Elucidating the fate of a mixed toluene, DHM, methanol, and i-propanol plume during in situ bioremediation

•A subsurface model to analyse the performance of an actively operating field-scale enhanced bioremediation scheme.•Failure of the treatment system is linked to an inefficient oxygen injection pattern.•Model simulations suggest additional contaminant spillages resulted in contaminant fluxes increase that remained untreated.•Reactive transport modelling can play an important role in data analyses and for enhancing remediation efficiency.

Organic pollutants such as solvents or petroleum products are widespread contaminants in soil and groundwater systems. In-situ bioremediation is a commonly used remediation technology to clean up the subsurface to eliminate the risks of toxic substances to reach potential receptors in surface waters or drinking water wells. This study discusses the development of a subsurface model to analyse the performance of an actively operating field-scale enhanced bioremediation scheme. The study site was affected by a mixed toluene, dihydromyrcenol (DHM), methanol, and i-propanol plume. A high-resolution, time-series of data was used to constrain the model development and calibration. The analysis shows that the observed failure of the treatment system is linked to an inefficient oxygen injection pattern. Moreover, the model simulations also suggest that additional contaminant spillages have occurred in 2012. Those additional spillages and their associated additional oxygen demand resulted in a significant increase in contaminant fluxes that remained untreated. The study emphasises the important role that reactive transport modelling can play in data analyses and for enhancing remediation efficiency.