Is it the end of the pipe, or a mid-pipe exposure? I would never leave a piece of exposed PVC in the middle of a completed job.
What are you calling risers? Is it a 1/2" or 3/4" nipple, a pop-up spray head, or a 1/4" micro-spray semi-hard line? Normally the risers should be close to plumb. PVC nipples can bend a little in the heat, but you should be able to get them pretty close if they were installed with a swing joint. 1/4" risers will never be plumb without a stake. Some installers will perferate the poly and plug the riser in. Sometimes it's plumb, most times not, because poly will move.
Mick
It's the end of the pipe protruding perpendicular to the ground, not exposed, buried pipe.
Maybe riser is incorrect. It's a tube in the flower beds upon which there is a spray head at the top.
Thank you for your reply.