Case-by-Case MACT or Subpart DDDDD MACT?
Many major sources of hazardous air pollutant (HAP) emissions with boilers that will be subject to the recently signed Boiler MACT standards have previously opted to obtain "case-by-case" MACT permits in North Carolina. Compliance with case-by-case MACT requirements for many sources is required in 2014.

In some cases, the NC Division of Air Quality's case-by-case MACT permits that were issued for certain types of boilers are not substantially less stringent than EPA's new standards, which will not require compliance with the most substantive of the requirements (e.g., emissions standards) until 2016.
If you obtained such a permit, you may want to carefully compare your current emission limits against the new limits and determine whether switching to the new Boiler MACT standard to allow more time for initial compliance is beneficial.