| 1. |
- Villain, Lucile, et al.
(författare)
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Evaluation of the effectiveness of backfilling and sealing at an open-pit mine using ground penetrating radar and geoelectrical surveys, Kimheden, northern Sweden
- 2014
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Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 73:8, s. 4495-4509
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Tidskriftsartikel (refereegranskat)abstract
- At Kimheden, a small copper mine in northern Sweden, reclamation of the two open pits was investigated using ground penetrating radar and geoelectrical multiple-gradient array measurements. The pits had been backfilled with waste rock, with a dry cover being applied on top in 1996 in order to reduce the influx of oxygen to the sulphidic mine waste and the subsequent production of acid mine drainage. The dry cover consists of a sealing layer of clayey till and a protective layer of unsorted till. As geochemical sampling in the drainage from the pits had previously revealed the continued release of contaminating oxidation products, the purpose of the geophysical survey undertaken in 2010 was to identify deficiencies in the cover or other pathways for oxygen to reach the waste rock. The radar images did not reveal any damage in the sealing layer but risks of deterioration of the cover in the long term were identified with both the radar and geoelectrical data. The radar localised regions of thinner protective layer where the sealing layer could be exposed to frost action. The geoelectrical measurements indicated the existence of seepage through the dry cover that presented a risk of erosion of the sealing layer. 2-D inversion of geoelectrical data also imaged some pathways of groundwater around the main pit. The results from the geophysical investigations were used together with other site data in order to show that both deficiencies in the cover and superficial fractures in the pit walls may explain an ongoing influx of oxygen to the mine waste.
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| 2. |
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| 3. |
- CHIRINDJA, FARISSE JOAO, et al.
(författare)
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Combined electrical resistivity tomography and magnetic resonance sounding investigation of the surface-water/groundwater interaction in the Urema Graben, Mozambique
- 2016
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Ingår i: Hydrogeology Journal. - : Springer Science and Business Media LLC. - 1431-2174 .- 1435-0157. ; 24:6, s. 1583-1592
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Tidskriftsartikel (refereegranskat)abstract
- This study focusses on the hydrogeology of Urema Graben, especially possible interactions between surface water and groundwater around Lake Urema, in Gorongosa National Park (GNP). Lake Urema is the only permanent water source for wildlife inside GNP, and there are concerns that it will disappear due to interferences in surface-water/groundwater interactions as a result of changes in the hydraulic environment. As the lake is the only permanent water source, this would be a disaster for the ecosystem of the park. The sub-surface geology in Urema Graben was investigated by 20 km of electrical resistivity tomography (ERT) and three magnetic resonance sounding (MRS) surveys. The average depth penetration was 60 and 100 m, respectively. The location of the ERT lines was decided based on general rift morphology and therefore orientated perpendicular to Urema Graben, from the transitional areas of the margins of the Barue platform in the west to the Cheringoma plateau escarpments in the east. ERT and MRS both indicate a second aquifer, where Urema Lake is a window of the first upper semi-confined aquifer, while the lower aquifer is confined by a clay layer 30–40 m thick. The location and depth of this aquifer suggest that it is probably linked to the Pungwe River which could be a main source of recharge during the dry season. If a dam or any other infra-structure is constructed in Pungwe River upstream of GNP, the groundwater level will decrease which could lead to drying out of Urema Lake.
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| 4. |
- Legchenko, Anatoly V., et al.
(författare)
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Experimental verification of advanced SNMR modeling
- 2014
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Konferensbidrag (refereegranskat)abstract
- Whatever would be the practical implementation of Surface Nuclear Magnetic Resonance (SNMR) survey, inversion is based on forward modeling of the magnetic resonance response. Consequently, the mathematical model is a crucial point for inversion. We have developed advanced mathematical model that allows computing magnetic resonance signal from 3D targets both in FID (free induction decay) and SE (spin echo) modes. This model takes into account both time and lateral variations of the earth's magnetic field, water temperature and electrical resistivity of the subsurface but also the effect of magnetic rocks on MRS signal. For experimental verification of the modeling routine we used two bulk water reservoirs. One-dimensional (1-D) measurements were performed in winter from the ice surface in the Baltic Sea (Sweden) and 3-D verification was made using an artificial water pool located in the southern part of the New Caledonia Island. Modeling was carried out taking into account reservoir geometry and local conditions obtained from independent measurements. We have found a good correspondence between observed and theoretical signals for both FID and SE measurements. At our knowledge, SNMR modeling was never compared with field data obtained under all mentioned above conditions.
