Consultation on the Two-dim

Exposure Rainfall-Runoff As

(TERRA) Watershed Model a

in the FIFRA Ecological Risk A

for Antimicrobial Uses of C

FIFRA SCIENTIFIC ADVISORY PANEL

Consultation

October 25-26, 2011

U.S. Environmental Protection Agency

Office of Pesticide Programs

Washington, DC
EPA Review of the TERRA Mode

Goodwin Creek Scenario as Us

Antimicrobial Copper Exposure A

Dr. Stephen Wente, EPA

FIFRA SCIENTIFIC ADVISORY PANEL

Consultation

October 25-26, 2011

U.S. Environmental Protection Agency

Office of Pesticide Programs

Washington, DC
Presentation Outline

z EPA’s Review of the TERRA Modelz EPA’s Review of the Goodwin Creez Exposure Modeling for Antimicrobi
EPA’s Review of TERRA 
Features and Computational R

z Features of the TERRA model

 Fully-distributed watershed model Small time-step (1 minute or less) used withi

events

 Calibrated to site-specific data

z Computational resource requirements ar

 Extensive GIS data required Calibration for site-specific scenarios required Computer processing requirements dependen

resolution
z Large grid-cell size (~90m) hinders repres

engineered water conveyance structures

z Designed to move water away from home

erosion, and be stable (impervious materi

z Continuous pathway for water from origin 

waterbodies of concern

 Shingles to roof gutter to downspout to dr

gutter to storm sewer to pond, stream or 

Engineered Water Conveyance 
Engineered Water Conveyance Sy

(cont.)

z Prediction quality as urban characteristics 

 Water is more likely to be moved by engineer

conveyance systems

 Therefore, water movement is less related to 

elevation and more related to finer-scale engiconveyance systems

Rural Suburban 

Less engineered Hydrology M
z Proportion of watershed in 

impervious surfaces

z Connectivity of impervious 

pixels

z Artificial dilution volume 

(runoff) contributed by large impervious pixels

Spatial Resolution Issues

90m 
Proportion of Impervious Su

z Averaging properties 

across grid-cells results in few truly impervious cells

z Finer resolution:

 Reduces averaging across 

grid-cells 

 More accurate distribution 

of pervious and impervious cells
Grid-Cell Connectivity of 

Impervious Surfaces

z Continuous impervious flow 

paths

 At 2 acres/grid-cell not many 

continuous flow paths could be represented in watershed

 Finer resolution would allow 

more flow paths
Dilution Water Volume

z A 3-cell flow path at 90m 

resolution (green) occupies 6 acres

z A 9-cell flow path at 30m 

resolution (blue) occupies 2 acres

z Finer resolution reduces 

area needed to represent an impervious flow path
Resolution and Landscape I

z Need finer resolution for:

 Proportion and distribution of pervious/imperviou Connectivity of impervious surfaces Reduction of artificial dilution volumes Representing a variety of landscapes

z Requires additional computational resouz Fewer impervious flow paths would:

 Result in more copper infiltration in soil Lower predicted copper concentrations

z Question: Does a lower grid-cell resoluti

produce lower copper concentrations? 
EPA’s Review of th

Goodwin Creek Scen
How Does Goodwin Creek C

Other Watersheds across th

Watershed

Characteristic Actual S

Land Use 60% pasture and 25% forest 89% 

9% 

Average Annual Rainfall 55.4 inches Runoff Capacity 71% C soil CN 71-86 Resid
Factors Affecting Model-Predict

Estimated Environmental Conce

z Model estimate location: 

watershed terminus vs. loworder streams

z Location of residential structures 

and density relative to water bodies

z Vegetative buffer configurationz Storm sewers

Watershed AreaStream ChannelsMonitoring Stations
Hydrology Calibration Meth

z Calibration based on: 

 Pastured/forested watershed hydrology and  Sediment load data

z Applied to a suburban scenarioz Question: Are any additional calibration 

necessary?
Comparison of Model Prediction

Model Shingles Tr

EPA Impervious 23 μg/L 

EPA Pervious ND μg/L 

TERRA 7.1 μg/L 

z Pervious vs. impervious surfacesz Question: Does the 90m-resolution TERRA 

Goodwin Creek scenario produce realistic exposure estimates?
Dissolve Cu Concentration (ug/L)

0 5 10 15 20 25 

Cumulative Probability

0.00.20.40.60.81.0

EPA Impervious

TERRA

EPA Pervious

Shingle Model Predictions Compar

Urban Site Dissolved Copper Conc
Wood Treatment Model Prediction

to USGS Urban Site Dissolved Cop

Concentrations
Exposure Modeling 

Antimicrobial Pesticid
Antimicrobial Use Patterns

1. Agricultural Premises and 

Equipment

2. Food Handling/Storage 

Establishments, Premises, and Equipment

3. Commercial, Institutional and 

Industrial Premises, and Equipment

4. Residential and Public Access 

Premises

5. Medical Premises and 

Equipment

6. Human Drinkin

Systems

7. Materials Pres8. Industrial Proc

Systems

9. Antifouling coa10. Wood Preserv11. Swimming Poo12. Aquatic Areas
Antimicrobial Models: What 

z Many antimicrobial pesticides tend to enter the a

environment indirectly via wastewater treatmenor from end-uses that lead to direct contact with 

z In addition to OPP-wide models, AD utilizes:

 E-FAST: Exposure and Fate Assessment Screening 

• DtD: Down-the-Drain• PDM: Probabilistic Dilution Model 

 MAM-PEC: Marine Antifoulant Model to Predict En

Concentrations

 PRZM/EXAMS
Antimicrobial Models: What 

z Antimicrobials Division is in need of mod

fully characterize surface water exposure antimicrobial pesticides with land uses. Lmodel(s) with ability to:

 Model environmental exposure from residen

treated wood, i.e. roofing shingles, fences an

 Model sporadic rural uses of antimicrobial wo

preservatives, i.e. railroad ties, fences and ut
Antimicrobial Models: What 

(continued)

z Ideally, model(s) would include scenarios specif

patterns of antimicrobial pesticides. These wou

 Loading from leaching (continuous over the lifetim

article)

 Variety of runoff pathways from use site including

• Direct and indirect runoff to surface water• Degrees of interception of runoff across pervious a

surfaces (rural to urban landscapes)

• Interception by water conveyance structures

 Variety and density of structures treated with ant

pesticides
Questions