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Total Maximum Daily Loads

Background

Under section 303 (d) of the Clean Water Act, states are required to identify surface waters that do not or are not likely to attain water quality standards, even after point sources of pollution have complied with at least the minimum technology-based requirements. Once these nonattainment waters have been identified, the states must establish and submit to the U.S. Environmental Protection Agency (USEPA) a priority ranking and schedule for the development of Total Maximum Daily Loads (TMDLs).

A TMDL enumerates the maximum level of a pollutant that a surface waterbody can receive and still meet water quality standards. The TMDL then distributes that acceptable pollutant loading among the various point and nonpoint sources for that pollutant. It should be noted that TMDLs are pollutant specific. Therefore, a single waterbody can have more than one TMDL, depending upon the pollutants contributing to its degradation.

The Michigan Department of Environmental Quality (MDEQ) has identified 268 waterbodies in Michigan requiring a total of 301 TMDLs. Michigan uses a five year rotating watershed approach for environmental monitoring and National Pollutant Discharge Elimination System (NPDES) permit reissuance. This five year cycle, along with several other criteria including USEPA’s direction to have all TMDLs developed by 2011, was used by MDEQ to establish the development schedule.

Sixty-four of the 301TMDLs in the state are in Southeast Michigan, including waterbodies in all seven Southeast Michigan counties. The nonattainment waters in Southeast Michigan includes portions of both rivers and lakes. They range in size from 0.1 to 54 miles (rivers and streams) and between three and 1280 acres (lakes). Several TMDLs have already been completed; however, the majority are scheduled to be developed between 2000 and 2011.

In an area where a TMDL has been developed, it can serve as a guide to communities in the development and implementation of nonpoint source control programs. In areas waiting for a TMDL to be developed, the subwatershed planning process could be used to ensure consideration of local concerns in the TMDL development or, perhaps, result in the achievement of water quality standards prior to the TMDL being established, negating the need for their development.

For example, under the Michigan Storm Water General Permit, municipalities must prepare a Watershed Management Plan and a Storm Water Pollution Prevention Initiative. In a nonattainment area, the management plan could identify the maximum pollutant loadings that the waterbody can receive and still meet water quality standards, as well as estimate the loadings from various sources and identify management strategies. The pollution prevention initiative could then ensure the implementation of appropriate management practices.

TMDL Schedule - Monroe County*