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4th EEGS Meeting
- Conference date: 14 Sep 1998 - 17 Sep 1998
- Location: Barcelona , Spain
- ISBN: 978-94-6282-127-9
- Published: 14 September 1998
1 - 100 of 236 results
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Spectral characteristics at a former industrial site using complex resistivity
Authors A. Binley, A. Eriksen, J. Gascoyne, T. Nguyen and A. KemnaThere is growing interest in using geophysical techniques for characterising former industrial, or 'brown field', sites. In particular, Olhoeft (1996) and others have prompted a number of studies into the use of speetral geo-electrical properties for assessing levels of contamination in sites polluted by hydrocarbons. We report here on the results of a recent survey using complex resistivity to assess the value of resistivity spectra in improving our understanding of the subsurface properties at a former industrial site and the extent of hydrocarbon contamination at the site.
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A new method and instrumentation for the soil contamination survey
More LessThe new introduced method for the soil contamination survey is based on the analysis of the soil gas or vapour. This newly developed method offers fast andreliable location of contaminant sourees and trajectories of the contaminant spread. Gas from the pore space in soil and rock formations is commonly known as soil vapour. The composition of this phase, in particular the présence and concentration of organic compounds, reveals vital information about pollution of the subsurface environment. Organic compounds constitute a group of contaminants which impact severely on groundwater resources. The presence and distribution of such pollutants can be detected by a new established technique known as a Soil Vapour Analysis ("SVA") or Soil Vapour Survey ("SVS").
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Using subsurface geophysics to avoid environmental degradation while enhancing oil recovery from a producing field
Authors A. Bouvier and T. TantawyThe Tengiz oil field in KAZAKHSTAN, located on the northern and eastern shores of the Caspian Sea, is a major oil field where Russia initiated production more than 25 years ago. In the past three years, Tengiz Chevron Oil (TCO) increased production significantly and was recently considering drilling new holes to boost output. To help to the selection of drilling locations, a 3D seismic survey using both vibrators and dynamite was conducted on the 400 km2 producing field. Because the location accuracy of the current buried pipe network is not sufficiently precise on available maps, a reconnaissance test took place at specific sites where old and recent pipes are known to exist. Most of these sites were also selected for their proximity to sensitive structures : plan facilities, manifold, dike edging the sea and office buildings where safety distances from seismic sources had to be determinated with a view to a forthcoming 3D seismic reflection survey.
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Air pollution mapping by portable sensors and DGPS positioning
Authors M. Fernetti, M. Gasparini, G. Manzoni and A. PurgaIn 1994 we applied the satellite positioning method to environmental monitoring (Camus et al., 1994, Cefalo P.,1996). A Carbon Monoxide electrochemical sensor was mounted on a car together with a GPS positioning sensor. The car was driven along the streets of Trieste center and the concentration of this gas was measured every two seconds. By properly choosing the urban route with crossing streets, the data were processed in the form of contour levels, so allowing a mapping of the CO concentration. The data were also processed as street pollution profil es. The sensor has a delayed response of about 9 seconds. Moreover, the CO concentration as measured outside a vehicle suffers a lot of transient peaks due to the exhaustion of any car or motorbyke close to the sensor. Nevertheless immediatly repeated passages on the same street displayed the same concentration within 20%, which is quite a significant result if the measurement campaign is devoted to alert authorities and people of the dangerous pollution.
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Magnetic mapping of soil pollution around a glass factory of Bratislava, Slovak Republic
By O. DurzaHeavy metals are important in several ways: many are used industrially in technologically advanced countries, some are physiologically essential for plants and animals - and thus have a direct bearing on human health and agricultural productivity - and many are significant as pollutants of ecosystem throughout the world. Heavy metals in soils have received increasig attention in recent years. Metals, which accumulate in the human body, such as Cd, Hg and Pb, are particular cause for concern. There have been reports of deaths and illness related to environmental Cd and Hg poisoning, and elevated levels of Pb in the blood of infants are becoming more common. These findings have provided a stimulus for more comprehensive studies of known or suspected areas of pollution and for complementary investigations of the chemical behavior of heavy metals in soils. A current method of a lithogeochemical mapping has supposed sampling of a definite soil horizon and following chemical analysis of the elements. Recent studies have shown that under certain conditions magnetic susceptibility can be used as a proxy parameter for the detection of higher heavy metals contents in soils. There were verified in many papers ( Durza et al 1993, 1996; Strzyszcz, Magiera 1996, Versteeg 1996; Kapièka 1997; Hoffman 1997; ...) that detected higher values of magnetic susceptibility of soils' samples above background indicate higher concentration of heavy metals in soil. There were recommended by Mikajev and Zogolev (1990) to use soil kappa-metry like a preliminary method that enable to border zones .Increased geochemical activity", to bring down a bulk of works and to change flexibly the method of mapping.
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Mapping of complex hydrocarbons contaminant using geoelectric and electromagnetic methods
Authors A. Godio and G. MorelliA combined geophysical survey was carried out in a oil refinery to study the complex hydrocarbon contamination of the soil and the near surf ace aquifer, resulting from several years of leakage of hydrocarbon products. A near surf ace level characterized by a strong reflector was weIl detected using Ground Penetrating Radar; lateral changes of the strength of the reflection and the subsequent drilling confirmed the existence of a free phase of hydrocarbon in the vadose zone above the water tabIe. Because of the limited thickness of the layer embedded with the residual oil, the geoelectrical resistivity measurements were not effective for detecting this level. The resistivity measurements pointed out very low values in the upper zone of the aquifer; this effect can be associated to complex chemical reactions between the dissolved hydrocarbon phase and the aquifer system. These effects were investigated using high resolution geoelectrical tomography. Soil data resulting from several boreholes confirmed the reliability of the geophysical response. Geochemical and physical analysis of the soil and groundwater samples, combined with the geophysical investigation, allowed the definition of a reliable model ofthe polluted area.
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Combined geophysical monitoring of a controlled LNAPL-Release
Authors M. Gruhne, F. Borner, R. Giese, Th. Richter and U. PippigThe exploration of contaminated sites represents a demanding task. Geophysical methods are predestined to deliver a high resolved spatial distribution of underground parameters. A promising strategy is to combine several geophysical methods. The development of qualified equipment and interpretation techniques should take place under undisturbed conditions. A large scale hydraulic experiment was carried out in February 1998 at VEGAS-facility (Versuchseinrichtung zur Grundwasser- und Altlastensanierung) at University of Stuttgart. One main part of the research doing there at VEGAS consists in the investigation of movement and spreading of non-aqueous phase liquids (NAPL' s) in the vadose zone. The objective was to monitor a hydraulic experiment using geophysical methods (complex conductivity tomography and cross-borehole radar tomography) and nongeophysical procedures (TDR, fluid level measurements, fluid pressure measurement).
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Geophysical characterization of groundwater protective layers
More LessTo enable an effectice proteetion of near surface groundwater reservoirs against pollution from agriculture, industry or waste disposals the protective qualities of the unsaturated layers on top of the aquifer must be quantified. On that basis the risk of groundwater contamination can be mapped and endangered regions can be protected be governmental regulations. A mean for the protective qualities can be the percolation time from the surface to the groundwater saturated zone. While groundwater is moving through the unsaturated layer the concentration of contaminants is reduced by biological and chemical processes. These processes are time consuming, and as a rule of thumb a percolation time of at least 10 years can offer an effective proteetion of our groundwater resources.
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Laboratory investigations to prove low concentrations of hydrocarbons in soils
Authors N. Klitzsch, F. StalImaeh and F. JacobsThe most ecological way to clean soils from organic contaminants is biological remediation. In addition to chemical analyses, geophysical measurements are an useful instrument to monitor the remediation process. Geophysical measurements can provide information of three-dimensional distributions for several parameters, e.g. temperature and resistivity (related to salt and moisture content), which are interesting for the remediation process. In a project supported by the Centre for Environmental Research Leipzig - Halle the possibilities to detect low concentrations of hydrocarbons in soils with geophysical measurements are investigated. The laboratory study is focussed on the speetral induced polarization (SIP) method. Additionally, nuclear magnetic resonance (NMR) measurements are carried out in order to understand petrophysical processes influencing electrical spectra.
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Frequency and DC electrical Behaviour of polluted sediments in industrial areas: field and laboratory investigations
More LessThe aim of this research is to find the class and the quantity of pollutants in soils and rocks on the bases of the different electrical behaviour of organic compounds and metallic ions at the solid-liquid interface, as function of electrical frequency in the DC-.;-.200kHzrange. This research started from previous laboratory studies of the polluted sample electrical responses. The electrical behaviour of these samples has been analysed following the method of Losito et al.(1985) pointed out to investigate the phyllosilicate electrical properties. The method starts from the waveform analysis of the electrical signals, that are strongly distorted by the double-layers of clay minerals. The classical THD% (% Total Harmonie Distortion) and the HD%(co) parameters, used in this analysis, are also strictly dependent of the pollutant molecular size and give an "electrical signature" ofthe pollutant-mineral interaction. On the base of the said laboratory results, a Geoelectrical Integrated Method (GIM) has been performed and tested to investigate and monitor the presence of chemical and organic pollutants near riverbed, water tables, and urban waste deposits.
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Geophysical studies for geoecological monitoring in Belarus
Authors I. A. Busel, V. V. Kazaryan and V. G. LobodenkoIn spite of their informative value, geophysical methods have not always being used in full measure at geological prospecting and monitoring. Let' s consider, as an example, the case history of point pollution of geological medium from oil boreholes drilling products.
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Complex investigation of radon concentrations in soil gas and electrical tomography in Lithuanian Karst Region
Authors D. Michelevicius and R. SeckusThe national radon survey in Lithuania started in 1995. Measurements have been performed in 400 randomly selected detached houses. Two separate used by inhabitants rooms used to be selected for measurements. E-PERM electrets by Rad Elec Inc were used for registration of indoor radon concentrations. The measurements were performed during heating season for 3 or more weeks. The results indicate dependenee of indoor radon concentrations on location of house. Five regions have been detected with average indoor radon concentrations exceeding the national level (55 Bq m") by almost two times. Houses with indoor radon concentrations higher than internationally recommended and nationally adopted levels of action (400 Bq m-3 for existing and 200 Bq m-3 for new houses) have been detected during the survey. One more region with elevated indoor radon concentrations has been identified in the karstic area near Birzai. For identification of this region the data available in the Lithuanian Geological Survey have been used because the measurements in randomly selected houses have been unable to disclose uniquity of this region. Analysis of results shows with small exceptions that the main souree of indoor radon in Lithuania is soiI. Since it is necessary to create the system of radon risk mapping selective measurements of radon concentrations in the soil air have been performed. Electrical tomography measurements were also included in order to get a possible correlation between distribution of radon concentration in soil gas and apparent resistivity anomalies of subsurface.
