This page provides guidance for MS4 (Municipal Separate Storm Sewer System) permittees who have permit requirements for chloride total maximum daily load wasteload allocations.

Total Maximum Daily Loads (TMDLs)

Currently there are two approved total maximum daily load (TMDLs) for Brown’s Creek and Miller Creek that include MS4 (Municipal Separate Storm Sewer System) wasteload allocations (WLAs) for thermal loading. Brown’s Creek is impaired for aquatic life due to a lack of cold water fish assemblage. Miller Creek is impaired for aquatic life due to a lack of cold water fish assemblage and elevated water temperature.

Permit requirement

Section 22.7 of the MS4 permit contains the following requirement: If the permittee has an applicable WLA for temperature that includes a reduction greater than zero percent (i.e., City of Duluth, City of Hermantown, City of Rice Lake, City of Stillwater, MnDOT Outstate, St. Louis County, University of Minnesota - Duluth, and Lake Superior College), the permittee must maintain a written plan that identifies specific activities the permittee will implement to reduce thermal loading during the permit term. The written plan may include, but is not limited to:
a. implementation of infiltration BMPs such as bioinfiltration practices;
b. disconnection and/or reduction of impervious surfaces;
c. retrofitting existing structural stormwater BMPs; or
d. improvement of riparian vegetation.

MS4s with applicable temperature WLAs
Link to this table

TMDL Project MS4 with a WLA for temperature
Browns Creek TMDL Stillwater City
Miller Creek TMDL Duluth City
Hermantown City
Rice Lake City
MnDOT Outstate
St. Louis County
University of Minnesota-Duluth
Lake Superior College

Guidance for meeting temperature TMDL permit requirements

The TMDL reports for Browns Creek and Miller Creek provide information on potential BMPs/activities that may be included in the written plan to reduce heat and meet the requirements of Section 22.7.

Brown’s Creek TMDL

Miller Creek TMDL