Salt a growing problem for Minnesota’s water

In the early 2000’s, Heinz Stefan, a civil engineering professor at the University of Minnesota’s St. Anthony Falls Laboratory asked a simple question, “What happens to all of the salt we put on roads during the winter?” By 2008, Stefan and his research team were able to share the unfortunate answer – it ends up in our lakes, rivers, streams and groundwater.

^{Swimming in Tanner’s Lake, Oakdale, one of 50 metro area lakes that are classified as impaired by chloride (salt). These lakes are still safe for swimming and recreation but don’t support the diversity of fish and aquatic life that they used to.}

In fact, the researchers determined that salt levels had grown so rapidly from 1984 to 2005 that some metro area lakes were no longer “turning over” in the spring and fall. Instead, saltwater in the lakes, which is heavier than freshwater, was sinking to the bottom and staying there, preventing bottom-dwelling fish and organisms from getting the oxygen they need to survive. Water monitoring programs had been underestimating the problem for years because they primarily collected water samples from the surface of lakes during the summer. If left unchecked, Stefan’s team predicted that the salinity of nearly 40 metro area lakes would double within the next 50 years.

This news propelled the Minnesota Pollution Control Agency (MPCA) into action, working with partners in the Twin Cities region to develop a chloride management plan.

^{The map above shows locations of lakes and streams that are impaired by chloride (red) or at high risk of becoming impaired (yellow).}

Currently, fifty of Minnesota’s lakes and streams are labeled as impaired because they have chloride levels too high for fish and other aquatic life. An additional 75 water bodies are labeled as “high risk” because they have chloride levels near the threshold for impairment. In addition, 37% of shallow aquifer monitoring wells in the Twin Cities area have chloride concentrations that exceed the water quality standard, and 27% have chloride concentrations higher than EPA drinking water guidelines.

Affected lakes and streams in the east metro include Judicial Ditch 2 through Forest Lake (impaired), which flows into the Sunrise River (high risk); Clearwater Creek between Bald Eagle and Peltier Lakes in Hugo/Centerville (high risk); Long Lake in Stillwater (high risk); Tanners Lake in Oakdale (impaired); Battle Creek and Carver Lakes in Woodbury (impaired); and Battle Creek (impaired) and Fish Creek (high risk), which flow into the Mississippi River on the lower east side of St. Paul.

^{Battle Creek Lake in Woodbury is another local lake classified as impaired for too much chloride.}

Overall, the MPCA has determined that road salt is responsible for 42% of the chloride in groundwater, lakes and streams. Each winter, Minnesotans dump approximately 730 million pounds of salt on roadways and parking lots – 600 million pounds in the metro area alone. Two other major sources of chloride that area less well-known include agricultural fertilizers (23% of the total chloride) and water softeners, which account for up to 65% of the chloride discharged from municipal wastewater treatment plants and also contribute to groundwater contamination in regions where septic systems are used.

University of Minnesota and others are currently researching new technologies that could reduce our need for salt, including novel applications of porous pavement, nano-technology and solar roads that prevent ice from adhering to pavement, salt-free water softeners, and chemical alternatives to road salt. Meanwhile, here are two ways that you can help to reduce salt use this year:

1) Check your water softener. Conventional water softeners treat hard water by exchanging the hard minerals with sodium and potassium ions. When the system is ‘full,’ it resets or regenerates by sending a pulse of salt water through the system. If you are using more than one 40lb bag of salt a month, you could optimize your softener’s efficiency by extending the time between regeneration cycles or consider buying a new water softener. Another tip? Don’t soften ALL of your water; only soften the water from your hot water taps versus cold water drinking taps.

2) Send your property manager to a certification training. Washington County is co-hosting a SMART Salt Certification Training for Property Managers on Tuesday, Nov. 2, 9am-1pm: https://tinyurl.com/smartsalt. During this free online workshop participants will learn how to improve winter maintenance, save money, and manage legal issues, liability, and regulatory requirements without compromising public safety.

Attending this workshop helped Mayo Clinic to reduce its winter salt use by 60 percent without any increase in slips and falls, and enabled City of Minnetonka to reduce its salt use by more than 50 percent. Funding for this training is provided by the MPCA, with support from the Clean Water Fund, and contributions from Dakota and Washington Counties.