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12th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 14 Mar 1999 - 18 Mar 1999
- Location: Oakland, California, USA
- Published: 14 March 1999
41 - 60 of 108 results
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Integrated Use Of Continuous Seismic-Reflection Profiling And Ground-Penetrating Radar Methods At John’S Pond, Cape Cod, Massachusetts
Authors C.J. Powers, F.P. Haeni and Spence SmithContinuous seismic-reflection profiling (CSP) and ground-penetrating radar (GPR) surveys
were conducted by the U.S. Geological Survey in April 1998 over the northern part of
John’s Pond, a glacial kettle pond southeast of Otis Air National Guard Base, Cape Cod, Massachusetts.
The surveys were conducted to delineate the types and thickness of sedimentary
units that may control the infiltration of contaminated groundwater into John’s Pond.
Sand-and-gravel deposits, collapse features and recent organic sediments were imaged
with the CSP and GPR methods. Hummocky to chaotic reflections were interpreted as sandand-
gravel deposits. Slightly wavy, parallel reflections located in depressions in the sand-andgravel
deposits were interpreted as filled collapse features. Lower amplitude, horizontal, laminar
reflections were interpreted as organic sediments. Entrapped methane gas within some of
the organic sediments created a reflection zone that obscured deeper reflections in the CSP
records.
The CSP and GPR methods provide complementary information over most of the surveyed
part of the pond. The methods detect similar interfaces, but a particular interface may
produce a stronger reflection in one record than in the other. For example, regions of the pond
containing organic sediments with entrapped methane gas, which prevent penetration of the
acoustic signal, were penetrated and imaged by GPR. Conversely, regions of the pond containing
electrically conductive sediments or deep water, which attenuate the GPR signal, were imaged
using CSP. The CSP and GPR data were interpreted to generate a bathymetric map and a
map of sediment type and thickness beneath John’s Pond.
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Temporal Saltwateref’F’Ects On A Porous Sand Derived From Geophysical Monitoring Through A Tidal Cycle At Crescent Beach State Park, Maine
Authors S.K. Sandberg and L.D. SlaterThis paper presents results of an experiment in which data from a combination of geophysical
methods (resistivity, induced polarization, electromagnetic profiling, and magnetic profiling)
were used to identify shallow geologic and hydrogeologic structure, and to provide a model for
groundwater flow in a dynamic beach environment. Based on this study, the beach appears to be
underlain by a thin beach sand, overlying bedrock. Within the overlying sediments, a patch of
glacial till was mapped toward the ocean side of the beach. Bedrock has lithologic variability, as
evidenced by a non-uniform magnetic response. In particular, a northeast-southwest trending
magnetic body, believed to be a basalt dyke, was detected by its magnetic response.
During the transgressive phase of the tidal cycle, saline groundwater flow appeared to be quite
rapid, extending ahead of the surfical water by at least 4 m, as evidenced by the electromagnetic
response. During the regressive phase, a slug of saline water remained up beach from the high
tide mark for several hours prior to draining. Also during this regression, we observed
electromagnetic evidence for two fracture zones, or other preferential groundwater flow
pathways. These fracture zones appear to contain a relatively constant concentration of saltwater,
while surficial sediments above and to the side are flushed with fresh groundwater during tidal
regression.
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Time-Domain Electromagnetic Techniques To Study South Florida Aquifers
Authors Paul J. Wolfe, Benjamin H. Richard, Erin E. Sesslar and Steven EdlavitchTime-domain electromagnetic soundings were acquired at 38 locations along profiles in
the Big Cypress National Preserve in southwest Florida to interpolate the thickness of the fresh
water aquifer between widely spaced boreholes. A Geonics EM-47 system with a 160m
transmitter wire was used for data acquisition. Since larger loops provide larger dipole moments
we used the largest practical configuration. A 20m by 20m loop was used at most sites, although
at a few sites we were restricted to a 12m by 28m loop. To determine the consistency of the data
obtained with the various loop sizes, we performed soundings using different loop configurations
at several locations. Soundings were taken with loop sizes ranging from 40m to 5m squares.
