FACT SHEET
Mercury and Air Toxics Standards: Proposed Revised Supplemental Finding
and Results of the Residual Risk and Technology Review
OVERVIEW
•	On December 27, 2018, the U.S. Environmental Protection Agency (EPA) proposed to revise
the Supplemental Cost Finding for the Mercury and Air Toxics Standards (the MATS rule), as
well as the Clean Air Act (CAA) required risk and technology review (RTR).
•	After taking account of both the cost to coal- and oil-fired power plants of complying with
the MATS rule (costs that range from $7.4 to $9.6 billion annually) and the benefits
attributable to regulating hazardous air pollutant (HAP) emissions from these power plants
(quantifiable benefits that range from $4 to $6 million annually), as EPA was directed to do
by the United States Supreme Court (Michigan v. EPA), the Agency proposes to determine
that it is not "appropriate and necessary" to regulate HAP emissions from power plants
under Section 112 of the CAA.
•	This revised finding would correct flaws in the Agency's 2016 Supplemental Finding on this
issue.
•	The emission standards and other requirements of the MATS rule, first promulgated in
2012, would remain in place, however, since EPA is not proposing to remove coal- and oil-
fired power plants from the list of sources that are regulated under Section 112 of the Act.
•	EPA is also proposing or taking comment on other MATS-related issues in this action.
o EPA is proposing the results of the risk and technology review required by section
112. The proposed RTR shows that no additional regulations are required,
o EPA is also soliciting comment on establishing a subcategory for emissions of acid
gas HAP from existing electric utility steam generating units (EGUs) firing eastern
bituminous coal refuse.
•	EPA will take comment on this proposal for 60 days after publication in the Federal Register
and hold at least one public hearing. Details about the public hearing will be available in a
future Federal Register notice.
REVISED SUPPLEMENTAL FINDING
Action
•	EPA is proposing that it is not "appropriate and necessary" to regulate HAP emissions from
coal- and oil-fired power plants under section 112 of the CAA because the costs of such
regulation grossly outweigh the quantified HAP benefits.
•	EPA has reexamined the cost analyses presented in the 2016 Supplemental Finding and
proposes to determine that neither of the Finding's approaches to considering cost satisfies
the Agency's obligation under CAA section 112(n)(l)(A) as interpreted by the Supreme
Court in Michigan.
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•	EPA proposes the 2016 Supplemental Finding erred in its consideration of cost. Specifically,
we find that what was described in the 2016 Supplemental Finding as the preferred
approach, or "cost reasonableness test," does not meet the statute's requirements to fully
consider costs, and was an unreasonable interpretation of the CAA mandate.
•	In this proposal, EPA uses a different consideration of cost for purposes of the appropriate
and necessary finding, one that aligns with the purpose of CAA section 112(n)(l)(A) as set
forth in Michigan.
•	EPA proposes to find that equal reliance on the particulate matter (PM) air quality co-
benefits projected to occur as a result of the reductions in HAPs was flawed as the focus of
CAA section 112 is HAP emissions reductions.
•	EPA proposes to directly compare the cost of compliance with MATS with the benefits
specifically associated with reducing emissions of HAP in order to satisfy our duty to
consider cost in the context of the CAA section 112(n)(l)(A) appropriate and necessary
finding.
•	A proper consideration of costs demonstrates that the total cost of compliance with MATS
($7.4 to $9.6 billion annually) dwarfs the monetized HAP benefits of the rule ($4 to $6
million annually).
•	While there are unquantified HAP benefits and significant monetized PM co-benefits
associated with MATS, the Administrator has concluded that the identification of these
benefits is not sufficient, in light of the gross imbalance of monetized costs and HAP
benefits, to support a finding that it is appropriate and necessary to regulate EGUs under
CAA section 112.
•	Further, EPA is proposing that making this determination that it is not "appropriate and
necessary" would not remove coal- and oil-fired EGUs from the list of affected source
categories for regulation under section 112 nor would it affect the 2012 MATS, which would
stay in place.
•	EPA is taking comment on alternative interpretations of the effects of its proposed finding.
Specifically, EPA is taking comment on whether it has the authority or obligation to remove
coal- and oil-fired EGUs from the CAA list of affected source categories and rescind MATS.
Background
•	The CAA lays out a multi-step process for regulating HAP emissions from power plants. The
process includes looking at whether it is "appropriate and necessary" to regulate coal- and
oil-fired power plants for HAPs- referred to as an A&N Finding; taking an action to "list"
EGUs for HAP regulation under section 112 of the CAA; and setting HAP emission standards
•	In December 2000, pursuant to CAA section 112(n)(l)(A), EPA determined it was
"appropriate and necessary" to regulate coal- and oil-fired EGUs under CAA section 112(d)
and added such units to the CAA section 112(c) List of Categories of Major and Area
Sources.
•	In 2005, EPA issued a final rule that reversed the A&N Finding, removed coal- and oil-fired
EGUs from the CAA section 112(c) list, and established standards for mercury emissions
under CAA section 111 (Clean Air Mercury Rule or CAMR).
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•	In 2008, in New Jersey v. EPA, the D.C. Circuit Court vacated the delisting and CAMR, ruling
that EPA's reversal of its A&N Finding did not remove coal- and oil-fired EGUs from the CAA
section 112(c) source category list and that the Agency failed to comply with the CAA
section 112(c)(9) requirements for delisting a source category.
•	In 2012, EPA reaffirmed its initial 2000 A&N Finding and finalized MATS, which regulates
HAP from coal- and oil-fired EGUs.
•	In 2015, in Michigan v. EPA, the Supreme Court ruled that the Agency erred when it
determined cost did not have to be considered when making the A&N Finding. The D.C.
