Chlorine
Dioxide
Environmental
Modeling
Chapter
Case
4023
Genevieve
Angle
Office
of
Pesticide
Programs
Antimicrobials
Division
U.
S.
Environmental
Protection
Agency
1200
Pennsylvania
Avenue,
NW
Washington,
DC
20460
June
28,
2005
Page
2
of
89
INTRODUCTION
This
document
provides
estimated
environmental
concentrations
(
EECs)
in
the
receiving
body
of
water
from
the
use
of
chlorine
dioxide
(
ClO2)
and
sodium
chlorite
(
ClNaO2)
in
once­
through
industrial
water
systems.
The
Probabilistic
Distribution
Model
version
4
(
PDM4)
was
used
to
evaluate
the
chlorine
dioxide
and
sodium
chlorite
concentration
in
stream
water.
Using
a
steam
electric
power
plant
as
the
representative
facility,
the
number
of
days
that
the
concentration
in
the
water
body
exceeded
threshold
levels
was
estimated.
Three
stream
flow
scenarios
were
modeled:
low
(
approximately
100
million
gallons
per
day
(
MGD)),
medium
(
approximately
500
MGD),
and
high
(
approximately
1000
MGD).
Intermittent
and
continuous
feed
application
of
chlorine
dioxide
and
sodium
chlorite
were
also
modeled.
The
probability
of
exceeding
a
given
concentration
of
concern
at
a
particular
dose
rate
(
intermittent:
0.1,
25,
and
800
ppm
and
continuous:
0.1,
2.0,
and
800
ppm)
and
flow
rate
(
low­
approximately
100
MGD;
mediumapproximately
500
MGD;
high­
approximately
1000
MGD)
over
the
time
period
of
60
days
was
calculated
and
presented
in
tabular
form
for
sodium
chlorite
or
chlorine
dioxide.
It
is
believed
that
the
single
label
with
the
800
ppm
dose
rate
will
be
either
cancelled
or
amended
by
the
registrant
to
delete
this
dose.

OVERVIEW
OF
PDM4
PDM4
calculates
downstream
chemical
concentrations
from
a
chemical
discharge
using
the
probabilistic
distribution
model.
The
algorithm
used
is
taken
from
DiToro,
1984.
A
simple
mass
balance
approach
forms
the
basis
of
PDM.
However,
the
input
variables
are
not
single
point
estimates,
because,
in
reality,
these
variables
are
not
constant.
Streams
follow
a
highly
variable
seasonal
flow
pattern
and
numerous
variables
in
a
manufacturing
process
can
affect
the
chemical
concentration
and
flow
rate
of
the
effluent.
PDM4
models
the
stream
flow
as
constantly
changing
and
calculates
the
probability
that
the
concentration
in
a
given
target
stream
will
exceed
some
target
value.
Specifically,
it
calculates
the
percent
of
days
per
year
that
the
concentration
of
concern
is
exceeded.
PDM4
uses
probability
distributions
as
inputs
and
calculates
the
resulting
probability
distribution
of
the
concentration
in
the
stream.

INPUTS
Power
Plant
Information
In
modeling
the
fate
of
chlorine
dioxide
and
sodium
chlorite
in
the
receiving
body
of
water,
the
following
assumptions
were
made
regarding
the
representative
power
plant
to
be
modeled:

$
The
7Q10
flow
rate
(
a
flow
rate
that,
once
every
ten
years,
a
stream
is
expected
to
be
below
for
seven
consecutive
days)
was
assumed
to
be
the
normal
cooling
water
flow
rate.
This
value
was
chosen
because
it
is
assumed
that
electric
plants
would
need
to
have
a
steady
supply
of
cooling
water,
and
the
7Q10
flow
reflects
a
rate
that
could
be
maintained
continuously
by
the
power
plant.
This
is
a
worst
case
scenario
since
electric
plants
may
Page
3
of
89
use
more
cooling
water
under
normal
conditions,
though
at
a
greater
risk
of
running
out
of
usable
water.
For
lack
of
better
data,
these
values
were
used.

$
It
is
assumed
that
the
system
is
running
without
any
noticeable
fouling,
so
that
only
maintenance
applications
of
the
chemical
are
necessary.

$
The
dose
rates
used
for
modeling
were
0.1,
2.0,
and
800
ppm
for
continuous
feed
and
0.1,
25,
and
800
ppm
for
intermittent
feed.
These
values
represent
the
low­
end,
high­
end,
and
maximum
dose
rates
stated
on
product
labels.
It
is
believed
that
the
single
label
with
the
800
ppm
dose
rate
will
be
either
cancelled
or
amended
by
the
registrant
to
delete
this
dose.

$
In
modeling
intermittent
feed
operation,
it
is
assumed
that
one
application
per
day
for
15
minutes
is
sufficient
to
achieve
initial
control
and
to
maintain
subsequent
control.
This
is
based
on
the
labeling
for
similar
uses
of
other
pesticides.

PDM4
Model
Inputs
A
summary
of
the
input
parameters
is
described
below.
To
see
the
complete
input
and
output
files,
please
refer
to
the
appendix
of
this
report.

$
Release
Days
­
It
has
been
assumed
that
the
product
is
released
365
days
a
year.

$
Loading
­
The
following
equations
were
used
to
calculate
the
loading
(
kg/
site/
day):

Continuous
Feed
Scenario­
Calculation
for
Loading
(
kg/
site/
day):

7Q10
Flow
(
MLD)
*
106
(
Conversion
factor
for
million
liters/
day
to
liters/
day)
(
Equation
#
1)
*
1
(
kg
water/
liter
of
water)
*
dose
rate
(
kg/
kg)

Dose
rate
(
kg
of
chemical/
kg
of
water)
=
dose
rate
(
ppm)
*
10­
6
(
Equation
#
2)

Where:
ppm
=
10­
6
kg
of
chemical/
kg
of
water
Intermittent
Feed
Scenario­
Calculation
for
Loading
(
kg/
site/
day):
One
application
per
day
for
15
minutes:

[
7Q10
(
MLD)
*
106
(
Conversion
factor
for
million
liters/
day
to
liters/
day)
(
Equation
#
3)
*
1
(
kg
water/
liter
of
water)
*
dose
rate
(
ppm)]
*
(
0.25/
24)

Dose
rate
(
kg
of
chemical/
kg
of
water)
=
dose
rate
(
ppm)
*
10­
6
(
Equation
#
4)

Where:
ppm
=
10­
6
kg
of
chemical/
kg
of
water
Note:

The
7Q10
flow
rate
(
a
flow
rate
that,
once
every
ten
years,
a
stream
is
expected
to
be
below
for
Page
4
of
89
seven
consecutive
days)
was
assumed
to
be
the
cooling
system
flow.

The
dose
rates
for
continuous
use
were
0.1,
2.0,
and
800
ppm.

The
dose
rates
for
intermittent
use
were
0.2,
25,
and
800
ppm.
It
was
assumed
that
one
application
per
day
for
15
minutes
(
0.25
hr)
is
sufficient
to
achieve
initial
control
and
to
maintain
subsequent
control.

$
Concentration
of
Concern
(
COC)
­
PDM4
is
designed
to
report
the
number
of
days
that
the
concentration
in
the
water
body
exceeds
a
COC
that
has
been
specified
by
the
user.
For
this
study,
the
model
was
run
multiple
times
using
different
COCs
to
determine
a
curve.
The
COCs
considered
for
each
flow
regime
are
as
follows:
1,
3,
7,
57,
115,
132,
264,
288,
660,
5060,
7500,
10120,
15000,
25300,
and
37500
ppb.
These
COC
values
were
derived
from
studies
of
the
sensitivity
of
various
species
to
sodium
chlorite/
chlorine
dioxide.

The
input
parameters
are
summarized
in
Table
1
below.

Table
1.
PDM4
Model
Inputs
Parameter
Value
Rationale
Industry
Type
Steam
Electric
Power
Plants
(
SIC
#
4911)
Various
NPDES
EPA
assumption
as
being
the
representative
facility
for
once­
through
industrial
water
systems
using
pesticides.

Release
Days
365
EPA
assumption.

Loading
Refer
to
Equations
#
1
&
#
2
for
continuous
loading
and
Equation
#
3
&
#
4
for
intermittent
loading
calculation
For
intermittent
feed
operation,
it
is
assumed
(
based
on
labeling
for
similar
uses
of
other
pesticides)
that
one
application
per
day
for
15
minutes
is
sufficient
to
achieve
initial
control
and
to
maintain
subsequent
control.

Concentration
of
Concern
1,
3,
7,
57,
115,
132,
264,
288,
660,
5060,
7500,
10120,
15000,
25300,
37500
ppb
A
range
was
used
to
determine
a
curve.
The
range
is
based
on
the
sensitivity
of
different
species
to
sodium
chlorite/
chlorine
dioxide.

