B­
1
State
of
Oregon
Department
of
Environmental
Quality
Memorandum
Date:
4/
16/
98
To:
File
From:
Bob
Baumgartner
Subject:
Columbia
Slough
Winter
Dissolved
Oxygen
Analysis
Background:
The
Columbia
Slough
is
water
quality
limited
(
WQL)
for
dissolved
oxygen.
Pulses
of
low
dissolved
oxygen
concentrations
are
associated
with
deicing
events
at
the
Port
of
Portland
international
airport
(
PDX).

The
federal
Clean
Water
Act
requires
that
pollution
control
plans
defined
as
Total
Maximum
Daily
Loads
(
TMDLs)
be
established
for
WQL
limited
streams.
The
federal
Clean
Water
Act
requires
TMDLs
to
be
established
with
existing
data,
include
a
reasonable
margin
of
safety
to
cover
uncertainty
with
existing
knowledge,
establish
a
load
for
background
where
possible,
and
allow
for
future
growth
and
development.

The
TMDL
for
dissolved
oxygen
defines
separate
loading
capacities
(
LC)
which
varies
with
stream
flow
and
the
dissolved
oxygen
criteria
applied.
In
order
to
establish
allocations
that
reflect
the
pulses
of
storm
driven
events
the
LC
also
varies
by
the
duration
of
the
low
dissolved
oxygen
events.
The
State
dissolved
oxygen
criteria
varies
in
relationship
to
the
duration
of
the
low
oxygen
event.
The
instantaneous
instream
DO
should
not
fall
below
4
mg/
l,
the
seven
(
7)
day
average
of
the
daily
minimums
should
not
fall
below
5
mg/
l,
and
the
lowest
thirty
(
30)
day
average
of
the
daily
means
should
not
fall
below
6.5
mg/
l.

The
loading
capacity
(
LC)
and
margin
of
safety
(
MOS)
are
estimated
using
both
existing
field
data
and
available
literature.
This
memorandum
summarizes
the
available
information
that
was
used
to
identify
the
loading
capacity
and
subsequent
allocations.
The
approach
used,
as
are
all
models,
is
a
simplification
of
reality.
The
discharges
are
assumed
to
be
plug
flows.
The
available
data
and
literature
were
used
to
select
reasonable
model
inputs.
Field
conditions
were
selected
to
represent
likely
worst
case
scenarios.

The
TMDL
distributes
allocations
to
the
three
(
3)
defined
sources;
de­
icing
loads,
storm
water
loads,
and
background.
The
storm
water
load
is
further
subdivided
between
loads
regulated
by
the
designated
management
agencies
and
permitted
industrial
storm
water.

AMBIENT
DATA:

The
Columbia
Slough
is
listed
as
being
WQL
based
on
observation
of
substandard
dissolved
oxygen.
The
instream
dissolved
oxygen
is
influenced
in
part
by
the
instream
BOD5
concentrations.
Temperature
directly
influences
the
dissolved
oxygen
concentration
by
establishing
the
level
of
saturation
and
indirectly
by
controlling
the
rate
of
reactions
that
influence
B­
2
dissolved
oxygen
levels.
Much
of
the
ambient
data
is
available
in
a
series
of
documents
and
memoranda
published
by
Portland
State
University
(
PSU)
and
supported
by
the
City
of
Portland
(
Wells(
1992),
Wells
and
Berger
(
1995)
Wells
et
al
(
1996)).
Much
of
this
information
is
also
reviewed
and
presented
in
the
Columbia
Slough
Water
Body
Assessment
(
CH2MHill
1995)
conducted
for
the
City
of
Portland.
Ambient
data
is
available
from
the
City
of
Portland
and
from
DEQ.

Ambient
Dissolved
Oxygen
Data:
Substantial
review
of
historical
dissolved
oxygen
data
is
contained
in
the
Water
Body
Assessment
(
CH2MHill
1995).

Field
data
for
dissolved
oxygen
can
be
reviewed
to
determine
the
magnitude
of
the
DO
problems.
Comparison
of
the
ambient
conditions
associated
with
depressed
oxygen
can
be
used
to
define
the
conditions
that
result
in
the
low
oxygen.

Critical
conditions
for
low
dissolved
oxygen
appear
to
occur
following
freezing
weather,
followed
by
warm
rain
with
increasing
temperature
in
the
receiving
stream.
In
the
Lower
Columbia
Slough
increasing
stage
from
the
Willamette
appears
to
be
associated
with
depressed
oxygen.
This
is
likely
due
to
increased
residence
time
and
reduced
aeration.

Several
periods
of
low
dissolved
oxygen
have
been
observed
in
both
the
Lower
and
Upper
Columbia
Slough.
Continuous
monitoring
data
collected
by
the
City
of
Portland
is
the
most
robust
record
of
the
low
DO
occurrences.
Some
ancillary
data
may
also
be
recorded,
however,
coincident
instream
BOD
data
is
sparse.
Low
dissolved
oxygen
data
have
been
observed
and
associated
with
de­
icing
events
for
several
years.
This
data
is
summarized
in
Table
1.

The
February
1995
low
DO
event
in
the
Lower
Slough
occurred
following
a
cold
period
when
instream
temperatures
increased
and
river
stage
increased
due
to
high
water
in
the
Willamette
River.
Increasing
stream
temperatures
also
occurred
at
MCDD1
during
the
event.

Wells
and
Berger
(
1996)
discuss
the
two
(
2)
significant
low
dissolved
oxygen
events
observed
during
late
1995,
early
1996.
The
events
occurred
following
cold
periods
followed
by
rain.
Figure
1
shows
the
decreasing
instream
DO
levels
as
the
instream
temperature
began
to
rise.
Table
1,
Dissolved
Oxygen
Data
Lower
Columbia
Slough
Date
DO
Location
of
DO
Load
Estimate
High
BOD
1/
10­
25/
95
1
SJB
2/
4­
9/
95
<
5
SJB
2/
19­
24/
95
0
SJB
2/
21/
95
0
Landfill
12/
10/
95
0
N.
Denver
1/
28/
96
>
4
N.
Denver
1/
18/
96
2/
10/
96
0
N.
Denver
2/
4­
5/
96
2/
15/
96
4
SJB
2/
4
­
5/
96
12/
30/
96
>
1
N.
Denver
78
Upper
Columbia
Slough
1/
15­
25/
95
>
4­
2
MCDD1
2/
5­
19,95
>
5>
4
MCDD1
75
11/
16/
95
>
5
MCDD1
1/
28/
96
>
2
MCDD1
1/
18­
30/
96
2/
3­
4/
96
>
1
MCDD1
2/
4­
5/
96
B­
3
Instream
conditions
are
characterized
by
warming
stream
temperatures
and
stagnation
in
the
Lower
Slough
due
to
increased
stage
because
of
high
water
in
the
Willamette.
The
low
DO
events
lasted
from
5
to
10
days
in
the
Lower
Slough.
No
oxygen
sag
was
observed
at
stations
upstream
of
the
airport
discharge.
Similar
physical
conditions
and
low
dissolved
oxygen
were
observed
in
December
1996­
January
1997.
Continuous
data
recorded
in
December
1996­
January
1997
shows
the
dissolved
oxygen
sag
becoming
apparent
at
RM
6.9
as
early
as
12/
27­
28.
At
N.
Denver
Bridge
the
minimum
dissolved
oxygen
of
0.99
mg/
L
occurred
at
2100
hours
at
12/
30/
96
and
recovery
began
by
the
end
of
the
day,
12/
31.
Near
RM
2.9
the
minimum
DO
occurred
near
0500
on
1/
4/
97,
several
days
later
than
when
peak
BOD5
measures
were
recorded.
However,
BOD5
concentrations
would
also
be
reduced
by
degradation
rates.
The
plug
of
low
DO
occurred
about
4.3125
days
later
at
RM
2.9.
The
average
velocity
was
estimated
as
the
difference
in
time
from
minimum
DO
divided
by
distance
(
3.8
miles/
4.3
days)
as
0.054
f/
s,
similar
to
the
velocities
estimated
using
observed
BOD5
data.
Observed
stream
temperature
near
5.2
C
had
begun
to
increase
by
the
time
the
minimum
DO
was
recorded
at
RM
6.7
Stream
temperatures
had
increased
substantially
to
near
7.1
C
by
the
time
the
minimum
DO
was
recorded
near
RM
2.9.
Willamette
River
stage
was
near
10.3
feet
during
this
period.

Previous
storm
monitoring
in
the
Slough
did
not
suggest
reduced
dissolved
oxygen
associated
with
storm
water
discharge
(
City
of
Portland
BES,
1989).
There
were
three
storm
event
monitoring
efforts
conducted
by
the
City
of
Portland
on
May
22,
April
21
and
May
2,
1988.
The
dissolved
oxygen
during
these
events
was
not
reduced
to
near
water
quality
standards
during
these
surveys.

