Abstract: In this study, the application of the Well Reversal Technique (WRT) and the impact of reversal time on the efficiency of uranium mining via In-Situ Leaching (ISL) were investigated. A prevalent issue in ISL mineral extraction is the formation of stagnant zones caused by limited access of the lixiviant, which leads to increased operating expenditures. The WRT, which involves altering the function of some wells from injection to production or vice versa, is a potential solution to this problem. The efficiency of WRT is heavily dependent on the well pattern and reversal time. Two commonly used well patterns in ISL are the 9-spot (row arrangement) and 7-spot (hexagonal arrangement). The objective of this study was to determine the optimal reversal time for a 9-spot well pattern through mathematical modeling of hydrodynamic and physico-chemical processes and subsequent economic assessment. A mathematical model of uranium extraction processes was developed using the principles of mass conservation, Darcy’s, and mass action laws. The results obtained for a 9-spot well pattern without reversal, with two reversal options, and a 7-spot scheme were analyzed comparatively. The 7-spot scheme without reversal was found to be the most effective of the options examined. The application of WRT on a 9-spot well pattern allows to enhance production efficiency to a level comparable to that of a 7-spot well pattern. Additionally, the effect of reversal time on recovery was studied based on two well reversal options. The results from calculation revealed that the optimal scenario was when the well reversal is conducted immediately after the time point at which the average concentration of the pregnant solution in the production wells reaches its peak value. The overall efficiency of WRT application was determined through economic calculations of capital (CAPEX) and operating (OPEX) expenditures. Based on economic calculations, it was determined that the utilization of WRT results in a 3–18% increase in mineral production efficiency for a 9-point scheme, depending on the chosen reversal method.

Abstract: CONTEXT Ancient irrigation systems (AISs) have been providing a multitude of ecosystem services to rural farming and urban communities in Asia and Africa, especially in arid and semi-arid climatic areas with low rainfall. Many AISs, however have now been degraded. A systematic analysis of AISs on their typologies, causes of degradation, and their ecosystem services is lacking. OBJECTIVE The objective of this review was to synthesize the knowledge on AISs on their typologies, status and causes of degradation, ecosystem services and functions, and identify gaps in research in Asia and Africa. METHOD A critical review of peer-reviewed journal papers, conference and workshop proceedings, book chapters, grey literature, and country reports was conducted. Qualitative and quantitative information from journal papers were used to conceptualize the typologies and analyze the status and causes of degradation, and ecosystems services and functions provided by the AISs. RESULTS AND CONCLUSION Based on the review, we classified AISs into three groups by source of irrigation water: Rainwater harvesting system (RHS) with small reservoirs, ground water based system, and floodwater based system. The RHSs, which used to receive reliable rainfall and managed by well cohesive social organizations for their maintenance and functioning in past, have now been silting due to extreme rainfall pattern and breakdown of the cohesive organizations in recent decades. In ground water based systems, indiscriminate development of deep tube wells causing siltation of channels has been a major challenge. In floodwater irrigation systems, irregular rainfall in the highlands and the breakage of irrigation structures by destructive floods were the main causes of degradation. Lack of maintenance and increased soil erosion, inadequate skilled manpower, and declining support from the government for repair and maintenance were the main causes of degradation of all AISs. The main ecosystem service provided by all AISs is water for agriculture. In tank- and pond-based systems, fish farming is also practiced. Tank irrigation systems provide various types of provisioning, regulatory, cultural and supporting services, especially in India and Sri Lanka. Ground water based systems provide water for domestic purposes and various cultural services. Floodwater based systems provide water for power generation and wildlife habitat maintenance and help in flood control. SIGNIFICANCE The knowledge generated through the review provide evidence-based information, and help aware governments, private sectors and development agencies for improved policy planning and decision making, and prioritizing the restoration, rehabilitation, and management of various AISs.

