Document ID: EPA-HQ-OW-2002-0049-0179
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2003-03-19T05:00Z

QUESTIONS
FOR
TRAVELING
SCREEN
MANUFACTURERS
Received
from
Trent
Gathright
on
9/
11/
2002.

REPLACING
COARSE
MESH
TRAVELING
SCREENS
WITH
FINE
MESH
TRAVELING
SCREENS
The
following
questions
inquire
about
replacing
coarse
mesh
traveling
screens
with
fine
mesh
traveling
screens.
Note
that
replacement
screens
will
have
fish
baskets
for
use
with
a
return
system.
If
you
perform
this
kind
of
work,
please
answer
the
following
questions:

The
following
questions
cover
the
breadth
of
information
being
sought
but
admittedly
are
somewhat
extensive.
Those
shown
in
non­
bold
print
are
generally
require
brief
or
quality
responses
and
are
intended
to
be
discussed
over
the
phone.
Questions
in
bold
print
may
require
research
and
may
best
be
presented
in
a
follow­
up
context.

General
1.
In
consultations
and/
or
projects,
how
often
do
you
encounter
site
conditions
at
existing
intakes
where
the
existing
screens
cannot
be
readily
accessed
via
crane?

In
approximately
25
years
of
experience,
we
see
+/­
40
%
of
the
Traveling
Screens
that
are
housed
in
buildings
that
require
the
dis­
assembly
of
the
screens
prior
to
removal.
Therefore,
these
are
not
"
readily
accessible"
for
immediate
removal.
This
is
of
course
a
rough
estimate.

2.
What
range
of
screen
mesh
opening
sizes
do
you
consider
to
be
"
fine
mesh?"
When
facilities
examine
and/
or
select
finer
mesh
to
reduce
entrainment,
what
is
the
most
common
mesh
size?
Are
there
any
differences
in
the
fine
mesh
sizes
commonly
evaluated
and/
or
selected
for
new
intakes
versus
existing
intake
retrofits?

The
old
common
"
rule
of
thumb"
for
the
mesh
size
of
traveling
screens
is
½
the
diameter
of
the
condenser
tube,
therefore
97%
of
existing
"
Thru
Flow"
type
traveling
screens
contain
3/
8"
square
opening
mesh.
We
consider
anything
between
½
"
to
¼
"
opening
to
be
coarse
mesh
and
3/
16"
and
smaller
to
be
"
fine"
mesh.
We
have
retrofitted
a
number
of
screens
with
1/
8"
opening
both
on
fish
handling
and
none
fish
handling.
I
personally
performed
a
number
of
experiments
in
1983
to
1986
on
the
result
of
Fish
as
they
encounter
traveling
band
screens.
This
was
the
first
work
actually
observing
fish
"
underwater"
through
ports
in
the
sides
of
the
flume.
The
results
conclude
that
"
smooth"
top
mesh
(
woven
wire
mesh
pressed
flat
on
the
upstream
side
to
provide
a
smooth
surface
to
prevent
descaling)
with
a
slotted
opening
typically
1/
8"
wide
x
½
"
tall.
Many
screens
with
3/
8"
and
¼
"
square
openings
are
just
large
enough
to
allow
juvenile
fish
to
become
lodged
in
the
mesh
opening.
New
intakes
are
typically
retrofitted
with
1/
8"
x
½
"
Smooth
Top
mesh
if
fish
handling
is
required,
(
based
on
the
work
performed
by
Fletcher
&
Gathright).
3.
What
is
the
range
and
typical
spacing
between
multiple
screen
units
at
most
existing
intakes?
In
other
words
how
wide
are
the
columns/
walls
at
the
screen
location?
How
close
can
they
be,
if
space
limitation
is
an
issue?
How
much
of
the
well
width
does
the
screen
panel
cover?