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Detection of anti-personnel landmines (APL) by integration of TEM-resistivity and IR surface temperature data
By C. OelsnerEvery year some 20.000 civilians are killed by landmines (UN estimates). Even if at the Ottawa Conference a convention against anti-personell landmines (APL) was signed, the old problem of mined areas remains still existent. Due to the Ottawa Convention there are following tasks among others: - mined are as must be identified, marked, and feneed as soon as possible, - all mines in these mined areas must be destroyed within 10 years. These problems up to now merely have been solved by deminers with different fully developed magnetic anomaly detection systems. Before the Ottawa Convention, mine producing industries have advertised their products under the aspects of "difficult or even impossible -detectability by conventional demining processes due to minimum iron content of the mines. Therefore the new task, which geophysics has to solve is as follows: detection of a very low conductive target in a very shallow depth from 5 cm to 20 cm. Additional disadvantage are the small sizes of the mines, which go down to diameters of approximately 5 cm. It is evident, that the methods being used must belong to those of remote sensing. In contrast to other geophysical targets a false result of measurement and interpretation will have catastrophic consequences. By UN a detection security of 99% is required. Additional demand is to reduce the rate of false alarm. From geophysical point of view this problem reminds of' 'squaring the circle
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LNAPL Detection using ground penetrating radar
By L. OrlandoHere are reported the results obtained from the application of the georadar method for the detection ofLNAPL (Light Non-Aqueous Phase Liquids) when they are floating on the water table. In order to do this study it was necessary to fust consider the georadar response on a theoretical model, which would respond in the closest possible manner to the actual case, and then move on to the field data. The studies on the theoretical model and on the field data have shown that it is not possible to individuate the presence of light hydrocarbons floating on the water table without resorting to the evaluation of attributes. Among the numerous attributes, in this work, only the instantaneous amplitude, phase and frequency were taken into consideration. Among these attributes, the instantaneous amplitude and frequency allow detection of hydrocarbons, while the instantaneous phase gives only a better lateral continuity of reflectors.
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The ground soiling by petroleum and other organic liquids: detection and study by GPR and seismic
Authors M. B. Rapoport and V. I. RyjkovOne of the main kinds of environmental pollution is the pollution of the ground with petroleum and other organic fluids, incJuding chemical wastes. Emission from oil wells, breakage of pipelines, leakages from huge reservoirs at the refineries, chemical plants, military bases, filling stations, airports etc- at first should belocalized and observed. Among geophysical methods to be used for studying such pollutions preferenee is given by us to impulse wave methods-GPR [1] and seismic. Although there are principal differences in the character of waves, both methods allow to make the zones of pollution contrast enough at the images obtained.
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Detection of hydrocarbon contaminated soil with radiomagnetotellurics
More LessSoH contamination caused by hydrocarbons is a problem for the reorganisation of closed factories and tank farms. It is necessary to determine the kind and content of the contaminants. Soil samples lead to reliable results but the detailed investigation of an area requires a large number of boreholes, which are usually quite expensive. Radiomagnetotellurics (RMT) is comparable to the known VLF-R method but uses a broader frequency range (10-240 kHz). Electromagnetic sounding is possible by using several radio transmitters with different frequencies. The horizontal electric field in the direction of the radio transmitter and the horizontal magnetic field perpendicular to this direction are observed. From the ratio of the amplitudes of these fields the apparent resistivity is derived. The phase between the two fields yields the second measured value.
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DC resistivity and time-domain induced polarization survey for the study of ground-water contamination in Bahia, Brazil
Authors A. Rühlow, B. Tezkan and O. A. L. de LimaDC Resistivity measurements were used to identify residual contaminant accumulation in sandstone aquifers by means of conductive anomalies. The contaminated regions were distinguished from conductive lens es of clay by simultaneously coIlected lP data, what would not have been possible by use of the method of DC resistivity alone.
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Construction of a 3D hydrogeological model using 2D resistivity imaging to determine potential contaminant pathways
Authors A. C. Vickery and B. A. HobbsThe City of Edinburgh Council is currently redeveloping the West Granton area in north Edinburgh, Scotland. The area has accommodated heavy industrial use for the past 150 years and consequently has numerous possible contaminant sources. A major concern for potential groundwater pollution is the emergence of contaminants on the neighbouring foreshore. This paper concentrates on the sites of two former oil distribution terminals that have been acquired for remediation and redevelopment. Figure 1 locates the old installations used for the storage of various hydrocarbons. By 1987, all the storage tanks and surface structures were dismantled to ground level. Contaminated made ground was cleared from the eastern most site which was awarded a certificate of remediation.
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Can resistivity methods be used to locate heave metal contaminated soils?
Authors C. Bernstone and T. DahlinThere are a large number of contaminated sites in Sweden requmng some form of remediation. In many cases the contaminants are heavy metals; here the level of contamination is often unknown. A typical investigation scheme includes chemical sampling to map the extension of the contaminant at the specific sites. Benefits could be derived from the use of additional methods, such as geophysics, to achieve a means of interpolating the result from the chemical sampling scheme. This is rather straightforward for some types of contaminants, e.g., brines that are highly conductive. An essential demand is, however, that there be a large enough contrast between composition of the natural geological environment and that of the contaminated area. In the case of high concentrations of heavy metals, a detectable physical anomaly can be expected, at least in theory. However, heavy metals are easily adsorbed into clays and organic soils. lts detection probably relies on the ohmic conductance, which can contribute to the current paths (i.e., not only electrolytic conductance) .
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Unconventional geoelectrical methods to observe the diffusion processes of contaminants in porous media
Authors V. Copertinn, V. Cuomo, G. di Bello, V. Lapenna, S. Piscitelli, V. Telesca and S. TroisiA geophysical survey, based on unconventional geoelectrical prospecting methods, was carried out in a controlled test site located in Montalto Uffugo (CS), Southem Italy. The main objective of the study is to outline the complex geological features of subsurface and to gain information about the hydrogeological features of the investigated area. Subsequently, the geoelectrical measurements will be used to control the time evolution and spatial distribution of contaminants and to analyze the correlation between the soil resistivity and the hydraulic characteristics of aquifer.
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Application of geophysical methods for studies of sites, polluted with old war ammunition
Authors D. Kolarov, W. Spyra and H. PetzoldOn the most part of Brandenburgland during the Second World war some battle collisions passed. As the result on battle fields a lot of different ammunitionfrom shellsplintersof grenades and mines up to non burst airbombshave remained.On the other hand Brandenburg land develops widely coal industry. As is known in south part of Brandenburgland there are some open mines for coal production.The presence of huge amountof ammunition'srests convertsa developmentof new coal deposits to very difficult anddangerousbusiness.
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Environmental mapping using airborne geophysics in Finland
Authors J. Lerssi, T. Jokinen, J. Lohva and R. PuranenGeological Survey of Finland (GSF) has carried out systematic airborne geophysical surveys in Finland since 1951. The second program started in 1972 using a flight altitude of 30-40 meters and line spacing of 200( 100) meters (Lohva et al, 1996; Peltoniemi, 1986). Today 80 % of the country has been measured. The measurements have been made with fixed-wing aircraft. The differential GPS is utilised in navigation. In lowaltitude measurements the following systems are in use: magnetic, gamma radiation and EM. Total magnetic field is measured with a wingtip gradiometer. The horizontal spacing between the magnetic gradiometer sensors is 21 meters. Earth's gamma radiation is measured with a spectrometer which utilises a 41 litres NAI crystal detector. The electromagnetic unit is dual frequency vertical coplanar coil equipment (Poikonen et al, 1998). The frequencies are 3.1 kHz and 14.4 kHz and coil separation is 21.4 m. The survey results are used in mineral exploration and geological mapping, recently also increasingly in environmental applications. GSF has recently conducted aerogeophysical studies of some contaminated are as in Finland (Lerssi et al, 1997). Ämmässuo is a modern, municipallandfill of Helsinki. Landfill area has been mapped three times, first in the national airborne mapping program (1984) before the operation of the landfill started. The 1993 and 1997 monitoring surveys were carried out in the same north-south flight direction as in 1984 but using tighter (100 meters) line spacing. Magnetic anomalies indicate metallic waste and metal constructions. Comparison of 1984, 1993 and 1997 EM maps of Ämmässuo indicate small changes, which have been estimated guantitatively by layer model and 3-D model interpretation. By total radiation map, it was possible to estimate changes of moisture and soil thickness. Lievestuore pulp millled its waste effluent during 1935-1967 to the nearby Koivusensuo mire, where the Lipeälampi waste pond was formed. GSF carried out airborne measurements and ground surveys around the waste pond. The electric conductivity of the efflucent (mainly sodium lignosulfonate) is high and its spreding into the soils can thus be deciphered by electric methods. The AEM anomalies indicate that the most heavily polluted mire area extends north- and southwards from the pond, which was verified by ground conductivity logging (Puranen et al. 1997). Logging and seismie results were also used as a reference material in interpretation and modelling of effluent plume migration.
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Time domain induced polarisation experiments on gasoline contaminated samples
Authors E. Martinho and F. AlmeidaRecently environmental studies have used geophysical methods to delineate oil contaminated sites (Vanhala, 1997). Organic liquids have a high resistivity and thus induction methods are not weil adapted to fine contaminated areas. On the other hand Induction Polarisation has been widely recognised as a useful method for the detecting organic electrical response In field ( Vanhala et al, 1992) and in laboratory (Vanhala et Soininen. 1995) experiments. The later author had a frequency domain approach (SIP) to the problem. On the other hand our initial work carried out in the time domain (Sumner, 1976) and is still in a laboratory phase. In order to study the induced polarisation effect in gasoline contaminated soil samples a GPIB controlled system was developed to carry out electrical measurements as it is shown in Fig.l. This System is able 10 obtain measurements at a rate of ten samples per second. Specially developed porous ceramic electrodes were built to obtain suitable electrical current contacts. Non polarizable electrodes SilverlSilver Chloride were used to measure potential.
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Analysis of ground penetrating measurements of a tar lake
Authors B. Forkman and C. SeegraefIn this paper we combine two relatively new methods to analyse a tar lake. The ground penetrating radar measurement has become a quite important method for the analysis of near-surface conditions. The method is based on the spreading of highfrequency electromagnetic waves and on the validation of Maxwell equations. The wavelet-transform (WT) is used for the analysis of measured data. This transform can be used for the time frequency analysis, for the filtering of data and for the detection of the interference of different signal parts. The WT depends on different functions, the socalled wavetet functions, which have different properties.
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Testfield for studies of sites polluted with old war ammunition with geophysical methods
Authors I. Wolfgang Spyra, S. Reinhardt, H. Petzold and D. KolarovOn most parts of Federal State Brandenburg battle collisions took place during the Second World War. As the result, a lot of different ammunition from shell-splinters of grenades and mines up to non burst airbombs have remained on battle fields. On the other hand. Brandenburg develops widely coal industry. As is known, there are open mines for brown-coal production in the southern part of Brandenburg. The presence of a huge amount of ammunition's rests converts the development of new coal deposits to very difficult and dangerous business.
