Flow zones in unsaturated soil due to barometric pumping

الملخص EN

The study of gas flow in unsaturated soil is important for better modeling of volatile organic compounds (VOCs) transport.

A gas flow in unsaturated soil can be induced naturally by the atmospheric pressure fluctuation.

Oscillations in barometric pressure are both diurnal, corresponding to daily heating and cooling of the atmosphere, and of longer time periods, resulting from the passage of weather fronts.

Daily variations will average about 4 to 5 mbar while those due to weather front passage can be 25 mbar or more.

A one-dimensional conceptual model was used to investigate the advective gas flow zones in the subsurface induced by the natural atmospheric pressure fluctuation.

From analytical solution, it is clear that the gas phase inside unsaturated zone moves with sinusoidal velocity whose amplitude decrease with depth.

Two zones can be distinguished.

First in which the gas phase can reach the soil surface and continuously mixed with clean air.

The depth "Penetration Depth" of this zone may range from 0.05m to 0.8m.

Second is "Oscillation Zone" in which the air oscillates around its original position but still remains in the soil.

Maximum air displacement toward the upper boundary may reach 0.24m when the depth of the lower impermeable boundary is 10m.

This displacement is more as the lower impermeable boundary is deeper.

The mixing of air above penetration depth with clean air above soil surface and the oscillation of air below penetration depth may have a significant effect on natural VOCs transport and fate in the soil region within