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5th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems
- Conference date: 26 Apr 1992 - 29 Apr 1992
- Location: Oakbrook, Illinois, USA
- Published: 26 April 1992
40 results
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Marine Seismic-Reflection Profiling To Define Hydrogeologic Continuity At Camp Lejeune, North Carolina
Authors Alex P. Cardinell and Steven A. BergContinuous marine seismic-reflection-profiling data were correlated with
land-based borehole geophysical and lithologic data to define the hydrogeologic
framework of Camp Lejeune Marine Corps Base in part of the Coastal Plain
Province of southeastern North Carolina. Marine seismic profiling was
particularly useful at Camp Lejeune because 25 percent of the study area is
covered by the New River estuary system.
A medium-power, wide-frequency seismic system was used to collect
continuous single-channel, shallow-marine seismic-reflection-profiling data for
more than 100 miles of transects across the estuary. Positioning of the boat
equipped with seismic instruments was controlled by an onboard integrated
navigation system; LORAN C and Global Positioning Systems' were integrated to
continuously plot boat position.
Onshore borehole geophysical and lithologic data were compared with
seismic data. A borehole acoustic-velocity log was used to generate an average
acoustic-velocity curve for the sediment, which was then used to convert the
seismic travel time to depth. The acoustic-velocity, single-point resistance,
and gamma-ray log data were adjusted for altitude and dip and correlated with
the seismic data.
Hydrogeologic sections constructed using these correlations show that the
combined thickness of the surficial, Castle Hayne, and Beaufort aquifers ranges
from approximately 200 feet at the western edge of the study area to approximately
490 feet at the eastern edge. Three sections of buried river channel
have been identified within the Castle Hayne aquifer underlying the New River
by seismic-reflection-profiling data. One of these channels has been correlated
with well-log data. Buried channels, if filled with permeable material,
can function as conduits for ground-water flow, thereby facilitating movement
of contaminants from land surface, or saltwater migration from the estuary to
supply wells.
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Identification Of A Multiaquifer Ground-Water Crosscontamination Problem In The Stockton Forjmation By Use Of Borehole Geophysical Methods, Hatboro, Pennsylvania
Authors Ronald A. Sloto, Paola Macchiaroli and Michael T. TowleAbandoned industrial and public supply wells and improperly constructed monitoring wells open to
multiple water-bearing zones in the Triassic Stockton Formation in Pennsylvania short circuit the
ground-water-flow system and are conduits for contaminant transport. Borehole geophysical methods
were used to construct a three-dimensional lithostratigraphic model, identify fluid-producing and
fluid-receiving zones (fractures), measure vertical borehole-fluid movement, and serve as the basis for
proper design and construction of monitoring wells. Natural-gamma, single-point-resistance, caliper,
fluid-temperature, and fluid-resistivity logs were run in 16 boreholes 149 to 470 feet deep.
The lithostratigraphic model of the dipping sedimentary rocks of the Stockton Formation primarily is
based on natural-gamma, single-point-resistance, and caliper logs. Geophysical logs from one borehole
were compared to a 200-foot-long rock core from that borehole to determine the relative response
of the geophysical logs to lithology. This comparison was used as the basis for litbologic interpretation
of the geophysical logs of the other boreholes. The interpreted lithostratigraphy correlates well from
borehole to borehole.
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Subsurface Charact!Bization Using Integrated Geophysical Methods: A Case History
Authors John J. Nicholl and Kathryn CainA geotechnical assessment was made of the Northwest Boundary Containment System (NWBCS) at the Rocky
Mountain Arsenal near Denver, Colorado. This assessment was conducted to support the Interim Response
Action (IRA) Alternative Assessment addressing the NWBCS Long-Term Improvements IRA, and was designed
to evaluate the present groundwater and recharge system, assess potential contaminant bypass of the system, and
identify remediation requirements of the system. Geophysical techniques were used as part of the geotechnical
assessment. Three surface geophysical techniques were used including seismic refraction, electromagnetics (EM),
and electrical resistivity soundings. Additionally, limited downhole geophysical logging was conducted for
correlation with surface geophysical data. The field program included approximately 32,000 linear feet of seismic
refraction data, 52,000 linear feet of EM data, 13 resistivity soundings using the Schlumberger electrode array,
and downhole geophysical logging in two boreholes. Seismic refraction data were combined with lithologic log
data to produce a map of the top of a sand and gravel unit that overlies the bedrock Denver Formation. Data
from the EM survey were combined with lithologic log data to produce a map of the top of the Denver
Formation. The resistivity and downhole results were used to augment the seismic and EM data. The results
of the geophysical investigation provided additional information for defining the location and geometry of
paleochannels and aided characterization of the interface between the Denver Formation and overlying alluvium.
EM results were particularly useful in providing information about the paleotopography of the Denver Formation
in areas where borehole data were sparse, allowing the detection of several previously unknown small
paleochannels in the Northwest Boundary area. Geophysical results allowed further refinement of the main
paleochannel and its orientation at the southwest end of the boundary system and confirmed the presence of a
suspected paleochamtel northeast of the system. All geophysical results, along with drilhng data, were then
incorporated into the hydrogeologic and contaminant transport models of the boundary system to aid evaluation
of its present and future effectiveness.
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Proper Appllcatlon Of Borehole Geophysical Techniques To The Evaluation Of A Carbonate Aquifer: A Case Histor
More LessThis paper documents a petrographic and petrophysical analysis of a water
supply test hole drilled in southwest Texas. The six inch hole penetrated the lower
Cretaceous Georgetown and Kiamichi Formations to a depth of 520 feet.
Initial analysis of the hole was ambiguous. Density and sonic porosities
were as high as 22% and 30%, respectively. However, an air-lift test of the well
produced only 35 gallons of water per minute. Further analysis of the well was
deemed necessary.
A petrographic examination of the drill cuttings was conducted to resolve
the discrepancy between the high porosity and low water production rates and to
determine if water production could be enhanced by acidizing or fracturing the
well. The logs were also analyzed in an attempt to resolve the discrepancy
between the density and sonic porosity values. Recommendations were made
regarding the most effective methods for evaluating subsequent wells.
Petrographic analysis of the cuttings revealed that the rock is a slightly
shaly, fossiliferous limestone with isolated moldic and micro-intergranular porosity.
While total porosity is high, effective porosity is very low. Neither fracturing nor
acidizing the well would significantly increase permeability and specific yield.
