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Soviet: atmospheric testing also was the greatest contributor to 

 radioactive contamination of Alaska and northern Canada. 



The severity of the contamination decreased dramatically 

 after the 1963 Limited Test Ban Treaty — especially in Alaska and 

 Canada — but Soviet underground nuclear weapons testing and 

 peaceful nuclear explosions continued. Russian statements 

 indicate over 130 peaceful nuclear explosions for mining, seismic 

 sounding, or creation of underground storage cavities were 

 conducted throughout the Soviet Union. A few of these explosions 

 were part of a program to develop the capability to excavate 

 canals using nuclear explosions. These crater-producing 

 explosions produced widespread contamination. In an August 1987 

 test, for example, the concrete plug placed to contain the 

 explosion was blown out of the tunne-l, and radioactive material 

 spewed into the atmosphere. Some of the other explosions may 

 havs contaminated the local groundwater, and a few may have 

 leaked radioactive materials. Except for tests at Novaya Zemlya, 

 which sometimes spread contamination into the broader Arctic 

 environment, these leaks probably produce only limited local 

 cont2UDination . 



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