Impaired Waters and TMDLs
Frequently Asked Questions

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The "303(d) Impaired Waters List" pertains to Section 303(d) of the Clean Water Act which states that waters that are not meeting their designated uses (fishing, swimming) due to pollutants must be placed on this list. The 303(d) Impaired Waters List is updated every two years. Wisconsin is required to develop TMDLs, Total Maximum Daily Loads, for water on this list. (Learn More...)

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The most recent (proposed) updates to the list are available online in DRAFT form for the Year 2010 Water Quality Report to Congress (and Impaired Waters List Update), which will be sent to USEPA in April, 2010. (Learn More...)

There are two types of pollution: point source and nonpoint source. Point sources are pollution sources that discharge effluent directly into the stream. An example would be cooling water from a factory discharged into an adjacent river. Effluent limitations are set by WPDES (Wisconsin Pollutant Discharge Elimination System) permits. Many water quality impairments in Wisconsin waters are due to nonpoint source pollution. Nonpoint sources include: agriculture, forestry, construction sites, urban runoff and more. (Learn More...)

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Water Quality Standards are rules established by the state of Wisconsin to protect the Great Lakes, the connecting waters, and all other surface waters of the state. These rules define the water quality goals for waterbodies in Wisconsin. These rules help protect the uses of the lake or the stream, the habitat for fish in the stream and include procedures to protect high quality waters. (Learn More...)

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A TMDL, or a Total Maximum Daily Load, is a quantitative analysis of the amount of a particular pollutant or load a stream or lake can allow before exceeding water quality standards. A TMDL can be used to implement water quality standards.(Learn More...)

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TMDLs are required under the Clean Water Act for all impaired waters. In order for a state to receive grants for the Clean Water Act the state must produce TMDLs. TMDLs are developed to set loading allocations of nonpoint sources to the impaired waters. Point source permits must be consistent with approved TMDLs.(Learn More...)

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The information provided in TMDLs may assist counties in competing for grants for implementation projects (such as TRM grants). TMDLs attempt to answer how much nonpoint source management is needed to have adequate water quality.

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The Clean Water Act provisions for TMDLs and corresponding federal rules do not create regulatory requirements. State nonpoint source performance standards and prohibitions will apply. (Learn More...)

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The critical condition can be thought of as the "worst case" scenario of environmental conditions in the waterbody in which the loading expressed in the TMDL for the pollutant of concern will continue to meet water quality standards. Critical conditions are the combination of environmental factors maintaining the water quality criterion and have an acceptably low frequency of occurrence.

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The total load capacity is the wasteload allocation (WLA: amount of load from point sources) plus the load allocation (LA: amount of load from nonpoint sources) plus the margin of safety (MOS).

TMDL (Total Load Capacity) = WLA + LA + MOS

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The margin of safety accounts for the discrepancies or uncertainties in the analysis.

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TMDLs take into consideration seasonal variation as it applies to the change of flow conditions, pollutant discharges, and designated uses throughout the year.

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The EPA requires that states have a public comment period for at least 30 days on the TMDL. Wisconsin has a 30-day public comment period in which news releases are sent out and the copies of the TMDL and public notice are posted on the WDNR's TMDL website. Written comments may be mailed to the WDNR prior to EPA submission and approval of the TMDL.

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Wisconsin must provide reasonable assurance that nonpoint sources will meet their allocated amount of reductions as stated in the TMDL. Possible methods include developing nonpoint source pollution plans or implementing best management plans (BMPs) in the watershed. A variety of grants may be available to assist counties with implementing BMPs to meet the reduced load allocations in the TMDL.

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Waterbodies that have written and approved TMDLs will be monitored on a regular basis until water quality standards have been met. Frequency of monitoring will be determined for each TMDL.