The CO2-Vadose Project: Dynamics of the natural CO2 in a carbonate vadose zone

► Monitoring strategy of gas phases based on preliminary modelling. ► Natural CO2 dynamics in the carbonate vadose zone. ► Abiotic parameters playing on the variations of CO2 concentration. ► Role of establishing a natural baseline in the monitoring of the CO2 storage sites. The CO2-Vadose Project aims at developing a facility around a cavity in a former underground quarry to perform experimental releases of a CO2 leakage under controlled conditions in order to study its migration along the carbonate vadose zone and to test geochemical and geophysical detection techniques. The paper aims to understand the natural CO2 dynamics in the vadose zone and to establish a natural baseline which differentiates it from an induced CO2 leakage. The location of the sensors is made on the basis of preliminary numerical modelling. The biological production of CO2 is variable in time and space. There are a lot of environmental parameters responsible for changes in CO2 concentrations to measure for understanding the natural CO2 dynamics. The CO2 moves from the soil to the atmosphere primarily by diffusion through air-filled pores. The air–water filled porosity of the soil can have a significant effect on the CO2 movement in the soil. The CO2 moves from the soil to the depth by diffusion through air-filled pores and piston effect. This study shows that it should be possible to detect a leakage with a greater sensitivity by installing the CO2 probes at a depth greater than 2m, where the biogenic CO2 production is reduced.