Abstract

A previous1 paper indicated that phenol transport was controlled by slow molecular diffusion in emulsion as the rate-determining step. Based on the transfer mechanism field dispersive model and a lab CFSTR model were built to model the time-dependent phenol concentration in emulsion and the flowing stream. Both models predicted that the produced phenol concentration monitored at an observation well will rise sharply and then decline gradually as the phenol flux emerging rom the entrapped emulsion decreases with time. For the CFSTR model phenol production is characterized by three process parameters, namely delay time to. the specific surface area/wellbore dilution term As, and reduced flow rate. q = v/L, which can be determined by a peak comparison method. The simplicity makes these models extremely valuable in estimating the size configuration and location of the spill, the time dependent phenol spatial distribution and the time required for phenol concentration to declineto an environmentally acceptable level These models are well suited to the water pollution problems associated with any chemical spills.

Introduction

In response to the bitumen spill at Cold Lake and the associated potential problem of groundwater contamination by phenol a leaching experiment1 was carried out in the lab using produced emulsion and fresh water. The purpose of the lab test was to identify and measure the critical transport parameters for phenol under well-controlled conditions. In the study, slow molecular diffusion of phenol within the oil phase of the emulsion was identified as the rate-determining step. This transfer mechanismwas adequately described by a de-coupled second-order diffusion equation from which the diffusion coefficient of phenol in emulsion was found to be 2.2 ×10−8cm2/s at 4 °C. In this paper, a similar unsteady-state formulation is developed to model field phenol response in a flowing aquifer in direct contact With the contaminated zone.

Theory

Three assumptions are made in building the model: al Emulsion is modelled as a single homogeneous phase with rapid phenol transfer between thebitumen and the emulsified water phases. Phenol diffusion within the emulsion is so slow that the phenol concentration at the water-emulsion. Interface Is zero and thephenol flux Is independent of the low phenol concentration In the leaching water. This "decoupled" condition has been explicitly stated and verified In a previous paper1. l An offset observation well Is produced at such a low rate that it does not affect the aquifer flow pattern. In the formation c) For simplicity, the emulsion-aquifer contact is assumed to be in a semi-infinite plane. The emulsion is immobile while the aquifer is flowing at a constant velocity v. A time-dependent finite, continuous line sourcedischarging into a moving 2 dimension infinite sheet with thickness σz The geometry is shown schematically in Fig. 1 The emulsion pad on the x-z plane is in contact with fresh water flowing in the × direction. The emulsion pad has a length L in the × direction and infinite In the z direction, i.e. .. L1 → ∞.

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