1. Defining the various subsoil "environments

Boreholes can be used to "probe" the ground, providing information on the pollutants emitted into the soil by a site's industrial activity. This activity may be ongoing or have taken place in the past. Chemical impacts on the soil are sometimes visible (hydrocarbons, odorous solvents), but will generally be detected and quantified by analyses carried out on samples taken at depth by drilling. Generally speaking, three types of "medium" can be sampled and analyzed: soil, soil gas and groundwater.

Soil is a solid medium made up of particles (sand, clay, limestone, etc.) that may or may not be welded together. The voids between these particles constitute the "porosity" of the soil or rock. These voids exist in the pores between particles, or in fractures in the rock (as in limestone or granite, for example). This porosity contains water and gases. Soil gases are only...