Exploratory drilling will begin in August to probe the riverbed under the Healdsburg Memorial Bridge, part of the initial work for a major rehabilitation of the span scheduled for next year.
The drilling is to ascertain soil characteristics that will determine the design of a new centerpiece and foundation for the 91-year-old Russian River crossing.
"We're shooting for the first week of August," Public Works Director Mike Kirn said of when work will start. "There's still a couple of loose ends we need to tie up with regulatory agencies and scheduling with the driller."
The work is expected to take two days, during which the bridge will be closed to motor vehicles. Bicycles and pedestrians will be able to use it.
The closure is insignificant compared to the 18 to 24 months the bridge is expected to be shut to all traffic after major work begins in mid-2013.
The planned $12 million rehabilitation and retrofit involves bolstering the rusting structure to withstand earthquakes, flooding and erosion. It includes sandblasting and painting, repairing damaged structural members, installing a new deck and making railing safety improvements.
Nearly 90 percent of the funding comes from federal programs, but the city must come up with about $1.4 million for its share. Healdsburg intended to use about $1 million in redevelopment money toward the bridge work, funds that are now in question after the state dissolved redevelopment programs earlier this year.
City officials hope some redevelopment money will be available, but the city also could use funds it gets from gas taxes.
Regardless of the source, Mayor Gary Plass expects the project will proceed.
"I feel we have a strong commitment not only from the City Council, but the community. Unless that changes we are doing our best to find funding," he said.