IGAG, National Research Council, SP 35d, 9 - 00010, Montelibretti (RM), Italy.
IGAG, National Research Council, SP 35d, 9 - 00010, Montelibretti (RM), Italy.
J Contam Hydrol. 2024 Apr;263:104342. doi: 10.1016/j.jconhyd.2024.104342. Epub 2024 Apr 15.
A recent diesel spill (dated January 2019 ± 1 month) in a refilling station is investigated by the Radon deficit technique. The primary focus was on quantifying the LNAPL pore saturation as a function of duration of ageing, and on proposing a predictive model for on-site natural attenuation. A biennial monitoring of the local fluctuating shallow aquifer has involved the saturated zone nine times, and the vadose zone only once. Rn background generally measured in external and upstream wells is elaborated further due to the site characteristics, using drilling logs and phreatic oscillations. Notably, this study marks the first application of the Rn deficit method to produce a detailed Rn background mapping throughout the soil depth. Simultaneously, tests are performed on LNAPL surnatant samples to study diesel ageing. In particular, they are focused on temporal variations of LNAPL viscosity (from an initial 3.90 cP to 8.99 cP, measured at 25 °C, after 34 months), and Rn partition coefficient between the pollutant and water (from 47.7 to 80.2, measured at 25 °C, after 14 months). Rn diffusion is also measured in different fluids (0.092 cm s, 1.14 × 10 cm s, and 2.53 × 10 cm s at 25 °C for air, water and LNAPL, respectively) directly. All parameters and equations utilized during this study are introduced, discussing their influence on Radon deficit technique from a theoretical point of view. Experimental findings are used to mitigate the effect of LNAPL ageing and of phreatic oscillations on determination of LNAPL saturation index (S.I.). Finally, S.I. dataset is discussed and elaborated to show the pollutant attenuation across subsurface over time, induced by natural processes primarily. The proposed predictive model for on-site natural attenuation suggests a half-removal time of one year and six months. The significance of such models lies in their capability to assess site-specific reactions to pollutants, thereby enhancing the effectiveness of remediation efforts over time. These experimental findings may offer a novel approach to application of Rn deficit technique and to environmental remediation of persistent organic compounds.
最近一次（2019 年 1 月±1 个月）在加油站发生的柴油泄漏事件，采用氡亏缺技术进行了调查。该技术的主要关注点是量化随着老化时间的 LNAPL 孔隙饱和度，并提出一种现场自然衰减的预测模型。对当地波动浅层含水层的两年一次监测涉及了饱和带九次，而只有一次涉及了非饱和带。由于场地的特点，进一步详细阐述了外部和上游井中普遍测量的Rn 背景，使用了钻井记录和潜水位波动。值得注意的是，这项研究首次应用氡亏缺方法，在整个土壤深度生成了详细的 Rn 背景图。同时，对 LNAPL 表层样品进行了测试，以研究柴油老化。特别是，它们集中在 LNAPL 粘度的时间变化上（从最初的 3.90cP 到 34 个月后的 8.99cP，在 25°C 下测量），以及污染物和水之间的 Rn 分配系数（从 14 个月后的 47.7 到 80.2，在 25°C 下测量）。Rn 扩散也在不同的液体中进行了测量（在 25°C 下，空气、水和 LNAPL 中的扩散系数分别为 0.092cm/s、1.14×10cm/s 和 2.53×10cm/s）。本研究中使用的所有参数和方程均已引入，并从理论角度讨论了它们对氡亏缺技术的影响。实验结果用于减轻 LNAPL 老化和潜水位波动对 LNAPL 饱和度指数（S.I.）确定的影响。最后，讨论和阐述了 S.I.数据集，以显示随着时间的推移，主要是自然过程导致的地下污染物衰减。提出的现场自然衰减预测模型表明，半去除时间为一年零六个月。此类模型的意义在于它们能够评估特定场地对污染物的反应，从而随着时间的推移提高修复效果。这些实验结果可能为氡亏缺技术的应用和持久性有机化合物的环境修复提供一种新方法。
