An unconfined aquifer extends over an area of 1 km^2 and has hydraulic conductivity, total porosity and specific retention of 20 m per day, 30% and 10%, respectively. After pumping some groundwater from this aquifer, the water table dropped to a depth of 20 m from the ground level. If the water table was initially at 14.5 m below the ground level, the change in groundwater storage in million cubic meters would be _______________