Modelling groundwater processes in a carbonate catchment: a case study from the Madonie area (Northern Sicily)

This study reports on the results of a hydrogeochemical survey carried out in the Madonie area, a carbonate massif located in Palermo Province, Northern Sicily. The large dataset (226 collected sites) is used to highlight the processes controlling the distribution of dissolved chemicals in groundwaters; and, more importantly, to develop a general model (based on reaction-path modelling, and using the EQ3/6 code) of rock–water reactions in a carbonate environment. The investigated groundwater samples have conductivity between 31.7 and 8220 lS/cm; their total dissolved solids (TDS) content is higher near the coast area, where the seawater contribution becomes important. Calcium and HCO 3 excess concentrations in groundwaters, with respect to the meteoric water–seawater mixing line, suggest that water–rock interactions in carbonate aquifers play a major role on water chemistry. Using the dataset, reaction-path modelling is used to simulate the evolution of groundwaters upon interaction with carbonate rocks. Model simulations are performed in time mode, taking into account the mineralogical composition of Madonie carbonate rocks, and the different dissolution rates of each dissolving mineral. The model results of reaction path calculations are in fair agreement with analytical data for natural waters, demonstrating the likelihood of model assumptions, and supporting further the relevance of carbonate dissolution in determining the chemistry of fluids in the investigated area. The developed model is useful for low-temperature weathering of carbonate mineral in general, and is thus likely to apply in a variety of geological contexts.