1 Exposure Modeling Public Meeting ( EMPM )
March 19 , 201 3 Agenda and Abstracts

Time Presentation Number and Title Presenter (s)

9:00

– 9:10 Welcome and Introductions Marietta Echeve r ria, Gabe
Rothman , and Jim Carleton

9:10

- 9:20 Opening Remarks Don Brady EPA Updates and Presentations

9:20

– 9: 45 PRZM GW: Implementation and Case Studies Reuben Baris , Michael Barrett, Rochelle Bohaty, Marietta Echeverria, Dirk Young, and
James Wolf

9:45

– 10: 10 Surface Water Calculator Dirk Young

10:10

– 1 0 : 35 Rice Modeling: A Case Study Chuck Peck

10: 35

– 1 0 : 45 Break

10:45

– 11:10 Status of Drinking Water Intake Watershed PCA Development Project J im Carleton

11:10

– 11:35 Spatial Aquatic Model (SAM) Pilot Project Nelson Thurman

11:35

– 12:00 Audrey III

– A Tier II Plant Exposure Estimation Tool R. David Jones, Chuck Peck, and Frank Farruggia

12:00

– 1:0 0 Lunch

Public Presentations

1:0 0

– 1:3 0 Implementation of Vegetative Buffer Strip Effectiveness in Removing Pesticides in Regulatory

Assessments Bjoern Roepke, Russell L. Jones, and George Sabbagh

1:30

– 2:0 0 iSTREEM®

– A Web

- Based River Ch emical

C oncentration E stimation M odel Xinhao Wang and Paul DeLeo

2:0 0

– 2: 30 M onitoring and Modeling the Fate and Transport of a
Pesticide Metabolite from Groundwater Recharge to Drinking Water R. Sur , T. Oertel, M. Himml,
and G. Görlitz

2:30

– 2:4 5 Break

2:45

– 3:15 Development and Validation of an Approach for Modeling Pyrethroid Residues in Urban Streams Michael Winchell, Scott Jackson, and Gary Mitchell

3:15

– 3:45 Evaluation of a Simplified SWAT Model Approach for
Prediction of Insecticide Concentrations in a Small Watershed in Northwestern Oregon Natalia Peranginangin, Michael

F . Winchell, and Solomon Folle

3:45

– 4:00 Meeting Wrap

- Up2 

## Abstracts

1. PRZM GW: Implementation and Case Studies Reuben Baris, Michael Barrett, Rochelle Bohaty, Marietta Echeverria, Dirk Young,
James Wolf
Environmental Fate and Effects Division. United States E nvironmental Protection Agency

The Pesticide Root Zone Model for Groundwater (PRZM

- GW) was developed by U.S. EPA as a regulatory model to estimate pesticide concentrations in drinking water for vulnerable groundwater supplies. PRZM

- GW permits assessment of multiple years of pesticide use and is being used by U.S. EPA’s Office of Pesticide Programs to conduct standard screening (Tier I) and refined (Tier II) drinking water assessments. Input parameters for PRZM

- GW include pesticide fate properties, environmental factors such as soil type, aquifer depth and weather, and ag ronomic practices, including application method, timing, and frequency of application. PRZM

GW output data include peak and time

- weighted drinking water concentrations. This presentation will review the conceptual model and model evaluation, including

com parisons to water monitoring data. The presentation will also discuss the implementation of PRZM

- GW for screening and refined drinking water assessments. Case studies will be presented to illustrate how PRZM

- GW is being used in drinking
water assessment s.

2. Surface Water Calculator Dirk Young Environmental Fate and Effects Division. United States Environmental Protection Agency

EFED will soon release a new Surface Water Calculator (SWC) that will replace PE5 and EXPRESS. The new SWC will include a new version of PRZM (PRZM5), an EXAMS replacement (the VVWM), and a new user interface. These programs will retain the most user

- requ ested features of the older programs, implement bug fixes, and improve maintainability. PRZM5 is upgraded to 100% standard Fortran 2003

-- no compiler

- specific extensions and no obsolete functions such as goto exist in PRZM5. PRZM5 eliminates non

- working, co nceptually problematic, unused, and redundant routines such as Monte Carlo, MOC, VADOFT, Nitrogen Simulation, biphasic degradation, and lateral flow. In a subtle but major revision, the time loop has been streamlined to a single daily loop from the old PRZ M convoluted looping system that involved an inner day loop, a middle year loop, and an outer month loop. The VVWM is a close replica of the two

- compartment subset of EXAMS, with the exception that VVWM has an option for changing the water body volume as a result of water inputs and outputs. Finally, the user interface was designed by developers with first

- hand knowledge of the way that EPA performs pesticide risk assessments and will be intuitive in its operation and installation.3 3. Rice Modeling: A Case S tudy Chuck Peck Environmental Fate and Effects Division. United States Environmental Protection Agency

EFED uses the Tier I rice model, which employs a pesticide’s application rate and adsorption coefficient, to develop estimated environmental concentrations (EECs) and estimated drinking water concentrations (EDWCs). While this model is useful for screening pesticides that are not harmful to human health or ecological receptors, it is not effective in refining estimates when risks of concern ar e triggered or for estimating chronic concentrations. Over the past few years, EFED has developed the Pesticide Flooded Application Model (PFAM) to refine aquatic exposure assessment for applications to rice or other flooded agricultural crops.
PFAM add s the capability to account for water and pest management practices, degradation in soil and aquatic environments, as well as post processing of discharged paddy waters to a stream, index reservoir, farm pond, or other user

defined receiving water. We will report on a case study of a drinking water exposure assessment for an herbicide applied to rice, which explores the use of PFAM and other approaches in an effort to refine chronic drinking water exposure estimates. This presentation will highlight the ca se study, the methods used to develop EDWCs, and the updates made to PFAM.