Typical
spacing
between
screens
is
normally
+/­
2'­
6"
due
to
the
civil
works
wall
between
adjacent
cells.
The
screens
overlap
above
deck
by
+/­
1'­
0"
thus
allowing
approx.
1'­
6"
between
most
Thru
Flow
Band
Screens.
Dual
Flow
Conversion
screens
eliminate
this
clearance
problem.
We
will
discuss
this
in
greater
detail
later.
The
most
common
width
channel
is
11'­
2"
(
although
there
are
wider
and
narrower
installations)
thus
allowing
a
10'­
0"
effective
width
Thru
Flow.
The
frame
of
the
screen
fits
into
guide
slots
embedded
in
the
civil
walls
and
contains
the
chain
tracks.
Each
side
frame
absorbs
approx.
7"
thus
the
rule
of
thumb
is
that
the
effective
width
of
a
screen
is
normally
1'­
2"
less
than
the
channel
width.

4.
How
practical
is
it
to
replace
screen
panels
only,
versus
replacing
the
entire
mechanical
unit?
When
finer
mesh
is
required,
how
practical
or
common
is
it
to
replace
screen
panels
only?
What
is
the
deciding
factor?
What
are
the
relative
cost
savings
compared
to
replacing
the
entire
screen
unit?

It
is
of
course
more
practical
to
only
replace
the
mesh
unless
it
involves
fish
handling.
The
old
method
typically
referred
to
as
a
"
Ristroph"
screen
literally
adds
a
bucket
(
like
a
house
gutter)
to
the
bottom
lifting
shelf
of
each
basket
(
panel).
However
this
method
has
been
well
proven
that
it
SIGNIFICANTLY
adds
to
fish
mortality.
The
"
bucket"
not
only
absorbs
mesh
room
but
creates
a
vortex
in
the
bucket
that
slams
the
juvenile
fish
against
the
mesh
again
and
again
eventually
leading
to
mortality.
We
therefore
created
a
NEW
basket
design
that
converts
the
structural
cross
members
(
i.
e.
basket
rails)
into
a
hydraulically
stabilized
area
that
actually
attracts
the
juvenile
fish
as
they
get
close
the
screen.
The
old
method
caused
fish
to
avoid
the
screens
due
to
the
vortex
in
the
bucket
as
all
fish
have
an
inherent
"
pressure
sensitive
live"
that
runs
longitudinally
along
their
body.
Thus
they
react
quickly
to
changes
in
pressure.
The
new
method
creates
a
sheltered
zone
that
they
seek
and
are
therefore
quickly
removed
form
the
intake.
This
new
method
is
referred
to
as
S.
I.
M.
P.
L.
E.
TM
(
Stabilized
Integrated
Marine
Protective
Lifting
Environment)
developed
by
this
author
and
his
associate
engineer.
Although
a
screen
may
be
retro
fitted,
this
would
include
all
new
baskets,
extending
the
height
of
the
head
section
to
accommodated
fish
sprays,
changing
the
housings
to
accommodate
fish
sprays
and
fish
troughs,
a
larger
drive
to
accommodate
the
unbalanced
load,
etc 
therefore
the
only
thing
typically
salvaged
is
the
frame
and
head
shaft
or
about
25%
of
the
cost
of
a
new
screen.
It
is
therefore
recommended
that
NEW
screens
be
installed
vs.
retro
fitting.

5.
Can
wedge
wire
type
screen
panels
be
used
on
traveling
screens?

Yes
wedge
wire
can
be
used
but
this
is
cost
prohibitive
vs.
using
Smooth
Top
mesh.
Wedge
wire
is
about
3
times
more
expensive
than
regular
mesh
and
2
times
more
expensive
than
smooth
top
mesh.
6.
What
problems
may
be
encountered
in
replacing
coarse
mesh
with
fine
mesh
traveling
screens
(
either
screen
panel
only
or
entire
unit).
What
are
the
typical
solutions?
Specifically,
­
Problems
with
collection
of
additional
debris?
­
Problems
with
increase
in
through
screen
velocity?
­
Other
problems
(
describe)

­
Debris
collection
is
actually
increased
although
some
minor
problems
are
encountered
with
debris
in
the
fish
troughs
if
filamentatious
algae
is
encountered.