Occasional
periods
of
reduced
oxygen
are
apparent
in
the
field
data
that
are
not
known
to
be
associated
with
de­
icing
events.
This
field
data
would
suggest
conditions
other
than
de­
icing
influence
ambient
dissolved
oxygen
levels.
Simulations
presented
by
Wells
and
Berger
(
1995)
indicate
oxygen
reduction
during
storm
events
to
near
the
dissolved
oxygen
standard
after
the
estimated
de­
icing
load
was
eliminated.
The
simulations
suggests
that
storm
water
and
CSOs
may
reduce
dissolved
oxygen
in
the
Slough,
however,
the
storm
water
induced
reduction
of
dissolved
oxygen
is
not
well
defined
with
existing
data.

Ambient
BOD
measures:
Ambient
BOD
concentration
is
the
result
of
natural
background
contribution,
source
loading
of
BOD,
and
decay.
Where
information
of
source
loads
and
background
are
known
or
can
be
reasonably
approximated,
ambient
measures
of
BOD
can
be
compared
to
estimates
of
loading
and
dilution
to
determine
if
such
estimates
appear
to
reasonably
explain
the
observed
conditions.
Where
associated
with
hydraulics
data,
observed
changes
in
ambient
BOD
concentration
may
be
used
to
estimate
instream
decay
rates.
Dissolved
Oxygen
and
Temperature
in
the
Lower
slough
following
De­
icing
0
2
4
6
8
10
16­
Dec
21­
Dec
26­
Dec
31­
Dec
5­
Jan
10­
Jan
Date
mg/
l
,
C
Temp.
at
NDB
Temp.
SJB
DO
at
NDB
DO
at
SJB
Figure
1,
Dissolved
Oxygen
and
Temperature
in
the
Lower
Slough
B­
4
Instream
BOD5
concentrations
reported
by
the
City
Portland
vary
from
greater
than
detection
to
below
detection
(
Nancy
Hendricksen,
BES,
personnel
communication)
(
Figure
2).
Maximum
recorded
concentrations
are
75
mg/
l
BOD5
.
Well
defined
spatial
trends
are
not
apparent
in
the
data
provided
by
the
City
of
Portland.
Using
the
existing
information
the
estimated
mean
BOD5
concentration
in
the
Columbia
Slough
is
2.5
mg/
l
BOD5
A
maximum
instream
BOD
of
150
mg/
l
is
presented
graphically
as
BODu
by
Wells
and
Berger
(
1995)
for
the
Columbia
Slough
near
Alderwood.
Measured
BOD5
of
>
70
mg/
l
is
illustrated
for
near
MCDD4,
and
>
60
mg/
l
near
NE
Alderwood
in
February
1995.
During
deicing
events
in
1995­
1996
the
observed
oxygen
demand
concentrations
reported
by
the
City
of
Portland
frequently
exceed
the
maximum
reporting
level
of
20
mg/
l
BOD5
(
Nancy
Hendricksen,
personnel
communication).

Similar
elevated
levels
of
BOD5
( 
80
mg/
L)
are
reported
by
the
City
of
Portland
during
a
December
1996/
January
1997
event.
Instream
data
were
collected
by
the
City
of
Portland
to
evaluate
the
pulses
of
low
DO
from
de­
icing
events.
This
data
demonstrates
that
pulses
of
high
BOD
periodically
move
through
the
Columbia
Slough.
The
timing
and
concentrations
of
the
peak
BOD5
at
different
locations
may
be
used
to
calculate
deoxygenation
rates
and
travel
times.
The
peak
BOD5
concentration
data
drops
from
>
78
to
52
mg/
l
between
river
miles
6.7
and
1.2
(
Figure
3).
The
peak
BOD5
concentration
occurred
several
(
1.9­
2.8)
days
later
at
river
mile
1.2
than
at
river
mile
6.7.
The
difference
in
peak
concentrations
suggest
relatively
slow
velocities
(
0.08
­
0.12
f/
s).
Relatively
high
(
0.14­
0.20
/
day)
BOD5
loss
rates
(
Kr)
may
be
estimated
by
solving
for
Kr
using:
BOD
BOD
e
rm
RM
K
X
v
r
1
2
6
7
.
.
=
.
However
the
peak
BOD5
data
near
river
mile
1.2
is
potentially
influenced
by
dilution
from
the
Willamette
and
dispersion.
Instream
BOD5
data
suggest
that
peak
concentrations
near
RM
6.7
were
missed
by
the
ambient
monitoring.
Similarly
the
peak
BOD5
concentrations
near
RM
1.2
are
not
known.
The
BOD5
concentrations
near
river
mile
2.9
suggest
a
plug
of
BOD5
on
the
order
of
four
(
4)
days
passed
through
the
Lower
Slough.
This
observation
is
consistent
with
the
general
length
of
the
DO
sag
observed
near
Denver
Bridge.

Ambient
Temperature:
Cursory
observation
of
available
data
indicates
stream
temperatures
were
near
5C
as
measured
at
St.
Johns
Bridge
at
the
initiation
of
the
February
1995
de­
icing
event
(
Wells
et
al
1996).
Over
the
next
several
days
the
dissolved
oxygen
dropped
to
anoxic
conditions
and
the
temperature
increased
to
approximately
10C.
A
similar
increase
in
temperature
through
the
low
dissolved
oxygen
event
was
observed
during
January
1997.
Similarly,
at
MCDD1
the
dissolved
oxygen
generally
drops
as
temperature
increases.
Minimum
temperatures
were
near
4C.
Reduced
Instream
BOD,
City
of
Portland,
All
station
y
=
­
0.8397x
+
0.9395
R2
=
0.9626
­
2
­
1
0
1
2
3
4
5
­
4
­
3
­
2
­
1
0
1
2
3
4
Z
Log(
n)
BOD
Figure
2,
BOD
Distribution
Columbia
Slough
BOD(
5)

0
10
20
30
40
50
60
70
80
12/
30/
96
12/
31/
96
1/
1/
97
1/
2/
97
1/
3/
97
1/
4/
97
Date
mg/
l
RM
6.7
RM
2.9
Figure
3,
BOD
by
date
and
location
B­
5
dissolved
oxygen
conditions
occurred
at
temperatures
in
the
range
of
7.5C
to
12C.
Continuous
monitoring
data
was
collected
by
the
City
of
Portland
between
Julian
Day
27
and
70
(
figure
25
Wells
and
Berger)
in
the
Upper
and
Lower
Slough.
This
data
shows
that
the
dissolved
oxygen
depressions
observed
occurred
during
periods
where
temperature
was
near
9C
in
the
Lower
Slough
(
St.
Johns
Bridge)
and
near
8C
in
the
Upper
Slough
(
MCDD1)

Willamette
River
stage:
The
stage
of
the
Willamette
river
can
substantially
influence
how
fast
water
moves
through
the
Lower
Columbia
Slough.
As
stage
increases,
water
backs
up
into
the
Columbia
Slough,
resulting
in
reduced
velocity,
longer
residence
time
(
stagnation)
and
reduced
calculated
aeration
rates
(
Wells
and
Berger
1995).
The
Willamette
river
stage
frequently
exceeded
15
feet
MSL
and
occasionally
exceeded
20
feet
MSL
during
the
winter
1996/
97.
The
12­
day
averages,
estimated
to
be
the
residence
time
of
water
in
the
Slough
at
high
stage
and
low
flow,
frequently
approached
or
exceeded
a
stage
of
15
feet
MSL
(
see
Figure
4).
The
City
of
Portland
(
1989)
reports
that
stage
levels
in
the
Columbia
Slough
of
14
to
17
feet
are
routinely
reached.

RATES:
Estimates
of
the
loading
capacity
of
the
Columbia
Slough
are
dependent
upon
estimates
of
the
rates
of
reaction.
The
principle
rates
that
influence
dissolved
oxygen
in
this
analysis
are
the
rate
at
which
deoxygenation
(
Kd)
occurs
from
BOD
and
the
rate
of
oxygen
brought
back
into
the
Slough
from
aeration
(
Ka).
Temperature
influences
both
of
these
rates
and
so
is
important
in
estimating
the
loading
capacity.
The
dispersion
rate
(
Ex)
can
also
significantly
influence
the
loading
capacity
for
the
short
term
pulse
loads
of
oxygen
demand.

Calculation
of
Biochemical
Deoxygenation
(
decay)
Rate
(
kd)
Estimates
of
Kd
were
derived
from
UBOD/
BOD5
information
presented
in
the
Final
Evaluation
of
Alternatives
for
controlling
the
Environmental
Impacts
of
De­
icing,
LTI
CH2M­
Hill,
4/
29/
1996
(
deicing
study)
and
from
percent
theoretical
oxygen
demand
at
five
days
information
provided
by
Union
Carbide
Corporation
as
part
of
information
provided
during
public
hearings.
The
Union
Carbide
data
showed
that
most
of
the
theoretical
oxygen
demand
was
consumed
within
20­
days.
The
theoretical
oxygen
demand
therefore
provides
a
reasonable
estimate
of
the
UBOD.
Kd
was
calculated
by
two
methods;
a
simple
method
based
on
the
mathematical
relationship
between
BODu
and
BOD5,
and
a
least
squared
regression
analysis
of
the
data.
The
following
section
discusses
both
methods.

