Updated Guidance for SO2 Area Designations- Part 1

The Updated Guidance for Sulfur Dioxide Area Designations was released by EPA on March 20, 2015. The main purpose of this document is to define the schedule and process for designating areas for the 2010 primary 1-hour SO2 NAAQS.

EPA issued the first round of SO2 designations in August 2013. However, three lawsuits were filed against EPA for not designating all portions of the country by the June 2013 deadline. As a result of this litigation, on March 2, 2015 EPA was ordered by the Court to complete the remaining SO2 designations for the rest of the country in three additional rounds.

Round 2
The second round of designations includes areas that have newly monitored violations of the 2010 1-hr SO2 standard and contain stationary sources that either:

  • Emitted more than 16,000 tons of SO2 in 2012 or,
  • Emitted more than 2,600 tons of SO2 and had an annual emission rate of at least 0.45 lbs SO2/MMBtu in 2012, and
  • Have not been announced for retirement.

Here are the important dates for Round 2:

  • 09/18/2015: Deadline for states to provide updated recommendations and supporting information to EPA
  • 01/22/2016: EPA notifies states about any intent to change their recommended designation status (120-day letter)
  • 02/03/2016: EPA publishes the state’s attainment recommendations along with EPA’s intended modifications and start of a 30-day public comment period
  • 04/08/2016: Deadline for states to provide additional information for EPA to consider before final designations are issued
  • 07/02/2016: EPA promulgates final SO2 area designations.

Round 3
This round includes the remaining undesignated areas that do not have an installed and operating SO2 monitoring network. This round is expected to cover most undesignated areas for those states choosing to follow the modeling approach. For these areas the important date is:

  • 12/31/2017: Deadline for EPA to designate the remaining undesignated areas that do not have an SO2 monitoring network in place and operation al by January 1, 2017.

Round 4
This round includes areas that implement the monitoring instead of the modeling approach. EPA expects to provide guidance related to the monitoring approach in the anticipated SO2 Data Requirements Rule (DRR). You can read the proposed rule HERE.  The areas that choose the monitoring approach would need to have a monitoring protocol in place by July 2016 and an installed and operating SO2 monitoring network by January 1, 2017. The areas under Round 4 would need to monitor SO2 ambient concentrations for at least 3 years (2017-2019).

Here is a summary of the important dates for Round 4 areas:

  • 07/01/2016: Annual monitoring network plans due to the EPA regional administrator
  • 01/07/2017: SO2 monitors are required to be operational
  • 12/31/2020: Deadline for EPA to designate areas using monitoring approach to characterize SO2 air quality.

Summary and Discussion
EPA is currently under a Court order to complete the 1-hour SO2 designation process in the time frame described above. There is still some time (but not much) to provide additional information to the state agencies to show compliance through modeling before an area is designated as non-attainment by EPA. Modeling is the preferred option due to its lower cost and effort involved compared with the monitoring approach.

Facilities with modeling SO2 exceedances should try to refine their emissions and explore mitigation techniques that can produce modeling runs that show compliance with the 1-hour SO2 NAAQS. Another option for these facilities is to refine the building dimensions entered into AERMOD. This can be done with the use of wind tunnel derived Equivalent Building Dimension (EBD) which has proven very useful in overcoming the overstated downwash effects due to BPIP generated dimensions. EBDs can be most effective for complex and elongated buildings, streamlined structures (e.g., hyperbolic cooling towers), and lattice structures. In most cases, the predicted AERMOD concentrations are reduced to a reasonable level – many times to less than half of what they would be with BPIP generated building dimensions. This is the case because the building wake algorithm in AERMOD/PRIME is based on wind tunnel studies developed for specific building dimensions, but when outside of these dimensions the theory falls apart and produces unrealistically high concentrations. However, EBD can match the theory and produce more accurate results.

Facilities must take a proactive approach in achieving favorable dispersion modeling runs. Otherwise, the only option left is to conduct ambient monitoring which entails a greater expense and a very tight schedule related to submission of monitoring plans and deployment/operation of the monitoring network.

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