A percentage that represents the number of molecules of a compound removed or
destroyed in an incinerator relative to the number of molecules that entered
the system. (For example, a DRE of 99.99 percent means that 9,999 molecules are
destroyed for every 10,000 that enter. The percentage 99.99 is known as
"four nines." For some pollutants, the Resource Conservation and
Recovery Act (RCRA) removal requirement may be as stringent as "six
nines.")