UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460



### MEMORANDUM O r F I ChOF

PREVbN TI ON

. PEST I C ID ES

. AN D

1 0X I C SUBSTANCES

PC Code: 118203

DP Barcode: 413592

August 12, 2013



### SUBJECT: Revised Drinking Water Exposure Assessment for Saflufenacil: New Chemical

Use pattern on Rice and Cha n ge in Label Application Rates for Other Crops.

TO: Bethany Benbow, Ri sk Manager Reviewer Kathryn Montague, M.S., Risk Manager, Rm 23

Danie l Kenny, Branch Chief

AND:



### FROM: Herbicide Branch Registration Division (RD) (7505P)

George F. Kramer, Ph.D., Chemist

Charles Smith, Acting Branch Chief

Risk Assessment Branch I

Health Effects Divi sion (7509P)

Mohammed Ruhman, Ph.D., Senior

# Agrol)O'l!~mgi!§·s~tJ/t~~;:::=;;;;;:;;Q~§~b~:;=~~~ Environmental Risk Branch 5 ...,.__- 

## fYI/JS!2ol3

Environmental Fate and Effects Division (7507P)

# THROUG**Shamim,** Ph.D., Branch Chie f

# ~ l.v-

# t/c~ Environmental Risk Branch 5

Env ir onmental Fate and Effects Division (7507P)



### I. EXECUTIVE SUMMARY

This is a revi s ion for previously calculated ti er I scree ning le vel EDWCs for sa flufenacil total

tox ic residues. The revision i s necessary due to the proposed new use pattern on rice (EPA Reg.

No. 7969-278) and the changes in lab e l application rates for some u ses (EPA Reg. No. 7969- 323). These revised EDWCs may be used in support of human health risk assessment.

The revised highest maximum EDWCs are 133.1 ppb for acute and 120.4 ppb for chronic

r esu lting from use on dry-seeded rice (Tier I Rice modeling).

1

### 2 This conclusion is based on the following EDWC results: (1) For surface water : 13 3.1 ppb acute and 12 0 .4 ppb chronic resulting from use on dry

seeded rice ( Tier I Rice modeling) and 11.9 ppb acute and 7.4 ppb chronic from

ap p lication to crops other than rice ( Tier I FIRST modeling) ; and

(2) For ground water : 69.2 ppb acute and 51.5 p pb chronic ( PRZM

- GW modeling using WI SANDS scenario)

.

It is noted that the maximum of the previously calculated EDWCs was obtained from modeling using an older version of the current PRZM

- GW with input parameters that are different from

the current PRZM

- GW

. Table 1 contains a summar y of previous results noting that reasons for

t he revision are detailed in section II (Background), below.

Table 1 Previously calculated 1

- in

- 10

- year EDWCs for the proposed saflufenacil uses contained

in E DWC Memo dated April, 15, 2009 (DP Barcode: 349860 )

Source (Tier: Model) Peak Exposure (μg/L) Annual Mean Exposure (μg/L)

Surface water (Tier I: FIRST) 37.3 23.8 Ground water (PRZM GW) 180 173



### The above stated values represent upper

- bound estimates of total concentrations that might be found in surface water and ground wate r due to the use of saflufenacil as a herbicide on the

current /proposed use patterns. If more information or refinement is needed, please call Mohammed A. Ruhman at (703) 605

- 0644 or email: ruhman.mohammed@epa.go v



### II. BACKGROUND

Two drinking water exposure assessments were conducted :

(1) A surface/ground drinking water exposure assessment for s ection 3 new chemical uses on agricultural and non

- agricultural areas ( Appendix 1 ): This assessment reported the modeled

EDWC s for the stressor (i.e., residues of concern) in drinking water resulting labeled uses at
that time

. This assessment was based on the following :

a. L abeled uses : Christmas trees, Citrus, Conifer and hardwood plantations, Corn (field, sweet, and pop), Cotton, Fallow and post

- harvest, Grape vines, Legume vegetables, Non

agricultural areas, Pome fruits, Small grains, Sorghum, Soybeans and Sunflower;

b. F ive labels: BAS 800 04H (FiRoCrop: Saflufenacil 29.74%); BAS 804 00H (LegVeg: Saflufenacil 17.80% + Imazethapyr 50.20%); BAS 781 02H (Saflufenacil 6.24% +

