Carlo Lucchetti

Tracing NAPLs contamination in the vadose zone using soil radon

Frequent spills of Non-Aqueous Phase Liquids (NAPLs), such as petroleum products or chlorinated solvents, occur all around the world contaminating the soil vadose zone or the aquifer. In order to trace the presence of these substances, radon concentration in soil gas can be employed because of its high solubility in NAPLs. Radon available in the soil pores accumulates in the NAPLs producing a local decrease of its concentration in the vicinity of contaminated areas. Thus radon minima in the vadose zone can be used to localize NAPL plumes indirectly.The suitability of this method is here checked by laboratory simulation of a gasoline spill within a known volume of soil. Radon activity concentration strongly drops down right after the injection of gasoline and progressively increases in the following days. This trend is compared with data from a simultaneous experiment carried out on a volume of the same soil, not contaminated by NAPL.Finally, an example of field measurements within a site affected by NAPL contamination is documented. Mapping of soil radon concentration at 80 cm depth shows an area where radon deficit is evident. This region is aligned along the directions of the groundwater flow induced by pumping for safety operation of the plant. Radon negative anomalies are not due to low gas permeability and are not correlated with soil CO2. The comparison of soil gas data with those from nearby background areas confirm the soundness of premises.

Laboratory simulation of recent NAPL spills to investigate radon partition among NAPL vapours and soil air

Soil radon is employed to trace residual NAPL (Non-Aqueous Phase Liquid) contamination because it is very soluble in these substances and is strongly depleted over polluted volumes of the subsoil. The solubility of radon into NAPL vapors, generally poorly considered, is investigated here, either as growth of radon exhalation from a material contaminated with increasing volumes of kerosene, or as radon partition between liquid kerosene, water and total air, considered ad the sum of kerosene vapors plus air.

Anatomy of a fumarolic system inferred from a multiphysics approach

Fumaroles are a common manifestation of volcanic activity that are associated with large emissions of gases into the atmosphere. These gases originate from the magma, and they can provide indirect and unique insights into magmatic processes. Therefore, they are extensively used to monitor and forecast eruptive activity. During their ascent, the magmatic gases interact with the rock and hydrothermal fluids, which modify their geochemical compositions. These interactions can complicate our understanding of the real volcanic dynamics and remain poorly considered. Here, we present the first complete imagery of a fumarolic plumbing system using three-dimensional electrical resistivity tomography and new acoustic noise localization. We delineate a gas reservoir that feeds the fumaroles through distinct channels. Based on this geometry, a thermodynamic model reveals that near-surface mixing between gas and condensed steam explains the distinct geochemical compositions of fumaroles that originate from the same source. Such modeling of fluid interactions will allow for the simulation of dynamic processes of magmatic degassing, which is crucial to the monitoring of volcanic unrest.