Enhancing the information content of geophysical data for nuclear site characterisation

Our knowledge and understanding to the heterogeneous structure and processes occurring in the Earth’s subsurface is limited and uncertain. The above is true even for the upper 100m of the subsurface, yet many processes occur within it (e.g. migration of solutes, landslides, crop water uptake, etc.) are important to human activities. Geophysical methods such as electrical resistivity tomography (ERT) greatly improve our ability to observe the subsurface due to their higher sampling frequency (especially with autonomous time-lapse systems), larger spatial coverage and less invasive operation, in addition to being more cost-effective than traditional point-based sampling. However, the process of using geophysical data for inference is prone to uncertainty. There is a need to better understand the uncertainties embedded in geophysical data and how they translate themselves when they are subsequently used, for example, for hydrological or site management interpretations and decisions. This understanding is critical to maximize the extraction of information in geophysical data. To this end, in this thesis, I examine various aspects of uncertainty in ERT and develop new methods to better use geophysical data quantitatively. The core of the thesis is based on two literature reviews and three papers. In the first review, I provide a comprehensive overview of the use of geophysical data for nuclear site characterization, especially in the context of site clean-up and leak detection. In the second review, I survey the various sources of uncertainties in ERT studies and the existing work to better quantify or reduce them. I propose that the various steps in the general workflow of an ERT study can be viewed as a pipeline for information and uncertainty propagation and suggested some areas have been understudied. One of these areas is measurement errors. In paper 1, I compare various methods to estimate and model ERT measurement errors using two long-term ERT monitoring datasets. I also develop a new error model that considers the fact that each electrode is used to make multiple measurements. In paper 2, I discuss the development and implementation of a new method for geoelectrical leak detection. While existing methods rely on obtaining resistivity images through inversion of ERT data first, the approach described here estimates leak parameters directly from raw ERT data. This is achieved by constructing hydrological models from prior site information and couple it with an ERT forward model, and then update the leak (and other hydrological) parameters through data assimilation. The approach shows promising results and is applied to data from a controlled injection experiment in Yorkshire, UK. The approach complements ERT imaging and provides a new way to utilize ERT data to inform site characterisation. In addition to leak detection, ERT is also commonly used for monitoring soil moisture in the vadose zone, and increasingly so in a quantitative manner. Though both the petrophysical relationships (i.e., choices of appropriate model and parameterization) and the derived moisture content are known to be subject to uncertainty, they are commonly treated as exact and error‐free. In paper 3, I examine the impact of uncertain petrophysical relationships on the moisture content estimates derived from electrical geophysics. Data from a collection of core samples show that the variability in such relationships can be large, and they in turn can lead to high uncertainty in moisture content estimates, and they appear to be the dominating source of uncertainty in many cases. In the closing chapters, I discuss and synthesize the findings in the thesis within the larger context of enhancing the information content of geophysical data, and provide an outlook on further research in this topic

The emergence of hydrogeophysics for improved understanding of subsurface processes over multiple scales

Geophysics provides a multi-dimensional suite of investigative methods that are transforming our ability to see into the very fabric of the subsurface environment, and monitor the dynamics of its fluids and the biogeochemical reactions that occur within it. Here, we document how geophysical methods have emerged as valuable tools for investigating shallow subsurface processes over the past two decades and offer a vision for future developments relevant to hydrology and also ecosystem science. The field of “hydrogeophysics” arose in the late 1990s, prompted, in part, by the wealth of studies on stochastic subsurface hydrology that argued for better field-based investigative techniques. These new hydrogeophysical approaches benefited from the emergence of practical and robust data inversion techniques, in many cases with a view to quantify shallow subsurface heterogeneity and the associated dynamics of subsurface fluids. Furthermore, the need for quantitative characterization stimulated a wealth of new investigations into petrophysical relationships that link hydrologically relevant properties to measurable geophysical parameters. Development of time-lapse approaches provided a new suite of tools for hydrological investigation, enhanced further with the realization that some geophysical properties may be sensitive to biogeochemical transformations in the subsurface environment, thus opening up the new field of “biogeophysics”. Early hydrogeophysical studies often concentrated on relatively small ‘plot-scale’ experiments. More recently, however, the translation to larger-scale characterization has been the focus of a number of studies. Geophysical technologies continue to develop, driven, in part, by the increasing need to understand and quantify key processes controlling sustainable water resources and ecosystem services

Feasibility of remote evaporation and precipitation estimates

Remote sensing by means of stereo images obtained from flown cameras and scanners provides the potential to monitor the dynamics of pollutant mixing over large areas. Moreover, stereo technology may permit monitoring of pollutant concentration and mixing with sufficient detail to ascertain the structure of a polluted air mass. Consequently, stereo remote systems can be employed to supply data to set forth adequate regional standards on air quality. A method of remote sensing using stereo images is described. Preliminary results concerning the planar extent of a plume based on comparison with ground measurements by an alternate method, e.g., remote hot-wire anemometer technique, are supporting the feasibility of using stereo remote sensing systems

FLOWPATH 2019 – NATIONAL MEETING ON HYDROGEOLOGY

FLOWPATH 2019, the 4th National Meeting on Hydrogeology, was held in Milan from 12th to 14th June 2019. According to the aim of the previous Editions of FLOWPATH, held in Bologna (2012), Viterbo (2014) and Cagliari (2017), the conference is an opportunity for Italian hydrogeologists to exchange ideas and knowledge on different groundwater issues. The objectives of the conference are: – To promote dialogue and exchange of scientific knowledge among young hydrogeologists; – To deepen the theoretical and practical aspects of our understanding on groundwater; – To update all the stakeholders, researchers and professionals on recent challenges in the hydrogeological sciences; – To encourage researchers, professionals and administrators to contribute to the improvement of water resources management

