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Latest News On The 1-Hour SO2 NAAQS Implementation Process

Posted: May 10th, 2012

Author: All4 Staff 

On April 12, 2012, U.S. EPA’s assistant secretary Gina McCarthy recently sent letters to States outlining updates to the implementation procedures of the 1-hour sulfur dioxide (SO2) National Ambient Air Quality Standard (NAAQS). The major news is that U.S. EPA has put a hold on the modeling requirement for individual sources for inclusion in the June 2013 Maintenance State Implementation Plan (SIP).  ALL4’s Colin McCall broke the news on April 20, 2012 in his blog post “Urgent – SO2 Implementation Update”.

Now that we’ve had some time to digest the news I thought it was a good time to update everyone on the latest information.  The letter sent to states from Gina McCarthy stated that stakeholder meetings would be held to address two (2) main topics:

  1. How best to assess compliance with the SO2 NAAQS (e.g., by defining and establishing a robust, representative monitoring network for SO2 across the country and/or by applying the appropriate modeling approach).
  2. How to implement the approach (e.g., implementation options and SIP timelines for areas in which violations are identified).

These stakeholder meetings have been scheduled and will be broken into the following three (3) sessions:

  1. Session 1: Environmental and Public Health Organization Representatives – May 30, 2012, Washington, DC
  2. Session 2:  State and Tribal Representatives – May 31, 2012, Research Triangle Park, NC
  3. Session 3:  Industry Representatives – June 1, 2012, Research Triangle Park, NC

U.S. EPA has indicated that the issues that will be discussed during each of the sessions will be outlined in a white paper.  In addition a summary of comments from the stakeholder meetings will also be posted on the same website following the conclusion of all three (3) meetings.  ALL4 also plans on attending at least one (1) if not all three (3) of the sessions.  For industry that could potentially be affected by the SO2 NAAQS implementation, we strongly recommend attending Session 3.  This is your time to provide valuable input into the process of determining how States (and facilities) will be assessing compliance with the SO2 NAAQS.

It should be noted that the stakeholder meetings will not be addressing the level of the 1-hour SO2 NAAQS.  The 1-hour SO2 NAAQS is a primary standard meaning that it is put in place to be protective of human health and therefore it is extremely unlikely that the 75 ppb standard will be changed.  In addition it should also be noted that the letters sent to States in no way are related to modeling requirements under the Prevention of Significant Deterioration (PSD) permitting program.  If modeling requirements for SO2 are tripped for the PSD permit program, a demonstration showing compliance with the 1-hour SO2 NAAQS is still required following procedures laid out in 40 CFR Part 51 Appendix W – “Guideline on Air Quality Models.”  However, if anyone would like to comment on issues related to permit modeling, the U.S. EPA has put a second extension on the comment period for the 10th Conference on Air Quality Modeling held in Research Triangle Park, NC on March 13-15, 2012.  The extension was put into place to address the late release of “Case Studies for 1-hour NO2 and SO2 NAAQS” conducted by the AERMOD Implementation Workgroup (AIWG) which can be found here.

Based on the changes made to the 1-hour SO2 NAAQS implementation process, ALL4 offers the following advice to our clients:

  • Be involved in the stakeholder meetings.
  • U.S. EPA’s original proposed 1-hour SO2 NAAQS implementation approach involved the installation of new ambient monitoring stations.  The location of the monitoring stations in a given census statistical area was to be based on a factor equal to the product of SO2 annual emissions and population in that area.  The basis of this proposed approach was to place ambient monitors in areas where the general public was most likely to be exposed to short-term peaks of SO2 concentrations.  This original approach could be more favorable than specific modeling demonstrations provided that the ambient monitors are placed in areas of the general population and not located along facility fencelines.  The proposal is technically justifiable but would need to be weighed versus the cost and time it would take to implement such a monitoring program.
  • ALL4 continues to recommend that facilities conduct exploratory modeling to assess your status with the 1-hour SO2 NAAQS for planning purposes.  The only thing that we recommend differently with the changes made to the implementation process is to conduct the modeling through legal counsel under an attorney-client privilege arrangement to keep the results confidential.
  • Be aware that there could still be a modeling requirement that comes out of the stakeholder meetings for the SO2 SIP Implementation.  Also, be aware that there could be a monitoring requirement that comes out of the stakeholder meetings as well.
  • Modeling under PSD for the SO2 1-hour NAAQS remains a requirement under each program, as applicable.


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