UNITED
STATES
ENVIRONMENTAL
PROTECTION
AGENCY
WASHINGTON,
D.
C.
20460
OFFICE
OF
PREVENTION,
PESTICIDES
AND
TOXIC
SUBSTANCES
TO:
Christina
Scheltema
Betty
Shackleford
Michael
Goodis
Special
Review
and
Reregistration
Division
(7508C)

FROM:
James
Wolf
ERB3
Environmental
Fate
and
Effects
Division
(7507C)

DATE:
November
20,
2001
RE:
Disulfoton
residues
in
ground
water
found
in
the
Virginia
BMP
Study:

BMP
Impacts
on
Nitrate
and
Pesticide
Transport
to
Groundwater
in
the
Nomini
Creek
Watershed.
Final
Report
Report
No.
NC­
0298
S.
Mostaghimi,
S.
Shukla,
and
P.
W.
McClellan.
1998.
Biological
Systems
Engineering
Department
Virginia
Polytechnic
Institute
and
State
University
Blacksburg,
VA
#
The
ground
water
monitoring
component
was
started
in
1986
and
ended
in
June,
1997.

#
Nomini
Creek
Watershed
is
located
in
Westmoreland
County,
Va.
The
1463
ha
watershed
has
typical
Coastal
Plain
land
use
49%
cropland,
47%
woodland,
and
4%
used
for
homestead
and
roads
(different
reports
has
slightly
different
breakdown,
but
have
the
same
major
uses).
Average
annual
precipitation
is
102
cm,
with
most
of
the
rainfall
occurring
between
April
and
September.
Most
ground
water
recharge
occurs
in
late
Fall
or
early
spring.

#
Nomini
Creek
Watershed
is
located
in
the
Coastal
Plain
Physiographic
providence.
Soils,
geology
and
topography
are
similar
to
the
of
the
unglaciated
Atlantic
Coastal
Plain.
2
Soils
are
mostly
Ultisols.
The
major
soil
series
are
Suffolk
and
Rumford.
These
soils
cover
91
percent
of
the
area
and
have
similar
physical
properties.

Soil
Taxonomy
Sulfolk
Coarse­
loamy,
siliceous,
thermic
Typic
Hapudults
Rumford
Coarse­
loamy,
siliceous,
thermic
Typic
Hapudults
The
Coastal
Plain
has
been
identified
as
a
vulnerable
area
to
ground
water
contamination.
Other
vulnerable
regions
have
also
been
identified.
The
soils
could
also
be
used
to
identify
possible
problem
areas.
(Can't
be
done
by
tomorrow).
These
are
vulnerable
soil
for
leaching.

#
Agriculture
is
primarily
row
crops.
Major
crops
are
corn,
soybeans,
and
small
grains
(wheat
and
barley).
Typical
rotation
is
conventionally­
tilled
corn,
followed
by
small
grains
with
no­
till
soybeans
planted
in
the
small
grain
residues.
Occasionally,
full
season,
conventionally­
tilled
soybeans
is
also
grown.
USDA
Ag
Statistics
do
not
report
tobacco
production
for
Westmoreland
County.
Potatoes
are
reported
to
be
produced,
but
production
appears
to
be
declining.

#
Study
Objective
to
study
the
quality
of
surface
and
ground
water
as
influenced
by
the
agricultural
practices
in
the
watershed.

#
Monitoring
consisted
of
two
(2)
runoff
and
surface
water
monitoring
stations;
seven
rain
gauges;
one
weather
station;
and
eight
(8)
ground­
water
monitoring
wells
(GN1
to
GN8).
The
ground
water
wells
were
located
primarily
in
agricultural
areas.
These
wells
were
drilled
in
pairs,
100
­
150
meters
apart,
with
one
in
pair
located
hydraulically
downgradient
of
the
other.

