Jean-Michel Lemieux

Dynamics of groundwater recharge and seepage over the Canadian landscape during the Wisconsinian glaciation

Received 30 May 2007; accepted 12 October 2007; published 15 February 2008. [1] Pleistocene glaciations and their associated dramatic climatic conditions are suspected to have had a large impact on the groundwater flow system over the entire North American continent. Because of the myriad of complex flow-related processes involved during a glaciation period, numerical models have become powerful tools for examining groundwater flow system evolution in this context. In this study, a series of key processes pertaining to coupled groundwater flow and glaciation modeling, such as densitydependent (i.e., brine) flow, hydromechanical loading, subglacial infiltration, isostasy, and permafrost development, are included in the numerical model HydroGeoSphere to simulate groundwater flow over the Canadian landscape during the Wisconsinian glaciation (�� 120 ka to present). The primary objective is to demonstrate the immense impact of glacial advances and retreats during the Wisconsinian glaciation on the dynamical evolution of groundwater flow systems over the Canadian landscape, including surface-subsurface water exchanges (i.e., recharge and discharge fluxes) in both the subglacial and the periglacial environments. It is shown that much of the infiltration of subglacial meltwater occurs during ice sheet progression and that during ice sheet regression, groundwater mainly exfiltrates on the surface, in both the subglacial and periglacial environments. The average infiltration/exfiltration fluxes range between 0 and 12 mm/a. Using mixed, ice sheet thickness–dependent boundary conditions for the subglacial environment, it was estimated that 15–70% of the meltwater infiltrated into the subsurface as recharge, with an average of 43%. Considering the volume of meltwater that was generated subsequent to the last glacial maximum, these recharge rates, which are related to the bedrock type and elastic properties, are historically significant and therefore played an immense role in the evolution of groundwater flow system evolution over the Canadian landmass over the last 120 ka. Finally, it is shown that the permafrost extent plays a key role in the distribution of surface-subsurface interaction because the presence of permafrost acts as a barrier for groundwater flow.

CO2-depleted warm air venting from chrysotile milling waste (Thetford Mines, Canada): Evidence for in-situ carbon capture from the atmosphere

We have discovered diffuse warm air vents at the surface of a chrysotile milling waste heap at the Black Lake mine, Thetford Mines, Quebec, Canada. The venting areas are inconspicuous, except in winter when the vents form snow-free areas of unfrozen ground, each with a surface area of 1–15 m 2 . The temperature and chemical composition of the warm air vents have been monitored from March 2009 to July 2010. The temperature of the warm air and ground surface at the venting sites ranged from 6.6 to 20.0 °C, whereas that of the ambient air ranged from −13.2 to 20.0 °C. The difference between atmospheric and vent air temperatures is greater in cold-weather months. The warm air has low CO 2 content, but has otherwise normal atmospheric gas composition. Warm air volumetric flow varies from 2.1 to 19.9 L/m 2 /s in winter, when it contains between 2 . In summer, the venting areas are more diffuse, with volumetric flow rates ranging from 0.5 to 1.5 L/m 2 /s, and are less depleted in CO 2 (260–370 ppm). Frozen ground is likely focusing airflow in winter compared to summer. We present a conceptual model in which air enters the steep flanks of the chrysotile milling waste heap, into which CO 2 reacts with Mg-rich minerals, stripping CO 2 from air by exothermic mineral carbonation reactions. Considering the surface area of summer and winter venting areas, flow rates, and concentration of CO 2 in warm air vents, we estimate that the Black Lake mine heap passively captures at least 0.6 kt CO 2 per year.