­
The
"
Through
screen
velocity"
can
be
reduced
slightly
with
a
Thru
Flow
type
screen
and
often
greatly
with
a
Dual
Flow
Conversion
screen.
Both
would
utilize
the
S.
I.
M.
P.
L.
E.
basket
that
increases
basket
percent
open
area.

­
Typical
solutions
the
replacement
of
the
entire
screens
with
a
prior
study
of
the
most
common
debris
encountered.

7.
Can
replacement
of
through
flow
with
dual
flow
(
double
entry
single
exit)
screens
be
used
to
increase
screen
area
and
thus
reduce
through
screen
velocities
and
reduce
impingement?

Yes.
We
have
provided
a
number
of
Dual
Flow
Conversion
Fish
Handling
Band
Screens
(
Dunkirk,
Medicine
Hat,
Barking
Reach)
to
reduce
velocity.
The
effective
width
of
the
screens
can
be
increased
as
the
panels
(
baskets)
are
parallel
to
the
channel
vs.
perpendicular.
Normally
the
deck
opening
parallel
to
the
channel
is
only
+/­
5'­
4"
but
the
deck
is
typically
a
concrete
walk
way
only
about
1'­
0"
thick
and
can
be
easily
removed
by
cutting
to
allow
for
a
DFC.

8.
What
is
the
%
open
space
for
typical
coarse
mesh
traveling
screens
(
e.
g.,
3/
8
inch)
that
were
evaluated
and/
or
installed
at
power
plant
intakes
in
the
past?
If
not
known,
what
is
a
typical
wire
gauge?
What
is
the
%
open
space
for
different
sized
fine
mesh
screens?

Typically
67.9
percent
open
area
(
opening)^
2
/
(
opening
+
wire
dia.)^
2.
The
most
common
is
3/
8"
square
with
14
Ga.
(
0.080"
diameter
wire).

9.
Are
you
aware
of
any
recent
retrofit
installations
where
the
system
capacity
or
flow
volume
was
not
increased,
yet
substantial
civil/
structural
modifications
were
necessary?
If
so:
NO,
not
on
retro
fits.
The
only
reductions
we
have
seen
are
on
new
installations
where
the
velocity
is
limited.
­
What
was
done
and
why?
­
What
was
the
facility
name
and
location?
­
What
were
costs
or
who
can
we
contact
for
cost
information?
Equipment
Costs
10.
EPA
previously
obtained
1999
costs
for
single
entry
single
exit
traveling
screens
with
the
structural
component
made
of
carbon
steel
coated
with
epoxy
paint
and
screens
made
of
304
stainless
steel,
with
non­
metallic
baskets.
Can
you
provide
delivered
equipment
costs
for
comparable
(
freshwater)
fine
mesh
(
using
most
common
mesh
size
from
above)
screen
units
with
widths
in
the
range
of
5,
10,
14
­
15
ft
and
well
depths
in
the
range
of
10,
25,
50,
75,
&
100ft?
The
1999
traveling
screen
costs
included:
­
Non­
metallic
fish
handling
panels
­
Spray
systems
­
Fish
trough
­
Housings
and
transitions
­
Continuous
operating
features
­
Drive
unit
­
Frame
seals
­
Engineering
Budget
Prices
for
Fish
Handling
Thru
Flow
Band
Screens
Application:
Fresh
Water
(
Primarily
Epoxy
Coated
Carbon
Steel
with
Stainless
Steel
Mesh
and
Fasteners)
Effective
Width
(
ft.)
Depth
(
ft)
5'­
0"
10'­
0"
14'­
0"