The
three
different
flow
regimes
considered
power
plants
with
average
stream
flow
rates
of
100
"

10
MGD
(
million
gallons
per
day),
500
"
50
MGD,
and
1000
"
50
MGD,
respectively
(
or
378.5
"
37.85,
1982.5
"
189.25,
and
3785
"
189.25
million
liters
per
day).
These
plants
were
pulled
from
a
database
of
NPDES
plant
codes
based
on
the
above
criteria
of
flow
regime.
Tables
2,
3,
and
4
below
show
details
regarding
the
power
plants
and
their
cooling
streams.
Twelve
different
sites
throughout
the
United
States
were
tested
in
the
model
from
the
low
and
medium
stream
flow
regimes,
and
six
were
tested
from
the
high
flow
regime.
Page
5
of
89
Table
2.
Low
Flow
(
100
MGD1)
Stream
Specifications
NPDES
Mean
Stream
Flow
(
MLD1)
Mean7Q102
Stream
Flow
(
MLD1)

IA0033235
401.08
2.84
PA0002062
391.05
4.09
LA0003042
383.57
44.57
MI0038172
379.25
13.97
OK0002682
363.06
3.37
WV0005525
358.67
14.56
IL0036919
355.83
3.89
LA0036145
354.06
13.56
UT0000116
351.97
32.39
TX0054500
351.57
26.85
PA0008443
336.52
12.64
IL0048321
336.36
97.05
1.
MGD=
Million
gallons
a
day;
MLD=
Million
liters
a
day
2.
Seven
consecutive
days
of
lowest
stream
flows
over
a
ten
year
period
Table
3.
Medium
Flow
(
500
MGD1)
Stream
Specifications
NPDES
Mean
Stream
Flow
(
MLD1)
Mean7Q102
Stream
Flow
(
MLD1)

MA0004367
2029.15
226.78
IA0000108
1973.2
61.30
NM0000108
1970.38
5.92
FL0025526
1959.16
653.08
IN0032948
1948.06
152.81
TX0001163
1867.21
11.37
OH0010421
1840.04
59.80
IN0041246
1819.99
167.19
PA0002054
1792.41
114.97
MN0000906
1749.68
28.94
NH0001431
1733.51
75.69
IN0038806
1715.15
58.19
1.
MGD=
Million
gallons
a
day;
MLD=
Million
liters
a
day
2.
Seven
consecutive
days
of
lowest
stream
flows
over
a
ten
year
period
Table
4.
High
Flow
(
1000
MGD1)
Stream
Specifications
NPDES
Mean
Stream
Flow
(
MLD1)
Mean7Q102
Stream
Flow
(
MLD1)

GA0004341
3964.96
837.51
WA0003280
3831.92
591.87
Page
6
of
89
KS0079057
3757.2
20.42
NC0005088
3693.64
812.48
SC0001104
3652.9
50.25
IL0002186
3635.95
1169.28
1.
MGD=
Million
gallons
a
day;
MLD=
Million
liters
a
day
2.
Seven
consecutive
days
of
lowest
stream
flows
over
a
ten
year
period
RESULTS
PDM4
calculates,
for
each
reach,
the
percent
of
days
per
year
that
a
reach
would
have
concentrations
above
a
particular
COC.
These
values
were
averaged
within
each
of
the
three
different
flow
regimes
(
i.
e.,
low,
medium,
and
high),
giving
average
percentages
of
exceedence.
EPA
also
looked
at
the
worst
case
scenarios
for
the
low,
medium,
and
high
stream
flows
considered.
These
calculations
were
performed
separately
for
intermittent
and
continuous
feed
scenarios.
Dose
rates
considered
were
0.1,
25,
and
800
ppm
for
the
intermittent
feed
scenario
and
0.1,
2.0,
and
800
ppm
for
the
continuous
feed
scenario.
EPA
also
calculated
the
chance
of
exceeding
a
particular
COC
over
time
periods
of
48
hours
(
2
days),
96
hours
(
4
days),
21
days,
and
60
days
for
sodium
chlorite
and
chlorine
dioxide.

Results
for
Intermittent
Feed
Scenario
Results
for
the
intermittent
feed
scenario
at
dose
rates
of
0.1,
25,
and
800
ppm
are
presented
in
Tables
5,
6,
and
7,
respectively.
Taking
these
percentages
and
multiplying
by
365
days
a
year,
one
can
calculate
the
number
of
days
out
of
the
year
the
chlorine
dioxide
and
sodium
chlorite
concentration
in
the
water
will
be
greater
than
any
given
COC.
For
example,
taking
the
0.1
ppm
dose
rate,
and
considering
a
COC
of
57
ppb,
the
average
exceedence
rates
for
each
of
the
three
stream
flow
categories
(
i.
e.,
low,
medium,
and
high
flow)
can
be
calculated
as
follows:

Dose
rate
=
0.1
ppm
Low
flow
regime
(
100
MGD),
1.89e­
4
[
LF
percent
days
57
ppb
COC
exceeded]/
100
*
365
=
6.90
e­
4
days/
yr
Medium
flow
regime
(
500
MGD),
2.63e­
5
[
MF
percent
days
57
ppb
COC
exceeded]/
100
*
365
=
9.6
e­
5
days/
yr
High
flow
regime
(
1000
MGD),
4.60e­
6
[
HF
percent
days
57
ppb
COC
exceeded]/
100
*
365
=
1.67
e­
5
days/
yr
For
comparison,
taking
the
25
ppm
and
800
ppm
dose
rate,
and
considering
the
same
COC
of
57
ppb,
the
average
exceedence
rates
for
each
of
the
three
stream
flow
categories
(
i.
e.,
low,
medium,
and
high
flow)
can
be
calculated
as
follows:

Dose
rate
=
25
ppm
Low
flow
regime
(
100
MGD),
15.3
[
LF
percent
days
57
ppb
COC
exceeded]/
100
*
365
=
2.04
days/
yr
Medium
flow
regime
(
500
MGD),
19.9
[
MF
percent
days
57
ppb
COC
exceeded]/
100
*
365
=
Page
7
of
89
72.6
days/
yr
High
flow
regime
(
1000
MGD),
33.7
[
HF
percent
days
57
ppb
COC
exceeded]/
100
*
365
=
123
days/
yr
Dose
rate
=
800
ppm
Low
flow
regime
(
100
MGD),
67.0
[
LF
percent
days
57
ppb
COC
exceeded]/
100
*
365
=
245
days/
yr
Medium
flow
regime
(
500
MGD),
85.4
[
MF
percent
days
57
ppb
COC
exceeded]/
100
*
365
=
312
days/
yr
High
flow
regime
(
500
MGD),
84.1
[
HF
percent
days
57
ppb
COC
exceeded]/
100
*
365
=
307
days/
yr
Although
fluctuations
can
be
seen,
the
general
trend
is
that
the
numbers
of
days
the
COC
is
exceeded
in
a
year
increases
as
the
concentration
of
the
chemical
increases.

Table
5.
Average
Percent
of
Days
COC
Exceeded
Intermittent
Feed
Scenario
(
Dose
=
0.1
ppm)
COC1
(
ppb)
LF2
Percent
Days
COC
Exceeded
(%)
LF­
Standard
Deviation
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
MF­
Standard
Deviation
(%)
HF4­
Percent
Days
COC
Exceeded
(%)
HF­
Standard
Deviation
(%)

1
2.69
5.58
2.73
2.78
4.4
3.66
3
0.515
1.56
0.246
0.285
0.35
0.415
7
0.115
0.386
2.43e­
02
4.00e­
02
2.69e­
02
4.05e­
02
57
1.89e­
04
6.52e­
04
2.63e­
05
6.12e­
05
4.58e­
06
9.74e­
06
115
6.17e­
06
2.13e­
05
2.00e­
06
4.87e­
06
1.38e­
07
3.12e­
07
132
2.90e­
06
1.00e­
05
1.17e­
06
2.88e­
06
6.71e­
08
1.53e­
07
264
4.16e­
08
1.44e­
07
6.78e­
08
1.74e­
07
1.43e­
09
3.40e­
09
288
2.32e­
08
8.00e­
08
4.64e­
08
1.20e­
07
8.55e­
10
2.03e­
09
660
4.00e­
11
1.38e­
10
1.00e­
09
2.84e­
09
5.01e­
12
1.22e­
11
5060
0.00
0.00
1.39e­
14
4.75e­
14
6.29e­
19
1.54e­
18
7500
0.00
0.00
1.16e­
15
4.02e­
15
3.02e­
20
7.39e­
20
10120
0.00
0.00
1.51e­
16
5.24e­
16
7.72e­
22
1.89e­
21
15000
0.00
0.00
1.02e­
17
3.53e­
17
2.74e­
24
6.71e­
24
25300
0.00
0.00
1.80e­
19
6.24e­
19
4.50e­
26
1.10e­
25
37500
0.00
0.00
3.21e­
21
1.11e­
20
1.63e­
29
4.00e­
31
Page
8
of
89
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)

