UNEP Case Study
UNEP endorses thick salt and clay formations for the permanent storage of difficult to manage wastes*
Difficult to manage chemical wastes like mercury (sic) can be permanently stored in geological cavities (e.g. in an underground mine). The intent is to permanently isolate wastes from the biosphere by including it as completely and permanently as possible in a suitable host rock via several natural and artificial barriers. A detailed case-by-case evaluation of the suitability of any such facility is critical to its effectiveness.
Potential host rocks include the following:
i) Salt rock:
Considered impermeable to liquids and gases and a very effective barrier for long-term storage of hazardous waste. A minimum thickness of the salt layer, however is needed to ensure safe encapsulation. Few countries have suitable formations.
ii) Clay formations:
Also considered as very good barrier. The sealing and permanent isolation from the biosphere may be achieved through a multi-barrier system. Thus, the isolating potential is safeguarded by geological (e.g. host rock formation of practically impermeable formations, overlaying clay layer) and engineered (e.g. chemical properties of the waste, packaging) elements. In order to ensure environmentally sound permanent storage, mercury wastes are stored:
*Practical Sourcebook on Mercury Waste Storage and Disposal, 2015, UNEP, pg 58 and 59.