Countermeasure against plant root intrusion into capping in Ningyo-toge Environmental Engineering Center

Masunaga, Kosuke; Saito, Hiroshi; Sato, Hisakazu*

Ningyo-toge Environmental Engineering Center has carried out remediation activities for Ningyo-toge Uranium Mine, now out of service for mining in accordance with the Mine Safety Law, to ensure the radiation protection from the exposure pathways to humans in future and to prevent the occurrence of mining pollution. Some remediation activities has already done so far, including capping construction for the upstream of mill tailings pond by the end of FY2012. The purpose of the capping is to reduce dose rate radon exhalation rate and rain infiltration rate of the pond, which is considered as the most prioritized facility to remediate.Post-remedial maintenance must be reduced just like to lower the burden of water treatment in future by capping construction as is written above. For the reason, plant root intrusion, its long-term impact to the function of the capping and countermeasure have been studied as plant is expected to intrude into the pond through its surface as capping. The result shows that annual herbs will intrude followed by perennials herbs and woody plants which constitutes forest eventually. Also, it is estimated that the long-time duration makes it easier for woody plants to intrude before vegetation becomes dense if vegetation is subject to natural succession. For these reasons, controlled vegetation is thought to be suitable compared with natural vegetation. Also, in terms of factors including economy, tolerance to cold climate and root depth, grass-felt with the seedlings of Gramineae is chosen as most suitable countermeasure against erosion.