MnDOT and local agencies control stormwater runoff from roadways through a range of settlement, filtration and infiltration facilities, such as wet ponds, infiltration basins, trenches and swales. Infiltration facilities have been used for more than 30 years, but a high rate of failure has been tied to inaccurate determination of soil infiltration rates. Researchers developed new tools and protocols to provide designers and engineers with the accurate infiltration measures they need, from initial site selection through construction. These tools and methods will support the development of successful stormwater infiltration facilities along Minnesota roadways.Continue reading Stormwater Bioslope Site Monitoring Continues Using Local Filter Media
Researchers have found that peat has high potential to replace commercial compost in MnDOT’s standard bioslope and bioswale design for roadside ditches, and that taconite tailings performed comparably to the sand currently specified in MnDOT designs, with the additional benefit of removing phosphates.
Finding alternatives to commercial compost and sand for use in bioswales will help MnDOT meet regulatory requirements for stormwater runoff, while reducing the costs and environmental effects of transporting and storing these materials.
“The results of this project will very much facilitate the development of green infrastructure by reducing its cost to MnDOT and Minnesota local agencies, helping them to do more with less,” said Dwayne Stenlund, Erosion Control Specialist, MnDOT Erosion Control and Stormwater Management.
What Was Our Goal?
The objective of this project was to evaluate peat and muck excavated from construction activities, taconite tailings from area mining operations, and other stormwater quality filter media for use in bioswales and bioslopes along Minnesota highways. Laboratory and field tests of these products would examine their capacity to absorb water, retain pollutants and support plant growth to determine if they are beneficial and practicable in these designs.
What Did We Do?
Researchers began by conducting a comprehensive literature review on the use of bioslopes and bioswales as stormwater treatment best management practices. Then they collected peat and muck near a highway construction project, as well as locally sourced sand, compost, taconite tailings and commercial peat.
These materials, as well as various combinations of materials, were used in laboratory experiments to determine how well they:
- Absorbed water, using a falling head test to measure saturated hydraulic conductivity, which indicates the rate at which water infiltrates a material.
- Retained pollutants, using leaching experiments to quantify how well they removed copper, lead, zinc, nitrate and phosphate.
- Sustained plant growth, using bioassays and greenhouse studies.
Finally, researchers conducted pilot field tests on three plots containing a 50/50 percent peat and sand mixture, and another three plots with a 50/50 percent compost and sand mixture. Between April and August of 2017, they monitored water infiltration, discharge water quality and vegetation establishment for these sites.
What Did We Learn?
“Ultimately, a combination of peat and taconite tailings will compare favorably with current MnDOT specifications for bioslope and bioswale design,” said Kurt Johnson, Research Fellow, University of Minnesota Duluth Natural Resources Research Institute.
Researchers found that peat has a strong potential for replacing commercial compost in MnDOT’s standard bioslope and bioswale designs, and that taconite tailings also performed comparably to the sand currently specified in these designs. However, muck has little potential to replace commercial compost or peat due to its low permeability, poor infiltration and filtration properties, and lack of support for plant growth.
Results for the three properties of interest follow:
- Infiltration rate: While muck had an unacceptably low hydraulic conductivity, peat performed at least as well as compost, and taconite tailings as well as sand. Pilot tests showed that a 50/50 mix of peat and taconite tailings had a similar water storage capacity to a 50/50 mix of compost and sand.
- Pollution retention: Muck absorbed only 50 percent of metals; salvaged peat, commercial peat and compost performed well, absorbing more than 80 percent. However, only taconite tailings showed the potential to remove phosphate. None of the materials removed nitrate.
- Plant growth: Mixtures of compost or peat with sand or taconite tailings all performed well in providing a viable substrate for plant growth. Mixes containing compost performed the best in plant growth trials. Muck was difficult to mix with any other material, and its value for plant growth was minimal. Greenhouse study results showed no difference between sand and taconite tailings in their effect on plant growth response.
In a second phase of this project, “Development and Regionalization of In Situ Bioslopes and Bioswales,” MnDOT will conduct further laboratory tests on alternative materials for bioslopes and bioswales, and expand field tests to several sites in Minnesota that have been constructed using these materials. Researchers also recommend the development of specifications and detail drawings for the use of these materials.
This blog pertains to Report 2017-46, “Comparing Properties of Water Absorbing/Filtering Media for Bioslope/Bioswale Design,” published November 2017.
Minnesota’s transportation research governing boards put a new emphasis on financial benefits when selecting next year’s round of transportation research projects.
MnDOT’s Transportation Research Innovation Group (TRIG) and the Local Road Research Board announced their Fiscal Year 2016 funding awards this week after hearing proposals from researchers in several states. They selected 20 research proposals hall-marked by novel approaches to improving the environment, increasing transportation safety, improving construction methods and boosting the bottom line.
“We asked the principal investigator to present the safety and financial benefits up front, and how they can be implemented to improve the transportation system and economic viability of Minnesota,” said MnDOT Research Management Engineer Hafiz Munir. “We’re making a point early in the process to identify those potential benefits, quantify them and document them in our tracking system.”
Researchers will test new technology that could make crack-free pavements; find better, faster and less expensive ways to reclaim roads; and even explore how to use waste material from road construction projects as part of the landscaping to absorb water runoff.
Links are provided below to brief descriptions of each of the projects:
Bridges and Structures
- Concrete Grinding Residue: Its Effect on Roadside Vegetation and Soil Properties (MnDOT)
- Comparing Properties of Water Absorbing/Filtering Media for Bioslope/Bioswale Design (MnDOT)
- Salt Brine Blending to Optimize Deicing and Anti-Icing Performance and Cost Effectiveness, Phase III (MnDOT)
- Expanding the Success of Salt-Tolerant Roadside Turfgrasses through Innovation and Education (LRRB)
- Pothole Prevention and Innovative Repair (LRRB/MnDOT)
Materials and Construction
- Evaluation of Stabilized Full Depth Reclamation (LRRB/MnDOT)
- MnPAVE-Rigid 2.0 (MnDOT)
- A Mechanistic Design Approach for Novel Graphene Nanoplatelet (GNP) Reinforced Asphalt Pavements for Low Temperature Applications (MnDOT)
- Performance Monitoring of Olmsted County CR 117/104 (MnDOT)
- Slope Stabilization and Repair Solutions for Local Government Engineers (LRRB)
- Life-Cycle Cost Analysis Tool for Minnesota Pavements (LRRB)
- Exploring the Walking Tolerance of Transitway Users (MnDOT)
- Refining Return on Investment Methodology/Tool for MnPASS (MnDOT)
Policy and Planning
- The Futures Project: Planning for Technology Change (LRRB/MnDOT)
Traffic and Safety
- Examining Signing Options for Improving Safe Driving Behaviors in Work Zones (LRRB/MnDOT)
- Assessing the Impact of Pedestrian-Activated Crossing Systems (MnDOT)
- Development of Travel Time Reliability Measurement System (MnDOT)
- Weigh-In-Motion (WIM) Sensor and Controller Operation and Performance Comparison (MnDOT)
- Investigate the Effectiveness of Bluetooth Low Energy (BLE) Technology to Trigger In-Vehicle Messages At Work Zones (MnDOT)