Soil venting project

The problem is described by a 2D, time-dependent, multiphase porous media flow model. Sorption of the pollutants to the soil surface is included. The SPRINT2D software is used as a basis for the simulator, with a new Galerkin Finite Element module incorporating an upstream stabilisation technique. Automatic spatial mesh adaptivity is shown to provide significant efficiency and accuracy benefits.

A full report on the first phase of this project is available as a School of Computing Research Report.

The figure below is a schematic representation of the problem. The solution domain is one half of the vadose zone -- the unsaturated region between the surface of the ground and the water table -- with the vent lying on an axis of symmetry. In the 2D problem solved thus far the vent is represented as a point source. For the initial conditions it is assumed that the spill has already occurred and that oil (and water) exist at residual saturations. All components are assumed to have partitioned between the phases so that conditions of thermodynamic and hydrostatic equilibrium exist. Pollutant concentrations fall to zero at the ground surface in the region outside the impermeable cover.



The figures below show (1) mass fraction of volatile oil in the gas phase, (2) pressure, and (3) the spatial mesh, at approximately 16 hours of venting at a rate of 0.01 kg of the air/vapour mixture per second (equivalent to about 8 litres). The influx of clean air (i.e. zero mass fraction of oil -- coloured red) from the atmosphere can be clearly seen.



Clicking here will take you to a series of images showing the development over time of the concentration and the mesh from the start of the venting process -- up to 90000 seconds (approximately 25 hours).

Work is ongoing to resolve some outstanding modelling issues as well as to extend the functionality of the simulator.

Acknowledgements: Dr Keith McFarlane, HSE Solutions, Shell Research and Technology Centre at Thornton.

Last Modified: 02Aug00