Pit in basement.. what's it for??

[The old college try]

I'm not even sure if this qualifies as a plumbing discussion item, but there is some sort of pit in the center of my basement laundry room floor. There's a slight depression in the floor in this area and a large metal cap (about 5" diameter) which I always thought was some sort of floor drain. I just decided to go pull it off to check it out since I'm getting ready to perform radon mitigation. I discovered that there is a pit that's about 2 feet deep. I can't see the sides, so I have no idea how large it really is. Any idea what this is or what it's for?? Oh yeah.. house is 80 years old. Could it be some sort of sump or have something to do with the old septic system???? Looks pretty gross. If I didn't know any better I'd think there used to be a toilet on this nasty looking thing.
Any thoughts would be appreciated. I'm thinking about just sealing it up.

 

[Redwood]

Hard to say without seeing it myself. It may be a floor drain with a drywell under the floor.

 

[Sponsor]

 

[The old college try]

Is it likely, if this is a drywell, that it may tie into the sump? My sump has 2 drain tiles coming into it, but they're completely plugged. I'm wondering if this may lead there. Also, I'm wondering if this is just a big collection point for the radon gas that I'm going to try to get rid of.

 

[Redwood]

Could very well be.

 

[Bob NH]

You aren't trying to get rid of radon gas that is collecting somewhere.

Radon gas is everywhere under the floor.

You are trying to maintain a slight vacuum (about 1" water column) under the floor. That depends on having a porous material under the concrete so the air and radon can get to the vacuum pipe. If there is a pipe in that drain going to a dry well or a sump then it won't be effective as a place to create the vacuum under the whole floor.

After you connect the vacuum pipe to the floor so it can collect air and radon that flows through the porous material under the concrete, you must seal any cracks in the floor, other openings, around the edges of the floor, and around any plumbing through the floor. You can caulk around the base of any toilets or shower pans so you don't have to take them up.

 

[The old college try]

Ok, so I'm trying to decide the best way to seal this thing up when I perform the mitigation. One concern is that I don't want to lose a floor drain in case of emergency. One thought is to set a floor drain at the location of that existing cover and trench a pipe over to the sump pit which currently accepts water from the washing machine. If I do this, I assume I'd need to put a trap in the line to prevent any smells from the sump pit from coming up through the floor and to prevent radon from finding it's way out of the sump. Do I need to be concerned about the sump pump sucking the water out of the trap?

 

[Furd]

There's no question that it is an old floor drain and I think it is quite possible that it could just be a dry well. It wouldn't take much to sledge hammer that into a big enough hole to see around a bit better and if it were my basement I would want to see how large it was. It may be that a fair amount of your basement floor is unsupported because of erosion.

Back when I was a kid (a long time ago) my parent's house had a stairwell to an outside entrance to the basement. The stairwell had a drain fitting exactly like that one only the cover was perforated. Inside the basement some twenty feet or so away was a similar drain fitting next to where the laundry tub piping went under the floor. My daddy told me that there was a pipe connecting the two floor drains but it was plugged up and that was why the outside one didn't drain.

When it rained the stairwell would collect water until it came under the door. One summer (when I was a teenager) I decided to see if I could clear the dirt from this outside drain. I ended up breaking out the drain and started digging. There was no pipe to be found. I ended up putting in a plastic catch basin and a condensate pump I found somewhere. I used a float switch for a bilge pump (yes, it was rated for 120 volts AC also) and ran power to the pump. I put in a discharge pipe that ran back to the driveway and then used concrete topping mix to grout in the catch basin and installed the grate.

Anyway, long story but I wanted you to know that there isn't necessarily a pipe to your sump down there and it could be an erosion problem you might want to investigate.

 

[Bob NH]

Ok, so I'm trying to decide the best way to seal this thing up when I perform the mitigation. One concern is that I don't want to lose a floor drain in case of emergency. One thought is to set a floor drain at the location of that existing cover and trench a pipe over to the sump pit which currently accepts water from the washing machine. If I do this, I assume I'd need to put a trap in the line to prevent any smells from the sump pit from coming up through the floor and to prevent radon from finding it's way out of the sump. Do I need to be concerned about the sump pump sucking the water out of the trap?

You can run a pipe from the drain to the sump but you must do some sealing.

1. The joints in the line from the drain to the sump pit must be sealed.
2. If the sump pit is exposed to the atmosphere of the basement, then the inlet from earth drains to the sump pit should enter below the water level that is maintained in the sump pit or those inlets should have traps to prevent air from the basement from entering the earth under the floor, and then your radon fan system, thereby reducing the vacuum available to remove the radon.
3. The pipe from the drain to the sump need not be trapped if that is its only inlet.
4. There must be a seal around the outside of the drain to the concrete floor, and the connection to the sump pit must be sealed, to prevent air from the basement from entering your radon fan system through a crack around the drain fittings.
5. The area around the sump pit must be sealed to the floor to prevent air from the basement from entering your radon fan system through a crack around the sump pit.
6. The sump pit must be plastic or some other material that is air-tight.

The purpose of all of the sealing is to prevent air from the basement or outdoors from entering the suction side of your radon fan where it will diminish the vacuum, and therefore the effectiveness of the mitigation system.

 

[The old college try]

So, does the sump pit need to be vented for the sump pump to work properly?

 

[Furd]

It's pretty unlikely that you could get your sump to be vacuum tight but yes, they do need to be vented for proper pump operation. Further, if it was pressure/vacuum tight no water would flow into the sump for the pump to remove.

 

[njmaan]

looks like an old radon mitigation system

Hi,

It looks like an old radon mitigation system, I would measure th eradon levels in the house.

The best solution, I came across, to mitigate high levels of radon is to use an in-line radon fan.

I have reduced the level of radon from 15 pCi/L (maximum acceptable in USA is 2 pCi/L) to 0.4 pCi/L by using this type of system.

I have took steps to measure the radon levels only after a friend has been diagnosed with an early form of lung sarcoma (cancer) - he had 21 pCi/L in his basement home office.

You can get additional information about radon mitigation and risks at

http://handyowner.com/2008/08/17/ins...gation-system/
http://handyowner.com/2008/08/15/rad...y-killing-you/

Cheers!

 

[Toolaholic]

Run water in the distant sinks beyond this ,Get a flashlight look and listen.
May be a drain cleanout You would want to keep. I think Your seeing radon EVERYWHERE ! SLOW DOWN