4. Status of Drinking Water Intake Watershed PCA Development Project Jim Carleton Environmental Fate and Effects Division. United States Environmental Protection Agency

EFED uses percent cropped area (PCA) adjustment factors in its drinking water assessments to account for the fact that watersheds supporting surface drinking water sources may not be devoted entirely to crop agriculture. The first PCAs were based on cropped acreage s initially within 8

- digit HUCs (USGS Hydrologic Unit Code “cataloguing units”). Acting in collaboration with USGS, EFED has recently developed a dataset of 4,840 quality

- assured watersheds for the locations of drinking water intakes that supply community water systems in the United States with raw water. EFED has developed and validated PCAs for these watersheds, compared them against existing HUC

- based PCAs, and evaluated their use in modeling through comparisons of PCA

- modified PRZM/EXAMS results again st available pesticide monitoring data. This talk will provide an update on, and overview of the results of this project.4 5. Spatial Aquatic Model (SAM) Pilot Project

Nelson Thurman
Environmental Fate and Effects Division. United States Environmental Protection Agency

A key question pesticide aquatic exposure assessments need to address is whether a pesticide, when used a ccording to its label, will occur in water at concentrations that may adversely impact human health or aquatic species and, if so, how often and where will these impacts likely to overlap with the populations at risk.

In order to improve current aquatic exposure assessments without increasing the workload for the risk assessor, EFED is developing a Spatial Aquatic Model (SAM). SAM will use mappable data and model routines to automate the scenario

- building and modeling steps, allowing EFED risk assessors to more effectively and effic iently characterize the spatial extent of any areas that may exceed levels of concern for a pesticide use. Such areas could be matched to drinking water intakes (for human health) or habitat (for aquatic species) to inform risk management decisions.

The current pilot project will incorporate spatial variability in hydrology, soil, land use, crop, agricultural practices, and climate

- related parameters. Results of this regional pilot will be used to inform the development of a national spatial aquatic model . The framework for the expanded model will allow incremental updates to EFED’s current aquatic modeling framework in order to incorporate better data and modeling routines as they become available.

Ultimately, SAM will be a desktop or web application c apable of estimating pesticide concentrations in water for use in regulatory purposes, as well as exploring risk mitigation options. The model will be amenable to methods for automating data input and for providing outputs in terms of summary tables and ma ps as needed. The automated process will allow risk assessors to devote more time to analyzing and characterizing results and working with risk managers to evaluate mitigation options
as needed.

This presentation will provide an overview of the goals, conceptual approach, inputs, and expected outputs for a regional pilot underway to develop a working version of
SAM.

6. Audrey III

– A Tier II Plant Exposure Estimation Tool R. David Jones , Chuck Peck, and Frank Farruggia5 Environmental Fate and Effects Divisi on. United States Environmental Protection Agency

This presentation will discuss the current progress toward a replacement for the Agency’s existing plant exposure model TerrPlant . Audrey III will be built into the Agency’s new PRZM

- EXAMS modeling shell and will rely on the same scenarios used for aquatic exposure assessment. Like TerrPlant, it will generate exposure estimates for plants in both terrestrial and semi

- aquatic habitat s. Conceptual models for both environments will be presented. The terrestrial conceptual model is based on a Plant Exposure Zone (PEZ), whose width is determined by distance from the edge of field traveled by overland flow and whose depth is determined by the plant root zone. Exposure will be estimated for loading from runoff, eroded sediment, and spray drift; exposure outside the PEZ will be estimated for spray drift only. For semi

aquatic environments, concentrations will be estimated using VVWM (Variabl e Volume Water Model) using a shallow wetland.

7. Implementation of Vegetative Buffer Strip Effectiveness in Removing Pesticides in Regulatory Assessments Bjoern Roepke, Russe ll L. Jones, and George Sabbagh Bayer CropScience

During the past decade signifi cant advances have been made in the modeling of pesticide removal by vegetative buffer strips. Several models have been developed and tested. Comparisons of model predictions with measured data have also been performed. In the U.S. interest in such mode ling effectiveness of buffer strips for pesticide removal has been shown by registrants and regulators, but such modeling has not yet been incorporated into regulatory risk assessments. In Europe modeling of buffer strip effectiveness has been included in to mitigation incorporated into surface water risk assessments. This paper will review the developments in modeling of pesticide removal by vegetative buffer strip and the development of scenarios and software tools for implementing vegetative buffer stri p modeling in European assessments.

