4/
7/
04
1
Scenario­
Specific
Field
Drainage
and
Water
Body
Sizes
Donna
Randall
and
Marietta
Echeverría
Office
of
Pesticide
Programs,

Environmental
Fate
and
Effects
Division
4/
7/
04
2
CA
Almond,
ChemB
4/
7/
04
3
Overview
°
National/
Regional
Risk
Assessment
Context

Crop
scenarios

"
Standard"
surface
water
body
and
field
size
dimensions
°
Sources
of
national/
regional
information
°
Options
evaluated
for
use
of
this
information
°
Proposed
scenario­
specific
values
4/
7/
04
4
National/
Regional
Risk
Assessment
Concept
At
Level
I
and
II
a
given
crop
scenario
is
used
as
a
surrogate
to
assess
the
risk
from
pesticide
use
on
that
crop
across
the
U.
S.
or
given
region
4/
7/
04
5
Crop
Scenarios
°
Crop
scenario
­
selected
combination
of
climatological,
soil,
and
cropping
practice
conditions
°
Four
categories
(
national,
regional,

organophosphate
cumulative,
or
local)


Cropping
practice
and
climatological
conditions
­

representative
of
main
crop
growing
area

Soil
series
­
vulnerable
to
soil
erosion
within
main
crop
growing
area
represented

Set
of
"
standard"
crop
scenarios
have
been
developed

Developed
on
an
as
needed
basis
4/
7/
04
6
"
Standard"
Surface
Water
Body
and
Field
Size
Dimensions
Treated
Field
Drainage
Area
(
DA)
­
10
ha
Surface
Area
1
ha
Depth
2
meters
Relationship
based
on
DA/
VC
1.5
acres/
acre­
ft
(
5
m2/
m3)

Volume
Capacity
(
VC)

20,000
m3
4/
7/
04
7
Origin
of
"
Standard"
Water
Body
Dimensions
and
Field
Size
°
Evaluation
of
original
model
performed
using
data
from
a
site
in
Georgia
°
Size
of
water
body
selected
as
representative
for
the
southeast

Depth
(
6
ft

2
m,
rounded)


Surface
area
(
2
acres

1
ha,
rounded)

°
Field
size
back­
calculated
using
USDA
(
1982)

DA/
VC
information
for
the
southeast

(
2
acres)(
6
ft)(
2
acres/
acre­
ft)
=
24
acres

rounded
to
10
ha

Due
to
rounding

DA/
VC
of
"
standard"
is
1.5
acres/
acre­
ft
4/
7/
04
8
Other
Model
Considerations
Regarding
Field
Size
°
Additional
model
assumptions
dependent
on
10
ha

Homogeneous
soil
series
across
treated
field

100
percent
planted
in
the
same
crop

100
percent
of
area
treated

Sufficient
drainage
area
to
support
a
small,

permanent
surface
water
body
4/
7/
04
9
Sources
of
National/
Regional
DA/
VC
Ratios
and
Water
Depths
°
Small
water
sources
used
for
irrigation,
recreation,
fire
protection,

livestock
watering,
fish
production,

waterfowl
and
other
wildlife
(
USDA,

1997)

°
Drinking
water
reservoirs
(>
956,000
m3)
(
Ruddy
and
Hite,
1990)
4/
7/
04
10
USDA
Recommended
DA/
VC
for
Small
Permanent
Water
Body
4/
7/
04
11
USDA
Recommended
Depth
for
a
Small
Permanent
Water
Body
4/
7/
04
12
Development
of
Scenario­

Specific
Values
4/
7/
04
13
Runoff
Direct
Precipitation
Overflow
Evaporation
Minimum
Level
Maximum
Level
Varying
Volume
Water
Body
4/
7/
04
14
Minimum
Depth
Maximum
Depth
(
Dmax)

Volume
capacity
(
VC)

Surface
area
(
SA)

Drainage
area
(
DA)

Size
Parameters
Affecting
Volume
4/
7/
04
15
Outline
1.
Options
for
assigning
size
parameter
values
2.
Sensitivity
of
VVWM
to
Dmax
3.
Comparison
of
VVWM
using
"
standard"
size
values
and
scenariospecific
values
4/
7/
04
16
Assigning
Size
Parameter
Values
For
CA
fruit
and
FL
sugarcane:

°
Dmax
was
set
to
USDA
recommended
minimum
depth
value
°
DA/
VC
ratio
was
set
to
highest
USDA
recommended
drainage
area
per
unit
storage
capacity
4/
7/
04
17
(
b)
FL
sugarcane
CA
fruit
Depth
Guidelines
and
Crop
Scenarios
4/
7/
04
18
(
b)
FL
sugarcane
CA
fruit
DA/
VC
Guidelines
and
Crop
Scenarios
4/
7/
04
19
Options
for
Assigning
Size
Parameter
Values
°
With
the
scenario­
specific
Dmax
and
DA/
VC
and
relationship
VC
=
SA
×
Dmax:

