Document ID: EPA-HQ-OW-2002-0049-0167
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2003-03-19T05:00Z

­
1­
2.2
New
Larger
Intake
Structure
for
Decreasing
Intake
Velocities
The
efficacy
of
traveling
screens
can
be
affected
by
both
through­
screen
and
approach
velocities.
Through­
screen
velocity
affects:
the
rate
of
debris
accumulation;
the
potential
for
entrainment
and
impingement
of
swimming
organisms;
and
the
amount
of
injury
that
may
occur
when
organisms
become
impinged
and
a
fish
return
system
is
in
use.
Performance,
with
respect
to
impingement
and
entrainment,
generally
tends
to
deteriorate
as
intake
velocities
increase.
For
older
intake
structures,
the
primary
function
of
the
screen
was
to
ensure
downstream
cooling
system
components
continued
to
function
without
becoming
plugged
with
debris.
The
design
often
did
not
take
into
consideration
the
effect
of
through­
screen
velocity
on
entrainment
and
impingement
of
aquatic
organisms.
For
these
older
structures,
the
standard
design
value
for
through­
screen
velocity
was
in
the
range
of
2.0
to
2.5
fps
(
Gathright
2002).
These
design
velocities
were
based
on
the
performance
of
coarse
mesh
traveling
screens
with
respect
to
their
ability
to
remove
debris
as
quickly
as
it
collected
on
the
screen
surface.
As
demonstrated
in
the
Facility
Questionnaire
database,
actual
velocities
may
be
even
higher
than
standard
design
values.
These
higher
velocities
may
result
from
cost­
saving,
site­
specific
designs
or
from
an
increased
withdrawal
rate
compared
to
the
original
design.

As
described
previously,
solutions
considered
for
reducing
entrainment
on
traveling
screens
are
to
replace
the
coarse
mesh
screens
with
finer
mesh
screens
or
to
install
fine
mesh
screen
overlays.
However,
a
potential
problem
with
replacing
the
existing
intake
screens
with
finer
mesh
screens
is
that
a
finer
mesh
will
accumulate
larger
quantities
of
debris.
Thus,
retrofitting
existing
coarse
mesh
screens
with
fine
mesh
may
affect
the
ability
of
screens
to
remove
debris
quickly
enough
to
function
properly.
Exacerbating
this
potentia
problem
is
finer
mesh
may
result
in
slightly
higher
throughscreen
velocities
(
Gathright
2002).
If
the
debris
problems
associated
with
using
fine
mesh
occur
on
a
seasonal
basis,
then
one
possible
solution
(
see
Section
2.1,
above)
is
to
use
fine
mesh
overlays
during
the
period
when
sensitive
aquatic
organisms
are
present.
This
solution
is
predicated
on
the
assumption
that
the
period
of
high
debris
loading
does
not
substantially
coincide
with
the
period
when
sensitive
aquatic
organisms
are
most
prevalent.
When
such
an
approach
is
not
feasible,
some
means
of
decreasing
the
intake
velocities
may
be
necessary.

The
primary
intake
attributes
that
determine
intake
through­
screen
velocities
are
the
flow
volume,
effective
screen
area,
and
percent
open
area
of
the
screen.
The
primary
intake
attributes
that
determine
approach
velocity
are
flow
volume
and
cross­
sectional
area
of
the
intake.
In
instances
where
flow
volume
cannot
be
reduced,
a
reduction
in
intake
velocities
can
only
be
obtained
in
two
ways:
for
through­
screen
velocities,
an
increased
screen
area
and/
or
percent
open
area,
or
for
approach
velocity,
an
increased
intake
cross­
sectional
area.
In
general,
there
are
practical
limits
regarding
screen
materials
and
percent
open
area.
These
limits
prevent
significant
modification
of
this
attribute
to
reduce
through­
screen
velocities.
Thus,
an
increase
in
the
screen
area
and/
or
intake
cross­
sectional
area
generally
must
be
accomplished
in
order
to
reduce
intake
velocities.
For
technology
options
that
rely
on
the
continued
use
of
traveling
screens,
a
means
of
increasing
the
effective
area
of
the
screens
is
warranted.
EPA
has
researched
this
problem
and
has
identified
the
following
three
approaches
to
increasing
the
screen
size:
­
2­
1.
Replace
existing
through
flow
(
single
entry­
single
exit)
traveling
screens
with
dual­
flow
(
double
entry­
single
exit)
traveling
screens.
Dual­
flow
screens
can
be
placed
in
the
same
screen
well
as
existing
through
flow
screens.
However,
they
are
oriented
perpendicular
to
the
orientation
of
the
original
through­
flow
screens
and
extend
outward
towards
the
front
of
the
intake.
Installation
may
require
some
demolition
of
the
existing
intake
deck.
This
solution
may
work
where
screen
velocities
do
not
need
to
be
reduced
by
a
large
amount.
This
technology
has
a
much
improved
performance
with
respect
to
debris
carry
over
and
is
often
selected
based
on
this
attribute
alone
(
Gathright
2002;
see
also
Section
2.1.4).

