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Computing the Effective Diffusion Coefficient



The effective diffusion coefficient for layer i of a porous media can be estimated using the Millington relationship:


Contaminant Terms:


Soil Terms:


The overall effective diffusion coefficient for systems composed of m layers (e.g., capillary fringe and the unsaturated zone) is:
where Li is the thickness of layer i, LT is the distance between the source of contamination and the bottom of the slab (sum of all layer thicknesses) and Di eff is the effective diffusion coefficient for layer i.


The overall effective diffusion coefficient used in determining target soil-gas concentrations only considers diffusion through the single-layer unsaturated zone.

The overall effective diffusion coefficient used in determining target groundwater concentrations incorporates both diffusion through the capillary fringe and diffusion through the unsaturated zone.

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