Inversion of the sounding data gave similar models for the various configurations. As
anticipated the larger loops gave better deep data. Another concern was the effect of overhead
power lines in some of the sounding areas. To establish the effects of the wires a set of
walkaway soundings were conducted. These showed no measurable effect due to the wires. The
interpreted data indicate that the subsurface is generally well represented by a two or three-layer
model of saturated fresh water over brackish water carbonates. Borehole information indicates
that a low permeability zone acts as an aquitard between the two zones. The results found a
fairly constant depth to the interface along a 24km north-south transect and a 15km east-west
transect. Two areas showed anomalous depths that may indicate leakage through the aquitard.
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Boise Hydrogeophysical Research Site (Bhrs): Objectives, Design, Initial Geostatistical Results
Authors Warren Barrash, Tom Clemo and Michael D. KnollThe Boise Hydrogeophysical Research Site (BHRS) is a wellfield developed in a shallow,
coarse (cobble-and-sand), alluvial aquifer with the goal of developing cost-effective methods for
quantitatively characterizing the distribution of permeability in heterogeneous aquifers using
hydrologic and geophysical techniques. Responses to surface geophysical techniques (e.g., seismic,
radar, transient electromagnetics) will be calibrated against a highly characterized control volume
(the wellfield) with 3-D distributions of geologic, hydrologic, and geophysical properties determined
from extensive field measurements. Also, these data sets will be used to investigate relationships
between properties and to test petrophysical models. Well coring and construction methods, and the
well arrangement in the field, are designed to provide detailed control on lithology and to support
a variety of single-well, crosshole, and multiwell geophysical and hydrologic tests. Wells are
screened through the cobble-and-sand aquifer to a clay that underlies the BHRS at about 20 m depth.
In addition, the wellfield design optimizes well-pair distances and azimuths for determination of
short-range geostatistical structure. Initial geostatistical analysis of porosity data derived from
borehole geophysical logs indicates that the omnidirectional horizontal experimental variogram for
porosity (possible proxy for log permeability) is best fit with a nested periodic model structure.
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Geophysical Surveys Across The Boise Hydrogeophysical Research Site To Determine Geophysical Parameters Of A Shallow, Alluvial Aquifer
At the Boise Hydrogeophysical Research Site (BHRS), we are characterizing the
hydrogeophysical parameters of a cobble-and-sand, unconfined aquifer using a wide variety of
geophysical methods. Our goal is to develop methods for mapping variations in permeability by
combining non-invasive geophysical data with hydrologic measurements. We are using seismic,
ground penetrating radar, and electrical methods in a variety of configurations to provide images
of and parameter distributions at the BHRS. Issues such as resolution, depth of penetration, and
the ability to image the desired parameters will help determine the most effective methods.
Supporting data sets from the BHRS include core analyses and geophysical logs from 18 wells at
the site. We will use these data to verify our geophysical interpretations. The various geophysical
methods and acquisition geometries, combined with the well control, will provide an outstanding
data set to characterize the heterogeneity of the subsurface beneath this alluvial aquifer, and find
ways to map permeability with geophysical information.
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Permeability Estimation Using Spectral Induced Polarization Measurements
Authors John T. Sturrock, David P. Lesmes and F. Dale MorganMany different models have been developed for the hydraulic permeability of
sedimentary rocks and soils. Generally, the models fall into two basic categories: fluid flow
through equivalent tubes and fluid flow around grains. Although different in approach, both tube
and grain models have been observed to produce reasonable results. The major obstacle to in-situ
permeability prediction is accurately estimating the relevant model parameters such as porosity,
specific surface area, tortuosity, and grain/pore size distribution. Spectral Induced Polarization
(SIP) measurements are sensitive to many of the same micro-geometricalparameters which are
required for permeability prediction. The objective of this paper is to test a new methodology
for inverting broadband SIP measurements for micro-geometricalparameters and then to use the
derived model parameters to estimate the sample permeabilities. A series of laboratory
experiments were performed using five different sandstone samples, for which the hydraulic
permeability, porosity, specific surface area, and SIP response was measured over the frequency
range of 10” to lo6 Hz. The SIP data were then used to independently estimate the formation
factor, porosity, specific surface area, surface fractal dimension and the grain size distribution of
each sample. As has been previously demonstrated, we observe that the IP response at a fixed
frequency increases with the specific surface area of the sample. However, permeability
estimates based on surface area alone are inaccurate. Much more robust permeability estimates
are obtained when using the grain size distribution obtained in the inversion of the broadband SIP
data.