Numerical investigation of methane and formation fluid leakage along the casing of a decommissioned shale gas well

Methane and brine leakage rates and associated time scales along the cemented casing of a hypothetical decommissioned shale gas well have been assessed with a multiphase flow and multicomponent numerical model. The conceptual model used for the simulations assumes that the target shale formation is 200 m thick, overlain by a 750 m thick caprock, which is in turn overlain by a 50 m thick surficial sand aquifer, the 1000 m geological sequence being intersected by a fully penetrating borehole. This succession of geological units is representative of the region targeted for shale gas exploration in the St. Lawrence Lowlands (Quebec, Canada). The simulations aimed at assessing the impact of well casing cementation quality on methane and brine leakage at the base of a surficial aquifer. The leakage of fluids can subsequently lead to the contamination of groundwater resources and/or, in the case of methane migration to ground surface, to an increase in greenhouse gas emissions. The minimum reported surface casing vent flow (measured at ground level) for shale gas wells in Quebec (0.01 m3/d) is used as a reference to evaluate the impact of well casing cementation quality on methane and brine migration. The simulations suggest that an adequately cemented borehole (with a casing annulus permeability kc ≤ 1 mD) can prevent methane and brine leakage over a time scale of up to 100 years. However, a poorly cemented borehole (kc ≥ 10 mD) could yield methane leakage rates at the base of an aquifer ranging from 0.04 m3/d to more than 100 m3/d, depending on the permeability of the target shale gas formation after abandonment and on the quantity of mobile gas in the formation. These values are compatible with surface casing vent flows reported for shale gas wells in the St. Lawrence Lowlands (Quebec, Canada). The simulated travel time of methane from the target shale formation to the surficial aquifer is between a few months and 30 years, depending on cementation quality and hydrodynamic properties of the casing annulus. Simulated long-term brine leakage rates after 100 years for poorly cemented boreholes are on the order of 10−5 m3/d (10 mL/d) to 10−3 m3/d (1 L/d). Based on scoping calculations with a well-mixed aquifer model, these rates are unlikely to have a major impact on groundwater quality in a confined aquifer since they would only increase the chloride concentration in a pristine aquifer to 1 mg/L, which is significantly below the commonly recommended aesthetic objective of 250 mg/L for chloride.

Three-dimensional numerical simulations of methane gas migration from decommissioned hydrocarbon production wells into shallow aquifers

Three-dimensional numerical simulations are used to provide insight into the behavior of methane as it migrates from a leaky decommissioned hydrocarbon well into a shallow aquifer. The conceptual model includes gas-phase migration from a leaky well, dissolution into groundwater, advective-dispersive transport and biodegradation of the dissolved methane plume. Gas-phase migration is simulated using the DuMux multiphase simulator, while transport and fate of the dissolved phase is simulated using the BIONAPL/3D reactive transport model. Methane behavior is simulated for two conceptual models: first in a shallow confined aquifer containing a decommissioned leaky well based on a monitored field site near Lindbergh, Alberta, Canada, and secondly on a representative unconfined aquifer based loosely on the Borden, Ontario, field site. The simulations show that the Lindbergh site confined aquifer data are generally consistent with a 2 year methane leak of 2–20 m3/d, assuming anaerobic (sulfate-reducing) methane oxidation and with maximum oxidation rates of 1 × 10−5 to 1 × 10−3 kg/m3/d. Under the highest oxidation rate, dissolved methane decreased from solubility (110 mg/L) to the threshold concentration of 10 mg/L within 5 years. In the unconfined case with the same leakage rate, including both aerobic and anaerobic methane oxidation, the methane plume was less extensive compared to the confined aquifer scenarios. Unconfined aquifers may therefore be less vulnerable to impacts from methane leaks along decommissioned wells. At other potential leakage sites, site-specific data on the natural background geochemistry would be necessary to make reliable predictions on the fate of methane in groundwater.

Physically Based Groundwater Vulnerability Assessment Using Sensitivity Analysis Methods

A general physically based method is presented to assess the vulnerability of groundwater to external pressures by numerical simulation of groundwater flow. The concept of groundwater vulnerability assessment considered here is based on the calculation of sensitivity coefficients for a user-defined groundwater state for which we propose several physically based indicators. Two sensitivity analysis methods are presented: the sensitivity equation method and the adjoint operator method. We show how careful selection of a method can significantly minimize the computational effort. An illustration of the general methodology is presented for the Herten aquifer analog (Germany). This application to a simple, yet insightful, case demonstrates the potential use of this general and physically based vulnerability assessment method to complex aquifers.

