Multidisciplinary subsurface monitoring for a better understanding of Soil Aquifer Treatment capacity applied on coastal operational wastewater treatment plant (Agon-Coutainville, France)

International audienceUnconfined coastal aquifers are potentially subject to both saline intrusion near the seashore and over discharge of treated wastewater in the surficial environment during the tourist season. In Agon-Coutainville (Normandy, France), managed aquifer recharge (MAR) system, combined with Soil Aquifer Treatment (SAT), was integrated as part of the full-scale operational wastewater treatment plant. Such integrated natural/engineered water treatment system ensure the sustainability of the seaside activities (seafood production, beach) and locally supply freshwater for the irrigational needs of the golf course. Concerning the MAR system, the secondary treated wastewater is infiltrated alternatively into three natural reed bed areas before reaching the sand dune aquifer and thus to enhance the quantity of freshwater in the aquifer. Treated wastewater potentially contains various compounds (chemical, virus, pathogen) which can, however, affect the groundwater quality. Nevertheless, some of these compounds are partly removed, during the SAT. To assess performance and efficiency of the integrated system in the natural environment, we have designed and performed an innovating and multidisciplinary monitoring dedicated to 1) spatial evolution of the freshwater generating by the MAR system, 2) mean residence time of water during SAT and 3) potential reactivity occurring during SAT. Spatial field campaigns and tracer tests were conducted by associating classical and innovative approaches including physico-chemical measurements and quantitative analyses, non target analysis for screening organic compounds, ecotoxicological bioassays, online biomonitoring BACTcontrol® system to detect fecal contamination and online system monitoring device dedicated to saline intrusion. Results show that the MAR system provides a freshwater barrier in the aquifer which is seasonally affected by saline intrusion. A part of the aquifer is assessed for freshwater potential production regardless of the natural and anthropogenic recharge. SAT mean residence time is around two weeks that allows SAT reactivity and thus increases quality of the pumped groundwater. This novel subsurface monitoring provides a better understanding of the SAT capacity to enhance the quantity of freshwater and improve its quality

Incorporation of metals into calcite in a deep anoxic granite aquifer

Understanding metal scavenging by calcite in deep aquifers in granite is of importance for deciphering and modeling hydrochemical fluctuations and water–rock interaction in the upper crust and for retention mechanisms associated with underground repositories for toxic wastes. Metal scavenging into calcite has generally been established in the laboratory or in natural environments that cannot be unreservedly applied to conditions in deep crystalline rocks, an environment of broad interest for nuclear waste repositories. Here, we report a microanalytical study of calcite precipitated over a period of 17 years from anoxic, low-temperature (14 °C), neutral (pH: 7.4–7.7), and brackish (Cl: 1700–7100 mg/L) groundwater flowing in fractures at >400 m depth in granite rock. This enabled assessment of the trace metal uptake by calcite under these deep-seated conditions. Aquatic speciation modeling was carried out to assess influence of metal complexation on the partitioning into calcite. The resulting environment-specific partition coefficients were for several divalent ions in line with values obtained in controlled laboratory experiments, whereas for several other ions they differed substantially. High absolute uptake of rare earth elements and U(IV) suggests that coprecipitation into calcite can be an important sink for these metals and analogousactinides in the vicinity of geological repositories

Simulation of the impact of SO2 co-injected with CO2 on the reservoir- rock reactivity

