Sempra Energy's two California utilities plan to file with California regulators by the end of this month to proceed with a new natural gas transmission pipeline link in the heart of San Diego County and the center of the population at the southern end of the state.

Dubbed the "Pipeline Safety & Reliability Project" (PS&RP), the $600 million plan calls for a new 47-mile 36-inch diameter pipeline from an existing transmission metering station in the north end of San Diego County, following roughly the route of an existing 16-inch diameter transmission pipeline into the Miramar area, which includes a major naval air facility northeast of downtown San Diego.

Sempra's San Diego Gas and Electric Co. (SDG&E) and Southern California Gas Co. (SoCalGas) utilities will jointly file for PS&RP by the end of September with the California Public Utilities Commission (CPUC). With the CPUC's go-ahead in 2017, the utilities hope to have the new gas transmission link in place by 2020, an SDG&E spokesperson told NGI on Friday. Following the new line's start, the existing 16-inch diameter transmission pipeline will be converted to a lower pressure distribution pipeline, she said.

California's extensive intrastate north-to-south pipeline system, operated by Pacific Gas and Electric Co. (PG&E) and the two Sempra utilities, has come under closer CPUC scrutiny in the past five years since the rupture of a PG&E high-pressure transmission pipeline in San Bruno that killed eight people and injured scores of others in 2010 (see Daily GPISept. 22, 2010). California's utilities have been scrambling to complete multi-year, multi-billion-dollar pipeline enhancement and safety programs.

This latest Sempra proposal is separate from a proposed north-south transmission pipeline addition already pending at the CPUC by SoCalGas to upgrade its extensive in-state system with a rebuilt compressor station and a new 65-mile, 36-inch diameter north-south pipeline link (see Daily GPIMay 7). This project carries a price tag of $855.5 million, meaning Sempra is proposing nearly $1.5 billion in gas transmission upgrades over the next five years.

The joint SDG&E-SoCalGas project would start at the existing Rainbow metering station that SDG&E maintains near the north San Diego County-Riverside County border, which is the starting point for an existing 30-inch diameter gas transmission pipeline that goes south into downtown San Diego via a mostly coastal route.

Under updated state/federal safety/maintenance requirements, the existing 16-inch diameter pipeline, built in 1949, must be pressure tested or replaced under the utility's ongoing pipeline safety and enhancement program, the SDG&E spokesperson said. "Rather than take it out of service for pressure testing, we believe the right decision is to replace the transmission component of the new line; we would lower that pressure and incorporate it into our distribution system," she said.

This pipeline, which is being tested internally in various segments, can continue to safely serve as a transmission pipeline for the interim period while the new line is being permitted and constructed, the spokesperson said.

Additional capacity from the new line would total about 200 MMcf/d and would help balance the load for the two transmission pipelines ultimately bringing gas into the San Diego load center. Currently, the 30-inch diameter line carries the bulk of the supplies (90%) with the 16-inch diameter line carrying the rest. SDG&E is shooting for closer to a 50-50 balance with the new pipeline.

"Now the whole system relies on essentially one pipeline, where with the new line there would be some redundancy to the system," said the spokesperson, adding that the vast majority of the new pipeline -- 97% -- will go under existing streets and roadways.