Locating underground sewer pipes

Underground sewer pipes should be a minimum 300mm deep to the top of the pipe, unless under concrete, and can be buried many meters below the ground. If you have a broken sewer pipe or blocked sewer drain you may want to find it fast, as these can present health risks. If you want to undertake a renovation or excavations, you will need to know where the underground sewer pipes are buried so that you do not damage them.

Damaged sewer pipes are health risks and can cost thousands to repair. You may want to lay a new concrete driveway and you should know the state of your sewer drains before you lay fresh concrete over them.

Dial Before You Dig plans only show the utility’s sewer mains and branch lines up to the boundary of the property and in easements running through properties. They do not show the location of privately owned underground sewer pipes.

If you are undertaking mechanical or vigorous excavations in the vicinity of an underground sewer pipe, once you have settled on the location of the sewer pipe you must dig it up by hand or hydrovac to expose it and prove its actual location. Do not attempt to prove its location with mechanical excavators apart from Hydrovac excavations. If we plan to mechanically excavate within .75 meters of a sewer pipe, we will expose it by shovel or hydrovac first.

Some councils require work as executed drainage plans be submitted for approval and future records once a private sewer drain has been laid and tested. These plans can be very accurate and will provide a good indication of the location the sewer drains for domestic and commercial buildings. Contact your council or planning authority to see if they have a record of the sewer installation and plans.

I have never witnessed marker tape indicating that there is a sewer pipe below. I have been working as a plumber, drainer since 1985. If you come across marker tape while mechanically excavating anywhere, stop digging immediately. Marker tape is the best indication that you are directly above a vital underground service. You must either move your excavation or expose the underground service by shovel or hydrovac method.

Underground metal sewer pipes are rare, but they can be the easiest to find. They are generally large diameter utility mains. Metal pipes are conductive. Therefore, a metal detector in the hands of an experienced operator may be all that you need. We prefer to induce an electronic signal into the metal pipes and then use a locating device with an inbuilt receiver to find that signal. This method is very accurate and allows us to determine the depth of the underground sewer pipe. We may also use a CCTV drain camera with a locating sonde attached. We use a receiver to locate the signal transmitted from the sonde back to the ground. This method is extremely accurate and provides a lot of information about the internal condition of the drain.

Underground clay sewer pipes are usually used for sewer mains and private sewer systems. The diameter is 100mm and larger. This allows access for a CCTV drain camera with a locating sonde attached. We use a receiver to locate the signal transmitted from the sonde back to the ground. This method is extremely accurate and provides a lot of information about the internal condition of the drain. It is the best method for finding the exact location of blockages and breaks. Occasionally the clay sewer drain will be so badly blocked that the electric eel cable and cutter will not pass through the blockage. In these cases, we induce a signal into the metal eel cable.

We then use a locator with inbuild receiver to locate the eel cable inside the clay sewer pipe.

Underground plastic sewer pipes are usually used for sewer mains and private sewerage systems. The diameter is 65 mm and larger. This allows access for a CCTV drain camera with a locating sonde attached. We use a receiver to locate the signal transmitted from the sonde back to the ground. This method is extremely accurate and provides a lot of information about the internal condition of the drain. It is the best method for finding the exact location of blockages and breaks in plastic sewer drains.

Occasionally sewer drains will be so badly blocked that a CCTV drain camera cannot be inserted into them and the jetter or electric eel cable and cutter will not pass through the blockage. In these cases, if we can get the eel cable and cutter all of the way to the blockage, we will induce a signal into the metal eel cable. We then use a locator with inbuilt receiver to locate the signal emitted from the eel cable inside the sewer pipe.