A contractor for the U.S. Army Corps of Engineers next week will begin removing boulders — the largest of which is up to 20 tons — above some homes in Moanalua Valley.

Prometheus Construction will remove five boulders on a hillside above about three homes on Ala Mahina Place. Prometheus plans to begin work on Tuesday and is expected to complete the nearly $309,000 project by the end of October.

The largest boulder is about the size of a small truck and weighs probably 15 to 20 tons, said Cliff Tillotson, Prometheus vice president and project manager. The others are about 3 tons, he said.

Moanalua Valley resident Lisa Hall noticed one of the boulders on a slope behind the home she rents right after she moved in in March and has worried about it tumbling down.

"It looks like it's going to fall any minute," she said. "It's a round boulder about the size of a Volkswagen, and it doesn't look like anything is holding it up there.

"Just looking at it is enough to scare you."

The company plans to put in fencing, break the boulders into pieces and airlift the rocks by helicopter. People who live in the homes below the boulders will only have to evacuate while the rocks are airlifted away, which should take a couple of hours or so, Tillotson said.

The project was initiated by concerns from Moanalua Valley residents and a subsequent inquiry from U.S. Sen. Daniel K. Inouye's office in February, the Army Corps of Engineers said.

The boulders are on a hillside about 260 feet above street level, said Dino Buchanan, spokesman for the Army Corps of Engineers Honolulu District.

The Army is working on the project because the boulders are just inside Tripler Army Medical Center's property line, he said.

The federal government has removed boulders in Moanalua Valley before.

Following heavy rains and landslides that damaged properties near Tripler Army Medical Center in late 2003, the Corps of Engineers identified more than a dozen boulders that needed to be removed.

Prometheus was hired for the $1.4 million project and in 2005 demolished the boulders and installed safety catchment fences in Moanalua Valley along Ala Aolani Street and Ala Aoloa Loop.

In 2004, the Navy spent about $225,000 to secure a 60-ton boulder perched more than 100 feet above Ala Lani Street on the opposite side of the valley.

More needs to be done, said state Rep. Glenn Wakai, D-31st (Moanalua Valley, Moanalua, Salt Lake). Wakai said the Navy has identified 49 sites on the Red Hill side of the valley as being problematic, and that he and Inouye have been working on securing $6 million for rockfall mitigation efforts there.

"We hope to get it in next year's budget," Wakai said. "If there's anything good about this entire situation, at least we can tap into federal funds."

Reach Lynda Arakawa at larakawa@honoluluadvertiser.com.