Salt continues to pollute Minnesota lakes and streams

This year, the Minnesota Pollution Control Agency (MPCA) is adding Long Lake in Stillwater to the list of lakes and streams impaired by chloride (salts), bringing the statewide total to 54. Other local water bodies already listed as impaired by chloride include Tanners Lake in Oakdale, Battle Creek and Carver Lakes in Woodbury, and Battle Creek.

^{The map above shows lakes and streams in the Twin Cities metro that were classified as impaired (red) or at-risk (yellow) from chloride pollution as of 2020. This year, Long Lake in Stillwater is one of four new water bodies to be listed as impaired.}

Salts are commonly used to help melt ice on sidewalks, parking lots, and roads during the winter. However, when the ice melts, it carries the salt with it into nearby lakes, streams, and wetlands. Unlike phosphorus, which is taken up by aquatic plants and algae in the water, chloride continues to accumulate over time. Once concentrations are high enough, the chloride becomes toxic to fish and invertebrates and can even prevent lakes from turning over the in spring and fall. Species such as trout and the mayflies that they eat are particularly vulnerable to chloride pollution.

In addition to road salts, two other major sources of chloride water pollution include water softener salt and agricultural fertilizers (most often potassium chloride).

For more than ten years, the MPCA has offered a training and certification program for winter maintenance professionals, in partnership with Fortin Consulting. The program offers three separate tracks for roads, parking lots and sidewalks, and property managers, and focuses on strategies for reducing overall salt use without impacting public safety. Some of the recommended best practices include: pretreating pavement before it snows to prevent ice from adhering; using pavement temperature sensors to select the best product for weather conditions (sodium chloride does not work when the pavement is colder than 15°F); using a liquid brine instead of rock salt to reduce waste; and plowing early and often.

^{Above: Pretreatment (sometimes called anti-icing) before snow helps to prevent ice from adhering to pavement. Photo from cleanwatermn.org.}

To date, 20,000 people have participated in Minnesota’s chloride training program, including public works staff people from most of the larger cities in Washington County. Fortin has also begun partnering with Wisconsin Salt Wise to offer the training programs in Wisconsin.

Concerns about salt pollution have also led many communities to explore alternative solutions for dealing with winter snow and ice. In 1988, Holland, Michigan installed a snowmelt system that uses waste heat from power generation to run hot water beneath streets and sidewalks in the downtown area. The system can melt one inch of snow per hour and helps to keep the pavement clear and dry, even in the middle of winter.

^{In Holland, Michigan, waste heat from power generation is used to heat water, which is circulated through 120 miles of plastic tubing underneath the streets and sidewalks. Photo from City of Holland.}

Some communities have begun adding beet juice, a bi-product of sugar production, to their brine solutions. The beet sugar enables sodium chloride to work at colder temperatures and reduces the overall volume of salt needed to clear roads. There are also cities in Wisconsin using left-over salt brine from cheese production on their roads.

In some parts of the country, road crews use sand and gravel, in lieu of salt. This helps to provide traction for vehicles, but doesn’t actually melt the ice. Sand and gravel does need to be swept-up and collected in the spring, however, otherwise it can smother roadside vegetation and silt-in nearby lakes and streams. A final strategy for some far-north and alpine locations is to skip the gravel, sand and salt altogether and require drivers to use spiked wheels or chains on their tires instead.