On June 4, 2019, the Washington Department of Ecology (Ecology) formally proposed changes to the state's toxic air pollutant (TAP) permitting program in WAC 173-460. The TAP program is part of the Notice of Construction (NOC) air permitting program, which requires evaluation of TAP emissions prior to issuance of an air permit. For each TAP, the rule specifies a de minimis emission rate threshold above which permitting is required, a Small Quantity Emission Rate (SQER) threshold above which dispersion modeling is required, and an Acceptable Source Impact Level (ASIL) against which the dispersion modeling results are compared.

The proposed rule changes involve a reevaluation of the list of TAPs and their relevant thresholds (de minimis, SQER, and ASIL). Key proposed changes include:

  • Adding 45 new TAPs to the list.
  • Removing 8 TAPs from the list, including the removal of ammonium sulfate by industry petition.
  • Relaxing ASILs for 23 TAPs based on more current toxicological data. Some of these changes would impact TAPs that are frequently evaluated for permitting projects, such as acrolein, ammonia, benzene, manganese compounds, methanol, and methylene chloride. Additionally, Ecology proposed ASILs for methyl mercury and dimethyl mercury, which currently do not have ASILs.
  • Tightening of ASILs for 67 TAPs based on more current toxicological data. Some of these changes would impact TAPs that are frequently evaluated for permitting projects, including arsine, asbestos, benz(a)anthracene), benzo(b)fluoranthene, benzo(j)fluoranthene, benzo(k)fluoranthene, chlorine, chromic (VI) acid, chromium (VI) and compounds, elemental mercury, and perchloroethylene.
  • Recalculating SQER values for all TAPs based on updated dispersion modeling.
  • Recalculating de minimis values to be equal to 5 percent of the corresponding SQER.

Many industry stakeholders had hoped the proposed rule would remove NO2, SO2, and CO from the TAP list, since those pollutants are already regulated under the permitting rules as criteria pollutants. However, the proposed rule leaves these three pollutants on the TAP list. Additionally, Ecology is not proposing changes to the problematically-low ASIL for diesel engine particulate.

If you have any questions about the proposed TAP rule changes, please contact Aaron Day at a aday@trinityconsultants.com or (253) 867-5600.