A clay 18m thick has hydraulic conductivity 10^-8m/s. The clay suports a thin layer of soil saturated with water; the clay is underlain by a thick gravel aquifer. If the pressure head at the base of the clay is 27m of water, how much water leaks from the aquifer across the clay to the surface over one hectare each day (1 h=10,000m^2). Hint: it may help to conceptualise this problem by putting in 2 imaginary piezometers: one in the thin soil layer above the clay, and the other to the base of the clay. Visualise the level of water in each piezometer.