­
C­
1­
APPENDIX
C
Calculation
Methods
and
GENEEC2
Model
Input/
Output
Tables
Showing
Estimated
Environmental
Concentrations
(
EECs)
for
Direct
Application
to
Water
In
addition
to
crop
and
non­
crop
terrestrial
uses,
imazapyr
can
be
applied
directly
to
surface
waters
for
control
of
aquatic
weeds.
Estimations
of
aquatic
EECs
resulting
from
direct
application
to
water
have
not
changed
substantially
from
the
April
2003
EFED
drinking
water
assessment
in
support
of
new
uses
for
aquatic
weeds.
However,
the
current
label
(
8/
25/
03)
for
HABITATTM
herbicide
indicates
that
a
one­
half
mile
setback
from
drinking
water
intakes
is
required.
EFED
does
not
currently
have
an
approved
policy
for
calculating
EECs
in
water
bodies
where
pesticides
are
applied
with
a
set
back
distance
from
drinking
water
intakes.
Therefore,
the
half
mile
setback
distance
was
not
considered
in
April
2003
assessment,
and
is
not
considered
here.
As
a
result,
the
assessment
presented
herein
is
more
conservative
than
one
where
a
setback
distance
is
considered.

To
assess
exposure
concentrations
for
direct
application
of
imazapyr
to
control
aquatic
weeds,
EFED
used
as
a
reference
or
benchmark
water
body
the
standard
EFED
pond
used
for
estimating
ecological
exposure
to
aquatic
organisms
from
runoff
of
chemicals
applied
terrestrially.
The
standard
pond
allows
for
dissipative
or
degradative
processes
once
the
chemical
reaches
the
pond.
A
complete
description
of
the
standard
pond,
including
its
dimensions,
volume,
and
chemical
characteristics
are
given
in
the
general
description
for
the
EFED
GENEEC2
surface
water
model
which
is
available
at
the
EPA
internet
site:

http://
www.
epa.
gov/
oppefed1/
models/
water/
geneec2_
description.
htm
EECs
for
Direct
Application
of
Imazapyr
to
GENEEC2
Ecological
Pond
In
order
to
have
a
standard
aquatic
environment
in
which
all
chemicals
could
be
assessed
and
compared
on
an
equal
footing,
EFED
developed
a
"
standard
agricultural
field­
farm
pond"
scenario
for
all
aquatic
exposure
assessments.
This
"
standard
pond"
scenario
assumes
that
rainfall
onto
a
treated,
10
hectare
agricultural
field
causes
pesticide­
laden
runoff
into
a
one
hectare,
20,000
cubic
meter
volume,
2.00
meter
deep
water­
body.
Although
this
`
standard
scenario'
was
designed
to
predict
pesticide
concentrations
in
the
standard
farm
pond,
it
has
been
shown
to
be
a
good
predictor
of
upper
level
pesticide
concentrations
in
small
but
ecologically
important
upland
streams
(
Effland
et
al.,
1999).
By
simple
calculation,
and
assuming
no
attenuating
factors
such
as
foliar
interception,
direct
application
at
the
maximum
rate
of
1.5
pounds
ae/
acre
to
the
entire
surface
area
of
a
two
meter
deep
"
standard
pond"
yields
a
acute,
peak
concentration
of
84
:
g/
L
(
ppb).
Direct
application
of
1.5
pounds
of
imazapyr
to
the
surface
of
water
bodies
1.0
feet
and
­
C­
2­
3.0
feet
deep
would
produce
acute,
peak
concentrations
of
552
and
184
:
g/
L
(
ppb),
respectively.

Aquatic
EECs
for
the
direct
application
of
imazapyr
to
surface
waters
as
well
as
aerial,
ground,
and
granular
applications
modeled
using
the
GENEEC2
ecological
pond
scenario
are
presented
in
Table
IIIB­
2.
If
imazapyr
is
applied
directly
to
the
entire
surface
of
the
GENEEC2
pond
and
uniformly
mixed
throughout
its
volume,
the
maximum
pond
concentration
of
imazapyr
is
calculated
by
simply
dividing
the
total
mass
of
pesticide
applied
to
the
pond
by
its
volume
at
three
water
depths.

The
"
standard
pond"
has
a
surface
area
of
1.00
hectares
and
is
2.00
meters
deep,
therefore,
it
has
a
volume
of
20,000
cubic
meters
or
2.00
x
107
liters
(
L).
The
maximum
imazapyr
application
rate
derived
from
the
label
is
1.50
lb/
acre,
and
since
1.00
lb/
acre
is
equivalent
to
1.121
kg/
ha,
the
application
rate
is
equivalent
to
1.682
kg/
ha
or
1.682
x
109
:
g/
ha.
Thus,
the
peak
concentration
for
imazapyr
is:

(
1.682
x
109
:
g/
ha
x
1.00
ha)/(
2.00
x
107
L)
=
84.1
:
g/
L
(
ppb)

Direct
application
of
1.5
pounds
of
imazapyr
to
the
surface
of
a
water
body
2.0
meters
deep
would
produce
an
acute
concentration
of
84.1
:
g/
L
(
ppb).
Direct
application
of
1.5
pounds
of
imazapyr
to
the
surface
of
water
bodies
1.0
feet
and
3.0
feet
deep
would
produce
acute
concentrations
of
552
and
184
:
g/
L
(
ppb),
respectively.
Calculated
concentrations
can
be
found
in
Table
C­
1,
below.

Table
C­
1:
Direct
Application
of
1.5
Pounds
per
Acre
to
the
Surface
of
Water.

