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To eradicate Minamata Disease, caused by the discharge of sewage containing methyl mercury and its accumulation in fish and shellfish through the food cycle, a large-scale sediment disposal project was conducted with special care taken to prevent new pollution resulting from the project itself. The basic approach to sediment disposal was to construct a highly watertight revetment to reclaim the inner area of the bay and then confine sediment dredged from the remaining contaminated area in the reclamation area through surface treatment. Before sediment disposal, boundary nets were installed to enclose the work area to prevent the mixing of contaminated and noncontaminated fish. Dredging work was successfully carried out by using four cutterless suction dredgers, newly developed in advance for minimizing resuspension of sediments. Dredged material was discharged into the reclamation area, filled up to sea level, and covered with a sandproof membrane, lightweight volcanic ash earth, and mountain soil.
mercury-contaminated sludge, dredging, sediment disposal
Director, Construction Bureau, Ministry of Transport, Niigata,