Abstract

This report describes the use of a systematic method for comparing options for the long-term management and retirement of surplus mercury in the Unites States. The method chosen is the Analytical Hierarchy Procedure as embodied in the Expert Choice 2000 software. The goals, criteria, and intensities were established and inputted into the Expert Choice software.

A limited scope decision-analysis was performed; two general types of treatment technologies were evaluated (stabilization/amalgamation and selenide). These were combined with four disposal options:

• In a Resource Conservation and Recovery Act (RCRA)-permitted landfill
• In a RCRA-permitted monofill
• In an engineered below-ground structure
• In a mined cavity

In addition, there were three storage options for elemental mercury:

• In an above-ground RCRA-permitted facility
• In a hardened RCRA-permitted structure
• In a mined cavity

Altogether, 11 options were chosen for examination with the decision-making tool. Results of a base-case analysis were generated together with variations on the results: assuming that only benefits (noncost criteria) or only costs are important.

Results show that the landfill options are preferred independent of the treatment technology. The storage options rank next, followed by the treatment technologies combined with monofills, bunkers, or mined cavities. The landfill choice was the least expensive option and this clearly outweighs the relatively unfavorable ranking if cost is a factor. If the cost is not an important factor, however, the three storage options occupy the first three places in the "noncosts only" ranking.

The standard storage option ranks least favorably of all in risks to the public, the workers, and the risk of susceptibility to terrorism. Although none of the options has a high risk, the fact that the standard storage option would have large quantities of elemental mercury in a nonhardened, above-ground structure suggests that the risks were somewhat higher than those for other options. Storage options also received unfavorable ranking because of high operating costs. High operating costs are incurred when:

• Storage continues for a long period (even relatively small per annum costs will add up)
• Storage is not a means for permanent retirement of bulk elemental mercury, and it is assumed that a treatment and disposal technology will be adopted

This is enough to drive the storage options out of first place in the base-case ranking. However, the analysis would support continued storage for a short period (up to a few decades) followed by a permanent retirement option. This would allow time for the treatment technologies to mature.

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Paul Randall

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