The basement in our cooperative occasionally backs up with sewage, creating an obviously unpleasant situation. We've hired a plumbing service to look into the problem, and they recommended that we "jet" the sewage lines twice a year to clear clogs and keep the waste water flowing freely. Another plumber we've consulted suspects the problem is more than just a clogged line because a sinkhole has developed on the property, which he thinks is caused by a damaged pipe underneath. We don't want to pay a plumber to clean the sewer line if it needs to be repaired or replaced, but on the other hand, we don't want to dig up the ground to check the pipe's condition if it just needs cleaning. Is there a way to check the pipe without digging? And how do we know if we can get by with repairing the pipe instead of replacing it outright, which I assume is a lot more expensive?
Sewage backups pose health risks caused by contamination from harmful bacteria and mold, so your building's problem needs to be addressed as quickly as possible. A blocked or broken sewer line is the obvious culprit. Fortunately there is a noninvasive way of checking the condition of the pipe as well as a less intrusive and less expensive way to repair the pipe than digging up the ground. If the pipe is badly damaged or collapsed, however, there's no alternative other than excavating and replacing the section of pipe—and possibly the entire line.
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 (terra cotta), brick, or PVC and measure from four inches in diameter to 30 inches or more, with eight- to 12-inch diameter pipes the most common. City mains are usually much larger, many of them measuring 40 inches to 100 inches or more in diameter. A building's sewer or storm line runs approximately 10 feet below ground.
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.
Pipes can clog from years of accumulated muck that hasn't been cleaned, as well as from a build-up of calcium deposits that form a crusted coating, especially if the building's water is hard. Concrete, brick, and clay pipes can last 40 years or longer, while cast iron and PVC pipes have an average lifespan of approximately 60 years.
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. Additionally, excavating doesn't reveal what's going on inside the pipe. With a video probe, 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. The camera is directed inside the building's sewer line and then the other way toward the city's main. 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. If the scale and corrosion is very thick, or tree roots have infiltrated the pipe through cracks, a pneumatic-powered rotating cutter inserted into the pipe may be required to clear the line. As a general maintenance item, an annual jet cleaning is a good idea, though your plumber's suggested twice-per-year regimen is probably unnecessary.
The decision to repair or replace a pipe will largely be determined by the extent of damage. 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. In CIPP, the pipe is first jet cleaned from the inside to remove any corrosion, deposits, or debris. An inflatable felt liner is then cut to the length of pipe being repaired and saturated with an epoxy resin on the outside. The wet liner is inserted into the pipe, and hot water or steam is poured in, inflating the liner so it presses against the pipe's inner wall, filling cracks, minor holes, and worn surfaces with the epoxy resin. 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.
The main advantage of the CIPP method is that, as the name implies, the pipes are repaired in place, eliminating the need for excavation and pipe replacement (which is why it's also known as "trenchless technology"). In addition, the epoxy-lined walls of the cured-in-place pipe are smoother than concrete, cast iron, or clay pipes, so they are more resistant to corrosion and calcium build-up and allow a greater flow of water. Companies that manufacture and install CIPP claim the epoxy-cured pipes last 50 years or more.
If the sewer line damage is limited to small areas, then the pipe can be patched or repaired if it's made of concrete or brick. If, however, the pipe has collapsed or suffered large holes or other significant defects, then either the entire pipe or at least sections of it will need to be replaced, which entails digging up the ground. The video probe will determine which areas of the sewer line are most badly damaged or blocked. The sinkhole that has developed on your cooperative's property indicates that underneath the hole there may be a pipe with a sizeable break, and that it has likely filled with soil, pipe debris, surrounding groundwater, and possibly even tree roots, creating the blockage.
You'll need to hire an engineering firm to specify the size and location of the replacement piping and areas of repair, and the details of the piping connections. The replacement piping should be the same kind as the existing piping, so concrete pipes would be replaced with concrete pipes, and so forth. Sewer pipes sections are typically 5 to 10 feet long.
Before excavating, you'll need to hire a testing company to perform a ground-penetrating radar survey of the property to locate and mark other utility lines, such as gas, electric, domestic or fire water, phone, fiber, etc., 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.
Keep in mind that your cooperative is responsible for the entire length of the sewer line, from inside the building to where it connects to the city main underneath the street, beyond the cooperative's 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. Also, the excavated ground, sidewalks, driveways, landscaping, street furniture, signs, etc. must be restored to their previous condition. In addition to the DOT permit, you'll need work permits from the New York City Department of Environmental Protection and the Department of Buildings.
The cooperative may need to shut off the water to the building for a brief period (from mid-morning to afternoon, for example) while the pipes are being repaired or replaced. If the work takes longer, then 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.Replacing a sewer line is no doubt a major project, but once it's completed and assuming it's cleaned regularly, your cooperative should not have to worry about it again for a long time.
Stephen Varone, AIA is president and Peter Varsalona, PE is principal of RAND Engineering & Architecture, PC. This column was originally published in the June 2009 issue of Habitat Magazine.
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