title: Hydrothermal gases in a shallow aquifer at Mt. Amiata, Italy: insights from stable isotopes and geochemical modelling.
abstract: We investigate the interaction between hydrothermal gases and groundwater in a major aquifer exploited for potable supply in the geothermal-volcanic area of Mt. Amiata, Central Italy. Two springs and two wells located on different sides of the volcanic edifice have been repeatedly sampled over the last 11 years. More than 160 chemical analyses and 10 isotopic analyses of total dissolved carbon (δ(13)C - total dissolved inorganic carbon (TDIC) = -15.9 to -7.8 ‰ vs. V-PDB) and sulphate (δ(34)S-SO4 = -6.9 to 5.1 ‰ vs. V-CDT) have been processed with geochemical modelling techniques. Best-fitting conditions between analytical data and model outputs have been achieved by numerical optimization, allowing for a quantitative description of gas-water-rock interactions occurring in this aquifer. Numerical calculations support a conceptual model that considers water-rock interactions to occur in the volcanic aquifer after inflow of deep-seated gases (CO2(g) and H2S(g)), and total conversion of H2S(g) to SO4, in the absence of mixing with geothermal waters from reservoirs currently exploited for electricity generation.
authors.affiliation: a Consiglio Nazionale delle Ricerche (CNR) - Istituto di Geoscienze e Georisorse (IGG), Area della Ricerca del CNR , Pisa , Italy.
authors.forename: Lisa
authors.initials: L
authors.lastname: Pierotti
authors.affiliation: a Consiglio Nazionale delle Ricerche (CNR) - Istituto di Geoscienze e Georisorse (IGG), Area della Ricerca del CNR , Pisa , Italy.
authors.forename: Gianni
authors.initials: G
authors.lastname: Cortecci
authors.affiliation: a Consiglio Nazionale delle Ricerche (CNR) - Istituto di Geoscienze e Georisorse (IGG), Area della Ricerca del CNR , Pisa , Italy.
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Gherardi
mesh_terms: D002247:Carbon Isotopes / Q000032:analysis; D004784:Environmental Monitoring; D005740:Gases / Q000032:analysis*; D045482:Hot Springs / Q000032:analysis* / Q000737:chemistry; D007558:Italy; D008962:Models, Theoretical
chemical_list: D002247:Carbon Isotopes; D005740:Gases
keywords: Carbon-13; Italy; Mt.Amiata volcano; gas–water–rock interaction; shallow aquifer; sulphur-34