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ENTERGY CORP. v. RIVERKEEPER, INC. 

Opinion of the Court 

EPA, 475 F. 3d 83, 99–100 (2007).  The issue for our deci-
sion is whether, as the Second Circuit held, the EPA is not 
permitted  to  use  cost-benefit  analysis  in  determining  the 
content of regulations promulgated under §1326(b). 

I 
Petitioners  operate—or  represent  those  who  operate—
large  powerplants.    In  the  course  of  generating  power, 
those plants also generate large amounts of heat.  To cool 
their  facilities,  petitioners  employ  “cooling  water  intake
structures” that extract water from nearby water sources.
These structures pose various threats to the environment, 
chief  among  them  the  squashing  against  intake  screens 
(elegantly  called  “impingement”)  or  suction  into  the  cool-
ing system (“entrainment”) of aquatic organisms that live
in  the  affected  water  sources.    See  69  Fed.  Reg.  41586.
Accordingly,  the  facilities  are  subject  to  regulation  under 
the  Clean  Water  Act,  33  U. S. C.  §1251  et  seq.,  which 
mandates: 

“Any standard established pursuant to section 1311 
of this title or section 1316 of this title and applicable 
to  a  point  source  shall  require  that  the  location,  de-
sign,  construction,  and  capacity  of  cooling  water  in-
take  structures  reflect  the  best  technology  available 
impact.” 
for  minimizing  adverse  environmental 
§1326(b). 

Sections 1311 and 1316, in turn, employ a variety of “best
technology”  standards  to  regulate  the  discharge  of  efflu-
ents into the Nation’s waters. 

The  §1326(b)  regulations  at  issue  here  were  promul-
gated by the EPA after nearly three decades in which the 
determination  of  the  “best  technology  available  for  mini-
mizing  [cooling  water  intake  structures’]  adverse  envi-
ronmental  impact”  was  made  by  permit-issuing  authori-
ties on a case-by-case basis, without benefit of a governing