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Hydrogeologic Parameters Of Reclaimed Coal Strip Mines From Borehole Geophysical Surveys
Authors D.M. Diodato and R.R. ParizekTwo nuclear methods were used to quantify hydrogeologic parameters in the
unsaturated zone of a reclaimed and revegetated coal strip mine spoil pile in Clarion,
Pennsylvania. These investigations were part of an ongoing acid mine drainage
abatement demonstration project. Quantitative descriptions of physical properties
affecting fluid flow in deep strip mine spoil piles were previously unavailable. In
order to quantify moisture content, bulk density, porosity, and unsaturated hydraulic
conductivity, six 6.4 m seamless aluminum neutron access tubes were installed in
boreholes at the site. These were probed with Am-Be (neutron) and Cs-137 (gammagamma)
probes on 7 different dates.
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Magnetqmetry As A Tool To Map Subsurface Conditions In An Abandoned Iron Ore Mining District In New Jersey
Authors K.K. Cohen, N.N. Moebs and M.A. TrevitsAbandoned underground coal and metal mines present a number of environmental risks to communities.
Ground subsidence resulting from the collapse of mine workings ranks high among these risks.
Collapse or subsidence of the ground surface can result in safety hazards to residents, property
damage, and loss of land use. Field methods that provide geotechnical information about the
underground mine configuration and stability of the mine overburden are needed. In the past, a number
of site specific geophysical tools such as seismic techniques, gravity surveys, and electromagnetic
methods have been used in an attempt to acquire subsurface mine and overburden rock mass
information. This study investigates the use of magnetic mapping as a tool to delineate shafts and
underground workings responsible for ground instability in an abandoned metal-mining district of New Jersey.
The Township of Mine Hill, New Jersey has been plagued by subsidence for decades due to
unpredictable failure of portions of more than 20 abandoned iron ore mines which riddle the subsurface
of this community. Historical records indicate that mining started during the early 1700’s and continued
until 1966 with the closing of the last mine. Ore production was from high grade magnetite deposits
intruded into Precambrian crystalline rocks. Due to the high magnetic susceptibility contrast between
the ore and country rock, and a rather uniform orientation of the deposits, a unique opportunity was
available to delineate the abandoned mine workings using ground magnetic surveys.
Several abandoned mines in the Township of Mine Hill were selected for investigation. Historical mine
maps were used to design a gridded station array, and a proton precession magnetometer was used to
conduct a ground survey over each mine. Modeled anomalies computed from historical mine maps and
other available subsurface information were compared to anomalies observed in the field. Results
suggest that magnetometry is useful in delineating the condition and location of mine workings. This
information could be useful for subsequent remediation and land use planning for undermined areas.
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Time Domain Electromagnetic Measurements To Determine Water Quality In Tee Floridan Aquifer
Authors Pieter Hoekstra, Jim Hild and David TothThe Floridan aquifer system is one of the most productive
aquifers in the world. This aquifer system underlies an area of
about 100,000 square miles in southern Alabama, south-eastern
Georgia, southern South Carolina, and all of Florida. The
Floridan aquifer system provides water for several large cities,
including Savannah and Brunswick in Georgia; and Jacksonville,
Tallahassee, Orlando, and St. Petersburg in Florida. Locally,
the Floridan is intensively pumped for industrial and irrigation
supplies. During 1985, an average of about 3 billion gallons per
day of fresh water was withdrawn from the Floridan for all
purposes (Miller, 1990). Despite the huge volumes of water that
are being withdrawn from the aquifer system, water levels have
not declined greatly except locally where pumpage is concentrated.
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Continuous Electrical Resistivity Surveys Along The Lake Michigan And Green Bay Coastlines Of Wisconsin
More LessElectrical resistivity depth soundings were obtained at 15
meter intervals along the entire Lake Michigan and Green Bay
shorelines of Wisconsin using a towed resistivity system
developed for this purpose. The electrical longitudinal
conductance for the bottom sediments, derived from the sounding
data, was empirically related to hydraulic leakance. The
hydraulic leakance was obtained from the direct measurement at
selected locations of bottom sediment seepage. The empirically
derived relationship was combined with ground water flow models
to estimate ground water flux on a nearly continuous basis along
the shorelines. The resulting flux estimates spatially vary from
-15 cubic meters per day per kilometer to 560 cubic meters per
day per kilometer of shoreline. The average input to Lake
Michigan was estimated to be 480 cubic meters per day per
kilometer of shoreline and this estimate is within the range
exhibited by previous estimates.
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Use Of Ground-Penetrating Radar And Continuous Seismic-Reflection Profiling On Surface-Water Bodies In Environmental And Engineering Studies
By F.P. HaeniGround-penetrating radar (GPR) and continuous seismic-reflection
profiling (CSP) on shallow rivers, lakes, and ponds are efficient and
economical ways of obtaining subsurface hydrologic and geologic information
for environmental and engineering studies. These methods are similar in
that they produce continuous subsurface profiles, are easy to use, and the
records can be straightforward to interpret. They are dissimilar in that GPR
cannot penetrate electrically conductive water or subsurface sediments, and
CSP usually cannot operate in water less than 5 ft (feet) deep.
GPR records collected on a lake in New Hampshire have been interpreted
to estimate the depth to bedrock and to evaluate the grain-size
characteristics of the underlying stratified drift at the lakeshore
boundary. In a pond in Massachusetts, CSP and GPR were used to determine
the depth to bedrock and the grain-size characteristics of the subbottom
materials in part of the pond. Water-column multiple reflections, depth and
conductivity of water and subsurface materials, and diffractions degraded
the quality of the GPR records.
CSP records collected in the Connecticut River near Hartford,
Connecticut were used to estimate the depth of till and bedrock interfaces
and to evaluate the grain-size characteristics of subsurface materials.
Interpreted CSP records also can indicate bedding planes within consolidated
rock units. Water-column multiple reflections and very shallow water
degraded the quality of the CSP records.
GPR and CSP methods have been used to delineate infilled scour holes
near bridge piers. Scour holes that have been filled with up to 8 ft of
loose sand have been mapped during engineering-scour studies near a bridge
in Connecticut.
Because GPR and CSP operate on different principles, the two
geophysical methods complement each other. Depending on the required depth
of penetration and the degree of resolution needed, one or both of these
methods can be used to acquire accurate and reliable subsurface hydrologic
and geologic information critical to environmental and engineering studies.