Dimethenamid

- P 55.04%); BAS 800 01H (TNV: Saflufenacil 70%); and BAS 800 02H (SharpenTM: Saflufenacil 12.27%);

c. A maximum label rate consisting from a single application rate of 0.356 lb a.i/A for use on

Christmas t ree, conifer, and hardwood plantat ions and non

- agricultural areas ( SharpenTM

label ) ; d. The maximum rate of 0.356 lb a.i/A used in all surface/ground water modeling; and

e. The stressor included parent compound and it ’ s degradates M800H01, M800H02, M800H07,

M800 H08, M800H15, M800H22 ; and

### 3 f. Tier I FIRST modeling for surface water and older version of PRZM

- GW for ground water. In this respect it is noted that input parameters for the current PRZM

- GW are different

.

Reported EDWCs for this assessment is summarized in Table 2

.

Table 2 Previously calculated 1

- in

- 10

- year EDWCs for the proposed saflufenacil uses reported

in EDWC Memo dated April, 15, 2009 (DP Barcode: 349860, Appendix 1 )

Source (Tier: Model) Peak Exposure (μg/L) Annual Mean Exposure (μg/L)

Surface water (Tier I: FIRST) 37.3 23.8 Ground water (Tier II: PRZM GW) 180 173



### (2) A surface d rinking water exposure a ssessment for section 3 new chemical use on rice “Pre

plant burn

- down” ( Appendix 2 ) This assessment was based on the following:

a. Labeled use : pre

- plant/pre

- flood use on rice only ; b. A suggested label amendment ( Sharpen EPA Reg. No. 7969

- 278) ;

c. A maximum label rate consisting from single maximum application rate of 0.0445 lb a.i/A ; d. Crop

- specific use restrictions/limitations that include (1) DO NOT a pply after rice planting; (2) DO NOT i rrigate (flush) between application and rice seeding ; (3) DO NOT i nitiate

perma nent flood to rice fields until 30 days or more after planting ; and (4) DO NOT a p ply within 45 days of permanent flooding in water

- seeded rice paddies ;

e. The stressor included parent compound and it ’ s degradates M800H01, M800H02, M800H07, M800H08, M800H15, M800H22 ; and

f. Tier I Rice Model (ver. 2) modeling which allows aerobic soil degradation of the pre

- flood applied chemical in addition to partitioning and degradation in the rice paddy for the left over

chemical residues.

Reported EDWCs for this assessment is summarized in Table 3

.

Table 3 Surface water E DWCs f or the propos ed new use on ri ce as reported in EDWC Memo

dated March

, 03 , 20 11 (DP Barcode: 384975

, Appendix 2 )

Holding Time Peak (μg/L) Annual Mean (μg/L)

1

- day 45.57 41.22

3

- day 45.50 41.19

21

- day 45.04 40.78



### This current revised assessment is based on the proposed new use pattern on r ice (EPA Reg. No.

7969

- 278) 1 

### and the master label for saflufenacil formulations (EPA R eg. No. 7969

- 323 ) 2



### . Based on these two labels, this assessment took in consideration the following:

1 

### EPA Reg. No. 7969

- 278 (Sharpen ® 

### Powered by KIXOR ® 

### Herbicide) : A supplemental Label For broadleaf weed control in rice production

. 2 

### EPA Reg. No. 7969

- 323 (KIXOR ® 

### Herbicide): A broad leaf herbicide for use in field and row agricultural crops, bearing and nonbearing tree and vine crops, and in non

- crop

.

### 4 (a) The maximum application rate for all crops, includin g rice, is 0.134 lb a.i/A instead of

0.356 lb a.i/A ; (b) Changes in values for t he aerobic soil half life and partitioning coefficient (K

oc 

### ) which is

entered in the current version of PRZM

- GW (refer to Table 4 )

.

Table 4 A summary of the difference in input parameters between older version of PRZM

- GW (strikethrough parameters) and the current PRZM

- GW version (parameters in normal text).

