The Clean Air Act Amendments of 1990 (CAAA) brought about new awareness regarding the overall health-effects of stationary source fossil combustion emissions. Title III of the CAAA identified 189 pollutants, including mercury, as hazardous or toxic and required the Environmental Protection Agency (EPA) to evaluate their emissions by source, health effects and environmental implications, including the need to control these emissions. These pollutants are collectively referred to as air toxics or hazardous air pollutants (HAPs). The provisions in Title III specific to electric generating units (EGU) were comprehensively addressed by DOE’s National Energy Technology Laboratory (NETL) and the Electric Power Research Institute (EPRI) in collaborative air toxic characterization programs conducted between 1990 and 1997. This work provided most of the data supporting the conclusions found in EPA's congressionally mandated reports regarding air toxic emissions from coal-fired utility boilers; the Mercury Study Report to Congress (1997)¹ and the "Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units -- Final Report to Congress" (1998).² The first report identified coal-fired power plants as the largest source of human-generated mercury emissions in the U.S. and the second concluded that mercury from coal-fired utilities was the HAP of "greatest potential concern" to the environment and human health that merited additional research and monitoring.

Top 6 Sources of Mercury Emissions in the US1

Subsequently, data were gathered in response to EPA's 1998 Information Collection Request (ICR).³ EPA, in cooperation with NETL, refined the total mercury emission inventory from coal-fired plants and ascertained the mercury control capabilities of existing and potential emission control technologies. Results of this work, and an independent evaluation of mercury health impacts by the National Academy of Sciences (NAS), culminated in EPA's decision in December 2000 to regulate the mercury emissions (and other air toxics the Agency deemed necessary) from coal-fired and oil-fired power plants.⁴ In their regulatory determination, EPA concluded that there was a "plausible link" between emissions of mercury from coal-fired electric utility steam generating units and the bioaccumulation of methyl mercury in fish and other animals that eat fish. Because human exposure to mercury occurs primarily through consumption of contaminated saltwater or freshwater fish, further control of coal- and oil-fired power plants was determined to be necessary.

The Mercury Cycle5 (click to enlarge)

The Legislative/Judicial/Regulatory Process Leading to Current Proposed Regulations⁶

The EPA is only permitted to regulate HAP emissions from electric utilities based upon section 112 of the CAA if it determines that such regulation is appropriate and necessary. On December 14, 2000, EPA concluded that, in accordance with the CAA, the regulation of mercury emissions from electric utilities was "appropriate and necessary," and therefore added electric generating units (EGUs) to the list of source categories to be regulated under section 112.⁷

This regulatory finding had an additional implication relating to a 1998 legal settlement agreement between the EPA and the National Resources Defense Council (NRDC). This agreement was made to avoid litigation over the agency's regulation of mercury emissions from EGUs. One of the terms of the agreement was that if the EPA found that regulation of mercury emissions from EGUs was appropriate and necessary on or before December 15, 2000, they would be required to propose a rule to regulate mercury emissions, pursuant to section 112 of the CAA, by December 15, 2003. Further, they were required to take "final action" on the proposed rule by December 15, 2004.⁸

On March 15, 2005 EPA finalized an alternative regulatory approach in two separate rulemaking actions. The first rule revised the December 2000 regulatory finding and removed ("delisted") coal- and oil-fired utilities from the section 112 source categories list.⁹ The second rule finalized standards of performance for mercury from new and existing coal-fired EGUs. That rule is commonly referred to as the Clean Air Mercury Rule (CAMR).¹⁰ CAMR was a two-phase market based "cap and trade" program developed under section 111 of the CAA that included provisions for trading and banking and the use of mercury emission allowances to account for annual mercury emissions.¹¹

The rules which delisted EGUs from the section 112 list of affected sources and led to the development of CAMR were challenged by a group of 15 states, additional government agencies, and various environmental groups. On February 8, 2008, the US Court of Appeals for the DC Circuit determined that the "delisting" rule was illegal because EPA did not make the specific findings required by section 112 before removing a source from the list. Because coal-fired EGUs are listed sources under section 112, regulation of existing coal-fired EGU mercury emissions under section 111 is prohibited, effectively invalidating CAMR's regulatory approach. Accordingly, the court granted both petitions and vacated both rules.¹² The Utility Air Regulatory Group (UARG) filed a petition for reconsideration with the US Supreme Court to review the February 8, 2008 findings on September 16, 2008,¹³ and EPA filed a similar petition on October 17, 2008.¹⁴

While the US Supreme Court hearing was pending, the American Nurses Association filed a mandatory duty suit on December 18, 2008 to compel EPA to establish standards in accordance with the requirements of section 112. The suit alleged that EPA had failed to establish maximum achievable control technology (MACT) standards for coal- and oil-fired electric generating units by December 20, 2002,¹⁵ which was the date required for establishment of standards after a substance was listed under section 112 (i.e., two years following the listing date).

The US Supreme Court denied UARG’s petition for reconsideration¹⁶ and accepted the government’s request to drop its petition on February 23, 2009. This decision obligated EPA to regulate HAPs from the utility sector in accordance with the specifications of section 112 of the CAA.

