Example : At one location on the ground a porous layer lies above an impervious stratum. The thickness of this porous layer is 7 meters.

Water table also lies in the porous layer and it is at the depth of 1.5 m below the ground surface.

A test well is drilled into the ground which penetrates the whole thickness of this permeable layer. Through this well the water is pumped out at the rate of 100 liters per second.

The drawdown of the water table because of this pumping out is observed by making observation wells at a distance of 7 m and 21 m from the test well.

The drawdown observed at 7 m is 3 m and at 21 m it is 0.8 m.

What is the coefficient of permeability of that porous layer of soil?

Answer :