In
table
2.4
of
the
de­
icing
study,
values
from
five
day
(
CBOD5)
and
Ultimate
(
CBODu)
were
provided
for
both
propylene
and
ethylene
glycol
and
from
Type
1
and
Type
2
aircraft
de­
icing
fluids.
Knowing
the
CBOD5
and
BODu
the
Kd
rate
was
calculated
as:
K
Log
BOD
BOD
T
d
n
U
=
 
 (
)
1
5
.
Daily
and
12­
day
average
stage
0
5
10
15
20
25
30
9/
8/
95
10/
28/
95
12/
17/
95
2/
5/
96
3/
26/
96
5/
15/
96
7/
4/
96
Date
MSL
Stage
12­
D
avg
Figure
4,
Daily
and
12
day
average
stage
B­
6
The
Kd
values
calculated
from
the
various
data
reported
varied
from
0.05/
day
to
0.24/
day
with
a
median
of
0.143/
day
and
a
standard
deviation
of
0.06.
The
rates
were
presumed
to
be
measured
at
20C.
The
calculated
deoxygenation
rates
are
similar
to
the
range
of
0.1/
day
­
0.2/
day
at
20
C
used
by
Wells
and
Berger
(
1995)
in
their
modeling
efforts,
and
are
similar
to
and
slightly
less
than
estimated
from
limited
instream
data
collected
during
December
1996,
January
1997.

Biochemical
deoxygenation
rates
expressed
as
a
percentage
of
the
theoretical
oxygen
demand
were
presented
by
Union
Carbide
for
three
(
3)
temperature
ranges
of
4,
10,
and
20C
for
both
ethylene
and
propylene
glycol.
The
Kd
was
calculated
by
empirical
regression
of
Log
BOD
BOD
vs
T
n
t
u
(
)..
1 
The
slope
of
the
regression
provides
a
measure
of
the
Kd.
As
seen
in
Figure
5,
for
propylene
glycol,
Kd
was
calculated
to
be
0.127
for
data
presented
at
20
C.

Cursory
observation
of
the
raw
data
indicates
that
there
is
a
considerable
lag
phase
in
the
deoxygenation
tests,
especially
at
the
4C
temperature
test.
Derivation
of
kd
using
the
regression
equation
appears
to
be
less
influenced
by
the
lag
than
would
similar
derivation
using
the
simple
calculations.
The
observed
lag
phase
could
result
in
an
underestimation
of
the
decay
rate
once
the
bacterial
population
was
established.
For
ethylene
glycol
the
observed
Kd
was
0.043/
day
using
all
data
(
Figure
6).
Presuming
that
any
lag
phase
was
complete
within
10­
days
a
higher
Kd
of
0.049/
day
was
derived.
Partially
acclimated
bacteria
were
used
in
the
original
tests.

To
model
the
loading
capacity
of
BOD,
the
median
Kd
of
0.143
at
20C
was
used.
Empirical
Derivation
of
Decay
Rates
for
Propylene
glycol
at
20C
y
=
­
0.1274x
­
0.0834
­
3
­
2.5
­
2
­
1.5
­
1
­
0.5
0
0
5
10
15
20
Time
(
days)
LN(
1­

BODt/
UBOD)

Figure
5,
regression
analysis
for
propylene
glycol
Kd
for
Ethylene
Glycol
at
4C
y
=
­
0.0428x
+
0.129
R2
=
0.9668
­
1.5
­
1
­
0.5
0
0.5
0
10
20
30
40
Days
Figure
6,
regression
analysis
for
ethylene
glycol
B­
7
Influence
of
Temperature
on
Kd
Reports
provided
by
Union
Carbide
contained
deoxygenation
data
for
three
temperature
ranges.
Observed
Kd
was
derived
for
each
of
the
three
temperatures
(
4,
10,
20C)
included
in
the
study.
The
influence
of
temperature
on
Kd
was
expressed
as
theta
where:
K
K
d
d
t
t
=
 

20
20
 (
)
and
calculated
directly
as:
K
K
t
t
20
1
20
 
=
 
for
each
temperature
(
10,
4
C).

The
decay
rates
were
calculated
as
a
percentage
of
the
theoretical
oxygen
demand.
The
decay
rates
appear
consistent
with
those
reported
earlier.
The
regression
(
Reg)
rates
were
described
above,
the
simple
rates
are
the
median
values
of
the
Kd
determined
independently
for
each
temperature.
The
influence
of
temperature
expressed
as
theta
has
a
median
value
of
1.102
and
a
standard
deviation
of
0.027.
These
results
are
summarized
in
Table
2.

The
calculated
theta
is
within
the
upper
range
of
values
typically
used
for
carbonaceous
BOD
originating
from
municipal
wastewater
treatment
plants
(
Thomann
and
Mueller
1991
=
1.04,
Tchoboanogolous
and
Schroeder
(
1985)
(
1.135
in
Wells
and
Berger
1995).
The
influence
on
temperature
is
similar
to
that
used
by
Wells
and
Berger
in
their
modeling
efforts.
The
formulation
used
by
Wells
and
Berger
would
reduce
deoxygenation
rates
more
severely
below
6
C,
and
less
severely
above
6
C
than
the
calculated
theta
of
1.1.

A
theta
value
of
1.10
is
used
in
the
loading
capacity
modeling.

Calculation
of
Aeration
Rate
(
Ka):
A
variety
of
aeration
rates
have
been
suggested
for
use
in
the
Columbia
Slough
model.
PDX
presented
Ka
in
the
range
of
3.1­
4.0/
day
from
field
data
collected
in
April
1996.
The
field
data
was
interpreted
to
suggest
that
the
aeration
rates
used
by
Wells
and
Berger
of
less
than
1/
day
may
underestimate
aeration.
The
wide
discrepancy
may
reflect
the
variability
that
could
be
observed
in
the
Columbia
Slough
system.
Aeration
rates
are
often
expressed
as
a
mathematical
function
of
stream
depth
and
velocity.
Both
velocity
and
depth
vary
independent
of
flow
in
the
Columbia
Slough.

Lower
Slough
aeration
rates:
In
the
Lower
Slough,
during
the
winter,
the
stream
depth
is
often
controlled
by
the
river
stage
of
the
Willamette
and
Columbia
Rivers.
When
the
Willamette
river
stage
is
high,
water
backs
up
into
the
Columbia
Slough
resulting
in
reduced
advective
flow
out
of
the
Slough.
Cursory
observation
of
available
continuous
monitoring
data
suggest
that
critically
low
dissolved
oxygen
levels
(
anoxic)
are
associated
with
high
river
stage.
During
the
1995
oxygen
depletion
event
the
Table
2,
Calculated
decay
rates
and
theta
Propylene
Ethylene
T
Reg
Simple
Reg
Simple
20
0.127
0.138
0.188
0.151
10
0.066
0.067
0.066
0.055
4
0.053
0.026
0.042
0.028
Theta
10
1.07
1.07
1.11
1.11
4
1.06
1.11
1.09
1.11
B­
8
river
stage
increased
from
near
6
ft
MSL
to
13
feet
MSL.
Aeration
rates
have
not
been
measured
during
the
periods
of
critically
low
dissolved
oxygen.

Aeration
rates
were
initially
estimated
using
an
O'Connor­
Dobbins
equation
(
K
u
h
a
=
12
9
1
2
3
2
.
).

Stream
velocity
(
u)
was
estimated
using
generalized
stream
cross
section
data
and
discharge.
Results
were
compared
to
detention
time
nomographs
presented
by
Wells
and
Berger
(
1995).
Velocity
estimates
using
generalized
stream
physical
conditions
are
similar
to
the
velocities
estimated
using
continuous
monitoring
data
collected
in
December
1996­
January
1997
of
0.05
to
0.12
f/
s
at
relatively
high
stage
(
5­
15
MSL)
and
discharges
of
less
than
250
cfs
(
Figure
7).

Depth
(
h)
was
estimated
as
the
difference
between
bottom
elevations
reported
by
Wells
and
Berger
(
1995)
and
stage.
As
seen
in
Figure
8
and
Table
3,
the
resulting
estimates
of
aeration
suggest
that
at
the
annual
high
stream
stages
typically
observed
of
>
15ft
MSL,
the
aeration
rates
would
be
substantially
lower
than
at
a
more
typical
summer
low
flow
range
of
6
feet
MSL.

