Possible Foundation Watering System?

First post here, my apologies if it’s in the wrong category.

My wife and I recently moved into a new house in Lewisville, TX. I had a Rachio Gen 2 at our old house, so naturally getting a Rachio was one of the first things we did to keep up with our new lawn.

I removed a Hunter controller that had 6 zones hooked up to it. The previous owners only had 5 zones labeled on that controller.

I have a mystery zone 6 that I am trying to figure out what it is for. When I activate it and go to the water meter, I do see it moving, however I cannot locate where it is watering. My Dad told me that one of his properties in the area had a dedicated zone to water the foundation. I searched all of the valves, and did locate this one that appears abnormally deep (1.5-2’ deep if I had to guess).

Does this seem likely to be for foundation watering? If so, any other North Texans have suggestions as to how frequently and how long to use this type of system? I would assume it would be best to be on its own separate fixed schedule…

Thanks in advance for any help or input!