This article was originally published in Catalyst, August 2022.
Ongoing research is looking into the possibility of using local industrial waste for roadside stormwater construction projects. This would help reduce material and transportation costs and put otherwise wasted materials to use.
Continue reading Treating Stormwater with Local By-Products Reduces Road Construction Costs, Minimizes WasteThe city of Shoreview, Minnesota was on the right track when it took the unusual step of paving a residential neighborhood with pervious concrete to help control stormwater and pollutant runoff into a nearby lake, according to a recently released seven-year performance study.
Typically used for parking lots and sidewalks, porous paving material allows stormwater to filter through the pavement and an aggregate base into the soil rather than run off the pavement and drain into storm sewers.
Shoreview bucked convention by using pervious concrete in a traffic application — low-volume, low-speed roads in the Woodbridge neighborhood near Lake Owasso. The city thought pervious pavement could help meet community sustainability goals and federal clean water regulations by reducing pollutants in waterways and groundwater while keeping water safely off driving surfaces.
Traditionally, pervious concrete hadn’t been used for roadways because engineers didn’t consider it strong enough for traffic (this and other projects have now demonstrated its application for low-volume roads like neighborhood streets). The impact on ride quality, tire-pavement noise and filtration was also not well understood, particularly in cold climates with freeze-thaw cycles like those in Minnesota.
Pervious concrete also presented a maintenance challenge: Organic debris, sand and other grit can clog the pavement’s pores. Periodic vacuuming is required to maintain the intended flow of water through the pavement. Concerned about how best to maintain the pavement and interested in tire-pavement noise levels and filtering performance, Shoreview, MnDOT and the Local Road Research Board monitored the Woodbridge roadways for seven years.
Shoreview replaced 9,000-square -feet of asphalt roads with 7 inches of pervious concrete over 18 inches of coarse aggregate base; near the lake, highly drainable sand served as the base. About twice each year for five years, researchers tested sound absorption, water infiltration and ride quality one day after the pavement had been vacuumed. In 2015, they repeated these tests without vacuuming the day before.
The pervious pavement performed well in filtering stormwater. By 2012, at least 1.3 acre-feet of water had filtered through the pavement and ground, and by 2015, nearly 2 acre-feet of water had filtered through the surface—all of which would otherwise have run directly into Lake Owasso.
Water infiltration and sound absorption rates were higher than traditional concrete, although rates declined over time because organic material continued to clog pavement pores despite vacuuming twice a year.
Initial construction of the pervious concrete streets and stormwater filtration system was slightly more costly than construction of comparable asphalt pavement with culverts. Life-cycle costs, including projections of maintenance costs over 15 years, however, showed somewhat lower costs for pervious pavement. While the pervious concrete pavement may require diamond grinding after 10 years, monthly vacuuming could make this unnecessary. Asphalt pavement would typically require a mill-and-overlay at year 15, and culverts would require periodic cleaning.
Additional benefits of the pervious pavement system that were not included in cost calculations—but were clearly significant—included complying with the federal Clean Water Act, recharging groundwater and avoiding direct pollution of Lake Owasso. Shoreview’s investment in pervious concrete has paid off economically and environmentally.
For additional information about this line of research, see these resources:
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.
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.
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:
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.
“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:
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.
The Tailgate Test Kit quickly and easily identifies flocculants that reduce turbidity in construction stormwater discharge. The mobile test setup efficiently determines which of the many available products works best for a particular construction site. In this study, 13 product combinations were tested. A short list of five tests was developed, as well as worksheets to aid in calculating the amount of flocculant needed and developing scale-up procedures.
“The Tailgate Test Kit is a cost-effective innovation that will help us determine the flocculant and quantity of product to use in the field and in real time,” said Dwayne Stenlund, Natural Resources Program Coordinator, MnDOT Environmental Stewardship.
“It’s important to add to the body of knowledge in this area,” said Joel Toso,
Senior Water Resources Engineer, Wenck Associates, Inc. “The Tailgate Test Kit is already being used in the field to help both contractors and maintenance workers make decisions.”
What Was the Need?
Stormwater runoff from construction sites often carries sediment from soil erosion, causing the water to become cloudy or turbid. Federal, state and local stormwater regulations prohibit construction sites from discharging water that is too turbid into the environment. Instead, the runoff must be sent to ponds to allow the sediment to settle to the bottom of the pond. The remaining clear effluent may then be discharged from the site.
The chemicals in flocculants speed up the sediment settling process by causing the sediment particles to clump together and fall to the bottom more rapidly. A number of flocculating agents are commercially available. The most effective agent for a specific situation is generally deter-mined by testing various flocculants with water samples in a lab. This selection process usually takes one or two days. Only after the appropriate flocculant is selected can the entire pond be treated.
To speed up this process, MnDOT has developed the Tailgate Test Kit, a series of tests that can be conducted in the field to determine the most effective flocculant, as well as the correct amount, for a specific construction site and soil type. What used to take a day or two to process in the lab now can be accomplished by field crews in an hour or two on the tailgate of a truck, enabling workers to begin treating the ponded turbid water much more quickly.