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Determining Elastic Soil Properties At Small Strains
More LessGeotechnical and geophysical techniques have been combined to determine the elastic
parameters of a series of lacustrine clays at a location where series of highway underpasses
are to be constructed. Piezocone penetrometer and triaxial tests on borehole core samples
allowed variations of the soil structure and the shear modulus /J over a range of larger
strains to be measured. The small-strain behavior of p was established from seismic
measurements. Extremely low ,U values of less than 50 MPa and Poisson’s ratios near 0.5
for small strains were found. Together with experience gained from the first construction
phase, these results will be used to optimize the design of construction process.
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Predicting Clay Content And Poroszty From Gamma-Ray And Conductivity Logs
Authors Wendy W. Corona and Gary MavkoAs the first step in predicting flow properties from geophysical logs, a gamma-ray
log was used to predict clay volume fraction (& 0.021), and the conductivity log was used
to predict porosity fraction (& 0.029) in the Oak Ridges Moraine (ORM) complex,
Ontario. First, empirical relations between the gamma-ray count and lab-measured clay
volume were derived and used to predict clay volume throughout the entire well for five
different lithologies. Then, Archie’s Law was used with a clay correction to calculate
formation factor. Finally, relations between lab-measured porosity and predicted
formation factor were derived and used to predict porosity throughout the entire well for
each lithology.
In the Aurora well, we reasonably predicted the volume fraction of clay and
porosity, and were able to identify known aquifer and aquitard units using the computed
formation resistivity factor. The porosity and formation factor pseudo-logs may be used
to model permeability at the well. The derived cementation factors were: m = 1.6 in the
sands, silts and gravels; m = 1.8 in the silt/clay rythmite series; and m = 1.3 in the poorly
sorted, clayey silt tills.
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Accounting For Saturation Heterogeneity In Obtaining Estimate Of Water Content From Dielectric Data
Authors Christina Y. Chan and Rosemary J. KnightMeasurements of dielectric constant can be used to determine water content or saturation in
the vadose zone; estimates of these parameters are needed in modeling contaminant transport. If a
sedimentary system is a homogeneous mixture, the dielectric constant-water content or saturation
relationship can be described by the time propagation (TP) model. If the sedimentary system
consists of thin layers, effective medium theory (EMT) describes the system; whereas if the system
consists of thick layers, ray theory describes the system.
In this paper, we present a flow chart for determining water content and saturation from
field measurements. In this procedure we look only at binary (e.g. clay-sand) sedimentary
systems and assume that if layers are present they are parallel to the surface. Using dielectric
measurements taken perpendicular to the surface of the earth and measurements taken parallel, we
can determine whether the system is homogeneous or layered. We then use the dielectric
measurements and lithologic information determined from direct sampling to calculate the water
content and saturation of the system. This method not only gives the global water content and
saturation of the whole system, but also gives the water contents and saturations of the two
different sedimentary layers if they are present. We also present examples of the error that can be
incurred if this method is not followed and an incorrect relationship is used to interpret to dielectric
data.
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Influence Of Microstructural Properties On Geophysical Measurements In Sand-Clay Mixtures
Authors Dorthe Wildenschild, Jeffery J. Roberts and Eric D. CarlbergWe have performed a series of laboratory experiments on saturated sand-clay
mixtures. Measurements include frequency-dependent electrical properties using the
four-electrode technique (10 mHz to 1 MHZ), permeability, porosity, and acoustic
velocities. We mixed clean Ottawa (quartz) sand with Na-montmorillonite (Wyoming
bentonite) in a number of different configurations containing 0 to 10% clay: as a
dispersed mixture, as discrete clay clusters, and arranged in distinct layers. Solutions of
CaC.& ranging from 0.0005 N to 0.75 N (0.05 to 64 mS/cm) and deionized water were
used as saturating fluids. We found the electrical properties to be dependent on clay
content, fluid conductivity, and microstrudure in a complex fashion. Increasing fluid
conductivity and increasing clay content generally resulted in higher electrical
conductivity. For an individual sample, two main regions of conduction exist: a region
dominated by surface conduction and a region where the ionic strength of the
saturating fluid controlled conduction. The sample geometry (dispersed, nondispersed,
or layered clay configuration) was found to greatly affect the magnitude of the surface
conductance in the range of low fhrid conductivity.