5
7
9
11
13
15
50
100
150
200
250
300
0
0.2
0.4
0.6
0.8
1
1.2
Surface
MSL
Calculated
Ka
(
Occonner­
Dobbins)
Using
Surface
Water
MSL
and
Discharge
for
the
lower
Columbia
Slough
1­
1.2
0.8­
1
0.6­
0.8
0.4­
0.6
0.2­
0.4
0­
0.2
Figure
8,
Ka,
Discharge,
Stage
Wind
induced
aeration
may
become
an
important
contributor
to
the
oxygen
balance
under
conditions
of
high
stage
and
low
velocity.

Upper
Slough
aeration
rates:
Stream
stage
in
the
Upper
Slough
is
regulated
for
flood
control
and
stream
depth
is
not
necessarily
a
function
of
discharge.
In
the
Upper
Slough
the
stage
is
not
directly
related
to
the
Willamette
River
stage.
Aeration
rates
were
estimated
using
generalized
stream
geometry
data
and
discharge
(
Figure
9).
Results
were
compared
to
detention
time
data
presented
by
Wells
and
Berger
(
1995).
The
generalized
aeration
rates
may
approximate
averaged
conditions,
they
will
not
represent
specific
locations.
The
Upper
Slough
is
deeper
and
wider
near
MCDD1
resulting
in
reduced
aeration
rates
compared
to
the
estimated
aeration
rates
for
the
rest
of
the
Upper
Slough
5
7
9
11
13
15
50
100
150
200
250
300
0
0.1
0.2
0.3
0.4
0.5
0.6
f/
s
MSL
Estimate
Velocity
by
Stage
and
Discharge
0.5­
0.6
0.4­
0.5
0.3­
0.4
0.2­
0.3
0.1­
0.2
0­
0.1
Figure
7,
Stage,
Discharge,
Velocity
cfs/
MS
L
5
10
15
20
100
0.65
0.13
0.06
0.03
200
0.98
0.19
9
0.08
0.05
300
1.16
0.23
0.10
0.06
Table
3:
Lower
Slough
Est.
Ka
B­
9
(
Table
4).
The
observed
dissolved
oxygen
sags
near
MCDD1
may
be
a
function
of
the
lower
aeration
rates.
The
estimated
aeration
rates
for
the
Upper
Slough
can
exceed
those
estimated
for
the
Lower
Slough.
Similar
to
the
Lower
Slough
the
aeration
rates
are
much
lower
at
a
relatively
high
stage
MSL
of
8
feet
as
compared
to
a
MSL
of
6
feet.
Estimated
Ka
is
much
lower
at
MCDD1.

Effect
of
wind
on
aeration
rates:
The
equation
used
to
calculate
aeration
is
appropriate
for
moderately
deep
to
deep
channels
(
1ft
<
H
<
30
ft)
with
velocities
in
the
range
of
0.5
fps
<
U
<
1.6
fps
(
EPA
Technical
Guidance
Manual
for
Performing
Waste
Load
Allocations,
1992).
Velocities
for
the
Columbia
Slough,
during
critical
time
periods,
range
from
0.05
fps
to
0.12
fps.
Using
the
O'Connor
Dobbins
formula
may
underestimate
the
aeration
rate,
as
Ka
approaches
zero
as
the
depth
increases.
For
these
two
reasons,
the
O'Connor
­
Dobbins
formula
may
be
inappropriate
for
the
Columbia
Slough.

Due
to
low
velocities,
with
deep
and
stagnant
waters,
the
Columbia
Slough
system
is
similar
to
a
lake.
DEQ
evaluated
equations
for
calculating
gas
transfer
rates
(
KL)
and
Ka
for
lakes
and
reservoirs.
In
such
waterbodies
the
effect
of
wind
on
reaertion
may
be
significant.
Banks
and
Herrera
(
Thomann
and
Mueller,
1987)
suggest
the
following
equation
to
estimate
KL.

K
U
U
U
L
w
w
w
=
 
+
0
728
0
317
0
0372
1
2
2
.
.
.

where
U
is
wind
speed
in
m/
s
and
KL
is
the
wind
driven
oxygen
transfer
coefficient
in
m/
day.

To
determine
an
appropriate
KL
for
the
aeration
calculations,
wind
data,
Willamette
River
stage
data
and
Columbia
Slough
DO
data
were
evaluated
for
time
periods
when
DO
levels
dropped
to
anoxic
conditions.
Using
hourly
average
wind
speed
for
the
period
of
February
15­
22,
1995,
values
for
KL
were
calculated
using
the
Banks
and
Herrera
equation.
A
minimum
daily
average
KL
which
represented
the
critical
conditions
was
estimated.
A
minimum
daily
average
Ka
(
reaeration
coefficient)
was
calculated
using
the
following
equation:

K
K
H
a
L
=
/
where
H
is
depth
of
the
waterbody.

Effect
of
temperature
on
Ka:
6
8
10
50
100
300
0
0.5
1
1.5
2
2.5
3
3.5
4
Ka
MSL
Q
Upper
Slough
Aeration
(
O'Conner­
Dobbins)

Figure
9,
Ka,
Stage,
Discharge
Upper
Slough
At
MCDD
1
cfs/
M
SL
6
8
10
6
8
10
50
1.6
0.6
0.3
0.09
0.06
0.04
100
2.3
0.8
0.4
0.12
0.08
0.06
300
3.9
1.4
0.7
0.21
0.15
0.10
Table
4:
Ka
generalized
for
the
upper
Slough
and
for
MCDD1
B­
10
The
reaeration
coefficient
was
adjusted
for
temperature
(
at
8
°
C)
using
the
following
equation:
K
K
a
a
t
t
=
 

20
20
 (
)

No
specific
information
is
available
for
estimating
the
influence
of
temperature
on
aeration
rates.
The
standard
default
theta
of
1.024
(
USEPA)
is
recommended.
The
minimum
daily
average
KL
was
estimated
as
0.577
m/
day
and
the
minimum
daily
average
Ka
was
estimated
as
0.107
at
8
°
C.

Effect
of
dispersion
on
instream
BOD:
In
any
river,
there
is
mixing
that
occurs
along
the
river
due
to
horizontal
and
vertical
gradients
in
velocity.
This
phenomenon
is
known
as
longitudinal
dispersion,
and
preliminary
calculations
indicate
that
peak
downstream
BOD
concentrations
will
be
reduced
if
dispersion
is
considered
in
the
dissolved
oxygen
analysis.
The
Port
of
Portland
calculated
dispersion
coefficients
(
Ex)
from
reaeration
studies
conducted
during
April,
1996.
Ex
was
estimated
to
be
2.3
ft2/
sec
and
26.8
ft2/
sec,
at
flow
rates
in
the
Upper
Slough
of
50
cfs
and
75
cfs,
respectively.
The
pumping
rates
at
MCDD1
were
assumed
to
be
75
cfs
and
300
cfs,
respectively.
DEQ
estimated
Ex
using
the
following
equation
(
Thomann,
1987):

E
U
B
HU
x
=
 
34
10
5
2
2
.
(
)
*
where
U
is
the
mean
velocity
in
fps,
B
is
the
mean
width
in
feet,
H
is
the
mean
depth
in
feet,
and
U*
is
the
shear
velocity
in
fps.

Estimates
of
Ex
obtained
by
this
method
were
of
the
same
order
of
magnitude
for
each
selected
flow
as
those
calculated
by
the
Port
of
Portland.
DEQ
used
Ex
values
of
2.0
ft2/
sec
for
100
cfs
and
20
ft2/
sec
for
both
200
cfs
and
300
cfs.

Results
of
sensitivity
analyses
demonstrate
that
dispersion
affects
the
peak
instream
BOD
values
for
short
term
discharges
(<
1.5
days).
During
short
discharge
periods,
the
BOD
load
acts
as
a
plug
moving
through
the
Slough.
Increasing
the
discharge
period
results
in
the
Port's
discharge
acting
as
a
continuous
discharge,
with
dispersion
becoming
insignificant.
To
simplify
the
analysis,
the
time
of
the
Port's
discharge
is
limited
to
one
day.

Time
to
critical
deficit
:
The
dissolved
oxygen
reaches
a
maximum
deficit
at
a
"
critical
time"
when
the
uptake
of
oxygen
by
the
BOD
is
balanced
by
input
of
oxygen
from
the
air:
t
K
K
Log
K
K
D
K
K
K
L
c
a
d
n
a
d
a
d
d
*
(
{
(
)
}
=
 
 
 
1
1
0
0
,
where
D0
is
the
initial
oxygen
deficit
and
Lo
is
the
initial
BODu.
Under
current
conditions
the
Columbia
Slough
becomes
so
heavily
loaded
with
organic
material
that
oxygen
will
approach
depletion,
and
anaerobic
conditions
will
result.
The
start
of
the
anaerobic
condition
occurs
prior
to
the
point
where
critical
oxygen
deficit
would
occur.
Assuming
no
other
sources,
the
point
of
recovery
from
anaerobic
conditions
will
be
dependent
upon
the
aeration
rates.
Under
the
anaerobic
conditions
the
rate
of
BOD
decay
will
be
satisfied
by
the
aeration
rate.

