An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

National Pollutant Discharge Elimination System (NPDES)

Whole Effluent Toxicity (WET) NPDES Spreadsheet

This spreadsheet can be used to analyze valid acute or chronic WET test data using statistical approaches. The results generated by the spreadsheet can be used by NPDES permit writers for reasonable potential (RP) determinations in accordance with EPA’s TSD (see pages 53-57, Chapter 5) and for NPDES WET compliance determinations (see TSD pages 112-113, Chapter 6). NPDES permittees and WET testing laboratories may also find the spreadsheet helpful when analyzing valid WET test data.

Disclaimer: Please note that neither the EPA nor any of its employees assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information disclosed. Furthermore, the NPDES WET Spreadsheet is supplied “as-is” without guarantee or warranty, expressed or implied, including without limitation, any warranty of merchantability or fitness for a specific purpose.