Leaking Underground Plumbing

[Clarky]

I'm a new member to TFP and have been getting acquainted with the site and the methodology. Currently working through a variety of issues with pool chemistry but have discovered a non-chemistry issue which I need help with. The area I live in has water restrictions so I haven't water the lawn for some time. Noticed a "green oasis" of grass in my backyard and started to dig and found a leaking +/- 2" PVC pipe which appeared to be previously repaired. It's the pipe on the left in the below pic.



I believe its a secondary return to the spa which is active when the main pool water is being circulated. I want to repair it but have two questions: 1) How do I cut off supply so I don't have water gushing out and 2) Does my assumption that it's a return to the spa make sense.

Below is a picture of my system, I believe it is the L-shaped connection to the return on the left.



Thank you for any assistance or guidance you can provide.

 

[JVTrain]

If you close the 3 way valve above the small elbow, that will prevent water flow to the line from the return side. (Handle should be rotated to the right, opposite of where it is in the picture) Then you'll have to close it off at the spa somehow, and expandable plug or two that fits inside the spa return(s) should to the trick.

To me though, because it's a smaller diameter, it would be more likely that it goes to a waterfall, slide or pressure side cleaner port rather than the spa.

Ohh and welcome to TFP!

 

[Clarky]

Thank you, that is helpful and makes me question my initial assumption that it's a return to the spa. The pool has one main drain, one skimmer, three return jets and a connector on the pool wall which I believe was for a pool cleaner (it has water flowing out of it). No slide, but when the main pool is circulating, their is a return that is active in the spa that is designed to cause the spa to spill over into the pool. I'm now wondering if the leaking line goes to the pool cleaner port. Any thoughts on how to identify the culprit?

Additionally, there are 5 larger dimension lines in the hole, am I correct in assuming the following:
1 is supply side to main pool drain;
1 is supply side to main spa drain:
1 is return to spa;
1 is return to pool:
1 is to spa air blower;

Also, forgot to mention I lose approximately 8" of water overnight in the spa and seem to gain approximately 2" in the pool, could this be related or just another problem? Had the jandy valves rebuilt when I replaced the filter thinking that was the cause, but it didn't effect the flow from the spa to the pool.

Sorry for all the questions, really appreciate the help.