Status of Outstanding SO2 NAAQS Designations



In June 2010, the U.S. Environmental Protection Agency (EPA) promulgated the new 1-hour sulfur dioxide (SO2) National Ambient Air Quality Standard (NAAQS) at a level of 75 parts per billion based on the 3-year average of the annual 99th percentile of 1-hour daily maximum concentrations.

On August 5, 2013, EPA initially designated 29 areas in 16 states as nonattainment with the 2010 SO2 standard (Round 1). Air quality monitoring in each of these areas measured violations of the standard based on 2009 - 2011 data. EPA set a timeline for states to submit State Implementation Plans (SIPs) to demonstrate how these areas will meet the new standard, with initial submittals by April 2015. At that time, EPA intended to address designations for the remainder of the country in future actions.

Accelerated Timeline Set

However, on March 2, 20151, as a result of litigation between EPA, Sierra Club, and Natural Resources Defense Council, the U.S. District Court for the Northern District of California directed EPA to complete designations for all remaining areas in the country in up to three additional rounds of designations. The intent of the litigation was to accelerate the schedule and determination of nonattainment status of the 2010 1-hour SO2 standard surrounding large SO2 sources. The resulting schedule includes the timelines described below:

Round 2
July 2, 2016 - The deadline for EPA to designate two categories of areas:

  1. Areas that have monitored violations of the 2010 SO2 standard based on 2013 - 2015 air quality data
  2. Areas that contain any stationary source not announced for retirement that in 2012 either (a) emitted more than 16,000 tons of SO2 or (b) had an average emission rate of at least 0.45 lbs. SO2/MMBtu
  3. ‚ 

Round 3
December 31, 2017 - The date by which EPA must complete an additional round of area designations addressing areas where states have not installed and begun operating a new SO2 monitoring network which meets EPA's specifications referenced in an anticipated final "Data Requirements Rule for the 1-hour SO2 primary NAAQS".

Round 4
December 31, 2020 - The date by which EPA must designate all remaining areas

SO2 Designation Guidance

On March 20, 2015, in a memorandum to Regional Air Division Directors, EPA provided updated guidance for areas designated as nonattainment with the 2010 SO2 standard. The memorandum identifies factors for determining boundaries for areas designated as nonattainment, attainment, and unclassifiable. The memorandum also discusses EPA's intent to utilize the proposed SO2 Data Requirements Rule (DRR) that requires states to gather and submit information to EPA regarding analysis of areas with larger sources of SO2 emissions. This information would be used as part of the future designations decision process. As proposed, states could use either monitoring or modeling to characterize SO2 air quality in the vicinity of large SO2 sources.

Also on March 20, 2015, EPA sent letters to 28 states that have areas scheduled to be addressed in the next round (Round 2) of designations for the 2010 SO2 standard. In these letters, EPA stated that air quality in parts of these states may be impacted by large sources of SO2 emissions. In addition, EPA stated that air quality monitors in some of these states are measuring preliminary violations of the standard. EPA also informed seven tribes that they may be impacted by nearby sources of SO2 emissions. The list of 68 power plants and new monitored violations can be referenced here

EQ Summer 2015 - Status of Outstanding..

Two guidance documents made available by EPA in January 2014 provide technical assistance to states (and sources) on the use of modeling and monitoring to determine if an area meets the 2010 SO2 standard. The December 2013 draft documents are SO2 NAAQS Designations Modeling Technical Assistance Document and SO2 NAAQS Designations Source-Oriented Monitoring Technical Assistance Document available here

For the round of designations due by July 2, 2016, EPA has requested that states provide updated recommendations and supporting information by September 18, 2015. EPA recognizes that the tight timeline will not allow the use of data from the installation of any new SO2 ambient monitoring sites and therefore the expectation would be for the use of source modeling for this round of designations.

A number of states are currently conducting studies to respond to EPA by September 18, 2015, for both the listed sources and the monitored violations. In many cases the studies are intended to limit the size of the nonattainment area. Typically, default nonattainment areas include whole counties unless a demonstration can be made that a smaller area better reflects the characteristics of the sources in the area, topographical features, and local meteorology.

States are also planning for Round 4 (new monitored areas and all remaining areas), which EPA is to designate by December 31, 2020. States are required to submit ambient monitoring plans to EPA by July 2016 for those facilities that plan to conduct ambient air monitoring. To establish a 3-year ambient monitoring dataset, new monitoring networks must begin operation by January 1, 2017.

Facilities that have an annual emission rate greater than 1,000 tons per year inside Core-Based Statistical Areas (CBSAs) greater than 1 million people or that emit more than 2,000 tons per year outside CBSAs of more than 1 million people are encouraged to monitor the associated ongoing regulatory developments. This may include conducting in-house dispersion modeling to determine if the facility will show violation of the standard or to determine the site location of potential ambient air monitor(s).

Trinity can provide strategic assistance in both understanding the proposed rules and technical guidance as well as implementing programs to achieve near-term and ongoing compliance.

1 On April 30, 2015, the states of North Dakota, Arizona, Kentucky, Nevada, Louisiana, and Texas filed a notice appealing the settlement to the U.S. Court of Appeals for the 9th Circuit. The notice of appeal does not discuss the reason the states seek to overturn the EPA settlement agreement, but a successful appeal could potentially benefit states by creating unclassifiable versus nonattainment status designations.