The two small ones are two inch diameter, the big one is four inch; they're black PVC with hammered in caps (that I can easily pull out by hand). I dug down another foot or so and from what I could see they just continue straight down.
Pretty much all my utilities flow past that spot so they could be related to almost anything. In particular the sewer goes past there so I think they might be an outside sewer access. Kind of wierd that's there three of them though instead of just one.
I don't think that we have any kind of french drain system, though it would make sense to have a low point there with a french drain drawing the water off.
Anyhoo, kind of curious what they are before I cover up that spot with a bunch of rock and dirt to raise it up. Photos backing up :