Sewer-Pipe Primer: Two Engineers Explain When to Repair or to Replace

In New York City, buildings are required to have separate sewer and storm-water lines. In many properties, the two pipes merge right before leaving the building and combine to form one line, which connects to the city's main below the street. If the city has separate sewer and storm water mains in front of the property, then the building's lines must connect to each main separately.

Sewer and storm lines are typically made of concrete, cast iron, clay (terracotta), brick or PVC and measure from four inches in diameter to thirty inches or more, with eight- to twelve-inch diameter pipes the most common. City mains are usually much larger. A building's sewer or storm line runs roughly 10 feet below ground.

Roots of the Problem

Underground pipes, especially concrete, brick, and clay, are subject to decay from groundwater and shifts in the surrounding soil. Once a pipe breaks, soil, tree roots (and occasionally small animals) can enter, blocking the flow of waste water. If the break is large enough, the pipe will act as a conduit for large amounts of soil and groundwater, which can create a depression, or sinkhole, in the ground above.

The most effective way to check the condition of your sewer line is with a video probe, which avoids the expensive and time-consuming method of digging up the ground to check the condition of the pipe. A specially fitted camera on the end of a cable is inserted through the pipe's trap (the "U"-shaped bend), located just inside the building. A video monitor displays cracks, loose joints, intruding roots and other defects in the pipe and their locations, as well as clogs and built-up residue.

If the video probes show the sewer pipe to be in good overall condition, and the backups are attributable to minor clogs and build-up, then a thorough cleaning using high-powered jets with multiple heads should do the trick of removing the muck and blockage. As a general maintenance item, an annual jet cleaning is a good idea.

Something Old, Something Pneumatic

If the scale and corrosion is very thick, or tree roots have infiltrated the pipe, a pneumatic-powered rotating cutter inserted into the pipe may be required to clear the line.

If the video probe shows that the pipe has minor cracks, or the interior surface of a concrete pipe is worn or pitted, then a method of repair called cured-in-place pipe (CIPP) may be used. Here, the pipe is first jet-cleaned, then an inflatable felt liner is cut to the length of pipe, saturated with an epoxy resin on the outside and installed so that it presses against the pipe's inner wall, filling cracks, minor holes and worn surfaces. After the resin cures, the liner is deflated and extracted, leaving behind the hardened resin, which now forms a seamless, structurally sound pipe within a pipe. A robotic cutting tool restores the holes where other pipes connect to the line.

If the pipe has collapsed or suffered large holes or other significant defects, then either the entire pipe or sections of it will need to be replaced, which entails digging up the ground. You'll need an engineering firm to specify the size and location of the replacement piping and areas of repair. Replacement piping should be the same kind as the existing piping, so concrete pipes would be replaced with concrete pipes, and so forth.

Where the Bodies Are Buried

Before excavating, you'll need to hire a testing company to perform a ground-penetrating radar survey to locate and mark other utility lines, such as gas, electric or phone that could be damaged during the digging. Once the damaged pipes are dug up and removed, the replacement pipes have to be set at the proper depth and slope so the unpressurized water can flow from the building to the city main.

Your condo or co-op is responsible for the entire length of the sewer line, from inside the building to where it connects to the city main, beyond the property line. A work permit from the New York City Department of Transportation will be required if you are replacing sections of piping that run on the city's property. Additionally, you'll need work permits from the New York City Department of Environmental Protection and the Department of Buildings.

You may need to shut off the water to the building for a brief period while the pipes are being repaired or replaced. If the work takes longer, a temporary bypass system can be set up for drainage until the new or repaired pipes are in place. Before the building's sewer line is connected to the city's main, it must be tested to make sure all the joints are tight.

Stephen Varone and Peter Varsalona are principals at Rand Engineering & Architecture.

For more, see our Site Map or join our Archive >>