Geochimica delle acque di Galleria Italia (Abbadia San Salvatore, Siena)

This paper presents and discusses the geochemical and isotopic data obtained on the waters from Galleria Italia (Abbadia San Salvatore) during a discontinuous monitoring carried out from January 2009 to April 2017. The Galleria Italia waters are characterized by a Ca-SO4 composition, slightly acidic pH (â?^6), salinity around 1000 mg/L, high concentrations of Fe, Al and Mn, and they are rich in dissolved CO2. These waters represent the only drainage of the complex system of galleries in the mining area of Abbadia San Salvatore. Therefore, they are of interest for understanding the geochemical processes and mixing between shallow waters with those of probable deep origin. This is due to the fact that after the closure of the mining activity at Abbadia San Salvatore, all accesses to the galleries were shut down for safety reasons. This makes impossible to verify what happens inside the complex water flow system inside the galleries from which the cinnabar was extracted for the production of liquid mercury. In February 2009 and January 2010, large quantities of Al-, Fe- and Mn-rich red-colored waters poured outside Galleria Italia, leaving a reddish-colored deposit characterized by relatively high concentrations of Al, Fe, As and other metals. These flood waves, likely due to intense precipitations event, highlighted the potential hazard of Galleria Italia. The red-colored waters were, indeed, able to reach the Pagliola Creek and then flow into the Paglia River and finally reach the Tiber River, raising particularly important environmental issues. The geochemical data showed that the chemical composition is not only modified in the case of the above events, suggesting that the system is highly dynamic and the geochemical observations only allow to make speculations on what is happening as the meteoric waters enters the various galleries. At present, however, the Galleria Italia waters are the only fluid vehicle that can allow a sort of "mining surveillance" and, in this paper, some geochemical parameters were identified in order to attempt to predict the repetition of events such as those that occurred between 2009 and 2010. As things stand, no interventions inside the galleries can be done and if new flood waves will occur they cannot be controlled.