Geological carbon sequestration (GCS) is necessary to help meet goals for emissions reduction, but groundwater contamination may occur if CO₂ and/or brine were to leak out of deep storage formations into the shallow subsurface. For this study, a natural analogue was investigated: in the Virgin River Basin of SW Utah, water with moderate salinity and high CO₂ concentrations is leaking upwards into shallow aquifers that contain heavy-metal-bearing concretions. The aquifer system is comprised of the Navajo and Kayenta formations, which are pervasive across southern Utah and have been considered as a potential GCS injection unit where they are sufficiently deep. Numerical models of the site were constructed based on measured water chemistry and head distributions from previous studies. Simulations were used to improve understanding of the rate and distribution of the upwelling flow into the aquifers, and to assess the reactive transport processes that may occur if the upwelling fluids were to interact with a zone of iron oxide and other heavy metals, representing the concretions that are common in the area. Various mineralogies were tested, including one in which Pb²⁺ was adsorbed onto ferrihydrite, and another in which it was bound within a solid mixture of litharge (PbO) and hematite (Fe₂O₃). Results indicate that metal mobilization depends strongly on the source-zone composition and that Pb²⁺ transport can be naturally attenuated by gas-phase formation and carbonate-mineral precipitation. These findings could be used to improve risk assessment and mitigation strategies at geological carbon sequestration sites.

Thematic collection: This article is part of the Geoscience for CO₂ storage collection available at: https://www.lyellcollection.org/cc/geoscience-for-co2-storage

地质碳固存（GCS）是帮助实现减排目标所必需的，但是如果CO ₂和/或盐水要从深层储层泄漏到浅层地下，则可能会污染地下水。在这项研究中，研究了一种天然类似物：在西南犹他州的维尔京河流域，盐度适中且CO ₂含量高的水浓缩物向上泄漏到含有重金属的凝结层的浅层含水层中。含水层系统由Navajo和Kayenta地层组成，遍及犹他州南部，被认为是潜在的GCS注入单元，其深度足够大。该站点的数值模型是基于先前研究中测得的水化学和水头分布而构建的。通过模拟可以更好地理解上升流进入含水层的速率和分布，并评估如果上升流流体与氧化铁和其他重金属（代表了固结体）相互作用时可能发生的反应性传输过程。在该地区很常见。测试了各种矿物学，包括其中一种Pb ²⁺将其吸附到三水铁矿上，再将其结合在石渣（PbO）和赤铁矿（Fe ₂ O ₃）的固体混合物中。结果表明，金属的迁移在很大程度上取决于源区的组成，并且Pb ^2+的传输可以通过气相形成和碳酸盐-矿物质沉淀而自然衰减。这些发现可用于改善地质碳固存地点的风险评估和缓解策略。

专题收集：本文是可用于以下位置的Geoscience for CO ₂储存集合的一部分：https://www.lyellcollection.org/cc/geoscience-for-co2-storage