Turbidity TMDL

Turbidity Impairment
A water body is considered impaired if it fails to meet one or more water quality standards. Federal standards exist for basic pollutants such as sediment, bacteria, nutrients and mercury. The Clean Water Act requires the MPCA to identify and retore impaired waters.

The water quality standard for turbidity is 25 NTU. If 10% of the samples taken are higher than 25 NTU, the water is placed on the EPA's 303(d) impaired waters list. In the last 10 years, water quality data on the Pomme de Terre show that 61% of the water samples tested higher than 25 NTU.

In 2002, the stretch of the Pomme de Terre from Muddy Creek to Marsh Lake was placed on EPA's impaired waters list for excessive levels of turbidity. Once a water body is placed on the list, the federal Clean Water Act requires the completion of a TMDL study. Work on the Pomme de Terre turbidity TMDL report began in February of 2008. This TMDL will identify the sources of turbidity in the watershed and allocate needed reductions among them. Once the TMDL report is approved by the EPA, a detailed implementation plan will be developed with stakeholder input. This plan will identify best management practices that will help meet the necessary TMDL load reductions.

The MPCA has a Turbidity Fact Sheet available online.

The following are pictures of erosion issues on the Pomme de Terre that can lead to high turbidity.

Bank wash, no streambank stabilizing plant materials.
Photo taken by Brett at 500th Avenue.

Bank sloughing, large amounts of sediment enter the river channel.
Photo taken at 270th Avenue.

Example of a grassed waterway leading to an eroded bank.
Photo taken at 500th Avenue.