Southern California Gas Co. (SoCalGas) plans to ramp up major transmission pipelines that have been idled as state regulators pressure the utility over its lack of natural gas in storage.

The California Public Utilities Commission (CPUC) called out SoCalGas for lagging behind its projected storage volumes this summer and fall. CPUC in a letter to the company said further outages on the  pipelines are problematic as the winter heating season nears. The situation adds to the uncertainty over whether or not extreme peak-day loads can be satisfied this winter in Southern California.

Three major transmission pipelines for feeding out-of-state gas supplies into the greater Los Angeles metropolitan area have been up and down ever since an explosion and fire disrupted operation in October 2017. The incident ripped apart a portion of SoCalGas' Line 235 in the middle of a sparsely populated part of the high desert, 150 miles northeast of Los Angeles. The line is set to return to service at reduced operating pressure in mid-October.

The 125-mile, 140 MMcf/d Line 3000 from the California-Arizona border to the Newberry Springs compressor station was returned to service late last year after a long outage, but it also is operating at reduced pressure. The third pipeline -- the 270 MMcf/d Line 4000 -- from the border to the Los Angeles metro area was taken out of service again last month and is scheduled to come back in November.

SoCalGas Senior Vice President Rodger Schwecke attributes most of the delays to changes in technology applied to pipeline integrity through inline inspections, difficult terrain in the high desert, which switches from 1,000 to 3,000-foot elevations, and multiple pipe segments being repaired or replaced.

"The process of evaluating the integrity of pipelines and the tools to perform the evaluations have improved greatly over the years," said Schwecke, who heads gas transmission, storage and engineering. "As a result, pipeline operators have access to greater and greater volumes of data on pipe conditions that require further analysis." The "validation" step is what takes all the time, he said.

In its latest order related to SoCalGas winter reliability, the CPUC noted that the continued below-pressure operations and out-of-service status means "SoCalGas is unlikely to be able to close its [current] storage inventory gap and it may fall further behind," before the start of the winter heating season on Nov. 1.

The three pipelines, when running at normal pressure and loads, carry nearly 1 Bcf/d of supplies. SoCalGas officials declined to say at what pressures the lines are operating at and what their collective throughput would be when they are all back online later this year.

Pipeline jurisdiction can also complicate the process of running lines at full capacity. A variety of regulatory agencies oversee portions of the gas pipelines, including the Pipeline and Hazardous Materials Safety Administration, the CPUC and the state Department of Conservation's Division of Oil, Gas and Geothermal Resources. Furthermore, the California Air Resources Board or regional air quality management boards have jurisdiction over pipeline emissions.