POWER February 2013 - 50

COOLING WATER MANAGEMENT
screen and they are unable to escape. Some
organisms may pass through the screening
system and the intake structure and travel
through the entire cooling system including
pumps, condenser tubes, and discharge
pipes. This is referred to as entrainment, and
it can lead to mortality rates that sometimes
approach 100%.
But just because a power plant withdraws
water from a river, lake, or estuary doesn't
mean it has a measurable impact on aquatic
life. For example, Ron Stohlmann, lead mechanical/civil
engineer with OPPD, said a
2008 test of a Beaudry water intake protection
screen at the utility's 650-MW, five-unit
North Omaha Station on the Missouri River
had to rely on " fish interdiction " to increase
the number of fish in front of the screen to
test its effectiveness. In other words, power
plant personnel had to bring in fish from
elsewhere in the river to successfully conduct
the tests. " The reality is our intakes aren't
impacting fish populations, " Stohlmann said.
" The proof is we had to go get fish to find an
adequate sample for testing. " He said the tests
validated earlier studies concluding that the
station's water intake structures caused little
if any impingement or entrainment. Indeed,
the EPA said that few if any studies exist that
quantify impingement and entrainment at facilities
that withdraw less than 100 mgd. In
general, Midwest power plants located on
rivers may have little if any impingement
problem, particularly compared with plants
located on ocean estuaries.
" I would recommend that existing
screens don't stand a chance with the standards, "
said Gregory L. Howick, PhD.,
senior aquatic ecologist with engineering
firm Burns & McDonnell. " My feeling
is that when you look at a new traveling
screen system with its plumbing and space
requirements compared with what we have
1. Here fishy, fishy. Personnel at Omaha
Public Power District's (OPPD's) North Omaha
Station had to bring in fish from elsewhere in
the Missouri River to test the effectiveness of
a water intake screen. " The reality is our water
intakes aren't impacting fish populations, "
an OPPD official said. Courtesy OPPD
State Actions Related to Cooling Water Use
Federal regulations are only one part of efforts
to regulate water use at power plants
to reduce the likelihood of impingement
and entrainment. State environmental
protection officials also have put forth
rules on the issue. Prominent among them
are recent rulemakings in New York and
California.
In July 2011, the New York State Department
of Environmental Conservation
finalized a rule requiring power plants and
other industrial facilities in the state to
use the Best Technology Available (BTA)
to protect aquatic wildlife when seeking
cooling water intake permits. The policy
is aimed at reducing fish kills by 90%. The
department said more than 17 billion fish
of all life stages (eggs, larvae, juveniles,
and adults) are entrained or impinged annually.
It said steam electric power plants
account for the majority, though not all,
of this industrial cooling impact, with
some power plants using more than a billion
gallons of water every day for cooling
purposes.
The policy identifies closed-cycle
cooling or its equivalent as the performance
goal for BTA. It acknowledged,
however, that closed-cycle cooling is
not always an available technology for
existing facilities. The performance goal
of the policy allows facilities to propose
an alternative technology or operational
measure, such as flow reduction, to
achieve reductions in impact equivalent
to what could be realized with cooling
towers. The department said this would
provide flexibility to the industry in designing
a mitigative system while ensuring
that aquatic impacts are reduced to
the greatest extent possible.
Meanwhile, in California, the State Water
Board (SWB) adopted a policy in May
2010 on the " Use of Coastal and Estuarine
Waters for Power Plant Cooling. " The policy
establishes technology-based standards
to implement 316(b) and applies to the
19 existing power plants (including two
nuclear plants) that currently have the
ability to withdraw more than 15 billion
gallons per day from coastal and estuarine
waters using a single-pass system. Closedcycle
wet cooling was selected as BTA, and
permittees must either reduce intake flow
50
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and velocity or reduce impacts to aquatic
life by other means.
Pacific Gas & Electric said that under
this policy, a nuclear review committee is
studying the feasibility and cost of a retrofit
at its Diablo Canyon nuclear station.
The study was to be completed by 2013.
Based on the results, if the SWB determines
that the costs to install cooling towers are
" wholly out of proportion " to the costs it
considered in developing the policy, or if
the installation of cooling towers would
be " wholly unreasonable " after considering
non-cost factors (such as engineering
and permitting constraints and adverse
environmental impacts), Diablo Canyon
could be granted a variance and allowed
to continue operating its once-through
cooling system and mitigate its impacts.
The utility estimated the cost to retrofit
Diablo Canyon at more than $4.5 billion.
On the issue of impingement, the EPA's
approach is to require facilities either to
install screens that will remove aquatic
life from in front of the intake structure
and return them to the water unharmed,
or reduce the velocity of water entering
the intake structure to 0.5 feet per
second. That velocity is considered slow
enough to enable aquatic life to avoid becoming
impinged.
Alden Lab's Gregory Allen said the impingement
section sets high performance
standards for traveling screens installed
on water intakes. He said the proposed requirement
of an 88% annual survival rate
among aquatic life washed off the screens
represents a " pretty high bar for those
screens " based on existing technology
and studies. Meeting those survival standards
" could be a challenge " to achieve,
depending on the fish species present at
the plant. Industry hopes the final EPA
rule will focus less on performance and
more on the fact that appropriate technology
has been installed. Allen said little if
any modification to civil structures likely
would be needed to install rule-compliant
technology, a considerable cost savings.
Meanwhile, existing screens would likely
need to be modified or replaced entirely
with a bucket-like mechanism that lifts
fish away from the intake and returns
them to the water.
POWER | February 2013
http://www.powermag.com
POWER February 2013

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