Island Lake Reservoir Development Update: Minnesota Power's Proposed Work Plan

Strategic Insights -

Minnesota Power has submitted an update to the Federal Energy Regulatory Commission regarding the Island Lake Reservoir Development project, part of the St. Louis River Hydroelectric Project. The proposed work plan involves conducting additional geotechnical tests and explorations to confirm the stability of the Main Dam at the Island Lake Reservoir. The tests, including Cone Penetration Tests (CPT) and geoprobes, are expected to take approximately two days to complete, with a team of experts working on the project.

Key Takeaways:

  • The proposed work plan includes conducting approximately eight 15 to 20-foot deep Cone Penetration Tests (CPT) at 100 foot intervals along the length of the dam crest to confirm relative density.
  • The additional CPTs are shallow compared to the 2023 exploration, which included deeper CPTs and Standard Penetration Tests.
  • The work team, consisting of Twin Ports Testing and GEI, will use the same drilling equipment and procedures as used in the 2023 geotechnical exploration.
  • Daily reports, including headwater and tailwater readings, will be emailed to Ms. Angela Damron of the FERC-CRO.
  • Any aberrant conditions encountered during the investigation will be reported according to FERC's previous authorization letter dated December 1, 2023.

Statistics:

  • Approximately eight 15 to 20-foot deep Cone Penetration Tests (CPT) will be performed at 100 foot intervals along the length of the dam crest.
  • The tests are expected to take approximately two days to complete.
  • The work team will use the same drilling equipment and procedures as used in the 2023 geotechnical exploration.
  • Daily reports will be emailed to Ms. Angela Damron of the FERC-CRO.
  • The previous geotechnical exploration in 2023 included deeper CPTs and Standard Penetration Tests.

Sources:

  • A letter from Kevin Griebenow, PE, Electronically Filed Regional Engineer Federal Energy Regulatory Commission, dated May 15, 2025.
  • A letter from GEI Consultants, Inc., dated July 11, 2025.
  • A letter from Matthew J. Ryan, PE, Chief Dam Safety Engineer, dated September 5, 2025.