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Near Surface 2006 - 12th EAGE European Meeting of Environmental and Engineering Geophysics
- Conference date: 04 Sep 2006 - 06 Sep 2006
- Location: Helsinki, Finland
- ISBN: 978-90-73781-62-7
- Published: 04 September 2006
101 - 120 of 142 results
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Confirmation of the Geophysical Site Characterization Results by Tunnel Observations at Olkiluoto
Authors C. Cosma, N. Enescu, H. Ahokas, E. Heikkinen and T. AhokasA project for geological disposal of spent nuclear fuel deep into Finnish bedrock has been run now since 1988 in Eurajoki Olkiluoto, western Finland (Anttila et al. 1999, Enescu et al. 2004). The related research and development tasks are carried out by Posiva Ltd. A multiphase characterization with geological, hydrological, geophysical and hydrochemical methods have been run from ground surface and boreholes. One of the crucial tasks in the early investigation phases were recognition of avoidable volumes of bedrock, which are more fractured (faulted), sheared or altered rock sections in the bedrock mass of generally high quality. The initial design of underground spaces has based on interpretations of these ground and borehole studies. The excavation of access tunnel leading to future underground investigation facilities started in 2003. The tunnel profile is 6 m and its raise is 1/10. Tunnel will reach the level -420 m by 2010 then characterization will be continued at the -400…-500 m depth levels until 2020. Current tunnel length is 1030 m, and depth 100 m from ground level. The tunnel offers a new view for characterization and confirmation of the observations. The progress makes it possible to implement a prediction and confirmation cycle.
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Continuous Pollution Monitoring by Pulse-Neutron-Neutron-Technique
More LessAlong Neutron-decay-curves a fully approach to elemental detection is featured. By mean of countrates elements and compounds may be identified over pregiven monitoring periods till the exhausting of the physical neutron source. The pulse neutron monitoring is equally effective for water and soil. Experiments and fieldtestd have shown, that the majority of potential pollutants (organic and inorganic) may be identified at least in the ppm-range.
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Study of Pollution of the Subsoil Under Slurry Ponds
Authors E. Aracil, P. Martínez-Pagán, U. Maruri, A. Faz and J. VallésSlurry is the residual material formed from solid and liquid animal wastes, water from drinking trough, and the cleaning of stables. This intensive livestock activity in some farms in the Region is more than 20 years old. The slurry ponds, owing to the typical nature of slurry, are sources of potential contamination: eutrophization of the aquatic environment, contamination of subterranean water with nitrates and soils, salinization, phototoxicity and nutritional imbalance in plants.
In order to study the temporal evolution of these effects on the subsoil in two slurry ponds located near Lorca (Murcia, SE Spain), geophysical techniques were employed specifically 2D and 3D electrical tomography. Use of these non-destructive geophysical techniques intends to evaluate if 2D and 3D electrical tomography is capable of revealing possible leakage of contamination in the subsoil through the seasonal monitoring of the slurry-soil interaction.
The results had confirmed that this technique is suitable for this type of study in the first 15 meters according to the contrast of resistivity between the material of subsoil and the slurry. The results clearly reflect what the direction and depth of filtration is.
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Solution of Near Surface Environmental Problems Using TAU-Transformation of IP Data
Authors M. Dobroka, E. Turai and P. VassIn this paper a generalization of the TAU-transform method introduced by Turai (1985) is presented. On combining the TAU transform method and the tools of inverse problem theory a general algorithm for the determination of the time-constant spectrum of the polarizability data (deduced from time-domain IP measurements) is available for the general case of continuous spectra (Turai, Dobróka, 2001). In the practice we use global inversion method for determination the time-constant spectra.
Induced Polarization is a very useful geophysical method also in the detection and haracterization of environmental spots mainly waste sites.
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Resistivity Survey to Assess Corrosion along a Proposed Pipeline Route in the Niger Delta
Authors A. I. Olayinka and M. A. Oladunjoyeis marshy or swampy. The Wenner and Schlumberger arrays were adopted for topsoil and subsoil resistivity determinations, respectively. Along the pipeline route 85 profiles and 85 sounding stations were occupied while at the flow station 40 profiles and 40 soundings were carried out in a grid form w. Measurements were taken in both N-S and W-E directions and the averaged values employed for interpretation. The results show that the resistivity of the subsoil along the pipeline route ranges between 2 and 233 Ώm (mean = 48 ± 29 Ώm); its thickness ranges between 1.6 and 17.5m (mean = 6.3 ± 3.0m). The resistivity of the subsoil within the flow station varies between 13 and 165 Ώm (mean = 42 ± 27 Ώm) while the thickness varies from 2.4 – 28.5m (mean = 8.5 ± 4.9m). Very low subsoil resistivities were obtained in areas dominated by mangrove plants, due to the influence of saline water. Any underground metallic piping or structure is liable to corrosion.
