The U.S. Environmental Protection Agency (EPA) has finalized amendments under the Clean Water Act that require permit applicants under the National Pollutant Discharge Elimination System (NPDES) program to use "sufficiently sensitive" methods for analyses of pollutants.

According to the EPA Water Permits Division, the purpose of this rulemaking is to clarify that NPDES applicants and permit holders must use approved analytical methods capable of detecting and measuring the pollutants at, or below, the applicable water quality criteria or permit limits. These amendments modify existing NPDES application, compliance monitoring, and analytical methods regulations.

The EPA and state permit authorities use data from the NPDES application to determine the presence and level of pollutants in an applicant's discharge. This data is then used to determine if effluent limits are needed in the applicant's NPDES permit. Therefore, it is critical that applicants provide data measured at levels that will be meaningful to the decision-making process.