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Subject: Office of Wastewater Management - Improving water quality in impaired waterbodies


Improving water quality in impaired waterbodies
pending the Establishment of a TMDL

Listing Impaired Waterbodiees and Establishing TMDLs

States and Territories identify impaired waterbodies, those not meeting water quality standards. Lists of these waterbodies are provided to the public and EPA every two years. States then establish TMDLs for waterbodies on the list. TMDLs specify the reductions needed to meet water quality standards and allocate those reductions among the sources in the watershed. TMDLs can take up to 15 years to establish.

The National Discharge Elimination System (NPDES) Program

The NPDES program protects public health and the environment through the issuance of permits to dischargers of pollutants from a point source into waters of the United States. These permits contain enforceable limitations and requirements that ensure that water quality standards will be met.

The Relationship Between Water Quality Standards, the TMDL Program and the NPDES Program

Water Quality Standards and TMDLs are in part, implemented through NPDES permits. While TMDLs are being established, NPDES permits may be issued to dischargers provided the discharge will not cause or contribute to a violation of water quality standards. After TMDLs are established, NPDES permits may be issued to new dischargers and reissued to existing dischargers provided the limitations and requirements within such permits are consistent with the TMDL.

How Can Water Quality Be Improved in Impaired Waterbodies As TMDLs are Being Established?

Proposed Revisions to the NPDES and WQS Regulations:


EPA is proposing to require certain dischargers seeking to add new pollutant loads to an impaired waterbody to offset their proposed discharge.. These dischargers will need to offset any increase in a pollutant(s) for which the waterbody is impaired by a specified amount.

What is an Offset?

An offset is a reduction in pollutant loads of a particular pollutant(s). These reductions can be obtained from an existing point source(s) and/or an existing nonpoint source(s).

Who must obtain an offset?

Dischargers who will be required to obtain these offsets are large new dischargers and large existing dischargers undergoing a significant expansion.

When must these offsets be obtained and for how long must they be maintained?

Offsets must be obtained before the discharger begins discharging. Offsets must be maintained until TMDLs are established and implemented.

Reissuing Expired Permits in Impaired Waterbodies

States with approved NPDES programs issue permits to point sources within their jurisdiction. When these permits expire, the State typically issues the permittee a new permit. In some instances, these permits expire and the permittee operates under an expired permit. Some of these expired permits are inconsistent with water quality standards. Authorizing discharges under these permits frustrates the goals of the Clean Water Act by delaying the implementation of needed water quality-based effluent limitations. In these instances and when the State fails to act, EPA is proposing to allow the Regional Administrator to reissue these permits consistent with water quality standards.

This page last updated on August 12, 1999