Parameter (units) Value Source and Calculation Procedure

Soil Metabolism

Half

- life (days) 

### 6,833 90 th percentile half

- l ife using four soils with half

- life values of 987; 1,433; 1,822; and 9,613 ( MRID 47445901)

Koc (mL/g O.C) 5.9 (the

mean of the

lowest reported

K OC values)



### 24 Overall average value calculated for all of the constituents of the
stressor ( MRIDs 47127829 and 47127830) as shown in the following Table :

Stressor Constituents Soil 1 Soil 2 Soil 3 Soil 4 Soil 5

Parent 9.3 19 22 23 25

Metabolite M1 4.8 7 7.1 8.6 13

Metabolite M2 0 6.7 10 12 13

Metabolite M7 3.3 32 59 67 97

Metabolite M8 4.8 5.6 7.1 12 18

Metabolite M22 0 5.2 6.4 13 23

Overall Average 

### 24

Overall Median 

### 13

(c) The change in crop

- specific use restrictions/limitations for rice which includes:

• The pesticide can be applied to drilled, dry and water

- seeded rice;

• The 1 s t 

### application: A maximum of 0.089 lb a.i/A (0.1 kg/ha) is applied pre

- plant through pre

- emergence “within 3 days of rice planting” ;

• The 2 nd 

### application: A maximum of 0.045 lb a.i/A (0.0 5 kg/ha) is applied as a

post

- emergence weed control that may be applie d either before or after flooding only when rice has reached the 2

- leaf stage ;

• The 1 st 

### and 2 nd 

### application may be applied sequentially but the two applications should be separated by at least 14 days;

• The maximum seasonal rate should not exceed 0.134 lb a. i/A (0.150 kg/ha); and

• Water may be released from treated fields after 7

- days following th e “last?” pesticide application noting that t he life cycle of rice is assumed to be a minimum of 110 day . Thus, water is released is released after 110+7= 11 7 days wh ich is 72 days after flooding in dry

- seeded rice and 117 days after flooding in water seeded

rice

. In rice, the length for the recognized growth stages is highly dependent on variety, type of rice culture (i.e., dry or water seeded), temperature and other environmental conditions 3 

### . For example, germination occurs within two days when temperatures are between 70° to 97°F; below

3 

### Rice Growth and Development by Karen Moldenhauer and Nathan Slaton : URL http:/ / baegrisk.ddns.uark.edu/ test/ Books/ PDF/ chapter1sl3.pdf

### 5 or above this temperature, germination requires more time

. Therefore, the following variable time periods were reported for rice gr owth stages in the same reference:

• From planting

, through germination/seedling emergence

, to the 2 nd 

### leaf stage: 8

- 3 0 days ;

• From planting, through the 2 nd 

### leaf stage to the start of internode elongation (the green ring stage) : 44 to 112 days ; and

• L ife cycl e of rice cultivars in Arkansas ranges from 110 to 150 days from germination to maturity

.

In the rice label, the 2 nd 

### application ( post

- emergence weed control) may be applied before or after flooding when rice has reached the second leaf stage up to intern ode elongation. This means that the window for the second application is from 45 to 112 days after planting. However, the

label states that the minimum time intervals between the 1 st 

### and second application is 14 days

and that was the interval used in model ing.

Based on rice culture, growth stages and label specific use restrictions/limitations, the following may be stated:

(1) In dry seeded rice: the 1 st 

### application within 3 days of planting and the 2 nd 

### application within 14 days of the 1 st 

### application with f looding occurring within 30 to 45 days of planting (normal agronomic practice in dry seeded rice). (2) In water seeded rice: the 1 st 

### application within 3 days of planting and the 2 nd 

### application within 14 days of the 1 st 

### application with flooding occurring at planting (water

- seeded).

Saflufenacil and its residues (the stressor) is expected to be highly persistent in soils before flooding (t 1⁄2 ranges 987 to 9,613 days ; 6,833 days is used in modeling “ 90 th % value” ) but it is expected to be less persistent in the rice paddy after flooding (aerobic aquatic 

### t 1⁄2= 415.7 days; 1,247 days is used in modeling “3x the single value”).

Based the fate properties of the stressor and all of the label and rice agronomic practices, the following may be considered as the most co nservative exposure scenarios:

(1) For dry seeded rice: the 1 st 

### application at planting, the second application 14 days after planting and flooding at 45 days after planting; and (2) For water seeded rice: the 1 st 

### application at planting, the second application 1 4 days after planting and flooding at planting

.

