Category Archives: Environment

Environment, Materials and Construction, research

Industrial by-products prove sustainable options for managing roadside stormwater

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Reprinted from CTS News, March 25, 2025

Roadside soil plays a crucial role in stormwater management. Naturally vegetated roadsides can filter and control runoff, helping to keep pollutants out of bodies of water and minimizing flooding to communities. However, soil left behind from road construction does not adequately support filtration and plant growth unless it’s amended with organic matter—and traditional mixtures for doing so, such as with sand and compost, can be costly and resource-intensive. 

sample plots
Field plots adjacent to the Natural Resources Research Institute parking lot were used to test the infiltration capacity, pollutant removal, and vegetative support capabilities of the soil mixtures.

To find a more sustainable solution, U of M researchers partnered with MnDOT and the Minnesota Local Road Research Board. Building on previous research, a team led by CTS scholar David Saftner, principal investigator and associate professor in the UMD Department of Civil Engineering, tested sustainable roadside soil mixtures using locally available waste materials and by-products generated from forestry, agriculture, and industrial activities.

In this project, nine materials were selected for testing, including a peat/biochar mix; dredged river sediment; pine and ash sawdust; VersaLime (a by-product of sugar beet processing); lime mud, bottom ash, and degritter (from a pulp and paper mill); and recycled concrete aggregate (RCA). All nine materials proved efficient at removing pollutants, though some were more effective than others. After extensive laboratory testing, the five top-performing materials were selected and used to create three engineered soil blends:

  • RCA (80%) and ash sawdust (20%)
  • RCA (80%) and peat/biochar (20%)
  • Dredge sediment (80%) and degritter (20%)

Field testing of these three engineered soil blends took place in outdoor plots. The team studied infiltration rate, pollutant removal, and plant growth from grass and flower seed. Through a life-cycle assessment, the researchers also evaluated material collection and transport, energy demand, human health and ecosystem impacts, climate change, and water use.

Their research revealed that all three engineered soil blends were effective at capturing and filtering the first inch of excess stormwater runoff, offering a viable alternative to traditional soil mixes. Other key findings: 

  • Of the engineered soil mixes, organic and coarser materials were better at allowing water to pass through.
  • Greenhouse tests showed promising plant growth, while field plots experienced challenges—possibly due to seasonal dryness.
  • The dredge sediment and degritter soil mix had substantially higher impacts than the other two soil mixes as well as the most CO2 emissions.
  • The RCA and ash sawdust soil mix had the lowest impacts, with the RCA and peat/biochar soil mix producing similar results.

Based on their findings, a design guide was developed for road engineers outlining best practices for using local by-products and waste materials to create engineered soil mixes while still adhering to regulatory standards. These recommendations are designed to be standard, common, and repeatable. 

“This was a great project and I’m especially happy with the design guide,” Saftner says. “Determining how to implement new procedures is tougher than using tried-and-true methods. Our hope is that the guide will simplify things for practicing engineers looking for more cost-effective, sustainable, and locally sourced solutions.”

The study results also highlighted many of the benefits of engineered soil mixtures including the reuse of waste materials, reduced spending on sand and compost, lower transportation costs, and fewer environmental impacts of transporting material. 

Further research on the reuse of waste materials includes another multi-phased project incorporating biochar. The first phase of that project should be finished this summer, with the second phase kicking off in summer 2026.

—Krysta Rzeszutek, CTS digital editor

Related Resources

Environment

Reusing Local By-Products to Create Sustainable Roadside Soil 

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Vegetated roadsides in Minnesota help control stormwater quantity and pollutant levels before the water reaches lakes, streams and communities. Because leftover soil from road construction generally does not support filtration and plant growth, MnDOT and local engineers have continued research to identify organically rich, locally available industrial by-products to amend the soil. Engineered soil mixes with materials such as dredge sand, coarse street sweepings and ash sawdust show high potential for providing a sustainable, efficient solution. 

Continue reading Reusing Local By-Products to Create Sustainable Roadside Soil  →
Environment, Maintenance Operations, research

Updated stormwater guide reflects new research, experience

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Reprinted from Catalyst, December 16, 2024

Effective stormwater management is essential for maintaining healthy urban environments, but it requires consistent monitoring and maintenance to prevent costly failures—something that municipalities across the state have struggled with for years.

At a recent CTS webinar, Andy Erickson, research manager at the University of Minnesota’s St. Anthony Falls Laboratory and CTS scholar, guided more than 160 attendees through recent changes made to the Minnesota Stormwater Inspection and Maintenance Resource Guide. The original guide, published in 2009, has been revised to incorporate more than a decade’s worth of field applications, research, and practical experience. The updated resource aims to improve the inspection, operation, and maintenance of stormwater management practices across the state, providing practitioners with essential tools to optimize stormwater management and increase cost-effectiveness.

Stormwater management is crucial for controlling urban runoff, and systems such as green infrastructure and low-impact development reduce pollution before stormwater is sent to lakes, rivers, and streams. However, these systems require regular upkeep to remain effective, and maintenance challenges arise from their passive nature and logistical issues in large urban areas. One key problem is the lack of on-site staff for monitoring and making the proactive inspections vital for preventing failures. Regular maintenance can reduce costs by avoiding the need for major repairs, but municipalities may still struggle to stay within their maintenance budgets, as funding for upkeep is often inadequate compared to the cost of new infrastructure.

