One woman's quest for geological understanding!

NSGG Postgraduate Research Symposium 2017

I attended (and presented at) my first NSGG event yesterday!NSGG

The Postgraduate Research Symposium 2017 was focussed on the application of geophysical methodologies in geohazards assessment to mark the Geological Society’s “Year of Risk”, and showcased a wide variety of applications – it was incredibly interesting!

Presentations:
  • Ground-penetrating radar survey in Ireland –overkill or a viable asset for archaeological survey?
    A Green
  • Kurtosis statistics as an indicator of the precision of migration velocity analysis.
    A. Harding and A. Booth
  • Predicting optimal forensic remote sensing and near – surface detection methods.
    M.I. Quick
  • Monitoring subsidence related to relict salt mines using long-term time-lapse microgravity, Marston, Cheshire, UK.
    C.J. Rowell and J.K. Pringle
  • Geophysical indicators of slope stability at the Hollin Hill LandslideObservatory: initial findings from repeated geophysical surveys.
    J Whiteley
  • A hydrogeological assessment of a small peat bog in South Wales,using an integrated approach.
    E. Hudson
  • Improved characterisation and modelling of measurement errors inelectrical resistivity tomography (ERT) surveys.
    C.M. Tso, A. Binley and O. Kuras
  • Integrated geophysical methods in meteorite impact investigation:case studies of Mahsuri Ring, Langkawi and Bukit Bunuh, Perak, Malaysia.
    H. Saleh, A.R. Samsudin, U. Umar Hamzah, M.A.A. Jelani, M.H. Arifin and N. Sulaiman
  • Subglacial Aquifer Characterisation using Multichannel Analysis of Surface Waves and Time -Domain Electromagnetic Techniques.
    S. Prise, A. Booth, P. Livermore and J. West.
  • Understanding how valley -glacier overdeepenings affect seasonaland glacial dynamics.
    W. Higson
  • Quantum Technology gravity sensors –first steps to aerial sensing.
    D. Roberts, L. Earl, M. Wright, M. Uddin, N. Metje and M. Holynski
Posters
  • Assessing surface and subsurface hydrological contamination at an abandoned metal mine in Mid-Wales, UK.
    E. Hudson
  • Geophysical ground survey investigation for the possible HS2 route through Rugeley, Staffordshire, UK.
    J. Francis and Z. Lloyd.
  • A preliminary Ground Penetrating Radar study of fluvial architectures at Spireslack, Ayreshire, Scotland.
    J.T. Ainsworth, A.J. Mitten and J.K. Pringle

I have added the abstracts to the presentations / posters presented at this NSGG event below, but for those interested, these can also be downloaded here (Original images not included in the below).

Ground-penetrating radar survey in Ireland – overkill or a viable asset for archaeological survey?
Ashely Green
Department of Archaeology, Anthropology and Forensic Science, Faculty of Science and Technology, Bournemouth University, Poole, Dorset, UK BH12 5BB

Modern rubbish and ferrous contamination often hinder data interpretability in archaeogeophysical surveys, especially in built environments. In Ireland groundwater retention and high attenuation materials often negatively impact the potential depth of investigation and further inhibit data interpretability. A majority of geophysical surveys in Ireland have been conducted on national road schemes with passive magnetic techniques (Bonsall et al. 2014). Recently, however, there has been resurgence in incorporating high-resolution geophysical survey into research frameworks as a means to identify new sites and target excavations. As a result, further analysis of the merits of ancillary techniques, such as ground-penetrating radar (GPR), and higher resolution survey are necessary.

To ascertain the viability of high-resolution GPR surveys for delineating large structural and small non-structural anthropogenic features the Black Friary (County Meath) and Forth Maigh Leana (County Offaly) were surveyed using multiple techniques (GPR, gradiometry, and electromagnetic induction). GPR, a rarely used technique, proved useful in detecting targets of interest and offered improved data visualization and interpretability on these sites, thus indicating its potential value to subsequent surveys.

Further investigations of the practicality of GPR surveys in Ireland will be conducted in counties Meath and Offaly, with extension to other regions with variable local geology.

