The Sonoma County Board of Supervisors on Tuesday formally approved the $84 million project to expand Charles M. Schulz-Sonoma County Airport to enable more daily commercial flights.

The project next goes to federal officials who must sign off before any construction begins.

The board's 4-0 decision came with a minor change to include analysis of public health and the environment in a future planned study of impacts associated with the expansion.

Supervisor Mike McGuire, who represents the airport area, pushed strongly for the condition, saying the Windsor area would bear the brunt of construction activity and other impacts associated with airport growth.

Three other supervisors ultimately agreed to the additional study work, which is set to happen when the county-owned facility reaches about 474,000 passengers per year, more than double its current level. Supervisor Valerie Brown was absent Tuesday, attending to a family health situation.

The formal approval came two weeks after the board's preliminary endorsement of the project and roughly 13 years after the county launched its latest move toward expanding the airport.

In the short term, the project calls for $42.7 million in safety upgrades that would extend the main runway by 885 feet to 6,000 feet and add 200 feet to the second runway.

Over a longer term, the airport would add a new passenger terminal, control tower, air cargo facility and other upgrades. The timing of those improvements depends on attracting more airlines to the county-owned airport.

About 95 percent of the expansion costs, including the short and long-term upgrades, would be financed with federal aviation grants.

The airport's lone commercial carrier, Alaska Airlines, currently offers five flights a day. The upgrades would allow up to 21 flights daily, a threshold authorized by the county's general plan but not possible with the current infrastructure.

The county is in talks with Alaska and Frontier Airlines about additional flights, but neither company has made commitments.

"Hopefully the airlines see the benefit of the project and when we get those upgrades complete we can get the additional service we've been asking for," said Jon Stout, the airport manager.

Business and tourism interests gave strong backing to the project, while some airport-area residents and environmental advocates expressed concerns about noise, air quality and habitat impacts.

The formal vote Tuesday authorized the runway improvements while approving an updated airport master plan, a general plan amendment and the project's final environmental impact report.

A separate vote authorized an amended contract in the amount of $2.6 million with Mead and Hunt, Inc., an architectural and engineering firm, for design and land acquisition services related to the runway upgrades.

Given a go-ahead by federal officials, the runway work could begin in July or August.

You can reach Staff Writer Brett Wilkison at 521-5295 or brett.wilkison@pressdemocrat.com.