QUANTIFYING AQUEOUS PHASE RELATIVE PERMEABILITY VARIATIONS DURING DISSOLUTION OF ENTRAPPED NAPL

Non-Aqueous Phase Liquids such as organic compounds are major sources of groundwater contamination throughout the world. The non-uniform distribution of these contaminants as NAPL pools and NAPL residuals introduce additional spatial heterogeneity in the hydrogeological parameters such as porosity and permeability. The existing models have repeatedly used models developed based on two phase flow experiments such as Corey's and Wylie's equations which relate relative permeability to effective water saturation. It is hypothesized that the pattern of changes in relative permeability as the NAPL dissolves is quite different from the relative permeability variations during two phase flow. Hence the use of the empirical relationships developed for relative permeabilities as a function of effective permeabilities for the case of dissolving NAPL pools is questionable.

In this study, column dissolution experiments were conducted in a simplified heterogeneous system and the changes in relative permeabilities were quantified by measuring differential pressures at various time points. The NAPL saturations were also quantified as the NAPL dissolved by estimating aqueous phase concentrations and applying mass balance. These experimental data when compared to the existing correlation predictions proved our hypothesis that the relative permeability variations as the NAPL dissolves slowly over time is quite different from the pattern of variations as the NAPL drains. A total of 12 experiments were conducted to quantify the relative permeability variations with time using different initial NAPL saturations and sand grain sizes. A new correlation was developed to predict relative permeability for known NAPL saturations for the NAPL dissolution scenario. The correlation was also verified with an independent data set. Sensitivity analysis was also conducted to study the impact of ground water flow velocities on the correlation. Using the data collected in these experiments an improved mass transfer correlation was also developed to predict the NAPL transfer into the aqueous phase. Both these correlations were plugged into an improved model for NAPL contaminant transport with dissolution to predict aqueous phase concentrations over time.