Characterization of low-enthalpy geothermal resources and evaluation of potential contaminants
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Characterization of low‑enthalpy geothermal resources and evaluation of potential contaminants Franco Frau1 · Rosa Cidu1 · Giorgio Ghiglieri1 · Guglielmo Angelo Caddeo1 Received: 25 May 2020 / Accepted: 6 August 2020 © Accademia Nazionale dei Lincei 2020
Abstract The use of renewable resources alternative to fossil fuels, thus contributing to the reduction of CO2 emissions, requires the assessment of eventual negative impacts on the environment. This study was devoted to the characterization of lowenthalpy geothermal resources and the potential contamination of geothermal effluents into the aquatic system. Thirty-five groundwater samples were collected in the Campidano (southern Sardinia, Italy), an area showing heat flow anomalies and thermal occurrences. Hydrogeological features inferred by literature were implemented by data acquired at each sampling site. Physical–chemical parameters, major, minor and trace components in groundwater were determined, together with the isotopic composition of the water. Six hydrogeological units with variable permeability were identified. According to geological and hydrogeological modeling, four of the six units appeared hydraulically connected, although not everywhere. The predominant groundwater flow was seen from north-east to south-west. The water temperature was in the range 17–42 °C, pH ranged from 6.7 to 8.6, dissolved oxygen varied from 1 km, would rise up along faults or fractured zones in the granitic–metamorphic Paleozoic basement. Maximum temperatures of 90 °C in the thermal reservoir were estimated by silica and Na–K–Ca geothermometers. The δ18O enrichment shift occurring at high temperature was not observed. Due to high concentrations of some contaminants (e.g. Mo, W, B, F −), geothermal effluents derived from exploitation should be either re-injected or treated before discharge for avoiding the contamination of aquatic systems. Keywords Thermal water · Hydrogeology · Geochemistry · Trace elements · Contaminants · Sardinian resources
1 Introduction Electronic supplementary material The online version of this article (https://doi.org/10.1007/s12210-020-00950-6) contains supplementary material, which is available to authorized users. * Rosa Cidu [email protected] 1
Department of Chemical and Geological Sciences, University of Cagliari, Blocco A, Monserrato, Italy
Due to the increasing demand for renewable and clean energy resources, the geothermal energy is attracting relevant attention worldwide because it can provide energy 24-h-a-day (Li et al. 2018), and can allow significant reduction of C O 2 emissions, as compared to the use of fossil fuel power plants (Yousefi et al. 2019). An estimation of worldwide applications of geothermal energy for
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direct utilization at the end of 2014 was 70,885 MWt, corresponding to a 46.2% increase over the 2010 data (Lund and Boyd 2016). Direct use of geothermal energy—such as heating/cooling of buildings, balneology, aquaculture, heat supply for greenhouse and factories—can be sometimes
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