Link to City of Madison Website

Link to EcoMelt Website

Excess Salt and Sand Use in Deicing the Wingra Watershed
Rachel Byrd-Felker, Kelli Matya, Hannah Drechsel
 

Abstract

Distribution of road salt and sand (mixed with salt) throughout the winter months is an essential part of drivers’ safety in Madison. However, the overuse of road salt also has important and potentially harmful effects on the environment. Specifically, the overuse of this product can affect the groundwater quality, thus affecting the health of the watershed at large. In response to this issue we measured both the percentage of salt within sand piles throughout the city, and the weight of salt leftover after snowfalls on the Edgewood Campus. To test the salt levels within the sand piles, we filtered the sand through water, and then used a Hach test to determine the level of chloride remaining in the sand. After a snowfall, we collected one square meter of salt from varying locations throughout the Edgewood Campus, and then weighed them to determine the amount of excess salt. Initially, we had hypothesized that the salt levels both in the sand piles and in the campus area would be excessive. Our results from the Edgewood Campus supported our hypothesis, and through the great variation of salt distributed between areas, implied that a consistent system for salt distribution is lacking on the Edgewood Campus. Our hypothesis was not supported in the case of the sand testing, as our results showed that less than 4% of the total weight of the salt piles was made up of sand. Once again, the variation within our results implied a need for the development of a more consistent salting plan from the City of Madison.

Introduction

While conducting research on the level of salt concentration in different areas of the Wingra Watershed, we began learning about the connection between changing chloride levels within the Watershed between the 1940’s and the present and the implementation of road salt deicing programs throughout the city. Although deicing is a fundamental part of maintaining drivers’ safety within the Madison area, over use of road salt has been shown to have the potential to harm fish and other aquatic organisms as they enter local bodies of water (City of Madison Salt Report, 2004-2005). In the winter of 1959, the City of Madison began applying road salt as a deicing agent throughout the city. Correspondingly, beginning in the winter of 1961, levels of sodium chloride (salt) in Lake Wingra began to rise. By 1972, the chloride level in Lake Wingra was 58mg/L, and the City of Madison was using approximately 5600 tons of salt on Madison roads (City of Madison Salt Report, 2004-2005). In 1973, the Madison Common Council implemented a plan to reduce the amount of road salt used within the Wingra Watershed areas. The original goal of this plan was to reduce the amount of salt being used to roughly 50% of the amount used in the winter of 1973. However, in 2004-2005, 48% more salt was used than in the year the program was implemented, and the chloride levels in Lake Wingra had climbed to 79.4 mg/L (City of Madison Salt Report, 2004-2005).
Edgewood College uses the Eco-Melt brand of road salt on its campus. This brand is a mixture of sodium chloride, magnesium chloride and the “ultimate accelerator”, which the company did not define. The Eco-Melt company suggests using the product only on “quality concrete that is air entrained” and more than one year old (www.ossian.com/Ecomelt_frames.htm), and warns that the product’s repeated use in areas with shrubbery or grass could cause damage. Eco-melt suggests using ¼ to ½ cup of salt per square meter.
After reviewing the history of salt use in Madison provided in the City of Madison Road Salt Report and the information provided on the Eco-Melt website, the negative impacts of over-use of road salt became evident. According to the road salt report, when snow and ice melt, dissolved road salt is carried into lakes and local water bodies through storm water runoff and into ground water. The chloride ions from road salt cannot be dissolved by natural biological processes and as a result all the chloride from the road salt reaches the body of water. At high levels of concentration, the chemicals from road salt have toxic effects on animal and plant life within the water. Due to the fact that sodium moves quickly through the environment when dissolved, there is also a risk of dissolved sodium being absorbed into the soil and groundwater, and hence our drinking water. The use and overuse of road salt, therefore, have profound implications on several aspects of our watershed.
An alternative to the overuse of road salt has been providing the public access to sand throughout Madison neighborhoods to assist with road deicing. These public sand collection sites are based in parks throughout Madison. The minimum amount of salt needed to prevent the sand from freezing is 4% (Salt and Highway Deicing, Vol. 42, No.2). In the winter of 2004-2005, 3,926 tons of sand was used throughout the Madison area, with a 10% salt make up (City of Madison Salt Report 2004-2005).
We decided to research both aspects of this issue in regards to the Wingra Watershed. We wanted to determine both if the amount of salt being used for deicing purposes within the Watershed was excessive , as well as whether the amount of salt being added to the public sand collection sites exceeded the 4% maximum. To address the salt aspect of the question, we turned to the parking lots and sidewalks in the Edgewood College Campus. We hypothesized that the amount of salt being used in this area was, in fact, excessive, resulting in leftover salt in the parking lots and sidewalks after the initial melting of ice and snow. In order to address the sand issue, we turned to the public sand collection sites. We hypothesized the amount of salt added to these collection sites was well over the 4% maximum.

