An experimental investigation of nonaqueous phase liquid dissolution in saturated subsurface systems: Steady state mass transfer rates

Abstract

Results of an experimental investigation into steady state dissolution of nonaqueous phase liquids (NAPLs) entrapped within water saturated porous media are presented. The influence of porous media characteristics, NAPL type, and aqueous phase velocity on NAPL dissolution rates is explored through evaluation of a series of laboratory column studies. For many of the conditions tested, measured organic solute concentrations in the column effluents were below solubility limits, indicating nonequilibrium conditions. Entrapped NAPL distributions are examined and shown to depend upon porous media grading and mean grain size. Experimental results reveal a dependence of dissolution rate on the distribution pattern of entrapped NAPL, as well as upon aqueous phase velocity. A phenomenological model for the mass transfer process is developed which incorporates grain size parameters as surrogate measures of NAPL distribution. An additional set of column experiments, employing another porous medium and NAPL type, confirm the usefulness of the model as a predictor of steady state mass transfer rates in similar systems.