The bearing capacity of sand deposit will remain same until water table rises to a depth less than width of footing i.e. 1.5m below footing.
When water table rises to 3m and 1.5m below footing, the bearing capacity remains same.
But when water table rises to 0.5m below footing bearing capacity would change. 
∴ Footing rests on surface of a sand deposit i.e.

D_f = 0 (Because footing resting on the surface) and C = 0 (Because of sand deposit)
∴ q_u and q_nu both are equal because D_f = 0

∴ When water table is far below the base of the footing, bearing capacity was estimated as       600 kN/m²