A quantitative redox zonation model for developing natural attenuation-based remediation strategy in hydrocarbon-contaminated aquifers

Abstract

Natural attenuation (NA) is a cost-effective and sustainable clean up technique for remedying groundwater contaminants, especially hydrocarbons, and redox zonation is a crucial subdivision of NA. However, the present Terminal Electron Acceptor Processes (TEAPs) approach, established in the 1990s, does not adequately determine the redox boundary, and is therefore unsuitable for the updated concept of the redox transition zone (RTZ) gradually confirmed in recent years. To compensate for this shortcoming, the quantitative model, integrating statistical analysis of metabolic consuming electron acceptors with the microbial growth mechanism, was improved. Furthermore, to illustrate the application of this model, one petroleum contaminated site in North China was studied. The redox boundaries of certain electron acceptors were defined as 3.72–32.68, 1.81–6.10, 0.51–1.49 and 85.83–167.62 mg/L, respectively, measured by NO3−, Mn2+, Fe2+ and SO42−. Estimated by TEAPs, groundwater was determined as exhibit sulfate reduction, superimposed with nitrate, manganese, and iron reduction, indicating that RTZs were ubiquitous. Thus, it can be concluded that the model is feasible and, particularly useful for RTZ definition. Additionally, the results imply that the model not only can be used for developing a NA-based remediation strategy in hydrocarbon-contaminated aquifers but also can be applied in other aquifers where the microbial mechanism is similar.