| 1. |
- Martin, T., et al.
(författare)
-
Inversion of hydraulic conductivity from Induced Polarisation, Part B: field examples from five countries
- 2021
-
Ingår i: Conference Proceedings, NSG2021 1st Conference on Hydrogeophysics. - : European Association of Geoscientists & Engineers. ; 2021
-
Konferensbidrag (refereegranskat)abstract
- The knowledge about the hydraulic conductivity of the subsurface is crucial to know as it is a main parameter for groundwater flow characterization within an aquifer. The geophysical method time-domain Induced Polarisation has been shown to be useful for estimating the hydraulic conductivity. By using a new inversion approach, where we directly invert for hydraulic properties as inversion parameters, the estimation of the hydraulic conductivity can be improved. We have measured at several test sites across five European countries, all characterized by unconsolidated sediments, but with differences in terms of the water electrical conductivity. In particular, at the Zeeland site in the Netherlands, a strong gradient in the water electrical conductivity is present since a freshwater lens is overlaying the sea water. A very good agreement between the hydraulic conductivity values from the inversion with the present hydraulic model can be observed, despite of the high water electrical conductivity, which makes it challenging to identify the clay layers at the site. Similar results were achieved for the other tests sites. Therewith, this new methodology might open the way for reliable, cost-effective geophysical estimation of hydraulic conductivity in the field.
|
|
| 2. |
- Arvidsson, M., et al.
(författare)
-
Resistivity imaging as a tool for rock quarry planning
- 2007
-
Ingår i: Near Surface 2007. - 9781629937960
-
Konferensbidrag (refereegranskat)abstract
- In the aggregate industry the use of geophysical measuring is rare. The aim of this project is to investigate how geophysical instruments can be a tool in prospecting for rock quarries, and also how they can be a help in which direction they should expand in. To have control over the quality of the aggregates is important and therefore to know when the rock mass is changing is of interest for the production. Two quarries, with different properties, were investigated with different geophysical methods, of which only the result from the electrical measurement is presented here. The fracture frequency was measured as well for comparison. The depth to the bedrock is visible in the inverted resistivity sections for the two sites, and an estimation of the quantity of the till is possible to make. It is also shown that the fracture frequency affects the resistivity of the bulk mass. The results also show that the resistivity imaging is well suited for detecting anomalies in the rock mass, which might affect the production.
|
|
| 3. |
- Chirindja, F. J., et al.
(författare)
-
Reconstructing the formation of a costal aquifer in Nampula province, Mozambique, from ERT and IP methods for water prospection
- 2017
-
Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 76:1
-
Tidskriftsartikel (refereegranskat)abstract
- In continental margin basins, the hydrogeological setting is complex due to transgression/regression events that removed old sediments in the basin and formed new geologic units. Due to the geological complexity, the use of vertical electrical sounding has proven to be insufficient for groundwater explorations. The lack of understanding the geological underground has resulted in many boreholes with low yield or poor water quality. By performing electrical resistivity tomography (ERT) and induced polarization (IP) measurements in 11 villages in Mongicual district, three different layers covering the basement were identified: a weathered autochthon layer, a weathered allochthon layer (paleo-coastal dune) and eolian white sand layer. The drilling at successful boreholes penetrates formations where the resistivity value is between 220 and 770 Ωm, whereas at unsuccessful boreholes the lower parts of the drilled range have resistivity values higher than 770 Ωm. Also, the thickness ratio of the weathered and semi-weathered layer in the unsuccessful boreholes is less than 1/3, whereas in all successful boreholes the ration is higher than 1/2. The difference between autochthon and allochthon layers was detected by heavy minerals content in the red eolian sand layer (Tupuito formation) that increased the chargeability value. The groundwater with a conductivity higher than 2000 µS/cm is linked to the white eolian sand. The surface extension of white eolian sand layer is small to be mapped; therefore, by mapping the eolian white sand formation and the use of ERT and enhanced with IP method would lower the failure rate.
|
|
| 4. |
- Dahlin, T., et al.
