Revised Rock Island Dam Drilling Program Plan Meets Federal Energy Regulatory Commission Requirements

Strategic Insights -

The Public Utility District No. 1 of Chelan County, Washington has submitted a revised drilling program plan for the Rock Island Hydroelectric Project to the Federal Energy Regulatory Commission (FERC). The plan addresses 11 FERC comments and revisions made to ensure compliance with regulatory requirements. Key changes include the relocation of boring RA-PZ-1 to the upstream side of the water-retaining feature, updating the typical standpipe piezometer installation in abutments, and providing additional figures to illustrate instrumentation installation details.

Key Takeaways:

  • The revised drilling program plan addresses 11 FERC comments and revisions, ensuring compliance with regulatory requirements.
  • Boring RA-PZ-1 has been shifted upstream outside the impervious fill to confirm the assumed headwater elevation on the upstream side of the cutoff wall.
  • Figure 28 has been updated to reflect bentonite-cement grout or neat-cement grout as appropriate for standpipe piezometer installation in abutments.
  • Additional figures have been added to illustrate the typical vibrating wire piezometer, inclinometer, and extensometer installation details.
  • Section 4.2.1 has been updated to clarify that sonic boring equipment will be used to drill to the bottom of the hole and seat the casing 5 feet into the rock.
  • Daily readings of the 3D joint meters along the north abutment gravity structure and drop gate structure will be performed during drilling operations to monitor for adverse movements.
  • The District has updated the Drilling Guidelines to recommend the use of cement-bentonite grout instead of bentonite chips for backfilling boreholes prior to installing piezometers.
  • The resumes of additional personnel have been added to the DPP for consideration as lead drillers, geotechnical leads, and field geologists/geotechnical engineers.
  • Table 10-1 has been updated to reflect the personnel changes at the FERC Portland Regional Office following Mr. Douglas Johnson's retirement.

Statistics:

  • 11 FERC comments and revisions were addressed in the revised drilling program plan.
  • The revised drilling program plan includes updates to Figures 28, 29, and 30 to illustrate instrumentation installation details.
  • Daily readings of the 3D joint meters will be performed for 365 days during drilling operations.
  • 6 additional personnel have been proposed to support the drilling activities.
  • September 19, 2025 is the desired completion date for FERC's timely review and authorization to proceed.

Sources:

  • Acting Portland Regional Engineer, D2SI-PRO Federal Energy Regulatory Commission to Public Utility District No. 1 of Chelan County, Washington, August 14, 2025
  • Federal Energy Regulatory Commission (FERC) comments and revisions, July 18, 2025
  • Public Utility District No. 1 of Chelan County, Washington, Rock Island Dam Drilling Program Plan Revision 1, August 14, 2025