The PDF document on this page is part of the information collection from the More Useful Links section of the Water Models page.

Modeled concentrations of pesticides in surface waters are multiplied by a percent cropped area (PCA) to account for the areal fraction of a watershed that may be treated with a particular pesticide based on the pesticide uses and the land cover types (i.e., crops) associated with those uses. The PCA-adjusted concentrations are used as the estimated drinking water concentrations (EDWCs) in human health risk assessment.

The United States Environmental Protection Agency (USEPA), Office of Pesticide Programs (OPP) initiated a peer review of an earlier draft of this document (titled Development of Community Water System Drinking Water Intake Percent Cropped Area Adjustment Factors for use in Drinking Water Exposure Assessments, dated 10/10/2012). Internal and external experts who were familiar with the datasets used in the calculation of Percent Cropped Area (PCA) adjustment factors or with occurrence of pesticides in drinking or surface water were asked to provide comments on the document and respond to charge questions. Consistent with USEPA’s Peer Review guidelines, the feedback from reviewers was carefully considered and this document was updated accordingly.

• Development of Community Water System Drinking Water Intake Percent Cropped Area Adjustment Factors for use in Drinking Water Exposure Assessments: 2014 Update (PDF)(111 pp, 4 MB)
  Watersheds large enough to support a drinking water facility are generally not comprised of only one land cover type, nor planted completely with a single crop. In order to account for variability in land cover, the USEPA uses percent cropped area (PCA) adjustment factors to reflect the percentage of a watershed that is covered by a particular land cover type and/or crop.