The Osamu Utsumi Mine located at the Poços de Caldas plateau, Minas Gerais state, Brazil, was the first uranium mine exploited in the country, in the Poços de Caldas Mining-Industrial Complex (CIPC) of the Nuclear Industries of Brazil (INB). The operational phase for extracting and processing uranium lasted from 1982 to 1995, when activities were interrupted initiating the decommissioning process. INB had the liability for presenting a mine closure plan following requirements of IBAMA (Brazilian Institute of Environment and Renewable Natural Resources) and CNEN (National Nuclear Energy Commission). Several studies have been conducted to provide useful information to support the establishment of the closure plan. The low grade uranium deposit occurring mainly in the form of pitchblend was associated with a primary mineralization of Zr, REEs, U,Th, Mo. The pyrite present in the rock played an important role in the generation of acid drainage. It was evidenced that the acid drainage from the open pit, waste rock piles and tailings dam is of utmost relevance due to environmental impact and neutralization costs. Two major water courses, the Antas River flowing to Poços de Caldas city and the Soberbo River flowing to Caldas city, have been potentially contaminated by receiving releases of the mining and milling operation, thereby impairing hydric system quality. Huge amounts of waste rocks corresponding to 45 x 106 m3 were dumped into several piles around the mine pit. The largest waste rock pile (WRP-4) has a surface area of 569 x 103 m2 and a deposited volume of 12.4 x 106 m3 in the valley of Consulta stream of the Rio Verde basin. A Plan for Environmental Remediation (PRAD) was developed guided by a Reference Term written by the Environmental and Nuclear regulators to provide solutions for site decommissioning encompassing the mine pit, waste rock piles, tailings dam and industrial area. The present study is based on a comprehensive sampling of the WRP-4 and the tailings dam performed for chemical and radiological characterization and will be thorougly discussed.