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 concentrations of U in natural waters are usually low, being typically less than 4 μg/L in river water, around 3.3 μg/L in open seawater, and usually less than 5 μg/L in groundwater. Higher concentrations can occur in both surface water and groundwater and the range spans some six orders of magnitude, with extremes in the mg/L range. However, such extremes in surface water are rare and linked to localized mineralization or evaporation in alkaline lakes. High concentrations in groundwater, substantially above the WHO provisional guideline value for U in drinking water of 30 μg/L, are associated most strongly with (i) granitic and felsic volcanic aquifers, (ii) continental sandstone aquifers especially in alluvial plains and (iii) areas of U mineralization. High-U groundwater provinces are more common in arid and semi-arid terrains where evaporation is an additional factor involved in concentrating U and other solutes. Examples of granitic and felsic volcanic terrains with documented high U concentrations include several parts of peninsular India, eastern USA, Canada, South Korea, southern Finland, Norway, Switzerland and Burundi. Examples of continental sandstone aquifers include the alluvial plains of the Indo-Gangetic Basin of India and Pakistan, the Central Valley, High Plains, Carson Desert, Española Basin and Edwards-Trinity aquifers of the USA, Datong Basin, China, parts of Iraq and the loess of the Chaco-Pampean Plain, Argentina. Many of these plains host eroded deposits of granitic and felsic volcanic precursors which likely act as primary sources of U. Numerous examples exist of groundwater impacted by U mineralization, often accompanied by mining, including locations in USA, Australia, Brazil, Canada, Portugal, China, Egypt and Germany. These may host high to extreme concentrations of U but are typically of localized extent. The overarching mechanisms of U mobilization in water are now well-established and depend broadly on redox conditions, pH and solute chemistry, which are shaped by the geological conditions outlined above. Uranium is recognized to be mobile in its oxic, U(VI) state, at neutral to alkaline pH (7–9) and is aided by the formation of stable U–CO3(±Ca, Mg) complexes. In such oxic and alkaline conditions, U commonly covaries with other similarly controlled anions and oxyanions such as F, As, V and Mo. Uranium is also mobile at acidic pH (2–4), principally as the uranyl cation UO22+. Mobility in U mineralized areas may therefore occur in neutral to alkaline conditions or in conditions with acid drainage, depending on the local occurrence and capacity for pH buffering by carbonate minerals. In groundwater, mobilization has also been observed in mildly (Mn-) reducing conditions. Uranium is immobile in more strongly (Fe-, SO4-) reducing conditions as it is reduced to U(IV) and is either precipitated as a crystalline or ‘non-crystalline’ form of UO2 or is sorbed to mineral surfaces. A more detailed understanding of U chemistry in the natural environment is challenging because of the large number of complexes formed, the strong binding to oxides and humic substances and their interactions, including ternary oxide-humic-U interactions. Improved quantification of these interactions will require updating of the commonly-used speciation software and databases to include the most recent developments in surface complexation models. Also, given their important role in maintaining low U concentrations in many natural waters, the nature and solubility of the amorphous or non-crystalline forms of UO2 that result from microbial reduction of U(VI) need improved quantification. Even where high-U groundwater exists, percentage exceedances of the WHO guideline value are variable and often small. More rigorous testing programmes to establish usable sources are therefore warranted in such vulnerable aquifers. As drinking-water regulation for U is a relatively recent introduction in many countries (e.g. the European Union), testing is not yet routine or established and data are still relatively limited. Acquisition of more data will establish whether analogous aquifers elsewhere in the world have similar patterns of aqueous U distribution. In the high-U groundwater regions that have been recognized so far, the general absence of evidence for clinical health symptoms is a positive finding and tempers the scale of public health concern, though it also highlights a need for continued investigation.

Abstract: The rapid rate of urban expansion with its associated physical development in recent years conflicts with the urban ecosystem and the services it provides. In most Sub-Saharan African cities, rapid urban expansion often does not conform to existing spatial plans. Physical developments are sometimes carried out in unauthorized areas, contributing to urban floods. The Sub-Saharan African regions’ flood management strategies mainly focus on engineering solutions but have not been fully functional in mitigating urban floods. There is a scarcity of knowledge on how urban flood-related NBS measures can be part of the spatial development in Sub-Saharan African cities for effective flood management. In order to address this gap, this study employed content and text analysis of policy documents and interviews to understand how current spatial and flood mitigation schemes in Accra, Ghana reflect possible NBS applicability and identify possible approaches to integrating NBS into existing planning schemes to prevent urban floods. The study found that Accra’s spatial plans and flood mitigation schemes reflect a possibility of NBS integration. Additionally, the study unveiled techniques for integrating NBS measures and possible implementation barriers and facilitation in the Ghanaian context, which can be linked to combating the challenges that the Ghanaian spatial planning and flood management authorities face. The research, therefore, contributes to knowledge of how NBS can be integrated into spatial planning systems and flood mitigation schemes in Sub-Saharan African regions.