Table
6.
Average
Percent
of
Days
COC
Exceeded
Intermittent
Feed
Scenario
(
Dose
=
25
ppm)
COC1
(
ppb)
LF2
Percent
Days
COC
Exceeded
(%)
LF­
Standard
Deviation
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
MF­
Standard
Deviation
(%)
HF4­
Percent
Days
COC
Exceeded
(%)
HF­
Standard
Deviation
(%)

1
73.3
37.8
90.8
17.5
90.4
18.7
3
61.0
40.4
79.5
27.8
79.5
36.9
7
49.3
38.3
66.3
28.2
73.4
40.4
57
15.3
19.9
19.9
17.5
33.7
23.5
115
7.43
11.7
9.18
9.23
15.7
11.3
132
6.29
10.3
7.63
7.75
12.9
9.44
264
2.49
5.28
2.47
2.51
3.96
3.35
288
2.20
4.83
2.09
2.12
3.33
2.90
660
0.631
1.86
0.338
0.375
0.491
0.56
5060
8.39e­
03
2.89e­
02
8.74e­
04
1.84e­
03
4.79e­
04
9.06e­
04
7500
2.34e­
03
8.07e­
03
2.37e­
04
5.23e­
04
8.78e­
05
1.75e­
04
10120
7.74e­
04
2.67e­
03
8.62e­
05
1.95e­
04
2.28e­
05
4.69e­
05
15000
1.50e­
04
5.20e­
04
2.20e­
05
5.13e­
05
3.58e­
06
7.65e­
06
25300
1.21e­
05
4.20e­
05
3.26e­
06
7.87e­
06
2.68e­
07
5.97e­
07
37500
1.40e­
06
4.84e­
06
7.09e­
07
1.75e­
06
3.39e­
08
7.78e­
08
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)

Table
7.
Average
Percent
of
Days
COC
Exceeded
Intermittent
Feed
Scenario
(
Dose
=
800
ppm)
COC1
(
ppb)
LF2
Percent
Days
COC
Exceeded
(%)
LF­
Standard
Deviation
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
MF­
Standard
Deviation
(%)
HF4­
Percent
Days
COC
Exceeded
(%)
HF­
Standard
Deviation
(%)

1
99.9
0.437
99.9
0.152
100
0
3
97.5
7.01
99.6
0.982
100
0
7
91
20
98.5
3.38
99.6
0.711
57
67
40.2
85.4
24.3
84.1
30.3
115
58.7
40.2
77.2
28.3
78.2
38.2
Page
9
of
89
COC1
(
ppb)
LF2
Percent
Days
COC
Exceeded
(%)
LF­
Standard
Deviation
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
MF­
Standard
Deviation
(%)
HF4­
Percent
Days
COC
Exceeded
(%)
HF­
Standard
Deviation
(%)

132
56.9
39.9
75.2
28.5
77.3
39
264
46.8
37.6
63
27.9
71.9
40.5
288
45.4
37.1
61.2
27.7
71.1
40.5
660
31.5
31.1
41.9
25.3
59.2
37.6
5060
5.01
8.72
5.87
6.01
9.83
7.36
7500
2.95
5.95
3.07
3.13
4.97
4.07
10120
1.92
4.39
1.74
1.76
2.75
2.46
15000
1.07
2.84
0.755
0.775
1.15
1.17
25300
0.473
1.45
0.215
0.255
0.303
0.365
37500
0.244
0.795
7.59e­
02
0.106
9.72e­
02
0.131
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)
Page
10
of
89
Figure
1
shows
the
same
data
as
Tables
5,
6,
and
7.
As
expected,
the
general
trend
in
all
three
flow
regimes
for
each
dose
rate
is
that
the
percent
of
days
the
COC
is
exceeded
decreases
as
the
COC
is
increased.
Figure
1
also
shows
the
similarities
between
the
three
stream
flow
regimes
for
each
of
the
dose
rates
that
were
modeled.

Figure
1:
Average
Exceedence
Rates
(
Intermittent
Feed)
Dose
Rates
of
0.1,
25,
and
800
ppm
1E­
11
1E­
10
1E­
09
1E­
08
1E­
07
1E­
06
1E­
05
0.0001
0.001
0.01
0.1
1
10
100
1
10
100
1000
10000
100000
Concentration
of
Concern
(
ppb)
Percent
of
Days
Exceeded
Per
Year
(%)

Low
Flow
(
Dose=
0.1
ppm)
Medium
Flow
(
Dose=
0.1
ppm)
High
Flow
(
Dose=
0.1
ppm)
Low
Flow
(
Dose=
25
ppm)
Medium
Flow
(
Dose=
25
ppm)
High
Flow
(
Dose=
25
ppm)
Low
Flow
(
Dose=
800
ppm)
Medium
Flow
(
Dose=
800
ppm)
High
Flow
(
Dose=
800
ppm)

Tables
8,
9,
and
10
list
the
calculations
for
those
power
plants
with
the
highest
exceedence
rates
for
each
of
the
three
stream
flow
regimes
for
dose
rates
of
0.1
ppm,
25
ppm,
and
800
ppm,
respectively.

Although
fluctuations
can
be
seen,
the
general
trend
is
that
the
percent
of
days
the
COC
is
exceeded
in
a
year
increases
as
the
dose
rate
of
the
chemical
increases.
A
hundred
percent
exceedence
indicates
that
the
COC
will
be
exceeded
every
day
in
a
year;
therefore
this
value
represents
the
absolute
maximum.
Page
11
of
89
Table
8.
Worst
Case
Scenarios:
Percent
of
Days
COC
Exceeded
Intermittent
Feed
Scenario
(
Dose
=
0.1
ppm)
COC1
(
ppb)
LF2­
Percent
Days
COC
Exceeded
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
HF4­
Percent
Days
COC
Exceeded
(%)

1
19.2
8.87
9.4
3
5.47
0.941
1.08
7
1.34
0.137
0.106
57
2.26e­
03
1.99e­
04
2.44e­
05
115
7.40e­
05
1.59e­
05
7.73e­
07
132
3.47e­
05
9.41e­
06
3.78e­
07
264
4.99e­
07
5.82e­
07
8.37e­
09
288
2.77e­
07
4.03e­
07
5.00e­
09
660
4.79e­
10
9.80e­
09
3.00e­
11
5060
0.00
1.650e­
13
3.770e­
18
7500
0.00
1.390e­
14
1.810e­
19
10120
0.00
1.820e­
15
4.630e­
21
15000
0.00
1.220e­
16
1.640e­
23
25300
0.00
2.160e­
18
2.700e­
25
37500
0.00
3.850e­
20
9.790e­
29
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)

Table
9.
Worst
Case
Scenarios:
Percent
of
Days
COC
Exceeded
Intermittent
Feed
Scenario
(
Dose
=
25
ppm)
COC1
(
ppb)
LF2­
Percent
Days
COC
Exceeded
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
HF4­
Percent
Days
COC
Exceeded
(%)

1
100
100
100
3
100
100
100
7
99.2
99.5
99.8
57
55.8
62.1
55.8
115
35.3
32.1
26.6
132
32.1
26.7
22.7
264
18.2
7.9
8.62
288
16.8
6.52
7.46
660
6.51
1.21
1.45
5060
0.1
6.18e­
03
2.31e­
03
7500
2.79e­
02
1.73e­
03
4.44e­
04
Page
12
of
89
COC1
(
ppb)
LF2­
Percent
Days
COC
Exceeded
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
HF4­
Percent
Days
COC
Exceeded
(%)

10120
9.26e­
03
6.40e­
04
1.18e­
04
15000
1.80e­
03
1.67e­
04
1.91e­
05
25300
1.45e­
04
2.56e­
05
1.48e­
06
37500
1.68e­
05
5.74e­
06
1.92e­
07
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)

Table
10.
Worst
Case
Scenarios:
Percent
of
Days
COC
Exceeded
Intermittent
Feed
Scenario
(
Dose
=
800
ppm)
COC1
(
ppb)
LF2­
Percent
Days
COC
Exceeded
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
HF4­
Percent
Days
COC
Exceeded
(%)

1
100
100
100
3
100
100
100
7
100
100
100
57
100
100
100
115
99.9
100
100
132
99.9
99.9
100
264
98.7
99.2
99.6
288
98.4
98.9
99.4
660
89.2
92
92.8
5060
28.1
20.5
18.2
7500
20.3
10.1
10.4
10120
15.3
5.25
6.36
15000
9.99
2.25
3.03
25300
5.08
0.846
0.949
37500
2.77
0.363
0.343
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)

Tables
11,
12,
and
13
show
the
average
of
all
power
plants
modeled,
and
compares
these
values
to
the
average
of
the
three
worst­
case
scenarios
that
were
presented
in
Tables
8,
9,
and
10,
respectively.
At
the
0.1
ppm
dose
level
the
difference
between
the
average
and
worst­
case
scenarios
is
about
an
order
of
magnitude
for
COCs
above
115
ppb.
At
the
25
ppm
dose
level
the
average­
case
is
50%
of
the
worst­
case
for
COCs
above
57
ppb.
At
the
800
ppm
dose
level
the
Page
13
of
89
average­
case
is
50%
of
the
worst­
case
scenarios
for
COCs
above
5060
ppb.
These
results
demonstrate
that
as
the
concentration
of
a
chemical
is
increased,
the
difference
in
the
days
the
COC
is
exceeded
seems
to
decrease
between
the
average
and
worse
case
scenarios.

