Abstract
Chlorinated hydrocarbons (CHC) are the volatile substances and exist in the unsaturated zone as volatilized, dissolved CHC and dense non-aqueous phase liquid (DNAPL). Recently, a vacuum extraction method is enlisted as the best recovery method for the unsaturated soil contaminated by CHC. In order to make an effective in situ remediation by this method, it is indispensable to understand the mechanism of transport of CHC gas by advection, dispersion and volatilization as well as the transport through water phase in unsaturated and saturated zones. In this paper, the effect of vacuuming out of soil gas in the field has been evaluated by the numerical simulation. In the numerical model, the cylindrical flow equations and transport equations in water and gas phases and a two layer model for volatilization and dissolution are developed, successfully. As a result it is noticed that the magnitude of designed pressure drop due to pumping, which induces the advection towards the vacuuming well, should be sufficiently enough compared with the dispersion towards the radial direction due to the CHC gas concentration gradient in order to achieve the remediation effectively. Therefore, the vacuuming pressure needs to be determined in terms of the fluxes of advection and dispersion. Besides, the decreasing rate of CHC gas concentration decelerates due to the increasing volatilization from the water phase at the region where the CHC gas concentration decreases by pumping.