The
expectation
of
the
TMDL
will
be
to
eliminate
the
anaerobic
conditions.
Once
the
TMDL
is
successful
dissolved
oxygen
will
not
fall
below
water
quality
standards.
If
the
residence
time
of
B­
11
water
in
the
Columbia
Slough
is
longer
than
the
time
to
critical
deficit
then
the
loading
capacity
is
established
by
the
critical
oxygen
deficit.
If
the
residence
time
of
water
in
the
Slough
is
less
than
the
time
to
critical
oxygen
deficit
the
loading
capacity
is
defined
by
the
dissolved
oxygen
deficit
that
occurs
at
the
time
water
leaves
the
Columbia
Slough
and
is
diluted
by
water
from
the
Columbia
and
Willamette
Rivers.

The
potential
range
for
time
to
critical
dissolved
oxygen
deficit
was
calculated
for
a
range
of
Kd
and
 d
as
defined
above,
and
for
a
range
of
the
estimated
Ka
and
 a
with
an
assumed
standard
error
of
0.03
(
USEPA).
An
initial
oxygen
deficit
of
zero
was
assumed.
A
total
of
1000
calculations
representing
the
potential
ranges
of
Ka
and
Kd
as
adjusted
by
temperature
were
made
for
defined
conditions
of
temperature
and
flow.
The
median
calculated
Tc
for
a
flow
of
100
cfs
and
stage
of
15
MSL
was
>
22
days
(
Figure
10).

Residence
time
is
dependent
upon
the
stage
and
discharge
(
Table
5).
The
time
to
critical
deficit
is
dependent
substantially
on
the
aeration
and
deoxygenation
rates,
which
in
turn
are
dependent
upon
temperature,
stage,
and
discharge.
However,
under
the
assumed
reasonable
worst
case
conditions
it
appears
the
time
to
critical
deficit
is
likely
to
be
greater
than
the
residence
time
of
water
in
the
Columbia
Slough.
The
LC
is
determined
by
the
residence
time
of
water
in
the
Slough.

OXYGEN
DEMAND
LOADS:
The
instream
dissolved
oxygen
is
in
part
dependent
upon
the
loads
of
oxygen
demanding
material
discharged
to
the
Slough.
The
relative
contribution
of
sources
varies
depending
upon
whether
rainfall
runoff
or
deicing
is
occurring.
The
substantive
loads
that
are
estimated
with
existing
data
include
the
de­
icing
loads,
storm
water
loads,
and
the
net
background
loads.
Critical
Time
@
100
cfs,
15MSL
0
50
100
150
200
250
300
5
10
15
20
25
30
35
40
45
More
Days
Frequency
.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
90.00%
100.00%

Frequency
Cumulative
%

Figure
10,
Time
to
critical
DO
deficit
Q/
MSL
10
15
20
100
7.6
11.2
11.7
200
3.3
4.9
5.1
300
2.8
3.5
3.7
Table
5:
Estimated
Residence
Time,
Lower
Slough
only
B­
12
Combined
Sewer
Overflows:
A
substantial
oxygen
demand
loads
is
contributed
by
CSOs.
Current
efforts
will
largely
eliminate
the
CSOs.
With
elimination
the
WLA
for
CSOs
will
be
zero
and
are
therefore
not
further
evaluated
as
part
of
the
TMDL.

Sediment
Oxygen
Demand:
Sediment
oxygen
demand
(
SOD)
can
substantively
influence
dissolved
oxygen.
A
single
measure
of
SOD
in
the
Columbia
Slough
of
2g
02/
m2/
day
is
similar
to
the
sediments
of
other
Western
Oregon
rivers.
Sediment
oxygen
demand
is
influenced
by
ambient
temperature
with
a
default
theta
(
 )
of
1.072
(
USEPA).
The
SOD
was
presumed
not
significant
compared
to
other
sinks
of
oxygen
for
this
analysis.

De­
icing
Loads:
De­
icing
loads
to
the
Columbia
Slough
were
estimated
using
COD
measures
and
presumed
flow
by
Fish
(
1996).
Wells
and
Berger
(
1995)
estimated
contributions
from
de­
icing
by
using
field
data
and
estimates
for
rates
of
aeration
and
deoxygenation.
No
direct
instream
information
is
available
to
demonstrate
the
influence
that
the
de­
icing
loads
have
on
instream
BOD5
concentrations.
Estimates
of
the
influence
of
de­
icing
loads
were
compared
to
instream
concentrations
using
simple
dilution
calculations
and
the
results
may
be
compared
to
instream
BOD5
measures.
Unfortunately,
available
instream
measures
occurred
during
different
periods
than
the
measured
de­
icing
loads.
The
instream
concentrations
would
also
be
influenced
by
several
processes
such
as
dispersion
and
decay.
Comparisons
may
only
provide
an
approximation
of
whether
the
observed
instream
concentrations
are
within
a
reasonable
order
of
magnitude
of
what
would
be
expected
by
de­
icing
loads.

De­
icing
loads
of
BOD
were
estimated
by
Fish
(
1996)
for
events
in
January
and
February
of
1996.
The
BOD5
concentrations
were
estimated
from
COD
data
using
empirical
correlations
developed
for
the
airport.
The
loads
were
estimated
using
presumed
"
worst
case"
pumping
discharge
rates.
Peak
loads
calculated
for
the
February
event
were
on
the
order
of
3.1
lb./
second
at
6,470
mg/
l
BOD5.
During
the
January
event
peak
loads
were
on
the
order
of
2
lb./
second
at
1784
mg/
l
BOD5.
The
resulting
instream
concentrations
are
not
available.
Estimates
of
loads
using
presumed
flow
ranges
are
similar
to
observed
peak
instream
BOD5.
B­
13
The
instream
BOD5
concentrations
resulting
from
the
estimated
de­
icing
loads
can
be
estimated
by
a
simple
mass
balance
using
presumed
stream
flow
(
Figure
11).
This
exercise
demonstrates
that
loads
would
be
periodic
pulses
moving
through
the
Columbia
Slough.
Subsequent
dispersion
would
reduce
maximum
concentrations
and
act
to
spread
out
the
period
of
the
pulse.

During
the
January
event
the
loads
were
derived
principally
from
subbasin
six
(
6)
of
the
Port.
Since
flow
data
was
not
readily
available
the
instream
concentrations
was
calculated
for
three
(
3)
assumed
discharge
rates
(
150,
200,
300
cfs)
and
an
ambient
concentration
of
1
mg/
l
BOD5
(
Figure
11).
On
other
occasions
instream
measures
of
>
80
mg/
l
have
been
reported.
The
reported
instream
BOD5
levels
of
>
80
mg/
l
do
not
appear
unreasonable
for
peak
ambient
concentrations
for
an
event
of
this
magnitude.

Maximum
instream
concentrations
were
estimated
for
the
February
1996
event
for
presumed
ambient
flows
of
between
200
and
1,000
cfs
and
background
BOD5
of
1
mg/
l
(
Figure
12).
Instream
flow
and
BOD5
measures
are
not
available.
Significant
deicing
load
contributions
occurred
for
both
subbasin
six
(
6)
and
seven
(
7).
The
peak
loads
for
both
were
assumed
to
occur
simultaneously.

The
Willamette
river
was
near
or
above
flood
stage
during
this
period.
However,
the
actual
flow
rate
in
the
Slough
is
not
known.
Peak
BOD5
loads
in
the
range
of
observed
peak
concentrations
of
80
mg/
l
or
greater
would
not
be
unreasonable.

Storm
water
BOD5
loads:
Numerous
efforts
have
been
made
to
estimate
the
BOD
contribution
of
storm
water
to
the
Slough
system.
Storm
water
BOD5
loading
have
been
estimated
for
the
City
of
Portland
as
part
of
earlier
CSO
studies.
Wells
and
Berger
(
1995)
estimated
storm
water
loads
through
calibration
of
receiving
water
quality
models.
Municipal
storm
water
permits
predicted
storm
water
loads
using
runoff
equations
and
assigned
concentrations
using
field
data.
Each
of
these
efforts
is
discussed
below.

Urban
runoff
modeling
(
SIMPTM)
conducted
by
OTAK
estimated
an
overall
storm
water
BOD5
of
 
5
mg/
l
for
the
City
of
Portland.
The
SIMPTM
model
used
local
rainfall
data,
and
Bellevue
Instream
BOD
using
assumed
flow,
January
18­
19
event
0
20
40
60
80
100
120
140
0
5
10
15
20
Hours
BOD5
150
200
300
Figure
11,
Instream
BOD
Estimated
BOD
using
Estimated
Peak
Mass
Load,
February
Event
and
Assumed
Discharge
0
50
100
150
200
250
0
200
400
600
800
1000
Discharge
mg/
l
BOD
Figure
12,
Estimated
BOD
B­
14
NURP
data
supplemented
with
data
collected
in
Portland.
The
SIMPTM
program
simulates
pollutant
loading
from
land
use
and
incorporates
the
influence
of
local
drainage
conveyance
systems
on
the
total
loading
of
particulate
and
associated
parameters,
such
as
BOD.