Groundwater occurrence in cold environments: examples from Nunavik, Canada

Water availability and management issues related to the supply of drinking water in northern communities are problematic in Canada. While rivers and lakes are abundant, they are vulnerable to contamination and may become dry in winter due to freezing. Groundwater can often provide a more secure and sustainable water source, however its availability is limited in northern Canada due to the presence of permafrost. Moreover, the exploitation of northern aquifers poses a dual challenge of identifying not only permafrost-free areas, but also permeable areas which will allow groundwater recharge and exploitation. Suitable aquifers are not as common in northern Canada since the shallow subsurface is mostly composed of low-permeability crystalline rocks or unconsolidated sediments of glacial origin that are highly heterogeneous. In order to investigate groundwater occurrence and associated geological contexts in Nunavik (northern Quebec, Canada), along with exploring how these resources will evolve in response to climate change, field and compilation work were conducted in the surroundings of the four villages of Salluit, Kuujjuaq, Umiujaq and Whapmagoostui-Kuujjuarapik. These villages are located in different permafrost zones, ranging from continuous to discontinuous, as well as in different geological environments. It was found that despite the ubiquitous presence of permafrost, unfrozen aquifers could be identified, which suggests that groundwater may be available as a source of drinking water for small communities. Expected climate change, with predicted permafrost thawing and increases in temperature and precipitation, should enhance groundwater availability and may contribute to a more secure source of drinking water for northern communities.RésuméLes questions de disponibilité et de gestion de l’eau liées à l’approvisionnement en eau potable dans les communautés du nord sont problématiques au Canada. Alors que les rivières et les lacs sont abondants, ils sont vulnérables aux contaminations et peuvent s’assécher en hiver en raison du gel. Les eaux souterraines peuvent souvent fournir des ressources en eau plus sures et durables, cependant leur disponibilité est limité dans le nord du Canada à cause de la présence du pergélisol. De plus, l’exploitation des aquifères du nord pose un double défi d’identification non seulement des zones libres de pergélisol, mais aussi des zones perméables qui permettront la recharge des eaux souterraines et leur exploitation. Des aquifères appropriés ne sont pas aussi communs dans le nord du Canada, du fait que le soussol peu profond est surtout composé de roches cristallines de faible perméabilité ou des sédiments non consolidés d’origine glaciaire qui sont très hétérogènes. Afin d’étudier l’occurrence des eaux souterraines et les contextes géologiques associés au Nunavik (nord du Québec, Canada), en explorant la façon dont ces ressources vont évoluer en réponse au changement climatique, des travaux de terrain et de compilation ont été menés dans les environs des quatre villages de Salluit, Kuujjuaq, Umiujaq et Whapmagoostui-Kuujjuarapik. Ces villages sont situés dans différentes zones de pergélisol, allant du continu au discontinu, ainsi que dans différents environnements géologiques. Il a été constaté que, malgré la présence omniprésente du pergélisol, des aquifères non affectés par le gel ont pu être identifiés, ce qui suggère que les eaux souterraines peuvent être disponibles en tant que source d’eau potable pour de petites communautés. Le changement climatique attend, avec une prévision d’un dégel du pergélisol et une augmentation de la température et des précipitations, devrait améliorer la disponibilité des eaux souterraines et peut constituer une ressource en eau potable plus sûre pour les communautés du Nord.ResumenLas cuestiones de disponibilidad y manejo en relación con el suministro de agua potable son problemáticas en las comunidades del norte de Canadá. Mientras que los ríos y lagos son abundantes, ellos son vulnerables a la contaminación y pueden llegar a estar secos en invierno