人形峠環境技術センターにおける覆土表層に対する植物根侵入対策について

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

桝永 幸介; 齊藤 宏; 佐藤 寿一*

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

人形峠環境技術センターでは、鉱山保安法に基づき、人に対する危害及び鉱害防止の観点からウラン鉱山の跡措置を進めている。そのうち、鉱さいたい積場の跡措置の一環として、廃砂たい積場に雨水浸透量、放射線量およびラドン散逸量低減化を目的として平成24年度までに覆土を施工した。今後において維持管理を低減化していくなかで、周辺から覆土表層への植物根の侵入が予想されることから、植物根の侵入が長期的に覆土の機能に及ぼす影響調査および植生による対策の検討を行った。その結果、覆土には最初に一年草が、次いで多年草が侵入し、その後、周辺樹林を構成する木本類が侵入するものと推測された。維持管理の観点から、自然育成では植生が疎らな状態にある期間が長く木本類の侵入を助長することから、人為的な植生導入について検討し、植生シート工によるイネ科による対策が優れていると判断した。

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.