Potential Pb+2 mobilization, transport, and sequestration in shallow aquifers impacted by multiphase CO2 leakage: a natural analogue study from the Virgin River Basin in Southwest Utah

Geological carbon sequestration (GCS) is necessary to help meet emissions reduction goals, 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 southwest Utah, water with moderate salinity and high CO2 concentrations is leaking upward 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 Pb+2 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 Pb+2 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

Paradise from Cataclysm: Zion Canyon’s Sentinel Landslide

Zion Canyon hosts millions of visitors each year, yet few are aware of the massive prehistoric landslide that played an important role in shaping the iconic landscape. South of the Sand Bench trailhead and bridge, a large hill encroaches on the canyon bottom around which the North Fork Virgin River flows. North of the bridge, Zion Canyon’s fl at bottom stretches into the distance. The hill is part of an enormous rock avalanche deposit known as the Sentinel slide that is nearly 2 miles (3.2 km) long and more than 650 feet (200 m) thick. After failure, the Sentinel rock avalanche dammed the North Fork Virgin River creating a lake (known as Sentinel Lake) which persisted for approximately 700 years (Grater, 1945; Hamilton, 1976; Castleton and others, 2016). Over the course of the lake’s lifetime, sediment settled at the bottom of the lake to create thick deposits of mud, clay, and sand. Sediment eventually fi lled in the canyon bottom behind the landslide dam, and the lake ceased to exist. Th ese sediment layers are still visible today and are responsible for the remarkably fl at fl oor of upper Zion Canyon (Grater, 1945; Hamilton, 2014; Castleton and others, 2016).