Table
11.
Total
Average
Exceedence
Rates
vs.
Worst­
Case
Exceedence
Rates
Intermittent
Feed
Scenario
(
Dose
=
0.1
ppm)

Percent
of
Days
COC
Exceeded
(%)
COC
(
ppb)

Total
Average
Average
of
the
Three
Worst
Case
Scenarios
(
Table
8)

1
3.27
12.5
3
0.37
2.5
7
5.53e­
02
0.528
57
7.32e­
05
8.27e­
04
115
2.77e­
06
3.02e­
05
132
1.38e­
06
1.48e­
05
264
3.70e­
08
3.63e­
07
288
2.35e­
08
2.29e­
07
660
3.49e­
10
3.43e­
09
5060
4.63e­
15
5.49e­
14
7500
3.87e­
16
4.64e­
15
10120
5.05e­
17
6.06e­
16
15000
3.40e­
18
4.08e­
17
25300
6.01e­
20
7.21e­
19
37500
1.07e­
21
1.28e­
20
Page
14
of
89
Table
12.
Total
Average
Exceedence
Rates
vs.
Worst­
Case
Exceedence
Rates
Intermittent
Feed
Scenario
(
Dose
=
25
ppm)

Percent
of
Days
COC
Exceeded
(%)
COC
(
ppb)

Total
Average
Average
of
the
Three
Worst
Case
Scenarios
(
Table
9)

1
84.8
100
3
73.4
100
7
63.0
99.5
57
23.0
57.9
115
10.8
31.3
132
8.95
27.2
264
2.97
11.6
288
2.54
10.3
660
0.486
3.06
5060
3.25e­
03
3.62e­
02
7500
8.87e­
04
1.00e­
02
10120
2.94e­
04
3.34e­
03
15000
5.87e­
05
6.62e­
04
25300
5.22e­
06
5.75e­
05
37500
7.14e­
07
7.57e­
06
Page
15
of
89
Table
13.
Total
Average
Exceedence
Rates
vs.
Worst­
Case
Exceedence
Rates
Intermittent
Feed
Scenario
(
Dose
=
800
ppm)

Percent
of
Days
COC
Exceeded
(%)
COC
(
ppb)

Total
Average
Average
of
the
Three
Worst
Case
Scenarios
(
Table
10)

1
99.9
100
3
99
100
7
96.4
100
57
78.8
100
115
71.4
100
132
69.8
99.9
264
60.6
99.2
288
59.2
98.9
660
44.2
91.3
5060
6.91
22.3
7500
3.66
13.6
10120
2.14
8.97
15000
0.99
5.09
25300
0.33
2.29
37500
0.139
1.16
To
calculate
the
chance
of
exceedence
of
sodium
chlorite
and
chlorine
dioxide
over
a
consecutive
number
of
days,
the
following
assumptions
were
made:

$
The
chance
of
exceedence
on
any
given
day
at
a
site
is
independent
of
whether
exceedence
occurred
on
previous
days.

$
Although
the
percentages
calculated
by
PDM
express
the
chance
of
exceedence
during
at
least
part
of
a
day,
it
is
assumed
for
this
calculation
that
the
percentages
calculated
by
PDM
imply
exceedence
over
the
total
day.

Based
on
these
assumptions,
the
following
formula
can
be
used
to
calculate
the
probability
of
exceedence
over
N
consecutive
days:

%
probability
=
(
Probability
of
Exceedence
per
Day/
100%)
N*
100%

Tables
14
through
22
show
the
results
of
these
calculations.
These
tables
can
be
used
to
determine
an
appropriate
COC,
based
on
the
level
of
risk
that
is
deemed
acceptable.
The
choice
between
using
either
the
total
average
column
or
the
worst­
case
scenarios
average
column
will
depend
on
how
conservative
a
value
is
deemed
necessary.
Page
16
of
89
Table
14.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Intermittent
Feed
Scenario,
Dose
=
0.1
ppm,
Low
Flow
Regime
(
100
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
7.24e­
02
5.24e­
05
1.06e­
31
6.10e­
93
3
2.65e­
03
7.03e­
08
8.87e­
47
­­
a
7
1.32e­
04
1.75e­
10
1.88e­
60
­­
a
57
3.57e­
10
1.28e­
21
­­
a
­­
a
115
3.81e­
13
1.45e­
27
­­
a
­­
a
132
8.41e­
14
7.07e­
29
­­
a
­­
a
264
1.73e­
17
2.99e­
36
­­
a
­­
a
288
5.38e­
18
2.90e­
37
­­
a
­­
a
660
1.60e­
23
2.56e­
48
­­
a
­­
a
5060
­­
a
­­
a
­­
a
­­
a
7500
­­
a
­­
a
­­
a
­­
a
10120
­­
a
­­
a
­­
a
­­
a
15000
­­
a
­­
a
­­
a
­­
a
25300
­­
a
­­
a
­­
a
­­
a
37500
­­
a
­­
a
­­
a
­­
a
a
Probability
is
less
than
10­
100.

Table
15.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Intermittent
Feed
Scenario,
Dose
=
0.1
ppm,
Medium
Flow
Regime
(
500
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
7.45e­
02
5.55e­
05
1.44e­
31
1.48e­
92
3
6.05e­
04
3.66e­
09
1.62e­
53
­­
a
7
5.90e­
06
3.49e­
13
1.25e­
74
­­
a
57
6.92e­
12
4.78e­
25
­­
a
­­
a
115
4.00e­
14
1.60e­
29
­­
a
­­
a
132
1.37e­
14
1.87e­
30
­­
a
­­
a
Page
17
of
89
Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
264
4.60e­
17
2.11e­
35
­­
a
­­
a
288
2.15e­
17
4.64e­
36
­­
a
­­
a
660
1.00e­
20
1.00e­
42
­­
a
­­
a
5060
1.93e­
30
3.73e­
62
­­
a
­­
a
7500
1.35e­
32
1.81e­
66
­­
a
­­
a
10120
2.28e­
34
5.20e­
70
­­
a
­­
a
15000
1.04e­
36
1.08e­
74
­­
a
­­
a
25300
3.24e­
40
1.05e­
81
­­
a
­­
a
37500
1.03e­
43
1.06e­
88
­­
a
­­
a
a
Probability
is
less
than
10­
100
Table
16.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Intermittent
Feed
Scenario,
Dose
=
0.1
ppm,
High
Flow
Regime
(
1000
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
0.194
3.75e­
04
3.25e­
27
4.050000e­
80
3
1.23e­
03
1.500e­
08
2.660e­
50
­­
a
7
7.24e­
06
5.240e­
13
1.060e­
73
­­
a
57
2.10e­
13
4.400e­
28
­­
a
­­
a
115
1.90e­
16
3.630e­
34
­­
a
­­
a
132
4.50e­
17
2.030e­
35
­­
a
­­
a
264
2.04e­
20
4.180e­
42
­­
a
­­
a
288
7.31e­
21
5.340e­
43
­­
a
­­
a
660
2.51e­
25
6.300e­
52
­­
a
­­
a
5060
3.96e­
39
1.570e­
79
­­
a
­­
a
7500
9.12e­
42
8.320e­
85
­­
a
­­
a
10120
5.96e­
45
3.550e­
91
­­
a
­­
a
15000
7.51e­
50
­­
a
­­
a
­­
a
Page
18
of
89
Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
25300
2.03e­
53
­­
a
­­
a
­­
a
37500
2.66e­
60
­­
a
­­
a
­­
a
a
Probability
is
less
than
10­
100.

