Stabilization and decommissioning of the Sillamäe Radioactive Tailings Pond, Estonia

The paper presents experiences gained and progress achieved during the currently ongoing stabilization and dry-decommissioning of the Sillamäe Radioactive Tailings Pond (area: 50 ha, vol.: 8 Mill m 3 ) in Eastern Estonia. The Sillamäe Tailings Pond is located next to the shoreline of the Baltic Sea near Sillamäe town (17.000 inhabitants). Tailings from uranium ore processing (1948–1977), from uranium related processing (1977–2003) and liquid oil-shale ashes from the local power plant have been discharged into the Tailings Pond. Initial evaluations carried out after Estonia’s independence in the 1990’s identified insufficient safety of the Tailings Pond for radiological, environmental and geotechnical reasons. Contaminated seepage was entering the Baltic Sea. The about 25 m high northern tailings dam was effected by marine erosion and dam safety was found to be insufficient. Therefore the multi-national Sillamäe Radioactive Tailings Pond Remediation Project was launched in 1998 jointly financed by Norway, Sweden, Finland and Denmark, Nordic Environmental Finance Corporation (NEFCO), EU and Estonia. ÖKOSIL Ltd. (Tallinn, Estonia) was contracted by NEFCO to become responsible for project steering and for implementing the newly developed radiation protection program. In addition ÖKOSIL Ltd. is the Employer for all decommissioning works. WISMUT GmbH (Chemnitz, Germany) is responsible for designing and planning of dry-decommissioning and for monitoring of the construction works of the ongoing project. Initial stabilization measures carried out from 2001 to 2003 are presented enclosing a shore protection embankment (1080 m), a pile grillage along the northern dam toe (690 m, 15–17 m deep CFA-piles), a diaphragm wall (580 m; depth 12–18 m), a large drainage trench including a gravel-filled drainage ditch (520 m). Reshaping of the tailings dams with respect to long term dam stability and contouring of the pond area with respect to long-term settlement portions started in 2003 building up a ridge-type surface contour. The paper finally presents the future decommissioning progress enclosing final covering of the whole Sillamäe Tailings Pond by a multi-layer type cover and long-term monitoring after closure.