Arguably, the most important European legislation relevant to landfill containment is embodied within the Council Directive of 17 December 1979 on the protection of groundwater against pollution caused by certain dangerous substances (80/68/EEC) (CEC 1979).
The Annex to this Directive contains two lists of generic as well as specific compounds or substances.
List I contains the most damaging substances and their direct discharge to groundwater, that is without percolation through an unsaturated zone, is prohibited. Indirect discharge of List I substances is permissible only where prior investigation shows the groundwater to be permanently unsuitable for other uses. Direct and indirect discharges of
List II substances may be authorised only after prior investigation and should be limited so as to avoid pollution of the groundwater by those substances (Article 3.2; CEC 1979). List II includes, amongst others, ammoniacal nitrogen (NH3-N), and it must be assumed that Article 3.2 would encompass landfill leachates, since this constituent is singularly the most long lived and potentially problematical gross component of landfill generated liquors.
The severity of the Directive is mitigated by two factors:
Groundwater (Article 1.2(a); CEC 1979) is understood to be water that is below the surface in a zone of saturation, implying that indirect discharge through an unsaturated zone, in which attenuating processes remove the
polluting potential, is acceptable;
An exemption is made (Article 2(b); CEC 1979) for discharges that contain substances in lists I and II in a quantity or concentration so small as to obviate any present or future danger of deterioration in the quality of the receiving
Taken together, these Articles suggest that controlled release of contaminants is permissible, so long as it is by indirect discharge and that attenuation in the unsaturated zone protects the groundwater.
More recently, a proposal for a Council Directive on the landfill of waste (91/C 190/01), submitted to the Commission on 23 April 1991 tightened the provisions of the Groundwater Directive by laying down landfill containment criteria irrespective of site specific conditions and knowledge of attenuation mechanisms.
Annex I (Section 8) of the draft Directive requires that, with the exception of landfills for inert wastes only, the following containment criteria must be met, either by the presence of in situ natural strata, or to the same level of hydraulic containment by engineering measures (synthetic liners or amended soils):
- minimum thickness of 3 metres;
- maximum hydraulic conductivity of 1 x 10^-9 m sec.
For engineered liners in clay the thickness is normally 1 metre, minimum at a maximum hydraulic conductivity of 1 x 10^-9 m sec.
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