The Charles M. Schulz-Sonoma County Airport has received a $1 million federal grant for environmental work associated with its runway expansion project, Rep. Mike Thompson, D-St. Helena, announced Monday.

The project’s environmental mitigation costs, to deal with endangered plant and animal species, have run to $21 million, mostly borne by the county. The $53 million runway project is 90 percent federally funded.

Thompson helped secure a $40 million Department of Transportation grant last year for the bulk of the project to extend the two runways and add safety improvements at the county’s only commercial airport. Officials hope the improved main runway, which will open this fall, will attract more commercial airline service.

Thompson called the project “a cornerstone of economic development in our region for years to come.”

“It’s important that we protect our local environment as this project continues, and these funds will help us do just that,” he said in a statement.

Measures to address impacts on endangered tiger salamanders and Burke’s goldfields were required to secure federal funding for the project.