A demonstration scale CO2 injection trial has been proposed in the Glenhaven area of the Surat Basin for investigating the feasibility of CO2 geological storage. The Precipice Sandstone is the targeted reservoir, with the Evergreen Formation the cap-rock. During CO2 storage, injected CO2 will dissolve into formation water and the resulting acidification induces water-rock reactions. These reactions have the potential for mobilisation of metals associated with the mineral phases. Subsequent water-rock interactions have the potential to limit that mobility. This presentation will describe the data that was used to build a reactive transport model to predict potential impacts to water quality. Drill core from the site was characterised including mineralogy, total metals and extractable metals; in addition, trace metal content in specific minerals was determined by synchrotron X-ray fluorescence microscopy. Based on porosity, permeability and mineralogy, several hydrostratigraphic units were identified in the Precipice Sandstone. The lower Precipice Sandstone is quartz-rich while the upper Precipice Sandstone and Evergreen Formation are more mineralogically diverse with increasing feldspar and clay content, as well as some heavily carbonate cemented sections. All of the hydrostratigraphic units contain traces of sulphides and carbonate cements containing iron, arsenic, lead and a number of additional transition metals. Experiments were performed at reservoir pressure and temperature conditions to react pure CO2 and impure CO2-SO2-NO-O2 with low salinity formation water and the different drill core lithologies. Metals such as lead and iron were released during siderite, calcite, chlorite and sulphide dissolution, while arsenic increased to lower concentrations. In the upper Precipice Sandstone, pH buffering and elevated O2 content resulted in Fe-oxyhydroxide precipitation and incorporation or adsorption of metals and arsenic in secondary precipitates. Geochemical modelling of the experiments accurately reproduced the dissolution, precipitation and adsorption reactions for the different hydrostratigraphic units. Reactive transport modelling showed mobilisation of metals, and if sinks for the released metals were not present, lead and arsenic would have exceeded water quality guidelines within the plume. Accounting for the precipitation of carbonate minerals and Fe-oxyhydroxides plus the associated adsorption resulted in significant attenuation of predicted dissolved concentrations of lead and arsenic.