Serving Our Hometowns: PG&E Teams Reroute Gas Lines as Integrity of Novato Landslide Looms Large

By Melissa Subbotin

Northern California has been saturated by three months of storms that have brought down thousands of trees, electric poles and triggered flooding and landslides. Through it all, PG&E was prepared and in position to battle the inclement conditions to restore customers.

This was the case last week when a waterlogged hillside in the North Coast Region gave way, triggering a landslide where two natural gas transmission lines were buried. These gas lines serve a population of more than 250,000 in Marin County. Both lines were impacted by the initial slide but remained intact.

Teams of PG&E engineers, geoscience experts, safety specialists and gas construction crews among others quickly assembled to assess the integrity of the failing slope and the pipelines within. They determined that an emergency plan would be necessary to avert further impact to the pipelines. If the landslide remained stable, there would be no interruption to gas service. But with another storm looming on the horizon, there was concern that the landslide would continue to grow. It was water rather than hope that was most likely to spring eternal at this incident location.

[Watch a video about the project]

'High propensity for slope failure'

PG&E's Geoscience team saw there was "high propensity for further slope failure especially given the incoming inclement weather," and noted that the slide was continuing to move. Given the assessments of the hillside's integrity, they concluded that we should be prepared for further impact to the pipelines.

The pipelines, one buried in the debris and another exposed along the hillside were threatened if another, perhaps larger, slide initiated. The line buried in the slide appeared to have moved several feet. Since the condition could not be assessed, operating pressure was essentially reduced to zero. This left only one feed to Marin County that was exposed and at the head of the landslide.

It was determined that a new and rerouted pipeline would be necessary to ensure there would be no gas disruption to customers in Marin County who rely on this vital source of energy.

So began the race against the clock. Typically, the work to reroute a pipeline can take weeks to complete, and often months of planning and preparations before a shovel enters the ground.

"We safely and swiftly executed a truly impressive feat. The different teams that came together were safety focused, mission driven and creative from design to implementation. Other agencies' support and cooperation were integral to our ability to complete this before Tuesday's storms. I haven't seen a project of this scale executed in this short of a window. From GeoSciences' hourly monitoring of the slide movement to GTGC and GPOM's efforts to construct and tie-in the bypass, I'm very proud of PG&E and our response," said PG&E's Chris Warner, senior director, Gas Transmission Engineering.

Fast and safe construction and testing

By Sunday morning, most of the new line was welded and in place. On Monday afternoon, it was being prepared to be tied in, including a hydrostatic pressure test where the water-filled pipeline is pressurized to several times normal operating pressure. This test is an industry standard PG&E applies to all new transmission lines before they are entered into service.

On Tuesday, (March 28), ahead of the incoming storm, PG&E brought the line into service. The two pipelines located within the slide zone were taken out of service. And while nobody can predict what will come of the hill following more rainy weather, the one thing we know for sure is that customers in Marin County are able to rely upon the natural gas service that PG&E is proud to have the opportunity to deliver for them.