The EPA’s Office of Air Quality Planning and Standards recently issued guidance on how information on prescribed fires on wildland may be factored into exceptional events demonstrations required by Section 319(b) of the Clean Air Act (CAA). If the Agency accepts a state’s exceptional event demonstration, air pollution resulting from the event is excluded from data used to determine an area’s attainment or nonattainment under the CAA’s National Ambient Air Quality Standards (NAAQS). In a 2016 rule, the Agency stated that an exceptional event demonstration must address six elements. For example, the state must provide data that show “a clear causal relationship between the specific event and the monitored exceedance or violation.” The state must also demonstrate that “the event was both not reasonably controllable and not reasonably preventable.” A third criterion, and one particularly relevant to prescribed burns, is that the demonstration must show that the event “was caused by human activity that is unlikely to recur at a particular location or was a natural event.” Unlikely to recur at a particular location is a somewhat slippery term that warrants clarification.

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3-year recurrence criterion

A human activity that is unlikely to recur at a particular location and that can contribute to an NAAQS violation can cover multiple types of events, including a chemical spill or other industrial accident and a structural fire. In such cases, the state can present strong evidence that the event is unlikely to recur at a particular location. However, the demonstration must meet a 3-year recurrence criterion. In the 2016 rule, the EPA explains:

“We measure the 3-year period backwards from the date of the most recent event (e.g.,for an event occurring on May 1, 2016, the 3-year period would be May 1, 2013, through May 1, 2016). [I]f there have been two prior events of a similar type (i.e.,a similar event type generating emissions of the same pollutant whether flagged or the subject of a demonstration) within a 3-year period in ‘a particular location,’ the third event, for which the demonstration is being prepared (or would be prepared), would generally not satisfy the ‘human activity that is unlikely to recur at a particular location’ criterion and, thus, would not qualify as an exceptional event. If an event type has not previously occurred within a given air quality control region in the 3 years preceding the submittal of an exceptional events demonstration for an event that has occurred recently, the EPA will consider this recent event to be a ‘first’ event and will generally consider that event type to be unlikely to recur in the same location.”

Sustaining wildland

But the 3-year benchmark for recurrence for most “human activities that are unlikely to recur” does not apply to prescribed fires.  The EPA defines “prescribed fires” as controlled, typically small, and contained events that are unlikely to produce a problematic quantity of emissions. In its new guidance, the Agency notes that in some situations, prescribed fires happening more frequently than three times in 3 years can be considered unlikely to recur. The EPA states:

“Rather than using [the 3-year] benchmark for prescribed fire on wildland, the exceptional events rule states that recurrence for prescribed fires is defined by either ‘the natural fire return interval or the prescribed fire frequency needed to establish, restore and/or maintain a sustainable and resilient wildland ecosystem contained in a multi-year land or resource management plan with a stated objective to establish, restore and/or maintain a sustainable and resilient wildland ecosystem and/or to preserve endangered or threatened species through a program of prescribed fire.’ Thus, the recurrence frequency for prescribed fire is specific to the ecosystem and resource needs of the affected area.”

The guidance goes on to note that the recurrence provision for a prescribed fire on wildland is intended to reduce the risk of catastrophic wildfire and recognizes that land managers often pursue these benefits through a program of prescribed fires. Other uses of prescribed fires that would fall under the provision include burning of debris for land clearing, agricultural burning, and burning of logging slash on land used for commercial timber sale.

Consult with EPA

The guidance advises that air agencies that receive exceptional event demonstrations should consult with their EPA regional offices regarding how to characterize a “particular location” for purposes of addressing the “human activity unlikely to recur at a particular location” criterion.

“Ultimately, EPA will determine the bounds for ‘a particular location,’” states the Agency.