The risk is linked to the drilling wastes and cuttings from the well (liquids and solids) stored at rig site before proper trucking, treatment and dumping in authorized sites. Wastes are temporarily stored in waterproof basins to avoid any seepage or contamination of the soil; the wastes composition in the basin is routinely controlled.
The risk of impacting soil from the rig site in its wide area is prevented by the laying of a geomembrane below the top soil of the site. A properly design drainage network will convey the waters in pits from which the fluids will be collected and trucked to authorized disposal sites. In case of heavy rains, an overflow separator will divert the "first rain waters".