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- Conferences
5th EEGS-ES Meeting
- Conference date: 06 Sep 1999 - 09 Sep 1999
- Location: Budapest, Hungary
- ISBN: 978-94-6282-119-4
- Published: 06 September 1999
1 - 20 of 196 results
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Use of Euler deconvolution in recognising magnetic anomalies of archaeological objects
By M. El ErakiThis paper deals with the three dimensions magnetic interpretation of the buried archaeological bodies using Euler deconvolution. Euler's homogeneity relationship offers a quasi-automated way to derive plan location and depth estimates of buried archaeological objects, such as kilns, walls and tombs, from a gridded magnetic data set. Euler's homogeneity equation relates the magnetic field and its gradient components to the location of the source, with the degree of homogeneity expressed as a structural index. The structural index is a measure of the fall-off rate of the field with distance from the source and provides a way to discriminate between different source shapes. The method is also insensitive to field distortion caused by permanent magnetisation of source objects. Euler deconvolution method has been applied to data collected over Tell Basta historical site, Zagazig, Egypt. The analyses of the data sets have provided characteristic Euler deconvolution signatures and structural indices associated with typical buried archaeological bodies. The solutions obtained indicate the ability to quickly and accurately map the location and depth of buried archaeological objects from gridded magnetic survey data. The revealed depths to the different discontinuities agree fairly well with the archaeological evidences excavated later.
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Geophysical investigations of a possible impact structure near Raabs/Austria
Authors D. Kostial, F. Kohlbeck and C. KöberlA circular depression of about 400m diameter is located in the vicinity of Raabs/Austria (Fig.1). The question arose whether this structure could have been caused by an impact. The structure is very flat, about 5m of depth, whereas impact structures of this diameter should have a depth of at least 40m. However the circular shape of the flat central plane and the steep flanks resemble a crater that could have been filled by sediments at a later time. There are no rock exposures in the near vicinity, therefore shocked quartzes to prove the impact could not be found. The surrounding rock material is gneiss and amphibolite. Impact craters are associated with a low density zone of destroyed rock in the centre caused by the impact shock wave. This low density area can be recognised by different geophysical methods. At the Raabs site refraction-seismic, gravimetric, magnetic and geoelectric studies have been made. The refraction-seismic were carried out at two perpendicular profiles and indicated virgin rock with velocities of up to 6000m/s no deeper than 8m below the surface in the centre. Gravimetric and magnetic studies were carried out at stations on a regular grid of 50m mesh size covering the structure and extending to the outside region. In the centre measurements were taken on a more dense grid with 10m of mesh size. One line striking N-S was used for a comparison of all geophysical methods that had been applied. It was found that the gravity anomalies did not follow the shape of the surface. The Bouguer anomalies shown in fig. 2 are dipping about from SW to NE without any relation to the topography. 2-D modelling along the profiles was carried out. The models suggested that the amphibolite was dying out toward N beneath the structure. The depth to the solid rock found by the models fit the depth found by the seismic studies. Fig.3 shows the free air anomalies along the N-S profile passing the centre and the geological interpretation. A small micro-gravity high located near the centre is well defined and also shown. A correlation with a nearby magnetic high was suspected but could not be verified. EM34 measurements were taken along two profiles crossing the whole structure, whereas multielectrode measurements were made on a small profile in the centre only. The conductivities found with the EM34 showed an anomaly in the centre which could not be correlated with the seismics carried out on the same line. The Schlumberger measurements showed low resistivities (142 Ohmm) at the surface and high resistivities (1200 Ohmm) at a depth of 8m indicating solid rock. Very high magnetic anomalies have been found within a small region in the centre. This zone could not be identified by the other methods. The conclusion drawn from the measurement is, that the structure cannot have been caused by an impact. The comparison of the methods with each other shows a general agreement concerning the main structure. However, some differences and details could not be recognised by all methods.
