Exposure Modeling Public Meeting

(EMPM)

03-24-14

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Karen Milians, 

Meridith Fry, and Dirk Young
Background

Quality Control (QC) Testing Plan 

PE5 vs. SWCC

QC Testing Results

Conclusions

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EXposure Analysis Modeling System 

(EXAMS, Vers. 2.95)

Variable Volume Water Model 

(VVWM)

PE5

Pesticide Root Zone Model 

(PRZM 5)

GUI

Pesticide Root Zone Model 

(PRZM 3, Vers. 3.12)

Surface Water 

Concentration Calculator 

(SWCC)

USEPA, 2013. Young, D. PRZM5 Manual; USEPA, 2013. Variable Volume Water Model. 3
USEPA, 2013. Young, D. PRZM5 Manual; USEPA, 2013. Variable Volume Water Model.

 SWCC allows more flexibility, user features and 

characterization as well as correcting bugs and eliminating 

inefficiencies

 SWCC will “behave" like PE5

 Easier to maintain in house

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 SWCC output should be similar to equivalent PE5 output

 Modifications are justifiable

 Debugged routines (e.g. Erosion, Runoff Parent/Degradate)

 GUI catches errors and program does not crash

 Documentation is clear and adequate

 Overall the SWCC must be easy to use, and intuitive in its 

execution

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PRZM Scenario Chemical EXAMS scenario

IL corn Atrazine1 Index reservoir

IL corn Fipronil2 Eco

IL corn Captan3 Index reservoir

IL corn X4 Index reservoir/Eco

Criteria

1Relatively persistent herbicide with low sorption. 

2Moderately persistent insecticide with moderate sorption.

3Fungicide with rapid degradation and low sorption.

4Relatively immobile compound.

WQTT Advisory Note: Standard Approach for Quality Control (QC) Reviews of PRZM/EXAMS Interfaces and Models. Dated: September 15, 2008.

Other scenarios tested:

• CA citrus

• MS cotton

• CA lettuce

• FL carrot

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0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

Atrazine Fipronil Captan Chem X

Peak

4 day

21 day

60 day

Output value from SWCC

Output value from PE5

Ratio = 

Criteria

Atrazine - Relatively persistent herbicide (304 days) with low sorption (88 L/kg). 

Fipronil - moderately persistent insecticide (33.7 days) with moderate sorption (727 L/kg).

Captan - fungicide with rapid degradation (3.75 days) and low sorption (200 L/kg).

Chemical X - moderately persistent (54 days) and immobile compound (4751300 L/kg). 7
More Impact 

Method of Calculating Chronic Concentration 

Degradate Fix

T-Band Application Fix

High Koc input value

Less Impact 

Curve Number Implementation 

Erosion Correction

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Concentration of pesticide 

in water (ppb)

Day 1 Day 2

PE5 chronic values

Day 3

SWCC chronic values

Captan

CA lettuce

Water 

concentration

PE5

(ppb)

SWCC

(ppb)

1-in 10 Peak 6.54 6.54

1-in 10 4 day 5.43 0.570

1-in-10 21 day 2.82 0.109

9 1-in-10 60 day 1.13 0.0380
0

1

2

3

PARENT WC (kg/m3)

DEG1 WC (kg/m3)

Concentration (kg/m3)

•Mass Balance Analysis

•Fundamental parameters were 

isolated

•Stable degradate

•Aqueous Aerobic Metabolism halflife of 365 days. 

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Parameter PE5 SWCC

Henry’s Law Constant value (HLC) Yes No

Temperature at which degradation 

applies

Assume 25oC Not only 25oC

Photolysis Reference Latitude (o) Assume 40 Not only 40

Chemical Application Method (CAM) 1,2,3, ... Presented slightly different 

but similar capabilities 

Degradates No capabilities Sequential only

Pond/IR Only one at a time Run both simultaneously 

Weather parameter Hidden Presented when running the 

model 

Output report Input and output 

values (notepad)

Input/output values are 

tabulated in tables, graph 

with the modeled results and 

characterization in the water 

body (Word doc)

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 SWCC output should be similar to equivalent PE5 output

 When not equal an explanation was provided

 Modifications are justifiable

 Changes were documented and reviewed by WQTT

 Debugged routines

 Erosion, Runoff, Parent/Degradate, Spray Drift, T-band application, 

high Koc input value

 GUI catches errors and program does not crash

GUI captured all errors and did not crash

 Documentation is clear and adequate

PRZM5, VVWM and user manual were reviewed by the Team

 Overall the SWCC must be easy to use, and intuitive in its execution

 The team reported SWCC is easy to use 12
SWCC has been pushed in EFED’s computer

Evaluation period six months was recommended 

with revision as needed

Tier I scenario will be developed

Public releases is imminent 

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