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Use Of Marine-Seismic Profiling To Study Ground-Water Contamination At Aberdeen Proving Ground, Maryland
More LessContinuous high-frequency marine-seismic profiling was used to define the extent of geologic units offshore
of J-Field, Aberdeen Proving Ground, Maryland, during March and April of 1988. J-Field was used by the U.S. Army
for disposal of chemical warfare agents, munitions, and organic solvents from the early 1920’s through the 1970’s. A
major concern at this site has been the discharge of contaminated ground water into offshore areas and eventually into
the Chesapeake Bay. A 150-foot-deep paleochannel containing Pleistocene fluvial and estuarine sediments was
identified from onshore geologic borings. The paleochannel sediments consist of three geologic units: a basal unit of
gravel and sand, a middle unit of silty clay, and an overlying unit of interbedded clay and sand. The seismic profiles
identified the extent of these units and were used to map them in offshore areas. An accurate knowledge of the
distribution of the geologic units in onshore and offshore areas is important to the investigation because the coarsegrained
paleochannel sediments could provide a preferential flow path for hazardous wastes and the fine-grained
sediments could impede their movement. The seismic data were also used in a ground-water-flow model of the study
area to define the boundary conditions and to aid in the design of the finite-difference grid.
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A Waterborne Geophysical Technique For Assisting Proposed Dredging Projects
Authors Keith J. Sjostrom, Robert F. Ballard Jr. and Richard G. McGeeEach year, the U.S. Army Corps of Engineers spends millions of dollars
world-wide on river and harbor maintenance and ship channel realignment
projects. Currently, the Corps relies on drilling and laboratory testing
programs to assess marine sediments in terms of material type, density, and
thickness for the purposes of characterizing proposed dredging sites. But
sampling and coring programs are costly and provide only discontinuous information
about the material characteristics.
In 1988, the Corps of Engineers launched a major research and development
initiative called the Dredging Research Program (DRP) directed toward
developing new or better technologies to improve subbottom sediment characterization,
increase dredging efficiency, and reduce the overall costs of dredging
and sampling operations. The U.S. Army Engineer Waterways Experiment
Station (WES) heads this initiative. Through the combined effort of the
Hydraulics Laboratory and Geotechnical Laboratory, the focus of one of its
work units is to remotely and efficiently determine the characteristics of
subbottom marine sediments using acoustic impedance information together with
limited drilling.
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The Model Se880 Sonar Image And Record Enhancement System
Authors P.A. Baxter and R.J. MillsThe Sonar Image and Record Enhancement project, a two phase collaborative research and
development project, was awarded and part funded by the UK Department of Trade and
Industry to GeoAcoustics Limited, formerly Ferranti ORE Limited. Heriot Watt University
and British Geological Survey were subcontracted to the research. Professor Larry Mayer,
a marine geologist from Dalhousie University, Halifax, Canada is a consultant to this group.
In addition several institutes and research centres have provided valuable feedback of
information in using the system that has resulted in improved data acquisition.
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Azimuthal Resistivity Techniquib And Tke Directional Variations Of Hydraulic Conductivity In Glacial Sediments
Authors William A. Sauck and Scott M. ZabikField and analog tank model studies were done to examine the response of various
electrode arrays and to try to develop an optimum field technique. Field studies were on
fractured tills and on glacial outwash fan deposits. In the latter, anisotropy in electrical
resistivity (and by inference, the hydraulic conductivity) is a result of primary depositional
structures, principally the stacked braided stream channels. Schlumberger, Wenner, Pole-
Dipole, Pole-Pole and other modified arrays were tested. Various ways of normalizing and
plotting the results were developed. All arrays showed clear anisotropy effects and there is no
single best array or field technique which is most sensitive to anisotropy. Choice of technique
depends on the size of the field crew, access or ease of installing remote electrodes, and size
of the field or open space. Clearly, a Vertical Electrical Sounding (VES) must first be done
near a control well in the area to establish the appropriate electrode spacings for investigating
the depth range of interest. Field studies at one outwash fan site concentrated on vertical
variations, where. 12 azimuthal plots were made for a full range of current electrode halfspacings
of 1 to 100 m about one central point. A second phase of the work at this site studied
lateral variations, k the center point was moved 180 m laterally to obtain a measure of the
local geologic “noise” or variability. The lateral variability was less for larger electrode
spacings, as these sampled and averaged over a much larger volume.
The tank modeling was done to study the effects of the distance laterally and vertically
from the top of the fracture(s) to the array center point. The azimuthal apparent resistivity
diagram changed significantly with lateral position relative to a single “fracture”. For the
application of azimuthal resistivity techniques to fracture and joint investigations, a number of
azimuthal surveys at closely spaced points must be done to remove ambiguities caused by
unknown fracture spacing, and by unknown lateral distance to the nearest fracture. For multisheet
models, increasing the thickness of a homogeneous overburden eliminated the “Paradox
of Anisotropy” effect and rotated the ellipse 90 degrees.
Azimuthal surveys should prove to be useful at sites where detailed ground water flow
models are required, as resistivity azimuthal effects of 10 - 40% are common and presumably
the directional hydraulic conductivity variations may have similar magnitudes. The
disadvantage of the technique is that it is cumbersome and requires a large circular open space
free of interfering conductors; thus it is not applicable at many sites. The information
provided, however, is unattainable by any other means within reasonable economic limits.
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Refraction Seismic Survl3Y Of Some Thick Till In Southeast Alaska
More LessA geotechnical investigation was conducted in a small, steep, tidewater glaciated valley
in southeastern Alaska. The geotechnical drilling program encountered unanticipated
overburden thicknesses in excess of 100 feet on one side of the valley. A refraction seismic
survey was conducted to augment the geotechnical program. Interesting aspects of the
geophysical survey included the remote location; logistics to and at the tent camp; limited
helicopter use; the steep and rugged forested terrain; the availability of drill hole information;
the combination of doing shallow and deep looking surveys; the deep depth of investigation
which required long lines, long off-end shots, and large explosive charges; and the snow cover
and the short amount of daylight during the early winter survey.
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Combined Seismic Reflection And Refraction Methods In Coastal Engineering Site Investigation
Authors Robert J. McDonald, Peter J. Brabham and Michael BrooksA combined seismic reflection and refraction approach to coastal site investigation is
described using case studies at two sites in South Wales, UK. The land-based surveys, using the
BISON 9024 seismograph, were carried out in the intertidal zone with a target depth of 4m to
40m below surface.