A Review on Applications of Time-Lapse Electrical Resistivity Tomography Over the Last 30 Years : Perspectives for Mining Waste Monitoring

"Mining operations generate large amounts of wastes which are usually stored into large-scale storage facilities which pose major environmental concerns and must be properly monitored to manage the risk of catastrophic failures and also to control the generation of contaminated mine drainage. In this context, non-invasive monitoring techniques such as time-lapse electrical resistivity tomography (TL-ERT) are promising since they provide large-scale subsurface information that complements surface observations (walkover, aerial photogrammetry or remote sensing) and traditional monitoring tools, which often sample a tiny proportion of the mining waste storage facilities. The purposes of this review are as follows: (i) to understand the current state of research on TL-ERT for various applications; (ii) to create a reference library for future research on TL-ERT and geoelectrical monitoring mining waste; and (iii) to identify promising areas of development and future research needs on this issue according to our experience. This review describes the theoretical basis of geoelectrical monitoring and provides an overview of TL-ERT applications and developments over the last 30 years from a database of over 650 case studies, not limited to mining operations (e.g., landslide, permafrost). In particular, the review focuses on the applications of ERT for mining waste characterization and monitoring and a database of 150 case studies is used to identify promising applications for long-term autonomous geoelectrical monitoring of the geotechnical and geochemical stability of mining wastes. Potential challenges that could emerge from a broader adoption of TL-ERT monitoring for mining wastes are discussed. The review also considers recent advances in instrumentation, data acquisition, processing and interpretation for long-term monitoring and draws future research perspectives and promising avenues which could help improve the design and accuracy of future geoelectric monitoring programs in mining wastes.

The utility of geophysical techniques to image the shallow subsurface in karst areas in Missouri

This dissertation is composed of three papers, which are focused on the utility of geophysical techniques to imaging the shallow subsurface in karst areas in Missouri. In the first paper, ground penetrating radar (GPR) and time domain electromagnetic metal detector (TDEM-MD) methods were effectively deployed in an investigation of the cemetery with the intent of locating unmarked graves. The outcome of this study is to expand the knowledge of GPR and TDEM-MD methods, to locate unmarked graves in cemeteries. The study concluded that the GPR method is superior than TDEM-MD to locate buried caskets in cemetery investigations. In the second paper, optimum field parameters of multi-channel analysis of surface waves (MASW) method were investigated in karst terrain and constrained with electrical resistivity tomography (ERT) data interpretation. Determinations were made based on the comparative analysis of MASW and ERT data results. It is concluded that the use of MASW method in karst terrain with smaller array provides good quality data. In the third paper, ERT and MASW methods were effectively used to map the bedrock of study area by using shear wave velocity and resistivity values. It was observed that the bedrock in some study areas was difficult to recognize, because of the dry soils or moist soils were intact with bedrock. The results of this study indicate that ERT and MASW methods are suitable for mapping bedrock in a karst environment --Abstract, page iv

The lethal and sublethal effects of anti-sea lice chemotherapeutants in marine benthic and pelagic invertebrates

The salmon aquaculture industry has become a major contributor to the Canadian economy, however, many practices including sea lice pest management strategies have resulted in the contamination of the environment near these operations. Compounds used in sea lice control include Salmosan® (active ingredient [AI] azamethiphos), Paramove®50 (AI hydrogen peroxide), ivermectin (IVM) and SLICE® (AI emamectin benzoate [EMB]). Salmosan® and Paramove®50 are water-soluble formulations applied as bath treatments, whereas IVM and SLICE® are in-feed additives that are hydrophobic and partition to sediment with persistent physicochemical properties. This research assessed both the lethal and sub-lethal effects of these compounds on non-target benthic and pelagic invertebrates at environmentally relevant concentrations. A short-term fertilization success bioassay using the sea urchin Strongylocentrotus purpuratus was performed using pest management application-level concentrations of Salmosan® and Paramove®50 in seawater. Paramove®50 significantly inhibited fertilization success with a calculated IC50 value of 7.27 mg/L; Salmosan® only marginally inhibited fertilization at the highest concentration (IC50 > 100 µg/L). Avoidance behaviour and oxygen consumption were assessed in the benthic amphipod, Eohaustorius estuarius, and the polychaete Nereis virens, following sub-chronic exposure to environmentally relevant sediment concentrations (< 5 µg/kg) of EMB, IVM and a combination of both (EMB/IVM). E. estuarius avoided sediment containing IVM and EMB/IVM ratio concentrations containing 25 and 50 µg/kg IVM, while N. virens avoided sediment with 50 and 200 µg/kg IVM and 0.5, 5, 50 and 200 µg/kg EMB/IVM ratio. Impaired burrowing and locomotory behaviour in N. virens was also observed with both treatments. Oxygen consumption was significantly decreased in E. estuarius and increased in N. virens when exposed to EMB, IVM and EMB/IVM at concentrations < 5 µg/kg over a 28-d exposure period. This research provides evidence of impacts to S. purpuratus, E. estuarius and N. virens from anti-sea lice chemotherapeutant exposure at environmentally relevant concentrations and will supplement regulatory decisions and management policies associated with chemicals used in aquaculture in Canada

Applied Geochemistry with Case Studies on Geological Formations, Exploration Techniques and Environmental Issues

Geochemistry has become an essential subject to understand our origins and face the challenges that humanity will meet in the near future. This book presents several studies that have geochemistry as their central theme, from the description of different geological formations, through its use for the characterization of contaminated sites and their possible impact on ecosystems and human health, as well as the importance of geochemical techniques as a complement to other current scientific disciplines. Through the different chapters, the reader will be able to approach the world of geochemistry in several of its subfields (e.g. environmental, isotope, or biogeochemistry) and learn through practical cases