International audienceAn important aspect in CO2 storage in geological media is the quality requirements put on the gases to be stored in terms of risk management. This study investigates and compares, through reactive transport modelling, the potential short-term (5y) reactivity of CO2 gas streams ˗ pure or containing ancillary gaseous compounds (SO2 : 0˗1.5% Wt) ˗ with the reservoir-rock of a limestone aquifer at 75°C. The modelling approach simulates the co-injection of CO2-(SO2) gases, through injection of CO2 (under supercritical form) and simultaneous injection of a SO2 (as a dissolved species solution) rich brine with TOUGHREACT [1]. The numerical simulation results indicate the development of an acidification front (pH < 5) following the progression of the gas migration in the reservoir. After an injection period of 5 years, the acidified zone extends up to 500 m from the injection well, independently of the impurity percentage of the CO2 gas stream. In close proximity of the injection well (0-10m), substantial calcite dissolution, together with albite and K-feldspar dissolution, result in a drastic increase of the permeability (1 order of magnitude) and porosity (x2). When CO2 is injected alone, anhydrite also precipitates in this reservoir zone. Significant calcite dissolution is also predicted in the zone 50-100m ˗ a highly reactive zone˗ resulting in a local permeability and porosity increase. Because of its high solubility, SO2 mainly remains in the brine (SO2 content lower in the CO2-rich phase than in the injected gas stream), decreasing its pH/Eh (relatively to pure CO2). Dissolved SO2 is lowly reactive with reservoir minerals

Diverse fractionation patterns of Rare Earth Elements in deep fracture groundwater in the Baltic Shield – Progress from utilisation of Diffusive Gradients in Thin-films (DGT) at the Äspö Hard Rock Laboratory

International audienc

Cerium Sequestration in Fractures in the Upper Kilometer of Granitoids, SE, Sweden

This study seeks to define geochemical processes governing the accumulation and sequestration of Ce in granitoidic fractures down to &gt;700 m depth, revealing past intrusions of oxygenated waters. The fracture coatings (secondary mineral precipitates in open fractures) gathered from the study area (Laxemar, SE Sweden) are characterized by high levels of Ce (Fig. 1b) compared to host rock cocentration (average: 86 ppm, n=65) and show a striking feature of distinct positive Ce anomalies (CeWN*=1.21-3.95, n=8) in the uppermost 20 m of the bedrock (Fig. 1a). Cerium and Mn X-ray absorption spectroscopy (XAS) of selected fracture coatings, together with existing data (e.g. fracture mineralogy and groundwater chemistry), indicate that: (1) Ce(IV) occurs down to c.a. 70 m depth and is exclusively associated with Mn oxides which occur as todorokite and triclinic birnessite as suggested by Mn EXAFS spectra; (2) Since Mn is largely speciated as Mn2+ in the present bedrock groundwaters, the Ce(IV)-bearing Mn oxides most probably resulted from oxidative weathering of wall rock and fracture coating minerals when oxygenated waters intruded into the bedrock (down to several hundred meters depth) during deglacation events (&gt;13000 BP); (3) Unlike other samples, clear XAS features of a poorly-crystalline hexagonalbirnessite-like phase and larger proportion of aqueous Mn2+ were observed in the sample with strikingly positive Ce anomaly (CeWN* = 3.95) (Fig. 1b) at the depth of 0.87 m, suggesting an ongoing dynamic accumulatinon of Ce(IV), i.e. dissolution and reprecipiation of Mn oxides while Ce(IV)- enriched residue largely remained

Cerium Sequestration in Fractures in the Upper Kilometer of Granitoids, SE, Sweden

This study seeks to define geochemical processes governing the accumulation and sequestration of Ce in granitoidic fractures down to &gt;700 m depth, revealing past intrusions of oxygenated waters. The fracture coatings (secondary mineral precipitates in open fractures) gathered from the study area (Laxemar, SE Sweden) are characterized by high levels of Ce (Fig. 1b) compared to host rock cocentration (average: 86 ppm, n=65) and show a striking feature of distinct positive Ce anomalies (CeWN*=1.21-3.95, n=8) in the uppermost 20 m of the bedrock (Fig. 1a). Cerium and Mn X-ray absorption spectroscopy (XAS) of selected fracture coatings, together with existing data (e.g. fracture mineralogy and groundwater chemistry), indicate that: (1) Ce(IV) occurs down to c.a. 70 m depth and is exclusively associated with Mn oxides which occur as todorokite and triclinic birnessite as suggested by Mn EXAFS spectra; (2) Since Mn is largely speciated as Mn2+ in the present bedrock groundwaters, the Ce(IV)-bearing Mn oxides most probably resulted from oxidative weathering of wall rock and fracture coating minerals when oxygenated waters intruded into the bedrock (down to several hundred meters depth) during deglacation events (&gt;13000 BP); (3) Unlike other samples, clear XAS features of a poorly-crystalline hexagonalbirnessite-like phase and larger proportion of aqueous Mn2+ were observed in the sample with strikingly positive Ce anomaly (CeWN* = 3.95) (Fig. 1b) at the depth of 0.87 m, suggesting an ongoing dynamic accumulatinon of Ce(IV), i.e. dissolution and reprecipiation of Mn oxides while Ce(IV)- enriched residue largely remained

