Lake Superior South Watershed Total Maximum Daily Load Report

The Clean Water Act, Section 303(d) requires total maximum daily loads (TMDLs) be determined for surface waters that do not meet applicable water quality standards necessary to support their designated uses (e.g., propagation and maintenance of a healthy fish community and associated aquatic life and habitats, swimming). A TMDL determines the maximum amount of a pollutant a receiving water body can assimilate while still achieving water quality standards. This TMDL study addresses the portion of the Lake Superior South (LSS) Watershed (Hydrologic Unit Code [HUC] 04010102) that is located north and east of the Lester River Watershed in northeastern Minnesota. TMDLs have been developed for six impaired streams in the watershed; all six streams are provided with a total suspended solids (TSS) TMDL and one stream is provided with an Escherichia coli (E. coli) TMDL. Forest and wetland land cover are dominant in all of the impaired watersheds with the exception of Skunk Creek. Skunk Creek, the only stream impaired for E. coli, passes through Two Harbors and has a large amount of developed lands (39%) in its watershed. Streams in the watershed transition from headwaters with low slope to high slope, bedrock-controlled areas near Lake Superior. Eroding banks and bluffs, roads and road crossings, and watershed runoff are all significant sources of sediment in the watershed. Geomorphic analysis and other field data have identified priority locations where erosion is likely contributing to impairment. Many of these areas correspond to soils with high clay content and higher stream power. Potential sources of E. coli in the Skunk Creek Watershed include watershed runoff, failing septic systems and other sources of untreated wastewater, wildlife, and pets. The pollutant load capacity of the impaired streams was determined through the use of load duration curves. These curves represent the allowable pollutant load at any given flow condition. Water quality data were compared with the load duration curves to determine load reduction needs. A 10% explicit margin of safety (MOS) was incorporated into all TMDLs to account for uncertainty. The implementation strategy highlights an adaptive management process to achieving water quality standards and restoring beneficial uses. Implementation strategies include stormwater and wastewater management, addressing sources of untreated wastewater (e.g., failing septic systems, leaky infrastructure), stormwater management, streambank restoration and stabilization, buffers, timber harvesting management, guidance for ditch maintenance and culvert design, culvert and road crossing upgrades, pet and wildlife waste management, and education and outreach.