Methods

Due to the fact that our project centers on two separate questions, we devised distinct research procedures for each part of our project. In order to conduct our research on the sand, we first discovered the placement of the public sand buckets in the west side of Madison. These sites were Elver Park, Olin Park, Garner Park, Glenway Golf Course, and Spring Harbor Park (cityofmadison.com/streets). Unfortunately, we were unable to collect sand from Olin or Spring Harbor Park due to lack of availability. Therefore, our final study included Elver Park, Garner Park, and Glenway Golf Course. We obtained a one cup sample of sand from the top of the sand pile at each of these locations. We then filtered the salt from the sand in 200ml of de-ionized waster to determine the salt to sand ratio in the sample. After two separate filtering processes we tested the water to obtain the level of sodium chloride that was filtered from the sand. To do so we used a Hach test kit measuring with both high and low range kits. Low range measures from 5-400 mg/L and the high range measures for 500-100,000 mg/L. The different ranges were needed to test the samples due to the differing levels of sodium chloride in each sample taken.
To determine the percentage of salt in each sample of sand we first figured out how much salt was removed from each sample during the Hach Testing process. We converted the milligrams per liter found to the number of grams in the two liters used to dissolve the salt from the sand. Once this number was found, we then divided it by the original dry weight of each sample, coming up with the percentage of salt in each sample based on weight. Through a weight test, we found that sand weighs 1.4 times the amount of the same amount of salt. Therefore, we multiplied our percentage based on weight by 1.4 to find the percent based on volume.
In order to research the salt level in the Edgewood College parking lot, we needed to wait until the first snowfall of the season, when the salting began. After a snowfall, we waited until the salt had melted the snow from the parking lot, and therefore served its purpose. Generally, we collected the salt 1-2 days after the snowfall. We then used a quadrat to take random samples of salt from different areas of the parking lot. By using a quadrat, we were able to limit the area being tested to one square meter. In order to obtain these salt samples, we threw the quadrat on the ground, and then swept the salt from that area into a plastic bag. Our use of the quadrat could not be 100% random due to cars in parking lot and other obstructions; therefore we were forced to test based on space limitations. After performing four samples of this kind, we weighed the salt to determine the amount of salt left over after the snow had melted. Before weighing, we used forceps to remove as many impurities, such as rocks and sticks, from the salt as possible.

Results

Table 1 shows the difference between the initial sand and salt weight and the weight after the sand had been flushed. This information was used to determine the percentage of salt that had been present in the sand. We found results ranging from 2.6% to 4.3%.

Table 1: (The initial weight of sand used and the weight of sand after two salt filtration processes. Also, the difference between the initial sand weight and the weight after the two salt filtration processes.)

Table 2 shows the Hach Test results converted from mg/L to grams. This conversion was used to determine the amount of chloride removed from the sand by weight and volume. By weight, we found chloride levels ranging from .03% to 2%. By volume, we found chloride levels ranging from .042% to 2.8%.

Table 2: (Hach Test results after first filtration process and second filtration process, determining the chloride level in water in mg/L.)

 

Table 3: Table 3 shows the quantity of salt found in one square meter areas of the Edgewood College parking lots and sidewalks.

Discussion
After completing all of out tests, we found that the sand and salt ratio either did not exceed the maximum salt quantity of 4%, or was almost exactly at the limit. Although these salt levels were much lower than we had hypothesized, they still raise certain concerns regarding the distribution of the salt within the sand piles. The fact that the salt content varied significantly depending on location indicates that there is no strict procedure for the combining of the salt and sand. Therefore, it is highly probable that salt concentration is higher in different places within the sand pile, as well as at varying locations. This scenario brings up many issues in regards to the protocol used by Madison City workers while distributing the salt and sand. Based on the implications of our results, it seems as though it would be advisable for the City of Madison to develop a more concrete and consistent manner of combining the salt and the sand, which would avoid any potential overuse.
The salt collection we performed on the Edgewood Campus sidewalks and parking lots indicated a gross overuse of salt throughout the winter. We conducted the salt collection at least 24 hours after the snowfall. By this point, the initial ice and snow from the fall had melted in these areas. All the salt we collected, then, was excess, and hence unnecessary. This shows that the individuals responsible are distributing the salt indiscriminately. Also, the amount of salt we collected from varying spots on campus was drastically different, ranging from less than one gram to nearly 750 grams. This incredible discrepancy suggests that Edgewood, like the City of Madison, has failed to formulate a solid, coherent plan for salt distribution.

References

City of Madison Road Salt Report—2004-2005. Prepared by John Hausbeck, Kirsti Sorsa, Tommye Shneider, Madison Department of Public Health.

Ecomelt website. www.ossian.com/Ecomelt.frames__htm.

Walker, Donald, P.E,.“The Truth About Sand and Salt for Winter Maintenance”, Salt and Highway Deicing, Vol. 42, No. 2. Summer, 2005.

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