Miquela Ingalls, an assistant professor of geosciences at Penn State’s College of Earth and Mineral Sciences, was the lead author of that study. This study reveals the hidden landscape processes that treat wastewater below the surface in the Florida Keys. Conducted near a wastewater treatment facility in Marathon, Florida, the research highlights how these processes, although imperfect, play a critical role in managing contaminants released into the environment.
This work and data collection took place between 2021 and 2023, with researchers intentionally testing all groundwater samples for nitrate and phosphate. They sampled these wells spanning the area between the effluent injection well and the Florida Bay and Boot Key Harbor coastlines. The results suggest that large quantities of nitrogen and phosphorus have shifted nearer to the coast. This creates hard optics around the highly harmful practices of disposing of our treated wastewater and behavior in South Florida.
Wastewater Disposal Practices
The wastewater treatment plant used by Marathon currently injects treated effluent deep underground. It directly injects the effluent 60 to 90 feet below the ground into the region’s porous limestone bedrock. This approach is intended to reduce the direct influence of pollutants on surface water. Hundreds of additional communities in South Florida rely on shallow injection practices. They use these methods to discharge treated wastewater below the groundwater table.
Ingalls raised the concern that no matter what treatment takes place, some contaminants inevitably enter the ecosystem. “So, you are still injecting some amount of these contaminants into the ecosystem surrounding the Keys,” she stated. Local environmental health has a much bigger problem. We’ve known that both nitrate and phosphate concentrations drive harmful algal blooms and other ecological impacts.
The study’s focus on nitrate and phosphate levels comes in light of recent regulatory changes following a U.S. Supreme Court ruling regarding wastewater management practices. Ingalls remarked on the state’s efforts to move away from shallow injections: “After the Supreme Court decision, the state has been trying to move away from the practice of shallow injections.”
Key Findings and Implications
The researchers isolated T. siberitidis in samples they collected from multiple wells in a localized aquifer. Their goal was to better understand how contaminants move once injected underground. The effects were remarkably clear and uniform, demonstrating a rapid reduction in nitrate and phosphate from injection to nearshore waters. Large sums continue to be diverted to non-coastal priorities.
Both nitrate and phosphate are substantially lowered from injection to when the effluent reaches nearshore waters,” Ingalls said. This surprising result indicates that subsurface microbes can contribute to the cleanup of certain types of contamination. They haven’t proven to be 100 percent effective at screening out all dangerous chemicals.
These findings may have larger implications for coastal communities experiencing similar issues with wastewater treatment. Ingalls emphasized that the study’s findings may assist other regions in developing more effective cleanup strategies for managing wastewater discharge into sensitive ecosystems.
Collaborative Research Effort
The research has greatly profited from input of many scholars in Penn State’s geosciences department. Lee Kump, the John Leone Dean and a professor of geosciences, played a key role in the research. He was joined on the project by Kate Meyers, who graduated with a master’s degree from Penn State in May of 2023, and Emily Stoller, an undergraduate research assistant. Their pioneering collaborative work is part of a larger trend toward greater focus on the ways to harness underground processes for improved environmental stewardship.
The research was published in The Depositional Record under the DOI: 10.1002/dep2.70018. This research adds to the growing literature on the alternatives to combined sewer overflow control practices. It reiterates the need to proactively mitigate any environmental effects, which includes utilizing enhanced filtration technology.