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Nonpoint source TMDL implementation

Nonpoint source pollution continues to be a primary cause of water quality problems in Wisconsin. The state has numerous lakes, streams, and rivers that are not meeting water quality standards and are considered to be "impaired" as a result of nonpoint source pollution impacts.

As required by the federal Clean Water Act, the DNR addresses waters impaired by nonpoint source pollution by establishing a "Total Maximum Daily Load" (TMDL). The goal of a TMDL analysis is to calculate a pollutant budget: sources of pollutants are identified and then reductions are given to various sources (municipalities, industries, agriculture) in order to meet water quality standards.

A TMDL is often expressed as an equation: TMDL = WLA + LA + MOS.

Where the TMDL is equal to the wasteload allocation (WLA) plus the load allocation (LA) plus a margin of safety (MOS). The TMDL analysis determines the allowable load and provides the basis for establishing or modifying controls on pollutant sources. This load is then allocated to point source discharges ("wasteload allocations") and nonpoint source discharges ("load allocations") to the impaired waters.

While TMDL development is a requirement of the federal Clean Water Act, TMDL implementation authority rests with the states. States are charged with ensuring the necessary actions are taken so that the loading of the pollutant of concern does not exceed the TMDL and associated wasteload and/or load allocations.

The goal of nonpoint source-related TMDL implementation is to maximize opportunities for restoration of impaired waters by prioritizing and targeting available programmatic, regulatory (such as the ag. performance standards), financial (such as Targeted Runoff Management Grants), and technical resources.

TMDL implementation is an adaptive and holistic process, uniting point and nonpoint source pollution control in a watershed-based approach. Implementing plans to achieve TMDL targets for polluted runoff from cities, construction sites, farms and roads is a challenging process that requires the collaboration of diverse stakeholders and a substantial commitment of public and private dollars.

To learn more about Wisconsin’s TMDLs and TMDL implementation, visit the DNR’s TMDLs page.