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The Environmental Protection Agency’s (EPA’s) proposed Air Toxics Rule will mark the first federal limits on hazardous air pollutants (HAPs) — including mercury — in U.S. history. The HAPs to be controlled include mercury, lead, arsenic, hydrogen chloride (HCl), hydrogen fluoride (HF), dioxins/furans and other toxic substances identified by Congress in the 1990 amendments to the Clean Air Act (CAA). The rule establishes “maximum achievable control technology” (MACT) limits for many of these and has therefore adopted the nickname “Utility MACT.”  The law requires EPA to base the MACT on the top 12 percent of units “for which the Administrator has data.”  The 12 percent of units equaled 131 units by EPA’s count. Consequently, EPA used data from 131 units to develop the proposed MACT limits.

Utility MACT does not require emission limits for organic HAPs or dioxins/furans. The rulemaking also allows SO2 as a surrogate option for acid gas HAPs, which means most power producers that already have scrubbers for SO2 control will not need additional controls for acid gas HAPs. Utility MACT also allows for alternative compliance by averaging among similar units within one plant. 

Utility MACT includes mandatory performance testing for both the surrogate and the pollutant. Also, “operating limits” on control equipment must be continuously monitored and maintained within “tight constraints,” even if continuous emissions monitoring systems (CEMS) are used to demonstrate compliance.

Since no CEMS currently exist for total  particulate matter (PM)—filterable plus condensable—selected as the surrogate for non-mercury metallic HAPs, this is sure to cause a number of challenges.

Mercury control regulations enforced by many states already require 80 to 95 percent mercury capture rates.  But because Utility MACT covers more than just mercury, even a power plant that has technology for a state mercury regulation may still need to install additional control technology in order to capture another emissions type. 

Ultimately, what is most important is that benefits generated by Utility MACT outweigh compliance costs. EPA estimates the Utility MACT would generate $140 billion in annual health and welfare benefits in 2016. EPA also admits the ruling would impose costs of about $11 billion a year on the U.S. economy.  However, EPA’s number crunching has been questioned by a number of industry groups, including the Electric Reliability Coordinating Council (ERCC).  (Power Engineering, 10/1/2011)