Work Package # 5

Infiltrating groundwater removes a small part of the CO₂ produced in the soil and stores this as dissolved carbonate in the subsurface for long periods of time. We will investigate how to enhance and optimize the uptake of CO₂ in aquifers by the infiltrating groundwater as a way of capturing CO₂ from the atmosphere.

Field sites will be established in a forested area and on arable land, both on soils that are free of CaCO3. The plots will be instrumented to measure the production of CO₂ in the soil, CO₂ exchange between soil and atmosphere, the transport of CO₂ through the unsaturated zone and the uptake of CO₂ into the saturated groundwater zone. Chemical interactions between dissolved CO₂ and solids will be studied by monitoring changes in water composition in soil, unsaturated and saturated zones. Temporal and spatial variation in soil moisture will be measured, by high-resolution cross-borehole geophysical methods, to estimate groundwater recharge, and the transport of dissolved carbonate.

Mesocosm experiments will be carried out, in the laboratory, to screen various soil treatments for their potential to increase the production and transport of CO₂ in the soil. Treatments comprise mineral addition of CaCO3, ultramafic rock or ground concrete, and the use of various plants and irrigation practices. The most promising treatments will be tested on the field plots.

Reactive transport of CO₂ and water between soil and saturated groundwater zone will be modelled using the model-code developed in WP2 and the CO₂ production in the soil under the various treatments will be quantified by a mass balance approach based on the main fluxes of carbon.