On April 16, the U.S. Environmental Protection Agency (EPA) completed a reconsideration of the appropriate and necessary finding for the Mercury and Air Toxics Standards (MATS), which it said corrected flaws in the 2016 supplemental cost finding while ensuring that power plants will emit no more mercury to the air than before.

After considering compliance costs relative to the hazardous air pollutants benefits (HAP) of MATS, the EPA said it is not “appropriate and necessary” to regulate electric utility steam generating units under section 112 of the Clean Air Act (CAA).

The EPA also took final action on the residual risk and technology review (RTR) that is required by CAA section 112. The results from the RTR showed that emissions of HAP have been reduced such that residual risk is at acceptable levels, that there are no developments in HAP emissions controls to achieve further cost-effective reductions beyond the current standards.

The EPA determined that no changes to the MATS rule were warranted.

The EPA said it is maintaining its mercury and air toxics emissions standards as EPA Administrator Andrew Wheeler announced nearly a year ago.

The EPA has decided to not remove coal- and oil-fired power plants from the list of affected source categories for regulation under the Clean Air Act, so MATS will remain in effect.

The EPA performed this task in response to the U.S. Supreme Court ruling in 2015 that the EPA had failed to consider the cost of compliance when proposing regulation of hazardous air pollutants from coal- and oil-fi red power plants.

The EPA said MATS was projected to cost up to $9.6 billion annually while the monetizable benefits derived from mercury emission reductions were valued at up to $6 million annually.

On April 9, the EPA established a new subcategory under the MATS rule electric utility steam generating units (EGUs) that burn eastern bituminous coal refuse (EBCR).

It will also establish new emission standards for these facilities to control acid gas hazardous air pollutant emissions. The new subcategory and emission standards will affect six existing EGUs that burn EBCR. All are small units operating in Pennsylvania or West Virginia. As a result of this final rule, the EPA said it does not expect emissions to increase above current levels.