Regulatory Update   |   Jan 15th, 2015 Proactive Positioning for the Imminent SO2 Data Requirements Rule


Following the establishment of a stringent 1-hour Sulfur Dioxide (SO2) National Ambient Air Quality Standard (NAAQS), the US Environmental Protection Agency (EPA) is now proceeding with its implementation plans to assure that all areas of the US will comply with the new NAAQS. The geographic areas of the US determined to have ambient air concentrations above the new NAAQS and therefore designated as nonattainment areas are illustrated in a map provided by EPA. If your facility is within one of these 29 nonattainment areas, you already know you face rigid compliance requirements.

All other SO2 sources will soon discover what requirements they will face as state and local permitting agencies develop plans for achieving or maintaining NAAQS attainment. These plans will need to comply with the final Data Requirements Rule, expected to be promulgated in early 2015.

Based on the proposed rule, it is likely that most, if not all, SO2 sources in the US will be affected and will need to work with their permitting agency to establish a NAAQS attainment strategy that may include air dispersion modeling and/or ambient air monitoring. There is no mystery as to which sources will be affected by the rule; EPA published a list that may include as many as 443 facilities that emit as little as 1,000 tons of SO2 per year. If your facility is included on this list, or if you are a smaller source that may contribute to your region or geographic area exceeding or violating the NAAQS, you should take action now. Some suggestions are provided below to help develop your strategy for demonstrating compliance.

The Proposed Rule

EPA created a 1-hour average NAAQS for SO2 and is responsible for identifying areas across the US that do not meet that standard. However, in many locations, EPA was unable to designate as either an attainment area (meets the standard) or a non-attainment area (NAA: does not meet the standard). On April 17, 2014, EPA proposed a Data Requirements Rule that mandated individual state air quality agencies give EPA data to complete their SO2 attainment classifications for the “undesignated” areas within the state. EPA gave the states two options to choose for the area designation process: develop and use air quality monitoring data or perform air dispersion modeling analyses of the sources of interest.

The areas of most interest to EPA are those that have major or large emission sources of SO2 with the potential to pose a threat to the NAAQS. The proposed rule includes suggestions of potential options to consider in establishing source size or emission level thresholds to which the rule would apply. The options include three population-weighted emission thresholds for states to use to target facilities to model or monitor the emission of:

  • Option 1 — Sources greater than 1,000 tons per year of SO2 in areas with a population of greater than 1 million, and sources greater than 2,000 tons everywhere else. [EPA’s Preferred option as of now ]
  • Option 2 — Sources greater than 2,000 tons per year of SO2 in areas with a population of greater than 1 million, and sources greater than 5,000 tons everywhere else.
  • Option 3 — Sources greater than 3,000 tons per year of SO2 in areas with a population of greater than 1 million, and sources greater than 10,000 tons everywhere else.

The Timeline

Depending on the option selected by the state or regulatory agency to demonstrate compliance, there are two timelines to follow. While emission options and timelines are being worked through by EPA, states are expected to develop protocols based on their choice of either a monitoring or modeling approach. By January 2016, each state must submit its list of targeted sources (e.g. “Option 1” sources) along with which data collection approach it has chosen. Depending on the method chosen, the timeline will be established as shown in this graphic.

Action You Should Take Now

If a state or permitting agency decides to adopt a dispersion modeling approach for a specific area or source, emission limits for a targeted facility will be based on compliance scenarios modeled by the state. If your facility is on this path, it is a good idea to perform some preliminary modeling of the source(s) in question to understand the potential ramification of a modeled compliance demonstration on the allowable emission rate for those sources. This information will be very helpful in developing a compliance strategy that can be used for internal planning, well before the State must take action.

If dispersion modeling is not the preferred option by the state, then consider identifying and screening potential locations where the state should install ambient monitors that would yield representative impact data for your facility. This data will help you understand the most appropriate location for monitors and provide informed feedback to the regulatory agency as they develop a monitoring program. This input will be invaluable to assure that the final monitor site selection will collect ambient air data that are representative of your sources’ contribution and the offending concentrations can be attributed to the appropriate sources. The availability of these data will ensure that your sources will be treated fairly in setting the eventual emission rates that demonstrate compliance with the NAAQS.

Do you have plans in place to meet compliance requirements? Please share your questions, challenges and best practices in the comments section below.

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