Salt Use and Snow Removal: Effects and Alternatives
Snow is an overwhelming part of our life up here in the northern states. Some people celebrate the coming snow storms by bundling up and enjoying the brisk air, while others bundle up and retreat indoors. And yet, others slide their warm boots on, don their hats and choppers, and head directly into whatever snow event drops on our heads, whether that be flurries, blizzard, or freezing rain.
I'm talking about the plow drivers who work during the worst weather Minnesota offers up. Did you know that Minnesota has over 130,000 (!) miles of roadways? That's a lot of roads to build, repair, maintain, protect, and plow and those 130,000 miles don't clear themselves!
But, why are we talking about snow removal in April? Two reasons: I wanted to show off the plow-naming contest MNDoT held this winter. Central Minnesota is now home to the plow named "Darth Blader," a grand name, right? You can check out the rest of the winners of the 7 other districts here (special shoutout to my favorite, "Ope, Just Gonna Plow Right Past Ya")
The second, and more important, reason we're bringing up the topic of snow removal is that right now, as the snow piles are melting into oblivion, the salt and brine solutions used to treat the roads and keep our vehicles on-road are now being carried away by run-off into nearby watersheds and soil.
The Purpose of Salt During Snow Events
So, why do we use salt and brine mixtures in snow removal? The main reason is to lower the temperature at which ice forms. According to the Crow Wing County Highway Department Snow and Ice Operations Methodology statement, standard road salt is most effective at temperatures above 15°F, but effectiveness degrades at lower temperatures and is completely ineffective at 0°F. If you want to get technical, salt keeps the water molecules from forming ice crystals. The salt must be in a solution with water for this to work, which is why a brine is used.
Brine is usually applied to roads before the snow flies. The resulting salt residue is activated once the precipitation actually hits. The brine keeps the snow or ice from bonding to the roads, which also makes any snowfall easier to remove later. (Not to mention, keeps our vehicles from careening off the road!)
The Effect of Salt Use on the Environment
All things said and done, over 365,000 tons of salt are used for deicing in the Twins Cities Metropolitan Area every year. That's just the metro area. Think of how much is spread out on all of roads in the state. Proper application of these methods can reduce collisions by up to 93% (according to the American Highway Users Alliance). There's really nothing as effective as using road salt. However, there are significant downsides to utilizing it. Let's look at some sectors where the detriment can be seen.
Effects on Plants & Soil
Sodium and chloride ions (which form road salt) separate when dissolved in water. Plants are affected by the dissolved salt. These ions can displace other minerals in the soil and plants will absorb them instead of their preferred nutrients, leading to poor development and growth.
In addition to poor growth, if the ground is saturated with too much salt, native plant species will simply be unable to seed where they prefer. Water that would normally be available to plant roots, will instead be absorbed by the salt. This leads to dehydration of the plants.
Moreover, if native plants are unable to thrive in a saline-based soil, other more competitive non-native plants will simply outcompete. This can be detrimental to the entire ecosystem, as everything is connected. Change the soil, change the plants ability to grow there. Change the plants, change the animals.
Effects on Water
A recent study has found that "37% of the drainage area of the contiguous US has experienced an increase in salinity over the past 50 years, citing road salt as the dominant source in colder regions." This is a growing concern, as once salt is introduced to an ecosystem, it can be difficult to remove. It can only be removed through transport (via rivers or runoff) or diluted via freshwater coming in (like rain or snow). However, transport can be non-existent in certain areas, like aquafers or lakes. If sodium is added to these bodies of water, negative effects will be seen in relation to fish and other aquatic organisms.
Another effect noted is the change in water density. Water polluted by road salt is denser than freshwater, leading to saltwater to rest at the bottom of waterbeds. This will lead to chemical stratification, which will prevent the natural occurrence of "lake-mixing" every year. Without proper oxygen levels at depths throughout the body of water, aquatic insects and fish that thrive at the bottom, will cease to be able to survive. That's bad news for an ecosystem!
What Are the Alternatives?
This table shows some of the alternative deicers in MNDoT's arsenal. Alternative deicers are other mineral salts containing chloride ions, such as calcium chloride, magnesium chloride and potassium chloride, but these are more prohibitively expensive. Some areas alternate these with salt applications to help with costs and only are only used when temperatures get to well-below the proven effectiveness of just salt.
These alternatives have fewer environmental effects, but are more expensive and consume oxygen as they decompose, causing oxygen depletion in water (leading to problems in lakes and other bodies of water.)
The main goal from MNDoT is that they are just going to try to use less salt. They have implemented plans to more thoroughly measure how much salt is applied. This will lead to a fuller understanding of how much salt is needed to be used. With this knowledge, they can better predict proper amounts for certain situations and then only apply the minimum. Yet, unless a more sustainable additive can be found (one that can be an effective deicer as well as be non-harmful to the environment), we may see some irreparable damage in the future. Something everyone is trying to avoid.