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25th Symposium on the Application of Geophpysics to Engineering & Environmental Problems
- Conference date: 25 Mar 2012 - 29 Mar 2012
- Location: Tucson, USA
- Published: 25 March 2012
1 - 100 of 195 results
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Application of Ground Penetrating Radar and Electrical Resistivity Techniques for Subsurface Stratigraphic Mapping in Southwestern Nigeria
Authors O. Fayemi and A.A. AdepelumiThe frequent building collapses in Nigeria have been attributed to lack of pre-construction investigations that will assist engineers obtain in-situ geotechnical information and the structural subsurface settings are often ignored; and when done, it is haphazardly. To address this issue and demonstrate the importance of such survey, a combined Ground Penetrating Radar (GPR) and Vertical Electrical Sounding (VES) data was acquired in a part of Southwestern Nigeria. A 200 MHz antenna was used for the data acquisition along four traverses. The data were subjected to standard GPR processing techniques, and attributes analyses such as instantaneous-frequency, amplitude and phase. Also, for comparative and engineering characterization purposes, longitudinal conductance and coefficient of anisotropy were computed from the VES results and used for determining the competency of the bedrock. From the GPR results, it was observed that the subsurface mapped is characterized by an erosional truncated, low angle, southerly dipping, tangential reflections. Further, stratified rocks dipping at an angle of 32º occurs between 1.0 to 4.5 m depth in all the GPR sections; these strata were truncated by topsoil at shallow depths. Also, some of the sections depict ancient channel structures that have a dimension of 70 m by 40m. The resistivity data suggest that the study area is characterized by four distinct geoelectric sequences. These sequences are comprised of topsoil, which is composed of clayey-sand to lateritic clay whose thickness ranges between 0.25 m – 8.12 m; weathered bedrock with a thickness of 3.84mto 12.61m; stratified bedrock with a thickness ranging between 0.33m – 7.51m and the fresh bedrock. These results reveal that the study area is characterized by a complex subsurface geology. The area has low to moderate longitudinal conductance and anisotropy coefficient values which suggest that incompetent to semi-competent bedrock exists beneath the subsurface. A good correlation between the GPR and resistivity derived thicknesses was established.
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Geophysical and Geotechnical Features of the Levee Systems Damaged by the East Japan Earthquake
By T. InazakiLevee systems in Kanto Region, central Japan, were severely damaged at many places caused by the long-lasting strong ground motion of the magnitude (Mw) 9.0 East Japan Earthquake, which occurred at 05:46 UTC on Friday, 2011 March 11, even located more than 400 km far from the epicenter. Since 2005, we have conducted integrated geophysical surveying for the safety assessment of levee systems at 39 actual levee sites in Japan. Among them, severe damage took place in two sites by the East Japan Earthquake just at the anomaly part delineated by the survey. The anomaly part in one site was characterized as low S-wave velocity and low resistivity both for levee body and substrata. After the earthquake, we conducted comparative surveying on the same levee but the damaged part of which had been soon repaired. As a result, the characteristic low S-wave velocity and low resistivity zone was again identified just at the damaged or repaired part where substantial top subsidence had occurred. This suggests a physical model that nonlinear loosening of underlying clay layers had caused the ground failure and resulted in the damage of levee systems. The other site, where large sliding had taken place on a levee slope during the earthquake attack, was featured by the existence of high resistivity anomaly in the levee body. The anomaly was also identified by the comparative surveying at the same part in the line where the slope sliding had occurred. A different type of levee failure mechanism was interpreted as resulting from high contrast of physical properties in levee body, based on our integrated geophysical surveys. Thus the corresponding survey results lead us to the usefulness of the integrated geophysical surveying for understanding levee failure mechanism and for the assessment of present conditions of levee systems attacked by the earthquake.
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MAPPING FRACTURES IN VERTICAL ROCK CUTS USING A 400 MHZ GROUND PENETRATING RADAR ANTENNA
Authors Adnan Aqeel, Norbert Maerz and Neil AndersonParallel to sub-parallel hidden discontinuities to the slope face of a sandstone bedrock were effectively mapped at four different stations in central Missouri using a continuous-distance-mode ground penetrating radar system equipped with a 400 MHz monostatic antenna. At each station, a suite of 2-D ground penetrating radar profiles were acquired along multiple closely spaced traverses. A small wheel was appropriately and significantly attached to the used antenna to fit with the distance mode that was used in our GPR common offset survey. The exposed rock surfaces were relatively smooth which help to place directly the used attached-wheel 400 MHz antenna on the slope face of the bedrock and record the data effectively.
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NUMERICAL MODELING TO ASSESS THE IMPACT OF POSITIONAL ERRORS DURING THE ACQUISITION OF WATERBORNE CONTINUOUS RESISTIVITY MEASUREMENTS
Authors Brad Hansen and Adam PidliseckyWaterborne continuous resistivity profiling (WCRP) permits rapid collection of direct current (DC) resistivity data over water by means of towing a multi-electrode cable streamer behind a moving vessel. During WCRP electrical current is injected using a pair of electrodes, while multiple potential measurements are made using other pairs of electrodes. This acquisition results in a near continuous profile of measured resistances along the survey path. These data are then processed/inverted to produce a 2.5D resistivity model, which can be used to interpret physical subsurface properties (i.e. lithology, and pore fluid conductivity).
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MONITORING SALT REMEDIATION BY INTEGRATING 3D ELECTRICAL RESISTIVITY TOMOGRAPHY AND POINT CHEMISTRY SAMPLING USING KRIGING WITH LOCAL VARYING MEAN
Authors Franklin Head, Laurence Bentley and Michael CallaghanSalt-affected soils are a common problem for the hydrocarbon industry. A remedial tile drain system was installed at a former oil and gas production facility to collect saline leachate and route it for disposal. Our objective is to evaluate the effectiveness of irrigation during a salt flushing experiment within a 20 by 20 m test plot.
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THREE-DIMENSIONAL RESISTIVITY IMAGING FOR DETERMINATION OF AIR-FILLED PORE SPACE IN THE DESIGN OF GROUNDWATER AIR SPARGING SYSTEMS
Authors Boyce Clark, Mark Klemmer and Bill ZahniserTypical methodologies for determining well spacing in groundwater air sparge systems, such as water table response, dissolved oxygen measurements, and conservative gaseous tracers have been known to give semi-quantitative estimates of the radius of influence. Placement of observation wells that intersect established air channels can lead to data that are very different than wells that do not intersect, while two such wells could be located only a short distance apart. Non-invasive geophysical methods such as electrical resistivity (ER) can provide more detailed data over a larger area, alleviating the data density issues associated with typical test methods. Data are presented from two sites with existing air sparge systems that were not performing to expectations, ER surveys were conducted to evaluate the air-filled pore space induced by the operating air sparge wells. The air sparge systems were turned off in advance for a baseline survey with no air-filled pore space. Multiple repeat surveys were then collected at progressively increasing air flow rates to evaluate differences in radius of influence or volume of air-filled pore space. An increasing area of resistivity values during air sparging at an increased flow rate is attributed to pore-water displacement by injected air, resulting in decreased relative electrical conductivity. This conclusion is supported by direct measurments at various observation wells of dissolved oxygen concentration and changes in depth to water.
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3-D GPR IMAGING ON DIFFICULT TERRAIN: EXAMPLES FROM THE PYRAMID COMPLEX OF PHARAOH SENWOSRET III AND THE THEBAN TEMPLE OF FEMALE PHARAOH TAUSRET (EGYPT)
Authors Douglas Sassen, Lawrence Berkeley and Pearce Paul CreasmanMany of the undisturbed areas of ancient Egyptian temples and pyramid complexes are situated in locations of adverse terrain, inhibiting archaeological excavation. Ground-penetrating radar (GPR) imaging of these difficult terrains can provide archaeologists with insights otherwise only available from excessively expensive or dangerous excavations. GPR imaging algorithms used on data from these terrains must allow for uneven sampling grids and missing traces, while compensating for surface topography and antenna patterns. We introduce an adaption to the Kirchoff topographic migration method that includes compensation for antenna patterns through a heuristic solution to the total field pattern of an antenna over a half space. The compensation of the antenna pattern is based on a stable inverse weighting of the total field pattern from numerical and analytical solutions. We also discuss surveying and interpolating surface topography, calculation of surface normals, pre- and post-processing of the data, attribute extraction, and other concerns for conducting successful remote sensing in Egypt. Examples of the application of this method include surveys from the Middle Kingdom pyramid complex of pharaoh Senwosret the III at Dahshur (ca. 1850 BC), and the New Kingdom Theban temple complex of the female pharaoh Queen Tausret (ca. 1180 BC), West Bank, Luxor, Egypt.
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MAPPING SUBSURFACE CAVITIES AND FRACTURES USING INTEGRATED SURFACE AND BOREHOLE GEOPHYSICS NEAR A SUPERFUND SITE SOUTH OF ROCKFORD, ILLINOIS
Authors Ryan Adams and Phillip CarpenterThe ACME Superfund site is one of many Superfund sites in Northern Illinois. This 20 acre (8.1 ha) site was contaminated by various volatile organic compounds (VOC’s) and heavy metals during the 1960-1980s. These contaminants have seeped into the Wise Lake dolomite (Galena Group) and contaminated local ground water supplies. The field site is located immediately south and hydrologically downgradient of the ACME site, where up to 10 m of unconsolidated sediments overlie the fractured and karstic Wise Lake Formation in a small valley adjacent to residential wells.
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FACILITATING LONG-TERM OUTBACK WATER SOLUTIONS (FLOWS) IN SOUTH AUSTRALIA: THE ROLE OF AIRBORNE GEOPHYSICS
By Tim MundayMining and energy development in South Australia’s far north is set to have significant consequences for the water resources of the region. These sectors generate significant economic value to the State and their support remains a priority for the government. The scale of the planned developments and the potential from current exploration programs facilitated by the South Australian Government through the Plan for Accelerated Exploration (PACE) Program will result in a substantial increase in infrastructure requirements, including access to water resources and Aboriginal lands for exploration and potential mine developments. Increased demand for water and in particular groundwater is compromised by the limited knowledge we have about these resources. This includes information about their character, variability, sustainability and their relationship to environmental and cultural assets, which is most notable in the priority areas for development. There is a recognised need to develop this knowledge so that water is not a limiting factor to development.
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ASSESSING CULTURAL (ELECTRICAL) INTERFERENCE OF DEEP WENNER RESISTIVITY SOUNDINGS AT FLOOD CONTROL STRUCTURES (DAMS) FOR SUBSIDENCE HAZARD STUDIES IN THE DESERT SOUTHWEST
Authors Michael Rucker and Sean HulburtFlood control structures (FRS) or dams in the desert southwest are commonly located at the margins of deep alluvial basins that are subject to groundwater pumping-induced subsidence. Safety assessment of these facilities includes characterizing the existing or potential future hazard to these structures due to subsidence. Differential subsidence can lead to changes in surface hydrology and flood storage capacity, and possible earth fissuring that could cause cracking in an FRS or its’ foundation, resulting in possible piping erosion failure of the FRS during a flood event. Resistivity is an excellent reconnaissance tool to assess compressible basin alluvium that is prone to subsidence. However, with typical water table depths of 30 to over 100 meters, and potential bedrock depths underlying alluvium ranging from 0 to over 300 meters, resistivity soundings require large arrays. The authors use array electrode a spacing up to 300 meters for this work.
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THE DARDADINE PALAEOCHANNEL PROJECT: USING AIRBORNE GEOPHYSICS TO SUPPORT REGIONAL COMMUNITIES IN WESTERN AUSTRALIA
Authors Tim Munday and Jasmine RutherfordHydrogeological investigations in the early 1990s confirmed that the West Arthur Shire in Western Australia’s south west contained the remnants of an ancient palaeodrainage system. Drilling revealed the presence of palaeochannel sediments, containing groundwater that has since been used to develop and support regional town water supplies and local farm water systems. Airborne electromagnetic (AEM) data have been employed to better define the location of these palaeovalleys and the quality of the contained groundwater. In this paper we describe the results from one such survey, which used the SkyTEM TDEM system to accurately locate and characterise aquifers within the Dardadine palaeochannel located near the town of Darkan. The aim of the survey was to identify the location of the palaeochannel, the thickness and width of palaeochannel sand aquifer and to generate a water resource (groundwater quality) map. A secondary, but equally important objective (from a management perspective) was to better understand the connection between aquifers developed in the regolith adjacent to the palaeochannel.