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Saturation and contamination dependence of electrical properties in the MHz range
Authors C. Urban, J. Schonart and A. WellerThe application of electrical and electromagnetic measurements on geotechnical and environmental problems requires detailed knowledge of the influence of lithology, pore structure and pore filling on the electrical properties of rocks. Former investigations at frequencies up to 1 MHz (Kulenkampff, 1994) have shown that frequency dependent electrical measurements yield especially information about parameters describing the pore structure due to polarization effects caused by electrochemical reactions at the internal surface. Only for highly porous media, pore filling considerably affects the complex conductivity spectra. This is one reason for the strong deviations between the results of measurements and mixing formulas like complex reflection index method (CRIM) or Bruggernann-Hanai-Sen-Shen (BHSS) which ignore surface effects (Urban, 1995). The aim of the presented work is to examine the influence of saturation and contamination of samples of different lithology and known pore structure on the electrical properties in the Mhz range to provide a data base for the interpretation of electromagnetic field measurements. Furthermore, the investigations should result in a quantification of the relation between electrical parameters and pore structure controlling the hydraulic and diffusive transport of pore fluids.
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Measurements and estimates of tracer diffusion in the NW Mediterranean Sea
Authors J. M. Redondo, M. O. Bezerra, M. R. Soler and I. R. CantalapiedraThe eddy diffusivities in the ocean exhibit a large variation and show a marked anisotropy, not only horizontal values are much larger than vertical ones but there is a strong dependenee on the spatial extent of the tracer dye or pollutant. In the case of oil spilIs, these are strongly influenced by the buoyancy and horizontal diffusion depends on ambient factors such as wave activity, wind and currents.
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The main problems of the technogenic radioactive water reservoirs safety on Techa River (South Ural)
Authors G. Batrak and S. SemenovDuring the creation of armament plutonium at the PO Mayak in the South Ural, the acute problem of utilization and storage of low-Ievel liquid nuc1ear wastes arises. The technology allows to discharge them into the open storage reservoirs without hydroisolation of reservoirs, whereas in the USA, bottom and sides of reservoirs are cemented or paved with asphalt. During the exploitation of storage reservoirs, there arises the danger of their overfilling or out-break, as weIl as of seepage through their body and foundation. The problem will be less acute, if the ways of rational reservoir control are found.
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Georadar, electromagnetic, and magnetic studies of a landfill and its host sediments
Authors R. De Iaco, H. Horstmeyer, D. E. Boerner, F. Lehmann and A. GreenMany landfills are currently causing severe environmental problems, such as ground-water contamination. In view of the large number of poorly documented landfills, fast and inexpensive methods for investigating the shallow subsurface are becoming increasingly important. We have tested a variety of non-intrusive geophysical methods at a landfill located within glacio-fluvial sediments in northwestern Switzerland. Three-dimensional georadar, frequency-domain electromagnetic (EM31), and mag net ie surveys have been conducted over part of the landfill and adjacent undisturbed ground. Dense sampling of the subsurface, a self-designed algorithm for sealing the georadar data in a way that suppressed prominent noise, and application of NMO corrections were important steps for obtaining detailed and accurate images of the investigated area. From borehole information, reflections from interfaces between different gravel sheets and from the top of the underlying lacustrine layer could be identified. Timeslices revealed a general SW-NE flow-direction of the ancient river system that deposited the gravels and sands. The lacustrine sediments are an aquitard in this region. Interpolation of the aquitard, an important barrier for contaminants emanating from the landfill, between surveyareas northwest and southeast of the landfill, provide us with an estimate of the maximum dep th of the waste disposal site.
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Evaluation of an old waste disposal site contamination, using electrical methods
Authors F. P. O. Figueiredo and A. I. S. AndradeA case of chemical pollution induced by an abandoned disposal site located on an alluvial plain has been investigated through geophysical prospection. The aim of the geophysical survey was the delimitation of the shape/dimension of the conductive contaminated plume, .which the landfill has been inducing. The plume goes down to a depth that ranges between lOm to 80 mand the resistivity of the contaminated sediments is approximately 50 ohm.m.
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The use of geophysical techniques for the detection and characterization of landfill in areas of urban development
Authors A. Granda and J. C. CamberoThe growth of some Spanish eities has created the need to develop urbanistic projects in its surroundings, on lands that in many cases have been affected by the activity of the city itself, and specifically by the existence of garbage deposits or different kinds of waste products. The nature and characteristics or these waste deposits usually differ in every case, since they may correspond to urban solid waste with a great presence of organic matter, or inert spillings caused by industrial activities. The existence of these deposits is known with a higher or lower degree of accuracy in some cases, while it is absolutely unknown in others, because the old deposits were conditioned for a subsequent use of the ground in a way that after several years it would be impossible to identify their location just by observing the site.
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Non-invasive geophysical mapping of chemical waste deposits and flow-paths
Authors R. D. Ogilvy, D. Beamish, P. I. Meldrum and R. MossA non-invasive geophysical survey has been undertaken to characterise the extent of contamination associated with chemical wastes deposited in dis-used sandstone quarries. The specific aims of the geophysical survey were: - to delineate the concealed edges and base of the quarries prior to the siting of sampling and monitoring boreholes - to assess whether waste fluids had invaded the surrounding sandstones and to map these contaminant migration pathways, prior to intrusive sampling A secondary aim was to assess the general capabilities and reliability of geophysical methods for waste site characterisation in this environment.
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Optimum model in 2D geoelectrical imaging : example from a dump site with high resistivity contrasts
Authors A. I. Olayinka and U. YaramanciModelling and inversion of synthethic data over 2D geologie models have shown that, at high resistivity contrasts, there could be an increase in the model misfit between the inverted model and the true model for successive iterations. Hence, the optimum model is attained at a low iteration number. A case history, from data measured over a waste dump site, is given in which the optimum model is the structure at the second iteration; the inverted resistivities are very low at less than 30 Om down to a depth of about 10 m. These are consistent with the analyses of surface - and ground - water which indicate the presence of a low resistivity contaminant.
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Electrical tomography survey of a landfill site
Authors M. Pokar and M. H. LokeThere are an estimated 230 landfills in Malaysia, some of which are located near communities and water sourees. Besides contamination of ground water due to chemical leachates, gas migration can also be a serious problem. Landfill gases are formed during the decomposition of organic wastes and consists of a mixture of methane (C~), carbon dioxide (C02), nitrogen (N2) and volatile organics. The use of 2D electrical tomography surveys (Griffiths and Barker 1993) to map various features in landfill sites was investigated in this research. Tests with synthetic data for different landfill models were first conducted. Surveys were also carried out to delineate the various fill materials, map leachate movement and gas accumulations. The results from two of the survey lines with possible gas traps are given in this paper.
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The conductivity structure beneath the industrial waste site Mellendorf as derived by radiomagnetotellurics (RMT)
By B. TezkanIn Europe, especially in Germany, the application of geophysical methods to waste site explorat ion becomes inereasingly important since their contribution 1.0 the pollution risk estimation has been recognized. Applied geophysics can offer many techniques for the non-invasive mapping of waste sites and should be considered as a main source of information about interesting borehole locations. Between 1960 and 1989 an automobile company used a sand pit located in Mellendorf near Hannover for the disposal of magnesium dross and other industrial waste. After its recultivation, the waste site was covered by a layer containing soil, sand with gravel and clay. Fig.1 shows a geological stratification beneath the survey area derived from boreholes on the waste site (Renno and Christofzik, 1987).
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Three-dimensional inversion of induced rolarization data from simulated waste
Authors A. Weller, M. Seichter and W. FrangosThe Idaho National Laboratory (INEL) Cold Test Pit (CTP) has been carefully constructed to simulate stored hazardous waste occurrences. In order to test various methods of non-invasive subsurface waste location techniques, a simulated waste pit has been constructed using safe materiaIs, and designed to resembie old waste pits as closely as possible. This Cold Test Pit (CTP) has been investigated by a number of workers using several different methods. The present work was carried out as part of the Electromagnetic Integrated Demonstration (EMID), which also inc1udes an assortment of electromagnetic techniques (pellerin and Alumbaugh, 1997). The CTP was constructed as a 13 x 70 m trench, segmented by transverse berms into cells. The southern-most cell investigated in the EMID project, contains stacked drums and boxes and a variety of randomly positioned barrels, pipes, a large metal tank, etc., this location is referred to as the Large Object Pit (LOP). The buried drums located in the center of the trench inc1ude both cardboard and metal drums containing scrap metal and nonmetallic materiais. The cell is described as being a three-meter waste seam with about 1.5 m of soil cap, thus the depth of the bottom of the waste is about 4.5 m. The cap is composed of c1ay-rich soil trucked in from other areas of the INEL complex. Host material is local soil overlying resistive Snake River basalt.
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Assessment of non controlled land-fillings by geochemical and geophysical methods. Llobregat Delta (Barcelona, Spain).
Authors X. Font, A. Navarro, L. Rivero, A. Casas, J. Noguera and F. MartînezThe problems associated with municipal, abandoned or non-controlled landfills are of general concern, specially because of the interactions between the hazardous content of the leachates derived from them and groundwater. MacFarlane and others (1983) were the pioneers on this type of studies, later on, Cherry and others (1996) did more specific research on heavy metal thermodynamic with emphasis on providing data to assess or validate mathematical models at Borden landfill site (Canada). The main objective of this study was to characterise contaminated sites provoked by noncontrolled sand and gravel extraction quarries filled with urban, construction, industrial and chemical wastes. Using combined geochemical and geophysical data is possible to characterise contamination extension of the groundwater superficial aquifer and to deduce possible implications of water flux through landfillings.
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Geophysical measurements for assessment leakage risk in underground waste storage
By H. MarcakThere are hundreds of kilometres of underground tunnels in the coal mining are as in Upper Silesia and in the copper mining area in Lower Silesia. This empty underground area seems to be very good place for waste deposits. Materials with different levels of toxicity may be stored in these places, when the safety of the place are taken into account. Furthermore according to polish law a system of barriers must be constructed such sites. However, a catastrophic scenario must be considered. In this scenario, the stability of underground caves are disturbed; barriers are destroyed, water fIows into caves and contaminants leave the storage. Consequently, the design of an environmentally safe underground storage system and the control of its safety is achallenge for research workers.
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Diagnosis of waste landfills by infrared thermography
Authors C. Sirieix, L. Rouvreau, L. Bertrand, M. Frappa and C. BloquetIncreasingly strict legislation concerning the management and storage of waste is leading to the creation of a new generation of landfills, as weil as to the remediation or closure of older sites. Thus there is the problem of the long term surveillance of the old sites and the control of the new one. The mass of waste is often a black box in which intense, complex and poorly understood physico-chemical processes occur. If they cannot be controlled, they must be regularly monitored in order to intervene as rapidly as possible if the process warrants it. The thermal activity of a site is directly related to exothermal chemical activity of waste. This chemical activity produces biogases who accumulates in some particular places. Landfill managers have difficulty in characterising site activity and its change with time. There are two phenomena to control : accumulation of biogases like methane and leakage in the new sites and increasing temperature with the risk of fire underground in the old sites. Infrared thermography can be used to establish this thermal activity. We'lI described this two kind of applications.
