Operation Groundhog is reported to be a joint US/Kazakh/Russian program to secure radioactive residues of Soviet-era nuclear bomb tests. In 2003, reports appeared in Science magazine that the program included paving some areas with thick layers of reinforced concrete to protect plutonium contaminating the ground, in order to prevent terrorists from acquiring contaminated material for making a dirty bomb.
References
Operation Groundhog Wikipedia(Text) CC BY-SA