Trying to understand an access hole in my basement slab and capped pipes inside.

I have a square access hole in my basement slab. I removed the steel cover and found the ends of 3 plastic pipes, capped, at the bottom of the hole. 2 of the pipes are 4-inch black drain pipes that come up on a slant and appear to lead down and away from the house, towards the street. The other pipe is about 6-inch diameter, and appears to go downward. The access hole is full of water - lots of rain lately. Any idea whether these are drains or what their purpose may be? How should I investigate and confirm? Would it be a bad idea to undo any of the caps to see if they drain? The house was built in '87. Poured concrete foundation.

Any advice would be greatly appreciated.