The EPD has updated their Guideline for Ambient Impact Assessment of Toxic Air Pollutants ("the Guideline"). This latest revision is dated March 2017 and was uploaded to EPD's website on April 19, 2017. The last revisions to the Guideline were approved over 19 years ago. The purpose of EPD's toxics Guideline document is to provide a guide for estimating the environmental impact of sources of toxic air pollutants (TAP) and demonstrating compliance with Georgia Rules. The new Guideline supersedes all previous versions of the Guideline. The new Guideline will be used by EPD in the review of all air quality applications for permits to construct or modify potential sources of air pollutants including an increase in TAP emissions or emissions of a TAP not previously emitted.

Previous to this latest update, specific pollutant toxicity data needed to be evaluated to identify pollutants that were TAPs and to develop each pollutant's Allowable Ambient Concentrations (AAC). In order to demonstrate compliance, the maximum ground level concentration for each TAP was then determined through air dispersion modeling and compared to the AACs.

With the revised 2017 Guideline, EPD institutes a definitive list of toxic air pollutants, establishes predetermined AACs, and introduces Minimum Emission Rates (MER) for each pollutant. The MERs were developed using worst case dispersion scenarios and, per the Guideline, are applicable to point sources only. If the facility-wide pollutant emissions are below the MER, no further analysis is required for that pollutant. If the facility-wide pollutant emissions are greater than the MER, the maximum ground level concentration is determined through air dispersion modeling and compared to the predetermined AAC. As of the revised 2017 Guideline, only those pollutants in the list of TAPs need to be evaluated for compliance.