The reflection data show a dominant frequency of 550Hz which, coupled with seismic
velocities averaging 16OOm/s, produces a quater-wavelength vertical resolution of 0.7m. Results
have imaged local rockhead and lithological boundaries in the overlying unconsolidated
sediments. Comparisons of hammer, buffalo gun and detonator sources are shown and their
relative suitability for use in the intertidal zone is discussed.
In interpreting shallow reflection data the requirement of rockhead depth control from
seismic refraction surveying and/or boreholes is emphasised. This is of particular importance if
the bedrock is deeply weathered and has a lower acoustic impedance contrast with overlying
sediments than other reflecting interfaces. Combined refraction and reflection surveys can
provide detailed information on rockhead depth and overlying sediment geometries. This
information can be valuable to the coastal engineer in both the design and location of man-made
structures.
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Studies In P-Wave And S-Wave Seismics
Authors C. Richard Bates, David Phillips and James HildThe technique of compressional (P) wave refraction is
routinely used in geotechnical and hydrogeological surveys.
Developments over the last 10 years in field procedures and
methods of data analysis have greatly increased the utility of
this technique in mapping targets in the shallow environment.
Nonetheless, two problems associated with hidden layers are often
cited as serious shortcomings with the technique, namely mapping
the top of the hidden layer and mapping boundaries below the
hidden layer. If a hidden layer is not identified in the data,
the errors in depth calculations can be significant. Lankston
(1989) has demonstrated the use of the general reciprocal method
(GM) for recognizing a hidden layer and mapping of boundaries
below the layer. Once recognized, the errors in depth
calculations are reduced but are still greater than. for problems
where a hidden layer does not exist. This reason is often used
to justify more costly P-wave reflection surveys.
While not routinely applied in shallow investigations,
horizontally polarized shear waves can yield additional
information. Shear (S) wave velocity is largely dependent on the
shear modulus or stiffness of a material and is virtually
unaffected by degree of saturation. As a result of the different
nature of S-wave propagation, S-waves may often show boundaries
not seen in P-wave surveys and equally the P-wave may show
boundaries S-waves do not.
The combined use of both P and S-wave seismics are described
for two site surveys. Lithology logs were available for both
sites and the seismics investigation formed part of a more
comprehensive geophysical feasibility study.
The hidden layer problem is often encountered in shallow
unconsolidated sediment/bedrock surveys where "velocity
inversionsl' and "layers too thin" are common. Boundaries can be
mapped below hidden layers with GRM. Also, by using both P and
S-waves, additional boundaries can be mapped that would not have
'been seen using one technique in isolation.
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Schlumberger Soundings ,And Sand-Column Resistmty Testing For Determining Stream-Aquifer Connection Great Sand Dunes Natl. Monument., Colorado
Authors Eric J. Harmon and Marilyn F. HajicekThe Great Sand Dunes National Monument, located in south-central Colorado, is comprised of
approximately 4002 Km of Holocene eolian sand dunes together with several surface streams and their
associated riparian ecosystems. The dune field and its two major physiographic boundaries, i.e. Sand
Creek on the north and Medano Creek on the south, together form a complex and unique system for the
study of eolian transport and recycling, including an unusual streamflow phenomenon known as bedform
dependent pulsating flow. Federal officials perceived that a very large ground-water pumping
project proposed for an area less than ten miles north of Sand Creek threatened its flow, and thus its
associated physical transport phenomena andriparian ecosystem, as well as Federal reserved water rights
decreed to the National Monument. The magnitude of the threat depends upon the degree of hydraulic
connection between the surface flow in Sand Creek and the underlying aquifer system.
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Hydraulic Aquifer Characteristics Determined From Resistivity Sounding Parameters Using Empirical Formulae And Geostatistical Techniques
Authors V.D.A. Coetsee, R. Meyer, C.D. Elphinstone, H. Bezuidenhout and A. WatsonGeohydrological data obtained through pump tests, are typically scarce and expensive.
Geophysical observations on the other hand are less expensive and can be obtained more
readily. Where geophysical observations can be shown to correlate with geohydrological
properties the potential exists for augmenting a sparse geohydrological data set with
predictions based on geophysical observations.
This paper describes the results obtained with the direct current resistivity method, using
the Vertical Electrical Sounding (VES) technique in defining certain aquifer characteristics,
i.e. transmissivity and porosity. In the past many attempts have been made to establish
empirical hydrogeophysical relationships, without understanding the physical principles of
the problem completely.
The complicated relationship that exists between formation geometrical factors, and the
governing ground water and current flow equations, resulted in the use of geostatistics to
interpolate hydraulic values to unknown points in the aquifer, using direct current
resistivity parameters.
In this study results from the use of empirical methods, geostatistical methods like kriging
and co-kriging are compared. Advantages and disadvantages in applying these
geostatistical techniques are discussed.
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Application Of Magnetic And Electromagnetic Methods To Metal Detection
Authors Robert H. Gilkeson, Stephen R. Gorin, Roy F. Weston and Douglas E. LaymonMagnetic and electromagnetic methods are routinely used to search for buried metal targets on
environmental sites. The methods are used to explore directly for buried tanks, buried pipe lines,
and individual or caches of buried steel drums. In addition trenches that contain hazardous waste
may also contain enough metallic debris to be detected with these methods.
Surveys are often performed with both methods to collect four different but complimentary
measurements. The two magnetic measurements are total intensity of the magnetic field and
vertical gradient of the magnetic field. The two electromagnetic measurements are quadrature
component (apparent conductivity) and in-phase component (metal detection). Electromagnetic
measurements are sensitive to all types of metal whereas magnetic measurements only detect
ferromagnetic metals. The Geonics EM-31 D terrain conductivity meter is a popular instrument for
environmental surveys. The instrument will simultaneously measure apparent conductivity and
presence of buried metal. The depth of investigation with electromagnetic methods is in part
controlled by instrument design. Therefore, this paper presents findings on detection of buried
metal that are specific to the Geonics EM-31 D instrument.
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Ground Penetrating Radar Survey Design
Authors A.P. Annan and S.W. CoswayEffective ground penetrating radar (GPR) surveys entail substantial planning if the surveys
are to meet pre-defined objectives. For many years, GPR has often been used with
unrealistic expectations in the mind of the end user of the data. The tools for survey design
are available and should be used routinely by geophysicists contemplating GPR surveys.