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A 3D Constant Offset GPR Survey on Ilhavo Landfill
Authors M. J. Senos Matias and H. HermosilhaThe degradation of sealed landfills can be hazardous but can also be of economic interest as biogas is produced. The internal landfill characterization can be investigated by geophysical methods. Here in a preliminary GPR survey, with a 100MHz antenna, was carried out and the results obtained allowed the interpretation of the landfill base, identification of high attenuation zones, interpreted as leachate accumulation, diffraction zones, interpreted as metallic objects and, finally, landfill collapsed areas.
The integration of several 2D profiles into a 3D block allows the analysis of lateral and depth continuity of the interpreted events.
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Hydrocarbon Plume Attenuation Monitoring with Electrical Methods
By J. C. GourryIn the framework of a research programme on natural attenuation of hydrocarbon and chlorinated solvents, geophysical methods have been evaluated for pollutant plume evolution monitoring in ground water. Test site is an ancient cokery plant where 2 large leaking coal tars have polluted ground water since decades. Hydrocarbon plume which is mainly composed of dense (DNAPL) coal tars, few light (LNAPL) hydrocarbon compounds with sulphate and nitrate which are by-products of coal refinery. Ground water table is situated around 25 to 30 m deep. Clay aquitard is around 60 m deep above the chalk aquifer.
Since 3 years, pollutant plume is monitored with a buried electrode configuration (resistivity and chargeability and electrical tomography profiles. Surface geophysical measurements are compared to chemical analysis (anions, cations, total hydrocarbon, and polycyclic aromatic hydrocarbons) and physical-chemical parameters (pH, Eh, conductivity) loggings in boreholes.
As hydrocarbon biodegradation strongly modifies electrical properties in soils and in ground water, hydrocarbon DNAPLs are characterized by conductive plumes. Geophysics showed agriculture water pumping and chalk fracturing influence on plume migration. The good correlation between chemical and geophysical parameters proves that electrical methods are effective for hydrocarbon plume monitoring and long term plume modelling.
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The Demonstration of Monitored Natural Attenuation in Oil-Contaminated Test Site near City of Hanko in Southern Finland
Authors P. Hänninen, T. K. T. Huotari, P. Lintinen and K. S. JørgensenIn this EU-Life-funded project we demonstrate the feasibility of MNA as a remediation technique for oil-contaminated sites in southern Finland. The study site, Trollberget, is an abandoned dumpsite outside the City of Hanko. ERT was used to map the hydrogeological and geological properties of the study site. The ERT measurements revealed clearly conductive zones near and at the place of the oil dump site. Also automatic monitoring stations were installed for monitoring the ground water. The ground water was at the highest level in wintertime and at the lowest in late summer. Ground water EC was anomalous high in monitoring site. Still, the ground water EC showed clear decreasing trend during the monitoring time. On-line monitoring of soil and groundwater conductivity together with electrical resistivity soundings seem to be promising monitoring tools for addressing biological activity.
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3D Resistivity Mapping of Aged Hydrocarbon-Contaminated Site
More LessResistivity and GPR surveys were conducted to characterize a former gas station site contaminated with fuel hydrocarbons. The results of geophysical investigations, incorporated with soil boring data provided the shallow geologic structure of (1) upper soil unit of mostly boulders and rock fragments, (2) lower soil unit of sediments and/or residual soils weathered from the bedrock, and (3) granite bedrock. The water table of the site is located in the lower soil unit, and the elevation of water table varies with topography from approximately 1.5 to 3 meters in depth. 3-D inversion of resistivity data have shown that the aged hydrocarbon-contaminated soils show low resistivity anomalies attributed to the biodegradation of petroleum hydrocarbons, and that the fuel hydrocarbons leaked from the USTs and fuel lines at the station have migrated downgradient over the water table toward the streamlet, and that most of petroleum-impacted zone lies near the water table in the smear zone within the lower soil unit. The study results also demonstrated that the geophysical methods, as a non-invasive environmental sounding technique, can be a very useful tool for characterization of the contamination sites.