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| 5. |
- Perttu, Nils
(författare)
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Assessment of hydrogeological and water quality parameters, using MRS and VES in the Vientiane Basin, Laos
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Water is essential for all life on the planet, sustaining and ensuring the earth's ecosystem. Groundwater from a global perspective provides about 50% of the potable water supplies, 40% of the industrial water and 20% of the irrigated agriculture. For drinking water, deep groundwater has many advantages compared to surface water and shallow groundwater, since it demands little or no treatment and the access is secured against temporary droughts. However, salinity in deep groundwater is common in coastal areas and in areas where rock salt is occurring naturally in the soil and bedrock. Drilling wells is expensive and unprofitable if it is made without knowing the groundwater potential and the location of salt affected groundwater. Vertical Electrical Soundings (VES) has been widely used to characterize aquifers and to identify salt affected water since there may be a relation between the conductivity of the aquifer and the salinity of the water. However, it is not possible to distinguish high conductive groundwater from e.g. increased clay content. Magnetic Resonance Sounding (MRS) gives a direct image of the water content of the ground and hence the vertical distribution of an aquifer. By combining MRS with VES, salt affected groundwater could be distinguished from high conductive sediments and freshwater aquifers. The aim of this study is to define and characterize water bearing geological formation and to test the possibility of using geophysical techniques to determine hydrogeological parameters and water quality parameters relating to salinity in the Vientiane basin, Laos. The investigation area is part of the Khorat Plateau where halite is naturally occurring as shallow as 50 m in depth in the Thangon Formation. In total, 32 sites and 28 sampled wells, located in three different areas were investigated. MRS and VES recognized the stratigraphic unit N2Q1-3, consisting of alluvial unconsolidated sediments, as the main water bearing unit. The aquifer thickness varies between 10 to 40 m and the depth to the main aquifer range from 5 to 15 m. The water content is here relatively high, up to 16 % and decay times varying between 100 and 400 ms, suggest a mean pore size equivalent to medium sand to gravel. The resistivity is highly variable, but usually around 10-100 ohm-m, which suggests fresh water. Hydraulic and storage related parameters such as transmissivity, hydraulic column, specific yield and specific storage have been estimated from MRS and transverse resistance has been estimated from VES. MRS together with VES has also shown to be a useful and important tool in identifying the salt related clay layer of the Thangon Formation. This layer is characterized by low water content and a resistivity lower than 5 ohm-m. This formation can be found in all 3 areas on depth of 20 to 50 m. Several approaches have been used to look for a relation between the water conductivity collected from wells and the aquifer conductivity determined from VES, including Archie's law. The best correlation is achieved using a linear fit between VES conductivity and water conductivity for deep wells (EC[μS/cm ]= 0.3821VES[μS/cm], R2=0.81). The conductivity of water from shallow wells does not show any relation to VES conductivity (R2=0.09). This is probably because deep wells usually have higher conductivity than shallow wells and hence contributing more to the aquifer conductivity. Interpolated maps of TDS in area 3 from deep wells together with maps of the conductivity of the bottom layer and aquifer layer, MRS transmissivity and hydrostatic column indicates that the salt originate from the underlying layer situated beneath the main aquifer. The most important water quality parameters influencing the water conductivity are TDS, hardness and chloride, which all have a high correlation to the EC of water and thus VES conductivity. This makes MRS and VES a very promising tool for guidance of future drillings and water quality estimation.
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| 6. |
- Perttu, Nils, et al.
(författare)
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Characterization of aquifers in the Vientiane Basin, Laos, using magnetic resonance sounding and vertical electrical sounding
- 2011
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Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 73:3, s. 207-220
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to define and characterize water bearing geological formation and to test the possibility of using geophysical techniques to determine the hydrogeological parameters in three areas in the Vientiane basin, Laos. The investigated areas are part of the Khorat Plateau where halite is naturally occurring at depths as shallow as 50 m in the Thangon Formation. Magnetic Resonance Sounding (MRS) has been used in combination with Vertical Electrical Sounding (VES) in different geological environments. In total, 46 sites have been investigated and the MRS and VES recognized the stratigraphic unit N2Q1-3, consisting of alluvial unconsolidated sediments, as the main water bearing unit. The aquifer thickness varies usually between 10 and 40 m and the depth to the main aquifer range from 5 to 15 m. The free water content is here up to 30%, and the decay times vary between 100 and 400 ms, suggesting a mean pore size equivalent to fine sand to gravel. The resistivity is highly variable, but usually around 10-1500 Ω-m, except for some sites in areas 1 and 2, where the aquifer is of low resistivity, probably related to salt water. Hydraulic and storage-related parameters such as transmissivity, hydraulic column, have been estimated from the MRS. The MRS together with VES has been shown to be a useful and important tool for identifying and distinguishing freshwater from possible salt-affected water as well as the salt-related clay layer of the Thangon Formation. This clay layer is characterized by very low free water content and a resistivity lower than 5 Ω-m and can be found in all 3 areas at depths from 15 to 50 m
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| 7. |
- Perttu, Nils, et al.