This paper presents basic guidelines for selecting operating frequency, station spacing, line
spacing, and antenna orientation. In addition, the fundamental methods for assessing
suitability of a GPR survey for a specific application are outlines.
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Improved Gpr Interpretation From Analysis Of Buried Target Polarization Properties
Authors Roger Roberts, Jeffrey J. Daniels and Leon PetersGround penetrating radar (GPR) investigations are often focused on the detection
of subsurface targets such as barrels, pipes, and isolated patches of
contaminants. Unfortunately many study areas also contain undesirable signals
from other objects such as logs, concrete, and disrupted soil. Knowledge of the
polarization properties of targets with different degrees of symmetry coupled with
GPR data containing polarization information enhances the interpretation of GPR
data over complex subsurface zones.
An ongoing study at The Ohio State University is investigating GPR polarization
with an array of antennas pulled by hand or towed behind an all-terrain vehicle.
The two-channel GPR system contains a switch that alternates radiation from one
antenna to a transmit antenna orthogonal to the first antenna. The receive
antennas are in a crossed-dipole configuration located at the center of the array.
Parallel, perpendicular, and cross polarization data. are received from subsurface
targets from the two orthogonal transmit antennas.
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Geophysics And The Solvents-In-Groundwater Program
By J.D. RedmanThe University of Waterloo has an active research program studying the application of geophysical methods
to subsurface contaminant detection and delineation. As part of the Solvents-in-Groundwater Program, the
focus of our recent research efforts has been on the class of contaminants referred to as dense nonaqueous
liquids (DNAPLs).
During the past two years, we have perfomed geophysical monitoring of controlled DNAPL spills in a natural
sandy aquifer. The aquifer was isolated from the surrounding environment by steel sheet-pile walls driven
into an underlying aquitard.
The geophysical monitoring of the first injection of 231 litres of DNAPL into a 3m x 3m x 3.5m deep cell
consisted of in situ dielectric permittivity monitoring, ground penetrating radar(GPR) and in situ resistivity
measurements. All of these techniques detected changes in the measured physical properties during and
following the injection. The GPR monitoring was limited in scope and the data quality, as expected, was
affected adversely by the small size of the cell and the numerous metallic monitoring devices installed in the cell.
The experience gained during this first injection experiment was applied to the methodology used for
extensive geophysical monitoring in the much larger 9m x 9m x 3.3m cell. In this cell, 770 litres of DNAPL
were injected, and monitoring was performed using neutron, den&y, and induction logging, borehole radar,
surface GPR, and in situ resistivity and dielectric permittivii devices. Most of the geophysical methods
successfully monitored the migration of the DNAPL during and following the injection.
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Effects Of Acquisition System Parameters On Refraction Survey Data
Authors T. Kanemori, Finn B. Michelsen and John H. MimsThe seismic refraction method is ideal for a variety of applications where large
features that are characterized by an abrupt increase of the seismic velocity need to be
delineated, such as the depth to the water table or the depth to basement rock. Over the
years, the techniques used to acquire and process seismic refraction data have changed
slowly. Most of the current techniques used for refraction processing were developed from
the late 1930’s to the early 1960’s (e.g., Hagiwara and Omote, 1939; Hagedoorn, 1959;
Hawkins, 1961). The most recent advance in seismic refraction processing, the Generalized
Reciprocal Method, was first published in 1980 (Palmer, 1980). Since the early 1970’s,
computer programs have been developed to facilitate processing of seismic refraction data
(e.g., Scott and Markiewicz, 1990). Most of these programs have merely changed the
processing platform from drafting boards to computer monitors with little modification to
the processing procedures.
The most recent developments for the refraction method have involved the data
acquisition systems. Features such as analog and digital filtering, IFP, and automatic gain
setting have become standard on many seismic data acquisition systems. These features
have made recording systems easier to operate and the recorded seismic traces appear to
be more robust. The results of theoretical calculations, numerical model studies, and field
tests, however, demonstrate the need to fully understand how changes to the acquisition
system settings affect the first break signal.
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Geophysical Investigation And Characterization With Usrads
Authors C.R. Flynn, M.S. Blair and J.E. NyquistThis paper describes two recent case histories in which commercially available geophysical
instruments were used with an innovative tracking and mapping system called USRADS
(UltraSonic Ranging And Data System) that automates data location and collection. USRADS uses
ultrasonics to provide real-time surveyor positioning and radio links to transmit the surveyor data
to an on-site computer for storage and real-time display. USRADS uses a standard 386 computer
for data collection and includes real-time color display of the findings. It also includes numerous
analysis and display formats for on-site, as well as utilities to facilitate post-process analysis of the
findings.
The objective of one project was to locate several suspect waste disposal trenches and to map their
boundaries. The second was to locate and map the presence of subsurface unexploded ordinance
(UXO) at a suspect artillery impact area. A Geonics EM31 terrain conductivity meter interfaced to
USRADS was used to map the suspect trenches. A Schonstedt GA-52C magnetometer interfaced
to USRADS was used to map the subsurface UXO. Correlation of findings to known site features
and additional knowledge about the sites indicates that these efforts did locate and map the
geophysical features including the suspect waste trenches and the subsurface UXO. Images of the
findings generated on-site and during post-processing are included.
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Geophysical Techniques For Characterizing Shallow Velocity-Attenuation Models
Authors G.I. Al-Eqabi and R.B. HerrmannKnowledge of seismic shear wave velocity and Q is required for both seismic
hazard analysis and the siting of critical structures since these parameters govern
the transmission of the seismic signal from the earthquake to the site and also
control the site response itself. These parameters vary spatially and may not be
readily available. The purpose of this paper is to show how these can be
estimated using surface-wave analysis techniques.
Data from USGS refraction surveys in Maine were selected which show dispersed
short-period Rg waves (fundamental mode Rayleigh waves). Processing techniques
applied to the data include filtering, waveform inversion of selected trace,
phase velocity stacking, interactive amplitude processing, inversion of dispersion
parameters for a layered shear-wave velocity and Q model, and finally verifying
the derived velocity-attenuation models by comparing both shape, absoluteamplitude
and arrival times of synthetic and observed time series. The resultant
velocity models show that the shear-wave velocity varies between 2.43-2.81
km/set for surface layer and Qp is less than 50 in the upper kilometer of the
metamorphic terrain of Maine. The models correlate with the type of geologic
rocks encountered. While the study focused on upper crustal structure, the techniques
and experimental procedure can be used for shallow site characterization
by appropriate scaling of the data acquisition.
