If toxic waste containg cyanide is not disposed of properly, it may drain into ponds, streams, sewers, and reservoirs.
There is usually cyanide in toxic waste. 
The passage does not say whether there is usually Cyanide  in toxic waste. It can be in it, but no way to know if it is usually in it. 
( z1 cyanide :location ( z2 waste :mod ( z3 toxic ) ) :frequency ( z4 usual ) )