### 6 

### III. D RINKING WATER EXPOSURE MODLING

1. Surface Water Modeling

a. All Crops Except Rice

The FQPA Index Reservoir Screening Tool (FIRST v1.1.1, Mar. 25, 2008; USEPA, 2008 ) was used in modeling EDWCs for drinking wat er from surface water sources. FIRST is a Tier I screening model that simulates the upper

- end exposure of the standard water body, the Index Reservoir, to pesticide residues in runoff and spray drift from an application within the standard

watershed. Peak and annual mean EDWCs are generated to estimate acute and chronic exposure. The Index Reservoir covers 5.2 hectares (ha) with an average depth of 2.74 meters (m) in a standard watershed of 172.8 ha. A more detailed description of the index reservoir wat ershed

can be found in Jones et al ., 1998. The FIRST model and user’s manual are available from the

EPA Water Models web

- page (USEPA, 2009). Input parameters, for modeling the stressor, are

summarized in Table 5 and modeling results are summarized in Tabl e 6

.

Table 5 FIRST input parameters for the total residues of saflufenacil based on the maximum

seasonal application among all use patterns

Input Parameter Value Comments Source

Application rate (lbs a.i./A) 0.134 Maximum proposed single application

rat e. Proposed label.

Number of applications per

year 1 Maximum proposed number of applications per year at the maximum proposed single application rate. Proposed label. Percent cropped area 100% Default for non

- agricultural uses. Effland et al. , 1999 Orga nic Carbon Partition Coefficient (K OC ) (L/kg OC ) 24 Refer to Table 4, above for calculation procedure MRID 47127829

MRID 47127830

Aerobic soil metabolism

half

- life (days) 6,833 Represents the upper 90% confidence

bound on the mean of four half

- lives

for th e residues of concern. MRID 47445901

Wetted in? No Not required. Proposed label.

Method of application Aerial Proposed application method of highest potential spray drift. Proposed label. Solubility in water (ppm) 2100 Solubility in pH 7 water. MRID 471 27819 Aerobic aquatic metabolism

half

- life (days) 1,247 Represents 3x the single available

half

- life for the residues of concern. MRID 47127827

Aqueous photolysis half

- life (days) 90.9 Represents the maximum environmental photo transformation

half

- life f or the residues of concern. MRID 47699901



### Table 6 FIRST modeling output (ppb).

Peak EDWC (Acute) Annual Average (Chronic



### 11.873 7.346

### 7 (b) Rice

Tier I v2.0 rice model was used to generate estimated drinking water concentrations (EDWC) of

saflufenacil res idues of concern that may occur in surface water used as drinking water. The tier

I v2.0 rice model is a modification of the same model ( v1.0). The two versions of the model rely on an equilibrium partitioning concept to provide EDWCs resulting from appli cation of pesticides to rice paddies. When a pesticide is applied to a rice paddy, the model assumes that it will instantaneously partition between a water phase and a sediment phase. Although v 1.0 of the model does not account for pesticide degradation , v2.0 accounts for degradation in the rice paddy using the aerobic aquatic half

- life. It is noted however, that both versions of the model produces the same peak concentration in water on the day of treatment and may produce similar

concentrations thereaf ter, depending on the aerobic aquatic degradation rate of the compound. Peak concentrations of rapidly degraded compounds in released tail

- water following a holding period will be lower than those produced by v1.0 of the model, as will any chronic

concent rations averaged over time.

Both versions of the model, do not account for mass transfer between the aqueous phase and the sediment, volatilization, dilution, drift or other dissipation processes. It should be stated that v01

of the model was calibrated to generate estimates that are consistent with or conservative for dissolved concentrations measured within rice paddies and in discharged paddy water. The

model was not evaluated or calibrated for concentrations measured in sediment and does not

account for residues partitions to suspended sediment. Currently, v02 of the model is considered to be a provisional model.