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Integrated geophysical studies of St.Lawrence monastery's basements
Authors V. S. Safronov, D. K. Bolshakov, M. V. Kalisheva, I. N. Modin and A. Ju. PalenovIntegrated geophysical studies are carried out on St. Lawrence monastery's territory in Kaluga. The task of meals building basement's rests study in St. Lawrence monastery were considered. Magnetic, resistivity, GPR survey and metal detectors were used here. The main feature of the survey is a high amount of metal rubbish on territory (in particular in the uppermost layer). For example sheets of roofing iron at the total area about 20 sq. m were found here. Such strong source of noise could prevent not only magnetic prospecting, but also resistivity and georadar survey. Therefore geophysical studies of the area were conducted with preliminary searches of iron rubbish with metal detectors (TM-808, White's and ÑZ-7, Fisher) and its extraction. Magnetic prospecting Difficulties for magnetic survey were represented not only by metal rubbish, but also by high level of industrial noise, because the monastery is on Kaluga town territory. We used two proton magnetometers MMP-203, manufactured at St.-Petersburg enterprise «Geologorazvedka». To avoid the short period and high intensity variations (up to 50 nT) we used synchronous measurement's technology: the measurements on the area (13 x 20 m) and at base variational station were made simultaneously. The survey grid was 0.5 x 1 m. The survey accuracy consisted ± 5 nT (Fig. 1). The magnetic data interpretation was carried out with computer program DIPOLS-3 (K.M.Ermokhine), where field modeling is based on a dipole source method. Estimated anomalous magnetic field is presented at Fig.2. The model of the object producing such a field a field is presented at Fig. 3. Resistivity survey The survey territory was mapped by resistivity method with gradient array in two stages. At the first stage the current line was placed in S-N direction and measuring profiles were laid parallel to current line. Then the whole array was rotated on 90° (in E-W direction) and the survey was repeated. The area 18 x 25 m was mapped. The current line ÀÂ has length 50 - 60 ì, electric current value was 10 mA, frequency 4.88 Hz. Length of a measuring dipole was 0.5 m. The survey grid was 1 x 0.5 m. Resistivity instrument included the current generator (produced by ISR), and two measuring units ERA. The interpretation in accordance with the survey technology was carried out in two stages. At first stage the data for two different current line directions were analyzed separately, and then results for different polarizing fields' directions were united to receive a general map
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Geoenvironmental danger for Boyana church (Sofia, Bulgaria)
By M. MatovaIntroduction The Boyana church is a remarkable monument of the Middle Age history of the country. It is a subject of special protection from the side of UNESCO and the Bulgarian State. The small Boyana church was built in a quiet place, far away from the of the ancient Sofia city, near to the Vitosha mountain foots. The church was painted in the XIII century. The Christian icons of the church present one of the most important manifestations of the Bulgarian Renaissance.
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Multipurpose Geophysical Investigation on buda Castle Hill
Authors I. Holczinger, M. Pattanyús-Á., Zs. Prónay, L. Hermann and Zs. NyáriThe Buda Castle Hill in Budapest with its natural and artificial relics is an invaluable part of World’s Heritage. Cellars and caves, castle-walls and retaining walls, dwelling houses and palaces are the components which are in a tight relationship with each other and the urban environment too. The geological milieu is formed of marl covered by limestone and topsoil. The task of geophysics - on the basis of long-term city-planning - was to investigate the geological structure (especially the relief of the rock bed) and to detect archeological objects in three different areas.
