# Environmental Modeling Public Meeting

September 20, 2011 Rochelle F. H. Bohaty, PhD Office of Chemical Safety and Pollution Prevention

Office of Pesticide Programs Environmental Fate and Effects Division

1 Disclaimer: Views expressed in this presentation are those of the presenter and may not represent EPA’s current thinking or policy.

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## Background  

## Conceptual Model  

# Model Selection  Field Studies  

## Evaluation  Monitoring Programs  

# Implementation ◦ Project Schedule

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### Vulnerable private drinking water wells in the vicinity of agricultural environments  

### The conceptualization of the groundwater scenario evolved from meetings between EPA and PMRA and from advice taken from the 2005 N-Methyl Carbamate SAP meetings (USEPA, 2005a, 2005b). 4

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## 22 models were considered in primary screen ◦ Considerations included:  familiarity with and scope of the model  knowledge of programming language  continued technical support  public access  runtime 

###  reviewability  

## Three finalist models were identified ◦ Pesticide Emission Assessment at Regional and Local Scales (PEARL) 

## ◦ Pesticide Root Zone Model (PRZM) ◦ Leaching Estimation and Chemistry Model (LEACHM)

56 

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## Acceptable studies  

## Areas susceptible to leaching  

## Use of tracer  

# Sampling: soil cores, pore water, and groundwater  

## Temperature probes7 

## Field- scale leaching studies/prospective groundwater studiesMeasured Soil Temperature LEACHM PRZM PEARL

89

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## Models performed similar for soils prone to leaching  

## Additional screening required

10 

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# Selection of Pesticide Root Zone Model (PRZM) ◦ EPA and PMRA currently use PRZM for modeling runoff ◦ PRZM uses a capacity type algorithm for water flow rather than the more complex Richard’s Equation 

## ◦ EPA maintains PRZM ◦ PRZM is freely available11

0.001 0.01 0.1 1 10 100 1000 10000 100000

0.001 0.01 0.1 1 10 100 1000 10000 PREDICTED

NAWQA OBSERVED CONCENTRATION (PPB) 

### Florida Citrus 

## Water Monitoring Data Comparison: non-targeted12

Pesticide Peak

NAWQA Concetration (PPB) Hydrolysis t1/2

(days) Aerobic t1/2

(days) Koc Malathion 0.1 6.21 3 151 Carbaryl 0.781 12 12 198 Azinphos -methyl 0.18 37 95 700 Chlorpyrifos 0.07 72 76.9 6070 Propanil 0.21 Stable 0.5 487 Thiobencarb 0.036 Stable 40 909 Ethalfluralin 0.09 Stable 138 4000 Dacthal 10 Stable 20 5000 Trifluralin 0.15 Stable 219 7300 Benfluralin 0.006 Stable 65 10750 Pendimethalin 0.12 Stable 172 20000 Actual hydrolysis rate is slower than modeled hydrolysis rate. • pH dependent Modeled rate was faster than environmental metabolism, • lab rate faster than environmental rate • lack of data Mobility in soil is faster than model simulation • Preferential flow • Micro particle transport 

### Other factors?? Use scenarios13

Milestone/Specific Task Due Date Final Report (joint with PMRA) Under Peer Review (with PMRA) Attachment 1: Scenario Development Guidance (joint with PMRA) Completed Attachment 2: Chemical Input Parameter Guidance (joint with PMRA) Completed Guidance for use of PRZM- GW in Drinking Water Assessments (EPA specific) In progress User guidance for PRZM- GW/ PRZM- GW GUI (EPA specific) In progress Implementation and Director’s Approval Late Fall 201114 

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## EFED is working with HED on determining appropriate “standard” exposure durations for model outputs15 

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## EFED is working on identifying scenarios for standard use in risk assessment  

## EFED is incorporating mitigation measures
—i.e. less vulnerable soils, greater depth to groundwater, well setbacks, etc.
—into user guidance 

## EPA Project Team ◦ Reuben Baris ◦ Michael Barrett 

### ◦ Rochelle Bohaty ◦ Dirk Young ◦ James Wolf  

## PMRA Project Team ◦ Greg Malis ◦ Ian Kennedy  

## WQTT Management Representative ◦ Marietta Echeverria  

## WQTT Science Advisors ◦ Jim Hetrick ◦ Nelson Thurman  

## WQTT Co- chairs ◦ Rochelle Bohaty ◦ Andrew Shelby 16