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: The sandstone-hosted uranium mineralization areas in the Sanzhao Sag of the northern Songliao Basin have been newly identified. The target stratum is the Upper Cretaceous Sifangtai Formation and the uranium mineralization mainly occurs in the bottom of Sifangtai Formation, corresponding to channel sand bodies in meandering river system, characterized by medium to fine-grained sandstone. This study proposes the uranium metallogenic model through petrographic observation, whole rock geochemistry, mineralogical study of uranium occurrence form (SEM), organic matter rock–eval pyrolysis analysis (REP) and in-situ sulfur isotope determination of different generations of pyrite by LA-MC-ICP-MS. Compared with the sandstones collected in barren reduction and oxidization zones, the mineralized sandstones show obvious increase in the contents of TOC, total sulfur, Y and U. Petrographic observations indicate that organic matters are mainly inherited from land plants. REP data display that the organic matter (OM) disseminated in the sandstone has very low hydrogen index (HI) from around 0 to 21 mg HC/g TOC and varied oxygen index (OI) from 44 to 115 mg CO2/g TOC, corresponding to Type Ⅳ kerogen (degraded kerogen). There are two types of coffinite with different grain size, micro-particles (μm-sized) and large aggregates (generally up to 100 μm) respectively. The coffinite micro spherules exhibit short rod-like or worm-like morphology occurring in clay matrix and cell cavities in degradofusinite or around subidiomorphic-idiomorphic pyrite. The coarse-grained coffinite contains other mineral facies (e.g. pyrite, quartz) and some of large coffinite aggregates display thrombolite-type microbial structures. The irregular pyrite relict particles in coarse-grained colloidal coffinite have light sulfur isotope compositions characterized by δ34S values from –39.96‰ to –49.89‰. The δ34S values of colloidal pyrite in replacement of OM or of the sub-idiomorphic FeS2 cement filling in the cavities of OM range from –52.77‰ to –13.88‰. Some of sub-idiomorphic pyrite cement and idiomorphic crystal have the heavier signature from – 27.06‰ to + 14.23‰. The light sulfur isotope signature suggests that the sulfur originates from bacterial sulfate reduction (BSR). The OM replacement by pyrite and the highest OI values recorded by REP in uranium mineralized samples are lines of evidence of biodegradation. Bacteria use the organic matter as food source and produce isotopically light reduced sulfur species. Oxygenated uranium-bearing waters infiltrated through the denudated windows at Daqing placanticline into the porous reduced sandstones deposited in the Sanzhao Sag. Uranium was indirectly reduced by BSR-derived iron disulfides or directly reduced by sulfate-reducing bacteria.

Abstract: The recharge of stream water below the baseflow water table can mobilize groundwater contaminants, particularly redox-sensitive and sorptive metals such as uranium. However, in-situ tracer experiments that simulate the recharge of stream water to uranium-contaminated groundwater are lacking, thus limiting the understanding of the potential mechanisms that control the mobility of uranium at the field scale. In this study, a field tracer test was conducted by injecting 100 gal (379 l) of oxic river water into a nearby suboxic and uranium-contaminated aquifer. The traced river water was monitored for 18 days in the single injection well and in the twelve surrounding observation wells. Mobilization of uranium from the solid to the aqueous phase was not observed during the tracer test despite its pre-test presence being confirmed on the aquifer sediments from lab-based acid leaching. However, strong evidence of oxidative immobilization of iron and manganese was observed during the tracer test and suggested that immobile uranium was likely in its oxidized state as U(VI) on the aquifer sediments; these observations ruled out oxidation of U(IV) to U(VI) as a potential mobilization mechanism. Therefore, desorption of U(VI) appeared to be the predominant potential mobilization mechanism, yet it was clearly not solely dependent on concentration as evident when considering that uranium-poor river water (\textless0.015 mg/L) was recharged to uranium-rich groundwater (≈1 mg/L). It was possible that uranium desorption was limited by the relatively higher pH and lower alkalinity of the river water as compared to the groundwater; both factors favor immobilization. However, it was likely that the immobile uranium was associated with a mineral phase, as opposed to a sorbed phase, thus desorption may not have been possible. The results of this field tracer study successfully ruled out two common mobilization mechanisms of uranium: (1) oxidative dissolution and (2) concentration-dependent desorption and ruled in the importance of advection, dispersion, and the mineral phase of uranium.

Abstract: The safety of uranium tailings pond is closely related to social stability and economic development, so it is necessary to improve the emergency management of uranium tailings pond to ensure its safety by adjusting the emergency plan. The Interpretive Structural Model (ISM) is used to analyze the structural relationship between the main risk factors leading to the occurrence of emergencies. The results show that attention should be paid to the risk factors originating from humans and infrastructures, and effective management measures should be adopted in the process of emergency management, for example, people build tighter employee access system, clarify the responsibilities of employees at all levels, and improve monitoring and organizational means. According to the results of ISM analysis, a structural risk control system can be constructed, and a defensive barrier that can effectively block the risk coupling transmission can be designed to prevent the risk from being transformed into an event. For other risks, system resilience management should be strengthened to respond to risks. The process is set as emergency response and accident response. Different management objects use different management methods to make emergency management work efficiently.

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.