Sprinkler Archaeology

Today I set to dig out one of the many Agapanthuses in my yard, and as I was digging ALL of the roots out, I hit PVC pipe.



Because we're not the first owners of this house, we don't know where everything in the yard is, so this was a pleasant (although not surprising) find.

1. I believe this to be the pipe in which the sprinkler timer wiring is, because it is not sealed.
2. I believe this to be one of the pipes installed under the walkway when the house was built. Doesn't go to anything, but I wonder if this is also for wires?
3. I believe this to be the sprinkler's water supply since the pipe is sealed.

I was going to plant something in place of the Agapanthus, but was wondering: (for now) should I simply leave this hole filled in, just in case we need to access it again during landscaping? Our sprinklers in their current state actually work well and are well-positioned for the landscape plan we have. (Although we will be adding one more station in the back, I hope it's already wired for it)...

Would love to hear your thoughts.