Reference:

  • Bonsall J, Gaffney C, and Armit I (2014). Preparing for the Future: A reappraisal of archaeo- geophysical surveying on National Road Schemes 2001-2010. University of Bradford report for the National Roads Authority, 1-151.

Kurtosis statistics as an indicator of the precision of migration velocity analysis
Anne Harding and Adam Booth
School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.

Ground-penetrating radar (GPR) is a well-established technique for detailed and continuous imaging of the subsurface, for purposes including archaeology. Although GPR quality is often suitable for archaeological interpretation, the accuracy of the implied subsurface structure can be limited. While migration algorithms can improve this, the implementation of migration is often compromised because i) migration and depth velocity are based on a single velocity estimate from common-offset GPR data, and ii) the effect of topography on the migrated output is often neglected. These compromises can be jointly circumvented using an approach to migration velocity analysis (MVA; Allroggen et al., 2015) that honours topographic variation.

However, quantification of the success of each migration scheme is often determined by subjective methods. Here, we present the use of the kurtosis statistic to objectify the performance of migration. Kurtosis is a statistical property of the amplitude distribution of a signal (Langet et al., 2014) and has been used in seismic reflection processing to find the “best-focussed” parts of a migrated seismic image (Burnett and Fomel, 2011). Since migration at the correct velocity should focus a hyperbola in a GPR profile at its apex (Grasmueck et al., 2005) and reduce amplitudes elsewhere in the profile, the amplitude distribution of the GPR profile should become less outlier prone, resulting in a higher kurtosis. Therefore, the kurtosis approach can be implemented to GPR to provide an objectified way of examining the performance of MVA, determining the optimal migration velocity for the subsurface and evaluating the precision with which this is calculated.

We consider the implementation of migration schemes incorporating topography to archaeological GPR data recorded close to the site of Old Scatness broch (Sumburgh, Shetland; Dockrill et al, 2010), and use the kurtosis statistic to objectively evaluate their performance.

Kurtosis statistics provide a means of assessing the reliability of a migrated image. However, they may also provide an important source of precision information where migration velocities are used for estimating quantitative properties (e.g., in the evaluation from pipe radius from diffraction curvature (Shihab et al., 2005)).

References:

  • Allroggen, N., Tronicke, J., Delock, M. and Boniger, U. 2014. Topographic migration of 2D and 3D ground- penetrating radar data considering variable velocities. Near Surface Geophysics, 13(3), pp. 253-259.
  • Burnett, W. and Fomel, S. 2011. Azimuthally anisotropic 3D velocity continuation. International Journal of Geophysics, 2011. p. 8 (Article ID 484653).
  • Dockrill, S.J., Bond, J.M., Turner, V.E., Brown, L.D., Bashford D.J. Cussans, J.E. and Nicholson, R.A. 2010. Excavations at Old Scatness, Shetland, Volume 1. Shetland Heritage Publications, 978-0-9557642-5-7.
  • Grasmueck, M., Weger, R. and Horstmeyer, H. 2005. Full-resolution 3D GPR imaging. Geophysics, 70(1), pp. K12-K19.
  • Langet, N., Maggi, A., Michelini, A. and Brenguier, F. 2014. Continuous Kurtosis-based migration for seismic event detection and location, with application to Piton de la Fournaise Volcano, La Réunion. Bulletin of the Seismological Society of America, 104(1), pp. 229-246.
  • Shihab, S. and Al-Nuaimy, W. 2005. Radius estimation for cylindrical objects detected by ground penetrating radar. Sensing and Imaging, 6(2), pp. 151-166.

Predicting optimal forensic remote sensing and near-surface detection methods

Megan Ivy Quick
Natural Sciences and Psychology, Liverpool John Mores University, Liverpool, L3 3AF, UK.

