Assessment of CO2 health risk in indoor air following a leakage reaching unsaturated zone: results from the first representative scale experiment

International audienceLeakage of CO2 from geological reservoirs is one of the most fearsome unexpected scenarios for CO2 storage activities. If a leakage reaches the ground level, exposure to high CO2 concentrations is more likely to occur in low ventilated spaces (pit dug in the ground, basement, building) where CO2 could accumulate to high concentrations. Significant literature and models about indoor exposure resulting from intrusion of soils gases in building are available in several domains (e.g., contaminated soils, radon, etc.). However, there is no guarantee that those approaches are appropriate for the assessment of consequences of CO2 leakage due the specificity of CO2 and due to the singularities of the source in case of leakage from anthropic reservoirs. Furthermore, another singularity compared to conventional approaches is that the risk due to CO2 exposure should be evaluated considering acute concentrations rather than long term exposure to low concentrations. Thus, a specific approach is needed to enable a quantitative assessment of the risk for health and living in indoor environment in case of leakage from a reservoir reaching the unsaturated zone below the buildings. We present the results of the IMPACT-CO2 project that aims at understanding the possible migration of CO2 to indoor environment and to develop an approach to evaluate the risks. The approach is based on modelling and experiments at laboratory scale and at field representative scale. The aim of the experiment is to capture the main phenomena that control the migration of CO2 through unsaturated zone, and its intrusion and accumulation in buildings. The experimental results will also enable numerical confrontation with tools used for risk assessment. Experiments at representative scale (Figure 1) are performed on the PISCO2 platform (Ponferrada, Spain) specifically instrumented and designed for understanding the impacts of CO2 migration towards the soil surface. The experiment is composed of a 2.2 m deep basin filled with sand upon which a specifically designed cylindrical device representing the indoor condition of a building (with controlled depressurization and ventilation) is set up. The device includes a calibrated interface that represents a cracked slab of a building. The injection of CO2 is performed at the bottom of the basin with a flow rate in the range of hundreds of g/d/m². The first results show that the presence of a building influences significantly the transport of CO2 in the surrounding soil leading to two competing phenomena: 1) seepage in the atmosphere mainly controlled by diffusion gradient and 2) advective/diffusive flux entering the building due to the depressurization. Models have been established to quantitatively assess the proportion of CO

Management of uncertainties on parameters elicited by experts – Applications to sea-level rise and to CO 2 storage operations risk assessment

International audienceIn a context of high degree of uncertainty, when very few data are available, experts are commonly requested to provide their opinions on input parameters of risk assessment models. Not only might each expert express a certain degree of uncertainty on his/her own statements, but the set of information collected from the pool of experts introduces an additional level of uncertainty. It is indeed very unlikely that all experts agree on exactly the same data, especially regarding parameters needed for natural risk assessments. In some cases, their opinions may differ only slightly (e.g. the most plausible value for a parameter is similar for different experts, and they only disagree on the level of uncertainties that taint the said value) while on other cases they may express incompatible opinions for a same parameter. Dealing with these different kinds of uncertainties remains a challenge for assessing geological hazards or/and risks. Extra-probabilistic approaches (such as the Dempster-Shafer theory or the possibility theory) have shown to offer promising solutions for representing parameters on which the knowledge is limited. It is the case for instance when the available information prevents an expert from identifying a unique probability law to picture the total uncertainty. Moreover, such approaches are known to be particularly flexible when it comes to aggregating several and potentially conflicting opinions. We therefore propose to discuss the opportunity of applying these new theories for managing the uncertainties on parameters elicited by experts, by a comparison with the application of more classical probability approaches. The discussion is based on two different examples. The first example deals with the estimation of the injected CO 2 plume extent in a reservoir in the context of CO 2 geological storage. This estimation requires information on the effective porosity of the reservoir, which has been estimated by 14 different experts. The Dempster-Shafer theory has been used to represent and aggregate these pieces of information. The results of different aggregation rules as well as those of a classical probabilistic approach are compared with the purpose of highlighting the elements each of them could provide to the decision-maker (Manceau et al., 2016). The second example focuses on projections of future sea-level rise. Based on IPCC's constraints on the projection quantiles, and on the scientific community consensus level on the physical limits to future sea-level rise, a possibility distribution of the projections by 2100 under the RCP 8.5 scenario has been established. This possibility distribution has been confronted with a set of previously published probabilistic sea-level projections, with a focus on their ability to explore high ranges of sea-level rise (Le Cozannet et al., 2016). These two examples are complementary in the sense that they allow to address various aspects of the problem (e.g. representation of different types of information, conflict among experts, sources dependence). Moreover, we believe that the issues faced during these two experiences can be generalized to many risks/hazards assessment situations. References Manceau, JC., Loschetter, A., Rohmer, J., de Lary, L., Le Guénan, T., Hnottavange-Telleen, K. (2016). Dealing with uncertainty on parameters elicited from a pool of experts for CCS risk assessment. Congrès λµ 20 (St-Malo, France). Le Cozannet G., Manceau JC., Rohmer, J. (2016). Bounding probabilistic sea-level rise projections within the framework of the possibility theory. Accepted in Environmental Research Letters

