Bonneville County engineers recommend relocating gas line under Sand Creek Bridge; commissioners take matter under advisement

Bonneville County officials on Jan. 27 reviewed engineering options for the 49th North (Sand Creek) bridge and heard a recommendation to relocate an Intermountain Gas pipeline that runs through the proposed abutment area.

Drew Mappen of Horox Engineers said the project team compared a soil-reinforced GRS-IBS abutment (which the engineers estimate would cost roughly $300,000 for the abutment) to higher-cost alternatives and concluded the existing pipeline sits in direct conflict with the proposed abutment. “We recommend … to have the gas line relocated and avoid any risk there,” Mappen said, citing both short-term construction hazards and long-term liability concerns.

Why it matters: the county’s preferred abutment type minimizes construction complexity and cost but, according to Horox, would place heavy construction equipment and settlement stresses near the buried pipeline. Horox said pile-driven abutments that would bridge the pipeline would raise construction costs to roughly $800,000, while drilled-shaft solutions could increase costs to about $1,000,000.

Intermountain Gas personnel described what moving the line would entail. Renny Sorensen, Intermountain Gas manager of engineering services, said the company would need to trench a new alignment along the canal banks and get the replacement pipeline across the canal before water is in place. “When we actually do do the tie over, … we would need to run a 12-inch bypass line … and be able to maintain flow through that bypass while we were to tie over the main line,” Sorensen said, and he noted that some tieovers would likely have to wait until late spring or summer when flows are low enough.

Jake Robinson, Intermountain Gas field operations supervisor, cautioned that operating on bypass would restrict work and increase risk on site. “It is gonna put a huge restriction on the work being done on the site,” Robinson said, noting the need to eliminate the chance of errors while the system is bypassed.

County staff and Horox discussed schedule and phasing. Horox said engineering time to redesign a different abutment type would be limited but that the principal impacts would be higher construction costs and schedule delay; the firm suggested phasing work (for example, building one abutment and half the superstructure first) if additional time is needed.

Decision and next steps: an unidentified speaker moved to take the proposal under advisement and revisit it next week; Terry Tanayo seconded the motion. The commission voted in the affirmative and the chair said the motion carried. Commissioners directed staff to place the item on next Tuesday’s agenda and asked Horox to issue a memo summarizing the findings for commissioner review.

What remains unresolved: the county has not decided whether to require relocation of the pipeline, redesign the abutment, or accept additional schedule and cost risk; commissioners will consider a written recommendation next week. The meeting record notes the abutment-cost comparisons and the pipeline-relocation logistics but does not specify who will pay relocation costs if the county requires the line to be moved.