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Significance of magnetic and induced polarization responses over municipal solid waste facilities
Authors N. Abu-Zeid, M. Marcheti, G. Santarato and M. PaiolaImpacts of improperly managed old Municipal Solid Wastes (MSW), especially those uncontrolled and/or illegal, not only deteriorate the environment by posing it to hazards leading to soil and groundwater eontamination, but also grave the economy as remedy costs ean be very high. Therefore, the best way to proteet the environment is to minimise negative impacts of MSW and to associate them with an efficient monitoring system not only during the feasibility study but also during the whole life of the facility.
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Application of electromagnetic reflection method (EMR) to investigate confined and perched aquifers
By F. BahloulThere are many reasons to drill a hole, for example test borings for local geological sampling, groundwater monitoring or shotpoint drilling for seismic investigation. Previous knowledge about areas endangered by artesian water is important to avoid drilling in these areas. Undesired artesian water outflow can be dangerous and causes a lot of damages. Perched and confined aquifers are common in areas of push moraines due to the interlocking of glacial sand, till and boulder clay. The groundwater levels change abruptly in steps because of steeply dipping thin layers with low perrneability between the sand layers ofthe aquifers. Owing to the differences of the electrical properties (dielectric constants and conductivity) between soils or rocks and water, electromagnetic energy is reflected at boundaries of material with different water content, since the water changes the relative permittivity of most soils or rocks by a factor 5-6. This fact makes the groundwater table a good reflector of electromagnetic energy if it is associated with a steep change in the soil's water content. The aim of the present paper is to demonstrate the possibility of using electromagnetic reflection method (EMR) to detect some groundwater table anomalies (mainly steps or a discontinuity) and its interpretation combined with the known geological and hydrogeological information to predict artesian waterand perched aquifers.
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Geophysical investigations of alluvial aquifers in Zimbabwe
More LessGeophysical investigations were carried out on shallow alluvial aquifers in conneetion with sand rivers in Zimbabwe. The primary methods used were OC resistivity imaging and ground penetrating radar (GPR). The investigated sites are situated on so called sand rivers. i.e. rivers with a seasonal surface flow. The strata of principal interest, for local water supply and subsistence irrigation purposes, are alluvial sands present in the active stream channel or beneath flood plains. The alluvium in the present stream channels consists of coarse grained sand, generally with a groundwater table within a couple of metres depth. These shallow aquifers are widespread in the dryer parts of Zimbabwe, as well as other countries in the region. Since resource development is possible with locally sustainable technology, it is of high potential value. Investigations were carried out at two sites on the Umzingwani River and one on the Shangani River with results that agree well, which is also supported by previous research (Owen 1989)'. The geophysical surveys have been presented in detail by Einarsson et al. (1994), Ekström et al. (1996) and Beekman and Liberg (1997).
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Geophysical imagery of strand zone
Authors J. C. Courryl and P. WatremezThis work belongs to a project for the use of geophysical techniques in the strand zone (i.e. the area situated between the low and the high tide, by extension in our work, the area between the lower level of sea and the back dune). A large part of French coasts are constituted of beach dunes which are moved by winds. The main problems of coast management are water resources management due to the saline intrusion, bedrock mapping for civil engineering problems and dune stabilization. For structural geology, usual geophysical techniques are seismic, but which is expensive. Saline intrusion are detected with electrical sounding, but is a punctual technique. The aim was to use low cost continuous methods. We tested a methodology coupling continuous electromagnetic techniques and electrical soundings. We supposed that this combination of techniques could answer to the problem of bedrock mapping and water levels detection.
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Geophysical prospecting of bedrock aquifers in Finland
By E. LanneThere are about 5.2 million inhabitants in Finland, most of which live in the Southernmost part of the country. 86 per cent of the population is connected to cooperative or public water supplies. In 1995, the average water consumption was about 260 litres per capita per day. The proportion of groundwater of the total water withdraval is about 58 per cent. The official water policy prefers ground water aquifers, because the quality of surface-water varies seasonally and is exposed to environmental risks.
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Application of the surface proton magnetic resonance method for the detection of fractured granite aquifers
Authors A. V. Legchenko, J. M. Baltassat, A. Beauce, M. A. Makki and B. A. AI-GaydiThe Surface Proton Magnetic Resonance (PMR) method was developed in Russia in early eighties for investigation of sedimentary aquifers. However, the magnetic resonance signal is also produced by water in any other types of rocks. It makes possible application of the PMR for water detection in fractured aquifers where traditional geophysica! methods are less effective. Results of the water prospecting project carried out in Saudi Arabia are presented. Investigated aquifers there are essentially composed of metasediments ("black slate"), granite, grandiorite and diorite. During the hydrogeological survey achieved by ANTEA in April of 1996 two promising areas for water supply were emphasized. In order to detect fractured zones these areas were then studied by BRGM using the Horizontal Loop Electromagnetic (HLEM) method. As HLEM anomalies nothing teil us about water in the fractures, exploration boreholes were also drilled and tested where these anomalies were observed. Totally 17 PMR soundings were carried out in April of 1997 using the NUMIS PMR instrument. Eight of them were performed just close to existing boreholes which have various yields ranging from 0 up to 22 m3/h. The aim of these measurements was to calibrate the PMR response. The other soundings were performed along profiles in order to investigate the lateral extends of the waterful fractured zones. Generally a good correlation between drilling and PMR results was observed. Thus, it was demonstrated that the PMR is a useful tooi for optimal location of productive boreholes in a fractured granite hydrogeological environment. For example, referring to the project in Saudi Arabia, if the PMR measurements would have been carried out at an intermediate stage between the HLEM survey and the drillings, the number of boreholes could be reduced at least twice without any loss of information.
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Application of geophysical methods to quantify hydraulic parameters in a complex porous aquifer a case history Pfynwald - Wallis - Switzerland
Authors R. Monnet, D. Chapellier and J. FurrerThe characterization of boundaries and hydraulic properties of the layers through which the water flows in complex saturated porous aquifers is only possible through numerous measurements in wells and boreholes including also intensive geophysical surveys. Within the framework of the research project entitled « Fluid and mass transport in porouss medium: quantification and comparison of hydrogeological. geophysical and hydrochemical methods. Example of the alluvial aquifer in The Bois de Finges (Pfynwald) » financed by the Swiss National Science Foundation, a 30 meters deep borehole was drilled in the vicinity of four shallower holes reaching 15 meters.
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Combined electrical resistivity and pumping test modelling
Authors J. Moore, R. Barker and A. HerbertContaminant transport issues, coupled with advanced numerical modelling techniques have led to an increased demand for quantitative descriptions of groundwater systems. To determine the distribution of hydraulic parameters, resistivity techniques have been employed to complement conventional hydraulic tests. The electrical resistivity of a saturated rock or sediment is a function of the porosity, the electrical resistivity of the saturating fluid, the resistivity of the solid rock or sediment. the surface conductance of the rock or soil and the tortuosity of the electrical and fluid path. It is generally assumed that for most formations with low c1ay content the electrical current is conducted electrolytically through the pore waters (Urish, 1981). This has led to numerous attempts to define a relationship between electrical resistivity and hydraulic conductivity. However, both direct and inverse relationships have been reported, thus highlighting the dominanee of surface conductance effects and the problerns incurred by neglecting its importance (Huntley, 1986).
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High resolution electrical monitoring of fluid flow through the unsaturated zone of a sandstone aquifer
Authors V. Hatzichristodulu, R. Barker and J. TellamThe unsaturated zone is very important, not only in water resource evaluation but in contaminant transport as weIl, particularly in siting waste disposal facilities and in remediating contaminated sites. Therefore, new approaches are required so that the three dimensional detail of the zone is determined. The aims of this work are: • to test the usefulness of high resolution electrical tomography in mapping the three dimensional movement of water in the unsaturated zone and • to provide a further understanding of the processes involved in the unsaturated zone flow. To achieve the above, a high resolution imaging system was installed at a research site at the University of Birmingham. The research site consists of an Environmental Agency observation borehole and 3 piezometers, together with unsaturated zone instrumentation which has enabled groundwater levels and moisture contents to be monitored for the last two years (Digges La Touche, 1998). Two more boreholes will be drilled at the site later this year. The new imaging system is used to monitor fluid movement in the unsaturated zone over an extended period of time and during short term pumping tests. The observations may be related to the properties of the subsurface and variations in recharge.
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Tests of the SGW-NMR technique within two aquifer characterization projects in the Iberian Peninsula
Authors J. Roy, A. Marques da Costa, M. Lubczynski and C. OwuorThe management of GroundWater (GW) resources implies, ahead of any exploitation scenario, an inventory and characterization of such resource. This is a multidisciplinary task, in which a whole array of techniques are used but the Surface version of the GroundWater Nuclear Magnetic Resonance teclmique (SGW-NMR) appears to have a potential role. NMR techniques are used in state-of-the-art applications such as medical imaging, chemical structure analysis and hydrocarbon resources exploration and quantification. The SGW-NMR technique is an implementation of this technology for the purpose of non-invasive investigations of groundwater from the earth's surface. The SGW-NMR technique has been described, among others, by Goldman et al. (1994) and Lieblich et al. (1994). The introduetion of a commercial SGW-NMR system by IRIS Instruments in the Spring of 1996, marketed under the name of NUMIS PMR, was followed with interest at ITC and elsewhere. Such interest is based on the potentialof this non-invasive technique in the domain of groundwater exploration and quantification. In fact, of high interest to us is its capacity to identify the hydrostratigraphy of the flow system, to quantify the effective porosity and to provide information related to pore size distribution and therefore to hydraulic conductivity of in-situ subsurface materials from surface measurements only (i.e. without using boreholes). This information is available in a sounding mode (i.e. as a function of depth) and is measured over a large volume of materials (106 to 107 m') so that seale effect, as observed with point souree hydraulic determinations i.e. pumping tests, are minimized (Lubczynski et al, 1997).
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A combined application of high resolution reflection seismics and TDEM for detailed study of the coastal aquifer of Israel
Authors V. Shtivelman and M. GoldmanAn integrated geophysical study, including high-resolution reflection seismies and TDEM, was recently carried out at several sites along the Mediterranean coast of Israel (Fig. 1). The coastal aquifer consists of the Quatemary sequence of marine and continental deposits composed predominantly of calcareous sandstone (the Kurkar unit) and including a number of clay layers. Calcareous sandstones are generally porous and hydrologically conductive and considered aquifers, whereas clays are impermeable and act as aquicludes. In the places where the clays are thick and extensive enough, they divide the aquifer into distinct subunits. Fig. 2 represents lithologicallog from borehole 12/A in which various Kurkar units are designated as KAl through KA7. The sequence rests on impermeable black shales and clays of the Saqiye group of Pliocene - Miocene age. The aquifer suffers from severe salinization caused by seawater encroachment reaching as far as 1 km from the sea shore. The general objective of the geophysical survey was a detailed study of the coastal aquifer and, in particular, subdivision of the aquifer into subaquifers separated by impermeable units and evaluation of water quality within each subaquifer. At first stage, the survey was carried out at the Nitzanim site, where several observational wells were located and used for correlation purposes. Then the survey was continued to other areas where the hydrogeological control was limited by a single well at each site. The results of the survey are represented here by an example of the Nitzanim area.