Police investigators need to locate buried forensic targets, such as clandestine graves, accurately, quickly and efficiently. Remote sensing and near-surface detection methods, though increasingly used in criminal investigations, are not always successful in locating clandestine graves, especially in variable terrains and climates. As Davenport (2001) states “there is no remote sensing method that will consistently find a body or physical evidence”. At present poor choices of detection methods are sometimes made either because of personal preference, what instruments are available or through unguided trial and error, resulting in poor outcomes and wasted time. There has been little published research on choosing optimum remote sensing methods for a particular site and evidence being sought.

This research therefore aims to build and test a computer-based system which will rank remote sensing detection methods by considering the properties of the target and its environment, thus improving detection method choices and the rate of recovery of buried targets. The research began by assembling current best survey practices by a literature review and approaching expert surveyors from forensic science and archaeology, to collate a database of what methods are currently being used to detect buried forensic targets.

The aim of the research is to bridge the gap in the research by encouraging the flow of information to improve the computer-based system by building wider relationships across the professional forensic field. The intention is to create closer inter- disciplinary collaborations and, produce standardised and improved search protocols.

Reference

  • Davenport GC, (2001). Remote sensing applications in forensic investigations. Historical Archaeology, 35(1), 87-100.

Monitoring subsidence related to relict salt mines using long-term time-lapse microgravity, Marston, Cheshire, UK

Cathrene J. Rowell and Jamie K. Pringle
School of Geology, Geography and the Environment, William Smith Building, Keele University, Keele, Staffs, ST5 5BG, UK.

The Cheshire Basin contains >4.5km of Permo-Triassic red beds, including the Mercia Mudstone Group (MMG) which accumulated in playa and tidal-flat environments. The MMG is the host to two major halite formations: The Northwich and Wilkesley Halite formations, which have been commercially exploited. Both rock salt and brine has been extracted from mainly two horizons of the Northwich Halite Formation in the Cheshire Basin in various locations, and rock salt is still mined in nearby Winsford, Cheshire.

Surface subsidence resulting from salt mining and brine pumping in Northwich, and the surrounding areas in Cheshire, has occurred since Medieval times. This has varied in severity, with evidence of subsidence ranging from topographic depressions to catastrophic surface collapse from the mid-18th Century onwards.

To detect, characterise and monitor areas susceptible of subsidence, near-surface geophysics has been applied. A section of the Trent and Mersey Canal, in Marston (Northwich), crossing 3 abandoned salt mines has been the focus of long-term microgravity surveys for >10 years. The data collected over this period shows consistent, deepening negative anomalies at the margin between the Adelaide and Old Marston relict mine workings, as opposed to over the mines themselves. By correlating microgravity data with mine plans, boreholes and sedimentary logs, 2D gravity models have been produced: the anomalies are interpreted as upwardly propagating voids, and associated collapse material. A void feature at the point of the microgravity excursion has been confirmed by intrusive investigations. Finally, investigation of the canal water depths and the underlying silt accumulation on the canal floor has been undertaken to ascertain any connection to underlying mines and potential canal collapse. This study further demonstrates the importance of time- lapse microgravity surveys to facilitate the identification and monitoring of at-risk areas, with a view to mitigating the risk of catastrophic surface subsidence.

Geophysical indicators of slope stability at the Hollin Hill Landslide Observatory: initial findings from repeated geophysical surveys

James Whiteley
British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK

Infiltration of rainwater into landslide systems due to increased effective rainfall is one of the leading contributing factors to the failure of unstable slopes in the UK. An increase in rainfall intensity in recent years elevates the likelihood of slope failure, and in turn increases risk from landslide hazards. Preventative remediation of all potential slope failures is an unfeasible approach to solving the problem, and therefore robust methodologies are required for long-term assessment of unstable slopes in order to predict and manage these future failure events.

This presentation shows the initial findings from some of the first combined surveys that have been undertaken as part of a PhD project at the BGS landslide observatory based at Hollin Hill, North Yorkshire. The project focuses on the monitoring of the Hollin Hill landslide using non-intrusive geophysical methods. The approaches used include active and passive seismic methods, including P-wave and S-wave seismic refraction tomography (SRT), multichannel analysis of surface waves (MASW) and permanent broadband seismometer stations, integrated into the ongoing programme of research using a permanently installed electrical resistivity tomography (ERT) array at the site. Ultimately the project aims to characterise and observe changes in subsurface properties that precede landslide failure, using seismic methods to inform on geo-mechanical property changes, and geo-electrics to monitor variations in hydrodynamics linked to seasonal variations in climate.

