I have a 75 year old home. I decided to put in a shower in my basement. While digging through the concrete floor to make room for the drain I encountered a cavity of about 3' by 4' under the floor with concrete sides and maybe 2' deep. It is about half full of water that does not smell. It appears clean. I pumped out the water and in a couple hours the water came right back up to the exact same level. I assume it is ground water.
I'm wondering what I should do about it, if anything. I mean it's been there for 75 years and I don't have water in the basement. I don't want to fix something that is not broken but I don't know if this is not a normal thing either.
Could I install the shower and backfill and just leave as is (out of sight out of mind) or should I take measures to deal with the ground water?
I am inclined to agree with Brian. If you have no drain near by the problem, good chance you have a high water table in your area. In my experiece do not go with out of site out if mind. I recomend you get someone in to take a look at it. You may need a sump hooked up.
Brian is correct. You clearly have a high water table. The 3'x4' cavity you talk about is called a sump pit. It sounds like at one point it was in use but someone over time poured concrete over it. Not a problem until you decided to put a shower in. In Durham we deal with it all the time.
My advice to you is to relocate your sump pit with a sump pump outside of your new bathroom location. Hire a reputable licensed plumber (through Trusted Pros) who has knowledge of installing drains while working with ground water. A pressure test and slope test will have to be done on the drains in order to pass inspection.
If you ignore these steps (out of sight) and a handyman does the work and the plumbing joints are not 100%, you have just given the ground water a possible escape route via your shower drain to enter your house...meaning that it isn't the potential water from the shower drain leaking out that is the problem, it is the ground water leaking into the pipe that poses the risk should the water table rise due to heavy rain and melting snow.
Below is a picture where the water table was literally underneath the concrete slab in a school we renovated. We dug a small pit for the ground water to collect where we pumped it out while installing the new drain lines.
Thank you Brian, Manuel, and Andrew.
I do have a floor drain so maybe a simple plan is to leave a line in the old sump pit, build the shower, and have an exterior pump hooked up so I can pump water out of the pit and into the floor drain if I need to. That make sense?
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