In
the
MS4
permit
applications
the
overall
average
BOD5
load
is
dependent
upon
the
mix
of
land
use,
runoff
coefficients
used
for
each
land
use
and
assigned
BOD5
concentration.
The
simulations
do
not
account
for
any
losses
of
BOD5
through
the
storm
water
system.
This
information
was
used
to
develop
storm
water
loading
estimates
for
the
Columbia
Slough
as
part
of
the
Columbia
Slough
Water
Body
Assessment
(
CH2MHill
1995).

Wells
and
Berger
(
1995)
cite
calibration
with
field
BOD5
and
dissolved
oxygen
data
as
demonstrating
that
the
estimates
made
by
OTAK
better
fit
observed
conditions
than
the
more
simple
models
used
to
develop
storm
water
permit
estimates.
As
part
of
the
calibration
efforts
to
better
represent
observed
instream
DO
and
BOD5
Wells
and
Berger
reduced
storm
water
concentrations
as
estimated
in
the
Water
Body
Assessment
(
CH2Mhill,
1995)
by
50%
and
75
%.
Although
this
calibration
improved
model
comparison
to
field
conditions
Wells
believed
additional
reduction
may
be
warranted.

Table
6
summarizes
these
storm
water
BOD
estimates.

Table
6:
Summary
of
estimates
of
storm
water
BOD
concentration
DEQ
initially
used
11
mg/
L
as
the
concentration
of
BOD5
from
storm
water
in
the
estimation
of
the
BOD
loading
capacity.
The
City
of
Portland
commented
that
the
representative
storm
water
BOD5
concentrations
should
be
reduced
from
11
mg/
L
to
near
5
mg/
L.
To
respond
to
this
comment,
DEQ
estimated
the
storm
water
BOD
concentration
by
two
methods:
calculation
of
a
flow
weighted
mean
urban
runoff
concentration
and
solution
of
a
simple
mass
balance.
These
two
methods
are
discussed
in
detail
below.

Flow
weighted
mean
method:
A
flow
weighted
mean
urban
runoff
BOD5
concentration
for
the
Columbia
Slough
was
derived
using
land
use
distributions
and
associated
event
mean
concentrations.
The
results
of
this
calculation
are
summarized
in
Table
7.
Source
mg/
L
BES­
SIMPTM
(
mean)
5.2
Gresham
MS4
(
mean)
5
Portland
MS4
(
mean)
19
WBA
CH2MHill
(
mean)
21
Wells
and
Berger
calibration
(
mean)
11
(
50%
reduction
of
initial
calibration)
B­
15
Table
7:
Flow
weighted
man
The
calculated
weighted
mean
concentration
of
20.39
mg/
l
BOD5
is
greater
than
the
recommended
5
mg/
l
to
represent
urban
runoff.
The
BOD
associated
with
land
use
classification
for
vacant
and
open
spaces
were
below
the
proposed
5
mg/
l
BOD5.
The
land
use
classifications
for
residential,
industrial,
commercial,
and
traffic
corridor
had
event
mean
concentrations
exceeding
the
proposed
5
mg/
l.
Available
data
suggest
that
industrial
storm
water
provides
a
significant
contribution
to
the
overall
storm
water
BOD5
loads
to
the
Columbia
Slough.
Industrial
storm
water
has
higher
BOD5
concentrations
than
other
land
uses.

Mass
balance:
A
simple
comparison
of
dilution
rates
and
instream
concentrations
can
be
used
to
estimate
storm
water
concentrations.
This
approach
is
similar
to
the
calibration
efforts
used
by
Wells
and
Berger
for
a
single
event.
A
calibrated
SWMM
model
was
used
to
estimate
urban
storm
water
flows
and
transport
these
flows
through
the
Slough.
Backwater
and
tidal
effects
were
ignored.
Dilution
was
estimated
by
assuming
a
constant
background
flow
of
75
cfs
in
the
Slough.
The
BOD
concentration
uninfluenced
by
storm
water
was
assumed
to
consistent
with
the
median
BOD
of
2.5
mg/
l
BOD5.
The
dilution
was
calculated
for
each
day
and
specific
location
where
BOD
was
monitored
in
the
Slough.
The
storm
water
concentration
was
then
directly
calculated
as:

{
}
C
Q
Q
Q
C
C
C
d
storm
background
simulate
background
observed
background
observed
=
 
 
+
.
The
simple
mass
balance
provides
an
indication
of
how
close
calibrated
storm
water
concentrations
from
multiple
sampling
efforts
rather
than
a
single
effort
would
compare
to
the
simulated
storm
water
runoff
concentrations.
The
results
of
this
calculation
are
summarized
in
Table
8.

Table
8,
storm
water
BOD5
concentrations
This
analysis
suggest
that
the
City
of
Portland's
calibration
estimate
that
storm
water
typically
contributes
5
mg/
l
BOD5
to
the
Slough
is
reasonable.
The
interquartile
range
for
estimated
BOD
from
storm
water
varies
from
2
to
>
15
mg/
l.
Mean,
median,
and
geometric
mean
estimates
varied
between
5.3
to
28
mg/
l,
but
were
typically
less
than
11
mg/
l.
The
highest
estimates
may
reflect
the
influence
of
de­
icing
materials
on
instream
BOD5
concentrations
used
to
calculate
storm
water
loads.
The
reason
for
the
LAND
USE
EMC
RUN
OFF
AREA
Residential
9.35
0.39
0.105
Industrial
54.05
0.68
0.14
Commercial
10.78
0.82
0.164
Open
3.84
0.14
0.132
Vacant
3.84
0.41
0.438
Traffic
13.65
0.91
0.023
(
average)
15
Sum
(
BOD*
Runoff*
area)
=

Sum
(
Runoff*
area)
20.39
MCDD1
LOWER
RM
6.9
LOWER
RM
4.9
25%
2.0
2.0
2.0
Mean
28
8.6
11.4
Median
6.0
8.8
7.7
Geomean
7.0
5.3
8.3
75%
15.6
11.7
7.4
B­
16
discrepancy
between
the
estimates
based
on
instream
calibration
and
the
storm
water
model
estimated
are
not
known.
Substantial
errors
could
occur
because
of
uncertain
estimates
for
dilution,
hydrologic
transport,
loss
mechanisms,
and
uncertain
load/
land
use/
runoff
estimates.

It
appears
reasonable
to
conclude
that
the
instream
BOD5
concentrations
are
less
than
would
be
expected
from
simple
dilution
models
using
storm
water
concentrations
estimated
using
simple
runoff
models
(
i.
e.
the
flow
weighted
mean
method).
The
reduction
is
on
the
order
of
50%
of
the
load,
and
may
be
greater.
However,
further
decrease
beyond
the
proposed
50%
reduction
may
imply
precision
that
does
not
exist.
The
storm
water
BOD5
contribution
is
therefore
estimated
as
10
mg/
L.

Background
BOD5
­
BODu:
The
background
BOD5
as
applied
represents
the
concentration
of
BOD5
originating
from
natural
anthropogenic
sources
other
than
storm
water
and
de­
icing
loads.
The
mean
(
log­
normalized)
of
2.5
mg/
l
BOD5
may
provide
a
site
specific
estimate
of
background
BOD5
that
is
consistent
with
the
relatively
high
range
of
BOD
observed
in
the
Slough
compared
to
other
western
Oregon
streams.

A
background
flow
of
70
CFS
is
consistent
with
the
volume
of
water
reported
in
the
Columbia
Slough
Water
Body
Assessment
for
groundwater
and
upstream
sources
of
water.

No
direct
measure
of
the
background
ultimate
oxygen
demand
have
been
made.
The
background
BOD
deoxygenation
rate
was
presumed
to
be
the
same
as
the
rate
for
glycols.
This
rate
may
be
greater
than
occurs
for
background
BOD
and
provides
a
conservative
estimate
of
BODu.

(
BOD
BOD
e
u
Kd
=
 
 
5
5
1
*
.)
The
estimated
BODu
is
 
4.9
mg/
l.

DERIVATION
OF
THE
TMDL
(
LC
WLA
LA
MOS):
A
dissolved
oxygen
TMDL
is
derived
for
the
Columbia
Slough
using
a
very
simple
analytical
solution
to
a
dissolved
oxygen
balance.
A
much
more
complex
model
is
available.
However,
the
lack
of
robust
synoptic
data
sets
providing
coincident
loading
and
ambient
information
results
in
substantial
uncertainty
for
describing
the
observed
oxygen
depletion
in
the
Slough.
Additionally,
the
uncertainty
on
the
decay
rates
of
glycols
and
the
influence
of
temperature
on
decay
rates
increases
the
opportunity
for
discussion
and
debate
about
model
calibration
and
application
for
the
development
of
TMDLs.
The
lack
of
coincident
ambient
data
and
uncertainty
about
decay
rates
results
in
a
large
number
of
degrees
of
freedom
and
a
more
complex
evaluation
may
not
be
more
precise
than
a
simple
approach.