The Hollin Hill site comprises a slow moving earth slide-earth flow within the Lower Jurassic Lias Group, and initial seismic refraction surveys have shown good agreement with the previous geological and geomorphological models of the site.

Although the slope is subject to constant creep processes, discrete failure events at the landslide are primarily driven by seasonal climatic variation, with larger failure events related to water infiltration more common in the winter and spring months.

References

  • Merritt AJ, Chambers JE, Murphy WE, Wilkinson PB, West LJ, Gunn DA, Meldrum PI, Kirkham M and Dixon N, (2013). 3D ground model development for an active landslide in Lias mudrocks using geophysical, remote sensing and geotechnical methods. Landslides, 11(4), 537-550.

Peatland Hydrology: A future at risk. A hydrogeological assessment of a small peat bog in South Wales, using an integrated approach

Emily Hudson
College of Science, Swansea University, Swansea, SA2 8PP, UK

Pyllau Cochion peat bog in Carmarthenshire, Wales, represents one of the most southerly and marginal peatlands in the UK. Recognized for the crucial role they play in greenhouse gas cycling; peatlands are particularly effective carbon sequesters. However, with predicted climatic changes, the future of these important ecosystems is potentially at risk.

This project aims to carry out a hydrogeological assessment of this small peatbog using an integrated approach. Water is the key modulator of peatland accumulation and subsequent carbon storage capacity, by producing the saturated conditions necessary for the formation of peat. If the water table becomes unstable, active accumulation will cease and existing peat will be exposed to the atmosphere. Oxygenation of peat enables full decomposition, which could lead to the catastrophic emission of CO₂. The integrated approach aims to use a variety of techniques, including slug-testing, permeameters, piezometers and water sampling; to elucidate the geometry, anatomy, hydrology and quality of the peatland. This in turn provides the necessary input parameters for a groundwater flow model. It is this model which will be used to assess the current and future hydrogeological functioning of the bog, as well as whether factors such as microtopography, vegetation, fire, and seasonality play modulating roles.

Geophysical methods were utilized, with Ground Penetrating Radar (GPR) used to locate the base of the peat. Manual probing showed basal depths ranging from 30- 720 cm, meaning a 30 MHz antenna was chosen to ensure adequate signal depth penetration. Eight transects were completed, covering the bog in six parallel and two perpendicular lines. By recording the two-way travel time (TWTT) of returned signals at 1m intervals along each transect, the base of the peat was located in all cases. The strongest reflection seen in all profiles was taken to be indicative of the peat- mineral soil interface. As the bog is underlain by clay, it was supposed that the abrupt change in water content and bulk density at the basal interface was responsible for producing such a strong reflection. Two steep basins were also found, with maximum basal depths reaching 9 m. Internal reflections were seen within the larger of the two basins, at around 350 cm. These were proposed to be a result of a change in peat type, from humousy to more herbaceous; with the change in bulk density creating the reflections in the radar profiles.

By employing geophysics to locate the base, the geometry of the bog can be inputted to form the basis of the groundwater flow model. Furthermore, initial volume estimates have also been made. This shows how geophysical techniques have been integral to the project so far. Other techniques, such as Electrical Resistivity Tomography (ERT) and Self Potential (SP) surveys, are being considered as additional geophysical techniques which may be employed to help better understand where the majority of flow occurs within the bog.

Improved characterisation and modelling of measurement errors in electrical resistivity tomography (ERT) surveys

Chak-hau Michael Tso 1, Andrew Binley1, and Oliver Kuras2
1 Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK
2 British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK

Measurement errors can play a pivotal role in geophysical inversion. Most inverse models require users to prescribe or assume a statistical model of data errors before inversion. Wrongly prescribed errors can lead to over- or under-fitting of data, however, the derivation of models of data errors is often neglected. With the heightening interest in uncertainty estimation within hydrogeophysics, better characterisation and treatment of measurement errors is needed to provide improved image appraisal.

