Nelson Environmental's soil remediation facility at Malahat Business Park. Direct Fired Thermal Desorption (TDU) removes organic contaminants from soil, sludge or sediment by heating them in a machine called a “thermal desorber” to evaporate the contaminants. The evaporation process volatilizes the organic contaminants in the soil into a vapour phase (gases) which in turn, separates them from the solid material and destroys them.