Workers yesterday chipped away at two large boulders that rolled into the back of an apartment building last week at the Kalihi Valley Homes public housing complex.

Royal Contracting Co. workers used a 40-pound jackhammer, 60-pound "splitter" and 90-pound "buster" to tear away large chunks of the two boulders, the bigger of which was about 8 feet in diameter.

The contractor estimated at about midday that it might take up to 10 days to finish the $50,000 boulder removal contract, said Moani Wright-Van Alst, spokeswoman for the Honolulu Board of Water Supply.

Nine families living in the building have been temporarily relocated.

Wright-Van Alst said the Board of Water Supply owns almost all the hillside from which the boulders tumbled down at about 8:30 a.m. Friday.

"There is one privately owned lot up above there, but most of the property is owned by the Board of Water Supply," Wright-Van Alst said.

The two boulders tore through a chain-link fence about 60 feet up the hillside behind the row of two-story walk-up apartments.

They came to rest on a sidewalk in the laundry area behind the building. One of the boulders flattened a 3-inch-diameter steel clothesline post and half-crushed what appeared to be a washing machine or dryer. No one was injured.

Wright-Van Alst said the Board of Water Supply immediately contracted with an engineering company to check on the stability of other boulders on the hillside behind the apartments.

While the two boulders may be split up into smaller pieces farly rapidly, those pieces will have to be broken down further and hand-carried to a debris bin and then trucked off for final disposal, Wright-Van Alst said.

The apartment buildings are stacked in rows along the hillside, preventing heavy equipment from gaining access to the area where the boulders landed.

Eight of the nine relocated families will stay in vacant units at the complex until an assessment of the hillside's stability is completed, said Alan Sarhan, a planner with the Hawai'i Housing Authority. The other family moved in with relatives or friends at another housing project, he said.

Sarhan said he won't be able to say how soon the families will be allowed to return to their apartments until after the agency has had a chance to review the assessment of the hillside's stability.