Historically, NPDES permits have been written to limit the discharge of conventional and toxic pollutants on a chemical-specific basis or using whole effluent toxicity.  This approach is straightforward, but sometimes can result in overprotective -- as well as underprotective -- permit limits. Simply controlling the substances discharged does not assure the biological integrity of water resources, because that integrity depends on a combination of chemical, physical, and biological processes.  Successful protection of water quality requires monitoring and assessment tools that measure both the interacting processes and the collective result of these processes. Chemical analyses, whole effluent toxicity testing, physical habitat assessment, and bioassessment are tools that have a unique role in the NPDES permitting process. The information provided from the integrated use of all four tools strengthens permitting decisions.

The following case studies provide examples of the importance of bioassessment information in the NPDES permitting process.

• Multiple Benefits in a County's Stormwater Control Program in Maryland
• Prioritizing Problem Discharges in Florida
• Support for Permit Limits in Ohio