Sensitivity of Predicted DNAPL Source Zone Longevity to Mass Transfer Correlation Model

Abstract

Despite significant research into the topic for 20 years, the interrelationship of DNAPL source zones and downgradient aqueous-phase contaminant concentrations is poorly understood. A number of experimentally derived correlation models have been published to describe mass transfer from the non-aqueous to the dissolved phases. This study examines the sensitivity of DNAPL migration, dissolution and transport simulations in homogeneous and heterogeneous porous media to the choice of mass transfer expression using six published, experimentally derived correlation models. One-dimensional simulations illustrate the sensitivity of predicted effluent concentrations to the employed dissolution model. This sensitivity is observable in the magnitude of dissolved phase concentrations, the length of time during which contaminated groundwater effluxes through the column, and the pattern of dissolved phase concentrations observed over time. Two-dimensional simulations of a realistic DNAPL release into a heterogeneous porous medium illustrate that the dissolution model employed significantly impacts predicted behaviour. Source zone life spans were observed to vary by greater than an order of magnitude, and maximum observed aqueousphase concentrations were observed to vary from the solubility limit to less than one-third that value. This study suggests that attempting to infer DNAPL source configuration from downgradient concentrations or to predict site remediation times remains uncertain until such time as a comprehensive mass-transfer expression is derived and validated. INTRODUCTION NUMERICAL MODEL RESULTS AND ANALYSIS CONCLUSIONS REFERENCES