In Minnesota’s metro region, areas of shallow groundwater show increasing evidence of chloride contamination from winter road maintenance operations, particularly deicing. More than a quarter show chloride concentrations at the maximum contaminant level for municipal drinking water. In addition, 123 lakes and rivers show chloride impairment or risk of impairment for aquatic life. Chlorides are now considered the second most important threat, after phosphorus, to Minnesota’s urban waters.
The City of Edina, with funding from the Local Road Research Board, hired the University of Minnesota to analyze chloride accumulation in city snowmelt following winter maintenance operations to learn how to most effectively adjust its deicing strategies to reduce chloride contamination.
Over two winters, researchers collected data from city deicing operations and correlated it with chlorides present in meltwater runoff. A sampler box collected data continuously, and snow pile cores were also analyzed. Snowplow operators then examined the results during workshops, yielding innovative ideas for reducing salt use.
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.
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.
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.
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.
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.
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.
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.
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.
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.
To mark Earth Day 2016, MnDOT Research Services is taking a glance at five stellar examples of current research projects at MnDOT that involve pollution control, wetland mitigation, road salt reduction and new ways of recycling pavement.
Soil carried away in stormwater runoff from road construction sites can pollute lakes and rivers.
Stormwater settling ponds provide a place for this sediment to settle before the water is discharged into local bodies of water. However, since stormwater ponds have limited space, a mechanism is needed to remove clean water from the pond to prevent the overflow of sediment-laden water.
MnDOT-funded researchers designed temporary stormwater ponds with floating head skimmers that can remove clean water from the surface of the settling pond, using gravity to discharge water into a ditch or receiving body.
The study, which was completed in spring 2014, identified five methods for “skimming” stormwater ponds that can improve a pond’s effectiveness by 10 percent. MnDOT researchers also created designs for temporary stormwater ponds on construction sites with the capacity to remove approximately 80 percent of suspended solids.
These designs will help contractors meet federal requirements for stormwater pond dewatering. Researchers also determined how often a pond’s deadpool must be cleaned, based on watershed size and pool dimensions.
Stormwater can pick up chemicals and sediments that pollute rivers and streams. Roadside drainage ditches, also known as swales, lessen this effect by absorbing water. But until recently, MnDOT didn’t know how to quantify this effect and incorporate it into pollution control mitigation measures.
In a study completed in fall 2014, researchers evaluated five Minnesota swales, measuring how well water flows through soil at up to 20 locations within each swale.
A key finding: grassed swales are significantly better at absorbing water than expected, which may reduce the need for other, more expensive stormwater management practices, such as ponds or infiltration basins.
This could save MnDOT and counties significant right-of-way and construction costs currently expended on more expensive stormwater management techniques.
Road salt is used for de-icing roadways during winter months, but can have a negative impact on the environment.
This research, which was just approved for funding through the Minnesota Local Road Research Board in December 2015, will investigate the reduction in road salt application during winter months that can be attained with permeable pavements, while still providing for acceptable road safety.
Some initial investigations (see previous study) suggest that road salt application can be substantially reduced, even eliminated, with permeable pavement systems. The proposed research will investigate this hypothesis more thoroughly, and further document the reduction in road salt application that can be expected with permeable pavement.
Road construction in northeast Minnesota often causes wetland impacts that require expensive mitigation. However, borrow areas excavated for road construction material can be developed into wetland mitigation sites if hydric vegetation, hydric soils and adequate hydrology are provided. Fourteen wetland mitigation sites were constructed north of Virginia, Minnesota along the U.S. Trunk Highway 53 reconstruction project corridor and evaluated for wetland. The sites were established with the goal of mitigating for project impacts to seasonally flooded basin, fresh meadow, shallow marsh, shrub swamp, wooded swamp, and bog wetlands. All but one of the sites consistently meet wetland hydrology criteria.
The sites contain a variety of plant communities dominated by wet meadow, sedge meadow, and shallow marsh. Floristic Quality Assessment (FQA) condition categories for the sites range from “Poor” to “Exceptional.”
According to the research report published in March 2016, these sites have shown the potential for creating mitigation wetlands in abandoned borrow pits in conjunction with highway construction. Adaptive management, particularly water level regulation, early invasive species control, tree planting, and continued long-term annual monitoring can make mitigation sites like these successful options for wetland mitigation credit.
MnDOT already extends the lives of some old concrete highways by paving over them with asphalt instead of tearing them up. Now MnDOT hopes to add a third life for these old concrete roads by using a process called cold in-place recycling to re-use that existing asphalt pavement when it reaches the end of its life.