2.
Replace
the
function
of
the
existing
intake
screen
wells
with
larger
wells
constructed
in
front
of
the
existing
intake
and
hydraulically
connected
to
the
intake
front
opening.
This
approach
retains
the
use
and
function
of
the
existing
intake
pumps
and
pump
wells
with
little
or
no
modification
to
the
original
structure.
A
concern
with
this
approach
(
besides
construction
costs)
is
whether
the
construction
can
be
performed
without
significant
downtime
for
the
generating
units.

3.
Add
a
new
intake
structure
adjacent
to,
or
in
close
proximity
to,
the
existing
intake.
The
old
intake
remains
functional,
but
with
the
drive
system
for
the
existing
pumps
modified
to
reduce
the
flow
rate.
The
new
structure
will
include
new
pumps
sized
to
pump
an
additional
flow.
The
new
structure
can
be
built
without
a
significant
shutdown
of
the
existing
intake.
Shutdown
would
only
be
required
at
the
final
construction
step,
where
the
pipes
from
new
pumps
are
connected
to
the
existing
piping
and
the
pumps
and/
or
pump
drives
for
the
existing
pumps
are
modified
or
replaced.
In
this
case,
generating
downtime
is
minimized.
However,
the
need
for
new
pumps,
and
the
modification
to
existing
pumps
that
reduce
their
original
flow,
entail
significant
additional
costs.

Option
3
is
a
seemingly
simple
solution
where
the
addition
of
new
intake
bays
adjacent
or
in
close
proximity
to
the
existing
intake
would
add
to
the
total
intake
and
screen
cross­
sectional
area.
A
problem
with
this
approach
is
that
the
current
pumping
capacity
needs
to
be
distributed
between
the
old
and
new
intake
bays.
Utilizing
the
existing
pump
wells
and
pumps
is
desirable
to
help
minimize
costs.
However,
where
the
existing
pumps
utilize
single
speed
drives,
the
distribution
of
flow
to
the
new
intake
bays
would
require
either
an
upstream
hydraulic
connection
or
a
pump
system
modification.
Where
the
existing
intake
has
only
one
or
two
pump
wells
a
hydraulic
connection
with
a
new
adjacent
intake
bay
could
be
created
through
demolition
of
a
sidewall
downstream
of
the
traveling
screen.
While
this
approach
is
certainly
feasible
in
certain
instances,
the
limitations
regarding
intake
configurations
prevents
EPA
from
considering
this
a
viable
regulatory
compliance
alternative
for
all
but
a
few
existing
systems.
A
more
widely
applicable
solution
would
be
to
reduce
pump
flow
rate
of
the
existing
pumps
either
by
modifying
the
pump
drive
to
a
multi­
speed
or
variable
speed
drive
system,
or
by
replacing
the
existing
pumps
with
smaller
ones.
The
new
intake
bays
would
be
constructed
with
new
smaller
pumps
that
produce
lower
flow
rates.
The
combined
flows
of
the
new
and
older,
modified
pumps
satisfies
the
existing
intake
flow
requirement.
The
costs
of
modifying
existing
pumps,
plus
the
new
pumps
and
pump
wells,
represents
a
substantial
cost
component.

Option
2
does
not
require
modifications
or
additions
to
the
existing
pumping
equipment.
In
this
­
3­
approach
a
new
intake
structure
to
house
more
and/
or
larger
screen
wells
would
be
constructed
in
front
of
the
existing
intake.
The
old
and
new
intake
structures
could
then
be
hydraulically
connected
by
closing
off
the
ends
with
sheet
pile
walls
or
similar
structures.
EPA
is
not
aware
of
any
installations
that
have
performed
this
retrofit
but
it
was
proposed
as
an
option
in
the
Demonstration
Study
for
the
Salem
Nuclear
Plant
(
PSE&
G
2001).
In
that
proposal
the
new
screens
were
to
be
dualflow
screens
but
the
driving
factor
for
the
new
structure
was
a
need
to
increase
the
intake
size.