The
federal
Clean
Water
Act
clearly
states
two
(
2)
conditions
that
influence
the
TMDL.
The
TMDLs
need
to
be
established
with
existing
data.
The
TMDL
needs
to
contain
an
appropriate
margin
of
safety
to
account
for
existing
lack
of
knowledge.

The
phased
TMDL
approach
allows
the
refinement
of
the
initial
TMDL
if
more
or
better
information
becomes
available.
The
implementation
plan
can
include
efforts
to
obtain
information
B­
17
needed
to
modify
the
TMDL.
The
phased
TMDL
approach
allows
the
TMDL
to
be
modified
using
information
developed
during
previous
phases.

Initial
TMDL
A
simple
oxygen
balance
was
developed
to
identify
the
initial
TMDL
and
to
test
the
sensitivity
of
the
various
rates
and
coefficients
on
the
potential
TMDLs.
Estimates
of
the
stream
loading
capacity
were
determined
using
the
best
available
information
on
deoxygenation
and
aeration
rates,
and
the
influence
of
temperature
on
these
rates.
A
reasonable
critical
condition
for
dissolved
oxygen
concentration
was
used
to
define
the
loading
capacity.

The
simple
oxygen
balance
provides
a
means
to
discuss
and
evaluate
alternative
allocation
strategies
and
is
presented
in
terms
of
the
oxygen
deficit
at
a
time
(
t):

{
}
{
}
{
}
DO
DO
K
K
K
e
e
BOD
DO
DOe
s
t
d
a
d
K
t
K
t
u
s
K
t
d
d
a
 
=
 
 
+
 
 
 

0
0
,
where
S
=
saturation.

The
initial
TMDL,
including
a
margin
of
safety
can
be
described
using
the
simple
oxygen
balance.
The
simple
oxygen
balance
was
modified
to
include
the
influence
of
dispersion
on
pulse
loads
of
BOD.
As
a
result
of
this
modification,
the
de­
icing
events
are
restricted
to
a
single
day.

This
information
can
be
used
to
determine
whether
further
model
refinement
is
needed
to
reduce
the
existing
uncertainty.
Reducing
uncertainty
will
in
effect
allow
a
shift
of
the
margin
of
safety
to
specific
waste
loads.
This
information
may
be
used
to
focus
discussion
on
what
data
and
information
is
needed
to
refine
the
understanding
of
the
oxygen
depletion
in
the
Columbia
Slough.

Because
of
the
magnitude
of
the
observed
DO
problems
it
is
reasonably
assumed
that
further
model
refinement
will
occur.
To
date
the
information
needed
has
not
been
collected.
A
phased
TMDL
will
assure
that
the
information
needed
will
be
collected
in
a
timely
manner
and
that
controls
will
be
implemented
with
an
appropriate
margin
of
safety.

From
the
information
reviewed
above
the
reasonable
design
conditions
for
determining
the
loading
capacity
(
LC)
are:

Kd(
20)
=
0.143/
day
(
at
20C)
Kd(
8)
=
0.045/
day
(
at
8C)
Theta
Kd
=
1.10
Theta
Ka
=
1.024
Ka
=
0.107/
day
(
at
8C)
Temperature
=
8
C
Background
BOD5
=
2.5
mg/
l,
Background
BODu
=
4.9
mg/
l
Storm
water
BOD5
=
10
mg/
L
De­
icing
Bod5
=
range
of
100
to
2000
mg/
L
to
meet
dissolved
oxygen
criteria
time
of
discharge
=
1
day
Exx
(
dispersion)
=
2
for
Q
<
100
CFS
Exx
(
dispersion)
=
20
for
Q>
200
CFS
Q
(
total
flow)
=
2.83
m/
s
(
100
CFS),
5.66
m/
s
(
200
CFS),
8.5
m/
s
(
300
CFS)
B­
18
The
residence
time
of
water
for
calculating
minimum
dissolved
oxygen
condition
includes
the
travel
time
from
the
airport
to
MCDD1
in
the
Upper
Slough,
and
for
the
travel
time
through
the
Lower
Columbia
Slough.
At
a
stage
of
15
MSL
in
the
Lower
Slough
the
residence
time
varies
from
a
<
5
days
to
near
12
days
depending
on
discharge
(
Table
9).

Table
9,
residence
time
(
days)

The
design
conditions
represent
the
best
estimate
of
model
input
values
and
a
reasonable
set
of
hydraulic
and
temperature
conditions
that
have
been
observed
to
generate
critical
dissolved
oxygen
depletion
in
the
Columbia
Slough.

Hydraulic
conditions
are
different
between
the
Upper
and
Lower
Slough.
The
preliminary
analysis
suggest
that
the
Lower
Slough
is
more
likely
than
the
Upper
Slough
to
have
reduced
oxygen
levels
due
to
elevated
BOD.
Allocations
are
established
to
achieve
the
DO
criteria
in
the
Lower
Slough.

The
simple
oxygen
balance
was
solved
to
determine
the
loading
capacity
of
instream
BOD.
The
objective
of
the
LC
is
to
achieve
dissolved
oxygen
criteria
of
6.5
mg/
l
as
a
long
term
average,
5.0
as
an
event
minimum
average,
and
4.0
as
an
absolute
minimum.
The
criteria
are
used
to
define
the
LC
for
an
event
hourly
maximum,
event
mean,
and
long
duration
discharge.
This
approach
allows
the
LC
and
subsequent
WLAs
to
vary
dynamically
with
pulse
events
of
the
storm
water
driven
loads.

Allocation
Strategy:
Several
allocation
strategies
are
available.
The
three
(
3)
principle
allocations
are
for
background,
storm
water,
and
de­
icing
loads.
The
TMDL
is
described
as
the
instream
target
BOD5
concentration
and
varies
with
flow
(
TMDL
(
kg/
d)
=
BOD5(
mg/
l)
*
Q(
m/
s)
*
conversion
factor).

Several
alternatives
were
evaluated
for
distributing
loads
between
storm
water
and
de­
icing
loads.
From
this
review
there
appears
to
be
two
(
2)
reasonable
strategies.

1)
Allocate
the
storm
water
loads
at
their
current
estimated
concentration
and
loads.
The
reduction
in
loads
needed
to
achieve
the
LC
would
be
taken
from
the
de­
icing
load.

2)
Equal
relative
efforts:
Under
the
equal
relative
effort
alternative
the
reduction
of
both
storm
water
and
de­
icing
loads
is
proportional
to
the
calculated
increase
in
BOD5
in
the
Columbia
Slough.
There
are
two
(
2)
alternative
methods
used
to
define
what
is
equal
equivalent
effort.
Information
presented
by
Wells
and
Berger
(
1995)
was
used
as
the
reference
condition
for
deriving
equal
relative
efforts.
The
WLA
would
be
determined
as
the
reduction
from
the
existing
reference
condition.
The
initial
allocation
reduced
4.5
pounds
of
de­
icing
load
for
each
pound
of
storm
water.
Alternatively,
if
the
mass
ratio
is
perceived
to
be
the
equitable
representation
of
equivalent
effort
there
would
be
3.8
pounds
BOD
reduced
in
de­
icing
load
for
each
pound
of
storm
water
(
Table
10).
Q
Lower
Upper
Residence
100
11.2
2
13.2
200
4.9
1
5.9
300
3.5
1
4.5
B­
19
Table
10,
equal
mass
reduction
calculation
The
relative
influence
of
storm
water
loads
would
be
unique
for
each
set
of
streamflow,
runoff,
and
de­
icing
event
conditions.
The
relative
load
is
also
dependent
upon
the
uncertain
estimates
of
both
storm
water
and
deicing
quality
and
loads.
The
relative
reduction
is
unique
for
each
condition.
It
would
not
be
possible
to
derive
unique
reductions
for
each
condition.

Reasonable
Margin
of
Safety:
A
TMDL
must
be
established
with
a
reasonable
margin
of
safety
to
account
for
uncertainty
in
existing
information
on
loads
and
receiving
water
response.
The
margin
of
safety
also
needs
to
account
for
the
uncertainty
in
achieving
the
assigned
load
allocations.
A
substantial
amount
of
uncertainty
exists
in
the
current
estimates
of
the
loading
capacity.
A
margin
of
safety
of
20%
was
assigned
to
the
estimates
of
LC
for
the
three
(
3)
flow
regimes
and
three
(
3)
oxygen
criteria.