debido a la congelación. El agua subterránea puede proporcionar a menudo una fuente de agua más segura y sostenible, sin embargo, su disponibilidad es limitada en el norte de Canadá debido a la presencia de permafrost. Por otra parte, la explotación de los acuíferos del norte plantea el doble reto de identificar las áreas no sólo libres de permafrost, sino también las zonas permeables que permitan la recarga y la explotación de los acuíferos. Los acuíferos adecuados no son comunes en el norte de Canadá ya que el subsuelo poco profundo está compuesto principalmente por rocas cristalinas de baja permeabilidad o sedimentos no consolidados de origen glacial que son altamente heterogéneos. Con el fin de investigar la ocurrencia del agua subterránea y contextos geológicos asociados en Nunavik (norte de Quebec, Canadá), junto con la exploración de cómo estos recursos van a evolucionar en respuesta al cambio climático, se llevaron a cabo trabajos de recopilación y de campo en el entorno de cuatro pueblos, Salluit, Kuujjuaq, Umiujaq y Whapmagoostui-Kuujjuarapik. Estos pueblos se encuentran en distintas zonas de permafrost, que van desde continuo a discontinuo, así como en diferentes entornos geológicos. Se encontró que, a pesar de la presencia generalizada de permafrost, se pudieron identificar acuíferos no congeladas, lo que sugiere que el agua subterránea puede estar disponible como una fuente de agua potable para las comunidades pequeñas. El cambio climático previsto, con el pronosticado deshielo del permafrost y el aumento de la temperatura y la precipitación, debería mejorar la disponibilidad de agua subterránea y puede contribuir a una fuente más segura de agua potable para las comunidades del norte.摘要与北部社区饮用水供水有关的水资源可用量及管理在加拿大存在着一些问题。加拿大 河流和湖泊众多, 容易受到污染, 由于冰冻, 这些河流和湖泊变干涸。地下水可常常 提供更安全和更持久的水源, 然而, 在加拿大北部由于存在着永久冻土, 水源可用量 受到限制。另外, 北部的含水层开采对确定无永久冻土区和可以进行地下水补给和开 采的的永久冻土区提出了双重挑战。在加拿大北部合适的含水层并不常见, 因为浅层 地表以下主要由透水性低的结晶岩或冰川来源的松散沉积物组成. 为了调查(加拿大 魁北克北部)努那维克地下水赋存情况和相关的地质背景, 连同探索这些资源是怎样 针对气候变化演化的, 在Salluit、Kuujjuaq、Umiujaq 和 Whapmagoostui-Kuujjuarapik四个村庄进行了室外和综合研究工作。这些村庄位于连续、不连续的永久冻 土带及不同地质环境中。研究发现, 尽管普遍存在着永久冻土, 但非冰冻的含水层仍 可识别, 这表明地下水可以作为小型社区的饮用水水源使用。预料的气候变化、加上 预测的永久冻土融化及温度和降水的增加应该增加地下水可利用量, 并且为北部社区 更安全的饮用水源做出贡献.ResumoQuestões sobre a disponibilidade e gestão da água relacionadas com o abastecimento de água potável em comunidades do norte são problemáticas no Canadá. Enquanto rios e lagos são abundantes, eles são vulneráveis à contaminação e podem tornar-se secos no inverno devido ao congelamento. Água subterrânea muitas vezes pode prover uma fonte de água mais segura e sustentável, no entanto a sua disponibilidade é limitada no norte do Canadá, devido à presença de pergelissolos (permafrost). Além disso, a exploração dos aquíferos do norte têm um duplo desafio de identificar não só áreas livres de pergelissolos, mas também áreas permeáveis que permitam a recarga e exploração dos aquíferos. Aquíferos adequados não são tão comuns no norte do Canadá já que a subsuperfície rasa é maioritariamente composta por rochas cristalinas de baixa permeabilidade ou sedimentos não consolidados de origem glacial que são altamente heterogêneos. A fim de investigar a ocorrência de água subterrânea e contextos geológicos associados em Nunavik (norte de Quebec, Canadá), juntamente como a forma de exploração destes recursos ira evoluir em resposta às alterações climáticas, a compilação e o trabalho de campo foram realizados no entorno das quatro aldeias de Salluit, Kuujjuaq, Umiujaq e Whapmagoostui-Kuujjuarapik. Estas aldeias estão localizadas em diferentes zonas de permafrost, que vão de contínuo a descontínuo, bem como diferentes ambientes geológicos. Foi descoberto que, apesar da presença ubíqua de pergelissolos, aquíferos descongelados podem ser identificados, o que sugere que a água subterrânea pode estar disponível como fonte de água potável para pequenas comunidades. Mudanças climáticas esperadas, com o descongelamento previsto do pergelissolo e aumento na temperatura e precipitação, deve aumentar a disponibilidade de água subterrânea e pode contribuir para uma fonte de água potável mais segura para as comunidades do norte.

