Road Salt use on the Edgewood Campus
Monica Zillner

Introduction

Methods

Results

Discussion 

Link to Full Report (pdf)

Link to Slide Show on Salt Movement Through Watershed (pdf)

Introduction

Road salt is used to melt ice and snow in parking lots, on roads, and on sidewalks. Chloride levels in Lake Wingra have risen since use of road salt began being used as a de-icer. Before salting, levels were below 10 mg/L. Since salt practices have been instituted, levels often surpass 75 mg/L, particularly after the spring snowmelt (WRM Workshop, 1999).

Road salt moves through the watershed by drying and being transported by wind, running downhill, infiltrating soil and groundwater, or may be sprayed or splashed onto vegetation along salting areas. Road salt negatively affects the health of the watershed, including its vegetation and drinking water. Edgewood contributes to the chloride levels in Lake Wingra through use of road salt on campus parking lots and sidewalks. The sidewalks are salted by College staff and the parking lots by a private contractor. To determine if Edgewood uses more road salt than necessary to de-ice, I collected road salt that remained after melting of snow and ice from Edgewood parking lots and sidewalks.

Back to top

Methods

• All the salt was collected from ¼ meter square quadrat samples using a brush.
• 5 sidewalk and 2 parking lot locations were sampled on 12/1/2008, 12/6/2008 and (sidewalks only) 2/27/2009 following snow events (See map).
• At the time of collections, snow and ice were not present in sampling areas, indicating melting had already occurred.
• Samples were cleared of debris and weighed.
• Salting guidelines from the City of Madison were used to determine the recommended amount of salt to apply to a square meter: 12 grams. This amount was used to make an estimate of how much salt had melted previous to sampling and an estimate of total campus use, based on paved impervious acreage.
• I used data from the City of Madison to determine how many times and how much road salt is applied annually to streets in the Lake Wingra Watershed.

Figure 1. Map with labeled sampling sites. ¤ represents parking lots. ☐ represents sidewalks.

Back to top 

Results 

• Edgewood campus applies an estimated average excess of 129 grams per square meter on sidewalks and 86 grams per square meter on parking lots (Figure 3).
• More road salt than is needed to de-ice was applied in every sampling. Almost 12 times the amount needed to de-ice was applied to sidewalks, and 8 times the amount needed to de-ice was applied to parking lots (Figure 4).
• Annually, Edgewood uses an estimated 188 tons of road salt, 169 of which can be considered excessive.
• Edgewood applies 7.7 tons of road salt per acre of paved surface and the City of Madison applies 2.1 tons of road salt per acre of streets (Figure 5).

Figure 2. Result of Samples. The average salt/meter² indicates the amount of excess road salt.

Figure 3. Comparison of excess road salt on sidewalks and parking lots.

Figure 4. Comparison of the estimated total annual salt use on Edgewood Campus, road salt used to de-ice, and excess amounts of road salt.

Figure 5. Comparison of ton of road salt per acre that the City of Madison and Edgewood Campus use.

Back to top 

Discussion 

• The current de-icing practices of Edgewood College result in excessive use of road salt.
• Edgewood’s contribution of road salt into the Lake Wingra Watershed, and consequently, sodium chloride levels, is significant. Edgewood applies nearly four times as much road salt per acre as does the City of Madison to maintain its streets.
• Together, the City of Madison and Edgewood contribute 983 tons of road salt annually to the Lake Wingra Watershed; of that, Edgewood’s estimated contribution is 19%.
• Future studies should consider the correlation between weather events and salting, and take more samples from more locations.
• Edgewood College should consider training for employees to raise awareness about concerns related to road salt use and instruction on application methods to apply an amount that is less excessive.
• Edgewood College should review its criteria for determining when road salt is needed on sidewalks and parking lots. Trucks responsible for the parking lots may recalibrate spreaders to apply less road salt.
• Thorough shoveling and plowing before applying road salt reduces the amount needed.
• Alternatives to road salt, such as calcium magnesium acetate (CMA) should be considered to mitigate negative effects on watershed health.

Back to top