The pollutant travel time through compacted soil material (i.e., when a pollutant introduced at the top first appears at the bottom) cannot be accurately predicted from the permeability (saturated hydraulic conductivity) alone. The travel time is also dependent on the effective porosity of the material; i.e., the portion of the total porosity that contributes significantly to fluid flow. Pollutant travel time is directly proportional to effective porosity and thickness of a compacted layer and inversely proportional to permeability and hydraulic gradient. The total porosity is calculated from measurements of bulk and particle density. Pore size distribution information is obtained from the cumulative porosity curve of the sample as measured by mercury-intrusion porosimeter. The paper also compares measured and predicted solute breakthrough times for three compacted soil materials.