline tracer on
reflections from transmissive fractures.
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Combination Of Downhole Gamma Logging And Soil Vapor Measurements To Track Low Level Chlorinated Solvent Contamination In The Deep Vadose Zone
Authors Rich Meixner, Dan Blout, Betsy Hovda, Bill Crawford, Duane Newell, Jim Viellenave and Richard HeibelDownhole gamma logging and a soil vapor investigation were used to identity an
unknown source and the subsurface pathway of chlorinated solvents migrating to ground
water at 110’ below ground surface (bgs). Thirty (30) borings were installed using Direct
Push Technology with 1.75” OD, 1 .OO” ID drive pipe to as deep as 67’ at a New Mexico
State Highway and Transportation Department Maintenance Yard in Deming, NM. While
the pipe was still in the ground, each hole was gamma logged to establish optimum
vertical locations for the installation of permanent soil vapor implant points. Two to four
points were then installed in 2-to-11 foot thick sand filter-pack beds, separated by granular
bentonite grout, in each boring. The borings were then completed as monitoring wells
with traffic covers. Soil gas samples were collected from each vapor implant point and
analyzed in a mobile environmental laboratory using EPA method 8010 (modified) for
chlorinated volatile organic compounds, including 1,l -dichloroethene (DCE), 1,l
dichloroethane (DCA), and 1 , 1, 1 trichloroethane (TCA). Confirmation analyses were run
by GC-MS onsite. The resulting three-dimensional representation clearly identified the
source area and a plume declining in concentration and descending in depth toward the
known area of ground water contamination. The gamma logging was instrumental in the
vertical placement of vapor implant points to obtain optimum gas samples, immediately
above potential low-permeability layers. Because the Direct Push borings were installed
without soil sampling or examination, the gamma logging was very useful in the
characterization of subsurface lithology for assessing source location and vapor plume
pathways.
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Mapping Hydraulically Permeable Fractures Using Directional Borehole Radar And Hole-To-Hole Tomography With A Saline Tracer
Authors David L. Wright and John W. LaneReflection-mode borehole radar and transmission-mode radar tomograms image heterogeneity in the
electromagnetic properties of rock. Heterogeneity may be produced by interfaces between different rock
types, foliation, and fracturing. In crystalline rock, hydraulic flow is primarily through fracture networks
rather than through the rock matrix. Borehole radar methods have been applied to help map flow paths
in crystalline rock. Correlation of features identified in borehole radar reflection records and tomograms
with hydraulic flow paths is generally uncertain because the records show responses to heterogeneity of
all- kinds, not just to hydraulically permeable fractures. Even in lithologically uniform rock, it is often
not possible to distinguish fractures of high hydraulic permeabilities from those with low permeabilities.
It is possible to “erase” signatures from lithologic interfaces and rock fabric to identify the signatures of
hydraulically permeable fractures by using a saline tracer in fractured crystalline rock because the
electrical properties of the rock, except for the fractures that are open to infiltration by the brine solution,
remain the same after the injection of the brine and may be removed by examining differences. Saline
tracer experiments were carried out in 1995, 1996, and 1997 in the FSE well field at the Mirror Lake
fractured-rock hydrology research site in Grafton County, New Hampshire. Comparisons of results from
directional radar reflection surveys to well-to-well difference attenuation tomography in the same pairs
of wells show generally good correspondence between the location of radar reflections and attenuation
anomalies. Our results demonstrate the advantage of using a saline tracer for before-and-after difference
mapping of hydraulically permeable fractures in lithologically heterogeneous rock and the utility of the
coordinated use of directional borehole radar and hole-to-hole radar tomography.
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