**4.3. Solid TE-NORM waste**

For TE-NORM-contaminated scale, sludge, and soils with very low levels of radioactivity, a suitable disposal option is to spread over the ground and mix with non contaminated soils, to dilute the contaminated soils and reduce the radioactivity level to background levels. This type of disposal is often the most cost-effective [48]. Subsurface disposal options include under‐ ground injection and down hole encapsulation. This type of disposal is widely acknowledged as one of the most environmentally sound methods of disposing TE-NORM-contaminated sludge. The two common forms of subsurface disposal are:

