1. Björn Södermark Swedish Environmental Protection Agency
Underground storage in bedrock – the Swedish solution for mercury waste
Björn Södermark
Swedish Environmental Protection Agency

3. Terminal storage in bedrock is the best solution
Rely on the capabilities of nature to withstand its own forces and those of man
Supplement with technical measures
The conclusion of our surveys and analyses is, that a terminal storage deep down in bedrock is the best solution. We base this opinion on the experience and knowledge we have in Sweden from several hundred years of mining and more than twenty years of research regarding a terminal storage in bedrock for nuclear waste.
Storage underground in deep bedrock relies on the capability of nature itself, in the form of the surrounding bedrock, to provide protection of the waste from the forces of nature and of man.
Supplementary technical measures are needed to compensate for lack of knowledge and unforeseen events, but also to get some freedom of action when choosing the method for treating the waste and choosing the site for the storage facility.

4. Fundamental properties of the surrounding bedrock
Prevention and remediation:
A stable physical and chemical environment and low groundwater flows
Long transport paths; high capacity for sorption, matrix diffusion and dilution
No supervision and maintenance needed
The fundamental properties of the surrounding bedrock, we want to use, are the capability of prevention and the capacity of remediation. The bedrock will provide long-term protection against physical and chemical changes, which will result in a stable environment suitable for terminal storage. In combination with technical barriers and pre-treatment of the waste, this will render it possible to keep leaching of mercury from the waste at a minimum.
Moreover, the surrounding bedrock will constitute a buffer against any mercury that does in fact leach out of the waste. The quantity of mercury able to reach the surrounding environment will be very small, even seen over a time scale of several thousand years.
Finally, but not least important, a storage in bedrock doesn´t need supervision and maintenance and thereby won´t be a burden on future generations.

5. Recommendations
Waste containing more than 1 per cent mercury should be terminally stored in bedrock
The mercury in the waste should be extracted and converted to an insoluble form
The storage facility should be located at least 400 m below ground in granite bedrock, preferably adjacent to an existing mine
The waste owners have the responsibility for building and running a storage facility
The following proposal was put forward in the official report presented in June 2001:
·        Waste containing more than one per cent mercury by weight should be terminally stored in bedrock within five year.
·        (Even waste containing at least 0.1 per cent mercury by weight shall be stored deep underground within five years should it be deemed justified.)
Also, in the report there are recommendations about extracting the mercury from the waste and convert it into an insoluble form, like e.g HgS. The conversion probably will be a technically difficult task and a costly operation. On the other hand, the disposal costs can be reduced by using an existing mine for the storage. The report concludes that there may be several advantages in storing the waste in granite bedrock adjacent to one of our many existing mines in Sweden.