Minnesota's stormwater environment is characterized by wet summers and snowy winters, with a diverse range of water bodies and groundwater. Learn more about the state's surface water challenges, regulations and solutions.

Stormwater in Minnesota

Due to its location Minnesota experiences a wide range of temperatures and climatic conditions that make stormwater a significant issue: the state can experience over four inches of rain a month during summer, mostly from thunderstorms, and over nine inches of snowfall per month over winter.

This rainfall and melting ice and snow fall onto and pass over impermeable surfaces such as roads (Minnesota has an estimated 285,000 lane miles of road surface), parking lots and roofs, picking up pollutants and carrying them to drainage networks and bodies of water. This stormwater pollution presents significant environmental hazards that can affect wildlife and residents alike.

Cold weather stormwater presents particular issues—not only does melting snow and ice pick up pollutants from surfaces, but that snow and ice itself is already loaded with contaminants that settle onto it while it is still frozen and accumulate until the thaw. Add to this the grit and salt that is spread onto road surfaces and it is clear northern states like Minnesota face a unique stormwater pollution challenge.

Minnesota surface water treatment priorities

With over 10,000 lakes and thousands of rivers and wetlands, Minnesota is defined by its bodies of water: not only do these waters supply water to homes and businesses, but they also provide recreational and tourism opportunities and act as critical habitats for wildlife. Minnesota has 80 major watersheds, most of which are characterized by large or moderate river systems. Protecting and maintaining the water quality of these water bodies is therefore a high priority for the state.

As part of its stormwater management strategy, Minnesota has identified that it is more cost-effective to protect high-quality waterways than to restore already degraded waterways, so the Minnesota Pollution Control Agency (MPCA), the Minnesota Department of Natural Resources (DNR), and the Board of Soil and Water Resources give priority to stormwater protection projects.

The MPCA identifies a number of different types of pollution as of particular concern to Minnesota’s water quality:

• 1,4-dioxane
• Bacteria and microorganisms
• Chloride
• Heavy metals such as lead, chromium, arsenic, cadmium and mercury
• Nutrients, such as nitrogen and phosphorus
• Perchloroethylene/tetrachloroethylene (PCE or Perc)
• Petroleum
• Per- and polyfluoroalkyl substances (PFAS)
• Polycyclic aromatic hydrocarbons (PAHs)
• Sediment or TSS, including contaminated sediments

According to the MPCA, as of 2022 there were over 2,900 water bodies with more than 6,000 impairments resulting from the above pollutants. Effects included unhealthy conditions for wildlife, contamination with substances such as mercury, nutrient spills, and increased turbidity due to sediment.

Chloride

Chloride is a pollutant of focus deriving in part from Minnesota’s northern climate, as salts such as sodium chloride, magnesium chloride and calcium chloride that are spread onto winter roads dissolve into meltwater and make their way into aquatic environments and aquifers. Agriculture, water treatment and domestic water softening are also significant sources of chloride.

Once in the environment chloride persists and accumulates, so the state has implemented the Minnesota Statewide Chloride Management Plan, which is aimed at reducing chloride use and controlling its discharge into the environment.

Groundwater

More than 75% of the residents of the state receive their drinking water from groundwater sources, and it also provides the majority of water used by agriculture for irrigation, so preventing contamination of these aquifers and underground water sources is a high priority.

To this end the DNR has drafted a Groundwater Strategic Plan that aims to improve understanding and implementation of sustainable groundwater practices for the state.

Stormwater regulations in Minnesota

As is common across the US, Minnesota’s stormwater regulations are derived from the 1972 Clean Water Act (CWA) and the related National Pollutant Discharge Elimination System (NPDES). While the EPA bears ultimate responsibility for the CWA and NPDES, the agency delegates local authority to the states. In Minnesota the EPA delegates authority for local management and enforcement of regulations to the MPCA.

The MPCA’s Stormwater Program implements both the requirements of the CWA and also the Minnesota State Disposal System, to reduce pollution, manage surface water runoff and protect the environment and water bodies within the state.

The Stormwater Program has three main areas of focus:

• Construction stormwater
• Industrial stormwater
• Municipal Separate Storm Sewer System (MS4) stormwater

General stormwater permits are administered for each of these three areas, with each type of permit incorporating both federal and state requirements for stormwater management within the state of Minnesota.

In addition to general permitting, Minnesota has embraced Green Infrastructure and, more specifically, Green Stormwater Infrastructure practices. These design philosophies focus on keeping and using precipitation and other surface water close to its point of origin, prioritizing philosophies such as runoff reduction, recycling and reuse.

Stormwater monitoring in Minnesota

A key component of Minnesota’s stormwater quality program is monitoring. In order to insure that lakes and rivers meet water quality standards, regular monitoring is carried out to achieve three main objectives:

• Water condition, by testing water quality and gauging the levels of target pollutants of concern
• Problem investigation, to identify the sources and causes of any water quality issues
• Effectiveness, to assess how well water quality management actions and initiatives

The MPCA completed the first ten-year water quality monitoring program of its 80 watersheds in 2018, and it is underway with its second.