The
amount
of
uncertainty
associated
with
the
selection
of
Kd,
 kd,
Ka,
and
 ka
was
determined
by
defining
probability
density
functions.
The
mean
and
defined
standard
deviation
for
Kd,
and
 kd
are
described
above.
The
calculated
Ka,
and
 ka
were
assigned
a
coefficient
of
variation
of
0.03
from
USEPA
guidelines
for
conducting
uncertainty
analysis
(
QUAL2EU).
All
distributions
were
presumed
to
be
normal.
The
loading
capacity
was
determined
as
the
Lo
that
would
create
a
deficit
equal
to
the
difference
between
saturation
and
the
state
water
quality
standard
(
dispersion
was
not
included
in
this
analysis):
DO
DO
K
K
K
e
e
s
stnd
d
d
a
K
t
K
t
d
a
 

 
 
 
 
(
)
.
The
dissolved
oxygen
was
assumed
to
be
initially
at
saturation.
The
residence
time
of
water
in
the
Slough
was
derived
above
and
estimated
to
be
less
than
the
critical
time
for
achieving
minimum
dissolved
oxygen.
The
distribution
of
calculated
loading
capacities
is
presented
in
Figure
13.

The
calculation
of
LC
depends
on
both
the
selection
of
a
reference
residence
time
and
the
physical­
hydraulic
conditions
used.
The
approach
used
presumed
reasonable
worst
case
physical
hydraulic
conditions
of
a
15
ft
MSL
stage,
and
a
temperature
of
8C.
The
loading
capacity
was
determined
for
a
criteria
of
4.0
mg/
l
DO.
A
greater
loading
capacity
would
be
expected
under
less
severe
hydraulic
conditions.
A
greater
range
for
loading
capacity
would
be
estimated
if
the
stage,
temperature,
and
residence
time
were
allowed
to
vary,
however
the
LC
is
described
for
specific
discharge
levels.
A
discharge
of
200
cfs
was
used
in
the
uncertainty
analysis.
C
Q
Mass
Storm
10
345.0
18596
de­
ice
2000
6.5
70070
BKG
2.5
70.0
943
8.7
BKG
+
Storm
39
BKG
+
Storm
+
de­
ice
39/
8.7
=
4.5
Mass
de­
ice
/
Mass
Storm
:
70070/
18596
=
3.8
Histogram
0
50
100
150
200
250
300
350
10
15
20
25
30
35
40
45
50
55
60
65
70
More
BOD(
5)
BIN
Range
Frequency
.00%
10.00%
20.00%
30.00%
40.00%
50.00%
60.00%
70.00%
80.00%
90.00%
100.00%

Frequency
Cumulative
%

Figure
13,
distribution
of
estimated
LC
B­
20
An
appropriate
margin
of
safety
needs
to
provide
reasonable
assurance
that
achievement
of
the
WLAs
will
result
in
achievement
of
water
quality
standards.
The
margin
of
safety
should
also
provide
an
objective
measure
of
the
uncertainty
with
existing
knowledge.
The
allocation
to
the
margin
of
safety
may
be
redistributed
if
additional
information
is
developed
which
improves
the
precision
of
the
estimated
loading
capacity.

Table
11,
range
of
LC
The
margin
of
safety
was
defined
as
a
function
of
the
normal
variate
(
z)
for
the
range
of
LC
(
Figure
14).
Over
68%
of
the
values
fall
between
+/­
1z,
and
over
95%
of
the
values
fall
between
+/­
2z.
A
range
of
1z
indicates
the
most
likely
range
and
2z
represents
the
reasonably
potential
range
(
Table
11).

The
MOS
is
calculated
as:
215
168
215
.
.

.
 
,
=
21.8%,
 
20%.
This
value
represents
one
standard
deviation
around
the
average
LC
calculated.
A
MOS
of
20%
is
applied
to
all
flow
rates
and
DO
criteria.
Allocating
a
margin
of
safety
reduces
the
amount
of
BOD
that
may
be
distributed
to
other
sources.
Additional
data
could
act
to
reduce
the
MOS
and
allow
some
of
the
mass
to
be
reallocated.

TMDL
LC,
WLAs,
LA
s:
Allocations
are
expressed
as
a
loading
capacity
that
varies
with
flow
as
determined
for
a
reasonable
design
condition.

The
allocations
are
distributed
to
three
(
3)
classes
of
sources;
background,
storm
water
and
deicing
The
storm
water
loads
are
divided
between
permitted
industrial
storm
water
and
urban
runoff
from
areas
managed
by
the
designated
management
agencies.
The
storm
water
and
deicing
loads
are
for
those
loads
that
reach
the
Columbia
Slough,
rather
than
those
loads
that
are
generated.
Both
storm
water
and
de­
icing
loads
may
be
treated
between
where
they
are
generated
and
the
Slough.
A
20%
margin
of
safety
is
taken
from
the
LC
and
reserved.

The
allocation
for
the
airport
is
divided
between
the
Port
of
Portland
(
PDX)
and
the
Oregon
Air
National
Guard
(
ANG).

Storm
water
runoff
allocations
have
been
split
between
industrial
and
urban
runoff.
The
storm
water
target
loads
may
also
be
expressed
as
an
event
mean
target
concentration.
The
storm
water
BOD5
reaching
the
Columbia
Slough
is
allocated
to
46%
originating
from
permitted
industrial
storm
water
and
54%
from
other
urban
runoff.
Distribution
of
estimated
LC
for
BOD(
5)

1
10
100
­
5
­
4
­
3
­
2
­
1
0
1
2
3
4
5
Z
mg/
l
Figure
14:
Estimated
LC
vs
Normal
Variate
(
Z)

z
LC
(
mg/
l)
BOD5
%
difference
Low
High
Low
Avg.
High
Range
(
avg.­
low)/
avg.
1.95
1.98
13.3
21.5
35.6
22.3
38.0%
1.00
1.00
16.8
21.5
27.9
11.1
21.8%
B­
21
Future
Growth
and
Development
From
application
of
the
SIMPTM
model
the
City
of
Portland
predicted
a
150%
increase
in
storm
water
pollutant
loading
over
current
loads
to
the
Columbia
Slough
(
City
of
Portland
1989).
Future
growth
therefore
receives
1/
3
of
the
storm
water
allocation.

The
allocation
of
mass
loads
is
summarized
in
Table
12.

Table
12,
BOD
allocations
REFERENCES
CH2MHill
1995,
Waterbody
Assessment
Columbia
Slough
TMDL
Development,
written
for
the
City
of
Portland.

City
Of
Portland,
Bureau
of
Environmental
Services,
1989,
Columbia
Slough
Planning
Study
Background
Report.

EPA,
1992,
Technical
Guidance
Manual
for
Performing
Waste
Load
Allocations,
Book
ii:
Streams
and
Rivers.

Fish,
William,
Ph.
D.,
1996,
Portland
International
Airport
Deicing
Impact
Study
1995­
1996,
Final
Report,
Prepared
for
the
Port
of
Portland.

Hendrickson,
Nancy,
1997,
Discussion
of
City
of
Portland
BOD
data.

Thomann,
Robert,
and
Mueller,
John,
1987,
Principles
of
Surface
Water
Quality
Modeling
and
Control,
Harper
and
Row,
Publishers,
Inc.

Wells
S.
A.,
and
C.
J.
Berger
(
1995)
Hydraulic
and
Water
Quality
modeling
of
the
Upper
and
Lower
Columbia
Slough:
Model
calibration,
verification,
and
management
alternatives
report
for
1992­
1995.
Research
supported
by
the
City
of
Portland
BES.
Flow
(
m3/
sec)
BKG
Future
Growth
DMA
Industrial
SW
PDX
ANG
MOS
TMDL
WLA
to
achieve
4.0
mg/
L
DO
criteria,
BOD5,
kg/
day
2.83
428
188
201
175
3342
413
1200
5947
5.66
428
869
931
809
8752
1082
3237
16108
8.50
428
1585
1702
1479
11641
1439
4568
22842
11.33
428
2435
2608
2267
17679
2185
6981
34583
WLA
to
achieve
5.0
mg/
L
DO
criteria,
BOD5,
kg/
day
2.83
428
187
200
174
2801
346
1034
5170
5.66
428
854
914
795
7225
893
2784
13893
8.50
428
1553
1664
1446
9645
1192
3992
19920
11.33
428
2361
2529
2198
14825
1832
6089
30262
WLA
to
achieve
6.5
mg/
L,
DO
criteria,
BOD5,
kg/
day
2.83
428
183
198
172
1978
244
801
4004
5.66
428
822
889
773
4935
610
2114
10571
8.50
428
1500
1607
1396
6652
822
3132
15537
11.33
428
2251
2411
2095
10504
1298
4795
23782
B­
22
Wells
S.
A.,
C.
J.
Berger,
and
M.
B.
Eberle
(
1996).
Modeling
and
Monitoring
the
Columbia
Slough
System
1995/
1996.
Research
supported
by
the
City
of
Portland.,
BES.
