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The results from initial testing performed by the Minnesota Department of Health. This testing was performed in two rounds, and each set of results is shown above. Rosemount continues to work with MDH to better understand manganese levels for all city wells and will post those results as they are received.

In 2019, the Minnesota Department of Health conducted testing in Rosemount as part of an unregulated contaminants study showing some city wells have manganese levels that exceed recommended health guidelines.

Manganese is a naturally occurring element found in rocks and soil often found in Minnesota ground and surface water. The human body needs some manganese to stay healthy, but too much can be harmful. Frequent testing by the city and MDH shows the municipal public water supply continues to meet all Safe Drinking Water Act standards.

Manganese is unregulated and does not have an enforceable standard. However, the MDH-recommended health guidelines include:

1. For those with an infant (less than 1 year of age) who drinks water or drinks formula made with tap water, a safe level of manganese in your water is 100 parts per billion or 100 micrograms per liter (μg/l) or less.

2. For those with an infant who never drinks water or drinks formula made with tap water, a safe level of manganese in your water is 300 ppb or 300 μg/l or less.

3. If everyone in a household is more than 1 year old, a safe level of manganese in your water is 300 ppb or 300 μg/l or less.

In addition, the Environmental Protection Agency has a secondary maximum contaminant level which is a nonmandatory water quality standard for manganese of 50 ppb or 50 μg/l. That is an aesthetic standard due to the possibility of stained fixtures and laundry.

Rosemount’s municipal water supply consists of nine city wells and four water towers. The water mixes in the mains and towers and is then distributed to the consumer’s tap. Because of this mixing, the actual level of manganese at each drinking water tap is unknown but would likely be below 100 micrograms per liter (μg/l).

More information is available at the MDH webpage at www.health.state.mn.us. Search for Manganese in Drinking Water.

A two-page information sheet can be found at: https://www.health.state.mn.us/communities/environment/water/docs/contaminants/mangnsefctsht.pdf

City actions

As an initial step, Well 7 has been put in a backup status, meaning it would only run as a last resort, such as a major structure fire. The city has also contracted with an engineering firm to do a review and provide recommendations to reduce the impact of the manganese. The city will voluntarily begin testing for manganese, in addition to the Department of Health’s required monthly bacteria testing, to better understand manganese levels in the system.

Rosemount is also in the initial planning process for constructing a water treatment plant that would be located behind Fire Station 2 on Connemara Trail.

In addition to the city water system, many rural households in Rosemount rely on private wells for their water supply. Existing manganese data from private water wells in Rosemount indicate 39 percent of well water samples exceed the drinking water guidance of 100 micrograms per liter.

Water softeners or reverse osmosis treatment systems can effectively reduce the manganese. Later this summer, to help residents and the city better understand manganese and other potential contaminants, Dakota County will be sending free water test kits to all Rosemount households that use private wells, and sharing the results with those residents.

Contact Vanessa Demuth at Vanessa.demuth@co.dakota.mn.us or 952-891-7010 with any questions or concerns.

For additional comments or questions, contact the Public Works Department at 651-322-2022. The annual water quality report is available for public review on the city website at https://www.ci.rosemount.mn.us/255/Water-Quality-Report.

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