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Gravity method - an effective way to prospect groundwater areas in Finland
Authors T. Valli and A. MattssonIn Finland the glasiofluvial formations, like sandy eskers and end morraines, are the most important storages of groundwater. Because of the growing risk of pollution, the mapping and protection of aquifers has become an important target of the environmental research. A typical survey area is usually large, e.g 40 km', so there is a need for regional prospecting. The Geological Survey of Finland (GTK) has developed an useful methodology which gives regional information of the bedrock topography and the thickness of overburden. It is based mainly on the gravity interpretations.
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Shallow geophysical methods applied to support hydrological research in experimental catchments
More LessThree geophysical techniques have been applied within a complex man effected catchment (Vallcebre in Catalunya). The techniques explored included geoelectrical, seismies and some early attempts to apply a Ground Penetrating Radar (GPR) methodology. This area has a complex hydrology and the system is dominated by abandoned agricultural terraces and man made ditches. The work shows the possibility to acquire key hydrological parameters used in the construction of models and to demonstrate how the shallow geophysical methods can be used within experiments to visualize 3D hydrological flow processes.
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Geophysical investigations of groundwater relevant subsurface structures in Northern Germany
Authors H. Wiederhold and R. KirschBeside the salt domes the subsurface structure in Northem Germany and adjacent countries is characterized by a system of glacial channels and valleys that are cut into Tertiary sediments down to a depth of more than 500 m (Fig. 1). They are filled with Quatemary sediments and are not visible from the surface. This kind of subsurface structure is highly important for the hydrogeological conditions. The glacial valleys can be filled with sandy material and thus be a good groundwater reservoir or conneet upper and deeper aquifers (Fig. 2, left) or they can be filled with low permeable clay bearing moraine material and so interrupt or disconneet the aquifers (Fig. 2, right). Normally a mixture of both extreme positions can be found, also a valley can show lateral changes in the hydrogeological characterization.
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Performance evaluation of DC resistivity and time-domain EM sounding as used in a complicated groundwater survey of the Batinah coastal plain, Oman
Authors A. AI-Ismaily and R. J. SporryThe Batinah coastal plain is located on the northem margin of the Northern Oman Mountains and stretches for a bout 300 km along the Gulf of Oman (Figure I). Scarce groundwater resources have been intensively exploited for agriculture, industrial and domestic use. The study area, Eastem Batinah, covers some 60x35 km and involves a coastal aquifer which is cornposed of alluvial fan and coastal deposits consisring rnostly of (partly) cemented gravels, sands and silts. Saline water intrusion poses a serious threat to a sustainable water supply. In the recent past, the district has been the subject of intensive geophysical exploration for various purposes. Among them are reflection seismics for hydrocarbon exploration, high resolution aeromagnetics and low density gravity for regiorial surveys. Since 1984 a number of dedicated groundwater surveys were executed, including Schlumberger De resistivity soundings (119), TDEM soundings (500) and wireline logging of a large number of monitoring and production boreholes (109).
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Outlining complicated subsurface geological conditions by elaborating 1-D electrical soundings for hydrogeological purposes
Authors J. Alexopoulos and T. PapadopoulosSubsurface investigations for hydrogeological purposes using geophysical (mainly geoelectrical) methods are widely used today. For geoelectrical methods, the array type and the way the electrodes are expanded, are highly depended on the nature of the hydrogeological target, the depth of investigation and the strike of the geological setting. For deep investigations (ABI2=1000 m), the Schlumberger array is more suitable and is mostly used, although the dipole-dipole array gives similar results. In addition, the inherent difficulty of interpreting 1D Schlumberger soundings, arising from non horizontal layering and lateral variations, has recently been faced by proposing several methods, for recognizing lateral resistivity inhomogeneities (Renning and Tennensen 1990) and detecting them by combining the Schlumberger sounding array with two dipole-dipole soundings (Morris et.al. 1997). During the last two decades emphasis has also been given among the geophysicists, to develop 2D interpretation algorithms for a reliable earth structure simulation (Dewand Morrison 1979, Barker 1981, Dahlin 1993, Loke and Barker 1994). Furthermore, it has been pointed out that in some cases the 1D approximation of Schlumberger curve interpretation is adequate (Beard and Morgan 1991, Morris et. al. 1997). In contrast, less attention has been paid among the geophysicists on the role of the in situ electrical measurements, mainly because of the diversity of the measured values, and dealing with detailed surface geology observations. Bath investigations can contribute to the construction of a reliable 2D structure.
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The geophysical electromagnetic prospection in the spatial location of the travertine deposits of the Banyoles depression (Girona). geological and hydrological implications
Authors D. Brusi, L. Palli, C. Roqué, I. Capellà, A. Pujadas and M. VehiThe results of the application of the geophysical electromagnetic prospection methods in the resolution of the problems of the spatial location of the travertine quaternary formations of the Banyoles depression are presented.
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A combined geophysical survey for hydrogeological purposes in north-eastern Italy
Authors A. Godio, P. Chiara, C. Conforto Galli and M. NaldiAn extended geophysical survey using electromagnetic and electrical methods (EM-34, VLF and YES) has been carried in a mountainous area in North-Eastern Italy (Southern Alps). The purpose of the geophysical survey was to provide information on the subsoil for the best location of water wells. Several profiles were performed using a frequency domain low induction system with 20 mand 40 m separation distance between the two coils in order to obtain information on the electrical resistivity at the target depth (about 30-50 m). The resistivity values were calibrated using the results of some vertical electrical soundings. The electromagnetic survey was completed with VLF profiles along the same profiles of the low induction survey. Attention was focused on the faults, which are the potential groundwater path-ways, to their direction and structural features (infilling, opening, etc.). The geophysical results were calibrated through the drilling of a borehole, which confirmed the reliability of the geological model.
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A comparison between DC-resistivity and electromagnetic methods for mapping sea water intrusion in the Llobregat delta
Authors M. Himi, L. Bagán, J. M. Carmona and A. CasasDC-resistivity and electromagnetic techniques are widely used to measure the electrical resistivity/conductivity of materials in the subsurface. Variationsin these two parameters are caused by changes in the soil characteristics -structure, clay content, degree of water saturation and conductivity of this water-. Taking advantage of the relationship between electrical conductivity and chloride ion ie concentration, we have attempted to map the saltwater intrusion in the Llobregat delta (Barcelona). For this purpose two different surveys have been conducted: vertical electrical sounding and electromagnetic mapping. This study allows us to compare the results and to contrast the obtained efficiency using each technique.
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Geoelectrics in detecting palaeochannel features of quaternary alluvial deposits: Villorba (Treviso - Italy)
More LessThe Department of Geology and Geophysics of the Padova University and the Department of Applied Geophysics of the Charles University in Prague are participating in a project "Contaminant impact on hydrogeological structures". The project is a part of a program supporting the cooperation between the Italian Foreign Office and the East- and Central European Countries. An important contribution to this project has been done by the Department of Applied Geophysics ofthe the Paris University. One of the sites chosen for geophysical studies is the industrial zone of the Villorba Village affected by the groundwater pollution. The rough plume extent was identified by means of chemical analysis of water samples collected from the local wells. The weil distribution being related to the water dernand do not allow a precise reconstruction of groundwater flow.
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GPR Profiling at the 'Güell d'Hurno' spring and Nere river discharge-measurement weir (Vall d'Aran, NE Spain)
Authors R. Lázaro, J. M. Carmona, X. Font and A. CasasIn 1995, a hydrogeologie study was carried out in the Nere river catchment basin to assess the real hydraulic resources and the possibilities of harnessing the river for generating electricity. The following aspects were studied: 1) Assessment of available water resources and their temporal distribution 2) Identification of the main water souree 3) Calculation of exploitable water volumes 4) Possibility of increasing the water flow the spring surroundings Besides to the study of the meteorologieal, hydrologie and hydrogeochemical attributes, a geophysical prospecting survey was carried out by GPR with the aim of determining the geometrie boundaries in the spring zone and locating the impervious basement in a weir used as a gauging station.
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Gravity and seismic reflection applied to the hydrogeological research in a large Alpine valley
Authors A. Rosselli, R. Olivier and G. VeroneseThe determination of the bedrock morphology is an important parameter for the purpose of the hydrogeological research. In the case of large alpine valleys the bedrock depth may vary from few hundreds to thousand meters. Furthermore, structural differences in the sedimentary body, generally linked to lateral valley contribution, are another important parameter to take into account. In the outline of a research project of the Geological Survey of the Province of Trento (ltaly), several gravity profiles was measured in the Adige valley, neighboring the urban area of Trento. A 2.5 D model was elaborated on the base of the gravity data. Geology, borehole information and seismie reflection was used to constrain the 2.5D gravity modeling.
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Hydrogeological and geophysical investigation for evaluating the salt/fresh water distribution in Saidia plain (North-Eastern Morocco)
Authors K. Walraevens, N. El Ualimi, A. Chaouni Alia and E. BeeuwsaertNorth-eastern Morocco has a Mediterranean c1imate, with low rainfall, which is irregularly distributed both within the year and over succeeding years. The c1imate is very dry in summer, and moderately to weakly humid in winter. The coastal area shows groundwater salinization, which is due to the presence of connate saltwater or to sea water intrusion. Low salinity water resources are scarcc, and should be carefully managed. The present study focuses on an aquifer system in the Mediterranean coastal area of northeastern Morocco. It is situated in the most easterly coastal plain, up to the Aigerian border: the eastern part of Saidia plain. This plain is mostly dispersely populated, with agricultural activity, while the city of Saidia is a summer resort. In the western part, outside the studied area, a large sea fish farm is causing extensive groundwater salinization by leakage from sea water filled basins. Saidia plain is an elongated area, squeezed in between the Ouled Mansour hills and the sea. To the east, it is bounded by the Aigerian border, following the Kiss River. From north to south, several parts, occurring as longitudinal, parallel strips, can be distinguished (fig. I): the shore, the northern dunes, the Sareg mud flat, the southern dunes, and finally the Merzakan mud flat, up the Ouled Mansour hills.
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Optimization of water wells through conventional logs
Authors J. M. Dîaz Curiel, D. Martin, N. Caparrini and A. MaldonadoThe need of increasing the quality of water wells is contributing to extend the use of geophysical well logging, as an essential technique to optimize the exploitations and to control of the ground-water resources also. Besides the development of new technologies and interpretation methods, the popularisation of this technique requires the optimization of the results obtained from the different welllogs (even maintaining the employment of a relative low cost devices), arousing the interest of the technicians involved with the different fields related with boreholes. In this communication, we present a summary of the conventional weIl logs with a higher hydrogeological application, The possibilities of each of them are pointed out in a schematic way. Overall, the use of geophysical logs in the hydrogeology's field can be divided in two main groups: the conventional logs used during the drilling phase, which will determine the constructive characteristics of the borehole, and the specific logs used in casing(piped) boreholes, which will define the optimum design of the exploitation.
