De Simone Gabriele, Lucchetti Carlo, Pompilj Francesca, Galli Gianfranco, Tuccimei Paola, Curatolo Pierpaolo, Giorgi Riccardo
Università"Roma Tre", Dipartimento di Scienze, Largo San Leonardo Murialdo 1, 00146 Roma, Italy.
Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma 1, Via di Vigna Murata 605, 00143, Roma, Italy.
J Environ Radioact. 2017 May;171:138-147. doi: 10.1016/j.jenvrad.2017.02.014. Epub 2017 Feb 27.
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. The values from the two instruments were cross-calibrated through specifically designed laboratory experiments and compared. The results are in agreement within the error range, so the presence of significant NAPL vapors, eventually absorbed by drierite, was ruled out. This is in agreement with low concentrations of soil VOCs. Accordingly, the radon-deficit is ascribed to the residual NAPL in the soil pores, as shown very well also by the obtained maps. Preferential areas of radon-deficit were recognised, as in previous surveys. An average estimate of 21 L (17 Kg) of residual NAPL per cubic meter of terrain is provided on the basis of original calculations, developed from published equations. A comparison with direct determination of total hydrocarbon concentration (23 kg per cubic meter of terrain) is provided.
2016年冬季，在意大利罗马一个受煤油污染的场地进行了一次土壤氡亏缺调查，以评估非饱和带中残留的非水相液体（NAPL）成分造成的污染，并研究蒸汽羽流的作用。事实上，氡在残留的NAPL中比在空气或水中更易溶解，但实验室实验表明，它也优先分配到运输它的NAPL蒸汽中，并且可能影响土壤氡的分布模式。设计了特定的实验配置并应用于一个31个监测站的网格来验证这一假设；将两台RAD7型氡监测仪串联放置，并连接到打入地下80厘米深处的空心探头顶部；第一台仪器直接连接到探头上，接收潮湿的土壤气体，进行计数，然后通过一个干燥剂（无水硫酸钙）圆筒输送到第二台监测仪，该圆筒可捕获水分，最终捕获NAPL挥发性成分以及溶解在蒸汽中的氡。通过专门设计的实验室实验对两台仪器的数据进行交叉校准并比较。结果在误差范围内一致，因此排除了存在大量最终被无水硫酸钙吸收的NAPL蒸汽的可能性。这与土壤挥发性有机化合物（VOCs）的低浓度情况相符。因此，氡亏缺归因于土壤孔隙中的残留NAPL，这也很好地体现在所得到的地图中。与之前的调查一样，识别出了氡亏缺的优先区域。根据已发表的公式进行原始计算，得出每立方米地形中残留NAPL的平均估计量为21升（17千克）。并提供了与直接测定总烃浓度（每立方米地形23千克）的比较结果。
