PACIFICA -- The Highway 1 bypass tunnels at Devil's Slide will open a year later than previously announced, resulting in a higher construction bill for taxpayers, according to state transportation officials.

Caltrans can't say how much money the delay will cost because it must negotiate with the construction firm. The agency contracted in 2006 with Kiewit Pacific Co., a subsidiary of Omaha, Neb.-based Kiewit Corp., to build the twin tunnels through a mountain between Montara and Pacifica, and route traffic onto a new 1,000-foot cantilevered bridge on the Pacifica side.

At the time, Caltrans agreed to pay $272 million for the tunnels and $42 million for the bridge, provided the roadway would open in late 2011.

Kiewit revised the timeline in October 2010 based on construction delays and then projected further delays a few months ago, according to Caltrans spokesman Bob Haus. The public was never officially notified, except for the fact that the Caltrans website was quietly updated to say the tunnel would open in "late 2012."

Kiewit officials referred questions to Caltrans at Caltrans' request, they said.

Haus said the delays started piling up when Kiewit discovered unpredictable rock and soil patterns in the final third of the tunnel excavation.

The conditions changed so frequently -- from hard rock to soft soil and back again -- that crews needed to employ many different kinds of machinery. Each new machine caused a delay, especially when Kiewit was blasting rock away, because it required removing the ventilation system.

Haus said Kiewit had completed scores of rock core samples before starting the project, but "you never know what kind of geological conditions you'll encounter until you strike it."

He added that the earth movement had altered the top of one tunnel and caused a delay while it was reinforced.

Kiewit won the contract to reroute the narrow, washout-prone stretch of coastal highway by promising a quicker and less-expensive job than another bidder.

Assemblyman Jerry Hill, D-San Mateo, said he is worried about what he sees as a pattern at Kiewit of bidding low, then adding delays and higher bills.

"I'm concerned this may be part of a larger entrenched history ... my office is going to be looking into it," Hill said. He also criticized the lack of public disclosure; even he wasn't notified of the yearlong delay until he heard some rumors and asked Caltrans about it.

Kiewit's change order claims must be negotiated with Caltrans before being paid.

"There is no final dollar amount. Every change order is an estimate until it's final," said Brigetta Smith, director of external affairs for Caltrans. "We don't give out estimates because it's not a true reflection of what the final cost will be."

Smith said that, so far, Caltrans has paid out $245 million of the $272 million in its contact with Kiewit. Construction money comes from the Federal Emergency Relief Administration.

A year's delay means an extra winter of wet-weather driving at Devil's Slide, which has been closed several times, sometimes for months, because of erosion and rock slides.

In fact, Caltrans plans to close one lane of Highway 1 from Aug. 8-19 to repair a section of roadway between Pacifica and Devil's Slide that has been subject to rock slides.

Contact Julia Scott at 650-348-4340.