
C:\
dmautop\
temp\
DCTM_
ARP.
wpd
MEMORANDUM
TO:
File;
Carey
Johnston,
USEPA/
EAD
FROM:
Mary
Willett
and
Mark
Briggs,
ERG
DATE:
July
15,
2004
SUBJECT:
Screen
Configurations
This
memorandum
documents
the
information
gathered
from
Johnson
Screens
on
the
geometry
and
flow
profile
to
prevent
entrainment
and
impingement
of
marine
life
on
cooling
water
intake
structures
per
the
proposed
CWA
316(
b)
Phase
III
rule.
Included
as
attachments
to
this
memo
are
design
information
and
typical
configurations
for
screening
systems
on
cooling
water
intake
structures
(
Attachment
1)
and
telephone
correspondence
between
ERG
and
Johnson
Screens
(
Attachment
2).

Simple
Pipe,
Caisson,
and
Submersible
Pump
Intake
Screens
Simple
pipes,
caissons
and
submersible
pumps
used
for
cooling
water
extraction
can
be
fitted
with
pre­
manufactured
cylindrical
wedge
wire
screens
to
prevent
entrainment
and
impingement
of
marine
life.
These
screens,
manufactured
by
Johnson
Screens1
can
be
manufactured
from
stainless
steel
or
a
copper­
nickel
alloy
("
Z­
Alloy")
if
additional
bio­
fouling
resistance
is
required.
All
cylindrical
wedge
wire
screens
purchased
from
Johnson
Screens
are
designed
to
provide
a
cooling
water
through­
put
velocity
of
less
than
0.5
feet
per
second
(
ft/
s)
2.
Wedge
wire
screen
openings
on
Johnson
Screens
vary
depending
on
size
of
the
organisms
that
will
be
entrained.
Typically,
screen
openings
range
between
0.002
and
0.25
inches.
The
size
of
the
screen
opening
is
selected
based
on
the
smallest
marine
organism
that
the
facility
is
trying
keep
from
being
entrained.
Design
information
on
cylindrical
wedge
wire
screens
is
included
in
Attachment
1
of
this
memo.

Simple
pipes,
caissons
and
submersible
pump
cooling
water
intake
structures
(
CWIS)
with
openings
less
than
40
to
50
feet
can
also
be
fitted
with
an
air
sparging
system
(
Johnson
Screens
"
Hydroburst"
system)
to
periodically
remove
bio
growth.
The
air
sparging
system
includes
an
air
compressor
system,
piping
and
valves,
and
controls.
The
system
delivers
a
timed
burst
of
air
through
the
screens
in
or
der
to
knock
off
any
growth
(
e.
g.,
zebra
mussels)
from
the
surface.
According
to
Linda
Cook
at
Johnson
Screens2,
air
sparge
systems
on
CWIS
are
typically
not
required
at
depths
below
50
feet
due
to
limited
bio­
growth.
Memorandum
2
July
2004
Page
2
C:\
dmautop\
temp\
DCTM_
ARP.
wpd
Sea
Chest
Screens
Johnson
Screens
also
manufactures
flat
panel
wedge
wire
screens
with
no
sharp
edges
that
can
be
placed
over
existing
sea
chests3.
These
screens
have
smooth
surfaces
to
minimize
the
risk
of
injury
to
fish
and
prevent
entrainment.
Slot
sizes
are
selected
based
on
the
smallest
size
of
marine
organism
that
the
facility
is
trying
to
prevent
entrainment.
Slot
sizes
on
flat
panel
screens
are
as
small
as
0.002
inches,
and
have
high
open
areas
to
allow
natural
flow
with
no
turbulence.
Information
on
flat
panel
screens
for
fish
protection
is
included
in
Appendix
A
of
this
memo.
Unlike
cylindrical
screens
placed
on
simple
pipes,
caissons,
and
submersible
pumps,
flat
panel
screens
can
not
limit
flow
velocity
to
less
than
0.5
fts
and
therefore
have
no
impingement
prevention
qualities.
Sea
chests
require
installation
of
horizontal
flow
diverters
to
lessen
the
flow
velocity
and
decrease
impingement.

References
1.
Johnson
Screens,
1950
Old
Highway
8
NW,
New
Brighton,
MN.
Telephone:
(
651)
636­
3900,
internet:
www.
johnsonscreens.
com
2.
Telephone
conversation
between
Ms.
Linda
Cook,
Johnson
Screens
(
651­
636­
3900)
and
Mark
Briggs,
ERG,
May
18,
2004.

3.
Email
communication
between
Ms.
Linda
Cook,
Johnson
Screens
(
email:
cookls@
johnsonscreens.
com)
and
Mark
Briggs,
ERG
(
email:
mark.
briggs@
erg.
com)
Memorandum
2
July
2004
Page
3
C:\
dmautop\
temp\
DCTM_
ARP.
wpd
Attachment
1
Johnson
Screens
Product
Literature
Memorandum
2
July
2004
Page
4
C:\
dmautop\
temp\
DCTM_
ARP.
wpd
Attachment
2
Telephone
Correspondence
