Professor George Pinder of the University of Vermont gave one of the keynote addresses in the WIT Advanced Seminars Summer Series, the subject of the lecture being “Simulation of Microbial Transport in Aquifer Contamination”.

Professor Pinder is the most well known scientist in the field of aquifer contamination and has participated in many research projects and well known cases worldwide, some of them very much in the public domain.

His talk concentrated on the case of alcohol-assisted bioremediation. This consists of applying an alcohol flush to the subsurface to degrade the microbics. The work involved the simulation of the effects of this process to the non-aqueous phase liquids (NAPLS).

He presented the governing equations representing air, water and NAPLS. Complications arise from the change of phase of the components and the fact that the NAPLS can dissolve into the gas phase or solidify. In mathematical terms, there are at least 10 unknown per node in the numerical model.

Professor Pinder presented some examples of bioremediation using the computer model that he has developed. They represent the NAPL species resolution and the microbial degradation. The results also show the amount of oxygen, nitrogen and microbes present. The differing percentages of these species can accelerate the microbial degradation.

The model was applied to the field investigation of a CIBA site. The company stored chemicals in two lined pools. Unfortunately the chemicals contained in the pools dissolved the liners and eventually reached the aquifer. The contaminant consisted of a series of NAPL’s contaminant species, mainly Chlorobenzenes and Trichlorobenzene, and CIBA explained that the two do not degrade at the same rate. Oxygen and nutrients were injected into the aquifer to regrade the chemicals.

The numerical model representation of the problem involved approximately 15,000 unknowns and the code was run for 30 days with different inputs, including alcohol flush.

As a conclusion, Professor Pinder explained that 3D simulation of bioremediation is now feasible, and alcohol flush performs better than other methods.

The lecture was followed by a very lively discussion which included many comments and suggestions.