City of San Carlos - Frequently Asked Questions (FAQs)


PG&E Gas Line 147

Home > ... > PG&E Pipeline 147 > Frequently Asked Questions (FAQs)

What action did the City take regarding its safety concerns about Line 147?

Once the City learned about the content of the PG&E engineer's emails questioning the line's safety written in 2012, City staff asked PG&E to shut down the pipeline as a safety precaution, but were refused. The City went to San Mateo County Superior Court and obtained a temporary injunction against PG&E, requiring that Line 147 be shut off. The City Council immediately met and declared a State of Emergency. The City requested that the California Public Utilities Commission (CPUC) review the safety of Line 147, and hired its own expert to help evaluate PG&E claims that the line was safe to operate. In response, the CPUC ordered PG&E to lower the operating pressure of Line 147 to 125 psig (per square inch gauge) and close the line at both ends.  The City subsequently hired Dr. Glen Stevick of Berkeley Engineering and Research to conduct a technical evaluation of Line 147.  Dr. Stevick was selected because he specializes in Failure Analysis and Design of Structures, Consumer Products, Industrial and Medical Equipment. However, during the hearing to consider repressurizing Line 147, the CPUC did not allow the City to present its case to keep the pressure down to no more than 240 psig until further investigation of the line and allowed PG&E to fully pressurize the line to 330 psig.  Upon release of PG&E emails concerning pre-hearing communications between PG&E and CPUC Commissioners and staff, the City called the Governor to investigate the CPUC.  Emails are available for viewing here.

The City has been working closely with PG&E on the safe operation of Line 147 by keeping residents informed of the development of Line 147 through community letters, news releases and meetings.  Furthermore, at the urging of the City, PG&E conducted an inline inspection of the entire length of Line 147. The inline inspection revealed some areas of concern, which PG&E is excavating and repairing as needed.

What is PG&E Natural Gas Transmission Line 147 and where is it located?
Line 147 is a 20-inch high pressure natural gas transmission pipeline that is 3.8 miles long and runs from the Interstate 280 corridor, through San Carlos (roughly along Brittan Avenue), to the intersection of Old County Road and Commercial Avenue, where it connects with PG&E high pressure natural gas Line 101, that runs north and south along the Peninsula. 

See the map.

Aside from Line 147, are there any other high pressure natural gas transmission lines that run through San Carlos?
Yes. Line 101, another high pressure natural gas transmission pipeline, runs north and south along the Peninsula, and in San Carlos, underneath Old County Road.  The City does not have any data on the condition of this gas line.  To understand the current condition of Line 101, please contact PG&E directly at 1-800-743-5000 or visit

The California Public Utilities Commission (CPUC) gave PG&E permission to operate Line 147 at a maximum operating pressure of 330 psig. Why does the City believe that the pressure should be lower?
The City hired an engineering expert, Dr. Glen Stevick, to evaluate the same data PG&E and the CPUC used to determine the maximum allowable operating pressure of 330 psig (per square inch gauge) on Line 147.  Dr. Stevick's evaluation concluded that Line 147 is safe to operate only up to 240 psig due to the unknown features of Line 147 (which PG&E has admitted to) and the requirements of the Code of Federal Regulations governing steel pipelines used for high pressure gas transmission. Line 147 has been operating at approximately 125 psig and will remain at this lower pressure until all inspection and repair work is complete and the CPUC approves raising the pressure.

Click here for the City of San Carlos' conclusion based on Dr. Stevick's findings.

