New research shows fluctuating water tables can accelerate contaminant breakdown

Ecohydrology Research Group members have co-authored a new study examining how fluctuations in groundwater levels can influence the remediation of petroleum-contaminated soils. The article, “Effects of water table fluctuations on naphthalene degradation: Soil column experiment and modeling,” was recently highlighted in a CSA News Science Brief and published in the Vadose Zone Journal.

Using a 300-day soil column experiment, researchers compared petroleum-contaminated soils exposed to repeated drainage and rewetting cycles with soils maintained under stable saturated conditions.

Results showed that fluctuating water tables significantly enhanced contaminant removal, with more than 91 percent of contamination degraded under fluctuating conditions, compared with approximately 60 percent under stable conditions. The researchers found that falling water tables increased oxygen availability within the soil, stimulating aerobic microbial activity, while rising water tables promoted anaerobic processes. Together, these alternating conditions accelerated the degradation of naphthalene and other petroleum-related compounds.

The study also identified an important environmental trade-off. Although fluctuating water levels improved contaminant breakdown, they also led to higher greenhouse gas production, with cumulative carbon dioxide and methane emissions approximately doubling compared with stable water table conditions.

In addition to the laboratory experiments, the team developed a reactive transport model that successfully reproduced the observed degradation patterns. The findings highlight the importance of considering water table fluctuations as an active factor in contaminated site management. Understanding the connections between hydrology, microbial activity, contaminant degradation and greenhouse gas production could help improve environmental risk assessments and inform more effective remediation strategies.

The study was co-authored by Mehdi Ramezanzadeh, Fereidoun Rezanezhad, Stephanie Slowinski, Jane Ye, Marianne Vandergriendt, David Rudolph, Neil Thomson, and Philippe Van Cappellen.

Read the original news post here: https://uwaterloo.ca/water-institute/news/changing-water-levels-can-accelerate-cleanup-petroleum

Read the CSA News Science Brief here: https://www.sciencesocieties.org/publications/csa-news/2026/august/water-levels-accelerate-cleanup

Read the full research article here: https://acsess.onlinelibrary.wiley.com/doi/10.1002/vzj2.70081