Guoxiang Liu

Date of Graduation


Document Type



With anthropogenic activities, the concentration of CO2 in the atmosphere has dramatically risen, very likely resulting in global warming and climate change. Capturing and disposing of the produced CO2 in geological formations can mitigate this problem provided that there is no substantial leakage from the subsurface back to atmosphere for hundreds of years. The detection of any CO2 leakage is essential to verify that the sequestration is effective, to initiate corrective actions if leakage is discovered, and to accurately assign storage credits in a "cap and trade" regulatory system. Natural fluctuations in atmospheric pressure are one factor that influences the motion of gas (including fugitive CO2) in the vadose zone. Rising pressure induces a flow of air into the subsurface; falling pressure induces a flow of soil gas into the atmosphere. This research focuses on modeling the flow in the vadose zone in response to barometric pumping and on determining the effectiveness of a scheme to harness this phenomenon to improve the sensitivity of CO2 detection plans by concentrating the flow of soil gas from a large area into a small vent tube. The proposed method requires that some tens of square meters of ground surface be covered by an impermeable membrane. In the center of the covered area is a one way vent valve which opens when the flow is out of the ground. The method has been adapted from a technique that has been used to remediate volatile organic chemical spills. Several scenarios were tested that vary the amplitude and period of barometric pressure variation, soil permeability, water table elevation, leakage rate, and size of plenum area. Effects of wind speed and rainfall were investigated as well. The results show that barometric pumping is significant for CO2 migration in the near-surface of vadose zone. The effects of barometric pumping decrease with depth The results demonstrate that the proposed vent valve system concentrates the leaking CO2 which allows for earlier detection with fewer sensors.