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Application of Geomagnetic, Geoelectric and GPR Surveying to Archaeological studies
More LessThe ruins of the Roman-age town, Aquincum, can be found in the northern part of today's Budapest. Geophysical exploration for the Aquincum Museum started in October 1997 on a test area opposite to the museum. On one side, a main road and a railway with high voltage cable, on the other sides living houses border the area. Due to the artificial noises, the area was a good site to test how the different geophysical methods work in such environment. Magnetic method, direct current resistivity mapping and ground penetrating radar were tested. Aim of the work was mapping the ancient Roman town, which is presently covered by soil. An area of 3200 m2 was surveyed in a grid with spacing of 1 m, using proton precession magnetometer of GEOMETRICS G856 (sensitivity 1 nT). The magnetic field varies hundreds of nT in a few seconds period due to the electromagnetic noise of the city (Fig. 1). The amplitude of the magnetic anomalies caused by the archaeological objects is a few tens of nT. Due to the high frequency noise, interpolation of the data of a base station cannot be used to correct the measured data. This problem was solved by connecting the base station instrument and the measuring instrument by a cable and using an outer trigger to start the measurement. The measured data were corrected for the variation in time, the low-frequency, space-domain components were removed by a high-pass filter, the high-frequency, space-domain noises were smoothed by an optimum filter, the data were reduced to the pole, and finally, the magnetic field was downward continued. The synchronous measurement between the base and measuring instruments highly reduced the noise. To further reduce the noise, 5 measurements were made in each point in a smaller area of 300 m2. The mean of the measured values was taken. The repeated measurements resulted in a significant improvement of the quality and reliability of the magnetic map. The result of the repeated measurements is shown in the insert in Fig. 3. The resistivities of the limestone walls and the covering soil differ significantly. This initiated the idea of testing geoelectric methods in the area. DC measurements were made in an area of 50x40 meter using dipole-dipole electrode configuration. The length of the source and potential dipoles was 1 meter. The distance between the centres of dipoles was 2 meters. This electrode configuration gives information from a depth of about 1 meter. To speed up the profiling a "double-fork" electrode system has been constructed. The whole configuration was moved by one meter in the consecutive measurements. East-west as well as south-north profiles were measured. About 4500 data points were available for processing. An apparent resistivity map was computed from the combination of the two direction profiling (Fig. 3).
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The Application of Geophysical methods to resolve a fascinating archaeological query
By G. RanieriThe most interesting cultural characteristics in Sardinia are defined by the presence of more than seven thousand ancient buildings called ‘nuraghe.’ They are three thousand years old. Their impressiveness bears witness to the great capability of building of the ancient Sardinian population. In fact Sardinia is the only part of the world where ‘nuraghe’ occur. The nuragic civilization constructed varied building forms: towers with ‘tholos’ rooves, huts, sacred wells, multi-towered castles and so on. Well construction in very soft, fractured rocks and in coastal areas also demonstrated the great capability in searching for water, a rare resource on the island of Sardinia. The ‘Cuccuru su Nuraxi’ well in the village of Settimo S.Pietro near Cagliari the capital of Sardinia, is of particular interest. The well is more than thirty metres deep, two metres large and is covered by granite and sandstone blocks, fifty centimetres thick . The well head is eleven metres deep, in a room with a tholos roof. The well and the room are underground. A vertical stair leads to the summit of a hill where nuraghe artifacts are found (figure 1). From the exterior, the system appears as a regular conical hill formed by marl rocks. The context is formed by Miocene marl. Other irregular conical hills are found. Beyond archaeological interest, construction details along with the geological constitution of the hill pose some fascinating queries: Is the well an isolated sacred well, or is it inserted into a majestic castle and is it a water supply well? Was the well constructed upwards or downwards? Is the hill natural or artificial? What methods have they used to find water (there is still water in the well!) under marl formation? To answer these questions , crucial for the planning of archaeological excavations, geophysical surveys are carried out. Taking advantage of the conical form of the hill, we executed: three horizontal seismic tomographies at different levels; many gravimetric `Nettleton' profiles; a pole- pole electrical survey. The seismic tomographies show a relative high velocity zone only in the section around the well (figure 2) and constant velocity in the other sections. The tomographies were made with different shots-geophones array to verify the anomaly zones. They probably show the well in side a larger nuragic structure. Nettleton profiles have been utilized to determine the density of the hill (1.88 g/cm3), as well as to identify differences from right trend probably corresponding to voids. The well is very well indicated and a zone of 1.5 g/cm3 seems to indicate an old excavation (a trench ?). The pole-pole electric survey shows resistive anomalies which can be attributed to nuragic walls around the known well.
