The dark stain on the bottom of the wall comes from water leaking through into the basement.
A new sump pump will pump out the water instead of letting it sit on the floor.
DryZone decided years ago that we need to protect the home against unexpected leaks on the wall. If a wall leaks, it will most likely happen in the bottom 2 feet, so we use a CleanSpace wall liner to direct the flow to the drains.
Once all the pipes are in place, we fix the concrete floor. The new concrete will dry and you won't have to lose any amount of floor space.
These are some great pictures of WaterGuard, a drainage pipe system for basement.