Sep 29, 2016

Rethinking Runoff

Study evaluates capture & treatment of highway runoff

New research being conducted at the University of Guelph in Ontario, Canada, tackles some of the most challenging aspects of urban storm water management by designing and testing new methods and materials for the capture and treatment of highway runoff. 

Multi-lane, high-volume roadways are essential to the movement of people and goods. Unfortunately, roadways also have been flagged as one of the leading causes of watercourse degradation and impairment in Canada and the U.S. Petroleum hydrocarbon, heavy metal, sediment, nutrient and road salt runoff leads to aquatic habitat degradation and puts drinking water supplies at risk.

My research uses a multi-pronged approach to deal with highway pollutant runoff. In regions experiencing road salting as part of normal winter operations, the challenge lies in optimizing salt use. While road salt is harmful to the environment, it increases commuter safety and saves lives. With this problem and no widely available, cost-effective alternatives to road salt, I focused on its efficient application to regional highways. Our team monitored three sites in the greater Toronto area to develop an accurate method of estimating melt using common meteorological parameters. 

Before and after each run, we weighed our salt spreaders in a controlled drainage area and measured the amount of fuel consumed. Meltwater flows in these areas were measured using area-velocity sensors installed in storm water pipe. Snow depletion was monitored using ultrasonic snow depth sensors. Such accurate measurement allowed me to develop a calculator to optimize the amount of salt needed to regain bare, drivable pavement in situations that also used conventional plowing. 

To address the issue of heavy metals and sediment washing off of roadways, the second prong of my research used high concentrations of synthetic road runoff filtered through soil columns amended with varied treatment materials derived from waste byproducts. The synthetic runoff used ultra-high concentrations of multiple heavy metal types to saturate the amendments undergoing testing and simulate 20 years of exposure in the field. We included road salt in our pollutant mix because we were interested in potential leaching or displacement issues that may exist. 

Using cheap, locally abundant materials from steel mills, coal mines and drinking water treatment plants, the tested amendments were able to remove up to 98% of the long-term pollutant load, usually within the top 10 to 15 cm of each soil column. It is exciting to think blast furnace slag can be repurposed to improve highway runoff water quality, despite not being widely considered. 

The last phase of my doctoral research included the development and testing of a field-scale pilot site along Highway 401, which is Canada’s busiest highway. With the support of Ontario’s Ministry of Transportation, we scaled our work to test our models and materials in real-world conditions. We also expanded our scope to address thermal mitigation and groundwater protection.

I am hopeful my research will lead to new, economical designs for roadside ditches that provide positive drainage and water quality improvements. The potential to improve the methodology used in road salt applications can save money and reduce environmental impact. Finally, treating steel slag as a valuable resource rather than a waste product constitutes another way we can reduce impact on the environment.   

About the author

Bill Trenouth is an engineering Ph.D. candidate at the University of Guelph. Trenouth can be reached at [email protected].

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