Cross Bore in a Sewer Line: What It Is and What to Do Now
A cross bore is a utility line that was bored straight through a sewer pipe. The one that matters most is a natural gas line pushed through a sewer lateral during trenchless installation. It can sit there for years without anyone noticing, until a stoppage builds up on it and someone sends a cutting head down the line.
If you see one on your monitor: stop. Do not cut, pull, or jet at it. Call the gas utility, and if there is any sign of a leak, get everyone clear and call 911 from a safe distance.
How cross bores happen
Gas services and other utilities are often installed by horizontal directional drilling (HDD) or other trenchless methods. The bore head can’t see what it’s going through. If a sewer lateral wasn’t located first, the drill can pass right through it and pull the new line in behind.
NASSCO’s cross bore specification guideline defines a cross bore as an intersection of an existing underground utility or structure by a second utility, with direct contact that compromises the integrity of either one. The same guideline notes that for most utilities, trenchless installation began in the mid-1970s while cross bore inspection did not gain prominence until the late 2000s. That gap is why older, undiscovered “legacy” cross bores are a known problem.
Why it’s dangerous
The gas line passes through the sewer. Debris builds up on it, the line slows or stops, and a plumber or drain cleaner is called. A mechanical cutter or root saw spinning in that pipe can slice the plastic gas line. Gas then enters the sewer and can travel back into the building through dry traps and floor drains. Utilities list fire and explosion as the risk.
That is why cross bore guidance to drain cleaners is consistent: assume an unexplained obstruction in a lateral could be a cross bore until you have seen it on camera.
What it looks like on camera
What you may see:
- A round pipe crossing the bore, usually side to side, sometimes at an angle. Plastic gas lines are commonly yellow; PG&E also mentions orange.
- A clean-edged hole in the sewer wall where the bore went through, sometimes with mud or soil around it.
- Debris hung up on the crossing: paper, wipes and grease wrapped around the line.
- A cable or conduit instead of a gas line. Electric, telecom and water lines can also be cross-bored. Treat any unexpected crossing pipe or cable as a utility until the owner confirms otherwise.
It can also be hidden. A cross bore that only clipped the pipe may show as a crack, fracture or new mud in the line. NASSCO’s guideline points out that cracks, fractures and broken pipe near a bore path can indicate a near miss. See cracked sewer pipe.
What to do the moment you see it
| Do | Don’t |
|---|---|
| Stop the machine and leave the line in place | Run a cutter, root saw or chain head into it |
| If you smell gas or hear hissing: evacuate, then call 911 and the gas utility from a safe distance | Try to shut off the gas or pull the line out |
| If there’s no sign of a leak: call the gas utility’s number and report a possible cross bore | Jet at the crossing to “clear it” |
| Save the recording with footage, clock position and a sonde locate on the surface | Keep working on the stoppage “just to get it flowing” |
| Tell the property owner not to use the drains until the utility clears it | Assume it’s a root or a broken pipe |
A camera with a transmitter in the head helps here. Locating and marking the crossing on the surface gives the utility an exact spot to dig. See sewer cameras with a locator.
Before you clear a line: prevention habits
Utilities and industry groups give drain cleaners the same checklist:
- Contact 811 (your state’s one-call system) before drain cleaning where a cross bore is possible, as the Cross Bore Safety Association recommends.
- Ask the owner about recent gas, fiber or electric work in the street or yard.
- Scope first when the stoppage is outside the building, especially if the line clears partway and then stops at the same footage.
- Start with non-cutting tools. PG&E tells sewer cleaners to use minimally invasive equipment such as a snake or water jet before any cutting tool.
- Check your blades after clearing for yellow or orange plastic, and watch for bubbling in standing water.
- Look for a sewer tag. Some utilities leave a tag at the cleanout or under the kitchen sink with a number to call before clearing a blocked line.
Cross bore programs
Many gas utilities run cross bore programs. Two types show up in their materials:
- Prevention programs scope sewers before and after new trenchless installs, so a strike is caught before anyone is at risk.
- Legacy programs go back through older areas that were bored before inspection was standard, often by scoping laterals and mains from the main or through cleanouts.
Some utilities state that they cover the cost of sewer repairs when one of their cross bores is found, and some hire outside contractors with push and lateral-launch cameras to do the inspections. Details vary by utility, so call and ask before any repair.
Put cross bore protocol in writing for every tech who runs a machine: scope before cutting on lateral stoppages, and one number to call if a pipe shows up where it shouldn't. It's also worth covering in your pricing; see how much to charge for a sewer camera inspection.
FAQ
What should I do if I find a gas line in a sewer lateral?
Stop work and do not cut, pull or jet at it. If you smell gas or hear a leak, get everyone out and call 911 and the gas utility from a safe distance. If there is no sign of a leak, leave the line alone and call the gas utility's number so they can confirm and repair it. Keep the video.
Who pays to fix a cross bore?
That depends on the utility and local rules. Some gas utilities run cross bore programs and state that they cover the sewer repair when one of their lines is found in a sewer. Call the utility and ask how their program works before any repair starts.
Do I need to call 811 before clearing a drain?
811 is the call-before-you-dig line, and the Cross Bore Safety Association recommends that plumbers contact the one-call system before drain cleaning work where a cross bore is possible. Check your state's one-call rules for what applies to drain cleaning versus excavation.
What color is a gas line on camera?
Plastic gas service lines are commonly yellow, and some utilities also mention orange. PG&E tells sewer cleaners to check their tool blades for yellow or orange plastic after clearing a line. Color is a clue, not proof, so treat any unexpected pipe crossing a sewer as a possible gas line.