What agency regulates PG&E's natural gas pipeline operations?
The California Public Utilities Commission (CPUC).  The CPUC regulates privately-owned electric, natural gas, telecommunications, water, railroad, rail transit and passenger transportation companies, in addition to authorizing video franchises.  The CPUC has five Governor-appointed Commissioners whose role is to: ensure that consumers have safe, reliable utility service at reasonable rates; protect against fraud; and promote the health of California's economy.  For more information about the CPUC, please visit

What can residents do to help ensure that the high pressure gas lines that run through San Carlos are safe?
It is important that residents stay informed of the issues involving gas lines and other regulated utilities in the community.  The California Public Utilities Commission (CPUC) holds public meetings regularly to discuss various issues related to regulating utilities.  For the CPUC's public meeting schedule and topics, please click here. The public is also encouraged to share feedback, comments and concerns with our state and federal representatives.  The City of San Carlos is currently represented by State Senator Jerry Hill, Assembly Member Kevin Mullin, Congresswoman Jackie Speier, Senator Dianne Feinstein and Senator Barbara Boxer.  

Of course, if a natural gas smell is ever detected, call PG&E's emergency service center at 1-800-743-5000 to report it.  In the event of an emergency, call 911 immediately.

What is a hydrostatic pressure test and how did the test affect the conditions of Line 147?
A hydrostatic pressure test involves pressurizing a section of pipe with water to a much higher level than the pipe will ever operate with natural gas.  The test is performed to validate the safe operating pressure of the pipeline.  This method was approved by the California Public Utilities Commission (CPUC) as a means of ensuring pipeline safety for all regulated natural gas providers in California.  PG&E performed a hydrostatic pressure test on Line 147 in 2011.  Because hydrostatic pressure tests put the pipe in a much greater pressure than it normally operates, there is a possibility that the test itself could damage the pipe.  In the November 2012 email from a PG&E engineer, he expressed concern that because older pipe was found in Line 147, it could have been cracked as a result of the hydrostatic test conducted on the line in 2011.  For more information about hydrostatic testing, please click here.

What is psi and psig?
The pressure of the line is measured in pounds per square inch and/or pounds per square inch gauge. There are units of measuring gas pressure in a pipeline of confined space.  A high pressure natural gas transmission line such as Line 147 operates at a typical pressure of 330 pounds per square inch gauge through the pipeline.

What is the current status of PG&E's Line 147?
At the urging of the City, PG&E conducted an inline inspection of the entire length of natural gas pipeline to verify the integrity of Line 147.  The inline inspection started in January 2015 and after several delays, was completed in early 2016. Since that time, PG&E has excavated several sections of the pipe to confirm results of the inline inspection and conduct needed repairs. This work continues.

Once all of the repair work is complete, PG&E will have a better understanding of what is under the ground, as will the City. PG&E will then ask the CPUC to increase the pressure of the line back to 330 psig.

What is the safety concern related to the PG&E Line 147?
The City of San Carlos became aware of a series of internal PG&E e-mails that disclosed alarming information about the condition of Line 147.  The PG&E engineer who wrote the emails disclosed that the pipeline contains certain sections made up of a "thin wall" pipe made of materials manufactured in 1929, rather than the late 1950's as PG&E's records indicated.  He was concerned that the hydrostatic pressure test that was performed in 2011 may have caused additional cracking in the pipe, and that the surface of the pipe had external corrosion with fatigue cracks, and questioned, "Are we sitting on a San Bruno situation?" This revelation was particularly alarming to the City for obvious reasons.  Line 147 runs through a densely populated area near many homes in San Carlos.

Whom should I contact for more information about the pipeline?
Please contact California Public Utilities Commission (CPUC) staff at 415-703-2782.

Why does the City disagree with PG&E's assertion that Line 147 is safe?
PG&E has admitted that the records for Line 147 are not complete, traceable and verifiable for about 25% of the length of the line, meaning that PG&E is not sure what type of pipe is under the ground for about one mile of Line 147.  This uncertainty leads the City to believe that PG&E should not be operating the line at 330 psig (the maximum allowable pressure approved by the CPUC), but maintain a lower the pressure to no more than what is allowed under the Code of Federal Regulations when the line contains unknown pipe materials.  Internal inspection of Line 147 is necessary to determine what damage may have been caused by past hydrostatic pressure testing. PG&E continues to inspect the line to gather information about the line and determine its safety. Until both the inspection and repair work are complete and the City has an opportunity to review the results, the City continues to be concerned.