In June 2012, the North Carolina General Assembly passed House Bill 952 (HB952) which addressed reforms to the Air Toxics Rules in North Carolina.  The main purpose of the bill was to provide an exemption to those sources that were already subject to certain Federal emission requirements (e.g. NESHAP).  The intent of the revisions was to lessen the burden on those facilities to include modeling compliance demonstrations under a state program at the same time they had to comply with Federal rules which were at least as stringent.  While the North Carolina Division of Air Quality (NCDAQ) amended its rule under 15A NCAC 02Q .0700 to exclude sources subject to a NESHAP, there has been a lot of ambiguity surrounding the following portion of HB952 (referred to herein as the "unacceptable risk clause"):

"...Department shall review the application to determine if the emission of toxic air pollutants from the source or facility presents or would present an unacceptable risk to human health."

An unacceptable risk demonstration typically consists of an air dispersion modeling analysis with impacts below the acceptable ambient levels (AAL).  The "unacceptable risk clause" shifts the burden of performing the "unacceptable risk" analysis from the applicant to the North Carolina Division of Air Quality (NCDAQ).  However, should NCDAQ identify any model impacts in excess of the AAL in their analysis, they will not allow the permit application review to proceed until the applicant "resolves the modeling issue."  As such, the applicant may end up having to model, even in cases where they would otherwise be exempt per 2Q .0700.  Further, that modeling analysis may have to include unplanned refinements such as emission reductions from the submitted application, stack height increases and/or other source configuration changes.

If you elect to submit the application that includes an increase of air toxics emissions in excess of the Toxics Permitting Emission Rates (TPER), without modeling, NCDAQ may request stack/source data so that they can complete their own modeling analysis.  The permit application review will not be complete until that analysis has been finalized.  In the event that any modeled exceedances of the AAL are shown, the applicant will then have to refine the facility emissions or sources to resolve the modeling issue, which will further delay the permit application process.  As such, depending on the magnitude of TAP emissions and considerations such as planned stack height and property parcel size, it may be in the best interest of the applicant to complete the modeling analysis as part of the initial application submittal package.

For sources and/or facilities that do not qualify for the NESHAP or other air toxics exemption, compliance modeling continues to be a required part of any permitting action involving an increase in any toxic air pollutant with facility-wide emissions in excess of the TPER.  If you have any questions regarding toxics modeling applicability to a specific project or in general, feel free to contact Jon Hill via phone at (919) 462-9693 or email.