The National Science Foundation could take until the end of 2026 to complete an environmental review for a potential investment in the proposed Thirty Meter Telescope on Hawaii island.

The agency announced Monday that its environmental review process, begun in 2022, will take more time than previously expected, in part because of delays for required formal consultation with Native Hawaiians under Section 106 of the National Historic Preservation Act.

NSF also said the need for more time for its environmental review was influenced by considerations including potential environmental impacts and advancements in analytical methods, such as the appropriate incorporation of Indigenous knowledge.

“In allowing more time to carry out these activities, NSF remains dedicated to making well-informed decisions that balance scientific advancement with environmental stewardship and respect for Indigenous cultural heritage,” the agency said.

Under federal rules the agency had two years to complete an environmental impact statement report after issuing a notice of intent to prepare such a report. NSF issued its notice July 19, 2022.

The agency previously anticipated that it would publish a draft EIS in 2023 followed by a final EIS this year. The draft report has yet to be completed.

Some of the delay stems from an estimated 7,000 verbal and written comments provided before and after initial public meetings in 2022 that followed an informal outreach effort that included “talk story” sessions from August 2020 to November 2021.

The nation’s leading funder of science research is considering an investment of potentially $800 million or more in the planned $2.65 billion TMT project after opponents blocked construction of the telescope atop Mauna Kea in 2015 and 2019.

Polling has indicated that a majority of Hawaii residents support the next-generation telescope, but the project has been a source of protest largely by many Native Hawaiians who consider the mountain a sacred place.