Assessment of CO2 Health Risk in Indoor Air Following a Leakage from a Geological Storage: Results from the First Representative Scale Experiment

If a leakage of CO2 out of a geological reservoir were to happen and to reach the vadose zone below a building, CO2 could migrate through the vadose and the building's slab and accumulate in the building, leading to possible acute risk for the inhabitants. A representative-scale experiment, including a prototype for a building, was developed to better understand and quantify this possible risk. It brought fruitful directions for further modeling work, since unexplained CO2 peaks were observed in the prototype. Numerical simulations were carried out to address the variability of CO2 concentrations considering the influence of soil and building properties as well as meteorological conditions, with promising results for risk analysis

Mitigation and remediation technologies and practices in case of undesired migration of CO2 from a geological storage unit—Current status

International audienceOne of the main objectives of operators and regulators involved in CO2 geological storage activities is to ensure that the injected CO2 will remain safely in the underground for a long period of time. Therefore, in addition to the screening and evaluation of the performance of a potential CO2 storage site, risks of unwanted migration in the subsurface should be addressed and adequately managed. This can include the use of methods to mitigate those risks and ultimately to remediate potential adverse effects. This paper reviews the status of knowledge with regards to the mitigation and remediation technologies, from mature techniques adapted from other fields, such as oil and gas industry and environmental clean-up, to research topics offering potential new possibilities. Several categories can be defined: (1) interventions on operational or decommissioned wells to re-establish their integrity; (2) pressure/fluid management techniques for countering the leakage driving forces and/or removing the leaking fluids; (3) emerging technologies providing new mitigation opportunities for controlling undesired CO2 migration; (4) techniques to remediate the impacts potentially induced by such a migration. This technical state of the art is completed by the actual practices in the emerging field of CO2 geological storage established from the regulatory requirements and guidelines, and from the experience gained in existing storage projects over the world. This article concludes on important best practices stemming from this review and on future challenges in terms of research topics and operational needs

La gestion des incertitudes sur des paramètres estimés par un groupe d’experts pour l’analyse des risques du stockage de CO2

Pour les exploitations du sous-sol, les données géologiques sont souvent peu nombreuses lorsque les projets sont à un stade précoce de développement, et le recours à l’avis d’experts est fréquent. Il est alors nécessaire de gérer les informations fournies par plusieurs experts, potentiellement conflictuelles. Sur un cas d’étude dédiée au stockage géologique du CO2, deux approches différentes ont été appliquées pour la gestion des incertitudes sur la valeur d’un paramètre estimée par 14 experts différents, une approche classique de type probabiliste ainsi qu’une approche basée sur la théorie de Dempster-Shafer. Les résultats sont discutés pour aider à la prise de décision.Handling potentially conflicting information coming from experts when other available data are scare or inexistent is an important issue for subsurface operations, especially for projects in the early stages of development. On a case study dedicated to the CO2 geological storage technology, two different approaches have been considered to deal with the uncertainties on a parameter value estimated by 14 different experts: a classical probabilistic approach and an approach based on the Dempster-Shafer theory. The results are discussed regarding their ability to help decision-making

Potential impacts of leakage from CO2geological storage ongeochemical processes controlling fresh groundwater quality : A review

International audiencetLeakage of CO2or brine coming from CO2geological storage sites constitutes a risk for overlying freshgroundwater resources. One of the main risks is the potential alteration of groundwater quality by theintrusion of contaminants such as trace elements. This paper reviews studies that address the potentialimpacts of CO2geological storage leakage on fresh groundwater quality.Leakage can directly modify the chemical properties of fresh water (pH, redox potential, chemicalcomposition) and, as a result, indirectly modify the effect of biogeochemical processes controlling traceelement availability. The ability of a CO2or brine leak to introduce or mobilize trace elements and poten-tially degrade the quality of water in an overlying aquifer depends on the composition and quantityof the leaking fluids, the nature of the solid phases making up the aquifer (buffering and scavengingcapacity) and the concentrations of undesirable or toxic elements that can be mobilized following anysuch modification. Furthermore, hydrogeological conditions will control the potential dissemination intogroundwater. To date, studies have shown that trace elements can be significantly mobilized without nec-essarily exceeding quality thresholds. In a few cases where aquifers are naturally rich in trace elements(i.e. whose natural concentrations in groundwater are already high), CO2is able to mobilize these traceelements (e.g. Fe, Mn, Ni, As, Ba, U) and increase concentrations up to or exceeding threshold values.This literature review provides a return on experience essential for both assessing biogeochemicalrisks prior to the installation of future CO2geological storage sites and designing and installing freshgroundwater quality monitoring networks