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Shallow Reflection Seismics Using Firecrackers As The Source
Authors Chien-Ying Wang, Deng-Bo Chen and Dao-Tze TsaiDue to the high resolution requirement of shallow reflection seismics, a
firecracker source was invented to generate high frequency signals used in
studying shall ow structures. Except for a slightly lower energy level, the
firecracker source has proved to be efficient, portable, cheap and safe. Its
performance was satisfactory. In this paper, a field test in a good
reflection area was conducted to exhibit high frequency signals among the
massive noises of groundroll when delineating the underground layers. By
setting the geophones at the near as well as the far offset distances, we
obtain different but compatible seismic profiles which could provide us with
different structural details. Careful and properly adjusted field procedure
has always been a key factor for successful shallow seismic reflection studies.
The other purpose of this paper is to use the firecracker source for
investigation of near-surface faults whose locations are only grossly known.
Three seismic lines, one used in detecting the Hsincheng fault and the other
two the Shihtan fault, were shot. They all resul,t in good reflection images
illustrating the structural variation across the fault. This kind of
near-surface fault mapping provides very detailed information about the
fault and the structure, which can be used to understand the faulting
processes during the earthquake. It is believed that the developed technique
could work equally well for other engineering applications. On account of
the outstanding achievements of firecracker source, we may expect a wider
acceptance of this powerful method for shallow structure studies in the future.
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Surface And Borehole Radar Monitoring Of A Dnapl Spill In 3D Versus Frequency, Look Angle And Time
Authors K.A. Sander, G.R. Olhoeft and J.E. LuciusAs part of the University of Waterloo continuing experiments at Canadian Forces
Base Borden (CFB), a controlled spill of perchloroethylene, a dense nonaqueous phase
liquid (DNAPL), was monitored by a variety of geophysical methods. Surface ground
penetrating radar (GPR) at 300,500, and 900 MHz and hole-to-hole GPR at 160 MHz were
periodically measured at the site for 340 hours. This report presents the results of the first
66 hours of 500 MHz surface data and an example of the 900 MHz data at 14 hours. The
surface data were acquired on a one meter grid in both directions across a nine meter by
nine meter experimental cell. The borehole radar data were acquired between 8 wells
circling the spill point on a 3 meter radius, using all 28 combinations of non-repeating holeto-
hole pairs, each at 14 different depths in the cell at 25 cm intervals. The resulting multidimensional
(x, y, z, time, frequency, look angle) dataset clearly outlines the movement of
the DNAPL horizontally and vertically, and the interactions of the DNAPL with the
heterogeneous sand matrix. Subtle changes in grain size distribution and the resultant
capillary forces in the sand caused the DNAPL to spend more time and distance in
horizontal travel than vertical travel.
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A Summary Of Methods For Locating And Mapping Fractures And Cavities With Emphasis On Geophysical Methods
Authors Richard C. Benson and Lynn YuhrAssessing the existence, location and mapping of geologic anomalies, such as fractures, cavities within soil
and rock are common to both engineering and hydrologic project needs. Spatial considerations of such a
site characterization must address the detection probabilities involved by using boreholes alone. Spatial
considerations must also include the characteristic dimensions of the fracture/cavity system, including
size, depth and perkxlicity and an appreciation of methods other than drilling to improve the probability of
detection.
A summary of the common methods available for fracture and cavity detection mapping (non-geophysical
as well as geophysical) are presented along with their spatial sampling and limitations. The remote sensing
and geophysical methods are but a small part of this list. However, they include some of the most effective
methods for fracture and cavity detection and mapping. They cover the complete range of spatial
sampling, from regional to no more than the localized borehole wall. The airborne, remote sensing,
surface, and downhole geophysical methods along with methods that can be used on water covered areas
are identified along with their spatial sampling capabilities. An understanding of the tools available and
their spatial sampling limitations are a necessary part of planning and carrying out an effective
fracture/cavity investigation.
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Fracture Detection With Sellsmlc Crosshole Tomography For Solution Control In A Stope
Authors James A. Jessop, Michael J. Friedel, Michael J. Jackson and Daryl R. TweetonAs part an environmental assessment for the application of in situ leaching in an
underground mine, the U.S. Bureau of Mines conducted a seismic crosshole tomographic
investigation at the Colorado School of Mines experimental mine near Idaho Springs, CO.
Seismic tomography was used to detect fractured regions as part of an investigation aimed at
providing information that will help mining companies control solution during stope leaching.
Whole waveform data provided both direct P-wave and S-wave traveltimes for input to the
Bureau’s curved ray tomography program MIGRATOM, based on Huygens’ principle of
wavefront propagation.
The heterogeneous velocity distribution observed is attributed to the presence of both
natural and blast induced fractures. The effectiveness of the tomographic method was
corroborated by noting that low velocity zones occurred where water was lost in boreholes.
The pre- and post-blast P-wave tomograms showed similar velocity distributions. This
similarity in velocity tomograms suggests that the blast energy was contained resulting in
minimal extension of existing fractures. Where changes in velocity were observed, they
correlated to either natural fractures or blast induced damage. Tomograms also were
produced showing the variation in dynamic elastic properties, including Poisson’s ratio,
Young’s, shear, and bulk moduli. Such dynamic elastic properties assist in solving
engineering problems associated with deformation, stability and blast design.
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The Relationship Between Lineaments And Fractures In Chad Basin
Authors Solomon A. Islorho, Karen S. Taylor-When and Tom. O. NkereuwemOne of the problems facing drought stricken parts of the world is the location of potable
sources of water. The apparent increase in global temperature is also of great concern in
those areas that are thirsty and as a result any available source of water needs to be
monitored and understood for management purposes. Recent studies in the drought striken
Sahel region (especially Chad Basin) indicate the presence of fractures within and near
Lake Chad. This paper looks at the use of geophysics to determine a fracture near the lake
shore and how this might be related to geochemical water quality of the region.
In the summer of 1991, a transect twenty kilometers in length was chosen perpendicular
to a lineament that was inferred from Landsat images. This was mapped using electrical
resistivity method (using Strata Scout and ABEM Terrameter) that utilized both the
Wenner and Schlumberger arrays for both sounding and profiling. The profile shows a
number of minor anomalies with a major anomaly that corresponds to the fracture that
was mapped from the Landsat images. There is no topographic feature that corresponds to
the anomaly or lineament in the field. Water samples were also collected in the field to see
the influence of the fracture on the water quality of the region.