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EARTH’S FIELD NMR FOR REMOTE DETECTION OF OIL UNDER ARCTIC SEA-ICE
Authors Eiichi Fukushima, Andrew McDowell and Stephen AltobelliRemote detection techniques of accidental oil spills under ice are needed to support oil spill response in the Arctic. The various techniques tried so far have not been fully satisfactory. We present preliminary considerations of Earth’s field NMR (EFNMR) from the ice surface for this purpose.
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Uncertainty in Near-Surface Refraction Seismology
By D. PalmerUncertainty in the tomographic inversion of near-surface seismic refraction data can be separated into aleatory variability, which describes the misfit errors and epistemic uncertainty, which describes the suite of acceptable models. Common default implementations of refraction tomography usually focus on reducing aleatory variability and frequently disregard epistemic uncertainty. In this study, the tomograms generated with three models of the seismic velocities in both the weathering and in the sub-weathering, using the generalized reciprocal method (GRM), are consistent with the traveltime data. However, only one tomogram is consistent with the optimum XY value and the attributes derived from the head wave amplitudes and seismic velocities. This study demonstrates that epistemic uncertainty can be explicitly addressed with the GRM, because the most probable tomogram can be selected objectively from a number of acceptable alternatives. The GRM-based tomogram successfully detects, defines and differentiates narrow regions with low seismic velocities which represent shear zones and a massive sulfide ore body. None of these zones is detected with the tomogram generated with the default starting model consisting of smooth vertical velocity gradients. It is concluded that minimizing epistemic uncertainty through the use of the most appropriate starting model is more important than minimizing aleatory variability.
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COMBINING FREQUENCY-DEPENDENT TRAVELTIME TOMOGRAPHY AND FREQUENCY-DOMAIN WAVEFORM TOMOGRAPHY FOR NEAR-SURFACE SEISMIC REFRACTION DATA
Authors Colin Zelt, Jianxiong Chen and Priyank JaiswalSeismic refraction surveys and tomographic methods are commonly used to characterize the near-surface. The advantage of traveltime tomography is its robustness because it uses only traveltimes. Its disadvantage is that it provides relatively low spatial resolution velocity models. The advantage of waveform tomography is its ability to provide high-resolution models. The disadvantage of waveform tomography is its strong dependence on an accurate starting model since it is a very nonlinear inverse problem. The spatial resolution of traveltimes data is related to the Fresnel zone, which can be very wide, whereas for waveform data it is related to the seismic wavelength, typically a smaller length scale by comparison. A new integrated strategy for deriving velocity models from nearsurface seismic refraction data using two complementary tomographic methods is presented.
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FINDING A DEEP BURIED BEDROCK HIGH USING GEOPHYSICS AND REMOTE SENSING AT A FLOOD CONTROL STRUCTURE (DAM) DURING A SUBSIDENCE HAZARD STUDY IN THE DESERT SOUTHWEST
Authors Michael Rucker and Sean HulburtSafety assessment of flood control structures (FRS) or dams located in alluvial basins in the desert southwest commonly includes characterizing the existing or potential future hazard to these structures due to ground pumping-induced subsidence. Differential subsidence can lead to changes in surface hydrology and flood storage capacity, and possible earth fissuring that might cause a piping erosion FRS failure during a flood event. For these studies, the authors typically use deep Wenner array resistivity as a reconnaissance tool to assess compressible basin alluvium and possible relatively shallow (<300 meters depth) bedrock.
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CHARACTERISATION OF BURIED SUBAQUEOUS OUTWASH STRUCTURE BY INTEGRATION OF BOREHOLE AND GEOPHYSICAL DATA
More LessSince 2009, the environment ministry of Quebec (Canada) funded a huge characterization program aiming to improve the knowledge of the groundwater resources throughout the southern part of Quebec. Our research group was mandated to characterize the region of Montérégie Est that covers an area of approximately 9000 km2 at South-East of Montreal. The surveyed area has approximately 577 000 inhabitants, of which 28% use groundwater as a source of supply.
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THE USE OF AIRBORNE EM AS AN AID TO UNDERSTANDING AQUIFERS SYSTEMS IN SOUTH AUSTRALIA’S ARID REGIONS: A CASE STUDY ON THE CAPABILITY OF DIFFERENT SYSTEMS
Authors Yusen Ley-Cooper and Tim MundayThe Musgrave province, located in South Australia’s far north-west, is experiencing accelerated minerals exploration partly in response to new State Government initiatives. Access to water may become a fundamental infrastructure requirement to support developments emerging from these activities. Our current knowledge of the local and regional groundwater systems, the architecture of aquifers, groundwater quality, availability and sustainability is very limited. Current understanding for the area suggests that fractured rock aquifer systems predominate with local palaeovalleys also present. Groundwater is the primary source of water for the indigenous communities and for pastoral purposes. Given its importance for these purposes and given the potential for increased demand, it has been recognised that a more thorough assessment is needed to inform the development of appropriate management policies.
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MOBILE ACOUSTIC SUBSURFACE SENSING (MASS) FOR THE SUBSURFACE PROPERTIES OF PAVEMENTS
Authors Yinghong Cao, Yifeng Lu, Yi Zhang, Gregory McDaniel, Ming Wang and Ralf BirkenSurface waves have been extensively utilized to detect the properties of subsurface materials for geological inspections in many non-destructive testing methods, such as the Spectral Analysis of Surface Waves (SASW) and Multi-channel Analysis of Surface Waves (MASW). In recent years, these stationary measurement methods were also applied to concrete and pavement structures. Most of these implementations are still using contact sensors, such as accelerometers and geophones. The test efficiency is also significantly limited by the conventional inversion algorithms, which were established on the iterative forward analysis with trial solutions. These drawbacks don’t meet the challenges of fast inspection for highway pavements.
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COMPARING SHEAR WAVE VELOCITY MEASUREMENTS FROM MASW AND DOWNHOLE SEISMIC METHODS
Authors Ahmed Ismail, Andrew Stumpf, Neil Anderson and William DeySeismic shear wave velocity profiles were acquired from 10 boreholes in central Illinois and compared to shear wave velocity profiles generated from the multichannel analysis of surface wave (MASW) data acquired at the borehole locations. The main objective was to determine if the shear wave velocity measurements from the MASW are reliable and can be used to characterize the glacial geology in central Illinois. The boreholes penetrated through glacial sediment consisting of multiple units of till, sandy silt, sand and gravel, and silty clay. The downhole data were acquired in PVC-cased holes drilled to depths ranging from 30 to 60 m using a three-component downhole geophone and a surface source. Travel times of the first-arrival seismic waves were analyzed using the direct and interval methods to generate 1-D seismic velocity profiles. The MASW profiles were acquired using 24-channel engineering seismograph with 1.5 m geophone spacing. The data were analyzed to generate 1-D velocity profile at each borehole location. Correlating the velocity profiles from both methods shows that the velocity values compare fairly well and demonstrate that the MASW is a reliable method to measure shear wave velocity of the subsurface materials.
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USE OF ELECTRICAL METHODS TO CHARACTERIZE PREFERENTIAL GROUND WATER FLOW IN ENBANKMENT DAMS
Authors Andre Revil and Abdel JardaniA method is proposed to localize preferential fluid flow pathways in earth dams and embankments based on time-lapse self-potential measurements associated with salt tracer injection upstream. This salt tracer is carried along the ground water flow paths by advection and hydrodynamic dispersion. A network of non-polarizing electrodes located at the ground surface is connected to a highly sensitive voltmeter and used to record the resulting electrical field fluctuations occurring over time at the ground surface. The transport of the salt through the conductive porous materials changes the localized streaming potential coupling coefficient associated with the advective drag of the excess of charge of the pore water and is also responsible for a diffusion current associated with the salinity gradient. Therefore, monitoring of the electrical field at the ground surface can be used to localize a pulse of saline water over time, and to determine its velocity. Possibly in real time This method can be used to track highly localized flow pathways characterized by high permeability that could not be monitored with DC resistivity tomography, which is limited in this regard because of temporal resolution.
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INTERPRETING NUCLEAR MAGNETIC RESONANCE RELAXATION MEASUREMENTS IN UNSATURATED POROUS MEDIA
Authors Sam Falzone and Kristina KeatingNear-surface geophysical applications of nuclear magnetic resonance (NMR) have primarily focused on interpreting NMR measurements under the assumption that the measured volume is fully saturated; however, as NMR is used for a wider set of near surface applications, an improved understanding of NMR measurements of unsaturated porous media will be needed. Our research focuses on using laboratory measurements to understand the relationship between the NMR relaxation time (T- 2) and the water content of unsaturated porous geologic material. A limited number of recent studies have determined how the shape and magnitude of the T2-water content relationship varies with the surface-area-to-volume ratio (S/V) of a porous media. Although it is well known that in fully-saturated porous material T2 is affected by the surface relaxivity (a parameter that quantifies the ability of a pore surface to enhance relaxation) as well as S/V, there have been no studies that explore the effect of surface relaxivity on the T2-water content relationship. We will present results from a laboratory study designed to understand the effect of both surface relaxivity and S/V on the T2-water content relationship.
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UNDERSTANDING THE SPATIOTEMPORAL DISTRIBUTION OF SOIL MOISTURE AT INTERMEDIATE SPATIAL SCALES USING GEOPHYSICAL METHODS
Authors Trenton Franz, Ty Ferre and Marek ZredaThe spatiotemporal distribution of soil moisture is critical for partitioning the water, energy, and carbon cycles at a variety of scales. In drylands, soil moisture is intimately linked to rainfall recycling shown through autocorrelation with future events. In this research, we investigate different soil moisture datasets collected at various scales from the Santa Rita Experimental Range in southern Arizona and Tonzi Ranch in northern California. We will present a series of electromagnetic induction surveys (EMI) that were collected within the footprint of a continuously recording cosmic ray probe (COSMOS). By performing the surveys within a COSMOS footprint we are able to better understand and interpret the information from the less rigorous but data rich EMI surveys. With this spatial information we are able to better understand the controls of topography, texture, and soil depth on the organization of vegetation at the landscape scale. Finally, we are able to quantify the uncertainty and support volume of each instrument through modeling experiments with the goal of obtaining more accurate information about the inferred fluxes.
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Use of Electrical Resistivity Surveying to Evaluate Collapse Potential Related to Road Construction over a Cave
Authors D.W. Lambert, G.L. Adams and B. FodorGeophysical surveying using the electrical resistivity method was used to help determine the potential for collapse that could occur resulting from the construction of a road over a known cave in the City of Kirkwood (City), Missouri. The City is installing a new water main which will require construction of an access road through Koestering Park. Underlying the park is historic Watson Cave, which was mapped in 1961. The width and height of the cave varies and appears to be influenced by the presence of vertical fractures that have been widened by solutioning. The depth to the top of the cave is unknown. Exploration by non-intrusive electrical resistivity surveying was performed rather than drilling or test pit exploration because the City desired to limit damage to the cave and densely wooded areas within the park. Electrical resistivity data were collected using a dipole-dipole array along the proposed road alignment. The data exhibited a valuable signature of a high-resistivity anomaly due to the presence of this cave of known dimensions. Based on the survey results, the depth to the top of the cave was estimated to be approximately 30 feet. Also identified, however, were nine other high-resistivity anomalies (possible voids) along the proposed road alignment. The interpretation of these anomalies, in some cases, suggested possible depths to voids of less than seven feet. It was concluded that the limited traffic loads caused by low speed construction-type vehicles would not significantly increase the potential for cave collapse at Watson Cave due to the approximately 30-foot depth of the feature. However, the interpreted shallower features have a comparatively higher potential for collapse. Recommendations included using a Bailey bridge to span large features and using a geogrid-reinforced crushed rock mat to distribute/dissipate heavy wheel loads over narrower features.
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A COMPARISON OF AEM INVERSION METHODS FOR DISCONTINUOUS PERMAFROST NEAR FORT YUKON, ALASKA
Authors Burke Minsley, Leif Cox, Ross Brodie, Glenn Wilson, Jared Abraham and Micheal ZhdanovPermafrost is a predominant physical feature of Arctic and sub-Arctic regions, and is sensitive to climate change. How warming of the permafrost affects near-surface hydrologic processes, ecosystems, and infrastructure is not clearly understood. A better understanding of the dynamic distribution and physical properties of permafrost, from continuous to discontinuous, provides knowledge of how the permafrost may change in the future and help inform engineering and sustainable management strategies. In June 2010, the US Geological Survey acquired 875 line km of RESOLVE frequency-domain airborne electromagnetic (AEM) data over a ~300 sq. km block near Fort Yukon in Alaska for imaging permafrost characteristics at various scales.