(författare)
-
Data quality quantification for time domain IP data acquired at a former waste deposit in Lund
- 2012
-
Konferensbidrag (refereegranskat)abstract
- Tests were done measuring resistivity and time domain induced polarisation using standard multi-core cable spreads and a special layout with separate cable spreads for transmitting current and measuring potentials. For both types of cables spreads both normal and reciprocal measurements were done in order to estimate the measurement errors. The tests were done on a former landfill in Lund in Sweden. The electrode contact was favourable with resistances of some hundred ohm. The results gave low average error levels for both types of cable spreads, but the single cable spread showed a larger variation with more scatter in the IP data. Data for both types of spreads gave very consistent models that delineate the lateral distribution of waste as well as the contaminant leachate flow path. The results agree well with observations of contaminant outflow and test pit results. It is concluded that the standard approach with a single cable spread is adequate for a site with favourable characteristics as the one studied here.
|
|
| 5. |
- Dahlin, T., et al.
(författare)
-
Embankment dam seepage evaluation from resistivity monitoring data
- 2008
-
Konferensbidrag (refereegranskat)abstract
- Methods for monitoring seepage are important for dam safety of embankment dams. Increased seepage may be associated with internal erosion in the dam, and internal erosion is one of the main reasons for dam failures. Internal erosion progresses inside the dam, and is difficult to detect by conventional methods. Therefore, there is a need for new or improved methods. The resistivity method is a non-destructive method that may accomplish this task. A method for evaluating the seepage from resistivity monitoring data is theoretically described and tested for four selected areas in the foundation of the Sädva dam. Seasonal resistivity variations are apparent in the reservoir as well as inside the dam. The four selected areas represent areas with low, via intermediate to high variations in the seasonal resistivity variation. The areas are compared qualitatively and thereby permeable zones within the dam may be identified. Quantitative assessment of the seepage flow is also carried out as an initial test of the described method. It is concluded that the experiences from the Sädva dam are valuable for the application of the resistivity method on embankment dams. The presented method is a promising first step for quantitative assessment of seepage.
|
|
| 6. |
- Dahlin, T., et al.
(författare)
-
Geoelectrical resistivity monitoring for localizing gas at Landfills
- 2009
-
Ingår i: Near Surface 2009 : 15th European Meeting of Environmental and Engineering Geophysics - 15th European Meeting of Environmental and Engineering Geophysics. - 9073781728 - 9789073781726
-
Konferensbidrag (refereegranskat)abstract
- In order to assess the potential of electrical resistivity for imaging gas migration at landfills, two relatively well-known sites - one bioreactor landfill and a conventional landfill - have been monitored successively. A three-dimensional resistivity image could be constructed every two hour on both sites. Meteorological parameters were monitored at the same time, with one measurement taken every hour. Methane concentration was measured in the air at several occasions, the pore pressure was monitored at two locations and some relative estimations of moisture in the top layer were made at the second site. The results show imperfect but interesting correlations between the different parameters and give a hint of how the method could be refined. The resistivity depends on several parameters, but the areas where the resistivity is most variable seem to be clearly related to higher gas emissions.
|
|
| 7. |
- Dahlin, T., et al.
(författare)
-
Pilot study of using resistivity-IP, magnetometry and slingram for separation of industrial waste
- 2012
-
Ingår i: Near surface geoscience 2012.
-
Konferensbidrag (refereegranskat)abstract
- A controlled experiment was carried out by doing geophysical measurements on a purpose-built heap consisting of two different industrial waste fractions, called NF ( non-ferrous metal) and SLF (shredder light fraction), from the recycling plant of Stena Metall in Halmstad, Sweden. The purpose of the experiment was to see if it was possible to distinguish the different types of material using geophysics. Resistivity-IP, magnetics and slingram were measured over the test heap. The results gave distinctly different signatures for the different materials. In conclusion the test shows a large potential for the tested methods for material characterisation of buried waste in connection with landfill mining.
|
|
| 8. |
- Dahlin, T., et al.