EPA
initially
developed
rough
estimates
of
the
comparative
costs
of
applying
option
2
versus
option
3
(
in
the
hypothetical
case
the
intake
area
was
doubled
in
size).
The
results
indicated
that
adding
a
new
screen
well
structure
in
front
of
the
existing
intake
was
less
costly
and
therefore,
this
option
was
selected
for
consideration
as
a
compliance
technology
option.
This
cost
efficiency
is
primarily
due
to
the
reuse
of
the
existing
intake
in
a
more
cost
efficient
manner
in
option
2.
However,
option
2
has
one
important
drawback:
it
may
not
be
feasible
where
the
sufficient
space
is
not
available
in
front
of
the
existing
intake.
To
minimize
construction
downtime,
EPA
assumes
the
new
intake
structure
is
placed
far
enough
in
front
of
the
existing
intake
to
allow
the
existing
intake
to
continue
functioning
until
construction
of
the
structure
is
completed.

Scenario
Description
In
this
scenario,
modeled
on
option
2
described
above,
a
new
reinforced
concrete
structure
is
designed
for
new
through­
flow
or
dual­
flow
intake
screens.
This
structure
will
be
built
directly
in
front
of
the
existing
intake.
The
structure
will
be
built
inside
a
temporary
sheet
pile
coffer
dam.
Upon
completion
of
the
concrete
structure,
the
coffer
dam
will
be
removed.
A
permanent
sheet
pile
wall
will
be
installed
at
both
ends,
connecting
the
rear
of
the
new
structure
to
the
front
of
the
old
intake
structure
hydraulically.
Such
a
configuration
has
the
advantage
of
providing
for
flow
equalization
between
multiple
new
intake
screens
and
multiple
existing
pumps.
The
construction
includes
costs
for
site
development
for
equipment
access.
Capital
costs
were
developed
for
the
same
set
of
screen
widths
(
2
feet
through
140
feet)
and
depths
(
10
feet
through
100
feet)
used
in
the
traveling
screen
cost
methodology.
Bets­
fit,
second­
order
equations
were
used
to
estimated
costs
for
each
different
screen
well
depth,
using
total
screen
width
as
the
independent
variable.
Construction
duration
is
estimated
to
be
nine
months.

Capital
Costs
Capital
costs
were
derived
for
different
well
depths
and
total
screen
widths
based
on
the
following
assumptions.

Design
Assumptions
­
Onshore
Activities
°
Clearing
and
grabbing:
this
is
based
on
clearing
with
a
dozer,
and
clearing
light
to
medium
brush
to
4"
diameter;
clearing
assumes
a
40
feet
width
for
equipment
maneuverability
near
the
shore
line
and
500
feet
accessibility
lengthwise
at
$
3,075/
acre
(
RS
Means
2001);
surveying
costs
are
estimated
at
$
1,673/
acre
(
R
S
Means
2001),
covering
twice
the
access
area.
­
4­
°
Earth
work
costs:
these
include
mobilization,
excavation,
and
hauling,
etc.,
along
a
water
front
width,
with
a
500­
foot
inland
length;
backfill
with
structural
sand
and
gravel
(
backfill
structural
based
on
using
a
200
HP
bulldozer,
300­
foot
haul,
sand
and
gravel;
unit
earthwork
cost
is
$
395/
cu
yd
(
R
S
Means
2001)
°
Paving
and
surfacing,
using
concrete
10"
thick;
assuming
a
need
for
a
20­
foot
wide
and
2­
foot
long
equipment
staging
area
at
a
unit
cost
of
$
33.5/
sq
yd
(
R
S
Means
2001)

$
Structural
cost
is
calculated
@
$
1250/
CY
(
R
S
Means
2001),
assuming
two
wing
walls
1.5
feet
thick
and
26
feet
high,
with
10
feet
above
ground
level,
and
36
feet
long
with
16
feet
onshore
(
these
walls
are
for
tying
in
the
connecting
sheet
pile
walls).

$
Sheet
piling,
steel,
no
wales,
38
psf,
left
in
place;
these
are
assumed
to
have
a
width
twice
the
width
of
the
screens
+
20
feet,
with
onshore
construction
distance,
and
be
30
feet
deep,
at
$
24.5/
sq
ft
(
R
S
Means
2001).