On December 24, 2009 EPA approved an Information Collection Request (ICR) requiring all US power plants with coal- or oil-fired EGUs to submit emissions information for use in developing the Utility MACT emission standards.¹⁷

To resolve the mandatory duty suit filed by the American Nurses Association, on April 15, 2010 EPA entered into a consent decree which obligated them to sign for publication in the Federal Register a notice of proposed rulemaking setting forth proposed emission standards for coal- and oil-fired EGUs pursuant to CAA section 112 no later than March 16, 2011. The consent decree also requires EPA to establish final emission standards for coal- and oil-fired EGUs no later than November 16, 2011.¹⁸

Regulatory Actions

As required by the American Nurses Association consent decree, on March 16, 2011 the EPA Administrator signed the proposed air toxics MACT rules for coal-fired and oil-fired EGUs.¹⁹ This proposed regulation was published in the Federal Register on May 3, 2011.²⁰

The mercury and air toxics standards will affect EGUs that burn coal or oil for the purpose of generating electricity for sale and distribution through the national electric grid to the public. These include investor-owned units as well as units owned by the Federal government, municipalities, and cooperatives that provide electricity for commercial, industrial, and residential uses.²¹

EPA estimates that there are approximately 1,350 units affected by this action. Approximately 1,200 existing coal-fired units and 150 oil fired units at about 525 power plants.²¹

The proposed toxics rule would reduce emissions of heavy metals, including mercury (Hg), arsenic, chromium, and nickel, and acid gases, including hydrogen chloride (HCl) and hydrogen fluoride (HF). These toxic air pollutants are known or suspected of causing cancer and other serious health effects.²¹ EPA estimates the proposed mercury MACT limits would result in a 90% reduction in mercury emissions from coal-fired EGUs.

EPA has identified two different subcategories of coal-fired EGUs, two different subcategories of oil-fired EGUs, and a subcategory for units that combust gasified coal or solid oil (integrated gasification and combined cycle (IGCC) units) based on the design of the various types of boilers at different power plants. The proposed air toxics rule includes emission standards and other requirements for each subcategory.²¹

The consent decree further requires that final utility air toxics rules be signed by the EPA Administrator by November 16, 2011.

State Mercury Regulations

¹Mercury Study Report to Congress
²Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units -- Final Report to Congress
³ Information collection request for electric utility steam generating unit mercury emissions information collection effort
⁴ Fact sheet, EPA to regulate mercury and other air toxics emissions from coal- and oil-fired power plants
⁵Tetra Tech, Inc. 2010, Figure used with permission from graphic creator Reed C. Harris
⁶Legal Analysis and Background on the EPA’s Proposed Rules for Regulating Mercury Emissions from Electric Utilities, Updated May 10, 2004
⁷Electric Utility Steam Generating Units Section 112 Rule Making
⁸Natural Resources Defense Council v. EPA, Stipulation for Modification of Settlement Agreement, No. 92-1415 (D.C. Cir. Nov. 17, 1998)
⁹Revision of December 2000 Regulatory Finding on the Emissions of Hazardous Air Pollutants from Electric Utility Steam Generating Units and the Removal of Coal- and Oil-fired Electric Utility Steam Generating Units from the Section 112(c) List ; Final Rule, Federal Register / Vol. 70, No. 59 / Tuesday, March 29, 2005
¹⁰Standards of Performance for New and Existing Stationary Sources: Electric Utility Steam Generating Units; Final Rule, Federal Register /Vol. 70, No. 95 /Wednesday, May 18, 2005
¹¹NETL Development and Testing of Mercury Control Technology for Coal-Fired Power Plants: A U.S. Department of Energy R&D Program
¹²United States Court of Appeals for the District of Columbia Circuit, No. 05-1097
¹³Supreme Court of the United States, Utility Air Regulatory Group, Petitioner, v. State of New Jersey, et al., Respondent, No. 08-352, September 17, 2008
¹⁴In the Supreme Court of the United States, Environmental Protection Agency, Petitioner, v. State of New Jersey, et al.
¹⁵In the United States District Court for the District of Columbia, American Nurses Association, et al., Plaintiffs, Lisa Jackson, Administrator, United States Environmental Protection Agency, and United States Environmental Protection Agency, Defendants
¹⁶In the Supreme Court of the United States, Utility Air Regulatory Group, Petitioner, v. State of New Jersey, et al., Respondents., Environmental Protection Agency, Petitioner, v. State of New Jersey, et al., Respondents., Nos. 08-352 & 08-512
¹⁷USEPA Air Toxics Standards for Utilities
¹⁸In the United States District Court for the District of Columbia, American Nurses Association, et al., Plaintiffs, Lisa Jackson, Administrator, United States Environmental Protection Agency, and United States Environmental Protection Agency, Defendants., Case 1:08-cv-02198-RMC Document 33 Filed 04/15/10
¹⁹US EPA Air Toxic Standards for Utilities
²⁰Federal Register: May 3, 2011 (Volume 76, Number 85)][Proposed Rules][Page 24975-25147]
²¹US EPA fact sheet proposed mercury and air toxics standards
²²Federal Register: May 3, 2011 (Volume 76, Number 85)][Proposed Rules] [Page 25027]
²³US EPA Letter from Gina McCarthy to Lee Zeugin (UARG), May 18, 2011
²⁴National Association of Clean Air Agencies, State Utility Mercury/Toxics Programs