Table
17.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Intermittent
Feed
Scenario,
Dose
=
25.0
ppm,
Low
Flow
Regime
(
100
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
53.7
28.9
0.147
8.06e­
07
3
37.2
13.8
3.10e­
03
1.32e­
11
7
24.3
5.91
3.55e­
05
3.72e­
17
57
2.34
5.48e­
02
7.56e­
16
1.21e­
47
115
0.552
3.05e­
03
1.95e­
22
1.82e­
66
132
0.396
1.57e­
03
5.91e­
24
8.30e­
71
264
6.20e­
02
3.84e­
05
2.09e­
32
5.92e­
95
288
4.84e­
02
2.34e­
05
1.55e­
33
3.51e­
98
660
3.98e­
03
1.59e­
07
6.32e­
45
­­
a
5060
7.04e­
07
4.96e­
15
2.51e­
84
­­
a
7500
5.48e­
08
3.00e­
17
5.67e­
96
­­
a
10120
5.99e­
09
3.59e­
19
­­
a
­­
a
15000
2.25e­
10
5.06e­
22
­­
a
­­
a
25300
1.46e­
12
2.14e­
26
­­
a
­­
a
37500
1.96e­
14
3.84e­
30
­­
a
­­
a
a
Probability
is
less
than
10­
100.
Page
19
of
89
Table
18.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Intermittent
Feed
Scenario,
Dose
=
25
ppm,
Medium
Flow
Regime
(
500
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
82.4
68
13.2
0.306
3
63.2
39.9
0.809
1.05e­
04
7
44
19.3
1.79e­
02
1.95e­
09
57
3.96
0.157
1.89e­
13
8.53e­
41
115
0.843
7.10e­
03
1.66e­
20
5.90e­
61
132
0.582
3.39e­
03
3.41e­
22
8.94e­
66
264
6.10e­
02
3.72e­
05
1.76e­
32
3.65e­
95
288
4.37e­
02
1.91e­
05
5.29e­
34
1.62e­
99
660
1.14e­
03
1.31e­
08
1.28e­
50
­­
a
5060
7.64e­
09
5.84e­
19
­­
a
­­
a
7500
5.62e­
10
3.15e­
21
­­
a
­­
a
10120
7.43e­
11
5.52e­
23
­­
a
­­
a
15000
4.84e­
12
2.34e­
25
­­
a
­­
a
25300
1.06e­
13
1.13e­
28
­­
a
­­
a
37500
5.03e­
15
2.53e­
31
­­
a
­­
a
a
Probability
is
less
than
10­
100.

Table
19.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Intermittent
Feed
Scenario,
Dose
=
25
ppm,
High
Flow
Regime
(
1000
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
81.7
66.8
12
0.234
3
63.2
39.9
0.809
1.05e­
04
7
53.9
29
0.151
8.75e­
07
57
11.4
1.29
1.20e­
08
4.55e­
27
115
2.46
6.08e­
02
1.30e­
15
5.68e­
47
Page
20
of
89
Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
132
1.66
2.77e­
02
2.10e­
17
4.32e­
52
264
0.157
2.46e­
04
3.56e­
28
7.27e­
83
288
0.111
1.23e­
04
9.36e­
30
2.22e­
87
660
2.41e­
03
5.81e­
08
3.26e­
47
­­
a
5060
2.29e­
09
5.26e­
20
­­
a
­­
a
7500
7.71e­
11
5.94e­
23
­­
a
­­
a
10120
5.20e­
12
2.70e­
25
­­
a
­­
a
15000
1.28e­
13
1.64e­
28
­­
a
­­
a
25300
7.18e­
16
5.16e­
33
­­
a
­­
a
37500
1.15e­
17
1.32e­
36
­­
a
­­
a
a
Probability
is
less
than
10­
100.

Table
20.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Intermittent
Feed
Scenario,
Dose
=
800
ppm,
Low
Flow
Regime
(
100
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
99.8
99.6
97.9
94.2
3
95.1
90.4
58.8
21.9
7
82.8
68.6
13.8
0.349
57
44.9
20.2
2.23e­
02
3.67e­
09
115
34.5
11.9
1.38e­
03
1.31e­
12
132
32.4
10.5
7.20e­
04
2.03e­
13
264
21.9
4.80
1.19e­
05
1.64e­
18
288
20.6
4.25
6.28e­
06
2.65e­
19
660
9.92
0.985
2.91e­
09
7.92e­
29
5060
0.251
6.30e­
04
4.97e­
26
9.78e­
77
7500
8.70e­
02
7.57e­
05
7.35e­
31
1.55e­
90
10120
3.69e­
02
1.36e­
05
8.90e­
35
­­
a
Page
21
of
89
Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
15000
1.14e­
02
1.31e­
06
4.14e­
40
­­
a
25300
2.24e­
03
5.01e­
08
1.49e­
47
­­
a
37500
5.95e­
04
3.54e­
09
1.37e­
53
­­
a
a
Probability
is
less
than
10­
100.

Table
21.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Intermittent
Feed
Scenario,
Dose
=
800
ppm,
Medium
Flow
Regime
(
500
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
99.8
99.6
97.9
94.2
3
99.2
98.4
91.9
78.6
7
97.0
94.1
72.8
40.4
57
72.9
53.2
3.64
7.72e­
03
115
59.6
35.5
0.436
1.81e­
05
132
56.6
32.0
0.252
3.74e­
06
264
39.7
15.8
6.11e­
03
9.13e­
11
288
37.5
14.0
3.32e­
03
1.60e­
11
660
17.6
3.08
1.17e­
06
2.15e­
21
5060
0.345
1.19e­
03
1.38e­
24
1.31e­
72
7500
9.42e­
02
8.88e­
05
1.70e­
30
1.69e­
89
10120
3.03e­
02
9.17e­
06
1.13e­
35
­­
a
15000
5.70e­
03
3.25e­
07
2.73e­
43
­­
a
25300
4.62e­
04
2.14e­
09
9.58e­
55
­­
a
37500
5.76e­
05
3.32e­
11
3.06e­
64
­­
a
a
Probability
is
less
than
10­
100.
Page
22
of
89
Table
22.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Intermittent
Feed
Scenario,
Dose
=
800
ppm,
High
Flow
Regime
(
1000
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
100
100
100
100
3
100
100
100
100
7
99.2
98.4
91.9
78.6
57
70.7
50.0
2.63
3.07e­
03
115
61.2
37.4
0.572
3.91e­
05
132
59.8
35.7
0.449
1.95e­
05
264
51.7
26.7
9.80e­
02
2.53e­
07
288
50.6
25.6
7.75e­
02
1.29e­
07
660
35.0
12.3
1.65e­
03
2.18e­
12
5060
0.966
9.34e­
03
6.98e­
20
3.57e­
59
7500
0.247
6.10e­
04
4.20e­
26
6.04e­
77
10120
7.56e­
02
5.72e­
05
1.68e­
31
2.29e­
92
15000
1.32e­
02
1.75e­
06
1.88e­
39
­­
a
25300
9.18e­
04
8.43e­
09
1.29e­
51
­­
a
37500
9.45e­
05
8.93e­
11
5.51e­
62
­­
a
a
Probability
is
less
than
10­
100.

Results
for
Continuous
Feed
Scenario
Results
for
the
continuous
feed
scenario
at
dose
rates
of
0.1
ppm,
2.0
ppm
and
800
ppm
are
presented
in
Tables
23,
24,
and
25,
respectively.
The
values
were
calculated
in
the
same
manner
as
the
intermittent
values.
Page
23
of
89
Table
23.
Average
Percent
of
Days
COC
Exceeded
Continuous
Feed
Scenario
(
Dose
=
0.1
ppm)
COC1
(
ppb)
LF2
Percent
Days
COC
Exceeded
(%)
LF­
Standard
Deviation
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
MF­
Standard
Deviation
(%)
HF4­
Percent
Days
COC
Exceeded
(%)
HF­
Standard
Deviation
(%)

1
62.7
40.4
81.2
27.1
80.6
35.6
3
47.6
37.9
64.1
28
72.4
40.5
7
33.6
32.2
44.9
25.8
61.5
38.5
57
5.44
9.26
6.45
6.59
10.9
8.04
115
2.08
4.64
1.94
1.96
3.08
2.71
132
1.7
4.02
1.47
1.48
2.3
2.12
264
0.592
1.76
0.305
0.344
0.441
0.509
288
0.515
1.56
0.246
0.285
0.35
0.415
660
0.119
0.4
2.56e­
02
4.19e­
02
2.85e­
02
4.28e­
02
5060
2.64e­
04
9.13e­
04
3.47e­
05
8.01e­
05
6.60e­
06
1.40e­
05
7500
4.44e­
05
1.53e­
04
8.52e­
06
2.02e­
05
1.00e­
06
2.20e­
06
10120
9.81e­
06
3.39e­
05
2.79e­
06
6.76e­
06
2.00e­
07
5.00e­
07
15000
1.10e­
06
3.80e­
06
6.02e­
07
1.49e­
06
2.72e­
08
6.26e­
08
25300
4.20e­
08
1.00e­
07
6.83e­
08
1.76e­
07
1.45e­
09
3.43e­
09
37500
3.00e­
09
9.45e­
09
1.19e­
08
3.17e­
08
1.39e­
10
3.35e­
10
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)

Table
24.
Average
Percent
of
Days
COC
Exceeded
Continuous
Feed
Scenario
(
Dose
=
2.0
ppm)
COC1
(
ppb)
LF2
Percent
Days
COC
Exceeded
(%)
LF­
Standard
Deviation
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
MF­
Standard
Deviation
(%)
HF4­
Percent
Days
COC
Exceeded
(%)
HF­
Standard
Deviation
(%)

