Integrating climate resilience in the water sector in the Caribbean: Moving from regional to national action

Climate-sensitive sectors such as water are central to sustainable development in the Caribbean. Strengthening regional and national capacity to respond to climate change, to mainstream climate resilience, and to design transformative sector- wide interventions is therefore a key priority under the ACP-EU-CDB National Disaster Risk Management (NDRM) programme. As part of this initiative, Phase I of the “Planning for the Integration of Climate Resilience in the Water Sector in the Caribbean project” (The Project) produced a package of training materials, tools, guidelines and technical notes to help water professionals and other practitioners mainstream climate resilience in the water sector. The training materials provide a framework to strengthen water sector resilience across multiple facets including assets and infrastructure, policies, plans, strategies and institutions. The training materials were developed and refined through country case study applications in Grenada and St. Kitts & Nevis. A regional Training of Trainers event bringing together representatives from the borrowing member countries (BMCs) of the Caribbean Development Bank (CDB) was subsequently held to improve the capacity of national professionals and practitioners to identify, plan and implement climate resilient development pathways in the water sector. Phase II of The Project subsequently applied the training materials, tools, guidelines and technical notes to two new case study countries, Dominica and Antigua & Barbuda. These additional pilot applications further demonstrated the applicability of the approaches in countries where the water supply and services were severely affected by Hurricanes Maria (Dominica) and Irma (Antigua & Barbuda) in September 2017. This paper showcases the outcomes and deliverables of The Project, highlights lessons learned during applications in the case study countries and takes a critical look at actions required to support the shift from regional to national actions to accelerate the integration of climate resilience across CDB’s BMCs

Spectral induced polarization and electrodic potential monitoring of microbially mediated iron sulfide transformations

Stimulated sulfate-reduction is a bioremediation technique utilized for the sequestration of heavy metals in the subsurface.We performed laboratory column experiments to investigate the geoelectrical response of iron sulfide transformations by Desulfo vibriovulgaris. Two geoelectrical methods, (1) spectral induced polarization (SIP), and (2) electrodic potential measurements, were investigated. Aqueous geochemistry (sulfate, lactate, sulfide, and acetate), observations of precipitates (identified from electron microscopy as iron sulfide), and electrodic potentials on bisulfide ion (HS) sensitive silver-silver chloride (Ag-AgCl) electrodes (630 mV) were diagnostic of induced transitions between an aerobic iron sulfide forming conditions and aerobic conditions promoting iron sulfide dissolution. The SIP data showed 10m rad anomalies during iron sulfide mineralization accompanying microbial activity under an anaerobic transition. These anomalies disappeared during iron sulfide dissolution under the subsequent aerobic transition. SIP model parameters based on a Cole-Cole relaxation model of the polarization at the mineral-fluid interface were converted to (1) estimated biomineral surface area to pore volume (Sp), and (2) an equivalent polarizable sphere diameter (d) controlling the relaxation time. The temporal variation in these model parameters is consistent with filling and emptying of pores by iron sulfide biofilms, as the system transitions between anaerobic (pore filling) and aerobic (pore emptying) conditions. The results suggest that combined SIP and electrodic potential measurements might be used to monitor spatiotemporal variability in microbial iron sulfide transformations in the field

Geophysical monitoring and reactive transport modeling of ureolytically-driven calcium carbonate precipitation

Ureolytically-driven calcium carbonate precipitation is the basis for a promising in-situ remediation method for sequestration of divalent radionuclide and trace metal ions. It has also been proposed for use in geotechnical engineering for soil strengthening applications. Monitoring the occurrence, spatial distribution, and temporal evolution of calcium carbonate precipitation in the subsurface is critical for evaluating the performance of this technology and for developing the predictive models needed for engineering application. In this study, we conducted laboratory column experiments using natural sediment and groundwater to evaluate the utility of geophysical (complex resistivity and seismic) sensing methods, dynamic synchrotron x-ray computed tomography (micro-CT), and reactive transport modeling for tracking ureolytically-driven calcium carbonate precipitation processes under site relevant conditions. Reactive transport modeling with TOUGHREACT successfully simulated the changes of the major chemical components during urea hydrolysis. Even at the relatively low level of urea hydrolysis observed in the experiments, the simulations predicted an enhanced calcium carbonate precipitation rate that was 3-4 times greater than the baseline level. Reactive transport modeling results, geophysical monitoring data and micro-CT imaging correlated well with reaction processes validated by geochemical data. In particular, increases in ionic strength of the pore fluid during urea hydrolysis predicted by geochemical modeling were successfully captured by electrical conductivity measurements and confirmed by geochemical data. The low level of urea hydrolysis and calcium carbonate precipitation suggested by the model and geochemical data was corroborated by minor changes in seismic P-wave velocity measurements and micro-CT imaging; the latter provided direct evidence of sparsely distributed calcium carbonate precipitation. Ion exchange processes promoted through NH4+ production during urea hydrolysis were incorporated in the model and captured critical changes in the major metal species. The electrical phase increases were potentially due to ion exchange processes that modified charge structure at mineral/water interfaces. Our study revealed the potential of geophysical monitoring for geochemical changes during urea hydrolysis and the advantages of combining multiple approaches to understand complex biogeochemical processes in the subsurface

