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An Experimental Investigation of Rate‐Limited Nonaqueous Phase Liquid Volatilization in Unsaturated Porous Media: Steady State Mass Transfer
Author(s) -
Wilkins Mark D.,
Abriola Linda M.,
Pennell Kurt D.
Publication year - 1995
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/95wr01677
Subject(s) - volatilisation , porous medium , mass transfer , vadose zone , dissolution , péclet number , sherwood number , tetrachloroethylene , grain size , groundwater , soil science , phase (matter) , porosity , materials science , chemistry , mineralogy , environmental chemistry , chromatography , environmental science , geotechnical engineering , thermodynamics , soil water , geology , composite material , trichloroethylene , reynolds number , nusselt number , physics , organic chemistry , turbulence
Results of one‐dimensional soil column experiments are presented to evaluate the factors influencing volatilization of entrapped nonaqueous phase liquids (NAPLs) in unsaturated sandy porous media. Three‐phase fluid saturations measured in Ottawa and Wagner sands were found to depend upon porous media grain size and distribution, with residual water and NAPL saturations ranging from 8 to 16% and 4 to 10%, respectively. In general, residual NAPL saturations were 2–3 times less than NAPL entrapped in similar two‐phase (organic‐water) systems. During volatilization of three single‐component NAPLs (styrene, toluene, and tetrachloroethylene), contaminant vapor phase effluent concentrations deviated from local equilibrium values by 10–40% for pore velocities ranging from 0.25 to 1.5 cm/s. In contrast to NAPL dissolution, mass transfer rates were found to decrease with decreasing soil mean grain size. An empirical correlation based on the modified Sherwood number and Peclet number was developed which incorporates the soil mean grain size as a surrogate measure of NAPL distribution. The utility of this model is demonstrated for the prediction of steady state volatilization rates in independent NAPL‐porous media systems.