AGENDA

U.S. ENVIRONMENTAL PROTECTION AGENCY (EPA) 

FIFRA SCIENTIFIC ADVISORY PANEL (SAP) 

OPEN MEETING 

SEPTEMBER 15 - SEPTEMBER 17, 2015

FIFRA SAP WEB SITE http://www.epa.gov/scipoly/sap/ 

DOCKET NUMBER: EPA–HQ–OPP–2015–0424

U.S. ENVIRONMENTAL PROTECTION AGENCY

CONFERENCE CENTER LOBBY LEVEL

ONE POTOMAC YARD (SOUTH BLDG.)

2777 S. CRYSTAL DRIVE, ARLINGTON, VA 22202

Development of a Spatial Aquatic Model (SAM) for Pesticide Assessments

Please note that all times are approximate (see note at the end of the Agenda).

Day 1 

Tuesday, September 15, 2015

9:00 A.M. Opening of Meeting and Administrative Procedures -- Fred Jenkins, Ph.D.,

Designated Federal Official, Office of Science Coordination and Policy, EPA 

9:05 A.M. Introduction and Identification of Panel Members – Stephen Klaine, Ph.D., 

FIFRA Scientific Advisory Panel Chair 

9:10 A.M. Welcome and Opening Remarks – James Cowles, Ph.D., Deputy Division 

Director, Environmental Fate and Effects Division, Office of Pesticide Programs (EFED, OPP), 

EPA

9:20 A.M. Background, Objectives, and Conceptual Model – Nelson Thurman, M.S., 

Environmental Fate and Effects Division, Office of Pesticide Programs EPA

9:45 A.M. Model Components – Meridith Fry, Ph.D., Environmental Fate and Effects 

Division, Office of Pesticide Programs EPA

10:30 A.M. Break

10:45 A.M. Data Inputs – Michelle Thawley, M.S., Environmental Fate and Effects Division, 

Office of Pesticide Programs, EPA

11:45 A.M. Lunch 
1:00 P.M. Accounting for Time of Travel – James Carlton, Ph.D., Environmental Fate and 

Effects Division, Office of Pesticide Programs), EPA

1:45 P.M. Defining Likely Pesticide Application Window – Paul Mastradone, Ph.D., 

Environmental Fate and Effects Division, Office of Pesticide Programs, EPA

2:30 P.M. Break

2:45 P.M. Wrap-up -- Nelson Thurman, M.S., Environmental Fate and Effects Division, Office 

of Pesticide Programs, EPA

3:00 P.M. Public Comments 

4:30 P.M. Adjourn

Day 2 

Wednesday, September 16, 2015

9:00 A.M. Opening of Meeting and Administrative Procedures – Fred Jenkins, Ph.D.,

Designated Federal Official, Office of Science Coordination and Policy, EPA 

9:05 A.M. Introduction and Identification of Panel Members – Stephen Klaine, Ph.D., 

FIFRA Scientific Advisory Panel Chair

9:10 A.M. Public Comments Continued

10:00 A.M. Charge to Panel

Question 1. The conceptual watershed model for the Spatial Aquatic Model (SAM) accounts for 

spatial and temporal variability in soil, land cover, weather, and crop/management inputs and 

integrates outputs at watershed pour points by area-weighting. 

a. Please discuss the strengths and limitations of the conceptual watershed model for 

representing spatial and temporal variability in pesticide concentrations in water. 

b. Please comment on how clearly this conceptual approach is explained. What additional 

documentation, description, and/or characterization is necessary to ensure clarity and 

transparency?

10:45 A.M. Break
11:00 A.M. Charge to Panel

Question 2. Please comment on the model organization and improvements to model code.

a. SAM is organized into three components (scenario generator, hydrology, and calculator) 

to reduce redundant calculations, increase model efficiency, and make use of preprocessing for creating standalone scenarios and hydrology (Section 2.1). USEPA OPP 

found this to be the best approach for handling the large quantity of the spatial and 

temporal inputs, while preserving the user’s ability to run unique simulations every time. 

Please comment on the separation of independent processes (e.g., hydrology, pesticide 

transport) to maximize computational efficiency and minimize user run-time.

b. USEPA OPP has improved the PRZM model code to eliminate inefficiencies and 

excessive calculations. For example, simplifying the soil into a single surface layer, as 

described in Section 2.1.1, increased computational time by 10-fold with negligible 

change in results. Please comment on this general approach to improve the model’s 

speed and efficiency without sacrificing accuracy and provide any additional 

recommendations for improving model efficiency. 

12:15 P.M. Lunch

1:15 P.M. Charge to Panel

Question 3. Section 2.3 describes initial model evaluation steps for SAM to evaluate model 

uncertainty, sensitivity, and performance in comparison to measured (monitoring) data. 

Additional model evaluations occur in Sections 4.4 and 5.3. 

a. What additional sensitivity analyses would the SAP recommend for model evaluation?

b. Current model evaluation compared SAM estimates to available atrazine monitoring data 

collected at daily to weekly intervals. Given the importance of robust, frequently-sampled 

monitoring data for evaluation, what additional monitoring or other types of data are 

currently available to test and evaluate how well SAM meets EPA objectives of 

transparent processes and clear, consistent, and reasonable products for risk 

assessments and risk characterization?

