I have never had foundation or ground water problems in my basement but I did have a sewar problem and as part of a recent replacment of that, I had a back flow valve installed that looks like this:
(source: a-to-zplumbing.com)
I have been periodically checking it, and recently I found that there were a couple inches of water in the pit. It was perfectly clear with no odor. We recently had a thaw so I figured it was a little bit of ground water flowing under the foundation. I checked it for a week or so after and observed the water level drop.
Today I opened it to find the valve almost completely submerged in water, though the water level was still about 12" below the floor. We had quite a bit of rain the last week, however in order to rule out the valve itself leaking, I tried to shop-vac the water out. I filled my shop-vac completely in a few seconds and water flowed back into the pit, which leads me to beleive that there is quite a bit of water underneeth my basement floor. The water supply enters my house about a foot from this pit.
I do not see any other evidence of moisture anywhere on the basement floor.
My biggest concern is that water will fill the pit completely and flood my basement.
Is it normal to find this much water under a basement floor after wet periods and is there a possibility of the pit overflowing, or am I only noticing this now because I have a big hole in my floor?
Best Answer
The fact that the water is seen in the pit only after a rain is a good thing, meaning your water table is not the problem, because that would mean a sump pump for sure. I think you are just seeing this because the valve is only 2' from the wall. Normally, it was dissipating. You had a good wall/slab system that wasn't leaking until a hole got poked in the slab for the repair
Some grading of the soil alongside this wall for better runoff might be in order. Any drainspouts nearby?
Some ad-hoc pump automation in the pit would give you some peace of mind until you can get outside for some landscaping.
Self contained sump pump
To verify gutters-to-storm drain are intact and not leaking down at the slab level,
Put a bottle of easter egg dye into the storm drain connection. If you see the color in the pit, I would disconnect the downspouts and direct them into the yard.
A pain for mowing, but the flip up ones work well. In our area, downspouts were connected into the floor drains and thence to the sewer. In the 1990s, we had to cap the connection with concrete or face a fine.