Mill Creek TMDL
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Purpose

Mill Creek is a 47-mile tributary of the Wisconsin River. The stream originates in the City of Marshfield and has minimal streamflow in the upper reaches. The Marshfield WWTP discharges to the headwaters of Mill Creek and contributes more than 90% of the streamflow at the point of discharge. The upper 14 miles of the stream is listed in NR 104 as a Limited Aquatic Life variance stream and the lower 33 miles is classified as Fish and Aquatic life waters. Mill Creek is also listed as an impaired waterbody on EPA’s 303d list for low dissolved oxygen, which required the Department to develop a TMDL for the stream. The stream is impacted by stormwater run-off from Marshfield, sedimentation, barnyard and cropland run-off, flashy streamflow, channel ditching, streambank erosion, ammonia toxicity and nutrient enrichment. Large volumes of stormwater scours streambeds, erode streamsbanks, and carries sediment, nutrients, and other pollutants to surface waters. August 2000 HBI results suggest there is a significant organic loading to the stream. Water samples collected in the winter of 2000 (before the new treatment plant was built) found ammonia concentrations high enough to cause chronic toxicity to aquatic life based on EPA criteria. Since Mill Creek is currently classified as Limited Aquatic Life, the WWTP in Marshfield has no ammonia limit.

Objective

Mill Creek in Wood and Portage Counties is impaired due to one or more pollutants and associated quality impacts. Mill Creek has been on the CWA 303(d) impaired waters list since 1998 for Total Phosphorus. The TMDL is in development. Projects for this area include: Mill Creek SWAT Modeling (UWSP), Mill Creek Nutrient Management Planning, (Portage Co. and Golden Sands RC&D),

Outcome

The work done for this TMDL was integrated into the Wisconsin River TMDL. The Wisconsin River TMDL was approved 04/26/2019.

Related Reports

Run Project Summary Report
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Targeted Monitoring
Special Project
Mill Creek TMDL
2013
Complete
 
Reports and Documents
Mill Creek Watershed (CW11) Goals and Priorities Image
 
Activities & Recommendations
TMDL Development
Mill Creek is a 47-mile tributary of the Wisconsin River.Mill Creek is also listed as an impaired waterbody on EPA?s 303d list for low dissolved oxygen, which required the Department to develop a TMDL for the stream.
 
Watershed
Mill Creek
 
Waters
Mill Creek
Monitoring Data