Crossbore Inspection Program

Clogged sewer line? ALWAYS call us first at (650) 329-2579 to have the line cleared of a potential crossbore.

The City of Palo Alto started its proactive safety program to investigate unintended crossings between natural gas service pipelines and sanitary sewer laterals, known as crossbores. 

In July 2011, the City began the first phase of the program and contracted with a sanitary sewer inspection company to assess the sanitary sewer collection system for crossbores. Over 18,000 sanitary sewer laterals were identified as potential cross bores. Churches and schools were inspected first, followed by various downtown neighborhoods, and completed with other remaining locations throughout the City. This project was completed in 2013. The contractor attempted to investigate  approximately 13,000 of the 18,0000 sanitary sewer laterals. Of the 13,000 sanitary sewer lateral anticipated to be inspected, around 7,000 sanitary sewer laterals were completed successfully.   During the 2011- 2013 crossbore investigation period, 26 natural gas pipeline crossbores were located and repaired. 

The City of Palo Alto leads the utility industry with its proactive natural gas safety programs.
Starting in 2011, we added a new component to our program---checking privately-owned sewer lines 
to ensure that there are no natural gas lines accidentally crossbored through them.

 Crossbore Situation
 Correct Alignment
Correct alignment


Check out this short video recently created by the Mayor's Youth Video Corp to get some background on the crossbore issue and an update on how the City's inspection program is addressing it.

The City of Palo Alto will begin the second phase of the natural gas safety program in August 2019 to investigate unintended crossings between natural gas service pipelines and sanitary sewer laterals. The City is contracting with AIMS Companies to perform the second phase of the natural gas safety crossbore inspection program. Critical facilities or high occupancy buildings will be inspected first then residential areas will be assessed. 

Initial coordination with the City to schedule the sanitary sewer lateral inspection is not required.  AIMS Companies trucks will inspect all identified sanitary sewer laterals in the second phase of the safety program. If contract workers have issues accessing the properties sanitary sewer lateral, notification will be provided by a letter or door hanger requesting the property occupant call and schedule an appointment for inspection.


  •  Call 811 if you are planning on digging in your yard to check where your utility lines are. 
  •  Do not use a sanitary sewer clearing machine to clear the sanitary sewer lateral until the obstruction has been assessed.
  •  If you smell a strong odor of natural gas or notice bubbles rising in the toilet bowl, immediately leave the premises while leaving exits open. From a safe distance, call 911 and City of Palo Alto Utilities at (650) 329 – 2579.
  •  Additional cross bore information is available in our brochure – click here.

Frequently Asked Questions

  1. What is a cross bore? Cross bore is the unintended conflict between one utility line through a portion of another utility line. This situation typically happens during construction using “horizontal directional drilling” or underground pneumatic boring. Our current safety program is focused on identifying natural gas cross bores where natural gas service pipelines pass through sanitary sewer pipelines.
  2. How can a natural gas pipeline run through a sanitary sewer lateral without the utility’s knowledge? Since the tunnel drilling equipment is designed to cut right through rock and other hard surfaces without stopping, it can easily pass through a sewer pipe without giving the operator any indication that this has happened.
  3. What is Horizontal Directional Drilling (HDD)?  HDD is a method of trenchless construction where pipelines are installed underground. In the 1970s, the City began installing natural gas pipelines on customers’ private property through horizontal directional drilling. This eliminated the need to excavate across properties for the connection between the gas meter at the house and the gas distribution main in the street.

What to expect when we're inspecting: 

What is the City’s current inspection program? Since 2001, all Capital Improvement Gas Main Replacement Projects have included the requirement to video inspect sanitary sewer laterals and assess them for cross bore. In 2011, City started the cross bore safety program. There are over 18,000 sanitary sewer laterals identified for inspection. By end of 2013, approximately 72% of 18,000 were inspected and 26 gas cross bore were found. From 2014 to present, City is has its contractors perform video inspection after the installation of a new gas service pipeline on private property.