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Control network (/T for the investigation of the marine intrusion in Castell de Ferro (Granada, Spain)
Authors D. A. Martin Sánchez, J. Diaz Curiel, A. Maldonado and N. CaparriniThe detection in every moment of the interphase (fresh/salt water) implies a great advantage controlling the advance of the marine intrusion. In this respect, the simultaneous and continuous measurement of the conductivity and the temperature in a sufficient number of borings, looks like the very best solution for this control. This publication shows the experience achieved by the Instituto Tecnológico Geominero de Espafia (I.T.G.E) and the Engineering Geology Department of the Madrid School of Mines in the coastal aquifer of the Gualchos in Caltell de Ferro, Granada province, where a control network was designed, optimised and installed. Through the analytic investigation of the results, a series of mathematic approximations have been obtained in a fast and simple way to show the possible processes of advance or regression of the sea interphase.
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H-Sense': harbour sediment mapping using Chirp reflection surveys in Norway and Sweden
Authors P. M. Maurenbrecher and T. WeverThe EdgeTech (4-24 kHz -Fish) is used in the range of 4 to 16 kHz to map the most recent, usually contaminated, top layer in the harbour and estuaries of the low tidal harbours of Bergen, Norway and Gothenburg, Sweden. The principal objective is to relate distribution patterns of the sediments with natural and man-induced processes such as sediment supply, currents, waves. storms, and vessel movements. In February and March surveys were carried out which covered the harbour areas of Bergen and Gothenburg. Both surveys succeeded in not only mapping the top sediments but also in obtaining profiles at Bergen in water depths exceeding 300 m despite the signal return period exceeding the transmission periods. In the Gothenburg estuary reflectors were obtained from 40 m below seabed despite the high frequency range of the Chirp signal showing profiles infilled channels (see Figure 2). The initial results for the H-SENSE study (Harbours: Silting and Environmental Sedimentology European) are presented for two harbour basins in Bergen and Gothenburg respectively. The study is being carried out jointly between universities and institutes in Sweden. Norway, the UK. Netherlands and Latvia within the EC-Directorate General 6 (Transport) research programme.
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Seismic amplitude versus offset analysis of gas hydrates
Authors A. Mazzotti and S. GrionWe describe the application of AVO (Amplitude Versus Offset). analysis and high resolution velocity analysis to evaluate the elastic properties of Bottom Simulating Reflectors located in the South Shetland margin and in the South Chile offshore. Two marine seismic data sets are available for the study and were subjected to a full amplitude-preserved processing. This presented some difficulties due to the presence of noise related to the bad weather conditions during the acquisition. For this reason, after array directivity compensation and geometrical spreading correction, surface consistent amplitude corrections were applied and particular attention was given to the picking of the AVO trend of the target reflectors. This AVO has been used for a single interface elastic inversion of the PP reflection coefficient. The results given by high resolution velocity analysis, based on the a priori estimation of the wave let, and by AVO inversion indicate that both the South Chile and the South Shetland Bottom Simulating Reflectors are associated with interfaces showing high P-wave velocity (Vp) in the upper medium, followed by a consistent drop in Vp and in VpNs ratio in the lower medium. These results are consistent with the presence of a layer fully saturated and consolidated by gas hydrates overlying unconsolidated sediments with free gas (partial) saturation.
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The SEISCAN image archive: an exercise in environmental geophysics
Authors P. R. Miles, M. Schaming, A. Casas, M. Sachpazi and A. MarchetriSeveral hundred thousand kilometres of marine seismic reflection records collected up to 30 years ago remain only as paper records; and this applies to European Exclusive Economie Zone (EEZ) surveys alone. These data records were collected during scientific programmes by academie institutions since the 1960s. Owing to deteriorating recording media (magnetic tape) and the absence of appropriate instrumentation these data cannot be re-played. Often the records remain boxed and un-referenced while gradually deteriorating; those of greater interest having suffered more by handling. SEISCAN is a project to rescue these early seismic records which, with few exceptions, have not been archived in any photographic or other reproducible form. The 3-year project is funded by the European Commission MAST-III Supporting Initiative Programme and involves 5 European partner institutions. These partners will oversee an initial phase compiling seismic record metadata prior to digital scanning and image processing. The image database created will not involve any cost to the contributing organisations.
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The Ricker pulse and sediment density measurement by acoustics
By N. RoosnekMeasuring the density of sediment in delta harbours is a major issue in proper harbor management. These measurements are carried out in the port of Rotterdam by nuclear radiation absorption. Carrying out sediment measurements by acoustics might be possible. The gradient of the sediment density causes sound echoes. Assuming that there is a one-to-one relation between impedance and density, a measure for the gradient is obtained by deconvolution of the echo. Integration of the gradient after correcting for the loss of the probing acoustic pulse gives a measure for density. To obtain the sign information a wide frequency-banded signal has to be used. Such a signal can be generated by nonlinear acoustics.
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Beach dewatering system, results from a pilot plant installation in the Ebro Delta
Authors J. Serra, R. Bautista, C. Montori and L. Parente MaiaBeach erosion problem has been considered and combated for a long time by different solutions since the loss of beaches has a direct impact on local economy, mainly the touristic one. Hard structures defences are in comparison with soft engineering solutions less effective and environmentally acceptables, and between the last ones the Beach Dewatering System, or BMS, has been tested in the regressive deltaic coast of the Ebro delta. The system is based in the lowering of the water table and the creation of an unsatured zone in the beach face that facilitates the percolation of the water from the up and backwash. With the less water in the backwash and reduced surge height, less sand will be brought back to sea and then trapped in the beach face (Vesterby 1997; Oversen 1992). Because of the complexity of the beach structure and controlling parameters, a geophysical support by seismic or georadar of that sedimentary bodies can help the knowledge and the response of the system.
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High resolution marine seismic surveying as quality control tool for the construction industry
Authors G. U. J. Swoboda and D. OrlowskyMulti Channel Marine Seismics is well known for Oil and Gas surveying. The application of this technique at problems of the construction industry or at engineering problems needs some modifications of the seismic equipment and high accuracy in evaluating geometric parameters. The result of these modifications is the hydro-acoustic measurement system. It examines with sound waves in the range from 50 Hz to 25 KHz the underground of shallow water. Targets are reservoirs, rivers and objects in waterfilled construction areas The penetration into the bottom is down to 30m under the sea floor, depending on the seismic impedance between the layers. The use of high frequencies allows measurements of small layers in the range of one decimeter. Inevitable for good results and high resolution ist the digital seismic postprocessing of the multichannel dataset.
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Flow paths in a full scale model
Authors S. A. al Hagrey, T. Schubert-Klempnauer, O. Wachsrnuth, J. Michaelserr and R. MeissnerFor the restoration of groundwater and for an assessment of its pollution by agrochemical, e.g. pesticides, and industrial contaminants, an intensive study of flow processes through the unsaturated near surface vadose zone is necessary. Such a study is being presently carried out by a joint effort of the Institute of Geophysics and the Institute of Water Management and Landscape Ecology of Kiel University. It was known from many field experiments with tracers that rain water does not penetrate the upper vadose zone as a uniform water "front", but prefers "preferentiaI" flow paths (ScanIon et al., 1997: Hagrey & MichaeIsen 1996). This is due to organic heterogeneities caused by wormholes and roots and by inhomogeneities like a variability of soil textures, background humidity or water repellence (Ritsema et al., 1993; Hagrey & MichaeIsen, 1998). A preferential flow leads to an increase of flow velocity and diminishes the filter effect of the subsurface (Kung, 1993). A full-scale model of homogeneous sand regarding the vadose zone, was needed to develop a suitable high resolution mapping technique in space and time, using different geophysical and hydrological sensors to be distributed in the sand.
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Nuclear well logging in soils calibration of slim hole nuclear tools gamma-gamma and neutron-thermal neutron
Authors L. Baron and D. ChapellierThe calculation of elasticity parameters by sonic and ultra sonic wave propagation in saturated soils using Biot's theory needs the following variables : forpiation density and porosity (p, ø), compressional and shear wave velocities (Vp, Vs), fluid density, viscosity and compressibility (Pfi Ilfi Ki), matrix density and compressibility (p" K), The first four parameters can be determined in situ using logging probes. Because fluid and matrix characteristics are not modified during core extraction, they can be obtained through laboratory measurements. All parameters necessitate precise calibrations in various environments and for specific range of values encountered in soils. The slim diameter of boreholes in shallow geophysics and the high cost of petroleum equipment demand the use of specific probes, which usually only give qualitative results. The measurement 'of density is done with a gamma-gamma probe and the measurement of hydrogen index, in relation to porosity, by a neutron probe. The first step of this work has been carried out in synthetic formations in the laboratory using homogeneous media of known density and porosity. To establish borehole corrections different casings have been used. Finally a comparison between laboratory and in situ data in cored holes of known geometry and casing has been performed.
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Tomographic resistivity 3D mapping: filter coefficients and depth correction
Authors P. Cosentino, D. Luzio and R. MartoranaIn this paper further adjustments are presented regarding the method given by Cosentino et al. (1995, 1997) to construct rapidly 3D tomographic pictures from resistivity data. The purpose of the procedure (a filtered back-projection of the experimental data) is to obtain 2D or 3D pictures which match as closely as possible the geometry of the structures which are being investigated. In order to optimize the target some problems should be solved. Firstly, one should try to detect correctly the depth of electrical discontinuities (or anomalous bodies); secondly and not less important, one should try to determine the size as weIl the shape of the structures which are buried. In this paper we study the conneetion between the resistivity of the anomalous bodies and their effect on the apparent resistivity distribution. The results suggest that is best to optimize the values of the filters using also the negative values of the influence coefficients; they give also some information which appear useful to improve the estimate of both the depth and geometry of the bodies.
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Comparative study relating the specific water content deduced from the neutron-neutron and electromagnetic conductivity logs
Authors I. M. Fernández, J. Estaire and A. CarbóThis paper presents the transformation of the neutron-neutron and conductivity logs to specific water content. The transformation of the neutron-neutron log is made using calculated curves deduced from calibration bank, and the transformation of the conductivity log is made using laboratory data obtained in borehole samples. Out of the logs of specific water content obtained by these two procedures of calculation it is posible to draw conclusions concerning the quality of the methods and the correct application of these logs in the determination of the specific water content.
