The potential effects of CO2 leakage from CCS sites on soil leachate chemistry

Abstract:

Monitoring of potential leakages and its effect on the soil environment are essential to ensure long term feasibility of the carbon capture and storage (CCS) projects. When high concentration of CO₂ is leaked into the soil system, the soil chemical environment will be changed. We hypothesized that soil pH will decrease sharply in response to the high soil CO₂, but we also expect that it would gradually resume because of the buffering capacity of the soil. The mechanisms of the soil’s buffering capacity could be dissolution of carbonate minerals and organic matter, which could result in production of dissolved organic and inorganic carbon (DOC and DIC) in the soil and leachate. In addition, changes in cation exchange capacity (CEC) induced by high CO₂ can lead to mobilization of base cations due to replacement by H⁺, Al³⁺ and Mn²⁺. This study aims at investigating changes in soil leachate chemical parameters when the soil was injected with 100% CO₂ for four weeks (28 days). Custom made plexiglass pots (30 cm × 20 cm × 20 cm) have been filled with organic rich soil (10 cmm depth) overlaid with mineral soil (15 cm). The pots were injected with 100% CO₂ at a flow rate of 400 cm³ min^-1. Separate control groups were made with no injection and N₂ injection. All the treatments have 9 replicates. The 300 ml of tap water was watered down in the pots three times a week. Leachates collected are analyzed for the soil pH and EC. Leachates are filtered through 0.2 µm membranes for analysis of DOC, DIC, and metal concentrations. After 4 wk of incubation, organic and mineral soils will be destructively sampled and analyzed for total organic and inorganic carbon and CEC. Knowledge of changes in leachate chemistry will allow us to quantify the mobilization of chemical parameters in well-drained soils under the potential influence of high soil CO₂. Furthermore, effect on leaching may give indirect information about consequent changes in groundwater chemistry.