2:30 P.M. Break

2:45 P.M. Charge to Panel

Question 4. To substantially lessen the number of scenarios and improve computational speed of 

the model, USEPA OPP evaluated the option of grouping soil map units into classes based on 

factors that have the greatest impact on pesticide loss due to runoff and erosion (USDA water 
quality index, described in Section 3.3). A comparison of runoff volume, pesticide mass, and 

pesticide concentration outputs showed little difference between the two approaches. Please 

comment on any implications for using soil grouping classes for watershed-scale 

modeling. 

4:00 P.M. Charge to Panel

Question 5. In order to generate the soil-land cover-weather station scenarios needed for 

modeling, USEPA OPP took spatial data at different scales and re-gridded them to the same 

scale for aggregation (Section 3.2). Based on comparative testing of the model (Sections 2.3, 

4.4, and 5.3), this appears to be a feasible approach. Please comment on the implications for 

aggregating spatial inputs across varying scales. 

4:45 P.M. Adjourn

Day 3 

Thursday, September 17, 2015

9:00 A.M. Opening of Meeting and Administrative Procedures – Fred Jenkins, Ph.D.,

Designated Federal Official, Office of Science Coordination and Policy, EPA 

9:05 A.M. Introduction and Identification of Panel Members – Stephen Klaine, Ph.D., 

FIFRA Scientific Advisory Panel Chair

9:10 A.M. Follow-up from the Previous Day Discussions 

9:20 A.M. Charge to Panel (Cont’d)

Question 6. As described in Sections 5.1 and 5.2, USEPA OPP has evaluated an approach for 

representing concentrations at the pour points of drainage networks that involves aggregating 

upstream drainage areas into integer-day stream travel-time zones, and the use of 

mathematical convolution to represent in-stream dispersive spreading of both influent runoff 

volumes and pesticide masses. Please comment on the use of this approach, and on any 

modifications or alternative approaches that USEPA OPP might consider for 

accomplishing the same ends.

10:00 A.M. Charge to Panel

Question 7. USEPA OPP has not yet investigated possible adaptations of the approach referred 

to in Q8 to simulate reactive and/or sorbing chemicals. Please comment on the potential for 

modifying this approach to simulate such chemicals. 
a. Given the risk assessment purpose of SAM, please comment on the applicability of the 

described approach in dual-compartment (aqueous and benthos) systems for 

representing chemical decay and sorption during transport in surface waters across a 

range of spatial scales.

b. Please recommend any watershed-scale monitoring datasets that may be suitable for 

use in evaluating estimated concentrations of pesticides that sorb non-negligibly to 

sediment, and any possible sources of data for representing the benthic sediment layer 

in surface waters throughout the country.

11:00 A.M. Break

11:15 A.M. Charge to Panel

Question 8. Pesticide applications often depend on planting dates, crop growth, and harvest 

dates, which vary with weather. To improve upon the initial approach of stratifying planting 

and harvesting dates within states by using a Plant Hardiness Zone map (Section 3.1.4), 

USEPA OPP tested the potential for using empirical data (USDA weekly crop progress 

reports) and, where such data are incomplete, crop growth models (Section 5). 

a. Please comment on the use of crop planting dates and growth stages to provide 

reference points for pesticide application windows. How applicable is this approach for 

predicting the application window for all types of conventional pesticides (e.g., 

herbicides, growth regulators, fungicides, insecticides, etc.). For pesticide or pest types 

for which this approach may not work, what alternative methods are available? 

b. As noted in Section 4.2, empirical crop progress data are not available for all crops, all 

areas, or all years. Please recommend any additional data sources that could provide 

useful information on spatial and temporal (year-to-year) variability in crop planting, 

growth, and harvesting dates for use in modeling.

c. Where empirical data are missing, USEPA OPP explored the possibility of using crop 

growth/phenology models such as growing degree days (GDD) to fill in missing data. 

Please comment on the number of crops with available GDD models and availability of 

alternative models/data for other crops or crop groupings.

12:00 P.M. Lunch
1:00 P.M. Charge to Panel (Cont’d)

Question 9. The test version of SAM provides the user with options for defining the extent of the 

pesticide application window and the distribution of pesticide applications across that 

window (e.g., uniform distribution, triangular distribution). Crop progress reports or, in their 

absence, crop growth models, offer an option for defining the application window and shape 

of the distribution (Section 5). Please comment on the use of empirical data or models to 

define the distribution of pesticide applications within an application window.

2:30 P.M. Closing Remarks – Stephen Klaine, Ph.D., FIFRA Scientific Advisory Panel Chair

Fred Jenkins, Ph.D., Designated Federal Official, Office of Science Coordination and Policy, 

EPA 

3:00 P.M. Adjourn

Note: Please be advised that agenda times are approximate; when the discussion for one 

topic is completed, discussions for the next topic will begin. For further information, please 

contact the Designated Federal Official for this meeting, Dr. Fred Jenkins, via telephone:

(202) 564-3327; fax: (202) 564-8382; or email: jenkins.fred@epa.gov.