Need Salt?

By Tim Gates, Greening the IU Health Center Intern

With winter weather upon us, snow is on the ground, and once again we find ourselves pouring millions of tons of salt on the roadways, sidewalks, and doorsteps. In fact over 22 million tons of sodium chloride is used on our roadways every winter, and has been increasing an average of 7% every year. In the United States, we use 13 times more salt on roadways than is used by the entire food processing industry.[1]

1

The reasons we use so much sodium chloride are pretty simple; it lowers the freezing temperature of water and thus melts snow and ice, and it is incredibly cheap. But do these benefits outweigh the costs? We all know that splashing salt from roadways can reek havoc on our vehicles, but those same splashes have major effects along roadways eroding soil, killing trees and other plant life, and polluting watersheds.

The biggest concern with the heavy use of salt on roadways is the effects it has on water quality. Studies of metropolitan areas have shown that 70 percent of the salt applied to roads stays within the region’s watershed. [2] This percentage would obviously vary depending on the geographical layout of different population areas and their proximity to water bodies, but here in Southern Indiana, we can safely assume that most of the salt applied to roadways stays within our regions watershed. In fact, recent research from IU SPEA professor Todd Royer found that, during a 28-month period that included two winters, the salinity of the streams near Ellettsville and parking lot outflows was greatest during winter. Though this may seem obvious, it is always a good to gather quantitative data to reinforce what many view as a common assumption. [3]

The technique of applying salts was first used on US roadways in the 1950’s, and since then concentrations of sodium chloride have been building in lakes, rivers, streams, and water tables. [4] Such large accumulations of sodium chloride has an effect on plant and animal life, aquatic life, and in drinking water from wells. The EPA even lists chloride as a “Nuisance Chemical” in drinking water and has created non-mandatory water quality standards to address the issue.  Chloride also has the ability to corrode pipes, which can be very costly and stain water fixtures such as sinks and tubs. [5]

The effects it has on aquatic plant and animal life are even greater. When salt dissolves it releases a heavy influx of sodium and chloride ions that disrupt the ability of freshwater organisms to regulate how fluid passes in and out of their bodies. It has also been shown to decrease biodiversity in wetland areas, altering the development of wood frogs, decreasing the number and types of fish available, and increasing mortality rates of organisms that rely on an aquatic system. [6] When sodium chloride accumulates in fresh water bodies, salty pockets can form near the bottom surface and create biological dead zones. Increases in sodium and chloride have also been shown to increase mobilization of heavy metals in the soil along major highways. [7]

So, what is being done to address this problem? There are lists of alternative chemicals that can be used, such as magnesium chloride, potassium acetate, and potassium chloride, but these can also can be much more expensive, and they often require municipalities to invest in new or upgraded equipment. [8] Plus, replacements can come with their own environmental issues. However, there are plenty of ways to cut back on their salt usage.

Weather monitoring is key no matter the size of the project. Applying deicer just before a storm hits makes it so snow can’t adhere to the ground, and is usually more efficient than waiting until after the snow has fallen. And since sodium chloride doesn’t work below 15 degrees Fahrenheit, getting an accurate read on pavement temperature helps cut down on waste as well. In Wisconsin, the Department of Transportation has been using economical techniques like anti-icing and pre-wetting pavement, which can lower the amount of salting compounds that needs to be applied. Liquid anti-icing chemicals sprayed on pavement before a forecasted storm or frost event are effective in reducing or preventing snow and ice from bonding with the pavement surface, which can make cleanup more efficient. [9]

So, next time you hear of a big snow or frost coming, try to spread your deicer before the snow hits in order to maximize its efficiency and minimize its use. If you don’t make it in time though, there is always a shovel! When asked by the Bloomington Herald, Todd Stevenson, drainage engineer for the Monroe County Highway Department, said he doesn’t use any deicer, but just a snow shovel on his sidewalks.”The main reason we don’t use salt is that we have a concrete driveway and salt degrades concrete,” Stevenson said. [10]

1. http://minerals.usgs.gov/minerals/pubs/commodity/salt/myb1-2008-salt.pdf

2. http://www.eurekalert.org/pub_releases/2009-02/uom-uom021009.php

3. http://newsinfo.iu.edu/news/page/normal/23680.html

4. http://www.dnr.state.mn.us/volunteer/janfeb10/road_salt.html

5.http://water.epa.gov/drink/contaminants/secondarystandards.cfm

6. http://www.newyorkwater.org/downloadedArticles/ENVIRONMENTANIMPACT.cfm

7. http://www.dnr.state.mn.us/volunteer/janfeb10/road_salt.html

8. U.S. Green Building Council L.E.E.D. Operations & Maintenance Manual v 3.0, pg.11, Site Selection Credit 2

9. http://dnr.wi.gov/wnrmag/2010/02/salt.htm

10. http://newsinfo.iu.edu/news/page/normal/23680.html

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