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Method of the equivalent dipole sources in the processing of results of the magnetic gradiometer surveys
Authors E. E. Nikitina and S. A. TikhotskyMeasurement of the vertical gradient (pseudo-gradient) of the magnetic field instead of total field measurement is one of the most popular methods in performing the high-accurate magnetic surveys especially when the noise level is very high. The process of transformation of the measured pseudo-gradient field into the total field is associated with the problem of the reconstruction of the long-wave field constituent. The common way in solving this problem is to add some small number of measurements of the total field T. Further processing of the survey results almost always includes the separation of the anomalous field into the constituents, associated with the distinct groups of sources. The traditional method in solving of formulated problems is the spectral operator application [e.g. C. Fechant, D. Orseau and N Florsch, 1998]. According to our experience spectral methods are not accurate enough and it could lead to the appearance of the false anomalies. These effects are due to the inaccurate Fourie series summation and edge effects (Gibbs effect). Following the ideas of V. Aronov (1963) and A. Bjerhammar (1964) we suggest an alternative method based on the simultaneous approximation of the measured values of the pseudo-gradient and the total field values by the model field of the equivalent dipole sources system. This algorithm allows us to calculate any magnetic field transformations, interpolation of the field values and to separate field into constituents. Let N be the number of the pseudogradient measurements (Gi) and M - the number of total field measurements Tj. N>M; i=1,..,N; j=N+1,..,N+M. We approximate these measurements by the system of K≤ N+M dipoles situated at some points (xk, yk, zk), k=1,..,K, in the lower half-space. In general magnetic moments of the dipoles mk can be determined from the following minimum condition:
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Enhancement and filtering of magnetic data in archeological sites
Authors F. Maurizio, F. Giovanni, P. Gaetano and R. Antonio.This work focuses on exploration of an archaeological site by magnetic survey. The aim of the survey is to evidence the presence of structures connected to an ancient Italic civilisation by means of new techniques for anomaly residuation and signal enhancement. The ancient settlement is located near S. Maria a Vico village, placed on a terrace of fluvial origin. The terrace is engraved in travertines covered by alluvial sediments and ash pyroclastic of Somma-Vesuvius and Flegrean Fields. In these sediments, altered by the weathering and about 3 meters thick, the remnants of proto-historical settlement to be investigated are buried. S. Maria a Vico is about 10 km far from Pontecagnano, site of a very important archeological deposit associated to the "Villanoviana" culture (Peninsular Italy, IX - VII century B. C.). Although the ancient site of S.Maria is associated to the "Tombe a fossa" culture, it was influenced by Villanoviana culture, being linked to the Etrurian-Campanian area and to the Greek colonies of the Ionian Sea. Excavation works, carried out in 1986 and 1991, did not allow to get clear elements about organization of the ancient settlement. Most of the remnants allow to estimate an age between VII and VI century B. C to the settlement.
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Monte Carlo simulation in geophysical site investigation
More LessGeophysical methods can substantially benefit the process of site investigation. It is equally true however that their full potential goes unrealised too often. A more rigorous and open approach to geophysical site assessment and forward modelling (i.e. geophysical `desk study') would go a long way to improving this situation. It is illustrated how the uncertainties involved in designing a geophysical investigation - for example uncertainties in the size and nature of the target, the accuracy and repeatability of measurements, the presence of cultural noise and the limitations of interpretation - can in many cases be understood and managed more clearly using a statistical method such as the Monte Carlo method. Examples of the application of such a method are described in the context of geophysical applications in site investigation. This type of approach can play a crucial role in defining the parameters of the investigation to an agreed or acceptable level of confidence. The approach can also aid the geophysicist in the design of the investigation and it improves clients' appreciation of the processes involved in designing, carrying out and interpreting the geophysical element of site investigation.
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Extremely fast IP used to delineate buried landfills
Authors N. R. Carlson, C. Mauldin Mayerle and K. L. ZongeDetermining the location of old, poorly documented buried landfills has become a significant concern in many places where development is hindered. Today new methodology provides a means for the efficient acquisition of induced polarization and resistivity data. Case studies of five landfills verified the accuracy of the technique and the acquisition speed of the system. At all sites IP anomalies (> 3 milliseconds) correspond to solid waste verified by drilling and trenching. Using a multiplexer capable of interfacing between a multichannel receiver, a transmitter and 30 electrodes allowed IP and resistivity data acquisition at extremely fast rates. Data acquisition in the dipole-dipole configuration consisted of a station spacing of 2.3 meters and a dipole size of 4.6 meters with twelve points collected along each diagonal (n=0.5, n=1.0, …n=6). The electric-field signal was sensed at the receiver site using tin-coated copper braid electrodes. A time domain, 0.5 Hz signal was used, stacking and averaging eight cycles to minimize random noise. Measuring all data points at least twice established repeatability of the data. A crew of three can acquire 3300 data points plus repeats in one day (approximately 800 line meters).
