Do you see any leak inside after our big rainstorms? If not, you should have no problem. Just fill the depression with soil. If you want to improve the drainage from outside, you have to dig about 3 feet deep at least. Examine the foundation from the outside. If there are cracks I would use some asphalt pitch and coat the area and put a piece of blue styrofoam over it. Then fill the rest with crushed stone or gravel.