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The Application Of Shallow Geothermal Exploration Methods To Detect High Permeability Features In Groundwater Flow Systems
By John JansenAn exploration method using shallow soil temperature
measurements as an exploration tool to find permeable bodies at
depth in an impermeable matrix is described. The depth of seasonal
soil temperature variation is discussed. A method of measuring
soil temperatures below the depth of seasonal variation is
described. Simple finite difference modeling techniques to predict
thermal anomaly characteristics are presented. Case histories are
presented which demonstrate the application of the method for
groundwater.
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Integrated Geophysical Studies Over Buried Valleys
Authors Paul J. Wolfe and Benjamin H. RichardIntegrated geophysical studies of four buried valleys have been completed in
Southwestern Ohio’. All of the areas have been overridden by two or more Pleistocene
glaciers and each valley contains sequences of till, outwash, and lacustrine deposits. This
paper summarizes the results of those studies and proposes a strategy for shallow geophysical
investigations in glaciated areas. The techniques used in the integrated studies were gravity,
magnetics, resistivity, ground penetrating radar, seismic refraction, and seismic reflection.
Certain combinations of geophysical techniques can be most cost effective but it is
important to clearly define the goals of the study and to understand the existing field
conditions before designing the geophysical survey. If only general depth to water table and
bedrock are needed and there is essentially no cultural development in the area, electrical
methods are inexpensive and fast. If there is no clay and the groundwater is low in mineral
content, then ground penetrating radar can be quick and inexpensive.
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Cokriging Surface Elevation And Seismic Refraction Data For Bedrock Topography
Authors J.E. Nyquist, W.E. Doll, R.K. Davis and R.A. HopkinsAnalysis of seismic refraction data collected at a proposed site of the Advanced Neutron Source
(ANS) Facility showed a strong correlation between surface and bedrock topography. By combining
seismically determined bedrock elevation data with surface elevation data using cokriging, we were
able to significantly improve our map of bedrock topography without collecting additional seismic data.
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Seismic Reflectlon/F?Efractlon Survey To Characterize The Subsurface At An Npl Site In The Mojave Desert
More LessIn July and August 1991, a seismic reflection and refraction survey was performed at the Marine Corps
Logistic Base (MCLB) in Barstow, California. The purpose of the survey was to determine the
configuration of: 1) bedrock, 2) the water table, 3) confining layers, and to precisely locate faults; mostly
the Waterman, that may affect contaminant pathways.
The site is on the National Priority List (NPL) with known contamination from solvents and petroleum
hydrocarbons. The MCLB is located within an alluvial basin in the Mojave block, a large wedge shaped
fault block bounded by the San Andreas and Garlock Faults.
The seismic survey was performed in support of the Remedial Investigation/Feasibility Study being
conducted by the Navy. it was designed to be innovative in response to the depth and nature of various
geologic formations, especially in light of difficufties experienced in collecting data in this desert region.
The Bison Model 9048 seismograph was used to record data generated by the Bison Elastic Wave
Generator Ill. The data was processed by using Seistrix 2386 for reflection and Firstpix and Gremix for
refraction. A split-spread array allowed for the extraction of both CDP reflection data and forward and
reverse refraction data. A total of ten miles of data were shot within a ten day period. Vertical seismic
profiling (VSP) was performed in four wells to assist in interpreting the surface information.
Combining data from the two techniques suggest that there is a mounding of water at the en echelon
faults which cut across the highlands into the alluvium. Faults not only displace the bedrocks but,
extend into sediments near the surface. The seismic survey provided a picture of the subsurface which
will assist in planning future work.
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Geophysical Detection Of Hydrocarewn And Organic Chemical Contamination
More LessUnambiguous detection of hydrocarbon and organic contamination is the most
difficult task for noninvasive geophysical methods at hazardous waste sites. The difficulty is
two-fold: 1) the low level of geophysical contrast that these contaminants provide against the
background soil and rock, and 2) the low level of contaminant concentration considered to
be of regulatory concern. Yet, electrical and electromagnetic methods can sometimes
detect some hydrocarbon and organic contaminants. The important questions are what
levels of contamination can be reliably detected and where? The most important
consideration in answering these questions is the level of interaction that occurs between the
contaminating chemical and the host matrix materials. The most obvious of contaminants
are those which either are insoluble in water or which chemically react with clay minerals.
The best understood examples are tetrachlorethene (common dry cleaning solvent) and
toluene (common industrial solvent and principle component in gasoline). Both have low
solubility in water, high electrical resistivity and low dielectric permittivity. Thus, both are
visible to ground penetrating radar (though toluene floats on the water table while
tetrachlorethene sinks). Toluene is also catalyzed on the surface of montmorillonite to
polymerize into bibenzyl, and the electrochemistry of the polymerization reaction is
observable with the complex resistivity technique. Some organic contaminants such as
alcohols, which dissolve in water, are essentially without geophysical trace. In between are
interactions such as insoluble lenses floating on the water table, suppression of the capillary
fringe, change in soil wetting, interference with cation exchange, and others, such as a
change in the background geological noise statistics, that sometimes produce a detectable
geophysical signature. Few geophysical signatures are unique indicators of hydrocarbon or
organic chemical contaminants, but repeated measurements with time can often detect the
movement of contaminant fluids, more uniquely indicating their presence. No hydrocarbon
or organic chemical contaminant produces a geophysical contrast that is observable at the
parts-per-billion concentration level of regulatory concern. Even when the contaminant
itself produces no detectable direct geophysical signature, sometimes it may be found by
indirect means through the use of geophysical mapping and characterization of
geohydrological heterogeneity as a guide to drilling likely traps of the contaminant.
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Site Studies Of Ground Penetrating Radar For Monitoring Petroleum Product Contaminants
Authors Jeffrey J. Daniels, Roger Roberts and Mark VendlGround penetrating radar (GPR) provides a possible means of mapping
hydrocarbons in the vadose zone. Results of controlled surveys in a sand test pit
at The Ohio State University demonstrate conclusively that there is a clear high
amplitude GPR anomaly over plastic containers containing diesel fuel and
containers containing the host sand material saturated with diesel fuel.