What Was Our Goal?
The overall goal of this study was to build upon the findings of several recent research projects, including “Flocculation Treatment BMPs for Construction Water Discharges” (2014-25), by developing and improving field methods to reduce total suspended sediment from construction stormwater runoff. A specific aim was to create a method for work crews to test water samples in the field using a mobile test toolkit that contains flocculants identified in previous research. Other goals included determining the most effective amount of the flocculant needed, developing the calculations needed for scale-up once the best product is identified and implementing a test for residual unreacted product.
What Did We Do?
To identify a variety of flocculant product types to evaluate with the Tailgate Test Kit, the research team summarized stormwater best management practices from the literature and from other departments of transportation. Since the effectiveness of product types varies depending upon soil and sediment types and environmental conditions, researchers conducted 13 tests of nine flocculant products (alone and in combination) taken from five distinct product classifications: mineral, polyacrylamide, chitosan, bio-polymer and anionic polyacrylamide. They also tested water samples from eight locations in Minnesota to ensure a cross section of representative samples.
What Did We Learn?
Using the results from these tests, the research team developed a short list of five tests that could be conducted in the field and incorporated in the Tailgate Test Kit. The five tests represent a range of flocculant product classifications and reduce the time required to complete the tests.
The team also prepared worksheets with mixing and dosing guidance to help users identify the most effective amount of product to achieve the target turbidity goal. Finally, the team developed scale-up procedures to aid in using test results to determine full-scale dosing rates on-site and procedures for testing new flocculant products.
The researchers investigated four methods for testing residual flocculant to detect any unreacted product in a sample. A preferred method was not identified during the course of this research but would still be a desirable research outcome.
What’s Next?
Next steps for this research effort include field implementation and new product evaluation.
First, investigators recommend developing a training module and field guide for using the Tailgate Test Kit to encourage implementation of the mobile kit throughout the state. If users understand how it works and how to use the test results for scale-up calculations, they will be more likely to use it.
Second, the product list should be kept current by testing additional flocculant products. It may also be beneficial to create a category for flocculants on the MnDOT Approved/Qualified Products List.
Finally, methods to identify residual and unreacted flocculant product need to be developed. If excess flocculant product is used in field tests, the residues will eventually have to be collected and removed for disposal. Minimizing the excess flocculant used at construction sites is desirable.
This post pertains to Report 2017-32, “Tailgate Test Kit for Determining Appropriate Sediment Reducing Chemicals and Dose Rates,” published July 2017.
The same chemicals used to treat drinking water might now be able to treat stormwater runoff to reduce the amount of pollutants entering Minnesota lakes and rivers from road construction sites.
A research project headed by Mankato State University and funded by the Minnesota Department of Transportation has identified three chemical flocculants that are effective at removing a broad range of Minnesota soils from water.
“Water is leaving construction sites carrying too much sediment,” said Minnesota State University-Mankato Environmental Engineering Professor Steve Druschel. “Chemical treatment has been used to treat drinking water for 70 to 80 years, and our thought was to try it in construction as well.”
Recent MnDOT research has investigated monitoring the amount of sediment in stormwater runoff and using temporary ponds to let sediment settle out of stormwater before it runs off the construction site. MnDOT also wanted to examine the possibility of treating construction runoff with flocculants, which are chemicals that cause suspended sediment to form clumps that quickly settle out of the solution.
Researchers tested 21 chemicals to see how well they could remove 57 types of soil from water. While no chemical was effective for the entire range of Minnesota’s soils, three chemicals were broadly effective on a range of samples.
The research will contribute to improved treatment of stormwater runoff from construction sites and reduce the amount of sediment pollution entering the state’s rivers and lakes.
Although flocculants have been used to treat drinking water for seven decades, there has been only limited testing of their use in treating construction runoff. Research was needed to evaluate the effectiveness of this approach.
chemical and mounting it above the water (as shown here), although thorough mixing must be ensured. MnDOT hopes to develop a system that will automatically dispense a precise dose based on the amount of sediment in the water.
Since it is not feasible for workers to constantly monitor sediment concentration in stormwater runoff, MnDOT hopes to leverage the knowledge gained from this project to develop an automated system that measures the amount of sediment in runoff and automatically adds the appropriate dose of flocculant to treat the water.
“We’re trying to develop a portable water treatment plant that can be applied to construction projects to deliver clean runoff water after a storm,” said MnDOT Environmental Specialist Dwayne Stenlund.
Any chemicals recommended for field usage will need to be approved by the Minnesota Pollution Control Agency, and methods for disposing of used chemicals will need to be identified as the environmental impacts of residual chemicals are unknown.
*Editor’s note: This article was adapted from the September-October 2014 issue of our Accelerator newsletter. Read it online or sign up for your free subscription.
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