Locating buried sewer manholes

So I have an unusual situation in my park where the previous owner hired a shoddy company to repave the roads last time, and some of the sewer covers that give access to the sewer main were paved over. I’ve walked the property several times, and cannot locate where they are. I have no good sewer schematics, and have contacted the city for the original building plans and they do not have anything helpful either.

I’m worried that if the park were to have a backup in the main sewer line it would be really bad right now. I’m guessing the plumbers would have to dig up the line just to snake it out.

Does anyone have any creative ideas on how I could locate those paved over sewer covers? I’ve tried looking up metal detector services in the city but the only outfit I could find said they probably couldn’t locate it with the equipment they have. (sewer covers are usually made of steel, and a standard metal detector isn’t designed to detect steel)

So here is what I would do. You can hire a drain cleaning company to video the sewer lines. The vid has direction and distance on the tape- so they can locate problems. With that info you should be able to pinpoint the risers to the drain cleanouts or manhole covers. We have used this type of service several times and the quality of vid is very good.

If… you were not looking in paved areas, you can also use a smoker. You use a special machine that fills the lines with smoke, and you look for the places it sneaks up through the dirt.

One last thing- you can use a sewer snake machine with a locate wire on it. Once the wire is in the sewer, you put a tone generator on it. Then you can use a utility locate wand on the surface to map the system.

good luck to you