10
$
69,648
$
87,453
$
100,732
Approx.
HP
3/
4
1
3
20
$
89,028
$
109,202
$
123,622
Approx.
HP
1
2
5
30
$
108,408
$
135,251
$
166,961
Approx.
HP
2
5
7.5
40
$
127,788
$
153,688
$
178,154
Approx.
HP
3
7.5
10
50
$
151,500
$
222,853
$
249,921
Approx.
HP
5
10
15
60
$
170,880
$
256,415
$
290,556
Approx.
HP
7.5
15
20
Budget
Prices
for
Fish
Handling
Thru
Flow
Band
Screens
Application:
Brackish
Water
(
Primarily
316
Stainless
Steel
with
Stainless
Steel
Mesh
and
Fasteners)
Effective
Width
(
ft.)
Depth
(
ft)
5'­
0"
10'­
0"
14'­
0"

10
$
137,903
$
182,226
$
213,436
20
$
176,275
$
227,544
$
261,937
30
$
214,648
$
281,822
$
353,765
40
$
253,020
$
320,239
$
377,482
50
$
299,970
$
464,359
$
529,547
60
$
338,342
$
534,291
$
615,647
If
we
are
unable
to
obtain
updated
costs
we
may
use
the
ENR
Construction
Cost
Index
which
results
in
a
capital
cost
increase
of
9%
when
updating
1999
costs
to
July
2002.
Do
you
feel
that
this
reasonably
reflects
the
actual
changes
over
this
period?

Yes
as
we
normally
use
an
inflation
rate
of
2.5%
so
3%
over
3
years
is
a
good
number.

11.
What
equipment
materials
do
you
recommend
(
or
are
commonly
selected)
for
corrosive
environments,
such
as
brackish
and
saltwater?
What
is
the
most
common
material
selected
for
saltwater
environments?
­
Carbon
Steel
with
epoxy
coating
(
freshwater)
This
is
also
very
common
for
sea
water
with
sacrificial
zinc
anodes
for
the
frames
and
even
the
basket
frames.
­
304
Stainless
Steel
 
Never
for
brackish
as
304
does
not
stand
up
to
chlorides.
­
316
Stainless
Steel
­
Most
of
the
plate
material
is
now
dual
certified
as
316L,
which
is
used
to
prevent
crevice
crack
corrosion
from
the
carbides
that
would
normally
surface
with
plain
316.
Of
course
the
non
welded
items
such
as
the
mesh
and
fasteners
would
be
316SS.
­
70/
30
Copper
Nickel
 
Once
in
25
years
for
an
Alaskan
project.
­
90/
10
Copper
Nickel­
Very
rarely.
­
Other
(
Describe)­
For
warm
seawater
(
i.
e.
countries
closer
to
the
equator)
it
now
common
to
see
requirements
for
316Ti
(
316
with
Titanium)
as
well
as
317
SS.
12.
Can
you
provide
equipment
costs
of
this
corrosion
resistant
equipment
or
provide
relative
equipment
cost
difference
compared
to
freshwater
unit,
such
as
a
cost
factor
or
percent
increase?

See
the
above
chart
for
brackish
/
seawater
applications.

13.
What
water
bodies
are
experiencing
problems
with
Zebra
mussels
and
how
much
extra
are
the
equipment
costs
for
special
alloy
construction
or
comparable
materials?

Zebra
mussels
are
fresh
water
mollusks
that
came
over
from
Russia
ships
and
were
discharged
into
the
Great
Lakes
via
the
ships
bilge
water.
These
are
now
common
in
every
water
body
that
connects
to
the
Great
Lakes.
They
do
not
like
warm
temperatures
yet
but
they
are
adapting
and
moving
down
the
Mississippi.
There
are
paints
with
musselcides
(
i.
e.
copper
based
paints)
that
supposedly
will
kill
mussels
but
they
last
so
long
before
being
rendered
ineffective.
This
is
too
general
of
a
question
to
give
you
a
quantitative
answer.
We
suggest
incorporating
debris
filters
just
upstream
of
the
condensers
to
prevent
macrofouling
as
mussel
larvae
are
to
fine
to
screen
out
at
the
raw
water
intake.

14.
If
you
indicated
replacing
screen
panels
only
is
practical,
can
you
provide
estimates
of
the
costs
for
replacing
the
panels
only,
including
both
equipment
and
installation?
NOT
only
is
this
not
practical
it
would
also
not
be
functional.