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OPTIMIZING ERT SURVEYS FOR TUNNEL DETECTION
Authors Tomas Goode and Ty FerreWe consider the problem of designing an electrical resistivity tomography (ERT) survey that is best able to discriminate a subsurface target among a population of similar targets. The targets being considered are horizontal buried tunnels with circular cross sections. Potential target tunnels vary in their radius and depth but, they have a constant electrical conductivity. They are evaluated singly, embedded in a homogeneous background with a differing electrical conductivity.
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MONITORING A NOVEL APPROACH TO MONITOR ENHANCED RECHARGE WITH TIME LAPSE GRAVITY
Authors Ty Ferre, Deborah Tosline and Damian GoschWe present work conducted in cooperation with the Bureau of Reclamation as part of their Enhanced Recharge Demonstration Project. The purpose of this project was to monitor the performance of a novel recharge enhancement approach based on diverting water from a main channel through a secondary channel within the floodplain. We located gravity stations along a 75 m transect that was perpendicular to the channels and extended from the midpoint between the main and excavated channels. We monitored over a period of 75 days. During this period, seepage loss measurements and streambed hydraulic conductivity measurements showed decreasing infiltration capacity with time. This response may be due to deposition of fine sediments and/or biological activity. Gravity responses mirrored these changes, showing rapid increases in water mass at early time, followed by a slow, steady decrease in stored mass. In addition, the gravity measurements gave a unique perspective on the extent of lateral movement of infiltrated water. Based on these results, we suggest that gravity monitoring could be a key component of monitoring of water movement adjacent to natural and engineered channels.
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GRAVITY-MEASURED WATER STORAGE CHANGE AND SUBSURFACE HYDRAULIC PROPERTIES AT A MANAGED RECHARGE FACILITY IN TUCSON, USA.
Authors Jeffrey Kennedy, Ty Ferre, Benjamin Creutzfeldt and Andreas GüntnerThe storage of subsurface water is central to Arizona’s future sustainable water supplies. Presently large amounts of water delivered from the Colorado River by Central Arizona Project canals (over 400,000 acre-feet/year permitted capacity) are stored underground at artificial recharge facilities to augment future water supplies. As the demand for Colorado River water increases and the energy required to transport, store, and recover this water becomes more costly, the importance of proper management and siting of recharge facilities increases. In this study, we combine different gravimeters (superconducting, absolute, and spring gravimeters) and advanced analysis methods to improve monitoring of subsurface storage and the characterization of subsurface hydraulic properties at Tucson Water’s Southern Avra Valley Storage and Recovery Project (SAVSARP) infiltration basins.
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SIMULTANEOUS PROXIMAL SENSING OF SOIL PHYSICAL, CHEMICAL, AND BIOLOGICAL PROPERTIES
Authors Erik Lund and Chase MaxtonSoil electrical conductivity (EC) sensing can rapidly delineate areas of contrasting soil properties within agricultural fields. Unless the signal is responding to a dominant soil property such as salinity or claypan, calibrating the signal in farm fields to specific properties has proven difficult. As a result, while the practice of soil EC mapping is receiving widespread acceptance in commercial agriculture, it is being adopted primarily as a soil pattern delineator. Recent advancements in proximal soil sensing allow for the mapping of soil properties such as organic matter using an optical sensor, and pH using an electrochemical sensor, along with soil EC. Also, elevation data from GPS receivers can provide co-located information about the topography of the field. When fields are mapped with all these sensors mounted on one platform, and calibration soil sample data are available, multivariate analysis techniques can be applied to calibrate the sensor readings to specific soil properties. Results from a multi-field, multi-state study show effective calibrations can be accomplished to a variety of soil properties using this sensorfusion approach.
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A SIMPLE AND EFFECTIVE DATA ACQUISITION PLANNING, PROCESSING AND GUIDANCE SYSTEM FOR CONDUCTING PARALLEL SWATH ELECTROMAGNETIC SURVEYS USING GEM 2 IN SUBSURFACE DRIP IRRIGATION MONITORING, POWDER RIVER BASIN, WYOMING
More LessThe National Energy Technology Laboratory and the U.S. Geological Survey are collaborating with BeneTerra LLC to comprehensively monitor a sub-surface drip irrigation (SDI) system at a site in the Powder River Basin (PRB) of Wyoming. Irrigation water for the SDI system is coalbed natural gas (CBNG) co-produced water. The study is being conducted at the Headgate Draw area, located approximately 17 km south of Arvada, Wyoming at the confluence of Crazy Woman Creek and the Powder River. The study site encompasses six alfalfa fields and covers an approximate area of 1.2 km2 (Figure 1).
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FIFTH YEAR OF SUBSURFACE DRIP IRRIGATION MONITORING USING GEM2 ELECTROMAGNETIC SURVEYS, POWDER RIVER BASIN, WYOMING
By James SamsThe National Energy Technology Laboratory and the U.S. Geological Survey are collaborating with BeneTerra LLC to comprehensively monitor a sub-surface drip irrigation (SDI) system at a site in the Powder River Basin (PRB) of Wyoming. Irrigation water for the SDI system is coalbed natural gas (CBNG) co-produced water. The study is being conducted at the Headgate Draw area, located approximately 17 km south of Arvada, Wyoming at the confluence of Crazy Woman Creek and the Powder River. The study site encompasses six alfalfa fields and covers an approximate area of 1.2 km2.
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UNKNOWN BRIDGE CHARACTERISTICS PROGRAM
More LessThe unknown bridge foundations issue remains one of the most persistent problems facing the bridge engineering community. Bridges are classified as having unknown foundations when the type (spread footing, piles, columns), material (steel, concrete, or timber), dimensions (length, width, or thickness), reinforcing, and/or elevation are unknown (HEC 18). The national cooperative highway research program (NCHRP) Project 21-5 devoted considerable effort in developing new test methods to address this issue and some good progress was reported. However, there are still concerns on the reliability of the available technologies and associated costs.
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A HYBRID METHOD FOR FIRST BREAK AUTO PICKING
By Don ZhaoFirst break picking is a basic procedure in first arrival tomography. There are a few of first break auto picking approaches available, such as energy ratio, AIC, and tracking. These methods work well with noise free data, but applied to field data, none of them are robust and large bias from the desired picks may present. A hybrid auto picking method is proposed. It first uses the energy ratio to generate a sketch of T-X curve, from which a velocity versus offset function is built, then employs AIC approach with the search range limited by the velocity versus offset function, finally adjusts the picks by correlation of the wavelet of adjacent traces. This method is proven by lots of experiments with a variety of data in refraction and cross-well tomography.
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3D GPR Real-Time Automated Detection of Buried Utilities
Authors P. Mazzucchelli, D. Molteni, N. di Buono and E. Cottinomini-trench" technique (addressed in ITU L.83 recommendation) requires that non-destructive mapping of buried services enhances its productivity to match the improvements of new digging equipment. Therefore, the development of a fully automated and real-time 3D GPR processing system plays a key-role in overall optical network deployment profitability. We propose a novel processing scheme whose goal is the automated processing and detection of buried targets, that can be applied in real-time to 3D GPR array system (16 antennas, 900 MHz central frequency). After the standard pre-processing steps, the antenna records are continuously focused during acquisition, by the mean of Kirchhoff depth-migration algorithm, to build pre-stack reflection angle gathers G(x, θ; v) at nv different velocities. The analysis of pre-stack reflection angle gathers plays a key-role in automated detection: by the mean of correlation estimate computed for all the nv reflection angle gathers, targets are identified and the best local propagation velocities are recovered. The data redundancy of 3D GPR acquisitions highly improves the proposed automatic detection reliability. The proposed approach allows to process 3D GPR data and automatically detect buried utilities in real-time on a laptop computer, without the need of skilled interpreters and without specific high performance hardware. More than 100 Km of acquired data prove the feasibility of the proposed approach.
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NEURAL NETWORK AND SUPPORT VECTOR MACHINE CLASSIFICATION OF UXO USING MAGNETICS FINITE ELEMENT MODELING DATA
Authors Matthew Bray, Curtis Link and Clifton YoumansA recently completed Montana Tech study used finite element modeling to calculate magnetic dipole moments for realistic unexploded ordnance (UXO) shapes found at Montana Army National Guard training sites. The modeling approach compared predictions from a simple prolate spheroid model, typical for conventional modeling, with a complex shape constructed using computer aided design (CAD). The complex shapes embody all of the features of the actual UXO bodies. Results showed that the larger, more accurate dipole moments calculated from the complex shape can be used to adjust the dipole moment discrimination level, ultimately reducing the number of targets to be dug.
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CALIBRATING SEISMIC REFRACTION MEASUREMENTS FOR ACCURATE AQUIFER VOLUME ESTIMATION IN A TROPICAL AREA: CAIRNS, AUSTRALIA
Authors Douglas Desper, Curtis Link and Paul NelsonThe Cairns (Australia) Regional Council on Water and Waste is committed to maintaining long term viability of the water supply to the rapidly increasing population of the Cairns region while ensuring a sufficient and safe water supply to maintain the natural environmental values of the rainforests, rivers, and reefs. Currently, the Copperlode Falls Dam supplies the majority of the water to the Cairns region, but this water source will not be sufficient to sustain the projected future growth of the area. The Council is investigating the feasibility of the nearby Mulgrave River Aquifer to supply the future water needs for the Cairns region while at the same time maintaining an equitable distribution of water among domestic, industrial, commercial, and agricultural users.
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MULTIPLE SEISMIC METHODS AND GRAVITY FOR DEFINING THE ANCESTRAL MISSOURI RIVER CHANNEL NEAR GREAT FALLS, MT, USA
Authors Curtis Link and Larry SmithStarting fall 2011 and continuing into spring 2012, the seismic prospecting class at Montana Tech designed and carried out a project focused on defining the preglacial paleochannel of the Missouri river near Great Falls, MT, USA. Although local water well driller’s logs can be interpreted unambiguously to determine presence of the channel, the well control, although dense in developed areas, is sparse throughout the area of interest. Approximate depth to the paleochannel is estimated at approximately 30-100m. As the paleochannel represents a prolific aquifer, there is significant interest in accurately locating it for future development and irrigation use.
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DETECTING BLIND FAULTS USING RAYLEIGH WAVE REFLECTIVITY
Authors Craig Hyslop and Robert StewartFinding faults near the surface is important for construction and engineering applications. It is difficult to locate them because there is often no surface expression, i.e. they are blind faults. We have developed a novel method for extracting Rayleigh wave reflectivity from sharp boundaries and tested it on modeled and field data. Rayleigh waves are particularly suited to detecting blind faults because of their presence extending into the shallow subsurface. Others have studied the complex wavefield due to heterogeneous impedance contrasts in the near surface scattering Rayleigh waves into P, S, and other Rayleigh waves. However, if contrasts are conformed to a boundary, such as a fault, scattered waves give way to reflected waves and a less complex wavefield. To find reflectivity, we determine phase velocity and amplitude for the outgoing Rayleigh wave and deconvolve the reflected wave with the outgoing wave while in a phase matched domain.
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VARIABILITY OF GRM AND REFRACTION TOMOGRAPHY RESULTS EXAMPLE: WATER RESOURCE INVESTIGATIONS IN WESTERN MASSACHUSETTS
More LessFive linear seismic surveys were conducted at the Clark Art Institute in Williamstown, MA to locate water-bearing bedrock fractures. Supply wells and return wells are needed to support an open-loop geothermal system requiring 550 gpm, with future expansion of the system planned.
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UNDERSTANDING GEOLOGIC CONTROLS ON GROUNDWATER USING BOREHOLE GEOPHYSICS EXAMPLE: LANDFILL IN EAST-CENTRAL NEW YORK
More LessBorehole geophysical logging of five bedrock wells was performed as part of a bedrock characterization study in support of groundwater investigations near a landfill in east-central New York. The investigation area is situated within an upland valley. Although the regional hydraulic gradient was generally understood, factors controlling variations in the groundwater flow patterns and potential vertical and horizontal pathways for landfill leachate around the vicinity were not. Contaminants of primary concern within the areas of investigation include VOCs in groundwater at concentrations above drinking water standards.