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Resistivity Imaging for Mapping of Groundwater Contamination at the Municipal Landfill La Chureca, Managua, Nicaragua
Authors L. T. Dahlin, K. Forsberg, A. Nilsson and P. FlyhammarThe purpose of this study was to map and describe groundwater contaminations at the La Chureca landfill. The groundwater level in the landfill is higher than in the surrounding area creating a local deviation from the regional groundwater flow. Due to this the contaminated groundwater from the landfill spreads out in the nearby soil and groundwater. The resistivity imaging results clearly show a top layer of around 10 metres thickness with low resistivity, where the resistivity has an inverse correlation with distance to the landfill. The soil samples show that the upper 10 m of the soil consists of loose permeable volcanic ashes with high water content, which are followed by a compact impermeable layer of tuff. The correlation between low resistivity and contaminated groundwater is confirmed by chemical analyses of groundwater samples. The compact layer of tuff appears impermeable enough to stop the contamination from penetrating deeper than approximately 10 m, which is supported by the resistivity imaging that show no traces of low resistivity below the top layer. Based on the combined results the contamination plume seems to stretch around 400 m in the southern direction and not more than 1000 m in the western direction.
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Rapid Accurate Evaluation of Permeable Zones for Reclaimed Water Recharge at Begur (Spain) from Electrical Resistivity Tomography
Authors A. Casas, J. C. Tapias, M. Himi, A. Masachs, L. Rivero and M. SalgotWhen trying to perform an integrated management of water resources, groundwater volumes can be increased by reusing reclaimed water for recharge. Reclaimed wastewater is a valued non-conventional resource in arid and semi-arid areas where water is scarce, but also in the Mediterranean countries because of the wide rainfall irregularity. Understanding in detail the structure and properties of the vadose has nowadays become crucial for recharging with reclaimed effluents, to ensure an effective percolation through the soil and an adequate treatment.
One of the easiest and cost-effective techniques for producing a large amount of information on aquifer geometry and subsoil properties is electrical imaging technique. The underlying objective of this paper was to test the advantage of using this geophysical method for the continuous characterization of the subsoil structure around the Begur treatment plant, where treated wastewater is discharged and reused in a Soil-Plant-Aquifer system. The good results of wastewater application to the area are also discussed.
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Analysis of GPR Trace Attributes and Spectra for LNAPL Contaminated Ground
Authors H. Marcak and T. GolebiowskiThe paper presents results of GPR measurements carried out over areas contaminated with LNAPL products. The mean traces from clear and contaminated parts of the ground were calculated. For mean traces the signal attributes and spectra were determined. The changes in GPR trace attributes and spectra for clear and contaminated areas of the ground were analysed by their comparison.
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Long-Term Application of GPR Technique for Estimation of Ground Contamination Degree
Authors A. Dolgiy, A. A. Dolgiy, V. Markulis and V. ZolotarevIn this paper practical results of the long-term (1999-2005) application of Ground Penetrating Radar (GPR) technique for estimation of electrical parameters of contaminated ground are presented. Contamination was caused by oil product leakage from pipeline. GPR technique includes a procedure of GPR profiling and application of Common-Midpoint (CMP) method. The GPR data allowed to acquire values of thickness of ground layers and their relative dielectric permittivity. These values were connected with the degree of ground contamination which was attested by measurements of a floating layer thickness of oil products in observation wells. These procedures were repeated during 6 years with the objectives to find steady time correlation of GPR data with ones acquired by attesting method. The GPR data allowed to monitor changes of oil contaminant concentration in the ground for optimal execution of environmental remediation actions and to detect in May 2005 the place of oil leakage from buried pipeline. After pipeline repairing the degree of ground contamination was decreased up to 10% in autumn 2005 comparing with 2004.
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The Application of the Ground Penetrating Radar (GPR) as a Non Intrusive Method to Measure Soil Water Content
More LessThis paper assesses the use of the ground penetrating radar, GPR, for measurement of soil water content. Results of laboratory Constant Mid Point tests, performed on an apparatus developed for this purpose, were analysed, on the basis of Time Domain Reflectometry theory. All tests were performed on sand. Electromagnetic pulses velocities were measured in a dry sample (w ~ 2%) and a saturated sample (w ~ 24%) under steady-state conditions and in unsaturated samples under transient conditions. Based on laboratory results, a theoretical equation is proposed in order to forecast electromagnetic pulse velocity in unsaturated mediums, showing a good agreement with experimental results.
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Challenges in Gamma Ray Interpretation - A Case History from Rautuvaara Mine Tailins
Authors P. O. Turunen and E. V. LanneWater is an important attenuator, amplifier and carrier of gamma radiation, especially if the radiation originates from the decay series of uranium. In mine tailings the water is often acid and it leaches uranium and transports it to new locations. One of the members of the decay series, radon, is likewise transported by flowing water. Movements of uranium or its daughters violate the secular equilibrium, and pose problems in the interpretation of field measurements. A gamma radiation anomaly at a certain position does not necessarily mean the presence of uranium, neither does the absence of radiation necessarily mean the absence of uranium. Further, the water causes characteristic changes to the gamma spectrum of bismuth, which may be used to get a rough estimation of the amount of water in the earth materials.
