This article presents the results of groundwater monitoring over a period of six years and the interpretation of these results by a reactive transport model, following an In Situ Recovery (ISR) test on the Dulaan Uul uranium deposit in Mongolia. An environmental monitoring survey was set up using 17 piezometers, from which it has been possible to describe the changes in the water composition before, during and after the ISR test. The water quality before the start of mining activities rendered it unfit for human consumption. During and after the test, a descent of the saline plume was observed, resulting in a dilution of the injection solutions. After a rapid decrease to pH = 1.13 during the production phase of the ISR test, the pH stabilized at around 4 in the production area and 5.5 below the production cell one year after the end of the test. Uranium and radium were being naturally attenuated. Uranium returned to background concentrations (0.3 mg/L) after two years and the measured ²²⁶Ra concentrations represent no more than 10% of the expected concentrations during production (75 Bq/L). The modeling of the contaminants of concern mobility, namely pH and concentrations of sulfate, uranium and ²²⁶Ra, is based on several key complementary mechanisms: density flow, cation exchange with clay minerals and co-precipitation of ²²⁶Ra in the barite. The modeling results show that the observed plume descent and sulfate dilution can only be predicted if consideration of a high-density flow is included. Similarly, the changes in pH and ²²⁶Ra concentration are only correctly predicted when the cationic exchanges with the clays and the co-precipitation reaction within the barite using the solid solution theory are integrated into the models. Finally, the proper representation of the changes in water composition at the scale of the test requires the use of a sufficiently fine mesh (1 m × 1 m cell) to take into account the spatial variability of hydrogeological (permeability distribution in particular) and geological (reduced, oxidized and mineralized facies distributions) parameters.

本文介绍了对蒙古Dulaan Uul铀矿床进行的原位恢复（ISR）测试后，六年来进行的地下水监测结果，并通过反应输运模型对这些结果进行了解释。使用17个压力计建立了环境监测调查，从中可以描述ISR测试之前，之中和之后水成分的变化。采矿活动开始之前的水质使其不适合人类消费。在测试期间和之后，观察到盐水羽流下降，导致注射液被稀释。在ISR测试的生产阶段中，pH迅速降低至1.13之后，测试结束一年后，pH在生产区域中稳定在大约4，在生产单元以下稳定在5.5。铀和镭自然衰减。两年后铀恢复到本底浓度（0.3 mg / L），并进行了测量²²⁶ Ra浓度不超过生产期间预期浓度（75 Bq / L）的10％。涉及流动性的污染物（即pH值和硫酸盐，铀和²²⁶ Ra的浓度）的建模基于几个关键的互补机制：密度流动，与粘土矿物的阳离子交换以及重晶石中²²⁶ Ra的共沉淀。建模结果表明，只有考虑到高密度流量，才能预测观察到的羽流下降和硫酸盐稀释。同样，pH值和²²⁶的变化仅当使用固溶理论将与粘土的阳离子交换和重晶石内的共沉淀反应整合到模型中时，才能正确预测Ra浓度。最后，在测试规模上正确表示水成分的变化，需要使用足够细的网格（1 m×1 m单元），以考虑水文地质学（特别是渗透率分布）和地质学的空间变异性（还原，氧化和矿化的相分布）参数。