A Concord firm has been selected to oversee a major rehabilitation of Interstate 680 in the San Ramon Valley.

Caltrans officials announced Wednesday they have selected Bay Cities Paving & Grading Inc. to resurface and rebuild the busy freeway.

The firm's $49.8 million bid was the lowest of 10 bids submitted for the project. A construction schedule is expected to be released soon.

Caltrans officials have said preliminary work might begin this winter, but the bulk of the reconstruction will start in the spring.

The original completion date was winter 2012, but that date is now in doubt.

The $74 million freeway reconstruction was scheduled to start last month, but the state budget stalemate put it on hold.

The project will cover eight miles of I-680 from Rudgear Road in Walnut Creek to Alcosta Boulevard in Dublin. It includes the repaving of all lanes of the freeway as well as improvements on the 39 ramps. 

Overpass bridges and freeway shoulders also will be repaired. The southbound carpool lane will be extended from Rudgear Road to Livorna Road in Alamo.