How is this sewer vent pipe meant to be capped?

Question

My house is connected to public sewer. There's a ~100ft setback between the house and the road, and in that area, there are two pipes I think are associated with the sewer. One is a white pipe coming out of the ground near the road that is well sealed, and the other is an open pipe that seems like it's meant to be allow airflow but keep rain out.

Here's that white pipe near the road:

Here's the other pipe, same diameter, with its lid on and off:

The issue, as shown in the last two images, is that the cap for the pipe near the house is not attached at all. The diameter of the cap is about the same as the diameter of the green fitting in the black pipe, so the cap's screws have no way to get into or under the green fitting. Also, the green fitting is snugly in the black pipe but it can easily be lifted up and out of the black pipe by hand. I'm unsure if that fitting is meant to be 'locked on' to the black pipe. We've had some very windy days and surprisingly, this went undisturbed and unnoticed.

How is this meant to be setup? What part do I need to swap out to remedy this? It seems like I just need a bigger cap so it can go over the green fitting and 'lock on' to it using the green screws. I'm assuming a 'snug' fit of the green fitting into the black pipe is sufficient.

Edit in Feb 6: I confirmed this is a sewer pipe - it goes fairly deep and I see water flow through it when the shower is on. I also saw we have a sewer vent up at the roof, so this is not the only vent and might just be for access.

Answer 1

Is it possible that you have a dry well? And that's an overflow?

The green fitting in the lawn looks like part of an overflow emitter - https://www.ndspro.com/products/drainage/pop-up-emitters.html

And the spherical cap looks like a mushroom vent cap. https://www.oatey.com/products/oatey-mushroom-vent-cap--1469620693

So I'd guess the center of the overflow got lost and someone dropped the vent cap on the hole to stop dirt/leaves washing down it.

Answer 2

The first one is a sewer cleanout. It's the last access point after your home plumbing but before the sewer drop dumps into the street line. The cap is so a plumber can access it with a snake or camera.

The second one looks to be an emitter connected to a stormwater drainage system. Generally your gutter downspouts are piped directly into PVC pipe and carried away from the foundation where the water can be discharged safely over the lawn. There is supposed to be another green plastic part on there that has broken off. The emitter caps are easy to find at hardware stores and usually just push into the pipe stub.