Design
Assumptions
­
Offshore
Components
°
Structure
width
is
20%
greater
than
total
screen
width
and
20
ft
front
to
back
°
Structural
support
consists
of
the
equivalent
of
four
3­
foot
by
3­
foot
reinforced
concrete
columns
at
$
935/
cu
yd
(
R
S
Means
2001)
plus
two
additional
columns
for
each
additional
screen
well
(
a
2­
foot
wide
screen
assumes
an
equivalent
of
2­
foot
by
2
feet
columns)
°
Overall
structure
height
is
equal
to
the
well
depth
plus
10%
°
The
elevated
concrete
deck
is
1.5
ft
thick
at
$
42/
cu
yd
(
R
S
Means
2001)
°
Dredging
mobilization
is
$
9,925
if
total
screen
width
is
greater
than
10
feet;
is
$
25,890
if
total
screen
width
is
10
feet
to
25
feet;
and
is
$
52,500
if
total
screen
width
is
greater
than
25
ft
(
R
S
Means
2001)
°
The
cost
of
dredging
in
the
offshore
work
area
is
$
23/
cu
yd
to
a
depth
of
10
feet
°
The
cost
of
the
temporary
coffer
dam
for
the
structure
is
$
22.5/
sq
ft
(
R
S
Means
2001),
with
total
length
equal
to
the
structure
perimeter
times
a
factor
of
1.5
and
the
height
equal
to
1.3
times
well
depth.

Field
Project
Personnel
Not
Included
in
Unit
Costs:

°
Project
Field
Manager
at
$
2,525
per
week
(
R
S
Means
2001)
°
Project
Field
Superintendent
at
$
2,375
per
week
(
R
S
Means
2001)
°
Project
Field
Clerk
at
$
440
per
week
(
R
S
Means
2001).

The
above
cost
components
were
estimated
and
summed
and
the
costs
were
expanded
using
the
following
cost
factors.

Add­
on
and
Indirect
Costs:

°
Construction
Management
is
4.5%
of
direct
costs
°
Engineering
and
Architectural
fees
for
new
construction
is
17%
of
direct
costs
°
Contingency
is
10%
of
direct
costs
°
Overhead
and
profit
is
15%
of
direct
costs
­
5­
Screen
Width
2
5
10
20
30
40
50
60
70
84
98
112
126
140
Depth
(
Ft)
10
$
280,000
$
320,000
$
880,000
$
1,010,000
$
1,220,000
$
1,370,000
$
1,520,000
$
1,680,000
$
1,850,000
$
2,080,000
$
2,330,000
$
2,590,000
$
2,860,000
$
3,140,000
25
$
540,000
$
600,000
$
1,880,000
$
2,090,000
$
2,390,000
$
2,620,000
$
2,860,000
$
3,100,000
$
3,350,000
$
3,700,000
$
4,070,000
$
4,440,000
$
4,830,000
$
5,230,000
50
$
1,130,000
$
1,240,000
$
4,190,000
$
4,570,000
$
5,030,000
$
5,420,000
$
5,820,000
$
6,230,000
$
6,650,000
$
7,240,000
$
7,840,000
$
8,640,000
$
9,090,000
$
9,740,000
75
$
1,770,000
$
1,920,000
$
6,650,000
$
7,190,000
$
7,810,000
$
8,370,000
$
8,940,000
$
9,510,000
$
10,090,000
$
10,920,000
$
11,760,000
$
12,610,000
$
13,480,000
$
14,360,000
100
$
2,480,000
$
2,690,000
$
9,420,000
$
10,130,000
$
10,930,000
$
11,660,000
$
12,400,000
$
13,150,000
$
13,900,000
$
14,970,000
$
16,060,000
$
17,160,000
$
18,280,000
$
19,410,000
°
Permits
are
2%
of
direct
costs
°
Metalwork
is
5%
of
direct
costs
°
Performance
bond
is
2.5%
of
direct
costs
°
Insurance
is
1.5%
of
direct
costs.

Table
2­
30
presents
the
total
capital
costs
for
various
screen
well
depths
and
total
screen
widths.
No
distinction
was
made
between
freshwater
and
brackish
or
saltwater
environments.
Figure
13
plots
the
data
in
Table
2­
30
and
presents
the
best­
fit
cost
equations.
The
shape
of
these
curves
indicates
a
need
for
separate
equations
for
structures
with
widths
less
than
and
greater
than
10
feet.
In
general,
however,
the
Phase
II
compliance
applications
of
this
technology
option
included
only
new
structures
greater
than
10
feet
wide.

