Abstract: The pore structure of uranium-bearing sandstone is one of the critical factors that affect the uranium leaching performance. In this article, uranium-bearing sandstone from the Yili Basin, Xinjiang, China, was taken as the research object. The fractal characteristics of the pore structure of the uranium-bearing sandstone were studied using mercury intrusion experiments and fractal theory, and the fractal dimension of the uranium-bearing sandstone was calculated. In addition, the effect of the fractal characteristics of the pore structure of the uranium-bearing sandstone on the uranium leaching kinetics was studied. Then, the kinetics was analyzed using a shrinking nuclear model, and it was determined that the rate of uranium leaching is mainly controlled by the diffusion reaction, and the dissolution rate constant (K) is linearly related to the pore specific surface fractal dimension (DS) and the pore volume fractal dimension (DV). Eventually, fractal kinetic models for predicting the in-situ leaching kinetics were established using the unreacted shrinking core model, and the linear relationship between the fractal dimension of the sample’s pore structure and the dissolution rate during the leaching was fitted.

Abstract: Despite the attention currently given to the potential environmental benefits of large-scale forest planting, there is a shortage of clear observational evidence regarding the effects on river flows, and what there is has often been contradictory or inconclusive. This paper presents three independently conducted paired-catchment forestry studies covering 66 station-years of flow measurements in the UK and Ireland. In each case coniferous evergreen trees were removed from one catchment with minimal soil disturbance while the adjoining control catchment was left unchanged. Trees were removed from 20% – 90% of the three experimental basins. Following woodland removal there was an increase in dry weather baseflow at all sites. Baseflows increased by about 8% after tree removal from a quarter of the Hore basin and by 41% for the near-total cut at Howan. But the changes were more complex for peak flows. Tree harvesting increased the smallest and most frequent peak storm flows, indicating that afforestation would lead to the suppression of such events. This was however restricted to events well below the mean annual flood, indicating that the impact of forests upon the largest and most damaging floods is likely to be limited. Whilst a forest cover can be effective in mitigating small and frequent stormflows it should never be assumed to provide protection against major flood events.

Abstract: Qanat is a passive (unpumped) horizontal well (or a slant well with a very mild inclined angle) that is capable of extracting water from aquifers by gravity. Many qanats are constructed along the radius of the alluvial fan wedge-shaped aquifers. Analytical modeling of such a qanat-aquifer system provides great benefit for quickly screening different designs of qanats and accessing the performance of qanat discharge in the field. The previous analytical modeling of discharge of qanats, however, did not consider the wedge-shaped aquifers. Thus, the goal of this research is to obtain semi-analytical solutions of discharge variations of qanats in alluvial fan aquifers with nearby pumping wells, subjected to areal recharges due to rainfall. The uniform head boundary is considered inside the qanat (because of its enormous permeability in respect to the background aquifer). The influences of the aquifer lateral boundaries on discharge of qanat and its sensitivity to hydraulic and geometric parameters are explored. The influences of the lateral boundaries on the discharge of qanat due to areal recharge and nearby pumping wells discharge are also explored. The results of this study can be utilized for multiple purposes: 1) to predict the discharge of qanat in an alluvial fan aquifer and explore the influences of the areal recharge and nearby pumping well discharge; 2) to estimate the hydraulic parameters of the alluvial fan aquifer depleted by a qanat; 3) to determine the location of the nearby pumping well to minimize its influences on the discharge of a qanat; 4) to calculate the water budgets of aquifers depleted by qanats and pumping wells and replenished by areal recharge among other applications. This paper is an extension to the work presented by Sedghi and Zhan (2020) (which concerns an infinite unconfined aquifer) for an unconfined alluvial fan aquifer setting.

Abstract: Despite numerous studies, there are many knowledge gaps in our understanding of uranium (U) contamination in the alluvial aquifers of Punjab, India. In this study, a large hydrogeochemical dataset was compiled to better understand the major factors controlling the mobility and enrichment of uranium (U) in this groundwater system. The results showed that shallow groundwaters (\textless60 m) are more contaminated with U than from deeper depths (\textgreater60 m). This effect was predominant in the Southwest districts of the Malwa, facing significant risk due to chemical toxicity of U. Groundwaters are mostly oxidizing and alkaline (median pH: 7.25 to 7.33) in nature. Spearman correlation analysis showed that U concentrations are more closely related to total dissolved solids (TDS), salinity, Na, K, HCO3−, NO3− Cl−, and F− in shallow water than deep water, but TDS and salinity remained highly correlated (U-TDS: ρ = 0.5 to 0.6; U-salinity: ρ = 0.5). This correlation suggests that the salt effect due to high competition between ions is the principal cause of U mobilization. This effect is evident when the U level increased with increasing mixed water species (Na-Cl, Mg-Cl, and Na-HCO3). Speciation data showed that the most dominant U species are Ca2UO2(CO3)2− and CaUO2(CO3)3−, which are responsible for the U mobility. Based on the field parameters, TDS along with pH and oxidation-reduction potential (ORP) were better fitted to U concentration above the WHO guideline value (30 μg.L−1), thus this combination could be used as a quick indicator of U contamination. The strong positive correlation of U with F− (ρ = 0.5) in shallow waters indicates that their primary source is geogenic, while anthropogenic factors such as canal irrigation, groundwater table decline, and use of agrochemicals (mainly nitrate fertilizers) as well as climate-related factors i.e., high evaporation under arid/semi-arid climatic conditions, which result in higher redox and TDS/salinity levels, may greatly affect enrichment of U. The geochemical rationale of this study will provide Science-based-policy implications for U health risk assessment in this region and further extrapolate these findings to other arid/semi-arid areas worldwide.

Abstract: The long-lived radio-krypton isotope 81Kr (t1/2 = 2.29 × 105 yr) is an ideal tracer for old groundwater age dating in the range of 105–106 years which goes beyond the reach of radio-carbon (14C) age dating. Analytical breakthrough made over the last two decades in Atom Trap Trace Analysis (ATTA) has enabled the use of this isotope with extremely low abundance (81Kr/Kr = 6 × 10−13) to be used as a practical dating tool for very old groundwater. The International Atomic Energy Agency aims to provide this new isotope tool for better groundwater resource management of Member States and developed a field sampling device to collect dissolved gas samples from groundwater and a system to separate and purify trace amounts of krypton from the gas samples for the ATTA analysis. The design, setup and performances of our sampling and purification systems are described here. Our system can produce a high purity aliquot of about 5 μL of krypton from 5 L of air sample (recovery yield of >90%). The samples made by our system were confirmed to be acceptable for the ATTA analysis.