Here we focus on the role of measurement errors in electrical resistivity tomography (ERT). We have analysed two time-lapse ERT datasets: one contains 96 sets of direct and reciprocal data collected from a surface ERT line within a 24h timeframe; the other is a two-year-long cross-borehole survey at a UK nuclear site with 246 sets of over 50,000 measurements. Our study includes the characterisation of the spatial and temporal behaviour of measurement errors using autocorrelation and correlation coefficient analysis. We find that, in addition to well-known proportionality effects, ERT measurements can also be sensitive to the combination of electrodes used, i.e. errors may not be uncorrelated as often assumed. Based on these findings, we develop a new error model that allows grouping based on electrode number in addition to fitting a linear model to transfer resistance.

The new model explains the observed measurement errors better and shows superior inversion results and uncertainty estimates in synthetic examples. It is robust, because it groups errors together based on the electrodes used to make the measurements. The new model can be readily applied to the diagonal data weighting matrix commonly widely used in common inversion methods, as well as to the data covariance matrix in a Bayesian inversion framework. We demonstrate its application using extensive ERT monitoring datasets from the two afore-mentioned sites.

Integrated geophysical methods in meteorite impact investigation: Case studies of Mahsuri Ring, Langkawi & Bukit Bunuh, Perak, Malaysia.

Hardianshah Saleh1,3, A.R. Samsudin2, U. Umar Hamzah2, M.A.A. Jelani1,4, M.H. Arifin2 and N. Sulaiman2

1 School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK
2 Universiti Kebangsaan Malaysia, 43600 UKM, Bangi Selangor, Malaysia
3 Universiti Malaysia Sabah, Jalan UMS, 88400, Kota Kinabalu, Sabah, Malaysia
4 Universiti Malaysia Terengganu, 21030 Kuala Terengganu, Terengganu, Malaysia

The evidence of shock metamorphisms (suevite breccia) at Bukit Bunuh (BB) in Lenggong, Perak and circular geomorphology in Mahsuri Ring (MR), Langkawi indicates of meteorite impact. Integrated geophysical methods – resistivity imaging, seismic refraction, gravity and magnetic survey – were carried out to investigate the existence of impact crater with covering approximately 10 km2 for both case studies area.

The results of Bouguer anomaly map showed that BB impact crater has a diameter of approximately 2.5 km and shows good correlation with result from seismic and resistivity, which located at the centre of the interpreted crater. The impact structure was successfully modeled as a complex impact crater with maximum depth of about 300 m. The Bouguer anomaly map also shows the possible occurrences of at least two more impact craters located in the northeast and southeast areas of the BB crater and these structures need further investigation for confirmation. While for MR cases, Bouguer gravity map shows relatively low negative anomaly with rounded shaped contour around the suspected crater area. This anomaly was interpreted as a remnant of meteorite impact structure with distorted shaped crater in the study area. The structure of the crater interpreted has a diameter of approximately 1.5 km. The impact structure has been modelled as a simple type crater in order to determine the thickness of the low density sedimentary fill.

In conclusion, integrated geophysical method shows the possible occurrences of at least two impact craters located at Bukit Bunuh with complex crater structure. While for Mahsuri Ring cases, there is an indication of subdued magnetic anomaly in the region within the impact crater and interpreted as simple crater structure.

Subglacial Aquifer Characterisation using Multichannel Analysis of Surface Waves and Time-Domain Electromagnetic Techniques

Siobhan Prise, Adam Booth, Phil Livermore, Jared West School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK

The contribution of glaciers and ice-sheets to global sea level is becoming significantly important as more evidence suggests this will increase in the coming decades (Bell, 2008). The subglacial hydrology exerts a substantial control on the flow dynamics of glaciers and ice masses (Bell 2008). Surface meltwater entering moulins, crevasses, and fractures is channelled to the bedrock through a combination of storage elements and transport pathways; however both englacial and subglacial drainage systems are imprecisely known (Rennermalm et al. 2013). Subglacial water influences ice flow by modulating basal friction, the strength of subglacial sediments and its potential to deform. Glacio-geophysical methods are needed for monitoring, imagining and mapping subglacial sediments and drainage system.

