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Road salt lingers in Madison’s watersheds, drinking water | Environment

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Road salt lingers in Madison’s watersheds, drinking water
Environment, Health
Road salt lingers in Madison’s watersheds, drinking water

Report: Decades of salt use causes chloride levels in watershed to rise   

Every winter, George Dreckmann, the public information officer for the Streets Division, faces numerous complaints from the public about bad road conditions, asking the department to use more salt in their communities.
 
"It is our policy to not apply salt to residential streets to protect our lakes and groundwater," responded Dreckmann to one resident's complaint via e-mail.
 
The road salt, also known as sodium chloride, doesn’t simply vanish after winter. As a study led by the University of Minnesota conducted in the Minneapolis-St. Paul area revealed, nearly 70 percent of the road salt applied in the metro area remains in the watersheds. Increased salt in area waters affects aquatic ecosystems, cars and infrastructure, as well as the quality of drinking water.
 
Madison adopted road salt for winter maintenance first in 1959. As a result of 50 years of salt use, chloride levels in watersheds continue to rise, according to the 2012 Road Salt Report prepared by Environmental Protection Lead Worker from the Department of Public Health for Madison and Dane County, Rick Wenta, and his colleague Kirsti Sorsa, the environmental technical services supervisor.
 
In 2012, average chloride level in Lake Wingra reached 115 mg/L, a 130-percent increase over the preceding three decades. Chloride in other Yahara Lakes -- Monona, Mendota, Kegonsa, Waubesa -- is accumulating at a higher rate, though the current levels are much lower than Lake Wingra’s concentration, according to the report.
 
 
 
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The lakes' chloride concentrations are still a long way below 230 mg/L limit, the so-called Criterion Continuous Concentration for freshwater established by the U.S. Environmental Protection Agency, which is the highest level to which "an aquatic community can be exposed indefinitely without resulting in an unacceptable effect."
 
But, "we can't continue that forever," said Wenta, concerning the growing environmental levels of sodium and chloride.
 
As a major contributor to salt discharge, the Streets Division endeavors to reduce its salt use. It constricts salt application to the so-called "salt roads," which include main arterials, bus routes, roads around schools, hospitals, and fire stations -- nearly covering one third of the city's streets, said Dreckmann.
 
For the remaining two thirds considered residential streets, the division only applies sand on them if requested, though sand still contains about 5 percent salt to keep it from freezing.
 
The department also stops using salt if the temperature drops below 12 degrees F when salt is no longer effective, said Dreckmann.
 
The amount of salt use, however, is still increasing. The total road salt use reached 7,716 tons in the 2011-2012 winter, double the volume used in the winter of 1982. It peaked at 17,993 tons in the winter of 2007-2008, a particularly snowy season.
 
As the city grows, so expand the salt roads, said Wenta. However, after comparing the growth in salt use to the miles of salt roads, Wenta found that these two trends were not parallel, meaning that "they [in the Streets Division] are using more salt for the same amount of streets."
 
"I think over time you just get [an] increasing service level, where you just become accustomed to driving on a dry street," said Wenta. "There is nobody really pushing back and saying we have to cut this back … people will complain if the roads aren’t in the condition that they are used to."
 
Yet the road salt makes its way into the lakes as well as the groundwater, which is a source of Madison's drinking water.
 
The EPA set a National Secondary Standard for chloride in drinking water at 250 mg/L. And its recommendation for sodium in drinking water is 20 mg/L, though the EPA website said "this guidance level for sodium needs updating, and is probably low."
 
Sodium and chloride concentrations continue to rise in some of Madison's drinking wells, especially those wells located near main thoroughfares. For example, in 2012, a well near University Avenue, well number 14, ranks highest in both chloride (109.2 mg/L) and sodium (37.4 mg/L) concentrations, which increased by 70 and 65 percent respectively in last decade.
 
Chloride and sodium concentrations in Madison's drinking water wells
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1. Bubble diameter is proportional to chloride concentration.
2. Data source: Department of Public Health for Madison & Dane County
 
"Right now it's really not an issue," said Wenta, equating salt in daily water consumption from the most impacted wells to the excess salt consumed in a piece of bread.
 
According to a Public Health Department report released in 2011, even for individuals on a restricted salt diet, the sodium concentrations in the city of Madison water supply are “unlikely to cause any adverse health effects,” though such individuals do need to consider the salt in water when calculating their daily intake.
 
Yet, “this level is likely to be revised upward in the future,” said Joseph Grande, water quality manager for the Madison Water Utility. “Trends at the city wells are likely to continue for chloride and sodium due to use of deicing salt on roads, private parking lots, and neighborhood sidewalks.”
 
The Streets Division did test a couple of alternatives to reduce salt use but, “without a great deal of success,” said Dreckmann.
 
They tested beet juice in the winter of 1999-2000, calcium magnesium acetate the next winter, and calcium chloride brine as a pre-wetting agent from 2004 to 2006. They also tried salt brine from 2009 to 2010, which turned out to be the only promising practice.
 
But alternatives are not friendlier to the environment, said Dreckmann. Basically, they consist of another kind of salt, which still discharges chloride into environment, or an organic compound which can deposit nutrients and disrupt the existing ecosystems in the lakes. These alternatives are also more expensive, said Dreckmann.
 
"We keep trying different things," he said. "But we haven’t found anything yet that really does what we’d like it to."
 
Efforts from the city of Madison alone may be not enough to effectively reduce salt use. Commercial roads, parking lots, and sidewalk use also contribute much to the total volume of salt discharge. In addition, there are many other communities and private businesses using road salt around the Yahara lakes.
 
"Madison’s salt reductions may be negated by the overall deicer use in the lake basins," according to the 2012 Road Salt Report.
 
Other concerns that go against reducing road salt use refer to driver safety during winter. Wenta cited a study in southern Sweden, which shows that "highest accident risk was associated with road slipperiness due to rain or sleet on a frozen road surface." It concluded that to reduce the accident rate under such circumstances, drivers need to be warned about poor conditions, so they will slow down and be more attentive, said Wenta.
 
Madison residents have to re-adapt to the changing environment, said Dreckmann. For example, people need to prepare good tires for winter, drive slower, and "get up earlier in the morning in order to get to work," he said.
 
Dreckmann believes that a major obstacle in reducing salt use is lack of public awareness.
 
"In January nobody cares about the lakes," said Dreckmann with a laugh; people only think about the health of the lakes when they use them in summer.
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