A section of canal 200 m long and 10 m wide is being deepened 1 m by means of a dredge. The effluent from the dredging operation is found to have a unit weight of 12.5 kN/m". The soil at the bottom of the canal has an in-place unit weight of 18.6 kN/m". The specific gravity of the soil grains is 2.69. If the effluent is to be pumped out at the rate of 500 litres/minute, how many operational hours would be required to complete the dredging work?