Here in North Carolina, our snowstorms (or often sleetstorms) are few and far between. As such, we may not think about snow as stormwater – and snowmelt as stormwater runoff. Though the risk for flooding is lower, transportation of pollutants is still an important consideration when preparing your home for inclement weather. Importantly, we tend to introduce a new pollutant into the mix when it might snow: salt.
Salt can come in many forms (think table salt, rock salt, brine) and with different chemical constituents, but the common denominator among salts we use to address ice concerns is that they contain chloride: sodium chloride (NaCl), magnesium chloride (MgCl2), and calcium chloride (CaCl2) most commonly. Chloride is of concern because it does not biodegrade, nor do organisms uptake and repurpose it naturally. This means all of the salt we apply – to our roads, sidewalks and driveways – is going to end up in the surrounding environment.
There are a few different ways that these chloride salts make their way into our ecosystems and waterways. Driving on salted roads can spray the salt onto vegetation and soils adjacent to the roadways, which can impact the growth of vegetation – altering the habitat and impacting native species. The chloride can then migrate into groundwater, which can degrade municipal and personal water supplies over time. When the snow melts, those salts can get carried into the stormwater system. In places like North Carolina, with Municipal Separate Storm Sewer Systems (MS4), these salts are delivered directly to our streams.
High concentrations of salt can be extremely detrimental to aquatic life, both flora and fauna. Thankfully in North Carolina, we do not have to apply salt frequently, but even occasional shocks to the system can hurt sensitive wildlife. In particular, macroinvertebrates are sensitive to increased salinity – and reduced macroinvertebrate population and diversity impacts the whole aquatic food web.
The brine applied to roads has a much lower rate of runoff than plain rock salt, which means that brine impacts ecosystems a bit less. Brine is typically 20-30% salt. Hydrating the salt in advance helps it stick to the road. Though the salt will still enter the environment, the overall chlorine measured in adjacent soils and waterways is significantly lower when compared to levels seen with rock salt. It is also worth noting that salt, particularly rock salt, is corrosive to both infrastructure and cars.
Some states are starting to use beet juice in their road brine to reduce the total salt load, while maintaining the benefits of treating the roadways. The beet juice is water-soluble, non-corrosive, and created as a byproduct of agricultural processing. As a relatively new technology, scientists are still researching possible ecosystem impacts of the use of beet juice on aquatic organisms.
There are many reasons to consider alternative solutions to putting rock salt down on your property. You may want to apply an inert substance like sand (which will not dissolve), to increase traction without impacting water quality. Some websites may recommend coffee grounds for a similar application, however the nutrients in coffee grounds may cause adverse impacts to water quality. Salt only helps melt snow at temperatures around freezing, so it may not be particularly helpful for your residence. Consider investing in a good snow shovel, enlisting the help of friends, kids, or neighbors, and only clearing when you need to. Snowstorms are rare here – if you are able, take the time to enjoy it!