Previous study1–3 indicated that phenol transport from spilled bitumen into flowing aquifer was controlled by slow molecular diffusion of phenol in bitumen as the ratedetermining step. This simplified de-coupled transfer mechanism has led to a 2 dimensional planar flow analytical solution, which described the time-dependent phenol concentration in a flowing stream4. The model predicted that the produced phenol concentration monitored at an observation well would rise sharply and then decline gradually as the phenol flux emerging from the bitumen surface was decreasing with time. The simplicity makes the model valuable in estimating the size, configuration and location of the spill as well as the produced phenol concentration, the time-dependent phenol spatial distribution and the time required for phenol concentration to decline to an environmentally acceptable level by natural dispersion in the aquifer. Reversible adsorption of phenol on sand surface is studied and incorporated into the model in this paper using a chromatographic transformation technique. It is found that phenol propagation is retarded by a delay factor related to the adsorption and desorption characteristics of phenol in accordance with the chromatographic theory. The enhanced model with adsorption mechanism is well suited to other water pollution problems arising from chemical spills.
Canada has an estimated 400 billion m3 of heavy oil deposit mainly located in Alberta and Saskatchewan. Heavy oil is a viscous tar-like liquid or semi-solid, it has a density of close to one and a viscosity as high as 1 million mPa.s at reservoir conditions. It has been reported that bitumen as well as conventional oil contains water soluble toxic compounds such as phenols1,5, carboxylic acids, anhydrides, ketones and other high molecular weight acidic compounds generically classified as humic acids (Blum et al. 1986). During a heavy oil spill such as the one reported by Imperial Oil at Cold Lake in 19881,7, the spilled bitumen can be in contact with the flowing water in the surface aquifer. These compounds, which are soluble both in oil and water, can leach slowly into the water contacted by the bitumen, posing a threat of groundwater contamination to the environment. To assess the environmental impact of groundwater contamination that can result from a spill, experiments1,2 were designed and conducted in the lab to study the rate of the release of phenol from bitumen into flowing fresh water. Molecular diffusion of phenol in bitumen was identified as the rate-determining step and this transfer mechanism was adequately described by ade-coupled second-order convective-dispersive equation from which the diffusion coefficients of phenol were determined1 to be 2.2×10−8 cm2/s at 4 °C in water-bitumen emulsion and 4.0 ±0.3x10−8 cm2/s at 22 °C in bitumen2 respectively.
The idealized "de-couple" assumption enables the development of an unsteady-state formulation derived from Green's function and convolution theory to describe phenol distribution in a flowing aquifer in contact with bitumen as well as the phenol concentration produced from a sampling observation well4. This paper, which is a continuation of the model development work, described the results and the mathematical process to incorporate the effect of reversible adsorption into the model using a chromatographic transformation technique.