1.
Set
SA
to
1
ha,
derive
VC
and
DA
2.
Set
VC
to
20000
m3,
derive
SA
and
DA
3.
Set
DA
to
10
ha,
derive
VC
and
SA
°
CA
fruit,
FL
sugarcane
with
short­
lived
ChemA
and
long­
lived
ChemB
4/
7/
04
20
10
20
18
10
328
400
DA
(
ha)
10156
20000
18288
609
20000
24384
VC
(
m3)
5553
10936
10000
250
8202
10000
SA
(
m2)
­­­­­­­­­­­­­­­
1.8
­­­­­­­­­­­­­­­

­­­­­­­­­­­­­­­
2.4
­­­­­­­­­­­­­­­

Dmax
(
m)
­­­­­­­­­­­­­­­
3
­­­­­­­­­­­­­­­

­­­­­­­­­­­­­­­
50
­­­­­­­­­­­­­­­

DA/
VC
(
acre/
acre­
ft)
Option
3
Option
2
Option
1
Option
3
Option
2
Option
1
FL
sugarcane
CA
fruit
Parameters
Parameter
Values
4/
7/
04
21
Summary
of
Results
°
Differences
in
water
body
volume
magnitude,
but
no
difference
in
temporal
pattern
°
Chemical
mass
and
water
body
volume
affected
proportionally
°
No
difference
in
concentration
4/
7/
04
22
CA
Fruit,
ChemB
4/
7/
04
23
CA
Fruit,
ChemB
4/
7/
04
24
Outline
1.
Options
for
assigning
size
parameter
values
2.
Sensitivity
of
VVWM
to
Dmax
3.
Comparison
of
VVWM
using
"
standard"
size
values
and
scenario­
specific
values
4/
7/
04
25
Sensitivity
of
VVWM
to
Dmax
°
Dmax
was
set
to
the
(
1)
minimum,

(
2)
average
and
(
3)
maximum
value
from
range
°
DA
set
to
10
ha
°
VC
derived
from
DA/
VC
ratio
°
SA
derived
from
VC
and
Dmax
4/
7/
04
26
Parameter
Values
­­­­­­­­­­­­­
10156
­­­­­­­­­­­­­

­­­­­­­­­­­­­
609.4
­­­­­­­­­­­­­

VC
(
m3)
2.13
1.98
1.83
3.05
2.74
2.44
Dmax
(
m)
4760
5216
5553
199.9
222.1
249.9
SA
(
m2)
­­­­­­­­­­­­­­­
10
­­­­­­­­­­­­­­­

­­­­­­­­­­­­­­­
10
­­­­­­­­­­­­­­­

DA(
ha)
­­­­­­­­­­­­­­­
3
­­­­­­­­­­­­­­­

­­­­­­­­­­­­­­­
50
­­­­­­­­­­­­­­­

DA/
VC
(
acre/
acre­
ft)
Max.

Avg.

Min.

Max.

Avg.

Min.
FL
sugarcane
CA
fruit
Parameters
4/
7/
04
27
Summary
of
Results
°
Concentration
using
minimum
>
average
>
maximum
depth
value
°
Inverse
relationship
with
volume
during
dry
periods,
larger
surface
area
greater
evaporation
°
Average
difference
in
daily
concentration:


CA
fruit:
~
10­
25%


FL
sugarcane:
~
2­
5%
4/
7/
04
28
CA
Fruit,
ChemB
4/
7/
04
29
CA
Fruit,
ChemB
4/
7/
04
30
Outline
1.
Options
for
assigning
size
parameter
values
2.
Sensitivity
of
VVWM
to
Dmax
3.
Comparison
of
VVWM
using
"
standard"
size
values
and
scenariospecific
values
4/
7/
04
31
Scenario­
Specific
CA
Fruit
4/
7/
04
32
Scenario­
Specific
CA
Fruit,
ChemA
4/
7/
04
33
Scenario­
Specific
CA
Fruit,
ChemB
4/
7/
04
34
Scenario­
Specific
FL
sugarcane
4/
7/
04
35
Scenario­
Specific
FL
sugarcane,
ChemA
4/
7/
04
36
Scenario­
Specific
FL
sugarcane,
ChemB
4/
7/
04
37
Proposed
Approach
&

Summary
4/
7/
04
38
Proposed
Scenario
Specific
Approach
°
Retain
historic
standard
field
area
10
ha
for
all
crop
scenarios

Other
options
result
in
field
areas
>
500
acres

Runoff
model
not
appropriate
for
this
size
field

Gross
failure
of
soil
series
homogeneity
assumption

Would
require
a
percent
crop
treated
adjustment
°
Initial
(
and
maximum)
water
depth
set
to
the
minimum
value
at
the
crop
scenario
location
from
the
USDA
(
1997)
water
depth
map
°
Volume
calculated
from
maximum
DA/
VC
ratio
value
at
the
crop
scenario
location
from
USDA
(
1997)
DA/
VC
map
4/
7/
04
39
Examples
of
Proposed
Scenario­
Specific
Water
Body
Size
Values
1523
714
2.1
20
R
KS
sorghum
2539
1190
2.1
12
OP,
R
TX
sorghum
10156
5553
1.8
3
R
FL
sugarcane
609
250
2.4
50
OP,
R
CA
fruit
(
m3)

(
m2)

(
m)

(
acre/

acre­
ft)

Category
Crop
scenario
VC
SA
Dmax
DA/
VC
°
Currently
there
are
over
60
crop
scenarios
