A job site requires an excavation of a circular area with a diameter of 100 m to a depth of 15m. The soil permeability k = 2.010-5 m/s. Multiple 200-mm-diameter deep wells are used for dewatering at an excavation site. The height of the phreatic level above the impermeable layer before pumping is 15 m. The height of the phreatic level at the center of excavation pit after pumping is 5 m. Estimate the required number of deep wells