Mysterious 2nd hole in basement

Hello Everyone,
Today I unearthed the source of our great basement smell. When we purchased our house the basement had nasty carpet from 1989 (Year house was built) that looked like it was from the early 70s. Upon removal we found a 2nd hole in our basement. When we replaced the carpet we were told it would be fine to just cover it back up...
We used padding and a thicker carpet, which I imagine is a contributing factor to our problem. After 2-3 years in the summer it would smell and occasionally in the winter but not very often. Today was one of those smelly days so I ripped up the carpet as I'd had enough. I took pictures which I posted here.
I' m not certain but I think this is the main drain pipe to the city sewer and that square thing that's all rusted could be a check valve. It could also be a radon pit but I think that's less likely. This is merely a SWAG... I think my sewer must have a check valve as my neighbors bi-levels flooded while my full basement at what I was told is the lowest point in the sewer return on the street received not a drop of sewer backup, 2 or so years ago. You'll notice at the floor level WAY above that is another ominous sealed pipe. If that's a check valve in the pit, could that be the main sewer cleanout?

So now I'm left with the real question of what to do to get rid of the smell forever.!. The top of the hole appears to have been propped up with some wood for stabilization. That was pretty discolored and smelled quite rank. The bottom also exposes the rock underlayment for the drain tile I think is there.

While the thought of diggin in that hole and opening that cover turns my stomach it's probably the right thing to do, maybe? If it ain't broke should I leave it alone? My favorite idea so far is just pouring concrete in the damn hole... while I'm sure that's wrong that would be very satisfying. Perhaps I could just fill it with expansion foam so it could be dug out later? What would you do with a smelly hole? I'm open to all suggestions.

Looks like a back flow thing. If you have radon that would be good place to put that system in. I would find a way to seal the lid.
http://www.balkanplumbing.com/sewer...es/sewer-check-valves-backwater-check-valves/

Yes I was thinking the same.
Something like a 4 to 6 mil thick Polyethylene sheet(drop cloth) put between the lid and the enclosure. Followed by a slightly larger piece of the poly over the entire area of the lid and that cleanout plug. Below that carpet padding.

1/4" clear Lexan and seal it down with silicone.

nealtw said:

1/4" clear Lexan and seal it down with silicone.

Click to expand...

You have expensive taste. And a bump in the floor.
Or are you thinking as a replacement for the existing lid?

Diehard said:

You have expensive taste. And a bump in the floor.
Or are you thinking as a replacement for the existing lid?

Click to expand...

That was hardly a lid, yes I was thinking replace it.

You really think 1/4" lexan would be sufficient so that it feels solid if I were to walk on it? What if a 400Lb person jumped on it? I wouldn't trust the current lid with a 400Lb man even for standing, but I like to make my work "real good".

Okay then make it 1/4" steel plate!

6 mm= 1/4 inch, I think you will be impressed.

I know a guy with a plasma cutter so he's just going to make me an A36 carbon steel plate for $40. Found a load chart that looks like I'll be able to have 2, 300 pound men jump in the center and won't deflect enough to come off the inner lip. I don't have any 300Lb friends but maybe I'll show my kids jumping on it.

It is a backwater valve, the code says that there must be access to the backwater valve. this is what you d0
1) re move has much debris around the valve as possible. the go and buy some


Quick Plug Hydraulic Cement.
then mix it up and fill the area around and below but not on top of the back water valve .this will seal the bottom of the opening on the make sure that you can undo the four bolts on top of the valve and remove the lip. buy the way i would open the valve now and check that everything is operating normally , and also lubricate the valve hinge pin with plumbers grease and remove any debris .
then go and fashion a water proof lid to fix over the opening.
if you can i would not put the carpeting back over the lid. i would want to go back once a month and open the lid just to make sure no more water was coming in . if in a year everything was dry then go head and put the carpet back .

SO an update: the pit steel plate lid is great and works perfectly but before I put the carpet back I had a hunch so I opened it up and sure enough the whole hole stunk... and it stunk like sewer as always. SO I got in the hole and looked at the backwater valve lid and there were cracks masked with Dirt in the plastic cover. I assume the lid failed the last time there was a sewer back up which then worsened the issue. The bolts had eroded away so I drilled them out. 3 drilled successfully, one did not. I am having a metal lid made for this. I will then use some pump housing RTV gasket and 3 bolts to hold the 3 sides of the hole in place. A hose clamp and c clamp to hold the 4th corner of the lid in place, it's a little ghetto but it saves me 2 estimates of 10k to dig up the concrete and 3.5' down to the current valve.