Results of surveys at a site in Northern Indiana show a correlation between the
decrease of the GPR signal amplitude in the vicinity of the gasoline concentration
and the presence of gasoline. A decreased amplitude of the GPR signal is
present in the capillary fringe region above the water table at this site, suggesting
that vapor-phase hydrocarbons may affect the propagation of the
electromagnetic wave. Possible explanations for the observed high amplitude
reflections over the confined hydrocarbons in the test pit and the low amplitudes
in the field include: 1) the hydrocarbon product may be contained in small
dispersed concentrations in the vadose zone, or 2) the hydrocarbon product may
have a high loss tangent. Small dispersed concentrations of hydrocarbon
product above the water table cotild cause reflecting and diffracting boundaries,
resulting in many small isolated anomalies on a GPR record. A high loss tangent
for the hydrocarbon product could help to explain both the observed decrease in
amplitude for the electromagnetic wave propagating through the capillary fringe,
and the high amplitude reflections from the saturated hydrocarbons.
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Monltorlng A Controlled Injectlon Of Perchloroethylene In A Sandy Aquifer With Ground Penetrating Radar And Time Domain Reflectometry
Authors M.L. Brewster, J.D. Redman and A.P. AnnanA controlled injection of perchloroethylene (PCE) into a sandy aquifer was undertaken to investigate the
effectiveness of ground penetrating radar (GPR) and time domain reflectometry (TDR) for monitoring and
detecting the subsurface migration of organic solvents.
Surveys were performed at regular intervals during the 70 hour injection and for 38 days following the
injection. Background (pre-injection) surveys were conducted to assist in the discrimination between features
caused by PCE and those due to natural geologic variability.
PCE was chosen because it is a typical member of a class of groundwater contaminants known as dense
non-aqueous phase liquids or DNAPLs. Similar to other DNAPLs, PCE has a low dielectric permittivity relative
to pore water, therefore PCE saturated soils can be expected to have higher radar velocities.
Time domain reflectometry probes were used to measure vertical profiles of in situ dielectric permittiiity.
Decreases in dielectric permittiiity of up to 50% were observed where PCE had pooled on low permeability
lenses.
Initially, GPR reflection events were detected from pooling of the DNAPL on low permeability horizons at 1 m
depth. At later times pools were observed on successively deeper horizons. Velocity pullup of the underlying
aquitard event was also observed.
GPR and TDR provide effective methods for monitoring the progress of PCE migration in a saturated sandy
aquifer. Reflections and dielectric contrasts from PCE pools are of such a high magnitude that they may
often be distinguishable from geology without the benefii of background data. Wiih background data, zones
of residual level PCE saturations are resolvable with GPR and TDR.
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Geophysical Detection Of Perchloroethylene In A Sandy Aquifer Using Resistivity And Nuclear Logging Techniques
Authors George W. Schneider and John P. GreenhouseAs part of a larger programme to understand the behaviour of dense non-aqueous phase
liquids (DNAPLs) in the subsurface (Redman, 1992), a controlled release of 770 litres of
perchloroethylene (PCE) into a 9 by 9 metre cell within a sandy aquifer was monitored
geophysically during the summer of 1991. Surface and in situ resistivity, terrain conductivity
and neutron, induction, and density logging data were collected over a period of several weeks
to document the movement of the PCE away from the point of injection towards its final resting
place in pools on confining layers within the cell.
The very high resistivity of the PCE in its liquid state makes it a target for resistivity,
induction logging and terrain conductivity methods. Its high density, low hydrogen and high
chlorine content make it a good target, in principle, for density and neutron logs. For resistivity
measurements, two specifically designed in situ probes were installed one metre on either side
of the injection point. Two surface arrays were used to monitor apparent resistivity across the
diagonals of the cell. A resistivity scanning system was developed to ensure rapid acquisition
of surface and probe resistivity data. The density, neutron and induction logs were performed
on a regular basis in nine PVC-cased boreholes arranged on a 3 metre radius circle around the
injection point. In all cases, extensive background measurements were made.
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Use Of Resistivity Monitoring Systems To Detect Leaks From Storage Ponds
Authors Gregory P. Van, Stephen K. Park and Patrick HamiltonA resistivity monitoring system was installed beneath and around a fifty-five acre
evaporation pond at the Mohave Generating Station in Laughlin, Nevada. The system was
installed to detect leakage of brine from the pond. The system consists of sixty-three
electrodes which are placed in a 7 by 9 grid using a go-meter spacing.
The feasibility of using this monitoring system was demonstrated by a scaled-down field test.
This field test determined that distinct measurable changes in resistivity occur in response
to the influx of water into the vadose zone. A direct correlation of increases in measured
voltages relative to the amount of water put into the ground was observed. Threedimensional
numerical modeling of the leak, using a finite-difference code, confirmed that
the changes observed in the field test were due to the influx of water.
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Risk Assessment Of A Landfill Using Soil Gas Survey
More LessThe soil gas survey technique was applied at a codisposal facility to define the direction
and extent of a contaminated soil gas plume. A typical soil gas probe assembly was used to
collect soil gas samples from approximately 2.5 feet below the ground surface. Photovac lOS50
portable gas chromatographs (GC) were used for field analysis of approximately 120 samples
during three sampling events. In addition, air samples were taken from the landfill surface. Each
sample was analyzed for five target volatile organic compounds (VOCs): vinyl chloride 0/C),
1,l -dichloroethene (1,l -DCE), trichloroethene (TCE), tetrachloroethene (PCE), and benzene. The
main criterion for selecting these compounds was their level of toxicity.
The similarity of the soil gas contaminants to those measured at the landfill surface (flux
box) indicates that landfill air emissions may be a primary source for the compounds identified in
the soil gas. Potentially, the presence of a polyvinyl chloride (PVC) cap over the municipal/
industrial landfill could be forcing landfill gas out of the perimeter of the landfill into the adjacent
soil. Large amounts of landfill-generated methane may create a significant pressure gradient in the
landfill and cause a vapor phase plume to migrate in the direction of lower pressure off the landfill.
Soil gas is further considered to be a source of contamination for ambient air above ground.
An advective transport model was used to predict the concentrations of contaminants in air.
Ambient air monitoring results showed a good correlation with the values predicted by the models.
Traditionally, the soil gas survey technique is used to define the direction and extent of
contamination in soil and groundwater. In the present study, this technique was used innovatively
to define the soil gas plume and then for risk assessment purposes via the air-vapor pathway.
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