Yuzhou Luo, Nan Singhasemanon, Kean S. Goh

California Department of Pesticide Regulation

Sacramento, CA 95812

10/28/2014
CDPR’s Surface Water Protection Program (SWPP) is 

developing a consistent, transparent, and fast method 

for evaluating new AI registration packages

Initially designed for agricultural uses by generally 

following USEPA approaches for registration evaluation

Improvements under development, including urban 

pesticide uses, degradates, California receiving water...

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Residential (10ha) Commercial/industrial (10ha) Agricultural (10ha)

10 ha: USEPA recommended size of drainage area for modeling 

purpose in registration evaluation and risk assessment 3
No data: half-life, adsorption coefficients, etc., on

impervious surface are not available

No model is consistently used by USEPA for registration 

evaluation of urban pesticides

For post-use risk assessment, USEPA developed a 

modeling scenario for impervious surface

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The model (“PRZM/EXAMS”) with the modeling 

scenario (“San Francisco impervious surface”) is “the 

most suitable available modeling approach for 

impervious runoff” (USEPA EFED, 2013)

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The model (“PRZM/EXAMS”) with the modeling 

scenario (“San Francisco impervious surface”)

Known limitations on landscape description and 

simulation design, e.g.,

Nationwide suburban data: 1⁄4 acre house lot

Buildings all surrounded by lawns

Optimized lawn irrigation by soil moisture

No dry-weather runoff (urban drool) from paved areas

Assumed equal contributions of runoff from pervious and 

impervious surfaces

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Based on California conditions, to improve urban

landscape description represented in the modeling 

approach

To improve the simulation design for better prediction 

of EEC (estimated environmental concentration) from 

an urban catchment

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58 residential lots (1/4 acre 

each) in a 10-ha watershed 

(USEPA, 2007), linked to a 

USEPA pond (1ha*2m) 8
Impervious surface coverage (ISC): USGS landuse 

images, and Caltrans urban boundaries (for San 

Francisco-Oakland) 

Residential density: OEHHA urban survey (Sacramento,

Irvine, and Santa Cruz)

House footprint: American Housing Survey 2011 (for 

San Francisco)

3-ft walkway around a building

3-ft paved area adjacent to lawns subject to

unintended irrigation

Pre-scheduled irrigation: UCANR lawn watering guide

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USEPA SWPP

Overall impervious fraction 50% 83%

#lots per 10 ha watershed 58 201.6

Lot size 1/4 acre 1/12 acre

House footprint 1000 ft2(house) +

900 ft2(garage)

1500 ft2

Driveway 546 ft2 546 ft2

Sidewalk 268 ft2 135 ft2

Lawns 9075 ft2 653 ft2

Paved walkway round a

house

0 501 ft2

The above data are for residential watershed. Commercial/ 

industrial and urban right-of-way scenarios are also developed. 

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PRZM for pervious 

surface

EXAMS

PRZM for 

impervious 

surface

EXAMS

EEC=fP*EECP+fIMP*EECIMP

For residential, simplified as EEC=(EECP+EECIMP)/2

EEC = estimated environmental concentration; f = fractional 

area, “P” for pervious surface; “IMP” for impervious surface

10-ha watershed

USEPA pond 

(1ha*2m)

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Water Precipitation only Precipitation + irrigation

Permeability Pervious (f1) Impervious (f2) P (f3) IMP (f4)

Treatment Treated 

(ft1)

Untreatedft2 ft3 ft4

Pervious 

surface

Impervious 

surface

Precipitation

Irrigation (which may cause dryweather runoff)

treated untreated treated untreated

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PRZM for 

surface 1

PRZM for 

surface 2

PRZM for 

surface 3

PRZM for 

surface 4

EXAMS

Weighted 

Edge-of-field average

fluxes from each 

surface

Edge-of-field fluxes for 

the urban watershed

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Modeling

components

USEPA SWPP

Model PE5 (integrated PRZMEXAMS)PRZM and EXAMS, separate

simulations

Modeling 

scenario

2 surfaces, USEPA tier-2 

modeling scenarios for 

California

4 surfaces, modeling 

scenarios revised from 

USEPA

Landscape 

description

Residential;

Commercial/industrial;

Rights-of-way

Modified for residential and 

commercial/industrial; 

Rights-of-way (USEPA)

Simulation 

design

Run PRZM-EXAMS for 

each surface; report the 

averages of the two 

EXAMS results

Run PRZM for each surface; 

aggregated resulting fluxes 

before EXAMS simulation

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Upgraded to PRZM5/VVWM

Compared with landscape descriptions (“Aliso Viejo” 

scenario) in the SWMM modeling (Winchell et al., 

2014, PWG-ERA-11)

To refine application extent with urban insecticide 

survey results (Winchell, 2013, PWG-ERA-02b), e.g.,

Fraction of households using outdoor insecticides

Possibility of a pesticide AI used in each application

Percentage of surface area of a use site
SWPP Product Registration Review Process 

(http://www.cdpr.ca.gov/docs/emon/surfwtr/review.htm)

Part I “initial screening” (Luo and Deng, 2012a)

Part II “refined modeling” (Luo and Deng, 2012b)

Part III “urban module” (Luo, 2014)

User Manual (Version 3.1) (Luo and Singhasemanon, 2014)

Risk assessment for urban pesticide uses in “USEPA 

Effects Determinations for the California Red-legged 

Frog” (www.epa.gov/espp/litstatus/effects/redleg-frog)

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Yuzhou Luo, Ph.D.

Research Scientist III

CDPR/EM/SWPP

yuzhou.luo@cdpr.ca.gov

(916) 445-2090