Numerical modelling in support of a conceptual model for groundwater flow and geochemical evolution in the southern Outaouais Region, Quebec, Canada

A two-dimensional vertical-section numerical model for groundwater flow and transport using age, tritium and chloride was used to help validate a conceptual model of geochemical evolution within a representative regional-scale hydrogeological system in the Outaouais Region, Quebec, Canada. The flow system includes up to 30 m of Quaternary sediments and marine clays overlying fractured silicate rock of the Canadian Shield. Calibration of the regional flow model using observed piezometric levels and tritium concentrations showed that shallow groundwater flow is dominated by local flow systems limited to 30–40 m depth, 1–5 km long, and with groundwater residence times of 10–50 years. Intermediate systems, on the order of 5–15 km long, are less extensive than initially thought and are characterised by maximum depths of about 100 m and residence times of 200–6000 years. A model-calibrated hydraulic conductivity of 8 × 10−5 m.s−1 was required in the upper 50 m of the fractured bedrock. The active flow zone was inferred to extend to depths of about 100–150 m, with any deeper regional flow essentially negligible. Differences between tritium-based ages and simulated mean residence times were attributed to mixing of groundwater in open boreholes. Concentrations of 4He could be explained by diffusive transport from deeper and older groundwater, exacerbated by sampling. With new insight from the numerical modelling, the conceptual flow model has been updated to now include only a weak component of regional flow combined with significant local- and intermediate-scale flow systems connected to the upper fractured bedrock. The simulated flow system is also consistent with the geochemical evolution of the region, which is dominated by young Ca-HCO3-type waters in the unconfined aquifer and by older Cl− signatures from the remnant Champlain Sea seawater.

Representing Glaciations and Subglacial Processes in Hydrogeological Models: A Numerical Investigation

The specific impact of glacial processes on groundwater flow and solute transport under ice-sheets was determined by means of numerical simulations. Groundwater flow and the transport of δ18O, TDS, and groundwater age were simulated in a generic sedimentary basin during a single glacial event followed by a postglacial period. Results show that simulating subglacial recharge with a fixed flux boundary condition is relevant only for small fluxes, which could be the case under partially wet-based ice-sheets. Glacial loading decreases overpressures, which appear only in thick and low hydraulic diffusivity layers. If subglacial recharge is low, glacial loading can lead to underpressures after the retreat of the ice-sheet. Isostasy reduces considerably the infiltration of meltwater and the groundwater flow rates. Below permafrost, groundwater flow is reduced under the ice-sheet but is enhanced beyond the ice-sheet front. Accounting for salinity-dependent density reduces the infiltration of meltwater at depth. This study shows that each glacial process is potentially relevant in models of subglacial groundwater flow and solute transport. It provides a good basis for building and interpreting such models in the future.

Assessment of paleo-recharge under the Fennoscandian Ice Sheet and its impact on regional groundwater flow in the northern Baltic Artesian Basin using a numerical model