What may be the consequences of a CO 2 leakage? Insights from soil gas measurements in an urban area – Clermont-Ferrand, French Massif Central

International audienceThis project is aimed to better constrain the geographical distribution of CO 2 geological emanations in an urban context and to suggest recommendations for risk management. Natural emanations may have some similarities with emissions from an anthropogenic deep storage site that experiences unexpected gas releases. Such gas emanations may generate hazards to which local authorities have to face, especially those concerning human exposure. In 2015, the Regional Bureau of Environment, Physical Planning and Housing from the Auvergne District (DREAL) and the Clermont-Ferrand Urban Community (CLERMONT-CO) have co-financed site investigations to better characterize gas emanations over selected territories (7 cities) and to establish guidelines for the management of associated risks. Work has been done under the coordination of the Regional Prefecture. Located in the Northern part of the French Massif Central, the Clermont-Ferrand city is a populated city (c.a. 140 000 inhabitants) that is located mostly over quaternary volcanic rocks belonging to a former maar structure. To the East, volcanic rocks are progressively replaced by continental formations belonging to the Tertiary graben of Limagne. The limit between sedimentary domain and basement/volcanic domain is underlined by deep-rooted normal faults along which several well-known mineral springs are emplaced

Development of a phyto-stabilization strategy based on the optimization of endogenous vegetal species development on a former arsenic-bearing mine waste

International audienc

Sélection d'amendements pour diminuer la mobilité et la toxicité de polluants inorganiques (Pb, As, Ba, Zn) dans un déchet minier pour le développement d'un procédé de phytoremédiation

International audienceIn mining sites, the dispersion of solid particles of tailings, induces a risk of dispersion of toxic elements, in addition with potential pollution of groundwater and surface water through leaching. The development of a vegetal cover is one of the potential options to decrease the risks. However, the growth of plants on mine tailings is generally hampered by several parameters: acidity, lack of nutrients, poor texture and toxicity of metals and metalloids. Thus, amendments are necessary to overcome these limitations. A mine tailing material was sampled on a former silver and lead mining site. Chemical analysis indicated the following concentrations in pollutants: 26 432 mg.kg-1 Pb, 265 mg.kg-1 Zn, 1 063 mg.kg-1 Ba, 1134 mg.kg-1 As. The tailing is acidic, siliceous and coarse (76% of particles with size in the range of 315 µm - 2 mm). A cow manure and some ochre (iron oxide-hydroxide) material produced in the water treatment plant of a coal mine were tested, alone or in combination, to stabilize the most mobile toxic pollutant, Pb, while avoiding the mobilization of other toxic elements. Leaching and microcosm experiments were performed and showed that the Pb concentration in water, that was higher than 10 mg.L-1 with the not-amended tailing, was decreased by a factor ×100, while As, Zn and Ba concentration did not increase significantly. Ochre (added at 5% in weight/weight) allowed increasing pH and could adsorb some metals and metalloïds. The metabolic microbial diversity, evaluated using Ecolog® plates, was improved by all amendements after one month of incubation. Polymers were the most used substrates in the non-planted microcosms, after one month of incubation, suggesting a specialized microbial community. Planted microcosms revealed that the growth of ryegrass was significantly improved by the addition of ochre and manure : the biomass of ryegrass is 3.5 X (with 5% ochre and 2% manure) to 4.8 X (with 5% ochre and 0.15%) greater than in the condition of plants growing on unamended soil. The next experimental step will include the monitoring of phytostabilization at metric scale, in mesocosm, with a vegetal specie naturally present on Pontgibaud mine site, belonging to the Agrostis genus

Methodologies and technologies for mitigation of undesired CO 2 migration in the subsurface

