Abstract: The closed tailings pond，due to long-term stagnation and lack of maintenance，often faces the severe challenge of abnormal uplift of the phreatic line，which seriously threatens the stability of the pond body and the safety of the downstream area. This study focuses on a closed valley-type tailings pond that has been in operation for over 20 a. It addresses the engineering hazard of the main pond's phreatic line depth being only 0.9~1.25 m and the emergence of escape points on the slope. It thoroughly analyzes the causes and clearly points out that the absence of the initial pond's anti-filter system，the aging and blockage of the drainage facilities，and the lateral over-flow recharge from the two banks of the mountain are the three main controlling factors leading to the deep stagnant water. In response to the problem that conventional shal⁃ low drainage is difficult to penetrate the blocked area，the radiation well technology is adopted to construct a deep 3D active drainage network. Based on the in-situ monitoring data over the past 1 a and the numerical simulation results of Geo-Studio，the comprehensive assessment indicates that after the implementation of the radiation wells，the phreatic line of the main pond has been effectively reduced，the depth has been steadily increased to 3.40~3.82 m，completely eliminating the leakage hazard，and the spatial distribution of the seepage field has become more reasonable. Under the mechanical mechanism of the decline of the phreatic line and the recovery of the effective stress of the soil，the anti-sliding stability safety factor of the pond body has increased from the current 1.155 to 1.404，an increase of 22.1%，meeting the specification requirements and having a certain safety reserve. The research results have confirmed the effectiveness of the radiation well technology in solving the problem of deep stagnant water in closed tailings ponds，and can provide scientific basis and engineering reference for the seepage control and treatment of similar tailings ponds.

Key words: closed tailings ponds, phreatic line, seepage control