Molinero Jorge, Samper Javier
E.T.S. Ingenieros de Caminos, Canales y Puertos, Campus de Elviña, Universidad de A Coruña, 15192 A Coruña, Spain.
J Contam Hydrol. 2006 Jan 10;82(3-4):293-318. doi: 10.1016/j.jconhyd.2005.10.008. Epub 2005 Dec 5.
Final disposal of high-level radioactive waste in deep repositories located in fractured granite formations is being considered by several countries. The assessment of the safety of such repositories requires using numerical models of groundwater flow, solute transport and chemical processes. These models are being developed from data and knowledge gained from in situ experiments such as the Redox Zone Experiment carried out at the underground laboratory of Aspö in Sweden. This experiment aimed at evaluating the effects of the construction of the access tunnel on the hydrogeological and hydrochemical conditions of a fracture zone intersected by the tunnel. Most chemical species showed dilution trends except for bicarbonate and sulphate which unexpectedly increased with time. Molinero and Samper [Molinero, J. and Samper, J. Groundwater flow and solute transport in fracture zones: an improved model for a large-scale field experiment at Aspö (Sweden). J. Hydraul. Res., 42, Extra Issue, 157-172] presented a two-dimensional water flow and solute transport finite element model which reproduced measured drawdowns and dilution curves of conservative species. Here we extend their model by using a reactive transport which accounts for aqueous complexation, acid-base, redox processes, dissolution-precipitation of calcite, quartz, hematite and pyrite, and cation exchange between Na+ and Ca2+. The model provides field-scale estimates of cation exchange capacity of the fracture zone and redox potential of groundwater recharge. It serves also to identify the mineral phases controlling the solubility of iron. In addition, the model is useful to test the relevance of several geochemical processes. Model results rule out calcite dissolution as the process causing the increase in bicarbonate concentration and reject the following possible sources of sulphate: (1) pyrite dissolution, (2) leaching of alkaline sulphate-rich waters from a nearby rock landfill and (3) dissolution of iron monosulphides contained in Baltic seafloor sediments. Based on these results, microbially mediated processes are postulated as the most likely hypothesis to explain the measured increase of dissolved bicarbonates and sulphates after tunnel construction.
几个国家正在考虑将高放废物最终处置在位于裂隙花岗岩地层中的深部处置库中。对此类处置库安全性的评估需要使用地下水流、溶质运移和化学过程的数值模型。这些模型是根据从原位实验（如在瑞典阿斯波地下实验室进行的氧化还原带实验）中获得的数据和知识开发的。该实验旨在评估通道建设对被通道穿过的裂隙带水文地质和水化学条件的影响。除了碳酸氢根和硫酸根意外随时间增加外，大多数化学物质呈现稀释趋势。莫利内罗和桑珀[莫利内罗，J.和桑珀，J.裂隙带中的地下水流和溶质运移：瑞典阿斯波大规模现场实验的改进模型。水利研究杂志，42，特刊，157 - 172]提出了一个二维水流和溶质运移有限元模型，该模型再现了保守物质的实测水位下降和稀释曲线。在此，我们通过使用一个考虑了水相络合、酸碱、氧化还原过程、方解石、石英、赤铁矿和黄铁矿的溶解 - 沉淀以及Na⁺和Ca²⁺之间阳离子交换的反应性运移模型对其进行扩展。该模型提供了裂隙带阳离子交换容量和地下水补给氧化还原电位的现场尺度估计。它还用于确定控制铁溶解度的矿物相。此外，该模型有助于检验几个地球化学过程的相关性。模型结果排除了方解石溶解是导致碳酸氢根浓度增加的过程，并否定了以下硫酸根的可能来源：（1）黄铁矿溶解，（2）从附近岩石填埋场淋滤出富含碱性硫酸盐的水，以及（3）波罗的海海底沉积物中所含单硫化铁的溶解。基于这些结果，微生物介导的过程被假定为解释通道建设后溶解的碳酸氢根和硫酸根实测增加的最可能假设。
