I just laid the first section of my basement slab. I'm now preparing the area for the next section and discovered a small, half-rotted stump that is just at the level where I intend to lay my concrete. The subgrade is otherwise completely virgin, hardpacked ground. The stump is rotted enough to give me a soft area about 18" in diameter but solid enough in the middle that removing the whole thing would be pretty tough. The stump will obviously continue to rot if left in place so I'm thinking that this area will re-soften over time resulting in an unsupported area of the slab unless I completely remove the whole thing. Since the area is so small, could I just increase the slab thickness in an area of about 2x the diameter of soft area? Or is the best solution to just remove the whole thing and pack with gravel and lay the slab normally? Thanks.