Hydrogeological Behaviour and Geochemical Features of Waters in Evaporite-Bearing Low-Permeability Successions: A Case Study in Southern Sicily, Italy

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.

Supplement to the paper “Groundwater dynamics between Planinsko Polje and springs of the Ljubljanica River, Slovenia” from Blatnik et al. (2019) published in Acta Carsologica 48/2

The article of Blatnik et al. (2019) “Groundwater dynamics between Planinsko Polje and springs of the Ljubljanica River, Slovenia” published in Acta Carsologica, 48/2 focused on describing the hydrogeological behaviour of the aquifer between Planinsko Polje and the springs of the Ljubljanica River. The authors analysed the effect of different high water events that occurred between January 2015 and May 2018. Interpretations were based on hydrographs obtained by continuous measurements of water level, temperature and specific electric conductivity in selected ponors, springs and water active caves located in the area between Planinsko Polje and the springs of the Ljubljanica River. Through these interpretations, different conceptual hydrological models about the dynamics and directions of the flow in the aquifer have been proposed and tested. A flow connection was proposed between the Hrušica Plateau, estavelles located at the NW border of Planinsko Polje, and caves Gradišnica (W2) and Gašpinova Jama (W3) close to town Logatec. In this supplement, we provide new data recorded during an unusual hydrological event in August 2018. These further support and stress the importance of the connection between the Hrušica Plateau and Logatec region (W2 and W3).

Coastal aquifer hydrodynamics and salinity in response to the tide: case study in Lisbon, Portugal

The variability in dynamics and salinity of the coastal alluvial aquifer on which the city of Lisbon is located was evaluated. The evaluation was based on the analysis of level and groundwater electrical conductivity fluctuations depending on the tide in the Tagus River. The results obtained made it possible to recognize three sectors. First, a littoral sector where the variations in level and salinity are larger on the coast and decrease towards the innermost sections of the alluvial fan. Second, a sector close to the docks where there is greater dynamic and salinity variability than in the coastal sectors, as the excavations of the docks favour the tidal propagation towards the aquifer. And third, a sector located towards the apex of the alluvial fan associated with the dynamics of the stormwater channel. In this sector, the largest periodical water table fluctuations in the aquifer occur, since the freshwater that cannot drain towards the river enters the aquifer at high tide, causing a slight decrease in salinity content. On the basis of these results, conceptual models of hydrogeological behaviour were used to describe the spatial and temporal variations in the hydrodynamic and salinity characteristics of groundwater.

Field experimental cells to assess hydrogeological behaviour of store-and-release covers made with phosphate mine waste

A field investigation was conducted to evaluate the effectiveness of store-and-release (SR) covers made with different phosphate mine wastes in reducing water infiltration (system inclination and surface runoff were neglected) and controlling acid rock drainage (ARD) generation. Four instrumented experimental cells were constructed with different SR layer configurations (two thicknesses and three materials) placed over a capillary break layer. To assess the hydrogeological behaviour of these cover systems, volumetric water content, matric suction, and meteorological monitoring time trends were studied for a period of 1.5 years under actual and extreme conditions typical of an arid climate. Under natural climatic conditions, all net infiltration was released to the atmosphere by the physical process of evaporation (regardless of SR layer thickness and type). Although high surface matric suction (>3000 kPa) decreased the evaporation rate (or release capacity) during the drying period, field tests showed that the studied scenarios limited deep water infiltration even under extreme rainfall events. The release capacity of the SR layer was slightly lower for cover systems made with the finer-grained mine waste (phosphate limestone tailings). This study showed that, for a one-dimensional (1D) condition, the tested phosphate mine wastes have the appropriate hydrogeological properties to be used as components of SR covers under conditions at the Kettara mine site, located near Marrakech, Morocco.