4/
7/
04
1
A
Varying
Volume
Water
Body
Model
with
Daily
Parameter
Variations
Dirk
F.
Young
Environmental
Fate
and
Effects
Division
Office
of
Pesticides
4/
7/
04
2
Model
Design
Criteria
°
Capabilities
to
vary
water
body
volume
according
to
meteorological
conditions
°
Daily
variations
in
parameters
values
°
Fast
running
program
suitable
for
Monte
Carlo
simulations
°
EXAMS
algorithms
where
applicable
4/
7/
04
3
Runoff
Direct
Precipitation
Overflow
Evaporation
Minimum
Level
Maximum
Level
Varying
Volume
Water
Body
Model:

modeled
volume
change
4/
7/
04
4
Littoral
Input
(
runoff
and
erosion)
Washout
Varying
Volume
Water
Body
Model:

modeled
pesticide
processes
Mass
Transfer
Volatilization
Benthic
Input
(
erosion)
Metabolism
Hydrolysis
Photolysis
Metabolism
Hydrolysis
4/
7/
04
5
Effect
of
New
Temperature
Averaging
Routine
­
10
­
5
0
5
10
15
20
25
30
Jan­
61
Mar­
61
Jun­
61
Sep­
61
Dec­
61
Time
Temperature
(

C)
30­
Day
Backward
Avg
(
VVWM)

Calendar
Month
Avg
(
EXAMS)
4/
7/
04
6
Effect
of
New
Wind
Representation
0
2
4
6
8
10
12
14
Jan­
61
Mar­
61
Jun­
61
Sep­
61
Dec­
61
Time
WInd
Speed
(

m/

s)
Daily
Wind
Speed
(
VVWM)

Calendar
Month
Average
(
EXAMS)
4/
7/
04
7
Effect
of
New
Washout
Representation
0
0.5
1
1.5
2
0
200
400
600
Days
Washout
Rate
Coefficient
(

sec­

1
x
106)
Daily
Calculated
(
VVWM)

Overall
Average
(
Current
Method)
4/
7/
04
8
Modeling
of
Individual
Processes
°
All
processes
use
same
algorithms
as
EXAMS
°
EXAMS
has
been
the
accepted
standard
for
pesticide
risk
assessments
4/
7/
04
9
Fast
Running
Program
°
Analytical
solution
°
Meteorological
Information
is
processed
and
stored
for
multiple
runs
°
Bulk
of
program
takes
advantage
of
fast
array
operations
in
F90
°
30­
year
simulation
runs
in
less
than
a
second,
subsequent
runs
(
Monte
Carlo)

are
faster
4/
7/
04
10
Summary
of
Simplifying
Assumptions
°
Pesticide
mass
input
and
volume
changes
occur
instantaneously
at
the
beginning
of
the
day
°
Suspended
solids
mass
does
not
change
with
volume
°
Mass
transfer
coefficient
coupling
water
column
and
benthic
zone
does
not
change
with
volume
°
Photolysis
rate
coefficient
does
not
change
with
volume
4/
7/
04
11
80
85
90
95
100
0
4
8
12
Days
Relative
Volume
(%)
Volume
and
Mass
Assumptions
Instantaneous
Pesticide
Additions
4/
7/
04
12
Suspended
Solids,
Photolysis,
and
Mass
Transfer
Assumptions
SS
=
SS
4/
7/
04
13
Summary
of
VVWM
°
Varying
volume
accomplished
by
daily
time­
step
adjustments
°
Daily
parameter
variations
°
Fast
program
suitable
for
Monte
Carlo
°
Questions
concerning
assumptions
