Environmental Engineering Reference
In-Depth Information
- high sorption capacity, and
- low diffusion coefficient;
− composite lining systems using geomembranes can give important advantages
in both the short and long-term due to:
- reduction of hydraulic conductivity as a result of the attenuation of local
defects of both geomembrane and compacted clay, as shown by [DAN 93, GIR 89a,
GIR 89b, GIR 92]:
- better biogas control,
- minimization of desiccation problems,
- enhancement of waste degradation,
- enhancement of flow within the drainage layers toward the collection pipes
(i.e. minimization of ponding leachate on the liner), and
- the geomembrane on top of the clayey barrier can delay direct contact
between clay and leachate long enough for consolidation of the clay portion of the
composite system. This is due to the establishment of high effective stresses when
the waste is landfilled. In this way it is possible to reduce or avoid compatibility
problems [ROW 95a].
Construction details play a fundamental role in the final efficiency of the lining
system in terms of full-scale hydraulic conductivity.
16.6.1.
Hydraulic conductivity at the field scale
One of the key aspects related to pollutant containment systems is the hydraulic
conductivity of the mineral barriers at field scale. The work of Daniel [DAN 93] and
Daniel and Trautwein [DAN 95] has led to the establishment of recommendations
related to the effects of compaction procedures, water content and pretreatment.
Uncertainties in construction, flow through macropores, and spatial variability of
the hydraulic properties of compacted clay liners have been treated statistically and
validated via field test results by [BEN 94a, BEN 94b, JES 93] among others (Figure
16.10). Their main conclusions can be summarized as a mineral sealing layer,
consisting of four or more lifts, which compensates for the effect of spatial
variability of the hydraulic conductivity. There is little benefit if the number of lifts
is increased above four to six.
