1. General

There are three main types of containment, illustrated in figure 1 :

• surface containment, which consists of placing an impermeable blanket on the surface of the area to be isolated;

• vertical containment, achieved by building low-permeability screens around the perimeter of the site to be isolated;

• deep horizontal containment, designed to seal permeable zones beneath polluted soils, in order to stop pollutants migrating deep down.

Vertical confinement can take the form of :

• a complete peripheral containment surrounding the entire area to be isolated (figure