Adaptive Management for De-icing in Minnesota
by Larry Baker, WRS faculty, BBE
When I was a kid, school was called off when it snowed and we had the day off to go sled riding down the quarter mile street near our house. Today, that road would be salted, and schools rarely have “snow days”.
Unfortunately, road salt has more serious impacts than stealing snow days from our youth. Road salt use has increased in the U.S. by five-fold since the 1960s. Contamination from road salt has become one of the most serious urban pollutants for cities in cold climates. A 2015 MPCA study reported that salt use costs $0.4-1.2 billion per year in the Twin Cities, including costs of salt, labor, and equipment, damage to trees, and corrosion to bridges, pavement, and vehicles. Beyond the infrastructure costs, chloride from road salt is toxic to aquatic organisms, causing nearly 80 surface waters in the Twin Cities region to be designated as “chloride-impaired”(a legal designation) or at high risk for becoming impaired. Chloride also moves freely through soils, and hence is also accumulating in groundwater. For some deep stormwater drains, in the Twin Cities, chloride concentrations remain at levels toxic to aquatic organisms even in mid-summer, when baseflow (groundwater) dominates the flow.
Removing chloride from meltwater in storm sewers is not practical, so management must focus on source reduction – reducing the amount of chloride (in NaCl) that is applied. This is easier said than done, because de-icing is needed (to some extent) to enable safe winter travel. The question then becomes: what is the minimum amount of road salt needed to both protect the environment and provide adequate transportation mobility?
In a new project sponsored by the Local Roads Research Board, Bruce Wilson (WRS faculty) and Larry Baker (WRS faculty), in collaboration with the City of Edina (Ross Bintner and Jessica Vanderwerf Wilson) proposed using an adaptive management approach to solve this problem. The idea behind adaptive management is to guide actions through continuous feedback. In this case the “action” is road de-icing, and the feedback are “meltwater metrics”, such as melt efficiency (gallons of water melted by a lb of chloride) and event chloride load (lb Cl per event). The key will be to provide feedback to road crews in post-event workshops, to enable continuous learning (adaptation).
One snag in using adaptive management for de-icing operations is measuring flow and chloride concentrations in debris-laden, corrosive, meltwater flowing into storm grates under frigid conditions, transmitting data by the minute, with minimal maintenance.
This problem is being addressed in by three seniors in Bioproducts and Biosystems Engineering (BBE) – Tahni Jungst, Baily Rockwell and Jeff Tierney who are designing a novel sampling system to measure meltwater flow and runoff and chloride as part of a Senior Capstone project. Their goal is to develop is a system that is both robust and applicable to many urban watersheds. The students are utilizing their environmental engineering backgrounds, including hydraulics, thermodynamics, and statistics to develop the sampling system, aided Assistant Professor Dr. Peter Marchetto, whose research involves development of novel environmental monitoring systems. Their goal is to develop a system that could be patented and licensed to private company, which could produce commercial samplers for other cities.