This project is focused on developing non-conventional glacio-geophysical methodologies: Multichannel Analysis of Surface Waves (MASW) and Time-Domain Electromagnetic (TEM) methods for acquiring and interpreting field observations of the subglacial environment. A small amount of unfrozen water in sediment pores can lead to large S-wave velocity (Vs) decreases; therefore the Vs profile provides useful information on water content and degree of freezing in sediment pores (Johansen et al 2003). Additionally water has a very low resistivity compared to ice and frozen sediments. Electrical resistivity values decrease by several orders of magnitude when ice melts or liquid water is present in sediment pores. This allows resistivity to be used as an indicator of moisture content and temperature of subsurface materials.

A combined analysis, using a joint inversion technique, of MASW and TEM can quantify the groundwater contents of subglacial sedimentary basins exploiting the fact both data types are sensitive to porosity, permeability and liquid water content.

An MASW feasibility study has been conducted using modelled synthetic data and Antarctic MIDAS seismic data (a NERC funded project to identify the impact of melt on ice shelf dynamics and stability). This tested different survey design parameters for acquiring MASW seismic to identify properties of the subglacial sediment at Midtdalsbreen, an outlet glacier of the Hardangerjøkulen ice cap. Active source seismic data has been acquired on

Midtdalsbreen glacier using survey design parameters established from the MASW feasibility study and a hammer and plate source.

The presentation will include: conclusions from the feasibility study, preliminary results from the first field campaign at Midtdalsbreen, and implications for future study.

References

  • Bell RE (2008). The role of subglacial water in ice-sheet mass balance. Nature, 1, 297-304.
  • Johansen TA, Digranes P, van Schaak M and Lønne I (2003). Seismic mapping and modeling of near-surface sediments in polar areas. Geophysics, 68(2), 566-573.
  • Rennermalm AK, Moustafa SE, Mioduszewski J, Chu VW, Forster RR, Hagedorn B, Harper JT, Mote JL, Robinson DA, Shuman CA, Smith LC and Tedesco M (2013). Understanding Greenland ice sheet hydrology using an integrated multi-scale approach. Environmental Research Letters, 8, 015017.

Understanding how valley-glacier overdeepenings affect seasonal and glacial dynamics

Will Higson
School of Geography, University of Sheffield, Winter Street, Sheffield, S10 2TN, UK

Understanding glacial dynamics is a very complex issue that is of prime importance for understanding contribution of ice sheet and glacier melt to sea level. Numerous interacting factors are responsible for how and why a glacier flows the way it does, including for example, basal debris, meltwater and climate. Despite overdeepenings in the bedrock topography being considered commonplace in glacial environments, the processes within them are still poorly understood. Alpine glaciers offer easier access than that of ice sheets and therefore it is considered that from investigating the conditions where ponding occurs within valley glaciers that the work done can be extrapolated and scaled up to ice sheet levels.

Overdeepenings can cause certain phenomenon to occur at the ice/bed interface, such as supercooling or ponding. These processes occur due to the relative slope ratios of the ice surface to the bedrock. In order that the effects of these processes can be estimated and examined, data needs to be gathered as to the relative changes and morphology of the glacier. A multifaceted methodology combining high resolution photogrammetry of the surface as well as bedrock topography estimations is required. The fieldsite of the bottom 2 km of Findelen glacier was chosen, due to evidence from previous works as well as glacial modelling, that two distinct overdeepenings are present.