Due to a range of envir onmental and other factors, v01 of the rice model is expected to generate conservative EDWCs that exceed peak measu red concentrations of pesticides in water bodies well downstream of rice paddies by less than one order of magnitude to multiple orders of magnitude (USEPA, 2007b). Rice paddies are likely to be planted and harvested on or near the same date suggesting th at when paddy waters are released, an influx of saflufenacil residues from multiple locations to the waterways may be expected. Also, EDWCs are expected to be more conservative downstream of rice paddies in California and inland areas of the Southeastern U.S. where dilution is expected to occur. Tidal influences in surface waters of the coastal areas of the Southeastern United States may effectively reduce dilution of saflufenacil residues from discharged paddy water, lengthening the period of chronic saf lufenacil exposure in waterways influenced by rice paddies. In contrast, v02 of the rice model is expected to generate after peak concentrations that are lower than those generated by v01 for pesticides that are expected to degrade quickly in aquatic syste m s (short aerobic aquatic half

- lives). However, these

concentrations a re expected to be less conservative than those produced by v01 model but possibly more representative to actual conditions in the field where degradation is expected to take place. Tier I v1.0 rice model and associated users’ manuals may be downloaded from the

U.S. Environmen tal Protection Agency (EPA) w ater model s web

- page (USEPA, 2009).

E xposure was specifically assessed for the proposed use of saflufenacil on rice based on the

follo wing two conservative exposure scenarios ( refer to II (2) BACKGROUND section above for details used in identifying these two scenarios) :

### 8 (1) The first scenario f or dry seeded rice: the 1 st 

### application at planting, the second application 14 days after planting and flooding at 45 days after planting; and

(2) The second scenario f or water seeded rice: the 1 st 

### application at planting, the second application 14 days after planting and flooding at planting.

For dry seeded rice, M odeling was done in two stages:

(1) Stage 1: Field before flooding: to estimate the amount of pesticide left in the soil after the 45 day in which the rice paddy is not flooded

. The estimate was based on the aerobic soil degradation half

- life of 6,833 days for saflufenacil residues

. Stage 1 estima te that 99. 7 % of the applied pesticide was left, in the un

- flooded soil, after 45 days and two applications: one at 14 days from planting and the other after 45 days from planting ; and (2) Stage 2: Field after flooding (Rice paddy): to estimate daily concentra tions using the tier I

v2.0 rice model which takes into account degradation in the rice paddy. This degradation was based on 3 times the one aerobic aquatic half

- life of saflufenacil residues which was determined previously to equal 1,247 days (from 3 x 41 5.7). Other parameters used in modeling included: maximum application rate s (1 st 

### = 0.0 89 lb a.i/A and 2 nd 

### = 0.045 lb a.i/A,

the mean for partitioning coefficient (K

oc 

### ) = 24 L/kg, water column depth of 0 .1 meter (m)

, sediment depth of 0.01 m, sediment organi c fraction of 0.01, sediment bulk density of 1300 kg/m 3 

### , and sediment porosity of 0.509 (50.9%).

Modeling results are summarized in Table 7 , below.

Table 7 Tier I v2.0 R ice model output (EDWCs in ppb) for tail water following a 7 days holding period

S cenario Peak Annual Mean

The first scenario : dry seeded rice 13 3

. 1 12 0. 4

The second scenario for water seeded rice 1 29.8 1 17.5



### Data in Table 7 show that the maximum EDWC is 138.0 ppb for peak and 125.4 ppb for the

annual mean

.

### 9 Figure 1 Change in EECs with time following two applications in dry and water

- seeded rice (in dry seeded rice flooding is after 45 days of planting while it is at planting in water seeded rice)

### 10 

### 2. Ground Water Modeling
As per current EFED policy, ground water exposure was modeled using Tier I PRAZM

- GW

and SCI

- GROW models. Parameters used in modeling runs were as follows:

(1) Scenarios and application rates and associated parameters:

PRZM

- GW calls for using the six standard scenarios representing vulnerable ground waters,

name ly: (1) DELMARVA_STD GW, (2) FLCITRUS_STD GW, (3) FLPOTATO_STD, (4) GACOASTAL_STD GW, (5) NCCOASTAL _STD, and (6) WISANDS_STD GW. Table 8 contains a summary of the input parameters used in modeling.

