In February 1991, the law "On The Legal Status of the Territory Exposed to the Radioactive Contamination resulting from the ChNPP Accident" was passed, updating the borders of the Exclusion Zone and defining obligatory and voluntary resettlement areas, and areas for enhanced monitoring. The borders were based on soil deposits of strontium-90, caesium-137, and plutonium as well as the calculated dose rate (sieverts/h) as identified by the National Commission for Radiation Protection of Ukraine. Responsibility for monitoring and coordination of activities in the Exclusion Zone was given to the Ministry of Chernobyl Affairs.