Abstract
Knowledge about the hydrogeological behaviour of heterogeneous low-permeability media is an important tool when designing anthropogenic works (e.g., landfills) that could potentially have negative impacts on the environment and on people’s health. The knowledge about the biogeochemical processes in these media could prevent “false positives” when studying groundwater quality and possible contamination caused by anthropogenic activities. In this research, we firstly refined knowledge about the groundwater flow field at a representative site where the groundwater flows within an evaporite-bearing low-permeability succession. Hydraulic measurements and tritium analyses demonstrated the coexistence of relatively brief to very prolonged groundwater pathways. The groundwater is recharged by local precipitation, as demonstrated by stable isotopes investigations. However, relatively deep groundwater is clearly linked to very high tritium content rainwater precipitated during the 1950s and 1960s. The deuterium content of some groundwater samples showed unusual values, explained by the interactions between the groundwater and certain gases (H2S and CH4), the presences of which are linked to sulfate-reducing bacteria and methanogenic archaea detected within the saturated medium through biomolecular investigations in the shallow organic reach clayey deposits. In a wider, methodological context, the present study demonstrates that interdisciplinary approaches provide better knowledge about the behaviour of heterogeneous low-permeability media and the meaning of each data type.
Highlights
The Mediterranean region was affected by a pervasive “salinity crisis” during the Messinian, when it was progressively restricted and partially isolated from the Atlantic Ocean by a combinationAppl
A recession period was typically observed from late spring to early autumn, whereas recharge was typically observed from early autumn to spring (Figure 7)
The low bulk permeability of the studied medium is in agreement with the findings of other authors who performed pumping tests in similar Messinian successions in Southern Italy
Summary
The Mediterranean region was affected by a pervasive “salinity crisis” during the Messinian, when it was progressively restricted and partially isolated from the Atlantic Ocean by a combinationAppl. Sci. 2020, 10, 8177 of tectonic and glacio-eustatic processes [1,2,3,4] that resulted in the deposition of large volumes of evaporitic sediments [5,6]. The Messinian Sicilian Basins are very important geologic systems for analysing these evaporite successions, in view of their lateral variations and subsequent deformation [7]. Their syn-tectonic evolution is fundamental to reconstructing the timing and geometry of the propagating thrust belt [8,9]. Progressive filling of sub-basins led to the formation of aquifer systems characterised by the coexistence of very low permeability clay successions and evaporitic lenses/horizons [10]. From a hydrochemical point of view, both low- and high-salinity groundwaters may be found associated with the mineralogical features described above
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