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

• Main Authors: Barbara Nisi, Orlando Vaselli, Franco Tassi, Javier de Elio, Marcelo Ortega, Juan Caballero, Daniele Rappuoli, Luis Felipe Mazadiego
• Format: Article
• Language: English
• Published: Istituto Nazionale di Geofisica e Vulcanologia (INGV) 2014-08-01
• Series: Annals of Geophysics
• Subjects: Central Italy; Amiata volcano; Hydrothermal gases; CO_2; Environmental impact
• Online Access: http://www.annalsofgeophysics.eu/index.php/annals/article/view/6584

<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>₂</span>-rich (&gt;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>₂</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>₂</span> fluxes from both the two wells and soil from an area of about 653,500 m<span>²</span> located between them were measured. The two wells are emitting up to 15,000, 92 and 8 tons y<span>^-1</span> of CO<span>₂</span>, CH<span>₄</span> and H<span>₂</span>S, respectively, while the computed soil CO<span>₂</span> output was estimated at 4,311 ton y<span>^-1</span>. The spatial distribution of the CO<span>₂</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>₂</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>