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ANALYSIS OF THE IVI MINIVIBI PERFORMANCE FOR HIGH FREQUENCY REFLECTION DATA
Authors Craig Hendrix and Richard D. MillerUnderstanding the vibrator-earth response is a pivotal part in addressing problems that decrease the fidelity of vibroseis data. If the vibrator output (ground force) is known, raw vibroseis data can be optimized for resolution and signal-to-noise ratio of the seismic waveform. The source signature, however, is non-unique and varies from shotpoint to shotpoint and from sweep to sweep. Nonlinear complexities within the vibrator’s hydraulic system, tower structure, baseplate flexure, and the ground response to force exerted by the vibrator baseplate increase irregularities in the vibroseis signal. Measuring and analyzing the response of the vibrator baseplate to a specific drive signal can help determine optimal recording positions on the baseplate to recover the ground force signal. When used to correlate or deconvolve raw data, an accurate approximation of the vibrator output will increase data resolution.
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A NOVEL SURFACE NMR PULSE SEQUENCE FOR IMPROVED ESTIMATION OF LONGITUDINAL T1 RELAXATION TIMES
Authors Elliot Grunewald and David WalshObtaining estimates of permeability from NMR methods requires the ability to measure relaxation time parameters that are most sensitive to pore geometry. While surface-NMR (SNMR) measurements can reliably quantify the effective transverse relaxation time T2*, transverse relaxation times are sometimes dominated by the influence of magnetic geology. The longitudinal relaxation time T1 is known to provide a more robust link to pore geometry, but previous attempts to measure T1 by SNMR, have shown mixed success due to fundamental limitations the commonly applied “pseudo-saturation recovery” (PSR) experiment.
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GEOPHYSICAL RESULTS OF MAIN BARTON SPRINGS (PARTHENIA) AND THEIR IMPLICATIONS ON THE GROUNDWATER FLOW PATTERN INTO BARTON SPRINGS POOL, AUSTIN, TEXAS
More LessBarton Springs is a major discharge site for the Barton Springs Segment of the Edwards Aquifer and is located in Zilker Park in Austin, Texas. Barton Springs actually consists of four springs: 1) The Main Barton Springs discharges into the Barton Springs pool from the Barton Springs Fault and several outlets along a fault and from a cave, several fissures, and gravel-filled solution cavities on the floor of the pool west of the fault. The thin-bedded unit on the southwest side of the fault is the regional dense member, and the lower Georgetown Formation of the Edwards Group is exposed on the northeast side of the fault. The offset of the fault is between 40 and 70 feet (12 to 21 m). 2) Old Mill Springs is located in the sunken gardens southeast of the Barton Springs Pool and is primarily fed by relatively mineralized groundwater from the Saline-Line Flow Route. 3) Eliza Springs is also located along the Barton Springs Fault north of Barton Springs pool. 4) The Upper Barton Springs is located upstream of the Barton Springs pool on the south bank.
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GROUNDWATER QUALITY AND GEOPHYSICAL STUDIES IN THE VICINITY OF TAILING PONDS OF THERMAL POWER PLANTS NEAR NAGPUR IN INDIA
Groundwater quality and Geophysical studies have been carried out in a microwatershed surrounding the tailing ponds near Nagpur in India. The study assumes importance in view of the nearby habitations using the groundwater for their drinking requirements. The study area covers approximately 60 sq km. A network of observation wells (23 nos) has been set up for groundwater quality monitoring for the major cations/anions. The results indicate that SO4 concentration has been found to be very high in few wells in the downstream of the tailing ponds. Elevated fluoride concentration (>1.5 mg/L) has been observed in only one observation well.
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Shallow Electrical and Seismic Imaging of The Pineto Mud Volcano (Central Italy)
Authors P. Torrese, M. Rainone, S. Rusi and P. SignaniniShallow underground electrical and seismic imaging was undertaken at the Pineto (Central Italy) Mud Volcano site using 2D-3D electrical resistivity tomography (ERT) and 2D reflection seismic surveys. This mud volcano or mud lump (known by the local population as “Cenerone Mud Volcano”) appears as a dome of about 15x10 m in size. The height is approximately 2 m with a crater 2.5 m of diameter where emission of fluids and solids (cold brine, mud, gas) occurs. Upper Pliocene-Lower Pleistocene foredeep pelitic deposits (clays with silty-sandy levels) overlain by clayey-silty deposits outcrop in the area. Below the Middle Pliocene deposits, a NNW-SSE anticline which runs approximately 2 kilometers to the WSW of the site represents the main element of the compressional tecnonic setting. Ditchs and streams in the area run along fault systems that are oriented NW-SE and NE-SW. These could be related to the upward migration of deep mud fluids. 2D-ERT results were used to determine the geometry of the high conductivity body related to the uprising of mud fluids and detecting changes in deposits. Detailed geometry reconstruction of the shallow upward migration of mud fluids was obtained by using 3D-ERT. A shear wave reflection seismic survey was undertaken to determine stratigraphic limits and to assess the occurrence of fractured zones along which mud fluids could migrate towards the surface. The survey results revealed that the uprising of deep fluids doesn’t occur exactly below the mud volcano at present. Instead, a high conductivity body occurs at approximately 60 m to the ENE, within a fractured zone in the undercompacted clays. The probable occurrence of a high permeability layer approximately between 20 m and 30 m below ground level, confined by clay layers, gives rise to an overpressured mud reservoir. This is the source of mud fluids which flow to the surface through a mud conduit that appears nearly horizontal at depth and then inclined towards the surface up to the mud volcano crater.
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INVESTIGATION OF A COASTAL KARST AREA TO DELINEATE PREFERENTIAL GROUNDWATER FLOWPATHS USING MARINE AND TERRESTRIAL ELECTRICAL RESISTIVITY TOMOGRAPHY
Authors Yvonne O‘Connell, Eve Daly, Garret Duffy and Tiernan HenryA major karst region is located in the west of Ireland in an area comprising the Burren and Gort Lowlands. The geology of this area is dominated by Carboniferous limestones which have experienced extensive dissolution resulting in an underground network of karstified conduits and fissures that define the groundwater flow across the region. In addition, the groundwater discharge to the sea in this area is exclusively intertidal and submarine. Typical winter rainfall conditions result in the karst system becoming saturated. The gradient of groundwater flow is low resulting in temporary lakes (turloughs) in the area acting as large reservoirs which provide storage to enable the transmission of the large volumes of water in the system to the sea.
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EFFICIENT AND SCALABLE ALGORITHMS FOR THE INVERSION OF VERY LARGE AEM DATASETS
Authors Casper Kirkegaard and Esben AukenRecently the standard size of airborne electromagnetic (AEM) datasets has been growing rapidly, while many surveys at the same time focus on modern applications that require very high resolution. Often, the particular target structures of interest cannot be identified directly from the data and approximate inversions or data transform techniques also prove insufficient. This type of application includes environmental studies of aquifers, salinity and geology and also cases of relevance to the mining industry e.g. uranium exploration. In these cases highly accurate full non-linear inversion provides the only reliable solution, which is a computational challenge. In designing an inversion scheme for these types of problems it is further advantageous to utilize as many assumptions as possible. The target structures of interest can often be regarded locally one dimensional, quasi layered and spatially coherent which can be integrated in the inversion. If inverting multiple soundings at a time for a set of spatially constrained 1D models, information is allowed to propagate spatially and a vastly improved model result can be obtained. Ideally, entire surveys should be inverted at a time in huge constrained problems, but poor scaling properties of the underlying algorithms typically makes this impossible.
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COMPARISON OF TIME-LAPSE RESISTIVITY AND WELL DATA IN THE HYPORHEIC ZONE BENEATH STREAMS
Authors Jonathan Nyquist, Laura Toran, David O‘Donnell and Robert RyanCharacterization of the hyporheic zone beneath streams, where surface water and groundwater mix, is critical for understanding stream ecology and contaminant fate and transport. Tracer tests can identify storage zones, but cannot distinguish between tracer lingering in pools and subsurface storage. Wells monitor the subsurface, but prohibitively many may be required to avoid spatially undersampling the plume, and with mixed porosity sediment wells preferentially sample the more hydraulically conductive sediments. Additional information can be obtained by monitoring saline tracer using time-lapse resistivity – continuous spatial coverage and sensitivity to the tracer distribution irrespective of the hydraulic conductivity – at the expense of a more ambiguous interpretation.
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AIRBORNE ELECTROMAGNETIC SURVEYS FOR GROUNDWATER CHARACTERIZATION
Authors Jared Abraham, Burke Minsley, Paul Bedrosian, Bruce Smith and James CanniaAirborne electromagnetic (AEM) surveys provide densely sampled data over large areas (typically several hundred sq. km) that cannot be covered effectively using ground-based methods. AEM data are inverted to estimate the three-dimensional distribution of electrical resistivity structures from shallow depths to several hundred meters. These models convey unparalleled details that are used to make inferences about hydrogeologic properties and processes at the watershed and local scale. This information is being used in groundwater models that are critical to water management decisions, to better understand geologic frameworks, and to improve climate change models. The U.S. Geological Survey (USGS) has been engaged in the application of AEM to many watershed and local scale groundwater projects within United States. We present the results of several frequency- and time-domain AEM surveys acquired by the USGS that have been used for mapping alluvial valleys, buried glacial aquifers, fault-bounded basins, salinity problems, and understanding permafrost distributions.
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EXAMPLES OF THE CONTRIBUTION OF A-PRIORI INFORMATION TO IMPROVING INVERSION OF AEM DATA
Authors Andrea Viezzoli, Tim Munday, Antonio Menghini, Anne-Sophie Hřyer and Esben AukenWe present a simple yet rigorous way of adding a-priori information to inversion of Airborne EM data, using the Spatially Constrained Inversion. Resistivity models are constrained spatially to reflect the lateral homeogeneity expected from the geology. These constraints, that can be considered “soft a-priori”, are fitted together with the AEM data, during the inversion. Moreover “hard a-priori” can be added: they can be, e.g., downhole resistivity logs, geological contacts and layers, hydrogeological units. The a-priori information is treated as an extra data set, by taking into account location, values, uncertainty, and expected lateral variability. The information it contains is spread to the location of the neighbouring AEM soundings. These fields enter the SCI formulations, with the Obs matrix containing the data (AEM and a priori), the Roughening matrix the constraints, the error matrix the uncertainties for all datasets. Constraints and uncertainties are usually different depending on data types and geology. Different datasets, collected by various AEM systems, have been used.
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GROUND PENETRATING RADAR INVESTIGATIONS ON THE RELATIONSHIP BETWEEN SALINITY IN FLUIDFILLED HORIZONTAL SUB-WAVELENGTH ‘THIN-LAYER’ BEDROCK FRACTURES AND REFLECTION AMPLITUDES
Authors Carolyn Tewksbury-Christle and Gregory S. BakerSubsurface fracture characterization is crucial for hydrogeologic modeling as applied to both fresh water resources and contaminant studies. Current methods of fracture geometry estimation for incorporation into groundwater models use cores, boreholes, and surface expression that are extrapolated over the entire study area. Due to the ‘cubic law’ relationship between fracture aperture and discharge—e.g., doubling fracture aperture will result in an eight-fold increase in discharge—there is a critical need to accurately estimate the aperture. Previous theoretical formulations suggested a correlation between ground penetrating radar (GPR) reflection amplitude and fracture aperture as well as groundwater salinity.
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INFORMED INVERSION APPROACH TO ELECTRICAL RESISTIVITY IMAGING IN A FRACTURED-ROCK SETTING
Authors Judith Robinson, Timothy Johnson, Lee Slater, Dimitris Ntarlagiannis and Pierre LacombeCharacterization of fractured rock presents unique inversion challenges in electrical resistivity imaging (ERI). The standard, smoothness-constrained inversion assumptions cannot adequately account for discrete fractures. Similarly, a borehole boundary is a sharp physical contrast and is often a conductive conduit that is typically not adequately incorporated into the inversion. We conducted synthetic studies to examine alternative ERI model parameterization approaches to better represent a fractured rock setting. An unstructured tetrahedral mesh was used for the forward modeling in order to optimize flexibility in the incorporation of boreholes and known fracture locations. Modeling such small-scale features at the plot scale resulted in a finite element mesh with a large number of tetrahedral elements.