Water
Depth
Peak
Concentration
Maximum
4
Day
Average
Maximum
21
Day
Average
Maximum
60
Day
Average
Maximum
90
Day
Average
1.0
Foot
552
:
g/
L
(
ppb)
552
:
g/
L
(
ppb)
549
:
g/
L
(
ppb)
542
:
g/
L
(
ppb)
538
:
g/
L
(
ppb)

3.0
Foot
184
:
g/
L
(
ppb)
184
:
g/
L
(
ppb)
183
:
g/
L
(
ppb)
181
:
g/
L
(
ppb)
179
:
g/
L
(
ppb)

2.0
Meter
84.1
:
g/
L
(
ppb)
84.1
:
g/
L
(
ppb)
83.6
:
g/
L
(
ppb)
82.6
:
g/
L
(
ppb)
81.9
:
g/
L
(
ppb)

In
order
to
conveniently
use
the
built­
in
GENEEC2
routines
to
estimate
imazapyr
concentrations
in
the
pond
as
a
function
of
time
for
the
2.0
meter
water
depth,
one
can
adjust
the
application
rate
in
the
GENEEC2
terrestrial
routine
to
yield
the
directly
calculated
84.1
ppb
peak
concentration.
Since
GENEEC2
output
is
directly
proportional
to
application
rate,
one
may
simply
use
any
trial
terrestrial
output
(
within
compound
solubility
limits)
and
use
the
appropriate
proportionality
factor
to
generate
the
peak
concentration.
For
example,
if
the
terrestrial
single
application
rate
of
1.5
lb
/
acre
and
the
appropriate
chemical­
specific
inputs
for
imazapyr
are
used,
the
following
results
are
obtained:
­
C­
3­
GENEEC
(
Ecological
Pond)
Results
for
Terrestrial
Application
of
Imazapyr
RUN
No.
111
FOR
Imazapyr
ON
Any
Crop
*
INPUT
VALUES
*
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
NO­
SPRAY
INCORP
ONE(
MULT)
INTERVAL
Kd
(
PPM
)
(%
DRIFT)
ZONE(
FT)
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
1.500(
1.500)
1
1
0.07
11000.0
AERL_
B(
13.0)
.0
.0
FIELD
AND
STANDARD
POND
HALFLIFE
VALUES
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
METABOLIC
DAYS
UNTIL
HYDROLYSIS
PHOTOLYSIS
METABOLIC
COMBINED
(
FIELD)
RAIN/
RUNOFF
(
POND)
(
POND­
EFF)
(
POND)
(
POND)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
2062.00
2
N/
A
5.30­
657.20
.00
657.20
GENERIC
EECs
(
IN
MICROGRAMS/
LITER
(
PPB))
GENEEC
Version
2.0
Aug
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
MAX
4
DAY
MAX
21
DAY
MAX
60
DAY
MAX
90
DAY
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
90.10
90.02
89.56
88.50
87.70
Using
the
peak
concentration
of
90.1,
the
proportionality
factor
is
84.1/
90.10
or
0.9334.
The
pseudo­
application
rate
used
below
is,
therefore,
0.4472
x
1.50
lb/
acre
or
1.40
lb/
acre.

EECs
for
Direct
Application
of
Imazapyr
to
Ecological
Pond
(
2
meters
deep)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
RATE
(#/
AC)
No.
APPS
&
SOIL
SOLUBIL
APPL
TYPE
NO­
SPRAY
INCORP
ONE(
MULT)
INTERVAL
Kd
(
PPM
)
(%
DRIFT)
ZONE(
FT)
(
IN)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
1.400(
1.400)
1
1
0.07
11000.0
AERL_
B(
13.0)
.0
.0
FIELD
AND
STANDARD
POND
HALFLIFE
VALUES
(
DAYS)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
METABOLIC
DAYS
UNTIL
HYDROLYSIS
PHOTOLYSIS
METABOLIC
COMBINED
(
FIELD)
RAIN/
RUNOFF
(
POND)
(
POND­
EFF)
(
POND)
(
POND)
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
2062.00
2
N/
A
5.30­
657.20
.00
657.20
GENERIC
EECs
(
IN
MICROGRAMS/
LITER
(
PPB))
GENEEC
Version
2.0
Aug
1,
2001
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
PEAK
MAX
4
DAY
MAX
21
DAY
MAX
60
DAY
MAX
90
DAY
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
AVG
GEEC
­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­
84.09
84.02
83.59
82.60
81.85
For
a
peak
concentration
of
84.1
ppb
resulting
from
a
1.40
lb/
acre
application
rate,
the
corresponding
average
concentrations
for
other
time
periods
are
then
used
in
the
ecological
risk
assessment
for
the
appropriate
organisms.
Additionally,
with
all
other
inputs
being
equal,
GENEEC2
output
values
are
directly
proportional
to
the
application
rate.
Therefore,
the
ratio
­
C­
4­
between
the
peak
concentrations
for
the
1
foot
and
3
foot
water
depths,
and
the
peak
concentration
for
the
two
meter
depth,
can
be
used
to
calculate
concentrations
at
the
other
four
GENEEC2
output
intervals
(
Table
C­
1).

A
simpler,
equivalent,
general
method
of
calculation
(
tabulated
by
Dr.
DeWitt)
for
a
water
body
of
uniform
depth
is
to
divide
the
mass
of
pesticide
applied
per
unit
cross­
sectional
surface
area
by
the
volume
of
that
unit
water
column.
Concentrations
along
the
edge
of
a
standing
water
body
can
be
estimated
by
consulting
the
DeWitt
table
for
an
application
rate
of
1.5
lbs/
acre
applied
to
a
six
inch
depth
of
water.
Therefore,
a
uniform
application
of
1.5
lbs/
acre,
without
the
standard
EFED
assumption
of
instantaneous
mixing
throughout
the
water
body,
would
yield
an
estimated
edge­
of­
water
concentration
of
1100
ppb.