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Ultrasonic Characterization Of Synthetic Soils For Application To Near Surface Geophysics
Authors B.P. Bonner, P. Berge, C. Aracne-Ruddle, C. Bore, E. Hardy and C. TrombinoEffective seismic interrogation of the near subsurface requires that measured parameters, such as
compressional and shear velocities and attenuation, be related to important soil properties. Porosity,
composition (clay content), and fluid content and identification are of particular interest. The
ultrasonic (100-500 kHz) pulse transmission technique was used to collect data for highly attenuating
materials appropriate to the vadose zone. Up to several meters of overburden was simulated by
applying low uniaxial stress of 0.1 MPa to the sample. The approach has been to make baseline
measurements for pure quartz sand, because the elastic properties are relatively well known except at
the lowest pressures. Second phases are then added to modify the sample microstructure and
ultrasonic measurements are made to characterize the effect of the admixed second phase. Samples are
fabricated from Ottawa sand mixed with a swelling clay (Wyoming bentonite), and with a common
organic soil amendment, peat. Compressional (P) velocities are low, ranging from 169 to 360 m/s for
the mixtures at low stress. Shear (S) velocities are about half of the compressional velocity, but show
different sensitivity to microstructure. Adding clay increases the shear amplitude dramatically with
respect to P, and also changes the sensitivity of the velocities to load. These experiments demonstrate
that P and S velocities are sensitive to the amount and type of admixed second phase, even at low
concentrations. Other properties of the transmitted signals which include the ratio of S and P
amplitudes, velocity gradient with depth, and the frequency content of transmitted pulses, provide
additional information and are not now used in near-surface surveys.
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Comparing Geophysical Measurements To Theoretical Estimates For Soil Mixtures At Low Pressures
Authors P.A. Berge, J.G. Berryman, B.P. Bonner, J.J. Roberts and D. WildenschildRelationships between geophysical and hydrogeological properties are needed for
improving characterization of the subsurface at contaminated sites using geophysical
methods. As part of an on-going project with the goal of improving underground imaging,
we are developing rock physics theories for relating elastic wave velocities to soil
composition and fluid-flow parameters. Here we use effective medium theories to estimate
velocities of unconsolidated sand-peat moss mixtures and compare the estimates to
measured compressional and shear velocities from low-pressure laboratory experiments.
We found that a self-consistent effective medium theory model using sand and porous peat
as the constituents provides estimated velocities that are in good agreement with measured
velocities. Understanding the microstructural assumptions inherent in various mixture
theories guides the selection of appropriate theories for modeling velocities in soils.
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Saturation And Contamination Dependence Of Electrical Properties In The Mhz Range
Authors Andreas Weller, Claus Urban and Joachim SchonartA Dielectric Measurement System is used to investigate the influence of pore filling and
saturation on electrical permittivity and conductivity in a frequency range from 2 MHz to 1.3
GHz. The small size of the sample holder requires a special preparation method of the samples.
The influence of the geometry of the sample holder was investigated with synthetic samples of
known permittivity.
Only the experiments with glass beads and pure sand verified the validity of known mixing laws.
Samples with varying clay content reveal the dominant influence of clay minerals on electrical
permittivity. The large specific internal surface of clay minerals requires the consideration of
surface effects. Mixing laws considering only the volume fraction of the components fail to
describe the electrical properties of samples with strong surface effects. Temporal variation of
electrical properties are observed which are caused by the imbibition process after the injection.
The intrusion of hydrocarbon contaminants into the pore space resulted only in small changes of
electrical permittivity compared to significant changes due to varying water and clay content.
