Document ID: ./input/supremecourt_opinions/opinions/21pdf/20-1530_n758.pdf
Page Number: 28

22 

WEST VIRGINIA v. EPA 

Opinion of the Court 

plant operator can deploy to attain the emissions limits es-
tablished by the Clean Power Plan.  See supra, at 10.  The 
Mercury  Rule,  therefore,  is  no  precedent  for  the  Clean 
Power Plan.  To the contrary, it was one more entry in an
unbroken list of prior Section 111 rules that devised the en-
forceable  emissions  limit  by  determining  the  best  control
mechanisms available for the source.1 

This consistent understanding of “system[s] of emission 
reduction” tracked the seemingly universal view, as stated 
by  EPA  in  its  inaugural  Section  111(d)  rulemaking,  that 
“Congress intended a technology-based approach” to regu-
lation in that Section.  40 Fed. Reg. 53343 (1975); see id., at 
53341 (“degree of control to be reflected in EPA’s emission 
guidelines” will be based on “application of best adequately 
demonstrated  control  technology”).2   A  technology-based
standard, recall, is one that focuses on improving the emis-
sions performance of individual sources.  EPA “commonly 

—————— 

1 The dissent cites other ostensible precedents, see post, at 25–26, but 
they are also inapposite.  A few allowed cap-and-trade or similar averag-
ing measures as compliance mechanisms, like the Mercury Rule.  See, 
e.g., 60 Fed. Reg. 65402 (1995).  The others were not Section 111 rules. 
2 See  McGarity  165  (EPA  promulgates  “technology-based  new  source
performance  standards  that  require  the  implementation  of  the  ‘best 
available demonstrated’ technology”); P. McCubbin, The Risk in Technology-
Based  Standards,  16  Duke  Env.  L.  &  Pol’y  Forum  1,  46,  n. 180  (2003)
(Section 111 standards “are another set of technology-based standards”);
W. Wagner, The Triumph of Technology-Based Standards, 2000 U. Ill. 
L. Rev 83, 84, n. 4 (“Technology-based standards made their initial ap-
pearance” in “Section 111 of the Clean Air Act,” which “requires the EPA
to set technology-based emission limitations”).   

The  dissent  points  to  a  1977  amendment  to  Section  111  as  evidence 
that the 1970 Congress did not intend for EPA to establish this sort of
source-specific standard.  Post, at 10–11.  But it is clear that the 1977 
amendment was merely intended to prohibit power plants from adopting 
one specific kind of at-the-source measure—a switch from burning high-
sulfur  coal  to  low-sulfur  coal—and  was  not  intended  or  understood  to 
change  the  basic,  source-focused  regulatory  approach.    See  Wisconsin 
Elec. Power Co. v. Reilly, 893 F. 2d 901, 919 (CA8 1990) (explaining the
history); B. Ackerman & W. Hassler, Clean Coal/Dirty Air (1981) (same).