Soil is the unsealed top layer of land where plants may grow (art. 7, para. 4bis Environmental Protection Act EPA): it forms the substrate for natural vegetation and cultivated plants, acts as a filter, and is the buffer zone within which water, heat and air are brought into equilibrium. Soil can be subdivided into pedological horizons: the surface layer of the soil, horizon A (whose thickness may vary from 5 to 30 cm), contains humus, roots and living organisms; the underlying layer, horizon B (whose thickness reaches about 1.5 m) is a mineral layer, less rich in humus, and is made up of eroded minerals, and also represents the mineral transition layer located between horizon A and the subsoil. Taken together, horizons A and B constitute what is referred to as ‘excavated soil’.

In the annexes of the Soil Deterioration Prevention Ordinance (VBBo) are listed threshold values for many harmful substances: these limits serve to assess whether it is necessary to restrict the use of soil.

Depending on the type of land use (e.g. as agricultural land, gardens, playgrounds, etc.), the aforementioned ordinance contains the index, threshold and remediation values for many substances (inorganic elements and organic compounds ), as well as indices for evaluating the extent of erosion.