Stan Kohls, a third-year PhD candidate in civil and environmental engineering, is conducting an in-depth investigation into organic contaminants found in water systems. As a graduate research assistant at IIHR—Hydroscience and Engineering working with Professor Greg LeFevre’s lab, Kohls has been collaborating with the city of Coralville on a project funded by the Iowa Department of Transportation to explore innovative approaches to urban flood management practices to reduce contaminants from road runoff. Their team has established multiple research test sites along the historic 5th Street in Coralville, Iowa—a location that has faced significant water management challenges, particularly in the wake of the catastrophic 2008 flood. 

Through the project, Kohls and the research team are trying to understand the pathways of these organic contaminants once they’re released into the environment. The goal is to inform better design of nature-based stormwater management solutions using green infrastructure to remove organic contaminants.  

“Interestingly, the high-intensity rainfall we’ve experienced this year has allowed us to observe subtle variations in the chemical profiles of the samples we collect,” says Kohls. “This testing provides insight into what contaminants are being introduced into the system from roads, lawns, and surrounding areas, and helps to understand the potential impact of these systems on water quality.”  

Organic pollutants originate from sources such as tires, paint, and fertilizers, and are pervasive in the environment. Kohls’ research seeks to identify the specific compounds entering Coralville’s urban stormwater management practices, mainly bioretention cells, to develop methods for their removal. The bioretention cells are well engineered, consisting of multiple layers of rock, soils, and absorptive medium designed to hold and filter runoff. At the surface, the structures resemble planters, filled with native plants that contribute to the filtration process. Kohls’ team is experimenting with the role that fungi can play in degrading organic contaminants, rendering them far less harmful. While plants and bacteria are known to help remove nutrients and degrade some contaminants, fungi—especially mycorrhizal and white rot fungi—have the potential to further enhance contaminant removal by breaking down more stubborn pollutants. The goal is for the water to be much cleaner and safer by the time it reaches the Iowa River.  

These practices not only support healthier waterways but also contribute to flood prevention. However, the system’s efficiency presents its own research challenges. “Ironically, these bio cells are performing so well that they’re infiltrating water into the ground at a rapid rate,” says Kohls. “While this is the intended function, the rapid infiltration sometimes complicates the sampling process. It’s possible that we’ve over-engineered the system, in doing so, it’s almost too effective.” 

Kohls’ research has the potential to inform future efforts in both urban water quality management and flood prevention. By investigating how organic contaminants interact with engineered stormwater systems, their work provides valuable insights into the role of bioretention cells and other green infrastructure in reducing pollution from road runoff. The findings could lead to more effective infrastructure designs that not only mitigate flooding but also protect water quality. As the frequency and intensity of weather events increase, this research lays the groundwork for future studies aimed at optimizing stormwater management practices to better protect urban environments and their water resources. 

To learn more about their ongoing research, read their recent publication here: https://pubs.rsc.org/en/content/articlelanding/2024/em/d4em00275j