In 2023, a study in the Journal of Contaminant Hydrology described an MNA pilot project at a former chemical manufacturing site in Southern Italy. The contaminants found were a large area plume of chlorinated solvents (TCE, DCE, VC), and the researchers sought to use Monitored Natural Attenuation (MNA) to remediate the contamination. Their first task was to demonstrate that active biodegradation was happening, moving the concept from theory into practice.

The research team, including experts from Italy’s Apulia Region Environmental Agency (ARPA Puglia), used a high-tech analytical technique called CSIA to gather forensic evidence of biodegradation. Traditional methods generally measure changes in contaminant concentration over time, whereas CSIA measures isotopic composition within the contaminant molecules themselves. As microorganisms naturally degrade chlorinated compounds, they favor the breakdown of lighter carbon isotopes, leaving behind contaminant molecules containing a greater proportion of heavier carbon isotopes. In the laboratory, this slight change in isotopic ratio serves as an indicator of natural biodegradation processes occurring in the environment and verifies that natural degradation is happening, as opposed to simple dilution or dispersion of the contaminant. The measured difference in abundance between the two forms of the heavier carbon-13 isotope (δ¹³C) provides the identifying features of a reductive dechlorination process, where microorganisms break down the contaminant to facilitate cleanup.

By collecting water samples along the contaminant plume's flow path using this method, the researchers discovered where the isotopic ratios were still normal near the pollution source and became progressively heavier farther downgradient. This clearly indicated microbial degradation of the contaminants. Furthermore, the researchers identified where this degradation had ceased, enabling them to establish the exact boundaries of the treatment zone.

The most important breakthrough occurred when the researchers plugged their results into two commonly used simulation models (PHREEQC and BIOCHLOR-ISO), which not only confirmed the occurrence of degradation but also enabled them to predict future conditions at the site. Using the degradation rate values, the researchers determined that the site would be below acceptable levels for approximately 11 years following removal of the pollution source.

Why does this case from Italy, a region without formal MNA regulations, matter to U.S. practitioners? It provides a rigorous model capable of meeting stringent U.S. standards. Many U.S. Superfund and brownfield sites face the same problems; MNA (Monitored Natural Attenuation) is relatively inexpensive and has little environmental impact.

Yet, often the reason for a lack of adoption by regulators and stakeholders is that they seek evidence of the actual destruction of the contaminants by biodegradation, not just dilution and dispersion. This Italian case shows how an initial investment in advanced lab analysis can open up the possibility of a long-term, cost-effective cleanup solution—especially at sites with simple aquifers and active microbial populations.

This case study offers cleanup managers a clear, replicable approach by providing a simple, step-by-step process for use in their own projects:

• Generate forensic evidence of biodegradation by utilizing CSIA (Compound Specific Isotope Analysis).
• Use that isotopic data to develop a predictive timeline based on an easily interpreted model.
• Present the integration of these scientific data as required by your regulatory agency to demonstrate compliance with regulatory obligations.

By using this science-based process, the observation of MNA is transformed from a passive monitoring strategy into a scientifically defensible, active management plan.