On January 3, 2007, the US Environmental Protection Agency proposed a rule that would eliminate the "Once In-Always In" policy for Maximum Achievable Control Technology (MACT) Standards for air emissions. (See 72 Fed Reg 69.) The current policy establishes MACT Standard applicability at the time of the first substantive compliance date. Under current rules, facilities considered a major source as of that date are forevermore subject to that MACT Standard regardless of any further changes to the source. The proposed change in policy would allow a source that can reduce its facility-wide potential to emit below the major source thresholds (10 tons per year for any individual hazardous air pollutant [HAP] or 25 tons per year for all HAPs combined) to escape MACT obligations at any time, even after the MACT compliance date. This is designed to generate a continuing incentive for sources to reduce HAP emissions even after achieving compliance with the MACT Standard.

As proposed, this new rule would allow the following:

  • Facilities that have shut down a significant HAP source, or that have reformulated raw materials to reduce HAP emissions, may find their potential to emit has fallen below major source thresholds. By obtaining a permit amendment establishing the facility-wide potential to emit below the 10/25 major source thresholds, the facility may be excused from MACT requirements going forward.
  • Facilities that can reduce emissions below the 10/25 thresholds by installing a portion of the controls required for MACT compliance can avoid significant MACT-related compliance costs by obtaining an enforceable permit term limiting potential to emit (PTE).
  • Facilities that are currently relying on internal PTE calculations for non-major status may reduce their risk by accepting enforceable permit terms that serve to verify and substantiate the PTE calculation. While the US EPA has made clear that this cannot be used to avoid an agency enforcement action that has already been initiated, it should be effective to reduce the risk of future actions and citizen suits.