Environmental pollution is a significant concern around the landfill sites, waste repositories and other similar wastewater storage and treatment basin and ponds. Pumice is an abundant natural material in Kayseri, Turkey and therefore, permeability characteristics of pumice-bentonite mixtures were investigated in comparison with commonly used sand-bentonite mixtures. Four different bentonite contents (15, 20, 25 and 30%) and three grain size ranges (2.00 to 1.00; 1.00 to 0.50; 0.50 to 0.25 mm) of pumice and sand were used to determine the hydraulic conductivity of mixtures. Since it takes long time to determine the hydraulic conductivity of fine grained mixtures, empirical equations were developed between permeability and easily-determined geotechnical characteristics such as dry unit weight, moisture content, and swell potential of such mixtures. Pumice-based mixtures yielded identical permeability values for the same bentonite contents and size ranges. Overall evaluation of regression equations with regard to mean absolute error (MAE) and regression coefficients showed that while dry unit weight yielded the least MAE and the highest R² values for pumice-based mixtures, swelling potential yielded the best estimations for sand-based mixtures. Bentonite content of ≥ 30% is recommended for both pumice and sand-based mixtures with grain sizes between 2.00 and 0.50 mm and ≥25% for mixtures with grain sizes less than 0.50 mm.

Key words: Pumice, bentonite, mixtures, permeability.