There was a recent flood in my neighborhood that caused several wet basements (directly from the river, or indirectly through rising water levels). My house didn't suffer water damage but a week or two after the river receded, I noticed dark wet spots on the concrete floor of the basement. There are also some efflorescence visible.
A few contractors who have come to fix some foundation cracks (this was noticed before the flood) have said the dark patches is due to hydrostatic pressure but they don't recommend putting in a sump pump. One said he would do it but also said it won't solve the hydrostatic pressure problem.
My question is why won't a sump pump help? If water is trying to get into the basement wouldn't pumping it out alleviate the problem? or will installing a sump pump cause the water to overflow the hole and flood the basement anyway?