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US EPA’s New Drinking Water Assessment Methods – Are You Ready for the Changes?

Posted by Jenn Collins on February 9, 2021


By Raghu Vamshi, Senior Geospatial Scientist; vamshir@waterborne-env.com

Ensuring the safety of drinking water from potential contaminants is a shared priority for the US Environmental Protection Agency, environmental researchers, and industries alike. To this end, it is mission critical to stay well versed in the newest EPA methodologies including a deep understanding of the underlying databases, development tools, and assumptions.

The Safe Drinking Water Act (SDWA) was passed by Congress in 1974 and amended for updated actions in 1986 and 1996 to regulate the country’s public drinking water supply. Drinking water assessments for conventional pesticides are a critical part of SDWA. Just a few months ago, EPA formally announced two new methods updating the drinking water exposure assessment from surface water sources tools. The method changes provided by EPA are designed to:

  • Build new scenarios (a combination of crop, soil type, and weather data) for use in EPA’s Pesticide in Water Calculator, the standard water exposure model for both drinking water and aquatic wildlife;
  • Better account for variability in the agricultural area within a watershed that may contribute to a drinking water intake (Percent Cropped Area (PCA)) and incorporate data on the amount of a pesticide applied within a watershed for each use (Percent Crop Treated (PCT));
  • Outline methods to confidently use surface water monitoring data;
  • Derive and integrate pesticide-specific sampling bias factors to address temporal challenges with available monitoring data; and,
  • Use a weight-of-evidence approach to evaluate the relevance of monitoring sites to drinking water watersheds to address spatial limitations with available monitoring data.

Those involved in conducting drinking water assessments may have found the new approaches challenging and data intensive. Our geospatial scientists have meticulously worked through these challenges and are able to apply and even expand upon EPA’s methods to address chemical-specific challenges that arise in drinking water assessments. Our familiarity with the datasets and methodology used by EPA in these updates allowed us to apply the standard scenarios and use the source datasets to evaluate focused refinement opportunities.  Waterborne scientists will continue to watch this space for future EPA method changes and work to apply similar tools for ecological risk assessments and endangered species assessments.