1
95.5
11.6
99.3
1.64
99.9
0.145
3
84.5
28.5
96.7
6.87
98.1
3.58
7
74.4
37.2
91.6
16.3
91.4
16.7
57
48.4
38.1
65.2
28.1
72.9
40.5
115
36.9
33.8
49.6
26.4
64.7
39.5
132
34.6
32.7
46.3
26
62.5
38.8
264
22.9
25.9
30.2
22.4
47.6
32
288
21.6
24.9
28.3
21.7
45.3
30.7
660
10.3
14.9
13.1
12.6
22.5
15.9
5060
0.633
1.86
0.339
0.376
0.493
0.562
7500
0.334
1.06
0.124
0.161
0.167
0.214
10120
0.198
0.651
5.48e­
02
8.08e­
02
6.76e­
02
9.44e­
02
Page
24
of
89
COC1
(
ppb)
LF2
Percent
Days
COC
Exceeded
(%)
LF­
Standard
Deviation
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
MF­
Standard
Deviation
(%)
HF4­
Percent
Days
COC
Exceeded
(%)
HF­
Standard
Deviation
(%)

15000
9.18e­
02
0.31
1.76e­
02
3.00e­
02
1.85e­
02
2.86e­
02
25300
2.75e­
02
9.45e­
02
3.50e­
03
6.88e­
03
2.71e­
03
4.74e­
03
37500
9.33e­
03
3.21e­
02
9.82e­
04
2.06e­
03
5.55e­
04
1.05e­
03
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)

Table
25.
Average
Percent
of
Days
COC
Exceeded
Continuous
Feed
Scenario
(
Dose
=
800
ppm)
COC1
(
ppb)
LF2
Percent
Days
COC
Exceeded
(%)
LF­
Standard
Deviation
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
MF­
Standard
Deviation
(%)
HF4­
Percent
Days
COC
Exceeded
(%)
HF­
Standard
Deviation
(%)

1
100
2.20e­
06
100
2.20e­
06
100
0.00
3
100
2.20e­
06
100
2.20e­
06
100
0.00
7
100
1.80e­
06
100
3.48e­
05
100
0.00
57
100
6.05e­
02
100
0.0558
100
2.32e­
04
115
99.7
0.783
99.9
0.209
100
4.09e­
03
132
99.6
1.18
99.9
0.264
100
6.57e­
03
264
97.9
6
99.7
0.852
100
4.85e­
02
288
97.5
7.01
99.6
0.982
100
6.06e­
02
660
91.2
19.7
98.5
3.3
99.6
6.72e­
01
5060
67.9
40
86.2
23.5
84.9
28.9
7500
63.5
40.5
82
26.7
81.2
34.8
10120
59.9
40.3
78.3
28.1
78.8
37.7
15000
54.6
39.5
72.6
28.6
76.1
39.7
25300
46.8
37.6
63.1
27.9
71.9
40.5
37500
40.4
35.3
54.4
26.9
67.6
40.1
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)
Page
25
of
89
Figure
2
shows
the
same
data
as
Tables
23,
24,
and
25.
As
expected,
the
general
trend
in
all
three
flow
regimes
for
each
dose
rate
is
that
the
percent
of
days
the
COC
is
exceeded
decreases
as
the
COC
is
increased.
Figure
2
also
shows
the
similarities
between
the
three
stream
flow
regimes
for
each
of
the
dose
rates
that
were
modeled.

Figure
2:
Average
Exceedence
Rates
(
Continuous
Feed)
Dose
Rates
of
0.1,
2.0,
and
800
ppm
1E­
10
1E­
09
1E­
08
1E­
07
1E­
06
1E­
05
0.0001
0.001
0.01
0.1
1
10
100
1000
1
10
100
1000
10000
100000
Concentration
o
f
Concern
(
ppb)
Low
Flow
(
Dose=
0.1
ppm)
Medium
Flow
(
Dose=
0.1
ppm)
High
Flow
(
Dose=
0.1
ppm)
Low
Flow
(
Dose=
2.0
ppm)
Medium
Flow
(
Dose=
2.0
ppm)
High
Flow
(
Dose=
2.0
ppm)
Low
Flow
(
Dose=
800
ppm)
Medium
Flow
(
Dose=
800
ppm)
High
Flow
(
Dose=
800
ppm)

Tables
26,
27,
and
28
list
the
calculations
for
those
power
plants
with
the
highest
exceedence
rates
for
each
of
the
three
stream
flow
regimes
for
dose
rates
of
0.1
ppm,
2.0
ppm,
and
800
ppm,
respectively.

Although
fluctuations
can
be
seen,
the
general
trend
is
that
the
numbers
of
days
the
COC
is
exceeded
in
a
year
increases
as
the
dose
rate
of
the
chemical
increases.

Table
26.
Worst
Case
Scenarios:
Percent
of
Days
COC
Exceeded
Continuous
Feed
Scenario
(
Dose
=
0.1
ppm)
COC1
(
ppb)
LF2­
Percent
Days
COC
Exceeded
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
HF4­
Percent
Days
COC
Exceeded
(%)

1
100
100
100
3
98.9
99.3
99.7
7
91.5
93.8
94.7
57
29.5
22.6
19.7
115
16.2
5.96
6.98
132
14.1
4.28
5.48
264
6.17
1.12
1.32
Page
26
of
89
COC1
(
ppb)
LF2­
Percent
Days
COC
Exceeded
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
HF4­
Percent
Days
COC
Exceeded
(%)

288
5.47
0.941
1.08
660
1.39
0.143
0.112
5060
3.16e­
03
2.61e­
04
3.51e­
05
7500
5.31e­
04
6.57e­
05
5.37e­
06
10120
1.18e­
04
2.20e­
05
1.21e­
06
15000
1.32e­
05
4.90e­
06
1.55e­
07
25300
5.05e­
07
5.87e­
07
8.46e­
09
37500
3.28e­
08
1.08e­
07
8.22e­
10
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)

Table
27.
Worst
Case
Scenarios:
Percent
of
Days
COC
Exceeded
Continuous
Feed
Scenario
(
Dose
=
2.0
ppm)
COC1
(
ppb)
LF2­
Percent
Days
COC
Exceeded
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
HF4­
Percent
Days
COC
Exceeded
(%)

1
100
100
100
3
100
100
100
7
100
100
100
57
99.1
99.4
99.7
115
94.3
96
96.9
132
92.4
94.5
95.5
264
75.4
80.4
78.8
288
72.4
77.7
75.4
660
42.2
44.4
35.7
5060
6.53
1.21
1.46
7500
3.71
0.544
0.559
10120
2.26
0.276
0.247
15000
1.08
0.103
7.47e­
02
25300
0.327
2.33e­
02
1.22e­
02
37500
0.111
6.92e­
03
2.67e­
03
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)

Table
28.
Worst
Case
Scenarios:
Percent
of
Days
COC
Exceeded
Continuous
Feed
Scenario
(
Dose
=
800
ppm)
COC1
(
ppb)
LF2­
Percent
Days
COC
Exceeded
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
HF4­
Percent
Days
COC
Exceeded
(%)

1
100
100
100
3
100
100
100
7
100
100
100
Page
27
of
89
COC1
(
ppb)
LF2­
Percent
Days
COC
Exceeded
(%)
MF3­
Percent
Days
COC
Exceeded
(%)
HF4­
Percent
Days
COC
Exceeded
(%)

57
100
100
100
115
100
100
100
132
100
100
100
264
100
100
100
288
100
100
100
660
100
100
100
5060
100
100
100
7500
100
100
100
10120
100
100
100
15000
100
99.9
100
25300
99.6
99.2
99.6
37500
98.4
97.6
98.4
1.
COC
=
Concentration
of
Concern
2.
LF
=
Low
Flow
Regime
(
100
MGD)
3.
MF
=
Medium
Flow
Regime
(
500
MGD)
4.
HF
=
High
Flow
Regime
(
1000
MGD)

Tables
29,
30,
and
31
show
the
average
of
all
power
plants
modeled,
and
compares
these
values
to
the
average
of
the
three
worst­
case
scenarios
presented
in
Tables
26,
27,
and
28,
respectively.
At
the
0.1
ppm
dose
level,
at
higher
COC
values
(
i.
e.,
above
660
ppb),
the
worstcase
scenario
is
about
an
order
of
magnitude
higher
than
the
than
the
average.
At
the
2.0
ppm
dose
level
the
average­
case
scenario
is
50%
of
the
worst­
case
scenario
for
COC
values
of
132
ppb
and
15000
ppb.
The
percent
exceedence
of
the
average
and
worst­
case
scenario
for
2.0
ppm
for
concentrations
above
15000
ppb
is
about
equal.
At
the
800
ppm
level
the
average
and
worst­
case
scenarios
are
about
equal
for
dose
levels
between
1
ppb
to
15000
ppb.
At
the
800
ppm
dose
level
the
worst­
case
scenario
is
approximately
twice
the
average­
case
scenario
for
COC
values
greater
than
15000
ppb.