The study investigates the mechanism of glacial meltwater recharge under the Fennosciandian Ice Sheet during the last glacial maximum (LGM) and its impact on regional groundwater flow in the northern Baltic Artesian Basin (BAB) in Estonia and Latvia. The current hypothesis is that a flow reversal occurred in the BAB due to subglacial recharge during the LGM. This hypothesis is supported by an extensive dataset of geochemical and isotopic measurements in the groundwater of northern Estonia, exhibiting significant depletion in δ18O with respect to modern precipitation. To verify the consistency of this hypothesis and better understand groundwater flow dynamics during the LGM period, a numerical model is developed for this area. Two cross-sectional models have been created across the northern BAB, in which groundwater flow and the transport of δ18O have been simulated from the beginning of the LGM to present-day. Several simulations were performed with different subglacial boundary conditions, to investigate the uncertainty related to subglacial recharge of meltwater during the LGM and the subsequent flow reversal in the northern BAB. Several simulations provide a satisfying fit between computed and observed values of δ18O, which means that the hypothesis of subglacial recharge of meltwater is consistent with δ18O distribution. The numerical model suggests that preservation of meltwater in northern Estonia is controlled by confining layers and the proximity to the outcrop area of aquifers, located in the Gulf of Finland. The results also suggest that glacial meltwater has been preserved under the Baltic Sea in the Gulf of Riga.RésuméCette étude s’intéresse au mécanisme de recharge de l’eau de fonte glaciaire sous la calotte glaciaire fennoscandienne pendant le dernier maximum glaciaire (DMG) et son impact sur l’écoulement régional des eaux souterraines dans le nord du Bassin Artésien Balte (BAB) en Estonie et en Lettonie. L’hypothèse actuelle est qu’une inversion de la direction d’écoulement de l’eau souterraine s’est produite dans le BAB en raison de la recharge sous-glaciaire au cours du DMG. Cette hypothèse est étayée par un vaste ensemble de données géochimiques et isotopiques provenant du nord de l’Estonie, montrant une déplétion significative en δ18O dans les eaux souterraines par rapport aux précipitations modernes. Pour vérifier la cohérence de cette hypothèse et mieux comprendre la dynamique de l’écoulement des eaux souterraines au cours de la période du DMG, un modèle numérique est développé. Deux coupes verticales ont été créées dans le nord du BAB, dans lesquels l’écoulement de l’eau souterraine et le transport de δ18O ont été simulés depuis le début du DMG jusqu’à aujourd’hui. Plusieurs simulations ont été effectuées avec différentes conditions aux limites afin d’étudier l’incertitude liée à la recharge sous-glaciaire durant le DMG et l’inversion de l’écoulement subséquent dans le nord du BAB. Parmi ces simulations, de nombreuses produisent des résultats satisfaisants entre les valeurs calculées et observées de δ18O, ce qui signifie que l’hypothèse de recharge sous-glaciaire de l’eau de fonte est cohérente avec la distribution observée de δ18O dans le BAB. Le modèle numérique suggère que la préservation de l’eau de fonte dans le nord de l’Estonie est contrôlée par des couches de confinement et la proximité de la zone d’affleurement des aquifères, située dans le golfe de Finlande. Les résultats suggèrent également que l’eau de fonte glaciaire a été préservée sous la mer Baltique dans le golfe de Riga.ResumenEl estudio investiga el mecanismo de recarga de agua de deshielo glacial bajo la capa de hielo fenoscandiana durante el Último Máximo Glacial (LGM) y su impacto en el flujo regional del agua subterránea en la Cuenca Artesiana del Báltico (BAB) en Estonia y Letonia. La hipótesis actual es que se produjo una reversión del flujo en el BAB debido a la recarga subglacial durante el LGM. Esta hipótesis está respaldada por un extenso conjunto de datos de mediciones geoquímicas e isotópicas en las aguas subterráneas del norte de Estonia, que muestran un agotamiento significativo en δ18O con respecto a la precipitación moderna. Para verificar la consistencia de esta hipótesis y comprender mejor la dinámica del flujo del agua subterránea durante el período LGM, se desarrolla un modelo numérico para esta área. Se han creado dos modelos de corte transversal en el norte de BAB, en los que el flujo de agua subterránea y