Limestone aquifers constitute important drinking water resources but are vulnerable to groundwater contaminations. They are also known to be often heterogeneous. However, the hydraulic properties of their entire vadose zone and the relationship of these hydraulic properties with their mineralogical and geochemical characteristics remain rarely studied. The hydraulic properties of soft (soil, powdery limestone, and calcareous sand) and hard (limestone rock) materials sampled throughout the entire vadose zone profile of the Beauce limestone aquifer (France) were determined with the multistep outflow method applied using a triaxial system. Physical, mineralogical, and geochemical analysis brought valuable information about factors contributing to the heterogeneity of the hydraulic properties and helped understanding water flow pathways within the vadose zone. The hydraulic properties of the soft materials were strongly related to their physical properties but also to the proportion and the nature of clay minerals. The massive rock presented a few thin microfissures where calcite was replaced by phyllosilicates, thus increasing its water retention capacity. The low hydraulic conductivity of the massive rock could explain the occurrence of perched water tables in the vadose zone. The weathered rock displayed fissures and vugs and was also characterized by the presence of phyllosilicates. The development of a secondary porosity and footprints of water–rock interactions and mass transfers highlighted the transformation of the limestone rock into a more permeable material. This study also pointed out the need to characterize the impact of natural fractures observed at the core scale on the preferential water flow at the field scale.

中文翻译：

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脆弱石灰岩含水层非均质包气带水力特性与物质特征的关系

石灰岩含水层构成重要的饮用水资源，但容易受到地下水污染。众所周知，它们通常是异质的。然而，它们整个包气带的水力特性以及这些水力特性与其矿物学和地球化学特征的关系仍然很少被研究。在 Beauce 石灰岩含水层（法国）的整个包气带剖面中采样的软（土壤、粉状石灰岩和钙质砂）和硬（石灰岩）材料的水力特性是通过使用三轴系统的多步流出法确定的。物理、矿物学、地球化学分析提供了有关导致水力特性异质性的因素的宝贵信息，并有助于了解包气带内的水流路径。软材料的水力特性与其物理性质密切相关，但也与粘土矿物的比例和性质密切相关。块状岩石出现一些细小的微裂缝，其中方解石被页硅酸盐取代，从而增加了其保水能力。块状岩石的低水力传导率可以解释包气带中栖息地下水位的发生。风化的岩石显示出裂缝和孔洞，并且还以存在页硅酸盐为特征。次生孔隙度的发展以及水-岩相互作用和传质的足迹突出了石灰岩向更具渗透性的材料的转变。该研究还指出，需要表征在核心尺度观察到的天然裂缝对现场尺度优先水流的影响。