Abstract: Unconventional hydrocarbon production has become the target of an intensive environmental debate due to the risks it poses to water resources. Fracking, while enabling the extraction of oil and gas from ultra-low permeability reservoirs, also possesses the risk of polluting water systems through failures from hydraulic fracturing and its associated procedures. The need to foster national industrial development with a transitional energy matrix has led Brazil to discuss the environmental suitability before producing its large unconventional reserves. Many studies have highlighted the need for a robust environmental characterization before the development of the unconventional industry. In this sense, multiple environmental isotopes may work as a proxy for identifying water contamination right from the early stages. Environmental isotopes may also be applied to enhance the understanding of the natural geochemical processes intrinsic to a given area. This study presents an environmental isotopes baseline for the groundwater and riverine water systems within the São Francisco Basin, a proven tight gas reservoir in Brazil, in a pre-operational context. δ18O, δ2H, 3H, δ13C, and Δ14C were evaluated in three different seasons in groundwater and surface water samples, along with other auxiliary parameters such as physical-chemical parameters (in situ), major ions, and d-excess. The δ2H and δ18O in surface water shows an upstream → downstream enrichment trend, with some variations suggesting baseflow interactions in the surface water systems. An evaporation line for the study area was defined as δ2H = 4.6903 δ18O + 10.362. δ13C indicates a mutual dissolution of silicates and carbonates in the groundwater system and suggests a group of samples highly related to the recharge areas. Groundwater dating denotes the Serra da Saudade Formation as a modern fractured aquifer with a strong recharge capacity. These findings support stakeholders in environmental monitoring and management of the unconventional gas industry.

Abstract: The quantification of groundwater resources is essential especially in water scarce countries like Namibia. The chloride mass balance (CMB) method and isotopic composition were used in determining groundwater recharge along a precipitation gradient at three sites, namely: Tsumeb (600 mm/a precipitation); Waterberg (450 mm/a precipitation) and Kuzikus/Ebenhaezer (240 mm/a precipitation). Groundwater and rainwater were collected from year 2016–2017. Rainwater was collected monthly while groundwater was collected before, during and after rainy seasons. Rainwater isotopic values for δ18O and δ2H range from −10.70 to 6.10‰ and from −72.7 to 42.1‰ respectively. Groundwater isotopic values for δ18O range from −9.84 to −5.35‰ for Tsumeb; from −10.85 to −8.60‰ for Waterberg and from −8.24 to −1.56‰ for Kuzikus/Ebenhaezer, while that for δ2H range from −65.6 to −46.7‰ for Tsumeb; −69.4 to −61.2‰ for Waterberg and −54.2 to −22.7‰ for Kuzikus/Ebenhaezer. Rainwater scatters along the GMWL. Rainwater collected in January, February and March are more depleted in heavy isotopes than those in November, December, April and May. Waterberg groundwater plots on the GMWL which indicates absence of evaporation. Tsumeb groundwater plots on/close to the GMWL with an exception of groundwater from the karst Lake Otjikoto which is showing evaporation. Groundwater from Kuzikus/Ebenhaezer shows an evaporation effect, probably evaporation occurs during infiltration since it is observed in all sampling seasons. All groundwater from three sites plot in the same area with rainwater depleted in stable isotopic values, which could indicates that recharge only take place during January, February and March. CMB method revealed that Waterberg has the highest recharge rate ranging between 39.1 mm/a and 51.1 mm/a (8.7% – 11.4% of annual precipitation), Tsumeb with rates ranging from 21.1 mm/a to 48.5 mm/a (3.5% – 8.1% of annual precipitation), and lastly Kuzikus/Ebenhaezer from 3.2 mm/a to 17.5 mm/a (1.4% – 7.3% of annual precipitation). High recharge rates in Waterberg could be related to fast infiltration and absence of evaporation as indicated by the isotopic ratios. Differences in recharge rates cannot only be attributed to the precipitation gradient but also to the evaporation rates and the presence of preferential flow paths. Recharge rates estimated for these three sites can be used in managing the savannah aquifers especially at Kuzikus/Ebenhaezer where evaporation effect is observed that one can consider rain harvesting.

Abstract: Naturally occurring uranium geochemical anomalies, representative of the several thousand recognized in the Portuguese section of the Iberian Massif and outcropping in three target areas with a total of a few thousand square metres, were subjected to a detailed study (1:1000 scale) to evaluate the radiological health-risk on the basis of a dose assessment. To reach this goal some radioactive isotopes from the uranium, thorium and potassium radioactive series were measured in 52 samples taken from different environmental compartments: soils, stream sediments, water, foodstuff (vegetables) and air; external radiation was also measured through a square grid of 10×10m, with a total of 336 measurements. The results show that some radioisotopes have high activities in all the environmental compartments as well as a large variability, namely for those of the uranium decay chain, which is a common situation in the regional geological setting. Isotopic disequilibrium is also common and led to an enrichment of several isotopes in the different pathways, as is the case of 226Ra; maximum values of 1.76BqL−1 (water), 986Bqkg−1 (soils) and 18.9Bqkg−1 (in a turnip sample) were measured. On the basis of a realistic scenario combined with the experimental data, the effective dose from exposure to ionizing radiation for two groups of the population (rural and urban) was calculated; the effective dose is variable between 8.0 and 9.5mSvyear−1, which is 3–4 times higher than the world average. Thus, the radiological health-risk for these populations could be significant and the studied uranium anomalies must be taken into account in the assessment of the geochemical background. The estimated effective dose can also be used as typical of the background of the Beiras uranium metalogenetic province and therefore as a “benchmark” in the remediation of the old uranium mining sites.

Abstract: Uranium (U) roll-front deposits constitute a valuable source for an economical extraction by in situ recovery (ISR) mining. Such technology may induce changes in the subsurface microbiota, raising questions about the way their activities could build a functional ecosystem in such extreme environments (i.e.: oligotrophy and high SO4 concentration and salinity). Additionally, more information is needed to dissipate the doubts about the microbial role in the genesis of such U orebodies. A U roll-front deposit hosted in an aquifer driven system (in Zoovch Ovoo, Mongolia), intended for mining by acid ISR, was previously explored and showed to be governed by a complex bacterial diversity, linked to the redox zonation and the geochemical conditions. Here for the first time, transcriptional activities of microorganisms living in such U ore deposits are determined and their metabolic capabilities allocated in the three redox-inherited compartments, naturally defined by the roll-front system. Several genes encoding for crucial metabolic pathways demonstrated a strong biological role controlling the subsurface cycling of many elements including nitrate, sulfate, metals and radionuclides (e.g.: uranium), through oxidation-reduction reactions. Interestingly, the discovered transcriptional behaviour gives important insights into the good microbial adaptation to the geochemical conditions and their active contribution to the stabilization of the U ore deposits. Overall, evidences on the importance of these microbial metabolic activities in the aquifer system are discussed that may clarify the doubts on the microbial role in the genesis of low-temperature U roll-front deposits, along the Zoovch Ovoo mine.