Document ID: ./input/supremecourt_opinions/opinions/21pdf/20-1530_n758.pdf
Page Number: 82

26 

WEST VIRGINIA v. EPA 

KAGAN, J., dissenting 

operating to increase the strictness of emissions limits.

And the mercury rule itself was rooted in precedent.  A 
decade earlier, EPA had determined that States could com-
ply  with  a  Section  111(d)  regulation  for  municipal  waste
combustors  by  establishing  cap-and-trade  programs.    See 
40 CFR §§60.30a, 60.33b(d)(2) (1996).  And beyond Section 
111(d),  trading  and  other  tools  of  generation  shifting  be-
come still more common.  For decades, EPA has relied on 
those  pollution-control  techniques  in  rules  covering  new 
internal-combustion engines under Section 111(b), sources 
of nitrogen oxide under the NAAQS program, and motor ve-
hicles under Section 202(a).  See 73 Fed. Reg. 3595 (2008); 
71  Fed.  Reg.  39159  (2006);  63  Fed.  Reg.  57358–57359 
(1998); 48 Fed. Reg. 33456 (1983); see also Brief for Richard 
L. Revesz as Amicus Curiae 24–29 (collecting similar rules). 
No  doubt  the  majority  is  right  that  scrubbers  and  other 
“add-on controls” are “more traditional air pollution control 
measures.”  Ante,  at  23.    EPA  readily  acknowledged  that 
fact in developing the Clean Power Plan.  But the idea that 
the  Plan’s  reliance  on  generation  shifting  effected  some 
kind of revolution in power-plant pollution control?  No.  As 
I’ve noted before, power plants themselves use that method.
State environmental regulators use that method.  And EPA 
has used that method, including under the statutory provi-
sion invoked here. 

In  any  event,  newness  might  be  perfectly  legitimate—
even required—from Congress’s point of view.  I do not dis-
pute that an agency’s longstanding practice may inform a 
court’s  interpretation  of  a  statute  delegating  the  agency 
power.  See ante, at 20–21.  But it is equally true, as Brown 
&  Williamson  recognized,  that  agency  practices  are  “not
carved in stone.”  529 U. S., at 156–157 (internal quotation 
marks omitted).  Congress makes broad delegations in part 
so that agencies can “adapt their rules and policies to the 
demands of changing circumstances.”  Id., at 157.  To keep