In the northern regions of the U.S. and in Canada a water contaminant of
increasing concern is chloride. The source of chloride contamination is mostly sodium
chloride (NaCl) which is used in large quantities for road de-icing and for water
softening. Chloride enters into the environment easily in snowmelt runoff and in
wastewater treatment plant discharges. Because it is a fairly conservative material it can
travel long distances without assimilation. It affects the quality of aquatic ecosystems.
Because of its adverse effects on plants and aquatic animals, MPCA standards of
230mg/L and 800 mg/L have been set for chronic and acute exposure.
The Twin Cities Metropolitan Area (TCMA) is one of the regions where salt 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. 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 186 cities and townships. There are over 26,000 lane miles of roadways with
impervious surfaces in the TCMA.
In this report an inventory of the amount of road salt (NaCl) applied in the
TCMA each year is given. This study was not aimed at evaluating the effectiveness,
suitability or cost of using NaCl as a de-icer. In addition to the total amounts of salt used,
it is of interest to identify and quantify the metrics that determine the rates of road salt
application. The spatial and temporal scales will be large enough so that the results of this
study can be compared to other regions in northern climates.
Many sources of information regarding the use of road salt in the TCMA and the
state of Minnesota were consulted. In the TCMA, most municipalities and counties
purchase salt through contracts offered by the Material Management Division (MMD) of
the state of Minnesota. The average amount of reported salt use per winter season (2001
to 2006) was 236,800 tons per year and varied between 243,000 and 274,000 tons per
year. Relative to the sum of the contract amounts, the actual reported use was on average
93% for the TCMA.
Not all municipalities participate in the MMD contract or keep track of the actual
road salt applications. The amount of road salt used by municipalities without
information was estimated based on a per capita road salt use rate of 0.045 tons per
season per person. The rate was determined from the reported road salt use in the TCMA
covering about 90% of the population.
Minnesota Department of Transportation, Local Roads Research Board
Sander, Andrew; Novotny, Eric; Mohseni, Omid; Stefan, Heinz.
Inventory of Road Salt Use in the Minneapolis/St.Paul Metropolitan Area.
St. Anthony Falls Laboratory.
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