Isotope-Based Early-Warning Model for Monitoring Groundwater–Leachate Contamination Phenomena: First Quantitative Assessments

Groundwater contamination due to municipal solid waste landfills’ leachate is a serious environmental threat. Deuterium (2H) and oxygen (18O) isotopes have been successfully applied to identify groundwater contamination processes, due to interactions with municipal solid waste landfills’ leachate, including significant organic amounts. A parameter influencing the isotope content of deuterium and oxygen18 is the deuterium excess (d or d-excess). This paper presents a d-isotope-based model, defined early-warning model, depending on the assessment of the deuterium excess variations in groundwater samples. The isotopic results are corroborated with the trace elements’ concentrations (Fe, Mn, Ni, Co and Zn), suggesting that the methanogenic activity diminished under trace element limitation. This model provides the determination of an index, F, as the percentage variation of d-excess, which makes it possible to define an alert level system to assess and check groundwater contamination by leachate. The procedure shows that values of F index higher than 1.1 highlight possible contamination phenomena of groundwater due to leachate and, therefore, actions by the municipal solid waste landfill management are required. This early-warning model is presented by the application to a case study in Central Italy in order to evaluate innovative aspects and opportunities to optimize the model. The application of the procedure to the case study highlighted anomalous values of the F index for the samples AD16 (Fmax = 2.069) and AD13 (Fmax = 1.366) in January, April, July and October surveys as well as the boundary values (1 ≤ F ≤ 1.1) for samples AD73 (F = 1.229) and AD68 (F = 1.219) in the April survey. The proposed model can be a useful management tool for monitoring the potential contamination process of groundwater due to the presence of landfills with municipal solid waste, including a significant organic component.