In northern states of the U.S. and in virtually all provinces of Canada sodium
chloride is becoming a water contaminant of increasing concern. The source of
contamination is mostly anthropogenic: Salt (NaCl) is used in large amounts for road
deicing and water softening. Sodium chloride enters into the environment easily in
snowmelt runoff and from wastewater treatment plant discharges.
Sodium chloride is not removed by conventional waste water treatment. It is a
fairly conservative material and can travel long distances without assimilation. It affects
terrestrial and aquatic ecosystems. Because of its adverse effects on plants and aquatic
animals, water quality standards for Cl have been set, e.g. by the Minnesota Pollution
Control Agency (MPCA) at 230mg/L and 800 mg/L for chronic and acute exposure,
The Minneapolis/St. Paul (Twin Cities) Metropolitan Area (TCMA) is one of the
regions where sodium chloride is used for winter road maintenance and for water
softening. The TCMA is an urbanized area with a population of about 2.7 million people
in seven counties. It is located at about 45oN latitude and has a reputation of cold and
long winters. The TCMA is traversed by the Mississippi River and several of its
tributaries, and claims to have 949 lakes within its seven counties and over 188 cities and
townships. There are over 26,000 lane miles of roadways with impervious surfaces in the
In previous reports of this study we have given a budget for road salt applications
in the TCMA and field observations of salinity in lakes of the TCMA. The goal of this
study is to give an overview of measured chloride and sodium concentrations in
groundwater (wells) of the TCMA. The information will be compared to statewide
observations in Minnesota, and to other regions in northern climates. Changes in
groundwater salinity in the TCMA and Minnesota over time, particularly the last 50 years
are of particular interest, because it is suspected that aquifers are the ultimate recipients
(sinks) of some of the road salt applied at the ground surface. This study is not aimed at
evaluating the effectiveness, suitability or cost of using NaCl as a deicer.
Local Road Research Board, Minnesota Department of Transportation
Sander, Andrew; Novotny, Eric; Mohseni, Omid; Stefan, Heinz.
Potential for Groundwater Contamination by Road Salt in Minnesota.
St. Anthony Falls Laboratory.
Retrieved from the University of Minnesota Digital Conservancy,
Content distributed via the University of Minnesota's Digital Conservancy may be subject to additional license and use restrictions applied by the depositor.