Environmental Engineering Reference
In-Depth Information
Figure 16.14.
a) Range of diffusion coefficients for soils and mineral barriers;
and b) relative importance of diffusive and advective transport through
mineral barriers [MAN 00]
The contribution to the contaminant flux due to the hydrodynamic dispersion
(
D
d
), which is proportional to the effective seepage velocity (
v
), can be appreciated
by looking at Figure 16.15. The example refers to a landfill bottom barrier underlaid
by a flushing aquifer where it is assumed that the exit concentration is uniform. The
system can be analyzed in a first approximation referring to one-dimensional steady-
state conditions with downward pollutant migration through the landfill liner, ending
with perfect mixing with the underlying flushing groundwater. In the example in
Figure 16.15 it is possible to observe that using current input parameters for the
mineral barrier material used (see also Figure 16.16), the contribution of dispersion
to the total contaminant flux and concentration is always negligible.