Table
29.
Total
Average
Exceedence
Rates
vs.
Worst­
Case
Exceedence
Rates
Continuous
Feed
Scenario
(
Dose
=
0.1
ppm)

Percent
of
Days
COC
Exceeded
(%)
COC
(
ppb)

Total
Average
Average
of
the
Three
Worst
Case
Scenarios
(
Table
13)

1
62.7
100
3
47.6
99.3
7
33.6
93.3
57
5.44
23.9
115
2.08
9.70
132
1.70
7.94
264
0.592
2.87
288
0.515
2.50
660
0.119
0.548
5060
2.64e­
04
1.15e­
03
Page
28
of
89
Percent
of
Days
COC
Exceeded
(%)
COC
(
ppb)

Total
Average
Average
of
the
Three
Worst
Case
Scenarios
(
Table
13)

7500
4.44e­
05
2.01e­
04
10120
9.81e­
06
4.69e­
05
15000
1.10e­
06
6.09e­
06
25300
4.21e­
08
3.67e­
07
37500
2.74e­
09
4.70e­
08
Table
30.
Total
Average
Exceedence
Rates
vs.
Worst­
Case
Exceedence
Rates
Continuous
Feed
Scenario
(
Dose
=
2.0
ppm)

Percent
of
Days
COC
Exceeded
(%)
COC
(
ppb)

Total
Average
Average
of
the
Three
Worst
Case
Scenarios
(
Table
14)

1
98.2
100
3
93.1
99.7
7
85.8
98.1
57
62.1
97.2
115
50.4
89.5
132
47.8
87.5
264
33.6
67.2
288
31.7
53.2
660
15.3
27.9
5060
0.488
1.64
7500
0.208
0.727
10120
0.107
0.283
15000
4.26e­
02
9.62e­
02
25300
1.12e­
02
1.18e­
02
37500
3.62e­
03
3.20e­
03
Table
31.
Total
Average
Exceedence
Rates
vs.
Worst­
Case
Exceedence
Rates
Continuous
Feed
Scenario
(
Dose
=
800
ppm)

Percent
of
Days
COC
Exceeded
(%)
COC
(
ppb)

Total
Average
Average
of
the
Three
Worst
Case
Scenarios
(
Table
14)

1
100
100
3
100
100
7
100
100
57
100
100
115
99.9
100
132
99.8
100
Page
29
of
89
Percent
of
Days
COC
Exceeded
(%)
COC
(
ppb)

Total
Average
Average
of
the
Three
Worst
Case
Scenarios
(
Table
14)

264
99.2
100
288
99.0
100
660
96.4
100
5060
79.6
100
7500
75.5
100
10120
72.3
100
15000
67.8
99.9
25300
60.6
99.5
37500
54.1
98.1
To
calculate
the
chance
of
exceedence
of
a
given
COC
for
sodium
chlorite
over
a
consecutive
number
of
days,
the
following
assumptions
were
made:

$
The
chance
of
exceedence
on
any
given
day
at
a
site
is
independent
of
whether
exceedence
occurred
on
previous
days.

$
Although
the
percentages
calculated
by
PDM
express
the
chance
of
exceedence
during
at
least
part
of
a
day,
it
is
assumed
for
this
calculation
that
the
percentages
calculated
by
PDM
imply
exceedence
over
the
total
day.

Based
on
these
assumptions,
the
following
formula
can
be
used
to
calculate
the
probability
of
exceedence
over
N
consecutive
days:

%
probability
=
(
Probability
of
Exceedence
per
Day/
100%)
N*
100%

Tables
32
through
40
show
the
results
of
these
calculations.
These
tables
can
be
used
to
determine
an
appropriate
COC,
based
on
the
level
of
risk
that
is
deemed
acceptable.
The
choice
between
using
either
the
total
average
column
or
the
worst­
case
scenarios
average
column
will
depend
on
how
conservative
a
value
is
deemed
necessary.

Table
32.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Continuous
Feed
Scenario,
Dose
=
0.1
ppm,
Low
Flow
Regime
(
100
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
39.3
15.5
5.53e­
03
6.86e­
11
3
22.7
5.13
1.70e­
05
4.53e­
18
7
11.3
1.27
1.13e­
08
3.81e­
27
57
0.296
8.76e­
04
2.80e­
25
1.37e­
74
115
4.33e­
02
1.87e­
05
4.78e­
34
1.21e­
99
Page
30
of
89
Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
132
2.89e­
02
8.35e­
06
6.91e­
36
­­
a
264
3.50e­
03
1.23e­
07
1.65e­
45
­­
a
288
2.65e­
03
7.03e­
08
8.87e­
47
­­
a
660
1.42e­
04
2.01e­
10
3.86e­
60
­­
a
5060
6.97e­
10
4.86e­
21
­­
a
­­
a
7500
1.97e­
11
3.89e­
24
­­
a
­­
a
10120
9.62e­
13
9.26e­
27
­­
a
­­
a
15000
1.21e­
14
1.46e­
30
­­
a
­­
a
25300
1.77e­
17
3.14e­
36
­­
a
­­
a
37500
7.51e­
20
5.64e­
41
­­
a
­­
a
a
Probability
is
less
than
10­
100.

Table
33.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Continuous
Feed
Scenario,
Dose
=
0.1
ppm,
Medium
Flow
Regime
(
500
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
65.9
43.5
1.26
3.74e­
04
3
41.1
16.9
8.79e­
03
2.58e­
10
7
20.2
4.06
4.98e­
06
1.36e­
19
57
0.416
1.73e­
03
1.00e­
23
3.75e­
70
115
3.76e­
02
1.42e­
05
1.11e­
34
­­
a
132
2.16e­
02
4.67e­
06
3.26e­
37
­­
a
264
9.30e­
04
8.65e­
09
1.48e­
51
­­
a
288
6.05e­
04
3.66e­
09
1.62e­
53
­­
a
660
6.55e­
06
4.29e­
13
3.74e­
74
­­
a
5060
1.20e­
11
1.45e­
24
­­
a
­­
a
7500
7.26e­
13
5.27e­
27
­­
a
­­
a
10120
7.78e­
14
6.06e­
29
­­
a
­­
a
Page
31
of
89
Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
15000
3.62e­
15
1.31e­
31
­­
a
­­
a
25300
4.66e­
17
2.18e­
35
­­
a
­­
a
37500
1.42e­
18
2.01e­
38
­­
a
­­
a
a
Probability
is
less
than
10­
100.

Table
34.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Continuous
Feed
Scenario,
Dose
=
0.1
ppm,
High
Flow
Regime
(
1000
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
65
42.2
1.08
2.40e­
04
3
52.4
27.5
0.113
3.84e­
07
7
37.8
14.3
3.68e­
03
2.15e­
11
57
1.19
1.41e­
02
6.11e­
19
1.76e­
56
115
9.49e­
02
9.00e­
05
1.82e­
30
2.06e­
89
132
5.29e­
02
2.80e­
05
3.95e­
33
5.05e­
97
264
1.94e­
03
3.78e­
08
3.41e­
48
­­
a
288
1.23e­
03
1.50e­
08
2.66e­
50
­­
a
660
8.12e­
06
6.60e­
13
3.56e­
73
­­
a
5060
4.42e­
13
1.96e­
27
­­
a
­­
a
7500
9.76e­
15
9.53e­
31
­­
a
­­
a
10120
4.71e­
16
2.22e­
33
­­
a
­­
a
15000
7.40e­
18
5.47e­
37
­­
a
­­
a
25300
2.10e­
20
4.42e­
42
­­
a
­­
a
37500
1.93e­
22
3.73e­
46
­­
a
­­
a
a
Probability
is
less
than
10­
100.
Page
32
of
89
Table
35.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Continuous
Feed
Scenario,
Dose
=
25.0
ppm,
Low
Flow
Regime
(
100
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
91.2
83.2
38.0
6.31
3
71.4
51
2.91
4.09e­
03
7
55.4
30.6
0.201
1.97e­
06
57
23.4
5.49
2.41e­
05
1.23e­
17
115
13.6
1.85
8.08e­
08
1.05e­
24
132
12.00
1.43
2.09e­
08
2.21e­
26
264
5.24
0.275
3.60e­
12
3.89e­
37
288
4.67
0.218
1.06e­
12
1.17e­
38
660
1.06
1.13e­
02
1.86e­
19
5.89e­
58
5060
4.01e­
03
1.61e­
07
6.75e­
45
­­
a
7500
1.12e­
03
1.24e­
08
9.97e­
51
­­
a
10120
3.92e­
04
1.54e­
09
1.70e­
55
­­
a
15000
8.43e­
05
7.10e­
11
1.66e­
62
­­
a
25300
7.56e­
06
5.72e­
13
1.68e­
73
­­
a
37500
8.70e­
07
7.58e­
15
2.33e­
83
­­
a
a
Probability
is
less
than
10­
100.

