Characterizing the Recharge of Fractured Aquifers: A Case Study in a Flysch Rock Mass of the Northern Apennines (Italy)

12 springs from the northern Apennines of Italy were studied by means of a comprehensive hydrogeological investigation to unravel recharge processes taking place in a highly fractured slab of flysch rock hosting the corresponding aquifers. Several campaigns were carried out during the period 2005–2008 to gather springs’ discharge together with electrical conductivity and temperature data. Water samples were collected and allowed the determination of the major ions (Ca2+, Mg2+, Na+, K+, SO4 2−, HCO3 −, Cl−) and the isotopic content (δ18O). Additionally, groundwater discharge from 3 selected springs was measured continuously using pressure-transducers. Over the same period, reference δ18O values for rainfall and snow-melt water were collected monthly by a rain-gauge. Results highlighted an aquifer-like behavior of this slab of flysch rock. The springs are characterized by a Ca–HCO3 hydro-facies and an increase of groundwater mineralization has been noticed moving toward the base of the slab; the mean discharges are between 0.3 and 0.7 l·s−1 and suffered a marked variability during the year; the total maximum yield is about 155,000 m3 while the total discharge volume is around 320,000 m3·y−1. By processing the δ18O isotope values from springs (mean annual values ranged from −9.67 and −10.42 ‰) and by combining them with rainfalls datasets, results show that the main aliquot of recharge occurs in the winter—spring months and it is principally related to the solid precipitations (snow-melt)