15.
Please
provide
a
description
of
installation
methods
and
typical
costs
for
screen
units,
and
whether
you
perform
such
services
including
differences
for
wet
versus
dry
installation.
Also
discuss
relative
cost
of
removal
and
disposal
of
existing
screens
(
are
the
costs
minimal?).

Can
you
provide
us
with
a
list
of
benefits
that
Brackett
Green
will
receive
for
providing
this
information
free
of
charge
?

Screen
change
out
varies
from
site
to
site
based
on
the
screen
effective
width,
depth,
is
it
in
door
or
out
door,
how
close
can
you
get
a
crane,
does
it
have
to
come
out
in
pieces,
etc 
but
at
the
end
of
the
day
the
average,
typical,
cost
for
removing
the
old
screen
and
installing
a
new
screen
is
+/­
$
45,000
per
channel
(
or
per
well).

16.
Are
there
any
special
considerations
for
nuclear
facilities
(
e.
g.,
does
screen
framing
need
to
be
stronger
and
more
resistant
to
collapse)
and
how
do
the
special
considerations
affect
equipment
selection,
costs
and/
or
performance?
Are
there
any
other
situations
where
similar
requirements
are
common?
Can
you
provide
an
equipment
cost
factor
for
selecting
screens
that
meet
these
requirements
versus
typical
non­
nuclear
installations?

Nuclear
sites
can
vary
from
what
is
termed
as
"
C"
class
or
Commercial
class,
which
are
normal
screens
for
an
intake
that
is
not
seismically
qualified.
When
"
Q"
class
screens
are
required
for
seismically
qualified
intakes,
the
screen
price
can
be
as
much
as
50%
more
just
because
of
the
Quality
control
required
for
tractability.
17.
Would
converting
to
fine
mesh
screens
have
a
significant
effect
on
O&
M
costs?
If
so
how
much
and
why?

Yes
it
would
have
an
impact
as
the
screens
would
most
likely
operate
under
a
higher
differential
thereby
wearing
out
the
chain
quicker.

Construction
Duration
18.
When
replacing
existing
screen
units
(
or
screen
panels
only),
approximately
how
long
would
the
intake
bay
and/
or
pumping
unit
need
to
be
shut
down?

In
theory
only
1­
3days
but
in
actuality
this
would
normally
have
to
be
done
during
an
outage
to
accommodate
the
new
troughing,
piping,
etc 
so
we
would
suggest
a
2
week
turnaround
depending
on
if
old
screens
had
to
be
removed.

Testing
19.
Once
the
new
screens
are
installed,
what
kind
of
performance
testing
is
typically
required?
Is
this
often
part
of
the
package
if
you
perform
installation?
What
are
typical
costs
and
how
do
these
costs
compare
to
other
construction/
equipment
costs?
What
factors
affect
the
costs?

The
answer
to
this
depends
on
whether
you
are
referring
to
performance
of
fish
recovery
or
just
screen
operability.
Normally
a
fish
screen
has
to
be
reviewed
for
one
year
to
properly
account
for
all
of
the
indigenous
species
migrating
past
the
intake.

Testing
the
screens
for
operability
after
installation
is
often
in
our
package
but
normally
only
consists
of
1
to
3
days
of
field
service
to
make
recommendations
on
adjusting
the
sprays,
leveling
the
head
shaft,
checking
gaskets,
etc 

ADDING
FISH
HANDLING
AND
RETURN
The
following
questions
inquire
about
adding
a
fish
handling
and
return
system
to
an
intake
with
traveling
screens
where
no
fish
return
existed
before.
This
can
involve
either
retrofitting
existing
screens
with
fish
handling
features
or
putting
in
new
screening
units.
In
either
case,
the
questions
also
focus
on
the
costs
and
technical
aspects
of
the
addition
of
a
fish
return
sluice/
conduit
(
and
possibly
fish
pumps).