Table 8 PRZM

- GW and SCI

- GROW input parameters used for modeling saflufenacil

Parameter (units) Input Values

Data Source/Comments PRZM

- GW SCI

- GROW

Application Rate 0.150 Kg a.i/H a 0.134 lb a.i/A Suggested amendment to label: maximum rate is changed from 0.356 to 0.134 lb a.i/A

Hydrolysis Ha lf

- life Stabl e N/A MRID 47127823

Soil Metabolism

Half

- life (days) 6,833 1,628 90 th percentile half

- life for PRZM

- GW and

median half

- live for SCI

- GROW using four

soils with half

- life values of 987; 1,433; 1,822; and 9,613 ( MRID 47445901)

CAM (chemical Application M odel) 2 N/A As per guidance 1

Koc (mL/g O.C) 24 13 Average for PRZM

- GW and Median for

SCI

- GROW ( MRIDs 47127829 and

47127830 refer to Table 4 , above)

1 URL: http:// www.epa.gov/oppefed1/models/water/przm_gw/wqtt_przm_gw_guidance.htm



### Modeling results are summarized in Figure 2 for PRZM

- GW and Table 9 for SCI

- GROW and

PRZM

- GW

.

### 11 Figure 2 PRZM

- GW estimated drinking water concentrations (EDWCs μg/L 

### ) in ground water

res ulting from the stressor (total toxic residues of saflufenacil)

10 15 20 25 30 35 40 45 50 55 60 65 70 75

7

- Dec 6

- Jan 5

- Feb 7

- Mar 6

- Apr 6

- May 5

- Jun 5

- Jul 4

- Aug 3

- Sep 3

- Oct 2

- Nov 2

- DecEDWC (ppb)

Application Date 

### Highest Daily EDWCs Values

WI SANDS NC COASTAL DELMARVA

FL CITRUS FL POTATO GA COASTAL

### 12 Table 9 PRZM

- GW and SCI

- GROW estimated drinking water concentrations (EDWCs μg/L 

### ) in ground water resulting from the stressor (total toxic residues of saflufenacil)

PRZM

- GW SCI

- GROW

A

pplication

Dates Scenario* Highest Daily

Value Post Breakthrough Average Average Simulation Breakthrough Time
(Days/Years) Peak and Average

Mar 15 DELMARVA_STD 42.4 27.5 413.5849 (1.1)



### 160 ppb

SCI

- GROW

was developed using K OC 

### values ranging from

32

- 180 mL

g OC - 1 

### and

half

- lives

from 13

- 1000 days. Extrapolation beyond these

values will

increase the uncertainty of the ground

water
concentration . Therefore,

the results for this modeling

exercise are

not used in

this risk

assessment Mar 15 FLCITRUS_S TD 38.8 27.1 432.3471 (1.2 )

Mar 15 FLPOTATO_STD 28.4 19.2 749.658 (2 .1)

Mar 15 GACOASTAL_STD 19.7 15.2 1380.526 ( 3.8 )

Mar 15 NCCOASTAL_STD 39.6 30.9 1247.013 ( 3.4 )

Mar 15 WISANDS_STD 67.3 48.7 1248.434 ( 3.4 )

Apr 15 DELMARVA_STD 43 27.6 413.5849 (1.1)

Apr 15 FLCITRUS_STD 39.3 27.2 432.3471 (1.2 )

Apr 15 FLPOTATO_STD 28.1 19.2 749.658 (2 .1)

Apr 15 GACOASTAL_STD 19.6 15.3 1380.526 ( 3.8 )

Apr 15 NCCOASTAL_STD 39.6 30.8 1247.013 ( 3.4 )

Apr 15 WISANDS_STD 69.2 51.5 1248.434 (3.4)

Jan 15 DELMARVA_STD 44.2 27.4 413.5849 (1.1)

Jan 15 FLCITRUS_STD 40.9 27 432.3471 (1.2 )

Jan 15 FLPOTATO_STD 27.8 19.2 749.658 (2 .1)

Jan 15 GACOASTAL_STD 19.8 15.3 1380.526 ( 3.8 )

Jan 15 NCCOASTAL_STD 38.7 31.2 1247.013 ( 3.4 )

Jan 15 WISANDS_STD 62 .2 46.2 1248.434 ( 3.4 )

