Abstract The southeastern zone of Rome city is located at the northwest periphery of the quiescent Colli Albano volcano. This zone is characterized by the presence of a shallow (depth ~ 45–50 m) gas pressurized aquifer that produces gas blowouts when it is reached by wells. Three gas blowouts occurred in this zone in 2003, 2008 (another one was discovered during the present study) and 2016 and in this paper we describe in detail the latter two. The emitted gas consists mostly of CO2 (>90 vol%) and contains a low but significant quantity of H2S (0.3–0.5 vol%) and it has the highest helium isotopic R/Ra value (1.90) of all Colli Albani natural gas discharges, suggesting its likely magmatic origin. In both the described gas blowouts, dozens of families had to be prudentially evacuated from their houses and the emitted gas killed some animals. We monitored, continuously or by discrete surveys, the soil CO2 flux, the indoor and outdoor air concentration of CO2 and H2S, the environmental parameters and we checked whether the cementation of the gas releasing wells had been effective. In both cases, the upper part of the wells had been partly closed with an inflating packer to avoid free gas dispersion in atmosphere; as a consequence gas diffused laterally from the wells into the permeable surficial soil up to reach the nearest houses creating hazardous indoor conditions, particularly for CO2 in some basements. During the well cementation operations, and in one case because of the packer rupture, gas and nebulized water were freely discharged from the wells into the atmosphere, and high air CO2 and H2S concentrations were found. Fortunately gas was quickly dispersed by strong winds. The positive results obtained in all the studied gas blowouts demonstrate that our applied geochemistry approach represents a model of intervention useful for the assessment of the hazard associated to accidental endogenous gas release. This model is of fundamental importance also to overcome the risk problems created by accidental gas blowout from wells in an urbanized environment, up to the safe return of the people in their evacuated houses.

中文翻译：

---

罗马市（意大利）浅井气井喷出的内源性 CO2 和 H2S 的危险排放

摘要 罗马市东南部地带位于静止的科利阿尔巴诺火山的西北边缘。该区域的特点是存在浅层（深度约 45-50 m）的加压气体含水层，当井到达该含水层时会产生气体井喷。2003 年、2008 年（本研究中发现另一次）和 2016 年在该区发生了 3 次瓦斯井喷，本文对后两次进行了详细描述。排放的气体主要由 CO2 (>90 vol%) 组成，含有少量但大量的 H2S (0.3–0.5 vol%)，并且在所有 Colli Albani 天然气排放中具有最高的氦同位素 R/Ra 值 (1.90) ，表明它可能是岩浆成因。在所描述的两次气体井喷中，数十个家庭不得不谨慎地从他们的房屋中疏散，并且排放的气体杀死了一些动物。我们连续或通过离散调查监测土壤 CO2 通量、室内和室外 CO2 和 H2S 的浓度、环境参数，并检查放气井的固井是否有效。在这两种情况下，井的上部都用充气封隔器部分关闭，以避免游离气体扩散到大气中；因此，气体从井中横向扩散到可渗透的表层土壤中，直至到达最近的房屋，从而造成危险的室内条件，尤其是某些地下室的二氧化碳。在固井作业过程中，有一次由于封隔器破裂，气体和雾化水从井中自由排放到大气中，发现空气中CO2和H2S浓度很高。幸运的是，气体很快被强风吹散了。在所有研究的气体井喷中获得的积极结果表明，我们应用的地球化学方法代表了一种干预模型，可用于评估与意外内源性气体释放相关的危害。该模型对于克服城市化环境中由井中意外气体井喷造成的风险问题，直至人们安全返回已撤离的房屋也至关重要。