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OBTAINING VELOCITY MODELS FROM SYNTHETIC FIRST-ARRIVAL TRAVEL TIMES USING REFRACTION TOMOGRAPHY METHODS
Authors Julian Ivanov, Richard D. Miller, J. Tyler Schwenk and Shelby PeterieThe possibility to apply different approaches to first-arrival time analysis of seismic data was examined using a sample synthetic first-arrival data set calculated initially from an unknown velocity model. This model was intentionally created for the purposes of a blind test and it was designed to represent a realistic near-surface target. Using the provided synthetic first-arrival data set various velocity models were estimated based on the understanding of the wide range of possible solution that can exist when dealing with the inverse refraction-traveltime problem (IRTP). Solutions to the IRTP were obtained using the refraction-tomography inversion technique. Comparison with the synthetic velocity model showed that none of the obtained models was accurate enough. Next, efforts were applied to find out what inversion parameters, such as initial model, types and degrees of regularization, etc., are required that would obtain solutions that match closely the synthetic model. Other possible models demonstrating possible nonuniqueness will be provided for comparison, as well. Such a comparison is expected to provide more evidence about the possible degrees of nonuniqueness of the IRTP for this particular model and the key inversion parameters for finding this true synthetic model.
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MAPPING THE ARCHEOLOGICAL POTENTIAL OF THE ROTTERDAM HARBOR AREA (THE NETHERLANDS), USING MARINE GEOPHYSICS IN A MULTI-DISCIPLINARY AND MULTI-STAKEHOLDER STUDY.
Authors Marco de Kleine, Peter C. Vos, Bjorn Smit, Henk Weerts, Dimitri Schiltmans, Wil Borst and Wouter WaldusThe Port of Rotterdam (PoR) is expanding the ‘Maasvlakte’ harbor on reclaimed land. In order to connect this new land with the old harbor a deep channel (‘Yangtze Harbor’) will be dredged to a depth of 20 meters below sealevel. Previous work revealed a deltaic landscape with Late Paleolithic and Early Mesolithic archeological artifacts at depths of 17-20 meters. Prior to the dredging the archeological potential of the site had to be investigated. In order to obtain a scientific and economical justifiable approach, fitting within the limited time frame, all concerned parties worked in close collaboration: - Harbor authorities (PoR) - Cultural Heritage Agency/Authority (RCE) - The engineering company (PUMA) - Geological and archaeological research institutions Deltares, BOOR and ADC
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SIMULATING P-WAVE VELOCITY VARIATIONS DURING FLUID INFILTRATION IN THE VADOSE ZONE USING FINITE-DIFFERENCE SEISMIC MODELING IN A VISCOELASTIC MEDIA
Authors Rachel E. Storniolo and Gregory S. BakerHydrogeologic parameter estimation in the vadose zone is critical in a variety of environmental and engineering applications. However, moisture content in the vadose zone is difficult to properly constrain using traditional methods, because water saturation can be highly variable in space and time, and geologic materials can be anisotropic, heterogeneous, or both. We have previously proposed an in situ method for estimating field-saturated hydraulic conductivity using time-lapse seismic first-arrival tomography (TLSFT).
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MEC Target Classification using EM61 Interrogation during Reacquisition
Authors A. Z. Kostera, R. L. Satkin and K. W. BolerThe value of digital geophysical mapping (DGM) for the remediation of sites containing Munitions and Explosives of Concern (MEC) is well documented. In recent years, the state of the science has shifted to the application of classification techniques which limit intrusive operations to those DGM anomalies most likely to represent subsurface MEC. While new target classification techniques show significant promise, they are still impractical at many of the sites with more challenging terrain and vegetation conditions. This paper will describe the use of target interrogation during reacquisition using existing, proven technology which provides a real-time field alternative to anomaly classification applicable to most sites and with the potential to significantly reduce the number of DGM targets that require intrusive investigation. NAEVA utilized a differential reacquisition threshold and innovative methods of evaluating terrain response to eliminate subsurface targets that are unlikely to be subsurface MEC. During processing of DGM data, target selections must be made conservatively knowing that data are recorded at a single orientation (parallel to line direction) and that the instrument often will not pass over a subsurface object in a way that creates the maximum response amplitude. During target reacquisition, the original mapping instrument is maneuvered over an anomaly at multiple orientations until that maximum response is found. The first implication of this technique is that a less conservative criterion could be applied to the selection of targets than would be reasonable during data processing, thus reducing the number of targets that require intrusive investigation. In addition, the ability to evaluate anomaly characteristics from multiple orientations in real-time allows the skilled operator to make sound judgments about the nature of a subsurface anomaly in the presence of non-metallic terrain response. The size of the McClellan project offered NAEVA the opportunity to evaluate Geonics EM61- MK2 targeting and reacquisition peak response data with respect to the dig results for over 195,000 targeted DGM anomalies in terrain which is generally unfavorable for anomaly classification using existing (large) advanced sensors. An analysis of this data showed that the anomaly peak response measured during reacquisition could be utilized to eliminate a significant (10-20%) number of digs without significantly impeding the ability to detect and remove MEC. The classification of targets in areas exhibiting elevated terrain response were evaluated under two different scenarios and offered reductions in intrusive effort of more than 50%.
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A SENSITIVITY COMPARISON OF TWO COMMERCIAL TIME-DOMAIN EMI SENSORS FOR UXO DETECTION
Authors Matthew Casari and Lance BesawIn live-site unexploded ordnance (UXO) remediation, digital geophysical mapping (DGM) must be accomplished to assess potential targets of interest (TOI) in the affected area. The DGM process is extremely time-consuming and subsequently an expensive endeavor. To minimize the costs associated with DGM, towed electromagnetic induction (EMI) sensors or sensor arrays are employed to increase the coverage rates and provide large sets of data for “post-processing” evaluation. The performance of these DGM studies in effectively detecting TOI is largely dependent on the sensor characteristics, in particular the Signal-to-Noise Ratio (SNR) achieved across targets of varying size and depth. Additionally, the spatial resolution of the sensor arrays determines the accuracy with which TOI can be localized, potentially saving time in the UXO extraction phase. In this project, we collected data over UXO test lanes with two commercially available EMI sensors - the Geonics EM61-MK2 and the Minelab Single-Transmit Multiple Receive array. Interrogated targets range from 40mm projectiles to 81mm mortars buried at multiple depths and different orientations. These tests were conducted using the Scout UXO detection system, a trailer unit originally developed by Applied Research Associates, Inc. for the U.S. Army Night Vision Electronic Sensors Directorate Humanitarian Demining division to perform DGM on live-site, overseas clearance areas . The performance of these sensors are presented and compared based on the criteria of SNR, rate of coverage, TOI localization capability, and the ability to detect “difficult” (small) targets.
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MAN-PORTABLE TEMTADS 2X2 TIME-DOMAIN EMI SENSOR ARRAY FOR UXO CLASSIFICATION
Authors Daniel Steinhurst, Thomas Bell, James Kingdon and Glenn HarbaughUnexploded ordnance (UXO) contamination at former and current Department of Defense sites is an extensive problem. Site characterization and remediation activities conducted with the current state-of-the-art technologies at these sites often yield unsatisfactory results and are extremely expensive to implement. This is due in part to the inability of current technology to distinguish between UXO and nonhazardous items. Newly emerging electromagnetic induction (EMI) sensor technologies offer the ability to robustly distinguish between these two classes of objects. Early versions of these systems have tended to be large and designed for towed operation on open fields with good sky view for geolocation.
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APPLICATION OF ELECTRICAL RESISTIVITY TOMOGRAPHY IN MAPPING SUBSURFACE HYDROCARBON CONTAMINATION
Authors Elijah Ayolabi, Adetayo Folorunso and Samuel Idemseasonal variation in the water table which is usually close to the surface during rainy season) to the surface and downwardly at greater depth into the subsurface, through a porous medium – sandy layer. This may probably accounts for the reason while most of the handdug wells in the area are contaminated with hydrocarbon products.
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INCORPORATING DEPHASING DYNAMICS INTO SNMR FID INVERSIONS IN THE HIGH PLAINS AQUIFER
Authors Trevor Irons, Jared Abraham, James Cannia, Yaoguo Li and Jason McKennaWhile it is accepted that T2 and T2 * diverge under most surface NMR (SNMR) conditions, the mechanism for this difference is usually not accounted for in the forward modeling kernels. In SNMR T2 * is often used as a proxy for T2 in the equations used to map NMR to aquifer characteristics. The reason that T2 and T2 * are not equivalent is due to inhomogeneities in the static magnetic field. As the Larmor frequency is a function of the static field, any inhomogeneity causes the spins to dephase and lose coherence. This dephasing causes non-exponential decay in the recorded FID time series.
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JOINT USE OF SEISMIC REFLECTION AND TIME-DOMAIN ELECTROMAGNETIC METHODS TO AID GROUND WATER MODELING
Authors Jacob Sheehan, Phil Sirles, Nicole Pendrigh and Mayo ThompsonHigh resolution seismic reflection and time-domain electromagnetic geophysical surveys were conducted in support of subsurface characterization and ground water modeling at a site in Wyoming contaminated with TCE. Two kilometer-long seismic profiles reveal several discontinuous cemented layers within the overburden sediments, and also show evidence of several faults that could be correlated between the lines.
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LABORATORY MEASUREMENTS OF ACOUSTIC, ELECTRICAL RESISTIVITY, AND ERODIBILITY OF SOILS DURING A COMPACTION PROCESS
Authors Craig Hickey, Cameron Ehn, Gregory Hanson and Zhiqu LuCurrent geophysical techniques used in the assessment of the interior of earthen embankments include: acoustic/seismic, electro-magnetic and resistivity, gravity, and radar. The tradeoff associated with using geophysical techniques is that the measurements are sensitive to the distribution of the bulk “geophysical” properties (elasticity, electrical resistivity, dielectric constant, etc) in the subsurface.
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GEOSCIENTISTS WITHOUT BORDERS - LASTING CHANGES AT AN AFFORDABLE COST
Authors Rhonda Jacobs, Bernadette Ward and Debra StarnesThe effects of the first five completed Geoscientists Without Borders(R) projects show clearly the impact applied geophysics can have in remote, under-served, or underdeveloped areas of the world. The projects in West Sumatra, Honduras, India, Romania, and Thailand have had impacts that extend far beyond the actual project goals. Although these projects are not all located in undeveloped countries, it is lessons learned that are leading us to think of the benefits that can be gained using geophysics in such places.
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FULL WAVEFORM NON-LINEAR P AND S WAVE SEISMIC TOMOGRAPHY INVESTIGATION PERFORMED TO IDENTIFY KARST FEATURES AND BEDROCK TOPOGRAPHY WITHIN STORMWATER BASIN IN WESTERN US
Authors Christopher Buckman, Raye Lahti, Finn Michelsen and Lisa SheaA full waveform non-linear P and S wave seismic refraction tomography survey was performed to investigate potential karst and geologic subsidence features located within a proposed engineered stormwater control structure located in the western US. Work was conducted in the vicinity of solution features and subsurface voids identified during site regrading and preliminary cell construction. Original geomorphology and terrain of the area consisted of moderately to steep topography with interpreted northwest to southeast rending fractures. During site construction, highly variable bedrock topography and solution features were discovered and addressed through backfill and compaction. Preliminary survey results indicate areas of both subsidence and air-filled open fracture along coincident inferred joint traces.
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GEOPHYSICAL TECHNOLOGY TO SUPPLEMENT USACE NON-UXO SITE REDEVELOPMENT PROGRAMS
Authors Raye Lahti, Christopher Buckman and Andri HansonGeophysical surveys have become increasingly more valuable as a part of the site redevelopment strategy for the USACE. As a result of outdated facilities to include housing, administration and maintenance buildings, many active military installations have undergone recent redevelopment to accommodate returning military personnel and to upgrade existing infrastructure. As part of a collaborative subcontract agreements AMEC has provided geophysical consulting services on several projects at the U.S. Army’s Fort Campbell Military Reservation located near Clarksville, TN. As requested by the USACE, time-domain electromagnetic surveys were performed within 11 proposed redevelopment areas totaling 42 acres to aid in locating potential subsurface utilities, foundations, uncontrolled fill and engineered structures. These features, if encountered, may affect planned future land use and overall site redevelopment plans. This presentation provides a brief background of the application of geophysics to engineering and site redevelopment investigations, the supplemental information they provide to existing site conditions, and its applicability to other environmental and engineering disciplines. The integration of GIS databases with historical aerial imagery and geophysical datasets provide a reliable multifaceted information resource to the USACE redevelopment strategy. Geophysical investigations, when properly integrated and sequenced, can reduce costs, increase margins of safety, improve project efficiency, and enhance subsurface detail.
