Tag Archives: chlorides

Research Provides Foundation for Chloride Mitigation Efforts

The accumulation of chloride in our waters has become a widespread concern. In a recent study sponsored by MnDOT and the Local Road Research Board, researchers measured the transport and accumulation of chloride from road deicers in a metro-area watershed. The findings revealed a greater infiltration of chlorides into soil and subsurface waters than previously assumed.

“The results of this research provide us with knowledge we did not
have before,” says William Herb,a research associate with the University of Minnesota’s St. Anthony Falls Laboratory and the study’s principal investigator. “It will help investigators and policymakers explore ways to capture chlorides and mitigate their damaging environmental effects.”

Road salt (sodium chloride) is used in most states that experience snow and ice, with growing impact. For example, chloride levels in some lakes and streams in the Minneapolis–Saint Paul metro area exceed state and federal water quality
standards, and a recent study showed that levels in more than one-quarter of shallow groundwater wells in the metro were above drinking-water taste standards.

“This is a real concern because even in low concentrations, chloride can be lethal to sensitive plants and some aquatic species, and many of our lakes, wetlands, and streams show acute or chronic levels of chloride,” Herb says.

To learn how chlorides from road salt deicers are transported in urban watersheds, researchers installed field instruments at eight sites in a Roseville watershed. They monitored water and chloride levels nearly continuously over three winter seasons; this included runoff directly from sources (roads and parking lots), transport in ditches and sewer networks, and retention in and release from detention ponds and wetlands. Computer modeling was used to generalize results.

2017-50-p1-image
This drain along State Highway 36 was one of the roadway runoff discharge sources used in the study.

Overall, the team observed substantial chloride retention via infiltration to soils and groundwater. For example, monitoring the runoff from a vegetated highway ditch showed that more than 95 percent of the chloride applied to the highway infiltrated
from the ditch into the soil, and less than 5 percent was exported from the site in surface runoff. “Interestingly, substantial chloride export from the ditch was observed in November rainfall runoff prior to application of any new road salt for the upcoming winter, suggesting long-term storage in soils and groundwater in and near the ditch,” Herb says.

Researchers also found that winter rain-on-snow events and the first major
prolonged thaw each season moved surface chlorides most effectively into the watershed.

The research team then used the data and modeling to examine potential strategies for reducing or mitigating the spread of chloride, including capturing low flows, seasonal runoff capture, and capture based on salinity.

Wayne Sandberg, deputy director of the Washington County Department of Public Works, chaired the study’s technical advisory panel. “Based on this research, we now know that deicer chemicals are staying in the soil and moving in the watersheds, and this should change how we manage ice and snow control,” he says. “The next questions are what can we do with that knowledge and what changes can we make.”

This article originally appeared in CTSs Catalyst Newsletter, March 2018 and pertains to Technical Summary 2017-50TS. The full report, “Study of De-icing Salt Accumulation and Transport Through a Watershed” 2017-50, published December 2017 can be accessed at mndot.gov/research/reports/2017/201750.pdf.

10 Ways Transportation Research Keeps Minnesotans Moving in the Winter

As the first big snow and ice storms sweep through parts of Minnesota today, we’d like to remind you of some of our great winter weather research studies. Here’s a list of some of this winter-related research from MnDOT and the Local Road Research Board:

Living snow fences

Living snow fences are trees, shrubs, native grasses, wildflowers, or rows of corn crops located along roads or around communities and farmsteads. These living barriers trap snow as it blows across fields, piling it up before it reaches a road, waterway, farmstead or community. Through multiple research efforts, MnDOT continues to advance its practices for living snow fences. Willow plants, which are which are inexpensive and fast-growing, are a new form of snow fence. MnDOT has also developed a tool that allows the agency to better offer a competitive payment to farmers.

Related studies:

Permeable pavement

According to recent studies, researchers believe Minnesota could eliminate salt usage on low-volume local roads by switching to permeable pavements. Permeable pavements — pavements that allow water to seep through them — have been studied in some Minnesota cities, and a research project is currently underway to further investigate how much salt reduction can be expected.

Related studies:

Traffic recovery during winter storms

MnDOT’s Metro District developed a way to automatically determine when to stop plowing a highway after a snow storm. The method involves measuring traffic flow to determine when road conditions have recovered. Current practice calls for maintenance workers to visually inspect traffic lanes. The automated technique could potentially be more accurate and save time and costs.

Related study:

Salt and other deicing chemicals

Minnesota winters are no joke, and Minnesotans still need to get wherever they’re going despite harsh snow and ice conditions. That’s why MnDOT is constantly researching new and improved versions of salt and other deicing chemicals to keep roads safe at the least amount of damage to lakes, rivers and groundwater.

Related studies:

Snowplow blades

A couple years ago, MnDOT snowplow operators in southwestern Minnesota invented an experimental plow that uses the wind to cast snow from the road without impeding traffic or the operator’s view. This winter, MnDOT intends to test multiple types of snowplow blades as part of a larger research project comparing types of deicers.

Related study:

Snowplow technology

While a lot of research has been done on the plow itself, MnDOT hasn’t forgotten to invest in research to improve in-cabin snowplow technology as well. Some of the great technology recently developed to assist snowplow drivers, includes a driver assist application that a MnDOT plow driver used last winter to navigate a storm and rescue stranded motorists. The agency is also studying equipment factors that can cause fatigue in snowplow operators.

Related studies:

Salt-resistant grasses

When the snow melts every spring, the damage salt does to roadside grass is obvious. That’s why researchers have spent years looking into developing and implementing salt-tolerant grasses on roadside settings. The result of this effort has been the introduction and use of salt-tolerant sod and seed mixtures that are made up primarily of fine fescue species. MnDOT is also studying how chlorides are transported within watersheds in order to better focus efforts to reduce deicer usage in  areas where it will have the biggest environmental impact.

Related studies:

Cold-weather cracking prediction test

MnDOT has developed a test that can tell whether a contractor’s proposed asphalt mix will cause the road to crack in the winter. Building roads using better asphalt mixes leads to less cracking and fewer potholes. The test is expected to save the state about $2 million per year.

Related studies:

Pedestrian snow removal

It’s not all about cars and trucks. Minnesotans still ride bikes and walk in the winter. That why MnDOT assembled a comprehensive review of existing practices and policies from other states, as well as a summary of valuable publications that could be referenced while developing a new policy.

Related study:

Maintenance Decision Making

MnDOT research led to the development of a Maintenance Decision Support System and related components provide real-time, route-specific information to snow plow drivers, as well as recommended salt application levels. These recommendations have reduced chemical usage while still achieving performance targets for snow and ice clearance.

Related studies: