Dear members,
I would be grateful if I could have any advise on the issue of leachate
transport. It may not directly related to the urban drainage matter, but I
guess some of you have good background of groundwater hydrology.
I am working on a project of a final disposal site for municipal waste. The
land has quite special feature. The water table is very high (about half
meter deep from the ground surface). The groundwater is so saline (more
than sea water) that it is not used for any human purpose. The aquitard, in
which this groundwater is contained, has about 60m thickness and an aquifer
is lying beneath. This aquifer is used to supply potable water.
The permeability (or maybe should be called hydraulic conductivity) of the
aquitard is about 5 to 7 x 10 E -9 m/sec.
I found a report regarding the possible contamination of the underlying
aquifer with leachate. It says that it will take more than 200 years for
the leachate to reach the aquifer by dividing 60m by the permeability.
However, I wonder if this calculation is right because permeability is not
flow speed, and hydraulic gradient should be null since the aquitard is not
confined. Also, porosity should affect the flow speed.
I think the leachate travels only due to the diffusion, convection current
and other molecular movement.
May I hear your ideas about how the leachate will travel? Thank you for
your attention.
(for your information, the landfill has impermeable liners at the bottom,
thus the story above is only in case where leachate finds any migration
route.)
Ms. Noriko Otsuki
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