W. M. Keck Observatory officials on Tuesday disclosed the discovery of an oil leak from the hydraulic system supporting the Keck I telescope.

The state Department of Health was notified Monday even though the leak — described as small by Keck officials — was first detected April 19.

Hilton Lewis, director of the Mauna Kea observatory, acknowledged being slow to launch a full investigation into the problem. In a news release, he said it was a delay “that I regret and for which I take full responsibility.”

“We are now giving this investigation the full attention it requires as the top priority for the observatory,” Lewis declared.

In an interview, Richard Matsuda, Keck’s chief of operations, said staff technicians discovered the hydraulic oil seepage inside the telescope building on the pier wall supporting the Keck I, in an area normally concealed by drywall.

After technicians removed all of the remaining drywall from the pier at the base of the telescope Monday, they identified six areas where slow seepage may be occurring, he said.

Technicians also removed the drywall from Keck I’s twin telescope, Keck II, and found no oil seeping on Keck II’s pier.

On Monday technicians took samples of the red cinder on the ground below the floor of Keck I, and they appeared to be wet. That prompted an immediate notification to the state Department of Health, Matsuda said.

Absorbent mats and pads were used to soak up the oil and to prevent more from escaping the telescope building, he said.

The Aiea engineering firm Masa Fujioka and Associates, which specializes in environmental, geotechnical and hydrogeological consulting, was hired to conduct an independent investigation and recommend remedial measures, if necessary, in consultation with the state and the Office of Maunakea Management.

Keck I’s extensive hydraulic system has a total capacity of 550 gallons of oil and is topped off with fresh oil as needed, Matsuda said.

How much oil was leaked is unknown, but officials found no obvious dripping or pouring, he said, and it appears to be small.

Keck Observatory, featuring a pair of telescopes that are among the most scientifically productive on earth, experienced damage from the large 6.9 earthquake that rocked Hawaii island May 4, the day after Kilauea started its latest East Rift Zone eruption.

The quake knocked the Keck I’s mechanical bearing system out of operation for four days. The system is what keeps the telescope centered as it rotates. The Keck II telescope did not suffer any damage.

Whether the earthquake exacerbated the oil leak is unknown.

“That will be determined by an immediate investigation,” Matsuda said. “We’re really taking this seriously. We want to get this done as quickly as possible.”

Keck, officials said, is acting according to procedures set forth in the Hazard Evaluation and Emergency Response Office of the state Department of Health technical guidance manual. Additional updates will be issued as the investigation progresses and will be posted at Keck’s web site at keckobservatory.org/responsibility.