Depending on the site you have in mind, you may find that the major potential
hazard is not migration of any leachate leaks through the impervious layer but
rather direct leakage due to unforeseen human activities. Once leachate
starts moving underground, it presumably will travel on top of the impermeable
layer until it finds an easy means of moving downwards - typical leakage
points being abandoned wells, old trial exploration bores that were not
propoerly sealed afterwards, or even foundations for new buildings (but this
is most unlikely in your case, with a 60m deep layer). In developing
countries, where I work, these risks are usually more worrying than simple
geological ones, simply because effective control and regulation often does
not exist.
Richard Middleton,
Kalbermatten Associates,
Washington. DC, USA.
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