Claims about TMT’s impact on watershed are just plain false, according to expert, EIS

An artist's rendering of TMT against a backdrop of other Maunakea telescopes.
Don Thomas

The most vocal opposition to the Thirty Meter Telescope project has come from the perspective of the rights of indigenous people and the cultural significance of the site.

However, the project also has been criticized for fear that development on the site will contaminate or otherwise impact groundwater throughout the island. Some criticism — largely promulgated on social media — went so far as to speculate that the TMT project will seek to drill into groundwater at Maunakea’s summit.


Those fears are not credible, said geochemist Don Thomas, director for the Center for the Study of Active Volcanoes at the University of Hawaii Manoa Institute of Geophysics and Planetology.

“In this case, I can’t conceive of any way the project could impact the groundwater,” Thomas said.

Thomas said that part of what likely inspires such concerns is that the popular conceptual model of the island’s groundwater — often visualized as a coherent pool of water beneath the earth — is overly simplistic.

“This is not as simple as people imagine it is,” Thomas said.

The composition of the rock at Maunakea summit and the hydrology of the island suggests that, even were a contaminant to leach into the ground at the summit, it would take more than 2,000 years to reach sea level, if it ever reached sea level at all.

Groundwater at Maunakea’s summit would quickly encounter sheets of dense, nonporous rock within the Hawaiian volcanoes called volcanic dikes as it infiltrated downward. These dikes — which Thomas likened to plates of concrete, only denser — would slow the rate of downward water infiltration or halt it completely as water becomes trapped behind the naturally formed dike walls.

Furthermore, Thomas said, thanks to naturally occurring hydrogen and oxygen isotopes within water, it is possible to trace groundwater samples to the altitude of where they originated, as well as their ages.

Wells drilled near the shoreline around Hilo and Hamakua produced water that originated from between 7,000 feet and 8,000 feet above sea level — well below the TMT site, which sits at over 13,000 feet.

The water from those wells also was determined to be around 2,000 years old, suggesting that it takes about that long for water to infiltrate from 7,000 feet to sea level consumer wells, Thomas said.

“This stuff doesn’t move very fast,” Thomas said.

The 2010 environmental impact statement that was prepared for the TMT project states that all wastewater from the telescope will be transported from the site, not discharged at the summit, which is another falsehood spread on social media. Potable water will similarly be transported to the site.

The EIS determined the primary water-related impact the project will have on the environment is tied to the addition of new impermeable surfaces. Because water cannot permeate through pavement and buildings, the project could alter the dynamics of how precipitation enters the groundwater.

Thomas said this will not be a particularly significant change, however. Because there is very limited precipitation at the summit — part of what makes it a desirable location for a telescope, he added — the rate of rainfall recharge is already very low.

The limited precipitation at the summit also is part of why suggestions that TMT intends to drill into groundwater is unfeasible, Thomas said.

Because there is so little precipitation, Thomas said he would expect the nearest groundwater source from the summit to be between 2,000 and 3,000 thousand feet down, although he admitted that the Office of Maunakea Management has not allowed many hydrological studies at the summit, so the groundwater map of the mountain’s upper elevations is still largely unknown.

“Our understanding of this is improving, and I would like to see more get done,” Thomas said. “There’s still a lot we don’t know.”

Thomas said he has proposed installing pipes into the subsurface structure of the decommissioned Caltech Submillimeter Observatory, allowing the site to gather data on the mountain’s groundwater even after the building is dismantled and the site returned to nature.

Thomas also said that he “hopes nobody takes too seriously” social media claims that TMT needs a groundwater source to cool a hidden nuclear reactor within the facility.

TMT will draw its power from the same source as every other telescope on the mountain: HELCO’s energy grid.

Email Michael Brestovansky at

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