The problem occurred when high altitude winds blew the fallout down to St George where it precipitated out on to the top of the sand. The same sand they used both at St George as well as back at the sound studio in LA.
The reactors lost cooling from the earthquake and the fire engine hose lines did not properly deliver the cooling water due to piping issues. Those explosions occurred as the reactors were melting out. Now estimated to have already released 3 Chernobyl's of radiation contamination.