Two Minnesota streams, the Le Sueur River and the Little Beauford Ditch, violated the Minnesota Pollution Control Agency (MPCA) Chronic Water Quality Standard for Acetochlor and are included on the Minnesota 2008 Total Maximum Daily Load (TMDL) List of impaired waters (also known as the 303(d) list). Information on Minnesota's impaired waters and the TMDL Program.

The Little Beauford Ditch is a tributary of the Le Sueur River and is located in Blue Earth County south of the city of Mankato. The Le Sueur River watershed covers 712,000 acres and drains areas of Faribault, Freeborn, Steele, Waseca, Le Sueur and Blue Earth Counties before outletting into the Minnesota River near Mankato.

Including these two streams on the Minnesota list of impaired waters was based on two violations of the water quality standard within a three year period for each stream; the standard being an average acetochlor concentration exceeding 3.6 µg/L over four days (96 hours). The documented violations, which occurred in 2001 for the Le Sueur River and 2005 for the Little Beauford Ditch, are likely associated with run-off from storm events that occurred early in the growing season soon after acetochlor was applied to crop fields.

The MPCA and the MDA both have a responsibility to address these acetochlor water quality impairments. The MPCA is responsible for seeing that water quality impairments are corrected and the MDA is responsible for proper use of pesticides.

The MPCA and the MDA have worked together to develop a proposed “Acetochlor Impairment Response Plan” for the Le Sueur River and Little Beauford Ditch. It outlines specific activities to be completed or evaluated in response to the water quality impairments. Some of the activities are in direct response to the acetochlor water quality impairments; others are in response to the MDA’s on-going responsibility to assure pesticides are used in a manner that does not cause unreasonable adverse effects on the environment.

The Acetochlor Registration Partnership (ARP) is an active partner in addressing the acetochlor impairments. The ARP is composed of Dow AgroSciences and the Monsanto Company, two major manufacturers and distributors of acetochlor products.

An Acetochlor Impairment Response Plan Advisory Committee guides the development and implementation of the acetochlor impairment response.