Origin of the gases released from the Acqua Passante and Ermeta wells (Mt. Amiata, central Italy) and possible environmental implications for their closure

Abstract

<div class="page" title="Page 2"><div class="layoutArea"><div class="column"><p>The Mt. Amiata volcano (Tuscany, central Italy) hosts the second largest geothermal field of Italy. Its SW and NE sectors are characterized by the presence of several CO<span><sub>2</sub></span>-rich (>95% by vol.) gas discharges. An intense Hg mining activity had taken place from the 19th century up to the end of the ’70s, particularly close to Abbadia San Salvatore, during which two drillings (Acqua Passante and Ermeta) intercepted a CO<span><sub>2</sub></span>-rich gas fertile horizon. The related gases are emitted in the atmosphere since 1938 and 1959, respectively, causing severe concerns for the local air quality. In this work the results of a geochemical and isotopic survey carried out on these gas emissions from March 2009 to January 2014 are presented. CO<span><sub>2</sub></span> fluxes from both the two wells and soil from an area of about 653,500 m<span><sup>2</sup></span> located between them were measured. The two wells are emitting up to 15,000, 92 and 8 tons y<span><sup>-1</sup></span> of CO<span><sub>2</sub></span>, CH<span><sub>4</sub></span> and H<span><sub>2</sub></span>S, respectively, while the computed soil CO<span><sub>2</sub></span> output was estimated at 4,311 ton y<span><sup>-1</sup></span>. The spatial distribution of the CO<span><sub>2</sub></span> soil flux suggests the presence of preferential patterns, indicating sites of higher permeability. Since the local municipality is evaluating the possibility to plug the Ermeta vent, a temporarily closure should first be carried out to test the possible influence of this operation on the diffuse soil degassing of deep-originated CO<span><sub>2</sub></span> in the surrounding area. This implies that diffuse soil gases should carefully be monitored before proceeding with its definitive closure.</p></div></div></div>

A conceptual model for the Tufiño-Chiles-Cerro Negro (TCCN) geothermal system (Ecuador-Colombia): New insights into geothermal exploration from chemical and isotopic composition of hydrothermal fluids

“…Light hydrocarbons were determined by a Shimadzu 14A gaschromatograph equipped with a 10 m long stainless-steel column (ɸ = 2 mm) packed with Chromosorb PAW 80/100 mesh (coated with 23 % SP1700) and FID detector. Hydrogen sulphide concentrations were determined by analysing sulphate in the soda solution by ionchromatography after oxidation with H 2 O 2 , while acidimetric titration with 0.1 N HCl was used to analyse CO 2 dissolved in the soda solution as CO 3 2− (Capaccioni et al, 2014;Montegrossi et al, 2001;Nisi et al, 2013;Tassi et al, 2010). The analytical errors were < 5 % for the main gas components and < 10 % for minor and trace gas compounds (Capaccioni et al, 2014;Tassi et al, 2010).…”

Analysis of Natural and Power Plant CO2 Emissions in the Mount Amiata (Italy) Volcanic–Geothermal Area Reveals Sustainable Electricity Production at Zero Emissions

“…Given the survey area of 280 km 2 , a mean emission rate of 58 t/d km 2 was estimated based on the total natural soil CO 2 output. An emission rate of 115 t/d km 2 was estimated for the Bagni San Filippo high soil CO 2 flux area (A in Figure 5), while emission rates ranging from 154-200 t/d km 2 [15,35,36] were estimated from localized high soil CO 2 degassing areas only. The lower emission soil CO 2 flux area coincides with the upper slopes of the volcanic edifice, characterized by the presence of a climate forested zone, where an emission rate of 27 t/d km 2 was computed [16].…”

“…Many focused gas emissions are present and are mostly located outside of the volcanic massif. Gases are also discharged by cold springs and Ca-SO 4 -rich thermal springs [15,34] and in correspondence with the tunnels and infrastructures of abandoned Hg mines [35][36][37][38]. Several papers and databases report the position, chemical, and isotopic composition and flux rates of the gas emissions and thermal and cold springs (i.e., [14,15,35,39]).…”