廃砂たい積場覆土措置後の地下水変動

Changes in groundwater flow after remediation with capping for the Upstream of Mill Tailings Pond at Ningyo-toge Environmental Engineering Center

西田 伸穂; 小原 義之; 川本 勉

Nishida, Nobuho; Ohara, Yoshiyuki; Kawamoto, Tsutomu

日本原子力研究開発機構人形峠環境技術センターは、鉱山保安法等に基づき、事業休止中の核原料物質鉱山である人形峠鉱山、東郷鉱山の安全対策及び閉山措置(以下「鉱山跡措置という」)に取り組んでいる。鉱山跡措置の取り組みとして、平成23年度から同24年度に鉱さいたい積場のうち、廃砂たい積場で雨水浸透抑制及びラドン散逸抑制効果を確認するとともに、覆土の安定性について検証するため、暗渠設置及び覆土措置を行った。覆土安定性の検証については、廃砂たい積場の覆土措置前後の地下水量の変動を数値解析するとともに、鉱さいたい積場周囲のボーリング孔の水位、廃砂たい積場下流部から流出する湧水の調査を行った結果、地下水量が増加している可能性は高いが、設置した暗渠が十分な排水機能を有しており、地下水位は覆土部まで上昇していないと推定された。よって、現状の覆土構造の安定性に問題ないと考えられるが、今後も鉱さいたい積場周辺のボーリング孔水位、廃砂たい積場下流部の湧水量の監視を継続する。

Japan Atomic Energy Agency Ningyo-toge Environmental Engineering Center, has been conducting environmental remediation of the Ningyo-toge mine and Togo mine, after decades of mine-related activities including uranium exploration, mining and test milling were terminated, with doing safety measure, under Mining Safety law. As the one, culvert installation and multi-layered capping were performed at Upstream of Yotsugi Mill Tailings Pond to inspect about stability of multi-layered capping with checking rainwater infiltration restraint and radon dissipation inhibiting effect, from FY 2011 to FY 2012. And it was presumed possibility of amount of underground water is increased, as result of fluctuation numerical analysis for Upstream of Yotsugi Mill Tailings Pond before and after the multi-layered capping, and the water level of bowling holes around the Pond and spring water which flows from lower place of the Pond. But a culvert possesses enough drainage function and groundwater does not rise to the multi-layered capping part. Therefore, it is considered that there isn't problem to the stability of the current state of the multi-layered capping, but we will continue the monitoring of the water level of the bowling hole around the Pond, and the spring water which flows from lower place of the Pond.