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A Multidisciplinary Study of an Old Mine Waste Site in Sweden Using Geophysical, Geological and Geochemical Methods
Authors L. Persson, H. Holmström, K. Lax, L. Maxe, M. Ripa and T. SträngA multidisciplinary study has been carried out at an old mine site in the central part of Sweden. The mine dumps at smaller and medium sized old mines in Sweden can still pose a local threat to the surrounding environment as the waste is oxidised, which leads to the formation of acid water solutions and release of heavy metals.
The main objective of the study is to characterize the acid mine drainage in order to predict future problems and if necessary find efficient remediation methods, which also preserves the historical value of the site.
The preliminary results from one of the investigated mine areas show that the local environment is clearly affected by the waste rock from the mining activities. Both soil and water samples collected from the stream draining the deposit are characterised by low pH and high metal concentrations. The extension of the contaminated area could be mapped by electromagnetic and electric methods and the results from the geophysical measurements correlate very well with the geochemical data.
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Efficient High Resolution Subsurface Shear Wave Reflection Imaging in Sealed Urban Environments
Authors T. Beilecke, U. Polom and S. HoffmannSealed urban environments, associated traffic, and subsurface supply lines are normally considered very challenging terrains for high resolution seismic subsurface structure imaging. If cost efficiency is also taken into account, seismic measurements in urban areas are often considered expensive. Recently, a combination of a small shear-wave vibrator and a shear- wave land streamer was tested in Hanover, Germany as a tool for structure determination in cities. After two weeks of seismic data acquisition, not only the used SH shear-wave reflection exploration set-up proved to allow a comparably fast and trouble-free measurement progress, but also the inherent advantages of sealed terrain with respect to the absence of surface waves and in terms of uniform coupling has become apparent.
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Kars Investigation by Microgravity and MASW Coupling
By A. BitriA geophysical integrated approach for the detection and characterisation of karst structures in an urban environment was experimented. Microgravity was performed for void detection, together with Multi-channel Analysis of Surface Waves (MASW), aimed to the identification of mechanical weakness areas.
Microgravity evidenced negative anomalies corresponding to known conduits and identified the probable extensions of this network in unexplored areas. Control borings, located on these extensions, encountered several levels of water saturated voids, probably belonging to the shallowest part of the karstic system, overlying the main conduits. Simulations, using compact inversion approach for the size and density characterisation of environmental disturbances, confirmed this conclusion. In this context, gravity method proves suitable to the detection of karstic near-surface features.
The MASW method, that analyses the Rayleigh wave propagation, can characterise the mechanical behaviour of superficial formations and serve as indicators of subsurface heterogeneities, such as voids or fractures. The MASW evidenced disturbed zones superimposed to gravity anomalies, characterised by the appearance of several dispersion modes, velocity inversions and seismic markers attenuation. One of these features was characterised by low velocities and interpreted as a mechanical weakness area that was confirmed by pressure measurements in the boreholes.
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Detection of the Natural and Man-Made Cavities in a Urban Area in Lower Austria
Authors S. Seren and A. Eder-HinterleitnerNatural and man made cavities in an urban area constitute an important risk for the buildings. The cavities in the underground cause lowering then again different damages on the buildings. The activities for the preservation of the buildings and the estimation of the risk requires information about positions and dimensions of the cavities. In an urban area the investigation of the all geophysical methods is very difficult or often impossible. In order to detect the cavities in the urban area Marienhoehe/Maria Enzersdorf in lower Austria, which have induced a lot of damages on the buildings, seismic, resistivity and ground penetrating radar (GPR) are applied. In particular it was possible to localize zones with cavities by seismic methods. Subsequent the specifically targeted drillings confirmed the results of the seismic measuring. They prove the existence of natural and man-made cavities in gypsum which are accrued by mining activities more than one hundred years ago.
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Geotechnical Problems Caused by Abandoned Stone and Clay Mining Areas
Authors Z. Pronay, E. Törös, B. Neducza and R. Miskolczibánya (Budapest, Hungary) was the main source of building materials at the end of the XIX. Century. At that time it was a suburb but the growth of the city reached it in the next century. Later most of the open pits were filled by waste. It causes severe geotechnical problems on the residential areas and besides there is a continuous need the use the filled pits for building purposes. The geotechnical solution of the problems is rather easy but expensive. In most cases it would be enough to know the maps of the pit at the time of the closure but unfortunately most of them were lost. In other cases, mostly at open pits filled by waste the compaction and the decomposition of the organic materials cause problems over a long period. The waste is highly inhomogeneous, conventional geophysical methods, supposing layers, can’t image the pits with satisfactory results. Seismic tomography using different wave-types was used to map the outlines and the structure of the backfilled pits. Experiments were made to detect the gas content of the decomposed waste by using Vp/Vs ratio.
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