The Caltech Submillimeter Observatory

The California Institute of Technology (Caltech), in cooperation with the Hawaiʻi Department of Land and Natural Resources, has released its Draft Environmental Assessment and Anticipated Finding of No Significant Impact (DEA/AFONSI), which was prepared as part of the planning effort required prior to decommissioning the Caltech Submillimeter Observatory (CSO).

If the regulatory process is completed as currently anticipated, Caltech aims to begin removing the observatory and restoring the site by Summer 2022. It will be one of the first observatories removed under the 2010 Decommissioning Plan for Maunakea Observatories.

The DEA was prepared by Caltech’s consultant, Planning Solutions, Inc. (PSI). It addresses the potential environmental effects of the proposed decommissioning of the CSO. Hawaiʻi law requires an environmental review, due to the use of State land and the need for a Conservation District Use Permit. A copy of the DEA/AFONSI can be found here:

These four options are considered in the DEA:

  • Complete removal/full restoration (Caltech’s preferred alternative);
  • No action (an alternative that is recommended to be evaluated);
  • Complete removal/moderate restoration; and
  • Partial removal/moderate restoration.

The State Office of Environmental Quality Control is expected to announce the availability of the DEA on September 8, 2021 in The Environmental Notice. The DEA and information concerning a companion Conservation District Use Application will also be available online at Once published, the DEA will be subject to a 30-day public comment period. The deadline for comments on the DEA is October 8, 2021.

The public is invited to attend community meetings, which will be virtual due to continuing COVID-19 concerns. At the meetings, the proposed decommissioning will be described in detail and questions answered informally. Each meeting will present the same information; they are scheduled for:

  • Tuesday, September 28, at 11:30 a.m.;
  • Wednesday, September 29, at 4:30 p.m.;
  • Thursday, September 30, at 6:00 p.m.

On the day of the meetings, a link to join will become live at:

“Caltech invites the public to give its feedback on the draft EA,” said Caltech physics professor and CSO Director Sunil Golwala.

Public comments can be submitted to PSI via email or in writing:

  • Planning Solutions, Inc.
    Attn: Mākena White, AICP
    711 Kapiʻolani Boulevard, Suite 950
    Honolulu, Hawaiʻi 96813

“We will address the comments we receive on the Draft Environmental Assessment as quickly as possible, and hope that a Conservation District Use Permit is granted in early 2022, which would enable Caltech to begin the deconstruction and restoration in the summer of 2022,” said Golwala.

CSO is one of the first observatories on the mountain to undertake the decommissioning process. The CSO was formerly one of the world’s premier facilities for astronomical research and instrumentation development at submillimeter wavelengths.

The CSO‘s 10.4-meter radio telescope, which came online in 1987 for use in research by astronomers at Caltech and other institutions, was housed in a compact dome near the summit of Maunakea. The telescope was used by researchers, including more than 200 students, to open a new submillimeter window on the universe. A summary of CSO’s contributions to astronomy and astronomical instrumentation are available here: All the astronomical instruments were removed from the facility in 2015.