On July 10, 2010, the combustion (emissions) source exemption was removed from the NC Division of Air Quality (DAQ) air toxics regulations.  The combustion source exemption has been a key component of the NC air toxics regulations since the regulations were implemented in the early 1990s.  The removal of this exemption could require new or modified combustion sources to be evaluated under the air toxic regulations using the same procedures that have been used for process emission units since the regulations were developed in the early 1990s. 
   
Under this regulation change, the following new and modified combustion sources must now be included in an air toxics evaluation for a facility:

* Boilers
* Process heaters
* Internal combustion engines
* Space heaters
* Combustion turbines

With the removal of this key combustion exemption, each new or modified combustion source must be evaluated under the air toxics regulations as follows.  New and modified combustion sources (those emission sources listed above) must be evaluated for air toxics emissions increases.  For any increase in a toxic air pollutant (TAP) from a new or modified combustion source, every emission source at the site (all other existing combustion sources and process sources) must be evaluated to determine if the emissions of each increased TAP will trigger air toxics modeling.  This iterative analysis must be conducted for each TAP that is emitted from a new combustion source and for increased TAP emissions from a modified combustion source.  Dispersion modeling will be required for any TAP that is increased from a new or modified combustion source and for which the respective TAP on a facility-wide basis is emitted above the levels listed in 15A NCAC 2Q .0711.

TAP emissions netting as allowed within the rule is also an option for demonstrating compliance a new or modified combustion source.  The netting procedures, which can be utilized for new and modified emission units at a permitted facility that was in place as of September 30, 1993, are outlined in 2Q .0706. 

These regulation changes were discussed at the DAQ Outside Involvement meeting on November 8, 2010.  The DAQ indicated that an applicability guidance document should be available in the near future to assist with interpretation of this regulation change.

The NC Trinity offices are currently assisting clients with interpreting this regulation change for the permitting of new and modified combustion emission sources.   In providing this assistance, our offices are working with the DAQ to understand the permitting requirements for this rule change.  If you have any questions concerning this regulation change, please feel free to contact your local NC Trinity office.