Jul 15 DELMARVA_STD 43.6 27.1 413.5849 (1.1)

Jul 15 FLCITRUS_STD 43.8 26.9 432.3471 (1.2 )

Jul 15 FLPOTATO_STD 26.4 19.2 749.658 (2 .1)

Jul 15 GACOASTAL_STD 20.2 15.2 1380.526 ( 3.8 )

Jul 15 NCCOASTAL_STD 40.3 30.8 1247.013 ( 3. 4 )

Jul 15 WISANDS_STD 68 51 1248.434 (3.4 )

Jun 01 DELMARVA_STD 42.1 27.5 413.5849 (1.1)

Jun 01 FLCITRUS_STD 40.5 26.1 432.3471 (1.2 )

Jun 01 FLPOTATO_STD 27.4 19.2 749.658 (2 .1)

Jun 01 GACOASTAL_STD 19.8 15.3 1380.526 ( 3.8 )

Jun 01 NCCOASTAL_STD 39.7 30.7 1247.013 ( 3.4 )

Jun 01 WISANDS_STD 68.2 51.2 1248.434 ( 3.4 )

May 15 DELMARVA_STD 43 27.5 413.5849 (1.1)

May 15 FLCITRUS_STD 40.1 27.4 432.3471 (1.2 )

May 15 FLPOTATO_STD 28.2 19.2 749.658 (2 .1)

May 15 GACOASTAL_STD 19.8 15.3 1380.526 ( 3.8 )

May 15 NCCOASTAL_STD 39.9 30.7 1247.013 ( 3.4 )

May 15 WISANDS_STD 69 51.2 1248.434 (3.4 )

Oct 15 DELMARVA_STD 40.4 26.6 413.5849 (1.1)

Oct 15 FLCITRUS_STD 42 26.2 432.3471 (1.2 )

Oct 15 FLPOTATO_STD 29 19 749.658 (2 .1)

### 13 PRZM

- GW SCI

- GROW

A

pplication

Dates Scenario* Highest Daily

Value Post Breakthrough Average Average Simulation Breakthrough Time
(Days/Years) Peak and Average

Oct 15 GACOASTAL_STD 19.8 1 5.2 1380.526 ( 3.8 )

Oct 15 NCCOASTAL_STD 39.9 30.6 1247.013 ( 3.4 )

Oct 15 WISANDS_STD 64.4 50.3 1248.434 ( 3.4 )

Sep 15 DELMARVA_STD 40.3 26.8 413.5849 (1.1)

Sep 15 FLCITRUS_STD 42.9 26.2 432.3471 (1.2 )

Sep 15 FLPOTATO_STD 27.5 19.1 749.658 (2 .1)

Sep 15 GACOASTAL_STD 19.7 15.2 1380.526 ( 3.8 )

Sep 15 NCCOASTAL_STD 39.9 30.6 1247.013 ( 3.4 )

Sep 15 WISANDS_STD 65 50.8 1248.434 (3.4 )

Nov 15 DELMARVA_STD 41.3 26.5 413.5849 (1.1)

Nov 15 FLCITRUS_STD 42.2 26.3 432.3471 (1.2 )

Nov 15 FLPOTATO_STD 28 .2 19 749.658 (2 .1)

Nov 15 GACOASTAL_STD 20.1 15.2 1380.526 ( 3.8 )

Nov 15 NCCOASTAL_STD 39.1 30.6 1247.013 ( 3.4 )

Nov 15 WISANDS_STD 65.2 50 1248.434 (3.4 )



### Data in Table 9 show that the maximum EDWC is 69.2 ppb for peak and 51.5 ppb for the post

bre akthrough average with an average breakthrough time of 3.4 years.

LITERATURE CITATIONS

USEPA. 2009. Water Models. U.S. Environmental Protection Agency, Pesticides: Science and Policy. Last updated: Apr 23, 2008. Online at: http://www.epa.gov/oppefed1/models/water/

USEPA. 2007b. Bradbury, S. Guidance for Tier I Estimation of Aqueous Pesticide Concentrations in Rice Paddies. U.S. Environmental Protection Agency, Office of Prevention, Pestic ides and Toxic Substances, Environmental Fate and Effects Division. Internal Memorandum. May 8, 2007.