38. The final cover of a contaminated soil burial site consists of superposed layers and must comprise, from the bottom up, (1) an impermeable layer consisting of
(a) a layer of clay over which an impermeable synthetic membrane of a high density polyethylene type or having equivalent characteristics at least 1.5 mm thick is laid. The clay must have a minimum constant hydraulic conductivity equal to or less than 1 x 10-7 cm/s to a minimum depth of 60 cm after compaction; or
(b) 2 impermeable synthetic membranes of a high density polyethylene type or having equivalent characteristics at least 1.5 mm thick, separated by an appropriate protection layer.
If there is a physical or chemical inconsistency between the contaminated soils and the impermeable layer, a transition zone consisting of a layer of soil at least 15 cm thick, a geotextile or the equivalent must be laid out;
(2) a drainage layer at least 60 cm thick after compaction having a hydraulic conductivity equal to or greater than 1 x 10-3 cm/s or the equivalent;
(3) a protective layer consisting of soil having the characteristics and thickness that can protect the impermeable layer against frost and biointrusions. The layer may comprise the drainage layer and the layer of soil suitable for vegetation; and
(4) a layer of soil suitable for vegetation, at least 15 cm thick, must be sown in such way that revegetation takes place within 1 year. Notwithstanding the foregoing, the vegetation must not be such that it is likely to impair the impermeable layer.
The final cover must have a slope of at least 2% and not more than 30% to enable the flow by gravity of runoff away from the deposit areas and to limit soil erosion.