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What is the NPDES?


The National Pollutant Discharge Elimination System

The NPDES, or the National Pollutant Discharge Elimination System, is perhaps noted best by it's goal to eliminate discharge of pollutants into navigable waters by 1985. This goal was not realized, but remains a principle for establishing permit requirements. The NPDES act had an interim goal to achieve "water quality which provides for the protection and propagation of fish, shellfish, and wildlife and provides for recreation in and on the water" by July 1, 1983. This is more commonly known as the "fishable, swimmable" goal.

The first round of NPDES permits issued between 1972 and 1976 provided for control of a number of traditionally regulated pollutants, but focused on 5-day biochemical oxygen demand (BOD5), total suspended solids (TSS), pH, oil and grease, and some metals, by requiring the use of the Best Practicable Control Technology currently available (BPT). The Act established a July 1, 1977, deadline for all facilities to be in compliance with BPT. Additionally, the Act established the compliance deadline for installing Best Available Technology Economically Achievable (BAT) as July 1, 1983. Most of the major permits issued to industrial facilities in the first round of NPDES permitting contained effluent limitations based on Best Professional Judgment (BPJ) because regulations prescribing nationally uniform, technology-based effluent limitations were generally unavailable.

The 1977 amendments to the legislation, known as the Clean Water Act (CWA) of 1977, shifted emphasis from controlling conventional pollutants to controlling toxic discharges. This era of toxic pollution control is referred to as the second round of permitting. The concept of BAT controls was clarified and expanded to include toxic pollutants. Hence, the compliance deadline for BAT was extended to July 1, 1984. The conventional pollutants (BOD5, TSS, pH, fecal coliform and oil and grease) controlled by BPT in the first round of permitting were now subject to a new level of control, termed Best Conventional Pollutant Control Technology (BCT). The compliance deadline for meeting BCT was also July 1, 1984.

In addition to treatment technology-based standards, the Clean Water Act also required that minimum receiving water quality standards be achieved. Water quality standards are promulgated by the states. The Michigan standards are designed to not only protect for aquatic life ("fishable") and recreation ("swimmable"), but also for all other uses of the receiving waters, including agriculture, public and industrial water supply, and navigation.

On February 4, 1987, Congress amended the CWA with the Water Quality Act (WQA) of 1987. The amendments outlined a strategy to accomplish the goal of meeting water quality standards set by the States. The WQA required all States to identify waters that were not expected to meet water quality standards after technology-based controls on point sources have been imposed. The State must then prepare an individual control strategy to reduce toxics from point and nonpoint sources in order to meet the water quality standards. Among other measures, these plans were expected to address control of pollutants beyond technology-based levels.

The WQA once again extended the time to meet BAT and BCT effluent limitations. The new compliance deadline was no later than March 31, 1989. The WQA also established new schedules for industrial and municipal storm water discharges to be regulated by National Pollution Discharge Elimination System permits. Industrial storm water discharges must meet the equivalent of BCT/BAT effluent quality. Discharges from municipal separate storm sewer systems (MS4) require controls to reduce the discharge of pollutants to the maximum extent practicable (MEP). Additionally, the WQA requires EPA to identify toxics in sewage sludge and establish numerical limits to control these pollutants. The WQA also established a statutory anti-backsliding requirement that will not allow an existing permit to be modified or reissued with less stringent effluent limitations, standards, or conditions than those already imposed. There are a few situations under which exceptions can be made, including when the permittee was unable to achieve the previous permit limits and when production is increased.


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