“Since there are no operating staff on-site to see when these things fail or see what’s causing them to fail, we have to be proactive in our inspections,” Erickson said. That means inspectors must travel multiple times to locations spread out across the metro region—which significantly increases costs. “Depending on the size of the practice, your total maintenance cost might become more than your original construction cost within five years of the life of that practice,” he said. 

The 2024 update to the Minnesota Stormwater BMP Maintenance Resource Guide aims to address this issue by offering detailed instructions for inspecting and maintaining various stormwater systems. The updated guide includes inspection checklists in the form of fillable PDF documents. These checklists should streamline the inspection and documentation process and help inspectors assess site conditions, including vegetation health, erosion, and drainage performance. And the forms can be easily updated and reused, providing a practical tool for ongoing stormwater management. “The forms are not static, but rather are intended to serve as a resource that can be used and adapted to fit a jurisdiction’s particular needs,” Erickson explained.

Following items from the checklist, the guide provides specific maintenance recommendations based on inspection findings, including how to address issues such as erosion, vegetation dieback, and structural failures. 

“You can go through these to really home in on what maintenance is needed and when the maintenance is needed,” Erickson said.

The updated Minnesota Stormwater BMP Maintenance Resource Guide is now available online for download.

—Emma McIntyre, CTS communications intern

Related Resources

Environment

Creating a Leafy Boulevard: Best Practices for Tree Selection

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Boulevards play an important role along a roadway. This open space located just behind the curb provides snow storage for roads and sidewalks, a place for rain and runoff to soak into the ground, and attractive green space in our city neighborhoods. In addition to their aesthetic appeal, trees planted in the boulevard along a roadway offer valuable environmental benefits. They save energy and lower temperatures, reduce greenhouse gases, and reduce stormwater runoff.

Continue reading Creating a Leafy Boulevard: Best Practices for Tree Selection →
Environment, research

Revised Stormwater Maintenance Guide Updates Common Practices and Offers Innovative Options

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Practices for managing stormwater runoff have evolved over the years. Changes to regulations, land use and weather patterns impact how transportation agencies integrate stormwater control options into road and waterway networks. Local agencies have used a stormwater maintenance guide produced by the Local Road Research Board (LRRB) in 2009. Over a decade of new research and the development of new tools for stormwater control necessitated revisions to the guidance document. The updated Stormwater BMP Inspection and Maintenance Resource Guide provides recommendations for enhancing traditional stormwater practices and presents new, innovative strategies and guidance on stormwater best management practices (BMPs). 

Continue reading Revised Stormwater Maintenance Guide Updates Common Practices and Offers Innovative Options →
Environment, research

New Project: Assessing Effectiveness of Pond Sediment Removal for Phosphorus Management in Stormwater Ponds

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MnDOT manages rainwater runoff to keep pollutants like phosphorus from Minnesota’s lakes and streams. Stormwater retention ponds, an established management strategy, allow phosphorus to settle to the pond’s bottom but do require periodic cleanout.

Continue reading New Project: Assessing Effectiveness of Pond Sediment Removal for Phosphorus Management in Stormwater Ponds →
Environment, research

New Project: Investigating Real Storms and the Impact of Potential Climate Change Adaptations

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MnDOT designs stormwater management infrastructure based on historical rainfall data and traditional design assumptions, including rainfall intensity and distribution, rainfall event duration and existing moisture conditions. Stormwater management infrastructure designed using traditional design parameters determines the risk of flooding, property damage and human safety in communities. 

Continue reading New Project: Investigating Real Storms and the Impact of Potential Climate Change Adaptations →
Environment, research

Urban trees are litterbugs. Sweeping up after them could reduce stormwater pollution.

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Reprinted from Catalyst, September 11, 2024

A U of M study determined that the leaves, flowers, and seeds dropped by trees in urban areas are a big polluter of stormwater. The project researchers recommend street sweeping as one way to address this issue—and they provide guidance on how to effectively time and target sweeping efforts.

Continue reading Urban trees are litterbugs. Sweeping up after them could reduce stormwater pollution. →
Environment, Maintenance Operations, research

New Project: Cost Benefit Analysis for Sustainable Energy Building Upgrades at Safety Rest Areas and Travel Information Centers

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MnDOT manages over 50 large safety rest areas (SRAs) with several amenities and travel information centers (TICs) with expanded customer service. Many of the SRA and TIC buildings were built before the significant advancements in energy efficiency and building technology made in the past few decades.

Continue reading New Project: Cost Benefit Analysis for Sustainable Energy Building Upgrades at Safety Rest Areas and Travel Information Centers →
Bridges and Structures, Environment, research

New Project: Species from Feces: A New Tool to Identify Bats in Culverts and on Bridges

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Three bat species in Minnesota have been decimated due to white-nose syndrome. The northern long-eared bat is listed as endangered by the U.S. Fish and Wildlife Service, the tricolored bat listing is imminent, and the little brown bat listing is under consideration.

Continue reading New Project: Species from Feces: A New Tool to Identify Bats in Culverts and on Bridges →