Thermal Mitigation

Development in thermally sensitive areas is required to mitigate thermal pollution. Rainfall is heated after landing on hot impervious surfaces, with the resulting runoff then flowing into receiving waters where it mixes, and potentially increases the base temperature of the surface water.

Thermally sensitive areas are those within a watershed that drain to an existing or proposed Cold Water Community or Class I, II, or III Trout Stream, as designated by the Wisconsin Department of Natural Resources. These streams are capable of supporting cold water fish and other aquatic life.

Turning on the “Thermally Sensitive Areas” layer in the Land and Water Resources Viewer will allow evaluation of a particular site or parcel.

The stormwater management plan for sites in thermally sensitive areas shall include provisions and practices to reduce the temperate of runoff. If the following provisions are met, the site may be considered meeting the standard.

• Maximize use of light colored impervious surfaces (e.g. white roofs)
• Disconnect impervious surfaces
• Meet 90% infiltration standard
• Use a Dry Pond for treatment, instead of wet ponds
• Route all impervious runoff through an infiltration practice or Stone Crib