We just bought an older home that had new perimeter drainage system installed and a new sump pump installed that drains outside. The old sump was closed off and now there is signs of water leaching up mainly along the line from the old sump to the floor drain. There is crumbling cement, white powdery substance staining the floor and today actually in a few spots there is a white fuzzy substance appearing. Other cracks in the floor are now show signs of the leaching also. I am thinking the old sump is filling up and has no where to drain which is causing the problem.
Basement – Water leaching up through basement floor
basement
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In the end, I ended up using DRYLOK® LATEX CONCRETE FLOOR PAINT
It's holding up well so far, we'll see how it does over the next few years.
To answer "how much is too much," if it's causing dampness in the basement, wet concrete, efflorescence, etc. then it's too much. If the only reason you know about it is because of the new hole, then I would monitor it over a few months. It should eventually dry out. If it doesn't then you might look at a sump pump.
As to what to fill hole with, fill it with gravel to about 4-6" below the floor surface, then finish with concrete to match the surrounding area.
It's also worth taking a look at the grading outside your house, water show flow away from your foundation. Also make sure eaves are draining far enough away from your house.
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Best Answer
It may be the case that the old sump is filling up. I'd suggest opening up the floor and investigating as it's the only why to find out what's happening and fix the problem.
You could coat the floor with a water repellent sealer. This may stop the water from coming through the floor, but would not fix the underlying problem.
Also, check to make sure no household drains or exterior downspouts are being piped to the old sump location. This is easier said than done, but something to consider.
Otherwise, the white powdery substance is most likely efflorescence. This is a condition where salts are being moved out of the concrete due to the moisture moving through it. It's harmless to you but shows signs of a problem in the floor (likely due to the water).