Table
2­
30
Total
Capital
Costs
for
Adding
New
Larger
Intake
Screen
Well
Structure
in
Front
of
Existing
Shoreline
Intake
O&
M
Costs
No
separate
O&
M
costs
were
derived
for
the
structure
itself
since
the
majority
of
the
O&
M
activities
are
covered
in
the
O&
M
costs
for
the
traveling
screens
to
be
installed
in
the
new
structure.

Construction
Downtime
As
described
above,
this
scenario
is
modeled
after
an
option
described
in
a
316b
Demonstration
Study
for
the
Salem
Nuclear
Plant
(
PSE&
G
2001).
In
that
scenario
which
applies
to
a
very
large
nuclear
facility,
the
existing
intake
continues
to
operate
during
the
construction
of
the
offshore
intake
structure
inside
the
sheet
pile
cofferdam.
Upon
completion
of
the
offshore
structure
and
removal
of
the
cofferdam,
the
final
phase
on
the
construction
requires
the
shut
down
of
the
generating
units
for
the
placement
of
the
sheet
pile
end
walls.
The
feasibility
study
states
that
units
1
and
2
would
be
required
to
shut
down
for
one
month
each.
Based
on
this
estimate
and
the
size
of
the
Salem
facility
(
average
daily
flow
of
over
2
million
gpm),
EPA
has
concluded
that
a
construction
downtime
estimate
in
the
range
of
6
to
8
weeks
is
reasonable.
EPA
did
not
select
a
single
downtime
for
all
facilities
installing
an
offshore
structure.
Instead,
EPA
applied
a
six­
to
eight­
week
downtime
duration
based
on
variations
in
project
size,
using
design
flow
as
a
measure
of
size.
EPA
assumed
a
downtime
of
six
weeks
for
facilities
with
intake
flow
volumes
of
less
than
400,000
gpm;
seven
weeks
for
facilities
with
intake
flow
volumes
greater
than
400,000
gpm
but
less
than
800,000
gpm;
and
eight
weeks
for
facilities
with
intake
flow
volumes
greater
than
800,000
gpm.
­
6­
Application
The
input
value
for
the
cost
equation
is
the
screen
well
depth
and
the
total
screen
width
(
see
Section
2.1
for
a
discussion
of
the
methodology
for
determining
the
screen
well
depth).
The
width
of
the
new
larger
screen
well
intake
structure
was
based
on
the
design
flow,
and
an
assumed
through­
screen
velocity
of
1.0
fps
and
a
percent
open
area
of
68%.
The
same
well
depth
and
width
values
are
used
for
estimating
the
costs
of
new
screen
equipment
for
the
new
structure.
New
screen
equipment
consisted
of
fine
mesh
traveling
screens
with
fish
handling
and
return
system
(
Scenario
C).
­
7­
Figure
13
Total
Capital
Costs
of
New
Larger
Intake
Structure
y
=
21.95x
2
+
39599x
+
4E+
06
R
2
=
0.9993
y
=
159500x
2
­
1E+
06x
+
4E+
06
R
2
=
1
y
=
29.323x
2
+
72303x
+
9E+
06
R
2
=
1
y
=
26.224x
2
+
55249x
+
6E+
06
R
2
=
1
y
=
112000x
2
­
734000x
+
3E+
06
R
2
=
1
y
=
69167x
2
­
447500x
+
2E+
06
R
2
=
1
y
=
29500x
2
­
186500x
+
795000
R
2
=
1
y
=
16.983x
2
+
23081x
+
2E+
06
R
2
=
0.9998
y
=
12333x
2
­
73000x
+
376667
R
2
=
1
y
=
17.269x
2
+
14668x
+
737544
R
2
=
0.9996
$­

$
5,000,000
$
10,000,000
$
15,000,000
$
20,000,000
$
25,000,000
1
10
100
1000
Total
Effective
Traveling
Screen
Width
(
Ft)

Capital
Cost
2002
Dollars
well
depth
10
ft
well
depth
25
ft
wel
ldepth
50
ft
well
depth
75
ft
well
depth
100
ft
small
screens
well
depth
10
ft
Small
screens
well
depth
25
small
screens
well
depth
50
ft
small
screens
well
depth
75
small
screens
well
depth
100
ft
­
8­