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Slope Monitoring within Open-Pit Mines by Ground-Based Radar: Methodology, Data Processing and Case Studies Review
Authors F. Mariotti, G. Amoroso, D. Giudici, D. d‘Aria and P. FarinaOpen-pit mines are widely exploited to provide increasing-demand materials around the world. The peculiar extraction methods carried out during mining operations create steep slopes that need to be constantly monitored to ensure the safety of workers and machinery. Methods to reliably measure slope movements and possibly predict impending failures are paramount and constantly under study and improvement. Reliability allows in fact to reduce the false alarm events that cause stopping of the operations with impact on the productivity. Radar interferometry is a technique that has been widely demonstrated in the past to be able to measure millimetric deformations over a wide area (when the radar is mounted on space-borne platforms) or, more, recently, at a local scale with Ground-based radars. Radar interferometry needs two main conditions to work well: the imaged targets should provide sufficient back-scattered signal and this signal remains coherent in time. Open-pit mines offer very often the two conditions above, as the vertical walls ensure a good level of backscattered signal and the poor presence of vegetation, subject to random movement, ensures a huge number of measurement points. Also if these conditions are satisfied, the digital processing of the radar signal is fundamental to eliminate artifacts caused by the variability of the atmospheric conditions, that have to be removed from the raw data in order to obtain accurate displacement measurements and reliable alarms. The paper deals with the monitoring of the slope movements over a wide areas of open pit mines up to millimetric precision, presenting the radar technology, the data processing method and some real case studies. The key parameters and boundary conditions that impact the quality of the measurements are discussed and the results for different cases of movement (fast, slow, distributed or concentrated) are analyzed and presented.
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MONITORING IN SITU BIOREMEDIATION AT THE RIFLE, COLORADO IFRC SITE WITH NUCLEAR MAGNETIC RESONANCE AND MAGNETIC SUSCEPTIBILITY MEASUREMENTS
Authors Kristina Keating, Kenneth Williams, Dimitris Ntarlagiannis and Lee SlaterNuclear magnetic resonance (NMR) and magnetic susceptibility (MS) borehole logging measurements were collected at the Rifle Integrated Field Research Challenge (IFRC) site. The Rifle IFRC site is located at a former uranium oreprocessing facility in Rifle, Colorado. Although removed from the site by 1996, leachate from spent mill tailings has resulted in residual uranium contamination of both groundwater and sediments within the local aquifer. Since 2002, research at the site has primarily focused on quantifying uranium mobility associated with stimulated biogeochemical processes.
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GPR CHARACTERIZATION OF DISCRETE FRACTURES AND MONITORING OF CHANNELED FLOW: ELUCIDATING THE FORWARD MODEL
Authors George Tsoflias and Matthew BeckerGround penetrating radar (GPR) is an effective geophysical method for imaging fractures. Of interest to hydrogeologic studies of fractured aquifers is quantification of fracture aperture distribution and flow channeling. We present work relating GPR signal response to fracture aperture variability, water salinity changes and flow channeling. We show that characteristic and quantifiable reflected radar signal amplitude and phase responses relate to fracture aperture and fluid salinity. Radar signal amplitude increases as fracture aperture increases and as fluid electrical conductivity increases. Radar reflection phase is relatively insensitive to aperture change (at frequencies lower than 200 MHz) but highly responsive to fracture water electrical conductivity changes (up to 1 S/m). Contrary to conventional thin-layer theory expectation, lower frequency radar signals exhibit greater sensitivity to changes in fluid electrical conductivity than higher frequency signals. Threedimensional multi-polarization reflection imaging shows that aperture variability and flow channeling introduce significant polarization effects to the radar wavefields that need to be accounted for in order to quantitatively relate GPR reflection response to fracture aperture and water salinity. Increasing fluid salinity along flow channels results in increasing polarization effects on the recorded signals offering an additional GPR attribute to varying fluid salinity.
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ASSESSING THE ACCURACY OF ANOMALY DENSITY ESTIMATES USING TRANSECT SAMPLING METHODS FOR UXO SITE CHARACTERIZATION
By Craig MurrayThe Department of Defense is currently focusing its efforts to address formerly used defense site UXO contamination on the site characterization, or remedial investigation, phase of the CERCLA process. This effort includes acquiring data to estimate the cost of remedial alternatives. One of the important factors determining the cost of remedial actions is the anomaly density of the contaminated area. Geophysical transect sampling using electromagnetic or magnetic sensors is the most common method for mapping anomaly density at UXO contaminated sites, but the accuracy of those estimates is not well understood.
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MEASUREMENT OF FRACTURE/MATRIX HEAT EXCHANGE USING FIBER OPTIC DISTRIBUTED TEMPERATURE SENSING
Authors Adam Hawkins, Matthew Becker and George TsofliasFluid circulation in fractured geothermal reservoirs is often impacted by an uneven sweep of water between injection and pumping wells. This channelization of flow can result in poor circulation or, alternatively, premature thermal breakthrough. Although the phenomenon has been frequently recorded in the temperature history at production wells, temperature loss in the rock matrix cannot be monitored in geothermal reservoirs.
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USE OF ELECTRICAL RESISTIVITY AND SELF-POTENTIAL SURVEYS FOR DAM SEEPAGE INVESTIGATIONS
Authors Richard Markiewicz, Kristen Pierce and Dan LiechtyElectrical resistivity imaging (ERI) and self-potential (SP) surveys provide an effective means of delineating seepage conditions within earth embankment dams, levees, and other structures. Recent advances in resistivity tomography inversion allow reconstructing the resistivity structure at the embankment/foundation contact, implying that internal embankment erosion can be effectively inferred from surface measurements.
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USE OF GROUND PENETRATING RADAR FOR DAM SPILLWAY AND CONDUIT INVESTIGATIONS
Authors Richard Markiewicz, Dan Liechty, Kristen Pierce and Justin RittgersGround penetrating radar (GPR) is an effective tool for investigating defects in concrete structures. In a dams setting, concrete structures of interest include spillway slabs, outlet works conduits, and structures such as spillway gate buttresses.
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INVESTIGATION FOR HYDRAULIC CONDUITS INVOLVED IN SINKHOLE FORMATION THROUGH THE USE OF INTEGRATED SURFACE AND BOREHOLE GEOPHYSICS
Authors Lauren Schroeder and Phillip CarpenterThe Nachusa Grasslands Conservancy is located near Franklin Grove in northern Illinois. It was used previously for agriculture and is currently undergoing restoration into a natural prairie. A sinkhole, ~40m in diameter, exists in the northern portion of this area. At this location Ordovician age dolomite subcrops beneath St. Peter sandstone and several meters of unconsolidated sand, gravel and clay. Geophysical surveys were deployed to determine the location and nature of hydraulic conduits related to the sinkhole’s formation. The area surrounding the sinkhole was investigated using EM conductivity profiles, resistivity soundings, ground- penetrating radar (GPR) profiles, supplemented by Geoprobe® conductivity logs and soil cores. Resistivity soundings and the Geoprobe® logs suggest bedrock averages about ~5.0 m deep near the sinkhole. Core samples were also collected and are presently being examined. The EM conductivity profiles showed lateral variations of 1-2 mS/m, but lack the resolution needed to definitively locate conduits. GPR using 50 and 100 MHz antennas proved the best tool for examining the subsurface. These high resolution images show possible conduits as diffraction hyperbolas below the bedrock surface. The water table is not visible, suggesting it lies at least several meters below the bedrock surface. An area of suspected multiple, small conduits has been detected on the north side of the sinkhole trending northeast to southwest. Future work will include expanding the GPR survey grid for better coverage, followed by additional borings to confirm the existence of hydraulically active conduits.
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ELECTRICAL GEOPHYSICS FOR DEEP TUNNEL DETECTION AT A GOLD MINE REMEDIATION SITE
Authors Nicole Pendrigh, Phil Sirles, Paul Ivancie and Douglas LaBrecqueSurface and crosshole geophysical investigations, including time-domain dipoledipole resistivity and frequency domain Mise-a-la-Masse (MALM) surveys, were conducted on the Captain Jack Project, an EPA Superfund remediation site which includes the Big Five tunnel. The Mise-a-la-Masse survey used the main access tunnel as a transmitting electrode and recorded data on the surface above the tunnel using a pole-dipole configuration. The objectives of the surface geophysical investigation are two-fold: 1) Geologically characterize the host-rock and region in which the mineralized fault zone and associated mine tunnel system lies; and, 2) Determine the location of the mineralized zone and the associated tunnels, if possible.
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SENSITIVITY OF BOREHOLE NMR MEASUREMENTS TO WELL CONSTRUCTION AND DEVELOPMENT
Authors David Walsh, Elliot Grunewald, James Butler, Ed Reboulet, Steve Knobbe and Rosemary KnightIn this work we investigate the effect of different well construction methods, and well development activities, on borehole NMR measurements and borehole-NMRderived estimates of hydraulic conductivity. Nuclear magnetic resonance (NMR) measurements provide direct sensitivity to pore fluids enabling estimation of key petrophysical properties including porosity, bound/free fluid content, and permeability. In particular, the observed NMR relaxation time T2 is sensitive to the pore volume to surface ratio. Hence, any differences or changes in the physical pore-scale properties of a water-saturated formation due to well construction and/or development should logically be detectable by borehole NMR. To test this hypothesis, we used a variety of small diameter NMR logging tools at a wellcharacterized hydrologic test site in Lawrence Kansas.
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BOREHOLE GPR TO DETECT AND MAP DEVIATED H-PILE FOUNDATIONS
Authors Rowland French, Thomas Pennington, Roy Cook and Tammy CleysThe City of Portland, Oregon, has completed construction of a six mile long combined sewer overflow (CSO) tunnel on the east side of the Willamette River through downtown Portland. The tunnel is 24 feet in diameter at a depth of 80 to 100 feet below ground level, and was constructed using a tunnel boring machine (TBM). The preliminary tunnel alignment passed beneath a major elevated freeway interchange where it will negotiate a series of steel H-pile foundations that extend below the tunnel horizon. Given the soft soils at the site, it was anticipated that these H-piles may have deviated from vertical at the depth of the tunnel. If the TBM were to encounter a deviant H-pile considerable costs would be incurred for the tunneling operation, and the operation and integrity of the freeway interchange may be compromised.
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Airborne Time-Domain Electromagnetics for Three Dimensional Mapping and Characterization of the Spiritwood Valley Aquifer
Authors G.A. Oldenborger, A. J.-M. Pugin and S.E. PullanThe Geological Survey of Canada commissioned a helicopter-borne time-domain electromagnetic (HTEM) survey over a 1062 km2 area of the Spiritwood Valley in southern Manitoba to test the effectiveness of airborne time-domain electromagnetics for mapping and characterizing buried valley aquifers in the Canadian Prairies. The HTEM data exhibit rich information content; apparent conductivity maps clearly image the Spiritwood Valley in addition to a continuous incised valley along the broader valley bottom. We detect complex valley morphology with nested scales of valleys including at least three distinct valley features and multiple possible tributaries. Conductivity-depth images (CDI) derived from the TEM decays indicate that the fill materials within the incised valleys are more resistive than the broader valley fill, consistent with an interpretation of sand and gravel. Comparison of ground-based electrical resistivity and seismic reflection data allow for calibration of CDI models. Lateral spatial information is in excellent agreement between data sets. The seismic data reveal the presence of additional valley features that are not imaged by the HTEM data as having a distinct electrical signature, possibly due to diamicton fill. The CDI model underestimates the dynamic range of electrical conductivity while overestimating depths to valley bottoms; these issues may be associated with system limitations, system bandwidth, algorithm limitations and penetration depth. The integrated data sets illustrate that HTEM surveys have the potential to map complicated buried valley aquifers at a level of detail required for groundwater prospecting and management.
