Does road salt harm the environment?
Deicers, like road salt, make our roads safer during the winter, but over applying salt canposea very real threat to the health of our rivers and environment.
Water runs over the landscape after precipitation and melting events and picks up chemicals and pollutants along the way. Pollutants, like chloride-based deicers, eventually end up in rivers, streams, and lakes.
Chloride-based deicers can negatively impact water quality, aquatic life, vegetation, soil, pets, wildlife, road, and vehicles.
Pets and Wildlife
Pets and wildlife can be attracted to consume road salts either on their paws or on the sides of roads. Aside from the risk of potential collisions, animals consuming road salts can become sick or die if they ingest too much of, or the wrong kinds of deicers. Many declumping agents mixed with salt contain cyanide.
Putting our Three Rivers on a Low Salt Diet
Since 2010, Milwaukee Riverkeeper has worked with U.S. Geological Society (USGS) to monitor chloride levels in many of our local rivers and streams. In 2015, Fund for Lake Michigan funded the expansion and development of our road salt monitoring program to deepen our understanding of the local impacts of road salt application and boost community awareness of the issue.
In 2016, 20 volunteers helped Milwaukee Riverkeeper monitor 29 stations forchloride and conductivity. Our volunteer monitors collected conductivity data on days followingtrigger events whenlarge amounts of runoff is expected due to precipitation or melting.
Milwaukee Riverkeeper also presents the results of our road salt monitoring program and the negative impacts of road salt on our waterways throughout the Milwaukee River Basin.
Chloride Levels in the Milwaukee River Basin
Results indicate large amounts of salt enter our rivers as runoff during the winter months. Sites throughout the Milwaukee River Basin frequently reach chloride levels that are toxic to aquatic ecosystems from December to March. Our monitoring efforts resulted in four stream segments being listed by the Department of Natural Resources for chloride impairments.
Organisms living in stream segments impaired by chloride will be less competitive, less active, reproduce less, and depending on the concentration could be more likely to experience die-offs.
The Environmental Protection Agency (EPA) defines impaired waters as waterways that are considered to be too polluted or otherwise degraded to support local communities and or ecosystems.
In Wisconsin, waterways that exceed chloride standards of 395 mg/L for four days (chronic toxicity) or 757 mg/L (acute toxicity) on two separate occasions are considered to be impaired.
These standards are based on tolerance levels of aquatic ecosystems in Wisconsin. At these levels of chloride, native aquatic organisms are less likely to forage and reproduce.
Specific conductivity is a measure of the ability of water to conduct electricity. Measurements of specific conductivity are impacted by the presence of charged particles, both positive (cations) and negative (anions). Specific conductivity is naturally tied to the geology of streams, but it can also be impacted by discharges of charged particles into streams (e.g. chloride, phosphate, nitrate, heavy metals, etc.).
Chloride deicers will eventually becomesuspended in our waterways so the relationship between chloride and specific conductivity is a particularly important indicator for monitoring the impacts of road salt on our rivers.
Using specific conductivity measurements taken during each trigger event, and the relationship curve below, our volunteers were trained to predict when sites would surpass state standards for chloride and when it would be cost-effective to take a chloride sample.
When specific conductivity measurements indicate chloride levels might exceed the standards for toxicity, volunteers collect a water sample for four consecutive days. These samples are sent to the Wisconsin State Lab of Hygiene and analyzed for chloride concentration.
Since conductivity and chloride have such a strong relationship, after all of our data had been collected, Milwaukee Riverkeeper was able to use conductivity measurements from each sampling date and some trends from our previously collected chloride data to predict what chloride levels might have been on days that did not require the analysis of a chloride sample. As a result we can speculate what chloride levels might have been associated with the specific conductivity values that our Winter Watchdogs were seeing out on our rivers.
The data that our volunteers collected is valuable as a tool for understanding where our rivers are struggling with chloride exceedances, how frequently those events are occurring, and at what extent. Comparing locations that are struggling with high levels of chloride to those that aren’t will help us speculate what factors might be influencing those conditions. That means that down the road our monitoring can become more precise, and our messaging surrounding sustainable road salt usage can become more targeted and can be supported with more specific evidence.
Locally Impaired Waters
Our 2016-2017 road salt monitoring data identified nine stretched of streamsthat should be added to the impaired waters list based on state standards for chloride:
Oak Creek Airport Tributary, Crestwood Creek, North Branch Oak Creek, Beaver Creek, Indian Creek, Noyes Creek, Southbranch Creek, Honey Creek, and Brown Deer Park Creek