Abstract：
The processes leading to high levels of arsenic (As), iron (Fe), and manganese (Mn) in groundwater, in a naturally reducing aquifer at a controlled municipal landfill site, are investigated. The challenge is to distinguish the natural water-rock interaction processes, that allow these substances to dissolve in groundwater, from direct pollution or enhanced dissolution of hydroxides as undesired consequences of the anthropic activities above. Ordinary groundwater monitoring of physical-chemical parameters and inorganic compounds (major and trace elements) was complemented by environmental isotopes of groundwater (tritium, deuterium, oxygen-18 and carbon-13) and dissolved gases (carbon-13 of methane and carbon dioxide and carbon-14 of methane). Pearson/Spearman correlation indices, as well as Principal Component Analysis (PCA), were used to determine the main correlations among variables. The concurrent presence of As, Fe and CH4, as reported in similar anoxic environments, suggests that anaerobic oxidation of methane could drive the reductive dissolution of As-rich Fe(III)(hydro)oxides. Manganese is more sensitive to carbon dioxide, possibly due to a decrease in pH which accelerates the dissolution of Mn-oxides. Finally, we found that tritium and deuterium, which have been used for decades as leachate tracer in groundwater, may be subject to false positives due to the reuse of water recovered from leachate treatment (which has the same isotopic signature of leachate) within the plants, to comply with the requirements of the circular economy. The integration of the environmental isotope analysis into the traditional monitoring approach can effectively support the comprehension of processes. However, this strategy needs to be complemented by a good conceptual hydrogeological model and expert evaluation to avoid misinterpretations.
摘要：
导致高砷（As）的过程，铁(Fe),和地下水中的锰(Mn)，在受控市政垃圾填埋场的自然减少含水层中，正在调查。挑战是区分自然的水-岩相互作用过程，让这些物质溶解在地下水中，由于上述人类活动的不良后果，直接污染或氢氧化物的溶解增强。地下水的环境同位素（tri，氘,氧气18和碳13）和溶解气体（甲烷和二氧化碳的碳13和甲烷的碳14）。皮尔逊/斯皮尔曼相关指数，以及主成分分析(PCA)，用于确定变量之间的主要相关性。As的同时存在，Fe和CH4，在类似的缺氧环境中报告，表明甲烷的厌氧氧化可以驱动富As的Fe（III）（氢）氧化物的还原溶解。锰对二氧化碳更敏感,可能是由于pH降低加速了Mn氧化物的溶解。最后,我们发现了氚和氘,几十年来一直被用作地下水中的渗滤液示踪剂，由于在植物内对从渗滤液处理中回收的水(具有相同的渗滤液同位素特征)的再利用,可能会出现假阳性,符合循环经济的要求。将环境同位素分析集成到传统的监测方法中可以有效地支持对过程的理解。然而,这一战略需要辅之以良好的概念性水文地质模型和专家评估，以避免误解。
