At my work there is a proposed storm sewer system on hold because of an unidentified 3" black pipe running right smack dab down the middle of where the concrete pipe will go. The drawings were done in 2019 and show a dashed line with unkown between dashes. The engineer told me nobody would ever claim it back then.
Our best guess is old telephone system main trunk line or a really really high voltage electric line from long ago. So it's never a good idea to just chomp through it with the digging bucket of a giant Tonka toy. A phone company guru came out today to "sound" it. We have used a water powered knife to safely expose the cable. And he was going back to cave man mode where you whack it with a shovel and listen for the sound it makes. Thud equals a big group of copper cables wrapped in a rubber sleeve. Ring means it's plastic.
First thing is to wash off the pipe and look for details like texture or stripes. Wash off pipe but being 4 feet in the ground means it's in a shadow. Not when you have an 850 lumen Maglite dialed to spotlight aimed at it. It was fun watching people when I pulled out a 2C sized Maglite and they assume it's an old light bulb model. "Pffft, what's that guy doing with that old flashlight"… Then hit the on switch of the ML150 shorty and "tadah" suddenly "is that a Maglite?" lol.
Unfortuneately the light did not help. No stripes, no texture were seen. Time to sound it. Bump, bump. No thud, no ring. More of a "thwap" like clapping a pair of 2x4's together. Perhaps being 21 degrees outside may have been a factor? All I know is the guru is returning Monday with what he calls a monkey clamp to wrap around it and send sonar in both directions to see if he can find where that sound stops. That may determine if it's disconnected or still live. But he's also bringing with him THE GURU. He says "Tom will know, because if it belongs to us he probably installed it". We're talking like 1965 to 1970 or so.
But I did get a kick out of watching peoples eyes light up when that Maglite lit up that hole like sunshine on a cloudy day.