Carbon Capture and Storage (CCS) is a valuable climate-mitigation technology, which offers the potential to cost-effectively reduce the emissions associated with the burning of fossil fuels. However, there is a potential risk of a small portion of the stored CO₂ unintentionally migrating from a storage site to a shallow groundwater aquifer which is the final retaining zone for any migrated CO₂ before it escapes to the atmosphere. Hence, it is imperative to identify the physical retention mechanisms of CO₂ within a shallow aquifer. In this study 1.70 × 10² kg of CO₂ and noble gas tracers (He, Ar and Kr) were continuously injected into a groundwater aquifer over 28 days with the aim of identifying the mechanisms and amount of CO₂ retention. Among the tracers, Kr was found to be the earliest indicator of CO₂ migration. The other tracers – He and Ar – arrived later and exhibited diluted signals. The diluted signals were attributed to degassing of the plume mass (1.6 % of CO₂) during the early stages of CO₂ migration. Diffusion accelerated the dilution of the lighter elements at the plume boundaries. Consequently, the clear relation of the noble gases with the CO₂ proved that degassing and mixing primarily control the mass retention of CO₂ in shallow groundwater, and the relative importance of these processes varies along the evolving path of migrating CO₂.

碳捕集与封存（CCS）是一种有价值的减缓气候变化技术，它具有潜在的成本效益，可减少与燃烧化石燃料相关的排放。然而，存在潜在的风险，即一小部分存储的CO ₂意外地从存储位置迁移到浅层地下水蓄水层，这是任何迁移的CO ₂逃逸到大气之前的最终保留区。因此，必须确定浅层含水层中CO ₂的物理滞留机制。在这项研究中1.70×10 ² kg CO ₂并在28天之内将稀有气体示踪剂（He，Ar和Kr）连续注入地下水含水层中，以查明CO ₂保留的机理和数量。在示踪剂中，发现Kr是CO ₂迁移的最早指标。其他示踪剂-He和Ar-后来到达，并显示出稀释的信号。稀释的信号归因于在CO ₂迁移的早期羽状物质（CO _2的1.6％）脱气。扩散加速了烟羽边界处较轻元素的稀释。因此，稀有气体与CO ₂的明确关系证明，脱气和混合主要控制了CO ₂的质量保留。在浅层地下水中，这些过程的相对重要性沿CO ₂迁移路径的变化而变化。