Circuit Court remanded MATS, requiring the Agency to consider the cost of MATS relative to
the A&N Finding.
•	EPA's response to the remand was the 2016 Supplemental Finding, in which the Agency
concluded that the consideration of cost did not change its conclusion that it was
appropriate and necessary to regulate HAP emissions from coal- and oil-fired EGUs.
•	The 2016 Supplemental Finding drew additional legal challenges, including Murray Energy
Corp. v. EPA, which challenged the conclusions reached in EPA's Supplemental Finding.
•	In response to this challenge, in 2017, EPA moved the D.C. Circuit Court to hold the Murray
Energy Corp. v. EPA case in abeyance so the new Administration could have time to review
the 2016 Supplemental Finding.
RESIDUAL RISK AND TECHNOLOGY REVIEW
Action
•	EPA is proposing the results of the RTR of MATS that the Agency is required to conduct in
accordance with CAA section 112.
•	Residual Risk Review: The CAA requires EPA to assess the risk remaining after the
promulgation of final HAP standards. Based on the completed risk assessment, EPA has
determined that the residual risks due to emissions of HAPs from the coal- and oil-fired
EGUs source category are acceptable and that the current standards provide an ample
margin of safety to protect public health.
•	Technology Review: The CAA also requires EPA to assess, review and revise HAP standards,
as necessary, taking into account developments in practices, processes and control
technologies. Based on the technology review of MATS, no new developments in HAP
emission controls to achieve additional cost-effective reductions were identified.
•	EPA proposes that no revisions to MATS are warranted based on the results of these
reviews.
Background
•	Section 112 of the CAA requires EPA to regulate HAPs, from categories of industrial facilities
in two phases.
•	The first phase is "technology-based," where EPA develops standards for controlling the
emissions of HAPs from sources in an industry group or "source category" under section
112(d) of the CAA. These maximum achievable control technology (MACT) standards are
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based on emissions levels that are already being achieved by the best-controlled and lower-
emitting sources in an industry.
•	Within 8 years of setting the MACT standards, section 112(f)(2) of the CAA directs EPA to
assess the remaining health risks from each source category to determine whether the
standards protect public health with an ample margin of safety and protect against adverse
environmental effects. This second phase is a "risk-based" approach called residual risk.
Here, EPA must determine whether more health-protective standards are necessary.
•	Also, every 8 years after setting MACT standards, section 112(d)(6) of the CAA requires EPA
to review and revise the standards, if necessary, to account for improvements in air
pollution controls and/or prevention.
SOLICITATION OF COMMENT ON EASTERN BITUMINOUS COAL REFUSE SUBCATEGORY
Issue
•	EPA is considering establishing a subcategory for emissions of acid gas HAP from existing
EGUs firing eastern bituminous coal refuse.
•	EPA is requesting comment on establishing a subcategory and on the acid gas HAP emission
standards that would be established if such a subcategory were created.
•	The subcategory and standards would affect an estimated 10 existing EGUs (small units in
Pennsylvania and West Virginia) that use eastern bituminous coal refuse to generate
electricity.
•	Bituminous coal refuse-fired EGUs must install some sort of downstream acid gas control
technology to meet the final acid gas MATS standards and EPA believes that such control
technology would be expensive and potentially technically and practically infeasible to
retrofit on the small units that are currently firing eastern bituminous coal refuse.
Background
•	In 2011, EPA proposed hydrochloric acid (HCI) and sulfur dioxide (SO2) standards for all coal-
fired EGUs.
•	Public comments on the proposal claimed that the characteristics of coal refuse made it too
costly to comply with the acid gas HAP standards and requested a subcategory for EGUs
burning coal refuse.
•	EPA determined there was no basis for a subcategory and, in 2012, finalized HCI and SO2
standards that apply to all coal-fired EGUs.
•	EPA's decision was challenged, and, in 2014, upheld by the D.C. Circuit Court in White
Stallion v. EPA.
•	EPA received a petition for reconsideration requesting a subcategory for the acid gas
standards for EGUs burning all types of coal refuse, and EPA denied the petition.
•	EPA's denial of the petition was challenged, the petitioner claiming that its petition only
requested subcategorization for EGUs burning bituminous coal refuse, not for all coal refuse
EGUs (ARIPPA v. EPA).
•	In 2017, EPA asked the Court to hold the case in abeyance.
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HOW TO COMMENT
•	Comments on the proposal should be identified by Docket ID No. EPA-HQ-OAR-2018-0794,
and may be submitted by one of the following methods:
o Online: Go to https://www.regulations.gov and follow the online instructions for
submitting comments to Docket ID No. EPA-HQ-OAR-2018-0794.
o Email: Comments may be sent to a-and-r-Docket@epa.gov. Include Docket ID
No. EPA-HQ-OAR-2018-0794 in the subject line of the message,
o Fax: Fax your comments to: (202) 566-9744. Attention Docket ID No. EPA-HQ-
OAR-2018-0794.
o Mail: Environmental Protection Agency, EPA Docket Center (EPA/DC), Mail Code
28221T, Attention Docket ID No. EPA-HQ-OAR-2018-0794,1200 Pennsylvania
Avenue, NW, Washington, DC 20460.
o Hand/Courier Delivery: EPA Docket Center, Room 3334, EPA WJC West Building,
1301 Constitution Avenue, NW, Washington, DC 20004, Attention Docket ID No.
EPA-HQ-OAR-2018-0794. Such deliveries are only accepted during the Docket's
normal hours of operation, and special arrangements should be made for
deliveries of boxed information.
•	For additional information, including the full EPA public comment policy, please visit
https://www.epa
FOR MORE INFORMATION
• A copy of the proposed rule is available on EPA's website at https://www.epa.gov/mats
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