MTBE Attenuation in a Chalk Aquifer

A conceptual model of MTBE attenuation in a chalk aquifer was built and validated by both field observations and modeling following the accidental spill of storage tanks at a petrol station in southern England. It was shown: (1) Dual porosity transport plays an important role in MTBE attenuation in the chalk aquifer; (2) MTBE concentration measured in monitoring wells may depend more on dual porosity transport effects than degradation; (3) For this dual porosity aquifer (the Chalk) with its large portion of immobile water, a single porosity model is not able to predict the plume evolution. The dual porosity model was able to accurately produce the quick response of fracture transport and the measured concentration level at different distances and depths; (4) Examination of MTBE fate with lab measured MTBE degradation rates showed that MTBE is unlikely to degrade within the Chalk matrix. MTBE may be degraded in fractures with a maximum degradation rate (kMTBE-O2) of not more than 3.62E-12 mol/L/s; (5) Physical processes such as advection, dispersion, diffusion and dual porosity mass transfer are more important than degradation in controlling plume development in this system.