The surface systems contain of two layers, which in combination interrupt capillary flow and water infiltration into the landfill body.
The capillary-interrupting sealing system relies on principles of soil physics.
While coarse-grained soils (gravel) retain little volume of water against gravity, finer soils (sand) retain more. When building a two-layer-system with coarse-grained soil beneath and fine-grained soil on top, infiltrating water is held in the upper layer due to the matrix potential. This means that the pores in the upper layer are partly filled with water, in the coarse-grained soil there is no water. The unsaturated water conductivity in this state is much higher in the upper layer due to a higher content of water filled pores and a higher flow cross-section. In case of an effectual inclination of the system, the water flows in the finer soil layer without entering the coarse-grained one. The water percolates towards the edge of the landfill and drains out into the drainage system.
When installing such a system on a landfill, the overall and in particular the hydraulic characteristics of the soil have be analyzed and evaluated in advance. Therefore also a practical in-situ test is necessary. Commonly, the coarse-grained layer (“capillary block”) is installed with 20-30 cm depth; the finer soil (“capillary layer”) is installed with 40 cm depth. The capillary layer needs adequate water conductivity, therefore commonly sand is applied. When used as unique sealing element, the groundwater recharge rate may not exceed 20 mm/a. The system has to be covered by ≥ 1m recultivation layer.
Approximately 150.000 Euros per hectare.
Evidence of success
The practice provides a simple design of a surface sealing system which hinders from infiltration of water in to the landfill body.
The system needs inclination. No installation in areas with high precipitation rates as water saturation may lead to a breakthrough of water. For landfills with higher contaminated waste, installation just in combination with a geomembrane as the prevention from water infiltration is not perfectly.
Potential for learning or transfer
Most landfills in the EU have no base liner system. Leachates from the waste of landfills and can severely pollute the groundwater. Therefore a sealing system is necessary in order to protect environment and groundwater. The mentioned sealing system is a simple one and not as cost intensive as other ones with geomembranes and can be applied for landfill where non-hazardous wastes were disposed. The practice can be particularly applied in southern regions of Europe with low precipitation rates and for smaller landfill containing non-hazardous wastes. However, also the distribution of precipitation and the corresponding hydraulic conditions in the soil have to be considered here, as this may affect the function of the system.
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