Facilitating the deployment of CO2 storage by exploiting synergies with geothermal energy

International audienceGeological CO2 storage should play a crucial part in the net zero emissions by 2050 target, as suggested by recent reports from the IEA or the IPCC. It contributes first by decarbonising high-emission sector by storing CO2 emitted during energy and industrial production. It is also a key aspect for achieving technological CDR (Carbon Dioxide Removal). Methods such as BECCS (BioEnergy with Carbon Capture and Storage) and DACCS (Direct Air Capture with Carbon Storage) rely on geological storage. Yet, the deployment of full-scale storage projects to date has not reached an adequate pace of change in order to contribute significantly to reach the net zero objective. Many factors can explain this observation: difficulty of a reliable business case (economic barrier), lack of political support and awareness (political barrier), concerns over public opposition (societal barrier), knowledge of favourable subsurface conditions (geological barriers), etc. In some ways, CO2-EOR, which is a synergy between CO2 storage and hydrocarbon production, has played a role in helping the deployment of CO2 storage, by providing business case and demonstrating the viability for parts of the CCUS chain. However, CO2-EOR also often encounter negative appreciation for its direct connection to hydrocarbon production, and contribution to CO2 emissions. In this paper, we focus on the synergy between CO2 storage and geothermal energy. Several authors have proposed such synergies. Tillner et al. (2013) envisage the coexistence of CO2 injection and a geothermal doublet. Buscheck et al. (2016, 2017) propose to exploit the thermal (and physical) energy of brine produced when injecting CO2. Kervévan et al. (2017) propose to dissolve CO2 in the geothermal brine and to store the resulting fluid in saline aquifer by using a geothermal doublet. Pure CO2 has also been proposed as a geothermal working fluid instead of water, notably due to favourable thermodynamic properties. CO2 based geothermal systems encompass two concepts: i. CO2-EGS (Enhanced or Engineered Geothermal Systems) first proposed by Brown (2000); ii. CO2 Plume Geothermal (CPG) in hydrothermal reservoirs introduced by Randolph and Saar (2011). This study aims to propose a structured approach to evaluate to which extent a combination of CO2 storage and geothermal energy would facilitate the deployment of CO2 storage. It will compare the global performance of the various options for combining CO2 storage and geothermal energy with the expected performance of a conventional CO2 storage project in saline aquifer. The proposed approach is based on BRGM's new method for performance assessment of subsurface uses. The method defines "performance" as any required conditions that would contribute to meet the objectives of the project. For a CO2 storage project, performance is primarily measured in terms of the quantity of CO2 stored in the targeted reservoi

Population genetics of An. arabiensis in Senegal

Variation at nine microsatellite loci was investigated to understand how #Anopheles arabiensis$populations survive the dry season in the sahelian region of Senegal. Low estimates of genetic differentiation (FST equal to 0.012, RST equal to 0.009) between two populations, 250km apart, suggested extensive gene flow across this distance. Despite extreme seasonal fluctuation in abundance with dry season minima in which mosquitoes virtually disappeared, allele frequencies remained stable over time in the village of Barkedji from August 1994 to December 1997 (including four rainy seasons and three dry seasons). The effective population size (Ne) was estimated to be 601 with 95$ maintains large permanent deme spread out over large area. (Résumé d'auteur