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Apuan Alps, in north-western Tuscany (Italy), have a very complex geological structure. For this reason karst springs show very different behaviours according to the geological setting of aquifer systems. More than 80 springs are fed by carbonate aquifers; flow rates (Q) range from 10 to 1600 L/s, in average, temperatures range from 8 to 15 °C. Deep and very slow groundwater flow feed some low-thermal springs (20-30 °C). Major karst springs (Q > 100 L/s) are concentrated in two altimetry ranges, one from 200 to 300 m a.s.l. in the seaward side (SW-NW) and a second one from 500 to 600 m a.s.l. on the inner (NE-SE) side of the mountain range. Most of the springs are the final destination of large karst systems developed in meta-dolomite and marbles characterized by a very rapid flow. Some springs have a regular regime and are fed by bathyphreatic systems in metamorphic rocks or by carbonate aquifers with a major contribution of fissured drainage in non-metamorphic rocks. Large physical-chemical variations, both in space and time, are observed as a consequence of lithological heterogeneity, mixing processes and hydrodynamic conditions. Most waters are of the Ca-HCO3 type, but Ca-SO4 and Na-Cl facies are also present. A wide range of electrical conductivity is recorded, with values between 0.1 μS/cm and 10 μS/cm. Significant differences in the average isotopic signature (e.g. δ18O from -5.5 to -8.5‰) of the “base-flow” are registered due to the variability of hydrogeological basins dimension and their distribution in terms of altitude range and side. In some cases, springs with similar chemical features and located close to each other, point out very different isotopes signature, thus highlighting complicated flow path of groundwater. Furthermore, different seasonal evolutions of isotopic signatures are registered.

Water is an essential economic and social resource. It is also finite and vulnerable. For Europe, this generally accepted understanding has been translated into the European and National Directive (2000/60/EC, D.Lgs. 152/2006). This law has led to an increased awareness of the role of the resource and its importance in the socioeconomic, cultural, and political realms. To protect this resource, safeguard zones for drinking water sources must be delineated. In Italy, a drinking water source such as a well or spring is to be protected by means of a three-level safeguard zone: an absolute safety zone close to the source, a respect zone depending on groundwater travel time, and a Protection Zone. The aim of this paper is to describe an integrated methodology used to define the Protection Zone. The work, developed within the framework of a project of the Institute of Geosciences and Earth Resources (IGG-CNR) and funded by the Tuscany Region Administration through “Consorzio Lamma”, focused on the delineation of the Protection Zones for several abstraction points located throughout the regional territory. The proposed methodology for protecting drinking water sources described in this paper integrates geological, hydrogeological, and hydrogeochemical methodologies. The approach includes a definition of the hydrostratigraphy of the aquifer systems, estimates of the water volume, and the quantification of inflows and outflows, as well their interrelationships. By means of this integrated methodology, fifteen Protection Zones were defined; each of these zones was divided in two areas according to their relative importance to supplying a drinking water source. The Protection Zones were further validated by means of hydrogeological and isotopic budget calculations.