20.
Do
you
sell
fish
return
retrofit
systems
for
existing
traveling
screens?
Yes.
Can
most
existing
screens
be
retrofitted
without
replacing
the
entire
unit?
No,
most
cannot
but
some
can.
We
would
estimate
that
maybe
30%
of
existing
sites
could
upgrade
without
replacing
the
entire
unit.
Many
sites
could
all
into
this
but
it
is
economically
logical
to
do
this
as
the
parts
and
modifications
required
approach
60
to
70%
of
the
cost
of
a
new
machine,
then
enter
the
warranty
issue
into
the
picture
and
most
clients
opt
for
a
new
screen.
When
is
it
more
practical/
economical
to
replace
the
whole
screening
unit?
70%
of
the
time.
What
are
the
costs
for
adding
fish
buckets,
spray
systems
and
troughs
either
in
relation
to
other
costs
cited
or
for
equipment
sizes
described
earlier?
35­
40
%.
How
much
would
the
addition
of
fish
buckets
only
reduce
cost
over
replacing
entire
screen
unit?
Not
acceptable.

21.
How
do
you
determine
the
design
flow
volume
for
the
fish
return
conduit?
Based
on
velocity.
Generally,
what
proportion
of
the
intake
flow
is
diverted
to
the
fish
return?
Impossible
to
quantify
as
the
same
width
machine
would
require
the
same
fish
spray
water
but
the
depth
could
be
2
to
3
times
greater.

22.
Do
you
design,
provide,
or
install
fish
return
equipment
such
as
pumps
and
return
conduit?
We
can
supply
the
fish
return
troughs.
If
so:
­
How
are
the
return
pipes/
flume
configured
and
sized?
Per
site.
­
Is
there
a
minimum
diameter
to
accommodate
large
fish?
Large
fish
are
not
the
object
but
the
pipe
must
handle
the
water
volume.
­
What
are
typical
slopes
and
velocities?
1/
16"
per
foot
to
1/
8"
per
foot.
Velocity
can
be
state
specific
based
on
getting
the
fish
out
of
the
trough.
­
If
pipes
are
used,
do
they
tend
to
flow
full?
No.
­
What
materials
of
construction
are
used
for
fish
return
conduits
(
fiberglass)?
Fiberglass.

23.
EPA
Survey
data
show
few
existing
traveling
screen
return
systems
use
fish
pumps.
Under
what
circumstances
would
fish
pumps
be
necessary?
Would
not
recommend
them.

24.
Do
you
have
any
cost
data
to
share
for
adding
fish
return
systems,
especially
fish
pumps
and
return
conduits?
In
general,
what
are
typical
equipment
and
installation
unit
costs
for
the
conduit
and
support
structure
for
return
flows
associated
with
intakes
with
capacities
of
5,000
GPM
to
500,000
GPM?
If
not
available,
who
should
we
contact
for
more
information?
Fish
return
systems
would
run
+/­
$
25,000
depending
on
how
many
screens
and
how
far
they
had
to
discharge.

25.
What
is
the
typical
range
of
return
conduit
lengths?
75
to
150
feet.
How
does
water
body
type
influence
return
conduit
length?
If
it
is
tidal,
it
must
discharge
both
directions.
For
example,
do
lengths
tend
to
be
shorter
for
non­
tidal
rivers
and
streams?
Longer.

26.
Would
there
be
any
difference
in
intake
downtime
when
adding
fish
handling
features
compared
to
downtime
for
screen
replacement?
Yes
because
of
the
additional
piping,
controls,
troughs,
etc 
for
the
fish
handling
screens.
For
normal
screen
replacement,
we
have
done
these
in
as
little
as
12
hours
each.

27.
What
additional
O&
M
cost
would
be
associated
with
a
fish
return
system
besides
the
operation
of
the
screens?
Fish
spray
wash
water
only
as
it
is
really
a
passive
conduit.

28.
The
total
average
water
required
for
a
fish
screen
including
the
debris
spray,
inside
fish
spray,
outside
fish
spray
and
trough
make
up
water
is
74.5
GPM
per
foot
of
effective
width.
(
not
the
40
to
50
quoted
during
our
telecon).