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SELF-POTENTIAL DATA ACQUISITION USING WIRELESS SENSOR NETWORKS
Authors Justin Rittgers, Brian Hoenes, Kerri Stone and Scott IkardWith the advent of wireless geophysical sensor networks in the form of highly sensitive, multi-functional, accurately time-synchronized and spatially located motes, continuous and automated geophysical monitoring of earthen dams and levees will soon be an economical approach to risk mitigation. While standard wired geophysical surveys such as Self Potential (SP), Electrical Resistivity Tomography (ERT) and seismic refraction or surface wave profiling can be extremely useful in characterizing earthen embankments, they constitute an expensive one-time investigation with the shortcoming of not being able to provide preemptive monitoring or early detection of developing seepage zones or structural weaknesses. Standard one-time geophysical surveys also exhibit added risks including potentially insufficient data coverage, inaccurate or noisy data and ultimately inconclusive results. Conversely, a permanently installed network of wireless motes across the length of an earthen structure would offer accurate, comprehensive and continuous monitoring.
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GEOPHYSICAL SIGNATURES OF CRACKING AND SELF-HEALING OF SOILS DURING LAB-SCALE SIMULATIONS
Authors Justin Rittgers and Minal ParekhInternal erosion in earthen embankments occurs when a critical combination of hydraulic gradient, in-situ stress conditions, soil porosity and intrinsic permeability results in uncontrolled seepage and the transport and migration of soil particles in localized areas. Concentrated embankment seepage and erosion will also occur within open cracks that can result from strong-motion earthquakes and uneven or discontinuous settlement. Acoustic methods in combination with electrical geophysical methods have not been used yet as a tool for detection, characterization and continuous monitoring of subsurface internal erosion initiation in its early stages. Passive acoustic emission (AE), self potential (SP) and cross-hole tomography (CT) are being investigated for suitability as long-term, remote and continuous monitoring techniques for internal erosion and cracking of embankment dams.
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A GPR ARRAY SYSTEM FOR TRAFFIC EMBEDDED MONITORING OF BRIDGES AND ROADWAYS
Authors Charles Oden and Ralf BirkenThe Versatile Onboard Traffic Embedded Roaming Sensors (VOTERS) project provides a framework to shift from periodical localized inspections to continuous network-wide health monitoring of roadways and bridge decks using Vehicles Of Opportunity (VOO). VOOs (e.g. commercial fleet vehicles) navigate through daily traffic going about their normal business and provide a low-cost data collection platform for repeatedly scanning roads and bridges in a geographic area of interest (i.e. a metropolitan area). A VOTERS concept compatible Ground Penetrating Radar (GPR) array is one of the key subsurface sensing technologies under development with the requirements of being low-cost, small, and fast enough to collect data at meaningful spatial sampling intervals while driving at regular traffic speeds.
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DETECTING FRACTURE-DRIVEN HYDROLOGIC ANISOTROPY USING AZIMUTHAL SEISMIC FIRST-ARRIVAL TOMOGRAPHY (ASFT)
Authors Matthew Edmunds, Gregory S. Baker, David Watson and Scott BrooksThe Oak Ridge Integrated Field Research Challenge (ORIFRC) project is funded by the U.S. Department of Energy’s (DOE’s) Subsurface Biogeochemical Research (SBR) Program in order to study the various biogeochemical processes involved in the remediation as well as natural attenuation of a large contaminant plume that is extant in the vicinity of the former S-3disposal pond area in Oak Ridge, TN. A part of this work has been to characterize the movement of this groundwater/contaminant plume with the use of seismic first-arrival tomography (SFT).
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NEAR-SURFACE SEISMIC SURVEYING ALONG THE GREEN VALLEY FAULT, SAN FRANCISCO BAY AREA, CALIFORNIA
Authors Mitchell Craig, Uyanga Ganbaatar and Joanne ChanSeismic reflection surveying was conducted at the Green Valley fault, located in the San Francisco Bay Area, California, with the goal of identifying subsurface stream channels for use in measuring fault offset and slip rate. Three 180-m long, fault-parallel profiles were recorded in 2009 near the site of previous paleoseismologic investigations, including near-surface geophysical surveys. A previous seismic refraction survey identified a trough-shaped, low velocity body on the east side of the fault at depths of 5-12 m, interpreted as a stream channel truncated by the Green Valley fault. The present work was undertaken with the goal of finding the corresponding portion of the channel on the west side of the fault, presumably offset to the north due to motion on the fault during approximately the past 10 ka. Seismic reflection data were recorded in order to obtain higher-resolution and more extensive coverage. The new survey provided excellent resolution of near-surface stratigraphy at depths of 80-375 m, but did not provide sufficient resolution at shallower depths to permit correlation with data from the earlier seismic refraction survey, which had a maximum depth penetration of only about 15 m. The new reflection data appear to image lateral variations in fluvial stratigraphy at depths of approximately 100 m that could be used to measure fault offset in a future study.
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GEOPHYSICAL ANALYSIS OF THE UPPER SIX METERS OF SOIL, EAST-CENTRAL DUGWAY PROVING GROUND, IN SUPPORT OF MILITARY AND HOMELAND SECURITY INTERESTS
Authors Kevin Parkman, Lee Perren, Seth Broadfoot, Jason McKenna and Lillian WakeleyOctober 2010 field investigations in the east-central part of Dugway Proving Ground included geophysical investigations coupled with extensive soil sampling and field investigations of stratigraphy in support of military and homeland security interests.
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DEPTH OF CINDER DEPOSITS AND WATER-STORAGE CAPACITY AT CINDER LAKE COCONINO COUNTY, AZ
Authors Jamie Macy, Lee Amoroso, Jeffrey Kennedy and Joel UnemaThe 2010 Schultz fire northeast of Flagstaff, Arizona burned over 14,000 acres on the east side of the San Francisco Mountain from June 20 to July 3. As a result, several drainages in the burn area are now more susceptible to increased frequency and volume of runoff and downstream areas are more susceptible to flooding. Resultant flooding in areas down-gradient of the burn has resulted in extensive damage to private lands and residences, municipal water lines, and roads. Coconino County, which encompasses Flagstaff, has responded by deepening and expanding a system of roadside channels. These channels move flood water away from communities and into an area of open Forest Service lands, known as Cinder Lake, where rapid infiltration can occur. Water that has been recently channeled into the Cinder Lake area has infiltrated into the volcanic cinders and could eventually migrate to the deep regional groundwater flow system that underlies the area. It is unknown as to how much water can potentially be diverted into Cinder Lake, and Coconino County is interested in determining how much storage is available. The U.S. Geological Survey conducted geophysical surveys and drilled four boreholes to determine the depth of the cinder beds and their capacity for potential water storage. Results from the geophysical surveys and boreholes indicate that the cinders are underlain by basalt at about 30 ft below land surface. Total porosity for the upper 30 ft of cinders was calculated at 43 percent for an area of 300 acres surrounding the boreholes, which yields a total potential subsurface storage for Cinder Lake of 3,900 acre-ft. Ongoing monitoring of storage change in the Cinder Lake area was initiated using a network of gravity stations.
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CREDIBILITY OF THE OPTIMUM XY SPACING OF THE GENERALIZED RECIPROCAL METHOD IN INTERPRETATION OF SHALLOW REFRACTION SEISMIC DATA
By Hamdy SeisaThe shallow seismic refraction technique has inherent problems, such as the undetected layers, ambiguities, first and later arrivals. Other main problems are related to the interpretation techniques themselves. Most of them are restricted to simple models, but the generalization is responsible to false interpretations The Generalized Reciprocal Method (GRM) is suggested to be used for mapping subsurface structures with lateral variations. This method depends mainly on a heuristic single parameter called the optimum XY distance. At the optimum XY separation, the rays to each geophone emerge from near the same point on the refractor. Since the GRM has heuristic assumptions and has no mathematical derivation, more uncertainties are raised in its application, even in case of simple models. The lack of constant XY spacing in all cases (except the horizontal ones) will lead to more uncertainties in its application. The optimum XY value is based on a heuristic determination and it is always a doubtful matter. The uncertainties of the optimum XY spacing will be discussed on two synthetic models.
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LINKING LABORATORY MEASUREMENTS OF GEOPHYSICAL PROPERTIES TO ENGINEERING PROPERTIES, QUANTITATIVE AND QUALITATIVE MINERALOGY, AND FIELD DATA
Authors Ryan North, William Folks, Julie Kelley and Jason McKennaNear-surface geophysics spans a wide range of methodologies and applications but one common theme is the desire to understand the relationships between the properties of the soil and the measurement methods. As part of a multi-year series of projects the U.S. Army Engineer Research and Development Center has been performing field geophysical data collections and soil sampling on multiple scales at a range of locations both domestically and internationally. This presentation will cover the range of measurements that have been performed to fully characterize the geophysical properties (electrical resistivity, magnetic susceptibility, dielectric permittivity, p-wave and s-wave velocities, moisture content measured with lowfield nuclear magnetic resonance), engineering properties (grain size distribution, moisture content, compressive and shear strength), and qualitative and quantitative mineralogy (X-Ray Diffraction, X-Ray Fluorescence, Scanning Electron Microscopy, Differential Thermal Analysis, Differential Scanning Calorimetry, Thermal Gravimetric Analysis). The geophysical properties have been measured over a frequency range from 10 mHz to 8.5 GHz. There will also be a discussion of some of the methodologies that have been employed for analysis and interpretation of individual results and also how to link the physical properties across disciplines. A dataset of this size requires several types of analyses to identify correlations in physical properties and allow more detailed explorations of the relation between physical properties.
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EXPLORING THE POTENTIAL OF NEAR-SURFACE GEOPHYSICAL METHODS TO DELINEATE A SHALLOW HARDPAN IN A SOUTHEASTERN U.S. SANDY COASTAL PLAIN SOIL
Authors Barry Allred, Hamid Farahani and Ahmad KhalilianA hardpan, which is a dense soil layer near the ground surface, is an undesirable feature of many soils in the Southeast U.S., especially sandy Coastal Plain soils. Shallow hardpans restrict root growth and water penetration through the soil profile, in turn reducing the effective crop root zone and thereby limiting crop production. Knowledge of hardpan existence, depth, and spatial extent is valuable, and can be used by farmers to improve soil, water, and crop management. This hardpan problem is similar to challenges faced with claypan soils in the Midwest U.S. (i.e., Missouri), where electromagnetic induction (EMI) geophysical methods have been successfully tested by investigators for determining claypan depth and spatial extent. Consequently, near-surface geophysical methods may also supply useful information on hardpan depth and spatial extent. Three near-surface geophysical methods were therefore tested on a hardpan present in an agricultural field near Blackville, South Carolina. The three near-surface geophysical methods evaluated were; 1) apparent soil electrical conductivity (ECa) mapping of the top 0.3 m and 0.9 m of the soil profile using an on-the-go resistivity measurement system, 2) ECa mapping of the top 0.75 m and 1.5 m of the soil profile using EMI, and 3) subsurface imaging using ground-penetrating radar at three different antenna frequencies. Near-surface geophysical results were then compared to cone penetrometer measurements and analysis of soil samples to determine the strengths and weaknesses of each near-surface geophysical method for providing insight on hardpans within agricultural settings.
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Optimizing the Metalmapper for Static "Cued ID" Measurements over UXO
Authors D.D. S. Snyder and C. P. OdenThe MetalMapper is a commercially available advanced EM system that includes an array of 3 transmitter loops and 7 tri-axial receiver cubes that is used for detecting and classifying UXO. In the current instrument, the number of receivers was determined by hardware limitations (24 analog channels max), and the receivers were positioned to provide uniform coverage when deployed for mapping surveys. With support from SERDP, we have undertaken a model study aimed at answering important questions about the optimality of the MetalMapper antenna configuration when deployed for static cued ID measurements. These questions include: Is there a significant advantage to tri-axial receiver loops as compared to a single loop receiver?; Are 7 tri-axial receivers necessary or might we obtain similar performance from an array of 5 tri-axial receivers that are better positioned? Our study extends earlier studies by Grimm and Sprott (Grimm 2002) at Blackhawk Geoservices (now Zapata/Blackhawk) and Smith et al (Smith 2005) at Lawrence Berkeley Labs. Those studies have guided us during the early development of the MetalMapper and its forbearer, the AOL system. Using synthetic data sets for a conductive and permeable sphere placed at random locations beneath the MetalMapper, we show that the current MetalMapper receiver array performs better than either an array of 7 single-component (dBz/dt) receivers or an array of 5 tri-axial receivers having several different dimensions. We obtained similar performance when we tested these arrays with a second synthetic data set that better simulates a UXO. Our study also confirms empirical observations from past demonstrations of the MetalMapper that the quality of shape-based target parameters is significantly degraded when the target has a horizontal offset from the center of the MetalMapper array of more than 40cm.
