Overall investigation of the influence on environment from Koshkar-Ata tailing pond and rehabilitation measures

The tailing pond KOSHKAR-ATA, representing the drain-free settling pool for industrial, toxic, chemical and radioactive wastes, as well as for ordinary domestic waste, is located 5 km northward to Aktau city in Mangystau oblast (Kazakhstan) in close vicinity of the Caspian Sea shore. The hollow of KOSHKAR-ATA was used since 1965 as storage for toxic and radioactive waste from chemical-hydrometallurgical and sulfur-acid plants that processed local uranium ore reach in phosphor. According to data of the Mangystau Regional Ecology department (Aktau), the amount of radioactive waste (RAW) disposed in the tailing pond is about 360 million tons with total activity of 11000 Ci. There has been studied in details present radio-ecological state of the tailing pond and obtained quantitative data characterizing current ecological status of air, water and soil at KOSHKAR-ATA and adjacent territories. During field investigations in 2003 there has been performed for the first time mapping of water phase and shore exposed surface of the tailing pond KOSHKAR-ATA. Currently, area of the water phase is estimated to be 42.5 km2 with shore exposed surface of 34.5 km2. Based on obtained data there was created a database with GIS elements 'KOSHKAR-ATA' enabling to obtain reliable information on concentrations of main dose-forming radionuclides in environmental objects. To polish rehabilitation technology for the shore exposed zone of the tailing pond KOSHKAR-ATA in its southern part was chosen a most characteristic control site 100 x 90 m. Reclaiming of the site was performed by backfilling of the site surface with 25 cm of radiation-clean sand-clay material. Preliminary assessment of the effectiveness for this reclaiming method (by backfilling with sand-clay material) demonstrates considerable improvement of radiation characteristics of the site. Comparative analysis of available materials showed advantages of sand-clay soils due to, first of all, availability and relative low price of this material. Clay in this soil prevents dusting and serves as an additional barrier to radon emanation. As well, cover with sand-clay soil will stimulate vegetation growth and prevention wind erosion. In order to stop further unauthorized proliferation of radioactive waste it is planned to take rehabilitation measures at the territory of the near-surface disposal of KOSHKAR-ATA tailing pool in 2005. It is supposed to cover it with a 0.5 m-thick layer of soil-rock. For land filling it is supposed to take soil-rocks from a protective ditch around the tailing pool what will also help to reconstruct the ditch that come tumbling down over the years and to prevent access of population and cattle to the hazardous site. (authors)