What is this plumbing puzzle?

[desertOasis]

This pipe and weird end cap comes out of the ground behind the filter housing for our pond/waterfall. Note that one of the 6 caps on top is missing (?). I became aware of it when it started spraying a jet of water into the air. It is definitely part of the pond plumbing; when I turned off the pump it stopped spraying.

Is it some kind of relief valve system? I will open up the filter tomorrow to take a look, but it was completely cleaned out and new cartridges installed not long ago.

 

[alexmaras]

I've seen similar caps for splitting PVC pipe into multiple sprinkler lines before, it could be that? Would be good to get a photo with the cap in focus.

 

[YippeeSkippy]

It looks to me that its a part of a inground water circulation system that appears to have been taken off service?

 

[desertOasis]

Mystery solved by coincidence. I thought it was part of the pond pump plumbing. It's actually as YippeeSkippy guessed. It's on one of the irrigation lines for the plants around the house. I didn't know that because water has never come out of it before. I guess pressure finally blew out one of the caps. Maybe during some previous ownership it was used. I plan to just cap off the pipe.

Thanks for the suggestions!

Ron