What is the City’s schedule of cross bore inspections?  Cross Bore Verification Program Phase 2 will begin in August 2019. The City will inspect the remaining 8,549 sanitary sewer laterals from the 1st phase of the Cross Bore Verification Program. The 2nd phase of the program will inspect 2,500 sanitary sewer laterals for cross bore to be completed by the end of June 2021. The remaining 6,049 sanitary sewer laterals will be prioritized in the next phases of the  Cross Bore Verification Program.  

Will I be notified when my property is inspected? The City contractor, AIMS Companies, will distribute notification to each property owner at least seven (7) days prior to the commencement of inspection activity. If re-inspection is required or if private property access is necessary to complete the inspection, the City contractor will notify the property owner 24 hours prior to the inspection. If the inspection does not occur after 20 days from the original notification, the City contractor will send another set of notification to the property owner.

Do the City contractors carry ID? The City contractor will wear an identification card at all times during the inspection activity. Residents or property owners can verify the Contract workers by calling the City of Palo Alto Utilities Engineering at (650) 329 – 2168.

What happens if my sewer line can't be easily inspected? The City’s contractor will place door hangers at each residence that require further investigation. These door hangers request that the affected property owner schedule an appointment for an on-site inspection. 

Will the City pay for a private sewer inspection before the City inspects my private sewer line? The City will not cover the inspection done by your own sewer cleaning professional. Property owners are responsible for all expenses incurred by sanitary sewer lateral inspection performed your own plumber (i.e., Non-City hired contractor).

Will the City inspect for cross bores other than sanitary sewer lines and natural gas service pipelines? The 2nd phase of Cross Bore safety program will only focus on identifying crossbores resulting from the intersection between natural gas service pipelines and sanitary sewer laterals.

More crossbore background:

  • How many crossbores are in Palo Alto?  During the 1st phase of Cross Bore Verification Program from 2011 to 2013,  56 crossbores were identified. Of the 56 cross bores identified, 26 were natural gas.
  • Are there cross bores involving other utilities? (electric, cable and water)? There are 30 cross bores identified that are not natural gas cross bore in the 1st phase of the program.
  • How many crossbores have resulted in fires or explosion in Palo Alto? None. 
  • Is the City now inspecting every sewer line in Palo Alto? In 2014, the city started conducting post video inspection after new installation of natural gas service pipelines.
  • How will the City be changing installation and inspection practices in the future so that cross bores are eliminated? The City will have multiple phases to complete and to clear from cross bore the remaining 8,549 sanitary sewer laterals from 1st phase of the Cross Bore Safety program. The 2nd phase of the project will inspect 2,500 sanitary sewer laterals. The remaining 6,049 sanitary sewer laterals will be prioritized in future phases of the program. From 2014 to present, the newly installed natural gas service pipelines require post-construction video inspection of sanitary sewer laterals.
  • Doesn’t the building inspection department have to approve the installation or replacement of natural gas lines to ensure that they are safe? No. Utility owned infrastructure is regulated by the U.S. Department of Transportation and natural gas infrastructure matters are not subject to local building codes. 
  • Does the City have records of the private sewer line? No. The City does not have records of  the private sewer line because local building codes do not require the submission of record drawings which would reflect what was installed by the plumber. Also, the property owner may make additional repairs or changes to the sewer line at a later time after a permit has been issued. For these reasons, the exact location of a private  sanitary sewer lateral is still not known. 
  • Will I see higher gas or wastewater rates as a result of this program? No, this program is funded through the Utilities Department's existing preventative maintenance program. 
  • What will it cost to fix this problem? Council approved $1,905,475 for the 2nd Phase of Cross Bore Safety Program over a two-year period.
  • How do I make sure to get the latest information? Sign up on our email list to get updates on programs, rebates and workshops, or go to our Twitter Feed or Facebook page to get the latest.