International audienceThe development and implementation of the CO2 Capture and Storage (CCS) technology is highly dependent on the assurance of the storage process safety with regards to a potential CO2 leakage from the target zone. Low permeability caprocks are viewed as critical element for a safe containment of CO2 in the target storage formation. As a result, the presence of any potential pathway is of a major concern since it may allow buoyant CO2 to migrate along and reach an overlying formation or be emitted at the surface, potentially impacting drinking water resources or sensitive stakes at the surface. Undesired CO2 migration may occur through man-made (abandoned and operational wells) and/or natural (caprock sealing defects including faults, fractures and high permeability areas) pathways. Managing a potential CO2 leakage risk scenario is of first importance and a dedicated, site-specific strategy has to be set up. The storage safety could be guaranteed through an adequate site selection and characterization leading to the choice of a site where the evolution of the CO2 plume and potential impacts of the storage are judged acceptable. Specifically to this given storage site, a proper risk-management process should be set up to anticipate the potential deviations from this acceptable behavior, including assessing the risks, monitoring the site to detect any potential loss of confinement, mitigating any potential leakage and remediating possible impacts.This study is focused on the risk treatment stage, more specifically on the methodologies and technologies for mitigation and remediation of unpredicted CO2 migration in the subsurface. To date this subject has not been addressed effectively although it is currently receiving more attention from the industrial and scientific communities. This evolution may be linked with the new regulations on CO2 geological storage, notably in Australia, Europe and in the USA, which specify requirements on mitigation and remediation methods.A comprehensive knowledge of mitigation techniques is needed to meet these requirements, which can be summarized with the three following categories:- Technical issue – the first challenge is to determine which ones of the existing technologies applied on the source, the transfer pathway or directly on the impacts may be adapted to avoid, reduce or correct any potential impacts induced by a CO2 migration. In other words, these are the scientifically conceivable measures;- Operational issue – from an operational perspective, the maturity of a technology is essential to ensure its feasibility. The achievability of one measure is dependent on additional criteria especially on the balance between the benefits (impact avoided) and the costs (economiccosts and potential environmental negative impacts of the measure). The second challenge is therefore to specify properly those criteria for the measures and to develop tools to assess the relevance of each conceivable measures;- Implementation issue – the third challenge is, based on the knowledge available at a given time, to produce an intervention plan as required by the above-cited regulations. This plan should answer to the identified risk events, and also prepare the operator and the competent authority to make an informed decision for choosing the best mitigation and/or remediation option at the time of the detection of an abnormal behavior in the CO2 storage complex.The technical issue has already been tackled and with several technical papers devoted to specific techniques aiming at reducing the potential risks and impacts of CO2 based on either existing work conducted in other fields (e.g. oil and gas industry, soil or water remediation) or specifically developed for CO2 storage. However, new categories of remediation techniques have recently appeared based on newly emerging technologies. In addition there is a need of comparative data to help operators to select the most adapted measure. Decision-making tools are also required to balance the benefits gained by the implementation of a mitigation measure and its economic costs and potential environmental impacts. Finally, there is a lack of integrated studies on the mitigation plan setting-up process. For instance, no comparison between the different intervention strategies of existing and future CO2 storage projects has been published. There is thus a need of gathering the best practices for mitigation of undesired CO2 migration based on the scientific literature and experience gained from various CO2 geological projects.In line with these statements, BRGM and IRIS conducted a literature and experience review on the methodologies and technologies for mitigation of undesired CO2 migration in the subsurface on behalf of the IEA Greenhouse Gas R&D Program.The state of knowledge of CO2 leakage mitigation and remediation technologies has been first presented from a technical point of view. Thus, for different scenarios, the potential actions for avoiding, reducing or correcting impacts caused by an unwanted CO2 migration have been reviewed. The choice of the appropriate measure strongly depends on the nature of the leak. The intervention on leakage through man-made pathways (well remediation) stems from the oil and gas industry experience, and for some of them are considered as standard operations. However, in some cases of man-made leakage pathways, and more importantly in most cases of natural ones, the operator may not be able to rely on the well engineering experience, and may rather rely on either fluid management techniques or new breakthrough technologies for modifying the leaking paths or fluid properties. In case of an impacting CO2 migration, measures may be applied to remediate environmental impacts.The state of knowledge presented in this study integrates both measures that are standard and technically feasible at the present time as well as innovative and under development ones. For each measure and when possible, a technical description of the intervention technique, generic cost and time elements (intervention delay, efficiency time duration) as well as a discussion on the maturity of the technique are provided. Decision-making tools (cost-benefit, cost-effectiveness and multi-criteria analyses) integrating those criteria to help choosing the optimal series of remediation actions are presented in this study. The third part of the work is a review of the existing plans and guidelines for designing such intervention plans. A qualitative survey has been performed among a list of CO2 and natural gas storage sites. Recommendations – research and development directions or best practices - are proposed according to the outcomes of the entire study