8. iSTREEM®

– A Web

- Based R i ver Chemical Concentration Estimation Model Xinhao Wang 1 and Paul DeLeo 2

1 University of Cincinnati

2 American Cleaning Ins titute

iSTREEM ® is a web

- based computer model that predicts the concentration of chemicals used in ‘down

- the

- drain’ products, such as consumer use pesticides, in the effluent of more than 10,000 wastewater treatment plants throughout the continental United States, their resultant mixing zones, riverine concentrations and drinking water intake concentrations downstream of wastewater discharges. The model has been scaled at both the national level (e.g., approximately 30,000 river reaches covering over 200,000 river miles ) and at the regional/watershed scales (e.g., Trinity River, TX; Willamette River, OR). The model permits exposure6 estimates to humans or ecological receptors from ingredients used in consumer products.

iSTREEM ® is a valuable new tool being made available to the public at no cost by the American Cleaning Institute to promote product stewardship and regulatory compliance for chemical suppliers and manufacturers of formulated products of all sizes. For more infor mation about iSTREEM®, go to: http://www.aciscience.org/iSTREEM.aspx

.

9. Monitoring and Modeling the Fate and Transport of a Pesticide Metabolite from Groundwater Recharge to Drinking Water
R. Sur 1 , T. Oe rtel 2 , M. Himml 3 , G. Görlitz 4

1 Bayer CropScience LP, Environmental Safety

2 Water Works

3 GEOBIT

4 Bayer CropScience AG, Environmental Safety

The duration and extent of future drinking water exposure was investigated for a pesticide metabolite caused by long

- time application of a plant protection product in
an orchard within the catchment area of a water works from 1993 to 2006. The leaching of the metabolite into groundwater under the orchard was calculated
with the 1

- dimensional leaching model PEARL based on the actual pesticide use history and using local soil and weather data for model parameterization. The further dilution during transport in the aquifer to the drinking water abstraction point was simulated using a 2

- dimensional modeling approach a pplying HYDRUS

- 2D. Horizontal hydraulic conductivities in the aquifer for model input were experimentally
determined across the catchment.

Monitoring results from several wells within the catchment confirm the results of the simulations. In total, a tran sfer factor of ca. 20 between the concentration of the metabolite in groundwater recharge and in raw water for drinking water production was calculated. The drinking water exposure is predicted to remain constant until 2015 and to terminate by 2025.

10. Devel opment and Validation of an Approach for Modeling Pyrethroid Residues in Urban Streams Michael Winchell, Scott Jackson, and Gary Mitchell Stone Environmental Inc.

Pyrethroid insecticides have been detected in urban waterways throughout California and other regions. Modeling pyrethroid environmental fate in a residential setting can help us to better understand the sources, transport pathways, and mitigation strategi es for reducing environmental concentrations of pyrethroids. Currently, there is not a standard modeling approach for estimating environmental7 concentrations of pesticides in an urban environment. One modeling approach is to adapt an urban water quality m odel, the Storm Water Management Model (SWMM) to serve this purpose. To test the suitability of SWMM in predicting urban pesticide exposure, the model was applied to a heavily developed residential neighborhood in southern California. This neighborhood was modeled because of the data available from monitoring of flow and pyrethroid concentrations conducted there over a several year period. One of the primary inputs to the model, the wash

- off characteristics of the pyrethroid, were calibrated to observed plo t

- scale data for both impervious and pervious turf surfaces. A statewide survey regarding the spatial and temporal patterns of pyrethroid applications was used in structuring the SWMM model to allow realistic application variability throughout the neighbor hood. Because of their direct effects on “dry weather” wash

- off and storm drain residues, residential outdoor water use practices represented another important component to the model structure and parameterization. The hydrologic component of the model was calibrated to 1 years’ worth of hourly flow data measured from a stormwater outfall draining the neighborhood. Pyrethroid samples from both storm and non

- storm periods were compared with the SWMM model predictions to assess the model performance. This pre sentation will report on the model development, calibration results, and the potential for utilizing this modeling approach as part of a standardized risk assessment process and as a tool for evaluating the potential benefits of best management practices.

11. Evaluation of a Simplified SWAT Model Approach for Prediction of Insecticide Concentrations in a Small Watershed in Northwestern Oregon Natalia Peranginangin 1 , Michael F. Winchell 2 , and Solomon Folle 3

1 Syngenta Crop Protection, LLC

2 Stone Environmental, Inc.

3 University of Minnesota

The need for a modeling approach to estimate pesticide concentrations in flowing water bodies has become increasingly important due to the endangered species assessment process. To address this need, a modeling approach using the Soil and Water Assessment Tool (SWAT) was developed and tested for a widely used corn herbicide on 30 watersheds across the corn belt and southern US. The assessment evaluated the ability of SWAT to predict pesticide concentration distributions using a simplified parameterization approach. The encouraging results from this study led to the application of the methodology to an insecticide in a different geographic region, Northwest Oregon. In stark contrast to the original watersheds studied, the Oregon watershed modeled included heterogeneous cropping patterns with a more variable pesticide use pattern. Simulation results from the Northwest Oregon watershed will be presented.