Gas Pipeline Construction Relied Heavily On HDD To Minimize Environmental Impacts

The recently completed Line 108 Replacement Project, an 11 mile long natural gas pipeline for Pacific Gas & Electric (PG&E) in northern California, featured the use of horizontal directional drilling (HDD) for portions of the pipeline installation beneath two rivers and two extremely sensitive natural areas.

Without this innovative approach, as well as other measures designed to minimize environmental impacts, the project likely never would have come to fruition.

Extensive growth throughout the Sacramento area necessitated the replacement of an existing 16 inch diameter gas transmission line that dated to the 1930s. PG&E’s Sacramento Local Gas Transmission System serves about 600,000 customers in some of the fastest growing counties in the state, including Sacramento County. PG&E anticipates this transmission system will serve approximately 22,330 new customers annually during the next several years. Most of them will be served by Line 108.

To take advantage of PG&E’s existing land rights, the alignment of the 24 inch diameter replacement line generally follows the existing pipeline. The pipeline connects the Thornton Meter Station, located just south of the Mokelumne River in San Joaquin County, to the Elk Grove Station, located just south of Elk Grove Boulevard in Sacramento County.

Beginning at the Thornton Meter Station, the replacement pipeline crosses the Mokelumne and Cosumnes rivers and extends north for slightly more than three miles along the east side of the tracks of the Union Pacific Railroad (UPRR). The pipeline then crosses under the UPRR line and Franklin Boulevard, before continuing north for roughly another three miles. At this point, Franklin Boulevard veers west, and the pipeline passes beneath it and continues north for nearly three miles along the west side of the UPRR line.

At the community of Franklin, the pipeline turns west, passing under a short stretch of Bilby Road before turning north and continuing for roughly another mile under Franklin Boulevard. After the intersection of Franklin Boulevard and the UPRR line, the pipeline runs along the west side of the tracks for the final mile, where it ends at the Elk Grove Station.

In addition to the replacement of Line 108, PG&E installed a pressure limiting station at the Elk Grove Station. At press time, the utility was in the process of removing a bridge that once supported the pipeline where it crossed the Cosumnes River. Removal of the bridge is the final element of the overall project.

Evaluating The Impacts
Although most of the pipeline extends through agricultural areas, the alignment also crosses numerous environmentally sensitive areas, including the two rivers, two critical natural areas and a variety of other habitats. As a result, the Line 108 Replacement Project required extensive environmental analysis and careful planning to avoid or minimize environmental impacts.