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NSG2023 2nd Conference on Hydrogeophysics
- Conference date: September 3-7, 2023
- Location: Edinburgh, United Kingdom
- Published: 03 September 2023
20 results
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Unsupervised Machine Learning Assisted Hydrogeophysical Borehole Logging Inversion for Robust Aquifer Characterization
Authors M. Abdelrahman and N. SzaboSummaryThis research proposes an integrated algorithm that uses an unsupervised machine learning technique, specifically the new K-mean clustering, for automatic aquifer characterization using hydrogeophysical borehole logging data. The MFV-cluster algorithm was employed to determine layer boundaries and petrophysical parameters automatically. The viability of the suggested process was evaluated using synthetic and field data, and it was found to be effective in distinguishing between various forms and providing a preliminary estimate for layer thicknesses. The integration between the new cluster technique and interval inversion can help with the automatic detection of both the geometrical and petrophysical parameters. The field data used in the study showed a shaly sand pattern response. The MFV clustering technique was applied to this field data and was able to distinguish between various forms and provide a preliminary estimate for layer thicknesses. The results of the statistical evaluation of synthetic data contaminated by 30 percent of outliers prove a high dependency on the initial location of the centroid. The interval inversion approach enhances the number of inverted data points by representing the petrophysical parameters as a continuous function.
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Investigation of the Hydrogeology at a Chalk Cliff Site in Normandy Using Multiple Research Approaches
Authors T. Junique, C. Fauchard, R. Antoine, V. Guilbert, B. Beaucamp, C. Ledun, S. Costa, O. Maquaire, R. Davidson and N. CoppoSummaryThis study uses a multidisciplinary approach combining optical and geophysical methods to analyze the stability and seawater intrusion in chalk cliff at Sainte-Marguerite-sur-Mer, Normandy (France). Techniques employed include photogrammetry, thermal infrared spectroscopy (TIR), electrical resistivity imaging (ERI) and the towed transient electromagnetic (tTEM) method.
The study focused on a 20–40 meter high cliff with a rocky platform at its feet. A visible and thermal photogrammetric model were made in September 2022. A total of six ERI profiles were carried out. The tTEM survey provided a resistivity mapping of the plateau as well as at the foot of the cliff.
ERI and tTEM methods identified the presence of a conductive body interpreted as a saturated saline to brackish aquifer beneath the cliff, with marine intrusion only in the southwestern part. The interface between the salt water and the aquifer shows instabilities with haline convection and upwelling of brackish water at different places on the rock platform to the northeast. TIR spectroscopy complements ERI by helping to identify areas vulnerable to collapse at the top of the cliff.
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Characterization of a Coastal Aquifer Prone to Saline Intrusion through Integration of Electrical and Seismic Data
Authors M. Cercato, G. De Donno, D. Melegari and G. Penta de PeppoSummaryIn this work, we present an integration of electrical and seismic data for the characterization of a coastal aquifer prone to saline intrusion. The main goal is to achieve a near-surface reconstruction of the unconsolidated lithotypes (mainly sands) and to image lateral transition of the hydrogeological parameters as saturation or permeability.
To this end we select two areas within the Circeo National Park (Central Italy), where we combine electrical resistivity tomography (ERT) and time-domain induced polarization (TDIP) and multichannel analysis of surface waves (MASW) at site A and ERT and seismic refraction tomography (SRT) at site B.
Through inversion of ERT/TDIP data for Cole-Cole parameters at site A, we achieve a first-approximation prediction of the permeability, to be used for rapid hydro-geophysical screening of the coastal areas. On the other hand, the joint inversion of ERT and SRT data at site B allows to discern a lateral transition likely related to a variation of the groundwater level.
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Prestack Least-Squares Reverse Time Migration for Ground Penetrating Radar
Authors L. Xu, J. Irving and K. HolligerSummaryGround-Penetrating Radar (GPR) is a non-destructive geophysical technique used for imaging the subsurface. In this study, we introduce prestack least-squares reverse time migration (LSRTM) for GPR imaging, formulating it as a linear optimization problem to accurately represent the primary reflection physics. Using an adapted version of Marmousi model as an example, we demonstrate the superiority of LSRTM over post-stack reverse time migration (RTM) in terms of model resolution, finer interface representation, and improved illumination of deep structures. We use data misfit to show that LSRTM effectively utilizes almost the full spectrum of the data for imaging, resulting in higher-resolution images. This research contributes a valuable methodology for improving GPR imaging with important potential applications in a wide range of near-surface studies. Future research will explore LSRTM’s resilience against noise and incomplete data, its application to non-zero-offset data, and algorithmic improvements for more efficient and user-friendly deployment.
