South Metro Mississippi River Total Suspended Solids Total Maximum Daily Load

The South Metro Mississippi River Total Suspended Solids (TSS) TMDL has been under development since 2004 as a companion project to the Lake Pepin eutrophication TMDL, initiated the same year. A river model extending from Lock and Dam 1 to Lock and Dam 4 was developed to allow analysis of both turbidity and eutrophication impairments, and interactions between the two. After the model was completed in 2008, the MPCA put the issues of turbidity and eutrophication on separate tracks, starting with the development of site-specific standards and proceeding to the writing of TMDL documents. The MPCA sent the U.S. Environmental Protection Agency (EPA) a proposed site-specific TSS standard for the South Metro Mississippi in 2010, replacing the statewide turbidity standard for these reaches and providing the basis for the South Metro Mississippi TSS TMDL. The EPA gave its final approval to the proposed standard on November 8, 2010. The present TMDL applies to the TSS-impaired reach extending from River Mile 844 at the confluence with the Minnesota River to River Mile 780, in upper Lake Pepin. The TMDL addresses water quality impairment in this impaired reach, in addition to the accelerated in-filling of Lake Pepin with sediment.