A site consists of a homogeneous dense silty sand layer of 9 thickness, which is underlain by an impervious stiff clay stratum. The initial water table was at 2 depth below the ground level. A pumping test was carried out by pumping out water at the rate of 0.6 . Observation wells were dug into the ground at 15 and 40 distances from the center line of the well. At steady state (i.e., when there was no change in water levels in the observation wells), the water levels in the two wells dropped by 550 and 150 , respectively.

Determine the hydraulic conductivity of the clayey sand layer.