Table
36.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Continuous
Feed
Scenario,
Dose
=
25
ppm,
Medium
Flow
Regime
(
500
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
98.6
97.2
86.3
65.6
3
93.5
87.4
49.4
13.4
7
83.9
70.4
15.8
0.517
57
42.5
18.1
1.26e­
02
7.16e­
10
115
24.6
6.05
4.03e­
05
5.36e­
17
Page
33
of
89
Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
132
21.4
4.6
9.49e­
06
8.61e­
19
264
9.12
0.832
1.20e­
09
6.32e­
30
288
8.01
0.641
3.07e­
10
1.28e­
31
660
1.72
2.94e­
02
2.90e­
17
1.09e­
51
5060
1.15e­
03
1.32e­
08
1.36e­
50
­­
a
7500
1.54e­
04
2.36e­
10
9.16e­
60
­­
a
10120
3.00e­
05
9.02e­
12
3.27e­
67
­­
a
15000
3.10e­
06
9.60e­
14
1.43e­
77
­­
a
25300
1.23e­
07
1.50e­
16
2.66e­
92
­­
a
37500
9.64e­
09
9.30e­
19
­­
a
­­
a
a
Probability
is
less
than
10­
100.

Table
37.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Continuous
Feed
Scenario,
Dose
=
25
ppm,
Low
High
Regime
(
1000
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
99.8
99.6
97.9
94.2
3
96.2
92.6
66.8
31.6
7
83.5
69.8
15.1
0.454
57
53.1
28.2
0.131
5.80e­
07
115
41.9
17.5
1.07e­
02
4.51e­
10
132
39.1
15.3
5.17e­
03
5.66e­
11
264
22.7
5.13
1.70e­
05
4.53e­
18
288
20.5
4.21
6.00e­
06
2.32e­
19
660
5.06
0.256
2.49e­
12
1.35e­
37
5060
2.43e­
03
5.91e­
08
3.55e­
47
­­
a
7500
2.79e­
04
7.78e­
10
4.75e­
57
­­
a
10120
4.57e­
05
2.09e­
11
2.68e­
65
­­
a
Page
34
of
89
Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
15000
3.42e­
06
1.17e­
13
4.08e­
77
­­
a
25300
7.34e­
08
5.39e­
17
1.24e­
94
­­
a
37500
3.08e­
09
9.49e­
20
­­
a
­­
a
a
Probability
is
less
than
10­
100.

Table
38.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Continuous
Feed
Scenario,
Dose
=
800
ppm,
Low
Flow
Regime
(
100
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
100
100
100
100
3
100
100
100
100
7
100
100
100
100
57
100
100
100
100
115
99.4
98.8
93.9
83.5
132
99.2
98.4
91.9
78.6
264
95.8
91.9
64.0
28
288
95.1
90.4
58.8
21.9
660
83.2
69.2
14.5
0.398
5060
46.1
21.3
2.95e­
02
8.17e­
09
7500
40.3
16.3
7.22e­
03
1.47e­
10
10120
35.9
12.9
2.12e­
03
4.42e­
12
15000
29.8
8.89
3.03e­
04
1.70e­
14
25300
21.9
4.80
1.19e­
05
1.64e­
18
37500
16.3
2.66
5.42e­
07
2.41e­
22
a
Probability
is
less
than
10­
100.
Page
35
of
89
Table
39.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Continuous
Feed
Scenario,
Dose
=
800
ppm,
Medium
Flow
Regime
(
500
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
100
100
100
100
3
100
100
100
100
7
100
100
100
100
57
100
100
100
100
115
99.8
99.6
97.9
94.2
132
99.8
99.6
97.9
94.2
264
99.4
98.8
93.9
83.5
288
99.2
98.4
91.9
78.6
660
97
94.1
72.8
40.4
5060
74.3
55.2
4.42
1.35e­
02
7500
67.2
45.2
1.55
6.74e­
04
10120
61.3
37.6
0.587
4.22e­
05
15000
52.7
27.8
0.12
4.53e­
07
25300
39.8
15.9
6.32e­
03
1.00e­
10
37500
29.6
8.76
2.80e­
04
1.37e­
14
a
Probability
is
less
than
10­
100.

Table
40.
Percent
Probability
of
Exceedence
Over
Consecutive
Days
Continuous
Feed
Scenario,
Dose
=
800
ppm,
High
Flow
Regime
(
1000
MGD)

Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
1
100
100
100
100
3
100
100
100
100
7
100
100
100
100
57
100
100
100
100
115
100
100
100
100
Page
36
of
89
Number
of
Consecutive
Days
COC
(
ppb)
48
hrs
(
2
days)
96
hours
(
4
days)
21
days
60
days
132
100
100
100
100
264
100
100
100
100
288
100
100
100
100
660
99.2
98.4
91.9
78.6
5060
72.1
52
3.21
5.43e­
03
7500
65.9
43.5
1.26
3.74e­
04
10120
62.1
38.6
0.672
6.19e­
05
15000
57.9
33.5
0.323
7.64e­
06
25300
51.7
26.7
9.80e­
02
2.53e­
07
37500
45.7
20.9
2.68e­
02
6.26e­
09
a
Probability
is
less
than
10­
100.

UNCERTAINTIES/
LIMITATIONS
The
following
limitations
apply
to
the
results
of
this
model:

$
The
PDM4
database
contains
data
on
steam
electric
power
plants
in
the
United
States.
In
the
database,
no
differentiation
was
made
between
those
power
plants
that
used
a
once­
through
cooling
water
system
and
those
that
did
not.
In
the
absence
of
better
data,
it
was
assumed
that
all
powerplants
in
the
database
used
once­
through
cooling
water
systems,
and
that
the
amount
of
cooling
water
used
in
normal
conditions
was
equal
to
the
7Q10
flow.

$
It
has
been
assumed
that
a
15
minute
daily
maintenance
dose
application
of
the
chemical
is
sufficient
to
maintain
control.
This
assumption
is
based
on
labeling
for
similar
uses
of
other
pesticides.
Page
37
of
89
$
PDM4
is
a
screening­
level
model.
Screening­
level
models
are
rarely
if
ever
used
as
the
sole
justification
for
regulatory
decision­
making
at
EPA.
Additional
data
and
more
rigorous
tools
are
used
to
improve
the
estimates
of
exposures
and
risks
for
such
decisions.
Results
may
not
accurately
reflect
all
of
the
information
and
data
used
by
EPA
to
make
a
regulatory
decision
on
a
chemical.

$
For
large
once­
through
cooling
water
systems,
the
product
label
states
a
quantity
of
product
to
be
used
that
is
very
large.
For
example,
a
system
with
a
flow
rate
of
100
MGD
would
require
20,000
lbs
of
product
per
day
if
the
product
is
applied
continuously
at
the
maximum
rate
listed
on
the
label
(
i.
e.,
0.2
lbs/
1000
gal).
For
lack
of
better
information,
the
application
rates
stated
on
the
label
were
used
for
this
model.

REFERENCES
Cloete
TE,
Smith
Z,
Saayman
G.
A
Cooling
Water
System
as
a
Biofilm
Reactor
for
the
Treatment
of
Municipal
Wastewater.
Water
SA
Vol.
25
No.
3
July
1999.
Available
on
website
http://
www.
wrc.
org.
za.

Dang
W,
1996.
Antimicrobial
Pesticides,
Uses,
Human
Exposures,
and
Risk
Assessments.
March,
1996.

DiToro,
D.
M.
1984.
Probability
Model
of
Stream
Quality
Due
to
Runoff.
ASCE.
Journal
of
Environmental
Engineering.
110(
3):
607­
628.

EFAST
Help,
beta
version,
2004.

Genest,
Dan,
Dominion
Power.
Telephone
interview.
June
14,
2004.
Page
38
of
89
Appendix
Input
and
Output
Files
for
PDM4
Page
39
of
89
High
Flow,
Continuous
Feed
Page
40
of
89
Page
41
of
89
Page
42
of
89
Page
43
of
89
Page
44
of
89
Page
45
of
89
Page
46
of
89
Page
47
of
89
Page
48
of
89
High
Flow,
Intermittent
Feed
Page
49
of
89
Page
50
of
89
Page
51
of
89
Page
52
of
89
Page
53
of
89
Page
54
of
89
Page
55
of
89
Medium
Flow,
Continuous
Feed
Page
56
of
89
Page
57
of
89
Page
58
of
89
Page
59
of
89
Page
60
of
89
Page
61
of
89
Page
62
of
89
Page
63
of
89
Medium
Flow,
Intermittent
Feed
Page
64
of
89
Page
65
of
89
Page
66
of
89
Page
67
of
89
Page
68
of
89
Page
69
of
89
Page
70
of
89
Page
71
of
89
Page
72
of
89
Low
Flow,
Continuous
Feed
Page
73
of
89
Page
74
of
89
Page
75
of
89
Page
76
of
89
Page
77
of
89
Page
78
of
89
Page
79
of
89
Page
80
of
89
Page
81
of
89
Page
82
of
89
Page
83
of
89
Low
Flow,
Intermittent
Feed
Page
84
of
89
Page
85
of
89
Page
86
of
89
Page
87
of
89
Page
88
of
89
Page
89
of
89