A GPR survey of the area was carried out in early February due to the low temperatures and therefore less meltwater equating to clearer results of bedrock from the GPR. Using MALA Ground penetrating radar, it was possible to measure the bedrock topography beneath the glacier to a higher degree of accuracy than estimates from the previously used glacial ice thickness models. It is the hope that this, combined with high quality digital elevation models (DEMs) and 3D orthomosiacs achieved from unmanned aerial vehicles (UAVs) will give us the best estimates as to how the bedrock beneath glaciers can affect the dynamics of the glacier itself both in terms of surface velocities and melt on seasonal and annual timescales. It is hoped that from these fieldworks and coming fieldworks in the summer, that a complete estimate and 3D model can be produced of the bedrock topography beneath Findelen Glacier, and glacial processes confirmed.

Quantum Technology gravity sensors – first steps to aerial sensing

Daniel Roberts1, Luuk Earl1, Michael Wright1, Mohammed Uddin1, Nicole Metje, Michael Holynski1.

1 UK National Quantum Technology Hub, Sensors and Metrology, School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT
2 School of Civil Engineering, University of Birmingham, Birmingham, B15 2TT

The UK Government has recognised that recent advances in science, engineering and manufacturing capabilities presents a major national opportunity. The Quantum Technology (QT) Hub in Sensors and Metrology at the University of Birmingham is one of four QT hubs created within the National QT Programme. The University of Birmingham is developing QT gravity sensors to look through the ground which have a significantly higher sensitivity, enabling them to detect features currently undetectable – such as buried tunnels and mine workings. Research to date has indicated a 1.5 – 2.0 increase in detectability, bringing some buried features now into view (Boddice et al., 2016). This has the potential to revolutionise the way in which geophysical investigations are undertaken.

Microgravity data is currently collected by geophysicists, but for most commercial applications relies on the microgravity sensor being placed on the ground surface to take measurements in a grid making surveys over large areas time consuming. In addition, challenges exist in mountainous regions with little-to-no access or densely populated cities that are congested with people, vehicles and buildings. These difficulties can be overcome by using aerial surveys. This paper will highlight the initial steps undertaken to develop a drone to include a QT gravity sensor. One key challenge is to provide a stable environment for a magneto-optical trap (MOT) that can be mounted onto the bottom of a drone and flown over an area to collect readings.

The MOT is the key element for a QT gravity sensor as it traps the ultra-cold atoms in a stable environment and ultimately interrogate these with a laser. The next stage of this project is to develop an interferometer small enough and efficient enough to measure the minute variations of gravity.

Reference:

  • Boddice D, Metje N, Tuckwell G (2016). The potential for quantum technology gravity sensors. European Geosciences Union General Assembly, April, Vienna, Austria.

Assessing surface and subsurface hydrological contamination at an abandoned metal mine in Mid-Wales, UK

Emily Hudson
College of Science, Swansea University, Swansea, SA2 8PP, UK

The mining and processing of metal ores in the UK has left behind a legacy of environmental degradation, and the abandonment of metal mines still poses a significant contamination threat to terrestrial and fluvial environments. Esgair Mwyn is an abandoned metal mine in Mid-Wales, which has been mined since Roman times, primarily for lead and zinc. However, since its abandonment, the site has been discharging waters loaded with heavy metals downstream into the Afon Meurig, contributing to its heavy metal concentrations that far exceed acceptable Environmental Quality Standards (EQS) established under the Water Framework Directive (WFD). Therefore, the aim of this project was to work in conjunction with Natural Resources Wales (NRW) to investigate surface and subsurface hydrological contamination at the site, in the hopes of informing future remediation strategies.

To investigate the above ground hydrological contamination occurring, salt water dilution gauging was performed. This allowed the flow rates of the primary surface streams at the site to be calculated, and this information was subsequently combined with the results of water sampling. From this, the daily metal export from the site was quantified, and the inputs of the main streams apportioned. It was discovered that 876 g of dissolved Pb, Zn, Cu and Cd were leaving the site each day in the Nant y Garw. This watercourse is fed by the four primary streams running over the site, each of which contributed varying proportions to the overall metals seen.

