ORIGINAL ARTICLE Hydrogeochemical study of an ophiolitic aquifer: a case study of Lago (Southern Italy, Calabria) T. Critelli • G. Vespasiano • C. Apollaro • F. Muto • L. Marini • R. De Rosa Received: 18 March 2014 / Accepted: 11 January 2015 Ó Springer-Verlag Berlin Heidelberg 2015 Abstract A hydrogeochemical survey was carried out in the area of Lago (Calabria region, Southern Italy) and outcropping geological units were classified from the hydrogeological point of view, to explain the evolution of local groundwaters. In addition, reaction path modeling was performed to simulate the evolution of groundwaters upon interaction with local metabasalts, phyllites, and serpentinites, by means of the EQ3/6 software package, version 8.0. Simulations were carried at constant temper- ature of 14.1 °C, which reproduces the average tempera- ture of local groundwaters. Three different simulations have been performed for the average metabasalt fixing the fugacity of CO 2 at either 10 -2.4 bar (mean value), 10 -2.0 bar (mean value ? 1r), or 10 -2.9 bar (mean value - 1r). The simulation for the average serpentinite and phyllite was carried out at the mean value of the fugacity of CO 2 (10 -2.4 bar). All evidences acquired in this study, namely the hydrogeological framework, the chemical analysis of local groundwaters and the results of reaction path mod- eling, consistently point out that groundwater circulation under ordinary hydraulic gradient, primarily occurs in the ophiolitic sub-complex and that dissolution of metabasalts and serpentinites controls the chemical characteristics of the groundwaters from the study area. Keywords Hydrogeology  Water–rock interaction  Hydrochemical modeling  Metamorphic rocks Introduction Water–rock interaction (WRI) has attracted increasing attention in the last 50 years. The interest of the world’s science community on this topic is explained by the fact that processes collectively termed as WRI are omnipresent in our planet and have been (and still are) relevant for geologic evolution. The most important WRI processes are calcite dissolution and precipitation, gypsum dissolution and precipitation, pyrite oxidation and formation of hydrous ferric oxide, silicate mineral dissolution (feldspars, micas, chlorites, amphiboles, olivines, and pyroxenes) and clay mineral formation (kaolinitization, laterization, and illitization), dolomite dissolution and calcite precipitation (dedolomitization), dolomite formation (dolomitization), sulfate reduction and pyrite formation, silica precipitation, evaporation, and cation exchange (Nordstrom 1977). WRI has an important control on the chemistry of nat- ural waters, leading to the formation of numerous hy- drogeochemical types (Shvartsev 2008). In particular, close to the Earth surface, weathering of primary (rock-forming) minerals causes the release of dissolved constituents to natural waters, with rocks acting as the main sources of chemical elements (Guagliardi et al. 2013a, b). However, several minerals (e.g., Al-silicates) dissolve incongruently, in that their dissolution is accom- panied by precipitation of secondary sparingly soluble solid phases, such as clay minerals and oxy-hydroxides (Apollaro et al. 2007b, 2013a; Scarciglia et al. 2008; Perri et al. 2014). Moreover, weathering is chiefly promoted by CO 2 which is converted to hydrogen carbonate. T. Critelli  G. Vespasiano  C. Apollaro (&)  F. Muto  R. De Rosa Department of Biology, Ecology and Earth Sciences (DIBEST), University of Calabria, via Ponte Bucci 4, cubo 15B, 87036 Arcavacata di Rende, CS, Italy e-mail: apollaro@unical.it L. Marini Consultant in Applied Geochemistry, 55049 Viareggio, LU, Italy 123 Environ Earth Sci DOI 10.1007/s12665-015-4061-z