(författare)
-
Resistivity-ip characterisation and short term monitoring at filborna waste deposit
- 2012
-
Ingår i: 74th European Association of Geoscientists and Engineers Conference and Exhibition 2012 Incorporating SPE EUROPEC 2012 : Responsibly Securing Natural Resources - Responsibly Securing Natural Resources. - 9781629937908 ; , s. 4667-4671
-
Konferensbidrag (refereegranskat)abstract
- Buried waste in old landfills is an increasing problem as cities expand and grow into areas with former waste deposits. In order to be able to manage and as far as possible reclaim land in such areas, better tools are needed for mapping and characterisation of buried waste and contaminated land. Other problems associated with landfills are leachate water and methane emissions. In the results presented internal landfill structure was successfully mapped using a combination of resistivity and time-domain IP. Differences in electrical properties can be related to different types of materials, and the groundwater level is outlined. Furthermore the results indicate that leachate water migrates into a former stream under the landfill. Variations in resistivity linked to variation in fluid and gas content were captured by short term monitoring. A rainfall event that occurred during the monitoring period acts as an infiltration test and the changes in resistivity outlines the water migration pattern. The results show the potential of resistivity monitoring for tracing fluid migration in the ground, and also shows patterns that may be due to increasing gas contents in line with previous studies.
|
|
| 9. |
- Dahlin, T., et al.
(författare)
-
Urban underwater ERT for site investigation in lake Mälaren, Sweden
- 2016
-
Ingår i: 22nd European Meeting of Environmental and Engineering Geophysics, Near Surface Geoscience 2016.
-
Konferensbidrag (refereegranskat)abstract
- An underwater ERT survey was made along a planned road tunnel for The Stockholm Bypass Project (Förbifart Stockholm). The aim was to assess the ability to identify variations in the depth of the bottom sediments, as well as variations in rock quality and the possible presence of weak zones in the rock. Reference data from a seismic survey and geotechnical drilling was used for evaluation the result. An underwater layout of 121 underwater and 37 land based electrodes at a separation of 5 m was used. Repeated measurements were made to assess the temporal variation in urban noise, which lead to doing the actual survey during the quiet night hours. The resistivity data are of good quality and the inversion results in low residuals. The invested section shows a low resistivity layer corresponding to sediments on top of bedrock with varying resistivity, where the interpreted depth to bedrock is in good accordance with the reference data. A major low resistive zone corresponds well with poor quality rock according to drilling and a low velocity zone.
|
|
| 10. |
- Johansson, S., et al.
(författare)
-
The potential of X-ray tomography and image analysis for interpretation of spectral induced polarization measurements
- 2017
-
Ingår i: Conference Proceedings, 23rd European Meeting of Environmental and Engineering Geophysics. - Netherlands : EAGE Publications BV. - 9789462822238
-
Konferensbidrag (refereegranskat)abstract
- The spectral induced polarization (SIP) method is a promising method for many near surface applications, including characterization of contaminated soil. In this study, SIP measurements, high-resolution X-ray tomography and image analysis are combined to investigate clean and tetrachloroethylene (PCE) contaminated sand. This is the first known combination of these methods and the aim of this paper is to demonstrate some powerful possibilities of using X-ray tomography in SIP research. X-ray tomography enables a direct visual control of the sample conditions and quantification of relevant sample properties via image analysis techniques. The image stacks from were processed with image analysis techniques, so that individual grains and PCE phases could be extracted from the sample volume. This enabled calculations of relevant sample properties such as PCE blob volumes, grain diameter,-surface area and-eccentricity as well as bulk porosity, specific surface area to pore volume and proportion of high-density grains. We conclude that the combination of SIP measurements and X-ray tomography have a great potential of increasing the understanding of SIP mechanisms in geological materials. The tomography results can be used both to calculate properties relevant for SIP interpretation as well as 3D modelling of the pore space.
|
|
