On July 18, 2018, the Washington Department of Ecology (Ecology) announced that the agency is initiating rulemaking to update the state's permitting rules for toxic air pollutants in WAC 173-460. This would be the first major revision since the current version of the rule was established in 2009.

The rulemaking process will include several elements. First, Ecology plans to update the list of toxic air pollutants regulated by the rule by evaluating the following possible changes:

  • Add or subtract chemicals based on current inhalation toxicity information available from EPA, California Office of Environmental Health Hazard Assessment (OEHHA), and the Agency for Toxic Substances and Disease Registry (ATSDR).
  • Review an industry request to remove ammonium sulfate from the list of toxic air pollutants.
  • Evaluate whether criteria pollutants (NOx, SO2, and CO) currently listed as toxic air pollutants should be removed from the list

Ecology also proposes to recalculate many of the numerical thresholds used in the current rule. The following recalculations are proposed.

  • Recalculate acceptable source impact levels (ASIL) used to determine whether dispersion modeling shows acceptable results. Additionally, Ecology will evaluate whether to establish additional ASIL for certain groups of chemicals (dioxin-like compounds, polycyclic aromatic hydrocarbons) and treat each of those groups of chemicals as a single toxic under the rule. Ecology will also be evaluating whether to include early life adjustment factors when deriving ASILs for chemicals that are considered to cause cancer through a mutagenic mode of action.
  • Recalculate small quantity emission rate (SQER) thresholds used as screening thresholds to determine whether dispersion modeling is required. The recalculation will be based on the updates to the ASIL values and the use of current AERSCREEN dispersion modeling.
  • Recalculate the de minimis emission rates used to determine whether a proposed project triggers toxic air pollutant permitting provisions. The recalculation will be based on the updates to the ASIL values.

An initial stakeholder meeting was scheduled for August 20, 2018, with additional meetings taking place in the Fall of this year. Ecology plans to propose an updated rule in Spring 2019, and finalize the rule in Fall 2019.

Concurrently, Ecology also announced that the agency is initiating an exploratory rulemaking process to consider other changes to the WAC 173-460 rules. Ecology will be gathering input over the next year on other possible rule changes, which may lead to future rulemaking efforts.

If you have any questions about the toxic air pollutant rulemaking, please contact Aaron Day, Principal Consultant, at (253) 867-5600.