Characteristic
(m)
Value
Well
GN1
GN2
GN3
GN4
GN5
GN6
GN7
GN8
Well
depth
13.7
12.8
15.2
13.7
16.5
12.0
15.8
11.9
GW
depth
Mean
10.3
9.
6
13.1
9.
4
12.9
8.
2
13.3
8.
6
"
Max.
12.0
10.8
14.0
12.7
13.9
9.
1
14.4
9.
6
"
Min
8.
5
7.1
11.5
7.
0
11.3
7.
0
11.8
7.
4
#
Approximately
monthly
samples
were
taken
from
each
monitoring
well
and
analyzed
for
a
number
of
analytes
including
22
pesticides.
QA/
QC
procedures
were
followed.
3
#
Herbicide
and
insecticide
application
information
in
the
watershed
were
obtained
from
farmer
surveys.
The
rate
and
time
of
herbicide
application
was
dependent
on
the
crop
rotation
adopted
by
the
farmer.
Corn
is
usually
planted
between
late
April
and
early
May.
Post­
emergence
sprays
applications
occur
in
early
July.
The
timing
and
application
rates
of
insecticides,
applied
individually
or
in
combination,
in
the
watershed
depending
on
the
type
and
extent
of
the
insect
problem
observed.

Note:
the
label
does
allow
for
fall
application
to
wheat.
Perhaps
fall
application
and
greater
fall
recharge
resulted
in
the
observed
concentration
(2.87
µg/
L).
Possible
mitigation
option?

#
Disulfoton
sampling
results
and
detection
statistics
in
the
Nomini
Creek
Watershed
(Table
15,
after
Mostaghimi,
1998).
These
are
disulfoton
parent.

Pesticide
Total
Samples
Detections
1
Detection
2
Frequency
(percent)
Concentration
(µg/
L)

Max
Mean
SD
Disulfoton
1010
10
1.0
2.87
0.39
0.32
Pre­
BMP
3
(5/
86
­
10/
88)

229
7
3.1
2.87
0.52
Post
BMP
4
(11/
89
­
9/
96)

693
3
0.4
0.10
0.08
1
Number
of
samples
with
detectable
levels
of
pesticide
2
(samples
with
detectable
levels
of
pesticide
*
100)/
total
number
of
samples
3
Before
agricultural
Best
Management
Practice
(BMP)
implemented
in
watershed.
4
Following
the
implementation
of
BMP
within
the
watershed.

Note:
I
only
had
(raw)
data
through
1990.
Thus,
I
only
had
6
of
the
10
detections,
mean
was
0.57
µg/
L,
which
is
only
slightly
greater
than
the
mean
with
7
samples
(pre­
BMP).

Disscussion
and
recommendation:

The
following
table
was
included
in
Feb.
7,
2000
Additional
Clarification
of
Disulfoton
GroundWater
Monitoring
Data
Assessment.
In
a
recent
discussion
about
a
"chronic"
exposure
for
ground
water
the
following
suggestions
was
put
forth
(mean
=
1.49
µg/
L
=
(2.87
+0.1)/
2
for
well
site
GN3.
Considering
there
are
many
"monthly
samples,
with
most
being
less
than
the
detection
limit,
a
lower
mean
is
probably
justified
(disulfoton
parent
only).
The
mean
of
all
the
detections
is
0.39
µg/
L,
the
mean
of
the
pre­
BMP
is
0.52
µg/
L,
and
post­
BMP
is
0.08
µg/
L.
Without
specifically
estimating
a
concentration,
I
think
that
as
far
as
parent
disulfoton
goes,
the
average
concentration
would
be
expected
to
be
considerably
less
than
the
DWLOC
of
1.2(?).
4
Summary
of
Disulfoton
Detections
in
ground
water
from
the
eight
ground­
water
monitoring
wells
in
Nomini
Creek
Watershed
(Virginia),
during
1986
and
1987.

Sampling
Date
Well­
Site
Number
Concentration
(µg/
L)

11/
5/
86
GN3
2.87
11/
5/
86
GN6
0.04
3/
13/
87
GN4
0.10
8/
20/
87
GN1
0.13
8/
20/
87
GN2
0.16
8/
20/
87
GN3
0.10