Subsurface hydrological contamination was investigated using geophysics. Electrical Resistivity Tomography (ERT) was employed to study the subsurface of three main areas of the site: the tailings lagoon wall, main spoil heap, and northern field; and this was done along eight transects. Seepage was proposed to be occurring within the tailings lagoon wall, thus allowing waters with extremely high heavy metal concentrations to escape downstream. The spoil heap surface was inferred to be preventing mass saturation and mobilization of water, with the loose, dry surface impeding percolation into the spoil. The large field adjacent to the main spoil heap was found to have high heavy metal mobilization potential, due to the extreme saturation of the subsurface, and the presence of spoil deposits at the heads of several surface streams. However, the morphological characteristics of the field mean that this potential is not fully realized, and the area is acting as a passive wetland treatment type system.

By utilizing geophysical and hydrological investigative techniques, both surface and subsurface hydrological contamination at the site was calculated and apportioned. This led to several proposals for remediation of the site, including diversion ditches and channelization, capping of the spoil heap, wetland establishment, as well as both passive and active water treatment systems.

Geophysical ground survey investigation for the possible HS2 route through Rugeley, Staffordshire, UK
James Francis and Zach Lloyd
School of Geology, Geography and the Environment, William Smith Building, Keele University, Keele, Staffs, ST5 5BG, UK.

A multi-geophysical and geotechnical site investigation was conducted along a portion of the proposed High Speed 2 (HS2) corridor near Rugeley, Staffordshire. The investigation focused on characterising the upper layers of the superficial geology as well assessing their potential to cause geotechnical issues following the construction of HS2. The area’s geology consists of Alluvium and river terrace deposits derived from the River Trent that overly mudstones of the Mercia Mudstone group and Sandstone of the Bromsgrove Sandstone Formation. The study examined areas of soft soils, gravel deposits, possible shallow sedimentological structures, water table variations and a possible bedrock horizon.

Geophysical data was collected using Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) to visualise the subsurface. Geotechnical data was gathered using a PANDA Dynamic Cone Penetrometer (CPT) which allowed for preliminary characterisation of the upper 4m of soil from a ground engineering perspective. The engineering specifications of HS2 allow for only 4mm of vertical deflection during operation, it is therefore imperative that all efforts be made to identify areas where displacement greater than this threshold could arise. The data from the site implies the presence of potentially problematic ground, leading the authors to propose extensive further investigation prior to construction.

A preliminary Ground Penetrating Radar study of fluvial architectures at Spireslack, Ayreshire, Scotland

Joseph T Ainsworth, Andrew J. Mitten and Jaime K. Pringle
School of Geology, Geography and the Environment, William Smith Building, Keele University, Keele, Staffs, ST5 5BG, UK.

Ground Penetrating Radar (GPR) is a near-surface geophysical technique, and has been previously used to obtain 3D sedimentary architectures of both modern and ancient fluvial successions. Obtaining multiple 2D profiles behind outcrop exposures should allow 3D architectures to be extracted and then used to create high-resolution deterministic 3D numerical models.

This research has collected a GPR dataset at Spireslack quarry in Glenbuck, Ayrshire, Scotland. Spireslack quarry is an ex-open case coal mine and is presently designated as SCARP (Scottish Carboniferous Research Park), a long term educational resource exposing Carboniferous geology.

This preliminary study collected 2D profile behind the B1 outcrop face exposing channelized fluvial features; here the soil was thinnest, giving the best chance of good signal penetration. A Sensors&Software PulseEKKO™ 100 system was used to collect both 50 MHz and 100 MHz frequency data, to determine the optimal equipment, resolution and achievable depth. Data was then processed using REFLEXW™ v.3 software before being incorporated into Schlumberger PETREL™ software to create a 3D model.

GPR results imaged a fluvial channel and point bar set that had significant di-electric permittivity contrasts. Penetration depths were ~20 m, depending upon GPR antenna frequency. A very near-surface, thick limestone bed, dominated the profiles at the very near surface.

Study implications suggest GPR is promising at this location to allow the capture of 3D sedimentary architectures, although recommendations should be to collect further data using lower (25 MHz) frequency profiles and where overlying soil has been removed.

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