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The Minnesota Department of Transportation is working to minimize impacts from road de-icing on the environment. 2015 MPCA Low Salt-Diet for MN Waters 2014 USGS Report - Urban Stream Contamination Increasing Rapidly Due to Road Salt (150 KB) 2012 - Ice School:Melding the science and craft of winter road maintenance (164 KB) 2005 - Minnesota Snow and Ice Control Field Handbook for Snowplow Operators (460 KB pdf - new window) promotes understanding the tools, best practices, and limitations for snow and ice control. More info at LTAP (exit site). Road Salt: Can we have safe roads and healthy streams?Why do we salt our roads? Duluth, Minnesota receives an average of 84 inches of snow per year; most of it falls in the month of January with an average temperature of 8.4 °F. The resulting snow and ice covered roads combined with steep hills can lead to pretty hazardous driving conditions. Without salt, snow and ice accumulate on roads and bond to the pavement, making it difficult to remove with snow plows. Salt applied to the surface causes some of the snow and ice to melt. The meltwalter combines with the salt to create a liquid called brine. The brine moves the salt around and contines the melting process. Traffic across partially melted ice patches breaks them apart so that plows can remove them. Are there alternatives? The Minnesota Department of Transportation is constantly looking for mothods of ice removal that are more effective and environmentally friendly than salt. Recognizing the corrosive and environmentally damaging nature of winter deicing salt, department maintenance forces have been going on a "reduced salt diet."
Click here to find out! Visit the MPCA's Road Salt and Water Quality website for more information and watch an instructional video by Forin Consulting about winter driveway and sidewalk maintenance.
Wisconsin, Michigan and Iowa residents:Become an Urban Salt Monitoring Volunteer! Find out more. |
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Equipment and procedural improvements have resulted in lower salting rates while maintaining public safety. Understanding the groundwater contamination potential of salt storage, all salt stockpiles are stored indoors. Runoff collection systems are being installed around salt and sand stockpiles and truck washing areas. Maintenance yard housekeeping practices are designed to minimize salt brine runoff. Mn/DOT snowplow operators from Alexandria to Zumbrota have a new tool in their snow fighting arsenal -an anti-icing solution. Liquid chemicals are applied to the roadway before a storm to prevent ice and snow from bonding with the pavement surface. Consider it a pre-emptive strike before the storm. Mn/DOT first experimented with anti-icing in the 1990's; now it's a standard winter practice statewide. Does road salt impact Duluth Streams? All contaminants to our streams are potentially harmful to the organisms that live there. Chloride (one of the components of road salt) is toxic to fish if the level is over 230 mg/L for a tenth of an organisms life span (100 - 200 days for brook trout) or a maximum of 860 mg/L for short periods of time. DuluthStreams doesn't monitor the chloride levels in its streams, but it does monitor electrical conductivity (EC25); a measure of water's ability to conduct an electric current directly related to the total dissolved chloride content of the water. NRRI developed the following relationship between EC25 and the chloride levels of the road salt used by the city of Duluth:
The chronic chloride level of 230 mg/L is equivalent to a conductivity of about 960 µS/s. The following graph shows chloride levels in Chester Creek after a early winter snowfall and snowmelt. Before the road salt entered the creek, EC25 was around 300 µS/s, far below the chronic level of 960 µS/s. When runoff entered the creek, EC25 peaked at about 1600 µS/s, far below the maximum level of 2830 µS/s.
To learn more about this graph, and to see similar graphs from Kingsbury and Tisher Creek, go to the Chester Creek Storm Graph page. As long as the choride levels in the streams remains within these boundaries, road salt isn't causing long-term problems for organisms in the streams. What else do we know about salt effects in the environment? More info about salt impacts on organisms is on our second page. You also may want to read about the USGS monitoring of Shingle Creek (a metro-area creek which is thought to be adversely impacted by decades of de-icing salt applications). Salt Application Rates in Duluth, Minnesota: These guidelines are used by City of Duluth Employees to determine how much salt (in pounds per mile) they need to apply to the roads to keep them safe. Workers re-evaluate weather conditions several times during the day to keep our roads safe while using the minimum amount of salt necessary.
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