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Relations between natural gamma radiation, mineralogical and chemical properties of clays and muds from the Aveiro region - Portugal
Authors A. C. Galhano, J. Saraiva, L. Torres. F. Rocha and C. GomesThe Aveiro region (Fig. I) corresponds to the northern sector of the Portuguese Occidental Meso-Cenozoic sedimeritary basin. At the Aveiro region the upper Cretaceous is represented by the "Argilas de Aveiro" formation (Campanian-Maastrichtian), which are composed of greenish clays and marls intercalated with thin dolomitic layers. In the region, the outcrops of this formation are relatively extensive, with a maximum length (oriented N-S) of about 20 Km and a maximum width of about 5 Km, partially covered by quaternary old beach and alluvial deposits.
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Subsurface resistivity imaging using two single-step algorithms
Authors M. Gasulla, J. Jordana and R. Pallás-ArenyThis paper compares two single-step algorithms to obtain 2D subsurface resistivity images based in the sensitivity theorem The first algorithm is based in the Marquardt-Levenburg method whereas the second algorithm uses a weighted backprojection technique. An approximate' analytical solution yields the data (surface potential) for a spherical anomaly immersed in a homogeneous medium when using dipole-dipole and Schlumberger-based electrode arrays A fidelity measure quantifies the reconstruction error of each algorithm, which is defined as squared inner product of the normalized difference between the true resistivity profile and the estimate. The Marquardt-Levenburg method yields smaller errors but requires a damping factor that must be obtained experimentally. The reconstruction algorithms have been validated experimentally by placing a spherical object in a plastic water tank. Data for the dipole-dipole array are less accurate at higher depths because of the small voltages detected. Errors in the reconstructed image because of the uncertainty in electrode positioning and the finite dimensions of the phantom are partially canceled by taking a reference measurement.
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Tomographic and spectrometric sonic measurements at historical buildings
Authors H. Lindner and C. PretzschnerThe estimation of seismic veloeities in rocks with ultrasonic transmission methods is well known. Our idea is both to apply the tomographic method and to prove the usefulness of spectrometric analysis of sonic signals transmitted through materials of old buildings. The advantage of tomography is that it produces a two-dimensional picture of physical properties inside the rock. Fig. I shows this principle of transmission measurements around the surface.
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Application of electrical tomography in environmental study of oil pipeline zone in Luthuanian karst region
Authors D. Michelevicius, V. Narbutas and R. SeckusThe geological and hydrogeological and geomorphological conditions have been investigated along the oil pipeline dislocated in the Northern Lithuanian karst region. The pipeline crosses a region of geological and natural preservation - a zone of intense karstification. A particularly distinct karst structure is being seen between Roveja and Apascia rivers. Karstic subsurface represênts a vulnerable environment, where potable groundwater aquifer can be easily polluted. The objectives were to evaluate already caused and potential damage to nature as weIl as ecological hazards factors in various places along the 18 km long pipeline profile. Electrical tomography measurements have been performed along more than 50 profiles of this region. Also borehole drilling was involved for further interpretation of geoelectrical modeis. 32 control wells up to 20 m deep and 6 wells up to 35 m deep have been drilled.
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Resistivity and lP probability tomography in near-surface geophysics
Authors D. Patella and P. MaurielloWe describe a new tomographic method for the interpretation of resistivity and induced polarization (lP) field data. In recent years, tomographic imaging of geophysical data has become an important topic, due to the need of a high-resolution approach to the delineation ofburied structures, mainly in near-surface exploration (Noel and Xu, 1991; Loke and Barker, 1996). Our approach to tomographic interpretation of resistivity and lP data differs from standard inversion schemes, since it is essentially based on a probabilistic point of view.
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Drilling and borehole geophysics in alpine permafrost
Authors D. S. Vonder Muehll and C. HauckDrilling in mountain permafrost is quite different from drilling at other places: the inhomogeneous formation consisting of 'hard' rocks and 'soft' ice, and the temperature close to the melting point of ice are the most difficult of several factors. A number of parameters can be measured along the borehole facilitating the understanding of surface geophysical investigations and of ongoing processes in the permafrost Here, we present all overview of experiences from several permafrost drill sites and list some possibilities for drilling and borehole geophysical rrieasurements in mountain permafrost. This includes the saving and analysis of cores, borehole television camera, borehole logging and long-term monitoring installations (temperature, deformation). The aim of the borehole logging (Gamma-ray, Gamma- Gamma, Neutron-Neutron, Resistivity, Sonic) is to determine the thickness of the perennial frozen debris layer above the bedrock and to investigate P-wave velocity, resistivity and ice content of the whole permafrost body. In addition, main results from several permafrost boreholes in the Swiss Alps and Svalbard (Spitsbergen) are presented.
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Elastic moduli from sonic log with high resolution
Authors C. Pretzschner and H. LindnerThe travel time of seismic waves with frequencies up to 20 kHz is measured in borehole acoustics. Registration of the acoustic wavetrain (Fullwave Sonic-Log) allows the estimation of the dynamic elastic moduli of the formation in situ. But use of this method presupposes the traveling of longitudinal (P-) and transversal (S-) waves only as refracted waves along the borehole. In practice, the formation in the near borehole is altered or damaged by the drilling process. If the source to receiver offset (spacing) is short, as is usual in engineering, the measured results mainly reflect the velocity of this altered zone. In this case the measured arrival times will tend to be greater than those of a homogeneous formation and will depend on the penetration depth of acoustic waves through the formation (Fig. 1). Because of higher penetration depth sondes with longer spacings register the true formation velocity - by loss of structural-resolution - more exactly.
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Application of borehole log data for determination and mapping of filtration parameters
By R. SeckusThe accurate determination of the filtration parameters of thick aqueous complexes that comprise sandy and clayey beds using the traditional hydraulical tools is rather problematic. It is because under unconfined aquifer conditions values of the calculated parameters depend on both duration and intensity of pumping. Additionally, the parameters that calculated from pumping test's data characterize only a small locality. Consequently, extrapolation of the results for a larger territory requires particular approach. The application of wireline log data for this purpose could be successful if relations between the hydrogeological and geophysical parameters would be established. A correlation between permeability and formation factor in clean terrigenous formations is theoretically well known. However, presence of clay particles affects the process of conductivity that results in necessity to apply corrections while formation factor is being calculated. The empirical relationship between the corrected formation factor and permeability was derived using data of detailed hydrogeological-geophysical investigation in 28 borehole. The boreholes have penetrated approximately 200-220 m of the Upper- Middle Devonian water-bearing terrigenous complex within a well field for public water supply of Panevezys town in Central Lithuania. According to this relationship the average values of permeability and hydraulic conductivity were calculated using log data from more than 200 boreholes. As a result, maps of these parameters were compiled for the territory of the Baltic artesian basin.
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Paleoclimate reconstractions on the base of geothermal borehole data for Russian Platform
More LessCollection and analysis of temperature logs for different regions of the former USSR could be the basis for geothermal mapping of territories connected with possibility of radioactive wastes disposal investigation and for future monitoring of burial areas. Geothermal data base of the Scientific Council on Geothermal Problems of Russian Academy of Sciences includes sorne thousandes of temperature logs for different regions of the former USSR. The temperature logs have been combined from 1930 on the base of geothermal measurements in hydrogeological and oil boreholes. Not all regions are investigated quite weIl. The temperature logs quality is different for different areas. The lithological columns and hydrogeological regime description exist not for all territories.
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What is the role of well logging in environmental and engineering geophysics ?
Authors M. Ali Riahi and R. NazarianIn this paper different aspects of desirable conditions In shallow weIl logging and various corrections that one must employ to provide a good picture of geological structures for important engineering purposes like dam constructions is presented. To examine the proposed corrections electrical weIl logging data of Salman Dam site were chosen. The dam site area was located in south central part of Zagros mountain ranges, Shiraz, Iran. In this project, nine boreholes and totally six thousand meters of weIl logging experiment including temperature, normal, sp, natural gamma, caliper, gamma-gamma and a case of fluid resistivity testing were logged. The results revealed temperature anomaly of about 5C, presence of low resistivity layers, under ground hot water flow and a minor fault impression,
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Computer processing of acoustic full wavetrains recorderd with LSS device
Authors M. Bala and J. JarzynaP-wave and S-wave velocities determined from acoustic full waveforms together with density log resuIts provide unique information on elastic moduli of rocks, while the Stoneley wave slowness gives knowledge of fissuring and permeability of investigated formations. Transit interval times of P-waves, S-waves and Stoneley wave as weIl as their respective amplitude and phase spectra may be obtained using computer programs for interpretation of wavetrains.
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Seismic tomography for rock quality characterization
Authors A. E. Bracci, E. Lucchi and C. B. DyerThe tomographic survey described in this paper was carried out in Montereale Valcellina (pordenone, N-E Italy) where a dam has been under construction and the rock formation on the two sides of the valley had to be consolidated. The purpose of the geophysical study was to form an image of the velocity field over the survey region from which the conditions of the rock could be interpreted.
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Electrical resistivity tomography for petrophysical investigation
Authors A. Just, T. Küpper, D. Kürschner, J. Kulenkampff and F. JacobsDetermination of physical parameters of rock samples is essential to characterize their composition and structure. One of these parameters is electrical resistivity. Depending on porosity, resistivity of the pore fluid, saturation degree and matrix properties (esp. ore and graphite content, clay content), it thus yields information about these quantities. There are different methods for its determination as integral value over the sample (TELFORD et al. 1990 a.o.). RAUEN & SOFFEL (1995) have developed a method for the determination of transversal anisotropy. But it is not possible to estimate the spatial resistivity distribution within the core by these methods. Therefore we applied the principle of tomography. With this method we are able to detect and quantify anomalies due to fractures, cristallization of mobilisates, or spatial variations of the the pore fluid.
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Evaluation of the Police cretaceous basin using well log techniques
More LessDuring a three-year regional hydrogeological project realised in the Police Cretaceous Basin (Fig. 1) all available well-Iogging data from hydrogeological boreholes were re-interpreted (33 boreholes in total). Hydrogeological bodies defined in the Basin (Fig. 2) were identified after their geophysical properties (Fig. 3) and groundwater flow was determined in particular boreholes (Figs. 4a, b). In this way well-Iogging supported significantly other methodical approaches and yielded important data for a regional hydrogeological conclusions and implementation of a numerical model of regional groundwater flow.
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Detection of a geological barrier by electrical resistivity tomography using buried electrodes
Authors B. Ullrich and M. HeydeckeElectrical Resistivity Tomography (ERT) methods have been applied within a disturbed till complex to assist in the detection of a geological barrier on a waste deposit site. Crossborehole, single-borehole and hole-to-surface direct current (DC) electrical measurements were performed. For this studies electrodes were fixed to the well-tubes at a distance of 0.5 m to each other during casing installation. Sets of pole-pole data were aquired and inverted using a SIRT-algorithm to produce resistivity images. Due to the spacing of the electrodes the achieved image resolution and depth of investigation of these techniques are between typical values of surface surveys and logging measurements. Additionally single-borehole measurements were evaluated yielding synthetic electrical logs, simulating Laterlog 7, short norm al and long normal logging tooI measurements, respectivily. The cross-borehole and single-borehole inversion results as well as the computed synthetic logs show clear resistivity contrasts between different types of unconsolidated sediments. Resistivity changes obtained from the ERT-methods image the geological structure. In comparision with surface measurements, well logging and drilling results it helps to find a consistent modell of the geological barrier.
