Under the Clean Water Act (CWA), the U.S. Environmental Protection Agency (EPA) established the National Pollutant Discharge Elimination System (NPDES) permitting program as a means of controlling the discharge of wastewater to national surface water supplies. The NPDES program is used within the CWA to help prevent the discharge of "toxic materials in toxic amounts" to the nation's waterways.
Historically, NPDES permits have contained discharge water quality limits based on specific parameters such as pH, chemical oxygen demand (COD), biological oxygen demand (BOD) and the priority pollutants. These parameters can be measured using standard laboratory equipment and procedures. Protocols and quality assurance procedures have long been established for quantifying these parameters. Thus, compliance or noncompliance was established easily by performing a chemical analysis of theÊ wastewater and comparing the results to the discharge limits.