Rock Placement Used To Stabilize Gas Pipelines In Idaho’s Pend Oreille River

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By David Dixon, Snelson Companies, Sedro Woolley, WA
Gas Transmission Northwest LLC, a natural gas pipeline system owned by TransCanada, contracted Snelson Companies, Inc.  (A PLH Group Company) of Sedro Woolley, WA to perform maintenance activities near a section of its natural gas pipelines that crosses the Pend Oreille River west of Sandpoint, ID.
  Ongoing monitoring of the system showed a natural washing away of the riverbed under the pipelines that required construction activities to ensure that the pipelines are properly supported for continued safety and reliable operation.
  To re-establish riverbed support, Snelson is placing pre-washed natural stones under segments of the 2,200-foot section of the two concrete-encased 30-inch diameter pipelines. The angular shaped stones, ranging in size from 1 to 4 inches, will reduce the amount of fine particles in the water, which will lessen the amount of turbidity created while doing the work.
  Snelson’s  field operations began arriving July 24, 2013 to attend pre-job meetings and begin planning and engaging subcontractors and securing materials. A worksite was set up on the TransCanada right-of-way near Sagle on the south shores of Pend Oreille River. C. E. Kramer initially installed walkways and docks and continued on the project as a subcontractor, providing tug support for moving the barges and installation anchors.
  A 440-ton lattice boom crane was set up along the lake on a pad to relay rock and equipment to the barges that will transport the rock to the work area. A 60 x 90 sq-ft work barge and two 20 x 40 sq-ft rock transfer barges have been assembled to perform the work.
  On August 22, approximately one month later, the work barge was launched with a CAT 336 trackhoe with a tremie tube system along with a Cat 320 trackhoe, double drum winches and Associated Underwater Services’ (AUS)  diving shack and equipment ready to start work.
  Once the barges were in place, anchors were set and AUS completed a Multi-Beam underwater survey of the pipeline in preparation for placement of the rock. Throughout the rock placement operations, AUS provided daily precise placement support of the rock with its sonar equipment and Remote Operated Vehicle (ROV).
  Over the course of the project some 5,000 tons of rock will be placed. At PLN deadline time, Snelson said they will be placing rock for two more weeks, followed by at least two weeks of demobilization
  As to challenges, crews had to deal with sensitive lake resources, public marine and worker safety, heavy boat traffic, high summer recreational activity, increased vehicle traffic on roadways, scrutiny from the U.S. Corps of Engineers and U.S. Fish and Wildlife Department and diving to 70 foot depths.
  So far, the project has progressed very smoothly with zero incidents under the oversight of John Kennedy, general superintendent of Snelson Companies Marine Division. Other key Snelson personnel included Jason Alvord, project manager, Jeff Fox, foreman; Mark Madison, safety, Brett Bushman, purchasing and Office Manager David Dixon.
  Safety is upmost importance to TransCanada and Snelson Companies  Inc. This has been very evident on the progression of the project both from the viewpoint of the workers, TransCanada and the public. The Marine Division of the Bonner County Sheriff’s office also proved to be of great assistance, along with C.E. Kramer that provided tugboat support.
  TransCanada personnel included: Richard Torres, project manager, Gordon Brochard, chief inspector and Darrin Moe, environmental specialist.