Document ID: ./input/supremecourt_opinions/opinions/08pdf/07-588.pdf/07-588.pdf
Page Number: 8.0

Cite as:  556 U. S. ____ (2009) 

5 

Opinion of the Court 

percent from the calculation baseline”; a subset of facilities
must  also  reduce  entrainment  of  such  aquatic  organisms
by  “60  to  90  percent  from  the  calculation  baseline.”    40 
CFR  §125.94(b)(1),  (2);  see  §125.93  (defining  “calculation 
baseline”).  Those targets are based on the environmental 
improvements  achievable  through  deployment  of  a  mix  of
remedial technologies, 69 Fed. Reg. 41599, which the EPA 
determined  were  “commercially  available  and  economi-
cally practicable,” id., at 41602. 

In  its  Phase  II  rules,  however,  the  EPA  expressly  de-
clined to mandate adoption of closed-cycle cooling systems
or  equivalent  reductions  in  impingement  and  entrain-
ment, as it had done for new facilities subject to the Phase
I rules.  Id., at 41601.  It refused to take that step in part 
because of the “generally high costs” of converting existing
facilities  to  closed-cycle  operation,  and  because  “other 
technologies approach the performance of this option.”  Id., 
at  41605.  Thus,  while  closed-cycle  cooling  systems  could 
reduce  impingement  and  entrainment  mortality  by  up  to
98 percent, id., at 41601, (compared to the Phase II targets
of  80  to  95  percent  impingement  reduction),  the  cost  of 
rendering  all  Phase  II  facilities  closed-cycle-compliant 
would  be  approximately  $3.5  billion  per  year,  id.,  at 
41605,  nine  times  the  estimated  cost  of  compliance  with
the Phase II performance standards, id., at 41666.  More-
over, Phase II facilities compelled to convert to closed-cycle
cooling systems “would produce 2.4 percent to 4.0 percent
less  electricity  even  while  burning  the  same  amount  of
coal,” possibly requiring the construction of “20 additional
400–MW  plants  . . .  to  replace  the  generating  capacity
lost.”  Id.,  at  41605.  The  EPA  thus  concluded  that  “[a]l-
though  not  identical,  the  ranges  of  impingement  and
entrainment reduction are similar under both options. . . .
[Benefits  of  compliance  with  the  Phase  II  rules]  can  ap-
proach those of closed-cycle recirculating at less cost with
fewer implementation problems.”  Id., at 41606.