Chemical composition of the uranium tail storages at Kadji-Sai (Southern Shore of Issyk-Kul Lake, Kyrgyzstan)

In 1996, an abandoned uranium mine was re-discovered in the Djilubulak ephemeral stream valley on the southern shore of Issyk-Kul - one of the largest and most pristine lakes in the world. The tail storages from the past mining may pose a pollution hazard to the lake water and sediments. A chain of six protective pools interconnected by drain pipes descend from the abandoned mine and processing plant down the Djilubulak stream valley. To assess the effectiveness of these catch pools and the scale of pollution risk the investigation of tail storages composition was performed. As a result, three sources of anomalous radioactivity were discovered: 1. Natural brown coal with the mean total radioactivity value not exceeding 16 kBq kg^-1, with U being in state of equilibrium with Ra. 2. Ashes depleted in U (relative to Ra) with the mean radioactivity reaching 49 kBq kg^-1, mostly due to the Ra content. 3. Clay and silt from the artificial protective pools where U activity (up to 2-2.5 kBq kg^-1) significantly exceeds that of Ra indicating recent process of U enrichment. Uranium in these pools is accompanied by very high contents of heavy metals such as Cu, Zn, Cd, Ni, Cr, and to a smaller degree Pb, Mo, Hg, Ag. From the upper catch pool to the lower ones the content of U and some heavy metals diminishes. Within the two lowest pools neither U nor heavy metal contents exceed background values (U < 0.1 kBq kg^-1). It appears that the system of catch pools effectively protects Lake Issyk-Kul from inorganic pollutants at the present time. However, a flash flood or other catastrophic event could breach the catch pool dams and carry radioactive elements and heavy metals into the Djilubulak stream valley and the lake.