Soil radon survey to assess NAPL contamination from an ancient spill. Do kerosene vapors affect radon partition ?

A soil radon-deficit survey was carried out in a site polluted with kerosene (Rome, Italy) in winter 2016 to assess the contamination due to the NAPL residual component in the vadose zone and to investigate the role of the vapor plume. Radon is indeed more soluble in the residual NAPL than in air or water, but laboratory experiments demonstrated that it is also preferentially partitioned in the NAPL vapors that transport it and may influence soil radon distribution patterns. Specific experimental configurations were designed and applied to a 31-station grid to test this hypothesis; two RAD7 radon monitors were placed in-series and connected to the top of a hollow probe driven up to 80-cm depth; the first instrument was directly attached to the probe and received humid soil gas, which was counted and then conveyed to the second monitor through a desiccant (drierite) cylinder capturing moisture and eventually the NAPL volatile component plus the radon dissolved in vapors.

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.