(författare)
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Determining water quality parameters of aquifers in the Vientiane Basin, Laos, using geophysical and water chemistry data
- 2011
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Ingår i: Near Surface Geophysics. - : Wiley. - 1569-4445 .- 1873-0604. ; 9:4, s. 381-395
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study is to test the possibility of using magnetic resonance sounding (MRS) and vertical electrical sounding (VES) together with groundwater chemistry data from shallow and deep wells to distinguish freshwater aquifers from salt affected groundwater and moreover determine water quality parameters directly from geophysical data. Three study areas within the Vientiane Basin, including 46 sites and 38 sampled wells, have been chosen for the study. The main water quality parameters affecting the water conductivity in the Vientiane Basin are total dissolved solids (TDS) and hardness and to a minor extent chloride, which all have shown to have fairly high correlation to the electrical conductivity (EC) of groundwater. The resistivity of the aquifers is highly variable but is most often above 4 Ωm, suggesting fresh water. No wells in the investigated areas have water quality parameters exceeding the limit for unacceptable drinking or irrigation water. There is a fairly strong relationship between the conductivity of water from deep wells and the conductivity of the main water bearing layer determined by VES, where the best fit is obtained using: EC[μS/cm] = 0.4694VES[μS/cm], R2 = 0.69. However, due to equivalence in the VES interpretation and the difficulty to estimate the resistivity contribution from finer sediments, the equation may be seen and used as guidance to good water quality only within the Vientiane Basin area or in other areas with similar geology. The MRS results have been used to identify water layers in the VES inversion results to decrease the uncertainty in the interpretation The combination of MRS and VES techniques has been successful in distinguishing high conductive clay and mudstone from water bearing layers and moreover freshwater aquifers from salt affected water. Altogether, this makes MRS and VES very promising tools for guidance of future drilling and water quality estimation.
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| 8. |
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| 9. |
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| 10. |
- Perttu, Nils, et al.
(författare)
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Magnetic resonance sounding and radiomagnetotelluric measurements used to characterize a limestone aquifer in Gotland, Sweden
- 2012
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Ingår i: Journal of Hydrology. - : Elsevier BV. - 0022-1694 .- 1879-2707. ; 424-425, s. 184-195
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Tidskriftsartikel (refereegranskat)abstract
- Almost all drinking water in Gotland is groundwater and is mainly found in karst limestone. However, the unpredictable location and geometry of the karst cracks and caverns makes it very difficult to estimate groundwater storage and movement, as well as contaminant transport. The aim of this study was to test the performance of different geophysical techniques like Magnetic Resonance Sounding (MRS), Radiomagnetotelluric (RMT), Vertical Electrical Sounding (VES) and Ground Penetrating Radar (GPR) to characterize aquifers in Gotland, in respect to geometry and storage as well as connectivity over a wider area. The investigated area is located on the south-eastern part of Gotland. The geology here is dominated by 50 to 60 m thick successions of limestone that gradually turn into marlstone. The use of multiple techniques has shown to give a more coherent interpretation. However, the shallow penetration depth of GPR and the lack of soil cover in some places of the investigated area limit the use of geoelectrical methods and GPR. With MRS, water are found down to 60 m in depth, with a maximum water content at depths of 20 to 30 m. This coincides with the most resistive sections of the limestone. The water content varies between 0 and 3%, with a relaxation time (T1MRS) less than 400 ms suggesting that the aquifer is hosted in small fractures, molds and vugs rather than larger karst fractures and caverns. Two potential aquifers were identified with MRS, possibly separated by marlstone. From modelling it can be seen that such boundary separating two aquifer apart can be more easily discriminated in the N/S-, than in the E/W direction. In summary, MRS is therefore the only method in this survey that can detect and determine the vertical and lateral distribution of water within the aquifer together with the total volume of free water. The RMT method has shown to be effective in characterizing the limestone/marl interface, but also to locate anomalous low resistive zones, possibly associated with salt water. RMT also helps to constrain the final MRS model by choosing a suitable regularization for the MRS 3D inversion. All together, the combination of MRS and RMT seems most efficient of the tested methods and therefore most promising for future groundwater explorations in geological environments like in eastern Gotland.
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