Construction of the new Napa River bridge at First Street is going at a furious pace to beat the winter rains.

Workers have been laboring 10 hours a day, six days a week and are prepared to add a seventh day if necessary, Jason Holley, the city of Napa engineer in charge of the project, said last week.

The general contractor, American Civil Constructors, is up against a tight deadline to finish work in the river by Oct. 15, a requirement of the Regional Water Quality Control Board, Holley said.

Demolition of the old concrete bridge, built in 1914, was wrapping up last week, leaving just six and a half weeks to build the piers and abutments for the new bridge, he said.

“It’s a very tight schedule. We’re confident we can get it done,” Holley said.

Workers are finishing the process of sinking sheet piles for cofferdams that will hold back the river, creating dry pockets for the construction of abutments and piers.

Over the next two to three weeks, workers will pound some 200 steel piles, each 85 feet long, into the river bed. The piles will be surrounded with concrete, becoming the foundation of the new span.

While sinking sheet piles for the cofferdams was loud, pounding foundation piles will be louder, Holley said. To speed up work, the contractor may bring in a second hammer so that two piles can be sunk at the same time, he said.

It’s essential that the foundation of the new bridge be completed by Oct. 15 so that construction of the deck can occur over the winter months, Holley said.

If for some reason the foundation is not completed by mid-October, work might not be able to resume in the river bed until next July.

Work is allowed in the waterway only between July 15 and Oct. 15 to protect fish that might be present during periods of elevated river flows, Holley said.

If Oct. 15 approaches and winter rains have held off, the city might be able to get a permit extension until Oct. 31, but this cannot be counted on, Holley said.

The new bridge will be higher and longer than the old one, eliminating a flood obstruction. The price tag for the project is $15.1 million, with the federal government paying 88.5 percent of most costs, Holley said. The city is paying the rest.

The reinforced concrete in the old bridge is being recycled for new construction projects, Holley said. The city saved the plaque on the old bridge for a future historical display, he said.

First Street isn’t scheduled to be reopened to traffic until July 2009. In the meantime, vehicles are being detoured to Lincoln Avenue and Third Street.

The construction is occurring adjacent to Copia, which remains fully open. The privacy of Copia’s gardens and outdoor dining at Julia’s Kitchen is partially protected by 10-foot fences that have been painted green.

Part of Copia’s north garden was wiped out by the construction of a temporary access road for deliveries. Copia salvaged a number of displaced olive trees, Holley said.