Geophysical characterization of subsurface biofuel contamination and biodegradation

In the last two decades, the production of ethanol (EtOH), one of the most common biofuels in the USA, has substantially increased due to regulations aiming at reducing air pollution and providing a supplement to petroleum. Scenarios of large spills of EtOH during production, transportation and at storage facilities are likely. Accidental release of EtOH and its persistence in the subsurface pose threats to human health and the environment, including the deterioration of municipal water supplies. Thus, there is a need to develop adequate monitoring tools to help with the remediation efforts of subsurface EtOH contamination. Ethanol presence, interaction and biodegradation could substantially alter the electrical properties of geologic materials, thereby potentially leading to distinctive geophysical responses. This dissertation demonstrates the potential application of non-invasive and cost effective complex resistivity (CR) technique for the characterization of biofuel contamination and biodegradation in the subsurface. The first research topic examined the electrical geophysical signatures arising from groundwater contamination by EtOH. Conductivity measurements were performed at the laboratory scale on EtOH-water mixtures (0 to 0.97 v/v EtOH) and EtOH-salt solution mixtures (0 to 0.99 v/v EtOH) with and without a sand matrix. A mixing model was used to simulate electrical conductivity as a function of EtOH concentration in the mixture. It was found that increasing EtOH concentration resulted in a decrease in measured conductivity magnitude ( ), which reflected changes in relative strength of the types of interactions occurring in EtOH-water mixtures. The second research topic explored the electrical properties associated with EtOH-clay interactions using CR measurements on laboratory columns of varying ethanol (EtOH) concentration (0% to 30% v/v) in a sand-clay (bentonite) matrix. A Debye Decomposition approach was applied to fit the CR data. Overall, the results showed a significant suppression (P ≤ 0.001) of the clay driven polarization with increasing EtOH concentration. The suppression effects are associated with alterations in the electrical double layer (EDL) at the clay-fluid interface due to strong EtOH adsorption on clay and complex intermolecular EtOH-water interactions. The persistent EtOH adsorption on clay also indicated strong hysteresis effects in the electrical response. The third research topic investigated changes in electrical properties during EtOH biodegradation processes in sand matrix using CR measurements in conjunction with geochemical data analysis on microbial stimulated (inoculation of bacterial cells) and control (without bacteria inoculation) columns. A Debye Decomposition approach was applied to fit the CR data. Overall, the results showed a clear distinction between the bio-stimulated and control columns in terms of real ( ) and imaginary ( ) conductivity, phase ( ) and apparent formation factor (Fapp). Temporal geochemical changes and high resolution scanning electron microscopy imaging corroborated the CR findings, thus indicating the sensitivity of CR measurements to EtOH biodegradation processes.Ph.D.Includes bibliographical referencesIncludes vitaby Yves Robert Personn

The use of Natural Gas Vehicles in underground facilities: Application to the PARIS-LA-DÉFENSE underground network

International audienceConsidering the current strong development of natural gas vehicles and their use in many underground infrastructures, this paper focuses on the corresponding risk induced in such situations. It consists in applying the analysis of the consequences of the huge and complex underground network of the La Défense business center, in the suburbs of Paris. The different types of natural gas vehicles were considered, compressed natural gas (CNG) and liquified natural gas vehicles (LNG). Based on existing knowledge in risk analysis, the main dangerous phenomena that can occur for those vehicles, jet fire, vapor cloud explosion, and tank burst, were all considered and modeled for each technology. To evaluate the release source term, the very beginning for both jet fire and flammable cloud characterization, the classic gas release model was used while considering the pressure decrease in the tank to get the mass release time variation. This was mainly interested in estimating the resulting jet fire heat release rate and duration and the corresponding impact on the global heat release curve. As far as vapor cloud explosion (VCE) is concerned, the worst-case situation, more precisely the largest flammable mass is obtained in the first seconds following the release beginning. The specificity for VCE represents the tunnel confinement's influence on the pressure wave propagation. In such an environment, the commonly used multi-energy approach, based on semi-spherical wave propagation is inappropriate, reflexion phenomena should be introduced to provide a better prediction. The consequence modeling shows that, for both technologies, the worst dangerous phenomena remain the tank burst, especially for LNG where the lethal effect may affect most of the people present in the tunnel, for CNG lethal effect should reach 30 m and more for the same tank burst scenario. This huge consequence highlights the importance of preventing its occurrence through the efficiency of dedicated safety measures but also fire prevention since such a tank burst is induced by a fire in the surrounding of the tank. For the jet fire case, the consequences are a global vehicle heat release rate increase, during the gas release, while this could influence the efficiency of the tunnel ventilation, this does not significantly modify the thermal consequences for people. Regarding the vapor cloud explosion, lethal overpressure would affect passengers of the few closest vehicles for LNG and users in an area of 4 to 20 m centered on the vehicle for CNG