A layer of clay 5 m thick overlies a deposit of sand 5 m thick, which is underlain by rock. The water table in the sand is sub- artesian with a level at 2 m below ground level. The saturated unit weights of the clay and sand are 21 and 18 kN/m^3, respectively. Determine the total stress, the pore water pressure, and the effective stress at the top and bottom of the sand.