Need advice on a garden pond

edwardbarnett

We have a large sitting area in our front yard full of gardenias. In the middle, there is an open area measuring approximately 10 x 12 feet. My wife and I would like to build a small pond there with a waterfall and a bench next to it. I believe the pond itself will be about 8 feet x 6 feet in size. My wife and 10-year-old child would like to keep some small fish there, which could also fight mosquitoes and algae.
That's my problem. An irrigation system with 7 coverage zones is installed on the lawn in front of the house. None of the sprinkler heads are in the garden, but I have no idea where the pipes for the system go. The previous owner died and took his knowledge of the system with him. I don't want to risk breaking the PCV pipe if it ends up right under this area, so what would be the best way to figure out where these pipes go? I assume that the pipes will be no more than 6-8 inches below the surface, right? If this is the case, can I just gradually scrape the surface to a depth of about 8 inches, and if I don't hit anything, it's probably safe to continue to 2 feet?
Thank you in advance for any advice on this.