el transporte de δ18O se han simulado desde el comienzo del LGM hasta la actualidad. Se realizaron varias simulaciones con diferentes condiciones de contorno subglacial, para investigar la incertidumbre relacionada con la recarga subglacial de agua de deshielo durante el LGM y la reversión de flujo posterior en el BAB norteño. Varias simulaciones proporcionan un ajuste satisfactorio entre los valores computados y observados de δ18O lo que significa que la hipótesis de la recarga subglacial de agua de deshielo es consistente con la distribución δ18O. El modelo numérico sugiere que la preservación del agua de deshielo en el norte de Estonia está controlada por las capas de confinamiento y la proximidad al área de afloramiento de los acuíferos, ubicada en el Golfo de Finlandia. Los resultados también sugieren que el agua de deshielo glacial se ha preservado bajo el mar Báltico en el Golfo de Riga.摘要本研究调查了末次冰期芬诺斯堪的纳维亚大冰盖下面冰川融水补给机理及其对爱沙尼亚和立陶宛波罗的海自流盆地北部地下水流的影响。目前的假设是由于末次冰期的亚冰川补给,波罗的海自流盆地出现水流逆转。这个假设得到了爱沙尼亚北部地下水中地球化学和同位素测量结果大量的数据集支持,显示出现代降水中有大量的δ18O消耗。为了证明这个假设的一致性以及更好地了解末次冰期地下水流动力学,针对本地区建立了数值模型。在整个波罗的海自流盆地建立了两个剖面模型,在模型中,模拟了末次冰期到现今地下水流和δ18O的传输。采用不同的亚冰期边界条件进行了几次模拟,以调查与末次冰期间融水亚冰期补给有关的不确定性及随后发生的波罗的海北部水流逆转。几次模拟的结果显示δ18O计算值和观测值非常匹配,这意味着融水亚冰期补给的假设与δ18O分布一致。数值模型表明,爱沙尼亚北部融水的保存受到承压层以及至位于芬兰湾的含水层出露区的距离的控制。结果还表明,冰川融水储存于里加湾波罗的海之下。ResumoO estudo investiga o mecanismo de recarga por derretimento sob o lençol de gelo da Fenoscândia durante o Último Máximo Glacial (UMG) e seu impacto no fluxo regional das águas subterrâneas no norte da Bacia Artesiana do Báltico (BAB) na Estônia e na Letônia. A hipótese atual é que uma reversão de fluxo ocorreu na BAB devido à recarga subglacial durante o UMG. Esta hipótese é embasada por um extenso conjunto de dados de medições geoquímicas e isotópicas nas águas subterrâneas do norte da Estônia, exibindo depleção significativa de δ18O comparada à precipitação moderna. Para verificar a consistência desta hipótese e entender melhor a dinâmica do fluxo das águas subterrâneas durante o período do UMG, um modelo numérico é desenvolvido para esta área. Dois modelos transversais foram criados em todo o norte da BAB, em que o fluxo de águas subterrâneas e o transporte de δ18O foram simulados desde o início do UMG até o presente. Diversas simulações foram realizadas com diferentes condições de contorno subglaciais, para investigar a incerteza relacionada à recarga subglacial de água de degelo durante o UMG e a subsequente reversão de fluxo no norte da BAB. Várias simulações fornecem um ajuste satisfatório entre valores simulados e observados de δ18O, o que significa que a hipótese de recarga subglacial de água de degelo é consistente com a distribuição de δ18O. O modelo numérico sugere que a preservação da água de degelo no norte da Estônia é controlada por camadas confinantes e pela proximidade com a área de afloramento dos aquíferos, localizada no Golfo da Finlândia. Os resultados também sugerem que a água derretida glacial foi preservada sob o Mar Báltico, no Golfo de Riga.

Atmospheric carbon mineralization in an industrial-scale chrysotile mining waste pile

Magnesium-rich minerals that are abundant in ultramafic mining waste have the potential to be used as a safe and permanent sequestration solution for carbon dioxide (CO2). Our understanding of thermo-hydro-chemical regimes that govern this reaction at an industrial scale, however, has remained an important challenge to its widespread implementation. Through a year-long monitoring experiment performed at a 110 Mt chrysotile waste pile, we have documented the existence of two distinct thermo-hydro-chemical regimes that control the ingress of CO2 and the subsequent mineral carbonation of the waste. The experimental results are supported by a coupled free-air/porous media numerical flow and transport model that provides insights into optimization strategies to increase the efficiency of mineral sequestration at an industrial scale. Although functioning passively under less-than-optimal conditions compared to laboratory-scale experiments, the 110 Mt Thetford Mines pile is nevertheless estimated to be sequestering up to 100 tonnes of CO2 per year, with a potential total carbon capture capacity under optimal conditions of 3 Mt. Annually, more than 100 Mt of ultramafic mine waste suitable for mineral carbonation is generated by the global mining industry. Our results show that this waste material could become a safe and permanent carbon sink for diffuse sources of CO2.