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Environmental assessment of municipal waste dump sites with electrical resistivity and induced polarization multielectrode methods
Authors V. Iliceto and G. MorelliA high resolution electrical resistivity and induced polarization survey was carried out inside and around a modern municipal waste dump site located in the Venice province, eastern Italy. The waste dump area is adjacent to two parallel rivers (Brenta and Bacchiglione), so that part of the measurement arrays had to be layed out directly on fluvial argins. The complex aquifer system was only partially known before the survey, although many boreholes were drilled in the past, before and after the construction of the dump site. However, the geology of the site is characterized by alternate thick clay and silt aquitards that should have guaranteed the protection of deeper aquifers. The most important things to assess with geophysical methods were the presence of higher permeability layers or lenses and the potential leakage from the waste area towards the above mentioned rivers or the adjacent farm land. The instrumentation used is a time domain resistivity/IP meter that allows for automatic SP compensation and digital stacking, with 1200 W maximum power and programmable IP windows. Special multi-core cables were constructed to ease the operations with up to 64 electrodes. The electrodes were made with standard copper-coated iron rods, that seemed to produce very low spurious polarization effects (although a cross-check with non polarizable porous pots is not easy to perform in multielectrode configuration). Different array configurations (Wenner, Dipole-Dipole) and different electrode spacings (2 to 5 meters) were tested, trying to optimize the results in terms of noise reduction and spatial resolution obtained. The data sets were interpreted using different 2D resistivity/IP inversion software, especially to test the influence of different IP modeling strategies on the final results. An example of a Resistivity / IP reconstructed section over the center part of the landfill is shown in the figure below: the solid waste mass appeared to be more resistive (25 -> 50 Ohm*m) than background soil (clay, pit and silty sand, ranging from 8 to 15 Ohm*m) and highly polarizable (over 20 mV/V). The IP results enabled to distinguish between different media having high conductivity, as clays or silty sands saturated with leachate originated by the waste. In fact, in the left part of the section a low resistivity layer ( 8 -> 15 meters depth, resistivity 4-5 Ohm*m) corresponds to a high chargeability zone, indicating a potential leakage from the bottom of the landfill (this older part was not protected with HDPE coating). From the center to the right of the section (the newer part of the landfill, with HDPE installed below 8 meters of waste) the chargeability decreases rapidly with depth to the low values encountered outside the area as well. In this case the conductive layer can be explained with the presence of a clay aquitard, indicated by the borings.
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Combined use of tem and RMT for the investigation of waste disposal sites
Authors S. Greinwald, A. Hördt, A. Hoheisl, G. Schaumann and B. TezkanAbout 25 km northwest of Hannover at Mellendorf a former sand pit was filled with industrial waste between about 1960 and 1980. The contents is mainly magnesium drosses. In 1987 the top of the site was sealed with a 1.5 m thick cover to avoid penetration of water into the waste. This was important because the bottom of the disposal at a depth of about 15 m below surface was not sealed. 1996 and 1997 TEM- (Transient Electromagnetic) and RMT-(Radio Magnetotelluric) measurements were carried out over the deposit. Goal of the combined use of RMT and TEM was a complete investigation of the vertical and horizontal resistivity distribution within the deposit and the directly surrounding area. The RMT measurements covered the deposit with a 10 m by 10 m grid, using four frequencies between 16 kHz and 200 kHz. For each frequency a pair of transmitters was chosen perpendicular to each other and located in the directions of the long and short axis of the deposit. For the TEM measurements the Protem 47 unit (Geonics) was used in an inloop configuration, the receiver being located at the centre of 50 m * 50 m transmitter loops. The interpretation of the data was performed in three steps. In a first step a one-dimensional inversion of the TEM data was used based on a three layer starting model. In the same step the interpretation of the RMT-data was based on a two-dimensional model. Secondly, for a further explanation of the RMT and the TEM data three-dimensional models were applied, based on the results of the preliminary interpretation of each method separately. Finally a three-dimensional model fitting both data sets was developed. The basic principle for determining the optimum model for both methods was to use the RMT-results for the top layers down to a depth of approximately 17 m and below that the results from the TEM data. This led to a final model combining the high resolution of the RMT method for the top layers and the better resolution at greater depth penetration of the TEM system. This model was further optimized, using trial and error, the only possible way at the moment. Figure 1a shows the combined model, which uses two different resistivity distributions for the western and eastern part of the deposit. The interesting result is that the high conductivity of the deposit extends to a greater depth than that of the former sand pit. The most likely explanation of the extension of the low resistivity below the known deposit depth is a leakage of waste water from the deposit into the ground below. To prove the validity of this result, modeling tests were undertaken with a reduced depth extend of the conducting layers for both sections of the deposit, the western (fig. 1b) and the eastern part (fig. 1c). Both models could not satisfactorily explain the measured data. This verifies with increased reliability the resistivity distribution of the optimized model shown in fig. 1a.