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Integrated use of Spatial and Time-Lapse TEM Data for Accurate Mapping of Saltwater Intrusion
Authors J.C. Zamora-Luria, P. McLachlan, L. Liu, D. Grombacher and A.V. ChristiansenSummarySaltwater intrusion in coastal aquifers threatens water security for millions of people worldwide. Mapping and monitoring of saltwater intrusion is crucial for effective groundwater management. In this study, a comprehensive approach to mapping saltwater intrusion is presented, which combines spatial and time-lapse transient electromagnetic (TEM) surveys. A case study was conducted in southeastern Denmark, where changes in the sea level and groundwater recharge have significant impacts on saltwater intrusion. The towed transient electromagnetic system (tTEM) was used to collect the spatial data, while the monitoring TEM (mTEM) system collected the time-lapse data. The tTEM surveys allowed for the spatial resolution of resistivity patterns, while the mTEM instrument permitted monitoring of dynamic processes. The integration of both surveys provides a more accurate and comprehensive understanding of the distribution and movement of saltwater intrusion in the study area.
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Automated Processing of a Large-Scale Airborne Electromagnetic Survey by Deep Learning
Authors M.R. Asif, M.A. Kass, R. Westerhoff, Z. Rawlinson, A.V. Christiansen and T. BordingSummaryModern airborne electromagnetic (AEM) surveys generate large data sets spanning over thousands of line kilometres. Some portions of these data sets are often unusable due to couplings with infrastructure, such as power lines and fences. The inversion of coupled data results in spurious subsurface features, which may give erroneous geological interpretations and, in turn, biased decision-making. To mitigate this, the corrupted data are often culled manually before inversion, which is a labour-intensive and time-consuming task, and requires specialized expertise.
To address this challenge, we have developed a deep learning expert system that automates the AEM data processing workflows. Our method employs a deep convolutional auto-encoder to identify corrupted data and is designed to generalize across diverse geological conditions and survey areas. In this study, we evaluate the generalization performance of our method on a large AEM survey conducted in Northland, New Zealand. Our approach processes 6471 line kilometres of data in 15 minutes and identifies corrupted data, showing strong spatial correlation. The inversion results reveal very few potential anomalies, which are undergoing manual inspection. Overall, our proposed approach demonstrates high-quality data processing with minimal quality inspection required, making it a promising solution to automate AEM data processing workflows.
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Small Coil Surface Nuclear Magnetic Resonance in Dynamic River Systems in New Zealand
Authors M. Vang, D. Grombacher, J.J. Larsen and S. WilsonSummaryBraided river systems are a major contributor to groundwater recharge in New Zealand. To identify subsurface structures in these environments is paramount to understand the complex interactions with underlying aquifers. The sediments in these systems are extremely resistive and electromagnetic methods are unable to resolve these impermeable layers as resistivities exceed 500ohmm. Borehole recovery is poor in the river due to the large cobbles which is the main sediment in the aquifer. Therefore, identifying these hydrological important layers remains a challenge.
We propose using surface nuclear magnetic resonance the aquifer and aquitards based on their free water contents. We acquired 77 SNMR soundings in three river systems in New Zealand which all have impermeable structures underneath a saturated aquifer. Lateral constrained inversion was implemented to resolve the shallow structures while maintaining the lateral coherency expected in these river systems. We distinguish between the layers by their free water content, i.e., high water contents in the aquifer and low water contents in the aquitard. Good agreement with adjacent boreholes shows the ability to map these important hydrological layers inductively with the SNMR in high density mapping campaigns.
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Hydrogeophysical Investigation for the Monitoring of the Unsaturated Zone Hydrology during an Infiltration Experiment
Authors A. Papadopoulos, A. Kallioras, G. Apostolopoulos and S. KarizonisSummaryAn integrated study with the combination of TDR, ERT and GPR was designed for the continuous monitoring of the unsaturated zone during an infiltration experiment. Time-lapse 3D ERT images depicted the spatiotemporal movement of the infiltrating water both laterally and vertically and coincide with TDR data obtained in a 3D array, in terms of flow directionality and velocity. GPR adds valuable insight regarding the extent of the infiltration process and the lateral water movement, as well as the existence of some possibly less permeable horizons, detected by TDR as well, that impede the lateral movement of the water. It is envisioned that by using conductive water, the contribution of ERT and GPR in some hydrological investigations will be enhanced.
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Comparison of Hydrogeological Properties Based on DCIP, Surface NMR and Hydraulic Tests
Authors T. Martin, T. Dahlin, D. Grombacher, A. Kass, A. Mendoza and C. ButronSummaryThe success and the costs of infrastructure projects depends to a large extent on a reliable characterisation of the subsurface. Information about the groundwater is crucial to protect groundwater resources and to avoid stability problems. Usually, drillings followed by hydraulic tests are conducted which are reliable but expensive and only give punctual information. The use of the geophysical methods Induced Polarisation (IP) and Nuclear Magnetic Resonance (NMR) can help to optimise drillings since they can give information about the hydraulic conductivity (K), the water content and the pore space characteristics. The combined methods were tested at three Swedish sites to investigate how reliably the hydrogeological properties of the underground can be characterised on a field scale. At the test site shown as example, it was accompanied by slug tests and the hydraulic profiling tool (HPT), where we could identify layers with different intrinsic permeabilities based on the IP data. Furthermore, we found that the water content is decreasing with depth. The comparison of the geophysical results with HPT and slug tests shows a correlation but more improvements regarding the K estimation from the IP data needs to be made.
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Geophysics to Mitigate Brownification of Lake Water – First Results
Authors T. Martin, E. Hiss, J. Rankinen, C. Klante and T. DahlinSummaryBrownification of surface waters, or browning, describes the increase of water colour in water systems. This phenomenon occurs due to an increase in dissolved organic carbon and iron concentrations. Browning is a major environmental concern, as it has negative effects on both water quality, and therewith the drinking water production, and the health of aquatic ecosystems. The aim of two research projects is to find mitigation measures to decrease the browning but also to monitor these changes. That is planned in the surrounding of Lake Bolmen, located in the South of Sweden. One part of the project is geophysical investigations. With the help of the direct current induced polarization (DCIP) and ground penetrating radar (GPR) methods, we want to characterise the underground, investigate the connection between surface water and groundwater and find a link between the electrical IP properties and the browning. During the first reconnaissance measurements we observed a connection between the chargeability and the browning of the sampled water. In the next step, a DCIP monitoring system will be set up to observe and follow the changes over several seasonal periods.
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Use of Geoelectrical Data for Coastal Aquifer Characterization and Management (Torredembarra, Spain)
Authors A. Sendrós, I. Cubides, A. García-Bertran, R. Lovera, A. Urruela, M. Himi, L. Rivero, R. Garcia-Artigas and A. CasasSummaryThe aquifers of the Spanish Mediterranean coast are generally subjected to intense exploitation to meet the growing water supply demands. The result of the exploitation is the salinization due to the marine saltwater intrusion, causing a deterioration in the quality of the water pumped and limiting its use for certain needs of the community. To prevent the deterioration, a groundwater control network usually allows a precise knowledge of the areas affected by saltwater intrusion, but not the extent of the saline plumes. Moreover, the characterization of aquifer systems requires a model that defines the geometry of aquifer formations. For this objective, we have integrated data of hydrogeological, hydrogeochemical, electrical resistivity subsoil data to establish a hydrogeological model of the coastal aquifer of Torredembarra (Tarragona, NE Spain). In this research, we have carried out a regional scale study of the aquifer system to define the areas prone to be affected by the saline intrusion. The obtaining results could be used as a support tool for the evaluation of the most favourable areas for groundwater withdrawal, as well as assessing vulnerability to contamination of aquifers, enabling the protection and control of the most susceptible areas to be polluted by saltwater intrusion.
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Modelling Approaches in Frequency Domain Electromagnetics and Applied in Shallow Groundwater Investigations
By P.J. SaksaSummaryPresentation discusses the 1-D modelling software developed and modelling usage. It is connected to NOVEL-EM called groundwater monitoring system used at several Finnish mine sites with more than ten years of experience. NOVEL-EM processing does not require special modelling itself but supplementing processing can give insight to subsurface variations and allows more accurate parameter calculations for groundwater layers. Solving hydrological soil parameters, however, adds new challenges for input data.
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Electrical Resistivity Tomography to Measure and Monitor Hydrodynamic Heterogeneities in a Malawian Agricultural Alfisol
Authors R. Swift, J. Boyd, J. Chambers, P. Wilkinson, I. Sandram, N. Magwero, A. Gregory, R. Whalley, P. Meldrum, J. Chimungu, C. Inauen, H. Harrison, P. Nalivata, F. Nguyen and M. LarkSummaryConservation Agriculture (CA) is an agricultural method that has been shown to provide crop resilience to drought. In order to better understand the hydrodynamics in soils cultivated using CA, we installed geophysical monitoring equipment and co-located pedophysical point sensors. Cross-borehole Electrical Resistivity Tomography (ERT) monitoring datasets from Chitedze Agricultural Research Station, Lilongwe, Malawi, are discussed alongside sensor derived moisture content data.
We have revealed a complex spatiotemporal pattern of near surface moisture dynamics that would be difficult to characterise using point sensors alone, and observe some differences between soils under CA and those farmed conventionally. Additionally, a varying relationship between moisture content and electrical resistivity is discovered with increasing depth. Ongoing work includes developing ERT derived soil moisture estimates - potentially using multiple relationship models for differing depths - and analysing these thoroughly to better understand how hydrodynamics in CA treated soils differs from soils tilled conventionally.
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Coupled Hydrogeophysical Modelling as a Tool for Determining Unsaturated Soil Parameters in Landslides.
Authors J. Boyd, J. Chambers, P. Wilkinson, E. Bruce, O. Kuras, P. Meldrum, B. Dashwood and A. BinleySummaryMoisture content is a well-known factor driving unstable slopes to failure, which result in landslides that can negatively affect societies and local economies. Managing this geohazard therefore requires knowledge of the hydrological states of slopes. While traditional methods of slope investigation provide accurate and discrete information about material properties, geophysical methods can provide spatial information about the internal geometry and electrical properties of slopes. Furthermore, the electrical properties of geological materials are highly dependent on their saturation level, and therefore it possible to constrain the hydrological properties of slopes via the use of a petrophysical transfer function, which describes how these electrical properties change with saturation. We contend that recent research shows it is possible to couple hydrological and geoelectrical modelling to produce a ‘coupled’ model that benefits from both geophysical and hydrological information to better constrain hydrological flow parameters in near surface materials. We show results of ‘hydro-geophysical coupled’ modelling can recover the van Genutchen soil water retention curve parameters. We use a Markov chain Monte-Carlo approach to couple our models and we study an active landslide in Lias mudrocks, North Yorkshire, UK, instrumented with a geoelectrical monitoring system and weather station that provide hydrological forcing data.
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From Near Surface Geophysics to Groundwater Reservoir Characterisation and Establishment of New Water Work
Authors P. Gisselø and K. EjsbølSummaryThe public water supply in the municipality of Varde in the southwestern Jutland, Denmark, is threatened by poor water quality.
Contents of pesticides in shallow unprotected aquifers, high iron content especially in buried valley aquifers, saltwater issues in some deep aquifers and organic content (brown water) in Miocene aquifers and aquifers related to interglacial layers have forced the water supply to find new aquifers with good water quality in the Varde area. It has been difficult to fully understand the complex geological settings formed by glacial tectonics with huge impact on near surface geology.
In the past 10 years airborne and ground based electromagnetic geophysical surveys have been carried out. The results have been followed up with drillings in the Vittarp area located 10 km northwest of Varde. These investigations have finally provided valuable information, and the detection, of the around 135 m deep buried Vittarp valley with a deep and well protected aquifer which fulfils the demands to excellent water quality and quantity.
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Mine Water Geothermal Research Facilities at the UK Geoenergy Observatory in Glasgow, UK
SummaryThe UK Geoenergy Observatory in Glasgow facilitates collaborative research to improve understanding of subsurface processes, environmental and induced change related to mine water energy. It provides scientific and engineering infrastructure for investigating the shallow, low-enthalpy geothermal energy and thermal storage resources available in abandoned and flooded coal mine workings.
Borehole monitoring capability includes hybrid fibre-optic distributed temperature sensing for passive monitoring or for performing heat pulse tests in active mode, as well as arrays of permanently installed ERT downhole electrodes to measure subsurface electrical resistivity, enabling both in-hole and cross-hole tomography for tracking subsurface changes in 4D. Together with pressure data from downhole data loggers and monitoring of flow and heat pump/chiller operation, this provides an at-scale field laboratory for evaluating the engineering and energy performance of the components of mine water geothermal systems.
An initial hydrogeological and hydrochemical conceptual model has been developed using borehole, pump test and baseline monitoring data. Integrated analysis of hydrogeological, geoelectrical, thermal and geochemical data provides a much more comprehensive understanding of geothermal processes in low-temperature mine water systems. Insights gained from research undertaken during commissioning will enable science users to tailor and optimise their proposals for research and innovation at the Glasgow Observatory.
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Improvements in Gravity Precision Provide Enhanced Opportunities in Hydrological Monitoring
By O. EikenSummaryThere has been little discussion on how to balance various gravity surveying sensors in a survey setup to best address hydrological monitoring challenges. Here we report on recent improvements in CG-6 relative gravimeters. The smaller and lighter case makes it easy to operate. Data processing from desert and seafloor environments show clear improvements over CG-5. The tilt susceptibility effect seems to be reduced. Our experiences are that 1 µGal or better repeatability can be regularly achieved. The relation between cost and precision may be predicted and the value of information compared against station spacing, to find the highest net value of information. Gravimetry provide unique and accurate measurements of bulk mass changes. While arial surveys may cover an aquifer reservoir, the higher precision and denser time-sampling of superconducting gravimeters can give control points. Combination in the same monitoring program may be termed “hybrid gravimetry”. Recent improvements in precision, instrument footprint and efficiency extend possibilities for useful and valuable gravity monitoring. While the feasibility of hydrological gravity monitoring has been proven, projects have not been done at regular basis by authorities or others. We believe sub-µGal resolution at reasonable cost provide new opportunities for more extensive monitoring.
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A Phased Approach to Mapping a Contaminant Plume
Authors A. Verweerd and A. O’ReillySummaryA discussion on a phased approach of mapping a contaminant plume using ERT through a mixture of industrial and rural environments. By building on the results of each survey, the interpretation could be expanded to depths normally uncertain as stand-alone results.
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An Integrated Approach to Characterise the Subsurface Using Near-Surface Geophysical Methods
Authors J. Dildar, M. Manzi, S. Gomo, T. Abiye and M.K. RapetsoaSummaryOne of the most precarious aspects of mining economics for underground mining includes properly managing groundwater. The area of interest, Tharisa Mine, is located on the southwestern limb of the Bushveld Igneous Complex that hosts world-class platinum group metal deposits in South Africa. The aim is to investigate and image the near-subsurface architecture in a shallow profile. This will be achieved by using stable isotopes (δ18O and δ2H) and radioactive isotopes of water (δ3H) to refine the understanding of conceptual groundwater flow and water source for the mine. Further, geophysical methods comprising electrical resistivity tomography, multichannel analysis of surface waves, seismic and magnetic assist in delineating fluid migration pathways and lineaments to authenticate the isotope results. Integrating the results gives the following initial outcomes of groundwater inflow volumes into the open pit: 1) Distinct fracture systems/zones and fluid migration pathways are delineated; 2) a larger aquifer volume is accessed through continuous mine development, promoting increasing groundwater inflows; 3) the aquifer material’s ability to transmit and store groundwater is amplified during mining activities; and 4) the main sources of water in the mine include mixing surface and deep water sources, recycling of water possibly via lineaments and tailing dam seepages.
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Monitoring the Remediation of Organic Contaminants by Colloidal Activated Carbon: a Spectral Induced Polarization Study
Authors A. Almpanis, L. Slater and C. PowerSummaryColloidal activated carbon (CAC) filters are becoming a popular option to remediate groundwater contaminated by DNAPLs and a real-time monitoring approach is desirable to assess its effectiveness. In this study, the spectral induced polarization (SIP) technique is evaluated for its applicability as a monitoring tool for DNAPL adsorption within CAC-filters. The adsorption of low-concentration (50 mg/L) tetrachloroethylene (PCE) in a CAC-filter was examined using a set of dynamic column experiments combined with SIP monitoring. The initial flushing of CAC into inert porous media was tracked by SIP monitoring, with an increase in both real and imaginary components of the complex conductivity. The CAC was then flushed out of the column via groundwater, leaving behind only carbon particles that will later adsorb the PCE. The process of flushing the CAC by groundwater indicated a decrease in both the SIP real and imaginary conductivities, with the imaginary holding a small amount of polarizability, which is likely associated with the remaining carbon particles. Finally, dissolved phase PCE was injected through the column, with insignificant changes in the simultaneous SIP response. This study suggests that SIP can monitor CAC within porous media but is insensitive to the low concentrations of dissolved phase PCE.
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