Applying Radon Deficit Technique to study a recent gasoline spill in Rome

Radon deficit technique was applied to monitor a gasoline contamination in the urban area of the city of Rome. The site is a pump station characterized by volcanic and alluvial deposits and a shallow aquifer. Rn deficit was periodically measured in groundwater to monitor the areal and vertical distribution of NAPL (Briganti et al. 2021) in order to assess the distribution of the plume. Rn deficit allows to locate Non-Aqueous Phase Liquid (NAPL) pollution due to preferential solubility of this gas in NAPLs than in water or air contained in soil pores (Schubert, 2015). The study was carried out for a year to value the impact of groundwater fluctuations on data collected. Two different methods were used to measure Rn content in groundwater. The first one consists in inserting PDMS-AC (polydimethylsiloxane and activated carbon) accumulators that selectively absorb 222Rn. They are impermeable to groundwater and humidity occurring in the wells (Voltaggio & Spadoni, 2013). After reaching equilibrium in two weeks, the Rn accumulated by PDMS-AC was counted using high resolution gamma-spectrometry. The second method measures Rn values by Durridge RAD7 every three months, analyzing water sampled in 12 purged wells. The results obtained show the possibility to reconstruct the NAPL plume better by the comparison of the Rn defict data with the changes of the groundwater level during the year. The assessing of the contaminant volumes and the improvement of remediation activities are the most direct outcomes. References Briganti A., Voltaggio M., Tuccimei P. snd Soligo M. (2021). Using 222-Radon as tracer for areal and vertical distribution of hydrocarbon contaminations. In: Abstract Book, Geology without borders- 90° Congresso della Società Geologica Italiana, 14-16 September, Trieste, 175. Doi: 10.3301/ABSGI.2021.03 Schubert M. (2015). Using radon as environmental tracer for the assessment of subsurface Non-Aqueous Phase Liquid (NAPL) contamination - A review. Eur. Phys. J. Spec. Top. 224, 717-730. Doi:10.1140/epjst/e2015-02402-3 Voltaggio M. & Spadoni M. (2013). Determination of 222Rn in water by absorption in polydimethylsiloxane mixed with activated carbon and gamma-ray spectrometry: An example application in the radon budget of Paterno submerged sinkhole (Central Italy). Applied Geochemistry, 34, 65-74. Doi:10.1016/j.apgeochem.2012.12.012