Pit in my basement

[moto]

My house has an addition, put on in 1980, with a basement under it. In the basement, there is a pit, roughly 18" by 18" by 24" deep. There is no water in it at the moment, but most times of the year it is about half full of water. There is a large pipe coming in from the side, that is capped off.

What is this for?

[pushkins]

It looks like a clean-out point for your waste lines, though I'm not so sure why it is half full of water for half the year.
Where does the water come from, up from below or is it filling from water on the basement floor ?

[Gregg]

Looks like a sump pit to me.Where I live a sump pit is required but the installation of a pump is up to the homeowner. If you want, add a sump pump and discharge line.

[moto]

Where does the water come from, up from below or is it filling from water on the basement floor ?

The basement floor is always dry, so the water must be coming up from below. I think the water table must be lower at this time of year, so no water in the pit at the moment.

[Wgoodrich]

Someone may have tapped a new daylight outlet to finish grade draining your outside perimeter drain. They may have installed an outside cistern and pumped the subsurface water to the surface then drained away from the house. If they did either of the above then they probably would have plugged off the inside drain pit to protect from inside flooding. If I were you I would go around the house looking for a new cistern or to low lying finish grade areas or a nearby creek looking for a new daylight outlet. This would give you answers to what you seek about that pit plugged off.

Just a thought

Wg

[moto]

I remembered I have an old diagram of the drainage for my house:

http://members.shaw.ca/redf4/LotPlan.jpg

If I'm understanding it correctly, most of the drain tile for the house is connected to the storm sewer system (at the top of the diagram).

The drain tile for the garage and carport are connect to a pit in the backyard. Would that be a "dry well"?

I appear to also have two connections to the sanitary sewer (along the bottom of the picture).

The pit in the basement is the "x" inside the box, shown in the addition. It seems to connect to the drain leading to the storm sewer.

Old houses seem to be full of mysteries...

[pushkins]

There ya go, the pit was in place to collect rising ground water and take it out via the (capped) pipe to the sewer system as per your picture.

[Wgoodrich]

What I read is that your house was originally with a perimeter drain system that drained into the city sewage system. Later in years many cities have addressed overloading of the wastewater treatment plants due to storm drains requiring homeowners to separate non sewage drain water from the sewage drain system and hook it to the storm drainage system that might have been installed after the original construction. Your plan states you have a gravity perimeter subsurface drain system that drains into the city strom drain system no after it was revised.

This is good news especially with the city storm drain being 5 feet deeper than the house perimeter drainage system. Bad news is you may experience a wetness or flooding during a 100 year flood event due to overloaded city storm drainage system. You are one of the few that have a way to address an overloaded city strom drain system by partially loosening the plug in your pit and pumping the water draining into that pit to the outside through a window on top of the grass away from the house during this 100 year adverse flooding event. Just remember do not remove the cap in that pit during flooding because water will rush up about 4' above your basement floor inside your basement due to back pressure from your city strom drainage system. This 100 year event would normally only last about 4 days on the average before your city storm drain can catch up with the onslot of massive rain periods.

If I were you I would leave things as they are considering yourself safe until a 100 year flood event. Then you will still have time to rent a pump to assist during that adverse flooding period minimizing any damage due to that 100 year event.

Just my opinion

Wg

[moto]

Thanks, guys, for the insight into the mysteries of my old house.

A couple more pictures. On the wall next to the basement pit, there is a capped-off pipe coming through the wall. Outside, the pipe comes up from the ground and extends up to a height of about 7 feet. Any ideas what that is for?

[joed]

That pipe looks like a vent line. I wonder if this used to be sewage ejector pit. Could this house have been on a septic and they added sewers at some time?

[Wgoodrich]

Looks like there may be a time in the past there was an oil tank for an oil furnace along that wall using that pipe as a vent pipe to the oil tank.

Wg

[moto]

The house might have had a septic system when it was built in 1955. The large pipe in the pit is about 5 feet below grade -- would they have put a pipe to the septic tank that far down?

The small pipe is part of the addition (1980), so would not have been part of the septic system.

The house originally had oil heat; I'm not sure when it was converted but there is no sign of an oil tank ever being in the basement.