An unconfined aquifer is called to be 32 m thick below the water table. A constant discharge of 2 cubic metres per minute is pumped out of the aquifer by a tubewell till the water level in the tubewell becomes steady. Two observation wells at distances of 15 m and 70 m from the tubewell show falls of 3 m and 0.7 m respectively from their static water levels. Determine the permeability of the aquifer.