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New DPR Model for Surface Water Assessment
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By  Lisa M. Campbell and Susan Hunter Youngren, Ph.D.

The California Department of Pesticide Regulation (DPR) announced on February 26, 2015, a revision to the process for evaluation of the potential for a pesticide to move off-site into surface water when the pesticide is used in an urban area. The former evaluation method followed the U.S. Environmental Protection Agency (EPA) approach with California specific parameters. This revision will continue to use the EPA approach but allow incorporation of a module specific for California urban settings.

Potential adverse impacts on surface water from use of pesticides are assessed in California by DPR’s Environmental Monitoring Branch’s Surface Water Protection Program (SWPP) using EPA methodology. The SWPP uses the EPA evaluation method for proposed agricultural pesticide registrations based on PE5 (PRZM-EXAMS version 5) and Tier 2 modeling scenarios but there have been no consistent methods for assessing potential pesticide runoff on impervious surfaces in an urban setting. The new California urban module includes the following improvements that are designed to be further representative of urban conditions in California:

* Introduction of four types of surfaces by permeability and water sources;
* Consideration of pesticide transport induced by dry-weather runoff from impervious surfaces;
* Separation of impervious and pervious portions in the modeling scenarios;
* Use of prescheduled lawn irrigation;
* Characterization of residential and commercial/industrial areas to reflect California urban conditions; and
* Aggregations of water, sediment, and pesticide yields for the urban watershed.

The urban model is designed particularly for evaluating pesticides applied outdoors in areas with large amounts of impervious surfaces such as residential areas, commercial/industrial facilities, and highway and road rights-of-way applications. Pesticide products of interest would be those that have the potential for impact to surface waters through overspray to impervious surfaces in these areas