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Data Requirements Rule (DRR): An Update on the 1-Hour SO2 NAAQS

Posted: July 31st, 2014

Author: All4 Staff 

Back in July 2010, the United States Environmental Protection Agency (U.S. EPA) published a final 1-hour sulfur dioxide (SO2) National Ambient Air Quality Standard (NAAQS).  In his blog, Colin McCall outlined the potential implications of the new SO2 NAAQS, pointing out that while “the final [SO2] NAAQS as established was extremely stringent to nobody’s surprise, the way U.S. EPA proposed to implement the standard was quite surprising, however.”  The surprise at the time was in the proposal to use air dispersion modeling to establish attainment and nonattainment designations for the 1-hour NAAQS.  After a winding road that included a pause in the process, stakeholder meetings, and much discussion around how attainment designations should look, the U.S. EPA has recently been providing guidance on how state and local air agencies should characterize air quality.  For a detailed look into the SO2 NAAQS Implementation as of March 2014, check out Colin’s blog, here.

On April 17, 2014, the U.S. EPA proposed the Data Requirements Rule (DRR) that directs air agencies to provide air quality data by using a combination of ambient air quality monitoring and air quality dispersion modeling to characterize current air quality in specific areas.  These areas do not have sufficient air quality monitoring data in place right now to identify maximum 1-hour SO2 concentrations. With the public comment period having come to a close on July 14, 2014, it is time to look closely into the rule itself and reexamine its possible implications.  While there is still uncertainty as to how U.S. EPA will address public comments in the final DRR, one (1) thing is for certain: facilities subject to a specific evaluation under the rule will bear the cost of either dispersion modeling or the implementation of an enhanced monitoring network.

In the proposed rule, the U.S. EPA proposed a schedule for state and local air agencies to provide air quality data to the U.S. EPA.  The U.S EPA’s proposal provides state and local air agencies with two (2) options to characterize air quality:

  1. Dispersion modeling of actual source emissions, or
  2. Appropriately sited ambient air quality monitors.

The data would then be used by the U.S. EPA in two (2) future rounds of NAAQS area designations in 2017 (for facilities/areas where dispersion modeling is used) and 2020 (for facilities/areas where new ambient monitors are used).  

The DRR also includes options for emissions thresholds in order to identify the facilities around which air agencies would need to characterize SO2 air quality.  These options would include lower annual emissions thresholds for facilities located in metropolitan areas greater than 1 million in population and higher emission thresholds for facilities outside of those areas. The options comprise:

  1. Sources greater than 1,000 tons per year of SO2 in metro areas with a population of greater than 1 million, and sources greater than 2,000 tons everywhere else.
  2. Sources greater than 2,000 tons per year of SO2 in metro areas with a population of greater than 1 million, and sources greater than 5,000 tons everywhere else.
  3. Sources greater than 3,000 tons per year of SO2 in metro areas with a population of greater than 1 million, and sources greater than 10,000 tons everywhere else.

The U.S. EPA is proposing Option 1, which would require ambient air quality characterization around sources with emissions greater than 1,000 tons per year that are located within a core based statistical area (CBSA) having 1,000,000 or more persons, and around sources with emissions greater than 2,000 tons per year located outside CBSAs having 1,000,000 or more persons. Based upon 2011 emissions data and 2012 census estimates, Option 1 would identify 443 sources that account for 75% of the total SO2 emissions inventory located in areas currently not designated.  Facilities with annual emissions in excess of the Option 1 thresholds should be gaining an understanding of how the DRR will impact them.  However, smaller facilities located nearby facilities defined in the options above may also be included in the evaluation, so understanding your neighbors and their emissions profiles is equally important.

Now is the time for those facilities that will be impacted by the DRR to start considering how to address the ensuing modeling and monitoring costs and what compliance approach is the right fit.  The dispersion modeling could result in the establishment of new short-term emission limits that are based on modeled compliance with the 1-hour NAAQS.  If dispersion modeling isn’t used, those facilities will be largely responsible for the funding, installation, operation, and maintenance of a new ambient monitor or monitors and the resulting logistical considerations that go with it.  Preliminary normalized dispersion modeling can be conducted to determine the locations and number of monitors that could be recommended by the state agency after finalization of the DRR.  ALL4 would be happy to assist you in evaluating the recommendations outlined here, so feel free to contact Colin McCall at (678) 460-0324 x206 with questions about this article or about the SO2 NAAQS in general.


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