What is a sewer line slab leak?
A sewer line slab leak is a crack, break or failed joint in a drain pipe under your concrete floor. Unlike water supply leaks, drain leaks aren't under pressure, so your water meter won't show them. Signs include sewer odors, slow or gurgling drains, damp spots on the floor, and pests such as drain flies.
In many older Woburn homes, the main drain runs under the basement floor slab before leaving the house. These lines are often cast iron, which can rust and crack after many decades. Some mid-century homes may also have clay or Orangeburg (tar paper) pipe in the sewer lateral outside.
Signs of a leaking drain under the slab
- Sewer smell in the basement or lower floor.
- Slow drains or gurgling toilets on the lowest level.
- Damp or stained spots on the basement floor.
- Backups in a floor drain.
- Drain flies or roaches coming from floor areas.
- New cracks in the floor near drains.
Think you have a slab leak?Call now to talk it through and get connected with a local Woburn plumber.
Call (781) 483-8802How is a drain leak under the slab found?
Drain leaks under the slab are found with a video camera inspection and a hydrostatic test. The camera travels through the pipe to show cracks, breaks, roots or separated joints. The hydrostatic test plugs the drain and fills the line with water. If the water level drops, the line is leaking.
- Camera inspection through a cleanout or fixture opening.
- Locate the problem with a sonde (transmitter) on the camera head, so the spot is marked from above.
- Hydrostatic test to confirm the line holds water.
- Review footage with you and explain the repair options.
Drain line repair options
| Option | How it works | Best for |
|---|---|---|
| Spot repair | Open the floor, replace the broken section | One break in an otherwise sound line |
| Cured-in-place lining | Resin liner forms a new pipe inside the old one | Cracks and minor corrosion, no collapse |
| Section replacement | Replace a longer run of pipe under the floor | Badly rusted cast iron, several breaks |
| Pipe bursting (outside) | Pulls new pipe through the old one underground | Sewer lateral from house to street |
Learn more about trenchless options on our epoxy pipe lining page.
How much does sewer line slab leak repair cost?
Repairing a drain line averages about $800 to $5,000 in 2026 national cost guides, depending on the damage, where the break is, and how hard it is to reach. Camera inspection is often a separate charge. Longer runs of failed cast iron or trenchless lining can cost more.
- Camera inspection and locating
- Pipe material (cast iron, PVC, clay)
- Depth and length of the damaged run
- Concrete and flooring restoration
- Cleanup if sewage has soaked flooring
Water running where it shouldn't?Call any time, day or night. Every hour of leaking adds to the damage.
Call (781) 483-8802When is a drain leak an emergency?
Sewage backing up into your home is a health risk. Stop using water, keep people and pets away from the area, and call for emergency service. Soaked flooring and drywall exposed to sewage usually need removal and professional water damage restoration.
Preventing drain line problems
- Don't pour grease or fats down drains.
- Flush only toilet paper, not wipes, even "flushable" ones.
- Get a camera inspection if you buy an older home.
- Deal with slow drains early, before they signal a bigger problem.
Who is responsible for the sewer line?
In most cities, the homeowner is responsible for the drain pipes inside the house and the sewer lateral that runs to the public sewer main. The city usually maintains the main line in the street. Rules can differ, so if the problem is near the street, call Woburn's public works department to ask where your responsibility ends.
Leaks inside the house or under your basement floor are almost always the owner's to repair. Getting a camera inspection first shows exactly where the break is before any work is planned.
Related slab leak services
Most requestedSlab Leak Detection
Pinpoint hidden leaks under concrete with pressure, acoustic and thermal testing.
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TrenchlessEpoxy Pipe Lining
Seal pinholes and cracks from inside the pipe with little digging.
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CleanupWater Damage Restoration
Dry out floors and walls and lower the risk of mold.
Explore →Sewer Line Slab Leak Repair across Woburn, MA
We connect homeowners and property owners across Woburn, MA 01801 with local pros for sewer line slab leak repair, including Downtown Woburn, North Woburn, East Woburn, Walnut Hill and Cummingsville. See all Woburn service areas.
Sewer Line Slab Leak Repair FAQs
Will my water meter show a sewer line leak?
No. Drain lines only carry water when fixtures drain, so the meter won't move. Camera inspection and hydrostatic testing are used instead.
Is a sewer smell in the basement always a slab leak?
Not always. A dry floor drain trap or a loose toilet seal can also cause odors. If the smell stays after you pour water into floor drains, have the lines inspected.
How long do cast iron drain pipes last?
Cast iron drain pipe often lasts many decades, but it rusts from the inside over time. Pipes from the mid-1900s or earlier are worth inspecting.
Can a drain line under the slab be lined instead of dug up?
Often, yes, if the pipe isn't collapsed. A camera inspection shows whether cured-in-place lining is an option.
Get a free estimate from a local proOne call connects you with a slab leak specialist near you.
Call (781) 483-8802