Groundwater in the Great Lakes Basin

INTRODUCTION
Salt is commonly used as a de-icing and anti-icing
agent and to a lesser extent as a dust suppressant.
Road salt is generally sodium chloride (NaCl). Other
compounds that are also used, but to a much smaller
extent, include calcium chloride (CaCl 2
), potassium
chloride (KCl) and magnesium chloride (MgCl 2
)
(Environment Canada, 2001). Environment Canada has
defined road salt that contains inorganic chloride salts
as toxic under the Canadian Environmental Protection
Act, 1999 (Environment Canada, 2001). However, road
salt still has not been officially listed on the List of
Toxic Substances (ECO, 2007; RiverSides Stewardship
Alliance and Sierra Legal Defence Fund, 2006).
Application Rates
Average road salt use in Canada has risen from 4.9
million tonnes during 1997-1998 (Environment Canada,
2001) to 6.8 million tonnes in 2003 (RiverSides
Stewardship Alliance and Sierra Legal Defence Fund,
2006). It is estimated that of this amount 2 million
tonnes are spread in Ontario (ECO, 2007), and about
500,000 to 600,000 tonnes are utilized by the Ontario
Ministry of Transportation on 16,500 kilometres of
provincial highway (Bradshaw, 2008b). This equates to
an application rate of 30.3 to 36.4 tonnes/km.
In the United States annual road salt use fluctuates
from 10 to 20 million tons per year (Schueler, 2005)
and road salt use in the United States has increased a
hundred fold from 1940 to
2005 (Jackson and Jobbágy,
2005). It is estimated that
9.5 million tons of salt
is added to runoff in the
United States every year
(Stefan and Mohseni, 2007).
Three-quarters of all road
salt used in the United
States is deposited on the
roads within six of the Great
Lakes states: New York,
Ohio, Michigan, Illinois,
Pennsylvania and Wisconsin
(Jackson and Jobbágy, 2005).
Fond du Lac County, Wisconsin, used 3,357 tons of
road salt in December 2007 in comparison to the 464
tons used in December 2006 (Zezima, 2008). The
Wisconsin Department of Transportation estimated
that more than 700,000 tons would be used on state
highways in 2008, a 73% increase over 2007 (Bergquist,
2008). New Hampshire is estimated to have used twice
as much road salt in 2007 as in 2006 (Zezima, 2008).
State roads alone in Michigan during 2007-2008 had
more than 757,000 tons applied (State of Michigan,
2008). Gladwin County, Michigan, deposited 2,700
tons during January 2008, the same amount used for the
entire winter season in 2006-2007 (“Road salt,” 2008).
Toronto uses an estimated 125,000 to 140,000 tonnes
of road salt each winter (Ferenc and Kalinowski, 2008;
Gray, 2004). An additional 1,000 tonnes is purchased by
Toronto GO transit for areas such as platforms (Ferenc
and Kalinowski, 2008). By February 2008, Toronto had
already applied 100,000 tonnes (Bradshaw, 2008a) and
it is estimated that 170,000 tonnes would be applied in
total for the 2007-2008 year (Bradshaw, 2008b).
Toxicity
Road salt is toxic to animals and native plants, results
in groundwater and surface water contamination
and may produce adverse health effects in humans
(RiverSides Stewardship Alliance and Sierra Legal
Defence Fund, 2006; Jackson and Jobbágy, 2005;
Environment Canada, 2001)(Figure 1). The effects are
Watershed Pollutants and Urban Toxics
However, these numbers
are likely a gross underestimation
for the winter of
2007-2008. An unusually
harsh winter resulted in
record high road salt usage
throughout much of the
United States and Canada.
Figure 1.
Chloride concentrations in the Credit River downstream of the Town of Orangeville
are rising over time
Source: Aaron Todd, Environmental Monitoring and Reporting Branch, MOE
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