Cold in-place recycling (CIR) uses existing pavements, without heat, to create a new layer of pavement. It involves the same process of cold- central plant mix recycling (which is being employed by MnDOT for the first time on two shoulder repair projects this year), but it is done on the road itself by a train of equipment. It literally recycles an old road while making a new road.
CIR has been in use in Minnesota for 20 years, but only with hot-mix asphalt (HMA) over gravel roads. The purpose of a new study, which was approved for funding in April 2016, is to validate Iowa’s promising new practice using CIR on bituminous over concrete.
In this research project (see proposal), MnDOT will use cold-in-place recycling to replace the asphalt pavement on a concrete road and then evaluate it for several years, comparing it also with control sections.
Along with the potential of a better service life, the cost of CIR is much lower than new hot mix asphalt (HMA). Therefore, a 20-percent to 30-percent price reduction per project may be realized.
For Minnesota’s roadside grasses, life isn’t easy. To survive, grass must be able to withstand extreme stresses including drought, heat, disease, soil compaction, poor quality soils, and high levels of road salt. Ideally, it could survive all that while still looking lush and green.
“Many roadsides, especially in metropolitan areas, need to look good,” says Eric Watkins, associate professor in the Department of Horticultural Science. “In addition to aesthetics, quality roadside vegetation is needed to prevent erosion and maintain water quality from roadside runoff.”
In 2010, MnDOT noticed a number of its new sod and seed plantings were failing and asked U of M experts to take a look at its specification. “We saw the problem immediately,” Watkins says. “The specification was for a mix with a lot of Kentucky bluegrass, which needs a great deal of care and watering. There was clearly an opportunity for improvement.”
During the next several years, Watkins’ team, led by former graduate student Josh Friell, worked to identify the best seed and sod for use along Minnesota’s roadsides in research sponsored by the Minnesota Local Road Research Board and MnDOT. Findings are now available in a final report.
The study was completed in several stages. First, many different types of cool-season grasses were planted in the fall and assessed the following spring to determine their ability to establish and survive on roadsides in Minnesota. Next, researchers looked at the salt tolerance of those grasses.
“In cold-weather climates like Minnesota’s, salt tolerance is required because of the application of deicing salts in the winter,” Watkins explains. “To determine if a grass species could stand up to this stress, we applied different levels of salt solution to the different grass species in a greenhouse. We identified several types of fescue grass as the most salt tolerant.”
Based on the results of the first two stages, researchers developed and tested 50 different grass mixtures along Minnesota’s roadsides and evaluated the survival and performance of those plantings for two years. In addition, each mixture was planted under a movable rain-out shelter to determine drought tolerance. This phase of the study resulted in the identification of a mix of three types of fescue for planting on roadsides in Minnesota.
Finally, researchers needed to find out if the new grass mixture would work as sod (sod growers need to be able to harvest it properly from their sod fields). “Most sod currently grown in Minnesota is Kentucky bluegrass, which isn’t the best for winter survival when salt stress is a problem,” says Watkins. “We grew 51 different grass mixtures as sod for 22 months and found that contrary to popular belief, fine fescue mixtures produced sod of acceptable strength for harvest.”
MnDOT has applied the research to standard specifications for construction activities for salt-tolerant sod products, salt/shade/drought-tolerant turf seed mixtures, and a third-party certification program for ensuring performance standards are met based on past and current research results, says Dwayne Stenlund, MnDOT erosion control engineering specialist. Researchers are also working with the state’s sod growers to produce sod grown from the new seed blends.
Moving forward, the researchers plan to continue their work to improve Minnesota’s roadside grass plantings. “The reality is that the success of sod or seed plantings depends on a number of factors, including time of year, amount of water, soil preparation, temperature, and sod harvest depth,” Watkins says. “In our next project, beginning this spring, we will identify the most important factors for the success of roadside plantings and sod cultivation, and then help MnDOT update the specifications for managing new installations.”
MnDOT is testing a mobile road condition monitor that uses infrared technology to detect hazardous ice, snow or wet conditions without even touching the pavement.
Maintenance crews hope the device, called the High Sierra Surface Sentinel, could help them better determine when it’s time to apply salt when they’re plowing. The mobile sensor reports air temperature, surface temperature and road friction data.
“The biggest reason we’re looking at this is for the friction reading,” said MnDOT Salt Solutions Coordinator Joe Huneke. “Typically, when operators are patrolling their route and the road looks like it’s getting icy, they’ll err on the side of caution and apply salt — and it may not need it.”
The device being tested by snow and ice crews in northern Minnesota would also provide real-time surface weather conditions. Currently, plow operators and supervisors must enter road conditions into a computer or relay them by phone, a time-consuming process that operators are not always able to perform in a timely manner.
The biggest potential benefit, however, is lower salt consumption.