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Large-Scale Geophysical Mapping And Its Application For Ground Water Protection In Urban Areas.
Authors Kurt I. Sørensen and Verner H. SøndergaardThe water supply in Denmark strongly relies on ground water, but pure water may soon be in
short supply. The Danish Parliament has therefore decided, that protection of ground water
against polution should be intensified by means of protection zones and area1 planning activities,
which means that for instance urban expansion will be under stronger control.
In order to act on a proper basis the knowledge about the geological and hydrogeological
situation has to be considerably improved. Over the next 10 years some 140 million US dollars
will be spent to obtain a better geological mapping of recharge areas with great drinking
water interests. These areas add up to a total of some 15.000 km2 in Denmark.
Geophysical methods, especially electrical and electromagnetic methods, are expected to
play an important role, accounting for more than half of the 140 million dollar mapping
expenses.
A large scale mapping project around the City of Aarhus has provided good experiences
about using high density geophysical measurements combined with drillings covering large
areas.
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Geophysical Imaging Of A Former Landfill And Its Associated Leachate Plume
An integrated geophysical investigation was conducted at a closed landfill site
(LF-30) at the decommissioned Wurtsmith Air Force Base (WAFB), Oscoda, MI in May
and June of 1998. Frequency domain horizontal loop electromagnetic (HLEM),
magnetic, self-potential (SP), electrical resistivity (ER), and ground penetrating radar
(GPR) methods were used. The site is nearly flat topographically, with less than two
meters of local relief, and is covered by dense tree growth approximately 23 years old.
Previous hydrogeologic investigations show PCE, TCE, DCE, vinyl chloride, and BTEX
are the main constituents of a leachate plume emanating from the landfill. Additionally,
the landfill plume contains elevated levels of total dissloved solids(TDS) leached from
the fill material, causing groundwater plume conductivities three times background
values. Groundwater flow in the area is toward the northeast and discharges into Van
Etten Lake.
All of the methods utilized in this study were successful in delineating the landfill.
The electromagnetic and magnetic data suggest the existence of eight separate clustered
burial cells (and one outlier) containing significant amounts of metal within the landfill.
Additionally, areas of fill are characterized by attenuated GPR signals and very low
apparent resistivities compared to background. Furthermore, the EM and SP surveys
were most effective in delineating an anomalous zone approximately 1600 R wide, where
boundaries are coincident with the lateral boundaries of the BTEX plume as determined
by scattered monitor wells. The difference in size between the small LF-30 landfill and
the much larger associated plume width, suggest the possibility of an additional source.
Therefore, it is likely that another landfill (LF-3 l), located up gradient from LF-30, is a
major contributor to this contaminant plume.
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The Temporal Variation Of A Saltwater Contaminant Plume As Evidenced Through Long-Term Resistivity Monitoring
Authors Gail Lipfert, Stewart Sandberg, Lee Slater, Andrew Reeve and Marc LoiselleThe site of a formerly uncovered sand/salt pile in Verona, Maine was used to investigate
the changes in resistivity over time of a fractured bedrock ground-water system. Terrain
conductivity of the area immediately down-slope from the site of the former sand/salt pile was
measured using a small horizontal loop electromagnetic (EM) profiling technique. High terrain
conductivity measurements delineate the contaminant plume. In areas where overburden is
shallow, anomalies in terrain conductivity along traverses indicated fracture locations. The angular
shape of the plume of high terrain conductivity represents the orientations of regional and local
bedrock fractures and indicates fracture control of the ground-water flow. A permanent array of
electrodes was established along six of the EM traverses and electrical resistivity measurements
were taken every one to two weeks over a five-month period. A correlation of rain events to
apparent resistivity changes are attributed to the migration of the plume.
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Applications Of Some New Techniques To Detect Groundwater Contamination At Mine Tailings Dams
Authors G. Buselli and K. LuWe have recently applied electrical and electromagnetic methods to two
environmental problems at minesites: firstly, to an acid mine drainage problem at the
tailings dam of a disused pyrite mine at Brukunga, South Australia, and secondly, to
the detection of any seepage from a tailings dam at the operating Ranger minesite,
Northern Territory, Australia. Using these examples, we stress the importance of the
use of combined methods for both measurement and interpretation of data.
At the first minesite, we used a combination of direct current (DC), transient
electromagnetic (TEM) and self-potential (SP) surveys to locate the source of
groundwater entering the tailings dam and to map the depth to water-table over the site.
At the second minesite, more extensive experimental surveys have been made with
these and the induced polarization (IP) method. The surveys include the use of a 2D
array of electrodes and measurements with a multichannel data acquisition system.
Results of a previous airborne electromagnetic survey have been interpreted using
newly-developed conductivity-depth imaging software.
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A Mise A La Masse Survey To Track Ground Water Cokduits In Weathered Bedrock Near A Salvage Yard
Authors John Jansen, Phillip Osborn and Michael WilsonA series of monitoring wells were installed as part of a ground water investigation around
a salvage yard. Most of the wells encountered relatively dense silty clay deposits and
shale. A few wells hit voids related to a paleochannel system filled with high TDS
ground water. A mise a la masse survey was conducted to map the trend of the
paleochanneis by placing a current electrode inside a monitoring well completed in a
channel feature. The survey identified the area of highest hydraulic conductivity and the
trend of the major channel system. The survey also appears to have mapped individual
minor channel features. The survey results were used to predict the trend of the
paleochannel system to the east of the site. The predicted location of the paleochannels
was confirmed by a test drilling program.
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An Integrated Approach To Monitoring A Field Test Of In Situ Contaminant Destruction
The development of in situ thermal remediation techniques requires parallel development
of techniques capable of monitoring the physical and chemical changes for purposes of
process control. Recent research indicates that many common contaminants can be
destroyed in situ by hydrous pyrolysis/oxidation (HPO), eliminating the need for costly
surface treatment and disposal. Steam injection, combined with supplemental air, can
create the conditions in which HP0 occurs. Field testing of this process, conducted in the
summer of 1997, indicates rapid destruction of polycyclic aromatic hydrocarbons (PAHs).
Previous work established a suite of underground geophysical imaging techniques capable
of providing sufficient knowledge of the physical changes in the subsurface during thermal
treatment at sufficient frequencies to be used to monitor and guide the heating and
extraction processes. In this field test, electrical resistance tomography (ERT) and
temperature measurements provided the primary information regarding the temporal and
spatial distribution of the heated zones.
Verifying the in situ chemical destruction posed new challenges. We developed field
methods for sampling and analyzing hot water for contaminants, oxygen, intermediates
and products of reaction. Since the addition of air or oxygen to the contaminated region is
a critical aspect of HPO, noble gas tracers were used to identify fluids from different
sources. The combination of physical monitoring with noble gas identification of the native
and injected fluids and accurate fluid sampling resulted in an excellent temporal and spatial
evaluation of the subsurface processes, from which the amount of in situ destruction
occurring in the treated region could be quantified. The experimental field results
constrain the destruction rates throughout the site, and enable site management to make
accurate estimates of total in situ destruction based on the recovered carbon. As of
October, 1998, over 400,000 kg (900,000 lb) of contaminant have been removed from the
site; about 18% of this has been destroyed in situ.
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Induced Polariza Tion Imaging Of A Jet Fuel Plume
Time-domain induced polarization data has been collected and analyzed for a site at the
Otis ANGB, Massachusetts Military Reservation, Cape Cod, Massachusetts. The
specific plume is designated FS- 12 and is due to break in the subsurface fuel transport
pipeline. Approximately 70,000 gallons of jet fuel were spilled in the early 1970’s. The
predominant contaminants are benzene and ethyl dibromide (EDB).
The data have been inverted to give resistivity and chargeability tomograms to depths of
300 feet and 1400 feet in extent. We also processed the IP time domain signals for short
and long times separately and produced a time domain gross spectral chargeability
difference. Both the chargeability and spectral chargeability difference show good
agreement with the known location of the plume from sampling wells.
The IP mapping provides detailed information that cannot otherwise be obtained from the
sparse borehole distribution.
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