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.
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.