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INTEGRATED, STUDENT-LED HYDROGEOPHYSICAL INVESTIGATIONS AT A SUSPECTED CENTRAL TEXAS SINKHOLE
A suspected sinkhole (Quadborder Sink) with unknown hydrogeological significance in a central Texas metropolitan area provided a research topic that was addressed by a group of graduate and undergraduate students during a semester-long hydrogeophysics class. These students designed geophysical field experiments using frequency-domain electromagnetic induction, electrical resistivity, groundpenetrating radar (50 and 100 MHz), microgravity, and seismic refraction methods, acquired data at the field site over multiple weekends, processed data, presented field results in weekly classes, and integrated results in a jointly written, comprehensive class report. Each of the methods provided useful information to establish the likely presence of a sinkhole and its lateral extent, the thickness and lithologic character of the sinkhole fill, the possible presence of an underlying shallow void in this karstic area, likely areas of preferential hydrologic recharge, and the character of the shallow interface between clastic fluvial and lacustrine fill and carbonate bedrock. Strengths of the approach included application of multiple geophysical methods to a single hydrogeologic problem of concern to residents and a local governmental agency. Weaknesses included the inability to spend adequate time and effort to apply advanced processing steps to the datasets acquired using different methods and maximize the benefits of multiple geophysical approaches to a common problem.
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FULL WAVEFIELD SEISMIC ANALYSIS BENEATH THE A.V. WATKINS DAM, UTAH
A reliable measure of seismic properties as a function of depth is important to the Bureau of Reclamation’s comprehensive and accurate appraisal of site response (ground motion and acceleration) along specific segments of A.V. Watkins Dam in Box Elder County, Utah. A series of seismic data sets were acquired along coincident profile lines at the downstream toe of A.V. Watkins Dam. Three distinctly different surveys, each tailored to a different portion of the wavefield, were optimally acquired and processed. Two three-quarter-mile-long high-hazard portions of the embankment were targeted for this study.
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EARTHEN EMBANKMENT DAM INSPECTION USING ELECTRICAL RESISTIVITY TOMOGRAPHY
Authors Jared Case, Craig Hickey and Gregory HansonTwo quarter scaled experimental embankment dams were constructed at the USDA ARS Hydraulic Engineering Research Unit in Stillwater, Ok. These dams were constructed with two internal compromised zones that would be susceptible to seepage and piping. The zones consist of a sandy region and a region compacted at a lower moisture content. Preliminary measurements were performed on the dam during construction to gain initial resistivity of the zones and the dam body. These measurements showed that there was a good contrast between the zones and the dam body. This will make the anomalous zones easily visible in our initial tomograms. Electrical resistivity surveys have been performed on the embankments for over the course of a year to monitor changes in electrical signatures of the dam due to environmental changes and cyclic loading and unloading of the reservoir. Also forward modeling was performed using the EarthImager 2D imaging software. These models will help predict changes in the resistivity of these zones due to infiltration of water from the reservoir or from rainfall and also due to the removal of fines/clay content during piping. Field measurements are then going to be compared to the forward model predictions. [This research was funded by the Department of Homeland Security-sponsored Southeast Region Research Initiative (SERRI) at the Department of Energy’s Oak Ridge National Laboratory.]
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USING ERT TO LOCATE A HISTORICAL MINE TUNNEL
Authors Douglas LaBrecque, Russell Brigham, Brady Flinchum, Nicole Pendrigh, Phil Sirles and Paul IvancieExisting tunnels in historical mine sites often serve as conduits for acid mine drainage thus, delineating them can be important in remediating these sites. In a recent field study, electrical resistivity tomography was successfully used to locate a tunnel in a former mining district in the Rocky Mountains of Colorado. Prior to the ERT survey, a combination of historical mine data and surface geophysical surveys were used to find the approximate location of the tunnel. This culminated in drilling of boreholes on both sides of the location of the tunnel. Cross-borehole ERT was then used to provide a final estimate of the tunnel location. Surface-to-hole ERT surveys were conducted near a second, known portion of the tunnel to determine the feasibility of finding the tunnel using only a single borehole. In addition to the ERT surveys, an electrode was placed inside the entrance to the tunnel and used to perform mise-a-la-masse (MALM) surveys with receiving electrodes at the surface and in the borehole.
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INVESTIGATING THE SPECTRAL INDUCED POLARIZATION RESPONSE OF A CRUDE OIL SPILL SITE UNDERGOING INTRINSIC BIOREMEDIATION
Authors Farag Mewafy, Estella Atekwana, Dale Werkema, Dimitris Ntarlagiannis, Lee Slater and Andre RevilThe spectral induced polarization (SIP) technique holds great promise for detecting oil contaminated sites due to its sensitivity to physicochemical processes occurring during intrinsic bioremediation. Many studies have investigated the SIP response due to oil contamination; however, the mechanisms resulting in the SIP response resulting from oil contamination are not completely understood. An oil spill at Bemidji, MN occurred in 1979, when a high pressure crude oil pipeline ruptured, releasing 1,700,000 L of oil.
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CHEMOMETRIC DESIGN OF EXPERIMENTS APPLIED TO PHYSICOCHEMICAL AND GEOPHYSICAL LABORATORY EXPERIMENTS
By Dale WerkemaChemometrics design of experiments and analysis applied to physicochemical and geophysical laboratory experiments potentially enable more robust experimentation. Chemometrics extracts information from empirical chemical systems, physical systems, industrial processes, or other experiments. It is essentially an interdisciplinary science incorporating applied multivariate statistics and mathematics with the goal of exploring problems in chemistry, biology, engineering, industrial processes, and the medical fields, for example. This presentation presents results from two laboratory geophysical experiments performed to evaluate the physicochemical response to various experimental treatments in an aqueous solution and a sand matrix.
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GEOPHYSICAL INVESTIGATION AT THE PROPOSED CONCENTRATOR AREAS, IN AN IMPORTANT PROJECT IN SOUTH OF PERU, USING MEASUREMENTS OF COMPRESSIVE (P) AND SHEAR (S) WAVES.
More LessBefore evaluating the final location of the future facilities we need to characterizer and describe the soil foundation. One of the studies that we development to support our future decisions is the measurements of compressive (P) and shear (S) waves. The investigation of the ground site (in the Concentrator Areas) was conducted through geophysical testing using the seismic refraction test method, and surface wave measurement methods such as the multichannel analysis of surface waves (MASW) method and the multichannel array of microtremors (MAM) method. From the interpretation of the velocity of compressive (P) and shear (S) waves, the thickness and stiffness of soil layers at the project site were determined. The geophysical investigation was carried out to estimate the soil profile in the foundation areas of the projected facilities, through the determination of the velocity of propagation of both P (Vp) and S (Vs) waves in the ground, using surface seismic refraction tests for P-wave measurements, and MASW/MAM tests for Swave velocities.
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20+ YEARS OF EXPERIENCE, OBSERVATIONS, AND LESSONS LEARNED OF WITH THE MODERN DIGITAL ACOUSTIC TELEVIEWERS, AND THEIR IMPACT ON DATA QUALITY AND WITH FOCUS ON PRODUCTION MINING APPLICATIONS. PART I – BASIC THEORY, APPLICATIONS, PROCESSING STEPS, RESOLUTIO
Authors Robert Crowder and John StowellThe modern slimhole digital acoustic televiewer has been applied for the last 20+ years for a variety of applications from ground water to rock mass evaluation to casing inspection. After an extended period of limit application, the technology is now widely accepted and hundreds of tools are in the market place and routinely being applied by service and in-house groups around the world. During this time, a number of lessons have been learned and observations noted. Understanding and learning from these observations and details are critical in insuring highest quality and correct application of the data. Despite the great advances in instrumentation, lack of training with resulting mistakes in acquisition, common misconceptions and errors in the processing and interpretation of the data lead generate bad data that is frequently not identified.
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PART II – DATA QUALITY ISSUES, SOURCES OF ERROR, NUMEROUS DATA EXAMPLES, AND GUIDELINES FOR QC.
Authors John Stowell and Robert CrowderEnhancements in acquisition and processing software allow many people to collect acoustic televiewer data with minimal training. However, these tools are extremely sophisticated and flexible and it is easy to generate data with significant error. These errors can occur in data acquisition from misunderstanding image orientation scheme and requirements; use of magnetic centralizers or housing; use in a magnetic environment; from in correct tool sample decisions and logging too fast. They can also occur from tool orientation sensor or software failure. The most common issues with data quality are tool centralization and borehole fluid conditions and incorrect presentation scales. Accessory logs accompanying the image data can frequently be used to identify these data issues.
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QUANTITATIVE ANALYSIS OF MAGNETIC ANOMALIES IN THE EASTERN MEDITERRANEAN: A REVIEW
More LessMagnetic anomalies observed in the Eastern Mediterranean are characterized by strongly inclined magnetization (about 45o). It should be noted that the method “reduction to pole”, which often are used in the conditions of inclined magnetization, is limited by situation when all disturbing bodies in the studied area are magnetized parallel to the geomagnetic field and have subvertical dipping. Only in this case the magnetic fields recalculation will be correct and the obtained graphs will be symmetric and then may be used for further interpretation by conventional methods. Other disturbing factors are rugged terrain relief, unknown level of the normal magnetic field and complex geological media.
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Electrical Geophysics for Assessing Permafrost Conditions along Highway Infrastructure
Authors G.A. Oldenborger, C.W. Stevens and S.A. WolfeThe Yellowknife region, part of the Slave Geological Province, falls within the extensive discontinuous permafrost zone in Canada. A large degree of economic development is routed through Yellowknife from the mineral-rich North Slave. Despite the mineral-rich nature of this region, surficial sediment maps and knowledge of permafrost conditions are only now being established in detail. Permafrost and associated ground ice can significantly affect land-based infrastructure through influence on ground stability and drainage patterns. As such, geoscience information contributing to permafrost characterization is critical for understanding risks to roads which are vital to Northern economic development. The 100 km stretch of the chip-sealed Highway 3, west of Yellowknife, presently experiences instabilities including settlement, heave, and rotations related to transitions between differing terrain and drainage conditions within the discontinuous permafrost. Electrical resistivity data were collected over identified terrain types, and across potential terrain transitions and thaw fronts based on the hypothesis that permafrost distribution and conditions vary with terrain type. Processed resistivity models indicate distinct electrical signatures for most of the terrain types which would allow for extensive geophysical characterization complimentary to landscape mapping, temperature data and shallow boreholes. The resistivity models also exhibit features indicative of the base of ice-bonded permafrost, ice-rich sediment and thaw zones, which can be correlated with terrain features of sediment type and drainage. Observed resistivity anomalies indicate thaw zones related to existing and past road infrastructure, which help in understanding conditions causing highway subsidence.
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BOREHOLE IP RESPONSE IN TRADITIONAL AND NON-TRADITIONAL TARGETS USING VARIABLE INJECTION TIMES
Authors Robert Crowder, John Stowell and James LoCocoA borehole IP probe with fully digitized waveforms has been tested in both hard rock and sedimentary lithologies. In many cases, the response has been as expected, and the results are presented for measurements made in pyritic and sulphide dominated targets. Field data sets have led to questions regarding depth of investigation of the multi-electrode device, and whether different chargeabilities should be expected, based on geometrical considerations. Possible mathematical solutions to this apparent behavior are discussed.
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ALIS- GPR 3-D IMAGING FOR HUMANITARIAN DEMINING
Authors Motoyuki Sato, Kazunori Takahashi and Yuya YokotaHumanitarian demining is very important issue not only in mine affected courtiers but also for the courtiers which are technically, politically and financially supporting the mine affected courtiers. In order to achieve higher efficiency of the mine clearance operation, new technologies can significantly contribute to the societies. Since 2002, Tohoku University, Japan has developed a sensor system “ALIS” for humanitarian demining. ALIS is a hand-held dual sensor, which combines an electromagnetic induction sensor (EMI) and a Ground Penetrating Radar (GPR). We need to establish a high-resolution, high-precision GPR system for this task. In order to reconstruct 3D GPR image with high resolution, the position tracking of the antenna is a key issue. We have developed a sensor tracking system with CCD camera and image processing. Although this is a hand-held system, GPR data can be processed with location information, therefore we can obtain 3-D GPR image on site. We think it is a quite unique system, and validated its potential in real operations. We have tested ALIS in Cambodia and found that it can eliminate more than 70% metal fragments. Since 2009, 2 sets of ALIS have detected more than 80 anti-personnel mines, and cleared more than 137,000m2 in Cambodia.
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