“Sometimes you get a light cold snow event where it might look like there’s a little ice on the road, but, in fact, you have good friction numbers and you don’t need salt. Once you put chemical down, you’re committed to it,” Huneke said.
District 1 snow and ice crews are evaluating the unit pictured below for its accuracy and effectiveness in determining slippery conditions. It will be compared with another device tested in District 3 that also uses infrared technology to determine how slippery the road is, and technology being tested in District 6 that uses gravitational force to determine the road surface friction.
MnDOT’s Office of Maintenance has its own research program designed to let maintenance personnel test innovative ideas to keep our roads smooth, snow-free and safe. They even put out a monthly bulletin featuring new ideas and technologies. (You can find the back issues here.)
Excalibur and the High Roller may be closed for the season, but Valleyfair Amusement Park still has one attraction open for the season: a driving track for Minnesota snowplow drivers.
MnDOT-funded researchers are studying the effects of weather and vehicle traffic on different deicing treatments in the parking lots of Valleyfair and Canterbury Park in Shakopee, Minn.
It’s been a busy winter, but each week MnDOT Metro District snowplow drivers make one last stop before heading home, to apply different combinations of salt and anti-icing chemicals to nine 1,000-foot driving lanes. They also drive over each lane multiple times to test the effect of traffic.
“We’re running trucks up to 30 miles per hour with different speeds, wind conditions, traffic conditions and pre-wetting chemicals,” said Steve Druschel, a researcher with the Minnesota State University, Mankato. “Each lane is its own experimental unit.”
Professor Druschel’s students will review more than 17,000 photos from time-lapsed cameras to document how the snow melted in each experimental run.
“The influence of factors like pavement type and age, traffic volume, truck proportion, weather conditions and sun presence will be assessed to evaluate which techniques have special advantages for certain situations or roadways,” said Maintenance Research and Training Engineer Tom Peters.
In 2010, Druschel tested 25 anti-icing compounds in 1,500 different combinations in a laboratory to study the effectiveness of different deicers.
“Public work superintendents commented, ‘Great work. It looks good, except it’s all in the lab. Beakers aren’t what people drive on,’ ” Druschel said. “So we’re taking it from the two-inch ice cup to the real world in phase two of this study.”
With rock salt prices quadrupled, finding the most cost-effective methods of treatment is important.
This latest research will help determine the best times for applying anti-icing treatments and examine whether certain chemicals — such as a pre-storm liquid treatment that costs twice as much — melt enough snow to be worth the extra cost.
Test runs in Shakopee are strictly experimental, but in Mankato students are analyzing how real-world salting treatments are working on the North Star Bridge.
An article in the Mankato Free Press tells how Druschel’s team is collecting road melt runoff and documenting bridge traffic. (Big trucks, for instance, squeeze more water out of the snow.)
Students plan to use time-lapsed photos, along with weather data and snowplow records, to determine what chemical treatments worked best – and when.
With the multi-pronged research project, Druschel hopes to put definitiveness to what some snowplow drivers have already tried in the field.
“The key to it is not so much that we’re so smart and we have a better idea or are inventing something new,” he said. “We’re just trying to enhance what they are already doing.”
Salt Brine Blending to Optimize Deicing and Anti-Icing Performance –Technical Summary (PDF, 1 MB, 2 pages) and Final Report (PDF, 11 MB, 151 pages) (previous study)
Even naturally derived products like corn syrup and beet juice can impact the environment when applied to salt mixtures for winter roadways.
A wide range of products, including the ones mentioned above, are added to deicing mixes to limit the amount of salt needed for Minnesota roads each winter. However, although information is available about the corrosive properties of various deicing chemicals, less is known about the toxicity of these compounds, especially to the aquatic environment.
Thanks to a recently completed project sponsored by the Clear Roads Pooled Fund, MnDOT winter maintenance personnel will better understand the relative toxicity of eight common deicing agents, which also include non-organics like Magnesium Chloride, Calcium Chloride and Potassium Acetate.
“Because the state has been trying a lot of different alternative chemicals, we wanted to get a better handle on the environmental impacts,” said MnDOT engineer Tom Peters, the technical liaison for the 26-member, Minnesota-led pooled fund for winter maintenance research.
In January, researchers plan to release a concise summary of the toxicity rankings to help winter highway maintenance managers consider both expected levels of service and potential harm to the environment when selecting a deicer.
Minnesota is the lead state for the Clear Roads Pooled Fund, which conducts rigorous testing of winter maintenance materials, equipment and techniques. Other recent and upcoming research (see our Technical Summary on the program) includes a winter maintenance cost-benefit analysis toolkit, snow removal techniques at extreme temperatures and environmental factors that can cause fatigue in snowplow operators.
You can learn more about Clear Roads via the project’s e-newsletter.