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Helicopter electromagnetic & magnetic surveying applied to a pipeline construction project in Canada
Authors A. Bouvier, P. Elkaim and G. HodgesFor construction Companies, the cost of a pipe laying project in a remote region depends on the risks taken when selecting a final pipe path according to the expected ground conditions within the first three to five metres of soil. Proper evaluation of the three engineering soil type distribution: unconsolidated, swampy deposits, loose ground (easily excavated), and hard rock (require drilling and blasting), is crucial to define the construction and environmental risks. It requires a costly and time consuming on-site investigation based on outcrop mapping and hand auger drilling. At best if access and logistics permit it, discontinuous soil sampling may be carried out along the proposed pipe path. For major pipeline projects, the selection of an appropriate path with respect to the lithological conditions is ensured through a helicopter-borne geophysical investigation combining electromagnetic and magnetic techniques. Electromagnetic data depict the surficial and near-surface apparent resistivity and discriminate between conductive layers (clay, marl, graphitic schist, salty formation..) and resistive ones ( dry sand, gravel, limestone, siltstone, sandstone, quartzite, gneiss, granite and volcanic rocks) . Magnetic data allow to distinguish between sedimentary and igneous rocks based on their magnetic susceptibility, which is several decades higher for igneous rocks. Methodology: a primary electromagnetic field is generated through transmitting coils using different frequencies in the 400 Hz – 100 000 Hz range. In a conductive body, eddy currents induce a secondary field, the component values of which (phase and amplitude) depend on the soil conductivity and are measured by a receiving coil. Transmitted frequency and depth of penetration share an inverse relationship whereby the higher the frequency, the shallower the depth, as expressed by the following formula: P = ½ Π √ 10 ρ/f where P is the depth of penetration (km), ρ is the ground resistivity (Ωm) and f is the frequency (Hz). This also means that the higher the soil conductivity (1/ρ), the shallower the penetration. The total intensity of the geomagnetic field is measured with a cesium vapor magnetometer simultaneously. Dighem method: the geophysical instruments are housed in a 8 metre long « bird » which is towed 30 m below a helicopter . Five pairs of coils (two coaxial and three coplanar) constitute the Dighem V electromagnetic system. A Geometrics 822A magnetometer is located between the transmitting and receiving coils. The helicopter flies lines at an altitude of 60 m and a speed of 100 km/h, maintening a ground clearance of 30 m for the bird. Along each line, an electromagnetic measurement is taken every tenth of a second, which represents a distance on the ground of about 3 m. The lines are positioned using an on board Ahstec GG24 GPS receiver, giving a lateral accuracy of about one meter.
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Locating burried waste using geomagnetic survey
Authors A. Kohler, S. Puszta and P. SteinbachDuring the operation of a refrigerator factory in the 50’s, 60’s and 70’s drummed hazardous wastes were dumped and covered with soil illegally in sand pits located near to the factory. About 20 years later the during an overall environmental remediation project these illegal waste disposal sites were excavated and restored. The locations of these dumping sites were determined by aerial photographs, and using local people recalls. As work progressed new reports were made to local government and factory management about waste dumping sites, all of which were examined by means of excavating, visual inspection, waste (if found), soil, and sometimes groundwater sampling. Originally 7 waste disposal sites were assigned for examination, the final number of the examined sites was fourteen. No. 14 site (WDS-14) was reported by an excavator operator of a sand mine, who actually was ordered to dig a trench, later in wich he witnessed dumped drums. Because of subsequent mining operations, and land use change the operator could not identify the location of a reportedly 40 x 2 meters trench, only approximately within a 100 x 100 meter area. The site was first excavated at several locations based upon the operator’s memory, but nothing was found, not even soil disturbance. As the operator insisted on the existence of the dump a geomagnetic survey was chosen to scan the area for geomagnetic anomalies, which could indicate burried metal objects. The site was prepared by creating a 20 x 20 m grid oriented to magnetic north, and handed over to the geomegnetic surveyors. Using fluxgate gradiometer one considerable anomaly and several disturbances were found within the area of interest. However, the proof of the existece of buried drums demanded systematic survey. A 120 x 120 meter area was systematically surveyed with a proton procession magnetometer. Measurements were taken at a 1 x 1 m grid, which means 12000 measurement points. The sensitivity of the instrument was 0,1 nT, and the probe was held at a 0,7 m level from ground surface. Data processing started with diurnal correction. This was followed by noise reduction as such reduction to the pole (resulted the elimination of anomalies that had permanent magnetic effect, since it could be presumed, that the burried objects have only induced magnetization). Geological effects (low frequency noises, e.g. facies changes, clay lenses etc.) were removed by band pass filtering and high frequency noises were compensated by optimum smoothing filtering. The picture of the burried objects was sharpened by downward continuation, and the result was visualized as a colour picture.
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Detection of old waste depostits and their contamination by using geophysical methods: Two case studies
Authors S. S. Seren and N. H. BlaumoserWaste deposits constitute a massive risk for the environment. Their re-development needs most exact information about their extent, content and their geological situation. This information can be improved cost-effectively and fast utilizing non-destructive geophysical methods, such as magnetic, electromagnetic and geoelectrical field measurements. To demonstrate the effectiveness and advantages resulting from combining these methods, two case studies are presented. 1) Waste deposit in Molln, Upper Austria: The waste of an aluminium-factory was deposed in a river. No precautions were made. The records showed no details about the quantity of the waste and the extent of the polluted area. Using geoelectrical-Wenner-array-measurements these informations could be retrieved. A 3m-array-distance was choosen for this purpose. The boundary of the waste deposit and even areas of high contaminations could be determined with high precision. The waste deposit showed lower apparant resistivity values than its surroundings, which consists of sand and gravel - both showing very high apparent resistivity values (> 500 Ohm-m). In addition, using two deep soundings after Schlumberger the specific resistivity of the waste deposit and of its surroundings could be determined. 2) Waste deposit in Karling, Upper Austria: The waste deposit, probably containing common house-garbage, was surveyed using magnetic, electromagnetic and geoelectrical methods. Based on five geoelectrical deep soundings after Schlumberger the hydrological and geological situation in the aerea of the waste deposit was determined. A 12 m thick ground-water-layer was endangered by this feature. At a depth of 18 m a layer showed up, which can play an important factor during a future re-development of the waste site. Electromagnetic and magnetic (total intensity and gradiometer) surveys were carried out with a measurement distance of 5x10m. The electromagnetic survey showed clearly the surrounding of the waste deposit and a strong contamination. The magnetic survey showed areas of strong anomalies, which are not typical for a normal household-waste. Hence, in the investigated area one should also expect to find steel barrels, car-wracks etc.
