Environmental Engineering Reference
In-Depth Information
active management, a higher amount of pollutant is caught by the leachate collection
system and removed outside the landfill and towards leachate treatment plants. In
the case of quickly degrading pollutants, both concentration and cumulative
contaminant flux can be lower for passive management than for active management
even though the degradation of the pollutant can be much faster in wet than in dry
conditions, corresponding to active and passive management respectively.
On the basis of the previous observation, it is apparent that landfill design should
be based on case-by-case analysis. This must consider not only the lining system
features, subsoil, climate conditions and waste types, but also the different
aspects of
landfill management, the waste mass and its distribution within the deposit, and the
time history of the cover construction.
16.4. Functions, performance and modeling
Referring to the three basic components of a containment system for waste
deposits, i.e. bottom, side and top liners, it is possible to briefly summarize their
main functions as follows:
− The
bottom liner
must reduce the advective and diffusive contaminant
migration toward the underlying soil and/or aquifer by as much as possible. The
performance of the bottom barriers is fundamentally governed by the following
parameters: field hydraulic permittivity and diffusivity, chemical compatibility,
sorption capacity, and service life. On the other hand the performance of filters and
drainage layers are fundamentally governed by the capacity to avoid clogging,
which in turn is influenced by the type of waste and landfill management (in terms
of waste temperature and water content). On the basis of direct field observations, it
has been shown that the clogging trend in the leachate collection and removal
system is reduced by increasing the seepage velocity of the leachate. Therefore the
higher the hydraulic conductivity and the gradient (i.e. slope of the landfill bottom),
the higher the service life and efficiency of the drains can be.
− The drainage component of the
side liner
is far less demanding than for the
bottom liner due to the generally high hydraulic gradients along the side slopes. On
the other hand, the side lining must be able to control migration into the vadose zone
of the biogas located above the leachate table inside the landfill. This task is
particularly delicate, since most of the accidents that have occurred in the past few
years in MSW landfill have been related to biogas escape [KJE 95, WIL 95]. In the
case of capping systems, one of the most important future research challenges is to
make reliable models and related parameters available to enable the effective design
of liners with respect to gas migration control [BOU 00, VAN 04].