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Karst cavities detection investigations: a case study in Kuwait
Authors W. A. Abdullah, M. A. Mollah and N. M. Al-MutairiA thorough investigation program for the detection and delineation of karst cavities was undertaken in Al-Dhahar area, Kuwait. The investigation program included, topographical and aerial, geophysical and geotechnical and geological investigations. The investigations result indicated that the karst cavities encountered had the form of thin interconnected tunnels network. There was, in general, a good correlation between the topographical, geophysical, geological and geotechnical investigations in terms of delineating the locations and nature of karst cavities. However, the geophysical investigation presented few cases of mismatching with the other investigations. The inconsistency might be attributed to either the thin, interconnected tunnels network nature of the karst cavities or due to the incorrect presentation of the gravity contour maps,
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Application of the "impact echo method" to the detection of underground cavities part I: theory and finite element modelling
Authors Ch. Leonard, B. Piwakowski, I. Shahrour, O. Abraham and Ph. CêteThe aim of this paper is to model, by means of the finite element method (FEM), the detection of underground cavities using the "impact echo method" (IEM). The detection of holes by the IEM relies on the analysis of multiple reflections of the compression wave (echoes) between the surface and the hole. The presence of echoes in the recorded signal induces, in the frequency domain, a resonance effect which can be related to the depth of the hole. In order to enhance the performance of IEM, the signal should be analysed in a carefully chosen temporal window (so that the energy of the surface waves does not mask the relevant information). An original time-frequency analysis approach is used. It enhances the resonance frequency determination and helps "choosing an optimum temporal window of observation. The obtained results enabled us to determine the parameters which may influence the resolving power of the method and to define a theoretical thresholds of detection. The experimental verification of these results, performed in real field conditions, is presented in a second part [6].
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Application of the "impact echo method" to the detection of underground cavities part II: field experiments
Authors O. Abraham, Ph. Cötel, Ch. Leonard, B. Piwakowski and I. ShahrourThis paper presents the practical verification of the theoretical results obtained in Part 1. The "impact echo method" (IEM), is applied in order to verify the possibility of detection of holes in concrete and cavities in soiI. The advantages of IEM are its simplicity and low cost. It only requires one sensor, an impulsive seismic source and a single channel acquisition system. An original time-frequency analysis procedure which enables the automatic research of an optimum temporal window of observation is used. The joint procedure including acquisition and processing is further referred as Time Frequency Analysis of Seismie Reflection (TFASR). The field experiments were performed on sites where the positions of voids are known. In the case of concrete, the experiments were undertaken on a slab with three thicknesses (0.2m, 0.35m and 0.5m) within which some pipes of different diameters and polystyrene blocks were hidden at various depths. In the case of real underground cavities, the experiments were conducted in an "ideal" setting, because the cavities are located near the surface, in chalk. Their depth varies between 3.5 m and 8 m, and their size varies between 4 m and 12 m.
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The resistivity method in void detection
More LessThe detection of void and/or partially filled caves has been attempted using all the surface geophysical methods. However, the microgravity and the resistivity seems to be the most suitable methods, although, nowadays, the radar has a more and more important role in this domain. The resistivity method has been used by several authors, Spiegel et al. (1980), D. L. Smith (1986), Andrade Afonso (1987), Andrade Afonso et al. (1989). Spiegel et al. (1980) considered the caves as void zones using the integral equation method. to obtain the solution for the pole-dipole array. Andrade Afonso (1987) and Andrade Afonso et al. (1989), generalized this method for the dipole-dipole array. However, the method is unstable for voids close to the terrain surface. So, we tested the hypothesis of approaching, for numerical proposals, the void zones to areas of high resistivities in relation to the surrounding environment. The results obtained in an automated electric analogie test tank (2,lx1,25x1,25 m), filled with a 26 Ohmxm copper sulphate aqueous solution, and in the field (caves with known geometry) were compared with the numerical results obtained by the mentioned method and with the results obtained using numerical techriiques (A. Dey et al,1979: N. C. Smith et al., 1984 and Sasaki, 1989) suitable for continuous media. The experiment al pseudo-sections for the pole-dipole, as well as, for the dipole-dipole arrays fit very well with the numerical ones.
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Cavity detection in urban zones of mexico city
Authors R. E. Chávez, A. Tejero and J. UrbietaCavities and shallow fractures on mined regions beneath urban sites of Mexico City are a highrisk problem. Electric tomography has been applied to successively detect and map these types of structures to the western side of the city. The method developed by Loke and Barker was employed to image the real electrical distribution at depth. GPR (Ground Penetrating Radar) was also used to confirm the results obtained. The area selected possesses a high rare of population and is found in the hilly portion of the city, within the Mexican Valley. Results are very encouraging, demonstrating that a multicornponent geophysical survey help to locate and characterize areas of high risk.
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Study of voids and cavities using GPR
Authors V. Pérez Graia, L. G. Pujades, J. A. Canas, J. Clapés, R. Osorio, F. Garcia and O. CasellesGround Penetrating Radar is an excellent non-destructive tooI for ground evaluations. These studies are done in pIaces where it is important to obtain information, for example, in areas where special constructions will be built or where a special use will be performed. Holes caused by flowing water, that erodes the ground materials or by their dissolution can damage the constructions performed there. The contrast between the electromagnetic parameters of the ground materials and the air or water ones, usually existing in these cavities, causes great reflections. Radar data, in areas where a cavity is placed, shows astrong reflection, which denotes the contact between .the ground and the filling material. Also, the bottom of the cavity is usually observed. So, the presence of multiple reflections is usual in these studies. The void size to be detected mainly depends of the materiaIs, the centre frequency and the bandwidth of the antenna and the speed of the antenna movement. To determine the GPR resolution it is necessary a full study of every case: equipment employed frequencies, distribution of the profiles and a preliminary geological study. Three different examples of voids are presented. The first is a great cavity caused by the dissolution of the salt. The second is the presence of small holes in the contact of different materiaIs, caused by the flowing water through the sand existing between conglomerate layers. Finally, the last is the erosion between the tunnel facing tile and the rock of the mountain where it is located. The observed radar images are discussed.
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Detection of voids in an active open air coal mine
Authors J. L. Plata and J. RodaSeveral geophysical tests have been done with the objective of selecting the most suitable geophysical method to detect the presence of the voids produced by an old underground coal mine, where the system known as "rooms and pillars" were used. The final aim is to ensure the security conditions for people and machinery during the excavation of a new open pit mine, made to recover the coal left by the old one; many of the galleries may be nowadays collapsed by falling of the roof and swelling of the clay, but some of them can constitute cavities. The coal seams have the geometric disposition shown in fig. 1; in the actual mining system, starting from a situation like the one indicated by the line AA of fig. 1, geophysical surveys are carried out on platforms like a-a, to try and know the presence of voids inside the shadowed zone, before going on digging to reach the new situation indicated by line BB. Due to the metroIogicaI requirements of most of the different geophysical methods, measurements have to be made in absence of mining activity; another conditioning for the geophysical works is the rough topography of the surrounding area and of the mine itself, which is continuously modified, allowing a very short time to make the diagnosis for the presence of cavities. So, the main characteristics of this surveys are the detection of a group of connected voids, overlaying at several depths, with the limitations which represent the mine labours.
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Detection and characterization of near surface small karstic cavities using integrated geophysical surveys
Authors D. Rousset, P. Genthon, H. Perroud and G. SénéchalAnalyzing fluid and heat transfer in a karstic zone requires a good knowledge of reservoirs and "pipes" involved in water circulation. Exploration geophysics offers several tools to deal with such problems. The studied area, the Baget Massif, Ariège, France (tig 1) is characterized by the existence of decametric caves, acting as reservoirs and smaller features connecting them. The aim of this work is to test the ability of near surface geophysics to detect such karstic pipes. We chosed a test site where hydrological data suggest the circulation of water under the topographic surface. The studied area has been comprehensively surveyed using microgravity, high resolution seismics, radar and DC resistivity techniques. The intill of the valley is composed of recent alluvial sediments, covering the limestone bedrock.
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Using resistivity technique for locating air-filled cavities and data inversion
Authors A. Denis, N. Rahmani and D. BreysseThe presence of an underground air-filled cavity modifies the distribution of the electrical potential. One of the weak points of the resistivity method for the detection of air-filled cavities is the data processing required for quantifying depth and size of an air-filled cavity. One possible way is to use data inversion. At first, numerical computations have been undertaken to look for the major parameters influencing the measurements in an air-filled cavity detection problem with resistivity technique. Then an original inverse approach of resistivity measurements is proposed. In this approach apparent resistivity is a multivariate function, variables being the depth (H), size (X, Y, Z) and surface location (Xa). Thus we have: Pa = f (H, X, Y, Z, Xa). With numerical computations three different data bases are built. Experimental data are compared to theoretical data from the different data bases by using error criteria which allow us to get depth, size and surface location of the cavity. Finally, one example of the results obtained by this inversion approach is gi ven on real field data
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Detection of underground cavaties using radar surveys and electrical imaging
Authors G. Dittrich and B. UllrichThe investigation of the inner structures of historical buildings and their foundations is a rather sofisticated task. Because of different high amplitude disturbance sources geomagnetic surveys are not successful. Gravimetric effects of cavities and tombs inside the buildings are too low in comparison to the effects from the walls and ceilings. Only ground penetrating radar measurements and geoelectric methods have proved to be an effective tool to locate the different targets and to determine their three dimensional shape. A number of applications of these methods are widely documented in the literature. Objects of interest may he cavities, tombs, crypts, foundation structures or the condition of the walls. Classical geoelectric measurements inside of historical buildings are often difficult or impossible. In most of the cases it is necessary to drill holes to coupling the current and potential electrodes with the soil. The application of methods using the electrostatic quadrupol may overcome this problem. However, such investigations requires special measurement equipment. In the present work we integrated the high resolution GPR-measurements with three dimensional conductivity information, yielded from non-destructive geoelectrical measurements. This geoelectric examinations were carried out using special electrodes and standard measurement equipment. The target of the investigation was the detection of different subsurface structures inside the St.Trinitatis church of Meissen/Saxony.
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Geophysical detection of cavities in subsoil studies for building
By M. G. GarciaSeveral studies of cavity detection by geophysical methods, mainly with ground penetrating radar, are presented in this paper. They are in conncetion with the requirements of the construction industry (buildings, roads, urban infrastructures, etc.), environmental studies or research tests. Most of them correspond to Oviedo surroundings in the Asturias region (Northern Spain). Some types of cavities exhibit a characteristic geophysical response to local effects. I consider a classification in two general types: artificial originated cavities and natural cavities. Most of the artificial cavities can be attributed to a mining origin or infrastructures, and the correspondents to a natural origin are related to different geological contexts: cavities in cretaceous sands and karstic cavities.
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