Landfilling of Waste

12. Restoration

12.1 Definition and strategy
12.2 Physical design
12.3 Final covering
12.3.1 General remarks
12.3.2 Cultivation purposes
12.3.3 Other purposes

12.1 Definition and Strategy

A landfill must be given aftercare so that the objectives for the future use of the land can be fulfilled. The restoration of a landfill must be so designed that the future site appears as an aesthetic entity.

The final covering must be carried out continuously so that each cell of a landfill unit receives its final cover as and when the cell reaches the contemplated profile.

The restoration must be seen in the light of the wish to allow the landfill to pass from the active to the passive phase as soon as possible.

A tight final cover is therefore unacceptable on landfills that require active environmental protection systems. In the long term, impermeable liners cannot be regarded as completely tight. That would imply a risk of putting off a potential pollution to the time when the active environmental protection systems have become passive.

12.2 Physical Design

The physical profile of the future landscape for a landfill should be determined before the landfill is established. The design is limited by a number of factors that must be taken into consideration. The most important ones are dealt with below.

The starting point for the landscape of the restored landfill is the future use of the land.

Regardless of the future use the restored landfill must appear as an aesthetic entity. It should therefore have an appearance which is adapted to the landscape in the region. To achieve this, the design should be made by a person with knowledge of landscaping - such as a landscape architect.

If the area is subsequently to be used for agricultural purposes with frequent machine tillage, the surface gradients should not exceed about 1:10.

To avoid erosion in surfaces with final cover, the surface gradients should nowhere exceed 1:3.

The natural run-off of water must be safeguarded in such a manner that no areas will occur within the landfill area with increased influx of surface water and an associated increase in the production of leachate.

Generally speaking, the filling heights should be as great as possible so that optimum use is made of the liner-covered areas. There should be no areas where the filling height is less than 5 to 7 metres. However, where active environmental protection systems are to be installed on the landfill, allowance must be made for the leaching behaviour of the waste. Thus, the maximum filling height in such places should be determined on the assumption that the active environmental protection systems can be made passive not more than 30 years after the landfilling has ceased, cf. Chapters 2, 4, and 11.

Finally, filling heights around leachate and inspection wells should not be excessive, as this may curb the realistic prospects of maintaining and inspecting the collection wells and/or their installations.

12.3 Final Covering

The shape of the final cover depends, firstly, on the landfill unit receiving the final cover and, secondly, on the future use of the land.

12.3.1 General remarks

Final covering rate

Under normal circumstances the final covering of the individual landfill units should proceed in keeping with the filling of waste.

However, the effect of the final cover on the generation should be considered carefully in relation to the leaching behaviour of the waste in each landfill unit. Thus, allowance must be made for the fact that not later than 30 years after the end of landfilling the leachate from the relevant landfill unit must be acceptable in the groundwater of the area.

The layer of soil used for final covering will have an impact on the storage of water in the final cover - resulting in a reduction of infiltration to the waste. The type and thickness of the layers of soil must therefore be chosen in accordance with the desired effect.

Generally speaking, the final cover should be seeded or planted just after final covering has been done. There may, however, be circumstances in certain landfill units that would render this inappropriate. The effect of the vegetation must therefore be assessed.

12.3.2 Cultivation purposes

In the case of areas that are to be used for cultivation, the guidelines of the Ministry of Agriculture for aftercare of areas for cultivation must be followed.

The cultivation layer should consist of an upper cambium of about 0.2 metres of topsoil and a lower cambium containing clay and silt, so that dessication is prevented and roots can develop.

The soil should be spread so as to avoid compression through traffic. If compression does occur, the soil should be loosened by grubbing.

Cultivation layers without root barriers are established with a total layer thickness of at least 1.7 metres. This will prevent contact between the roots of the crop and the waste.

If a root barrier is installed in the form of, e.g., an 0.15-metre layer of gravel, the thickness of the cultivation layer can be reduced to 1.0 metre. The root barrier should be laid out on a trimmed covering layer.

12.3.3 Other purposes

If the future area is to be used for purposes other than cultivation, the primary object of the final covering is to prevent freezing of the waste and to ensure that the contemplated future use of the land is possible. In this case the thickness of the final cover should be at least one metre.

In connection with certain future uses of the land any free infiltration to the waste will be prevented.

In these cases it is necessary to make a concrete estimate of the effect on the leaching behaviour of the waste - so as to make sure that the active environmental protection systems can be made passive not more than 30 years after the landfilling ceased.