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Waste disposal site mapping using the CVES method
Authors M. Ezersky and A. Beckctions were constructed using Res2Dinv software, which is a computer program for rapid 2D resistivity inversion using the least-squares method by Loke and Barker (1996)1. The waste disposal site is 300x500m and consists of non-organic materials (mostly building waste), layered alternately with thin, sandy-loamy layers and underlain by a thick layer of dune sands. Visual inspection of the site revealed that, apart from bricks, wood and concrete fragments, there was also a substantial number of metallic objects randomly distributed throughout the waste volume. The sandy-loamy layers retain moisture whereas the sand is drained, thus there is a significant difference in electrical resistivity between the waste and the natural sandy base layer. At the northern and eastern sides of the site, the waste layer is higher than the sandy basement, while at the southern and western sides, both the waste and the basement are at the same level. It was, therefore, possible to correct the thickness of the waste layers using a forward calibration measured at the waste outcrops. Five CVES lines, totaling 1500 meters in length, were carried out in the waste disposal area. Fig. 1 shows a typical geoelectric cross-section of Line 2. Two layers are clearly observed: the upper layer (waste) is characterized by resistivities of 5-50 ohm-m, while the lower sandy layer has resistivities of 100-500 ohm-m. The corresponding interfaces are shown by dashed lines. The field between these interfaces may be interpreted as a “transition” zone, i.e. a sandy layer with different electrical properties. The results of the survey are shown in Fig. 2 as an lateral changes of the thickness of the waste layer. The map shows that the thickness of the waste layer varies from 0-30 m. The thickest part (more than 32 m) is located in the center of the map. An example of waste disposal site mapping using the CVES method with 2D inversion technique is given. This is one of the few geophysical methods that can be used successfully to map such heavily heterogeneous structures.
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Seismic investigations of waste disposals and biogas detection
Authors B. Elek, Zs. Prónay, L. Hermann and E. TörösThe investigation of waste disposals is not an easy task in geophysics. The general approximations, like homogeneous, near horizontal layers are not valid. That’s why besides conventional seismic methods new developments are necessary. On some recultivated old waste disposals the accumulation of organic originated gases (biogases) can endanger buildings, which is an other challenge for geophysics. ELGI has driven a project to try to solve those problems. The first step was to make test measurements on a typical location, and to compare and evaluate the results of different seismic methods. P-, S-wave refraction, reflection, diving wave tomography and surface-wave methods were tested. In deep seismics AVO (Amplitude-Versus-Offset) analysis seems to be the proper tool for direct gas detection, but in shallow cases the poor signal to noise ratio of reflected signals makes its application impossible. In highly inhomogeneous medium new methods needed. The first results are promising, on the test location the gas accumulation could have been detected and evaluated by drilling. In the recent years we want to continue the project to investigate more waste disposals for further testing of our method.
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Application of induced polarization and radiomagnetotellurics to a waste site in Nortii Cologne
Authors M. Hönig, S. Recher, B. Tezkan and F. M. NeubatuerThe application of geophysical methods to waste site exploration becomes increasingly important. On a waste site in Longerich measurements have been taken out using time domain dipole-dipole induced polarisation and frequency domain EM (RMT). The Time Domain IPequipment consists of a transient electromagnetic recording system and a portable transmitter whereas the RMT-method uses remote radio stations (10-300 kHz). The aim of the poster is to show first results of the survey and some details about the IP-equipment and measurement setup.
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Complez geophysical survey of an abandoned soviet military area polluted by the LNAPL in the creatceous of Bohemia
More LessIntroduction In the frame of the Czech-Italian joint research project "Groundwater movement and contamination risk of hydrogeological structures", a set of geophysical methods has been tested in an abandoned soviet military area with an airport for fighters near to the provincial town Mimon. Pollution history The selected test site has an extent 300 m2 and is situated in the area of the railway terminal, where the hydrocarbon products have been transferred from tank wagons to underground storage tanks. The leakage of tubes and bad insulated high volume tanks - getting rusty during the 30 years long period and finally being perforated - caused serious groundwater LNAPL pollution with first meters of the kerosene at the water table, with vadose zone pollution and traces of dissolved hydrocarbons in groundwater. The remedial activities (pumping fluids from clean-up wells situated in the dense network 10 x 10 m, bioventing, venting) are running continuously from 1993 under the supervision of the KAP Company. Under present conditions, the light heating oils and kerosene contaminate irregularly the vadose zone, in addition - after 3 year remedial activities - create thin layer above the groundwater level
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