CHARGE QUESTIONS:

FIFRA Scientific Advisory Panel Consultati on on the Two-dimensional Exposure RainfallRunoff Assessment (TERRA) Waters hed Model and Its Use in th e FIFRA Ecological Risk Assessment for Antimicrobial Uses of Copper

October 25-26, 3011

The purpose of this FIFRA Scientific Advisory Panel (SAP) meeting is to seek consultation on the usefulness of the Two-dimensional E xposure Rainfall-Runoff Assessment (TERRA) 1 model as an aquatic exposure assessment tool – specifically for evalua ting the antimicrobial uses of copper and potentially for wider use. The EPA is seeking the Panel’s in put on the three charge questions listed below. Char ge question one focuses on the TERRA model’s attributes and the general capabilities necessary for mo deling pesticides used in urba n settings. The second charge question focuses on the Goodwin Creek Waters hed and the national application of this watershed. And lastly, ch arge question three focuses on model calibration.

Charge Question 1

The three most prevalent antimicrobial uses of copper include antifoulant pa ints, roofing shingles and wood preservatives. The Antimicrobials Division used a basic field scale modeling approach, including maximum use rates, realisti c heavy rainfall events, the assumption of high leaching rates, and storm-water conveyance via impervious surfaces, to estimate potential high end aquatic exposure from copper’s use as an an timicrobial pesticide in roofing shingles and treated wood. The American Chemistry Counc il (ACC) has proposed the TERRA Model as an alternative and more refined way to assess aquatic exposure due to the two major urban antimicrobial uses of copper, in wood preservatives and in roofing shingles, on a watershed scale level.

a) What does the Panel believe are the adva ntages and/or limitations of assessing antimicrobial uses of copper from roofing shingles and wood preservatives with TERRA, a spatially-explicit, watershed scale model? Ar e there other models that the Panel feels should be considered for use by OPP in estima ting exposure to copper from its use as an antimicrobial pesticide, specifically in roofing shingles and wood preservative? b) In the opinion of the Panel, what attributes of an urban watershed model are the most critical and why does the Panel regard these at tributes as critical? Does the TERRA model possess these attributes? c) Please discuss whether TERRA has the modeling capabilities necessary for it to be applied to other urban metal exposure assessments fo r antimicrobial pesticides as well as what modifications, if any, would be needed to assess exposure to other metals used as pesticides. d) In the opinion of the panel what further de velopment and/or assessm ent is necessary to prepare the TERRA model for use as an exposure assessment tool by the EPA?

1 Please note that the name of the model under review was recen tly changed from Two-dimensional Runoff, Erosion, and Export (TREX) to Two-dimensional Exposure and Rainfall-Runoff Analysis (TERRA). This name change was made to avoid confusion with the Terrestrial Residue Exposure (T -REX) model that OPP uses to estimate pesticide concentrations for avian and mammalian food items. (Unite d States Environmental Protection Agency. 2008. Terrestrial Residue Exposure Model Version 1.4.1. www.epa.gov/oppefed1/m odels/terrestrial/trex).Charge Questions 2

EPA employs a tiered strategy to assess aquatic exposure. The first tie r facilitate s the rapid screening of pesticide uses fo r potential risk issues, while the second tier refines exposure estimates by utilizing a field scal e model and site specific properties . This process is designed to incorporate additional data (e.g., site specific properties) for e ach progressive tier. EPA has historically employed field scale models to assess aquatic exposure in support of national pesticide registrations. The TERRA model, un like other models used by OPP, is a fully distributed, spatially-explicit wa tershed model. It has mode l capabilities of distributing differences in hydrology, meteorology, soil proper ties, and pesticide uses across a watershed. These model capabilities require consideration in terms of th e proper scale of the exposure
assessment.

a) Are the appropriate pathways (e.g. engineered water conveyance structures) for modeling urban antimicrobial uses of copper within th e Goodwin Creek scenario currently included in the framework of the TERRA model? What , if any, additional pathways are necessary to appropriately estimate exposure concentrations? b) What are the most important attributes to c onsider when selecting and designing an urban watershed modeling scenario ? In the opinion of the Pa nel, where does the Goodwin Creek watershed fall within a distribution of the nation’s urban watersheds? Also, given that the model does not account for storm dr ains, how does this compare to watersheds nationwide?

Charge Question 3

Watershed-scale models require calibration to account for complex watershed-dependent hydrology and environmental fate processes. Model calibrations have been conducted by altering saturated hydraulic conductivity, Mannings N, soil erodibi lity factors, la nd cover factors, and chemical partitioning coefficients. In contrast, the OPP field-scale models such as PRZM/EXAMS are not calibrate d for site-specific hydrology, etc

.

The TERRA model utilizes a simulated urban wate rshed that was calibrated to the hydrology and sediment loads of Goodwin Creek. Because th e Goodwin Creek watershed is a predominately pastured/forested watershed, the EPA has conc erns that the calibration processes may not adequately represent urban hydrologic and chemical transport processes.

a) Please discuss the implications of waters hed land use patterns on model calibration. What types of impacts could these have on the estimated exposure concentrations of copper? b) Please indicate any unique cal ibration issues that should be considered when simulating an urban, residential watershed.