Sodium bentonite samples were obtained from seven bentonite mining pit stockpiles. Swell index, fluid loss and hydraulic conductivity testing of the sodium bentonite was performed at two different laboratories. The major objectives of the study were: • To determine the correlation, if any, between swell index, fluid loss and hydraulic conductivity. • To examine the sensitivity of swell index (ASTM D 5890) to variations in the test procedures.

There was a poor correlation between swell index and hydraulic conductivity. There was a good correlation between fluid loss and hydraulic conductivity. A swell index ⩾19 mL and fluid loss ⩽16 mL appeared sufficient to yield a hydraulic conductivity of 5 × 10^-9 cm/sec at 5 psi confining pressure.

Swell index testing was performed with varying the number of scoops of bentonite dispensed into a graduated cylinder and with three different types of reagent water (distilled/deionized, deionized and tap water).