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Mercury and Air Toxics Standards

History of the MATS Regulation

Early 1990s

The Clean Air Act provides that EPA must take several steps before regulating air toxics emissions (such as mercury) from power plants. Deadlines for these steps were specified in a legal settlement of related litigation filed in the early 1990s. 

October 1994

EPA enters settlement agreement providing that by November 15, 1995, it would complete its "Utility Air Toxics Study"(5 pp, 31 K, About PDF) to Congress; determine whether its is "appropriate and necessary" to regulate power plants under Clean Air Act section 112; and, if so, to issue such regulations by November 15, 2000. The parties subsequently agreed to extend the deadline for completing the Utility Air Toxics study until February 1998. EPA also agreed to solicit additional information from power plants and to use such information for making its appropriate and necessary determination.

December 1997

EPA analyzed mercury emissions from power plants and other industrial sources, the health and environmental impacts of those emissions and available control technologies. These findings were issued as a "Mercury Study Report to Congress" in December 1997.

February 1998

In the "Utility Air Toxics Study" report to Congress, issued in February 1998, EPA focused on power plants, analyzing emissions of toxic air pollutants, including mercury.

November 1998

Deadline for EPA to determine whether it is "appropriate and necessary" to regulate power plant emissions under CAA section 112 is extended until December 15, 2000. EPA further agrees to issue proposed and final power plant mercury emission standards by December 15, 2003 and December 15, 2004, respectively.

December 2000

EPA announced its finding that it was "appropriate and necessary" to regulate coal- and oil-fired electric utilities under section 112 of the Clean Air Act. This finding, known as the Utility Air Toxics Determination (PDF)(7 pp, 254 K, About PDF) triggered a requirement for EPA to propose regulations to control air toxics emissions, including mercury, from these facilities by December 15, 2003.

January 2004

On January 30, 2004, EPA proposed a rule with two basic approaches for controlling mercury from power plants. One approach would require power plants to meet emissions standards reflecting the application of the "maximum achievable control technology" (MACT) determined according to the procedure set forth in section 112(d) of the Clean Air Act. If implemented, this proposal would reduce nationwide mercury by 14 tons or about 30 percent by early 2008. A second approach proposed by EPA would create a market-based "cap and trade" program that, if implemented, would reduce nationwide utility emissions of mercury in two phases. When fully implemented mercury emissions would be reduced by 33 tons (nearly 70 percent). EPA proposed to pursue the cap and trade approach either under Section 111 or Section 112 of the Clean Air Act.

EPA also proposed to revise its December 2000 finding that it is "appropriate and necessary" to regulate utility hazardous air emissions using the MACT standards provisions (section 112) of the Clean Air Act.

March 2004

On March 16, 2004, EPA proposed a supplement to its January 2004 proposal (PDF)(75 pp, 442 K, About PDF). This action provided details on the proposed mercury trading program and methodologies for measuring mercury emissions.

April 2004

To afford the public with an additional opportunity to comment on EPA's proposal, EPA agreed to extend the deadline for issuance of the final power plant mercury rule from December 15, 2004 to March 15, 2005.

December 2004

On December 1, 2004, EPA issued a Notice of Data Availability (NODA) (15 pp, 89 K, About PDF) summarizing the modeling analyses presented by EPA and the commenters, and soliciting comment on the inputs and assumptions underlying those analyses. The NODA also sought comment on EPA’s benefits assessment. The public comment period closed January 3, 2005.

March 2005

On March 15, 2005, EPA issued the final Clean Air Mercury Rule.

The Clean Air Mercury Rule established “standards of performance” limiting mercury emissions from new and existing utilities and created a market-based cap-and-trade program to reduce nationwide utility emissions of mercury in two phases.

February 2008

On February 8, 2008, the D.C. Circuit vacated EPA's rule removing power plants from the Clean Air Act list of sources of hazardous air pollutants. At the same time, the Court vacated the Clean Air Mercury Rule. Read the Court's Opinion (PDF)(18 pp, 51 K About PDF(US Court of Appeals, District of Columbia Circuit website)

EPA announced plans to propose air toxics standards for coal- and oil-fired electric generating units by March 16, 2011 and finalize a rule by November 16, 2011.

February 2009

On February 6, 2009, the Department of Justice, on behalf of EPA, asked the Supreme Court to dismiss EPA’s request (petition for certiorari) that the Court review the D.C. Circuit Court’s vacatur of the Clean Air Mercury Rule (CAMR). Read the Acting Solicitor General’s motion.

On February 23, 2009, the Court also denied the Utility Air Regulatory Group’s request to review the U.S. Circuit Court of Appeals decision.

December 2009

On December 24, 2009, EPA approved an Information Collection Request (ICR) requiring all US power plants with coal-or oil-fired electric generating units to submit emissions information for use in developing air toxics emissions standards. Additional details about the final ICR can be found on the Clean Air Act Standards and Guidelines for Electric Utilities webpage.

March 2011

On March 16, 2011, EPA proposed a rule that would reduce emissions from new and existing coal- and oil-fired power plants. This proposed rule would replace the court-vacated Clean Air Mercury Rule.