REMEDIATION WORK FOR MERCURY CONTAMINATED BAY - EXPERIENCES OF MINAMATA BAY PROJECT, JAPAN

The Minamata Bay remedial project, which commenced in 1977, was completed in 1990. 1.5 million m3 of mercury contaminated sediment were treated by careful dredging and confined reclamation. A contaminated area of 2 million m2 in Minimata Bay was decontaminated. During this large project, we have faced several technical problems. Some of the experiences are expected to be useful for planning remedial works of other areas. The following topics are presented width technical details: a. initial distribution of mercury in the bottom sediment, b. monitoring system design and monitoring committee, c. dredging work with specially designed vessels, d. sand capping over reclaimed sediment for confinement. e. residual mercury after dredging. Economic considerations were important, but we gave a higher priority to safety. For the remediation, we had to use every possible technique in order to minimize secondary pollution.