The former Hg-mining area of Abbadia San Salvatore (Mt. Amiata, central Italy): geochemical investigation vs. remediation activities

Abstract: The mining activity of the Hg(HgS)-rich ore deposits in the Mt. Amiata district started at the end of the 19th century and terminated in 1982 since the demand of mercury dramatically collapsed, mostly because of the elevated toxicity of the various forms into which this element is found in atmosphere, hydrosphere, biosphere and pedosphere. The dismission of mercury basically started after the Minamata event. Among the many Mt. Amiata mining areas, that of Abbadia San Salvatore was the most important center of exploitation of cinnabar and production of liquid mercury. A lot of scientific studies and reports evidenced that the mining and industrial activity has caused a significant impact able to affect all the environmental matrices. To facilitate the activities in the mining concession (ca. 65 ha), the area was divided in 6 units according to the increasing concentration of mercury. Unit 6 is indeed the most critical, since it hosts the Gould furnaces and condenser lines, where gaseous elemental mercury (GEM) reaches concentrations even >50,000 ng/m3 , a multi-layer shallow aquifer strongly affected by the presence of dissolved and suspend mercury (up to 200 µg/L) and contaminated soils where the contents are up 2%, likely deriving from the tailings stored in this area and the old furnaces. In the other units, the monitoring activity allowed to plan specific solutions to reduce the presence of high concentrations of GEM that, in most cases, were >2000 ng/m3 , i.e., well above the threshold limit required by regional authority to consider reclaimed a specific site by GEM, i.e., 300 and 500 ng/m3 in outdoor and indoor environments, respectively. A pilot well is instead planned to verify which procedures are to be adopted to restore the concentration of mercury in the shallow aquifer below 5 µg/L, in order to discharge the Hg-low content waters into surface waters. Two different techniques were satisfactorily tested. As far as the soil matrix is concerned, there is no other option but to impermeabilize it to avoid any contact between the meteoric water and the Hg-rich soils. In this study, we review the geochemical activity carried out in the environmental matrices inside the former mining area of Abbadia San Salvatore and adjacent areas as part of the remediation program aimed at restoring and allocating the area to an archeometallurgical museum and public park as a result of the 2008 agreement between the previous owner of the mining concession (ENI-Agip Division) and the Municipality of Abbadia San Salvatore