Effective Porosity and Seepage Velocity in Column Tests on Compacted Clay

A series of column and tank tests were conducted using bromide to estimate seepage velocity through compacted clays. Bromide concentrations in effluent and sectioned-core pore water were measured. The seepage velocity estimated from the concentration-depth profile data obtained from sectioned-core pore water samples was approximately 50% greater than that estimated from the breakthrough curve data. The discrepancy is thought to be caused by the soil sample compression during coring and sectioning. The effective porosities estimated from the column/tank breakthrough curves ranged from 89 to 104% of the total porosities determined from the weight-volume phase relationship. The hydrodynamic dispersion coefficient had a linear relationship with the seepage velocity. When the mass transport parameters of contaminants through a soil liner are to be estimated using column tests, it is recommended that tracer tests be conducted for the correct estimation of the seepage velocity.