[en] The report outlines the Office of Supervising Scientist (OSS) activities for the period 1 July 1990 to 30 June 1991. Relations between the OSS, the Northern Territory authorities and the mining company have improved over the past year though there has been non-agreement over some technical issues such as the need for, and the effectiveness of, a seepage surveillance system, and the requirement for collection of seepage from the Ranger tailings dam. OSS still has misgivings about the lack of precision in wording in places in the Ranger Authorization and in approvals issued to the companies. Issues connected with the protection of people and the environment from uranium mining in the Region can be complex, and their proper examination can require access to extensive data and detailed information. It is reported that the mining companies have built up, over the years, strong environment programs and a large body of data. Regulatory action has ensured that the both Nabarlek and Ranger, water Management and control systems have been operated to restrict the quantities of contaminants dispersed to the environment. To date, the contaminants released have been at levels which could be assimilated without causing undesirable effects to the wider environment. The future environmental challenges will be to restore the Nabarlek mine site to an acceptable condition and to ensure that contaminant dispersal does not continue to increase at Ranger. 15 tabs., 21 figs