SANTA ROSA -- The Sonoma County Board of Supervisors today officially signed off an $84 million safety upgrade and expansion of Charles M. Schulz--Sonoma County Airport but tabled a proposed health and noise study on the project.

Today's 4-0 vote, with Supervisor Valerie Brown absent, was the last hurdle before federal officials must approve the plan, which would extend the runway to allow for mid-sized commercial aircraft. The board originally approved the project Jan. 10.

The supervisors agreed to add language that addresses environmental and public health concerns for possible study as construction progresses at the airport. One trigger for further study will come if and when  ridership more than doubles at the airport. In 2011, the number of passengers going through the airport reached an all-time high of 207,188, a 9.8 percent increase over 2010.

Airport staff said they're hoping for Federal Aviation Administration approval by this April. If so, construction could begin as soon as August.

About 95 percent of the the safety upgrades and expansion would be paid for by federal aviation grants. The first phase of construction -- the safety measures -- would cost about $42 million.

The remainder of the price tag would go toward toward improvements to the control tower, a new passenger terminal and cargo space. Timing of the latter would depend on attracting more airlines and passenger volume.

The upgrades and expansion include fixing blind spots on the main runway and extending it by 885 feet to 6,000 feet, along with extending a second runway by 200 feet to 5,002 feet. That would allow for larger and more frequent commercial aircraft to land and depart from the county.  Proponents say that would  ease the reliance on San Francisco and Oakland airports while boosting the local economy. 

The county General Plan allows for up to 21 commercial flights per day by 2030. But airport officials say that's unattainable with the current runway and needed repairs.

Separately, the board voted in favor of a contract worth $2.6 million for Mead and Hunt, Inc., a national architecture and engineering firm with offices in Santa Rosa, for services related to improvements to the airport's runways.