In order to determine the average permeability of a bed of sand 12.5 m thick overlying an impermeable stratum, a well was sunk through the sand and a pumping test carried out. After some time the discharge was 850kg/min and the drawdowns in observation wells 15.2m and 30.4m from the pump were 1.625 m and 1.360 m respectively. If the original water table was at a depth of 1.95 m below ground level, find the permeability of the sand (in m/s) and an approximate value for the effective grain size.
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